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Micro‐sized bismuth (Bi) is recognized for its high volumetric capacity and suitable working potential, making it a promising anode candidate for sodium‐ion batteries (SIBs). However, its substantial volume changes and slow reaction kinetics during cycling detrimentally affects the SIB performance. Theoretical prediction uncovers a previously unexplored favorable attribute that bonding between nitrogen within a carbon coating and Bi atoms facilitates Na+ ingress into the Bi bulk, significantly enhancing Bi‐Na alloying reactions, mitigating volume expansion, and preventing Na‐dendrite formation. Experimentally, the study innovatively engineers a flower‐like micro‐sized Bi encapsulated within an elastic, nitrogen‐doped carbon framework (FBi@NC) working as an efficient anode for SIBs. This design enables FBi@NC anode achieving a high tap density of 2.86 g cm−3 and delivering a remarkable volumetric capacity of 1100 mAh cm−3 at 1 mA cm−2. It also exhibits exceptional rate capability (368.2 mA h g−1 at 30 A g−1) and super durable cyclability (10 000 cycles with 318.8 mA h g−1 at 5 A g−1, retaining 82% capacity). Full cells with Na3V2(PO4)3 cathodes demonstrate superior rate and cycling performances. Crucially, this study elucidates the underlying Na+‐storage mechanisms and the contributory factors to performance enhancement, providing vital insights for the development of high‐energy and stable SIBs. [ABSTRACT FROM AUTHOR]

Alloying‐type antimony (Sb) with high theoretical capacity is a promising anode candidate for both lithium‐ion batteries (LIBs) and sodium‐ion batteries (SIBs). Given the larger radius of Na+ (1.02 Å) than Li+ (0.76 Å), it was generally believed that the Sb anode would experience even worse capacity degradation in SIBs due to more substantial volumetric variations during cycling when compared to LIBs. However, the Sb anode in SIBs unexpectedly exhibited both better electrochemical and structural stability than in LIBs, and the mechanistic reasons that underlie this performance discrepancy remain undiscovered. Here, using substantial in situ transmission electron microscopy, X‐ray diffraction, and Raman techniques complemented by theoretical simulations, we explicitly reveal that compared to the lithiation/delithiation process, sodiation/desodiation process of Sb anode displays a previously unexplored two‐stage alloying/dealloying mechanism with polycrystalline and amorphous phases as the intermediates featuring improved resilience to mechanical damage, contributing to superior cycling stability in SIBs. Additionally, the better mechanical properties and weaker atomic interaction of Na−Sb alloys than Li−Sb alloys favor enabling mitigated mechanical stress, accounting for enhanced structural stability as unveiled by theoretical simulations. Our finding delineates the mechanistic origins of enhanced cycling stability of Sb anode in SIBs with potential implications for other large‐volume‐change electrode materials. [ABSTRACT FROM AUTHOR]

Prussian blue analogues (PBAs) are promising cathode materials for sodium‐ion batteries (SIBs) due to their tunable chemistry, open channel structure, and low cost. However, excessive crystal water and volume expansion can negatively impact the lifetime of actual SIBs. In this study, a novel iron nitroprusside: Fe[Fe(CN)5NO] (PBN) was synthesized to effectively eliminate the detrimental effects of crystal water on the reversible capacity and cycling stability of PBA materials. Experiments and DFT calculations demonstrated that PBN has lower crystal water and volume expansion compared to Fe[Fe(CN)6] (PB). Also, the N=O bond in PBN significantly reduces the diffusion potential of Na+ in the skeleton. Without any modification, the cathode material exhibited a capacity of up to 148.6 mAh g−1 at 50 mA g−1 as well as maintained 102.9 mAh g−1 after 200 cycles. This work expands our knowledge of the crystal structure of PBA cathode materials and facilitates the rational design of high‐quality PBA cathodes for SIBs. [ABSTRACT FROM AUTHOR]

