Specific Energy Storage Research Articles

Experimental investigation on high energy-density and power-density hydrated salt-based thermal energy storage

• High energy and power density hydrated salt-based TES device. • Performance evaluation of TES device at different conditions for hot water heating. • Phase-change temperature of 50 ℃ and phase-change enthalpy of 184.5 kJ·kg −1 . • Energy storage density is 2.6 times higher than that of conventional water tank. • High energy storage density (∼88.4 kWh·m −3 ) and high power density (669.9 W·kg −1 ) Thermal energy storage based on phase change materials (PCMs) plays a key role in bridging the gap between energy supply and demand for renewable energy applications. Hydrated salt is one kind of the most promising PCMs due to high phase-change enthalpy, non-flammability and low cost. Herein, we design and fabricate a lab-scale high energy-density and power-density thermal energy storage (TES) device using hydrated salt-based phase change composite (PCC). The thermophysical properties of the hydrated salt-based PCC are characterized and the thermal performances of the PCC-based TES device are analyzed at different operating conditions during charging and discharging processes. The Differential Scanning Calorimeter (DSC) analysis shows that the PCC has high phase-change enthalpy of 184.5 kJ·kg −1 and suitable phase-change temperature of 50 ℃ for hot water heating. The experimental results show that the PCC-based TES device exhibits high specific energy storage density up to 88.4 kWh·m −3 , approximately 2.6 times higher than the conventional water tank storage device. In discharging process, the PCC-based TES device exhibits high energy density (∼81.6 kWh·m −3 ), high efficiency (∼92.3 %), high power density (∼669.9 W·kg −1 ), and stable output hot water temperature (45 ∼ 47 ℃) at different water flow rates (0.42 ∼ 2.42 L·min −1 ) and inlet cold water temperatures (8 ∼ 25 ℃).

Opportunistic soaring by birds suggests new opportunities for atmospheric energy harvesting by flying robots.

The use of flying robots (drones) is increasing rapidly, but their utility is limited by high power demand, low specific energy storage and poor gust tolerance. By contrast, birds demonstrate long endurance, harvesting atmospheric energy in environments ranging from cluttered cityscapes to open landscapes, coasts and oceans. Here, we identify new opportunities for flying robots, drawing upon the soaring flight of birds. We evaluate mechanical energy transfer in soaring from first principles and review soaring strategies encompassing the use of updrafts (thermal or orographic) and wind gradients (spatial or temporal). We examine the extent to which state-of-the-art flying robots currently use each strategy and identify several untapped opportunities including slope soaring over built environments, thermal soaring over oceans and opportunistic gust soaring. In principle, the energetic benefits of soaring are accessible to flying robots of all kinds, given atmospherically aware sensor systems, guidance strategies and gust tolerance. Hence, while there is clear scope for specialist robots that soar like albatrosses, or which use persistent thermals like vultures, the greatest untapped potential may lie in non-specialist vehicles that make flexible use of atmospheric energy through path planning and flight control, as demonstrated by generalist flyers such as gulls, kites and crows.

Current developments in composite phase change materials for thermal energy storage application: A review

The development of secure, sustainable, affordable energy is a prime challenge for the worldwide power sector. Upgradation of energy efficiency and acceptance of renewable energy sources are practical approaches to address environmental issues. The isothermal functioning of the storage process and peak-energy storage density are favorable characteristics of phase change materials. An effort has been made in this review paper to compile the ongoing R and D work integrating C-PCMs in solar thermal energy storage systems. Not all predefined properties required for a perfect thermal-storage system can be discovered in an individual material. The inferior properties of available PCMs can be improved by correcting system arrangement or blending additives. The desirable characteristics of PCMs essentially thermophysical, chemical, kinetic, economics, safety, availability, etc. are important selection parameters for a specific energy storage application. This work explores the recent status of experiment work about the fabrication, characterization procedures of C-PCMs. The experimentation preferred for fabrication of C-PCMs by adopting metal foam techniques and carbon materials are summarized categorically.

On Capacitance and Energy Storage of Supercapacitor with Dielectric Constant Discontinuity.

