Control of nanoparticle dispersion, SEI composition, and electrode morphology enables long cycle life in high silicon content nanoparticle-based composite anodes for lithium-ion batteries

Abstract

Striking a balance between high theoretical capacity, earth abundance, and compatibility with existing manufacturing infrastructure, silicon is one of the few materials that meet the requirements for a next-generation anode for rechargeable lithium-ion batteries. Due to complications with extreme volume changes during charging/discharging and reactive interfacial chemistries, the cycle life of silicon-based composite anodes is unacceptable for broad use. Developing a majority silicon composite anode formulation that overcomes these challenges and is compatible with current industrial manufacturing practices requires materials and chemical engineering solutions that account for both electrode morphology and interfacial chemistry. Here, we synthesize surface-functionalized silicon nanocrystals that enable a highly dispersed and homogeneous slurry that can easily be integrated into a standard electrode fabrication process. We use this formulation to fabricate a 76 wt% silicon composite electrode. We show that the contents and the morphology of the silicon electrolyte interphase – a determining factor for the cycle life of silicon-based anodes – can be controlled with a post-synthetic thermal curing procedure. The curing process removes the organic surface functional groups used initially to enable dispersion in the slurry. Removing the organic surface coating reduces the cell impedance, improves the silicon utilization for lithium storage, and boosts the coulombic efficiency to values > 99.9% when electrochemically cycled. When paired with a capacity-matched lithium nickel manganese cobalt oxide LiNi_0.8Mn_0.1Co_0.1O₂ cathode, the cell retains 72% of its capacity after 1000 charge/discharge cycles while delivering an initial anode specific capacity of nearly 1000 mA h g⁻¹ and an areal capacity of 2.55 mA h cm⁻².