Search

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...

Propylene carbonate (PC) is an electrolyte co-solvent with a wide working temperature range, which can improve the performance of lithium ion batteries (LIBs). Unfortunately, PC co-intercalates into graphite with lithium ions leading to exfoliation and rapid capacity decay. Incorporation of low concentrations of Cs + or K + ions as additives improves the performance by inhibiting graphite exfoliation and leading to better first cycle efficiency. The electrochemical behavior of graphite anodes with a series of electrolytes containing added alkaline metal acetate salts, Li, Na, K, and Cs, has been investigated. Cells containing K and Cs acetate have the highest first cycle efficiency and reversible cycling capacity. In an effort to better understand the role of the cation on performance, the solid electrolyte interphase (SEI) on the graphitic anodes cycled with the different electrolytes has been investigated via a combination of X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Infrared Spectroscopy (ATR-IR), Transmission electron microscopy (TEM) and Inductive coupled plasma mass spectrometry (ICP-MS). The presence of the heavier cations (K and Cs) leads to a thinner SEI with higher LiF content which is likely responsible for the performance enhancement.

The electrochemical performance of hard carbon (HC)/Na cells with NaPF 6 in a mixture of EC/DEC (1:2, v/v) has been investigated in the voltage range of 0.05–2 V. An initial reversible capacity of 162 mAh g − 1 is observed. With continuous cycling, the reversible capacities fluctuate slightly and obtain a value of 183 mAh g − 1 on the 25th cycle. Ex-situ surface analysis of cycled HC electrodes has been conducted by a combination of scanning electron microscopy (SEM), infrared spectroscopy with attenuated total reflectance (IR-ATR) and X-ray photoelectron spectroscopy (XPS). The ex-situ surface analysis suggests that the major composition of solid electrolyte interphase (SEI) formed on the surface of HC electrode is sodium ethylene dicarbonate (SEDC) and NaF with lower concentrations of sodium alkyl carbonates and Na 2 CO 3 which is similar with that reported in lithium ion batteries.

International audience; Bacteria tumble periodically, following environmental cues. Whether they can tumble near a solid surface is a basic issue for the inception of infection or mineral biofouling. Observing freely swimming Escherichia coli near and parallel to a glass surface imaged at high magnification (Â100) and high temporal resolution (500 Hz), we identified tumbles as events starting (or finishing, respectively) in abrupt deceleration (or reacceleration, respectively) of the body motion. Selected events show an equiprobable clockwise (CW) or counterclockwise change in direction that is superimposed on a surface CW path because of persistent propulsion. These tumbles follow a common long (about 300 5 100 ms, N ¼ 52) deceleration-reorientation acceleration pattern. A wavelet transform multiscale analysis shows these tumbles cause in-plane diffusive reorientations with 1.5 rad 2 /s rotational diffusivity, a value that compares with that measured in bulk tumbles. In half of the cases, additional few-millisecond bursts of an almost equiprobable CW or counterclockwise change of direction (12 5 90 , N ¼ 89) occur within the reorientation stage. The highly dispersed absolute values of change of direction (70 5 66 , N ¼ 89) of only a few bursts destabilize the cell-swimming direction. These first observations of surface tumbles set a foundation for statistical models of run-and-tumble surface motion different from that in bulk and lend support for chemotaxis near solid surface.

The structure and composition of lithium ion solvation spheres of electrolyte solutions composed of common lithium salts (LiTFSI, LiPF6, LiBF4, and LiClO4) dissolved in aprotic polar linear and cyclic carbonate solvents (propylene carbonate (PC) or dimethyl carbonate (DMC)) have been investigated via a combination of FTIR, 13C NMR spectroscopy, and density functional theory (DFT). Results from the two different spectroscopic methods are in strong agreement with each other and with predictions from quantum chemistry calculations. The coordination of the carbonyl oxygen of the solvents to the lithium cation is observed by IR spectroscopy. The ratio of coordinated to uncoordinated PC and DMC has been used to determine solvent coordination numbers which range from 2 to 5 depending on salt, solvent, and concentration. The relative stability of the lithium–anion solvates were examined using DFT employing the cluster-continuum approach including changes to the intensity and frequency of the IR bands along with t...

