Potassium-ion Capacitors Research Articles

Fast potassium migration in mesoporous carbon with ultrathin framework boosting superior rate performance for high-power potassium storage

Potassium-ion based electrochemical energy storage devices are an emerging technology for large-scale energy storage owing to the abundance of low-cost potassium resources. Nevertheless, the sluggish kinetics and substantial volume variations of anode materials lead to poor rate capability and insufficient cyclability. Herein, a mesoporous carbon with an ultrathin framework (MCUF) was designed as an anode material to achieve stable and high-power potassium storage performance. The ultrathin framework as well as its mesoporous structure synergistically realize excellent potassium storage cyclability and high-rate performance by accommodating substantial volume variations and promoting fast potassium diffusion. The potassium storage characteristics of the MCUF were revealed using electrochemical analyses, in situ XRD characterizations, and DFT calculations, identifying a surface-dominated potassium storage behavior with excellent electrochemical kinetics, high-power capability, and reversibility. Furthermore, the MCUF was used as an anode to assemble novel non-flammable potassium-ion capacitors that exhibited excellent cyclability (with a capacity retention of 89.2% after 6000 cycles), outstanding rate performance, and high energy/power densities (120.2 Wh kg−1 and 16.7 kW kg−1, respectively). Accordingly, our work affords new insights into understanding the potassium storage mechanism in carbon materials and constructing non-flammable high-safety and high-performance potassium-ion capacitors.

Fast potassium storage in porous CoV2O6 nanosphere@graphene oxide towards high-performance potassium-ion capacitors

The increasing demand to develop sustainable energy storage equipment has aroused interest for potassium-ion capacitors (PICs), owing to their high abundance and low cost of potassium sources. Nevertheless, the practical application of PICs is impeded by the lack of suitable anode materials with high performance. Here we demonstrate a solvothermal-assisted synthesis of porous CoV2O6 nanosphere@graphene oxide (GO) composites as the anode material of PICs for the first time. Benefiting from the well-designed porous nanostructure and high-conductivity carbon incorporation, the hybrid composite delivers an initial high discharge capacity (264 mAh g−1, 1 A g−1) and superior rate capability (97 mAh g−1, 10 A g−1). Moreover, the electrochemical reaction mechanism of CoV2O6 involving an intercalation followed by conversion reaction is comprehensively revealed by first-principles calculations (DFT), ex-situ X-ray photoelectron spectroscopy as well as ex-situ high-resolution transmission electron microscopy. Meanwhile, the DFT also indicates that CoV2O6 possesses high electron/K-ion conductivity and low diffusion barriers for K+ intercalation. Consequently, PICs coupling the CoV2O6@GO anode and activated carbon cathode display a high energy/power density (78.2 Wh kg−1 and 22,500 W kg−1) as well as an ultralong lifespan over 3000 cycles. The work delves metal vanadate as high-performance anode for PICs and may provide innovative insight into electrode structure building in rechargeable metal-ions chemistry.

Nitrogen/oxygen dual-doped hierarchically porous carbon/graphene composite as high-performance anode for potassium storage

Although potassium-ion batteries (PIBs) are considered as promising candidate to lithum-ion batteries (LIBs) in the area where energy density is no longer the top priority, developing suitable anodes for PIBs is still a big challenge because of the large radius of potassium-ion, which limits the rate performace and cyclic stability. Herein, nitrogen/oxygen dual-doped hierarchically porous carbon/graphene composite (NOPC@G) has been prepared for potassium-ion storage. Thanks to the heteroatom-rich porous structure and conductive network induced by graphene, the ion diffusion and electronic transmission are enhanced, which make NOPC@G exhibit outstanding potassium storage performance in terms of high specific capacity (445 mAhg−1), high rate capability (112 mAhg−1 at 40 C) and excellent cyclic stability. Furthermore, when used as anode for potassium-ion capacitors (PICs), NOPC@G also exhibits an impressive electrochemical performance with a maximum energy density of 153 Wh kg−1 (with a power density of 120 W kg−1) and a maximum power density of 22.98 kW kg−1 (with an energy density of 57 Wh kg−1). The simple synthesis route combined with the desirable electrochemical performance makes NOPC@G a promising anode for potassium storage.

