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Pyromellitic diimide-based copolymers and their application as stable cathode active materials in lithium and sodium-ion batteries Nicolas Zindy, J. Terence Blaskovits, Catherine Beaumont, Julien MichaudValcourt, Hamidreza Saneifar, Paul A. Johnson, Daniel Bélanger, and Mario Leclerc Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b02862 • Publication Date (Web): 12 Sep 2018 Downloaded from http://pubs.acs.org on September 12, 2018

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Chemistry of Materials

Pyromellitic diimide-based copolymers and their application as stable cathode active materials in lithium and sodium-ion batteries Nicolas Zindy,† J. Terence Blaskovits,† Catherine Beaumont,† Julien Michaud-Valcourt,† Hamidreza Saneifar,‡ Paul A. Johnson,† Daniel Bélanger‡* and Mario Leclerc†* † ‡

Département de chimie, Université Laval, Québec, QC, Canada, G1V 0A6. Département de chimie, Université du Québec à Montréal (UQÀM), Montréal, QC, Canada, H3C 3P8

ABSTRACT: Organic molecules are emerging candidates for the next generation of cost-effective active materials of Li-ion batteries. Small diimide building blocks such as pyromellitic diimide (PMDI) have attracted much attention due to their high theoretical capacity. Many strategies have been undertaken to limit the well-known phenomenon of dissolution of the active material in the electrolyte. Such strategies include the preparation of salts and the synthesis of polyimides or macrocycles. Since dibromopyromellitic dimiide exhibits almost no sp2 cross-coupling polymerization reaction by conventional synthetic routes (Suzuki-Miyaura or Migita-Stille), we used PMDI as an aromatic C-H bond-bearing unit for direct (hetero)arylation polymerization (DHAP) with 1,4-dibromobenzene as comonomer as a new stabilization strategy. DHAP proved to be an effective tool in the preparation of this polymer, yielding a number average molecular weight of up to 31 kDa. We studied the effect of side-chain engineering using variable chain lengths, cross-linked structures and thermocleavable functional groups. Practical potential limits of 1.65 to 2.50V vs. Li/Li+, wherein two distinct redox phenomena appear, and a galvanostatic high rate limit of 2C were determined. Galvanostatic measurements at C/20 show a starting normalized capacity of 0.94 decreasing to 0.48 after more than 80 days (50 cycles). A maximum discharge capacity of 73 mAh/g as a first cycle was obtained for a polymer of this family at C/10. Density functional theory calculations were applied to understand the higher corrected redox potentials obtained by cyclic voltammetry for sodium ion over lithium ion batteries.

INTRODUCTION Since the advent of π-conjugated polymers, a large library of organic semiconducting materials has been synthesized, allowing for their use in several applications ranging from the production and transport to conversion and storage of energy (i.e. solar cells, transistors, light-emitting diodes, electrochemical capacitors and rechargeable batteries).1-4 These materials are generally synthetized via Migita-Stille5 or SuzukiMiyaura6 cross-coupling methodologies relying on the preparation of monomers functionalized with organotin or organoborane compounds, respectively. Direct (hetero)arylation polymerization (DHAP) is an emerging polymerization technique which uses reactive aromatic C-H bonds (primarily thiophene derivatives) with dibrominated arenes7 to produce corresponding π-conjugated polymers in fewer steps, a more cost-efficient way and with increased atom economy than traditional organometallic polymerization techniques.8-11 Also, further benefits arise from reduced toxicity and increased stability of the compounds involved, compared to the organotin functional groups necessary for Migita-Stille polymerization.12 However, despite the synthetic advantages of DHAP, there are very few examples for the C-H activation of aryl derivatives, due to the higher activation barriers of arenes.13 To our knowledge, only three arene monomers have been reported to successfully copolymerize via DHAP to yield linear π-conjugated polymers with an acceptable degree of polymerization, namely 1,2,4,5-tetrafluorobenzene (TFB),14 2,2',3,3',5,5',6,6'-octafluorobiphenyl (OFBP)15 and 5,6-

difluoro-2,1,3-benzothiadiazole (DFBT)16. It is important to highlight that the presence of fluorine atoms for all three monomers is necessary to increase the reactivity of the adjacent CH bonds. This occurs by increasing the kinetics of the concerted metalation-deprotonation (CMD) transition state.12 Furthermore, other arenes of significant interest in organic electronics, specifically 5H-[1,2,5]thiadiazolo [3,4-f]isoindole5,7(6H)-dione (TDID)17 and pyromellitic diimide (PMDI),18 have shown that they could be coupled by direct C-H activation only when an excess of the brominated derivative is present (up to tenfold for the latter), indicative of insufficient reactivity for polymerization. Along these lines, PMDI-based π-conjugated polymers may provide interesting cost-efficient active electrode materials for lithium-ion batteries (LIBs). The PMDI unit has already been extensively studied for this purpose in its salt,19,20 polyimide2125 and macrocyclic26 forms, exhibiting a discharge capacity of up to 227 mAh/g, an average discharge voltage of up to 2.3 V at a cycle rate up to 0.5C. These strategies limit the known issue of the dissolution of small organic molecules into the electrolyte.27 Recently, many investigations in the field have focused on different p-doped polymer electrodes. These have been designed to be applied as matrices and coatings with the aim of enhancing the conductivity as well as flexibility of electrode materials or even be used as active material.28-34 Examples include polyanilines, poly(3,4etylenedioxythiophene)s, polypyrroles and polythiophenes. In contrast, polythienopyrrolediones, recently reported by our

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Figure 1. Former strategies using the chemistry of pyromellitic dianhydride, as compared the present approach, which exploits the reactivity of the pyromellitic diimide C-H bonds to prepare π-conjugated polymers via C–H activation. In this way, the effect of side-chains on the the imide function could be studied.

