Sodium superionic conductor (NASICON)-type conducting ceramic Li 1+x Al x Ti 2−x (PO 4 ) 3 (LATP) has been regarded as one of the most promising candidates for high-safety and high-energy density solid-state Li metal batteries (SSLMBs) because of its high ionic conductivity and good chemical stability. However, the large interfacial impedance and instability between the solid electrode and LATP electrolyte severely hinder its practical application in solid-state batteries. To overcome this technical challenge, we demonstrate a polymer–ceramic–polymer composite electrolytes (PCPCEs) prepared through drop casting, which ameliorates the interfacial stability between the solid electrolyte and the electrode. PCPCEs with an ideal ambient-temperature ionic conductivity can drastically reduce the interfacial resistance between the LATP and solid electrodes and effectively avoid a direct reaction and contact between them. As a result, the interfacial impedance decreases from 30,000 to 280 Ω for the Li–LATP interfaces and from 40,000 to 800 Ω for the LATP–LiFePO 4 (LFP) interfaces. Meanwhile, the polarization voltage of the Li||PCPCEs||Li symmetric cell reduces from 1.5 V to 100 mV. The solid-state Li metal batteries assembled with a Li metal anode , LFP cathode, and PCPCEs exhibit a desired initial discharge capacity of 152.5 mAh g −1 and a good cycling performance at 0.1 C for 25 °C. This study provides a prospective insight to improve the poor interface between the solid electrode and inorganic conducting ceramic.
The large scale application of solid state lithium metal batteries based on NASICON-type Li 1+x Al x Ti 2-x (PO 4 ) 3 (LATP) electrolyte has been hindered by insufficient ion conductivity and interface instability due to the spontaneous Ti 4+ reduction reaction between Li metal and LATP. To address these issues, Li 1.7 Al 0.3-x Bi x Ti 1.7 (PO 4 ) 3 (0 ≤ x ≤ 0.03) (LABTP) electrolytes were prepared, and the influence of Bi substitution on the microstructure and conductivity of LATP were investigated. Suitable amount of Bi substitution accelerates densification and improves the ionic conductivity . Furthermore, unlike commonly used polyethylene oxide (PEO) and polyvinylidene difluoride (PVDF), polyvinylbutyral (PVB)-based quasi-solid electrolytes with LABTP is first-time proposed to improve the compatibility and stability of the LATP/Li interface. The synergistic effect of Bi doping and PVB reduces the reduction reaction of Ti 4+ . Small voltage hysteresis is observed in the corresponding Li||Li symmetric cells. The solid-state Li|LABTP@PVB|LiFePO 4 full cell can deliver a high capacity of 146.2 mAh g −1 and a stable cycling performance without reduction after 200 cycles.
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