Designed Nanoarchitectures by Electrostatic Spray Deposition for Energy Storage

Feδ+ diaspora titanium dioxide and graphene: A study of conductive powder materials and coating applications

Developing new conductive primers to ensure electrostatic spraying is crucial in response to the call for lightweight production of new energy vehicles. We report a stabilized material, Fe-T/G, of Fe-doped TiO2 composite graphene synthesized by a simple hydrothermal and electrostatic self-assembly method. The resistivity decreases from 0.9165 Ω·cm to 0.0943 Ω·cm for T/G. XPS and EPR confirm that Fe3+ is doped into the TiO2 lattice to generate OVs, and Feδ+ is introduced to activate the surrounding Fe-Ti active sites to break the obstruction of the Ti-O bond and build the Ti-O-C and Feδ+-O-C bonds between TiO2 and graphene to connect the two tightly. Multiple electron transfer channels promote Feδ+ impurity energy levels in the TiO2 valence and conduction bands to build electron leaping pathways, enhancing the electron transport ability. Based on this, Fe-T/G can be used as a conductive coating material to develop various insulator surfaces. With Fe-T/G powder material and PVDF, a conductive primer coating can be made and overlaid on a plastic plate to simulate actual applications. The resistance can still be maintained below 25 Ω·cm. Through contact angle experiments, it has been confirmed that the superhydrophobic surface has a water contact angle of 142.8°, with self-cleaning potential.

Multiobjective Optimization Strategy for Enhancing the Efficiency and Quality of Organic Thin-Film Manufacturing with Electrohydrodynamic Atomization Coating

Electrohydrodynamic atomization coating technology is well-suited for micro-/nanoscale thin-film additive manufacturing. However, there are still some challenges in quality control and parameter adjustment during the coating process. Especially when coating on nonconductive and nonhydrophilic substrates, film quality and thickness uniformity are difficult to control. This paper proposes an optimization strategy for enhancing the efficiency and quality of thin-film manufacturing on nonconductive, nonhydrophilic glass substrates. In this paper, a visual inspection system was developed for in situ inspection and identification of droplet deposition states in the substrate surface. Then, the statistical relationship between the operating parameters and the quality of the deposition state was analyzed by response surface methodology. On this basis, machine learning models and intelligent recommendation frameworks for small data sets were developed to rapidly optimize operating parameters and improve the quality of thin-film coating. Optimization strategy developed by applying the principles of statistical modeling, analysis of variance, and global optimization are more efficient and less costly than traditional parameter screening methods. The experimental results show that optimum deposition quality can be obtained with the recommended operating parameters. And, validation results show a 12.8% improvement in film thickness uniformity. At the same time, no mura defects appeared on the thin-film surface. The proposed optimization strategy can improve the efficiency and quality of additive manufacturing of micro and nano thin films and is beneficial for advancing industrial applications of the electrohydrodynamic atomization coating.

Design of Coatings for Sulfur-Based Cathode Materials in Lithium-Sulfur Batteries: A review

Lithium-sulfur batteries (LSBs) are considered next-generation energy storage and conversion solutions owing to their high theoretical specific capacity and the high abundance/low-cost of sulfur-based cathode materials. However, LSBs still encounter significant challenges, including the low conductivities of sulfur-based materials, severe volumetric expansion of sulfur during the discharge process, and the persistent "shuttle effect" of polysulfides. In recent years, a tremendous amount of research has been conducted to address the above challenges by developing coating and compositing materials and corresponding fabrication strategies for sulfur-based cathode materials. In this study, the surface coating, compositing materials, and fabrication methodologies of LSB cathodes are comprehensively reviewed in terms of advanced materials, structure/component characterization, functional mechanisms, and performance validation. Some technical challenges are analyzed in detail, and possible future research directions are proposed to overcome the challenges toward practical applications of lithium-sulfur batteries.

