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Numerical Analysis of Distribution and Evolution of Reaction Current Density in Discharge Process of Lithium-Ion Power Battery

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The reaction current density is an important process parameter of lithium-ion battery, significantly influencing its electrochemical performance. In this study, aimed at the discharge process of lithium-ion power battery, an electrochemical-thermal model was established to analyze the distribution of the reaction current density at various parts of the cathode and its evolution with the time of discharge, and to probe into the causes of distribution and evolution. The investigation revealed that the electrochemical-thermal coupled model showed more accurate compared to the single electrochemical model, which was more obvious in high rate discharge. The results demonstrated that the conductivity of solid and liquid-phases was an important factor affecting the distribution of the reaction current density. Moreover, the uniformity of the distribution of the current density was related to the rate of utilization of the active materials in the electrodes. By optimizing the porosity and thickness of the electrode, not only the distribution of the current density was improved, but also the rate of utilization of the active materials in the electrodes and the energy density of batteries were significantly enhanced.
Journal of The Electrochemical Society,161 (8) E3021-E3027 (2014) E3021
0013-4651/2014/161(8)/E3021/7/$31.00 ©The Electrochemical Society
Numerical Analysis of Distribution and Evolution
of Reaction Current Density in Discharge Process
of Lithium-Ion Power Battery
Yiwei Tang, Ming Jia,zJie Li, Yanqing Lai, Yun Cheng, and Yexiang Liu
School of Metallurgy and Environment, Central South University, Changsha 410083, China
The reaction current density is an important process parameter of lithium-ion battery, significantly influencing its electrochemical
performance. In this study, aimed at the discharge process of lithium-ion power battery, an electrochemical-thermal model was
established to analyze the distribution of the reaction current density at various parts of the cathode and its evolution with the time
of discharge, and to probe into the causes of distribution and evolution. The investigation revealed that the electrochemical-thermal
coupled model showed more accurate compared to the single electrochemical model, which was more obvious in high rate discharge.
The results demonstrated that the conductivity of solid and liquid-phases was an important factor affecting the distribution of the
reaction current density. Moreover, the uniformity of the distribution of the current density was related to the rate of utilization of the
active materials in the electrodes. By optimizing the porosity and thickness of the electrode, not only the distribution of the current
density was improved, but also the rate of utilization of the active materials in the electrodes and the energy density of batteries were
significantly enhanced.
© 2014 The Electrochemical Society. [DOI: 10.1149/2.004408jes] All rights reserved.
Manuscript submitted January 21, 2014; revised manuscript received February 19, 2014. Published March 4, 2014. This paper is
part of the JES Focus Issue on Mathematical Modeling of Electrochemical Systems at Multiple Scales.
Lithium-ion battery is low maintenance with a series of advantages
such as high voltage, high energy density, long cycle life, and no
“memory effect”13; therefore, it has been extensively employed in
portable electronic products and become a preferred battery of choice
for electric vehicles and hybrid electric vehicles.4The study of Li-ion
battery is of significant scientific and technological interest. In recent
years, the new energy vehicle market has developed rapidly; thus, to
satisfy the needs for the Li-ion battery with higher single capacity and
specific energy, the battery manufacturers are encouraged to improve
their electrode design. Therefore, it is extremely important and urgent
to analyze in depth the dynamics of Li-ion power battery because it is
inevitably necessary to increase the battery power.
The research conducted on the Li-ion batteries is based on the ex-
perimental approach; thus, to gain insight into the characteristics of the
battery and to examine its performance, different experiments would
have to be performed. Operating mechanism of the battery can be well
understood by the visual data obtained from the experiments and by
summarizing the related criterion for electrode design by comparing
the effect of different electrode designs on the battery performance.
