Silicon‐Microtube Scaffold Decorated with Anatase TiO2 as a Negative Electrode for a 3D Litium‐Ion Microbattery

An optimized scaffold based on silicon microtubes is designed to increase the surface capacity of 3D lithium‐ion microbatteries. High‐depth, mechanically robust microstructures are fabricated using microelectronic facilities. Conformal deposition of anatase TiO₂ is achieved using atomic layer deposition, realizing the targeted improvement for microbatteries; a surface capacity of 0.2 mA h cm^–2 at a charge rate of C/10 is obtained in standard liquid electrolyte. This work paves the way for the fabrication of solid‐state 3D Li‐ion microbatteries with an efficient 3D scaffold.     

An Ultrahigh Energy Density Quasi‐Solid‐State Zinc Ion Microbattery with Excellent Flexibility and Thermostability

The rapid development of smart wearable and integrated electronic products has urgently increased the requirement for high‐performance microbatteries. Although few lithium ion microbatteries based on organic electrolytes have been reported so far, the problems, such as undesirable energy density, poor flexibility, inflammability, volatility toxicity, and high cost restrict their practical applications in the above‐mentioned electronic products. In order to overcome these problems, a low cost quasi‐solid‐state aqueous zinc ion microbattery (ZIMB) assembled by a vanadium dioxide (B)‐multiwalled carbon nanotubes (VO₂ (B)‐MWCNTs) cathode, a zinc nanoflakes anode, and a zinc trifluoromethanesulfonate‐polyvinyl alcohol (Zn(CF₃SO₃)₂‐PVA) hydrogel electrolyte is exploited. As expected, the ZIMB exhibits excellent electrochemical performance, e.g., a high capacity of 314.7 µAh cm^?2, an ultrahigh energy density of 188.8 µWh cm^?2, and a high power density of 0.61 mW cm^?2. Furthermore, the ZIMB also shows high flexibility and excellent high temperature stability: the capacity has no obvious decay when the bending angle is up to 150° and the temperature reaches 100 °C. The ZIMB provides a way to develop next‐generation miniature energy storage devices with high performance.     

In Situ Generation of Artificial Solid‐Electrolyte Interphases on 3D Conducting Scaffolds for High‐Performance Lithium‐Metal Anodes

Rational structure design of the current collector along with further engineering of the solid‐electrolyte interphases (SEI) layer is one of the most promising strategies to achieve uniform Li deposition and inhibit uncontrolled growth of Li dendrites. Here, a Li₂S layer as an artificial SEI with high compositional uniformity and high lithium ion conductivity is in situ generated on the surface of the 3D porous Cu current collector to regulate homogeneous Li plating/stripping. Both simulations and experiments demonstrate that the Li₂S protective layer can passivate the porous Cu skeleton and balance the transport rate of lithium ions and electrons, thereby alleviating the agglomerated Li deposition at the top of the electrode or at the defect area of the SEI layer. As a result, the modified current collector exhibits long‐term cycling of 500 cycles at 1 mA cm^?2 and stable electrodeposition capabilities of 4 mAh cm^?2 at an ultrahigh current density of 4 mA cm^?2. Furthermore, full batteries (LiFePO₄ as cathode) paired with this designed 3D anode with only ≈200% extra lithium show superior stability and rate performance than the batteries paired with lithium foil (≈3000% extra lithium). These explorations provide new strategies for developing high‐performance Li metal anodes.     

Ultrafast All‐Solid‐State Coaxial Asymmetric Fiber Supercapacitors with a High Volumetric Energy Density

Fiber‐supercapacitors (FSCs) are promising energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. Currently, a major challenge for FSCs is achieving ultrahigh volumetric energy and power densities simultaneously, especially when the charge/discharge rates exceed 1 V s^?1. Herein, an Au‐nanoparticle‐doped‐MnO_x@CoNi‐alloy@carbon‐nanotube (Au–MnO_x@CoNi@CNT) core/shell nanocomposite fiber electrode is designed, aiming to boost its charge/discharge rate by taking advantage of the superconductive CoNi alloy network and the greatly enhanced conductivity of the Au doped MnO_x active materials. An all‐solid‐state coaxial asymmetric FSC (CAFSC) prototype device made by wrapping this fiber with a holey graphene paper (HGP) exhibits excellent performance at rates up to 10 V s^?1, which is the highest charge rate demonstrated so far for FSCs based on pseudocapacitive materials. Furthermore, our fully packaged CAFSC delivers a volumetric energy density of ≈15.1 mW h cm^?3, while simultaneously maintaining a high power density of 7.28 W cm^?3 as well as a long cycle life (90% retention after 10 000 cycles). This value is the highest among all reported FSCs, even better than that of a typical 4 V/500 µA h thin‐film lithium battery.     

