Rapid Energy Release Research Articles

Giant Protostellar Flares: Accretion-driven Accumulation and Reconnection-driven Ejection of Magnetic Flux in Protostars

Abstract Protostellar flares are rapid magnetic energy release events associated with the formation of hot plasma in protostars. In the previous models of protostellar flares, the interaction between a protostellar magnetosphere with the surrounding disk plays crucial role in building-up and releasing the magnetic energy. However, it remains unclear if protostars indeed have magnetospheres because vigorous disk accretion and strong disk magnetic fields in the protostellar phase may destroy the magnetosphere. Considering this possibility, we investigate the energy accumulation and release processes in the absence of a magnetosphere using a three-dimensional magnetohydrodynamic simulation. Our simulation reveals that protostellar flares are repeatedly produced even in such a case. Unlike in the magnetospheric models, the protostar accumulates magnetic energy by acquiring large-scale magnetic fields from the disk by accretion. Protostellar flares occur when a portion of the large-scale magnetic fields are removed from the protostar as a result of magnetic reconnection. Protostellar flares in the simulation are consistent with observations; the released magnetic energy (up to ∼3 × 1038 erg) is large enough to drive observed flares, and the flares produce hot ejecta. The expelled magnetic fields enhance accretion, and the energy build-up and release processes are repeated as a result. The magnetic flux removal via reconnection leads to redistribution of magnetic fields in the inner disk. We therefore consider that protostellar flares will play an important role in the evolution of the disk magnetic fields in the vicinity of protostars.

Monitoring gear surface degradation using cyclostationarity of acoustic emission

Abstract This paper aims at establishing a correlation between gear wear in spur gears and the statistical properties of AE signals. A generalised Gaussian cyclostationary model is proposed for AE signals measured on gears. This choice is motivated by the characteristics of lubricated contact in spur gears, combining non-stationarity (i.e. cyclostationarity) and non-Gaussianity (i.e. impulsiveness). The former is due to the cyclic kinematics of gear tooth meshing, which leads to a periodicity in the statistics of the AE signal, while the latter is caused by rapid energy release from asperity deformation during gear tooth contact. Two gear wear indicators are defined and estimated based on this assumption (cyclic kurtosis and cyclic scale parameter) and their evolution is monitored against direct measurements of surface degradation in an endurance test. Results show that the proposed indicators are sensitive to monitoring wear phenomena on gear tooth surfaces.

(Invited) Understanding Downstream Risk from Lithium-Ion Battery Thermal Runaway & Designing for Safety

With continued advances in battery technologies, batteries have become one of the leading solutions for not only portable power applications but also energy storage applications. Because of the high energy density in advanced batteries, one key safety goal is preventing the unintended release of stored energy. A catastrophic failure of a battery pack can occur if one or more cells in the battery pack undergo a thermal runaway event that results in a rapid release of the stored energy in the battery. Thermal runaway can lead to a release of flammable gases and heat, which can potentially result in fire and explosions. The design of effective thermal management systems or fire mitigation systems requires proper quantification of the thermal failure characteristics. This presentation will detail several research activities that have been developed to analyze and quantify thermal safety aspects of batteries, as well as to identify/quantify potential toxicology hazards. This process involves real-time gas analysis from lithium-ion battery failure events, as well as post-failure composition analysis and identification of gas combustion properties. The implications of this work toward designing for safety and integration into risk analyses will be discussed.

Study on Rock Burst Event Disaster and Prevention Mechanisms of Hard Roof

Coal mining under hard roofs is jeopardized by rock burst‐induced hazards. In this paper, mechanisms of hard roof rock burst events and key techniques for their prevention are analyzed from the standpoint of energy evolution within geological conditions typical of the hard roofs found in Chinese coal mines. Equations used to calculate the total strain energy densities of the coal‐rock mass and hard roof working face are derived. Moreover, several failure‐causing energy evolution rules are analyzed under various conditions. Various rock roof and coal mass thicknesses and strengths are considered, and a method of preventing hard roof rock burst events is proposed. The results obtained show that rock burst events can be facilitated by high stress concentrations, significant accumulation of strain energy in the coal‐rock mass, and rapid energy release during roof breakage. The above conditions are subdivided into two classes: energy accumulation and energy release. The total strain energies of the coal mass and working faces in the roof are positively correlated with the roof thickness, roof strength, and coal mass strength. The coal mass strength primarily influences the overall accumulation of energy in the working face, and it also has the largest effect on the total energy release (i.e., the earthquake magnitude).

