Lithium Iron Phosphate (LiFePO4) Batteries forMarine Applications
Many thanks to Armin Pauza for this very interesting article aboutthe latest developments in lithium ion battery technology whichwill soon be available in Australia. For the technically challenged there is a summary at theend.
Overview of Existing BatteryTechnology
Up to the present time the boat owner has only hadavailable one type of battery chemistry to serve a multitude ofmarine applications. This of course is the lead acid battery. Thereare two main variations to the lead acid battery depending upon itsspecific application.
Broadly speaking the lead acid engine start or “cranking battery”is designed to provide a short, high power burst of electricalcurrent to crank over either petrol or diesel engines whilestarting.
The other main type of lead acid battery is the deepcycle or gel/AGM type which is used to provide sustained power forelectrical devices and equipment over a long period. This is thetype of battery which provides house power on boats and is alsoused for backup power in UPS systems (uninterruptible powersupplies) and for stationary solar powerapplications.
Both types of lead acid batteries however havesevere limitations.
Lead acid batteries are extremely heavy and while weight may not bean important factor for batteries in a stationary environment, foruse in a motive application such as a boat or car having to “carry”such a heavy dead weight (particularly in racing applications) doesnot make much common sense. In addition lead acid batteries containmany nasty chemicals such as sulphuric acid and toxic heavy metalslike lead which are potentially hazardous for theenvironment.
Lead is a very heavy metal and for many years thesearch has been on to make a better battery that is also lighter inweight.
Development of Lithium Batteries
Lithium is the logical choice since it is thelightest metal known to man. However in addition to being extremelylight in weight, lithium is also extremely reactive and for thisreason pure lithium metal is never found in nature. Lithium metalis manufactured from lithium salts which are extracted throughmining activities. Lithium ion batteries have been available forseveral years for many consumer applications.
As with lead acid batteries, lithium batteries alsoare available in several chemistries, each having their particulargood and bad points. The earliest lithium battery chemistries whichbecame a commercial reality and which are still in use today forconsumer items like mobile phones, notebook computer and camcordersetc. are cobalt oxide lithium ion and manganese lithium ionbatteries. These batteries both have extremely high energydensities but have the disadvantage that in large formatapplications and in cases where many separate cells are used whichcan become unbalanced during several charge cycles, they canpotentially become dangerous and a risk of fire or explosion is apossibility.
While these batteries are generally considered quitesafe in small format applications such as for mobile phones and thelike (generally one cell only is used therefore this is why thebattery voltage of a typical mobile phone battery is 3.6 -3.7volts) there could be disastrous consequences should a largelithium battery of this chemistry fitted to a boat catchfire.
In the mid 1990’s Dr John B Goodenough and his research team from theUniversity of Texas developed material used to make the Lithium Iron Phosphate battery(LiFePO4 for short). Dr Goodenough patented his invention and gavepermission to Phostech Lithium/Hydro Quebec Canada to manufacture this material in commercial quantities for theproduction of LiFePO4 batteries which would be a superiorreplacement for lead acid batteries.
More information about Phostech Lithium can beobtained here.
Advantages of Lithium Batteries
Unlike the hazardous nature of the earlier chemistrylithium battery types, lithium iron phosphate batteries areextremely stable and safe to use. This safety combined with theirlight weight has found wide use for these batteries for militaryapplications and now for the emerging electric vehicle market. Theyare in fact even safer than lead acid batteries and do not sufferfrom some of the problems which are inherent to lead acid batteriessuch as, thermal runaway, sulphation when left in a dischargedcondition and high rates of self discharged if notused.
A great advantage of LiFePO4 batteries is their extremely longlife. For a standby power application such as battery could beexpected to have a life of up to 20 years.
Lead acid batteries generally have a life of only a few hundreddeep charge cycles while a quality lifepo4 battery can typically becharged in excess of 2000 times and there are lifepo4 cells whichare currently under test at the US Department ofEnergy Laboratories in New Mexico which have recentlypassed 7000 cycles and are still working.
Though not as high in energy density as the earlierlithium battery types, the lithium iron phosphate battery still hasa far higher energy density compared to the lead acid battery ascan be seen from the graph below.
In recent years large format LiFePO4 batteries havebeen made to replace lead acid batteries and are now being widelyused for battery packs for electric vehicles as well as hybridelectric cars. They are also being used in high power electriccordless power tools.
Benefits To The Boat Owner Of A Quality LiFePO4Battery
Lithium iron phosphate is a truly multi-applicationbattery so the same battery can be used for both high powerapplications such as engine cranking as well as for housepower.
Another major factor which should be taken intoconsideration when replacing a lead acid battery with a LiFePO4battery is that due to the higher energy density and greaterperformance of the lithium battery often a smaller battery can beused which will provide equivalent performance to the original leadbattery. For many applications a 60Ah lithium battery will provideequivalent performance to a 100Ah lead acid battery.