Facile and Scalable Preparation of Ruthenium Oxide‐Based Flexible Micro‐Supercapacitors

Tremendous efforts have been invested in the development of the internet of things during the past 10 years. Implantable sensors still need embedded miniaturized energy harvesting devices, since commercialized thin films and microbatteries do not provide sufficient power densities and suffer from limited lifetime. Therefore, micro‐supercapacitors are good candidates to store energy and deliver power pulses while providing non‐constant voltage output with time. However, multistep expensive protocols involving mask aligners and sophisticated cleanrooms are used to prepare these devices. Here, a simple and versatile laser‐writing procedure to integrate flexible micro‐supercapacitors and microbatteries on current‐collector‐free polyimide foils is reported, starting from commercial powders. Ruthenium oxide (RuO₂)‐based micro‐supercapacitors are prepared by laser irradiation of a bilayered tetrachloroauric acid (HAuCl₄ · 3H₂O)–cellulose acetate/RuO₂ film deposited by spin‐coating, which leads to adherent Au/RuO₂ electrodes with a unique pillar morphology. The as‐prepared microdevices deliver 27 mF cm^?2/540 F cm^?3 in 1 m H₂SO₄ and retain 80% of the initial capacitance after 10 000 cycles. This simple process is applied to make carbon‐based micro‐supercapacitors, as well as metal oxide based pseudocapacitors and battery electrodes, thus offering a straightforward solution to prepare low‐cost flexible microdevices at a large scale.     

2D Amorphous V2O5/Graphene Heterostructures for High‐Safety Aqueous Zn‐Ion Batteries with Unprecedented Capacity and Ultrahigh Rate Capability

Rechargeable aqueous zinc‐ion batteries (ZIBs) are appealing due to their high safety, zinc abundance, and low cost. However, developing suitable cathode materials remains a great challenge. Herein, a novel 2D heterostructure of ultrathin amorphous vanadium pentoxide uniformly grown on graphene (A‐V₂O₅/G) with a very short ion diffusion pathway, abundant active sites, high electrical conductivity, and exceptional structural stability, is demonstrated for highly reversible aqueous ZIBs (A‐V₂O₅/G‐ZIBs), coupling with unprecedented high capacity, rate capability, long‐term cyclability, and excellent safety. As a result, 2D A‐V₂O₅/G heterostructures for stacked ZIBs at 0.1 A g^?1 display an ultrahigh capacity of 489 mAh g^?1, outperforming all reported ZIBs, with an admirable rate capability of 123 mAh g^?1 even at 70 A g^?1. Furthermore, the new‐concept prototype planar miniaturized zinc‐ion microbatteries (A‐V₂O₅/G‐ZIMBs), demonstrate a high volumetric capacity of 20 mAh cm^?3 at 1 mA cm^?2, long cyclability; holding high capacity retention of 80% after 3500 cycles, and in‐series integration, demonstrative of great potential for highly‐safe microsized power sources. Therefore, the exploration of such 2D heterostructure materials with strong synergy is a reliable strategy for developing safe and high‐performance energy storage devices.     

