An Aqueous Conducting Redox-Polymer-Based Proton Battery that Can Withstand Rapid Constant-Voltage Charging and Sub-Zero Temperatures

Article abstract of DOI:10.1002/anie.202001191

Electrodes based on organic matter operating in aqueous electrolytes enable new approaches and technologies for assembling and utilizing batteries that are difficult to achieve with traditional electrode materials. Here, we report how thiophene-based trim

Full text of DOI:10.1002/anie.202001191

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: An aqueous conducting redox polymer based proton battery
that can withstand rapid constant-voltage charging and sub-zero
temperatures
Authors: Christian Strietzel, Mia Sterby, Hao Huang, Maria Strømme,
Rikard Emanuelsson, and Martin Sjödin
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202001191
Angew. Chem. 10.1002/ange.202001191
Link to VoR: http://dx.doi.org/10.1002/anie.202001191
http://dx.doi.org/10.1002/ange.202001191

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
An aqueous conducting redox polymer based proton battery that
can withstand rapid constant-voltage charging and sub-zero
temperatures
Christian Strietzel, Mia Sterby, Hao Huang, Maria Strømme, Rikard Emanuelsson★, and Martin Sjödin★
C. Strietzel, Dr. M. Sterby, Dr. H. Huang, Prof. M. Strømme, Dr. R. Emanuelsson, Prof. M. Sjödin
Nanotechnology and Functional Materials, Department of Materials Science and Engineering, The Ångström Laboratory, Uppsala University
Box 534, SE-751 21 Uppsala, Sweden
Rikard.Emanuelsson@angstrom.uu.se, Martin.Sjodin@angstrom.uu.se
Supporting information for this article is given via a link at the end of the document.
Abstract: Electrodes based on organic matter operating in aqueous
electrolytes enable new approaches and technologies for
assembling and utilizing batteries that are difficult to achieve with
traditional electrode materials. Here, we report how thiophene-based
trimeric structures with naphthoquinone or hydroquinone redox-
active pendent groups can be processed in solution, deposited, dried
and subsequently polymerized in solid state to form conductive
(redox) polymer layers without any additives. Such post-deposition
polymerization offers efficient use of material, high mass loading (up
to 10 mg/cm2) and good flexibility in the choice of substrate and
coating method. By employing these materials as anode and
cathode in an acidic aqueous electrolyte a rocking-chair proton
battery is built. The battery shows good cycling stability (85% after
500 cycles), withstands rapid charging, with full capacity (60 mAh/g)
reached within 100 seconds, allows for direct integration with
photovoltaics, and retains its favorable characteristics even at -
24 °C.
The vast majority of these concepts requires significant amounts
of conducting additives, often different forms of carbon, as most
organic materials are insulators. Consequently, while the
theoretical specific capacity of these battery materials might be
high, the effective capacity is considerably lower (Supporting
Information (SI) table S1). Moreover, a polymeric binder is often
needed to ensure good adhesion and material cohesion. These
insoluble additives complicate the solution processing of the
electrode material, required for assembly techniques such as
spray coating, screen printing, ink-jet printing or dip coating.
Another approach to tackling these issues is to attach redox-
active groups to pi-conjugated structures, e.g. thiophene or
pyrrole, which upon polymerization form a conductive polymer
(CP) backbone, resulting in so-called conducting redox polymers
(CRPs).[11b, 13] CRPs require no additives as the CP backbone
serves a dual purpose: i) to facilitate electron transport through
the material while the redox-active pendant stores the charge
and ii) to reduce material solubility. Thus, the properties of the
pendants determine battery characteristics such as storage
capacity, voltage output, and available cycling chemistries. The
CRP approach results in other challenges with respect to
forming and processing the CPs.[14] The traditional method of
Introduction
With
a seemingly ever-increasing demand for secondary
electrical energy storage, research into how to utilize organic
matter as the active material in batteries has exploded.[1]
Environmentally benign and more economical than conventional
inorganic batteries,[2] together with a wide structural variety and
the possibility of tailoring their properties by chemical
modification are some of the envisioned benefits of batteries
based on redox-active organic molecules.[3] These could also
allow new ways to assemble and utilize batteries, including
bottom-up synthesis, the use of environmentally benign and safe
electrolytes based on water, the easy disposal of complete
battery cells with regular household waste collection, the
development of flexible batteries for wearable electronics and
the development of super-fast charging batteries.[4]
forming
conductive
polymers,
through
oxidative
electropolymerization from a monomer solution, is unsatisfactory
as it is difficult to scale and is limited to conducting substrates.