OH* Chemiluminescence Imaging of the Combustion Products From a Methane-Fueled Rotating Detonation Engine

Pressure gain combustion (PGC) has been conceived to convert fuel's chemical energy into thermal energy and mechanical energy, thereby reducing the entropy production in the process. Recent research has shown that the rotating detonation combustor (RDC) can provide excellent specific thrust, specific impulse, and pressure gain within a small volume through rapid energy release by continuous detonation in the circumferential direction. The RDC as a PGC system for power generating gas turbines in combined cycle power plants could provide significant efficiency gains. However, few past studies have employed fuels that are relevant to power generation turbines, since RDC research has focused mainly on propulsion applications. In this study, we present experimental results from RDC operated on methane and oxygen-enriched air to represent reactants used in land-based power generation. The RDC is operated at a high pressure by placing a back-pressure plate downstream of the annular combustor. Past studies have focused mainly on probe measurements inside the combustor, and thus, little information is known about the nature of the products exiting the RDC. In particular, it is unknown if chemical reactions persist outside the RDC annulus, especially if methane is used as the fuel. In this study, we apply two time-resolved optical techniques to simultaneously image the RDC products at framing rate of 30 kHz: (1) direct visual-imaging to identify the overall size and extent of the plume, and (2) OH* chemiluminescence imaging to detect the reaction zones if any. Results show dynamic features of the combustion products that are consistent with the probe measurements inside the rotating detonation engine (RDE). Moreover, presence of OH* in the products suggests that the oblique shock wave and reactions persist downstream of the detonation zone in the RDC.

Simulation of induced acoustic emission in fractured porous media

Acoustic/microseismic Emissions (AE) in naturally fractured porous media are the result of local instability along internal interfaces and the sudden release of strain energy stored in the rock matrix. This rapid release of energy, stimulates high-frequency components of the dynamic response of the rock mass, inducing mechanical wave propagation. In this article an enriched finite element model is employed to concurrently simulate the interface instability and the induced wave propagation processes in a fractured porous media. Harmonic enrichment functions are used in the context of the Generalized Finite Element Method (GFEM) to suppress the spurious oscillations that can appear in wave propagation/dynamic modelings using regular finite elements. To model the fractures, the Phantom Node Method (PNM) is employed with the GFEM. The frictional contact condition at material interfaces is modeled using a stable augmented Lagrange multiplier approach. Through various parametric studies it’s shown that (i) decreasing the permeability leads to an increase in the frequency and a decrease in the amplitude of the acoustic signal; (ii) increasing viscous damping leads to narrower frequency spectrum and decreased magnitude of the emitted acoustic signal; (iii) increasing damping leads to a transition from transient wave propagation to diffusion-dominated AE response; (iv) increasing interface friction leads to more pronounced stick-slip behavior and higher amplitude AE-without interface friction there is no AE. Lastly, the numerical illustrations demonstrate the superior capability of the enriched model (in comparison with regular finite element models) in suppressing the spurious oscillations in AE solutions.

Comparison of seismic effects during deep tunnel excavation with different methods

The rapid release of strain energy is an important phenomenon leading to seismic events or rock failures during the excavation of deep rock. Through theoretical analysis of strain energy adjustment during blasting and mechanical excavation, and the interpretation of measured seismicity in the Jin-Ping II Hydropower Station in China, this paper describes the characteristics of energy partition and induced seismicity corresponding to different energy release rates. The theoretical analysis indicates that part of the strain energy will be drastically released accompanied by violent crushing and fragmentation of rock under blast load, and this process will result in seismic events in addition to blasting vibration. The intensity of the seismicity induced by transient strain energy release highly depends on the unloading rate of in-situ stress. For mechanical excavation, the strain energy, which is mainly dissipated in the deformation of surrounding rock, releases smoothly, and almost no seismic events are produced in this gradual process. Field test reveals that the seismic energy transformed from the rock strain energy under high stress condition is roughly equal to that coming from explosive energy, and the two kinds of vibrations superimpose together to form the total blasting excavation-induced seismicity. In addition, the most intense seismicity is induced by the cut blasting delay; this delay contributes 50% of the total seismic energy released in a blast event. For mechanical excavation, the seismic energy of induced vibration (mainly the low intensity acoustic emission events or mechanical loading impacts), which accounts only for 1.5‰ of that caused by in-situ stress transient releasing, can be ignored in assessing the dynamic response of surrounding rock.

