We live in an increasingly wireless world, with billions of consumer batteries being used to power laptops, cell phones, flashlights, cameras, toys, and other consumer goods. Meanwhile, the rapid growth of the Industrial Internet of Things (IIoT) has accelerated demand for lesser known applications that are powered by industrial grade batteries which feature extended operating life, can survive extreme environments, and deliver periodic high pulses to power two-way wireless communications.
Applications that commonly require long-life industrial grade batteries include automated utility meters (AMR/AMI), automotive toll tags, GPS asset tracking devices, environmental sensors, structural stress sensors, M2M and system control and data acquisition (SCADA), data loggers, measurement while drilling, seismic monitoring and oceanographic equipment, to name a few.
Comparing primary (non-rechargeable) batteries
Numerous primary (non-rechargeable) battery chemistries are commercially available including alkaline, iron disulfate (LiFeS2), lithium manganese dioxide (LiMNO2), lithium thionyl chloride (LiSOCl2), and lithium metal oxide (see Table 1).
Alkaline cells are extremely inexpensive, but have major drawbacks, including low voltage (1.5 V), a limited temperature range (-0°C to 60°C), a high annual self-discharge rate that reduces life expectancy to 2-3 years, and crimped seals that may leak.
The low initial cost of an alkaline battery can also be very misleading for long-term deployments. To determine the total cost of ownership, you need to factor in all costs associated with future battery replacements, which can skyrocket if the wireless device is being deployed in a remote, difficult-to-access location.
Lithium battery chemistry is preferred for long-term deployments due its high intrinsic negative potential, which exceeds all other metals. As the lightest non-gaseous metal, lithium offers the highest specific energy (energy per unit weight) and energy density (energy per unit volume) of all available battery chemistries. Lithium cells operate within a normal operating current voltage (OCV) range of 2.7 to 3.6V. The absence of water enables lithium batteries to survive extreme temperatures without causing the constituents to freeze. Several primary lithium chemistries are commercially available, including:
- Lithium iron disulfate (LiFeS2) cells are relatively inexpensive, used mainly to deliver the high pulses required to power a camera flash. LiFeS2 batteries have performance limitations, including a narrow temperature range (-20°C to 60°C), a high annual self-discharge rate, and crimped seals that may leak.
- Lithium Manganese Dioxide (LiMNO2) cells, including the popular CR123A, provide a space-saving solution for cameras and toys, as one 3V LiMNO2 cell can replace two 1.5V alkaline cells. LiMNO2 batteries can deliver moderate pulses, but suffer from low initial voltage, a narrow temperature range, a high self-discharge rate, and crimped seals.
- Lithium thionyl chloride (LiSOCl2) batteries are manufactured two ways: spiral wound or bobbin-type construction. Bobbin-type LiSOCl2 batteries are better suited for long-life applications that draw low average daily current, delivering the highest capacity and highest energy density of any lithium cell, along with very low annual self-discharge rate (as low as .0.7% per year), the widest possible temperature range (-80°C to 125°C), and a glass-to-metal hermetically sealed can to resist leakage.
Achieving 40-year battery life
Bobbin-type LiSOCl2 batteries are not created equal, as the method of manufacturing and the quality of the raw materials can greatly impact battery operating life. For example, an inferior quality LiSOCl2 battery may have an annual self-discharge rate of up to 3% per year, losing 30% of its available capacity every 10 years. By contrast, a superior grade bobbin-type LiSOCl2 battery can feature an annual self-discharge rate as low as 0.7% per year, thus permitting certain wireless devices to operate for up to 40 years on a single battery.
Choosing a superior grade LiSOCl2 battery could substantially lower your total cost of ownership by eliminating future battery replacements over the expected lifetime of the device. Superior quality batteries utilize the highest grade of raw materials and are carefully manufactured using six sigma methodologies and statistical process controls (SPC) during all phases of manufacturing to ensure greater lot-to-consistency.
Not all bobbin-type LiSOCl2 batteries are manufactured to such high standards, so due diligence is required to verify that the batteries are UL-approved and offer a higher safety margin by being able to withstand extreme temperature, humidity, shock, vibration, and puncture. High self-discharge rates may not become apparent for years, so it is important to demand documented long-term test results along with in field data from batteries operating under similar loads and environmental conditions. Long-term lab test results and data from the field have been assembled by Tadiran to create a vast database that can be utilized to develop predictive models of long-term battery performance for all types of remote wireless applications.
Prioritize your battery performance requirements
Every wireless application is unique in terms of its battery performance requirements. Here are some of the most important performance variables:
- Energy consumed in ‘stand-by’ mode (the background current)
- Energy consumed during ‘active’ mode (including the size, duration, and frequency of pulses)
- Storage time (a battery will self-discharge during storage, diminishing its capacity)
- Thermal environments (including storage and in-field operation)
- Equipment cut-off voltage (as the battery’s capacity is exhausted, the voltage can drop too low for the device to operate; an effect that is magnified in extreme temperatures)
- Battery self-discharge rate (which can be higher than the average daily current consumed)
- Battery replaceability or rechargeability
- Total cost of ownership (initial purchase price along with all labor and material costs associated with future battery replacements, where applicable)
Trade-offs are often inevitable, so it makes sense to prioritize your list of desired attributes when specifying the power supply.
