Low Areal Capacity Research Articles

Efficient structural and compositional modulation of vanadium oxides for high-areal-capacity zinc-ion batteries

Although rechargeable aqueous zinc-ion batteries (RAZIBs) have been revitalized as competitive candidates for large-scale energy storage, the development of this technology is stalled by the underutilization of cathode materials due to sluggish reaction kinetics, resulting in low areal capacities that cannot meet the practical requirements. Herein, this study reveals a simple, efficient, and low-energy synthetic route to effectively convert relatively inactive α-V2O5 (131 mAh g−1 at 0.1 A g−1) into highly active MxV8O20·nH2O (MVO, M = Li, Na, and K) by liquid-phase dissolution-recrystallization reaction and chemical preintercalation under low-temperature conditions. Particularly, NaVO presents the most expansive diffusion channel, the highest specific surface area, and the smallest band gap, allowing faster electron/ion transport kinetics and better material utilization. With these features, NaVO accommodates electrolyte Zn2+ and H+ with good reversibility, showing high capacity (383 mAh g−1 at 0.1 A g−1) and rate-performance (207 mAh g−1 at 8 A g−1). More importantly, high-areal-capacity of 3.2 mAh cm−2 and remarkable cycle stability over 1500 cycles can be achieved from free-standing high-mass-loading electrode (∼14 mg cm−2) made of NaVO and multi-walled carbon nanotubes (MWCNTs). This work enriches the synthetic methods for obtaining high-performance vanadium-based host materials with practical areal capacity and cycle stability.

Pomegranate‐Inspired Cathodes Mitigate the Mismatch Between Carrier Transport and High Loading for Aqueous Zinc‐Ion Batteries

AbstractThe development of high‐energy‐density aqueous zinc‐ion batteries requires the preparation of cathodes with a thick layer of active material. However, the insulating nature and dissolution of vanadium‐based oxides lead to low areal capacity (0.1,1 mA h cm−2) during the charge/discharge cycle. Herein, V2O5 nanospheres are generated by anchoring onto the laser‐induced graphene (LIG) conductive network through defect‐induced adsorption, resulting in the formation of pomegranate‐like V2O5@LIG composites. The unique and abundant defect structure in the honeycomb LIG can trigger the formation of uniform V2O5 nanospheres with high specific surface area and interact electronically with V2O5 to enhance the electrical conductivity of the cathode materials up to four orders of magnitude. In contrast to conventional carbon materials that can cause steric hindrance for ion transport, the micropores within LIG shorten the ion transport path through the cathode. Concurrently, the pomegranate‐like encapsulated structure effectively prevents cathode material corrosion. Under a high‐loading mass of 17.1 mg cm−2, the full cell is stably cycled for 200 cycles, possessing a 92.5% capacity retention, and achieving a high areal capacity of 6.05 mA h cm−2.

Hierarchical porous N-doped carbon fibers enable ultrafast electron and ion transport for Zn-ion storage at high mass loadings

Zinc-ion capacitors (ZICs) are a promising and safe energy storage system for portable electronics but usually limited by relatively low areal capacity and energy density. Although increasing the mass loading has been suggested, thick electrode layers and clogged pores unavoidably lead to sluggish electron transport and ion diffusion as well as “dead volume” of active materials. Herein, a millimeter-scale 3D thick-network electrode, composed of closely intertwined hierarchical porous N-doped and free-standing carbon nanofibers (HPNCFs), was fabricated via carbonization of nanoscale zeolitic imidazolate framework (ZIF-8) particles embedded in electrospun polyacrylonitrile (PAN) nanofibers. With fast electron/ion transport, large ion-accessible surface area and high utilization rate of active materials, the mass loading of the HPNCFs electrode can reach 48.67 mg cm−2 with a thickness of 4.46 mm. Moreover, the HPNCFs-based ZICs can yield a superior areal/gravimetric capacity of 4.13 F cm−2 /280 F g−1, superior rate capability up to 193.7 F g−1 even at 100 A g−1, high energy density of 99.6 Wh kg−1, and long-term stability for 40,000 cycles. The straightforward approach can provide an opportunity to prepare efficient thick electrodes that could be applied in electrocatalysis, energy storage/conversion, and other electrochemical energy-related techniques.

