The "blood" of electric vehicles - an overview of electrolytes

first. Introduction

Electrolyte, known as the "blood" of electric vehicles, is an important part of the production of lithium-ion batteries, and has a direct impact on performance indicators such as energy density, cycle stability, and safety of lithium-ion batteries. Its main function is to provide a transmission environment for lithium ions between the positive and negative electrodes of the battery, and provide an important guarantee for lithium-ion batteries to obtain high voltage, long cycle life, and high energy density. Compared with other components such as positive electrode materials and negative electrode materials, electrolyte accounts for a relatively low proportion in the field of battery materials. In general, the electrolyte accounts for about 10% of the battery material cost.

From the performance point of view, the electrolyte needs to have high ionic conductivity, a wide electrochemical window, strong thermal stability and chemical stability and other excellent physical and chemical properties to ensure the efficient transmission of lithium ions between positive and negative electrodes and the safety and stability of the battery charge and discharge cycle. The electrolyte is mainly made of solute lithium salt, organic solvent and additives in a certain ratio. Among them, solute lithium salt is the most expensive part in the production of electrolyte, accounting for more than 50% of the total cost of electrolyte. The amount of organic solvent added is the largest, accounting for about 30% of the cost of electrolyte. Additives account for about 10% of the cost of the electrolyte.

Second, electrolyte classification and composition

The ideal electrolyte needs to have high conductivity, high thermal stability, high chemical stability, high electrical compatibility, low cost and other characteristics. Electrolyte is the function of ion transmission and conduction current in lithium/sodium ion batteries, which is the basic guarantee for the smooth charging and discharging of batteries. First of all, to play a good role in transporting ions, the electrolyte needs to have a high conductivity; In addition, the electrolyte also needs to have high thermal stability and chemical stability, will not easily occur thermal decomposition, can maintain a relatively stable temperature in a wide voltage range, and does not occur chemical reactions in the long cycle; Third, the electrolyte needs to have a high compatibility with the motor, can form a stable SEI film on the negative electrode, and finally, the high-volume use of the electrolyte needs to have green, low-cost and other characteristics.

The electrolyte plays a very important role in the energy density, wide temperature range application, cycle life and safety performance of lithium batteries. Lithium-ion battery electrolytes are mainly divided into liquid electrolytes, solid-liquid composite electrolytes and solid electrolytes. The liquid electrolyte can be divided into organic liquid electrolyte, water electrolyte and ionic liquid electrolyte. Solid electrolyte can be divided into inorganic solid electrolyte and solid polymer electrolyte. The liquid electrolyte is further divided into ester and ether based electrolyte, whose solvation effect and electric field drive are considered to be the main factors affecting Li+ migration, while the chain segment movement and vacancy migration in the polymer are considered to be the factors affecting Li+ migration in the solid electrolyte and the gel electrolyte.

(1) electrolyte solute

Solute is the supplier of lithium ions, which largely determines the physical and chemical properties of the electrolyte, and is the most important component of the electrolyte. At present, the solutes on the market mainly use lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and the new lithium salt lithium fluoride sulfonimide (LiFSI).

Lithium salt, that is, the solute in the electrolyte, is the most core component of the electrolyte and the highest cost ratio. Although there are many types of lithium salts, the ones suitable for lithium batteries are relatively limited, It mainly includes lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorosulfonimide (LiFSI), lithium dioxalate borate (LiBOB), lithium difluoroxalate borate (LiDFOB), lithium difluorophosphate (LiPO2F), lithium trifluoromethylsulfonimide (LiTFSI).

(2) electrolyte solvent

Organic solvent is the main component of liquid electrolyte, dissolve lithium salt and provide carrier for lithium ion, common organic solvents that can be used for lithium battery electrolyte are mainly divided into carbonate solvent and organic ether solvent. Lithium-ion battery solvents are mainly carbonate solvents, ether solvents, sulfur-containing organic solvents, including vinyl carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), tetrahydrofuran (THF), dimethyl ether (DME), dimethyl sulfoxide (DMSO), ethyl methyl sulfonate (EMS), etc. Most of the industry uses mixed solvents, commonly used electrolytic liquids are EC+DMC, EC+DMC+DEC, EC+DMC+EMC, EC+DMC+DEC and so on.

