Possibility of Using Petroleum Coke As Reducing Agent for V2O5 in Solid-Phase Synthesis of Li3V2(PO4)3

Abstract

Nowadays, electrochemical batteries are playing an important role in the development of technology in various fields – consumer electronics, electric transport, and stationary energy storage systems. The main requirements for modern batteries are high specific energy and low cost. State of art lithium-ion batteries have the highest specific energy, but their cost is quite high, and that limits their production volume. Therefore, a relevant problem is the development of new low-cost electrode materials with a high specific energy. One of the most promising compounds for positive electrodes of lithium-ion batteries is lithium vanadium phosphate Li3V2(PO4)3. It has the same safety in operation as LiFePO4, and at the same time has a higher specific capacity of 197 mA·h/g vs. 170 mA·h/g in LiFePO4, and provides lithium-ion batteries higher average discharge voltage. The lithium-ion batteries with positive electrodes based on Li3V2(PO4)3 have an average discharge voltage of 4.1 V and with LiFePO4 have 3.3 V [1]. The main raw material for lithium-vanadium phosphate is vanadium pentoxide (V2O5). V5+ reduces to V3+ in the process of synthesis Li3V2(PO4)3. The aim of the present work was to study the possibility of using petroleum electrode coke as a reducing agent in the solid-phase synthesis of lithium vanadium phosphate Li3V2(PO4)3. The following reagents were used: Li2CO3 (>99.9%), NH4H2PO4 (>98%), V2O5 (>99%), petroleum electrode coke. The reagents were milled to a homogeneous mixture in a mortar, then pressed into pellets in a hydraulic press at a pressure of 6 tons per cm2. The synthesis was carried out at a temperature of 800 °C in a tubular furnace in an argon atmosphere for 5 hours. Electrodes of the following composition (% wt.) were made of the synthesized material: 80% Li3V2(PO4)3, 10% Super P, 10% LA-132. 1M LiPF6 in mixture of DMC:EMC:EC:PA (1:1:2:1 by vol.) was used as an electrolyte, Celgard®3501 was used as a separator, lithium metal foil (100 µm) was used as the negative electrode. On the 1st cycle, the discharge capacity of the cells was 130 mA∙h/g(Li3V2(PO4)3) for cells being cycled in the potential range of 3.0-4.2 V and 160 mA∙h/g(Li3V2(PO4)3) in the range of 3.0-4.8 V. According to obtained results, it can be concluded that petroleum electrode coke can be used as a reducing agent in the solid-phase synthesis of Li3V2(PO4)3. In order to improve the characteristics of Li - Li3V2(PO4)3 cells, it is necessary to optimize the synthesis method. This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7), Russia.