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 of Si-nanoparticle/Li cells with different electrolytes has been investigated. Cells containing standard binary LiPF6/ethylene carbonate/ethyl methyl carbonate electrolytes have poor capacity retention (46 %) after 50 cycles. Cells cycled with fluoroethylene carbonate (FEC)-based electrolyte have much better capacity retention (74 %). The effect of incorporation of flame-retardant co-solvents triphenyl phosphate and dime- thyl methylphosphonate was investigated with both the standard and FEC electrolytes. The incorporation of the FR co-solvents did not significantly alter the performance of either electrolyte. Ex situ analysis via scanning electron microscopy, attenuated total reflectance infrared spec- troscopy, and X-ray photoelectron spectroscopy was con- ducted to gain a better understanding of the role of electrolyte in solid electrolyte interphase structure and stability.

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.

Control of electrode–electrolyte interfacial reactivity and the formation of the solid electrolyte interphase (SEI) layer is a key technology for high performance rechargeable lithium batteries. Here we present the first report on a promising interfacial approach for Sn–Ni electrode that the use of acid-resisting and -scavenging fluorine-dopant on Sn combined with acid-scavenging trimethyl phosphite electrolyte additive to LiPF6-contiaing carbonate-based organic electrolyte improves the interfacial stability of Sn to acidic electrolyte species. As a result, a stable SEI layer consisting of a plenty of carbonate decomposition products forms and cycling ability significantly improves, in contrast to less efficient SEI formation and rapid performance fade for the electrodes without fluorine-dopant or trimethyl phosphite additive.

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.

/EC:EMC. SEM imaging reveals that the facetting on higher surface energy plane of (101) is additionallydeveloped at the edges of an octahedron that is predominantly grown with the most thermodynamically stable(111) plane, which enhances interfacial reactivity. Fluorine-doping also increases the amount of interfaciallyreactive Mn

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.

cathodes upon oxidation of electrolyte during electrochemicalcycling was investigated. Information on the important factors for film formation on the cathode can facilitatethe design of additives that improve the properties of the cathode. Pyrazole is added to the electrolyte becauseit is readily oxidized to form a surface film on the cathode. The results of differential scanning calorimetry andFourier transform infrared spectroscopy (FTIR) showed that the active material played a dominant role in theinterfacial film formation with the electrolyte. Carbon black played a negligible role in the surface filmformation. Key Words : Li-ion battery, Li(Ni

Interfacial compatibility between the Si-Cu electrode and diluted ionic liquid electrolyte containing 50 vol.% of 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide (MPP-TFSI) and 50 vol.% dimethyl carbonate (DMC) in a lithium cell and dilution effect on surface chemistry are examined. ex-situ ATR FTIR analysis results reveal that the surface of the Si-Cu electrode cycled in the diluted ionic liquid electrolyte is effectively passivated with the SEI layer mainly composed of carboxylate salts-containing polymeric compounds produced by the decomposition of DMC. Surface species by the decomposition of TFSI anion and MPP cation are found to be relatively in a very low concentration level. Passivation of electrode surface with the SEI species contributes to protect from further interfacial reactions and to preserve the electrode structure over 200 cycles, delivering discharge capacity of > 1670 and capacity retention of 88% of maximum discharge capacity.

