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This work presents that Cu with atomic-scale spacings (ds) efficiently catalyses the electrochemical co-reduction of CO2 and NO3− to urea. Specifically, Cu with ds near 6 Å (6 Å-Cu) produces urea with a high yield rate and partial current density.

Quinones having a fully conjugated cyclic dione structure have been used as redox mediators in electrochemistry. 2,5-Di

Ten times heavy silver loading into a 3D scaffold via a strong Ag+–pN interaction between silver cations and argentophilic pyridinic nitrogen of melamine provides a strong lithiophilicity, largely improving lithium plating/stripping reversibility.

Very strong catalyst–support interaction was realized by supporting FePc with Ti3C2, encouraging biased electron transfer to Fe. 4e ORR activity was improved to suppress peroxide production and therefore to have ORR durability guaranteed.

High-energy density lithium-oxygen batteries (LOBs) seriously suffer from poor rate capability and cyclability due to the slow oxygen-related electrochemistry and uncontrollable formation of lithium peroxide (Li

Silicon microparticles (SiMPs), which have a high capacity, a high initial Coulombic efficiency, and a low volume-to-surface ratio compared with nanosized materials, are promising anode materials f...

The insertion of lithium into lithium manganese oxide spinel (LiMn2O4 (LMO) to Li2Mn2O4 (L2MO)) was used to store light energy as a form of chemical energy in a dye-sensitized photorechargeable bat...

Nickel-rich layered oxides (LiNi1–x–yCoxMnyO2; (1 – x – y) ≥ 0.6), the high-energy-density cathode materials of lithium-ion batteries (LIBs), are seriously unstable at voltages higher than 4.5 V ve...

A redox-active mixed ion and electron conductor (redox-active MIEC) is presented as a binder for the lithium titanate anodes of lithium-ion batteries. The redox-active MIEC binder (symbolized by PT*-GmCn) was designed to be (1) electrically conductive along its conjugated thiophene backbone (PT = polythiophene), (2) redox-active from its succinimide moiety (* = redox-active) and (3) ionically conductive by adopting glyme (G) branches. It was superior to the practically used PVdF binder in terms of lithium ion diffusivity and electrical conductivity (1.4× and 15 000×, respectively). High capacity was guaranteed, particularly at high rates due to its MIEC nature of PT*-GmCn, while an additional capacity was achieved from its redox activity.

The reversibility of lithium plating/stripping should be guaranteed in lithium metal batteries. Seriously localized lithium growth during plating leads to the dendritic evolution of lithium metal due to the uneven current distribution on the electrically conductive surface. Artificial protective layers covering electrodes (e.g., polymer film on copper foil) have been used to narrow the gap of the current density between positions on the conductive surface. Herein, we incorporated an active ingredient to attract lithium ions into the dendrite-suppressing layer. Pyridinic nitrogen of graphitic carbon nitride (g-C3N4) served as the lithium ion affinity center. Conformation of the nitrogen changed from pyridinic to graphitic in the presence of lithium ions, which confirms the coordination of lithium ion to the pyridinic nitrogen. Moreover, lithium ion conduction was facilitated in the presence of g-C3N4 layer probably via a site-to-site hopping mechanism. Lithium metal was plated between the g-C3N4 layer and the copper current collector (or the lithium metal). The homogeneous lithium nucleation expected from the active role of the pyridinic nitrogen (lithium ion affinity and facilitated ionic conduction) suppressed the dendritic growth of lithium metal and decreased the overpotential required for the initial metal nucleation. Due to the top-down ion flux regulation on the uppermost surface (or tip) of lithium metal, the reversibility of lithium plating/stripping was dramatically improved.

Although bimetallic materials with various structures have been used as anodes for advanced lithium ion batteries, structural degradation, caused during electrochemical reactions, leads to a shorte...

