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Engineered Electronic Contacts for Composite Electrodes in Li Batteries Using Thiophene-Based Molecular Junctions Ali Yassin,†,# Pablo Jimenez,‡,§ Bernard Lestriez,‡,§ Philippe Moreau,‡,§ Philippe Leriche,† Jean Roncali,† Philippe Blanchard,*,† Hélène Terrisse,‡ Dominique Guyomard,‡,§ and Joel̈ Gaubicher*,‡,§ †

Linear Conjugated Systems Group, MOLTECH Anjou, Université d’Angers, UMR-CNRS 6200, 2 boulevard Lavoisier, 49045 Angers, France ‡ Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 rue de la Houssinière, BP32229, 44322 Nantes Cedex 3, France § Réseau sur le stockage Electrochimique de l’Energie (RS2E), CNRS FR3459, 33 rue Saint Leu, 80039 Amiens Cedex, France S Supporting Information *

ABSTRACT: Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy experiments indicate that molecular junctions can be achieved between non-carbon-coated LiFePO4 (LFP) and multiwall carbon nanotubes (MWCNT) using a thiophene-based conjugated system which was designed to selectively functionalize these two different types of surfaces. The strategy enables the architecturing of the cathode electrode of lithium batteries, leading to a vast improvement in the component intermixing, which results in the individual MWCNT being nanocontacted at the surface of LFP grains. This advancement leads to much higher specific capacity, especially at high charge/discharge rates, for undensified electrodes of 2 mA h cm−2, for which the electronic wiring of the electroactive material is a critical issue. Furthermore, thanks to molecular junctions, better capacity retention comparable to that of carbon-coated LiFePO4 electrodes could be achieved. These results are expected to trigger the development of novel electron transport engineering methods, of special interest for industry-relevant thick battery electrodes.

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INTRODUCTION Compared to alternative electrochemical energy storage technologies, Li-ion batteries appear to be the most promising with respect to numerous applications.1,2 The cathode of a lithium battery is a complex composite material obtained by mixing the redox active material (AM) together with nonredox compounds, such as an electron-conducting additive (C) and a polymeric binder (B). Since the composite electrode must possess two percolating networks, electronic and ionic, its architecture (dispersion of the AM, C, and B ingredients, porosity, tortuosity, etc.) greatly influences electrode performance. In particular, the importance of electronic conductivity on battery performance (i.e., energy, power,3−8 and cyclability9−11) has been demonstrated several times for Li-ion, Li−metal− polymer batteries,12,60 and the future generation of semi-solid lithium rechargeable flow battery systems.13,14 Indeed, regarding contemporary batteries, and especially those with thick electrodes that are less costly (such electrodes are moderately densified to get open porosity), it is estimated that the 20−80% decrease in power performance stems from insufficient electronic conduction.12 In the particular case of nanocarbon decorated LiFePO4 (referred to as LFPC), which is at the heart of present-day electrified vehicle batteries,15 the contact resistance between clusters of LFPC grains is one of the © XXXX American Chemical Society

three major limitations with respect to electronic transport. The other two are ascribed to sp3 defects within the carbon shell,16 and to the contact resistance at the electrode/current collector interface.17,18 Intercluster contact resistance results in a conductivity drop of more than 2 orders of magnitude from the micrometric (clusters of LFPC grains) to the macroscopic (the whole electrode) scale.16 The design of enhanced electronic conductivity at different scales of the electrode is therefore a key challenge toward cheaper and more efficient batteries. However, it is not a trivial task because it relies on the use of conductive carbon additives which are difficult to disperse homogeneously owing to the unstable nature of colloidal electrode inks which can suffer from aggregation phenomena.19 Moreover, electron transport has been shown to occur through electron tunneling across surface layers, as is the case in adsorbed polymers and solid electrolyte interphases,20 and therefore cannot be controlled. Accordingly, since insulating binders have to be added, a compromise has to be reached between the electronic conductivity and the mechanical properties of the composite electrode.20 Received: March 20, 2015 Revised: May 6, 2015

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DOI: 10.1021/acs.chemmater.5b01049 Chem. Mater. XXXX, XXX, XXX−XXX