Thin Film Co3O4/TiO2 Heterojunction Solar Cells

Co₃O₄ is investigated as a light absorber for all‐oxide thin‐film photovoltaic cells because of its nearly ideal optical bandgap of around 1.5 eV. Thin film TiO₂/Co₃O₄ heterojunctions are produced by spray pyrolysis of TiO₂ as a window layer, followed by pulsed laser deposition of Co₃O₄ as a light absorbing layer. The photovoltaic performance is investigated as a function of the Co₃O₄ deposition temperature and a direct correlation is found. The deposition temperature seems to affect both the crystallinity and the morphology of the absorber, which affects device performance. A maximum power of 22.7 μW cm^?2 is obtained at the highest deposition temperature (600 °C) with an open circuit photovoltage of 430 mV and a short circuit photocurrent density of 0.2 mA cm^?2. Performing deposition at 600 °C instead of room temperature improves power by an order of magnitude and reduces the tail states (Urbach edge energy). These phenomena can be explained by larger grains that grows at high temperature, as opposed to many nucleation events that occur at lower temperature.     

Vertically Aligned Lithiophilic CuO Nanosheets on a Cu Collector to Stabilize Lithium Deposition for Lithium Metal Batteries

Uncontrollable dendrite growth hinders the direct use of a lithium metal anode in batteries, even though it has the highest energy density of all anode materials. Achieving uniform lithium deposition is the key to solving this problem, but it is hard to be realized on a planar electrode surface. In this study, a thin lithiophilic layer consisting of vertically aligned CuO nanosheets directly grown on a planar Cu current collector is prepared by a simple wet chemical reaction. The lithiophilic nature of the CuO nanosheets reduces the polarization of the electrode, ensuring uniform Li nucleation and continuous smooth Li plating, which is difficult to realize on the normally used lithiophobic Cu current collector surface. The integration of the grown CuO arrays and the Cu current collector guarantees good electron transfer, and moreover, the vertically aligned channels between the CuO nanosheets guarantee fast ion diffusion and reduce the local current density. As a result, a high Columbic efficiency of 94% for 180 cycles at a current density of 1 mA cm^?2 and a prolonged lifespan of a symmetrical cell (700 h at 0.5 mA cm^?2) can be easily achieved, showing a simple but effective way to realize Li metal‐based anode stabilization.     

Electrokinetic Phenomena Enhanced Lithium‐Ion Transport in Leaky Film for Stable Lithium Metal Anodes

The application of lithium (Li) metal anodes in Li metal batteries has been hindered by growth of Li dendrites, which lead to short cycling life. Here a Li‐ion‐affinity leaky film as a protection layer is reported to promote a dendrite‐free Li metal anode. The leaky film induces electrokinetic phenomena to enhance Li‐ion transport, leading to a reduced Li‐ion concentration polarization and homogeneous Li‐ion distribution. As a result, the dendrite‐free Li metal anode during Li plating/stripping is demonstrated even at an extremely high deposition capacity (6 mAh cm^?2) and current density (40 mA cm^?2) with improved Coulombic efficiencies. A full cell battery with the leaky‐film protected Li metal as the anode and high‐areal‐capacity LiNi_0.8Co_0.1Mn_0.1O₂ (NCM‐811) (≈4.2 mAh cm^?2) or LiFePO₄ (≈3.8 mAh cm^?2) as the cathode shows improved cycling stability and capacity retention, even at lean electrolyte conditions.     

Atomic Layer Deposition of Tin Monosulfide Thin Films

Thin film solar cells made from earth‐abundant, non‐toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se)₂ and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). In this report, pure, stoichiometric, single‐phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of bis(N,N′‐diisopropylacetamidinato)tin(II) [Sn(MeC(N‐ⁱPr)₂)₂] and hydrogen sulfide (H₂S) at low temperatures (100 to 200 °C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption (α > 10⁴ cm^?1) is observed throughout the visible and near‐infrared spectral regions. The films are p‐type semiconductors with carrier concentration on the order of 10¹⁶ cm^?3 and hole mobility 0.82–15.3 cm²V^?1s^?1 in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in‐plane direction.     

