Energy Density Requirements Research Articles

Synergy of Silicon-Graphene Anodes and Polymer-Ceramic Hybrid Separators for High Rate-Capable Lithium-Ion Batteries

With more and more electric vehicles (EV) hitting the market, the need for better and more robust energy storage system increases, and silicon has been a promising candidate for the next generation anode material to satisfy the high energy density and high-power requirements for electric vehicles because of its extremely high theoretical capacity. This has allowed the design of thinner electrodes to reduce the diffusion time scales and deliver a fast charge. However, at high charge and discharge rates, low electrical conductivity (~1.12 eV) of silicon hampers the battery performance. As a result, a lot of research has been conducted to improve the performance of silicon anodes using nanoscale carbon to increase the electrical conductivity. Graphene has been used to synthesize Si/Gr hybrid anodes due to its high conductivity.Graphene nanoribbons (GNRs) , a part of the graphene family, are one-dimensional graphene nanostructures which tune its electrical properties based on dimensional confinement. GNR has a higher conductivity than Graphene. It also has high aspect ratio and surface area to provide a strong conductive path along with mechanical strength to support the silicon anode. Due to presence of GNR, lithium-ion transport into silicon nanostructures was enhanced. As a result, 50% of graphene was replaced by 50% GNR with silicon nanoparticles to form anodes. Due to the highly conducting structure of GNR, capacity at high rates was significantly improved because of the improved silicon utilization. Since GNR’s dimensions are in nanometer range, connection with silicon nanoparticles is better. It not only improves silicon to silicon conductivity, but it also acts as a filler for better connection of graphene with silicon nanoparticles.Addition of graphene nanoribbons can improve the lithium-ion transport within the anode but to enhance the high charge transfer rate further, Si/GNR/Gr hybrid, high rate-capable anodes were paired with Polyimide (PI)/Polysilsesquioxane (PSSQ) hybrid separators which also shown to exhibit an improved charge transfer rate. At high rates such as 3C and 5C, the effect of separator on the cell performance becomes more prominent. While Celgard’s performance was very unstable at both 3C and 5C, at 3C, the cycling of hybrid separators did not get impacted, despite the relatively harsher conditions. This synergistic combination of high-rate capable silicon/graphene anode and hybrid separator outperformed the commercially used separator especially at high-rate cycling. Cells with Si/GNR/Gr anode paired with the PI/PSSQ separator delivered an impressive capacity of 1,000 mAh/g at high charge/discharge rates of 5C/5C.

Advancements and Challenges in the Synthesis of Oxymethylene Ethers (OMEs) as Sustainable Transportation Fuels.

The urgent need for sustainable alternatives to fossil fuels in the transportation sector is driving research into novel energy carriers that can meet the high energy density requirements of heavy-duty vehicles without exacerbating the climate change. This concept article examines the synthesis, mechanisms, and challenges associated with oxymethylene ethers (OMEs), a promising class of synthetic fuels potentially derived from carbon dioxide and hydrogen. We highlight the importance of OMEs in the transition towards non-fossil energy sources due to their compatibility with the existing Diesel infrastructure and their cleaner combustion profile. The synthesis mechanisms, including the Schulz-Flory distribution and its implications for OME chain length specificity, and the role of various catalysts and starting materials are discussed in depth. Despite advancements in the field, significant challenges remain, such as overcoming the Schulz-Flory distribution, efficiently managing water as an undesirable byproduct, and improving the overall energy efficiency of the OME synthesis. Addressing these challenges is crucial for OMEs to become a viable alternative fuel, contributing to the reduction of greenhouse gas emissions and the transition to a sustainable energy future in the transportation sector.

Comparative study of the reduction techniques of Graphene Oxide for Zinc Ion hybrid Storage Application

