The researchers proposed a new strategy to extend the recyclability of sodium ion battery by using copper sulfide as electrode material.

The researchers proposed a new strategy to extend the recyclability of sodium ion battery by using Cu2S as electrode material. This strategy has led to high-performance conversion reactions, and is expected to promote the commercialization of sodium ion batteries, because they will become a substitute for lithium ion batteries.

Professor Jong Min Yuk's team confirmed the stable sodium storage mechanism by using copper sulfide, which is an excellent electrode material resistant to pulverization and capable of inducing capacity recovery. Their research results show that when copper sulfide is used, the sodium ion battery will be charged once a day, and its life will exceed 5 years. What's more, copper sulfide, which is composed of rich natural materials such as copper and sulfur, is more cost competitive than lithium-ion batteries using lithium and cobalt.

Sandwich materials, such as graphite, as the commercial anode materials of lithium ion batteries, cannot be used for high-capacity sodium storage due to their insufficient interlayer spacing. Therefore, conversion and alloy reactive materials have been explored to meet higher anode partial capacity. However, these materials usually produce large volume expansion and sudden crystal changes, which lead to serious capacity degradation.

The research team confirmed that the semi coherent phase interface and grain boundary in the conversion reaction played a key role in realizing the pulverization resistant conversion reaction and capacity recovery respectively.

Most conversion and alloy reactive battery materials, due to their completely different crystal structures before and after reaction, have large volume expansion, and usually have serious capacity degradation. However, Cu2S undergoes a gradual crystallographic change, forming a semi coherent interface, and finally preventing the particle from crushing. Based on this unique mechanism, the research team confirmed that Cu2S has high capacity and high cycle stability regardless of its size and shape.

Professor Yuk said: "The sodium ion battery using copper sulfide can promote the development of sodium ion battery, which can help the development of low-cost energy storage system and solve the problem of micro dust."