A direct comparison of the cathode–electrolyte interface (CEI) generated on high-voltage LiNi0.5Mn1.5O4 cathodes with three different lithium borate electrolyte additives, lithium bis(oxalato)borate (LiBOB), lithium 4-pyridyl trimethyl borate (LPTB), and lithium catechol dimethyl borate (LiCDMB), has been conducted. The lithium borate electrolyte additives have been previously reported to improve the capacity retention and efficiency of graphite/LiNi0.5Mn1.5O4 cells due to the formation of passivating CEI. Linear sweep voltammetry (LSV) suggests that incorporation of the lithium borates into 1.2 M LiPF6 in EC/EMC (3/7) electrolyte results in borate oxidation on the cathode surface at high potential. The reaction of the borates on the cathode surface leads to an increase in impedance as determined by electrochemical impedance spectroscopy (EIS), consistent with the formation of a cathode surface film. Ex-situ surface analysis of the electrode via a combination of SEM, TEM, IR-ATR, XPS, and high energy XPS (HAXPES) suggests that oxidation of all borate additives results in deposition of a passivation layer on the surface of LiNi0.5Mn1.5O4 which inhibits transition metal ion dissolution from the cathode. The passivation layer thickness increases as a function of additive structure LiCDMB > LPTB > LiBOB. The results suggest that the CEI thickness can be controlled by the structure and reactivity of the electrolyte additive.Keywords: additive; cathode−electrolyte interface (CEI); electrolyte; high energy XPS (HAXPES); lithium ion battery;

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 the populations of the cis–cis and cis–trans conformers of DMC in the lithium ion solvation shell. Solvent coordination is dependent upon the nature of the salt. Weakly associating salts, LiTFSI, LiPF6, and LiClO4, dissociate to a similar degree with LiPF6 being the most dissociated, while LiBF4 had significantly less dissociation in both solvents. This investigation provides significant insight into the solution structure of commonly used LIB electrolytes over a wide range of salt concentrations.

Thermal behavior of the solid electrolyte interphase (SEI) on a silicon electrode for lithium ion batteries has been investigated by TGA. In order to provide a better understanding of the thermal decomposition of the SEI on silicon, the thermal decomposition behavior of independently synthesized lithium ethylene dicarbonate (LEDC) was investigated as a model SEI. The model SEI (LEDC) has three stages of thermal decomposition. Over the temperature range of 50–300 °C, LEDC decomposes to evolve CO2 and C2H4 gases leaving lithium propionate (CH3CH2CO2Li) and Li2CO3 as solid residues. The lithium propionate decomposes over the temperature range of 300–600 °C to evolve pentanone leaving Li2CO3 as a residual solid. Finally, the Li2CO3 decomposes over 600 °C to evolve CO2 leaving Li2O as a residual solid. A very similar thermal decomposition process is observed for the SEI generated on cycled silicon electrodes. However, two additional thermal decomposition reactions were observed characteristic of LixPOyFz at 300 °C and the polyimide binder at 550 °C. TGA measurements of Si electrodes after various numbers of cycles suggest that the LEDC on Si electrodes thermally decomposes during cycling to form lithium propionate and Li2CO3, resulting in increased complexity of the SEI.

ZnCo2O4 nanocluster particles (NCPs) were prepared through a designed hydrothermal method, with the assistance of a surfactant, sodium dodecyl benzene sulfonate. The crystalline structure and surface morphology of ZnCo2O4 were investigated by XRD, XPS, SEM, TEM, and BET analyses. The results of SEM and TEM suggest a clear nanocluster particle structure of cubic ZnCo2O4 (~100 nm in diameter), which consists of aggregated primary nanoparticles (~10 nm in diameter), is achieved. The electrochemical behavior of synthesized ZnCo2O4 NCPs was investigated by galvanostatic discharge/charge measurements and cyclic voltammetry. The ZnCo2O4 NCPs exhibit a high reversible capacity of 700 mAh g−1 over 100 cycles under a current density of 100 mA g−1 with an excellent coulombic efficiency of 98.9% and a considerable cycling stability. This work demonstrates a facile technique designed to synthesize ZnCo2O4 NCPs which show great potential as anode materials for lithium ion batteries.

