Lithium Iron Phosphate (LiFePO4) Batteries

for recreational users including camper trailers, boating and 4WD applications

 

 

 

 

 

    This article explains the basic features regarding the latest developments in lithium ion battery technology which have recently become available to Australian recreational users.

 

    Up to the present time the camper trailer owner has only had available one main type of battery to serve a multitude of remote power applications. This of course is the lead acid battery. There are two main variations to the lead acid battery depending upon its specific application. This is the engine start (or “cranking”) battery and the deep cycle variety with main types in that family being the gel and AGM sealed lead acid types.

 

    Broadly speaking the lead acid engine start battery is designed to provide a short, high power burst of electrical current to crank over a gasoline engine while starting.

 

    The other main type of lead acid battery is the deep cycle type which is used to provide sustained power for electrical devices and equipment over a long period. This is the type of battery which is the best choice to power most common electrical appliances used by camper trailer owners- either directly 12 volts from the battery itself or 240 volts from an inverter connected to the battery.

 

    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 such as a fixed solar power installation, for use in a motive application such as in a camper trailer, having to “carry” such a heavy dead weight 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.

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 lithium metal is never found in its pure metallic form in nature.

 

    Lithium metal is manufactured from lithium salts which are extracted through mining activities.

Lithium ion batteries have been available for several years now and are in use in 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 computers and camcorders etc. are cobalt oxide lithium ion and manganese lithium ion batteries. These batteries both have 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, there is the risk they can potentially become dangerous with a possibility of fire or explosion occurring under certain circumstances..

 

    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 in a camper trailer catch fire.

 

    There are several documented examples where the more hazardous chemistry of lithium ion batteries (lithium cobalt oxide) has caught on fire and an example of this in recent years which many people may be aware of is several instances where laptop computer batteries caught on fire. This resulted in a manufacturer recall of millions of batteries used in these laptop computers.

 

    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 by going to http://www.lifebatt.com/phosteclithium.pdf

 

    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 commercial applications such as in the recreational user market. These batteries 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 discharge 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 quite 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.

 

 

 

  

    The benefits to the camper trailer owner of a quality LiFePO4 battery are many.

 

    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 of the main campervan towing vehicle as well as for power at the campsite in the place of a deep cycle/AGM lead acid battery.

 

    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 iron phosphate battery will provide equivalent performance to a 100Ah lead acid battery. A 12V 20Ah LiFePO4 battery is all that is required for a starting battery up to an engine size of 3000cc. This battery weighs just over 4kg.

 

    What many battery owners and users fail to realise about the lead acid battery is that its capacity (Ah) rating is usually specified at the 20 hour discharge rate. At high rates of discharge the useable 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 recharging.

 

    Another great benefit of these batteries for campervan owners is 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 area in a caravan or campervan without fear of a fire or explosion. Also due to the slim cylindrical nature of LiFePO4 cells a custom battery of virtually any shape or size can be custom manufactured which will fit into any tight space even if the space is of an unusual shape.

 

    To sum up, an overview of the benefits of Lithium Iron Phosphate batteries is as follows-

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

·        Half the weight of an equivalent capacity lead acid battery

·        Over 2000 deep 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, 14.6V 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 including inverted

·        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

 

    It will not be long before several brands of LiFePO4 batteries will be available to campervan owners. When selecting a particular brand the battery purchaser should consider a brand which uses cathode material manufactured by the inventor and patent holder of this technology (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 manufacturers do not pay royalties to the patent holder and as such the cathode powder used in their manufacture is of a much lower quality and the battery 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 the lead based battery.

 

    Lithium Iron Phosphate batteries are sure to revolutionise remote power requirements for camper trailer owners in coming years by enhancing the amount of power which can be stored in a given size battery thus allowing camper trailer owners access to a source of  longer sustained electrical current to power electrical equipment for longer while exploring the great outdoors.

 

Information provided by

Armin Pauza

General Manager & Principal Electrical Engineer

Lithium Batteries Australia

ph. 0420 948 757

info@lifebatt.com.au