However, the Li-ion battery is a closed chemical system with complex
internal structure and components; therefore, it is difficult to acquire
directly the distribution of its internal physical quantities from the
experiments in real time, which significantly affects the understand-
ing for the battery operation. Instead, real time management of the
electrochemical process can be effectively studied by applying the
computer numerical simulation technology to establish mathematical
models on the basis of a strict electrode dynamics theory framework
and enormous amount of accumulated battery data. The mathematical
models across multiple scales were widely used in understanding and
describing behaviors of Li-ion battery,58it forms the core of sys-
tems engineering approach for the optimal design of Li-ion battery.9
Newman et al.1017 applied Butler–Volmer equation to describe the
electrochemical process occurring between the interface of electrode
and electrolyte based on the porous electrode theory. Fick’s law was
used to describe the intercalation and deintercalation of the Li-ions
inside the active-material particles, and the mass transfer process of
the Li-ion in electrolyte was described using concentrated solution
theory. Moreover, the changes in the concentration distribution, elec-
trochemical potential, and exchange current density of the battery at
various parts with time of discharge were obtained from the calcu-
lation. Wang18 et al. applied the abovementioned model to study the
distribution and changes in local reaction current density during the
discharge process and to probe into the relationship between the reac-
tion current density and electrode design. However, this study ignored
the effect of temperature on the electrochemical process revealing that
a large error could be produced by the increase in temperature due to
a high-powered discharge of the battery.9Incorporation of the energy
conservation in the electrochemical process would be helpful to im-
prove the accuracy of model.19 Smith20 et al. and Ye21 et al. utilized
the electrochemical-thermal coupled model to study the relationships
of the temperature with the electrochemical reaction, as well as with
the key parameters such as the diffusion coefficients of the solid and
liquid-phases, indicating that the influence of temperature change on
the electrochemical parameters could not be neglected; and verify-
ing the accuracy of the model via experimental method. The reaction
current density is an important parameter in the operating process
of the Li-ion battery and significantly influencing its electrochemical
performance. To analyze the dynamics during operation and to ac-
quire a deeper understanding of the battery, real-time and quantitive
analysis should be conducted to study the parameters and the factors
influencing them.
In allusion to the Li-ion power battery; this study established a
one-dimensional electrochemical-thermal coupled model capable of
investigating the distributionand evolution of the local reaction current
density during discharge process by considering anode as an example.
The model was useful in analyzing the causes of distribution and
evolution; thus, further providing guidance for the design of Li-ion
power battery.
Model Development and Experimental
Taking into account the coupling relationship between electro-
chemical reaction and heat, an electrochemical thermal coupling
model was established to investigate the electrochemical process of
lithium ion battery. The schematic of the battery modeled in this study
is shown in Fig. 1. The complete electrochemical system is composed
of five media, namely negative current collector, negative electrode,
separator, positive electrode and positive current collector. The active
materials of solid electrodes are treated as homogenous media, and
are comprised with spherical particles.
Electrochemical model.— The model developed in this paper con-
siders porous electrode theory, Ohm’s law, concentrated solution the-
ory, intercalation /deintercalation kinetics and transport in solid phase
and electrolyte phase. The main governing equations and boundary
conditions required in this model are as follows:
... A complete DT technology system is shown in Fig 1. Fig 1: Schematic diagram of digital twin technology [14] The data assurance layer is used to realize the functions of collection, transmission, and storage of physical entity operation data. Data is the basis of the entire DT technology system [26] . All functions in the model and the interaction between virtual and real models will be performed around data. ...
... Mastali et al. [25] established the electrochemical-thermal coupling model of a large lithiumion battery to simulate the three-dimensional distribution of electrochemical and thermal variables in the battery and verified the accuracy of the model through experiments. Tang et al. [26] established an electrochemistry-thermal coupling model for battery discharge. After studying the distribution of cathodic reaction current density and the evolution of reaction current density with discharge time, it was found that the electrochemistry-thermal coupling model has higher accuracy than the single electrochemical model, especially at high discharge rates. ...
