Electrode Binder Research Articles

Molecular‐level Designed Polymer Electrolyte for High‐Voltage Lithium–Metal Solid‐State Batteries

AbstractIn solid polymer electrolytes (SPEs) based Li–metal batteries, the inhomogeneous migration of dual‐ion in the cell results in large concentration polarization and reduces interfacial stability during cycling. A special molecular‐level designed polymer electrolyte (MDPE) is proposed by embedding a special functional group (4‐vinylbenzotrifluoride) in the polycarbonate base. In MDPE, the polymer matrix obtained by copolymerization of vinylidene carbonate and 4‐vinylbenzotrifluoride is coupled with the anion of lithium‐salt by hydrogen bonding and the “σ‐hole” effect of the CF bond. This intermolecular interaction limits the migration of the anion and increases the ionic transfer number of MDPE (tLi+ = 0.76). The mechanisms of the enhanced tLi+ of MDPE are profoundly understood by conducting first‐principles density functional theory calculation. Furthermore, MDPE has an electrochemical stability window (4.9 V) and excellent electrochemical stability with Li–metal due to the CO group and trifluoromethylbenzene (ph‐CF3) of the polymer matrix. Benefited from these merits, LiNi0.8Co0.1Mn0.1O2‐based solid‐state cells with the MDPE as both the electrolyte host and electrode binder exhibit good rate and cycling performance. This study demonstrates that polymer electrolytes designed at the molecular level can provide a broader platform for the high‐performance design needs of lithium batteries.

Recent Advances in Porous Polymers for Solid-State Rechargeable Lithium Batteries.

The application of rechargeable lithium batteries involves all aspects of our daily life, such as new energy vehicles, computers, watches and other electronic mobile devices, so it is becoming more and more important in contemporary society. However, commercial liquid rechargeable lithium batteries have safety hazards such as leakage or explosion, all-solid-state lithium rechargeable lithium batteries will become the best alternatives. But the biggest challenge we face at present is the large solid-solid interface contact resistance between the solid electrolyte and the electrode as well as the low ionic conductivity of the solid electrolyte. Due to the large relative molecular mass, polymers usually exhibit solid or gel state with good mechanical strength. The intermolecules are connected by covalent bonds, so that the chemical and physical stability, corrosion resistance, high temperature resistance and fire resistance are good. Many researchers have found that polymers play an important role in improving the performance of all-solid-state lithium rechargeable batteries. This review mainly describes the application of polymers in the fields of electrodes, electrolytes, electrolyte-electrode contact interfaces, and electrode binders in all-solid-state lithium rechargeable batteries, and how to improve battery performance. This review mainly introduces the recent applications of polymers in solid-state lithium battery electrodes, electrolytes, electrode binders, etc., and describes the performance of emerging porous polymer materials and materials based on traditional polymers in solid-state lithium batteries. The comparative analysis shows the application advantages and disadvantages of the emerging porous polymer materials in this field which provides valuable reference information for further development.

The influence of intrinsically proton conductive electrode binder materials on HT-PEMFC performance

High temperature proton exchange membrane fuel cells (HT-PEMFCs) typically employ either acid-absorbing or hydrophobic electrode binders in their catalyst layers (CLs). A recently introduced alternative is the ionomeric binder PWN, poly(2,3,5,6-tetrafluorostyrene-4-phosphonic acid). In literature, PWN with a phosphonation degree of 70% was shown to remarkably improve HT-PEMFC performance. Here, we investigate the influence of the phosphonation degree (40–95%) of this ionomeric binder on HT-PEMFC performance. PWN is employed in the cathode CL and compared to the commonly used polytetrafluoroethylene (PTFE) binder. The electrochemical behavior is tested at 180 °C at ambient pressure under H2/air conditions using a commercial phosphoric acid (PA)-doped PBI-membrane. HT-PEMFCs with PWN generally outperform fuel cells (FCs) with PTFE after a full break-in regarding peak power density (PPD), activation overpotential (as studied by Tafel analysis), and reproducibility in the mass transport region. Further, PWN-electrodes show higher electrochemically active surface areas (ECSAs) than PTFE-electrodes after completing the break-in. We find that the phosphonation degree has a substantial impact on the PPD, with PWNs with lower phosphonation degrees (40–60%) outperforming highly phosphonated PWNs (70–95%). Taken together, PWN as an ionomeric electrode binder in HT-PEMFCs shows remarkable improvements in performance, but a precise adjustment of the phosphonation degree is required to obtain optimal results.