Chromospheric Response during the Precursor and the Main Phase of a B6.4 Flare on 2005 August 20

Abstract Solar flare precursors depict a constrained rate of energy release, in contrast to the imminent rapid energy release, which calls for a different regime of plasma processes to be at play. Due to the subtle emission during the precursor phase, its diagnostics remain delusive, revealing either nonthermal electrons (NTEs) or thermal conduction to be the driver. In this regard, we investigate the chromospheric response during various phases of a B6.4 flare on 2005 August 20. Spatiotemporal investigation of flare ribbon enhancement during the precursor phase, carried out using spectra images recorded in several wavelength positions on the Hα line profile, revealed its delayed response (180 s) compared to the X-ray emission, as well as a sequential increment in the width of the line profile, which are indicative of a slow heating process. However, the energy contained in the Hα emission during the precursor phase can reach as high as 80% of that estimated during the main phase. Additionally, the plasma hydrodynamics during the precursor phase, resulting from the application of a single-loop one-dimensional model, revealed the presence of a power-law extension in the model-generated X-ray spectra, with a flux lower than the RHESSI background. Therefore, our multiwavelength diagnostics and hydrodynamical modeling of the precursor emission indicates the role of a two-stage process. First, reconnection-triggered NTEs, although too small in flux to overcome the observational constraints, thermalize in the upper chromosphere. This leads to the generation of a slow conduction front, which causes plasma heating during the precursor phase.

Estimating the Relative Energy Content of Reactive Materials Using Nanosecond-Pulsed Laser Ablation

ABSTRACTRecently, a laboratory-scale method for measuring the rapid energy release from milligram quantities of energetic material has been developed based on the high-temperature plasma chemistry induced by a focused, nanosecond laser pulse. The ensuing exothermic chemical reactions result in an increase in the laser-induced shock wave velocity compared to inert materials. Laser-induced air shock from energetic materials (LASEM) provides a method for estimating the detonation performance of novel organic-based energetic materials prior to scale-up and full detonation testing. Here, the extension of LASEM to non-organic energetic materials is discussed. The laser-induced shock velocities from reactive materials such as Al/PTFE, Al/CuO, Al/Zr alloys, Al/aluminum iodate hexahydrate, and porous silicon composites have been measured; in many cases, the high sensitivity of the samples resulted in propagation of the reaction to the surrounding material, producing significantly higher shock velocities than conventional energetic materials. Methods for compensating for this effect will be discussed. Despite this limitation, the relative comparison of the shock velocities, emission spectra, and combustion behavior of each type of material provides some insight into the mechanisms for increasing the energy release of the material on a fast (μs) and/or slow (ms) timescale.

Investigation into Mechanism of Floor Dynamic Rupture by Evolution Characteristics of Stress and Mine Tremors: A Case Study in Guojiahe Coal Mine, China

In order to explore the mechanism of floor dynamic rupture, the current study adopts a thin plate model to further investigate the condition of floor failure. One of the possible explanations could be floor buckling due to high horizontal stress and dynamic disturbance ultimately leading to rapid and massive release of elastic energy thus inducing dynamic rupture. Seismic computed tomography and 3D location were employed to explore the evolution characteristics of floor stress distribution and positions of mine tremors. In the regions of floor dynamic rupture, higher P‐wave velocity was recorded prior to the dynamic rupture. On the contrary, relatively lower reading was observed after the dynamic rupture thus depicting a high stress concentration condition. Meanwhile, evolution of mine tremors revealed the accumulation and subsequent release of energy during the dynamic rupture process. It was further revealed that dynamic rupture was induced due to the superposition of static and dynamic stresses: (i) the high static stress concentration due to frontal and lateral abutment stress from coal pillar and (ii) dynamic stress from the fracture and caving of coal pillar, hard roof, and key stratum. In the later part of this study, the floor dynamic rupture occurrence process would be reproduced through numerical simulations within a 0.6 sec time frame. The above‐mentioned findings would be used to propose a feasible mechanism for prewarning and prevention of floor dynamic rupture using seismic computed tomography and mine tremors 3D location.

