Application Watch: Flexing Li-ion battery technology for wearables

The search for new design and fabrication strategies to make flexible Li-ion batteries (FLIBs) for wearable devices has been ongoing for years. It has led to innovations in electrode design and options in compatible electrolytes. Breakthroughs notwithstanding, this category remains at an early stage of development but will continue to flourish as development and adoption of wearable technology gather pace.

Driving FLIB R&D efforts are the opportunities that abound in this application, which include smart jewelry such as rings, wristbands, watches and pins, as well as body-mounted sensors, fitness trackers and smart clothing.

IDC reported that 444.7 million wearable devices shipped worldwide in 2020, increasing by 28 percent YoY despite the COVID-19 pandemic. This upsurge is attributed to the availability of disposable income as sheltering in place has limited access to most leisure activities. "The pandemic has also been good for the market as it has put health and fitness at the forefront of many consumers' minds," said Jitesh Ubrani, research manager for IDC mobile device trackers.

In China, wearables shipments rose to 110 million units in 2020, up 7.5 percent YoY. While this pales in comparison to the 37 percent YoY growth in 2019, there is market confidence that 5G developments and heightened health awareness will ensure a significant increase in the coming years.

Indeed, going by the projections, it is almost certain. According to IDTechEx, the global market for wearable devices will be valued at $100 billion and $150 billion in 2023 and 2026, from $40 billion in 2018.

This bodes well for the flexible batteries segment. Markets and Markets estimates growth will lead to $296 million in 2025 from $98 million in 2020 at a CAGR of nearly 25 percent.

In the area of research and development, this means great impetus to come up with more creative solutions, especially for FLIBs to withstand deformation yet deliver high capacity efficiently and safely.

An example is the spine-like battery designed by a research team led by Yuan Yang of Columbia University's engineering school. It has an energy density of 242Wh/L, shows a stable voltage when flexed and twisted, and maintains 94 percent of capacity even after 100 charge cycles. However, there is no available data on this breakthrough, that is, if it has gone past the prototype stage.

In China, there have been similar initiatives in the past three years led by Gotion, CATL and BattFlex. Since 2016, Wuhan-based BattFlex has been developing and manufacturing FLIBs, with current monthly capacity at 50,000 units. One of its product models for wearable devices has 5.7Wh rated power capacity, providing 1,500mAh capacity and 3.8V rated voltage.

Other Chinese suppliers, banking on the expected 10 to 15 percent demand increase in the coming years, are focusing on the wearables market. Shenzhen Bofuneng Battery Co. Ltd, one of the manufacturers interviewed by Global Sources Electronic Components for this article, built a new factory in 2020 to boost production capacity, which is now at 200,000 units. This will rise further with another facility scheduled to open in 2021.

There are more than a thousand suppliers making up the Li-ion battery manufacturing sector in China. This pool includes companies from Japan and South Korea such as Panasonic, TDK and LG Chem. Other key Chinese enterprises include AEC, Sunhe, PATL, EVE, Large and ATL.

Some of these manufacturers also offer other types of batteries and battery packs. Their shipments of Li-ion batteries account for 40 to 80 percent of output.

At least 60 percent of the companies are based in Guangdong, specifically in the cities of Shenzhen, Dongguan, Huizhou, Zhongshan and Zhuhai. They include the top 10 suppliers of Li-ion batteries for wearable devices, namely, AEC, Sunhe, PATL, Everpower, EVE, Great Power, Coslight, Highpower, McNair and Juheyuan.

There are also many manufacturers in Suzhou, Wuxi, Changzhou, Ningbo and Tianjin in east and north China.

De-facto wearables battery

Li-ion batteries are small, lightweight and have a long operating life, making them the power source of choice for wearable electronics. Their development continues to trend toward thinner and more flexible configurations that offer a bigger capacity for longer device use.

In China, typical Li-ion batteries for wearables come in variants with 3.6 to 3.8V rated voltage, 240 to 253Wh/L specific energy and 500-cycle life span. These usually have a less than 10 percent self-discharge after one month of storage under normal temperature.

Most manufacturers ensure their products meet quality, safety and environmental standards such as CE, UL and RoHS.

In the coming years, Chinese suppliers aim to reach 400Wh/L specific energy and up to 1,000-cycle life span. This is to expand their customization range and sharpen their competitive edge. Custom-made products, after all, are still their bread and butter, accounting for at least 30 percent to as much as 80 percent of shipments.

For anode and cathode materials, electrolytes and diaphragms, companies turn to domestic providers but also welcome requests for other sources of materials and components. Diaphragms, for instance, may come from Japan, South Korea or the Taiwan region.

So far this year, manufacturing input costs have stabilized after an increase in previous months that led to a 5 percent price adjustment. This is expected to hold for the remainder of 2021 and keep Li-ion battery quotes at current levels.

3.7V, 45mAh Li-ion battery

This PATL500823 model from Dongguan Perfect Amperex Technology Ltd is a 3.7V, 45mAh Li-ion battery with 0.2C standard and 1C maximum charge and discharge rates. The 5x8x23mm unit, with a 500-cycle life span, has charge and discharge temperatures of 0 to 45 C and -20 to 60 C. It meets CE, IEC 62133, RoHS, UL and UN 38.3 requirements.

An order of at least 3,000 units is required. Lead time is 15 days.

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Li-ion battery with 150mAh rated capacity

Rated at 150mAh, this 322331 Li-ion battery from Fello Tech Co. Ltd has 3.7V nominal voltage, 150mAh rated capacity, 1C maximum charge and discharge rate, and ≤60mohm internal impedance.

A 500-unit minimum order has a 10-day lead time.

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Li-ion battery, supports 400 cycles

Shenzhen Bofuneng Battery Co. Ltd markets this ICR Series of Li-ion batteries with 3.7V nominal and 4.2V maximum voltage, and 3V cut-off voltage. The charge and discharge temperatures are 0 to 45 C and -20 to 60 C, and the life span is 400 cycles.

The minimum order quantity is 100 units. Delivery takes five days.

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3.7V, 45mAh Li-ion battery

From Shenzhen Melasta Battery Co. Ltd, this LP054050 Li-ion battery has 3.7V nominal voltage, 45mAh capacity, 0.2C standard and 1C maximum discharge rates, and -10 to 45 C operating temperature. It lasts more than 500 cycles.

The supplier requires a 50-unit minimum order for delivery within 15 days.

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