Lithium-ion Capacitors Research Articles

Boosting High‐Voltage Dynamics Towards High‐Energy‐Density Lithium‐Ion Capacitors

Lithium‐ion capacitors (LICs) are becoming important electrochemical energy storage systems due to their great potential to bridge the gap between supercapacitors and lithium‐ion batteries. However, capacity lopsidedness and low output voltage greatly hinder the realization of high‐energy‐density LICs. Herein, a strategy of balancing capacity towards fastest dynamics is proposed to enable high‐voltage LICs. Through electrochemical prelithiation of Nb2C to be 1.1 V with 165 mAh g−1, Nb2C // LiFePO4 LICs show a broadened potential window from 3.0 to 4.2 V and an according high energy density of 420 Wh kg−1. Moreover, the underlying mechanism between prelithiation and high voltage is disclosed by electrochemical dynamic analysis. Prelithiation declines the Nb2C anode potential that facilitates electron transmission in the interlayer of two‐dimensional Nb2C MXene. This effect induces small drive force for Li+ ions deposition and hence weakens the repulsive force from adsorbed ions on the electrode surface. Benefiting from even more Li+ ions deposition, a higher voltage is eventually delivered. In addition, prelithiation significantly increases Coulomb efficiency of the 1st cycle from 74% to 90%, which is crucial to commercial application of LICs.

Natural Molybdenite as a High‐Capacity Anode Material for Fast‐Charging Lithium‐Ion Capacitors

Lithium‐ion capacitor (LIC) is a promising energy storage device, which combines double advantages of high‐energy lithium‐ion batteries (LIBs) and high‐power supercapacitors. However, the reported anode materials for LICs are synthesized based on the high‐purity chemicals under complicated and time‐consuming conditions, which exhibit a prohibitive cost in practical application. Herein, natural molybdenite is employed as the precursor to construct a high‐capacity and low‐cost anode material of LICs. Specifically, molybdenite is exfoliated into thin‐layer MoS2 under the interaction of hydrazine hydrate and sodium hydroxide, and then coupled with reduced graphene oxide to form a MoS2@rGO composite. Resulting from high reactive activity and structural stability, the MoS2@rGO anode shows excellent lithium‐ion storage performance including high specific capacity (936 mAh g−1 at 100 mA g−1) and rate capability (446 mAh g−1 at 5000 mA g−1). By using MoS2@rGO as an anode and activated carbon as a cathode, the assembled LIC device provides a maximum energy density of 105 Wh kg−1. Even at a high power density of 25 000 W kg−1, the energy density is still up to 65 Wh kg−1. This work provides a reference for the commercial utilization of natural molybdenum resources in the energy storage field.

Manufacture of Lithium Lanthanum Titanate Active Material as a Lithium-Ion Capacitor Anode Using Solid-State Reaction Methods

Lithium lanthanum titanate, Li0.2La0.6TiO3 (LLTO) was synthesized for the manufacture of lithium-ion capacitors using the solid-state reaction method. in this study, the active ingredients were synthesized using variations of lithium and lanthanum as raw materials. The raw materials used are Li2CO3, La2O3, and TiO2. The three raw materials were mixed according to the stoichiometric calculations then added 13 ml of Ethanol solution so that the raw materials were mixed evenly during the milling process for 5 hours. Sintering was carried out for 8 hours at 800oC and then at 1150oC for 12 hours. The sintered powder was ground using a mortar and pastel and then sieved on a 400 mesh sieve. The anode sheet was made by mixing the active ingredients: PVDF: Super-P with a composition of 85:10:5 by adding 3 ml of DMAC solvents. The characterization test was carried out using XRD while the electrochemical test used CV and EIS. The XRD result shows the formation of the main phase and the impurity phase with the main phase percent of 96.4%. From the results of electrochemical testing, the percentage of capacity is 73%.

