Is the use of lithium batteries in data centres already completely superior to lead-acid batteries?

Lithium batteries are a generic term for lithium metal batteries and lithium ion batteries, commonly referred to as lithium ion batteries, which are characterised by the absence of lithium in the metallic state and support repeated charging and discharging.

The history of lithium batteries is an interesting one. It was back in 1979 that Professor John Goodenough of Oxford University first demonstrated that lithium cobaltate could be used to make rechargeable batteries capable of storing energy.

In 1991, Sony combined a lithium cobaltate cathode with a carbon anode to produce the first commercially available rechargeable battery.

Since then, the technology has enabled portable computers and mobile phones to become smaller and more powerful. As the energy density and safety performance of lithium-ion batteries continue to improve and their cost continues to fall, lithium is increasingly in demand in communications, power, powered vehicles, data centres and other areas. 

Today, lithium batteries power almost every portable device on the planet, including mobile phones, laptops and tablets. Lithium batteries are also on their way to becoming the next generation of mainstream energy.

Disadvantages of Lead-acid Batteries in Data Centers

• Uninterruptible power supply auto shut down after unplanned power outage causes the battery to run out

• The battery needs to be inspected and discharged every quarter, increasing operation and maintenance costs

• No power supply priority, no high power supply level for important services

• The overall business interruption caused by UPS failure

The Computer Room Problem of Lead-acid Battery Centralized Power Distribution

Although lead-acid batteries appeared hundreds of years earlier than lithium batteries, and the products have matured, there are still many shortcomings that cannot be remedied technically. These shortcomings cause lead-acid batteries to have many problems when forming UPS units to provide backup power for data centers!

Low utilization rate of machine room space and high construction cost

• The space ratio between UPS Systems and IT equipment is approximately 1:3

• The load-bearing capacity of the data center computer room is approximately 16kN/m2

The future demand is not clear, and the elastic expansion is insufficient

• Long design demonstration cycle and large initial investment

• Early power supply equipment is often in light load operation

• Expansion and transformation and system cutover are difficult to implement

Stand-alone capacity is getting bigger and bigger, and it is difficult to operate and maintain

• Large UPS power supply requires professional UPS maintenance personnel

• Lead-acid batteries need regular inspections

• Rely on the stand-alone reliability of UPS Systems 

Why use Lithium Batteries?

Consumer electronics companies typically use lithium-ion cobalt batteries, which feature a capacity of a few amp hours. These uninterruptible power supply systems are equipped with rectangular lithium-manganese batteries with an installed capacity of 60 amp hours, offering a longer service life and multiple levels of fail-safe protection. They have an installed capacity of 60 amp-hours and feature a longer service life and multiple levels of fault protection. Individual modules and sometimes even individual cells are responsible for monitoring key performance parameters such as temperature, voltage and current. 

Sometimes the power cabinet or even the entire system can be responsible for such a monitoring process. Monitoring is necessary for full control of the charging and discharging process and to prevent critical heat generation and irreversible chemical processes from occurring. Lithium-ion batteries also offer higher energy density (Wh/kg) and higher output power density (W/kg). They are approximately three times lighter than lead-acid batteries for a similar energy storage capacity, which helps to reduce the total mass of the system by approximately 60-80%.

In recent years, data centres have been aiming to increase their power density given their space constraints and the need for more efficient operations. Making more efficient use of available space is one of the most relevant tasks for data centre owners. 

Compact lithium-ion batteries can reduce the area occupied by uninterruptible power supply systems by 50-80%. These batteries require less charging time and have a better self-discharge rate, which plays an important role in the event of frequent power outages. Lithium-ion batteries lose about 1-2% of their charge per month when they are left idle. 

The most important advantage is its long service life. Lead-acid batteries have a fairly short lifespan, from 3 to 6 years. Lithium-ion batteries, on the other hand, should have a service life of around 10 years. Depending on chemistry, technology and temperature, they are characterised by a charge efficiency of up to 5000 life cycles and are maintenance-free, whereas lead-acid batteries have an average charge efficiency of only 700 life cycles.

Ease of replacement

Every end customer eventually asks themselves the most important question. Is now the right time to upgrade our UPS systems to Li-Ion batteries? To answer this question, the first thing to consider is the availability of technical capabilities. Not all models of UPS will be able to use the new batteries and may require extensive hardware and embedded software upgrades. Even at the same nominal voltage, the characteristics of the battery charge and discharge can vary.

Typical UPS systems in data centres typically have a life expectancy of 10-15 years. Lead acid batteries have an operating life of 3-6 years, while lithium ion batteries have an operating life of 10 years or more. At the beginning of the UPS system's life (less than 5 years) it will prove useful to replace a significant proportion of the lead-acid batteries. 

However, when it comes to lithium-ion batteries, they are most likely to last until the day the UPS system fails. If your UPS system is nearing the mid-point of its useful life, the batteries may last longer and in most cases it does not make sense to replace them. 

At the end of their useful life, consideration should be given to replacing the entire UPS system with a new lithium-ion battery solution. However, even for an older UPS system, it may be expedient to install expensive batteries. You should take into account their decreasing price and the ratio of the maintenance costs of the old system to the full replacement cost.

Compared to lead-acid batteries, the total cost of ownership of a 10-year lithium battery (the average life of a data centre UPS) is down 39%. While this is an optimistic estimate, at least a 10% cost saving is guaranteed. Lithium-ion batteries have only one serious drawback - the initial investment is much higher. This is why large data centres have been pioneers when it comes to introducing new solutions. 

