High-Entropy Polymer Electrolytes Derived from Multivalent Polymeric Ligands for Solid-State Lithium Metal Batteries with Accelerated Li+ Transport.

Solid-state polymer-based electrolytes (SSPEs) exhibit great possibilities in realizing high-energy-density solid-state lithium metal batteries (SSLMBs). However, current SSPEs suffer from low ionic conductivity and unsatisfactory interfacial compatibility with metallic Li because of the high crystallinity of polymers and sluggish Li+ movement in SSPEs. Herein, differing from common strategies of copolymerization, a new strategy of constructing a high-entropy SSPE from multivariant polymeric ligands is proposed. As a protocol, poly(vinylidene fluoride-co-hexafluoropropylene) (PH) chains are grafted to the demoed polyethylene imine (PEI) with abundant -NH2 groups via a click-like reaction (HE-PEIgPHE). Compared to a PH-based SSPE, our HE-PEIgPHE shows a higher modulus (6.75 vs 5.18 MPa), a higher ionic conductivity (2.14 × 10-4 vs 1.03 × 10-4 S cm-1), and a higher Li+ transference number (0.55 vs 0.42). A Li|HE-PEIgPHE|Li cell exhibits a long lifetime (1500 h), and a Li|HE-PEIgPHE|LiFePO4 cell delivers an initial capacity of 160 mAh g-1 and a capacity retention of 98.7%, demonstrating the potential of our HE-PEIgPHE for the SSLMBs.

Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells.

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer-catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement.

Weakly coordinated Li ion in single-ion-conductor-based composite enabling low electrolyte content Li-metal batteries.

The pulverization of lithium metal electrodes during cycling recently has been suppressed through various techniques, but the issue of irreversible consumption of the electrolyte remains a critical challenge, hindering the progress of energy-dense lithium metal batteries. Here, we design a single-ion-conductor-based composite layer on the lithium metal electrode, which significantly reduces the liquid electrolyte loss via adjusting the solvation environment of moving Li+ in the layer. A Li||Ni0.5Mn0.3Co0.2O2 pouch cell with a thin lithium metal (N/P of 2.15), high loading cathode (21.5 mg cm-2), and carbonate electrolyte achieves 400 cycles at the electrolyte to capacity ratio of 2.15 g Ah-1 (2.44 g Ah-1 including mass of composite layer) or 100 cycles at 1.28 g Ah-1 (1.57 g Ah-1 including mass of composite layer) under a stack pressure of 280 kPa (0.2 C charge with a constant voltage charge at 4.3 V to 0.05 C and 1.0 C discharge within a voltage window of 4.3 V to 3.0 V). The rational design of the single-ion-conductor-based composite layer demonstrated in this work provides a way forward for constructing energy-dense rechargeable lithium metal batteries with minimal electrolyte content.

Modulating Ionic Transport and Interface Chemistry via Surface-Modified Silica Carrier in Nano Colloid Electrolyte for Stable Cycling of Li-Metal Batteries.

Tailoring the Li+ microenvironment is crucial for achieving fast ionic transfer and a mechanically reinforced solid-electrolyte interphase (SEI), which administers the stable cycling of Li-metal batteries (LMBs). Apart from traditional salt/solvent compositional tuning, this study presents the simultaneous modulation of Li+ transport and SEI chemistry using a citric acid (CA)-modified silica-based colloidal electrolyte (C-SCE). CA-tethered silica (CA-SiO2 ) can render more active sites for attracting complex anions, leading to further dissociation of Li+ from the anions, resulting in a high Li+ transference number (≈0.75). Intermolecular hydrogen bonds between solvent molecules and CA-SiO2 and their migration also act as nano-carrier for delivering additives and anions toward the Li surface, reinforcing the SEI via the co-implantation of SiO2 and fluorinated components. Notably, C-SCE demonstrated Li dendrite suppression and improved cycling stability of LMBs compared with the CA-free SiO2 colloidal electrolyte, hinting that the surface properties of the nanoparticles have a huge impact on the dendrite-inhibiting role of nano colloidal electrolytes.

Confronting Sulfur Electrode Passivation and Li Metal Electrode Degradation in Lithium-Sulfur Batteries Using Thiocyanate Anion.