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Scientific and reliable battery management systems (BMS) are the key to the safe and efficient application of lithium-ion battery energy storage systems. The traditional BMS has problems such as low computing resources and weak data processing ability, which makes the application of intelligent control algorithms and high simulation models limited. The digital twin (DT) technology characterized by the integration of information and physics has brought new opportunities for the development of BMSs. The creation of an intelligent BMS is accomplished through the creation of a DT that corresponds to the physical entities of the battery, virtual and real interactive feedback mechanisms, and data fusion. Systematically introduce the technical system and functions of the DT, including the data assurance layer, the modeling and calculation layer, the functional application layer, and the human-machine interaction layer. The key technologies, such as model modeling, data fusion, and mechanism model fusion, in the construction of battery DTs are analyzed. On this basis, the design framework of a lithium-ion BMS based on DT is clarified, with the goal of providing guidance and a reference for research into building an intelligent management system. 1. Introduction Under the background of "carbon peak, carbon neutral" green energy, energy storage systems have become a key link in building a new type of power system with new energy as the main body. The energy storage technologies can be divided into electrochemical energy storage, mechanical energy storage, and electromagnetic energy storage. Compared with other energy storage methods, electrochemical energy storage has the advantages of fast response, high conversion efficiency, a short construction period, and so on, making its application scale continue to expand [1]. Lithium-ion batteries have become the main technical route for electrochemical energy storage with the advantages of high energy density, long service life, and no memory effect [2]. Scientific and effective management of lithium-ion batteries is the premise for ensuring the safe and efficient use of the battery energy storage system and is also an important link to achieving low carbon. Because the traditional embedded lithium-ion battery management system has limited data processing capacity and computing resources and the complex management strategy and algorithm model cannot run on the BMS, it is still challenging to carry out scientific and effective management, operation, and maintenance of lithium batteries. The DT technology, characterized by the integration of information and physics, has attracted the attention of academic and industrial circles at home and abroad [3]. On the DT platform, the virtual model corresponding to the physical entity can be established, and the data such as the characteristics and performance of the physical entity can be described through the virtual model. The virtual model can also be used to predict the future development trend of the physical entity [4] , allowing for status monitoring, health diagnosis, future prediction, and performance optimization of the physical entity. NASA created the twin of the spacecraft in the Apollo program in 1969 [5]. The earth twin was placed to simulate and reflect the spacecraft's on-orbit working state in space, as well as the prediction and resolution of emergencies. With the continuous
... In other words, the effect of a spatially varying electrode composition is explored to ameliorate the otherwise inhomogeneous electochemical response of the LFP particles across the electrode thickness. [38][39][40][41][42][43] In general, it can be expected that grading will have greatest benefit in cases where the ionic and/or electrical transport of the electrode is most challenged i.e. relatively thick (>100 μm) electrodes with an active-rich (>90 wt%) formulation of intrinsic low conductivity (like LFP) materials, operating under high power requirements (>1 C). ...
... In terms of modelling, the LFP-based electrodes are described by a complex system of equation that capture charge and discharge hysteresis, 44,45 inhomogeneous electrode current distributions 38,39,44 and flat open-circuit-potentials. Because interpretation of model data solely from current/voltage data can be challenging, 46 we focus on validating the electrochemical model against more sensitive electrical impedance spectroscopy (EIS) data. ...
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Graded electrodes for Li-ion batteries aim to exploit controlled variations in local electrode microstructure to improve overall battery performance, including reduced degradation rates and increased capacity at high discharge rates. However, the mechanisms by which grading might deliver performance benefit, and under what conditions, are not yet fully understood. A Li-ion battery electrochemical model (a modified Doyle-Fuller-Newman type model capable of generating impedance functions) is developed in which local microstructural changes are captured in order to understand why and when graded electrodes can offer performance benefits. Model predictions are evaluated against experimental electrochemical impedance data obtained from electrodes with micro-scale, controlled variations in microstructure. A region locally enriched with carbon at the electrode/current collector interface is shown to significantly reduce the overpotential distribution across the thickness of a LiFePO$_4$-based Li-ion battery cathode, resulting in a lower charge transfer resistance and impedance. The insights gained from the LiFePO$_4$-based electrodes are generalised to wider design principles for both uniform and graded Li-ion battery electrodes.
