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Dual‐ion batteries (DIBs) inherently suffer from limited energy density. Proposed here is a strategy to effectively tackle this issue by employing locally ordered graphitized carbon (LOGC) cathodes. Quantum mechanical modeling suggests that strong anion–anion repulsions and severe expansion at the deep‐charging stage raise the anion intercalation voltage, therefore only part of the theoretical anion storage sites in graphite is accessible. The LOGC interconnected with disordered carbon is predicted to weaken the interlaminar van der Waals interactions, while disordered carbons not only interconnect the dispersed nanographite but also partially buffer severe anion–anion repulsion and offer extra capacitive anion storage sites. As a proof‐of‐concept, ketjen black (KB) with LOGC was used as a model cathode for a potassium‐based DIB (KDIB). The KDIB delivers an unprecedentedly high specific capacity of 232 mAh g−1 at 50 mA g−1, a good rate capability of 110 mAh g−1 at 2000 mA g−1, and excellent cycling stability of 1000 cycles without obvious capacity fading. [ABSTRACT FROM AUTHOR]

Potassium-ion batteries are a compelling technology for large scale energy storage due to their low-cost and good rate performance. However, the development of potassium-ion batteries remains in its infancy, mainly hindered by the lack of suitable cathode materials. Here we show that a previously known frustrated magnet, KFeC2O4F, could serve as a stable cathode for potassium ion storage, delivering a discharge capacity of ~112 mAh g−1 at 0.2 A g−1 and 94% capacity retention after 2000 cycles. The unprecedented cycling stability is attributed to the rigid framework and the presence of three channels that allow for minimized volume fluctuation when Fe2+/Fe3+ redox reaction occurs. Further, pairing this KFeC2O4F cathode with a soft carbon anode yields a potassium-ion full cell with an energy density of ~235 Wh kg−1, impressive rate performance and negligible capacity decay within 200 cycles. This work sheds light on the development of low-cost and high-performance K-based energy storage devices. The abundance and low cost of potassium makes potassium batteries a promising technology for large scale energy storage. Here the authors apply a previously known frustrated magnet, KFeC2O4F, as the cathode in which the unique structure and Fe2+/Fe3+ redox enable excellent cycling stability. [ABSTRACT FROM AUTHOR]

Sodium‐ion batteries (NIBs) are the most promising alternatives to lithium‐ion batteries in the development of renewable energy sources. The advancement of NIBs depends on the exploration of new electrode materials and fundamental understanding of working mechanisms. Herein, via experimental and simulation methods, we develop a mixed polyanionic compound, Na2Fe(C2O4)SO4⋅H2O, as a cathode for NIBs. Thanks to its rigid three dimensional framework and the combined inductive effects from oxalate and sulfate, it delivered reversible Na insertion/desertion at average discharging voltages of 3.5 and 3.1 V for 500 cycles with Coulombic efficiencies of ca. 99 %. In situ synchrotron X‐ray measurements and DFT calculations demonstrate the Fe2+/Fe3+ redox reactions contribute to electron compensation during Na+ desertion/insertion. The study suggests mixed polyanionic frameworks may provide promising materials for Na ion storage with the merits of low cost and environmental friendliness. [ABSTRACT FROM AUTHOR]

Capacity degradation by phase changes and oxygen evolution has been the largest obstacle for the ultimate commercialization of high‐capacity LiNiO2‐based cathode materials. The ultimate thermodynamic and kinetic reasons of these limitations are not yet systematically studied, and the fundamental mechanisms are still poorly understood. In this work, both phenomena are studied by density functional theory simulations and validation experiments. It is found that during delithiation of LiNiO2, decreased oxygen reduction induces a strong thermodynamic driving force for oxygen evolution in bulk. However, oxygen evolution is kinetically prohibited in the bulk phase due to a large oxygen migration kinetic barrier (2.4 eV). In contrast, surface regions provide a larger space for oxygen migration leading to facile oxygen evolution. These theoretical results are validated by experimental studies, and the kinetic stability of bulk LiNiO2 is clearly confirmed. Based on these findings, a rational design strategy for protective surface coating is proposed. Thermodynamic and kinetic reasons for structural instability of LiNiO2‐based cathode materials are studied by combined first‐principle calculation and experiments. Deep battery charging decreases oxygen reduction and induces strong thermodynamic driving force for oxygen evolution from surface and grain boundary. In contrast, oxygen evolution is kinetically prohibited in bulk phase, implying a promising direction for stabilizing these materials. [ABSTRACT FROM AUTHOR]

