Electrochemical-thermal Coupling Model Research Articles

Active equalization control strategy of Li‐ion battery based on state of charge estimation of an electrochemical‐thermal coupling model

Aiming at solving the problem of poor battery cell consistency caused by excessive decay of cell capacity or increased internal resistance during the operation of lithium-ion battery packs for vehicles, the paper proposes an active equalization control with 12-V power supply as an equalization energy source, which achieves efficient energy replenishment of individual cells with low power. The electrochemical-thermal coupling model of lithium-ion battery is built, and the order reduction of large-scale system theory ensures that the model had higher accuracy and lower amount of calculation, which is suitable for vehicle battery management system (BMS). Then the extended Kalman filter algorithm is used to calculate the real-time state of charge (SOC) of each cell and set as an equalization variable. The equalization simulation circuit is built with MATLAB/Simulink, the experimental platform of active equalization system for battery packs is constructed, and the battery packs are tested for equalization in static state. The simulation and experimental results show that the proposed active equalization control strategy can rapidly improve the voltage inconsistency between single cells, and the energy transfer efficiency can reach about 85% during the equalization process.

Thermal safety study of Li‐ion batteries under limited overcharge abuse based on coupled electrochemical‐thermal model

Many fire accidents of electric vehicles were reported that happened during the charging process. In order to investigate the reasons that lead to this problem, this paper studies the thermal safety of Li-ion batteries under limited overcharge abuse. A 3D electrochemical-thermal coupled model is developed for modeling thermal and electrochemical characteristics from normal charge to early overcharge state. This model is validated by experiment at charge rates of 0.5C, 1C, and 2C. The simulation results indicate that irreversible heat contributes most to temperature rise during the normal charge process, but the heat induced by Mn dissolution and Li deposition gradually dominates heat generation in the early overcharge period. Based on this, a threshold selection method for multistage warning of batteries overcharge is proposed. Among them, level 1 should be considered as a critical stage during the early overcharge process due to the deposited lithium starts to react with electrolyte at the end of level 1, where temperature rate increases to 0.5°C min−1 for 1C charge. While the thresholds of levels depend on charge rate and composition of battery. Furthermore, several critical parameters are analyzed to figure out their effects on thermal safety. It is found that the temperature at the end of overcharge is significantly influenced by the change of positive electrode thickness and solid electrolyte interface (SEI) film resistance. The final temperature increases by 17.5°C and 7.9°C, respectively, with positive electrode thickness ranging from 50 to 80 μm and SEI film resistance increasing from 0.002 to 0.03 Ω.

Cathode Chemistries and Electrode Parameters Affecting the Fast Charging Performance of Li-Ion Batteries

Abstract Li-ion battery fast-charging technology plays an important role in popularizing electric vehicles (EV), which critically need a charging process that is as simple and quick as pumping fuel for conventional internal combustion engine vehicles. To ensure stable and safe fast charging of Li-ion battery, understanding the electrochemical and thermal behaviors of battery electrodes under high rate charges is crucial, since it provides insight into the limiting factors that restrict the battery from acquiring energy at high rates. In this work, charging simulations are performed on Li-ion batteries that use the LiCoO2 (LCO), LiMn2O4 (LMO), and LiFePO4 (LFP) as the cathodes. An electrochemical-thermal coupling model is first developed and experimentally validated on a 2.6Ah LCO based Li-ion battery and is then adjusted to study the LMO and LFP based batteries. LCO, LMO, and LFP based Li-ion batteries exhibited different thermal responses during charges due to their different entropy profiles, and results show that the entropy change of the LCO battery plays a positive role in alleviating its temperature rise during charges. Among the batteries, the LFP battery is difficult to be charged at high rates due to the charge transfer limitation caused by the low electrical conductivity of the LFP cathode, which, however, can be improved through doping or adding conductive additives. A parametric study is also performed by considering different electrode thicknesses and secondary particle sizes. It reveals that the concentration polarization at the electrode and particle levels can be weaken by using thin electrodes and small solid particles, respectively. These changes are helpful to mitigate the diffusion limitation and improve the performance of Li-ion batteries during high rate charges, but careful consideration should be taken when applying these changes since they can reduce the energy density of the batteries.