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.

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.

•Characterization of the solid electrolyte interphase for sodium ion batteries•Reduction product of ethylene carbonate is similar for sodium and lithium.•The structure and function of the solid electrolyte interphase is similar for lithium and sodium ion batteries.The electrochemical performance of hard carbon (HC)/Na cells with NaPF6 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 Na2CO3 which is similar with that reported in lithium ion batteries.

A novel series of lithium alkyl trimethyl borates and lithium aryl trimethyl borates have been prepared and investigated as cathode film forming additives. The borates are prepared via the reaction of lithium alkoxides or lithium phenoxides with trimethyl borate. Incorporation of 0.5–2.0% (wt) of the lithium borates to a baseline electrolyte (1.0 M LiPF6 in 3:7 (EC/EMC)) results in improved capacity retention and efficiency of high voltage graphite/LiNi0.5Mn1.5O4 cells especially upon cycling at elevated temperature (55 °C). The improved performance results from the sacrificial oxidation of the lithium borate on the cathode surface to generate a cathode passivation film. The lithium borates can be readily structurally modified to act as a functional group delivery agent to modify the cathode surface. Ex situ surface analysis of the electrodes after cycling confirms that the lithium borates modify the cathode surface and generate a borate rich surface film which inhibits electrolyte oxidation and Mn dissolution.

We have synthesized the products of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) via lithium naphthalenide reduction. By analyzing the resulting solid precipitates and gas evolution, our results confirm that both FEC and VC decomposition products include HCO2Li, Li2C2O4, Li2CO3, and polymerized VC. For FEC, our experimental data supports a reduction mechanism where FEC reduces to form VC and LiF, followed by subsequent VC reduction. In the FEC reduction product, HCO2Li, Li2C2O4, and Li2CO3 were found in smaller quantities than in the VC reduction product, with no additional fluorine environments being detected by solid-state nuclear magnetic resonance or X-ray photoelectron spectroscopy analysis. With these additives being practically used in higher (FEC) and lower (VC) concentrations in the base electrolytes of lithium-ion batteries, our results suggest that the different relative ratios of the inorganic and organic reduction products formed by their decomposition may be relevant to the chemical composition and morphology of the solid electrolyte interphase formed in their presence.

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.Keywords: binders; formation; IR; SEI; silicon; XPS

•Effects of MEC on cycling ability of Si nanoparticle anodes was investigated.•MEC greatly improved capacity retention of Si anode compared to standard electrolyte.•High concentration of poly(MEC) was found in MEC-derived SEI.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.

The performance of different concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in propylene carbonate (PC) on a binder free (BF) graphite electrode has been investigated. Variation in the salt concentration results in a change in the reduction reactions at the electrode interface and the reversible cycling of the cell. Continuous electrolyte reduction is observed at low salt concentrations while reversible lithiation/delithiation is observed at high salt concentrations. Ex-situ surface analysis of the cycled electrodes has been conducted via infrared spectroscopy with attenuated total reflectance (IR-ATR) and X-ray photoelectron spectroscopy (XPS). The ex-situ surface analysis suggests that changes in the cycling performance correlate with changes in the composition of the solid electrolyte interface (SEI) on the surface of binder free (BF) graphite electrode. The improved cycling performance correlates with an increase in the LiF content of the SEI.

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.Keywords: electrolyte additives; ex-situ surface analysis; HAXPES; lithium ion battery; Silicon anode; solid electrolyte interface; XPS

Lithium-ion coin cells containing electrolytes with and without 1,3-propane sultone (PS) and vinylene carbonate (VC) were prepared and investigated. The electrochemical performance of the cells is correlated with ex situ surface analysis of the electrodes conducted by Fourier transform infrared and X-ray photoelectron spectroscopies and in situ gas analysis by online electrochemical mass spectrometry (OEMS). The results suggest that incorporation of both PS and VC results in improved capacity retention upon cycling at 55 °C and lower impedance. Ex situ surface analysis and OEMS confirm that incorporation of PS and VC alter the reduction reactions on the anode inhibiting ethylene generation and changing the structure of the solid electrolyte interface. Incorporation of VC results in CO2 evolution, formation of poly(VC), and inhibition of ethylene generation. Incorporation of PS results in generation of lithium alkylsulfonate (RSO2Li) and inhibition of ethylene generation. The combination of PS and VC reduces the ethylene gassing during formation by more than 60%.

