Study On Synthesis And Electrochemical Properties Of LiMo₂?M=Mn/Mo/V? Cathode Materials For Lithium-ion Battery

Layered LiMO₂ is considered to be a good lithium-ion battery cathode material because of its structure is advantageous to the de-intercalation/intercalation of lithium ions during the process of charging and discharging,In recent years,layered LiMnO₂ become one of the most attractive new cathode material for rechargeable lithium-ion batteries due to its high specific capacity?285 mAh/g?,high energy density and high environment acceptability.Researchers are mainly focused on orthorhombic LiMnO₂ and monoclinic LiMnO₂ during the studying of layered LiMnO₂.The structure of the orthorhombic LiMnO₂ relatively stable,preparation of monoclinic LiMnO₂ is difficult and limit its further application because of it belong to thermodynamic metastable phase.In addition,compared with traditional type of transition metal oxide,layered LiMoO₂ also become a new important lithium ion battery cathode material gradually due to its good thermal stability,high specific capacity,safe and good cycle performance,high environment acceptability.The main synthesis methods of layered LiMoO₂ is high temperature solid method,the process of this method is complex and reaction time is too long.Similarly,cathode material LiVO₂ in a similar situation,the synthesis method of LiVO₂ rely on the traditional high temperature solid method and hydrothermal method,but the capacity of cathode material LiVO₂ that synthesized by these methods is low.For these defects,this study use new methods to synthesize target products,compare with the traditional synthesis methods,the new methods have different advantages,simplified the experimental steps,improve the efficiency,improve the electrochemical properties of the materials at same time.In the synthesis and electrochemical properties of the LiMnO₂ :The layered LiMnO₂ with orthorhombic structure?o-Li MnO₂?and monoclinic structure?m-LiMnO₂?and the mix phase with m-LiMnO₂ and o-Li MnO₂ can be controlled synthesized via a one-step hydrothermal method.The final structure of product directly affected by temperature,reaction time,the molar ratio of Li/Mn and the concentration of alkaline solution.Electrochemical test results showed that under the condition of 0.1 C,the maximum discharge capacity of m-Li MnO₂ can reach219.8 mAh/g,but also exhibited poor cycle stability with a significant capacity loss after 50 cycles.Although the o-Li MnO₂ showed the lowest initial discharge capacity is 180 mAh/g,which demonstrated the best cycle stability and the reversible capacity.The mix phase with m-LiMnO₂ and o-LiMnO₂,however,combining withthe characteristics of both of them,exhibiting a high initial discharge capacity and better cycle performance.In the synthesis and electrochemical properties of the Li MoO₂: phase-pure LiMoO₂ was successfully synthesized by rheological phase reaction and solid state method.The results of phase characterization and electrochemical performance test showed that the sample consists of a single phase with a high degree of crystallinity at 750? calcined 12 h.The first discharge capacity of the material is 196.8 mAh/g at a rate of 0.05 C between 2.0 to 4.5 V.Close to the theoretical capacity means that lithium ion can be completely de-intercalation from materials.After 30 cycles,a discharge capacity of 138.2 mAh/g is still retained,which corresponds to 70%retention of the initial capacity.In the synthesis and electrochemical properties of the LiVO₂: Layered LiVO₂ was successfully synthesized by two-step reduction method.The crystallinity of as-prepared LiVO₂ by heating at 750°C for 12 h under a flowing argon atmosphere is good.The specific capacity of the material measured at 0.1 C is 197.4 m Ah/g in the voltage range of 1.0–4.5 V,68.5% of the initial discharge capacity is retained after 30 cycles.Compared with those LiVO₂ prepared by using citric acid and ascorbic acid?Vc?as carbon source,the electrochemical properties of LiVO₂ that use sucrose as carbon source is the best.