Gravimetric Energy Density Research Articles

A Study on the Reaction Mechanism of a Model Organic Cathode in Magnesium-Ion Batteries

The need for abundant, sustainable, and cost-effective energy storage technologies has been generating increased interests in batteries that rely on the use of earth abundant elements such as multivalent batteries. Those that utilize metallic anodes (Mg, Ca, Al) and organic cathodes are attractive as they can offer a path forward toward a competitive gravimetric energy density and in some cases fast charge capabilities. In particular, reports of a variety of Mg metal anode–organic cathodes batteries with good performances compel further research efforts of these systems and understanding of processes that govern their performances. However, studies of organic cathodes in competent, Cl– free Mg electrolytes remain limited, and the mechanisms that govern the cycling of these batteries are unclear. Herein, we assess the Mg battery performance using a typical benzoquinone type organic molecule in a competent Cl– free, single salt electrolyte and investigate the mechanisms at play. Combining the findings from battery and analytical studies reveal reversible structural transformations driven by a new precedence of a unique dissolution/precipitation mechanism. The implications of this mechanism on the performance of the battery are evaluated and discussed. The findings unveiled shed light onto potential challenges and opportunities with these systems and help guide future advancements.

High-Energy-Density Zinc–Air Microbatteries with Lean PVA–KOH–K2CO3 Gel Electrolytes

Small-scale, primary electrochemical energy storage devices ("microbatteries") are critical power sources for microelectromechanical system (MEMS)-based sensors and actuators. However, the achievable volumetric and gravimetric energy densities of microbatteries are typically insufficient for intermediate-term applications of MEMS-enabled distributed internet-connected devices. Further, in the increasing subset of Internet of Things (IoT) nodes, where actuation is desired, the peak power density of the microbattery must be simultaneously considered. Metal-air approaches to achieving microbatteries are attractive, as the anode and cathode are amenable to miniaturization; however, further improvements in energy density can be obtained by minimizing the electrolyte volume. To investigate these potential improvements, this work studied very lean hydrogel electrolytes based on poly(vinyl alcohol) (PVA). Integration of high potassium hydroxide (KOH) loading into the PVA hydrogel improved electrolyte performance. The addition of potassium carbonate (K2CO3) to the KOH-PVA gel decreased the carbonation consumption rate of KOH in the gel electrolyte by 23.8% compared to PVA-KOH gel alone. To assess gel performance, a microbattery was formed from a zinc (Zn) anode layer, a gel electrolyte layer, and a carbon-platinum (C-Pt) air cathode layer. Volumetric energy densities of approximately 1400 Wh L-1 and areal peak power densities of 139 mW cm-2 were achieved with a PVA-KOH-K2CO3 electrolyte. Further structural optimization, including using multilayer gel electrolytes and thinning the air cathode, resulted in volumetric and gravimetric energy densities of 1576 Wh L-1 and 420 Wh kg-1, respectively. The batteries described in this work are manufactured in an open environment and fabricated using a straightforward layer-by-layer method, enabling the potential for high fabrication throughput in a MEMS-compatible fashion.

Bilayer Dense-Porous Li7 La3 Zr2 O12 Membranes for High-Performance Li-Garnet Solid-State Batteries.

Li dendrites form in Li7 La3 Zr2 O12 (LLZO) solid electrolytes due to intrinsic volume changes of Li and the appearance of voids at the Li metal/LLZO interface. Bilayer dense-porous LLZO membranes make for a compelling solution of this pertinent challenge in the field of Li-garnet solid-state batteries (SSB). Lithium is thus stored in the pores of the LLZO, thereby avoiding i) dynamic changes of the anode volume and ii) the formation of voids during Li stripping due to increased surface area of the Li/LLZO interface. The dense layer then additionally reduces the probability of short circuits during cell charging. In this work, a method for producing such bilayer membranes utilizing sequential tape-casting of porous and dense layers is reported. The minimum attainable thicknesses are 8-10µm for dense and 32-35µm for porous layers, enabling gravimetric and volumetric energy densities of Li-garnet SSBs of 279Wh kg-1 and 1003Wh L-1 , respectively. Bilayer LLZO membranes in symmetrical cell configuration exhibit high critical current density up to 6mA cm-2 and cycling stability of over 160 cycles at a current density of 0.5mA cm-2 at an areal capacity limitation of 0.25 mAh cm-2 .

