(A) SEM and (B) TEM images of NVPOF at 144 h. (C) The cycling performance of NVPOF electrode at a current rate of 15 C. (A–C) Reproduced with permission from Ref. [164]. Copyright©2018, Elsevier Inc. (D) Schematic illustration of the time-dependent solvothermal reaction: self-sacrifice and Ostwald ripening mechanism from rough spheres to yolk-shell structure. (E–H) TEM images of products synthesized with different solvothermal times (1, 6, 24, and 48 h, respectively). Reproduced with permission from Ref. [165]. Copyright©2021, Elsevier. (I) Crystal structure of Na₂FePO₄F: view along [100]. Ion transport pathways (I, II, and III) are marked. Reproduced with permission from Ref. [167]. Copyright©2009, American Chemical Society. (J) TEM image of the as-synthesized double-shelled hollow Na₂FePO₄F/C sample. (K) Charge and discharge profiles of double-shelled hollow Na₂FePO₄F/C sample at various current rates. (J, K) Reproduced with permission from Ref. [168]. Copyright©2017, Springer Science Business Media, LLC. (L) Schematic of Na₄Fe₃(PO₄)₂(P₂O₇). Reproduced with permission from Ref. [169]. Copyright©2025, The Author(s). (M) Schematic illustration of NFPP@NFP@C-CC flexible electrode. Reproduced with permission from Ref. [171]. Copyright©2019, Elsevier B.V. (N) Voltage drops of THoCS and THoCS-0.6Ni at different rates. Reproduced with permission from Ref. [172]. Copyright©2024, Wiley-VCH GmbH.