Prussian Blue Cathode Research Articles

Central metal coordination environment optimization enhances Na diffusion and structural stability in Prussian blue analogues

Prussian blue analogues, particularly metal hexacyanoferrates with double octahedral coordination (DOC) structures, hold great promise as cathode materials for sodium-ion batteries. However, their practical application is hindered by limited structural stability and restricted ionic diffusion channels inherent to the DOC structure. In this study, we have successfully integrated a mixed tetrahedral and octahedral coordination (TOC) structure with the DOC structure by a dual polymerization and high-entropy strategy, thereby optimizing the central metal coordination environment in hexacyanoferrate cathodes. It leverages the TOC structure's superiorities in structural stability and ionic diffusion, resulting in a hexacyanoferrate-based cathode that exhibits exceptional performance, with a capacity retention of 81.6% after 1000 cycles at 0.5 A g-1 and high rate capabilities of 96.7 and 89.1 mAh g-1 at 0.5 and 1 A g-1, respectively. These findings not only underscore the potential of the TOC design for prussian blue cathodes but also pave the way for the development of high-performance, durable sodium-ion battery systems.

Synergistic Dual‐Additive Tailored Robust Interphase toward Enhanced Cyclability of Prussian Blue Cathode for K+ Storage

Synergistic Dual‐Additive Tailored Robust Interphase toward Enhanced Cyclability of Prussian Blue Cathode for K⁺ Storage

An Ultrastable Aqueous Ammonium-Ion Battery Using a Covalent Organic Framework Anode.

Aqueous ammonium ion batteries have garnered significant research interest due to their safety and sustainability advantages. However, the development of reliable ammonium-based full batteries with consistent electrochemical performance, particularly in terms of cycling stability, remains challenging. A primary issue stems from the lack of suitable anode materials, as the relatively large NH4 + ions can cause structural damage and material dissolution during battery operation. To address this challenge, an Aza-based covalent organic framework (COF) material is introduced as an anode for aqueous ammonium ion batteries. This material exhibits superior ammonium storage capabilities compared to existing anode materials. It operates effectively within a negative potential range of 0.3 to‒1.0 V versus SCE, achieves high capacity even at elevated current densities (≈74 mAh g-1 at 10 A g-1), and demonstrates exceptional stability, retaining a capacity over 20000 cycles at 1.0 A g-1. Furthermore, by pairing this COF anode with a Prussian blue cathode, an ammonium rocking-chair full battery is developedd that maintains 89% capacity over 20000 cycles at 1.0 A g-1, surpassing all previously reported ammonium ion full batteries. This study offers insights for the design of future anodes for ammonium ion batteries and holds promise for high-energy storage solutions.

Boosting the potassium storage property of spongia-like copper phosphide anode via nano-in-micro construction

Metal phosphides (MPs) show great promise as anode material in potassium-ion batteries (PIBs) owing to their cost-effectiveness and high theoretical capacity. Despite that, MPs anode usually manifests inferior poor cyclability as a result of dramatic volume fluctuation during discharge–charge cycling. Herein, a scalable salt template-assisted spray-drying method is developed to fabricate the porous carbon microspheres wrapped CuP2 nanoparticles (p-CuP2/C) with a nano-in-micro structure. The combination of the CuP2 nanoparticles, large meso-porous carbon microspheres can simultaneously offer plenty of reactive sites, promote electrolyte penetration, and maintain structural integrity. Additionally, the proposed synthesis strategy is suit for the industrial manufacture. As an anode for PIBs, the p-CuP2/C anode presents a high reversible capacity (494 mAh/g at 0.05 A/g), excellent cycling stability (a capacity degradation rate of 0.04 % per cycle during 2000 cycles at 2 A/g), and superior rate capability (244 mAh/g at 2 A/g). More impressively, pairing with a potassium Prussian blue cathode, the potassium-ion coin cell shows an excellent cycling lifespan with 87.1 % capacity retention after 200 cycles at a current density of 0.1 A/g, the assembled pouch cell also maintains stable cycling at 0.3 A/g over 80 cycles. This research could offer a facile approach to develop other advanced anodes with industrial practicability for alkali ion batteries.