Tri-sites co-doping: An efficient strategy towards the realization of 4.6V-LiCoO2 with cyclic stability

Lithium cobalt oxide (LCO) is extremely attractive for the volumetric and gravimetric energy density at high cut-off voltage, but the degradation issues we are always grappling with becomes much tougher. Here, an unconventional strategy of multi-sites co-doping is proposed using cheap and abundant elements like Na, Si, Al, Fe and F. By summarizing the fading behaviors of all the samples, the capacity fading shows a linear correlation with the doping elements. The optimized co-doping strategy enables each doping elements to achieve the full potential in the promotion of cyclic stability. The resultant LCO maintains a capacity retention of 81.8% after 500 cycles at 4.6 V of the full battery. Further evidences signify that the capacity fading in the early stage is mainly caused by surficial side reactions and the accompanying structural damage, while the fading in the later stage is due to particle cracking generated by the repeated planar gliding and the anabatic side reaction of the newly exposed surface. Therefore, not only the main factor of structural damage caused by surface side reactions should be considered, but more attention need to be paid on the planar gliding when designing more stable LCO. The tri-sites co-doping strategy, which can better integrate the inhibitory effect of different doping sites on planar gliding, provides a new idea for further improving the cyclic stability of high-voltage LCO.

Virtual screening of organic quinones as cathode materials for sodium-ion batteries.

High-throughput virtual screening (HTVS) has been increasingly applied as an effective approach to find candidate materials for energy applications. We performed a HTVS study, which is powered by: (i) automated virtual screening library generation, (ii) automated search on a readily purchasable chemical space of quinone-based compounds, and (iii) computed physicochemical descriptors for the prediction of key battery-related features of compounds, including the reduction potential, gravimetric energy density, gravimetric charge capacity, and molecular stability. From the initial virtual library of approximately 450k molecules, a total of 326 compounds have been identified as commercially available. Among them, 289 of the molecules are predicted to be stable for the sodiation reactions that take place at the sodium-ion battery cathodes. To study the behaviour of molecules over time at room temperature, we performed molecular dynamics simulations on a group of sodiated product molecules, which was narrowed down to 21 quinones after scrutinizing the key battery performance indicators. As a result, 17 compounds are suggested for validation as candidate cathode materials in sodium-ion batteries.

Activated Carbon-MnO2 Composite on Nickel Foam as Supercapacitors Electrode in Organic Electrolyte

Since energy storage is an essential component of global energy development, starting with batteries, fuel cells, and supercapacitors, it is an important topic of particular concern. Supercapacitors continue to be developed due to their high power density when compared to batteries, despite all of the benefits and drawbacks of the three. Activated carbon (AC) is materials that frequently utilized as a supercapacitor electrode due to the high surface area. Metal oxides such as manganese dioxide (MnO2) with high teoritical specific capacitance which loaded in activated carbon will caused an improvement on supercapacitors electrochemical performance. The composite was fabricated using blending method with a mass difference of MnO2, then deposited on a porous Ni-foam substrate. Ni-foam pores play as main role on the process of transferring electrolyte ions in the system so that the AC/MnO2 has, resulting a supercapacitor based AC-MnO2 15% nanocomposite with a gravimetric capacitance, energy density and power density of 79 F/g at 1 A/g, W/kg and Wh/kg respectively. The cell could maintain up to 93% after 100 cycles.

