Carbon LiFePO

Figure 29. Lhs Battery performance of a Li cell with LiFePO 4 as cathode and nano-Si02 (10 nm) in 1 M LiCFsSCVECLDMC (EC ethylene carbonate, DMC dimethyl carbonate).202 Rhs At the contact of anion adsorbing phases LiX is completely dissociated and Li+ mobile in the space charge region.

Keywords-. Li-ion battery, conducting polymers, polyaniline, polypyrrole, polythiophene, graphene, carbon nanotubes, LiFePO, MnO, V Oj, Si, SnO, Fe O, nanocomposites, intercalation, electrolyte, electrode, cathode, anode, energy density, power density, rate capability, voltage, current density, charge/discharge capacity, Nyquist plots, efficiency, cyclability... 

The reactions for the charge/discharge processes of Li-ion batteries (Scheme 7.1), if LiCoO and carbon are, respectively, used as cathode and anode, are shown by Equations 7.1-7.3 [11], Obviously, the conductivity in the electrode materials plays a vital role, because the high conductive electrode facilitates the transport of electrons and ions and fully fulfills the capacity of the active materials. However, most of the inorganic materials for either cathode or anodes [2,4],e.g., LiFePO, LiCoO, MnO, SnO, MoOj, and TiO, are limited by their low electronic conductivity. 

Carbon-coated LiFePO (C-LFP) composites incorporated with electro-chemically active conducting polymer polyaniline (PANI) were fabricated in situ by chemical oxidative polymerization as cathode for LIB. Specific capacities as high as 165 mAh/g at 0.2 C, 133 mAh/g at 7 C and 123 mAh/g at 10 C were observed in C-LFP/7 wt% PANI composite. The improved cyclability as compared with the parent C-LFP was due to PANI, which acts not only as an additional host for Li -ion insertion/extraction, but also as a binder to modify the electrode surface and a container for electrolyte to penetrate into C-LFP particles [55]. 

We have here exploited photoelectron spectroscopy using synchrotron radiation (PES-SR) to characterise the interface formed on carbon-coated LiFePO particles in the cathode of a lithium-ion battery after storage and electrochemical cycling at 23°C and 40 in a IM LiPF, mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The PES-SR technique facilitates non-destructive depth-profile analysis of the surface layer. An example is given in Figure 14. 

Most significantly, products from solvent reactions or decompositions (e.g., polycarbonates, semicarbonates and Li COj) could not be detected on the carbon-coated LiFePO surface. This indicates that the phosphate group does... 

Figure 14 P2p photoelectron spectroscopy (PES-SR) spectra for carbon-coated LiFePO electrodes cycled at 23°C (a) and 40°C (b). The spectra were obtained at photon energies of 454 and 1061 eV. Spectra are shown together with fitted peaks to clarify the peak assignments.

These results combine to indicate that the surface film formed on a carbon-coated LiFePO cathode will not serve to limit cell performance as the surface film appears to do for other cathode materials. 

Chen Z, Dahn JR (2002) Reducing carbon in LiFePO /C ctnnposile electrodes to maximize specific energy, volumetric energy and tap density. J Electrochem Soc 149 A1184-A1189... 

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