# High-capacity semi-organic polymer batteries: From monomer to battery in an all-aqueous process

Erik Schröter, Lada Elbinger, Manon Mignon, Christian Friebe, Johannes

Brendel, Martin Hager, Ulrich Schubert

► To cite this version:

Erik Schröter, Lada Elbinger, Manon Mignon, Christian Friebe, Johannes Brendel, et al. High-capacity semi-organic polymer batteries: From monomer to battery in an all-aqueous process. Journal of Power Sources, 2023, 556, pp.232293. 10.1016/j.jpowsour.2022.232293. hal-05093664

HAL Id: hal-05093664

https://hal.science/hal-05093664v1

Submitted on 2 Jun 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# High-capacity semi-organic polymer batteries: From monomer to battery in an all-aqueous process

Erik Schröter<sup>a, b</sup>, Lada Elbinger<sup>a, b</sup>, Manon Mignon<sup>c</sup>, Christian Friebe<sup>a, b</sup>, Johannes C. Brendel<sup>a</sup>, Martin D. Hager<sup>a, b</sup>, Ulrich S. Schubert<sup>a, b, *</sup>

<figure><img src="image_3.png" /></figure>

## HIGHLIGHTS

* New poly (TEMPO-methacrylamide) polymer synthesized.

* Obtainable through all-aqueous one-pot process.

* Enables aqueous semi-organic coin cells with zinc anodes.

* Stable long-term cycling at 1.5 V battery voltage.

* High-capacity coin cells from ultra-thick electrodes.

## GRAPHICAL ABSTRACT

<figure><img src="image_4.png" /></figure>

## ARTICLE INFO

### Keywords:

Semi-organic battery

High capacity

Aqueous battery

TEMPO

PTMAm

Coin cell

Battery testing

Ultra-thick electrode

Self-discharge

Float testing

Rate testing

## ABSTRACT

Aqueous Zinc-batteries comprising organic cathode materials represent interesting candidates for sustainable, safe, environmentally friendly, and highly flexible secondary energy storage system. Here, we demonstrate that such an oxygen-tolerant, semi-organic setup can conveniently be prepared in an all-aqueous process, including all steps from the initial polymerization to the coin cell assembly without the need of any intermediate purification steps, and still reach high energy densities of 2.55 mAh cm⁻². The TEMPO-modified and crosslinked poly (methacrylamide) cathode facilitates an excellent compatibility to the aqueous electrolyte and an efficient accessibility of the redox-active species due to the increased polarity of the material compared to the common poly(TEMPO-methacrylate) (PTMA). The material exhibits excellent stability (capacity retention of >99% after 1000 cycles at 5C) with low self-discharge and features high rate capabilities. The casting process from the aqueous slurry further appeared to be suitable for the preparation of ultra-thick but still homogeneous binder-free electrodes and exhibit total device capacities of approximately 4.5 mAh in a 2032-type coin cell. Since the overall process avoids harsh conditions or harmful solvents, is scalable, and relies on straightforward processing steps, it represents a promising step towards cost-effective and efficient rechargeable Zinc-based semi-organic batteries with competing capacities if further optimized.

<footnote><sup>a</sup> Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstraße 10, 07743, Jena, Germany</footnote>

<footnote><sup>b</sup> Center for Energy and Environmental Chemistry Jena (CEEC Jena), Friedrich Schiller University Jena, Philosophenweg 7a, 07743, Jena, Germany</footnote>

<footnote><sup>c</sup> Faculté des Sciences, Université de Montpellier, Place Eugène Bataillon, 34095, Montpellier Cedex 5, France</footnote>

<footnote>* Corresponding author. Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstraße 10, 07743, Jena, Germany.</footnote>

<footnote>E-mail address: ulrich.schubert@uni-jena.de (U.S. Schubert).</footnote>
# 1. Introduction

Organic electrode materials have gained enormous interest over the last 60 years [1–5]. Since materials from renewable organic sources are increasingly desired for flexible energy storage, considerable research efforts are made to advance this alternative technology to Li-ion batteries [6–9]. Considering sustainability, particularly oxygen-tolerating systems that are compatible with aqueous electrolytes are of interest and expected to represent an alternative to conventional metal-ion battery chemistries [10,11]. A variety of combinations have been presented and discussed in the literature, reaching from flexible thin-film or flow batteries to aqueous zinc-air batteries [12–14]. 2,2,6,6-Tetramethylpiperidinyloxyl (TEMPO) radical-based systems have been shown to exhibit outstanding cyclability among the reported organic compounds and are known to tolerate even the presence of oxygen in corresponding battery setups. This combination is favorable as both zinc and TEMPO-containing starting materials are readily commercially available, water compatible, oxygen-tolerating and enable straight forward processing [12,15–18]. Furthermore, concentrated zinc salt solutions reveal a high theoretical capacity and elemental zinc shows a specific capacity of 825 mAh g⁻¹, which makes zinc an attractive counterpart for the characterization of the TEMPO-containing cathode [19]. The most well-known TEMPO derivative, poly (TEMPO-methacrylate) (PTMA), was pioneered by Nakahara and coworkers in 2002 [20]. Since then, it has emerged as a gold standard in terms of cathode material, and it has been functionalized and structurally altered [21–24]. Many contenders have to compete with it in terms of cyclability, stability, and synthetic availability [3,25]. Despite the excellent tolerance, solid-state batteries featuring an aqueous electrolyte that comprise PTMA polymers have not been presented to date, which might be related to the hydrophobicity of the polymer. In accordance, aqueous processing of PTMA materials remains a challenge. Only recently, we could present a procedure to synthesize crosslinked PTMA nanoparticles in an aqueous process, which was adapted from a common emulsion polymerization procedure [26]. The synthesis yielded a suitable cathode material after oxidation, with excellent cycling properties in a hybrid battery setup with a capacitor anode. The presented emulsion approach bears key advantages in terms of a cost-effective synthesis, but nevertheless the resulting PTMA remains incompatible with aqueous electrolytes since the reactive TEMPO moieties remain mostly inaccessible due to the hydrophobic nature of the polymer backbone. An interesting approach to increase the compatibility of TEMPO-based polymers with aqueous systems relies on more hydrophilic backbones as it has been demonstrated by the Nishide group. Firstly, a hydrophilic TEMPO-bearing poly(vinylether) (PTVE) was presented in 2009 [27]. PTVE was obtained by an Ir-catalyzed coupling of 4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxyl (TEMPOL) and vinyl acetate to yield the TEMPO vinyl ether. The monomer was polymerized cationically with trifluoroborane-diethyl ether. In a semi-organic setup utilizing a zinc anode and PTVE electrodes of 35 to 1000 nm thickness, 65% of the initial capacity could be retained after 500 consecutive cycles at 60C charging current [27]. However, the authors reported limited long-term cyclability, insufficient hydrophilicity and limited working film thickness, which was referred to the solubility of short polymer chains leading to inhomogeneities in the redox-active films. In a second step to address these challenges, acrylamide-based TEMPO-bearing polymers (PTAm) have been presented by the same group. In particular, the latter displayed a higher degree of swelling in water but remained insoluble in its neutral state. Furthermore, the acrylamide materials revealed high compatibility with a poly(viologen)-based anode and retained 80% of the initial capacity after 2000 cycles at 60C in 100 nm thick films [15]. Only recently, devices were reported that combine excellent charge/discharge rates with high capacities using carbon nanotubes as current collector, which emphasizes the potential of such more hydrophilic polymers in batteries. Nevertheless, all these polymers still required organic solvents during their synthesis and processing of the

corresponding electrodes [15,28]. For instance, PTAm was obtained after free radical polymerization of a TEMPO-acrylamide monomer in acetic acid with subsequent oxidation in tetrahydrofuran with meta-chloroperbenzoic acid in very small batch sizes.