The increasing demand for low cost and high energy storage devices has given rise to the hybrid supercapacitor device. To overcome the safety issues of the Lithium and Sodium-based devices Zinc ion hybrid supercapacitors (ZIHSCs) are a promising alternative. These devices amalgamate the energy density and power density requirements which makes them suitable for varied applications. The device construction comprises of a zinc anode, zinc-based electrolyte and capacitive type cathode material. Carbon based nanomaterials such as reduced graphene oxide (RGO) are predominantly used as potential cathodes. The strategies involved in obtaining RGO changes the structural characteristic of the samples. This study compares three different strategies such as Chemical reduction (c-RGO), Microwave reduction (m-RGO) and Solar reduction (s-RGO). It was observed that the employment of each these techniques render the change in the physical properties of the materials like number of defect, change in the surface are, porosity and in-situed developed functional group, especially oxygen species. These changes were analyzed thoroughly by various techniques like Raman, Fourier, X-ray diffraction and X-Ray photoelectron spectroscopy. The overall study reveals that solar reduction route shows enhanced surface area and porosity and decrease in defect concentration. Further due to this enhanced property in s-RGO the zinc ion storage capacitance of the fabricated ZIHSC was 200 F/g with a high cyclic stability of 5100 cycles at a current density of 10 A/g. The enhanced energy density thus obtained was 111 Wh/kg corresponding to a power density of 10 KW/kg.

Working Fluid Selection and Thermodynamic Optimization of the Novel Renewable Energy-Based RESTORE Seasonal Storage Technology

Abstract Seasonal-based energy storage is expected to be one of the main options for the decarbonization of the space heating sector by increasing the renewables dispatchability. Technologies available today are mainly based on hot water and can only partially fulfill the efficiency, energy density and affordability requirements. This work analyzes a novel system based on pumped thermal energy storage (PTES) concept to maximize renewables and waste heat exploitation during summer and make them available during winter. Organic fluid-based cycles are adopted for the heat upgrade during hot season (heat pump (HP)) and to produce electricity and hot water during cold season (power unit (PU)). Upgraded thermal energy drives an endothermic reaction producing dehydrated solid salts, which can be stored for months using inexpensive and high energy density solutions. This paper focuses on thermodynamic cycles design, comparing the performance attainable with several working fluids. Two different configurations are investigated: coupled systems, sharing the fluid and heat exchangers in both operating modes, and decoupled systems. A preliminary economic assessment completes the study, including a sensitivity analysis on electricity and heat prices. Cyclopentane is identified as a promising working fluid for coupled systems, reaching competitive round trip efficiencies (RTEs), maximizing the ratio between performance and HX surfaces, without excessive turbomachinery volume ratios and volumetric flows. Economic analysis shows that solutions with lower efficiency, but also lower capital cost, can achieve competitive payback times (PBT). On the contrary, decoupled systems are less attractive, as they reach slightly higher thermodynamic performance, but require higher capital costs, possibly being of interest only in specific applications.

Coordinated power management strategy for reliable hybridization of multi-source systems using hybrid MPPT algorithms

This research discusses the solar and wind sourcesintegration in aremote location using hybrid power optimization approaches and a multi energy storage system with batteries and supercapacitors. The controllers in PV and wind turbine systems are used to efficiently operate maximum power point tracking (MPPT) algorithms, optimizing the overall system performance while minimizing stress on energy storage components. More specifically, on PV generator, the provided method integrating the Perturb & Observe (P&O) and Fuzzy Logic Control (FLC) methods. Meanwhile, for the wind turbine, the proposed approach combines the P&O and FLC methods. These hybrid MPPT strategies for photovoltaic (PV) and wind turbine aim to optimize its operation, taking advantage of the complementary features of the two methods. While the primary aim of these hybrid MPPT strategies is to optimize both PV and wind turbine, therefore minimizing stress on the storage system, they also aim to efficiently supply electricity to the load. For storage, in this isolated renewable energy system, batteries play a crucial role due to several specific benefits and reasons. Unfortunately, their energy density is still relatively lower compared to some other forms of energy storage. Moreover, they have a limited number of charge–discharge cycles before their capacity degrades significantly. Supercapacitors (SCs) provide significant advantages in certain applications, particularly those that need significant power density, quick charging and discharging, and long cycle life. However, their limitations, such as lower energy density and specific voltage requirements, make them most effective when combined with other storage technologies, as batteries. Furthermore, their advantages are enhanced, result a more dependable and cost-effective hybrid energy storage system (HESS). The paper introduces a novel algorithm for power management designed for an efficient control. Moreover, it focuses on managing storage systems to keep their state of charge (SOC) within defined range. The algorithm is simple and effective. Furthermore, it ensures the longevity of batteries and SCs while maximizing their performance. The results reveal that the suggested method successfully keeps the limits batteries and SCs state of charge (SOC). To show the significance of system design choices and the impact on the battery’s SOC, which is crucial for the longevity and overall performance of the energy storage components, a comparison in of two systems have been made. A classical system with one storage (PV/wind turbine/batteries) and the proposed system with HESS (PV/wind turbine system with batteries). The results show that the suggested scenario investigated with both wind and solar resources appears to be the optimum solution for areas where the two resources are both significant and complementary. The balance between the two resources seems to contribute to less stress on storage components, potentially leading to a longer lifespan. An economical study has been made, using the Homer Pro software, to show the feasibility of the proposed system in the studied area.

