A Strategy to Improve Cyclic Performance of LiNi_0.5Mn_1.5O₄in a Wide Voltage Region by Ti-Doping

A strategy to improve cyclic performance of 5 V spinel LiNi 0.5 Mn 1.5 O 4 in a wide voltage region (4.95–2.0 V) by Ti-doping has been proposed and demonstrated for the first time. The effects of Ti substitution for Mn on the structure and electrochemical properties of the LiNi 0.5 Mn 1.5− x Ti x O 4 (0 ≤ x ≤ 0.6) during cycling between 4.95 and 2.0 V were investigated. X-ray diffraction (XRD) results show that all of these materials are cubic spinel structure with a space group of Fd m , where their unit cell parameter a increases with the substituting amount of Mn by Ti, which is in agreement with the fact that the ionic radius of Ti 4+ (74.5 pm) is much larger than that of Mn 4+ (67 pm). Electrochemical test results show that proper amount of Ti substitution for Mn is able to significantly improve the cyclic performance of LiNi 0.5 Mn 1.5− x Ti x O 4 spinel during cycling at 4.95–2.0 V, especially for the capacity retention of the ca. 2.7 V plateau. Take LiNi 0.5 Mn 1.0 Ti 0.5 O 4 as an example, the capacity retention in the upper (4.95–3.0 V) and lower voltage (3.0–2.5 V) regions after 100 cycles are 57.1% and 79.8%, respectively, while they are only 47.0% and 24.5% for un-substituted LiNi 0.5 Mn 1.5 O 4 sample, respectively.