Controlling Electrodeposition in Nonplanar High Areal Capacity Battery Anodes via Charge Transport and Chemical Modulation.

Controlling the morphological evolution of electrochemical crystal growth in battery anodes is of fundamental and practical importance, particularly towards realizing practical, high-energy batteries based on metal electrodes. Such batteries require highly reversible plating/stripping reactions at the anode to achieve a long cycle life. While conformal electrodeposition and electrode reversibility have been demonstrated in numerous proof-of-concept experiments featuring moderate to low areal capacity (≤3 mA h/cm2) electrodes, achieving high levels of reversibility is progressively challenging at the higher capacities (e.g., 10 mA h/cm2), required in applications. Nonplanar, "3D" electrodes composed of electrically conductive, porous substrates are conventionally thought to overcome trade-offs between reversibility and capacity because they hypothetically "host" the electrodeposits in an electronically conducting framework, providing redundant pathways for electron flow. Here, we challenge this hypothesis and instead show that a nonplanar substrate with moderate electrical conductivity (ideally, with an electrical conductance similar to the ionic conductance of the electrolyte) and composed of a passivated cathode-facing surface efficiently regulates electro-crystallization. In contrast, an architecture with a high intrinsic electrical conductivity or with a high electrical conductivity coating on the front surface results in dominantly out-of-plane growth, making the 3D architecture in effect function as a 2D substrate. Using Zn as an example, we demonstrate that interconnected carbon fiber substrates coated by SiO2 on the front and Cu on the back successfully ushers electroplated Zn metal into the 3D framework at a macroscopic length scale, maximizing use of the interior space of the framework. The effective integration of electrodeposits into the 3D framework also enables unprecedented plating/stripping reversibility >99.5% at high current density (e.g., 10 mA/cm2) and high areal capacities (e.g., 10 mA h/cm2). Used in full-cell Zn||NaV3O8 batteries with stringent N/P ratios of 3:1, the substrates are also shown to enhance cycle life.

Monolithic Microparticles Facilitated Flower-Like TiO2 Nanowires for High Areal Capacity Flexible Li-Ion Batteries.

Flexible lithium-ion batteries (FLIBs) are intensively studied using free-standing transition metal oxides (TMOs)-based anode materials. However, achieving high areal capacity TMO-based anode materials is yet to be effectively elucidated owing to the poor adhesion of the active materials to the flexible substrate resulting in low active mass loading, and hence low areal capacity is realized. Herein, a novel monolithic rutile TiO2 microparticles on carbon cloth (ATO/CC) that facilitate the flower-like arrangement of TiO2 nanowires (denoted ATO/CC/OTO) is demonstrated as high areal capacity anode for FLIBs. The optimized ATO/CC/OTO anode exhibits high areal capacity (5.02 mAh cm-2@0.4mA cm-2) excellent rate capability (1.17 mAh cm-2@5.0mA cm-2) and remarkable cyclic stability (over 500 cycles). A series of morphological, kinetic, electrochemical, in situ Raman, and theoretical analyses reveal that the rational phase boundaries between the microparticles and nanowires contribute to promoting the Li storage activity. Furthermore, a 16.0 cm2 all-FLIB pouch cell assembled based on the ATO/CC/OTO anode and LiNiCoMnO2 cathode coated on ATO/CC (ATO/CC/LNCM) exhibits impressive flexibility under different folding conditions, creating opportunity for the development of high areal capacity anodes in future flexible energy storage devices.