Photo-rechargeable batteries (PRBs) benefit from their bifunctionality covering energy harvesting and storage. However, dim-light performances of the PRBs for indoor applications have not been reported. Herein, we present an external-power-free single-structured PRB named a dye-sensitized photo-rechargeable battery (DSPB) with an outstanding light-to-charge energy efficiency (ηoverall) of 11.5% under the dim light condition. This unprecedented ηoverall was attributed to the thermodynamically-favorable design of the DSPB that maximizes the working potential. At high-power irradiation, the kinetically-fast but thermodynamically-unfavorable iodine mediator (I−/I3−) showed the highest charge and discharge capacities even if its discharge voltage was lowest. Under dim-light for indoor applications, however, the thermodynamically-favorable but kinetically-slow copper complex mediator (Cu+/2+(dmp)2) showed energy density and efficiency superior to I−/I3− because its kinetics did not limit the harvesting capacity. The successful demonstration of the ability of the DSPB to operate a temperature-sensing IoT device only by indoor light opens the possibility of realizing indoor-light-harvesting PRBs.

The continued demand for long-lasting batteries essentially drives us to contribute to a development of high-performance cathode materials, because a cathode material which is one of essential components in Li-ion batteries (LIBs) critically determines an overall energy density of a battery. High-capacity Ni-rich NCM (x > 80%, LiNixCoyMnzO2, x+y+z=1) cathode materials have been regarded as one of the most promising candidates to realize high-energy density Li-ion batteries. However, the complete application has been limited due to some critical problems, especially the unstable interfacial stability resulting from the massive formation of residual lithium compounds and the severe electrolyte decomposition. In this study, we investigate the roles of fullerene-based electrolyte additive in Ni-rich NCM-based LIB system and reveal that the fullerene-based additives functionalized with malonic acid moieties, MA-C60, effectively stabilize the unstable interface of Ni-rich cathodes, which are demonstrated by combined experimental and computational studies. According to differential electrochemical mass spectroscopy (DEMS), nuclear magnetic resonance (NMR) analysis and the first principles calculation, the MA-C60 additives deactivate reactive radical species (O2 •-, LiOCO3 •, and Li(CO3)2 •) induced by electrochemical oxidation of residual lithium compound, Li2CO3 on the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode surface thanks to a highly favorable affinity of the malonic acid moieties with the reactive radical species. Furthermore, the additive mitigates the parasitic reaction of residual lithium compounds with LiPF6 through the formation of a stable cathode-electrolyte interphase. These roles of the new additive effectively prevent an aging in the cell system by suppressing attacking the interface of Ni-rich cathodes against the harmful reactive oxygen species and drastically enhance the cyclic performance over 400 cycles (nearly ~50 % improvement of capacity retention). Our work offers the potential of new-type of fullerene-based additive for the stable cathode-electrolyte interphase and would help to realize a commercialization of high-energy density LIB cathodes. Figure 1

The concentration polarization, in addition to the activation and ohmic polarizations, limits the fast operation of electrochemical cells such as Li-ion batteries (LIBs). We demonstrate an approach...

Plating-stripping reversibility of lithium metal is improved by reinforcing the solid-electrolyte interphase layer by inorganic nanobeads. The outmost solid-electrolyte interphase shell is clearly identified, which is the passive layer formed on current collectors (or lithium metal) before the first lithium metal deposition. The outmost shell is intrinsically brittle and fragile so that it is easily broken by lithium metal dendrites growing along the progress of plating. Lithium metal deposit is not completely stripped back to lithium ions. On the other hand, lithium metal cells containing inorganic nanobeads in electrolyte show high reversibility between plating and stripping. The nanobeads are incorporated into the outmost shell during its formation. The nanobead-reinforced outmost shell having mechanically durable toughness suppresses dendritic growth of lithium metal, not allowing the dendrites to penetrate the shell. In addition to the mechanical effect of nanobeads, the LiF-rich solid-electrolyte interphase layer formation is triggered by HF generated by the reaction of the moisture adsorbed on oxide nanobeads with PF6−. The LiF-rich composition is responsible for facile lithium ion transfer through the passive layers.

Partially hydrous RuO2 nanocluster embedded in a carbon matrix (x-RuO2@C with x = hydration degree = 0.27 or 0.27@C) is presented as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) for water splitting. Symmetric water electrolyzers based on 0.27-RuO2@C for both electrodes showed smaller potential gaps between HER and OER at pH 0, pH 14 and even pH 7 than conventional asymmetric electrolyzers based on two different catalysts (Pt/C || Ir/C) that have been known as the best catalysts for HER and OER respectively. Moreover, 0.27-RuO2@C showed another bifunctional electroactivity for fuel cell electrochemistry involving hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) that are the backward reactions of HER and OER respectively. Pt-level HOR electroactivity was obtained from 0.27-RuO2@C, while its ORR activity was inferior to that of Pt with 200 mV higher overpotential required. The tetra-functionality of 0.27-RuO2@C showed the possibility of realizing single-catalyst regenerative fuel cells.

