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Zhang et al. Energy Mater 2023;3:300008 https://dx.doi.org/10.20517/energymater.2022.71 Page 11 of 13

[39]
the enhanced conductivity in Co Ni HCF . Furthermore, the calculated results based on density
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functional theory (DFT) [Figure 6C and D] prove that the energy migration barriers of Na -ions in
+
Co Ni HCF are lower than that in CoHCF, which is consistent with GITT experiment results. Schematic
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illustrations of the structures of Co Ni HCF and CoHCF unit cell of calculation model are shown in
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Supplementary Figure 11. All of these calculations demonstrate that the electronic conductivity, redox
activity and ion mobility of Co Ni HCF are enhanced effectively than those of un-substituted sample
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(CoHCF), which provides enlightenment that a small amount of Ni in the lattice of PBAs can promote the
electron transfer and ion diffusion, as well as stabilize the frameworks.
CONCLUSIONS
In conclusion, to address the low actual specific capacity, poor cycling and poor rate capability of CoHCF as
the cathode material of SIBs, partial substitution of Co by Ni is proposed in low-defect and Na-enriched
CoHCF sample. The introduction of Ni inhibits large lattice distortion during cycling, improves the
electronic conductivity and reduces the migration barrier of sodium ions. Benefiting from the structural
effect of Ni substitution, Co Ni HCF not only exhibits high capacity up to 142.2 mAh g , but also achieves
-1
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high capacity retention of more than 80% after 500 cycles at room temperature. Even at such a low
temperature of -30 °C, a reversible two-phase transition between monoclinic phase and cubic phase is
occurred due to adequate sodium-ions insertion and extraction, which provides a high specific capacity of
109 mAh g . Moreover, Co Ni HCF also shows stable electrochemical performance at high temperatures
-1
0.3
0.7
of 45 °C and 60 °C owing to suppressed lattice variation and stable framework. It demonstrates that Ni-
substituted double redox active PBAs are potential candidates for cathode material in all-climate sodium-
ion batteries due to their unique structural characteristics. However, Co and Ni are too expensive to apply
on a large scale, so the exploration of the next generation of low-cost all-climate sodium-ion batteries is
worth studying.

DECLARATIONS
Authors’ contributions
Methodology, formal analysis and writing manuscript: Zhang J, Wan J
Data analysis and technical support: Ou M, Liu S, Huang B
Data acquisition: Xu J, Lin Y
Supervision, writing - review and editing: Sun S, Xu Y, Fang C, Han J

Availability of data and materials
The data supporting our findings can be found in the Supplementary Material.

Financial support and sponsorship
This work was supported by National Natural Science Foundation of China (Grant No. 52172201, 51732005,
51902118, 52102249), China Postdoctoral Science Foundation (Grant Nos. 2019M662609 and
2020T130217), and the international postdoctoral exchange fellowship program No. PC2021026 for
financial support. We thank the Analytical and Testing Centre and the State Key Laboratory of Materials
Processing and Die & Mould Technology and the Experiment Center for Advanced Manufacturing and
Technology in School of Mechanical Science & Engineering of HUST for the material characterization.

Conflicts of interest
All authors declared that there are no conflicts of interest.