High-energy and high-power Li-rich nickel manganese oxide electrode materials

A lithium-rich nickel-manganese oxide compound Li_x(Ni_0.25Mn_0.75)O_y (x > 1) was synthesized from layered Na_0.9Li_0.3Ni_0.25Mn_0.75O_δ precursor using a lithium ion-exchange reaction. The electrochemical behavior of the material as a cathode for lithium batteries, and a preliminary discussion of its structure are reported. The product Li_1.32Na_0.02Ni_0.25Mn_0.75O_y (IE-LNMO) shows broad X-ray diffraction peaks, but possesses a high intensity sharp (003) layering peak and multiple peaks with intensity in the 20–23° 2θ region which suggest Ni–Mn ordering in the transition metal layer (TM). Li/IE-LNMO cells demonstrate very stable reversible capacities of 220 mAh/g @ 15 mA/g and possess extremely high power of 150 mAh/g @ 1500 mA/g (15C). The Li/IE-LNMO cell dQ/dV plot exhibits three reversible electrochemical processes due to Ni/Mn redox behavior in a layered component, and Mn redox exchange in a spinel component. No alteration in the dQ/dV curves and no detectable change in the voltage profiles over 40 cycles were observed, thus indicating a stable structure for lithium insertion/extraction. This new material is attractive for demanding Li-ion battery applications.