Exploring the Five Main Lithium-Ion Battery Chemistries for UPS Use Cases

 

DECEMBER 14, 2023

 

by J.J. Hocken, Product Manager Batteries & DC Technologies

In this edition of The Runaway Review, we will explore the five major lithium-ion battery chemistries that are currently available in the UPS battery backup industry. We will briefly define the specific attributes of each chemistry and the different use cases that may apply.

 

Knowing the main attributes and the primary optimal use cases for each lithium-ion chemistry will enhance the safety of the UPS system design and reduce operational downtime. 

Lithium Manganese Oxide (LMO) 

LiMn₂O₄

 

LMO has low internal cell resistance that enables fast charging and high-current discharging. It is typically mixed with NMC, and the NMC improves specific energy and prolongs the life span of the battery.

 

The result is a power dense battery with a relatively long life that can discharge quickly and safely. The typical LMO UPS battery use case is not intended for long discharges in energy capacity and is best used for traditional UPS mission critical applications of 3 -15-minute backup times. 

 

 

Lithium Nickel Manganese Cobalt Oxide (NMC) 

LiNiMnCoO₂

 

NMC is one of the most versatile battery chemistries, largely due to the two main elements in the chemical structure. The first is Nickel, which is known for its high specific energy but poor stability. The second is Manganese, which has the structure stability to gain low internal resistance with a low specific energy. The many different combinations available can be used to tailor the battery cells to be either an energy cell or a power cell.

 

In UPS applications, the NMC battery chemistry can be utilized in both a traditional mission critical use case or possibly a grid interactive energy capacity use case, depending on the overall NMC’s chemical properties. 

 

 

Lithium Iron Phosphate (LFP) 

LiFePO₄

 

LFP* can be kept at high voltages for prolonged periods and tends to be more tolerant of full charge conditions than other lithium-ion battery chemistries. Additionally, the lithium phosphate in this battery chemistry can self-discharge at higher rates, causing cell balancing issues as the battery ages.

 

LFP is known for its flat discharge voltage profile. Typically, LFP has a lower energy capacity, but a higher power density. In energy storage, LFP is typically used at lower discharge C rates from .5C to .25C. There are some LFP chemistries that mix in other lithium-ion, such as NMC, to increase the energy density.

 

LFP is a suitable choice for UPS mission critical applications with shorter runtimes given the energy and power density attributes. Due to the lower energy density, it typically has a larger overall UPS battery system footprint than other chemistries for the same system runtime.

 

The LFP chemistry is suitable for high cycle life usage but with controlled extended discharge time periods like many solar and battery energy storage use cases. 

 

*The LFP described is a traditional LFP battery chemistry and not a hybrid mix with other chemistries.

 

 

Lithium Nickel Cobalt Aluminum Oxide (NCA) 

LiNiCoAlO₂

 

NCA adds aluminum to lithium nickel oxide. The aluminum supports this chemistry with enhanced stability. NCA has good specific power and a long design life span. NCA is extremely popular as an energy cell in energy storage and electric vehicles and has a high energy capacity.

 

Presently, it is uncommon to see NCA in the UPS industry as other chemistries are more dominant. This may change as more grid interactive use cases are designed in UPS applications. NCA is a battery that does well with constant discharge cycles of 1C or below, as high discharge rates can reduce its design life.

 

 

Lithium Titanate (LTO) 

Li₂TiO₃

 

In LTO, the graphite in the anode is replaced with titanate. The cathode can be either LMO or NMC. The titanate in the anode allows the chemistry to have faster charging rates while also increasing the cycle life of the battery.

 

LTO technology is typically more expensive due to the titanate cost and the overall process of how the battery is produced. The chemistry is very safe and has an extended life span if used properly. It has a lower specific energy than other lithium-ion battery chemistries. 

 

In the UPS industry, LTO in general has a slight disadvantage in overall footprint and power density due to the lower cell voltage. However, LTO is still a viable option for mission critical applications and some grid interactive use cases.  

 

 

Importance of choosing the right lithium-ion battery chemistry for your use case

Batteries are stored energy devices from which other pieces of equipment or electric circuits pull or draw power. Batteries have different internal resistances, impedances, charge rates, discharge rates, power ratings, energy capacity ratings, and stability properties. Using a battery that is not well-suited for the use case can lead to safety issues and/or thermal runaway.

 

A common mistake is to misuse the battery chemistry of the backup system by imposing that system discharge/charge rates and overall cycle rates not intended for that battery chemistry. This can cause excessive thermal stress, erratic operation, and battery design degradation. The correct battery system is the chemistry that meets the goals of the system. Those goals may include, but are not limited to:

• Economics: CAPEX & OPEX goals of the project
• Safety: The acceptable risk and safety goals of the project
• Sustainability: The design life, carbon footprint, and emissions goals of the project
• Design: The power, energy, cycle rates, footprint, and overall use case goals of the project

Interested in what lithium-ion battery chemistries Mitsubishi Electric currently offers?

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