As lithium-ion battery technology matures, it is widely used in various industries, resulting in a rapid increase in production and sales. However, since lithium-ion batteries generally only have a service life of about 5 to 8 years, it will inevitably bring about an explosive growth of waste lithium-ion batteries. The technical and safety requirements for the recycling of lithium batteries are becoming increasingly demanding, and the correct handling and resolution of the cost and safety risks in the recycling process is an important issue in the development of lithium batteries today.

Is there a recycling value of lithium batteries?

As we know, lithium batteries contain about 15% cobalt, 25% iron, 0.1% lithium, 14% copper, and 4.7% aluminum, and these metals have a high recycling value. According to market estimates, the average revenue per ton of cathode scrap cobalt-lithium film is about $9,000.

Since high value-added metals such as lithium, cobalt, nickel, etc. are mainly found in cathode materials in used lithium ion batteries, the current research on recycling of lithium ion batteries mainly focuses on cathode materials, so generally speaking, the recycling process of used lithium ion batteries is the separation, purification and reuse of high value-added metal elements in cathode materials. Scrap lithium ion battery contains a large number of cobalt, lithium, copper, manganese and other metal elements, as well as lithium hexafluorophosphate, polyvinylidene fluoride and other harmful toxic substances, resource recovery and harmless treatment is of great significance.

So, What are the recycling steps for lithium-ion power batteries?

Lithium ion battery recycling can be divided into three parts: pretreatment, secondary treatment and deep treatment.

(I) Pre-treatment
The lithium ion battery still has some residual charge inside when it is recycled, and toxic HF will be formed when it encounters moisture; therefore, the lithium battery must be pretreated to fully deplete its charge before recycling.

Currently, there are two main treatment methods: immersion method and resistance method. Immersion mainly releases the charge by sodium chloride solution, and in order to prevent the generation of toxic gases, the battery is placed in dilute alkaline water, the reaction formula is: HF+NaOH → NaF+H2O, then crushed at low temperature and physically sorted according to the different material densities of the battery casing and separator, and the proportion of positive and negative electrodes.

(II) Secondary treatment
The secondary treatment is to separate the anode and cathode active materials from the substrate, generally using heat treatment, electrolysis and organic solvent dissolution method, and the heat treatment method is relatively simple, convenient operation is widely used. The cell is placed at a certain temperature, and the material is separated by the volatilization and decomposition of PVDF. At 370°C to 400°C, PVDF decomposes, and at 600°C to 700°C, the aluminum foil melts due to the combustion reaction of the conductive additive.

The secondary treatment can also be performed by organic solvent dissolution and alkaline dissolution. Organic solvents can dissolve PVDF very effectively and partially recover the electrolyte at the same time, generally NMP, DMF, DMAC, DMSO and other organic solutions can be used for treatment, at a temperature higher than 70 ℃, PVAF dissolution reached the maximum degree, the solubility of 211 g/L, 177 g/L, 218 g/L, 241 g/L respectively. After a comparative study, DMSO has the highest solubility for waste lithium ion batteries, and has the excellent performance of environmental protection, low cost, and non-toxic, etc. When the temperature is below 65℃, the aluminum foil obtained after 90min treatment can be directly used for recycling.

(III) Deep treatment
Deep processing is a key step in the recycling of lithium-ion batteries, which mainly includes leaching and separation.

In the leaching process, there are two main types: microbial leaching and inorganic acid leaching.

A. Microbial Leaching: It is more commonly used because of its high efficiency, low cost and low difficulty. At present, as the waste lithium ion battery is mainly recycled by autotrophic bacteria, including ferrous oxide microspirochetes, sulfur oxide-thiobacillus and ferrous oxide thiobacillus, etc., through the physiological reaction of the bacteria to promote their own growth and regeneration process, the metabolic acid can be used to carry out the leaching process of waste lithium ion power battery. In the experiment, we used Cu 2+ as the catalyst, and the leaching efficiency of Co 2+ was as high as 99% after six days with 0.85g/L catalyst, while the leaching efficiency of Co 2+ was greatly reduced to 40.3% after ten days without Cu 2+ as the catalyst. The results show that Cu 2+ has a significant effect on the recycling efficiency of LiCoO2.

