High-voltage Electrode Materials Research Articles

Integrated Supervised and Unsupervised Machine Learning Approach to Map the Electrochemical Windows Over 4500 Solvents for Battery Applications.

The compatibility between solvent electrolytes and high-voltage electrode materials represents a significant impediment to the progress of rechargeable metal-ion batteries. Rapidly identifying suitable solvent electrolytes with optimized electrochemical windows (ECWs) within an extensive search space poses a formidable challenge. In this study, we introduce a combined supervised and unsupervised (clustering) machine learning (ML) approach to discern distinct clusters of solvent electrolytes exhibiting varying ECW ranges. Through supervised machine learning, we have accurately predicted optimal solvent electrolytes with desired ECWs from a vast pool of 4882 solvents. Our ML model boasts superior accuracy compared to previously reported data from density functional theory (DFT). Besides, the exploration of the vast solvent space through K-means clustering (unsupervised approach) yields 11 optimal clusters, each encompassing different solvents characterized by diverse ECW ranges and frequencies. The expedited reduction of solvent space achieved through clustering occurs within a very short time frame and with minimal resource expenditure. Consequently, this method is highly capable of streamlining the subsequent experimental investigations for battery applications, avoiding the need for a trial-and-error approach.

Towards the 4 V-class n-type organic lithium-ion positive electrode materials: the case of conjugated triflimides and cyanamides.

Organic electrode materials have garnered a great deal of interest owing to their sustainability, cost-efficiency, and design flexibility metrics. Despite numerous endeavors to fine-tune their redox potential, the pool of organic positive electrode materials with a redox potential above 3 V versus Li+/Li0, and maintaining air stability in the Li-reservoir configuration remains limited. This study expands the chemical landscape of organic Li-ion positive electrode chemistries towards the 4 V-class through molecular design based on electron density depletion within the redox center via the mesomeric effect of electron-withdrawing groups (EWGs). This results in the development of novel families of conjugated triflimides and cyanamides as high-voltage electrode materials for organic lithium-ion batteries. These are found to exhibit ambient air stability and demonstrate reversible electrochemistry with redox potentials spanning the range of 3.1 V to 3.8 V (versus Li+/Li0), marking the highest reported values so far within the realm of n-type organic chemistries. Through comprehensive structural analysis and extensive electrochemical studies, we elucidate the relationship between the molecular structure and the ability to fine-tune the redox potential. These findings offer promising opportunities to customize the redox properties of organic electrodes, bridging the gap with their inorganic counterparts for application in sustainable and eco-friendly electrochemical energy storage devices.

Bio-Based Polyhydroxyanthraquinones as High-Voltage Organic Electrode Materials for Batteries.

Organic materials have gained much attention as sustainable electrode materials for batteries. Especially bio-based organic electrode materials (OEMs) are very interesting due to their geographical independency and low environmental impact. However, bio-based OEMs for high-voltage batteries remain scarce. Therefore, in this work, a family of bio-based polyhydroxyanthraquinones (PHAQs)-namely 1,2,3,4,5,6,7,8-octahydroxyanthraquinone (OHAQ), 1,2,3,5,6,7-hexahydroxyanthraquinone (HHAQ), and 2,3,6,7-tetrahydroxyanthraquinone (THAQ)-and their redox polymers were synthesized. These PHAQs were synthesized from plant-based precursors and exhibit both a high-potential polyphenolic redox couple (3.5-4.0 V vs Li/Li+) and an anthraquinone redox moiety (2.2-2.8 V vs Li/Li+), while also showing initial charging capacities of up to 381 mAh g-1. To counteract the rapid fading caused by dissolution into the electrolyte, a facile polymerization method was established to synthesize PHAQ polymers. For this, the polymerization of HHAQ served as a model reaction where formaldehyde, glyoxal, and glutaraldehyde were tested as linkers. The resulting polymers were investigated as cathode materials in lithium metal batteries. PHAQ polymer composites synthesized using formaldehyde as linker and 10 wt % multiwalled carbon nanotubes (MWCNTs), namely poly(THAQ-formaldehyde)-10 wt % MWCNTs and poly(HHAQ-formaldehyde)-10 wt % MWCNTs, exhibited the best cycling performance in the lithium metal cells, displaying a high-voltage discharge starting at 4.0 V (vs Li/Li+) and retaining 81.6 and 77.3 mAh g-1, respectively, after 100 cycles.

