Additive-Free Organic Radical Batteries Prepared through Electrochemical Polymerization of TEMPO-Decorated Terthiophene

12 Pages·4.215 MB·English

by  Christian Friebe*, Clara Zens, Stephan Kupfer ,  Ulrich S. Schubert

pubs.acs.org/JPCC Article
Additive-Free Organic Radical Batteries Prepared through
Electrochemical Polymerization of TEMPO-Decorated Terthiophene
Christian Friebe,* Clara Zens, Stephan Kupfer, and Ulrich S. Schubert
CiteThis:https://doi.org/10.1021/acs.jpcc.2c08069 ReadOnline
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s. ABSTRACT: Batteries based on organic active materials offer a
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at 11:ely sh (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) units through elec-
3 at trochemical polymerization of suitable monomers directly onto the
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O ons ofthesystemwithratecapabilitiesofupto20%capacityretentionat50Candagoodlong-termstabilitywithacapacitylossofonly
SCptio 0.03% per cycle.
Ao
AIS Ves for
L Pelin 1. INTRODUCTION band structure enabling them to reversibly store several
DEuid Nowadays,thedemandanddevelopmentofelectronicdevices chargesperpolymerchain.10−13Theelectronicbandstructure
V gg further provides an intrinsic conductivity, diminishing the
UNIharin opforatallblkeindapspilsicainticornesa,sinsgucshteaadsilym. oInbileparptihcounlaers, somrallsmaanrdt demand for conductive additives. Many types of conjugated
ed via s.org/s pteacchknaoglionggie,sinthcarteaosefferthae lonweedwefigohrt naenwd heinghergmyecshtoanraicgael tpioolny,merersndcearninaglsothbeemsysnutihteabsilzeedfourtiliizningsiteulecptrreoppaorlaytmioenrizoa-f
wnloadpubs.ac Tfleoxdibaiyl’istysoalsutiwoenlsl raeslyamlooswtlyproincel,ithhiiguhm-siotanbibliatyttearnieds,swahfeitcyh. teolecbtreodaenfiolmbsst.1ru4cYtievte,wdhisaatdsveaenmtaegdetosibnecea,ndaudevatnotagtheeprsoevmeid-
Dos:// intrinsically possess a number of disadvantages. Most conductor-like behavior, the polymers’ redox potentials are
p
htt prominently, they pose the hazard of fire or even explosions determined by their state of charge. Thus, no stable charging
ee if damaged, thereby constituting a major risk for their and discharging capacities and voltages can be attained.14
S application.1,2 Furthermore, their commercial production Consequently, this first approach was eventually abandoned.
suffers from several drawbacks, e.g., the ecologically harmful Stable organic radicals form another class of suitable energy
exploitation of precarious metals, such as cobalt, manganese, storage materials. The first time they were utilized as active
and nickel,3 as well as the need for their disposal or material was in 2002 by Nakahara et al.15 As the name
recycling.4,5 A promising new approach toward sustainable suggests, these molecules possess an unpaired electron
energystoragesolutionsisprovidedbyorganicbatteries.Here, stabilized by electron resonance or sterically demanding
the active material is not composed of metals and their substituents. During charging, the radical is oxidized or
oxides6,7 but of organic molecules or polymers, which can be
reduced,formingastablenonradicalmolecule.Thisunderlying
potentially produced from renewable resources.8 Moreover,
electron transfer does not involve large structural changes,
organic active materials enable the cheap and straightforward
production of mechanically flexible thin-film devices, as
Received: November17,2022
comprehensivecastingtechniques,likedoctorblading,printing
Revised: January2, 2023
(e.g.,inkjetprinting,screenprinting),orroll-to-rollprocessing,
can be utilized.9
Among the classes of organic redox-active materials,
conjugated polymers are investigated already since the 1980s
and are well-known to feature a semiconductor-like electronic
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allowing for high electron transfer rates, and thus, high 2.3. Electrochemistry. Electrochemical characterization
achievable charging/discharging currents and power den- was carried out according to a standard procedure.23 Cyclic
sities.16 voltammetry experiments were performed using a Biologic
The preparation of redox-active materials via the electro- VMP 300 potentiostat at room temperature under argon
chemical polymerization of suitable substituent-bearing elec- atmosphere.Solutionsconsistedof3mLofCH Cl with0.1M
2 2
tropolymerizable units is a well-known technique toward both Bu NPF and 5 mg of the studied compound. A three-
battery active materials17−20 and other electroactive com- ele4ctrode6setupwithaglassy-carbonworkingelectrode(3mm
pounds.21,22 The most apparent advantage is the direct diameter), a platinum wire counter electrode, and a AgNO /
3
formation of the insoluble polymer on the electrode that is Ag/CH CN reference electrode was used. After the measure-
3
later used within the battery, circumventing the polymer ments, ferrocene was added and measured to have a reliable
processing involving grinding, suspending, homogenizing, and potential reference (ferrocenium/ferrocene, Fc+/Fc). Electro-
coating of the composite slurry. Furthermore, the incorpo- polymerization tests were carried out using the same setup.
