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Li plating as unwanted side reaction in commercial Li-ion cells – A review

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Abstract

Deposition of Lithium metal on anodes contributes significantly to ageing of Li-ion cells. Lithium deposition is connected not only to a drastic limitation of life-time, but also to fast-charging capability and safety issues. Lithium deposition in commercial Li-ion cells is not limited to operation conditions at low temperatures. In recent publications various types of commercial cells were investigated using complimentary analysis methods. Five cell types studied in literature (18650, 26650, pouch) serve as a basis for comparison when and why Li deposition happens in commercial Li-ion cells. In the present paper, we reviewed literature on (i) causes, (ii) hints and evidences for Li deposition, (iii) macroscopic morphology of Li deposition/plating, (iv) ageing mechanisms and shapes of capacity fade curves involving Li deposition, and (v) influences of Li deposition on safety. Although often discussed, safety issues regarding Li deposition are not only limited to dendrite growth and internal short circuits, but also to exothermic reactions in the presence of Lithium metal. Furthermore, we tried to connect knowledge from different length scales including the macroscopic level (Li-ion cells, operating conditions, gradients in cells, electrochemical tests, safety tests), the microscopic level (electrodes, particles, microstructure), and the atomic level (atoms, ions, molecules, energy barriers).

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... However, it is broadly believed that the graphite anode is the major obstacle to the high-rate charging capability of commercial LIBs. The redox potential of graphite anodes (~0.1 V versus Li/Li + ) is close to that of Li-metal plating (0 V versus Li/Li + ) and easily falls below 0 V when charging with high SOC, high charging current, and low temperature due to enlarged overpotential polarization [13][14][15][16][17][18]. This favorably accelerates Li plating along the edge plane of the graphite surface, which competes with the Li-ion intercalation process in the graphite bulk phase. ...
... Therefore, a high charging rate expedites Li plating. During the de-intercalation or stripping process, a part of Li metal may lose electrical contact with the anode and form isolated Li islands (referred to as dead Li) on the anode surface [16,20,40]. The formation of dead Li will not only accelerate the aging effect of cells but also increase internal resistance [41,42]. ...
... On the full-cell level, the ratio of negative-to-positive areal capacity (N/P ratio) is also an important factor in influencing Li plating behavior. The N/P ratio is typically in the range of 1.0 to 1.2 to avoid Li plating [16]. In fact, the N/P ratio is also a dynamic process varying with charging current density. ...
Article
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As the world enters into the era of electrifying transportation for cleaner energy, lithium-ion battery (LIB)-powered electric vehicles have drawn great attention in recent years. However, the fast-charging capability of LIBs has long been regarded as the technological obstacle to the wider adoption of battery electric vehicles (BEVs) in the market. A substantial challenge associated with fast charging is the formation of Li plating on the graphite anode as it is the major contributor of side reactions during cell operations. In this review, the fundamentals of Li plating and corresponding influencing factors (including state of charge [SOC], charging current density, temperature, and N/P ratio) for the Li-ion intercalation process are first elucidated under fast-charging conditions. Furthermore, conventional strategies to suppress Li plating by enhancing ion transport kinetics between interface and electrode through anode engineering and electrolyte design are also summarized and analyzed. Then, innovative strategies for achieving ultrahigh SOC of anodes by regulating Li plating morphology on host materials to construct hybrid anode storage are discussed in detail. Two types of strategies are compared in terms of cell performance, process simplicity, and safety concerns. Last, we highlight some research orientations and perspectives pertaining to the development of hybrid anode storage, providing effective approaches to address Li plating issues for fast-charging LIBs.
... The calendar ageing rate increases with a higher state of charge (SOC) and operational temperatures, while it decreases over time due to the formation of the solid electrolyte interphase (SEI) layer, which develops proportionally to the inverse of square root of time 2 . Conversely, the rate of cycling ageing is influenced by several factors: it increases with the C-rate, SOC, and higher temperatures, and also accelerates under lower temperatures due to lithium plating 2, 3 . ...
... This study exclusively focuses on cyclic ageing due to cells experiencing the same calendar ageing rate when the temperature distribution is homogeneous and the cell is resting. 4. The ageing mechanism considered in this study is the SEI formation, which is the main ageing process in most graphite-based lithium-ion batteries 3 . Lithium plating is not considered since it mainly occurs under low temperature or high C-rate conditions 3 . ...
... Most previous studies rely on 2D models, which cannot fully capture real-time temperature changes or distribution throughout the entire cycling process. In these studies, the temperature gradient is often set to a constant value (e.g. a 5°C increment in Liu et al.'s study13 ; a fixed gradient of 12.5°C or 25°C in Marlow et al.'s study 12 ).3. Most research has focussed on interconnection resistance and welding techniques to optimise module-level variances. ...
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The distribution of current/voltage can be further regulated by optimising the electrical connection topology, considering a particular battery thermal management systems. This study numerically investigates a 4P6S battery module with two connection topologies: 1) a straight connection topology, where the sub-modules consist of parallel-connected cells that are serial connected in a linear configuration, and 2) a parallelogram connection topology, where the sub-modules are serial connected in a parallelogram configuration. We find that the straight topology is more advantageous, as it allows the temperature gradient to be distributed among the parallel-connected cells in the sub-modules, mitigating over(dis)charging. Consequently, it achieves a 0.8% higher effective capacity than the parallelogram topology at 1C discharge, along with a higher state of health at 80.15% compared to 80% for the parallelogram topology. Notably, the straight topology results in a maximum current maldistribution of 0.24C at 1C discharge, which is considered an acceptable trade-off.
... For example, charging a 7.5 Ah cell at 1 C rate at 0 • C would result in a significant 3.6% capacity loss [42]. The three following main variables cause the power and energy densities of a lithium-ion battery to decrease at low temperatures, especially when charging: 1. inadequate charge-transfer rate; 2. low solid diffusivity of lithium ions in the electrode; and 3. reduced ionic conductivity in the electrolyte [43][44][45]. Ionic conductivity in the electrolyte diminishes, which causes an increase in cell internal resistance; nevertheless, this is not the primary issue with low-temperature charging. Lithium plating at low temperatures, where lithium ions collect at the interface between carbon particles and electrolytes, may be primarily caused by poor Li+ diffusivity inside the electrodes [46,47]. ...
... During fast charging, there is a greater chance that the charging rate will surpass the intercalation rate. The quantity of Li + ions transferred during the charge-transfer process from the cathode to the anode per unit of time rises at a high C-rate [44]. High SOC has a great impact on the lithium plating. ...
... Battery degradation affects each battery cell in the battery energy storage system (BESS), which in turn causes capacity fading throughout the system. Waldmann et al. estimated an 18% capacity fade in lithium Li 0.89 NiCoO 2 during the first charge discharge cycle [44]. Generally, BESS is made up of multiple interconnected batteries, and the system's total performance and storage capacity are impacted by the individual cells' deterioration combined. ...
Article
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Batteries play a crucial role in the domain of energy storage systems and electric vehicles by enabling energy resilience, promoting renewable integration, and driving the advancement of eco-friendly mobility. However, the degradation of batteries over time remains a significant challenge. This paper presents a comprehensive review aimed at investigating the intricate phenomenon of battery degradation within the realm of sustainable energy storage systems and electric vehicles (EVs). This review consolidates current knowledge on the diverse array of factors influencing battery degradation mechanisms, encompassing thermal stresses, cycling patterns, chemical reactions, and environmental conditions. The key degradation factors of lithium-ion batteries such as electrolyte breakdown, cycling, temperature, calendar aging, and depth of discharge are thoroughly discussed. Along with the key degradation factor, the impacts of these factors on lithium-ion batteries including capacity fade, reduction in energy density, increase in internal resistance, and reduction in overall efficiency have also been highlighted throughout the paper. Additionally, the data-driven approaches of battery degradation estimation have taken into consideration. Furthermore, this paper delves into the multifaceted impacts of battery degradation on the performance, longevity, and overall sustainability of energy storage systems and EVs. Finally, the main drawbacks, issues and challenges related to the lifespan of batteries are addressed. Recommendations, best practices, and future directions are also provided to overcome the battery degradation issues towards sustainable energy storage system.
