Silicon Forging Ahead for Higher-Performance Battery Anodes

General Motors’ new joint-research agreement with OneD underscores the promise of silicon-anode development.

The Sinanode anode-coating process, says OneD, leverages readily available, cost-efficient processing machinery. (OneD)

Silicon-infused anodes, already widely considered one of the most promising candidate technologies for the next significant performance-improvement phase of electric-vehicle (EV) lithium-ion batteries, enjoyed a significant boost in September 2022, when GM and OneD Battery Sciences revealed a joint research and development agreement to study the potential to use OneD’s silicon nanotechnology in GM’s Ultium battery cells. General Motors and Volta Energy Technologies also invested in a $25-million Series C funding for OneD, a move interpreted by some as a vote of confidence that silicon-anode technology is poised to make a comparatively imminent impact on EV battery development.

OneD silicon-graphite comparisons_gallery Comparison of “carbon-trapped” silicon-infusion method versus use of silicon nanowires to integrate silicon in graphite for anode coating. (OneD)

The interest from GM is based on silicon’s ability to markedly improve the energy density of lithium-ion batteries while at the same time reducing cost and cutting recharging times. It’s a performance-enhancement trifecta that has several battery developers scrambling to bring the technology to volume-production scale. In addition to OneD, companies such as Sila Technologies, StoreDot Enevate and Group 14 Technologies, to name a few, are working to perfect the materials and manufacturing processes that will enable silicon-anode performance gains. Tesla and Porsche currently have EV batteries leveraging some degree of silicon-anode technology, which helps to explain both brands’ leadership in certain battery-performance qualities.

OneD’s silicon nanotubes enable highly-efficient lithium-ion transfer but mitigate the propensity of silicon to expand with rising temperature. (OneD)

In a release announcing the joint-research collaboration, GM reiterated that it designed its Ultium battery platform for flexibility, “so we can continuously improve our cells as battery technology advances,” said Kent Helfrich, GM chief technology officer, VP of GM research and development, and president of GM Ventures. The research, the two companies said, will focus on OneD’s Sinanode platform, a novel process for blending silicon onto the anode battery cells by fusing silicon nanowires into the “EV-grade” graphite already being supplied to all major battery manufacturers.

Critically, said OneD CEO and co-founder Vincent Pluvinage in an interview with SAE Media, one of Sinanode’s prime attractions is its ability to be efficiently and cost-effectively incorporated into today’s established EV-battery graphite production process.

Advancing the basics

Although graphite (carbon) has served as the industry’s stalwart anode material during lithium-ion batteries’ early volume-production phases, OneD and its competitors know that silicon’s unique properties can greatly enhance the performance of batteries with graphite-only anodes. The challenge is how to incorporate silicon with graphite to derive the most performance benefit — and do it within the constraints of a constantly pressured cost structure that virtually demands battery prices are markedly reduced if EVs are to sell in high volumes in almost every world region.

OneD’s Sinanode process is claimed to be a comparatively inexpensive method for creating silicon-infused graphite material ready for use in conventional battery-cell manufacturing processes. (OneD)

OneD’s Pluvinage insists that incorporating the silicon-graphite matrix material that is central to the company’s Sinanode platform and process actually will reduce cost compared to a conventional graphite-only anode because OneD’s less-expensive silicon nanowires displaces a considerable amount of the costlier graphite. Reduced overall material cost and OneD’s capital-friendly Sinanode process are the company’s compelling advantages, Pluvinage said.

“If you take graphite today — if you use artificial graphite — it costs about $8 per kilogram, which means that it costs about $6.50 per [battery] kilowatt-hour. The cost of putting in the nanowires — the nanowires can store a lot more in energy — is very little,” Pluvinage said. “It’s less than $2 per kilowatt-hour variable cost. But you use far less graphite. So, if you use two-thirds less graphite, you end up with a total [anode] cost that may be around $3 per kilowatt-hour instead of $6.50 per kilowatt-hour.”

Comparison of key properties of graphite and silicon as they relate to use in batteries. (Sila Technologies)

Sinanode is compatible with natural and artificial graphite, Pluvinage asserts. “We can work with suppliers of natural graphite and we can work with suppliers of synthetic graphite. We can process their graphite so that the little silicon hairs are inside the core of those commercial graphites. And that’s very good, because we don’t spend a penny making the substrate. It is already in production and already qualified with EV cell factories.”