High-voltage (4.1 V) organic electrode material with an oxygen redox center

We reported an oxygen-containing 4.1 V-class high-voltage organic redox-active compound, dibenzo-1,4-dioxin (DD), which shows one of the highest redox potential among organic electrode materials reported thus far.

Ionic Conductivity Enhancement of Li2ZrCl6 Halide Electrolytes via Mechanochemical Synthesis for All-Solid-State Lithium-Metal Batteries.

Superionic halides have returned to the spotlight of solid electrolytes because of their satisfactory ionic conductivity, soft texture, and stability toward high-voltage electrode materials. Among them, Li2ZrCl6 has aroused interests since abundant Zr element can reduce the cost of large-scale synthesis. However, the related research is very limited, including the detailed parameters during synthesis and the possible strategies for enhancing ionic conductivity. In this work, we have systematically investigated the effects of synthesis parameters on the structure and ionic conductivity of Li2ZrCl6 during the ball-milling annealing process. It is found that mild heat treatment (100 °C) can largely enhance the ionic conductivity of ball-milled electrolytes by 2-3 times, which has not been previously reported. Such enhancement is mainly attributed to the network-like micromorphology composed of nanorods, nanowires, or nanoballs, which is beneficial for lithium ion migration. Finally, the modified Li2ZrCl6 (4.46 × 10-4 S cm-1 @ RT) is also proved to be applicable in LiNi0.8Mn0.1Co0.1O2/ Li2ZrCl6/ Li6PS5Cl/Li-In all-solid-state lithium metal batteries (ASSLMBs). It presents high initial charge capacity of 176.4 mAh g-1 and satisfactory cycle stability since a discharge capacity of 90.8 mAh g-1 is maintained after 40 cycles at 0.1 C. The Li2ZrCl6 electrolytes synthesized via the mechanochemical method is promising to be applied in the high-voltage ASSLMBs, and its ionic conductivity can be enhanced by the strategies provided in our work.

Encapsulating Cu2Se into 3D porous carbon as high-voltage electrode materials for aluminum-ion batteries

In this work, a neoteric Cu2Se@C positive electrode material for AIBs, which Cu2Se nanoparticles encapsulated into three-dimensional (3D) porous carbon derived from HKUST-1 (MOF-199), has been fabricated through a synchronous carbonization-selenization strategy. Al/Cu2Se@C batteries not only display high discharge plateau of 1.83 V and reversible capacity of 276.2 mA h g−1 under the current density of 200 mA g−1, but also show decent cycling stability with a retention of 54.4 mA h g−1 at 800 mA g−1 after 200 cycles. The good Al storage performance of Cu2Se@C relies on its unique porous carbon structure, which plays an important role in improving the electrical conductivity of the electrode material, buffering the volume expansion, and providing channels for Al3+ migration. A new opportunity toward the development of high performance and low cost AIBs is demonstrated in this work.

A novel phosphonium ionic liquid electrolyte enabling high-voltage and high-energy positive electrode materials in lithium-metal batteries

The synthesis of a new ionic liquid (IL), consisting of the symmetric tetra-butyl-phosphonium (P4444+) cation and the (nonafluorobutanesulfonyl)(trifluoromethanesulfonyl)imide (IM14–) anion, via a facile and environmentally-friendly aqueous route is reported. The novel P4444IM14 IL demonstrates excellent thermal and electrochemical stability (beyond 6 V vs. Li+/Li0 (against Ni-foil)) in combination with good near-room temperature conductivity and ionic liquid characteristics, such as non-measurable volatility and exceptional flame-retardant properties. Employed as electrolyte component in Li-metal cells together with the high-voltage, Li1.2Ni0.2Mn0.6O2 positive electrode material, enables an initial discharge capacity of 264 mA h g-1 at 12.5 mA g−1 and improved initial Coulombic efficiency. Additionally, the discharge capacity retention is promising (92.3% after 50 cycles and 84.4% after 100 cycles) when compared with using a conventional organic carbonate-based electrolyte (55.5% after 50 cycles). Further development of this ionic liquid electrolyte may facilitate the practical application of Li-metal anodes in high-voltage/high-energy lithium batteries.