Acid-assisted synthesis of core-shell Prussian blue cathode for sodium-ion batteries

In recent years, core–shell structured Prussian Blue Analogues (PBAs) have been considered as highly promising cathode materials for sodium-ion batteries. Reducing production costs and simplifying the preparation method for core–shell PBAs have also become crucial considerations. This paper presents a novel approach for the first time: by acid-treating the as-synthesized solution from a simple coprecipitation reaction, a high-crystallinity, sodium-rich Mn2+-doped iron hexacyanoferrate (Fe/MnHCF) shell material is self-grown on the surface of manganese hexacyanoferrate (MnHCF). This method significantly improves the electrochemical properties of the MnHCF material. The core–shell structured PBA exhibits excellent cycling performance (with a capacity retention of 95.5 % for 400 cycles at 1 A/g) and high rate performance (134.2mAh/g@10 mA/g, 95.2mAh/g@1 A/g). In this article, we explore the growth mechanism of the high-sodium content, high-crystallinity shell structure and introduce a green chelating agent that is better suited for the crystallization of Mn and Fe-type PBA systems. Our study demonstrates that Mn2+ doping enhances the conductivity of the shell material. Meanwhile, the heterojunction structure of MnHCF@Fe/MnHCF conducive to charge separation and migration. This straightforward synthesis strategy offers a novel approach for fabricating high-performance core–shell structured Prussian Blue Analogue materials.

(Invited) Research and Development Trends in Sodium-Ion Batteries

Lithium-ion batteries (LIBs) are the most used energy storage technology for electronic devices and electric vehicles. However, the increasing demand for lithium may make it difficult to support the widespread use of LIBs in electric vehicles, utility grids, and other applications. Therefore, developing alternative technologies to LIBs is critical for large-scale energy storage. Studies suggest that using sodium-ion batteries with renewable energies can significantly reduce the cost of electricity. Despite the lower energy density, sodium-ion batteries are appealing for several reasons: (1) sodium is abundant, (2) less critical components are used, and (3) the manufacturing knowledge of LIBs can be used. Herein, we report for the first time a hydrothermal synthesis of a new class of sodium-rich cathode material with the formula Na3+xNixV2-x(PO4)2F2O that could enable the compensation of the irreversible sodium loss in the first charge in a full cell with hard carbon. Trends in sodium-ion batteries will be discussed, considering the new developments in layered oxides, oxy-fluoro-phosphates, and Prussian blue cathodes.

High-Entropy Prussian Blue Analogues as High-Capacity Cathode Material for Potassium Ion Batteries

Potassium ion batteries, due to their similar electrochemical principles to lithium-ion batteries and the abundance of metal sources, are considered one of the alternatives to lithium-ion batteries. The development of new cathode materials has always been a research focus in this field. Among them, Prussian blue materials, with their three-dimensional open and flexible metal framework structure, can efficiently and reversibly store potassium ions. However, Prussian blue cathode materials still face issues such as poor reversibility and low capacity, which limit their application scope. This study investigates the preparation of high-entropy Prussian blue analogues materials to enhance electrochemical performance. The doping of five different transition metals (Fe2⁺, Co2⁺, Cu2+, Ni2+, and Mn2+) sharing the same nitrogen coordination sites results in a configurational entropy greater than 1.5 R for the material. HEPB-1 cathode material (K1.75Mn0.26Fe0.01Ni0.01Cu0.08Co0.09 [Fe(CN)6]0.66·0.83H2O) shows better electrochemical performance, with the initial discharge capacity of 86.69 and 74.51 mAh g−1 (capacity retention is 75.2% after 100 cycles) at 20 and 100 mA g−1, respectively. The research results have provided new insights for the further development and application of potassium ion batteries.