Brewery waste derived activated carbon for high performance electrochemical capacitors and lithium-ion capacitors

In this study we report about the synthesis and characterization of an activated carbon (AC) displaying very large surface area (∼3600 m2 g−1) obtained from a cheap and abundant brewery waste product (Brewer's spent grains, BSG). AC based electrodes prepared from BSG demonstrated a very high specific capacitance (46 F g−1) and capacitance retention when evaluated in symmetric Electrical Double Layer Capacitors (EDLCs) devices with organic electrolytes. We showed that these electrodes can be successfully utilized for the realization of lab scale EDLCs and Lithium-ion Capacitors exhibiting very high energy and power densities as well excellent cycling stability (85% capacitance retention after 200 h of float test). Considering these results, the BSG-derived AC can be certainly considered as very promising material, which can contribute to the development of high performance, cost effective and eco-friendly high-power devices.

Sizing of Hybrid Supercapacitors and Lithium-Ion Batteries for Green Hydrogen Production from PV in the Australian Climate

Instead of storing the energy produced by photovoltaic panels in batteries for later use to power electric loads, green hydrogen can also be produced and used in transportation, heating, and as a natural gas alternative. Green hydrogen is produced in a process called electrolysis. Generally, the electrolyser can generate hydrogen from a fluctuating power supply such as renewables. However, due to the startup time of the electrolyser and electrolyser degradation accelerated by multiple shutdowns, an idle mode is required. When in idle mode, the electrolyser uses 10% of the rated electrolyser load. An energy management system (EMS) shall be applied, where a storage technology such as a lithium-ion capacitor or lithium-ion battery is used. This paper uses a state-machine EMS of PV microgrid for green hydrogen production and energy storage to manage the hydrogen production during the morning from solar power and in the night using the stored energy in the energy storage, which is sized for different scenarios using a lithium-ion capacitor and lithium-ion battery. The mission profile and life expectancy of the lithium-ion capacitor and lithium-ion battery are evaluated considering the system’s local irradiance and temperature conditions in the Australian climate. A tradeoff between storage size and cutoffs of hydrogen production as variables of the cost function is evaluated for different scenarios. The lithium-ion capacitor and lithium-ion battery are compared for each tested scenario for an optimum lifetime. It was found that a lithium-ion battery on average is 140% oversized compared to a lithium-ion capacitor, but a lithium-ion capacitor has a smaller remaining capacity of 80.2% after ten years of operation due to its higher calendar aging, while LiB has 86%. It was also noticed that LiB is more affected by cycling aging while LiC is affected by calendar aging. However, the average internal resistance after 10 years for the lithium-ion capacitor is 264% of the initial internal resistance, while for lithium-ion battery is 346%, making lithium-ion capacitor a better candidate for energy storage if it is used for grid regulation, as it requires maintaining a lower internal resistance over the lifetime of the storage.

Holey Ti3C2 MXene-Derived Anode Enables Boosted Kinetics in Lithium-Ion Capacitors.

Lithium-ion capacitors (LICs) attract enormous attention because of the urgent demands for high power and energy density devices. However, the intrinsic imbalance between anodes and cathodes with different charge-storage mechanisms blocks the further improvement in energy and power density. MXenes, novel two-dimensional materials with metallic conductivity, accordion-like structure, and regulable interlayer spacing, are widely employed in electrochemical energy storage devices. Herein, we propose a holey Ti3C2 MXene-derived composite (pTi3C2/C) with enhanced kinetics for LICs. This strategy effectively decreases the surface groups (-F and -O) and generates expanded interplanar spacing. The in-plane pores of Ti3C2Tx lead to increased active sites and accelerated lithium-ion diffusion kinetics. Benefiting from the expanded interplanar spacing and accelerated lithium-ion diffusion, the pTi3C2/C as an anode implements excellent electrochemical property (capacity retention about 80% after 2000 cycles). Furthermore, the LIC fabricated with a pTi3C2/C anode and an activated carbon cathode displays a maximum energy density of 110 Wh kg-1 and a considerable energy density of 71 Wh kg-1 at 4673 W kg-1. This work provides an effective strategy to achieve high antioxidant capability and boosted electrochemical properties, which represents a new exploration of structural design and tuneable surface chemistry for MXene in LICs.

