Introduction to the resource utilization and environmental control technology of waste lithium-ion batteries

　　With the increasing use of batteries in daily life, the production and sales of batteries are increasing day by day, and then a large number of waste batteries are recycled and disposed of. Based on the recycling of used lithium-ion batteries, this article introduces the composition of used lithium-ion batteries and the current domestic and international recycling and treatment technologies for used batteries, as well as the "directional cycle" technology from used batteries to battery materials. The environmental pollution problem of "heavy metal-ammonia nitrogen compound wastewater" encountered in the process of utilization, proposed a control solution.

　　Abstract: With the increasing use of batteries in daily life, the production and sales of batteries are increasing day by day, and then a large number of waste batteries are recycled and disposed of. Based on the recycling of used lithium-ion batteries, this article introduces the composition of used lithium-ion batteries and the current domestic and international recycling and treatment technologies for used batteries, as well as the "directional cycle" technology from used batteries to battery materials. The environmental pollution problem of "heavy metal-ammonia nitrogen compound wastewater" encountered in the process of utilization, proposed a control solution.　　 Introduction 　　 With the continuous growth of human society's energy demand, the battery, as a portable energy storage device, accounts for an increasing proportion in people's daily life, becoming one of the third largest consumer products [1]. In 2010, China’s output of lithium batteries reached 1.35 billion, and continued to increase at an average annual growth rate of 15%. China has become the world’s largest producer, consumer and exporter of lithium batteries. Due to the widespread use of lithium batteries, the amount of scrap will inevitably increase substantially. Lithium batteries contain chemical substances such as lithium hexafluorophosphate, organic acid esters, copper, cobalt, nickel, and manganese. These substances will cause environmental pollution when they enter the environment during landfill, incineration, and recycling of batteries in small and indigenous smelters. Injury to the human body. Therefore, the development of waste lithium-ion battery recycling technology is not only conducive to environmental protection, but also has greater economic benefits [2]. 1 Lithium-ion battery composition The outer layer of the lithium-ion battery is wrapped in plastic, aluminum, and iron shells, and the inner layer is divided into positive electrode active material, negative electrode active material, aluminum or copper foil current collector, binder and polyethylene or polypropylene porous diaphragm Materials, electrolyte (carbonate organic solvent) and dissolved electrolyte salt (generally LiPF6) and other parts [2]. Among them, the positive active material is multi-site lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, and the like. The negative electrode active materials are mostly graphite carbon powder, 　　 lithium titanate, etc. Taking lithium cobalt oxide battery as an example, the average content of lithium cobalt oxide battery is 12%-18% cobalt, 1.2%-1.8% lithium, 8%-10% copper, 4%-8% aluminum, and 30% shell alloy. Metals are primary resources and have great recycling value. In particular, the metal cobalt and nickel are more expensive, and they are important raw materials indispensable for the construction of the national economy and national defense, as well as necessary materials for high, precise and cutting-edge technology.　　2Recycling and processing technology of waste lithium-ion batteries 　　Currently, research on the recycling and utilization of used lithium-ion batteries mainly focuses on the recovery and utilization of cobalt in lithium cobalt oxide batteries. After discharging and disassembling the waste lithium ion battery, according to the main technology used in the recycling process, the recycling process of the waste lithium battery can be divided into three major types: fire method, wet method and biological method. kind. 2.1 Fire method Fire method mainly uses high temperature incineration to decompose and remove the organic matter that plays a role in bonding, so as to realize the separation between the constituent materials of the lithium battery, and at the same time, it can oxidize, reduce and decompose the metal and its compound in the battery, and then volatilize in the form of vapor. Later, it is collected by condensation and other methods [3]. Research by Sony/Sumitomo Corporation in Japan shows that the incineration of undismantled waste lithium batteries below 1000°C can effectively remove the electrolyte and diaphragms and other organic substances contained in them to achieve the cracking of the battery. The residual substances after incineration include Fe, Cu, Al, etc., can be separated from each other by sieving and magnetic separation [4].　　