Exploring High-Voltage Sulfate Cathodes for Low-Temperature Thermal Batteries

Thermal batteries have high specific energy and can operate in harsh environments, making them suitable for military and aerospace applications. However, existing cathode materials do not meet the high power and energy density requirements of advanced military systems. This urgent need motivates the development of new high-performance cathodes. Sulfates, as polyanionic compounds with highly electronegative anions, often exhibit higher voltages than phosphates. This high voltage should match the high power output needs of thermal battery cathode, though few studies explore sulfate. In this of case, NiSO4, CoSO4, and CuSO4 were investigated as cathode materials for thermal battery. They all have higher voltage and greater specific capacity at 450 °C (cut-off voltage is 75% of peak voltage) than at 500 °C or higher. Compared with other temperatures, the peak voltage of CoSO4 cathode at 450 °C is 2.23 V and the specific capacity is 296 mAh g−1. While CuSO4 showed modest capacity at 450 °C, its high voltage of 2.5 V makes it a promising high energy density cathode. This work provides new insights into cathode materials for high power and energy density thermal batteries.

Optimal Design of Boundary Angle for Gas Foil Thrust Bearing Thermal Performance

As the energy density and efficiency requirements of air compressors continue to increase, gas foil thrust bearings face a high risk of thermal failure due to their elevated speed and limited cooling space. This paper proposes a novel structure for gas foil thrust bearings with enhanced thermal characteristics. A thermo-elastic–hydrodynamic model is developed using a thermal-fluid–solid interaction approach to investigate aerodynamic and thermal performance. The load capacity and thermal characteristics of nine different boundary angles are analyzed. The model is validated, and the actual characteristics of gas foil bearings with various boundary angles are examined using a test rig. The results indicate that, compared to conventional gas foil thrust bearings with a boundary angle of 0°, the new structure with a boundary angle ranging from −10° to −5° not only maintains the load carrying capacity but also improves thermal characteristics. Furthermore, this improvement becomes more pronounced with higher rotational speeds. Therefore, the proposed optimization is advantageous in reducing the risk of thermal failure.

Recent advances in separator design for lithium metal batteries without dendrite formation: Implications for electric vehicles

Electric vehicle (EV) technology addresses the challenge of reducing carbon and greenhouse gas emissions. The power battery, which serves as the energy source for EVs, directly impacts their driving range, maximum speed, and service life. Considering the high energy density requirements for future EVs, lithium metal anodes possess several advantages such as high theoretical capacity, high energy and power density, and low electrochemical reduction potential which enable them to be a promising material for next-generation batteries. However, lithium metal anodes suffer from short cycle life and safety concerns due to the formation of dendritic and moss-like metal deposits that impede battery performance and reliability. This review will feature the recent advancement of functional separators to tackle these challenges. Firstly, this review presents a comprehensive review of the growth mechanism of lithium dendrites and delineates the underlying processes leading to battery failure. This aims to deepen understanding, which serves as a fundamental basis for classifying separators. Then, according to the growth of lithium dendrites and the failure process of lithium metal batteries, namely lithium-ion nucleation, growth of lithium dendrites, penetration of lithium dendrites into the separator, thermal runaway and even failure of the battery, four types of functional separators for different stages are proposed. The functions of these types of separators are to prevent the nucleation of lithium ions and regulate the uniform deposition of lithium ions, detect and eliminate dendrites, increase the mechanical strength of the separator and enhance the thermal stability and flame-retardancy of the separators, respectively. Finally, the recent advances of the above strategies are reviewed and discussed, existing critical problems are identified, and the future perspective of functional separators for the safety of lithium metal batteries is also discussed.