group, display n-type electrochemical behavior.35 Similarly, PMDI-based π-conjugated polymers could exhibit n-type properties comparable to the naphthalene diimide-bithiophene copolymer already used as an electrode active material exhibiting a discharge capacity of 54 mAh/g with an average discharge voltage of 2.5 V.36 The latter material has previously shown fast cycle rate of up to 100C with almost full utilization of the active cathode material combined with impressive stability for an organic material. Besides, despite an early interest in sodium-ion batteries (SIBs),37,38 the commercial success of LIBs has kept research into sodium-based analogs in the shadows. However, with recent concerns regarding the availability of lithium, SIBs have been regarded as a promising alternative to LIBs, particularly for large scale applications.39-41 Carbonyl compounds are potential candidates for SIBs.30,42 Moreover,

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the imide functional group has already been proven effective when it is used in sodium-ion battery devices.29,43,44 Herein, we report the DHAP of PMDI, the first example of polymerization via direct C–H activation of a non-fluorinated six-membered arene. PMDI was copolymerized with 1,4dibromobenzene to yield copolymers which were studied for their application as a Li-ion and Na-ion cathode active materials. This led us to explore the engineering of the imide functional group through varying the length of alkyl side-chains and using cross-linked and thermocleavable chains, as schematized in Figure 1. SIBs were made and compared to LIBs to highlight the effect of ion size (Li vs. Na) on interactions between the ion and the bridging carbonyl groups that occur within these polymers. Density functional theory (DFT) calculations were undertaken to explain the difference in cyclic voltammetry experiments and the surprisingly good performance of SIBs made with PMDI-based polymers.

EXPERIMENTAL SECTION Synthesis of monomers. As shown in Scheme 1, the anhydride functionalities of commercially available pyromellitic dianhydride (1) undergo imidization with an amine followed by the condensation of the resulting amic acids to afford the corresponding N-substituted pyromellitic diimide (M1, M2 and 3). Then, both alcohol groups on intermediate (3) and both diimide groups on commercially available (4) react with an alkylchloroformate (2) synthesized beforehand (see SI) to produce the carbonate- and carbamate-containing monomers M3 and M4, respectively. M1’ was synthesized using a twostep imidization protocol reported in the Supporting Information.

Scheme 1. Synthesis of monomers (M1, M2, M3, M4), and their corresponding polymers P1, P2 and P3. Also shown are M1-based crosslinked polymers P1C(5%) and P1C(10%) using 5% and 10% of the two-headed monomer M1’, respectively.


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Synthesis of polymers. Polymerization reactions are presented in Scheme 1. Five alternating copolymers (P1, P1C(5%), P1C(10%), P2 and P3) were synthesized via direct (hetero)arylation polymerization (DHAP) between their respective monomer and 1,4-dibromobenzene. No coupling reaction is observed with M4 under the same conditions. In addition to the other advantages described above, DHAP was used for the polymerization of PMDI due to the low coupling efficiency of dibromopyromellitic diimide with the MigitaStille and Suzuki-Miyaura methods.45,46 Preparation of electrodes. The composite electrodes were prepared from a mixture of 30 wt.% polymer, 60 wt.% acetylene black (conductive carbon, Alfa Aesar, 99.5%) and 10 wt.% polyvinylidene fluoride as binder (PVDF, Sigma Aldrich). The solid mixture was crushed with an agate mortar and pestle and N-methyl-2-pyrrolidone (NMP) was added to afford a mixture with a polymer concentration of 30 mg/mL. The mixtures were then ball milled for one hour and deposited on an aluminum foil using a doctor-blade technique (set to a thickness of 150 µm) and dried at 80 °C under vacuum overnight. The electrode was then punched into a 12 mm diameter disk and assembled in a glovebox into CR2032-type coin cells for electrochemical measurements, with metallic lithium foil (0.6 mm (Sigma)) as the counter and reference electrode and a Celgard-2400 membrane as the separator. All potentials are reported vs. Li/Li+. The mass loading of the electrode was between 0.36 mg/cm2 and 0.78 mg/cm2. The electrolyte was 1M LiPF6 in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volumetric ratio of 1:1:1 (LP71 from BASF). Cyclic voltammetry (CV) and galvanostatic charge/discharge curves of half-cells were recorded using a VMP3 potentiostat from Bio-Logic. Capacities of the electrodes were calculated based on the mass of polymer materials. For sodium-based batteries, sodium ACS reagent dry cubes (Sigma) were cut and used as the counter and reference electrode. The 1M NaPF6 electrolyte was prepared by mixing sodium hexafluorophosphate 98% (Sigma) and anhydrous EC (BASF), DEC (BASF), DMC (BASF) in a volumetric ratio of 1:1:1 and stirred at 60 °C for 18h in glove box.

RESULTS AND DISCUSSION Synthesis. The copolymerization conditions used in this work were elaborated from an analysis of small molecule coupling between N-alkyl pyromellitic diimide and bromobenzene. Coupling conditions leading to a pyromellitic diimide conversion of up to 100% with 94% of the desired disubstituted product was found with only one of the optimization conditions attempted): Pd(OAc)2 (0.05 eq.), P(o-OMeC6H4)3 (0.20 eq.), Cs2CO3 (3 eq.), PivOH (1 eq.), toluene (0.5 mol/L), 120 °C (see the Supporting Information for a list of conditions tested). These conditions were then used for the copolymerization of PMDI with 1,4-dibromobenzene without success. We observed the formation of a viscous beige solution upon start of the reaction. To understand the cause of this, we heated PMDI and Cs2CO3 alone in toluene at 120 °C. A white viscous mixture was formed within minutes. We therefore attributed this effect to the complexation of Cs+ ions by the PMDI imides. This phenomenon was successfully suppressed by replacing Cs2CO3 with K2CO3. However, no polymerization occurred under the new reaction conditions, as no solid was obtained upon precipitation of the crude reaction mixture in methanol after heating for 16 hours. Finally, P(o-

(a)

(b)

Figure 2. (a) Conversion of P3 to P3(clvd). (b) Thermogravimetric analysis curve labeled with the corresponding polymeric species.