Synthesis and Electrochemical Properties of Mg-Substituted Ni/Mn-Based High-Voltage Spinel Oxides

1. Introduction Currently, research on layered and rocksalt Li-rich materials is being actively conducted as a high-capacity positive electrode material for lithium ion batteries, and now it is widely accepted that large capacity originates from oxygen redox reaction.[1] Oxygen redox is proposed to be activated for oxygen ions with a Li-O-Li configuration.[2] It was also reported that oxygen redox is activated for Li-rich manganese spinel-type oxides, i.e., Li[Li x Mn2–x ]O4.[3] Nevertheless, its origin of activation of anionic redox for spinel-type oxides is not known. In this study, LiMg y Ni0.5-y Mn1.5O4, which is solid solution samples between LiNi0.5Mn1.5O4 and LiMg0.5Mn1.5O4, is targeted as positive electrode materials with anionic redox for spinel-type oxides. Mg ions have a high ionic bonding nature with oxygen, and thus better reversibility for anionic redox is anticipated.[1] We report the impact of Mg substitution on reversibility of Ni cationic and O anionic redox in the spinel framework structure, and the possibility of 5 V-class high-voltage electrode materials with excellent capacity retention is discussed. 2. Experimental LiMg y Ni0.5-y Mn1.5O4 (0 ≤ y ≤ 0.5) were synthesized from mixtures of Li2CO3, Mg(OH)2, Ni(OH)2 and Mn2O3 by two-step solid-state reaction at 950 oC for 6 h to 700 °C for 48 h in air atmosphere. Characterization of LiMg y Ni0.5-y Mn1.5O4 were conducted by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the evaluation of electrochemical properties, composite electrodes consisting of 80 wt% active material, 10 wt% AB, and 10 wt% PVdF, and were casted on aluminum foil. 1.0 M LiPF6 dissolved in ethylene carbonate (EC)/dimethyl carbonate (DMC) (3/7 by volume) solution was used as electrolyte. 3. Results and Discussion XRD patterns of LiMg y Ni0.5-y Mn1.5O4 (0 ≤ y ≤ 0.5) are assigned into the spinel structure with space group of Fd-3m. From SEM images, particle sizes of LiMg y Ni0.5-y Mn1.5O4 are estimated to be ~4 μm. No difference in particle sizes regardless of chemical compositions is observed. Figure 1 compares charge/discharge curves of LiMg y Ni0.5-y Mn1.5O4. After 5 cycles, the non Mg-substituted sample, LiNi0.5Mn1.5O4, delivers 135 mAh g−1 of the discharge capacity in a lithium cell when the cut-off voltage is set to 5.3 V. After 50 cycles test, discharge capacity of LiNi0.5Mn1.5O4 is decreased to 125 mAh g-1. On the other hand, significant improvement of cyclability is evidenced for the partially Mg-substituted samples. No capacity fading and no increase in polarization is observed for LiMg0.06Ni0.44Mn1.5O4 even charge to 5.3 V vs. Li for 50 cycles at a rate of 10 mA g-1. On the basis of these findings, Mg substitution is proposed to be effective to reduce electrolyte decomposition and improve structural stability upon high-voltage exposure. Nevertheless, the further enrichment of Mg ions in the structure results in loss of reversible capacity, and anionic redox seems to be inactive for LiMg0.5Mn1.5O4. From these results, factors affecting electrode performance of high voltage spinel with cationic/anionic redox will be discussed in detail.References(1) N. Yabuuchi, Chem. Rec., 19, 703 (2019).(2) D.-H. Seo, Nature Chem., 8, 692 (2016).(3) E. Iwata et al., and T. Ohzuku, Electrochemistry, 71,1187 (2003). Figure 1

Layered manganese oxide Mn5O8 as a structural matrix for fast lithium and magnesium intercalation

