Remote wireless devices demand specialized batteries that are capable of withstanding harsh environments for extended periods, even decades.

Battery-powered devices are being deployed throughout the industrial internet of things (IIoT) in harsh environments and remote sites, where they are exposed to temperature extremes, long storage times, high pulse requirements and other performance challenges.

Designing a battery-powered solution that can perform reliably in harsh environments is no easy task. So, to better understand this challenge, I contacted the engineers at Tadiran Batteries, the company that introduced the first ultra-long-life lithium battery for remote wireless applications nearly 50 years ago. The first Tadiran batteries were used in automatic meter reading by water and gas utilities.

The experts at Tadiran informed me that the rapidly expanding IIoT has increased demand for low-power devices for use at remote locations and harsh environments, most of which are ill-suited for consumer grade batteries. While everyday alkaline batteries may be great for delivering continuous high-rate current (i.e., powering a flashlight) they are ill-designed for industrial applications due to a very high self-discharge rate (up to 60% per year), low energy density (potentially requiring more batteries), and a propensity to freeze due to their water-based chemistry.

More often than not, industrial applications require workhorse batteries that can operate reliably for extended periods. This is especially crucial for deployments in hard-to-access locations where battery replacement is excessively expensive and sometimes dangerous. Consider, for example, a battery that powers a wireless structural stress sensor mounted beneath a bridge truss. Accessing this device to replace the battery is a prohibitively expensive undertaking, requiring scaffolding, safety netting and safety harnesses. Besides the labor expense, there is also the risk of valuable data being lost during downtime.

For a seismic monitor sitting on the ocean floor, the battery cannot be replaced. If it dies prematurely, so does the device. Remote applications such as these demonstrate the need for ultra-long-life battery-powered solutions that lower the cost of ownership by minimizing the need for future battery replacement.

Of all available primary (non-rechargeable) battery chemistries, the #1 option for long-term deployments– especially for IIoT applications such as asset tracking, safety systems, tank level and flow measuring, environmental monitoring, and more – is bobbin-type lithium thionyl chloride (LiSOCl₂). This unique chemistry offers major performance advantages, including a wider temperature range, higher capacity and energy density to support miniaturization, and, most importantly, an extremely low annual self-discharge rate that allows certain devices to last up to 40 years.

Figure 1. A Resensys structural stress sensor mounted to the underside of a bridge truss. Bobbin-type LiSOCl2 batteries power remote communications while maximizing battery operating life. Source: Resensys

Bobbin-type LiSOCl₂ batteries are ideal for use in wireless devices that principally operate on low-level base current during ‘standby’ mode, alternating with periodic high pulses to power wireless communications. To generate high pulses, a bobbin-type LiSOCl₂ battery is paired with a patented hybrid layer capacitor (HLC). In addition to storing high pulses, the HLC features a unique end-of-life voltage plateau, which can be interpreted to deliver money-saving ‘low battery’ status alerts.

Temperature extremes

All batteries have temperature limitations that, when exceeded, can result in degraded performance or battery failure. This holds especially true for alkaline and consumer grade rechargeable Li-ion batteries (try starting a car or recharging it on a sub-zero day). Conversely, LiSOCl₂ chemistry freezes at -105° C, which is ideal for use in the cold chain. Bobbin-type LiSOCl₂ cells also perform well in excessive heat, remaining stable at up to +125° C, which is ideal for applications such as deep hold drilling, car windshields, and autoclave sterilization.

Low self-discharge rates

Self-discharge refers to the current leakage that continually occurs when a battery is inactive or is being stored as chemical reactivity burns up energy. In fact, many low-power devices exhaust more energy from self-discharge than is required to operate the device. How do bobbin-type LiSOCl₂ batteries deliver a self-discharge rate of under 1% per year? It has largely to do with the passivation effect.

Passivation occurs when a thin film of lithium chloride (LiCl) forms on the surface of the anode to create a protective layer that acts as a physical barrier to separate the anode from the cathode, thus reducing the chemical reactions that cause self-discharge.

An experienced battery manufacturer can effectively harness the passivation effect through the use of proprietary manufacturing methods and higher quality raw materials. As a result, a superior quality bobbin-type LiSOCl₂ battery can feature a self-discharge rate as low as 0.7% per year whereas a lower quality battery can experience a much higher self-discharge rate of up to 3% per year. This difference may not seem so significant until you realize that a 3% annual loss of energy translates into a 30% capacity loss every 10 years, making 40-year battery life unachievable.

Compact, convenient design

Bobbin-type LiSOCl₂ batteries also promote miniaturization by packing more power into smaller spaces, which is accomplished through a unique combination of higher capacity and higher energy density (710 Wh/kg) with an open circuit voltage of 3.6 V. For example, a single 3.6V bobbin-type LiSOCl₂ cell can replace two 1.5 V batteries.

Figure 2. Oceantronics’ GPS/ice buoy being retrieved by helicopter for use in experiments measuring wind, temperature, sunlight and ice thickness near the North Pole. Bobbin-type LiSOCl2 batteries reduced size and weight by more than 90%. Oceantronics’ original battery pack (left) used 380 alkaline D-size cells weighing 54 kg while the redesigned battery pack (right) combines 32 bobbin-type LiSOCl2 D-size cells and 4 hybrid layer capacitors (HLCs) weighing just 3.2 kg. Source: Sigrid Salo NOAA/PMEL

Better batteries by design

While bobbin-type LiSOCl₂ batteries offer extended battery life, this benefit can be difficult to quantify using short-term testing to predict long-term battery performance. Fortunately, Tadiran has solved this problem with a huge database amassed over decades using test results from random customer-supplied batteries taken from the field. This long-term data enables Tadiran to generate highly accurate predictive models by comparing new applications to actual devices that have been operating for extended periods under comparable loads and environmental conditions.

Identifying the right battery is complex decision-making process. Therefore, it pays to consult with an experienced applications engineer to review your application-specific requirements. The easiest way to begin this process is by submitting an online application questionnaire to the experts at Tadiran by visiting tadiranbat.com.