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After the publication of the article there were many comments about the dangers of Li-Ion solutions for server and data centers. Therefore, today we will try to figure out what is the difference between industrial lithium-based solutions for a UPS and a battery in your gadget, how battery operating conditions differ in a server room, why a Li-Ion phone battery lasts no more than 2-3 years, and in a data center this figure will increase to 10 years or more. Why the risks of lithium ignition in the data center / server room are minimal.
Yes, accidents on UPS batteries are possible regardless of the type of energy storage devices, but the myth of the “fire hazard” of industrial solutions based on lithium is not true.
After all, many have seen with a lithium battery in a car moving on a highway? So let's see, let's see, let's compare...
Here we see a typical case of uncontrolled self-heating, thermal runaway of the phone battery, which led to such an incident. You say: WOW! It's just a phone, only a madman would put it in a server room!
I am sure that after studying this material, the reader will change his point of view on this issue.
The current situation in the data center market
It's no secret that building a data center is a long-term investment. The price of only engineering equipment can be 50% of the cost of all capital costs. The payback horizon is approximately 10-15 years. Naturally, there is a desire to reduce the total cost of ownership throughout the entire life cycle of the data center, and along the way, also compact the engineering equipment, freeing up space for the payload as much as possible.
The optimal solution is industrial UPSs of a new iteration based on Li-Ion batteries, which have long since got rid of "childhood diseases" in the form of a fire hazard, incorrect charge-discharge algorithms, and have acquired a mass of protective mechanisms.
With the increase in the capacity of computing and network equipment, the demand for UPS is growing. At the same time, the requirements for battery backup time increase in case of problems with centralized power supply and / or failures when starting a backup power source in the case of using / having a diesel generator set.
There are two main reasons, in our opinion:
- The rapid growth of the volume of processed and transmitted information
For example, the , which
need to be saved and processed. - Growth of electric energy consumption dynamics. Despite the general trend of reducing the energy consumption of IT equipment, reducing the specific energy consumption of electronic components.
Graph of energy consumption of just one operating data center
The same trend is demonstrated by data center market forecasts in our country.According to the site, the total number of rack spaces put into operation is more than 20 thousand. according to the CNews Analytics report. According to consulting agencies, by 20 it is projected to increase the number of rack spaces to 2017. That is, in two years the real capacity of the data center can double. What is it connected with? First of all, with the growth of the volume of information: both stored and processed.
In addition to clouds, players rank the development of data center capacities in the regions as growth points: they are the only segment where there is a reserve for business development. According to IKS-Consulting, in 2016 the regions accounted for only 10% of all resources offered on the market, while the capital and the Moscow region occupied 73% of the market, and St. Petersburg and the Leningrad region - 17%. In the regions, there is still a shortage of data center resources with a high degree of fault tolerance.
By 2025, according to forecasts, the total amount of data in the world will increase 10 times compared to 2016.
Still, how safe is lithium for a server or data center UPS?
Disadvantage: high cost of Li-Ion solutions.
The price of lithium-ion batteries is still high compared to standard solutions. SE estimates that the initial cost for high power UPSs over 100 kVA for Li-Ion solutions will be 1,5 times higher, but ultimately the savings in ownership will be 30-50%. If we make comparisons with the military-industrial complex of other countries, then here is the news about the launch in with Li-Ion batteries. Quite often, lithium-iron-phosphate batteries (on the photo - LFP) are used in such solutions due to their relative cheapness and greater safety.
The article mentions that $100 million was spent on new batteries for the submarine, let's try to recalculate in other values ...4,2 thousand tons - underwater displacement of the Japanese submarine. Surface displacement - 2,95 thousand tons. As a rule, 20-25% of the weight of the boat is batteries. From here we take about 740 tons - lead-acid batteries. Further: the mass of lithium is approximately 1/3 of lead-acid batteries -> 246 tons of lithium. At 70 kWh/kg for Li-Ion, we get about 17 MWh of battery array power. And the difference in the mass of the batteries is about 495 tons ... Here we do not take into account , in which one submarine needs 14,5 tons of silver, and at a cost they exceed lead-acid batteries by 4 times. Let me remind you that Li-Ion batteries are now 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 entails a change in its seaworthiness, stability ... They probably had to add weapons on board in order to return the design values of the weight of the boat.
Lithium-ion batteries also weigh less than lead-acid batteries, so the design of the Soryu-class submarine had to be redesigned somewhat to maintain ballasting and stability.
