In-depth analysis of sulfide solid state battery industry

On December 12, Factorial Inc. announced that its first sulfide all-solid-state battery has been extended to 40Ah, which can be used for a sample of the power battery specification, using a new dry electrode process to prepare the positive electrode.

At present, the industrialization process of all-solid-state batteries is accelerating, and sulfide solid-state batteries, as one of them, are regarded as key research and development routes because of their high ionic conductivity and low Young's modulus characteristics. CATL, Tinci Materials, Beijing Weilan, Jiangsu Qingtao, QuantumScape, Solid Power, Samsung SDI, LG New Energy, Toyota and other domestic and foreign enterprises have accelerated the layout. According to relevant data, it is expected that by 2030, the demand for sulfide solid electrolytes is expected to reach 20,000 tons, and the market space is 10.6 billion yuan. 

The energy density of liquid batteries faces a bottleneck

The energy density of liquid batteries is difficult to improve, and there is still a gap from the goal. Conventional lithium-ion batteries are composed of four major materials, such as positive electrode, negative electrode, diaphragm, electrolyte and auxiliary materials. At present, the energy density of lithium-ion batteries that can be mass-produced and commercialized can reach about 300Wh/kg, but it is difficult to further improve.

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This is because the energy density of lithium-ion batteries mainly depends on the increase of the material gram capacity, and the use of high specific capacity of positive and negative electrode materials will cause a decline in safety performance, therefore, the need to balance the energy density and safety of the battery. With the continuous development of the new energy automobile industry, there is still a large demand for lithium-ion batteries with high energy density.

According to the power battery development roadmap formulated by the China Society of Automotive Engineering, the specific energy of high-end power battery cells should reach more than 350Wh/kg in 2025, more than 400Wh/kg in 2030, and more than 500Wh/kg in 2035. Generally speaking, the upper limit of the energy density of the traditional liquid lithium-ion battery is recognized as 350Wh/kg, and its actual specific energy is difficult to reach 400Wh/kg, and there is still a large gap from the planning goal.

Solid-state batteries offer advantages in terms of energy density and safety

Solid-state batteries can increase battery energy density. Solid-state battery is a battery technology that replaces the electrolyte in a traditional liquid battery with a solid electrolyte. Compared with liquid batteries, the positive and negative electrode materials of solid-state batteries are similar, the difference is the use of solid electrolytes.

There are several ways to improve battery energy density: Solid state batteries can use higher battery capacity lithium metal as a negative electrode. Because the solid electrolyte has strong mechanical properties, it can inhibit the growth of lithium dendrites, realize the application of lithium metal, and improve the energy density of the smart battery. Solid state batteries can fully utilize the positive electrode material capacity. The solid electrolyte can withstand higher voltages than the electrolyte, achieving further development of the positive electrode material capacity, thereby increasing the battery energy density.

Sulfide electrolyte is expected to be industrialized

The sulfide electrolyte has excellent properties. Compared with oxide and polymer electrolytes, sulfide electrolyte has a higher ion conductivity, which can reach 10-3S/cm at room temperature, and is an ideal solid-state battery electrolyte material.

The electrolytes of silver-germanium sulfide have outstanding advantages and are expected to be industrialized in the future. Li6PS5X (X=Cl, Br, I) sulfide electrolyte is a kind of crystalline structure, which has the advantages of low cost, high room temperature conductivity (10-2S/cm), simple synthesis, and better electrochemical stability than other sulfides. However, the Li6PS5Cl electrolyte also has the disadvantages of poor air stability, poor compatibility with the positive electrode material, and instability with lithium metal.

At present, the main measures to improve its performance are element doping, positive electrode coating, lithium alloy negative electrode and composite solid electrolyte. In general, silver germanite electrolytes, especially those containing halogens, are one of the most promising inorganic solid electrolytes due to their high room temperature lithium ion conductivity, relatively low cost and high stability and electrode compatibility in sulfide electrolytes, and are expected to be the first to achieve industrialization in the future.

