Foil Anode Research Articles

Triple engineering boosts high-performance accordion-like vanadium oxide for practical aqueous zinc-ion batteries

Vanadium oxide is one of promising cathode materials for aqueous zinc-ion batteries (ZIBs), but the low electrical conductivity and slow ion diffusion kinetics of vanadium oxide lead to low practical capacity and poor cycling life, which limits further commercialization development. Herein, this study proposes a triple engineering strategy of N-doping, oxygen vacancies and crystal water to achieve the high-performance of V2O5 by a simple stirring method. N doping can improve the electrical conductivity of the materials, oxygen vacancies can modulate the electronic structure, and the crystal water can effectively shield the electrostatic effect. First-principles calculations confirmed that the incorporation of the triple engineering strategies can effectively reduce of the energy band gap and Zn2+ diffusion barrier of V2O5, and promote the intercalation dynamics of Zn2+. As a result, the prepared N-doped V2O5-x·nH2O achieves an outstanding specific capacity of 607.74 mAh/g at 0.1 A/g, and cycling stability. Moreover, based on the above advantages, the practical 21700-type cylindrical battery assembled with this N-doped V2O5-x·nH2O cathode and Zn foil anode, presenting a maximum capacity of 393.5 mAh at 0.4 A. This high performance of vanadium oxide cathode shows a good practical prospect in aqueous cylindrical ZIBs.

Study of the Rolling Effect on MoS2-Carbon Fiber Density and Its Consequences for the Functionality of Li-Ion Batteries.

In this study, an electrode slurry composed of molybdenum disulfide (MoS2) and vapor-grown carbon fiber (VGCF) prepared through a solid-phase synthesis method was blade-coated onto copper foil to form a thick film as the anode for lithium-ion batteries. In previously reported work, MoS2-based lithium-ion batteries have experienced gradual deformation, fracture, and pulverization of electrode materials during the charge and discharge cycling process. This leads to an unstable electrode structure and rapid decline in battery capacity. Furthermore, MoS2 nanosheets tend to aggregate over charge and discharge cycles, which diminishes the surface activity of the material and results in poor electrochemical performance. In this study, we altered the density of the MoS2-carbon fiber/Cu foil anode electrode by rolling. Three different densities of electrode sheets were obtained through varying rolling repetitions. Our study shows the best electrochemical performance was achieved at a material density of 2.2 g/cm3, maintaining a capacity of 427 mAh/g even after 80 cycles.

Effects of oxygen sources on the growth characteristics and dielectric properties of atomic-layer-deposited TiO2 films for aluminum electrolytic capacitors

TiO2 is a promising high dielectric material which can be introduced into aluminum anode foils for realizing miniaturization, lightweight, and high quality of aluminum electrolytic capacitors because of its excellent permittivity. However, the complex porous framework of etched aluminum foil gives rise to the low step coverage and residual carbon impurities of TiO2 films, which can restrict the specific capacitance improvement. In this work, the TiO2 films were deposited by atomic layer deposition (ALD) using O3, O2 plasma (O2*), H2O as oxygen sources, respectively. The effects of oxygen sources on step coverage, carbon impurity content, crystalline structure, oxygen vacancies (OVs) concentration and band gap (Eg) of TiO2 films were studied. Besides, the capacitor performances of aluminum foils were investigated. The O3–TiO2 films showed the best conformability and the least carbon impurity content, while the O2*-TiO2 films exhibited the lowest step coverage due to the directionality of plasma. And the highest carbon impurity content in H2O–TiO2 films was caused by the poor reactivity of H2O. Moreover, the anatase TiO2 peak intensity of H2O–TiO2 films through sintering and anodization was the highest due to the highest deposited mass. The O3–TiO2 films were found to be optimally insulating by characterization of OVs concentration and Eg. Surprisingly, the composite dielectric films using O3 as oxygen source exhibited the excellent withstanding voltage of 21.9 V, while the specific capacitance of 159.9 μF cm-2 was maintained, and there were about 45.89% and 33.63% enhancements in the specific capacitance and CV compared with those without TiO2. These outstanding properties demonstrate that O3 is more favorable for depositing high-performance ALD TiO2 films on aluminum electrolytic capacitors.

