EV Battery Technology,part 2

EV-210b

This course is presented as part of Evannex Universitya free, open learning environment that presents concise, video-based mini-courses for those who have interest in electric vehicles (EVs)

Building a better batteryWhy cant we build a higher capacity EV batteryWhats the challenge?geometric constraintsweight constraintstechnological metrics

Source: http://batteryuniversity.com/learn/article/batteries_for_electric_cars

We left part 1 of this EVU mini-course by asking the question:

>> Why cant we build higher capacity, cheaper EV batteries?The answer is that we can, but the technology is complex.

>>So, whats the battery capacity and cost challenge?>> Inside an EV, there is a limited space and a limited geometry in which we can place a battery.Therefore, we need to design and build batteries with higher energy density per cubic cm to overcome the geometric constraints.>> But there are also weight constraints. Every additional pound that the electric motor must move forward reduces the EV range for a given battery>> Finally, there are other technological metrics.Each of these must be considered as new battery chemistries are developed. The metrics can be represented using a radar diagram (shown on the right of your screen) that provides what well call a footprint for the battery.

Lets consider each of the metrics separately.

Specific Energyspecific energyis the capacity of the battery measured in energy output per unit weight (e.g., kWh/kg)the challengeGasoline, 13 kWh per kilogramover 100 times more energy density than a Li-ion batterygoal to double or triple specific energy

Source: http://www.mpoweruk.com/chemistries.htm

The first technological metric well consider for EV batteries is specific energy.

>> Specific energy is the capacity of the batterythe amount of energy it can deliver until it is depleted. >> Specific energy is measured in energy output per unit weight (e.g., kWh/kg)

Because the Ev competes directly with ICE vehicles, >> the ultimate challenge is to achieve the specific energy of Gasoline. Gas delivers 13 kWh per kilogramover 100 times more energy density than a Li-ion battery.Its highly unlikely that batteries will every achieve the specific energy of gasoline, so for now, >> the goal is to double or even triple the specific energy of EV batteries

Battery CostIncorporates the costs of:manufacture of battery cellsthe battery management subsystem:thermal management systemsafety systempower management systemsupport hardwarepower electronics, wiring harnesses, pack housing

Source: http://costing.irena.org/charts/electric-vehicles.aspx

The second technological metric is cost.

Battery cost is the primary reason why current EV buyers pay a price premium for EVs.

>> Cost is a function of:>> the manufacturing costs for battery cellsthe individual batteries that are the building blocks for an EV battery>> the costs of the battery management system and its related subsystems>> thermal management system that controls battery temperature>> safety system that is design to recognize any safety problems and protect the integrity of the battery>> power management system that controls power flow into and out of the EV battery >> support hardware that incorporates power electronics, wiring harnesses, pack housing

The chart on the right of the screen provides a typical cost breakdown for an EV battery pack. The battery cells represent 50% of overall battery cost, with other electronics, control systems, management systems and business costs representing the other half.

Life Spanthe number of charging cycles that a battery can accommodate before losing 20+ percent of its capacitya function of:temperaturebattery performance and life span degrades at temps above 86 deg Fcharge protocolwhether charging regularly occurs in a fully depleted battery or one that has significant capacity leftdegree of charging to the batterys limit

Source: http://jervisdabreo.com/thetechcorner/battery-life-vs-battery-lifespan/

The third technological metric is battery life span. Every battery degrades as the number of charging cycles grows.

A batterys life span is:>>the number of charging cycles that a battery can accommodate before losing 20+ percent of its capacity>> Its a function of:>> temperaturebattery performance and life span degrades at temps above 86 deg F>> charge protocolwhether charging regularly occurs in a fully depleted battery or one that has significant capacity left,>> and the degree to which the battery capacity is charged to its limit

Today, battery costs are high. Therefore, life span is a major concern because the cost of battery replacement for an EV is significant.

Performancethe ability of a battery to meet it power and recharging requirements, regardless of its environment

to operate effectively in various climatesextreme temperatures can impact battery capacity by 20 - 30%the time required to achieve a full charge

The fourth technological metric is performance.An EV battery must provide the power needed, when needed without fail.>> Performance is a somewhat vague term that addresses the ability of a battery to meet it power and recharging requirements, regardless of its environmentThis includes:>> the ability to operate effectively in various climates;>>for example, extreme temperatures can impact battery capacity by 20 - 30%In fairness, it should be noted that extreme temperatures also effect the range of ICE vehicles, sometimes significantly.>>Finally, performance also alludes to the time required to achieve a full charge with higher performing battery taking less time for a full charge.

SafetyFew verified safety issues with EV batteriesBUT, media obsessionTherefore, sophisticated safety subsystem is mandatoryensures no thermal runaway monitors charging and overall power output

The fifth technological metric is safety, normally considered in the context of battery fires or other reactions that might endanger the driver or passengers.

There are well over 150,000 vehicle fires in the U.S every year with approximately 350 deaths and almost 2000 serious injuries. 99.99 percent occur in ICE vehicles.

>> To date, there have been few verified safety issues with EV batteries and/or EVs in general,

>> BUT the media seems obsessed with any fire that might be even remotely related to the EV battery. The most celebrated cases occurred when three different Tesla Model S vehicles has fires during 2013, its first full year on the market. The media reported these events as if car fires were rare. They are not.

Heres a comment on these incidents from MIT Technology Review: In two cases, the cars ran over large metal objects at highway speed; the third car hit a concrete wall. No one was hurt: a warning system allowed the drivers to pull the car over and get out before smoke started coming from the battery pack, and the design of the battery pack slowed the spread of the fire, which never made it into the passenger compartments.

However, public perception is reality, and for that reason,

>> a sophisticated safety subsystem and robust battery enclosures are mandatory elements of the battery management system.

The safety subsystem>> ensures no thermal overload >> controls run-away charging or operation

Specific Powerthe amount of power delivered per kilogrambatteries with high specific power can discharge electricity rap[idly in powerful burstsEV batteries with high specific power allow their vehicle to accelerate rapidlydesign trade-off: high specific power increases the cost per kWh of storage capacity

Power

The last technological metric is Specific power, sometimes referred to as the power to weight ratio.

Specific power is>> the amount of power delivered per kilogram for any object that produces power as outputFor ICE vehicles, specific power often refers to the power produced by an ICE vs. the weight of the engine.For EVs, it refers to the power produced by the battery vs. the weight of the battery.

>> batteries with high specific power can discharge electricity rapidly in powerful bursts

With the observable benefit that >> EV batteries with high specific power allow their vehicle to accelerate rapidly

>>The design trade-off is that high specific power increases the cost per kWh of storage capacity

Li-Ion Chemistries

Source: Boston Consulting Group, http://www.bcg.com/documents/file36615.pdf

The Boston Consulting Group used the six battery metrics we just discussed to create footprints for 5 different lithium Ion chemistries. A quick scan of the footprints indicates that Lithium Titanate batteries, based on advanced nanotech, offers low cost and reasonable specific power, a very long life span, and good performance (particularly their ability to recharge quickly), but relatively poor specific energy, meaning that battery capacity would suffer.

A detailed discussion of the footprint for each of these battery chemistries is beyond the scope of this mini-course, but the interested reader should use the link provided to learn more.

a free study guide for all EVU mini-courses is available for download from our website For a complete list of mini-courses and the study guide, visit: www.evannex.com

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