Polyimides: Promising Energy-Storage Materials

Organic Carbonyl Compounds for Sodium-Ion Batteries: Recent Progress and Future Perspectives

Sodium-organic batteries, which use organic materials as the electrodes in sodium-ion batteries, are an attractive alternative to conventional lithium-ion batteries for next-generation sustainable and versatile energy storage devices owing to the abundant sodium resources and environmental friendly features. However, organics used in sodium-ion batteries also encounter some issues such as low redox potential, high solubility in the electrolyte, and low conductivity. In response, altering the aromatic system/attaching electron-withdrawing groups, constructing polymers, and incorporating a conductive matrix are effective strategies. This review summarizes and briefly discusses recent organic carbonyl compounds for sodium-organic batteries from the viewpoint of function-oriented design, including function evolution from small-molecule compounds to polymers, then composites, and finally flexible electrodes. In particular, as a timely overview, carbonyl-based organic flexible electrodes for sodium-organic batteries are also highlighted for the first time.

Recent Progress in Polymeric Carbonyl-Based Electrode Materials for Lithium and Sodium Ion Batteries

Advancement in mobile electronics is driving progress in lithium ion batteries. Recently, organic electrode materials have emerged as promising candidates for lithium ion batteries due to their high theoretical capacity, ease of synthesis, versatility of structure, and abundance. Polymerization is a strategy used to overcome the issues associated with small organic molecules for charge storage application. The focus of this review is on the most recent progress in the field of polymeric carbonyl materials for lithium ion batteries (LIBs) and sodium ion batteries (SIBs). Advantages of organic electrode materials, device architecture, and charge storage mechanism are discussed. Challenges associated with carbonyl-based electrodes and some recent solutions are outlined. Later, a comparison of theoretical capacity, practical capacity, and cyclic life are presented for different carbonyl systems. Capacity-fading phenomena and structural degradation during charging are discussed where necessary. Some key parameters for the design of flexible batteries are highlighted and an overview of some recent contributions of our group in this field are reported. Finally, some future prospects for researchers in this field are outlined.

Robust Micron-Sized Silicon Secondary Particles Anchored by Polyimide as High-Capacity, High-Stability Li-Ion Battery Anode

Silicon is an attractive high-capacity anode material for lithium-ion battery. With the help of nanostructures, cycling performance of silicon anode has improved significantly in the past couple of years. However, three major shortcomings associated with nanostructures still need to be addressed, namely, their high surface area, low tap density, and poor scalability. Herein, we present a facile and practical method to produce micron-sized Si secondary particle cluster (SiSPC) with a high tap density and a low surface area from bulk Si by high-energy ball-milling. By coupling SiSPC with a mechanically robust polyimide binder, more than 95% of the initial capacity is retained after 500 cycles at 3500 mA g^-1 (1C rate). Reversibility of electrode thickness change is confirmed by in situ dilatometry. In addition, the polyimide binder suppresses the surface reaction of the particles with electrolyte, resulting in a high Coulombic efficiency of 99.7%. Excellent cycling performance is obtained even for thick electrodes with an areal capacity of 3.57 mAh cm^-2, similar to those in commercial lithium-ion batteries. The presented Si electrode system has a high volumetric capacity of 598 mAh cm^-3, which is higher than that of the commercial graphite anode materials.

Azo Compounds Derived from Electrochemical Reduction of Nitro Compounds for High Performance Li-Ion Batteries

Organic compounds are desirable alternatives for sustainable lithium-ion battery electrodes. However, the electrochemical properties of state-of-the-art organic electrodes are still worse than commercial inorganic counterparts. Here, a new chemistry is reported based on the electrochemical conversion of nitro compounds to azo compounds for high performance lithium-ion batteries. 4-Nitrobenzoic acid lithium salt (NBALS) is selected as a model nitro compound to systemically investigate the structure, lithiation/delithiation mechanism, and electrochemical performance of nitro compounds. NBALS delivers an initial capacity of 153 mAh g^-1 at 0.5 C and retains a capacity of 131 mAh g^-1 after 100 cycles. Detailed characterizations demonstrate that during initial electrochemical lithiation, the nitro group in crystalline NBALS is irreversibly reduced into an amorphous azo compound. Subsequently, the azo compound is reversibly lithiated/delithiated in the following charge/discharge cycles with high electrochemical performance. The lithiation/delithiation mechanism of azo compounds is also validated by directly using azo compounds as electrode materials, which exhibit similar electrochemical performance to nitro compounds, while having a much higher initial Coulombic efficiency. Therefore, this work proves that nitro compounds can be electrochemically converted to azo compounds for high performance lithium-ion batteries.

