Nickel@Nickel Oxide Core–Shell Electrode with Significantly Boosted Reactivity for Ultrahigh‐Energy and Stable Aqueous Ni–Zn Battery

The main bottlenecks of aqueous rechargeable Ni–Zn batteries are their relatively low energy density and poor cycling stability, mainly arising from the low capacity and inferior reversibility of the current Ni‐based cathodes. Additionally, the complicated and difficult‐to‐scale preparation procedures of these cathodes are not promising for large‐scale energy storage. Here, a facile and cost‐effective ultrasonic‐assisted strategy is developed to efficiently activate commercial Ni foam as a robust cathode for a high‐energy and stable aqueous rechargeable Ni–Zn battery. 3D Ni@NiO core–shell electrode with remarkably boosted reactivity and an area of 300 cm² is readily obtained by this ultrasonic‐assisted activation method (denoted as SANF). Benefiting from the in situ formation of electrochemically active NiO and porous 3D structure with a large surface area, the as‐fabricated SANF//Zn battery presents ultrahigh capacity (0.422 mA h cm^?2) and excellent cycling durability (92.5% after 1800 cycles). Moreover, this aqueous rechargeable SANF//Zn battery achieves an impressive energy density of 15.1 mW h cm^?3 (0.754 mW h cm^?2) and a peak power density of 1392 mW cm^?3, outperforming most reported aqueous rechargeable energy‐storage devices. These findings may provide valuable insights into designing large‐scale and high‐performance 3D electrodes for aqueous rechargeable batteries.     

All‐Cellulose‐Based Quasi‐Solid‐State Sodium‐Ion Hybrid Capacitors Enabled by Structural Hierarchy

Na‐ion hybrid capacitors consisting of battery‐type anodes and capacitor‐style cathodes are attracting increasing attention on account of the abundance of sodium‐based resources as well as the potential to bridge the gap between batteries (high energy) and supercapacitors (high power). Herein, hierarchically structured carbon materials inspired by multiscale building units of cellulose from nature are assembled with cellulose‐based gel electrolytes into Na‐ion capacitors. Nonporous hard carbon anodes are obtained through the direct thermal pyrolysis of cellulose nanocrystals. Nitrogen‐doped carbon cathodes with a coral‐like hierarchically porous architecture are prepared via hydrothermal carbonization and activation of cellulose microfibrils. The reversible charge capacity of the anode is 256.9 mAh g^?1 when operating at 0.1 A g^?1 from 0 to 1.5 V versus Na⁺/Na, and the discharge capacitance of cathodes tested within 1.5 to 4.2 V versus Na⁺/Na is 212.4 F g^?1 at 0.1 A g^?1. Utilizing Na⁺ and ClO₄^? as charge carriers, the energy density of the full Na‐ion capacitor with two asymmetric carbon electrodes can reach 181 Wh kg^?1 at 250 W kg^?1, which is one of the highest energy devices reported until now. Combined with macrocellulose‐based gel electrolytes, all‐cellulose‐based quasi‐solid‐state devices are demonstrated possessing additional advantages in terms of overall sustainability.     

Walnut‐Like Multicore–Shell MnO Encapsulated Nitrogen‐Rich Carbon Nanocapsules as Anode Material for Long‐Cycling and Soft‐Packed Lithium‐Ion Batteries

Metal oxide‐based nanomaterials are widely studied because of their high‐energy densities as anode materials in lithium‐ion batteries. However, the fast capacity degradation resulting from the large volume expansion upon lithiation hinders their practical application. In this work, the preparation of walnut‐like multicore–shell MnO encapsulated nitrogen‐rich carbon nanocapsules (MnO@NC) is reported via a facile and eco‐friendly process for long‐cycling Li‐ion batteries. In this hybrid structure, MnO nanoparticles are uniformly dispersed inside carbon nanoshells, which can simultaneously act as a conductive framework and also a protective buffer layer to restrain the volume variation. The MnO@NC nanocapsules show remarkable electrochemical performances for lithium‐ion batteries, exhibiting high reversible capability (762 mAh g^?1 at 100 mA g^?1) and stable cycling life (624 mAh g^?1 after 1000 cycles at 1000 mA g^?1). In addition, the soft‐packed full batteries based on MnO@NC nanocapsules anodes and commercial LiFePO₄ cathodes present good flexibility and cycling stability.     

