Li-rich layered oxides have attracted much attention for their potential application as cathode materials in lithium ion batteries, but still suffer from inferior cycling stability and fast voltage decay during cycling. How to eliminate the detrimental spinel growth is highly challenging in this regard. Herein, in situ K(+)-doped Li1.20Mn0.54Co0.13Ni0.13O2 was successfully prepared using a potassium containing α-MnO2 as the starting material. A systematic investigation demonstrates for the first time, that the in situ potassium doping stabilizes the host layered structure by prohibiting the formation of spinel structure during cycling. This is likely due to the fact that potassium ions in the lithium layer could weaken the formation of trivacancies in lithium layer and Mn migration to form spinel structure, and that the large ionic radius of potassium could possibly aggravate steric hindrance for spinel growth. Consequently, the obtained oxides exhibited a superior cycling stability with 85% of initial capacity (315 mA h g(-1)) even after 110 cycles. The results reported in this work are fundamentally important, which could provide a vital hint for inhibiting the undesired layered-spinel intergrowth with alkali ion doping and might be extended to other classes of layered oxides for excellent cycling performance.

Multicomponent spinel metal-oxide assembled mesoporous microspheres, promising anode materials for Li-ion batteries with superior electrochemical performance, are usually obtained using different kinds of precursors followed by high-temperature post-treatments. Nevertheless, high-temperature calcinations often cause primary particles to aggregate and coarsen, which may damage the assembled microsphere architectures, leading to deterioration of electrochemical performance. In this work, binary spinel metal-oxide assembled mesoporous microspheres MnCo2O4 were fabricated by one-step low-temperature solvothermal method through handily utilizing the redox reaction of nitrate and ethanol. This preparation method is calcination-free, and the resulting MnCo2O4 microspheres were surprisingly assembled by nanoparticles and nanosheets. Two kinds of MnCo2O4 crystal nucleus with different exposed facet of (1̅10) and (11̅2̅) could be responsible for the formation of particle-assembled and sheet-assembled microspheres, respectively. Profiting from the self-assembly structure with mesoporous features, MnCo2O4 microspheres delivered a high reversible capacity up to 722 mAh/g after 25 cycles at a current density of 200 mA/g and capacities up to 553 and 320 mAh/g after 200 cycles at a higher current density of 400 and 900 mA/g, respectively. Even at an extremely high current density of 2700 mA/g, the electrode still delivered a capacity of 403 mAh/g after cycling with the stepwise increase of current densities. The preparation method reported herein may provide hints for obtaining various advanced multicomponent spinel metal-oxide assembled microspheres such as CoMn2O4, ZnMn2O4, ZnCo2O4, and so on, for high-performance energy storage and conversion devices.

rate capability. [ 12,13 ] In contrast, spinel cathodes exhibit a high-rate capability due to the effi cient 3D diffusion of lithium ions, nevertheless the discharge capacity is low, only about 130 mA h g −1 . [ 14,15 ] Then, a highly interesting, but also challenging question appears: can the rate capability be much improved by introducing spinel component into the layered oxides? Previous investigations have shown that the cubic close-packed oxygen arrays in both the layered and spinel oxides are structurally compatible. [ 16 ] Therefore, it is possible to integrate the Li-rich layered and spinel oxides into a composite, which might show both a high capacity and an excellent rate capability.Much effort has been devoted to the preparation of composites that intergrate both layered Li-rich oxides and spinel oxides (i.e., spinel-layered materials), which have led to several high-energy and power electrodes, [17][18][19][20] such as the outstanding cathode materials of spinel/ layered heterostructure, [ 17 ] [ 18 ] Unfortunately, most synthetic methods still suffer from several shortcomings. For instance, it is diffi cult to obtain a homogeneous mixture of layered and spinel oxides. The preparation procedures are always tedious, which may introduce uncertain factors in reproducing the electrochemical performance. On the other hand, metal-ion impurities, such as K + , were inevitably introduced into the fi nal products. In particular, the synthetic methods ever reported cannot allow the control over the morphology to give microspheres of spinellayered materials, due to the multiple transition metal ions and phases involved. As a consequence, spherical spinel-layered cathode materials are highly necessary, which expect to impose a signifi cant impact on electrochemical performance (especially for rate capability) of Li-ions batteries.Here, we report on the preparation of a spinel-layered Lirich Li-Mn-Co-O microsphere using a solvothermal-precursor method. This method is an extension of ther oxalate-precursor method, [ 21 ] which has been successfully applied to prepare Lirich layered composite cathodes. This new method has the advantages of the oxalate-precursor method where lithium ions and transition metal ions are precipitated simultaneously in the absence of alkali metal ions to form uniform precursors, and provides the possibility for regulation of spherical morphology and dimension. Based on previous results, [ 16,22 ] we Li-rich layered materials are considered to be the promising low-cost cathodes for lithium-ion batteries but they suffer from poor rate capability despite of efforts toward surface coating or foreign dopings. Here, spinel-layered Li-rich Li-Mn-Co-O microspheres are reported as a new high-rate cathode material for Li-ion batteries. The synthetic procedure is relatively simple, involving the formation of uniform carbonate precursor under solvothermal conditions and its subsequent transformation to an assembled microsphere that integrates a spinel-like component with a layered component by a heat...

