Self-discharge Of Supercapacitors Research Articles

Nitrogen-Doped Cellulose-Derived Porous Carbon Fibers for High Mass-Loading Aqueous Supercapacitors.

Biomass-based porous carbon with renewability and flexible structure tunability is a promising electrode material for supercapacitors. However, there is a huge gap between experimental research and practical applications. How to maintain good electrochemical performance of high mass-loading electrodes and suppress the self-discharge of supercapacitors is a key issue that urgently needs to be addressed. The structure regulation of electrode materials such as heteroatom doping is a promising optimization strategy for high mass-loading electrodes. In this work, nitrogen-doped cellulose-derived porous carbon fibers (N-CHPCs) were prepared by a facile bio-template method using cotton cellulose as raw material and urea as dopant. The prepared N-CHPCs have high specific surface area, excellent hierarchical porous structure, partial graphitization properties and suitable heteroatom content. The assembled high mass-loading (12.8 mg cm-2; 245 μm) aqueous supercapacitor has excellent electrochemical performance, i. e., low open-circuit voltage attenuation rate (21.39 mV h-1), high voltage retention rate (78.81 %), high specific capacitance (295.8 F g-1 at 0.1 A g-1), excellent area capacitance (3.79 F cm-2 at 0.1 A g-1), excellent cycling stability (97.28 % over 20,000 cycles at 1.0 A g-1). The excellent performance of high mass-loading N-CHPCs is of great significance for their practical applications in advanced aqueous supercapacitors.

Constructing bilayer heterogeneous organogel electrolytes of Lewis acidic/basic polymers to suppress self-discharge of supercapacitors

Flexible supercapacitors with fast charging rate, long cyclic lifetime and high power density, but often suffer from their rapid self-discharge process, which remains a big challenge for their widely commercial application. Here, we for the first time report a bilayer heterogeneous organogel electrolyte (BHOE) consisting of a layer of Lewis acidic polymer (LAP) and a layer of Lewis basic polymer (LBP), to develop high-performance flexible supercapacitors with slow self-discharge process. The existing strong coordination interaction between the charged LAP (or LBP) and its counter anions (or cations) can effectively restrict the diffusion of ions accumulated on/in the electrodes into or throughout the bilayer electrolyte, which endowed the charged BHOE-based supercapacitor with slow self-discharge time (9.7 h) from its open-circuit voltage to the half, more than ten times longer than those (0.9 h) of devices based homogeneous LAP or LBP electrolytes. Furthermore, the BHOE-based supercapacitor possessed high capacitance retention up to 95 % after thousands of folding cycles, suggesting excellent mechanical flexibility. This study provides a novel strategy to build high-performance flexible supercapacitors with slow self-discharge, which is great meaningful for their practical application in the near future.

Reduced self-discharge of supercapacitors based on surfactant-functionalized NiAl layered double hydroxide

Nickel aluminum layered double hydroxide (NiAl LDH) is an important pseudocapacitive electrode material for its low cost, facile preparation method, and high specific capacity. Due to the lack of chemical stability, however, NiAl LDH-based supercapacitors typically suffer from fast self-discharge. Herein, we report that NiAl LDH functionalized with sodium dodecyl sulfonate (SDS) can show much suppressed self-discharge for supercapacitors assembled from NiAl LDH positive electrodes and activated carbon negative electrodes. Compared to pristine NiAl LDH, the introduction of SDS in NiAl LDH leads to slower decay of open circuit voltage (26.7 vs. 11.6 h for a voltage decay from 1.6 to 0.42 V), reduced leakage current (1.2 vs. 0.17 mA at a charging voltage of 1.6 V), and improved capacitance retention (77 % vs. 49 % after resting for 4 h). The slower self-discharge can be attributed to the negatively charged hydrophobic layer on the surface of SDS-functionalized NiAl LDH particles so that the access of OH− ions to the electrode surface is impeded. As a result, the oxidization of OH− as a main process for the self-discharge of NiAl LDH is largely suppressed.