Chitin as a universal and sustainable electrode binder for electrochemical capacitors

We have introduced chitin-bound, activated carbon-based electrode materials dedicated to supercapacitors operated on different electrolyte environments. As a chitin solvent, we have used our original mixture system containing an ionic liquid (1-ethyl-3-methylimidazolium acetate) and a viscosity reducing agent (dimethyl sulfoxide). The prepared electrode material has been tested in terms of morphological, physicochemical, and electrochemical properties. The most attention has been paid to studying the electrochemical performance of composite electrodes in the most common types of liquid electrolytes, i.e. aqueous, organic and ionic liquid electrolytes. A comparative study of the assembled supercapacitors has been made in terms of specific capacitance, charge propagation, cycle stability, and power/energy density. As was demonstrated, the proposed electrode binder material features a very attractive attribute appearing as versatility in terms of employed electrolyte. Regardless of the type of used electrolyte, chitin-bound electrodes display high specific capacitance (128–142 F g−1), good rate capability (up to 92% capacitance retention under 15 A g−1), and excellent cycle stability (75–99% of an initial capacitance). Taking into account the natural origin of chitin and the excellent electrochemical efficiency of tested devices, it appears that synthesized electrode materials represent a promising and green alternative for the development of environmentally benign supercapacitors.

(Invited) Anion Exchange Membrane Fuel Cells in LIME Laboratory: From Commercial Polymers Towards Biomass Based Materials

Anion exchange membrane fuel cells (AEMFCs) are clean energy conversion devices that are an attractive alternative to the more common proton exchange membrane fuel cells, because they present the advantage of not using noble metals as catalysts for the oxygen reduction reaction (ORR). Unfortunately the low durability of anion exchange membranes (AEMs) in basic conditions limits their use on a large scale. The International Laboratory "Ionomer Materials for Energy" (LIME) group has extensively worked on synthesis of ionomers applying different strategies to mitigate the damaging effect of alkaline media on anion exchange membranes: the delocalization of the positive charge, the introduction of a long chain to separate the charge and the backbone [1], the introduction of a second phase, backbone without ether groups, and recently the use of biomass to prepare more sustainable materials for fuel cells. In this presentation, after a short overview on the progress made on anionic membranes based on commercial polymers, such as polysulfone (PSU) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) [2], I will focalize on the synthesis of the new ionomer poly(alkylene biphenyl butyltrimethyl ammonium) (ABBA) with a backbone devoid of alkaline-labile C-O-C bonds and with quaternary ammonium groups grafted on long side chains [3]. The ionomer was achieved by metalation reaction on 2-bromobiphenyl, followed by the introduction of the long chain with 1,4-dibromobutane. The precursor was polycondensed and then quaternized using trimethylamine (TMA). The reaction is efficient, well controllable and easy to modulate. The ability to form stable solutions over several months, combined with the spacing of the positive charge from the backbone, the flexibility due to the quaternary carbon in the matrix and the high IEC values such as 2.5 meq/g, allows us to consider this ionomer a good candidate as an electrode binder and AEM. Other synthesis of backbones without ether linkage was explored e.g. a crosslinked poly(vinylbenzylchloride-co-hexene) copolymer grafted with N,N-dimethylhexylammonium groups [4]. The copolymerization was achieved by the Ziegler–Natta method, employing the complex ZrCl4 (THF)2 as a catalyst. The resulting aliphatic ionomer showed good alkaline stability, after 72 h of treatment in 2M KOH at 80 °C the remaining IEC of 76% confirmed that ionomers without ether bonds are less sensitive to a SN2 attack. The ionic conductivity of blended membrane with polyvinyl alcohol (PVA) at 25 °C in the OH− form was 29.5 mS/cm. The last part of presentation will be focus on a more sustainable fuel cell, based on heterocycle building blocks exploiting biomass resources.

Electrode Ionomer Accelerated Stress Test Applied to High Oxygen Permeability Ionomer in Fuel Cells