Scalable Fabrication of Quasi-One-Dimensional van der Waals Ta2Pt3Se8 Nanowire Thin Films via Solution Processing for NO2 Gas Sensing over Large Areas

Solution-based processing of van der Waals (vdW) one- (1D) and two-dimensional (2D) materials is an effective strategy to obtain high-quality molecular chains or atomic sheets in a large area with scalability. In this work, quasi-1D vdW Ta2Pt3Se8 was exfoliated via liquid phase exfoliation (LPE) to produce a stably dispersed Ta2Pt3Se8 nanowire solution. In order to screen the optimal exfoliation solvent, nine different solvents were employed with different total surface tensions and polar/dispersive (P/D) component (P/D) ratios. The LPE behavior of Ta2Pt3Se8 was elucidated by matching the P/D ratios between Ta2Pt3Se8 and the applied solvent, resulting in N-methyl-2-pyrrolidone (NMP) as an optimal solvent owing to the well-matched total surface tension and P/D ratio. Subsequently, Ta2Pt3Se8 nanowire thin films are manufactured via vacuum filtration using a Ta2Pt3Se8/NMP dispersion. Then, gas sensing devices are fabricated onto the Ta2Pt3Se8 nanowire thin films, and gas sensing property toward NO2 is evaluated at various thin-film thicknesses. A 50 nm thick Ta2Pt3Se8 thin-film device exhibited a percent response of 25.9% at room temperature and 32.4% at 100 °C, respectively. In addition, the device showed complete recovery within 14.1 min at room temperature and 3.5 min at 100 °C, respectively.

Controllable synthesis of crystalline germanium nanorods as anode for lithium-ion batteries with high cycling stability

Germanium (Ge) nanomaterials have emerged as promising anode materials for lithium-ion batteries (LIBs) due to their higher capacity compared to commercial graphite. However, their practical application has been limited by the high cost associated with harsh preparation conditions and the poor electrode cycling stability in charging and diacharging. In this study, we successfully synthesized crystalline Ge nanorods through the reaction of intermetallic compound CaGe and ZnCl2. Ge nanorods with different morphologies and crystallinity can be obtained through precisely controlling the reaction temperature. When employed as electrodes for LIBs, the Ge nanorods demonstrate exceptional long-term cyclic stability. Even after 1000 cycles at a high rate of 2C (1C = 1600 mA g-1), it exhibits a remarkable reversible capacity of around 1000 mAh/g. Furthermore, such Ge electrode displays excellent cycling performance across a wide temperature range. And it could achieve reversible capacities of 1267, 832, and 690 mAh/g, with the rate of 1C, at temperatures of 20, 0, and -20 °C, respectively. Above all, our study offers a cost-effective approach for the synthesis of crystalline Ge nanorods, addressing the concerns associated with high production costs. And the application of Ge nanorods as anode materials in LIBs over a wide temperature range opens up new possibilities for the development of advanced energy storage systems.

Efficient preparation of uniform germanane nanosheets as anode with high-cycling stability in lithium-ion batteries

Two-dimensional germanane (2D GeH) is considered to be a potential anode material for lithium-ion batteries (LIBs) due to the unique structure and properties. In this study, an effective method for synthesizing GeH is proposed, involving the etching of ball-milled CaGe2 with dilute hydrochloric acid at room temperature for a short duration. The resulting GeH nanosheets exhibit uniformity and high yield without the need for harsh reaction conditions or repeated ultrasound and centrifugation treatments. Comparative analysis reveals that GeH fabricated using this method exhibit superior cycling stability when employed as electrode in LIBs in comparison with reported techniques. Specifically, the as-prepared GeH anode can achieve a specific capacity of 1320 mAh/g after 400 cycles at 0.2C (1C = 1600 mAh/g) and 1020 mAh/g after 1000 cycles at 1C. Furthermore, GeH//LiFePO4 full cell is assembled for evaluating its practical applications. The specific capacity remains stable, maintaining 108 mAh/g after 140 cycles at a current density of 1C (1C = 170 mAh/g). The results confirm that the nano refinement process presented in this study effectively simplifies the synthesis process and significantly enhances the anode stability of GeH materials in LIBs applications. Importantly, this work provides a promising and versatile approach for the mass production of 2D electrode materials with improved electrochemical performance.

