Capacity Fading Analysis Of Commercial Lithium Ion Batteries

Driven by the challenge of fossil energy shortage and environmental pollution,people are making great efforts to develop renewable clean energy technology around the world.Energy storage devices are vital to utilizing novel energy resources efficiently.Lithium ion batteries(LIBs),which have already been widely used in the field of 3C consumer electronics and electric vehicles,still stand out among all kinds of advanced energy storage technologies because of their high energy/power density,high energy efficiency,long cycling life,wide working temperature window,high reliability,low self-discharge rate and environmental friendly.However,there are still many probabilities where the failure of LIBs may occur during the process of manufacturing,transportation,usage and maintenance.These failing modes like capacity fading,cycling life decreasing and rate capability degradation are detrimental to a stable energy storage device.Though,like anything else,every lithium ion battery will inevitably fail in the end,expand the operating life can be achieved by failure analysis.Based on the results of failure analysis we can rationally optimize the performance of LIBs including safety,reliability,and so on.In the early 1950s,the researchers abroad had been carried out the Failure Mode and Effects Analysis(FMEA)of LIBs and accumulated its database,while the research of the LIBs5 FMEA in China was still in the preliminary stage of exploration and focused on the factors affecting the performance of the battery.The FMEA is difficult to carry out because of the complex internal battery system and various batteries9 failure cause.In order to explore reasonable commercial LIBs’ failure analysis process and research methods,we do some works as follows:1.A systematic and detailed illustration including the analysis scheme design and test methods choice for the main components(cathode,anode,separator and current collector)was exemplified by the case of failure analysis on a commercial power battery whose material system was unknown.The information of each part is collected efficiently to judge the main composition of materials and possible synthesizing methods.The test and analysis process is universal for the other Li-ion batteries,and will lay the foundation for the failure analysis of Li-ion batteries.2.The failure analysis conducted on the capacity degradation of a commercial power battery is reported in this thesis based on accumulation of battery material analysis.The possible factors leading to the battery performance declination are listed.The contribution of each factor to the capacity loss is quantified.We conducted non-destructive test and postmortem test on the whole-battery scale and electrode material level.The involved testing methods include Electrochemical Impedance Spectroscopy(EIS)9 X.ray diffraction(XRD),Fourier Transform Infrared Spectroscopy(FTIR),Inductive Coupled Plasma Emission Spectrometer(ICP),Scanning Electron Microscope(SEM),Transmission Electron Microscope(TEIVD and X-ray photoelectron spectroscopy(XPS).Electrochemical analytical methods such as incremental capacity analysis and differential voltage analysis are also performed.In the aspect of the anode,the loss of lithium-ion inventory related to solid electrolyte interface(SEI)formation leads to about 52%of battery capacity 1oss.The phenomenon caused by the Fe which came from the cathode promote the growth of SEI when it arrived at the surface of the anode.The highlights of above work are mainly focused on these aspects:1.Basing on the research of the whole system and all components of LIBs in the global,a new and efficient failure analysis procedure was explored for LIBs and an actual case was taken as an example for explaining above procedure.2.Quantitative analysis about the related failure factors of the capacity loss was achieved according to the characterization and analysis of all parts of the battery for avoiding the interference of various factors in the failure analysis of commercial battery systems,3.Discussing the main reasons for the decrease of active lithium ion content.