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We propose P3-K0.54[Co0.5Mn0.5]O2, which is rationally designed as a promising cathode material for high-performance potassium-ion batteries (KIBs). Its composition adopts the use of the valence state of Mn above 3.5 + to minimize the disruptive effect of Jahn–Teller distortion in the MnO6octahedra during the electrochemical reaction. Unlike other types of layered materials that suffer from the sluggish diffusion of large potassium ions accompanying multi-step voltage profiles, P3-K0.54[Co0.5Mn0.5]O2delivers a high specific discharge capacity of 120.4 mAh (g-oxide)−1with smooth charge and discharge curves. First-principles calculations predict an activation barrier energy of ∼260 meV for a large K+diffusion, which is comparable to those observed in conventional layered cathode materials for lithium-ion batteries. As a result, even at 500 mA g−1, P3-K0.54[Co0.5Mn0.5]O2is able to deliver a high discharge capacity of 78 mAh g−1, which is a retention of 65% versus the capacity obtained at 20 mA g−1. Combination studies using operandoX-ray diffraction, the ex-situX-ray absorption near-edge structure, and first-principles calculations elucidate the nature of the excellent potassium storage mechanism of K0.54[Co0.5Mn0.5]O2. This work provides a new insight for the development of efficient cathode materials for KIBs.

The O3-type Na[Ni1–x–yCoxMny]O2cathodes have received significant attention in sodium-ion batteries (SIBs) due to their high energy density. However, challenges such as structural instability and interfacial instability against an electrolyte solution limit their practical use in SIBs. In this study, the single-crystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2(SC-NCM) cathode has been designed and synthesized to effectively relieve the degradation pathways of the polycrystalline O3-type Na[Ni0.6Co0.2Mn0.2]O2(PC-NCM) cathode for SIBs. The mechanically robust SC-NCM due to the absence of pores in the particles enhances tolerance to particle cracking, resulting in stable cycling performance with a cycle retention of 73% over 350 cycles. Moreover, the proposed SC-NCM is synthesized using a simple and cost-effective molten-salt synthetic route without the complex quenching process typically associated with PC-NCM synthesis methods, showing good practical applicability. This study will provide an innovative direction for the development of advanced cathode materials for practical SIBs.

Lithium-ion batteries (LIBs) are widely used in various electronic devices and have garnered a huge amount of attention. In addition, evaluation of the intrinsic properties of LIB cathode materials is of considerable interest for practical applications. Therefore, through first-principles calculations based on the density functional theory, we investigated the structural, electronic, electrochemical, and kinetic properties of mixed transition metals, that is, Ni-substituted LiMnPO4(LMP) and LiMnPO4F (LMPF) cathode materials, that is, LiMn0.5Ni0.5PO4(LMNP) and LiMn0.5Ni0.5PO4F (LMNPF), respectively, which have not been extensively studied. We also evaluated their delithiated phases, that is, Mn0.5Ni0.5PO4(MNP) and Mn0.5Ni0.5PO4F (MNPF). Our calculations suggest that Ni substitution significantly affected the structural and electrochemical properties. After Li insertion, the MNPF unit-cell volume increased by about 8%, lower than that of pristine MnPO4F. The Li intercalation voltage also increased in LMNP (4.27 V) and LMNPF (5.23 V). In addition, the migration barrier was calculated to be 0.4 eV for LMNPF, lower than that of LMPF. This study may provide insights for developing LMNP and LMNPF cathode materials in LIB applications.

P2-type layered oxides have been considered promising candidates as cathodes for sodium-ion batteries (SIBs) owing to their high capacity and high rate capability. However, because of the difficulty involved in forming hierarchical microstructures, it remains challenging to develop high energy density P2-type layered oxides with good electrochemical performance and high electrode density. In this study, we demonstrate the feasibility of P2-type Na0.65[Ni0.17Co0.11Mn0.72]O2as a very efficient cathode material for high energy density SIBs by synthesizing a micron-sized hierarchical structure via the coprecipitation route. The as-prepared P2-type microsphere cathode constructed from nanoscale primary particles provides a sufficient interface between the electrodes and the electrolyte solution, which enables to shorten the transport pathways for Na+ions and electrons. Simultaneously, the hierarchical microstructure enhances the structural stability and high tap density (∼1.18 g cm–3). Benefiting from these merits, the proposed P2-type microsphere Na0.65[Ni0.17Co0.11Mn0.72]O2displays a high discharge capacity of 187 mA h g–1at 12 mA g–1and an exceptional cycle retention of 74.7% after 500 cycles, even at the high current density of 600 mA g–1. In addition, the high tap density of this P2-type microsphere enhances the density of composite cathodes, which translates to a high volumetric energy density of 340 W h L–1based on the overall volume of the cathode active mass and the aluminum foil current collector.

Cationic alteration related to a sodium super ion conductor (NASICON)-structured Na3V2(PO4)3(NVP) is an effective strategy for formulating high-energy and stable cathodes for sodium-ion batteries (SIBs). In this study, we altered the structure of NVP with dual cations, namely, Cr and Fe, to develop Na3V1.5Cr0.4Fe0.1(PO4)3cathodes for SIBs with high-rate capability (∼71 mAh g–1at 100 C) and an extreme cycle life output (∼75 mAh g–1with 95% capacity retention for 10,000 cycles). These excellent electrochemical properties can be ascribed to the synergistic effects of Cr and Fe in the NVP structure, as verified experimentally and theoretically. Therefore, the proposed cosubstitution method can enhance the performance of SIBs by improving their structural stability, electronic conductivity, and phase-change behavior.