Following our previous emulsion approach, we tried to adapt the aqueous process to similar, more hydrophilic TEMPO derivatives in order to combine advantages of an all-aqueous synthesis and processing with the good compatibility with water-based electrolyte systems for high-capacity batteries. For this purpose, tetramethylpiperidine methacrylamide was copolymerized with a compatible bifunctional methacrylamide to yield a crosslinked precursor polymer, which was subsequently oxidized to the desired PTMAm. Due to the increased hydrophilicity of the monomer, the initial emulsion process could be adapted to a precipitation polymerization circumventing the need of any surfactant. In terms of device fabrication, we focused on a semi-organic system using zinc as anode material, which is particularly attractive due to high theoretical battery charging/discharging rates and energy densities, as well as its large-scale availability. We considered that the high energy density that the Zn/Zn²⁺ redox couple offers can only be exploited with such an aqueous-compatible organic polymer, which ensures the above-mentioned high accessibility even if very thick electrodes are considered. In a first attempt to characterize the potential of the new material, the polymer composites were prepared in a stepwise manner including intermediate isolation and purification steps. Furthermore, a solvent-based process was used in this first approach for the subsequent slurry preparation and electrode fabrication. However, we additionally investigated an alternative and more sustainable processing pathway. In this procedure, all intermediate steps are circumvented and a one-pot, all-aqueous approach for the preparation of a battery composite is established, starting from the monomers and including the electrode formation, which can easily be scaled up. The flexibility and robustness of the process enabled the preparation of cathodes with dry thicknesses of up to 2 mm without addition of any additional binder. These electrodes were as well tested in a coin cell setup to realize high-capacity, secondary batteries.

# 2. Results and discussion

## 2.1. Monomer and polymer synthesis

The monomer tetramethyl-4-piperidyl methacrylamide (TEMPOAm) was obtained by reaction of 4-amine-2,2,6,6-tetramethylpiperidine with methacryloyl chloride at 0 °C (see SI, Scheme S1) in accordance with literature reported procedures [10,11]. To our surprise the monomer appears to be fully soluble in water at elevated temperatures (50 to 80 °C) at 0.3 M concentration. This property distinguishes the more hydrophilic methacrylamide already from the more common tetramethyl-4-piperidyl methacrylate (TEMPOMA) and prompted us to adapt our previously reported emulsion polymerization process [26]. Initial tests, however, revealed that a precipitate is formed upon polymerization, which led directly to a fine dispersion of the corresponding polymer in aqueous solution. We therefore abandoned the use of any surfactants and tested a direct precipitation polymerization of TEMPOAm (Scheme 1) in combination with a compatible methacrylamide-based crosslinker (see Supporting Information for further details on the synthesis). Even in presence of 3 mol% of crosslinker, a powdery precipitate is formed, which could easily be filtered off and redispersed. Apparently, the precipitation process prevents an uncontrolled and full crosslinking of all the formed polymer, which simplifies further processing considerably since additional milling or grinding steps are not necessarily required.

Afterwards, the electrochemical activity of the TEMPO group is introduced by oxidation of the polymer in an aqueous suspension [29]. Interestingly, no further solubility mediators must be added to enable access to high degrees of oxidation (>75%) as PTMAm is water swappable. In comparison, the preparation of similarly crosslinked PTMA
requires addition of ethanol during the oxidation step, to enable suffi-
cient swelling of the material. This difference again corroborates the
significantly higher hydrophilicity of PTMAm compared to PTMA.
PTMAm shows a specific capacity of 112.6 mAh g⁻¹ and can, therefore,
be compared to literature-known active materials PTMA (111 mAh g⁻¹),
PTVE (135.9 mAh g⁻¹), and PTAm (119.6 mAh g⁻¹) of the same cross-
linker to monomer ratio. Our first batch of crosslinked PTMAm material
exhibited a degree of oxidation of 76.8 ± 5.4% as analyzed by electron
paramagnetic resonance (EPR) spectroscopy. The formation of the
nitroxide (Scheme 2) was further supported by infrared spectroscopy
(Fig. 2, further information in Supporting Information), since the signal
at 1464 cm⁻¹, related, amongst others, to the N-O-stretching vibration,
is enhanced [30]. However, as the signal can also be assigned to methyl-
and methylene-based stretching vibrations, this is not an unambiguous
proof for the oxidation. This also accounts for the pronounced shoulder
at 1180 cm⁻¹, which can be observed for the oxidized product. This
signal has previously been reported by Nolte *et al.* and was assigned for a
TEMPO small molecule [31]. Additional thermogravimetric analysis and
difference scanning calorimetry data is given in the Supporting Infor-
mation (Fig. S1, Fig. S3).

For this first investigation, we subsequently subjected the orange
polymeric material to milling at 0 °C in order to obtain a more uniform
fine powder. Unlike PTMA, the milling process does not lead to melting
of the oxidized polymers and yielded an even, powdered material, that
can be used to form smooth electrode layers. However, it has to be
mentioned that this step might be skipped since the synthesis directly led
to a powder-like material after lyophilization although featuring a
somewhat coarser particle distribution, which we considered detri-
mental for the initial preparation of thin electrode layers.

The oxidized polymer powder was subsequently used as an active
material in a zinc coin cell setup to characterize the cycling behavior of
the crosslinked, insoluble and hydrophobic active material in detail. The
material was suitable for two different processing routes. First, the
standard synthesis route with individual purification was used and the
material was utilized in a wet processing that uses NMP as solvent and
PVDF as binder. A second procedure was performed in an all-aqueous
process, without purification and with aqueous slurry preparation
either directly from the reaction mixture or utilization of a lyophilized
sample, which does not exclude reaction impurities. While the first route
is used for general characterization of the material, the latter route
enabled high-capacity batteries and also aqueously processed standard-
sized characterization cells. The preparation pathways are summarized
in Fig. 1.

