Preparation and characterization of sub-micro LiNi_(0.5-x)Mn_(1.5+x)O_4 for 5 V cathode materials synthesized by an ultrasonic-assisted co-precipitation method

摘要

Sub-micro spinel LiNi_(0.5-x)Mn_(1.5+x)O_4 (x < 0.1) cathode materials powder was successfully synthesized by the ultrasonic-assisted co-precipitation (UACP) method. The structure and electrochemical performance of this as-prepared powder were characterized by powder XRD, SEM, XPS, CV and the galvanostatic charge-discharge test in detail. XRD shows that there is a small Li_yNi_(1-y)O impurity peak placed close to the (400) line of the spinel LiNi_(0.5-x)Mn_(1.5+x)O_4, and the powders are well crystallized. XPS exhibits that the Mn oxidation state is between +3 and +4, and Ni oxidation state is +2 in LiNi_(0.5-x)Mn_(1.5+x)O_4. SEM shows that the prepared powders (UACP) have the uniform and narrow size distribution which is less than 200 nm. Galvanostatic charge-discharge test indicates that the initial discharge capacities for the LiNi_(0.5-x)Mn_(1.5+x)O_4 (UACP) at C/3, 1C and 2C, are 130.2, 119.0 and 110.0mAhg~(-1), respectively. After 100 cycles, their capacity retentions are 99.8%, 88.2%, and 73.5%, respectively. LiNi_(0.5-x)Mn_(1.5+x)O_4 (UACP) at C/3 discharge rate exhibits superior capacity retention upon cycling, and it also shows well high current discharge performance. CV curve implies that LiNi_(0.5-x)Mn_(1.5+x)O_4 (x < 0.1) spinel synthesized by ultrasonic-assisted co-precipitation method has both reversibility and cycle capability because of the ultrasonic-catalysis.