ration of a semiconducting polymer backbone, as for most of Electropolymerized films were flushed with the pure solvent
the electropolymerizable polymers, renders the usage of
and immersed in a fresh electrolyte solution to measure CV.
conductive additive unnecessary.14 Consequently, in this 2.4. Battery Building. Polymer electrodes were prepared
work, we combine the most established stable organic radical
through electropolymerization using a three-electrode setup,
(2,2,6,6-tetramethylpiperidin-1-yl)oxyl(TEMPO)withapoly-
which consisted of a carbon paper working electrode (11 mm
thiophene backbone, the latter being built up via electro-
diameter,onlythecentral6mmdiameterexposedtosolution,
chemical polymerization to prepare in situ polymerized,
weighed before the experiment), a platinum wire counter
additive-free electrodes for organic batteries.
electrode, and a AgNO /Ag/CH CN reference electrode. 10
Inarecenttheory-drivenstudy,23wecoulddemonstratethat 3 3
mgofthemonomerin5mLoftherespectivesolventwith0.1
the introduction of an electron-withdrawing linker within a
M supporting electrolyte was used. Standard electropolymeri-
charged monomer species leads to the localization of the
zation parameters were as follows: −0.5 to 1.4 V (vs AgNO /
charge solely on the TEMPO. Thereby, a spontaneous 3
Ag)potentialrange,100mV·s−1scanrate,and150cycles.The
reduction of the TEMPO or oxidation of the thiophene
obtained films were thoroughly flushed with the pure solvent,
backbone and a resulting drop in capacity is prevented. These
driedunderairfor2days,andweighedtodeterminethemass
phenomena had been observed in former investigations
of the deposited polymer. The obtained electrodes showed
employing a thiophene backbone connected by an aliphatic
linker to a TEMPO.24 Furthermore, we revealed that the areal loadings of 2−3 mg·cm−2.
Solubility tests were carried out as follows: polymer films
lengthoftheC-chainofthelinkerhasamajorinfluenceonthe
were prepared on carbon paper as described above from a
potential coupling between the thiophene backbone and the
CH Cl /Bu NPF electrolyte. The dried films were then
TEMPO moiety. Namely, the addition of only one methylene 2 2 4 6
placed in pure solvents and allowed to rest for 24 h. Of the
unittothelinkerledtoadecreaseofthepotentialcouplingby
obtained solutions, 1 mL was taken, diluted, and analyzed by
more than one order of magnitude. However, a high potential
means of UV−vis absorption spectroscopy (PerkinElmer
coupling is necessary to permit an efficient intramolecular
charge transfer between the TEMPO unit and the thiophene Lambda 750).
backbone during the charging and discharging processes. Coin cells were built using a CR2032 housing, a polymer
Furthermore, computational modeling revealed that electron- carbon paper electrode as the positive pole, an oversized
withdrawing linkers do not affect the redox potential of the activated carbon counter electrode (9 mm diameter, prepared
TEMPO significantly. However, the (oligo)thiophene’s as described in the literature25) as the negative pole, a
oxidation is significantly shifted to higher potentials (by Whatman GF/D separator (19 mm diameter), and 250 μL of
around 0.6 eV). Hence, a C1 linker bearing an electron- the electrolyte (respective solvent with 1 M supporting
withdrawing group exhibits the best performance within the electrolyte).
proposed set of monomers. 2.5.BatteryTests.Cyclicvoltammogramsofthecellswere
Consequently, in this study, we present a thorough measuredwithinavoltagerangeof0.2−1.0Vwith0.1,0.2,0.5,
investigation of two TEMPO-decorated thiophene species, and 1.0 mV·s−1.