Microwave-assisted synthesis of carbon dots modified graphene for full carbon-based potassium ion capacitors

Potassium ion batteries or capacitors are a promising technology for large-scale energy storage due to the abundant resource and low cost of potassium. However, the development of stable electrode materials with high capacity, capable rate ability, and excellent cycling stability remains a challenge. Herein, carbon dots modified reduced graphene oxides (LAP-rGO-CDs) are designed and synthesized via a rapid and green microwave-assisted method with l-Ascorbic acid 6-palmitate (LAP) as the reducing agent. LAP-rGO-CDs present enlarged interlayer spacing and faster ion transfer rate owing to the introducing of carbon dots. Serving as a potassium ion battery electrode, LAP-rGO-CDs showed a high specific capacity of 299 mAh g−1 at 1 A g−1 and excellent cycling stability. Moreover, a LAP-rGO-CDs//AC full carbon-based potassium ion capacitor is assembled and displays a maximum energy density of 119 Wh kg−1 and a power density of 5352 W kg−1. This work demonstrates the potential application of LAP-rGO-CDs for high-performance potassium ion storage.

Status of rechargeable potassium batteries

Future renewable energy integrated grid systems require rechargeable batteries with low cost, high safety, and long cycle life. The much higher abundance of sodium and potassium compared to lithium in earth crust indicates that rechargeable sodium and potassium batteries are attractive replacements for lithium-ion batteries. Rechargeable potassium batteries have gained tremendous attention during the past decade. However, the development of rechargeable potassium batteries is still in its infancy. This review summarizes the recent technological developments in rechargeable potassium batteries. First, we summarize the latest achievements of active materials design, mechanistic understanding, and exploration of new active materials. We propose new directions in tuning the architecture and enhancing the electrochemical performances of high-performance anodes and cathodes. Second, we also summarize the advances that have been achieved in the new configurations of rechargeable potassium battery systems (potassium-ion capacitors, potassium dual ion batteries, potassium-sulfur batteries, and potassium-oxygen batteries). Finally, we propose future directions and design strategies that could be employed to advance rechargeable potassium batteries toward commercial applications. In this review, a large family of rechargeable batteries based on potassium as charge carrier are summarized. Rechargeable potassium ion batteries include potassium-ion batteries, potassium-ion capacitors, potassium-ion-based dual ion batteries, potassium-sulfur batteries, and potassium-oxygen batteries. Future directions and design strategies that could be employed to advance rechargeable potassium batteries toward commercial applications are proposed. • Rechargeable potassium ion battery as a promising rechargeable battery system. • Current status and future research trends of rechargeable potassium batteries. • Strategies for developing practical anodes and cathodes for potassium batteries. • Recent advances of different configurations of rechargeable potassium batteries.

Armoring Black Phosphorus Anode with Stable Metal–Organic-Framework Layer for Hybrid K-Ion Capacitors

HighlightsThe ultrathin metal–organic-framework (MOF) interphase layer with high mechanical/chemical stability was in situ grown on black phosphorus nanosheets (BPNSs).MOF interphase layers as an ordered porous and robust protective layer can facilitate K ion diffusion and accommodate the volume change of the electrode.Benefiting from the improved reaction kinetics and enhanced electrode stability, the BPNS@MOF anode for potassium-ion capacitors exhibits outstanding cycle performance.

Carbon-coated WS2 nanosheets supported on carbon nanofibers for high-rate potassium-ion capacitors

A freestanding anode of carbon-coated WS2 nanosheets supported on carbon nanofibers (C-WS2@CNFs) is designed for fabricating high-rate potassium-ion capacitors.

Sulfur-Rich Graphene Nanoboxes with Ultra-High Potassiation Capacity at Fast Charge: Storage Mechanisms and Device Performance.

It is a major challenge to achieve fast charging and high reversible capacity in potassium ion storing carbons. Here, we synthesized sulfur-rich graphene nanoboxes (SGNs) by one-step chemical vapor deposition to deliver exceptional rate and cyclability performance as potassium ion battery and potassium ion capacitor (PIC) anodes. The SGN electrode exhibits a record reversible capacity of 516 mAh g-1 at 0.05 A g-1, record fast charge capacity of 223 mA h g-1 at 1 A g-1, and exceptional stability with 89% capacity retention after 1000 cycles. Additionally, the SGN-based PIC displays highly favorable Ragone chart characteristics: 112 Wh kg-1at 505 W kg-1 and 28 Wh kg-1 at 14618 W kg-1 with 92% capacity retention after 6000 cycles. X-ray photoelectron spectroscopy analysis illustrates a charge storage sequence based primarily on reversible ion binding at the structural-chemical defects in the carbon and the reversible formation of K-S-C and K2S compounds. Transmission electron microscopy analysis demonstrates reversible dilation of graphene due to ion intercalation, which is a secondary source of capacity at low voltage. This intercalation mechanism is shown to be stable even at cycle 1000. Galvanostatic intermittent titration technique analysis yields diffusion coefficients from 10-10 to 10-12 cm2 s-1, an order of magnitude higher than S-free carbons. The direct electroanalytic/analytic comparison indicates that chemically bound sulfur increases the number of reversible ion bonding sites, promotes reaction-controlled over diffusion-controlled kinetics, and stabilizes the solid electrolyte interphase. It is also demonstrated that the initial Coulombic efficiency can be significantly improved by switching from a standard carbonate-based electrolyte to an ether-based one.

