A recent study published in Advanced Energy and Sustainability Research examined the fabrication of nanoporous helium-silicon thin films using a plasma-assisted co-deposition process, offering a novel approach for lithium-ion battery anodes.
By creating a high-density helium plasma environment, researchers achieved controlled implantation of helium atoms into silicon layers, producing thin films with significant porosity. These co-deposited films were evaluated for their lithium-ion storage capacity and cycling stability, demonstrating their potential for enhanced battery performance.
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Background
The demand for high-performance lithium-ion batteries (LIBs) has driven research into advanced anode materials that exceed the capabilities of conventional graphite electrodes. Silicon (Si) is a promising candidate due to its theoretical capacity of approximately 3600 mAh g-1—over ten times that of graphite.
However, its practical application is limited by a substantial volume expansion of up to 400 % during the lithiation and delithiation processes. This expansion generates mechanical stress, often leading to Si detachment from the electrode.
To address these challenges, researchers are developing porous Si structures that accommodate volume changes while increasing the surface area for electrolyte interaction. This study investigates the potential of He-Si co-deposited layers to improve LIB performance by optimizing their morphological and electrochemical properties.
Fabrication and Characterization
The He-Si co-deposition process was carried out in a high-density helium plasma environment, allowing simultaneous deposition of Si atoms and He ions onto a copper (Cu) substrate. The experiments were conducted using a linear plasma device known as Co-NAGDIS, which uses a DC arc discharge to generate plasma. Deposition parameters, including He flux and substrate temperature, were systematically varied to study their impact on thin film formation.
The deposition temperature ranged from 473 to 773 K to maintain optimal thin film structure. The resulting films were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to examine surface morphology and microstructural features. Thermal desorption spectroscopy (TDS) was used to measure He atom implantation efficiency, and porosity levels were quantified between 0.3 and 0.74 based on He flux and substrate bias adjustments.
Results and Discussion
The co-deposition method successfully produced Si-thin films with porosity levels optimized for lithium-ion transport while minimizing stress during electrochemical cycling. Discharge capacity evaluations under various cycling conditions revealed that film structure significantly influenced performance. The best-performing sample, designated Si1, demonstrated an initial discharge capacity of nearly 3000 mAh g-1, retaining about 1800 mAh g-1 after 100 cycles. This capacity retention indicates that the porous structure effectively supported cycling stability.
The study also examined the effect of substrate temperature on the amorphous structure of Si during deposition. At 523 K, amorphous Si was successfully deposited, contributing positively to electrochemical performance. Additionally, He atom implantation played a key role, as early analyses suggested that Cu atom diffusion into the Si layer enhanced conductivity and improved lithium-ion transport.
Cycling tests showed an increase in Coulombic efficiency over time, indicating stable structural integrity and good electrochemical behavior. These findings suggest that He-Si co-deposition thin films hold promise for high-performance LIB applications.
Future research should focus on optimizing the co-deposition process and enhancing the interface between the anode material and the electrolyte, which is essential for the advancement of all-solid-state batteries. The insights gained from this research contribute to the development of more efficient and durable LIBs, addressing key challenges in energy storage technology.
Journal Reference
Kajita S., et al. (2024). Nanoporous Helium–Silicon Co-Deposition Thin Film via Plasma-Assisted Process for Lithium-Ion-Battery Anodes. Advanced Energy and Sustainability Research, 2400300. DOI: 10.1002/aesr.202400300, https://advanced.onlinelibrary.wiley.com/doi/10.1002/aesr.202400300