Finely Crafted 3D Electrodes for Dendrite‐Free and High‐Performance Flexible Fiber‐Shaped Zn–Co Batteries

Rechargeable aqueous Zn‐based batteries, benefiting from their good reliability, low cost, high energy/power densities, and ecofriendliness, show great potential in energy storage systems. However, the poor cycling performance due to the formation of Zn dendrites greatly hinders their practical applications. In this work, a trilayer 3D CC‐ZnO@C‐Zn anode is obtained by in situ growing ZIFs (zeolitic‐imidazolate frameworks) derived ZnO@C core–shell nanorods on carbon cloth followed by Zn deposition, which exhibits excellent antidendrite performance. Using CC‐ZnO@C‐Zn as the anode and a branch‐like Co(CO₃)_0.5(OH)_x·0.11H₂O@CoMoO₄ (CC‐CCH@CMO) as the cathode, a Zn–Co battery is rationally designed, displaying excellent energy/power densities (235 Wh kg^?1, 12.6 kW kg^?1) and remarkable cycling performance (71.1% after 5000 cycles). Impressively, when using a gel electrolyte, a highly customizable, fiber‐shaped flexible all‐solid‐state Zn–Co battery is assembled for the first time, which presents a high energy density of 4.6 mWh cm^?3, peak power density of 0.42 W cm^?3, and long durability (82% capacity retention after 1600 cycles) as well as excellent flexibility. The unique 3D electrode design in this study provides a novel approach to achieve high‐performance Zn‐based batteries, showing promising applications in flexible and portable energy‐storage systems.     

Cactus‐Like NiCoP/NiCo‐OH 3D Architecture with Tunable Composition for High‐Performance Electrochemical Capacitors

To effectively enhance the energy density and overall performance of electrochemical capacitors (ECs), a new strategy is demonstrated to increase both the intrinsic activity of the reaction sites and their density. Herein, nickel cobalt phosphides (NiCoP) with high activity and nickel cobalt hydroxides (NiCo‐OH) with good stability are purposely combined in a hierarchical cactus‐like structure. The hierarchical electrode integrates the advantages of 1D nanospines for effective charge transport, 2D nanoflakes for mechanical stability, and 3D carbon cloth substrate for flexibility. The NiCoP/NiCo‐OH 3D electrode delivers a high specific capacitance of ≈1100 F g^?1, which is around seven times higher than that of bare NiCo‐OH. It also possesses ≈90% capacitance retention after 1000 charge–discharge cycles. An asymmetric supercapacitor composed of NiCoP/NiCo‐OH cathode and metal–organic framework‐derived porous carbon anode achieves a specific capacitance of ≈100 F g^?1, high energy density of ≈34 Wh kg^?1, and excellent cycling stability. The cactus‐like NiCoP/NiCo‐OH 3D electrode presents a great potential for ECs and is promising for other functional applications such as catalysts and batteries.     

Layered P2‐Type K0.65Fe0.5Mn0.5O2 Microspheres as Superior Cathode for High‐Energy Potassium‐Ion Batteries

Potassium‐ion batteries have been regarded as the potential alternatives to lithium‐ion batteries (LIBs) due to the low cost, earth abundance, and low potential of K (?2.936 vs standard hydrogen electrode (SHE)). However, the lack of low‐cost cathodes with high energy density and long cycle life always limits its application. In this work, high‐energy layered P2‐type hierarchical K_0.65Fe_0.5Mn_0.5O₂ (P2‐KFMO) microspheres, assembled by the primary nanoparticles, are fabricated via a modified solvent‐thermal method. Benefiting from the unique microspheres with primary nanoparticles, the K⁺ intercalation/deintercalation kinetics of P2‐KFMO is greatly enhanced with a stabilized cathodic electrolyte interphase on the cathode. The P2‐KFMO microsphere presents a highly reversible potassium storage capacity of 151 mAh g^?1 at 20 mA g^?1, fast rate capability of 103 mAh g^?1 at 100 mA g^?1, and long cycling stability with 78% capacity retention after 350 cycles. A full cell with P2‐KFMO microspheres as cathode and hard carbon as anode is constructed, which exhibits long‐term cycling stability (>80% of retention after 100 cycles). The present high‐performance P2‐KFMO microsphere cathode synthesized using earth‐abundant elements provides a new cost‐effective alternative to LIBs for large‐scale energy storage.     

