Lithium Iron Phosphate (LiFePO4) Batteries

Many thanks to Armin Pauza for this very interesting article about the latest developments in lithium ion battery technology which will soon be available in Australia. For the technically challenged there is a summary at the end.

 

Overview of Existing Battery Technology

Up to the present time the boat owner has only had available one type of battery chemistry to serve a multitude of marine applications. This of course is the lead acid battery. As discussed in detail in a previous article on batteries, there are two main variations to the lead acid battery depending upon its specific application.
Broadly speaking the lead acid engine start or “cranking battery” is designed to provide a short, high power burst of electrical current to crank over either petrol or diesel engines while starting.

The other main type of lead acid battery is the deep cycle or gel/AGM type which is used to provide sustained power for electrical devices and equipment over a long period. This is the type of battery which provides house power on boats and is also used for backup power in UPS systems (uninterruptible power supplies) and for stationary solar power applications.

Both types of lead acid batteries however have severe limitations.
Lead acid batteries are extremely heavy and while weight may not be an important factor for batteries in a stationary environment, for use in a motive application such as a boat or car having to “carry” such a heavy dead weight (particularly in racing applications) does not make much common sense. In addition lead acid batteries contain many nasty chemicals such as sulphuric acid and toxic heavy metals like lead which are potentially hazardous for the environment.

Lead is a very heavy metal and for many years the search has been on to make a better battery that is also lighter in weight.

 

Development of Lithium Batteries

Lithium is the logical choice since it is the lightest metal known to man. However in addition to being extremely light in weight, lithium is also extremely reactive and for this reason pure lithium metal is never found in nature. Lithium metal is manufactured from lithium salts which are extracted through mining activities. Lithium ion batteries have been available for several years for many consumer applications.

As with lead acid batteries, lithium batteries also are available in several chemistries, each having their particular good and bad points. The earliest lithium battery chemistries which became a commercial reality and which are still in use today for consumer items like mobile phones, notebook computer and camcorders etc. are cobalt oxide lithium ion and manganese lithium ion batteries. These batteries both have extremely high energy densities but have the disadvantage that in large format applications and in cases where many separate cells are used which can become unbalanced during several charge cycles, they can potentially become dangerous and a risk of fire or explosion is a possibility.

While these batteries are generally considered quite safe in small format applications such as for mobile phones and the like (generally one cell only is used therefore this is why the battery voltage of a typical mobile phone battery is 3.6 -3.7 volts) there could be disastrous consequences should a large lithium battery of this chemistry fitted to a boat catch fire.

In the mid 1990’s Dr John B Goodenough and his research team from the University of Texas developed material used to make the Lithium Iron Phosphate battery (LiFePO4 for short). Dr Goodenough patented his invention and gave permission to Phostech Lithium/Hydro Quebec Canada to manufacture this material in commercial quantities for the production of LiFePO4 batteries which would be a superior replacement for lead acid batteries.

More information about Phostech Lithium can be obtained here.

 

Advantages of Lithium Batteries

Unlike the hazardous nature of the earlier chemistry lithium battery types, lithium iron phosphate batteries are extremely stable and safe to use. This safety combined with their light weight has found wide use for these batteries for military applications and now for the emerging electric vehicle market. They are in fact even safer than lead acid batteries and do not suffer from some of the problems which are inherent to lead acid batteries such as, thermal runaway, sulphation when left in a discharged condition and high rates of self discharged if not used.

A great advantage of LiFePO4 batteries is their extremely long life. For a standby power application such as battery could be expected to have a life of up to 20 years.
Lead acid batteries generally have a life of only a few hundred deep charge cycles while a quality LiFePO4 battery can typically be charged in excess of 2000 times and there are LiFePO4 cells which are currently under test at the US Department of Energy Laboratories in New Mexico which have recently passed 7000 cycles and are still working.

Though not as high in energy density as the earlier lithium battery types, the lithium iron phosphate battery still has a far higher energy density compared to the lead acid battery as can be seen from the graph below.

In recent years large format LiFePO4 batteries have been made to replace lead acid batteries and are now being widely used for battery packs for electric vehicles as well as hybrid electric cars. They are also being used in high power electric cordless power tools.

Benefits To The Boat Owner Of A Quality LiFePO4 Battery

Lithium iron phosphate is a truly multi-application battery so the same battery can be used for both high power applications such as engine cranking as well as for house power.

Another major factor which should be taken into consideration when replacing a lead acid battery with a LiFePO4 battery is that due to the higher energy density and greater performance of the lithium battery often a smaller battery can be used which will provide equivalent performance to the original lead battery. For many applications a 60Ah lithium battery will provide equivalent performance to a 100Ah lead acid battery.

This difference in performance can clearly be seen if both battery types are compared side by side in high current drain applications (for example if used to power an electric trolling motor). What many people fail to realise about a lead acid battery is that its capacity (Ah) rating is usually specified at the 20 hour discharge rate. At high rates of discharge the capacity is reduced due to “Peukert’s Effect”. A typical 100Ah lead acid battery when discharged in an hour or two may have an actual measured capacity of as little as 60-70Ah.

