Hybrid energy storage devices (HESDs) combining the energy storage behavior of both supercapacitors and secondary batteries, present multifold advantages including high energy density, high power density and long cycle stability, can possibly become the ultimate source of power for multi-function electronic equipment and electric/hybrid vehicles in. Hybrid devicesElectrode materialsMatching principlesBatteriesWith the increasing concerns on the environmental issues and the critical demands in clean and sustainable energy resource of human society, the construction of advanced energy-storage devices with high energy density, high power density, long-cycle life is becoming a worldwide important topic,,,,,,,. Supercapacitors (SCs) and secondary batteries (SBs) have been widely studied as energy storage devices with broad application prospects. The secondary battery has a high energy density (30–200 Wh kg−1), but a low power density (<1 kW kg−1) and poor cycling stability, which is insufficient in the industrial applications,. Supercapacitors, on the other hand, with charge transfer merely limited at the electrolyte/electrode interface, have the characteristics of long life (~100000 times) and high power density (~10 kW kg−1), but their energy density is relatively low (< 20 Wh kg−1). An apparent solution is to manufacture a new kind of hybrid energy storage device (HESD) by taking the advantages of both battery-type and capacitor-type electrode materials,,, which has both high energy density and power density compared with existing energy storage devices (Fig. 1). Thus, HESD is considered as one of the most promising next-generation energy storage systems.Comparing the charge storage behavior of SBs with the SCs can help one to. In terms of ion transport kinetics, energy storage materials can be divided into capacitive energy storage materials and battery-type energy storage materials. The capacitance material demonstrates a surface control charge storage kinetics, while battery-type material shows typically diffusion controlled kinetics.Supercapacitors can be classed as electrochemical double-layer capacitors (EDLCs) and pseudocapacitors. Generally, the EDLCs take advantage of the electronic charge storage induced by the electrochemical double layer of high-surface area carbons, whereas the pseudocapacitors rely on those electroactive phases, which undergo faradaic redox processes limited to the electrode-electrolyte interface leading to a so-called pseudocapacitance,.As the energy storage device combined different charge storage mechanisms, HESD has both characteristics of battery-type and capacitance-type electrode, it is therefore critically important to realize a perfect matching between the positive and negative electrodes. The overall performance of the HESDs will be improved if the two electrodes are well.