Novel investigation strategy for mini‐channel liquid‐cooled battery thermal management system

Many researchers have focused on liquid-cooled devices with simple structure and high efficiency, which promoted the gradual development of the mini-channel liquid-cooled plate battery thermal management system (BTMS), due to the advancement of liquid cooling technology. This paper has proposed an electrochemical-thermal coupling model to numerically predict the thermal behavior of the battery pack in different parameters of mini-channel cold plates and optimize the parameter combinations. The effects of cooling plate width, mini-channel interval, and inlet mass flow rate on the heat dissipation performance of the system were analyzed at a constant C-rate to provide a reliable experimental basis for the optimization model. Results indicate that increasing the cold plate width and the inlet mass flow rate reduce the temperature and temperature gradients. In addition, the minimum temperature difference is obtained at the mini-channel interval of 6 mm. The optimum cooling plate width (90 mm), mini-channel interval (4 mm), and inlet mass flow rate (80 g/s) are determined using the orthogonal test, analysis of variance, and comprehensive analysis of multi-index results. The addition of an auxiliary cooling system based on the optimized combination further reduces the maximum temperature and temperature difference of the battery pack by 4.9% and 9.2%, respectively. The developed strategy and methods can further improve the performance of the BTMS and provide a reference for the development of a compact battery pack at high discharge rates for engineering applications.

Effects of discharge rate on electrochemical and thermal characteristics of LiFePO4/graphite battery

The discharge rate has great influences on the electrochemical reaction rate and heat generation in lithium ion batteries. In order to simulate the discharge process and investigate the effects of discharge rate on electrochemical and thermal characteristic, a one-dimensional electrochemical-thermal coupled model has been developed for a prismatic LiFePO4 battery cell unit. The model is validated by experimental data for electrochemical and thermal performance. The electrochemical and thermal behaviors of the battery cell at different discharge rate are investigated in detail.The results show that the spatial and temporal distributions of the electrochemical reaction rate and the generated heat are non-uniform. The non-uniformity becomes aggravated at higher discharge rates. The averaged reaction heats in both positive and negative electrodes are mainly determined by the entropy change, while the averaged heat from polarization and ohmic heat across the cell unit have regular changes with time. Furthermore, the polarization heat is the main part of the total heat generation in a lithium-ion battery cell unit. With the increases of discharge rate, the polarization heat remains the main part of heat production, but its proportion decreases slightly, while the proportion of the ohmic heat increases.

SOC Oriented Electrochemical-Thermal Coupled Modeling for Lithium-Ion Battery

This paper proposes an electrochemical-thermal coupling model for state of charge (SOC) estimation of lithium-ion batteries (LIBs). In this paper, to solve two numerical problems in the quasi two-dimensional model of LIBs, a simplified one-dimensional model is built. Considering that the parameters in the model are affected by temperature, the internal parameters of the battery which obey the Arrhenius equation are introduced. Based on the simplified one-dimensional model, the electrochemical-thermal coupling model is built. Finally, an adaptive SOC observer based on electrochemical-thermal coupling model is designed. The simulation results show that the electrochemical-thermal coupling model can be effectively applied to SOC estimation.

The effect of electrode design parameters on battery performance and optimization of electrode thickness based on the electrochemical–thermal coupling model

Schematic of the lithium-ion battery and description of the P2D electrochemical model.

