Fabrication of High‐Power Li‐Ion Hybrid Supercapacitors by Enhancing the Exterior Surface Charge Storage

Abstract

However, low conductivity, diffusion limitations, and large structural deviations have so far been major obstacles for its application in hybrid systems.As a general rule for supercapacitor devices, the electrochemical performance needs to be confi ned to experimental timescales, i.e., on the order of minutes or seconds. [ 1,17 ] Nevertheless, for hybridized Li-HECs, the kinetics imbalance between the two ends impedes the full realization of the high power concept, leading to insuffi cient performance at high currents. In most cases, desirable energy storage (30-90 Wh·kg −1 ) can only be obtained at the expense of the power performance (<3 kW·kg −1 ), [5][6][7]19,22 ] which is far lower than the power performance targets required for new-generation electric vehicles (15 kW·kg −1 ). [ 18 ] Therefore, it will be a major challenge to design electrodes that can overcome the kinetics mismatch as well as achieve rapid electrochemical processes. [ 23 ] With larger external surface areas and shorter ion diffusion paths, various nanoarchitectures show an effective response to rapid redox reactions. [ 3,24 ] In particular, it was demonstrated that nanoscale architectures of less than 10 nm could enable pseudo-capacitance to overcome diffusion limitations for most reactions that occur at/near the surface. [ 25 ] Correspondingly, three-dimensional (3D) architectures with an interconnected carbon matrix render continuous and effi cient electrical conductive networks with electron supplies that guarantee electrochemical reactions at high power. [ 26 ] Here, we present high-power Li-ion hybrid supercapacitors (Li-HSCs) from the prospective of both single electrodes and devices, with two ends concurrently constructed with delicately engineered 3D hierarchical structures to overcome the kinetics discrepancy ( Figure 1 ). A well-designed MnO-graphene composite (MnO@GNS) was devised as the anode with MnO nanocrystals (≈5 nm) homo-dispersed in the 3D architecture, while 3D hierarchical porous N-doped carbon (HNC) was used as the cathode with thin nanosheets forming the overall multi-porous framework. These scaffolds allow fast kinetics with ion diffusion paths narrowed down to ultrafi ne scales, as well as maximum exposure of the exterior surface. Both porous 3D electrodes with 2D ultrathin subunits facilitate high-power charge storage near the surface. The beneficial surface decoration of heteroatoms further improves the pseudo-capacitance performance of HNC, leading to higher capacitance than conventional carbon materials. As expected, the originally-devised hybrid Li-HSCs achieve attractive energy storage of 127 Wh·kg −1 electrodes , and even remains as high as 83.25 Wh·kg −1 at a battery-inaccessible power density of 25 kW·kg −1 with rapid charging within 8 s. Such a coherent design marks a new strategy for rationally fabricating hybrid devices with both high energy and power density by enhancing the exterior surface charge storage.Electrical energy-storage (EES) systems are anticipated to satisfy the increasing demand for large...

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Filling and unfilling carbon capsules with transition metal oxide nanoparticles for Li-ion hybrid supercapacitors: towards hundred grade energy density

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