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Safety First: Mobile Cart Batteries that Protect Against Fire

January 2, 2018
Author: Definitive Technology Group

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Since the United States mandated the nationwide use of electronic medical records in healthcare, mobile computer carts have enabled countless healthcare facilities to record and access medical data at the point of care. Carts are also used for telemedicine, computerized prescriptions, and for administering medications - they have become indispensable in the modern healthcare environment.

To get the most out of your investment in mobile computer carts, it's crucial that you make the investment in mobile computer cart battery systems that help to maximize up-time - after all, what good is a mobile computer cart that's plugged into a wall charger? Still, it's important to choose a product that's operationally safe and doesn't put the welfare of your healthcare workers or patients at risk.

In this article, we'll discuss the importance of safety when choosing a battery system for your mobile computer carts. We'll assess different types of battery chemistry and their relative safety, introduce some terminology that will help you understand what to expect from any battery product that your facility purchases, and inform you about the most important features to look for when putting safety first at your healthcare organization.

Battery Terminology that You Need to Know

Later in this article, we'll be comparing some different types of batteries across several dimensions that indicate their operational capacity and safety parameters. Let's start with a quick glossary of terms that you can apply to understand the differences:

Battery Chemistry - Batteries pump electrons using chemical reactions. Different batteries use different types of chemical reactions to facilitate this process. Lead, nickel, and lithium are the most common types of battery chemistry, with lithium-ion being the most widely used for rechargeable batteries. Battery chemistry has implications for what equipment can be used to charge the battery and how the battery can be disposed of safely.

Specific Energy - Specific energy is very similar to "battery capacity". This metric defines battery capacity in terms of weight, with the units Wh/kg. Specific energy is calculated by taking a one-kilogram battery with a known battery chemistry and measuring how much power it outputs over a one-hour period. For example, if your computer needs 200W/h of power, a battery with a specific energy of 20Wh/kg can be used to power it, but you'll need a 10kg unit! Specific energy tells you what mass of battery will be required to meet your power consumption needs.

Thermal Runaway - The chemical reactions in a battery are exothermic, meaning that they produce heat. Sometimes, when the battery system malfunctions and cannot dissipate heat adequately, the battery overheats and can lead to a thermal explosion. This is known as thermal runaway. It is important to choose a battery system that safeguards against thermal runaway by using less reactive anode and cathode materials.

Why Choose Lithium Ion Batteries?

Lead-acid batteries were invented in the mid-1850s, whereas Lithium Ion battery systems have only been around since the early 1900s, so what makes these batteries superior to their predecessors? For starters, the chemical properties of lithium ions make them the ideal power system. Lithium is the lightest of all metals, has the greatest electro-chemical potential, and provides the greatest specific energy per weight of any battery chemistry available.

In the early 90s, cell phone manufacturers discovered that metallic lithium batteries were inherently unsafe, and research shifted towards using lithium ions in non-metallic solutions for rechargeable batteries. This led to the creation of all of the most popular lithium-ion battery types today.

Advantages of Lithium-ion batteries include high specific energy and high load capabilities, long battery life cycles, extended shelf life with minimal maintenance, and high capacities. Still, lithium-ion technology must be combined with the best available materials to produce a battery that is both safe and effective. In the next section, we'll look at the various battery types that have been developed with Lithium ions, their applications, and key differences in their safety features.

Types of Lithium-Ion Batteries

Lithium Cobalt Oxide (LCO) - This battery chemistry is most commonly used in mobile phones, tablets, laptops, and cameras. These batteries provide excellent specific energy at 150-200Wh/kg, meaning that a very lightweight battery can power a simple electronic device like a tablet or laptop computer. One major shortcoming of these batteries is that they can overheat at relatively low temperatures of as little as 150 degrees Celsius (302 Fahrenheit). The biggest problem with any battery that has Cobalt within its chemistry is that when it catches fire, the battery 'feeds' itself the oxygen it requires to continue burning. This battery fire is very difficult to extinguish and presents a very serious problem. - Cobalt batteries should not be used in mobile workstations.

Lithium Manganese Oxide (LMO) - LMO batteries are commonly used with power tools and some medical devices. They have a specific capacity of 100-150Wh/kg, slightly lower than LCO batteries, but a greater power output, which makes them ideal for devices that require high power outputs for a short duration. This limits their suitability for mobile computer carts, where power consumption is steady and predictable for long periods. LMO batteries typically have a thermal runaway temperature of 250 degrees Celsius, or 482 degrees Fahrenheit.

Lithium Nickel Manganese Cobalt Oxide (NMC) - With a capacity of 150-220Wh/kg, NMC batteries provide both high power and high capacity. The thermal runaway temperature of 210 degrees Celsius makes these batteries safer than LCO batteries, but not as resistant to overheating as LMO batteries. The biggest problem with NMC batteries is that they are cost prohibitive when looking at their total cost of ownership compared to other battery types. An NMC battery will need to be replaced 5X compared to a LiFe.

Lithium Iron Phosphate (LiFe) -  LiFe batteries are the safest form of lithium ion batteries currently available, and are ideally suited to portable and stationary applications that require high endurance batteries, rather than high power output or specific capacity. Though the specific capacity of LiFe batteries is typically just 90-120Wh/kg, the thermal runaway temperature is a whopping 270 degrees Celsius (518 Fahrenheit). LiFe batteries offer a steady discharge that can power your mobile workstations while maintaining a low operating temperature. Additionally, they can last 5+ years without requiring a replacement.

Fanless Design Adds Another Layer of Safety

Definitive Technology Group offers a Lithium Iron Phosphate battery system that's specially designed to promote safety in mobile computer cart applications. The most significant additional feature we've added is a fan-less design. Cooling fans are often incorporated in many batteries, but these devices malfunction frequently.

If a device relies on a fan to stay cool, what happens when the fan is jostled loose or collects dust? The battery system overheats and a thermal runaway may occur, resulting in personal injury or damage to your facility. Fanless cooling improves efficiency and run-time, reduces maintenance costs and limits the risk of spreading airborne substances.

Additional Safety Tips for Operating Rechargeable Batteries

Conclusion

Choosing a mobile cart battery that protects against fire is as simple as understanding the various battery systems available, the chemistry they use, and the safety features they include. Choose a battery system with a high threshold for thermal runaway, such as a Lithium-Iron-Phosphate battery. For added safety, opt for a model with fanless cooling, minimizing the possibility that a simple mechanical failure could lead to a fire.

It's important to choose a battery system that meets your power and weight requirements, but you should never compromise safety for power output.



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