The classical density functional theory (CDFT) is applied to investigate influences of electrode dielectric constant on specific differential capacitance and specific energy storage of a cylindrical electrode pore electrical double layer. Throughout all calculations the electrode dielectric constant varies from 5, corresponding to a dielectric electrode, to 108 corresponding to a metal electrode. Main findings are summarized as below. (i): By using a far smaller value of the solution relative dielectric constant , which matches with the reality of extremely narrow tube, one discloses that a rather high saturation voltage is needed to attain the saturation energy storage in the ultra-small pore. (ii): Use of a realistic low value brings two obvious effects. First, influence of bulk electrolyte concentration on the is rather small except when the electrode potential is around the zero charge potential; influence on the curve is almost unobservable. Second, there remain the and enhancing effects caused by counter-ion valency rise, but strength of the effects reduces greatly with dropping of the value; in contrast, the and reducing effects coming from the counter-ion size enhancing remain significant enough for the low value. (iii) A large value of electrode relative dielectric constant always reduces both the capacitance and energy storage; moreover, the effect of the value gets eventually unobservable for small enough pore when the value is beyond the scope corresponding to dielectric electrode. It is analyzed that the above effects take their rise in the repulsion and attraction on the counter-ions and co-ions caused by the electrode bound charges and a strengthened inter-counter-ion electrostatic repulsion originated in the low value.

Influence of ion structure and solvent electric dipole on ultrananoporous supercapacitor: a lattice model study

A five-state modified BEG model is proposed for describing electrolyte in polar solvent in cylindrical electrode pore in which only one row of particles can be stationed. Two properties the closest to the actual situation of the aqueous electrolyte are integrated into the model: cation is dimer comprised of two tangentially tethered hard spheres of different diameters: one is charged, while the other is neutral, and polar solvent is modeled as neutral hard sphere with an electric dipole. The system partition function is obtained by numerically solving maximum real root of characteristic equation of Kramers-Wannier transfer matrix. The model is used to investigate effects of ion structure and electric valence, solvent electric dipole, and cylindrical pore radius on specific differential capacitance and specific energy storage of the resulting supercapacitor. Main findings are briefly described below. (i) The dimer counter-ion electric valence does not exert obvious influence on the saturation value of the but reduces the threshold electrode potential strength beyond which the value is just reached. (ii) Whether the dimer counter-ion is monovalent or bivalent, the peak height and the value tend to rise with the dimer neutral site size decreasing, but influence of the value on the value is very small. Only when the value is small enough, the value rises a little with decrease of the value. (iii) Increase of solvent electric dipole moment (whether by increasing the dipole charge or dipole length) always raises the value, and enlarges width of the pure solvent domain or zero and zero domain around the zero electrode potential, but does not change the value obviously. (iv) With the pore size increasing, the value reduces and the value increases. So, using small size pore is favorable to improve the supercapacitor performance from the perspective of energy storage and electrode potential applied. (v) The three parameters: dipole charge, and dipole length, are cooperative in influencing the value.

Natural iron ores for large-scale thermochemical hydrogen and energy storage

A stable energy supply will require balancing the fluctuations of renewable energy generation due to the transition to renewable energy sources. Intraday and seasonal storage systems are often limited to local geographical or infrastructural circumstances.This study experimentally verifies the application of inexpensive and abundant natural iron ores for energy storage with combined hydrogen and heat release. The incorporated iron oxides are reduced with hydrogen from electrolysis to store energy in chemically bonded form. The on–demand reoxidation releases either pure hydrogen or high-temperature heat as valuable products. Natural iron ores as storage material are beneficial as the specific costs are lower by an order of magnitude compared to synthetic iron oxide-based materials.Suitable iron ores were tested in TG analysis and in a 1 kW fixed-bed reactor. Siderite, a carbonate iron ore, was verified as promising candidate, as it shows significantly lower reaction temperatures and twice the storage capacity over other commercial iron ores such as ilmenite. The specific storage costs are as low as 80–150 $ per MWh hydrogen stored, based on the experimental in-situ tests. The experimentally determined volumetric energy storage capacity for the bulk material was 1.7 and 1.8MWhm−3 for hydrogen and heat release, respectively. The raw siderite ore was stable for over 50 consecutive cycles at operating temperatures of 500–600 °C in in-situ lifetime tests.The combination of high abundance, low price and reasonable capacity can thus result in very low specific energy storage costs. The study proofs that suitable natural iron ores are an interesting economic solution for large-scale and seasonal energy storage systems.