## 2.2. Film preparation and electrochemical characterization

To evaluate the battery performance of the crosslinked PTMAm, the
literature standard processing route was followed from the solid poly-
mer to the aqueous coin cell. For this, graphite discs were prepared, and
electrode slurries were prepared from PVDF, N-methylpyrrolidone
(NMP) and the polymeric active material, according to the literature
standard processing steps [26]. Through simple drop casting, electrodes

for the usage in coin cells were obtained. The drop casting method was
chosen due to the inconsistent layer thickness of the graphite which
complicates the material loading calculation for the coin cells in case a
blade casting process is chosen. If the template that is casted on is not
equally thick over the complete casting area, the mass of the template
cannot be approximated by weighing a representative amount of equally
sized punched out template discs. Consequently, the mass of the dried
active material cannot be determined after the blade casting, when the
weight of the used graphite disc is not known. The material loading
amounted approximately 49 µAh cm⁻² (referred to the theoretical ca-
pacity). Subsequently, the electrodes were assembled to coin cells with
oversized zinc sheet counter electrodes and three different Zinc-salt
electrolytes. The utilized zinc salts comprised the triflate (OTf), tri-
fluoromethylsulfonylimide (TFSI), and perchlorate. All these salts are
known from different zinc battery systems and were expected to perform
equally. 2 M concentration in aqueous solution led to pH values of
approximately 2.5 for all the considered electrolytes. The investigated
materials, pH values and electronic conductivities are summarized in
Table 1.

Fig. 3 displays the cyclic voltammograms of the semi-organic coin
cells. All supporting electrolytes enable a reversible peak shape with a
half wave potential of 1.45 to 1.49 V (Table 1). However, peak shapes
differ slightly, with the Zn(ClO₄)₂ electrolyte exhibiting the most even
oxidation and re-reduction peaks. Furthermore, it could be shown that
the square root of the applied scanning speeds correlates linearly with
the maximum peak currents upon the oxidation and the re-reduction
signal, indicating reversible redox behavior exhibited by the TEMPO
moiety for all the tested electrolyte systems (see Supporting Informa-
tion, Fig. S5). While electrolyte anions have been shown to influence a
radical battery’s working voltage, in the present case, the potentials
differ only slightly [17].

## 2.3. Battery testing and cycling performance

For the initial battery tests and proof of cyclability, similar condi-
tions were applied to the semi-organic aqueous zinc cells as for the
emulsion-polymerized, non-aqueous PTMA batteries from Münch *et al.*
A rate testing experiment was performed, which subjects the prepared
coin cells to charging/discharging at rates between 0.2C and 50C.

The batteries exhibited a smooth charging/discharging plateau be-
tween 1.4 and 1.5 V. The rate tests began with five cycles at 1C, followed
by 0.2C and 0.5C, whereupon the rates were increased up to 50C
(Fig. 4). At 0.2C, the cells revealed their maximum active material uti-
lization, which was observed for all supporting electrolytes. In more
detail, 84% of the theoretical charging capacity (112.6 mAh g⁻¹ for
PTMAm) can be addressed at 1C, and 91% at 0.2C for the Zn(OTf)₂
electrolyte. For ZnTFSI₂, 70% charging capacity is reached at 1C and
85% at 0.2C. For Zn(ClO₄)₂, at 1C, 88% can be addressed and 93% are
reached at 0.2C. These values refer to the theoretical capacity, consid-
ering an active polymer with 100% degree of oxidation. As the real
degree of oxidation is lower, the achieved values can be considered as
excellent material usage. This material utilization is further proof for the

<figure><img src="image_5.png" /><figcaption>Scheme 1. Schematic representation of the polymerization procedure to yield the crosslinked polymer.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Scheme 2.** Schematic representation of the oxidation procedure to yield the crosslinked PTMAm polymer 4.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Fig. 1.** Schematic summary of the processing routes from the starting materials to the investigated coin cells. Literature procedure (top) is added as comparison. The standard PTMA route (mid) was performed as reference to current literature and the all-aqueous route (bottom) is added. Orange fields symbolize the utilization of organic solvents during the step, yellow indicates organic but sustainable solvents and green refers to aqueous processing steps. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 2.** FT-IR spectra of unoxidized (blue) and oxidized (red) polymer (the nitroxide vibration is indicated at 1464 cm⁻¹). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

<table><caption>**Table 1**

Composition of the supporting electrolyte and half-wave potentials as obtained by cyclic voltammetry.</caption><thead><tr><th>Crosslinker [%]</th><th>Supporting electrolyte</th><th>Concentration [M]</th><th>Half-wave potential (vs. Zn²⁺/Zn) [V]</th><th>pH-value</th></tr></thead><tbody><tr><td>3</td><td>Zn(OTf)₂</td><td>2</td><td>1.49</td><td>2.77</td></tr><tr><td>3</td><td>ZnTFSI₂</td><td>2</td><td>1.45</td><td>2.42</td></tr><tr><td>3</td><td>Zn(ClO₄)₂</td><td>2</td><td>1.47</td><td>2.28</td></tr></tbody></table>

hydrophilic nature of the polymer electrodes as a high number of redox-active moieties can be addressed in the cell. At increasing rates, the addressed capacity decreases continuously. Nevertheless, relative capacities of >50% can still be achieved even at rates of 50C, although differences between the electrolytes become apparent. In comparison, the Zn(ClO₄)₂ electrolyte led to the highest capacity retention under higher charging currents with the ZnOTf₂ system close by. In case of ZnTFSI₂, however, the material utilization is more significantly reduced when higher charging rates are applied. We assume that this is due to the low polarity of the TFSI-anion which can result in weak interactions between the polar polymer and the supporting electrolyte, impeding the
<figure><img src="image_9.png" /><figcaption>Fig. 3. Cyclic voltammetry measurements of 3% crosslinked PTAMm/Zn coin cells at 0.1, 0.2, 0.5, and 1.0 mV·s⁻¹ scanning speeds and varying supporting electrolyte: a) 2 M Zn(OTf)₂, b) 2 M ZnTFSI₂, c) 2 M Zn(ClO₄)₂. Associated half-wave potentials are given in Table 1.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Fig. 4. Charging rate tests for 3% crosslinked PTAMm/Zn batteries with a) 2 M Zn(OTf)₂, b) 2 M ZnTFSI₂ and c) 2 M Zn(ClO₄)₂ aqueous solution as supporting electrolyte. Normalized average discharge capacities during the rate tests are depicted in diagram d).</figcaption></figure>

