Wet Procedure-Driven Performance Enhancement of Poly-Crystalline Cathodes in All-Solid-State Batteries
Authors: Kim Doohun 
Published: December 2024

As the demand for electrical energy continues to rise, battery systems have gained significant attention. All-solid-state batteries (ASSBs) have emerged as promising candidates for the next generation of energy storage systems due to their enhanced safety and high energy density. By replacing the flammable organic liquid electrolytes used in conventional lithium-ion batteries (LIBs) with solid-state alternatives, ASSBs offer enhanced safety features, eliminating risks of leakage, fire, and explosions. Furthermore, recent research efforts have been directed towards improving energy density by increasing the capacity of nickel-rich layered oxide cathode materials (NCM), facilitating safer and more efficient energy storage system[1].

Conventional dry methods for manufacturing bulk-type electrodes in all-solid-state batteries (ASSBs) are limited in scalability, posing challenges for commercialization. Wet-slurry casting methods are essential for synthesizing large-area cathodes; however, difficulties arise due to the severe reactivity between sulfide solid electrolytes (SEs), such as Li6PS5Cl (LPSCl), and polar solvents like N-Methyl-2-pyrrolidone (NMP).

Kim et al. proposed an infiltration method as a solution to address this issue. By elevating the temperature during the infiltration process, we enhance the molecular motion of the SE, facilitating its efficient incorporation into the cathode structure. This approach enabled the fabrication of a high-energy-density NCM622/Li–In half cell with a capacity of 136 mA h g-1 and a loading level of 17 mg cm-2. Electrochemical testing with cathode materials of varying particle sizes revealed that hybrid cathodes containing a mixture of large and small particles exhibited optimal SE infiltration, minimizing void formation within the electrode. Among the fabricated ASSBs, those with SE–NCM electrodes comprising a blend of active materials demonstrated superior electrochemical performance, achieving a capacity of 108.6 mA h g-1[2].

In this study, a scalable infiltration sheet-type process was used to fabricate composite electrodes with different cathode-material morphologies for ASSBs. LPSCl-infiltrated polycrystalline electrodes showed an excellent retention performance and rate capability. Galvanostatic intermittent titration technique (GITT) analysis and transmission electron microscopy (TEM) confirmed severe polarization and the presence of a rock-salt-structure layer in single-crystalline cathode particles. In contrast, composite electrodes comprising polycrystalline cathode materials infiltrated with the SE LPSCl showed an excellent electrochemical performance owing to intimate electrode–electrolyte interfacial contact. The as-fabricated poly-NCM infiltration electrodes showed an excellent electrochemical performance (with an initial discharge capacity of 196 mA h g−1, a discharge capacity of 112 mA h g−1 at a high rate of 2 C, and a retention of 81 % after 30 charge–discharge cycles). The infiltration method proposed in this study could enable the fabrication of high-performance composite electrodes for ASSBs in the future.