Ralf Wagner

University of Münster | WWU · Institute of Physical Chemistry, MEET battery research center

In this work, we investigate the electrochemical and safety performance of the glyoxalic acyclic acetals, namely 1,1,2,2-tetramethoxyethane (TME) and 1,1,2,2 tetraethoxyethane (TEE) as substituted solvents for linear organic carbonates in propylene carbonate (PC)-based electrolytes in LiNi0.6Mn0.2Co0.2O2∣∣graphite cells. By means of conductivity me...

Due to its well-balanced properties, lithium hexafluorophosphate (LiPF6) remains the most widely adopted conducting salt in state-of-the-art non-aqueous, aprotic liquid electrolytes used in lithium ion batteries (LIBs). However, the relatively high reactivity of LiPF6 can cause issues such as bulk electrolyte deterioration including formation of to...

Modelling and numerical simulations play a vital role in the design and optimization of electrochemical energy storage devices. In this study, a general physics-based model is developed to describe Hybrid Asymmetric Capacitors (HACs). A one-dimensional cell is constructed with one faradaic electrode, a separator and a capacitive electrode. The mode...

Compared to the commercially used state-of-the art non-aqueous organic carbonate solvent-based electrolytes, acetonitrile (AN)-based electrolytes have the advantage of enabling higher conductivity and lower viscosity values. The beneficial influence of adding fluoroethylene carbonate (FEC), thus enabling AN compatibility with graphite anodes, in di...

Energy storage is considered a key technology for successful realization of renewable energies and electrification of the powertrain. This review discusses the lithium ion battery as the leading electrochemical storage technology, focusing on its main components, namely electrode(s) as active and electrolyte as inactive materials. State-of-the-art...

State-of-the-art (SOTA) liquid electrolyte/polyolefin separator setups used in lithium ion batteries suffer from the hazard of leakage and high flammability. To address these issues, phosphonate, a flame retarding moiety, is chemically bonded to a polymer matrix to fabricate a non-flammable gel polymer electrolyte (GPE). The obtained phosphonate-ba...

A poly(vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP)-based gel polymer electrolyte (GPE) containing propylene carbonate (PC)-based liquid electrolyte was developed to enhance the safety performance of LiNi0.5Mn0.3Co0.2O2/graphite (NMC532/graphite) lithium ion batteries. The PC-based liquid electrolyte (PEV-LE) consists of 1 mol L⁻¹ LiPF6...

Energy storage is considered a key technology for successful realization of renewable energies and electrification of the powertrain. This review discusses the lithium ion battery as the leading electrochemical storage technology, focusing on its main components, namely electrode(s) as active and electrolyte as inactive materials. State-of-the-art...

It is widely accepted that for electric vehicles to be accepted by consumers and to achieve wide market penetration, ranges of at least 500 km at an affordable cost are required. Therefore, significant improvements to lithium-ion batteries (LIBs) in terms of energy density and cost along the battery value chain are required, while other key perform...

In this work, we present a comprehensive study on the influence of lithium phosphorus oxynitride (LIPON) as a possible “artificial SEI layer” on the electrochemical performance of pure silicon (Si) thin film electrodes for a possible application in microbatteries or on-chip batteries. Si thin film anodes (140 nm) with and without an additional amor...

Abstract To improve the intrinsic safety of lithium ion batteries (LIBs) by preventing cells from a thermal runaway, we studied two carbene adduct electrolyte additives. The recently synthesized compounds (1,3-dimethylimidazolidin-2-μm-trifluoroborate (NHC-BF3) and 1,3-dimethylimidazolidin-2-μm-tetrafluorotrifluoromethylphosphate (NHC-PF4CF3)) were...

Increasing specific energy of lithium ion battery cells (LIBs) and their cycle life requires deeper understanding of complex processes taking place during the cell operation. This work focuses on the electrode potential development and the interactions between negative and positive electrode in a quasi LIB full cell by applying over-discharge condi...