Realizing fast plating/stripping of high-performance Zn metal anode with a low Zn loading

Zn metal batteries and capacitors (ZMBs/ZMCs) are gaining significant attention due to their low cost, high safety, and high theoretical capacity. However, the low utilization of Zn metal decreases the coulombic efficiency. Here, we present a novel approach to enhance the conductivity of host materials by utilizing a 3D conductive structural network of copper mesh. The 3D copper mesh serves as a high-conductive matrix and additionally coating it with Zn serves as a Zn source. Finally, a flexible reduced graphene oxide (rGO) was deposited on the Zn-coated copper mesh as an anode protective layer. The conductive copper mesh renders a fast plating/stripping of Zn and enables more contact of Zn with the electrolyte. The flexible rGO film deposited on Zn-coated copper mesh alleviates the local charge accumulation and inhibits corrosion. As a result, the Zn-coated copper mesh anode modified with rGO (RCZ) exhibited a longer lifespan of 200 h than the Zn-coated planar copper foil anode which cycled only for 30 h. The RCZ||AC full capacitor obtained high capacity retention of 97.9% after 9000 times cycling. The RCZ anode integrates the merits of 3D structure matrix and rGO realizing a dual-functionalized Zn metal anode. The conductive matrix strategy sheds light on other metal batteries.

Non-flammable long chain phosphate ester based electrolyte via competitive solventized structures for high-performance lithium metal batteries

Safety remains a persistent challenge for high-energy–density lithium metal batteries (LMBs). The development of safe and non-flammable electrolytes is especially important in harsh conditions such as high temperatures. Herein, a flame-retardant, low-cost and thermally stable long chain phosphate ester based (tributyl phosphate, TBP) electrolyte is reported, which can effectively enhance the cycling stability of highly loaded high-nickel LMBs with high safety through co-solvation strategy. The interfacial compatibility between TBP and electrode is effectively improved using a short-chain ether (glycol dimethyl ether, DME), and a specially competitive solvation structure is further constructed using lithium borate difluorooxalate (LiDFOB) to form the stable and inorganic-rich electrode interphases. Benefiting from the presence of the cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) enriched with LiF and LixPOyFz, the electrolyte demonstrates excellent cycling stability assembled using a 50 μm lithium foil anode in combination with a high loading NMC811 (15.4 mg cm−2) cathode, with 88% capacity retention after 120 cycles. Furthermore, the electrolyte exhibits excellent high-temperature characteristics when used in a 1-Ah pouch cell (N/P = 0.26), and higher thermal runaway temperature (238 °C) in the ARC (accelerating rate calorimeter) demonstrating high safety. This novel electrolyte adopts long-chain phosphate as the main solvent for the first time, and would provide a new idea for the development of extremely high safety and high-temperature electrolytes.

Revealing the alkali ions effects in potential shift and Zn dendrites suppression via electrolyte concentration regulation in aqueous zinc ion batteries

The energy density of aqueous reachable batteries (ARBs) is limited by the output voltage in the aqueous electrolyte. Herein, low-cost aqueous hybrid electrolytes composed of ZnSO4 and K2SO4 dual salts effectively improve the output voltage and suppress the zinc dendrites. The aqueous full cells assembled with potassium zinc hexacyanoferrate (KZnHCF) cathodes and zinc foil anodes reach an output voltage of 1.92 V and an energy density of 107.6 Wh kg−1. It is demonstrated the reversible insertion/extraction of K+ at the cathodes and uniform zinc deposition/striping at the anode in hybrid electrolyte via a series in-situ and ex-situ investigation. The dual salt electrolyte can not only satisfy the reversible capacitive dominated process at the cathodes but also suppress the zinc dendrite. Density functional theory (DFT) calculation demonstrates the K+ preferential intercalation mechanism of KZnHCF in hybrid electrolyte and the inhibition effect of K+ insertion on Zn2+ insertion. This strategy presents a promising approach for development of high performance and low-cost aqueous electrolyte.

