Historically, creating a thin phone often meant compromising on battery life, as manufacturers opted for slimmer, less robust batteries. But what is the value of a sleek device if it can't keep up with daily demands? Fortunately, advancements in silicon-carbon battery technology may offer a solution. This exciting innovation has been under research for decades and is gradually becoming mainstream, with several notable products already utilizing it.
Fitness trackers like the Whoop have employed a silicon-carbon battery since 2021, showcasing the technology's potential. Recently, Chinese brands such as Xiaomi and Honor have also integrated this battery type into their devices. OnePlus has adopted it in its OnePlus 13, while Nothing has made it a feature of its latest Phone (3). This technology's application varies depending on the phone's form factor, with foldable phones benefiting from thinner designs while traditional candy bar phones enjoy enhanced battery capacities.
Apple is set to unveil the highly anticipated iPhone 17 Air this week, rumored to be an astonishing 5.5 mm thick, making it the slimmest iPhone to date. It is speculated that Apple will incorporate a silicon-carbon battery to maintain or even match the expected battery life of a modern iPhone, despite its reduced thickness.
Most smartphones today fall within the 8 to 9 mm thickness range. For instance, the Samsung Galaxy S25 Ultra measures 8.2 mm, while the iPhone 16 Pro Max is 8.25 mm thick. However, manufacturers are eager to shed weight and have introduced an array of super-slim devices in 2025. Samsung's Galaxy S25 Edge debuted at just 5.8 mm, and the Galaxy Z Fold7 impressively measures 4.2 mm when unfolded. Huawei's tri-folding Mate XT Ultimate takes the crown at 3.6 mm unfolded, with smaller brands like Tecno also joining the trend with a 5.93 mm handset.
In this new era of thin smartphones, only a few manufacturers, such as Huawei and Honor, have begun to leverage silicon-carbon batteries. In contrast, Samsung seems to be taking a more conservative approach, relying on traditional lithium-ion batteries while enhancing display efficiency to offset smaller battery sizes. Despite these efforts, the Galaxy S25 Edge's battery performance has still been underwhelming.
To grasp the significance of silicon-carbon batteries, it's essential to understand their mechanics. In traditional lithium-ion batteries, lithium ions flow between the anode and cathode during discharge and charging cycles. Typically, the anode is made of graphite. However, a silicon-carbon battery replaces the graphite anode with a silicon-carbon composite. Silicon can store approximately ten times more lithium ions by weight than graphite, as explained by Rick Luebbe, CEO of Group14, a leader in silicon battery technology.
The graphite anode occupies a significant portion of a lithium-ion battery—about 60%, depending on design. By substituting a silicon anode, manufacturers can achieve higher energy density and save space. Companies like Group14 provide powdered silicon-carbon anodes to battery manufacturers, allowing them to easily transition from graphite to this innovative material without significant interruptions in production.
Smartphone manufacturers can adopt one of two strategies when utilizing silicon-carbon batteries. They can maintain the same thickness while increasing the battery's energy capacity, as seen with the OnePlus 13, or they can slim down the device, keeping energy capacity similar but benefiting from the space saved. Brands like Honor, OnePlus, and Nothing have opted for the former, maintaining standard thicknesses while increasing battery capacities.
However, Apple appears to be pursuing the latter strategy with the iPhone 17 Air, rumored to feature a reduced battery capacity of around 2,900 mAh, a significant decrease compared to previous models. To compensate, Apple is expected to implement power-saving technologies, including a more efficient C1 modem that debuted with the iPhone 16e.
Despite the advantages, silicon batteries come with their own set of challenges. One significant issue is that silicon expands when it lithiates, potentially up to three times its original volume. This expansion poses safety risks and has been the focus of extensive research. The carbon component of silicon-carbon batteries plays a crucial role in mitigating this expansion, allowing the battery to maintain stability and prolong cycle life.
Vincent Chevrier from Cyclikal emphasizes that while silicon is set to become a staple in lithium-ion batteries, the high cost associated with silicon-carbon technology could hinder widespread adoption. Moreover, claims regarding energy density improvements may be exaggerated; actual gains are likely to be around 10% with standard integration.
As smartphone technology continues to evolve, the introduction of silicon-carbon batteries presents exciting possibilities. However, the increasing demand for power-hungry features, such as artificial intelligence capabilities, may offset the potential benefits of enhanced battery capacity. The upcoming iPhone 17 Air will serve as a crucial test case, exploring whether a thin and lightweight design can coexist with satisfactory battery life. Only time will tell if this innovative approach will resonate with consumers and shape the future of mobile devices.