The need to factor in extreme environments and high pulse requirements
Consumer batteries do not perform well in extreme environments. A prime example is the cold chain, where wireless devices continually monitor the transport of frozen foods, pharmaceuticals, tissue samples, and transplant organs at controlled temperatures as low as -80°C. Bobbin-type LiSOCl2 batteries are uniquely suited for the cold chain due to their high specific energy (energy per unit weight), high energy density (energy per unit volume), and their non-aqueous electrolyte, as the absence of water allows specially modified cells to operate in extreme temperatures ranging from -80°C to 125°C. Wireless devices connected to the IIoT may also require high pulses of energy to support two-way wireless communications, remote shut-off capabilities, and other advanced functionality.
High pulse requirements can sap battery energy, and thus shorten battery operating life. To conserve energy, most IIoT-enabled wireless devices are intelligently designed using low power components, ICs, and circuitry, along with the use of a low power communications protocol such as ZigBee, WirelessHART, Bluetooth, DASH7, INSTEON, or Z-Wave. Energy consumption is further minimized by operating mainly in a “stand-by” state that draws nominal amounts of current, periodically querying the data, and only becoming “active” for brief intervals to manage data retrieval and wireless communications.
Standard bobbin-type LiSOCl2 batteries are designed to deliver low rate power, experiencing a temporary drop in voltage, or transient minimum voltage (TMV) when high pulses are drawn. This problem can be easily solved by combining a standard bobbin-type LiSOCl2 cell with a patented Hybrid Layer Capacitor (HLC). The battery and HLC work in parallel, with the standard cell supplying the background current while the single-unit HLC acts like a rechargeable battery to store and deliver high pulses. As a bonus, the HLC features a unique end-of-life performance curve with a measurable a voltage plateau that can be interpreted to issue low battery status alerts.
Supercapacitors often perform the same function in consumer electronics but are ill suited for industrial applications due to their inherent drawbacks, including a high self-discharge rate (up to 60% per year) and a limited temperature range that prohibits their use in harsh environments. A supercapacitor made up of two 2.5 V capacitors in series also requires a balancing circuit, which draws additional current.
Growing demand for energy harvesting
Certain remote wireless devices consume enough average daily energy to quickly exhaust a primary battery, thus requiring the use of an energy harvesting device in combination with a consumer or industrial grade rechargeable Lithium-ion (Li-ion) battery to store the harvested energy.
The most popular version of the consumer grade Li-ion battery is the ubiquitous 18650 cell, which was designed and manufactured by manufacturers of laptop computers. These cells can operate for approximately 5 years and 500 full recharge cycles with a temperature range of -20 to 60°C, as this is all that their intended application required. As consumer grade Li-ion cells age, they also experience a gradual degradation of the cathode, making them less receptive to future recharging, which further reduces their operating life.
To overcome these limitations, industrial grade rechargeable Li-ion batteries were developed that can operate maintenance-free for up to 20 years and 5,000 full recharge cycles. These cells feature a low annual self-discharge rate, a small form factor, and no degradation of the cathode, a common problem for consumer grade Li-ion batteries (see Table 2).
Industrial grade Li-ion batteries can also be recharged in extreme temperatures (-40°C to 85°C), and, unlike consumer batteries, they can deliver the high pulses required for two-way wireless communications (up to 15A pulses for a AA-sized cell).
Some real-life examples from the IIoT
IPS solar-powered parking meters provide true wireless connectivity to the IIoT, with industrial grade rechargeable Li-ion batteries being utilized to save millions of dollars by eliminating the need to hard-wire metropolitan sidewalks. These wireless networked solar powered parking meters feature state-of-the-art functionality such as multiple payment system options; access to real-time data; integration to vehicle detection sensors; user guidance and enforcement modules. All parking meters are wirelessly networked to a comprehensive web-based management system. Small photovoltaic (PV) panels capture the sun’s energy, with industrial grade rechargeable Li-ion batteries storing the energy and delivering the high pulses required to power two-way wireless communications, ensuring 24/7/365 system reliability for up to 20 years.
Another notable example is Cattlewatch, where a small percentage of cows are outfitted with solar-powered transmitters powered by industrial grade rechargeable Li-ion batteries, while the remainder of the herd wears collars powered by long-life primary lithium batteries. Together, these devices form a wireless mesh network that permits ranchers to remotely manage the entire herd by continually monitoring animal health status and GPS location, and receiving alerts about unusual animal behavior that could indicate the presence of poachers or predators.
The emergence of the IIoT has created dynamic opportunities for industrial grade batteries, including bobbin-type LiSOCl2 batteries that can operate for up to 40 years and rechargeable Li-ion batteries that operate for up to 20 years and 5,000 full recharge cycles. Understanding the performance differences between consumer and industrial grade batteries is essential to specifying the ideal power supply based on application-specific requirements.