Regulating the synergy coefficient of composite materials for alleviating self-discharge of supercapacitors

Supercapacitor is an efficient energy storage device, yet its wider application is still limited by self-discharge. Currently, various composite materials have been reported to have improved inhibition on self-discharge, while the evaluation of the synergistic effect in composite materials is challenging. Herein, pairs of intercalation type pseudocapacitive niobium oxides are pre-lithiated and coupled to construct conjugatedly configured supercapacitors, within which the cathode and anode experience identical reaction environment with single type of charge carrier, thus providing ideal platform to quantify the synergistic effect of composite materials on the self-discharge process. By using titanium dioxide as the stabilizer, we have compared how the modes of forming composite would influence the self-discharge performance of the active composite materials with similar ratio of the constituent materials. Specifically, core@shell Nb2O5@TiO2 composite using TiO2 as the shell shows significantly higher synergy coefficient (µ = 0.61, defined as the value that evaluates the synergistic effect between composite materials, and can be quantified using the overall performance of the composite, performance of individual component as well as the ratio of the component.) than other control group samples, which corresponds to the highest retained energy of 63% at 100 h. This work is expected to provide a general method for quantifying the synergistic effect and guide the design of composite materials with specific mode of forming the composite.

Deterministic Effect of the Solid-State Diffusion Energy Barrier for a Charge Carrier on the Self-Discharge of Supercapacitors

Deterministic Effect of the Solid-State Diffusion Energy Barrier for a Charge Carrier on the Self-Discharge of Supercapacitors

Binder-controlled pore size distribution of carbon electrodes to mitigate self-discharge of supercapacitors

Self-discharge, which refers to voltage depression when a power source is removed, is a crucial issue for supercapacitors (SCs). Self-discharge results in Coulombic efficiency loss and energy dissipation, and thus restricts the charge storage performance of SCs. A cost-effective and facile strategy for addressing self-discharge is newly developed in this work. It is found that self-discharge involves charge redistribution and Faradaic side reactions, which are closely associated with the pore size of activated carbon electrodes. Importantly, the pore size distribution (and thus self-discharge) can be controlled by the binder type. Specifically, a binder that maintains high macropore and mesopore fractions can effectively mitigate self-discharge. The fundamental reasons for this finding are examined. The effects of the charging rate, holding time at the full charging voltage, operation temperature, and charging cutoff voltage on the self-discharge of SCs prepared using various binders are investigated. The data reveal that binder selection also influences SC reliability in terms of the aging rate at elevated temperature and high voltage, leakage current, and gas evolution during operation.

Self-Discharge of Supercapacitors: A Review

The literature on the self-discharge of supercapacitors is reviewed, the advantages of electrochemical supercapacitors over batteries are formulated. The principal disadvantage of the electrochemical supercapacitors is their rapid self-discharge. A study of self-discharge of electrochemical supercapacitors was conducted; methods of the self-discharge studying, the effect of functional carbon groups on the self-discharge, the self-discharge mechanisms and mathematical modeling of the self-discharge are described. The development of new supercapacitor devices destined to minimize the self-discharge is described, including additives to the electrolyte, solid-state supercapacitors, electrochemical supercapacitors with ion-exchange membranes, the using of pure electrolytes, methods of the electrode chemical modification to slow down self-discharge. A study of self-discharge of electrochemical supercapacitors with electrodes based on activated carbon cloth CH 900 (the Kuraray Co. production) and 1 M MgSO4 aqueous electrolyte is conducted. The rate of self-discharge after ~70 min after its start is found to be proportional to the charging voltage. The voltage dependence of the self-discharge rate at 2000 min after its start goes through a minimum. This minimum is explained, firstly, by a significant contribution to the capacity from the Faradaic redox-reaction pseudo-capacity involving the functional groups; secondly, the very presence of these groups increases the self-discharge rate. It is the former factor that dominates in the low-voltage region; the second one, in the high voltage region.

Self-Discharge of Supercapacitors: A Review

Self-Discharge of Supercapacitors: A Review

Screening the deep eutectic electrolytes for supercapacitors with alleviated self-discharge

The functional groups in HBD for deep eutectic electrolytes have a profound impact on the self-discharge of supercapacitors.

