As one of the most promising cathodes for Li‐ion batteries, Li‐rich layered oxides suffer from low Coulombic efficiency, severe capacity fading, and voltage decay, which are related to the aggregated Li@Mn6 superstructure units. Herein, a Co‐free Li‐rich oxide Li[Li1/4Mn1/2Ni1/6Al1/12]O2 through Al substitution of Co in Li[Li1/4Mn1/2Ni1/6Co1/12]O2, is designed. Combining the average structural refinement with the detailed local structural/chemical analysis, it is found that the introduced Al ions occupy the Mn sites in Li@Mn6 superstructure units, which further induces the partial replacement of the central Li ions in Li@Mn6 units by Ni2+. The modified superstructure units stabilize the anionic framework and suppress structural degradation during long‐term cycling. A superior cyclability (a capacity retention of 91.4% after 500 cycles at 1 C) is achieved. This work not only deepens the understanding into the mechanism of Al substitution, but also provides a novel route to design high‐performance Li‐rich cathodes by modifying the local functional units.

The cathode materials work as the host framework for both Li + diffusion and electron transport in Liion batteries. The Li + diffusion property is always the research focus, while the electron transport property is less studied. Herein, we propose a unique strategy to elevate the rate performance through promoting the surface electric conductivity. Specifically, a disordered rock-salt phase was coherently constructed at the surface of LiCoO 2 , promoting the surface electric conductivity by over one magnitude. It increased the effective voltage (V eff ) imposed in the bulk, thus driving more Li + extraction/insertion and making LiCoO 2 exhibit superior rate capability (154 mAh g À 1 at 10 C), and excellent cycling performance (93 % after 1000 cycles at 10 C). The universality of this strategy was confirmed by another surface design and a simulation. Our findings provide a new angle for developing high-rate cathode materials by tuning the surface electron transport property.

Alkali metals have low potentials and high capacities, making them ideal anodes for next‐generation batteries, but they suffer major problems, including dendrite growth and low Coulombic efficiency (CE). Achieving uniform metal deposition and having a reliable solid electrolyte interphase (SEI) are the basic requirements for overcoming these problems. Here, a general remedy is reported for various alkali‐metal anodes by the supramolecularization of alkali‐metal cations with crown ethers that follows a size‐matching rule. The positively charged supramolecular complex provides electrostatic shielding layers to regulate metal deposition and suppress dendrite formation. More promisingly, it reforms electric double layers and drives the production of organic‐dominated SEIs with improved flexibility that can accommodate large volume changes. The high flexibility of SEIs during metal deposition and dissolution reduces the amount of dead metal and improves CE and cycling stability. Specifically, a 200% excess Li‐based full cell has a capacity retention of ≈100% after 100 cycles. This crown‐like supramolecularization strategy is a new chemistry that may be used for the production of dendrite‐free metal‐anode‐based batteries not limited to the cases with alkali metal. It is also expected as a practical technology to improve the uniformity of coatings produced in the electrodeposition industry.

energy density among the reported cathode materials, thus dominates the current battery market for electronics. [3,4] The practical reversible capacity of LCO is only ≈160 mA h g −1 with a cutoff voltage of 4.35 V, far below the theoretical capacity (274 mA h g −1 ), thus there is still a large space for expanding the capacity. [5,6] Further increasing the charging cutoff voltage is the most effective approach to extract more Li + from the LCO framework. [7,8] For example, La-and Al-co-doped LCO offered an initial capacity of ≈190 mA h g −1 with a cut-off voltage of 4.5 V and retained 96% capacity after 50 cycles, [9] and Ti-Mg-Al co-doped LCO offered an initial capacity of 202 mA h g −1 with a cut-off voltage of 4.6 V and retained 86% capacity after 100 cycles. [10] However, the origin of structural stability by these trace doping remains unclear, which restricts the further development of high-voltage LCO.Our recent work revealed the structural differences between regular LCO and high-voltage LCO at the atomic level, and correlated the curvature of the Co-O layers near the surface with structural instability. [11] Li's group reported a hybrid Co cation and O anion redox occurred at a high voltage of 4.6 V. [12] As shown in Scheme 1a, the generated Co 4+ and O − species at high potentials would induce the severe surface side reactions, including the catalytic decomposition of the carbonate-based electrolyte, and the lattice O loss in the form of CO 2 . Such O loss would lead to the irreversible Co migration, formation of dense Co 3 O 4 spinel phase at the surface that would block Li + diffusion, [13] and lattice distortion in the bulk evolving into microcracks upon cycling. [14] Aiming to effectively resolve these critical issues, surface engineering is proved to be a direct and efficient strategy. [15] Lu's group reported the ternary lithium, aluminum, fluorine-modified LCO with improved cycling stability when operating at 4.6 V. [16] However, the active material was covered with a large amount of Al 2 O 3 and LiAlO 2 particles rather than a uniform coating layer, and it was still susceptible to HF attack from the electrolyte, thus the interfacial stability and structural integrity deteriorated upon longterm cycling. LCO with modified surface by electrochemically stable solid electrolyte Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 was prepared through mechanical mixing followed by a high-temperature annealing process to mitigate the catalytic effect of surficial Co 4+ species at LiCoO 2 (LCO) is the most successful cathode material for commercial lithium-ion batteries. Cycling LCO to high potentials up to 4.5 V or even 4.6 V can significantly elevate the capacity but cause structural degradation due to the serious surface side reaction between the highly oxidized Co 4+ and O − species with organic electrolytes. To tackle this concern, a new strategy, constructing cation and anion dual gradients at the surface of LCO (DG-LCO), is proposed. Specifically, the electrochemically inactive cation and anion are selected to substitu...