Layered Mn5O8 is considered as low-cost and high-voltage electrode materials for storing Na+ ions in aqueous media. Herein we provide the first report on the intercalation of Li+ and Mg2+ ions into layered Mn5O8 in non-aqueous electrolytes. The layered oxide Mn5O8 is simply prepared by a thermal decomposition of freshly precipitated γ-MnOOH at 500 °C for a short heating time. The morphology of Mn5O8 consists of well-crystalized nanoparticles with rod-like shape. The intercalation properties of Mn5O8 are examined galvanostatically in half lithium-ion cells. Two type of electrolytes are utilized: lithium and magnesium electrolytes containing 1 M LiPF6 in EC:DMC and 0.5 M MgTFSI in diglyme. Because of the layered structure, specific morphology and mixed oxidation states of manganese ions, layered Mn5O8 is able to intercalate reversibly and in high-amount both Li+ and Mg2+ ions in lithium and magnesium electrolytes. In lithium electrolyte, Mn5O8 exhibits high specific capacity (about 180 mAh/g at C/20), excellent rate capability (about 120 mAh/g at C1) and good cycling stability (the Coulombic efficiency more than 99% at C1). The mechanism of the electrochemical reaction is discussed on the basis of ex-situ HR-TEM and electron paramagnetic resonance spectroscopy (EPR). The storage capability of Mn5O8 will, most probably, be of significance for understanding the electrochemical behavior of layered Mn-based oxides in non-aqueous electrolyte.

Probing Mg Intercalation in the Tetragonal Tungsten Bronze Framework V4Nb18O55.

While commercial Li-ion batteries offer the highest energy densities of current rechargeable battery technologies, their energy storage limit has almost been achieved. Therefore, there is considerable interest in Mg batteries, which could offer increased energy densities in comparison to Li-ion batteries if a high-voltage electrode material, such as a transition-metal oxide, can be developed. However, there are currently very few oxide materials which have demonstrated reversible and efficient Mg2+ insertion and extraction at high voltages; this is thought to be due to poor Mg2+ diffusion kinetics within the oxide structural framework. Herein, the authors provide conclusive evidence of electrochemical insertion of Mg2+ into the tetragonal tungsten bronze V4Nb18O55, with a maximum reversible electrochemical capacity of 75 mA h g-1, which corresponds to a magnesiated composition of Mg4V4Nb18O55. Experimental electrochemical magnesiation/demagnesiation revealed a large voltage hysteresis with charge/discharge (1.12 V vs Mg/Mg2+); when magnesiation is limited to a composition of Mg2V4Nb18O55, this hysteresis can be reduced to only 0.5 V. Hybrid-exchange density functional theory (DFT) calculations suggest that a limited number of Mg sites are accessible via low-energy diffusion pathways, but that larger kinetic barriers need to be overcome to access the entire structure. The reversible Mg2+ intercalation involved concurrent V and Nb redox activity and changes in crystal structure, as confirmed by an array of complementary methods, including powder X-ray diffraction, X-ray absorption spectroscopy, and energy-dispersive X-ray spectroscopy. Consequently, it can be concluded that the tetragonal tungsten bronzes show promise as intercalation electrode materials for Mg batteries.

Investigation of Hydrogen Peroxide Formation After Underwater Plasma Discharge

This paper reports investigations on the formation of hydrogen peroxide resulting from micro-pulse plasma discharges obtained in pin-to-pin configuration underwater. In particular, this study reports the influence of the discharge regime (cathode regime with and without breakdown, and anode regime) as well as that of the discharge energy (from 10 to 45 mJ per pulse). It has been shown that the H2O2 production is higher for high energy and anode regime. In addition, the variation of the pulse width (from 50 to 500 µs) highlights the dependence of the chemical processes induced by the discharge according to the regime. Considering two different electrode materials (tungsten and platinum), we do not observe any significant influence of the electrode material on the H2O2 production, whereas the injected energy depends on the high voltage electrode material. Finally, the erosion of the electrodes have been studied using in-situ optical microscopy and SEM. It is shown that the erosion mechanisms strongly depend on materials, regimes and the polarity of the electrodes.