An autotransferable alloy overlayer toward stable sodium metal anodes

Sodium (Na) metal anodes receive significant attention due to their high theoretical specific energy and cost-effectiveness. However, the high reactivity of Na foil anodes and the irregular surfaces have posed challenges to the operability and reliability of Na metals in battery applications. In the absence of inert environmental protection conditions, constructing a uniform, dense, and sodiophilic Na metal anode surface is crucial for homogenizing Na deposition, but remains less-explored. Herein, we fabricated a Tin (Sn) nanoparticle-assembled film conforming to separator pores, which provided ample space for accommodating volumetric expansion during the Na alloying process. Subsequently, a seamless Na-Sn alloy overlayer was formed and transferred onto the Na foil during Na plating through a separator-assisted technique, thereby overcoming conventional operational limitations of metallic Na. As compared to traditional volumetrically expanded cracked ones, the present autotransferable, highly sodiophilic, ion-conductive, and seamless Na-Sn alloy overlayer serves as uniform nucleation sites, thereby reducing nucleation and diffusion barriers and facilitating the compact deposition of metallic Na. Consequently, the autotransferable alloy layer enables a high average Coulombic efficiency of 99.9 % at 3.0 mA cm−2 and 3.0 mAh cm−2 in the half cells as well as minimal polarization overpotentials in symmetric cells, both during prolonged cycling 1200 h. Furthermore, the assembled Na||Sn-1.0h-PP||Na3V2(PO4)3@C@CNTs full cell delivers high capacity retention of 97.5 % after 200 cycles at a high cathodic mass loading.

Green biomediated synthesis of anodized WO3 nanocatalysts using Melia azedarach leaves extract for the energetic transition: Solar hydrogen and Li-ion batteries

This study reports the bio-mediated synthesis of tungsten trioxide nanostructures from aqueous extracts of Melia azedarach (L.) dry leaves. The synthesis was carried out by electrochemical anodization of tungsten foils in the presence of different volume percentages of leaves extracts. These nanostructures were afterwards completely characterized by Field-Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), impedance measurements, linear sweep voltammetry in the presence of simulated solar light and UV-Vis spectroscopy. Finally, these nanoelectrodes were used as (photo)electrocatalysts in the photoelectrochemical water splitting process to obtain green hydrogen and as anodes in Li-ion rechargeable batteries. Nanostructures fabricated with 5% M. azedarach leaves extract provided the best (photo)electrocatalytic behavior for both applications, since in that biogenic electrolyte, thin nanorods arranged in very porous and spongy layers were formed. Therefore, the significant increase in specific surface area found for nanostructures fabricated following this green route, in comparison with the blank sample (i.e., nanostructure formed following a non-green route), was essential to enhance their performance as promising efficient (photo)electrocatalysts.

Improvement Synthesis of Graphene Oxide Yield in Two Steps of Intercalation and Oxidation of Flexible Graphite Foil by Electrochemical Exfoliation

Synthesis of high quality and quantity of graphene by cost-effective methods are highly desirable for various application. In electrochemical exfoliation, graphite foil has been used as carbon source for the synthesis of high yield of graphene flakes. Electrochemical exfoliation is one of the faster and cheaper method to synthesize graphene sheets. In this work, five different types of concentration of sulphuric acid were used for electrochemical exfoliation. The electrochemical cell design where graphite foil as anode and copper foil as cathode which were connected to DC power supply of 5V. To examine the morphology scanning electron microscope (SEM) was employed in which the sheet structures with large lateral dimension and thin graphene flakes. Furthermore, X-ray diffraction (XRD) revealed that exfoliated graphene samples showed a significant peak at about 2θ = 26º corresponded to graphite.

Tunable electrical and mechanical properties of anode foils for aluminum electrolytic capacitors prepared by additive manufacturing technology

An additive manufacturing technology was used to produce anode foils with different polystyrene microsphere (PSM). The effect of PSM addition in the range of 0–20 vol% on the specific capacitance and bending strength of the anode foils was investigated. Scanning electron microscopy analysis confirms the presence of pores in the anode foils, which is attributed to the addition of PSM. The porosity and pore diameter of the anode foils increase with increasing PSM content, resulting in an initial increase and then a decrease in specific capacitance, as well as a gradual increase in bending strength. At a PSM addition of 12.5 vol%, the anode foils exhibit a high specific capacitance of 0.927 μF/cm2 and a bending strength of over 120 times greater, meeting the specific capacitance and bending strength requirements for anode foils in aluminum electrolytic capacitors. These findings suggest that incorporating PSM into anode foils is an effective method for adjusting their specific capacitance and bending strength.

