SoftBank Corp. and Enpower Japan Corp.
Successfully Develop All-Solid-State Batteries
with High Energy Density

350 Wh/kg battery cell and charge-discharge curve

SoftBank and Enpower Japan previously succeeded in the development and verification of all-solid-state batteries with specific energy of 300 Wh/kg by reducing the interface resistance between the cathode and solid electrolyte layer, reducing the weight ratio of the solid electrolyte in the cathode mixture, and reducing the thickness of the solid electrolyte layer. This time, to further increase specific energy, development has been focused on improvement of the homogeneity of the materials to reduce interface resistance.

Solid electrolyte, unlike liquid electrolyte, shows low adhesion on the interface of the cathode active material and solid electrolyte. This increases the interface resistance related to ion conductivity, which cause reduction of battery capacity, decrease in output characteristics and cycle life characteristics, and leads to difficulties in formation of the interface between the cathode active material and solid electrolyte, and solid electrolytes themselves.

To solve these issues, SoftBank and Enpower Japan succeeded in the homogenization of the solid electrolyte by controlling the particle size of the solid electrolyte by means of adjustment of the particle size in the raw materials and improvement of the grinding process, as well as improving the dispersion of particles in the film formation process. This approach improved the dispersion of the conductive material, increasing the utilization rate of the cathode active material, and improving the smoothness of the electrode layer to form a good interface between the electrodes, which realized a high capacity over a large area and suppressed short circuits. As a result, the companies succeeded in increasing the specific energy of the all-solid-state battery cell with lithium metal anode to 350 Wh/kg.

Regarding circle life characteristics, SoftBank and Enpower Japan have achieved 200 cycles at the electrode level, but the short circuit occurring during cycles remains as an issue in large-area pouch cells. Both companies will continue to develop further homogenization technology for materials and electrodes to make it possible to prevent a short circuit for the large-area electrodes or the stacked structure.

SoftBank and Enpower Japan will continue research and development to increase the capacity of next-generation batteries, aiming to achieve specific energy of 400 Wh/kg in 2024 fiscal year, and then, in 2026 fiscal year, increase the battery life to more than 1000 cycles. They will also develop core technologies to reduce pressure in compression mechanism. This will contribute to further improvement of the solid-state batteries performance and promote the batteries practical use, while also promoting the battery use in the aviation field, including HAPS and drones, as well as in IoT devices and automotive applications, thereby contributing to solve current social issues in a multi-faceted way using next-generation batteries.

All-Solid-State Battery Development by SoftBank