Study On LiFePO₄/Li₄Ti₅O₁₂Battery

Due to the high rate and long cycle life capability, LiFePO₄and Li₄Ti₅O₁₂could beused as cathode and anode of LFP/LTO lithium-ion battery respectively, to supply electricvehicle with high energy density and high power density. In this thesis, we firstcharacterized and evaluated the cathode and anode materials of LFP/LTO battery, and thenstudied the performance of LFP/LTO pouch battery with different binder, conductive carbon,separator and electrolyte.The cathode material LFP-3and anode material LTO-1were nanoparticles shown byXRD and SEM analysis. Their electrochemical performance was tested in CR2032coincells with Li metal reference electrode. The specific capacity corresponding to Li-ioninsertion and de-insertion in LFP-3at0.1C reached158.1mAh·g^-1and158.8mAh·g^-1, at5C reached124.5mAh·g^-1and118.1mAh·g^-1respectively, showing that LFP-3had a highspecific capacity at high rates. The specific capacity corresponding to Li-ion insertion andde-insertion in LTO-1at0.1C reached165.7mAh·g^-1and165.2mAh·g^-1, at10C reached108.8mAh·g^-1and108.8mAh·g^-1respectively. After100cycles at1C, the specific capacityof LTO-1remained94.7%. LTO-1was identified to have high rate performance and longcycling stability. Therefore, LFP-3and LTO-1are the better choice of cathode and anodematerials of LFP/LTO battery which can be charged and discharged quickly.Effects of materials used in LFP/LTO pouch battery on its performance wereinvestigated. In the aspect of binders in the positive electrode, two binders with differentrelative molecular masses were tested. It was found that binder B-a is better than others forthe discharge performance at high rate and low temperature. However binder B-b is betterthan others for the performance of high rate charge and cycle life. For the conductivecarbons in the negative electrode, ECP and SP were investigated. It was found that ECPexhibited better performance at high discharge and charge rate and longer cycling life thanSP. But ECP has the same discharge performance at low temperature with SP. As toseparators, both of Separator-A and Separator-C were stable at high temperature,Separator-A performs better at high rates due to its low resistance, but has no differencewith Separator-C for low temperature discharge performance. Separator-C, on the otherhand, displayed a longer cycle life than Separator-A. In the aspect of electrolytes, E-2had the minimum effect on battery polarization, but E-4had a much better performance at lowtemperature.The energy density of LFP/LTO pouch battery reached58Wh·kg^-1, its maximum peakpower density reached1kW·kg^-1and its cycle life reached more than2500times whencharged at5C and discharged at2C. The LFP/LTO battery has a promising developmentpotential.