All-solid-state lithium batteries can overcome the serious safety defects of current commercial lithium-ion batteries, and at the same time further increase energy density. It is a disruptive technology for new energy vehicles and energy storage industries. However, because the core material of all-solid-state lithium batteries, the solid-state electrolyte, is difficult to balance performance and cost, industrialization still faces huge obstacles.
In order to meet the needs of practical applications, the solid-state electrolyte of all-solid-state lithium batteries needs to meet at least three conditions: high ionic conductivity (over 1 millisiemens per centimeter at room temperature), good deformability (realized at 250 to 350 MPa more than 90% dense), and sufficiently low cost (less than 50 US dollars per kilogram). The oxide, sulfide, and chloride solid-state electrolytes that have been widely studied at present cannot meet these conditions at the same time.
In this research, Ma Cheng no longer focused on any of the above-mentioned oxides, sulfides, and chlorides, but turned to oxychlorides, and designed and synthesized a new type of solid electrolyte-lithium zirconium oxychloride. This material has a strong cost advantage. If it is synthesized with hydrated lithium hydroxide, lithium chloride, and zirconium chloride, its raw material cost is only 11.6 US dollars per kilogram. However, if hydrated zirconium oxychloride, lithium chloride, and zirconium chloride are used for synthesis, the cost of lithium zirconium oxychloride can be further reduced to about 7 US dollars per kilogram, which is far lower than the current most cost-effective solid-state electrolyte zirconium chloride. Lithium ($10.78 per kg), and less than 4% of sulfide and rare earth-based, indium-based chloride solid electrolytes.
While having a strong cost advantage, the comprehensive performance of lithium zirconium oxychloride is comparable to that of the most advanced sulfide and chloride solid electrolytes. Its room temperature ionic conductivity is as high as 2.42 millisiemens per centimeter, exceeding the 1 millisiemens per centimeter required for applications, and ranks among the top among all kinds of solid electrolytes reported so far. At the same time, its good deformability enables the material to reach 94.2% densification under a pressure of 300 MPa, which can well meet the application requirements, and is also better than sulfide and chloride solid electrolytes (equal to less than 90% dense under pressure).
Experiments have proved that the all-solid-state lithium battery composed of lithium zirconium oxychloride and high-nickel ternary positive electrode has demonstrated excellent performance: under the condition of fast charging for 12 minutes, the battery can still successfully cycle at room temperature for more than 2000 cycles .
According to the researchers, lithium zirconium oxychloride can achieve performance similar to that of the most advanced sulfide and chloride solid-state electrolytes at the current lowest cost, which is of great significance to the industrialization of all-solid-state lithium batteries. The reviewers considered the discovery "very novel and original" and considered the lithium zirconium oxychloride material "promising" and "beneficial to the commercialization of solid-state battery technology."