Self-discharge mitigated supercapacitors via hybrid CuO-nickel sulfide heterostructure for energy efficient, wireless data storage application

With the surge of demand for instant high power in miniaturized electronic and mechanical systems, supercapacitors (SCs) are considered as one of the viable candidates to fulfill the requirements. Thus, long-term resilience and superior energy density associated with self-discharge in SCs are obviously critical, but securing electrode materials, which can meet both benefits of SCs and persist charged potential for a comparatively prolonged duration, are still elusive. Herein, hierarchically refined nickel-sulfide heterostructure (CuO-NS) on CuO (CO) scaffold is achieved through optimized film formation, exhibiting a threefold improvement in the essential electrochemical characteristics and outstanding capacitance retention (∼5% loss). Self-discharge behavior and its mechanism are systematically investigated via morphological control and nanostructural evolution. Furthermore, significant mitigation of self-discharge owing to an increase in surface area and refined nanostructure is displayed. Remarkably, CuO-NS2 (20 cycle overcoating) based SC can retain over 60% of the charged potential for a complete voltage holding and a self-discharge test for 16 h. An appealing demonstration of wireless power transmission in burst mode is demonstrated for secure digital (SD) card data writing, powered by SCs, which substantiates that it can be readily leveraged in power management systems. This enables us to realize one of the envisioned applications soon.

Effects of electrode mass loading on the self-discharge of supercapacitors

Electrode mass loading is an important device parameter for supercapacitors and its effect on electrochemical properties such as energy density, rate performance, and cycle stability has been widely reported. However, how the self-discharge of supercapacitors varies under different mass loadings has not been examined systematically. In this study, we prepared porous activated carbon (AC) electrodes with a series of mass loadings and investigated their self-discharge behavior. It is found that with the increase in mass loadings, the decay rates of open circuit voltages (OCVs) are reduced substantially. Specifically, when the electrode mass loading increased from 0.6 to 10.6 mg cm−2, the cell OCV decay rate at a charging voltage of 1.6 V dropped from 1.07 to 0.05 mV mF−1 hr−1, indicating much slower self-discharge rates at higher mass loadings. Analysis of the self-discharge mechanism suggests that faradaic reactions are the major self-discharge processes for the supercapacitors after float charging. While the OCV decays due to both activation-controlled and diffusion-controlled faradaic reactions are reduced at high mass loadings, the self-discharge attributing to diffusion-controlled faradaic reactions is more affected due to the deeper pores and longer diffusion paths for electrolyte and reactive species in thicker electrodes.

Polydopamine-coated graphene for supercapacitors with improved electrochemical performances and reduced self-discharge

Graphene-based supercapacitors have attracted significant attention owning to the high specific surface area and electrical conductivity of graphene with the potential to deliver superior energy and power performances than other supercapacitor materials. However, graphene-based supercapacitors inevitably have self-discharge behavior like any other supercapacitors, resulting in rapid voltage drop and limiting their applications for long-term energy storage. Reported methods for mitigating the self-discharge of graphene-based supercapacitors are often associated with deteriorated performances such as decreased specific capacitances or rate performances. Here we report that self-polymerized dopamine on the surface of graphene can reduce the self-discharge of supercapacitors while achieving improved specific capacitance and rate performance. Specifically, a 40% increase in specific capacitance (150.8 vs. 108.0 F g–1 at 0.1 A g–1), much improved capacitance retention at high currents (80% vs. 55% at 10 A g–1), and a 37% reduction in open circuit voltage (OCV) decay rate (0.33 V vs. 0.52 V in 12 h) were attained simultaneously after PDA-coating on graphene. Analysis of the open circuit potential attenuation of both positive and negative electrodes of the supercapacitors suggests that the coating of PDA suppressed the self-discharge caused by diffusion-controlled faradaic reaction process. This can be attributed to the catechol and amine functional groups of PDA which not only offered additional pseudocapacitance when the electrodes were charged but also served as trapping sites for dissolved impurity ions and oxygen molecules so that the reactions of these species on graphene surface were impeded during open circuit test, leading to both improved energy storage performances and reduced self-discharge rate.

