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A new family of fluorine-free solid-polymer electrolytes, for use in sodium-ion battery applications, is presented. Three novel sodium salts withdiffuse negative charges: sodium pentacyanopropenide (NaPCPI), sodium 2,3,4,5-tetracyanopirolate (NaTCP) and sodium 2,4,5-tricyanoimidazolate (NaTIM) were designed andtested in a poly(ethylene oxide) (PEO) matrix as polymer electrolytes for anall-solid sodium-ion battery. Due to unique, non-covalent structural configurations of anions, improved ionic conductivities were observed. As an example, “liquid-like” high conductivities (>1 mS cm−1) were obtained above 70 °C for solid-polymer electrolyte with a PEO to NaTCP molar ratio of 16:1. All presented salts showed high thermal stability and suitable windows of electrochemical stability between 3 and 5 V. These new anions open a new class of compounds with non-covalent structure for electrolytes system applications.

We hereby present the new class of ionic liquid systems in which lithium salt is introduced into the solution as a lithium cation−glyme solvate. This modification leads to the reorganisation of solution structure, which entails release of free mobile lithium cation solvate and hence leads to the significant enhancement of ionic conductivity and lithium cation transference numbers. This new approach in composing electrolytes also enables even three-fold increase of salt concentration in ionic liquids.

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Nowadays, technology of the renewable batteries is based on Li-ion technology. Due to development of such technologies, large growth of the marked demands on the batteries of this type is expected. It is due to the intensive impact put on technologies of the electric cars and large-scale batteries dedicated to storage of energy from renewable sources. Unfortunately, global lithium resources, currently estimated at 29 million tonnes, are not sufficient to fulfill these demands. Therefore, studies on batteries which are alternative to lithium-based energy sources are conducted intensively. A natural candidate to replace the lithium is sodium. Standard potential of the Na/Na+ (-2.71 V) is similar to the potential of Li/Li+ (-3.05 V). Sodium is the most abundant alkali metal on Earth’s crust and therefore the above-mentioned problems of the use of the lithium do not occur in case of sodium or Na-ion batteries. Moreover, sodium materials are cheaper than lithium. The first successful attempt to use sodium in batteries took place in 1967, after the discovery of the ionic conductivity of the β-alumina (Na2O·11Al2O3). Sodium cations were responsible for the ionic transport in this system. The ionic conductivity of this material was approximately 10 S/cm at 300°C. As β-alumina does not exhibit electronic conductivity, it was judged as a promising, ceramic electrolyte. On this basis, high temperature, sodium-sulfur battery (with sodium and sulfur as electrode materials) was constructed. The range of the operating temperatures for this battery was 300-400°C, OCV was between 2.1 V and 1.8 V (at the final stage of discharge). Though the good reversibility, the battery did not achieve the commercial success due to high operating temperature, problems related to the corrosion of the electrodes, low safety of use. Also the aspect of the overcharge control remained unsolved, which was of high importance because of very high internal resistance of the fully charged cell. Simultaneously, studies on the Na/NiCl2 battery were conducted. The design of this system was similar to the Na / S cell. The liquid sulfur cathode was replaced by solid nickel chloride. Additionally, an electrolyte intermediate (NaAlCl4) was used in order to enhance contact between the solid cathode and solid electrolyte. This battery was characterized with better safety of use (mainly due to the fact that there was no metal sodium in the battery when it was installed- the anode material was produced at the anode during the first charging) and operated at lower temperatures (250-350°C). Also high OCV (about 2.5 V) was advantage of the proposed battery. Na-NaSICON-S battery, designed in 2000, became real success. The system exhibited very high energy density. On the other hand, the problem of the high temperature of work at which the batteries are working (270-350°C) remained unsolved. High-temperature sodium cells, despite the many benefits are not competitive in many applications. The construction of the power source for the portable device needs to be simple and safe. When application of the battery in the uninterruptible power source (UPS) is taken into consideration, the battery should work no later than 1 s after switching on. These expectations cannot be fulfilled by the high-temperature battery. The idea of the low-temperature sodium battery may be realized by preparing the system which is analog of the lithium anode or Li-ion battery. The main issue deciding on the successful application of the sodium battery is stability of the interface between sodium or Na-ion anode and the electrolyte. This limits possible range of the solvents to the polyethers, as organic carbonates as well as their mixtures are unstable versus metallic sodium and Na-ion anode. In the presentation, we present conductivity and CV results of the Na-based electrolytes. The compositions of the electrolytes were optimized in order to obtain system of highest conductivity. The obtained data were confronted with spectroscopic studies of the system in order to discuss the influence of the salt concentration and temperature on the formation of the various ionic agglomerates.

