Improved Energy Density Research Articles

VOx anchored Ti3C2Tx MXene heterostructures for high-performance 2.2 V supercapacitors

Pseudocapacitive materials with superior electrochemical properties have attracted significant interest in developing high-performance supercapacitors. Herein, VOx anchored Ti3C2Tx MXene pseudocapacitive materials are synthesized via a solvothermal method to synergize metallic electrical conductivity and redox activity. Pure vanadium oxide synthesis results in VO2 formation, while in the presence of Ti3C2Tx, quasi-metallic V2O3 and VO2 (VOx) are observed due to the decomposition of surface functionalities of Ti3C2Tx. The growth of the V2O3 phase increases with an increase in the weight concentration of Ti3C2Tx. The optimal composition of heterostructure delivers a specific capacitance of 364 F g−1 in a stable potential window of −0.9 V–1 V, surpassing the specific capacitance of pure VO2 (245 F g−1) and Ti3C2Tx (140 F g−1) in 0.5 M K2SO4 electrolyte. Furthermore, the developed symmetric supercapacitor (SSC) delivers an energy density of 45.7 Wh kg−1 at a power density of 1.1 kW kg−1 with cyclic stability of 78 % for 10000 cycles with a self-discharge open circuit potential of 1.34 V. This work highlights a strategy to develop anodic and cathodic active pseudocapacitive material based SSC to improve energy density and mitigate self-discharge.

Functional Electrolyte Additives for Sodium‐Ion and Sodium‐Metal Batteries: Progress and Perspectives

AbstractSodium‐based rechargeable batteries are considered one of the strongest contenders for the next generation of power storage devices. Functional electrolytes with additives play a crucial role in influencing the electrochemical performance of sodium‐based batteries. The addition of small doses of additives can greatly enhance the electrolyte, improving energy density, cycling performance, and safety. This paper presents an overview of recent research focused on novel additives for sodium‐ion batteries (SIBs) and sodium‐metal batteries (SMBs). The additives are categorized based on their specific functions, including film‐forming, flame retardant, overcharge protection, high‐voltage, acid and water removal, inhibition of gas production, high and low temperature and protection of sodium metal anode. The working mechanisms for these additives are thoroughly explained. Finally, potential future research directions are proposed.

Emerging Two–Dimensional Intercalation Pseudocapacitive Electrodes for Supercapacitors

AbstractThe growing need for efficient energy storage has spurred advancements in supercapacitors (SCs), aiming to offer high power and energy density simultaneously. While SCs offer longer cycles and higher power density values, their low energy densities limit practical applications. In response, pseudocapacitive materials have emerged, leveraging reversible Faradaic reactions at or near the surface for enhanced energy storage. This approach surpasses the constraints of the electrical double layer in SCs and the mass transfer constraints of batteries. Progress in asymmetric supercapacitors and high mass loading has improved energy density values, yet maintaining high mass loading without compromising power density remains a hurdle. Advancements in pseudocapacitance through intercalation during charging/discharging processes, especially in layered structures like graphite, graphene, transition metal oxides (TMOs) transition metal dichalcogenides (TMDCs), MXenes, and metal–organic frameworks (MOFs) have proven significant. The intercalated species induce reversible or irreversible structural changes, contributing to the physicochemical characteristics of the electrode materials. Exploring the intercalation mechanism in bulk two‐dimensional (2D) materials reveals distinct differences that enhance our understanding and improve electrochemical properties for superior energy storage. Finally, an in‐depth exploration of the intercalation pseudocapacitance in 2D materials such as TMDCs and MXenes underscores their significance, setting a benchmark for future electrochemical studies in the subsequent advancement of SCs research.