Biodegradable wood plastic composites with phase change microcapsules of honeycomb-BN-layer for photothermal energy conversion and storage

A novel thermal energy storage (TES) composites system consisting of the microPCMs based on n-octadecane nucleus and SiO2/honeycomb-structure BN layer-by-layer shell as energy storage materials, and wood powder/Poly (butyleneadipate-co-terephthalate) (PBAT) as the matrix, was created with the goal of improving the heat transmission and photothermal responsiveness of building materials. The microPCMs were made via mini-emulsion interfacial polycondensation and electrostatic self-assembly to anchor BN on the surface of the SiO2 shell. The two kinds of microPCMs we designed had regular spherical morphology, BN was successfully anchored outside the SiO2 shell, showing a honeycomb structure and good heat storage performance (140.4 J/g and 140.6 J/g). The thermal energy storage wood plastic composites (TES WPCs) had considerable energy storage capacity and temperature regulation ability. The TES WPCs with the unique honeycomb structure of BN-MicroPCMs (BN-WPC) had better heat transfer performance and photothermal conversion efficiency (69.54%), and the thermal conductivity, specific heat capacity and energy storage efficiency of which were increased by 75.06%, 87.06% and 200% respectively. Meanwhile, the unique honeycomb structure strengthened the interfacial bond strength of TES WPCs and brought satisfactory mechanical strength, and the tensile strength, elongation at break, bending strength and bending modulus of BN-WPC are increased by 51.16%, 97.01%, 81.28% and 742.74%, respectively compared with the WPC added with S-MicroPCMs (S-WPC). These results indicated that this research by designing the BN honeycomb structure layer on the traditional microPCMs surface, obtained the rapid thermal response of high-performance TES WPCs in residential construction, thermal energy storage, solar energy collection system and thermal regulation has broad application prospects.

Dual-electroactive metal–organic framework nanosheets as negative electrode materials for supercapacitors

Exploring high-efficiency and robust multifunctional negative electrode materials are vital to develop high-performance asymmetric supercapacitors (ASCs). As one class of important functional materials, metal–organic frameworks (MOFs) have been widely applied in adsorption/separation, optoelectronics, sensing, catalysis, and energy storage fields, but they are rarely served as negative electrodes for construction of ASCs. Herein, the novel electrochromic MOFs-based hierarchical nanosheets (called EV-HNSs) that self-assembled from negative electroactive organic viologen ligands and europium ions, are successfully synthesized through a solid-state precursor and surfactant dual-template-directed approach, and employed as negative electrode of supercapacitors. The obtained EV-HNSs show high areal capacity (186.25 mF cm−2 at 1 mA cm−2), excellent cycling stability, and good rate capability under the voltage from −0.9 to −0.1 V (vs. Ag/AgCl), superior to their bulk counterparts. Especially, during the charge and discharge process, such EV-HNSs display a smart potential-correlated electrochromic feature. The color of EV-HNSs electrode turns from colorless to bright purple when the voltage gets negative, and then it can go back reversibly. Their distinct dual-electroactive composition, molecular stacking mode, and hierarchical porous nanosheet assembly structures endow the specific energy storage performance of EV-HNSs. Next, by choosing the electrodeposited MnO2 as positive electrode, the EV-HNSs//MnO2 ASCs are further fabricated, which manifest satisfactory operating voltage (1.55 V) and high areal energy density (9.4 μWh cm−2 at 775 μW cm−2), outperforming most of reported ASCs devices. This work may shed light on developing hierarchical MOFs-nanosheets-based multifunctional negative electrodes, and promote their applications in smart energy storage devices or other clean energy options.