"Water-in-Deep Eutectic Solvent" Gel Electrolytes Synergistically Controlled by Solvation Regulation and Gelation Strategies for Flexible Electronic Devices.

Recent developments in flexible electronics have heightened the need for electrolytes with high safety, ionic conductivity, and electrochemical stability. However, neither conventional organic electrolytes nor aqueous electrolytes can meet the above requirements simultaneously. Herein, a novel "water-in-deep eutectic solvent" gel (WIDG) electrolyte synergistically controlled by the solvation regulation and gelation strategies is reported. The water molecules introduced into deep eutectic solvent (DES) participate in the solvation structure regulation of Li+, thus endowing the WIDG electrolyte with high safety, thermal stability, and outstanding electrochemical performance, including high ionic conductivity (∼1.23 mS cm-1) and a wide electrochemical window (∼5.4 V). Besides, the polymer in the gel interacts with DES and H2O, further optimizing the electrolyte with excellent mechanical strength and higher operating voltage. Benefiting from these advantages, the lithium-ion capacitor constructed by WIDG electrolyte presents a high areal capacitance of 246 mF cm-2 with an energy density of 87.3 μWh cm-2. The use of the gel enhances the electrode structure stability, resulting in desirable cycling stability (>90% capacity retention after 1400 cycles). Moreover, the WIDG-assembled sensor exhibits high sensitivity and rapid real-time detection of motion. This work will provide guidelines for designing high-safety and high-operating-voltage electrolytes for flexible electronics.

A Safer High-Energy Lithium-Ion Capacitor Using Fast-Charging and Stable ω-Li3 V2 O5 Anode.

Lithium-ion capacitors (LICs) are flourishing toward high energy density and high safety, which depend significantly on the performance of the intercalation-type anodes used in LICs. However, commercially available graphite and Li4 Ti5 O12 anodes in LICs suffer from inferior electrochemical performance and safety risks due to limited rate capability, energy density, thermal decomposition, and gassing issues. Here a safer high-energy LIC based on a fast-charging ω-Li3 V2 O5 (ω-LVO) anode with a stable bulk/interface structure is reported. The electrochemical performance, thermal safety, and gassing behavior of the ω-LVO-based LIC device are investigated, followed by the exploration of the stability of the ω-LVO anode. The ω-LVO anode exhibits fast lithium-ion transport kinetics at room/elevated temperatures. Paired with an active carbon (AC) cathode, the AC||ω-LVO LIC with high energy density and long-term endurability is achieved. The accelerating rate calorimetry, in situ gas assessment, and ultrasonic scanning imaging technologies further verify the high safety of the as-fabricated LIC device. Theoretical and experimental results unveil that the high safety originates from the high structure/interface stability of the ω-LVO anode. This work provides important insights into electrochemical/thermochemical behaviors of ω-LVO-based anodes within LICs and offers new opportunities to develop safer high-energy LIC devices.

Insights into Formation and Li‐Storage Mechanisms of Hierarchical Accordion‐Shape Orthorhombic CuNb2O6 toward Lithium‐Ion Capacitors as an Anode‐Active Material

The orthorhombic CuNb2O6 (O–CNO) is established as a competitive anode for lithium‐ion capacitors (LICs) owing to its attractive compositional/structural merits. However, the high‐temperature synthesis (>900 °C) and controversial charge‐storage mechanism always limit its applications. Herein, we develop a low‐temperature strategy to fabricate a nano‐blocks‐constructed hierarchical accordional O–CNO framework by employing multilayered Nb2CTx as the niobium source. The intrinsic stress‐induced formation/transformation mechanism of the monoclinic CuNb2O6 to O–CNO is tentatively put forward. Furthermore, the integrated phase conversion and solid solution lithium‐storage mechanism is reasonably unveiled with comprehensive in(ex) situ characterizations. Thanks to its unique structural merits and lithium‐storage process, the resulted O–CNO anode is endowed with a large capacity of 150.3 mAh g−1 at 2.0 A g−1, along with long‐duration cycling behaviors. Furthermore, the constructed O–CNO‐based LICs exhibit a high energy (138.9 Wh kg−1) and power (4.0 kW kg−1) densities with a modest cycling stability (15.8% capacity degradation after 3000 consecutive cycles). More meaningfully, the in‐depth insights into the formation and charge‐storage process here can promote the extensive development of binary metal Nb‐based oxides for advanced LICs.

