Novel Nonthermal Plasma Injector for the in-Flight Synthesis and Coating of Battery Materials
Authors: Iannitto Robyn , Filice Dante , Asgarian Ali , Li Gaofeng , Coulombe Sylvain 
Published: December 2024

As CO2 emissions continue to rise and the demands for electric vehicles and energy storage grow, efforts need to be made to produce higher performing lithium ion batteries (LIBs). Therefore, it is critical to improve the performance of the anode materials. Graphite has gained recognition as the most popular anode for commercial LIBs due to its low cost, low toxicity and cycle stability. However, there are a number of disadvantages with graphite, such as its limited storage capacity, which hinders further LIB development. As a result, silicon has emerged as a promising anode material due to its high charge storage capacity, which is approximately 10 times larger than graphite. Despite this, silicon as an anode for LIBs faces its own challenges, namely its extreme volume expansion during the lithiation and delithiation process, which leads to poor cycle performance. To combat this, silicon nanoparticles with carbon coatings have been identified as a promising candidate for LIBs anodes. The carbon will provide continuous conduction during cycling and prevent pulverization, and the core-shell structure will reduce volumetric expansion and therefore improve the anode stability.

Ideally, silicon nanopowder (core) with carbon coating (functional shell) should be integrated in a single process. This would prevent the synthesized nanoparticle from immediately oxidizing upon contact with air or agglomerating, irreversibly affecting the sought-after surface properties. However, the successful one-step synthesis of core-shell nanopowders still remains a challenge. Therefore, the bottleneck for the integration of silicon anodes with carbon coatings into LIBs is the development of a cost-effective and environmentally friendly synthesis method.

A number of industries have adopted inductively coupled plasma (ICP) reactors since they are well-suited for large scale production of nanopowders, but these currently lack the ability for in-situ modification of nanopowder surfaces. This is where non-thermal plasmas (NTPs) come into play. NTPs host high-temperature electrons that initiate the formation of chemical radicals and ions in the gas phase which, upon reaction with a nanopowder surface, form coatings and/or graft functional groups. In this work, we developed a novel radial non-thermal plasma injector that can be added to our ICP reactor for the in-flight synthesis and coating of nano silicon with carbon. Here, we show that ICP produces nano silicon particles which is then coated by an organic carbon layer in-flight by the NTP injector using an Ar/C2H6 gas mixture. To evaluate the success of the injector, the phase composition was evaluated using x-ray diffraction (XRD), the morphology and particle size was confirmed using scanning electron microscopy (SEM) and the chemical composition was validated using energy dispersive X-ray analysis (EDX). The novel NTP injector developed in this work coupled with ICP provides an efficient pathway for the synthesis of core-shell anodes necessary for further battery development.