Vincent Pluvinage, OneD co-founder and CEO, said adding performance-enhancing silicon nanowires to battery-grade graphite can reduce overall battery cost . (OneD)

The anode material-cost savings, multiplied by the 75-kWh to 100-kWh battery pack typical of most current EVs, amounts to significant cost reduction, Pluvinage said. And crucially, the Sinanode process of getting the silicone nanowires blended with graphite and then into the battery cells also is claimed to be a low-impact investment. Pluvinage said to go from the current projected pilot-manufacturing of Sinanode-enhanced battery packs to much higher volumes will take some time.

OneD plans to collaborate with GM on a pilot-production phase “that allows us to process large enough quantities of the material so that our customers can make 5000 or 10,000 battery packs. "And that’s necessary,” he said. “Once you optimize the EV cell, you need to make that many battery packs in order to do all the safety qualifications, pre-production. And so that takes a couple of years.”

From there, the focus will be on scaling for high volume. “Large-scale manufacturing is to be able to process tens of thousands of tons, so that the [Sinanode] material can be used in a million, 2 million, 3 million EVs. Now, what is totally unique about our relationship with GM and our business model, is that the large-scale manufacturing is not going to be built by OneD,” Pluvinage said. Instead, he added, OneD will license its process to be incorporated into existing battery manufacturers’ production process and facility footprint — all with comparatively low-cost and high-throughput equipment, he said, including machines already in use to fabricate solar cells.

“If you go, for example, to China to a company like Longi, which is the largest supplier of solar cells in the world, you see hundreds and hundreds of those machines. There are suppliers in

the United States — we use a supplier in New York called CVD Equipment Corporation,” Pluvinage said. “It is so efficient that instead of putting the wafers to make solar cells inside the machine, in the tube that comprises those machines, we put the reactor that we designed, which is the graphite in which we are going to grow the silicon nanowires. A single machine, which costs a few million dollars, can produce enough anode material for two gigawatt-hours of anode.”

Energy density, charging-time upgrades

Although EV consumers will directly benefit from the reduced cost structure silicon-infused battery anode material is claimed to provide, they may be as pleased with the added EV performance it promises. OneD and other silicon-anode developers expect new silicon-intensive lithium-ion batteries to address anxiety about driving range and also cut recharging times — both significant barriers to consumer acceptance.

Israel-based StoreDot, for example, said in 2021 that it intends to have its patented “silicon-dominant anode” Extreme Fast Charge (XFC) lithium-ion battery in production “via traditional certified lithium-ion battery manufacturing lines in 2024,” the company said in a release. And StoreDot also said it reached a framework agreement with China-based Eve Energy Co. Ltd. to produce engineering samples of the XFC battery and to create a venture for mass production.

OneD’s Pluvinage said the company expects its silicon nanowire-infused graphite anode technology to provide significant gains over current lithium-ion batteries. “If you look at the mobility of electrons along nanowires,” he said, “it’s even faster than in graphite. The lithium ions [the battery’s electricity carrier] can get in and out very easily, because there is nothing in their way and the radius is so thin and so small that they get in and out of the silicone very quickly.”

The 20% silicon and its presence in the unique structure of nanowires allows a tripling of the anode’s energy density, Pluvinage said. Increases in charging speeds and driving range — or reduction in size of an EV’s battery pack — will depend on an individual battery manufacturer or automaker’s deployment of the technology. For recharging times, StoreDot claims its battery technologies “will deliver 100 miles in 5 minutes by 2024, 100 miles in 3 [min.] by 2028 and 100 [miles] in 2 [min.] within a decade.”

“If you look at the total market between now and 2030, we need to reach for example 40 percent, 50 percent [EV] market penetration. That means that the vast majority of the market cannot afford an EV today,” Pluvinage said. “What the world needs is an EV that can sell for less than $30,000, has a range of more than 300 miles and can charge from 10 percent to 80 percent in less than 30 minutes. Nobody makes that. That’s why we like GM. Because as [GM CEO] Mary Barra said, ‘Our goal is to make EVs affordable, and we want to produce millions of them.’ So that’s a perfect match between their goals and our goal.”