A Large-Area Patterned Hydrogen-Bonded Organic Framework Electrochromic Film and Device

Fabrication of a patterned hydrogen-bonded organic framework (HOF) films on a large scale is an extreme challenge. In this work, a large area HOF film (30 × 30 cm2 ) is prepared via an efficient and low-cost electrostatic spray deposition (ESD) approach on the un-modified conductive substrates directly. Combining the ESD with a template method, variously patterned HOF films can be easily produced, including deer- and horse-shaped films. The obtained films exhibit excellent electrochromic performance with multicolor change from yellow to green and violet, and two-band regulation at 550 and 830 nm. Benefiting from the inherently present channels of HOF materials and the additional film porosity created by ESD, the PFC-1 film could quickly change color (within 10 s). Furthermore, the large-area patterned EC device is constructed based on the above film to prove practical potential application. The presented ESD method can be extended to other HOF materials; thus, this work paves a feasible path for constructing large-area patterned HOF films for practical optoelectronic applications.

Mass Production of Customizable Core-Shell Active Materials in Seconds by Nano-Vapor Deposition for Advancing Lithium Sulfur Battery

Rational design and scalable production of core-shell sulfur-rich active materials is vital for not only the practical success of future metal-sulfur batteries but also for a deep insight into the core-shell design for sulfur-based electrochemistry. However, this is a big challenge mainly due to the lack of efficient strategy for realizing precisely controlled core-shell structures. Herein, by harnessing the frictional heating and dispersion capability of the nanostorm technology developed in the authors' laboratory, it is surprisingly found that sulfur-rich active particles can be coated with on-demand shell nanomaterials in seconds. To understand the process, a micro-adhesion guided nano-vapor deposition (MAG-NVD) working mechanism is proposed. Enabled by this technology, customizable nano-shell is realized in a super-efficient and solvent-free way. Further, the different roles of shell characteristics in affecting the sulfur-cathode electrochemical performance are discovered and clarified. Last, large-scale production of calendaring-compatible cathode with the optimized core-shell active materials is demonstrated, and a Li-S pouch-cell with 453 Wh kg^-1 @0.65 Ah is also reported. The proposed nano-vapor deposition may provide an attractive alternative to the well-known physical and chemical vapor deposition technologies.

Honeycomb ZrCo Intermetallic for High Performance Hydrogen and Hydrogen Isotope Storage

Hydrogen isotope storage materials are of great significance for controlled nuclear fusion, which is promising to provide unlimited clean and dense energy. Conventional storage materials of micrometer-sized polycrystalline ZrCo alloys prepared by the smelting method suffer from slow kinetics, pulverization, disproportionation, and poor cycling stability. Here, we synthesize a honeycomb-structured ZrCo composed of highly crystalline submicrometer ZrCo units using electrospray deposition and magnesiothermic reduction. Compared with conventional ones, honeycomb ZrCo does not require activation and exhibits more than 1 order of magnitude increase in kinetic property. Owing to low defects and low stress, the anti-disproportionation ability and cycling stability of honeycomb ZrCo are also obviously higher than those of conventional ZrCo. Moreover, the interfacial stress (due to hydrogenation/dehydrogenation) as a function of particle radius is established, quantitatively elucidating that small-sized ZrCo reduces stress and pulverization. This study points out a direction for the structural design of ZrCo alloy with high-performance hydrogen isotope storage.

