In the development process of smartphones, "making them thin" often requires sacrificing battery capacity. But if the phone becomes thinner and the battery is not enough, how can the experience start?Today, the increasingly mature silicon-carbon battery technology may be the answer to this problem.This technology has been quietly developed for decades and is beginning to become commercially available. Whoop sports bracelets have used silicon-carbon batteries since 2021. Chinese mobile phone brands Xiaomi and Honor have recently used this technology in some models, while new phones such as OnePlus 13 and Nothing Phone (3) have also followed suit.

Currently, this technology is being implemented in two directions: foldable screen mobile phones use it to achieve even more extreme thinness and lightness, while traditional candy bar machines use it to increase battery capacity.

It is reported that Apple will release iPhone 17 Air this week, which may be only 5.5 mm thick, making it the thinnest iPhone in history. The key technology behind it that may keep its battery life from shrinking is probably silicon-carbon batteries.

The “frivolous” war begins again

Currently, the thickness of mainstream smartphones is mostly between 8 and 9 mm. For example, the Samsung Galaxy S25 Ultra is 8.2 mm thick, the iPhone 16 Pro Max is 8.25 mm, and the Google Pixel 10 Pro XL is about 8.5 mm thick. But in 2025, mobile phone manufacturers have once again launched an "ultra-thin phone war."

This spring, Samsung launched the Galaxy S25 Edge, which is only 5.8 mm thick, while its recently released Galaxy Z Fold7 is only 4.2 mm when unfolded. Huawei's tri-folding model Mate XT Ultimate is only 3.6 mm thick when unfolded, setting a new record. Even smaller brands such as Tecno have joined the fray, exhibiting an ultra-thin concept phone at MWC 2025, and then officially released a 5.93 mm thick mass production model.

Of course, this is not the first time that the mobile phone industry has pursued “thinness” as a selling point. As early as around 2010, a similar competition was staged. In September 2012, when Apple released the 7.6mm-thick iPhone 5, it first emphasized that it was "the thinnest phone we've ever made" and was even claimed to be the world's number one at the time. Since then, various thinner products have emerged one after another. For example, the OPPO R5 in 2014 is only 4.85 mm thick.


In this new round of "ultra-thin machine war", currently only a few brands such as Huawei and Honor use silicon-carbon batteries. Samsung appears to be more cautious, still choosing traditional lithium-ion batteries, and instead improving the energy efficiency of the screen to make up for the reduction in battery capacity. This strategy is not difficult to understand given the brand’s past “black history” with batteries. However, judging from actual performance, the Galaxy S25 Edge’s battery life is still not ideal.

So, what exactly is a silicon-carbon battery? How can it affect the experience of iPhone 17 Air?

What is a silicon carbon battery?

In a lithium-ion battery, when the phone discharges during use, lithium ions move from the negative electrode (i.e., the anode) to the positive electrode (i.e., the cathode). When charging a device, lithium ions move from the cathode back to the anode, and the cycle repeats. The anode material of traditional batteries is mainly graphite.

"Silicon-carbon battery" is not actually a new battery type. In essence, it is still a lithium-ion battery, but the traditional graphite anode is replaced by a silicon-carbon anode. Rick Luebbe, CEO of silicon battery manufacturer Group14, said that the theoretical lithium storage capacity of silicon far exceeds that of graphite, that is, the number of lithium ions stored per unit weight of silicon is about 10 times that of graphite. This means that the silicon-carbon anode can hold more lithium ions at the same weight, significantly increasing the energy density of the battery.

In addition, graphite anodes often occupy a considerable amount of space inside traditional lithium-ion batteries (up to 60% in some designs). Silicon-carbon composite materials have higher lithium storage efficiency, which can reduce the volume required for the anode and leave more space for battery design.This can be used to enlarge the cathode and further increase the total capacity, or to achieve a thinner design of the entire machine.

At present, the upstream of silicon-carbon batteries is mainly driven by material companies, such as Group14, Sila Nanotechnologies, Enovix, etc. They do not directly manufacture batteries, but focus on producing silicon-carbon composite anode materials (often supplied in powder form), which battery manufacturers (such as ATL) integrate into batteries. This "material substitution" production method can be adapted to existing production lines and is less difficult to transform.

Terminal brands currently adopt two product strategies: one is to make smartphones with roughly the same thickness as previous models, but increase the battery capacity; the other is to maintain roughly the same energy capacity as previous models and use the saved space to make the phone thinner.

Manufacturers such as Honor, OnePlus and Nothing use silicon-carbon battery technology in their latest candy bar phones. Most of these devices maintain standard thickness while increasing battery capacity. The OnePlus 13, for example, has a larger 6,000mAh battery and is thinner than its predecessor, but its 8.5mm thickness is still comparable to most traditional phones.

