Potassium-ion Hybrid Capacitors Research Articles

Molten-salt-induced interpenetrated meso/macro porous structural hard carbon derived from chitosan for enhanced potassium ions storage

Hard carbon materials are commonly used as anode materials for environmentally friendly potassium-ion energy devices due to excellent development prospects. However, the poor conductivity and unsatisfactory rate performance of hard carbon limit their development. Herein, chitosan was chosen as the carbon precursor to prepare interpenetrated meso/macro-porous structural hard carbon (PC) formed by the template agent NaCl in the molten state at high temperature as the anode for potassium-ion batteries. PC with a high content of pyridinic N, pyrrolic N, and CO bonds can provide a high reversible capacity of 280.1 mAh g−1 at the current density of 0.05 A g−1, and show an improved rate performance of 173.8 mAh g−1 at 1.0 A g−1. Galvanostatic charge/discharge (GCD) curves do not exhibit an obvious plateau, indicating that surface adsorption is dominant in the potassium ions storage mechanism. The high K+ diffusion coefficient indicates that the interconnected meso/macro structure allows potassium ions to diffuse faster in PC. Therefore, using activated carbon (AC) as the cathode and PC as the anode, a potassium-ion hybrid capacitor (PIHC) is fabricated, which can achieve an energy density of 130 Wh kg−1 at the current density of 0.05 A g−1 and an energy density of 62 Wh kg−1 at 1.0 A g−1.

Lignin organic molecule aggregate derived turbine-like nanocarbon with high nitrogen doping for potassium ion hybrid capacitors

Potassium-ion hybrid capacitors (PIHCs) represent a burgeoning class of electrochemical energy storage devices characterized by their remarkable energy and power densities. Utilizing amorphous carbon derived from sustainable biomass presents an economical and environmentally friendly option for anode material in high-rate potassium-ion storage applications. Nevertheless, the potassium-ion storage capacity of most biomass-derived carbon materials remains modest. Addressing this challenge, nitrogen doping engineering and the design of distinctive nanostructures emerge as effective strategies for enhancing the electrochemical performance of amorphous carbon anodes. Developing highly nitrogen-doped nanocarbon materials is a challenging task because most lignocellulosic biomasses lack nitrogen functional groups. In this work, we propose a general strategy for directly carbonizing supermolecule-mediated lignin organic molecular aggregate (OMA) to prepare highly nitrogen-doped biomass-derived nanocarbon. We obtained lignin-derived, highly nitrogen-doped turbine-like carbon (LNTC). Featuring a three-dimensional turbine-like structure composed of amorphous, thin carbon nanosheets, LNTC demonstrated a capacity of 377 mAh g−1 when used as the anode for PIHCs. This work also provides a new synthesis method for preparing highly nitrogen-doped nanocarbon materials derived from biomass.

Optimizing the performance of a graphite anode for innovative metal-ion batteries and hybrid capacitors

Herein, we present an optimum method for maximizing the electrochemical performance of graphite anodes using two heat treatment methods involving graphite intercalated compound (GIC) group within graphite, namely, thermal shock (TS; directly input target temperature) and gradual heating (GH; including ramping time). Different heating methods for preparing expanded graphite (EG) involve different reactions, relaxation times, and diffusion pathways for the diffusion of metal ions into EG. We find that rapidly shocking the layered structure can facilitate faster lithium and potassium ion diffusion from EG (TS) (heated for 30 min) via different intercalation/deintercalation processes compared to that from EG (GH). Consequently, EG (TS) exhibits the most significantly improved electrochemical performance among the lithium and potassium ion half-cells. For full lithium-ion hybrid capacitors (LIHCs), EG (TS)||activated carbon (AC) shows reasonable values of maximum power density (2.8 kW kg−1 with 59.12 Wh kg−1) and energy density (196.41 Wh kg−1), demonstrating its ultrahigh durability (capacity retention: 70.01%) over 12000 cycles at 2.0 A g−1. In addition, for potassium-ion hybrid capacitors (PIHCs), reasonable performance is achieved (average capacity of 82.02 mAh g−1 at 1.0 A g−1 over 2000 cycles with 94.35% capacity retention), demonstrating the high efficiency of PIHCs for substituting LIHCs without any systematic alterations.

