BioAccess created an alternative version of its single-use, handheld bone drill using TLM-1550HP lithium metal oxide batteries instead of alkaline cells.

Miniaturized, feature-rich devices are driving a growing need for reliable and cost-effective power management solutions using lithium battery technology.

Primary lithium batteries are commonly utilized in single-use devices as well as in applications that require exceptionally long battery life without worrying about battery status (i.e. automatic external defibrillators). Lithium chemistry is also preferred for devices that need to be small, lightweight, and ergonomically designed. Certain lithium chemistries are also well adapted to the high temperatures associated with autoclave sterilization cycles as well as the extremely low temperatures required by the medical cold chain.

Why lithium?

First utilized in pacemakers during the 1960s, primary lithium batteries now power all types of medical devices, including automatic external defibrillators, surgical saws, drills, robotic inspection systems, RFID asset tracking tags, infusion pumps, bone growth stimulators, glucose monitors, blood oxygen meters, cauterizers, and other medical devices.

Lithium batteries are the preferred choice for many of today’s advanced medical devices because they offer the highest specific energy (energy per unit weight) and energy density (energy per unit volume) of any battery type. Lithium cells, all of which use a nonaqueous electrolyte, also have nominal open circuit voltages of between 1.7 and 3.9V. However, the use of non-aqueous electrolytes results in relatively high internal impedance.

Lithium chemistries also offer an extended temperature range, made possible by the absence of water and the chemical and physical stability of the materials. Lithium thionyl chloride cells provide the widest temperature range of all (-55oC to +125oC) and can be specially modified to withstand temperatures as low as -80°C to support the medical cold chain, delivering continuous power even at extremely cold temperatures to permit around-the-clock monitoring of pharmaceuticals, transplant organs and tissue samples that are frozen or packed in dry ice.

Not created equal

Within the category of lithium primary batteries, numerous competing chemistries are available, each offering certain advantages and disadvantages.

First utilized in pacemakers during the 1960s, primary lithium batteries now power all types of medical devices, including this wireless blood oxygen meter.

Li/MNO2 (lithium manganese dioxide) batteries, originally designed for consumer items such as toys and cameras, are now commonly utilized in glucose monitors. Li/MNO2 cells feature relatively low cost and high current-pulse capabilities, but suffer from high self-discharge and low energy density, which makes for bulky devices. Likewise, Li/MNO2 cells have a limited temperature range of -10ºC to 60ºC.

Li/SO2 (lithium sulfur dioxide) batteries, found in certain types of external defibrillators, are capable of delivering high current-pulses at low temperatures, but tend to be larger and heavier than other lithium chemistries. Li/SO2 cells also suffer from higher selfdischarge, which limits their potential service life.

Li/SOCL2 (lithium thionyl chloride) cells are ideally suited for low-current applications where a steady low current (micro amps to low milli amps) is applied for an extended period of time. They feature high energy density, high capacity, and low self-discharge rate, and feature an operating life as long as 25+ years. Certain bobbin-type lithium thionyl chloride cells also can operate in extreme temperatures ranging from -80oC to 125°C.

A hybrid version of the lithium thionyl chloride cell, the PulsesPlus battery, combines the advantages of lithium thionyl chloride chemistry with a hybrid layer capacitor to deliver high current-pulses. This hybrid cell is ideal for use in automatic external defibrillators (AEDs) and similar applications that generally operate with a low background current (sleep mode) but require periodic high-current pulses (in the multi-amp range). PulsesPlus cells also offer the potential for an end-of-life indication when the battery has depleted 90 to 95% of its original capacity. This end-of-life feature can be useful for critical applications where the “readiness status” of the device needs to be continually monitored.

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