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

Abstract

A fundamental study of interfacial phenomena on a Si(100) single crystal electrode in organic carbonate-based electrolytes was carried out. The SEI formation on the Si(100) single crystal electrode was investigated as a function of the electrolyte composition, electrode potential and Li x Si lithiation degree. Fourier transform infrared spectroscopy (FTIR) and X-ray photon spectroscopy (XPS) studies of the SEI layer during early stages of SEI formation indicate a strong dependence of the SEI composition on the electrolyte composition. However, the influence of the electrolyte composition becomes negligible at low potentials, when lithium alloys with Si and forms amorphous Li Currently, graphite is the most common negative electrode material in commercial lithium ion batteries for portable electronics. [1][2][3] However, lithium ion batteries for large-scale transportation applications require new inexpensive electrode materials with higher specific capacity. For decades, silicon has been considered as a promising negative electrode material, mainly because of its high specific capacity of ca. 3500 mAh/g 4 and its abundance in the earth crust. [4][5][6] The key problems that prevent its widespread use are large, up to ∼300 % volumetric changes during lithiation/delithiation processes and interfacial instability of lithium silicides in organic solvent based electrolytes. 6-12The resultant poor electrochemical cycling performance and large irreversible capacities during formation and operation of the Si negative electrode contribute to rapid degradation and failure of the battery. 6,7,13 The solid electrolyte interphase (SEI) layer, which forms at the electrode/electrolyte interface during the initial charge/discharge cycles, is the key component that determines the long-term stability and cycling behavior of carbonaceous and intermetallic negative Li-ion battery electrodes.14-16 Electrolyte reduction and SEI layer formation on a Si electrode usually take place at potentials below 1.8 V vs. Li/Li + and accompany the formation of Li-Si phases, the so-called "Si-Li alloying" process at E <0.4 V vs. Li/Li + . 17 The exact mechanism of the SEI formation processes on Si, the SEI composition and the effect on the Si electrode electrochemical cycling performance is not well understood. 18 On the other hand, SEI-forming electrolyte additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are known to alter the composition and properties of the SEI on Si and improve the electrode electrochemical performance. [19][20][21] Interestingly, recent model studies on Sn single crystal electrodes in organic carbonate electrolytes revealed a strong correlation between the crystal surface orientation and the SEI composition.22,23 A similar study of the composition of the SEI on a silicon monocrystal electrode showed strong effects of different SEI formation protocols, presence/absence of intrinsic SiO 2 , electrolyte composition and impurities e.g., HF. [24][25][26] Also graphite exhibits different SEI layer compos...

A Robust Solid Electrolyte Interphase Layer Augments the Ion Storage Capacity of Bimetallic‐Sulfide‐Containing Potassium‐Ion Batteries

“…[37] Compared with KPF-EP (74 %), the initial CEs of electrode using KFSI-EP was 78 %, which is higher than others.This result is attributed to the formation of thin and robust SEI layers using this type of electrolyte.Because of the higher CE, our electrode using this type of electrolyte is helpful for increasing the utilization rate of the cathode in the full battery. [37] Compared with KPF-EP (74 %), the initial CEs of electrode using KFSI-EP was 78 %, which is higher than others.This result is attributed to the formation of thin and robust SEI layers using this type of electrolyte.Because of the higher CE, our electrode using this type of electrolyte is helpful for increasing the utilization rate of the cathode in the full battery.…”

Calendar and Cycle Life of Lithium-Ion Batteries Containing Silicon Monoxide Anode

“…The SEI forming reactions usually happen at >0.7V (∼0.9 V for FEC reduction and ∼0.7-0.8V for EC reduction). 19,20 The OCV of SiO anode is ∼0.55 V. Therefore a reasonable explanation to this phenomenon is that the reactions are already mass transport controlled, and not kinetically controlled.…”

Structural Study of Electrochemically Lithiated Si(111) by using Soft X‐ray Emission Spectroscopy Combined with Scanning Electron Microscopy and through X‐ray Diffraction Measurements

“…Figure a shows a typical cyclic voltammogram of the Si(111) electrode measured in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solution (1:1 v/v %) containing 1 m LiPF 6 , when the potential was scanned between 2.4 V (vs. Li/Li + ), that is, the open‐circuit potential, and 0.01 V at a scan rate of 1 mV s −1 . In the cathodic scan, a small peak attributed to solid electrolyte interphase (SEI) formation was observed around 1.4 V and a current corresponding to lithiation of Si started to flow at approximately 0.08 V. In the anodic scan, broad peaks corresponding to the delithiation of Si were observed at 0.30 and 0.50 V. Figure b shows the time profiles of current density and potential, when the potential was scanned from 2.4 to 0.01 V and the potential was maintained for 1 h. When the potential was kept at 0.01 V, the cathodic current corresponding to lithiation of Si increased, reached a maximum, gradually decreased, and then became constant at approximately −0.1 mA cm −2 . For the preparation of the EC‐LiSi sample, the electrode was disconnected just after 1 h, as indicated by arrow (x) in Figure b.…”