Techno-Economic Development Methodology for Mini-Environments in Battery Cell Production

Due to the rising interest in electric vehicles, the demand for more efficient battery cells is increasing rapidly. To support this transformation, battery cells must become cheaper and environmentally friendly. Energy consumption during production is a major driver of costs and CO2 emissions. To fulfill societal demand, higher gravimetric and volumetric energy density of lithium-ion battery cells are required. Since these materials are significantly more sensitive to moisture, the production conditions need to be adapted accordingly. Therefore, the preparation of clean and extremely dry atmospheric conditions is crucial for production of high-quality battery cells. The technology approach "Mini-Environment" enables the substitution of conventional clean- and dry-rooms for significant energy and cost savings. However, the diverse product- and process-specific characteristics along the value chain require individual solutions to enable Mini-Environments for highly automated battery cell production. Due to multiple interacting requirements and characteristics, such as operator interventions, logistics interfaces and air handling procedures, there is a very high diversity of variants for the machine equipment design. Moreover, typical methodological procedures for development of quality-oriented and energy efficient production machines remain less applicable to the early stages of technological development. Both issues lead to the research questions, how to identify the independencies between costs, air handling, product and process characteristics and how to reach the most techno-economical machine design. To answer these questions, a systematic techno-economic development procedure was conducted. Following a four-phase analytical approach, based on an extended morphological box, cost analysis, techno-economic utility analysis and sensitivity loop, different Mini-Environment concepts were constructed, analyzed and cross-evaluated. The study also forecasts the CO2 emission rate reduction and cost savings compared to alternative machine concepts. In summary, a fully interlinked system design was adapted on a cell assembly line with a cost-saving potential of 56% for future battery cell production.

Boosting the crystallinity of novel two-dimensional hexamine dipyrazino quinoxaline-based covalent organic frameworks for electrical double-layer supercapacitors

A novel and conjugated 2D 250-HADQ COF exhibits a high specific surface area and excellent thermal stability yielding high values of gravimetric capacitance and energy density in two-electrode double-layer supercapacitor cells.

Positioning hydrogen reaction sites by constructing CdS/CoNiMoS4 heterojunctions for efficient photocatalytic hydrogen evolution.

The high gravimetric energy density of hydrogen makes it an ideal chemical fuel to address the issues of fossil fuel depletion and environmental pollution. Even though transition metal sulfides (TMSs) have been extensively investigated as substitutes for noble metals, their effectiveness is still doubtful for practical applications. Herein, we introduce a facile and general strategy to fabricate heterojunctions with CdS nanorods and a multimetallic transition metal sulfide (CoNiMoS4) for enhanced photocatalytic activity. The CdS/CoNiMoS4 heterojunction will serve as a dual-function photocatalyst with enhanced visible light absorption capability offered by CdS and high charge transfer efficiency provided by CoNiMoS4 nanostructures. Moreover, CdS/CoNiMoS4 nanostructures exhibit the best photocatalytic performance to generate H2 with an amount of 31.9 mmol g-1 h-1, with a distinguished stability for over 25 h. This synthetic approach may offer a new strategy to create diverse heterojunctions with Earth-abundant multimetallic components, which may broaden their scope of application in catalysis.

Improved strategies for ammonium vanadate-based zinc ion batteries.

Aqueous zinc ion batteries (ZIBs) are becoming increasingly popular as a new form of resource for electrochemical energy storage due to their high safety, affordability, availability of natural zinc resources, and high gravimetric energy density. However, the development of high-performance ZIB cathode materials remains a great challenge because current ZIB cathode materials tend to have low conductivity and relatively complex energy storage mechanisms. Compared with other cathode materials, ammonium vanadate-based materials have been extensively investigated as cathode materials for ZIBs due to their plentiful availability and high potential capacity. In this review, we highlight the mechanisms and challenges of ammonium vanadate-based materials and summarize the progress in improved strategies including the design of different morphologies, doping with different impurities, the introduction of different intercalators, and combination with other materials for high-performance ZIBs. Finally, the paper also provides an outlook on the future challenges and development prospects of ammonium vanadate-based cathode materials in ZIBs.