NiCo2O4 on monolithic 3DGF/CNT for high performance hybrid zinc batteries

Hybrid Zn-Air and Zn-MX (MX refers to metal species with cation redox properties) batteries that combine the merits of both types are attracting increasing interest. However, the low areal capacity of the Zn-MX segment hinders their applications toward power resilience. Increasing the electrochemically active material loading is critical to achieving sufficient capacity but poses a challenge for conventional electrodes to maintain fast gas diffusion, which is necessary for the Zn-air function. Herein, we report an advanced, monolithic, carbon-based current collector by growing carbon nanotubes (CNT) onto a 3D graphene network (3DGF). The porous and highly conductive current collector readily accommodates more electrochemically active material, NiCo2O4 (NCO), thereby improving the Zn-NCO segment’s capacity without sacrificing the Zn-air segment’s performance. The 3DGF/CNT/NCO electrode was fabricated into a hybrid Zn battery which achieved a superior areal specific capacity of 2.87 mAh cm−2 at 5 mA cm−2, almost threefold of previously reported values, and an impressive rate capability and cycling stability with 98% of original capacity retained after 1000 cycles at 20 mA cm−2 charging/discharging current density. This work showcases 3DGF/CNT as an advanced current collector architecture for new and novel batteries.

Decoupling Electrochromism and Energy Storage for Flexible Quasi-Solid-State Aqueous Electrochromic Batteries with High Energy Density.

Currently, reported aqueous electrochromic batteries (ECBs) show only limited capacity with insufficient energy density and power density. Such a limitation is naturally imposed by the rationale that the cathode of ECBs stores charge by an ion intercalation/deintercalation mechanism, where the inherent inhibition of ion diffusion and structural collapse of cathode materials through repetitive charge/discharge cycles lead to low areal capacity and unsatisfactory electrochemical performance with short lifetime. Herein, we decouple the dual functions of electrochromism and energy storage in conventional cathodes of ECBs by introducing a polyaniline/triiodide composite cathode that is in situ formed by direct electrolysis of an iodide-based quasi-solid-state aqueous electrolyte during charging. When paired with a zinc metal anode, the composite cathode can synergistically utilize the electrochromic property of polyaniline, the high-efficiency energy storage of the Zn-I2 system, as well as the effective anchorage of polyiodide by polyaniline to suppress the shuttle effect of triiodide. By selecting 1-butyl-3-methylimidazolium ion (BMI+) as the cation, a liquid-solid cathode/quasi-solid-state electrolyte interface can be achieved to facilitate the interfacial charge transfer, rendering quasi-solid-state aqueous electrochromic batteries with a high areal capacity of 1363 μAh cm-2, energy density of 1650 μWh cm-2, and power density of 5186 μW cm-2.

Self-Standing Porous Carbon Electrodes with Lean Electrolyte and High Areal Capacity Conditions for Rechargeable Lithium–Oxygen Batteries

Rechargeable lithium–oxygen batteries (LOBs) have the highest theoretical energy densities of all the lithium-based batteries; however, the key challenges facing them are excessing electrolyte amounts and operating at low areal capacity conditions. Thus far, few studies have investigated the performance of the LOBs under practical conditions using appropriate technological parameters. In this study, we prepared a series of carbon-black based self-standing membranes with different pore structures. The self-standing carbon membranes, which were prepared by applying a non-solvent-induced phase separation (NIPS) technique have investigated the relationship between the physicochemical properties and battery performance at low electrolyte/areal capacity ratio (E/C < 10 g/Ah) condition. As a result, the discharge capacity exhibits a clear correlation with the physicochemical property. On the other hand, the cycle number of the LOBs did not simply correlate with the total discharge capacity of the self-standing carbon electrodes. Interestingly, it is observed that the self-standing electrode mainly composed of a unique mesoporous structure exhibits superior cycle performance under small E/C conditions (E/C < 5 g/Ah). Therefore, a turbostratic morphology with a three-dimensional hexagonal array of the unique mesoporous structure is beneficial for exhibiting superior LOB performance under lean electrolyte condition (Figure 1). We believe that the results obtained in the present study give an insight into the development of a new direction for the material design of porous carbon electrodes for achieving a high LOB performance and long cycle life of practical significance. Figure 1