Organic solvent is the largest component in electrolyte products, accounting for more than 80% of the quality of electrolyte products. Organic solvents are mainly used to dissolve lithium salts and provide transport environment for lithium ions. It should have the characteristics of high dielectric constant, low melting point, high boiling point, good chemical stability and low viscosity. Common electrolyte organic solvents include carbonates, ethers and new fluorinated solvents. At present, more than 95% of the solvents commercially used in the market are mainly organic carbonate solvents. According to their molecular structure, carbonate solvents can be further divided into cyclic carbonate (ethylene carbonate, propylene carbonate, etc.) and chain carbonate (dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.). Generally speaking, cyclic carbonate solvent has higher dielectric constant and ionic conductivity, but larger viscosity. The viscosity of the chain carbonate solvent is small and the dielectric constant is low. At the same time, the physical and chemical properties of different electrolytes are different, and the compatibility with positive and negative electrode materials is also different. Therefore, the current commercial electrolyte generally uses several carbonate solvent mixing systems. Among them, the most used solvents are dimethyl carbonate, vinyl carbonate, methyl ethyl carbonate and diethyl carbonate, and their total demand accounts for more than 93% of the total demand for organic solvents in the electrolyte. The production of electrolyte is very sensitive to the content of moisture and impurities, so the purity of organic solvents is high, and the purity of battery-grade organic solvents is generally required to reach 99.99%.

(3) Additives

Electrolyte additive refers to the additive added to the electrolyte to improve the electrochemical performance of the electrolyte and improve the quality of the cathode deposition, which plays a crucial role in improving the specific performance of the electrolyte and is an important part of the electrolyte. The difference in electrolyte products is mainly reflected in the formulation of the customer's needs and the additives to improve the performance, especially with the battery factory's performance requirements for safety, charge and discharge ratio, cycle life, high voltage characteristics and so on. The additive has the characteristics of small dosage and remarkable effect, and can significantly improve the performance of lithium batteries without increasing the production cost and changing the production process. The additives of electrolyte can be divided into negative film forming additives, high temperature additives, low temperature additives, conductive additives, neutralizing additives, flame retardant additives, rate additives, anti-overcharge additives, water control and HF content additives according to their functions.

Third, the production of electrolyte related process flow

(1) The electrolyte production process is mainly composed of solvent preparation, solvent purification, preparation, post-treatment and filling. Among them, preparation means that according to the electrolyte formula and the sequence of material addition, the purified solvent, solute, additive and other raw materials are added to the preparation kettle to stir and mix thoroughly, which directly determines the performance indicators of the electrolyte and is the core of the electrolyte production process. The main process steps are as follows: 1. Rectification and dehydration: The organic raw materials used are respectively treated with rectification or dehydration to meet the standards for the use of lithium-ion battery electrolyte. In the rectification or dehydration stage, the items that need to be tested for organic solvents are: purity, moisture, and total alcohol content.

2. Feed mixing: According to the ratio of materials and the order of addition, the organic solvent is added to the reaction kettle in turn to stir and mix well, and then the required solute and electrolyte additives are added through the special feed port of lithium salt or the glove box. From the beginning to the end of adding materials, the stirring speed and temperature of the reactor should be controlled. Different material ratio mixing time is different, but must make the electrolyte mixed evenly, at this time the electrolyte test items are: moisture, conductivity, chroma, acidity.

3. Filling: The liquid electrolyte that has passed the test is poured into the qualified packaging barrel, filled with argon gas protection, and finally enters the warehouse for delivery. Due to the physical and chemical properties of the electrolyte itself, the stored electrolyte should be used in a short period of time to prevent the deterioration of the electrolyte caused by environmental factors.

(2) Main equipment for electrolyte production:

(1) Raw material storage tank for storing large amounts of solvents in the formula;

(2) Transfer tank, transfer storage of solvent;

(3) molecular sieve (water removal column) to remove the water in the solvent, to prevent the solvent water is too high;

(4) Filter to prevent the molecular sieve from being taken away in the water removal column and filter the finished product before filling;

(5) Measuring tank, measuring and weighing according to the formula;

(6) Mixing kettle, solvent, solute, additive and other raw material mixing. In addition, there are glove boxes, air compression equipment, chiller, hot water unit, drying room or hot bath, vacuum equipment, liquid nitrogen, electrolyte packaging bucket, pure water equipment, various platform scales, gas chromatograph, moisture meter, conductivity meter, density meter and so on.

