Attainable Energy Density Research Articles

Urea-treatment of CoOx carbon nanofibers to improve the electrochemical performance of supercapacitor using aqueous electrolytes

Supercapacitors (SCs) play a crucial role in flexible electronics, necessitating innovative approaches to enhance surface faradaic reactions and minimize faradaic diffusion while using aqueous electrolytes. Thus, the urea treatment of cobalt oxide (CoOx)-decorated carbon nanofibers (CNFs) is proposed in this study to decrease the contribution of faradaic diffusion-limited current. Flexible CoOx/CNF electrodes were obtained by annealing ZIF-67-grafted polyacrylonitrile (PAN) fibers via a wet chemical method. The urea treatment of CoOx/CNFs increased the content of sp2-hybridized carbon and pyridinic nitrogen, as confirmed by X-ray photoelectron spectroscopy, effectively enhancing conductivity and pseudocapacitive charge storage capability via nitrogen doping. Notably, urea-treated CoOx/CNF electrode samples exhibited a capacitance of 750 mF cm−2 at a scan rate of 10 mV s−1, while retaining more than 81 % capacitance at a higher scan rate of 100 mV s-1. The cyclic voltammetry curves during variable bending angle testing (0°, 45°, and 90°) exhibited negligible changes, indicating the excellent flexibility of the SCs. The CoOx/CNFs and urea-treated CoOx/CNFs exhibited 80 % and 91 % capacitance retentions, respectively, after 10,000 galvanostatic charge and discharge cycles. Furthermore, the attained energy densities of 76 and 61 µWh cm−2 at the respective power densities of 2 and 20 mW cm−2 indicated the excellent electrochemical performance of the optimal urea-treated CoOx/CNF electrode.

Micropillar‐based channel patterning in high‐loading graphite anodes for superior Li‐ion batteries

AbstractThis study presents a low‐cost, one‐step electrode patterning method that uses a template with micropillars to indent a hexagonal array of channels in high‐loading graphite anodes for faster electrolyte infiltration and Li‐ion transport. In contrast to prior studies on using laser micro‐machining, active material losses could be completely avoided by the proposed methodology. The process can also be made roll‐to‐roll and continuous. Furthermore, the very small volume fraction of the introduced channels (<1 wt.%) has little impact on practically attainable energy density or specific energy. Yet, thus introducing pore channels significantly reduces electrolyte infiltration time and improves rate performance.

Tailoring NiCoCu layered double hydroxide with Ag-citrate/polyaniline/functionalized SWCNTs nanocomposites for supercapacitor applications.

Supercapacitors have substantially altered the landscape of sophisticated energy storage devices with their exceptional power density along with prolonged cyclic stability. On the contrary, their energy density remains low, requiring research to compete with conventional battery storage devices. This study addresses the disparities between energy and power densities in energy storage technologies by exploring the integration of layered double hydroxides (LDH) and highly conductive materials to develop an innovative energy storage system. Four electrodes were fabricated via a hydrothermal process using NiCoCu LDH, Ag-citrate, PANI, and f-SWCNTs. The optimal electrode demonstrated exceptional electrochemical properties; at 0.5 A g-1, it possessed specific capacitances of 807 F g-1, twice as high as those of the pure sample. The constructed asymmetric supercapacitor device attained energy densities of 62.15 W h kg-1 and 22.44 W h kg-1, corresponding to power densities of 1275 W kg-1 and 11 900 W kg-1, respectively. Furthermore, it maintained 100% cyclic stability and a coulombic efficiency of 95% for 4000 charge-discharge cycles. The concept of a supercapacitor of the hybrid grade was reinforced by power law investigations, which unveiled b-values in the interval of 0.5 to 1. This research emphasizes the considerable potential of supercapacitor-grade NiCoCu LDH/Ag-citrate-PANI-f-SWCNTs nanocomposites for superior rate performance, robust cycle stability, and enhanced energy storage capacity.