Revealing the Charge Storage Mechanism in Porous Carbon to Achieve Efficient K Ion Storage.

Constructing a porous structure is considered an appealing strategy to improve the electrochemical properties of carbon anodes for potassium-ion batteries (PIBs). Nevertheless, the correlation between electrochemical K-storage performance and pore structure has not been well elucidated, which hinders the development of high-performance carbon anodes. Herein, various porous carbons are synthesized with porosity structures ranging from micropores to micro/mesopores and mesopores, and systematic investigations are conducted to establish a relationship between pore characteristics and K-storage performance. It is found that micropores fail to afford accessible active sites for K ion storage, whereas mesopores can provide abundant surface adsorption sites, and the enlarged interlayer spacing facilitates the intercalation process, thus resulting in significantly improved K-storage performances. Consequently, PCa electrode with a prominent mesoporous structure achieves the highest reversible capacity of 421.7 mAh g-1 and an excellent rate capability of 191.8 mAh g-1 at 5C. Furthermore, the assembled potassium-ion hybrid capacitor realizes an impressive energy density of 151.7Wh kg-1 at a power density of 398W kg-1. The proposed work not only deepens the understanding of potassium storage in carbon materials with distinctive porosities but also paves a path toward developing high-performance anodes for PIBs with customized energy storage capabilities.

Pyridine N‐Modulated Adsorption Equilibrium of Highly Dispersed Atomic W‐P Clusters toward Advanced Potassium‐Ion Hybrid Capacitors

AbstractImproving the atomic utilization of storage sites and developing isotropic transport characteristics become crucial to enhance the performance of potassium‐ion hybrid capacitors (PIHCs), and the disordered strategy and coordination modulation of the electrodes can satisfy the above structure‐activity requirements. Herein, the highly dispersed atomic W‐P clusters are chosen as a platform for the electronic restructuring. Studies and calculations indicate that replacing O in W‐O2/P2 with pyridine N can modulate the electron distribution and electronegativity, and enrich the edge‐dangling bonds of the amorphous clusters (W‐N2/P2), resulting in proper adsorption equilibrium and high affinity for K+ storage. In addition, the clusters have isotropic and bulk‐phase‐indifferent fast ion storage, and in situ protection of carbon nanosheets can provide stable support for ion storage and electron transfer in the clusters. As an anode, the composite (W‐N/P@C) exhibits superior storage properties of K+ (reversible capacity of 181.6 mAh g−1 after 3000 cycles at 5.0 A g−1), with high energy density (163.7 Wh Kg−1) at the high‐power output (3500 W Kg−1) in PIHCs. This work systematically delineates the effects of disordered design and pyridine N‐coordination on energy storage, and provides new research ideas for studying high‐performance PIHCs.

Unveiling the Synergy of Architecture and Anion Vacancy on Bi2Te3-x@NPCNFs for Fast and Stable Potassium Ion Storage.

