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.

A. J. Bhattacharyya et at, in preparation. The courtesy of Prof. J.-M. Tarascon, Universite de Picardie Jules Verne, of providing the LiFePO,i samples is acknowledged. 

In this work, we perform a sensitivity analysis of selected parameters of a commercial 26650 LiFePO/graphite cell and investigate their effect on the simulated impedance spectrum. Basic values such as layer thickness and particle radii are taken from literature and preceding measurements. The model implemented within the commercial Finite Element Method (FEM) software COMSOL Multiphysics is then solved in the frequency domain. To demonstrate the capabilities of this method, variations in state of charge, particle radius, solid state diffusion coefficient and reaction rate are analysed. These parameters evoke characteristic and also unusual properties of the observed impedance spectrum. 

The Li+ ion batteries generally produce an output voltage of approximately 3.5 V with the Li-based cathode materials such as LiCoO, LiMn O, LiFePO, etc. 

Additional experiments were also performed for a large number of cycles, which showed different capacity tendency as compared to the rate. An unusual behavior was the best capacity retention over 160 cycles is observed at high rates. For instance, the full cell cycled at C/2,1 C and 2 C exhibited 20, 30 and 56 mA h g", while the capacity was 82 mA h g" when cycled at 5 C. A lithium-ion cell based on titanium oxide nanotubes and bare LiFePO exhibited only 70 mA h g" at C/10 at the first reversible cycle [167]. The increased capacity in batteries using coated Ti02 can be ascribed to an improvement of the Li ion diffusion when Li3P04 layer is applied. Moreover, a reduced contact area between the electrodes and the electrol5fre can be achieved. 

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. 

The initial overpotential of PPy/LiFePO was greatly reduced after the first charge reaction, and after the initial 10 cycles, the specific capacity of the electrode increased to 132 mA h g L Figure 7.2d displays the obviously enhanced rate capabilities of the PPy/LiFePO as compared with LiFePOyC/PTFE (75 20 5 in wt.%) cathode composites for rates ranging from C/5 to 5C. It was speculated that the oxidation of the polymer led... 

Figure 7.2 Scanning electron microscopy (SEM) images of an electrochemically deposited PPy/LiFePO composite film on a stainless-steel mesh, (a) Around a hole and (b) enlarged image (scale bars 85.7 and 19.9 pm, respectively), (c) Charge-discharge curves and (d) rate capabilities of PPy/LiFePO and PPy/C/PTFE composite electrodes. Panels (a, b, c, and d) are reproduced with permission [40]. Copyright 2007, WUey.

Figure 7.4 (a) First charge-discharge profiles (C/15 rate) of the LiFePO nanorods (40 ... 

Hsu K-F, Tsay S-Y, Hwang B-J. Synthesis and characterization of nano-sized LiFePO cathode materials prepared by a citric acid-based sol-gel route. J Mater Chem 2004 14 2690-5. 

LiFePOypolythiophene composites were also synthesized by in-situ polymerizing thiophene monomers on the surface of LiFePO particles to improve the electronic conductivity and electrochemical properties of LiFePO for LIB cathode application. The as-prepared composites showed... 

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]. 

Orthorhombic LiFePO of the olivine structure forms FePO during charging/ discharging, and two crystal phases exist during charging/discharging thus it exhibits a flat discharge curve. The accurate crystal structure of orthorhombic... 

PjOio) ", or polymetaphosphate (P 03 )" can be easily produced. Iron phosphates such as olivine LiFePO, pyrophosphate LiFeP O, and Fe (P207)3 that show similar discharge plateaus at 3 V are attractive as rare metal free cathodes. Especially, olivine LiFePO has the highest theoretical capacity (170 mAh/g) in the iron-based polyanionic cathodes. 

The following features of the improved LiFePO have drawn attention for its use as a next-generation cathode candidate ... 

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