Further insights into structural diversity of phosphorus-based decomposition products in lithium ion battery electrolytes via liquid chromatographic techniques hyphenated to ion trap-time-of-flight mass spectrometry

Article abstract of DOI:10.1021/acs.analchem.8b05229

This study illustrates the high complexity of phosphorus-based decomposition products in thermally treated state-of-the-art lithium ion battery (LIB) electrolytes. Liquid chromatographic techniques hyphenated to ion trap time-of-flight mass spectrometry reveal 122 different organophosphate (OP) and organofluorophosphate (OFP) species, the majority of which are not reported in the literature so far. The application of hydrophilic interaction liquid chromatography and reversed-phase chromatography enables the investigation of the acidic as well as nonacidic spectrum of aging products. Furthermore, the generation of high structure certainty by consideration of (i) mass accuracy of the precursor ions and subsequent MS^2/3 fragments, (ii) fragment intensity distribution in the mass spectra, and (iii) retention times in hydrophilic interaction liquid chromatography (HILIC) and reversed-phase (RP) separation allows a target analysis of further work in the LIB electrolyte context. In an ethyl methyl carbonate-based battery electrolyte, 82 OP compounds, 27 OFPs, and 13 cyclic O(F)Ps are identified. Additionally, the formation of 8-membered organo(fluoro)phosphate rings in lithium ion battery electrolytes is reported for the first time. Since the high toxic potential of organo(fluoro)phosphates has emerged interest in safety assessments of electrolytes, the knowledge of possibly formed substances supports further quantification approaches and toxicological assessments compared to nontarget investigations.

Full text of DOI:10.1021/acs.analchem.8b05229

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Article
Further insights into structural diversity of phosphorus-
based decomposition products in lithium ion battery
electrolytes via liquid chromatographic techniques
hyphenated to ion trap - time of flight mass spectrometry
Jonas Henschel, Luca Schwarz, Frank Glorius, Martin Winter, and Sascha Nowak
Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.8b05229 • Publication Date (Web): 12 Feb 2019
Downloaded from http://pubs.acs.org on February 20, 2019
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Further insights into structural diversity of phosphorus-based
decomposition products in lithium ion battery electrolytes via liquid
chromatographic techniques hyphenated to ion trap - time of flight
mass spectrometry
Jonas Henschela, J. Luca Schwarzb, Frank Gloriusb, Martin Wintera,c and Sascha Nowaka*
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a
University of Münster, MEET Battery Research Center, Corrensstraße 46, 48149
Münster, Germany
b
University of Münster, Institute of Organic Chemistry, Corrensstraße 40, 48149
Münster, Germany
c Helmholtz-Institute Münster, IEK-12, FZ Jülich, Corrensstraße 46, 48149 Münster,
Germany
Keywords
Lithium ion battery electrolyte, organo(fluoro)phosphates, LC-IT-TOF-MS, non-target
analysis
Abstract
This study illustrates the high complexity of phosphorus-based decomposition products in
thermally treated state-of-the-art lithium ion battery (LIB) electrolytes. Liquid chromatographic
techniques hyphenated to ion trap time of flight mass spectrometry reveals 122 different
organophosphate (OP) and organofluorophosphate (OFP) species, the majority of them not
reported in literature so far. The application of hydrophilic interaction liquid chromatography
and reversed-phase chromatography enables the investigation of the acidic as well as non-
acidic spectrum of aging products. Furthermore, the generation of high structure certainty by
consideration of (i) mass accuracy of the precursor ions and subsequent MS2/3 fragments,
(ii) fragment intensity distribution in the mass spectra as well as (iii) retention times in HILIC
and RP separation allows a target analysis in further work in the LIB electrolyte context. In an
ethyl methyl carbonate-based battery electrolyte 82 OP compounds, 27 OFPs and 13 cyclic
O(F)Ps are identified. Additionally, the formation of 8-membered organo(fluoro)phosphate
rings in lithium ion battery electrolytes is reported for the first time. Since the high toxic
potential of organo(fluoro)phosphates emerged interest in safety assessments of
electrolytes, the knowledge of possibly formed substances supports further quantification
approaches and toxicological assessments compared to non-target investigations.
*Corresponding author: e-mail address: sascha.nowak@uni-muenster.de
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1 Introduction
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Since its market introduction in the early 1990s, the lithium ion battery (LIB) took over the
market of energy storage in portable electronics like power tools, laptops and smartphones.
Nowadays, the demand is still rising due to upscaling of LIBs for e.g. stationary energy
storage systems (EES), plug-in hybrid electric vehicles (PHEVs) or fully electrified vehicles
(EVs).1,2 In particular, LIBs offer a high operating cell voltage (>3.5 V) and specific energy /
energy density on cell level (260 Wh kg-1 / 700 Wh L-1) compared to other battery systems,
accompanied with outstanding energy efficiency and cycle life.3,4 Recently, improvements in
gravimetric and volumetric energy densities enabled the application in the automotive sector.
For the approach to desired energy densities research aligned to new, high capacity and
high voltage electrode materials is nescessary.5–7 In theory, the LIB is based on redox
reactions between two electrodes, referred to as anode and cathode, whereas, as anode
commonly carbonaceous materials are used and as cathode materials lithium transition
metal oxides (LiTMO2; TM: Mn, Co, Ni).5,8 Additionally, an separator which is soaked with
electrolyte is located between the electrodes.9
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The state-of-the-art electrolyte formulation is based on lithium hexafluorophosphate (LiPF6)
as conducting salt, dissolved in a mixture of a linear and a cyclic organic carbonate solvent
(e.g. ethyl methyl carbonate and ethylene carbonate, respectively). They exhibit the best
compromise in terms of viscosity, conductivity, temperature range and stability, however,
suffering from high reactivity of LiPF6 to moisture as well as its redox instability.10–13
Electrolyte decomposition is one of various and highly complex degradation mechanism
reported in battery cell components which is often referred to as aging. Additionally, among
other also in literature reported degradation mechanisms were (i) particle cracking, (ii)
transition metal dissolution, (iii) metallic lithium deposition or iv) contact losses to the current
collectors of the respective active material.14–16 One electrolyte-based aging phenomenon
that is actually desired is the formation of interphases at the respective electrodes like the
solid electrolyte interphase (SEI) on the anode17 or the cathode electrode interphase (CEI) on
the cathode which are mainly generated during the first charging process of the battery cell.18
These interphases are electronically insulating but ionically conductive, thus, ensuring Li ion
movement and protecting the electrolyte from further oxidation/reduction at the respective
electrode surfaces. Their composition and physicochemical properties have a crucial
influence on the performance and lifetime of a LIB cell.19–21
However, the instability of electrolytes leads to undesirable side reactions. Plakhotnyk et al.