Apple appears to be taking the second approach, but with some reservations. Rumor has it that the battery capacity of the iPhone 17 Air will be around 2900mAh, which is significantly lower than the previous model., especially with the 6.6-inch screen size. However, Apple is likely to make up for the capacity gap through collaborative optimization of software and hardware, including more energy-efficient self-developed modems (such as C1 chips) and system-level power consumption management, in an effort to make battery life close to traditional models.

However, Apple and its main material suppliers have not yet confirmed whether silicon-carbon battery technology is used in the iPhone 17 Air.

What are the disadvantages of silicon-carbon batteries?

Although silicon-carbon batteries have shown potential in terms of energy density and thin and light design, they still have several obvious shortcomings that restrict their large-scale application.

First, silicon materials undergo significant volume expansion during charging and discharging. Lubbe explains that raw silicon can expand up to three times in volume after lithium ions are embedded in it. Although slight swelling is common in lithium-ion batteries, drastic changes in silicon materials can easily lead to damage to the electrode structure and loss of active materials, which in turn affects battery life and even causes safety hazards, such as battery bulges or short circuits.

To solve this problem, researchers have worked for decades to curb expansion through "carbon frame" structures. Each company uses different patented processes. For example, Group14 uses porous carbon materials (pore diameter less than 10 nanometers, reaching the molecular level) as a carrier to partially fill the pores with silane gas, leaving about half of the space. During the lithiation process, the expansion of silicon will fill these reserved gaps, thereby controlling the volume change inside the particles, avoiding overall deformation of the battery, and improving structural stability and cycle life.

Vincent Chevrier, a partner at battery consulting firm Cyclikal and a veteran of 15 years of silicon research, said,Even with technological breakthroughs, silicon-carbon batteries still face cost issues.

The silane gas used by companies like Group14 improves performance but costs up to ten times as much as solid silicon. This not only increases the material pressure on battery manufacturers, but may also push up the selling prices of end electronic products. For example, there are market rumors that the starting price of the iPhone 17 Air may be US$1,099, which is US$200 higher than the iPhone 16 Plus it is expected to replace. In addition to factors such as tariffs, the application of new battery materials is also an important reason.

Chevalier also pointed out that there is still controversy over the actual performance indicators of silicon-carbon batteries. Some companies claim that the energy density of their products is 50% higher than traditional lithium-ion batteries, but he believes that if they simply replace the graphite anode without redesigning the battery unit,The actual improvement is usually only about 10%. Even after overall optimization, the increase in energy density is difficult to exceed 30%.

In terms of cycle life, silicon-carbon batteries are currently inferior to traditional graphite systems. The so-called cycle life refers to how many complete charge and discharge cycles a battery can undergo before its capacity decays to 80%. The more cycles, the longer the battery life.

Theoretically, the cycle life of graphite batteries can reach 5,000 times, while Group14's silicon-carbon composite material has only about 1,000 times, which translates into a lifespan of about three years, depending on the user's charging habits.

However, Chevalier also emphasized that even existing batteries using graphite anodes cannot reach 5,000 charging cycles in actual use. The reason is that manufacturers like Apple will try to increase battery energy density as much as possible in order to extend daily battery life, which virtually increases the pressure on the battery. The result: Although iPhones can be used for daily use, the batteries are often not as durable as new after two years. According to Apple’s official data, taking the iPhone 16 as an example, its battery can still maintain about 80% of its capacity after 1,000 charging cycles.

Therefore, even if it switches to silicon-carbon materials in the future, the battery life of Apple mobile phones may not be significantly improved.

New features consume more power

Although battery technology continues to advance, especially the application of new materials such as silicon-carbon anodes, which has brought new possibilities for improving battery performance,At the same time, there are always new technologies emerging that use up the extra power brought by improved battery performance.

Nowadays, more and more artificial intelligence functions running locally on the device are becoming new "power consumers." This means that even if manufacturers successfully increase battery capacity or reduce size through silicon-carbon batteries, the actual increase in battery life experienced by users may be consumed by new features, and the overall battery life experience may not be significantly improved.

Taking the iPhone 17 Air as an example, Apple is taking advantage of the energy density and volume of silicon-carbon anode materials to create an extremely thin and light product, while striving to maintain a battery life level close to that of a regular iPhone, without sacrificing screen size.This design direction may also be exploring the path for the future folding screen iPhone., ensuring that it can still maintain a relatively thin shape in the unfolded state.

As for whether Apple can find a balance between slim design and sufficient battery life, we will have to wait until we can finally try the iPhone 17 Air in person.