Towards sustainable solar energy solutions: Harnessing supercapacitors in PV systems

The integration of supercapacitors in photovoltaic (PV) energy systems holds immense potential for enhancing energy storage, reliability, and efficiency. This article provides a comprehensive overview of recent advancements, challenges, and opportunities in the utilization of supercapacitors within PV systems. Fundamental principles of supercapacitor operation, including charge storage mechanisms and electrode materials, are discussed, highlighting their unique advantages such as high power density and rapid charge/discharge capabilities. Various integration strategies, including parallel and series configurations, as well as system-level control algorithms, are examined to optimize energy management and performance. Case studies and real-world examples demonstrate the effectiveness of integrated PV and supercapacitor systems across different applications and scales. According to the results of the research, 235 publications have been made on the subject in the last fifteen years and the number of publications has doubled in the last five years. Additionally, future research directions focus on improving energy density, efficiency, and cost-effectiveness, as well as addressing challenges related to temperature sensitivity and system scalability. Overall, the integration of supercapacitors in PV systems offers promising solutions for advancing sustainable energy solutions and accelerating the transition towards a cleaner, greener future.

Alternative inner filling and outer surface coating of BNNT by Tungsten(VI) oxide for supercapacitor electrode

The motivation behind this research is to address the need for advanced energy storage materials by exploring the selective filling and coating of boron nitride nanotube (BNNT) with tungsten(VI) oxide (WO3) to enhance the pseudocapacitive performance. In this study, we present a novel synthesis method that allows precise control over the extent of filling and coating, aiming to create tailored hybrid structures. Morphological and structural analysis confirm the filling and coating of BNNT by WO3. Inner filling and outer surface coating of BNNT by WO3 significantly impact on the electrochemical properties. The filling of WO3 within the BNNT can enhance the stability of the system, whereas outer surface coating of BNNT by WO3 improves the capacitive performances. The role of BNNT influences both these phenomena by acting as electrolyte transportation channel as well as stabilizing the WO3. In three electrode study, WO3 coated BNNT showed the maximum specific capacitance of 856 F/g at 1 A/g. An asymmetric supercapacitor device using WO3 coated BNNT as positive electrode revealed the maximum specific capacitance of 137 F/g at 2 A/g current density with an improved energy density of 52 W h/kg. The WO3 coated BNNT-based asymmetric supercapacitor device also showed ∼81 % specific capacitance retention after the completion of 10,000 GCD cycles, whereas WO3 filled BNNT-based supercapacitor device demonstrated better stability (∼94 % specific capacitance retention) due to the filling and stabilization of pseudocapacitive WO3 by BNNT.

Role of Salt Concentration in Stabilizing Charged Ni-Rich Cathode Interfaces in Li-Ion Batteries.

The cathode-electrolyte interphase (CEI) in Li-ion batteries plays a key role in suppressing undesired side reactions while facilitating Li-ion transport. Ni-rich layered cathode materials offer improved energy densities, but their high interfacial reactivities can negatively impact the cycle life and rate performance. Here we investigate the role of electrolyte salt concentration, specifically LiPF6 (0.5-5 m), in altering the interfacial reactivity of charged LiN0.8Mn0.1Co0.1O2 (NMC811) cathodes in standard carbonate-based electrolytes (EC/EMC vol %/vol % 3:7). Extended potential holds of NMC811/Li4Ti5O12 (LTO) cells reveal that the parasitic electrolyte oxidation currents observed are strongly dependent on the electrolyte salt concentration. X-ray photoelectron and absorption spectroscopy (XPS/XAS) reveal that a thicker LixPOyFz-/LiF-rich CEI is formed in the higher concentration electrolytes. This suppresses reactions with solvent molecules resulting in a thinner, or less-dense, reduced surface layer (RSL) with lower charge transfer resistance and lower oxidation currents at high potentials. The thicker CEI also limits access of acidic species to the RSL suppressing transition-metal dissolution into the electrolyte, as confirmed by nuclear magnetic resonance (NMR) spectroscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES). This provides insight into the main degradation processes occurring at Ni-rich cathode interfaces in contact with carbonate-based electrolytes and how electrolyte formulation can help to mitigate these.