Mechanism of influence of separator microstructure on performance of lithium-ion battery based on electrochemical-thermal coupling model

Separator is an important component of lithium-ion battery,and the microstructure of separator has an important influence on the performance of lithium-ion battery.In the present paper,an electrochemical-thermal full coupling model is developed to accurately describe the complex physicalchemical phenomena in lithium-ion battery in charge and discharge process.The simulation results by the present model are closer to the experimental results than those by the previously published model.What is more,the present model is widely used to investigate the effects of the separator porosity and tortuosity on the performance of lithium-ion battery,respectively.The simulation results show that with separator porosity decreasing or separator tortuosity increasing,the output voltage,maximum discharge capacity and average output power of lithium-ion battery decrease,and the lithium-ion battery surface temperature and its rising rate increase.In the initial stage of discharge,when the separator porosity decreases or separator tortuosity increases to a certain degree,the output voltage of lithium-ion battery first decreases and then increases.The smaller the separator porosity or the higher the separator tortuosity,the larger the range and rate of reducing the output voltage of lithium-ion battery become and the longer the rise time needs in the initial stage of discharge.To ensure that the output voltage of lithium-ion battery is higher than the cut-off voltage,the separator tortuosity must be less than the critical tortuosity (It is equal to the separator tortuosity of the lithium-ion battery with the lowest output voltage,which is just equal to the cut-off voltage in the initial stage of discharge).Finally,a comprehensive analysis is conducted on the dynamic distribution of the electrochemical parameters and various heat productions in lithium-ion battery during charge and discharge.It can be clearly found that the electrochemical reactions in the end of discharge,the diffusion coefficients and the conduction coefficients of Li<sup>+</sup> of electrolyte in the initial and middle stage of discharge are mainly influenced by the separator porosity and tortuosity.The research results in the present paper not only provide theoretical and technical support for the separator microstructure design and optimization,but also has important realistic meanings for improving or perfecting the preparation technology of the separator.

Modeling the effect of two-stage fast charging protocol on thermal behavior and charging energy efficiency of lithium-ion batteries

Abstract To enable fast charging of lithium ion batteries, extensive attention is needed to reduce the heat generation rate to avoid thermal runaway. This work studies the impact of the fast charging protocol on thermal behavior and energy efficiency of a lithium ion battery cell for 30-minute charging with 80% rated capacity. A two-stage constant current (2SCC) charging protocol with different current level combinations is adopted to mitigate the temperature rise leading to thermal runaway and improve the charging energy efficiency, because different charging current will generate different rates of heat. An electrochemical thermal coupled model is developed to predict the heat generation rate, charging energy rate, and temperature rise with experimental validation. The simulation results indicate that the “high-low” charging protocols of the 2SCC fast charge can achieve a lower overall temperature rise and higher charging energy efficiency than both the “low-high” charging protocols and the standard one-stage constant current (1SCC) charging. Compared to the 1SCC charge, the 2SCC charging protocol can improve the overall charging energy efficiency by 1%. Additionally, the impact of the 2SCC charging protocol on the thermal behavior under different initial cell temperatures and the heat transfer coefficients are discussed.

Numerical modeling and analysis of thermal behavior and Li+ transport characteristic in lithium-ion battery

A lithium-ion battery is consist of numerous electrochemical cell units connected in parallel. The performance of lithium-ion battery is closely related to thermal and Li+ transport behavior in lithium-ion battery. It is essential to pay attention to the heat transfer and mass diffusion in the lithium-ion battery. The outside cooling condition and the geometrical structure will result in uneven thermal and electrochemical distribution on the cross section. A 2D (two-dimensional) electrochemical-thermal coupled model was developed for LiFePO4 battery to investigate the uneven thermal and electrochemical distribution. The potential distribution and electrochemical reaction rate were focused on both in spatial view and temporal view. The potential distribution both in cathode and anode, and the electrochemical reaction rate on the cross section showed an obvious non-uniformity in the spatial distribution. This non-uniformity was mainly determined by the geometrical structure of the battery. In the temporal view, non-uniformity index of current density was defined and presented a parabolic trend during the discharging process. Also, there was a heating effect of tab on the electrode material region of battery, due to the higher heat generation rate and lower heat capacity of tab during the discharge process. Discharging area on the tab directly determined and significant affected the current density and the temperature distribution on the tab respectively. In the design of battery cell and battery pack, the structure of tab and connecting method between batteries must be considered to avoid local higher current density or contact electric resistance and corresponding higher temperature region and to improve the performance of battery.

