Lightweight Carbon-Metal-Based Fabric Anode for Lithium-Ion Batteries

Lithium-ion battery electrodes are typically manufactured via slurry casting, which involves mixing active material particles, conductive carbon, and a polymeric binder in a solvent, followed by casting and drying the coating on current collectors (Al or Cu). These electrodes are functional but still limited in terms of pore network percolation, electronic connectivity, and mechanical stability, leading to poor electron/ion conductivities and mechanical integrity upon cycling, which result in battery degradation. To address this, we fabricate trichome-like carbon-iron fabrics via a combination of electrospinning and pyrolysis. Compared with slurry cast Fe2O3 and graphite-based electrodes, the carbon-iron fabric (CMF) electrode provides enhanced high-rate capacity (10C and above) and stability, for both half cell and full cell testing (the latter with a standard lithium nickel manganese oxide (LNMO) cathode). Further, the CMFs are free-standing and lightweight; therefore, future investigation may include scaling this as an anode material for pouch cells and 18,650 cylindrical batteries.

Plasma Surface Treatment of Cu Current Collectors for Improving the Electrochemical Performance of Si Anodes

The practical utilization of Si electrodes is hindered by their substantial volume expansion during alloying and dealloying processes, which causes mechanical damage and separation from Cu current collectors. To alleviate the problem of Si composite detachment from Cu current collectors, the surface of the Cu current collectors is modified using atmospheric oxygen plasma. Plasma treatment improves the wetting ability of the Cu current collectors and, consequently, the coating quality of the Si electrodes. The uniform distribution of the Si electrode components reduces the sheet resistance and improves the adhesion properties of the Si electrodes containing surface-modified Cu current collectors. As a result, the volume expansion of Si during alloying and dealloying is reduced; this results in an excellent rate capability of 1584 mA h g-1 at a current density of 3.6 A g-1 (135% that of bare Cu) and excellent cycle performance of 1545 mA h g-1 after 300 cycles (Si electrodes with bare Cu exhibit 930 mA h g-1). Therefore, the developed plasma treatment method for Cu current collectors is expected to be an economical and efficient approach for improving the Li-ion battery performance.

Overcoming Challenges: Extending Cycle Life of Aqueous Zinc-Ion Batteries at High Zinc Utilization through a Synergistic Strategy

Aqueous zinc-ion batteries (AZIBs) face challenges in achieving high energy density compared to conventional lithium-ion batteries (LIBs). The lower operating voltage and excessive Zn metal as anode pose constraints on the overall energy storage capacity of these batteries. An effective approach is to reduce the thickness of the Zn metal anode and control its mass appropriately. However, under the condition of using a thin Zn anode, the performance of AZIBs is often unsatisfactory. Through experiments and computational simulations, the electrode structural change and the formation of dead Zn as the primary reasons for the failure of batteries under a high Zn utilization rate are identified. Based on this understanding, a universal synergistic strategy that combines Cu foil current collectors and electrolyte additives to maintain the structural and thermodynamic stability of the Zn anode under a high Zn utilization rate (ZUR) is proposed. Specifically, the Cu current collectors can ensure that the Zn anode structure remains intact based on the spontaneous filling effect, while the additives can suppress parasitic side reactions at the interface. Ultimately, the symmetric cell demonstrates a cycling duration of 900 h at a 70% ZU, confirming the effectiveness of this strategy.

Toward Sustainable Li-S Battery Using Scalable Cathode and Safe Glyme-Based Electrolyte

The search for safe electrolytes to promote the application of lithium-sulfur (Li-S) batteries may be supported by the investigation of viscous glyme solvents. Hence, electrolytes using nonflammable tetraethylene glycol dimethyl ether added by lowly viscous 1,3-dioxolane (DOL) are herein thoroughly investigated for sustainable Li-S cells. The electrolytes are characterized by low flammability, a thermal stability of ∼200 °C, ionic conductivity exceeding 10-3 S cm-1 at 25 °C, a Li+ transference number of ∼0.5, electrochemical stability window from 0 to ∼4.4 V vs Li+/Li, and a Li stripping-deposition overpotential of ∼0.02 V. The progressive increase of the DOL content from 5 to 15 wt % raises the activation energy for Li+ motion, lowers the transference number, slightly limits the anodic stability, and decreases the Li/electrolyte resistance. The electrolytes are used in Li-S cells with a composite consisting of sulfur and multiwalled carbon nanotubes mixed in the 90:10 weight ratio, exploiting an optimized current collector. The cathode is preliminarily studied in terms of structure, thermal behavior, and morphology and exploited in a cell using standard electrolyte. This cell performs over 200 cycles, with sulfur loading increased to 5.2 mg cm-2 and the electrolyte/sulfur (E/S) ratio decreased to 6 μL mg-1. The above sulfur cathode and the glyme-based electrolytes are subsequently combined in safe Li-S batteries, which exhibit cycle life and delivered capacity relevantly influenced by the DOL content within the studied concentration range.

Engendering High Energy Density LiFePO4 Electrodes with Morphological and Compositional Tuning

Improving the energy density of Li-ion batteries is critical to meet the requirements of electric vehicles and energy storage systems. In this work, LiFePO₄ active material was combined with single-walled carbon nanotubes as the conductive additive to develop high-energy-density cathodes for rechargeable Li-ion batteries. The effect of the morphology of the active material particles on the cathodes' electrochemical characteristics was investigated. Although providing higher packing density of electrodes, spherical LiFePO₄ microparticles had poorer contact with an aluminum current collector and showed lower rate capability than plate-shaped LiFePO₄ nanoparticles. A carbon-coated current collector helped enhance the interfacial contact with spherical LiFePO₄ particles and was instrumental in combining high electrode packing density (1.8 g cm^-3) with excellent rate capability (100 mAh g^-1 at 10C). The weight percentages of carbon nanotubes and polyvinylidene fluoride binder in the electrodes were optimized for electrical conductivity, rate capability, adhesion strength, and cyclic stability. The electrodes that were formulated with 0.25 wt.% of carbon nanotubes and 1.75 wt.% of the binder demonstrated the best overall performance. The optimized electrode composition was used to formulate thick free-standing electrodes with high energy and power densities, achieving the areal capacity of 5.9 mAh cm^-2 at 1C rate.

Intertwined CNT Assemblies as an All-Around Current Collector for Volume-Efficient Lithium-Ion Hybrid Capacitors

The increasing demands for conversion systems for clean energy, wearable devices powered by energy storage systems, and electric vehicles have greatly promoted the development of innovative current collectors to replace conventional metal-based foils, including those in multidimensional forms. In this study, carbon nanotubes (CNTs) with desirable features and ease of processing are used in the preparation of floating catalyst-chemical vapor deposition-derived CNT sheets for potential use as all-around current collectors in two representative energy storage devices: batteries and electrochemical capacitors. Due to their short and multidirectional electron pathways and multimodal porous structures, CNT-based current collectors enhance ion transport kinetics and provide many ion adsorption and desorption sites, which are crucial for improving the performance of batteries and electrochemical capacitors, respectively. By assembling activated carbon-CNT cathodes and prelithiated graphite-CNT anodes, high-performance lithium-ion hybrid capacitors (LIHCs) are successfully demonstrated. Briefly, CNT-based LIHCs exhibit 170% larger volumetric capacities, 24% faster rate capabilities, and 21% enhanced cycling stabilities relative to LIHCs based on conventional metallic current collectors. Therefore, CNT-based current collectors are the most promising candidates for replacing currently used metallic materials and provide a valuable opportunity to possibly redefine the roles of current collectors.

