IIoT-connected devices using two-way wireless communications require specialized power management solutions.

The use of an ultra-long-life lithium battery can translate into significant cost savings over the life of a remote wireless device by eliminating the labor and logistical expenses involved in battery replacement. Extended battery life is especially important for remote wireless devices being deployed in remote locations and harsh environments where battery replacement is extremely cost prohibitive or impossible and where continuous data integrity is essential.

Demand for battery-powered remote wireless devices has exploded across the Industrial Internet of Things (IIoT), which encompasses a wide array of applications ranging from supervisory control and data acquisition (SCADA) to automated process control, machine-to-machine (M2M), machine learning and artificial intelligence (AI)-enabled predictive maintenance programs, to name a few. 

Battery-powered devices are used to monitor structural stress to critical infrastructure, seismic activity and environmental conditions, tank levels and pipeline flow, GPS and RFID asset tracking, safety systems and more. Increasingly, these IIoT-connected devices use two-way wireless communications with specialized batteries required to extend product longevity, improve reliability, reduce long-term maintenance costs, support predictive maintenance programs and more (see sidebar “Ayyeka: Wastewater Management Application”).

Ayyeka: Wastewater management application

Ayyeka, a company that specializes in remote monitoring applications, is using AI-enabled smart sensors to revitalize hard infrastructure, including solid waste and wastewater management, public utilities, transportation, energy exploration and distribution, smart cities, environmental monitoring and more. These remote wireless devices permit two-way communications to maximize operational efficiency, detect unusual events, enable predictive maintenance and repairs and help counter growing cyber security threats. The Tadiran bobbin-type LiSOCl2 batteries in these devices support predictive maintenance programs and improve device reliability and longevity. 

Most low-power applications require primary batteries

The vast majority of low-power devices operate mainly in a standby state that draws small amounts (microamps) of average current interrupted by periodic pulses in the multiamp range. Numerous primary (non-rechargeable) lithium ion battery chemistries are available for such low-power applications, each offering unique performance benefits and tradeoffs. 

These chemistries include alkaline, iron disulfate (LiFeS2), lithium manganese dioxide (LiMnO2), lithium thionyl chloride (LiSOCl2), and lithium metal-oxide. 

Bobbin-type LiSOCl2 batteries are overwhelmingly preferred for long-term deployments due to their high capacity and energy density, wide temperature range and an incredibly low annual self-discharge rate of less than 1% per year for some cells.

There are also low-power applications that draw higher amounts of average energy measurable in milliamps with pulses in the multiamp range—enough to prematurely exhaust a non-rechargeable battery. These applications often require some form of energy harvesting device in combination with a rechargeable Lithium-ion (Li-ion) battery to store the harvested energy.

Industrial grade TLI Series rechargeable Li-ion cells have been developed that far exceed the capabilities of consumer grade Li-ion batteries. TLI Series batteries can operate for up to 20 years and 5,000 full recharge cycles and can be charged and discharged at extremely cold temperatures.

The importance of very low self-discharge

The two-way wireless communications used by IIoT connected devices requires specialized power management solutions. These devices employ a variety of energy-saving strategies to maximize battery life, including the use of a low-power communications protocol (i.e., WirelessHART, ZigBee, LoRa, etc.), low-power chipsets and proprietary software that minimizes energy consumption during active mode. While helpful to extending battery life, these energy-saving techniques are often overshadowed by the energy losses caused by battery self-discharge.

Self-discharge is common to all batteries as chemical reactions occur even when a cell is disconnected or in storage. The annual self-discharge rate of a cell can vary significantly based on a number of factors including the choice of chemistry, the design of the cell, its current discharge potential, the quality of the raw materials and the harnessing of the passivation effect.

Unique to liSOCl2 batteries, passivation involves a thin film of lithium chloride (LiCl) that forms on the surface of the lithium anode that greatly reduces its reactivity while not in use. LiSOCl2 cells made with bobbin-type construction feature a smaller active surface area to limit reactivity, thus enhancing the passivation effect with the tradeoff being an inability to deliver high-rate current. Cells made with spiral wound construction feature a greater surface area for reactivity to occur, thus permitting higher rates of energy flow with the tradeoff being a higher rate of self-discharge.

Whenever a continuous load is placed on an inactive LiSOCl2 cell, the passivation layer causes initial high resistance and a temporary dip in voltage until the discharge reaction begins to dissipate the LiCl layer—a process that keeps repeating each time the battery becomes inactive. The ability to harness the passivation effect can be affected by such variables as the cell’s current capacity, length of storage, storage temperature, discharge temperature and prior discharge conditions, as removing the load from a partially discharged cell increases the level of passivation relative to when it was new. The passivation effect also must be carefully managed to avoid the possibility of over-restricting energy flow.

Experienced battery manufacturers can optimize the passivation effect by using higher quality raw materials and through proprietary manufacturing processes.

Challenges of powering two-way wireless communications

Standard bobbin-type LiSOCl2 cells provide an excellent solution for maximizing the passivation effect but are unable to deliver the high pulses required for two-way wireless communications due to their low-rate design.

This challenge was addressed with the introduction of PulsesPlus batteries that combine a standard bobbin-type LiSOCl2 cell that delivers low-level background current with a patented hybrid layer capacitor (HLC) that stores and delivers high pulse current.

This hybrid battery technology provides a valuable alternative to supercapacitors that store pulsed energy electrostatically rather than chemically. Mainly found in consumer applications, supercapacitors are generally ill-suited for long-term industrial deployments due to a variety of serious drawbacks including short-duration power, linear discharge qualities that prevent use of all the available energy, low capacity, low energy density and high annual self-discharge rates (up to 60% per year). Supercapacitors linked in series also require the use of cell-balancing circuits, which add cost, increase bulkiness and consume added energy to further accelerate the self-discharge rate.

LiSOCl2 batteries are not created equal

Significant differences exist between competing bobbin-type LiSOCl2 cells. For example, a superior quality bobbin-type LiSOCl2 battery can feature a self-discharge rate as low as 0.7% per year, able to retain more than 70% of its original capacity after 40 years. By contrast, an inferior quality cell can have an annual self-discharge rate of up to 3% per year, losing 30% of its capacity every 10 years, making 40-year battery life unachievable.
Superior quality LiSOCl2 batteries are not easily distinguishable since the long-term effects of a higher annual self-discharge rate can take years to become apparent. In addition, the predictive models used to estimate expected battery life tend to underestimate the passivation effect as well as the impact of prolonged exposure to extreme temperatures. Various testing procedures have been developed to estimate battery life, with the most reliable predictor being long-term data from actual devices in the field with similar energy consumption profiles and environmental conditions.

When extended battery life is essential, it pays to perform added due diligence. Start by demanding fully documented long-term product test results along with historical in-field test data from comparable applications.

Thorough evaluation can help users achieve significant long-term savings while enhancing the reliability of remote wireless device.

This feature will appear in the November 2025 issue of Automation.com Monthly: AI and Digital Transformation.