Experimental investigations on the correlations between the structure and thermal-electrochemical properties of over-discharged ternary/Si-C power batteries

© 2021 John Wiley & Sons Ltd. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1002/er.7274The thermal safety of power lithium-ion batteries（LIBs） has seriously affected the booming development of electric vehicles (EVs). Especially, owing to the requirement of high energy density, thermal runaway (TR) easily occurs in LIBs, resulting in a higher heat generation rate. Over-discharging is recognized as a common cause for TR. In the present research, the correlations between the structure and thermal-electrochemical properties of an over-discharged ternary/Si-C battery at room and high temperatures were investigated. The heat generation mechanisms of the batteries due to the maximum surface temperature and peak temperature difference variations during fast charging and discharging processes were investigated. Moreover, the electrochemical performances parameters of the batteries, such as voltage changing trend, discharge time, discharge capacity, internal resistance, electrochemical impedance spectroscopy (EIS) spectra, were analyzed. When the battery was discharged at 2.0C and 55°C, its maximum temperature and highest temperature difference reached 91.34°C and 13.24°C, respectively, finally resulting in a sharp decline in electrochemical performance. Furthermore, the root reasons for performance degradation and heat generation intensification of the over-discharged battery (ODB) were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The cause of the aforementioned phenomenon is due to irreversible damage of the electrode materials. This research not only reveals the relevant relationship between the thermal behavior and the microscopic structure of the over-discharged ternary/Si-C battery under various temperature conditions but also provides valuable insights for improving the safety of LIBs modules even packs.Peer reviewe

Design of the flame retardant form-stable composite phase change materials for battery thermal management system

Phase change materials have attracted significant attention owing to their promising applications in many aspects. However, it is seriously restricted by some drawbacks such as obvious leakage, relatively low thermal conductivity, and easily flame properties. Herein, a novel flame retardant form-stable composite phase change material (CPCM) with polyethylene glycol/epoxy resin/expanded graphite/magnesium hydroxide/zinc hydroxide (PEG/ER/EG/MH/ZH) has been successfully prepared and utilized in the battery module. The addition of MH and ZH (MH:ZH = 1:2) as flame retardant additions can not only greatly improve the flame retardant effect but also maintain the physical and mechanical properties of the polymer. Further, the EG (5%) can provide the graphitization degree of residual char which is beneficial to building a more protective barrier. This designation of CPCM can exhibit leakage-proof, high thermal conductivity (increasing 400%–500%) and prominent flammable retardant performance. Especially at 3C discharge rate, the maximum temperature is controlled below 54.2 °C and the temperature difference is maintained within 2.2 °C in the battery module, which presents a superior thermal management effect. This work suggests an efficient and feasible approach toward exploiting a multifunctional phase change material for thermal management systems for electric vehicles and energy storage fields

Experimental and Numerical Investigation on an Integrated Thermal Management System for the Li-Ion Battery Module with Phase Change Material

Lightweight power battery modules with outstanding thermal performance are urgently required given the rapid development of electric vehicles. This study proposes a composite phase change material coupled with forced convection as an integrated thermal management system (ITMS) with the aim to control the temperature’s rising tendency and maintain the temperature distribution uniformly within an appropriate range among the battery modules. The thermal behavior effects of airflow rates on the thermal management system were investigated in detail by combining experiments and numerical simulations. Comparisons were conducted between an air cooling system with an optimum flow rate and the ITMS. Experimental results revealed that the cooling effect of the ITMS was better than that of the forced cooling system at a 3 m/s airflow rate. The maximum temperature in the designed battery module was limited to 63.2°C. The maximum temperature difference was limited to 4.8°C at a 4 C discharge rate. This research indicates that the ITMS is an effective and optimized approach to control and balance the temperature among battery modules, thereby providing engineers with design optimization strategies for similar systems