Synthesis And Electrochemical Characterizations Of Carbon Coated Li₃V₂（PO₄）₃Cathode Materials

In recent years, due to the high energy density, reusable, long cycle life,environmental benefits, lithium ion secondary battery has been widely used in themobile phone, notebook and portable electronic devices. In addition, the research oflithium ion secondary battery has been mature in the field of electric vehicles. As themost important factor of the performance and the research of electrode materials hasalways been one of the keys. The early time of lithium ion technology was solelydevoted to oxide cathode materials, such as LiCoO2, LiMn2O4and LiNiO2. However,there still exist some disadvantages such as short cycle life, strong toxicity, safetyissue. Thus, a new type of lithium ion secondary battery cathode material still need toresearch. Recently, Goodenough et al., basing on the research of the poly anionicelectrode materials, has succeeded in finding LiFePO4cathode material that has manyexcellent electrochemical properties. Similar like LiFePO4materials, Li3V2(PO4)3material has the NASICON structure. Therefore, the electrochemical cycle stability,charging and discharging work platform as well as the safety performance and so on,should be all excellent. Besides the cathode electrode materials, lithium ion secondarybattery anode material also has an important influence on the electrochemicalproperties. The commercial anode material is graphite. Graphite which has theoreticalspecific capacity372mAh/g can match with the most common cathode materials.However, with the deep research of the lithium ion battery cathode materials,electrode materials with higher specific capacity appear constantly. As a result, newanode materials can replace graphite also has become the research focus. As a newanode material, Li4Ti5O12has some advantages such as stable structure and its zero‘‘straining electrochemical. Besides,The cycling voltage of Li4Ti5O12with respect tolithium metal is relatively higher than that of graphite. Therefore, compared withgraphite, Li4Ti5O12has long cycle life and higher safety. Therefore, this paper studiesLi3V2(PO4)3/Li4Ti5O12new lithium-ion battery system.First of all, we successfully prepared carbon coated Li3V2(PO4)3by using carbon thermal reduction process in800oC, the synthesis of pure phase has a monoclinalstructure and space group is P21/n. SEM illustrates that the material is composed ofwell-dispersed secondaryparticles,the average particle size of the powders is about2um. HRTEM shows that a small amount of carbon penetrated into the Li3V2(PO4)3crystallite to form a Li3V2(PO4)3-C interface film with thickness about10nm. Ramanshows that the carbon on the surface of coated Li3V2(PO4)3material is the amorphousnature of the residual carbon.Then, we study the electrochemical performance of Li3V2(PO4)3in differentvoltage range. The first discharge specific capacity is121mAh/g at the currentdensity of30mA/g in the voltage window of3.0-4.3V, after50cycles the dischargespecific capacity is119.5mAh/g, capacity only loses1.5mAh/g, the cycle stability ofthe material is very excellent. At the same current density, The first discharge specificcapacity is158.5mAh/g in the voltage window of3.0-4.8V, after50cycles thedischarge specific capacity is only130mAh/g, capacity loses28.5mAh/g. Bycomprehensive comparison, Li3V2(PO4)3shows better electrochemical performance in3.0-4.3V voltage.Finally, we focus on the electrochemical performance of Li3V2(PO4)3/Li4Ti5O12in different voltage range. The first discharge specific capacity of Li3V2(PO4)3/Li4Ti5O12is125.1mAh/g at the current density of17mA/g in the voltage window of1.5–2.9V, after30cycles the discharge specific capacity is102.9mAh/g, capacityloses22.2mAh/g, the capacity retention is only82.2%. At the same currentdensity,The first discharge specific capacity of Li3V2(PO4)3/Li4Ti5O12is145.6mAh/gin the voltage window of1.5–3.3V, after30cycles the discharge specific capacity is110.8mAh/g, capacity loses34.8mAh/g, the capacity retention is76.1%. So theelectrochemical performance in the voltage window of1.5-2.9is better than that of inthe voltage window of1.5-3.3.Through the study of this article, we have with deeper understand in Li3V2(PO4)3/Li4Ti5O12, which is very meanful. We think that the research of Li3V2(PO4)3with other anode materials have a certain guided role in future.