Abstract: State of the art electrolytes for lithium ion batteries (LIBs) consist of a lithium salt dissolved in a mixture of cyclic and linear carbonates, mainly using ethylene carbonate (EC), dimethyl carbonate (DMC) and/or diethyl carbonate (DEC). Notwithstanding many beneficial properties, e.g. high conductivity and low viscosity, the thermal operation window is limited especially in regards to low volatility and flammability. To overcome well-known drawbacks of carbonate based solvents, alternative solvents are desired to simultaneously expand the operating temperature range, improve the safety and maintain excellent electrochemical performance. As conductive salt, LiPF 6 is still the lithium salt of choice. However, it suffers from drawbacks related to trace amounts of water as well as its decomposition at high temperatures. Lithium bistrifluoromethanesulfonimide (LiTFSI) represents a promising alternative salt for LIB technology to possibly overcome the aforementioned challenges. However, an additional challenge in LITFSI based electrolytes is set on the dissolution of the aluminum current collector at already moderate potential values ( 〈 4V vs. Li/Li + ) when using carbonate based solvents. The goal of our research was to develop new safer electrolyte formulation based on non-carbonate based single solvents with LiPF 6 or LiTFSI as conducting salt. In this work, an ester functional group was introduced to the nitrile molecular structure to support salt dissociation and to enhance the compatibility towards lithium metal and graphite based anodes. The basic framework for the possible structures was either R1-COO-R2, whereas two different linkages of the nitrile moiety were possible. In the first one, nitrile functionality is positioned on the acid part of the ester, whereas in the second it is situated on the alcohol part. In order to select the best possible combination of ester and nitrile moieties, a computational screening by means of theoretical calculations of the main physical and electrochemical properties was preceded. Over 2000 possible structures were calculated in regards to important parameters namely viscosity and pkA value as well as the melting point. All possible molecules were divided into the two possible linkages. Methyl 3-cyanopropanoate (MCP) and, methyl 2-cyano-2-methylpropionate (MCMP) were identified as the two most promising candidates for the acid linkage. Two additional compounds, namely methyl cyanoacetate (MCA) and ethyl-2-cyano-2-methylpropionate (EMCP) were included for better evaluation of the results obtained by theoretical calculations. For the second possibility, three molecules were synthesized, namely 2-cyanoethyl acetate (CEA), 2-cyanoethyl 2,2,2-trifluoracetate (CFA) and 2-cyanopropan-2-yl acetate (CYA) as depicted in Figure 1. In the frame of this work, the newly proposed electrolyte solvents were analyzed in regards to their liquid window, viscosity and conductivity. In our study, a very good agreement between theoretical and experimental results was obtained. Additionally, all possible solvents were screened with respect to their compatibility to graphite based anodes. We found that it is necessary to use a film-forming additive. This study showed that possible acid linked candidate proved to be MCP and the best alcohol linked proved to be CEA, which were not the ideal candidates in regards to their physicochemical properties. After having identified the two most suitable candidates, experiments in full cell setups with 4 V cell chemistry were performed. As we used a single solvent approach, the obtained results were compared with 1 M LiPF 6 in PC based electrolytes containing FEC as film forming additive and additionally to a state of the art electrolyte: 1 M LiPF 6 in EC:DMC (1:1 by wt.). These experiments showed that at moderate cycling rates of 1 C the proposed electrolytes perform comparable to the carbonate based electrolytes. To further evaluate the thermal properties of the electrolytes, Heat-wait-search (HWS) tests were performed to determine the onset temperature value for a thermal runaway. Furthermore, the compatibility of MCP and CEA with the alternative conductive salt LiTFSI was investigated, showing that the cyanoester based solvents show negligible to no corrosion behavior on the aluminum current collector in comparison to the carbonate based solvents. In conclusion, we present a complete study obtained from selected theoretical calculations of a promising new class of solvents for the implementation of MCP and CEA in full cell set-up as possible alternative solvents for LiPF 6 and LiTFSI. Comparable thermal and electrochemical behavior in comparison to a one solvent carbonate based system and better thermal behavior in comparison to a two solvent carbonate based system was recognized. Figure 1

