Researchers Develop a New Lithium-Ion Silicon Anode Battery Design That Could Provide a Longer EV Range and Power Portable Devices

Traditional lithium-ion battery designs use graphite as the anode material, which has an energy density of around 370 mAh/g (milliampere hour per gram). Silicon provides better performance because it has an energy density of up to 3,600 mAh/g, which is almost 10x what graphite offers. This means replacing graphite with silicon as the anode material could potentially multiply the range of EV batteries, running the vehicle for up to 10 times the distance for the same battery weight. But there is a catch. Silicon expands rapidly by over 300–400% or 3–4X during charging, which makes it crack and degrade, resulting in a shorter battery lifespan. On the other hand, graphite is stable and durable throughout the charging process, and these properties have made it the dominant anode material in the market. So to achieve the high energy density provided by silicon anodes, the challenge is to manage the silicon expansion, and researchers from the University of Surrey have developed a solution that can solve this problem.

Silicon-Carbon Nanotube Battery Anode

Published in ACS Applied Energy Materials, the research by a team from the University of Surrey introduces a structure known as VISiCNT, which is short for Vertically Integrated Silicon-Carbon Nanotube. This novel lithium-ion battery anode provides some of the highest energy storage capacities ever reported in Lithium-ion battery prototypes with silicon-carbon nanotube anodes while maintaining a stable structure after hundreds of charging cycles.

To develop this structure, the team grew a dense forest of carbon nanotubes directly onto a copper foil, then coated this forest using a thin layer of silicon. This method creates a flexible and conductive scaffold that can absorb the expanding silicon layer during charging, while maintaining the battery’s energy storage density and performance long term.

The results from this design showed promising results because the anode was able to store more than 3,500 mAh/g in lab tests, which is almost at the limit of the energy density that silicon anodes can provide. This figure is significantly higher than the 370 mAh/g provided by graphite anodes, and the tests also proved better stability and performance after subjecting the silicon-carbon nanotube anode to multiple charging cycles.

The lead author of the study and research fellow at the University of Surrey’s ATI (Advanced Technology Institute) stated that this VISiCNT design provides a practical route towards harnessing silicon’s huge energy storage capacity without sacrificing cycle life. Since this design also supports fast charging, it provides a much-needed breakthrough towards bringing the world closer to having EVs that can cover extremely long ranges or carry heavy loads, particularly in the trucking industry.

Why This VISiCNT Growing Approach Is Matters

This method of manufacturing silicon anodes is critical in the success of these lithium-ion batteries because the carbon nanotubes are grown directly on copper (a metal that is already widely used in commercial batteries) using a scalable manufacturing process. As a result, it could be relatively easy to integrate VISiCNT growing into existing industrial lithium ion battery production lines.

Carbon nanotubes provide several advantages when used as part of the anode. These include providing a large surface area while being lightweight, superior thermal and electrical conductivity, and superior tensile strength. However, their absence of a voltage plateau, large first cycle loss, and formation of an unstable solid electrolyte interphase layer makes them suboptimal.

To ensure optimal performance, these nanotubes are usually used as additives to silicon or graphite composites, which ensures charge transport efficiency and reversibility. This requires harsh chemical treatments or mechanical processing, all of which compromise their intrinsic properties. On top of that, alignment and random dispersion issues affect the charge transport process’ effectiveness. So ensuring direct contact between each nanotube and the copper current collecting layer is critical towards achieving optimal battery performance. Additionally, factors like carbon nanotube length and structural quality are difficult to control in solution-based processes, yet they impact performance.

CVD vs. PTCVD

Chemical Vapor Deposition (CVD) provides a better alternative for growing carbon nanotubes on copper than solution-based processes because it ensures superior structural integrity, which eliminates the need for polymeric binders. Additionally, it simplifies the tailoring of various carbon nanotube parameters, such as diameter, length, metallicity, and density. However, direct growth of the nanotubes on copper using this method is challenging. These nanotubes must first be grown on rigid, insulating materials, such as aluminum oxide, at high temperatures (over 600°C), then transferred to the copper conductive surface. This complicates the manufacturing process and makes it difficult to scale.

To avoid these challenges, this research team used the PhotoThermal Chemical Vapor Deposition (PTCVD) method, which relies on light (laser or UV) to drive the reaction, making it possible to grow the carbon nanotubes directly on copper (with aluminum or iron catalysts in between) at lower temperatures with higher precision and faster localized deposition. This method provided high-quality carbon nanotube growth at a quick rate of  21 μm/min, making it viable for scaling up through roll-to-roll production.

Professor Ravi Silva, a Director and Principal Investigator of the ATI stated that this research is important towards bringing carbon nanotube silicon anodes out of the lab and into real-world manufacturing, where these structures can be grown at speed, after which the silicon layer applied above them can be tailored to provide maximum stability over many more charging cycles.

Silicon is deposited via RF sputtering in the last step, and it is done at room temperature under a 3 mTorr chamber pressure using a 20 sccm argon atmosphere. In the lab, this process formed a 99.999% high purity undoped silicon layer at a deposition rate of 0.13 Å/s, which provided a power density of 0.66 W·cm–2.

All these production processes can be introduced into existing lithium-ion battery production lines with minimal disruption.

What This Means For Battery Storage

As the demand for compact energy storage solutions that charge faster and last longer grows, this VISiCNT solution offers a promising route towards achieving that dream coupled with easy manufacturability, so the time to market might be shorter. This could be the key towards powering the next generation of EVs, consumer devices, solar energy storage, and microelectronics solutions.