Boron doping modulates the electrostatic interaction of Na-O bond for inducing P2/O3 biphasic structure in layered oxide cathode

Abstract

Sodium-ion batteries (SIBs) are promising for large-scale energy storage, yet developing cathode materials with both high capacity and long-term stability remains challenging. Herein, the strategy of modulating the electrostatic interaction of Na-O bonds via polarization effect through boron doping is proposed, enabling the precise construction of the P2/O3 biphasic structure. A series of Na0.8Fe1/3Ni1/3Mn1/3BxO2 (x = 0.00-0.08) cathode materials are synthesized. At low x doping levels, the material exhibits the O3 phase, while the P2/O3 biphasic structure emerges starting at x = 0.05. With increasing boron content, the Na-O bond electrostatic interaction weakens and the R value increases, which facilitate the emergence of the P2 phase. Among the samples, the Na0.8Fe1/3Ni1/3Mn1/3B0.05O2 cathode, has the optimal biphasic ratio comprising 10.3% P2 and 89.7% O3, endowing it with as low as 1.38% volume variation during charge/discharge, as identified by in situ X-ray diffraction measurement. It achieves an optimal balance of electrochemical performance, delivering a remarkable cycling stability with a capacity retention of 92.24% after 200 cycles at 1 C and a sufficient capacity of 100.2 mAh g-1 at 0.1C. This work demonstrates that B3+ doping effectively tailors Na-O bond chemistry to construct a stable P2/O3 biphasic structure, offering a viable approach for designing high performance layered oxide cathodes for sodium-ion batteries.