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.

No abstract

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–Ni composite nanoparticles have been produced by a single and continuous plasma spray physical vapor deposition (PS-PVD) from Si and Ni powder feedstocks and their electrochemical performances as anode in lithium-ion batteries (LiB) are investigated. Si nanoparticles with 20–40 nm on which Ni is directly attached with Si/NiSi2 epitaxial interface are formed spontaneously through co-condensation of high temperature elemental gas mixtures during PS-PVD. When only a little amount of Ni is added to Si, the effect of the epitaxial Ni attachment on the Si nanoparticles becomes evident; the cycle capacity is appreciably improved to reach a 1.6 times higher capacity than that of the Si only cell after 50 cycles, due to reduced charge-transfer resistance and nanosized Si particle. In contrast, excessive Ni addition to Si feedstock leads to formation of various silicides as a result of the accelerated silicidation during PS-PVD, which results in a significant decrease in the cycle capacity due to reduction of the active Si phase amount despite reduced charge-transfer resistance.

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.