... Lithium plating can be confirmed through various techniques such as Nuclear-Magnetic-Resonance (NMR), X-Ray-Photoelectron-Spectroscopy (XPS) and semi-quantitative Glow-Discharge-Optical-Emission-Spectroscopy (GD-OES) depth profiling after postmortem analysis of cells. Operando measurements, including neutron scattering and measurements of anode potentials via introducing reference electrodes in full cells, can also provide evidence of metallic lithium deposition [221]. ...
... The aging inhomogeneity of lithium-ion cells was confirmed with postmortem coin cell analysis exploiting XPS, Scanning-Electron-Microscope (SEM) and NMR [221,201,58,232]. The post-mortem analysis techniques can directly reflect the morphological and chemical changes but are always costly and time-consuming [222]. ...
Thesis
https://cuvillier.de/en/shop/publications/9107-multimodal-on-board-aging-estimation-of-lithium-ion-batteries-via-charging-behavior-observation
... This is a worst-case assumption using the maximum open circuit voltage of the battery. During the heating process, the voltage will drop according to eqn (5). Furthermore, to keep the inductance low to reduce cost and space, the switching frequency should be high. ...
... The short time was set to Dt S = 4 ms, resulting in a peak current of I Max = 254 A when the battery is fully charged with U Batt = 54 V. However, during the heating process, the voltage will decrease due to the discharge current and the resulting voltage drop as described by eqn (5). ...
Article
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In many cases, batteries used in light e-mobility vehicles such as e-bikes and e-scooters do not have an active thermal management system. This poses a challenge when these batteries are stored in sub-zero temperatures and need to be charged. In such cases, it becomes necessary to move the batteries to a warmer location and allow them to acclimatize before charging. However, this is not always feasible, especially for batteries installed permanently in vehicles. In this work, we present an internal high-frequency AC heater for a 48 V battery, which is used for light electric vehicles of EU vehicle classes L1e and L3e-A1 for a power supply of up to 11 kW. We have taken advantage of the features of a damped oscillating circuit to improve the performance of the heater. Additionally, only a small inductor was added to the main current path through a cable with three windings. Furthermore, as the power electronics of the heater is part of the battery main switch, fewer additional parts inside the battery are required and therefore a cost and space reduction compared to other heaters is possible. For the chosen setup we reached a heating rate of up to 2.13 K min⁻¹ and it was possible to raise the battery temperature from −10 °C to 10 °C using only 3.1% of its own usable capacity.
... 2. What are the promising test strategies, and what are the limitations of a specific test strategy, for example extreme stress factors? 3. How do we model the accelerated ageing aiming at reliable and fast predictions that can be transferred to normal operating conditions? As the lifetime and degradation of lithium-ion batteries are highly relevant, there is published work that addresses ageing mechanisms and ageing effects at the cell or system level [7][8][9][10][11] and ageing-related test methods. [12][13][14] Furthermore, there are reviews on specific stress factors, [15][16][17][18] as well as operation [19] and fast charging strategies. ...
... For a detailed discussion of ageing mechanisms, their potential interaction and relation to stress factors the reader is kindly referred to other review articles. [7][8][9][10][11] In this section, we discuss the stress factors SoC, temperature, C-rates, and tests without rests for calendar and cyclic ageing tests and how they can be used to accelerate ageing characterisation with AAM. In this context, acceleration compares to an application scenario in which the battery is operated at an average SoC of around 50 % with an average DoD of 50 %, a temperature of 25°C and moderate C-rates, including many rest periods. ...
Article
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For the battery industry, quick determination of the ageing behaviour of lithium‐ion batteries is important both for the evaluation of existing designs as well as for R&D on future technologies. However, the target battery lifetime is 8–10 years, which implies low ageing rates that lead to an unacceptably long ageing test duration under real operation conditions. Therefore, ageing characterisation tests need to be accelerated to obtain ageing patterns in a period ranging from a few weeks to a few months. Known strategies, such as increasing the severity of stress factors, for example, temperature, current, and taking measurements with particularly high precision, need care in application to achieve meaningful results. We observe that this challenge does not receive enough attention in typical ageing studies. Therefore, this review introduces the definition and challenge of accelerated ageing along existing methods to accelerate the characterisation of battery ageing and lifetime modelling. We systematically discuss approaches along the existing literature. In this context, several test conditions and feasible acceleration strategies are highlighted, and the underlying modelling and statistical perspective is provided. This makes the review valuable for all who set up ageing tests, interpret ageing data, or rely on ageing data to predict battery lifetime.
... Furthermore, a high SOC decreases the potential of the negative electrode that is highly lithiated, allowing for a thermodynamic process where lithium is deposited on the electrode instead of being intercalated during charging. To avoid this problem and to prevent the negative electrode from being fully lithiated, battery manufacturers design this electrode with 10% of the positive-electrode capacity [226,233]. In addition to the SOC, the temperature also influences the batteries' degradation; once the high temperature increases, the SEI solubility can create lithium crystals less permeable to Li + , which increases the negative electrode impedance [226,233]. ...
... To avoid this problem and to prevent the negative electrode from being fully lithiated, battery manufacturers design this electrode with 10% of the positive-electrode capacity [226,233]. In addition to the SOC, the temperature also influences the batteries' degradation; once the high temperature increases, the SEI solubility can create lithium crystals less permeable to Li + , which increases the negative electrode impedance [226,233]. ...
Article
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Lithium-Ion Batteries (LIBs) usually present several degradation processes, which include their complex Solid-Electrolyte Interphase (SEI) formation process, which can result in mechanical, thermal, and chemical failures. The SEI layer is a protective layer that forms on the anode surface. The SEI layer allows the movement of lithium ions while blocking electrons, which is necessary to prevent short circuits in the battery and ensure safe operation. However, the SEI formation mechanisms reduce battery capacity and power as they consume electrolyte species, resulting in irreversible material loss. Furthermore, it is important to understand the degradation reactions of the LIBs used in Electric Vehicles (EVs), aiming to establish the battery lifespan, predict and minimise material losses, and establish an adequate time for replacement. Moreover, LIBs applied in EVs suffer from two main categories of degradation, which are, specifically, calendar degradation and cycling degradation. There are several studies about battery degradation available in the literature, including different degradation phenomena, but the degradation mechanisms of large-format LIBs have rarely been investigated. Therefore, this review aims to present a systematic review of the existing literature about LIB degradation, providing insight into the complex parameters that affect battery degradation mechanisms. Furthermore, this review has investigated the influence of time, C-rate, depth of discharge, working voltage window, thermal and mechanical stresses, and side reactions in the degradation of LIBs.
... [17] Consequently, fewer Li + ions were embedded in the electrodes than those extracted during the charge-discharge process. [18] Figure S4 (Supporting Information) displayed the cycling performance of the electrodes with different pre-lithiation time. When the pre-lithiation time did not exceed 5 min, the specific capacity increased as the pre-lithiation time increased. ...
Article
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The hard carbon (HC) anode materials demonstrate high capacity and excellent rate performance in lithium‐ion batteries. However, HC anodes suffer from excessive loss of Li⁺ ions during the formation of the solid electrolyte interphase (SEI) film, leading to poor cycling stability, which hinders their large‐scale applications. Herein, a facile pre‐lithiation strategy is proposed to achieve multi‐functional precompensation of carbon nanofibers (CNFs) anodes. Both experimental and density functional theory (DFT) calculation results revealed that the strategy compensated for the loss of Li⁺ ions and reacted with four structures of CNFs during pre‐lithiation, including tiny graphite domains, CO‐containing functional groups, defects, and micropores. Furthermore, the lithium in pre‐lithiated carbon nanofibers (pCNFs) existed in various forms, consisting of LiC24 and LiC18, Li─O─C, quasi‐metallic lithium, and Li⁺ ions. Moreover, the uniformly distributed lithium on the surface of pCNFs induced the formation of denser and more robust LiF/Li2CO3‐rich SEI film, which promoted Li⁺ ions transport. As a result, pCNFs showed more stable cycling performance (369.8 mAh g⁻¹, almost no decay for 1500 cycles). This work provides deeper insight into chemical pre‐lithiation and offers a simple and mild strategy for highly stable batteries.