Silane-based self-assembly was employed for the surface modification of carbon-coated Si electrodes and their surface chemistry and electrochemical performance in battery electrolyte depending on the molecular structure of silanes was studied. IR spectroscopic analyses revealed that siloxane formed from silane-based self-assembly possessed Si-O-Si network on the electrode surface and high surface coverage siloxane induced the formation of a stable solid-electrolyte interphase (SEI) layer that was mainly composed of organic compounds with alkyl and carboxylate metal salt functionalities, and PF-containing inorganic species. Scanning electron microscopy imaging showed that particle cracking were effectively reduced on the carbon-coated Si when having high coverage siloxane and thickened SEI layer, delivering > 1480 mAh/g over 200 cycles with enhanced capacity retention 74% of the maximum discharge capacity, in contrast to a rapid capacity fade with low coverage siloxane.

Among advanced materials studied to enhance the performance and energy storage of Li ion batteries, silicon nanoparticles have shown great potential as an anode material with its high theoretical gravimetric capacity of approximately 4200 mAh/g which is ~10 times higher than that of the commercially used anode material graphite. Nevertheless, the volume expansion of ~400% during the lithiation causes the electrode to suffer from rapid degradation, thus leading to poor cycle life. In this study we discuss the surface modification of silicon nanoparticles with citric acid for better cycling performance and capacity retention of silicon based electrodes. The objective of the study is to form a protective layer on silicon nanoparticles that will reduce the strain caused by volume variation due to lithiation and delithiation in the cycling process. Cycling performance studies have been conducted on 50% silicon containing electrodes as well as graphite silicon composite electrode (70:15 weight % respectively). Both types of electrodes have shown promising cycling performance data when the surface of was functionalized with citric acid. The results indicate good capacity retention of ~60% after 50 cycles from surface modified silicon electrodes as opposed to 45% with the surface unmodified electrode. Chemical and surface analytical techniques such as Fourier transformation infrared spectroscopy(FTIR), Xray photoelectron spectroscopy (XPS), hard x-ray photoelectron spectroscopy (HAXPES), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), electrochemical impedance spectroscopy was used to analyze the nanoparticle surface as well as the solid electrolyte interphase formed on the electrodes to further understand how this protective layer improve the performance and the results of this study will be discussed. Figure 1

Interfacial structures of electrode–current collector and electrode–electrolyte have been designed to be stabilized for improved cycling performance of amorphous silicon (Si) that is considered as an alternative anode material to graphite for lithium-ion batteries. Interfacial structural stabilization involves the interdigitation of Si electrode–Cu current collector substrate by anodic Cu etching with thiol-induced self-assembly, and the formation of self-assembled siloxane on the surface of Si electrode using silane. The novel interfacial architecture possesses promoted interfacial contact area between Si and Cu, and a surface protective layer of siloxane that suppresses interfacial reactions with the electrolyte of 1 M LiPF6/ethylene carbonate (EC):diethylene carbondate (DEC). FTIR spectroscopic analyses revealed that a stable solid electrolyte interphase (SEI) layer composed of lithium carbonate, organic compounds with carboxylate metal salt and ester functionalities, and PF-containing species formed when having siloxane on Si electrode. Interfacially stabilized Si electrode exhibited a high capacity retention 80% of the maximum discharge capacity after 200 cycles between 0.1 and 1.5 V vs. Li/Li+. The data contribute to a basic understanding of interfacial structural causes responsible for the cycling performance of Si-based alloy anodes in lithium-ion batteries.

Formation of the SEI layer on Si–Cu film electrode in the ionic liquid electrolyte of 1 M lithium bis(trifluoromethylsulfonyl)imide/1-methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide (LiTFSI/MPP-TFSI) was investigated using ex-situ ATR FTIR and X-ray photoelectron spectroscopy. The SEI layer is found to be composed of organic and inorganic compounds that are the decomposition products of MPP cation and TFSI anion, and effectively passivate the electrode surface during initial cycling. Formation of a stable SEI layer leads to an excellent capacity retention 98% of the maximum discharge capacity, delivering discharge capacities of >1620 mAhg−1 over 200 cycles. The data contribute to a basic understanding of SEI formation and composition responsible for the cycling performance of Si-based alloy anodes in ionic liquid electrolyte-based rechargeable lithium batteries. Keywords: Rechargeable lithium batteries, Si-based anode, Ionic liquid electrolyte, SEI layer

