The Li-ion and the Mouse

Lithium-ion batteries have many advantages, but they’ve historically been tied up by the higher CAPEX they demand. Prices have however come down substantially over the last decade. With the technology no longer being held back by prohibitive prices, lithium-ion batteries have become an attractive choice for datacenters.

In technology, some tipping points happen fast, while others seem to take place in slow motion. Lithium-ion batteries have already completely taken over many types of devices and equipment. It’s difficult to imagine a modern smartphone or electric automobile, for instance, using anything other than a lithium-based chemistry these days. The reason is simple: no other mass-producible technology offers the same energy density, longevity, performance, and low self-discharge in such compact dimensions.

What’s been holding the li-ions at bay?

So why aren’t all datacenters using lithium-ion batteries by now? One might wonder if it could have something to do with safety. Lithium-ion batteries can in fact combust or even explode if improperly handled or damaged. Such cases involving consumer batteries are well known from the airline industry, for instance.

Lead-acid chemistry not without risks, either

But lead acid batteries are not entirely without risk themselves. Sure, with a time-honored technology such as lead acid, there is an extensive body of knowledge about how to safely manufacture and maintain these types of batteries. In the datacenter industry, most UPS systems were built for them and everyone knows what to expect and how to handle things. The main hazard from lead acid batteries involves the hydrogen gas produced when the battery charges, but the associated risks can be easily minimized with proper equipment and facilities.

Specifically, when charging a lead-acid battery, a portion of the charging current will electrolyze water contained in the electrolyte. This generates oxygen and hydrogen which in some types of batteries is vented to its surroundings. When the mixture of hydrogen in the air rises about 4%, it can explode if ignited. So, improperly maintained lead-acid batteries can be a fire hazard. But modern VRLA (valve-regulated lead acid) batteries prevent the emission of hydrogen almost completely. The only time a VRLA battery would release hydrogen into its surroundings is in the event of a critical pressure buildup that forces the safety valve to open. The rest of the time, nearly all (up to 99%) of the hydrogen produced is recombined with oxygen to form water inside the sealed battery. This reduces the risk of explosion greatly but also has the beneficial side effect of returning the water that is recombined back to the electrolyte, eliminating the need to add water to the battery at regular intervals. All-in-all, this makes VRLA batteries a very safe and proven technology.

They can run away, but you don’t need to hide from li-ions

Lithium-ion batteries, on the other hand, have seen their reputations tarnished because of a few highly publicized incidents. In most cases, the cause of a li-ion accident is thermal runaway due to mishandling or a violent impact. Because of the much higher energy density in lithium-ion batteries, the possibility of thermal runaway is higher than with lead-acid chemistries, particularly vented batteries. But lithium-ion batteries come in a variety of different chemistries including lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, and lithium titanate. Each chemistry has its unique advantages with regard to safety, energy, performance, and cost.

Furthermore, modern li-ion battery packs of the kind used in datacenter applications include a number of active and passive design features to prevent thermal runaway at the cell, module, and system levels. As a result, statistically, li-ion batteries have become incredibly safe over the years. Safety is no longer any reason to avoid lithium-ion chemistries in the data center.

Temperature matters

Another benefit or advantage of li-ion batteries that should not be underestimated is the higher operating temperature of Li-Ion against VRLA. This means: Less cooling is required for li-ion batteries, and this saves energy consumption and reduces costs for cooling – an important factor for data center applications.

 Li-Ion batteries are capable to operate in ambient 35℃ normally without cooling. In contrast to this, traditional VRLA batteries don’t like temperatures over 20℃, because higher temperatures above 20° C decrease VRLA battery lifetime.

Show me the money

With far greater energy density, lower floor space requirements, and considerably lower operating costs, what could still be holding us back from deploying li-ion batteries in our data centers? The most obvious reason is capital expenditure. For the equivalent energy capacity, li-ion solutions still cost anywhere from double to triple what the equivalent lead acid batteries cost to acquire. Even so, li-ion is now a highly economic alternative when considering the entire useful life of the battery. This was not necessarily the case as little as just a few years ago. The reason is that the cost of lithium-ion batteries has plummeted this decade. Whereas prices per kWh have sunk to under $200 now, lithium-ion batteries in 2010 cost five times as much as they do today. So, just a few short years ago, these batteries were in fact prohibitively expensive. Not everyone may be aware of how the math for datacenter UPS batteries has recently changed.

That’s totally expensive! Or not?

The most convincing argument for lithium-ion batteries is their low total cost of ownership. And that derives mainly (but not exclusively) from their considerably longer useful life. VRLA batteries in medium-sized UPS applications only last somewhere between three to six years. A lithium ion battery of the same capacity can be expected to easily last over 10 years, in most cases 12 or more. With the planned life of a UPS often somewhere between 10 and 15 years, that means a lithium-ion battery can last for the entire useful life of the UPS system. With VRLA technology, you would need to replace the batteries at least twice and possibly three times during the same period. This generates significant costs which can exceed the premium you pay up front to acquire lithium-ion batteries.

Put your batteries on a diet

Lithium-ion batteries can also take up 90% less floor space in the data center, leaving you more room for compute or storage capacity or, alternatively, reducing your space requirements and lease or construction costs. They also weigh considerably less (-86%), which reduces transportation costs by meaningful amounts. Another factor to consider are energy costs, which for li-ion can up to 50% lower than what the equivalent VRLA would consume over the same period. So although the $/Watt acquisition costs for li-ion can be double that of a comparable VRLA battery, operating costs for VRLA over a ten year period can be triple those of li-ion, outweighing the cheaper acquisition cost of the VRLA system and batteries for as much as a 25% cost reduction over 10 years.

Outlook

We’re getting a lot of inquiries about li-ion UPS systems these days. It’s no wonder. In addition to the benefits mentioned above, lithium-ion systems are also generally more sophisticated and customers can put them on their CAN bus. They charge faster, which can be an advantage in certain situations. But with the electrification of the transportation sector now underway, some of the natural resources required to build these batteries are in short supply. The price of cobalt in particular has risen sharply. There are efforts to use substances such as polymers to replace at least some of the cobalt in these batteries, but polymers have drawbacks as well (swelling).

Therefore it is difficult to tell whether the price of li-ion batteries will continue sink as rapidly as it has in recent years. That doesn’t have to be a concern, however, so long as the benefits from a total-cost-perspective are there, and now they clearly are. The steadily declining prices of lithium-ion batteries in recent years have been like a tiny mouse, knawing away at the rope around the lion’s neck until one day, the beast was freed. And that day has come.

Sources: https://about.bnef.com/blog/rapid-growth-data-centers-boon-lithium-batteries/