showed a reaction route for the decomposition of LiPF6 where the assumed equilibrium of
LiPF6 and LiF/PF5 is disrupted by trace amounts of water reacting with PF5 to highly reactive
POF3 and hydrofluoric acid (HF).22 After further conversions with water and organic
carbonates, the reaction cascade concludes in the formation of organofluorophosphate
(OFP) and organophosphate (OP).23,24 Mechanism of formation of these phosphorus esters
has been reported in recent years.25–29 This decomposition behavior is an aging process in
LIBs, whereas organo(fluoro)phosphate (O(F)P) products excite interest regarding their
toxicity and the safety of LIBs due to their structural similarity to pesticides and nerve
agents.25 Especially OFP possess the same characteristic P-F bond as chemical warfare
agents (CWA) which interact irreversibly with the catalytic active site of the
acetylcholinesterase enzyme (AChE).30 The inhibition of the catalytic triad, and therefore the
cleaving of acetylcholine at the synapses, results in the permanent stimulation of
neuromuscular junctions ending up to paralysis or decease. For instance, the CWA sarin
exhibits a median lethal dose (LD50) of 1.08 mg kg-1 body weight, some OFPs identified in
LIBs show comparable LD50 values (Figure 1).31 Alteration in structure and polarity of O(F)Ps
changes the properties, modulate the inhibition to reversible or quasi-irreversible and
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requires toxicological investigation. Besides the decomposition to volatile, non-acidic
compounds, incomplete saturation of side chains ends into P-OH groups and acidic O(F)Ps.
Sarin
O
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Irreversible
active site
binding
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Dimethyl ethyl
phosphate
Diethyl
Dimethyl
Serine 200
Catalytic triad
fluorophosphate fluorophosphate
Figure 1: Interaction of CWA sarin at the catalytic triad active side of acetylcholinesterase
and homologue structures identified in LIBs. Mode of action modelled on Dvir et al..32
The formation of decomposition products correlates strongly with the applied solvents in the
LIB electrolyte. Ethylene carbonate undergoes a single-electron ring opening process at the
electrode surface, C2-based alkoxy groups form side chains of OFPs with terminal groups
depending on the formulation of the linear organic carbonate.33–35 The use of dimethyl
carbonates leads entirely to methylation while ethyl methyl carbonates lead to a mixture of
terminal ethyl and methyl groups, increasing the potential variety of formed OFPs
drastically.36 For structural investigations of O(F)Ps in LIB electrolytes Kraft et al. proved the
comparability of the accelerated thermal aging at 80 °C to electrochemical aging
experiments.24
While organophosphorus compounds were considered and investigated as flame retardant
additives since the 1970s, the first discovery of O(F)Ps in LIBs due to electrolyte
decomposition was shown by Gachot et al. in 201127, accompanying with increased research
interest via numerous analytical approaches like ion chromatography (IC), gas
chromatography (GC) or nuclear magnetic resonance spectroscopy (NMR).37–44 Today’s
common technique for the investigation of non-acidic O(F)Ps and carbonate-based
decomposition products is GC hyphenated to flame ionization detector or mass spectrometry
(MS). However, due to the harmful properties of formed HF and high salt concentration, a
sample pretreatment is mandatory.45,46 Furthermore, the identification of acidic O(F)Ps and
ionic aging products is realized via chromatographic techniques based on capillary
electrophoresis (CE) as well as one and two-dimensional IC.36,47 Nonetheless, the
instrumental afford of these approaches is the separation of small molecules from acidic to
non-acidic properties combined with a high structural variety. For a comprehensive
qualitative and quantitative investigation, the application of different chromatographic
instruments and detection techniques is required. This is crucial for the quantification of
O(F)Ps as no analytical standards are available for this material class due to its potential
harmful properties. However, plasma-based detection via phosphorus proved to be the most
promising approach to overcome the lack of analytical standards, thus, offering quantification
of O(F)Ps.30 Therefore, inductively coupled plasma-mass spectrometry (ICP-MS)
hyphenations were reported.38,39 Molecular mass spectrometry with fragmentation
possibilities (MSn) with collision cells or ion traps (IT) and high mass resolution time of flight
detection (TOF) were applied for the identification.48
High performance liquid chromatography (HPLC) is a promising separation technique due to
the high variety of retention mechanisms, depending on physicochemical properties of the
stationary and mobile phase. In the field of LIB electrolyte investigations, classic reversed-
phase (RP) chromatography has been reported.49–53 Nevertheless, the HPLC allows to
separate non-acidic molecules with an hydrophobic stationary phases as well as acidic
molecules by changing the separation mode to hydrophilic interaction liquid chromatography
(HILIC)54,55. HILIC enables the conversion of the chromatographic order of RP separation
and allows the comprehensive investigation of O(F)Ps by using a single instrument set-up
with two different stationary phases. For structure elucidation of decomposition products in
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LIB electrolytes not only an effective separation is required, but also good mass accuracy by
high resolution mass spectrometry and fragmentation information.56 Thus, a hybrid ion trap-
time of flight-mass spectrometer (IT-TOF-MS) is the method of choice to generate high
certainty in structure elucidation without analytical standards.
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In this work, a HPLC-IT-TOF-MS hyphenation was performed for comprehensive O(F)Ps
structure elucidation by applying two different liquid chromatographic techniques. To
generate the highest possible structural diversity of phosphorus-based species in LIB
electrolytes, thermal decomposition was induced at 80 °C for three weeks. Acidic O(F)Ps
were separated via HILIC for identification, non-acidic structures by changing the separation
mode to a RP chromatography. 118 structures could be identified, including constitutional
isomers. The knowledge of the complexity of O(F)Ps allows the progression from unknown
target analysis to a target analysis in LIB electrolytes. Accompanied with the identification of
main decomposition products, quantitative information enables the approximation to risk
assessments for the recycling of end-of-life LIBs as well as safety assessments concerning
abuse and accident cases in home storage or EVs.
