I interviewed Honor and OnePlus about their silicon-carbon battery tech — Apple and Samsung are quickly falling behind

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It’s pretty clear that standard Lithium-ion (Li-ion) cells with traditional graphite anodes have hit a limit when it comes to energy density. By adding silicon content to the anode, Si-C batteries offer vastly higher capacities in the same physical space. But silicon in anodes expands and contracts a lot during charges and discharges, and is challenging to integrate safely into cells. And that’s where each manufacturer’s secret sauce comes in.

(Image credit: Tom’s Guide / Myriam Joire)

Flagship-level capability does not necessarily require sacrificing a slim, lightweight in-hand experience.

Hope Cao, Honor

The most immediate consumer benefit of Si-C batteries is their profound impact on industrial design. Since these cells deliver significantly higher energy densities, manufacturers like Honor, OnePlus, and Oppo are able to offer thinner form factors with outstanding battery life. This also makes Si-C batteries ideally suited for folding phones like the Honor Magic V6 and Oppo Find N6, or ultra-sleek flagships like the OnePlus 15.

For Honor, Si-C batteries are critical to the company’s folding phone strategy. Keeping these devices highly pocketable requires a split battery design with two smaller, thinner cells. Thanks to Si-C batteries, the Magic V6 manages to pack up to 7,150mAh into a chassis that’s merely 8.75mm thick when folded. Honor”s Cao emphasizes that “Flagship-level capability does not necessarily require sacrificing a slim, lightweight in-hand experience.”

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OnePlus is focused on using Si-C batteries to improve the look and feel of traditional candy-bar smartphones, noting that consumers are showing a “fresh appetite for compact flagships”. Si-C batteries allow the company to slightly reduce device thickness while greatly increasing battery capacity. As a result, the OnePlus 15, which boasts a 7,300mAh Si-C battery, combines a slim, premium design with industry-leading battery life. It’s no wonder that it has the best phone battery life of any device that Tom’s Guide has tested.

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We do not foresee Si-C anode batteries becoming cheaper than conventional graphite-anode cells in the near term.

Rudolf Xu, OnePlus

Despite all the aforementioned benefits, the transition to Si-C batteries faces a couple of significant hurdles. As you’d expect, Si-C batteries are fundamentally more difficult to manufacture and more expensive than standard Li-ion cells.

Honor is transparent about the higher cost, and states that Si-C batteries are typically 20% to 40% more expensive to manufacture than Li-ion batteries at the cell level. This premium reflects higher material costs, stricter production environments, and more complex manufacturing processes the company has developed to mitigate the rapid expansion and contraction of silicon in anodes while charging and discharging.

OnePlus also confirms that Si-C batteries are more expensive. Xu is candid about current prices, saying, “We do not foresee Si-C anode batteries becoming cheaper than conventional graphite-anode cells in the near term.”

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The challenge with using silicon in anodes is its extreme volatility. As the silicon in the anode absorbs lithium ions, it expands drastically, which creates extreme mechanical stress within the cell. Both companies overcome this obstacle in their Si-C batteries through impressive engineering feats.

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Given how much silicon in anodes expands while charging, and the resulting mechanical stress, both companies have taken exceptional steps to ensure that their Si-C batteries remain safe and durable for years to come. This includes extreme testing that exceeds the certification requirements used for Li-ion cells.

​Honor’s testing goes far beyond industry standards. Besides obtaining mandatory CB (IEC 62133), UKCA (UK Conformity Assessed), and CE (European Union) certifications, the company subjects its Si-C batteries to tests in extreme conditions to ensure stability. As Cao notes, “In response to the unique expansion characteristics of Si-C batteries, Honor conducts even more rigorous evaluations, such as puncture resistance tests, extreme stress tests, structural deformation tests, and high-temperature stability tests.”

​OnePlus is similarly thorough, and runs more than seventy unique tests on its Si-C batteries. The company evaluates cells in a broad range of temperature, voltage, and stress conditions to make sure its Si-C batteries meet strict durability and safety targets. According to Xu, device longevity is critical to OnePlus, and the Silicon NanoStack battery used in the OnePlus 15 is designed to maintain “over 80% of its original health after 4 years of use.”

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So there you have it. After hearing from experts at Honor and OnePlus, two leaders in the field of Si-C batteries, I hope you have a better understanding of what this technology brings to the table — the benefits, the limitations, and the remaining challenges. What’s abundantly clear is that Si-C batteries today aren’t some exotic fad. They are a mature, safe, and durable technology that drastically improves the smartphone user experience, and are here to stay.

With Chinese manufacturers relentlessly marching forward, it’s only a matter of time until Apple, Google, and Samsung join the Si-C battery party. And that’s a good thing, because their manufacturing volume and marketing power will make this technology accessible to everyone — in other words, ubiquitous. After all, who doesn’t want a fast-charging smartphone with two-day battery life?