2-Carboxyethylgermanium sesquioxide as a promising anode material for Li-ion batteries.

We propose here the strategy of using Ge sesquioxide [O1.5GeCH2CH2CO2H]n (2-carboxyethylgermanium sesquioxide, 2-CEGS), in lieu of GeO2, as a promising, energy-intensive, and stable new source system for building lithium-ion anodes. Due to the presence of the organic substituent, the formed polymer has a 1D or a 2D space organization, which facilitates the reversible penetration of lithium into its structure. 2-Carboxyethylgermanium sesquioxide is common and commercially available, completely safe and non-toxic, insoluble in organic solvents (which is important for batteries use) but soluble in water (which is convenient for manufacturing diverse materials from it). This paper reports on preparing its micro- (flower-shaped agglomerates of ~1 mum thick plates) and nano-forms (needle-shaped 2-CEGS nanoparticles of ~500 x (50-80) nm) using common methods available in laboratory and industry such as vacuum and freeze-drying of aqueous solutions of 2-CEGS. The lithium half-cells anodes based on 2-CEGS show a capacity of ~400 mA h g-1 for microforms and up to 700 mA h g-1 for nano-forms, which is almost two times higher than the maximal theoretical capacity of graphite. These anodes are stable during the cycling at various rates. The results of DFT simulation suggest that Li atoms form the stable Li2O with the oxygen atoms of 2-CEGS, and actual charge-discharge cycle involves deoxygenated GeC3H5 molecules. Thus, capital ES, Cyrillic3 chains loosen the anode structure compared to pure Ge improving its ability to accommodate Li ions.