Luminescence of Molecular Nitrogen Nanoclusters Containing Stabilized Atoms.

We studied the luminescence of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms. Optical spectra were observed during the destruction of these ensembles of nanoclusters accompanied by a rapid release of chemical energy stored in the samples. Several interesting features were observed including a broad band near λ ≈ 360 nm, which was identified as emission corresponding to 2Ag→1Ag transition of N4(D2h) polymeric nitrogen. Also the sharp lines at λ ∼ 336 and 473 nm were observed, and their assignments to ND radicals are discussed.

Generation of shock lamellae and melting in rocks by lightning‐induced shock waves and electrical heating

AbstractThe very rapid energy release from impact events, such as those resulting from lightning strikes or meteorites, can drive a variety of physical and chemical processes which alter rocks and result in the formation of natural glasses (i.e., fulgurites and tektites). Fulgurite is the vitrified soil, sand, or rock resulting from lightning strikes. A thunderbolt is associated with air temperatures of up to 105 K, which can heat rocks to >2000 K within tens of microseconds. The rapid fusing and subsequent quenching of the surface of the rock leaves a distinctive, thin, garbled coating composed of a glassy to fine‐grained porous material. Previous studies on rock fulgurites found planar deformation features in quartz crystals within the target rock substrate, evidence of strong shock waves during fulgurite formation. In this paper, we simulated the shock pressure and temperature caused by an idealized lightning impact on rocks and compared the model results with observations on rock fulgurites from the literature. Our model results indicate that a lightning strike can cause >7 GPa pressure on the rock surface, generate a layer of fulgurite (of radius ∼9 cm), and leave a burned region (of radius ∼11 cm). The fulgurites found on rock surfaces share many features with sand fulgurites, but their spatial distribution is completely different, as sand fulgurites are hollow tube structures. Our study on rock fulgurites provides an indirect constraint on the energy of a lightning event and also demonstrates that the presence of shock features in rocks cannot be taken as unequivocal evidence for impact events.

Particle acceleration with anomalous pitch angle scattering in 2D magnetohydrodynamic reconnection simulations

The conversion of magnetic energy into other forms (such as plasma heating, bulk plasma flows, and non-thermal particles) during solar flares is one of the outstanding open problems in solar physics. It is generally accepted that magnetic reconnection plays a crucial role in these conversion processes. In order to achieve the rapid energy release required in solar flares, an anomalous resistivity, which is orders of magnitude higher than the Spitzer resistivity, is often used in magnetohydrodynamic (MHD) simulations of reconnection in the corona. The origin of Spitzer resistivity is based on Coulomb scattering, which becomes negligible at the high energies achieved by accelerated particles. As a result, simulations of particle acceleration in reconnection events are often performed in the absence of any interaction between accelerated particles and any background plasma. This need not be the case for scattering associated with anomalous resistivity caused by turbulence within solar flares, as the higher resistivity implies an elevated scattering rate. We present results of test particle calculations, with and without pitch angle scattering, subject to fields derived from MHD simulations of two-dimensional (2D) X-point reconnection. Scattering rates proportional to the ratio of the anomalous resistivity to the local Spitzer resistivity, as well as at fixed values, are considered. Pitch angle scattering, which is independent of the anomalous resistivity, causes higher maximum energies in comparison to those obtained without scattering. Scattering rates which are dependent on the local anomalous resistivity tend to produce fewer highly energised particles due to weaker scattering in the separatrices, even though scattering in the current sheet may be stronger when compared to resistivity-independent scattering. Strong scattering also causes an increase in the number of particles exiting the computational box in the reconnection outflow region, as opposed to along the separatrices as is the case in the absence of scattering.

Sensitivity analysis of the seismic demands of RC moment resisting frames to different aspects of ground motions

SummaryA weight vector representing the relative importance of various characteristics of ground motions (GMs) and a conditioning intensity measure (IM) are required to be able to use the generalized conditional IM framework for the purpose of GM selection. An inappropriate weight vector may result in the biased distributions of some important characteristics of GMs and, consequently, the bias in the structural responses. This article aims to provide the analyst with the understanding of which properties of GMs are important in capturing the accurate structural responses, to specifically assign a suitable weight to them and to select an appropriate conditioning IM as well. To this end, 4 reinforced concrete buildings, located at the site in which the seismic hazard is dominated by shallow crustal earthquakes, are considered. The findings reveal that the appropriate weight vectors depend on the characteristics of the employed structural systems. In addition, the role played by each IM in capturing the true structural responses changes over different earthquake intensity levels implying that different weight vectors are required over different earthquake levels. Furthermore, this study shows that, even in case of shorter‐duration GMs from shallow events, GM duration should be incorporated in GM selection as it has effects on the peak‐based structural responses in the earthquake levels beyond the level of 2%‐in‐50‐years. Specifically, the findings reveal that in case of shallow events, unlike large magnitude earthquakes, the shorter the duration of GM the more rapid release of energy and, consequently, the larger the peak‐based structural responses.