2.2 Wet Method 　　wet method is to first classify lithium batteries, then dissolve, separate, and extract with an appropriate solvent to obtain the corresponding metal and metal compound materials [5]. Nan Junmin [6] and others first leached and removed aluminum with an alkaline solution, and used a mixed system of sulfuric acid and hydrogen peroxide to dissolve the electrode material of the lithium ion battery, and then used the extractants AcorgaM5640 and Cyanex272 to extract copper and cobalt. The recovery rate of copper can be Up to 98%, the recovery rate of cobalt can reach 97%, and the remaining lithium can be precipitated in the form of lithium carbonate with sodium carbonate. These materials can be used as precursors for the preparation of lithium cobalt oxide electrode materials for lithium ion batteries. The process does not need to separate the positive and negative electrodes, and the used extractant has a good separation effect, and can be reused after elution; at the same time, the recovered material can be used to prepare electrode materials, which increases the economic benefit of recovery.　　 Wu Fang [7]’s method is similar. Use alkali to dissolve battery materials and remove 90% of aluminum in advance. Then use the H2SO4+H2O2 system to acid leaching the filter residue. The filtrate after acid leaching contains Fe2+, Ca2+, Mn2+ and other impurities. P2O4 (dioctyl phosphate) is used to extract a mixture of cobalt and lithium, and then P5O7 (organic phosphoric acid extractant) 1) Extraction and separation of cobalt and lithium, recovery of cobalt sulfate by back extraction, and recovery of lithium carbonate by deposition of raffinate, thereby recovering cobalt and lithium from waste lithium ion secondary batteries. The obtained lithium carbonate meets the requirements of a zero-grade product, and the primary lithium precipitation rate is 76.5%.　　2.3 Biological method 　　Biological method uses the metabolic process of the microorganisms with special selectivity to realize the leaching of cobalt, lithium and other elements. Debaraj Mishra et al. [8] used a kind of acidophilus called Acidithiobacillus-ferrooxidans, which can use sulfur and ferrous ions as energy sources to metabolize products such as sulfuric acid and ferric ions, thereby contributing to waste lithium-ion batteries. Dissolution of metal elements.　　 From the perspective of the aforementioned waste lithium-ion battery recycling method, the use of fire method has higher requirements for equipment and energy consumption. The cost of removing aluminum and copper in the wet process is relatively high, and it only separates and purifies a certain metal element in the electrode material into a basic chemical raw material, which has great limitations. Although biological leaching technology has the advantages of low cost and low pollution, it is still in the research stage. With the diversified development of battery cathode materials, the recovery method for cobalt in lithium cobalt oxide batteries is no longer applicable. The recovery of lithium ion batteries is not limited to resource utilization, but should also include harmless disposal.　　3 directional cycle technology 　　 waste lithium ion battery recycling technology is not complicated, the key is that the recycling technology can be industrialized and scaled up. This technology uses an advanced sorting and identification system to physically remove waste lithium-ion batteries, and uses internationally leading extraction separation and solid-phase synthesis technology to completely "direct cycle" waste batteries into high-end energy storage electrode materials[9] , To truly realize the short-range, energy-saving and high-efficiency of the recycling process of used batteries. The technological process flow chart is shown in Figure 1.

