Thermal hazard evaluations of 18650 lithium-ion batteries by an adiabatic calorimeter

In this study, the thermal hazard features of various lithium-ion batteries, such as LiCoO₂ and LiFePO₄, were assessed properly by calorimetric techniques. Vent sizing package 2 (VSP2), an adiabatic calorimeter, was used to measure the thermal hazards and runaway characteristics of the 18650 lithium-ion batteries under an adiabatic condition. The thermal behaviors of the lithium-ion batteries were obtained at normal and abnormal conditions in this study. The critical parameters for thermal hazardous behavior of lithium-ion batteries were obtained including the exothermic onset temperature (T ₀), heat of decomposition (ΔH), maximum temperature (T _max), maximum pressure (P _max), self-heating rate (dT/dt), and pressure rise rate (dP/dt). Therefore, the result indicates the thermal runaway situation of the lithium-ion battery with different materials and voltages in view the of TNT-equivalent method by VSP2. The hazard gets greater with higher voltage. Without the consideration of other anti-pressure measurements, different voltages involving 3.3, 3.6, 3.7, and 4.2 V are evaluated to 0.11, 0.23, 0.88, and 1.77 g of TNT. Further estimation of thermal runaway reaction and decomposition reaction of lithium-ion battery can also be confirmed by VSP2. It shows that the battery of a fully charged state is more dangerous than that of a storage state. The technique results showed that VSP2 can be used to strictly evaluate thermal runaway reaction and thermal decomposition behaviors of lithium-ion batteries. The loss prevention and thermal hazard assessment are very important for development of electric vehicles as well as other appliances in the future. Therefore, our results could be applied to define important safety indices of lithium-ion batteries for safety concerns.     

Thermal instability of organic esters and ethers with deposited lithium in lithium-ion battery

The thermal instabilities of deposited lithium with electrolytes in lithium-ion batteries are simulated by the reactions between metallic lithium with organic esters and ethers. Exothermic onset temperatures and enthalpy changes are measured and analyzed by differential scanning calorimetry. In this study, heat of reactions in lithium with eight different formations of esters and ethers are determined which are consistent to the data of lithiated graphite (LiC₆) reacted with electrolytes in literature. Furthermore, violently exothermic reactions with enthalpy larger than 1,000 J g^?1 and onset temperature lower than 120 °C are further conducted by the confinement test to verify the worst scenarios and consequences of lithium-ion batteries encountered any kind of abuses. Thermal instability of metallic lithium with organic esters in descending order determined to be Li + EB (70 °C)>Li + MB (73.1 °C)>Li + EA (90.8 °C). Finally, thermal hazard data such as onset temperature, maximum self-heat rate, maximum temperature, and maximum pressure of lithium reacted with esters and ethers are compared, evaluated, and some conclusion and suggestions are made.     

Self-reactive rating of thermal runaway hazards on 18650 lithium-ion batteries

Vent sizing package 2 (VSP2) was used to measure the thermal hazard and runaway characteristics of 18650 lithium-ion batteries, which were manufactured by Sanyo Electric Co., Ltd. Runaway reaction behaviors of these batteries were obtained: 50% state of charge (SOC), and 100% SOC. The tests evaluated the thermal hazard characteristics, such as initial exothermic temperature (T ₀), self-heating rate (dT?dt ^?1), pressure-rise rate (dP?dt ^?1), pressure temperature profiles, maximum temperature, and pressure which were observed by adiabatic calorimetric methodology via VSP2 using customized test cells. The safety assessment of lithium-ion cells proved to be an important subject. The maximum self-heating rate (dT?dt ^?1)_max and the largest pressure-rise rate (dP?dt ^?1)_max of Sanyo 18650 lithium-ion battery of 100% SOC were measured to be 37,468.8???C?min^?1 and 10,845.6?psi?min^?1, respectively, and the maximum temperature was 733.1???C. Therefore, a runaway reaction is extremely serious when a lithium-ion battery is exothermic at 100% SOC. This result also demonstrated that the thermal VSP2 is an alternative method of thermal hazard assessment for battery safety research. Finally, self-reactive ratings on thermal hazards of 18650 lithium-ion batteries were studied and elucidated to a deeper extent.     