Ultrafast microwave heated form-stable thermal package providing operating temperature for PEO all-solid-state batteries

All-solid-state batteries (ASSBs) have been regarded as satisfying future energy storage devices owing to the advantages of notably high energy density and outstanding safety. However, their attainable energy density, especially in poly(ethylene oxide) (PEO)-based ASSBs, is limited by low operating ambient temperature due to sluggish lithium-ion transport of solid electrolyte. Herein, a functional anti-leakage skeleton (alumina ceramic and boron nitride) with efficient graphene-modified phase change material (GPCM) and microwave thermal energy storage system is proposed for providing the operating temperature of ASSBs. The composite, prepared by alumina ceramic fiber, boron nitride, and GPCM, presenting excellent thermal properties such as great enhancement of thermal conductivity (64.6%) and low enthalpy loss (11.27%). The superior thermal effect is confirmed by experiments and simulations of microwave absorption. Through microwave irradiating the ASSBs wrapped with the composite, ASSBs can realize cold-starting in 1 min from room temperature in a fast, safe and low-power heating pathway. Significantly, the combination of multi-scale characteristics in graphene increases the thermal energy generated by the composite during microwave processing. Furthermore, the composite material (GPBC), used as portable auxiliary heating equipment, enables the ASSB to exhibit 92% capacity of those ASSBs placed in 55 °C ovens at 1C. This work provides a distinctive route to achieve efficient and extensive applications of ASSBs through external preheating.

Toward Practical Solid-State Lithium–Sulfur Batteries: Challenges and Perspectives

ConspectusThe energy density of the ubiquitous lithium-ion batteries is rapidly approaching its theoretical limit. To go beyond, a promising strategy is the replacement of conventional intercalation-type materials with conversion-type materials possessing substantially higher capacities. Among the conversion-type cathode materials, sulfur constitutes a cost-effective and earth-abundant element with a high theoretical capacity that has a potential to be game-changing, especially within an emerging solid-state battery configuration. Employment of nonflammable solid electrolytes that improves battery safety and boosts the energy density, as lithium metal anodes are also viable. The long-standing inherent problem of conventional lithium–sulfur batteries, arising from the reaction intermediates dissolved in liquid electrolytes, can be eliminated with inorganic solid ion conductors. In particular, the highly conducting and easily processable lithium-thiophosphates have successfully enabled the lab-scale solid-state lithium–sulfur cells to achieve close-to-theoretical capacities. For applications requiring safe, energy-dense, lightweight batteries, solid-state lithium–sulfur batteries are an ideal choice that could surpass conventional lithium-ion batteries.Nevertheless, there are challenges specific to practical solid-state lithium–sulfur batteries, beyond the typical challenges inherent to solid-state batteries in general. While the conversion reaction of sulfur realizes a large specific capacity, the associated significant total volume changes of the active material results in contact losses among the cathode components and, consequently, decreases reversible capacity. Additionally, the ionically and electronically insulating active material requires composite formation with solid electrolytes and electron-conductive additives to secure sufficient ion and electron supply at a triple-phase boundary. However, the compositing process itself makes the carrier transport pathways very tortuous and requires the balancing of carrier transport and optimization of the attainable energy density. Lastly, the requirement of a high interfacial area to establish sufficient triple-phase boundaries promotes the degradation of the solid electrolytes, and the formation of less-conductive interphases further deteriorates the transport in the composites.This Account focuses on the challenges associated with developing practical solid-state lithium–sulfur batteries and provides an overview over recently developed concepts to tackle these critical challenges: (1) Introduction of the conversion efficiency to enable quantitative assessments of the impact of chemo-mechanical failure. (2) For long-term cycling, the electrolyte degradation at the interface and the electrochemical activity of the formed interphases come into play. Practical stability tests with increased interfacial areas and subsequently altered reversal potentials can quantify the magnitude of the electrolyte degradation and confirm influences of reversible redox activity of the interphases. (3) Monitoring the effective conductivity in the composites clarifies correlations between transport and cyclability, further highlighting the need of quantitative measurements to address the composite carrier transport. (4) Impedance spectroscopy combined with transmission-line model analysis as a function of applied potentials can visualize the stability window of good effective ion transport to utilize both the capacity contributions from redox-active interphases and the high ionic conductivity. In the end, a roadmap toward the practical solid-state lithium–sulfur batteries will be presented.

