Ultrasonic Lithium Battery Scanning Imaging Technology And Its Application

As the most successful electrochemical energy storage device,lithium battery is widely used in new energy vehicles,mobile electronic products,power grid energy storage and other fields,and is a crucial link in the sustainable development of society.The improvement of the performance of lithium batteries is inseparable from the in-depth research on its working and aging mechanism.However,commercial batteries usually have closed outer packaging,which will block the transmission of visible light,infrared light,electron beam and other information carriers,resulting in difficulties in the non-destructive characterization of their internal structure changes.At present,there is a lack of effective characterization methods for nondestructive and in-situ imaging analysis of electrolyte infiltration,gas generation,lithium dendrite growth,and physical contact at the interface in commercial lithium batteries.Therefore,this paper proposes to develop a new ultrasonic transmission scanning technology,which utilizes the sensitivity of acoustic waves to the battery structure change to carry out in-situ non-destructive imaging of the battery,and then obtains the state changes information of the battery.The main works and achievements of this paper include the following aspects:(1)A set of ultrasonic in-situ detection and imaging equipment for lithium-ion batteries with independent intellectual property rights,and matching data acquisition and analysis software,have been developed to realize non-destructive imaging of electrolyte infiltration,gas production by side reaction,lithium plating,interface contact changes,etc.,with the inplane resolution of sub-millimeter level.The equipment has been successfully applied to the lithium battery research and development of Huawei,BYD,Tongji University,China Automotive Engineering Research Institute,etc.well-known enterprises and research institutes.(2)In this paper,the nondestructive imaging of electrolyte infiltration in the battery was realized by using ultrasonic technology.By studying the electrolyte infiltration path and time after injection under different structures and sizes,a non-empirical method to determine the minimum amount of electrolyte injection in the battery was creatively proposed.By comparing the bad wetting region before and after the formation of the battery,it is revealed that the bad infiltrating of the electrolyte will leads to the lithium plating on the negative electrode.(3)The side reactions at the electrolyte-electrode interface of lithium batteries were studied by ultrasonic imaging technology.Through non-destructive imaging of the gas generated by the side reaction during the battery working process,the intensity of the side reaction was explored,and a method that can quickly estimate the electrolyte matching degree was proposed.In addition,by characterizing the side reaction gas caused by lithium plating,information of the lithium plating time,degree and region inside the battery can be nondestructively achieved.(4)The aging process of lithium batteries was investigated by ultrasonic imaging technology,while the phenomenon of "unwetting" during the aging process of batteries was proposed and observed.The research proved that the "unwetting" is one of the main reasons for the rapid capacity decay of the battery under the deep cycles,and is also one of the reasons for the rapid death of the anode-free lithium battery.Furthermore,the periodic "unwetting" effect caused by the reversible volume expansion was proposed and observed experimentally,which provides theoretical guidance and experimental support for researchers to further understand the battery failure mechanism and establish the aging predict model.(5)Ultrasonic imaging technology was applied to non-destructively study the interface stability of polymer solid-state lithium pouch battery.The side reaction between residual solvent and lithium metal in the polymer solid-state electrolyte prepared by the blade casting method was found.Moreover,the dynamic process of the interface contact improvement with the heat treatment time increase inside the polymer solid-state battery,manufactured by the hot press method,was observed.In addition,by analyzing the ultrasonic image change of polymer solid lithium battery during the aging process,it is proved that the interfacial resistance increase is caused by the growth of the passivation layer rather than the formation of the interfacial gap.