... Using the electrochemical-thermal coupling model, many researchers have focused on the mechanism of heat generation inside the battery, including the variation of heat generation of different heat sources with charge-discharge depth, 14,15 the uneven distribution of overpotential and local current density, 16,17 the heat generation distribution inside the battery 18 and the heat generation at different conditions, 19,20 etc. Others focus on the influence of external heat transfer parameters, 18,21 battery shape, 22,23 and current collecting tab 24 on the thermal characteristics of the battery. ...
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This paper presents an electrochemical-thermal coupling model of 5Ah NCA-graphite pouch battery to analyze the heat generation mechanism. The simulation result indicates that the total heat generation increases with current and the polarization heat is dominant. The total heat generation of the negative electrode is higher than that of the positive electrode, while the electrochemical reaction heat and ohmic heat of the positive electrode are higher than those of the negative electrode. Ffour design parameters were selected, and their effects on electrochemical-thermal characteristics and the heat generation from different heat sources were analyzed in detail. The results indicate that the increase of capacity and decrease of discharge temperature can be achieved by decreasing the radius of positive/negative particles (Rp/Rn) and increasing the initial electrolyte concentration (cl,0) in a reasonable range. Rp and Rn are proportional to polarization heat and ohmic heat, Rp is proportional to electrochemical reaction heat and Rn is inversely proportional. cl,0 does not affect on electrochemical reaction heat, it is proportional to ohmic heat and inversely proportional to polarization heat. The sensitivity order of the design parameters is as follows: Rp > Rn > cl,0 > SEI film resistance (Rsei).
... Three of these four dimensionless ratios are involved in the effective conductivities of both the solid matrix and solution phase. Tang et al. [26] numerically investigated the various values of these effective conductivities. ...
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Reaction rate distribution across porous electrodes in Li-ion battery applications largely determines the overall battery performance. In the present work, expressions for the reaction rate distribution across porous electrodes are analytically derived and analyzed for small current and short time applications. The dependency on the effective ionic and electronic conductivities is systematically investigated and discussed. It is found that in the case of equal effective electronic and ionic conductivities, the reaction rate distribution is symmetric around the electrode mid-point. Small conductivities induce the charge-transfer reaction to preferentially occur at the interface of the current collector and separator, while high conductivities make the reaction rate distribution uniform across the electrode thickness. In the case of unequal conductivities, a decrease in the effective electronic conductivity shifts the reaction rate distribution towards the electrode/current collector interface. In contrast, a decrease in the effective ionic conductivity shifts the reaction rate distribution towards the electrode/separator interface. It is also found that the reaction rate distribution shows saturating behavior when the effective electronic or ionic conductivity grows infinitely. A further increase in the effective ionic or electronic conductivity does not lead to any further reaction rate distribution changes.
Battery modeling has become increasingly important with the intensive development of Li‐ion batteries (LIBs). The porous electrode model, relating battery performances to the internal physical and (electro)chemical processes, is one of the most adopted models in scientific research and engineering fields. Since Newman and coworkers’ first implementation in the 1990s, the porous electrode model has kept its general form. Soon after that, many publications have focused on the applications to LIBs. In this review, the applications of the porous electrode model to LIBs are systematically summarized and discussed. With this model, various internal battery properties have been studied, such as Li+ concentration and electric potential in the electrolyte and electrodes, reaction rate distribution, overpotential, and impedance. When coupled with thermal, mechanical, and aging models, the porous electrode model can simulate the temperature and stress distribution inside batteries and predict degradation during battery operation. With the help of state observers, the porous electrode model can monitor various battery states in real‐time for battery management systems. Even though the porous electrode models have multiple advantages, some challenges and limitations still have to be addressed. The present review also gives suggestions to overcome these limitations in future research. The present paper has systematically reviewed applications of porous electrode models to Li‐ion batteries (LIBs), including simulations of performance‐related characteristics, overpotential and impedance, temperature and stress distributions, battery degradation, online extraction of battery status, and other applications. With porous electrode modeling reviewed, the challenges and future developments have been stressed to broaden design perspectives and enhance LIBs performance.
