Electrical-thermo Model Based Optimal Structure Design Of Large-format Pouch-type Lithium-ion Batteries

Lithium-ion batteries(LIBs)have been widely used in the field of electric vehicles because of their high energy density and long cycle life.However,in recent years,the frequent occurrence of LIBs caused widespread concern of the whole society.Electrical and thermal non-uniformity behaviors in large-format pouch-type LIBs would increase the risks of safety,durability and reliability.This study investigates the spatial non-uniformity reduction strategy of both electrical and thermal parameters by means of optimal structure design of LIBs.(1)A thermal-electrical model of LIBs is firstly constructed,in which the parameters are optimally tuned from the battery testing profiles.The performance of the thermal-electrical model is verified by the constant current discharge test of commercial LIBs at different rates.(2)Two uniformity indices of state of charge(SOC)and temperature are proposed to characterize the electrical and thermal uniformities respectively.A bi-objective mixed-integer nonlinear programming(MINLP)model is then formulated for the optimal structure design of LIBs,in which both SOC and temperature uniformityindices are simultaneously minimized.A simple weighted strategy is used to reformulate the bi-objective MINLP model into a single-objective MINLP model.A surrogate model based optimization method is utilized to efficiently solve the weighted single-objective black-box MINLP problem.The MINLP results show that both electrical and thermal uniformities can be significantly improved by means of optimally designing the structure of LIBs.It is thus indicated that the proposed electrical and thermal characteristics simultaneous optimization approach could be greatly helpful not only for improving the active material utilization efficiency,but also for avoiding local hot spot to some extent during the battery operation.