Hello, friends!
After the publication of the article there were many comments regarding the dangers of Li-Ion solutions for servers and data centers. Therefore, today we will try to understand the differences between industrial lithium solutions for UPSs and the batteries in your gadgets, how the operating conditions of batteries differ in servers, why a Li-Ion battery in a phone lasts no more than 2-3 years, while in a data center this figure can increase to 10 years or more. Why the risks of lithium fires in data centers/servers are minimal.
Yes, accidents with UPS batteries can occur regardless of the type of energy storage, but the myth of the 'flammability' of industrial lithium solutions is not true.
After all, many have seen that with a lithium battery in a moving car, right? So let’s take a closer look, analyze, and compare…
Here we see a typical case of uncontrolled self-heating, thermal runaway of a phone battery that led to such an incident. You might say: 'LOOK! This is just a phone, only a madman would put that in a server room!'
I am confident that after studying this material, the reader will change their viewpoint on this issue.
The current situation in the data center market
It is no secret that building a data center is a long-term capital investment. The price of engineering equipment alone can account for 50% of all capital expenditures. The payback period is approximately 10-15 years. Naturally, there is a desire to reduce the total cost of ownership throughout the entire lifecycle of the data center, while also maximizing the space available for useful loads.
The optimal solution is industrial UPS systems of a new iteration based on Li-Ion batteries, which have long overcome the 'growing pains' in the form of flammability, incorrect charge-discharge algorithms, and have gained numerous protective mechanisms.
With the increase in computing and networking equipment capacities, the demand for UPS systems is growing. At the same time, the requirements for the autonomous operation time of batteries in case of issues with centralized power supply and/or failures during the startup of backup power sources in case of using/having DGs are also increasing.
In our opinion, there are two main reasons for this:
- The rapid growth of processed and transmitted information volumes
For example, , which
needs to be stored and processed. - The growth dynamics of electrical energy consumption. Despite the overall trend of decreasing energy consumption of IT equipment, there is a reduction in specific energy consumption by electronic components.
The energy consumption chart of a single operational data center
This same trend is reflected in data center market forecasts in our countryAccording to the website, the total number of commissioned rack spaces exceeds 20 thousand. "The number of commissioned rack spaces among the 20 largest data center service providers increased by 3% in 2017, reaching 22.4 thousand (data as of October 1, 2017)," says the CNews Analytics report. Consulting agencies estimate that by 2021, the number of rack spaces will increase to 49 thousand. This means, in two years, the actual capacity of data centers could double. What is this related to? Primarily, the growth in information volumes: both stored and processed.
In addition to cloud services, players identify the development of data center capacities in the regions as a growth point: they are the only segment where there is still potential for business development. According to IKS-Consulting, in 2016, regions accounted for only 10% of all resources offered in the market, while the capital and the Moscow region accounted for 73% of the market, and St. Petersburg and the Leningrad region accounted for 17%. There continues to be a shortage of data center resources with high fault tolerance in the regions.
By 2025, according to forecasts, the total data volume in the world will increase tenfold compared to 2016.
Still, how safe is lithium for UPS in a server room or data center?
Disadvantage: high cost of Li-Ion solutions.
The price of lithium-ion batteries remains high compared to standard solutions. According to SE, the initial costs for powerful UPS over 100 kVA for Li-Ion solutions will be 1.5 times higher, but in the end, total ownership savings will be 30-50%. Comparing with the military-industrial complex of other countries, here is the news about the launch of with Li-Ion batteries. Lithium iron phosphate batteries (shown in the photo - LFP) are often used in such solutions due to their relative affordability and higher safety.
The article mentions that $100 million has been spent on new batteries for the submarine; let's try to convert this into other metrics...4,200 tons - underwater displacement of the Japanese submarine. Surface displacement is 2,950 tons. Typically, 20-25% of the mass of the boat consists of batteries. Therefore, we take approximately 740 tons — lead-acid batteries. Next: the mass of lithium is about 1/3 of lead-acid batteries -> 246 tons of lithium. At 70 kWh/kg for Li-Ion, we get approximately 17 MWh of battery array capacity. And the difference in battery mass is approximately 495 tons... Here we do not take into account , which require 14.5 tons of silver for one submarine, and their cost exceeds lead-acid batteries by 4 times. I remind you that Li-Ion batteries are currently only 1.5-2 times more expensive than VRLA, depending on the power of the solution.
