Last developments in polymers for wearable energy storage devices

Currently, portable energy storage devices are lacking in the overall performance characteristics needed to meet desired energy and power density performance demands. Furthermore, these performance demands for long-lasting energy storage devices for portable electronics continue to constantly increase. Batteries remain the main source of portable energy storage, but they generally lack the pulsed-power delivery capability required by many applications, as well as have limited cycle life. Thus, improvements in devices that show a high operational cycle life in addition to delivering high energy and power densities are extremely desirable over a wide range of physical sizes, footprints, and power delivery capabilities. Conventional electrostatic capacitors provide some of these benefits compared to batteries, including high power density and extended cycle life, but are lacking in the energy density capability required to replace batteries in many applications.Electrochemically-based double-layer capacitors (EDLCs) or ultracapacitors offer a promising solution to bridging the gap between maintaining the high-power density capability of electrostatic capacitors while providing a path to improving the energy density to be comparable to batteries –significantly broadening their applicability. An EDLC’s power density and energy density are based on the highly reversible surface charge adsorption-based mechanism of energy storage. This provides benefits in terms of high frequency responses as well as providing a route to supply power for longer duration pulses. Additionally, since the stored capacity is based on the surface charge adsorption-based energy storage, it provides an essentially indefinite lifespan as long as the materials do not degrade. However, current EDLC technologies still provide significantly lower energy density than is available from batteries. This energy density gap must be narrowed if the EDLCs are going to make further inroads toward replacing batteries.The capacitance and energy density are driven by the electrode’s available solution-accessible surface area. Thus, our approach to increasing the energy density of electrochemical capacitors is through the development of carbon nanotube-based electrode structures with a precise, highly controlled and ordered nanostructured porosity. To further improve power and energy density, these electrode structures are used in combination with an ionic liquid electrolyte with high voltage window, thus providing an increased operating voltage. While traditional electrode materials are generally comprised of randomly ordered porous structures, we have developed electrodes with an adjustable and highly controlled pore structure that provide very high surface area. These electrodes are produced using a nanotemplated approach that allows for preparation of high surface area aligned and vertically oriented carbon nanotube (CNT)-based electrodes. The templated approach has the added benefit of a achieving a greater areal CNT density than available in traditional carpet-grown CNT forests as well as providing more uniform and controllable CNT outer and inner diameters. The ability to control these dimensions allows for tailoring the electrode geometry for a specific electrolyte.Ionic liquids are becoming increasingly popular in a variety of applications as a result of their unique properties and highly tailorable chemistry. In electrochemical applications, their large voltage stability window, low vapor pressure, excellent thermal stability at temperatures above most organic solvents’ boiling points, and lower temperature conductivity make them an excellent electrolyte choice. Ionic liquids are ideal for use in higher temperature electronics applications, especially in small-scale microelectronics formats where confined spaces make efficient heat removal very difficult. By making use of ionic liquid electrolytes and optimizing the interaction of the electrolyte with our templated CNT electrodes, we have developed an energy storage technology with high-energy density and high-power density.In this talk, we will discuss the challenges and solutions to scaling up the fabrication and testing of reproducible, nanostructured electrodes from 3.14 cm2 or smaller single-sided lab cells to multiple 200 cm2 electrodes on both sides of an aluminum current collector. We will discuss the electrode fabrication scale-up and performance validation from small coin or disc cells tested in a glove box to larger area sealed pouch cells with integration of an optimized ionic liquid electrolyte. We discuss cell fabrication challenges and solutions including verifying the performance of the electrodes as they are scaled up, and the cell fabrication including ensuring the electrode and separator are reliably wetted with the ionic liquid electrolyte. The challenges of optimizing the practical tradeoff of electrode active depth and minimizing the current collector thickness as we move the electrode and overall cell design to a fully packaged cell while maintaining the optimized electrochemical performance characteristics will be discussed.[DISTRIBUTION STATEMENT A. Approved for public release; Distribution is unlimited 412TW-PA-21154]