charge equilibration during the charging/discharging reactions. For the present system, the migration of the counter anions of the supporting electrolyte into the polymer matrix is particularly important as they are required by the cathode material for the charge equilibration upon charging. Apparently, the perchlorate counterion matches the polymer polarity requirements, which leads to reversible redox chemistry and efficient migration of the ion into the polymer matrix. Another set of 1C cycles was tested after charging with the highest rate of 50C. The initial capacity observed for the first 1C cycling can be reobtained rebutting any sign of degradation of the active materials for all utilized electrolytes. Therefore, the decrease in capacity is related to an intrinsic resistance of the cells and a limited diffusion rate of the ions, which might reflect the observed differences between the applied electrolytes. In general, the full addressability of the material at higher charging/discharging currents appears to be limited due to a hampered migration of the supporting electrolytes into the composite matrix or even within the electrolyte solution. Therefore, for all supporting electrolytes, we observe a reduced utilization of the active material at higher cycling rates. For the PTAm polymer, presented by Koshika et al., higher material usage values have been presented, but, the authors investigated only very thin electrode films of 50 nm to 3.2 µm thickness [15]. Furthermore, Hatakeyama-Sato et al. presented another outstanding

amide-coupled TEMPO-polymer, which was applicable in high-capacity batteries and yielded 80% of capacity retention at a charging rate of 10C in electrodes of millimeter-range thickness [32]. This emphasizes the application potential for the hydrophilic polymers that feature amide-connected redox active groups.

Moreover, the self-discharge of the semi-organic aqueous cells was investigated in identical coin cells. For this purpose, the active material was charged and left under OCV conditions for 12, 24, 48 and 72 h. After this time, the discharge capacity was compared with the charge capacity prior to the OCV phase. This method was presented recently by Gerlach et al. and can yield precious information about the shelf life of the device, which is rarely presented in literature [33]. The percentage of capacity retained after self-discharge is shown in Fig. 5. The lowest self-discharge is obtained from the Zn(ClO₄)₂ cells, which retain approximately 90% of capacity after up to 24 h OCV. These values are higher compared to the ZnTFSI₂ and Zn(OTf)₂ electrolytes, which immediately drop to around 80% of original capacity after OCV for 12 to 24 h. Additional capacity is lost when the cell is left at OCV for longer times. However, it can be noted that for all cells, the highest amount of capacity is lost directly after starting the OCV technique. The cells comprising the Zn(ClO₄)₂ electrolyte still maintained 87% of their capacity after 72 h. Generally, the self-discharge in the cells can be
<figure><img src="image_11.png" /><figcaption>Fig. 5. a) Percentage of retained capacity after self-discharge for the PTMAm/Zn batteries with three different supporting electrolytes. b) Discharging capacities during float tests for the PTMAm/Zn cells. Voltage of 1.7 V was held for 10 h, then five cycles of 1C charging rate were performed. The initial discharge capacity of each supporting electrolyte system is greater than for the next four cycles due to the preceding voltage hold time.</figcaption></figure>

explained by the presence of smaller, soluble polymer fragments, which can act as redox shuttles between the electrodes, leading to charge equilibration when no external voltage is applied.

Float testing was performed for 500 h to check the material's resilience under stressful charging conditions (Fig. 5). All supporting electrolytes showed stable behavior during the float tests with minor capacity fading after 500 h. 97% and 98% of discharge capacity are retained for the triflate and the perchlorate salt, respectively. A capacity retention of 96% is obtained for ZnTFSI₂. It must be noted that for all investigated supporting electrolytes, the initial discharge capacity after the 10 h hold time is significantly higher compared to the following four cycles. However, ZnTFSI₂ led to a higher difference between the first and the next four cycles per cycling loop. The initially achieved discharge capacity directly after the 10 h holding period suggested the presence of TEMPO-moieties that are not addressed during cycling at 1C but can be reached when the maximum charging voltage is held for longer time periods. This can be seen from the stable discharge capacities during the subsequent four cycles at 5C after the initial discharge after the 10 h time period. The other electrolytes did not display such a pronounced

difference between the first and the subsequent cycles. This strategy, to combine float testing and self-discharge evaluation for organic battery material characterization, has been shown by Gerlach *et al*. recently and has been adapted from super capacitor research [33]. Float testing and self-discharge evaluations are currently not performed extensively in literature for organic coin cell materials; however, we expect such investigations to deliver valuable information about shelf life, stability and feasibility of the active materials for practical use.

To investigate the long-term stability of the synthesized material, the coin cells were further cycled at 5C for at least 20 days, which corresponds to >1000 cycles. The obtained efficiencies and charge/discharge capacities are depicted in Fig. 6. All utilized electrolytes in combination with the redox-active materials are suitable for long-term cycling and form stable batteries with excellent cyclability.

However, some differences could be again observed comparing the different electrolytes. The lowest capacity fade is observed for the Zn (ClO₄)₂ supporting electrolyte, which leads to a capacity retention of 99.7% after 1000 consecutive cycles at 5C charging rate. The cell exhibits a material usage of 76.8%, which is comparable to the results of

<figure><img src="image_12.png" /><figcaption>Fig. 6. Efficiency (green) and charge (blue) and discharge (red) curves for the long-term cycling of the PTMAm electrodes at 5C utilizing a) Zn(OTf)₂, b) ZnTFSI₂ and c) Zn(ClO₄)₂ supporting electrolytes. An overview for the material usage (green) and capacity retention (blue) after 1000 consecutive cycles at galvanostatic cycling is given in diagram d). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>
the rate dependency tests (Fig. 6). A similar behavior is observed for the Zn(OTf)₂ electrolyte, which shows a capacity retention of 98.5% after 1000 cycles. The material usage is, however, slightly lower with 74.3% of the initial capacity. While the capacity retention for the TFSI electrolyte is the lowest, at 97.7%, this value can still be considered sufficient for most potential applications. However, the material usage of 52.4% is rather low compared to the other electrolytes. Again, Koshika et al. reached higher values due to the utilized lower electrode thickness [15]. This is in good accordance with the previous results, suggesting the perchlorate to be most suitable for the PTMAm electrodes while the TFSI salts are less favorable. However, all electrolytes yielded batteries that were able to be cycled for over 1000 cycles. Only thereafter some of the TFSI- or OTf-based cells resulted in shot-circuits, which is supposedly a result of dendrite formation at the zinc counter electrode. This is concluded from the fact that the batteries restarted the cycling after a longer time period under short-circuit conditions, which may be caused by the detachment of the zinc dendrites from the zinc electrode surface, disabling the short-circuit (see Supporting Information, Fig. S7). For the Zn(ClO₄)₂-containing cells, this behavior was not observed. Next to the dendrite growth, other detrimental processes originating on the zinc anode can be considered for the present cell chemistry. In the acidic media that have been investigated, a hydrogen evolution reaction cannot be completely denied and is expected to be closely related to the dendrite formation. Further general zinc electrode corrosion or passivation can be expected at the low pH-values present [34–36]. However, we expect the most harming effect in our batteries to be dendrite growth as it causes battery failure after ca. 1000 consecutive cycles. Generally, the kind and concentration of supporting electrolyte anions is expected to play an important role for the reversibility of the zinc anode. However, the comparably high concentrated supporting electrolyte solution yielded working zinc electrode with all supporting electrolytes.