Carbon Nano-Onion-Encapsulated Ni Nanoparticles for High-Performance Lithium-Ion Capacitors

Lithium-ion capacitors (LICs) feature a high-power density, long-term cycling stability, and good energy storage performance, and so, LICs will be widely applied in new energy, new infrastructure, intelligent manufacturing. and other fields. To further enhance the comprehensive performance of LICs, the exploration of new material systems has become a focus of research. Carbon nano-onions (CNOs) are promising candidates in the field of energy storage due to the properties of their outstanding electrical conductivity, large external surface area, and nanoscopic dimensions. Herein, the structure, composition, and electrochemical properties of carbon nano-onion-encapsulated Ni nanoparticles (Ni@CNOs) have been characterized first in the present study. The initial discharge and charge capacities of Ni@CNOs as anodes (in half-cells (vs. Li)) were 869 and 481 mAh g−1 at 0.1 A g−1, respectively. Even at a current density of 10 A g−1, the reversible specific capacity remained at 111 mAh g−1. Ni@CNOs were used as anode materials to assemble LICs (full pouch cells (vs. activated carbon)), which exhibited compelling electrochemical performance and cycle stability after optimizing the mass ratio of the positive and negative electrodes. The energy density of the LICs reached 140.1 Wh kg−1 at 280.2 W kg−1 and even maintained 76.6 Wh kg−1 at 27.36 kW kg−1. The LICs also demonstrated excellent cycling stability with a 94.09% capacitance retention over 40,000 cycles. Thus, this work provides an effective solution for the ultra-rapid fabrication of Ni-cored carbon nano-onion materials to achieve high-performance LICs.

Mechanically flexible reduced graphene oxide/carbon composite films for high-performance quasi-solid-state lithium-ion capacitors

Practical applications of diverse flexible wearable electronics require electrochemical energy storage (EES) devices with multiple configurations. Moreover, to fabricate flexible EES devices with high energy density and stability, organic integration from electrode design to device assembly is required. To address these challenges, a free-standing reduced graphene oxide (rGO)/carbon film with a unique sandwich structure has been designed via the assistance of vacuum-assistant filtration for lithium-ion capacitors (LICs). The graphene acts as not only a binder to construct a three-dimensional conductive network but also an active material to provide additional capacitive lithium storage sites, thus enabling fast ion/electron transport and improving the capacity. The designed rGO/hard carbon (rGO/HC) and rGO/activated carbon (rGO/AC) free-standing films exhibit enhanced specific capacities (513.7 mA h g−1 for rGO/HC and 102.8 mA h g−1 for rGO/AC) and excellent stability. Moreover, the integrated flexible quasi-solid-state rGO/AC//rGO/HC LIC devices possess a maximum energy density of 138.3 Wh kg−1, a high power density of 11 kW kg−1, and improved cycling performance (84.4% capacitance maintained after 10,000 cycles), superior to the AC//HC LIC (43.5% retention). Such a strategy enlightens the development of portable flexible LICs.

Equivalent Circuit Model for High-Power Lithium-Ion Batteries under High Current Rates, Wide Temperature Range, and Various State of Charges

The most employed technique to mimic the behavior of lithium-ion cells to monitor and control them is the equivalent circuit model (ECM). This modeling tool should be precise enough to ensure the system’s reliability. Two significant parameters that affect the accuracy of the ECM are the applied current rate and operating temperature. Without a thorough understating of the influence of these parameters on the ECM, parameter estimation should be carried out manually within the calibration, which is not favorable. In this work, an enhanced ECM was developed for high-power lithium-ion capacitors (LiC) for a wide temperature range from the freezing temperature of −30 °C to the hot temperature of +60 °C with the applied rates from 10 A to 500 A. In this context, experimental tests were carried out to mimic the behavior of the LiC by modeling an ECM with two RC branches. In these branches, two resistance and capacitance (RC) are required to maintain the precision of the model. The validation results proved that the semi-empirical second-order ECM can estimate the electrical and thermal parameters of the LiC with high accuracy. In this context, when the current rate was less than 150 A, the error of the developed ECM was lower than 3%. Additionally, when the demanded power was high, in current rates above 150 A, the simulation error was lower than 5%.