And what about the Japanese? They remembered too late that "lightening the boat" by 700 tons leads to changes in its seakeeping qualities and stability... They probably had to add armaments on board to restore the design weight distribution values of the boat.
Lithium-ion batteries also weigh less than lead-acid batteries, so the design of the Soryu-class submarine had to be slightly modified to maintain ballast and stability.
In Japan, two types of lithium-ion battery systems have been created and brought to operational status: lithium nickel cobalt aluminum oxide (NCA) produced by GS Yuasa and lithium titanate (LTO) produced by Toshiba. The Japanese fleet will use NCA-type batteries; according to Kobayashi, Australia recently proposed LTO-type batteries for use on Soryu-class submarines in a recent tender.
Knowing the meticulous attitude towards safety in the Land of the Rising Sun, one can assume that lithium safety issues have been resolved, tested, and certified.
Risk: flammability.
Here we will address the purpose of the publication, as there are diametrically opposed opinions regarding the safety of these solutions. But that's all preamble; what do we have with specific industrial solutions?
We have already discussed security issues in our , but let’s revisit this topic once more. Let us refer to the diagram that examined the protection level of the module and cell of the LMO/NMC battery manufactured by Samsung SDI, used in the UPS by Schneider Electric.
The chemical processes were discussed in the article by the user Let’s start with the general case of the risk flowchart and the causes of lithium-ion cell ignition.
And closer? The photo is clickable.
The initial flowchart of risks and causes of ignition (Safety Hazard) of the lithium-ion cell fromthe scientific article Since, depending on the chemical structure of the lithium-ion cell, there are differences in the thermal runaway characteristics of the cell, we will focus here on the process described in the article concerning the lithium-nickel-cobalt-aluminum cell (based on LiNiCoAIO2) or NCA.
The process of accident development in the cell can be divided into three stages:
Stage 1 (Onset). Normal operation of the cell, when the temperature rise gradient does not exceed 0.2 °C per minute, and the cell temperature does not exceed 130-200 °C depending on the chemical structure of the cell;
- Stage 2, heating (Acceleration). At this stage, the temperature rises, the temperature growth gradient increases rapidly, and there is active heat release. In general, this process is accompanied by gas emission. Excessive gas release must be compensated by the activation of the safety valve.
- Stage 2, heating (Acceleration). At this stage, the temperature rises, the temperature gradient increases rapidly, and there is active heat energy release. Typically, this process is accompanied by gas emissions. Excessive gas release must be compensated by the activation of the safety valve;
- Stage 3, thermal runaway. The battery heats up above 180-200 degrees. At this point, the cathode material undergoes a disproportionation reaction and releases oxygen. This is the level of thermal runaway, as a mixture of flammable gases with oxygen may occur, leading to self-ignition. However, this process can sometimes be managed; for instance, if the external factors change, thermal runaway can stop in some cases without fatal consequences for the surrounding space. The integrity and functionality of the lithium cell after these events are not considered.
The temperature of thermal runaway depends on the cell size, cell design, and material. The temperature of thermal runaway can range from 130 to 200 degrees Celsius. The time of thermal runaway can vary, taking minutes, hours, or even days...
What about the LMO/NMC type cells in lithium-ion UPS?
To prevent contact between the anode and the electrolyte, a ceramic layer is used in the cell (SFL). Lithium ion movement is blocked at 130 degrees Celsius.
In addition to the protective ventilation valve, a protection system against overcharging (Over Charge Device, OSD) is used, which works in tandem with an internal fuse and disconnects the damaged cell, preventing the thermal runaway process from reaching dangerous levels. Moreover, the internal OSD system will trigger earlier, at a pressure of 3.5 kg/cm², that is, half of the activation pressure of the cell's protective valve.
By the way, the cell fuse will activate at currents exceeding 2500 A within no more than 2 seconds. Suppose the temperature gradient reached a reading of 10 degrees Celsius per minute. In 10 seconds, the cell would increase its temperature by about 1.7 degrees while in the runaway mode.
The three-layer separator in the cell during overcharging will block the transition of lithium ions to the anode of the cell. The blocking temperature is 250 degrees Celsius.
Now let's look at what we have with the cell temperature; let's compare at which stages different types of protection are triggered at the cell level.
— OSD system – 3.5±0.1 kg/cm² <= external pressure
Additional protection against overcurrents.
