Estimation of temperature distribution of LiFePO<Subscript>4</Subscript> 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.     

电动汽车锂离子电池热管理系统研究进展

锂离子电池作为电动汽车最广泛使用的动力源,对工作温度高度敏感,为保证其高性能和安全运行,电池热管理系统必不可少.本文综述了近年来锂离子电池热管理系统的研究进展.首先讨论了由高低温环境和电池温度不均匀引起的临界热问题.在此基础上,对设计原则和现有的电池热管理系统进行了广泛的介绍和阐述.然后进一步分析了用于未来电池热管理系统的热电器件和内部加热方法等新兴技术.分析表明,被动和主动冷却/加热方法的组合有望满足苛刻的热要求,特别是在功率波动剧烈的动态条件下.此外,电池在变工况下所输出的电流、电压等均不相同,因此建议对电动汽车动力电池进行动态性能实时管理,从而延长电池使用寿命。     

Preparation of Schiff base surfactant and its application in alkaline zinc-nickel batteries

A Schiff base surfactant 2-octanone ethylenediamine (OED) was in this study designed to improve the performance of alkaline zinc-nickel batteries that were synthesized and characterized by IR and XRD. Electrochemical experimental results showed that addition of OED surfactant in both zinc electrode and electrolyte effectively inhibited self-corrosion of zinc electrode and improved performance of zinc-nickel battery charge and discharge. The battery capacity can keep almost 70 % of the theoretical capacity after 30 times cycles. The batteries also showed better performance, lower resistance, and longer cycle life with addition of surfactant, which can be attributed to fact that the zinc electrode surface had good adsorption capacity and coordination with zinc ions in the presence of surfactant.     

A facile pyrolysis method to prepare vanadium oxides for high performance aqueous Zn-ion battery

Vanadium oxides, as one of the most promising cathode materials for zinc ion batteries, have attracted extensive attention in recent years. Different from the generally used hydrothermal and solvothermal methods to adjust the composition, structure, morphology and electrical properties of vanadium oxides, we firstly adopt a simple pyrolysis method to synthesize a series of vanadium oxides and use them as cathode materials for aqueous Zn-ion battery, whose electrochemical performances is superior to most state-of-the-art vanadium oxides. The as-obtained V₄O₇ under the calcination temperature of 700 °C exhibits excellent zinc ion storage performance with maximum specific capacity of 367.2 mAh g⁻¹ at the current density of 1 A g⁻¹, about 84.9% capacity retention after 100 cycles, excellent rate performance, high capacity. In addition, a series of structural and electrochemical characterization are used to reveal the possible mechanism of charge and discharge.     

Cycle-life and degradation mechanism of LiFePO<Subscript>4</Subscript>-based lithium-ion batteries at room and elevated temperatures

Cycle-life tests of commercial 22650-type olivine-type lithium iron phosphate (LiFePO₄)/graphite lithium-ion batteries were performed at room and elevated temperatures. A number of non-destructive electrochemical techniques, i.e., capacity recovery using a small current density, electrochemical impedance spectroscopy, and differential voltage and differential capacity analyses, were performed to deduce the degradation mechanism of these batteries. To further characterize their internal materials, we disassembled the batteries, and material analyses were performed. All results indicated that loss in active lithium was the main reason for battery aging, and the cells showed diverse recession of active materials at different temperatures. In addition, high discharge rate and growing impedance lead to a capacity fall down at 25 °C at approximately 300–500 cycles.     

基于电化学-热耦合模型研究隔膜孔隙结构对锂离子电池性能的影响机制

隔膜孔隙结构对锂离子电池性能具有重要的影响,本文提出了可准确描述充放电过程中锂离子电池内部复杂物理化学现象的电化学-热耦合模型,发现该模型较文献中模型的计算结果更接近实验测试数据.利用该模型探讨了隔膜孔隙率与扭曲率分别对锂离子电池性能的影响规律,发现减小孔隙率或增大扭曲率,电池输出电压、最大放电容量和平均输出功率均不断降低,电池表面温度和温升速度均不断升高;当孔隙率减小或扭曲率增大到一定程度时,放电初期电池输出电压均会出现先下降后回升的现象,且孔隙率越小或扭曲率越大,其下降的幅度越大、速度越快,回升所需时间也越长;要确保其不低于截止电压,隔膜扭曲率必须小于临界扭曲率(其下降至最低点刚好等于截止电压时的隔膜扭曲率).综合分析了放电过程中电池内部各电化学参量和产热量的动态分布规律,发现隔膜孔隙率和扭曲率主要影响放电末期电极膜片内部电化学反应以及其他放电时刻电解液中有效Li~+扩散(传导)系数.     