Perfluorosulfonic acid (PFSA) polymer electrolytes are widely used in proton exchange membrane (PEM) fuel cell fabrication for the membrane separator and the electrode binder. The PEM serves to electrically insulate the cathode catalyst layer (CCL) from anode catalyst layer (ACL), provide proton conduction between both CCL and ACL, as well as prevent gas crossover. PFSA ionomers are also used in the CCL and ACL to mechanically bind the catalyst particles into thin-films, provide proton conduction between the PEM and catalyst surface, and produce a high proton reactant concentration at the oxygen reduction reaction catalyst. Despite their versatility to be used as a membrane and catalyst binder, the typical PFSA ionomers pose challenges due to the high oxygen transport resistance that is introduced by the thin ionomer films over the catalyst. In recent years, novel high oxygen permeability ionomers (HOPIs) have been developed as the successor to the traditional Nafion™ PFSA ionomers. Despite their remarkable results as a catalyst binder due to their increased oxygen transport rates, less is known regarding their degradation and functional lifetime. Although accelerated stress tests (ASTs) for platinum (Pt)/Pt-alloy catalysts, carbon supports, and membranes are well-established and commonly applied, there is no standard and easily implemented AST for electrode ionomers. One challenge is that membrane ASTs usually quantify the fluoride emission rate (FER) to assess chemical degradation, which is difficult to apply for electrode PFSA ionomer when also using a PFSA membrane because the FER is overwhelmed by membrane signal. In addition, changes in OCV and H2 crossover are not directly indicative of electrode ionomer degradation. Furthermore, concomitant degradation of the catalyst and support can interfere with interpreting electrode ionomer degradation. Here we present an effective and easily applied electrode ionomer chemical AST protocol that can be used to evaluate degradation in the functionality of the electrode ionomer. The approach borrows the chemical AST conditions of the chemical membrane AST’s open circuit voltage (OCV) hold and avoids excessive potential cycling to minimize catalyst and support degradation that will elicit changes in electrode properties separate from ionomer degradation. During the AST, we measure the cathode’s proton conduction resistance, oxygen permeability, and electrochemically surface area (ECSA) to evaluate the degradation of the ionomer’s functionality. Thus, this protocol can be used to assess if more complex and time consuming analyses of ionomer durability are needed as new chemistries emerge. Here we present results of this AST to both conventional PFSA ionomers and HOPIs.

The Influence of Polar Functional Groups in Melt-Blended Polymers Used As New Solid Electrolytes for Lithium Batteries.

Following the COP26 Summit in November 2021, more than hundred countries pledged to reach zero-emission by 2070 at the latest and the major car manufacturers committed to selling only electric vehicles by 2040. Currently, lithium-ion batteries (LIBs) are among the most widely used storage systems because of their high energy and power densities and long lifespan.1 The early LIBs are composed of intercalation electrodes, electronically isolated by an ion-conducting organic liquid electrolyte. However, the use of liquid electrolytes presents some disadvantages – especially in regard to consumer safety – related to short-circuits and potential leakages of the flammable liquid solvent. Moreover, in the case of lithium metal batteries, the combination of a liquid electrolyte and a high-capacity lithium metal anode leads to the uncontrolled deposition of lithium during the reduction, forming dendrites between the electrodes. A promising way to avoid this instability and improve battery safety is to replace the liquid electrolyte with an ion-conducting solid electrolyte.2 Among them, solid polymer electrolytes (SPEs) represent one of the most attractive alternatives due to their capacity to effectively conduct ions and higher mechanical resistance than their liquid counterparts.3 An important criterion for selecting polymers for use in SPEs is their ability to dissolve lithium salts through polar functional groups. Salt dissolution results in the replacement of ion-ion interactions in the lithium salt, with ion-dipole interactions in the polymer. The transport mechanisms of these ion-conducting materials differ from those of liquid electrolytes. Cation transport in polymer involves two steps which are considered to be dissociated or not, depending on the model chosen (Arrhenius or Vogel-Tamman-Fulcher, respectively). The application of one of these models provides interesting information on the ionic mobility dynamics in SPEs and, in particular, on the interplay between ionic jumps and polymer chain mobility. According to previous studies, higher segmental motions in the amorphous phase of polymers mainly provide ionic transport, which explains the limited ionic conductivity of SPEs at ambient temperature (less than 10-5 S/cm).Another major limitation of SPEs is primarily related to their dual role as electrolyte and binder in composite electrodes, which requires contradictory requirements to be met. Indeed, SPEs must have both sufficient flexibility to allow good interfacial contact between the electrode components and sufficient rigidity to limit short circuits.Polymer blending has emerged as an economic and effective technique to develop new SPEs which may simultaneously combine properties of each polymer and control the intrinsic properties of the resulting blend by adjusting the formulation.4 Moreover, polymer blends can be obtained by a solvent-free processing method, which reduce SPE toxicity and production time and cost. However, polymer blending makes both the salt dissociation processes and the ionic transport more difficult to understand as both polymers can dissolve lithium salts with their polar groups. Each polymer has different ionic transport properties depending on its architecture and thermal properties. Currently, no systematic survey comparing the ability of polymers with various functional groups to dissolve lithium salts in blends has thus far been conducted.In this presentation, we will discuss the salt dissociation ability of polar functional groups in various polymer blend SPEs. These groups are limited to those that are most commonly present in SPEs : ether, nitrile, carbonate, ester, alcohol and amide.5 The blends presented have been obtained by extrusion, which allows the effect of solvents on salt/polymer interactions to be neglected. Coupled FTIR, EDX and 7Li NMR analyses allow the interactions between LiTFSI and the polymer blends to be determined with a good degree of certainty. Our original study combines experimental and theoretical approaches to determine effects of polymers’ lithium salt solvating ability on blend electrolyte properties. Finally, this survey highlights an ideal polymer couple with the most promising and complementary properties, usable as SPE for LIBs. Indeed, this blend presents encouraging properties, compared to single-polymer SPEs, such as higher ionic conductivities over a wide temperature range, as well as improved mechanical and thermal stability properties and cycling performances. References Xie, W., Liu, X., He, R., Li, Y., Gao, X., Li, X., Peng, Z., Feng, S., Feng, X. and Yang, S. Journal of Energy Storage 2020, 32, 101837.Chen, R., Qu, W., Guo, X., Li, L. and Wu, F. Materials Horizons 2016, 3, 487-516.Gray, F. M. Solid polymer electrolytes, VCH New Tork 1991.Caradant, L., Lepage, D., Nicolle, P., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2020, 4943-4951.Caradant, L., Verdier, N., Foran, G., Lepage, D., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2021. Figure 1