Acoustic Emission from Organic Martensites.

In salient effects, still crystals of solids that switch between phases acquire a momentum and are autonomously propelled because of rapid release of elastic energy accrued during a latent structural transition induced by heat, light, or mechanical stimulation. When mechanical reconfiguration is induced by change of temperature in thermosalient crystals, bursts of detectable acoustic waves are generated prior to self-actuation. These observations provide compelling evidence that the thermosalient transitions in organic and organic-containing crystals are molecular analogues of the martensitic transitions in some metals, and metal alloys such as steel and shape-memory alloys. Within a broader context, these results reveal that, akin to metallic bonding, the intermolecular interactions in molecular solids are capable of gradual accrual and sudden release of a substantial amount of strain during anisotropic thermal expansion, followed by a rapid transformation of the crystal packing in a diffusionless, non-displacive transition.

Acoustic Emission from Organic Martensites

AbstractIn salient effects, still crystals of solids that switch between phases acquire a momentum and are autonomously propelled because of rapid release of elastic energy accrued during a latent structural transition induced by heat, light, or mechanical stimulation. When mechanical reconfiguration is induced by change of temperature in thermosalient crystals, bursts of detectable acoustic waves are generated prior to self‐actuation. These observations provide compelling evidence that the thermosalient transitions in organic and organic‐containing crystals are molecular analogues of the martensitic transitions in some metals, and metal alloys such as steel and shape‐memory alloys. Within a broader context, these results reveal that, akin to metallic bonding, the intermolecular interactions in molecular solids are capable of gradual accrual and sudden release of a substantial amount of strain during anisotropic thermal expansion, followed by a rapid transformation of the crystal packing in a diffusionless, non‐displacive transition.

Acoustic emission signature of mechanical failure: Insights from ring‐shear friction experiments on granular materials

AbstractThe generation of acoustic emission (AE) in a material relates to the rapid energy release process, which delivers important information concerning the failure mechanism for stressed geologic materials. Here we report on ring‐shear friction experiments to investigate the mechanical behavior and AEs for sheared granular materials with different particle sizes under constant normal stress and a range of shear rates. Results show that the mechanical behavior of shear resistance, sample compaction and slip displacement, and the release of acoustic energy can be affected by both shear rate and particle size. The main AEs are strongly correlated with the global mechanical failure, and the maximum absolute amplitude of AEs generally increases with increase of the magnitude of stress drops. By analyzing the event sequences, it is found that the onset of AEs precedes the beginning of stress drop, which provides more useful information on the failure mechanisms of geologic granular materials.

Predicting rock burst hazard with incomplete data using Bayesian networks

Rock burst is a dynamic process of sudden, rapid and violent release of elastic energy accumulated in rock and coal masses during underground activities. It can lead to casualties, to failure and deformation of the supporting structures, and to damage of the equipment on site; hence its prediction is of great importance. This paper presents a novel application of Bayesian networks (BNs) to predict rock burst. Five parameters —Buried depth of the tunnel (H), Maximum tangential stress of surrounding rock (MTS) (σθ), Uniaxial tensile strength of rock (UTS) (σt), Uniaxial compressive strength of rock (UCS) (σc) and Elastic energy index (Wet)— are adopted to construct the BN with the Tree augmented Naïve Bayes classifier structure. The Expectation Maximization algorithm is employed to learn from a data set of 135 rock burst case histories, whereas the belief updating is carried out by the Junction Tree algorithm. Finally, the model is validated with 8-fold cross-validation and with another new group of incomplete case histories that had not been employed during training of the BN. Results suggest that the error rate of the proposed BN is the lowest among the traditional criteria with capability to deal with incomplete data. In addition, a sensitivity analysis shows that MTS is the most influential parameter, which could be a guidance on the rock burst prediction in the future.

