PO43− polyanion-doped Li-rich layered oxides offer excellent energy density retention during long cycling due to the stronger anion bonding of PO43− polyanions to transition metal cations.

No abstract

Enhancement of the discharge capacity, high-rate capability, and cycle stability of the Li-rich layered Li(Li 0.17 Ni 0.25 Mn 0.58 )O 2 oxide with a large specific capacity is highly significant for high energy lithiumion batteries. In this work, the Li-rich layered Li(Li 0.17 Ni 0.25 Mn 0.58 )O 2 oxide is prepared by a spray-drying method. The surface modification with the Li-Mn-PO 4 is introduced onto Li-rich layered Li(Li 0.17 Ni 0.25 Mn 0.58 )O 2 oxide for the first time. It is demonstrated that the surface of Li(Li 0.17 Ni 0.25 Mn 0.58 ) O 2 grains is coated with the thin amorphous Li-Mn-PO 4 layer (5 wt%). With increasing calcination temperature after the surface coating, a strong interaction can be induced on the interface between the amorphous Li-Mn-PO 4 layer and the top surface of Li(Li 0.17 Ni 0.25 Mn 0.58 )O 2 grains. As anticipated, the discharge capacity and high-rate capability are obviously improved for the Li-Mn-PO 4 -coated sample after calcination at 400 C, while excellent cycle stability is obtained for the Li-Mn-PO 4 -coated sample after calcination at 500 C as compared with the as-prepared Li(Li 0.17 Ni 0.25 Mn 0.58 )O 2 oxide during cycling. Apparently, the interface interaction between the amorphous Li-Mn-PO 4 layer and the top surface of Li(Li 0.17 Ni 0.25 Mn 0.58 )O 2 grains is responsible for the improvement of the reaction kinetics and the electrochemical cycle stability of Li-Mn-PO 4 -coated samples.

5Li-rich layered oxides have been intensively investigated as cathode for high energy lithium-ion batteries. However, oxygen loss from the lattice in the initial charge and the gradual structural transformation during cycling can lead to a capacity degradation and potential decay for the cathode materials. In this work, Sn 4+ is used to partially substitute Mn 4+ to prepare a series of Li(Li 0.17 Ni 0.25 Mn 0.58-x Sn x )O 2 (x = 0, 0.01, 0.03, and 0.05) samples through a spray-drying method. Structure characterization reveals that the 10 Sn 4+ substituted samples with a suitable amount show a low cation mixing, indicating an enhanced ordered layer structure. Moreover, the metal-oxygen (M-O) covalency is gradually decreased with increasing Sn 4+ amount. It is shown from the initial charge-discharge curves that Sn 4+ substituted samples present a shorter charging potential plateau at 4.5 V (vs Li/Li + ), implying that oxidation of the O 2ion to O 2 is suppressed by Sn 4+ substitution and lead to the minor structural change. Among the Sn 4+ substituted 15 samples, the Li(Li 0.17 Ni 0.25 Mn 0.55 Sn 0.03 )O 2 sample exhibits a higher capacity retation of 86% after 400 cycles at 0.1 C rate and 92 % after 200 cycles at 1 C rate, showing an excellent cycle stability and highrate capability as compared with the as-prepared sample. The electrochemical performance improvement can be attributed to the influence of Sn such as enlarging Li ion diffusion channel due to large ionic radius of Sn 4+ substitution with respect to Mn 4+ , higher bonding energy of Sn-O than Mn-O, and weakening M-20 O covalency. All the influence is favorable for stabilization of the host lattice in Li-rich layered oxides. 65 the lithium ion diffusion channel and decrease the M-O covalency in Li-rich layered oxides. Correspondingly, the oxygen