namely a terthiophene with one TEMPO unit and a Investigations of the performance of the cells were
bithiophene with two TEMPO moieties, which were already conducted according to a previously established protocol.26
introduced in our previous work.23 We study their suitability Allcharge/dischargeexperimentswereperformedgalvanostati-
for electrochemical polymerization as well as the capability of cally using an upper charge voltage limit of 1.0 V and a lower
the resulting polymer films as cathodes in organic batteries. dischargelimitof0.2V.Allcelltestswerecarriedoutatroom
Furthermore, the experimental results are supported by an in- temperature.
depth quantum chemical analysis performed at the density Rate capability tests were executed with charge/discharge
functionalleveloftheory(DFT)toelucidatethenatureofthe currents corresponding to 1, 0.2, 0.5, 2, 5, 10, 20, and 50C,
underlyingredoxintermediatesaswellastoaddressstructure− whereas 1C corresponds to a theoretical charging time of 1 h.
property relationships. For each current, five cycles were carried out. Two cells per
configurationwerebuiltandtested;thestatedvaluesaremean
2. EXPERIMENTAL SECTION
values.
2.1. Materials and Instrumentation. All materials were Long-term cycling experiments were conducted with a
obtained from commercial sources. Solvents were distilled charge/dischargecurrentcorrespondingto2C.Intotal,atleast
prior to use. 3000 charge/discharge cycles were performed. Three cells per
2.2. Synthesis. The syntheses of monomers 1 and 2 were configurationwerebuiltandtested;thestatedvaluesaremean
carried out as described previously.23 values.
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Scheme 1. Synthesis of TEMPO-Bearing Electropolymerizable Thiophene Monomers 1 and 2
Figure 1.EPRspectraof (a) 1 and(b)2 (1 mM indeoxygenated toluene).
Self-discharge experiments were carried out applying a 2.6. Morphology. Scanning electron microscopy (SEM)
current corresponding to 1C. The experiment started with imaging was performed with a Sigma VP field emission
scanningelectronmicroscope(Carl-ZeissAG,Germany)using
discharging to completely empty the battery. The first cycle
an InLensand SE detector with accelerating voltages of 6 and
startedwithafullchargingprocess,followedbyanopen-circuit
10 kV, respectively.
period for 12 h and complete discharging of the remaining
2.7. Computational Details. Molecules 1 and 2 were
charge. The second, third, and fourth cycles were executed
optimized as neutral (singlet), cationic (doublet), and
similarly but with open-circuit periods of 24, 48, and 72 h, dicationic (triplet) species within ORCA 5.0.3.27,28 DFT was
respectively. applied using the range-separated functional ωB97X-D3,29
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Figure2.Cyclicvoltammogramsof(a)1and(b)2insolutioninvolvingonlythefirst(black)orthefirsttwo(red)anodicprocessesat100mV·s−1
(1mg·mL−1in CHCl with0.1 MBuNPF).
2 2 4 6
which was previously applied successfully to investigate the
electrochemical properties of related organic radicals.23,30
Furthermore, Ahlrichs’ def2-svp basis set was utilized for all
DFTcalculations.31 Implicitsolventinteractions(CH Cl ,ε=
2 2
8.93, n = 1.4242) were taken into account by the conductor-
like polarization continuum model.32 Vibrational mode
analysis verified that all ground-state geometries are (local)
minima on their respective potential energy surfaces.