Compensating effect of self-assembled capsule towards enhanced structural stability of prussian blue cathodes for sodium-ion batteries

The Prussian Blue analog (PBA) is a promising sodium-ion cathode material with high theoretical capacity and relatively easy to synthesize. One of the Prussian Blue analogs, sodium manganese hexacyanoferrate (NaxMn[Fe(CN)6], MnHCF), experiences significant initial capacity decrease due to Jahn–Teller distortion depending on the sodium content. In contrast, Sodium copper hexacyanoferrate (NaxCu[Fe(CN)6], CuHCF) exhibits lower reversible sodium-ion content compared to MnHCF and exhibits excellent cycling stability. We designed direct-strike coprecipitation process to synthesize nanocomposite of PBAs. The proposed encapsulated composite has been successfully synthesized by encapsulating MnHCF with self-assembled CuHCF, leading to substantial improvement in the cycling performance of MnHCF. The encapsulated composite demonstrated a capacity of 106.2 mAh g−1 even at high current rate. Regarding cycle stability, it retained over 68 % of its initial capacity even after 500 cycles. The ion conductivity was calculated through the Galvanostatic intermittent titration test (GITT), and the encapsulated composite exhibited higher ion conductivity than pristine MnHCF. Ex-situ post-analysis was conducted to confirm structural evolution of samples. The severe structural collapse of MnHCF led to electrode damage, whereas the encapsulated composite demonstrated excellent electrode condition. The encapsulated composite exhibited superior performance in full-cell tests as well.

Photothermal Enhancement of Prussian Blue Cathodes for Li-Ion Batteries.

Photoenhanced batteries, where light improves the electrochemical performance of batteries, have gained much interest. Recent reports suggest that light-to-heat conversion can also play an important role. In this work, we study Prussian blue analogues (PBAs), which are known to have a high photothermal heating efficiency and can be used as cathodes for Li-ion batteries. PBAs were synthesized directly on a carbon collector electrode and tested under different thermally controlled conditions to show the effect of photothermal heating on battery performance. Our PBA electrodes reach temperatures that are 14% higher than reference electrodes using a blue LED, and a capacity enhancement of 38% was achieved at a current density of 1600 mA g-1. Additionally, these batteries show excellent cycling stability with a capacity retention of 96.6% in dark conditions and 94.8% in light over 100 cycles. Overall, this work shows new insights into the effects leading to improved battery performance in photobatteries.

Bismuth: An Epitaxy-like Conversion Mechanism Enabled by Intercalation-Conversion Chemistry for Stable Aqueous Chloride-Ion Storage.

The exploitation of new anion battery systems based on high-abundance oceanic elements (e.g., F-, Cl-, and Br-) is a strong supplement to the current metal cation (e.g., Li+, Na+) battery technologies. Bismuth (Bi), the rare anion-specific anode species nearest to practical application for chloride ion storage, is plagued by volume expansion and structure collapse due to limited control of its conversion behavior. Here, we reveal that a unique epitaxy-like conversion mechanism in the monocrystalline Bi nanospheres (R3m group) can drastically inhibit grain pulverization and capacity fading, which is enabled by Cl- intercalation in their interlayer space. The Bi nanosphere anode can self-evolve and transform into a rigid BiOCl nanosheet-interlaced structure after the initial conversion reaction. With this epitaxy-like conversion mechanism, the Bi anode exhibits a record-high capacity of 249 mAh g-1 (∼1.2 mAh cm-2) at 0.25 C and sustains more than 1400 h with 20% capacity loss. Pairing this anode with a Prussian blue cathode, the full battery can deliver an ultrahigh desalination capacity of 127.1 m gCl gBi-1. Our study milestones the understanding of conversion-type anode structures, which is an essential step toward the commercialization of aqueous batteries.

