A New Electrochemical Energy Storage Material-Intercalation-Type Niobium-Based Anode Material

High-performance lithium-ion batteries（LIBs）with four essential requirements of long-term cyclability,large reversible capacities,fast charging performance and elevated safety are intensively pursued for electric vehicles（EVs）.In recent years,niobium has been considered as one of the most promising anode materials for lithium storage due to its rich niobium chemical properties and open crystal structure.However,the exploration of niobates is still insufficient.Therefore,it is necessary to explore newNb-based anode materials to improve the electrochemical properties of niobium-based oxide materials.（1）CuNb₃O₈ was developed as a new niobium-based material for the cathode of lithium battery,and the CuNb₃O₈ particles with 0.2-1μm particle size distribution were successfully synthesized and prepared by a simple ball milling and solid-phase sintering method.CuNb₃O₈ can be identified as a monoclinic phase（P/21a space group）,CuNb₃O₈ open and robust framework is constructed byNb O₆ octahedra linked by Cu O₄ tetrahedra through sharing O^2–.CuNb₃O₈ structural and appearance advantages give excellent electrochemical properties,including large reversible capacity(231.8 m Ah g^-1 at 0.1C),first cycle coulomb efficiency（75.8%）,safe operating potential（～1.53V vs.Li/Li⁺）,and cycle stability（capacity retention of 60.0%after 100 cycles at 1C）.（2）A new type ofNb-rich oxide,NaNb₁₃O₃₃,has been developed and prepared as a new type of unembeddedNb-based anode material.High purity NaNb₁₃O₃₃ micron particles were successfully prepared by secondary sintering method.NaNb₁₃O₃₃ has a very stable like shears Re O₃ crystal structure（C2/m space group）,and its structural units are composed ofNb O₆ octahedra and Na atoms linked by sharing O^2–.Open and stable crystal structure gives NaNb₁₃O₃₃ showed excellent electrochemical performance,which has the larger A-B-Alayer spacing faster lithium-ion diffusion rate,higher specific capacity(0.1 C to 330 m Ah g^-1),excellent performance ratio and safe working potential（～1.51 V vs Li/Li⁺）,and long cycle stability（10 C under capacity to keep 99.1%after 1000 cycles）.In-situ X-ray diffraction characterization verified the excellent structural stability and electrochemical inversibility of NaNb₁₃O₃₃,revealing that the main embedding and exiting reaction of lithium-ions occurs on the（110）plane during the embedding and exiting process.Through in-situ transmission electron microscopy,it was accidentally found that during the process of charging and discharging,due to the formation of holes in the material itself,the strain of NaNb₁₃O₃₃single crystal in the electrochemical reaction was alleviated,the volume change of the actual reaction was reduced,and the structural deterioration of the material itself was significantly reduced during the electrochemical reaction.In addition,Li Ni_0.5Mn_1.5O₄//NaNb₁₃O₃₃,Li Fe PO₄//NaNb₁₃O₃₃,Li Ni_0.8Co_0.1Mn_0.1O₂//NaNb₁₃O₃₃ full cells show excellent electrochemical properties,it is further proved that NaNb₁₃O₃₃ has potential practical applications.Therefore,as an anode material,NaNb₁₃O₃₃ perfectly meets the four key requirements of high energy density,high power density,high safety and long cycle performance of on-board power lithium-ion batteries,making it a promising anode material for lithium-ion batteries.