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Chemistry of Materials

Scheme 1. (A) Engineered Electronic Contacts between the MWCNT Carbon Additive and the AM Particle by Using Thiophene-Based π-Conjugated Systems Functionalized with Phosphonic and Pyrene Groups; (B) Molecular Structures of P3TPPO and P3T

diffusive or “‘incoherent”’ tunneling. According to Frisbie and co-workers,39 the conductance, G, associated with coherent tunneling current can be expressed as G = 2e2T/h, where T is a function that relates to the efficiency of the molecule to transport electrons from one contact to the other. T can be divided into three components, T = TlcTrcTmol, where Tlc and Trc refer to the electron transfer at each of the two contacts and Tmol to the ability of the molecule to transport charges. Tmol generally depends exponentially on the molecule length d, such as in Tmol = k0e−βd, where k0 is a pre-exponential factor and β is a structure-dependent attenuation factor that describes the decay of electronic coupling between the substrates as the distance between them increases. The value of the attenuation factor, β, depends significantly on the molecular structure of the bridge. For a vacuum gap between two metals with work functions of 5.0 eV, a β value of 2.8 Å−1 is predicted while it decreases to ca. 1.0 and 0.5 Å−1, respectively, for alkane and conjugated molecular junctions. Conjugated systems are thus more favorable for tunneling transport.40 In addition, a molecular junction with weak contacts (large Tlc and Trc) can reduce the conductance, G. This is likely to be the case when molecular interaction with the two substrates is ensured by physisorption rather than chemisorption.41 Accordingly, to improve charge transport within a composite electrode, we hereby propose to connect the carbon additives, namely, multiwall carbon nanotubes (MWCNT), to the active material, namely, non-carbon-coated LiFePO4 (LFP), by short molecular junctions (≈2 nm) (Scheme 1A). A thiophene-based π-conjugated molecule, P3TPPO (Scheme 1B), was designed to form a molecular junction by selectively functionalizing each of the two types of surface using a pyrene and a phosphonic group, respectively. While tunneling transport is expected for such short junctions, the redox properties of the thiophene-based π-conjugated system may also promote hopping transport. In addition, π-stacking interactions between the pyrene unit of P3TPPO and MWCNT were preferred over covalent anchoring to avoid the formation of sp3 defects while still allowing electronic coupling via supramolecular interactions. We describe here the synthesis and the optical and electrochemical properties of the functionalized conjugated molecule P3TPPO. In parallel, a reference π-conjugated analogue molecule, P3T, bearing one pyrene unit and devoid of any phosphonic acid moiety was also synthesized (Scheme 1B). In the latter case, the absence of an acid group is expected to prevent any formation of molecular bridging between the MWCNT and the LFP. Functionalized MWCNT with these

To date, improved charge transport has been achieved by Wu and co-workers who designed a so-called double nanocarbon decorated LiFePO4 nanocomposite where LFPC particles are embedded at the surface of carbon nanotubes upon sucrose carbonization.21 Alternatively, Grätzel’s group offers strategies based on the use of redox molecular mediators,22 redox polymers with “swing” redox active molecules tethered to the polymer backbone,23 and redox shuttle24 to directly wire uncoated LiFePO4 (referred to as LFP) particles to the current collector. In general, Grätzel’s methods are based on the electron−hole transport from the redox active molecules to the LFP particles. Therefore, two essential conditions need to be fulfilled to get reversible storage in LFP: (i) the adsorbed molecules should be percolated to allow for cross-surface charge transfer (as is the carbon coating proposed by Armand)25,26 and (ii) the redox potential of the molecule should match the Fermi level of LiFePO4/FePO4. Kavan et al. implemented this solution by adsorbing a Ru−bipyridine complex on the LFP surface.27,28 However, in this case, a small amount of single-wall carbon nanotubes should be bound to the Ru complex to allow for discharging of FePO4 particles. Another approach, proposed by Goodenough and co-workers, consists of replacing the carbon additive by a direct connection of LFPC particles to the current collector via conductive polyaniline or polypyrrole polymers: upon oxidation, the polymer enters its conducting state, therefore allowing fast cycling of the LFPC particles.29−31 Schougaard and co-workers also used poly(3,4-ethylenedioxythiophene) derivatives to replace the carbon coating of LFPC.32 Aside from Wu et al.,21 however, these publications aim at bypassing the use of carbon additives within composite electrodes and do not, therefore, directly tackle the contemporary concerns of industry-relevant electrodes. In this sense our approach diverges from these works since it proposes a way of controlling and improving the charge transport occurring in traditional porous electrodes by engineering the electronic contacts between the carbon additive and the active material using molecular junctions. Many research papers have focused on how molecules transport charge33 by means of experimental34−36 and theoretical37,38 investigations. Both tunneling and hopping mechanisms can be considered. In principle, tunneling electron transport occurs over short distances (60%) to prevent Li-ion diffusion limitations. Typical voltage composition curves are reported in Figure 5A.