Advanced multilayer model electrode for binder distribution within composite electrodes of lithium batteries

The loading levels of composite electrodes are increasing continuously to satisfy the energy density requirements of lithium-ion batteries (LIBs) in electric vehicles (EVs). Furthermore, a faster coating and drying process in the mass-production line yields a nonuniform binder distribution. Thus, it is necessary to understand its distribution within the composite electrode and control it for a better and more reliable electrochemical performance. Therefore, we propose the utilization of an advanced multilayer electrode model consisting of several electrode layers with different binder contents. Using these controlled electrode models, the adhesive strength within each layer was examined using a surface and interfacial cutting analysis system (SAICAS). This was followed by a composition analysis using EDX on each surface. Subsequently, the electronic conductivities of the model electrodes were measured using an electrode resistance meter to determine the bulk and interfacial electrode resistances. Furthermore, the electrochemical properties of each model electrode were evaluated to correlate their relationships and design the optimum binder distribution. Thus, this multilayer model provides a highly effective platform for determining the optimum binder distribution in highly loaded composite electrodes for high-energy–density and long-lasting LIBs.

Thiophene organic molecules in-situ grafted mesoporous carbon promote high stable and high kinetic lithium-sulfur batteries

Lithium‑sulfur (LiS) batteries are widely regarded as the promising battery system that meet the high energy density requirement up to 500 Wh kg−1. However, the serious shuttle effect and poor reaction kinetics seriously slow down the practical application of LiS batteries. For both solid and liquid LiS batteries, holding sulfides by adsorptive and catalytic host is an indispensable strategy to improve their reaction kinetic. Carbonaceous materials have been widely used as the sulfur hosts due to their easy controlled morphologic, lightweight and low-cost. However, these advantages were usually shelved by their low wettability and poor adsorption to polysulfides. In this study, a high active and stable carbonaceous host was synthesized by in-situ grafting thiophene molecules on mesoporous carbon. Sulfur was further bond on the thiophene molecules to form an extremely stable electrode structure. More importantly, the electron-rich conjugated thiophene molecules, which with high ionic and electronic conductivity, can effectively improve the reaction kinetics of LiS batteries. This simple and reproducible cathode modification strategy provides a reliable reference for realizing the practical application of LiS batteries.

In situ fluoro-oxygen codoped graphene layer for high-performance lithium metal anode.

Because traditional lithium-ion batteries have been unable to meet the energy density requirements of various emerging fields, lithium-metal batteries (LMBs), known for their high energy density, are considered promising next-generation energy storage batteries. However, a series of problems, including low coulombic efficiency and low safety caused by dendrites, limit the application of lithium metal batteries. Herein, fluoro-oxygen codoped graphene (FGO) was used to modify the copper current collector (FGO@Cu). FGO-coated current collector provides more even nucleation sites to reduce the local effective current density. FGO is partly reduced during cycling and helps form stable LiF-rich SEI. Moreover, graphene's oxygen and fluorine functional groups reconstruct the current density distribution, promoting uniform lithium plating. The FGO@Cu current collector demonstrates superior properties than commercial Cu foil. The FGO@Cu delivers a 97% high CE for over 250 cycles at 1 mA cm-2. The FGO@Cu symmetrical battery cycled at 1 mA cm-2 for over 650 h. LiFePO4 fuel cell with a lithium-plated FGO@Cu collector as an anode exhibits superior cycling stability.

All-Solid-State Li-Metal Cell Using Nanocomposite TiO2/Polymer Electrolyte and Self-Standing LiFePO4 Cathode

Li-ion batteries (LIBs) represent the most sophisticated electrochemical energy storage technology. Nevertheless, they still suffer from safety issues and practical drawbacks related to the use of toxic and flammable liquid electrolytes. Thus, polymer-based solid electrolytes may be a suitable option to fulfill the safety and energy density requirements, even though the lack of high ionic conductivity at 25 °C (10−8–10−7 S cm−1) hinders their performance. To overcome these drawbacks, herein, we present an all-solid-state Li-metal full cell based on a three-component solid poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl) imide/titanium dioxide composite electrolyte that outclasses the conventional poly(ethylene oxide)-based solid electrolytes. Moreover, the cell features are enhanced by the combination of the solid electrolyte with a self-standing LiFePO4 catholyte fabricated through an innovative, simple and easily scalable approach. The structural, morphological and compositional properties of this system are characterized, and the results show that the electrochemical performance of the solid composite electrolyte can be considerably improved by tuning the concentration and morphology of TiO2. Additionally, tests performed with the self-standing LiFePO4 catholyte underline a good cyclability of the system, thus confirming the beneficial effects provided by the novel manufacturing path used for the preparation of self-standing electrodes.

