With the rapid development of the new energy industry, solid-state electrolytes, which have significant advantages in energy density and safety, have received widespread attention.

In recent years, Highrui Power has actively engaged in research in related fields, investing 5 million to build a solid-state battery material R&D laboratory, forming a complete platform for the development, preparation, and innovation of solid-state battery materials. In the future, it will continue to invest over 10 million to collaborate with upstream and downstream suppliers to construct a ton-level solid-state battery material industrial chain. Additionally, a project cooperation has been established with Central South University to achieve technology sharing, preparing to scale up laboratory-level results.

Types of oxide solid-state electrolytes

Solid-state electrolytes can be classified into polymer solid-state electrolytes and inorganic solid-state electrolytes based on the type of electrolyte. The representative system of polymer solid-state electrolytes is PEO (polyethylene oxide), while inorganic solid-state electrolytes mainly consist of oxides, sulfides, and halides. Among them, polymers have a lower performance ceiling, oxides are currently progressing rapidly, and sulfides have the greatest potential in the future.

Due to the high production cost of sulfide electrolyte powders, stringent environmental requirements, and high demands on electrode materials, as well as the fact that the liquid in batteries can damage the structure of sulfide materials, thus affecting battery performance, sulfides are difficult to apply effectively in semi-solid batteries. On the other hand, polymer electrolytes cannot meet the performance requirements of downstream manufacturers due to their material characteristics.

In the current semi-solid battery system, the combination of oxide electrolyte powders and the application of oxide and polymer electrolyte powders have become mainstream.

The ionic conductivity of oxide electrolytes generally ranges from 10-6 to 10-3 S/cm. Their dense morphology gives them higher mechanical strength, chemical/electrochemical stability, air stability, and a wider electrochemical window, and they are relatively cost-effective. They can be classified into crystalline and amorphous electrolytes based on their morphology.

1. Crystalline oxide electrolytes include perovskite-type (LLTO), anti-perovskite-type (LOC), garnet-type (LLZO/LLZTO), and fast ionic conductor-type (LATP/LZG), among others. Among them, perovskite-type (LLTO) has the highest crystal ionic conductivity among crystalline solid-state electrolytes and is relatively stable against lithium metal.

2. Amorphous solid-state electrolytes are mainly LiPON-type solid-state electrolytes, which have relatively low ionic conductivity but possess high chemical stability and a wide electrochemical window, making them suitable for thin-film batteries. Therefore, they have better application prospects in electronic devices with lower capacity requirements.

Different types of oxide electrolytes have variations in production costs and electrochemical performance due to their different materials, but they share a common disadvantage of high brittleness and high process requirements during preparation.

In addition, the interface contact between oxide solid-state electrolytes and electrode materials is poor, requiring methods such as interface modification to improve it. Currently, the material systems with high market recognition are LATP, LLZO, and LLTO. Among them, LATP has the lowest production cost, but Ti4+ is easily reduced by lithium, making it unstable against lithium metal; LLZO has the highest overall ionic conductivity and the best thermal stability, but contains rare metal elements, leading to high costs and high sintering temperatures, which can be optimized through modification (doping with elements like Al/Ta, substitution, surface coating, etc.); LLTO has the highest crystal conductivity but high grain boundary resistance, resulting in low overall conductivity; similarly, like LATP, it contains high-valent Ti ions, which are incompatible with lithium metal anodes.

Preparation process of oxide solid-state electrolytes

The preparation process of oxide solid-state electrolytes is mainly divided into solid-phase and liquid-phase methods.

Solid-phase method: Raw materials (lithium salts, lanthanum/zirconium/aluminum oxides, etc.) are crushed in proportion, repeatedly ball-milled, and sintered at high temperatures to obtain the product. The advantages are that raw materials are readily available, costs are low, and the process is simple. The disadvantages are high energy consumption, uneven grain size, and easy agglomeration, which affect product performance and require high grinding standards.

Liquid-phase method: Raw materials (lithium acetate, organic lanthanum/zirconium salts, etc.) are dissolved, mixed, reacted, dehydrated, and polymerized to form a sol/gel, and finally low-temperature calcined to prepare the product. The advantages are low energy consumption, uniform doping, controllable particle size, and the ability to nano-size. The disadvantages are high raw material costs and environmental issues, making it unfavorable for large-scale production.

From the product perspective, the particle size of oxide electrolyte powder products should reach the nanoscale to better leverage the material advantages; the uniformity of particles and whether they agglomerate also affect the final product's ionic conductivity and other properties (it is known that existing market products can achieve a maximum of 10-2 S/cm at room temperature); the surface stability of the product can enhance material compatibility and facilitate product storage and sales.

From the production perspective, large-scale production is a necessary path to reduce production costs, and currently, there are very few production lines in the industry chain with a capacity exceeding ton-level.

In summary, how to achieve low-cost, pollution-free large-scale continuous production of uniformly sized nanoscale solid oxide electrolyte powders is a pressing issue that the industry urgently needs to address.

Currently, the main application scenarios for oxide solid-state electrolytes are:

1. Oxides combined with polymers as composite solid-state electrolytes;

2. Oxide membrane coating layers;

3. As coating layers for active materials of positive and negative electrodes.

Before solid-state batteries are industrialized on a large scale, semi-solid batteries can effectively combine the advantages of solid and liquid electrolytes. Oxide electrolytes can relatively effectively address core issues such as conductivity (rate performance and low-temperature performance) and interface (cycle life) in semi-solid batteries, thus having a more optimistic market demand expectation.

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