Thermal runaway features of 18650 lithium-ion batteries for LiFePO4 cathode material by DSC and VSP2

In view of availability, accountability, and applicability, LiFePO₄ cathode material has been confirmed to be better than LiCoO₂ cathode material. Nevertheless, few related researches were conducted for thermal runaway reaction of the LiFePO₄ batteries. In this study, vent sizing package 2 (VSP2) and differential scanning calorimetry were employed to observe the thermal hazard of 18650 lithium-ion batteries and their content??LiFePO₄ cathode material, which were manufactured by Commercial Battery, Inc. Two states of the batteries were investigated, which was charged to 3.6?V (fully charged) and 4.2?V (overcharged), respectively, and important parameters were obtained, such as self-heating rate (dT?dt ^?1), pressure-rise rate (dP?dt ^?1), and exothermic onset temperature (T ₀). The results showed that T ₀ for fully charged is about 199.94?°C and T _max is about 243.23?°C. The entire battery for LiFePO₄ cathode material is more stable than other lithium-ion batteries, and an entire battery is more dangerous than a single cathode material. For process loss prevention, the data of battery of VSP2 test were applied as reference for design of safer devices.     

Study about thermal runaway behavior of high specific energy density Li-ion batteries in a low state of charge

Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.     

Electrolyte additives for improved lithium-ion battery performance and overcharge protection

Much effort is being expended on the development of smart, safe, high-power lithium-ion batteries that are also environmentally friendly. Scaled-up lithium-ion batteries still raise safety concerns, especially when they are overcharged. Therefore, efforts continue to improve the thermal and chemical stability of positive electrodes, negative electrodes, separators, and electrolytes within the battery to counter thermal runaway. This opinion discusses highlights of research on additives for nonaqueous electrolytes published during 2018 and 2019.     

金属锂电池的热失控与安全性研究进展

锂离子电池在便携式储能器件及电动汽车领域得到了广泛应用,然而频繁发生的电池起火爆炸事故,使热失控和热安全问题备受人们关注,目前已有多篇综述报道了缓解锂离子电池热失控的措施。相比于已经接近理论比能极限的锂离子电池,金属锂负极具有更高的比容量、更低的电势和高反应活性,但是不可控的锂枝晶生长,使得金属锂电池的热失控问题更为复杂和严重。针对金属锂电池的热失控问题,本文首先介绍了热失控的诱因及基本过程和阶段,其次从材料层面综述了提高电池热安全性的多种策略,包括使用阻燃性电解质、离子液体电解质、高浓电解质和局域高浓电解质等不易燃液态电解质体系,开发高热稳定性隔膜、热响应隔膜、阻燃性隔膜和具有枝晶检测预警与枝晶消除功能的新型智能隔膜,以及研究热响应聚合物电解质,最后对金属锂电池热失控在未来的进一步研究进行了展望。     

Li2S-P2S5体系电解质及其在全固态锂离子电池中的应用研究进展

全固态锂离子电池具有安全性能好、能量密度高、工作温区广等优点,被广泛应用于便携式电子设备。固态电解质是全固态锂离子电池的关键材料之一,其中的硫化物电解质具有离子电导率高、电化学窗口宽、晶界电阻低和易成膜等特点,被认为最有希望应用于全固态锂离子电池。本文综述了Li_2S-P_2S_5体系电解质的发展状况,包括固态电解质的制备、改性、表征以及电极/固态电解质之间的固-固界面的稳定兼容问题。本文还涉及了以Li_2S-P_2S_5为电解质的全固态锂离子电池性能的研究进展。     

Electrospun cellulose acetate/poly(vinylidene fluoride) nanofibrous membrane for polymer lithium-ion batteries

The membranes for gel polymer electrolyte (GPE) for lithium-ion batteries were prepared by electrospinning a blend of poly(vinylidene fluoride) (PVdF) with cellulose acetate (CA). The performances of the prepared membranes and the resulted GPEs were investigated, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), porosity, hydrophilicity, electrolyte uptake, mechanical property, thermal stability, AC impedance measurements, linear sweep voltammetry, and charge–discharge cycle tests. The effect of the ratio of CA to PVdF on the performance of the prepared membranes was considered. It is found that the GPE based on the blended polymer with CA:PVdF =2:8 (in weight) has an outstanding combination property-strength (11.1 MPa), electrolyte uptake (768.2 %), thermal stability (no shrinkage under 80 °C without tension), and ionic conductivity (2.61 × 10^?3 S cm^?1). The Li/GPE/LiCoO₂ battery using this GPE exhibits superior cyclic stability and storage performance at room temperature. Its specific capacity reaches up to 204.15 mAh g^?1, with embedded lithium capacity utilization rate of 74.94 %, which is higher than the other lithium-ion batteries with the same cathode material LiCoO₂ (about 50 %).     

Thermal runaway and fire behavior investigation of lithium ion batteries using modified cone calorimeter

The lithium ion battery has been widely used, but it has high fire risk due to its flammable materials. In this study, a series of combustion tests are conducted on the 18650-type lithium ion batteries using the modified cone calorimeter. The temperature and voltage variation of the battery, heat release rate and gas generation during combustion are measured in this study. The battery is heated evenly by the self-made heater, and the reliable trigger temperatures of thermal runaway are obtained for different states of charge (SOCs) batteries in this study. The fire behavior of the 100% SOC batteries is shown in this paper. The net heat absorption by the battery before thermal runaway is calculated based on the heat transfer theory. It ranges from 56.81 to 64.05 kJ for 0 to 100% SOC batteries, which shows a decreasing trend as SOC increases. The peak combustion heat release rate of 100% SOC batteries is 3.747?±?0.858 kW. CH₄ and CO gases are detected before and after thermal runaway. The generation of CO shows an increasing trend as SOC increases. Some suggestions on the early warning system of battery thermal runaway are proposed based on this study.

