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Nanoscale dendrite formation and mitigation in high-energy density metal anodes

Periodic Reporting for period 1 - NANODENDRITE (Nanoscale dendrite formation and mitigation in high-energy density metal anodes)

Reporting period: 2021-10-01 to 2023-09-30

Efficient and sustainable energy storage and conversion technologies are essential to replace our reliance on fossil fuels and transition to cleaner, affordable energy sources. Batteries play an essential role in the electrification of society. However, to meet the demands of modern applications, we need better battery technologies that offer larger storage capacities.

Lithium-ion batteries (LiBs) currently dominate the market in portable electronics, electric vehicles, and short-duration grid-scale storage. These batteries typically use graphite as a host material to store lithium. Storing lithium directly as metal, without the need for graphite, could significantly increase the energy these batteries can hold. But there is a problem: lithium metal batteries can develop detrimental structures called dendrites, which cause capacity losses by death of active material and safety issues. Understanding when and how these problematic dendrites and dead lithium form is crucial to prevent these issues and make this technology viable.

To address this challenge, the NANODENDRITE project focused on developing a new way to study how lithium metal gets stored within batteries. We have developed a modern electrochemical microscopy platform, allowing us to investigate battery processes at the nanoscale with high-throughput capabilities. By adding optical microscopy, we can dynamically watch lithium metal during battery operation. This new visualisation approach provides a promising avenue to find better strategies for smoother lithium deposition, which could lead to longer-lasting lithium metal batteries.
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.
The work carried out in this project was original and innovative, significantly advancing the state-of-the-art in scanning probe electrochemical microscopy for battery research across a wide range of materials. This means that these techniques can now be applied to investigate various battery-relevant processes at the nanoscale, including lithiation/delithiation, the formation of the solid-electrolyte interphase, and lithium metal plating and stripping. In addition, we successfully integrated electrochemical microscopy with in situ optical monitoring in a glovebox, opening up new possibilities for visualising the early stages of metal nucleation and growth in metal battery studies. The innovative multi-microscopy approach, developed in this project, has broad applicability beyond the battery field. For instance, it can be used to reveal new interfacial phenomena in other fields, such as energy conversion (electrocatalysis), corrosion, and electroplating.

Developing these novel tools to investigate battery processes is paramount to achieve new mechanistic information. This novel understanding may pave the way for strategies that minimise degradation and guide the development of improved battery materials, interphases, and interfaces. Ultimately, this can result in increased long-term stability and operation lifetimes for these energy storage devices. The advances made in this project are not limited to a specific type of battery chemistry or material, and could be extended to study more sustainable metals such as Na, K, Mg, and others. While the project primarily focused on fundamental developments, it holds significant potential for societal and economic impact in the future. These developments may be the foundation for the rational design of enhanced battery materials with better performance than those currently available, promising a brighter and more sustainable energy future.
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