Electron-outflowing heterostructure hosts for high-voltage aqueous zinc-iodine batteries

Enhancing the energy density is an imperative challenge in the advancement of aqueous zinc-iodine (Zn-I2) batteries, which hold great promise for grid energy storage systems. Achieving the reversible conversion reaction of high-valence iodine species, particularly I+/I0 redox chemistry, offers a substantial potential for improved energy density. In this study, we introduce a novel method of employing electron-outflowing heterostructured hosts to stabilize I+ ions in aqueous halide-free ZnSO4 electrolytes. Both experimental analyses and density functional theory (DFT) calculations reveal that the stabilization of thermodynamically unstable I+ cations originates from the charge transfer interaction between I+ ions and copper phthalocyanine (CuPc) within the hosts. The electron-outflowing effect resulting from the π-π conjugation between CuPc and the carbon framework in heterostructured hosts further intensifies the charge transfer interaction, leading to the reversible I+/I5− conversion reaction in Zn-I2 batteries. Consequently, this emerging redox reaction, validated by in-situ Raman and ex-situ ultraviolet-visible spectroscopy, introduces another voltage plateau at ∼1.6 V and enhances the energy density to 233.8 Wh kg–1 at 3.0 A g–1. This work showcases outstanding electrochemical performance for the Zn-I2 battery, providing valuable insights into advancing iodine redox chemistry featuring multiple electrons.

High-performance all-solid-state lithium batteries enabled by high-conductivity free-standing sulfide electrolyte membrane and Li-Zn/LiCl bifunctional interphase

All-solid-state lithium batteries (ASSLBs) empolying sulfide solid electrolyte and lithium metal anode can afford improved energy density and safety. However, their large-scale application is hampered by the rigidity of ceramic–based electrolyte and the inevitable growth of lithium dendrites. Herein, a novel, flexible, high-conductivity and free-standing sulfide electrolyte membrane (Li6PS5Cl-polypropylene carbonate6, (LPSCl-PPC6)) with a thickness of 60 μm is prepared via methodology of blade coating and hot pressing, which exhibits a high Li+ conductivity (3.1 × 10−3 S cm−1 at 25 °C) and a wide electrochemical window (4.7 V vs Li+/Li) at 25 °C. Additionally, a bifunctional interphase with Li-Zn/LiCl is implanted on lithium metal surface to enhance the stability of electrolyte/lithium anode, which effectively prevents the growth of lithium dendrites and the internal short circuit of lithium symmetric battery. Benefiting from the synergistic effect, the assembled ASSLBs of S-CNTs/LPSCl-PPC6/Li-Zn/LiCl|Li and LLZO@NCM93/LPSCl-PPC6/Li-Zn/LiCl|Li exhibit high initial capacity of 1183.5 mAh g−1 (193.6 mAh g−1) and exceptionally cyclic stability with capacity retention of 89.2% over 150 cycles at 0.05C (93.2% over 100 cycles at 0.1C). This highly conductive sulfide-based composite electrolyte and interface engineering provides a promising strategy for achieving high performance ASSLBs.

Entropy Stabilized Medium High Entropy Alloy Anodes for Lithium‐Ion Batteries

AbstractOne often proposed route to improved energy density for lithium‐ion batteries is to use alloy anodes, such as silicon, able to store large amounts of lithium. Mechanical instability caused by the large expansion and contraction associated with (de)lithiation, and hence bad cyclability, has, however, so far hindered progress. As proof‐of‐concept of a remedy, we here present BiSbSe1.5Te1.5, a medium high‐entropy alloy with improved cycling stability for conversion‐alloying (de)lithiation reactions. We attain five to twenty times more stable cycles than previously reported for comparable metal‐Se and ‐Te‐based anodes, with a very good reversible capacity (464 mAh g−1) for up to 110 cycles‐ and this without using any carbonaceous materials to create a composite. Altogether, this highlights how alloy engineering and increased entropy materials can stabilize conversion‐alloying electrodes.