Oxidative chemical polymerization is better for large scale
synthesis.[15] However, once the CP is formed, there is a strong
tendency for aggregation through pi-pi stacking, which makes
the polymer insoluble and hard to process further. The main
strategies for overcoming this issue have been to engineer
stable
polymer
suspensions,
as
with
poly(3,4-
ethylenedioxythiophene):poly(styrenesulfonate)
(PEDOT :PSS),[16] or by chemically modifying the monomers
with solubilizing groups.[17] The first method has limited versatility
and the second strategy limits further substitution of the
monomer. Limited substitution also hinders the use of solid state
polymerization methods developed for thiophene derivatives. [18]
This report discusses all-organic batteries assembled from
CRPs containing repeating terthiophene units, i.e. trimers,
allowing for what we call post-deposition polymerization of the
trimer layers. As opposed to previously reports on CRP
batteries[11b] this approach allows easy processing as the soluble
trimer can be solution-processed and then, after drying, the layer
can be polymerized in the solid state either by applying a
positive potential to the layer in the presence of an electrolyte
solution, or by dipping the layer into an oxidant solution. In
addition to permitting traditional, up-scalable layering techniques,
this method achieves 100% utilization of the precursor material
Batteries consisting of one organic and one inorganic electrode
have been extensively studied with the aim of maximizing cell
potential and investigating the characteristics of organic
electrode materials.[5] All-organic batteries are rarer,[6] but are
gaining in popularity, as exemplified by the pioneering work of
Nishide using organic radical batteries,[7] and Poizot using
lithiated tetrahydroxybenzoquinone.[8] Recently, the work of
Schubert’s, Gaubicher’s and Aziz’s groups on all-organic battery
concepts has also shown promising results.[9] There is a wide
range of organic battery concepts, for example the organic
electrode material can be either polymeric to prevent dissolution
in the electrolyte, or consist of single molecules with very low
5c, 10]
solubility in the chosen electrolyte.[4,
Electrolytes using
metal ions (e.g. Li, Na, Mg ions), molecular ions (e.g. tetraalkyl
ammonium), or protons (H+) have even been considered.[3b, 9d, 11]
Organic solvents are common but there are also examples using
ionic liquid or aqueous electrolytes.[9a, 12]
thus
minimizing
material
losses.
We
used
benzoquinone/hydroquinone (Q/QH2) and
1
This article is protected by copyright. All rights reserved.

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
Figure 1. Schematic representation of the all-organic battery concept, chemical structures/naming and polymerization method. The trimeric precursors (a) were
used in the post-deposition polymerization procedure (b) to form polymers with similar characteristics to those formed from monomeric units. In post-deposition
polymerization, the trimer is first dissolved in an organic electrolyte, followed by drop casting and drying. Subsequently, the trimer film is oxidized, either i)
electrochemically in an aqueous 0.5 M H2SO4 solution by cyclic voltammetry between 0.0 and 1.21 V vs SHE at 10 mV/s or by applying a potential of 0.81 V vs
SHE for 3000 seconds or ii) chemically by immersion into an acidic aqueous solution containing 1 M FeCl3 as oxidant, resulting in the formation of a black polymer
layer. The anode material (c) consisted of pEP(NQ)E, which was formed by oxidative polymerization of EP(NQ)E. Similarly, the cathode material pEP(QH2)E (d)
-
was formed from EP(QH2)E. Conductivity was achieved from a polythiophene backbone (e) that was oxidized/doped, e.g. with HSO4 . The battery (middle) was
assembled as an all-organic proton battery using 0.5 M H2SO4 (aq) electrolyte, which enabled a rocking-chair motion of the protons. The anode and cathode redox
activity relies on the two-electron two-proton (2e2H) redox process of the pendants (f and g). When the battery is charged, the quinone pendant groups are in the
Q and NQH2 states, for the positive electrode (cathode) and negative electrode (anode), respectively. During discharge, the active cathode material is converted
to QH2 while the anode is converted to NQ.
E = 3,4-ethylenedioxythiophene; NQ = naphthoquinone; NQH2 = naphthohydroquinone; P = 3,4-
propylenedioxythiophene; p = polymerized; Q = benzoquinone; QH2 = hydroquinone
naphthoquinone/naphthohydroquinone (NQ/NQH2) as capacity
carriers in the two-electron, two-proton (2e2H) redox reaction.
The use of naphtoquinone, instead of the previously reported
anthraquinone unit in the CRP,[11b] allow us to use an acidic,
aqueous electrolyte for the formation of a proton battery, where
the protons function as charge carriers in a rocking-chair motion
upon charge and discharge (Figure. 1). We have shown how
such a battery can be charged in mere seconds using a
constant-voltage charging method, and that this type of charging
is beneficial for the stability of the organic battery compared to
conventional constant-current charging. The battery can be
charged directly by an organic solar cell, no additional
electronics are needed, operates in sub-zero temperatures and
can be used to power e.g. a thermometer.
pendant group on the polymerizable unit. Crucially, we planned
for polymerization to be initiated only after monomer deposition,
rendering an insoluble polymer material immobilized on the
substrate surface and containing only the desired dopant.
