Custom Tailor Batteries for Maximum Performance

Summary

When it comes to powering remote wireless devices, there are no one-size-fits-all solutions. Choosing a battery should be like visiting a custom tailor shop, where an expert with decades of experience sizes you up for a beautiful garment that highlights your strengths and disguises your weaknesses. Similar expertise is required for specifying the optimal power supply solution that combines reliability, durability and long-term cost savings while minimizing tradeoffs.

Inexpensive off-the-shelf solutions may work for certain consumer electronic devices powered by alkaline or lithium-ion batteries, especially in situations where the batteries are easily replaceable and operate in moderate environments. However, consumer batteries rarely serve the needs of industrial applications involving hard-to-access locations, extreme environments and large-scale installations where multiple simultaneous battery failures could be highly disruptive—and expensive.

Expert fitting is necessary when specifying an ultra-long-life lithium battery as thorough due diligence is required to develop a clear understanding of the power requirements and challenges specific to each application. The entire selection process can be streamlined with the help of a qualified applications engineer who—with the help of proprietary data intelligence—can help you identify the optimal power supply solution that delivers the biggest bang for the buck.
 

Know your application

Too commonly, a one-size-fits-all mentality is followed throughout the battery specification process, as the power supply is often seen as an afterthought rather than an integral step toward optimal product performance. By thoroughly understanding your power requirements, then eliciting outside expertise to validate your choice of battery, you will be far more likely to ensure that your device will operate reliably for long-term deployments in remote or extreme environments, where battery replacement is either impractically expensive or impossible.

Design optimization begins with a thorough understanding of each application’s unique performance requirements. Certain fundamental questions must be answered. For example, is the device being used as a backup power source or as the main power supply? Does the application require extended shelf life? Is the amount of average current being drawn high enough to demand the use of an energy harvesting solution combined with an industrial grade rechargeable Li-ion battery to store the harvested energy?

Answers to these and other pertinent questions can vary significantly throughout the Industrial Internet of Things (IIoT), including applications such as supervisory control and data acquisition (SCADA), process control, industrial robotics, memory backup, asset tracking, safety systems, environmental monitoring, machine-to-machine (M2M), machine learning (ML), wireless mesh networks and many more.

Typical factors that require consideration when specifying a battery for a low-power remote wireless application include electrical, environmental and size and weight, requirements.

Electrical requirements. The ideal starting point is to know your specific requirements for maximum, nominal and minimum (cut-off) voltage, keeping in mind that a higher voltage battery could enable the use of fewer or smaller batteries. The math is simple: It takes at least two 1.5 V cells to deliver the same energy as a 3.6 V cell.

The total capacity of the battery, measurable in Ampere-hours (Ah), is also vital because it establishes the maximum theoretical life of the battery based on its calculated annual energy consumption. High capacity along with high energy density are essential to battery miniaturization.

Another important consideration is the average amount of current expected to be drawn as it allows you to calculate expected annual losses in available capacity. You must also factor in the potential need for high pulses, if required, to facilitate two-way wireless communications or other advanced functionality. High pulse requirements vary in their size, duration and frequency. When predicting expected capacity losses, you must also factor in the expected amount of time the battery will spend in storage where available capacity will be consumed by self-discharge.

Environmental requirements. Environmental factors can significantly influence overall battery performance. For example, long-term exposure to extreme temperatures can compromise battery performance by reducing available capacity, which causes voltage drops and delays, and by accelerating the battery’s self-discharge rate. Certain battery chemistries are far better adapted to operate reliably in extreme temperatures (see Table 1).


Table 1: Numerous primary lithium battery chemistries are available.
 
Understanding the operating environment is especially important for remote wireless devices designed for long-term deployments in extreme environments where you must calculate the expected maximum, average and minimum temperatures expected while in operation and during storage, including the percentage of time spent in each phase.

The widest temperature range of all (-80°C to 125°C) is provided by bobbin-type lithium thionyl chloride (LiSOCl₂) batteries, which are unrivaled in their ability to operate in extreme environments while delivering the highest capacity and energy density, potentially resulting in the use of fewer or smaller cells. Bobbin-type LiSOCl₂ batteries are also ideally suited for surviving humidity, shock and vibration.

Size and weight requirements. Allowable size and weight restrictions can have a major impact on the battery selection process. Many remote wireless devices need to be miniaturized for ease of transport, ergonomics or to accommodate severe space and weight restrictions. Reducing the size and weight of the battery also can mitigate the rising cost of transporting hazardous goods while meeting increasingly stringent UN and IATA shipping regulations.

Maximizing battery operating life

The longer a device can operate maintenance-free on its original battery, the higher the return on investment. Expected battery life can be calculated based on numerous factors, principally the cell’s total capacity, energy consumed while in operation and, most importantly, the cell’s annual self-discharge rate.