　　The key technologies of this technology process are: 　　(1) pretreatment process　　After the waste battery is crushed and sorted, the plastic and the diaphragm paper are separated by wind separation, the iron is separated by magnetic separation, and the copper and aluminum are separated by gravity to obtain the crude cathode material powder. (2) Synergistic extraction and separate extraction use P2O4 extraction to remove impurities. By controlling the pH of the water phase, impurities such as iron, zinc, copper, calcium, and magnesium in the water phase can be extracted into the organic phase. The raffinate components are mainly nickel, Mixed solution of cobalt and manganese. According to needs, P5O7 is used to extract and separate nickel and cobalt elements, and the pH is controlled to be 5 to 5.5. The cobalt element enters the organic phase and the manganese element remains in the water phase to obtain a cobalt-containing solution and a manganese-containing solution, respectively. (3) Synthesis process 1) Synthesis of nickel-cobalt-manganese lithium: Add an appropriate amount of nickel sulfate and manganese sulfate to a mixed solution containing nickel, cobalt, and manganese, and adjust the molar ratio of nickel, cobalt, and manganese in the solution according to the product brand; add The theoretical amount of precipitant and appropriate amount of ammonia are controlled by controlling the reaction temperature, time and pH of the solution to obtain the precursor precipitate with intact crystal form; the precursor precipitate and lithium carbonate are proportioned according to a certain ratio, and after the mixing is uniform, the separation is carried out. Step program temperature increase heat treatment, after cooling, obtain calcined lithium nickel cobalt manganese oxide product. 2) Synthesis of lithium cobaltate: add a theoretical amount of precipitant and an appropriate amount of ammonia to the cobalt solution, and control the reaction temperature, time and pH value of the solution to obtain a precipitate with intact crystal form; Proportioning, after mixing uniformly, step-wise temperature-programming heat treatment is performed, and after cooling, a calcined lithium cobalt oxide product is obtained. 3) Synthesis of lithium manganate: add a theoretical amount of precipitant and an appropriate amount of ammonia to the manganese-containing solution, and control the reaction temperature, time and pH value of the solution to obtain a precipitate with intact crystal form; press the precipitate with lithium carbonate After mixing in a certain proportion and evenly mixing, the stepwise temperature-raising heat treatment is carried out, and the calcined lithium manganate product is obtained after cooling. The pretreatment of 　　"directed circulation" process physically removes aluminum foil, copper foil, diaphragm paper, and steel shell, and uses a combination of collaborative extraction and separate extraction to directly prepare waste lithium-ion batteries into electrode materials. Compared with the traditional alkali-soluble acid impregnation, the method of preparing chemical salt by separate extraction is not only lower in cost, but also more environmentally friendly and has higher product added value. 4 Environmental control technology The main pollutant produced during the "directed cycle" production mode of waste lithium-ion battery recycling is "heavy metal-ammonia nitrogen" composite wastewater, according to the "Copper, Nickel and Cobalt Industrial Pollutant Discharge Standard" (GB25467-2010) Since January 1, 2012, the direct discharge of ammonia nitrogen from existing enterprises is limited to 8mg/L, total nickel is 0.5mg/L, and total cobalt is 1.0mg/L. Its control standards are much higher than the "Comprehensive Wastewater Discharge Standard" "(GB8978-1996), it can be seen that the country has become stricter and stricter on the discharge of heavy metals and ammonia nitrogen in sewage.　　 At present, the treatment methods of "heavy metal-ammonia nitrogen" composite wastewater can be roughly divided into three categories: chemical treatment, physical treatment, and biological treatment [10]. Zhong Li et al. [10, 11] compared the removal effect of MgO+H3PO4 and MgHPO4 on the pollutant NH3 in water, and found that the former agent is better, and its pH=9~11, n(Mg2+): n(PO3- 4): n(NH4+)=1:1:1, n(H3PO4):n(MgO)>1.5:1, the removal rate of ammonia nitrogen in wastewater is as high as 99%, and the ammonia concentration in the residual liquid after treatment is <1mg/ L. Huang Wenshui [12] and others used Na2HPO4 and MgSO4 experiments to further find that the dosage of phosphate has the greatest influence on the removal efficiency of ammonia nitrogen, followed by pH, and the dosage of Mg and reaction temperature have relatively little influence on it.　　 Using chemical methods alone to treat a large amount of wastewater will increase the cost of treatment, so it is restricted and cannot be applied on a large scale. The physical separation method is used to recover ammonia nitrogen resources through a self-made rectification deammonia device. After the ammonia nitrogen resources are recovered, the wastewater mainly contains heavy metals. Then, the process of dissolution, extraction, and impurity removal can be used to efficiently recover the precious metals and realize the resources. Chemical recycling, and can be applied to larger-scale sewage treatment.

　　This process utilizes the characteristics of ammonia solubility that fluctuates with temperature, and uses direct steam to distill ammonia: the feed ammonia and tower kettle are heated to about 90°C through a heat exchanger, and then enter the steam tower with a pressure of 0.12M～0.16MPa, using steam directly Carry out stripping distillation. The produced concentrated ammonia vapor is cooled by the heat exchanger and then enters the high-level ammonia absorber for recycling. The liquid phase after the ammonia vaporization directly enters the tower for reflux. The process flow is shown in Figure 2.

　　5 Conclusion The recycling of used lithium-ion batteries is a major event that benefits the country and the people. With the diversification of battery materials, the "directed cycle" technology has become the best way to dispose of used batteries due to its environmental protection, economy, and application. The comprehensive recovery rate has reached 98.5%, and large-scale production has been successfully realized, which is very worthy of promotion in the industry. Although the current recovery of valuable metal elements in waste lithium batteries has reached a high recovery rate, and can effectively control environmental pollution during the recycling process, the recovery and treatment of materials such as negative electrode materials and diaphragm paper is still in the initial stage. This will become a new technical issue.