Micro-cracking on the surface of zinc metal improves the cycle performance of aqueous zinc ion batteries

The notorious zinc dendrite is a severe constraint to the practical application of zinc-based batteries, as the metal tips growing vertically in two dimensions on the surface of the electrodes during cycling and loosely packed sharp edges may pierce through the diaphragm, posing a safety hazard. In this study, physical stress extrusion was used to generate micron- or submicron-sized cracks on zinc metal anodes, which significantly increased the specific surface area of the electrodes and mitigated the local current density of the electrodes. Zinc ion fluxes were significantly dispersed, producing a dense Zn2SO4(OH)6-xH2O (ZHS) layer, which differed distinctly from the by-products of the loose upright growth on the surface of Raw Zn (RZn). Additionally, three-dimensional structure of cracked zinc composition allows it to adjust the zinc volume variations during electroplating/stripping, and the abundance of nucleation sites significantly reduces the Zn polarization voltage, resulting in uniform Zn deposition. The average cycle life of the symmetric cell was >400 h at 1 mA cm−2 current density, and nearly 500 cycles at 5 mA cm−2 current density for the asymmetric cell, with an average Coulombic efficiency of 99.3 %. The activation energy substantially declined with the increase in Zn ion flux per unit time (29.615 KJ mol−1 vs. 44.041 KJ mol−1), demonstrating efficient desolvation kinetics. Furthermore, the Crack Zn || V2O5 full cell also exhibits outstanding self-discharge performance, with 85 % capacity retention in a 48 h resting charge/discharge testing, superior to the raw zinc foil anode (78.3 %). Herein, a method of creating microcrack configurations on the surface of zinc anodes using stress extrusion was presented, sparing the current density while optimizing the undesirable growth patterns of ZHS by-products.

Stable ultrathin lithium metal anode enabled by self-adapting electrochemical regulating strategy

Ultrathin lithium (Li) metal foils with controllable capacity could realize high-specific-energy batteries; however, the pulverization of Li metal foils due to its extreme volume change results in rapid active Li loss and capacity fading. Here, we report a strategy to stabilize ultrathin Li metal anode via in-situ transferring Li from ultrathin Li foil into a well-designed three-dimensional gradient host during a cycling process. A three-dimensional carbon fiber with gradient distribution of Ag nanoparticles is placed on the ultrathin Li foil in advance and acts as a Li reservoir, guiding Li deposition into its interior and thus alleviating the volume change of ultrathin Li foil anodes. Hence, a high reversibility of Li metal is achieved and Li pulverization is suppressed, which can be witnessed by a long cyclic life in the symmetric cells. The proposed method offers a versatile and facile approach for protecting ultrathin Li metal anodes, which will boost their commercial application process.

Effect of sintered aluminum powder layer structure on properties of sintered anode aluminum foil

The effects of the structure characteristics of sintered aluminum powder, such as particle size and thickness of the sintered aluminum layer, on the mechanical properties, electrochemical properties, and specific capacitance of sintered anode aluminum foil for electrolytic capacitors were investigated using scanning electron microscopy, adhesion and anti-bending tests, electrochemical tests, and specific capacitance tests. The results indicate that reducing the particle size while maintaining the same sintered layer thickness can enhance the specific capacitance of anode foils for aluminum electrolytic capacitors. The optimal particle size was found to be 2.25 μm. Increasing the thickness of the sintered layer can increase the specific capacitance, but it also leads to higher interface resistance and decreased anti-bending performance. The optimal comprehensive performance is achieved when the thickness of both sides of the sintered aluminum powder layer is approximately 65 μm. At this thickness, the specific capacitance is 1.1910 μF/cm2, the interface resistance is 511.5 Ω, and the number of bending can reach 85 cycles, satisfying the requirements of aluminum electrolytic capacitors.

