US researchers develop environmentally friendly method to reduce lithium-ion battery recycling costs

According to foreign media reports, nanoengineers at the University of California San Diego have developed a new process that can restore spent cathode materials to good condition and recycle lithium-ion batteries more cost-effectively. Compared with current methods, this process uses more environmentally friendly chemicals, can reduce energy consumption by 80-90%, and reduce greenhouse gas emissions by about 75%.

(Image source: UCSD)

This process is particularly suitable for positive electrodes made of lithium iron phosphate (LFP). LFP batteries have a longer lifespan, are safer, and because they do not use expensive metals such as cobalt or nickel, they are cheaper to manufacture than other lithium-ion batteries. Therefore, they are widely used in power tools, electric buses and energy grids. They are also the preferred battery for Tesla Model 3. Zheng Chen, a professor of nanoengineering at the school, said: "Considering these advantages, LFP batteries will have a more competitive advantage than other lithium-ion batteries in the market. However, similar to plastic recycling, these materials themselves are cheap, but the recycling cost is high."

The research team developed a new low-cost recycling process that can be operated at low temperatures (60 to 80 degrees Celsius) and ambient pressure, and consumes less electricity. In addition, the chemicals used, such as lithium salts, nitrogen, water and citric acid, are low-cost and non-hazardous. "The entire recycling process is very safe and does not require any special safety measures or equipment, so the recycling cost can be greatly reduced," said researcher Panpan Xu.

The researchers first ran a commercial LFP battery to lose half of its energy storage capacity. Then, they disassembled the battery, collected the cathode material powder, and soaked it in a solution containing lithium salt and citric acid. Next, they rinsed the solution with water, dried the powder, and heated it. Finally, they made a new cathode out of the powder and tested it in button cells and soft-pack batteries. The results showed that its electrochemical performance, chemical composition, and structure could be completely restored to its original state.

During battery operation, two types of structural changes in the positive electrode can cause its performance to deteriorate. The first is that the loss of lithium ions creates vacancies in the positive electrode structure; the second is that when iron and lithium ions exchange positions in the crystal structure, lithium ions are easily trapped and cannot continue to circulate in the battery. This process restores the positive electrode structure by replenishing lithium ions, making it easier for iron and lithium ions to return to their original positions. The latter is accomplished through citric acid, which acts as a reducing agent, transferring electrons to iron ions, making them non-positively charged, thereby minimizing electron repulsion, making it easier for iron ions to return to their original positions in the crystal structure, and releasing lithium ions to return to the cycle.

The researchers say the overall energy cost of the recycling process is low, but further research is needed to understand the logistics of collecting, transporting and processing battery materials in large quantities.