(Invited) Modelling and Experiments to Guide Scale-up of Structured Electrode Manufacturing for Fast-Charging and Long-Life Li-Ion Cells

Abstract

For widespread adoption of electric vehicles, lithium-ion batteries (LiBs) need to achieve energy densities of around 350 Wh/kg, cost less than $100/Wh, and be able to charge quickly within around 15 minutes. To achieve this aim, the material properties of lithium-ion electrodes need to be optimized across multiple length scales, from particle to cell. Leveraging advanced characterization techniques to acquire representative particle- and electrode-level microstructures, we develop models to simulate the behavior of individual particles and novel electrode architectures that are feasible to synthesize and scale up to manufacture high performance batteries. We then demonstrate manufacturing of the novel electrode architectures at pilot scale roll-to-roll processing using high-speed laser-ablation to tune the electrode architecture. Guided by multi-scale models, we observe substantial improvements in cell performance.For the particle level optimization, the primary objective is to develop a predictive cathode-particle cracking model that captures secondary-particle fracture dynamics, relate damage to observed capacity fade, and provide design criteria for future cathode development. The novel coupled electrochemistry-transport-mechanics model is implemented on realistic three-dimensional LiNixMnyCozO2 (NMC) secondary particles. Realistic secondary particles are generated using statistically representative particle generation software. The generated particle architecture is used in chemo-mechanical models to simulate Li (de)intercalation during cycling. The model considers diffusion-induced stress, mismatch strain, and damage evolution coupled through the spatial and temporal evolution of geometric, transport, and mechanical properties. Contrary to most cathode-cracking models, instead of a cohesive-zone implementation, a continuum-damage model is used. Additionally, the model simulates several realistic secondary particle geometries to study the effect of secondary-particle size and grain size on damage. The model is expected to provide insights into ideal cathode geometries (e.g., grain morphology, orientation, and particle sizes) and optimal cathode-sensitive charge-protocol development.For electrode level optimization, structuring the electrode with channels to provide straight diffusion paths along the electrode thickness is a promising approach with demonstrated improved capacity retention at fast charge. The optimal shape and spatial distribution of these channels, that together form the so-called Secondary Pore Network (SPN), taking into consideration the manufacturing technique limitations, is however still unknown. Battery manufacturing cost is another key limiting factor for the wide adoption of electric vehicles. The electrolyte wetting process is an expensive step as complete infiltration can takes days, thus requiring expensive storage space and time. Structured electrodes have also demonstrated reduced wetting time as channels offer highways indifferently for capillary-driven or concentration gradient-driven transport mechanisms. However, the optimal channel pattern for enhanced wetting is also unknown. In this work, we identify both optimal patterns, for fast charging, and for fast wetting, independently, through use of a genetic algorithm (GA). The final proposed structured electrode is therefore the baseline porous matrix, a Secondary Pore Network (SPN) tailored for fast charging, and a Tertiary Pore Network (TPN) tailored for fast wetting, with less than 10% of active material removed in total.High-speed laser-ablation is applied to manufacturing this electrode architecture. Laser ablation is a scalable technique for decreasing the effective tortuosity of electrodes by selectively removing material with high precision. Applied to thick electrode coatings, this work focuses on understanding the impact of laser ablation on electrode material properties at the beginning of life and synergistic impacts of ablated channels on cell performance throughout their cycle life. Post laser ablation, local changes in chemistry, crystallography, and morphology of the laser-impacted electrode regions are investigated. It is shown that femtosecond pulsed laser ablation can achieve high-rate material removal with minor material damage locally at the interface of the impacted zones. The capacity achieved during a 6C (10 min) constant-current constant-voltage charge to 4.2 V improved from 1 mAh cm−2 for the non-ablated electrodes to almost 2 mAh cm−2 for the ablated electrodes. This benefit is attributed to a synergistic effect of enhanced wetting and decreased electrode tortuosity. The benefit was maintained for over 120 cycles, and upon disassembly decreased Li-plating on the graphite anode was observed.From the particle to the electrode level, we demonstrate that there remains ample opportunity for optimizing the material properties of conventional electrode chemistries for faster charging and longer-life performance. Our combined use of advanced characterization, modelling, and data-guided manufacturing shows that a multi-scale and multi-modal approach can be applied to build electrodes from the particle up and achieve enhanced electrochemical performance at the cell level through advanced and scalable manufacturing techniques. Figure 1