Ultrananoporous supercapacitor with ionic liquid comprised of two-site cation: an Ising model study (II)

A four-state one-dimension discrete spin model with the nearest neighbor and partial next nearest neighbor lattice interactions is proposed for describing electrical double layer formed by ionic liquid in cylindrical pore that can accommodate only one row of particles. The model, in which cation is modeled as a dimer formed by two hard spheres (HSs): one is positively charged with diameter , while the other is neutral with diameter , and anion is modeled by charged HS with diameter , is designed to investigate effects of pore diameter , ion transfer free energy, ion size and electrical valence on behaviors of specific differential capacitance and specific energy storage and its saturation value . Relevant Kramers–Wannier transfer matrix is , which gives system partition function by numerically solving maximum real root of the relevant characteristic equation. Main findings are briefly described below. (i) The ion valence has little effect on the value, but does reduce the threshold voltage strength , beyond which the energy storage reaches . However, the ion valence (whether co- or counter-ion) raises both the and values as the relevant ion size decreases enough. (ii) Decreasing of the value weakly reduces the value, but raises the peak height and the value obviously; correlation between the value and value becomes stronger with the ions getting more pore hostile. (iii) With the counter-ion or co-ion charged site size decreasing, both the value and value rise. However, the effect of the co-ion charged site size is weakened as the co-ion gets more pore hostile, and the cation neutral site size influences on the value less than the cation charged site size does. (iv) Pore friendly co-ion or pore hostile counter-ion always helps in raising the value; the two have significant synergistic effect with the co-ion pore friendliness playing more important role than the counter-ion pore hostility.

N, P, O-codoped biochar from phytoremediation residues: a promising cathode material for Li–S batteries

Environment and energy are two key issues in today’s society. In terms of environmental protection, the treatment of phytoremediation residues has become a key problem to be solved urgently, while for energy storage, it tends to utilize low-cost and high specific energy storage materials (i.e. porous carbon). In this study, the phytoremediation residues is applied to the storage materials with low-cost and high specific capacity. Firstly, the phosphorous acid assisted pyrolysis of oilseed rape stems from phytoremediation is effective in the removal of Zn, Cu, Cd and Cr from the derived biochar. Moreover, the derived biochar from phytoremediation residues shows abundant porous structure and polar groups (–O/–P/–N), and it can deliver 650 mAh g−1 with 3.0 mg cm−2 sulfur, and keeps 80% capacity after 200 cycles when employing it as a sulfur host for lithium–sulfur (Li–S) batteries. Hence, phosphorous acid assisted pyrolysis and application in Li–S battery is a promising approach for the disposal of phytoremediation residues, which is contributed to the environmental protection as well as energy storage.

Regulation of the Interfaces Between Argyrodite Solid Electrolytes and Lithium Metal Anode.

Lithium-ion batteries (LIBs) are widely used in portable electronic devices, electric vehicles and large scale energy storage, due to their considerable energy density, low cost and long cycle life. However, traditional liquid batteries suffer from safety problems such as leakage, thermal runaway and even explosion. Part of the issues are caused by lithium dendrites puncturing the liquid electrolyte during cycling. In order to achieve the objective of higher safety and energy density, a rigid solid-state electrolyte (SSE) is proposed instead of liquid electrolyte (LE). Thereinto, sulfide SSEs have received of the most attention due to their high ionic conductivity. Among all the sulfide SSEs, argyrodite SSEs are considered to be one of the most promising solid-state electrolytes due to their high ionic conductivity, high thermal stability and good processablity. On the other hand, lithium metal is an ideal material for anode because of its high specific energy, low potential and large storage capacity. However, interfacial problems between argyrodite SSEs and the anode (interfacial reactions, lithium dendrites, etc.) are considered to be important factors affecting their availability. In this mini review, we summarize the behavior, properties and problems arising at the interface between argyrodite SSEs and anode. Strategies to solve interface problems and stabilize interfaces in recent years are also discussed. Finally, a brief outlook about argyrodite SSEs is presented.