A Novel High-Capacity Anode Material Derived from Aromatic Imides for Lithium-Ion Batteries

A novel anode material for lithium-ion batteries derived from aromatic imides with multicarbonyl group conjugated with aromatic core structure is reported, benzophenolne-3,3',4,4'-tetracarboxylimide oligomer (BTO). It could deliver a reversible capacity of 829 mA h g^-1 at 42 mA g^-1 for 50 cycles with a stable discharge plateaus ranging from 0.05-0.19 V versus Li⁺ /Li. At higher rates of 420 and 840 mA g^-1 , it can still exhibit excellent cycling stability with a capacity retention of 88% and 72% after 1000 cycles, delivering capacity of 559 and 224 mA h g^-1 . In addition, a rational prediction of the maximum amount of lithium intercalation is proposed and explored its possible lithium storage mechanism.

Amino group enhanced phenazine derivatives as electrode materials for lithium storage

The development of organic molecule-based batteries is hampered by stability issues caused by the dissolution of the active organic materials in electrolytes. Herein, phenazine (PNZ) and 2,3-diaminophenazine (DAP) are investigated as organic electrode materials. The presence of amino functional groups in DAP dramatically enhances its electrochemical performances due to suppressed dissolution in the electrolyte.

Conjugated Polymers for Flexible Energy Harvesting and Storage

Since the discovery of conjugated polymers in the 1970s, they have attracted considerable interest in light of their advantages of having a tunable bandgap, high electroactivity, high flexibility, and good processability compared to inorganic conducting materials. The above combined advantages make them promising for effective energy harvesting and storage, which have been widely studied in recent decades. Herein, the key advancements in the use of conjugated polymers for flexible energy harvesting and storage are reviewed. The synthesis, structure, and properties of conjugated polymers are first summarized. Then, their applications in flexible polymer solar cells, thermoelectric generators, supercapacitors, and lithium-ion batteries are described. The remaining challenges are then discussed to highlight the future direction in the development of conjugated polymers.

Self-Assembled Biomolecular 1D Nanostructures for Aqueous Sodium-Ion Battery

Aqueous sodium-ion battery of low cost, inherent safety, and environmental benignity holds substantial promise for new-generation energy storage applications. However, the narrow potential window of water and the enlarged ionic radius because of hydration restrict the selection of electrode materials used in the aqueous electrolyte. Here, inspired by the efficient redox reaction of biomolecules during cellular energy metabolism, a proof of concept is proposed that the redox-active biomolecule alizarin can act as a novel electrode material for the aqueous sodium-ion battery. It is demonstrated that the specific capacity of the self-assembled alizarin nanowires can reach as high as 233.1 mA h g^-1, surpassing the majority of anodes ever utilized in the aqueous sodium-ion batteries. Paired with biocompatible and biodegradable polypyrrole, this full battery system shows excellent sodium storage ability and flexibility, indicating its potential applications in wearable electronics and biointegrated devices. It is also shown that the electrochemical properties of electrodes can be tailored by manipulating naturally occurring 9,10-anthroquinones with various substituent groups, which broadens application prospect of biomolecules in aqueous sodium-ion batteries.

Aromatic Polyimide/Graphene Composite Organic Cathodes for Fast and Sustainable Lithium-Ion Batteries

A composite organic cathode material based on aromatic polyimide (PI) and highly conductive graphene was prepared through a facile in situ polymerization method for application in lithium-ion batteries. The in situ polymerization generated intimate contact between PI and electronically conductive graphene, resulting in conductive composites with highly reversible redox reactions and good structure stability. The synergistic effect between PI and graphene enabled not only a high reversible capacity of 232.6 mAh g^-1 at a charge-discharge rate of C/10 but also exceptionally high-rate cycling stability, that is, a high capacity of 108.9 mAh g^-1 at a very high charge-discharge rate of 50C with a capacity retention of 80 % after 1000 cycles. This improved electrochemical performance resulted from the combination of stable redox reversibility of PI and high electronic conductivity of the graphene additive. The graphene-based composite also exhibited much better performance than composites based on multi-walled carbon nanotubes and the conductive carbon black C45 in terms of specific capacity and long-term cycling stability under the same charge-discharge rates.

