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There are many different ways you could consider a product to be more environmentally friendly or not than another. Li-ion batteries do not contain hazardous materials while lead-acid batteries do (i.e., lead). Both battery types are recyclable; however, at present it is much easier in most regions of the world to recycle lead acid than larger format li-ion batteries used in UPSs and electric vehicles. For a complete picture of environmental impact, however, consider the entire carbon footprint over the course of the battery lifecycle. Carbon use accumulates throughout the product lifecycle:
- Raw material extraction
- Energy to produce and transport
- Operating energy to keep batteries charged and cooled
- Recyclability and impact on the earth when it is time to dispose
Previous analysis has shown that the operating losses (i.e., the energy used to keep the batteries charged) are, by far, the dominant driver of the carbon footprint of a UPS and its battery system over a 10 year life cycle. However, there is not a large difference in operating losses between the two systems. Which one edges out the other depends on the actual use case.
Lithium-ion batteries do require less energy to keep them charged than lead acid. The charge cycle is 90% efficient for a lithium-ion battery vs. 80-85% for a lead acid battery. Additionally, lead acid batteries self-discharge at a higher rate than Lithium-ion. These efficiency gains, however, are offset by the need for Li-ion to have a battery management system (BMS) to protect against short circuits and overcharging. This monitoring system consumes energy. So the total operating losses are very similar between the two.
With the dominant factor for determining a 10-15 year carbon footprint basically a wash, one must look to the other factors. Given that lithium-ion batteries containing landfill -safe materials are recyclable, and because their lifespan is 2-3 times longer than lead acid batteries, it can be argued that lithium-ion batteries are “greener”.
However, note that the recycling rate of lead from lead-acid batteries is 99% with over 90% of the batteries being collected (in North America…similar rates occur in Europe and Japan). The state of recycling for lithium-ion batteries, particularly the larger format ones (such as those used in electric vehicles and data center UPSs), is much less mature, however.