Potassium Prussian Blue Nanoparticles: A Low‐Cost Cathode Material for Potassium‐Ion Batteries

Potassium‐ion batteries (KIBs) in organic electrolytes hold great promise as an electrochemical energy storage technology owing to the abundance of potassium, close redox potential to lithium, and similar electrochemistry with lithium system. Although carbon materials have been studied as KIB anodes, investigations on KIB cathodes have been scarcely reported. A comprehensive study on potassium Prussian blue K_0.220Fe[Fe(CN)₆]_0.805?4.01H₂O nanoparticles as a potential cathode material is for the first time reported. The cathode exhibits a high discharge voltage of 3.1–3.4 V, a high reversible capacity of 73.2 mAh g^?1, and great cyclability at both low and high rates with a very small capacity decay rate of ≈0.09% per cycle. Electrochemical reaction mechanism analysis identifies the carbon‐coordinated Fe^III/Fe^II couple as redox‐active site and proves structural stability of the cathode during charge/discharge. Furthermore, for the first time, a KIB full‐cell is presented by coupling the nanoparticles with commercial carbon materials. The full‐cell delivers a capacity of 68.5 mAh g^?1 at 100 mA g^?1 and retains 93.4% of the capacity after 50 cycles. Considering the low cost and material sustainability as well as the great electrochemical performances, this work may pave the way toward more studies on KIB cathodes and trigger future attention on rechargeable KIBs.     

Ever‐Increasing Pseudocapacitance in RGO–MnO–RGO Sandwich Nanostructures for Ultrahigh‐Rate Lithium Storage

Lithium ion batteries have attained great success in commercialization owing to their high energy density. However, the relatively delaying discharge/charge severely hinders their high power applications due to intrinsically diffusion‐controlled lithium storage of the electrode. This study demonstrates an ever‐increasing surface redox capacitive lithium storage originating from an unique microstructure evolution during cycling in a novel RGO–MnO–RGO sandwich nanostructure. Such surface pseudocapacitance is dynamically in equilibrium with diffusion‐controlled lithium storage, thereby achieving an unprecedented rate capability (331.9 mAh g^?1 at 40 A g^?1, 379 mAh g^?1 after 4000 cycles at 15 A g^?1) with outstanding cycle stability. The dynamic combination of surface and diffusion lithium storage of electrodes might open up possibilities for designing high‐power lithium ion batteries.     

Bifunctional Separator with a Light‐Weight Carbon‐Coating for Dynamically and Statically Stable Lithium‐Sulfur Batteries

Sulfur is appealing as a high‐capacity cathode for rechargeable lithium batteries as it offers a high theoretical capacity of 1672 mA h g^?1 and is abundant. However, the commercialization of Li‐S batteries is hampered by fast capacity fade during both dynamic cell cycling and static cell resting. The poor electrochemical stability is due to polysulfide diffusion, leading to a short cycle life and severe self‐discharge. Here, we present the design of a bifunctional separator with a light‐weight carbon‐coating that integrates the two necessary components already inside the cell: the conductive carbon and the separator. With no extra additives, this bifunctional carbon‐coated separator allows the use of pure sulfur cathodes involving no complex composite synthesis process, provides a high initial discharge capacity of 1389 mA h g^?1 with excellent dynamic stability, and facilitates a high reversible capacity of 828 mA h g^?1 after 200 cycles. In addition, the static stability is evidenced by low self‐discharge and excellent capacity retention after a 3 month rest period.     

A High‐Power Symmetric Na‐Ion Pseudocapacitor

Batteries and supercapacitors are critical devices for electrical energy storage with wide applications from portable electronics to transportation and grid. However, rechargeable batteries are typically limited in power density, while supercapacitors suffer low energy density. Here, a novel symmetric Na‐ion pseudocapacitor with a power density exceeding 5.4 kW kg^?1 at 11.7 A g^?1, a cycling life retention of 64.5% after 10 000 cycles at 1.17 A g^?1, and an energy density of 26 Wh kg^?1 at 0.585 A g^?1 is reported. Such a device operates on redox reactions occurring on both electrodes with an identical active material, viz., Na₃V₂(PO₄)₃ encapsulated inside nanoporous carbon. This device, in a full‐cell scale utilizing highly reversible and high‐rate Na‐ion intercalational pseudocapacitance, can bridge the performance gap between batteries and supercapacitors. The characteristics of the device and the potentially low‐cost production make it attractive for hybrid electric vehicles and low‐maintenance energy storage systems.     