Probing electrochemical reactions in organic cathode materials via in operando infrared spectroscopy

Organic materials are receiving an increasing amount of attention as electrode materials for future post lithium-ion batteries due to their versatility and sustainability. However, their electrochemical reaction mechanism has seldom been investigated. This is a direct consequence of a lack of straightforward and broadly available analytical techniques. Herein, a straightforward in operando attenuated total reflectance infrared spectroscopy method is developed that allows visualization of changes of all infrared active bands that occur as a consequence of reduction/oxidation processes. In operando infrared spectroscopy is applied to the analysis of three different organic polymer materials in lithium batteries. Moreover, this in operando method is further extended to investigation of redox reaction mechanism of poly(anthraquinonyl sulfide) in a magnesium battery, where a reduction of carbonyl bond is demonstrated as a mechanism of electrochemical activity. Conclusions done by the in operando results are complemented by synthesis of model compound and density functional theory calculation of infrared spectra.

Metal-organic batteries are gaining traction as versatile, low-cost, and sustainable devices, although there are still few ways to probe internal behavior during use. Here, the authors explore organic-molecule structural changes within several battery systems by in operando infrared spectroscopy.

Azo compounds as a family of organic electrode materials for alkali-ion batteries

Organic compounds are desirable for sustainable Li-ion batteries (LIBs), but the poor cycle stability and low power density limit their large-scale application. Here we report a family of organic compounds containing azo group (N=N) for reversible lithiation/delithiation. Azobenzene-4,4'-dicarboxylic acid lithium salt (ADALS) with an azo group in the center of the conjugated structure is used as a model azo compound to investigate the electrochemical behaviors and reaction mechanism of azo compounds. In LIBs, ADALS can provide a capacity of 190 mAh g^-1 at 0.5 C (corresponding to current density of 95 mA g^-1) and still retain 90%, 71%, and 56% of the capacity when the current density is increased to 2 C, 10 C, and 20 C, respectively. Moreover, ADALS retains 89% of initial capacity after 5,000 cycles at 20 C with a slow capacity decay rate of 0.0023% per cycle, representing one of the best performances in all organic compounds. Superior electrochemical behavior of ADALS is also observed in Na-ion batteries, demonstrating that azo compounds are universal electrode materials for alkali-ion batteries. The highly reversible redox chemistry of azo compounds to alkali ions was confirmed by density-functional theory (DFT) calculations. It provides opportunities for developing sustainable batteries.

The rise of organic electrode materials for energy storage

Organic electrode materials are very attractive for electrochemical energy storage devices because they can be flexible, lightweight, low cost, benign to the environment, and used in a variety of device architectures. They are not mere alternatives to more traditional energy storage materials, rather, they have the potential to lead to disruptive technologies. Although organic electrode materials for energy storage have progressed in recent years, there are still significant challenges to overcome before reaching large-scale commercialization. This review provides an overview of energy storage systems as a whole, the metrics that are used to quantify the performance of electrodes, recent strategies that have been investigated to overcome the challenges associated with organic electrode materials, and the use of computational chemistry to design and study new materials and their properties. Design strategies are examined to overcome issues with capacity/capacitance, device voltage, rate capability, and cycling stability in order to guide future work in the area. The use of low cost materials is highlighted as a direction towards commercial realization.

Electron-poor arylenediimides

This review article highlights the emergence of eclectic molecular design principles to realize remarkably strong electron deficient arylenediimide molecules, aspects of their stability and associated applications.

Oxocarbon-functionalized graphene as a lithium-ion battery cathode: a first-principles investigation

In recent years, organic-based, especially carbonyl-based, Li-ion battery electrode materials have attracted great attention due to their low-cost, environmentally friendly nature and strong Li-ion bonding abilities.