Energy storage is a field which governs almost all aspects of daily life. Batteries and capacitors are utilised in devices at every scale, from mobile phones all the way up to the national grid. Efficient energy storage requires extensive research into chemistries and configurations, utilising novel materials to assemble devices. These often have a significant effect on features including the energy and power density of a cell. One such property is the pore structure of an electrode. Electrochemical Double-Layer Capacitors, also known as supercapacitors, utilise meso/microporous electrodes with a wide distribution of pore sizes. Larger pores typically facilitate ion diffusion and a high device power density, yet smaller micropores provide a large specific surface area for the electric double layer which facilitates a high device energy density. Recent advancements in post-lithium ion battery technology (such as lithium-sulphur and lithium air batteries) utilise these micropore surface areas for redox reactions. Developing accurate models of energy storage devices allows for the simulation of the processes within the cells without the need for expensive and time-consuming experimental testing. Many models have been developed in the past, however sweeping assumptions are often made with respect to the pore structure. These generally assume a uniform pore size and structure, and do not take into account the effects of different pore sizes present in a true electrode material. Pore network models are able to do this, but require complex or expensive pieces of software and a long simulation time. In this project, a novel continuum model of mass and charge transport has been developed catering for the many pore sizes in an electrode. This model allowed for the simple implementation of a pore size distribution into the simulation of the processes in several supercapacitor configurations, a lithium-sulphur battery, and two lithium-oxygen battery configurations. This novel approach involved characterising an electrode material through analysis of the pore structure and pore size distribution. A novel mathematical transient volume averaged model was developed to solve for the mass transport of species within pores of different sizes. The use of this model in each case demonstrated good agreement with experimental data and allowed for analysis of the effects of different pore structures on the activity of cells. It was found that larger pores (in the macropore region) facilitate mass transport of species, and smaller pores (in the micropore region) have a reduced rate of mass transport and a higher rate of reaction (in batteries) and stern layer formation (in supercapacitors). This novel model demonstrated the importance of modelling ion transport through multiple pore sizes of an electrode material. This model also addresses the need for more complex energy storage device simulation in a reasonable solving time without the need for expensive pieces of software.

Capacitive contribution matters in facilitating high power battery materials toward fast-charging alkali metal ion batteries

The growing number of energy consuming devices is driving an ever increasing demand for high efficiency, high capacity, and portable energy storage devices. In addition to higher levels of energy storage, there is a growing need for the capability to produce sustained high power pulses. For many applications, the energy storage devices must also provide a high cycle life to provide the sustained operation life, along with increased capability of providing high power over ever increasing pulse durations. Moreover, these energy storage devices are in demand over a wide range of sizes from chip-scale power storage to large-scale, kilovolt-level power delivery. Rechargeable batteries, in particular lithium ion, are well known and have been extensively developed for their high energy density, but their major drawback remains in their limited power density and cycle-life capability. Electrostatic capacitors, on the other hand, provide a high power density, and research has shown they have great potential for meeting the power and cycle life demands for the new energy storage device demands. However, for conventional electrostatic capacitors, the energy density and thus pulse power duration capability is very limited. Alternatively, electrochemically-based double-layer capacitors (EDLCs) or ultracapacitors, provide a pathway to an energy storage device that shows significant promise for delivering the high power density and high cycle life that is achievable with electrostatic capacitors, while providing a path to much greater energy storage and thus sustained long duration pulsed power delivery. Through the surface charge adsorption-based mechanism of energy storage utilized in EDLCs, it is possible to get high frequency response times while providing the ability to supply power for much longer periods of time than can be achieved with conventional capacitors. Despite this major benefit, currently available commercial EDLC devices still provide energy densities that are much lower than that of batteries. To increase the number of potential applications for EDLCs and displace batteries, the energy density must be increased. Thus the main focus of our ultracapacitor research, presented here, is increasing the energy density of ultracapacitors through the use of highly ordered nanostructured electrode materials, which are combined with a high voltage window ionic liquid-based electrolytes to increase the power and energy density.In EDLCs, the capacitance and corresponding energy storage capability are directly proportional to the electrode’s solution accessible surface area. To maximize this area, we have developed electrode structures with a tunable, highly controlled porosity that provides very high, electrolyte-accessible, surface area. We’ve developed a robust and scalable templated approach to allow the fabrication of high surface area carbon nanotube (CNT)-based electrodes with highly aligned and vertically-oriented CNTs. This approach provides an areal CNT density that is much greater than typical carpet-grown CNTs. Furthermore, through our templated fabrication approach, we can tune the electrode pore size, thus allowing us to optimize it for the specific electrolyte. Our approach, combining tuning of both the electrode and electrolyte, ensures maximum charge adsorption for energy storage, while maintaining excellent solution access for fast charge transport during charging and discharging, thereby ensuring power capability.Ionic liquids are becoming popular electrolytes for a range of applications because of their large voltage window, and chemical properties that can be tailored for the specific application. The use of ionic liquid electrolytes allows operation at higher cell voltages than the conventional aqueous or organic solution-based capacitors. Larger operation voltage further enhances the power and energy density in our capacitors. Additionally, since ionic liquids are nonflammable and have a negligible vapor pressure, they make the ideal electrolyte choice in higher temperature applications or for micro- and on-chip devices, where the removal of heat is difficult because of the confined space operating conditions. Through the use of designer electrolytes based on pure and mixed ionic liquids, and combining and optimizing the interaction of the electrolyte with our templated CNT electrodes, we are able to produce an energy storage technology which combines the optimal balance and benefits of high energy density and high-power density. This talk will detail our electrode development and device optimization efforts for our large format capacitors.[DISTRIBUTION STATEMENT A. Approved for public release; Distribution is unlimited 412TW-PA-20122]