... 4 The causes, mechanism, and mitigation strategies of Li plating are being intensively studied in order to address this important safety concern. 5,6 The thermodynamic condition for Li nucleation occurs when the graphite anode is at a lower voltage with respect to a standard Li metal reference electrode. 7,8 Nucleation is defined here and elsewhere as the first step in the conversion of a metastable phase into a stable form, e.g. the formation of dendritic crystals of snow during supercooling of water vapour. ...
Article
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Li plating on the anode is a side reaction in Li-ion batteries which competes with Li intercalation and leads to loss of capacity. Growth of Li clusters into dendrites is...
... Especially under the aspect of increasing volumetric energy densities, higher specific capacities, and new material generations, not only thermal and electrochemical but also mechanical interrelationships have to be considered [2]. Mechanical effects include reversible electrode expansion due to lithiation [3][4][5] or alloying processes [6,7], SEI (solid electrolyte interface) formation [8], Li-plating [9,10], and gas generation due to side reactions [11,12]. All mechanisms depend on the electrode materials used. ...
... This again underlines the detrimental effect of undissipated gas regarding enhanced lithium plating. Although, it is regularly reported in the literature that higher temperature improves (dis)charge kinetics and reduces the probability for lithium plating, 48,49 the detrimental effect of the undissipated gas overcompensates the positive effects of the higher temperature and favours lithium plating. 36,50 However, a negative effect of compression is visible for the cells cycled at 60°C. ...
Article
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Pressure is often applied to improve the performance of lithium ion batteries (LIBs) during cyclic aging. However, the reasons for the performance impact of compression is still unclear. For this, LiNi0.8Mn0.1Co0.1O2 (NMC811) based LIB pouch cells with graphite based and SiOx based negative electrodes were used. Further, the electrolyte composition was varied between vinylene carbonate (VC) -containing and VC-free electrolytes. The cells were cyclic aged at 20 or 60 °C under three different conditions: without compression, compression (∼1.9 bar) only during formation and compression during formation and cyclic aging. Compression during formation increased obtainable capacity and decreased capacity loss, if gassing was present. However, no additional long-term effect of cells where pressure was applied during formation was observed during cyclic aging without compression at 20 and 60 °C. Compression during cyclic aging increased the obtainable capacity, when the cells were gassing during cycling as at 60 °C. Otherwise, if the cells were not gassing, as at 20 °C, no further effect of compression was observed during cycling. The results highlight that pressure only had a beneficial effect if cells were gassing.
... 10,31,[49][50][51][52][53] Additionally, lithium plating promoted by high C-rates is considered a major factor contributing to the Loss of Lithium Inventory (LLI). 54,55 The overpotential of the side reaction causing lithium plating at the negative electrode is expressed as ...
Article
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Safety and maintaining high performance are key considerations during the operation of lithium-ion batteries. Battery degradation, in particular lithium plating and loss of active material, is often accelerated by fast charging. This study explores a strategy for the design of fast charging protocols that takes into account the influence of the variability between battery cells on factors that can impact degradation. We employ a non-intrusive polynomial chaos expansion to identify the key parameters for each degradation condition. We explore the reduction of battery degradation by adjusting constraints such as the maximum C-rate and voltage. Tight control of the key adjustable parameters contributes significantly to reducing the confidence interval of the degradation factors, allowing reduced charging time with minimal degradation. The application of our approach to two state-dependent fast charging protocols for a LiC6/LiCoO2 battery indicates the value in explicitly accounting for uncertainties when designing charging protocols that minimize degradation.
... Thus, lithium deposition is partially reversible, occurring in LIBs with different cathode materials (NCM [115], LCO [117], LFP [120]). The occurrence of lithium deposition is determined by the interplay of charging rate, temperature, and State of Charge (SOC), with lower temperatures, higher rates, and higher SOCs more prone to promoting lithium deposition [121]. Even under relatively mild conditions, lithium deposition may occur, due to factors such as reduced anode porosity and weakened ion transport caused by SEI growth [122]. ...
Article
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As the low-carbon economy continues to advance, New Energy Vehicles (NEVs) have risen to prominence in the automotive industry. The design and utilization of lithium-ion batteries (LIBs), which are core component of NEVs, are directly related to the safety and range performance of electric vehicles. The requirements for a refined design of lithium-ion battery electrode structures and the intelligent adjustment of charging modes have attracted extensive research from both academia and industry. LIB models can be divided into mechanism-based models and data-driven models; however, the distinctions and connections between these two kinds of models have not been systematically reviewed as yet. Therefore, this work provides an overview and perspectives on LIB modeling from both mechanism-based and data-driven perspectives. Meanwhile, the potential fusion modeling frameworks including mechanism information and a data-driven method are also summarized. An introduction to LIB modeling technologies is presented, along with the current challenges and opportunities. From the mechanism-based perspective of LIB structure design, we further explore how electrode morphology and aging-related side reactions impact battery performance. Furthermore, within the realm of battery operation, the utilization of data-driven models that leverage machine learning techniques to estimate battery health status is investigated. The bottlenecks for the design, state estimation, and operational optimization of LIBs and potential prospects for mechanism-data hybrid modeling are highlighted at the end. This work is expected to assist researchers and engineers in uncovering the potential value of mechanism information and operation data, thereby facilitating the intelligent transformation of the lithium-ion battery industry towards energy conservation and efficiency enhancement.
... [8] During the charge-discharge test, especially at high rates, Li + ions tend to accumulate on the surface and trigger lithium plating, which in turn affects the battery safety. [9] Therefore, excessive surface compaction not only affects the cycle life of the battery but also brings serious safety hazards. ...
Article
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The reduced surface porosity of highly compacted graphite anode after calendering is one of the major obstacles restraining the fast‐charging capability and low‐temperature adaptability of lithium‐ion batteries. In this work, through‐hole carbon spheres (THCS) synthesized by coaxial electrospinning and the following template sacrifice method are employed as a pore‐forming agent on graphite surfaces for the first time. The established gradient porosity architecture endows graphite anode with interconnected conductive networks and abundant Li⁺ transport channels. Therefore, the THCS pouch cell exhibits fast charging capability (charging efficiency of 49.2% at 5 C), superior cycling stability (96% capacity retention after 500 cycles at 1 C), and low‐temperature adaptability (high lithium plating resistance at −10 °C). By contrast, severe lithium‐plating behavior is observed in the blank pouch cell under the same testing conditions. It is believed that the facile and scalable gradient pore structure manufacturing technology will succeed in promoting the fast‐charging capability and low‐temperature adaptability of commercial Li‐ion batteries.
... [29][30][31][37][38][39][40][41] Importantly, however, the lithiation conditions utilized in this work are mild and therefore not conducive with Li plating on the surface of LiC6. 42,43 Interestingly, the appearance of the Li2C2 coincides with a change in color on the surface of LiC6 that is localized to the region exposed to the laser ( Figure 2b). As the laser power density is increased, there is an increase in the intensity of the Li2C2 peak relative to the other electrolyte peaks that occurs concurrently with an increase in the extent of discoloration on the surface of LiC6 ( Figure S4). ...
