MoCl 5 as a Cathode Material for Solid‐State Lithium Batteries: A Molecular Crystal With Zero‐Dimensional Building Blocks via Coordination Rearrangement

ABSTRACT Inorganic ionic crystals, characterized by extended lattices and strong ionic bonding, form the structural foundation of most cathode materials for lithium batteries. Yet, molecular crystals composed of zero‐dimensional building blocks have been largely overlooked. Their inherent structural fragility, dictated by weak van der Waals interactions, is widely presumed to preclude reversible Li + ion insertion. In this work, we challenge this assumption by providing molybdenum pentachlorides (MoCl 5 ), coupled with a halide solid electrolyte as a model system. We show that molecular crystal with zero‐dimensional building blocks can support highly reversible electrochemical lithiation. Operando synchrotron x‐ray absorption spectroscopy and x‐ray diffraction reveal that this reversibility is enabled by an electrochemically driven coordination rearrangement, in which discrete Mo 2 Cl 10 dimers reversibly transform into a framework of corner‐sharing MoCl 6 octahedra arranged in a zigzag motif. As a result, MoCl 5 delivers a specific capacity of 172 mAh g −1 and retains 85.6% of its capacity after 500 cycles in a solid‐state cell. These findings show that the coordination rearrangement enables the MoCl 5 molecular crystal to undergo reversible lithiation and delithiation, thereby pointing to a broader space for solid‐state intercalation electrochemistry in next‐generation energy storage materials.