Large volume strain and slow kinetics are the main obstacles to the application of high-specific-capacity alloy-type metal tellurides in potassium-ion storage systems. Herein, Bi2Te3-x nanocrystals with abundant Te-vacancies embedded in nitrogen-doped porous carbon nanofibers (Bi2Te3-x@NPCNFs) are proposed to address these challenges. In particular, a hierarchical porous fiber structure can be achieved by the polyvinylpyrrolidone-etching method and is conducive to increasing the Te-vacancy concentration. The unique porous structure together with defect engineering modulates the potassium storage mechanism of Bi2Te3, suppresses structural distortion, and accelerates K+ diffusion capacity. The meticulously designed Bi2Te3-x@NPCNFs electrode exhibits ultrastable cycling stability (over 3500 stable cycles at 1.0 A g-1 with a capacity degradation of only 0.01% per cycle) and outstanding rate capability (109.5 mAh g-1 at 2.0 A g-1). Furthermore, the systematic ex situ characterization confirms that the Bi2Te3-x@NPCNFs electrode undergoes an "intercalation-conversion-step alloying" mechanism for potassium storage. Kinetic analysis and density functional theory calculations reveal the excellent pseudocapacitive performance, attractive K+ adsorption, and fast K+ diffusion ability of the Bi2Te3-x@NPCNFs electrode, which is essential for fast potassium-ion storage. Impressively, the assembled Bi2Te3-x@NPCNFs//activated-carbon potassium-ion hybrid capacitors achieve considerable energy/power density (energy density up to 112 Wh kg-1 at a power density of 1000 W kg-1) and excellent cycling stability (1600 cycles at 10.0 A g-1), indicating their potential practical applications.

Engineering of edge nitrogen dopant in carbon nanosheet framework for fast and stable potassium-ion storage

Amorphous carbons are promising candidates as the anode materials for potassium-ion hybrid capacitors (PIHCs). The insufficient storage sites and inferior diffusion kinetics limit their potassium-ion storage capability. Edge nitrogen and morphology engineering are effective pathways to construct accessible active sites and enhanced diffusion kinetics. However, the organic integration of both pathways in amorphous carbon is still challenging. Herein, a “twice-cooking” strategy, including two-step carbonization processes at 700 °C, is designed to synthesize edge-nitrogen-rich lignin-derived carbon nanosheet framework (EN-LCNF). In the first-step carbonization process, the staged gas releases of CO and CO2 from CaC2O4 decomposition exfoliate the carbon matrix into a carbon nanosheet framework. In the second-step carbonization process, the generated CaO reacts with the cyanamide units of graphitic carbon nitride (g-C3N4) to form an edge-nitrogen-rich framework, which is then integrated into the meso-/macropores of carbon nanosheet framework through sp3-hybridized C–N bonds. EN-LCNF with a high edge-nitrogen level of 7.0 at.% delivers an excellent capacity of 310.3 mAh g−1 at 50 mA g−1, a robust rate capability of 126.4 mAh g−1 at 5000 mA g−1, and long cycle life. The as-assembled PIHCs based on EN-LCNF anode and commercial activated carbon cathode show a high energy density of 110.8 Wh kg−1 at a power density of 100 W kg−1 and excellent capacitance retention of 98.7% after 6000 cycles. This work provides a general strategy for the synthesis of edge-nitrogen-rich lignin-derived carbon materials for advanced potassium-ion storage.Graphical

Carbon cathode with heteroatom doping and ultrahigh surface area enabling enhanced capacitive behavior for potassium-ion hybrid capacitors

Carbon cathode with heteroatom doping and ultrahigh surface area enabling enhanced capacitive behavior for potassium-ion hybrid capacitors

Zinc sulfide quantum dots modified 3D Nitrogen-Doped framework carbon enhances the ion transport rate of potassium ion hybrid capacitors

The potassium-ion hybrid capacitor (PIHC) has garnered considerable attention due to its ability to leverage the advantages of both battery-type anodes and capacitor-type cathodes simultaneously. Nevertheless, the slow K+ transfer rate between the PIHC battery-type anode and capacitor-type cathode significantly impedes the overall performance. Herein, we have employed quantum-sized zinc sulfide (ZnS) immobilized within a three-dimensional N-doped porous carbon framework (ZnSQDS@3DNC) as a standalone anode. The corresponding three-dimensional N-doped porous carbon (3DNC) serves as the cathode, thereby constructing a PIHC device. The strong coupling between ZnS quantum dots and N-doped three-dimensional porous carbon material effectively enhances ion/electron transport, facilitating intercalation-conversion-exfoliation reactions and improving K+ transfer rates. The numerous active sites within the 3DNC significantly enhance the capacitance performance of the cathode, facilitating the reversible adsorption and desorption of FSI-. The values of DK+ have all been calculated to be within the range of 10-10 to 10-9 cm2 s−1, indicating the rapid diffusion capability of this ZnSQDs@3DNC structure. More impressively, the assembled PIHC device can achieve high energy densities of 179.9 Wh kg−1 at power densities of 200 W kg−1, with an ultralong cycling life over 10,000 cycles. This study serves to advance the development of metal-ion hybrid capacitors and provides direction for improving ion transport kinetics.