Nickel-rich layered metal oxide materials are prospective cathode materials for lithium ion batteries due to the relatively higher capacity and lower cost than LiCoO2. Nevertheless, the disordered arrangement of Li(+)/Ni(2+) in local regions of these materials and its impact on electrochemistry performance are not well understood, especially for LiNi(1-x-y)Co(x)Mn(y)O2 (1-x-y > 0.5) cathodes, which challenge one's ability in finding more superior cathode materials for advanced lithium-ion batteries. In this work, Ni-Co-Mn-based spherical precursors were first obtained by a solvothermal method through handily utilizing the redox reaction of nitrate and ethanol. Subsequent sintering of the precursors with given amount of lithium source (Li-excess of 5, 10, and 15 mol %) yields LiNi0.7Co0.15Mn0.15O2 microspheres with different extents of Li(+)/Ni(2+) disordering. With the determination of the amounts of Li(+) ions in transition metal layer and Ni(2+) ions in Li layer using structural refinement, the impact of Li(+)/Ni(2+) ions disordering on the crystal structure, valence state of nickel ions, and electrochemical performance were investigated in detailed. It is clearly demonstrated that with increasing the amount of lithium source, lattice parameters (a and c) and interslab space thickness of unit cell decrease, and more Li(+) ions incorporated into the 3a site of transition metal layer which leads to an increase of Ni(3+) content in LiNi0.7Co0.15Mn0.15O2 as confirmed by X-ray photoelectron spectroscopy and a redox titration. Moreover, the electrochemical performance for as-prepared LiNi0.7Co0.15Mn0.15O2 microspheres exhibited a trend of deterioration due to the changes of crystal structure from Li(+)/Ni(2+) mixing. The preparation method and the impacts of Li(+)/Ni(2+) ions disordering reported herein for the nickel-rich layered LiNi0.7Co0.15Mn0.15O2 microspheres may provide hints for obtaining a broad class of nickel-rich layered metal oxide microspheres with superior electrochemical performance.

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We initiated a self-adjusted oxygen-partial-pressure approach to prepare high-performance Li 2 MnO 3 -LiMO 2 cathode material. Four different lithium resources, lithium acetate, lithium hydrate, lithium carbonate, and lithium nitrate were used to create the local oxygen partial pressure over the samples. Since the melting points or decomposition temperatures for these lithium resources decrease in a sequence, Li 2 CO 3 z LiOH > LiNO 3 > CH 3 COOLi, the oxygen partial pressure of the four crucibles that contain these lithium salts increases in a sequence, S4 z S3 < S2 < S1 z air in muffle furnace (S1:and S4: Li 2 CO 3 ). Regardless of the lithium resources, the decomposed gases reduced the local oxygen partial pressures, leading to an incomplete oxidation of Mn ions in the final product Li[Li 0.14 Mn 0.47 Ni 0.25 Co 0.14 ]O 2 . That is, some of the Mn 3+ ions existed in the final product Li[Li 0.14 Mn 0.47 Ni 0.25 Co 0.14 ]O 2 , and the amount of Mn 3+ ions was closely related to the oxygen partial pressure. The lower oxygen partial pressure gave rise to a larger amount of Mn 3+ in the final products, as confirmed by X-ray photoelectron spectroscopy. Electrochemical tests showed that the products prepared using lithium carbonate exhibited the best electrochemical performance: the initial discharge capacity was 279.4 mA h g À1 at a current density of 20 mA g À1 , which remained as high as 187.2 mA h g À1 even at a much higher current density of 500 mA g À1 . Such excellent electrochemical performance could be ascribed to the presence of Mn 3+ that decreased the surface layer resistance and charge transfer resistance, and that further increased the conductivity and Li + ion diffusion coefficient.

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