Numerical study on tab dimension optimization of lithium-ion battery from the thermal safety perspective

Tab is related to the safety of the whole battery, it is crucial to optimize the tab dimension to reduce the battery temperature and improve the safety performance. An electrochemical-thermal coupling model for an 18.5 Ah pouch cell is proposed and the model is validated with experimental data. Using this model, the temperature distribution is investigated at four discharge rates of 0.5 C, 1 C, 2 C and 4 C, respectively. It is found that heat will be accumulated at the positive tab at high discharge rate. Then the thermal behavior is analyzed with different tab dimensions for 4 C discharge rate to determine an optimized tab dimension. The results indicate that widening and thickening the tab appropriately can significantly reduce the battery temperature and lead to more uniform temperature distribution. Eventually the tab with thickness of 0.2 mm, width of 35 mm and height of 20 mm are selected as the optimized tab design for this battery. Afterwards, the heat generation mechanism and characteristics are discussed at the optimized tab dimension, which indicates that the irreversible heat, especially the positive irreversible heat occupies an increasingly dominant position in the total heat generation rate with the increase of the discharge rate.

Investigation on lithium-ion battery electrochemical and thermal characteristic based on electrochemical-thermal coupled model

A lithium-ion battery consists of numerous electrochemical cell units, and is treated as an assembly of one dimensional (1D) cell unit connected in parallel. The electrochemical and thermal characteristics of 1D cell unit have a great influence on battery performance. The thermal behavior and the dynamic evolution of electrochemical reaction in the cell are simulated. At lower discharge rate, reversible heat dominates the heat generation, but the proportion of irreversible heat gradually increases with the discharge rate. Non-uniform distribution of heat generation and electrochemical reaction rate in the cell increase with the discharge rate. Temperature has little effect on average heat generation rate and mainly influences the distribution uniformity of electrochemical reaction rate and heat generation in the cell. The temperature distribution in a battery is researched based on multi-cell 1D model. It is found that temperature in the battery presents a parabolic distribution in the laminated direction and the temperature gradient significantly increases with the cells number, which is mainly induced from the lower heat conductivity in the laminated direction. The bulk temperature will be decreased and safety of battery will be improved with the increase of cooling strength, but the temperature difference within the battery will be significant increased simultaneously. The number of cell can’t exceed 80 for a monomer battery with this electrode thickness and an active battery thermal management system (such as forced air cooling and liquid cooling system) is also indispensable to keep the temperature difference and surface temperature in the reasonable range at 5C discharge rate. At the same time, the thickness of the battery need to be chosen based on the application.

Study of the thermal properties during the cyclic process of lithium ion power batteries using the electrochemical-thermal coupling model

In this work, a soft pack (20 Ah LiFePO4/MCMB) lithium ion battery is used as a prototype to develop a mathematical model and carry out a numerical simulation of the thermal properties associated with the cyclic process of a lithium ion power battery. This model incorporates the solvent reduction reaction on the anode, which is thought to be a dominant aging mechanism. Capacity fade is based on the loss of active lithium ions due to solvent reduction reaction on the anode and on the rise of anode film. The variation of internal ohmic heat, electrochemical reaction heat, and polarization heat of the battery during the constant-current discharge and constant-current and constant-voltage charge, as well as its relationship with capacity fading during the cyclic process are analyzed quantitatively. The results show that when a lithium ion battery is charging and discharging at a conventional rate, polarization and electrochemical reactions are the main causes for heat production. Capacity fading during the charging and discharge process affects both the charging and discharging time of the battery. It also affects the charging state of the electrode at a certain moment of charging or discharging, which changes the thermal behavior of the battery.

