Prussian Blue Analogue (PBA)-Zn aqueous batteries are attractive because of the high potential of PBA against Zn (~1.7 V), relative safety of the system, and high rate capability. But, despite the long cycle life of PBA half-cells, full PBA-Zn battery systems studied thus far have typically reported only up to 100 cycles and suffer significant capacity fade beyond that. In this work we demonstrate that the loss in capacity retention and cycle life is a combined effect of Zn 2+ ion poisoning at the PBA cathode, as well as dendrite formation in the zinc anode. We address both these issues via the use of a dual ion (Na + as the primary charge carrier) electrolyte and hyper-dendritic Zinc (HD Zn) as the anode. The copper hexacyanoferrate (CuHcf) vs. HD Zn system with Na + ion electrolyte demonstrated herein exhibits 90% (83%) capacity retention after 300 (500) cycles at a 5C rate and a 3% reduction in usable capacity from 1C to 5C. Detailed characterization is done using in situ synchrotron energy-dispersive XRD (EDXRD), conventional XRD, XPS, SEM, TEM, and electrochemical techniques.

h i g h l i g h t s g r a p h i c a l a b s t r a c t Electrochemical behavior of the LieBi system was investigated for liquid metal cells. Lithium insertion kinetics in liquid bismuth were studied in a threeelectrode cell. LijLiCleLiBrjBi cells showed long life, high efficiency, and low fade rate. System scalability demonstrated in prototypes with 10 and 100 times original capacity. Robustness shown by cooling to solidify cell, followed by heating and recycling. a b s t r a c tIn an assessment of the performance of a LijLiCleLiFjBi liquid metal battery, increasing the current density from 200 to 1250 mA cm À2 results in a less than 30% loss in specific discharge capacity at 550 C. The charge and discharge voltage profiles exhibit two distinct regions: one corresponding to a LieBi liquid alloy and one corresponding to the two-phase mixture of LieBi liquid alloy and the intermetallic solid compound, Li 3 Bi. Full cell prototypes of 0.1 Ah nameplate capacity have been assembled and cycled at 3 C rate for over a 1000 cycles with only 0.004% capacity fade per cycle. This is tantamount to retention of over 85% of original capacity after 10 years of daily cycling. With minimal changes in design, cells of 44.8 Ah and 134 Ah capacity have been fabricated and cycled at C/3 rate. After a hundred cycles and over a month of testing, no capacity fade is observed. The coulombic efficiency of 99% and energy efficiency of 70% validate the ease of scalability of this battery chemistry. Post mortem cross sections of the cells in various states of charge demonstrate the total reversibility of the Li 3 Bi solid phase formed at high degrees of lithiation.

a b s t r a c tPrussian blue analogue (PBA) material is a promising cathode for applications in Na-ion and K-ion batteries which can support high c-rates for charge and discharge. In this study, the material of composition [K 2 Cu II Fe II (CN) 6 ] was synthesized and its structural and electrochemical redox behavior was investigated with 5 different alkali insertion cations (Li + , Na + , K + , Rb + , Cs + ). Galvanostatic measurements indicate that the redox potential strongly depends on the ionic radius of the inserted cation. The redox potential varies by ∼400 mV between using Li + (0.79 Å ) or Cs + (1.73 Å ) in the electrolyte. The underlying modification of the Fe 2 + /Fe 3 + redox potential in PBA is proposed to be due to the weakening of the Fe-C bond in the material. This hypothesis is supported by XRD measurements which reveal that the lattice parameter of the de-intercalated host structure follows the same trend of monotonic increase with the cation size. The relatively minor volume changes accompanying the redox (1.2%-2.4%) allow the PBA to accommodate differently sized cations, although the structural hindrances are quite pronounced at high c-rates for the larger ones (Rb + and Cs + ). Cycle aging studies indicate that the minimum capacity fade rate is observed in case of K + and Rb + containing electrolyte. The peak intensity corresponding to the [220] crystallographic plane varies depending on the state of charge of PBA, since this plane contains the insertion cations. Owing to the sensitivity of the redox potential to the insertion cation coupled with the observed fast ion-exchange ability, the PBA material may find additional analytical applications such as ion sensing or filtration devices.