Synthesis and structure regulation of armor-wearing biomass-based porous carbon: Suppression the leakage current and self-discharge of supercapacitors

Biomass-based porous carbon is a very promising electrode material for supercapacitors, but adverse leakage current and self-discharge has hindered its practical applications. Herein, high-performance armor-wearing biomass-based porous carbon (NP-RHPC) was prepared with finely adjustable surface properties and micro-structure using rice husk as carbon source and coal pitch as chemical modification reagent. The synergetic effect of the stable biochar skeleton and the pitch carbon armor ensures NP-RHPC has low leakage current and self-discharge, long cyclic stability, and good rate performance. The leakage current and open circuit voltage attenuation rate of NP-RHPC are lower than those of N-RHPC without pitch carbon armor and the commercial capacitor carbon of YP-50F. The synthesized NP-RHPC has ideal specific capacitance of 209.2 F g−1 and the capacitance retention rate is up to 95.0% over 20,000 cycles at a high current density of 1.0 A g−1, which is higher than that of N-RHPC. This impressively long-term cyclic performance of NP-RHPC can be ascribed to the excellent electrical conductivity and especially the reduction of the unstable oxygen-containing groups. This study provides insights for the rational design of high-performance armor-wearing biomass-based porous carbon electrode material towards the advanced application of biomass and coal pitch in energy storage.

Self-discharge of a supercapacitor with electrodes based on activated carbon cloth

• Self-discharge of a supercapacitor with activated carbon cloth electrodes was investigated. • The dependence of the self-discharge rate on voltage has a minimum. • An equivalent electric circuit of a supercapacitor has been developed from impedance measurements. A study of the self-discharge of supercapacitor (SC) with electrodes based on the activated carbon (AC) cloth CH 900 of the Kuraray Company with an aqueous electrolyte of 1 M MgSO 4 was conducted. The elemental composition of the positive and negative electrodes after electrochemical treatment up to 1.6 V began to radically differ from each other. A very high concentration of hydrogen and oxygen appeared on the positive electrode, which is explained by the formation of functional surface groups (FSG). It was found that the logarithm of the self-discharge rate after 70 min is proportional to the charging voltage. Self-discharge rate dependences on the charge voltage after 1000 and 2000 min have its minimums. These minimums is explained by the action of two oppositely directed mechanisms. First, the pseudocapacity of Faraday redox reactions of FSG makes a significant contribution to the capacity, and second, the very presence of these groups increases the self-discharge rate. At low voltages, the first factor dominates, and at high voltages, the second factor. Based on impedance measurements for small self-discharge times, an equivalent electric circuit of the SC cell has been developed. It is shown that the resistance of the leakage current decreases with voltage increasing, which corresponds with measurements of the self-discharge rate. It is also shown that the self-discharge rate of the SC after 2000 charge–discharge cycles is lower than that corresponding to the initial state of the cell, which is explained by the presence of the FSG.

An Effective Designing of Supercapacitor Mitigating Self-Discharge

Supercapacitor is a kind of effective energy storage device with merits such as high power density, long cycling life and so on, but their application is limited nowadays compared to the application of batteries. One important restriction is because of the serious self-discharge in supercapacitors, and how to conquer the self-discharge problem is an important issue. In this article we propose an effective way to reduce self-discharge of the supercapacitor by carefully designing of activated carbon (ACs) electrodes and water-in salt electrolyte. The electrochemical characterization shows that our supercapacitor can have the ability to reduce self-discharge.

Binder-Controlled Pore Size Distribution of Carbon Electrodes to Mitigate Self-Discharge of Supercapacitors

Binder-Controlled Pore Size Distribution of Carbon Electrodes to Mitigate Self-Discharge of Supercapacitors

Self-discharge of supercapacitors based on carbon nanosheets with different pore structures