Energy-storage technologies, including supercapacitors with high power density and rechargeable batteries with high energy density, have attracted significant attention for applications in electric vehicles, power line conditioners, and load leveling of solar energy and wind power. However, for such applications, the demand for both high power density and energy density devices is becoming increasingly important. Thus, novel hybrid energy storage devices combining the advantages of supercapacitors and batteries is becoming a hotstopic in the energy storage research field. In previous work, the 3D nanostructured binder free electrodes have been shown to deliver high discharge capacity and excellent rate capability, which were assessed using Li-ion half cells [1-4], indicating that energy storage devices with high energy and power density may be achieved using such kinds of 3D electrodes. In this work, novel Li-ion full cells and supercapacitors were designed and fabricated using MnOx-based 3D electrodes, a manganese oxides based Li-ion full cell is shown in Figure 1a-c. The electrochemical performances of the different energy storage devices were assessed using a 3-electrode cell, as shown in Figure 1 d-f. The maximum energy density of the manganese oxides based Li-ion full cell is 223 Wh/kg at 146 W/kg. The Sn and Si based 3D anodes were also prepared and assessed using both Li-ion half cells and Li-ion full cells. Figure 1 (a)Figure 1 (b)Figure 1 (c)Figure 1 (d)Figure 1 (e) Figure 1: (a) Scheme of the manganese oxides based Li-ion full cell. S(T)EM images of the nanostructured LiMn2O4 cathode material (b) and the 3D C/MnOy/ACNTs anode materials (c). Two- and three-electrode charge (d) and discharge (e) voltage profiles of the manganese oxides based Li-ion full cell utilizing Li metal reference.

The prime importance in the energy storage field is to develop a new system that can combine high energy and power density. While lithium-ion batteries (LIBs) have become scientifically and commercially important because of their high energy densities, their power densities are not sufficient for emerging large-scale applications. Supercapacitors, on the other hand, are capable of delivering very high power due to their intrinsically fast surface-reaction mechanism, but they fail to meet high energy density requirements. This presentation proposes a new type of battery that adopts the fast surface reaction mechanism mimicking the supercapacitor without sacrificing energy density: an all-graphene energy storage device. The key advantages of an all-graphene energy storage device are that (i) both electrodes (a functionalized graphene cathode and a reduced graphene anode) exhibit fast surface reactions instead of intercalation while maintaining high energy density, and (ii) simple chemical modification of graphene yields either the anode or the cathode in a one-pot synthesis. Combined with controlled porous morphology and high electrical conductivity of graphene, the all-graphene energy storage device was capable of delivering a high energy of 195 Wh/kgtotal electrode, which is comparable to the energy density of conventional LIBs. The newly developed all-graphene energy storage device also retains 8.5 Wh/kgtotal electrode (energy) and 3,300 W/kgtotal electrode (power) at charge/discharge rates of just a few seconds. This energy and power performance perfectly spans the region that conventional LIBs and supercapacitors cannot reach. The performance and operating mechanism of an all-graphene energy storage device resemble those of both supercapacitors and batteries, blurring the conventional distinction between the two. This work sheds new light on the development of advanced energy-storage devices that bridge the performance gap between LIBs and supercapacitors. Presenting author: H. Kim E-mail: kimhaegyeom1@gmail.com Corresponding author: K. Kang E-mail: matlgen1@snu.ac.kr

Intercalation pseudocapacitance in electrochemical energy storage: recent advances in fundamental understanding and materials development

