Octahedral Microdistortion for Aqueous Ammonium-Ion Batteries

Ammonium-ion battery (AIB) is an emerging energy storage system, owing to its inherent safety and low cost. However, the large size of NH4+ and its strong interaction with the host lattice lead to severe stress accumulation and undesirable structural evolution. Here, we introduce Al3+ into vanadium oxide to modulate the occupancy of the V t2g orbital, thereby achieving a local chemical coordination manipulation. The electronic adjustment breaks the lattice symmetry and induces a VO6 octahedral distortion. This microdistortion acts as a built-in stress buffer that suppresses lattice breathing and accelerates electron transport. As a result, the AlVO electrode delivers 112 mAh g–1 at 2 A g–1, retains 91% of its capacity over 10000 cycles. The pouch cell also delivers a durable cycling stability, further confirming the feasibility of this strategy. These findings clarify the relationship between local distortion and electrochemical performance, providing a rational route to optimize electrodes through precise regulation of coordination environments.