(Battery Division Student Research Award Sponsored by Mercedes-Benz Research & Development) Quantitative SEI-Based Descriptors for Li metal Liquid Electrolyte Design

Energy density requirements for next-generation batteries make the Li metal anode a key candidate to replace graphite in Li-ion batteries due to Li’s improved capacity (3,860 mAh/g vs. 372 mAh/g). However, Li anodes display lower Coulombic efficiency (CE, <99.9%) than graphite (>99.95%), resulting in faster loss of reversible Li over cycling. This shortfall derives from parasitic Li-electrolyte reactions that lead to accumulation of inactive Li0 and electrolyte-derived byproducts, which result in the formation of a native solid electrolyte interphase (SEI) on Li. Despite the importance of the SEI, its properties and composition are challenging to probe experimentally due to its exceedingly low amount (sub-μmolLi/cm2/cycle at >99% CE). Consequently, the framework on which the understanding of SEI composition and function was built has largely been qualitative, and descriptors to CE have overwhelmingly focused on electrolyte-, as opposed to SEI-based, metrics.To bridge this gap, this collective work focuses on advancing experimental methodologies to precisely quantify (1) functional properties of native SEIs on Li and (2) their chemical composition, both in order to explore their relationships with CE. First, we use a combination of self-consistent measurements involving EIS and CV to measure rates of Li+ exchange across these native interfaces, revealing that this functional property varies across electrolytes, increasing from low to high CE. These experiments further reveal an evolution of Li+ exchange with cycling unique to high-CE electrolytes and that is tightly linked to rate capability. In particular, we find that SEIs of high-CE electrolytes can support Li+ exchange rates in excess of 1 mA/cm2, and increasing to >>10 mA/cm2 after SEI formation and cycling. In order to (2) explore which SEI phases tend to be favored at high CE, we leveraged the quantitative power of analytical tools such as GC, NMR and ICP-AES to measure byproducts of SEI formation. We developed a custom operando GC experiment to measure and chemically-resolve gas evolution in situ during Li cycling. With sub-nmol/min resolution, these revealed, quantitatively, that SEI formation reactions that release CO or CO2, thus leaving behind a decarbonylated/decarboxylated byproduct in the SEI are associated with higher CE. We also expanded our chemical quantification studies to postmortem cells using a titration scheme that was capable of quantifying with ~nAh resolution SEI phases such as ROCO2Li, Li2C2, Li2C2, LiF and P-containing phases, in addition to the inactive Li0 that accumulates on the anode after cycling. In carbonate-based electrolytes, it was found that salt-derived phases (LiF and P) comprised only ~5% of the SEI, with solvent-derived products being the majority of the SEI. Furthermore, it was found that Li2C2, a previously-unmeasured phase on Li, shows a strong anti-correlation with CE. More recently, we further expanded our titration strategy to include other previously-unmeasured phases in leading high-CE electrolytes. Altogether, chemical quantification of the SEI reveals quantitative “SEI fingerprints” that are unique to each electrolyte. Taken together, these quantitative SEI-based descriptors enable a new avenue for electrolyte engineering, informed by a fundamental understanding of the “optimal” Li SEI and their associated capacity loss mechanisms at high CE.

Design Strategies of Spinel Oxide Frameworks Enabling Reversible Mg-Ion Intercalation.