In order to realize electrochemically efficient hydrogen production, various endeavors have been devoted to developing hydrogen evolution reaction (HER) electrocatalysts having zero hydrogen binding energy (ΔGH⁎ = 0) for balancing between adsorption and desorption. This work demonstrated that nitrogen doping improved the HER activity of ruthenium oxide by letting its ΔGH⁎ approach zero or facilitating hydrogen desorption process. A highly nitrogen-doped ruthenium oxide catalyst guaranteeing the ruthenium-nitrogen intimacy was prepared by employing a polymer whose nitrogen-containing moiety (pyrrolidone) was strongly coordinated to ruthenium ion in the precursor solution prior to calcination. The less electronegative nature of nitrogen (when compared with oxygen) decreased the free energy uphill required for desorption of hydrogen intermediate species sitting on the nitrogen (H-*N to 1/2 H2 + *N) to make the desorption process more favored. Also, the nitrogen dopant facilitated OH- desorption from its neighboring ruthenium site (HO-*Ru + e- to HO- + *Ru) since the less electronegative nitrogen withdrew less electrons from the ruthenium site. The ruthenium-nitrogen intimacy of the catalyst more than doubled the electrocatalytic HER current from 33 mA cm-2 for an undoped RuO2 to 79 mA cm-2 for the nitrogen-doped RuO2 at -50 mVRHE.

Lithium metal has been considered as an anode material to improve energy densities of lithium chemistry-based rechargeable batteries (that is to say, lithium metal batteries or LMBs). Higher capacities and cell voltages are ensured by replacing practically used anode materials such as graphite with lithium metal. However, lithium metal as the LMB anode material has been challenged by its dendritic growth, electrolyte decomposition on its fresh surface, and its serious volumetric change. To address the problems of lithium metal anodes, herein, we guided and facilitated lithium ion transport along a spontaneously polarized and highly dielectric material. A three-dimensional web of nanodiameter fibers of ferroelectric beta-phase polyvinylidene fluoride (beta-PVDF) was loaded on a copper foil by electrospinning (PVDF#Cu). The electric field applied between the nozzle and target copper foil forced the dipoles of PVDF to be oriented centro-asymmetrically and then the beta structure induced ferroelectric polarization. Three-fold benefits of the ferroelectric nano-web architecture guaranteed the plating/stripping reversibility especially at high rates: (1) three-dimensional scaffold to accommodate the volume change of lithium metal during plating and stripping, (2) electrolyte channels between fibers to allow lithium ions to move, and (3) ferroelectrically polarized or negatively charged surface of beta-PVDF fibers to encourage lithium ion hopping along the surface. Resultantly, the beta-PVDF web architecture drove dense and integrated growth of lithium metal within its structure. The kinetic benefit expected from the ferroelectric lithium ion transport of beta-PVDF as well as the porous architecture of PVDF#Cu was realized in a cell of LFP as a cathode and lithium-plated PVDF#Cu as an anode. Excellent plating/stripping reversibility along repeated cycles was successfully demonstrated in the cell even at a high current such as 2.3 mA cm-2, which was not obtained by the nonferroelectric polymer layer.

A carbon electrode was designed to guarantee flexibility of symmetric electric double layer capacitors (EDLCs) based on its architecture. Three different dimensional carbon materials were combined ...

Highly oxygen evolution reaction (OER)-active electrocatalysts often exhibit improved OER durability in the presence of carbon corrosion or oxidation (COR) in the literature. The activity-durability coincidence of OER electrocatalysts was theoretically understood by preferential depolarization in galvanostatic situations. At constant-current conditions for a system involving multiple reactions that are independent and competitive, the overpotential is determined most dominantly by the most facile reaction so that the most facile reaction is responsible for a dominant portion of the overall current. Therefore, higher OER activity improves durability by mitigating the current responsible for COR. The activity-durability coincidence was then proved experimentally by comparing between two catalysts of the same chemical identity (MnCo2O4) in different dimensions (5 and 100 nm in size). Carbon corrosion responsible for inferior durability was suppressed in the smaller-dimension catalyst (MnCo2O4 in 5 nm) having...