MWCNT have been gained at the expense of initial OH groups of P3TPPO−MWCNT and LFP through Fe−O−P−C covalent bonding. This assertion is, in fact, duly substantiated by the occurrence of two new P−O stretching bands at lower wavenumbers in the vicinity of 1100 cm−1 in the case of MWCNT−P3TPPO−LFP (marked by arrows in Figure 3B). Study of Molecular Junction Impact on Electrode Morphology by Microscopy. The effect of P3TPPO on the morphology of the composite electrode based on a mixture of MWCNT and LFP was investigated by SEM and HRTEM (Figure 4).

Figure 5. (A) Galvanostatic charge−discharge profile on the second cycle at C/4 and C/2 rates on charge and discharge, respectively, for MWCNT−P3TPPO−LFP (red curve), MWCNT−LFPC (black curve), and MWCNT−LFP−blank (blue curve). (B) Corresponding power tests (signature curve) along with the capacity gain from MWCNT−LFP−blank to MWCNT−P3TPPO−LFP (green curve).

Figure 4. SEM images of (A) MWCNT−LFP−blank, (B) MWCNT− P3TPPO−LFP, and (C) MWCNT−P3T−LFP. (D) HRTEM image of MWCNT−P3TPPO−LFP at liquid nitrogen temperature showing an approximately 2 nm molecular junction between MWCNT and LFP nanoparticle (marked by an arrow).

In comparison to the blank, much better performance is clearly obtained at a C/2 discharge rate for the sample bearing molecular junctions. The latter is associated with the highest capacity (dx = 0.93, nearly 150 mA h g−1) and the smallest polarization reflecting good electronic wiring of the LFP particles. Performances are actually very similar to that obtained for LFPC, although we note a higher polarization is observed at the end of charge and discharge. This tendency that is maintained on subsequent cycles (Figure S4) could be due to Li intercalation kinetics slightly inhibited by molecules at the (010) surface plane. In contrast, a relatively high polarization is observed for MWCNT−LFP−blank as a direct consequence of nonhomogeneous and poorer electronic contact of the particles. We note that MWCNT−LFP−blank shows a capacity of nearly 125 mA h g−1, which is slightly lower than that measured by Masquelier and co-workers.59 However, in their case the 5 wt % carbon additive (Ketjen Black) that was involved is much more prone to yield homogeneous mixture than MWCNT. Furthermore, they used twice smaller LFP particles (∼140 vs 300 nm) and lower electrode loadings (∼1.5 vs 2 mA h cm−2). Figure 5B shows the influence of current density on gravimetric capacity, and confirms the crucial effect of molecular junctions at all rates from C/8 to 10C by promoting interfacial electron transfer from the MWCNT to the insulating LFP nanograins. The significant role of the molecular junction in engineering a superior electronic network is in fact confirmed by two-probe measurements of dc conductivity that is nearly 50 times higher for MWCNT−P3TPPO−LFP electrodes (2.5 × 10−4 S cm−1) than for MWCNT−LFP−blank ones (4.7 × 10−6 S cm−1) (Figure S5). These results would partly mirror the fact that

Comparison of the images obtained for MWCNT−LFP− blank (Figure 4A) and MWCNT−P3TPPO−LFP (Figure 4B) shows that the presence of P3TPPO greatly increases the dispersion of the MWCNT that seem to decorate the surface of LFP nanoparticles. Indeed, this observation does not apply to the blank sample (Figure 4A), which is mainly characterized by regions of LFP particles sitting next to MWCNT bundles. Thus, the role of P3TPPO is particularly significant. This effect is even more striking when observing the SEM image of MWCNT−P3T−LFP presented in Figure 4C: indeed, while πstacking functionalization of MWCNT by P3T was validated from cyclic voltammetry (see Figure S1), no evident change of morphology is observed when compared to the blank (4A) due to the absence of possible P−O−Fe bonds (Scheme 2). We note, however, that the surfactant/dispersant role of grafted P3TPPO on MWCNT could also favorably contribute to achieving a similar homogeneous mixing state in the MWCNT−P3TPPO−LFP sample. A typical image of HRTEM observations on MWCNT− P3TPPO−LFP carried out at low temperatures (liquid nitrogen), to obtain direct proof of the establishment of molecular junctions, is presented in Figure 4D (more images are reported in the Supporting Information). The contact region in between LFP nanoparticles and MWCNT is clearly characterized by the occurrence of organic matter (marked by an arrow) which was further observed to shrink, or even disintegrate, under the electron beam. We note that, regarding the HRTEM observation of the blank sample, we were able to F