Rate-limiting mechanism of all-solid-state battery unravelled by low-temperature test-analysis flow

All-solid-state batteries (ASSBs) with potentially improved energy density and safety have been recognized as the next-generation energy storage technology. However, their performances at subzero temperatures are rarely investigated, with rate-limiting process/mechanisms unidentified. Herein, the rate-limiting process/mechanisms for -40℃ ASSBs are accurately identified/analyzed by developing a standard test-analysis flow model. We reveal that the rate-limiting processes of LiCoO2 (LCO)+sulfide solid electrolyte (SE) composite cathode are the sluggish ion transport across unfavorable interfacial reaction layer and charge transfer at damaged LCO cathode surface. After inserting Li2ZrO3 (LZO) coating layer to suppress interfacial reactions, the rate-limiting process of LCO@LZO+sulfide SE composite cathode turns into the arduous ion transport across the interphase composed of the self-decomposition products of sulfide SE. Interestingly, by replacing sulfide SE with halide SE, LCO+halide SE composite cathode delivers fast charge transfer and the ion conduction through the thick SE separator becomes the rate-limiting process, thus enabling a superior capacity retention rate (41.4 %) at -40℃. Furthermore, the capacity retention of ASSB coupling LCO+halide SE composite cathode with Si anode can be boosted from 28.9 % to 38.6 % at -40℃ by employing superionic conductor with low activation energy. These successful identifications/modulations on rate-limiting process/mechanism and improvements on low-temperature performance demonstrate the significant role of this test-analysis flow in propelling the development of low-temperature ASSBs.

Research Progress and Optimization Strategies of Cathodes, Anodes and Electrolytes for Lithium-ion Batteries

The importance of lithium-ion batteries is becoming increasingly clear as the world's need for clean energy grows. However, the challenges of realizing their higher energy density, stability and safety remain to be overcome. This paper discusses the working principle of Li-ion batteries and the importance of their core components, then explores the research significance of cathode, anode materials and electrolytes, respectively, and describes the current mainstream materials and their current challenges and optimization strategies. In terms of positive electrode materials, this paper introduces mainstream materials such as Nickel Manganese Cobalt Oxide (NMC), Nickel Cobalt Aluminum Oxide (NCA), and Lithium Iron Phosphate (LFP), and puts forward strategies to improve energy density and enhance stability; in terms of negative electrode materials, this paper lists core materials such as graphite and silicon, and discusses the issues of volume change and how to improve stability, etc. In the electrolyte section, it not only introduces the mainstream electrolytes such as organic liquid electrolytes and solid electrolytes, but also analyzes and discusses the problems of how to improve their ionic conductivity. By synthesizing these reviews and strategies, this paper aims to promote the progress and development of lithium-ion battery technology and bring new research perspectives and values.

Superior Cyclic Stability and Capacitive Performance of Cation- and Water Molecule-Preintercalated δ-MnO2/h-WO3 Nanostructures as Supercapacitor Electrodes.

The large number of active sites in the layered structure of δ-MnO2 with considerable interlayer spacing makes it an excellent candidate for ion storage. Unfortunately, the δ-MnO2-based electrode has not yet attained the exceptional storage potential that it should demonstrate because of disappointing structural deterioration during periodic charging and discharging. Here, we represent that stable Na ion storage in δ-MnO2 may be triggered by the preintercalation of K ions and water molecules. Furthermore, the sluggish reaction kinetics and poor electrical conductivity of preintercalated δ-MnO2 layers are overcome by the incorporation of h-WO3 in the preintercalated δ-MnO2 to form novel composite electrodes. The composites contain mixed valence metals, which provide a great number of active sites along with improved redox activity, while maintaining a fast ion transfer efficiency to enhance the pseudocapacitance performance. Based on our research, the composite prepared from preintercalated δ-MnO2 with 5 wt % h-WO3 provides a specific capacitance of up to 363.8 F g-1 at a current density of 1.5 A g-1 and an improved energy density (32.3 W h kg-1) along with an ∼14% increase in capacity upon cycling up to 5000 cycles. Hence, the interaction between the preintercalated δ-MnO2 and h-WO3 nanorods results in satisfactory energy storage performance due to the defect-rich structure, high conductivity, superior stability, and lower charge transfer resistance. This research has the potential to pave the way for a new class of hybrid supercapacitors that could fill the energy gap between chemical batteries and ideal capacitors.

Redox-Active Phenanthrenequinone Molecules and Nitrogen-Doped Reduced Graphene Oxide as Active Material Composites for Supercapacitor Applications.