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Temperature is known to impact Li-ion battery performance and safety, however, understanding its effect on Li-ion batteries has largely been limited to uniform high or low temperatures. While the insights gathered from such research are important, much less information is available on the effects of non-uniform temperatures which more accurately reflect the environments that Li-ion batteries are exposed to in real world applications. In this paper, we characterize the impact of a microscale, temperature hotspot on a Li-ion battery using a combination of in situ micro-Raman spectroscopy, in situ optical microscopy and COMSOL Multiphysics thermal simulations. Our results show that mild temperature heterogeneity induced by the micro-Raman laser can cause lithium to locally leach out from different lithiated graphite phases (LiC6 and LiC12) in the absence of an applied current. The Li metal is found to be largely localized to the region heated by the micro-Raman laser and is not observed upon uniform heating to comparable temperatures suggesting that temperature heterogeneity is uniquely responsible for causing Li to leach out from lithiated graphite phases. A mechanism whereby localized temperature heterogeneity induced by the laser induces heterogeneity in the degree of lithiation across the graphite anode is proposed to explain the localized Li leaching. This study highlights the sensitivity of lithiated graphite phases to minor temperature heterogeneity in the absence of an applied current.
... Given that the capacity loss caused by both "dead" Li and organic SEI does not exhibit linearity with increasing charging intervals, we believe that the morphology of plated Li in stage III is dendritic, whereas in stage II is nuclei, which is based on the differences in reversibility and specific surface area between Li nuclei and Li dendrites. [8,24,26] ...
Article
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Li plating is widely known as the key factor leading to degradation and safety issues in lithium‐ion batteries (LIBs). Herein, the feasibility of monitoring the onset and progression of Li plating is proposed and justified in the graphite/LiFePO4 pouch cell by an operando impedance‐thickness combinational technique. First, as a proof‐of‐concept, the real‐time thickness/impedance variations of LIBs during charging at low temperature (≈0 °C) are obtained and dissected. Three distinct stages corresponding to different Li plating patterns are observed with the critical changing points of charge‐transfer resistance, which match well with the counterpoints in the differential thickness/capacity curves. Post‐mortem analysis by Mass Titration and Scanning Microscopy also indicate that these stages are Li intercalation, Li nucleation & nuclei growth, and Li dendrite growth, respectively. Thereafter, different cycling protocols are proposed and carried out to test the as‐mentioned Li plating processes by this novel technique. The results disclose that the extensive deposition of metallic Li significantly intensifies the loss of Li inventory, leading to cell aging or even a “capacity plunge”, and depict a safer boundary plot about preventing the occurrence of “Li plating” region. This work provides new insights on Li plating behavior and battery safety control under harsh operational conditions.
... Apart from SEI growth and its effect on cell performance, none of the formation variations in Figure 4a shows an anode potential notably below 0 V vs. Li/Li + , avoiding safety-critical lithium plating. [71] However, a recent study found that small amounts of plated lithium during formation have no significant effect on thermal cell safety and capacity retention during cycling. [72] Eventually, this provides headroom for a further reduction of formation time, e. g., via a model-based fast charge optimization. ...
Article
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The formation process of lithium‐ion batteries commonly uses low current densities, which is time‐consuming and costly. Experimental studies have already shown that slow formation may neither be necessary nor beneficial for cell lifetime and performance. This work combines an experimental formation variation with physicochemical cell and solid electrolyte interphase (SEI) modeling to reveal formation‐induced changes within the cells. Formation at C/2 without full discharge compared to a standard C/10 formation at 20 °C notably improves the discharge and charge capacities at 2C by up to 41 % and 63 %, respectively, while reducing the formation time by over 80 %. Model‐based cell diagnostics reveal that these performance gains are driven by improved transport in the anode electrolyte phase, which is affected by SEI formation, and by enhanced transport on the cathode side. Hence, the focus on the dense SEI layer is insufficient for a comprehensive understanding and, ultimately, optimization of cell formation. All formation procedures were also tested at temperatures of 35 °C and 50 °C. Despite often surpassing the 2C discharge capacity of the standard formation at 20 °C, these cells showed comparable or lower 2C charge capacities. This suggests a pivotal role of local temperature in the formation of large‐format cells.
... 38,39 Graphite encounters sluggish lithiation kinetics at high current density, which results in a decrease of anode potential to values lower than 0.1 V versus Li/Li + ; this leads to the unwanted Li plating and formation of dendritic Li on the graphite surface ( Figure 2D). 40 Highly reactive Li deposits on the anode surface induce parasitic reactions for the electrolyte components, leading to rapid capacity deterioration. Lithium dendrites gradually grow upon repeated cycling and can reach the cathode through the separator pores; hence, the cell is at the risk of experiencing a short circuit. ...
Article
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Global trends toward green energy have empowered the extensive application of high‐performance energy storage systems. With the worldwide spread of electric vehicles (EVs), lithium‐ion batteries (LIBs) capable of fast‐charging have become increasingly important. Nonetheless, state‐of‐the‐art LIBs have failed to satisfy the demands of prospective customers, including rapid charging, extended cycle life, and high energy density. Addressing these challenges through innovations in material science and other advanced battery technologies is essential for meeting the growing demands of prospective customers. Besides the choice of active materials, electrolyte formulation has a significant impact on the fast‐charging performance and cycle life of LIBs over a wide range of temperatures. The liquid electrolyte is typically composed of lithium salts to provide an ion source, solvents to carry Li⁺ ions, and functional additives to build a stable solid electrolyte interphase (SEI). To enable the fast movement of Li⁺ ions, the liquid electrolytes should have low viscosity and high ionic conductivity. Meanwhile, SEI layers must be thin, uniform and ionically conductive. Furthermore, the low binding energy of the solvent facilitates desolvation of the solvation sheath, enabling fast Li⁺ ion transport to the anode during fast charging. This review provides the latest insights into rapid Li⁺ ion transport during fast charging, focusing on ensuring a deeper understanding of liquid electrolyte chemistry. The involvement of existing electrolyte mechanisms in materials discovery will develop electrolyte engineering techniques to improve the fast‐charging performance of batteries over a wide temperature range and will also facilitate the development of EV‐adoptable advanced electrodes. image
... For instance, the measurement of distinct electrode impedances enables the decoupling of various side reactions within the battery, thereby deeply unraveling the mechanisms underlying battery failure [94]. Additionally, monitoring the anodic potential through reference electrodes assists in detecting lithium plating and enhances charging capability, ensuring both the safety and durability of the battery [95]. ...
Article
With the significant and widespread application of lithium-ion batteries, there is a growing demand for improved performances of lithium-ion batteries. The intricate degradation throughout the whole lifecycle profoundly impacts the safety, durability, and reliability of lithium-ion batteries. To ensure the long-term, safe, and efficient operation of lithium-ion batteries in various fields, there is a pressing need for enhanced battery intelligence that can withstand extreme events. This work reviews the current status of intelligent battery technology from three perspectives: intelligent response, intelligent sensing, and intelligent management. The intelligent response of battery materials forms the foundation for battery stability, the intelligent sensing of multi-dimensional signals is essential for battery management, and the intelligent management ensures the long-term stable operation of lithium-ion batteries. The critical challenges encountered in the development of intelligent battery technology from each perspective are thoroughly analyzed, and potential solutions are proposed, aiming to facilitate the rapid development of intelligent battery technologies.
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Low temperatures seriously affect the performance of lithium-ion batteries. This study proposes a non-destructive low-temperature bidirectional pulse current (BPC) heating method. Different from existing heating approaches, this method not only optimizes heating frequency and amplitude but also considers the optimization of the charge/discharge pulse duration ratio. To optimize the BPC heating strategy, a precise electro-thermal coupled model is established, and a neural network is employed to delineate the relationship among model parameters, temperature, and state of charge (SOC). Additionally, the interplay between the impedance of the graphite anode and that of the full cell is analyzed by constructing a three-electrode battery. Then, a novel full-cell-oriented lithium plating criterion is introduced. Finally, based on the constructed electro-thermal coupled model, lithium plating criterion, and terminal voltage constraint, a novel non-destructive BPC heating method is proposed. The results show a significant improvement in heating efficiency compared to conventional BPC heating. Especially for high SOCs, the heating power is increased at least 8 times. When the battery SOC is below 40 %, the average heating rate from −10 °C to 10 °C is 11.28 °C/min. Even at 90 % SOC, the heating rate remains at 2.88 °C/min. Furthermore, the capacity and impedance of a battery at 50 % SOC exhibit no significant changes after 60 heating cycles using the optimal BPC heating strategy at 100 Hz. These findings show that the optimized method proposed in this study has high heating efficiency and no damage to the battery.