High Loading Sulfur Cathodes by Reactive‐Type Polymer Tubes for High‐Performance Lithium‐Sulfur Batteries

AbstractSimultaneously attaining high gravimetric energy density (Eg) and volumetric energy density (Ev) in lithium‐sulfur (Li–S) batteries is a longstanding challenge that has to be solved for practical application, which demands breakthroughs in electrode materials with optimized functionality and structure. Herein, anthraquinone‐containing, reactive‐type polymer tubes (PQT) that can be used to regulate the redox chemistry of sulfur species are designed and prepared for practical Li–S batteries. PQT favors a similar redox potential window as sulfur, which effectively facilitates the immobilization and conversion of sulfur species through a reversible lithiation/delithiation process. Its tubular structure and high tap density is vital to the fabrication of intact electrode with high sulfur loading and minimizing electrolyte intake during battery operation. With all these contributions, Li–S battery with PQT/S cathode exhibits a stable cycling capacity (73% at 2.0 C over 1000 cycles), remarkable rate performance (514.2 mAh g−1 at 10 C), and a high areal capacity of 7.20 mAh g−1 with high sulfur loading under lean electrolyte condition. More importantly, the assembled Li–S pouch cell delivers an Eg of 329 Wh kg−1 and an Ev of 401 Wh L−1, which meets the requirement for practical operation.

Investigation of poly(3,6-dioxa-1,8-octane-dithiol)-based organosulfur polymer as the positive electrode material in rechargeable Li-S battery

The lithium-sulfur batteries (LISB) possess issues, such as insulating nature of sulfur, polysulfide shuttle, volume expansion and self-discharge, which impede its widespread commercialization. To address the insulating nature of sulfur, carbon-based materials were utilised. However, increasing the amount of carbon content in the cathode matrix reduces the specific capacity and the gravimetric energy density. To address the above-mentioned issues, we believe that these can be overcome by developing or utilising sulfur confining materials, favourably macromolecules, so-called organosulfur polymers, as suitable candidates and potential solution. Hence, we developed a sulfur rich organosulfur based polymer, sulfur-poly(3,6-dioxa-1,8-octane-dithiol) (PSDODT) via an inverse vulcanization reaction, as well as by changing the feed composition, and thus the sulfur content of the polymer. Then, the synthesized PSDODTs with various weight ratios of sulfur and DODT (30:70, 40:60, and 50:50) were used as an alternative to elemental sulfur, and these were also mixed with carbon host materials, such as carbon black (CB) and reduced graphene oxide (rGO). Subsequently, the electrochemical performances of these materials were evaluated as cathode materials for Li-sulfur batteries. Among the developed cathode materials, the 40S:60DODT-rGO composite showed enhanced specific capacity with good cyclic performances in comparison to the 30S:70DODT-CB combination. In addition to that, it has been identified from the results that the organosulfur based polymer PSDODT can be utilised as an alternative to conventional elemental sulfur, and this opens up some new research and development possibilities in the field of Li-sulfur batteries.

Photoliquefiable Azobenzene Surfactants toward Solar Thermal Fuels that Upgrade Photon Energy Storage via Molecular Design.

Photoresponsive phase change materials (PPCMs) are capable of storing photon and heat energy simultaneously and releasing the stored energy as heat in a controllable way. While, the azobenzene-based PPCMs exhibit a contradiction between gravimetric energy storage density and photoinduced phase change. Here, a type of azobenzene surfactants with balance between molecular free volume and intermolecular interaction is designed in molecular level, which can address the coharvest of photon energy and low-grade heat energy at room temperature. Such PPCMs gain the total gravimetric energy density up to 131.18 J g-1 by charging solid sample and 160.50 J g-1 by charging solution. Notably, the molar isomerization enthalpy upgrades by a factor of up to 2.4 compared to azobenzene. The working mechanism is explained by the computational studies. All the stored energy can release out as heat under Vis light, causing a fast surface temperature rise. This study demonstrates a new molecular designing strategy for developing azobenzene-based PPCMs with high gravimetric energy density by improving the photon energy storage.

