Cathode For Potassium-ion Batteries Research Articles

Tetrahedral Occupied V Ions Enabling Reversible Three-Electron Redox of Cr3+ /Cr6+ in Layered Cathode Materials for Potassium-Ion Batteries.

Reversible three-electron redox of Cr3+ /Cr6+ in layered cathode materials for rechargeable batteries is very attractive in layered cathode materials, which leads to high capacity and energy density for rechargeable batteries. However, the poor reversibility and Cr-ion migration make it very challenging. In this work, by introducing V ions into tetrahedral sites of layer-structured NaCrO2 , reversible three-electron redox of Cr3+ /Cr6+ is realized successfully in NaCr0.92 V0.05 O2 (NCV05) cathode for potassium-ion batteries with a cut-off voltage of 4.0V. V ions can weaken the attraction of Cr to electrons, leading to enhanced valence change of Cr ions. On the other hand, V in tetrahedral sites can facilitate the reversible migration of Cr between octahedral and tetrahedral sites via coulombic repulsion to realize the reversible redox between Cr3+ and Cr6+ during charge and discharge processes. In addition, V ions can inhibit the phase transition from O3 phase to O'3 phase during the charge process by adjusting the crystal lattices. As a result, the NaCr0.92 V0.05 O2 cathode exhibits a high reversible capacity of 130mAhg-1 with promising cycle stability and rate capability. The strategy opens new opportunity for developing high-capacity cathode materials for potassium-ion batteries.

Effects of Graphene Interface on Potassiation in a Graphene–Selenium Heterostructure Cathode for Potassium-Ion Batteries

Effects of Graphene Interface on Potassiation in a Graphene–Selenium Heterostructure Cathode for Potassium-Ion Batteries

Electro-activation to achieve entropy increase of organic cathode for potassium-ion batteries

Developing highly stable cathode materials is the key to achieving long-life K-ion batteries (KIBs). Considering that cathode with higher entropy can promote the ion adsorption process, we developed a method with heat treatment and synergistic electro-activation of 3,4,9,10-perylene-tetracarboxylic dianhydride (EA-PTCDA) to realize entropy increase in PTCDA, which achieves a stable K-ion storage. From our characterization results, the molecular stacking structure of EA-PTCDA and the C–O and C–H bending vibration at the edge position of PTCDA molecules decreased after electro-activation, indicating the achievement of entropy increase in the EA-PTCDA cathode. After treatment, our EA-PTCDA exhibits a high discharge capacity of 92 mA h g−1 after 100 cycles at 20 mA g−1 for KIBs. Even at a high current density of 200 mA g−1, our EA-PTCDA also maintains a discharge specific capacity of 66 mA h g−1 after 1000 cycles, showing shallow capacity decay. We believe that our method of achieving entropy increase in cathode materials based on electro-activation provides a reference for achieving high-performance KIBs.

Flower-like K1+δVOPO4F crystallite with a layered framework structure as a robust cathode for potassium-ion batteries

Flower-like K1+δVOPO4F crystallite with a layered framework structure as a robust cathode for potassium-ion batteries

Double-layer phosphates coated Mn-based oxide cathodes for highly stable potassium-ion batteries

Manganese rich oxides with layered structure are now being developed as cathodes for potassium ion batteries (PIBs). Nevertheless, poor cycling stability and sluggish electrochemical kinetics have hindered their practical applications. Here, we construct a thin K3PO4/MnPO4 layer, which has high conductivity of both electron and potassium-ion, on the surface of K0.5Mn0.8Co0.2O2 (KMCO) and achieve improved cycling stability and capacity rate when the composite is used as cathodes in PIBs. Comparing to the pure KMCO, the K3PO4/MnPO4-coated K0.5Mn0.8Co0.2O2 (P-KMCO) has higher electron and K-ion conductivity, less surficial oxygen loss and layered-to-spinel-to-rock salt tri-phase transition, and less internal lattice expansion and contraction in cycling, as studied by aberration-corrected scanning transmission electron microscopy and in-situ X-ray diffraction. The synthesized P-KMCO exhibits a highly reversible specific capacity (101.3 mAh g−1 at 0.1 A g−1), excellent rate performance and stellar capacity retention of 80% after 500 cycles at 1 A g−1 compared to pure KMCO (78.6 mAh g−1 at 0.1 A g−1 with 67.3% capacity retention). The P-KMCO electrode shows also a supreme electrochemical performance when assembled in pouch cells. First-principal calculations imply that the surface modification can effectively prevent TM ions dissolution and oxygen release while cycling. Like those developed in lithium-ion batteries, this work demonstrates that the appropriate surface engineering is also an effective approach to development stable cathodes of PIBs.