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Sodium-ion batteries are promising alternative to lithium-ion batteries and a case of study of many researchers. Researches from Warsaw University of Technology are constantly working on modern electrolytes, including NaPDI and NaTDI, that are promising for application in Na-ion batteries due to the easy synthesis path [1]. Also the new methods of electrodes’ active materials synthesis is essential topic of researches. The modification of the conditions of synthesis using wet impregnation method and different way of introduction of Li+ into active material by using various precursors in synthesis leads to changes of properties of the electrodes [2]. A huge issue for Na-ion batteries is finding a suitable anode. A novel idea is using Microwave Plasma Chemical Vapour Decomposition of SbxOy/C to achieve stable anode [3]. Presented research data is based on electrolytes containing imidazole salts and modern cathodes for Na-ion batteries. Due to the conducted measurement, the conductivity of the electrolytes containing NaTDI salt differ due to the used solvents in 0.75 M concentration solutions: 6.61 mS cm-1 in PC, 11.87 mS cm-1 in EC:DMC (1:1) and 15.56 mS cm-1 in EC:DME (1:1) [4]. The knowledge based on many years of experience in research on Li-ion batteries was essential for sodium analogues synthesis, which has promising properties. The optimization of the electrolytes compositions and adjustment of the cells work parameters with the new type of electrodes were a key issue during electrochemical tests. The presentation will be enriched by the determining parameters of the metallic sodium electrode. Also possible application of electrolytes and electrodes will be shown. Studies were funded by ENERGYTECH-1 project granted by Warsaw University of Technology under the program Excellence Initiative: Research University (ID-UB). [1] New Tailored Sodium Salts for Battery Applications, Anna Plewa-Marczewska, Tomasz Trzeciak, Anna Bitner, Leszek Niedzicki, Maciej Dranka, Grażyna Z. Żukowska, Marek Marcinek, and Władysław Wieczorek, Chem. Mater. 2014, 26, 17, 4908–4914 [2] Different strategies of introduction of lithium ions into nickel-manganese-cobalt carbonate resulting in LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode material for Li-ion batteries, Magdalena Zybert,, Hubert Ronduda, Anna Szczęsna, Tomasz Trzeciak, Andrzej Ostrowski,Elżbieta Żero, Władysław Wieczorek, Wioletta Rarog-Pilecka, Marek Marcinek, Solid State Ion. 2020, 348, 115273 [3] Microwave Plasma Chemical Vapor Deposition of SbxOy/C negative electrodes and their compatibility with lithium and sodium Hückel salts—based, tailored electrolytes, A. Bitner-Michalska, K. Michalczewski, J. Zdunek, A.Ostrowski, G. Żukowska, T. Trzeciak, E. Żero, J. Syzdek M.Marcinek, Electrochim. Acta 2016, 210, 395-400 [4] Liquid electrolytes containing new tailored salts for sodium-ion batteries, A. Bitner-Michalska, A. Krztoń-Maziopa, G. Żukowska, T. Trzeciak, W. Wieczorek, M. Marcinek , Electrochim. Acta 2016, 222, 108-115