Porous and Amorphous MnMo₃S₁₃ Chalcogel Electrode for High-Capacity Conversion-Based Lithium-Ion Batteries

While Li-ion batteries (LIBs) are a leading energy storage technology, their energy densities are limited by the low capacity of conventional intercalation cathodes, driving interest in high energy-density Li-S batteries that make use of conversion chemistry. Achieving high capacity, reversibility, and cycle stability, and controlling volume changes in conversion batteries during the charge-discharge process, however, remains challenging. Here, we present a porous, amorphous, sulfide-based MnMo₃S₁₃ chalcogel, which concurrently offers high capacity and cycle stability. The solution-processable room temperature synthesized MnMo₃S₁₃ (x = 0.25) chalcogel exhibits a local structure that resembles the Mo₃S₁₃ cluster with Mn²⁺ distributed across the Mo₃S₁₃ matrix, as determined by synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS). Ab initio molecular dynamics (AIMD) simulations reveal that Mn²⁺ incorporation shortens the polysulfide chain in the gel matrix compared to the Mo₃S₁₃ chalcogel, while forming a coordination environment with disulfide groups, analogous to the experimental findings. A Li/Mn_0.25Mo₃S₁₃ half-cell delivers 897 mAh g^-1 capacity during the first discharge and retains 571 mAh g^-1 capacity after 100 cycles at a C/3 rate. Distribution of relaxation time (DRT) unveils a stable solid-electrolyte interphase (SEI) formation upon cycling that enables charge-discharge reversibility. Here, the enhanced capacity retention and cycle stability compared to those of the Li/Mo₃S₁₃ cell are attributed to the reduced dissolution of active mass into the electrolyte, facilitated by the formation of shorter polysulfide chains within the Mn_0.25Mo₃S₁₃ structure and the strong affinity of Lewis-acidic Mn²⁺ for polysulfide anions generated during the charge-discharge process of the Li/Mn_0.25Mo₃S₁₃ cell. Thus, this work illustrates a design principle of material for high-capacity and cycle-stable Li-metal sulfide batteries.