Combining in situ electrochemistry, operando FTIR and post-mortem analyses to understand Co-Mn-Al spinels on mitigating shuttle effect in lithium-sulfur battery

Abstract

The spinel oxide Co2Mn0.5Al0.5O4 (CMA) was investigated as an additive onto the cathode of lithium-sulfur batteries. We demonstrate the polysulfide adsorption onto CMA, mitigating the shuttle effect, a well-known failure mechanism. The in situ electrochemical impedance spectroscopy and cyclic voltammetry tests evidenced that CMA facilitates the conversion of short-chain lithium polysulfides (LPS). The CMA reduced the maximum voltammetric current by approximately 20% compared to the AC/S cathode and facilitates the conversion of LPS into solid-liquid-solid species. High conversion efficiencies were verified after 315 cycles, resulting in 89% of capacity retention. Low CMA concentrations of up to 10 wt.% increased battery capacity and showed that CMA has high ionic conductivity, while moderate concentrations of approximately 50 wt.% improved cyclability but increased cell’s resistivity. This improvement in cyclability is related to LPS trapped at CMA which is demonstrated by micrographs, X-ray energy dispersive and photoelectron spectra of post-mortem samples. The byproducts formed after cycling until failure, were identified by Raman spectra and diffraction patterns. Fourier transform infrared spectroscopy operando analyses suggested electrolyte decomposition as a relevant cell failure mechanism. In conclusion, we demonstrated how CMA can trap LPS and enhanced initial capacity to 1000 mA h g-1sulfur cm-2 and improved cyclability for more than ∼360 cycles.