Constructing 3D Skeleton on Commercial Copper Foil via Electrophoretic Deposition of Lithiophilic Building Blocks for Stable Lithium Metal Anodes

Lithium (Li) metal has been regarded as the "Holy Grail" of Li battery anodes thanks to its high theoretic specific capacity and low reduction potential, but uneven formation of Li dendrites and uncontrollable Li volume changes hinder the practical applications of Li metal anodes. A three-dimensional (3D) current collector is one of the promising strategies to address the above issues if it can be compatible with current industrialized process. Here, Au-decorated carbon nanotubes (Au@CNTs) are electrophoretically deposited on commercial Cu foil as a 3D lithiophilic skeleton to regulate Li deposition. The thickness of the as-prepared 3D skeleton can be accurately controlled by adjusting the deposition time. Benefitting from the reduced localized current density and improved Li affinity, the Au@CNTs-deposited Cu foil (Au@CNTs@Cu foil) achieves uniform Li nucleation and dendrite-free Li deposition. Compared with bare Cu foil and CNTs deposited Cu foil (CNTs@Cu foil), the Au@CNTs@Cu foil exhibits enhanced Coulombic efficiency and better cycling stability. In the full-cell configuration, the Au@CNTs@Cu foil with predeposited Li shows superior stability and rate performance. This work provides a facial strategy to directly construct a 3D skeleton on commercial Cu foils with lithiophilic building blocks for stable and practical Li metal anodes.

Braided Fiber Current Collectors for High-Energy-Density Fiber Lithium-Ion Batteries

Fiber lithium-ion batteries represent a promising power strategy for the rising wearable electronics. However, most fiber current collectors are solid with vastly increased weights of inactive materials and sluggish charge transport, thus resulting in low energy densities which have hindered the development of fiber lithium-ion batteries in the past decade. Here, a braided fiber current collector with multiple channels was prepared by multi-axial winding method to not only increase the mass fraction of active materials, but also to promote ion transport along fiber electrodes. In comparison to typical solid copper wires, the braided fiber current collector hosted 139% graphite with only 1/3 mass. The fiber graphite anode with braided current collector delivered high specific capacity of 170 mAh‧g-1 based on the overall electrode weight, which was 2 times higher than that of its counterpart solid copper wire. The resulting fiber battery showed high energy density of 62 Wh‧kg-1.

Reconstruction of Solid Electrolyte Interphase with SrI2 Reactivates Dead Li for Durable Anode-Free Li-Metal Batteries

Without excess Li, anode-free Li-metal batteries (AFLMBs) have been proposed as the most likely solution to realizing highly-safe and cost-effective Li-metal batteries. Nevertheless, short cyclic life puzzles conventional AFLMBs due to anodic dead Li accumulation with a local current concentration induced by irreversible electrolyte depletion, insufficient active Li reservoir and slow Li+ transfer at the solid electrolyte interphase (SEI). Herein, SrI2 is introduced into carbon paper (CP) current collector to effectively suppress dead Li through synergistic mechanisms including reversible I-/I3- redox reaction to reactivate dead Li, dielectric SEI surface with SrF2 and LiF to prevent electrolyte decomposition and highly ionic conductive (3.488 mS cm-1) inner layer of SEI with abundant LiI to enable efficient Li+ transfer inside. With the SrI2-modified current collector, the NCM532/CP cell delivers unprecedented cyclic performances with a capacity of 129.2 mAh g-1 after 200 cycles.

Damage Caused by Material Defects of Carbon Composites Used on Various Types of Railway Pantographs

Mainstream materials of the railway pantograph strips are carbon composites. They are subject to wear during use, as well as various types of damage. It is important that their operation time is as long as possible and that they are not damaged, as it may damage the remaining elements of the pantograph and the overhead contact line. As part of the article, three types of pantographs were tested: AKP-4E, 5ZL, and 150 DSA. They had carbon sliding strips made of MY7A2 material. By testing the same material on different types of current collectors, it was possible to check what impact the wear and damage of the sliding strips has on (among others) the method of their installation, i.e., whether the damage to the strips depends on the type of current collector and what is the participation of damage caused by material defects. As a result of the research, it was found that the type of pantograph on which it is used has an undoubted influence on the damage characteristics of the carbon sliding strips, whereas the damage caused by material defects can be classified as a more general group-the group of damage of a sliding strip, which also includes overburning of a carbon sliding strip.

Porous Metal Current Collectors for Alkali Metal Batteries

Alkali metals (i.e., Li, Na, and K) are promising anode materials for next-generation high-energy-density batteries due to their superior theoretical specific capacities and low electrochemical potentials. However, the uneven current and ion distribution on the anode surface probably induces undesirable dendrite growth, which leads to significant safety hazards and severely hinders the commercialization of alkali metal anodes. A smart and versatile strategy that can accommodate alkali metals into porous metal current collectors (PMCCs) has been well established to resolve the issues as well as to promote the practical applications of alkali metal anodes. Moreover, the proposal of PMCCs can meet the requirement of the dendrite-free battery fabrication industry, while the electrode material loading exactly needs the metal current collector component as well. Here, a systematic survey on advanced PMCCs for Li, Na, and K alkali metal anodes is presented, including their development timeline, categories, fabrication methods, and working mechanism. On this basis, some significant methodology advances to control pore structure, surface area, surface wettability, and mechanical properties are systematically summarized. Further, the existing issues and the development prospects of PMCCs to improve anode performance in alkali metal batteries are discussed.

Toward High-Energy-Density Aqueous Lithium-Ion Batteries Using Silver Nanowires as Current Collectors

The lack of suitable lightweight current collectors is one of the primary obstacles preventing the energy density of aqueous lithium-ion batteries (ALIBs) from becoming competitive. Using silver nanowire (AgNW) films as current collectors and a molecular crowding electrolyte, we herein report the fabrication of ALIBs with relatively good energy densities. In the 2 m LiTFSI-94% PEG-6% H₂O solution, the AgNW films with a sheet resistance of less than 1.0 ohm/square exhibited an electrochemical stability window as broad as 3.8 V. The LiMn₂O₄//Li₄Ti₅O₁₂ ALIBs using AgNW films as the current collectors demonstrated an initial energy density of 70 Wh/kg weighed by the total mass of the cathode and anode, which retained 89.1% after 50 cycles.

Early Braking of Overwarmed Lithium-Ion Batteries by Shape-Memorized Current Collectors

In the context of the constant impending energy crisis, the lithium-ion battery as a burgeoning energy storage means is showing extraordinary talents in many energy relevant investigations. However, fire and explosion would probably occur when the battery is encountered with overheating, at which the shrinking of the separator routinely causes an internal short circuit. Herein, we develop a kind of novel shape-memorized current collector (SMCC), which can successfully brake battery thermal runaway at the battery internal overheating status. Unlike traditional current collectors made of commercial copper foils, SMCC is made of a micropatterned shape memory micron-sized film with copper deposition. SMCC displays ideal conductivity at normal temperatures and turns to be insulative at overheating temperatures. Following this principle, the battery consisting of an SMCC can run normally at temperatures lower than 90 °C, while it quickly achieves self-shutdown before the occurrence of battery combustion and explosion.

