(536g) Reactivity of an Alucone Thin Film Coating on a Lithiated Si Anode of Li-Ion Batteries

Lithium-ion batteries are one of the most common types of rechargeable batteries to power small, portable electronic devices. Current research efforts are focused on achieving the energy density required for electric cars and high-end portable electronics. Silicon anodes in Li-ion batteries yield higher theoretical capacities than graphite, the most common anode material; nevertheless, the significant volume changes occurring in the silicon anode during lithiation and de-lithiation limits its ability to retain capacity for an extended number of charge/discharge cycles. A solid electrolyte interphase (SEI) layer that naturally forms on the silicon surface from the reduction of the electrolyte components can improve the mechanical stability of the anode at the expense of hindering Li transport. In contrast, surface modification of the silicon anode may be a viable strategy to accommodate volumetric changes, preventing cracking and pulverization of the electrode, while maintaining or improving ionic and electric conductivity. Aluminum alcoxide (alucone) films to improve the stability of the anode have been successfully deposited and characterized on lithiated silicon surfaces, and reportedly become electronically conductive after Li atoms saturate the favorable sites of the film. In the present work, we use density functional theory and ab initio molecular dynamics simulations to study the reactivity of the film and the anode surface in contact with a typical organic solvent, ethylene carbonate. The solvent molecules are found to be able to penetrate the film and undergo reduction inside the film and at the film-anode and film-electrolyte interfaces via one- and two-electron mechanisms. Such reaction mechanisms are examined along with the structure, stability and suitability of the film to improve the anode, as well as the implications for the design of enhanced electrode materials for Li-ion batteries.