A High-Concentration Edge-Nitrogen-Doped Porous Carbon Anode via Template Free Strategy for High-Performance Potassium-Ion Hybrid Capacitors

Developing facile and economical strategies to fabricate nitrogen-doped porous carbon anode is desirable for dual-carbon potassium ion hybrid capacitors (PIHCs). Here, a high-concentration edge-nitrogen-doped porous carbon (NPC) anode is synthesized by a template-free strategy, in which the total content of pyrrolic nitrogen and pyridinic nitrogen accounts for more than 80% of the nitrogen atoms. As a result, the NPC anode displays a capacity of 315.4 mA h g −1 at a current rate of 0.1 A g −1 and 189.1 mA h g −1 at 5 A g −1 . Ex situ characterizations and density functional theory calculations demonstrate the high-concentration edge-nitrogen doping enhances K + adsorption and electronic conductivity of carbon materials, resulting in good electrochemical performance. The assembled NPC//CMK-3 PIHC delivers an energy density of 71.1 W h kg −1 at a power density of 771.9 W kg −1 over 8,000 cycles.

Redox-active electrolytes as a viable approach for the one-step assembly of metal-ion capacitors

The assembly of metal-ion capacitors is a very challenging task; the use of traditional metallic electrodes or sacrificial materials induces technical problems during cell assembly or affects its normal operation. Here, we report an efficient, one-step method for assembling metal-ion capacitors using redox-active electrolytes with thiocyanate-based salts. The addition of a redox-active salt compensates for the charge on the positive electrode while enabling the insertion of metal ions into the structure of the negative electrode. The proposed approach reduces assembly time and cost and results in increased specific energy compared to that from the traditional two-step assembled hybrid systems. Furthermore, we demonstrate that the proposed approach can be successfully implemented for sodium-ion and potassium-ion hybrid capacitors. Our results are supported by operando techniques and can potentially facilitate further research on metal-ion capacitors and applications of these devices.

Thermal Induced Conversion of CoFe Prussian Blue Analogs Nanocubes Wrapped by Doped Carbon Network Exhibiting Fast and Stable Potassium Ion Storage as Anode.

Prussian blue analogs (PBAs) show great promise as anode materials for potassium-ion batteries (PIBs) due to their high specific capacity. However, PBAs still suffer from the drawbacks of low electronic conductivity and poor structural stability, leading to inadequate rate and cyclic performance. To address these limitations, CoFe PBA nanocubes wrapped with N/S doped carbon network (CoFe PBA@NSC) as anode for PIBs is designed by using thermal-induced in situ conversion strategy. As expected, the structural advantages of nanosized PBA cubes, such as abundant interfaces and large surface area, enable the CoFe PBA@NSC electrode to demonstrate superior rate properties (557 and 131mAhg-1 at 0.05 and 10Ag-1 ) and low capacity degradation (0.093% per cycle over 1000 cycles at 0.5Ag-1 ). Furthermore, several ex situ characterizations revealed the K-ion storage mechanism. Fe+ and Co0 are generated during potassicization, followed by a completely reversible chemical state of iron while some cobalt monomers remained during depotassication. Additionally, the as-built potassium-ion hybrid capacitor based on CoFe PBA@NSC anode exhibits a high energy density of 118Whkg-1 . This work presents an alternative but promising synthesis route for Prussian blue analogs, which is significant for the advancement of PIBs and other related energy storage devices.

