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Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical–radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation. [ABSTRACT FROM AUTHOR]

The intrinsic iron(III) impurity center in polycrystalline lead titanate was investigated by means of high-frequency electron paramagnetic resonance spectroscopy in order to determine the local-environment sensitive fine-structure parameter D. At a spectrometer frequency of 190 GHz, a spectral analysis of a powder sample was unambiguously possible. The observed mean value D=+35.28 GHz can be rationalized if Fe3+ ions substitute for Ti4+ at the B site of the perovskite ABO3 lattice forming a directly coordinated FeTi′–VO·· defect associate. A consistent fit of the multifrequency data necessitated the use of a distribution of the D values with a variance of about 1 GHz. This statistical distribution of values is probably related to more distant defects and vacancies. [ABSTRACT FROM AUTHOR]

Aprotic lithium-oxygen (Li-O2) batteries have attracted considerable attention in recent years owing to their outstanding theoretical energy density. A major challenge is their poor reversibility caused by degradation reactions, which mainly occur during battery charge and are still poorly understood. Herein, we show that singlet oxygen (1Δg) is formed upon Li2O2 oxidation at potentials above 3.5 V. Singlet oxygen was detected through a reaction with a spin trap to form a stable radical that was observed by time- and voltage-resolved in operando EPR spectroscopy in a purpose-built spectroelectrochemical cell. According to our estimate, a lower limit of approximately 0.5 % of the evolved oxygen is singlet oxygen. The occurrence of highly reactive singlet oxygen might be the long-overlooked missing link in the understanding of the electrolyte degradation and carbon corrosion reactions that occur during the charging of Li-O2 cells. [ABSTRACT FROM AUTHOR]

High-frequency electron paramagnetic resonance (EPR) has been used to identify different manganese oxidation states in the 0.5 mol% MnO 2 -doped (100−x)Bi 0.5 Na 0.5 TiO 3 -xBaTiO 3 (BNT-xBT) solid solution with x=6. The as-sintered and air-annealed samples show two distinct EPR resonances that were assigned to Mn 2+ - and Mn 3+ -ions, respectively, incorporated at the Ti-site. The equilibrium between acceptor-type Mn″ Ti - and Mn′ Ti -states can be explained by the thermodynamic equilibration under air at the sintering temperature corresponding to [n]>[p], which yields an n-type Mn:BNT-6BT compound. [ABSTRACT FROM PUBLISHER]

The defect chemistry in the vicinity aliovalent acceptor-type transition-metal functional centers in piezoelectric perovskite oxides is characterized by means of multifrequency and multipulse electron paramagnetic resonance spectroscopy, assisted by density-functional theory calculations. The focus is on the formation of charged and neutral defect dipoles, which are discussed causing internal bias fields, as well as isovalent manganese substitutes. Based on this nanoscale characterization of the defect structure, its impact on macroscopic material properties is discussed. [ABSTRACT FROM AUTHOR]

The position of (FeZr,Ti′-VO••)• defect complexes in Pb[Zr0.52Ti0.48]O3 (PZT) piezoelectric ceramics was investigated by means of electron paramagnetic resonance (EPR) spectroscopy. The method of analysis pursued to obtain information on the (FeZr,Ti′-VO••)• position is to compare the EPR spectra of Fe3+-doped PZT specimen at different states, i.e., a powder that is representative for a system with considerably reduced amount of non-180° domain walls and a sintered ceramic of identical composition but with markedly developed domain structure. By considering the local site symmetry for the Fe3+-functional center, indirect evidence is obtained that the (FeZr,Ti′-VO••)• defect complexes are located within domains and not at domain walls. [ABSTRACT FROM AUTHOR]

The effect of Fe2O3-doping on the defect structure and piezoelectric properties of [Bi0.5Na0.5]TiO3 ceramics is studied by means of electron paramagnetic resonance spectroscopy. The results show that the Fe3+ functional centers are incorporated at the perovskite B-site, and clearly can be attributed to the formation of (FeTi′–VO••)• defect complexes with charge compensating oxygen vacancies. Correspondingly, they act as acceptors which promotes materials “hardening.” [ABSTRACT FROM AUTHOR]

