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The mechanism for the performance enhancement of lithium metal electrodes by fluoroethylene carbonate (FEC) is revealed. Electrolytes containing FEC, 1.2 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7, vol) with 10% FEC (mass %) and 1.2 M LiPF6 in FEC, improve the electrochemical performance of both Li∥Li and Cu∥LiFePO4 cells compared to the baseline electrolyte, 1.2 M LiPF6 in EC:EMC (3:7, vol). Ex situ surface analysis of lithium metal electrodes after the initial plating demonstrates that the solid electrolyte interphase (SEI) generated from FEC containing electrolytes is similar to the SEI generated from the baseline electrolyte, yet the corresponding Coulombic efficiencies are markedly different. Electron microscopy investigations reveal the presence of a unique SEI containing nanostructured LiF particles for the lithium electrode plated from the 1.2 M LiPF6 in FEC electrolyte. The presence of the nanostructured LiF particles correlate with the improved cycling performance, sugg...

Citric acid and its analogues have been investigated as surface-modifying agents for Si nanoparticle anodes using electrochemical cycling, attenuated total reflectance infrared (ATR IR), and X-ray photoelectron spectroscopy (XPS). A Si nanoparticle anode prepared with citric acid (CA) has better capacity retention than one containing 1,2,3,4-butanetetracarboxylic acid (BA), but both electrodes outperform Si-PVDF. The Si-CA anode has an initial specific capacity of 3530 mA h/g and a first cycle efficiency of 82%. Surprisingly, the Si-CA electrode maintains a high specific capacity of ∼2200 mA h/g after 250 cycles, corresponding to 64% capacity retention, which is similar to the Si prepared with long-chain poly(acrylic acid) (PAA). On the contrary, the silicon electrode prepared with PVDF has a fast capacity fade and retains only 980 mA h/g after 50 cycles. The IR and XPS data show that the Si-CA electrode has an SEI composed primarily of lithium citrate during the first 50 cycles, resulting from the electrochemical reduction of citric acid. Only low concentrations of electrolyte reduction products are observed. The lithium citrate layer derived from CA stabilizes the silicon surface and suppresses electrolyte reduction, which likely contributes to the enhanced cycling performance of the Si nanoparticle anode.

A novel polyimide has been investigated as a conductive binder for silicon electrodes. The electrochemical properties of a polyimide electrode, derived from pyromellitic dianhydride and 4,4′-oxydianiline, were characterized and the feasibility as a binder for silicon electrodes was investigated. When fully lithiated and delithiated (3 V–5 mV), the polyimide electrode demonstrates a large reversible capacity of 826 mAh g−1 in the first cycle. The ex situ IR spectra indicate that the carbonyl groups on imide rings are irreversibly reduced during earlier period of first lithiation. Further lithiation leads to removal of characteristic peaks of PO–PI as well as a significant decrease of peak intensities, which implies changes in chemical structure of the host material. Nevertheless, the PO–PI electrode delivers large reversible capacity in subsequent cycles. In the potential range that silicon operates (0.7 V–5 mV), the polyimide electrode remains in a highly lithiated state maintaining its electric conductivity. Silicon electrodes with polyimide binder exhibit superior capacity retention and coulombic efficiency in comparison to electrodes using insulating binders. The improvements are attributed to the reinforced electrical conductive network in the electrode laminate.

Methylene ethylene carbonate (MEC) has been investigated as an alternative additive to fluoroethylene carbonate (FEC) for Si nanoparticle anodes cycled with 1.2 M LiPF6/ethylene carbonate (EC): diethyl carbonate (DEC) (1:1, w/w) electrolyte. The Si electrodes cycled with 10% MEC-added electrolyte exhibit significantly improved capacity retention after 100 cycles compared to standard electrolyte (73% vs 46%). In addition, the Si electrode cycled with MEC additive has less damage from cracking than the standard electrolyte. Ex situ surface analyses via infrared and X-ray photoelectron spectroscopy reveal a solid electrolyte interphase (SEI) containing a high concentration of a poly(MEC), which is likely responsible for the improved performance of Si anodes. Keywords: Silicon anode, Electrolyte additive, Methylene ethylene carbonate, Solid electrolyte interphase, Surface analysis