DOI: 10.1021/acs.chemmater.5b01049 Chem. Mater. XXXX, XXX, XXX−XXX

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Chemistry of Materials molecular junctions enable many more MWCNT paths to percolate across the electrode thickness as suggested by SEM images (Figure 4). In fact, electronic limitations arising from contact resistance at the sample/collector interface, as well as from electron transport within the carbon percolation network and at contacts with the active material, are expected to impact performance at high rates.12 This corresponds to the trend observed in Figure 5B where the gain of capacity resulting from molecular junctions increases with the C rate. Considering electrodes were not calendared quite impressive capacities such as 100 mA h g−1 at 5C rate are still achievable for carbon free LFP electrodes of MWCNT−P3TPPO−LFP. Finally, it is instructive to note that molecular junctions enable similar performance than that obtained for carbon-coated LFP but without the need for mixing with MWCNT (Figure 5B) by ball milling. As far as our current strategy goes, it still remains to be proven that molecular junction can enhance the rate of the electron transfer through these engineered contacts. Even though tunnel transfer could be involved in the process, given the length of the present molecular junction, additional temperature-dependent characterizations of the electron transport still need to be performed to determine to what extent the redox state of the molecule influences electron transport. To gain better insight, we applied this molecular junction strategy with the same P3TPPO molecule to Li4Ti5O12 (LTO) electrodes with the same loadings. HRTEM experiments confirm that similar images to those presented for LFP electrodes are obtained upon establishment of molecular junctions. Indeed, LTO grains are nicely anchored on MWCNT (Figure S6), which is not the case for the blank sample. Quite surprisingly, however, unlike MWCNT− P3TPPO−LFP, the electrochemical performance of MWCNT−P3TPPO−LTO is worse than the blank at increasing C rates (Figure S7). Accordingly, a charge-hopping mechanism that would take place at higher potential as for LFP may also contribute to the charge transport through molecular junctions. This assumption is supported by CVs in Figure 2 that clearly show part of the P3TPPO electroactivity is superimposed onto that of LFP. The latter result therefore clearly highlights the effect of the redox state of the molecule when compared to that of the active material, and substantiates the crucial role of molecular junctions to carry the flow of the current load at nanocontacts. With regard to tunneling transfer, ongoing investigations using in situ broadband dielectric spectroscopy should yield valuable information regarding the role of the molecule design, as well as the influence of the anchoring groups on the electronic transfer.61 Cycle life was evaluated for MWCNT−LFP−blank and MWCNT−P3TPPO−LFP samples and compared to that obtained for carbon-coated LFPC. At this point, we would like to emphasize again that (i) our results were achieved for noncalendared electrodes prepared with (ii) a non-carboncoated LiFePO4. It is well-known that noncalendared electrodes with high active mass loading show poor cyclability and rate performance as a consequence of weak interparticle contacts.17,62 Figure 6 corroborates these finding and clearly highlights the crucial role of molecular junctions in preserving the initial capacity of uncoated LFP electrodes. Indeed, the capacity retention of the molecular-junction-based electrode (>95% upon 100 cycles) is improved with respect to the blank sample (88% after 100 cycles) and compares fairly well to that of the carbon-coated LFPC electrode.

Figure 6. Capacity retention at C/4 and C/2 rates on charge and discharge, respectively, for MWCNT−LFP−P3TPPO (red curve), MWCNT−LFPC (black curve), and MWCNT−LFP−blank (blue curve).

