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Lead acid battery or lithium ion?

Batteries are strange devices. Nobody wants them, but everybody needs them. They are only bought when required. How many people plan a trip to the local mall to window shop for batteries? They are a grudge purchase and only bought when absolutely necessary. A good salesman can sell you two pair of shoes, two cars and maybe two houses if you have the money, but he cannot sell you two SLI automobile batteries. When you do buy a battery whether a solar battery for a solar panel, an electric bike or a UPS and inverter battery backup system or a traction battery for forklifts don’t you wish you knew more about it? How do they work, what is the differences between types and models, and how about the different chemistries? They can be expensive. In a commercial or domestic application what is the payback, what is the life and the cost of replacement? The size you need, the space available, the energy efficiency and recharge time? And then, there is the hidden costs of safety, disposal and the carbon footprint. This article compares lead acid batteries with lithium ion batteries and addresses many of the misconceptions associated with both of these chemistries.

Dr Mike

The perception in the public domain is that lead acid batteries are old technology.  Lithium ion batteries has a different perception, it is modern, cleaner, it has 3 or 4 times the energy density and a longer cycle life. With all of this, what possible advantages could the 150-year old lead acid technology bring to the table?  Well actually, all is not as it seems, look behind the headlines at the data used in the marketing claims, then apply a bit of common sense, basic research and some rudimentary science. You will find that the real story is rather different. 

The first misconception concerns the volumetric and specific energy densities. The headline values of 4 to 5 times relate only to the specific energy density and to a limited number of lithium ion battery chemistries, some of which are still not in commercial use. Fig. 2 compares several cathodes for lithium ion battery cells these range from around 100 Wh/kg for the safest Li-FePO4 chemistry to over 200 Wh/kg for the nickel-cobalt-aluminium oxide variant. 

Figure 2 Energy densities of various battery chemistries at cell level

Energy Densities of different chemistry batteries
Energy Densities of different chemistry batteries

These values only apply to single cell level, not the pack or in-service condition.  Fig. 3 shows energy densities of different battery chemistries at cell and system level. The energy densities of lithium ion batteries cells are practically halved when fully installed with all the connections, cooling, safety and battery management equipment.

 

Figure 3 Comparison of Li-ion and Lead acid at cell and system level

Comparison of Li-ion and Lead acid at cell and system level
Comparison of Li-ion and Lead acid at cell and system level

 

The cell level advantage of 3 to 5 times the specific energy density is reduced to 2 to 3 times.  Dependent upon the lithium cathode chemistry we could almost be looking at parity between lithium ion batteries and lead acid batteries energy density for a fully installed battery system in some applications.

 

The other factor, that of cycle life, is also a source of confusion. How many cycles can a lithium ion battery perform before the capacity drops below 80% of its nameplate rating? Two, three thousand? Table 1 gives a summary of the different Li-ion cathode materials for performance and cycle life.

Table 1 Comparison of different cathode materials for Li-ion batteries

Comparison of different cathode materials for Li-ion batteries
Comparison of different cathode materials for Li-ion batteries

As can be seen, all fall within the 800 to 2000 cycle range. In comparison, a well-designed lead acid battery can easily achieve more than 1600 cycles to 80% DOD. So how does this all add up when considering cost of ownership? This brings us to the next point which is price. How much does a lithium ion battery cost compared to a lead acid battery? Naturally lithium ion batteries are more expensive but how much more. Again, this depends upon the level being considered. The press releases will tell us that Li-ion prices are falling and now are in the range of 2-3 times that of lead acid

 Really? I recently did a UK internet search to get prices on commercially available leisure batteries of 12V and 100 Ah for both lithium ion batteries and lead acid batteries. The mean prices were

lithium ion batteries $960 or $800/kwh 

Lead acid battery $215 or $180/kwh  

Obviously, the life of the lithium ion battery has to be 4 times that of the lead acid battery equivalent to get the same value. As we have seen, this is not the case.

Table 2 is a real-life situation comparing the economics of using lithium ion batteries and 2v battery in lead acid battery chemistry over different life periods.

Table 2 Operating costs for a telecoms tower in India

Operating costs for a telecoms tower in India
Operating costs for a telecoms tower in India

 In all cases lead acid batteries were the most cost effective even when a larger lead acid battery was fitted to give better charge acceptance and a longer cycle life. In this example the application was a telecoms tower in India. The same principle holds true in most applications and geographies, more so in colder climates. The other misconception is that Li-ion is a cleaner technology and less polluting than lead acid. The cradle to gate emissions for different battery chemistries is given in Figs. 5 and 6.

Figure 5 Schematic of cradle to gate principle for battery manufacturing 

Schematic of cradle to gate principle for battery manufacturing
Schematic of cradle to gate principle for battery manufacturing

This figure shows the boundary of operations for battery manufacture. From extraction and transport of raw materials right through all the processing steps to the point where the batteries are ready to ship.