Low‐Overpotential Li–O2 Batteries Based on TFSI Intercalated Co–Ti Layered Double Oxides

Lithium–oxygen batteries with an exceptionally high theoretical energy density have triggered worldwide interest in energy storage system. The research focus of lithium–oxygen batteries lies in the development of catalytic materials with excellent cycling stability and high bifunctional catalytic activity in oxygen reduction and oxygen evolution reactions. Here, a hierarchically porous flower‐like cobalt–titanium layered double oxide on nickel foam with intercalated anions of bistrifluoromethane sulfonamide (TFSI) is designed and prepared. When used as a binder‐free cathode for lithium–oxygen batteries, this material exhibits low polarization (initial polarization of 0.45 V) and superior cycling stability (80 cycles at a current density of 100 mA g^?1 at full discharge/charge). The high electrochemical performance of the cathode material is attributed to the good dispersion of binary elements in its host layer and good compatibility with lithium bistrifluoromethane sulfonamide electrolyte induced by intercalated guest anions of TFSI within its interlayer. This work provides a novel strategy for the fabrication of binder‐free cathodes based on layered double oxides for high‐performance lithium–oxygen batteries.     

Designing 3D Biomorphic Nitrogen‐Doped MoSe2/Graphene Composites toward High‐Performance Potassium‐Ion Capacitors

Potassium‐ion hybrid capacitors (KICs) reconciling the advantages of batteries and supercapacitors have stimulated growing attention for practical energy storage because of the high abundance and low cost of potassium sources. Nevertheless, daunting challenge remains for developing high‐performance potassium accommodation materials due to the large radius of potassium ions. Molybdenum diselenide (MoSe₂) has recently been recognized as a promising anode material for potassium‐ion batteries, achieving high capacity and favorable cycling stability. However, KICs based on MoSe₂ are scarcely demonstrated by far. Herein, a diatomite‐templated synthetic strategy is devised to fabricate nitrogen‐doped MoSe₂/graphene (N‐MoSe₂/G) composites with favorable pseudocapacitive potassium storage targeting a superior anode material for KICs. Benefiting from the unique biomorphic structure, high electron/K‐ion conductivity, enriched active sites, and the conspicuous pseudocapacitive effect of N‐MoSe₂/G, thus‐derived KIC full‐cell manifests high energy/power densities (maximum 119 Wh kg^?1/7212 W kg^?1), outperforming those of recently reported KIC counterparts. Furthermore, the potassium storage mechanism of N‐MoSe₂/G composite is systematically explored with the aid of first‐principles calculations in combination of in situ X‐ray diffraction and ex situ Raman spectroscopy/transmission electron microscopy/X‐ray photoelectron spectroscopy.     

Novel Insoluble Organic Cathodes for Advanced Organic K‐Ion Batteries

Organic redox‐active molecules are inborn electrodes to store large‐radius potassium (K) ion. High‐performance organic cathodes are important for practical usage of organic potassium‐ion batteries (OPIBs). However, small‐molecule organic cathodes face serious dissolution problems against liquid electrolytes. A novel insoluble small‐molecule organic cathode [N,N′‐bis(2‐anthraquinone)]‐perylene‐3,4,9,10‐tetracarboxydiimide (PTCDI‐DAQ, 200 mAh g^?1) is initially designed for OPIBs. In half cells (1–3.8 V vs K⁺/K) using 1 m KPF₆ in dimethoxyethane (DME), PTCDI‐DAQ delivers a highly stable specific capacity of 216 mAh g^?1 and still holds the value of 133 mAh g^?1 at an ultrahigh current density of 20 A g^?1 (100 C). Using reduced potassium terephthalate (K₄TP) as the organic anode, the resulting K₄TP||PTCDI‐DAQ OPIBs with the electrolyte 1 m KPF₆ in DME realize a high energy density of maximum 295 Wh kg^?1_cathode (213 mAh g^?1_cathode × 1.38 V) and power density of 13 800 W Kg^?1_cathode (94 mAh g^?1 × 1.38 V @ 10 A g^?1) during the working voltage of 0.2–3.2 V. Meanwhile, K₄TP||PTCDI‐DAQ OPIBs fulfill the superlong lifespan with a stable discharge capacity of 62 mAh g^?1_cathode after 10 000 cycles and 40 mAh g^?1_cathode after 30 000 cycles (3 A g^?1). The integrated performance of PTCDI‐DAQ can currently defeat any cathode reported in K‐ion half/full cells.     