Furthermore, polymerization should proceed under mild
conditions and, importantly, without re-dissolving the deposited
material. To achieve this we decided to add an additional
thiophene unit on both sides of a (functionalized) thiophene
monomer, forming a terthiophene trimer which we believed
could be conductive upon oxidation. This would allow
polymerization to propagate through the trimer layer to yield CPs
or CRPs. Oligomers would also exhibit lower oxidation potentials
compared to the monomer, allowing for milder polymerization
conditions.[19]
ethylenedioxythiophene (EDOT, E) or
Indeed,
while
a
monomeric
3,4-
a
hydroquinone-
Results and Discussion
functionalized EDOT (EQH2)[20] does not accomplish these
targets, utilizing a trimeric structure of thiophenes, EEE and
EE(QH2)E does (SI section S1 for synthetic details and
Post-deposition polymerization: We envisioned a method that
would reliably and smoothly result in a CP regardless of the
2
This article is protected by copyright. All rights reserved.

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
respectively. Note, for simplicity we refer to the polymers in their
discharged state [(pEP(QH2)E and pEP(NQ)E)] when discussing
these in general terms. A constant potential polymerization (0.81
V vs SHE for 3000 seconds) was used to achieve material
loadings above ~1 mg/cm2, since at this point polymerization
using cyclic voltammetry was ineffective, requiring many sweeps
for full polymerization (SI figure S28). Trimer layers up to 2
mg/cm2 could also be polymerized by dipping the trimer-coated
substrate into an oxidant solution containing 1 M FeCl3 (aq),
while higher loadings resulted in polymerization and subsequent
delamination preventing further investigation. In addition, we
confirmed that trimer layers with much higher mass loading, up
to 10 mg/cm2, 0.5 mm thick (vide infra), formed by sequential
drop casting/drying steps, also formed CRPs upon
polymerization using the electrochemical potential step method.
The polymeric materials were further analyzed by scanning
electron microscopy/energy-dispersive X-ray spectroscopy
(SEM/EDX) and infrared (IR) spectroscopy showing that the
atomic composition corresponds well to the theoretical
composition based on the polymers depicted in Figure 1 and
that the vibrational features are preserved from the trimer
precursor to the polymer (SI section S8). Thermogravimetric
analysis (TGA) suggested that both polymers were stable to well
above 150 °C.
characterization). Polymerization was achieved in line with the
approach detailed above. A solution of EEE or EE(QH2)E) was
drop-cast onto a conductive substrate and the solvent was
removed under vacuum (Figure 1b and SI section S1). The
electrode was then submerged in 0.5 M aqueous H2SO4 solution,
which does not dissolve the materials, and a potential was
applied to the trimer layer using a cyclic voltammetry voltage
profile. Monitoring the conductance in situ during the
voltammetric sweeps revealed that the conductance started to
increase sharply after a certain potential during the initial anodic
polarization, i.e. potential sweep from lower to higher voltages
(SI figure S20). Concurrently, the yellow/amber trimer layer
became black. The conductance reached a plateau which
remained during consecutive cycles, during both anodic and
cathodic sweeps, with no substantial change in conductance
over the potential interval 0.2-1 V vs a standard hydrogen
electrode (SHE). This is indicative of a CP and we interpreted
the increase in conductance observed during the initial anodic
sweep as polymerization of the trimeric layers. Using the same
protocol with a methyl end-capped trimer, MeEEEMe, which
cannot form a conducting polymer, nevertheless revealed a
small conductance increase upon oxidization (SI figure S21). As
hypothesized, the trimers are thus intrinsically conducting in
oxidized state and post-deposition polymerization was
successful since oxidation, and concomitant polymerization, can
propagate through the trimer layer by virtue of the inherent
Individual electrode evaluation: Successful CRP designs
require that the conductivity of the CP is sufficient in the
potential region where the pendant/capacity carrier redox
reaction occurs, a condition known as polymer-pendant group
redox matching.[11b, 23] From in situ conductance measurements
using interdigitated array (IDA) electrodes it was clear that
appreciable conductance was attained above 0 V and 0.1 V vs
SHE in pEP(QH2)E and pEP(NQ)E, respectively (Figure 2).