Coupling of reasonable micro-defect structure and multiple chemisorption sites for boosting the K+ storage capacity in dual-carbon potassium ion hybrid capacitors

Construction of hierarchical porous (meso‑microporous) carbonaceous anodes with reasonable-sized defects and rich active sites is important for enhancing K+ storage capacity. Here, we propose a strategy that can expand the microporous defects and synchronously introduce multiple chemisorption sites to synthesize phosphorus-nitrogen double-doped foamed porous carbon (PN-FPC). Interlaced and interconnected macropores in PN-FPC can effectively promote long-range mass transfer, while ultrathin carbon bubble walls with abundant meso‑micropores and chemisorption sites can maximize the utilization of active sites. Density-functional theory (DFT) calculations show that the P, N double-doped synergistically rational micro-defect structure significantly contributes to the reversible adsorption-desorption of K+. More importantly, the potassium-ion hybrid capacitors (PIHCs) composed of P, N double-doped activated porous carbon (PN-FAPC) as cathode and pre-activated PN-FPC as anode exhibited ultra-high energy density (155.6 Wh kg−1), power density (17,000 W kg−1), and ultra-long lifetime (90.9 % capacity retention after 10,000 cycles). This study not only provides new insights for the convenient synthesis of advanced carbonaceous anode materials, but also provides a deeper understanding for revealing the charge storage mechanism of PIHCs.

Ampere-hour-scale soft-package potassium-ion hybrid capacitors enabling 6-minute fast-charging

Extreme fast charging of Ampere-hour (Ah)-scale electrochemical energy storage devices targeting charging times of less than 10 minutes are desired to increase widespread adoption. However, this metric is difficult to achieve in conventional Li-ion batteries due to their inherent reaction mechanism and safety hazards at high current densities. In this work, we report 1 Ah soft-package potassium-ion hybrid supercapacitors (PIHCs), which combine the merits of high-energy density of battery-type negative electrodes and high-power density of capacitor-type positive electrodes. The PIHC consists of a defect-rich, high specific surface area N-doped carbon nanotube-based positive electrode, MnO quantum dots inlaid spacing-expanded carbon nanotube-based negative electrode, carbonate-based non-aqueous electrolyte, and a binder- and current collector-free cell design. Through the optimization of the cell configuration, electrodes, and electrolyte, the full cells (1 Ah) exhibit a cell voltage up to 4.8 V, high full-cell level specific energy of 140 Wh kg−1 (based on the whole mass of device) with a full charge of 6 minutes. An 88% capacity retention after 200 cycles at 10 C (10 A) and a voltage retention of 99% at 25 ± 1 °C are also demonstrated.

Freestanding fibers assembled by CoPSe@N-doped carbon heterostructures as an anode for fast potassium storage in hybrid capacitors

Although the fast development of potassium-ion hybrid capacitors (PIHC) recently, the issues such as the slow kinetics and poor durability of potassium ion hosts greatly restric their applications. Herein, a freestanding fiber (NHF fiber) with necklace-like configuration and CoPSe@N-doped carbon (CoPSe@NCNT) heterostructured units is introduced as the anode in PIHC. The highly porous network of NHF fiber facilitates the fast ion transports and promises the good high-rate property. Additionally, the nanoscle crystallites inside in-situ grown NCNT favor the high adaption to volume expansion/shrinkage and endow good structure stability during ion insertion/deinsertion. Density function theoretical (DFT) calculations disclose the CoPSe@NCNT heterostructure has improved intrinsic conductivity, fast potassium migration, and decreased energy barrier. Meanwhile, the finite element simulation analysis (FEA) reveals the decreased stress inside the NHF architecture during charge/discharge processes. Moreover, the electrochemical tests confirm the fast and durable properties of the CoPSe@NCNT NHF fibers for potassium storage. Furthermore, the PIHC full cell with the anode of CoPSe@NCNT NHF fiber is assembled, which obtains the superior energy/power densities and high capacity retention (89%) after 2000 cycles at 2 A g−1. When the polymer electrolyte is incooperated, the flexible PIHC device achieves the good pliability and good adaptation during wide temperature changes from −20 to 25 °C. Therefore, this work introduces a novel anode for fast potassium ion storage, and opens a new approach to assemble the power sources for flexible electronics in diverse conditions.

