Graphene-Wrapped Silicon Nanoparticles for All-Solid-State Lithium-Ion Batteries

Abstract

Current lithium-ion batteries consist of a graphite anode and a metal oxide cathode. Due to their relatively high energy density and rechargeability, they have enabled various applications over the past few decades. However, significant improvements to battery cost, performance, and safety for applications such as vehicle electrification require a shift to next-generation materials, such as silicon as an anode which offers higher capacity, as well as solid-state electrolytes (SSEs) which are non-flammable. Both of these technologies currently suffer challenges which have prevented their widespread adoption. Silicon suffers low conductivity, and large volume change on each cycle, subsequently causing loss in electrical contact and the formation of an unstable solid electrolyte interface (SEI) each cycle. This project aims to solve these challenges by wrapping silicon nanoparticles and a sacrificial spacing material with crumpled graphene sheets using a scalable, spray drying method, and coupling it with a solid electrolyte. The graphene shell provides electrical contact with the silicon and space for its expansion during lithiation. The solid electrolyte provides a safer alternative to liquid electrolytes, and further reduces the SEI formation which, with a liquid electrolyte, can leak into such crumpled structures. In this work we will present our initial results concerning how the spacing material affects the structure and how the overall structure can be modified by spray drying parameters to determine optimal conditions for capacity and cycle-life using, first, at typical, organic carbonate-based electrolyte. We will explore different spacing material candidates such as chitosan which, upon heat treatment of the sample, would not only provide space for the expansion of silicon, but the residual nitrogen-doped carbon would also act as a conductive filler inside the crumpled structure. Furthermore, we will investigate various binder systems and their impact on cycle-stability including polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), sodium alginate (SA), and cross-linked SA. Based on preliminary, both PAA and SA are shown to have improved performance compared to PVDF as well as higher cycle life, however, SA forms smoother, thinner electrode films. Cross-linked SA is also shown to increase the cycling life and decrease the capacity loss per cycle. We then explore powder mixing and solution infiltration methods to introduce high conductivity SSEs and their performance when coupled to the graphene-wrapped silicon anode structures.