New energy vehicles are one of China's strategic emerging industries, which is crucial for China's energy security and sustainable development strategy, and can help achieve carbon peak and carbon neutrality goals. The service life of power batteries is 5-8 years, and it is expected that over ten million tons of retired lithium-ion batteries will be urgently needed to be disposed of around 2030. Therefore, in the future, there will be a huge challenge in the recycling and treatment of a large number of retired lithium-ion batteries, and the development of green economic resource closed-loop utilization technology is crucial.

At present, domestic and foreign researchers mainly focus on the recovery of valuable metals from retired lithium-ion batteries. Waste negative electrode materials are usually treated by combustion, stacking, or as steelmaking additives, resulting in environmental pollution and resource waste. The quality of negative electrode graphite accounts for about 15% to 22% of the total weight of the battery, and the cost accounts for about 13% to 18% of the total cost of the battery. The future recycling amount is expected to exceed one million tons, and the market size will reach tens of billions of yuan. Graphite, as a key national strategic resource, if not properly disposed of, will result in huge resource waste and economic losses.

The research team addressed the problem of low Coulomb efficiency in the first cycle of waste graphite after impurity removal and recycling. By constructing a nano titanium niobate coating layer on the surface, and utilizing niobium based materials with high lithium intercalation working potential (greater than 1.5 V vs. Li+/Li), combined with their stable structure and high rate charge discharge ability, the damaged surface microstructure of the recovered graphite was coated and repaired, significantly improving the surface interface structure of the recovered graphite and stabilizing the formation of the SEI layer of the regenerated graphite. The PG TNO material after titanium niobate coating regeneration was tested, and compared to the impurity removed graphite before repair (63.1%), the first Coulombic efficiency of the modified regenerated graphite PG TNO reached 83.1%. The Coulombic efficiency of the battery after 500 cycles is greater than 99.7%, and the capacity retention rate is close to 90%. The related work was published in the internationally renowned journal Carbon under the title of Enhancing the compressed initial Coulombic efficiency of regenerated graphite anodes via the surface modification of a TiNb2O7 nanolayer. This work has been supported by major projects in Zhengzhou City (2019CXZX0074) and Henan Province Innovation Demonstration Project (No.201111311400).

High stability coating layer for surface interface construction in structural repair engineering

Charge and discharge curves of the first cycle Coulombic efficiency of the whole battery after coating with different cycles