Carbon-based supercapacitor electrodes are generally restricted in energy density, as they rely exclusively on electric double-layer capacitance (EDLC). The introduction of redox-active organic molecules to obtain pseudocapacitance is a promising route to develop electrode materials with improved energy densities. In this work, we develop a porous nitrogen-doped reduced graphene oxide and 9,10-phenanthrenequinone composite (N-HtrGO/PQ) via a facile one-step physical adsorption method. The electrochemical evaluation of N-HtrGO/PQ using cyclic voltammetry showed a high capacitance of 605 F g-1 in 1 M H2SO4 when the composite consisted of 30% 9,10-phenanthrenequinone and 70% N-HtrGO. The measured capacitance significantly exceeded pure N-HtrGO without the addition of redox-active molecules (257 F g-1). In addition to promising capacitance, the N-HtrGO/30PQ composite showed a capacitance retention of 94.9% following 20,000 charge/discharge cycles. Based on Fourier transform infrared spectroscopy, we postulate that the strong π-π interaction between PQ molecules and the N-HtrGO substrate enhances the specific capacitance of the composite by shortening pathways for electron transfer while improving structural stability.

Bipolar Current Collectors of Cu/polymer/Al Composite for Anode‐Free Batteries

AbstractThe all‐in‐one design of cathode and anode is a promising strategy to improve energy density and assembly efficiency for lithium batteries. However, it is an important prerequisite to combine negative and positive current collectors in a single sheet. Here, an asymmetric structure of bipolar composite current collector (BCCC), thin copper (Cu) and aluminum (Al) metal layers respectively deposited on each side of a thin polyethylene terephthalate (PET) polymer substrate is developed. Unlike conventional metal foils, the electronically insulative polymer blocks electron transfer between the cathode and anode coated on each side of BCCC. Buckling‐based mechanics measurement and molecular simulation are conducted to quantitatively evaluate the interfacial strength of metal/polymer, which is enhanced by introducing an intermediate chromium (Cr) layer. For applications in anode‐free wound batteries, the integrated sheet of separator/cathode/BCCC can simplify the alignment of the electrodes during the winding process. Without special surface and electrolyte optimizations, a higher Coulombic efficiency (99.1%) and larger capacity retention (50.0%) are achieved after 100 cycles in the LiNi0.8Co0.1Mn0.1O2 anode‐free battery than the battery using Cu foils.

X‐ray imaging for structural evolution and phase transformation dynamics of battery electrodes

AbstractThe impending energy crisis entails sustainable battery technologies with improved energy density, reliability, safety and lifetime. Hence, it is essential to gain detailed insights into the surface reactions, ionic diffusion, structural and morphological evolution, and degradation mechanisms of battery electrodes. Recently, X‐ray techniques emerged as revolutionary tools to reveal an in‐depth understanding of the battery during operations. This review provides an overview of the use of in situ/operando X‐ray techniques to understand the different functionalities of electrode materials inside the battery. It will focus on the phase transformation, structural evolution and dynamic properties of the battery electrodes, and discuss the relationship between battery failure and electro‐chemo‐mechanical failure in the electrode. Finally, the limitations of these methods are also discussed with the prospects for effective use of these techniques in the development of advanced battery technologies.

Polymer nanocomposite dielectrics for capacitive energy storage.

Owing to their excellent discharged energy density over a broad temperature range, polymer nanocomposites offer immense potential as dielectric materials in advanced electrical and electronic systems, such as intelligent electric vehicles, smart grids and renewable energy generation. In recent years, various nanoscale approaches have been developed to induce appreciable enhancement in discharged energy density. In this Review, we discuss the state-of-the-art polymer nanocomposites with improved energy density from three key aspects: dipole activity, breakdown resistance and heat tolerance. We also describe the physical properties of polymer nanocomposite interfaces, showing how the electrical, mechanical and thermal characteristics impact energy storage performances and how they are interrelated. Further, we discuss multi-level nanotechnologies including monomer design, crosslinking, polymer blending, nanofiller incorporation and multilayer fabrication. We conclude by presenting the current challenges and future opportunities in this field.