Analysis on the Fault Features for Internal Short Circuit Detection Using an Electrochemical-Thermal Coupled Model

The potential of internal short circuit (ISC) increases due to the attempt to cram more active materials in a limited volume, when designing battery with higher energy density. Since the mechanism of ISC formation in lithium ion batteries is still unclear, it is essential to develop effective ISC detection algorithm. This paper provides an in-depth analysis on the fault features for ISC detection using a validated electrochemical-thermal coupled model. The modelling analysis unveils the fault features of ISC, and the difference of state-of-charge and the heat generation power are regarded as promising indicators for further development of fault diagnosis algorithms.

Numerical simulation of transport characteristics of Li-ion battery in different discharging modes

A three-dimensional electrochemical-thermal coupling model of LiFePO4 battery was developed based on the real multi-layer structure. The model was developed to describe the discharge process of the battery in four modes: the constant current, constant overpotential, constant voltage and maximum power discharge processes. The electric conductivity of the electrode, the electric conductivity of the current collector, the ionic conductivity of the electrolyte and the diffusion coefficient of the electrolyte were considered. The results show that: (1) In the constant current discharge mode, the core electrochemical reaction area of the positive electrode moved towards the separator while that of the negative electrode moved towards the current collector due to the change of the electrolyte concentration. (2) In the constant overpotential discharge process, the change of the average chemical reaction rate and the decreasing rate of the current density increased with increasing overpotential. (3) In the constant voltage discharge process, the current density and the temperature increased when the electrode thickness was increased. (4) In the maximum power discharge process, the output power increased with increasing electrode thickness but decreased with increasing contact resistance at the same current density.

A comprehensive study on Li-ion battery nail penetrations and the possible solutions

Li-ion batteries are the state-of-the-art power sources for portable electronics, electric vehicles, and aerospace applications. The safety issues regarding Li-ion batteries arouse particular attentions after several accidents reported in recent years. Among various abuse conditions, nail penetration is one of the most dangerous for Li-ion batteries due to the accumulated heat generation, which could give rise to the thermal runaway and could damage entire energy storage system. In this paper, an electrochemical-thermal coupling model is developed to study the nail penetration process of Li-ion batteries. By introducing joule heating at the nail location, the model shows good agreement with the testing results. With this verified model, a comprehensive parametric study is carried out to investigate the effects of battery capacity, internal resistance, and nail diameter on the electrochemical and thermal behaviors of Li-ion batteries during the penetration processes. Furthermore, three possible solutions to prevent the thermal runaway, which includes decreasing the state of charge, improving heat dissipation, and increasing contact resistance, are compared and discussed in detail based on a series of simulations.

A novel 3D-layered electrochemical-thermal coupled model strategy for the nail-penetration process simulation

Abstract The safety is one of the persisting concerns related with Lithium-ion (Li-ion) batteries, among which the internal short-circuit is the most dangerous abusive situation and has always been the root cause for several catastrophic accidents in recent years. In this work, a 3D-layered electrochemical-thermal coupled model is employed to investigate the nail-penetration process in a Li-ion cell. The model is based on multilayer construction of a cell, and an effective strategy to evaluate the short-circuit area equivalent resistance (i.e. the equivalent resistance of short-circuit area that is caused by nail-penetration) during the penetration process is proposed. The developed model is proved to have capability of estimating the thermal runaway time, as well as the temperature distribution during nail-penetration process. It is also found that the active material loss during the nail-penetration process can be reconstructed by utilizing the developed model, which could provide understandings about the side reactions inside the cell during the nail-penetration process. The present study provides some insights about the nail-penetration process, and can be treated as a useful tool that helps the design of Li-ion cells for improving safety.

