RSCF №24-73-10157
(2024—2026)
Annotation
The binder is an important component of the electrode of both lithium-ion and other metal-ion batteries, and plays a significant role in determining their electrochemical characteristics. However, the importance of developing a high-performance binder is often underestimated, and to date, even basic ideas about the mechanism of interaction of the binder with the active material have not been fully formulated. Developing new binders is a complex task that requires collaboration between experts in various disciplines, including polymer science, electrochemistry, chemical engineering, and advanced materials characterization techniques.
The goal of the project is to study the influence of the nature and composition of multifunctional binders (ion- and/or electron-conducting) on the transport characteristics of composite electrodes of metal-ion batteries (MIB) and to develop a procedure for selecting the optimal composition of the electrode composite. It is known that the introduction of electron- and ion-conducting polymers into the binder composition can lead to an increase in the capacity and power of MIA electrodes, as well as an increase in their mechanical and electrochemical stability. However, the reasons for these effects have not been studied in detail. As a result, the creation of electrode composites based on various combinations of active material and binder is usually carried out by trial and error rather than by rational search for given parameters. Effective non-empirical selection of a binder that is well compatible with a specific active material is possible only on the basis of a fundamental understanding of the mechanism of their interaction.
As part of this project, a specially selected series of polymer binders will be obtained that differ in the ionic and electronic conductivity of the components.
The electrochemical characteristics of the resulting binders and their composites with the most promising cathode materials will be revealed using electrochemical methods such as galvanostatic charge/discharge (GCD), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic intermittent titration (GITT) and the potentiostatic intermittent titration method (PITT), as well as using direct conductivity measurement using the four-probe method and/or differential voltammetry on a comb microelectrode. In addition to electrochemical studies, the materials will be studied using electrochemical quartz microgravimetry (EQCM) and X-ray diffraction analysis. They will provide information on the distribution of Li+ between the phases of the composite electrode at different states of charge/discharge.
The obtained electrochemical and spectral data will be used to develop a Newman-type model that will describe the dynamics of a metal-ion battery, taking into account the specific features of the resulting composite electrodes, such as the ionic and electronic conductivity of both the binders and the active material, the structure of the interphase boundaries of the composite and charge transfer between phases. This model will provide an understanding of the influence of specific parameters of the binders and composite composition on the electrochemical response of the battery, which will ultimately simplify the procedure for selecting the optimal composition of the composite electrode and provide universal criteria for selecting a binder suitable for a specific type of cathode material. As a result, it will be possible to increase the charge/discharge rate of MIA with a constant composition of the active material by improving the transport characteristics of the binder.
Expected results
Multifunctional conductive polymer binders consist of three main components: conductive polymer (PP); an anion or polyanionic dopant, a polyelectrolyte (PE), responsible for stabilizing the conductive state of the PP, and a binder (adhesive) polymer (AD), which provides the required mechanical properties of the binder. PP provides electronic conductivity, while PE and AD provide ionic conduction pathways and determine the adhesive and mechanical properties of the binder. However, the role of such additional features in the overall performance of the binder is not usually discussed, and the selection of PE and AD is based on synthetic availability or price. This leads to empirical selection of the binder and often does not allow understanding the effects of interaction of the components of the functional binder with each other. The selection of the conductive and adhesive properties of a material for practical use can be simplified using mathematical models. Such models make it possible to take into account the complexity of charge transport in composite electrodes, namely, that some composites may be limited to a greater extent by ionic conductivity, while for others electronic conductivity is of decisive importance. In addition, increasing the adhesive properties of anionic polyelectrolytes compared to non-polar polymers can also play a decisive role in cell performance.
The main goal of the project is to separate and quantify bulk and interfacial electron and ion transport processes and determine their role in the electrochemical properties of the composite electrode. To achieve this goal, the following tasks will be solved:
- Obtain a series of multifunctional binders with a systematic change in a certain parameter (electronic and ionic conductivity, adhesion). This task will be accomplished by both changing the nature of PP (polythiophenes, polysalens, polypyrrole, polyaniline), PE (polystyrene sulfonate, polyvinyl sulfonate, poly(2-acrylamido-2-methyl-1-propanesulfonate)) and AD (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, polyvinyl alcohol), and by obtaining multifunctional binders with different contents of components (PP:PE:AD) of the same nature.
- Conduct an electrochemical study of the resulting binders (in order to establish their electronic and ionic conductivity, stable cycling potentials, charge transfer resistance, etc.), and also measure their adhesive and mechanical properties.
- Prepare and test electrodes based on the obtained binders and commercial active materials. LiFePO4, whose properties are well studied and whose low charge/discharge potential guarantees the stability of the polymer in contact with it, will be used as a reference active material for model development and tuning. Other promising active materials (for example, LNMO, NMC, sodium-ion cathode materials) will be used to study the possibility of improving their practical characteristics and assessing the stability of polymers in contact with a certain type of material. Each cathode material will, if possible, be represented by several samples (particles of different sizes and morphologies). Samples will be studied using SEM, XPS, EDX to characterize the composition, morphology and coating properties of these samples.
- Investigate the resulting composites using electrochemical methods (CV, GCD, DCVA, EIS, GITT, PITT, EQCM) and in situ physical methods (SEM, HR-TEM, AFM) in order to characterize and extract physicochemical parameters. From this study, using the results of electrochemical tests of pure binders (item 2) and the results of physicochemical characterization of composites (item 3), it will be established how the properties of the binder, morphology and composition of the composite correlate with the electrochemical response of the system.
- Next, based on the results of the above experiments, a mathematical model will be developed that takes into account both the properties of multifunctional binders and the properties of the composite. The model will numerically calculate the galvanostatic charge-discharge (GCD) and current-voltage (CV) curves of the composite electrodes. Many possible rate-limiting stages will be taken into account, among which may be interfacial transfer of ions, electrons, diffusion of charge carriers, phase growth rate in the active material, slow nucleation, etc. The resulting model will allow us to correlate the electrochemical response of the composite electrode with the characteristics and amount of the binder and, accordingly, will provide the ability to select optimal combinations of the composition of the binder and active material through a numerical experiment and, thus, will allow us to predict the composition of the optimal electrode composition with the least labor costs.
Publications
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