Anodes for Li-ion batteries based on titanium fluorides

The work is devoted to a comparative study of the electrochemical behavior and molecular level transformations in TiF3 and TiOF2 electrodes of Li-ion batteries at charge-discharge processes. Based on analysis of the electrode voltage profiles, we propose possible redox reactions which occur with the change of Ti oxidizing state. According to these models, titanium trifluoride has a reversible capacity of 600 mAh/g, TiOF2 of 395 mAh/g. It has been shown that titanium oxyfluoride is characterized by a long cycle life while specific capacity of the titanium trifluoride rapidly degrades. The degradation of TiF3 is associated with a temporal molecular ordering and decrease in the chemical activity of titanium and lithium fluoride formed during the reversible introduction of lithium. The related effect lies under the superreversibility phenomenon in TiOF2 electrodes (Coulomb efficiency more than 100%). The dependences of the equilibrium voltage and chemical diffusion coefficient of Li on the concentration of Li were determined from GITT analysis.