Molecular Engineering with Organic Carbonyl Electrode Materials for Advanced Stationary and Redox Flow Rechargeable Batteries

Organic carbonyl electrode materials that have the advantages of high capacity, low cost and being environmentally friendly, are regarded as powerful candidates for next-generation stationary and redox flow rechargeable batteries (RFBs). However, low carbonyl utilization, poor electronic conductivity and undesired dissolution in electrolyte are urgent issues to be solved. Here, we summarize a molecular engineering approach for tuning the capacity, working potential, concentration of active species, kinetics, and stability of stationary and redox flow batteries, which well resolves the problems of organic carbonyl electrode materials. As an example, in stationary batteries, 9,10-anthraquinone (AQ) with two carbonyls delivers a capacity of 257 mAh g^-1 (2.27 V vs Li⁺ /Li), while increasing the number of carbonyls to four with the formation of 5,7,12,14-pentacenetetrone results in a higher capacity of 317 mAh g^-1 (2.60 V vs Li⁺ /Li). In RFBs, AQ, which is less soluble in aqueous electrolyte, reaches 1 M by grafting -SO₃ H with the formation of 9,10-anthraquinone-2,7-disulphonic acid, resulting in a power density exceeding 0.6 W cm^-2 with long cycling life. Therefore, through regulating substituent groups, conjugated structures, Coulomb interactions, and the molecular weight, the electrochemical performance of carbonyl electrode materials can be rationally optimized. This review offers fundamental principles and insight into designing advanced carbonyl materials for the electrodes of next-generation rechargeable batteries.

An Aqueous Ca-Ion Battery

Multivalent-ion batteries are emerging as low-cost, high energy density, and safe alternatives to Li-ion batteries but are challenged by slow cation diffusion in electrode materials due to the high polarization strength of Mg- and Al-ions. In contrast, Ca-ion has a low polarization strength similar to that of Li-ion, therefore a Ca-ion battery will share the advantages while avoiding the kinetics issues related to multivalent batteries. However, there is no battery known that utilizes the Ca-ion chemistry due to the limited success in Ca-ion storage materials. Here, a safe and low-cost aqueous Ca-ion battery based on a highly reversible polyimide anode and a high-potential open framework copper hexacyanoferrate cathode is demonstrated. The prototype cell shows a stable capacity and high efficiency at both high and low current rates, with an 88% capacity retention and an average 99% coloumbic efficiency after cycling at 10C for 1000 cycles. The Ca-ion storage mechanism for both electrodes as well as the origin of the fast kinetics have been investigated. Additional comparison with a Mg-ion cell with identical electrodes reveals clear kinetics advantages for the Ca-ion system, which is explained by the smaller ionic radii and more facile desolvation of hydrated Ca-ions.

Organic Thiocarboxylate Electrodes for a Room-Temperature Sodium-Ion Battery Delivering an Ultrahigh Capacity

Organic room-temperature sodium-ion battery electrodes with carboxylate and carbonyl groups have been widely studied. Herein, for the first time, we report a family of sodium-ion battery electrodes obtained by replacing stepwise the oxygen atoms with sulfur atoms in the carboxylate groups of sodium terephthalate which improves electron delocalization, electrical conductivity and sodium uptake capacity. The versatile strategy based on molecular engineering greatly enhances the specific capacity of organic electrodes with the same carbon scaffold. By introducing two sulfur atoms to a single carboxylate scaffold, the molecular solid reaches a reversible capacity of 466 mAh g^-1 at a current density of 50 mA g^-1 . When four sulfur atoms are introduced, the capacity increases to 567 mAh g^-1 at a current density of 50 mA g^-1 , which is the highest capacity value reported for organic sodium-ion battery anodes until now.

High-Voltage Aqueous Magnesium Ion Batteries

Nonaqueous rechargeable magnesium (Mg) batteries suffer from the complicated and moisture-sensitive electrolyte chemistry. Besides electrolytes, the practicality of a Mg battery is also confined by the absence of high-performance electrode materials due to the intrinsically slow Mg²⁺ diffusion in the solids. In this work, we demonstrated a rechargeable aqueous magnesium ion battery (AMIB) concept of high energy density, fast kinetics, and reversibility. Using a superconcentration approach we expanded the electrochemical stability window of the aqueous electrolyte to 2.0 V. More importantly, two new Mg ion host materials, Li superconcentration approach we expanded the electrochemical stability window of the aqueous electrolyte to 2.0 V. More importantly, two new Mg ion host materials, Li₃V₂(PO₄)₃ and poly pyromellitic dianhydride, were developed and employed as cathode and anode electrodes, respectively. Based on comparisons of the aqueous and nonaqueous systems, the role of water is identified to be critical in the Mg ion mobility in the intercalation host but remaining little detrimental to its non-diffusion controlled process. Compared with the previously reported Mg ion cell delivers an unprecedented high power density of 6400 W kg ion cell delivers an unprecedented high power density of 6400 W kg while retaining 92% of the initial capacity after 6000 cycles, pushing the Mg ion cell to a brand new stage.

