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

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.