Effect of N-doping-derived solvent adsorption on electrochemical double layer structure and performance of porous carbon

N-doped porous carbon has been extensively investigated for broad electrochemical applications.The performance is significantly impacted by the electrochemical double layer(EDL),which is material dependent and hard to characterize.Limited understanding of doping-derived EDL structure hinders insight into the structure-performance relations and the rational design of high-performance materials.Thus,we analyzed the mass and chemical composition variation of EDL within electrochemical operation by electrochemical quartz crystal microbalance,in-situ X-ray photoelectron spectroscopy,and time-offlight secondary ion mass spectrometry.We found that N-doping triggers specifically adsorbed propylene carbonate solvent in the inner Helmholtz plane(IHP),which prevents ion rearrangement and enhances the migration of cations.However,this specific adsorption accelerated solvent decomposition,rendering rapid performance degradation in practical devices.This work reveals that the surface chemistry of electrodes can cause specific adsorption of solvents and change the EDL structure,which complements the classical EDL theory and provide guidance for practical applications.

Structure evolution of oxygen removal from porous carbon for optimizing supercapacitor performance

The presence of oxygen functional groups is detrimental to the capacitive performance of porous carbon electrode in organic electrolyte. In this regards, hydrogen thermal reduction has been demonstrated effective approach in removing the unstable surface oxygen while maintaining the high porosity of carbon matrix. However, the exact evolution mechanism of various oxygen species during this process, as well as the correlation with electrochemical properties, is still under development. Herein, biomass-based porous carbon is adopted as the model material to trace its structure evolution of oxygen removal under hydrogen thermal reduction process with the temperature range of 400–800 °C. The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700°C. XPS, TPRMS and Boehm titration results indicate that the oxygen elimination undergoes three distinctive stages(intermolecular dehydration, hydrogenation and decomposition reactions). The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700 °C. Benefiting from the stable electrochemical interface and the optimized porous structure, the as-obtained HAC-700 exhibit significantly suppressed self-discharge and leak current, with improved cycling stability, which is attributable to the stabilization of electrochemical interface between carbon surface and electrolyte. The result provides insights for rational design of surface chemistry for high-performance carbon electrode towards advanced energy storage.

Recent advances in carbon nanostructures prepared from carbon dioxide for high-performance supercapacitors

The burgeoning global economy during the past decades gives rise to the continuous increase in fossil fuels consumption and rapid growth of CO_(2) emission,which demands an urgent exploration into green and sustainable devices for energy storage and power management.Supercapacitors based on activated carbon electrodes are promising systems for highly efficient energy harvesting and power supply,but their promotion is hindered by the moderate energy density compared with batteries.Therefore,scalable conversion of CO_(2) into novel carbon nanostructures offers a powerful alternative to tackle both issues:mitigating the greenhouse effect caused by redundant atmospheric CO_(2) and providing carbon materials with enhanced electrochemical performances.In this tutorial review,the techniques,opportunities and barriers in the design and fabrication of advanced carbon materials using CO_(2) as feedstock as well as their impact on the energy-storage performances of supercapacitors are critically examined.In particular,the chemical aspects of various Cv2 conversion reactions are highlighted to establish a detailed understanding for the science and technology involved in the microstructural evolution,surface engineering and porosity control of CO_(2)-converted carbon nanostructures.Finally,the prospects and challenges associated with the industrialization of CO_(2) conversion and their practical application in supercapacitors are also discussed.

Insights into the thermochemical evolution of maleic anhydride-initiated esterified starch to construct hard carbon microspheres for lithium-ion batteries

Starch,as a typical polysaccharide with natural spherical morphology,is not only a preferred precursor for preparing carbon materials but also a model polymer for investigating thermochemical evolution mechanisms.However,starch usually suffers from severe foaming and low carbon yield during direct pyrolysis.Herein,we report a simple and eco-friendly dry strategy,by maleic anhydride initiating the esterification of starch,to design carbon microspheres against the starch foaming.Moreover,the infuence of ester grafting on the pyrolytic behavior of starch is also focused.The formation of ester groups in precursor guarantees the structural stability of starch-based intermediate because it can promote the accumulation of unsaturated species and accelerate the water elimination during pyrolysis.Meanwhile,the esterification and dehydration reactions greatly deplete the primary hydroxyl groups in the starch molecules and thus the rapid levoglucosan release is inhibited,which well keeps the spherical morphology of starch and ensures the high carbon yield.In further exploration as anode materials for Lithium-ion batteries,the obtained carbon microspheres exhibit good cyclability and rate performance with a reversible capacity of 444 m Ah g^(-1)at 50 m A g^(-1).This work provides theoretical fundamentals for the controllable thermal transformation of biomass towards wide applications.