Fast Ionic Storage in Aqueous Rechargeable Batteries: From Fundamentals to Applications

The highly dynamic nature of grid-scale energy systems necessitates fast kinetics in energy storage and conversion systems. Rechargeable aqueous batteries are a promising energy-storage solution for renewable-energy grids as the ionic diffusivity in aqueous electrolytes can be up to 1-2 orders of magnitude higher than in organic systems, in addition to being highly safe and low cost. Recent research in this regard has focussed on developing suitable electrode materials for fast ionic storage in aqueous electrolytes. In this review, breakthroughs in the field of fast ionic storage in aqueous battery materials, and 1D/2D/3D and over-3D-tunnel materials are summarized, and tunnels in over-3D materials are not oriented in any direction in particular. Various materials with different tunnel sizes are developed to be suitable for the different ionic radii of Li⁺ , Na⁺ , K⁺ , H⁺ , NH₄ ⁺ , and Zn²⁺ , which show significant differences in the reaction kinetics of ionic storage. New topochemical paths for ion insertion/extraction, which provide superfast ionic storage, are also discussed.

One-Step Prepared Water-Resistant Organic-Inorganic-Hybrid Perovskite Quantum Dots with Zn-Oxygen Vacancies for Attempts at Nitrogen Fixation

Applying organic-inorganic hybrid perovskite quantum dots (PQDs) to photocatalytic nitrogen fixation is hindered long-term by the inherent instability in water and tedious preparations. Here, to realize PQD-catalyzed photocatalytic N₂ reduction reaction (NRR), water-resistant PQDs are simply prepared through one-step electrospray synthesis in microseconds. During the fast electrospray, PQDs of Zn/PbO-doped methylammonium lead bromide (Zn/PbO/PC-Zn/MAPbBr₃ , MA: CH₃ NH₃ ) are prepared and part-encapsulated by polycarbonate. The synthesis maintains good water resistance, whose restriction on charge transport is overcome skillfully. Simultaneously, substitution of Zn with Pb on water-resistant surface is also achieved, which fabricates new Zn-oxygen vacancies (Zn-OVs) with Zn/PbO-Zn/MAPbBr₃ type I heterojunction. This facilitates efficient electron transfer from internal heterojunction interface of Zn/MAPbBr₃ PQDs to the surface of Zn/PbO. Demonstrated by theoretical calculations, Zn-OVs promote chemisorption and polarization of N₂ . In addition, s-electrons in exposed Zn become active due to changes of electron filling of Zn orbitals under OVs' co-doping. Thus, photocatalytic N₂ reduction reaction catalyzed by organic-inorganic hybrid PQDs is first achieved in aqueous phase without sacrificial agents being added. This initiates possibilities for photocatalytic applications of organic-inorganic hybrid PQDs in aqueous phase.

Two-Phase Transition Induced Amorphous Metal Phosphides Enabling Rapid, Reversible Alkali-Metal Ion Storage

Metal phosphides as anode materials for alkali-metal ion batteries have captured considerable interest due to their high theoretical capacities and electronic conductivity. However, they suffer from huge volume expansion and element segregation during repetitive insertion/extraction of guest ions, leading to structure deterioration and rapid capacity decay. Herein, an amorphous Sn_0.5Ge_0.5P₃ was constructed through a two-phase intermediate strategy based on the elemental composition modulation from two crystalline counterparts and applied in alkali-metal ion batteries. Differing from crystalline P-based compounds, the amorphous structure of Sn_0.5Ge_0.5P₃ effectively reduces the volume variation from above 300% to 225% during cycling. The ordered distribution of cations and anions in the short-range ensures the uniform distribution of each element during cycles and thus contributes to durable cycling stability. Moreover, the long-range disordered structure of amorphous material shortens the ion transport distance, which facilitates diffusion kinetics. Benefiting from the aforementioned effects, the amorphous Sn_0.5Ge_0.5P₃ delivers a high Na storage capacity of 1132 mAh g^-1 at 0.1 A g^-1 over 100 cycles. Even at high current densities of 2 and 10 A g^-1, its capacities still reach 666 and 321 mAh g^-1, respectively. As an anode for Li storage, the Sn_0.5Ge_0.5P₃ similarly also exhibits better cycling stability and rate performance compared to its crystalline counterparts. Significantly, the two-phase transition strategy is generally applicable to achieving other amorphous metal phosphides such as GeP₂. This work would be helpful for constructing high-performance amorphous anode materials for alkali-metal ion batteries.