Perovskite oxides have received considerable attention as useful electro-catalysts for Li-air batteries due to their properties of excellent catalytic activity, electrical conductivity, and durability. The nanostructure can enhance the electrochemical performance of perovskite oxides by enlarging the catalytic active sites. In this study, nano-size Nd0.67Sr0.33CoO3-δ (NSC) perovskite particles with a particle size of 20–50 nm and a specific surface area of 12.759 m2 g−1 were successfully synthesized by a microemulsion method. The NSC perovskite particles exhibit excellent electrocatalytic activity particularly in the oxygen evolution reaction (OER) with a high limiting current density of 33.68 mA cm-2 at 0.9 V vs. (Hg/HgO). This excellent catalytic activity can be ascribed to the existence of Co3+ and the enlarged surface area. Co3+ provides catalytically active site by forming Co3+/4+ redox couple and the enlarged surface increases active sites for reactants and catalyst particles. In this regard, nano-size NSC particles prepared by the microemulsion route provide excellent and stable electrochemical performance in the hybrid Li-air battery.

In this study, the fabrication of a high-performance electrothermal and anticorrosive transparent heating sticker employing a novel Ni/Ag hybrid microgrid electrode is reported. The proposed sticker not only exhibits an excellent optoelectronic performance (a sheet resistance of 4.3 Ω sq−1 at a transmittance of 96%) but also has a uniform heat distribution over its entire area owing to the electrical uniformity of the honeycomb-structured microgrid electrode. The transparent heating sticker reveals outstanding thermal and chemical stability with no electrode damage even in harsh environments such as high temperatures (300 °C) and atmospheres containing sulfur in excess, due to the anti-corrosion properties of nickel (Ni). The transparent heating sticker also exhibits a high saturation temperature of over 100 °C even at a low operating voltage (5 V) because highly thermally/electrically conductive silver (Ag) is employed as a base electrode material underneath Ni. Furthermore, a successful defogging test is demonstrated with an automobile side-view mirror using the transparent heating sticker, confirming its practical applicability. Accordingly, the proposed transparent heating sticker presents a unique opportunity for developing transparent heaters with superior chemical stability and a high electrothermal performance.

Cost-effective and environmentally friendly seawater-electrolyte-based batteries exhibit high energy density and demonstrate immense potential for use in future energy storage devices; however, lack of high-performance negative and positive electrodes significantly challenges their practical applications. In this study, N-doped and N,S-doped carbon nanospheres (referred to as NCSs and NSCSs, respectively) are synthesized via the pyrolysis of melanosomes, which is a bio-inspired polymer. Electrocatalytic activity measurements reveal the bifunctionality of the prepared catalysts. NSCSs exhibit a distinctively higher performance than NCSs when used as an air electrode in seawater batteries under ambient conditions (referred to as static mode hereafter). Further, due to the introduction of air flow into the seawater electrolyte (referred to as flow mode hereafter), NSCSs exhibit an improved cell discharge potential. The high performance of the cell is attributed to the high surface area, bifunctional electrocatalytic activity, generation of new active sites, improvement of spin density in NSCSs, and continuous flow of air to the electrolyte. The cell in the flow mode exhibits an overpotential gap of 0.56 V, a round-trip efficiency of 84%, a maximum power density of 203 mW g−1, and an outstanding cycling stability up to 100 cycles. The developed synthetic method provides an effective, scalable approach for doping binary or ternary atoms into the carbon host matrix, which can motivate further experimental and theoretical studies of electrode materials in various energy storage devices. In addition, the concept and results obtained by the introduction of air flow into the electrolyte can lead to the improvement of cell performance in terms of electrical energy efficiency, which can be exploited in various metal–air batteries.