OMe-C6H4)3 was replaced with P(t-Bu2)Me-HBF4 as the ligand and the heating temperature was increased to 125 °C. This catalytic system, which matches that used for the DHAP of the fluorinated arene 5,6-difluoro-2,1,3-benzothiadiazole,16 served as the reaction conditions for all polymerizations in this study. These conditions were used to produce the polymers P1 (Mn : 13 kDa, PDI : 1.6 (25 repeat units)), P1C(5%) (Insoluble), P1C(10%) (insoluble), P2 (Mn : 31 kDa, PDI : 2.1 (42 repeat units)) and P3 (Mn : 6 kDa, PDI : 1.2 (6 repeat units)), the latter being better represented by the term oligomer. The same protocol was applied to monomer M4 without success. It is suspected that the palladium catalyst is trapped between the imide ketone and the adjacent carbamate ketone. This may also occur for P3, but with less severity due to the longer distance between the imide ketone and the carbonate ketone, and would explain the low molecular weight materials obtained. It should be noted that P1 has short ethylhexyl sidechains and P2 longer octyldodecyl side-chains. P1C(5%) and P1C(10%) are crosslinked and use the same monomer M1 as in P1 but in each case a portion of M1 is replaced by the monomer M1', which acts as a "crosslinking agent" in a concentration of 5 and 10%, respectively. Finally, P3 was synthesized with a thermo-cleavable carbonate side-chain. P3(clvd) is the resulting polymer after heating to 300 °C (see Figure 2a). Carbonates have variable cleavage temperatures depending on their structure.47 In our case the cleavage temperature was expected to be approximately 300 °C due to the presence of a secondary carbon adjacent to the carbonate functional group. The result of heating is the controlled formation of a latent alcohol on the short residual alkyl chain as well as the release of CO2 and a volatile alkene at high temperature. TGA analysis carried out on P3 (Figure 2b) shows a mass loss, with an onset at around 300 °C with a plateau at 42.5 wt.%, which corresponds closely to the



difference of the molecular masses between P3(clvd) and P3 (0.414 for a ratio of 378.335 g/mol and 915.205 g/mol). Infrared spectra of P3 and P3(clvd) are presented in the Supporting Information.

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of 0.36 to 0.78 mg/cm2 and a thickness of 150 µm on the current collector. Each PMDI unit contains four carbonyl groups, two of which are located on each of the two imide groups. The cyclic voltammetry (CV) (at a scan rate of 0.1 mV/s) in a half-

(a)

(b)

(c)

(d)

(e)

Figure 3. (a) Two-step redox processes for P2. (b) Cyclic voltammograms of P2 (0.39 mg/cm2) at a scan rate of 0.1 mV/s. (c) First charge/discharge profile at a rate of C/20. (d) Long term stability of P2 (0.33 mg/cm2), theoretical capacity: 72 mAh/g; first cycle discharge capacity: 68 mAh/g) and (e) Rate capability of P2 (0.39 mg/cm2).

Redox and rate characteristics. We then compared the stability and capacity of the PMDI-based polymers depending on the nature of the side-chain. For all composite electrodes, a mixture of 30 wt.% polymer, 60 wt.% acetylene black and 10 wt.% binder was used and spread, to obtained a mass loading

cell configuration was first carried out on P2 in order to identify the redox potentials of this new family of PMDI-benzene copolymers. The analysis reveals two distinct reduction potentials (2.25 and 1.90 V) and two distinct oxidation potentials (2.30 and 2.00 V) (see Figure 3b, 70th scan). This corresponds


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to the two possible reversible redox processes of diimides from which its theoretical capacity (2e- / PMDI, doping level of 2.0) is determined (see Figure 3a). In the reduction process, it is understood that two out of four carbonyl groups are reduced diagonally where the oxygen atoms convert from a degree of oxidation of (-II) to (-III). The complete reduction of other carbonyl groups at lower potential (1.20 V vs. Li/Li+) is irreversible and leads to the degradation of the molecule.29-31,48 Incorporating PMDI into a conjugated polymer failed to prevent the degradation caused by the complete reduction of the four carbonyl groups. As seen in Figure 3b, the cyclic voltamogramme for the 70th cycle succeeds 69 cycles carried out between 1.65 and 2.5 V vs Li/Li+ without apparent degradation. Then, the lower cut-off potential is decreased to 1.0 V vs Li/Li+ for the 71th-74th cycles in order to reduce the third and fourth carbonyls. In these scans, there is a decrease in the current associated with the intensity of the original redox processes (Red1, Red2, Ox1 and Ox2), and by the 75th cycle (also in the potential window of 1.0 to 2.5 V vs Li/Li+), the redox waves above 1.7 V have completely vanished. This experiment allows to determine stability potential window of the polymer. Two parameters must be considered to evaluate the electrochemical performance, the potential of each electrode of the battery and their specific capacity. Firstly, PMDI shows two plateaus at about 2.25 and 1.90 V. Thus, it could be used as cathode with a Li anode to get a cell voltage of about 2.0 V or as anode with a high voltage cathode. This would require the use of an active cathode material with a potential of about 4 V to obtain a 2 V battery. Secondly, if the specific capacity of the anode and the cathode differs, the strategy is to balance their respective charge by using appropriate mass loading of active materials Figure 3c presents the potential profile for the first constant current charge/discharge cycle at C/20 rate (complete charge/discharge in 20 hours) during the n-doping-undoping processes. The potential profile exhibits a well-defined twostep reduction, which is in agreement with the potentials of the redox processes observed on the CV measurement (Figure 3b). Judging from the charge injection during n-doping, P2 undergoes an almost complete two-electron reduction, leading to a high n-doping level of 1.89. If considered as a Li storage material, the specific capacity of P2 under C/20 for the first cycle is 68 mAh/g, which is a normalized capacity of 0.94 relative to the theoretical capacity (Ct: 72 mAh/g, calculated for a 2electron redox process). CV and galvanostatic charge/discharge measurements of a reference electrode containing 90% acetylene black and 10% binder was carried out to ensure the very negligible contribution of acetylene black to the cathode capacity (see Supporting Information) Moreover, Figure 3c corresponds to the first cycle long term cycling stability of P2 presented in Figure 3d. The latter was carried out over 50 cycles, which corresponds to more than one month and a half of continuous galvanostatic charge/discharge cycling, in which a gradual decrease in capacity over time can be observed. This decrease is characterized by a coulombic efficiency of 95% for the first cycle, which then reaches values oscillating around 99% starting with the 12th cycle. The specific capacity of P2 at a rate of C/20 for the 50th cycle is 34 mAh/g, which corresponds to a normalized capacity of 0.48. Slow rates have the advantage of allowing all electroactive sites to undergo redox reactions and

