Microzone-explosion synthesis of porous carbon electrodes for advanced aqueous solid-state supercapacitors with a high-voltage gel electrolyte

A new microzone-combustion synthesis is proposed for preparing S, N-doped hierarchically porous carbons(CAC-CN) with a novel mixed microstructure of sp~2 short-range order area and sp~3 defective area,achieving a coexistence of high conductivity and high capacitance as well as good access for electrolyte.By engineering ‘‘water in salts" into a polymer matrix, a high-voltage(2.5 V) aqueous gel electrolyte(HGWIS) is prepared and used to construct an aqueous solid-state SCs by in situ polymerization between the electrodes. The good match of CAC-CN electrode and HG-WIS electrolyte endows the assembled devices with superior high energy density and excellent capacitance retention, also a good temperature robustness, as well a high flexibility in 0-180° bending cycles. This study indicates that the collaborative design strategy of electrode materials and electrolyte would be great potential in exploring advanced aqueous solid-state SCs.

Amorphous Se species anchored into enclosed carbon skeleton bridged by chemical bonding toward advanced K-Se batteries

Potassium-selenium(K-Se)batteries have attracted significant attention as one of the most promising alternatives of lithium-ion storage systems owing to high energy density and low cost.In the design of Se-based cathode materials,however,the low utilization rate of active Se and the rapid dissolution of polyselenides seriously weaken the capacity and cycle stability.Therefore,how to make full use of Se species without loss during the charge and discharge process is the key to design high-performance Se-based cathode.In this paper,a 3 D"water cube"-like Se/C hybrid(denoted as Se-O-PCS)is constructed with the assistance of Na_(2)CO_(3) templates.Thanks to the abundant carbonate groups(CO_(3)^(2-))originated from the Na_(2)CO_(3) templates,the molten Se species are firmly anchored into the pore of carbon skeleton by strong C-O-Se bonding.Thus,this unique Se-O-PCS model not only improves the utilization of active Se species,but also can reduce the contact with the electrolyte to inhibit the shuttle effect of polyselenides.Moreover,flexible carbon skeleton gives Se-O-PCS hybrid a good electrical conductivity and excellent structural robustness.Consequently,the resultant Se-O-PCS hybrid is endowed with an obviously enhanced K-ions storage property.

Realizing the Long Lifespan of Molybdenum Trioxide in Aqueous Aluminum Ion Batteries Through Potential Regulation

MoO_(3) is one of the most promising anode materials for aqueous aluminum batteries due to its high theoretical capacity and suitable aluminum insertion/de-insertion potential.However,the inferior cycling stability limits its further application,and the failure mechanism is still unclear.In this article,we provide a straightforward potential regulation technique to manage phase evolution during the charge/discharge process,which ultimately results in a markedly enhanced MoO_(3) electrode cycling stability.The failure mechanism study reveals that the excessive oxidation of the electrode during charge/discharge generates the H_(0.34)MoO_(3) phase,which has high solubility and is the primary cause of MoO_(3) deactivation.Although the dissolved Mo species will be deposited onto the electrode sheet again,the deposition is not electrochemically active and cannot contribute to the capacitance.Controlling the cutoff potential prevented the production of H_(0.34)MoO_(3),resulting in excellent cycling performance(80.1% capacity retention after 4000 cycles).The as-assembled α-MoO_(3)//MnO_(2) full battery exhibits high discharge plateaus(1.4 and 0.9 V),large specific capacity(200 mAhg^(-1) at 2 Ag^(-1)),and ultra-high coulombic efficiency(99%).The research presented here may contribute to the development of highly stable electrode materials for aqueous batteries.

