3D Electrode Architectures and Advanced Materials for Next-Generation Lithium-Ion Battery

Laser structuring has a huge impact on performances and operational lifetime of lithium-ion batteries. Optimized cell architectures including current collectors, separators, and electrodes are flanked by material concepts for the development of next-generation 3D lithium-ion batteries. Recently a new approach was established by merging 3D electrode, high-energy material and thick film electrode concepts. For this purpose ultrafast laser structuring for upscaling including roll-to-roll processing was established. Performance, degradation and failure processes were studied and correlated to the 3D electrode architectures. <i>Post-mortem</i> studies using laser-induced breakdown spectroscopy (LIBS) were carried out to illustrate the formation of new lithium diffusion pathways in 3D electrodes. In addition, 3D elemental mappings by LIBS were used to indicate starting points of cell degradation in coin and pouch cell designs. The studies were performed with NMC 622 as cathode and graphite as well as graphite/silicon as anode. Those materials are commonly used in lithium-ion batteries (LIBs). Due to the demand for a significantly increased energy density for xEVs (electromotive vehicles), there is worldwide a strong effort to increase the energy density on the battery level. Silicon has the benefit to provide one order of magnitude higher gravimetric energy density than graphite. However, a bottleneck of silicon as anode material is its huge volume change of about 300 % during electrochemical cycling. Volume change induces high compression and tension, which results in crack formation, continuous reformation of solid electrolyte interphase (SEI) layers, and subsequent electrode delamination from the current collector. Especially the compressive stress can restrict a complete fully lithiation in silicon and graphite and accelerates chemical degradation of the battery. In this study, thick film graphite, silicon, and silicon/graphite composite electrodes on the anode side and nickel-enriched NMC on the cathode side were developed. Subsequently, hole, grid, and line patterns were generated on electrodes by ultrafast laser ablation in order to reduce compressive stress during electrochemical cycling, to shorten the electrolyte diffusion distance and to reduce diffusion overpotential. The latter one is a critical issue in elevated power densities of the thick film electrodes, i.e., high mass loading. 3D elemental mapping by using LIBS could demonstrate that new lithium-ion diffusion pathways were generated along the structure's sidewalls and are activated with increasing power densities. It was shown that batteries with laser structured electrodes benefit from a homogenous lithiation as well as delithiation, reduced compressive stress, an overall improved electrochemical performance, and cell lifetime in comparison to batteries with unstructured electrodes. Cells with 3D micro-structured electrodes demonstrate an improved high rate capability and an increased battery lifetime. Laser structuring of electrodes offers a new manufacturing tool for next-generation battery production to overcome current limitations in electrode design and cell performance.