Lithium energy storage

Wednesday, November 4, 2020
Training

You've probably heard of it...

There has been so much talk around lithium batteries that we decided to clear up the air and look at the different variations that abound, so here goes. . . .!

But why Lithium?

Lithium is the lightest of all metals and Australia is the world’s number one producer, accounting for 47% of global lithium output.

It has the greatest electrochemical potential and provides the largest specific energy per weight compared to traditional battery materials.


Lithium: the process

Lithium-ion batteries use a cathode (positive electrode), an anode (negative electrode) and electrolyte as conductor. 

During discharge, the ions flow from the anode to the cathode through the electrolyte and separator and the direction the ions flow from the cathode to the anode is reversed when charging.



Lithium: graphite anode

Most companies shifted to a graphite anode to attain a flatter discharge curve.  The graphite aids in long term stability and is used in lead pencils. A future material that promises to enhance the performance of Li-ion is graphene. 

Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a two-dimensional honeycomb lattice. The name is a portmanteau of "graphite" and the suffix -ene, reflecting the fact that the graphite allotrope of carbon consists of stacked graphene layers.


The Lithium List

Lithium batteries come in a variety of mixtures and the mains ones include:


  • LCO — Lithium Cobalt Oxide (LiCoO2)
  • LMO — Lithium Manganese Oxide (LiMn2O4)                                
  • NMC — Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
  • LFP — Lithium Iron Phosphate (LiFePO4)
  • NCA — Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2)
  • LTO — Lithium Titanate (Li2TiO3)


Lithium Cobalt Oxide (LiCoO2) — LCO

Its high specific energy, good for mobile phones, laptops and digital cameras but has a major drawback in that it has a relatively short life span, low thermal stability and limited load capabilities so this means it is not really applicable for renewable energy storage applications.   


Lithium Manganese Oxide (LiMn2O4) — LMO

LMO has low internal resistance and good current handling combined with high thermal stability and enhanced safety but the cycle and calendar life are limited. Li-manganese is used for power tools, medical instruments, as well as some hybrid and electric vehicles.


Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2) — NMC

NMC combines nickel and manganese. Nickel is known for its high specific energy but poor stability, while manganese has the benefit of achieving low internal resistance but offers a low specific energy.

Combining the metals enhances each other's strengths which has made NMC a battery of choice for power tools, e-bikes and other electric powertrains.

Battery manufacturers are moving away from cobalt toward nickel cathodes because of the high cost of cobalt and to a lesser extent, environmental factors. Nickel-based systems have higher energy density, lower cost, and longer cycle life than the cobalt-based cells but they have a slightly lower voltage.


Lithium Iron Phosphate (LiFePO4) — LFP

The key benefits are high current rating and long cycle life with good thermal stability, enhanced safety and tolerance if abused. Li-phosphate is more tolerant to full charge conditions but has higher self-discharge than other Li-ion batteries, which can cause balancing issues with aging. 


Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2) — NCA

High specific energy, reasonably good specific power and a long lifespan, however it is not as safe as others on the list, and is generally quite costly. The aluminium adds stability. High energy and good power density makes NCA a candidate for EV powertrains.

Lithium Titanate (Li2TiO3) — LTO

Can be fast charged, has high discharge current of 10C, or 10 times the rated capacity and the cycle count is said to be higher than that of a regular Li-ion. 

Li-titanate is safe, has excellent low-temperature discharge characteristics but, at this stage, is expensive. Some uses include: electric powertrains, UPS and solar-powered street lighting.

The comparison

As with most things in life, there is a cost benefit analysis that drives the commercial realities of different battery technologies. As we can see from the Watt Hour per Kilogram chart below, NCA enjoys the highest specific energy however its safety challenges and cost make it less viable currently. Manganese and phosphate are superior in terms of specific power and thermal stability and have achieved relatively wide use, with Li-titanate having the best life span.


Image courtesy of Cadex

Currently NMC and LFP are the Lithium chemistries most utilised across residential and commercial renewable applications

Conclusion

There are many different lithium batteries out in the market from which to choose from. Some of the important criteria when looking at a potential candidate include thermal stability, energy density and longevity. 

Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2), NMC is used by quite a few manufacturers for energy storage solutions and EV’s with LiFePo4 also popular. In the years ahead, we anticipate a continual decline in the price of battery technology as well as an expansion in the range of suitable applications. Lithium is very useful in the creation of battery storage solutions, and by changing the composition with other materials it can be used across a wide variety of applications.


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