International lithium battery recycling technology route -Lithium - Ion Battery Equipment
The recycling process of waste lithium-ion batteries mainly includes pretreatment, secondary treatment and advanced treatment. Because there is still some electricity left in the waste battery, the pretreatment process includes deep discharge process, crushing and physical separation; The purpose of secondary treatment is to realize the complete separation of positive and negative active materials from the substrate. Heat treatment, organic solvent dissolution, alkali solution dissolution and electrolysis are commonly used to achieve the complete separation of the two; Advanced treatment mainly includes two processes: leaching and separation and purification to extract valuable metal materials [4]. According to the classification of extraction process, battery recovery methods can be mainly divided into three categories: dry recovery, wet recovery and biological recovery.(Lithium - Ion Battery Equipment)
Dry recycling
Dry recovery refers to the direct recovery of materials or valuable metals without solution and other media. Among them, the main methods are physical separation and high-temperature pyrolysis.
(1) Physical sorting method
The physical separation method refers to the disassembly and separation of batteries, and the crushing, sieving, magnetic separation, fine crushing and classification of battery components such as electrode active substances, collector fluid and battery shell to obtain valuable and high content substances. Shin et al. [6] proposed a method to recover Li and Co from the waste liquid of lithium ion battery by using sulfuric acid and hydrogen peroxide, including two processes: physical separation of metal particles and chemical leaching. The physical separation process includes crushing, screening, magnetic separation, fine crushing and classification. In the experiment, a group of rotary and fixed blade crushers are used for crushing, sieves with different apertures are used to classify and crush materials, and magnetic separation is used for further treatment to prepare for the subsequent chemical leaching process.
Based on the grinding technology and water leaching process developed by Zhang et al., Lee et al. and Saeki et al., Shu et al. developed a new method to recover cobalt and lithium from lithium sulfur battery waste by mechanochemical method. This method uses planetary ball mill to grind lithium cobalate (LiCoO2) and polyvinyl chloride (PVC) together in air to form Co and lithium chloride (LiCl) in mechanochemical formula. Subsequently, the grinding product is dispersed in water to extract the chloride. Grinding promotes mechanochemical reactions. With the grinding process, the extraction yield of Co and Li was improved. More than 90% Co and nearly 100% lithium were recovered after 30 min of grinding. At the same time, about 90% of chlorine in PVC samples has been converted into inorganic chlorides.
The operation of physical separation method is relatively simple, but it is not easy to completely separate lithium ion batteries. In addition, mechanical entrainment loss is easy to exist during screening and magnetic separation, and it is difficult to completely separate and recover metals.
(2) Pyrolysis
The high-temperature pyrolysis method refers to the high-temperature calcination and decomposition of lithium battery materials that have undergone preliminary separation treatment such as physical crushing, and the removal of organic adhesives, so as to separate the constituent materials of lithium battery. At the same time, the metal and its compounds in the lithium battery can be oxidized, reduced and decomposed, volatilized in the form of steam, and then collected by condensation and other methods.
Lee et al. used high-temperature pyrolysis method to prepare LiCoO2 from waste lithium-ion batteries. Lee et al. first heat treated LIB samples in a muffle furnace at 100~150 ℃ for 1h. Secondly, the heat treated battery is chopped to release the electrode material. The samples were disassembled with a high-speed pulverizer specially designed for the study. The samples were classified according to size, and the size range was 1~50mm. Then, conduct two steps of heat treatment in the furnace, the first at 100~500 ℃ for 30min, the second at 300~500 ℃ for 1h, and release the electrode material from the collector through vibration screening. Next, the cathode active material LiCoO2 is obtained by burning for 0.5~2h at 500~900 ℃, burning off the carbon and adhesive. The experimental data showed that the carbon and adhesive were burned off at 800 ℃.
The high-temperature pyrolysis treatment technology is simple in process, convenient in operation, fast in reaction and high in efficiency under high temperature environment, and can effectively remove adhesives; Moreover, the method does not require high components of raw materials, and is more suitable for processing large or complex batteries. However, this method requires high equipment; In the process of treatment, the decomposition of organic matter in the battery will produce harmful gas, which is not friendly to the environment. Therefore, purification and recovery equipment should be added to absorb and purify harmful gas to prevent secondary pollution. Therefore, the treatment cost of this method is high.