Asymmetric Fiber Supercapacitors Based on a FeC2O4/FeOOH-CNT Hybrid Material

The development of new flexible and lightweight electronics has increased the demand for compatible energy storage devices to power them. Carbon nanotube (CNT) fibers have long been known for their ability to be assembled into yarns, offering their integration into electronic devices. They are hindered, however, by their low intrinsic energy storage properties. Herein, we report a novel composite yarn, synthesized through solvothermal processes, that attained energy densities in the range between 0.17 µWh/cm2 and 3.06 µWh/cm2, and power densities between 0.26 mW/cm2 and 0.97 mW/cm2, when assembled in a supercapacitor with a PVDF-EMIMBF4 electrolyte. The created unique composition of iron oxalate + iron hydroxide + CNT as an anode worked well in synergy with the much-studied PANI + CNT cathode, resulting in a highly stable yarn energy storage device that maintained 96.76% of its energy density after 4000 cycles. This device showed no observable change in performance under stress/bend tests which makes it a viable candidate for powering wearable electronics.

A High‐Capacity, Long‐Cycling All‐Solid‐State Lithium Battery Enabled by Integrated Cathode/Ultrathin Solid Electrolyte

AbstractCurrent all‐solid‐state lithium battery (ASSLB) manufacturing typically involves laborious fabrication and assembly of individual electrodes and solid electrolyte, which inevitably result in large interfacial resistances. Moreover, due to the unfavorable mechanical strength, most solid electrolytes are fabricated to be overly thick and are incapable of retarding lithium dendrite formation. These factors limit the attainable energy density and cyclability of ASSLBs. Here, a novel integrated cathode/solid electrolyte for scalable ASSLB manufacturing is reported by directly fabricating an ultrathin yet robust fiber network reinforced solid electrolyte on the cathode. The integrated design allows continuous ion conduction at both the interface and the entire cathode, thereby considerably reducing interfacial resistance and enabling higher cathode loading. Meanwhile, the strong fiber network endows the solid electrolyte with an ultrasmall thickness and superior dendrite suppression capability. As a result, the newly‐developed Li/LiFePO4 ASSLB achieves a high capacity of 155.2 mAh g–1 at 0.5 C and 45 °C with capacity retention of 84.3% after 500 cycles. Even with a cathode loading of 13 mg cm–2, the battery still delivers a capacity of 124.1 mAh g–1. Additionally, a pouch cell with this integrated design displays good electrochemical performance and safety, showing great promise for practical applications.

Structural evolution and electrochemistry of the Mn-Rich P2– Na2/3Mn0.9Ti0.05Fe0.05O2 positive electrode material

Positive electrodes still limit the maximum attainable energy density of Na-ion batteries. Increasing the amount of electrochemically active transition metal is one way of improving energy density. However, this is complicated by the balance between initial capacity and structural stability/capacity retention. Here, the Mn-rich P2– Na2/3Mn0.9Fe0.05Ti0.05O2 is synthesised via the solid-state method and its structural evolution during operation, between 1.9 and 4.2 V, investigated. Through operando X-ray powder diffraction data, no evidence is found for the formation of Z, OP4 or O2 phases and the material primarily displays regions of two-phase coexistence. P2– Na2/3Mn0.9Fe0.05Ti0.05O2 delivers a second charge/discharge capacity of 152/164 mAh.g−1 at C/10, within the voltage range 4.0–2.0 V and retains 75% of the dis-charge capacity at the 50th cycle. A detailed comparison, in terms of both the electrochemical performance and structural evolution, to related Mn-rich phases is provided. The results further demonstrate that structural stability and battery performance can be improved through subtle co-substitutions.

