Cécile RIZZI1, Alexandros PLOUMISTOS1, Francisco FERNANDES2, Ana-Gabriela PORRAS-GUTIERREZ1, Anne-Laure ROLLET1, Juliette SIRIEIX-PLÉNET1, Laurent GAILLON1
1Sorbonne Universite?, CNRS, Physico-chimie des E?lectrolytes et Nanosyste?mes Interfaciaux, PHENIX, F-75005 Paris, France, Paris, France
2Sorbonne Universite?, CNRS, Collège de France, Laboratoire de chimie de la matière condensée de Paris, LCMCP, F-75005 Paris, France, Paris, France
Various materials such as alloy, conversion-type, silicon or carbon-based materials are theoretically capable of outperforming graphite as Li-ion battery (LIBs) anodes. Among alloy materials, tin exhibiting a high theoretical capacity, higher charge-discharge rates and better conductivity suffers, however, from a main drawback as a huge volume expansion occurs while cycling, leading to electrical contact loss and fracturing which are detrimental to the electrode and responsible for the short lifetime of the LIBs. Nanostructuring the active material allow to counter this. The development of a synthetic technique to produce Sn@SnOx core-shell nanoparticles in an ionic liquid (IL) [1] was reported by our group a few years ago. Nanoparticles (NPs) were uniform, with a very narrow size distribution, as their growth during reduction was effectively controlled via interactions with the imidazolium of the IL solvent. Results obtained from electrodes which were prepared using tin NPs were found wanting, as common binders and additives limited the accessibility of the nanoparticles and failed to prevent their structural damage during cycling of the batteries.
In this work, considering the fact that the morphology of the anode material has a large impact in the improvement on its electrochemical properties, various carbon-based materials were developed. IL from the imidazolium family could be combined with graphene-based matrix either by mixing or cation-grafting. An amino functionalized imidazolium ionic liquid was synthesized and used as an integral constituent of the anode. As for the matrix itself, graphene and its derivatives can organize in several different types of 3D structures with varying and tunable characteristics. [2] We investigated various conductive graphene-based scaffolds such as membrane and aerogels obtained by freeze casting techniques [3] that could allow to harness the favorable interactions between tin and the imidazolium ring grafted onto the matrix. Its porous network permits the fast diffusion of lithium ions straight to the Sn host NPs and the flexible, functionalized graphene sheets can absorb and contain the phase transformation of active materials during charge and discharge, keeping the NPs in place by preventing their migration and the aggregation of tin. At last, a further advantage could rely on the fact that the bis(trifluoromethane)sulfonimide anion, TFSI-, is known to take part in the formation of a stable solid electrolyte interface (SEI). As the system is both self-supporting and conductive, no additives are needed. It might be useful for the design of lighter batteries. The composite and each of its constituents have been characterized at the different stages of preparation by thermal analyses, NMR, SAXS, electron microscopy, XPS and electrochemical properties in batteries were evaluated.
REFERENCES
[1] N. Soulmi et al., 2017, Inorganic Chem. 56, 10099–10106.
[2] C.-N. Yeh et al., 2019, Nature Communications, 10, 1, 422-432 ; M. A. Worsley et al., 2010, J. Am. Chem. Soc. 132, 14067–14069.
[3] S. Christoph et al., 2018, Chemical Engineering J., 350, 20–28.