Concentration-Gradient Prussian Blue Cathodes for Na-Ion Batteries

Abstract

A concentration-gradient composition is proposed as an effective approach to solve the mechanical degradation and improve the electrochemical cyclability for cathodes of sodiumion batteries. Concentration-gradient shell NaxNiyMn1-yFe(CN)6• nH2O, in which the Ni content gradually increases from the interior to the particle surface, is synthesized by a facile co-2 precipitation process. The as-obtained cathode exhibits an improved electrochemical performance compared to homogeneous NaxMnFe(CN)6• nH2O, delivering a high reversible specific capacity of 110 mA h g-1 at 0.2 C and outstanding cycling stability (93% retention after 1000 cycles at 5 C). The improvement of electrochemical performance can be attributed to its robust microstructure that effectively alleviates the electrochemically induced stresses and accumulated damage during sodiation/desodiation and thus prevents the initiation of fracture in the particles upon long term cycling. These findings render a prospective strategy to develop high-performance electrode materials for sodium-ion batteries. TOC GRAPHICS Sodium ion batteries (SIBs) have been gaining increased attention as a potential energy storage device. 1-4 Compared to lithium, sodium is available abundantly and relatively inexpensive, thereby reducing the cost of the electrode material. Moreover, sodium has similar electrochemical properties to lithium and maintains a good reversibility in a variety of host materials. Hence,

Hexacyanoferrate‐Type Prussian Blue Analogs: Principles and Advances Toward High‐Performance Sodium and Potassium Ion Batteries

“…Reproduced with permission. [ 176 ] Copyright 2020, American Chemical Society. j) Schematic illustration of ion‐exchange formation of NaFeHCF@NaCuHCF and the SEM images of k) bare NaFeHCF and l) NaFeHCF@NaCuHCF.…”

“…Using the same method, Aifantis and co‐workers alleviated the electrochemically induced stress and damage of NaMnHCFs which is vulnerable to the Jahn–Teller effect of Mn 3+ . [ 176 ] The cycling stability is significantly improved by constructing a concentration gradient sample with ≈10% Ni enriched on the surface part, delivering an initial capacity of 110 mAh g ‒1 and 95% retention after 100 cycles at 0.2C (Figure 17g–i).…”

“…Exchange of anode or/and electrolytes gives more options to adjust the voltage and stability. Generally, nonaqueous Na‐ion full cells coupled with hard carbon (HC) [ 55,80,117,125,133,146,150,173,184 ] deliver the most promising voltage (2.75‒3.25 V) as compared to the use of other anodes such as TiO 2 , [ 122 ] TiS 2 , [ 176 ] Ni 0.67 Fe 0.33 Se 2 [ 221 ] and NaTi 2 (PO 4 ) 3 , [ 124,173,177 ] because of the lowest potential of HC (≈0.2 V vs Na + /Na). A NaFeHCF‐HC pouch cell is reported to demonstrate a lifetime over 1000 cycles at a current density of 100 mA g ‒1 with a plateau of 2.9 V. [ 117 ] The voltage of the full cells (nonaqueous) drops to the level of 1.2 V when NaTi 2 (PO 4 ) 3 is coupled, [ 124,173,177 ] but the capacity retention and rate capability are very attractive, especially when NiHCFs are used as cathode.…”

Structure and Properties of Prussian Blue Analogues in Energy Storage and Conversion Applications

“…Hu et al. [ 84 ] reported a concentration‐gradient Na x Ni y Mn 1− y Fe(CN) 6 · n H 2 O with high Ni content on the particle surface, the modified MnHCF delivered high reversible specific capacity of 110 mAh g −1 at 0.2 C, as well as outstanding cycling stability. Li et al.…”

Post‐Lithium‐Ion Battery Era: Recent Advances in Rechargeable Potassium‐Ion Batteries

“…In addition, because each formula unit of the HCF structure can transport two equivalents of alkali ions (Li + , Na + , or K + ) reversibly, it can provide a high specific capacity. Therefore, HCFs can be used as suitable cathode materials for a rechargeable battery, and have been widely studied in LIBs and SIBs [112–116] . In recent years, with the rapid development of PIBs, many HCF cathode materials have emerged.…”