Generally speaking, when the capacity of the lithium-ion power battery decays to 80% of the rated value, it needs to be decommissioned. At present, there are two main methods for the utilization of decommissioned power battery recycling technology in power battery recycling companies: cascade utilization and dismantling and recycling. Whether the decommissioned power battery can be used in cascades and its application field mainly depends on the remaining capacity of the battery. When the remaining capacity of the battery is 30% to 80%, it can be used in cascades.
When it is lower than 30%, it does not meet the standard of cascade utilization and should be dismantled and recycled. The new energy automobile industry is developing in full swing, and the supply of lithium resources is in short supply. The shortage of lithium resources has led to a prominent contradiction between the supply and demand of lithium materials. It is also particularly important to accelerate the development of the layout of the power battery recycling technology industry.
1. Recycling process of key components of lithium-ion battery
From the perspective of environmental protection, lithium-ion batteries are mainly composed of positive electrode active materials, negative electrode graphite, separator, electrolyte, conductive agent, organic binder and other materials. Moreover, the battery is rich in metal ions such as nickel, cobalt, and manganese, fluorine, and organic matter. These substances will cause serious damage to the ecological environment such as soil, water, and atmosphere. From the perspective of resource recycling, the proportion of cathode active materials in lithium-ion battery materials is generally higher than 30%, which fully reflects that lithium-ion batteries are rich in valuable metal elements.
The copper, cobalt and lithium content in decommissioned lithium battery materials is much higher than the copper and cobalt content in copper and cobalt concentrates and the lithium content in lithium ore. In the existing battery recycling technology, every ton of lithium-ion batteries recycled can generate about 5013 US dollars in profit. In battery recycling technology, before recycling the key materials of lithium batteries, pretreatment is required to separate materials with the same or similar physical properties, so as to reduce energy consumption and improve recycling efficiency.
Pretreatment mainly includes discharge deactivation treatment, heat treatment, dismantling, crushing and separation. The waste electrode materials obtained after pretreatment need to be further recycled. Although most of the research focuses on the recovery of valuable metals in cathode materials, more and more attention has been paid to the recovery of anode materials and electrolytes in battery recycling technology. At present, the industrial methods for disposing of used lithium-ion batteries are mainly through wet recycling and pyro-recycling processes, and of course direct recycling is also an important way.
2. Direct regeneration battery recycling technology
Generally speaking, the loss of lithium and the irreversible phase transition of the structure of cathode materials during long-term use are one of the main reasons for their failure. For some decommissioned lithium-ion batteries with low impurity content, it is possible to directly regenerate the material through lithium supplementation and roasting without destroying its chemical structure and causing secondary pollution.
In recent years, in order to avoid the difficulty of three wastes treatment and the decline in economic benefits caused by the long battery recycling technology process, simplifying the process is the most effective way to solve the above problems. Therefore, shifting the focus from extracting metals from waste cathode materials to directly repairing waste materials to obtain recycled cathode materials is an important development direction of battery recycling technology. Especially for materials with relatively low prices such as LFP and LMO, the cost advantage is more obvious.
3. Fire-metallurgy battery recycling technology
Pyrometallurgical battery recovery technology refers to the use of physical or chemical transformation at high temperature to recover and refine valuable metals from waste lithium-ion battery materials, and finally process the obtained alloy and slag separately and further purify the metal element. Due to its relatively simple operation and large processing capacity, it is widely used in industry, but it also has the defects of high energy consumption and low recovery rate.
In the early stage of pyrometallurgy, the waste batteries hardly went through any pretreatment, and the battery packs were directly disassembled and then calcined. This approach is economically feasible for spent batteries with a high content of precious metals, but difficult for batteries such as lithium iron phosphate or lithium manganate. Traditional pyrometallurgy has high energy consumption, large material loss, and produces toxic gases, and lithium cannot be recovered.
Therefore, there is a need to find alternative battery recycling technologies with high material recovery rates, lower energy consumption, and less environmental risk. For example, fire method combined with hydrometallurgy, vacuum evaporation and inert gas atmosphere roasting, etc. These methods can finally obtain lithium compounds, reducing lithium loss. The process of pyrotechnic treatment of waste lithium batteries includes: The battery is broken. Reduction roasting. Separation of alloy materials.