Effect of Electrolyte on the Stress-Strain Behavior of Polymer Binder in Commercial Rechargeable Battery Electrode

Commercial battery electrodes are composites made of active particles bonded to current collected by polymer binders. Binder not only keeps all the particles together but also provides the electrical network necessary for battery operation. Several studies showed that the mechanical behavior of the polymer binder is very important, and it governs the cyclic performance of batteries. To develop advanced degradation models of battery electrodes, the mechanical behavior of binders needs to be characterized. Recently, some studies developed experimental methods to characterize the mechanical behavior of polymer binders, which showed that the most widely used binder, polyvinylidene fluoride (PVdF), behaves as an elastic-viscoplastic material under the typical charge/discharge rates of battery electrodes. However, the time dependent behavior of PVdF is not the only characteristic behavior to keep in mind. It should be noted that the electrolyte interacts with the binder and potentially changes its mechanical behavior which has not been characterized before. Most of the existing studies were carried out under dry conditions (no electrolyte present), and no study exists on the understanding of how electrolyte solvents and salts affect the mechanical behavior of polymer binders. In this talk, we will present the effect of electrolyte on the stress-strain behavior PVdF binder.

(Invited) Conducting Polymers As Dual Charge Conductors for Electrochemical Systems

Electrically conductive polymers are a class of polymers, which can conduct electricity. Conductive polymers have found niche applications such as anti-statics. The electrochemical energy storage devices, especially lithium-ion rechargeable batteries, has grown significantly in the past two decades. Recently multifunctional conductive polymers have been designed as dual ion and electron transport materials, and synthesized through a thermal process. These class of dual charge conducting polymers play a significant role as electrode binders for Silicon (Si) and Tin (Sn) alloy based anode electrode. Si is an attractive candidate for lithium-ion batteries because it delivers 10 times greater theoretical (∼4200 mAh/g) specific capacity than that of a traditional graphite anode (∼370 mAh/g). However, the widespread application of silicon materials has remained a significant challenge because of the large volume change during lithium insertion and extraction processes, disrupting both the Si electrode surface and electrode mechanical integrity. This large volume change causes electrode failure, leading to loss of the electrical contact and drastic capacity fading. Nanosizing the Si and Sn based anode materials provides better performance, but poses significant challenges to manufacturing of the electrode, including particle aggregation, and difficulties in maintaining constant electrical contacts to the nanoparticles, and excessive surface area. Conductive polymer binders can play multiple functions for Si electrode, including improved adhesion and connectivity, lithium ion compensation, better ion and electric conductivity as well as surface and interface modification. Organic and polymer chemistry has provided almost infinity possibilities to modify the polymeric binders to include the desired functionalities. This presentation will discuss the specific molecular design principles and synthetic steps to realize the structures and functionalities of the binders, how these binders interact with different alloy materials, and the electrochemical performances of the electrodes based on these binders.