Damage grading system for severity assessment on concrete structure

Acoustic Emission (AE) is a high frequency stress wave generated by rapid release of energy in solid material due to changes such as crack initiation and growth. High sensitivity to crack growth, the ability to locate the source, its passive nature and the possibility to perform real-time monitoring are some of the attractive features of the AE technique. In spite of these advantages, challenges still exist in using the AE technique for monitoring applications, especially in the analysis of recorded AE data as large volume of data are usually generated during the monitoring process. The need for effective data analysis in a grading system can be linked to the main objective of this research; to develop a new standard grading system for severity assessment. In this research, the cyclic load test (CLT) method is the first method used for this evaluation system. This is a relatively new method that may provide better insights into structural integrity and also collaborates with the AE evaluation system. This study proposed and tested the absolute energy parameter in the evaluation for determining the damage level in Reinforced concrete RC structure. The Intensity Absolute Energy Analysis (IAEA) methods that involved the absolute energy parameter were investigated to determine the damage level in RC structure. This was found to provide encouraging results for the analysis of AE data parameters in determining the damage grading system. By addressing this primary issue, it is believed that this study can help improve the effectiveness of the AE technique for Structural Health Monitoring (SHM) in civil engineering.

One-step synthesis of architectural Ni3S2 nanosheet-on-nanorods array for use as high-performance electrodes for supercapacitors

Although a wide variety of three-dimensional porous electrode architectures have been created for supercapacitors to markedly enhance the charge and mass transfer associated with cycling, their low volumetric energy densities limit applications in many energy storage systems. In this work, we report a unique electrode architecture consisting of Ni3S2 nanosheet-onto-Ni3S2-nanorods grown on nickel foam and prepared using a simple one-step hydrothermal method. When tested as an electrode for a supercapacitor (using a three-electrode configuration), this material exhibited excellent rate capability and cycling stability at high cycling rates. The obtainable capacitance decreased by <42% as the current density was increased from 20 to 240 mA cm−2, and the capacity retained 89.3% of its initial value after 5000 cycles at a cycling rate of 120 mA cm−2. Further, an asymmetric supercapacitor consisting of the Ni3S2 nanosheet-onto-Ni3S2-nanorods electrode and an activated carbon (AC) electrode displayed a volumetric energy density as high as ~1.96 mWh cm−3, with the potential to bridge the performance gap between thin-film Li batteries and commercial AC//AC supercapacitors. The outstanding electrochemical performance is attributed to the good mechanical adhesion and electrical connection with the substrate, high contact area with the electrolyte and alleviated structural pulverization during the ion insertion/desertion process. It is predicted that the architectural Ni3S2-nanosheet-on-nanorods array prepared with this facile method offers great potential promise in large-scale energy storage device applications. An electrode material for considerably enhanced storage of electrical energy in supercapacitors has been developed by an international team. Supercapacitors offer high charge storage capacities and rapid energy release, but they typically have lower volumetric energy storage densities than rechargeable batteries, making them bulkier in comparison. Supercapacitor electrodes having high surface areas through nanoscale morphologies offer a solution but can be difficult to fabricate. Now, Meilin Liu from Georgia Institute of Technology in the USA, Chenghao Yang from South China University of Technology in China, and their colleagues have used a simple one-step hydrothermal method to fabricate an architecture based on nickel sulfide (Ni3S2) nanosheets and nanorods. Supercapacitors made from these materials showed a high volumetric energy density and a long durability. The researchers anticipate that this architecture will be useful for large-scale energy storage devices. Three kinds of Ni3S2 nanostructures, namely Ni3S2 nanorods, Ni3S2 nanosheet@nanorods and Ni3S2 multi-connected nanorods were prepared using a one-step hydrothermal process via controlling the temperature. Owing to the good mechanical adhesion and electrical connection with the substrate, high contact area with the electrolyte and alleviated structural pulverization during the ion insertion/desertion process, Ni3S2 nanosheet-onto-Ni3S2 nanorods exhibited excellent rate capability and cycling stability. Asymmetric supercapacitor consisting of Ni3S2 nanosheet @nanorods electrode and activated carbon (AC) electrode displayed a volumetric energy density of 1.96 mWh cm−3, which can be used to bridge the performance gap between thin-film Li batteries and commercial AC//AC supercapacitors.