Binder-free silicon (BF-Si) nanoparticle anodes were cycled with 1.2 M LiPF6 in ethylene carbonate (EC), fluoroethylene carbonate (FEC), or EC with 15% FEC (EC:FEC), extracted from cells and analyzed by Hard X-ray Photoelectron Spectroscopy (HAXPES). All of the electrolytes generate an SEI which is integrated with Si containing species. The EC and EC:FEC electrolytes result in the generation of LixSiOy after the first cycle while LixSiOy is only observed after five cycles for the FEC electrolyte. The SEI initially generated from the EC electrolyte is primarily composed of lithium ethylene dicarbonate (LEDC) and LiF. However, after five cycles, the composition changes, especially near the surface of silicon because of decomposition of the LEDC. The SEI generated from the EC:FEC electrolytes contains LEDC, LiF, and poly(FEC) and small changes are observed upon additional cycling. The SEI generated with the FEC electrolyte contains LiF and poly(FEC) and small changes are observed upon additional cycling. The stability of the SEI correlates with the observed capacity retention of the cells.

The cycling performance and SEI composition of Si nano-particle anodes in electrolytes containing 5–25 wt% fluoroethyelene carbonate (FEC) and 3–6 wt% vinylene carbonate (VC) has been investigated by a combination of by electrochemical cycling, electrochemical impedance spectroscopy, IR-ATR and XPS. The incorporation of FEC or VC changes the cycling performance, impedance, electrode morphology, and SEI structure of Si nano-particle electrodes. Cells cycled with standard carbonate electrolytes have poor capacity retention and the anode surface is primarily covered by lithium alkyl carbonates and lithium carbonate. The electrodes cycled in electrolyte containing 10–15 wt% FEC have the smallest impedance and best capacity retention. The reduction of electrolyte containing FEC forms a stable SEI consisting of poly(FEC), LiF, lithium carbonate and lithium alkyl carbonates. Reduction of electrolytes containing VC results in higher impedance and the generation of lithium carbonate, poly(VC) and traces of LiF, and lithium alkyl carbonates.

We present the first report on carbon fiber-interwoven amorphous nano-SiOx/graphene prepared by a simple and facile room temperature synthesis of amorphous SiOx nanoparticles using silica, followed by their homogeneous dispersion with graphene nanosheets and carbon fibers in room temperature aqueous solution. Transmission and scanning electron microscopic imaging reveal that amorphous SiOx primary nanoparticles are 20-30 nm in diameter and carbon fibers are interwoven throughout the secondary particles of 200-300 nm, connecting SiOx nanoparticles and graphene nanosheets. Carbon fiber-interwoven nano-SiO0.37/graphene electrode exhibits impressive cycling performance and rate-capability up to 5C when evaluated as a rechargeable lithium battery anode, delivering discharge capacities of 1579-1263 mAhg(-1) at the C/5 rate with capacity retention of 80% and Coulombic efficiencies of 99% over 50 cycles, and nearly sustained microstructure. The cycling performance is attributed to synergetic effects of amorphous nano-SiOx, strain-tolerant robust microstructure with maintained particle connectivity and enhanced electrical conductivity.

Lithium diffusivity of the silicon (Si)-based materials of Si-Cu and SiO x (x = 0.4, 0.85) withimproved interfacial stability to electrolyte have been determined, using variable rate cyclic vol-tammetry with film model electrodes. Lithium diffusivity is found to depend on the intrinsic prop-erties of anode material and electrolyte; the fraction of oxygen for SiO x (x = 0.4, 0.85), which isdirectly related to electrical conductivity, and the electrolyte type with different ionic conductivityand viscosity, carbonate-based liquid electrolyte or ionic liquid-based electrolyte, affect the lithiumdiffusivity. Keywords : Rechargeable lithium batteries, Si-based anode, Lithium diffusivity, Film model electrode ( Received September 23, 2013 : Accepted October 7, 2013) 1. Introduction There is an increasing need of high-energyrechargeable lithium batteries for their applications toelectric vehicles and stationary energy storage gridsystems. This represents the development need ofhigher capacity anode materials, and higher capacityand higher voltage cathode materials with a stablecycling ability and safer characteristics than the con-ventional ones.