Investigating Oxygen Reduction Reaction Using a Multiscale Modeling Approach for Polymer Electrolyte Membrane Fuel Cell

Cathode catalyst layer (CCL) modeling is an important tool in elucidating the coupled transport-reaction phenomena and optimizing electrode architectures for greater efficiency, power density, and durability and thereby, reducing fuel cell costs. State-of-the-art catalyst use a high surface area carbon black (HSC) that supports platinum (Pt) nanoparticles, where some of the Pt particles reside on the carbon surface and a significant fraction of particles are found in the nm-scale pores of the carbon support. Within the electrode, the catalyst in bound by a polymer electrode binder (i.e., ionomer) that coats the external surface of the catalyst but does not penetrate the internal pores that are filled with liquid water due to capillary condensation. The contact of ionomer with Pt is known to reduce electrocatalytic activity due to site-blocking by the ionomer anion as well as increase the oxygen transport resistance. There is very little prior work on modeling the distinct performance of the internal Pt and the external Pt in contact with the ionomer. Most prior attempts to model CCLs with HSC catalyst supports at the MEA-scale and cell-scale have used an uncoupled approach, that separately considered the transport to the internal and external Pt particles, not considering the combined flux of oxygen through the ionomer film. Thus, the prior uncoupled model could potentially underestimate the oxygen concentration drop through the ionomer film. Here, we have adopted a numerical model of the catalyst that simultaneously considers the transport to the internal and external Pt as well as the different transport properties in the water and ionomer domains in single primary particle of the catalyst. The single spherical catalyst support model is upscaled to a 3D fuel cell model using a parametric linear regression fitting to model the local source/sink terms in the CCL. This multi-scale model is then applied to study the impact of the catalyst morphology.This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.

Polymer electrolytes based on interactions between [solvent-Li+] complex and solvent-modified polymer

Poly(vinylidene fluoride) (PVDF) is the most popular electrode binder in the current lithium ion batteries (LIBs). Depending on solvent content, polymer electrolytes are classified into solid polymer electrolyte (SPE; solvent-free) and gel polymer electrolytes (GPE; solvent-rich). PVDF-based electrolytes with high contents of solvent undisputedly belong to GPE. However, the affiliation (SPE or GPE) of the PVDF-based electrolyte with low content of “solvent” is in argument as its “solvent” cannot be eliminated till 80 °C in vacuum and its structure and ion transport mechanism remain unclear. By a series of studies, we demonstrate that this is actually a polymer electrolyte based on the interactions between the [solvent-Li + ] complex and the polymer in structure and in Li-ion transport mechanism. The “residual solvent” (N,N-dimethylformamide, DMF, for example) plays critical roles in constructing the polymer electrolyte and in determining its ion transport and therefore such electrolyte cannot be assigned to any of the known polymer electrolytes. The Li + -associated DMF becomes difficult to be eliminated while the DMF-dehydrofluorinated PVDF has a larger dielectric constant, enhances the dissociation of the lithium salt and interacts with the [DMF-Li + ] complex, the charge carrier of the electrolyte. These [solvent-Li + ] complex-based polymer electrolytes have high ionic conductivity (10 −4 S cm −1 at room temperature), Li-ion transference number (0.44) and Young's modulus (45.87 MPa) and will find important applications in the solid lithium batteries and as an ion-conducting binder for the electrodes. These findings will enrich the gallery and deepen the fundamental understandings of the polymer electrolytes, spurring designing of novel electrolytes.

Polymer hydrogel based quasi-solid-state sodium-ion supercapacitor with 2.5 V wide operating potential window and high energy density

The present work reports a quasi-solid state sodium ion-based asymmetric supercapacitor (ASC) device with nitrogen-doped reduced graphene oxide (NrGO) and boron-doped reduced graphene oxide (BrGO) electrodes. The choice of NrGO (BrGO) for the cathode (anode) is accomplished through a computational investigation of electrode quantum capacitances based on density functional theory (DFT). Nanocellulose is used as an electrode binder due to its biodegradability, enhanced wettability, good ion permeability, and low cost. The NaClO4-PVA based hydrogel membrane is the separator-less quasi-solid state gel electrolyte in the fabricated device. The specific capacitance of the NrGO || BrGO ASC device is obtained as 251.2 F g−1, at a current density of 1 A g−1 with a wide potential window of 2.5 V which is better than the previous reports. This device offers a better performance in comparison to the rGO||rGO, NrGO||NrGO and BrGO||BrGO symmetric supercapacitor (SSC) devices due to the synergistic effect of non-faradic capacitance and pseudocapacitance. The ASC device shows an energy density of 54.5 Wh kg−1 at a power density of 1.25 kW kg−1 and significant capacitance retention of 84.8% after 10,000 cycles at a high current density of 15 A g−1.

Fluorinated Materials as Positive Electrodes for Li- and Na-Ion Batteries.

