Electrochemical Performance And Safety Evaluation Of LiFePO₄/Li₄Ti₅O₁₂ Lithium Ion Battery

LiFePO₄ cathode material gradually expands its market share for its low-cost and environmentally friendly. In this paper, graphite and Li₄Ti₅O₁₂ are researched as anodes, respectively, for LiFePO₄ lithium ion battery.(1) LiFePO₄ material was synthesized by solid state method which is feasible in industrial application. Two methods for introducing conductive carbon, coating and mixting, are applied to improve the conduction of LiFePO₄ cathode. It is considered that the connection between active material and conductive carbon determines the electrochemical performance of the lithium ion battery. It is also considered that the lower the particle size of conductive carbon, the higher the specific capacity will be achieved at low rates, but worse cycle performance at high rates.(2) 403562-type soft package LiFePO₄/graphite lithium ion batteries were designed and fabricated. The relative manufacture technique was detected. Statistic method was applied for the first time to research the relationship between the fabrication and the electrochemical performance. And some advices were approved to improve the specific capacity, specific energy, and product yield.(3) Electrochemical analysis for the 403562-type soft package LiFePO₄/graphite lithium ion batteries were implemented to figure out the gap between practical use and demands. It is considered that the graphite material is limiting the charge-discharge stability and safety performance of LiFePO₄/graphite cell, especially during cycling and under overcharge condition.(4) Solid state method was applied for synthesizing Li₄Ti₅O₁₂ material. And liquide electrolyte soft package 4050140-type LiFePO₄/Li₄Ti₅O₁₂ batteries were designed and fabricated for the first time. The cooperation of the two kinds of materials was researched and the electrochemical properties were detected. It is considered that the distinctive lithiation-delithiation plateaus of Li₄Ti₅O₁₂ deduce the side-reactions inside the cell, which is helpful to cycling stability. The overcharge performance of LiFePO₄/Li₄Ti₅O₁₂ cell was detected, and it is considered that the excellent thermal runaway resistibility of the LiFePO₄/Li₄Ti₅O₁₂ system is due to the infinitesimal crystal-distortion and preferable lithium ionic diffusion of Li₄Ti₅O₁₂. The anode excessive ratio and separater for the electrochemical and safety performances were also investigated.