Calcium-based composites directly irradiated by solar spectrum for thermochemical energy storage

The optical absorptance of calcium-based composites used in direct solar-driven calcium-looping thermochemical energy storage systems should be improved. Experimental data obtained by thermogravimetric analyzer (TGA) cannot adequately describe the realistic performance of such calcium-based composites. In this work, calcium-based composites filled in a fixed bed reactor were directly irradiated by concentrated sunlight to examine the performance of thermochemical energy storage under different light illumination conditions. The effects of doping content and concentration ratio of sunlight on the cycling performance of the modified calcium-based composites were investigated under direct solar-driven conditions. The Cr/Mn co-doped CaCO3-based materials with a molar ratio of Ca: Cr: Mn = 100:4:8 could be efficiently operated under direct sunlight irradiation conditions because of a high optical absorption of 73.22 %, achieving gravimetric energy densities of 1090 and 818 kJ/kg in the 1st and 10th cycles, respectively. The cycling performance of the calcium-based composites under different light illumination conditions was compared with that using the TGA device. By comparing the optimal performance in two operating modes, the cycling stability of the calcium-based composites attenuated faster in the solar-driven fixed bed reactor than in the TGA device, which was ascribed to the uneven temperature distribution in the solar-driven reactor. By preventing surface overheating or localized hot spots in a direct solar-driven reactor, cycling stability of the calcium-based composites can be enhanced. Based on this principle, we propose some improvement methods for ensuring uniform temperature distribution in CaCO3-based composites during the direct solar-driven calcination process.

Thin Solid Electrolyte Separators for Solid-State Lithium–Sulfur Batteries

The lithium-sulfur battery is one of the most promising "beyond Li-ion" battery chemistries owing to its superior gravimetric energy density and low cost. Nonetheless, its commercialization has been hindered by its low cycle life due to the polysulfide shuttle and nonuniform Li-metal plating and stripping. Thin and dense solid electrolyte separators could address these issues without compromising on energy density. Here, we introduce a novel argyrodite (Li6PS5Cl)-carboxylated nitrile butadiene rubber (XNBR) composite thin solid electrolyte separator (TSE) (<50 μm) processed by a scalable calendering technique and compatible with Li-metal. When integrated in a full cell with a commercial tape-cast sulfur cathode (3.54 mgS cm-2) in the presence of an in situ polymerized lithium bis(fluorosulfonyl)imide-polydioxolane catholyte and a 100 μm Li-metal foil anode, we demonstrate stable cycling for 50 cycles under realistic operating conditions (stack pressure of <1 MPa and 30 °C).

Flexible Freestanding Thin Polyethylene Oxide‐Based Film as Artificial Solid–Electrolyte Interface to Protect Lithium Metal in Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) that utilize sulfur and lithium (Li) metal as electrode materials are highly attractive for transportation applications due to their high theoretical gravimetric energy density. However, two major challenges currently impede the commercialization of LSB, which are the formation of Li dendrites and polysulfide shuttling. To mitigate these two effects, a protective film or artificial solid–electrolyte interface (SEI) can be applied directly to the Li‐metal surface. Herein, the preparation of freestanding polyethylene oxide (PEO)‐based films using tape casting as a scalable coating technique is presented. Moreover, the films are applied directly to the Li surface via a solvent‐free method. To demonstrate the suitability of the developed PEO‐based films, the long‐term cycling performance of the lithium–sulfur cells is discussed. It is shown that the cells with the Li‐metal surface protected by PEO‐based films achieve better stability and reproducibility, reaching ≈400 mA h g S−1 after 250 cycles compared to ≈200 mA h g S−1 after 250 cycles for the bare Li‐metal electrode. An extensive postmortem analysis of the Li‐metal electrode surface with scanning electron microscopy is additionally shown, revealing that the PEO‐based artificial SEIs form uniformly with a low level of defect layers at the interface with the Li‐metal electrode, which indicates the creation of a stable SEI.

Advances in Interfacial Engineering and Their Role in Heterostructure Formation for HER Applications in Wider pH