2. Wet recovery
The wet recovery process is to break up and dissolve the waste battery, and then use appropriate chemical reagents to selectively separate the metal elements in the leaching solution to produce high-grade cobalt metal or lithium carbonate for direct recovery. The wet recycling treatment is more suitable for recycling the waste lithium batteries with relatively single chemical composition, and its equipment investment cost is low, which is suitable for the recycling of small and medium-sized waste lithium batteries. Therefore, this method is also widely used at present.
(1) Alkali acid leaching method
Since the cathode material of lithium ion battery will not be dissolved in alkali solution, while the aluminum foil of the base will be dissolved in alkali solution, this method is often used to separate aluminum foil. When recovering Co and Li from the battery, Zhang Yang et al. used alkali to leach aluminum in advance, and then used dilute acid to soak to destroy the adhesion of organic matter to copper foil. However, alkaline leaching can not completely remove PVDF, which has adverse effects on subsequent leaching.
Most of the positive active substances in the lithium ion battery can be dissolved in acid, so the pretreated electrode materials can be leached with acid solution to separate the active substances from the collector fluid, and then the target metal can be precipitated and purified according to the principle of neutralization reaction, so as to achieve the goal of recovering high-purity components.
The acid solution used in acid leaching method includes traditional inorganic acid, including hydrochloric acid, sulfuric acid and nitric acid. However, in the process of leaching with inorganic strong acid, chlorine (Cl2), sulfur trioxide (SO3) and other harmful gases that have an impact on the environment are often produced, so researchers try to use organic acids to treat waste lithium batteries, such as citric acid, oxalic acid, malic acid, ascorbic acid, glycine, etc. Li et al. use hydrochloric acid to dissolve the recovered electrode. Since the efficiency of acid leaching process may be affected by hydrogen ion (H+) concentration, temperature, reaction time and solid liquid ratio (S/L), in order to optimize the operating conditions of acid leaching process, experiments were designed to explore the effects of reaction time, H+concentration and temperature. The experimental data show that when the temperature is 80 ℃, the concentration of H+is 4mol/L, the reaction time is 2h, and the leaching efficiency is the highest. Among them, 97% Li and 99% Co in the electrode material are dissolved. Zhou Tao et al. used malic acid as the leaching agent and hydrogen peroxide as the reducing agent to carry out the reduction leaching of the positive active substance obtained from the pretreatment, and studied the influence of different reaction conditions on the leaching rate of Li, Co, Ni, Mn in the malic acid leaching solution, so as to find out the best reaction conditions. The research data showed that when the temperature was 80 ℃, the concentration of malic acid was 1.2mol/L, the volume ratio of liquid to liquid was 1.5%, the ratio of solid to liquid was 40g/L, and the reaction time was 30min, the efficiency of malic acid leaching was the highest. The leaching rates of Li, Co, Ni, Mn were 98.9%, 94.3%, 95.1%, and 96.4%, respectively. However, compared with inorganic acid, the cost of organic acid leaching is higher.
(2) Organic solvent extraction
The organic solvent extraction method uses the principle of "similarity and compatibility" to physically dissolve the organic binder with appropriate organic solvent, so as to weaken the adhesion between the material and the foil and separate them.
In order to better recover the active materials of electrodes when recycling lithium cobalate batteries, Contesabile et al. used N-methylpyrrolidone (NMP) to selectively separate the components. NMP is a good solvent for PVDF (solubility is about 200g/kg), and its boiling point is high, about 200 ℃. The study used NMP to treat the active material at about 100 ℃ for 1h, which effectively realized the separation of the film and its carrier. Therefore, it was simply filtered out from the NMP (N-methylpyrrolidone) solution to recover the metal form of Cu and Al. Another advantage of this method is that the recovered Cu and Al can be directly reused after full cleaning. In addition, recycled NMP can be recycled. Because of its high solubility in PVDF, it can be reused for many times. Zhang et al. used trifluoroacetic acid (TFA) to separate cathode materials from aluminum foil when recycling cathode waste for lithium ion batteries. Polytetrafluoroethylene (PTFE) was used as the organic binder for the waste lithium-ion battery used in the experiment. The effects of TFA concentration, liquid-solid ratio (L/S), reaction temperature and time on the separation efficiency of cathode material and aluminum foil were systematically studied. The experimental results show that the cathode materials can be completely separated when the mass fraction of TFA is 15, the liquid-solid ratio is 8.0 mL/g, the reaction temperature is 40 ℃, and the reaction time is 180 min under proper stirring.
