Designing High-Performance Substrate Interfaces for Anode-Free Sodium Batteries

Background

Anode-free sodium batteries (AFSBs) represent a paradigm shift in sustainable energy storage, eliminating the need for pre-deposited sodium metal and relying instead on in situ Na plating onto a bare current collector during the first charge. This architecture offers unmatched advantages in terms of energy density, cost reduction, and safety. Sodium’s natural abundance and low cost make it an attractive alternative to lithium, particularly for large-scale stationary energy storage applications. However, challenges, including poor plating and stripping reversibility, dendrite formation, and unstable SEI growth on bare surfaces, have hindered commercial progress.

Ionic liquid (IL) electrolytes offer a transformative solution. Their inherent thermal stability, wide electrochemical window, and non-flammable nature make them ideal for addressing the interface and safety issues in AFSBs. Preliminary studies from my current project at IFM, Deakin University, have demonstrated that IL-based electrolytes can significantly boost initial Coulombic efficiency and improve sodium reversibility by stabilizing the Na-metal/SEI interface.

Research Gap

While early results are promising, critical gaps still hinder progress. For instance, the mechanism by which sodium metal nucleates and grows on modified copper substrates in ionic liquid (IL) environments remains unclear. Additionally, there is a lack of comprehensive studies that connect the surface chemistry of current collectors, the IL electrolyte composition, and the formation and evolution of the solid electrolyte interphase (SEI). Currently, no standardized protocols exist to fine-tune formation cycles or design current collectors that ensure smooth, dendrite-free sodium deposition (Carter et al., 2017

Lohani et al., 2022).

Aim

To advance the performance and stability of anode-free sodium batteries by engineering substrate interfaces that enable uniform, dendrite-free sodium deposition and long-term cycling efficiency using established ionic liquid electrolytes.

Objectives

1. Testing of modified (mechanical, chemical, and electrochemical) current collectors using benchmark ionic liquid electrolytes: Preliminary results at IFM (Deakin University, Australia) indicate that the substrate surface chemistry and morphology significantly affect the Initial Coulombic Efficiency (ICE) and long-term cycling of Anode-Free Batteries. The goal of this project is to identify and engineer current collector surfaces that are compatible with the chosen ionic liquid systems, enabling practical implementation of AFSBs. This research has substantial innovation potential, employing the following techniques: (a) Electrochemical modification-tailoring substrate properties to improve compatibility with existing IL electrolytes and sodium plating

(b) Chemical modification-using surface coatings to enhance substrate-electrolyte interactions and mitigate dendrite growth

(c) Mechanical modification- introducing micro-structuring or roughening to control sodium deposition for better stability and safety.

2. Current collector compatibility testing with selected ionic liquid (IL) electrolytes: Utilize benchmark ionic liquid electrolyte systems already developed at IFM to assess their interfacial compatibility with various modified current collectors. The focus will be on improving Na plating/stripping efficiency by identifying the optimal substrate conditions.

3. Optimize formation protocols: Design low-voltage and pulse-formation strategies to tune the SEI chemistry and maximize both initial Coulombic efficiency (ICE &gt

90%) and long-term average Coulombic efficiency (CE &gt

99%).

4. Study interfacial dynamics: Utilize in situ and ex-situ tools (XPS, Raman, NMR, EIS) to correlate electrolyte composition and CC surface chemistry with SEI evolution and failure mechanisms.

Significance

This project aims to unlock the full potential of AFSBs by addressing their most critical challenge: efficiently and stably cycling Na metal on bare substrates. By leveraging ionic liquid electrolytes and rational current collector engineering, this work will lay the groundwork for high-energy, long-life, and safe sodium batteries. The results will accelerate the commercialization of sodium-based battery technologies while reducing dependence on critical lithium resources.