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Power batteries are the core components of electric vehicles. It is generally believed that when the capacity retention rate is below 80%, they no longer meet the requirements of vehicles. Therefore, the issue of decommissioned power LiFePO4 battery recycling has surfaced.
In the past, the recycling of power batteries by enterprises was mainly LCO, NCM/NCA, but there was not much enthusiasm for LiFePO4 battery recycling. The reason is that the cost of existing recycling strategies and methods is high, while the value of LiFePO4 battery recycling is low. However, starting from May 2021, the growth rate of LiFePO4 battery shipments has surpassed that of ternary lithium batteries, reversing the trend in which the output of LiFePO4 batteries has been lower than that of ternary lithium batteries since 2018.
At the same time, LiFePO4 battery has a large market space in terms of energy storage, 5G base stations, new energy vehicles, and renewable energy grid integration in the future, and are expected to occupy a dominant position in the market for a long time in the future. The return of LiFePO4, coupled with the skyrocketing prices of phosphorus and lithium, brought about a direct change that people began to pay attention to the LiFePO4 battery recycling.
The average service life of lithium-ion batteries is 5 to 8 years. Due to the early application of LiFePO4 batteries, they will face problems such as scrapping earlier. 2020 will usher in the explosive period of LiFePO4 battery retirement.
It is estimated that from 2021 to 2030, the total amount of decommissioned power batteries for passenger cars and commercial vehicles in China will be nearly 7 million tons, and the corresponding waste LiFePO4 batteries will exceed 2 million tons. The huge amount of decommissioning poses serious challenges to the LiFePO4 battery recycling and the recycling of battery materials.
1. LiFePO4 battery recycling pretreatment
LiFePO4 battery recycling refers to the process of dismantling batteries, extracting or utilizing valuable metals. Due to the many components of used batteries, the first step in recycling requires a pretreatment step to separate the cathode active material from the battery casing, separator, current collector, electrolyte, carbonaceous additives, and battery hookup components.
Pretreatment requires dismantling of the shell and separation of the different valuable components. Use external resistors or immerse waste batteries in salt solution for discharge treatment to prevent electric shock, fire, explosion and some potential chemical hazards.
Then use machinery to directly crush the battery. The crushed components are sorted by specific gravity according to different properties such as density, particle size, magnetism and hydrophobicity, and the battery case, separator, plastic, aluminum foil, cathode and anode are initially separated, and then recycled separately.
2. Recycling of LiFePO4 battery cathode material in LiFePO4 battery recycling
At present, the research on waste LiFePO4 battery recycling mainly focuses on cathode materials. The lithium element in a fully discharged lithium-ion battery mainly exists in the cathode of the battery, and the cathode waste generated during the battery production process also has important recycling value.
At present, the mainstream process for the recovery of cathode active materials is the wet process, which mainly recovers the most economically valuable Li element, and can simultaneously recover Fe, Al and other metals.
Dissolve the cathode sheet with NaOH lye, make the current collector aluminum foil enter the solution in the form of NaAlO2, after filtration, the filtrate is neutralized with sulfuric acid solution, and Al(OH)3 is precipitated to realize the recovery of Al. The filter residue is a mixture of LiFePO4, conductive agent carbon black, and LiFePO4 surface-coated carbon.
There are two ways of LiFePO4 recycling in LiFePO4 battery recycling:
Method 1: In order to dissolve the filter residue with sulfuric acid and hydrogen peroxide, LiFePO4 enters the solution in the form of Fe2(SO4)3 and Li2SO4. The filtrate separated from the carbon impurities is adjusted with NaOH and ammonia water to adjust the pH value, the iron is first precipitated with Fe(OH)3, and the remaining liquid is precipitated with a saturated Na2CO3 solution to obtain Li2CO3;
Method 2: Based on FePO4 being slightly soluble in nitric acid, the positive electrode material filter residue is dissolved with nitric acid and hydrogen peroxide. Precipitation of FePO4 is formed first, and finally Fe(OH)3 is precipitated. The remaining acid solution is precipitated with saturated Na2CO3 solution to precipitate Li2CO3 to realize the separate precipitation and recovery of Al, Fe and Li.
3. LiFePO4 battery anode material recycling
With the widespread application of lithium-ion batteries, including 12v battery, 24v lithium battery, 36v lithium battery, etc., the demand for graphite anodes has also increased. The proportion of graphite in waste lithium batteries is 12% to 21% (mass fraction), which is a considerable amount.
In some countries that do not produce graphite or have low graphite reserves, such as the United States and some European countries, graphite is used as a key material. The recycled graphite powder is expected to be recycled and used in battery production after modification.
In addition, in the anode, copper foil is expensive and the recycling process is simple in LiFePO4 battery recycling, which has high recycling value. Anode materials can usually be recovered by heat treatment, leaching, or grinding flotation.
The researchers successfully regenerated graphite from spent lithium batteries through simple high-temperature smelting and sieving process steps. Calcined under 1673K nitrogen atmosphere for 4 hours, the current collector copper foil becomes spherical particles and is separated from graphite, and then regenerated graphite can be obtained by ultrasonic vibration and sieving. The purity of graphite recovered by this process can reach 99.5%, which meets the standard of battery grade graphite material.
4. Electrolyte material recycling in LiFePO4 battery recycling
In the power battery, the electrolyte accounts for about 15% of the battery cost, which contains relatively rich lithium ions and has a certain recycling value. At present, the recycling of electrolyte in LiFePO4 battery recycling includes vacuum pyrolysis treatment, organic solvent extraction recycling treatment, and CO2 supercritical recycling method.
Supercritical CO2 recycling of waste lithium-ion battery electrolyte refers to the process of using supercritical CO2 as an extraction agent to separate the lithium-ion battery separator and the electrolyte adsorbed in the active material.
Supercritical CO2 can effectively dissolve non-polar substances and can separate the electrolyte from spent lithium batteries. And CO2 is stable, non-toxic and cheap, and can realize the integrated operation of separation and recycling, so it plays a great role in the recycling process of lithium battery electrolyte.
5. Conclusion and outlook
In recent years, great progress has been made in the waste LiFePO4 battery recycling, but most of the research focuses on the recycling of cathode materials, and the research on the metal recycling mechanism in cathode materials is not in-depth, and the technology transformation is immature.
At the same time, the research on the selective separation and purification of various metals is still lacking. There are too few studies on the recovery of anode materials and electrolytes, and it is impossible to realize the recovery and reuse of high-value resources for full batteries.
In order to effectively improve the recycling efficiency and increase the economic value of waste LiFePO4 battery recycling, in-depth research should be carried out on cathode and anode materials, electrolyte recycling processes and principles, and a clean, environmentally friendly, and short-process recycling process should be developed. So that it can truly achieve high-efficiency and high-quality recycling of all components of used lithium-ion power batteries.
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