## 2.4. All aqueous one-pot procedure

The hydrophilic nature of the material does not only enable aqueous batteries but also an adaption of the processing strategies circumventing the need for any organic solvents. Moreover, the fact that all previous steps including the polymerization are aqueous-based made us consider a preparation procedure without any intermediate isolation and purification steps. After each reaction step, the necessary reactants were

added, and the reaction times were kept identical to the previous synthesis pathway. Starting with a quasi-one-pot synthesis, the initial precipitation polymerization was repeated, but the polymer dispersion was not filtered off. Subsequently, hydrogen peroxide was simply added to the suspension inducing the transformation of the secondary amine to the nitroxide moiety. Since the polymer was not dried previously, the swelling step could be already skipped.

For in-depth investigation of the battery material from the all-aqueous processing procedure, an aliquot of the reaction suspension was taken after the oxidation, and SuperP® conductive additive was added directly to the aqueous reaction mixture without lyophilization. It must be noted that for this procedure, no milling was applied to keep the procedure as straight-forward as possible and solely rely on the material hydrophobicity, instead of also increasing the surface area of the polymer particles, to facilitate addressing the TEMPO-moieties. To the SuperP® and reagent mixture, a small amount of carboxymethylcellulose (CMC) binder was added to enable smooth processing of the electrode slurry and to increase the adhesion of the electrode paste on the graphite templates. The aqueous slurry was again drop-casted on pre-weighed graphite sheets that were processed to coin cells after drying. The coin cell tests were performed according to the previous investigations and showed stable battery behavior. The first rate testing experiments are depicted in Fig. 7.

The obtained batteries revealed a rate capability that has similarly been shown for the NMP-processed cells. However, a pronounced charging capacity loss at higher rates occurred, which has not been visible for the conventionally prepared batteries in this order of magnitude. This is also visualized in Fig. 7, which indicates a strong capacity loss when a charging rate of 10C is exceeded. A possible explanation could be the missing milling step, which would yield smaller particle sizes and, consequently, shorter diffusion pathways. However, under moderate rates, the addressable capacity is comparable to the previous battery tests. The initially reachable 1C capacity can be reobtained after the charging rate test, which is desirable for reversible battery behavior. Again, the highest material usage is observed for Zn(ClO₄)₂ at 71.1% at 1C and 72.3% at 0.2C charging rate. As expected, this material usage drops further until nearly no material can be addressed at 50C, which is a difference from the composite from the initial tests. Here, the impurities and the water-soluble binder seem to impair the battery performance significantly. The corresponding

<figure><img src="image_13.png" /><figcaption>Fig. 7. Charging rate tests for 3% crosslinked PTMAm/Zn batteries (one-pot process) with a) 2 M Zn(OTf)₂, b) 2 M Zn(OTf)₂ and c) 2 M Zn(ClO₄)₂ aqueous solution as supporting electrolyte. The active material was obtained from one-pot preparation starting with the monomers. d) Comparison of the C rate test for the 3% crosslinked PTMAm/Zn batteries with different supporting electrolytes. Results from the standard processing procedure were included as a comparison between both routes.</figcaption></figure>
behavior is also seen for ZnTFSI₂ which exhibits 65.2% material usage at 1C and 72.0% at 0.2C and drops strongly afterwards until no material is used at 50C as was observed for the perchlorate salt. For Zn(OTf)₂, material usages of 63.5% at 1C and 65.4% at 0.2C where observed. While the material usage drops as before, 25.2% material is still used at 50C.

The self-discharge tests (Fig. 8) revealed a significant self-discharge for the Zn(ClO₄)₂, with only 20% of capacity remaining after 72 h OCV period. However, the capacity retention for ZnTFSI₂ and Zn(OTf)₂ is higher, while also 40% of initial capacity are lost, when the cells are kept at OCV for 72 h. Again, the strongest effect is observed in the first 12 h of OCV, leading to a 20% capacity loss. This can be related to larger particles detaching from the electrode surface after the charging step due to an expected pronounced swelling in the charged state. On the other hand, due to the one-pot-processing, remaining impurities of oxidation agents are present, which may cause interference. Tungstate salts show a very high redox activity themselves, which might be suitable for the catalyzed oxidation step but is apparently not beneficial for the performance of the coin cells. Furthermore, redox-active species might act as redox shuttling units, which can result in self-discharge through charge equilibration between the electrodes. Notably, the Zn(ClO₄)₂ supporting electrolyte results in the strongest self-discharge, while it yielded the lowest self-discharge values in the previous investigation for the conventionally prepared material. Apparently, the different electrolyte salts have a strong influence on the water solubility of the residual soluble hydrophilic polymer chains, resulting in different amounts of dissolved redox shuttles. Compared to PTMA, it can be expected that short chains of PTMAm are more soluble in the aqueous electrolytes due to their intrinsic hydrophilicity. This leads to more shuttling processes if short chains are present, compared to PTMA, which is rather hydrophobic. The float test data again showed similar trends as for the NMP-processed cells. The initial capacity after the hold time is significantly higher than for the consecutive four cycles, which follows the same mechanism as for the NMP-cells. However, the overall stability of the cycling is decreased, mainly in the case of the TFSI-electrolyte. Here, the discharge capacities vary strongly and fade significantly. Triflate and perchlorate led to a rather stable floating behavior.

Also, long-term cycling experiments have been performed for the one-pot reacted materials. The batteries revealed high capacity retentions with 99.1% after 500 cycles for the Zn(OTf)₂, 93.4% for ZnTFSI₂ and 96.2% for Zn(ClO₄)₂. For all electrolytes, high efficiencies are exhibited, but overall lower material usages are observed at a charging rate of 5C (Fig. 9). 46.5% of the theoretical capacity is used when the Zn(OTf)₂ electrolyte is used, 55.6% is achieved for the Zn(ClO₄)₂. Again, the lowest material usage is shown by the ZnTFSI₂ at 30.6%. Generally, Zn(ClO₄)₂ electrolyte batteries showed failure after few hundred cycles, while triflate and TFSI salts revealed higher cycle stabilities. Generally, the batteries exhibited lower lifetimes and

batteries failed quicker than before. Therefore, the capacity retention was calculated after 500 cycles. Generally, the capacity retentions suffer strongly, as can be seen from the fact that the one-pot-processed composite exhibit lower capacity retentions after 500 cycles than the previous batteries after 1000 cycles at 5C. This indicates that more optimization of the procedure is necessary to yield equally stable battery chemistries.