B Another acid leaching method is to leach the battery cathode material by inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and organic acids such as oxalic acid, citric acid and grapes acid. Oxalic acid, for example, is used to recycle the cobalt and lithium elements in the battery, and the leaching efficiency of the cobalt and lithium elements can be as high as 97%-98% after one and a half hours of stirring with H2C2O4 at 95°C and a solid to liquid ratio of 16g/L. In the inorganic acid treatment, the cobalt and lithium elements can be leached out of the cathode material by using inorganic acid. In the treatment of inorganic acid, the leaching efficiency of lithium battery was analyzed by using hydrochloric acid, sulfuric acid, and nitric acid, and the results showed that the leaching efficiency of Al, Ni, Co, and Li reached 82.1%, 92.1%, 85.3%, 85.3%, and 82.3%, respectively, after 20 hours of stirring with 4mol/L HCl at a solid-liquid ratio of 210g/L at 90℃. 83.5%.

In general, the leaching efficiency of inorganic acid is relatively high, but it produces a lot of toxic and harmful gases such as sulfur dioxide, nitrogen dioxide, etc., and the residual liquid is difficult to treat, often resulting in secondary pollution. The pH value of the organic acid effluent is lower and easier to handle, but the relative cost is higher.

The final separation and purification is mainly the separation and purification of Li, Ni 2+, Mn 2+, Co 2+, etc. in the leachate, the main methods are solvent extraction, chemical precipitation and electrochemical methods.

Chemical precipitation is mainly the precipitation of metal ions by specific precipitants to form the corresponding metal compound products. Common precipitating agents include potassium permanganate, ammonium oxalate, sodium carbonate, etc., which precipitate the corresponding metal ions at different pH values. For example, the combined use of NaOH, Na 2 CO 3, KmnO 4, etc., will give precipitation products such as MnO 2, LiCO 3, Ni (OH) 2, Co (OH) 2, etc., and the recoveries of Li, Ni 2+, Mn 2+, Co 2+ are 96.97%, 96.97%, 96.97%, 96.97%, and 96.97%, respectively. 97.45%, 96.99%, 98.25%.

Risk analysis of secondary contamination and safety during recycling of lithium batteries.

(i) Pre-treatment of security issues
Lithium-ion batteries are a type of hazardous waste that can explode during the disposal process, and because the electrolyte inside produces toxic HF when it is untreated, there is still a growing awareness of waste separation in China. Although the awareness of waste separation is gradually increasing in China, it is inevitable that some of the used lithium-ion power batteries are still in contact with wet garbage or moisture during transportation before disposal, which may produce toxic substances. Therefore, better protective measures must be taken before pretreatment, and efficient treatment must be carried out in an absolutely safe environment.

(II) Pollution Prevention and Safety Issues in Secondary Treatment
In the secondary treatment, heat treatment method often produces a large number of sulfur dioxide, nitrogen dioxide and other harmful gases, the atmosphere has a more serious pollution, at the same time, if the air circulation is not enough, a great safety hazard will occur. Therefore, in the heat treatment method, on the basis of air circulation, the gas is treated as secondarily as possible, and the toxic and harmful gases are reduced or even purified through chemical reactions. The residual liquid produced by the lye dissolution method often has a high pH value, is highly alkaline and very corrosive, and needs to be considered for recycling in the process of safety treatment.

IV. Development and Prospect
At present, the recycling technology of lithium ion battery only focuses on the recycling of electrode materials, but lacks the treatment of graphite and electrolyte. On the one hand, lithium ion battery contains many toxic and harmful elements and substances, if not treated scientifically and effectively, it will certainly pose a very serious threat to the environment. On the other hand, the used lithium ion battery contains a considerable grade of lithium, cobalt, nickel, manganese, aluminum, copper and other metal elements, some of these metals and their chemical products are relatively expensive, so if the used lithium ion battery can be scientifically and effectively recycled, it can not only effectively solve the plight of resources and the environment, but also create considerable economic gains, and achieve a virtuous cycle of sustainable development.