LiPF6 electrode materials

Composite electrodes made of two carbon components were evaluated experimentally as anodes for Li-ion batteries. The electrochemical activity of these electrodes in the reaction of reversible lithium intercalation ffom/to a solution of LiPF6 in ethyl carbonate and diethyl carbonate was studied. Compositions of the electrode material promising for the usage in Li-ion batteries were found. 

According to the Marcus theory [64] for outer-sphere reactions, there is good correlation between the heterogeneous (electrode) and homogeneous (solution) rate constants. This is the theoretical basis for the proposed use of hydrated-electron rate constants (ke) as a criterion for the reactivity of an electrolyte component towards lithium or any electrode at lithium potential. Table 1 shows rate-constant values for selected materials that are relevant to SE1 formation and to lithium batteries. Although many important materials are missing (such as PC, EC, diethyl carbonate (DEC), LiPF6, etc.), much can be learned from a careful study of this table (and its sources). 

Both carbon materials were tested for their initial electrochemical performance in the 2-electrode electrochemical cells with Li metal as a counter electrode. Our findings have shown that with both types of carbon materials, achieving near theoretical reversible capacity upon Li+ deintercalation was possible. Thus, in a typical half cell environment (a CR2016 type coin cell with graphite and Li metal electrodes, a 1M LiPF6,... 

The electrode active masses were prepared by mixing the active material with 10 wt.% of polyvynilidene fluoride slurred in 1-methyl-pyrrolidone solvent. The actual mass was then pasted onto one side of precleaned Co foil, dried for 4 h at 100°C, pressed and the disks of 15,6 mm diameter were cut and placed into the cell s coins. Large excess of Li metal (foil) was used as a counter electrode. 1M LiPF6 solution in mixture of ethylene carbonate (50 vol.%) and methyl carbonate was used as an electrolyte (Merck product LP30). 

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