With 65% rise in the global demand, green hydrogen (H2) as a clean energy carrier with high gravimetric energy density, has emerged as a premier candidate in the past decade. The production of sustainable and clean hydrogen through water electrolysis tends to majorly rely on electrocatalysts with the scope of achieving exceptional activity with low cost and excellent durability. The extensive use of high cost noble metal HER electrocatalysts in the industry diverts the attention to recent studies proposing that a proper design of non-noble metal heterostructure could show comparable electrocatalytic performance. Construction of interfaces appears as a solution to simultaneously address multiple challenges and, at the same time, take advantage of each component in constructing rich interfaces that could synergistically enhance the HER activity in acidic, alkaline, and neutral environments. This review describes the different forms of interfaces arising from different heterostructures at the structural and atomic level, underlining and correlating the principle mechanisms responsible for the performance enhancement in the HER electrocatalysts. The first part of the review recognizes the heterostructures at the micro/nano scale and at the scale focusing mainly of 2D materials. Further, the interfaces at the atomic level especially composed of chalcogenides, carbides, phosphides, and nitrides are analyzed comprehensively based on their electrochemical performance. Finally, the interfacial mechanisms arsing as a consequence of the heterostructure formation are briefly described and correlated to provide a better understanding in the future design of HER electrocatalysts.

Binder-Free Freestanding 3D Zn-Graphene Anode Induced from Commercial Zinc Powders and Graphene Oxide for Zinc Ion Battery with High Utilization Rate

Aqueous zinc-ion batteries (AZIBs) have received widespread attention owing to the increasing demand for safety and inexpensive batteries. However, a zinc metal anode suffers from dendrite growth during continuous cycling, and side reactions occurred on anode surface such as hydrogen evolution reaction (HER) and passivation. Moreover, the low utilization of Zn metal is also a neglected issue leading to a low energy density at the cell-level. Herein, a nondendrite Zn anode with high utilization was designed by spontaneous reaction of commercial Zn powders and graphene oxide (GO). The formed binder-free three-dimensional (3D) anode Zn_G achieves a cycling time over 550 h and extremely low voltage hysteresis of ∼20 mV with 7.4% DOD (130 h for Zn foil with 1.3% DOD and 80 h for Zn powders with 7.4% DOD) at a current density of 1 mA cm–2 in a symmetric cell. In Zn||MnO2 full batteries, Zn_G greatly enhances the gravimetric energy density on the cell level and achieved more than 1600 cycles much higher than Zn foil (Zn_F) with 700 cycles and Zn powders (Zn_P) with 500 cycles. The low N/P ratio of 3 also achieved high stability with 126 mAh g–1 and 74.5% retention after 1000 cycles.

Insights into the Importance of Native Passivation Layer and Interface Reactivity of Metallic Lithium by Electrochemical Impedance Spectroscopy.

Lithium-metal batteries offer substantial advantages over lithium-ion batteries in terms of gravimetric and volumetric energy densities. However, their widespread practical use is hindered by safety concerns, often attributed to the poor stability of the metallic lithium interface, where electrochemical impedance spectroscopy (EIS) can provide crucial information. The EIS spectra of metallic lithium electrodes proved to be more complex than expected, especially when studying thin lithium metal foils. Here, it is identified that charge-transfer impedance becomes one of the main components of the EIS spectra, the magnitude of which is found to be strongly dependent on the native passivation layer of metallic lithium and on the nature of electrolyte. "Asymmetricity" of the EIS spectra in symmetric cells when separated the working and counter electrode contributions to the total impedance using three-electrode cells is also identified.

Hybrid Aluminum-Ion Capacitor with High Energy Density and Long-Term Durability

Hybrid capacitors have been extensively investigated owing to their potential applications in advanced devices to satisfy the requirements of high-energy, high-power, and extended cycle life. With the aim of significantly improving the performance of such devices, we propose a novel hybrid aluminum-ion capacitor (AIC) utilizing pore-size-controlled activated carbon as the cathode, Al foil as the anode, and an AlCl3-based ionic liquid as the electrolyte. The AIC exhibits high gravimetric and volumetric energy densities (51 W h kg−1 and 28 mW h cm−3, respectively), exceeding those of electrochemical double-layer capacitors and comparable to those of Li-ion capacitors. The hybrid device also exhibits a long-term cycle life, with a capacitance retention of 97.9% after 10,000 cycles, and a coulombic efficiency of 97.6%–99.9% over a specific current range of 0.1–5.0 A g−1. Therefore, high-performance AICs, obtained by optimizing the electrode materials have the potential to be cost-effective and safe, with high-energy and power density.