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Power Battery Recycling Technology

- Sep 26, 2018 -

Due to the limited lifetime of lithium-ion batteries, a large number of used lithium-ion batteries have also been produced. A power battery shipment data is shown below

Power battery shipment statistics

1、Ladder utilization and raw material recovery

Retired power lithium batteries, the use of roads by the ladder, is the use of materials after the use of the ladder; direct material recycling is too small, no history, safety monitoring is not qualified.

Pursuing economic benefits is the driving force for business and social behavior. It is reasonable to use the ladder, to reduce the available value of the battery to below the maintenance cost, and then to recycle the raw materials to maximize the battery value. However, the actual situation is that the early power battery has poor traceability, and the quality and model are uneven. In the early stage, the risk of using the ladder was high, and the cost of eliminating the risk was high. Therefore, in the early stage of power battery recycling, the probability of the battery being removed was mainly based on raw material recovery.

Waste battery recycling industry chain

2、Positive metal material valuable metal extraction method

At present, the recycling of power lithium batteries does not completely recycle all kinds of materials on the entire battery. The types of positive electrode materials mainly include: lithium cobaltate, lithium manganate, ternary lithium, lithium iron phosphate and the like.

The cost of battery cathode material accounts for more than 1/3 of the cost of single cell. Since the negative electrode currently uses more carbon materials such as graphite, lithium titanate Li4Ti5O12 and silicon carbon negative S i/C are used less, so the current battery recycling technology is mainly aimed at The battery is recovered from the positive electrode material.

There are three main types of recycling methods for waste lithium batteries: physical law, chemical method and biological method. Compared with other methods, hydrometallurgy is considered to be an ideal recovery method due to its low energy consumption, high recovery efficiency and high product purity.

2.1、Physical law

The physical method utilizes a physical chemical reaction process to treat a lithium ion battery. Common physical and chemical treatment methods are mainly mechanical grinding and crushing flotation.

1) Mechanical grinding method

The mechanical grinding method is a method in which the thermal energy generated by mechanical grinding is used to cause the electrode material to react with the abrasive to convert the lithium compound originally bonded to the current collector into the salt in the electrode material. The recovery rates of different types of grinding aid materials are different. The higher recovery rate can be achieved: Co recovery rate is 98%, and Li recovery rate is 99%. The mechanical grinding method is also an effective method for recovering cobalt and lithium in waste lithium ion batteries. The process is relatively simple, but the requirements on the instrument are high, and it is easy to cause loss of cobalt and recovery of aluminum foil.

2) Broken flotation method

The crushing flotation method is a method for sorting the difference in physical and chemical properties of the surface of the material, that is, firstly, after the complete waste lithium ion battery is crushed and sorted, the obtained electrode material powder is subjected to heat treatment to remove the organic binder. Finally, flotation separation is carried out according to the difference in hydrophilicity between the surface of the lithium cobaltate and the graphite in the electrode material powder, thereby recovering the cobalt lithium compound powder. The crushing flotation process is simple in process, and the lithium cobaltate and the carbon material can be effectively separated, and the recovery rates of lithium and cobalt are high. However, since all the materials are crushed and mixed, it is difficult to separate and recover the subsequent copper foil, aluminum foil and metal shell fragments; and because the crushing easily causes the electrolyte LiPF6 to react with H2O to generate environmental pollution caused by volatile gases such as HF, it is necessary to pay attention to the crushing. method.

2.2、Chemical method

The chemical method is a method for treating a lithium ion battery by a chemical reaction process, and is generally classified into two methods: hydrometallurgy and pyrometallurgy.

1) Hydrometallurgy

Hydrometallurgy is a method of selectively dissolving a positive electrode material in a spent lithium ion battery with a suitable chemical reagent and separating the metal element in the leachate. The hydrometallurgical process is more suitable for recycling waste lithium batteries with relatively simple chemical composition. It can be used alone or in combination with high-temperature metallurgy. It has low requirements on equipment and low processing cost. It is a very mature treatment method suitable for small and medium-sized enterprises. Recycling of used lithium-ion batteries of scale.

2) Pyrometallurgy

Pyrometallurgy, also known as incineration or dry metallurgy, removes the organic binder in the electrode material by high-temperature incineration, and at the same time causes the metal and its compounds to undergo redox reaction, and recovers the low-boiling metal in the form of condensation. The compound is recovered by sieving, pyrolysis, magnetic separation or chemical methods of the metal in the slag. Pyrometallurgy has low requirements on the composition of raw materials, and is suitable for large-scale processing of more complex batteries. However, combustion will inevitably generate some exhaust gas to pollute the environment, and high-temperature treatment requires higher equipment. At the same time, it is necessary to increase purification and recovery equipment. The processing cost is higher.

2.3、Biological method

Biometallurgy is currently under study, which utilizes the metabolic processes of microbial fungi to achieve selective leaching of metallic elements such as cobalt and lithium. The bio-energy consumption is low, the cost is low, and the microorganisms can be reused, and the pollution is small; however, the cultivation of the microbial bacteria requires harsh conditions, the cultivation time is long, the leaching efficiency is low, and the process needs further improvement.

2.4、Lithium iron phosphate recovery partial cold door

Among the various power lithium batteries, only the lithium iron phosphate battery cathode material does not contain precious metals, but mainly consists of aluminum, lithium, iron, phosphorus and carbon. For this reason, companies are not enthusiastic about the recovery and decomposition of lithium iron phosphate. For the recovery of lithium iron phosphate batteries, there are few targeted studies.

