Page 141 - Read Online

Page 2 of 13 Zhang et al. Energy Mater 2023;3:300008 https://dx.doi.org/10.20517/energymater.2022.71

-1
Co Ni HCF delivers a high specific capacity of 142.2 mAh g at 0.2 C, an ultrahigh rate capability with
0.3
0.7
-1
126.2 mAh g at 5 C and excellent cycling stability with 80.9% capacity retention after 500 cycles at 5 C. Even at
-1
-30 °C, Co Ni HCF can provide a high capacity of 109 mAh g without an activation process. This work reveals
0.3
0.7
the great application prospect of PBAs for all-climate SIBs, especially at low temperatures.
Keywords: Prussian blue analogues, all-climate, sodium-ion batteries, CoHCF, Ni substitution
INTRODUCTION
The application of Lithium-ion batteries (LIBs) in the field of energy storage, especially at low temperatures,
has been limited due to the shortage of lithium resources, high raw material prices, and unsatisfactory low-
temperature performances. Having similar physical and chemical properties to lithium, low-cost sodium-
[1-3]
ion batteries (SIBs) are one of the potential options for large-scale energy storage . Meanwhile, the Stokes
radius of sodium-ion is smaller than that of lithium-ion, which is more conducive to kinetic transmission
and has better performance at subzero temperatures . In addition, in the cathode materials of SIBs,
[4,5]
Prussian blue (PB) and its analogues (PBAs, Na M[Fe(CN) ], M = Fe, Co, Mn, Ni, Cu, etc.) have an open 3D
6
2
framework structure, which can further improve the migration rate of Na -ions . However, the PBAs
+
[6-8]
+
synthesized via the conventional rapid precipitation process are always Na -deficient phase with large
amounts of water and Fe(CN) vacancies, which leads to low capacity and poor cycling and rate
4-
6
stability [9-11] . The use of chelates including sodium citrate , ethylenediaminetetraacetic acid (EDTA) ,
[13]
[12]
sodium carboxymethylcellulose (CMC) and additives such as surfactants and sodium salts has
[15]
[16]
[14]
improved the control of crystallization, which are propitious to increase sodium content and reduce defects
of PBAs.
Among the PBAs, nickel hexacyanoferrate (NiHCF) has only one redox center, severely limiting the
capacity, iron hexacyanoferrate (FeHCF) with low average voltage will also reduce the energy density, and
manganese hexacyanoferrate (MnHCF) is affected by Jahn-Teller effect, resulting in poor cycling
performance. Whereas, CoHCF shows attractive advantages such as high theoretical capacity, good voltage
platform and almost no Jahn-Teller effects [17-19] . However, even in the PB with perfect lattice, once the
material reaches its theoretical specific capacity (fully desodiated state), the material will undergo huge
volume change after almost all sodium ions are removed from the framework, resulting in stress and strain.
The accumulation of stress and strain causes large lattice distortion and even collapse of the lattice structure,
resulting in poor cycling stability . Therefore, many strategies have been proposed to stabilize the lattice
[20]
structures, including surface protective layers coating [21-23] , transition metal elements doping [24-26] , and
regulation of lattice water [27,28] . Qiao et al. constructed a semiconductor ZnO protective layer outside FeHCF
to form a physical barrier, which inhibited the decomposition of PB during the charging and discharging
process and improved the electrochemical performance . Wang et al. achieved Ni gradient doping from
[23]
surface to inside of FeHCF, in which the nickel-rich outer layer provided a stable framework structure and
the nickel-poor inner layer partly activated the electrochemical activity of Fe to increase the capacity .
[25]
Hu et al. used interstitial water as the pillar in the crystal frameworks to stabilize the lattice, which
effectively improved the cycling stability of PBAs . However, the lattice water occupies the Na sites, which
[27]
+
directly reduces the sodium content in the lattice and results in the decrease of specific capacity [29,30] .
Therefore, it is a great challenge to choose appropriate modification methods to balance high capacity and
cycle stability. Meanwhile, only under a stable frame structure, sodium ions can fully use the advantages of
3D channels in PBAs, exhibiting good rate and low-temperature performances, and be applied to all-climate
batteries.