Battery grade lithium carbonate background and overview
Lithium carbonate is widely used in the production of secondary lithium salts and metallic lithium products, and is the most critical product in the lithium industry. In the current actual production process of lithium carbonate, its main production raw materials come from salt lake brine and ore extracts. At present, in the production process of lithium carbonate in my country, the solid ore extraction method is mainly used, while abroad the salt lake brine extraction process is mostly used. At present, our country is also actively exploiting salt lake lithium resources, but due to limitations in technology, resources and other factors, the development speed is relatively slow. To this end, it is necessary to conduct in-depth research on the production and application of battery-grade lithium carbonate. Lithium carbonate is widely used in industrial production and is also one of the important raw materials in pharmacy. It also plays a very important role in the development of the chemical industry. In its actual production practice, lithium carbonate is divided into industrial grade lithium carbonate and battery grade lithium carbonate according to different purity. The chemical composition of battery-grade lithium carbonate is higher in purity and contains fewer impurities, which can effectively ensure battery performance. With the continuous development of the current industry, the purity requirements for lithium carbonate are also constantly increasing. Many industries directly require the use of battery-grade lithium carbonate. The requirements for the lithium carbonate process are getting higher and higher. Not only the quality of production is required, but also the production quality is required. size and modernization.
Battery grade lithium carbonate applications
Battery-grade lithium carbonate is a key raw material for the production of cathode materials for lithium-ion batteries. The cathode materials of lithium cobalt oxide batteries, lithium iron phosphate batteries, and ternary batteries are all synthesized based on battery-grade lithium carbonate. In addition, battery-grade lithium carbonate, as an electrolyte additive for lithium-ion batteries, can not only significantly improve the safety performance of the battery, but also extend its service life. Therefore, the improvement of the battery-grade lithium carbonate preparation process plays an important role in promoting the development of the lithium-ion battery industry.
Preparation of battery grade lithium carbonate
1. Direct preparation of battery-grade lithium carbonate from salt lake brine
Electrodialysis is a method for directly preparing battery-grade lithium carbonate from salt lake brine, and then extracting potassium from salt fields to form lithium boron
Brine is further treated with boron extraction to obtain boric acid products and lithium brine. The lithium brine is passed through an electrodialysis membrane to obtain a refined liquid. The refined liquid then passes through a nanofiltration membrane, an ion exchanger and forced evaporation to remove calcium, magnesium, boron and sulfate radicals. Finally, a concentrated lithium solution is obtained. The concentrated lithium reacts with sodium carbonate to obtain a lithium carbonate precipitate. After cleaning and drying, a battery-grade lithium carbonate product is obtained. This process can directly obtain battery-grade lithium carbonate with higher purity, but the operation process is cumbersome.
A method for preparing battery-grade lithium carbonate from brine using an ion exchange process. By extracting potassium from the concentrate
Add aluminum chloride hexahydrate to the subsequent salt lake brine to prepare new brine, and use a mixed alkali solution of sodium hydroxide and sodium carbonate to be added dropwise to the brine at the same time. After a full reaction, a low magnesium-rich lithium solution is obtained. The lithium-rich solution after magnesium removal is used to extract lithium through a manganese adsorbent, desorbed using hydrochloric acid solution or nitric acid solution, adjust the pH of the desorbed solution to 7-12 to obtain manganese hydroxide precipitate, and then filter, and the filtrate is concentrated to a lithium content of 20-30g/L, and filtered Remove sodium chloride, add sodium carbonate solution to the filtrate, filter and wash with water to obtain battery-grade lithium carbonate. This method not only solves the problem of magnesium recycling, but also controls the content of various impurity ions in the desorption solution. However, a large amount of sodium ions are introduced in the process, which may cause the sodium in the product to exceed the standard. It can be seen that the current method of directly preparing lithium carbonate from salt lake brine has a complicated process flow, and because the raw materials contain more impurities such as Na, Mg, and K, it is easy to cause the impurity content to exceed the standard. Therefore, currently, industrial lithium carbonate is mostly used as raw material to purify and prepare battery-grade lithium carbonate.
2. Method for purifying industrial grade lithium carbonate to prepare battery grade lithium carbonate
At present, the main methods for purifying industrial lithium carbonate to prepare battery-grade lithium carbonate include causticization method, recrystallization method, precipitation method, electrolysis method, hydrogenation method, etc.
1) Causticization method
By adding refined lime milk to the slurry of industrial lithium carbonate and deionized water, soluble lithium hydroxide is formed, while calcium impurities mainly precipitate in the form of calcium carbonate, and magnesium impurities form more insoluble magnesium hydroxide. Precipitate, remove calcium and magnesium impurities after filtration, and pass high-purity carbon dioxide into the filtered liquid to obtain lithium carbonate, which is further separated from other impurities. The lithium carbonate precipitate is dried to obtain a high-purity lithium carbonate product. The chemical reactions involved are as follows:
In addition, the causticization time, temperature and other conditions were studied, and it was concluded that the product prepared with the causticization time controlled at 100 minutes and the reaction temperature at 104°C has the highest purity. The causticization method can produce high-purity lithium carbonate from relatively cheap raw materials and minimize the loss of lithium by recycling the waste liquid from which high-purity lithium carbonate has been recovered. Jiangyi
Part of the available lithium is converted into lithium carbonate, and most of it is recovered as lithium hydroxide monohydrate. Most impurities are removed during the recovery process of lithium hydroxide monohydrate, thereby minimizing and controlling the accumulation of impurities. This method has strict requirements on the proportion of Li2CO3 and lime milk, the purity and temperature of lime milk, etc.
