According to statistics, in 2000, the consumption of lithium-ion batteries in the world was 500 million, and in 2015 it reached 7 billion. Since the service life of lithium-ion batteries is limited, a large number of waste lithium-ion batteries will follow. For example, in 2020, China will have more than 25 billion lithium batteries discarded, with a total weight of more than 500,000 tons. As an example of a ternary material battery, its positive electrode contains a large amount of precious metals, of which cobalt accounts for 5 to 20% and nickel accounts for 5 to 12%. Manganese accounts for 7~10%, Lithium accounts for 2~5% and 7% of plastics, and most of the metals contained are rare metals, which should be reasonably recycled and reused. For example, cobalt is widely used in various fields as a strategic resource. In addition to lithium batteries and high-temperature alloys, etc. It can be inferred that the precious metal recovery is huge.
A copy of the power battery shipment data is shown in the chart below. In accordance with the commercial vehicle service for 3 years, and the passenger vehicle service for 5 years, it is estimated that 2018 will experience a decommissioning climax of power lithium batteries. These decommissioned batteries There are two types of typical follow-up paths, either step-by-step or direct material recycling.
Power Battery Shipment Statistics
1 step utilization and raw material recovery
Lithium batteries that have been decommissioned for power use, and are used for road access, are recycled after the steps are used; direct material recovery is too small, no history, safety monitoring is not qualified, etc.
The pursuit of economic efficiency is the driving force for corporate and social behavior. According to reason, the use of ladders to reduce the available value of the battery to the maintenance cost, and then do raw material recovery, is to maximize the value of the battery. But the actual situation is that the early power battery Traceability is poor, quality, and model are uneven. Early battery use has a high risk of ladder utilization, eliminating the high cost of risk, so it can be said that in the early period of power battery recycling, the probability of battery removal is mainly based on raw material recovery.
Waste battery recycling industry chain
2 positive electrode material valuable metal extraction method
At present, the recovery of power lithium batteries does not fully recycle all kinds of materials on the entire battery. The types of cathode materials mainly include: lithium cobaltate, lithium manganate, lithium ternary, and lithium iron phosphate.
The cost of battery cathode material occupies more than 1/3 of the cost of a single battery. However, due to the current use of carbon materials such as graphite in the negative electrode, lithium titanate Li4Ti5O12 and silicon carbon negative electrode Si/C are used less frequently. Therefore, the current battery recovery technology is mainly aimed at It is battery cathode material recycling.
The recycling methods of used lithium batteries mainly include physical methods, chemical methods and biological methods. Compared with other methods, hydrometallurgy is considered to be an ideal one because of its low energy consumption, high recovery efficiency and high product purity. The recycling method.
2.1 Physical Law
The physical method utilizes the physical and chemical reaction process to process the lithium ion battery. The common physical treatment methods are mainly broken flotation and mechanical grinding.
1) Broken flotation method
Crushing and flotation is a method of sorting by using the difference in the physical and chemical properties of the surface of the material. That is, the entire waste lithium ion battery is first broken. After sorting, the obtained electrode material powder is heat-treated to remove the organic binder. Finally, according to the difference in the hydrophilicity of the lithium cobaltate and the graphite surface in the electrode material powder, flotation separation is performed to recover the cobalt lithium compound powder. The crushing flotation process is simple and can effectively separate the lithium cobalt oxide from the carbon material. The recovery rate of lithium and cobalt is relatively high. However, due to all the materials being crushed and mixed, it is difficult to separate and recover the subsequent copper foil, aluminum foil and metal shell fragments, and the electrolyte LiPF6 reacts with H2O to generate HF due to crushing. Volatile gases, such as environmental pollution, need to pay attention to the method of crushing.
2) Mechanical grinding method
The mechanical grinding method is a method in which the heat energy generated by mechanical polishing promotes the reaction between the electrode material and the abrasive, thereby converting the lithium compound originally bonded to the current collector into salts in the electrode material. Different types of grinding aid materials are recovered. The rate is somewhat different. Higher recoveries can be achieved: 98% recovery of Co and 99% recovery of Li. Mechanical grinding is also an effective method for recovering cobalt and lithium from used lithium-ion batteries. The process is relatively simple. , but the instrument requirements are high, and it is easy to cause the loss of cobalt and aluminum foil recovery.