Stretchable MXene/Thermoplastic Polyurethanes based Strain Sensor Fabricated Using a Combined Electrospinning and Electrostatic Spray Deposition Technique

In this work, a novel flexible electrically resistive-type MXene/Thermoplastic polyurethanes(TPU) based strain sensors was developed by a composite process of electrospinning (ES) and electrostatic spray deposition (ESD). Compared with other deposition processes, the sensing layer prepared by ESD has better adhesion to the ES TPU nanofiber membrane and is not easy to crack during the stretching process, thereby greatly improving the working range of the strain sensor. Furthermore, we obtained the sandwich structure easily by ES on the surface of the sensing layer again. This will help make the stress distribution more uniform during the stretching process and further increase the strain sensing range. The ESD-ES strain sensors were attached on skin to monitor various human motions. The results demonstrate that our ESD-ES strain sensors have wide application prospects in smart wearable device.

Challenges in Solvent-Free Methods for Manufacturing Electrodes and Electrolytes for Lithium-Based Batteries

With the ever-growing energy storage notably due to the electric vehicle market expansion and stationary applications, one of the challenges of lithium batteries lies in the cost and environmental impacts of their manufacture. The main process employed is the solvent-casting method, based on a slurry casted onto a current collector. The disadvantages of this technique include the use of toxic and costly solvents as well as significant quantity of energy required for solvent evaporation and recycling. A solvent-free manufacturing method would represent significant progress in the development of cost-effective and environmentally friendly lithium-ion and lithium metal batteries. This review provides an overview of solvent-free processes used to make solid polymer electrolytes and composite electrodes. Two methods can be described: heat-based (hot-pressing, melt processing, dissolution into melted polymer, the incorporation of melted polymer into particles) and spray-based (electrospray deposition or high-pressure deposition). Heat-based processes are used for solid electrolyte and electrode manufacturing, while spray-based processes are only used for electrode processing. Amongst these techniques, hot-pressing and melt processing were revealed to be the most used alternatives for both polymer-based electrolytes and electrodes. These two techniques are versatile and can be used in the processing of fillers with a wide range of morphologies and loadings.

Electrochemical double-layer capacitors with lithium-ion electrolyte and electrode coatings with PEDOT:PSS binder

Although typical electrochemical double-layer capacitors (EDLCs) operate with aqueous or lithium-free organic electrolytes optimized for activated carbon electrodes, there is interest in EDLCs with lithium-ion electrolyte for applications of lithium ion capacitors and hybridized battery-supercapacitor devices. We present an experimental study of symmetric EDLCs with electrolyte 1 M LiPF6 in EC:EMC 50:50 v/v and electrode coatings with 5 wt% SBR or PEDOT:PSS binder at 5 or 10 wt% concentration, where for the PEDOT:PSS containing electrodes pseudocapacitance effects were investigated in the lithium-ion electrolyte. Two different electrode coating fabrication methods were explored, doctor blade coating and spraying. It was found that EDLCs with electrodes with either binder had a stability window of 0–2 V in the lithium-ion electrolyte. EDLCs with electrodes with 10 wt% PEDOT:PSS binder yielded cyclic voltammograms with pseudocapacitance features indicating surface redox pseudocapacitance in the doctor blade coated electrodes, and intercalation and redox phenomena for the sprayed electrodes. The highest energy density in discharge was exhibited by the EDLC with doctor blade-coated electrodes and 10 wt% PEDOT:PSS binder, which combined good capacitive features with surface redox pseudocapacitance. In general, EDLCs with sprayed electrodes reached higher power density than doctor blade coated electrodes.

