Research On Detecting The Overcharge/Overdischarge Of The Power Batteries Based On Structure And Performance

The overcharge and overdischarge are the typical security problems of the electric vehicle power batteries during the applied process.To detect overcharge and overdischarge accurately is of great significance for the research and development,manufacture and routine maintenance of power batteries and the safety guarantee for the electric vehicle occupant.The commonly used detection methods based on electrochemical performance are susceptible to the interference factors such as aging,which leads to inaccurate and unreliable detection results.The electrochemical performance of the power batteries is the external performance of its internal structure,and its internal structure is the internal basis of electrochemical performance,and the two exist mutually reinforcing relationship.It is helpful to improve the accuracy and reliability of overcharge/overdischarge detection by combining structure detection with electrochemical performance detection.Therefore,a certain kind of lithium iron phosphate battery was regarded as the research object,and in order to detect overcharge/overdischarge of power batteries and its degree,the mehod for detecting overcharge/overdischarge of power batteries based on structure and performance was proposed.First of all,the mechanism of influence from overcharge/overdischarge on structural morphology and electrochemical performance of power batteries was studied.The gassing/copper precipitation,lithium dendrite/copper dendrite,the change of voltage and capacity that were caused by overcharge/overdischarge was discussed.On this basis,the characteristics of internal structure and electrochemical performance of overcharged/overdischarged batteries were summarized.Second,according to the principle of computer tomography and electrochemical performance measurement,the method of detecting the overcharge/overdischarge of the power batteries based on structure and performance was proposed.And the mechanism of the comprehensive application of tomography and electrochemical performance measurement to detect the overcharge/overdischarge of the power batteries was expounded.An image processing algorithm was designed to obtain the structure parameters of overcharged/overdischarged batteries(pixel quantity n_gas/n_Cu and its density distribution feature vector DDF).According to the principle of Levenberg-Marquardt algorithm and capacity increment analysis,the internal short circuit resistance R_s that was a parameters of short circuit model for overcharged/overdischarged power batteries was identified,and the characteristics of the change of the incremental capacity was analyzed.According to the principle of analytic hierarchy process,the state of overcharge/overdischarge（SOC_C and SOC_F）of the power batteries was estimated by combining the structure parameters with the performance parameters.Third,a certain type of lithium iron phosphate power batteries applied to vehicle was taken as the experimental objects,called experimental battery for short.The experiment system composed of overcharge/overdischarge experiment subsystem,electrochemical performance detection subsystem and computerized tomography detection subsystem was set up,in which the experiment was carried out to detect the batteries in different state of overcharge/overdischarge.Finally,by analyzing the tomographic image measurements data and electrochemical performance measurement data,the curves of the relation between(n_gas/n_Cu,R_s)and（SOC_C or SOC_F）were fitted by using nonlinear regression method.The change rule of the characteristics of density distribution feature and incremental capacity along with overcharge/overdischarge state was discussed.And the reliability and accuracy of the method for detecting the overcharge/overdischarge of the power batteries based on structure and performance was verified.