Tape-cast Ce-substituted Li₇La₃Zr₂O₁₂ electrolyte for improving electrochemical performance of solid-state lithium batteries

Solid-state lithium-metal batteries (SSLMBs) with a composite solid electrolyte (CSE) have great potential for achieving both high energy density and high safety and are thus promising next-generation energy storage devices. The current bottlenecks are a high electrode/electrolyte interface resistance and the limited Li⁺ conductivity of the solid electrolyte layer. To reduce the interface resistance, a tape casting method is used to directly deposit a CSE layer (∼20 μm) onto a model LiFePO₄ cathode. The CSE slurry infiltrates the cathode layer, forming a Li⁺ conduction network and ensuring intimate contact between the CSE and the cathode. The tape casting parameters, such as the polymer/Li salt ratio, inorganic filler fraction, and casting thickness, for the CSE layer are investigated. To increase Li⁺ conductivity, Ce substitution is conducted for Li₇La₃Zr_2−xCe_xO₁₂, x = 0-0.15. The effects of Ce content on the specific capacity, rate capability, and cycling stability of Li//CSE//LiFePO₄ cells are systematically studied. Li₇La₃Zr_1.9Ce_0.1O₁₂ (i.e., x = 0.1) is found to be the optimal composition; it outperforms Li₇La₃Zr₂O₁₂ and Li_6.25Ga_0.25La₃Zr₂O₁₂ in terms of CSE conductivity and SSLMB charge-discharge performance.