Combined DFT and experiment:Stabilizing the electrochemical interfaces via boron Lewis acids

The incorporation of boron into carbon material can significantly enhance its capacity performances.However,the origin of the promotion effect of boron doping on electrochemical performances is still unclear,in part due to the inadequate exposure of boron configurations resulting from the complexity of traditional carbon materials.To overcome this issue,herein,a series of boron-doped graphene with highly-exposed boron configurations are prepared by tuning annealing temperature.Then the correlation between boron configurations and the electrochemical performances is investigated.The combination of density-functional theory(DFT)computation and NH3-TPD/Py-FTIR indicates that the BCO_(2)configuration formed on the surface of graphene is easier to accept lone-pair electrons than BC_(2)O and BC_(3)configurations due to the stronger Lewis acidity.Such an electronic structure can effectively reduce the number of unstable electron donors and stabilize the electrochemical interface,which is proved by NMR,and critical for improving the electrochemical performances.Further experiments confirm that the optimized BG800 with the largest amount of BCO_(2)configuration presents ultralow leak current,improved cyclic stability,and better rate performance in SBPBF4/PC.This work would provide an insight into the design of high-performance boron-doped carbon materials towards energy storage.

Molecular-scale controllable conversion of biopolymers into hard carbons towards lithium and sodium ion batteries: A review

Hard carbons are widely investigated as potential anodes for lithium and sodium ion batteries owing to their internally well-tailored textures(closed pores and defects) and large microcrystalline interlayer spacing. The renewable biomass is a green and economically attractive carbon source to produce hard carbons. However, the chemical and structural complexity of biomass has plagued the understanding of evolution mechanism from organic precursors to hard carbons and the structure-property relationship.This makes it difficult to finely tune the microstructure of biomass-derived hard carbons, thus greatly restricting their high-performance applications. Most recently, the optimal utilization and controllable conversion of biomass-derived biopolymers(such as starch, cellulose and lignin) at the molecular level have become a burgeoning area of research to develop hard carbons for advanced batteries.Considering the principal source of carbonaceous materials is from biomass pyrolysis, we firstly overview the chemical structures and pyrolysis behaviors of three main biopolymers. Then, the controllable preparation of hard carbons using various physicochemical properties of biopolymers at the molecular level is systematically discussed. Furthermore, we highlight present challenges and further opportunities in this field. The Review will guide future research works on the design of sustainable hard carbons and the optimization of battery performance.

Utilizing the capacity below 0 V to maximize lithium storage of hard carbon anodes

Compared with conventional graphite anode,hard carbons have the potential to make reversible lithium storage below 0 V accessible due to the formation of dendrites is slow.However,under certain conditions of high currents and lithiation depths,the irreversible plated lithium occurs and then results in the capacity losses.Herein,we systematically explore the true reversibility of hard carbon anodes below 0 V.We identify the lithiation boundary parameters that control the reversible capacity of hard carbon anodes.When the boundary capacity is controlled below 400 mAh g−1 with current density below 50 mA g−1,no lithium dendrites are observed during the lithiation process.Compared with the discharge cut-off voltage to 0 V,this boundary provides a nearly twice reversible capacity with the capacity retention of 80%after 172 cycles.The results of characterization and finite element model reveal that the large reversible capacity below 0 V of hard carbon anodes is mainly benefited from the dual effect of lithium intercalation and reversible lithium film.After the lithium intercalation,the over-lithiation induces the quick growth of lithium dendrites,worsening the electrochemical irreversibility.This work enables insights of the potentially low-voltage performance of hard carbons in lithium-ion batteries.

