Study On The Influence Mechanism Of External Pressure On Lithium-ion Battery Cycle Life And Characteristics

At present,lithium ion battery is widely used as the power battery of electric vehicles due to its high specific energy and long cycle life.Power battery,as the core component of electric vehicles,has an important influence on the popularization of electric vehicles.Its aging mechanism and cycle characteristics have also been widely studied.In the battery use process,the external environment temperature,charge and discharge rate and charge and discharge cut-off voltage will affect the battery aging.Since the power batteries are stored in the battery pack during use,the batteries will be affected by external mechanical pressure.This paper studies the influence of external pressure on the battery cycle life and characteristics.The research object of this paper is a soft-pack ternary lithium ion battery produced by a company.The failure mechanism of the lithium ion battery is described from the influence of internal materials and external use environment,and the research status of the pressure characteristics of the lithium ion battery at home and abroad and the results of the previous team’s pressure experiment are introduced.By means of experiment and modeling,this paper mainly studies the following contents:(1)A comparison experiment was designed for the cycle life of the battery under constrained and unconstrained conditions.The influence mechanism of external pressure on the cycle life of the battery was explored by means of recording pressure changes,observation of scanning electron microscope and increment capacity analysis.(2)The effect of external pressure on the battery discharge rate was investigated by comparing the discharge capacity and the mechanism was analyzed by designing discharge experiments with different rates under different pressure gradients.(3)The second-order RC circuit model of lithium-ion battery was established,and the errors of the model under constrained and unconstrained conditions were compared,and the idea of introducing the influence of external pressure into the model parameters was proposed.The results show that appropriate external pressure is beneficial to prolong the cycle life of the battery.However,when the battery is in a fixed constraint,with the aging of the battery,the external pressure on the battery increases,which has a negative impact on the battery at the later stage of the cycle.Therefore,the elastic constraint method is more conducive to the positive effect of the external pressure.Under a small external pressure,the battery capacity is increased at a small rate of discharge of 0.1C,while the battery capacity decreases at a rate of discharge of 0.5C and above,and the greater the pressure,the more obvious the decrease.When the second-order RC model of lithium-ion battery is established under the condition of no pressure,the error increases obviously.Therefore,the influence of pressure on the parameters should be considered in the modeling of the battery.