How High-Content Silicon Anodes Can Reshape the EV Landscape
Research & Development

How High-Content Silicon Anodes Can Reshape the EV Landscape

Author: Solid Power Admin
Date Posted: 12.08.21

How High-Content Silicon Anodes Can Reshape the EV Landscape

Battery manufacturers are actively seeking next-generation cathode and anode materials, in both liquid and solid electrolyte systems, in order to bring better performing, lower-cost cells to market. Silicon anodes are particularly interesting to automakers and cell producers alike — in theory, silicon anodes are 10x more energy efficient than industry-standard graphite anodes. 

But silicon anodes pose their own challenges, and capacity retention is chief among them. The silicon in liquid-based Li-ion cells expands and contracts throughout charging and discharging, which can lead to mechanical issues that reduce the life of the cells. This swelling issue makes the EV use-cases of high-content silicon anodes in Li-ion questionable without a highly engineered, and often costly, approach. High contents of silicon in an all-solid-state cell, though, can eliminate these cycle life degradation problems while delivering specific energy that’s on par with lithium metal anode approaches. 

When combined with solid-state chemistry, silicon anodes have the potential to change EV battery landscape. Solid Power intends to commercialize high-content silicon cells in 2026 and internal testing shows the potential benefits. 

Increased Energy Density

At the cell level, the only way to dispel range anxiety concerns is through increased energy – both specific energy and energy density. The appeal of a more energy-dense battery directly impacts vehicle range. If energy goes up 35%, in theory, the range could also go up 35%. Currently, Tesla’s industry-leading 2170 batteries provide 260 Wh/kg. 

Solid Power’s all-solid-state silicon cells are expected to offer more energy compared to today’s best performing Li-ion cells. We also expect them to outperform cells anticipated to reach passenger vehicles in the middle part of the decade.. When tested internally, Solid Power’s coin pouch cells had a stack-level-specific energy of ~350 Wh/Kg. 

Faster Charging Speeds

Though EVs outperform their gas-powered predecessors in many ways, they can’t yet compete with fuel-up speed. In a gas-powered vehicle, drivers can fill their tank and get back on the road in mere minutes. When an EV is low on range, drivers face a longer wait. Fast-charging can take up to 40 minutes, enough time to make (and eat) a meal or watch an episode of a television show. For EV enthusiasts, these long charging times are a worthwhile inconvenience. But for would-be EV buyers, a ~40-minute charge could be enough to make them think twice about making the switch. High contents of silicon in the anode can help solve that problem. 

At near room temperature, our silicon cells showed the ability to charge at a 2C rate (~30 mins) every 5th  charge. Solid Power is working to take this further in future iterations, with the goal to provide a <15 min charge (10-90%). 

Wider Temperature Range

Li-ion batteries’ liquid electrolyte is sensitive to both high and low temperatures. They can lose energy efficiency when too cold, and become a fire hazard when too hot. Sulfide solid electrolytes, though, can better withstand extremes at both ends of the spectrum, which could lead to extended driving ranges in very hot temperatures. When combined with a high-content silicon anode, Solid Power’s low-temperature performance results are especially compelling, demonstrating stable charge and discharge at temperatures as low as -10° C. 

Goodbye to graphite?

Fine-tuning solid-state chemistry is already a challenge, and constantly evolving consumer and automaker demands add an extra layer of difficulty. Upon their introduction, silicon-based solid-state EV cells will be expected to meet — and exceed — the performance standards created through decades of continued Li-ion development. That’s a lot to ask of brand-new technology, but Solid Power is up to the task. 

Like Li-ion batteries, graphite anodes are here to stay — for now. But if our development is any indication, safer, higher-energy, and lower-cost high-content silicon EV cells could be a worthwhile alternative.