The solution structures of organic carbonate solvents (ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC)) as electrolyte solutions of LiPF6 were investigated with FTIR and NMR spectroscopy and DFT computational methods. Both coordinated and uncoordinated solvents are observed by IR spectroscopy, allowing the determination of solvent coordination numbers, which a range from 2 to 5. The predominant species in solution changes as a function of LiPF6 concentration. At low salt concentrations (<1.2 M), the predominant species is a solvent-separated ion pair, whereas at high salt concentrations (>2.0 M) the predominant species in solution is the contact ion pair. In mixed solvent systems (PC–DMC, PC–DEC, EC–DMC, or EC–DEC), the mixed solvated cations are observed in the presence of high concentrations of uncoordinated cyclic carbonate despite the much larger dielectric constant of the cyclic carbonates than dielectric constant of linear carbonate.

•A process to prepare novel stacked electrodes for lithium ion batteries was developed.•Coin cells were prepared and cycled with novel stacked anodes and cathodes.•Cells with novel stacked electrodes had similar cycling performance to traditionally prepared lithium ion cells.•SEM images suggest that the novel stacked electrodes have good stability after cycling.In an effort to reduce the cost of manufacturing lithium ion batteries, a novel approach is being developed to build a one piece integrated cell via layer by layer coating deposition rather than manufacturing separate pieces followed by electrode stacking and assembly. This new process would hold several advantages by providing excellent contact and thinner deposits, which will conserve space for energy storing materials while reducing production costs. Anode and cathode half stacks are made using a new process and the electrodes have been investigated in coin cells. Each half stack consists of a current collector, electrode, and separator combined into a single component. The stack cells successfully cycle as graphite stack/lithium and LiNi1/3Mn1/3Co1/3O2/lithium cells and together in graphite stack/LiNi1/3Mn1/3Co1/3O2 stack cell arrangements. Cross sectional SEM images show very little change in the anode and cathode materials indicating that the material is stable under typical cycling conditions and at moderately elevated temperature (55 °C). While the electrode stacks investigated are not optimized, the results support good cycling performance for a stacked cell design.

•EIS suggests higher cathode impedance for cells cycled to higher potential.•Ex-situ surface analysis used to investigate the surface of cycled electrodes.•Thicker surface films are generated after cycling at higher working potential.Layered Li(Ni1/3Co1/3Mn1/3)O2 (NCM) materials have been investigated at high working potential and elevated temperature to correlate electrochemical performance with changes to the electrode interface. Graphite/NCM cells were cycled to either 4.2 or 4.5 V vs Li/Li+ at room temperature (25 °C) followed by moderately elevated temperature (55 °C). Cells cycled to 4.2 and 4.5 V have similar capacity retention, but the cells cycled to 4.5 V have poorer first cycle efficiency, efficiency upon cycling at 55 °C, and greater increases in cell resistance. Surface analyses indicate thicker surface films on the cathode after cycling to 4.5 V, compared to cycling at a lower voltage of 4.2 V. The thicker surface film on the cathode is the result of electrolyte oxidation to generate poly(ethylene carbonate) and lithium alkyl carbonates. Electrochemical impedance spectroscopy of three-electrode cells reveals that the cathode dominates the cell impedance and the cathode impedance is much greater for cells cycled to 4.5 V than cells cycled to 4.2 V.

The reactions of lithium ion battery electrolyte (LiPF6 in ethylene carbonate/ethyl methyl, EC/EMC, 3:7 v/v) with and without added lithium bis(oxalato) borate (LiBOB) on the surface of high voltage LiNi0.5Mn1.5O4 cathodes has been investigated via a combination of electrochemical measurements, in situ gas analysis, and ex situ surface analysis. The oxidation of LiBOB on the cathode results in the generation of CO2 and a cathode passivation film containing borate oxalates. The cathode passivation film inhibits oxidation of the bulk electrolyte at high potential (>4.8 V vs Li/Li+).

