Characterizing Solid Electrolyte Interphase on Sn Anode in Lithium Ion Battery

Abstract

Tin (Sn) nanoparticle electrodes have been prepared and battery cycling performance has been investigated with 1.2 M LiPF 6 in ethylene carbonate (EC) / diethyl carbonate (DEC) electrolyte (1:1, w/w) with and without added vinylene carbonate (VC) or fluoroethylene carbonate (FEC). Incorporation of either VC or FEC improves the capacity retention of Sn nanoparticle electrodes although incorporation of VC also results in a significant increase in cell impedance. The best electrochemical performance was observed with electrolyte containing 10% of added FEC. In order to develop a better understanding of the role of the electrolyte in capacity retention and solid electrolyte interface (SEI) structure, ex-situ surface analysis has been performed on cycled electrodes with infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Hard XPS (HAXPES). The ex-situ analysis reveals a correlation between electrochemical performance, electrolyte composition, and SEI structure. Graphite has been widely used as an anode material in lithium ion batteries. However, there is significant interest in increasing the energy density of lithium ion batteries for electric vehicle applications.1 One method of current interest for increasing the energy density of lithium ion batteries includes the use of high capacity metal alloy anode materials, such as silicon (Si) and tin (Sn).2-6 Sn has almost three times more capacity (944 mAh/g) than graphite (372 mAh/g). However, a major challenge for the use Sn as an anode material is the large volume expansion/contraction during lithium insertion and extraction. The large surface area changes result in damage to the anode solid electrolyte interface (SEI) and continuous decomposition of the electrolyte. There have been many investigations of novel fabrication methods for Sn-based anodes to mitigate the problems with the SEI due to the volume changes.2,7-9 However, few investigations have focused on developing a better understanding of SEI formation on Sn anodes. [10][11][12] In order to develop Sn anodes for lithium ion batteries, a better understanding of the structure and function of the SEI on Sn is required.In this investigation, Sn nanoparticle electrodes were prepared and tested with different electrolytes. A standard electrolyte composed of 1.2 M LiPF 6 in EC/DEC with and without 5 or 10% of the SEI film forming additives FEC or VC has been investigated for optimization of an electrolyte formulation for Sn electrodes. 13 The cells have been analyzed via electrochemical cycling and electrochemical impedance spectroscopy. In order to develop a better understanding of the role of the electrolyte in SEI formation and stability, the Sn nanoparticle electrodes were extracted from cells and ex-situ surface analysis with infrared with attenuated total reflectance (IR-ATR), X-ray photoelectron spectroscopy (XPS) and Hard XPS (HAXPES) was conducted. While IR-ATR and XPS are frequently utilized analytical techniques for the investigation of the SEI, 14 HAXPES has been less utilized due to...

Microsized Sn as Advanced Anodes in Glyme‐Based Electrolyte for Na‐Ion Batteries

“…[33] The proportion of C-C(H) peak at 285 eV increases prominently after long cycling: an indication of the formation of sodium alkoxides (RCH 2 ONa) groups as a result of reduction of DGME. [34] Note also the appearance of another peak at 290 eV corresponding to the formation of Na 2 CO 3 .…”

Mechanisms for Stable Solid Electrolyte Interphase Formation and Improved Cycling Stability of Tin‐Based Battery Anode in Fluoroethylene Carbonate‐Containing Electrolyte

“…While once the SEI layer forms by FEC, the SEI is hold at a limited thickness by inhibition of further electrolyte decomposition, with EC the SEI seems to thicken by a continuous electrolyte decomposition with cycling, which is similar phenomenon to the case of silicon . This phenomena and performance fade significantly intensified on bulk Sn‐based anode …”

“…Surface degradation can also occur by the dissolution of surface oxide by HF. The most explored approaches to improve the interfacial (SEI) stability have been the use of electrolyte additives, such as phosphite and fluoroethylene carbonate (FEC) but just few studies have focused on investigating the SEI formation on Sn‐based anode . Despite some improvement, challenges in the improvement of performance and SEI stability still remain.…”

“…Carbon‐ and polymeric binder‐free film model electrodes deposited on electronically conductive substrate, which otherwise are necessary for porous bulk electrodes, generally possess a strong adherence to the substrate and a robust structure, and can provide high‐quality spectroscopic signals and a precise characterization of the SEI composition, which gives clear insights into electrode–electrolyte interfacial processes and reaction mechanisms, and failure mechanisms . Our earlier works on Sn‐ and silicon‐based film model electrodes suggested that a fundamental understanding of the mechanisms for interfacial reaction and the SEI formation helped find a path towards the SEI stabilization and performance improvement of porous bulk electrode materials . In the past study, we observed that doping of a small fraction of fluorine (F) to Sn–Ni film electrode induced the positive charge on the electrode surface, which behaved as an F anion‐capturing agent from HF inhibiting a direct HF‐attack, and as a resistor against PF 5 and PF 3 O Lewis acids .…”

“…FEC has been widely used as an SEI forming agent for alloy anode, mostly silicon . It was recently demonstrated that FEC is an efficient alternative solvent to EC of the conventional electrolyte, enhancing the cycling performance of Sn‐ and silicon‐based anodes . However, reaction mechanisms such as at what voltage and how FEC reduction begins and proceeds, consequently how the SEI layer forms at the surface of Sn‐based anode, and why FEC‐derived SEI is stable remain not understood.…”