Electrochemical Complexation of Polyatomic Aluminum Cations in Quinone-Type Organic Battery Electrodes Revealed By Solid-State NMR

Rechargeable aluminum batteries represent a significant area of opportunity for beyond-lithium-ion energy storage due to the high theoretical capacity (2980 mA∙h∙g-1, 8046 mA∙h∙mL-1), large earth abundance (8.23 wt.%), low cost, and safety of aluminum metal. Due to the stable native oxide layer that forms on aluminum, very few electrolytes are able to reversibly plate and strip aluminum at room temperature. Lewis acidic chloroaluminate ionic liquid electrolytes have demonstrated success in this regard; however, any cathode materials must also be (electro)chemical stable in this electrolyte. Electrode materials based on organic molecules have garnered attention due to their tunable structures and properties, enabling optimization for specific energy storage systems. Furthermore, diverse functional groups enable a range of possible charge storage mechanisms, many of which have yet to be explored in these systems. Like aluminum, organic materials are highly abundant and can be derived from various sources without geopolitical constraints. However, few Al-organic battery studies exist, and none so far have performed mechanistic analyses based on experimental data to identify conclusively the electroactive ions and their binding sites.Here, we present a rigorous analysis of charge storage mechanisms in quinone-type organic molecules for the first time, established through multi-dimensional solid-state nuclear magnetic resonance (ssNMR) spectroscopy in concert with quantum chemical calculations and electrochemical measurements. Indanthrone quinone (INDQ) is investigated for the first time as a model system due to its two distinct quinone functionalities and low solubility in many solvents. Through-space 27Al{1H} and 13C{1H} dipolar-mediated ssNMR techniques are used to establish the sub-nanometer proximities between polyatomic aluminum cations and specific moieties in the organic frameworks. Furthermore, dipolar-mediated ssNMR measurements are sensitive to both molecular dynamics and internuclear distances, which enables us to selectively filter out signals from residual liquid electrolyte, eliminating the need for solvent rinsing that can perturb the sample. Al-INDQ cells achieve reversible capacities of up to 240 mA∙h∙g-1 and maintain capacities >100 mA∙h∙g-1 at rates up to 2400 mA∙g-1. The enolization reaction and charge-balancing AlCl2 + cation complexation was established via dipolar-mediated ssNMR, findings that are corroborated through density functional theory (DFT) calculations. Other quinone-based organic structures with modified structures and compositions were also investigated using similar methods and will briefly be compared to INDQ. In aggregate, the quinone-based model systems serve as a basis to better understand how different functional groups, heteroatoms, and organic structures affect the electrochemical properties of rechargeable Al-organic batteries. The results yield strategies towards creating ‘designer’ organic electrode materials for rechargeable aluminum batteries.

Stoichiometry-Controlled Reversible Lithiation Capacity in Nanostructured Silicon Nitrides Enabled by in Situ Conversion Reaction.

In modern Li-based batteries, alloying anode materials have the potential to drastically improve the volumetric and specific energy storage capacity. For the past decade silicon has been viewed as a “Holy Grail” among these materials; however, severe stability issues limit its potential. Herein, we present amorphous substoichiometric silicon nitride (SiNx) as a convertible anode material, which allows overcoming the stability challenges associated with common alloying materials. Such material can be synthesized in a form of nanoparticles with seamlessly tunable chemical composition and particle size and, therefore, be used for the preparation of anodes for Li-based batteries directly through conventional slurry processing. Such SiNx materials were found to be capable of delivering high capacity that is controlled by the initial chemical composition of the nanoparticles. They exhibit an exceptional cycling stability, largely maintaining structural integrity of the nanoparticles and the complete electrodes, thus delivering stable electrochemical performance over the course of 1000 charge/discharge cycles. Such stability is achieved through the in situ conversion reaction, which was herein unambiguously confirmed by pair distribution function analysis of cycled SiNx nanoparticles revealing that active silicon domains and a stabilizing Li2SiN2 phase are formed in situ during the initial lithiation.

