Thomas Waldmann

Zentrum für Sonnenenergie und Wasserstoff-Forschung Baden-Württemberg · Accumulators Materials Research

It is known that both the material used in Li-ion battery cells, as well as their aging history and state of charge (SOC), strongly impact the safety of such cells. This study investigates the safety characteristics of new or aged 21700 cells containing silicon-graphite blend anodes together with Ni-rich NMC cathodes by accelerating rate calorimetr...

Competing effects of graphite and Si result in a complex temperature dependent performance and degradation of Li-ion batteries with Si-graphite composite anodes. This study examines the influence of varying the Si content (0 to 20.8 wt%) in Si-graphite composite anodes with consistent areal capacity and N/P ratio in full cells containing NMC622 cat...

This study presents a novel method for implementing internal temperature sensors in cylindrical lithium-ion batteries by laser ablation to enhance the understanding of thermal runaway (TR) behavior. Using commercial 21700 cells, Accelerating Rate Calorimetry (ARC) experiments were conducted at various states of charge. The results showed that inter...

In order to balance energy and power density of Li-ion batteries – and to ensure a long battery life – it is crucial to understand in detail how the composition and the microstructural design of the electrodes affects their capacity and kinetics. In our study we compare different commercial 21700 high-energy cells with very similar capacities (5 Ah...

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 co...

Li redistribution processes within Si-graphite composite (SiG) electrodes are analyzed using in situ and operando X-ray diffraction (XRD), ex situ light microscopy (LM), in situ optical microscopy of cross-sectioned full cells (CS-IOM), and 3D microstructure-resolved simulations of full cells. First, the lithiation behavior of graphite and SiG full...

Calendar aging of Li-ion batteries with Si/graphite electrodes was investigated within this study. A total of 121 single-layer pouch full cells with either graphite or Si/graphite (3.0 wt−%, 5.8 wt−% and 20.8 wt−% Si) anodes and NMC622 cathodes with the same N/P ratio were built on pilot-scale. Calendar aging was studied at SoC 30%, 60%, and 100%,...

The cycle life of Li-ion batteries is limited by aging on the material and electrode level. Prolonging the battery life helps increasing sustainability, reducing the dependency from critical raw materials, and safes costs. The first step in extending battery life is to understand the underlying degradation mechanisms. Post-Mortem analysis of commer...

Bending of electrodes in certain cell designs (cylindrical cells or flat wound jellyrolls) leads to curved electrodes (curvature κ). For double side-coated electrodes, this curvature leads to convex and concave sides of the coating. In this work, we describe the effect of curved electrodes on the microstructure and aging. From a simple elastic mode...

In this publication, different cell- and charging parameters (advanced fast-charging protocol, 21700 tab design, electrolyte composition) are changed in a systematic step-by-step approach to reduce charging time while keeping the anode and cathode cell chemistry and electrodes (graphite—NMC 622 full cell) unchanged. Preliminary tests were carried o...

Mixing graphite with Si particles in anodes of Li-ion batteries provides increased specific energy. In addition, higher Si contents lead to thinner anode coatings at constant areal capacity. In the present study, we systematically investigated the influence of the Si content on the susceptibility of Li plating on Si/graphite anodes. Si/graphite ano...

The safety of Li-ion batteries is the most critical of many important characteristics and must be carefully considered. However, depending on the aging conditions, safety of batteries can change drastically. We had recently introduced ARC-MS as a new tool for safety investigations, which is an updated accelerating rate calorimeter (ARC) combined wi...

Li metal deposition and internal short circuits (ISC) are directly observed in full cells using a cross-sectional in situ optical microscopy set-up. The cell chemistries under investigation are graphite/LFP and graphite/NMC 622. Direct observations are made on (i) lithiation gradients without Li metal deposition, (ii) Li metal deposition without IS...

We present an extensive analysis of Li-ion battery ageing via Arrhenius plots. The V-shaped Arrhenius plots show minima at an optimum temperature corresponding to the longest cycle-life. The V-shape of the Arrhenius plots signifies the crossover between the two dominating ageing mechanisms – solid electrolyte interphase (SEI) growth in the high tem...

A new semi-quantitative method based on Post-Mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling was developed to detect Li deposition on Si/graphite anodes. By means of the detected amounts of Li, Si and O in the GD-OES depth profiles, a corridor is determined, in which the minimum amount of Li deposition is found. Three d...

In Li-Ion batteries, the graphite anode undergoes chromatic changes from grey (unlithiated graphite) to blue (LiC 18 ) to red (LiC 12 ) to gold (LiC 6 ) during lithiation. ¹ When charged with high current rates, lithiation gradients are observable due to mass transport limitations within the anode. ² Due to high lithiation degrees at the surface, t...

The ageing rate and consequentially service life of mass-produced lithium-ion batteries depends on many external and internal factors. Some of the more important ones are the charge-discharge rate, ambient temperature, electrode thickness and state of health (SoH). This makes the estimation of the lifetime of battery cells very challenging and time...

Li‐ion cells of the industrially‐relevant 21700 format are investigated experimentally by systematic variation of their tab design. In order to observe effects of the tab design only, the cells were built on pilot‐scale using the same electrodes, electrolyte, and separator. Tabs were varied regarding (i) conventionally welded tabs, (ii) tabs made f...