2.2 Chemical method
Chemical method is the use of chemical reaction process of lithium-ion batteries, generally divided into pyrometallurgical and hydrometallurgical methods.
1) pyrometallurgy
Pyrotechnics, also known as incineration or dry metallurgy, removes organic binders in electrode materials by high-temperature incineration and simultaneously redoxes the metals and their compounds, recovering low-boiling metals in condensed form and The compound is used for sieving, pyrolysis, magnetic separation or chemical method recovery of the metal in the slag. The pyrometallurgy has low requirements for the composition of the raw materials, and is suitable for large-scale processing of more complicated batteries, but the combustion will certainly produce Part of the exhaust gas pollutes the environment, and high-temperature treatment also requires high equipment. At the same time, it also needs to increase purification and recycling equipment, and the cost of treatment is high.
2) Hydrometallurgy
Hydrometallurgy is a method of selectively dissolving the positive electrode material in a waste lithium-ion battery with a suitable chemical reagent and separating the metal elements in the leachate. The hydrometallurgical process is suitable for recovering a relatively single-use lithium battery that has a relatively simple chemical composition. Used alone, it can also be used in conjunction with high-temperature metallurgy, low equipment requirements, low processing costs, is a very mature processing method, suitable for the recycling of small and medium-sized waste lithium-ion batteries.
2.3 Biological methods
Biomass metallurgy is currently underway. It uses the metabolic processes of microbial flora to achieve the selective leaching of metal elements such as cobalt and lithium. Biological methods have low energy consumption, low cost, and can be reused by microorganisms with little pollution. However, the cultivation of microbial fungi requires harsh conditions, long incubation time, low leaching efficiency, and the process needs further improvement.
2.4 Iron phosphate recycling partial upset
Among various power lithium batteries, only the lithium iron phosphate cathode material is free of precious metals, but mainly composed of aluminum, lithium, iron, phosphorus, and carbon. As a result, the company is not enthusiastic about the recycling of lithium iron phosphate. For the recycling of lithium iron phosphate battery, there are few targeted studies.
The general treatment of lithium iron phosphate, the battery after the entire mechanical crushing, the use of polar organic solvents NMP or strong alkali dissolved in the separation of aluminum, the remaining material is a mixture of LiFePO4 and carbon powder. To the mixture of Li, Fe , P to adjust the molar ratio of the three elements in the material, and then ball-milled, LiFePO4 material can be re-synthesized after calcination at high temperature in an inert atmosphere, but the capacity of the material compared to the first synthesized lithium iron phosphate battery cathode material , Charge and discharge performance have declined. The failure of lithium iron phosphate battery cathode material oxidative decomposition, recovery of lithium, iron, phosphorus, carbon and reuse is the solution to the root cause of the recovery path.
Although there are few studies, some people are still doing it. For example, Zhuo Hongshuai developed a method to leach the spent lithium iron phosphate cathode material with a phosphoric acid system, and achieve better efficiency, low cost, and zero waste emission. Lithium, iron separation effect, comprehensive recovery of lithium, iron, phosphorus, carbon.
3 Hydrometallurgy is currently the main application technology
Through the research on the domestic and international lithium-ion battery recycling process, it can be seen that the recovery rate of the lithium-ion battery recycling using the physicochemical method is relatively low; the chemical method research is common, the application range is wide, and it is relatively feasible; the biological method is environmentally friendly, but it requires The time is too long to be further studied. Many studies on chemical methods have shown that the electrochemical performance of recycled materials obtained through hydrometallurgy through single pyrometallurgy is good, but the recovery of a single hydrometallurgy requires a large amount of reagents, not suitable Large-scale industrialization.