Graphic abstract

Finger directed surface charges for local droplet motion

Water droplets are expected to be employed as animated soft matter to mimic the behaviours of both nonliving objects and small living organisms. Local water droplet motion has attracted considerable interest and has expanded into various application areas because of its close relationship with processes associated with life. However, few approaches have been capable of independently manipulating local droplet motion without loss on a substrate due to the difficulty in shaping and focusing the motion route. Here, we demonstrate a non-contact electrostatic-powered local water motion strategy. The gradient of electrostatic charges in space guides the local drop motion without liquid loss in a controlled motion path. The local droplet motion on surfaces with varied wettabilities is discussed and compared. A unipolar electrostatic field is theoretically simulated. This work can introduce a finger-directed surface charge pattern and local droplet motion as a new variable in many droplet robot schemes and inspire next-generation liquid devices.

Scaling of roughness and porosity in thin film deposition with mixed transport mechanisms and adsorption barriers

Thin film deposition with particle transport mixing collimated and diffusive components and with barriers for adsorption are studied using numerical simulations and scaling approaches. Biased random walks on lattices are used to model the particle flux and the analogy with advective-diffusive transport is used to define a Peclet number P that represents the effect of the bias towards the substrate. An aggregation probability that relates the rates of adsorption and of the dominant transport mechanism plays the role of a Damkohler number D, where D≲1 is set to describe moderate to low adsorption rates. Very porous deposits with sparse branches are obtained with P≪1, whereas low porosity deposits with large height fluctuations at short scales are obtained with P≫1. For P≳1 in which the field bias is intense, an initial random deposition is followed by Kardar-Parisi-Zhang (KPZ) roughening. As the transport is displaced from those limiting conditions, the interplay of the transport and adsorption mechanisms establishes a condition to produce films with the smoothest surfaces for a constant deposited mass: with low adsorption barriers, a balance of random and collimated flux is required, whereas for high barriers the smoothest surfaces are obtained with P∼D^{1/2}. For intense bias, the roughness is shown to be a power law of P/D, whose exponent depends on the growth exponent β of the KPZ class, and the porosity has a superuniversal scaling as (P/D)^{-1/3}. We also study a generalized ballistic deposition model with slippery particle aggregation that shows the universality of these relations in growth with dominant collimated flux, particle adsorption at any point of the deposit, and negligible adsorbate diffusion, in contrast with the models where aggregation is restricted to the outer surface.

Bicontinuous transition metal phosphides/rGO binder-free electrodes: generalized synthesis and excellent cycling stability for sodium storage

Transition metal phosphides (TMPs) have received considerable attention owing to their great potential in energy conversion and storage technologies. Elaborate design and synthesis of various TMPs with abundant structures in order to meet the requirements of various applications is one of the major goals and challenges of sustainable chemistry. In this work, an electrostatic spray deposition (ESD) approach has been developed and has been demonstrated to be a general strategy to fabricate TMPs for the first time. Various bicontinuous TMPs/carbon nanocomposites can be constructed by this approach. This novel architecture, when applied in energy storage systems, can provide an efficient electron/ion mixed-conducting network, thereby inducing fast electron/ion transfer kinetics and enhancing the structural stability upon long term cycling. As proof of concept application, 3D porous Cu3P/rGO nanocomposites as modeling anodes for Na-ion storage show excellent cycling performance and remarkable rate capacities. The sodium storage mechanism is proposed to be a reversible conversion reaction. The microstructural evolution of the electrodes upon cycling correlates well with the capacity variation. The facile and versatile ESD technique is quite universal and can be further extended to various TMPs. This opens exciting opportunities for the incorporation of TMPs in a variety of new applications.

Electrodeposition Technologies for Li-Based Batteries: New Frontiers of Energy Storage

Electrodeposition induces material syntheses on conductive surfaces, distinguishing it from the widely used solid-state technologies in Li-based batteries. Electrodeposition drives uphill reactions by applying electric energy instead of heating. These features may enable electrodeposition to meet some needs for battery fabrication that conventional technologies can rarely achieve. The latest progress of electrodeposition technologies in Li-based batteries is summarized. Each component of Li-based batteries can be electrodeposited or synthesized with multiple methods. The advantages of electrodeposition are the main focus, and they are discussed in comparison with traditional technologies with the expectation to inspire innovations to build better Li-based batteries. Electrodeposition coats conformal films on surfaces and can control the film thickness, providing an effective approach to enhancing battery performance. Engineering interfaces by electrodeposition can stabilize the solid electrolyte interphase (SEI) and strengthen the adhesion of active materials to substrates, thereby prolonging the battery longevity. Lastly, a perspective of future studies on electrodepositing batteries is provided. The significant merits of electrodeposition should greatly advance the development of Li-based batteries.