Evaluating the Multifunctional Performance of Structural Composites for Thermal Energy Storage

The simultaneous need for high specific mechanical properties and thermal energy storage (TES) function, present in several applications (e.g., electric vehicles), can be effectively addressed by multifunctional polymer-matrix composites containing a reinforcing agent and a phase change material (PCM). The PCMs generally decrease the mechanical properties of the host structural composites, but a multifunctional composite can still be beneficial in terms of mass saving, compared to two monofunctional units performing the structural and heat management functions individually. To quantify any possible advantages, this paper proposes an approach that determines the conditions for an effective mass saving at the system level and ranks the investigated structural TES composites with a parameter called multifunctional efficiency. It is found that the potential mass saving is higher when the volume fraction of the reinforcement is kept constant also when the PCM fraction increases or when the single phases (reinforcement, PCM) are themselves multifunctional.

Comprehensive Survey of Various Energy Storage Technology Used in Hybrid Energy

Various power generation technologies, such as wind turbines and solar power plants, have been increasingly installed in renewable energy projects as a result of rising demand and ongoing efforts by global researchers to mitigate environmental effects. The sole source of energy for such generation is nature. The incorporation of the green unit into the power grid also results in volatility. The stabilization of frequencies is critical and depends on the balance of supply and demand. An efficient monitoring scheme called Load Frequency Monitoring (LFM) is introduced to reduce the frequency deviation from its natural state. Specific energy storage systems may be considered to improve the efficiency of the control system. The storage system contributes to the load rate, peak rushing, black start support, etc., in addition to high energy and rapid responsive features. A detailed study of different power storage systems, their current business scenario, and the application of LFM facilities, as well as their analysis and disturbance, is presented in this paper. According to the literature analysis, the current approaches can be divided into two categories: grid and load scale structures. This article also distinguishes between the organized aggregate system and the uncoordinated system control scheme, both of which have advantages and disadvantages in terms of technology.

Ising model study on effects of solvent electric dipole on ultrananoporous supercapacitor

A three-state one-dimensional Ising model is used to investigate effects of solvent electric dipole on specific differential capacitance Cd and energy storage per unit area E in shallow cylindrical pore. Maximum real root of the 16×16 Kramers-Wannier transfer matrix and the system partition function are obtained numerically. The present method is rather general in that it covers symmetry and asymmetry cases of both ion size and ion valence, but the solvent electric dipole effects are analyzed only in the cases of charge symmetry and asymmetry. Main findings are briefly described below. (i) High solvent pore affinity raises the saturation energy storage but at the cost of simultaneously raising the threshold surface potential strength. Encouragingly, the presence of high valence ion can raise the saturation energy storage to the same extent or to an even greater extent and in the meantime, threshold surface potential strength remains basically unchanged. (ii) For 2:1 type electrolyte, the Cd curves always present camel-shaped whether the solvent pore affinity is moderate (w0=6kBT) or even higher (w0=12kBT), and the solvent electric dipole moment is high or low. However, for 1:1 type electrolyte, the Cd curves can take bell-shaped as the solvent electric dipole moment is lower and the solvent pore affinity is moderate (w0=6kBT). (iii) Both the l parameter and b parameter have similar effects in influencing the Cd and .. profiles; what counts most is the value of the solvent electric dipole moment. (iv) Presence of the bivalent co-ion in the coexistence bulk causes two effects. First, the threshold surface potential strength reduces, and the supercapacitor reaches its saturation energy storage at a lower potential strength applied. Second, the pattern of growth of E with the surface potential strength is modified, the E rapidly reaches its saturation value once the threshold surface potential strength is reached; whereas in the absence of the bivalent co-ion, the E saturation value is reached more gently.