Enhancing the performance of carbon-based anode materials in Li-ion battery (LIB) systems is of considerable interest in terms of next-generation LIB host electrodes, because the unique reversible intercalation–de-intercalation process of such materials ultimately facilitates increases in LIB performance and longevity. This study explored the potential of a new class of carbon-based contorted hexabenzocoronene (c-HBC) as an anode material for high-performance LIB systems. The exploitation of the polymorphic crystalline nature of c-HBC resulted in successful development of a LIB anode based on a newly found crystal phase of trigonal R by solvent and subsequent thermal annealing. Our in-depth analysis based on cross-sectional transmission electron microscopy, grazing incidence X-ray diffraction, and computational investigation revealed further advantages of using contorted molecules in LIB systems. For instance, the resulting electrochemical characteristics using half-cell architecture clearly reflected single-stage Li insertion behavior associated with the large interspacing and short diffusion length of c-HBC molecule during the discharging process. In addition, the battery exhibited excellent rate capability and cycle endurance, highlighting the suitability of c-HBC as an anode material for high-performance LIBs.

We present a metal-ion-chelating organogel electrolyte, thermally gelated within cells, to solve the problems triggered by metal dissolution from cathodes of lithium ion batteries. The organogel significantly improved the capacity retention of lithium manganese oxide spinel during cycling. The organogel mitigated metal deposition on anodes by capturing metal ions (anode protection). Interestingly, the organogel inhibited metal dissolution by keeping dissolved metal ions highly concentrated around the cathode surface (cathode protection by Le Chatelier's principle).

A dendrite-free and chemically stabilized lithium metal anode is required for extending battery life and for the application of high energy density coupled with various cathode systems. However, uneven Li metal growth and the active surface in nature accelerate electrolyte dissipation and surface corrosion, resulting in poor cycle efficiency and various safety issues. Here, the authors suggest a thin artificial interphase using a multifunctional poly(styrene-b-butadiene-b-styrene) (SBS) copolymer to inhibit the electrochemical/chemical side reaction during cycling. Based on the physical features, hardness, adhesion, and flexibility, the optimized chemical structure of SBS facilitates durable mechanical strength and interphase integrity against repeated Li electrodeposition/dissolution. The effectiveness of the thin polymer film enables high cycle efficiency through the realization of a dendrite-free structure and a chemo-resistive surface of Li metal. The versatile anode demonstrates an improvement in the electrochemical properties, paired with diverse cathodes of high-capacity lithium cobalt oxide (3.5 mAh cm

Uniform zinc metal plating has been raised as a critical issue in zinc-based batteries. Randomly localized ions lead to severe zinc dendrite formation in liquid electrolyte due to nonuniform ion flux caused by electroconvective flow. One of the mitigating approaches is to use gel polymer electrolyte to regulate the ion flux for suppressing zinc dendrites by imparting viscoelasticity to the electrolyte and improving the ion transport along charged functional groups of polymer chains. However, to this date, the effectiveness of gel polymer electrolyte has been visualized using ex situ methods (e.g., scanning electron microscopy) that requires cell disassembly. And the underlying mechanism is poorly understood. Herein, we applied in situ optical microscopy with dark-field illumination and a transparent glass slide cell to visualize zinc metal plating in the gel polymer electrolyte. At a given current density, the morphological differences of plated zinc metal between the liquid and gel polymer electrolytes were compared. Our in situ optical microscopy platform successfully showed that the gel polymer electrolyte supported by cross-linked polyacrylic acid (PAA)/N,N’-methylenebisacrylamide (MBA) polymer framework significantly suppressed the dendrite formation in contrast to the liquid electrolyte during plating. In addition, at various current densities, the tendency of dendritic growth was observed and statistically compared in both electrolytes. The findings will be useful for future design of rechargeable zinc-based batteries.

Synergistic effects of dual homogeneous catalysts for chemical reactions have been reported. Double activation (chemical transformation process where both catalysts work in concert to activate reactants or intermediates) was often responsible for the synergistic effects of dual catalyst systems. Herein, we demonstrate the extension of the double activation from chemo-catalysis to electrocatalysis. The activity of low-cost cobalt oxide electrocatalysts for oxygen reduction reaction (ORR) was significantly improved by introducing secondary-amine-conjugated polymers (HN-CPs) as the secondary promoting electrocatalyst (shortly, promoter). It was proposed that HN-CPs activated neutral diatomic oxygen to partially charged species (O2δ-) in the initial oxygen adsorption step of ORR. Electron donation number of HN-CP to diatomic oxygen (δ in O2δ-) well described the order of activity improvement, i.e., polypyrrole (pPy) > polyaniline (pAni) > polyindole (pInd). The maximum overpotential gain at ~150 mV was achieved by using pPy with the highest δ. Also, it was confirmed that proton of HN-CP was transferred to single oxygen intermediate (*O) of ORR.

