| Development of manufacturing technology for bipolar all-solid-state batteries
All-solid-state battery, a battery in which the internal electrolyte is solid
No risk of explosion or fire, and battery volume is one-third.

The Korea Institute of Industrial Technology (KITECH) announced on the 17th that it has developed manufacturing technology for a bipolar all-solid-state battery that can reduce the volume of the battery pack while eliminating the risk of explosion and fire.

According to Japan's Fuji Economic Research Institute, the global solid-state battery market is expected to expand to approximately 28 trillion won by 2035.

An all-solid battery refers to a next-generation rechargeable battery in which the electrolyte between the positive and negative electrodes is changed from liquid to solid.

Currently commercialized secondary batteries are lithium-ion batteries that use flammable liquid electrolytes, and there is a risk of them expanding and exploding if they are overheated or overcharged.

The all-solid-state battery developed by the research team of Dr. Kim Ho-seong, Head of the Jeju Regional Headquarters of the Korea Institute of Science and Technology (KIST), is safe and free from the risk of explosion and fire because it uses oxide-based solid electrolyte materials.

The developed all-solid-state battery is designed and manufactured with a bipolar structure in which multiple unit cells are connected in series within a single cell stack, making it advantageous for achieving high voltage.

This allows the electric vehicle battery pack to be simplified, reducing the volume to approximately It is expected that the driving range can be improved by more than double while reducing it by one-third.

All-solid-state batteries are classified into oxide, sulfide, and polymer types depending on the type of solid electrolyte. The research team focused on manufacturing technology for high-strength composite solid electrolyte sheets using oxide-based materials, specifically Garnet LLZO (lithium-lanthanum-zirconium-oxygen), which is considered the most effective.

LLZO materials have excellent potential window (the voltage range in solid electrolyte materials where electrochemical oxidation or reduction reactions do not occur) and safety, but the manufacturing process cost is high and ion conductivity (the rate at which lithium ions diffuse within a solid) There have been difficulties in commercialization so far because the capacity and lifespan are relatively low (when low, capacity and lifespan also decrease).

Accordingly, the research team succeeded in minimizing the production cost of LLZO powder and nano-sizing the powder particles by introducing a low-cost continuous production process using a Taylor reactor (a chemical reactor utilizing the Taylor fluid flow principle).

The nano-grade LLZO solid electrolyte powder significantly reduced costs by shortening the sintering time by more than five times through doping with heterogeneous elements (gallium and aluminum), and improved the ion conductivity by more than three times to 1.75 x 10⁻³ S/cm.

The developed LLZO powder was combined with a small amount of high-strength ion-conductive binder to produce a composite solid electrolyte sheet with a thickness of about 50 to 60 µm, which is a key technology for improving the volumetric energy density of all-solid-state batteries to 445 Wh/L.

Furthermore, the research team increased the possibility of commercialization by producing a bipolar cell stack (37V, 8Wh) composed of 10 all-solid-state battery unit cells for the first time in Korea.

The manufactured cell stack is in the form of a large-area (11 cm x 12 cm) pouch outer material, and its safety has been verified as there was no ignition or explosion even when it was cut with scissors in the air while overcharged.

The unit cells used in the cell stack retained approximately 84% of the battery's initial capacity as a result of 400 charge-discharge cycles.Maintaining [it], the lifespan characteristics have been improved by more than 5 times compared to conventional all-solid-state batteries.

Dr. Kim Ho-sung stated, “With battery safety becoming critical due to the recent successive explosions and fires in renewable energy ESS, we have succeeded in securing next-generation solid-state battery manufacturing technology capable of replacing existing batteries using domestic technology.” He added, “The LLZO material manufacturing technology has already been transferred to a domestic company, and starting this year, we plan to focus on early commercialization by commencing cell stack commercialization.”