Self-discharge is an important factor to be considered for practical applications of supercapacitors (SCs). While the transport of electrolyte ions largely determines the rate performance of SCs, it also affects their self-discharge rate. In this work, three carbon materials, namely stacking carbon nanosheets (S-CNSs), double-layer carbon nanosheets (DL-CNSs), and flower-like carbon nanosheets (FL-CNSs), with similar pore sizes but different pore structures were synthesized. Due to the different pore structures and correspondingly different ion transport resistances, the rate performances increased from S-CNS, FL-CNS, to DL-CNS SCs. On the other hand, the self-discharge rates increased following the same order – the open circuit voltage dropped from 2.0 to 0.99, 0.74, and 0.53 V after 24 h for S-CNS, FL-CNS, and DL-CNS SCs, respectively. Analysis of the self-discharge processes indicates a combined diffusion-controlled and ohmic leakage self-discharge mechanism and a larger diffusion constant was found for DL-CNS than that of FL-CNS and S-CNS SCs, consistent with their order of self-discharge rates. The results of this work suggest that although fast ion transport is beneficial to the rate performance of SCs, it may also lead to fast self-discharge and limit the duration of energy storage.

Recent research advances of self-discharge in supercapacitors: Mechanisms and suppressing strategies

This review summarized and discussed the mechanisms of self-discharge supercapacitors, with a focus on suppressing strategies in terms of electrode, electrolyte, and separator. The remained challenges and the promising directions in suppressing the self-discharge of supercapacitors were also presented and summed up. Supercapacitors are one of the most promising energy storage devices in the fields of vehicle transportation, flexible electronic devices, aerospace, etc. However, the existed self-discharge that is the spontaneous voltage decay after supercapacitors are fully charged, brings about the wide gap between experimental studies and practical utilization of supercapacitors. Although eliminating the self-discharge completely is not reachable, suppressing the self-discharge rate to the lowest point is possible and feasible. So far, the significant endeavors have been devoted to achieve this goal. Herein, we summary and discuss the possible mechanisms for the self-discharge and the underlying influence factors. Moreover, the strategies to suppress the self-discharge are systemically summed up by three independent but unified aspects: modifying the electrode, modulating the electrolyte and tuning the separator. Finally, the major challenges to suppress the self-discharge of supercapacitors are concluded and the promising strategies are also pointed out and discussed. This review is presented with the view of serving as a guideline to suppress the self-discharge of supercapacitors and to across-the-board facilitate their widespread application.

Ion-Exchange Separators Suppressing Self-Discharge in Polymeric Supercapacitors

Author(s): Wang, K; Yao, L; Jahon, M; Liu, J; Gonzalez, M; Liu, P; Leung, V; Zhang, X; Ng, TN | Abstract: Supercapacitors offer superior cycle life and high power densities, but as energy storage devices, they are limited by self-discharge processes manifested as large potential decay and leakage current, resulting in loss of stored energy and low charging efficiency. To minimize Faradaic side reactions, this Letter has incorporated a sulfonate ion-exchange resin in separators to trap impurities and thereby suppress self-discharge in supercapacitors with PEDOT as redox electrodes. The versatile separator design is generally applicable to organic and aqueous electrolytes and compatible with a pH range of 0-14, while maintaining the device capacitance and rate performance. Temperature-dependent characteristics were analyzed to identify that the reduction of impurity concentration and diffusion was key to improve potential retention. Compared to devices using commercially available separators, the device here exhibited a lower leakage current and better charging efficiency. It was demonstrated to work with radio frequency energy-harvesting circuits and showed the potential to serve as an energy reservoir for wireless electronic applications.

Self-discharge of supercapacitors based on carbon nanotubes with different diameters

The self-discharge of supercapacitors was investigated using electrodes composed of multiwalled carbon nanotubes (MWCNTs) of three different diameters: 20, 30, and 50 nm, respectively. A combined self-discharge mechanism including both ohmic leakage and diffusion-controlled faradaic reaction was employed to fit the open circuit voltage (OCV) decays of the supercapacitors. The existence of both large inter-bundle pores and small intra-bundle pores in the MWCNT electrodes led to a two-stage diffusion-controlled faradaic reaction process - while the first stage can be described as a divided diffusion-controlled (DDC) process due to the diffusion of ions from both inter- and intra-bundle pores, and the second stage corresponds to a single diffusion-controlled (SDC) process mainly due to the diffusion of ions from the intra-bundle pores. The diffusion parameters obtained based on this model were consistent with the measured self-discharge rates which increased with the size of the MWCNTs. The results of this work demonstrate that electrode materials with wide pore size distributions may be associated with more complex self-discharge processes.