Spinel LiNi0.5Mn1.5O4 (LNMO) is a promising cathode candidate for the next‐generation high energy‐density lithium‐ion batteries (LIBs). Unfortunately, the application of LNMO is hindered by its poor cycle stability. Now, site‐selectively doped LNMO electrode is prepared with exceptional durability. In this work, Mg is selectively doped onto both tetrahedral (8a) and octahedral (16c) sites in the Fdtrue3‾ m structure. This site‐selective doping not only suppresses unfavorable two‐phase reactions and stabilizes the LNMO structure against structural deformation, but also mitigates the dissolution of Mn during cycling. Mg‐doped LNMOs exhibit extraordinarily stable electrochemical performance in both half‐cells and prototype full‐batteries with novel TiNb2O7 counter‐electrodes. This work pioneers an atomic‐doping engineering strategy for electrode materials that could be extended to other energy materials to create high‐performance devices.

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Lithium-rich metal oxides Li 1+z MO 2 (M = Ni, Co Mn, etc) are promising positive electrode materials for high-energy lithium-ion batteries, with capacities of 250-300 mAh.g -1 that closely approach theoretical intercalation limits. Unfortunately, these materials suffer severe capacity fade on cycling, amongst other performance issues. Whilst ion substitution can improve the performance of many of these materials, the underlying mechanisms of property modification are not completely understood. In this work we show enhanced performance of the Li 1+z MO 2 electrode, consisting of Li 2 MnO 3 (with C2/m space group) and LiMO 2 (with R3m space group) phases, and establish the effects of cationic and anionic substitution on the phase and structure evolution underpinning performance changes. Whist the undoped material has a high capacity of ~ 270 mAh.g -1 , only 79% of this remains after 200 cycles. Including ~ 2% Cr in the material, likely at the R3m metal (3a) site, improved cycle performance by ~ 13% and including ~ 5% F in the material, likely at the R3m oxygen (6c) site, enhanced capacity by ~ 4-5% at the expense of a ~ 12% decline in cycle performance. Moreover, Cr doping enhances energy density retention by ~ 13% and F doping suppresses this by 17%. We find that these changes arise by different mechanisms. Both anionic and cationic substitution promote faster Li diffusion, by 48% and 20%, respectively, as determined using cyclic voltammetry and leading to better rate performance. Unlike anionic substitution, cationic substitution enhances structural stability at the expense of some capacity, by suppressing lattice distortion during Li insertion and extraction. This work implicates strategic cationic-anionic co-doping for enhanced electrochemical performance in lithium-rich layered metal-oxide phases.ABSTRACT: Lithium-rich metal oxides Li 1+z MO 2 (M = Ni, Co Mn, etc) are promising positive electrode materials for high-energy lithium-ion batteries, with capacities of 250-300 mAh.g -1 that closely approach theoretical intercalation limits. Unfortunately, these materials suffer severe capacity fade on cycling, amongst other performance issues. Whilst ion substitution can improve the performance of many of these materials, the underlying mechanisms of property modification are not completely understood. In this work we show enhanced performance of the Li(Li 0.13 Ni 0.24 Co 0.12 Mn 0.5 )O 2 electrode, consisting of Li 2 MnO 3 (with C2/m space group) and LiMO 2 (with R3 ̅ m space group) phases, and establish the effects of cationic and anionic substitution on the phase and structure evolution underpinning performance changes. Whist the undoped material has a high capacity of ~ 270 mAh.g -1 , only 79% of this remains after 200 cycles. Including ~ 2% Cr in the material, believed to reside at the R3 ̅ m metal (3a) site, improved cycle performance by ~ 13% and including ~ 5% F in the material, believed to reside at the R3 ̅ m oxygen (6c) site, enhanced capacity by ~ 4-5% at the expense of a ~ 12% decline in cycle performa...

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Oxides composed of an oxygen framework and interstitial cations are promising cathode materials for lithium‐ion batteries. However, the instability of the oxygen framework under harsh operating conditions results in fast battery capacity decay, due to the weak orbital interactions between cations and oxygen (mainly 3d–2p interaction). Here, a robust and endurable oxygen framework is created by introducing strong 4s–2p orbital hybridization into the structure using LiNi0.5Mn1.5O4 oxide as an example. The modified oxide delivers extraordinarily stable battery performance, achieving 71.4 % capacity retention after 2000 cycles at 1 C. This work shows that an orbital‐level understanding can be leveraged to engineer high structural stability of the anion oxygen framework of oxides. Moreover, the similarity of the oxygen lattice between oxide electrodes makes this approach extendable to other electrodes, with orbital‐focused engineering a new avenue for the fundamental modification of battery materials.