Improved Functionality of Lithium‐Ion Batteries Enabled by Atomic Layer Deposition on the Porous Microstructure of Polymer Separators and Coating Electrodes

Atomic layer deposition (ALD) of Al₂O₃ is applied on a polypropylene separator for lithium‐ion batteries. A thin Al₂O₃ layer (<10 nm) is coated on every surface of the porous polymer microframework without significantly increasing the total separator thickness. The thin Al₂O₃ ALD coating results in significantly suppressed thermal shrinkage, which may lead to improved safety of the batteries. More importantly, the wettability of Al₂O₃ ALD‐coated separators in an extremely polar electrolyte based on pure propylene carbonate (PC) solvent is demonstrated, without any decrease in electrochemical performances such as capacity, rate capability, and cycle life. Finally, a LiCoO₂/natural graphite full cell is demonstrated under extremely severe conditions (pure PC‐based electrolyte and high (4.5 V) upper cut‐off potential), which is enabled by the Al₂O₃ ALD coating on all three components (cathode, anode, and separator).     

Rationally Designed Hierarchical TiO2@Fe2O3 Hollow Nanostructures for Improved Lithium Ion Storage

Hollow and hierarchical nanostructures have received wide attention in new‐generation, high‐performance, lithium ion battery (LIB) applications. Both TiO₂ and Fe₂O₃ are under current investigation because of their high structural stability (TiO₂) and high capacity (Fe₂O₃), and their low cost. Here, we demonstrate a simple strategy for the fabrication of hierarchical hollow TiO₂@Fe₂O₃ nanostructures for the application as LIB anodes. Using atomic layer deposition (ALD) and sacrificial template‐assisted hydrolysis, the resulting nanostructure combines a large surface area with a hollow interior and robust structure. As a result, such rationally designed LIB anodes exhibit a high reversible capacity (initial value 840 mAh g^?1), improved cycle stability (530 mAh g^?1 after 200 cycles at the current density of 200 mA g^?1), as well as outstanding rate capability. This ALD‐assisted fabrication strategy can be extended to other hierarchical hollow metal oxide nanostructures for favorable applications in electrochemical and optoelectronic devices.     

Solvent‐Free Synthesis of Thin,Flexible, Nonflammable Garnet‐Based Composite Solid Electrolyte for All‐Solid‐State Lithium Batteries

Thin solid‐state electrolytes with nonflammability, high ionic conductivity, low interfacial resistance, and good processability are urgently required for next‐generation safe, high energy density lithium metal batteries. Here, a 3D Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) self‐supporting framework interconnected by polytetrafluoroethylene (PTFE) binder is prepared through a simple grinding method without any solvent. Subsequently, a garnet‐based composite electrolyte is achieved through filling the flexible 3D LLZTO framework with a succinonitrile solid electrolyte. Due to the high content of garnet ceramic (80.4 wt%) and high heat‐resistance of the PTFE binder, such a composite electrolyte film with nonflammability and high processability exhibits a wide electrochemical window of 4.8 V versus Li/Li⁺ and high ionic transference number of 0.53. The continuous Li⁺ transfer channels between interconnected LLZTO particles and succinonitrile, and the soft electrolyte/electrode interface jointly contribute to a high ambient‐temperature ionic conductivity of 1.2 × 10^?4 S cm^?1 and excellent long‐term stability of the Li symmetric battery (stable at a current density of 0.1 mA cm^?2 for over 500 h). Furthermore, as‐prepared LiFePO₄|Li and LiNi_0.5Mn_0.3Co_0.2O₂|Li batteries based on the thin composite electrolyte exhibit high discharge specific capacities of 153 and 158 mAh g^?1 respectively, and desirable cyclic stabilities at room temperature.     

Structural and Electrochemical Study of Al2O3 and TiO2 Coated Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Material Using ALD

Nanolayers of Al₂O₃ and TiO₂ coatings were applied to lithium‐ and manganese‐rich cathode powder Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ using an atomic layer deposition (ALD) method. The ALD coatings exhibited different surface morphologies; the Al₂O₃ surface film appeared to be uniform and conformal, while the TiO₂ layers appeared as particulates across the material surface. In a Li‐cell, the Al₂O₃ surface film was stable during repeated charge and discharge, and this improved the cell cycling stability, despite a high surface impedance. The TiO₂ layer was found to be more reactive with Li and formed a Li_xTiO₂ interface, which led to a slight increase in cell capacity. However, the repetitive insertion/extraction process for the Li⁺ ions caused erosion of the surface protective TiO₂ film, which led to degradation in cell performance, particularly at high temperature. For cells comprised of the coated Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ and an anode of meso‐carbon‐micro‐beads (MCMB), the cycling stability introduced by ALD was not enough to overcome the electrochemical instability of MCMB graphite. Therefore, protection of the cathode materials by ALD Al₂O₃ or TiO₂ can address some of the capacity fading issues related to the Li‐rich cathode at room temperature.     