In Lithium-ion batteries, the graphite anode mainly contributes to the dilatation of the battery. Under the light microscope a distinct chromatic change can be observed during lithiation and de-lithiation due to the formation of graphite intercalation compounds (graphite: grey; LiC18: blue; LiC12: red; LiC6: gold). Using a novel cross-sectional in-...

A new semi-quantitative method was developed to detect Li deposition on Si/graphite anodes. This method is based on Post-Mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling. Based on the contents of Si, Li, and O in the GD-OES depth profiles, we define a corridor, in which the minimum amount of metallic Li on the anode is l...

A new in situ optical microscopy set-up is introduced which allows direct observation of cross-sections of Li-ion full cells in combination with simultaneous recording of electrochemical data. The method is validated by comparison of electrochemical data from coin full cells. Color changes give insights into processes on the electrode and particle...

In addition to the costs, high energy density, and fast-charging capability, safety of Li-ion batteries is most important-even after long-term usage or abusive conditions. A new combination of Accelerating Rate Calorimetry (ARC) coupled with a mass spectrometer (MS) [1] to study commercial 18650-type Li-ion cells will be shown. This novel ARC-MS se...

Li-ion batteries show a minimum of their aging rate at a certain temperature. This minimum in the corresponding Arrhenius plot expresses the longest cycle life at a certain C-rate. By characterizing aging of laboratory-made pouch cells and commercial 21700 cells as a function of C-rate and ambient temperature, we confirm that this minimum indeed sh...

Aim Safety is one of the most important parameters that control the extent of use and spread of lithium-ion batteries (LIBs) worldwide. With the progressive development of LIBs in energy density, improving their safety is becoming necessary for EV applications. Developing an analytical tool for on-line gas detection during the thermal runaway of LI...

One of the main problems in LIBs is the capacity fading due to the volume expansion of electrodes, which causes particles cracking, contact loss, delamination from current collectors, and SEI destruction [1,2]. Silicon as a promising negative electrode for LIBs suffers from structural change during de-/lithiation resulting in up to 300% volume expa...

In addition to the costs, high energy density, and fast-charging capability, safety of Li-ion batteries is very important-even after long-term usage or abusive conditions. In this research, a new combination of Accelerating Rate Calorimetry (ARC) coupled with a mass spectrometer (MS) [1] to study commercial 18650-type Li-ion cells is developed. Thi...

Li-ion cells of the industrially-relevant formats PHEV1 (prismatic), multi-layer pouch, and 21700 (cylindrical) are directly compared by experiments for the first time. All three cell formats were reproducibly built on pilot-scale with the same anode (graphite), cathode (NMC622), separator, and electrolyte allowing a direct comparison. The main dif...

Fast charging is considered to be a key requirement for widespread economic success of electric vehicles. Current lithium‐ion batteries (LIBs) offer high energy density enabling sufficient driving range, but take considerably longer to recharge than traditional vehicles. Multiple properties of the applied anode, cathode, and electrolyte materials i...

Driven by the rise of the electric automotive industry, the Li-ion battery market is in strong expansion. This technology does not only fulfill the requirements of electric mobility, but is also found in most portable electric devices. Even though Li-ion batteries are known for their numerous advantages, they undergo serious performance degradation...

Li-ion cells of the industrially-relevant 21700 format were built on pilot-scale with tabs made from (a) the electrodes’ current collecting foils (Al and Cu, “foil tabs”) in comparison with (b) conventional tabs (Al and Ni) welded to the electrodes’ current collecting foils (“welded tabs”). Both cell types use the same anode (graphite), cathode (NM...

The Cover Feature illustrates the operando analysis of gas evolving from an 18650‐type Li‐ion cell after provoked venting. This measurement became possible by coupling of accelerated rate calorimetry (ARC) to cause venting and thermal runaway of Li‐ion cells intentionally and gas analysis by mass spectrometry (MS). The molecules in the evolved gas...

Li plating, meaning the deposition of metallic Lithium on the negative electrode is considered as one of the major degradation mechanisms in Li-Ion batteries. Therefore, understanding the processes which occur between metallic Lithium and state-of-the-art electrode materials, mainly Graphite, is important to improve the life-time of Li ion cells. L...

Nowadays, long charging times have become one of the main limitations to a greater worldwide spread of electric vehicles (EV). Enabling high C-rates charging is a promising approach to eliminate this problem and alleviate range anxiety. When a battery is charged at high currents, several factors have to be taken into account. Temperature is certain...

Besides high energy density, fast‐charging capability, and costs, safety of Li‐ion batteries is fundamentally important – even after long‐term usage or abusive conditions. In this paper, a new combination of accelerating rate calorimetry (ARC) coupled with a mass spectrometer (MS), as well as cell resistance and audio recording was applied to study...

Cu dissolution in Li-ion cells during over-discharge to 0 V was investigated by Post-Mortem analysis. Commercial 18650 type cells with graphite anode and NMC/LMO cathodes as well as pilot-scale pouch full cells with graphite/NMC chemistry with reference electrode were investigated. The effects of discharge time at 0 V in the range of 100 h to 1000...

