Interface Engineering and Substrate Design for Anode-free Lithium Metal Batteries

Lithium metal batteries (LMBs), especially anode-free LMBs, have gained renewed attention because lithium metal offers an ultrahigh theoretical capacity (3860 mAh g-1) and the lowest electrochemical potential (−3.04 V versus the standard hydrogen electrode) among common metal anodes. These merits enable energy densities approximately double those of conventional lithium-ion batteries with graphite anodes. However, the practical application of LMBs remains limited by unstable cycling and safety risks, primarily due to uncontrolled lithium nucleation and growth, dendrite formation, and unstable solid electrolyte interphases (SEIs). This thesis investigates how substrate structure and interfacial design influence lithium deposition behaviour and reversibility. Emphasis is placed on understanding the role of copper (Cu) current collectors and two-dimensional (2D) materials in regulating lithium nucleation, growth, and SEI properties. I demonstrate that the microstructure of Cu current collectors, particularly grain size, has a significant impact on lithium nucleation and growth. Larger grains reduce the number of nucleation sites due to their lower grain boundary (GB) density, initially resulting in fewer yet denser lithium early-growth deposits. This early-stage behaviour suppresses inactive (“dead”) lithium accumulation during stripping and evolves to uniform, dense lithium deposition during cycles, resulting in enhanced cycling stability. Subsequently, to address the challenge of lithium dendrite growth, monolayer hexagonal boron nitride (hBN) was introduced as an artificial SEI in lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes. The hBN interfacial layer facilitates uniform lithium deposition and promotes the formation of a stable, inorganic-rich SEI. In addition, a salt-dependent mechanism of lithium behaviour with hBN was observed. In LiPF6-based electrolytes, lithium ions can transport through hBN, depositing beneath hBN. In contrast, lithium deposition occurs on top of hBN in LiTFSI-based electrolytes. This distinct behaviour in LiPF6-based electrolytes is attributed to the defect formation with the hBN lattice, facilitating lithium-ion transport. The defects may be induced by spontaneous interaction between hBN with PF6-. This interaction also promotes the formation of a LiF-rich SEI. As a result of these synergistic effects, the hBN/Cu electrode exhibits excellent cyclability. This study offers new perspectives on the deposition mechanisms of lithium on two-dimensional material interfaces and underscores the iii critical role of electrolyte composition in determining the interfacial behaviour of 2D materials in lithium metal batteries. Building on this, I further investigate defect engineering in graphene for anode-free LMBs. It should be noted that this foundational study in this thesis was conducted solely in a half-cell configuration (vs. Li/Li+) to validate the core concepts governing reversible lithium deposition in anode-less systems. Oxygen plasma treatment was employed to introduce functionalized defect sites on graphene. These controlled defects enhance the lithiophilicity of the graphene/Cu current collector, promoting uniform lithium deposition. In addition, defective graphene/Cu current collector facilitates the formation of a Li2O-rich SEI, which contributes to improved electrochemical performance. The increase of Li2O in SEI may result from the oxidation of both the graphene and the underlying Cu after plasma treatment. Together, these findings provide mechanistic insight into how substrate structure and interfacial chemistry influence lithium-metal behaviour. This thesis highlights the potential of tailored 2D materials and substrate engineering as effective strategies to enable stable, high-energy LMBs.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2025

Author dc:creator

• Zang, Han

Advisor dc:contributor.advisor

• Chhowalla, Manish

• 2D materials
• Batteries
• Lithium metal batteries

Licence

• https://www.repository.cam.ac.uk/bitstreams/3c1be1a5-b412-40c1-929f-bd54f9838265/download
• http://purl.org/NET/rdflicense/allrightsreserved

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.125308

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/395985