Thermal management is of upmost importance for the safe and efficient operation of lithium-ion batteries in electric vehicles. To this purpose it is required to develop reliable thermal models to assess the behavior of the battery under different operating and ambient conditions. In this work, it is proposed a three-dimensional thermal model of the 40Ah LiFePO4/ graphite prismatic battery, which is a particular type of the lithium-ion battery (LIB), and it is analyzed the uncertainty related to the base data needed to run the model. The base data comprises, among others, the battery material physical properties and their dependence on the temperature, and the special “double-coated electrodes” structure. The charge and discharge processes of the 40Ah LiFePO4/ graphite prismatic battery are tested experimentally to verify the reliability of the thermal model. The deviation of the thermal model predictions caused by the uncertainty of the physical parameters of the battery is fully investigated numerically. The influence of physical parameters on the predictions is verified for the battery surface temperature and temperature difference between the battery interior and the surface. For the range of the properties tested the highest deviations of the predicted surface temperature and the inside and surface temperature difference are 0.14°C and 0.93°C during discharge at room temperature, respectively. Based on this investigation, it is proposed a simplified one-dimensional thermal model, which has the potential of being an expedite way of calculating the temperature distribution inside most commercial prismatic batteries. The comparison of the temperature distribution predictions using the three-dimensional thermal model and the simplified model indicates that the temperature gradient predictions obtained with the two models are in close agreement; the maximum relative difference of the two models is only 0.5%. The simplified thermal model, in what concerns the uncertainty of the physical properties, may provide an easy-to-use preliminary tool to evaluate the temperature distribution related to prismatic batteries.
Lithium ion battery is nowadays one of the most popular energy storage devices due to its high energy, power density and cycle life characteristics. It has been known that the overall performance of battery depends on not only electrolyte and electrode materials, but also operation condition and choice of physical parameters. Designers need to understand the thermodynamic and kinetic characteristics of battery, which is costly and time-consuming by experimental methods. However, lithium ion battery is a complicated electrochemical system with multi physicochemical processes including the mass, charge, and energy conservations as well as the electrochemical kinetics. It not only has a typical multiple level arrangement: across the electrode level, cell level, and extending to the battery module level, which is different from the basic active material particle level arrangement, but also confronts the challenges to meeting the requirements for sorting and consistency method for battery. These facts increase the difficulties in designing the battery and evaluating the overall performance. Owing to the rapid development of multi-scale numerical simulation technology, the multi-scale mathematical models for lithium ion battery are developed to help battery designer comprehensively and systematically gain the interaction mechanisms between different physicochemical fields in the battery working process and analyze the regulations of these interaction mechanisms, which is significant in providing theoretical supports for designing and optimizing the battery systems. At present, multi-type lithium ion battery models coupled with many physicochemical processes have been developed on different scales to study different issues, such as thermal behavior, inner polarization, micro structure, inner stress and capacitance fading, etc. In this paper, we review the research statuses and development trends of multi-scale mathematical models for lithium ion battery. The primary theoretical models for lithium ion battery are systemized and their features, application ranges and limitations are also summarized. Furthermore, the future research area and the difficulty in industry application are discussed. All of these are helpful for the theoretic research and engineering application of the multi-scale numerical models for lithium ion battery.
