Intercalation Vanadium Based Anode Materials For Electrochemical Energy Storage

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,Li₃VO₄is of the most representative material.Li₃VO₄has a theoretical capacity of 394 mAh g^-1and 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 Cr³⁺doped Li₃VO₄compounds are synthesized by solid-state reaction.The obtained Li_3-xCr_2xV_1-xO₄compounds（x=0,0.01 and 0.02）have the same orthorhombic crystal structure（Pnm2₁space group）,suggesting the successful Cr³⁺doping in Li₃VO₄.Compared with Li₃VO₄,Li_2.98Cr_0.04V_0.98O₄exhibits a two orders of magnitude larger electronic conductivity.Additional benefits of the Cr³⁺doping include the increase of the Li⁺diffusion coefficient and the decrease of the particle size.Consequently,Li_2.98Cr_0.04V_0.98O₄displays not only a large reversible capacity.The“zero-strain”γphase Li_3.08Cr_0.02Si_0.09V_0.9O₄compounds were prepared by Cr³⁺-Si⁴⁺co-doping.“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_3.08Cr_0.02Si_0.09V_0.9O₄（γ-LCSVO）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.Li⁺sequentially inserted into the 4c（1）and 8b sites ofγ-LCSVO,but its maximum unit-cell volume variation was only～0.18%,the smallest among the explored“zero-strain”compounds.It mean strain originated from Li⁺insertion was only 0.07%.Consequently,bothγ-LCSVO nanowires（γ-LCSVO-NW）and micron-sized particles（γ-LCSVO-MP）exhibited excellent cycling stability with 90.1 and 95.5%capacity retentiaon after as long as 2000 cycles at 10C,respectively.Moreover,γ-LCSVO-NW andγ-LCSVO-MP respectively delivered large reversible capacities of 445.7 and 305.8 mAh g^–1at 0.1C,and retained 251.2 and 78.4 mAh g^–1at 10C.Additionally,γ-LCSVO showed a suitably safe operating potential of～1.0 V,significantly lower than that of the famous“zero-strain”Li₄Ti₅O₁₂（～1.6 V）.These merits demonstrate thatγ-LCSVO can be a parctical anode compound for stable,high-energy,fast-charging and safe Li⁺storage.