Bilayer Halide Electrolytes for All-Inorganic Solid-State Lithium-Metal Batteries with Excellent Interfacial Compatibility.

Inorganic solid-state electrolytes (ISSEs) have been extensively researched as the critical component in all-solid-state lithium-metal batteries (ASSLMBs). Many ISSEs exhibit high ionic conductivities up to 10-3 S cm-1. However, most of them suffer from poor interfacial compatibility with electrodes, especially lithium-metal anodes, limiting their application in high-performance ASSLMBs. To achieve good interfacial compatibility with a high-voltage cathode and a lithium-metal anode simultaneously, we propose Li3InCl6/Li2OHCl bilayer halide ISSEs with complementary advantages. In addition to the improved interfacial compatibility, the Li3InCl6/Li2OHCl bilayer halide ISSEs exhibit good thermal stability up to 160 °C. The Li-symmetric cells with sandwich electrolytes Li2OHCl/Li3InCl6/Li2OHCl exhibit long cycling life of over 300 h and a high critical current density of over 0.6 mA cm-2 at 80 °C. Moreover, the all-inorganic solid-state lithium-metal batteries (AISSLMBs) LiFePO4-Li3InCl6/Li3InCl6/Li2OHCl/Li fabricated by a facile cold-press method exhibit good rate performance and long-term cycling stability that stably cycle for about 3000 h at 80 °C. This work presents a facile and cost-effective method to construct bilayer halide ISSEs, enabling the development of high-performance AISSLMBs with good interfacial compatibility and thermal stability.

Understanding the Effect of Atomic-Scale Surface Migration of Bridging Ions in Binding Li3PO4 to the Surface of Spinel Cathode Materials.

Spinel cathode materials (e.g., LiMn2O4 and LiNi0.5Mn1.5O4) with strongly bonded surface coatings are desirable for delivering improved electrochemical performance in long-term cycling. Here, we report that the introduction of bridging ions such as Fe and Co, which can diffuse into both the spinel cathode materials and Li3PO4, the latter is found to cover the spinel surface in the form of dense and uniform particles (∼2-3 nm). Detailed structural analysis of the surface reveals that the bridging ions diffuse into the 16c site of the spinel structure to form ion-doped spinel cathode materials, which contribute to the formation of strong bonds between the surface and Li3PO4, possibly via spinel-(surface bridging ions)-Li3PO4 bonds. The critical role of the surface bridging ions is further investigated by heating the as-formed Li3PO4-coated spinel cathode materials (with bridging ions) to high temperatures, resulting in further diffusion of bringing ions from the surface to the interior of the spinel materials and consequently depletion of the surface spinel-(surface bridging ions)-Li3PO4 bonds. This leads to the gradual growth of surface Li3PO4 particles (∼20 nm) and the exposure of the spinel surface.