trimer conductance. Note, neither
E nor EQH2 could be
polymerized in this way, suggesting that the use of longer
oligomers is essential for the post-deposition polymerization
approach. In addition, electrochemical characterization shows
that the potential required to oxidize trimeric units is about 1 V
below the oxidation potential for monomeric compounds allowing
for the possibility to use water electrolytes during polymerization
without risking electrolyte degradation and generation of reactive
oxygen species (SI figure S23). Consequently, we concluded
that the lower oxidation potential and the finite conductivity of the
trimer upon doping are essential for this method to work. The
polymers produced, pEEE (i.e. PEDOT) and pEE(QH2)E,
displayed similar characteristics to polymers formed through
oxidative electropolymerization of EDOT (to PEDOT) and EQH2
(to pEQH2) (SI section S4).[20-21] Electrochemical quartz crystal
microbalance (EQCM) during polymerization indicated that the
polymers formed were short (nine thiophenes long on average),
in line with previous studies on PEDOT which found between 5
and 20 units[22] (SI section S4).
All-organic batteries: Confident of the applicability of post-
deposition polymerization, we designed a new set of trimers
based
on
a
central
quinone-functionalized
3,4-
propylenedioxythiophene (ProDOT, P) to which two EDOTs (E)
were attached at the α-positions to form an EPE trimer.
Synthetic availability and reduced complexity of the trimer and
polymer due to the lack of chirality of the functionalized ProDOT
were the main rationales behind this modification.
A
hydroquinone (QH2) or naphthoquinone (NQ) capacity carrier
was attached as a pendant group to the central ProDOT,
forming EP(QH2)E and EP(NQ)E, respectively (see SI section
S2 for synthetic details and full characterization). These trimers
were subsequently polymerized to form the redox-active
electrode materials pEP(QH2)E and pEP(NQ)E employed as
cathode (positive electrode) and anode (negative electrode),
Figure 2. Conductance response as measured by interdigitated array
electrode (grey) and cyclic voltammogram (cyan) at a scan rate of 10 mV/s in
a 0.5 M H2SO4 electrolyte for EP(QH2)E (a) and EP(NQ)E (b).
3
This article is protected by copyright. All rights reserved.

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
Figure 3. Individual electrode evaluation of pEP(QH2)E (black and orange) and pEP(NQ)E (grey and cyan) in 0.5 M H2SO4 (aq) using potential step charging (a)
followed by galvanostatic discharge (b) as well as traditional galvanostatic charge/discharge (c). Galvanostatic charge/discharge was performed at 3 C in all cases
and the potential profiles recorded during the first (pEP(QH2)E: black, pEP(NQ)E: cyan) and 100th (pEP(QH2)E: orange, pEP(NQ)E: grey) cycles are shown for
both materials. Panel (a) show the current profile during the potential step charging from ∼0.5 V to 0.81 V and 0.1 V vs SHE for pEP(QH2)E (black) and pEP(NQ)E
(grey), respectively. E = 3,4-ethylenedioxythiophene; NQ = naphthoquinone; P = 3,4-propylenedioxythiophene; p = polymerized; QH2 = hydroquinone
The potential for the Q/QH2 redox reaction in pEP(QH2)E is 0.67
V vs SHE in 0.5 M H2SO4 (aq) while the corresponding potential
for NQ/NQH2 in pEP(NQ)E is 0.27 V vs SHE. Around the
NQ/NQH2 redox peak, the conductance of pEP(NQ)E reached a
value of 30 mS and the Q/QH2 conversion was clearly within the
high-conductance region observed in pEP(QH2)E with an
observed conductance of 65 mS. Lowering the temperature to -
24 °C did not significantly affect the polymer conductance or the
redox matching condition indicating that efficient electron
transport provided by the polymer backbone was sustained even
at sub-zero temperatures (SI Figure S35 and S36). In addition to
the achieved redox matching condition the pEP(NQ)E redox
chemistry is just within the stability window of the electrolyte
making the NQ group ideal for use as pendent in anode material
for water-based CRPs. In both materials the conductance
provided by the polymer backbone was sufficient for efficient
electron transport so that no conducting additive was needed
and, when combined, they could yield a battery with a cell
voltage of 0.4 V. As stated above, the CRP design rely on the
pendent group to serve as capacity carrier and, from the cyclic
voltammetry response we estimated the capacity contribution
from the pendant redox chemistry to about 83 % and 80 % of the
total capacity in pEP(QH2)E and pEP(NQ)E, respectively. The
remaining capacity originates from doping of the polymer
backbone and, with around 20 % of the total capacity, this
suggest a doping level of half a charge per trimeric repeat unit.