Process optimization and cost reduction are the key factors for the high environmental requirements of sulfide electrolyte preparation. Although sulfide solid electrolyte has the advantages of high ion conductivity, it also faces application problems. Sulfide solid electrolyte is extremely unstable in the air, and is easy to react with water and oxygen to produce highly toxic hydrogen sulfide gas.

Therefore, the preparation and assembly of sulfide solid electrolyte must be carried out in an anhydrous and oxygen-free environment, and the preparation cost is greatly increased. In order to improve the air stability of sulfide electrolyte and achieve the purpose of reducing the cost, there are several methods: using additives to absorb hydrogen sulfide gas; Surface coating or passivation; Construction of sulfide-polymer composite electrolyte. Among them, the strategy of building composite electrolytes is expected to integrate the advantages of sulfide and polymer electrolytes, which may meet all the prerequisites for electrolyte materials and accelerate the commercialization of all-solid-state batteries

Sulfide offers the greatest potential for the future

Electrolyte: oxides + halides progress rapidly, sulfide has the greatest potential for development

Solid electrolyte is the key to achieve high safety, energy density, cycle life performance. According to the type of electrolyte, it can be divided into four routes: polymer, oxide, sulfide and halide. Sulphides have the greatest potential for development, and the popularity of halides is also increasing.

Polymers are not safe enough, the upper limit is low, and have been basically eliminated, mainly mixed with oxides/sulfides/halides. Oxide has the highest safety, general conductivity, the most difficult processing, low cost, but the texture is brittle, and it is mainly used for semi-solid. Sulfide has the greatest potential, high conductivity, easy processing, but the most difficult, high cost, poor stability, and long-term potential. Halides are between oxides and sulfides, the difficulty is that the reduction resistance is poor, the cost is low, and the progress is relatively fast in the past year.

Current status of solid-state battery development in China

China leads in the number of patents filed for solid electrolytes. According to the incoPat Patent database, as of June 25, 2024, there were 8,494 patent applications related to solid-state batteries. Given the 3-18 months between patent filing and publication, the actual number of patent filings in 2023 and 2024 is greater than the number of disclosures.

Among the top 10 patent applicants, Japan and South Korea are dominated by Toyota with 1,297 patents, followed by LG with 703 patents. In terms of the total number of national patent applications, China took the lead in the number of patent applications in solid electrolyte related fields, reaching 2,987 cases, accounting for 35.17% of the total number of patents, followed by the United States (1,507 cases), Japan (1,455 cases), and South Korea (790 cases). At present, China has shown a strong momentum of catching up in the field of solid-state batteries.

Many companies around the world have chosen sulfides as the key material for future all-solid-state batteries. Chinese enterprises aim to achieve the commercial production of all-solid-state batteries in 2027-2030, of which CATL has built a 10Ah all-solid-state battery verification platform, and is expected to achieve small-batch production of solid-state batteries in 2027; Tinci Materials sulfide solid electrolyte is in the pilot stage, and it is expected that the sulfide solid electrolyte kiloton production line will be completed in 2027.

Global enterprises choose sulfides as key materials for future all-solid-state batteries

Japan is mainly focused on sulfide research and development, plans to achieve all-solid-state batteries by 2030, and supports Toyota in 2027 to launch a range of 960 kilometers, charging only 10 minutes of pure electric plan. South Korea LG, Samsung SDI and other battery companies have chosen to lay out sulfide solid-state batteries, Samsung Group plans to fully put into production in 2027 all solid-state, to achieve mass production and loading applications. The United States Solid Power, QuantumScape and other companies are laying out sulfide solid-state batteries.

Conclusion

As an important development direction in the field of solid-state batteries, sulfide solid state batteries have become the focus of research worldwide due to their excellent ion conductivity, high room temperature conductivity and potential high energy density. Despite the challenges of high preparation environment requirements, poor stability and high cost, with technological progress and process optimization, sulfide solid-state batteries are expected to achieve industrialization in the next few years, promoting innovation in electric vehicles, energy storage battery and other fields.

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