     

新合成方法制备的LiCoO2正极材料的结构和电化学性能研究

采用新合成方法制备了锂离子二次电池正极材料LiCoO₂。通过ICP-AES、XRD、SEM、电化学方法等测试分析了所合成材料的物理性质和电化学性能，并与商品LiCoO₂材料作了对比研究。同时分别以国产MCMB和石墨作负极活性物质、合成的LiCoO₂作正极活性物质做成锂离子电池，对其电化学性能进行了测试。实验结果表明，所合成的LiCoO₂材料的电化学性能优于其它两种商品LiCoO₂材料，其初始放电容量为155.0 mAh·g^-1，50次循环后的容量保持率达95.3%，而且以此为正极的锂离子电池也表现出优良的电化学性能。计时电位分析结果还表明，合成的材料在充放电循环过程中发生了三次相转变过程，但相变过程具有良好的可逆性。     

Low-temperature synthesis of a green material for lithium-ion batteries cathode

Abstract

Battery technology is an important anthropogenic source of the heavy metals which are highly threatening to human health. A category of rechargeable lithium batteries that is of great interest is the set of batteries where the cathode material is a lithium iron phosphate (LiFePO₄). LiFePO₄ is an environmentally friendly and safe lithium-ion battery cathode material, but it has a key limitation, and that is its extremely low-electronic conductivity, a problem that can be greatly overcome by zinc-doping LiFePO₄. For the first time to our knowledge, a low-temperature method, that is advantageous both economically and technologically, for the synthesis of a zinc-doped LiFePO₄ is presented. Since the method appears to be applicable for synthesizing various zinc-doped LiFePO₄ compounds with the general formula LiFe_1?x Zn _x PO₄ (0<x<1), it is very promising for the production of a green cathode material for lithium-ion batteries.     

New electrolytes using Li2O or Li2O2 oxides and tris(pentafluorophenyl) borane as boron based anion receptor for lithium batteries

A new system of electrolytes has been developed and studied for lithium-ion batteries. This new system is based on the interactions between Li₂O or Li₂O₂ and tris(pentafluorophenyl) borane (TPFPB) in carbonate based organic solvents. This opens up a completely new approach in developing non-aqueous electrolytes. In general, the solubility of Li₂O or Li₂O₂ is very low in organic solvents and the ionic conductivities of these solutions are almost undetectable. By adding certain amount of tris(pentafluorophenyl) borane (TPFPB), one type of boron based anion receptors (BBARs), the solubility of Li₂O or Li₂O₂ in carbonate based solvents was significantly enhanced. In addition, the Li⁺ transference numbers of these new electrolytes measured were as high as 0.7, which are more than 100% higher than the values for the conventional electrolytes for lithium-ion batteries. The room-temperature conductivities are around 1 × 10⁻³ S/cm. These new electrolytes are compatible with LiMn₂O₄ cathode for lithium-ion batteries.     

Rational design on separators and liquid electrolytes for safer lithium-ion batteries

As the energy density of lithium-ion batteries (LIBs) continues to increase,their safety has become a great concern for further practical large-scale applications.One of the ultimate solution of the safety issue is to develop intrinsically safe battery components,where the battery separators and liquid electrolytes are critical for the battery thermal runaway process.In this review,we summarize recent progress in the rational materials design on battery separators and liquid electrolyte towards the goal of improving the safety of LIBs.Also,some strategies for further improving safety of LIBs are also briefly outlooked.     

Thermal behaviors of electrolytes in lithium-ion batteries determined by differential scanning calorimeter

Lithium-ion batteries have been widely used in daily electric appliance, but abusive accidents occurred from time to time. Lithium-ion batteries composed of various electrolytes (containing organic solvents, inorganic salts), binder, and electrode materials, which may be unstable under some abnormal conditions. The formulation or components of electrolytes played a crucial factor in affecting reactive hazards within the cell. In order to meet safety requirements of the lithium-ion batteries on electronic device, reseachers and scholars are continuing to do further studies on the important issues in relation to the lithium-ion batteries. This study aims to apply the differential scanning calorimeter for measuring the thermal or reactive hazards of the organic solvents related to the formulation of the electrolytes. Besides, thermal instabilities of lithiated graphite or deposited lithium with electrolytes were simulated by the reactions between metallic lithium (Li) and organic carbonates of linear and cyclic structures. Exothermic onset temperatures and enthalpy changes were measured and analyzed. Results showed that the thermal behaviors of these organic carbonates themselves or with lithium hexafluorophosphate liberated less enthalpy changes. However, violent exothermic reactions were detected between the linear or cyclic carbonates and lithium metal with larger enthalpy change larger than 1,000 J g^?1 of lithium. This can be observed by Li reacted with diethyl carbonate at surprisingly lower onset temperature about 46.6 °C.     