Probing the Role of Electrode Microstructure in the Lithium-Ion Battery Thermal Behavior

Safety and performance of lithium-ion batteries over a wide temperature window are of paramount importance, especially for electric vehicles. The safety concerns are predicated on the thermal behavior as the occurrence of local temperature excursions may lead to thermal runaway. In this work, the role of electrode microstructure and implications on the cell thermal behavior are examined. A microstructure-aware electrochemical-thermal coupled model has been proposed, which delineates the electrode-level thermal complexations due to the structure-transport-electrochemistry interactions. Detailed analysis of the spatio-temporal variation of the heat generation rates (ohmic, reaction and reversible contributions) for different electrode microstructural configurations is presented to explain the dominant factors causing temperature rise. The tradeoff between the cell performance and safety is discussed from an electrode-level, bottom-up view point. This study aims to provide valuable insights into potentially tuning electrode-level structural features as an internal safety switch toward limiting the Li-ion cell temperature rise during operation.

Safe Lithium-Ion Batteries? Predicting Performance over a Range of Operating Conditions

Electrochemical-thermal coupled modelling of lithium-ion batteries is used to simulate battery performance. Modelling can be used to investigate the effects of different materials and design parameters on battery performance and safety. Numerous models exist for lithium-ion batteries1 from microscopic through to module scale simulations. Majority of these models simulate cell performance under normal charge and discharge operation. Generally these models do not accurately predict cell behaviour outside of normal conditions, such as at high temperatures. Operating lithium-ion cells at high temperatures can lead to an internal thermal event and ultimately cell failure. A number of models have been developed to simulate cell behaviour outside normal conditions however these models do not include the performance of cells during normal operation. A model that simulates cell performance over a range of conditions is necessary to make an informed decision regarding material and design changes. This work aims to combine two existing models to create a new model for simulation of cell performance under normal and high temperature conditions. Two existing models were chosen to create the new model. The models were selected to meet the following criteria: 1) single cell model 2) stacked plate configuration 3) individual component layers modelled (no homogeneous core assumption) 4) includes temperature dependent material properties (or able to be included). The first is a 1D electrochemical-thermal reduced order model developed by Gambhire et al.2 for simulation under normal charge and discharge operation. The second is a 1D electrochemical-thermal coupled model developed by Wang et al.3 for simulating internal thermal events including decomposition reactions for each cell component. Key aspects of both models have been used to create a new model implemented in COMSOL Multiphysics®. The new model is expected to more accurately describe cell behaviour over a range of conditions. The results of this study will be presented at the conference. Acknowledgments: The authors acknowledge the funding support provided by the ARC Research Training Centre for Naval Design and Manufacturing, PMB Defence Engineering, and the CSIRO Manufacturing High Performance Metal Industries Program.

Estimation of temperature distribution of LiFePO4 lithium ion battery during charge–discharge process

Thermal issues of lithium ion batteries are key factors affecting the safety, operational performance, life, and cost of the battery. An electrochemical–thermal coupling model based on thermoelectrochemical basic data was established to investigate the thermal behavior of LiFePO4 lithium ion battery. In this paper, the finite element method was used for simulation of temperature field distribution inside battery during charge–discharge process, and the influence of the charge–discharge rate and ambient temperature on the distribution of temperature field was summarized. The results showed that the highest temperature of battery was recorded at the junction of negative and separator during charge–discharge process. At a low discharge current, the modeling results agreed well with the experimental data. When the ambient temperature was 303.15 K, the maximum temperatures inside the battery were 304.60, 304.83, 306.55, and 309.96 K for 0.1, 0.2, 0.5, and 1.0 C charge–discharge rates, respectively. If the ambient temperature increased to 323.15 K, the maximum temperatures were increased by 24.96, 27.91, 33.18, and 32.59 K for 0.1, 0.2, 0.5, and 1.0 C charge–discharge rates, respectively, and the homogenous temperature field distribution inside the battery was worse.