To the best of our knowledge, this is the best capacity retention obtained for uncoated LFP electrodes of loading as high as 2 mA h cm−2. This relatively good long-term stability of electrodes based on molecular junctions can be assigned to the presence of P3TPPO molecules, which leads to both π−π stacking anchoring on the MWCNT side and covalent grafting on the oxide side. This interpretation is in full agreement with capacity fade observed for electrodes exhibiting a lack of adhesion at interparticles contacts.63

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CONCLUSION This study describes a novel strategy for enhancing electronic transport within porous electrodes and is based on the implementation of nanometer-scale molecular junctions between the carbon additives and the redox active material of the Li-battery cathode. To that end, we designed and synthesized an extended thiophene-based π-conjugated system which is functionalized by a pyrene unit prone to developing π−π stacking with MWCNT, on one hand, and a phosphonic acid group able to interact with LiFePO4, on the other hand. By way of FTIR, SEM, and HRTEM, we demonstrate the achievement of unprecedented molecular junctions between MWCNT and LiFePO4, which have a tremendous impact on the morphology of electrodes and on electrochemical performance. To this purpose, a reference molecule devoid of a phosphonic acid group was also synthesized and used to establish the pivotal role of the second anchoring group in the formation of molecular junctions. Electrochemical tests in Li batteries, as well as dc conductivity measurements, clearly confirm the beneficial effects of this strategy. Accordingly, for undensified 2 mA h cm−2 electrodes of uncoated LiFePO4, a higher capacity gain is observed at increasing C rates, thereby affirming the key role of molecular junctions in engineering the contacts between the carbon additive network and LFP grains. Furthermore, the role of molecular junctions is not limited to capacity improvements since better capacity retention could be achieved. The latter is comparable to that of carbon-coated LFPC electrode. The numerous possible variations of our strategy certainly need further investigation, and many questions remain unanswered as to the physics of electron transport at macro-, meso-, and nanoscopic scales through these junctions. In this regard, the unexpected adverse effect of molecular junctions when replacing LFP by LTO, whose intercalation potential is G