Stabilizing superoxide (O2−) is one of the key issues of sodium-air batteries because the superoxide-based discharge product (NaO2) is more reversibly oxidized to oxygen when compared with peroxide (O22−) and oxide (O2−). Reversibly outstanding performances of sodium-oxygen batteries have been realized with the superoxide discharge product (NaO2) even if sodium peroxide (Na2O2) have been also known as the discharge products. Here we report that the Lewis basicity of anions of sodium salts as well as solvent molecules, both quantitatively represented by donor numbers (DNs), determines the superoxide stability and resultantly the reversibility of sodium-oxygen batteries. A DN map of superoxide stability was presented as a selection guide of salt/solvent pair. Based on sodium triflate (CF3SO3−)/dimethyl sulfoxide (DMSO) as a high-DN-pair electrolyte system, sodium ion oxygen batteries were constructed. Pre-sodiated antimony (Sb) was used as an anode during discharge instead of sodium metal because DMSO is reacted with the metal. The superoxide stability supported by the high DN anion/solvent pair ($${{\rm{CF}}}_{3}{{\rm{SO}}}_{3}$$ CF 3 SO 3 –/DMSO) allowed more reversible operation of the sodium ion oxygen batteries.

Antimony metal nanoparticles wrapped with a-few-layer graphene coat (Sb@Gn) were fabricated from their oxide form (Sb2O3) in a micrometer dimension using a novel two-step ball-milling process. The first mechanochemical process was designed to decrease the particle size of Sb2O3 microparticles for ensuring advantages of nano size and to subsequently coat the Sb2O3 nanoparticles with a-few-layer graphene (Sb2O3@Gn). The second metallomechanical ball-milling process reduced the oxide to its metal form (Sb@Gn) by the help of Zn as a metallic reductant. The graphene layer (@Gn) blocked the alloying reaction between Sb and Zn, limiting the size of Sb particles during the metallomechanical reduction step. During reduction, oxygen species were transferred from of Sb2O3 through @Gn to Zn along redox transfer pathways rather than direct mass transfer via unsaturated vacancies in the @Gn. the redox transfer involving oxidation of @Gn by O2− is plausible routes for O2− transfer in the metallomechanical reduction. The Sb@Gn anode exhibited outstanding capacity retention along charge/discharge cycles and improved rate capability in sodium-ion batteries. The @Gn provided conductive pathways to the Sb core and limited size expansion during sodium-lithium alloying.

Ruthenium oxide (RuO2) is the best oxygen evolution reaction (OER) electrocatalyst. Herein, we demonstrated that RuO2 can be also efficiently used as an oxygen reduction reaction (ORR) electrocatalyst, thereby serving as a bifunctional material for rechargeable Zn–air batteries. We found two forms of RuO2 (i.e. hydrous and anhydrous, respectively h-RuO2 and ah-RuO2) to show different ORR and OER electrocatalytic characteristics. Thus, h-RuO2 required large ORR overpotentials, although it completed the ORR via a 4e process. In contrast, h-RuO2 triggered the OER at lower overpotentials at the expense of showing very unstable electrocatalytic activity. To capitalize on the advantages of h-RuO2 while improving its drawbacks, we designed a unique structure (RuO2@C) where h-RuO2 nanoparticles were embedded in a carbon matrix. A double hydrophilic block copolymer-templated ruthenium precursor was transformed into RuO2 nanoparticles upon formation of the carbon matrix via annealing. The carbon matrix allowed overcoming the limitations of h-RuO2 by improving its poor conductivity and protecting the catalyst from dissolution during OER. The bifunctional RuO2@C catalyst demonstrated a very low potential gap (ΔEOER-ORR = ca. 1.0 V) at 20 mA cm−2. The Zn||RuO2@C cell showed an excellent stability (i.e. no overpotential was observed after more than 40 h).