Enlarging Zn deposition space via regulating Sn-induced effective interface for high areal capacity zinc-based flow battery

Zinc-based flow batteries (ZFBs) have aroused great favor in large-scale energy storage due to the high security and low cost. However, the low areal capacity arising from the limited space for Zn plating hinders the further development. Herein, a novel carbon felt-Sn-carbon felt sandwich host (CSCH) is designed and constructed. Benefiting from the strong chemical absorption and the dehydration effect on Zn(H2O)62+, the Sn activation layer in the CSCH demonstrates the lowest comprehensive resistance for Zn deposition. Thus, Zn is induced to nucleate preferentially on the Sn activation layer, and grows towards the membrane, regulating the spatial distribution of Zn electrochemical deposits, which remarkably improves the areal capacity and cyclic stability of Zn anode. Consequently, the zinc-bromine flow batteries equipped with CSCH electrodes can achieve the ultra-high areal capacity of 120 mA h cm−2 at 80 mA cm−2, and run stably for 140 h with average energy efficiency of 80.3% in the extreme condition (80 mA cm−2, 80 mA h cm−2). This innovative work will inspire future advanced designs for high areal capacity electrodes in ZFBs.

DNA-Guided Li2S Nanostructure Deposition for High-Sulfur-Loaded Li–S Batteries

The low areal capacity caused by low sulfur loading (<2.0 mg cm–2) and the poor sulfur utilization due to the insulating Li2S layer covering the cathode always limit the practical applications of lithium–sulfur batteries (Li–S batteries). Deoxyribonucleic acid (DNA)-controlled nucleation and growth of Li2S in the Li–S system were first studied in this work. The negatively charged sugar-phosphate backbone of DNA could attract Li+ ions and allow crystalline Li2S to grow along the DNA chains. The electrodeposition of Li2S with a unique three-dimensional nanostructure during the polysulfide conversion and deposition process was realized, which can not only boost electron and ion transport but also expose and retain more active sites in the cathode. A Li–S battery with ultrahigh sulfur loading of 10 mg cm–2 and a low electrolyte/sulfur ratio of 6.08 delivered a high areal capacity of 8.1 mA h cm–2, which is more than 2 times that of commercial Li-ion batteries, demonstrating a great enhancement of the Li–S battery compared to other studies. Therefore, this study provides an effective strategy of DNA-guided 3D Li2S deposition for achieving high-sulfur-loading Li–S batteries.

Thick‐Network Electrode: Enabling Dual Working Voltage Plateaus of Zn‐ion Micro‐Battery with Ultrahigh Areal Capacity

AbstractAqueous Zn‐ion micro‐batteries (AZMBs) have been recently shown to be promising integrated and safe micropower sources for portable electronics but with wide commercial adoption greatly constrained by their relatively low areal capacity. Although increasing the electrode thickness is proposed, the performance is compromised due to sluggish reaction kinetics, slow ion diffusion rate, and underutilization of active materials. Herein, the technique of utilizing a 3D thick‐network electrode, consisting of closely interweaved MnO2 nanowires (MnO2 NWs), silver nanowires (AgNWs), and carbon nanotubes (CNTs) is presented. The technique readily enables electrode realization up to a thickness of 351 µm, where the porous structure, high hydrophilicity, and fast electrolyte infiltration jointly contribute to fast kinetics. Matching with a Zn metal anode, the prototyped AZMBs acquire an ultra‐high areal capacity/power density of 809 µAh cm−2/1951 µW cm−2. Additionally, as MnO2 NWs and AgNWs collectively participate in the reaction as active substances, the AZMBs deliver dual voltage plateaus to further improve the areal energy density, realizing a maximum value of 896 µWh cm−2. The 3D thick‐network electrode supporting dual working voltage plateaus can provide a path forward for developing AZMBs with simultaneously ultra‐high areal capacity and energy density.