Tailoring Zr-doped tungsten bronze (Sr,Ba,Gd)Nb2O6 relaxor ferroelectric with high electrical insulation interface for dielectric capacitor

Tetragonal tungsten bronze structure (TTB) compounds have attracted tremendous interest for their applications in energy storage, especially as dielectric capacitor mediums. However, constrained by the inverse correlation of polarization and electric breakdown field in relaxor ferroelectrics, there is still a major challenge in improving energy density. To addresse this challenge, a viable strategy of constructing relaxor behavior with robust electrical insulation in TTB-type Sr0.485Ba0.47Gd0.03Nb2-xZrxO6 (SBN-Gd-Zrx) by introducing ZrO2 during the preparation process was proposed. By introducing Zr4+ in the B-site, we have revealed how Zr4+ affects the dielectric and ferroelectric characteristics to explore the intrinsic relaxation. Based on the analysis of Rietveld refinement against synchrotron X-ray powder diffraction and Raman results, the substitution of Gd3+ and Zr4+ for Sr2+ and Nb5+ in Sr0.53Ba0.47Nb2O6 caused a decline in tetragonality and a shrinkage of the unit cell due to the lattice defect of [GdSr]• and [ZrNb]', which mutually compensates effectively alleviate the distortion of BO6 and then favors the balance of polarization and dielectric constant. The accrual of additional ZrO2 at grain boundaries significantly enhances electrical insulation characteristics, as validated by complex impedance spectroscopy. At near room temperature, all Zr-doped SBN-Gd compounds of the series exhibit heightened relaxation and undergo a phase transition from ferroelectric to paraelectric. As a result, in tandem with the synchronous augmentation in breakdown electric field (EB) and saturation polarization (Pm), optimal energy storage characteristic is realized in the SBN-Gd-Zr0.2 sample. It attains a remarkable Wrec of 2.67 J/cm3 and an efficiency ƞ of 91.21 %, showcasing excellent suitability in terms of different frequencies and temperatures, which far exceeds that of Gd-modified SBN ceramics and pure SBN ceramics. These results exemplify an efficacious strategy for designing novel TTB dielectrics by coupling relaxor modulation with electrical insulation, and position them competitively for implementation in dielectric storage capacitors utilized in pulsed power devices.

Bridging the gap between academic research and industrial development in advanced all-solid-state lithium-sulfur batteries.

The energy storage and vehicle industries are heavily investing in advancing all-solid-state batteries to overcome critical limitations in existing liquid electrolyte-based lithium-ion batteries, specifically focusing on mitigating fire hazards and improving energy density. All-solid-state lithium-sulfur batteries (ASSLSBs), featuring earth-abundant sulfur cathodes, high-capacity metallic lithium anodes, and non-flammable solid electrolytes, hold significant promise. Despite these appealing advantages, persistent challenges like sluggish sulfur redox kinetics, lithium metal failure, solid electrolyte degradation, and manufacturing complexities hinder their practical use. To facilitate the transition of these technologies to an industrial scale, bridging the gap between fundamental scientific research and applied R&D activities is crucial. Our review will address the inherent challenges in cell chemistries within ASSLSBs, explore advanced characterization techniques, and delve into innovative cell structure designs. Furthermore, we will provide an overview of the recent trends in R&D and investment activities from both academia and industry. Building on the fundamental understandings and significant progress that has been made thus far, our objective is to motivate the battery community to advance ASSLSBs in a practical direction and propel the industrialized process.

The Nb–Ti–W–O system as safe high-power anodes for Li-ion batteries

New materials are currently needed to serve as anodes in Li-ion batteries for applications that require extreme safety, long lifetimes, high power and improved energy density.

Collaboratively improved energy density and efficiency in NaNbO3-based lead-free relaxor ferroelectrics via enhancing antiferrodistortion

A novel strategy for enhancing antiferrodistortion is proposed to effectively achieve simultaneously high energy density and efficiency in lead-free relaxor ferroelectric capacitors.