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2 Experimental
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2.1 Instrumentation
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Chromatographic method development and separation of decomposition products in LIB
electrolytes were performed on a Nexera X2 UHPLC system (Shimadzu, Kyoto, Japan)
hyphenated to an ion trap – time of flight (IT-TOF™) mass spectrometer (Shimadzu, Kyoto,
Japan). The flow rate and column temperature were set to 0.35 mL min-1 and 40 °C,
respectively. The injection volume was 1 µL. Shimadzu LCMS solution 3.80 was used for
LC-MS instrument control, data acquisition and data evaluation.
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NMR measurements were conducted on an Avance™ III HD (Bruker, Billerica, MA, USA) at
300 MHz (1H). Proton spectra were referenced to the solvent signal of CDCl3 at 7.26 ppm.
1H NMR shift simulations were performed on PerkinElmer ChemBioDraw 14.0.0.117.
2.1.1 Acidic organo(fluoro)phosphates
For the separation of acidic O(F)Ps analytes the hydrophilic interaction liquid
chromatography mode was used with an Hypersil GOLD™ SAX column (200×2.1 mm, 1.9
µm, Thermo Fisher Scientific Inc., Waltham, MA, USA). The mobile phase gradient consisted
of a 10 mmol L-1 aqueous ammonium formiate at pH 6.5 (A) and acetonitrile (B). The
optimized gradient started with 95% B and decreased to 90% within 5 min. Subsequently, the
mobile phase dropped to 75% within 0.1 min, decreased to 70% within 7 min and kept
constant for 2 min. After a further drop to 50% the gradient was kept constant for 10 min.
Finally, the column equilibrated at 95% B for 10 min. To protect the IT-TOF™ mass
spectrometer from high concentrations of conducting salt LiPF6, the flow line switched to the
MS after 2.5 min. Ionization was performed in ESI(-) mode at -4.5 kV. Curved desolvation
line and heat block temperature were 230°C, respectively and the nebulizer gas flow was 1.5
l min-1. The ion trap operated in automatic MS2 mode with an ion accumulation time of
10 msec in MS1 and 60 msec in MS2, leading to a loop time of 280 msec. The mass range
was set to m/z 80-250. The collision induced dissociation energy and gas flow were set to
30%. For further structure elucidation and confirmation purposes close to the limit of
detection, manual MS2 and varied ion trap parameters were used.
2.1.2 Non-acidic organo(fluoro)phosphates
Reversed-phase chromatography of non-acidic O(F)P analytes were performed on an
Hypersil GOLD™ C18 column (150×2.1 mm, 3 µm, Thermo Fisher Scientific Inc., Waltham,
MA, USA). The mobile phase gradient consisted of a 0.1% aqueous formic acid (A) and
acetonitrile (B). The optimized gradient started with 3% B from 0 to 5 min and increased to
70% within 11 min. Subsequently, the mobile phase kept constant at 70% for 4 min. Finally,
the column equilibrated at 3% B for 10 min. To protect the IT-TOF™ mass spectrometer from
high concentrations of conducting salt LiPF6, the flow line switched to the MS after 5 min.
Ionization was performed in ESI(+) mode at 4.5 kV. Curved desolvation line and heat block
temperature were 230°C, respectively and the nebulizer gas flow was 1.5 l min-1. The ion trap
operated in automatic MS2 mode with an ion accumulation time of 10 msec in MS1 and 60
msec in MS2, leading to a loop time of 280 msec. The mass range was set to m/z 100-300.
The collision induced dissociation energy and gas flow were set to 30%. For further structure
elucidation and confirmation purposes close to the limit of detection, manual MS2 and varied
ion trap parameters were used.
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2.2 Chemicals and materials
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Four different battery grade SelectiLyte™ electrolytes (BASF, Ludwigshafen am Rhein,
Germany) were investigated. All electrolytes contained 1 mol L-1 LiPF6 and vary in the
composition of linear and cyclic organic carbonates. LP30 consists of ethylene carbonate
(EC) and dimethyl carbonate (DMC) (50/50 wt%), LP40 of ethylene carbonate (EC) and
diethyl carbonate (DEC) (50/50 wt%), LP50 of ethylene carbonate (EC) and ethyl methyl
carbonate (EMC) (50/50 wt%) and LP572 of ethylene carbonate (EC), ethyl methyl carbonate
(EMC) and vinylene carbonate (30/70/+2 wt%). Acetonitrile (VWR International GmbH,
Darmstadt, Germany, LC-MS grade), ammonium formiate (MS grade, >99.0%), formic acid
(Sigma Aldrich Chemie GmbH, Steinheim, Germany, LC-MS grade), isopropanol (Merck,
Darmstadt, Germany, EMSURE©, 99.9% purity, for analysis) and deionized water (Millipore,
Molsheim, France, 18.2 MΩ cm-1) were used for the preparation of eluents. For thermal
experiments 10 mL gas-tight aluminum vials with butyl/polytetrafluoroethylene (PTFE) caps
were used (Leicht & Appel GmbH, Bad Gandersheim, Germany). All chemicals were used as
received.
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Gas-tight 10 mL aluminum vials were cleaned with isopropanol/MilliQ and dried in a vacuum
drying oven at 60 °C for 2 hours. 500 µL battery grade SelectiLyte™ were stored at 80 °C for
3 weeks. Samples were diluted 1/20 with acetonitrile for measurements.
2.4 Standard material synthesis
Unless otherwise noted, all reactions were carried out under an atmosphere of argon in
oven-dried glassware. The solvents used were purified by distillation over standard drying
agents and were stored over molecular sieves and transferred under argon. Except where
stated, the starting materials 1,2,4-triazole (Alfa Aesar, Karlsruhe, Germany), KOt-Bu (TCI,
Eschborn, Germany) phenyl phosphorodichloridate (Fluorochem, Hadfield, UK), triethylamine
(Acros Organics, Geel, Belgium) POCl3 and diethylene glycol (Sigma Aldrich, Steinheim,
Germany) were commercially available and used as received. Reaction temperatures are
reported as the temperature of the oil bath or metal block surrounding the vessel,
respectively.