Copper Foil Substrate Enables Planar Indium Plating for Ultrahigh‐Efficiency and Long‐Lifespan Aqueous Trivalent Metal Batteries

AbstractAqueous trivalent metal batteries represent a compelling candidate for energy storage due to the intriguing three‐electron transfer reaction and the distinct properties of trivalent cations. However, little research progress has been achieved with trivalent batteries due to the inappropriate redox potentials and drastic ion hydrolysis side reactions. Herein, the appealing yet underrepresented trivalent indium is selected as an advanced metal choice and the crucial effect of substrate on its plating mechanism is revealed. When copper foil is used, an indiophilic indium‐copper alloy interface can be formed in situ upon plating, exhibiting favorable binding energies and low diffusion energy barriers for indium atoms. Consequently, a planar, smooth, and dense indium metal layer is uniformly deposited on the copper substrate, leading to outstanding plating efficiency (99.8–99.9%) and an exceedingly long lifespan (6.4–7.4 months). The plated indium anode is further paired with a high‐mass‐loading Prussian blue cathode (2 mAh cm−2), and the full cell (negative/positive electrode capacity, N/P = 2.5) delivers an excellent cycling life of 1000 cycles with 72% retention. This work represents a significant advancement in the development of high‐performance trivalent metal batteries.

Alumina - Stabilized SEI and CEI in Potassium Metal Batteries.

Aluminum oxide (Al2O3) nanopowder is spin-coated onto both sides of commercial polypropene separator to create artificial solid-electrolyte interphase (SEI) and artificial cathode electrolyte interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm2-0.5 mAh/cm2 and 3.0 mA/cm2-0.5 mAh/cm2. Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo-stage focused ion beam (cryo-FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina-modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal - SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.

Alumina – Stabilized SEI and CEI in Potassium Metal Batteries

AbstractAluminum oxide (Al2O3) nanopowder is spin‐coated onto both sides of commercial polypropene separator to create artificial solid‐electrolyte interphase (SEI) and artificial cathode electrolyte interface (CEI) in potassium metal batteries (KMBs). This significantly enhances the stability, including of KMBs with Prussian Blue (PB) cathodes. For example, symmetric cells are stable after 1,000 cycles at 0.5 mA/cm2–0.5 mAh/cm2 and 3.0 mA/cm2–0.5 mAh/cm2. Alumina modified separators promote electrolyte wetting and increase ionic conductivity (0.59 vs. 0.2 mS/cm) and transference number (0.81 vs. 0.23). Cryo‐stage focused ion beam (cryo‐FIB) analysis of cycled modified anode demonstrates dense and planar electrodeposits, versus unmodified baseline consisting of metal filaments (dendrites) interspersed with pores and SEI. Alumina‐modified CEI also suppresses elemental Fe crossover and reduces cathode cracking. Mesoscale modeling of metal – SEI interactions captures crucial role of intrinsic heterogeneities, illustrating how artificial SEI affects reaction current distribution, conductivity and morphological stability.

Prussian blue/reduced graphene oxide composites cathode material via one-pot precipitation synthesis for enhancing capacity sodium metal pouch cell batteries

The popularity of sodium metal-ion batteries (SMBs) is increasingly displacing lithium-ion batteries (LIBs). Iron-based Prussian blue (Fe4[Fe(CN)6]3) analogs promise low-cost and easily prepared cathode materials for sodium metal-ion batteries. However, the effectiveness of these materials has consistently been attributed to their inadequate electrical conductivity. In this study, we employed a one-pot synthesis technique to prepare composites of Prussian blue (PB) and reduced graphene oxide (PB/rGO) with varying rGO concentrations. Ascorbic acid was utilized as a reducing agent to convert graphene oxide (GO) into reduced graphene oxide (rGO). Following optimization, the SMB coin cell with PB/rGO(5 %) electrode exhibited an initial specific discharge capacity of 91 mAh/g at a current density of 0.3C. This electrode had exceptional rate performance and remarkable capacity retention, with 75.3 % remaining after 2000 cycles. Furthermore, the pouch cell SMB using PB/rGO(5 %) showed a high capacity of 87 mAh/g at 0.05C with an energy density of 34 Wh kg−1 and good cycle ability over 500 cycles. Notably, the performance of the SMBs surpasses that of the PB cathode, making it highly advantageous for efficient sodium ion storage in SMBs.

