In concentrated propylene carbonate (PC)-based electrolyte solutions, reversible lithium intercalation and de-intercalation occur at graphite negative electrodes because of the low solvation number. However, concentrated electrolyte solutions have low ionic conductivity due to their high viscosity, which leads to poor electrochemical performance in lithium-ion batteries. Therefore, we investigated the effect of the addition of 1,2-dichloroethane (DCE), a co-solvent with low electron-donating ability, on the electrochemical properties of graphite in a concentrated PC-based electrolyte solution. An effective solid electrolyte interphase (SEI) was formed, and lithium intercalation into graphite occurred in the concentrated PC-based electrolyte solutions containing various amounts of DCE, while the reversible capacity improved. Raman spectroscopy results confirmed that the solvation structure of the lithium ions, which allows for effective SEI formation, was maintained despite the decrease in the total molality of LiPF6 by the addition of DCE. These results suggest that the addition of a co-solvent with low electron-donating ability is an effective strategy for improving the electrochemical performance in concentrated electrolyte solutions.
Lithium thionyl chloride (Li/SOCl 2) batteries exhibit the highest energy densities seen in commercially available primary batteries because of their high operating voltages and discharge capacities. They are widely used in various extreme environments; however, they show signs of degradation at high discharge currents. The discharge performance of Li/SOCl 2 is considered to be greatly dependent on the carbon materials used in the cathode. Therefore, suitable carbon materials must be chosen to improve discharge performances. In this work, we investigated the discharge properties of Li/SOCl 2 batteries in which the cathodes contained various ratios of acetylene black (AB) and multi-walled carbon nanotubes (MWCNTs) at high discharge currents. It was confirmed that the MWCNTs were effectively dispersed in the mixed AB/MWCNT cathodes. Moreover, the discharge capacity and operating voltage improved at high discharge currents in these mixed cathodes when compared with pure AB cathodes. It was found that the mesopores present in the cathodes have a strong impact on the discharge capacity, while the macropores present on the cathode surface influence the discharge properties at high discharge rates in Li/SOCl 2 batteries. These results indicate that the ratio of mesopores and macropores in the cathode is key to improving the discharge performance of Li/SOCl 2 batteries, as is the dispersion of the MWCNTs.
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