Phase-engineered cathode for super-stable potassium storage

The crystal phase structure of cathode material plays an important role in the cell performance. During cycling, the cathode material experiences immense stress due to phase transformation, resulting in capacity degradation. Here, we show phase-engineered VO2 as an improved potassium-ion battery cathode; specifically, the amorphous VO2 exhibits superior K storage ability, while the crystalline M phase VO2 cannot even store K+ ions stably. In contrast to other crystal phases, amorphous VO2 exhibits alleviated volume variation and improved electrochemical performance, leading to a maximum capacity of 111 mAh g−1 delivered at 20 mA g−1 and over 8 months of operation with good coulombic efficiency at 100 mA g−1. The capacity retention reaches 80% after 8500 cycles at 500 mA g−1. This work illustrates the effectiveness and superiority of phase engineering and provides meaningful insights into material optimization for rechargeable batteries.

Layered transition metal oxides prepared by plasma-enhanced sintering technique as environmentally stable cathode for potassium-ion batteries

Layered transition metal oxides are deemed the most promising cathode materials for potassium-ion batteries owing to their high energy density and scalable design. However, their inherent moisture sensitivity thwarts their potential commercial realization. Herein, we show the efficacy of plasma-enhanced sintering technique in enhancing the environmental stability of K0.6Ni0.2Co0.3Mn0.5O2 layered oxide. The attained K0.6Ni0.2Co0.3Mn0.5O2 microspheres manifest a potassium-deficient surface layer that significantly suppresses surface hygroscopicity. Consequently, K0.6Ni0.2Co0.3Mn0.5O2 can be kept and handled in ambient air condition, while yet achieve competitive potassium-ion storage performance compared with other reported layered cathode materials with similar composition and microstructures. Overall, this work accentuates plasma-enhanced sintering techniques as an effective strategy to circumvent the moisture sensitivity of potassium-containing layered metal oxides, leverageable to hygroscopic layered metal oxides for other energy storage systems.

Fine valence regulation of hydrated vanadium oxide as a novel cathode for stable potassium-ion storage.

Layered V10O24·nH2O with a large interlayer spacing of 14 Å is hydrothermally synthesized and used as a cathode for potassium-ion batteries. It exhibits a capacity of 110 mA h g-1 with a capacity retention of 99.2% over 700 cycles. Its storage mechanism is identified as pseudo-capacitive intercalation.

KVPO4F/carbon nanocomposite with highly accessible active sites and robust chemical bonds for advanced potassium-ion batteries

KVPO4F (KVPF) has been extensively investigated as the potential cathode material for potassium-ion batteries (PIBs) owing to its high theoretical capacity, superior operating voltage, and three-dimensional K+ conduction pathway. Nevertheless, the electrochemical behavior of KVPF is limited by the inherent poor electronic conductivity of the phosphate framework and unstable electrode/electrolyte interface. To address the above issues, this work proposes an infiltration-calcination method to confine the in-situ grown KVPF into the mesoporous carbon CMK-3 (denoted KVPF@CMK-3). The assembled KVPF@CMK-3 nanocomposite features three-dimensional interconnected carbon channels, which not only offer abundant active sites and significantly accelerate K+/electron transport, but also prevent the growth of KVPF nanoparticle agglomerates, hence stabilizing the structure of the material. Additionally, V–F–C bonds are created at the interface of KVPF and CMK-3, which reduce the loss of F and stabilize the electrode interface. Thus, when tested as a cathode material for PIBs, the KVPF@CMK-3 nanocomposite delivers superior reversible capacitiy (103.2 mAh g−1 at 0.2 C), outstanding rate performance (90.1 mAh g−1 at 20 C), and steady cycling performance (92.2 mAh g−1 at 10 C and with the retention of 88.2% after 500 cycles). Moreover, its potassium storage mechanism is further examined by ex-situ XRD and ex-situ XPS techniques. The above synthetic strategy demonstrates the potential of KVPF@CMK-3 to be applied as the cathode for PIBs.