Mesoporous hollow Fe4[Fe(CN)6)]3 hierarchical nanocrystal architecture for advanced sodium-ion batteries

Prussian blue (PB) has been broadly recognized as promising cathode materials for sodium-ion batteries (SIBs) due to its large interstitial space and robust frame structure, whereas their applications are impeded by unsatisfied long-term cyclability and poor rate capability due to its inherent lattice defects. Herein, we report to fabricate the mesoporous hollow Fe4(Fe(CN)6)3 (one kind of PB) hierarchical nanocrystal architecture by the hydrothermal crystallization and HCl etching of the mesoporous precursor Fe4[Fe(CN)6]3 cubic particles, leading to high crystallinity and large specific surface area. The resultant Fe4[Fe(CN)6]3 cathode for SIBs exhibits a good reversibility and cycling stability with a capacity retention of 75.6 % at 0.5 C after 200 cycles as well as superb rate capability featuring a stable discharge specific capacity of 30.2 mAh g−1 at as high as 10 C, demonstrating the fast kinetics and low polarization of electrochemical reaction, which might be ascribed to the unique architecture and high crystallinity. This offers a new route to designing PB cathode of for SIBs with high rate capabilities.

Advanced Prussian Blue Cathodes for Rechargeable Li-Ion Batteries

Taking advantage of fact that the surface electrons of metallic nanoparticles (NPs) can be effectively released even at a low voltage bias, we demonstrate an improvement in the electrochemical performance of nanosized Prussian Blue (PB)-based secondary batteries through the incorporation of bare Ag or Ni NPs in the vicinity of the working PB NPs. It is found that the capacity for electrochemical energy storage of the 17 nm PB-based battery is significantly higher than the capacity of 10 nm PB-based, 35 nm PB-based or 46 nm PB-based batteries. There is a critical PB size for the highest electrochemical energy storage efficiency. The full specific capacity CF of the 17 nm PB-based battery stabilized to 62 mAh/g after 130 charge–discharge cycles at a working current of IW = 0.03 mA. The addition of 14 mass percent of Ag NPs in the vicinity of the PB NPs gave rise to a 32% increase in the stabilized CF. A 42% increase in the stabilized CF could be obtained with the addition of 14 mass percent of Ag NPs on the working electrode of the 35 nm PB-based battery. An enhancement in CF was also found for electrodes incorporating bare Ni NPs but the effect was smaller.

Enhancing cyclic stability of Mn-based Prussian blue cathode for Potassium Ion storage by High-spin Fe substitution strategy

Aqueous K-ion batteries (AKIBs) are being considered as promising candidates, although they still confront numerous problems. Here we propose a high-spin Fe substitution method to enhance the long-term cyclic stability of Mn-based Prussian blue analogue (Mn-PBA) cathode. The prepared K1.86Mn[Fe(CN)6]0.96·0·19H2O (KMF) are electrochemically activated for 20-cycle CV scan in the hybrid electrolyte containing KNO3+Fe(NO3)3. The modified cathode (KMF-100) achieves a high capacity of 185.8 mAh g−1 and high-capacity retention of 89.8 % at 2 A g−1 after 1500 cycles (based on maximum capacity). The high-spin Fe substitution strategy not only activates the transition metal at high spin sites to contribute extra capacity, but also promotes the partial dissolved Mn2+ to return to the PBA in the hybrid electrolyte with Fe3+, relieving the Jahn-Teller effect of Mn(Ⅲ). In contrast, the KMF in the pure KNO3 electrolyte does not exhibit this behavior. The DFT calculation further demonstrate the reconstituted Prussian blue structure can increase the electrical conductivity and improve ion diffusion kinetics of the cathode material. Notably, it suppresses the change in C-Fe bond lengths during K-ion extraction, maintaining outstanding structural stability throughout cycle. This work provides a novel way to prepare high-stability manganese-based PBA cathode.