Salt anions with a high donor number (DN) enable high sulfur utilization in lithium-sulfur (Li-S) batteries by inducing three-dimensional (3D) Li2 S growth. However, their insufficient compatibility with Li metal electrodes limits their cycling stability. Herein, a new class of salt anion, thiocyanate (SCN- ), is presented, which features a Janus character of electron donor and acceptor. Due to a strong Li+ coordination by SCN- and the direct interaction of SCN- with polysulfide anions, the LiSCN electrolyte has a remarkably high lithium polysulfide solubility. This electrolyte induces 3D Li2 S formation and ameliorates cathode passivation, even more than Br- , a typical high DN anion. Moreover, SCN- forms a Li3 N-enriched stable SEI layer at the surface of the Li metal electrode, enhancing cycling stability. A Li-S battery with the LiSCN electrolyte shows high current density operation (2.54 mA cm⁻2 ) with high discharge capacity (1133 mAh g⁻1 ) and prolonged cycle life (100 cycles). This work demonstrates that the cathode and anode performance in a Li-S battery can be simply and concurrently enhanced by the single salt anion.

A Mesoporous Tungsten Oxynitride Nanofibers/Graphite Felt Composite Electrode with High Catalytic Activity for the Cathode in Zn-Br Flow Battery.

High electrochemical polarization during a redox reaction in the electrode of aqueous zinc-bromine flow batteries largely limits its practical implementation as an effective energy storage system. This study demonstrates a rationally-designed composite electrode that exhibits a lower electrochemical polarization by providing a higher number of catalytically-active sites for faster bromine reaction, compared to a conventional graphite felt cathode. The composite electrode is composed of electrically-conductive graphite felt (GF) and highly active mesoporous tungsten oxynitride nanofibers (mWONNFs) that are prepared by electrospinning and simple heat treatments. Addition of the 1D mWONNFs to porous GF produces a web-like structure that significantly facilitates the reaction kinetics and ion diffusion. The cell performance achieves in this study demonstrated high energy efficiencies of 89% and 80% at current densities of 20 and 80 mA cm-2 , respectively. Furthermore, the cell can also be operated at a very high current density of 160 mA cm-2 , demonstrating an energy efficiency of 62%. These results demonstrate the effectiveness of the mWONNF/GF composite as the electrode material in zinc-bromine flow batteries.

A Zinc-Bromine Battery with Deep Eutectic Electrolytes.

A deep eutectic solvent (DES) is an ionic liquid-analog electrolyte, newly emerging due to its low cost, easy preparation, and tunable properties. Herein, a zinc-bromine battery (ZBB) with a Zn-halide-based DES electrolyte prepared by mixing ZnBr2 , ZnCl2 , and a bromine-capturing agent is reported. The water-free DES electrolyte allows a closed-cell configuration for the ZBB owing to the prevention of Br2 evaporation and H2 evolution. It is found that the Cl- anion changes the structure of the zinc-halide complex anions and demonstrated that it improves the ion mobility and electrode reaction kinetics. The DES electrolyte with the optimized ZnCl2 composition shows much higher rate capability and a cycle life 90 times longer than that of a ZnCl2 -free DES electrolyte. A pouch-type flexible ZBB battery based on the DES electrolyte exhibits swelling-free operation for more than 120 cycles and stable operation under a folding test, suggesting its potential in consumer applications such as wearable electronics.

Regional Control of Multistimuli-Responsive Structural Color-Switching Surfaces by a Micropatterned DNA-Hydrogel Assembly.

Structural colors have advantages compared with chemical pigments or dyes, such as iridescence, tunability, and unfading. Many studies have focused on developing the ability to switch ON/OFF the structural color; however, they often suffer from a simple and single stimulus, remaining structural colors, and target selectivity. Herein, we present regionally controlled multistimuli-responsive structural color switching surfaces. The key part is the utilization of a micropatterned DNA-hydrogel assembly on a single substrate. Each hydrogel network contains a unique type of stimuli-responsive DNA motifs as an additional cross-linker to exhibit swelling/deswelling via stimuli-responsive DNA interactions. The approach enables overcoming the existing limitations and selectively programming the DNA-hydrogel to a decrypted state (ON) and an encrypted state (OFF) in response to multiple stimuli. Furthermore, the transitions are reversible, providing cyclability. We envision the potential of our method for diverse applications, such as sensors or anticounterfeiting, requiring multistimuli-responsive structural color switching surfaces.

Modulation of Solvation Structure and Electrode Work Function by an Ultrathin Layer of Polymer of Intrinsic Microporosity in Zinc Ion Batteries.

