Sodium-ion hybrid capacitors(SICs)have been proposed to bridge performance gaps between batteries and supercapacitors,and thus realize both high energy density and power density in a single configura-tion.Nevertheless,applications of SICs are severely restricted by their insufficient energy densities(＜100 Wh/kg)resulted from the kinetics imbalance between cathodes and anodes.Herein,we report a nanograin-boundary-rich hierarchical Co3O4 nanorod anode composed of～20 nm nanocrystallites.Extreme pseudocapacitance(up to 72％@1.0 mV/s)is achieved through nanograin-boundary-induced pseudocapacitive-type Na+storage process.Co3O4 nanorod anode delivers in this case highly reversible capacity(810 mAh/g@0.025 A/g),excellent rate capability(335 mAh/g@5.0 A/g),and improved cycle sta-bility(100 cycles@1.0 A/g with negligible capacity degradation).The outstanding performance can be credited to the hierarchical morphology of Co3O4 nanorods and the well-designed nanograin-boundaries between nanocrystallites that avoid particle agglomeration,induce pseudocapacitive-type Na+storage,and accommodate volume variation during sodiation-desodiation processes.Nitrogen-doping of the Co3O4 nanorods not only generates defects for extra surficial Na+storage but also increases the electronic conductivity for efficient charge separation and lowers energy barrier for Na+intercalation.Synergy of conventional reaction mechanism and pseudocapacitive-type Na+storage enables high speci-fic capacity,rapid Na+diffusion,and improved structural stability of the Co3O4 nanorod electrode.The SIC integrating this highly pseudocapacitive anode and activated carbon cathode delivers exceptional energy density(175 Wh/kg@40 W/kg),power density(6632 W/kg@37 Wh/kg),cycle life(6000 cycles@1.0 A/g with a capacity retention of 81％),and coulombic efficiency(～1 00％).

IMDEA Materials Institute,C/Eric Kandel 2,Getafe,Madrid 28906,Spain;Universidad Politécnica de Madrid,E.T.S.de Ingenieros de Caminos,28040 Madrid,Spain;Universidad Autónoma de Madrid,C/Francisco Tomás y Valiente,7,28049 Madrid,Spain;Surface Analysis Laboratory,Faculty of Engineering and Physical Sciences University of Surrey Guildford,Surrey GU2 7XH,United Kingdom

[1]Wenliang Feng;Venkata Sai Avvaru;Steven J.Hinder;Vinodkumar Etacheri-.High-energy sodium-ion hybrid capacitors through nanograin-boundary-induced pseudocapacitance of Co3O4 nanorods)[J].能源化学,2022(06):338-346

nanograin,nanocrystallites,Na+intercalation,Na+diffusion

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