Aging Mechanism of Mn-Based Prussian Blue Cathode Material by Synchrotron 2D X-ray Fluorescence

The aging mechanism of 10% and 30% nickel-substituted manganese hexacyanoferrate cathode material in aqueous zinc-ion batteries has been explored through the advanced synchrotron-based two-dimensional X-ray fluorescence technique. Thanks to the two-dimension modality, not only were the metal concentration dynamics throughout the entire electrodes followed during the aging process, but their spatial distribution was also revealed, suggesting the route of the material transformation. The dissolution of Mn and Ni, as well as the penetration of Zn inside the framework were detected, while the Mn aggregations were found outside the hexacyanoferrate framework. Additionally, the possibility of conducting X-ray absorption spectroscopy measurements on the regions of interest made it possible to explore the chemical state of each metal, and furthermore, synchrotron-based powder X-ray diffraction demonstrated the gradual structural modification in 30% Ni-containing sample series in terms of the different phase formation.

Sequentially epitaxial multi-shelled Mn-based Prussian blue cathode for highly stable sodium-ions batteries

The sodium manganese hexacyanoferrate (MnPB) has drawn widely attention as a remarkable cathode material for sodium-ions batteries owing to its high theoretical capacity (∼170 mAh g–1), environmental-friendly and low cost. However, it suffers from serious capacity fading and inferior cycling stability caused by the inevitable Jahn-Teller distortion and significant volume change during Na+insertion/extraction process. Herein, we propose a simple one-pot method for constructing a multi-shelled Mn-based Prussian blue through sequentially epitaxial growth CoPB and NiPB on the surface of MnPB (NiCoMnPB). The density functional theory calculations demonstrate the unequal affinities of different metal ions with various chelating agents (citrate and ferrocyanide), leading to the dissociation and recombination of metal ions and chelating agents in a certain order. Effectively inheriting merits of CoPB and NiPB, the NiCoMnPB reveals enhanced charge transfer kinetics, suppressed volume change and alleviative Jahn-Teller distortion during cycling, thereby exhibiting superior rate capacity (∼54.2 mAh g–1 at 3200 mA/g), long-term cyclic stability and capacity retention (∼76 % over 1000 cycles at 800 mA/g). This work provides a simple method to construct multi-shelled PBAs, which can integrate the virtues of different materials to ameliorate the electrochemical properties of initial materials.

Hollow Layered Iron-Based Prussian Blue Cathode with Reduced Defects for High-Performance Sodium-Ion Batteries.

Fe-based Prussian blue (Fe-PB) analogues have emerged as promising cathode materials for sodium-ion batteries, owing to their cost-effectiveness, high theoretical capacity, and environmental friendliness. However, their practical application is hindered by [Fe(CN)6] defects, negatively impacting capacity and cycle stability. This work reports a hollow layered Fe-PB composite material using 1,3,5-benzenetricarboxylic acid (BTA) as a chelating and etching agent by the hydrothermal method. Compared to benzoic acid, our approach significantly reduces defects and enhances the yield of Fe-PB. Notably, the hollow layered structure shortens the diffusion path of sodium ions, enhances the activity of low-spin Fe in the Fe-PB lattice, and mitigates volume changes during Na-ion insertion/extraction into/from Fe-PB. As a sodium-ion battery cathode, this hollow layered Fe-PB exhibits an impressive initial capacity of 95.9 mAh g-1 at a high current density of 1 A g-1. Even after 500 cycles, it still maintains a considerable discharge capacity of 73.1 mAh g-1, showing a significantly lower capacity decay rate (0.048%) compared to the control sample (0.089%). Moreover, the full cell with BTA-PB-1.6 as the cathode and HC as the anode provides a considerable energy density of 312.2 Wh kg-1 at a power density of 291.0 W kg-1. This research not only enhances the Na storage performance of Fe-PB but also increases the yield of products obtained by hydrothermal methods, providing some technical reference for the production of PB materials using the low-yield hydrothermal method.