Research On The Internal Short Circuit Problem Of The Vehicle Power Battery System

With the developing and popularizing of electric vehicles,the safety problem of lithium-ion power batteries becomes prominent.The internal short circuit(ISCr)is the critical step of the safety evolution of lithium-ion power batteries and is one of the main obstacles to solving the safety problem of lithium-ion power batteries.For the ISCr mechanism research before the application of batteries,new ISCr experiment methods are needed;for the safety purpose during the application of batteries,new ISCr detection methods are needed.In this dissertation,the research focuses on ISCr experiment methods and ISCr detection methods.The shape memory alloy(SMA)ISCr trigger method is invented,which is able to trigger all kinds of ISCr on demand with point contact.The Fusing Phenomenon of ISCr is discovered,the hypothesis of the Fusing Phenomenon’s entire life cycle is presented,and the pattern of ISCr evolution is revealed.The ISCr detection method based on the Parameter Effect and the Depleting Effect is invented,which makes the detection of the initial phase ISCr possible.The ISCr detection method based on the symmetrical loop circuit topology is invented,which overcomes the difficulty of the ISCr detection in parallel circuits and improves the initial phase ISCr detection efficiency greatly.Firstly,the SMA ISCr trigger method is invented based on the shape memory effect of SMA,which is able to trigger different types of ISCr on demand through point contact.The experiments have good reproducibility,the fabrication process of the experiment batteries is safe and simple.The most dangerous ISCr type,Al-Anode ISCr,and the most common ISCr type,Anode-Cathode ISCr,are analyzed through the experiments with the SMA ISCr trigger method.Comparing with the nail penetration test,the SMA ISCr trigger method has better repeatability and reliability.Secondly,the Fusing Phenomenon of ISCr is discovered through the analysis of the lithium dendrite melting scenario.The hypothesis of the Fusing Phenomenon’s entire life cycle is presented,which reveals the heating-melting period,the ion discharging period and the implosion period.Through the Al-Cu ISCr experiments,the Fusing Phenomenon is verified,the hypothesis of the Fusing Phenomenon’s entire life cycle is examined.The axisymmetrical local simulation model of Al-Cu ISCr Fusing is constructed to analyze the Fusing Phenomenon and its influence factors.Having the Fusing Phenomenon as the key node,a new ISCr developing diagram is presented,which interprets the ISCr evolution process.Thirdly,the Parameter Effect and the Depleting Effect of ISCr are discovered,which reveal the electrical features of ISCr batteries.Based on the significance criterion of the ISCr characteristic parameters,the ISCr detection method for series battery packs is invented.This ISCr detection method is able to detect the initial phase ISCr in series battery packs.Finally,the symmetrical loop circuit topology(SLCT)is invented.Based on the SLCT,the ISCr detection method for parallel battery packs is invented,which overcomes the difficulty of the ISCr detection in parallel circuits.Through this ISCr detection method,the accurate estimation of ISCr resistance is achieved,the detection speed of the initial phase ISCr is improved from the magnitude of days and hours to the magnitude of seconds.The research outputs provided technical guidance to the BMW Group.Several patents and copyright yielded by this research were purchased by the Daimler AG.