Comparatively speaking, hydrometallurgy is a kind of method with better overall performance in current extraction methods. Acid leaching is the most important link. Its main purpose is to transfer the target metal in the active material after pretreatment to the leachate. It facilitates subsequent separation and recovery processes. Traditional inorganic strong acids (HCl, HNO3 and H2SO4) have been widely used in leaching processes. However, toxic gases such as Cl2, SO3 and Nx are harmful to the environment during the leaching process. 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 the environmental impact while satisfying high efficiency. Secondary pollution.
The main steps of a typical wet extraction are: pretreatment → acid leaching → leaching solution leaching → separation and extraction → elemental precipitation.
3.1 preprocessing basic steps
Discard the used lithium battery in salt water, remove the outer packaging of the battery, and remove the metal shell to obtain the inner cell. The cell consists of the negative electrode, positive electrode, separator and electrolyte. The negative electrode is attached to the surface of the copper foil and the positive electrode is attached to the aluminum foil. On the surface, 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 raw material to be treated. Different processes have different follow-up processing means. The typical wet extraction procedure is as follows, from the '6', and feel:
1) LiCoO2 electrode powder is added to the sulfuric acid solution to maintain a specific solid-liquid ratio and mechanically stirred;
2) After ultrasonic leaching for 60 minutes, remove the residue and measure the concentration of each metal in the leachate;
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) Using P507-sulfonated kerosene system to extract cobalt and stripping with H2SO4 to obtain high-purity cobalt sulfate solution;
5) After the NaOH solution and the cobalt-rich solution are heated to boiling, alkali solution is added to the cobalt-rich solution until a large amount of blue precipitate is produced in the cobalt solution;
6) Seal the mouth of the beaker. After standing for 5 minutes, the blue precipitate completely transforms into pink precipitated sodium hydroxide and cobalt;
7) After washing several times, add ethanol as a dispersant to age, filter, filter the cake and dry it in a muffle furnace and calcine it to obtain a black powder of osmium tetroxide.
4 Technology Trends
At present, it is mainly for the recovery of precious metals in batteries. It ignores other relatively inexpensive materials such as electrolytes and separators, and fails to systematically recover the entire battery.
There were also reports of technologies other than mainstream methods that were involved in the recycling of other elements. At the end of 2016, a news release from the Tsinghua University Science and Technology Achievement Promotion Center in the magazine "Acetaldehyde Acetate Chemicals" stated that its team developed a kind of 'power'. Lithium battery rapid stripping and lithium cobalt short-term recycling technology', can efficiently extract precious metals in lithium batteries, copper, aluminum metal recovery rate of more than 98%, cobalt, lithium metal recovery rate of more than 95%.
In addition, a more comprehensive method has also been proposed. Gao Guilan proposed in his article “The Current Status of Recycling and Utilization of Lithium-ion Power Battery for Used Vehicles” to comprehensively use the ideas of various methods. The joint treatment method is 'fire method pretreatment+wet'. Acid recovery and metal precipitation 'recovery route, the route leaching of valuable metals by acid leaching, the traditional use of acid is mainly inorganic acid (HCl, H2SO4 and HNO3, etc.), but the type of inorganic acid corrosion of equipment , It is also harmful to the human body. Therefore, it is recommended to use organic acids of relatively mild nature (including malic acid, oxalic acid, and ascorbic acid, etc.) to replace it. This is not only environmentally friendly, but some organic acids are also reducing and can replace traditional 'organic acids'. + Reducing agent' system.
5 Summary
The current percentage of power lithium battery recycling is still relatively low. In a report, China's power lithium battery recycling rate is about 10%. Compared with the lead-acid battery industry, China's recycling rate is about 30%, and the United States The number has exceeded 90%, it can be said that 'circular economy'. Turned over, there is a huge market space.
However, the direct driving force of waste battery recycling is still on the cost-effectiveness of recycling. If the recycled materials play a beneficial role in reducing the battery cost for the entire industry, the recycled materials can be smoothly circulated, and the recycling of used batteries can really be done from 'Change to 'I do' come up. Because the data information is far from enough, there is no ability to figure out what exactly this turning point appears at. We can only say that truth is such a reason.