The effect of excess iron-doping in piezoelectric lead-zirconate-titanate (PZT) on the microstructure was investigated by means of transmission electron microscopy in conjunction with electron diffraction and energy dispersive x-ray spectroscopy analysis. Electron paramagnetic resonance (EPR) spectroscopy has been used to characterize the site of the iron functional centers. A crystalline secondary magnetic phase formed upon sintering, magnetoplumbite (PbFe12O19), has been unequivocally identified. Furthermore, the phase assemblage observed in the Fe3+-doped PZT 60/40 sample could be correlated with an exchange-coupled resonance in the EPR spectra. [ABSTRACT FROM AUTHOR]

Gadolinium(III)-modified polycrystalline lead titanate (PbTiO3) of 1.0 mol % dopant level was investigated by means of multifrequency electron paramagnetic resonance spectroscopy in order to determine sign and size of the local-environment sensitive finestructure parameter B20. The Gd3+ ions were assigned to substitute for Pb2+ at the A site of the perovskite ABO3 lattice, providing donor centers. The obtained value amounts to B20=0.776(2) GHz at ambient temperature and 0.860(2) GHz at 5 K, thus showing a considerable temperature dependence. A charge-compensation mechanism is proposed that is based solely on the creation of lead and oxygen vacancies. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In operando EPR spectroscopy is utilized to monitor redox processes in LCO. • In the pristine battery, Co2+ due to electrolyte decomposition was found. • A pure oxygen redox mechanism is found for standard battery cycling. • Cobalt remains redox inactive during charging and discharging. Abstract Electron paramagnetic resonance (EPR) spectroscopy was utilized in operando to analyze redox mechanisms in lithium cobalt oxide (LCO) cathode material during battery cycling. In the pristine battery, a considerable amount of paramagnetic Co2+ was detected that was formed during initial contact of the electrolyte with the LCO. The Co2+ got oxidized during the formation cycle. The absence of an EPR signal during subsequent battery cycles, irrespective of the state-of-charge, indicates that no EPR active Co4+ is formed. This suggests the presence of an anionic oxygen redox mechanism in the active material. [ABSTRACT FROM AUTHOR]

Abstract The composition of lithium manganese spinel Li 1+ x Mn 2− x O 4 (LMO) cathode materials for lithium-ion batteries is very sensitive with respect to temperature conditions during processing. Elevated calcination temperatures promote the formation of Li 2 MnO 3 secondary phase in addition to the spinel phase. Under heat treatments at lower temperature secondary-phase Li 2 MnO 3 can react with the LMO spinel main phase and form a new spinel phase with higher Li-content. This solid state reaction has been observed but its kinetic behavior has not been investigated. An experimental approach to monitor the change of Li 2 MnO 3 amount during heat treatment on lithium manganese spinel materials is addressed by implementing Electron Paramagnetic Resonance (EPR) spectroscopy. It is shown that for materials prepared initially at 1073 K, the reaction occurs from 673 K to 973 K and it is active between interface of spinel and Li 2 MnO 3. The Li 2 MnO 3 amounts after varied heating temperatures and holding times were quantified and analyzed. The reaction kinetics, based on a quantitative analysis of the EPR resonances, are discussed by using pseudofirst-order and second-order rate laws. Detailed data analysis indicates that the reaction follows different kinetics depending on the microstructure of Li 2 MnO 3. Highlights • The reaction between LMO spinel and secondary-phase Li 2 MnO 3 under heat treatment is monitored by EPR spectroscopy. • The kinetic behavior of this reaction has been analyzed by using pseudofirst-order and second-order rate laws. • The formation of LMO spinel from monoclinic Li 2 MnO 3 phase is visualized by SEM. • The impact of diffusion limit on a solid state reaction is confirmed from both the theory and experiment. [ABSTRACT FROM AUTHOR]

