Study On The Electrochemical Performance And Mechanism Of Lithium Vanadate Negative Electrode Materials For Lithium-ion Batterie

Vanadate compounds were considered as promising anode materials for power lithium-ion batteries because of its high theoretical capacity,low working potential and excellent rate performance.Among them,Li₃VO₄ is of the most representative material.Li₃VO₄ has a theoretical capacity of 394 m Ah·g^-1 and a low safety working platform（～1V）,which is considered as a potential commercial anode material for lithium-ion batteries.However,its low conductivities limited its rate performance and cycle performance,and its low coulomb efficiency may also need to be improved.In order to solve these problems,we adopt a series of doping to improve its electrochemical performance.A series of Ge⁴⁺doped Li₃VO₄ compounds are synthesized by solid-state reaction.The obtained Li_3+xGe_xV_1-xO₄ compounds（x=0.06,0.10,0.15 and 0.20）have the same orthorhombic crystal structure（Pnmb space group）,suggesting the successful Ge⁴⁺doping in Li₃VO₄.Additional benefits of the Ge⁴⁺doping include the increase of the Li⁺diffusion coefficient.Consequently,γ-Li_3.06Ge_0.06V_0.94O₄ displays not only a large reversible capacity(204 m Ah·g^-1 at 50 m A·g^-1)and superior cyclic stability(92.6%capacity retention after1000 cycles at 1000 m A·g^-1)but also decent rate performance(103 m Ah·g^-1 at 1000 m A·g^-1).“Zero-strain”compounds are ideal energy-storage materials for long-term cycling because they present negligible volume change and significantly reduce the mechanically induced deterioration during charging-discharging.However,the explored“zero-strain”compounds are very limited,and their energy densities are low.Here,we exploredγphase Li_3.09Ge_0.09V_0.91O₄（γ-LGVO-0.09）as an anode compound for lithium-ion batteries,and surprisingly found its“zero-strain”Li⁺storage during Li⁺insertion-extraction through using various state-of-the-art characterization techniques.The maximum unit-cell volume variation was only～0.016%,the smallest among the explored“zero-strain”compounds.Consequently,γ-LGVO-0.09 nanowires（γ-LGVO-0.09-NW）exhibited excellent cycling stability with 94.8/111.5%capacity retention after 1800/1500 cycles at 25/60℃and 4 A·g^-1,and large reversible capacities of 383 and 425 m Ah·g^-1 at 0.05 A·g^-1,and retained 209and 331 m Ah·g^-1 at 4 A·g^-1.Additionally,γ-LGVO showed a suitably safe operating potential of～1.0 V,significantly lower than that of the famous“zero-strain”Li₄Ti₅O₁₂（～1.6V）.These merits demonstrate thatγ-LGVO-0.09-NW can be a practical anode compound for stable,high-energy,fast-charging and safe Li⁺storage.