Mg2Nb34O87 Porous Microspheres for Use in High-Energy, Safe, Fast-Charging, and Stable Lithium-Ion Batteries.

M-Nb-O compounds are advanced anode materials for lithium-ion batteries (LIBs) due to their high specific capacities, safe operating potentials, and high cycling stability. Nevertheless, the found M-Nb-O anode materials are very limited. Here, Mg2Nb34O87 is developed as a new M-Nb-O material. Mg2Nb34O87 porous microspheres (Mg2Nb34O87-P) with primary-particle sizes of 30-100 nm are fabricated based on a solvothermal method. Mg2Nb34O87 has an open 3 × 4 × ∞ Wadsley-Roth shear structure and a large unit-cell volume, leading to its largest Li+ diffusion coefficients among all the developed M-Nb-O anode materials. In situ X-ray diffraction analyses reveal its high structural stability and intercalating characteristic. These architectural, conductivity, and structural advantages in Mg2Nb34O87-P lead to its most significant intercalation pseudocapacitive contribution (87.7% at 1.1 mV s-1) among the existing M-Nb-O anode materials and prominent rate capability (high reversible capacities of 338 mAh g-1 at 0.1C and 230 mAh g-1 at 10C). Additionally, this new material exhibits a safe operating potential (∼1.68 V), an ultrahigh initial Coulombic efficiency (94.8%), and an outstanding cycling stability (only 6.9% capacity loss at 10C over 500 cycles). All of these evidences indicate that Mg2Nb34O87-P is an ideal anode material for high-energy, safe, fast-charging, and stable LIBs.