Employees of the Faculty of Chemistry of Moscow State University were able to synthesize promising material for sodium-ion batteries. These batteries are considered a cheaper alternative to the widely used lithium-ion batteries.
The rapid development of lithium-ion battery technology in just a few decades has led to the massive proliferation of compact and capacious power supplies for numerous mobile devices, energy storage and even vehicles. However, a fundamental problem arose – with the current growth in consumption and the level of lithium mining technologies, its resources may be exhausted, moreover, this is not the cheapest raw material. A partial transition to an alternative charge carrier in batteries, sodium, can help solve the problem.
In terms of energy characteristics, the sodium-ion battery is close to lithium-ion, but its main working cation is about a hundred times cheaper than lithium (one ton of sodium carbonate costs $ 200, while lithium costs $ 20,000). In addition, the chemical properties of sodium make it possible to use light and cheap aluminum in the anode instead of heavy and expensive copper.
Unfortunately, a larger radius of the sodium ion compared to lithium ion leads to a decrease in the energy storage density in the electrode. With the same energy intensity, the battery is 30-50% more. This makes sodium-ion batteries less attractive for mobile devices, but for large batteries – say, in an electric car or stationary storage of electricity – they are quite suitable.
Specialists of the Department of Electrochemistry of Moscow State University, headed by a senior researcher, Ph.D. Oleg Drozhzhin, for the first time synthesized a new material for sodium-ion batteries – sodium-vanadium pyrophosphate – and characterized its electrochemical properties.
The energy intensity of the material reaches 420 W · h / kg. This is only 20% less than 530 Wh · kg / kg, an indicator of lithium-based LiCoO2 cathode material, and significantly higher than the energy intensity of many previously studied potential sodium cathode materials. An equally important advantage of the new material is an extremely small change in volume during charge-discharge. According to this indicator, equal to 0.5%, it is close to lithium-titanium spinel, which is used in electric vehicle batteries, since it is considered the most stable, powerful and safe anode material.
The sodium-vanadium pyrophosphate framework can reversibly donate and incorporate up to two sodium cations per unit cell. According to the total capacity of such cycling, approximately equal to 220 mA · h / g, pyrophosphate is a champion among similar materials. In addition, this means that it can potentially become the anode material of sodium-ion batteries. Chemists at Moscow State University plan to further improve the electrochemical properties of the compound by changing the initial oxidation state of vanadium and partially replacing it with other cations.