Formation of Mn–Ni Prussian Blue Analogue Spheres as a Superior Cathode Material for Potassium-Ion Batteries

Abstract

Potassium manganese hexacyanoferrate shows great potential as a cathode material for potassium-ion batteries (PIBs) due to its impressive electrochemical performance, abundant elements, and easy synthesis. However, severe capacity fading and poor K+ diffusion kinetics greatly limit its large-scale application. Herein, we propose a facile anion exchange method to construct Mn–Ni Prussian blue analogue (denoted MnNi-PBA) spheres. The introduction of Ni can stabilize the structure to enhance the cycling performance, and rich active sites can be provided by the formation of a unique porous spherical structure, thus enabling shorter ion diffusion pathways during charge/discharge. Consequently, the MnNi-PBA sphere cathode delivers an initial discharge capacity of 130.6 mAh g–1 at 10 mA g–1, an enhanced rate capability of 66.3 mAh–1 at 200 mA g–1, and a long cycle life with 83.8% capacity retention after 500 cycles. When assembled with a pitch-derived soft carbon anode, a full cell exhibits excellent cycling stability and rate performance. In addition, ex situ X-ray diffraction demonstrates that the MnNi-PBA spheres undergo reversible structural changes (monoclinic ↔ cubic) throughout the cycling process. Therefore, this work may offer a design strategy to synthesize Mn-based Prussian blue analogues for the application of PIBs.

Prussian blue analogues for potassium-ion batteries: insights into the electrochemical mechanisms

“…65,66 The two long axial Mn–N bonds (2.42 Å) can be weakened during the continuous lattice expansion/compression, possibly inducing the creation of inactive Mn sites by the dissolution of Mn ions in the electrolyte, as already widely reported in the literature for Mn-containing PBAs. 67–71 This observation might explain the modification of the mechanism and thus of the performance of MF21 during cycling, which becomes evident by looking at the derivative of the capacity of MF21 in half-cell after 1, 2, and 50 cycles (Fig. S11†).…”

“…[19][20][21] The promising electrochemical properties of Mn-and Fe-based PBAs have been reported for both aqueous and organic sodium-ion batteries (SIBs) 17,18,[22][23][24][25][26][27] and PIBs. 7,[28][29][30][31][32][33][34][35] Nevertheless, the order of the redox reactions at the two Mn and Fe sites is still a matter of debate: on the one hand, by comparing the signals of the TMs in the cyclic voltammetry (CV) signatures of different PBA compositions, the redox potentials of the TMs were found in the order of HS Fe 3+ /HS Fe 2+ < LS Fe 3+ /LS Fe 2+ < HS Mn 3+ /HS Mn 2+ . 32,33,36,37 On the other hand, from so X-ray absorption spectroscopy (sXAS), Pasta and co-workers proposed that the oxidation of LS Fe 2+ and HS Mn 2+ occurs simultaneously, yet the LS Fe 3+ /LS Fe 2+ couple was assigned at lower potential.…”

Progress of Prussian Blue and Its Analogues as Cathode Materials for Potassium Ion Batteries

“…Li's team proposed a simple anion exchange method to construct the MnÀ Ni co-doped PBA balls. [102] The unique porous spherical structure provided abundant active sites, thus shortened the ion diffusion path in the charge and discharge process (Figure 8g, h). The initial discharge capacity of the MnÀ Ni-PBA spherical cathode was 130.6 mA h g À 1 at 10 mA g À 1 , increased 66.3 mA/h at 200 mA g À 1 , and had a long cycle life after 500 cycles with a capacity retention rate of 83.8 %.…”

Molten-salt assisted synthesis of a high-performance oxide cathode for sodium-ion batteries: Na0.44MnO2as a case

“…These promising cathode materials are also being tested by researchers for potassium-ion batteries with larger carriers. [21][22][23] Among these, transition metal oxides have been widely studied by researchers due to their advantages of abundant resources and easy preparation. In general, transition metal oxides can be divided into layered and tunnel phases depending on their structures.…”