Effect of heat treatment on the interface resistance between LiFePO4 and Li7La3Zr2O12

All-solid-state lithium batteries are in great demand, but the problem of high interfacial resistance between the cathode and solid electrolyte needs to be addressed. The effect of heat treatment of the cathode half-cells on the LiFePO₄ | Li₇La₃Zr₂O₁₂ interfacial resistance was studied. According to differential scanning calorimetry, the interaction between the cathode material and Li₇La₃Zr₂O₁₂ begins at 699 °C. It was also shown via X-ray diffraction data that increasing the annealing temperature from 600 to 700 °C leads to the appearance of impurities related to the interaction of the solid electrolyte with LiFePO₄ (La₂Zr₂O₇ and LaFeO₃). A scanning electron microscopy study demonstrated that LiFePO₄ has good contact with ceramic electrolyte without and after heat treatment. The lowest resistance at the LiFePO₄ | Li₇La₃Zr₂O₁₂ interface (∼2000 and 30 Ohm cm² at 100 and 300 °C, respectively) was obtained for half-cells without heat treatment. Thus, heat treatment leads to an increase in the interfacial resistance caused by the interaction of LiFePO₄ with Li₇La₃Zr₂O₁₂