Atomic layer deposition regulating hydrated K2Ti6O13 nanobelts on graphene platform with accelerated solid solution potassiation for potassium ion capacitors

• K 2 Ti 6 O 13 (KTO) nanobelts are regulated on graphene by ALD pre-anchoring method. • The electrochemical performances surpass other KTO anodes for potassium ion storage. • Hydrated KTO endow itself with an accelerated solid solution potassiation mechanism. • PICs deliver high energy/power densities and a long cycle life. Potassium ion capacitors (PICs) represent a promising energy storage device with high energy and power densities for long stretches beyond the lithium and sodium storage chemistry of nowadays. As an analogous anode like lithium titanates, potassium titanates (KTO) are expected to be applied to PICs. Herein, hydrated KTO (K 2 Ti 6 O 13 ) nanobelts were regulated on graphene nanosheets by a method of atomic layer deposition (ALD) coupled with hydrothermal potassiation. The close correlation of KTO to the underneath graphene nanosheets favors the electron transport, the interweaved structure facilitates the permeation of electrolyte ions, and the chemically (interlayer) adsorbed water endows KTO with larger interlayer spacing, synergistically giving rise to an accelerated solid solution potassiation mechanism. Based upon this, superior specific capacity and rate capability (87 mAh g −1 @1 A g −1 ), as well as stability of the ALD KTO can be delivered, outperforming many performances of reported KTO anodes. The PICs exhibit simultaneously high energy/power densities (Max. 119.3 Wh kg −1 @117.5 W kg −1 , 4.7 kW kg −1 @35.3 Wh kg −1 ) as well as good capacity retention after 4,000 cycles. Our work demonstrates the great performance of ALD KTO anode and the promising application of PICs, which propose a delicate methodology of high performance K + storage anode materials.

Pseudocapacitive Crystalline MnCo2O4.5 and Amorphous MnCo2S4 Core/Shell Heterostructure with Graphene for High-Performance K-Ion Hybrid Capacitors.

Potassium-ion capacitors (KICs) have received a surge of interest because of their higher reserves and lower costs of potassium than lithium. However, the cycle performance and capacity of potassium devices have been reported to be unsatisfactory. Herein, a unique crystalline MnCo2O4.5 and amorphous MnCo2S4 core/shell nanoscale flower structure grown on graphene (MCO@MCS@rGO) was synthesized by a two-step hydrothermal process and demonstrated in KICs. The MCO@MCS@rGO exhibits improved electrical conductivity and excellent structural integrity during the charging and discharging process. The reasons could be attributed to the cavity structure of MCO, the mechanical buffer and high electrolyte diffusion rate of MCS, and the auxiliary effect of graphene. The electrical conductivity of MCO@MCS shows a specific capacity of 272.3 mA h g-1 after 400 cycles at 1 A g-1 and a capacity of 125.6 mA h g-1 at 2 A g-1. Besides, the MCO@MCS@rGO and high-surface-area activated carbon in KICs exhibit a relative energy density of 85.3 W h kg-1 and a power density of 9000 W kg-1 and outstanding cycling stability with a capacity retention of 76.6% after 5000 cycles. Moreover, the reaction mechanism of MCO@MCS@rGO in the K-ion cell was investigated systematically using X-ray diffraction and transmission electron microscopy, providing guidance on the further development of pseudocapacitive materials.

Dual Carbon Potassium-Ion Capacitors: Biomass-Derived Graphene-like Carbon Nanosheet Cathodes.