Exploring Ionic Liquid-Solvent Blend Formulations for the Stable Cycling of Li-Metal Anodes in Li-O2 Batteries

The scope of non-aqueous lithium-oxygen (Li-O2) battery chemistries as valuable “beyond Li-ion” energy storage technologies relies on complex cathode processes for the reversible generation of Li-oxide species.1 As such, the majority of Li-O2 battery research justifiably focuses on the (electro)chemistry of the cathode and the additional complications of applying Li-metal as the full-cell anode in Li-O2 cells have received less attention. It is highly desirable to utilize Li-metal anodes to maximize the attainable energy density of practical devices but the high reactivity of Li0, coupled with the tendency for dendrite formation, leads to severe cyclability and safety issues.2 In Li-O2 batteries, this is further complicated by the reactive nature of the cathode reaction intermediates and products. Therefore, in lieu of anode protection or separation, the electrolyte media needs to exhibit mutual stability/performance at the two contrasting interfacial environments to achieve a highly rechargeable system. In this regard, many interesting solvents utilized in Li-O2 battery investigations decompose readily in contact with Li-metal (e.g. DMSO, amides) and there has been some recent electrolyte literature showing methods for stabilizing Li plating/stripping in these solvents.3, 4 Furthermore, to also impede electrolyte evaporation via the cathode under dynamic gas-flow of an operating Li-O2 cell, candidate electrolytes must exhibit low vapor pressures. In this work, we report on the formulation and testing of liquid blend electrolytes based on Li-O2-cathode relevant components for the stable electroplating/stripping cycling at the Li-metal anode. Blends were prepared and studied through iterative formulations with selected molecular solvents, ionic liquids (ILs) and lithium salts. Therein, low boiling solvents (e.g. DME and acetonitrile) were immediately excluded, along with solvents known to decompose during O2 reduction at the cathode (e.g. organic carbonates). Galvanostatic cycling in symmetrical Li|electrolyte|Li cells was utilized under low current/capacity regimes to screen the electrolyte/electrode interfacial stability and under higher currents/capacities to compare performances with leading electrolytes for Li-anode application (generally not concerning Li-O2 cathode relevant materials). Furthermore, the application of asymmetric Li|electrolyte|Cu cells was used for the accurate determination of Coulombic efficiency of the Li plating/stripping process.5 Simple introduction of stable ILs into binary electrolyte formulations in rational quantities effectively stabilized otherwise reactive molecular solvents and the importance of Li+-cation solvation on solvent stabilization was further explored spectroscopically. Through further iterative improvements of more complex electrolyte formulations, over 3000 h of continued low current Li-plating/stripping cycling has been achieved (with >97% Coulombic efficiency of Li plating/stripping measured in Li|Cu cells). Higher Coulombic efficiencies and longer cycle lifetimes must be achieved under industrially relevant current densities to enable practical devices, but these results are notable given the electrolytes contain the highly reactive components considered useful at the Li-O2 cathode. D. Aurbach, B. D. McCloskey, L. F. Nazar, and P. G. Bruce, Nat. Energy, 1 16128 (2016). X.-B. Cheng, R. Zhang, C.-Z. Zhao, and Q. Zhang, Chem. Rev. (Washington, DC, U. S.), 117 (15), 10403-10473 (2017). M. Roberts, R. Younesi, W. Richardson, J. Liu, T. Gustafsson, J. Zhu, and K. Edström, ECS Electrochem. Lett., 3 (6), A62-A65 (2014). V. Giordani, W. Walker, V. S. Bryantsev, J. Uddin, G. V. Chase, and D. Addison, J. Electrochem. Soc., 160 (9), A1544-A1550 (2013). B. D. Adams, J. Zheng, X. Ren, W. Xu, and J.-G. Zhang, Adv. Energy Mater., 8 (7), 1702097 (2018).

Attainable Energy Density of Microbatteries

Attainable Energy Density of Microbatteries

3D Structuring of Thin Film Solid State Li-Ion Cells for Fast Charging Micro-Batteries

