Chemical valence electron-engineered LiNi0.4Mn1.5MtO4 (Mt = Co and Fe) cathode materials with high-performance electrochemical properties

Abstract

LiNi0.5Mn1.5O4 (LNMO) with a spinel crystalline structure exhibits excellent properties such as a high voltage of ~4.7 V and a fairly high theoretical capacity of ~147 mAh g−1 as well as low cost. However, LNMO cathode materials exhibit a deteriorated high-rate performance and capacity fading because of their low structural stability caused by dissolution of Mn ions into the electrolyte via the Jahn–Teller effect during the Li+ ion insertion/desertion process. Herein, to obtain electrochemical/structural stabilities and to prevent dissolution of Mn ions from pristine LNMO, we designed Mt-doped LNMO cathode materials (LiNi0.4Mn1.5MtO4) with different transition metal elements (Mt = Co and Fe) having a chemical valence electron of Mt3+ using a hydrothermal method. All samples exhibited that the Mt-doped LNMO structures were homogeneously doped with Co and Fe elements. Furthermore, compared with the undoped LNMO materials, the Mt-doped LNMO cathode materials showed superior electrochemical properties in terms of high discharge capacities (121.1 mAh g−1) at 120 mA g−1 and good cycle retentions (over 99.7%) after 200 cycles as well as improved high-rate performance, because of the well-engineered valance and disordered structure for the doping of Mt3+, preventing the dissolution of Mn ions via the Jahn–Teller distortion.