To satisfy the requirements for various highly regarded applications such as electric transportation systems and portable electronic devices, developing advanced energy storage devices with high energy density, power density, and long lifespan is significantly rising. Li-ion batteries (LIBs) and supercapacitors (SCs) are state-of-the-art energy storage technologies owing to their widespread usage in practical applications. However, LIBs and SCs cannot simultaneously meet high energy density, high power density, and long cyclic stability due to their storage mechanism, relying on their active materials. Li-ion hybrid capacitors (LIHCs) have attracted intensive attention due to their high energy and power density and long cyclability. LIHCs are composed of battery-type and capacitor-type electrodes, benefiting from the advantages of both LIBs and SCs. In this chapter, we briefly introduce the principle of LICs, classify battery- and capacitor-type electrode materials, and discuss the criteria for materials selection. Then, recent challenges and developments associated with LIHCs are discussed. Providing in-depth insights into designing electrode materials for LIHCs as the next generation of energy storage devices is the overall aim of this chapter.KeywordsEnergy storageLithium-ion hybrid capacitorLi-ion batterySupercapacitorActivated carbon

Energy storage devices have received a keen interest throughout the world due to high power consumption. A large number of research activities are being conducted on electrochemical double layer capacitors (EDLCs) because of their high power density and higher energy density. In the present study, an EDLC was fabricated using natural graphite based electrodes and ionic liquid (IL) based gel polymer electrolyte (GPE). The IL based GPE was prepared using the IL, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (1E3MITF) with the polymer poly(vinyl chloride) (PVC) and the salt magnesium trifluoromethanesulfonate (Mg(CF3SO3)2 - MgTF). GPE was characterized by electrochemical impedance spectroscopy (EIS), DC polarization test, linear sweep voltammetry (LSV) test and cyclic voltammetry (CV) test. The maximum room temperature conductivity of the sample was 1.64 x 10-4 Scm-1. The electrolyte was purely an ionic conductor and the anionic contribution was prominent. Fabricated EDLC was characterized by EIS, CV and galvanostatic charge discharge (GCD) tests. CV test of the EDLC exhibits a single electrode specific capacitance of 1.44 Fg-1 initially and GCD test gives 0.83 Fg-1 as initial single electrode specific discharge capacitance. Moreover, a good stability was observed for prolonged cycling and the device can be used for applications with further modifications.

The crucial request for alternative clean energy technologies to replace conventional fossil fuels and drive technological advancement in consumer and wearable electronics, electric vehicles etc. has led to great advancement in electrochemical energy storage systems research. The lithium-ion battery possesses high energy density while the supercapacitor can guarantee high power density. However, modern technologies such as integrated solar and wind energy solutions require a blend of high energy and power density devices, which is a great challenge. Presently, there is increased research interest in aqueous hybrid supercapacitors, a device capable of combining the high energy density of rechargeable batteries and the high-power density of electric-double layer capacitors.The current hotspot of the hybrid supercapacitor research is the zinc-ion hybrid supercapacitor owing to its several advantages such as the abundance of Zinc resource over lithium, high theoretical capacity of Zn, double charge transfer compared to univalent Lithium, environmental safety and high energy/power density. Wang et al first reported the carbon zinc-ion hybrid supercapacitor in 2018 by directly using zinc foil as anode and bio-carbon as cathode to realize long stability up to 20000 cycles. Next, Dong et al also developed an activated carbon-based zinc-ion hybrid supercapacitor which achieved a high energy density of ~84 Wh kg-1 and power density of 14.9 kW kg-1 in a potential window of 0.2 – 1.8 V. Despite the rapid advances over a short period in this class of energy storage devices, some problems still exist. The coulombic efficiency of Zinc-ion hybrid supercapacitors is inferior in low-cost ZnSO4 electrolytes owing to side reactions between the electrolyte and the Zn anode, while the mass loading of commonly used carbon cathode is extremely low (less than 2 mg cm-2). Importantly, the charge storage mechanism in zinc-ion hybrid supercapacitors is unclear.In this work, we developed high performance zinc-ion hybrid supercapacitors with superior charge storage, improved rate capability, and high power and energy density using a high mass density carbon anode with superior capacitive/pseudocapacitive storage. We successfully reveal that the charge storage of zinc-ion hybrid supercapacitors is extensively limited in zinc sulfate electrolytes and successfully address the coulombic efficiency problem using by modifying the electrolyte. Finally, using techniques such as in-situ Raman spectroscopy and X-ray diffraction analysis, we probe the charge storage mechanism and unravel a double cation charge storage mechanism, resulting in high energy density and extended potential window. Finally, our work provides crucial insights into understanding the charge storage process of zinc-ion hybrid supercapacitors and designing hybrid supercapacitors with new material chemistries.

