Initially, we focused on establishing and optimising scanning electrochemical cell microscopy (SECCM) in an argon-filled glovebox to investigate lithium-ion battery processes in nonaqueous solvents. To achieve this, we conducted a series of studies to examine Li-based battery processes in relevant model materials such as silicon. These studies helped us understand essential battery processes such as lithium delivery (lithiation) and the formation of the solid-electrolyte interphase (SEI). One of the early key achievements was advancing SECCM as a high-throughput technique for creating the SEI under a broad range of experimental conditions. [1] By combining SECCM with complementary techniques such as shell-isolated nanoparticles for Raman spectroscopy (SHINERS), we were able to determine the temporal dynamics in the SEI composition. This work was presented as oral contribution at the 32nd Topical Meeting of the International Society of Electrochemistry in Stockholm (Sweden). To provide a better understanding of how the SEI chemistry changes in function of experimental conditions, we successfully combined SECCM with secondary ion mass spectrometry (SIMS). [2] We also used focused ion beam (FIB) and scanning transmission electron microscopy (STEM) to examine interfacial degradation after Li delivery by SECCM, revealing that the structure of the electrode material significantly influences the interfacial degradation processes. [3] These studies were essential to progress SECCM for battery research. A review article discussing the recent advances in SECCM for correlative electrochemical multi-microscopy, including battery studies, was published. [4]
To study Li metal plating, the core objective of this project, we realised that coupling SECCM with in situ optical microscopy would provide significant opportunities. Therefore, a key technical development during the project was the integration of SECCM with interference reflection microscopy (IRM) in a glovebox. Firstly, the new setup was used to explore the lithiation of individual TiO2 nanoparticle clusters. [5] We developed a semi-automatic method that directed the SECCM probe to specific electrode locations using the in situ optical capabilities, increasing the efficiency of SECCM. We found that clusters of small TiO2 nanoparticles could rapidly store a significant amount of lithium under fast charging conditions.
The success of our optical/electrochemical integration was essential to study Li metal plating and stripping. The SECCM/IRM setup enabled us to examine the nucleation and growth of Li metal with high spatial resolution (~40 nm), fast time acquisition (ms), strong optical-electrochemical correlation, and high throughput capabilities for systematic screening of electrochemical conditions. We were able to visualise the spatiotemporal dynamics of Li plating and stripping at the nanoscale and study combinatorial plating under various current conditions and experimental durations. [6] We revealed in detail the local accumulation of inactive Li upon cycling, spatially-resolved coulombic efficiency mapping to identify regions on electrode surfaces where Li reversibility was hindered, and how local electrode topography and mass transport phenomena influenced the growth of Li structures, potentially impacting dendrite formation. Additionally, we conducted a study to understand the dynamics of Li nucleation and growth under a pulsed potential program, [7] a typical strategy to minimise dendrite formation. This study provided further insights and understanding of how dendrite formation could be mitigated, offering guidance for strategies that promote uniform nucleation and growth.
[1] Angew. Chem. Int. Ed. 61 (2022) e202207184.
[2] Small 19 (2023) 2303442.
[3] Nat. Sci. 3 (2023) e20210607.
[4] Cur. Opin. Electrochem. 42 (2023) 101405.
[5] Angew. Chem. Int. Ed. 62 (2023) e202214493.
[6] Submitted.
[7] In preparation.
