World Minerals and World Politics

Geometry of carbon supports significantly affected electrochemical durability of Pt/C (platinum electrocatalyst supported by carbon) for oxygen reduction reaction (ORR). Carbon nano-onion (CNO) was used as the support, which is characterized by its nanosize (similar to Pt size) and high curvature. Superior ORR durability was guaranteed by Pt/CNO due to (1) its <i>islands-by-islands</i> configuration to isolate each Pt nanoparticle from its neighbors by CNO particles; (2) highly tortuous void structure of the configuration to suppress Ostwald ripening; and (3) the <i>curvature-induced strong interaction</i> between CNO and Pt. The finding that highly curved carbon surface encourages electron donation to catalysts was first reported

Multiple Roles of Superoxide on Oxygen Reduction Reaction in Li⁺‑Containing Nonaqueous Electrolyte: Contribution to the Formation of Oxide as Well as Peroxide

Oxygen reduction reaction (ORR) on carbon in lithium-ion-containing nonaqueous electrolytes is supposed to follow a three-step mechanism: oxygen (O₂⁰) to superoxide (O₂^– or LiO₂) to peroxide (O₂^2– or Li₂O₂) to oxide (O^2– or Li₂O). This work attempts to solve three controversial issues: (1) whether the superoxide is really formed; (2) whether the superoxide can be stable or immediately converts to peroxide; (3) whether the formation of oxide is feasible at the typical discharge potentials of lithium–air battery or the discharge product is only peroxide. ORR on carbon was studied in LiClO₄ or LiPF₆ containing dimethyl sulfoxide. The staircase cyclic voltammetry combined with Fourier transform electrochemical impedance spectroscopy (SCV-FTEIS) was used for the <i>in situ</i> investigation of ORR during potential scans. Oxygen was quasi-reversibly reduced to superoxide in the first step. Superoxide showed chemical stability in electrolyte. The superoxide was further reduced to surface-adsorbed peroxide, and the reduction proceeded to produce oxide at higher overpotentials. We identified a novel chemical route resulting in oxide formation even at not-enough overpotentials: peroxide is reduced to oxide by superoxide as an <i>in situ</i> formed one-electron reducing agent. The electrolyte/electrode decomposition product, Li₂CO₃, was observed only in electrolyte with LiClO₄

Facile Route to an Efficient NiO Supercapacitor with a Three-Dimensional Nanonetwork Morphology

NiO nanostructures with three distinct morphologies were fabricated by a sol–gel method and their morphology-dependent supercapacitor properties were exploited. The nanoflower- shaped NiO with a distinctive three-dimensional (3D) network and the highest pore volume shows the best supercapacitor properties. The nanopores in flower-shaped nanostructures, offering advantages in contact with and transport of the electrolyte, allow for 3D nanochannels in NiO structure, providing longer electron pathways. The XPS and EIS data of the NiO nanostructure confirm that the flower-shaped NiO, which has the lowest surface area among the three morphologies, was effectively optimized as a superior electrode and yielded the greatest pseudocapacitance. This study indicates that forming a 3D nanonetwork is a straightforward means of improving the electrochemical properties of a supercapacitor

Succinonitrile as a Corrosion Inhibitor of Copper Current Collectors for Overdischarge Protection of Lithium Ion Batteries

Succinonitrile (SN) is investigated as an electrolyte additive for copper corrosion inhibition to provide overdischarge (OD) protection to lithium ion batteries (LIBs). The anodic Cu corrosion, occurring above 3.5 V (vs Li/Li⁺) in conventional LIB electrolytes, is suppressed until a voltage of 4.5 V is reached in the presence of SN. The corrosion inhibition by SN is ascribed to the formation of an SN-induced passive layer, which spontaneously develops on the copper surface during the first anodic scan. The passive layer is composed mainly of Cu­(SN)₂PF₆ units, which is evidenced by Raman spectroscopy and electrochemical quartz crystal microbalance measurements. The effects of the SN additive on OD protection are confirmed by using 750 mAh pouch-type full cells of LiCoO₂ and graphite with lithium metal as a reference electrode. Addition of SN completely prevents corrosion of the copper current collector in the full cell configuration, thereby tuning the LIB chemistry to be inherently immune to the OD abuses

Conducting Polymer-Skinned Electroactive Materials of Lithium-Ion Batteries: Ready for Monocomponent Electrodes without Additional Binders and Conductive Agents