Pseudocapacitive Potassium-Ion Intercalation Enabled by Topologically Defective Soft Carbon toward High-Rate, Large-Areal-Capacity, and Low-Temperature Potassium-Ion Batteries.

Carbonaceous materials are widely investigated as anodes for potassium-ion batteries (PIBs). However, the inferior rate capability, low areal capacity, and limited working temperature caused by sluggish K-ions diffusion kinetics are still primary challenges for carbon-based anodes. Herein, a simple temperature-programmed co-pyrolysis strategy is proposed for the efficient synthesis of topologically defective soft carbon (TDSC) based on inexpensive pitch and melamine. The skeletons of TDSC are optimized with shortened graphite-like microcrystals, enlarged interlayer spacing, and abundant topological defects (e.g., pentagons, heptagons, and octagons), which endow TDSC with fast pseudocapacitive K-ion intercalation behavior. Meanwhile, micrometer-sized structure can reduce the electrolyte degradation over particle surface and avoid unnecessary voids, ensuring a high initial Coulombic efficiency as well as high energy density. These synergistic structural advantages contribute to excellent rate capability (116mAhg-1 at 20 C), impressive areal capacity (1.83mAhcm-2 with a mass loading of 8.32mg cm-2 ), long-term cycling stability (capacity retention of 91.8% after 1200h cycling), and low working temperature (-10°C) of TDSC anodes, demonstrating great potential for the practical application of PIBs.

Performance of Air Electrode Catalysts in the Presence of Redox Mediators for High-Capacity Li–O2 Batteries

Lithium–oxygen batteries (LOBs) have usually been investigated at low current densities and low areal capacities due to small amounts of active materials supported on carbon papers, though they theoretically have high energy density. In addition, studies on catalysts have usually been conducted in the absence of redox mediators. In this study, we have investigated various catalysts at a high current density (0.4 mA cm–2), at a high areal capacity (4 mAh cm–2), and in the presence of dual redox mediators (RMs) of NO3– and Br–, using Ketjen black free-standing sheets (KBFSs; thickness: 270 μm) of high areal weight (6 mg cm–2). The RMs reduced the charge overvoltage even in the presence of catalysts, and catalysts also promoted Li2O2 decomposition in the presence of RMs. RuO2/KBFS, Ir-Co/N-KBFS, and Co/KBFS improved both cyclability and overvoltages compared with KBFS. RuO2/KBFS and Ir-Co/N-KBFS decomposed Li2CO3 at lower voltages than KBFS and exhibited less Li2CO3 residue after charge than KBFS. However, catalysts were coated with byproducts even in the presence of RMs during the discharge/charge tests.

Si–Ni-alloy-assisted very high-areal-capacity silicon-based anode on Ni foam for lithium ion battery

Silicon is investigated as an active material for the anode of lithium-ion battery (LIB) because of the 10 times higher specific capacity of silicon than graphite. In order to achieve a low internal resistance and high areal capacity of a silicon-based anode, metal foams are used as three-dimensional current collectors. However, unless the foam is densely compressed, active materials adhere loosely to the foam and suffer from loss of electrical contacts with the current collector. A densely compressed anode suffers from poor physical integrity without spare room for large volume expansion of silicon. By means of pyrolysis at 800 °C in argon of a mixture of silicon nanoparticles, phenolic resin binder, and Super P conductivity agent on the nickel foam, silicon reacts with nickel to form nickel silicide while the specially selected binder is graphitized to form a conductive and porous anode with a nickel foam current collector. We report 80-nm-silicon-based anode with a nickel foam, exhibiting excellent cycling performance and a high retained areal capacity of 6.5 mAh/cm2 after 50 cycles under a discharge/charge current density of 4 mA/cm2. For anode area of 1 cm2, it stores 23.4 C of charges at a current rate of 4 mA.