In Japan, two types of lithium-ion batteries have been created and brought to operational condition: lithium-nickel-cobalt-aluminum-oxide (NCA) manufactured by GS Yuasa and lithium-titanate (LTO) manufactured by Toshiba Corporation. The Japanese navy will use NCA-type batteries, with LTO-type batteries being proposed in a recent tender for use in submarines based on the Soryu type, according to Kobayashi, Australia.
Knowing the reverent attitude to safety in the Land of the Rising Sun, we can assume that lithium safety issues have been resolved, tested and certified.
Risk: fire hazard.
Here we will figure it out for the purpose of publication, since there are diametrically opposed opinions about the security of these solutions. But this is all poetry, but what about specific industrial solutions?
Security issues have already been discussed in our , but once again we will dwell on this issue. Let's turn to the figure, which considered the level of protection of the module and cell of the LMO / NMC battery manufactured by Samsung SDI and used as part of the Schneider Electric UPS.
Chemical processes have been covered in the user's article . Let's try to understand the possible risks in our particular case and compare them with multi-level protection in Samsung SDI cells, which are an integral part of the finished Type G Li-Ion rack as part of an integrated solution based on Galaxy VM.
Let's start with the general case of a block diagram of the risks and causes of a lithium-ion cell ignition.
Under the spoiler, you can study the theoretical issues of the risks of ignition of lithium-ion batteries and the physics of processesThe original block diagram of the risks and causes of ignition (Safety Hazard) of a lithium-ion cell from 2018 year.
Since, depending on the chemical structure of the lithium-ion cell, there are differences in the thermal runaway characteristics of the cell, here we will focus on the process described in the article in a lithium-nickel-cobalt-aluminum cell (based on LiNiCoAIO2) or NCA.
The development of an accident in a 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 itself does not exceed 130-200 °C, depending on the chemical structure of the cell;
- stage 2, warming up (Acceleration). At this stage, the temperature rises, the temperature growth gradient rapidly increases, and there is an active release of thermal energy. In general, this process is accompanied by the release of gases. Excessive outgassing must be compensated by actuation of the safety valve;
- stage 3, thermal runaway (Runaway). Battery heating over 180-200 degrees. In this case, the cathode material enters into a disproportionation reaction and releases oxygen. This is the level of thermal runaway, since in this case a mixture of combustible gases with oxygen may occur, which will cause spontaneous combustion. However, this process in some cases can be controlled, read - when the regime of external factors changes, thermal runaway in some cases stops without fatal consequences for the surrounding space. The serviceability and performance of the lithium cell itself after these events is not considered.
The thermal runaway temperature depends on cell size, cell design, and material. The thermal runaway temperature can vary from 130 to 200 degrees Celsius. Thermal runaway times can vary from minutes, hours, or even days…
And what about LMO / NMC type cells in lithium-ion UPSs?
– To prevent contact of the anode with the electrolyte, a ceramic layer is used in the composition of the cell (SFL). The blocking of the movement of lithium ions occurs at 130 gr.S.
– In addition to the protective vent valve, an overcharge protection system (Over Charge Device, OSD) is used, which works in tandem with an internal fuse and turns off the damaged cell, preventing the thermal runaway process from reaching dangerous values. Moreover, the operation of the internal OSD system will be earlier, when the pressure reaches 3,5 kgf / cm2, that is, half as much as the pressure of the cell safety valve.
By the way, the cell fuse will operate at currents above 2500 A in no more than 2 seconds. Assume that the temperature gradient has reached a reading of 10 C/min. In 10 seconds, the cell will have time to add about 1,7 degrees to its temperature while in overclocking mode.
– A three-layer separator in the cell in the overcharge mode will block the transition of lithium ions to the anode of the cell. The blocking temperature is 250°C.
Now let's see what we have with the cell temperature; Let's compare the stages at which different types of protections are triggered at the cell level.
– OSD system – 3,5+-0,1 kgf/cm2 <= external pressure
Additional overcurrent protection.
— safety valve 7,0+-1,0 kgf/cm2 <= external pressure
- fuse inside the cell 2 seconds at 2500A (over current mode)
The risk of cell thermal runaway directly depends on the degree/level of cell charge, more details here…Consider the effect of the cell charge level in the context of the risks of thermal runaway. Let's consider the cell temperature correspondence table from the SOC (State of Charge) parameter.
