Preparation And Performance Of Self-heating Electrodes For Low Temperature Lithium Ion Batteries

Conventional lithium-ion batteries usually perform at a specific operating temperature range.When the ambient temperature deviates from the applicable temperature range of the battery,those batteries would be difficult to discharge smoothly at low temperatures and could not work properly.By adjusting the positive and negative electrode material structure of the battery and optimizing the electrolyte components,the low-temperature performance of the lithium ion battery can be optimized to a certain extent.However,the low diffusion and migration rate of lithium ions in the battery system under low temperature environment could not be solved fundamentally.In view of this problem,we proposed to control the working environment temperature of the battery by means of heating,so as to fundamentally solve the series of problems faced by the battery when operating in a low-temperature environment.Specific research contents are as follows:(1)The heated lithium ion battery was designed by using nickel metal sheet inside the ordinary lithium ion battery as heating sheet.According to Adiabatic Rate Calorimeter(ARC)test and formula calculation,the specific heat capacity of the battery was 1.272J/(g.k).The stable heating effect was obtained by using the appropriate nickel sheet resistance design.Under the condition of 0.5C current charging and discharging at room temperature(25°C),after 105 cycles of the battery,the capacity retention rate of the battery was 92.8%,showing good cycling performance.Compared with conventional batteries,at low temperature of-20°C,when the battery was heated by nickel sheet,the charging capacity of the battery at-20°C would be increased by 34% and the discharge capacity would be increased by 19.9%.In the environment of-40°C,when the battery was not heated,the charging capacity would be approximately 0.In the heating state,the charging capacity of the battery was 7058 mAh,and the discharge capacity would be improved by 32.8%.The built-in heated nickel battery had better low temperature charge and discharge performance and higher discharge voltage platform.(2)Different materials were produced with using acetylene black,carbon nanotubes(CNT)and high-density polyethylene(HDPE)as raw materials by melt mixing.Conductive substance was consistent with acetylene black alone or acetylene black and CNT mixed.After testing,it was found that the conductivity of materials used a mixture of two conductive substances was better than that used a single conductive substance.At the same time,after adjusting the content of the conductive material,it was clearly that more conductive material content made composites have better conductive properties.However,with HDPE as the matrix,after using a single conductive material,mixing(super-p and CNT)conductive materials and changing the content of conductive materials,the PTC transition temperature of the prepared composites were still higher than 80 ?,so it was not suitable as a built-in heater.(3)Ni metal particles and HDPE were melt mixed to make composites,and different material characteristics were obtained by changing the content of Ni metal particles.The results showed that the higher the content of Ni particles in composites,the lower the resistivity and the smaller the thermal expansion coefficient of composites.When the content of Ni particles was 10 and 15Vol%,composites had PTC transition temperature at room temperature.And the melting temperature of composites decreased with the increased of the content of Ni particles.On the contrary,the crystallization temperature of the material increased.In addition,after heat treatment of the composite material system,the resistivity-temperature curve of the composite material changed at-40~80?.After heat treatment at 120 ? for 1h,the PTC strength of composites in the range of-40~80 ? would be increased by about 1.5.