High energy and power density are the main requirements of today’s high demanding applications in consumer electronics. Lithium ion batteries (LIB) have the highest energy density of all known systems and are thus the best choice for rechargeable micro-batteries. Liquid electrolyte LIBs present limitations in safety, size and design, where all-solid state thin film batteries are considered to overcome these restrictions for small devices. Although planar all-solid state thin film LIBs are at present commercially available, they provide low capacity (<1mAh/cm2) which limits their application scenario. By using micro-structured surfaces (i.e. 3D batteries) and appropriate conformal coating technologies (i.e. electrochemical deposition, ALD), the capacity can be increased while still keeping a high rate performance. The main challenges in the introduction of solid-state LIBs are low ionic conductance and limited cycle life time due to mechanical stress and shearing interfaces. Novel materials and innovative nanostructures have to be explored in order to overcome these limitations. Thin film 3D compatible materials need to provide with the necessary requirements for functional and viable thin-film stacks. Thin film electrodes offer shorter Li-diffusion paths which allow them to be used at ultra-fast charging rates while keeping their maximum capacities. Thin film electrolytes with intrinsically high ion conductivity (~10-3 S/cm) do exist, but are not electrochemically stable. On the other hand, electronically insulating electrolytes with a large electrochemical window and good chemical stability are known, but typically have intrinsically low ionic conductivities (<10-6S/cm). In addition, there is the need for conformal deposition techniques which can offer pinhole-free coverage over large surface areas with large aspect ratio features for electrode, electrolyte and buffer layers. In this paper, we present the fabrication of 3D thin-film batteries using high aspect ratio silicon pillar arrays providing area enhancement of over 25x. The pillars are conformally coated with LiMn2O4 (LMO) and LixTiO2 as positive and negative electrodes, respectively. For the electrolyte, thin-film composite electrolyte films are being developed. Where we currently focus on 60 μm high pillars with a 2 μm diameter and pitch, the energy and power output per unit area of the battery can be increased by scaling towards higher aspect ratio pillars. Indeed, by increasing the height of the pillars, more active material per unit area can be deposited, resulting in a higher capacity. Simultaneously, the power output of the battery improves due to the increased internal surface of the 3D battery. Notice that a similar approach is not possible with conventional thin-film batteries. Increasing the active film thickness in these batteries results in more capacity, but this goes at the cost of power output due to the increased resistance of the thicker active layers. In addition, by decreasing the pitch between the pillars, the film thickness can be scaled down. We show that the available capacity of both the manganate and titania based films can be increased by scaling down the film thickness below 100 nm without affecting cycle life time. The thinnest films show the highest volumetric capacity and the best cycling stability. The increased stability of the LMO films below 50 nm allows cycling in both the 4 and 3V potential region, resulting in a high volumetric capacity of 1.2Ah/cm3. The potential of 3D thin-film batteries with respect to attainable energy density and C-rate performance will be discussed. Figure 1

The concentration gradient flow battery as electricity storage system: Technology potential and energy dissipation

Unlike traditional fossil fuel plants, the wind and the sun provide power only when the renewable resource is available. To accommodate large scale use of renewable energy sources for efficient power production and utilization, energy storage systems are necessary. Here, we introduce a scalable energy storage system which operates by performing cycles during which energy generated from renewable resource is first used to produce highly concentrated brine and diluate, followed up mixing these two solutions in order to generate power. In this work, we present theoretical results of the attainable energy density as function of salt type and concentration. A linearized Nernst-Planck model is used to describe water, salt and charge transport. We validate our model with experiments over wide range of sodium chloride concentrations (0.025–3 m) and current densities (−49 to +33 A m−2). We find that depending on current density, charge and discharge steps have significantly different thermodynamic efficiency. In addition, we show that at optimal current densities, mechanisms of energy dissipation change with salt concentration. We find the highest thermodynamic efficiency at low concentrate concentrations. When using salt concentrations above 1 m, water and co-ion transport contribute to high energy dissipation due to irreversible mixing.