yield the highest capacities but also lead to side reactions and slow dissolution of the polymer into the electrolyte when the electrode is in the reduced state. Also, the rate capability of P2 was evaluated at different galvanostatic rates between C/2 up to 5C (Figure 3e). At each rate, 5 cycles were performed. A slight decrease of the capacity is observed for each set of C rates. When the capacity obtained at each rate is compared, a marginal drop is seen upon increasing the C rate from C/2 to C and from C to 2C. However, there is a collapse of the capacity when the C rate is raised to 5C, which establishes a practical limit not to be exceeded in terms of cycling rate for this polymer family. This is caused either by the slow redox reaction rate at the polymer redox sites, slow solid-state ion (Li+) transport, or poor electronic conduction. The latter two parameters could be mitigated by engineering the cathode formulation, (e.g. by changing the composition of the components of the electrode). Interestingly, when returning to C/2 rate, only a small loss of capacity is observed, indicating only a small degradation of the polymer electrode (vide supra). Among other things, with these initial analyses it was possible to establish the reference parameters for comparing the different polymers: a potential window between 1.65 to 2.5 V, between which the two reversible redox reactions occur and at a comparative galvanostatic rate of C/10, which is a conventional rate and is under the rate limitation observed here. Side-chain length. The length of the side chain can have a significant impact on the solubility of the monomer as well as that of the growing polymer. P1 with ethylhexyl side-chains and P2 with hexyldecyl side-chains have a number average molecular weight (Mn) of 13 kDa (PDI: 1.6) and 31 kDa (PDI: 2.1) respectively. Also, it is expected that a polymer with a high number of repeating unit is less soluble due to increased inter-molecular forces. Although good solubility during polymerization is desirable in order to obtain a polymer with the highest molecular weight possible, it is also desirable to have a low solubility in the mixture of solvents used as an electrolyte in the Li-ion battery (EC, DEC and DMC), to minimize polymer dissolution. There is a marked increase in normalized capacity from 0.32 to 0.78 for P1 to P2 (Figure 4b). This could be explained by the fact that P2 has a higher Mn than P1. However, it seems that the longer side-chains also benefit the stability of P2. The large increase in the normalized capacity of P2 over P1 suggests that the long non-polar sidechains also limit solubility in the polar electrolyte. The usefulness of long alkyl side-chains in limiting polymer dissolution into the electrolyte is also observed in the naphthalene diimide-bithiophene (NDI-BT) polymer, which has similar branched octyldodecyl side-chains and exhibits outstanding stability.36 By comparing P1 to P3, the size of the side-chain, rather than the number of repeating units (Mn), appears to have a greater impact on polymer stability. P3 has a Mn of 6 kDa versus 13 kDa for P1. These Mn values correspond to 6 repeat units for P3 (oligomer) compared to 25 repeat units for P1. Despite this, P3 offers a superior normalized capacity for all 10 cycles, indicating that the length of the polymer backbone does not govern dissolution in the electrolyte. It is rather likely due to the much longer non-polar methylpentadecyl (-C15H31) side-chains located on the P3 carbonate moiety, which has twice the number of methylene (-CH2-) groups than does P1 with its ethylhexyl (-C8H17) alkyl side chain. It would therefore be tempting to use the longest possible alkyl chains, but this approach would compromise the theoretical capacity of



the materials, which is inversely proportional to the mass of the repeating unit.

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such as acetone, hexane and CHCl3 as was desired, but consequently could not be characterized by GPC. However, they

(a)

(c)

(b)

Figure 4. (a) Loading, theoretical capacity and first cycle capacity of the structures investigated. (b) Comparison of galvanostatic measurements for polymers over 10 cycles at C/10 by normalized discharge capacity and (c) discharge capacity.