The Negative-Charge-Triggered "Dead Zone" between Electrode and Current Collector Realizes Ultralong Cycle Life of Aluminum-Ion Batteries

Typically, volume expansion of the electrodes after intercalation of active ions is highly undesirable yet inetvitable, and it can significantly reduce the adhesion force between the electrodes and current collectors. Especially in aluminum-ion batteries (AIBs), the intercalation of large-sized AlCl₄ ^- can greatly weaken this adhesion force and result in the detachment of the electrodes from the current collectors, which seems an inherent and irreconcilable problem. Here, an interesting concept, the "dead zone", is presented to overcome the above challenge. By incorporating a large number of OH^- and COOH^- groups onto the surface of MXene film, a rich negative-charge region is formed on its surface. When used as the current collector for AIBs, it shields a tiny area of the positive electrode (adjacent to the current collector side) from AlCl₄ ^- intercalation due to the repulsion force, and a tiny inert layer (dead zone) at the interface of the positive electrode is formed, preventing the electrode from falling off the current collector. This helps to effectively increase the battery's cycle life to as high as 50 000 times. It is believed that the proposed concept can be an important reference for future development of current collectors in rocking chair batteries.

Uniform Lithium Deposition Induced by ZnFx(OH)y for High-Performance Sulfurized Polyacrylonitrile-Based Lithium-Sulfur Batteries

Lithium metal batteries are emerging as the next generation of high-density electrochemical energy storage systems because of the ultra-high specific capacity and ultra-low electrochemical potential of the Li metal anode. However, the uneven Li deposition on commercial Cu current collectors result in low Coulombic efficiencies (CEs) and poor cycle life. In this research, we proposed the modification of ZnFx(OH)y on Cu foils to expand the lifespan. As-generated ZnLi alloy and LiF could promote uniform Li nucleation and deposition, thus resulting in an improved Li plating/stripping CE and extended cycle life. The Li-S battery with sulfurized polyacrylonitrile cathode and Li-ZnFx(OH)y@Cu anode (N/P ratio of 1.5:1) maintains 95% capacity after 60 cycles, proving the feasibility of ZnFx(OH)y@Cu for practical applications.

Facile Electroless Plating Method to Fabricate a Nickel-Phosphorus-Modified Copper Current Collector for a Lean Lithium-Metal Anode

The compatibility of current collectors with reactive Li is key to inducing stable Li cycling and prolonged cycle life of lean Li-metal batteries. Herein, a thin and uniform layer of Ni-P complex was built on the surface of a Cu current collector (NiP@Cu) via an efficient, controllable, and cost-effective electroless plating method. The thickness, morphology, composition, and roughness of the Ni-P deposition were successfully regulated. Lithiophilicity of the current collector was greatly improved by Ni-P deposition, which effectively reduced the Li nucleation overpotential and suppressed the Li dendrite growth. In addition, NiP@Cu promoted an inorganic LiF/Li₃P-rich solid electrolyte interphase to facilitate interfacial charge transfer and eliminate excessive side reactions between Li and the electrolyte. As a result, the Coulombic efficiency of half-cells remained above 98.5% for more than 400 cycles at 0.5 mA/cm² and 98.2% for more than 250 cycles at 1 mA/cm². Full cells with NiP@Cu also showed superior performance compared to those with bare Cu. This work proposes a promising surface modification method to develop a stable, dendrite-free, and cost-effective anode current collector for high-energy-density lean Li-metal batteries.

Interface Crystallographic Optimization of Crystal Plane for Stable Metallic Lithium Anode

Li metal, the ideal anode material for rechargeable batteries, suffers from the inherent limitations of uneven interface kinetics and dendrite growth. Herein, we tackle this issue by applying an interface crystallographic optimization strategy. We demonstrate a promising metallic Li anode design by introducing a customized magnetron sputtering layer of preferred orientation copper coating on the surface of a current collector. The sputtered Cu layer employed is stable against the highly reactive robust Li metal to render the surface lithiophilic and achieve promoted interface kinetics due to the perfect interface-crystal plane matching between the sputtered copper layer and premier Li metal. The dendrite-free Li anode sustains stable interface kinetics and achieves a stable life span of 200 cycles during the plating and stripping process in commercial carbonate electrolytes. This design based on crystallographic optimization provides important insights into the design principles of the Li metal anode as well as other alkali metal anodes (Na, K, Zn, Mg, and Al).

Hydrogels as Soft Ionic Conductors in Flexible and Wearable Triboelectric Nanogenerators

Flexible triboelectric nanogenerators (TENGs) have attracted increasing interest since their advent in 2012. In comparison with other flexible electrodes, hydrogels possess transparency, stretchability, biocompatibility, and tunable ionic conductivity, which together provide great potential as current collectors in TENGs for wearable applications. The development of hydrogel-based TENGs (H-TENGs) is currently a burgeoning field but research efforts have lagged behind those of other common flexible TENGs. In order to spur research and development of this important area, a comprehensive review that summarizes recent advances and challenges of H-TENGs will be very useful to researchers and engineers in this emerging field. Herein, the advantages and types of hydrogels as soft ionic conductors in TENGs are presented, followed by detailed descriptions of the advanced functions, enhanced output performance, as well as flexible and wearable applications of H-TENGs. Finally, the challenges and prospects of H-TENGs are discussed.

Effect of Contact Area and Shape of Anode Current Collectors on Bacterial Community Structure in Microbial Fuel Cells

Low electrical conductivity of carbon materials is a source of potential loss for large carbonaceous electrode surfaces of MFCs due to the long distance traveled by electrons to the collector. In this paper, different configurations of titanium current collectors were used to connect large surfaces of carbon cloth anodes. The current collectors had different distances and contact areas to the anode. For the same anode surface (490 cm²), increasing the contact area from 28 cm² to 70 cm² enhanced power output from 58 mW·m^-2 to 107 mW·m^-2. For the same contact area (28 cm²), decreasing the maximal distance of current collectors to anodes from 16.5 cm to 7.75 cm slightly increased power output from 50 mW·m^-2 to 58 mW·m^-2. Molecular biology characterization (qPCR and 16S rRNA gene sequencing) of anodic bacterial communities indicated that the Geobacter number was not correlated with power. Moreover, Geobacter and Desulfuromonas abundance increased with the drop in potential on the anode and with the presence of fermentative microorganisms. Electrochemical impedance spectroscopy (EIS) showed that biofilm resistance decreased with the abundance of electroactive bacteria. All these results showed that the electrical gradient arising from collectors shapes microbial communities. Consequently, current collectors influence the performance of carbon-based anodes for full-scale MFC applications.