Facile preparation of heteroatom S doped dumbbell-like hard carbon for boosting potassium-ion storage capability

Potassium-ion storage devices have gained increasing interest in applications such as large-scale energy storage and smart grids due to the advantages of high abundance, low cost, high working voltage, and fast charge transport in electrolytes. However, obtaining high-performance anodes with excellent rate performance and cycling stability remains a challenge due to the much larger size of K+ ions. In this contribution, heteroatom S doped dumbbell-like hard carbon (SDHC) are synthesized using sucrose as the carbon source. SDHC-700, which is carbonized at 700 °C, exhibits the highest sulfur doping degree (9.3 at.%), remarkable reversible capacity (416 mAh g-1 at 0.05 A g-1), and superb rate performance (174 mAh g-1 at 5.0 A g-1). Ex situ X-ray photoelectron spectroscopy (XPS) tests reveal that covalent C-S bonds can undergo a reversible reaction with K to form K2Sx. In situ electrochemical impedance spectroscopy (EIS) results suggest that the diffusion of long-chain potassium polysulfides may be the main reason for the degradation of SDHC during long-term cycling. Moreover, using SDHC-700 as the anode and commercial activated carbon as the cathode, a dual-carbon potassium-ion hybrid capacitor has been successfully constructed, which can deliver a high energy/power density of 96.5 Wh kg-1/160.3 W kg-1. This study provides a straightforward and practical approach for developing sulfur-doped hard carbons as high-performance anode materials for alkali metal ion storage.

Versatile potassium vanadium fluorophosphate (KVPO4F) composites as Dual-Function cathode and anode materials for Potassium-Ion hybrid capacitors

Potassium-based energy storage has emerged as a promising alternative for advanced energy storage systems, driven by the abundance of potassium, fast ion migration, and low standard electrode potential. Hybrid capacitors, which combine the desirable characteristics of batteries and supercapacitors, offer a compelling solution for efficient energy storage. In this study, we present the development of versatile composite materials, specifically potassium vanadium fluorophosphate (KVPO4F) composites, utilizing a sol–gel method. These composites enable tunable potassium storage and charge transport kinetics within regulated voltage windows, serving as both cathode and anode materials. The anode composite, composed of KVPO4F and hierarchical porous carbon (HPC), exhibited exceptional stability over 400 cycles within a low-voltage window. On the other hand, the cathode composite, consisting of battery-like KVPO4F and physisorption activated carbon (AC), demonstrated great potential as a cathode material, striking a balance between specific energy and cycle life within a regulated high-voltage window. By integrating KVPO4F/C as the anode and KVPO4F/AC as the cathode, we successfully created potassium-ion hybrid capacitors (PIHCs) that showcased an impressive capacity retention of 83% after 10,000 cycles within a high voltage window of 0.5–4.3 V. Furthermore, to explore the application of these materials in miniaturized energy storage, we fabricated potassium-ion micro hybrid capacitors (PIMHCs) with interdigitated electrodes. These devices exhibited a high areal energy density of 18.8 μWh cm−2 at a power density of 111.6 μW cm−2, indicating their potential for compact energy storage systems. The results of this study demonstrate the versatility and efficacy of the developed KVPO4F composite materials, highlighting their potential for future advancements in potassium-based energy storage technologies.

