Observation of High‐Capacity Monoclinic B‐Nb₂O₅ with Ultrafast Lithium Storage

Abstract Apart from Li₄Ti₅O₁₂, there are few anode substitutes that can be used in commercial high‐power lithium‐ion batteries. Orthorhombic T‐Nb₂O₅ has recently been proven to be another substitute anode. However, monoclinic B‐Nb₂O₅ of same chemistry is essentially inert for lithium storage, but the underlying reasons are unclear. In order to activate the “inert” B‐Nb₂O₅, herein, nanoporous pseudocrystals to achieve a larger specific capacity of 243 mAh g⁻¹ than Li₄Ti₅O₁₂ (theoretical capacity: 175 mAh g⁻¹) are proposed. These pseudocrystals are rationally synthesized via a “shape‐keep” topological microcorrosion process from LiNbO₃ precursor. Compared to pristine B‐Nb₂O₅, experimental investigations reveal that B‐Nb₂O_5−x delivers ≈3000 times higher electronic conductivity and tenfold enhanced Li⁺ diffusion coefficient. An ≈30% reduction of energy barrier for Li‐ion migration is also confirmed by the theoretical calculations. The nanoporous B‐Nb₂O_5−x delivers unique ion/electron transport channels to proliferate the reversible and deeper lithiation, which activate the “inert” B‐Nb₂O₅. The capacitive‐like behavior is observed to endow B‐Nb₂O_5−x ultrafast lithium storage ability, harvesting 136 mAh g⁻¹ at 100 C and 72 mAh g⁻¹ even at 250 C, superior to Li₄Ti₅O₁₂. Pouch‐type full cells exhibit the energy density of ≈251 Wh kg⁻¹ and ultrahigh power density up to ≈35 kW kg⁻¹.