The general treatment method of lithium iron phosphate, after the whole battery is mechanically pulverized, the aluminum is separated by using a polar organic solvent NMP or a strong alkali, and the remaining material is a mixture of LiFePO4 and carbon powder. Li, Fe, and P are introduced into the mixture to adjust the molar ratio of the three elements in the material, and then LiFePO4 material can be re-synthesized by ball milling and high temperature calcination under an inert atmosphere, but with the first synthesized lithium iron phosphate battery cathode material. In comparison, the material's capacity, charge and discharge performance have declined. The oxidative decomposition of the cathode material of the failed lithium iron phosphate battery, recovery of lithium, iron, phosphorus, carbon and reuse is the recovery path for the treatment of the standard.

Although there are few studies, there are still people who are doing it. For example, Zhu Hongshuai developed a method to leach the cathode material of the failed lithium iron phosphate battery with a phosphoric acid system, to achieve better lithium and iron separation effect by high efficiency, low cost and zero waste discharge method, and comprehensively recover lithium. Iron, phosphorus, carbon.

3、Hydrometallurgy is currently the main application technology

Through the research on the recovery process of lithium-ion batteries at home and abroad, it can be seen that the recovery rate of lithium ion batteries recovered by physical chemical method is low; the chemical method is common, the application range is wide, relatively feasible; the biological method is environmentally friendly, but it is required The time is too long and needs further study. Numerous studies on chemical methods have shown that the electrochemical properties of recycled materials obtained by single pyrometallurgy are not as good as those obtained by hydrometallurgy, but a large amount of reagents are required for single hydrometallurgical recovery, which is not suitable for large-scale industrial processing.

In comparison, hydrometallurgy is a relatively good method for comprehensive performance in current extraction methods, and acid leaching is the most important link. Its main purpose is to transfer the target metal in the pretreated active material to the leachate to facilitate the subsequent separation and recovery process. Traditional inorganic strong acids (HCl, HNO3 and H2SO4) have been widely used in the leaching process. However, in the leaching process, toxic gases such as Cl2, SO3, and Nx are associated with environmental hazards. Therefore, in recent years researchers have begun to pay attention to the role of organic acids (citric acid, oxalic acid, ascorbic acid, etc.) in the leaching process. Compared with traditional inorganic acids, organic acid leaching can reduce secondary pollution to the environment while meeting high efficiency.

The main steps of typical wet extraction are: pretreatment→acid leaching→leaching solution decontamination→separation extraction→element precipitation.

3.1、Basic steps of preprocessing

The used lithium battery is discharged into the brine to remove the outer packaging of the battery, and the metal steel shell is removed to obtain the inner battery. The battery cell is composed of a negative electrode, a positive electrode, a separator and an electrolyte. The negative electrode adheres to the surface of the copper foil, the positive electrode adheres to the surface of the aluminum foil, and the separator is an organic polymer; the electrolyte adheres to the surface of the positive and negative electrodes and is an organic carbonate solution of LiPF6.

3.2、a typical leaching extraction operation

From a complete cell, after pretreatment, it becomes a powdery material to be treated. Different processes and subsequent processing methods are quite different. Typical wet extraction steps are as follows:

1) Add LiCoO2 electrode powder to the sulfuric acid solution to maintain a specific solid-liquid ratio and mechanically stir;

2) After ultrasonic leaching for 60 min, the residue is filtered off, and the concentration of each metal in the leaching solution is measured;

3) Then add ammonium bicarbonate solution to adjust the pH value of the leachate, after standing and filtering, add a small amount of Na2S solution to remove copper;

4) extracting cobalt by P507-sulfonated kerosene system and stripping with H2SO4 to obtain high-purity cobalt sulfate solution;

5) After heating the NaOH solution and the cobalt-rich solution to boiling, add the alkali solution to the cobalt-rich solution until a large amount of blue precipitate is produced in the cobalt solution;

6) Seal the beaker mouth and let it stand for 5 minutes, then the blue precipitate completely transforms into a pink precipitated sodium hydroxide.

7) Washing several times, adding ethanol as a dispersing agent, aging, filtering, and drying the cake after drying at 105 ° C in a muffle furnace to obtain a black powder of tricobalt tetroxide.

4、Technology trend

At present, the precious metals in the battery are mainly recovered, and other relatively inexpensive materials such as electrolytes and separators are ignored, and the entire battery cannot be systematically recovered.

There are also techniques other than mainstream methods that are reported that involve the recycling of other elements. At the end of 2016, Tsinghua University Science and Technology Achievements Promotion Center released a message in the magazine "Acetaldehyde Acetic Acid Chemical" that its team developed a "power lithium battery rapid stripping and lithium cobalt short-range resource recovery technology", which can extract lithium efficiently. The precious metal in the battery, the recovery rate of copper and aluminum metal exceeds 98%, and the recovery rate of cobalt and lithium metal exceeds 95%.

In addition, a more comprehensive approach has been proposed. Gao Guilan puts forward the idea of comprehensively utilizing the strengths of various methods in his article "Recycling Status of Powered Lithium Ion Batteries for Waste Vehicles". The combined treatment method is the recovery route of “fire pretreatment + wet acid leaching + metal precipitation”. The route is leached by acid leaching method. The traditionally used acid is mainly inorganic strong acid (HCl, H2SO4 and HNO3, etc.) However, this type of inorganic acid is highly corrosive to equipment and harmful to the human body. Therefore, it is recommended to use a milder organic acid (including malic acid, oxalic acid and ascorbic acid) instead of environmental protection, and some organic acids are also Reducing, can replace the traditional "mineral acid + reducing agent" system.