2.4.1 2-hydroxy-1,3,6,2-trioxaphosphocane 2-oxide
The acidic standard was prepared following a literature procedure.57,58 To a solution of
1,2,4-triazole (207 mg, 3.00 mmol, 3.00 equiv.) and triethylamine (416 μL, 3.00 mmol,
3.00 equiv.) in 1,4-dioxane (5.0 mL) was added POCl3 (91.1 μL, 1.00 mmol, 1.00 equiv.)
dropwise at 0 °C. The mixture was allowed to warm to room temperature and stirred for
15 min. In a separate flask, diethylenglycole (85.3 μL, 0.90 mmol, 0.90 equiv.) was dissolved
in pyridine (8.0 mL). Then, the crude tri(triazolyl)phosphine oxide solution was added
dropwise to the diethylene glycol solution at room temperature. The mixture was stirred for
10 minutes, quenched with H2O (0.2 mL) and concentrated in vacuo. The residue was
dissolved in H2O (1.0 mL) and passed through a Dowex 50W×8/H+/resin (1 mL) with MeOH
and the filtrate was concentrated in vacuo. The residue was triturated with CH2Cl2 and
concentrated in vacuo to afford a colorless oil (54.1 mg) that was analyzed with
HILIC-IT-TOF-MS without further purification.
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2.4.2 2-phenoxy-1,3,6,2-trioxaphosphocane 2-oxide
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The intermediate for the synthesis of methyl and ethyl 8-membered rings
(cf. chapter 2.4.3/2.4.4) was prepared following a literature procedure.59 To a solution of
diethylene glycol (521 μL, 5.50 mmol, 1.10 equiv.) in pyridine (3.0 mL) was added phenyl
phosphorodichloridate (748 μL, 5.00 mmol, 1.00 equiv.) dropwise at 0 °C. The mixture was
stirred at room temperature overnight. The solids were removed by filtration and washed with
benzene. The filtrate was concentrated in vacuo and then dissolved in benzene. The
organics were washed with H2O, sat. NaHCO3 (aq.), dried over MgSO4 and concentrated in
vacuo to afford a colorless oil (246 mg) that used without further purification.
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2.4.3 2-methoxy-1,3,6,2-trioxaphosphocane 2-oxide
The first non-acidic standard was prepared following a literature procedure.60 Under air, to a
solution of crude 2-phenoxy-1,3,6,2-trioxaphosphocane 2-oxide (244 mg, 1.00 mmol,
1.00 equiv.) in MeOH (10.0 mL) was added KOt-Bu (112 mg, 1.00 mmol, 1.00 equiv.) at
room temperature. The mixture was stirred overnight at room temperature, quenched with
H2O, extracted with CH2Cl2. The organics were dried over MgSO4 and concentrated in vacuo
to afford a colorless oil that was analyzed with RP-LC-IT-TOF-MS without further purification.
2.4.4 2-ethoxy-1,3,6,2-trioxaphosphocane 2-oxide
The second non-acidic standard was prepared following a literature procedure.60 Under air,
to a solution of crude 2-phenoxy-1,3,6,2-trioxaphosphocane 2-oxide (52 mg, 0.21 mmol,
1.00 equiv.) in EtOH (10.0 mL) was added KOt-Bu (112 mg, 1.00 mmol, 4.76 equiv.) at room
temperature. The mixture was stirred overnight at room temperature, quenched with H2O,
extracted with CH2Cl2. The organics were dried over MgSO4 and concentrated in vacuo to
afford a colorless oil that was analyzed with RP-LC-IT-TOF-MS without further purification.
O
P
O
P
O
P
O
P
OH
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
a
b
c
d
Figure 2: Structures of synthesized standards 2-hydroxy-1,3,6,2-trioxaphosphocane 2-oxide
(a) and its phenyl (b), methyl (c) and ethyl ester (d).
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3 Results and discussion
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Structure elucidation of formed decomposition products required a separation of the
analytes. Due to their structural analogy the fragmentation pattern of O(F)Ps can be very
similar. Hence, the suggested structures were evaluated based on the (i) mass accuracy of
the precursor ions, and subsequent MS2/3 fragments, (ii) fragment intensity distribution in the
mass spectra as well as (iii) retention times in HILIC and RP separation. Furthermore, the
suggested structures were confirmed via the formation or absence in either exclusively
methyl groups containing LIB electrolyte (SelectiLyte™ LP30) or ethyl groups containing
electrolyte (SelectiLyte™ LP40). Separation of acidic species, containing a free P-OH bond,
was performed by HILIC on a strong anion exchange (SAX) stationary phase, whereas
separation of non-acidic species was obtained by reversed-phase chromatography with a
C18-based stationary phase.
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Despite the small number of reactants in LIB electrolytes the structural variety of
decomposition products concerning solvent-originated molecules led to many isobaric
interferences in extracted ion chromatograms (EICs) of possible O(F)Ps (Figure 3). This
emphasized the importance of high resolution mass spectrometry combined with
fragmentation information to obtain reliable results and avoid false positive results.
Nevertheless, at higher m/z ratios the high resolution reached its limit due to a more difficult
attribution of fragments while a partial-fragmentation of side chains occurred. Furthermore,
the structural variety increased up to 9 constitutional isomers (cf. m/z 273.110) and the
structure prediction software revealed several possible sum formula. Besides, signal
intensities decreased for higher mass-to-charge ratios, which diminished the MS3
fragmentation opportunity.
The following work is divided into three parts to classify phosphorus based decomposition
products of the hexafluorophosphate anion regarding their different structures with the same
head group and to keep track of the high variety.
Figure 3: Isobaric interferences of the extracted ion chromatogram of m/z 245.095 (ESI(+))
and two theoretical suitable OFP structures for this m/z ratio are depicted. MS2 showed no
phosphorus- or fluorine-based fragments whereas carbonate-originated characteristic
fragmentation occurred.