Comparative Study of Supercapacitor, Battery and Supercapattery

Nowadays, the consumption of fossil fuels is increasing, which means there may be some serious environmental problems caused by greenhouse emissions. Solar and wind electricity, for instance, are examples of renewable energy sources that are important for the growth of human society. However, due to their unpredictability, these energy sources are susceptible to the effects of the environment, including the weather. In order to continue using renewable energy sources, energy storage technology development will be crucial. These devices would be able to store energy under favorable external conditions and release it when the environment was not ideal for converting the renewable energy to electrical energy. There have been two main types of energy storage devices, which are respectively supercapacitor and battery. Supercapacitor has an outstanding energy density with a long-life cycle while there are still some challenges with the power density. Battery has an impressive power density while there are still some problems with the energy density. Therefore, a new type of energy storage device is highly required. So, more attention has been devoted to supercapattery, which could have both high power and energy density. This essay will introduce the working principle of supercapacitor, battery with more details. Next, there will be a comparison between supercapacitor and battery. Finally, supercapattery will be proposed, and there will be a simple introduction of Lithium-ion hybrid capacitor based on silicon carbon material.

MnCO3 Cuboids from Spent LIBs: A New Age Displacement Anode to Build High-Performance Li-Ion Capacitors.

The advantage of hybridizing battery and supercapacitor electrodes has succeeded recently in designing hybrid charge storage systems such as lithium-ion capacitors (LICs) with the benefits of higher energy than supercapacitors and more power density than batteries. However, sluggish Li-ion diffusion of battery anode is one of the main barriers and hampers the development of high-performance LICs. Herein, is introduced a new conversion/displacement type anode, MnCO3 , via effectively recycling spent Li-ion batteries cathodes for LICs applications. The MnCO3 cuboids are regenerated from the spent LiMn2 O4 cathodes by organic acid lixiviation process, and hydrothermal treatment displays excellent reversibility of 535 mAhg-1 after 50 cycles with a Coulombic efficiency of >99%. Later, LIC is assembled with the regenerated MnCO3 cubes in pre-lithiated form (Mn0 +Li2 CO3 ) as anode and commercial activated carbon (AC) as the cathode, delivering a maximum energy density of 169.4Whkg-1 at 25°C with ultra-long durability of 15,000cycles. Even at various atmospheres like -5and 50°C, this LIC can offer a energy densities of 53.8and 119.5Whkg-1 , respectively. Remarkably, the constructed AC/Mn0 + Li2 CO3 -based LIC exhibits a good cycling performance for a continuous 1000cycles with >91% retention invariably for all temperature conditions.

Novel Nonstoichiometric Niobium Oxide Anode Material with Rich Oxygen Vacancies for Advanced Lithium-Ion Capacitors