Uric Acid as an Electrochemically Active Compound for Sodium-Ion Batteries: Stepwise Na+-Storage Mechanisms of π-Conjugation and Stabilized Carbon Anion

Developing efficient sodium-ion-storage mechanisms to increase the energy capacity in organic electrodes is a critical issue even after this period of prolonged effort. Uric acid (UA), a simple organic compound with three carbonyl groups is demonstrated to be electrochemically active in the insertion/extraction of Na ions. Theoretical calculations and experimental characterizations reveal that the sodium-ion storage by UA is a result of the stepwise mechanisms of p-π conjugation and the carbon anion. Aside from C═O, the functional group C═C(NH-)₂ also provides an efficient Na-storage activated site in which the lone-pair electrons is stabilized through the planar-to-tetrahedral structural transition and low-energy orbital hybridization of N atoms. For further improvement of the electrochemical performance, a uric acid and carbon nanotube (UA@CNT) composite is prepared via a vacuum solution impregnation method. When employed as an anode material for sodium-ion batteries, the UA@CNT composite exhibits high specific capacity, excellent rate capability, and long cycling life even at high current densities. A reversible capacity of over 163 mA h g^-1 is maintained even after 150 cycles at a current density of 200 mA g^-1. The present study paves a way to develop reversible high-capacity organic electrode materials for sodium-ion batteries by a carbon-anion stabilization mechanism.

Crystal structure of N,N'-di-decyl-pyromellitic di-imide

The title compound, C30H44N2O4 [systematic name: 2,6-di-decyl-pyrrolo-[3,4-f]iso-indole-1,3,5,7(2H,6H)-tetra-one], consists of a central pyromellitic di-imide moiety with terminal decyl groups at the N-atom positions. The centre of the mol-ecule lies on a crystallographic inversion centre so the asymmetric unit contains one half-mol-ecule. The mol-ecule exhibits a rod-shaped conformation, like other similar compounds of this type, the distance between the ends of terminal decyl groups being 32.45 Å. The packing is dominated by a lamellar arrangement of the mol-ecules, which is reinforced by C-H⋯O hydrogen bonds and C-O⋯π inter-actions, forming a classic herringbone structure. The mol-ecular structure is consistent with the theoretical calculations performed by density functional theory (DFT).

Emerging Prototype Sodium-Ion Full Cells with Nanostructured Electrode Materials

Due to steadily increasing energy consumption, the demand of renewable energy sources is more urgent than ever. Sodium-ion batteries (SIBs) have emerged as a cost-effective alternative because of the earth abundance of Na resources and their competitive electrochemical behaviors. Before practical application, it is essential to establish a bridge between the sodium half-cell and the commercial battery from a full cell perspective. An overview of the major challenges, most recent advances, and outlooks of non-aqueous and aqueous sodium-ion full cells (SIFCs) is presented. Considering the intimate relationship between SIFCs and electrode materials, including structure, composition and mutual matching principle, both the advance of various prototype SIFCs and the electrochemistry development of nanostructured electrode materials are reviewed. It is noted that a series of SIFCs combined with layered oxides and hard carbon are capable of providing a high specific gravimetric energy above 200 Wh kg^-1 , and an NaCrO₂ //hard carbon full cell is able to deliver a high rate capability over 100 C. To achieve industrialization of SIBs, more systematic work should focus on electrode construction, component compatibility, and battery technologies.

Dispersion-Assembly Approach to Synthesize Three-Dimensional Graphene/Polymer Composite Aerogel as a Powerful Organic Cathode for Rechargeable Li and Na Batteries