Crosslinking. We then turned to crosslinking structural analogs of polymer P1 to evaluate the effect of crosslinking on limiting polymer dissolution. To do this, we chemically bound two PMDI units together via the imide group (M1') and substituted a small portion of M1 in the polymerization reaction with M1' to yield crosslinked polymers P1C(5%) and P1C(10%) (see Supporting Information for synthetic methodologies). These materials were insoluble in common solvents

formed a viscous gel in hot o-dichlorobenzene (o-DCB) which made it possible to wash them using the same process as the other polymers. The results obtained with this new crosslinked material showed a marked increase in the normalized capacity (0.32 to 0.56) from P1 to P1C(5%) and then a smaller increase (0.56 to 0.68) from P1C(5%) to P1C(10%) (Figure 4b). As anticipated, crosslinking greatly limits the initial loss in the electrolyte without reducing the theoretical capacity of the


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materials. This strategy is very promising because it is simple to implement on a wide range of monomers and can be combined with other complementary tools. However, it has the inherent disadvantage of yielding materials which cannot be fully characterized. Cleavable side-chains. When using cleavable side-chains, a soluble polymer can be readily synthesized and characterized, and then can be rendered insoluble with post-polymerization treatments to increase the theoretical capacity of the material. Side-chains do not contribute to the redox properties of the polymer and can be viewed as a ‘‘dead mass’’ that adds unnecessary weight to the active material, thereby lowering capacity. Another motivation for using a cleavable carbonate group is that it is stable in the potential window used in Li-ion battery applications since it is equivalent to the functional group of the solvents used in the electrolyte (ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC)).49 This makes it possible to use P3 as a relevant reference to P3(clvd) when comparing the performance of these two polymers. It should be noted that P3(clvd) has a theoretical capacity (Ct) 2.4-fold greater than P3 due to the absence of side-chains. However, the normalized capacities obtained are much lower for P3(clvd) with 0.06 versus 0.33 for P3 in the first cycle (Figure 4b). This means that even with a higher theoretical capacity, P3(clvd) exhibits a specific capacity of only 8 mAh/g versus 19 mAh/g for P3 during that cycle. This can be explained by the importance of the non-polar alkyl chains in preventing polymer dissolution in the polar electrolyte (vide supra) as observed in the present alkyl side-chain study. Even more importantly, P3(clvd) contains terminal alcohol groups which may have favourable interactions with the electrolyte. On the other hand, it is possible that the alcohols may participate in unwanted irreversible side reactions, which would lead to poor electrochemical cell performance. Sodium ion battery behavior and DFT calculations. For comparison purposes, the same type of electrolyte was used for LIBs and SIBs (LiPF6 in EC, DEC, DMC (1: 1: 1) and NaPF6 in EC, DEC, DMC (1: 1: 1), respectively). The potential values of the SIB are corrected by +0.33 V, which corresponds to the difference of the standard potential between the Li/Li+ and the Na/Na+ redox couples. The P2 electrodes were characterized by cyclic voltammetry at a scan rate of 0.1 mV/s from 2.40 to 1.20 V vs Na/Na+ (2.73 to 1.53 V vs Li/Li+ corrected). For the sodium system, the same two redox processes identified for the lithium system are observed (Figure 5a). It was found that the first reduction process (Red1) is more favorable with sodium ions (+0.18 V) than with lithium ions, while the second reduction process with sodium (Red2) remains approximately unchanged relative to the second reduction with lithium. Also, the oxidation potentials corresponding to the redox reaction with sodium ions are observed at a higher potential; +0.16 and +0.23 V for the first oxidation process (Ox1) for which there are two distinct phenomena, and +0.11 V for the second oxidation process (Ox2). This indicates that sodium is inserted more efficiently into the polymer structure during the first reduction, likely due to more favorable interactions, but that these interactions do not benefit the second reduction process. In order to explain these results, we turned to DFT calculations to explore conformational changes in the polymer upon reduction with both lithium and sodium. Calculations were undertaken with the CAM-B3LYP functional, the 6-31G(d)

basis set and the GD3BJ empirical dispersion using the Gaussian 09 package (revision E.01).50 The lowest energy conformer of the neutral PMDI-co-phenylene dimer (Dimer-R0) is linear along the conjugated backbone and the dihedral angle created by the two PMDI units (θ(Dih)) is 66° (Figure 5b). Many

(a

(b Dimer-R0

Dimer-R1Li

Dimer-R2Li

Dimer-R1Na

Dimer-R2Na

Figure 5. (a) Cyclic voltammograms of P2 with lithium and sodium anodes as counter and reference electrodes (corrected to lithium) at a scan rate of 0.1 mV/s. (b) DFT optimized structures of PMDI small molecule models for the unreduced polymer (Dimer-R0), and the polymer reduced with intercalated Li+ions (Dimer-R1Li and Dimer-R2Li) and Na+ ions (DimerR1Na and Dimer-R2Na). Oxygen-ion bond lengths, PMDIbenzene bond angles and PMDI-PMDI dihedral angles are shown. Structures were calculated at the CAM-B3LYP/6ACS Paragon Plus Environment 31G(d) level of theory with the GD3BJ empirical dispersion.