Understanding of the capacity fading for lithium-ion batteries will contribute to increasing the endurance of electric vehicles and avoiding rapid devaluation. Based on an electrochemical-thermal coupled model, a comprehensive physics-based cycle life model is developed for a LiFePO4 battery. The model takes the solid electrolyte interface (SEI) formation, Li plating and loss of active material (LAM) into consideration. The model can accurately predict the capacity fading of the battery under a wide range of operating temperatures and current rates (C-rates). The effects of C-rates and ambient temperatures on the capacity fading and the aging distribution inside a cell are extensively discussed. As the ambient temperature increases from -10 °C to 50 °C, the capacity fading decreases and then increases, and it can be divided into three stages. The LAM, both the LAM and SEI formation, and the SEI formation dominate the capacity fading in the first stage, the second stage and the third stage, respectively. The capacity fading in the second stage is the minimum and slightly affected by the ambient temperature. When the C-rate of cycles is 1 C, the ambient temperature range corresponding to the second stage is 20 °C ~ 30 °C. As the C-rate increases, the range will migrate to those with higher ambient temperature. When the charging C-rate increases from 4 C to 6 C, the aggravation of capacity fading is insignificant due to the fact that the charging rapidly changes into constant voltage charging. The Li plating primarily occurs in the region near to the separator, and restrains the SEI formation and the LAM in the region. The LAM in the region is more significant, which will be aggravated when the ambient temperature decreases or the C-rate increases.
Thermal management plays a vital role in ensuring that each single cell in the battery pack works within a reasonable temperature range while maintaining the temperature uniformity among the cells and battery modules in the pack as much as possible. In this study, an electrochemical–thermal model coupled to conjugate heat transfer and fluid dynamics simulations is utilized to accurately evaluate the thermal behavior of the battery pack. The effect of different cooling structures, the number of mini-channels, and the inlet mass flow rate on the temperature indexes of the battery pack are investigated by single-factor analysis method. Then, the simple and efficient orthogonal analysis and comprehensive analysis are used to obtain the optimal factor combination. Results show that the cooling structure design significantly affects the area where the highest temperature occurs in the battery pack. Meanwhile, case D can obviously improve the temperature indexes of the battery pack. The maximum temperature of the battery pack decreases as the number of mini-channels increases, but the downward trend decreases. On the basis of aforementioned work, the optimal combination can control the maximum temperature below 302 K and reduce the maximum temperature difference to 3.52 K. The research and optimization strategies in this paper can provide promising optimization solutions for battery thermal management systems.
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Capacity loss of a commercial graphite/LiFePO4 cell during either open-circuit-potential storage or under cycling conditions at 25 and 45 degrees C during one year is analyzed with the aid of postmortem analyses and simulations of the cell performance decay over the course of aging. An in-depth understanding of capacity-loss mechanisms under both storage and cycling conditions is gained by refining some parameters of a single-particle model of the cell at different extents of aging. The simulation-based analysis of the aging data reveals that the capacity fade during cell storage only results from the loss of cyclable lithium because of side reactions whereas the loss of graphite active material is an additional source of aging for the cells under cycling conditions. A simple kinetic analysis of electrode/electrolyte interactions is provided for the cells under storage conditions. Moreover, the growth of solid-electrolyte interphase (SEI) at the graphite electrode under storage conditions is simulated in order to refine the solvent-reduction kinetic parameters and solvent diffusion coefficient in the SEI layer. From the analysis, it is shown that the SEI growth during storage is under mixed kinetic/diffusion control. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.103112jes]
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This paper demonstrates the application of the coordinate-transformation approach developed elsewhere (Gomadam et al. J. Electrochem. Soc.. 150, A1339, 2003) in electrochemical-thermal modeling of spirally wound batteries. The approach presented here allows for easy adaptation of a two-dimensional electrochemical-thermal model of a plate-type cell (ie. a single rectangular anode-cathode couple) to a spirally-wound battery. Model predictions are presented and analyzed for situations when spiral heat conduction is important.