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The separation on C18-based stationary phases relies on the hydrophobic interaction of alkyl
chains with the analytes. Accordingly, retention of non-acidic OPs depended on the
hydrophobicity of molecules regarding the shielding of the polar phosphate head group due
to the three side chains and their length. Therefore, the retention times in Figure 4 increased
strongly from trimethyl phosphate (m/z 141.031, 6.6 min), to ethyl dimethyl phosphate
(m/z 155.047, 14.0 min), to diethyl methyl phosphate (m/z 169.063, 20.4 min) and to triethyl
phosphate (m/z 183.078, 23.6 min). The elongation of side chains by ethoxy groups
originating from EC led only to slightly increased retention times on the C18 stationary
phase, therefore, tris(2-ethoxyethyl) phosphate (m/z 315.157) eluted already after 26.2 min.
The integration of ethoxy groups into side chains enhanced the hydrophobicity only slightly,
whereas terminal hydroxyl groups at the side chains had a strong abridging influence on
retention times (see Table S1 m/z 185.058). Additionally, RP chromatography was capable
of separating several acidic species. These structures were not taken into account and are
discussed in HILIC results. A characteristic charge transfer to the side chain fragments in
positive ionization mode could have simplified the identification of acidic compounds with RP
retention but for the omnipresence of organic carbonate-based polymerization products in
LIB electrolytes isobaric interferences aggravated the identification especially for higher
masses.
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Figure 4: EICs from IT-TOF-MS in ESI(+) mode of non-acidic OPs in LP50 electrolyte
separated by RP chromatography.
MS2 fragmentation was performed to obtain further information about OP structures and, in
combination with the retention time in chromatography, was an important tool to distinguish
constitutional isomers. The prevalent fragmentation behavior of OPs was the loss of a single
or multiple side chains (see Figure 5). Therefore, the phosphate fragment was an indicator
for OPs with stable leaving groups like ethyl groups (loss of ethylene) or longer side chains.
Hence, methyl groups revealed to be bad leaving groups in the fragmentation process and
no phosphate fragments were detected. Structures with a single methyl group showed the
cleavage of the P-O bond and the release of methanol whereas two or three methyl groups
containing OPs exhibited the unlikely methane loss (Table S1 m/z 141.031, 185.058 and
215.068). Therefore, the absence of fragments indicated a structural feature as well as the
fragment intensity distribution, which was used to recognize homologous side chains.
Furthermore, the generation of characteristic fragments and short scan times of the
IT-TOF-MS in MS2 mode enabled the resolution of co-eluting constitutional isomers
(see Figure 6). Fragmentation within side chains occurred only with very low probability
leading to low intensities in MS2 spectra but increased with longer side chains and
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complicated clear attribution of signals to a specific isomer. With increasing m/z ratios, MS
spectra exhibited less characteristic fragments and MS3 experiments were in some cases
impossible due to insufficient signal intensities. This effect complicates the investigation of
high mass OPs and leads to the exclusion of possible OP signals.
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Figure 5: MS2 fragmentation pattern of three OPs in ESI(+) mode (a, b, c). Bond cleavages
and resulting fragments are indicted with different colors. Two MS3 spectra are depicted for
m/z 301.141 (d, e) showing side chain cleavage and fragmentation to the phosphate head
group.
The elongation of side chains with ethoxy groups and termination with methyl or ethyl groups
led to a high variety in structures, even at the same molecular mass by different conjunction
possibilities at three side chains. The retention behavior and formation of OP decomposition
products in thermally aged electrolytes were investigated until PO4-(C12H27O3). Despite this
limitation, over 60 structures were theoretically possible and 46 were identified by
RP-IT-TOF-MS, the majority not described in literature, yet. The number of identified
structures in LP30 and LP40 was significantly lower with 8 and 11 OPs, respectively. Only
structures with appropriate retention behavior, mass accuracy and MS2 fragmentation pattern
were considered and depicted in Table S1.
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Figure 6: EIC of the precursor 213.089 in ESI(+) mode and corresponding MS2 fragments.
Bond cleavage and resulting fragments are indicated with different colors. Different signal
maxima of fragment EICs indicate the co-elution of two constitutional isomers.
Acidic OP structures showed only poor retention on RP chromatography. Therefore, the
separation was performed in HILIC mode on a SAX column with negative electrospray
ionization for increased sensitivity. As a result of the negative ionization mode no non-acidic
OPs and only a few carbonate-based analytes were ionized, and the total ion current was
less complex. The retention mechanism changed completely from hydrophobicity and side
chain dependency to a characteristic anionic head group based separation with only minor
influence by side chains or their attached terminal hydroxyl groups. Nevertheless, enhanced
hydrophobicity led to slightly decreased retention times, thus, 26 acidic OP structures eluted
in a period from 9-12 minutes. A second group of acidic OPs with an additional hydroxyl
group at the phosphate showed high retention and peak broadening due to strong interaction
with anion exchange functional groups of the stationary phase. The elution time of this group
of signals ranged from 17-22 minutes (see Figure 7).
Remarkably, the PF6 anion showed very low retention in RP as well as in HILIC mode. This
retention behavior was beneficial to cut off the signal within the first 2.5 minutes of the
chromatography by a switching valve.
Figure 7: EICs from IT-TOF-MS in ESI(-) mode of acidic OP in LP50 electrolyte separated by
HILIC.
Fragmentation in negative ionization mode revealed to be analogous to the fragmentation in
positive ionization mode with the preferential cleavage of side chains and stable leaving
groups. Furthermore, better sensitivities for methanol loss at methylated OPs were shown.
The formation of PO3H fragments appeared to be common as well as fragments from
possible initial ring closure reactions with loss of a water molecule at terminal ethoxy groups
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(m/z 185.022) or from ethoxy groups formed after side chain cleavage accompanied with a
release of a stable leaving group (C2H4 or higher). 5-membered ring fragments (m/z 122.985)
showed comparably high intensities and therefore have a good stability. The setup of
HILIC-IT-TOF-MS revealed a total of 36 acidic OP in thermally aged LP50 electrolyte, for
LP30 14 and LP40 11 species, respectively (see Table S2).
