Single‐Crystal‐to‐Single‐Crystal Transformation in a Thermally Stable All‐Inorganic Polyoxoniobate Framework Boosts Lithium Ion Battery Anode Performance

Niobium oxides are considered as promising anode materials for lithium‐ion batteries (LIBs) due to their excellent rate‐performance. However, the practical application is hindered by their limited specific capacity. In this work, we report the first example of an all‐inorganic two‐dimensional niobate framework as anode material for LIBs. The title compound is based on antimony‐linked bivanadyl‐capped α‐Keggin polyoxoniobates as secondary building units. The compound undergoes a unique single‐crystal‐to‐single‐crystal (SCSC) transformation triggered by formic acid which results in the migration of a {VO} unit into the framework interlayer. This results in a 34% increase of the specific capacity, reaching 519 mAh g‐1 at 0.1 A g‐1, thereby surpassing most Nb‐based LIB anode materials. Experimental and theoretical calculations reveal that the SCSC transformation exposes more Li‐binding sites in the framework, and reduces the interlayer Li‐ion diffusion barrier, leading to a capacity increase. This work presents the first example of a SCSC transformation leading to enhanced LIB performance and offers atomic‐level insights into the design of advanced LIB anode materials.