At the beginning of September, the lithium sulfide track successively sent out signals of "increasing volume".

Tianqi Lithium announced at its semi annual performance briefing that the pilot project for producing 50 tons of lithium sulfide annually has started construction in Meishan, Sichuan, claiming to be "low-risk and capable of rapid mass production"; In mid August, Enjie Corporation announced that its 100 ton high-purity lithium sulfide pilot line had been completed, and a 10 ton sulfide solid electrolyte production line had been built; Earlier in July, Shanghai Xiba won the bid for research related assets of rare earth lithium sulfide and planned to expand production through joint ventures.

Recently, Yiwei Lithium Energy, Guoxuan High tech, Funeng Technology, Xinwangda, and Rongjie Shares have collectively disclosed the latest developments in sulfide all solid state battery products, which has once again attracted industry attention to the sulfide solid state battery route.

As a key material for sulfide solid electrolytes, lithium sulfide is particularly prominent in the industry for its ability to compete for production capacity under high technological barriers.

Industry insiders point out that the demand for lithium sulfide is expected to reach the level of hundreds of tons by 2025; By 2026, there is a high probability that the industry will move towards the thousand ton level, which is faster than the previous industry estimate of "2GWh corresponding to 500 tons of demand in 2027". The demand for lithium sulfide is clearly climbing at a faster pace.

Lithium sulfide:

Dual throat of cost reduction and performance

As a key precursor of sulfide solid electrolytes, lithium sulfide accounts for 77% to 80% of the cost of electrolyte materials, with current market prices reaching 3-4 million yuan/ton. Its cost reduction process directly determines the commercialization speed of solid-state batteries.

High purity lithium sulfide is the basis for preparing high-performance sulfide solid electrolytes.

Impurities in lithium sulfide, such as lithium oxide, lithium carbonate, polysulfides, carbon, etc., can cause a decrease in the ionic conductivity of sulfide solid electrolytes. Impurities may introduce non-ionic conductive impurities or accumulate at grain boundaries, hindering the transport of lithium ions.

If lithium sulfide contains impurities (such as lithium oxide, lithium carbonate, polysulfides, carbon, etc.), non-conductive impurities will be generated during high-temperature synthesis, blocking ion transport channels and significantly reducing ion conductivity. However, residual carbon or metal impurities can form leakage current inside the battery, which can easily lead to electrolyte decomposition or local lithium deposition, causing micro short circuits in the battery and posing serious safety hazards.

In addition, lithium sulfide has strong hygroscopicity, and residual moisture can cause hydrolysis reactions, leading to deterioration of material purity. During storage and preparation, water may generate impurities such as lithium hydroxide. The high ionic conductivity of sulfide solid electrolytes is highly dependent on precise stoichiometry, which also affects the stoichiometry and phase structure of the electrolyte, thereby reducing the ionic conductivity.

Some lithium sulfide companies have also provided feedback that the current requirements for lithium sulfide in the solid-state electrolyte process mainly include: carbon content within 0.1%, moisture content less than 100mg/kg, metal impurities less than 100mg/kg, and particle size less than 7um.

In terms of purity, the mainstream products in the current market are concentrated at 99.5% to 99.9%, but Mitsui Metal in Japan has launched high-end products with a purity of 99.95%, while domestic enterprises are accelerating the breakthrough of 99.99% level technology.

Enjie Co., Ltd. has shared the purity of lithium sulfide, and the quality of lithium sulfide should be mainly measured by its application performance in electrolytes and batteries, rather than necessarily pursuing higher as better. As a future bulk raw material, it is not necessarily required to have very high purity. Enjie, which uses carbon thermal reduction method to prepare lithium sulfide, can achieve 99.9% purity of lithium sulfide, but is currently promoting 99.5% purity lithium sulfide and sending samples and self testing feedback to downstream customers. 99.5% purity lithium sulfide can also meet the needs of electrolyte preparation.

Technological breakthroughs rely on accumulation

Hydrogen sulfide neutralization method takes the lead in scaling up

In 2025, enterprises that are laying out sulfide all solid state batteries, although their industrialization pace is not the same, are all moving further towards expanding capacity and increasing production capacity. The industry's demand for lithium sulfide is higher than expected, and lithium sulfide is also experiencing capacity expansion.

It is worth noting that different enterprises choose differentiated process routes based on their technological backgrounds and industrial accumulation. At present, the hydrogen sulfide neutralization method has taken the lead in achieving large-scale breakthroughs.

From the current industrialization layout, the processes selected by mainstream enterprises can be roughly divided into four categories:

1. Hydrogen sulfide neutralization method (hydrogen sulfide lithium hydroxide)

This route is represented by Shanghai Xiba (acquiring rare earth related assets of Youyan). Its technology is consistent with the principle of the benchmark lithium sulfide production technology in Japan, which uses the hydrogen sulfide lithium hydroxide preparation process.

With its profound experience in purification and impurity control in rare earth separation, Youyan Rare Earth has successfully solved the industrialization problems of impurity introduction and side reaction suppression in this process, achieving high purity (≥ 99.99%) and low-cost preparation of lithium sulfide.

This advantage has enabled its products to be validated by leading domestic battery manufacturers and Japanese and Korean manufacturers, and to occupy a high market share in the global market. And Shanghai Xiba is utilizing its unique experience in handling hydrogen sulfide in its traditional main business to further strengthen the environmental and cost advantages of this route.