Influence of the Polyacrylic Acid Binder Neutralization Degree on the Initial Electrochemical Behavior of a Silicon/Graphite Electrode

The role of the physicochemical properties of the water-soluble polyacrylic acid (PAA) binder in the electrochemical performance of highly loaded silicon/graphite 50/50 wt % negative electrodes has been examined as a function of the neutralization degree x in PAAH_1-xLi_x at the initial cycle in an electrolyte not containing ethylene carbonate. Electrode processing in the acidic PAAH binder at pH 2.5 leads to a deep copper corrosion, resulting in a significant electrode cohesion and adhesion to the current collector surface, but the strong binder rigidity may explain the big cracks occurring on the electrode surface at the first cycle. The nonuniform binder coating on the material surface leads to an important degradation of the electrolyte, explaining the lowest initial Coulombic efficiency and the lowest reversible capacity among the studied electrodes. When processed in neutral pH, the PAAH_0.22Li_0.78 binder forms a conformal artificial solid electrolyte interphase layer on the material surface, which minimizes the electrolyte reduction at the first cycle and then maximizes the initial Coulombic efficiency. However, the low mechanical resistance of the electrode and its strong cracking explain its low reversible capacity. Electrodes prepared at intermediate pH 4 combine the positive assets of electrodes prepared at acidic and neutral pH. They lead to the best initial performance with a notable areal capacity of 7.2 mA h cm^-2 and the highest initial Coulombic efficiency of around 90%, a value much larger than the usual range reported for silicon/graphite anodes. All data obtained with complementary characterization techniques were discussed as a function of the PAA polymeric chain molecular conformation, microstructure, and surface adsorption or grafting, emphasizing the tremendous role of the binder in the electrode initial performance.

Effect of Washing on the Electrochemical Performance of a Three-Dimensional Current Collector for Energy Storage Applications

The development of efficient materials for energy storage applications has attracted considerable attention, especially for supercapacitors and batteries that are the most promising and important power sources in everyday life. For this purpose, a suitable and efficient current collector must be determined and its behavior with respect to various solvents when it is used as an electrode material for energy storage applications should be understood. In this work, we studied the effect of washing three-dimensional nickel foam using different concentrations of hydrochloric acid and ethanol on the surface characteristics, electrochemical behavior, and storage performance of the foam. Additionally, we observed the different types of acidic treatments that improved the electrochemical and storage performances of the three-dimensional nickel foam. The surface characterization results show that acidic conditions with a concentration of 3M changes the surface morphology from a flat/hill-like structure to a nanosheet/nanoflake-like structure without any further treatment. This structure provides a nano-channel and a large number of surface charges during the electrochemical reaction. The results of this study show that pretreatment of 3D-NF is highly important and recommended. The present work also contributes to the knowledgebase on pretreatment of 3D-NF and its optimization.

Nanoscale Wrinkled Cu as a Current Collector for High-Loading Graphite Anode in Solid-State Lithium Batteries

Solid-state lithium batteries have been intensively studied as part of research activities to develop energy storage systems with high safety and stability characteristics. Despite the advantages of solid-state lithium batteries, their application is currently limited by poor reversible capacity arising from their high resistance. In this study, we significantly improve the reversible capacity of solid-state lithium batteries by lowering the resistance through the introduction of a graphene and wrinkle structure on the surface of the copper (Cu) current collector. This is achieved through a process of chemical vapor deposition (CVD) facilitating graphene-growth synthesis. The modified graphene/wrinkled Cu current collector exhibits a periodic wrinkled pattern 420 nm in width and 22 nm in depth, and we apply it to a graphite composite electrode to obtain an improved areal loading average value of ∼2.5 mg cm^-2. The surface-modified Cu current collector is associated with a significant increase in discharge capacity of 347 mAh g^-1 at 0.2 C when used with a solid polymer electrolyte. Peel test results show that the observed enhancement is due to the improved strength of adhesion occurring between the graphite composite anode and the Cu current collector, which is attributed to mechanical interlocking. The surface-modified Cu current collector structure effectively reduces resistance by improving adhesion, which subsequently improves the performance of the solid-state lithium batteries. Our study can provide perspective and emphasize the importance of electrode design in achieving enhancements in battery performance.

Vertically Aligned and Ordered Arrays of 2D MCo2S4@Metal with Ultrafast Ion/Electron Transport for Thickness-Independent Pseudocapacitive Energy Storage

Pseudocapacitance holds great promise for energy density improvement of supercapacitors, but electrode materials show practical capacity far below theoretical values due to limited ion diffusion accessibility and/or low electron transferability. Herein, inducing two kinds of straight ion-movement channels and fast charge storage/delivery for enhanced reaction kinetics is proposed. Very thick electrodes consisting of vertically aligned and ordered arrays of NiCo₂S₄-nanoflake-covered slender nickel columns (NCs) are achieved via a scalable route. The vertical standing ∼5 nm ultrathin NiCo₂S₄ flakes build a porous covering with straight ion channels without the "dead volume", leading to thickness-independent capacity. Benefiting from the architecture acting as a "superhighway" for ultrafast ion/electron transport and providing a large surface area, high electrical conductivity, and abundant availability of electrochemical active sites, the NiCo₂S₄@NC-array electrode achieves a specific capacity up to 486.9 mAh g^-1. The electrode even can work with a high specific capacity of 150 mAh g^-1 at a very high current density of 100 A g^-1. In particular, due to the advanced structure features, the electrode exhibits excellent flexibility with a unexpected improvement of capacity when being largely bent and excellent cycling stability with an obvious resistance decrease after the cycles. An asymmetric pseudocapacitor applying the NiCo₂S₄@NC-array as a positive electrode achieves an energy density of 66.5 Wh kg^-1 at a power density of 400 W kg^-1, superior to the most reported values for asymmetric devices with NiCo₂S₄ electrodes. This work provides a scalable approach with mold-replication-like simplicity toward achieving thickness-independent electrodes with ultrafast ion/electron transport for energy storage.

Porous Cu Film Enables Thick Slurry-Cast Anodes with Enhanced Charge Transfer Efficiency for High-Performance Li-Ion Batteries

The ever-growing demand for energy in the consumer market has put higher requirements on the energy density of Li-ion batteries. Many researchers have strived to discover new electrode materials with higher capacity, while little attention has been focused on improving the cell structure. How to increase the thickness of conventional slurry-cast electrodes as well as decrease the charge transfer resistance by improving the electrode structure is an urgent problem for enhancing the energy density of Li-ion batteries. Here, a porous Cu film is developed to replace the conventional Cu foil current collector, and a thick graphite anode (300 μm) is engineered by two-side slurry casting. The anode delivers a maximum capacity of 18 mAh cm^-2 or 301.3 mAh g^-1 under a highly active mass loading of 60 mg cm^-2, much higher than that fabricated on Cu foil. The assembled full cell with the graphite anode and the LiFePO₄ cathode achieves high energy densities of 36.2 mWh cm^-2 and 283.3 Wh kg^-1. Systematic experimental and simulation investigations reveal the enhanced performance benefits from the facilitated charge transfer efficiency by the porous Cu current collector. This work provides a new strategy for engineering thick electrodes for high-energy Li-ion batteries by improving the conventional electrode structure.