potential conformers were explored in order to locate the most stable sites for ion binding. For reduction with each of Li+ and Na+, these were found to be in the cavity formed between two adjacent imide carbonyls and the phenylene repeating unit. Out-of-plane binding involving nitrogen atoms or only one carbonyl did not stabilize the ion. Due to the smaller radius of the Li+ ion, a bend in Dimer-R1Li occurs in order for the ion to be efficiently chelated between the carbonyls, leading to LiO distances of 1.81 Å and a “bite” angle of 174° between the phenylene group and each of the adjacent PMDI units. The PMDI units also become planar with respect to one another (θ(Dih) = 0°) to reduce the oxygen-metal bond distance. For the reduction of the dimer with sodium (Dimer-R1Na), the optimal Na-O distances are much longer (2.10 Å) than the LiO distances in Dimer-R1Li, as would be expected for a larger ion. There is minimal change in the PMDI-phenylene bite angle (178°), and the distance between the carbonyl groups and the sodium ion is increased by means of a larger dihedral angle between the PMDI units (40°). From these results, it can be inferred that the polymer chain must be strained in order to accommodate the smaller Li+ ion, whereas the larger Na+ ion more readily stabilizes the reduced state. The absence of unfavorable torsion in the polymer chain explains the higher potentials of the Red1 and Ox1 processes involving Na+. One explanation to the peak splitting observed for sodium Ox1 curve could be that the polymer structure is able to fold more easily on the few remaining Na+ once it gets even more flexibility at low ions content. This could open the door to organic redox-active materials with cavity sizes tailored to accept specific ions. For instance, by changing the spacer between the PMDI units, larger or smaller ions could be accepted between the imine carbonyl groups. Upon a second reduction with lithium (Dimer-R2Li), the angles between the phenyl ring and the PMDI units return to 180° in order to accommodate the insertion of a second Li+ ion into the opposite carbonyl cavity. A wider angle between the carbonyl and the metal ion is necessary to achieve a Li-O bond distance similar to that of the first reduction (1.86 Å). The second reduction with sodium (Dimer-R2Na) has a similar effect, rendering the structure more planar. The similar Red2 potential curves obtained with Li and Na could be explained by the fact that following the first reduction, the polymer chain is already locked in a rigid conformation due to the metal ions bridging adjacent PMDI units. This would potentially make the rapid conformational change to accommodate the insertion of the Red2 ions more difficult. Also, it is unclear why both Li and Na Red2 operate at the same potential but that their related oxidation (Ox2) is more positive for sodium by 0.11 V. One explanation would be that the structure slowly stabilize after the Na ions insertion of Red2, releasing heat, before the Na Ox2 happens. We extended the size of the model systems to pentamers in order to explore longer-range ordering and to compare the relative free energies of the structures relative to the placement of the ions during the first reduction (all optimized geometries and free energies are given in the Supporting Information). As observed with the dimers, in the extended systems both Li+ and Na+ ions are most stable in the cavities between the PMDI carbonyls. A smaller distribution of relative free energies is observed for the various reduction motifs with sodium than with lithium. For instance, the difference in free energies (GREL) be-

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tween the various “diagonal” reductions through the PMDI unit and the “linear” reductions across one diimide unit is 7.5 kcal mol-1 for the polymer intercalated with lithium ions, versus only 2.5 kcal mol-1 for reductions with sodium. The comparable free energies of the possible sodium reduction motifs may explain the broader distribution of the oxidation and reduction potentials for the SIB. Analogous to the dimers, the higher difference in GREL among polymer conformers reduced with lithium is due to the more strained polymers conformations necessary to chelate the Li+ ions.

CONCLUSION We have synthesized a new series of PMDI-based redoxactive copolymers containing different side-chain substituents using a DHAP methodology. Galvanostatic performances with the polymers as cathode active materials in Li-ion batteries were undertaken, and conclusively exhibited the favorable effect of introducing longer alkyl side-chains and cross-linked structures on battery stability. Polymers with thermo-cleavable alkyl side-chains demonstrated low stability and poor output discharge capacity. DFT calculations explained the difference in cyclic voltammetry results obtained between lithium and sodium ion batteries by giving evidence of more favorable interactions of the imide with sodium ion over lithium ion due to the polymer cavities being more suited to the size of the sodium ion. This study could serve to rationally design the redox-active structures in new organic electrode materials. Since moderate molecular weight were obtained for our materials, it would be interesting to improve the catalytic system of the polymerization reaction and study the influence of the molecular weight for a given PMDI-based polymer.

ASSOCIATED CONTENT Supporting Information. Experimental protocols for the synthesis of monomers and polymers, optimization of polymerization conditions, UV-vis spectra, Coulombic efficiencies and computational data. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected] *E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by a grant to Mario Leclerc and Daniel Bélanger from the Centre Québécois sur les Matériaux Fonctionnels (CQMF) and Discovery Grants from the Natural Sciences and Engineering Research Council of Canada (NSERC/CRSNG). Compute Canada, Calcul Québec and Sharcnet are acknowledged for providing computational resources. Calculations were performed on the Graham cluster. The authors would thank Professors Gino DiLabio and Paul Ayers for helpful discussions during the preparation of this manuscript.