This difference in performance can clearly be seenif both battery types are compared side by side in high currentdrain applications (for example if used to power an electrictrolling motor). What many people fail to realise about a lead acidbattery is that its capacity (Ah) rating is usually specified atthe 20 hour discharge rate. At high rates of discharge the capacityis reduced due to “Peukert’s Effect”. A typical 100Ah lead acidbattery when discharged in an hour or two may have an actualmeasured capacity of as little as 60-70Ah.
As soon as a load is placed on a lead acid batterythere is a sudden drop or “sag” in voltage. The voltage continuesto decrease until the battery is completely discharged. By contrastthe discharge characteristic of a LiFePO4 battery is verydifferent. The discharge curve is close to being linear. Even undervery heavy electrical loads a LiFePO4 battery will maintain almostfull power with very little reduction in nominal voltage throughoutits discharge cycle until the battery becomes almost exhausted andin need of re-charging.
A good example of this effect in practical terms has been the useof this new lithium battery technology in yachts. For more than sixmonths now LiFePO4 batteries have been used as an engine startingbattery in several large yachts in Taiwan. An 80Ah lithium iron phosphate battery weighing only16.5kg has replaced the 240Ah lead acid starting batteries weighingover 40kg for starting the 380 horsepower marine diesel engines on several ofthese large Taiwanese yachts.
Another great benefit of these batteries for boatingapplications is due to their inherent safety features. Since theydo not produce flammable hydrogen under any circumstances (even ifovercharged) a LiFePO4 battery can be safely installed in aconfined place in a boat or ship without fear of a fire orexplosion. Also due to slim cylindrical nature of LiFePO4 cells acustom battery or virtually any shape can be made which will fitinto any tight space on a boat.
Another advantage of these batteries is their rapidcharge capability. LiFePO4 batteries can be re-charged extremelyquickly. This rapid charge capability comes by necessity sincethese batteries have been developed for use in the electric cars ofthe future.
For maximum life a discharged deep cycle lead acid battery shouldonly be trickle charged in 12–24 hours. By stark contrast a qualityLiFePO4 battery which is completely discharged can be brought backto a state of greater than 90% full charge in 15 minutes. For manyboating applications this rapid charge ability will be agodsend.
For example when an electric trolling motor battery has beendischarged, it would be possible to return to shore and rechargethe battery by a generator or mains and head off again with a fullycharged battery in less than an hour. The added benefit of theLiFePO4 battery is that since it is only half the weight of a leadacid battery for the same capacity it won’t break your back whileyou lift it out of the boat to carry it to the chargingsource.
An overview of the benefits of Lithium Iron Phosphate batteries
- Safe technology, will not catch fire or explode withovercharge
- Over 2000 discharge cycles life compared totypically around 300 for lead acid
- Double the usable capacity of similar amp hour leadacid batteries
- Virtually flat discharge curve means maximum poweravailable until fully discharged (no “voltage sag” as with leadacid batteries).
- High discharge rate capability, 10C continuous, 20C pulse discharge.
- Unlike lead acid batteries, can be left in apartially discharged state for extended periods without causingpermanent damage
- Extremely low self discharge rate (unlike lead acidwhich will go flat quite quickly if left sitting for longperiods)
- Does not suffer from “thermalrunaway”
- Can be used safely in high ambient temperatures ofup to 60 deg.C without any degradation inperformance
- 12.8V nominal, 8V maximum discharge, 14.65V maximumcharge voltage
- Can be connected in series for higher voltages orparallel for higher capacity.
- Absolutely maintenance free for the life of thebattery
- Can be operated in anyorientation
- Does not contain any toxic heavy metals such aslead, cadmium, nor any corrosive acids or alkalis thus makingLiFePO4 batteries the most environmentally friendly batterychemistry available
- LiFePO4 cells are of solid construction. There areno fragile/brittle plates made of lead which can be prone tofailure over time as a result of vibration.
- Can be safely rapidly recharged. When fullydischarged can be brought to a state of over 90% fully charged in15 minutes.
Availability of Lithium Batteries
It will not be long before several brands of LiFePO4 batteries willbe available to boat owners. When selecting a particular brand thebattery purchaser should consider a battery manufacturer who usescathode material supplied by Phostech Lithium Canada. Such a battery should come with a warranty of at least 3 yearsand more than 1000 charge cycles.
Due to the much higher initial cost of a LiFePO4 battery, severalcheap Chinese pirated copies have now entered the market. Theprospective battery purchaser should be very wary when consideringpurchasing one of these batteries since one reason for their lowerprice is that the Chinese battery cell manufacturers do not use thefinest grade of cathode powder available (and do not pay royaltiesfor this highest quality powder which is only available from thepatent holder, Phostech Canada). Since this Chinese manufacturedcathode powder is of inferior quality to that which comesfrom Canada, the performance and longevity of the final battery product can beexpected to have a much shorter lifespan combined with overallpoorer performance.
There are a handful of manufacturers of first gradequality Lithium Iron Phosphate batteries which will outlast severallead acid batteries and provide vastly superior performance to alead acid battery.
Lithium Iron Phosphate batteries are sure torevolutionise the marine industry in coming years by enhancing boththe performance and reliability of boats and their electricalsystems thus making for a more enjoyable and safer boatingexperience.
LiFePO4 for Marine