The experimental conditions for using organic solvent extraction to separate materials and foils are relatively mild, but organic solvents have certain toxicity, which may be harmful to the health of operators. At the same time, because different manufacturers have different processes for making lithium-ion batteries, the selected binders are different. Therefore, manufacturers need to choose different organic solvents when recycling waste lithium-ion batteries according to different manufacturing processes. In addition, cost is also an important consideration for large-scale industrial recovery and treatment operations. Therefore, it is very important to select a solvent with wide sources, appropriate price, low toxicity and wide applicability.
Dry recycling
Dry recovery refers to the direct recovery of materials or valuable metals without solution and other media. Among them, the main methods are physical separation and high-temperature pyrolysis.
(1) Physical sorting method
The physical separation method refers to the disassembly and separation of batteries, and the crushing, sieving, magnetic separation, fine crushing and classification of battery components such as electrode active substances, collector fluid and battery shell to obtain valuable and high content substances. Shin et al. [6] proposed a method to recover Li and Co from the waste liquid of lithium ion battery by using sulfuric acid and hydrogen peroxide, including two processes: physical separation of metal particles and chemical leaching. The physical separation process includes crushing, screening, magnetic separation, fine crushing and classification. In the experiment, a group of rotary and fixed blade crushers are used for crushing, sieves with different apertures are used to classify and crush materials, and magnetic separation is used for further treatment to prepare for the subsequent chemical leaching process.
Based on the grinding technology and water leaching process developed by Zhang et al., Lee et al. and Saeki et al., Shu et al. developed a new method to recover cobalt and lithium from lithium sulfur battery waste by mechanochemical method. This method uses planetary ball mill to grind lithium cobalate (LiCoO2) and polyvinyl chloride (PVC) together in air to form Co and lithium chloride (LiCl) in mechanochemical formula. Subsequently, the grinding product is dispersed in water to extract the chloride. Grinding promotes mechanochemical reactions. With the grinding process, the extraction yield of Co and Li was improved. More than 90% Co and nearly 100% lithium were recovered after 30 min of grinding. At the same time, about 90% of chlorine in PVC samples has been converted into inorganic chlorides.
The operation of physical separation method is relatively simple, but it is not easy to completely separate lithium ion batteries. In addition, mechanical entrainment loss is easy to exist during screening and magnetic separation, and it is difficult to completely separate and recover metals.
(2) Pyrolysis
The high-temperature pyrolysis method refers to the high-temperature calcination and decomposition of lithium battery materials that have undergone preliminary separation treatment such as physical crushing, and the removal of organic adhesives, so as to separate the constituent materials of lithium battery. At the same time, the metal and its compounds in the lithium battery can be oxidized, reduced and decomposed, volatilized in the form of steam, and then collected by condensation and other methods.
Lee et al. used high-temperature pyrolysis method to prepare LiCoO2 from waste lithium-ion batteries. Lee et al. first heat treated LIB samples in a muffle furnace at 100~150 ℃ for 1h. Secondly, the heat treated battery is chopped to release the electrode material. The samples were disassembled with a high-speed pulverizer specially designed for the study. The samples were classified according to size, and the size range was 1~50mm. Then, conduct two steps of heat treatment in the furnace, the first at 100~500 ℃ for 30min, the second at 300~500 ℃ for 1h, and release the electrode material from the collector through vibration screening. Next, the cathode active material LiCoO2 is obtained by burning for 0.5~2h at 500~900 ℃, burning off the carbon and adhesive. The experimental data showed that the carbon and adhesive were burned off at 800 ℃.
The high-temperature pyrolysis treatment technology is simple in process, convenient in operation, fast in reaction and high in efficiency under high temperature environment, and can effectively remove adhesives; Moreover, the method does not require high components of raw materials, and is more suitable for processing large or complex batteries. However, this method requires high equipment; In the process of treatment, the decomposition of organic matter in the battery will produce harmful gas, which is not friendly to the environment. Therefore, purification and recovery equipment should be added to absorb and purify harmful gas to prevent secondary pollution. Therefore, the treatment cost of this method is high.
2. Wet recovery
The wet recovery process is to break up and dissolve the waste battery, and then use appropriate chemical reagents to selectively separate the metal elements in the leaching solution to produce high-grade cobalt metal or lithium carbonate for direct recovery. The wet recycling treatment is more suitable for recycling the waste lithium batteries with relatively single chemical composition, and its equipment investment cost is low, which is suitable for the recycling of small and medium-sized waste lithium batteries. Therefore, this method is also widely used at present.