High-Voltage Stability in KFSI Nonaqueous Carbonate Solutions for Potassium-Ion Batteries: Current Collectors and Coin-Cell Components

Cu, Al, and 316L stainless steel are the main components of the current collectors and coin-type cells used in the characterization of potassium-ion battery (KIB) materials and are expected to be electrochemically inactive. Herein, their electrochemical stabilities in a nonaqueous potassium-bis(fluorosulfonyl)imide (KFSI)-based electrolyte are investigated. In dynamic- and transient-mode polarization, passivation of each metal is observed to occur below 3.9, 3.8, and 4.05 V versus K⁺/K for Cu, Al, and 316L stainless steel, respectively, which are considered the threshold potentials. The composition of the passive layers of each metal is determined using time-of-flight secondary-ion mass spectrometry. The passive layers of Cu and Al consist of Cu-O (CuO or Cu₂O) and Al-O (Al₂O₃), respectively, and 316L stainless steel is passivated with an outermost Cr-F (CrF₃) layer and an inner Cr-O (Cr₂O₃) layer. Above the threshold potentials, however, severe corrosion of each metal occurs accompanied by the dissolution of metal ions, which could affect the reliability of experimental results for KIBs using KFSI-based electrolytes.

Interfacial Engineering of a Heteroatom-Doped Graphene Layer on Patterned Aluminum Foil for Ultrafast Lithium Storage Kinetics

The design of the interfacial architecture between the electrode and the current collector in lithium-ion batteries (LIB) plays a key role in achieving ultrafast lithium storage kinetics with respect to efficient charge transfer and cycle stability. However, in recent years, despite considerable efforts in the structural and chemical engineering of active materials (anode and cathode materials), interfacial architectures between the electrode and the current collector have received relatively insufficient attention in the case of ultrafast LIBs. Here, the interface architecture of a micropatterned Al current collector with a heteroatom-doped graphene interfacial layer is developed using roll pressing and dip coating processes. The cathode electrode fabricated with the resultant current collector offers increased contact area with enhanced interfacial stability between the electrode and the current collector because of micropatterns with heteroatom-doped graphene formed on the current collector, leading to outstanding ultrafast cycling capacity (105.8 mA h g^-1) at 20 C. Furthermore, at extremely high rate and long-term cycling performance, significant ultrafast cycling stability (specific capacity of 87.1 mA h g^-1 with capacity retention of 82.3% at 20 C after 1000 cycles) is noted. These improved ultrafast and ultra-stable performances are explained in terms of the increased electron collection/provision site with a high contact area between the electrode and the current collector for enhanced ultrafast cycling capacity and the effective corrosion prevention of the current collector with fast charge transfer for ultrafast cycling stability.

Electrospun 3D Structured Carbon Current Collector for Li/S Batteries

Light weight carbon nanofibers (CNF) fabricated by a simple electrospinning method and used as a 3D structured current collector for a sulfur cathode. Along with a light weight, this 3D current collector allowed us to accommodate a higher amount of sulfur composite, which led to a remarkable increase of the electrode capacity from 200 to 500 mAh per 1 g of the electrode including the mass of the current collector. Varying the electrospinning solution concentration enabled obtaining carbonized nanofibers of uniform structure and controllable diameter from several hundred nanometers to several micrometers. The electrochemical performance of the cathode deposited on carbonized PAN nanofibers at 800 °C was investigated. An initial specific capacity of 1620 mAh g⁻¹ was achieved with a carbonized PAN nanofiber (cPAN) current collector. It exhibited stable cycling over 100 cycles maintaining a reversible capacity of 1104 mAh g⁻¹ at the 100th cycle, while the same composite on the Al foil delivered only 872 mAh g⁻¹. At the same time, 3D structured CNFs with a highly developed surface have a very low areal density of 0.85 mg cm⁻² (thickness of ~25 µm), which is lower for almost ten times than the commercial Al current collector with the same thickness (7.33 mg cm⁻²).

Quantitative Analyses of the Interfacial Properties of Current Collectors at the Mesoscopic Level in Lithium Ion Batteries by Using Hierarchical Graphene

At the mesoscopic level of commercial lithium ion battery (LIB), it is widely believed that the poor contacts between current collector (CC) and electrode materials (EM) lead to weak adhesions and large interfacial electric resistances. However, systematic quantitative analyses of the influence of the interfacial properties of CC are still scarce. Here, we built a model interface between CC and electrode materials by directly growing hierarchical graphene films on commercial Al foil CC, and we performed systematic quantitative studies of the interfacial properties therein. Our results show that the interfacial electric resistance dominates, i.e. ∼2 orders of magnitude higher than that of electrode materials. The interfacial resistance could be eliminated by hierarchical graphene interlayer. Cathode on CC with eliminated interfacial resistance could deliver much improved power density outputs. Our work quantifies the mesoscopic factors influencing the battery performance and offers practical guidelines of boosting the performance of LIBs and beyond.

Development of a Current Collector with a Graphene Thin Film for a Proton Exchange Membrane Fuel Cell Module

This paper constructs planar-type graphene thin film current collectors for proton exchange membrane fuel cells (PEMFCs). The present planar-type current collector adopts FR-4 as the substrate and coats a copper thin film using thermal evaporation for the electric-conduction layer. A graphene thin film is then coated onto the current collector to prevent corrosion due to electrochemical reactions. Three different coating techniques are conducted and compared: Spin coating, RF magnetron sputtering, and screen printing. The corrosion rates and surface resistances are tested and compared for the different coating techniques. Single cell PEMFCs with the developed current collectors are assembled and tested. A PEMFC module with two cells is also designed and constructed. The cell performances are measured to investigate the device feasibility.

Graphene-Modified 3D Copper Foam Current Collector for Dendrite-Free Lithium Deposition

Lithium (Li) metal is regarded as the ideal anode for rechargeable Li-metal batteries such as Li-S and Li-air batteries. A series of problems caused by Li dendrites, such as low Coulombic efficiency (CE) and a short circuit, have limited the application of Li-metal batteries. In this study, a graphene-modified three-dimensional (3D) Copper (Cu) current collector is addressed to enable dendrite-free Li deposition. After Cu foam is immersed into graphene oxide (GO) suspension, a spontaneous reduction of GO, induced by Cu, generates reduced graphene oxide on a 3D Cu (rGO@Cu) substrate. The rGO@Cu foam not only provides large surface area to accommodate Li deposition for lowering the local effective current density, but also forms a rGO protective layer to effectively control the growth of Li dendrites. As current collector, the rGO@Cu foam shows superior properties than commercial Cu foam and planar Cu foil in terms of cycling stability and CE. The rGO@Cu foam delivers a CE as high as 98.5% for over 350 cycles at the current density of 1 mA cm⁻². Furthermore, the full cell using LiFePO₄ as cathode and Li metal as anode with rGO@Cu foam as current collector (LiFePO₄/rGO@Cu-Li) is assembled to prove the admirable capacities and indicates commercialization of Li-metal batteries.

A Lightweight 3D Cu Nanowire Network with Phosphidation Gradient as Current Collector for High-Density Nucleation and Stable Deposition of Lithium

Lithium metal anodes with high energy density are important for further development of next-generation batteries. However, inhomogeneous Li deposition and dendrite growth hinder their practical utilization. 3D current collectors are widely investigated to suppress dendrite growth, but they usually occupy a large volume and increase the weight of the system, hence decreasing the energy density. Additionally, the nonuniform distribution of Li ions results in low utilization of the porous structure. A lightweight, 3D Cu nanowire current collector with a phosphidation gradient is reported to balance the lithiophilicity with conductivity of the electrode. The phosphide gradient with good lithiophilicity and high ionic conductivity enables dense nucleation of Li and its steady deposition in the porous structure, realizing a high pore utilization. Specifically, the homogenous deposition of Li leads to the formation of an oriented texture on the electrode surface at high capacities. A high mass loading (≈44 wt%) of Li with a capacity of 3 mAh cm^-2 and a high average Coulombic efficiency of 97.3% are achieved. A lifespan of 300 h in a symmetrical cell is obtained at 2 mA cm^-2 , implying great potential to stabilize lithium metal.