An investigation of the interrelationship of cycling performance, solution structure, and electrode surface film structure has been conducted for electrolytes composed of different concentrations of LiPF6 in propylene carbonate (PC) with a binder-free (BF) graphite electrode. Varying the concentration of LiPF6 changes the solution structure, altering the predominant mechanism of electrolyte reduction at the electrode interface. The change in mechanism results in a change in the structure of the solid electrolyte interface (SEI) and the reversible cycling of the cell. At low concentrations of LiPF6 in PC (1.2 M), electrochemical cycling and cyclic voltammetry (CV) of BF graphite electrodes reveal continuous electrolyte reduction and no lithiation/delithiation of the graphite. The solution structure is dominated by solvent-separated ion pairs (Li+(PC)4//PF6–), and the primary reduction product of the electrolyte is lithium propylene dicarbonate (LPDC). At high concentrations of LiPF6 in PC (3.0–3.5 M), electrochemical cycling and CV reveal reversible lithiation/delithiation of the graphite electrode. The solution structure is dominated by contact ion pairs (Li+(PC)3PF6–), and the primary reduction product of the electrolyte is LiF.

The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) 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. Cells were cycled with LiPF6 and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF6 electrolytes, the graphite SEI is nonuniform, ∼10–20 nm thick, and contains lithium ethyl carbonate (LEC), lithium methyl carbonate (LMC), and LiF. In cells containing EC/EMC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick, and predominantly contains LEDC, LMC, and LiF.

Methyl butyrate (MB) has been investigated as a co-solvent for lithium-ion battery electrolytes to improve the performance at low temperature (−10 to −30 °C). The cycling performance of graphite/LiNi1/3Co1/3Mn1/3O2 cells with 1.2 M lithium tetrafluorooxalatophosphate (LiFOP) in 2:2:6 EC/EMC/MB was compared to 1.2 M LiPF6 in both 3:7 EC/EMC and 2:2:6 EC/EMC/MB. The LiFOP/MB electrolyte has a good operational temperature window and comparable cycling performance to the LiPF6 electrolyte at both room temperature and low temperature (−10 °C). However, after accelerated aging the LiFOP/MB electrolyte has worse performance at very low temperature (−30 °C) compared to LiPF6 electrolytes. Ex-situ surface analysis was conducted by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transfer infrared spectroscopy to provide insight into the performance differences.

The cycling performance of LiPF4(C2O4) (LiFOP) electrolyte with propylene carbonate (PC) as a cosolvent is compared with LiPF6 electrolyte with ethylene carbonate (EC) as a cosolvent in the presence of different cathode materials, such as LiNi1/3Co1/3Mn1/3O2 and LiFePO4. The cycling performance of cells with LiFOP and PC is similar to cells with LiPF6 with EC at room temperature and superior at low temperature (−10 °C). After thermal abuse the room temperature performance of cells with LiFOP electrolyte and PC is worse than cells with LiPF6 and EC. A detailed analysis of the surface films on both the anode and the cathode via X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Fourier transfer infrared spectroscopy (FT-IR) in the attenuated total reflection (ATR) mode was conducted to provide a better understanding of performance differences.Highlights► New electrolyte for lithium ion battery electrolytes was investigated. ► LiPF4(C2O4) electrolytes with propylene carbonate is an alternative to state-of-art LiPF6 ethylene carbonate electrolytes. ► LiPF4(C2O4) allows reversible cycling in the presence of propylene carbonate. ► Surface analysis of the electrodes after cycling was conducted.

The preparation of methylene ethylene carbonate (MEC) and the incorporation of MEC into lithium ion batteries as an electrolyte additive were investigated. MEC is prepared in good yield by mercury catalyzed cyclization. Addition of low concentrations of MEC (1–2%) to 1 M LiPF6 in 3:7 ethylene carbonate/ethyl methyl carbonate improves the capacity retention of lithium ion batteries cycled at elevated temperature (60 °C). Ex situ surface analysis (XPS and FTIR) of the electrodes supports the presence of poly(methylene ethylene carbonate) on the anode surface. Modification of the anode solid electrolyte interphase (SEI) correlates with significant improvements in the cycling performance at 60 °C.Highlights► New additive for lithium ion battery electrolytes was investigated. ► New electrolytes improve cycle life of lithium ion batteries for electric vehicles. ► Surface analysis of the electrodes after cycling was conducted. ► Alternative thermal stabilizing additive to vinylene carbonate.