From the electrochemical characterization of the individual
electrodes it is thus clear that both pEP(QH2)E and pEP(NQ)E
meet the CRP design criteria of 1) processability, 2) redox
matching, allowing for efficient electron transport, 3) pendent
group dominated capacity that provides a well-defined voltage
output and 4) that the redox chemistry of both materials fall
within the stability window of the electrolyte. (SI section 5)
charging times, and also enables direct integration with an
energy-harvesting device such as a single junction solar cell
without any additional electronics for current control. In a three-
electrode setup, we applied a fixed potential, i.e. we performed a
potential step from ~0.45 to 0.81 V vs SHE, to pEP(QH2)E which
oxidized (charged) QH2 to Q. This potential step drew an initial
large current, starting at 45 A/g, which rapidly faded towards 0
A/g and the material reached its maximum achievable capacity
within 15 s (80 mAh/g achieved, theoretical capacity: 87 mAh/g)
(Fig. 3a - black). We maintained that potential more than five
times as long (100 s) as this was the time required to fully
charge the all-organic proton battery assembled (vide infra).
After 100 s the material was re-reduced by applying a CC at 3 C,
simulating a device drawing a current. Repeating 100 such
charge-discharge cycles retained 92 % of the initial capacity (Fig.
3b). Using CC galvanostatic charge-discharge at a rate of 3 C,
the initial capacity was slightly lower, around 75 mAh/g, and the
capacity during 100 cycles also faded somewhat faster (87 %
retention) than with the potential step charging (Fig. 3c). Similar
behaviour was observed for pEP(NQ)E but with somewhat
higher stability: Potential step charging from ~0.45 to 0.1 V vs
SHE, reducing NQ to NQH2, was complete within 45 s (Fig. 3a –
grey) and achieved 68 mAh/g (theoretical 75 mAh/g) upon
galvanostatic discharge and the capacity was practically
retained during 100 such cycles (Fig. 3b). Galvanostatic CC
charging/discharging (at 3 C) gave an initial capacity of 70
mAh/g and 90 % capacity retention after 100 CC cycles (Fig. 3c).
The specific capacities observed for pEP(QH2)E and pEP(NQ)E
were comparable to those of previously reported all-organic
batteries, if conducting and binder additives are taken into
consideration (SI table S1).
The above characteristics are for electrodes loaded with ~1 mg
of trimer corresponding to ~2 mg/cm2. However, for pEP(QH2)E
we reached up to at least 10 mg/cm2 without any additive or
binder with practically maintained specific capacity and very fast
charging using the potential step method (SI figure S38). For
pEP(NQ)E, higher loadings were more challenging as the
polymer did not achieve the same capacity without extensive
One interesting aspect of the CRP all-organic proton battery
design is that the battery can be charged not only by applying a
constant current (CC), i.e. galvanostatically, but also by applying
a fixed potential, i.e. constant voltage (CV), for a short period.
Using CV as the only means of charging allows much faster
4
This article is protected by copyright. All rights reserved.

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
pre-treatment. This was probably the result of inefficient wetting
of the more hydrophobic pEP(NQ)E, resulting in substantially
different ion transport during doping of the polymer backbone, as
suggested by EQCM data (SI figure S40). For pEP(NQ)E,
oxidation of the polymer backbone was associated with close to
zero mass changes and hence the charge balance has to be
attained from the combined uptake of negative ions from the
electrolyte and expulsion of cations, presumably protons,
already present in the polymer matrix. In clear contrast, polymer
backbone oxidation for pEP(QH2)E was associated with a mass
increase corresponding to a mass-per-mole charge of 99 g/mol,
which is close to the mass of HSO4- (Mw = 97 g/mol). The charge
balance is thus accomplished exclusively by anion uptake,
indicating that charge balancing by cation expulsion is not
favoured, presumably due to the possibility to accommodate
volume changes associated with exclusive charge compensation
by anion uptake. The extensive pre-treatment required for
pEP(NQ)E limited the characterization and battery test to ~2
mg/cm2, which was achieved without any pre-treatment.
found that the battery characteristics were well captured by the
combined properties of the two individual electrode materials.
That is, the average cell voltage (0.4 V) corresponded to the
difference in charge/discharge plateaus between pEP(QH2)E
and pEP(NQ)E and the capacity was comparable to the capacity
of the limiting pEP(NQ)E electrode. When CV charging, at a
voltage of 0.6 V was used the battery was fully charged within
100 s and we attribute the somewhat longer charging time to the
higher pressure inside the coin cell preventing swelling of the
polymer. Nonetheless, the battery was charged to 50 % within
10 s and 80 % after 25 s (Fig. 4a). The resulting discharge
capacity was around 60 mAh/g at 3 C, which is about 80 % of
the theoretical capacity of the pEP(NQ)E electrode (theoretical
capacity 75 mAh/g) . The battery retained 85 % of its initial
capacity after 500 cycles using CV charging followed by
galvanostatic discharge (Fig. 4b). Using galvanostatic CC for
both charging and discharging similarly resulted in an initial
discharge capacity of 60 mAh/g but only about 50 % of the initial
capacity was retained after 500 cycles (Fig. 4d). This shows that
the initial capacity was indifferent to the charging method used
and that CV charging can fully replace, and even outperform,
galvanostatic charging from a stability point of view despite the
high currents, which exceeded 30 A/g.