Hierarchically porous N-doped carbon framework with enlarged interlayer spacing as dual-carbon electrodes for potassium ion hybrid capacitors

Thanks to the high power/energy densities together with lower cost, potassium ion hybrid capacitors (PIHCs) have broad application prospects. Nevertheless, the significant volume changes during K+ intercalation/deintercalation together with the misfit between anode as well as cathode limit their further development. Herein, hierarchically porous nitrogen-doped carbon (N-HPC) is fabricated and used as two electrodes materials for PIHCs. The three-dimensional hierarchical porous structure and large interlayer distance of N-HPC afford enough space to alleviate the volume expansion of potassium. Furthermore, the suitable N doping enables additional active sites towards K+ storage and improves electrical conductivity of electrodes. Hence, the constructed PIHCs assembled with dual N-HPC electrodes deliver a high energy density of 103.5 Wh kg‒1 at 1000.0 W kg‒1. Meanwhile, the PIHCs devices also display superior cycling stability, achieving a capacity retention rate of 70.2% after 10,000 cycles at 1.0 A g‒1.Graphical Hierarchically porous nitrogen-doped carbon (N-HPC) is fabricated and used as two electrode materials for PIHCs. The three-dimensional porous structure of N-HPC, the larger inter-layer distance, and the synergy of N-doped introduction of more active sites make it have good magnification properties. At the same time, the assembled PIHCs cycle of 10000 laps has an excellent cycle retention rate.

Supermolecule-regulated synthesis strategy of general biomass-derived highly nitrogen-doped carbons toward potassium-ion hybrid capacitors with enhanced performances

Biomass-derived carbons are promising anodes in potassium-ion hybrid capacitors owing to their tunable structure and competitive cost-effectiveness. The intercalation of K+ ions into carbonaceous anode is a sluggish reaction due to the turbostratic structure and large radius of K+ ions, resulting in the inability to exploit its high capacity and high-rate capability. Nitrogen-doping strategy could enhance the K-ion storage performance by surface capacitive adsorption mechanism. Nevertheless, conventional nitrogen-doping strategies could only endow biomass-derived carbons with low nitrogen-doping levels (<10 at.%), owing to the general agglomeration issue of biomass molecules and the easy release of nitrogen dopant during carbonization. Herein, we proposed a supermolecule-regulated strategy, which enables the breakage of the agglomeration of lignin molecule and disperses lignin in Lewis alkali-acid coupled supermolecule through inter-molecule interactions between lignin and the supermolecule. The co-decomposition of supermolecule/lignin composite precursor could form a covalent-bonded graphitic carbon nitride/carbon intermediate, ensuring the high nitrogen doping level (17.0 at.%) in lignin-derived carbon. The obtained carbon anode delivered high reversible capacities and high-rate capability. All-carbon potassium-ion hybrid capacitors constructed by this carbon as both anode and cathode exhibited a high energy density and power density. This work proposes a general method for constructing highly nitrogen-doped carbon anodes with superior performances.

Stepwise induced passivation film formation on the surface of spherical hard carbons enabling ultra-stable potassium ions storage

Potassium-ion storage devices are seen as a form of prospective substitute for large-scale electrochemical energy storage because of the low cost and the fast charge transport in electrolytes. However, the rosy scenario is compromised by developing ultra-stable electrode materials to ensure long-term cycling performance. Herein, with sucrose as the carbon source, we construct two carbon materials, namely hard carbon spherules (HCS) and active hard carbons (AHCS), as anode and cathode materials, respectively, to fabricate high-performance potassium-ion hybrid capacitors (PIHC). Benefiting from the advantageous ionic conductivity and the comparatively stable passivation film, HCS bonding with sodium alginate delivers superior rate performance and high pseudocapacitive proportion. In situ electrochemical impedance spectroscopy and distribution of relaxation time analysis combined with ex situ scanning electron microscope images reveal that the formation of solid electrolyte interface on the surface of the HCS during the initial discharge can be explained as a gradually forming process. As expected, the HCS//AHCS PIHC device delivers a high energy density of 116 Wh kg−1 at a power density of 218 W kg−1 and exhibits an ultra-stable lifespan over 20000 cycles. This study provides a worthy reference for the value-added utilization of biomass in innovative potassium-based energy storage technology.