For such facilities, lowering TCO is more important than reaping any short-term benefits, and in this case even a small monetary saving can be significant. In addition, compact batteries make more efficient use of available space, while reliable monitoring systems ensure better safety and consistent performance. Lithium-ion batteries can operate at higher temperatures than VRLA without loss of capacity, thus reducing the load on the cooling system. 

Of course, there are even single-phase UPS with lithium-ion batteries. starting from the largest data centres and industrial applications, to small server rooms and even individual racks, there is a model for every application.

Uninterruptible Power Supply Battery Replacement--Lithium Battery

What are the advantages of lithium batteries as uninterruptible power supply alternatives to lead-acid batteries? In my opinion, the most basic thing is that the life of lithium batteries is 2-3 times that of lead-acid batteries, up to 10 years, so the uninterruptible power supply life expectancy is about 10 years, which makes UPS backup systems long lasting. In addition, the uninterruptible power supply and maintenance of lithium batteries are simpler, reducing operation and maintenance costs.

Lithium Battery Uninterruptible Power Supply Benefits

Save data center space

• No need for UPS battery backup room and battery room;

• Increase the utilization rate of computer room space by more than 30%

Reduce the load-bearing capacity of the data center

• The weight of the power supply is equivalent to that of IT equipment;

• Low floor load-bearing requirements;

• Reduce construction costs

Flexible on-demand configuration

• Modular design, deployment on demand;

• The early design goes online quickly;

• Easy to expand later

Reduce operating costs

• Hot-swappable, easy to maintain;

• The system can dynamically adjust the load rate;

• Good energy-saving effect

The introduction of lithium battery power improves the reliability and service life of the power supply system, reduces the weight of the equipment, and improves the space utilization of the data center.

What materials are recommended for lithium-ion batteries in data centres?

The 2019 Nobel Prize in Chemistry was awarded to John B Goodenough, M. Stanley Whittingham and Akira Yoshino for their contributions to the development of lithium-ion batteries.

In particular, John Goodenough became the oldest Nobel Laureate in history and his lifetime of exploration of lithium batteries is particularly admired, with lithium iron phosphate (LFP) as one of his key contributions, and lithium iron phosphate is also considered to be the safest and most environmentally friendly cathode material available for lithium-ion batteries.

Lithium, especially lithium iron phosphate in data centres and communications base stations, as the old man's name suggests, has been Goodenough.

Currently, the industry's mainstream lithium is divided into lithium cobaltate, lithium manganate, lithium iron phosphate and ternary lithium. Lithium cobaltate is mainly used in the mobile phone battery industry; lithium manganate is mainly used in the electric bicycle industry; lithium iron phosphate is widely used in bus / bus energy storage, energy storage power station; lithium ternary is widely used in home car / taxi energy storage, energy storage power station industry. Lithium iron phosphate and lithium ternary are commonly used in data centre scenarios, with lithium iron phosphate being more reliable and lithium ternary having an advantage in energy density.

Figure 2: Molecular structures of different Lithium-ion batteries.

Source: Soroosh Sharifi-Asl, et al., Oxygen Release Degradation in Lithium-ion Battery Cathode Materials: Mechanisms and Mitigating Approaches. Adv. Energy Mater. 2019, 1900551

Challenges for Data Center Lithium Applications

In addition to reliability and cost issues, there are also a number of issues that will be critical to the future adoption of lithium-ion in the data centre.

Challenge 1: Current equalisation between cabinets. When multiple cabinets are connected in parallel, current imbalance occurs due to inconsistent cell resistance and capacity and power distribution differences, especially for short-time discharge of large currents. As a result, overcurrent protection is triggered in each battery cabinet.

Challenge 2: Online capacity expansion of old and new battery cabinets. Partial failure is unavoidable in a Lithium-ion battery system. Capacity expansion is required due to load increase. New and old battery cabinets may be connected in parallel. If resistance and capacity are inconsistent when new and old battery cabinets are used together, serious bias current can be caused, and a battery cabinet can even be disconnected due to overcurrent.

Challenge 3: Voltage equalisation of cells connected in series. Inconsistency of cell resistance and capacity in a battery can cause cell charge overvoltage, rendering the entire battery system unable to be fully charged.

Challenge 4: Troubleshooting. If a battery module in a battery string is faulty, the entire battery string cannot work properly. Quick battery replacement is difficult.

Challenge 5: Fire control. If fire occurs in a Lithium-ion battery cabinet after Lithium-ion batteries are deployed in a modular data centre, it is hard to control the fire inside the cabinet and prevent it from spreading to ICT equipment nearby. 

Although UPS systems powered by lithium-ion batteries significantly reduce operating costs and total cost of ownership, a large proportion of customers still use VRLA time-of-use solutions. This can first be explained by the fact that it is the use of lithium-ion batteries that is beneficial from a long-term perspective. However, it does add significantly to the capital costs. In any case, customer interest in innovation is increasing year on year and will only continue to do so. For large data centres, the savings can be enormous, so lithium-ion power systems will increasingly be used in the enterprise sector. Lithium-ion chemistry is also advancing. Over time, new solutions and technologies will emerge and the price of lithium-ion batteries will fall further.

BSLBATT Uninterruptible Power Supply System (UPS)

BSLBATT's lithium battery Power backup systems adopts a line-interactive topology design, which can not only provide power outage protection for data centers, but also provide guaranteed power protection for desktop computers, workstations, personal electronic products, and home networks/VoIP. They provide analog sine wave battery backup power during power outages, maintain a stable voltage during power outages, and provide surge protection to prevent overvoltage and power spikes. Features include automatic voltage regulation (AVR), energy-saving design, data line protection and management software, which can easily control and monitor your UPS.