Construction of Frame-Structured Flexible MXene Film Electrode to Achieve High Areal Capacitance Micro-Supercapacitor

Two-dimensional MXene-based film materials as flexible electrodes have been widely studied in wearable microsupercapacitors(MSCs).However,the existence of strong van derWaals interactions leads to serious self-stacking ofMXene layers,resulting in poor ionic dynamics and loss of active sites,which causes MXene film electrodes to exhibit low capacitance and poor rate performance in practical studies.To solve this,a frame-structured hybrid film(labeled as CN-MX hybrid film)is constructed by introducing intercalating agents(nanometer g-C_(3)N_(4))into MXene layers.In this unique hybrid film,the g-C_(3)N_(4)nanoparticles rationally occupy the interspace between MXene layers so as to alleviate layer stacking,thus effectively expanding the electrochemically active surface and promoting proton transfer.Synergistic pseudocapacitance inducted by g-C_(3)N_(4)surface groups,consequently,the CN-MX hybrid film electrode achieves an enhanced capacitive capability.In the three-electrode system,this frame-structured film electrode exhibits an ultra-high areal capacitance of 1932.8 mF cm^(−2).The assembled symmetry flexible MSC device based on CN-MX hybrid film can achieve an energy density of 2.28μWh cm^(−2)at 0.075 mW cm^(−2),as well as a superior cyclic stability with 90.4%retention after 700 cycles in alternating 90o bending and releasing states,revealing its potential in practical applications.

Extremely high-rate aqueous supercapacitor fabricated using doped carbon nanoflakes with large surface area and mesopores at near-commercial mass loading

Achieving a satisfactory energy-power combination in a supercapacitor that is based on all-carbon electrodes and operates in benign aqueous media instead of conventional organic electrolytes is a major challenge. For this purpose, we fabricated carbon nanoflakes （20-100 nm in thickness, 5-μm in width） containing an unparalleled combination of a large surface area （3,000 m2-g-1 range） and mesoporosity （up to 72%）. These huge-surface area functionalized carbons （HSAFCs） also had a substantial oxygen and nitrogen content （N10 wt.% combined）, with a significant fraction of redox-active carboxyl/phenol groups in an optimized specimen. Their unique structure and chemistry resulted from a tailored single-step carbonization-activation approach employing （2-benzimidazolyl） acetonitrile combined with potassium hydroxide （KOH）. The HSAFCs exhibited specific capacitances of 474 F-g-1 at 0.5 A.g-1 and 285 F-g-1 at 100 A.g-1 （charging time 〈 3 s） in an aqueous 2 M KOH solution. These values are among the highest reported, especially at high currents. When tested with a stable 1.8-V window in a 1 M Na2SO4 electrolyte, a symmetric supercapacitor device using the fabricated nanoflakes as electrodes yielded a normalized active mass of 24.4 Wh-kg-1 at 223 W·kg-1 and 7.3 Wh·kg-1 at 9,360 W·kg-1. The latter value corresponds to a charge time of 〈3 s. The cyclability of the devices was excellent, with 93% capacitance retention after 10,000 cycles. All the electrochemical results were achieved by employing electrodes with near-commercial mass loadings of 8 mg-cm-2.

Dual carbon Li-ion capacitor with high energy density and ultralong cycling life at a wide voltage window

Using the same materials for the cathode and anode in energy storage devices could greatly simplify the technological process and reduce the device cost significantly.In this paper,we assemble a dual carbon-based Li-ion capacitor with the active materials derived entirely from a single precursor,petroleum coke.For the anode,petroleum cokederived carbon(PCC)is prepared by simple ball milling and carbonization,having a massive tap density(1.80 g cm^(-3))and high electrical conductivity(11.5 S cm^(-1)).For the cathode,the raw petroleum coke is activated by KOH(petroleum cokeactivated carbon(PC-AC)sample)to achieve a well-developed pore structure to meet a rapid capacitive behavior.As a result,in addition to the robust structural stability of both the anode and cathode,the assembled dual carbon Li-ion capacitor shows a high energy density(231 W h kg^(-1)/206 W h L^(-1))and ultralong cycling life(up to 3000/10,000 cycles)at a wide voltage window.The excellent electrochemical response and simple production process make the PCC materials have great potential for practical application.