Cell longevity: What you need to know

One of the common challenges for developers of IoT devices is longevity.

The power source, normally a primary battery, is a critical component that is expected to deliver consistent performance, often in remote or hard-to-reach environments, for years without replacement.

Here, we explore the importance of reliable long-life cells, and dig into the R&D that underpins how cells for IoT are designed with lifespan in mind.

The value of longevity

Primary lithium cells are widely used in IoT/IIoT devices due to their high energy density, low self-discharge rates, and extended shelf lives. That longevity is crucial for several reasons.

First, it massively reduces total cost of ownership by minimizing the need for site visits, labor (to change batteries) and equipment downtime. This is particularly true for devices deployed in remote or inaccessible installations (such as oil pipelines, smart meters, or wildlife tracking tags) where regular maintenance or battery replacement is impractical at best.

There are also significant environmental benefits as, put simply, fewer battery replacements also mean less electronic waste and fewer resources consumed over time.

That’s why several sectors in the IoT space are reliant on long-life power sources, for example:

Smart Metering: Smart electricity, gas, and water meters are often installed in locations with limited access and are expected to function continuously for up to 20 years.

Asset Tracking and Logistics: Devices used to monitor the condition, location, and status of goods in transit (e.g., cold chain logistics, fleet management, container tracking) rely on long-life batteries to operate for months or even years without intervention.

Industrial Automation: In IIoT applications for predictive maintenance, wireless sensors are deployed on rotating equipment, motors, or remote industrial sites and they require long-lasting power sources that can withstand extreme temperatures and vibrations.

Agriculture Monitoring: IoT solutions for agriculture – often deployed in ‘off-grid’ environments – require dependable long-life power sources for crop management, livestock management and more.

Take a closer look at IoT in Agriculture

Environmental Monitoring: Devices can be deployed to monitor air quality (helping to identify sources of pollution and inform corrective measures), carbon dioxide levels, risk of forest fires, and water quality in rivers, lakes, and oceans. These devices are often deployed in highly remote environments.

Security and Infrastructure Monitoring: Applications such as smart locks, motion detectors and sensors operate reliably over long periods. Battery longevity ensures that these systems remain active, and therefore effective, without frequent human interaction.

Healthcare: IoT has a range of uses in healthcare settings, such as patient monitors or drug delivery systems. These require batteries that are both long-lasting and safe to reduce the need for invasive procedures on patients for maintenance.

Finding the balance: R&D for long-life batteries 

To find out how batteries can be designed to optimize lifespan, we spoke to Dr. Herzel Yamin, Technical Manager for Connected Smart Energy (CSE) Division. He’s been working in R&D for primary cells for almost four decades and brings a wealth of knowledge about how long-life cells are developed to meet the needs of the IoT market.

How do you balance the need for both long-life and high power?

Fundamentally it comes down to four main things – cell construction, chemistry, technology and quality

Cell construction is very important.

We do everything possible to reduce the self-discharge of a cell. If your cell loses 3% of its capacity each year, then it’ll lose 60% over the course of 20 years and be unsuitable for many use cases. That’s why, in principle, we work towards developing cells with less than 0.5% self-discharge per year. That can mean sacrificing some other characteristics or behaviours in the battery, but it’s a necessity to achieve that long life.

One of the ways in which you do that is to reduce the surface area of the battery – which also makes it safer. But when you reduce the surface area through your cell construction it means that only a low current can be drawn.

So, to achieve higher power we deploy two techniques.

First, we maximise the current through additives in the electrolytes to improve the voltage characteristic of the cell. We can also bolster the power through a capacitor. In Tadiran Batteries (a subsidiary of Saft) we invented the hybrid layer capacitor (HLC) that could be used in parallel to the primary cell. While the cell delivers the energy, the HLC delivers the power, meaning you can draw very high current while maintaining a low self-discharge and longer lifespan.

Finally, you have to think about the impact of quality.

Innovation is important, but so too are good raw materials, and robust quality assurance and control processes. What you’re looking for in long-life cells are materials with less impurity and, as a result, better reliability and performance over a long time.

How do you go about testing a battery’s lifespan?

Of course, you cannot wait 20 years to be sure that the battery is performing as expected, so we have methods for testing it that allows us to give customers assurances about lifespan.

One thing we do is called accelerating storage. Here, we can place a battery in higher temperatures for a predetermined period before measuring the remaining capacity. Fundamentally you can put a cell in accelerated storage for six months to simulate 20 years of ‘in field’ life.

We also use a microcalorimeter to measure the heat that is emitted from a cell. That heat is a result of self-discharge, and so you can calculate exactly how much is being lost in certain temperatures and load profile.

When we talk to customers we ask where devices (and the batteries) will be deployed, taking into account seasonal variations in temperature and more, before we draw on our very large database to properly calculate how long a particular cell will perform as needed. Through extensive testing and refining of our database we’ve been able to get those estimates increasingly accurate, and we now model lifespan to within a 1-3% margin of error.

Are there things that developers can do to ensure the optimal lifespan of a cell is achieved?

Most definitely. Firstly, they can provide information about how and where a device will be used. For IoT devices it’s important to know the load profile and the current being drawn with each pulse – and that means knowing the pulse duration, amplitude and frequency. This will inform the optimal cell type for the device.

But it’s also important to make sure that devices and batteries are properly stored before they are deployed.

What’s next for R&D on lifespan? Is there more that can be done?

What we can do is look to increase the power capability, to help meet the demand for more powerful devices. There are things we can do here.

One is to develop the HLC further for really high-powered devices, but we also want to look at how we can optimize power without the need for a capacitor. That might be a case of changing the raw materials or additives, or it could be through changing internal design, or even in refining the processes of how we produce the battery. These are all things we explore to make sure we can improve performance without reducing the lifespan of a cell.