All-Solid-State Lithium Metal Batteries Operating at Near-Zero Pressure

All-solid-state batteries (ASSBs) have emerged as a promising next-generation energy storage technology, owing to their high energy density and enhanced safety compared to conventional liquid electrolyte-based systems. To further increase energy densities in sulfide-based ASSBs, lithium metal anodes have been extensively studied for their low reduction potential and high specific capacity. However, lithium metal’s tendency to creep into the solid electrolyte during charge/discharge cycles—exacerbated by volume expansion—often leads to internal short circuits and hampers stable operation. While ASSLMBs with sulfide-based solid electrolytes are promising due to their superior energy density and safety, this issue remains a significant barrier to their widespread practical deployment.
To mitigate lithium creep and improve battery stability, this work employs a dual-strategy approach. First, thioctic acid (TA), a self-polymerizing monomer, was introduced into the electrolyte and polymerized in-situ at elevated temperatures without the use of a catalyst. This process forms flake-like poly(thioctic acid) (poly(TA)) structures, which act to suppress lithium metal creep and inhibit dendrite growth. Second, a porous carbon matrix (PCM) was integrated as the current collector to alleviate mechanical stress at the lithium-electrolyte interface. The PCM channels lithium deposition within its porous architecture, promoting directional growth and reducing stress during plating. This strategy ensures stable operation even under low stack pressures.
Symmetrical Li-Li cell tests demonstrated the effectiveness of the TA-modified electrolyte. Cells incorporating 5% TA exhibited outstanding cycling stability, operating for over 3,500 hours at a current density of 1 mAh cm^-2 and 1 mA cm^-2, whereas cells with lower (3%) or higher (10%) TA content showed inferior performance due to either insufficient stabilization or increased internal resistance. Critical current density tests further supported the efficacy of 5% TA, with cells maintaining stability up to 2.9 mA cm^-2 compared to the control cells, which short-circuited at 1.7 mA cm^-2. X-CT analysis confirmed the orientation of poly(TA) flakes perpendicular to the applied pressure during hot pressing, effectively curbing lithium dendrite growth. Also, operando X-CT imaging during lithium plating in cells incorporating PCM revealed that lithium was deposited within the PCM pores, rather than at the electrolyte interface, which likely prevented lithium creep and further minimized stress.
To evaluate the combined effects of TA and PCM in a practical cell configuration, a coin-type Li-NCM full cell was fabricated and tested at room temperature. The full cell delivered high areal capacities of 2.4 mAh cm^-2 and maintained stable cycling for over 150 cycles, achieving a Coulombic efficiency of 73.4% after 150 cycles. The rate capability of the full cell was further tested at 55°C, demonstrating stable performance even under elevated current densities. This achieved areal capacity of 2.4 mAh cm^-2 significantly surpasses the previously reported benchmark of 0.8 mAh cm^-2 for similar ASSLMBs operating under low pressures (<1 MPa).
In conclusion, this study presents an effective solution to the challenge of lithium metal anode integration in ASSLMBs by combining the in-situ polymerization of TA with the mechanical reinforcement provided by a porous carbon matrix. The integration of these strategies enables stable, high-capacity operation at ambient temperature and low pressure, making significant progress toward the commercial viability of ASSLMBs for real-world applications.