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Lithium deposition on anode surfaces can lead to fast capacity degradation and decreased safety properties of Li-ion cells. To avoid the critical aging mechanism of lithium deposition, its detection is essential. We present workflows for the efficient detection of Li deposition on electrode and cell level. The workflows are based on a variety of complementary advanced physico-chemical methods which were validated against each other for both graphite and graphite/Si electrodes: Electrochemical analysis, scanning electron microscopy, glow discharge-optical emission spectroscopy and neutron depth profiling, ex situ optical microscopy, in situ optical microscopy of cross-sectioned full cells, measurements in 3-electrode full cells, as well as 3D microstructurally resolved simulations. General considerations for workflows for analysis of battery cells and materials are discussed. The efficiency can be increased by parallel or serial execution of methods, stop criteria, and design of experiments planning. An important point in case of investigation of Li depositions are rest times during which Li can re-intercalate into the anode or react with electrolyte. Three workflows are presented to solve the questions on the occurrence of lithium deposition in an aged cell, the positions of lithium deposition in a cell, and operating conditions which avoid lithium depositions in a cell.
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The measured heat flow of graphite/NMC lithium ion cells under charging conditions show a characteristic and easily identifiable signal at the onset of lithium plating on the graphite electrode. A marked decrease in heat flow signals the full lithiation of the graphite host. The origin of this signal is shown to arise from the combined effects of entropy and cell over potentials. This signal allows for an accurate measure of the maximum amount of lithium intercalation possible in the host. Metallic lithium deposition begins within 5–7 mAh/g after the heat flow begins to decrease. Two different types of graphite were examined; G25 and MCMB. The onset of lithium plating was detected at 336 mAh/g for the G25 graphite and 297 mAh/g for the MCMB graphite, yielding empirical formulas of Li0.888C6 and Li0.804C6, respectively. The effect of plated lithium on the electrode/electrolyte reactivity was also examined by precise measurement of the coulombic efficiency, parasitic thermal energy and cell capacity fade. These measurements then allowed for the calculation of the efficiency of lithium plating on the graphite surface: 0.98 and 0.97 for G25 and MCMB graphites, respectively.
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This paper deals with the occurrence of a graphite irreversible degradation mechanism in commercial Graphite (C) / lithium Nickel Manganese Cobalt oxide (NMC) lithium-ion batteries, challenging metallic lithium deposition as the major aging mechanism at low temperature cycling. In this study, commercial 16 Ah C/NMC Li-ion cells were aged during cycling at 5◦C at a rate of 1C between 2.7 V and 4.2 V (namely between 0 and 100% of state of charge (SOC), respectively), with significant performance fading after 50 cycles only, while up to 4000 cycles can be performed at 45◦C with the same commercial cells. The monitoring of the potential of each electrode during cycling has been performed through the successful introduction of lithium metal as reference electrode into the commercial cell. This technique demonstrated that it was more and more difficult to extract lithium ions from graphite particles to intercalate into the positive electrode as the number of cycles increased. Graphite electrodes remained unexpectedly lithiated after cells were dismantled in discharged state. A part of exchangeable lithium detected being trapped into the negative electrode as graphite intercalation compounds was observed with X-Ray Diffraction (XRD). Lithium-7 Nuclear Magnetic Resonance (⁷Li NMR) performed on graphite electrode led to the distinction between lithium intercalated into graphite, oxidized lithium in the Solid Electrolyte Interphase (SEI) and metallic lithium present in low amounts. Coupling Focused Ion Beam (FIB) / Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Photoelectron Spectrometry (XPS) techniques demonstrated the presence of an untypical layer composed of electrolyte degradation products, hindering graphite electrode pores, particularly concentrated in the regions corresponding to interparticle cavities where lithium was found enriched and trapped.
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Metallic lithium deposition is a typical aging mechanism observed in lithium-ion cells at low temperature and/or at high charge rate. Lithium dendrite growth not only leads to strong capacity fading, it also causes safety concerns such as short-circuits in the cell. In applications such as electric vehicles, the use of lithium-ion batteries combines discharging, long rest time and charging phases. It is foremost a matter of lifetime and safety from the perspective of the consumer or the investor. This study presents the post-mortem analyses of commercial 16 Ah Graphite/NMC (Nickel Manganese Cobalt layered oxide) Li-ion pouch cells. The cells were degraded by calendar aging at high temperature with or without periodic capacity tests. Unexpected local depositions of metallic lithium were confirmed on graphite electrodes by Nuclear Magnetic Resonance (NMR). Biphenyl, a monomer additive present in the liquid electrolyte, generates gas during its polymerization reaction occurring at high temperature and at high state of charge. As a result, dry-out areas are present between the electrodes leading to high impedance regions and no charge transfer between the electrodes. It is at the border of these areas that lithium metal is deposited.
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The contribution introduces a new theory explaining the capacity increase that is often observed in early stages of life of lithium-ion batteries. This reversible and SOC-depending capacity rise is explained by the passive electrode effect in this work. The theory assumes a slow, compensating flow of active lithium between the passive and the active part of the anode, where the passive part represents the geometric excess anode with respect to the cathode. The theory is validated using a systematic test of 50 cylindrical 8 Ah LiFePO4jGraphite battery cells analyzed during cyclic and calendaric aging. The cyclic aging has been performed symmetrically at 40 C cell temperature, varying current rates and DODs. The calendar aging is executed at three temperatures and up to four SOCs. The aging is dominated by capacity fade while the increase of internal resistance is hardly influenced. Surprisingly shallow cycling between 45 and 55% SOC shows stronger aging than aging at higher DOD and tests at 4 C exhibit less aging than aging at lower Crates. Aging mechanisms at 60 C seem to deviate from those at 40 C or lower. The data of this aging matrix is used for further destructive and non-destructive characterization in future contributions.
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During charging at low temperatures, metallic Lithium can be deposited on the surface of graphite anodes of Li-ion cells. This Li plating does not only lead to fast capacity fade, it can also impair the safety behavior. The present study observes the effect of rest periods between Li plating and subsequent accelerated rate calorimetry (ARC) tests. As an example, commercial 3.25 Ah 18650-type cells with graphite anodes and NCA cathodes are cycled at 0 °C to provoke Li plating. It is found that the rest period at 25 °C between Li plating and the ARC tests has a significant influence on the onset temperature of exothermic reactions (TSH), the onset temperature of thermal runaway (TTR), the maximum temperature, the self-heating rate, and on damage patterns of 18650 cells. The results are discussed in terms of chemical intercalation of Li plating into adjacent graphite particles during the rest period. The exponential increase of capacity recovery and TSH as a function of time suggest a reaction of 1st order for the relaxation process.
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Li[Ni0.42Mn0.42Co0.16]O2 (NMC442)/graphite pouch cells with an ethylene carbonate-containing or a fluorinated electrolyte were used to prepare charged electrodes for studies using “pouch bags”. Sealed pouch bags containing either lithiated graphite or delithiated NMC442 electrodes taken from pouch cells, and also “sister” pouch cells, were subjected to 500 h storage at elevated temperature. The electrodes recovered from the pouch bags and pouch cells after storage were studied using electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy while the gases generated were quantified using gas chromatography. The fluorinated electrolyte suppressed impedance growth of the positive electrode during storage but caused a large initial negative electrode impedance compared to the carbonate electrolyte. The solid electrolyte interface (SEI) formed by the fluorinated electrolyte at the graphite electrode hinders the consumption of CO2 generated at the delithiated NMC442 electrode, leading to more CO2 in pouch cells with fluorinated electrolyte than in cells with carbonate electrolyte. Hydrogen gas was only observed in pouch cells after storage and not in pouch bags which contained either a single negative electrode plus electrolyte or a single positive electrode plus electrolyte, suggesting the H2 results from a species created at one electrode which reacts at the other in a pouch cell.
