Study On The State Of Health Of Power Lithium Ion Battery For Electric Vehicle

Electric vehicle is a main direction of the future car development.Power batteries often function as the energy storage and supply of electric vehicles,whose performance will directly determine the performance of electric vehicles.At present,lithium-ion batteries are mainly used for the power battery electric vehicles so that researches related with lithium-ion batteries of electric vehicle power have become the major concerns of many companies and universities nowadays.In this paper,with the state of health(SOH)of lithium battery as the research direction,the author proposes two new methods of estimating and measuring the relative states of lithium-ion batteries.O ne is a new SOH estimation method for lithium-ion batteries,which is based on internal resistance to estimate the SOH of lithium-ion battery.The other is a new SOC measurement method of lithium-ion battery based on AC internal resistance.This method can not only measure the battery SOC,but also can protect the battery and slow battery SOH attenuation by correcting the lithium-ion battery in different SOH charge and discharge cut-off conditions.In this paper,the two kinds of electric vehicle powered lithium ion batteries----NCR18650 B battery manufactured by Panasonic Corporation of Japan and LR1865 AM battery manufactured by Tianjin Lishen Company----are selected as the experimental objects.The main work of this paper can be divided into the following aspects:Firstly,the author briefly introduces the necessity and significance of studying the health status of Li-ion battery as well as the current research status of SOH and SOC of lithium battery.And the definitions and calculation methods under different measurement methods are also described in this part.Then,a new SOC measurement method based on AC internal resistance is introduced in details.The test method of the related experiment is firstly described in this part,and then comes the description the special change phenomenon of the battery internal resistance in the process of charging and discharging.After that,the regular pattern of this phenomenon is summed up through the trial data analysis and calculation of a large number of experiments,which contributes to the proposal of a new SOC measurement method.This method can not only measure the battery SOC,but also can protect the battery and slow battery SOH attenuation by re-delineating the battery charge and discharge cut-off conditions.At last,the SOH estimation method based on internal resistance is presented thoroughly.In this part,the author firstly introduces the specific meaning of the internal resistance as well as the battery charge and discharge energy model used in this SOH estimation method.Then,the main body of my experiment is introduced that the method of SOH estimation of this new type lithium-ion battery is summarized through the analysis of a lot of experimental data.It proves in this paper that when combining these two methods: the SOH estimation method based on internal resistance and the new SOC measurement method based on AC internal resistance,we can not only estimate the SOH of the battery,but ca n also adjust the charge and discharge cut-off conditions of the battery under a certain SOH so as to achieve the the purpose of protecting the battery and delaying SOH attenuation that no other existing lithium SOH estimation methods can achieve.