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 1^st 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.

References

[1]. S.W. Choi, Da. H. Kim, S.H. Yang, M.Y. Kim, M. S. Lee, Journal of Industrial and Engineering Chemistry, 52 (2017), 314-320.