Enhanced constraint and catalysed conversion of lithium polysulfides: Via composite oxides from spent layered cathodes
Rechargeable lithium-sulfur (Li-S) batteries are regarded as a promising option for electrochemical energy storage systems. However, one of the key issues hindering their practical application is lithium polysulfide (LiPS) shuttling, which results in severe capacity decay and self-discharge. Separator-decoration with oxides has been demonstrated to be an effective strategy and has attracted widespread attention. But there has been no report about intergrown multi-phase composite oxides for separator modification. Herein, spent layered cathode (LiNi0.5Co0.2Mn0.3O2) derived layered-spinel-rocksalt intergrown oxides were firstly introduced and investigated. Unexpectedly superior performance was obtained with high reversible capacity and outstanding stability, which could be contributed by the entrapping and catalysis of LiPSs. The Li-S batteries with the spent multi-phase composite LiNi0.5Co0.2Mn0.3O2 show a low fading rate of 0.053% per cycle over 550 cycles at 1C rate, and high discharge capacities of 976.1, 916.7, 865.2, and 795.1 mA h g-1 at 0.5, 1, 2, and 3C rates, respectively. DFT calculation demonstrated that the spinel and rock-salt phases can provide more energetic reaction sites to strongly adsorb the LiPSs and accelerate the catalyzed conversion of LiPSs to Li2S/Li2S2. Moreover, our systematic experimental and theoretical investigation produced intriguing results, indicating that there is a synergistic effect between the spinel, rock-salt and layered phases. This study not only provides a high-value application of spent LiNi0.5Co0.2Mn0.3O2 but also demonstrates the potential of multi-phase composites to boost the performance of Li-S batteries.