Potassium-ion storage devices are attracting tremendous attention for wide-ranging applications on account of their low cost, fast charge transport in electrolytes, and large working voltage. However, developing cost-effective, high-energy electrodes with excellent structural stability to ensure long-term cycling performance is a major challenge. In this contribution, we have derived two different forms of carbon materials from almond shells using different chemical treatments. For instance, hard carbon (HC) and graphene-like activated carbon (AC) nanosheets are developed by employing simple carbonization and chemical activation routes, respectively. The resultant hard carbon (AS-HC) and activated carbon (AS-AC) exhibit outstanding electrochemical performance as negative and positive electrodes in a potassium-ion battery (KIB), respectively, through their tailor-made surface properties. These promising benefits pave a way to construct a biomass-derived carbon potassium-ion capacitor (KIC) by employing AS-HC as the negative electrode and AS-AC as the positive electrode in a K-based electrolyte. The as-fabricated KIC delivers a reasonable specific energy of 105 Wh/kg and excellent cycling life with negligible capacitance fading over 10 000 cycles. This "waste-to-wealth" approach can promote the development of sustainable KICs at low cost and inspire their use for fast-rate K-based energy storage applications.

Large interspaced layered potassium niobate nanosheet arrays as an ultrastable anode for potassium ion capacitor

Potassium-ion battery (KIB) is a promising technology for large-scale energy storage applications due to their low cost, theoretically high energy density and abundant resources. However, the development of KIBs is hindered by the sluggish K+ transport kinetics and the structural instability of the electrode materials during K+ intercalation/de-intercalation. In the present investigation, we have designed a potassium-ion capacitor (KIC) using layered potassium niobate (K4Nb6O17, KNO) nanosheet arrays as anode and orange-peel derived activated carbons (OPAC) as fast capacitive cathode materials. The systematic electrochemical analysis with the ex-situ characterizations demonstrates that KNO-anode exhibits highly stable layered structure with excellent reversibility during K+ insertion/de-insertion. After optimization, the fabricated KNO//OPAC delivers both a high energy density of 116 Wh/kg and high power density of 10,808 W/kg, which is significantly higher than other similar hybrid devices. The cell also displays long term cycling stability over 5000 cycles, with 87 % of capacity retention. This study highlights the utilization of layered nanosheet arrays of niobates to achieve superior K‐storage for KICs, paving the way towards the development of high‐performance anodes for post lithium‐ion batteries.

Nano-phosphorus supported on biomass carbon by gas deposition as negative electrode material for potassium ion batteries

This work presents a novel method for loading phosphorus nanoparticles by gas deposition. A large amount of nano phosphorus is loaded on the carbon matrix by the reaction of phosphine gas heating. The carbon is obtained by carbonization of hemp and has a natural porous structure. The combination of phosphorus and carbon in the form of C–O–P has better stability. The product obtained a stable capacity of 463 mAh/g at 0.04 A/g. There was still a reversible capacity of 270 mAh/g after continuous operation for 6 months at a high current density of 1 A/g, and the capacity retention rate was 96.7%. The excellent cyclic stability is due to new methods of phosphorus deposition. It can reach 10 times the running time of the same type of battery, which provides a new idea for preparing phosphor-doped electrode materials. Assembled into a potassium ion capacitor, an energy density of 294.2 Wh/kg can be obtained.

Emerging Potassium-ion Hybrid Capacitors.

As a new type of capacitor-battery hybrid energy storage device, metal-ion capacitors have attracted widespread attention because of their high-power density while ensuring energy density and long lifespan. Potassium-ion capacitors (KICs) featuring the merits of abundant potassium resources, lower standard electrode potential, and low cost have been considered as potential alternatives to lithium-/sodium-ion capacitors. However, KICs still face issues including unsatisfactory reaction kinetics, low energy density, and poor lifetime owing to the large radius of the potassium ion. In this Review, the importance of emerging potassium-ion capacitor is addressed. The Review offers a brief discussion of the fundamental working principle of KICs, along with an overview of recent advances and achievements of a variety of electrode materials for dual carbon and non-dual carbon KICs. Furthermore, electrolyte chemistry, binders as well as electrode/electrolyte interface, are summarized. Finally, existing challenges and perspectives on further development of KICs are also presented.

Hierarchically Engineered Nanocarbon Florets as Bifunctional Electrode Materials for Adsorptive and Intercalative Energy Storage.