Given the inherent features of open tunnel-like structures, moderate lithiation potential (1.0-3.0 V vs Li/Li+), and reversible redox couples (Nb5+/Nb4+ and Nb4+/Nb3+ redox couples), niobium-based oxides with Wadsley-Roth crystallographic shear structure are promising anode materials. However, their practical rate capability and cycling stability are still hindered by low intrinsic electronic conductivity and structural stability. Herein, ultrathin carbon-confined Nb12O29 materials with rich oxygen vacancies (Nb12O29-x@C) were designed and synthesized to address above-mentioned challenges. Computational simulations combined with experiments reveal that the oxygen vacancies can regulate the electronic structure to increase intrinsic electronic conductivity and reduce the Li+ diffusion barrier. Meanwhile, the carbon coating can enhance structural stability and further improve the electronic conductivity of the Nb12O29 material. As a result, the as-prepared Nb12O29-x@C exhibits high reversible capacity (226 mAh g-1 at 0.1 A g-1), excellent high-rate performance (83 mAh g-1 at 5.0 A g-1), and durable cycling life (98.1% capacity retention at 1.0 A g-1 after 3000 cycles). The lithium storage mechanism and structural stability of Nb12O29-x@C were also revealed by in situ X-ray diffraction (XRD), ex situ X-ray photoelectron spectroscopy (XPS), and ex situ Raman spectroscopy. When applied as the anode of lithium-ion capacitors (LICs), the as-built LIC achieves high energy density (72.4 Wh kg-1) within the voltage window of 0.01-3.5 V, demonstrating the practical application potential of the Nb12O29-x@C materials.

Battery-Type Lithium-Ion Hybrid Capacitors: Current Status and Future Perspectives

The lithium-ion battery (LIB) has become the most widely used electrochemical energy storage device due to the advantage of high energy density. However, because of the low rate of Faradaic process to transfer lithium ions (Li+), the LIB has the defects of poor power performance and cycle performance, which can be improved by adding capacitor material to the cathode, and the resulting hybrid device is also known as a lithium-ion battery capacitor (LIBC). This review introduces the typical structure and working principle of an LIBC, and it summarizes the recent research developments in advanced LIBCs. An overview of non-lithiated and pre-lithiated anode materials for LIBCs applications is given, and the commonly used pre-lithiation methods for the anodes of LIBCs are present. Capacitor materials added to the cathodes, and suitable separator materials of LIBCs are also reviewed. In addition, the polarization phenomenon, pulsed performance and safety issues of LIBCs and electrode engineering for improving electrochemical performance are systematically analyzed. Finally, the future research and development direction of advanced LIBCs is prospected through the discussion of the existing problems of an LIBC in which the battery material in the composite cathode is LiNixCoyMn1−x−yO2 (NCM).

Highly defective N-doped carbon/reduced graphene oxide composite cathode material with rapid electrons/ions dual transport channels for high energy density lithium-ion capacitor

The energy density of present Li-ion capacitors (LICs) is severely limited by the carbon-based cathode with supercapacitor properties. Herein, to address the low specific capacitance of the cathode, we prepared a structurally stable carbon composite consisting of polypyrrole-derived highly defective carbon nanotubes and highly conductive reduced graphene oxide (rGO) nanosheets, using a facile one-step hydrothermal self-assembly method. The highly defective structures serve as effective electrochemically active sites to enhance ion adsorption for high-performance capacitance characteristics. Meanwhile, the interconnected porous three-dimensional network structures constructed by one-dimensional carbon nanotubes and two-dimensional rGO nanosheets act as rapid electrons/ions dual transport channels, which synergistically promotes fast energy storage/release with abundant defect structures in the material. The carbon composite with optimized structure exhibits significantly improved specific capacitance of 160.6 F g−1 at 0.3 A g−1 and 91.0 F g−1 at a high current density of 60 A g−1 as a cathode material in half-cells pairing with lithium metal. Furthermore, the carbon composite was employed as a cathode paired with a carbon-coated FeOx (FeOx@N-3DG) anode for LIC applications, which demonstrates a superior energy density of 129.1 Wh kg−1 at a power density of 1.7 kW kg−1 and still maintains an outstanding energy density of 32.9 Wh kg−1 at an extremely high power density of 43.9 kW kg−1. The findings of this work provide an effective and rational strategy for designing high energy density LICs cathode materials.

