Academic literature on the topic 'Multi-valent batteries'

Research and development works in the field of multi-valent metal-ion batteries are intensified these days because of the abundance of multi-valent elements such as magnesium, aluminum, calcium and so on in the Earth’s crust. Magnesium-ion batteries are particularly important, because they have high theoretical volumetric capacity (3832 mAh cm-3) compared to that of well-known lithium-ion batteries (2062 mAh cm-3). However, there are potential challenges, typically, designing suitable electrolytes with sufficient ambient temperature ionic conductivities is a major challenge. In this work, a set of gel-polymer electrolytes based on poly (ethylene oxide) (PEO) host polymer and magnesium acetate (Mg(CH3COO)2) ionic salt have been synthesized and characterized by electrochemical impedance spectroscopy (EIS), DC polarization and linear sweep voltammetry (LSV) techniques. Among the compositions studied in this work, the optimized PEO-Mg(CH3COO)2-EC-PC electrolyte (6:14:40:40 wt.%) showed an ambient temperature ionic conductivity of 6.1x10-5 S cm-1. Ionic conductivity vs inverse temperature showed Arrhenius behavior with almost same activation energies (0.15 - 0.18 eV) for all the compositions. DC polarization studies performed with stainless steel blocking electrodes under an externally applied voltage of 1V showed that the highest conducting composition is dominantly an ionic conductor with an ionic transference number of 0.99. The electronic contribution to conductivity was found to be almost negligible, which is desirable to avoid short circuits within the cell. The LSV test on highest conducting composition revealed that the electrochemical stability window of these electrolytes is about 2.2 volts.

A new phenomenon of Li electrochemical (de)intercalation on the pure mineral clay materials has been evidenced for the first time. These tests are initialized by the idea of putting an electronic conducting polymer or a multi-valent metal oxide in the layer of the clay to modify the electronic properties and also to modulate the charge and discharge potential of the clay during the Lithium electrochemical (de)intercalation processing. In this paper, as the beginning of our research, we will first show the results of Lithium electrochemical charge and discharge processes on pure clay materials.

Because of their broad range of applications, electrochemical energy storage devices are the subject of a growing field of science and technology. Their unique features of high practical energy and power densities and low prices allow mobile and stationary applications. A large variety of electrochemical systems has been tailored for specific applications: Lithium-ion batteries for example have been optimized for mobile applications ranging from mobile phones to electric vehicles. On the other hand, sodium-sulphur accumulators – among others – have been developed for stationary applications to account for the capricious nature of renewable energies. Chemistry, physics and materials science have led to the optimization of existing cell-chemistries and the development of new concepts such as all-liquid or all-solid state batteries as well as high-energy density metal-air batteries. The aim of the BMBF (Federal Ministry of Education and Research, Germany)-financed project "CryPhysConcept" is to develop new concepts for electrochemical energy storage applying a crystallographic approach. First, a categorization of the main solid components of batteries based on their underlying working principles is suggested. Second, an algorithm for the identification of suitable new materials and material combinations, based on economical, ecological and material properties as well as crystallographic parameters, is presented. Based on these results, new concepts using multi-valent metal ions are proposed. Theoretical as well as experimental results including an iron-ion approach are presented.