Three-dimensional dendritic nanostructured carbon florets (NCFs) with tailored porosity are demonstrated as electrochemically versatile electrodes for both adsorptive and intercalative energy storage pathways. Achieved through a single-step template-driven approach, the NCFs exhibit turbostratic graphitic lamellae in a floral assembly leading to high specific surface area and multi-modal pore distribution (920 m2/g). The synergism in structural and chemical frameworks, along with open-ended morphology, enables bifunctionality of hard carbon NCFs as symmetric adsorptive electrodes for supercapacitors (SCs) and intercalation anodes for hybrid potassium-ion capacitors (KICs). Flexible, all-solid-state SCs through facile integration of NCF with the ionic-liquid-imbibed porous polymeric matrix achieve high-energy density (20 W h/kg) and power density (32.7 kW/kg) without compromising on mechanical flexibility and cyclability (94% after 20k cycles). Furthermore, NCF as an anode in a full-cell hybrid KIC (activated carbon as cathode) delivers excellent electrochemical performance with maximum energy and power densities of 57 W h/kg and 12.5 kW/kg, respectively, when cycled in a potential window of 1.0-4.0 V. The exceptional bifunctional performance of NCF highlights the possibility of utilizing such engineered nanocarbons for high-performance energy storage devices.

Hierarchical N-doped carbon nanosheets submicrospheres enable superior electrochemical properties for potassium ion capacitors

Hybrid ion capacitors show promise to bridge the gap between rechargeable batteries with high energy density and supercapacitors of high power. However, research efforts primarily focus on lithium-ion and/or sodium-ion based capacitors, potassium ion capacitor (KIC) is theoretically more sustainable and promising owing to the high abundance, low standard redox potential and low cost of the K sources. Herein, nitrogen-doped porous carbon submicrospheres derived from hierarchical micro-flowerlike polyimide superstructure are fabricated and investigated as novel anodes for excellent K ion storage. The effect of different electrolytes on potassium storage properties and the reaction kinetics are successfully revealed. A low cost nonaqueous KIC is assembled with commercial activated carbon as cathode and the polyimide derived carbon as anode. Benefiting from the unique structure characteristics of enriched active sites, high electronic conductivity, and the conspicuous pseudocapacitive effect of polyimide carbon, the as-fabricated device manifests the maximum energy density and power density of 90.1 Wh kg−1 and 3000 W kg−1, respectively. Even at 1540 W kg−1, the energy density still remains at 43.5 Wh kg−1. Moreover, the device achieves a near 100% Coulombic efficiency and favorable cycling stability over 5000 cycles at a current density 500 mA g−1.

Ionic Liquid Electrolytes Enabling the Development of Highly Efficient High-Voltage Potassium-Ion Full Cells with a Potassium Manganese Hexacyanoferrate Cathode

Potassium-ion (K-ion) batteries are a promising complementary technology to lithium-ion in which less scarce and less expensive elements can be used; potassium instead of lithium, aluminum instead of copper, and cobalt-free cathodes. They have the advantage over sodium-ion batteries in that graphite, the standard commercial anode for lithium-ion, can be used[1] and potassium has a lower reduction potential (K+/K) than that of sodium and even lithium. Currently, the research focus is on developing energy-dense, high-voltage cathode materials. Prussian blue analogues, with their open-framework structure, are well-suited to reversibly insert the relatively large potassium ion.[2] Potassium manganese hexacyanoferrate (KMF) is of particular interest due to its high theoretical capacity (155 mAh g-1) and high voltage (around 4 V vs. K+/K) making it one of the most promising K-ion candidate cathode materials.[3] However, significant challenges remain before KMF K-ion batteries are suitable for commercialization. Current collector corrosion at high voltages and material instability lead to low coulombic efficiency on cycling and severe capacity fade.[4]In this work we report a significant improvement in KMF electrode performance by utilizing a highly stable ionic liquid electrolyte. This electrolyte suppresses corrosion of the current collector and deleterious reactions on the cathode. Performance of the KMF material is significantly controlled by its composition and particle size, which can be controlled during synthesis. We employ high-throughput techniques to systematically study a wide synthesis parameter space in order to minimize hexacyanoferrate vacancy and water content whilst controlling for particle size. We found that changing particle size considerably impacted specific capacity and cyclability, and a compromise must be made. Our optimized KMF material had a specific capacity of 119 mA h g-1, a coulombic efficiency of 99.3%, and relatively good cyclability. Crucially, graphite also displayed excellent electrochemical performance in the same ionic liquid electrolyte (maintaining 99% of initial capacity after 400 cycles and a coulombic efficiency of more than 99.9%) and exhibited a highly reversible electrode reaction studied by in operando XRD. Optimized KMF | ionic liquid electrolyte | graphite full-cell chemistry reported here proves a viable strategy for highly efficient high-voltage potassium-ion batteries.[1] Komaba et al., Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors, Electrochemistry Communications (2015), 60, 172-175[2] Hurlbutt et al., Prussian Blue Analogs as Battery Materials, Joule (2018), 2, 10, 1950-1960[3] Bie et al., A novel K-ion battery: hexacyanoferrate(II)/graphite cell, J. Mater. Chem. A (2017), 5, 9, 4325-4330[4] Hosaka et al. Highly concentrated electrolyte solutions for 4 V class potassium-ion batteries, Chem. Commun. (2018), 54, 8387-8390