Suppressing Corrosion of Aluminum Foils via Highly Conductive Graphene-like Carbon Coating in High-Performance Lithium-Based Batteries

Aluminum foil is the predominant cathodic current collector in lithium-based batteries due to the high electronic conductivity, stable chemical/electrochemical properties, low density, and low cost. However, with the development of next-generation lithium batteries, Al current collectors face new challenges, such as the requirement of increased chemical stability at high voltage, long-cycle-life batteries with different electrolyte systems, as well as improved electronic conductivity and adhesion for new electrode materials. In this study, we demonstrate a novel graphene-like carbon (GLC) coating on the Al foil in lithium-based batteries. Various physical and electrochemical characterizations are conducted to reveal the electronic conductivity and electrochemical stability of the GLC-Al foil in both carbonate- and ether-based electrolytes. Full-cell tests, including Li-S batteries and high-voltage Li-ion batteries, are performed to demonstrate the significantly improved cycling and rate performance of batteries with the use of the GLC-Al foil as current collectors. The cell using the GLC-Al foil can greatly reduce the potential polarization in Li-S batteries and can obtain a reversible capacity of 750 mAh g^-1 over 100 cycles at 0.5C. Even with high-sulfur-loading cathodes, the Li-S battery at 1C still maintains over 500 mAh g^-1 after 100 cycles. In high-voltage Li-ion batteries, the GLC-Al foil significantly improves the high-rate performance, showing an increased retained capacity by over 100 mAh g^-1 after 450 cycles at 1C compared to the bare foil. It is believed that the developed GLC-Al foil brings new opportunities to enhance the battery life of lithium-based batteries.

A High-Surface-Area Carbon-Coated 3D Nickel Nanomesh for Li-O2 Batteries

Nanostructured electrodes show great promises for application in batteries and could improve their energy and power density. Herein, a carbon-coated 3D Ni nanomesh was used as an air cathode for non-aqueous Li-air (O₂ ) battery applications. A 3 μm thick 3D Ni nanomesh was fabricated, showing an excellent surface area/footprint area ratio (90 cm² :1 cm² ) and uniformly distributed pores, on which a conformal amorphous carbon coating was applied for the first time. This carbon-coated 3D Ni nanomesh showed an approximately 100 times larger charge-footprint capacity than that of the glassy carbon electrode. Owing to its tunable properties, a capacity higher than 6 mAh cm^-2 could be achieved for a carbon-coated 3D Ni nanomesh with a thickness of 100 μm, whereas the practical capacities of current air electrodes are in the range of 2 mAh cm^-2 .

Combining High Porosity with High Surface Area in Flexible Interconnected Nanowire Meshes for Hydrogen Generation and Beyond

Nanostructured metals with large surface area have a great potential for multiple device applications. Although various metal architectures based on metal nanoligaments and nanowires are well known, they typically show a tradeoff between mechanical robustness, high surface area, and high (macro)porosity, which, when combined, could significantly improve the performance of devices such as batteries, electrolyzers, or sensors. In this work, we rationally designed templated networks of interconnected metal nanowires, combining for the first time high porosity of metal foams, narrowly distributed macropores, and a very high surface area of nanoporous dealloyed metals. Thanks to their structural uniformity, the few-micron thick nanowire meshes are also remarkably flexible and durable. We show how the textural properties of the material can be precisely tuned to optimize the nanowire networks for applications in different devices. In an exemplary application in electrolytic production of hydrogen, thanks to its high surface area, a few-micron thick nanomesh outperformed a 300 times thicker nickel foam. Furthermore, thanks to its high porosity, the Pt-doped nanomesh surpassed a microporous Pt/C cloth, demonstrating benefits of the optimally designed nanowire structure for a simultaneous improvement and miniaturization of electrochemical devices. This work extends the potential of interconnected nanowires to multiple new research and industrial applications requiring highly porous and flexible conductive materials with a high surface-to-volume ratio.

Li2O-Reinforced Solid Electrolyte Interphase on Three-Dimensional Sponges for Dendrite-Free Lithium Deposition

Lithium (Li) metal, with ultra-high theoretical capacity and low electrochemical potential, is the ultimate anode for next-generation Li metal batteries. However, the undesirable Li dendrite growth usually results in severe safety hazards and low Coulombic efficiency. In this work, we design a three-dimensional CuO@Cu submicron wire sponge current collector with high mechanical strength SEI layer dominated by Li₂O during electrochemical reaction process. The 3D CuO@Cu current collector realizes an enhanced CE of above 91% for an ultrahigh current of 10 mA cm^-2 after 100 cycles, and yields decent cycle stability at 5 C for the full cell. The exceptional performances of CuO@Cu submicron wire sponge current collector hold promise for further development of the next-generation metal-based batteries.

Three-Dimensional Copper Foil-Powder Sintering Current Collector for a Silicon-Based Anode Lithium-Ion Battery

In this work, we propose a facile method for manufacturing a three-dimensional copper foil-powder sintering current collector (CFSCC) for a silicon-based anode lithium-ion battery. We found that the CFSCC is suitable as a silicon-based paste electrode, and the paste-like electrodes are commonly used in industrial production. Compared with flat current collectors, the CFSCC better constrained the silicon volume change during the charging-discharging process. The capacitance of electrodes with CFSCC remained as high as 92.2% of its second cycle after 40 cycles, whereas that of electrodes with a flat current collector only remained at 50%.

3D Hierarchical Porous Cu-Based Composite Current Collector with Enhanced Ligaments for Notably Improved Cycle Stability of Sn Anode in Li-Ion Batteries

A 3D porous Cu current collector used in Li-ion batteries can improve the cycling performance of Sn anodes with high specific capacity because of the accommodation of large volume expansion by the pores. However, the pure Cu ligament is too soft to endure enough stress from volume expansion, and then it leads to the fast fade of capacity because of the formation of cracks or the collapse of the 3D porous structure. In this study, a novel micro-nano 3D hierarchical porous Cu-based composite current collector with enhanced ligaments has been fabricated by one-step dealloying of the Cu-34Zn-6Al (wt %) precursor and subsequent heat treatment. The pore and microstructure evolutions during dealloying and heat treatment have been studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. To confirm the validity of the 3D porous Cu/β/γ composite current collector, Sn has been directly electroless plated on it in comparison with the porous pure Cu and the common Cu foil. It is found that the Sn-coated 3D hierarchical porous Cu/β/γ composite current collector with higher hardness shows significantly improved cycling stability compared with the Sn-coated 3D porous Cu current collector and the planar copper foil.