— pressure relief valve 7.0+-1.0 kgf/cm² <= external pressure
— fuse inside the cell for 2 seconds at 2500A (overload current mode)
The risk of thermal runaway in a cell directly depends on the state of charge of the cell; more details here...Let's consider the effect of the cell's state of charge in the context of the risks of thermal runaway. We will examine the temperature correspondence table of the cell based on the SOC (State of Charge).
The state of charge of a battery is measured in percentage and indicates what portion of the total charge remains stored in the battery. In this case, we are looking at the battery's overcharge mode. It can be concluded that depending on the chemical composition of the lithium cell, the battery may behave differently during overcharging and have varying tendencies toward thermal runaway. This is due to the differing specific capacity (Ah/gram) of various types of Li-Ion cells. The higher the specific capacity of the cell, the more rapid the heat generation will be during overcharging.
Furthermore, at 100% SOC, external short circuits often lead to thermal runaway of the cell. On the other hand, when the cell has a charge level of 80% SOC, the maximum temperature at which thermal runaway begins shifts upward. The cell becomes more resistant to failure modes.
Finally, for 70% SOC, external short circuits may not be a cause of thermal runaway at all. This means that the risk of cell ignition is significantly reduced, and the most likely scenario is merely the activation of the lithium battery's pressure relief valve.
Additionally, from the table, it can be concluded that LFP (purple curve) batteries typically exhibit a steep increase in temperature, meaning the 'heating' phase smoothly transitions into the 'thermal runaway' phase, and the system's resistance to overcharging is somewhat poorer. Batteries of the LMO type, as we see, exhibit a more gradual heating characteristic during overcharging.
IMPORTANT: When the OSD system is triggered, the cell is switched to bypass. This reduces the voltage on the rack, but it remains operational and sends a signal to the UPS monitoring system via the BMS system of the rack itself. In a classic UPS system with VRLA batteries, a short circuit or break within one battery in the string can lead to a complete UPS failure and a loss of IT equipment functionality.
Based on the above, the following risks remain relevant for the use of lithium solutions in UPS systems:
- Thermal runaway of the cell or module due to external short circuit – several levels of protection.
- Thermal runaway of the cell or module due to internal battery failure – several levels of protection at the cell and module level.
- Overcharging – protection through BMS plus all levels of protection for the rack, module, and cell.
- Mechanical damage – irrelevant for our case; the risk of this event is negligible.
- Overheating of the rack and all batteries (modules, cells). Not critical up to 70-90 degrees. If the temperature in the UPS installation room rises above these values, it indicates a fire in the building. Under normal operating conditions of the data center, the risk of this event is negligible.
- Reduced battery life at elevated room temperatures – prolonged operation at temperatures up to 40 degrees is acceptable without significant reduction in battery resources. Lead-acid batteries are very sensitive to any increase in temperature and reduce their remaining capacity proportionally to the increase in temperature.
Let's take a look at the risk flowchart for incidents with lithium-ion batteries in our data center and server use case. We will simplify the scheme a bit, as lithium UPS systems will operate under ideal conditions compared to the operating conditions of batteries in your gadget or phone.
CONCLUSION: Specialized lithium batteries for UPS data centers and server rooms have sufficient protection against emergency situations. The comprehensive solution provides numerous levels of diverse protection, and over five years of operational experience with these solutions assures a high level of safety for new technologies. Furthermore, it's essential to note that the usage of lithium batteries in our sector resembles 'greenhouse' conditions for Li-Ion technologies: unlike your smartphone in your pocket, the battery in a data center won't be dropped, overheated, drained daily, or actively used in backup mode.
To learn more and discuss a specific solution using lithium-ion batteries for your server room or data center, you can send a request to the email , or make a request on the company website .
OPEN TECHNOLOGIES – reliable comprehensive solutions from world leaders, tailored specifically to your goals and tasks.
Author: Oleg Kulikov
Lead Design Engineer
Department of Integration Solutions
Open Technologies Company
Only registered users can participate in the survey. , please.
What is your opinion regarding the safety and applicability of industrial solutions based on Li-Ion technologies?
16,2%It's dangerous, can self-ignite, I would never put it in my server room.
10,3%I'm not interested, and we periodically change classic batteries, and everything is fine.
16,2%I need to think about it, it might be safe and promising.
23,5%Interesting, I will consider the possibilities.
13,2%I'm interested! Invest once – and not worry about taking down the entire data center due to the failure of a single lead battery.
20,6%Interesting! The advantages far outweigh the downsides and risks.
68 users voted. 25 users abstained.
Source: habr.com