Silicon is one of the most promising anode materials because of its high theoretical capacity of 3579 mAh/g at room temperature which is ten times higher than graphite, a common anode currently used in commercial lithium ion batteries.1 However, Si has poor cycle life because of the massive volume change during cycling followed by the pulverization of active particles and the loss of electrical contact within electrode components. 1 Binder, usually long-chain polymers, are important electrode components that help to hold particles together and to current collector. Poly(vinylidene fluoride) (PVdF) has been widely used as binder in lithium ion batteries due to its good electrochemical and thermal stability and good adhesion to electrode material and current collector.2 The performance of Si with PVdF, however, has been reported to be poor.2 Recently, the cycle life of Si was greatly improved by using binders which contains a large quantity of –OH and –COOH such as sodium carboxymethylcellulose (CMC),2 poly(acrylic acid) (PAA).3 The formation of covalent bond and/or strong interaction of hydrogen bonds between silicon particles and binders are believed the reason for the improvement.4,5 However, there is no report on using small molecule carboxylic acids as binders in lithium ion batteries. In this study, Si electrode has been prepared with silicon nanoparticles (≤50nm), conductive carbon and carboxylic acids with ratio of 50:25:25. The Si electrode with PVDF binder was also prepared for comparison. The Si anodes were then evaluated in half cells with lithium metal as current collector and reference electrodes in 1.2M LiPF6/Ethylene carbonate (EC) : Dimethyl carbonate (DEC) without and with 10 wt.% additive. In the absence of additive, Si electrode with carboxylic acids show very high first cycle specific capacity and efficiency, ~3500 mAg/g and 79%, respectively. After 30 cycles, the electrode still maintains a capacity > 1500 mAh/g. On contrary, Si electrode with PVDF binder shows a low first discharge capacity and efficiency: 1700 mAh/g and ~60%, respectively. Furthermore, the capacity fades rapidly after first cycle. The dramatic improvement cycling performance of silicon NP electrodes with carboxylic acids over PVdF are believed due to the interaction of carboxylic acids with silicon particles. We will further discuss effects of carboxylic acids for enhancing cyclability of silicion nanoparticle anode in the meeting. Acknowledgement The authors gratefully acknowledge funding from Department of Energy Office of Basic Energy Sciences EPSCoR Implementation award (DE-SC0007074) Reference 1. M. N. Obrovac and L. Christensen, Electrochem. Solid-State Lett., 7, A93 (2004). 2. H. Buqa, M. Holzapfel, F. Krumeich, C. Veit, and P. Novák, J. Power Sources, 161, 617–622 (2006). 3. A. Magasinski, B. Zdyrko, I. Kovalenko, B. Hertzberg, R. Burtovyy, C. F. Huebner, T. F. Fuller, I. Luzinov, and G. Yushin, ACS Appl. Mater. Interfaces, 2, 3004–3010 (2010). 4. N. S. Hochgatterer, M. R. Schweiger, S. Koller, P. R. Raimann, T. Wöhrle, C. Wurm, and M. Winter, Electrochem. Solid-State Lett., 11, A76–A76 (2008). 5. J.-S. S. Bridel, T. Azaı, M. Morcrette, J.-M. M. Tarascon, D. Larcher, and T. Azaïs, Chem. Mater., 22, 1229–1241 (2010).