Abstract: Ni 1/3 Co 1/3 Mn 1/3 O 2 (NCM) cathode material can be charged to different potentials. When using the standard salt LiPF 6 , elevated cutoff potentials lead to increased energy densities and better energy quality, but reduce the cycle life dramatically. Metal dissolution is catalyzed by acids, like HF, derived from deterioration of the salt. To exclude the influence of HF, next to LiPF 6 the less hydrolysis sensitive LiBF 4 and the fluorine-free conducting salt LiClO 4 were investigated. To determine the metal dissolution behavior of NCM, these electrodes were stored in 1 M EC/DMC (1/1, by wt.) electrolyte containing different salts for 28 days at different states of charge. The measurement of metal ion content was carried out by inductively coupled plasma/optical emission spectrometry (ICP-OES) technique. Constant current cycling experiments were performed with different charge potential limits. In contrast to LiPF 6 , LiBF 4 showed suppressed metal dissolution and superior cycling performance with low capacity fading even at high cutoff-potentials (4.6 V vs. Li/Li + ). At low potentials, metal dissolution, as well as capacity fading, is rather low for LiClO 4 but escalates at potentials above 4.4 V vs. Li/Li + .

Abstract: Increasing energy consumption, shortages of fossil fuels, and concerns about the environmental impact of energy use, especially emissions of carbon dioxide, give fresh impetus to the development of renewable energy sources. However, many renewable energy sources, such as solar photovoltaic and wind are unavailable during extended periods of time. The generated power from these sources is always fluctuating due to the environmental status. Hence, with the advent of renewable energy, it is now indispensable that efficient energy storage systems are developed. One of the most promising storage systems to be employed in stationary energy storage applications are lithium-based batteries (LIB), mainly due to their high energy density, high power, and nearly 100% efficiency. The speed and scope of research and development of LIB make it critical for researchers to be aware of the progress in this field across different laboratories. Thus, in a first step, we aim at giving a general overview on the research activities in the field of LIB. To this end, we conduct a patent search on LIB and their main components. We identify the main fields of patent activity in LIB and give an overview on the state-of-the-art in LIB technology. In a second step and based on our first findings, we aim at forecasting possible future research trends among the various battery components, main materials, and dominant designs used in LIB.

Abstract: In order to increase the energy density of lithium ion batteries, lithium metal is an attractive anode material based on its high specific capacity and low electrochemical potential. However, a major drawback of lithium metal anodes comprises dendrite growth due to unstable solid electrolyte interphase (SEI) resulting in severe safety hazards. Polymer electrolytes constitute a viable alternative to commonly utilized liquid electrolytes and are able to suppress or even avoid dendrite growth thereby providing increased safety. In particular, single ion conducting polymer electrolytes are promising for application in lithium ion or lithium metal batteries. In contrast to common dual ion conducting electrolytes, single ion conductors afford high transference numbers, hence significantly reducing polarization effects as only lithium ions are mobile whereas anions are bound at the polymer backbone. In this contribution we present various single ion conducting polymers composed of AB-type alternating block copolymers in which the lithium ions are bound to the backbone (e.g., bis(4-carboxyl benzene sulfonyl)imide moieties). Systematic variation of the constituents can control the achievable properties including the morphology, electrical and electrochemical properties of the resulting polymers. The electrolyte membranes fabricated for application in lithium meatal batteries are blends of single ion conducting aromatic polymers and a flexible linear polymer such as poly(vinylidene fluoride-co -hexafluoropropylene (PVDF-HFP). The appropriate ratio of the polymer blends is evaluated to yield membranes (swollen with thermally stable solvent solutions of ethylene carbonate and propylene carbonate (EC: PC, 1:1, v/v)), with increased ionic conductivity, reduced solvent uptake as well as sufficient flexibility and mechanical stability as well as reduced solvent uptake. We present optimized routes for the synthesis of single ion conducting polymers and suitable membrane compositions. Furthermore, feasible relations of both structural and physicochemical properties of the polymer membranes are discussed, particularly with respect to underlying ion transport properties or transport mechanisms, in this way potentially enabling controlled modification or adjustment of either the chemical structures or electrochemical properties of the polymer membranes. A morphology analysis is performed using small angle X-ray scattering (SAXS), while nuclear magnetic resonance spectroscopy (NMR) and electrochemical data including impedance as well as dielectric loss spectra are combined to unravel the major ion transport mechanisms and ion mobility in addition to ionic conductivity, complex permittivity, self-diffusion coefficients and transference numbers. Both the oxidative and reductive stability as well as cycling performance in NMC/ lithium metal cells are also presented. Profound understanding of the ion transport mechanisms and property relations in single ion conducting polymer electrolyte membranes is essential and will allow to design future electrolyte membranes having desired properties. Thereby, the requirement for different applications can be met and the application of safe and highly performing lithium metal batteries can be enabled.