REFERENCES


Page 9 of 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(1) Lu, L. Y.; Zheng, T. Y.; Wu, Q. H.; Schneider, A. M.; Zhao, D. L.; Yu, L. P. Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem. Rev. 2015, 115, 12666-12731. (2) Wang, C. L.; Dong, H. L.; Hu, W. P.; Liu, Y. Q.; Zhu, D. B. Semiconducting Pi-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics. Chem. Rev. 2012, 112, 2208-2267. (3) Wong, M. Y. Recent Advances in Polymer Organic LightEmitting Diodes (PLED) Using Non-Conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts. J. Electron. Mater. 2017, 46, 6246-6281. (4) Shi, Y.; Peng, L. L.; Ding, Y.; Zhao, Y.; Yu, G. H. Nanostructured Conductive Polymers for Advanced Energy Storage. Chem. Soc. Rev. 2015, 44, 6684-6696. (5) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Stille Polycondensation for Synthesis of Functional Materials. Chem. Rev. 2011, 111, 1493-1528. (6) Sakamoto, J.; Rehahn, M.; Wegner, G.; Schlueter, A. D. Suzuki Polycondensation: Polyarylenes a La Carte. Macromol. Rapid Commun. 2009, 30, 653-687. (7) Pouliot, J. R.; Grenier, F.; Blaskovits, J. T.; Beaupre, S.; Leclerc, M. Direct (Hetero)Arylation Polymerization: Simplicity for Conjugated Polymer Synthesis. Chem. Rev. 2016, 116, 14225-14274. (8) Ackermann, L.; Vicente, R.; Kapdi, A. R. Transition-MetalCatalyzed Direct Arylation of (Hetero)Arenes by C-H Bond Cleavage. Angew. Chem., Int. Ed. 2009, 48, 9792-9826. (9) McGlacken, G. P.; Bateman, L. M. Recent Advances in ArylAryl Bond Formation by Direct Arylation. Chem. Soc. Rev. 2009, 38, 2447-2464. (10) Wencel-Delord, J.; Glorius, F. C-H Bond Activation Enables the Rapid Construction and Late-Stage Diversification of Functional Molecules. Nat. Chem. 2013, 5, 369-375. (11) Segawa, Y.; Maekawa, T.; Itami, K. Synthesis of Extended PSystems Through C-H Activation. Angew. Chem., Int. Ed. 2015, 54, 66-81. (12) Burke, D. J.; Lipomi, D. J. Green Chemistry for Organic Solar Cells. Energy Environ. Sci. 2013, 6, 2053-2066. (13) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. Analysis of the Concerted Metalation-Deprotonation Mechanism in Palladium-Catalyzed Direct Arylation Across a Broad Range of Aromatic Substrates. J. Am. Chem. Soc. 2008, 130, 10848-10849. (14) Wakioka, M.; Kitano, Y.; Ozawa, F. A Highly Efficient Catalytic System for Polycondensation of 2,7-Dibromo-9,9Dioctylfluorene and 1,2,4,5-Tetrafluorobenzene via Direct Arylation. Macromolecules 2013, 46, 370-374. (15) Lu, W.; Kuwabara, J.; Iijima, T.; Higashimura, H.; Hayashi, H.; Kanbara, T. Synthesis of Pi-Conjugated Polymers Containing Fluorinated Arylene Units via Direct Arylation: Efficient Synthetic Method of Materials for OLEDs. Macromolecules 2012, 45, 41284133. (16) Zhang, X.; Gao, Y.; Li, S.; Shi, X.; Geng, Y.; Wang, F. Synthesis of Poly(5,6-Difluoro-2,1,3-Benzothiadiazole-alt-9,9Dioctylfluorene) via Direct Arylation Polycondensation. J. Polym. Sci. Part a-Polymer Chem. 2014, 52, 2367-2374. (17) Blouin, N.; Krompiec, M.; Lohr, A., PCT Int Appl 67pp., 2015, WO2016066241. (18) Hameury, S; Kunz, S.; Sommer, M. Expanding the Scope of Electron-Deficient C-H Building Blocks: Direct Arylation of Pyromellitic Acid Diimide. ACS Omega 2017, 2, 2483-2488. (19) Renault, S.; Geng, J. Q.; Dolhem, F.; Poizot, P. Evaluation of Polyketones with N-Cyclic Structure as Electrode Material for ElectroChemical Energy Storage: Case of Pyromellitic Diimide Dilithium Salt. Chem. Commun. 2011, 47, 2414-2416. (20) Renault, S.; Mihali, V. A.; Edstrom, K.; Brandell, D. Stability of Organic Na-Ion Battery Electrode Materials: The Case of Disodium Pyromellitic Diimidate. Electrochem. commun. 2014, 45, 52-55. (21) Song, Z. P.; Zhan, H.; Zhou, Y. H. Polyimides: Promising Energy-Storage Materials. Angew. Chem., Int. Ed. 2010, 49, 8444-8448. (22) Tian, D.; Zhang, H. Z.; Zhang, D. S.; Chang, Z.; Han, J.; Gao, X. P.; Bu, X. H. Li-Ion Storage and Gas Adsorption Properties of Porous Polyimides (PIs). RSC Adv. 2014, 4, 7506-7510.

