Sn/Si/graphite composites for Li-ion storage characterized by physical, electrochemical and computational tools

A. RUDERMAN; S. SMREKAR; D. E. BARRACO; F. VACA CHAVEZ

Congreso; 7 th International Workshop on Lithium, Industrial Minerals and Energy; 2020

Sn and Si have proven to be promising active materials due to their high theoretical gravimetriccapacities of 994 mAhg −1 [1] and 3579 mAhg −1 [2], respectively. Unlike graphite, Sn and Si undergostructural changes during the lithiation process that produce an increase in their volume of about300% [3]. This expansion results in the cracking of the electrode, leading to a loss of interparticlecontact and the consequent capacity fading. There are many reports exploring different strategies toalleviate this huge volume expansion, in order to mitigate the mechanical strain, namely: i) reducethe particle size or ii) disperse the Si or Sn in a conductive matrix (e.g. carbon-based materials) inorder to accommodate the volume change [4-5].In a very recent work, using a simple high energy planetary ball milling technique, our researchgroup has proven that anodes composed of Tin-Silicon-microGraphite (Sn-Si-μG) have an improvedelectrochemical performance with respect to the pristine materials [6]. A systematic study ofSn/Si/graphite composite materials varying the content of each component was reported. Here, wego further with the characterization of this anode material, identifying the different lithiated phasesduring the charge/discharge processes. With this purpose, complementary ex-situ 7 Li MAS NMR, X-ray and TEM experiments on anodes with different active material compositions were carried out.Figure 1 shows the complex and asymmetric 7 Li NMR spectrum of the lithiated Sn/μG 2:1 anodetogether with the corresponding deconvolution. Using Lorentzian lineshapes the spectrum showsseven peaks, with chemical shifts between -9 ppm to 42 ppm attributed to different phase formedduring the process.Complementary to these studies and not only to get a better understanding about the results, but alsovalidate the assignations done, DFT calculations of the full discharged and charged states ofelectrodes prepared with Sn-Si-μG were performed. Results about the thermodynamic stability ofthe alloys vs. composing the battery?s anode at different potential and computational calculation ofthe NMR shielding tensor allowed us to