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Degradation in lithium ion (Li-ion) battery cells is the result of a complex interplay of a host of different physical and chemical mechanisms. The measurable, physical effects of these degradation mechanisms on the cell can be summarised in terms of three degradation modes, namely loss of lithium inventory, loss of active positive electrode material and loss of active negative electrode material. The different degradation modes are assumed to have unique and measurable effects on the open circuit voltage (OCV) of Li-ion cells and electrodes. The presumptive nature and extent of these effects has so far been based on logical arguments rather than experimental proof. This work presents, for the first time, experimental evidence supporting the widely reported degradation modes by means of tests conducted on coin cells, engineered to include different, known amounts of lithium inventory and active electrode material. Moreover, the general theory behind the effects of degradation modes on the OCV of cells and electrodes is refined and a diagnostic algorithm is devised, which allows the identification and quantification of the nature and extent of each degradation mode in Li-ion cells at any point in their service lives, by fitting the cells' OCV.
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Electroplating was first reported in 1801 by a British scientist, William Cruickshank, who described his experiments of depositing dendritic metallic lead and copper on a surface in the Journal of Natural Philosophy, Chemistry and the Arts. He used Volta piles of zinc and silver with ammonia soaked paper in between the layers. By attaching a silver wire to the bottom layer of zinc and the other to the top layer of silver of the Volta pile, and then placing the ends into a lead acetate solution, he was able to produce, fine needles of a metallic material at the silver wire. Gold electroplating experienced a revival in the late 1940s as gold became widely used in electric circuits due to its high conductivity and excellent corrosion resistance. The toxic gold mercury fire gilding process was replaced by the toxic gold-cyanide electroplating process, which was fortunately replaced by the development of the gold electrolyte systems with sulfite or no excess cyanide, has made the plating process less toxic for the operators and the environment.
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Lithium-ion batteries (LIBs) are attractive candidates as power sources for various applications, such as electric vehicles and large-scale energy storage devices. However, safety and life issues are still great challenges for the practical applications of LIBs. Metallic lithium plating on the negative electrode under critical charging conditions accelerates performance degradation and poses safety hazards for LIBs. Therefore, anode lithium plating in LIBs has recently drawn increased attention. This article reviews the recent research and progress regarding anode lithium plating of LIBs. Firstly, the adverse effects of anode lithium plating on the electrochemical performance of LIBs are presented. Various in situ and ex situ techniques for characterizing and detecting anode lithium plating are then summarized. Also, this review discusses the influencing factors that induce anode lithium plating and approaches to mitigating or preventing anode lithium plating. Finally, remaining challenges and future developments related to anode lithium plating are proposed in the conclusion.
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Lithium ion (Li-ion) batteries provide low mass and energy dense solutions necessary for space exploration, but thermal related safety concerns impede the utilization of Li-ion technology for human applications. Experimental characterization of thermal runaway energy release with accelerated rate calorimetry supports safer thermal management systems. ‘Standard’ accelerated rate calorimetry setup provides means to measure the addition of energy exhibited through the body of a Li-ion cell. This study considers the total energy generated during thermal runaway as distributions between cell body and hot gases via inclusion of a unique secondary enclosure inside the calorimeter; this closed system not only contains the cell body and gaseous species, but also captures energy release associated with rapid heat transfer to the system unobserved by measurements taken on the cell body. Experiments include Boston Power Swing 5300, Samsung 18650-26F and MoliCel 18650-J Li-ion cells at varied states-of-charge. An inverse relationship between state-of-charge and onset temperature is observed. Energy contained in the cell body and gaseous species are successfully characterized; gaseous energy is minimal. Significant additional energy is measured with the heating of the secondary enclosure. Improved calorimeter apparatus including a secondary enclosure provides essential capability to measuring total energy release distributions during thermal runaway.
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Improvement of life-time is an important issue in the development of Li-ion batteries. Aging mechanisms limiting the life-time can efficiently be characterized by physico-chemical analysis of aged cells with a variety of complementary methods. This study reviews the state-of-the-art literature on Post-Mortem analysis of Li-ion cells, including disassembly methodology as well as physico-chemical characterization methods for battery materials. A detailed scheme for Post-Mortem analysis is deduced from literature, including pre-inspection, conditions and safe environment for disassembly of cells, as well as separation and post-processing of components. Special attention is paid to the characterization of aged materials including anodes, cathodes, separators, and electrolyte. More specifically, microscopy, chemical methods sensitive to electrode surfaces or to electrode bulk, and electrolyte analysis are reviewed in detail. The techniques are complemented by electrochemical measurements using reconstruction methods for electrodes built into half and full cells with reference electrode. The changes happening to the materials during aging as well as abilities of the reviewed analysis methods to observe them are critically discussed.
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Deposition of metallic Li is a severe aging mechanism in Lithium-ion cells. This study evaluates the influence of the main operating parameters leading to deposition of Li: temperature, charging C-rate, and end-of-charge voltage. Therefore both, graphite anodes and NMC cathodes from commercial 16Ah pouch cells are reconstructed into 3-electrode full cells. The position of the reference electrode between anode and cathode allows acquiring anode potentials vs. (Li/Li+). Extensive evaluations of data reveal critical combinations of operating parameters to avoid Li deposition. The results from the reconstructed 3-electrode cells are compared with independently performed aging tests of the original 16Ah cells.
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Second-life applications of automotive lithium-ion batteries are currently investigated for grid stabilization. Reutilization depends on reliable projections of the remaining useful life. However, reports on sudden degradation of lithium-ion-cells near 80% state of health challenge these extrapolations. Sudden degradation was demonstrated for different positive active materials. This work elucidates the cause of sudden degradation in detail. As part of a larger study on nonlinear degradation, in-depth analyses of cells with different residual capacities are performed. Sudden degradation of capacity is found to be triggered by the appearance of lithium plating confined to small characteristic areas, generated by heterogeneous compression. The resulting lithium loss rapidly alters the balancing of the electrodes, thus generating a self-amplifying circle of active material and lithium loss. Changes in impedance and open-circuit voltage are explained by the expansion of degraded patches. Destructive analysis reveals that sudden degradation is caused by the graphite electrode while the positive electrode is found unchanged except for delithiation caused by side reactions on the negative electrode. Our findings illustrate the importance of homogeneous compression of the electrode assembly and carbon electrode formulation. Finally, a quick test to evaluate the vulnerability of cell designs toward sudden degradation is proposed.
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Two procedures to introduce a lithium metal reference electrode into commercially manufactured lithium-ion pouch cells (Kokam SLPB 533459H4) are described and compared. By introducing a stable reference potential, the individual behavior of the positive and negative electrodes can be studied in operando under normal cycling. Unmodified cells and half-cells made from harvested electrode material were cycled under identical conditions to the modified cells to compare capacity degradation during cycling and thus validate each modification procedure for degradation testing. A configuration that did not affect the performance of the cell over 20 cycles was successfully developed.
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Multi-dimensional modeling is a powerful approach to get access to internal variables such as current density or temperature distribution. In thiswork, an effective coupling approach is developed to describe the behavior of amodified commercial LFP/graphite cell during discharge. The model is based on a geometrical decomposition of the cell's features followed by a re-assembly by means of a scaled volume averaging method (SVAM). Following this approach, mass and charge transport within the porous electrode and separator domain, charge transport within the current collector domain and heat transport within the cell domain can be described in detail whereby the effective coupling method allows for precise spatially resolved simulation results within minutes. Simulated cell voltage profiles and internal temperature agree well with measurements which are performed and discussed in Part I. By addressing local potentials and internal temperature the model is validated more precisely than by measuring surface temperature and terminal voltage only. Additionally, a study on current density distribution, internal temperature and local state of charge is performed.