ConspectusReversible Mg2+ intercalation in metal oxide frameworks is a key enabler for an operational Mg-ion battery with high energy density needed for the next generation of energy storage technologies. While functional Mg-ion batteries have been achieved in structures with soft anions (e.g., S2- and Se2-), they do not meet energy density requirements to compete with the current rechargeable lithium-ion batteries due to their low insertion potentials. It emphasizes the necessity of finding an oxide-based cathode that operates at high potentials. A leading hypothesis to explain the limited availability of oxide Mg-ion cathodes is the belief that Mg2+ has sluggish diffusion kinetics in oxides due to strong electrostatic interactions between the Mg2+ ions and oxide anions in the lattice. From this assessment, it can be hypothesized that such rate limiting kinetic shortcomings can be mitigated by tailoring an oxide framework through creating less stable Mg2+-O2- coordination.Based on theoretical calculations and preliminary experimental data, oxide spinels have been identified as promising cathode candidates with storage capacity, insertion potential, and cation mobility that meet the requirements for a secondary Mg-ion battery. However, spinels with a single redox metal, such as MgCr2O4 or MgMn2O4, were not found to demonstrate sufficiently reversible Mg-ion intercalation at high redox potentials when coupled with nonaqueous Mg-electrolytes. Therefore, a materials development effort was initiated to design, synthesize, and evaluate a new class of solid-solution oxide spinels that can satisfy the required properties needed to create a sustainable Mg-ion cathode. These were designed by bringing together electrochemically active metals with stable redox potentials and charged states against the electrolyte, for instance, Mn3+, in combination with a structural stabilization component, typically Cr3+. Furthermore, common spinel structural defects that degrade performance, i.e., antisite inversion, were controlled to see correlation between structures and electrochemical overpotentials, thus controlling overall hysteresis. The designed materials were characterized by both short- and long-range structure in both ex situ and in situ modes to confirm the nature of solid-solution and to correlate structural changes and redox activity to electrochemical performance. Consistent and reproducible results were observed for facile bulk Mg2+-ion activity without phase transformations, leading to enhanced energy storage capability based on reversible intercalation of Mg2+, enabled by understanding the variables that control the electrochemical performance of the spinel oxide. Based on these observations, with proper materials design, it is possible to develop an oxide cathode material that has many of the desired properties of a Li-ion intercalation cathode, representing a significant mile marker in the quest for high energy density Mg-ion batteries.This Account describes strategies for the design and development of new spinel oxide intercalation materials for high-energy Mg-ion battery cathodes through a combination of theoretical and experimental approaches. We will review the key factors that govern the kinetics of Mg2+ diffusion in spinel oxides and illustrate how material complexity correlates with the electrochemical Mg2+ activity in oxides and is supported by secondary characterization. The understanding gained from the fundamental studies of cation diffusion in oxide cathodes will be beneficial for chemists and materials scientists who are developing rechargeable batteries.

Enhanced energy density and fast-charging ability via directional particle configuration

The limited energy density of lithium-ion capacitors poses a significant obstacle to their widespread application, primarily stemming from the inability of the electrodes to simultaneously fulfill both high energy density and rapid charging requirements. Experimental data demonstrate that a directional particle configuration can enhance charging speed while maintaining high-capacity density, but it is rarely discussed. Here, we have developed a particle-level electrochemical model capable of reconstructing an electrode with a directional particle configuration. By employing this method, an investigation was conducted to explore how the spatial morphology characteristics of particle configuration impact the energy storage characteristics of electrodes. Results demonstrate that rational particle configuration can effectively enhance the transport of lithium ions and create additional space for lithium-ion storage. With the same particle size distribution, the best electrode can increase the discharge capacity by up to 132.4% and increase the charging SOC by 11.3% compared to the ordinary electrode under the condition of 6 C. These findings provide a further understanding of the energy storage mechanism inside the anisotropic particle distribution electrode, which is important for developing high-performance lithium-ion capacitors.

A biocompatible and flexible supercapacitor for wearable electronic devices

In this work, a supercapacitor (SC) designed for flexible and wearable textile systems operating in environments similar to biological fluids is presented. Supercapacitor electrode (SE) uses electrodes composed of derivatized coumarin poly(3,4-ethylenedioxythiophene)/7-Hydroxy-4-phenyl-2H-chromen-2-one (SE1), poly(3,4-ethylenedioxythiophene)/7-Hydroxy-8-(((1-hydroxy-3-phenylpropan-2-yl)imino)methyl)-4-phenyl-2H-chromen-2-one (SE3) and poly(3,4-ethylenedioxythiophene/Ethyl-2-(((7-hydroxy-2-oxo-4-phenyl-2H-chromen-8-yl)methylene) amino)-3-(4-hydroxyphenyl) propanoate (SE4) in 3.0 M NaCl as the electrolyte. The SE4 shows ultra-high specific capacitance of 2852.6 F g−1 (14.3 F cm−2) at a current density of 1.0 A g−1 (5.0 mA cm−2). The energy and power densities of the symmetric supercapacitor consisting of SE4 were 46.7 Wh/kg and 800.0 W kg−1, respectively for 1.0 V and its specific capacitance is 672.6 F g−1. SC exhibits a capacitance retention of 113.6% by charging/discharging stability (15,000 cycles). Cyclic voltammograms generated by twisting and bending the flexible supercapacitor at various angles (0–180°) are successfully carried out. SC was made that shows the operation of a red LED light when charged with a battery. The device, created through the use of aqueous electrolyte systems such as Na+, Cl− ions, has demonstrated significant performance as a safe and sustainable way to meet the energy and power density requirements in wearable electronic systems.

