Microstructure and electrochemistry performance of the composite electrode prepared by spark plasma sintering

The 30%LiFePO4-55%Li1.5Al0.5Ge1.5(PO4)3-15%C composite electrodes were successfully prepared by spark plasma sintering, and the microstructure and electrochemistry performance were investigated. As sintered at 550 °C, the phase structure of the composite electrode remained unchanged. With the sintering temperature increasing, the Li1.5Al0.5Ge1.5(PO4)3 were decomposed and transformed into nanocrystals and impurity phases of AlPO4 and GeO2. The 3D-microstructure showed that abundant pores existed in the composite electrodes. The volume fraction and connectivity of these pores decreased with the sintering temperature. The initial discharge capacity of the composite electrode was 138 mAh·g−1 as sintered at 550 ℃, while it decreased monotonously with the sintering temperature. The decrease was related with the formation of impurities and closed pores. Moreover, the composited electrode sintered at 550 ℃ had severely capacity fading during electrochemistry cycles. By the EIS and postmortem analyses, it was determined that the capacity fading was due to the ion transport failure caused by the cracking during cycles.