Impact of LiAl Nucleation Kinetics on the Microstructural Evolution of Aluminum Foil Anodes in Lithium-ion Batteries

Aluminum foil anodes have the potential to significantly improve the energy density, safety, cost, and sustainability of Li-ion batteries (LIB). However, their adoption is limited by their notoriously poor cycle life, and the dramatic structural transformations of Al foil anodes during formation and cycling remain poorly understood. In this work, we investigate how the nucleation and growth kinetics of LiAl control the microstructural evolution and cycle life of Al foil anodes. First, we demonstrate the unique sensitivity of Al foil anodes to the cell design and cycling conditions and emphasize the necessity of electrochemical testing in practical full cells. Operando electrochemical impedance spectroscopy (EIS) is combined with scanning electron microscope (SEM) imaging of the lithiated foils to elucidate the relationships between LiAl nucleation kinetics and the resulting LiAl microstructure. Particularly, we investigate the effects of annealing the pristine foils, and controlling the overpotential and temperature during formation, showing that as-rolled foils lithiated at high overpotentials give a columnar LiAl microstructure. Finally, we show that uncontrolled LiAl nucleation during cycling quickly destroys this favorable columnar structure, and a significant improvement in cycle life of LiFePO4 || Al full cells is achieved by limiting the depth-of-discharge to <75%.

Self-mixing anti-corrosive Zn-In powder composite anode with ultra-long lifespan for aqueous zinc-ion battery

Appropriate design of electrode structure and chemistry for Zn metal anode is important to the kinetics and electrochemical stability of Zn in aqueous batteries. Herein, In modified Zn powder electrode with carbon nanofibers as the stable electric conductive matrix provides an effective approach to simultaneously enhance reaction kinetics and inhibit H2 generation reactions. The designed Zn–In powder electrode presents self-mixing In distribution within the electrode during cycling thus enabling superior anti-corrasion and stable conductive network that significantly alters the Zn deposition behavior. Instant 3D Zn deposition with super-fast interfacial kinetics is achieved due to favorable Zn nucleation and growth as well as suppressed side reactions. Stable cycling of over 6300 h is achieved, which is 30-fold longer lifespan than Zn foil anode. Even at 5 mA cm−2, 5 mAh cm−2 (depth of discharge: 31.1%), Zn–In powder anode still presents stable cycling of over 500 h and low polarization voltage. Ultra-long cycle life of over 20,000 cycles can be achieved for full cells using Zn–In powder electrode paired with V2O5 cathode. Modified composite Zn powder electrode provides an effective and practical approach to address the electrochemical stability of Zn-based anodes in rechargeable cells.

Marangoni‐Driven Self‐Assembly MXene As Functional Membrane Enables Dendrite‐Free and Flexible Zinc–Iodine Pouch Cells

AbstractZn metal is a promising anode material in aqueous batteries, but the direct use of Zn foil encounters severe issues of dendrite formation and side reactions, causing short cycle life. Conventional thick and rigid insulating protection layers may impede Zn ion diffusion and detach during mechanical deformation of the battery. Herein, a dendrite‐free zinc anode is demonstrated by grafting a thin (≈10 nm) Ti3C2Tx MXene functional membrane which is formed via Marangoni‐driven self‐assembly. The thin MXene membrane initiates uniform nucleation and promotes deposition of (002)‐oriented Zn in a lateral growth mode. Meanwhile, the membrane functions as a soft, stress‐adaptive, and protective layer to the underneath active zinc. This functional membrane renders Zn anode with improved cycling stability without notable dendrite formation or side‐reaction products. Flexible Zn─I2 pouch cells fabricated from the MXene‐covered Zn foil (20 µm thick) anode and a modified ZnI2 cathode demonstrate stable capacity up to 1500 cycles and unchanged voltage upon various mechanical deformations. This work affords new insights into designing functional soft membranes for constructing flexible Zn‐based energy devices.

Correlation between surface morphology and photocatalytic performance of electrochemically anodized SnO2 nanoparticles

Abstract Dependence of photocatalytic activity of tin oxide nanostructures (SnO2 NS) on the surface morphology is reported. In contrast to previous literature, an electrochemical anodization of Sn foils was successfully carried out to switch SnO2 porous into nanoparticles (NPs). Modifying the surface was limited to a short-time anodization between 10 and 20 min with fixing electrolyte concentration and anodization voltage. Semi-circular tetragonal-phased SnO2 NPs were figured out by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Also, fluorescence spectra confirm that the energy gap was expanded to 4.14 eV. Accordingly, high photo-efficiency (93.08 %) for degrading methylene blue (MB) dye was obtained. Therefore, unlike several studies on porous, the results suggest that the anodized nanoparticles are promising for high-performance catalysts.