2) Recrystallization method
The solubility of lithium carbonate in water has the characteristic of decreasing with increasing temperature, while the solubility of impurity ions generally increases with increasing temperature. Taking advantage of this characteristic, industrial grade lithium carbonate and deionized water are heated and stirred.Lithium carbonate is insoluble but impurities are dissolved. Impurities are removed by filtration and high-purity lithium carbonate is obtained after drying. During the operation, high-temperature dissolution and uniform stirring can accelerate the dissolution of impurities. This method is easy to operate and has good impurity removal effect, but the solubility of Li2CO3 is small, wall sticking phenomenon is prone to occur during the stirring process, resulting in high losses and a long operating cycle.
3) Precipitation method
A: Homogeneous precipitation method
LiOH solution is prepared by reacting industrial-grade lithium carbonate with milk of lime. High-purity CO(NH2)2 is added to the solution to precipitate large Li2CO3 crystals at once. The chemical reactions involved are as follows:
The homogeneous precipitation method uses CO cyclohexylamine carbonate (NH2)2 as a homogeneous precipitant, which can avoid the local reaction of too fast crystallization and precipitation, and is not prone to secondary aggregation. The generated Li2CO3 particles are large and do not contain solution inside the particles. impurity ions in the system. This reaction is carried out in an ammonia system, which is easy to introduce new impurities, and the residual problem of Li2CO3 is serious, and the recovery rate is low.
B: LiOH precipitation method
High-purity Li2CO3 can be obtained by reacting LiOH produced by the reaction of industrial-grade lithium carbonate and calcium hydroxide with high-purity NH4HCO3. This method introduces less impurity ions, and the residual ammonia in the product can be removed by drying. Pass CO2 into the LiOH solution and precipitate to prepare a high-purity Li2CO3 product. The purity of the Li2CO3 product in this method mainly depends on the purity of LiOH, and almost no impurity ions are introduced during the operation. This method is also the most direct and widespread method for preparing high-purity lithium carbonate.
4) Electrolysis
The diaphragm method electrolysis of lithium sulfate or lithium bicarbonate usually converts industrial grade Li2CO3 into lithium sulfate and lithium bicarbonate using sulfuric acid or CO2 gas. After ion exchange treatment, most impurity cations such as calcium and magnesium in the solution are removed. The resulting high-purity solution is used as the anolyte, and the LiOH solution is used as the catholyte. The two are separated by an ion selective permeability membrane. The schematic diagram of electrolysis principle is shown in Figure 1. During the electrolysis process, high-purity LiOH is obtained on the cathode chamber side. After passing high-purity CO2 into the LiOH solution, Li2CO3 precipitates are obtained, and then the battery-grade Li2CO3 product can be obtained by removing impurities and drying. The involvedelectrolytic formula is as follows:
The electrolysis of lithium sulfate uses Li2SO4 solution as the anode solution. During the electrolysis process, SO2-4 will inevitably be mixed into the cathode side. If Li2CO3 is prepared from this LiOH aqueous solution, there will be SO2-4 pollution. During electrolysis, a high concentration of H2SO4 is generated on the anode side, which causes the electrolytic cell to require relatively expensive corrosion-resistant materials. Moreover, electrolysis consumes a lot of electricity and has high requirements on the membrane. The electrolysis of lithium bicarbonate method can not only obtain high-purity lithium carbonate, but also reduce the cost of the electrolytic cell because non-corrosive CO2 gas is generated on the anode side.
5) Hydrogenation method
A: Hydroprecipitation method
Industrial-grade Li2CO3 is mixed with deionized water to form an aqueous solution slurry, and high-purity CO2 gas is passed into it to generate a LiHCO3 aqueous solution. The filtered filtrate is passed through a cationic methyltetrahydrofuran exchange resin to remove impurity ions such as calcium and magnesium. The impurity-free LiHCO3 reacts with high-purity LiOH to obtain Li2CO3 precipitate, which is filtered and rinsed with hot deionized water. After drying, the high-purity Li2CO3 product is obtained. The process flow is shown in the figure, and the chemical reaction formula involved is as follows:
Hydroprecipitation method is used to prepare high-purity lithium carbonate. Even if no impurity removal process is used, the purity of the product is relatively high. However, the degree of the second step of the reaction is difficult to control, the process is complicated, and the price of high-purity LiOH is high, which increases the cost. .
B: Hydrolysis method
Hydrogenation reaction is one of the key steps of this method. Through research on the purification of industrial grade lithium carbonate, it was found that hydrogenation time and hydrogenation temperature have a great impact on the purity and yield of lithium carbonate, but have no great impact on the content of calcium and magnesium impurities. The time of 40 minutes and the temperature of 25°C have the best effect. At the same time, increasing the stirring rate can increase the solubility of lithium carbonate. The decomposition of LiHCO3 is another key element of the method. The heating temperature is generally set at 80 to 90°C. When the temperature exceeds 90°C, the evaporation reaction will become extremely violent and a large amount of CO2 gas will be released at the same time, which may easily cause “tank leakage” accidents. Improper control of the experimental process can easily cause wall sticking. Phenomenon.
