Instantaneous formation of SiO_x nanocomposite for high capacity lithium ion batteries by enhanced disproportionation reaction during plasma spray physical vapor deposition

Abstract

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.

High Initial Coulombic Efficiency of SiO Enabled by Controlling SiO2 Matrix Crystallization

“…This indicates that the bare SiO is mainly amorphous without any long-range order. The bare SiO is a mixture of amorphous Si ( a -Si) and a -SiO 2 at the atomic level, and the mixture is thermodynamically unstable, so SiO is easily disproportionated at >900 °C. ,− , The XRD patterns of disproportionated SiO that was prepared at >900 °C show the presence of nanosized Si crystals and a -SiO 2 . − , The XRD change indicates that Si is easily crystallized during the disproportionation reaction at 900 °C, but a -SiO 2 still shows an amorphous phase even at 1200 °C. , Although the heating temperature was increased to 1200 °C to crystallize a -SiO 2 in SiO (Supporting Information, Figure S2), crystallization of SiO 2 was not completed yet. The SiO 2 matrix was partially crystallized to quartz and cristobalite, and SiO still maintained a predominantly amorphous SiO 2 matrix phase (Supporting Information, Figure S2a).…”

“…The bare SiO is a mixture of amorphous Si (a-Si) and a-SiO 2 at the atomic level, and the mixture is thermodynamically unstable, so SiO is easily disproportionated at >900 °C. 4,[10][11][12]18 The XRD patterns of disproportionated SiO that was prepared at >900 °C show the presence of nanosized Si crystals and a-SiO 2 . [10][11][12]18 The XRD change indicates that Si is easily crystallized during the disproportionation reaction at 900 °C, 20 but a-SiO 2 still shows an amorphous phase even at 1200 °C.…”

“…For instance, the disproportionation reaction of SiO at high temperatures separates SiO to Si and SiO 2 , but this separation is not effective in decreasing irreversible capacity to increase ICE. − Control of the Si/O ratio exploits the fact that Li reacts reversibly with Si and irreversibly with SiO 2 ; an increase in the ratio of Si yields an increase in the ICE of SiO but can reduce the capacity retention by a decrease in the portion of SiO 2 matrix that can be a buffer against large volume expansion. , The pre-lithiation process of SiO can remove the irreversible reaction of SiO 2 in SiO by electrochemically/chemically reacting SiO with a Li ion or Li metal before an electrochemical use. ,, However, this pre-lithiation process is not an efficient process due to being an additional time-consuming and tedious process. Furthermore, pre-lithiation consumes almost the same number of moles of Li ions as SiO to remove irreversible capacity caused by the reaction of SiO 2 with Li. ,, The large amount of LiOH·H 2 O in SiO was only used to fully transform the SiO 2 to lithium silicate (Li 4 SiO 4 ) phase before an electrochemical reaction like a pre-lithiation process. , As a result, these features can make the pre-lithiation process not easy for mass production of high-performance SiO material with high ICE.…”

“…7,9,17 The large amount of LiOH•H 2 O in SiO was only used to fully transform the SiO 2 to lithium silicate (Li 4 SiO 4 ) phase before an electrochemical reaction like a pre-lithiation process. 9,18 As a result, these features can make the prelithiation process not easy for mass production of highperformance SiO material with high ICE.…”

Potassium Ions Regulated the Disproportionation of Silicon Monoxide Boosting Its Performance for Lithium-Ion Battery Anodes

“…Many synthesis routes related to disproportionation introduce ball milling ways to achieve better SiO x anodes. , In Hwang’s work, for the sample milled for 24 h, a reversible capacity of 1270 mAh g –1 and a Coulombic efficiency of 71.8% were obtained at the first cycle . There are also many works that have assisted other technologies to realize disproportionation, for example, Homma et al and Tashiro et al produced a SiO x composite via plasma spray physical vapor deposition (PS-PVD), leading to a large capacity decrease at the initial stage of the cycles but stabilized capacities after five cycles. Based on the research of disproportionation, many other modifications of silicon monoxide used disproportionation before other specific methods. , However, disproportionation requires high temperatures and cannot solve the problems of unstable SEI formed on SiO particles.…”