Conference Paper
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The deposition of lithium on the surface of graphitic anodes in Lithium-ion batteries is a major concern about safety and lifetime of lithium-ion batteries. The deposition can be caused by high anodic overpotentials at low temperatures or exceeding a critical lithium ion concentration at the graphite particle surface. The prediction of the onset of lithium deposition by modelling is rather difficult because there are no reported values for the Li+ activity in the electrolyte or their changes during lithium ion insertion into graphite. Furthermore the modelling of the Li+ activity in the electrolyte is quite challenging because the needed parameters like the diffusion coefficient of Li+inside the particles depend strongly on the state of charge and the absolute value on the measuring method respectively the texture of the electrode coating [1]. The critical Li+ activity in the electrolyte in matters of a lithium deposition follows from the concentration dependency of the Li/Li+potential, which is described by the Nernst equation. In the present study, we take advantage of the concentration dependency and develop a 4-electrode cell design (Figure 1a), which allows to measure potential changes of the metallic lithium reference electrode of the standard three electrode setup. The potential shifts of the metallic lithium reference correlate directly with changes in the Li+ activity in the electrolyte. We studied the interaction of lithium transport and reaction kinetics in dependency of current density, temperature and active material of the anode and the cathode. The measurements indicate a direct correlation between changes in anodic and cathodic reaction kinetics and the Li+concentration in the electrolyte (Figure 1b). Based on the knowledge of the Li+activity and its variation, we were able to improve an operation strategy for Lithium-Ion batteries and match the cell components with each other in terms of avoiding lithium deposition.
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Application of Li-ion batteries for transportation not only requires long cycling life but also the preservation of the electrochemical performance during the resting period. For certain car usage this resting time could be predominant compared with the cycling activity and is referred to as calendar aging. To understand the aging mechanisms during calendar aging, an extensive post-mortem study was conducted on commercial 16 Ah NMC/graphite pouch cells stored at 5, 25, 45, and 60 °C. The post-mortem analyses were performed in parallel within three separate laboratories across Europe. They included visual inspection and structural and microstructural analysis along with a combination of analytical techniques to determine accurately the composition of positive (NMC) and negative (graphite) electrodes and the electrolyte. A direct correlation was established between the calendar-aging temperature and the degradation of the cells. The measurements revealed a severe deterioration phenomenon for the electrodes aged at 45 and 60 °C. These results are explained by the formation of a resistive interface on top of the negative electrodes due to a continuous and heterogeneous growth of a surface layer. Electrochemical impedance spectroscopy and electrochemical measurements confirm the resistance increase during cell degradation. At high temperatures, this occasionally leads to a Li deposition phenomenon. Nonetheless, we revealed that this degradation process does not affect the bulk structure of the materials but only the surface of the particles.
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In order to optimize the operating parameters of battery management systems for electric and hybrid vehicles, great interest has been shown in achieving the maximum permissible charging currents during recuperation, without causing a cell damage due to lithium plating, in relation to the temperature, charge quantity and state of charge. One method for determining these recuperation currents is measuring the cell thickness, where excessively high charging currents can be detected by an irreversible increase in thickness. It is not possible to measure particularly small charge quantities by employing mechanic dial indicators, which have a limited resolution of 1 μm. This is why we developed a measuring setup that has a resolution limit of less than 10 nm using a high-resolution contactless inductance sensor. Our results show that the permissible charging current I can be approximated in relation to the charge quantity x by a correlating function I=a/(x) which is compliant with the Arrhenius law. Small charge quantities therefore have an optimization potential for energy recovery during recuperation.
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This paper presents a numerical model used for analyzing heat propagation as a safety feature in a custom-made battery pack. The pack uses a novel technology consisting of an internal short circuit device implanted in a cell to trigger thermal runaway. The goal of the study is to investigate the importance of wrapping cylindrical battery cells (18650 type) in a thermally and electrically insulating mica sleeve, to fix the cells in a thermally conductive aluminum heat sink. By modeling the full-scale pack using a 2D model and coupling the thermal model with an electrochemical model, good agreement with a 3D model and experimental data was found (less than 6%). The 2D modeling approach also reduces the computation time considerably (from 11 h to 25 min) compared to using a 3D model. The results showed that the air trapped between the cell and the boreholes of the heat sink provides a good insulation which reduces the temperature of the adjacent cells during thermal runaway. At the same time, a highly conductive matrix dissipates the heat throughout its thermal mass, reducing the temperature even further. It was found that for designing a safe battery pack which mitigates thermal runaway propagation, a combination of small insulating layers wrapped around the cells, and a conductive heat sink is beneficial.
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A physics-based Li-ion battery (LIB) aging model accounting for both lithium plating and solid electrolyte interphase (SEI) growth is presented, and is applied to study the aging behavior of a cell undergoing prolonged cycling at moderate operating conditions. Cell aging is found to be linear in the early stage of cycling but highly nonlinear in the end with rapid capacity drop and resistance rise. The linear aging stage is found to be dominated by SEI growth, while the transition from linear to nonlinear aging is attributed to the sharp rise of lithium plating rate. Lithium plating starts to occur in a narrow portion of the anode near the separator after a certain number of cycles. The onset of lithium plating is attributed to the drop of anode porosity associated with SEI growth, which aggravates the local electrolyte potential gradient in the anode. The presence of lithium metal accelerates the porosity reduction, further promoting lithium plating. This positive feedback leads to exponential increase of lithium plating rate in the late stage of cycling, as well as local pore clogging near the anode/separator interface which in turn leads to a sharp resistance rise.
Article
Lithium plating is considered one of the most detrimental phenomenon in lithium ion batteries (LIBs), as it increases cell degradation and might lead to safety issues. Plating induced LIB failure presents a major concern for emerging applications in transportation and electrical energy storage. Hence, the necessity to operando monitor, detect and analyze lithium plating becomes critical for safe and reliable usage of LIB systems. Here, we report in situ lithium plating analyses for a commercial graphite||LiFePO4 cell cycled under dynamic stress test (DST) driving schedule. We designed a framework based on incremental capacity (IC) analysis and mechanistic model simulations to quantify degradation modes, relate their effects to lithium plating occurrence and assess cell degradation. The results show that lithium plating was induced by large loss of active material on the negative electrode that eventually led the electrode to over-lithiate. Moreover, when lithium plating emerged, we quantified that the loss of lithium inventory pace was increased by a factor of four. This study illustrates the benefits of the proposed framework to improve lithium plating analysis. It also discloses the symptoms of lithium plating formation, which prove valuable for novel, online strategies on early lithium plating detection.
Article
Lithium dendrite growth dynamics on Cu surface is first visualized through a versatile and facile experimental cell by in operando transmission X-ray microscopy (TXM). Galvanostatic plating and stripping cycle(s) are applied on each cell. Upon plating/stripping process at ~ 1 mA cm-2, mossy lithium was clearly found growing and shrinking on the Cu surface as the applying time increases. It is interesting to note that the aspect ratio (height/width) of deposited lithium has increased with charge passed during plating, indicating a faster growing from the base. In addition, the dendritic or mossy lithium have been also observed when various high current densities (25 mA cm-2, 12.5 mA cm-2 and 6.3 mA cm-2) were applied in different cycle, showing a severe dendritic lithium formation that could be induced by inhomogeneous current distribution. The clear structure of dead lithium is found after the cycling, which also shows a lower efficiency and higher hazard when applying a higher current density. This work explores TXM as a useful tool for in operando dynamic visualization and quantitative measurement of lithium dendrite which is difficult to achieve with ex situ measurements and other microscopy techniques. The understanding of growth mechanism from TXM can be beneficial for the development of safe lithium ion and lithium metal batteries.