A study on capacity and power fading characteristics of Li(Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>)O<Subscript>2</Subscript>-based lithium-ion batteries

The objective of this study is to find out the factor that accounts for the capacity fading and to predict the cycle life of lithium-ion batteries by the driving cycle test. A new method, incremental polarization resistance, is elected to analyze the gradation mechanism based on incremental capacity analysis. It is summarized that the two major factors, the loss of lithium ions and the cathode fading, make the capacity loss in different stages. In the first stage, the loss of lithium ions, caused by the solid electrolyte interface (SEI) lay reaction, is the main reason for battery degradation. In the second stage, the cathode starts to decay and make the capacity loss, because of the less intercalation in cathode. In the third stage, the cathode degradation gradually outpaces the loss of Li and becomes the limit factor for the battery recession. Finally, a cycle life model was established to predict the capacity loss with cycle numbers.     

锂-亚硫酰氯电池储存寿命研究

锂-亚硫酰氯电池作为一种免维护、高比能、长储存寿命电池,目前已经在以国防领域为代表的国民经济中得到了广泛应用;其储存寿命的考核在行业内尚属难题;通过广泛、深入地调研和对前期锂-亚硫酰氯电池储存数据的收集整理,研究了锂-亚硫酰氯电池的储存寿命影响因素及其试验评估方法;通过研究得知,锂-亚硫酰氯电池的储存寿命试验应尽早备样,若时间紧迫可通过加速试验方法;提出了通过等效储存试验时间来评估电池储存寿命及其可靠度的方法,指出当等效储存试验时间不足时,应安排样本进行容量回归分析,得出其退化规律;此外,还要对电池储存末期热性能进行分析;在以上工作基础上对电池储存寿命进行综合评估;最后,通过案例分析,进行了工程演算;为后续锂-亚硫酰氯电池储存寿命评估提供了参考。     

Expanding the metrology of Coulombic efficiency using neutron depth profiling

The metrology of Coulombic efficiency (CE) is widely used for the qualification of rechargeable batteries particularly in assessing their state of health and the expected lifetime. The quantity of CE is conventionally defined as the ratio of the electric charge capacity in one round-trip cycle of discharge and charge of a battery. For better diagnosis of the health, failure and lifetime of rechargeable batteries, it is desirable to expand the traditional CE of the round-trip electric charge to including that of the round-trip CE of ionic charges as well as those of single trip CEs of ionic/electric charges for charging and electric/ionic charges for discharging. To enable such expansion, in operando ion metrology is needed. For the mainstream technology of lithium-containing batteries, neutron depth profiling is one of the techniques suited for Li ion metrology. In this report, we demonstrate the application of in situ neutron depth profiling to expanding the metrology of Coulombic efficiencies to include all four CEs. The methodology of expanded CE is exemplified using measurements and analyses on a model battery of LiFePO₄ vs. Li.     

Characteristics of hydrogen storage alloy electrode with cupric oxide additive

Cupric oxide was used as a novel additive for the hydrogen storage alloy electrode in nickel metal hydride batteries. The influence of the cupric oxide on the discharge storage capacity (DSP) of the hydrogen storage alloy electrode was studied and the electrochemical properties of the electrode were investigated. The cupric oxide was verified to reduce to copper in the first charge and stably existed on the alloy surface in the following cycles. And the hydrogen storage alloy electrode with cupric oxide exhibited better high rate discharge capability and longer cycle life compared with the blank one. The cupric oxide greatly decreases the weight and volume of the hydrogen storage alloy electrode, and make it better meet the requirement as power sources for electric and hybrid vehicles.     

