Annotation

The composite electrodes of commercial metal-ion batteries consists of an active material, a conductive additive that provides electrical conductivity, and a non-conductive polymer that binds all components together. However, this widespread composition of the metal-ion electrodes faces the problem of component adhesion, i.e. does not provide optimal interfacial ion and electron transport between the electrolyte, the active material and the conductive additive. Thus, the transport characteristics of modern metal-ion batteries are limited by the adhesion characteristics and conductivity of the auxiliary components.

Novel ion- and electron-conducting binders have been studied broadly in recent years, since they can improve the adhesive characteristics, electronic and ionic conductivity, and can increase the homogeneity of the composite electrode in comparison with standard compositions.This improvement is of importance for the next generation of high performance, and durable batteries. The development of new binders is a very complex task, which is often solved by empirical search through components and compositions. The development of theoretical concept of ion and electron transfer within polymer binders and active material and at their interphases could shed light on how to simplify the search for optimal binder compositions with the most suitable properties. Nevertheless, there are still no models and approaches that adequately describe the mechanism of charge transfer within polymer binders and active material and at their interfaces.

The goal of the project is to develop a theoretical model describing ionic and electronic conductivity in complex composite electrodes, as well as the structure of electrical double layers (EDL) and adhesion between components. The model will take into account the interaction of multifunctional binders and the peculiarities of charge transfer within them and at their interphases, so it will provide an opportunity to compute optimal composition of composite electrodes and, thereby, will reduce the labor cost for finding the optimal composition.

The experimental part of the study will include the synthesis of a series of functional polymeric binders with different electrochemical properties. The binders will then be investigated by electrochemical methods such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), galvanostatic intermittent titration (GITT) and potentiostatic intermittent titration (PITT) and electrochemical microgravimetry on quartz piezoelectrode (EQCM). Then a mathematical model of a polymer binder will be developed. The model will take into account the polaron conductivity in conductive polymer component, that wiil enable satisfactorily describe their quasi-equilibrium response (PITT, GITT) and nonequilibrium response (CV, GCD).

The parameters obtained from the experimental study and modeling will be used as input data for the second theoretical model, which describes the entire composite electrode. In the second series of experiments, composite electrodes will be investigated by electrochemical methods, which will allow first tuning the model and then testing its predictive ability.

Expected results

Rate-capability, capacity and stability of metal-ion batteries strongly depend on the composition of composite electrodes. The main goal of the project is to develop a method for searching the optimal composition of a composite electrode. The method will take into account both the properties of the active material and the properties of binders and their mutual influence. To achieve this goal, it is necessary to solve the following tasks:

1. Investigate a set of ion- and electron-conducting polymer binders by electrochemical methods (CV, GCD, EIS, GITT, PITT, EQCM) in order to obtain the dependences of the diffusion coefficients, electronic conductivity, differential capacities and exchange currents on applied potential) and by SEM in order obtain their morphology.
2. Develop a mathematical model that describes the quasi-equilibrium charging curves (PITT, GITT) of polymer binders obtained in p.1.
3. Supplement the equilibrium model with number of rate-limiting non-equilibrium stages (such as slow ion diffusion, slow electron transport within the bulk, slow electron / ion transport at interphases, etc.). Fit the results of electrochemical measurements from p.1 with developed model, so the model verified.
4. Manufacture composite electrodes made from commercial active materials (LFP, LMNO) and ion- and electron-conducting polymers from p.1. Investigate the obtained electrodes with electrochemical methods.
5. Develop a model that describes galvanostatic charge-discharge curves (GCD) of composite electrodes. The model will use the data obtained from previous experiments and simulations as well as literature data on well-described compounds (LFP, LNMO) as initial parameter values. Number of possible rate-limiting stages will be taken into account, such as the interfacial ion and electron transfer, ion diffusion, polaron conductivity in conjugated polymer and phase transition in the active material, etc. The model will take into account the peculiarities of the interaction of the proposed polymer binders with the active material, which will provide understanding the complex mechanism by which composition of the electrode effects battery performance.

The project at RSCF website

Publications

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