## 2.5. High-capacity devices

After the one-pot oxidation step, a greater part of the reaction mixture was lyophilized and experiments to yield high-capacity batteries were performed. A summary of the processing steps towards batteries with ultra-thick electrodes is given in Fig. 10. For the first route, the obtained solid was processed into a very thick slurry by adding SuperP® as conductive additive and a small amount of water (for details, see the Supporting Information). It is noteworthy to mention that no ball milling process was utilized in both routes, simplifying the process significantly. Interestingly, no binder had to be added to the slurry under these conditions as the hydrophilic PTMAm appeared itself to be sufficient for binding the conductive agent and forming a homogenous matrix. The mixture was casted into a round shape and dried completely. The dry material could be put onto 15 mm graphite disks and soaked with the battery electrolyte, namely 2 M Zn(ClO₄)₂, over a few days. By this means, battery cells with an electrode loading of 45 mg cm⁻² were constructed. That exceeds the previous battery electrode loadings by 60 times and resulted in an average theoretical capacity of 5.5 mAh in the coin cell, which corresponds to approximately 3.1 mAh cm⁻² (4.5 mWh cm⁻² at a charging/discharging voltage of 1.45 V). This can be considered as a significant advantage, in comparison to the current literature which commonly utilizes material loadings of only 4–6 mg cm⁻² [9,37], 3–4 mg cm⁻² [38], or 2.5–10 mg cm⁻² [39].

Analogous to the previous investigations, the material was firstly subjected to CV analysis at low scanning rates on the one hand to prove the addressability of the redox-active material in the thicker electrode and, on the other hand, to maximize the wetting of the redox active material. The CV (Fig. S6) revealed a similar redox potential, 1.49 V (vs. Zn/Zn²⁺). Due to the expectedly high cell resistance, the oxidation and re-reduction signal are strongly separated in the CV. The material showed reversible oxidation and reduction behavior, even in the thick electrodes. Different scanning rates again suggested a reversible redox behavior; however, it must be noted that already scanning rates of 1.0 mV s⁻¹ lead to cell failure in some test cells, which is related to the extremely high peak currents that are achieved by those rates and the caused strong swelling behavior. Galvanostatic cycling was subsequently performed between 1.2 and 1.7 V. Notably, the voltage limits had to be adjusted when the thick electrodes are used, as deeper discharge revealed another charging/discharging plateau that did not appear to resemble a fully reversible redox process. The high-capacity

<figure><img src="image_14.png" /><figcaption>Fig. 8. a) Percentage of retained capacity after self-discharge for the one-pot prepared PTMAm/Zn batteries with three different supporting electrolytes. b) Discharging capacities during float tests for the one-pot prepared PTMAm/Zn cells. Voltage of 1.7 V was held for 10 h, then five cycles of 1C charging rate were performed. The initial discharge capacity of each supporting electrolyte system is greater than for the next four cycles due to the preceding voltage hold time.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Fig. 9.** Efficiency (green) and charge (blue) and discharge (red) curves for the long-term cycling of the PTMAm electrodes (one-pot process) at 5 C utilizing Zn(OTf)₂ (a), ZnTFSI₂ (b) and Zn(ClO₄)₂ (c) supporting electrolytes. An overview (d) for the material usage (green) and capacity retention (blue) after 350 consecutive cycles at galvanostatic cycling is given. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>**Fig. 10.** Schematic representation of the processing steps to yield high-capacity coin cells. Route I comprises casting, drying and soaking a composite plug with electrolyte. Route II comprises preparation of the coin cells, direct with an electrolyte-soaked composite slurry.</figcaption></figure>

batteries exhibit a stable charging plateau at 1.48 V and discharging plateau at 1.43 V (Fig. 11).

The missing binder does not seem to impair the battery performance.

Also, the present impurities that result from the reaction are not disturbing the cyclability. Therefore, the ultra-thick electrodes can be cycled stably at 0.1C (0.31 mA cm⁻²) charging rate for 45 cycles. Higher
<figure><img src="image_17.png" /><figcaption>**Fig. 11.** a) Cycling test for the high-capacity cells at 0.1C with charging (blue) and discharging (red) capacities. b) Every tenth cycle is depicted to visualize the charging/discharging plateau. After the first charging/discharging cycle, the cutoff voltage of 1.2 V was adjusted to 1.1 V. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>

charging rates repeatedly led to battery failures. The coin cells appeared to be pushed apart when the charging rates are too high. We expect this behavior to derive from the faster swelling of the active material at higher rates, without time to swell evenly distributed over the whole electrode surface. This effect can also be caused by inhomogeneous material distributions, which can ultimately lead to inhomogeneous swelling. However, a capacity retention of 94% after 45 cycles could be measured for the aqueous, binder-free, ultra-thick approach after cycling for 45 cycles at 0.1C.

It is also possible to prepare high-capacity cells without the need for soaking the battery materials with electrolyte for several days. Therefore, battery slurries were prepared by directly soaking the lyophilized material in aqueous 2 M Zn(ClO₄)₂ solution instead of deionized water and constructing the coin cells with the wet slurry. An additionally soaked separator is added to increase the overall amount of Zn(ClO₄)₂ in the cell as higher amounts of cathode material require a sufficient capacity of the counter electrode. This ultra-straightforward processing yielded working batteries with high capacities. During cycling, an initial equilibration period is observed with slightly fading charge/discharge capacities during the first ten cycles. This is referred to the swelling of the electrode in the charged state. It is possible that several redox-active moieties are addressed during the first cycles that are not active during the subsequent battery cycling. However, reversible battery behavior was observed with stable cycling at 0.1C for 80 cycles and a capacity retention of 93% after 45 cycles (Fig. 12). The redox potential is similar to the previously measured values. However, the charging plateaus appeared to be more constant and only a minor shift of the plateaus' position is observed. Comparable to the previous electrodes that were prepared by soaking a dried composite disk with the electrolyte, the higher charging rates of >0.2C led to battery failure.

Interestingly, the batteries utilize a high amount of active material despite the fact that the active material and the conductive agent are

simply ground in a mortar for a few minutes instead of homogenization in a shear rate stirrer. This indicates a sufficient electron conductivity in the cathode material and represents a highly promising approach towards practically applicable batteries. While the composition must be subjected to optimization to enable higher charging currents and higher cycle stability, the overall preparation process convinces due to its straightforward character, lack of swelling times and upscaling possibilities.

### 3. Conclusion

A TEMPO-carrying crosslinked active material, poly(TEMPO-methacryloylamide) (PTMAm), was synthesized in an all-aqueous synthesis procedure and was characterized in detail. The material precipitates from solution as a fine powder and is highly wetable and swellable in water, enabling the use of aqueous electrolytes in a coin cell setup, which has not been possible for the structurally related poly (TEMPO-methacrylate) (PTMA). By this strategy, the redox activity and the stable cycling behavior of the PTMA is retained while cycling the semi-organic battery in an aqueous electrolyte. Since aqueous electrolytes are cost-efficient, rather non-toxic and available in large quantities, they are in particular promising for energy storage devices. Together with the zinc counter electrode, the water compatibility, oxygen tolerance and the electrochemical working window of these electrolytes is fully used and a battery voltage of 1.5 V is achieved.

