Porous and Amorphous MnxMo3S13 Chalcogel Electrode for High-Capacity Conversion-Based Lithium-Ion Batteries

Abstract

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 Mn_xMo₃S₁₃ chalcogel, which concurrently offers high capacity and cycle stability. The solution-processable room temperature synthesized Mn_xMo₃S₁₃ (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.