A High‐Energy Aqueous Aluminum‐Manganese Battery

Rechargeable aluminum‐ion batteries have drawn considerable attention as a new energy storage system, but their applications are still significantly impeded by critical issues such as low energy density and the lack of excellent electrolytes. Herein, a high‐energy aluminum‐manganese battery is fabricated by using a Birnessite MnO₂ cathode, which can be greatly optimized by a divalence manganese ions (Mn²⁺) electrolyte pre‐addition strategy. The battery exhibits a remarkable energy density of 620 Wh kg^?1 (based on the Birnessite MnO₂ material) and a capacity retention above 320 mAh g^?1 for over 65 cycles, much superior to that with no Mn²⁺ pre‐addition. The electrochemical reactions of the battery are scrutinized by a series of analysis techniques, indicating that the Birnessite MnO₂ pristine cathode is first reduced as Mn²⁺ to dissolve in the electrolyte upon discharge, and Al_xMn_(1?x)O₂ is then generated upon charge, serving as a reversible cathode active material in following cycles. This work provides new opportunities for the development of high‐performance and low‐cost aqueous aluminum‐ion batteries for prospective applications.     

Molecularly Coupled Two‐Dimensional Titanium Oxide and Carbide Sheets for Wearable and High‐Rate Quasi‐Solid‐State Rechargeable Batteries

High‐performance, flexible, and lightweight powering electrodes are urgently needed to meet the increasing interest in deformable electronic devices, particularly those utilizing solid‐state electrolytes and performing at high charging rates, which unfortunately have remained a formidable challenge. Here, by regularly stacking two‐dimensional (2D) titanium oxide and carbide sheets, in which the two kinds of sheets are coupled at the molecular level, a self‐standing electrode is achieved with ideal mechanical durability and excellent electrochemical performance, including superb rate performance (delivering a capacity of 114 mAh g^?1 in 3.4 min) and good cycling stability (remaining >93% after 1000 cycles at 1000 mA g^?1). Profiting from these advantages, a flexible and safe full lithium‐ion battery, employing a poly(ethylene glycol) diamine‐based gel polymer as the electrolyte, possesses an excellent power density of 1412 W kg^?1 while maintaining a high energy density of 59 Wh kg^?1, which outperforms most documented flexible batteries that utilize liquid electrolytes and is even comparable with some cells using coin configurations. Importantly, the performance was well maintained under mechanical deformation and after multiple breaking and self‐healing cycles, demonstrating the feasibility for practical application in wearable powering devices. The results highlight the numerous possibilities for utilizing sheet materials to fabricate wearable electrode materials.     

A Cost‐Effective Mixed Matrix Polyethylene Porous Membrane for Long‐Cycle High Power Density Alkaline Zinc‐Based Flow Batteries

Alkaline zinc‐based flow batteries (ZFBs) have received considerable interest for renewable energy storage due to their attractive features of low cost and high energy density. However, a membrane with high stability, high selectivity, and high ion conductivity is in urgent need. Herein, an economical mixed matrix membrane with highly anti‐alkali microporous hollow spheres (denoted as DM‐HM) is developed in this work. With excellent chemical and mechanical stability, DM‐HM can achieve a high area capacity of 100 mA h cm^?2 for carbon felt (CF)||Zn@CF symmetrical flow battery, and thereby exhibits 500 stable cycles with a coulombic efficiency of 98.6% and an energy efficiency of 88.3% at 80 mA cm^?2 for alkaline zinc–iron flow battery. Additionally, with 44 wt% of hollow spheres inside matrix, DM‐HM can dramatically shorten the ion transport pathway and results in a very high power density battery. A kilowatt stack assembled with DM‐HM shows a very impressive performance, further confirming the practicability of this scalable mixed matrix membrane for alkaline ZFBs.     

Suppressing Manganese Dissolution in Potassium Manganate with Rich Oxygen Defects Engaged High‐Energy‐Density and Durable Aqueous Zinc‐Ion Battery

The manganese dissolution leading to sharp capacity decline as well as the sluggish reaction kinetic are still major issues for manganese‐based materials as aqueous zinc‐ion batteries (ZIBs) cathodes. Here, a potassium‐ion‐stabilized and oxygen‐defect K_0.8Mn₈O₁₆ is reported as a high‐energy‐density and durable cathode for neutral aqueous ZIBs. A new insight into suppressing manganese dissolution via incorporation of K⁺ ions to intrinsically stabilize the Mn‐based cathodes is provided. A comprehensive study suggests that oxygen defects improve electrical conductivity and open the MnO₆ polyhedron walls for ion diffusion, which plays a critical role in the fast reaction kinetics and capacity improvement of K_0.8Mn₈O₁₆. In addition, direct evidence for the mechanistic details of simultaneous insertion and conversion reaction based on H⁺‐storage mechanism is demonstrated. As expected, a significant energy output of 398 W h kg^?1 (based on the mass of cathode) and an impressive durability over 1000 cycles with no obvious capacity fading are obtained. Such a high‐energy Zn‐K_0.8Mn₈O₁₆ battery, as well as the basic understanding of manganese dissolution and oxygen defects may open new opportunities toward high‐performance aqueous ZIBs.     