The cycling performance of LiPF4(C2O4) electrolyte is compared with LiPF6 electrolyte in the presence of several different electrode materials. The cycling of MCMB/LiNi1/3Co1/3Mn1/3O2 and natural graphite/LiFePO4 cells provides very similar performance for both electrolytes. However, MCMB/LiMn2O4 cells have a lower initial reversible capacity with LiPF4(C2O4) electrolytes. A detailed analysis of the surface films on both the cathode and the anode via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) was conducted. The performance differences are attributed to the anode as opposed to the cathode.Highlights► New salt for lithium ion battery electrolytes was investigated. ► New electrolytes improve lithium ion batteries for electric vehicles. ► Surface analysis of the electrodes after cycling was conducted. ► LiPF4(C2O4) electrolytes are an alternative to state-of-art LiPF6 electrolytes.

The incorporation of additives designed to sacrificially react on the surface of cathode materials of lithium ion batteries has been investigated. Addition of low concentrations of inorganic additives including lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4)), and tetramethoxy titanium (TMTi) to 1 M LiPF6 in 1:1:1 EC/DEC/DMC improves the capacity retention of Li/Li1.17Mn0.58Ni0.25O2 cells cycled to 4.9 V vs. Li. Surface analysis of the cathode materials (XPS and IR) suggests that structure of the cathode surface film is modified by the presence of the additives resulting in a decrease in detrimental electrolyte oxidation reactions on the cathode surface.

Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of Nafion, as a surface supported acid catalyst. The addition of simple alkali metal halide salts, including NaCl, provides significant enhancement to the yield. The catalyst can be recycled suggesting possible extension into a continuous flow reactor for the synthesis of the biofuel precursors.

The solvation of LiPF6 by carbonate solvents (EC, DMC, and DEC) was investigated via 13C NMR chemical shift and 1H NMR diffusion coefficient experiments. The gradual addition of LiPF6 into a ternary solvent mixture results in a larger change in the chemical shift of EC than DMC or DEC suggesting that EC binds Li+ more strongly than DEC or DMC. The self diffusion coefficient of the carbonate solvents provides additional support for EC binding Li+ more strongly than DEC or DMC. Variable temperature NMR spectroscopic investigations support an increase in EC binding at low temperature and an enthalpic preference for the binding of EC to Li+.

Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of surface-supported Brønsted and Lewis acid catalysts. Nafion catalysts, in particular, have the potential to be recycled or applied to a continuous flow reactor for the synthesis of these biofuel precursors.Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of surface-supported Brønsted and Lewis acid catalysts. Nafion catalysts, in particular, have the potential to be recycled or applied to a continuous flow reactor for the synthesis of these biofuel precursors.

Commercial lithium-ion batteries have excellent performance at room temperature for a few years. However, the calendar life and thermal stability (>50 °C) need to be improved for many applications, including electric vehicles. We have conducted an investigation of the effect of thermal stabilizing additives, including dimethyl acetamide, vinylene carbonate, and lithium bis(oxalato) borate, on the performance of lithium ion batteries stored at 70 °C for one month. The reactions of the lithium hexafluorophosphate/carbonate electrolyte, with and without electrolyte additives, with the surface of the electrodes after initial formation cycling have been analyzed via a combination of IR-ATR and XPS.