Although batteries have been successfully employed in light-duty vehicles (hybrid and fully electric cars), batteries still find it is hard to satisfy power-hungry platforms such as trucks, trams, and buses. Conventional lithium ion batteries (LIB) could provide power density less than 3 kW/kg with relatively moderate energy density. On the other side, supercapacitors (SCs) that are known to provide power density of more than 10 kW/kg have a very low energy density of less than 1 Wh/kg and thus, SCs could not be used solely as energy storage. However, employing anode from LIB and electrode from SC together in a single system would benefit both high energy and power density, which system is-so called lithium ion capacitor (LIC). To date, so many attempts have been done to investigate the best anode material combination with activated carbon (AC) to obtain high performance LIC. The anode materials that are commonly utilized in LIB such as graphite, hard carbon, Li4Ti5O12 (LTO), Fe3O4, SnO2, and silicon based material have been extensively studied for LIC. Graphite that is known as an ubiquitous anode material in LIBs provided relatively high energy density of c.a. 100 Wh/kg and maximum power density of less than 2 kW/kg in LIC. Among all, LTO application was found to be the least desirable material for LIC since it provided relatively low maximum energy and power density, which was merely less than 40 Wh/kg and 2 kW/kg, respectively, due to its low conductivity and high voltage plateau at around 1.5 V. Grphene has been used to reinforce rate capability of Fe3O4 and it demonstrated promising energy density as high as 86 Wh/kg. However, the maximum power density of the enhaced electrode material was only 2.6 kW/kg. Higher power LIC can be achieved by harnessing hard carbon anode material, which displayed maximum power density of about 50 kW/kg. However, the high power density of hard caron in LIC was compensated by extremely low energy density of less than 2 Wh/kg. Herein, we investigate the electrochemical performance of LIC by using silicon oxycarbide (SiOC) as the anode and the AC from biomass (Zalacca salacca) peels as the cathode to provide massive power while maintaining the energy density relatively high. SiOC showed an outstanding rate capability performance indicated by relatively high discharge capacity of over than 200 mAh/g at current density of 80 A/g. The excelent rate capability was attributed to the fast lithium diffusion in SiOC, which was represented by high lithium diffusion coefficient (DLi+) of 5.1 × 10-6 cm2/s. Meanwhile, the AC derived from biomass is promising since its surface area (c.a. 2600 m2/g) and capacitance (163.7 F/g) was significantly higher than that of commercial AC. Combination of SiOC and AC derived from Zalacca salacca in a single unit of LIC could be used to provide a massive power density of 155kW/kg while maintained relatively high energy density of 25 Wh/kg. Moreover, the resulting LIC demonstrated highly stable cycle retention at high C-rate. After reaching equilbrium state, the cycle retention of LIC at 50C was 99.4% after more than 40,000 cycles. At higher C-rate of 100C, the cycle retention of the LIC was 99% even after more than 75,000 cycles. The present study indicates that LIC design based on SiOC and AC from Zalacca salacca peels is suitable for energy storage in high-duty platforms such as trucks, trams, and buses.

Higher-voltage asymmetric-electrolyte metal-air batteries

Sluggish kinetics severely limit the development of potassium-ion hybrid capacitors (PIHCs). Exposing active sites is recognized as an ideal strategy to resolve this issue, but the corresponding ma...

Because of the increasing demand for portable devices, renewable energy systems, and electric vehicles, energy storage system has been developed intensively over the past decade. Researchers have intensively studied low-cost, high energy density, high power density, and high-safety energy storage devices. Lithium-ion batteries (LIBs) have advantages of high energy density and no memory effect. However, the power density is relatively low. In contrast to LIBs, supercapacitors (SCs) exhibit high power density and long cycling life, but low energy density. Therefore, lithium ion capacitors (LICs) which combine the superiorities of LIBs and SCs has been announced recently in order to achieve both high energy density and power density. Polyoxometalates (POMs) are a class of anionic polynuclear transition metal oxides, and they possess multiple redox reactions which can store many charges per molecule. Hence, POMs have been employed as electrode materials for energy storage devices, such as LIBs, sodium-ion batteries (NIBs), and SCs, and most of them exhibit high capacity. In this work, a vanadium-based POM (V-POM) was utilized as anode material for LICs. V-POM exhibited high specific capacities as well as good cycling stability. A full cell comprised with V-POM anode and porous carbon cathode were assembled, and it showed high energy density and high power density. These results demonstrated that V-POM anode material is suitable for LIC applications. Furthermore, we also utilized several in operando techniques to investigate the charge storage mechanisms of this V-POM anode including X-ray Absorption Spectroscopy and X-ray diffraction.

