SoftBank Corp. (“SoftBank”) and Enpower Japan Corp. (“Enpower Japan”), a subsidiary of US-based Enpower Greentech Inc. (“Enpower Greentech”), have promoted the development of lightweight, large-capacity and high specific energy (Wh/kg) next-generation batteries with applications for IoT devices and cellular base stations. Both companies recently succeeded in the development of technologies that reduce interface resistance between the cathode and solid electrolyte layer and reduce the weight ratio of solid electrolyte to achieve high energy density. Both companies are also pleased to announce the successful verification of a high specific energy (300 Wh/kg) all-solid-state battery cell (ASSB) with lithium metal anode.
Widely used lithium-ion batteries use organic liquid electrolyte as ion conductor. In contrast, ASSB use solid electrolyte. Therefore, ASSB features include high safety and low risk of ignition or leakage of liquid electrolyte, which was an issue with lithium-ion batteries. Solid electrolyte is expected to improve lifetime and temperature characteristics and expand the operation voltage range since the material is more stable than the liquid electrolyte.
On the other hand, ASSB has issues with interface formation and weight increment. In the case of solid electrolyte, unlike liquid electrolyte, it is essential to form a suitable interface between the electrode material and the solid electrolyte because of the low adhesion between the cathode active material and the electrolyte, as well as increase interface resistance related ion conductivity, which cause reduction of battery capacity, output power characteristics, and lifetime characteristics. Solid electrolyte with a higher specific gravity than liquid electrolyte tends to increase the weight of batteries and ASSB have lower specific energy than current lithium-ion batteries.
To solve these issues, both companies successfully developed technology that reduces interface resistance between cathode active material and solid electrolyte, reduces the weight ratio of solid electrolyte in cathode mixture, thins solid electrolyte layer, and increases the specific energy to 300 Wh/kg. This energy value is the same as the maximum value of lithium-ion battery cell.
SoftBank and Enpower Japan will continue to conduct various research activities into high-capacity next-generation batteries to solve social issues through their business activities by making use of their technologies.