Preparation Of Low-temperature Preheating Electric Heating Film For Lithium Batteries And Its Performance Study

As the share of new energy vehicles in the domestic market at all levels gradually climbs,the performance requirements of lithium-ion power batteries(referred to as lithium batteries)are also increasing.The low temperature environment will have a greater impact on the charging and discharging performance of lithium batteries,and may even cause safety hazards to the driver and passengers.Low-temperature preheating is one of the core technologies of battery thermal management system,which is the key to mitigate the performance degradation of Li-ion battery in low-temperature environment.Electric heating film preheating is favored in the field of low-temperature preheating of lithium batteries because of its advantages of light weight and low cost,small space occupation and stable heating,etc.At present,the theoretical research on electric heating film preheating is relatively complete,and the breakthrough can be made from the electric heating film material to further improve the preheating effect.Therefore,the design of a new carbon electric heating film has important practical application value for the low temperature preheating of lithium batteries.In this paper,we analyze the influence of low temperature environment on the charging and discharging performance of lithium battery and propose a design of composite carbon system electric heating film with graphene and carbon nanotubes as conductive filler,waterbased acrylic resin as binder and polyurethane film as substrate.The thickness,square resistance,volume resistivity and electrothermal conversion rate are used as the performance evaluation indexes of the electric heating film,and the effects of carbon nanotube diameter,conductive filler ratio,ratio of conductive filler to binder,solid content of electric heating slurry and electric heating slurry coating amount on the performance of the electric heating film are investigated by single-factor experimental method,and the ratio of each component of the electric heating slurry is preferably selected.The effects of coating parameters(thickener content,narrow seam gap and coating speed)on the performance of electric heating film were investigated by single-factor experimental method;orthogonal experiments were designed to investigate the weights of the effects of coating parameters on the performance of electric heating film;a coating BP neural network prediction model was established,and the optimal combination of parameters for the prediction model was solved by using genetic algorithm.The results show that the experimental results verify the accuracy of the prediction model,and the film formation effect of the electric heating film prepared with the optimized coating parameters is better,and the electric heating performance is significantly improved.The experiments are conducted to compare the preheating effect of polyimide wide wire metal film and composite carbon electric heating film on the battery pack,and the equivalent simulation model is established to solve and analyze,and the experimental results are compared and verified;the effects of electric heating film arrangement and input power on the preheating effect of the battery pack are analyzed by numerical simulation.The results show that: the composite carbon film has better preheating effect and electrical heating performance;the experimental results of battery pack preheating fit well with the simulation results,which verifies the reliability of the simulation model;the temperature uniformity of preheating is better with the double-side arrangement of the film;the higher the input power of the film,the faster the preheating speed.