Interfacial Engineering of Na₃V₂(PO₄)₂F₃ Hollow Spheres through Atomic Layer Deposition of TiO₂: Boosting Capacity and Mitigating Structural Instability

Abstract

To mitigate the associated challenges of instability and capacity improvement in Na3V2(PO4)2F3 (NVPF), rationally designed uniformly distributed hollow spherical NVPF and coating the surface of NVPF with ultrathin (≈2 nm) amorphous TiO2 by atomic layer deposition is demonstrated. The coating facilitates higher mobility of the ion through the cathode electrolyte interphase (CEI) and enables higher capacity during cycling. The TiO2@NVPF exhibit discharge capacity of >120 mAhg−1, even at 1C rates, and show lower irreversible capacity in the first cycle. Further, nearly 100% capacity retention after rate performance in high current densities and 99.9% coulombic efficiency after prolonged cycling in high current density is reported. The improved performance in TiO2@NVPF is ascribed to the passivation behavior of TiO2 coating which protects the surface of NVPF from volume expansion, significantly less formation of carbonates, and decomposition of electrolyte, which is also validated through post cycling analysis. The study shows the importance of ultrathin surface protection artificial CEI for advanced sodium‐ion battery cathodes. The protection layer is diminishing parasitic reaction, which eventually enhances the Na ion participation in reaction and stabilizes the cathode structure.

High‐Entropy Co‐Free O3‐Type Layered Oxyfluoride: A Promising Air‐Stable Cathode for Sodium‐Ion Batteries

“…The lower area of C─O and carbonate peaks point toward the suppression of both interfacial parasitic reactions and electrolyte degradation at the cathode surface with Li inclusion in the structure, ultimately resulting in the lower carbonate content in the CEI. [ 50 ]…”

“…The lower area of C─O and carbonate peaks point toward the suppression of both interfacial parasitic reactions and electrolyte degradation at the cathode surface with Li inclusion in the structure, ultimately resulting in the lower carbonate content in the CEI. [50] Though Lithium substituted composition shows better cyclic stability, the mechanical stress due to repeated desodiationsodiation may generate cracks enabling the penetration of electrolyte and could result in deterioration of the structure. Therefore, post-mortem analysis (Figure S22a, Supporting Information) after 50 cycles (2-4 V) of charge-discharge for all three compositions is carried out.…”

The Distance Between Phosphate‐Based Polyanionic Compounds and Their Practical Application For Sodium‐Ion Batteries

“…Similarly, Mukherjee et al prepared Na 3 V 2 (PO 4 ) 2 F 3 with ultrathin amorphous TiO 2 layer (≈2 nm), and Na 3 V 2 (PO 4 ) 2 F 3 @TiO 2 has a larger capacity than bare Na 3 V 2 (PO 4 ) 2 F 3 , as shown in Figure 8g. [120] This can be attributed to the construction of TiO 2 coating, which can facilitate the migration of Na + through the cathode-electrolyte interphase (CEI) layer, leading to the rapid sodium-storage kinetics. Besides, the reversible capacity of Na 3 V 2 (PO 4 ) 2 F 3 @TiO 2 is still as high as 107 mAh g −1 (>16% improvement of bare Na 3 V 2 (PO 4 ) 2 F 3 ) after 200 cycles, since the TiO 2 layer can alleviate the volume expansion of cathode and the decomposition of the electrolyte.…”

“…g) First cycle of pure Na 3 V 2 (PO 4 ) 2 F 3 and Na 3 V 2 (PO 4 ) 2 F 3 @TiO 2 . Reproduced with permission [120]. Copyright 2021, Wiley-VCH.…”

Pore-forming mechanisms and sodium-ion-storage performances in a porous Na3V2(PO4)3/C composite cathode

“…14,15 The 3D porous framework structure is an ideal micromorphology for electrode materials, considering the following facts: 16,17 (1) the 3D porous framework can provide a sufficient buffering space for the stress and volume expansion produced in the electrode materials during the charging–discharging reaction, which significantly improves the cycling stability; 18 (2) the huge specific surface area can increase the contact area between electrode materials and the electrolyte, thereby enhancing the Na + -transport efficiency, and finally improving the rate performance of the electrode materials. 19 However, considering their complex elemental composition, it is a big challenge to design a fine hierarchical structure for cathode materials compared with that for their corresponding anode materials.…”