Two material synthesis and processing routes have been evaluated. The first route comprised the individual focus on each process step with separate purification steps, while the second involved one-pot processing from the monomers to the finished composite electrodes. For the first route, the material was synthesized stepwise and subsequently introduced into a coin cell battery setup utilizing zinc as counter electrode with three zinc-based supporting electrolytes under ambient conditions.

<figure><img src="image_18.png" /><figcaption>**Fig. 12.** a) Cycling behavior of high-capacity coin cells with charge (blue) and discharge (red) capacities, fabricated from a non-dried slurry that was fabricated with 2 M Zn(ClO₄)₂. b) Every tenth cycle is depicted to visualize the charge/discharge plateau. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)</figcaption></figure>
However, the cell preparation involved NMP as solvent, which was replaced in the subsequent all-aqueous preparation approach. The cells showed high material usage, good cyclability, and stable charging capacities at high efficiencies. The performance of the batteries strongly indicated that the PTMA-typical cycling behavior is retained and the hydrophilicity is efficiently introduced to the polymer. Thus, PTAM can be a valuable new alternative for PTMA where aqueous electrolytes are chosen – both in research applications but also for potential commercial scenarios.

For the latter, the second preparation approach is of particular importance. Here, the monomers were polymerized and oxidized without purification after each reaction step. Similar composite electrodes, utilizing PTAM, could then be obtained from this aqueous one-pot approach by adding conductive agent and a water-soluble binder to the reaction mixture. By this processing, toxic solvents are completely excluded from the processing procedure and binder-free electrodes can be realized. Also, no ball-milling was required as the fine polymer precipitate exhibited sufficient active material addressability. Again, this is attractive for a potential large-scale synthesis. At moderate cycling rates, the materials from this processing route reveal a similar behavior, which emphasizes the feasibility of aqueous one-pot processing for the poly (methacrylamide) material. However, the reaction-derived impurities in the second approach alter the cyclability of the batteries, with a slightly decreased capacity retention. Also, the rate capability suffers, as could be shown for all supporting electrolytes, which reveal significantly reduced material usages at elevated charging rates. Furthermore, self-discharge and floating tests have been performed, as previously presented by Münch et al. We expect these kinds of tests to be of high importance for future battery material characterizations as they deliver valuable information about shelf live or battery lifetimes under rather realistic conditions.

From a lyophilizate of the all-aqueous reaction, binder-free, high-capacity electrodes were prepared by casting a thick electrode slurry in a coin cell with subsequent drying. They revealed stable galvanostatic cycling at lower charging rates and a device capacity of approximately 4.5 mAh. These ultra-thick electrodes are a significant, roughly 10-fold, improvement in terms of capacity compared to the current literature. As an alternative processing route towards high capacities, the thick battery slurry was utilized directly as active cathode side in a coin cell. This preparation procedure yielded stably cycling batteries and, therefore, opens a completely new processing possibility of TEMPO-based polymer materials. Together with the compatibility with aqueous electrolytes, this processing procedure is highly attractive to greater-scale applications. The presented capacities approach the values of practically applicable commercial zinc primary cells. However, we presented secondary cells that feature the intrinsic advantage of charge/discharge compatibility. Furthermore, organic electrode materials have been shown to be compatible with inkjet- and screen-printing procedures. While the system requires further optimization and finetuning of the active material composition, the results are promising towards realizing a real alternative for established primary cells.

### CRediT authorship contribution statement

**Erik Schröter:** Conceptualization, (lead), Methodology, (lead), Validation, (lead), Data curation, (lead), Formal analysis, (lead), Visualization, (lead), Writing – original draft. **Lada Elbinger:** Conceptualization, (supporting), Investigation, (supporting), Writing – review & editing, Critical Review, (equal). **Manon Mignon:** Investigation, (lead), Writing – review & editing, Critical Review, (equal). **Christian Friebe:** Formal analysis, (supporting), Supervision, (of L. E.), Writing – review & editing, Critical Review, (equal). **Johannes C. Brendel:** Conceptualization, (supporting), Methodology, (supporting), Writing – review & editing, Critical Review, (equal). **Martin D. Hager:** Writing – review & editing, Critical Review, (equal), Supervision, (of E. S.), Funding acquisition, (equal). **Ulrich S. Schubert:** Writing – review & editing,

Critical Review, (equal), Supervision, (of E. S. und L. E.), Funding acquisition, (equal).

### Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Ulrich Schubert reports financial support was provided by Thüringer Aufbaubank. Johannes Brendel reports financial support was provided by Deutsche Forschungsgemeinschaft.

### Data availability

Data will be made available on request.

### Acknowledgements

We gratefully acknowledge the financial support of the Thüringer Aufbaubank (TAB, project 2019 FGR 0080). Johannes C. Brendel further thanks the German Science Foundation (DFG) for generous funding within the Emmy-Noether program (Project-ID: 358263073). We would also like to thank the Université de Montpellier for realizing the internship of Manon Mignon.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jpowsour.2022.232293.

### References

[1] N. Goujon, N. Casado, N. Patil, R. Marcilla, D. Mecerreyes, Prog. Polym. Sci. 122 (2021), 101449, https://doi.org/10.1016/j.progpolymsci.2021.101449.

[2] J. Heiska, M. Nisula, M. Karppinen, J. Mater. Chem. 7 (2019) 18735–18758, https://doi.org/10.1039/C9TA04328D.

[3] H. Nishide, Green Chem. 24 (2022) 4650–4679, https://doi.org/10.1039/D2GC00981A.

[4] B. Esser, F. Dolhem, M. Becuwe, P. Poizot, A. Vlad, D. Brandell, J. Power Sources 482 (2021), 228814, https://doi.org/10.1016/j.jpowsour.2020.228814.

[5] B. Esser, Organic Mater. 1 (2019) 63–70, https://doi.org/10.1055/s-0039-3401016.

[6] Z. Guo, Y. Ma, X. Dong, J. Huang, Y. Wang, Y. Xia, Angew. Chem. Int. Ed. 57 (2018) 11737–11741, https://doi.org/10.1002/ange.201807121.

[7] H. Nishide, K. Oyaizu, Science 319 (2008) 737–738, https://doi.org/10.1126/science.1151831.

[8] L. Yang, P. Wang, S. Zhang, Y. Wang, L. Zang, H. Zhu, J. Yin, H.Y. Yang, J. Mater. Chem. 8 (2020) 22791–22801, https://doi.org/10.1039/D0TA07267B.