Regulated electrochemical performance of manganese oxide cathode for potassium-ion batteries: A combined experimental and first-principles density functional theory (DFT) investigation

Potassium-ion batteries (KIBs) are promising energy storage devices owing to their low cost, environmental-friendly, and excellent K+ diffusion properties as a consequence of the small Stoke's radius. The evaluation of cathode materials for KIBs, which are perhaps the most favorable substitutes to lithium-ion batteries, is of exceptional importance. Manganese dioxide (α-MnO2) is distinguished by its tunnel structures and plenty of electroactive sites, which can host cations without causing fundamental structural breakdown. As a result of the satisfactory redox kinetics and diffusion pathways of K+ in the structure, α-MnO2 nanorods cathode prepared through hydrothermal method, reversibly stores K+ at a fast rate with a high capacity and stability. It has a first discharge capacity of 142 mAh/g at C/20, excellent rate execution up to 5C, and a long cycling performance with a demonstration of moderate capacity retention up to 100 cycles. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) simulations confirm that the K+ intercalation/deintercalation occurs through 0.46 K movement between MnIV/MnIII redox pairs. First-principles density functional theory (DFT) calculations predict a diffusion barrier of 0.31 eV for K+ through the 1D tunnel of α-MnO2 electrode, which is low enough to promote faster electrochemical kinetics. The nanorod structure of α-MnO2 facilitates electron conductive connection and provides a strong electrode–electrolyte interface for the cathode, resulting in a very consistent and prevalent execution cathode material for KIBs.

Fluorinated soft carbon as an ultra-high energy density potassium-ion battery cathode enabled by a ternary phase KxFC

Fluorinated carbons (CFx) have been widely applied as lithium primary batteries due to their ultra-high energy density. It will be a great promise if CFx can be rechargeable. In this study, we rationally tune the C-F bond strength for the alkaline intercalated CFx via importing an electronegative weaker element K instead of Li. It forms a ternary phase KxFC instead of two phases (LiF + C) in lithium-ion batteries. Meanwhile, we choose a large layer distance and more defects CFx, namely fluorinated soft carbon, to accommodate K. Thus, we enable CFx rechargeable as a potassium-ion battery cathode. In detail, fluorinated soft carbon CF1.01 presents a reversible specific capacity of 339 mA h g−1 (797 Wh kg−1) in the 2nd cycle and maintains 330 mA h g−1 (726 Wh kg−1) in the 15th cycle. This study reveals the importance of tuning chemical bond stability using different alkaline ions to endow batteries with rechargeability. This work provides good references for focusing on developing reversible electrode materials from popular primary cell configurations.

High crystallinity potassium nickel hexacyanoferrate nanoparticles synthesized by improved precipitation way as cathodes for potassium-ion batteries

Due to the unique three-dimensional tunnel structure, Prussian blue analogues can reversibly de/intercalate K+ in crystal lattice and show original electrochemical properties. However, crystal water and vacancy inevitably appear in the framework controlled by synthesis process, limiting severely the potassium storage. Herein, high crystallinity K1.86Ni[Fe(CN)6]0.87·□0.13·1.88H2O was synthesized through electrostatic assisted coprecipitation technology, which effectively increased the initial potassium content. Moreover, the microstructure is affected under the action of static electricity, resulting in a nano-structure and large specific surface area (102.5 m2 g−1). Compared with the sample without electrostatic field, its electrochemical performances can be significantly improved with a high initial coulombic efficiency of 85.5%, capacity retention of 90.3% after 503 cycles at 1C and rate capability of 49 mAh g−1 at 10C. The new method opens up a way for the performance improvement of other Prussian blue-based cathodes.

High-quality Prussian blue analogues K2Zn3[Fe(CN)6]2 crystals as a stable and high rate cathode material for potassium-ion batteries

High-quality Prussian blue analogues K2Zn3[Fe(CN)6]2 crystals with a uniform size distribution of ~1 µm have been synthesized via a facile pyrophosphate-assisted crystallization method at room temperature. Owing to its high crystallinity and structural regularity, the as-synthesized high-quality K2Zn3[Fe(CN)6]2 crystal can deliver a theoretical one K reversible capacity of 65.3 mAh g−1 at 50 mA g−1 based on [Fe(CN)6]3−/[Fe(CN)6]4−, high rate performance and an impressive long-term cycling performance (a capacity retention of 89.3% after 1000 cycles at 500 mA g−1)，showing great potentials as a low-cost and stable cathode for potassium ion batteries.

