Realization of "Fire-Resistant, High-Energy-Density Lithium-Ion Secondary Battery"

Semiconductor Energy Laboratory Co., Ltd. (SEL, Atsugi, Kanagawa; Chairman and CEO: Shunpei Yamazaki) has conducted safety verification experiments using nail penetration tests for lithium-ion secondary batteries intended for consumer electronics. In this verification, SEL applied its newly developed cathode active material, Ni-doped lithium cobalt oxide (LCNO™). This has enabled the realization of a lithium-ion secondary battery that possesses both fire resistance and high energy density. The LCNO™ battery developed by SEL has successfully improved fire resistance without compromising the high energy density inherent in lithium cobalt oxide (LCO) batteries. In nail penetration tests, the prototype LCNO™ battery did not ignite, showed no temperature rise on the cell surface, and confirmed that no thermal runaway occurred. Furthermore, LCNO™ exhibits improved discharge energy density (per weight) of the cathode material compared to commercial LCO products. The structural stability of LCNO™ plays a crucial role in achieving this performance. LiCoO₂ (LCO), a cathode active material, is known to degrade through repeated charge-discharge cycles. General LCO undergoes a phase transition to the H1-3 phase during charging, causing the CoO₂ layers to shift and preventing them from returning to their original state during discharge. The newly developed LCNO™ by SEL incorporates Ni and Mg into LCO. This allows Ni and Mg to enter the Li sites in the layered rock-salt structure of LCO, supporting the CoO₂ layers and ensuring the structure does not collapse even in a charged state. XRD measurements confirmed that LCNO does not transition to the H1-3 phase even at high-voltage charging of 4.6V or higher, but instead changes to a different crystal structure (O3' phase) than the O3 phase. We are confident that this development will contribute to the realization of a safe and secure society free from fire accidents.