Zinc ion batteries are promising candidates for large-scale energy storage systems. However, they suffer from the critical problems of insufficient cycling stability due to internal short-circuiting by zinc dendrites and zinc metal orphaning. In this work, a polymer of intrinsic microporosity (PIM-1) is reported as an ion regulating layer and an interface modulator, which promotes a uniform Zn plating and stripping process. According to spectroscopic analyses and computational calculations, PIM-1 enhances the reaction kinetics of a Zn metal electrode by altering the solvation structure of Zn2+ ions and increasing the work function of the Zn surface. As a result, the PIM-1 coating significantly improves the cyclability (1700 h at 0.5 mA cm-2 ) and Coulombic efficiency (99.6% at 3 mA cm-2 ) of the Zn/Zn2+ redox reaction. Moreover, the PIM-1 coated Zn operates for more than 200 h at 70% Zn utilization even under 10 mA cm-2 and 110 h at 95% Zn utilization of the Zn metal electrode. A Zn||V2 O5 full cell employing the PIM-1 layer exhibits seven times longer cycle life compared to the cell using bare Zn. The findings in this report demonstrate the potential of microporous materials as a key ingredient in the design of reversible Zn electrodes.

Hierarchical Wrinkle-Structured Catalyst Layer/Membrane Interface for Ultralow Pt-Loading Polymer Electrolyte Membrane Fuel Cells (PEMFCs).

The optimal architecture of three-dimensional (3D) interface between a polymer electrolyte membrane (PEM) and catalyst layer (CL) is one of the most important issues to improve PEM fuel cells' (PEMFCs) performance. Here, we report the fabrication of hierarchical wrinkled PEM/CL interface over a large area. We fabricated the hierarchical wrinkles on a multiscale from nanometers to micrometers by bottom-up-based facile, scalable, and simple method. Notably, it allows one to go beyond the limit of the catalyst utilization by extremely enlarged interfacial area. The resulting hierarchical wrinkled PEM/CL displays a dramatically increased electrochemically active surface area (ECSA) and power performance by the enhancement factors of 89% and 67% compared with those of flat interface, which is one of the best enhancements compared to previous PEMFCs. We believe the scalability of hierarchical wrinkled interface can be exploited to design advanced 3D interfaces for high-performance PEMFCs even with ultralow Pt-loading.

An electron-deficient carbon current collector for anode-free Li-metal batteries.

The long-term cycling of anode-free Li-metal cells (i.e., cells where the negative electrode is in situ formed by electrodeposition on an electronically conductive matrix of lithium sourced from the positive electrode) using a liquid electrolyte is affected by the formation of an inhomogeneous solid electrolyte interphase (SEI) on the current collector and irregular Li deposition. To circumvent these issues, we report an atomically defective carbon current collector where multivacancy defects induce homogeneous SEI formation on the current collector and uniform Li nucleation and growth to obtain a dense Li morphology. Via simulations and experimental measurements and analyses, we demonstrate the beneficial effect of electron deficiency on the Li hosting behavior of the carbon current collector. Furthermore, we report the results of testing anode-free coin cells comprising a multivacancy defective carbon current collector, a LixNi0.8Co0.1Mn0.1-based cathode and a nonaqueous Li-containing electrolyte solution. These cells retain 90% of their initial capacity for over 50 cycles under lean electrolyte conditions.

Light-Designed Shark Skin-Mimetic Surfaces.

Sharks, marine creatures that swim fast and have an antifouling ability, possess dermal denticle structures of micrometer-size. Because the riblet geometries on the denticles reduce the shear stress by inducing the slip of fluid parallel to the stream-wise direction, shark skin has the distinguished features of low drag and antifouling. Although much attention has been given to low-drag surfaces inspired from shark skin, it remains an important challenge to accurately mimic denticle structures in the micrometer scale and to finely control their structural features. This paper presents a novel method to create shark skin-mimetic denticle structures for low drag by exploiting a photoreconfigurable azopolymer. The light-designed denticle structure exhibits superior hydrophobicity and an antifouling effect as sharks do. This work suggests that our novel photoreconfiguration technology, mimicking shark skin and systematically manipulating various structural parameters, can be used in a reliable manner for diverse applications requiring low-drag surfaces.

Electrokinetic-Driven Fast Ion Delivery for Reversible Aqueous Zinc Metal Batteries with High Capacity.