Market research indicates that Shanghai Saiba ships 2 tons per month and expands to the hundred ton level by the end of the year. The company also revealed that in the future, after large-scale modulus production, the selling price is expected to be reduced from the current 3-4 million yuan/ton to "several hundred thousand yuan/ton".

Japan's Idemitsu Kogyo has a deep cooperation with Toyota, providing core material support for its plan to launch all solid state battery electric vehicles in 2027-2028. And this project has already received subsidies from the Japanese government. Currently. Idemitsu Xingchan Lithium Sulfide has operated two small-scale validation facilities and started the basic design of a large-scale experimental facility in October 2024. The plan is to build a thousand ton lithium sulfide production facility by June 2027.

2. Liquid phase method

Companies such as Tianci Materials, Huasheng Lithium Battery, and Haichen Pharmaceutical have chosen liquid-phase synthesis routes largely due to their years of technological accumulation in the fields of electrolytes and fine chemicals. The liquid-phase method involves chemical reactions in a solvent system, which is closely related to the formulation development, synthesis, and purification process of lithium-ion battery electrolytes.

Tianci Materials and Huasheng Lithium Battery have transferred their rich experience in solvent application, purification, and quality control in the development of electrolyte additives to the synthesis process of lithium sulfide, which enables better control of lithium sulfide particle size and significant long-term cost optimization potential.

In addition, as a traditional pharmaceutical enterprise, Haichen Pharmaceutical not only lays out the electrolyte track, but also applies its high-end advantages that have been deeply cultivated in the pharmaceutical field for many years, including precise control of synthesis processes, rigorous impurity removal technology, and pharmaceutical grade precision reaction management experience, to the research and trial production of lithium sulfide.

The company is attempting to migrate pharmaceutical grade purity control standards to the production process of lithium sulfide, in order to overcome the common problem of organic solvent residue in liquid-phase methods and improve product purity and batch stability. At present, the route is still in the stage of sample verification.

However, the liquid-phase method is still limited by residual organic solvents and complex impurity removal processes, resulting in its products still lacking advantages in purity and impurity content indicators compared to leading rare earth separation methods. Whether this technological route can ultimately break through the bottleneck of impurities and achieve high-purity and low-cost mass production is expected to be determined by the end of 2025 or 2026.

3. Lithium sulfur direct solid-phase method

Lithium industry giants represented by Ganfeng Lithium and Tianqi Lithium have chosen the solid-phase synthesis route starting from metallic lithium.

Although this method can produce products with extremely high purity (≥ 99.9%), it is considered difficult to scale due to the high price of metallic lithium, intense heat release during the reaction process, and the risk of explosion.

However, both companies are actively tackling the issues of process cost reduction and scaling up. Especially as lithium industry giants, the two companies have resource integration advantages in lithium metal costs. Ganfeng Lithium has achieved pilot testing at the 100 ton level, and its products have been certified by customers and have begun to be supplied; Tianqi Lithium recently launched a 50 ton pilot line in Meishan, Sichuan, emphasizing "low-risk, rapid mass production" and opening up the mass production path.

4. Carbon thermal reduction method

Enjie Corporation, Rongbai Technology and other battery material companies are focusing on this method, which stems from their profound technical accumulation in the treatment of battery powders such as positive electrode materials. Carbon thermal reduction method, as a mature powder material preparation technology, uses reducing agents such as glucose to convert lithium sulfate into lithium sulfide, which is also a cost-effective technology route. However, its industrialization faces core challenges such as high carbon residue and susceptibility to battery micro short circuits.

The cooperation between Hunan Enjie, a subsidiary of Enjie Group, and the technical team of Central South University is a key practice in the industrialization of this route. The technological advantages of Central South University in the field of powder material preparation provide key support for overcoming the challenges of agglomeration and surface structure damage in the micro nano process of sulfide powders. By jointly optimizing the grinding process and sintering system, Hunan Enjie has successfully built a 100 ton pilot line with a product purity of up to 99.9%.

But the company has shown a pragmatic market judgment on product positioning, and currently focuses on promoting products with 99.5% purity. Its viewpoint is that "as a future bulk raw material, it does not necessarily have to pursue extremely high purity", but rather values the practical application performance and comprehensive cost-effectiveness of the battery end. If this route can solve the problem of carbon residue while maintaining cost advantages, it also has the potential for large-scale production.

Equipment and process collaboration

Another challenge of scaling up

In addition to process selection, the development of specialized equipment has also become a key constraint on the mass production of lithium sulfide. Due to the strong corrosiveness, easy wall adhesion, and extreme sensitivity to water and oxygen of lithium sulfide, its production equipment needs to meet multiple requirements such as sealing, corrosion resistance, no wall hanging, and suitability for amplification.

At present, the industry commonly adopts three equipment solutions: full process dry room environment, modular equipment inside glove boxes, and fully sealed large-scale reaction devices. The third method, although the most difficult, can greatly enhance engineering capabilities and reduce costs for large-scale production. But the industry points out that equipment materials are currently the biggest problem, and even aviation grade alloys are difficult to meet all conditions.

At present, relying on the deep chemical background and process accumulation of the layout enterprise, the hydrogen sulfide lithium hydroxide method has taken the lead by half a position. But if other routes make breakthroughs in quality and cost, they may still reshape the competitive landscape. This will also depend on the improvement of engineering capabilities by enterprises based on their own advantages, achieving the unity of high quality, low cost, and large-scale.