Notably, many significant breakthroughs for a new generation of supercapacitors have been reported in recent years, related to theoretical understanding, material synthesis and device designs. Herein, we summarize the state-of-the-art progress toward mechanisms, new materials, and novel device designs for supercapacitors. Firstly, fundamental understanding of the mechanism is mainly focused on the relationship between the structural properties of electrode materials and their electrochemical performances based on some in situ characterization techniques and simulations. Secondly, some emerging electrode materials are discussed, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes, metal nitrides, black phosphorus, LaMnO, and RbAgI/graphite. Thirdly, the device innovations for the next generation of supercapacitors are provided successively, mainly emphasizing flow supercapacitors, alternating current (AC) line-filtering supercapacitors, redox electrolyte enhanced supercapacitors, metal ion hybrid supercapacitors, micro-supercapacitors (fiber, plane and three-dimensional) and multifunctional supercapacitors including electrochromic supercapacitors, self-healing supercapacitors, piezoelectric supercapacitors, shape-memory supercapacitors, thermal self-protective supercapacitors, thermal self-charging supercapacitors, and photo self-charging supercapacitors. Finally, the future developments and key technical challenges are highlighted regarding further research in this thriving field.

An aqueous rechargeable Zn//Co3 O4 battery is demonstrated with Zn@carbon fibers and Co3 O4 @Ni foam as the negative and positive electrodes, respectively, using an electrolyte of 1 m KOH and 10 × 10(-3) m Zn(Ac)2 . It can operate at a cell voltage as high as 1.78 V with an energy density of 241 W h kg(-1) and presents excellent cycling. The battery is also assembled into a flexible shape, which can be applied in flexible or wearable devices requiring high energy.

Supercapacitors have unique advantages over lithium ion batteries in high power delivery and long cycling life, and are emerging as attractive electrochemical energy storage devices for future electrical vehicle application. [1][2][3][4] However, supercapacitors deliver an unsatisfactory energy density. Intensive efforts have been devoted to the enhancement of their energy density to make it comparable to that of rechargeable batteries. Among the supercapacitor electrode materials, pseudocapacitive transition-metal oxides and electronically conducting polymers based on faradic redox charge storage have attracted signifi cant attention because of their higher energy density than those of electrochemical double-layer capacitive carbon materials. [ 5 , 6 ] Currently, the most investigated pseudocapacitive materials are always directed towards the cathode material, [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] whereas there are only a few reports on anode materials due to the unsatisfactory capacitive performance. [23][24][25][26][27][28] Among the various transition-metal oxides, V 2 O 5 possesses the unique advantages of high energy density [ 29 ] and wide potential window arising from its various vanadium oxidation states (V-II), [ 27 ] which render it a promising candidate as an anode material for supercapacitors. However, its poor electronic conductivity and high dissolution in liquid electrolyte are detrimental to high-rate and long-term cycling performance in electrochemical devices. The combination of V 2 O 5 with carbon nanotubes has been demonstrated to be an effective strategy to improve electronic transport, [ 10 , 30-32 ] but this kind of composite cannot prevent vanadium dissolution. In this work, polypyrrole (PPy)-known to be an electronic conductive polymer [ 33 , 34 ] -is grown uniformly on the surface of V 2 O 5 nanoribbon by using anionic dodecylbenzenesulfonate (DBS − ) as a surfactant. The obtained core-shell-structured PPy@V 2 O 5 nanocomposites is expected to resolve the above two problems simultaneously utilizing the electronic conductivity and polymeric coating effect of PPy ( Figure 1 a). [ 35 , 36 ] Electrochemical results demonstrate that our prepared PPy@V 2 O 5 nanocomposite exhibits excellent cycling and rate behavior, and is a promising candidate as an anode material for supercapacitors.The process for the growth of PPy on V 2 O 5 surface is schematically shown in Figure 1 b. The virgin V 2 O 5 nanoribbons were prepared by hydrothermal treatment of NH 4 VO 3 and poly(ethylene oxide)block -poly(propylene oxide)blockpoly(ethylene oxide) copolymer in acid solution at 120 ° C. [ 37 ] For the fabrication of the PPy@V 2 O 5 nanocomposite, V 2 O 5 nanoribbons were fi rst ultrasonically dispersed in water assisted by anionic surfactant dodecylbenzenesulfonate (DBS − ), with the hydrophilic head towards water phase. After addition of pyrrole, pyrrole monomer is supposed to adsorb on the V 2 O 5 surface via electrostatic interaction between anionic DBS − and protonated pyrro...

Due to the energy crisis within recent decades, renewable energies such as solar, wind and tide energies have received a lot of attention. However, these renewable energies are dependent on the time and season. Consequently, energy storage systems are needed to fully utilize these energies including their connection with smart grids. Aqueous rechargeable lithium batteries (ARLBs) may be an ideal energy storage system due to its excellent safety and reliability. However, since the introduction of ARLBs in 1994, the progress on improving their performance has been very limited. Recently, their rate performance, especially superfast charging performance, reversible capacity and cycling life of their electrode materials were markedly improved. The present work reviews the latest advances in the exploration of the electrode materials and the development of battery systems. Also the main challenges in this field are briefly commented on and discussed. Broader contextFor large-scale energy storage systems, their safety and reliability are more challenging than those required for electric vehicles. New rechargeable batteries are urgently needed. It has been well realized that an aqueous electrolyte is one of the safest choices for rechargeable batteries. In addition, the ionic conductivity of aqueous electrolytes is higher than those of nonaqueous and solid electrolytes, which is one prerequisite for a fast redox reaction, i.e., fast charge and discharge processes. In the case of aqueous rechargeable lithium batteries (ARLBs), the rst was invented in 1994. Only until recently has great progress been achieved. The main reasons are ascribed to the nanostructuring and surface coating on their electrode materials. The reversible capacities of their electrode materials are markedly increased, which can be similar to those achieved in organic electrolytes. Their cycling life is excellent. For example, in the case of LiMn 2 O 4 , its capacity retention can be 93% aer 10 000 full cycles. In addition, their electrode materials and the ARLBs can be charged at a super fast rate, which is comparable with gasoline lling for car engines. These progresses show that ARLBs provide another promising choice as a power source for smart grids and hybrid electric vehicles, and can assist the power sources of electric vehicles and range-extenders.