New hydrofluoroethers (HFEs), 2-trifluoromethyl-3-methoxy-perfluoro-pentane (TMMP) and 2-(trifluoro-2-fluoro-3-difluoropropoxy)-3-difluoro-4-fluoro-5-trifluoropentane (TPTP) were investigated as nonflammable electrolyte solvents for lithium ion batteries. Activation energies (ΔG∗dep) for desolvation of lithium ion (Li+) and lithium-solvation number (Ns) were evaluated for 1 M LiBETI/EC+DEC electrolytes with and without TMMP or TPTP in order to understand the mechanism of rate-capability improvement. The ΔG∗dep for the carbonate-mixed electrolyte (0.01–2 M of LiBETI/EC+DEC (50:50 in volume)) increased from 45.7 to 98.3 kJ mol−1 with a decrease in the LiBETI concentration. In comparison, ΔG∗dep was found lower (ΔG∗dep≈35 kJ mol−1) for TPTP-mixed electrolytes (LiBETI/EC+DEC+TPTP (5:45:50)) and much lower (ΔG∗dep≈25 kJ mol−1) for TMMP-mixed electrolytes (LiBETI/EC+DEC+TMMP (5:45:50)). Adding 60 vol% TPTP in EC+DMC (50:50) reduced both NEC and NDMC by 40%, exemplified by Raman spectroscopy with different concentrations of LiBETI (0.05–1.5 M) and DFT calculation. Thus, the rate-capability improvement by adding TMMP or TPTP is exerted by both enhancements of the intercalation kinetics and Li+ diffusion at the LiCoO2 interface, where HFEs preferentially exist by their affinity with the hydrophilic LiCoO2 cathode surface.
Fabrication of microscale lithium batteries has been required for various applications. A microarray configuration which is composed of interdigitated two comb-type electrodes is an appropriate form for the microscale battery. By an electrophoresis deposition (EPD), LiCoO2 was deposited only on the selected comb-type substrate successfully. The prepared LiCoO2 electrode can intercalate and deintercalate Li ion, indicating that the electrode can be used for cathode of the lithium battery. The discharge capacity of the electrode was 5.3 µA h cm−2 at 1 C and the capacity will be improved by optimization of the EPD condition.