Abstract: Abstract not Available.

Abstract: In pursuit of higher energy density in lithium-ion batteries, the general approach is focused on cathode materials that operate at high voltages and exhibit even higher specific charges. To enable the high-voltage application of the cathode, the electrolyte interface needs to be either thermodynamically or kinetically stable. For this reason, the stability of the electrolyte components towards oxidation, in particular, depending on their HOMO energy levels, is crucial. The theoretical calculation of the molecular orbital energies is a helpful and commonly used tool to predict the electrochemical stability[1]. Earlier studies demonstrated strong correlation between the HOMO energy and the pK a value, as both are depending on the electron affinity[2]. Having this in mind, here we report on the first study referring to a pK a value based selection procedure on development of new electrolyte components for the application in lithium-ion batteries. The identified trimethylsilyl(TMS)-based additives, which are known to scavenge HF and show sufficient oxidative stability, enable the application of LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) at an increased upper cut-off potential of 4.6 V vs. Li/Li + without severe degradation, leading to a 50% higher energy density[3]. The selected electrolyte additives were calculated by Hartee-Fock based molecular orbital energy calculations in respect to relevant electronic parameters, and were characterized by linear sweep voltammetry experiments on LiMn 2 O 4 (LMO) and constant current cycling experiments in NCM as well as in graphite half-cells. Furthermore, the reaction mechanism was investigated by impedance, SEM, XPS, NMR, GC-MS and ICP-OES techniques. The results reveal that the pre-selection of electrolyte additives by pK a value is a promising approach to identify suitable electrolyte components with high electrochemical oxidation stability. Several TMS-based electrolyte additives, which can considerably improve the capacity retention of NCM cathodes during cycling at high-voltage conditions from 53% (after 50 cycles, 1 M LiPF 6 in EC/DMC electrolyte) up to 99% in the same electrolyte containing 1wt-% of TMS based additive, were identified. Due to a higher stability towards oxidation, better leaving group ability and the formation of a more effective cathode passivation layer (CEI), the capacity retention increases with lower pK a value of the leaving group of the TMS based additives. The aforementioned findings provide new insights into the structure-property relationship of certain electrolyte additives, supporting the improvement of the prospective selection procedure of new electrolyte components in lithium-ion battery research. References: [1] Y.-K. Han, K. Lee, S.C. Jung, Y.S. Huh, Computational and Theoretical Chemistry, 1031 (2014) 64-68. [2] H.J. Soscún Machado, A. Hinchliffe, Journal of Molecular Structure: THEOCHEM, 339 (1995) 255-258. [3] D.R. Gallus, R. Schmitz, R. Wagner, B. Hoffmann, S. Nowak, I. Cekic-Laskovic, R.W. Schmitz, M. Winter, Electrochim Acta, 134 (2014) 393-398.

Abstract: Compared to the actual state of the art electrolyte (SOTA) for lithium ion batteries (LIBs), a novel electrolyte with better safety and lower costs and at the same time equal electrochemical performance was developed and investigated in this work. This electrolyte consists of a mixture of γ-Butyrolactone (GBL) as a solvent with fluoroethylene carbonate (FEC) as solid electrolyte interphase (SEI) additive and lithium tetrafluro borate (LiBF 4 ) as electrolyte salt. Raman spectroscopy measurements indicated that the salt is completely dissociated by the solvent GBL which is the reason for the enhanced ionic conductivity compared to the SOTA electrolyte. The oxidation stability of this mixture is sufficient for the use in actual LIBs. Cyclic voltammetry with a T44 graphite electrode revealed the positive influence of the SEI additive FEC. The addition of FEC (1 % by wt.) enabled fully reversible de-/ intercalation of lithium ions into graphite. Furthermore, 1 M LiBF 4 in GBL + FEC (1 % by wt.) improved the coulombic efficiency of T44 graphite in the first cycle of constant current cycling experiments and in addition, no capacity fading was observed after 50 cycles. On NCM electrodes a stable cycling was observed as well, obtaining similar performance compared to the SOTA electrolyte, even at an increased cut-off potential of 4.6 V vs. Li/Li + .