Fluorine is known to be a key element for various components of batteries since current electrolytes rely on Li-ion salts having fluorinated ions and electrode binders are mainly based on fluorinated polymers. Metal fluorides or mixed anion metal fluorides (mainly oxyfluorides) have also gained a substantial interest as active materials for the electrode redox reactions. In this review, metal fluorides for cathodes are considered; they are listed according to the dimensionality of the metal fluoride subnetwork. The synthesis conditions and the crystal structures are described; the electrochemical properties are briefly indicated, and the nature of the electron transport agent is noted. We stress the crucial importance of the elaboration processes to induce the presence of cation disorders, of anion substitutions (mainly F-/O2- or F-/OH-) or vacancies. Finally, we show that an accurate structural characterization is a key step to enable enhanced material performances to overcome several lasting roadblocks, namely the large irreversible capacity and poor energy efficiency that are frequently encountered.

Comparative Study on Chitosans as Green Binder Materials for LiMn2O4 Positive Electrodes in Lithium Ion Batteries

AbstractThe increasing demand for lithium ion batteries consequently involves research on environmentally benign materials and processing routes. Environmentally friendly cobalt‐free, and fluorine‐free electrodes processed without organic solvents were targeted as this approach combines high work safety and sustainability with good electrochemical performance. In this study, chitosan‐based biopolymers were synthesized and systematically investigated for the first time as “green” binders for positive electrodes utilizing LiMn2O4 (LMO). In particular, chitosans with different specifically designed low and high degrees of polymerization (DP), each with comparable degree of acetylation (DA), revealed insights into the impact on the mechanical and electrochemical performance of LMO positive electrodes. Herein, low DP chitosan provided twice the adhesion strength compared to the state‐of‐the‐art binder polyvinylidene difluoride (PVdF) in LMO electrodes, thus, showing the opportunity to reduce the binder content and increase the specific energy. Electrodes with DA<16 % chitosan‐based binder could deliver higher discharge capacities than cathodes using PVdF or chitosans with DA>16 % in LMO||Li metal cells. Cross‐linking of chitosans with citric acid (CA) was demonstrated to significantly increase the discharge capacity up to 80 mAh g−1 at 10 C charge/discharge rate.

Ionic Conductivity Enhancement Achieved by Binder in Electrodes and Its Influence in Supercapacitor

AbstractIonic conductivity is a critical factor affecting the electrochemical performance of double layer capacitor. Therefore, additional ion transport channels are introduced by using Nafion as binder in electrode. In this study, carbonized maple as active substance was mixed with binder of Nafion or PVDF to form electrodes. The electrode structures were obtained by scanning electron microscopy and N2 adsorption‐desorption isotherms with the aim of clarifying negligible differences in the microstructure and binding strength of electrodes with different binders. Furthermore, the two electrodes with different binders tested in KOH exhibited similar electrochemical properties. However, in H2SO4 electrolyte, the electrode containing Nafion showed a much higher specific capacitance than that of electrode using PVDF binder. To directly prove the high ionic conductivity of Nafion electrode, concentration battery was constructed using the two electrodes as separators to investigate their liquid junction potential. This study focused on the ionic conduction in electrodes, which could provide suggestions for electrode design, especially for the utilization of commercial supercapacitors.

Practical Approaches to Apply Ultra-Thick Graphite Anode to High-Energy Lithium-Ion Battery: Carbonization and 3-Dimensionalization.

Lithium-ion batteries with ultra-thick electrodes have high energy density and low manufacturing costs because of the reduction of the inactive materials in the same battery volume. However, the partial usage of the full capacity and the low rate capability are caused by poor ionic and electronic conduction. In this work, the effects of two approaches, such as electrode binder carbonization by heat treatment and 3-dimensionalization by the laser structuring of ultra-thick graphite anodes to lithium-ion batteries for high energy density, are investigated. During the heat treatment, the polyvinylidene fluoride (PVDF) binder is carbonized to form fluorinated graphitic carbons, thereby increasing the number of lithium-ion storage sites and the improvement of the electrode capacity by 14% (420 mAh g−1 and 20 mAh cm−2). Further, the carbonization improves the rate capability by 31% at 0.1 C by simultaneously reducing the ionic and electronic resistances. Furthermore, after the laser structuring of the carbonized electrode, the areal discharge capacity increases to 50% at the increasing current rates, resulting from drastically improved ionic conduction. In addition to the electrochemical characteristics, these two approaches contribute considerably to the fast wetting of the electrolyte into the ultra-thick electrode. The carbonization and laser structuring of the ultra-thick graphite anodes are practical approaches for high-energy batteries to overcome the thickness limitation.