Uniform Longitudinal Zinc Growth beyond Interface Guided by Anionic Covalent Organic Framework for Dendrite‐Free Aqueous Zinc Batteries

AbstractAqueous zinc (Zn) batteries hold considerable promise to address safety problems that frequently occur in electric vehicle cells or energy storage applications. However, Zn metal anode suffers seriously from dendrite, corrosion, and interface water decomposition in aqueous electrolytes, especially under large areal capacity or long charging duration. This is mainly because of the uneven longitudinal Zn growth induced by the anisotropic Zn2+ diffusion, which is usually neglected in a laboratory study with low areal capacity. Herein, we report an artificial interface of the anodic covalent organic framework (COF, which can be rapidly synthesized and facilely assembled with Zn anode in a large area) to guide the uniform longitudinal Zn growth for dendrite‐free Zn batteries. In‐situ optical microscope observes that compared with the bare Zn anode, COF interface can promote the formation of the smooth and dendrite‐free surface through spatial‐triggered uniform longitudinal Zn growth. Theoretical calculation uncovers that anodic COF with a negative charge at its N sites could attract Zn2+ to achieve uniform longitudinal Zn2+ diffusion. In addition, this COF interface with superior hydrophobicity could suppress water decomposition and Zn corrosion. Consequently, the COF‐functionalized Zn anode realizes a high coulombic efficiency under severe Zn plating/stripping conditions (10 mAh cm−2), contributing to a long Zn‐I2 full battery life of over 10000 cycles. This work highlights the high‐areal‐capacity Zn anode protection in external space beyond the interface.

High mass-loading and binder-free flexible vanadium-based oxide cathode for zinc-ion battery via a bridge of MXene

Flexible zinc-ion batteries (ZIBs) are promising power sources for portable devices due to their high safety and low production cost. However, the low mass-loading and limited areal capacity of cathode materials are the major problems blocking the practicability of ZIBs. Herein, a high mass-loading and binder-free flexible vanadium oxide ([email protected]) cathode with a large areal capacity was fabricated via the bridge effect of MXene. The functional MXene bridge induces the growth of the vanadium oxide active layer on the carbon cloth (CC) flexible substrate. The binder-free cathode can reduce the electrochemically inactive weight of the whole electrode, which enhances the energy density of ZIBs. Consequently, the [email protected] cathode (mass-loading of ∼7 mg cm−2) delivers a desirable areal capacity (2.36 mAh cm−2) and good cycling stability (capacity retention of 86.1% after 1200 cycles at 10 mA cm−2). Moreover, several ex-situ characterization results indicate that the reaction mechanism upon battery cycling is based on the reversible Zn2+/H+ (de)intercalation in the vanadium oxide interlayer. Furthermore, the assembled quasi-solid-state [email protected]//Zn flexible battery exhibits decent performance at different bending states. Such a bridge effect strategy sheds light on the construction of high mass-loading flexible electrodes for ZIBs applications.

High Areal Capacity and Long Cycle Life Flexible Mild Quasi‐Solid‐State Ag–Zn Battery with Dendrite‐Free Anode

Silver‐zinc (Ag–Zn) batteries are a promising battery system for flexible electronics owing to their high safety, high energy density, and stable output voltage. However, poor cycling performance, low areal capacity, and inferior flexibility limit the practical application of Ag–Zn batteries. Herein, we develop a flexible quasi‐solid‐state Ag–Zn battery system with superior performance by using mild electrolyte and binder‐free electrodes. Copper foam current collector is introduced to impede the growth of Zn dendrite, and the structure of Ag cathode is engineered by electrodeposition and chloridization process to improve the areal capacity. This novel battery demonstrates a remarkable cycle retention of 90% for 200 cycles at 3 mA cm−2. More importantly, this binder‐free battery can afford a high capacity of 3.5 mAh cm−2 at 3 mA cm−2, an outstanding power density of 2.42 mW cm−2, and a maximum energy density of 3.4 mWh cm−2. An energy management circuit is adopted to boost the output voltage of a single battery, which can power electronic ink display and Bluetooth temperature and humidity sensor. The developed battery can even operate under the extreme conditions, such as being bent and sealed in solid ice. This work offers a path for designing electrodes and electrolyte toward high‐performance flexible Ag–Zn batteries.

