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Mechanochemistry of advanced anode designs in Li-ion batteries

Subject Area Mechanics
Term from 2017 to 2022
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 386355213
 
Final Report Year 2022

Final Report Abstract

In this work coupled problems of mechanochemistry were considered, namely the stress-affected kinetics of a chemical reaction front propagation in solids. A coupling of mechanical stresses, diffusion, and chemical reactions was comprehensively investigated: analytically, numerically, and experimentally. The main results of this investigation are as follows: i. A numerical procedure was developed and verified for simulating the chemical reaction front propagation in elastic solids. The proposed numerical procedure was verified by comparison with the analytical predictions and also compared and cross-verified with CutFEM and IGA-based procedures. ii. The analytical procedure for a linear stability analysis of an equilibrium phase interface was extended to the case of a chemical reaction front. The stability of the propagating reaction front was studied numerically for cases of stable and unstable thermodynamic equilibrium interface positions; iii. The competition between the global kinetics of the interface propagation and the local kinetics of interface perturbations was demonstrated in the case of an unstable equilibrium interface position; iv. To qualitatively and quantitatively verify the proposed model experimentally a high-temperature storage test was carried out for microchips with eutectic SnAg solder ball grid arrays. Based on the experimental results, diffusion and reaction kinetics parameters for the case of intermetallic growth in the context of the chemical affinity tensor concept were obtained for the first time. As a result of setting and solving related problems of mechanochemistry based on the concept of the chemical affinity tensor models have been developed to describe lithization reactions occurring in the anodes of lithium-ion batteries. It was investigated how the rheological properties of the reaction product - viscosity, plasticity - affect the kinetics of the propagation of the reaction front. In the case of plasticity, the interaction between the reaction front and the boundary between the elastic and plastic regions was studied. It has been demonstrated that mechanical stresses generated by the transformation deformation can slow down and even block the propagation of the reaction front. For anodes based on composite materials, in the effective field approximation, a model has been developed to study the kinetics of chemical transformations in interacting inclusions of a composite material. In addition, a special case of a Si nano-particle embedded in a viscous matrix was considered for which a lithiation kinetics was also analyzed. In the context of using the buckling of anode structural elements as a mechanism for stress relaxation, the problem of buckling of a linear anode element caused by a chemical reaction is formulated and investigated. The time until loss of stability was determined. Various diffusion models have been developed and tested that take into account the effect of the stress-strain state on the diffusion flow, the presence of vacancies, and electromigration. The possibility and expediency of using various materials for the anode was experimentally investigated. A technological process for assembling a lithium-ion battery cell with silicon-based anode material has been developed and carried out. A design solution for a battery case with a sealed window was selected, assembled and tested for in-situ testing of Raman spectroscopy during the discharge/charge process. A Raman shift and a decrease in the intensity of the silicon peak in the process of discharging a battery cell were noted.

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