To address the issues of low specific capacity and poor cycle performance of Prussian blue analogues as cathode materials for sodium-ion batteries, this work performed surface etching modification on the synthesized Fe 0.8 Co 0.2 HCF with a regular cubic structure and optimized its electrochemical performance. The resulting grooved structure further enhanced the electrode material significantly. The results show that the etched sample delivers a discharge capacity of 153.3 mAh/g at 0.5 C and retains 83.3% after 200 cycles at 2 C. When the rate returns from 16 C to 0.5 C, the discharge capacity can be maintained at about 90.7%. Based on experimental analysis and theoretical calculation, the improved electrochemical performance of the etched sample is mainly attributed to the following three aspects: (1) fast diffusion of Na+; (2) reduced water content; (3) large contact area between electrode and electrolyte. [Display omitted] • Groove structures on Prussian blue analogues particles for cathodes of sodium-ion batteries were created by etching. • Etched samples have three advantages: (1) faster diffusivity of Na+; (2) lower water content; (3) larger specific area. • Etching process greatly improved the specific capacity of the samples at high rates. • Kinetic process of Na+ migration through grooves was revealed by density functional theory calculations. [ABSTRACT FROM AUTHOR]

The Prussian blue analogues (PBA) Na x MFe(CN) 6 (M = 3d transition metal) synthesized by conventional synthesis methods usually contain defects. This hinders our understanding of its intrinsic properties as a cathode material, and causes difficulties in designing composite electrodes with heterogeneous structures. In this work, we performed first-principles calculations to study the properties of Na x MFe(CN) 6 (M = Fe, Cr, Mn, Sc, Zn, V, Ti, Co, Ni, Cu) compounds as cathode materials for sodium-ion batteries, focusing on their structural stability, thermal effects and electrical performance during charging and discharging. The results confirm the strong correlation between the M element and the intrinsic characteristics of Na x MFe(CN) 6 in the process of inserting/extracting sodium ions, and revealed the thermodynamic mechanism of the apparent physical properties related to the sodium-ion concentration. Based on the intrinsic physicochemical properties of Na x MFe(CN) 6 systems, it is promising to develop sodium-ion cathode materials with complex heterostructures. First-principle computations demonstrate that Prussian blue analogues Na x MFe(CN) 6 (M = 3d transition metal) as the cathode material for Na-ion battery has the composition-dependent properties. [Display omitted] • Intrinsic structural stability, thermal effects and electrical performance of NaxMFe(CN)6 were studied. • Stability of cyanide-bridged bimetallic assemblies is associated with M-Na interaction. • Strong Jahn-Teller effect was found in NaxNiFe(CN)6 and NaxCuFe(CN)6. • NaxTiFe(CN)6 show the most stable voltage in the discharging process. • Temperature-induced volume effect of NaxCrFe(CN)6 is lower than other compounds. [ABSTRACT FROM AUTHOR]

Prussian blue analogues (PBA) are promising cathode materials because of their low-cost and wide diffusion tunnels for sodium ion batteries. However, several key challenges, such as low actual capacity and high voltage instability, restrain their further development. Here, we investigate the influence of pH value on the electrochemical performances of Na 2 MnFe(CN) 6 cathodes during co-precipitation process. When the pH equals to 3.0, the sample shows the high content of sodium, low contents of interstitial water molecules and Fe(CN) 6 defects, which achieves a high discharge capacity (~130.6 mAh g−1) and a capacity retention of 72% after 100 cycles at 1C. As the pH becomes 9.0, the sample exhibits an excellent high-rate capability, and the discharge capacity can still remain about 92% when the rate goes back to 0.1C from 5C. Besides, the sample also reveals capacity retention of about 80% after 100 cycles at 1C, which shows the best stability among all samples. The enhanced performances could be mainly ascribed to two aspects: on the one hand, the high content of Na+ contributes to high specific capacity; on the other hand, less Fe(CN) 6 defects are beneficial to Na+ ion diffusion and stabilize the structure during the Na+ insertion/extraction process. Unlabelled Image • The different PBM samples are successfully prepared by controlling pH value. • The effects of different pH value on the properties of PBM are discussed in detail. • The PBM-3 sample exhibits the highest content of sodium and discharge capacity. • The PBM-9 sample reveals capacity retention of about 80% after 100 cycles at 1C. [ABSTRACT FROM AUTHOR]