Sulfone-based electrolytes, known for their higher oxidative stability compared to the typically used organic carbonate-based electrolytes, are considered promising electrolytes for high voltage cathode materials towards the objective of obtaining increased energy density in lithium ion batteries. Nevertheless, sulfones suffer from high viscosity a...

The electrochemical and thermal stabilities of commonly used LiPF6/ organic carbonate-based electrolytes are still a bottleneck for the development of high energy density lithium ion batteries (LIBs) operating at elevated cell voltage and elevated temperature. The use of intrinsic electrochemically stable electrolyte solvents, e.g. sulfones or dini...

Increasing the specific energy of a lithium ion battery and maintaining its cycle life is a predominant goal and major challenge for electrochemical energy storage applications. Focusing on the positive electrode as the specific energy bottleneck, cycle life characteristics of promising layered oxide type active materials (LiMO2) has been thoroughl...

Increasing the operation voltage of electrochemical energy storage devices is a viable measure to realize higher specific energies and energy densities. A sufficient oxidative stability of electrolytes is the predominant requirement for successful high voltage applicability. The common method to investigate oxidative stability of LIB electrolytes i...

The next generation of lithium ion batteries (LIBs) with increased energy density for large-scale applications, such as electric mobility, but also for small electronic devices, e.g. micro-batteries and on-chip batteries, requires advanced electrode active materials with enhanced specific and volumetric capacities. In this regard, silicon (Si) as a...

The required boost in specific energy of lithium ion battery (LIB) cells can only be achieved by the increase of cell voltage and/or of the electrodes' specific capacities. In the latter regard, the positive electrode constitutes the specific energy bottleneck. Lithium transition metal oxides (LiMO2) like LiNixMnzCo1-x-zO2 (NMC) are regarded as the...

The kinetic stabilization of the cathode/electrolyte interface is essential to enhance cycle life and safety of lithium-ion batteries at high voltage application. The addition of only 2 wt.% Mg powder to the cathode slurry were found to significantly increase the cycle life of LiNi1/3Co1/3Mn1/3O2/Li half cells upon cycling to 4.6 V vs. Li/Li⁺, in t...

The further development of lithium ion batteries operating at high voltages requires basic understanding of the occur-ring capacity fade mechanisms. In this work, the overall specific capacity loss with regard to reversible and irreversible processes for LiNi1/3Co1/3Mn1/3O2 (NCM111)/Li half cells, cycled at a charge cut-off potential of 4.6 V vs. L...

Allylboronic acid pinacol ester (ABPE) was investigated as shutdown overcharge additive to increase the intrinsic safety of lithium ion cells during operation at elevated charge cutoff potentials up to 4.5 V vs. Li/Li+. It was demonstrated that the additive had no negative influence on the cycling performance of LiNi1/3Co1/3Mn1/3O2 (NMC-111)/graphi...

The long-term influence of the most commonly used conducting salt in electrolyte formulations, lithium hexafluorophosphate, on the aluminum current collector stability in high voltage lithium ion batteries was investigated. By means of different surface sensitive techniques (scanning electron microscopy, atomic force microscopy and X-ray photoelect...

In a lithium ion battery, balancing of active materials is an essential requirement with respect to safety and cycle life. However, capacity oversizing of negative electrodes is associated with decrease of specific energy/energy density. In this work, the required trade-off between maximized specific energy and minimized risk of lithium plating is...

The practically available specific energy of Li ion batteries (LIB) is highly depending on the used specific charge/discharge current, since the respective overpotentials of each electrode affect the two vital specific energy parameters, specific capacity and voltage. Focusing on the positive composite electrode as the specific energy bottleneck, t...

Here, we report on methyl 3-cyanopropanoate (MCP) in combination with the conductive salt lithium bis(trifluoromethane)sulfonyl imide (LiTFSI) as a safe single-solvent electrolyte for lithium-ion batteries (LIBs). To investigate the extent of anodic aluminum dissolution, an innovative electrochemical technique was introduced. Long-term full-cell [L...

