The batteries that do not have the value of cascading utilization in retired lithium iron phosphate batteries and the batteries that have been cascading utilization will eventually enter the dismantling and recycling stage. The difference between lithium iron phosphate batteries and ternary material batteries is that they do not contain heavy metals and are mainly recovered from Li, P, and Fe. The added value of the recovered products is low, and low-cost recovery routes need to be developed, mainly including pyrometallurgical and wet recovery methods.
1、 Fire recovery process
The traditional pyrometallurgical recovery method generally involves high-temperature incineration of electrode fragments to burn away the carbon and organic matter in the electrode fragments. The remaining ash that cannot be burned is ultimately screened to obtain fine powder materials containing metals and metal oxides. This method has a simple process, but a long processing flow and a low comprehensive recovery rate of valuable metals. The improved pyrometallurgical recovery technology involves removing organic binders through calcination, separating lithium iron phosphate powder from aluminum foil to obtain lithium iron phosphate material. Then, an appropriate amount of raw material is added to obtain the required molar ratio of lithium, iron, and phosphorus, and a new lithium iron phosphate is synthesized by high-temperature solid-phase method. According to cost estimation, the improved pyrometallurgical dry recycling of waste lithium iron phosphate batteries can achieve profitability, but the newly prepared lithium iron phosphate using this recycling process has many impurities and unstable performance.
2、 Wet recovery process
Wet recovery mainly involves dissolving metal ions in lithium iron phosphate batteries through acid-base solutions, and further extracting the dissolved metal ions in the form of oxides, salts, etc. through precipitation, adsorption, and other methods. During the reaction process, most reagents such as H2SO4, NaOH, and H2O2 are used. The wet recycling process is simple, with low equipment requirements, and is suitable for industrial scale production. It is the most researched by scholars and also the mainstream waste lithium-ion battery treatment route in China.
The wet recovery of lithium iron phosphate batteries mainly focuses on recovering the positive electrode. When using a wet process to recover lithium iron phosphate cathode, the first step is to separate the aluminum foil current collector from the active material of the cathode. One method is to use alkaline solution to dissolve the collection fluid, while the active substance does not react with the alkaline solution and can be obtained through filtration. The second method is to dissolve the binder PVDF in an organic solvent to separate the lithium iron phosphate cathode material from the aluminum foil. The aluminum foil is reused, and the active substance can be further treated. The organic solvent can be distilled to achieve its recycling. Compared to the two methods, the second one is more environmentally friendly and safe. One way to recover lithium iron phosphate from the positive electrode is to generate lithium carbonate. This recycling method has a lower cost and is adopted by most lithium iron phosphate recycling enterprises. However, the main component of lithium iron phosphate, iron phosphate (with a content of 95%), has not been recycled, resulting in resource waste.
A more ideal wet recovery method is to convert waste lithium ferrous phosphate cathode materials into lithium salts and iron phosphate, achieving full element recovery of Li, Fe, and P. To transform lithium ferrous phosphate into lithium salts and iron phosphate, ferrous phosphate needs to be oxidized to trivalent iron, and lithium can be leached using acid or alkali leaching. Scholars have used oxidation calcination to separate aluminum sheets and lithium iron phosphate, which are then leached and separated by sulfuric acid to obtain crude iron phosphate. The solution is then precipitated into lithium carbonate using sodium carbonate for impurity removal; The filtrate evaporates and crystallizes to obtain anhydrous sodium sulfate products for sale as by-products; The crude iron phosphate is further refined to obtain battery grade iron phosphate, which can be used for the preparation of lithium iron phosphate materials. After years of research, this process has become relatively mature.