V2O5 Nano‐Electrodes with High Power and Energy Densities for Thin Film Li‐Ion Batteries

Nanostructured V₂O₅ thin films have been prepared by means of cathodic deposition from an aqueous solution made from V₂O₅ and H₂O₂ directly on fluorine‐doped tin oxide coated (FTO) glasses followed by annealing at 500°C in air, and studied as film electrodes for lithium ion batteries. XPS results show that the as‐deposited films contained 15% V⁴⁺, however after annealing all the vanadium is oxidized to V⁵⁺. The crystallinity, surface morphology, and microstructures of the films have been investigated by means of XRD, SEM, and AFM. The V₂O₅ thin film electrodes show excellent electrochemical properties as cathodes for lithium ion intercalation: a high initial discharge capacity of 402 mA h g^?1 and 240 mA h g^?1 is retained after over 200 cycles with a discharging rate of 200 mA g^?1 (1.3 C). The specific energy density is calculated as 900 W h kg^?1 for the 1^st cycle and 723 W h kg^?1 for the 180^th cycle when the films are tested at 200 mA g^?1 (1.3 C). When discharge/charge is carried out at a high current density of 10.5 A g^?1 (70 C), the thin film electrodes retain a good discharge capacity of 120 mA h g^?1, and the specific power density is over 28 kW kg^?1.     

All‐Solid‐State Fiber Supercapacitors with Ultrahigh Volumetric Energy Density and Outstanding Flexibility

Fiber supercapacitors (FSCs) represent a promising class of energy storage devices that can complement or even replace microbatteries in miniaturized portable and wearable electronics. One of their main limitations, however, is the low volumetric energy density when compared with those of rechargeable batteries. Considering the energy density of FSC is proportional to CV² (E = 1/2 CV², where C is the capacitance and V is the operating voltage), one would explore high operating voltage as an effective strategy to promote the volumetric energy density. In the present work, an all‐solid‐state asymmetric FSC (AFSC) with a maximum operating voltage of 3.5 V is successfully achieved, by employing an ionic liquid (IL) incorporated gel‐polymer as the electrolyte (EMIMTFSI/PVDF‐HFP). The optimized AFSC is based on MnO_x@TiN nanowires@carbon nanotube (NWs@CNT) fiber as the positive electrode and C@TiN NWs@CNT fiber as the negative electrode, which gives rise to an ultrahigh stack volumetric energy density of 61.2 mW h cm^?3, being even comparable to those of commercially planar lead‐acid batteries (50–90 mW h cm^?3), and an excellent flexibility of 92.7% retention after 1000 blending cycles at 90°. The demonstration of employing the ILs‐based electrolyte opens up new opportunities to fabricate high‐performance flexible AFSC for future portable and wearable electronic devices.     

The Fast Charge Transfer Kinetics of the Lithium Metal Anode on the Garnet‐Type Solid Electrolyte Li6.25Al0.25La3Zr2O12

The charge transfer kinetics between a lithium metal electrode and an inorganic solid electrolyte is of key interest to assess the rate capability of future lithium metal solid state batteries. In an in situ microelectrode study run in a scanning electron microscope, it is demonstrated that—contrary to the prevailing opinion—the intrinsic charge transfer resistance of the Li|Li_6.25Al_0.25La₃Zr₂O₁₂ (LLZO) interface is in the order of 10^?1 Ω cm² and thus negligibly small. The corresponding high exchange current density in combination with the single ion transport mechanism (t⁺ ≈ 1) of the inorganic solid electrolyte enables extremely fast plating kinetics without the occurrence of transport limitations. Local plating rates in the range of several A cm^?2 are demonstrated at defect free and chemically clean Li|LLZO interfaces. Practically achievable current densities are limited by lateral growth of lithium along the surface as well as electro‐chemo‐mechanical‐induced fracture of the solid electrolyte. In combination with the lithium vacancy diffusion limitation during electrodissolution, these morphological instabilities are identified as the key fundamental limitations of the lithium metal electrode for solid‐state batteries with inorganic solid electrolytes.     

