Development in ionic liquid media of new synthesis processes for tin-based nanomaterials used as negative electrode for Li-ion battery

Tin is a promising alternative to replace graphite carbon as a negative electrode material in Li-ion batteries due to its high specific theoretical mass capacity of 993 mAh.g^-1. However, change in volume during lithiation leads to its mechanical degradation during the cycling, and consequently very short life of the material. To overcome this issue, the use of the intergranular space via the nano-structuration of the material combined by the addition of a carbon matrix or other inactive element vs. lithium (intermetallic alloys), which buffers drastically the volume expansion during the lithium alloying process, is employed. The aim of this work is to develop new processes for the synthesis of tin nanoparticles and tin-copper alloys in ionic liquid medium. Sn nanoparticles varying in size from 7 to 45 nm were synthesized, according to the cation-anion combination of the ionic liquid and from different metallic salts, as well as a nano-alloy compound, Cu6Sn5. The size of the nanoparticles is directly related to the nature of the anion although the cation has a privileged interaction with the metal surface of the nanoparticles. Once isolated from the ionic liquid, Sn and Cu6Sn5 nanoparticles have a core-shell architecture with a metallic or intermetallic crystalline core and an amorphous shell of tin oxides. A reversible conversion mechanism of the SnOx from the shell is highlighted for Sn-SnOx nanoparticles, with a high specific capacity of approximately 950 mAh.g^-1. Sn-Cu-SnOx nano-alloys have a capacity close to the theoretical for an alloy mechanism at more than 530 mAh.g^-1. (author)