Constructing a Heterostructural LiNi_0.4Mn_1.6O_4−δ Material from Concentration-Gradient Framework to Significantly Improve Its Cycling Performance

A heterostructural LiNi 0.35 Mn 1.65 O 4−δ -LiNi 0.5 Mn 1.5 O 4 was achieved via constructing the concentration-gradient material with an average composition of LiNi 0.4 Mn 1.6 O 4−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 LiNi 0.35 Mn 1.65 O 4−δ is encapsulated completely by a concentration-gradient shell with the outmost layer of LiNi 0.5 Mn 1.5 O 4 . 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 P 4 3 32 phase on the surface coordinates the high conductive Fd 3̅ m 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.