Constructing a Heterostructural LiNi0.4Mn1.6O4-δ Material from Concentration-Gradient Framework to Significantly Improve Its Cycling Performance.

A heterostructural LiNi0.35Mn1.65O4-δ-LiNi0.5Mn1.5O4 was achieved via constructing the concentration-gradient material with an average composition of LiNi0.4Mn1.6O4-δ. The as-obtained samples were characterized by cross-sectional scanning electron microscopy and energy dispersive X-ray spectrometry, and it was found that the core material LiNi0.35Mn1.65O4-δ is encapsulated completely by a concentration-gradient shell with the outmost layer of LiNi0.5Mn1.5O4. Demonstrated by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy analysis with a low-energy Ar neutral beam etching method, the structurally stable P4332 phase on the surface coordinates the high conductive Fd3̅m phase in the bulk without any detectable interface. At room temperature, the heterostructural samples deliver the initial discharge capacity of 145.1 mAhg-1 at 1 C, close to the theoretical capacity, and the capacity retention after 300 cycles was up to 96.5% of the first discharge capacity. Moreover, it shows excellent rate capability with discharge capacity of 144.3 mAhg-1 at 10 C and significantly improved cycling stability with capacity retention of 85.51% over 50 cycles between 3.0 and 4.95 V at 55 °C. The as-obtained material with coordination of two crystallographic structure domains is a promising cathode to develop high energy, high power, long lifespan, and low cost lithium-ion batteries.