The NASICON-type polyanionic compounds are promising cathode materials for sodium-ion batteries (SIBs) due to their robust framework and high work voltage. Motivated by the recent synthesis of high-performance Na4MnCr­(PO4)3(NMCP) [Adv. Mater.2020321906348] that exhibits a reversible three-electron process with a high energy density of 566.5 Wh/kg, we provide an in-depth theoretical study on the underlying mechanisms of ion diffusion and stability for a better understanding of the experimental results. We self-consistently calculate the Hubbard U parameters for Mn and Cr in the NMCP system using the linear response approach and successfully reproduce the three voltage plateaus observed in the experiment. At the low voltage plateau, the Na+ ions diffuse with both concerted and stepwise migration mechanisms, and the corresponding energy barrier is 0.18 and 0.21 eV. The synergy of these two mechanisms results in fast diffusion kinetics for the Na ion in NMCP. Besides, the redox couples of Mn2+/Mn3+, Mn3+/Mn4+, and Cr3+/Cr4+ are confirmed theoretically in good agreement with the experiment. Despite the distinct changes of O-2p states during the charging/discharging process, the NASICON framework of NMCP withstands the formations of O2 or (O2)2–, thus exhibiting high stability. Especially, we have identified the locking effect of Na+ ions at low Na+ concentration due to the large site energy difference and weak concerted migration, which can be effectively modulated by enlarging the lattice constants to improve the performance of NMCP during cycling.

Halide materials are of current interest as solid electrolytes for all-solid-state sodium-ion batteries (ASIBs), due to their good balance between ionic conductivity and electrochemical stability. In this work, by using density functional theory combined with deep potential model and grand potential phase diagram analysis, we report a new spinel chloride (Na 2 Y 2/3 Cl 4 ) and systemically evaluate its potential for the solid electrolyte. The spinel Na 2 Y 2/3 Cl 4 exhibits a high ionic conductivity of 0.94 mS/cm at room temperature and has a three-dimensional isotropic diffusion network comprised of face-sharing octahedra and tetrahedra. Further analysis of the diffusion mechanism indicates that the Na + conductivity mainly derives from Na ions in the 8a site while the Na ions in the 16d site are mainly used for forming the rhombus skeleton. Besides, the spinel Na 2 Y 2/3 Cl 4 has a wide electrochemical window of 0.59−3.76 V and good interfacial stability with high-voltage cathodes, which ensures its ability to improve the energy density of ASIBs. This study demonstrates the promising application of the spinel framework in sodium solid electrolytes and sheds new light on developing the halide-based solid electrolyte for ASIBs.

Among the key parts of metal-ion batteries, cathode materials significantly affect the energy density and cycling stability. However, due to the large size of K + , not much progress has been made on cathode materials for K-ion batteries (KIBs). In this study, using the Atomistic Line Graph Neural Network and first-principles calculations, for the first time we screen cathode materials for KIBs from 7385 topological quantum materials with high electronic conductivity and reversible capacity. The experimentally synthesized K 2 MnS 2 is discovered to have a reversible capacity of 203.8 mAh/g, an energy density of 564.5 Wh/kg, a small volume change of 6.4%, and multiple channels for K + transport with fast dynamics. Furthermore, K 2 MnS 2 shows high electrochemical interface stability with the reported solid electrolytes of K 4 V 2 O 7 , and K 3 NbP 2 O 9 . These findings suggest that topological quantum materials expand the design space of battery cathodes.

Disordered rock salt transition-metal oxides have emerged recently as promising electrodes for Li-ion batteries (LIBs). However, only two disordered rock salt (DRX) materials, Li 3 V 2 O 5 and Li 3 Nb 2 O 5 , have been studied as anodes so far, leaving numerous DRX compounds with vast compositions and exotic battery-related performance unexplored. Here, based on theoretical analyses and calculations, we propose a Ta pentoxide-based DRX anode with rich electrochemical properties, where the thermodynamic stability, average voltage, energy density, redox chemistry, and cation mobility are studied. Our results show that DRX-Li 3 Ta 2 O 5 can cycle three Li ions at an average voltage of 1.27 V, which is higher than that of DRX-Li 3 V 2 O 5 (0.73 V) but lower than that of DRX-Li 3 Nb 2 O 5 (1.76 V), falling in the optimal range for the high rate performance. More importantly, DRX-Li 3 Ta 2 O 5 exhibits a superhigh volumetric capacity of 1336 mAh cm −3 , which surpasses that of graphite, Li 4 Ti 5 O 12 , and DRX-Li 3 V 2 O 5 . Meanwhile, the unique geometry of DRX-Li 3 Ta 2 O 5 allows Li + to diffuse rapidly through channels with low diffusion energy barriers, and Ta 2 O 5 is electronically activated by inserting Li + into the available octahedral sites with enhanced orbital overlapping. Our work expands the family of DRX anode materials with new features.