Figure 6 Cradle to Gate CO2 emissions for different battery chemistries

CO2 emissions for different battery chemistries
CO2 emissions for different battery chemistries

This data from Argonne National Laboratories, show that the total manufacturing process including the extraction and transport of raw materials for lithium ion batteries are more than 4 times the lead acid value. Regarding the extraction of materials, the supply of basic cathode materials such as cobalt and manganese and lithium are not completely certain. The extraction and recovery processes exist but the number of mines and manufacturing sites may limit supply if demands significantly increases. The geo-political map also predicts uncertainty for some sources of these materials.

The recyclability and safety of these chemistries are important factors. It is known that almost all of the components in lead acid batteries are 100% recycled whereas there are no commercial processes for recycling lithium ion batteries. This situation is understandable when you consider that the more expensive components of Li, Co, Mn etc. are only a small fraction of the total lithium ion batteries. For example, Lithium is around 4% of the total cell weight. Add to this the obvious fact that Lithium is highly reactive (the basis of its high energy density), which understandably makes it expensive to extract from the waste. The additional factor of complexity with many different materials in its construction makes recycling difficult, both technically and economically. The result? There is simply no commercial incentive to recycle these batteries. For this reason, recycling facilities are still at pilot stage and mostly government funded.

At present the vast majority of scrapped lithium ion batteries are stockpiled waiting for either a technological breakthrough or legislation to force their recycling. If the latter were to be implemented then there would be a cost, ultimately to the consume. This would further increase the price of the Li-ion cell compared with lead acid.

Finally, we have safety. No lead acid battery to my knowledge has ever had a safety recall as we know is the case with Li-ion batteries in portable electronic devices and even electric vehicles. Fig. 7 shows what happened to a new hybrid Volvo in the UK just a couple of weeks ago. In this case its lithium ion batteries caught fire when on charge.

Figure 7 Fire caused by a Li-ion battery in a Volvo hybrid electric vehicle: April 2018-UK residence

Volvo car fire caused by li ion battery
Volvo car fire caused by li ion battery
firemen dousing the fire caused by a lithium battery
firemen dousing the fire caused by a lithium battery

Even when stored or transported lithium ion batteries have been the cause of seriously dangerous fires. Whilst these occasions are rare, they have to be acknowledged, and suitable safety equipment and battery management software have to be installed. The New York fire department for example are still in the process of deciding how to tackle lithium ion batteries fires. This would strongly suggest that existing safety measures for lithium ion batteries worldwide need to be reviewed.

 

The following is the view from the New York Fire Department:

 

News article quote: AWS utility drive Nov. 15, 2016   “Fire is not the biggest problem,” said Rogers. Firefighters are trained to deal with fires, he said, but they need to know what they are dealing with. Li-ion batteries can release toxic acids and flammable vapors. Some of those vapors are consumed by the fire, but if they are not, they could ignite or be a problem for firefighters. The biggest problem is what happens “post op,” that is, after the fire is extinguished. Even if a battery is shut down it could re-ignite for up to 72 hours, Rogers said.  -Lt. Paul Rogers Fire Department of New York’s hazardous materials operations division”

 

In summary, lithium ion batteries most certainly have better performance characteristics than lead acid. However, these advantages are severely reduced by the additional hardware associated with the safety and management requirements. The net result is that lead acid batteries have distinct advantages particularly when considering applications which are not restricted by weight or charge acceptance. The low purchasing price and low amortisation cost of lead acid combined with its low environmental impact and inherent safety, provide the following advantages:

  • Lower purchase price. The price is around one quarter of a Li-ion equivalent. The lower operating costs to give a lower total cost of ownership in the majority of applications.

  • Recyclability. Almost 100% of all lead acid battery materials are recycled. The scrap value can provide additional revenue of up to 20% of the battery material cost. Lithium batteries have no infrastructure or commercial process for recycling

  • Safety. The chemistry of lead acid is inherently safer than that of lithium ion batteries

  • Sustainability. There are many well established sources of supply for lead acid, particularly from recycling facilities. Lithium and other cathode materials may be supplied from politically sensitive areas. Both the current global materials extraction and manufacturing capability would not support a rapid increase in the production of Lithium ion batteries..

  • Carbon footprint. Lead acid battery manufacture has a cradle to gate carbon footprint one third of that of lithium ion batteries.

There we have it. A different picture to the one painted by the lithium ion battery companies. Whilst it cannot be argued that lead acid has an advantage in energy density, the point can be made that it is still a highly competitive technology and remains the best choice in many applications. Please email any questions to Dr Mike.  You can also reach out to us here.

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