Interpretation of the recycling of lithium iron phosphate battery cathode materials

Compared with ternary lithium batteries, lithium iron phosphate batteries have low cost, high safety and long cycle life. Recently, the CTP battery and blade battery launched by CATL and BYD have improved the volume energy density of lithium iron phosphate battery, enabling the cruising range of passenger cars to reach more than 500 kilometers. Ternary cobalt-nickel raw materials are precious metals with few reserves and high prices.

China mainly relies on imports, which limits its large-scale promotion and use in the future. Phosphorus, iron, and lithium, the main raw materials of lithium iron phosphate batteries, are rich in resources in China, suitable for large-scale promotion and use, and will have an important position in the future new energy development strategy.

At present, wind power, solar power generation, and grid energy storage mostly use lithium iron phosphate batteries in China, and almost all commercial electric vehicles and logistics-specific electric vehicles use lithium iron phosphate batteries.

New energy passenger car power batteries and motorcycle battery pack are mainly lithium iron phosphate batteries and ternary lithium batteries, but as 2022 will enter the subsidy-free era, car companies have turned to lithium iron phosphate batteries. With the continuous popularity of new energy vehicles and strong downstream demand, the price of lithium iron phosphate has also risen, and production capacity is in a hurry.

It is estimated that from 2020 to 2025, the demand for lithium iron phosphate cathode materials will increase from 200,000 tons to about 2 million tons, with an average annual growth rate of more than 50%. Lithium iron phosphate cathode waste will also increase in the same proportion. Starting from 2021, lithium iron phosphate power batteries after 2015 will enter the replacement and elimination period, and the supply of cathode powder after dismantling of lithium iron phosphate batteries will also increase significantly.

Therefore, for a long time to come, the comprehensive recycling technology of lithium iron phosphate battery waste will have huge market demand and economic benefits. Compared with the existing recovery technology in China, the new lithium iron phosphate comprehensive recovery process developed by this project can not only recover lithium carbonate, but also recycle iron phosphate as raw material for lithium iron phosphate synthesis, and can increase the recovery rate of lithium from about 75% to more than 90%.

Lithium iron phosphate cathode material recycling process

This project uses lithium iron phosphate cathode scraps and lithium iron phosphate cathode waste powder separated from lithium battery dismantling as raw materials. Using physical separation and wet recycling methods, lithium carbonate and iron phosphate are produced, which are used as raw materials for the precursor of lithium battery cathode materials.

The recovered graphite powder is used as raw material for the production of anode or conductive agents, and the aluminum foil is recycled into the traditional resource recovery system to realize the comprehensive recycling of waste lithium battery cathode materials.

This project realizes the wet process, which reduces the processing cost and improves the economic benefits. It is a new process for recycling lithium batteries with high efficiency, environmental protection and economy.

Physical separation

The lithium iron phosphate cathode sheet is crushed and screened, and the aluminum sheet and lithium iron phosphate cathode powder are peeled off.

Leaching

According to the metal element content of the cathode powder, add an appropriate amount of sulfuric acid, heat and stir for leaching, the leaching solution contains lithium, iron, phosphorus, and a small amount of other impurities, filter and separate carbon iron slag containing carbon slag and iron phosphate, and use the filtrate to extract lithium carbonate after removing impurities and purifying. The carbon slag is separated into graphite, and the graphite powder product is obtained after purification.

Lithium carbide

The purified lithium sulfate solution is separated by electrolysis to generate lithium hydroxide and sulfuric acid. Lithium hydroxide enters the carbonization reactor to form lithium carbonate precipitates, washed and dried, and jet crushed to obtain battery-grade lithium carbonate products, or to prepare lithium hydroxide monohydrate products through evaporation and crystallization.

The output of lithium hydroxide and lithium carbonate can be customized according to market conditions. The sulfuric acid generated by electrolysis is returned to the cathode waste leaching process.

Iron phosphate synthesis

Carbon iron slag dissolves iron phosphate, and the iron phosphate solution is added with ammonia water to adjust the acidity, and iron phosphate dihydrate is precipitated. After repeated washing, drying and roasting, the iron phosphate product is obtained.

Mother liquor treatment

The mother liquor after precipitating iron phosphate contains ammonium sulfate and a small amount of lithium carbonate. After heating, the ammonia gas is blown off, cooled and absorbed to obtain ammonia water, which is returned to the synthesis process to precipitate iron phosphate, and the deammonized solution is purified and concentrated for electrolytic extraction of lithium carbonate.

Technical characteristics of lithium iron phosphate cathode recycling process

The main problems in the current global recycling process are as follows:

At present, lithium iron phosphate cathode waste is used to extract lithium carbonate, and the mixture of iron phosphate and carbon slag produced cannot be used, and the recovery value is low. At the same time, solid waste needs to be treated, and the resource recovery rate is low;

After adding alkali in the extraction process, a large amount of sodium sulfate wastewater will be generated, and the discharge will pollute the environment. The cost of evaporation and recovery of sodium sulfate is too high, which affects the economic benefits of recovery.

In view of the problems existing in the existing lithium battery recycling process, the comprehensive recycling, economical and environmentally friendly new process developed by this project has the following advantages:

The new process developed by this project realizes the comprehensive recycling of resources. By separating lithium, iron and phosphorus, recycling lithium carbonate, iron phosphate products and graphite powder, the recycling of all elements is realized.

The new process uses electrolysis technology to process lithium-containing mother liquor, which improves the recovery rate of lithium and product purity. Sulfuric acid can be recycled, which eliminates the disadvantages of traditional processes that consume a large amount of acid and alkali and produce a large amount of sodium sulfate by-products with high processing costs. It reduces the cost of waste liquid treatment and improves the economic benefits of production.

The generation process basically realizes zero discharge of the three wastes.