2020年7月17日星期五

Nano Tungsten Oxide Applied in Cobalt-free Lithium Ion Battery

As one of the most hot topics recently, cobalt-free lithium ion battery is considered as an upgraded version of the current commercial ternary lithium ion battery. Because of their higher energy density and lower production costs, they are popular among many battery manufacturers. As a typical transition metal N-type semiconductor material, how should nano tungsten oxide be used in cobalt-free lithium battery?

Nano tungsten oxide can be used as a modifier for the anode material of cobalt-free batteries, and can also be used to produce high-performance anode materials. In terms of cathode materials, the use of WO3 can not only reduce the use of cobalt metal, but also effectively improve the specific capacity and thermal stability of the product. In terms of anode materials, the use of WO3 can significantly improve the rate performance and lithium storage kinetics.

nano tungsten oxide photo

As we all know, the biggest cost of new energy vehicles lies in power batteries. As far as the ternary lithium battery that currently dominates the market, the cobalt contained in it is a very important rare metal with a small distribution area and low output, making the cobalt price center of gravity relative to other rare metals for a long time. All are in a higher position, which greatly increases the production cost of power batteries.

At present, the price range of electrolytic cobalt is between 245~255 thousand RMB/ton, the price range of cobalt powder is between 266~269 thousand RMB/ton, cobalt sulfate is 4.45-4.70 million yuan/ton, cobalt chloride is between 54-57 thousand RMB /ton, tricobalt tetrachloride is between 175,000-180 thousand RMB /ton, cobalt chloride is 174~179 thousand RMB /ton. and cobalt sulfide is between 116~119 thousand RMB /ton.

cobalt free battery photo

In the context of the gradual retreat of subsidies for new energy vehicles in 2019 and the attack of COVID-19 in 2020, the removal of cobalt and chemical conversion have become the common choice of many power battery companies. In February 2020, the concept of Tesla's cobalt-free battery was introduced, and cobalt removal was pushed to the cusp. Various cobalt-free solutions gradually appeared in power battery companies.

Tungsten trioxide nanoparticles are often used by domestic researchers to replace the cobalt element in lithium ion batteries because of their unique physical and chemical properties. This is mainly because tungsten oxide has the characteristics of large specific area, high specific gravity, and good mechanical stability, which can significantly improve the specific energy density and thermal stability of the cathode material. This means that the positive electrode material containing tungsten trioxide is less likely to undergo thermochemical reaction with the electrolyte, thereby reducing the possibility of a sudden rise in partial pressure and temperature in the battery.

In order to further improve the capacity and charge-discharge rate performance of cobalt-free batteries, some researchers have indicated that tungsten trioxide powder can also be used to prepare the anode material. However, it should be noted here that tungsten trioxide needs to be compounded with graphene (RGO), which can significantly improve the overall electrochemical lithium storage performance of the composite material.

Due to the synergistic effect between tungsten trioxide and graphene, the reversible specific capacity of WO3/RGO nanocomposites at 0.1C rate is not only far superior to WO3 and RGO monomers, but also greater than the sum of the two monomers.

In addition, WO3/RGO nanocomposites also have stable cycling performance and good rate performance. After 100 cycles at 0.1C rate, its reversible specific capacity remains at 635mA/g, and the capacity retention rate is 83.4%; at 5C rate, its reversible capacity can still maintain 460mA/g, which is lower than the graphite negative electrode used in commercial lithium batteries. The theoretical specific capacity of the material (372mA/g) is much higher, which also indicates the potential application of the prepared tungsten trioxide/graphene composite material in a new generation of lithium ion batteries.

The vigorous development of cobalt-free batteries may help to further increase the demand for tungsten trioxide.

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