The ability of fast and safe charging is critical for the further success of lithium ion batteries in automotive applications. In state-of-the-art lithium ion batteries, the charging rate is limited by the onset of lithium plating on the graphite anode. Despite its high importance, so far no analytical technique has been available for directly measuring lithium plating during battery charge. Herein, we introduce operando electron paramagnetic resonance (EPR) spectroscopy as the first technique capable of time-resolved and quantitative detection of lithium metal plating in lithium ion batteries. In an exemplary study, the C-rate dependence of lithium metal plating during low-temperature charging at −20 °C is investigated. It is possible to quantify the amount of ‘dead lithium’ and observe the chemical reintercalation of plated lithium metal. In this way, it is possible to deconvolute the coulombic inefficiency of the lithium plating/stripping process and quantify the contributions of both dead lithium and active lithium loss due to solid electrolyte interphase (SEI) formation. The time-resolved and quantitative information accessible with operando EPR spectroscopy will be very useful for the optimization of fast charging procedures, testing of electrolyte additives, and model validation. [ABSTRACT FROM AUTHOR]

The interplay between aliovalent CuO doping and nonstoichiometry on the development of defect structures and the formation of secondary phases of antiferroelectric NaNbO3 ceramics has been investigated by means of x-ray diffraction (XRD), first-principles calculations using density functional theory (DFT), and electron paramagnetic resonance spectroscopy. The results indicate that, for stoichiometric 0.25 mol% CuO-doped NaNbOs, as well as for 2.0 mol% Nb-excess sodium niobate, the Cu2+ functional centers are incorporated at the Nb site (Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed). For reasons of charge compensation, two kinds of mutually compensating defect complexes (Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed) and (Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed) are formed where, for the niobium-excess compound, additionally, Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed contribute to the mechanism of charge compensation. In contrast, for 2.0 mol% Na-excess sodium niobate, a Na3NbO4 secondary phase has been detected by XRD, and only part of the Cu2+ forms these types of defect complexes. The major part of the Cu2+ is incorporated in a fundamentally different way by forming Cu2+-Cu2+ dimeric defect complexes. Germany [ABSTRACT FROM AUTHOR]

Abstract: The oxidation/reduction behavior of iron in the Sr[Ti1− y Fe y ]O x solid-solution system, for y ∈[0.002; 0.05], under various oxygen partial pressures was examined through the use of electron paramagnetic resonance (EPR) spectroscopy. The results indicate that iron has been induced to move between di- tri- and tetravalent oxidation states. This results with the centers functioning as either a source (oxidation) or as a sink (reduction) for electrons. In particular it is shown that the reducibility of iron decreases with increasing iron content. [Copyright &y& Elsevier]

This paper presents the utilization of hybrid carbon nano-tube (CNT) – manganese dioxide (MnO 2) tissues as air electrodes in nonaqueous aluminum- and lithium-based battery systems. The CNT tissues are impregnated with α-manganese dioxide nanoparticles via a straightforward binder-free ultrasonic treatment, thereby enabling an improved oxygen reduction reaction (ORR) catalytic activity. Half-cell potentiodynamic measurements along with full-cell discharge evaluations of Li- and Al-based battery systems are reported. Higher discharge potentials and capacities were obtained from generic and advanced hybrid CNT–MnO 2 air cathodes. The discharge products obtained on the air cathode surface were studied using high-resolution scanning electron microscopy. Their chemical compositions were evaluated using elemental mapping energy-dispersive X-ray spectroscopy. We complemented our analysis with density functional theory calculations of oxygen adsorption on MnO 2 and graphene. The modifications obtained for the discharge products in both systems, along with their improved distribution within the cathode surface, supported longer discharge processes without clogging the O 2 penetration pathways at the air cathode. The stability of the α-MnO 2 catalyst was studied using X-ray photoelectron spectroscopy and electron paramagnetic resonance spectroscopy, thereby indicating the ongoing formation of an outer MnF 2 shell layer, which affected the α-MnO 2 functionality, as an efficient ORR catalyst. [Display omitted] • A catalyst impregnation using a straightforward binder-free ultrasonic treatment. • An improved full-cell operation using hybrid CNT-MnO 2 air cathode. • Prolonged discharge process and better cyclability. • Discharge products modification in metal-air systems. [ABSTRACT FROM AUTHOR]