Synthesis And Electrochemical Performance Of Lithium (Sodium) Vanadium Oxides For Lithium-ion Batteries

Advanced rechargeable lithium-ion batteries?LIBs?have received extensive attentions because of a favorable combination of high voltage,high energy density,long cycling performance.Cathode materials as an indispensabl component play a critical role in electrochemical performance of lithium ion batteries.Current study on cathode materials was mostly focused on layered compounds LixMO2 and spinel compounds LixM2O4?M=Co,Ni,Mn,V and other transition metalions?.Shortage of cobalt resources results in high cost of LixCoO2,while LixNiO2 cathode materials with perfect crystal structure are very difficult to be prepared.Meanwhile,the capacity of LixMn₂O₄ decays rapidly over cycling.Lithium vanadium oxides as cathode materials are of low price,no contaminate,high capacity and facile synthesis are recognized as one of the most potential cathode materials for lithium ion batteries.In this paper,the synthesis parameters,formation mechanism and structures of various lithium vanadium oxides are systematically studied and discussed,and the lithium-ion batteries performance of the as-prepared various lithium vanadium oxides are evaluated.The results and discussion are shown as follows:?1?A variety of LiVO₃ compounds?LVO-350,LVO-400,LVO-450,andLVO-500?were synthesized via an aresorcinol-formalin assisted sol-gel method.The lithium ion intercalation/deintercalation mechanism of LiVO₃ wass investigated by XRD and TEM.The results reveaed that the initial lithium insertion/extraction reaction of LiVO₃ based on V5+/V4+ redox couple underwent a successive structural transition:monoclinic LiVO₃ transforms into cubic Li₂VO₃ upon lithium intercalation,followed by the lithiated Li₂VO₃ transforming into a more stable phase witha similar crystalline structure to monoclinic LiV3O8 upon initial lithium deintercalation.?2?In this work,sodium doped LiVO₃ cathode is proposed to achieve enhanced cycling performance for lithium ion battery?LIB?application.LixNa2-xV2O6?x=2,1.4,1 ·0?compounds have been prepared and characterized,and X-Ray diffraction patterns confirmed the successful Na doping with various amounts in the LiVO₃.The electrochemical performances of the various Na doped compounds LiVO₃,Li1.4Na0.6V2O6,LiNaV2O6,and NaVO₃ are evaluated by cyclic voltammetry,galvanostatic charge/discharge and electrochemical impedance spectroscopy.The results reveal that Na-doping amount strongly affects the electrochemical performance,and LiNaV2O6?x=1?is considered as the optimized Na doped com-pound for LIB cathodes.The LiNaV2O6 cathode displays enhanced cycling and rate performances as a specific capacity of 193 mAh g-1 at 0.5 C after 100 cycles is delivered.The enhanced performance is explained that the doping of Na can provide good channels and increase Li+ diffusion coefficient for lithium ion intercalation/deintercalation?3?NaV₃O₈ nanoplates with a thickness of approximately 50-200 nm,a length of 1-3 mm,and a width of 0.2-1 mm have been fabricated by using an in situ template method.The as-synthesized NaV₃O₈ nanoplates used as a LIB cathode material delivered a high reversible capacity of 230 mAh g-1,with a capacity retention of 93.4%for up to 200 cycles,while the specific capacity ratained 50%at a high current density of 6.4 A g-1?21.3 C?.The superior electrochemical performances are attributed to the fast lithium-ion diffusion kinetics and good structural stability.The excellent Li-storage properties,including high capacity,superior high-rate performance,and long cycle life,demonstrate that NaV₃O₈ nanoplates can be serveed as a potential cathode candidate for Li-ion batteries.