Rechargeable aqueous zinc-ion batteries (ZIBs) have attracted much attention recently due to the high abundance, low cost, high theoretical capacity up to 820 mAh g-1 with multi-valent charge carrier, and compatibility with aqueous electrolyte of the zinc anode.[1] Especially, the introduction of neutral or mild acidic electrolyte greatly improves the reversibility of zinc anode compared to conventional alkaline ZIBs.[2] Among all the cathode candidates, MnO2 is most attractive due to its relatively high energy density, low toxicity and low cost.[3] However, MnO2 electrode suffers from capacity fading during cycling mainly due to Mn dissolution and structural change. The addition of Mn2+ into the mild acidic electrolyte is a common method to suppress Mn dissolution.[4] Other strategies like structural design and surface coatings are also developed to suppress Mn dissolution.[5, 6] Though the cycle performance still cannot meet the demand of application, as the irreversible formation of inactive ZnMn2O4 during cycles still requires to be tackled. Here, we proposed Bi2O3 as a facile electrode additive in the electrode to suppress ZnMn2O4 formation and improve the cyclability of commercial electrolytic manganese dioxide (EMD). XRD, in-situ pH measurements and ICP tests suggest that inactive ZnMn2O4 is formed upon cycling due to the interaction between MnO2 and zincate ions in the electrolyte from localized increase in pH, and Bi2O3 dissolves into the electrolyte in the presence of zincate ions and forms a complex with the zincate ions to suppress the reaction pathway. A high capacity of 269 mAh g-1 is maintained at 100 mA g-1 after 50 cycles with a capacity retention of 91.5% when EMD with 10 wt% of Bi2O3 is tested in ZnSO4 electrolyte without Mn2+ additive. Combining both Bi2O3 electrode additive and Mn2+ electrolyte additive, EMD can maintain a stable capacity of 190 mAh g-1 for 1000 cycles at 1000 mA g-1 (about 3.3C). More characterizations are underway to further understand the role of Bi2O3 and the results will be shown during the meeting. Reference: [1] B. Tang, L. Shan, S. Liang, J. Zhou, Issues and opportunities facing aqueous zinc-ion batteries, Energy & Environmental Science, 12 (2019) 3288-3304. [2] J. Hao, X. Li, X. Zeng, D. Li, J. Mao, Z. Guo, Deeply understanding the Zn anode behaviour and corresponding improvement strategies in different aqueous Zn-based batteries, Energy & Environmental Science, 13 (2020) 3917-3949. [3] N. Zhang, X. Chen, M. Yu, Z. Niu, F. Cheng, J. Chen, Materials chemistry for rechargeable zinc-ion batteries, Chemical Society Reviews, 49 (2020) 4203-4219. [4] H. Pan, Y. Shao, P. Yan, Y. Cheng, K.S. Han, Z. Nie, C. Wang, J. Yang, X. Li, P. Bhattacharya, Reversible aqueous zinc/manganese oxide energy storage from conversion reactions, Nature Energy, 1 (2016) 1-7. [5] J. Huang, Z. Wang, M. Hou, X. Dong, Y. Liu, Y. Wang, Y. Xia, Polyaniline-intercalated manganese dioxide nanolayers as a high-performance cathode material for an aqueous zinc-ion battery, Nature communications, 9 (2018) 1-8. [6] B. Wu, G. Zhang, M. Yan, T. Xiong, P. He, L. He, X. Xu, L. Mai, Graphene scroll‐coated α‐MnO2 nanowires as high‐performance cathode materials for aqueous Zn‐ion battery, Small, 14 (2018) 1703850. Figure 1

Recently, new types of cation disordered rocksalt (DRS) have been reported which show good reversibility. In our study we combined the strategy of using high-valent cations with partial substitution of fluorine for oxygen anions in disordered rocksalt-structure phase to achieve optimal Mn2+/Mn4+ double-redox reaction in the composition system Li2MnxTi1-xO2F (1/3 ≤ x ≤ 1). we synthesized 4 different compositions (Li2MnIIIO2F, Li2MnII 1/3MnIII 1/3TiIV 1/3O2F, Li2MnII 1/2TiIV 1/2O2F and Li2MnII 1/3TiIII 1/3TiIV 1/3O2F). Two of them were synthesized for the first time, Li2MnII 1/3MnIII 1/3TiIV 1/3O2F and Li2Mn II 1/3TiIII 1/3TiIV 1/3O2F. By studying the electrochemical properties of different compounds we found that Ti+4 in the structure keeps Mn at the second state of charge, thus enabling a double redox reaction of Mn2+/Mn4+. By investigating the electrochemical properties of all samples we found that the sample with the composition Li2Mn2/3Ti1/3O2F showed the best electrochemical properties with initial high discharge capacity of 227 mAh g-1 in the voltage window of 1.5-4.3 V and 82% of capacity retentionafter 100 cycles. However, fluorination might lead to several issues such as synthesis limitation, lithium diffusion issues due to preferable strong Li-F bonds, etc. thus, two more different samples based on the Li2Mn2/3Ti1/3O2F composition were synthesized and their properties were investigated (Li1.5MnII 1/3MnIII 1/3TiIV 1/3O2F0.5 and Li1.25MnII 1/3MnIII 1/3TiIV 1/3O2F0.25) in order to find the proper amount of fluorine in the structure which promises the electrochemical behavior. In the following the effect of fluorine on lithium diffusion was investigated by ex-situ Raman studies. These studies shed light on the diffusion pathways of lithium ions during charge and discharge process. The structural characteristics are examined using X-ray diffraction patterns, Rietveld refinement, energy-dispersive X-ray spectroscopy and scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The oxidation states and charge transfer mechanism are also studied further using extended X-ray absorption fine structure and X-ray photoelectron spectroscopy in which the results approve the double redox mechanism of Mn2+/Mn4+ in agreement with Mn-Ti structural charge compensation. The findings pave the way for designing high capacity electrode materials with multi-electron redox reactions. References: [1]: Chen, R.; Ren, S.; Knapp, M.; Wang, D.; Witter, R.; Fichtner, M.; Hahn, H., Disordered Lithium‐Rich Oxyfluoride as a Stable Host for Enhanced Li+ Intercalation Storage. Advanced Energy Materials 2015, 5, (9), 1401814. [2]: Lee, J.; Kitchaev, D. A.; Kwon, D.-H.; Lee, C.-W.; Papp, J. K.; Liu, Y.-S.; Lun, Z.; Clément, R. J.; Shi, T.; McCloskey, B. D., Reversible Mn 2+/Mn 4+ double redox in lithium-excess cathode materials. Nature 2018, 556, (7700), 185-190.

