SoftBank Corp. announced last week the development of lightweight, large-capacity and high specific energy next-generation batteries with applications for IoT devices and cellular base stations. The former Sprint owner said the batteries were made in cooperation with Enpower Japan Corp., a subsidiary of U.S.-based Enpower Greentech Inc.
The key technology used, according to SoftBank, was to 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 also announced 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 uses 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. 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, according to SoftBank’s engineers.