(1) Alkali acid leaching method
Since the cathode material of lithium ion battery will not be dissolved in alkali solution, while the aluminum foil of the base will be dissolved in alkali solution, this method is often used to separate aluminum foil. When recovering Co and Li from the battery, Zhang Yang et al. used alkali to leach aluminum in advance, and then used dilute acid to soak to destroy the adhesion of organic matter to copper foil. However, alkaline leaching can not completely remove PVDF, which has adverse effects on subsequent leaching.
Most of the positive active substances in the lithium ion battery can be dissolved in acid, so the pretreated electrode materials can be leached with acid solution to separate the active substances from the collector fluid, and then the target metal can be precipitated and purified according to the principle of neutralization reaction, so as to achieve the goal of recovering high-purity components.
The acid solution used in acid leaching method includes traditional inorganic acid, including hydrochloric acid, sulfuric acid and nitric acid. However, in the process of leaching with inorganic strong acid, chlorine (Cl2), sulfur trioxide (SO3) and other harmful gases that have an impact on the environment are often produced, so researchers try to use organic acids to treat waste lithium batteries, such as citric acid, oxalic acid, malic acid, ascorbic acid, glycine, etc. Li et al. use hydrochloric acid to dissolve the recovered electrode. Since the efficiency of acid leaching process may be affected by hydrogen ion (H+) concentration, temperature, reaction time and solid liquid ratio (S/L), in order to optimize the operating conditions of acid leaching process, experiments were designed to explore the effects of reaction time, H+concentration and temperature. The experimental data show that when the temperature is 80 ℃, the concentration of H+is 4mol/L, the reaction time is 2h, and the leaching efficiency is the highest. Among them, 97% Li and 99% Co in the electrode material are dissolved. Zhou Tao et al. used malic acid as the leaching agent and hydrogen peroxide as the reducing agent to carry out the reduction leaching of the positive active substance obtained from the pretreatment, and studied the influence of different reaction conditions on the leaching rate of Li, Co, Ni, Mn in the malic acid leaching solution, so as to find out the best reaction conditions. The research data showed that when the temperature was 80 ℃, the concentration of malic acid was 1.2mol/L, the volume ratio of liquid to liquid was 1.5%, the ratio of solid to liquid was 40g/L, and the reaction time was 30min, the efficiency of malic acid leaching was the highest. The leaching rates of Li, Co, Ni, Mn were 98.9%, 94.3%, 95.1%, and 96.4%, respectively. However, compared with inorganic acid, the cost of organic acid leaching is higher.
(2) Organic solvent extraction
The organic solvent extraction method uses the principle of "similarity and compatibility" to physically dissolve the organic binder with appropriate organic solvent, so as to weaken the adhesion between the material and the foil and separate them.
In order to better recover the active materials of electrodes when recycling lithium cobalate batteries, Contesabile et al. used N-methylpyrrolidone (NMP) to selectively separate the components. NMP is a good solvent for PVDF (solubility is about 200g/kg), and its boiling point is high, about 200 ℃. The study used NMP to treat the active material at about 100 ℃ for 1h, which effectively realized the separation of the film and its carrier. Therefore, it was simply filtered out from the NMP (N-methylpyrrolidone) solution to recover the metal form of Cu and Al. Another advantage of this method is that the recovered Cu and Al can be directly reused after full cleaning. In addition, recycled NMP can be recycled. Because of its high solubility in PVDF, it can be reused for many times. Zhang et al. used trifluoroacetic acid (TFA) to separate cathode materials from aluminum foil when recycling cathode waste for lithium ion batteries. Polytetrafluoroethylene (PTFE) was used as the organic binder for the waste lithium-ion battery used in the experiment. The effects of TFA concentration, liquid-solid ratio (L/S), reaction temperature and time on the separation efficiency of cathode material and aluminum foil were systematically studied. The experimental results show that the cathode materials can be completely separated when the mass fraction of TFA is 15, the liquid-solid ratio is 8.0 mL/g, the reaction temperature is 40 ℃, and the reaction time is 180 min under proper stirring.
The experimental conditions for using organic solvent extraction to separate materials and foils are relatively mild, but organic solvents have certain toxicity, which may be harmful to the health of operators. At the same time, because different manufacturers have different processes for making lithium-ion batteries, the selected binders are different. Therefore, manufacturers need to choose different organic solvents when recycling waste lithium-ion batteries according to different manufacturing processes. In addition, cost is also an important consideration for large-scale industrial recovery and treatment operations. Therefore, it is very important to select a solvent with wide sources, appropriate price, low toxicity and wide applicability.
