Interface Improvement of Li_6.4La₃Zr_1.6Ta_0.6O₁₂@La₂Sn₂O₇ and Cathode Transfer Printing Technology with Splendid...

All-solid-state lithium batteries (ASSLBs) are regarded as the next-generation energy storage devices due to their superior safety and potential high energy density. In ASSLBs, a composite solid electrolyte is the most competitive candidate. The interface between the cathode and composite electrolyte and the interface between ceramic and polymers are important factors affecting the performance of solid-state batteries. The interface between the superionic conductor and polymer electrolyte (polyvinylidene fluoride) was modified by in situ synthesis of a pyrochlore-type La₂Sn₂O₇ (LSO) ceramic layer on the surface of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO). The synthesis of LSO consumes La in LLZTO, increases the concentration of lithium ions in LLZTO, and significantly improves the conductivity of the composite electrolyte (LLZTO@LSO-CSE). Compared with the pristine sample (3.15 × 10^-5 S cm^-1), the conductivity of LLZTO@0.9%LSO-CSE was improved by an order of magnitude (as high as 1.30 × 10^-4 S cm^-1). At the same time, the lithium-ion transference number of LLZTO@0.9%LSO-CSE and LLZTO@1.5%LSO-CSE was 0.42 and 0.44, respectively (LLZTO@0%LSO-CSE was 0.36). Meanwhile, the pyrochlore structure of LSO has the characteristics of fast energy storage and conversion, so the full cell LiFePO₄|LLZTO@LSO-CSE|Li showed superior rate capability and cycling stability. As anticipated, the discharge capacities of LiFePO₄|LLZTO@0.9%LSO-CSE|Li were 141.4 mA h g^-1 (1 C) and 128.1 mA h g^-1 (2 C), respectively. However, the discharge capacities of pristine batteries without LLZTO modification were 122.5 mA h g^-1 (1 C) and 88.7 mA h g^-1 (2 C). After 400 cycles, the discharge capacity of the LiFePO₄|LLZTO@0.9%LSO-CSE|Li remained at 110.6 mA h g^-1, the Coulomb efficiency was 99.4%, and the capacity retention rate was 72% compared to 75.5 mA h g^-1, 98, and 49% for the pristine one, respectively. In addition, the transfer printing (TP) technology was used to improve the interface between the cathode and the solid-state electrolyte, which immensely increased the energy density (without aluminum foil). Compared with the original interface impedance of 379 Ω, the interface impedance was significantly reduced to 213 Ω. This uniquely developed LLZTO@LSO-CSE combined with the TP technology can provide an effective approach for the development of all-solid-state batteries.