An interesting and effective route for improving battery performance using ferroelectric poly(vinylidene difluoride) (PVDF) polymer as a binder material is demonstrated in this work. A ferroelectric PVDF phase developed under the appropriate thermal annealing process enables generation of suitable polarization on active materials during the discharge and charge process, giving rise to longer capacity with lower overpotential at a high current rate. Electrochemical analysis including in situ galvanostatic electrochemical impedance spectroscopy and a galvanostatic intermittent titration measurement revealed that the ferroelectric binder effectively reduced Li-ion diffusion resistance and supported fast migration in the vicinity of active electrodes. Computational results further support that the binding affinity of the ferroelectric PVDF surface is much higher than that of the paraelectric PVDF, confirmed by ideally formed ferroelectric and paraelectric PVDF conformations with Li-ions. Furthermore, we consistently achieved high Li-ion battery (LIB) performance in full cell architecture consisting of a LTO/separator/LFP with a ferroelectric PVDF binder in the anode and cathode materials, revealing that the polarization field is important for fabricating high-performance LIBs, potentially opening a new design concept for binder materials.

Nitrogen-containing electrocatalysts, such as metal–nitrogen–carbon (M–N–C) composites and nitrogen-doped carbons, are known to exhibit high activities for an oxygen reduction reaction (ORR). Moreover, even if the mechanism by which nitrogen improves the activities is not completely understood, a strong electronic interaction between nitrogen and active sites has been found in these composites. Herein, we demonstrate a case in which nitrogen improves the electroactivity, but in the absence of a strong interaction with other components. The overpotentials of the ORR and oxygen evolution reaction (OER) on perovskite oxide catalysts were significantly reduced simply by mixing the catalyst particles with polypyrrole/carbon composites (pPy/C). Any strong interactions between pPy (a nitrogen-containing compound) and active sites of the catalysts are not confirmed. A scenario based on the sequential task allocation between pPy and oxide catalysts for the ORR was proposed: (1) molecular oxygen is incorporated into pPy as a form of superoxide (pPy^+O2^−), (2) the superoxide is transferred to the active sites of perovskite catalysts, and (3) the superoxide is completely reduced along the 4e ORR process.

Conversion-reaction-based anode materials for lithium ion batteries (LIBs) such as transition metal oxides have been considered as high-capacity alternatives to graphite. In the conversion reactions, interestingly, microparticles have been known to be superior to nanoparticles in terms of capacity retention along repeated cycles. In this work, a cross-linked two-component binder system of poly(acrylic acid) and carboxymethyl cellulose (PAA/CMC) was used for nanoparticular Co 3 O 4 . The binder was characterized by high modulus and strong bonding to the surface oxide of Co 3 O 4 . Even without carbon coating, the composite electrodes of nanoparticular Co 3 O 4 in the presence of PAA/CMC showed significantly enhanced cycle retention with improved reversibility of the conversion reaction.

Binder-free and bifunctional electrocatalysts have vital roles in the development of high-performance metal–air batteries. Herein, we synthesized a vanadium oxide (VO2) nanostructure as a novel binder-free and bifunctional electrocatalyst for a rechargeable aqueous sodium–air (Na–air) battery. VO2 nanostructures were grown on reduced graphene oxide coated on carbon paper, which had a carambola morphology. We confirmed the bifunctional nature of VO2 nanostructures by analyzing their electrocatalytic activity associated with the oxygen reduction reaction and oxygen evolution reaction. The reaction pathway associated with electrocatalytic activity was also affirmed by computational modeling and simulation studies. Thereafter, an aqueous Na–air cell was built using novel binder-free VO2 nanostructures as the air electrode. The fabricated cell displayed a 0.64 V overpotential gap, 104 mW g−1 power density at 80 mA g−1 current density, 81% round trip efficiency and good cyclic stability up to 50 cycles.