Free-standing Reduced Graphene Oxide/carbon Nanotube Paper for Flexible Sodium-ion Battery Applications

We propose a flexible, binder-free and free-standing carbonaceous paper fabricated via electrostatic spray deposition using reduced graphene oxide/carbon nanotube (rGO/CNT) as a promising electrode material for flexible sodium-ion batteries (NIBs). The as-prepared rGO/CNT paper exhibits a three-dimensional (3D) layered structure by employing rGO as conductive frameworks to provide sodium-storage active sites and CNT as spacer to increase rGO interlayer distance and benefit the diffusion kinetics of sodium ions. Consequently, the rGO/CNT paper delivers an enhanced sodium ion storage capacity of 166.8 mAh g^-1 at 50 mA g^-1, retaining an average capacity of 101.4 mAh g^-1 when current density sets back 100 mA g^-1 after cycling at various current rates. An average capacity of 50 mAh g^-1 at 200 mA g^-1 was stabilized when cycling up to 300 cycles. The well-maintained electrochemical performance of free-standing rGO/CNT paper is due to the well-established hybrid 3D nanostructures, which demonstrates our carbon based material fabricated by a facile approach can be applied as one of the high-performance and low-cost electrode materials for applications in flexible energy storage devices.

Advanced Thin Film Cathodes for Lithium Ion Batteries

Binder-free thin film cathodes have become a critical basis for advanced high-performance lithium ion batteries for lightweight device applications such as all-solid-state batteries, portable electronics, and flexible electronics. However, these thin film electrodes generally require modifications to improve the electrochemical performance. This overview summarizes the current modification approaches on thin film cathodes, where the approaches can be classified as single-phase nanostructure designs and multiphase nanocomposite designs. Recent representative advancements of different modification approaches are also highlighted. Besides, this review discusses the existing challenges regarding the thin film cathodes. The review also discusses the future research directions and needs towards future advancement in thin film cathode designs for energy storage needs in advanced portable and personal electronics.

Toward High Power-High Energy Sodium Cathodes: A Case Study of Bicontinuous Ordered Network of 3D Porous Na3 (VO)2 (PO4 )2 F/rGO with Pseudocapacitance Effect

Developing high power-high energy electrochemical energy storage systems is an ultimate goal in the energy storage field, which is even more difficult but significant for low-cost sodium ion batteries. Here, fluoride is successfully prepared by the electrostatic spray deposition (ESD) technique, which greatly expands the application scope of ESD. A two-step strategy (solvothermal plus ESD method) is proposed to construct a bicontinuous ordered network of 3D porous Na₃ (VO)₂ (PO₄ )₂ F/reduced graphene oxide (NVOPF/rGO). This two-step strategy makes sure that NVOPF can be prepared by ESD, since it avoids the loss of F element during synthesis. The obtained NVOPF particles are as small as 15 nm, and the carbon content is only 3.5% in the final nanocomposite. Such a bicontinuous ordered network and small size of electroactive particles lead to the significant contribution of the pseudocapacitance effect to sodium storage, resulting in real high power-high energy sodium cathodes. The cathode exhibits excellent rate capability and cycling stability, whose rate performance is one of the best ever reported in both half cells and full cells. Moreover, this work provides a general and promising strategy for developing high power-high energy electrode materials for various electrochemical energy storage systems.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion

This review provides insight into various nanostructures designed by spray pyrolysis and their applications in energy storage and conversion.