Carbons, Ionic Liquids, and Quinones for Electrochemical Capacitors

Carbons are the main electrode materials used in electrochemical capacitors, which are electrochemical energy storage devices with high power densities and long cycling lifetimes. However, increasing their energy density will improve their potential for commercial implementation. In this regard, the use of high surface area carbons and high voltage electrolytes are well known strategies to increase the attainable energy density, and lately ionic liquids have been explored as promising alternatives to current state of the art acetonitrile-based electrolytes. Also, in terms of safety and sustainability ionic liquids are attractive electrolyte materials for electrochemical capacitors. In addition, it has been shown that the matching of the carbon pore size with the electrolyte ion size further increases the attainable electric double layer (EDL) capacitance and energy density. The use of pseudocapacitive reactions can significantly increase the attainable energy density, and quinonic-based materials offer a potentially sustainable and cost effective research avenue for both the electrode and the electrolyte. This perspective will provide an overview of the current state of the art research on electrochemical capacitors based on combinations of carbons, ionic liquids and quinonic compounds, highlighting performances and challenges and discussing possible future research avenues. In this regard, current interest is mainly focused on strategies which may ultimately lead to commercially competitive sustainable high performance electrochemical capacitors for different applications including those requiring mechanical flexibility and biocompatibility.

Distributions of transverse energy and forward energy in 16O- and 32S-induced heavy ion collisions at 60A and 200A GeV.

Distributions of transverse energy, forward energy, and dET/dη from 60A GeV and 200A GeV induced16 and 200A GeV induced32 nuclear collision with C, Al, Cu, Ag, and Au are presented. The energy, projectile, target, and centrality dependences are shown and discussed within a simple Glauber spectator-participant model. Two universal parametrizations of the dET/dη distributions are presented together with various estimates of the nuclear stopping power and attained energy densities. An upper limit for γdirect/π0 in central collisions of 200A GeV S32+197Au is derived.Received 18 June 1991DOI:https://doi.org/10.1103/PhysRevC.44.2736©1991 American Physical Society

Experimental results from CERN on reaction mechanisms in high energy heavy ion collisions

Three main experimental results from CERN concerning reaction mechanisms in high energy heavy ion collisions are discussed: 1) the striking validity of the single particle picture, 2) the nuclear stopping power and 3) the attained energy densities.

Oxygen-induced reactions at 60A GeV and 200A GeV studied by calorimetry

Results based on calorimetric measurements are presented from reactions of 60A GeV and 200A GeV16O projectiles with C, Cu, Ag, and Au nuclei. Minimum-bias cross sections are discussed. Energy spectra measured at zero degrees and transverse-energy distributions for the pseudorapidity range 2.4≦η≤5.5 are shown. An analysis of the average transverse energy in terms of the number of participating nucleons and the number of binary nucleon-nucleon collisions is presented. Estimates of nuclear stopping and of attained energy densities are made.

Forward and transverse energy distributions in oxygen-induced reactions at 60 A GeV and 200 A GeV

Results are presented from reactions of 60 A GeV and 200 A GeV 16O projectiles with C, Cu, Ag, and Au nuclei. Energy spectra measured at zero degrees and transverse energy distributions in the pseudorapidity range from 2.4 to 5.5 are shown. The average transverse energy per participant is found to be nearly independent of target mass. Estimates of nuclear stopping and of attained energy densities are made.

Short pulse amplification in the presence of absorption

Energy amplification of short pulses in the presence of distributed absorption is analyzed and discussed. A short pulse is defined as a pulse length that is much shorter than the lasing state lifetime. It is shown that the energy density of a short pulse cannot be amplified indefinitely in the presence of nonsaturable absorption. In an active medium having a small signal gain g0 and a nonsaturable absorption α, the maximum attainable energy density is (Esat g0/α), where Esat is the medium saturation energy. High-energy densities are obtained at the expense of the extraction efficiency. An amplifier design can be optimized by choosing the appropriate parameters such as small signal gain and active medium gain length.

Quark-gluon plasma formation in the central rapidity region and finite size effects of colliding nuclei

The energy density of the central products in the ultra-relativistic heavy ion collisions are calculated. In our estimation, the special attention is paid to the space-time extension of the emission points of the secondary hadrons which are originate in the successive nucleon-nucleon interactions within the finite size of colliding nuclei. The average collision number per produced particle, in the final state interaction, is also calculated and is used as a criterion whether the system is thermalized or not. It turns out that the attainable energy density in the central heavy ion collision is sensitive to the spacetime extension of the emission points. However, if the incident energy and the mass numbers of colliding nuclei are high and large, we can get high enough energy density for the phase transition from a hadronic state to a quark-gluon plasma state.