[9] Z. Guo, Y. Ma, X. Dong, J. Huang, Y. Wang, Y. Xia, Angew. Chem. Int. Ed. 57 (2018) 11737–11741, https://doi.org/10.1002/anie.201807121.

[10] W. Liu, Z. Zhao, T. Li, S. Li, H. Zhang, X. Li, Sci. Bull. 66 (2021) 457–463, https://doi.org/10.1016/j.scib.2020.08.042.

[11] C. Han, J. Zhu, C. Zhi, H. Li, J. Mater. Chem. 8 (2020) 15479–15512, https://doi.org/10.1039/D0TA03947K.

[12] B. Häupler, C. Rössel, A.M. Schwenke, J. Winsberg, D. Schmidt, A. Wild, U. S. Schubert, NPG Asia Mater. 8 (2016), e283, https://doi.org/10.1038/amt.2016.82.

[13] W. Sun, F. Wang, B. Zhang, M. Zhang, V. Küpers, X. Ji, C. Theile, P. Bieker, K. Xu, C. Wang, M. Winter, Science 371 (2021) 46–51, https://doi.org/10.1126/science.abb9554.

[14] J. Winsberg, S. Muench, T. Hagemann, S. Morgenstern, T. Janoschka, M. Billing, F. H. Schacher, G. Hauffman, J.-F. Gohy, S. Hoeppener, M.D. Hager, U.S. Schubert, Polym. Chem. 7 (2016) 1711–1718, https://doi.org/10.1039/C5PY02036K.

[15] K. Koshika, N. Chikushi, N. Sano, K. Oyaizu, H. Nishide, Green Chem. 12 (2010) 1573, https://doi.org/10.1039/b926296b.

[16] K. Koshika, M. Kitajima, K. Oyaizu, H. Nishide, Green Chem. Lett. Rev. 2 (2009) 169–174, https://doi.org/10.1080/17518250903251775.

[17] Y. Luo, F. Zheng, L. Liu, K. Lei, X. Hou, G. Xu, H. Meng, J. Shi, F. Li, ChemSusChem 13 (2020) 2239–2244, https://doi.org/10.1002/cssc.201903083.

[18] Y. Deng, C. Teng, Y. Wu, K. Zhang, L. Yan, ChemSusChem (2022), e202102710, https://doi.org/10.1002/cssc.202102710.

[19] E. Grignon, A.M. Battaglia, T.B. Schon, D.S. Seferos, Science (2022), 104204, https://doi.org/10.1016/j.isci.2022.104204.

[20] K. Nakahara, S. Iwasa, M. Satoh, Y. Morioka, J. Iriyama, M. Suguro, E. Hasegawa, Chem. Phys. Lett. 359 (2002) 351–354, https://doi.org/10.1016/S0009-2614(02)00705-4.
[21] S. Wang, A.M.G. Park, P. Flouda, A.D. Easley, F. Li, T. Ma, G.D. Fuchs, J. L. Lutkenhaus, ChemSusChem 13 (2020) 2371–2378, https://doi.org/10.1002/cssc.201903554.

[22] Y. Feng, T. Suga, H. Nishide, Y. Ohki, G. Chen, S. Li, Macromol. Rapid Commun. 40 (2019), e1800734, https://doi.org/10.1002/marc.201800734.

[23] M. Khodeir, H. Jia, A. Vlad, J.-F. Gohy, Polymers 13 (2021), https://doi.org/10.3390/polym13081307.

[24] M. Khodeir, H. Jia, S. Antoun, C. Friebe, U.S. Schubert, Y. Lu, E. van Ruymbeke, J.-F. Gohy, J. Polym. Sci. 58 (2020) 1553–1563, https://doi.org/10.1002/pol.20200172.

[25] P. Rohland, E. Schröter, O. Nolte, G.R. Newkome, M.D. Hager, U.S. Schubert, Prog. Polym. Sci. (2021), 101474, https://doi.org/10.1016/j.progpolymsci.2021.101474.

[26] S. Muench, P. Gerlach, R. Burges, M. Strumpf, S. Hoeppener, A. Wild, A. Lex-Balducci, A. Balducci, J.C. Brendel, U.S. Schubert, ChemSusChem 14 (2020) 449–455, https://doi.org/10.1002/cssc.202002251.

[27] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Macromol. Chem. Phys. 210 (2009) 1989–1995, https://doi.org/10.1002/macp.200900257.

[28] W. Xue, H. Mutlu, H. Li, W. Wenzel, P. Theato, Polym. Chem. 12 (2021) 2643–2650, https://doi.org/10.1039/D0PY01421D.

[29] T. Janoschka, N. Martin, M.D. Hager, U.S. Schubert, Angew. Chem. Int. Ed. 55 (2016) 14427–14430, https://doi.org/10.1002/anie.201606472.

[30] Y. Yonekuta, K. Oyaizu, H. Nishide, Chem. Lett. 36 (2007) 866–867, https://doi.org/10.1246/cl.2007.866.

[31] O. Nolte, R. Geitner, M.D. Hager, U.S. Schubert, Adv. Energy Mater. 11 (2021), 2100931, https://doi.org/10.1002/aemn.202100931.

[32] K. Hatakeyama-Sato, H. Wakamatsu, R. Katagiri, K. Oyaizu, H. Nishide, Adv. Mater. 30 (2018), e1800900, https://doi.org/10.1002/adma.201800900.

[33] P. Gerlach, A. Balducci, Electrochim. Acta 377 (2021), 138070, https://doi.org/10.1016/j.electacta.2021.138070.

[34] Y. Shang, D. Kundu, Batter. Supercaps 5 (2022), https://doi.org/10.1002/batt.202100394.

[35] C. Han, W. Li, H.K. Liu, S. Dou, J. Wang, Nano Energy 74 (2020), 104880, https://doi.org/10.1016/j.nanoen.2020.104880.

[36] F. Wan, X. Zhou, Y. Lu, Z. Niu, J. Chen, ACS Energy Lett. 5 (2020) 3569–3590, https://doi.org/10.1021/acsenergylett.0c02028.

[37] W. Wang, V.S. Kale, Z. Cao, Y. Lei, S. Kandambeth, G. Zou, Y. Zhu, E. Abouhamad, O. Shekhah, L. Cavallo, M. Eddaoudi, H.N. Alshareef, Adv. Mater. 33 (2021), e2103617, https://doi.org/10.1002/adma.202103617.

[38] Y. Gao, G. Li, F. Wang, J. Chu, P. Yu, B. Wang, H. Zhan, Z. Song, Energy Storage Mater. 40 (2021) 31–40, https://doi.org/10.1016/j ensm.2021.05.002.

[39] Q. Zhao, W. Huang, Z. Luo, L. Liu, Y. Lu, Y. Li, L. Li, J. Hu, H. Ma, J. Chen, Sci. Adv. 4 (2018), eaao1761, https://doi.org/10.1126/sciadv.aao1761.