Li-rich manganese-based oxides (LRMOs) with high energy density have been intensively studied, but their practical use as cathode materials for lithium-ion batteries is still impeded by the shortcomings such as low initial coulombic efficiency, voltage decay and poor rate capability. To address these issues, element Nb is selected to bulk dope and simultaneously surface modify the hierarchical LiMnCoNiO spheres in this work. Synergistic effect of Nb doping and surface modification on the crystalline structure and electrochemical performance of the resultant LRMOs is characterized in detail. The results suggest that Nb ions are doped into the interlayer sites within the crystals while the LiMnO and LiNbO double layers are coated on the primary nanoparticles. The galvanostatic charge-discharge measurements reveal that the optimal LRMO-Nb2 sample can deliver the capacities of 286 and 167 mAh g at the rates of 0.1 C and 5 C, respectively, and retains a capacity of 191 mAh g at 1 C rate after 200 cycles. Ex-situ XRD patterns prove that the layered structure is strongly pillared by the interlayer-doped Nb during the delithiation/lithiation processes. Especially, some lithium vacancies formed around Nb ions can accelerate the diffusion of Li ions, which was proved by DFT calculations and experimental results. Our research demonstrates that cooperating of the interlayered doping of Nb with surface coating of LiNbO layer can improve rate capability and cyclability of the resultant LRMOs significantly.

中文翻译：

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层间掺杂与表面改性协同提升富锂锰基正极材料性能


具有高能量密度的富锂锰基氧化物（LRMO）已得到深入研究，但其作为锂离子电池正极材料的实际应用仍因初始库伦效率低、电压衰减和倍率性能差等缺点而受到阻碍。为了解决这些问题，在这项工作中，选择元素 Nb 来批量掺杂并同时对分层 LiMnCoNiO 球体进行表面改性。详细表征了 Nb 掺杂和表面改性对所得 LRMO 晶体结构和电化学性能的协同效应。结果表明，Nb 离子掺杂到晶体内的层间位点，而 LiMnO 和 LiNbO 双层则涂覆在初级纳米颗粒上。恒电流充放电测试表明，最佳的LRMO-Nb2样品在0.1C和5C倍率下的容量分别为286和167 mAh g，并在200次后在1C倍率下保留191 mAh g的容量。循环。非原位 XRD 图证明，在脱锂/锂化过程中，层状结构受到层间掺杂 Nb 的强烈支撑。特别是，Nb离子周围形成的一些锂空位可以加速Li离子的扩散，DFT计算和实验结果证明了这一点。我们的研究表明，Nb 的层间掺杂与 LiNbO 层表面涂层的配合可以显着提高所得 LRMO 的倍率性能和循环性能。