Adopting inorganic solid electrolytes (ISEs) is a promising approach to assemble batteries using Li metal anodes because of their superior Li-ion conductivity and high mechanical strength. This approach greatly improves the energy density and the safety of batteries. However, lithium dendrites still can pierce the bare ISE because of inhomogeneous current distributions at interfaces, leading to serious short circuits. This work proposes to reduce the interfacial resistance and prevent lithium dendrite growth simultaneously through in situ formation of interlayers enabled by a conversion reaction of MoS₂ layers coated on a bare Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZO) pellet. The interfacial resistance is reduced to only 14 Ω cm², with the overpotential decreasing notably. The critical current density of cells is improved from 0.7 mA cm⁻² to 2.2 mA cm⁻². Furthermore, short circuits are significantly suppressed above the critical current density with the potential diverging quickly. The cell can be recovered to some extent by applying an inverse potential for a short time. The comparison between XPS and XAS measurements reveals that the nanoscale thin MoS₂ layer in contact with the Li anode can be converted into an interlayer composed of Mo and Li₂S through the conversion reaction. The sluggish kinetics of the conversion reaction resulting from the poor electronic conductivity makes the in situ-formed interlayer kinetically stable, which can hinder further reaction of MoS₂ with Li effectively. Moreover, the in situ reaction could suppress the local tip electric field effect efficiently and make the current distribution more even. This study provides a new strategy to optimize the interface of anodes by screening for more candidates which undergo a conversion reaction.

The intercalation compounds with various electrochemically active or inactive elements in the layered structure have been the subject of increasing interest due to their high capacities, good reversibility, simple structures, and ease of synthesis. However, their reversible intercalation/deintercalation redox chemistries in previous compounds involve a single cationic redox reaction or a cumulative cationic and anionic redox reaction. Here we report an anionic redox chemistry and structural stabilization of layered sodium chromium sulfide. It was discovered that the sulfur in sodium chromium sulfide is electrochemically active, undergoing oxidation/reduction rather than chromium. Significantly, sodium ions can successfully move out and into without changing its lattice parameter c, which is explained in terms of the occurrence of chromium/sodium vacancy antisite during desodiation and sodiation processes. Our present work not only enriches the electrochemistry of layered intercalation compounds, but also extends the scope of investigation on high-capacity electrodes.