Battery Evolution: Understanding the Pros and Cons
Batteries are a part of our daily lives. The devices and systems they support are integral to a wide range of applications we use. Some battery types we are familiar with, while others we may not be aware of and therefore take for granted. So first, what is a battery?
A battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices†.
Simply put, a battery is a device that stores chemical energy and converts it to electric energy††. Primary (single-use or disposable) batteries are used once and discarded, as the electrode materials are irreversibly changed during discharge. A common primary example is the alkaline battery used for flashlights, television remotes and a multitude of portable electronic devices.
Examples of Primary Batteries
Secondary (rechargeable) batteries can be discharged and recharged multiple times using an applied electric current; the original composition of the electrodes can be restored by reverse current. Examples include the lead–acid batteries used in vehicles and lithium-ion batteries used for portable electronics such as laptops, digital cameras and mobile phones.
Examples of Secondary Batteries
Within the category of secondary batteries there is a specific designation for stationary batteries. Stationary batteries are designed for a fixed location (i.e., not moved) and permanently connected to the load and to the direct current. They come in a wide variety of designs for different applications. They are used for applications where power is necessary only on a standby or emergency basis and are infrequently discharged. Stationary batteries remain on a continuous float charge so they can be used on demand. Examples of applications using stationary batteries include engine generators and uninterruptible power supply (UPS) systems.
Battery Use in Daily Lives
So why should you care about battery types and uses? While you’re aware of being dependent on AA and AAA batteries, and care if your mobile phone and car battery are charged, it’s likely you rely on batteries more than you realize. For example, the bank account information you access online or at a cash machine likely resides on a computer server which relies on a UPS backed by a stationary battery, providing 100% uptime and availability.
Interruption in power to these servers, even for a fraction of a second, could not only interrupt the transaction but could result in an extended outage to accessing the information. Amplify this when the interruption affects thousands of users, and the result could be profound. A battery that is integral to the UPS will ensure power remains available to the server, and if the interruption is an extended event, the engine generator for the data center will receive an automated start command—using a starting battery—and replace the failed source of power so the server(s) can continue to operate.
Historical Batteries
In the telecommunications and UPS industries, the Vented Lead Acid (VLA) battery was the battery of choice for decades. VLA batteries were noted for their free electrolyte (an acid and water solution), that can be readily viewed through a transparent container.
VLA batteries required dedicated rooms for storage. The cells/jars were heavy and difficult to replace. They required regular maintenance including adding water that was lost during float charge. While cumbersome to store and maintain, they were well known, and users understood what was required.
A Significant Milestone
In the 1980s the battery industry announced a solution to the issues with the VLA battery. Behold, the valve regulated lead acid (VRLA) battery. The battery was sealed and the need to add water periodically was no longer necessary. It was touted as “maintenance free” by some.
However, that turned out to not be the case. Problems associated with the VRLA battery required development of test and monitoring equipment. The result was that a greater focus was required, not less. As the issues were identified and addressed, users came to understand what was required to help ensure availability and to identify potential problems.
Batteries Today
Fast forward to today. Over the past few years, a relatively new battery chemistry was introduced in the Mission Critical industry: lithium ion (Li-ion). The electric vehicle (EV) marketplace has been using Li-ion batteries for more than a decade. Keep in mind, this is a different application than the stationary battery represents. There have been some UPS manufacturers who claimed to have systems in use for similar time frames, but not on a scale large enough to instill greater confidence with experts and the general public. Additionally, Li-ion batteries have their fair share of incidents, including fires in EVs. Key to reducing/eliminating these incidents is gaining a better understanding of those risks and how to take action to prevent them from escalating or the proper response to a fire event.
In the case of the UPS application, the Li-ion battery must be monitored and controlled by a battery management system (BMS). The battery will not function, for safety reasons, without the BMS being active.
A BMS is any electronic system that manages a rechargeable battery (cell or battery pack), such as by protecting the battery from operating outside its safe operating area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and/or balancing it.‡
Li-ion batteries are typically organized in strings and can be connected in series, in parallel or a combination of both, to achieve whatever voltage and current is required for a given application, just as the lead-acid. However, the configuration is frequently in a more complex cell configuration within the individual battery pack.
The following table shows typical performance ranges for the kind of battery cells used in today’s UPS.
Add to the above the lighter weight, and it is a very attractive alternative to the lead-acid.
It is important to know that Li-ion is not a single technology, but a wide range of related electrochemistries. Li-ion technologies are attractive because of their high energy density. However, that feature also brings an increased level of risk as the nonaqueous electrolytes and other combustible materials in these cells can pose an increased fire hazard.
Looking specifically at Li-ion technologies, potential causes of safety events can be lumped into one of three categories:
- Overcharging
- Overtemperature
- Mechanical abuse
Codes and Standards
The recent development of new codes and standards relating to Li-ion systems has been rapid. NFPA 855, Standard for the Installation of Stationary Energy Storage Systems, includes strict spacing and maximum-energy limitations towards people occupied buildings. An alternate approach when trying to bypass these limitations is to show results of UL9540A, Standard for Test Method for Evaluation Thermal Runaway Fire Propagation in Battery Energy Storage Systems, testing to the AHJ and seek a waiver. The original intent was for UL9540A to be required in more exceptional cases, but now it is essentially mandatory. Compliance testing under UL1973 can be augmented with some additional metering to meet the requirements of UL9540A at the same time.
The rapid development of codes and standards relating to Li-ion safety is causing manufacturers to rethink their approaches to product design.
What Does All This Mean?
There is a lot of excitement around the increase in use of stored energy systems as an integral part of a sustainable future. Li-ion batteries have been the purported solution in many publications. Given what we know today—and if history offers insight into possible consequences of rapid change—we still have a lot to learn about Li-ion. The mining of minerals, their sources and the variety and of minerals that are used in their manufacture is one area that gives us pause. It is worth noting the recycling of Li-ion batteries is an aspect of the life cycle that has not been fully developed. The expectation is that demand will provide the solution(s) as needed.
There are a number of battery chemistries being introduced today that may offer alternatives to any one battery chemistry. And let us not forget the lead-acid battery is still in use and has been well understood for some time.
Many of those involved with stationary batteries believe there will be a variety of options in the future and selection of a specific battery may be driven by many factors.
Those of us in the Mission Critical segments of our society look at the rapid deployment as a double-edged sword. It’s great to see emerging uses of batteries in all applications. At the same time, it’s concerning we are not being more attentive to a more planful strategy during these coming years of transition. Personally, I look forward to the continued evolution of batteries, in a carefully regulated and thoughtful manner.