4. Hydrometallurgical battery recycling technology
Wet battery recycling technology refers to dissolving valuable metal oxides in positive electrode active materials into metal ions by leaching into the solution. Then, the leaching solution is subjected to precipitation, ion exchange, solvent extraction and electrolysis to remove impurities or separate metals to recover valuable metals. Hydrometallurgy has the advantages of low energy consumption and high recovery purity, but its process is complex and will produce a large amount of harmful emissions such as waste water and gas. Hydrometallurgy is one of the most important and widely used battery recycling technologies.
Typical hydrometallurgical steps include leaching, separation and purification. Leaching. The key step of hydrometallurgy, its main purpose is to make the material to be recovered into a solution state, which is convenient for material separation and purification. The leaching methods mainly include inorganic acid leaching, organic acid leaching, ammonia leaching and biological leaching. Bioleaching is the use of metal-enriching and metabolizing microorganisms such as bacteria or fungi to recover metals from used lithium-ion batteries.
Bioleaching has the advantages of environmental friendliness, low treatment and recovery requirements, and low cost, so it has attracted widespread attention. However, it is difficult to achieve large-scale industrial application at present. Separation and purification. Separation and purification are the final steps for hydrometallurgical battery recycling technicians, and commonly used separation processes include solvent extraction, chemical precipitation, and electrochemical deposition. Solvent extraction is widely used, and its advantages are high ion selectivity and extraction efficiency.
The disadvantage is that when it is used on a large scale, the cost of extractant invested in the early stage and the cost of waste treatment in the later stage are relatively high. The cost of hydroxide and carbonate used in chemical precipitation is low, so it has a good application prospect, but the precipitation process is more sensitive to the pH value of the leachate. Electrochemical deposition uses different electrode potentials to effectively separate metal ions in the leachate.
5. Graphite anode material recycling
Compared with cathode materials with high recycling value, the added value of anode is relatively low and it is more difficult in battery recycling technology. With the widespread application of lithium-ion batteries, the demand for graphite anodes has also increased. The proportion of graphite in waste lithium batteries is 12% to 21%, 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.
In addition, anode materials can also be used as raw materials to prepare other functional materials after recycling, so the recycling of anode materials also has important strategic significance and practical feasibility in battery recycling technology. Studies have shown that waste graphite anodes can be reused as high-capacity anodes for new batteries after regeneration, and the recycling process can not only recover valuable lithium elements, but also recover graphite for reuse. Anode materials can usually be recovered by heat treatment, leaching, or grinding flotation.
6. Lithium-ion battery electrolyte recycling
Power and energy storage lithium battery electrolytes are generally prepared from high-purity organic solvents, electrolyte lithium salts, and necessary additives and other raw materials in certain proportions under certain conditions. The proportion of electrolytes in batteries accounts for about 17%. When the electrolyte lithium salt enters the environment, it can undergo hydrolysis, decomposition and combustion chemical reactions to produce fluorine, arsenic and phosphorus-containing compounds, resulting in fluorine pollution, arsenic pollution and phosphorus pollution.
Organic solvents undergo chemical reactions such as hydrolysis, combustion, and decomposition to produce small molecular organic substances such as formaldehyde, methanol, acetaldehyde, ethanol, and formic acid. These substances are easily soluble in water and can cause water pollution and personal injury. Since the electrolyte itself is in a liquid state and is adsorbed in the separator and electrode active materials, its volatility is relatively high, and there are also problems such as low recovery rate and secondary pollution of waste liquid and gas.
Therefore, the recovery of the electrolyte is difficult in the battery recovery technology, and the recovery cost is relatively high. Although the recycling of electrolysis seems to be unprofitable, it still has a great impact on environmental protection, so it is also worthy of attention. At present, most of the processes do not consider the recovery and treatment of electrolyte, which brings great safety hazards to production and relatively serious environmental pollution.
At present, most of the methods used by lithium battery electrolyte companies to treat waste lithium-ion battery electrolyte are still in the laboratory stage, and most of them are manual operations. It is necessary to vigorously develop corresponding large-scale automatic processing equipment for production. Supercritical CO2 can effectively dissolve non-polar substances, and can separate electrolytes from spent lithium batteries. Moreover, CO2 is stable, non-toxic and cheap, and can realize the integrated operation of separation and recovery. It is considered to be a promising electrolyte treatment method.