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(6) Wu, M.-S.; Lee, J.-T.; Chiang, P.C.-J; Lin, J.-C. Carbon-Nanofiber Composite Electrodes for Thin and Flexible Lithium-Ion Batteries. J. Mater. Sci. 2007, 42, 259. (7) Striebel, K.-A.; Sierra, A.; Shim, J.; Wang, C.-W; Sastry, A.-M. The effect of compression on natural graphite anode performance and matrix conductivity. J. Power Sources 2004, 134, 241. (8) Gnanaraj, J.-S.; Cohen, Y.-S.; Levi, M.-D.; Aurbach, D. The effect of pressure on the electroanalytical response of graphite anodes and LiCoO2 cathodes for Li-ion batteries. J. Electroanal. Chem. 2001, 516, 89. (9) Shim, J.; Striebel, K.-A. Characterization of high-power lithiumion cells during constant current cycling: Part I. Cycle performance and electrochemical diagnostics. J. Power Sources 2003, 122, 188. (10) Lei, J.; McLarnon, F.; Kostecki, R. In Situ Raman Microscopy of Individual LiNi0.8Co0.15Al0.05O2 Particles in a Li-Ion Battery Composite Cathode. J. Phys. Chem. B 2005, 109, 952. (11) Kostecki, R.; Lei, J.; McLarnon, F.; Shim, J.; Striebel, K. Diagnostic Evaluation of Detrimental Phenomena in High-Power Lithium-Ion Batteries. J. Electrochem. Soc. 2006, 153, A669−A672. (12) Fongy, C.; Gaillot, A.-C.; Jouanneau, S.; Guyomard, D.; Lestriez, B. Ionic vs Electronic Power Limitations and Analysis of the Fraction of Wired Grains in LiFePO4 Composite Electrodes. J. Electrochem. Soc. 2010, 157, A885−A891. (13) Duduta, M.; Ho, B.; Wood, V.-C.; Limthongkul, P.; Brunini, V.E.; Carter, W.-C.; Chiang, Y.-M. Semi-Solid Lithium Rechargeable Flow Battery. Adv. Energy Mater. 2011, 1, 511. (14) Madec, L.; Youssry, M.; Cerbelaud, M.; Soudan, P.; Guyomard, D.; Lestriez, B. Electronic vs Ionic Limitations to Electrochemical Performance in Li4Ti5O12-Based Organic Suspensions for LithiumRedox Flow Batteries. J. Electrochem. Soc. 2014, 161, A693−A699. (15) https://www.autolib.eu/fr/ (accessed 01/13/2015). (16) Seid, K. A.; Badot, J.-C.; Dubrunfaut, O.; Levasseur, S.; Guyomard, D.; Lestriez, B. Multiscale electronic transport mechanism a n d t r u e c o n d u c t i v i t i e s in a m o r p h o u s c a r b o n − L i F e PO4nanocomposites. J. Mater. Chem. 2012, 22, 2641. (17) van Bommel, A.; Divigalpitiya, R. Effect of Calendering LiFePO4 Electrodes. J. Electrochem. Soc. 2012, 159, A1791−A1795. (18) Wu, H.-C.; Lee, E.; Wu, N.-L. High-temperature carbon-coated aluminum current collector for enhanced power performance of LiFePO4 electrode of Li-ion batteries. Electrochem. Commun. 2010, 12, 488. (19) Porcher, W.; Lestriez, B.; Jouanneau, S.; Guyomard, D. Optimizing the surfactant for the aqueous processing of LiFePO4 composite electrodes. J. Power Sources 2010, 195, 2835. (20) Guy, D.; Lestriez, B.; Bouchet, R.; Guyomard, D. Critical Role of Polymeric Binders on the Electronic Transport Properties of Composites Electrode. J. Electrochem. Soc. 2006, 153, A679−A688. (21) Wu, X.-L.; Guo, Y.-G.; Su, J.; Xiong, J.-W.; Zhang, Y.-L.; Wan, L.-J. Carbon-Nanotube-Decorated Nano-LiFePO4@C Cathode Material with Superior High-Rate and Low-Temperature Performances for Lithium-Ion Batteries. Adv. Energy Mater. 2013, 3, 1155. (22) Wang, Q.; Evans, N.; Zakeeruddin, S.-M.; Exnar, I.; Grätzel, M. Molecular Wiring of Insulators: Charging and Discharging Electrode Materials for High-Energy Lithium-Ion Batteries by Molecular Charge Transport Layers. J. Am. Chem. Soc. 2007, 129, 3163. (23) Wang, D.; Ela, S.-E.; Zakeeruddin, S.-M.; Pechy, P.; Exnar, I.; Wang, Q.; Grätzel, M. Polymer wiring of insulating electrode materials: An approach to improve energy density of lithium-ion batteries. Electrochem. Commun. 2009, 11, 1350. (24) Wang, Q.; Zakeeruddin, S.-M.; Wang, D.; Exnar, I.; Grätzel, M. Redox Targeting of Insulating Electrode Materials: A New Approach to High-Energy-Density Batteries. Angew. Chem., Int. Ed. 2006, 45, 8197. (25) Ravet, N.; Goodenough, J.-B.; Besner, S.; Simoneau, M.; Hovington, P.; Armand, M. Abstract n°127 presented at the 196th Meeting of the Electrochemical Society, Honolulu, HI, October 1999. (26) Ravet, N.; Besner, S.; Simoneau, M.; Vallée, A.; Armand, M. New Electrode Materials with High Surface Conductivity. Canadian Patent CA2270771, Apr 30, 1999.

roughly 2 V lower, shows that a charge-hopping mechanism may also contribute to the charge transport above 3 V vs Li+/ Li0 and substantiates the crucial role of molecular junctions to carry the flow of the current load at nanocontacts. It is clear that this novel concept will spark new developments with respect to the control and optimization of electron transport and transfer at the relevant contacts within electrodes destined for use in electrochemical storage devices. In this sense, these results may be of particular interest to those designing thick electrodes of high-energy density applications with high-power performance.

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ASSOCIATED CONTENT

S Supporting Information *

Complete description of all materials and experimental measurements, CVs, and HRTEM images for P3T samples, dc conductivity measurements, HRTEM images of MWCNT− P3TPPO−LTO, and additional electrochemical results including those related to LTO as well as full experimental procedure for the organic synthesis. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.5b01049.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Present Address #

Department of Chemistry, Functional Materials, Technische Universität Berlin, Hardenbergstr. 40, 10623 Berlin, Germany. E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS CNRS, University of Nantes, and the ANR program (no. ANR09-STOCK-E-02-01) are acknowledged for their financial funding. We express our gratitude to S. Levasseur (UMICORE) for the supply of the LFPC active material, and to B. Humbert (IMN) for the fruitful discussions. Jonhson Mattey is acknowledged for his donation of the PdCl2 used for the preparation of the Pd(PPh3)4 catalyst.

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REFERENCES

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DOI: 10.1021/acs.chemmater.5b01049 Chem. Mater. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.chemmater.5b01049 Chem. Mater. XXXX, XXX, XXX−XXX