Ni/Li exchange is a detrimental effect on electrochemical performances for high-Ni cathode materials (LiNi_xCo_yMn_zO₂, x ≥ 0.6). Adjusting Li-excess degree has been proved to be an effective way to optimize Ni/Li exchange in the materials. However, until now, how the Ni/Li exchange and thus the structural properties is affected by the Li-excess has not been understood and clearly elucidated in the literature. Herein, a feasible strategy is utilized to optimize Ni/Li exchange and the amount of anti-Li⁺ in LiNi_0.8Co_0.1Mn_0.1O₂ by mixing Ni_0.8Co_0.1Mn_0.1(OH)₂ precursor with different amounts of lithium sources during lithiation. It was found that morphology and phase stability of the material can be tuned with moderate excessive lithium. With 10% Li-excess, LiNi_0.8Co_0.1Mn_0.1O₂ exhibits an initial discharge capacity of 211.5 mAh·g^–1 at 0.1 C and maintains 93.3% of its initial capacity after 100 cycles at 1 C. Different technologies were used to characterize the materials and it shows that the formation of broader Li slab space, decreased anti-Ni²⁺ in Li layer, and gradient distribution of Ni³⁺ in the surface is contributed to moderate Li-excess in the materials. Broader Li slab space facilitates diffusion of Li⁺, decreased antisite-Ni²⁺ and gradient distribution of Ni³⁺ in materials surfaces optimizes the Ni/Li exchange. Based on these results, we thus believe that it is the moderate Li-excess in material that optimized the electrochemical performance of high-Ni cathode materials.

With high reversible capacities of more than 200 mAh/g, Ni-rich layered oxides Li[Ni_xCo_yMn_1–x–y]O₂ (x ≥ 0.6) serve as the most promising cathode materials for lithium-ion batteries (LIBs). However, the anisotropic lattice volume changes linked to their α-NaFeO₂ structured crystal grains bring about poor cycle performances for conventionally produced NCM materials. To deal with these issue, single-crystal µm-sized LiNi_0.8Co_0.1Mn_0.1O₂ rods was synthesized by a hydrothermal method. Compared with conventional synthesis methods, these LiNi_0.8Co_0.1Mn_0.1O₂ rods were calcined at a low temperature with excessive lithium sources, which not only reduces the sintering temperature but also ensures the mono-dispersed micrometer-scaled particle distribution. When used as the cathode material for LIBs, the as-prepared LiNi_0.8Co_0.1Mn_0.1O₂, with ordered layered-structure and low degree of cation mixing, shows excellent electrochemical performances. When sintered at 750 °C with 50% Li-excess, the cathode material delivered an initial discharge capacity of 226.9 mAh/g with Coulombic efficiency of 91.2% at 0.1 C (1 C = 200 mA/g) in the voltage range of 2.8‒4.3 V. When charge-discharged at 1 C for 100 cycles, discharge capacity of 178.1 mAh/g with the capacity retention of 95.1% are still obtained. The cycling stability at high cut-off voltage is also outstanding. These superior electrochemical properties should be related to the monodispersed micron scaled morphology which not only decreases the contact area between electrode and electrolyte but also mitigates the formation of microcracks. This low-temperature strategy of synthesizing single-crystal LiNi_0.8Co_0.1Mn_0.1O₂ rods should be able to provide a feasible method for synthesizing other single-crystal Ni-rich cathode materials with excellent electrochemical performances for LIB.

Lithium-rich layered oxides (LLOs) have been extensively studied as cathode materials for lithium-ion batteries (LIBs) by researchers all over the world in the past decades due to their high specific capacities and high charge-discharge voltages. However, as cathode materials LLOs have disadvantages of significant voltage and capacity decays during the charge-discharge cycling. It was shown in the past that fine-tuning of structures and compositions was critical to the performances of this kind of materials. In this report, LLOs with target composition of Li_1.17Mn_0.50Ni_0.24Co_0.09O₂ were prepared by carbonate co-precipitation method with different pH values. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and electrochemical impedance spectroscopies (EIS) were used to investigate the structures and morphologies of the materials and to understand the improvements of their electrochemical performances. With the pH values increased from 7.5 to 8.5, the Li/Ni ratios in the compositions decreased from 5.17 to 4.64, and the initial coulombic efficiency, cycling stability and average discharge voltages were gained impressively. Especially, the material synthesized at pH = 8.5 delivered a reversible discharge capacity of 263 mAh·g^-1 during the first cycle, with 79.0% initial coulombic efficiency, at the rate of 0.1 C and a superior capacity retention of 94% after 100 cycles at the rate of 1 C. Furthermore, this material exhibited an initial average discharge voltage of 3.65 V, with a voltage decay of only 0.09 V after 50 charge-discharge cycles. The improved electrochemical performances by varying the pH values in the synthesis process can be explained by the mitigation of layered-to-spinel phase transformation and the reduction of solid-electrolyte interface (SEI) resistance. We hope this work can shed some light on the alleviation of voltage and capacity decay issues of the LLOs cathode materials.

Spinel phase LiMn₂O₄ was successfully embedded into monoclinic phase layeredstructured Li₂MnO₃ nanorods, and these spinel-layered integrate structured nanorods showed both high capacities and superior high-rate capabilities as cathode material for lithium-ion batteries (LIBs). Pristine Li₂MnO₃ nanorods were synthesized by a simple rheological phase method using α-MnO₂ nanowires as precursors. The spinel-layered integrate structured nanorods were fabricated by a facile partial reduction reaction using stearic acid as the reductant. Both structural characterizations and electrochemical properties of the integrate structured nanorods verified that LiMn₂O₄ nanodomains were embedded inside the pristine Li₂MnO₃ nanorods. When used as cathode materials for LIBs, the spinel-layered integrate structured Li₂MnO₃ nanorods (SL-Li₂MnO₃) showed much better performances than the pristine layered-structured Li₂MnO₃ nanorods (L-Li₂MnO₃). When charge-discharged at 20 mA·g^-1 in a voltage window of 2.0-4.8 V, the SL-Li₂MnO₃ showed discharge capacities of 272.3 and 228.4 mAh·g^-1 in the first and the 60th cycles, respectively, with capacity retention of 83.8%. The SL-Li₂MnO₃ also showed superior high-rate performances. When cycled at rates of 1 C, 2 C, 5 C, and 10 C (1 C = 200 mA·g^-1) for hundreds of cycles, the discharge capacities of the SL-Li₂MnO₃ reached 218.9, 200.5, 147.1, and 123.9 mAh·g^-1, respectively. The superior performances of the SL-Li₂MnO₃ are ascribed to the spinel-layered integrated structures. With large capacities and superior high-rate performances, these spinel-layered integrate structured materials are good candidates for cathodes of next-generation high-power LIBs.