Aqueous zinc (Zn) metal batteries (ZMBs) are considered a promising candidate for grid-scale energy storage due to their freedom from fire hazards. However, a limited reversibility of Zn metal electrode caused by dendritic Zn growth has hindered the advent of high-capacity Zn metal batteries (>4 mAh cm-2 ). Herein, it is reported that fast electrokinetic Zn-ion transport extremely improves the Zn metal reversibility. It is revealed that a negatively charged porous layer (NPL) provides the electrokinetic Zn-ion transport by surface conduction, and consequently impedes the depletion of Zn-ion on electrode surface as indicated by numerical simulations and overlimiting current behavior. Due to the quick Zn-ion delivery, a dendrite-free and densely packed Zn metal deposit is accommodated inside its pores. With the introduction of the NPL, the cycling stability of Zn symmetric cell is enhanced by 21 times at 10 mA cm-2 /10 mAh cm-2 . Average Coulombic efficiency of 99.6% is achieved over 500 cycles for electrodeposition/stripping at 30 mA cm-2 /5 mAh cm-2 on NPL-Cu electrode. Furthermore, a high-capacity Zn/V2 O5 full cell with the NPL exhibits an extraordinary stability over 1000 cycles at a capacity of 4.8 mAh cm-2 .

Lithium Dendrite Suppression with a Silica Nanoparticle-Dispersed Colloidal Electrolyte.

Developing a safe and long-lasting lithium (Li) metal battery is crucial for high-energy applications. However, its poor cycling stability due to Li dendrite formation and excessive Li pulverization is the major hurdle for its practical applications. Here, we present a silica (SiO2) nanoparticle-dispersed colloidal electrolyte (NDCE) and its design principle for suppressing Li dendrite formation. SiO2 nanoclusters in the NDCE play roles in enhancing the Li+ transference number and increasing the Li+ diffusivity in the vicinity of the Li-plating substrate. The NDCE enables less-dendritic Li plating by manipulating the nucleation-growth mode and extending Sand's time. Moreover, SiO2 can interplay with the electrolyte components at the Li-metal surface, enriching fluorinated compounds in the solid electrolyte interface layer. The initial control of the Li plating morphology and SEI structure by the NDCE leads to a more uniform and denser Li deposition upon subsequent cycling, resulting in threefold enhancement of the cycle life. The efficacy of the NDCEs has been further demonstrated by the practical battery design, featuring a commercial-level cathode and thin Li-metal (40 µm) anode.

Light-induced surface patterning of alumina.

Micro/nano-patterned alumina surfaces are important in a variety fields such as chemical/biotechnology, surface science, and microelectro-mechanical systems. However, for patterning alumina surfaces, it still remains a challenge to have a lithographic tool that has large flexibility in design layouts, structural reconfigurability, and a simple fabrication process. In this work, a new alumina-patterning platform that uses a photo-reconfigurable azobenzene-alumina composite as an imprinting material is presented. Under far-field irradiation, the azobenzene-alumina anisotropically flows in the direction parallel to the light polarization. Accordingly, an arbitrarily designed azobenzene-alumina composite by imprinting can be deterministically reconfigured by light polarization and irradiation time. The photo-reconfigured azobenzene-alumina is then converted to pure alumina through calcination in an air atmosphere, which provides thin crack-free alumina patterns with a high structural fidelity. The novel combination of photo-reconfigurable azobenzene moieties and an alumina precursor for imprinting the material provides large flexibility in designing and controlling geometric parameters of the alumina pattern, which potentially offers significant value in various micro/nanotechnology fields.

Programmable Fabrication of Submicrometer Bent Pillar Structures Enabled by a Photoreconfigurable Azopolymer.

Anisotropic small structures found throughout living nature have unique functionalities as seen by Gecko lizards. Here, we present a simple yet programmable method for fabricating anisotropic, submicrometer-sized bent pillar structures using photoreconfiguration of an azopolymer. A slant irradiation of a p-polarized light on the pillar structure of an azopolymer simply results in a bent pillar structure. By combining the field-gradient effect and directionality of photofluidization, control of the bending shape and the curvature is achieved. With the bent pillar patterned surface, anisotropic wetting and directional adhesion are demonstrated. Moreover, the bent pillar structures can be transferred to other polymers, highlighting the practical importance of this method. We believe that this pragmatic method to fabricate bent pillars can be used in a reliable manner for many applications requiring the systematic variation of a bent pillar structure.

High-Energy Efficiency Membraneless Flowless Zn-Br Battery: Utilizing the Electrochemical-Chemical Growth of Polybromides.