A Novel Real-Time State-of-Health and State-of-Charge Co-Estimation Method for LiFePO_4 Battery

The state of charge(SOC) and state of health(SOH) are two of the most important parameters of Li-ion batteries in industrial production and in practical applications.The real-time estimation for these two parameters is crucial to realize a safe and reliable battery application.However,this is a great problem for LiFePO_4 batteries due to the large constant potential plateau in the charge/discharge process.Here we propose a combined SOC and SOH co-estimation method based on the experimental test under the simulating electric vehicle working condition.A first-order resistance-capacitance equivalent circuit is used to model the battery cell,and three parameter values,ohmic resistance(R_s),parallel resistance(R_p) and parallel capacity(C_p),are identified from a real-time experimental test.Finally we find that R_p and C_p could be utilized to make a judgement on the SOH.More importantly,the linear relationship between C_p and the SOC is established to make the estimation of the SOC for the first time.     

A dynamic capacity fading model with thermal evolution considering variable electrode thickness for lithium-ion batteries

Capacity is one of the key parameters to characterize the performances of lithium-ion batteries. Heat generation analysis is essential to evaluate the safety of batteries. To figure out the effects of electrode thickness on capacity fade and thermal behaviors, a capacity fading model is proposed considering reaction kinetics and mass transfer processes on solid electrolyte interface (SEI) layers coupled with thermal evolution. Simulations are conducted on seven LiFePO₄ batteries with variable electrode thicknesses. Results show that, with the increase of electrode thickness, the capacity losses of batteries deteriorate, and the total heat generation aggravates. For the battery with thick electrode, both the polarization overpotential and the gradient of lithium ion concentrations on particle surfaces of active materials increase on the edges, and then decrease perpendicularly to the cathodes. Under the adiabatic conditions, the temperature of battery (with anode 68 μm and cathode 140 μm) is increased to over 130 °C at the sixth cycle. The temperature of batteries declines when discharging in the beginning and then rises, which is noticeable for the batteries with thin electrodes. The proposed model and the simulation results would provide deep insights into both design and operation of batteries.     

Influence of charge rate on the cycling degradation of LiFePO<Subscript>4</Subscript>/mesocarbon microbead batteries under low temperature

The lithium-ion batteries show extremely poor cycling performance at low temperature. The main degradation mechanism is not clear. To address the fading mechanism, the cycling degradation of commercial LiFePO₄/mesocarbon microbead (MCMB) batteries under various charge rate (1/10C, 1/3C, 1/2C, and 1C) at ?10 °C is systematically investigated using nondestructive tests combining with post-mortem analysis. The low-temperature charging under high charge rates of 1/3C, 1/2C, and 1C results in severe lithium plating, which leads to extremely serious capacity loss. In contrast, no lithium plating occurred under low charge rate of 1/10C. The lithium plating on the anode surface leads to consumption of active lithium ions and electrolyte, which causes the capacity decay and increases ohmic resistance (R _b) with cycling number under high charge rates. The lithium plating on the anode surface is partially reversible, which brings about the capacity recovery of batteries after 80 cycles at 25 °C. The above results are proved by the followed post-mortem measurements. The evolution of the surface morphologies of MCMB electrodes upon cycling shows that a layer composed of rod-like lithium is formed on the anode surface.     

Fading analysis of the Li(NiCoMn)O<Subscript>2</Subscript> battery under different SOC cycle intervals

In a review of literature on operating conditions, such as temperature, materials, cutoff voltage, and current rate, state-of-charge (SOC) interval has attracted less attention regarding research on cell fading. Lithium-ion cells as power source practically applied to electric vehicles (EVs) are seldom operated in the entire SOC interval, which means that lithium-ion cells are employed in a certain SOC interval. However, the SOC interval that facilitates the increase of the life span of the cell remains unknown. In the current study, several cells are tested over different SOC intervals and discharge rates. In-depth analysis is performed on the influence of the two factors on cell fading. The incremental capacity and incremental resistance methods are used to analyze capacity fading and resistance evolution. The electrochemical mechanism analysis of cell fading is studied and discussed, showing that SOC interval influences the rate of cell degradation. Results show that a low SOC interval prolongs the life span of cell use if other operating conditions are similar. Therefore, the study provides a theoretical framework and reference for the cell maintenance of EVs.     