Ionization potentials were calculated based on Gibbs free
energiesoftheinvolvedredoxintermediatesof1and2aswell
as of the Fc+/Fc reference. In a similar fashion, Gibbs free
energies of ferrocene (singlet; Fc) and its singly oxidized
quartet species (Fc+) were obtained at the B3LYP33,34/def2-
svp31 leveloftheoryinCH Cl (SMD;soluteelectrondensity
2 2
variant of the integral equation formalism of the polarizable
continuum model35) using Gaussian 16.36
3. RESULTS AND DISCUSSION
3.1. Synthesis. The syntheses of potential monomers 1
and 2 (Scheme 1) were already presented in our previous
publication.23 Both monomers are based on commercially
availablebromo-functionalizedter-andbithiophene,whichare
converted to the respective carboxylic acids. The latter is
achievedviaaprocedureadaptedfromtheliterature37through
the lithiation of the bromo species and subsequent
carboxylation with dry ice. The obtained thiophene carboxylic
acidsarefurtherreactedwiththerespectiveTEMPOamineor
alcohol toward the TEMPO-thiophene compound using 1-
ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) as a
Figure3.Electroniccharacterandionizationpotentialspredictedby
mild and well-known activation reagent.38 DFTforthe(a)non-oxidizeddoublet,(b)singlyoxidizedsinglet,and
Both compounds were characterized by EPR spectroscopy (c)doublyoxidizeddoubletspeciesof1.Chargesandspinstatesare
to confirm the activity of the radical. For 1, the typical three- indicated in parenthesis (singlet: S, doublet: D). Spin densities are
line pattern of the TEMPO moiety is found (Figure 1a), shown for (a, c) open-shell intermediates and (b) highest occupied
originatingfromtheinteractionoftheradicalelectronwiththe molecularorbital inthe caseof closed-shellspecies.
nuclear spin of the adjacent nitrogen atom. In contrast, the
EPR spectrum of 2 shows a five-line pattern (Figure 1b), possessachemicallyreversibleprocessatahalf-wavepotential
indicating an interaction of the radical electrons with the E of0.37 V (vs Fc+/Fc),which is assignedto thenitroxide-
1/2
nuclear spins of both nitroxide nitrogen atoms39 and, thus, a oxoammonium redox couple.16 The linear dependence
spatial proximity of the two TEMPO units. between peak current and the square root of the scan rate
3.2. Electrochemistry. The TEMPO-thiophene com- (see Figure S2) indicates a diffusion-controlled process. As
poundsweresubsequentlycharacterizedbycyclicvoltammetry expected,bothspeciesshowasecond,irreversiblesignalwithin
(CV)tostudytheirelectrochemicalbehavior(Figure2).Both the measured range, which is assigned to the oxidation of the
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Figure 4.Electropolymerization testsformonomers (a)1 and (b)2 (1 mg·mL−1 inCHCl with0.1 MBuNPF, 100mV·s−1).
2 2 4 6
Scheme 2. Representation of the Electropolymerization of TEMPO-Terthiophene 1 Yielding Polymer P1
and without any rereduction peak and only negligible changes
for the first process.
3.3. Computational Studies. Computational studies at
thedensityfunctionalleveloftheoryusingtherange-separated
ωB97X-D329 functional were performed to assess the electro-
chemicalpropertiesof1and2in-depthatthemolecularlevel.
Forthispurpose,thenon-oxidizeddoublet,thesinglyoxidized
singlet,andthedoublyoxidizeddoubletspeciesof1aswellas
the non-oxidized triplet, the singly oxidized doublet, the
doubly oxidized singlet, and triplet species and, finally, the
triply oxidized doublet of 2 were fully optimized in CH Cl
2 2
usingapolarizablecontinuummodel.Forin-depthinformation
regardingthecomputationalsetup,thereaderisreferredtothe
Computational Details.
The neutral ground state of 1 involves dihedral angles
betweenthethiophenesof162and143°(Figure3a).Thefirst
oxidationwasdeterminedtobelocalizedontheTEMPOunit,
where the π* is mainly involved as evident from the spin
Figure5.CyclicvoltammogramoftheelectropolymerizedP1filmat NO
different scan rates (on glassy carbon in CHCl with 0.1 M density, shown in Figure 3a, and the highest occupied
2 2
BuNPF). molecularorbitalofthesinglyoxidizedintermediate,illustrated
4 6
in Figure 3b. This first oxidation event is predicted to hardly
ter-/bithiophene moiety.40 For 1, the incorporation of the influence the structure of 1. Based on the simulated free
secondprocess(E at0.85VvsFc+/Fc)leadstoanimmediate energiesoftheinvolvedredoxspecies,DFTyieldstheTEMPO
p
increase of the reverse reduction signal intensities, hinting to oxidation at an energy of 0.52 eV vs Fc+/Fc. The second
an electropolymerization reaction. In contrast, the second oxidation event was determined at 0.81 eV vs Fc+/Fc and is
signalof2occursatahigherpotential(E at1.48VvsFc+/Fc) localized on the terthiophene moiety (i.e., π ) as illustrated
p thio
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Figure6.CyclicvoltammogramsofP1-basedcoincellsatdifferentscanratesusingdifferentelectrolytes(acetonitrilewith1M(a)BuNPF,(b)
4 6
BuNClO,(c) BuNTFSI,or (d)Pyr TFSI).