An Ultrastable Nonaqueous Potassium‐Ion Hybrid Capacitor

Potassium‐ion hybrid capacitors (PIHCs) show great potential in large‐scale energy storage due to the advantages of electrochemical capacitors and potassium‐ion batteries. However, their development remains at the preliminary stage and is mainly limited by the kinetic imbalance between the two electrodes. Herein, an architecture of NbSe₂ nanosheets embedded in N, Se co‐doped carbon nanofibers (NbSe₂/NSeCNFs) as flexible, free‐standing, and binder‐free anodes for PIHCs is reported. The NbSe₂/NSeCNFs with hierarchically porous structure and N, Se co‐doping afford highly efficient channels for fast transportation of potassium ions and electrons during repeated cycling process. Furthermore, excellent electrochemical reversibility of the NbSe₂/NSeCNFs electrode is demonstrated through in situ XRD, in situ Raman, ex situ transmission electron microscopy and element mapping. Thus, PIHCs with the NbSe₂/NSeCNFs anode and active carbon cathode achieve a high energy of 145 W h kg^?1 at a current density of 50 mA g^?1, as well as an ultra‐long cycle life of over 10 000 cycles at a high current density of 2 A g^?1. These results indicate that the assembled PIHCs display great potential for applications in the field of ultra‐long cycling energy storage devices.     

Electrochemically Derived Graphene‐Like Carbon Film as a Superb Substrate for High‐Performance Aqueous Zn‐Ion Batteries

3D graphene, as a light substrate for active loadings, is essential to achieve high energy density for aqueous Zn‐ion batteries, yet traditional synthesis routes are inefficient with high energy consumption. Reported here is a simplified procedure to transform the raw graphite paper directly into the graphene‐like carbon film (GCF). The electrochemically derived GCF contains a 2D–3D hybrid network with interconnected graphene sheets, and offers a highly porous structure. To realize high energy density, the Na:MnO₂/GCF cathode and Zn/GCF anode are fabricated by electrochemical deposition. The GCF‐based Zn‐ion batteries deliver a high initial discharge capacity of 381.8 mA h g^?1 at 100 mA g^?1 and a reversible capacity of 188.0 mA h g^?1 after 1000 cycles at 1000 mA g^?1. Moreover, a recorded energy density of 511.9 Wh kg^?1 is obtained at a power density of 137 W kg^?1. The electrochemical kinetics measurement reveals the high capacitive contribution of the GCF and a co‐insertion/desertion mechanism of H⁺ and Zn²⁺ ions. First‐principles calculations are also carried out to investigate the effect of Na⁺ doping on the electrochemical performance of layered δ‐MnO₂ cathodes. The results demonstrate the attractive potential of the GCF substrate in the application of the rechargeable batteries.     

Magnesium Anodes with Extended Cycling Stability for Lithium‐Ion Batteries

Magnesium as a promising alloy‐type anode material for lithium‐ion batteries features both high theoretical specific capacity (2150 mAh g^?1) and stack energy density (1032 Wh L^?1). However, the poor cycling performance of Mg‐based anodes severely limits their application, mainly because high‐impedance films can grow easily on the surface of Mg and cause diminished electrochemical activity. As a result, the capacities of reported Mg anodes fade quickly in less than 100 cycles. To improve the stability of Mg anodes, 3D Cu@Mg@C structures are prepared by depositing Mg/C composite on 3D Cu current collectors. The resulting 3D Cu@Mg@C anodes can deliver an initial capacity of 1392 mAh g^?1. With a second‐cycle capacity of 1255 mAh g^?1, 91% can be retained after 1000 cycles at 0.5 C. When cycled at 2 C, the initial capacity can be maintained for 4000 cycles. This remarkably improved cycling performance can be attributed to both the 3D structure and the embedded carbon layers of the 3D Cu@Mg@C electrodes that facilitate electrical contact and prevent the growth of high‐impedance films during cycling. With 3D Cu@Mg@C anodes and LiFePO₄ cathodes, full cells are assembled and charging by a rotating triboelectric nanogenerator that can harvest mechanical energy is demonstrated.