Battery evaluation: We then proceeded to assemble all-organic
proton batteries in the discharged state using pEP(QH2)E and
pEP(NQ)E as cathode and anode, respectively, to evaluate if
similar characteristics could be achieved for battery cells. We
Figure 4. Battery evaluation at RT (a-d) and -24°C (e-f). Current profile (a) during the constant voltage charging at RT with 50 % of charge reached after around
6.5 seconds (black area under graph), voltage profiles (b) for the first (cyan) and 500th (grey) cycles (85% retention after CV charging and CC discharging at 3C).
A galvanostatic C-rate stud at RT (c) with C-rates corresponding to 0.6 A/g (cyan), 1.1 A/g (grey) and 5.5 A/g (black). Voltage profile (d) for the first cycle (cyan)
and 500th cycle (grey) (50% retention after cycling at 3C, ~95% Coulombic efficiency). The corresponding C-rate study (e) for a battery operating at -24°C with C-
rates corresponding to 0.6 A/g (cyan), 1.1 A/g (grey) and 3 A/g (black). Voltage profile (f) for the first cycle (cyan) and 500th cycle (grey) (~98% retention after
cycling at 3C, ~100% Coulombic efficiency). The capacity retention and Coulombic efficiency for all cycles can be found in Figure S42.
5
This article is protected by copyright. All rights reserved.

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
We rationalized the improved stability as involving detrimental side reactions that competed with the redox conversion during
charging. With CV charging, most of the current was consumed by the redox conversions, which are presumed to be much faster
than the side reactions. Interestingly, a traditional C-rate study of the battery showed that galvanostatic charging of the battery was
not particularly fast, compared to CV charging. This was especially clear when different CC charging currents, i.e. different C-rates,
were used (Fig. 4c). At 5.5 A/g (100 C), only 20 mAh/g of the material could be accessed. At first this seems contradictory, but it
effectively highlights the benefit of the CV charging method. With galvanostatic charging, the IR drop (or ohmic drop) increases
linearly with charging current and is constant throughout the charging process, assuming that the resistance is independent of the
state of charge. With increased current the potentials that the electrodes experience at the cut-off voltage thus decrease and increase
linearly for the positive and negative electrodes, respectively. Hence, as the charging current increases the effective voltage will
decrease and, accordingly, the state of charge changes with that. With constant potential charging, the initial current is large and so
is the IR drop. However, as the current rapidly decreases so does the IR drop and, at the end of the charging process, the effective
voltage is likely to be quite close to the voltage applied, leading to full capacity utilization. Needless to say, the gain in capacity
utilization and speed is at the expense of energy efficiency as the charging voltage exceeds the discharge voltage, and this has to be
considered. Nevertheless, the feasibility of utilizing CV charging shows that the battery can withstand high charging currents without
sacrificing cycling stability and is therefore practical in situations where the charging currents are variable, e.g. when using
photovoltaics for charging. To show this direct integration without any additional electronics, we connected the battery to a
commercial organic photovoltaic cell with a rated output of 0.6 V at 6-10 mA under full sun. The battery was fully charged in 100 s by
simply connecting it to the solar cell exposed to a one sun equivalent light (SI figure S44). Next, we turned to explore the possibility of
using the battery at sub-zero temperatures for low temperature applications. In order to prevent freezing the electrolyte, that rendered
the battery inactive, the sulfuric acid concentration was increased from 0.5 M to 3.3 M thus inducing a freezing point depression to -
27°C.[24] With the higher electrolyte concentration galvanostatic cycling of the battery at -24°C afforded a discharge capacity of 60
mAh/g up to 1.1A/g and 40 mAh/g at 3 A/g (Figure 4e). Hence, capacity and the rate capability were largely unaffected by the
reduced temperature. In line with the hypothesis presented above that capacity fading is due to kinetically unfavourable side
reactions, the cycling stability is improved with capacity retention of 98% after 500 cycles and a coulombic efficiency around 100%
(Figure 4f). For some applications an acidic liquid electrolyte is unpractical due to the risk of leakage and we therefore explored the
possibility to use the CRP battery together with a polymer-gel electrolyte. By confining the liquid electrolyte using a poly(vinyl alcohol)
gel a proof-of-principle device was produced with close to identical cycling characteristics as the liquid electrolyte analogue (SI Fig.
S45). Finally, we used the batteries to power a thermometer chosen to demonstrate an application in, for example, monitoring
packaging temperatures during transportation. Two batteries (containing ~1 mg material/electrode) in series to achieve a higher
voltage powered the thermometer for more than one hour, with gradually fading display intensity (SI figure S46).