A detailed investigation of the effect of the thermal stabilizing additive, propane sultone (PS), on the reactions of the electrolyte with the surface of the electrodes in lithium-ion cells has been conducted. Cells were constructed with meso-carbon micro-bead (MCMB) anode, LiNi0.8Co0.2O2 cathode and 1.0 M LiPF6 in 1:1:1 EC/DEC/DMC electrolyte with and without PS. After formation cycling, cells were stored at 75 °C for 15 days. Cells containing 2% PS had better capacity retention than cells without added PS after storage at 75 °C. The surfaces of the electrodes from cycled cells were analyzed via a combination of TGA, XPS and SEM. The addition of 2% PS results in the initial formation of S containing species on the anode consistent with the selective reduction of PS. However, modifications of the cathode surface in cells with added PS appear to be the source of capacity resilience after storage at 75 °C.

A series of regioregular poly(3-alkylthiophene)s with substituent groups R = C22H45, C24H49, C26H53, and C28H57 were synthesized. All of the materials can form a mesophase by rapid quenching from the isotropic melt. The ease of mesophase formation depends upon the length of the alkyl group, with the longer side chains leading to mesophase formation at lower quenching rates. Variable temperature reflection and fluorescence spectroscopy of thin films and differential scanning calorimetry and variable temperature X-ray diffraction on powders were used to study the thermal behavior of the new polymers. All of the materials studied showed a two-step thermochromic transition from the mesophase, and endotherms in the thermograms could be assigned to melting of each phase. The data indicate that π−π stacking is an important contributor to the thermochromism observed in these compounds while the interaction between the alkyl side chains controls mesophase formation.

Thermal reactions between cathode particles (LiNi0.8Co0.2O2, LiCoO2, LiMn2O4 and LiFePO4) and ternary electrolyte (1.0 M LiPF6 in 1:1:1 diethyl carbonate/dimethyl carbonate/ethylene carbonate) with or without the thermal stabilizing additive dimethyl acetamide (DMAc) have been investigated. Ternary electrolyte reacts with the surface of lithiated metal oxides (LiNi0.8Co0.2O2, LiCoO2 and LiMn2O4) upon storage to corrode the surface and generate a complex mixture of organic and inorganic surface species, but the bulk ternary electrolyte does not decompose. There is little evidence for reaction between the surface of carbon coated LiFePO4 and ternary electrolyte upon storage at elevated temperature (>60 °C), but the bulk ternary electrolyte decomposes. Addition of DMAc to ternary electrolyte reduces the surface corrosion of the lithiated metal oxides and stabilizes the electrolyte in the presence of LiFePO4.

The addition of some small molecules can red shift UV-Visible absorption and quench the fluorescence of poly(3-octadecylthiophene).

The thermal reaction of ternary electrolyte (1.0 M LiPF6 in 1:1:1 ethylene carbonate/dimethyl carbonate/diethyl carbonate) with mesocarbon microbeads (MCMB) particles was investigated by the combined use of NMR, GC–MS, FTIR-ATR, TGA, XPS and SEM/EDS-element map. The thermal decomposition of ternary electrolyte is not inhibited by the presence of MCMB particles. The chemical composition and morphology of the surface of MCMB particles changes significantly upon storage in the presence of ternary electrolyte. Electrolyte decomposition products including oligocarbonates, oligoethylene oxides, polyethylene oxide (PEO), lithium fluorophosphates (LixPOyFz), and lithium fluoride are deposited on the surface of MCMB particles. The concentration of decomposition products on the surface of MCMB increases with increased storage time and temperature. The addition of dimethyl acetamide (DMAc) impedes the thermal decomposition of the electrolyte and deposition of electrolyte decomposition products on the surface of MCMB.

Poly[3-(oligoethylene oxide)-4-methylthiophene] is doped by HCl in aqueous solution in the absence of oxygen and undergoes dramatic solvatochromism in water–ethanol mixtures.

Hexamethylphosphoramide (HMPA) was investigated as a flame retarding additive for lithium-ion batteries. The flammability, electrochemical stability, conductivity, and cycling performance of electrolytes containing HMPA were studied. The addition of HMPA to electrolytes comprising solutions of LiPF6 in organic carbonates provided a significant reduction in the flammability of the electrolyte. However, the HMPA caused a slight decrease in the conductivity and electrochemical stability window of the electrolyte. Cycling performance of coin cells containing HMPA modified electrolytes was diminished.

P-Substituted poly(p-phenylenephosphine)s were prepared via palladium catalyzed carbon–phosphorus bond formation.