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Organic materials such as polyanthraquinone sulfide (PAQS) are receiving increased attention as electrodes for energy storage systems owing to their good environmental compatibility, high rate capability, and large charge-storage capacity. However, one of their limitations is the solubility in organic solvents typically composing the electrolytes. Here, the solubility of PAQS was tested in 17 different solvents using UV/Vis spectroscopy. The results show that PAQS exhibits a very wide range of solubility according to the nature of the solvent and the obtained trend agrees well with the predictions from Hansen solubility analysis. Furthermore, the transport properties (conductivity, σ, and viscosity, η) of selected electrolytes composed of non-solubilising solvents with 1 m LiTFSI are compared and discussed in the temperature range from -40 °C to 80 °C. In the second part of this study, the electrochemical characterization of PAQS as electrode material in selected pure or mixture of solvents with 1 m LiTFSI as salt was made in half-cells by a galvanostatic method. In a methylglutaronitrile (2MeGLN)-based electrolyte that exhibits low solubility of PAQS, it appears that the capacity fade is intricately linked to the large irreversibility of the second step of the redox process. Although the standard cyclic carbonate solvents mixture (ethylene carbonate and propylene carbonate) led to rapid capacity fade in the initial 10-15 cycles owing to their high solubilising ability. Finally, it is shown that a pure linear alkylcarbonate (dimethyl carbonate) or binary mixture of ether-based (dioxolane/dimethoxy ethane) electrolyte is much more compatible for enhanced capacity retention in PAQS with more than 120 mAh g for 1000 cycles at 4 C.

Atomistic simulation techniques are used to perform a comparative study of intrinsic defects, dopant incorporation and protonic groups in two lanthanum phosphate compounds, namely, the orthophosphate (LaPO 4 ) and the ultraphosphate (LaP 5 O 14 ). The suitability of dopant incorporation predicted from the dopant solution energies (with Ca and Sr the most favorable) is in excellent agreement with trends in ionic conductivity from recent experimental investigations. The defect chemistry of the phosphates related to protonic defects and oxygen vacancies created from extrinsic doping is investigated. The results indicate favorable orientations for the protonic defect within the structures. The binding energies for proton-dopant interactions indicate that defect association may occur. In LaPO 4 it was observed that the relaxed local atomic structure around an oxygen vacancy is analogous to the formation of a P 2 O 7 pyrophosphate anion.

One of the primary causes of aging in supercapacitors are the irreversible faradaic reactions occurring near the operating-voltage limit that lead to the production of gases resulting in device swelling, increased resistance, and lowering of the capacitance. In this study, a protic deep eutectic solvent (DES) consisting of mixture of lithium bis(fluorosulfonyl)imide (LiFSI) with formamide (FMD) as H-bond donor (x =0.25; C=2.5 m LiFSI) is investigated as electrolyte for activated carbon (AC)-based electrical double layer capacitors (EDLCs). Characterization of the viscosity, conductivity, and the ionicity of the electrolyte in a wide range of temperatures indicates >88 % salt dissociation. In situ pressure measurements are performed to understand the effect of cycling conditions on the rate of gas generation, quantified by the in operando pressure variation dP/dt. These measurements demonstrate that about 25 % of the faradaic reactions leading to gas generation are electrochemically reversible. Cell aging studies demonstrate promising potential of the LiFSI/FMD as a protic electrolyte for AC-based EDLCs and high energy density close to 30 Wh kg at 2.4 V.

Current proton exchange membranes (PEM) are based on polymeric materials such as perfluorosulfonic acid (Nafion™), which have an upper limit to their temperature of operation (<100°C). To overcome this limitation, ceramic PEM materials are being investigated for transportation applications, where operating temperatures in the range of 200°–600°C are desired. In this study, the conductivity behavior of lanthanum orthophosphate (LaPO4) has been compared and contrasted with lanthanum ultraphosphate (LaP5O14) in order to better understand crystal structure—proton conduction relationships in ceramic materials. The conductivity of the lanthanum phosphates (doped and undoped) was measured using impedance spectroscopy in the temperature range 300°–600°C. The conductivity of 5 mol% Sr2+‐doped LaP5O14 (1.01 × 10−4 S/cm, 600°C) was found to be an order of magnitude higher than similarly doped LaPO4 (7.00 × 10−6 S/cm, 600°C), which is a well‐investigated proton conducting material. In addition, it was observed that the activation energy for protonic conduction was much lower for doped LaP5O14 (0.80 ± 0.01 eV) as compared with LaPO4 (1.09 ± 0.01 eV). A hypothesis relating the oxygen‐to‐oxygen ion distance in a material to the activation energy for proton conduction is presented and the experimental results obtained have been critically examined on the basis of the hypothesis and other relevant literature. From this analysis, it is shown that the condensed nature of the phosphate anion in LaP5O14 can provide low‐energy avenues for proton transport within the material leading to enhanced conductivity in the material. Limitations of the currently proposed model for proton conduction along with some other plausible explanations for the conductivity enhancement have also been discussed.