NiTiHf shape memory alloys as phase change thermal storage materials

Motivated by the recent advancements demonstrating the effectiveness of NiTi shape memory alloys (SMAs) as high figure of merit (FOM) phase change materials (PCMs) for thermal management and storage, NiTiHf SMAs were explored as candidate solid-solid PCMs with high temperature capability. Differential scanning calorimetry and Archimedes’ method were used to determine the transformation temperatures, thermal hysteresis, enthalpy of transformation, and density of several different NiTiHf SMAs with varying compositions. Ni50.3Ti29.7Hf20 (at. %) demonstrated a high transformation enthalpy of 32.5 J/g, a relatively low thermal hysteresis of 31°C and a thermal conductivity of 11.19 Wm−1K−1 in the austenite phase. In general, NiTiHf SMAs exhibited FOM values an order of magnitude higher than traditional PCMs and up to about 120 % higher than the FOM value measured in binary NiTi SMAs. The clear trends relating transformation temperatures, transformation enthalpy, and thermal hysteresis to composition presented here provide for tunability of NiTiHf SMAs to specific thermal energy storage applications through composition control. High FOM values combined with transformation temperatures surpassing 500°C allows NiTiHf alloys to populate previously empty regions of FOM vs. transformation temperature property space for high FOM PCMs.

Ragone Plots for Electrochemical Double‐Layer Capacitors

AbstractThe Ragone plot (RP) compares devices in energy and power density characteristics, helping engineers decide on a specific energy storage system for technological applications. RP would contrast the performance of several technologies together under similar boundary conditions. Unfortunately, that is not what is happening for electrochemical double‐layer capacitors (EDLCs) because conditions for calculating energy and power are not standardized in the literature, resulting in severe discrepancies in the obtained values. With this widespread misconception, RP may become an unreliable tool for characterizing EDLCs. An intervention in this vital issue now becomes necessary. To put action on that, a rational strategy for dealing with measurements needed for EDLCs and calculations to prepare a reliable RP is reported here. This manuscript presents a step‐by‐step procedure to provide a correct RP. Also, simple theoretical demonstrations of how to get each fundamental equation are presented. In general, this work contributes as a guide to obtain reliable RPs for EDLCs.

(Invited) Microstructural Design Strategies of Sulfur Electrodes for High Specific Energy Lithium/Sulfur Cells

Lithium (Li) ion batteries have been regarded as major contributors to the energy solution and they have been intensively developed in terms of performance, cost and lifetime to meet the demands of emerging applications such as electric vehicle and energy storage systems for power grids. One of major goals of Li rechargeable battery development is to enhance its energy storage capability while reducing its weight or volume. In this regard, a lithium/sulfur (Li/S) cell has attracted great attentions of battery researchers because the Li/S cell offers large theoretical specific energy of 2600 Wh/kg that is ~ 5 times larger than that of conventional Li ion cells (500~600 Wh/kg). With consideration of the current state-of-the art of the Li ion cells that delivers specific energy of 150~250 Wh/kg, the Li/S cell has obvious potential to compete with the conventional Li ion cells for applications that require high specific energy storage capability.High specific energy of the Li/S cell is mainly attributed to high theoretical capacity of S electrode (Li2S: 1675 mAh/gS) where two Li ions can be stored per one S atom. To achieve near theoretical capacity of the S electrode, several challenges associated with the S electrode need to be overcome, that are (1) poor electrical conductivity of S (and Li2S) (2) lithium polysulfide (Li-PS) shuttle and irreversible deposition of Li2S onto Li electrode[1] (3) structural changes of the S electrode due to the large volume change of S particles, and the formation and deposition process of Li-PS species.[2] In recent years, dramatic enhancement of electrochemical utilization of S has been reported by developing advanced S-based active materials that significantly improve electrical conductivity and durability of the S electrodes. In the most of those design, the confined S particles are encapsulated within the electronically conductive porous matrix or coated onto S-philic functional materials so that electronic conductivity of the S electrode is improved while S loss by Li-PS shuttle is suppressed during the cell operation.Despite the advancement in the S-based active materials, current state-of-the art of the Li/S cell is still not satisfactory, thus further development strategies of S electrodes are required for the advanced Li/S cells demanding long life and high performance. Complex and simultaneous electrochemical processes of S electrode that involve formation and deposition of Li-PS intermediates occur during Li/S cell operation, and kinetic of the electrochemical process are strongly depend on structure of liquid electrolyte/solid S electrode interface. Therefore, rational microstructural design of the S electrode and maintaining the microstructure of the S electrode during the Li/S cell operation will play a key role to achieve high performance and durable Li/S cells. Implementation of specially treated membrane[3] or interlayer[4] are known to be very efficient methods for this purpose, but we still need to develop structural control methodologies to design microstructural of S electrodes.Amongst various S/carbonaceous composites, a S/graphene oxide (S/GO) composite has been investigated as one of promising composite materials for S electrode.[5] The major benefit of the use of the GO in the S electrode is S-philic property of the GO that comes from oxygen-containing functional groups existing on large surface area of the GO. The key strategies for the efficient use of GO’s functionality to accommodate S species within the S/GO electrode is to maintain large surface area of the GO by minimizing restacking of individual GO sheets during entire material synthesis and electrode manufacturing processes. In this presentation, multifaceted approaches to develop rational design of the S/GO composites and electrode, from nano- to macro-scale, will be introduced. These approaches seek to identify the most effective solutions to mitigate current major challenges of S electrodes, such a porous electrode design strategies for the advanced Li/S cells, in particular, the new discoveries of (1) a three-dimensionally aligned structure of battery electrodes consisting of few-microns-thick material arrays with 10−20 μm interlayer spacings[6] (2) reticulated structure of S-nitrogen-doped graphene oxide (NrGO) composite electrode[7] will mainly be discussed. References Y. V. Mikhaylik et al., J. Electrochem. Soc. 2004, 151, A1969–A1976.R. Elazari et al., J. Electrochem. Soc. 2010, 157, A1131–A1138.B-C. Yu et al., K. Park, J.-H. Jang, J. B. Goodenough, ACS Energy Lett. 2016, 1, 633–637.A. Manthiram et al., Adv. Mater. 2015, 27, 1980–2006.L. Ji et. al., J. Am. Chem. Soc. 2011, 133, 18522–18525.Y. Hwa et al., Nano Lett. 2019, 19, 4731–4737.Y. Hwa et al., Mater. Horiz. 2020, 7, 524–529.