Influence of film-forming additives on the interface performance of potassium ion battery cathode

The addition of electrolyte additives is widely regarded as one of the most effective methods of improving the electrochemical performance of a battery. This study uses succinonitrile as a typical representative of nitrile film-forming additives to improve the film-forming stability of δ-MnO2/KMnF3 as the potassium ion battery cathode. The strong interaction between the –CN group of the nitrile and the metal ion on the cathode surface will enhance the stability of the solid electrolyte interface film. Electrochemical impedance spectroscopy is used to study the interface phenomena during charge and discharge. The mechanism of the film-forming additives is predicted and explained. These new design concepts will create a higher possibility of improving the battery cycle stability.

Preparation of K2Fe[Fe(CN)6] nanoparticles by improved electrostatic spray assisted precipitation technology as potassium-ion battery cathodes

Prussian blue analogues, which have a stable structural framework and larger ion migration channels, are currently one of the most potential cathodes for potassium ion batteries. However, Prussian blue-based materials are susceptible to preparation conditions, resulting in vacancy defects and crystal water in structures, which seriously restricts the exertion of electrochemical properties. Herein, a novel preparation technology-an electrostatic spray assisted coprecipitation way protected by inert atmosphere is proposed and applied to the synthesis of K2Fe[Fe(CN)6] materials. The effects of preparation process on the crystallinity, microstructure and potassium storage performances of K2Fe[Fe(CN)6] are systematically discussed. The results prove that K2Fe[Fe(CN)6] synthesized by the new preparation process has good crystallinity (K1.56Fe[Fe(CN)6]0.89·□0.11·1.86 H2O), small particle size (~20 nm) and high specific surface area (104.31 m2 g−1), and finally exhibits excellent electrochemical performance, including an superb cycling stability of 89 mAh g−1 after 503 cycles at 0.5 C and rate capability of 82 mAh g−1 at 10 C. In addition, this preparation technology also provides a new strategy for the microstructure and performance optimization of other Prussian blue-based materials.

Ion-exchange-assisted Li0.27K0.72Ni0.6Co0.2Mn0.2O2 cathode in potassium-ion batteries

A Li0.27K0.72Ni0.6Co0.2Mn0.2O2 (LKNCM) cathode for potassium-ion batteries (PIBs) was obtained from LiNi0.6Co0.2Mn0.2O2 (NCM622) via ion exchange. In-situ X-ray diffraction and high-resolution transmission electron microscopy analyses showed the morphological and structural changes that occur during K+-ion insertion. Particularly, the primary particles became porous, and the (003) interlayer distance expanded from 4.76 to 6.50 Å, providing a potassiation/depotassiation framework. Inductively coupled plasma-optical emission spectroscopy revealed that 0.72 mol of K+ ions were inserted into the Li-extracted NCM622 cathode per formula unit, indicating that the amounts of extracted Li+ and inserted K+ were similar. The developed LKNCM cathode exhibited a theoretical capacity of 160.79 mAh g−1 and an initial discharge capacity of 106.95 mAh g−1 with an average potential of 3.1 V vs. K/K+. These results demonstrate that ion exchange enables layered NCM cathodes for lithium-ion batteries to be applied as cathodes for PIBs.

Unraveling the role of ion-solvent chemistry in stabilizing small-molecule organic cathode for potassium-ion batteries

Redox-active organic cathodes are promising high-capacity and low-cost electrode materials for potassium-ion batteries (KIBs), but usually suffer from poor cyclability due to the severe dissolution and notorious K dendrites. Herein, the effects of salt concentrations and solvents on the performance of potassium-organic batteries based on a typical phenothiazine derivative, methylene blue (MB), are explored, and the high-concentration potassium bis(fluorosulfonyl)amide-based ether electrolyte is versatile to achieve long lifespan. The high donor number and strong solvation ability of ether solvent endow MB cathode with high voltage plateaus and reversible capacity as compared to the carbonate counterpart. Moreover, the enhanced interactions of K+-ether and anion-participated ion-ether complexes in concentrated electrolyte not only decrease the amount of free solvent, but also contribute to forming highly ionic-conducting and thin anion-derived interphase layers, which effectively mitigate the shuttle effect and inhibit K dendrite growth. Consequently, MB cathode exhibits a high capacity of 139.5 mAh g−1 after 500 cycles at 0.1 A g−1, and long-term cycling stability for 4500 cycles. The good performance of full cells matched with graphite anode further demonstrates the feasibility of MB as KIB cathode. This work highlights the roles of ion-solvent chemistry in stabilizing small-molecule organic cathodes, which may bring new insights in the electrolyte design for wide organic electrode-based battery systems.