The state of charge of the battery is measured as a percentage and shows how much of the total charge is still stored in the battery. In this case, we are considering the battery recharge mode. It can be concluded that, depending on the chemical composition of the lithium cell, the battery can behave differently when overcharged and have a different tendency to thermal runaway. This is due to the different specific capacity (A * h / gram) of various types of Li-Ion cells. The greater the specific capacity of the cell, the more rapid will be the heat release during recharging.
In addition, at 100% SOC, an external short often results in thermal runaway of the cell. On the other hand, when the cell has a charge level of 80% SOC, the maximum temperature of the beginning of the thermal runaway of the cell is shifted upwards. The cell becomes more resistant to emergency modes.
Finally, for 70% SOC, external short circuits may not cause thermal runaway at all. That is, the risk of cell ignition is significantly reduced, and the most likely scenario is only the lithium battery safety valve tripping.
In addition, it can be concluded from the table that the LFP (purple curve) of the battery usually has a steep slope of temperature rise, that is, the “warm-up” stage smoothly turns into the “thermal runaway” stage, and the overcharging stability of this system is somewhat worse. Batteries of the LMO type, as we can see, have a smoother warm-up characteristic when recharging.
IMPORTANT: when the OSD system is triggered, the cell is reset to bypass. Thus, the voltage on the rack is reduced, but it remains in operation and gives a signal to the UPS monitoring system through the BMS system of the rack itself. In the case of a classic UPS system with VRLA batteries, a short circuit or open circuit inside one battery in the string can lead to the failure of the UPS as a whole and the loss of IT equipment.
Based on the foregoing, for the case of using lithium solutions in a UPS, the following risks remain relevant:
- Thermal runaway of a cell, module as a result of an external short circuit - several levels of protection.
- Thermal runaway of a cell, module as a result of an internal battery failure - several levels of protection at the level of the cell, module.
- Overcharge - protection by means of BMS plus all levels of protection of the rack, module, cell.
- Mechanical damage is irrelevant for our case, the risk of an event is negligible.
- Rack and all batteries (modules, cells) overheated. Uncritical up to 70-90 degrees. If the temperature in the UPS installation room rises above these values, then this is already a fire in the building. Under normal data center operating conditions, the risk of an event is negligible.
- Reduced battery life at elevated room temperatures - long-term operation at temperatures up to 40 degrees is allowed without a noticeable decrease in battery life. Lead batteries are very sensitive to any increase in temperature and will reduce their remaining life in proportion to the increase in temperature.
Let's take a look at the accident risk flowchart with lithium-ion batteries in our data center, server room use case. Let's simplify the circuit a little, because lithium UPSs will be operated in ideal conditions, if we compare the operating conditions of the batteries in your gadget, phone.
CONCLUSION: Specialized lithium batteries for UPS data centers, server rooms have a sufficient level of protection against emergency situations, and in the complex solution a large number of degrees of various protection and more than five years of experience in operating these solutions allow us to speak of a high level of safety of new technologies. Among other things, do not forget that the operation of lithium batteries in our sector looks like "greenhouse" conditions for Li-Ion technologies: unlike your smartphone in your pocket, no one will drop the battery in the data center, overheat, discharge it every day, actively use in buffer mode.
To learn more and discuss a specific Li-Ion battery solution for your server room or data center, please send an email request. or by making a request on the company's website .
OPEN TECHNOLOGIES – reliable integrated solutions from world leaders, adapted specifically to your goals and objectives.
Author: Kulikov Oleg
Lead Design Engineer
Department of Integration Solutions
Open Technologies Company
Only registered users can participate in the survey. , you are welcome.
What is your opinion on the safety and applicability of industrial solutions based on Li-Ion technologies?
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Present in several = 16,2%Dangerous, self-igniting, in no case will I put it in my server room.11
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Present in several = 10,3%I'm not interested, and so we periodically change classic batteries, and everything is OK.7
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Present in several = 16,2%We need to think, perhaps it is safe and promising.11
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Present in several = 23,5%Curious, I'll consider the possibilities.16
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Present in several = 13,2%Interested! Invest once - and not be afraid to fill up the entire data center due to the failure of one lead battery.9
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Present in several = 20,6%Interesting! The benefits far outweigh the downsides and risks.14
68 users voted. 25 users abstained.
Source: habr.com