First-Principle Insights Into Molecular Design for High-Voltage Organic Electrode Materials for Mg Based Batteries.

Low cost, scalability, potentially high energy density, and sustainability make organic magnesium (ion) battery (OMB) technologies a promising alternative to other rechargeable metal-ion battery solutions such as secondary lithium ion batteries (LIB). However, most reported OMB cathode materials have limited performance due to, in particular, low voltages often smaller than 2 V vs. Mg2+/Mg and/or low specific capacities compared to other competing battery technologies, e.g., LIB or sodium ion batteries. While the structural diversity of organic compounds and the large amount of possible chemical modifications potentially allow designing high voltage/capacity OMB electrode materials, the large search space requires efficient exploration of potential molecular-based electrode materials by rational design strategies on an atomistic scale. By means of density functional theory (DFT) calculations, we provide insights into possible strategies to increase the voltage by changes in electronic states via functionalization, by strain, and by coordination environment of Mg cations. A systematic analysis of these effects is performed on explanatory systems derived from selected prototypical building blocks: five- and six-membered rings with redox-active groups. We demonstrate that voltage increase by direct bandstructure modulation is limited, that strain on the molecular scale can in principle be used to modulate the voltage curve and that the coordination/chemical environment can play an important role to increase the voltage in OMB. We propose molecular structures that could provide voltages for Mg insertion in excess of 3 V.

Dilution of the Electron Density in the π-Conjugated Skeleton of Organic Cathode Materials Improves the Discharge Voltage.

Organic compounds are promising candidates as battery materials because they can be sourced from sustainable resources, have tunable structures, and are cheap. However, the working voltage of battery cells containing organic compounds as positive electrodes is relatively lower than that of those containing an inorganic counterpart. In this work, a strategy was developed to increase the discharge voltage of battery cells by diluting the electron density of N-based redox centers in conjugated organic materials. In electron-rich heterocyclic compounds that utilize N as the redox center, pentatomic rings such as carbazole derivatives exhibited a higher atomic-dipole-moment-corrected Hirshfeld charge population compared with hexatomic rings, which led to a significant increase in the oxidation potential. As a result, polymeric indolocarbazole derivatives showed a high discharge voltage of 3.7-4.3 V vs. Li+ /Li and good cycling performance. Such a strategy can be used to design high-voltage organic electrode materials containing other redox centers.

Na7V3(P2O7)4as a high voltage electrode material for Na-ion batteries: crystal structure and mechanism of Na+extraction/insertion byoperandoX-ray diffraction

The crystal chemistry and the electrochemical properties of Na7V3(P2O7)4as a high voltage cathode material upon Na+extraction/insertion were investigated byoperandoX-ray diffraction.

Ionic liquid electrolytes based on sulfonium cation for lithium rechargeable batteries

We report the preparation and characterization of ionic liquid electrolytes composed of the ionic liquid triethyl sulfonium bis(trifluoromethylsulfonyl imide) ([S222TFSI]) and four different lithium salts, namely lithium bis(trifluoromethylsulfonyl imide) (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6) and lithium trifluoromethanesulfonate or lithium triflate (LiFSI). Among the electrolytes we studied, [S222TFSI] – LiTFSI has the lowest viscosity. DSC analysis showed that all these ionic liquid electrolytes have their melting peak below −5 °C, confirming that they are in liquid state over the temperature range at which batteries are usually required to operate. The ionic conductivity at room temperature is in the order of 10−3 S cm−1 and increases to 10−2 S cm−1 at higher temperatures. The [S222TFSI] – LiTFSI electrolyte system is electrochemically stable up to 5 V against lithium metal which indicates the feasibility of using it with high voltage electrode materials. Reversible redox process of lithium stripping/deposition in this electrolyte was observed in cyclic voltammetry by the appearance of redox peaks in both forward and reverse scans within the voltage range, −0.4 V–2.5 V. In addition to correlating the viscosity of the prepared electrolytes with their ionic conductivity as a function of temperature, as a proof of concept, we demonstrate the electrochemical performance of the electrolyte in a coin cell configuration with lithium iron phosphate (LiFePO4) cathode. We observed voltage plateaus around 3.5 V and 3.28 V during the first galvanostatic charging and discharging steps, respectively.