P2‐K0.76Fe0.2Mg0.1Mn0.7O2made from earth‐abundant elements for rechargeable potassium ion battery

AbstractDue to the large volume change, limited energy density, large safety problems, and other factors restricting the development of potassium ion battery in the process of charge and discharge, the research on the cathode materials of potassium ion battery is an indispensable part. In this article, we designed and predicted P2‐type structures by introducing “cationic potential” that captures the key interactions of the layered materials. The precursors of the designed potassium ion battery cathode materials were obtained by co‐precipitation method. Through component analysis, the experimental conditions most in line with the theoretical content of precursors were found. The cathode material was synthesized by solid phase method. This material has a highly reversible K+insertion/deinsertion effect. The initial discharge specific capacity of the battery appears at about 47 mAh/g. After 30 charge‐discharge cycle tests, the discharge specific capacity of the battery drops to about 33 mAh/g, and the retention rate is about 70%.

A P3-Type K1/2Mn5/6Mg1/12Ni1/12O2 Cathode Material for Potassium-Ion Batteries with High Structural Reversibility Secured by the Mg-Ni Pinning Effect.

Mn-based layered oxides are very attractive as cathodes for potassium-ion batteries (PIBs) due to their low-cost and environmentally friendly precursors. Their transfer to practical application, however, is inhibited by some issues including consecutive phase transitions, sluggish K+ deintercalation/intercalation, and serious capacity loss. Herein, Mg-Ni co-substituted K1/2Mn5/6Mg1/12Ni1/12O2 is designed as a promising cathode material for PIBs, with suppressed phase transitions that occurred in K1/2MnO2 and improved K+ storage performance. Part of Mg2+ and Ni2+ occupies the K+ layer, playing the role of a "nailed pillar", which restrains metal oxide layer gliding during the K+ (de)intercalation. The "Mg-Ni pinning effect" not only suppresses the phase transitions but also reduces the cell volume variation, leading to the improved cycle performance. Moreover, K1/2Mn5/6Mg1/12Ni1/12O2 has low activation barrier energy for K+ diffusion and high electron conductivity as demonstrated by first-principles calculations, resulting in better rate capability. In addition, K1/2Mn5/6Mg1/12Ni1/12O2 also delivers a higher reversible capacity owing to the participation of the Ni element in electrochemical reactions and the pseudocapacitive contribution. This study provides a basic understanding of structural evolution in layered Mn-based oxides and broadens the strategic design of cathode materials for PIBs.

O3-Type NaCrO2 as a Superior Cathode Material for Sodium/Potassium-Ion Batteries Ensured by High Structural Reversibility.

O3-type NaCrO2 is attracting increasing attention as potential cathode material for sodium-ion batteries (SIBs). Bare NaCrO2 is usually synthesized by a solid-state reaction and suffers from serious capacity decay and poor power capability. Modification by coating is an effective method to improve the electrochemical properties, but it inevitably reduces the energy density. To avoid the decrease of energy density and optimize the electrochemical performance, a specific route, i.e., a freeze-drying-assisted sol-gel method, has been adopted to synthesize bare NaCrO2 in this work. Three-phase coexistence during charging is confirmed for the first time, which contributes to delaying the disappearance of the O3 phase and then improving the structural reversibility, resulting in superior cycle stability (∼50% capacity retention after 3000 cycles at 5C). Meanwhile, as-synthesized NaCrO2 delivers an outstanding rate capability (82.1 mAh g-1 at 50C), which is attributed to the fast Na+ diffusivity and high electronic conductivity proved by density functional theory (DFT) calculations. It is worth mentioning that NaCrO2 also exhibits excellent electrochemical properties when used as a cathode for potassium-ion batteries (PIBs). This work provides new perspectives on the structural evolution of NaCrO2, and the results are expected to contribute to the development of SIBs and PIBs.