Ultrathin 3 V Spinel Clothed Layered Lithium-Rich Oxides as Heterostructured Cathode for High-Energy and High-Power Li-ion Batteries

In an attempt to overcome the drawbacks of high-capacity layered lithium-rich cathodes xLi2MnO3·(1–x)LiMO2(0<x<1,M=Mn,Ni,and Co),the spinel clothed layered heterostructured materials,x’Li4Mn5O12·(1–x’)Li[Li0.2Mn0.55Ni0.15Co0.1]O2(x’=0.01,0.03,0.05)have been proposed and synthesized as high-performance cathode materials for high-energy and high-power Li-ion batteries.Based on the characterizations of X-ray diffraction(XRD),transmission electron microscopy(TEM),Raman scattering spectroscopy,it is indicated that ultrathin 3 V spinel Li4Mn5O12 has been successfully clothed on the layered lithium-rich cathode.Electrochemical tests demonstrate the sample 0.01Li4Mn5O12·0.99 Li[Li0.2Mn0.55Ni0.15Co0.1]O2 with an ultrathin clothing layer of spinel phase,exhibits the highest reversible capacity of 289.4 mAh g^(-1) and maintains 259.8 mAh g^(-1) after 80 cycles at 0.1 C rate.Meanwhile,it delivers outstanding rate discharge capacities of 229.4 mAh g^(-1) at 1 C,216.8 mAh g^(-1) at 2 C and 184.4 mAh g^(-1) at 5 C as well as alleviated voltage fade.It is believed the ultrathin clothing spinel layer plays a vital role in the modification of the materials kinetics,and structural and electrochemical stability of the heterostructured cathode.

Advanced Electrode Materials in Lithium Batteries:Retrospect and Prospect

Lithium-(Li-)ion batteries have revolutionized our daily life towards wireless and clean style,and the demand for batteries with higher energy density and better safety is highly required.The next-generation batteries with innovatory chemistry,material,and engineering breakthroughs are in strong pursuit currently.Herein,the key historical developments of practical electrode materials in Li-ion batteries are summarized as the cornerstone for the innovation of next-generation batteries.In addition,the emerging electrode materials for next-generation batteries are discussed as the revolving challenges and potential strategies.Finally,the future scenario of high-energy-density rechargeable batteries is presented.The combination of theory and experiment under multiscale is highlighted to promote the development of emerging electrode materials.

Influence of co-solvent hydroxyl group number on properties of water-based conductive carbon pastes

A series of water-based conductive carbon pastes were prepared by wet ball milling, followed by vacuum defoaming using isopropyl alcohol, propylene glycol or glycerin as co-solvents. Screen printing was then used to prepare conductive patterns. To determine the influence of co-solvent hydroxyl group number on the properties of water-based conductive carbon pastes, the rheological properties of the pastes and the surface morphologies and conductivities of the printed patterns were characterized. The results show that paste viscosity increased with the number of hydroxyl groups and the latter also affected thixotropy. In addition, the boiling points and surface tensions of the co-solvents increased consistently with hydroxyl group number, affecting the hydrodynamic flow. The conductive carbon paste created using propylene glycol as a co-solvent was the best for screen printing because of its weak coffee-ring effect and appro- priate rheological properties, resulting in a smooth coating surface and uniform deposition of the fillers. The resistivity of the pattern printed using paste PG, containing the closest packing of conductive carbon black particles, was 0.44 Ω cm.

A High Energy Density Self-supported and Bendable Organic Electrode for Redox Supercapacitors with a Wide Voltage Window

Redox-active organic electrode materials are highly desirable in realizing next-generation all-in-one bendable electronic systems.Herein,a novel flexible supercapacitors(SCs)electrode is fabricated from poly(anthraquinonyl sulfide)(PAQS)and single-walled carbon nanotubes(SWCNTs)suspension by a simple vacuum filtration and named as PAQS-SWCNTs.The PAQS-SWCNTs electrode offered an initial capacitance of 223 F·g^-1 and outstanding capacitance retention up to 78.4%after 3×10^4 charge-discharge cycles at 0.5 A·g^-1 current density.In a high potential range(0-3 V)and aprotic electrolyte,the PAQS-SWCNTs electrodes in coin cell exhibited an outstanding energy density of 69 Wh·kg^-1 at a power density of 90.6 W·kg^-1,whereas in the fabricated flexible SCs it retained 63.2 Wh·kg^-1.The PAQS-SWCNTs electrodes also showed extraordinary performance at a higher current density(20 A·g^-1)and maintained a specific capacitance of 55 and 47 F·g^-1 for coin and flexible SCs,respectively.Moreover,the flexible SC is further verified to be able to illuminate up multiple LEDs.These futuristic findings showed that the SCs assembled with flexible PAQS-SWCNTs electrodes have potential application in energy-storage devices and make them highly appealing for future redox supercapacitors.