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Several LiFePO 4 /C composites were prepared and characterized electrochemically in lithium half-cells. Pressed-pellet conductivities correlated well with the electrochemical performance in lithium half-cells. It was found that carbon structural factors such as sp 2 /sp 3 and disordered/graphene ͑D/G͒, as determined by Raman spectroscopy, and H/C ratios determined from elemental analysis influenced the conductivity and rate behavior strongly. The structure of the residual carbon could be manipulated through the use of additives during LiFePO 4 synthesis. Increasing the pyromellitic acid ͑PA͒ content in the precursor mix prior to calcination resulted in a significant lowering of the D/G ratio and a concomitant rise in the sp 2 /sp 3 ratio of the carbon. Addition of both iron nitrate and PA resulted in higher sp 2 /sp 3 ratios without further lowering the D/G ratios or increasing carbon contents. The best electrochemical results were obtained for LiFePO 4 processed with both ferrocene and PA. The improvement is attributed to better decomposition of the carbon sources, as evidenced by lower H/C ratios, a slight increase of the carbon content ͑still below 2 wt %͒, and more homogeneous coverage.

An electrolyte based on the new salt, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), is evaluated in combination with nano-Si composite electrodes for potential use in Li-ion batteries. The additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are also added to the electrolyte to enable an efficient SEI formation. By employing hard X-ray photoelectron spectroscopy (HAXPES), the SEI formation and the development of the active material is probed during the first 100 cycles. With this electrolyte formulation, the Si electrode can cycle at 1200 mAh g(-1) for more than 100 cycles at a coulombic efficiency of 99%. With extended cycling, a decrease in Si particle size is observed as well as an increase in silicon oxide amount. As opposed to LiPF6 based electrolytes, this electrolyte or its decomposition products has no side reactions with the active Si material. The present results further acknowledge the positive effects of SEI forming additives. It is suggested that polycarbonates and a high LiF content are favorable components in the SEI over other kinds of carbonates formed by ethylene carbonate (EC) and dimethyl carbonate (DMC) decomposition. This work thus confirms that LiTDI in combination with the investigated additives is a promising salt for Si electrodes in future Li-ion batteries.

The effect of filler surface group on the conductivity, ion−ion, ion−polymer interactions, and microstructure of PEG−LiClO4−Al2O3 composite polymer electrolytes is studied. It is shown that the addition of fillers results in an increase in ionic conductivity of polyether electrolytes observed in the narrow lithium salt concentration range. The position of conductivity maximum depends on the type of the surface groups of the filler and results from the Lewis acid−base type interactions between filler surface centers, ions, and ether oxygen base groups. These interactions are reflected by changes in the polymer chain flexibility observed by DSC and rheological experiments as well as microstructural changes due to polymer−filler−Li+ interactions as revealed by FT-IR experiments. Finally, the addition of the filler results in the changes in ionic associations as studied by FT-IR and by applying the Fuoss−Kraus formalism to the salt concentration dependence of the molar conductivity of the composite electrolytes studied.

Abstract13 C-carbon black substituted composite LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes were tested in model electrochemical cells to monitor qualitatively and quantitatively carbon additive(s) distribution changes within tested cells and establish possible links with other detrimental phenomena. Raman qualitative and semi-quantitative analysis of 13 C in the cell components was carried out to trace the possible carbon rearrangement/movement in the cell. Small amounts of cathode carbon additives were found trapped in the separator, at the surface of Li-foil anode, in the electrolyte. The structure of the carried away carbon particles was highly amorphous unlike the original 12 C graphite and 13 C carbon black additives. The role of the carbon additive, the mechanism of carbon retreat in composite cathodes and its correlation with the increase of the cathode interfacial charge-transfer impedance, which accounts for the observed cell power and capacity loss is investigated and discussed. [1,5]. Possible causes of the increase in cathode impedance and irreversible charge/discharge capacity loss include the formation of an electronic and/or ionic barrier at the cathode surface [6,7,8]. This is consistent with our earlier studies [9,10], in which we demonstrated that the non-uniform kinetic behavior of the individual oxide particles was attributed to the degradation of the electronically conducting matrix in the composite cathode upon testing. Carbon additive rearrangement in portions of the tested LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes and/or thin film formation on the surfaces of carbon and oxide particles is closely linked with the observed isolation of oxide active material.Because the composite cathodes typically consists of an active material, two types of carbon additive, and a binder, suitable instrumental techniques must be applied to obtain lateral resolution comparable to the size and morphology of electrode surface features. In situ and ex situ application of non-invasive and non-destructive microscopies and spectroscopies, including Raman, fluorescence spectroscopy, SEM, and AFM to characterize physico-chemical properties of the electrode/electrolyte interface at nanometer resolution provide unique insight into the mechanism of specific chemical