Silicon, due to its large specific capacity, is regarded as one of the most promising negative electrode materials for lithium ion batteries despite critical drawbacks associated with large volume change upon lithiation/de-lithiation. Although nano-sized silicon particles have been employed to mitigate the failures and related techniques have achieved considerable improvements, current materials do not meet the demand of commercial applications. Thus, a systematical approach to elucidating failure mechanisms is necessary to further improve electrochemical performances of the silicon electrode. Here, the evolution of voltage profiles recorded during cycling was thoroughly analyzed and thereby the failure mechanisms are proposed. The main failure mechanism of the silicon electrode is related to an inability to fully de-lithiate due to resistance increases during discharging, which are mostly contact and SEI resistance. The capacity retention was significantly improved by lowering discharge cut-off voltage and by introducing electrolyte additives, in which reduce the resistances during discharging.

The surface reactions of electrolytes with a silicon anode in lithium ion cells have been investigated. The investigation utilizes two novel techniques that are enabled by the use of binder-free silicon (BF-Si) nanoparticle anodes. The first method, transmission electron microscopy with energyndispersive X-ray spectroscopy, allows straightforward analysis of the BF-Si solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Coin cells (BF-Si/Li) were cycled in electrolytes containing LiPF6 salt and ethylene carbonate or fluoroethylene carbonate solvent. Capacity retention was significantly better for cells cycled with LiPF6/FEC electrolyte than for cells cycled with LiPF6/EC electrolyte. Our unique combination of techniques establishes that for LiPF6/EC electrolyte the BF-Si SEI continuously grows during the first 20 cycles and the SEI becomes integrated with the BF-Si nanoparticles. The SEI predominantly contains lithium ethylene dicarbonate, LiF, and LixSiOy. BF-Si electrodes cycled with LiPF6/FEC electrolyte have a different behavior; the BF-Si nanoparticles remain relatively distinct from the SEI. The SEI predominantly contains LiF, LixSiOy, and an insoluble polymeric species. The depth dependence of structure of the SEI was further investigated by Hard X-ray photoelectron spectroscopy (HAXPES). Finally, the effect of different binders including PVDF, CMC, and PAA on the surface of silicon nanoparticles and on the structure of the SEI will be discussed. We gratefully acknowledge funding from Department of Energy office of Basic Energy Sciences EPSCoR Implementation award (DE-SC0007074).

Silicon is one of the most promising candidates for an anode material in LIBs due to the high theoretical capacity, 3580 mAh/g. This theoretical capacity is ~10 times that of commercial graphite (372 mAh/g) currently used in lithium ion batteries. However the silicon electrodes have a very large volume expansion (300–400%) during lithiation resulting in instability of the solid electrolyte interphase (SEI) and poor capacity retention. The two most frequently utilized SEI stabilizing additives are vinylene carbonate (VC) and fluoroethylene carbonate (FEC). A systematic comparison of the effects of added FEC or VC at multiple concentrations is being conducted with uniform silicon nano-particle electrodes. Capacity retention of Li/silicon nano-particle cells with different concentrations of VC and FEC in 1.2 M LiPF6 in 1:1 EC/DEC have been investigated. The capacity fades very rapidly for the baseline electrolyte. Incorporation of FEC at any of the concentrations investigated (5, 10, 15, or 25 %) results in significant improvements in capacity retention. Interestingly, intermediate concentrations of FEC 10-15 % give the best capacity retention suggesting that lower concentrations do not generate a sufficiently stable SEI while higher concentrations may results in increased cell resistance. Cells containing added VC do not have significantly better performance than the cells containing the baseline electrolyte. Incorporation of 3 % VC results in cells with very similar capacity fade to the baseline electrolyte, while cells containing 6 % VC have an odd intermittent behavior which may be due to high cell impedance as evidenced by electrochemical impedance spectroscopy. The cycling efficiencies correlate very well with the capacity retention. Cells containing 10-15 % FEC have the best efficiencies (~99 % for cycles 10-50), while cells containing the baseline electrolyte or electrolyte with added VC have lower efficiencies ( Ex-situ surface analysis of the electrodes after cycling via a combination of SEM, XPS and FT-IR will be reported. Structural characterization of the SEI will lead to a better understanding of the source of performance enhancement due to the incorporation of added FEC. Acknowledgements This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No 6879235 under the Batteries for Advanced Transportation Technologies (BATT) Program.