4 4 4 1,4
by the spin density of the doubly oxidized doublet species radical centers are chemically interacting, thus impacting the
(Figure 3c). In contrast to the TEMPO-based oxidation, the oxidationoftheneighboringradicalunit.Finally,theoxidation
second oxidation event leads to more pronounced structural of the bithiophene moiety is calculated at 1.31 eV vs Fc+/Fc
changes as given mainly by the planarization of terthiophene. (FigureS1h).Interestingly,theoxidationpotential(vsFc+/Fc)
In a similar fashion, the electrochemical properties of 2 and ofthetriplyoxidizeddoubletspeciesiswith4.24eVveryhigh
itssingly,doubly,andtriplyoxidizedspecieswereinvestigated. (Figure S1i). Hence, the simulations suggest an incomplete
However, since 2 features two TEMPO moieties, oxidation
oxidationoftheredox-activegroupsin2.However,duetothe
potentials have been calculated for two doubly oxidized
absence of counter ions in this computational approach, the
species, namely, for a singlet featuring two oxidized TEMPOs
oxidation potentials for highly charged species may be
and a triplet with one oxidized TEMPO and a hole at the
significantly higher in comparison to the experimental setup,
bithiophene. The equilibrium structure of the neutral ground
where charges formed through redox processes are counter-
stateof2featuresadihedralanglebetweenthetwothiophenes
balanced by electrolyte ions.41
of about 50° so that both TEMPOs are pointing toward the
In summary, DFT systematically overestimates the exper-
same direction in favor of dispersive interactions between the
imentaloxidationpotentialsby∼0.1eV.Thisslightdivergence
TEMPOs (see Figure S1d). This is in accordance with the
from the experimental results mainly originates from the
recordedEPRdata,whichsuggestaninteractionoftheradical
approximate treatment of electron correlation as well as from
moietiesin2(seeabove).Analogueto1,oxidationofoneand
two TEMPOs hardly has any influence on the structure of 2 the applied implicit solvent model, where no electrolytes were
(FigureS1d−g).Oxidationofthethiophenebackboneleadsto considered, and from the ferrocene reference. In fact, explicit
planarization of the thiophene dihedral (145°, Figure S1h,i). interactionswiththesolventandtheelectrolytemightstabilize,
OxidationpotentialsofoneandtwoTEMPOsarepredictedto in particular, the triply oxidized redox intermediate of 2.
be 0.51 and 0.65 eV (vs Fc+/Fc), respectively (Figure S1f,g). Overall,thegoodagreementbetweentheoryandexperimentis
Therefore, despite the formally symmetric nature of 2, both highly encouraging for future theory-driven design studies.
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Figure 7. Time−voltage curves of P1-based coin cells. The first five cycles of galvanostatic charge/discharge experiments at 1C are depicted.
Different electrolyteswereused consistingof acetonitrileand (a) BuNPF,(b) BuNClO,(c) BuNTFSI,and (d)Pyr TFSI (1 M).
4 6 4 4 4 1,4
3.4. Electropolymerization Tests. Subsequently, electro- which are coupled to every thiophene unit via short amide
polymerization tests were carried out for 1 and 2. For this linkers in2,are crucialatthis point.Thisis also supportedby
purpose, solutions that were similar to the CV experiments the computational results (see above), which show that the
were prepared and potential cycling was applied using a TEMPO−TEMPO interactions even prevent the coplanariza-
standard three-electrode CV setup.The potential ranged from tion of the oxidized bithiophene unit, potentially impeding a
−1.0V (vsFc+/Fc)upto thesecondanodic processasfound successful electropolymerization.42
duringtheCVstudies.Uponcyclingof1,thecurrentincreased After the successful electropolymerization yielding P1, the
continuously with the cycle number (Figure 4a). The peak resulting thin film on the working electrode was washed with
currents of the, TEMPO-related, first redox process increase the pure solvent and immersed in a fresh, monomer-free
linearlyforaboutfivecycles.Then,thegrowthdiminishesand electrolyte. CVs at different scan rates, five cycles each, were
the increase continues with a lower slope but still linearly measured to test the basic electrochemical stability of the
(Figure 4a, inset). This observation indicates a successful electropolymerizedfilm.Theobtainedvoltammograms(Figure
deposition of the TEMPO moiety, most likely reaching a full 5) revealed a broad anodic redox process with a convenient
firstlayerataroundthefifthcycle.Inaddition,abroadeningof electrochemical stability of the polymer film, rendering the
the signal occurs, which is assigned to the formation of oligo- prepared material suitable for subsequent battery studies.
