Electrochemical properties of natural graphite in the electrolyte solutions containing propylene carbonate and nonflammable organo-fluorine compounds for lithium-ion batteries

Achiha Takashi

doi:10.7209/tanso.2010.135

High improvement in the battery performances such as low temperature characteristics, thermal stability and high rate charge/discharge is urgently requested. Because EC-based solvents should be used for graphite anode, lithium-ion batteries currently used have difficulty for the use at low temperatures. In the present study, surface fluorination using F₂, ClF₃, NF₃ and plasma-treatment was applied to natural graphite samples. Surface fluorination highly increased surface disorder in all fluorinated natural graphite samples, reducing the electrochemical decomposition of PC. Due to decrease in the decomposition of PC, first coulombic efficiencies increased by 10–20%.<br>High safety is one of the most important issues for the application of lithium-ion batteries to hybrid cars and electric vehicles because lithium-ion batteries use flammable organic solvents. Organo-fluorine compounds are new candidates since fluorine substitution of organic compounds reduce HOMO level, i.e. increases oxidation stability. In the present study, thermal and electrochemical oxidation stability of organo-fluorine compound-mixed electrolyte solutions was evaluated, and charge/discharge characteristics of natural graphite were investigated using fluorine compound-mixed electrolyte solutions. It was found that organo-fluorine compounds improved thermal and electrochemical oxidation stability of electrolyte solutions, and highly increased first coulombic efficiencies for graphite in PC-containing electrolyte solution.

Electrochemical properties of natural graphite in the electrolyte solutions containing propylene carbonate and nonflammable organo-fluorine compounds for lithium-ion batteries

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