Ionic conductivity and electro/chemical compatibility of Li₁₀SnP₂S₁₂ electrolytes play crucial roles in achieving superior electrochemical performances of the corresponding solid-state batteries. However, the relatively low Li-ion conductivity and poor stability of Li₁₀SnP₂S₁₂ toward high-voltage layered oxide cathodes limit its applications. Here, a Br-substituted strategy has been applied to promote Li-ion conductivity. The optimal composition of Li_9.9SnP₂S_11.9Br_0.1 delivers high conductivity up to 6.0 mS cm⁻¹. ⁷Li static spin-lattice relaxation (T₁) nuclear magnetic resonance (NMR) and density functional theory simulation are combined to unravel the improvement of Li-ion diffusion mechanism for the modified electrolytes. To mitigate the interfacial stability between the Li_9.9SnP₂S_11.9Br_0.1 electrolyte and the bare LiNi_0.7Co_0.1Mn_0.2O₂ cathode, introducing Li₂ZrO₃ coating layer and Li₃InCl₆ isolating layer strategies has been employed to fabricate all-solid-state lithium batteries with excellent electrochemical performances. The Li₃InCl₆-LiNi_0.7Co_0.1Mn_0.2O₂/Li₃InCl₆/Li_9.9SnP₂S_11.9Br_0.1/Li-In battery delivers much higher discharge capacities and fast capacity degradations at different charge/discharge C rates, while the Li₂ZrO₃@LiNi_0.7Co_0.1Mn_0.2O₂/Li_9.9SnP₂S_11.9Br_0.1/Li-In battery shows slightly lower discharge capacities at the same C rates and superior cycling performances. Multiple characterization methods are conducted to reveal the differences of battery performance. The poor electrochemical performance of the latter battery configuration is associated with the interfacial instability between the Li₃InCl₆ electrolyte and the Li_9.9SnP₂S_11.9Br_0.1 electrolyte. This work offers an effective strategy to constructing Li₁₀SnP₂S₁₂-based all-solid-state lithium batteries with high capacities and superior cyclabilities.

Lithium halide electrolytes show great potential in constructing high-energy-density solid-state batteries with high-voltage cathode materials due to their high electrochemical stability and wide voltage windows. However, the high cost and low conductivity of some compositions inhibit their applications. Moreover, the effect of electronic additives in the cathode mixture on the stability and capacity is unclear. Here, the Y³⁺ doping strategy is applied to enhance the conductivity of low-cost Li₂ZrCl₆ electrolytes. By tailoring the Y³⁺ dopant in the structure, the optimal Li_2.5Zr_0.5Y_0.5Cl₆ with high conductivity up to 1.19 × 10⁻³ S cm⁻¹ is obtained. Li_2.5Zr_0.5Y_0.5Cl₆@CNT/Li_2.5Zr_0.5Y_0.5Cl₆/Li_5.5PS_4.5Cl_1.5/In-Li solid-state batteries with different carbon nanotube (CNT) contents in the cathode are fabricated. The stability and electrochemical performances of the cathode mixture as a function of CNT content are studied. The cathode mixture containing 2% (wt.) CNT exhibits the highest stability and almost no discharge capacity, while the cathode mixture consisting of Li_2.5Zr_0.5Y_0.5Cl₆ and 10% (wt.) CNT delivers a high initial discharge capacity of 199.0 mAh g⁻¹ and reversible capacities in the following 100 cycles. Multiple characterizations are combined to unravel the working mechanism and confirm that the electrochemical reaction involves the 2-step reaction of Y³⁺/Y⁰, Zr⁴⁺/Zr⁰, and Cl⁻/Cl_x⁻ in the Li_2.5Zr_0.5Y_0.5Cl₆ electrolyte. This work provides insight into designing a lithium halide electrolyte-based cathode mixture with a high ionic/electronic conductive framework and good interfacial stability for solid-state batteries.