In this work, we perform a comprehensive study of five phenomena of LiNi 1-2x Co x Mn x O 2 (NCM) (x = 0–1/3) cathodes at the end of charge (phase reaction, crack propagation, Li-Ni exchange, phase transition, and oxygen evolution), using first-principle calculations within the DFT + U framework. Based on our results, we have located the obstacles toward unity efficiency and revealed that the degradation strongly depends on the Ni concentration and the depth of charge. The threshold capacities for degradation of Li y Ni 1-2x Co x Mn x O 2 are 130–140 mA·hg −1 (y < 0.5) for 1/4 ≤ x = 1/3 (33.33–50% of Ni), and 200–210 mA·hg −1 (y < 0.25) for 0 ≤ x = 1/4 (50–100% of Ni), respectively. For 1/4 ≤ x = 1/3, our results show that the origin of the degradation is the oxidation of O 2− , which is the result of the pining of O-p and Ni-d bands at the valence band edge. For 0 ≤ x = 1/4, lattice distortion and Li-Ni exchange are the mechanisms responsible for the degradation of the cathode material, leading to severe structural instabilities in the Ni-rich region (x = 0.1). Our findings will help to rationally design NCM cathode materials with high-energy density, also providing possible solution mechanisms to the degradation factors, such as doping, coating or novel nanostructures, like core-shell or concentration gradient cathodes. [ABSTRACT FROM AUTHOR]

Conventional interatomic potential methods for Li-ion battery cathode materials normally use fixed-charge models, which are not accurate enough to model the dynamical oxidation state change of transition metals during electrochemical reactions. In order to enable more accurate large-scale simulations for battery cathode materials, here we report a semiempirical interatomic potential of the Li-Ni-O ternary system based on an advanced dynamic charge method: Charge-Transfer Modified Embedded-Atom Method (CT-MEAM). The potential is parameterized by fitting the atomic Bader charges and energy-strain curves of the LiNiO 2 cathode material under uniaxial, biaxial and hydrostatic strains to results obtained with ab initio density-functional theory (DFT) calculations. A variety of structural, electrochemical and dynamical properties derived from the fitted CT-MEAM potential are observed to be in excellent agreement with previous DFT and experimental data. The transferability of the potential is validated by comparing relative phase stabilities and charge distribution states within the ternary Li-Ni-O systems. Our results support the capability of the present CT-MEAM to model complex ternary transition metal oxides. This method will facilitate not only the optimal design of Lithium-ion battery cathode materials, but also other transition metal oxide-based applications involving electrochemical reactions. [ABSTRACT FROM AUTHOR]

• Synergies effect enhance electrochemistry performance in Ni/GDY composite material. • A very low overpotential of 12 mV archive in Ni/GDY composite. • The cycle efficiency archive 98.5%, and have a cycle time of up to 2200 h in Ni/GDY. The growth of lithium dendrites during repeated deposition or dissolution is a key issue that inhibits lithium metal anodes for high energy density batteries. Here, we demonstrate nickel-anchored graphdiyne materials by solvothermal method on three-dimensional copper foam and apply them to Li metal deposition and stripping. The graphdiyne has a very high Li storage capacity, but poor Li affinity. On the other hand, Ni is highly lithiophilicity and the rich nanoporous structure of graphdiyne provides a stable Li deposition interface, enabling high-efficiency and high-capacity Li deposition and stripping. Ni-anchored graphdiyne modified copper foam substrate can achieve high-area, high-rate dendrite-free Li deposition and stripping. The deposition and stripping of 1 mA h cm−2 of lithium at a current density of 1 mA cm−2 show an overpotential of about 12 mV, high cycle efficiency of 98.5%, and a cycle time of up to 2200 h. The cycle efficiency can reach 98% at higher current density and higher lithium deposition and stripping amount. We assemble a full battery with Ni/GDY@Li using LiFePO 4 as the cathode material, showing excellent capacity and cycling stability. [Display omitted] [ABSTRACT FROM AUTHOR]