Rapid growth of mobile and even wearable electronics is in pursuit of high-energy-density lithium-ion batteries. One simple and facile way to achieve this goal is the elimination of nonelectroactive components of electrodes such as binders and conductive agents. Here, we present a new concept of monocomponent electrodes comprising solely electroactive materials that are wrapped with an insignificant amount (less than 0.4 wt %) of conducting polymer (PEDOT:PSS or poly­(3,4-ethylenedioxythiophene) doped with poly­(styrenesulfonate)). The PEDOT:PSS as an ultraskinny surface layer on electroactive materials (LiCoO₂ (LCO) powders are chosen as a model system to explore feasibility of this new concept) successfully acts as a kind of binder as well as mixed (both electrically and ionically) conductive film, playing a key role in enabling the monocomponent electrode. The electric conductivity of the monocomponent LCO cathode is controlled by simply varying the PSS content and also the structural conformation (benzoid-favoring coil structure and quinoid-favoring linear or extended coil structure) of PEDOT in the PEDOT:PSS skin. Notably, a substantial increase in the mass-loading density of the LCO cathode is realized with the PEDOT:PSS skin without sacrificing electronic/ionic transport pathways. We envisage that the PEDOT:PSS-skinned electrode strategy opens a scalable and versatile route for making practically meaningful binder-/conductive agent-free (monocomponent) electrodes

Activity-Durability Coincidence of Oxygen Evolution Reaction in the Presence of Carbon Corrosion: Case Study of MnCo₂O₄ Spinel with Carbon Black

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 more numbers of active sites per a fixed mass

Influence of the Lithium-Ion Concentration in Electrolytes on the Performance of Dye-Sensitized Photorechargeable Batteries

Dye-sensitized photorechargeable batteries (DSPBs) have recently gained attention for realizing energy recycling systems under dim light conditions. However, their performance under high storage efficiency (i.e., the capacity charged within a limited time) for practical application remains to be evaluated. Herein, we varied the lithium (Li)-ion concentration, which plays a dual role as energy charging and storage components, to obtain the optimized energy density of DSPBs. Electrochemical studies showed that the Li-ion concentration strongly affected the resistance characteristics of DSPBs. In particular, increasing the Li-ion concentration improved the output capacity and decreased the output voltage. Consequently, the energy density of the finely optimized DSPB improved from 8.73 to 12.64 mWh/cm3 when irradiated by a 1000-lx indoor light-emitting-diode lamp. These findings on the effects of Li-ion concentrations in electrolytes on the performance of DSPBs represent a step forward in realizing the practical application of DSPBs

Amphi-Active Superoxide-Solvating Charge Redox Mediator for Highly Stable Lithium–Oxygen Batteries

A multifunctional electrolyte additive for lithium oxygen batteries (LOBs) was designed to have (1) a redox-active moiety to mediate decomposition of lithium peroxide (Li2O2 as the final discharge product) during charging and (2) a solvent moiety to solvate and stabilize lithium superoxide (LiO2 as the intermediate discharge product) in electrolyte during discharging. 4-Acetamido-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidin-1-yl)oxyl) or AAT was employed as the additive working for both charge and discharge processes (amphi-active). The redox-active moiety was rooted in TEMPO, while the acetamido (AA) functional group inherited the high donor number (DN) of N,N-dimethylacetamide (DMAc). Integrating two functional moieties (TEMPO and AA) into a single molecule resulted in the bifunctionality of AAT (1) facilitating Li2O2 decomposition by the TEMPO moiety and (2) encouraging the solvent mechanism of Li2O2 formation by the high-DN AA moiety. Significantly improved LOB performances were achieved by the superoxide-solvating charge redox mediator, which were not obtained by a simple cocktail of TEMPO and DMAc

Fire-Inhibiting Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries

Herein, we present a gel polymer electrolyte (GPE) improving nonflammability of lithium-ion batteries (LIBs) by blocking radical-initiated chain reactions which cause thermal runaway and finally fire issues. The polymer that makes up the nonflammable GPE was (1) soluble in carbonate electrolytes, (2) cross-linkable in the presence of a popularly used lithium salt such as LiPF6, (3) gelated only with 2 wt % in electrolytes, and (4) radical-scavenging by its functional side chains. Electrolytes having the polymer were thermally gelated within battery cells after the cells were assembled by a conventional way. LIB cells with the GPE were durable against external thermal and mechanical shocks without sacrificing cell performances. The high transference number of lithium ions and liquid-equivalent ionic conductivity of the GPE at only 2% solid content having a stable solid-electrolyte interphase layer formed even improved cell performances at normal operation conditions

Fire-Inhibiting Nonflammable Gel Polymer Electrolyte for Lithium-Ion Batteries

Herein, we present a gel polymer electrolyte (GPE) improving nonflammability of lithium-ion batteries (LIBs) by blocking radical-initiated chain reactions which cause thermal runaway and finally fire issues. The polymer that makes up the nonflammable GPE was (1) soluble in carbonate electrolytes, (2) cross-linkable in the presence of a popularly used lithium salt such as LiPF6, (3) gelated only with 2 wt % in electrolytes, and (4) radical-scavenging by its functional side chains. Electrolytes having the polymer were thermally gelated within battery cells after the cells were assembled by a conventional way. LIB cells with the GPE were durable against external thermal and mechanical shocks without sacrificing cell performances. The high transference number of lithium ions and liquid-equivalent ionic conductivity of the GPE at only 2% solid content having a stable solid-electrolyte interphase layer formed even improved cell performances at normal operation conditions