Conclusion
In this report we have presented an all-organic CRP-based aqueous proton battery assembled from functionalized trimeric thiophene
units. The post-deposition polymerization allows interesting possibilities with regard to processability and electrode assembly as it
can be entirely solution based. Furthermore, we have shown how these materials withstand charging by applying a constant voltage,
resulting in a fully charged battery within mere minutes that allows for direct integration with e.g. photovoltaic devices. In addition, we
show that the battery can be used down to -24°C without significant loss in performance. As a future development both voltage (0.4
V) and capacity (60 mAh/g) in the battery could be improved by optimization of the CRP components. In particular, quinone pendant
groups providing higher potentials, e.g. catechol[25] or dihydroxyanthraquinones[9d], would make better use of the stability window of
water. The capacity could be improved by optimizing the linkage unit as well as increasing the number of redox groups per repeat
unit in the polymer similar to our previous studies. Nevertheless, the present battery shows, as a proof-of-concept, that it is possible
to construct additive-free all-organic aqueous batteries of the rocking-chair type using protons as cycling ions. Aqueous proton
batteries similar to that presented here would allow new exciting, safe, affordable and environmentally friendly substitutions for
conventional batteries.
Acknowledgements
This work was funded by the Swedish Energy Agency, the Carl Trygger Foundation, the Olle Engqvist Byggmästare Foundation, the
ÅForsk Foundation and the Research Council Formas. We thank Dr. U. Zimmermann for help with the solar cell experiments and A.
Mancebo Romero for valuable assistance with battery material preparation.
Conflict of interest
C.S., R.E. and M.Sj. have applied for a patent (1950142-8 Sweden, Conducting redox oligomers) for the trimer molecules described
herein. All other authors declare no competing financial interests.
Keywords: Quinones • Electrochemistry • Organic battery • Conducting redox polymers • Electrical energy storage
6
This article is protected by copyright. All rights reserved.

10.1002/anie.202001191
Angewandte Chemie International Edition
RESEARCH ARTICLE
[1]
[2]
[3]
[4]
[5]
a) M. Armand, J. M. Tarascon, Nature 2008, 451, 652; b) P. Poizot, F. Dolhem, Energy Environ. Sci. 2011, 4, 2003.
G. Majeau-Bettez, T. R. Hawkins, A. H. Strømman, Environ. Sci. Technol. 2011, 45, 4548.
a) Z. Song, H. Zhou, Energy Environ. Sci. 2013, 6, 2280; b) D. Larcher, J. M. Tarascon, Nat. Chem. 2015, 7, 19.
J. Kim, J. H. Kim, K. Ariga, Joule 2017, 1, 739.
a) B. Häupler, A. Wild, U. S. Schubert, Adv. Energy Mater. 2015, 5, 1402034; b) V.-A. Oltean, S. Renault, M. Valvo, D. Brandell,
Materials 2016, 9, 142; c) T. B. Schon, B. T. McAllister, P.-F. Li, D. S. Seferos, Chem. Soc. Rev. 2016, 45, 6345.
P. Poizot, F. Dolhem, J. Gaubicher, Curr. Opin. Electrochem. 2018, 9, 70.
a) H. Nishide, S. Iwasa, Y.-J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004, 50, 827; b) K. Nakahara, K. Oyaizu, H.
Nishide, Chem. Lett. 2011, 40, 222; c) T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 1627.
H. Chen, M. Armand, M. Courty, M. Jiang, C. P. Grey, F. Dolhem, J.-M. Tarascon, P. Poizot, J. Am. Chem. Soc. 2009, 131, 8984.
a) P. Sofia, S. A. B. Yuman, E. Chris, M. Philippe, G. Dominique, P. Philippe, O. Fabrice, G. Joël, Adv. Energy Mater. 2018, 8,
1701988; b) S. Perticarari, E. Grange, T. Doizy, Y. Pellegrin, E. Quarez, K. Oyaizu, A. J. Fernandez-Ropero, D. Guyomard, P.
Poizot, F. Odobel, J. Gaubicher, Chem. Mater. 2019, 31, 1869; c) A. Wild, M. Strumpf, B. Häupler, M. D. Hager, U. S. Schubert,
Adv. Energy Mater. 2016, 1601415; d) L. Tong, Y. Jing, R. G. Gordon, M. J. Aziz, ACS Appl. Energy Mater. 2019, 2, 4016.
S. Muench, A. Wild, C. Friebe, B. Häupler, T. Janoschka, U. S. Schubert, Chem. Rev. 2016, 116, 9438.
a) M. Yao, H. Sano, H. Ando, T. Kiyobayashi, Sci. Rep. 2015, 5, 10962; b) R. Emanuelsson, M. Sterby, M. Strømme, M. Sjödin, J.
