The Electrochemical Performances of Metal Ions and F- Co-Substituted Li4Ti5O12
The graphite is usually selected as anode material of commercial lithium-ion batteries, because of its large theoretical capacity (372 mAh g-1) and reversible charged-discharge for Li+, but the potential safety problem is dendritic lithium growth on the anode surface during the charging and discharging. Li4Ti5O12 has almost no formation of SEI layer and dendritic lithium growth on the electrode surface during charging/discharging because its high flat operating voltage of about 1.5 V. To overcome the demerit of insulating property of Li4Ti5O12, doping the structure with small amounts of various transition metal ions have been tried.
The investigation of electrochemical performances of Al3+ and F- co-substituted compounds was previously done. But, the electrochemical performance of co-substituted specimen was worse than the Al3+ substituted one.
The electrochemical perfomances of the eight kinds of F- and metal ions (Fe, Mg, Ag, Zn, Sr, Sn Mo, and Co ions) co-doped Li4Ti5O12 specimens were studied. Among them, the cycle retention was best in F- and Co ion co-doped sample. The capacity of F- and Mg ion co-substituted one was largest. The capacity of all the co-substituted samples was larger than pure Li4Ti5O12. The good cycle performance was explained by the relative bonding strength between metal ion and oxygen ion.