Carbon composites of silicon (Si), silicon monoxide (SiO) or silicon suboxide (SiO x ) are considered as alternative anode materials to graphite for rechargeable lithium batteries, due to the high theoretical capacity of 3579 mAh/g for Si at room temperature and safer operation voltage above lithium. The Si, however, suffers from capacity fade due to large volume change upon lithiation and delithiation during cycling. This leads to electrochemical and mechanical particle disintegration. SiO and SiO x are favored with respect to cycling stability despite sacrificing the capacity, as lithium oxide (Li2O) and lithium silicates formed during initial lithiation better accommodates significant volume change of Si.Interfacial processes for Si anode with LiPF6-containing electrolyte, which is another cause for particle disintegration and performance fade, have been established as LiPF6 decompose and produce Lewis acids (PF5, PF3O) and HF (LiPF6 → LiF + PF5; PF5 + H2O → PF3O + 2HF) that can undergo electrophilic attack to the surface of Si anode and participate in electrochemical reduction leading to Si deactivation. This restricts the formation of a stable SEI and charge-discharge cycling stability. Extensive research efforts have been made to improve interfacial stability and cycling performance of SiOx-based carbon composite.We have been developing a new synthetic method and mechanistic investigation of surface-protected SiO x , (x < 0.5) nanoparticles and their carbon composites for attaining stabilized electrode performance. Here we report a facile preparation, and material and electrochemical characterization of amorphous nano-SiO x and its graphite composite with homogeneous compositional distribution. Artificial SEI-capped SiO x nanoparticles were synthesized by a chemical reduction of silicon tetrachloride and in-situ capping with a surface protective hydrophobic layer. The hydrophobic surface nature led to an easy and homogeneous dispersion of SiO x nanoparticles with graphite powders in n-methylpyrrolidinone (NMP) just by room temperature mixing for the preparation of slurry. Artificial SEI-capped nano-SiO x /graphite (50:50 wt%) electrodes consisted of the active material (70 wt%), carbon black (15 wt%) and binder (15 wt%) were fabricated onto a copper foil, followed by vacuum drying at 110 °C overnight. Cycling ability of the composite electrode was evaluated using coin half-cell cells with a lithium foil as a counter electrode and the baseline electrolyte of 1M LiPF6/EC:EMC (3:7 volume ratio) or that with a new carbonate-based solvent, and polyethylene separator, between 0.01 to 1.5 V at a constant current density of 300 mA/g (~0.3C). SEM and elemental mapping images (Figure 1A) of nano-SiOx/graphite reveal a uniform distribution of carbon (green) and silicon (red) atoms over bulk composite. Large micron carbon particles are of graphite and relatively small ones are of carbon black, respectively. Figure 1B shows the voltage profiles of nano-SiO x /graphite electrode measured at 0.3C. The initial charge and discharge capacity are 1370 and 1010 mAh/g, respectively, resulting in the initial coulombic efficiency of 74 %. Coulombic efficiency increases to higher than 98 % after the fifth cycle. Discharge capacity is retained as 931 mAh/g after 100 cycles (Figure 1C), corresponding to capacity retention of 91%. The excellent cycling stability is ascribed to homogenous dispersion of SiO x and graphite powders, accommodation of volume change of SiO x by oxygen and graphite, and enhanced interfacial stability by artificial SEI. Further discussion of the high-rate capability, and the SEI formation and stability and their correlation to cycling performance would be presented in the meeting. Acknowledgments This work was supported partly by the Korean Ministry of Education and National Research Foundation through the Human Resource Training Project for Regional Innovation (2012026203) and partly by the Converging Research Center Program (2013K000214) through the Ministry of Science, ICT & Future Planning.

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.

not Available.

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.

not Available.

not Available.

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.

not Available.

not Available.

not Available.