(23) Wu, H. P.; Shevlin, S. A.; Meng, Q. H.; Guo, W.; Meng, Y. N.; Lu, K.; Wei, Z. X.; Guo, Z. X. Flexible and Binder-Free Organic Cathode for High-Performance Lithium-Ion Batteries. Adv. Mater. 2014, 26, 3338-3343. (24) Meng, Y. N.; Wu, H. P.; Zhang, Y. J.; Wei, Z. X. A Flexible Electrode Based on a Three-Dimensional Graphene NetworkSupported Polyimide for Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2, 10842-10846. (25) Wu, H. P.; Yang, Q.; Meng, Q. H.; Ahmad, A.; Zhang, M.; Zhu, L. Y.; Liu, Y. G.; Wei, Z. X. A Polyimide Derivative Containing Different Carbonyl Groups for Flexible Lithium Ion Batteries. J. Mater. Chem. A 2016, 4, 2115-2121. (26) Kim, D. J.; Hermann, K. R.; Prokofjevs, A.; Otley, M. T.; Pezzato, C.; Owczarek, M.; Stoddart, J. F. Redox-Active Macrocycles for Organic Rechargeable Batteries. J. Am. Chem. Soc. 2017, 139, 6635-6643. (27) Williams, D. L.; Byrne, J. J.; Driscoll, J. S. A High Energy Density Lithium/Dichloroisocyanuric Acid Battery System. J. Electrochem. Soc. 1969, 116, 2-4. (28) Chen, J.; Liu, Y.; Minett, A. I.; Lynam, C.; Wang, J. Z.; Wallace, G. G. Flexible, Aligned Carbon Nanotube/Conducting Polymer Electrodes for a Lithium-Ion Battery. Chem. Mater. 2007, 19, 35953597. (29) Ji, L. W.; Yao, Y. F.; Toprakci, O.; Lin, Z.; Liang, Y. Z.; Shi, Q.; Medford, A. J.; Millns, C. R.; Zhang, X. W. Fabrication of Carbon Nanofiber-Driven Electrodes from Electrospun Polyacrylonitrile/Polypyrrole Bicomponents for High-Performance Rechargeable Lithium-Ion Batteries. J. Power Sources 2010, 195, 2050-2056. (30) Guo, C. X.; Wang, M.; Chen, T.; Lou, X. W.; Li, C. M. A Hierarchically Nanostructured Composite of MnO2/Conjugated Polymer/Graphene for High-Performance Lithium Ion Batteries. Adv. Energy Mater. 2011, 1, 736-741. (31) Qie, L.; Chen, W. M.; Wang, Z. H.; Shao, Q. G.; Li, X.; Yuan, L. X.; Hu, X. L.; Zhang, W. X.; Huang, Y. H. Nitrogen-Doped Porous Carbon Nanofiber Webs as Anodes for Lithium Ion Batteries with a Superhigh Capacity and Rate Capability. Adv. Mater. 2012, 24, 20472050. (32) Jeong, J. M.; Choi, B. G.; Lee, S. C.; Lee, K. G.; Chang, S. J.; Han, Y. K.; Lee, Y. B.; Lee, H. U.; Kwon, S.; Lee, G.; Lee, C. S.; Huh, Y. S. Hierarchical Hollow Spheres of Fe2O3@Polyaniline for Lithium Ion Battery Anodes. Adv. Mater. 2013, 25, 6250-6255. (33) Liu, B. R.; Soares, P.; Checkles, C.; Zhao, Y.; Yu, G. H. Three-Dimensional Hierarchical Ternary Nanostructures for HighPerformance Li-Ion Battery Anodes. Nano Lett. 2013, 13, 3414-3419. (34) Wu, H.; Yu, G. H.; Pan, L. J.; Liu, N. A.; McDowell, M. T.; Bao, Z. A.; Cui, Y. Stable Li-Ion Battery Anodes by in-Situ Polymerization of Conducting Hydrogel to Conformally Coat Silicon Nanoparticles. Nat. Commun. 2013, 4, 1-6. (35) Robitaille, A.; Perea, A.; Belanger, D.; Leclerc, M. Poly(5Alkyl-Thieno 3,4-c Pyrrole-4,6-Dione): A Study of Pi-Conjugated Redox Polymers as Anode Materials in Lithium-Ion Batteries. J. Mater. Chem. A 2017, 5, 18088-18094. (36) Liang, Y. L.; Chen, Z. H.; Jing, Y.; Rong, Y. G.; Facchetti, A.; Yao, Y. Heavily N-Dopable Pi-Conjugated Redox Polymers with Ultrafast Energy Storage Capability. J. Am. Chem. Soc. 2015, 137, 4956-4959. (37) Whittingham, M. S. Chemistry of Intercalation Compoundsmetal Guests in Chalcogenide Hosts. Prog. Solid State Chem. 1978, 12, 41-99. (38) Nagelberg, A. S.; Worrell, W. L. Thermodynamic Study of Sodium-Intercalated TaS2 and TiS2. J. Solid State Chem. 1979, 29, 345-354. (39) Kim, S. W.; Seo, D. H.; Ma, X. H.; Ceder, G.; Kang, K. Electrode Materials for Rechargeable Sodium-Ion Batteries: Potential Alternatives to Current Lithium-Ion Batteries. Adv. Energy Mater. 2012, 2, 710-721. (40) Pan, H. L.; Hu, Y. S.; Chen, L. Q. Room-Temperature Stationary Sodium-Ion Batteries for Large-Scale Electric Energy Storage. Energy Environ. Sci. 2013, 6, 2338-2360. (41) Palomares, V.; Serras, P.; Villaluenga, I.; Hueso, K. B.; Carretero-Gonzalez, J.; Rojo, T. Na-Ion Batteries, Recent Advances and



Present Challenges to Become Low Cost Energy Storage Systems. Energy Environ. Sci. 2012, 5, 5884-5901. (42) Wang, S. W.; Wang, L. J.; Zhu, Z. Q.; Hu, Z.; Zhao, Q.; Chen, J. All Organic Sodium-Ion Batteries with Na4C8H2O6. Angew. Chem., Int. Ed. 2014, 53, 5892-5896. (43) Sharma, P.; Damien, D.; Nagarajan, K.; Shaijumon, M. M.; Hariharan, M. Perylene-Polyimide-Based Organic Electrode Materials for Rechargeable Lithium Batteries. J. Phys. Chem. Lett. 2013, 4, 3192-3197. (44) Banda, H.; Damien, D.; Nagarajan, K.; Hariharan, M.; Shaijumon, M. M. A Polyimide Based All-Organic Sodium Ion Battery. J. Mater. Chem. A 2015, 3, 10453-10458. (45) Shao, J. J.; Chang, J. J.; Dai, G. L.; Chi, C. Y. Pyromellitic Diimide-Based Copolymers for Ambipolar Field-Effect Transistors: Synthesis, Characterization, and Device Applications. J. Polym. Sci. Part a-Polymer Chem. 2014, 52, 2454-2464. (46) Kola, S.; Tremblay, N. J.; Yeh, M. L.; Katz, H. E.; Kirschner, S. B.; Reich, D. H. Synthesis and Characterization of a Pyromellitic Diimide-Based Polymer with C- and N-Main Chain Links: Matrix for Solution-Processable N-Channel Field-Effect Transistors. ACS Macro Lett. 2012, 1, 136-140. (47) Van Speybroeck, V.; Martele, Y.; Waroquier, M.; Schacht, E. Ab Initio and Experimental Study on Thermally Degradable Polycar-

Page 10 of 10

bonates: The Effect of Substituents on the Reaction Rates. J. Am. Chem. Soc. 2001, 123, 10650-10657. (48) Han, X. Y.; Chang, C. X.; Yuan, L. J.; Sun, T. L.; Sun, J. T. Aromatic Carbonyl Derivative Polymers as High-Performance Li-Ion Storage Materials. Adv. Mater. 2007, 19, 1616-1621. (49) Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22, 587-603. (50) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria G. E.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A.; Bloino, J.; Janesco, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, Jr. J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, Revision E.01 Gaussian, Inc., Wallingford CT. 2016.

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