Epitaxial Welding of Carbon Nanotube Networks for Aqueous Battery Current Collectors

Carbon nanomaterials are desirable candidates for lightweight, highly conductive, and corrosion-resistant current collectors. However, a key obstacle is their weak interconnection between adjacent nanostructures, which renders orders of magnitude lower electrical conductivity and mechanical strength in the bulk assemblies. Here we report an "epitaxial welding" strategy to engineer carbon nanotubes (CNTs) into highly crystalline and interconnected structures. Solution-based polyacrylonitrile was conformally coated on CNTs as "nanoglue" to physically join CNTs into a network, followed by a rapid high-temperature annealing (>2800 K, overall ∼30 min) to graphitize the polymer coating into crystalline layers that also bridge the adjacent CNTs to form an interconnected structure. The contact-welded CNTs (W-CNTs) exhibit both a high conductivity (∼1500 S/cm) and a high tensile strength (∼120 MPa), which are 5 and 20 times higher than the unwelded CNTs, respectively. In addition, the W-CNTs display chemical and electrochemical stabilities in strong acidic/alkaline electrolytes (>6 mol/L) when potentiostatically stressing at both cathodic and anodic potentials. With these exceptional properties, the W-CNT films are optimal as high-performance current collectors and were demonstrated in the state-of-the-art aqueous battery using a "water-in-salt" electrolyte.

Spherical Li Deposited inside 3D Cu Skeleton as Anode with Ultrastable Performance

Porous current collectors are conducive to enhance the property of Li metal anode. Unfortunately, congestion in diffusion path during plating process damages the effects of current collectors. Herein, we developed a 3D Cu skeleton with open micrometer-sized pores by NaCl-assisted powder-sintering method. The unobstructed pores of 3D Cu skeleton help to reduce congestion during plating, thus most of Li deposited inside the current collector. Besides, the large smooth surface promotes the deposition of Li with smooth spherical shape, which mitigating Li dendrite growth. As a result, better safety and rechargeability of Li metal anode were achieved in this design.

Hierarchically Mesostructured Aluminum Current Collector for Enhancing the Performance of Supercapacitors

Aluminum (Al) current collector is one of the most important components of supercapacitors, and its performance has vital effects on the electrochemical performance and cyclic stability of supercapacitors. In the present work, a scalable and low-cost, yet highly efficient, picosecond laser processing method of Al current collectors was developed to improve the overall performance of supercapacitors. The laser treatment resulted in hierarchical micro-nanostructures on the surface of the commercial Al foil and reduced the surface oxygen content of the foil. The electrochemical performance of the Al foil with the micro-nanosurface structures was examined in the symmetrical activated carbon-based coin supercapacitors with an organic electrolyte. The results suggest that the laser-treated Al foil (laser-Al) increased the capacitance density of supercapacitors up to 110.1 F g^-1 and promoted the rate capability due to its low contact resistance with the carbonaceous electrode and high electrical conductivity derived from its larger specific surface areas and deoxidized surface. In addition, the capacitor with the laser-Al current collector exhibited high cyclic stability with 91.5% capacitance retention after 10 000 cycles, 21.3% higher than that with pristine-Al current collector due to its stronger bonding with the carbonaceous electrode that prevented any delamination during aging. Our work has provided a new strategy for improving the electrochemical performance of supercapacitors.

Performance-Enhanced Activated Carbon Electrodes for Supercapacitors Combining Both Graphene-Modified Current Collectors and Graphene Conductive Additive

Graphene has been widely used in the active material, conductive agent, binder or current collector for supercapacitors, due to its large specific surface area, high conductivity, and electron mobility. However, works simultaneously employing graphene as conductive agent and current collector were rarely reported. Here, we report improved activated carbon (AC) electrodes (AC@G@NiF/G) simultaneously combining chemical vapor deposition (CVD) graphene-modified nickel foams (NiF/Gs) current collectors and high quality few-layer graphene conductive additive instead of carbon black (CB). The synergistic effect of NiF/Gs and graphene additive makes the performances of AC@G@NiF/G electrodes superior to those of electrodes with CB or with nickel foam current collectors. The performances of AC@G@NiF/G electrodes show that for the few-layer graphene addition exists an optimum value around 5 wt %, rather than a larger addition of graphene, works out better. A symmetric supercapacitor assembled by AC@G@NiF/G electrodes exhibits excellent cycling stability. We attribute improved performances to graphene-enhanced conductivity of electrode materials and NiF/Gs with 3D graphene conductive network and lower oxidation, largely improving the electrical contact between active materials and current collectors.

Curious Case of Positive Current Collectors: Corrosion and Passivation at High Temperature

In the evaluation of compatibility of different components of cell for high-energy and extreme-conditions applications, the highly focused are positive and negative electrodes and their interaction with electrolyte. However, for high-temperature application, the other components are also of significant influence and contribute toward the total health of battery. In present study, we have investigated the behavior of aluminum, the most common current collector for positive electrode materials for its electrochemical and temperature stability. For electrochemical stability, different electrolytes, organic and room temperature ionic liquids with varying Li salts (LiTFSI, LiFSI), are investigated. The combination of electrochemical and spectroscopic investigations reflects the varying mechanism of passivation at room and high temperature, as different compositions of decomposed complexes are found at the surface of metals.

Thin Coating of Microporous Organic Network Makes a Big Difference: Sustainability Issue of Ni Electrodes on the PET Textile for Flexible Lithium-Ion Batteries

Poly(ethylene terephthalate) fibers (PET-Fs) were coated with microporous organic networks (MONs) by the Sonogashira coupling of tetra(4-ethynylphenyl)methane with 1,4-diiodobenzene. Ni was deposited on the PET-F@MON via electroless deposition. Interestingly, although Ni on the PET-F showed a sharp decrease in conductivity in repeated bending tests, the PET-F@MON@Ni showed excellent retention of conductivity. We suggest that thin MON layers play roles of an efficient binder for Ni attachment to fibers and a structural buffer for the relaxation of bending strain. The positive effect of MON was supported by scanning electron microscopy studies of the PET-F@Ni or PET-F@MON@Ni retrieved after 2000 bending numbers. Although Ni on the PET-F showed severe detachment after bending tests, PET-F@MON@Ni retained the original morphologies. The pouch cells of lithium-ion batteries fabricated using PET-F@MON@Ni as the current collectors showed excellent performance against bending.

Novel Co2 VO4 Anodes Using Ultralight 3D Metallic Current Collector and Carbon Sandwiched Structures for High-Performance Li-Ion Batteries

A novel spinel Co₂ VO₄ is studied as the Li-ion battery anode material and it is sandwiched with a 3D ultralight porous current collector (PCC) and amorphous carbon. Co₂ VO₄ demonstrates the high capacity and excellent cyclability because of the mixed lithium storage mechanisms. The 3D composite structure requires no binders and replaces the conventional current collector (Cu foil) with a 3D ultralight porous metal scaffold, yielding the high electrode-based capacity. Such a novel composite anode also enables the close adhesion of Co₂ VO₄ to the PCC scaffold. The resulting monolithic electrode has the rapid electron pathway and stable mechanical properties, which lead to the excellent rate capabilities and cycling properties. At a current density of 1 A g^-1 , the PCC and carbon sandwiched Co₂ VO₄ anode is able to deliver a stable reversible capacity of about 706.8 mAh g^-1 after 1000 cycles. Generally, this study not only develops a new Co₂ VO₄ anode with high capacity and good cyclability, but also demonstrates an alternative approach to improve the electrochemical properties of high capacity anode materials by using ultralight porous metallic current collector instead of heavy copper foil.