Commercial-Level Energy Storage via Free-Standing Stacking Electrodes

Summary Pseudocapacitors with a fast faradic redox reaction during the electrochemical charge/discharge process hold great promise for delivering high power and high energy. Here, we used emerging oxygenated carbon nitride (OCN) as a model for nitrogen- and oxygen-enriched carbons and found an anion-selective charging behavior in aqueous electrolytes. The N- and O-mediated hydroxyl anion-selective charging originates from inbuilt surface-positive electrostatic potential localized at heptazine and quaternary N atom structural units. The carbon atoms in heptazine adjacent to pyridinic N act as the electron transfer active sites for faradic pseudocapacitance. The OCN free-standing films (FSFs) were developed as current collector-free electrodes, and stacking OCN FSFs can confer a cell with loading weight over a commercial level. For demonstration, a symmetrical cell with 17.7 mg cm−2 delivers an energy of 140.9 mW h at a high power of 2,499.9 mW, and almost 100% capacitance retention after 20,000 charge/discharge cycles at 50 mA.

In-Situ Characterization of the Li-Al System at Elevated Temperatures

We will describe our platform for ex- and in-situ characterization of lithium ion electrode and electrolyte materials over a wide range of temperatures, and our use of this platform to characterize phase formation and dissociation in the Li-Al system. Aluminum electrodes have been studied for use in lithium electrochemical cells for more than 40 years. Electrochemical insertion of lithium in to aluminum at very high temperatures (>400 °C) follows the equilibrium phase diagram; studies at e.g. room temperature only demonstrate the formation of LiAl. The formation of the other expected Li-Al phases, Li3Al2 and Li9Al4, is thought to be inhibited by slow diffusion of Li in LiAl. Aluminum is available in a wide variety of morphologies and manufacturing-induced microstructures and as such is a model test platform for deconvoluting the effects of microstructure, diffusion, and phase formation in metal alloy electrodes. Our core enabling technology is an adaptable high-temperature compatible cell design inspired by high-temperature compatible primary cell hardware and adapted from earlier work. Our double-ended glass-to-metal Conflat cells are compatible with low and high voltage electrode materials, adjustable (and commercially-relevant) electrode thicknesses and stack pressures, and can maintain ultra-high vacuum (<10-7 Pa) tight seals at temperatures up to 415 °C. Results from in-situ cycling of a Conflat cell with lithium and aluminum foil electrodes at 110 °C are presented in Fig. 1. Three voltage plateaus are evident, and the step changes between plateaus roughly correspond with the expected phase transition compositions (i.e. LiAl for Li/Al = 0 <–> 1, Li3Al2 for Li/Al = 1 <–> 1.5, Li9Al4 for Li/Al = 1.5 <-> 2.25). XRD patterns collected at room temperature (ex-situ) at three indicated compositions (x1, x2, x3) are also provided in Fig. 1. Patterns collected from samples cycled to 200 mV vs. Li metal on insertion (x1) and 150 mV vs. Li metal on removal (x3) indicate LiAl and Li3Al2 are present, as expected. However, the XRD pattern collected from the sample cycled to 40 mV vs. Li metal on removal (x2) indicates Li1.77Al, rather than Li9Al4, is present at a composition of Li/Al = 2.2. Li9Al4 has been detected in samples cycled in different conditions (temperature, current density, voltage limits, sample morphology etc.) The discrepancy between measured and expected phase composition at x2 (Li/Al = ~2.2 vs. ~1.8, respectively) is attributed to consumption of lithium in solid-electrolyte interphases (SEI). Li3Al2 (at composition x3, Li/Al = 1.8) has a similar discrepancy (expected composition of Li/Al = 1.5). Known phase transitions can therefore be used as guideposts to quantify SEI formation. XRD results shown in Fig. 1 and described above were collected by cooling and then disassembling Conflat cells and incorporating the lithiated electrode in a polypropylene encapsulated sample holder. A major advantage of Conflat cell technology is the ability to bolt-on new functionality without compromising cell performance. Conflat flanges incorporating x-ray transparent windows are now being incorporated in to our cells. We will present ex- and in-situ (variable temperature cycling, room temperature XRD, with and without cell disassembly) and in-operando (integrated variable temperature cycling and XRD, without cooling) results from aluminum thin films and (much thicker, but still thin) aluminum foils to map out phase formation as a function of temperature, sample morphology, and static and dynamic stress. This data, when coupled with insight in to Li diffusion rates and nucleation barriers for the various Li-Al phases, will enable a more complete understanding of ion mobility and phase formation and stability in the Li-Al and other metal alloy systems. Figure 1

