Preparation and cycling performance of Al3+and F− co-substituted compounds Li4AlxTi5−xFyO12−y

Li4AlxTi5−xFyO12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al3+ and F− ions entered the structure of spinel-type Li4Ti5O12. Charge–discharge cycling results at a constant current density of 0.15 mA cm−2 between the cut-off voltages of 2.5 and 0.5 V showed that the Al3+ and F− substitutions improved the first total discharge capacity of Li4Ti5O12. However, Al3+ substitution greatly increased the reversible capacity and cycling stability of Li4Ti5O12 while F− substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al3+–F−-co-substituted specimen was better than the F−-substituted one but worse than the Al3+-substituted one.