Comparative performance study of electric vehicle batteries repurposed for electricity grid energy arbitrage

Electric vehicle (EV) batteries can provide extended value beyond EV service if they are repurposed for a “second life” in electricity grid applications. However, because batteries from different EV makes and models vary significantly by size, shape, chemistry, and thermal management, there is uncertainty regarding their relative performance in second-life applications. This experimental study evaluates seven different EV batteries in their original modules and/or packs, featuring four unique positive active materials, two negative active materials, three cell formats, and four thermal management designs. Each battery is subjected to deep-discharge cycling at 4 h, 2 h, and 1 h constant-power rates to emulate performance in electricity grid energy arbitrage. Test results are evaluated based on six battery performance metrics in three key performance categories, including two energy metrics (usable energy capacity and charge–discharge energy efficiency), one volume metric (energy density), and three thermal metrics (average temperature rise, peak temperature rise, and cycle time). Significant differences in performance arise from the variety of chemistries and thermal management systems tested, dominating any influence from battery state of health. Chevrolet Volt and EnerDel batteries (both from hybrid EVs using NMC chemistry) give the best usable energy capacity (≥94%) and energy efficiency (≥97%), while Tesla Model S batteries (from long-range EVs using NCA chemistry) give the lowest usable energy capacity (≥84%) and energy efficiency (≥89%). However, the ModelS batteries give roughly double the energy density (half the physical footprint) of the Volt and EnerDel batteries. The Volt battery experiences no more than 2 °C of warming even during a 1 h discharge, thanks to its active (forced) liquid thermal management and high energy efficiency. This contrasts with the Leaf and Lishen batteries, which use passive (natural convection) thermal management and consequently experience over 17 °C of warming during a 1 h discharge, and then require over 4 h of standby time to cool down by less than 10 °C. Novel analytical techniques are applied to the experimental results to rank the tested EV batteries in the three aforementioned performance categories to illustrate their relative commercial performance expectation in second-life energy arbitrage. This new performance ranking system can be employed by industry in conjunction with economic models to select the most appropriate used EV batteries for specific energy storage applications.