Embedded Ag Grid Electrodes as Current Collector for Ultraflexible Transparent Solid-State Supercapacitor

Flexible transparent solid-state supercapacitors have attracted immerse attention for the power supply of next-generation flexible "see-through" or "invisible" electronics. For fabrication of such devices, high-performance flexible transparent current collectors are highly desired. In this paper, the utilization of embedded Ag grid transparent conductive electrodes (TCEs) fabricated by a facile soft ultraviolet imprinting lithography method combined with scrap techniques, as the current collector for flexible transparent solid-state supercapacitors, is demonstrated. The embedded Ag grid TCEs exhibit not only excellent optoelectronic properties (R_S ∼ 2.0 Ω sq^-1 and T ∼ 89.74%) but also robust mechanical properties, which could meet the conductivity, transparency, and flexibility needs of current collectors for flexible transparent supercapacitors. The obtained supercapacitor exhibits large specific capacitance, long cycling life, high optical transparency (T ∼ 80.58% at 550 nm), high flexibility, and high stability. Owing to the embedded Ag grid TCE structure, the device shows a slight capacitance loss of 2.6% even after 1000 cycles of repetitive bending for a bending radius of up to 2.0 mm. This paves the way for developing high-performance current collectors and thus flexible transparent energy storage devices, and their general applicability opens up opportunities for flexible transparent electronics.

Anode-Free Sodium Battery through in Situ Plating of Sodium Metal

Sodium-ion batteries (SIBs) have been pursued as a more cost-effective and more sustainable alternative to lithium-ion batteries (LIBs), but these advantages come at the expense of energy density. In this work, we demonstrate that the challenge of energy density for sodium chemistries can be overcome through an anode-free architecture enabled by the use of a nanocarbon nucleation layer formed on Al current collectors. Electrochemical studies show this configuration to provide highly stable and efficient plating and stripping of sodium metal over a range of currents up to 4 mA/cm², sodium loading up to 12 mAh/cm², and with long-term durability exceeding 1000 cycles at a current of 0.5 mA/cm². Building upon this anode-free architecture, we demonstrate a full cell using a presodiated pyrite cathode to achieve energy densities of ∼400 Wh/kg, far surpassing recent reports on SIBs and even the theoretical maximum for LIB technology (387 Wh/kg for LiCoO₂/graphite cells) while still relying on naturally abundant raw materials and cost-effective aqueous processing.

Three-Dimensional Adhesion Map Based on Surface and Interfacial Cutting Analysis System for Predicting Adhesion Properties of Composite Electrodes

Using a surface and interfacial cutting analysis system (SAICAS) that can measure the adhesion strength of a composite electrode at a specific depth from the surface, we can subdivide the adhesion strength of a composite electrode into two classes: (1) the adhesion strength between the Al current collector and the cathode composite electrode (FAl-Ca) and (2) the adhesion strength measured at the mid-depth of the cathode composite electrode (Fmid). Both adhesion strengths, FAl-Ca and Fmid, increase with increasing electrode density and loading level. From the SAICAS measurement, we obtain a mathematical equation that governs the adhesion strength of the composite electrodes. This equation revealed a maximum accuracy of 97.2% and 96.1% for FAl-Ca and Fmid, respectively, for four randomly chosen composite electrodes varying in electrode density and loading level.

Free-Standing Copper Nanowire Network Current Collector for Improving Lithium Anode Performance

Lithium metal is one of the most attractive anode materials for next-generation lithium batteries due to its high specific capacity and low electrochemical potential. However, the poor cycling performance and serious safety hazards, caused by the growth of dendritic and mossy lithium, has long hindered the application of lithium metal based batteries. Herein, we reported a rational design of free-standing Cu nanowire (CuNW) network to suppress the growth of dendritic lithium via accommodating the lithium metal in three-dimensional (3D) nanostructures. We demonstrated that as high as 7.5 mA h cm(-2) of lithium can be plated into the free-standing copper nanowire (CuNW) current collector without the growth of dendritic lithium. The lithium metal anode based on the CuNW exhibited high Coulombic efficiency (average 98.6% during 200 cycles) and outstanding rate performance owing to the suppression of lithium dendrite growth and high conductivity of CuNW network. Our results demonstrate that the rational nanostructural design of current collector could be a promising strategy to improve the performance of lithium metal anode enabling its application in next-generation lithium-metal based batteries.

Reduced Graphene Oxide Films with Ultrahigh Conductivity as Li-Ion Battery Current Collectors

Solution processed, highly conductive films are extremely attractive for a range of electronic devices, especially for printed macroelectronics. For example, replacing heavy, metal-based current collectors with thin, light, flexible, and highly conductive films will further improve the energy density of such devices. Films with two-dimensional building blocks, such as graphene or reduced graphene oxide (RGO) nanosheets, are particularly promising due to their low percolation threshold with a high aspect ratio, excellent flexibility, and low cost. However, the electrical conductivity of these films is low, typically less than 1000 S/cm. In this work, we for the first time report a RGO film with an electrical conductivity of up to 3112 S/cm. We achieve high conductivity in RGO films through an electrical current-induced annealing process at high temperature of up to 2750 K in less than 1 min of anneal time. We studied in detail the unique Joule heating process at ultrahigh temperature. Through a combination of experimental and computational studies, we investigated the fundamental mechanism behind the formation of a highly conductive three-dimensional structure composed of well-connected RGO layers. The highly conductive RGO film with high direct current conductivity, low thickness (∼4 μm) and low sheet resistance (0.8 Ω/sq.) was used as a lightweight current collector in Li-ion batteries.

Synthesis and applications of carbon nanomaterials for energy generation and storage

The world is facing an energy crisis due to exponential population growth and limited availability of fossil fuels. Over the last 20 years, carbon, one of the most abundant materials found on earth, and its allotrope forms such as fullerenes, carbon nanotubes and graphene have been proposed as sources of energy generation and storage because of their extraordinary properties and ease of production. Various approaches for the synthesis and incorporation of carbon nanomaterials in organic photovoltaics and supercapacitors have been reviewed and discussed in this work, highlighting their benefits as compared to other materials commonly used in these devices. The use of fullerenes, carbon nanotubes and graphene in organic photovoltaics and supercapacitors is described in detail, explaining how their remarkable properties can enhance the efficiency of solar cells and energy storage in supercapacitors. Fullerenes, carbon nanotubes and graphene have all been included in solar cells with interesting results, although a number of problems are still to be overcome in order to achieve high efficiency and stability. However, the flexibility and the low cost of these materials provide the opportunity for many applications such as wearable and disposable electronics or mobile charging. The application of carbon nanotubes and graphene to supercapacitors is also discussed and reviewed in this work. Carbon nanotubes, in combination with graphene, can create a more porous film with extraordinary capacitive performance, paving the way to many practical applications from mobile phones to electric cars. In conclusion, we show that carbon nanomaterials, developed by inexpensive synthesis and process methods such as printing and roll-to-roll techniques, are ideal for the development of flexible devices for energy generation and storage - the key to the portable electronics of the future.