Synthesis of PANI/rGO composite as a cathode material for rechargeable lithium-polymer cells

Graphene oxide (GO) was synthesized by an improved Hummers method and then reduced with NaBH₄; GO became rGO with regular layered structure. Polyaniline (PANI)/rGO composite was prepared by a adsorption double oxidant method with rGO as a template. Some physical characterization methods (Fourier transform infrared spectroscopy analysis, X-ray diffraction, scanning electron microscope, and transmission electron microscope) were used to analyze the morphology and crystallinity of the composite. The electrochemical properties were characterized by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge, and rate capability. The first discharge specific capacity of the rPANI/rGO and PANI/rGO was 181.2 and 147.8 mAh/g. After 100 cycles, the capacity retention rate was still 90.2 and 88.9% separately, and the coulombic efficiency of batteries is close to 100%. These results demonstrate the composite has exciting potentials for the cathode material of lithium-ion battery.     

Numerical modeling of lithium ion battery for predicting thermal behavior in a cylindrical cell

The thermal behavior of lithium ion battery during charge and discharge is investigated by a numerical simulation. The commercially available cylindrical 18650 battery is modeled in this study. Two different models are used. The porous electrode model is simulated to obtain the Li content inside the particles. The transient thermo-electric model is used to predict the temperature distribution inside the cell. The results suggest that the increase in temperature during discharge is higher than that during charge. The temperature difference between charge and discharge is decreased with increasing C-rates. At a rate of 1C, the discharge temperature increases with a waving region at the beginning, whereas the charge temperature increases until certain point and then decreases. The thermal behavior is closely related to the change in entropy and applied current.     

Understanding oxygen reactions in aprotic Li-O_2 batteries

Although significant progress has been made in many aspects of the emerging aprotic Li-O_2 battery system, an indepth understanding of the oxygen reactions is still underway. The oxygen reactions occurring in the positive electrode distinguish Li-O_2 batteries from the conventional Li-ion cells and play a crucial role in the Li-O_2cell's performance(capacity, rate capability, and cycle life). Recent advances in fundamental studies of oxygen reactions in aprotic Li-O_2 batteries are reviewed, including the reaction route, kinetics, morphological evolution of Li_2O_2, and charge transport within Li_2O_2. Prospects are also provided for future fundamental investigations of Li-O_2 chemistry.     

Lithium intercalation in MoO3-nH2O

Oxide-hydrates of molybdenum (OHM) are of interest as lithium insertion electrodes for rechargeable lithium batteries because they offer wide operating temperature, long shelf life and low cost. We have studied the electrochemical characteristics of Li/OHM batteries using two types of commercial materials. Results are as follows. (a) The discharge potential (Φ) ranges between 3.0 and 1.5 V and it is a function of the water content into the cathode. (b) The electro-insertion of Li occurs mainly in two steps in the compositional range 0<x(Li)<1.5. (c) The discharge/charge (Φ-x) curves are very well fitted using a theoretical relationship based on the mean field approximation of a lattice-gas model including an ion-ion interaction term. (d) Kinetics show that Li-ions are highly mobile in the OHM framework. Long-term cycling has been investigated and a detailed analysis of the residual fading capacity during cycling is given. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

光伏发电系统充放电控制策略研究

本对光伏发电系统中影响蓄电池寿命各因素进行了简单分析,并在此基础上提出了一种新的充放电控制策略。实验结果证明该控制策略能较显提高蓄电池的放电容量。     

Graphites for Li-ion cells: Study of the irreversible capacity using differential capacity analysis

The aim of this work is to examine the performance and in particular the irreversible capacity of synthetic graphites. Our analysis is based on the evaluation and study of the differential capacity (dx/dV), computed by numerical differentiation of the galvanostatic curve. The dx/dV curve shows a series of peaks that correspond to potential plateaus. The area under each peak results in the charge related to the particular process, and by peak de-convolution analysis we can determine the charge consumed by or released from each process. This approach enables us to identify the processes involved (formation of SEI, solvated Li co-intercalation, cell self discharge, etc.). Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.