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3.2 Structure elucidation of organofluorophosphates
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The separation of non-acidic OFPs with RP chromatography showed only the formation of
mono fluorinated OFPs which indicates a low stability of difluoroalkyl phosphate
intermediates. Formation of fluoroalkyl side chains was not observed. This structural change
shifted the retention time to slightly lower values due to the higher polarity of fluorine atoms,
but overall the retention behavior was similar to non-acidic OPs (see Figure 8). The
remaining P-F bond reduced the number of side chains to two and therefore decreased the
amount of possible structures and constitutional isomers. Hence, the number of non-acidic
OFPs was 15 in the LP50 electrolyte, 3 in the LP40 and 4 in the LP30, respectively, and are
depicted in Table S3.
Figure 8: EICs from IT-TOF-MS in ESI(+) mode of non-acidic OFPs in LP50 electrolyte
separated by RP chromatography.
The retention and fragmentation behaviors of non-acidic OFPs in positive ionization mode
were similar to those of OPs due to the structural homology (Table S3). Stabilization by ring
formation was not observed for non-acidic OFPs in positive mode whereas terminal ethoxy
groups led to 5- and 8-membered ring fragments for acidic structures due to HF loss and the
cleavage of fluorine which was detected for methyl fluorophosphates (m/z 112.981).
Characteristic fragmentation pattern of OFPs with terminal methyl or ethyl groups are
depicted in Figure 9.
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Figure 9: Fragmentation patterns of different OFPs in ESI(-) (a, b) and ESI(+) modes (c, d).
Characteristic bond cleavages and resulting fragments are indicated with different colors.
In agreement to the results of non-acidic OFPs, acidic fluoroalkylation products were not
detected. The structure of the acidic head group, especially number of fluorine present,
showed a remarkable influence on the retention on the SAX stationary phase. Thus, the
retention times raised from 1.4 min (hexafluorophosphate), to 3.1 min (difluorophosphate)
and to 7.9 min for mono-fluorinated structures (Figure 10). The effect of side chain
composition was negligible. Nevertheless, several co-eluting mono-fluorinated structures
were identified by their fragmentation pattern and due to the low structural variability with 3 of
4 fixed conjunctions at the phosphorus atom constitutional isomers could be excluded.
Figure 10: EICs from IT-TOF-MS in ESI(-) mode of acidic OFPs in LP50 electrolyte
separated by HILIC.
12 acidic OFP structures were identified in LP50, 7 in LP30 and 4 in LP40, respectively
(Table S4). The mitigated formation of high molecular ethyl-based OFPs could indicate a
higher stability of DEC-based electrolytes. Nonetheless, predictions regarding the stability of
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different electrolyte formulations were difficult since the pristine water content is the crucial
parameter for promoted electrolyte degradation in relation to the used linear organic
carbonate. Overall, the lower structural variability is reflected by the number of formed acidic
and non-acidic O(F)Ps in thermally aged LIB electrolytes due to more fixed side groups. The
formation of compounds with elongated side chains is theoretically less likely. This is in good
agreement since detected signals were close to the limit of detection of the instrument.
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3.3 Structure elucidation of cyclic organo(fluoro)phosphates
Heterocyclic 5-membered or 8-membered rings suffer from high ring strain. Therefore, cyclic
O(F)Ps represent an unexpected group of decomposition products in LIB electrolytes. In
contrast to 8-membered rings, 5-membered rings have been reported in literature.41 Thus,
assignments of 8-membered rings were confirmed by synthesized standards and a possible
formation scheme based on literature is shown in Figure 11.27,61,62 Ethylene oxide polymers
generated under EC addition and subsequent decarboxylation are substrate for the ring
organophosphate compounds, presumably.
Figure 11: Decomposition of LiPF6 and ethylene carbonate leading to 8-membered ring
organophosphates. Pristine electrolyte composition is indicated in blue, features from
degraded electrolyte in red. Scheme adapted and expanded from Lee et al., Sloop et al. and
Gachot et al..27,61,62
Several ring structures were identified in thermally aged LIB electrolytes with side chains
having terminal methyl or ethyl but no hydroxyl groups (cf. Table 5). The increase in chain
length led to higher retention times in RP chromatography with a small abridging effect after
extension with an oxygen atom and higher retention times for 8-membered compared to
5-membered ring isomers (Figure 12).
Figure 12: EICs from IT-TOF-MS in ESI(+) mode of cyclic OPs in an LP50 electrolyte
separated by RP chromatography.
Fragmentation of cyclic O(F)Ps showed primary the afore mentioned chain cleavage as well
as a ring opening reaction in 8-membered rings with a presumably subsequent re-forming of
a 5-membered ring. Thus, the decomposition of LIB electrolytes to 8-membered rings is
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confirmed by the fragmentation pattern of synthesized standards as well as the retention
behavior of the analytes. Additionally, this disproved both the formation of terminal vinyl
groups or interferences with in-source fragmentations, which might cause the same m/z ratio.
Retention times of one acidic and two non-acidic synthesized standards were in accordance
to samples (Figure 13). The cleavage of an ethyl group from m/z 197.058 with a stable
neutral loss of ethane indicated that an 8-membered ring exists (Figure 14). Furthermore, the
fragmentation pattern of the 8-membered methylated ring and the 8-membered free acid ring
were identical to the analytes in the sample. The ring opening reaction is probably induced
by a C-O cleavage, leading to a nucleophilic attack and ring closure at the phosphorus atom
and the subsequent release of ethanol. Additionally, NMR data showed no evidence of a
vinyl group in the estimated region of 5.0 – 5.5 ppm in the non-acidic methylated standard
(cf. Figure S1).
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Figure 13: HILIC (ESI(-) m/z 167.012) and RP (ESI(+) m/z 183.042, 197.057)
chromatograms of three 8-membered rings formed in LIB electrolyte LP50 in comparison to
synthesized standards.
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Figure 14: Fragmentation pattern of different cyclic O(F)Ps (a, b, c) and synthesized standard
(d) in ESI(+) mode. Characteristic bond cleavages and resulting fragments are indicted with
different colors.
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Overall, 14 different cyclic O(F)P structures were identified in LP50, 6 in LP30 and 4 in LP40,
respectively. This unexpected group revealed the possible presence of several further kinds
of decomposition products in LIB electrolytes. These findings emphasized the importance of
qualitative and quantitative consideration of phosphorus-based aging products for the
evaluation of safety concerns as well as performance impacts.
