Analysis of SiO Anodes for Lithium-Ion Batteries

Abstract

The chemical structure of SiO ͑silicon monoxide͒ anodes has been analyzed using X-ray photoelectron spectroscopy ͑XPS͒. Vapor deposition was used to form SiO anodes on Cu film. XPS analysis was performed on anodes at each of three stages: after deposition, after initial charge, and after discharge. The results of this analysis were then evaluated in terms of the anode's respective electrochemical characteristics. It has been found that some Si remains oxidized in the full charge state and that lithium silicates are formed. The lithium silicates serve as a buffer with respect to changes in anode volume.The high energy density of lithium-ion rechargeable batteries would seem to make them especially promising candidates for meeting future requirements for large capacity batteries. However, the capacity of the material conventionally used for their anodes, graphite, is increasingly approaching its theoretical limit of 372 mAh/g, which would be insufficient for meeting the needs of future portable electronic equipment. 1,2 That is why much research has been devoted to the development of new anode materials, and substances which can absorb and retain lithium appear to be particularly promising in this respect. Silicon, which has a capacity ten times that of graphite, is one such substance. 3,4 Unfortunately, however, with silicon the expansion and contraction of lithium alloy during chargedischarge processes would lead to a pulverization of the active materials, and the resulting poor electrical contact between the current collector and the active materials would mean the degradation of capacity over a relatively small number of cycles. 5 As an alternative, SiO appears particularly promising because of its long cycle life. 6 It also has the advantage of absorbing and retaining a large quantity of lithium, which gives it a higher energy density than lithium-graphite. In order to determine the reasons for the good cycle characteristics of SiO, however, it is important to learn more about the chemical structure of SiO anodes. In this study, we have used X-ray photoelectron spectroscopy ͑XPS͒ to determine that chemical structure, and we have also investigated the electrochemical reaction of SiO with lithium. ExperimentalA SiO thin film about 2 m in thickness was prepared on a flat Cu film by vapor deposition. The background pressure was 1 ϫ 10 −6 Pa, and the deposition pressure was 1 ϫ 10 −4 Pa. X-ray diffraction ͑XRD͒ analysis of as-deposited SiO thin film was performed with Rigaku, RINT-2050. SiO anodes cut from this twolayer film were incorporated into coin-type electrochemical cells having lithium metal counter electrodes. The electrolyte was 1 M LiPF 6 in ethylene carbonate ͑EC͒:diethyl carbonate ͑DEC͒ ͑30:70 by volume͒. The electrochemical performance of these coin cells was measured for a 1/40 C current rate during initial charge and discharge operations, which were performed for a 0-2.5 V range. After initial charge and initial discharge, the anodes were removed in an Ar atmosphere, washed a number of times with DE...

The Mechanism of SEI Formation on a Single Crystal Si(100) Electrode

“…25,33,34,36 Additionally, peaks of Li x Si at 98.4 eV and 98.9 eV are clearly identifiable. 25,33,34,36 The presence of Li-Si bonds is not attributed to a Li-Si alloying reaction because it happens at potentials above 0.5 V. 17 However, the intrinsic SiO 2 layer on Si(100) reacts with Li + , resulting in a partial conversion of the surface oxide to Li 2 O and lithium silicates Li 2 Si 2 O 5 at 0.5 V. [37][38][39][40] The presence of SiOF in the samples from FEC-and VC-containing electrolytes as indicated by the signals at 105.1 and 105.6 eV, is fully consistent with the corresponding F 1s XPS spectra ( Figure 6). 33,34,36 The Si-O peaks from SiO 2 at 103.6 and 104.2 eV 19,33,34,36 and a small amount of lithium silicates at 101.0 and 101.6 eV 33,34,36 can also be observed.…”

Kinetics of Electrochemical Insertion and Extraction of Lithium Ion at SiO

“…[5][6][7][8][9][10][11][12][13] SiO shows a small volume change because it contains a relatively small amount of Si element that is active for the alloying reaction. The discharge capacity of SiO electrodes was reported to be over 600 mAh g −1 in several papers, [9][10][11][12] which is much higher than that of a graphite electrode ͑372 mAh g −1 ͒. To commercialize the SiO electrode, we need to consider the rate performance in addition to the energy density.…”

Silicon Based Composite Anode for Lithium Ion Battery

“…The nano-silicon then reacts with Li and forms Li-Si alloy (Lee & Lee, 2004). Contrary to this explanation (Miyachi et al, 2006) showed through O 1s spectra analysis that during the first lithiation process a direct absorption of Li by SiO takes place giving rise to the formation of Li 4 SiO 4 and Li 2 O. Among the composites prepared, the 24 h ball-milled sample exhibits higher reversible capacity.…”