Lead-acid is getting lighter

Future endeavors tomaximize the lead-acidbattery’s energy densityshow great promise asmanufacturers develop newways to make currentcollectors more efficientand take up less space. This leaves more room foractive material, improvingthe battery’s power-per-pound. Lowering theweight-to-power output isan important benefit forPlug-in Hybrid and ElectricDrive vehicles, whereweight is a critical issue in performance.

Hybrid Electric Vehicles (HEV)

Next Generation Lead-Acid Technology:Performance Enhanced Through Creativity

Dramatic improvements in theperformance of lead-acid batterieshave come about not through the useof rare or expensive materials, butthrough the creative use of the rawmaterials that lead-acid manufacturershave been using for decades.

e novel use of standard, readilyavailable materials has enabledengineers to achieve the technologicalbreakthroughs that are making a newgeneration of affordable, efficient andenvironmentally safe lead-acidbatteries available for use in hybridelectric vehicles, the electric powergrid, and other energy storageprograms.

e addition of certain types ofcarbon to the traditional lead-acidbattery has led to the production of new lead-acid designs. ese arebreaking performance standards andpositioned to become the low-costalternative to batteries produced withnickel metal hydride (NiMH) orlithium ion(Li-Ion) technology.

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the facts about

• Energy Storage/StandbyLead-acid – The most efficient technology

• Motive PowerLead-acid – The best overall solution

• Hybrid Electric Vehicles (HEV)Lead-acid is getting lighter

• Safety and ReliabilityLead-acid – A longer track record in safety and reliability than otherrechargeable battery technologies

• Sustainability/RecyclingLead-acid – One of the highest recycling rates on the planet

In one such design, called theUltraBattery, a supercapacitor carbonelectrode is combined with the lead-acid battery’s negative plate to betterregulate the flow (charge anddischarge) of energy, therebyextending the power and life of thebattery itself. e Advanced Lead-Acid Battery Consortium (ALABC)tested the UltraBattery in a HondaInsight HEV. e vehicle easilysurpassed the 100,000-mile durabilitytest without any conditioning orequalization treatment.

ere are other novel lead-acid designswhich replace the negative leadelectrode entirely with a pure carbonelectrode to form an asymmetricsupercapacitor, or that use carbon asan electrode substrate. Among otherbenefits, these modifications candramatically reduce the weight of the battery.

As the lead-acid industry continues itsbreakthrough work on incorporatingcarbon and supercapacitors in batteriesto improve their performance, significantprogress also is being made in anotherkey area: the commercialization ofbipolar technology. Bipolar technologycan help produce batteries that willachieve the goals of more power and asmaller footprint, both very important inmaking hybrid electric vehicles moreaffordable for consumers.

e majority of batteries are madewith conventional ‘monopolar’technology, which uses two plates percell. It then connects those cells in aseries of metallic connectors outside of the cells or through a wall.

While bipolar and monopolar designsshare the same lead-acid chemistry,they differ in that bipolar battery cellsare stacked so that the negative plateof one cell becomes the positive plateof the next. e cells are separatedfrom each other by the bipolar plate,which allows each cell to operate inisolation from its neighbor.

is construction reduces the powerloss that is normally caused by theinternal resistance of the cells. At eachend of the stack, single plates act asthe final anode and cathode. isconstruction leads to reduced weightsince there are fewer plates and busbars are not needed to join cellstogether. e net result is a batterydesign with higher power and lessweight than conventional monopolarlead-acid batteries.

Weight is not a limitingfactor in most hybridvehicle designs:

Although lead-acid haslower specific energy thannickel metal hydride (NiMH)or lithium ion, batteries inHEVs are rather small (about1kWh) so the weight penaltyof adopting lead-acid ismodest – especially sincelead-acid does not need thesupplementary battery and12 V starter motor thatsupports NiMH in lowtemperature conditions, or the cell-by-cell batterymanagement that lithium ionmust have to ensure safety.

For years, scientists have known thatthe accumulation of lead sulfate canprevent lead-acid batteries fromachieving the sustained level of high-rate partial state of charge (HRPSoc)operation required for heavy dutyperformance in hybrid electric vehiclesand other energy storage applications.

is problem would occur whenever a lead-acid battery’s ‘state-of-charge’remained significantly below 100%for a sustained period. Conversely,whenever the battery’s state-of-chargewould rise much above 70 percent, it could not accept a recharge fromeither a regenerative braking system or a charge from the engine itself.

One solution has been to insert asuper-capacitor into the battery to actas a ‘buffer’ to manage the high-ratecharge/discharge process so that theunit can operate successfully within a state-of-charge window below 70 percent.

Carbon + Supercapacitor = Performance Breakthrough The Commercialization of Bipolar Technology

New lead-acid battery technology hassharply reduced the accumulation oflead sulfate deposits that previouslyinhibited the performance of lead-acidbatteries in HEV or other HRPSoCapplications. is benefit has extendedthe life of traditional lead-acidbatteries three-fold, enabling largescale deployment of micro andmedium hybrids with significant fueleconomy and emissions savings atvery low cost.

Lead-Acid + Carbon: Enabling Micro Hybrids for the Masses

Bipolar 4V

Monopolar 4V

Source: ALABC

Source: ALABC

Separator Separator

PbO2 Pb PbO2 CarbonElectrode

UltraBattery CarbonElectrode

Lead-Acid Cell Asymmetric Supercapacitor