Here we present a novel methodology to measure the alkaline stability of anion conducting polymers to be used as anion exchange membranes and anion exchange ionomers for fuel cells. The new ex situ technique simulates the environment of an anion exchange membrane fuel cell (AEMFC) during operation, where nucleophilic and basic OH − species in the absence, or with a scarce amount of water, attack the functional groups of the ionic polymer. Using this technique, we clearly show the critical effect of water molecules on the alkaline stability of quaternary ammonium (QA) cations commonly used as functional groups in AEMFCs. The results show that as the water content is reduced, the QA cations are more rapidly degraded in the presence of OH − at room temperature. With an increasing number of water molecules solvating the hydroxide, its nucleophilicity and basicity are hindered, and the QA degradation is significantly slowed. These results indicate that the currently used aqueous alkali ex situ tests to measure anion exchange membrane (AEM) stability may lead to false positive stability results where anion conducting polymers may appear more alkali stable than they really are.

A 3D hybrid zinc formate framework, [NH(4)][Zn(HCOO)(3)], possessing an acs topology, shows a high degree of mechanical anisotropy and negative linear compressibility (NLC) along its c axis. High-pressure single-crystal X-ray diffraction studies and density functional theory calculations indicate that contraction of the Zn-O bonds and tilting of the formate ligands with increasing pressure induce changes in structure that result in shrinkage of the a and b axes and the NLC effect along c.

Mg­(N­(SO2CF3)2)2 (MgTFSI2) solutions with dimethoxyethane (DME) exhibit a peculiar behavior. Over a certain range of salt content, they form two immiscible phases of specific electrolyte concentrations. This behavior is unique, as both immiscible phases comprise the same constituents. Thus, this miscibility gap constitutes an exceptionally intriguing and interesting case for the study of such phenomena. We studied these systems from solutions structure perspective. The study included a wide variety of analytical tools including single-crystal X-ray diffraction, multinuclei NMR, and Raman spectroscopy coupled with density functional theory calculations. We rigorously determined the structure of the MgTFSI2/DME solutions and developed a plausible theory to explain the two-phase formation phenomenon. We also determined the exchange energy of the “caging” DME molecules solvating the central magnesium ion. Additionally, by measuring the ions’ diffusion coefficients, we suggest that the caged Mg2+ and TFSI– move as free ions in the solution. Knowledge of the arrangement of the solvent/cation/anion structures in these solutions enables us to explain their properties. We believe that this study is important in a wide context of solutions chemistry and nonaqueous electrochemistry. Also, MgTFSI2/DME solutions are investigated as promising electrolyte solutions for rechargeable magnesium batteries. This study may serve as an important basis for developing further MgTFSI2/ether based solutions for such an interesting use.

Ni-rich Li-based layered Ni, Co, and Mn (NCM) materials have shown tremendous promise in recent years as positive electrode materials for Li-ion batteries. This is evident as companies developing batteries for electrical vehicles are currently commercializing these materials. Despite the considerable research performed on LiNiαCoβMnγO2 systems, we do not yet have a complete atomic level understanding of these materials. In this work we study the cationic ordering, thermodynamics, and diffusion kinetics of LiNi0.5Co0.2Mn0.3O2 (NCM-523). Initially, we show that cationic ordering can be predicted employing cheap atomistic simulations, instead of using expensive first-principles methods. Subsequently, we investigate the electrochemical, thermodynamic and kinetic properties of NCM-523 using density functional theory (DFT). Our results demonstrate the importance of including dispersion corrections to standard first principles functionals in order to correctly predict the lattice parameters of layered cathode materials. We also demonstrate that a careful choice of computational protocol is essential to reproduce the experimental intercalation potential trends observed in the LiNi0.5Co0.2Mn0.3O2 electrodes. Analysis of the electronic structure confirms an active role of Ni in the electrochemical redox process. Moreover, we confirm the experimental finding that on complete delithiation, this material remains in an O3 phase, unlike LiCoO2 and NCM-333. Finally, we study various pathways for the Li-ion diffusion in NCM-523, and pinpoint the preferred diffusion channel based on first principles simulations. Interestingly, we observe that the Li diffusion barrier in NCM-523 is lower than that in LiCoO2.

This paper is dedicated to studies of the electrochemical behavior, the structural and thermal features of the Ni-rich LiNi 0.5 Co 0.2 Mn 0.3 O 2 undoped and Al-doped (∼0.01 at.%) materials for positive electrodes of lithium batteries. We have found that structural characteristics of these materials are quite similar from the crystallographic point of view. It was demonstrated that Al substitution in the doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 is preferred at Ni sites over Co sites, and the thermodynamic preference for Al 3+ substitutions follows the order: Ni>Co>Mn. The lower capacity fading of the Al-doped electrodes upon cycling and aging of the cells in a charged state (4.3 V) at 60 • C, as well as more stable mean voltage behavior, are likely due to the chemical and structural modifications of the electrode/solution interface. The Al-doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes demonstrate also lower resistances of the surface film and charge-transfer as well as lower activation energies for the discharge process. From XPS studies we conclude that the modified stable and less resistive interface on the Al-doped particles comprises the Li + -ion conducting nano-sized centers like LiAlO 2 , AlF 3 , etc., which promote, to some extent, the Li + ionic transport to the bulk. A partial layered-to-spinel transformation was established upon cycling of LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathodes.One of the major challenges in lithium batteries technology is, undoubtedly, the further improvement of battery components -electrodes, solutions, and separators. 1-7 Among several modern strategies to improve electrochemical performance and structural characteristics of materials for positive electrodes, doping has attracted the attention of scientists over the years. This is due to the effectiveness of dopants in stabilizing the structure of materials (even in minute amounts) and thus to increase the electrochemical cycling activity and to diminish the heat evolution of the electrodes in a charged state. A variety of dopant ions, like Co 2+ , Al 3+ , Ti 4+ , Zr 4+ , Zn 2+ , Fe 3+ , Cu 2+ , and Cr 3+ , has been used to improve the stability, morphology and microstructure of cathode materials, to enhance the electrode cycleability and rate capability, and to reduce capacity fading upon cycling. 8-13 For instance, doping of LiNi 0.5 Mn 0.5 O 2 with Co, Al, Ti resulted in decrease of the irreversible capacity loss and in almost no capacity fading of the doped electrodes. 14,15 In a systematic study of the Al-doped Ni-rich electrodes (LiNi 0.8 Co 0.15 Al 0.05 O 2 ), which are promising materials for use in batteries for electromotive applications, the authors have shown high cycling stability of these electrodes upon accelerated testing. 16 Several other doping metals, such as silver, magnesium, cobalt, gallium, lanthanum, bismuth, 17-19 as well as non-metallic ions (boron, fluorine), 20,21 were also explored in an attempt to increase the electrochemical cycling behavior of cathodes (both of layered and spinel structures) and to reduce their in...