(Invited) Electrochemical Pumping for Hydrogen Storage and Distribution in the Natural Gas Pipeline

Over the next decade, the production and use of hydrogen in various sectors of the global economy is anticipated to grow significantly. It is an already important feedstock in the production of ammonia and desulfurization of fuels in addition to being used in metals refining and as a coolant in thermal electric power plants. More recently, hydrogen is being considered for long-term seasonal energy storage for energy derived from renewables like solar and wind. To alleviate the severe costs of building out completely new infrastructure, the U.S. natural gas pipeline represents an enticing proposition for hydrogen storage and a potential distribution network from centralized production facilities. Embrittlement concerns of the pipeline with hydrogen limit the hydrogen partial pressure/concentration of hydrogen to be stored. Because many end use applications often require high purity hydrogen, it is necessary to separate/de-blend hydrogen from natural gas and compress it at the point-of-use. This talk presents high-temperature polymer electrolyte membrane (HT-PEM) electrochemical hydrogen pumps for separating hydrogen from gas mixtures. Hydrogen purification to +99% from syngas (25mol% hydrogen and 40mol% carbon monoxide (CO)) at 1 A cm-2 and cell voltage of 0.4 V with an electrochemical hydrogen pump was demonstrated. About 90% of hydrogen used in the United States today derives from steam-reformed natural gas that contains large concentrations of CO – which is a potent platinum electrocatalyst poison at temperatures below 100 °C. The hydrogen purification from syngas was possible with an electrochemical hydrogen pump operated at 220 °C and by using: i.) an ion pair HT-PEM that exploits electrostatic interactions to prevent phosphoric acid leaching at elevated temperatures from the membrane matrix and in the presence of water and ii.) a phosphonic acid ionomer electrode binder. The membrane electrode assembly (MEA) with the said materials and platinum on carbon (Pt/C) electrocatalyst was also effective for purifying hydrogen from other types of reformed hydrocarbons with different CO and hydrogen concentrations. Unexpectedly, operating the HT-PEM hydrogen pump at 220 °C minimized CO impact on cell polarization. At this temperature, cell polarization was governed by the hydrogen concentration in the gas feed. These observations motivate future work to develop new electrodes and electrode binders that can extract, purify, and compress hydrogen with feed streams that have low hydrogen content and contain other constituents in natural gas (methane, ethane, t-butyl mercaptan, etc).

(Invited) In-Situ Nanoscale Coatings on Silicon Anodes

One of the directions being pursued for next generation electrochemical cells is the incorporation of elemental silicon into a lithium-ion battery anode. Silicon's high storage capacity and abundance make it an appealing material for lithium-ion cells. While many studies revolve around its mechanical issues (high volume expansion) and coulombic efficiency on cycling, a major roadblock to its use is its poor calendar life. On standing while charged, silicon based electrodes are observed to lose capacity (active lithium). Since this type of test does not involve particle breakdown, losses due to issues associated with parasitic currents are in part derived from the high reactivity of charged silicon anodes with the surrounding electrolyte and electrode binder. In this talk we will be discussing a new concept that deactivates the redox activity of the silicon surface while maintaining the high lithium-ion conductivity of the highly charged surface phases. We have found that by selectively adding alkaline earth cations to the surface, a more electron precise phase (i.e. Li14MgSi4 vs Li15Si4) forms that acts to change the phase evolution moving away from phases formed by gradual one-electron oxidation in the binary lithium-silicon system. Various studies show that the parasitic currents are seen to drop with addition and cycling with extended calendar life observed. Mechanistic studies will be presented that highlight magnesium addition to the electrolyte and electrode and the role of time on the surface phases.

Influence of Acetylation and Polymerization Degree of Chitosan As Green Binder Material for LiMn2O4 Positive Electrodes in Lithium Ion Batteries

The increasing market of lithium ion batteries within the climate crisis consequently leads to a need of environmentally friendly battery materials and production. Organic solvents, fluorinated binders and toxic transition metals are common components in state-of-the-art batteries. Aqueously processed ecofriendly electrodes are reported showing high electrical performance combined with high work safety and sustainability. In this study, the biopolymer chitosan is investigated electrochemically and mechanically as green binder for positive electrodes utilizing lithium manganese oxide (LiMn2O4; LMO) for the first time. Therefore, chitosans were tailored to a high and low degree of polymerization (DP) and three comparable degrees of acetylation (DA). The systematical comparison of these binder materials reveals insights into the impact of polymer binder properties on the electrochemical performance of positive electrodes. Low DP chitosan show a higher adhesive strength than high DP chitosans or PVdF, while chitosan-based electrodes with DA<16% deliver higher discharge capacities and Coulombic efficiencies in T-type cells than with DA>16% or even with the state-of-the-art binder polyvinylidene difluoride (PVdF). Crosslinking of chitosans with citric acid (CA) further increases discharge capacities up to 80 mAh g-1 at 10C and shows again a superior electrochemical performance with sustainable battery materials. Figure 1