and polythiophene chains, constituting semiconductive struc- To gain insight into the morphology of the prepared films,
tures with broad redox signals.40 Together, these findings scanning electron microscopy (SEM) was used. The obtained
indicate the successful electropolymerization of 1 over several images(seeFigureS3)revealedthepresenceofanunderlying,
cycles forming multiple layers of TEMPO-bearing polythio- completed film with spherical structures on top. The latter
phene toward P1 (Scheme 2). In contrast, for 2, no current form agglomerates of different sizes in the micrometer scale.
increasewasobtainedduringcycling(Figure4b),showingthat Higher magnifications reveal that the underlying film is
this monomer seems to be unsuitable for electropolymeriza- likewise composed of agglomerated spherical structures,
tion. Most likely, interactions among the TEMPO moieties, suggesting that the film is formed starting from several
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Figure8.ExemplaryratecapabilitytestsofP1-basedcoincells.Charge/dischargecurrentsof0.5−50Cwereappliedwithfivecyclespercurrent
value.Different electrolyteswere usedconsisting ofacetonitrile and(a) BuNPF, (b)BuNClO,(c) BuNTFSI, and(d) Pyr TFSI (1 M).
4 6 4 4 4 1,4
spherical cores that grow and agglomerate through the course For details about the coin cell preparation, see Section 2.
of electropolymerization. A similar behavior was observed in The electrolyte for the electropolymerization toward the
previous thiophene-based electropolymerization studies.43 polymer electrodes consisted of dichloromethane and the
3.5. Battery Building. Upon electropolymerization and respective salt intended to be used in the later battery.
electrochemicalcharacterizationofP1,coincellswerebuiltfor 3.6. Battery Characterization. The prepared coin cells
battery tests. First, a suitable battery electrolyte had to be were initially characterized via cyclic voltammetry (Figure 6).
For all four electrolytes used, stable voltammograms were
foundsincedichloromethanewasexcludedduetoitsveryhigh
obtained at scan rates from 0.1 to 1.0 mV·s−1. The obtained
volatility. Thus, solubility studies were carried out using N,N-
half-wave voltage, corresponding to the expected working
dimethylformamide (DMF), N-methylpyrrolidone (NMP),
voltage of the battery, was around 0.6 V for all systems.
acetonitrile, 1,3-dioxolane/dimethoxyethane (DOL/DME; v:v
Subsequently, P1-based coin cells were studied through
1:1), and ethylene carbonate/dimethyl carbonate (EC/DMC;
galvanostatic charge/discharge experiments. The voltage
v:v 3:7). Of the tested solvents, acetonitrile turned out to be
curves of the first five cycles for each electrolyte are depicted
the most suitable, while the other solvents led to significant
inFigure7.FortheBu NPF -basedcells,chargeanddischarge
UV−vis absorption signals due to dissolution of the polymer 4 6
voltage plateaus are visible at around 0.6 V, reflecting the
(seeFigureS4).Hence,celltestswereexecutedusingdifferent
relatedcyclicvoltammogramandconfirmingthebasiccharge/
acetonitrile-based electrolytes; namely, tetrabutylammonium dischargecapabilityofthesystem.InthecaseoftheBu NClO
4 4
hexafluorophosphate (Bu4NPF6), tetrabutylammonium per- electrolyte, the voltage plateaus are only very weakly visible,
chlorate (Bu4NClO4), tetrabutylammonium bis- indicating a lower suitability of the system. The utilization of
(trifluoromethane)sulfonimide (Bu NTFSI), and 1-butyl-1- the Bu NTFSI electrolyte leads, again, to distinct voltage
4 4
methylpyrrolidinium bis(trifluoromethane)sulfonimide plateausat0.6V,whiletheusageofPyr TFSI resultsinonly
1,4
(Pyr TFSI) were utilized as supporting electrolytes. negligible plateau-like features. In contrast, the voltage curves
1,4
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Figure9.MeandischargecapacitydependingontheappliedcurrentduringratecapabilitytestsofP1-basedcoincells.Charge/dischargecurrents
of 0.5−50C were applied with five cycles per current value. Different electrolytes were used consisting of acetonitrile and (a) BuNPF, (b)
4 6
BuNClO,(c) BuNTFSI,and (d) Pyr TFSI (1 M).