The mechanism of the spontaneous intercalation of Li metal into graphite electrodes is highly relevant for aging mechanisms and pre-lithiation of Li-ion cells. In the present work, we introduce a method to investigate this mechanism via measuring the open-circuit-potential (OCP). Experiments without electrolyte, with organic solutions without and w...

A method based on glow discharge optical emission spectroscopy (GD‐OES) depth profiling is developed to detect copper deposition on graphite electrodes for the first time. Commercial 18650 cells with graphite anodes were subject to Cu dissolution by over‐discharge to 0 V. On a first approach, the depth profiles for Cu show significant differences f...

Li-ion cells of the classic 18650 format are directly compared with the new 21700 format regarding electrochemical, thermal, and geometrical properties. Both types of cells were reproducibly built on pilot scale with the same electrodes, separator, and electrolyte allowing a direct comparison for the first time. Internal temperature sensors give in...

Li plating is a severe and safety relevant aging mechanism which has to be avoided. A new 4-electrode operando pouch full cell, with two Li reference electrodes is developed. The voltage shifts between the two Li metal electrodes are correlating directly with changes in the Li+ activity a[Li+] in the electrolyte in front of the anode surface. We ta...

The addition of Si compounds to graphite anodes has become an attractive way of increasing the practical specific energies in Li‐ion cells. Previous studies involving Si/C anodes lacked direct insight into the processes occurring in full cells during low‐temperature operation. In this study, a powerful combination of operando neutron diffraction, e...

Due to their extreme volume expansion, Si/C-composites suffer from fracture or delamination and consequent capacity fading during the Li-ion cell operation. One approach to reduce the electrical contact loss and improve the performance is the application of mechanical pressure on the cell. Therefore, a comprehensive aging study of Si/C|NMC811 pouch...

Novel mobile and stationary applications require batteries with increasing energy density / specific energy, fast-charging capability, ¹ and long life-time – while maintaining a high safety level. However, there is a dearth of knowledge on the interactions between these parameters. Additionally, the data sheets of commercial cells contain usually o...

Si as active material has become a prominent candidate as anode material for high-energy Li-ion cells. Unfortunately, Si in Si/C anodes is hard to quantify by established methods, e.g. with ICP-OES no depth profile can be obtained and HF is needed for digestion. Here, we present a semi-quantitative depth profiling method based on glow discharge opt...

Addition of a certain amount of Si to state of the art graphite anodes has become the most prominent option to increase the energy density of Li-ion cells. However, the distribution of Si in the depth of Si/C anodes is difficult to measure with established methods. In this paper, we present a semi-quantitative depth profiling method based on glow d...

Si/C composite anodes are of great interest for increasing the energy density of Li-ion cells. We report the applicability of the glow discharge optical emission spectroscopy (GD-OES) technique to detect and quantify the Si distribution in Si/C composite anodes. The calibration was developed in the range of 0–100 wt.-% Si by lab coated samples, whi...

The standard format for cylindrical Li-ion cells is about to change from 18650-type cells (18mm diameter, 65mm height) to 21700-type cells (21mm diameter, 70mm height). We investigated the properties of five 18650 cells, three of the first commercially available 21700, and three types of the similar 20700 cells in detail. In particular, the (i) spe...

Lithium deposition on graphite anodes is an unwanted side reaction in lithium ion batteries, which significantly contributes to accelerated ageing of the cells. Lithium deposition is connected not only to a drastic decrease of lifetime , but also limits fast-charging capability and can cause severe safety issues due to increased exothermic reaction...

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 publicat...

Li-ion cells are used in a variety of mobile and stationary applications. Their use must be safe under all conditions, even for aged cells in second-life applications. In the present study, different aging mechanisms are taken into account for accelerating rate calorimetry (ARC) tests. 18650-type cells are cycled at 0◦C (Li plating expected) and at...

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...

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 combine...

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....

Commercialization of many Li-ion cell chemistries is hindered by undesirable processes occurring during usage of Li-ion batteries, limiting their lifetime. One such process is the development of temperature gradients, especially in large-format cells, leading to uneven utilization of electrode material.1 Such inhomogeneity could locally accelerate...

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 appli...

Commercialization of many Li-ion cell chemistries is hindered by undesirable processes occurring during usage of Li-ion batteries, limiting their lifetime. One such process is the development of temperature gradients, especially in large-format cells, leading to uneven utilization of electrode material. ¹ Such inhomogeneity could locally accelerate...

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 disa...

Due to the high chemical reactivity of metallic lithium, safety and life-time of Lithium-ion cells are closely related to the aging phenomenon of lithium plating [1–5]. Lithium plating on graphite anodes can occur during charging at low temperatures, high C-rates, and high states-of-charge [1,3,4]. However, lithium deposition depends also on the co...

Li-ion batteries are good candidates for electric vehicles and stationary applications due to their high power and energy densities. It is well known that the lifetime of lithium ion batteries is limited by undesirable side reactions. Moreover, these side reactions can affect different parts of the battery including the electrolyte, the active mate...