Thin, Conformal Carbon-Coating of Silicon-Phosphorus Nanoparticle Agglomerates for Lithium-Ion Battery Anodes

Abstract

Efforts to further enhance the capabilities of silicon as a lithium-ion battery anode are continuing into the realm of chemical composition. Adding varying amounts of other elements can significantly alter the material properties or side reactions, which influence electrochemical performance. Additionally, tuning the chemical composition combined with surface modifications can better enable application of silicon anodes in other devices such as hybrid supercapacitors.Prior work, among others, has shown different performance enhancement regimes depending on how much phosphorus is added to silicon-containing anodes [1, 2]. In particular, the amount of phosphorus from ppm levels to majority atomic fraction can result in enhancement in the conductivity, diffusivity, or forming altogether a wholly new protective matrix [3]. However, while the rate capability has been enhanced only primarily for delithiation, silicon-phosphorus (SiPx) anodes still suffer from similar capacity degradation issues as pure silicon anodes.In the present work, we attempt to address the capacity degradation issue by using a thin, conformal carbon coating to modify the solid-electrolyte interface (SEI) reaction. Firstly, amorphous nanoparticles of SiPx with a few atomic percent of phosphorus are prepared using silane and phosphine co-pyrolysis. Using an oscillating furnace at 800 degrees Celsius under a low flow of acetylene in Ar carrier gas, we are able to produce consistent, uniform carbon films on nanoparticle agglomerates with select thicknesses between 2 and 10 nm, validated using low voltage scanning transmission electron microscopy (LV-STEM), as shown in Figure 1. By comparing Si- and SiPx-containing anodes in electrochemical half cells, we can reproduce the rate capability results while demonstrating the effect of carbon coating on cycle life and capacity retention. Furthermore, the carbon coating’s effect on volume expansion for Si- and SiPx-containing anodes is studied in situ using an electrochemical dilatometer in half cell configuration.[1] Y. Domi, H. Usui, M. Shimizu, Y. Kakimoto, H. Sakaguchi, ACS Applied Materials & Interfaces 2016, 8, 7125-7132.[2] S. Huang, L.-Z. Cheong, D. Wang, C. Shen, ACS Applied Materials & Interfaces 2017, 9, 23672-23678.[3] F. T. Huld, S. Y. Lai, W. M. Tucho, R. Batmaz, I. T. Jensen, S. Lu, O. E. Eleri, A. Y. Koposov, Z. Yu, F. Lou, ChemistrySelect 2022, 7, e202202857. Figure 1