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Sulfide-based all-solid-state batteries, often referred to as the “dream battery,” typically require strong external pressure to maintain contact between the electrodes and solid electrolyte during operation, making heavy pressure equipment essential.

A POSTECH research team has developed a new battery technology that can operate stably without applying strong external pressure inside the battery.

The battery maintained more than 70% of its initial performance even after repeated charge and discharge cycles under ultra-low pressure.

POSTECH announced on the 14th that a joint research team led by Professor Sujin Park of the Department of Chemistry and Professor Changshin Jo of the Department of Battery Engineering and Department of Chemical Engineering successfully reduced the pressure dependence of sulfide-based all-solid-state batteries by developing a thin hybrid interfacial layer combining MXene, silicon, and silver.

MXene is a two-dimensional nanomaterial known for its excellent electrical conductivity. The research findings were published in the international journal Advanced Energy Materials on the 15th of last month.

All-solid-state batteries use solid electrolytes instead of flammable liquid electrolytes, offering enhanced safety and high energy-storage capacity. Sulfide-based solid electrolytes, in particular, have attracted considerable attention as next-generation battery materials due to their excellent electrochemical performance.

However, both the electrodes and electrolyte in sulfide-based all-solid-state batteries are solid materials.

During repeated charging and discharging, solid electrodes undergo slight changes in volume, which can create microscopic gaps at the interface between the electrodes and the solid electrolyte.

These gaps interfere with the pathways through which lithium ions and electrons move, reducing battery performance.

To minimize these gaps, conventional sulfide-based all-solid-state batteries must be continuously compressed under pressures reaching several tens of atmospheres.

This requires separate pressure-control equipment, increasing the weight and volume of the battery and creating challenges for commercialization.

Instead of relying on external pressure, the research team introduced a buffer layer between the electrode and electrolyte.

The team fabricated an ultra-thin interfacial layer just 2–4 micrometers (μm) thick and inserted it between the lithium anode and the solid electrolyte.

The interfacial layer consists of three materials.

MXene serves as the structural framework of the layer. Its stacked, two-dimensional structure can flex as the electrode undergoes changes in volume, helping prevent the formation of gaps at the interface.

The researchers also incorporated silicon and silver into the MXene layer.

The two materials regulate lithium growth through different mechanisms.

Silicon remains in place within the interfacial layer and serves as a nucleation site where lithium can accumulate.

Silver, meanwhile, moves along with lithium and creates new sites for lithium growth.

By working in a complementary manner, the two materials help distribute lithium growth more evenly rather than allowing lithium to become concentrated in specific locations.

When the research team tested an all-solid-state battery equipped with the MXene–silicon–silver interfacial layer, the battery operated stably at a pressure of approximately 0.2 MPa.

This represents a substantial reduction compared with conventional silicon-based all-solid-state batteries, which typically require pressures of around 5 MPa to operate.

According to the research team, this is the first reported all-solid-state battery capable of operating at a pressure as low as 0.2 MPa.

The researchers also confirmed the performance of the technology in a battery using a high-energy-density NCM811 cathode, a material widely used in electric vehicle batteries.

Under ultra-low-pressure conditions, the battery retained 72.4% of its initial capacity after 200 charge–discharge cycles.

A 3 × 3 cm pouch-type battery tested under the same conditions also retained 82.7% of its initial performance after 200 cycles.

The research team expects that reducing the reliance on external pressure-control equipment could help decrease the weight and volume of all-solid-state battery systems while increasing their practical energy density.

Professor Changshin Jo said, “We expect this research to provide a new direction for realizing stable all-solid-state batteries through the design of the materials and structure of the interface itself.”