Graphitic Carbon Nitride Induced Micro‐Electric Field for Dendrite‐Free Lithium Metal Anodes

Uncontrolled dendrites resulting from nonuniform lithium (Li) nucleation/growth and Li volume expansion during charging cause serious safety problems for Li anode‐based batteries. Here the coating of nickel foam with graphitic carbon nitride (g‐C₃N₄) to have a 3D current collector (g‐C₃N₄@Ni foam) for dendrite‐free Li metal anodes is reported. The lithiophilic g‐C₃N₄ coupled with the 3D framework is demonstrated to be highly effective for promoting the uniform deposition of Li and suppressing the formation of dendrites. Both density functional theory calculations and experimental studies indicate the formation of a micro‐electric field resulting from the tri‐s‐triazine units of g‐C₃N₄, which induces numerous Li nuclei during the initial nucleation stage, effectively guiding the following Li growth on the 3D Ni foam to be well distributed. Furthermore, the 3D porous framework is favorable for absorbing any volume change and stabilizing the solid–electrolyte interphase layer during repeated Li plating/stripping. As such, a Li metal anode based on the g‐C₃N₄@Ni foam has a remarkable electrochemical performance with a high Coulombic efficiency (98% retention after 300 cycles), an ultralong lifespan up to 900 h, as well as a low overpotential (<15 mV at 1.0 mA cm^?2) at a Li deposition of 9.0 mA h cm^?2.     

Alkaline Polymer Membrane‐Based Ultrathin,Flexible, and High‐Performance Solid‐State Zn‐Air Battery

The increasing demand for portable and wearable electronics requires lightweight, thin, and highly flexible power sources, for example, flexible zinc‐air batteries (ZABs). The so‐far reported flexible ZAB devices mostly remain bulky, with a design consisting of two relatively thick substrates (e.g., carbon cloths and/or metal foams) and a gel electrolyte‐coated separator in between. Herein, an ultrathin (≈0.2 mm) solid‐state ZAB with high flexibility and performance is introduced by directly forming self‐standing active layers on each surface of an alkaline polymer membrane through an ink‐casting/hot‐pressing approach. A Fe/N‐doped 3D carbon with hierarchic pores and an interconnected network structure is used as cathode electrocatalyst, so that the backing gas‐diffusion layer (e.g., carbon cloth) can be abandoned. What is further, a microstructure‐modulating method to significantly increase the FeN₄ active sites for oxygen reduction reaction is developed, thus significantly boosting the performance of the ZAB. The assembled solid‐state ZAB manifests remarkable peak power density of 250 mW cm^?3 and high capacity of 150.4 mAh cm^?3 at 8.3 mA cm^?3, as well as excellent flexibility. The new design should provide valuable opportunity to the portable and wearable electronics.     

Tailoring Lithium Deposition via an SEI‐Functionalized Membrane Derived from LiF Decorated Layered Carbon Structure

Lithium (Li) metal is a key anode material for constructing next generation high energy density batteries. However, dendritic Li deposition and unstable solid electrolyte interphase (SEI) layers still prevent practical application of Li metal anodes. In this work, it is demonstrated that an uniform Li coating can be achieved in a lithium fluoride (LiF) decorated layered structure of stacked graphene (SG), leading to the formation of an SEI‐functionalized membrane that retards electron transfer by three orders of magnitude to avoid undesirable Li deposition on the top surface, and ameliorates Li⁺ ion migration to enable uniform and dendrite‐free Li deposition beneath such an interlayer. Surface chemistry analysis and density functional theory calculations demonstrate that these beneficial features arise from the formation of C–F_x surface components on the SG sheets during the Li coating process. Based on such an SEI‐functionalized membrane, stable cycling at high current densities up to 3 mA cm^?2 and Li plating capacities up to 4 mAh cm^?2 can be realized in LiPF₆/carbonate electrolytes. This work elucidates the promising strategy of modifying Li plating behavior through the SEI‐functionalized carbon structure, with significantly improved cycling stability of rechargeable Li metal anodes.