Aqueous Zn-Br batteries (ZBBs) offer promising next-generation high-density energy storage for energy storage systems, along with distinctive cost effectiveness particularly in membraneless and flowless (MLFL) form. Unfortunately, they generally suffer from uncontrolled diffusion of corrosive bromine components, which cause serious self-discharge and capacity fade. An MLFL-ZBB is presented that fundamentally tackles the problem of bromine crossover by converting bromine to the polybromide anion using protonated pyridinic nitrogen doped microporous carbon decorated on graphite felt (NGF). The NGF electrodes efficiently capture bromine and polybromide anions at the abundant protonated nitrogen dopant sites within micropores and facilitate effective conversion of bromine into polybromides through electrochemical-chemical growth mechanism. The MLFL-ZBBs with NGF exhibit an extraordinary stability over 1000 charge/discharge cycles, with an energy efficiency over 80%, the highest value ever reported among membraneless Zn-Br batteries. Judicious engineering of an atomistically designed nanostructured electrode offers a novel design platform for low cost, high voltage, long-life cycle aqueous hybrid Zn-Br batteries.

Catalytic production of impurity-free V3.5+ electrolyte for vanadium redox flow batteries.

The vanadium redox flow battery is considered one of the most promising candidates for use in large-scale energy storage systems. However, its commercialization has been hindered due to the high manufacturing cost of the vanadium electrolyte, which is currently prepared using a costly electrolysis method with limited productivity. In this work, we present a simpler method for chemical production of impurity-free V3.5+ electrolyte by utilizing formic acid as a reducing agent and Pt/C as a catalyst. With the catalytic reduction of V4+ electrolyte, a high quality V3.5+ electrolyte was successfully produced and excellent cell performance was achieved. Based on the result, a prototype catalytic reactor employing Pt/C-decorated carbon felt was designed, and high-speed, continuous production of V3.5+ electrolyte in this manner was demonstrated with the reactor. This invention offers a simple but practical strategy to reduce the production cost of V3.5+ electrolyte while retaining quality that is adequate for high-performance operations.

Tuning Two Interfaces with Fluoroethylene Carbonate Electrolytes for High-Performance Li/LCO Batteries.

Various electrolytes have been reported to enhance the reversibility of Li-metal electrodes. However, for these electrolytes, concurrent and balanced control of Li-metal and positive electrode interfaces is a critical step toward fabrication of high-performance Li-metal batteries. Here, we report the tuning of Li-metal and lithium cobalt oxide (LCO) interfaces with fluoroethylene carbonate (FEC)-containing electrolytes to achieve high cycling stability of Li/LCO batteries. Reversibility of the Li-metal electrode is considerably enhanced for electrolytes with high FEC contents, confirming the positive effect of FEC on the stabilization of the Li-metal electrode. However, for FEC contents of 50 wt % and above, the discharge capacity is significantly reduced because of the formation of a passivation layer on the LCO cathodes. Using balanced tuning of the two interfaces, stable cycling over 350 cycles at 1.5 mA cm-2 is achieved for a Li/LCO cell with the 1 M LiPF6 FEC/DEC = 30/70 electrolyte. The enhanced reversibility of the Li-metal electrode is associated with the formation of LiF and polycarbonate in the FEC-derived solid electrolyte interface (SEI) layer. In addition, electrolytes with high FEC contents lead to lateral Li deposition on the sides of Li deposits and larger dimensions of rodlike Li deposits, suggesting the elastic and ion-conductive nature of the FEC-derived SEI layer.

High-Rate Cycling of Lithium-Metal Batteries Enabled by Dual-Salt Electrolyte-Assisted Micropatterned Interfaces.

We present a synergistic strategy to boost the cycling performance of Li-metal batteries. The strategy is based on the combined use of a micropattern (MP) on the surface of the Li-metal electrode and an advanced dual-salt electrolyte (DSE) system to more efficiently control undesired Li-metal deposition at higher current density (∼3 mA cm-2). The MP-Li electrode induces a spatially uniform current distribution to achieve dendrite-free Li-metal deposition beneath the surface layer formed by the DSE. The MP-Li/DSE combination exhibited excellent synergistic rate capability improvements that were neither observed with the MP-Li system nor for the bare Li/DSE system. The combination also resulted in the Li||LiMn2O4 battery attaining over 1 000 cycles, which is twice as long at the same capacity retention (80%) compared with the control cells (MP-Li without DSE). We further demonstrated extremely fast charging at a rate of 15 C (19.5 mA cm-2).