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4 Conclusion
This study reveals the high structural variety of phosphorus-based decompositions products
in thermally aged lithium ion battery electrolytes by the hyphenation of liquid chromatography
to IT-TOF-MS. Additionally, it reports the applicability of HILIC with a strong anion exchange
column for the separation of acidic O(F)Ps as well as a successful reversed phase
chromatography of non-acidic O(F)Ps. This allows a comprehensive, qualitative investigation
with a single instrument setup. Besides the formation of longer side chains with higher
variation and structural isomers, organophosphates with 8-membered ring structure are
identified for the first time and confirmed with synthesized standards. For standard-less
identification high mass resolution, fragmentation pattern and intensity distribution, achieved
with IT-TOF-MS, are considered, combined with the retention behavior on two orthogonal
separation techniques as well as different electrolyte formulations. In thermally aged
ethyl methyl carbonate containing battery electrolyte (LP50) 82 OPs, 27 OFPs and 13 cyclic
O(F)Ps are identified. For the only ethyl groups containing solvent in LP40 the number
declines expectably to 22, 7 and 4, respectively. In LP30, dimethyl carbonate solvent, the
amount is also lower with 22, 11 and 6, respectively.
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The results illustrate the complex decomposition possibilities of the conductive salt LiPF6 and
the range of O(F)P-based structures with potentially tremendous toxicity. These contribute to
the significance of toxicological investigations for risk assessments of LIB electrolytes. The
specific toxicity may change accompanied with structural variety, and therefore consideration
of qualitative and quantitative information is important. This study gives an overview on
121 phosphorus-based decomposition products in LIB electrolytes and enables a target
analysis for quantitative speciation approaches with ICP-MS techniques which are necessary
for a significant safety assessment.
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5 Conflict of interest
There are no conflicts to declare.
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6 Acknowledgements
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The authors would like to acknowledge the German Federal Ministry of Education and
Research for funding the project “Cell-Fi” (03XP0069B).
7 Supporting information
The reader is kindly referred to the supporting information to obtain following information:
Tables S1-S5: Structure suggestions with underlying MS identification data
Figure S1: 1H-NMR of synthesized standard 2-methoxy-1,3,6,2-trioxaphosphocane 2-oxide
8 References
1
2
3
4
5
6
Z. P. Cano, D. Banham, S. Ye, A. Hintennach, J. Lu, M. Fowler and Z. Chen, Nat.
Energy, 2018, 3, 279–289.
R. Wagner, N. Preschitschek, S. Passerini, J. Leker and M. Winter, J. Appl.
Electrochem., 2013, 43, 481–496.
R. Schmuch, R. Wagner, G. Hörpel, T. Placke and M. Winter, Nat. Energy, 2018, 3,
267–278.
P. Meister, H. Jia, J. Li, R. Kloepsch, M. Winter and T. Placke, Chem. Mater., 2016,
28, 7203–7217.
F. Schipper, E. M. Erickson, C. Erk, J.-Y. Shin, F. F. Chesneau and D. Aurbach, J.
Electrochem. Soc., 2017, 164, A6220–A6228.
J. Kasnatscheew, M. Evertz, B. Streipert, R. Wagner, R. Klöpsch, B. Vortmann, H.
Hahn, S. Nowak, M. Amereller, A. C. Gentschev, P. Lamp and M. Winter, Phys.
Chem. Chem. Phys., 2016, 18, 3956–3965.
7
T. Placke, R. Kloepsch, S. Dühnen and M. Winter, J. Solid State Electrochem., 2017,
21, 1939–1964.
8
9
Y. P. Wu, E. Rahm and R. Holze, J. Power Sources, 2003, 114, 228–236.
R. W. Schmitz, P. Murmann, R. Schmitz, R. Müller, L. Krämer, J. Kasnatscheew, P.
Isken, P. Niehoff, S. Nowak, G. V. Röschenthaler, N. Ignatiev, P. Sartori, S. Passerini,
M. Kunze, A. Lex-Balducci, C. Schreiner, I. Cekic-Laskovic and M. Winter, Prog. Solid
State Chem., 2014, 42, 65–84.
10
L. Terborg, S. Nowak, S. Passerini, M. Winter, U. Karst, P. R. Haddad and P. N.
Nesterenko, Anal. Chim. Acta, 2012, 714, 121–126.
11
12
K. Xu, Chem. Rev., 2004, 104, 4303–4417.
S. Wiemers-Meyer, S. Jeremias, M. Winter and S. Nowak, Electrochim. Acta, 2016,
222, 1267–1271.
13
I. Cekic-Laskovic, N. von Aspern, L. Imholt, S. Kaymaksiz, K. Oldiges, B. R. Rad and
M. Winter, Top. Curr. Chem., 2017, 375, 1–64.
ACS Paragon Plus Environment

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Analytical Chemistry
1
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5
6
7
8
9
14
15
16
M. Börner, F. Horsthemke, F. Kollmer, S. Haseloff, A. Friesen, P. Niehoff, S. Nowak,
M. Winter and F. M. Schappacher, J. Power Sources, 2016, 335, 45–55.
M. Evertz, F. Horsthemke, J. Kasnatscheew, M. Börner, M. Winter and S. Nowak, J.
Power Sources, 2016, 329, 364–371.
A. Friesen, F. Horsthemke, X. Mönnighoff, G. Brunklaus, R. Krafft, M. Börner, T.
Risthaus, M. Winter and F. M. Schappacher, J. Power Sources, 2016, 334, 1–11.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
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40
41
42
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44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
17
18
M. Winter, Z. Phys. Chem., 2009, 223, 1395–1406.
H. Buqa, R. I. R. Blyth, P. Golob, B. Evers, I. Schneider, M. V. Santis Alvarez, F.
Hofer, F. P. Netzer, M. G. Ramsey, M. Winter and J. O. Besenhard, Ionics (Kiel).,
2000, 6, 172–179.
19
20
21
22
23
E. Peled and S. Menkin, J. Electrochem. Soc., 2017, 164, A1703–A1719.
K. Xu, Chem. Rev., 2014, 114, 11503–11618.
X. Yu and A. Manthiram, Energy Environ. Sci., 2018, 11, 527–543.
A. V. Plakhotnyk, L. Ernst and R. Schmutzler, J. Fluor. Chem., 2005, 126, 27–31.
W. Weber, R. Wagner, B. Streipert, V. Kraft, M. Winter and S. Nowak, J. Power
Sources, 2016, 306, 193–199.