Diverse LiPF6 hydrolysis products evolve during lithium-ion battery cell operation at high operation voltages and high operation temperatures. However, their influence on the electrode/electrolyte interfaces is not yet investigated and understood. In this work, literature-known hydrolysis products of LiPF6 dimethyl fluorophosphate (DMFP) and diethy...

Thanks to its high operating voltage, LiNi0.5Mn1.5O4 (LNMO) spinel represents a promising next-generation cathode material candidate for Li ion batteries. However, LNMO based full-cells with organic carbonate solvent electrolytes suffer from severe capacity fading issues, associated with electrolyte decomposition and concurrent degradative reaction...

A new method for the in operando analysis of evolving gases during cyclic aging of lithium ion batteries (LIBs) was developed to better assess safety concerning cell processes, especially those arising from the electrochemical degradation of the lithium hexafluorophosphate LiPF6/organic carbonate solvent based electrolyte. For electrochemical chara...

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 wi...

Further development of high voltage lithium-ion batteries requires electrolyte formulations stable against oxidation or measures to generate a protective cathode/electrolyte interface (CEI) film. In the frame of this work, the actually counterintuitive concept of using metal ions as electrolyte additives to stabilize the CEI has proven to be succes...

The electrochemical aging of commercial non-aqueous lithium hexafluorophosphate (LiPF6)/organic carbonate solvent based lithium ion battery electrolyte has been investigated in view of the formation of ionic and non-ionic alkylated phosphates. Subject was a solvent mixture of ethylene carbonate/ethyl methyl carbonate EC:EMC (1:1, by wt.) with 1 M L...

The 1st cycle Coulombic efficiency (CE) of LiNi1/3Co1/3Mn1/3O2 (NCM) at 4.6 V vs. Li/Li+ has been extensively investigated in NCM/Li half cells. It could be proven that the major part of the observed overall specific capacity loss (in total 36.3 mAh g-1) is reversible and induced by kinetic limitations, namely an impeded lithiation reaction during...

The presented work was focused on the development of a new liquid chromatography-tandem quadrupole mass spectrometry method (LC MS/MS) for the identification and quantification of organophosphates in lithium hexafluorophosphate (LiPF6) based lithium ion battery electrolytes. The investigated electrolyte consists of 1 M LiPF6 dissolved in ethylene-/...

In pursuit of higher energy density in lithium-ion batteries (LIBs), a most promising approach focuses on cathode materials that operate at higher potentials and exhibit even higher specific charges than present LIB cathodes charged up to only 3.8 to 4.3 V vs. Li/Li+. To enable a high-voltage (HV) application of the cathode, the "by-materials", in...

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 s...

The thermal aging process of a commercial LiPF6 based lithium ion battery electrolyte has been investigated in view of the formation of volatile phosphorus-containing degradation products. Aging products were analyzed by GC-MS. Structure determination of the products was performed by support of chemical ionization MS in positive and negative modes....

LiNi1/3Co1/3Mn1/3O2 (NCM) cathode material can be charged to different potentials. When using the standard salt LiPF6, elevated cut-off potentials during charge lead to increased capacity and energy density during discharge, but reduce the cycle life dramatically. Metal dissolution is promoted by acids, like HF, derived from deterioration of the el...

Ni1/3Co1/3Mn1/3O2 (NCM) cathode material can be charged to different potentials. When using the standard salt LiPF6, 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...

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. T...

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 ex...

The electrochemical performance of propylene carbonate (PC) based electrolytes with methyl vinyl sulfone (MVS) and ethyl vinyl sulfone (EVS) as film-forming additives on graphite electrode was studied. The results indicate that already small amount of these additives is able to form a stable SEI and thus successfully prevent exfoliation of the grap...

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 carbo...

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. With the advent of renewable energy, it is now indispensable that efficient energy storage systems have to be developed. One o...