Fourth, electrolyte market situation

Statistics show that in 2023, the global shipments of lithium-ion battery electrolyte reached 1.312 million tons, an increase of 25.8%, of which China's electrolyte shipments were 1.138 million tons, an increase of 27.7%, and the global share of China's electrolyte shipments continued to increase to 86.7%. From the perspective of market size, the global electrolyte market size in 2023 will be 52.21 billion yuan (69.05 billion yuan in 2022), a year-on-year decline of 36.7%, mainly due to the decline in electrolyte prices. In December 2023, the average sales price of electrolyte in China has fallen to less than 30,000 yuan/ton. It is predicted that the global electrolyte demand will reach 2.726 million tons in 2025, and the electrolyte demand will exceed 8 million tons in 2030. However, according to the current expansion plan of major enterprises, by 2025, the planned capacity of China's electrolyte enterprises has exceeded 8 million tons, and the competition in the future electrolyte industry will be more intense, and enterprises with cost and technological advantages can stand out in the competition. Global lithium-ion battery shipments will reach 1926.0GWh and 5004.3GWh in 2025 and 2030, respectively.

From the perspective of China's major electrolyte enterprises in 2023, Tianci Materials ranked first with shipments of nearly 400,000 tons, and its domestic market share was 34.7%, which declined compared with 2022. Statistics show that the fastest year-on-year growth in the first ten enterprises in 2023 is BYD, whose shipments increased by 86.3% year-on-year, and the domestic market share increased to 16.7%, replacing new Zhou Bang ranked second. In 2023, the total shipment of more than 50,000 tons of enterprises also include new Zhou Bang, Ruitai new materials and Kunlun new materials three enterprises, of which Kunlun new materials with nearly 60,000 tons of shipments narrowed the gap with the first echelon enterprises and opened the distance with Farnwright, Zhuhai Sawei and other second echelon enterprises.

1. Guangzhou Tianci High-tech Materials Co., Ltd. was established in June 2000, the main business is lithium-ion battery materials, daily chemical materials and specialty chemicals two business segments. Since its establishment, it has continued to develop the two business segments of lithium-ion battery materials, daily chemical materials and specialty chemicals. Tianci Materials has 33 wholly-owned subsidiaries and 17 holding subsidiaries. As a supplier of world-class brands, Tianci Materials is an international first-class fine chemical enterprise and electrolyte leading enterprise with greater influence and leading demonstration role in the industry.

Tianci Materials' domestic electrolyte production bases include Longshan base, Sichuan base, Fenghuang Wu base, Liyang base, Ningde + Fuding base, Jiangmen base and so on. At present, Tiansi Materials has no electrolyte production base in North China.

In 2022, Tianci Materials achieved operating income of 22.317 billion yuan, an increase of 101.22% (net profit attributable to shareholders of listed companies was 5.714 billion yuan, an increase of 158.77%; Among them, the net profit attributable to listed companies after deducting non-recurring profit and loss was 5.539 billion yuan, an increase of 155.38% year on year. Among them, the operating income of lithium-ion battery materials business was 20.822 billion yuan (accounting for 93.30% of revenue), and the sales volume of electrolyte increased by 122% year on year. Daily chemical materials and specialty chemicals operating income of 1.135 billion yuan, other operating income of 360 million yuan.

2. Shenzhen Xinzhoubang Technology Co., LTD., founded in 1996 and listed on Shenzhen Stock Exchange GEM in 2010, is a global leader in electronic chemicals and functional materials. The company focuses on the research and development, production and sales of battery chemicals, capacitor chemicals, organic fluorine chemicals and semiconductor chemicals, and is committed to providing customers with first-class "one-stop" product solutions. The company is headquartered in Shenzhen, now Guangdong, Jiangsu, Fujian, Hunan, Hubei, Poland, the United States and other production bases, and Japan, South Korea and other foreign branches, the total number of employees more than 3000 people.

Since its establishment, the company has always attached great importance to research and development and technological innovation, and the annual research and development investment exceeds 7% of the turnover. After more than 20 years of development, has built a set of lithium battery chemicals, capacitor chemicals, organic fluorine chemicals, semiconductor chemicals and LED packaging materials research, development, technical services, testing and verification and information management in one of the new Zhou Bang Research Institute. It has established industry-university-research cooperation with Peking University, South China University of Technology, Southern University of Science and Technology, Shanghai Jiao Tong University, Hong Kong Polytechnic University and other universities and research institutions. It has a number of research and development platforms such as the National CNAS accredited Testing Experiment Center, Guangdong Province Engineering Technology Research and Development Center, Southern University of Science and Technology New Zhou Bang energy materials Joint Laboratory. For many years, the company's electrolyte shipments have always ranked among the top three in the industry. In 2021, the market accounted for 17.6%, and in 2022, the shipments exceeded 100,000 tons, accounting for 12.3% of the market share. In 2023, the new Zhoubang electrolyte shipment market accounted for 11.9%, ranking third in electrolyte shipments.