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liFePO4 Battery Research

This article explains the basic features regarding the latestdevelopments in lithium ion battery technology which have recentlybecome available to Australian users.

 

Up to the present time there has only had available one maintype of battery to serve a multitude of remote power applications.This of course is the lead acid battery. There are two mainvariations to the lead acid battery depending upon its specificapplication. This is the engine start (or “cranking”) battery andthe deep cycle variety with main types in that family being the geland AGM sealed lead acid types.

 

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

 

The other main type of lead acid battery is the deep cycle typewhich is used to provide sustained power for electrical devices andequipment over a long period. This is the type of battery which isthe best choice to power most common electrical appliances eitherdirectly 12 volts from the battery itself or 240 volts from aninverter connected to the battery.

 

Both types of lead acid batteries however have severelimitations.

 

Lead acid batteries are extremely heavy and while weight may notbe an important factor for batteries in a stationary environmentsuch as a fixed solar power installation, for use in a motiveapplication such as in aviation, boating, 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 suchas sulphuric acid and toxic heavy metals like lead which arepotentially hazardous for the environment.

 

Lead is a very heavy metal and for many years the search hasbeen on to make a better battery that is also lighter in weight.Lithium is the logical choice since it is the lightest metal knownto man. However in addition to being extremely light in weight,lithium is also extremely reactive and for this reason lithiummetal is never found in its pure metallic form in nature.

 

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

Lithium ion batteries have been available for several years nowand are in use in many consumer applications.

 

As with lead acid batteries, lithium batteries also areavailable in several chemistries, each having their particular goodand bad points. The earliest lithium battery chemistries whichbecame a commercial reality and which are still in use today forconsumer items like mobile phones, notebook computers andcamcorders etc. are cobalt oxide lithium ion and manganese lithiumion batteries. These batteries both have high energy densities buthave the disadvantage that in large format applications and incases where many separate cells are used which can becomeunbalanced during several charge cycles, there is the risk they canpotentially become dangerous with a possibility of fire orexplosion occurring under certain circumstances..

 

While these batteries are generally considered quite safe insmall format applications, such as for mobile phones and the like(generally one cell only is used therefore this is why the batteryvoltage of a typical mobile phone battery is 3.6 -3.7 volts) therecould be disastrous consequences should a large lithium battery ofthis chemistry fitted in an aircraft, boat or camper trailer catchfire.

 

There are several documented examples where the more hazardouschemistry of lithium ion batteries (lithium cobalt oxide) hascaught on fire and an example of this in recent years which manypeople may be aware of is several instances where laptop computerbatteries caught on fire. This resulted in a manufacturer recall ofmillions of batteries used in these laptop computers.

 

In the mid 1990’s Dr John B Goodenough and his research teamfrom the University of Texas developed material used to make theLithium Iron Phosphate battery (LiFePO4 for short).


Dr Goodenough patented his invention and gave permission toPhostech Lithium/Hydro Quebec Canada to manufacture this materialin commercial quantities for the production of LiFePO4 batterieswhich would be a superior replacement for lead acid batteries.

 

 

Unlike the hazardous nature of the earlier chemistry lithiumbattery types, lithium iron phosphate batteries are extremelystable and safe to use. This safety combined with their lightweight has found wide use for these batteries for militaryapplications and now for commercial applications. These batteriesare 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 discharge if not used.

 

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 of EnergyLaboratories in New Mexico which have recently passed 7000 cyclesand are still working.

Though not quite 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.

 

The benefits of a quality LiFePO4 battery are many!

 

Lithium iron phosphate is a truly multi-application battery sothe same battery can be used for both high power applications suchas engine cranking as well as for general house power in the placeof a deep cycle/AGM lead acid battery.

 

Another major factor which should be taken into considerationwhen replacing a lead acid battery with a LiFePO4 battery is thatdue to the higher energy density and greater performance of thelithium battery, often a smaller battery can be used which willprovide equivalent performance to the original lead battery. Formany applications a 60Ah lithium iron phosphate battery willprovide equivalent performance to a 100Ah lead acid battery. A 12V20Ah LiFePO4 battery is all that is required for a starting batteryup to an engine size of 3000cc. This battery weighs just over 4kg.

 

What many battery owners and users fail to realise about thelead acid battery is that its capacity (Ah) rating is usuallyspecified at the 20 hour discharge rate. At high rates of dischargethe useable capacity is reduced due to “Peukert’s Effect”. Atypical 100Ah lead acid battery when discharged in an hour or twomay 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 asudden drop or “sag” in voltage. The voltage continues to decreaseuntil the battery is completely discharged. By contrast thedischarge characteristic of a LiFePO4 battery is very different.The discharge curve is close to being linear. Even under very heavyelectrical loads a LiFePO4 battery will maintain almost full powerwith very little reduction in nominal voltage throughout itsdischarge cycle until the battery becomes almost exhausted and inneed of recharging.

 

Another great benefit of these batteries is their inherentsafety features. Since they do not produce flammable hydrogen underany circumstances (even if overcharged) a LiFePO4 battery can besafely installed in a confined area without fear of a fire orexplosion. Also due to the slim cylindrical nature of LiFePO4 cellsa custom battery of virtually any shape or size can be custommanufactured which will fit into any tight space even if the spaceis of an unusual shape.

 

To sum up, an overview of the benefits of Lithium Iron Phosphatebatteries is as follows:

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

·        Half the weight ofan equivalent capacity lead acid battery

·        Over 2000 deepdischarge cycles life compared to typically around 300 for leadacid

·        Double the usablecapacity of similar amp hour lead acid batteries

·        Virtually flatdischarge curve means maximum power available until fullydischarged (no  "voltage sag" as with lead acid batteries)

·        High discharge ratecapability, 10C continuous, 20C pulse discharge


·        Unlike lead acidbatteries, can be left in a partially discharged state for extendedperiods without causing permanent damage

·        Extremely low selfdischarge rate (unlike lead acid which will go flat quite quicklyif left sitting for long periods)

·        Does not suffer from"thermal runaway" 

·    Can be used safely in high ambienttemperatures of up to 60 deg.C without any degradation inperformance

·        12.8V nominal, 8Vmaximum discharge, 14.6V maximum charge voltage

·        Can be connected inseries for higher voltages or parallel for higher capacity.

·        Absolutelymaintenance free for the life of the battery

·        Can be operated inany orientation including inverted

·       Does not contain any toxicheavy metals such as lead, cadmium, nor any corrosive acids oralkalis thus making LiFePO4 batteries the most environmentallyfriendly  battery chemistry available

 

liFePO4 Battery Research


 

Lithium Iron Phosphate batteries are sure to revolutioniseremote power requirements in coming years by enhancing the amountof power which can be stored in a given size battery thus allowingaccess to a source of  longer sustained electrical current topower electrical equipment for longer.
 

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