Explosion Strategy Engineering Oxygen-Functionalized Groups and Enlarged Interlayer Spacing of the Carbon Anode for Enhanced Lithium Storage

Amorphous carbon monoliths with tunable microstructures are candidate anodes for future lithium-based energy storage. Enhancing lithium storage capability and solid-state diffusion kinetics are the precondition for practical applications. Transforming intrinsic oxygen-rich defects into active sites and engineering enlarged interlayer spacing are of great importance. Herein, a novel explosion strategy is designed based on oxalate pyrolysis producing CO and CO2 to successfully prepare lignin-derived carbon monolith (LSCM) with active carbonyl (C═O) groups and enlarged interlayer spacing. Explosion promotes the demethylation of methoxyl groups and cleavage of carboxyl groups to form C═O groups. CO2 etches carbon atoms in a short time to improve the heteroatom level, expanding the interlayer spacing. ZnC2O4 is decomposed at 400 °C, simultaneously producing CO and CO2, which constructs less C═O groups and large interlayer spacing. MgC2O4 is decomposed at 450 and 480 °C, staged-weakly producing CO and CO2, which constructs more C═O groups and larger interlayer spacing. CaC2O4 is decomposed at 480 and 700 °C, staged-uniformly producing CO and CO2, which constructs abundant C═O groups and largest interlayer spacing. The LSCM prepared by staged-uniform explosion exhibits high lithium storage capacity, superior rate capability, and cycling performance. The assembled lithium ion capacitor device achieves excellent energy/power densities of 78 Wh kg-1/100 W kg-1 and superior durability (capacitance retention of 8 4.6% after 20,000 cycles). This work gives a novel insight to engineer advanced oxygen-functionalized carbons for enhanced lithium storage.

Dual-functionally modified N/S doped hierarchical porous carbon and glycerol-engineered polyacrylonitrile carbon nanofibers combine for high-performance lithium-ion capacitors

Designing cathode and anode materials that can accommodate capacity and rate performance is a significant challenge in developing lithium-ion capacitors (LICs). Herein, we synthesize a unique N/S dual-doped hierarchical porous carbon (NSC) under the effect of pore distribution modification and heteroatom doping. The nanosheet shape and pore distribution of NSC are highly adjustable, while it demonstrates a reversible capacity that is tens of times more than that of unaltered pristine active carbon. Meanwhile, the prepared glycerol-engineered polyacrylonitrile nanofiber (GPN) form a fast conducting network in the presence of glycerol and carbon nanotubes (CNTs) and exhibit a 300% higher capacity compared to pure polyacrylonitrile nanofibers at 5 A g−1. On this premise, the constructed highly stable LIC (NSC//GPNx@CNTs) can achieve an energy density of 131.48 Wh kg−1 and have an excellent capacity retention rate (93.5%) over 10,000 cycles at a high current density (5 A g−1). This work may lead to new avenues for the preparation of heteroatom-doped porous carbon and redefine the electrode matching of highly stable LICs.

Excellent Metal Phosphide Electrode for Potassium Ion Hybrid Capacitors: The Case of Carbon Nanotube-Wrapped AgP2

Potassium-ion hybrid capacitors (PIHCs) have received extensive attention due to combining the advantages of high energy density of batteries and high power density of capacitors and are economically advantageous alternatives to lithium-ion hybrid capacitors. Metal phosphides are potential anode materials for K+-storage with high theoretical capacity, relatively low working potential, thermal stability, and metal characteristics. Nevertheless, high-performance metal phosphide materials for PIHC applications have proven to be challenging due in part to the dissatisfied electronic conductivity, irreversible deterioration of the structure, and high electron transfer resistance. In this work, we synthesize carbon nanotube (CNT)-wrapped AgP2 via a wet-ball milling (WBM) approach to prepare the electrode slurry. Simultaneously with electrode cycling, the in situ formed Ag nanocrystals increased the electrical conductivity and formed Ag-P composites that easily adsorbed more K+, the framework of CNTs effectively reduced the capacity fading caused by material refinement, and a large surface area is provided to facilitate electrolyte penetration. Owing to these advantageous merits of AgP2/CNT electrodes, the assembled PIHC exhibits a high energy/power density of 37.3 Wh kg–1/12207.3 W kg–1, respectively, and remarkable cycling life over 2000 cycles. These promising results reveal that the design interfacial engineering of the CNT-wrapped AgP2 scaffold provides a clue to propel the development of metal phosphide-based hybrid capacitors.