To understand the thermal effect of polymer Li-ion cells during the discharge process, an electrochemical thermal coupling model was established to investigate the thermal behavior of the cell. The average deviation and variance between the modeling results and the experimental data at 3C discharge rate were 0.57 K and 0.15, thus it was concluded that the modeling results agreed well with the experimental data. Also, the model is used to analyze the temperature distribution affected by discharge rate and cooling condition. The average heat production rate of the cells shows an increasing trend throughout the discharge process; it is increased significantly at both the beginning and the end of discharge. At a high discharge current, the irreversible heating which is proportional to the square of the current density, is the major heat generation source inside the battery. At a low discharge current, the heat production rate is dominated by reversible entropic heat. Improving cooling temperature could lower the average temperature during the discharge process. When the heat coefficient is 5 W/(m(2).K), the average temperature rises of the battery cells are 6.46 K, 17.67 K, 27.53 K for 1C, 3C, 5C discharge rates respectively. If the heat coefficient increases to 25 W/(m2.K), the average temperatures of the battery cells are reduced by 2.91 K, 4.68 K, 5.62 K for 1C, 3C, 5C discharge rates, respectively, but the inner temperature difference would be increased.
Dissolution of active material is one of the primary reasons for capacity fade in lithium-ion batteries, particularly at elevated temperatures. The effects of the volume fraction changes due to dissolution in both the active and inert material phases in composite Li-ion electrodes are investigated by a thermal-electrochemical coupled model. The study reveals that the changes in effective transport properties result in a reduction in the electrochemical reaction rate and an increase in the cell resistance, reducing capacity. The simulation results are also used to map the nature of the effects of dissolution of the active particles on the capacity decrease during cycling with different conditions, including temperature and voltage range. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3516619] All rights reserved.
An isothermal model for the electrochemical behavior of a commercial graphite/LiFePO4 cell at 25 and 45 degrees C is developed. Although it does not embed any special feature of the porous electrodes and of the two-phase process of the LiFePO4 electrode, proper account of the experimental charge/discharge (from C/10 to 1C) and path-dependence effects of the commercial cell is achieved. The LiFePO4 electrode is treated based on a resistive-reactant concept with multiple particles whereas a single-particle approach is used to model the graphite electrode. In order to refine the model parameters for each electrode, half cells are made either from the recovered LiFePO4 or graphite electrodes vs. a Li counterelectrode. A detailed experiment/simulation analysis of half-cell and complete-cell data unfolds the impact of uniaxial pressure on the galvanostatic charge/discharge limitation and path dependence of the LiFePO4 electrode in the coin cell and the commercial cell.
An electro-thermal cycle life model is developed by incorporating the dominant capacity fading mechanism to account for the capacity fading effect on the lithium ion battery performance. This model is comprehensively validated in three different aspects: (1) Electrochemical performance with different discharge C_rates (C/10, 1C, 3C) and different ambient temperature (0 °C, 25 °C, 45 °C, 60 °C); (2) battery surface temperature and center temperature during 6 C_rate constant current charge–constant voltage charge–constant current discharge (CC–CV–CC); (3) the amount of capacity fade indicated by the discharge potential curves of different cycle conditions. The feasibility of using the dominant factor only to represent the overall capacity fading in model is verified, and the model is used to predict OCV–SOC curves of cycled battery. To recover the capacity fade of cycled battery, either charging the negative electrode of fully discharged battery or charging the positive electrode of fully charged battery, could be an effective method, and possible capacity recovering design is presented. The decreasing trend of thermodynamic parameter Ea with increasing C_rate in the capacity fading function is deduced with increasing battery temperature when increasing discharge C_rate.
Local current density is an important parameter in battery modeling, which affects the performance of lithium-ion batteries. In this study, we take LiFePO4 cathode material as an example. A simplified mathematical model has been developed to study the internal mechanism of the electrode. According to the results of the model, the local current density distribution has a regular change at different time in the discharge process. The parameter “critical thickness” as an optimized variable has been presented for battery design. By qualitative analysis to estimate the critical thickness under different condition, we can optimize the design parameter of a battery according to the practical demand.