Dual Performance Electrodes for Li-S and Li-Ion Batteries

New classes of materials were investigated as potential negative electrodes for Li-ion and Li-S batteries. FeSnS₂, Fe₂SnS₄ and CuSnS₂ without any carbon coating were synthetized by solid state reactions. According to their active elements, tin and sulfur, these materials can be cycled in two different potential windows: [0-1V] vs. Li⁺/Li in the Li-ion system (active window of Sn) and [1.2-2.7V] vs. Li⁺/Li in the Li-S system (active window of sulfur), using LP30 (1M LiPF₆ 1:1 EC:DMC) and LiTFSI (1M LiTFSI, 2:1 DME:Diox) as electrolyte, respectively.  In both systems, there is a major issue that limits the development of those systems to take into consideration. During cycling of tin particles versus lithium, an alloying process (Snà Li₇Sn₂) with a volume expansion of 243% of the electrode material takes place, leading to a loss of electric contact in the particles and significant fading. In the Li-S system, lithiation leads to the development of soluble species in the electrolyte (polysulfides) that affect the cycling stability and cause significant fading. For this study, we decided to cycle these materials in two different potential windows and to have a look at the morphology of the electrodes after cycling. By using this approach, we were able to cycle at a rate of 1C (loading of 3-4mg/cm²) for at least 500 cycles and obtained more than 900 mAh/g for the Li-S system and more than 800mAh/g for the Li-ion system, with a coulombic efficiency of around 99%. In both case, the non-active materials (Cu, Fe), as well as S in the active window of Sn, and Sn in the active window of S seemed to be able to buffer both the volume changes of the Sn particles and impede the polysulfide shuttle of the sulfur particles. The impact of the electrolyte on the cycling properties, as well as the role of the electrolyte additive and the different cycling properties will be discussed and compare to the reference sample SnS₂ already described in the literature. In situ XRD and post mortem analysis will be further discussed to understand the reaction mechanism of this new promising class of anode materials.