Article
The aging behavior of commercially produced 18650-type Li-ion cells consisting of a lithium iron phosphate (LFP) based cathode and a graphite anode based on either mesocarbon microbeads (MCMB) or needle coke (NC) is studied by in situ neutron diffraction and standard electrochemical techniques. While the MCMB cells showed an excellent cycle life with only 8% relative capacity loss (i.e., referenced to the capacity after formation) after 4750 cycles and showed no capacity loss on storage for two years, the needle coke cells suffered a 23% relative capacity loss after cycling and a 11% loss after storage. Based on a combination of neutron diffraction and electrochemical characterization, it is shown that the entire capacity loss for both cell types is dominated by the loss of active lithium; no other aging mechanisms like structural degradation of anode or cathode active materials or deactivation of active material could be found, highlighting the high structural stability of the active material and the excellent quality of the investigated cells.
Article
The development of high-capacity rechargeable and safe metallic lithium negative electrodes for next-generation batteries requires an in-depth understanding of reasons for nonuniform lithium plating during lithium-metal battery charge. It drives the interest for the tools enabling efficient monitoring of electrochemical interfaces where lithium electrodeposition occurs. We report on a three-electrode electrochemical cell designed to track lithium electrodeposition from aprotic electrolytes by neutron reflectometry (NR) in the specular reflectivity mode. We performed a case study of Li plating from LiClO4 solution in propylene carbonate. The sensitivity was optimized by tuning the neutron scattering contrast for a given electrode material (Cu film) and the electrolyte, which was done employing a deuterated solvent. The analysis of the scattering length density (SLD) profiles derived from the modeling of the reflectivity data clearly demonstrated that the deposition of nm-thin Li layers above initially formed solid-electrolyte interphase (SEI) layer can be detected and their roughness, which is a characterizing parameter of electrodeposition nonuniformity, can be estimated. It makes NR a proper tool for further studies of “dendritic” lithium growth.
Article
Established safety of lithium ion batteries is key for the vast diversity of applications. The influence of aging on the thermal stability of individual cell components and complete cells is of particular interest. Commercial 18650-type lithium ion batteries based on LiNi0.5Co0.2Mn0.3O2/C are investigated after cycling at different temperatures. The variations in the electrochemical performance are mainly attributed to aging effects on the anode side considering the formation of an effective solid-electrolyte interphase (SEI) during cycling at 45 °C and a thick decomposition layer on the anode surface at 20 °C. The thermal stability of the anodes is investigated including the analysis of the evolving gases which confirmed the severe degradation of the electrolyte and active material during cycling at 20 °C. In addition, the presence of metallic lithium deposits could strongly affect the thermal stability. Thermal safety tests using quasi-adiabatic conditions show variations in the cells response to elevated temperatures according to the state-of-charge, i.e. a reduced reactivity in the discharged state. Furthermore, it is revealed that the onset of exothermic reactions correlates with the thermal stability of the SEI, while the thermal runaway is mainly attributed to the decomposition of the cathode and the subsequent reactions with the electrolyte.
Article
The understanding of the aging behavior of lithium ion batteries in automotive and energy storage applications is essential for the acceptance of the technology. Therefore, aging experiments were conducted on commercial 18650-type state-of-the-art cells to determine the influence of the temperature during electrochemical cycling on the aging behavior of the different cell components. The cells, based on Li(Ni0.5Co0.2Mn0.3)O2 (NCM532)/ graphite, were aged at 20 °C and 45 °C to different states of health. The electrochemical performance of the investigated cells shows remarkable differences depending on the cycling temperature. At contrast to the expected behavior, the cells cycled at 45°C show a better electrochemical performance over lifetime than the cells cycled at 20°C. Comprehensive post-mortem analyses revealed the main aging mechanisms, showing a complex interaction between electrodes and electrolyte. The main aging mechanisms of the cells cycled at 45 °C differ strongly at contrast to cells cycled at 20 °C. A strong correlation between the formed SEI, the electrolyte composition and the electrochemical performance over lifetime was observed.
Article
In this work, lithium plating is investigated by means of voltage relaxation and in situ neutron diffraction in commercial lithium-ion batteries. We can directly correlate the voltage curve after the lithium plating with the ongoing phase transformation from LiC12 to LiC6 according to the neutron diffraction data during the relaxation. Above a threshold current of C/2 at a temperature of −2 °C, lithium plating increases dramatically. The results indicate that the intercalation rate of deposited lithium seems to be constant, independent of the deposited amount. It can be observed that the amount of plating correlates with the charging rate, whereas a charging current of C/2 leads to a deposited amount of lithium of 5.5% of the charge capacity and a current of 1C to 9.0%.
Article
Using cyclic voltammetry (CV), in-situ scanning tunneling microscopy (STM) and electrochemical quartz crystal microbalance (EQCM) the initial stages of lithium deposition on Au(111) from a solution of lithium bis(trifluoromethylsulfonyl)imide in the commercially available ionic liquid 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPipTFSI) were investigated. We could identify three distinct cathodic peaks in the potential range from 0 to -2.5 V (vs. Pt quasi-reference electrode), corresponding to different lithium deposition modes. While in the potential region of the under-potential deposition (UPD) (-1.2 to -1.8 V) the growth of monoatomic high islands (300-370 pm) takes place, Li bulk deposition occurs at potentials <-2.3 V. Finally, the third peak at 0 V, which only appears after a previous bulk deposition, is connected to a strand-like growth of lithium at (111) terraces with a uniform orientation over the whole substrate. Interestingly, once reaching a step-edge, the one-dimensional growth continues into the electrolyte, indicating the initial stages of Li dendrite formation.
Article
Parallel connections can be found in many battery applications. Therefore, it is of high interest to understand how the current distributes within parallel battery cells. However, the number of publications on this topic is comparably low. Furthermore, the measurement set-ups are often not clearly defined in existing publications and it is likely that additional impedances distorted the measured current distributions. In this work, the principles of current distributions within parallel-connected battery cells are investigated theoretically, with an equivalent electric circuit model, and by measurements. A measurement set-up is developed that does not significantly influence the measurements, as proven by impedance spectroscopy. On this basis, two parameter scenarios are analyzed: the ΔR scenario stands for battery cells with differing impedances but similar capacities and the ΔC scenario for differing capacities and similar impedances. Out of 172 brand-new lithium-ion battery cells, pairs are built to practically represent the ΔR and ΔC scenarios. If a charging pulse is applied to the ΔR scenario, currents initially divide according to the current divider but equalize in constant current phases. The current divider has no effect on ΔC pairs but, as a rule of thumb for long-term loads, currents divide according to the battery cell capacities.
Article
Measuring the thickness change of lithium-ion cells is a reliable method to detectthe intercalation stages of the electrodes, thickness increase during cycling and lithium plating. In this study, we introduce an innovative method to measure the thickness change of a pouch cell at multiple positions during operation. Using this technique, we disclose a local overshoot in the thickness change during fast charging near the current collector tabs at 25 °C, which significantly increases at 17 °C and is not detectable at 40 °C. As the cells show a better cycling stability at higher temperatures, the observed overshoot in thickness increase can be attributed to a failure mechanism. Opening the cells after cycling revealed that the anode was covered by a thick surface layer, so the failure mechanism is estimated to be lithium plating.
Article
Durability and performance of Li-ion cells are impaired by undesirable side reactions, observed as capacity decrease and resistance increase during their usage. This degradation is caused by aging mechanisms on the material level including surface film formation, especially in the case of graphite-based anodes. The present study evaluates the applicability of glow discharge optical emission spectroscopy (GD-OES) as a powerful tool to study aging-induced film formation on graphite anodes of Li-ion cells, including deposition of metallic Li. The technique provides depth-resolved information on elemental distribution in the samples from the anode surface to the current collector (through-plane resolution). Additionally, conducting GD-OES depth profiling at different positions of an aged graphite anode reveals differences in surface film growth across the anode plane (in-plane resolution). After verification of the GD-OES method by well-established analytical techniques, aged anodes from commercial state-of-the-art Li-ion cells are analyzed. The results show through-plane and in-plane inhomogeneity in surface film growth: local island-like Li deposition is revealed for 16Ah pouch cells cycled at 45°C and high charging current density while a more homogeneous Li plating gradient is found for cycling 26650-type cells at -20°C.