The Influence of Polar Functional Groups in Hot-Melt Extruded Polymer Blend Electrolytes for Solid-State Lithium Batteries

Following the COP26 Summit in November 2021, more than hundred countries pledged to reach zero-emission by 2070 at the latest and the major car manufacturers committed to selling only electric vehicles by 2040. Currently, lithium-ion batteries (LIBs) are among the most widely used storage systems because of their high energy and power densities and long lifespan.1 The early LIBs are composed of intercalation electrodes, electronically isolated by an ion-conducting organic liquid electrolyte. However, the use of liquid electrolytes presents some disadvantages – especially in regard to consumer safety – related to short-circuits and potential leakages of the flammable liquid solvent. Moreover, in the case of lithium metal batteries, the combination of a liquid electrolyte and a high-capacity lithium metal anode leads to the uncontrolled deposition of lithium during the reduction, forming dendrites between the electrodes. A promising way to avoid this instability and improve battery safety is to replace the liquid electrolyte with an ion-conducting solid electrolyte.2 Among them, solid polymer electrolytes (SPEs) represent one of the most attractive alternatives due to their capacity to effectively conduct ions and higher mechanical resistance than their liquid counterparts.3 An important criterion for selecting polymers for use in SPEs is their ability to dissolve lithium salts through polar functional groups. Salt dissolution results in the replacement of ion-ion interactions in the lithium salt, with ion-dipole interactions in the polymer. The transport mechanisms of these ion-conducting materials differ from those of liquid electrolytes. Cation transport in polymer involves two steps which are considered to be dissociated or not, depending on the model chosen (Arrhenius or Vogel-Fulcher-Tammann, respectively). The application of one of these models provides interesting information on the ionic mobility dynamics in SPEs and, in particular, on the interplay between ionic jumps and polymer chain mobility. In the Arrhenius model, ionic jumps occur between coordinating sites, without taking into account the influence of segmental relaxation. Conversely, the VTF equation implies a strong relationship between these parameters. According to previous studies, higher segmental motions in the amorphous phase of polymers mainly provide ionic transport, which explains the limited ionic conductivity of SPEs at ambient temperature (less than 10-5 S/cm).Another major limitation of SPEs is primarily related to their dual role as electrolyte and binder in composite electrodes, which requires contradictory requirements to be met. Indeed, SPEs must have both sufficient flexibility to allow good interfacial contact between the electrode components and sufficient rigidity to limit short circuits.Polymer blending has emerged as an economic and effective technique to develop new SPEs which may simultaneously combine properties of each polymer and control the intrinsic properties of the resulting blend by adjusting the formulation.4 Moreover, polymer blends can be obtained by a solvent-free processing method, which reduce SPE toxicity and production time (no solvent evaporation). However, polymer blending makes both the salt dissociation processes and the ionic transport more difficult to understand as both polymers can dissolve lithium salts with their polar functional groups. Each polymer has different ionic transport properties depending on its architecture and thermal properties. Currently, no systematic survey comparing the ability of polymers with various functional groups to dissolve lithium salts in blends has thus far been conducted.In this presentation, we will discuss the salt dissociation ability of polar functional groups in various polymer blend SPEs. These groups are limited to those that are most commonly present in SPEs : ether, nitrile, carbonate, ester, alcohol and amide.5 The blends presented have been obtained by extrusion, which allows the effect of solvents on salt/polymer interactions to be neglected. In this work, coupled FTIR, EDX and 7Li NMR analyses allow the interactions between LiTFSI and the polymer blends to be determined with a good degree of certainty. Our original study combines experimental and theoretical approaches to determine effects of polymers’ lithium salt solvating ability on polymer blend electrolyte properties and represents an advancement in understanding and optimizing polymer selection for SPEs, used in lithium-ion batteries. References Xie, W., Liu, X., He, R., Li, Y., Gao, X., Li, X., Peng, Z., Feng, S., Feng, X. and Yang, S. Journal of Energy Storage 2020, 32, 101837.Chen, R., Qu, W., Guo, X., Li, L. and Wu, F. Materials Horizons 2016, 3, 487-516.Gray, F. M. Solid polymer electrolytes, VCH New Tork 1991.Caradant, L., Lepage, D., Nicolle, P., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2020, 4943-4951.Caradant, L., Verdier, N., Foran, G., Lepage, D., Prébé, A., Aymé-Perrot, D. and Dollé, M. ACS Applied Polymer Materials 2021. Figure 1