Reversible Multielectron Redox Chemistry in a NASICON-Type Cathode toward High-Energy-Density and Long-Life Sodium-Ion Full Batteries.

Na-superionic-conductor (NASICON)-type cathodes (e.g., Na3 V2 (PO4 )3 ) have attracted extensive attention due to their open and robust framework, fast Na+ mobility, and superior thermal stability. To commercialize sodium-ion batteries (SIBs), higher energy density and lower cost requirements are urgently needed for NASICON-type cathodes. Herein, Na3.5 V1.5 Fe0.5 (PO4 )3 (NVFP) is designed by an Fe-substitution strategy, which not only reduces the exorbitant cost of vanadium, but also realizes high-voltage multielectron reactions. The NVFP cathode can deliver extraordinary capacity (148.2mAhg-1 ), and decent cycling durability up to 84% after 10000 cycles at 100 C. In situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy characterizations reveal reversible structural evolution and redox processes (Fe2+ /Fe3+ , V3+ /V4+ , and V4+ /V5+ ) during electrochemical reactions. The low ionic-migration energy barrier and ideal Na+ -diffusion kinetics are elucidated by density functional theory calculations. Combined with electron paramagnetic resonance spectroscopy, Fe with unpaired electrons in the 3d orbital is inseparable from the higher-valence redox activation. More competitively, coupling with a hard carbon (HC) anode, HC//NVFP full cells demonstrate high-rate capability and long-duration cycling lifespan (3000stable cycles at 50 C), along with material-level energy density up to 304Whkg-1 . The present work can provide new perspectives to accelerate the commercialization of SIBs.

Towards a Fully-Quantitative Picture of SEI Chemical Composition and Its Native Li+ Exchange in Liquid Electrolytes

Energy density requirements for next-generation batteries make the lithium (Li) metal anode a key candidate to replace graphite in lithium-ion batteries due to Li’s improved capacity (3,860 mAh/g vs. 372 mAh/g). However, Li anodes display lower Coulombic efficiency (CE, <99.9%) than graphite (>99.95%),1 resulting in faster loss of reversible Li over cycling. This shortfall derives from parasitic Li-electrolyte reactions that lead to accumulation of inactive Li0 and electrolyte-derived byproducts, which result in the formation of a native solid electrolyte interphase (SEI) on Li. In addition to contributing to capacity loss, the SEI also has the important role of regulating Li+ exchange between Li and the electrolyte, which may affect Li plating morphology and reversibility.2 Despite significant advances, the framework on which the understanding of SEI composition and function was built has largely been qualitative, often due to experimental limitations and/or lack of self-consistent techniques.To bridge this gap, my thesis work focuses on advancing experimental techniques and methodologies to precisely quantify the chemical composition and rates of Li+ exchange in native SEIs. Using a combination of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), self-consistent rates of Li+ exchange are reported across a wide range of electrolytes.3 Notably, we found that native SEIs formed in high CE electrolytes displayed consistently higher rates of Li+exchange. The improved transport in high-CE electrolytes was found to emerge after an SEI formation cycle, and amplified over cycling, indicating that fast Li+ exchange is beneficial to Li reversibility.In order to identify which SEI phases grant high-CE electrolytes their beneficial functional properties, we also developed and expanded upon a series of titration experiments based on GC, ICP-AES and NMR that can track an extended array of key SEI phases: semicarbonates (ROCO2Li), lithium carbide (Li2C2), olefins (RLi), LiF, P-containing phases, and total Li loss.4 In the 1 M LiPF6 EC/DEC electrolyte, we demonstrate chemical resolution up to 71% of Li loss and 33% of SEI loss. Among the quantifiable SEI phases, ROCO2Li was consistently the major phase, but its proportions were invariant with CE. Instead, Li2C2, a minor phase, exhibited clear inverse correlation with CE. We also demonstrate further quantitative chemical resolution can be achieved with online GC, which can differentiate between the different types of semicarbonate (i.e., which “R” in ROCO2Li) and alkoxide phases that form on Li.5 Altogether, these results add further nuance to the current understanding of SEI composition and their function, which we hope will allow more quantitative electrolyte design. Hobold, G. M.; Lopez, J.; Guo, R.; Minafra, N.; Banerjee, A.; Shirley Meng, Y.; Shao-Horn, Y.; Gallant, B. M., Moving Beyond 99.9% Coulombic Efficiency for Lithium Anodes in Liquid Electrolytes. Nat. Energy 2021, 6 (10), 951-960. Zheng, J.; Kim, M. S.; Tu, Z.; Choudhury, S.; Tang, T.; Archer, L. A., Regulating Electrodeposition Morphology of Lithium: Towards Commercially Relevant Secondary Li Metal Batteries. Chem. Soc. Rev. 2020, 49 (9), 2701-2750. Hobold, G. M.; Kim, K.-H.; Gallant, B. M., Beneficial Vs. Inhibiting Passivation by the Native Lithium Solid Electrolyte Interphase Revealed by Electrochemical Li+ Exchange. 2022. Hobold, G. M.; Gallant, B. M., Quantifying Capacity Loss Mechanisms of Li Metal Anodes Beyond Inactive Li0. ACS Energy Lett. 2022, 7 (10), 3458-3466. Hobold, G. M.; Khurram, A.; Gallant, B. M., Operando Gas Monitoring of Solid Electrolyte Interphase Reactions on Lithium. Chem. Mater. 2020, 32 (6), 2341-2352.