The Role of High Voltage Electrode Material in the Inactivation of E. coli by Direct-in-Liquid Electrical Discharge Plasma

This work investigates the effect of high voltage (HV) electrode material of a point-plane plasma reactor on the inactivation rate of E. coli in both direct plasma and post-discharge inactivation processes. For the direct plasma processes, nickel chromium alloy, iron, tungsten and copper were used as HV electrode materials. In comparison with the other three materials, a significantly higher inactivation rate of E. coli was achieved with copper as the HV electrode. The inactivation effect was demonstrated to be mainly associated with the toxicity of copper ions, rather than from copper nanoparticles released from the electrode during the treatment. Similarly, for the post-discharge inactivation process, a higher E. coli inactivation rate was achieved in both post-plasma and plasma-treated water treatment using copper as the HV electrode, as compared to the tungsten control case. Increased inactivation rates are a result of a synergistic action between copper ions and the hydrogen peroxide generated by the plasma.

Advanced Polymer Electrolyte with Enhanced Electrochemical Performance for Lithium-Ion Batteries: Effect of Nitrile-Functionalized Ionic Liquid

High-voltage electrode materials are beneficial for developing high-power-density lithium-ion batteries. The anodic voltage stability of electrolytes is a major challenge for high-voltage lithium b...

(Keynote) Polyanionic Compounds for K-Ion Batteries

We reported the high working voltage of K-ion battery (KIB) comparable to Li-ion and higher than Na-ion thanks to the standard potential of potassium is lower than those of lithium and sodium in non-aqueous electrolyte [1,2]. In 2015, our group reported graphite negative electrode delivering 250 mAh g-1 or higher with excellent reversibility [1]. Furthermore, a Prussian blue analogue (PBA) of K2Mn[Fe(CN)6] demonstrated highly reversible potassium insertion/extraction and 4 V operation, realizing a 4 V-class K2Mn[Fe(CN)6]/graphite full cell [3]. The previous studies revealed that a three-dimensional open framework structure of PBAs is suitable for insertion/extraction of large K+ ion. Addition to the PBAs, polyanionic compounds are potential positive electrode materials for KIBs due to their open framework structure and inductive effect. In this talk, our recent studies on potassium insertion into various polyanionic compounds, such as heterosite FePO4, KFePO4, KMnPO4, K2FeP2O7, K2MnP2O7, KVPO4F, KVOPO4, monoclinic KFeSO4F, and orthorhombic KFeSO4F (o-KFeSO4F) [4,5], will be presented to give a perspective of potassium insertion material design. Because K+ ion is too large to occupy the octahedral site in heterosite FePO4 prepared from olivine-type LiFePO4, the crystallinity of heterosite FePO4 significantly decreases after potassium insertion. On the other hand, KVPO4F, KVOPO4, and o-KFeSO4F possess the KTiOPO4-type structure providing large channels to diffuse K+ ion and show the reversible potassium insertion/extraction properties and excellent rate performance. These results indicate that the crystal structure plays a key factor for reversible potassium insertion and rate performance. Moreover, the average discharge voltage of KVPO4F and KVOPO4 is as high as 4 V in a K half-cell. That of o-KFeSO4F is 3.6 V, which is notably high redox potential of Fe2+/Fe3+ due to the strong inductive effect of SO4 2- and F- on the Fe2+/3+ couple. The cycling stability of these high-voltage electrode materials is highly improved by using highly concentrated potassium salt solutions [6]. From these results, we will present our future insight into electrochemical potassium insertion chemistry for high voltage battery applications.