Although the volume of antimony tremendously expands during the alloying reaction with sodium, it is considered a promising anode material for sodium-ion batteries (SIBs). Repeated volume changes along the sodiation/desodiation cycles encourage capacity fading by triggering pulverization accompanying electrolyte decomposition. Additionally, the low cation transference number of sodium ions is another hindrance for application in SIBs. In this work, a binder was designed for the antimony in SIB cells to ensure bifunctionality and improve (1) the mechanical toughness to suppress the serious volume change and (2) the transference number of sodium ions. A cross-linked composite of poly(acrylic acid) and cyanoethyl pullulan (pullulan-CN) was presented as the binder. The polysaccharide backbone of pullulan-CN was responsible for the mechanical toughness, while the cyanoethyl groups of pullulan-CN improved the lithium-cation transfer. The antimony-based SIB cells using the composite binder showed improved cycle life with enhanced kinetics. The capacity was maintained at 76% of the initial value at the 200th cycle of 1C discharge following 1C charge, while the capacity at 20C was 61% of the capacity at 0.2C, implying that the composite binder significantly improved the sodiation/desodiation reversibility of antimony.

Reactive oxygen species or superoxide (O2-), which damages or ages biological cells, is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C60) was used as a superoxide disproportionation chemocatalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm-2) with 0.5 mAh cm-2 cutoff survived up to 50 cycles after MA-C60 was introduced to the electrolyte. Moreover, the SOD-mimetic catalyst increased capacity, e.g., more than a 6-fold increase at 0.2 mA cm-2. The experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60.

Alloys are recently receiving considerable attention in the community of rechargeable batteries as possible alternatives to carbonaceous negative electrodes; however, challenges remain for the practical utilization of these materials. Herein, we report the synthesis of germanium-zinc alloy nanofibers through electrospinning and a subsequent calcination step. Evidenced by in situ transmission electron microscopy and electrochemical impedance spectroscopy characterizations, this one-dimensional design possesses unique structures. Both germanium and zinc atoms are homogenously distributed allowing for outstanding electronic conductivity and high available capacity for lithium storage. The as-prepared materials present high rate capability (capacity of ~ 50% at 20 C compared to that at 0.2 C-rate) and cycle retention (73% at 3.0 C-rate) with a retaining capacity of 546 mAh g−1 even after 1000 cycles. When assembled in a full cell, high energy density can be maintained during 400 cycles, which indicates that the current material has the potential to be used in a large-scale energy storage system., Alloy anode materials are receiving renewed interest. Here the authors show the design of Ge-Zn nanofibers for lithium ion batteries. Featured by a homogeneous composition at the atomic level and other favorable structural attributes, the materials allow for impressive electrochemical performance.

Germanium nanoparticles were synthesized and subjected to study as anode materials for lithium ion batteries and sodium ion batteries. Laser pyrolysis of GeH4 was used to produce germanium nanoparticles and the average diameter of these nanoparticles was easily controlled by regulating sensitizer gas flow rates during the process. 60 and 10 nm diameter nanoparticles were synthesized and micron-size powder was purchased and these three pure germanium powder samples were tested as the anode materials of lithium ion batteries and sodium ion batteries in terms of cycle retention, long term cycles and the kinetics of reactions. Experimental results showed that the smallest powder sample which is synthesized, average 10 nm, exhibited excellent performances in both kinds of batteries. According to the results, the characteristics of batteries improved as the size of germanium powder decreased consistently. Pure germanium was thoroughly investigated as an anode of metal-ion batteries with regard to its powder size. The experimental data and synthesis approach of germanium nanoparticles suggested in this research would be a good example for the utilization of elemental germanium in high performance batteries.

Aprotic lithium-oxygen batteries (LOBs) have been considered as one of the high-energy-density alternatives to replace currently available lithium ion batteries. Highly reactive superoxide as the discharge intermediate of LOBs triggers side reactions to deteriorate LOB performances. Also, high overpotential is required to oxidize the discharge product Li2O2 during charge due to the non-conductive nature of Li2O2. Herein, we present 4-carboxy-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO-COOH) as a superoxide dismutase mimetic bifunctional mobile catalyst soluble in electrolytes for improving LOB performances. The role of TEMPO-COOH is two-fold: (1) the chemo-catalyst to catalyze superoxide disproportionation reaction for suppressing the superoxide-triggered side reactions during discharge; and (2) the redox mediator to oxidize Li2O2 in a kinetically effective way for reducing the overpotential during charge. The use of the mobile catalyst in LOB cells resulted in the 4-fold increase in cycle life from 50 cycles to 200 cycles as well as the 4-fold increase in the discharge capacity, significantly reducing the overpotential during charge.