Examining the Electrochemical Properties of Hybrid Aqueous/Ionic Liquid Solid Polymer Electrolytes through the Lens of Composition‐Function Relationships

AbstractSolid polymer electrolytes (SPEs) have the potential to meet evolving Li‐ion battery demands, but for these electrolytes to satisfy growing power and energy density requirements, both transport properties and electrochemical stability must be improved. Unfortunately, improvement in one of these properties often comes at the expense of the other. To this end, a “hybrid aqueous/ionic liquid” SPE (HAILSPE) which incorporates triethylsulfonium‐TFSI (S2,2,2) or N‐methyl‐N‐propylpyrrolidinium‐TFSI (Pyr1,3) ionic liquid (IL) alongside H2O and LiTFSI salt to simultaneously improve transport and electrochemical stability is studied. This work focuses on the impact of HAILSPE composition on electrochemical performance. Analysis shows that an increase in LiTFSI content results in decreased ionic mobility, while increasing IL and water content can offset its impact. pfg‐NMR results reveal that preferential lithium‐ion transport is present in HAILSPE systems. Higher IL concentrations are correlated with an increased degree of passivation against H2O reduction. Compared to the Pyr1,3 systems, the S2,2,2 systems exhibit a stronger degree of passivation due to the formation of a multicomponent interphase layer, including LiF, Li2CO3, Li2S, and Li3N. The results herein demonstrate the superior electrochemical stability of the S2,2,2 systems compared to Pyr1,3 and provide a path toward further enhancement of HAILSPE performance via composition optimization.

Bifunctional lithiophilic carbon fibers with hierarchical structure for high-energy lithium metal batteries

Lithium (Li) metal is an impeccable candidate anode for satisfying the energy density requirements of next-generation Li batteries. However, Li dendritic growth and fragile solid-elecrolyte interphase (SEI) caused by the high reactivity between Li and electrolyte are the primary challenges for its large-scale applications. Herein, a bifunctional lithiophilic hierarchical substrate composed of high-density nitrogen-doped carbon nanotubes and Co nanoparticles encapsulated in graphene (Co@G) decorated carbon fibers (Co-N-CNT-CF) can modulate the structural dimensions and hierarchy of Li nucleation/growth and alleviate Li volume expansion, achieving the homogeneous Li plating/stripping behavior. Density functional theory (DFT) calculations and experimental results confirm the highly lithiophilicity of the substrate, which exhibits a low Li nucleation overpotential, enhanced Coulombic efficiency (CE), small voltage hysteresis, and ultrastable lifespan without dendritic formation. As coupled with the thick LiFePO4 and LiCoO2 (∼2 mA h cm−2) cathodes, the Co-N-CNT-CF@Li composite anode (N/P = 3) enables a high reversible capacity, high Li utilization, and improved cycle stability. This work engineers a hierarchical structure of the three-dimensional (3D) lithiophilic carbon substrate for realizing highly reversible, dendritic-free Li metal anodes.