4 4 4 1,4
Figure10.Exemplarylong-termcyclabilitytestsofP1-basedcoincells.Acharge/dischargecurrentof2Cwasappliedoveratleast3000cycles.
Different electrolyteswereused consistingof acetonitrileand (a) BuNPF and (b)BuNTFSI(1 M).
4 6 4
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Figure11.Benchself-dischargetestsofP1-basedcoincells.Thecellswerechargedat1C,letrestfordifferentdurations,anddischargedat1C.
Different electrolyteswereused consistingof acetonitrileand (a) BuNPF,(b) BuNClO,(c) BuNTFSI,and (d)Pyr TFSI (1 M).
4 6 4 4 4 1,4
of Bu NClO - and Pyr TFSI-based cells show, instead of the Tostudythepolymer’ssuitabilityforrepeatedchargingand
4 4 1,4
TEMPO-based plateaus, more distinct capacitive features, discharging, long-term cyclability tests were carried out.
most likely related to the polythiophene moieties or the Bu NPF - and Bu NTFSI-based electrolytes were selected for
4 6 4
activated carbon counter electrode. theseexperimentsduetotheirmostpromisingpreviousresults.
For rate capability tests, galvanostatic charge/discharge P1-basedcoincellswerepreparedandchargedanddischarged
cycling was carried out at different currents, from 0.5 to atacurrentof2Cforseveralthousandcycles(Figure10).The
50C, for each electrolyte (Figure 8). In the case of the cells using Bu NPF showed a mean initial discharge capacity
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Bu NPF -based electrolyte, a maximum discharge capacity of of 26 mAh·g−1, which corresponds to 43% of C and
4 6 theo
29mAh·g−1(correspondingto48%ofthetheoreticalcapacity decreasedto9 mAh·g−1overthecourseof3000cycles,which
C of 60 mAh·g−1) was achieved (Figure 9). At higher is a loss of 0.041% per cycle. The usage of the Bu NTFSI-
theo 4
currents,thecapacityisexpectedlylowerbutstillat6mAh·g−1 based electrolyte led to an initial mean discharge capacity of
at50C(correspondingto21%ofthecapacityat0.5C).Forthe only 16 mAh·g−1 (27% of C ) decreasing to 7 mAh·g−1,
theo
Bu NClO electrolyte,however,thecapacityat0.5Cisonly20 which corresponds to a loss of 0.029% per cycle. Hence, the
4 4
mAh·g−1 (33% of C ) and only 0.4 mAh·g−1 at 50C (2% of dischargecapacitiesoftheBu NTFSI-basedcoincellsareabit
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C ), while the Bu NTFSI-based system shows a capacity of lowerthanforBu NPF butwithloweroverallcapacityvalues.
0.5C 4 4 6
16 mAh·g−1 (27% of C ) at 0.5C and 1.6 mAh·g−1 (10% of Cyclicvoltammogramswererecordedprevioustoandafterthe
theo
C )at50C.Finally,thePyr TFSI-basedelectrolyteleadsto long-term cycling, revealing a significantly diminished redox
0.5C 1,4
a maximum capacity of 18 mAh·g−1 (30% of C ), signal (see Figure S8). Notably, while a distinct redox signal
theo
maintaining 2.7 mAh·g−1 (15% of C ) at 50C. Out of the remains for the Bu NPF -containing cells, no peak is
0.5C 4 6
four tested electrolytes, again, Bu NPF revealed the best observable anymore for the Bu NTFSI-based electrolyte. The
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performance for both the capacity utilization and rate observed capacity loss is most likely caused either by
capability. decomposition of the redox-active moieties (TEMPO) or by
J https://doi.org/10.1021/acs.jpcc.2c08069
J.Phys.Chem.CXXXX,XXX,XXX−XXX