Hexacyanoferrates and related cyanometallates exhibit model electron transfer properties that are of importance to many electrochemical and related applications. In particular homo- and heterometallic cyanide bridged networks and derived materials have proven to exhibit very rich and diverse electrochemical properties. Their redox properties can be tuned by adjusting stoichiometry and oxidation state of the constituent metal centers, incorporation of interstitial ions, or preparation methods. Polynuclear cyanometallates are promising open-framework systems for low-cost electrochemical energy storage applications. Both soluble and insoluble analogues of Prussian blue have been explored as cathode materials with lithium, sodium, potassium, magnesium, calcium, and even zinc intercalated ionic carriers. Electrochromic devices are another promising area for employing the unique properties of cyanometallates. Prussian blue itself exhibits electrocatalytic properties toward hydrogen peroxide, and it has been used for biosensing and amperometric detection of glucose, L-cysteine, and glutamate. Also removal of radioactive cesium ions from contaminated water has been successfully achieved with Prussian blue and its metal substituted analogues. It is well-established that the choice of redox-active charge-storage material has a significant impact on the performance of a redox flow battery. The concentration of redox centers and their reaction kinetics have an influence on the available current densities and, thus, the power of the device. Remembering the requirement of good solubility of redox species, the semi-solid slurry approach (provided that the dispersion is homogeneous) represents another effective way to improve the volumetric capacity of the redox electrolyte (i.e. of the electrolyte with dissolved redox couples). An interesting approach to improve current densities involves application of circulating suspensions of electroactive materials. Prussian blue and its metal (Fe, Co, Ni, etc.) substituted analogues, which are electroactive mixed-valence inorganic systems, exhibit very rich and diverse electrochemistry. Their electrochemical properties that can be tuned through the variation of the material composition. Special attention will be paid to the formation of stable colloidal suspensions of truly mixed-valence fast-conducting Berlin Green, iron(III) hexacyanoferrate(III,II), together with multi-layered clay-like nickel(II) hexacyanoferrate(III) structures characterized by fast potassium counter-cation motion. It can be hypothesized that the proposed system could serve as the catholyte redox suspension containing large population of mixed-valence redox centers and capable of fast charge propagation and, consequently, yielding fairly large current densities. The materials can also be explored for sorption of large concentrations of Zn2+ ions and for the improvement of the Zn2+/Zn chemistry. While the application of Zn2+/Zn as the anode active system is well established in redox flow batteries, we are going to address and minimize limitations that include the efficiency of zinc deposition and the hydrogen evolution reaction taking place at the potentials where Zn is electrodeposited. The increase of current density could be achieved not only by reducing the viscosity of the electrolyte, thus accelerating charge-carrier transport, but also – by referencing to our experience with mixed-valent nickel hexacyanoferrate system as charge relay for dye-sensitized solar cells – through improvement of the dynamics of charge propagation by improving mobility of charge compensating counter-ions.