Am. Chem. Soc. 2017, 139, 4828.
[6]
[7]
[8]
[9]
[10]
[11]
[12]
a) Y. Liang, Y. Jing, S. Gheytani, K.-Y. Lee, P. Liu, A. Facchetti, Y. Yao, Nat. Mater. 2017, 16, 841; b) R. Emanuelsson, C.
Karlsson, H. Huang, C. Kosgei, M. Strømme, M. Sjödin, Russ. J. Electrochem 2017, 53, 8; c) D. Moia, A. Giovannitti, A. A.
Szumska, I. P. Maria, E. Rezasoltani, M. Sachs, M. Schnurr, P. R. F. Barnes, I. McCulloch, J. Nelson, Energy Environ. Sci. 2019,
12, 1349.
[13]
a) C. Karlsson, C. Strietzel, H. Huang, M. Sjödin, P. Jannasch, ACS Appl. Energy Mater. 2018, 1, 6451; b) X. Jia, Y. Ge, L. Shao,
C. Wang, G. G. Wallace, Acs Sustain. Chem. Eng. 2019, 7, 14321.
[14]
[15]
[16]
[17]
J. Kim, J. Lee, J. You, M.-S. Park, M. S. A. Hossain, Y. Yamauchi, J. H. Kim, Mater. Horiz. 2016, 3, 517.
H. Bagheri, Z. Ayazi, M. Naderi, Anal. Chim. Acta 2013, 767, 1.
M. Lefebvre, Z. Qi, D. Rana, P. G. Pickup, Chem. Mater. 1999, 11, 262.
a) G. Zotti, S. Zecchin, G. Schiavon, L. B. Groenendaal, Macromol. Chem. Phys. 2002, 203, 1958; b) R. H. Karlsson, A. Herland,
M. Hamedi, J. A. Wigenius, A. Åslund, X. Liu, M. Fahlman, O. Inganäs, P. Konradsson, Chem. Mater. 2009, 21, 1815; c) Kim, L.
Chen, Gong, Y. Osada, Macromolecules 1999, 32, 3964.
[18]
a) H. Meng, D. F. Perepichka, M. Bendikov, F. Wudl, G. Z. Pan, W. Yu, W. Dong, S. Brown, J. Am. Chem. Soc. 2003, 125, 15151;
b) H. Meng, D. F. Perepichka, F. Wudl, Angew. Chem. Int. Ed. 2003, 42, 658; c) H. Meng, D. F. Perepichka, F. Wudl, Angew.
Chem. 2003, 115, 682; d) H. J. Spencer, R. Berridge, D. J. Crouch, S. P. Wright, M. Giles, I. McCulloch, S. J. Coles, M. B.
Hursthouse, P. J. Skabara, J. Mater. Chem. 2003, 13, 2075; e) S. Chen, B. Lu, X. Duan, J. Xu, J. Polym. Sci., Part A: Polym.
Chem. 2012, 50, 1967.
[19]
a) K. Oka, O. Tsujimura, T. Suga, H. Nishide, B. Winther-Jensen, Energy Environ. Sci. 2018, 11, 1335; b) T. Abdiryim, R. Jamal, C.
Zhao, T. Awut, I. Nurulla, Synth. Met. 2010, 160, 325.
[20]
[21]
[22]
M. Sterby, R. Emanuelsson, X. Huang, A. Gogoll, M. Strømme, M. Sjödin, Electrochim. Acta 2017, 235, 356.
M. Sterby, R. Emanuelsson, F. Mamedov, M. Strømme, M. Sjödin, Electrochim. Acta 2019, 277.
a) T. Takano, H. Masunaga, A. Fujiwara, H. Okuzaki, T. Sasaki, Macromolecules 2012, 45, 3859; b) A. Ugur, F. Katmis, M. Li, L.
Wu, Y. Zhu, K. K. Varanasi, K. K. Gleason, Adv. Mater. 2015, 27, 4604; c) I. Zozoulenko, A. Singh, S. K. Singh, V. Gueskine, X.
Crispin, M. Berggren, ACS Appl. Polymer Mater. 2019, 1, 83.
[23]
[24]
[25]
L. Yang, X. Huang, A. Gogoll, M. Strømme, M. Sjödin, J. Phys. Chem. C 2015, 119, 18956.
T. B. Reddy, D. Linden, Lindens Handbook of Batteries, McGraw-Hill, 2010.
D. Chhin, L. Padilla-Sampson, J. Malenfant, V. Rigaut, A. Nazemi, S. B. Schougaard, ACS Appl. Energy Mater. 2019, 2, 7781.
7
This article is protected by copyright. All rights reserved.