Three-Dimensional Vanadium and Nitrogen Dual-Doped Ti3C2 Film with Ultra-High Specific Capacitance and High Volumetric Energy Density for Zinc-Ion Hybrid Capacitors.

Zinc-ion hybrid capacitors (ZICs) can achieve high energy and power density, ultralong cycle life, and a wide operating voltage window, and they are widely used in wearable devices, portable electronics devices, and other energy storage fields. The design of advanced ZICs with high specific capacity and energy density remains a challenge. In this work, a novel kind of V, N dual-doped Ti3C2 film with a three-dimensional (3D) porous structure (3D V-, N-Ti3C2) based on Zn-ion pre-intercalation can be fabricated via a simple synthetic process. The stable 3D structure and heteroatom doping provide abundant ion transport channels and numerous surface active sites. The prepared 3D V-, N-Ti3C2 film can deliver unexpectedly high specific capacitance of 855 F g-1 (309 mAh g-1) and demonstrates 95.26% capacitance retention after 5000 charge/discharge cycles. In addition, the energy storage mechanism of 3D V-, N-Ti3C2 electrodes is the chemical adsorption of H+/Zn2+, which is confirmed by ex situ XRD and ex situ XPS. ZIC full cells with a competitive energy density (103 Wh kg-1) consist of a 3D V-, N-Ti3C2 cathode and a zinc foil anode. The impressive results provide a feasible strategy for developing high-performance MXene-based energy storage devices in various energy-related fields.

Enhancing Durability and Capacity Retention of Ultrafine-Grained Aluminum Foil Anodes in Lithium-Ion Batteries.

In this study, we present our successful fabrication of commercial-grade pure aluminum anode foil (99.5%, 2NAl) with an ultrafine-grained (UFG) microstructure and high hardness, achieved through cold rolling. Under identical rolling conditions, a coarse-grained microstructure with a low hardness was attained from the high-purity Al foil (99.99%, 4NAl). The UFG 2NAl foil exhibited enhanced lithium-ion diffusivity and reduced nucleation and activation overpotentials for forming the β-LiAl phase compared to the 4NAl foil. The high-density grain boundaries in the UFG 2NAl foil facilitated the rapid formation of a uniform β-LiAl phase layer on its surface, thereby mitigating mechanical damage within the β-LiAl phase layer caused by volume changes during the lithiation and delithiation processes. The high hardness of the UFG 2NAl sample effectively prevented macroscopic plastic deformation during cycling, thus preserving the integrity of the β-LiAl phase layer and inhibiting the formation of cracks within the unreacted Al matrix. The collective advantages of reduced overpotential, enhanced Li-ion diffusivity, and high resistance to mechanical damage and plastic deformation in UFG 2NAl contribute to its superior durability and capacity retention compared to the high-purity Al in electrochemical cycling.

Highly Fluorinated Interphase Enables the Exceptional Stability of Monolithic Al Foil Anode for Li‐Ion Batteries

AbstractDirectly using aluminum (Al) foil as anode material offers a streamlined manufacturing process by eliminating the need for conductive additives, binders, and casting procedures. Nonetheless, monolithic Al foil anodes often suffer from mechanical failure and poor cyclability, posing challenges for practical adoption. In this study, a high‐concentration ether‐based electrolyte is employed to boost the durability of the Al foil anode. In contrast to traditional low‐concentration electrolytes, the use of 5 m lithium bis(fluorosulfonyl)imide in 1,2‐dimethoxyethane promotes the priority decomposition of anions, leading to the creation of a fluoride‐rich solid electrolyte interphase (SEI) layer with exceptional structural modulus and high ion conductivity. These outcomes, coupled with Al's superior compatibility in the chosen electrolyte, enable a record‐breaking cycle life of up to 400 cycles for Li//Al half‐cells, when operated at a high areal capacity of 1 mAh cm−2. In full‐cell configurations, an outstanding capacity retention is also observed, with 96.9% after 150 cycles even under practical conditions involving a 40 µm thin Al foil and a 7.4 mg cm−2 LiFePO4 cathode. These results not only mark the pioneering use of high‐concentration ether‐based electrolyte systems in Al foil anodes but also showcase the high potential for developing low‐cost and high‐energy Al foil‐based LIBs.