Polymer cathode materials are promising alternatives to inorganic counterparts for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) due to their high theoretical capacity, adjustable molecular structure, and strong adaptability to different counterions in batteries, etc. However, they suffer from poor practical capacity and low rate capability because of their intrinsically poor conductivity. Herein, we report the synthesis of self-assembled graphene/poly(anthraquinonyl sufide) (PAQS) composite aerogel (GPA) with efficient integration of a three-dimensional (3D) graphene framework with electroactive PAQS particles via a novel dispersion-assembly strategy which can be used as a free-standing flexible cathode upon mechanical pressing. The entire GPA cathode can deliver the highest capacity of 156 mAh g^-1 at 0.1 C (1 C = 225 mAh g^-1) with an ultrahigh utilization (94.9%) of PAQS and exhibits an excellent rate performance with 102 mAh g^-1 at 20 C in LIBs. Furthermore, the flexible GPA film was also tested as cathode for SIBs and demonstrated a high-rate capability with 72 mAh g^-1 at 5 C and an ultralong cycling stability (71.4% capacity retention after 1000 cycles at 0.5 C) which has rarely been achieved before. Such excellent electrochemical performance of GPA as cathode for both LIBs and SIBs could be ascribed to the fast redox kinetics and electron transportation within GPA, resulting from the interconnected conductive framework of graphene and the intimate interaction between graphene and PAQS through an efficient wrapping structure. This approach opens a universal way to develop cathode materials for powerful batteries with different metal-based counter electrodes.

Three-Dimensional Arylene Diimide Frameworks for Highly Stable Lithium Ion Batteries

Lithium ion batteries are the best commercial technology to satisfy the energy storage needs of current and emerging applications. However, the use of transition-metal-based cathodes precludes them from being low-cost, sustainable, and environmentally benign, even with recycling programs in place. In this study, we report a highly stable organic material that can be used in place of the transition-metal cathodes. By creating a three-dimensional framework based on triptycene and perylene diimide (PDI), a cathode can be constructed that mitigates stability issues that organic electrodes typically suffer from. When a lithium ion battery is assembled using the PDI-triptycene framework (PDI-Tc) cathode, a capacity of 75.9 mAh g^-1 (78.7% of the theoretical value) is obtained. Importantly, the battery retains a near perfect Coulombic efficiency and >80% of its capacity after cycling 500 times, which is the best value reported to date for PDI-based materials.

Electrochemical and structural investigation of the interactions between naphthalene diimides and metal cations

Cyclic voltammetry and X-ray diffraction studies reveal the strength and nature of the interactions between Li⁺/Mg²⁺ and reduced naphthalene diimides.

Crystal structure of N,N'-di-benzyl-pyromellitic diimide

The title compound, C24H16N2O4 [systematic name: 2,6-di-benzyl-pyrrolo-[3,4-f]iso-indole-1,3,5,7(2H,6H)-tetra-one], consists of a central pyromellitic di-imide moiety with terminal benzyl groups at the N-atom positions. The mol-ecule is located about an inversion centre, so the asymmetric unit contains one half-mol-ecule. In the mol-ecule, both terminal phenyl groups, tilted by 72.97 (4)° with respect to the mean plane of the central pyromellitic di-imide moiety (r.m.s. deviation = 0.0145 Å), are oriented away from each other, forming an elongated S-shaped conformation. In the crystal, mol-ecules are connected via weak C-H⋯O hydrogen bonds and C-H⋯π inter-actions, resulting in the formation of supra-molecular layers extending parallel to the ab plane.

Highly durable organic electrode for sodium-ion batteries via a stabilized α-C radical intermediate

It is a challenge to prepare organic electrodes for sodium-ion batteries with long cycle life and high capacity. The highly reactive radical intermediates generated during the sodiation/desodiation process could be a critical issue because of undesired side reactions. Here we present durable electrodes with a stabilized α-C radical intermediate. Through the resonance effect as well as steric effects, the excessive reactivity of the unpaired electron is successfully suppressed, thus developing an electrode with stable cycling for over 2,000 cycles with 96.8% capacity retention. In addition, the α-radical demonstrates reversible transformation between three states: C=C; α-C·radical; and α-C- anion. Such transformation provides additional Na+ storage equal to more than 0.83 Na+ insertion per α-C radical for the electrodes. The strategy of intermediate radical stabilization could be enlightening in the design of organic electrodes with enhanced cycling life and energy storage capability.

Achieving High Aqueous Energy Storage via Hydrogen-Generation Passivation

A new design strategy for polyimides/carbon nanotube networks is reported, aiming to passivate the hydrogen-evolution mechanism on the molecular structures of electrodes, thus substantially boosting their aqueous energy-storage capabilities. The intrinsic sluggish hydrogen-evolution activity of polyimides is further passivated via Li(+) association during battery charging, leading to a much wider voltage window and exceptional energy-storage capability.