As soon as a load is placed on a lead acid battery there is a sudden drop or “sag” in voltage. The voltage continues to decrease until the battery is completely discharged. By contrast the discharge characteristic of a LiFePO4 battery is very different. The discharge curve is close to being linear. Even under very heavy electrical loads a LiFePO4 battery will maintain almost full power with very little reduction in nominal voltage throughout its discharge cycle until the battery becomes almost exhausted and in need of re-charging.

A good example of this effect in practical terms has been the use of this new lithium battery technology in yachts. For more than six months now LiFePO4 batteries have been used as an engine starting battery in several large yachts in Taiwan. An 80Ah lithium iron phosphate battery weighing only 16.5kg has replaced the 240Ah lead acid starting batteries weighing over 40kg for starting the 380 horsepower marine diesel engines on several of these large Taiwanese yachts.

Another great benefit of these batteries for boating applications is due to their inherent safety features. Since they do not produce flammable hydrogen under any circumstances (even if overcharged) a LiFePO4 battery can be safely installed in a confined place in a boat or ship without fear of a fire or explosion. Also due to slim cylindrical nature of LiFePO4 cells a custom battery or virtually any shape can be made which will fit into any tight space on a boat.

Another advantage of these batteries is their rapid charge capability. LiFePO4 batteries can be re-charged extremely quickly. This rapid charge capability comes by necessity since these batteries have been developed for use in the electric cars of the future.
For maximum life a discharged deep cycle lead acid battery should only be trickle charged in 12–24 hours. By stark contrast a quality LiFePO4 battery which is completely discharged can be brought back to a state of greater than 90% full charge in 15 minutes. For many boating applications this rapid charge ability will be a godsend.
For example when an electric trolling motor battery has been discharged, it would be possible to return to shore and recharge the battery by a generator or mains and head off again with a fully charged battery in less than an hour. The added benefit of the LiFePO4 battery is that since it is only half the weight of a lead acid battery for the same capacity it won’t break your back while you lift it out of the boat to carry it to the charging source.

An overview of the benefits of Lithium Iron Phosphate batteries

• Safe technology, will not catch fire or explode with overcharge

• Over 2000 discharge cycles life compared to typically around 300 for lead acid

• Double the usable capacity of similar amp hour lead acid batteries

• Virtually flat discharge curve means maximum power available until fully discharged (no “voltage sag” as with lead acid batteries).

• High discharge rate capability, 10C continuous, 20C pulse discharge.

• Unlike lead acid batteries, can be left in a partially discharged state for extended periods without causing permanent damage

• Extremely low self discharge rate (unlike lead acid which will go flat quite quickly if left sitting for long periods)

• Does not suffer from “thermal runaway”

• Can be used safely in high ambient temperatures of up to 60 deg.C without any degradation in performance

• 12.8V nominal, 8V maximum discharge, 14.65V maximum charge voltage

• Can be connected in series for higher voltages or parallel for higher capacity.

• Absolutely maintenance free for the life of the battery

• Can be operated in any orientation

• Does not contain any toxic heavy metals such as lead, cadmium, nor any corrosive acids or alkalis thus making LiFePO4 batteries the most environmentally friendly battery chemistry available

• LiFePO4 cells are of solid construction. There are no fragile/brittle plates made of lead which can be prone to failure over time as a result of vibration.

• Can be safely rapidly recharged. When fully discharged can be brought to a state of over 90% fully charged in 15 minutes.

Availability of Lithium Batteries

It will not be long before several brands of LiFePO4 batteries will be available to boat owners. When selecting a particular brand the battery purchaser should consider a battery manufacturer who uses cathode material supplied by Phostech Lithium Canada. Such a battery should come with a warranty of at least 3 years and more than 1000 charge cycles.

Due to the much higher initial cost of a LiFePO4 battery, several cheap Chinese pirated copies have now entered the market. The prospective battery purchaser should be very wary when considering purchasing one of these batteries since one reason for their lower price is that the Chinese battery cell manufacturers do not use the finest grade of cathode powder available (and do not pay royalties for this highest quality powder which is only available from the patent holder, Phostech Canada). Since this Chinese manufactured cathode powder is of inferior quality to that which comes from Canada, the performance and longevity of the final battery product can be expected to have a much shorter lifespan combined with overall poorer performance.

There are a handful of manufacturers of first grade quality Lithium Iron Phosphate batteries which will outlast several lead acid batteries and provide vastly superior performance to a lead acid battery.

Lithium Iron Phosphate batteries are sure to revolutionise the marine industry in coming years by enhancing both the performance and reliability of boats and their electrical systems thus making for a more enjoyable and safer boating experience.

Armin Pauza
General Manager & Principal Electrical Engineer
Lithium Batteries Australia
info@lifebatt.com.au