Film model electrodes of silicon oxide (SiOx) with various oxygen content (x = 0.4, 0.85, 1.0 and 1.3) have been studied for the effects of oxygen content and interfacial reaction behavior on cycling ability. IR and XPS analyses on the origin of initial charge plateau in 1M LiPF6/EC:DEC indicate that the contribution of electrolyte reduction to the plateau is far larger than the formation of lithium silicates, lithium oxide and silicon. Higher oxygen content of SiOx induces to decrease initial electrolyte reduction, whereas larger fraction of oxides is subjected to dissolution by acid (e.g., HF)-etching. Cycling ability at higher oxygen content however is remarkably improved when constructing a surface protective siloxane network at the electrodes using silane electrolyte additive. The SiO1.0 electrode exhibits superior capacity retention of 84% at the 200th cycle delivering discharge capacity of 1206–1017 mAh/g. The SEI layer formed over surface siloxane network consists of a plenty of organic compounds and lithium carbonate, in contrast to mainly inorganic salts and organic phosphorus fluoride compounds upon cycling without silane adidtive. A better protection and passivation of electrode surface should be of the effects of siloxane network, and in that fashion cycling ability is greatly stabilized.

The effects of different binders, polyvinylidene difluoride (PVdF), poly(acrylic acid) (PAA), sodium carboxymethyl cellulose (CMC), and cross-linked PAA-CMC (c-PAA-CMC), on the cycling performance and solid electrolyte interphase (SEI) formation on silicon nanoparticle electrodes have been investigated. Electrodes composed of Si-PAA, Si-CMC, and Si-PAA-CMC exhibit a specific capacity ≥3000 mAh/g after 20 cycles while Si-PVdF electrodes have a rapid capacity fade to 1000 mAh/g after just 10 cycles. Infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) reveal that PAA and CMC react with the surface of the Si nanoparticles during electrode fabrication. The fresh Si-CMC electrode has a thicker surface coating of SiOx than Si-PAA and Si-PAA-CMC electrodes, due to the formation of thicker SiOx during electrode preparation, which leads to lower cyclability. The carboxylic acid functional groups of the PAA binder are reactive toward the electrolyte, causing the decomposition of LiPF6 and dissolution of SiOx during the electrode wetting process. The PAA and CMC binder surface films are then electrochemically reduced during the first cycle to form a protective layer on Si. This layer effectively suppresses the decomposition of carbonate solvents during cycling resulting in a thin SEI. On the contrary, the Si-PVDF electrode has poor cycling performance and continuous reduction of carbonate solvents is observed resulting in the generation of a thicker SEI. Interestingly, the Lewis basic -CO2Na of CMC was found to scavenge HF in electrolyte.

Siloxane-capped amorphous nano-SiOx/graphite was prepared by simple reduction and self-organization, and facile particle dispersion. 92% capacity retention of the composite anode is ascribed to effective accommodation of the volume change, and uniform distribution of SiOx on the graphite matrix.

The authors of the above-mentioned article would like to state that on page 3031, in the later part of Section 3.3, Cyclic voltammetry, n error in the calculation of lithium diffusivity has been uncovered. For obtaining the slope of Ip vs. 1/2, current density was used, which as wrong. According to Randles-Sevcic equation, current, not current density had to be used. The corrected text is provided below: The slope of Ip vs. 1/2 was used for the preliminary calculation of diffusivity [30] assuming that the anodic peak current corresponds o the removal of 2.33 Li+ ions from Li2.33Si, and using the theoretical molar volume of Li2.33Si [31]. The determined diffusivity was .35 × 10−13 cm2/s. This value is approximately three orders lower than ∼1.12 × 10−10 cm2/s of graphite powder electrode for the formation f LiC6 [32]. The authors would like to apologize for any inconvenience caused.

Control of electrode–electrolyte interfacial stability and the composition of the solid electrolyte interphase (SEI) layer is a promising approach for improved cycling performance of silicon-based anode material for rechargeable lithium batteries. Here we demonstrate that a room temperature ionic liquid electrolyte effectively passivates the surface of the SiO1.3 electrode and significantly enhances cycling ability in contrast to the commercial liquid electrolyte. The SiO1.3 electrode, prepared by pulsed laser deposition, showed 88% capacity retention in the ionic liquid electrolyte of 1 M LiTFSI/Py13TFSI delivering 1058–930 mA h g−1 over 200 cycles. Results from infrared and X-ray photoelectron spectroscopic analyses suggest that the presence of organic SEI compounds consisting of the pyrrolidinium cation and TFSI anion and their decomposition products on the oxygen-abundant SiO1.3 surface confers interfacial stability and cycling stability.