All batteries experience some amount of self-discharge, as chemical reactions consume small amounts of energy even when the device is not in use or is disconnected. Self-discharge can be significantly minimized by controlling the passivation effect, which involves a thin film of lithium chloride (LiCl) that encircles the anode of an unused battery to limit its chemical reactions. Passivation is a repeating phenomenon. Whenever continuous current is drawn from an unused cell, there is an initial period of high resistance combined with a temporary drop in voltage until the protective layer begins to dissipate, also known as depassivation. This phenomenon occurs whenever an LiSOCl₂ remains in a dormant state for extended periods.

Passivation varies based on many variables including the cell’s current discharge capacity, the length of storage, storage temperature, discharge temperature and prior discharge conditions, as partially discharging a cell and then removing the load will lessen passivation effect over time.

Competing bobbin-type LiSOCl₂ batteries vary significantly in terms of their ability to harness the passivation effect, thus impacting their self-discharge rate. For example, the highest quality LiSOCl₂ batteries can feature a self-discharge rate as low as 0.7 percent per year, retaining nearly 70 percent of their original capacity after 40 years. Conversely, inferior quality LiSOCl₂ cells can have an annual self-discharge rate of up to 3 percent per year, causing roughly 30 percent of the cell’s available capacity to be consumed every 10 years, making 40-year battery life unachievable. If the application demands an ultra-long-life battery, this becomes a critical consideration.

High pulses drive wireless communications

Certain low-power remote wireless devices require high pulses of up to 15 A to initiate and power two-way wireless communications. Standard bobbin-type LiSOCl₂ cells cannot generate such high pulses due to their low-rate design. As a result, a hybrid solution is required that combines the use of a standard bobbin-type LiSOCl₂ cell that delivers low-level base current along with a patented hybrid layer capacitor (HLC) that generates pulses of up to 15A. As cell capacity starts approaching its end-of-life, the patented HLC experiences a unique voltage plateau that can be measured and interpreted to deliver “low battery” status alerts.

Consumer devices often use supercapacitors for similar purposes. However, supercapacitors are ill-suited for most industrial applications due to serious limitations such as short-duration power, linear discharge qualities that do not allow for the use of all available energy, low capacity, low energy density and very high self-discharge rates up to 60 percent per year. When linked in series, supercapacitors also require the use of bulky expensive cell-balancing circuits that drain additional current, which further reduces battery operating life.
 

An expert can help

The ideal battery-powered solution should last for the entire lifetime of the device, thereby eliminating the need for costly battery change-outs. This is especially important for ultra-long-life deployments.

However, short-term test data is often inaccurate in predicting long-term battery performance, which makes it difficult to distinguish a higher quality cell from a lower quality battery. This is where the advice of an experienced applications engineer becomes advantageous to making an informed choice. An experienced applications engineer can assist you in performing thorough due diligence by reviewing your power requirements, then recommending the solution that best suits your application. The applications engineer can also help you interpret the test data, bearing in mind that the most reliable predictor of expected battery life is in-field test data derived from similar devices operating under equivalent loads and environmental conditions.
 

Water/wastewater application

Ayyeka is a developer of remote monitoring technologies that provide digital transformation for critical infrastructure. The company’s technology embeds edge AI into field assets. With its combination of edge, Internet of Things (IoT) and AI/machine learning (ML), it propels the critical infrastructure space, enabling infrastructure stakeholders to create, manage and use remote field assets data.

Ayyeka’s AI-enabled smart sensors monitor sensors used in solid waste and wastewater management (Figure 1), public utilities, transportation, energy exploration and distribution, smart cities, environmental monitoring and other hard infrastructure. Tadiran bobbin-type LiSOCl₂ batteries power two-way wireless communications to maximize operating life, detect unusual events, enable predictive maintenance and repairs, and counter cyber security threats.

Structural integrity application

Resensys provides a powerful platform for remote monitoring of strain (stress), vibration (acceleration), displacement, crack activity, tilt, inclination, temperature and humidity. For protecting infrastructure systems against aging and malfunction, the company developed a global network to supply its high precision, durable and reliable structural monitoring solutions to customer applications including bridges, tunnels, buildings, dams and cranes.

Resensys wireless sensors are mounted beneath bridge trusses (Figure 2) to measure structural stress. These locations are highly inaccessible and use of a bobbin-type LiSOCl₂ battery serve to maximize return on investment by maximizing the operating life and increasing product reliability in extreme temperatures.

Final thoughts

Choosing the ideal battery for a low-power remote wireless device involves numerous considerations including potential trade-offs. Therefore, it pays to have a qualified applications engineer assist you when performing your due diligence. This collaborative approach can result in a custom-tailored solution that serves to extend battery life, increase reliability and maximize your return on investment.

_{This article was published in the January/February 2025 edition of Automation.com Montly.}