All-solid-state lithium batteries can overcome the serious defects in the safety of current commercial lithium-ion batteries, and further improve the energy density, which is a disruptive technology for new energy vehicles and energy storage industry. However, because the core material of all-solid-state lithium batteries - solid electrolyte - is difficult to balance performance and cost, the industrialization of this technology is still facing huge obstacles. On June 27, Professor Ma Cheng of the University of Science and Technology of China reported a new solid electrolyte, which has similar comprehensive properties to the current most advanced sulfide and chloride solid electrolytes, but the cost is less than 4% of the latter, which is suitable for industrial applications. The result is described as "A cost-effective, ionically conductive and compressible oxychloride solid-state electrolyte for stable all-solid-state lithium-based  "batteries" was published in the internationally renowned academic journal Nature Communications.

In order to meet the needs of practical applications, the solid electrolyte of all-solid-state lithium batteries needs to have at least three conditions at the same time: high ionic conductivity (more than 1 millisiemens per centimeter at room temperature), good deformability (more than 90% dense at 250-350 mpa), and low enough cost (less than $50 per kilogram). However, the oxide, sulfide and chloride solid electrolytes that have been widely studied at present cannot meet these conditions at the same time. As brittle ceramics, oxides are generally not deformable. Sulfides and most chlorides are costly, in the order of at least $200 per kilogram. The only exception among these materials is lithium zirconium chloride, but its ionic conductivity is well below 1 millisiemens per centimeter.

In this study, Professor Ma no longer focused on any of the above-mentioned oxides, sulfides and chlorides, but turned to oxychlorides and designed and synthesized a new solid electrolyte - lithium zirconium oxychloride. This material has a strong cost advantage. If it is synthesized with hydrated lithium hydroxide, lithium chloride, zirconium chloride, its raw material cost is only 11.6 US dollars per kilogram, which well meets the above requirements of 50 US dollars per kilogram. If it is synthesized with hydrated zirconium chloride, lithium chloride, and zirconium chloride, the cost of lithium zirconium chloride can be further reduced to about $7 per kilogram, which is far lower than the current most cost-effective solid electrolyte lithium zirconium chloride ($10.78 per kilogram), and less than 4% of sulfide and rare earth and indium chloride solid electrolytes. While having a strong cost advantage, the comprehensive performance of lithium zirconium oxychloride is comparable to 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. At the same time, its good deformability makes the material 94.2% dense at 300 mpa pressure, which is also more than the level required for applications (more than 90% dense at 250-350 mpa). The all-solid-state battery, composed of lithium zirconium oxychloride and a high-nickel ternary positive electrode, demonstrated extremely excellent performance: under the conditions of 12 minutes of fast charging, the battery still succeeded in stable cycling at room temperature for more than 2000 cycles.

The discovery of lithium zirconium oxychloride has made a breakthrough in both performance and cost of solid electrolyte, which is of great significance to the industrialization of all-solid lithium batteries. The reviewers described the discovery as "innovative and original" and said the lithium zirconium oxychloride material was "promising" and "beneficial for the commercialization of solid-state battery technology."

Related paper information：https://www.nature.com/articles/s41467-023-39522-1

(School of Chemistry and Materials Science, Department of Scientific Research)
Source: China University of Science and Technology News