Spinel LiNi0.5Mn1.5O4 and its derivatives as cathodes for high-voltage Li-ion batteries

The spinel material LiNi_0.5Mn_1.5O₄ displays a remarkable property of high charge/discharge voltage plateau at around 4.7 V. It is a promising cathode material for new-generation lithium-ion batteries with high voltage. Recently, a lot of researches related to this material have been carried out. In this review we present a summary of these researches, including the structure, the mechanism of high voltage, and the latest developments in improving its electrochemical properties like rate ability and cycle performance at elevated temperature, etc. Doping element and synthesizing nanoscale material are effective ways to improve its rate ability. The novel battery systems, like LiNi_0.5Mn_1.5O₄/Li₅Ti₄O₁₂ with good electrochemical properties, are also in progress.     

锂离子电池高电压电解液的研究现状

目前提高锂离子电池能量密度的途径主要有提高锂离子电池的工作电压和应用高工作电压的正极材料,因此,锂离子电池高电压电解液的研究和开发势在必行。本文概述了锂离子电池电解液和高电压电解液的特点,介绍了前线轨道理论中的HOMO和LUMO对电解液设计的指导意义。尤其是结合日本知名企业和科研机构在高电压电解液方面的研究成果,阐述了两种实现电解质高电压化的途径,即提高溶剂本身的耐氧化性和使用添加剂,总结了氟代酯、氟化醚、硼酸酯、砜类和耐氧化添加剂等用于高电压电解液中的关键物质类型,并讨论了目前高电压电解液研究开发所带来的启示。     

New experimental heat capacity and enthalpy of formation of lithium cobalt oxide

The heat capacity of LiCoO₂ (O3-phase), constituent material in cathodes for lithium-ion batteries, was measured using two differential scanning calorimeters over the temperature range from (160 to 953) K (continuous method). As an alternative, the discontinuous method was employed over the temperature range from (493 to 693) K using a third calorimeter. Based on the results obtained, the enthalpy increment of LiCoO₂ was derived from T = 298.15 K up to 974.15 K. Very good agreement was obtained between the derived enthalpy increment and our independent measurements of enthalpy increment using transposed temperature drop calorimetry at 974.15 K. In addition, values of the enthalpy of formation of LiCoO₂ from the constituent oxides and elements were assessed based on measurements of enthalpy of dissolution using high temperature oxide melt drop solution calorimetry. The high temperature values obtained by these measurements are key input data in safety analysis and optimisation of the battery management systems which accounts for possible thermal runaway events.     

Thermal properties and kinetics study of charged LiCoO2 by TG and C80 methods

The thermal stability of lithium-ion battery cathode could substantially affect the safety of lithium-ion battery. In order to disclose the decomposition kinetics of charged LiCoO₂ used in lithium ion batteries, thermogravimetric analyzer (TG) and C80 microcalorimeter were employed in this study. Four stages of mass losses were detected by TG and one main exothermic process was detected by C80 microcalorimeter for the charged LiCoO₂. The chemical reaction kinetics is supposed to fit by an Arrhenius law, and then the activation energy is calculated as E _a=148.87 and 88.87 kJ mol⁻¹ based on TG and C80 data, respectively.     

Effect of Al2O3 -coating on the electrochemical performances of Li3V2(PO4)3/C cathode material

The effect of Al₂O₃ -coating on Li₃V₂(PO₄)₃/C cathode material for lithium-ion batteries has been investigated. The crystalline structure and morphology of the synthesized powders have been characterized by XRD, SEM, and HRTEM, and their electrochemical performances are evaluated by CV, EIS, and galvanostatic charge/discharge tests. It is found that Al₂O₃ -coating modification stabilizes the structure of the cathode material, decreases the polarization of electrode and suppresses the rise of the surface film resistance. Electrochemical tests indicate that cycling performance and rate capability of Al₂O₃-coated Li₃V₂(PO₄)₃/C are enhanced, especially at high rates. The Al₂O₃-coated material delivers discharge capacity of 123.03 mAh g^?1 at 4 C rate, and the capacity retention of 94.15 % is obtained after 5 cycles. The results indicate that Al₂O₃ -coating should be an effective way to improve the comprehensive properties of the cathode materials for lithium-ion batteries.