For a more convenient and safer power storage device that answer market demand
The world is moving towards realizing by 2050 a carbon-neutral society, which is a society in which greenhouse gas emissions are substantially cut to zero.
Considering the trends of the times, SEL has started research and development of rechargeable batteries from 2009.
With safety as our top priority, we strive to develop rechargeable batteries with high energy density, long life, and robustness against demanding environments.
We also work on new technologies such as flexible batteries, nonflammable batteries, and battery protection circuits that will enable next-generation power storage devices.
SEL owns many patents in Japan (e.g., JP Patent Nos. 6736241, 6736243) and abroad regarding rechargeable batteries, and we work to create interest in our technology for other companies to utilize.
Demand for lithium-ion batteries are higher than ever for us to reduce carbon emissions. SEL will work to improve the technology.
Development of materials and devices
Aiming for the ultimate energy storage device, SEL has been thoroughly researched and developed materials and devices that make up batteries to improve battery properties.
Graphene Net Electrode －High-performance electrode－Graphene net electrodes mean electrodes using graphene net as a conductive additive. Technology with graphene net[1, 2] enables rechargeable batteries to have electrodes with a high-performance conductive network and output characteristics with high energy density.
Graphene oxide (GO) is an oxidized material in a single-layer form separated from graphite, which has many functional groups and thus is easily dispersed into solvent and suitably used for coating. Being reduced after coating, GO can be used as graphene net.
▲Graphene net electrode’s surface (a) and cross section (b) of SEM image
 The 60th Battery Discussion Meeting Manuscript book 1G04 (2019)
 M.Yamakaji et al., “High Performance Lithium Ion Battery Using Graphene Net Electrode,” ECS Trans., 50(26), 329 (2013).
LiCoO2 －Positive electrode material standing high voltage－SEL is also working on the development of positive electrode materials that are hardly degraded even with high charging voltage, 4.6 V(vs Li/Li+) through the improvement of lithium cobalt oxide (LiCoO2) widely used as a positive electrode material of a lithium-ion battery.
LiCoO2 exhibits large degradation while increasing its capacity by an increase in charging voltage, and also exhibits large degradation as the temperature rises.
SEL has fabricated a positive electrode material whose degradation can be suppressed even with high charging voltage.
▲LiCoO2 capacity dependence on voltage
Exhibit at IEDM2019 (Dec. 9 to 11, 2019)
Utilizing our advanced flexible technology, SEL has developed flexible batteries compatible with in-house developed flexible displays.
For its wide application range, e.g., wearable device
In 2013, we showcased an OLED flexible display incorporating our flexible battery at FPD International 2013 (exhibition for display) and were awarded “Outstanding Achievement Prize” for “Flexible display, lighting, and battery using oxide semiconductor”.
Our flexible battery has flexibility and durability against bending and stretching over 10,000 times, as well as having general battery performance.
▲Bending test conditions
 R.Tajima et al., “Truly wearable display comprised of a flexible battery, flexible display panel, and flexible printed circuit,” J. Soc. Inf. Disp., 22(5), 3237 (2014).
Nonflammable electrolyte for nonflammable battery
To achieve high-safety battery operating stably even in harsh environment, we are striving for the development of nonflammable electrolytes.
SEL demonstrated displays incorporating batteries which operate at 0℃ and 100℃ at Display Innovation 2014 (exhibition for display) in 2014.
 J.Ishikawa et al., “Flame-resistant and Heat-resistant Lithium-ion Battery Used to Operate Heat-resistant OLED,” SID Symp. Dig. Tech. Pap., 46, 143 (2015).
Battery system for ensuring safety
Battery Protection Control Circuit (BTOS®)Our aim is highly functional and safety power storage system achieved by the synergistic effect of the battery and the oxide semiconductor (OS) technologies in which SEL has been engaged since 2008.
BTOS[5, 6] is original system constructed by SEL, in which batteries and OS technologies are combined to protect and control the batteries.
BTOS has 10 functions listed below and can be applied to all lithium-ion secondary batteries. The BTOS technology enables, in advance, anomaly detection of micro short-circuit causing ignition and heat generation. This system is a promising technology to prevent accidents due to the batteries.
▲Functions of lithium-ion secondary battery protection control circuit
 S.Fukai et al., “Current Monitor Circuit with Cascode Amplifier Using Crystalline IGZO FETs Compatible with Low-Voltage Input to Detect Micro Short-Circuit in Lithium Ion Battery,” Ext. Abstr. Solid State Devices and Materials, 707 (2019).
Anomaly Detection with AI for Rechargeable batteriesWe are developing safe control system of rechargeable batteries such as lithium ion batteries with AI technology.
SEL battery R&D environment
SEL has created a fulfilling environment to work on the R&D of a variety of materials and devices that make up batteries as well as on the prototype of complete cells.
Endurance testCharge-discharge tests are conducted to evaluate performance of batteries, such as endurance.
*BTOS is a registered trademark of Semiconductor Energy Laboratory Co., Ltd. (Japanese trademark registration No. 6146374).