24
25
V. Kraft, W. Weber, M. Grützke, M. Winter and S. Nowak, RSC Adv., 2015, 5, 80150–
80157.
C. L. Campion, W. Li, W. B. Euler, B. L. Lucht, B. Ravdel, J. F. DiCarlo, R.
Gitzendanner and K. M. Abraham, Electrochem. Solid-State Lett., 2004, 7, A194–
A197.
26
27
C. L. Campion, W. Li and B. L. Lucht, J. Electrochem. Soc., 2005, 152, A2327.
G. Gachot, P. Ribière, D. Mathiron, S. Grugeon, M. Armand, J.-B. Leriche, S. Pilard
and S. Laruelle, Anal. Chem., 2011, 83, 478–485.
28
L. Terborg, S. Weber, F. Blaske, S. Passerini, M. Winter, U. Karst and S. Nowak, J.
Power Sources, 2013, 242, 832–837.
29
30
31
32
B. Vortmann, S. Nowak and C. Engelhard, Anal. Chem., 2013, 3433–3438.
S. Nowak and M. Winter, J. Electrochem. Soc., 2015, 162, A2500–A2508.
S. Nowak and M. Winter, Molecules, 2017, 22, 403.
H. Dvir, I. Silman, M. Harel, T. L. Rosenberry and J. L. Sussman, Chem. Biol. Interact.,
2010, 187, 10–22.
33
34
35
36
37
F. Horsthemke, A. Friesen, L. Ibing, S. Klein, M. Winter and S. Nowak, Electrochim.
Acta, 2019, 295, 401–409.
I. A. Shkrob, Y. Zhu, T. W. Marin and D. Abraham, J. Phys. Chem. C, 2013, 117,
19255–19269.
D. Ortiz, V. Steinmetz, D. Durand, S. Legand, V. Dauvois, P. Maître and S. Le Caër,
Nat. Commun., 2015, 6, 1–8.
V. Kraft, M. Grützke, W. Weber, J. Menzel, S. Wiemers-Meyer, M. Winter and S.
Nowak, J. Chromatogr. A, 2015, 1409, 201–209.
L. Terborg, S. Weber, S. Passerini, M. Winter, U. Karst and S. Nowak, J. Power
Sources, 2014, 245, 836–840.
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Page 20 of 21
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Y. Stenzel, M. Winter and S. Nowak, J. Anal. At. Spectrom., 2018, 33, 1041–1048.
J. Menzel, H. Schultz, V. Kraft, J. P. Badillo, M. Winter and S. Nowak, RSC Adv.,
2017, 7, 39314–39324.
7
8
9
40
41
42
43
44
45
46
V. Kraft, W. Weber, B. Streipert, R. Wagner, C. Schultz, M. Winter and S. Nowak,
RSC Adv., 2015, 6, 8–17.
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60
W. Weber, V. Kraft, M. Grützke, R. Wagner, M. Winter and S. Nowak, J. Chromatogr.
A, 2015, 1394, 128–136.
M. Grützke, V. Kraft, B. Hoffmann, S. Klamor, J. Diekmann, A. Kwade, M. Winter and
S. Nowak, J. Power Sources, 2015, 273, 83–88.
X. Mönnighoff, A. Friesen, B. Konersmann, F. Horsthemke, M. Grützke, M. Winter and
S. Nowak, J. Power Sources, 2017, 352, 56–63.
M. Grützke, V. Kraft, W. Weber, C. Wendt, A. Friesen, S. Klamor, M. Winter and S.
Nowak, J. Supercrit. Fluids, 2014, 94, 216–222.
F. Horsthemke, A. Friesen, X. Mönnighoff, Y. P. Stenzel, M. Grützke, J. T. Andersson,
M. Winter and S. Nowak, RSC Adv., 2017, 7, 46989–46998.
M. Grützke, X. Mönnighoff, F. Horsthemke, V. Kraft, M. Winter and S. Nowak, RSC
Adv., 2015, 5, 43209–43217.
47
48
M. Pyschik, M. Winter and S. Nowak, Separations, 2017, 4, 1–11.
C. Schultz, S. Vedder, M. Winter and S. Nowak, Anal. Chem., 2016, 88, 11160–
11168.
49
50
M. Tochihara, H. Nara, D. Mukoyama, T. Yokoshima, T. Momma and T. Osaka, J.
Electrochem. Soc., 2015, 162, A2008–A2015.
S. Takeda, W. Morimura, Y. H. Liu, T. Sakai and Y. Saito, Rapid Commun. Mass
Spectrom., 2016, 30, 1754–1762.
51
52
C. Schultz, S. Vedder, M. Winter and S. Nowak, Spectrosc. Eur., 2016, 28, 21–24.
C. Schultz, V. Kraft, M. Pyschik, S. Weber, F. Schappacher, M. Winter and S. Nowak,
J. Electrochem. Soc., 2015, 162, A629–A634.
53
C. Schultz, S. Vedder, B. Streipert, M. Winter and S. Nowak, RSC Adv., 2017, 7,
27853–27862.
54
55
56
A. J. Alpert, J. Chromatogr., 1990, 499, 177–196.
P. Jandera, Anal. Chim. Acta, 2011, 692, 1–25.
A. Schwarzenberg, F. Ichou, R. B. Cole, X. Machuron-Mandard, C. Junot, D. Lesage
and J. C. Tabet, J. Mass Spectrom., 2013, 48, 576–586.
57
58
59
60
61
62
I. Staatz, U. H. Granzer and H. J. Roth, Liebigs Ann. Chem., 1989, 51–57.
J. Jankowska and J. Stawinski, J. Synth., 1984, 408, 408–411.
C. L. Penney and B. Belleau, Can. J. Chem., 1978, 56, 2396–2404.
W. G. Wadsworth and W. S. Wadsworth, J. Am. Chem. Soc., 1983, 105, 1631–1637.
J. C. Lee and M. H. Litt, Macromolecules, 2000, 33, 1618–1627.
S. E. Sloop, J. B. Kerr and K. Kinoshita, J. Power Sources, 2003, 119–121, 330–337.
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