Energy storage systems are vital components to the success of emerging technologies such as renewable resources harvesting technologies and electric vehicles. Commercially, rechargeable Li-ion batteries (LIBs) and electrochemical capacitors (ECs) share the majority of energy storage systems markets. While LIBs are known for high energy density (≈ 240 Wh/kg) and ordinary power density (≈ 1000 W/kg), ECs have high power density (>10000 W/kg) and cyclability (>100000 cycles) but low energy density (≈ 5 Wh/kg)1. For past two decades, a new energy storage device has been studied to hybridize the two technologies by combining an EC cathode and a rechargeable battery's anode and achieve a balanced performance2. The hybridized device is commonly known as hybrid electrochemical capacitor (h-EC) or asymmetrical electrochemical capacitors which is intended to have a power density higher than rechargeable batteries and energy density higher than ECs. The initial study of the designed system comprised of nanostructured Li4Ti5O12 negative electrode accompanied with activated carbon as positive electrode. The performance showed similar cyclability to non-aqoues EDLC electrodes and 500% energy storage improvement2. Unlike the negative electrode materials, positive electrodes are believed to be more sensitive in determining the overall performance of the h-ECs due to the huge gap between the capacity of electrodes half-cells2,3. Thus, higher capacitance positive electrodes are perused using higher surface area and/or pseudocapacitance properties. The primary material for the positive electrode is carbonaceous materials with by high surface areas, such as biomass-derived doped and un-doped activated carbon1,3–5, 3D graphene/carbon composite6. Nonetheless, heteroatom-doped graphene, which has shown to increase the conductivity and activate the pseudocapacitance feature to enhance the capacitance, has rarely been reported as a cathode for hybrid electrochemical capacitors7,8. Herein, we demonstrate a high energy density of 106.2 Wh/kg at high power density 14160 Wh/kg hybrid electrochemical cell by hybridizing highly crumpled nitrogen-doped graphene with carbon-coated nano-sized silicon [Figure 1a, b]. Furthermore, the crumpled nitrogen-doped graphene was synthesized by a two-step method which led to a surface area of 1200 m2/g and high pore volume 4.5 cm3/g9. In addition, the long cycling performance has shown a capacity retention of 78% after 5000 cycles at high rate 1A/g [Figure 1c]. Carbon coating silicon anode proved to be highly advantageous for both cycling the h-EC and storing energy at higher power density. While 88% was of the initial capacity was preserved for carbon-coated silicon, only 63% was maintained for bare nano-sized silicon after 1000 cycles [Figure 1d]. Reference: Yi, R. et al. High-performance hybrid supercapacitor enabled by a high-rate Si-based anode. Adv. Funct. Mater. 24, 7433–7439 (2014).Amatucci, G. G., Badway, F., Du Pasquier, A. & Zheng, T. An Asymmetric Hybrid Nonaqueous Energy Storage Cell. J. Electrochem. Soc. 148, A930 (2001).Li, B. et al. Nitrogen-doped activated carbon for a high energy hybrid supercapacitor. Energy Environ. Sci. 9, 102–106 (2016).Sun, F. et al. High-energy Li-ion hybrid supercapacitor enabled by a long life N-rich carbon based anode. Electrochim. Acta 213, 626–632 (2016).Jain, A. et al. Activated carbons derived from coconut shells as high energy density cathode material for Li-ion capacitors. Sci. Rep. 3, 3002 (2013).Zhang, F. et al. A high-performance supercapacitor-battery hybrid energy storage device based on graphene-enhanced electrode materials with ultrahigh energy density. Energy Environ. Sci. 6, 1623 (2013).Wei, D. et al. Synthesis of n-doped graphene by chemical vapor deposition and its electrical properties. Nano Lett. 9, 1752–1758 (2009).Mendoza-Sánchez, B. & Gogotsi, Y. Synthesis of Two-Dimensional Materials for Capacitive Energy Storage. Advanced Materials 6104–6135 (2016). doi:10.1002/adma.201506133Song, J., Yu, Z., Gordin, M. L. & Wang, D. Advanced Sulfur Cathode Enabled by Highly Crumpled Nitrogen-Doped Graphene Sheets for High-Energy-Density Lithium-Sulfur Batteries. Nano Lett. 16, 864–870 (2016). Figure 1