High-performance potassium ion capacitors enabled by hierarchical porous, large interlayer spacing, active site rich-nitrogen, and sulfur Co-doped carbon

Potassium ion hybrid capacitors (PIHCs) have drawn considerable attention due to the fact that they can combine the merits of high energy density of potassium ion batteries (KIBs) and high power density of supercapacitors. However, the sluggish kinetics caused by the large radius of K+ largely hinder the practical application of PIHCs. In this work, we report a nitrogen and sulfur co-doped 3D hierarchical porous carbon (N, S-3DHPC-600) as an anode for KIBs, possessing boosted potassium storage performance in terms of high reversible capacity, superior durability and rate capability. This N, S-3DHPC-600 electrode provides a large surface area, highly interconnected micro/mesoporosity, high ratio of pyridinic N/pyrrolic N and enlarged interlayer distance, which could promote the fast intercalation/deintercalation of K+, improve the surface charge capacity and maintain the structural stability of electrode material. As expected, a PIHCs device is constructed by employing this N, S-3DHPC-600 as an anode and AC-800 as a cathode, delivering exceptionally high energy/power densities (130.6 Wh Kg−1/16800W Kg−1), as well as a long cycle life (86.8% capacity retention after 5000cycles).

Sulfur-nitrogen rich carbon as stable high capacity potassium ion battery anode: Performance and storage mechanisms

Combined sulfur and nitrogen (S ​= ​12.9 ​at.%, N ​= ​9.9 ​at.%) rich carbons are synthesized for potassium ion anode applications. The low-surface-area carbons (56 ​m2 ​g−1) have sulfur covalently bonded to the structure, with minimum unbound “free” sulfur. This allows for exceptional rate capability and stability: Capacities of 437, 234 and 72 mAh g−1 are achieved at 0.1, 1 and 10 ​A ​g−1, with 75% retention at 2 ​A ​g−1 after 3000 cycles. These are among the most favorable capacity-cyclability combinations reported in potassium ion battery carbon literature. As a proof of principle, the carbons are incorporated into a potassium ion capacitor with state-of-the-art energy and power (e.g. 110 ​W ​h ​kg−1 at 244 ​W ​kg −1). According to XPS analysis, the reaction of nitrogen with K+ is distinct from that of K+ with sulfur. The N and N–O moieties undergo a series of complex multi-voltage reactions that result in both reversible and irreversible changes to their structure. The K–S reactions involve a combination of reversible adsorption and reversible formation of sulfides, thiosulfate and sulfate. GITT and EIS analysis indicate that incorporation of S into the N-rich carbon increases the K+ solid-state diffusion coefficient by factors ranging from ~3 to 8, depending on the voltage. The diffusivities are asymmetric with charging vs. discharging, signifying distinct reaction pathways. The covalently bound sulfur also has a positive influence on the solid electrolyte interphase (SEI) formation, at early and at prolonged cycling.

Excellent Electrochemical Performance of Potassium Ion Capacitor Achieved by a High Nitrogen Doped Activated Carbon

Supercapacitors, due to their unique high-power characteristics, are bound to occupy a place in the field of energy storage. Carbon-based supercapacitor is one of the most promising in all material systems. In this work, N-doped/graphene composite activated carbon (AC) is prepared through a facile method as electrodes for the comparison between an aqueous system and an organic system. The obtained AC shows high surface areas of 1600 m2 g−1 with a high N content of 11.7 wt% and is simultaneously applied to lithium-ions capacitor (LIC), sodium-ions capacitor (NIC) and potassium ion capacitor (KIC). Electrochemical evaluations indicated that the high N-doped activated carbon-based LIC, NIC and KIC possess different performance and energy storage mechanisms. The KIC exhibits the highest energy density of 50 Wh kg−1 at 0.4 A g−1 and the most stable cycle performance of three capacitors. This work reveals differences among the three types of ion capacitors, providing clues for the development of high power-energy and long life ion supercapacitors. Moreover, KIC has better performance than LIC, and the reserve of K is much higher than Li, which makes KIC a better application prospect.