Benchmarking the Electrochemical Degradation Behavior of Aluminum Foil Anodes for Lithium-Ion Batteries

Aluminum is an attractive candidate for replacing graphite anodes in lithium-ion batteries because it has high specific capacity (990 mAh g-1), and directly using aluminum foil as the anode structure eliminates the need for slurry-coating processes. However, achieving highly reversible lithiation and delithiation of aluminum is challenging due to volume changes during transformation, sluggish lithium-ion transport through the surface oxide layer, and poor initial Coulombic efficiency which all lead to degradation during cycling. Previous studies have focused on understanding the fundamental electrochemical reaction and material transformation behaviors of aluminum, yet there has not been a focus on how different aluminum alloy compositions behave and degrade under electrochemical cycling conditions. In this work, we carry out comprehensive electrochemical testing to benchmark the performance of three different aluminum alloy foils under different cycling conditions. We found that for foils of constant thickness, all foil compositions exhibit a power-law dependence of cycle life on the areal capacity lithiated per cycle, revealing that degradation is significantly accelerated when high areal capacities are used each cycle. Furthermore, the composition of the aluminum alloy was found to strongly affect the Coulombic efficiency over the first 10 cycles, with higher purity foils exhibiting higher Coulombic efficiency. Finally, ex situ scanning electron microscopy and operando optical microscopy revealed different reaction mechanisms and mechanical degradation behavior amongst the different alloys. Based on understanding these various parameters, we showed how full cells with aluminum anodes can be cycled for hundreds of cycles at relatively low areal capacities. The improved understanding of the behavior of aluminum foil anodes herein paves the way for future work intended to engineer aluminum-based foils with enhanced stability.

Toward High‐Areal‐Capacity Electrodes for Lithium and Sodium Ion Batteries

AbstractIn recent decades, extensive nanomaterials and related techniques have been proposed to achieve high capacities surpassing conventional battery electrodes. Nevertheless, most of them show low mass loadings and areal capacities, which deteriorates the cell‐level energy densities and increases cost after the consideration of inactive components in batteries. Achieving high‐areal‐capacity is essential for those advanced materials to move out of laboratories and into practical applications, yet remains challenging due to the decreased mechanical properties and sluggish electrochemical kinetics at elevated mass loadings. In this paper, the previously reported strategies for promoting areal lithium storage performance, including material‐level designs, electrode‐level architecture optimization, and novel manufacturing techniques are reviewed. Sodium‐ion battery electrodes are discussed subsequently, emphatically on its difference with those for lithium storage. Pouch‐cell‐level energy densities based on high‐areal‐capacity electrodes with different thicknesses are also estimated. For each category of these strategies, working principles, advantages, and possible problems are analyzed, with typical examples presented in detail and a summary table comparing the structures and achieved performance. Finally, the features of the high‐areal‐capacity electrodes demonstrated in this review are concluded, and overlooked issues and potential research directions in this field are summarized.

Rationalized design of hyperbranched trans-scale graphene arrays for enduring high-energy lithium metal batteries.

Lithium (Li) metal anode have shown exceptional potential for high-energy batteries. However, practical cell-level energy density of Li metal batteries is usually limited by the low areal capacity (<3 mAh cm−2) because of the accelerated degradation of high–areal capacity Li metal anodes upon cycling. Here, we report the design of hyperbranched vertical arrays of defective graphene for enduring deep Li cycling at practical levels of areal capacity (>6 mAh cm−2). Such atomic-to-macroscopic trans-scale design is rationalized by quantifying the degradation dynamics of Li metal anodes. High-energy Li metal cells are prototyped under realistic conditions with high cathode capacity (>4 mAh cm−2), low negative-to-positive electrode capacity ratio (1:1), and low electrolyte-to-capacity ratio (5 g Ah−1), which shed light on a promising move toward practical Li metal batteries.