Silicon nanoparticles (Si-NPs) have been produced by plasma spray physical vapor deposition at throughput as high as 1 kg h−1 (17 g min−1) and the effect on the battery performance is investigated. When the Si powder feed-rate is changed from 1 to 17 g min−1, although the average primary particle size increases to 50 nm, the cycle capacity of the batteries using these Si-NPs is improved slightly owing to their less agglomerated structure. In contrast, when Ni is added to Si feedstock, the cycle capacity is improved at 1 g min−1 due to modified Si-NP structure having SiNi2 interface. Whereas, the batteries with the Si-NP produced at 17 g min−1 shows significant decrease in the cycle capacity because of the excess Ni silicide formation that is resulted from the elevated co-condensation point and the increased reaction area at high throughputs despite the constant Ni concentration in the feedstock.
Nanocomposite SiOx particles have been produced by a single step plasma spray physical vapor deposition (PS-PVD) through rapid condensation of SiO vapors and the subsequent disproportionation reaction. Core-shell nanoparticles, in which 15 nm crystalline Si is embedded within the amorphous SiOx matrix, form under typical PS-PVD conditions, while 10 nm amorphous particles are formed when processed with an increased degree of non-equilibrium effect. Addition of CH4 promotes reduction in the oxygen content x of SiOx, and thereby increases the Si volume in a nanocomposite particle. As a result, core-shell nanoparticles with x = 0.46 as anode exhibit increased initial efficiency and the capacity of lithium ion batteries while maintaining cyclability. Furthermore, it is revealed that the disproportionation reaction of SiO is promoted in nanosized particles attaining increased Si diffusivity by two orders of magnitude compared to that in bulk, which facilitates instantaneous composite nanoparticle formation during PS-PVD.
Si nanoparticles with the averaged primary particle size ranging from 20 to 175 nm have been produced by plasma spray physical vapor deposition (PS-PVD) at different powder feed rates from 0.6 to 25.4 g min−1. High-order agglomerates as large as 10 µm are found to form especially at low powder feed rate, while such large agglomerates are suppressed when the particle size becomes greater than 100 nm at high powder feed rate. The electrochemical cells using Si nanoparticles smaller than 100 nm retain relatively high capacity with reasonable cycle stability, while the capacity drops rapidly for the cells with Si greater than 100 nm due partly to an increased charge transfer resistance. Moreover, ultrasonic particle breakup reveals that absence of large agglomerates as large as 10 µm are beneficial in reducing the charge-transfer resistance and in improving the cycle stability. Although oxygen content increases with decreasing the particle size, slow oxidation upon collection of the particles after PS-PVD successfully suppresses excessive oxidation, leading to negligible influence on the initial efficiency.
Si nanowires/nanorods are known to enhance the cycle performance of the lithium-ion batteries. However, viable high throughput production of Si nanomaterials has not yet attained as it requires in general expensive gas source and low-rate and multiple-step approach. As one of the potential approaches, in this work, we report the fast-rate Si nanorod synthesis from low-cost powder source by the modified plasma flash evaporation and the fundamental principle of structural formation during gas co-condensation. In this process, while Si vapors are formed in high temperature plasma jet, molten copper droplets are produced separately at the low temperature region as catalysts for growth of silicon nanorods. Si rods with several micrometers long and a few hundred of nanometers in diameter were produced in a single process at rates up to 40 µm s−1. The growth of the Si nanorods from powder source is primarily characterized by the vapor–liquid–solid growth which is accelerated by the heat extraction at the growth point. The battery cells with the Si nanorods as the anode have shown that a higher capacity and better cyclability is achieved for the nanorods with higher aspect ratios.
Spherical titanium particles have been produced from hydride-dehydride titanium raw powders using an inductively coupled plasma spray system. Taking into account the variously modified particle morphologies with different plasma conditions, the effect of powder loading on spheroidization was quantified and evaluated in terms of the altered particle heating capabilities. The averaged particle heat transfer coefficient was found to vary with powder feeding rate and associated strongly with Ar–H2 gas thermal conductivity. Furthermore, there observed a most efficient particle heating condition for each powder feeding rate, but the efficient heating condition tends to vaporize small raw powders and increase the overall oxygen content unintentionally as a result of the attachment of satellites nanoparticles on spherical particles. It is therefore important that the plasma input power is optimally controlled with particular attention to the altered degree of heat transfer especially for the case of small powder injection.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.