Researchers in South Korea have confirmed the mechanism of deterioration occurring inside the anodes of solid-state batteries and have demonstrated the possibility of stable operation of these batteries in a low-pressure environment.
The Korea Institute of Science and Technology (KIST) announced on Nov. 12 that a research team led by Dr. Jeong Hun-ki of the Energy Storage Research Center had identified factors causing rapid capacity decline and shortened lifespan when operating solid-state batteries under pressure levels similar to those in lithium-ion batteries.
Solid-state batteries replace the liquid electrolyte used for ion transfer between the anode and cathode with a solid, making them non-flammable and resistant to fire or explosion risks. They are also resilient against temperature changes and external impacts, earning them the nickname “dream batteries.”
However, solid-state batteries face “interfacial deterioration,” where the interface between the solid electrolyte and the electrodes detaches due to volume changes in the anode and cathode during charging and discharging cycles. Previously, high external pressure was necessary to prevent this phenomenon.
Past studies primarily attributed the short lifespan of solid-state batteries to losses at the electrode interfaces, without a clear assessment of the causes in low-pressure operating environments.
The research team created coin-shaped solid-state batteries with sulfide-based solid electrolytes and operated them under the low pressure of 0.3 MPa, akin to coin-shaped lithium-ion batteries, and conducted 50 charge-discharge cycles.
The results confirmed that deterioration in a low-pressure environment was caused by cracks in the anode material and irreversible anodic phase changes. Irreversible anodic phase changes lead to the collapse of the anode structure, significant capacity reduction, and thermal instability.
Additionally, by substituting lithium in the anode with the isotope lithium-6 and employing “time-of-flight secondary ion mass spectrometry,” the research team verified that lithium consumption within the anode impacts the overall cell capacity.
During the charge-discharge cycles, sulfur – a decomposition product of the solid electrolyte – penetrated the cracks inside the anode material, forming lithium sulfide, a non-conductive byproduct. This depleted the active lithium ions, promoting anodic phase changes and reducing the capacity of the solid-state battery.
The researchers believe this finding could provide clues for solving the issue of shorter lifespans of solid-state batteries compared to lithium-ion batteries in low-pressure environments.
Dr. Jeong Hun-ki emphasized, “For the commercialization of solid-state batteries, it’s essential to develop new anode and cathode materials that can operate in unpressurized or low-pressure environments. Applying low-pressure solid-state batteries in large-scale applications like electric vehicles could be highly beneficial, as it would allow the use of existing lithium-ion battery manufacturing facilities.”
These research findings were featured as the cover article in the international journal Advanced Energy Materials on Oct. 27.