EV Battery Technology,part 1

EV-210a

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)

EV BatteriesBaseline requirements:handle high power (up to 100 kW) inputfrom chargingfrom regenerative brakinghave significant storage capacitysmall EV, between 4 and 30 kWhlarger BEVs, over 60 kWhtwo major battery chemistriesLithium Ion, Li-ionNickel metal hydrid, NiMH

EV batteries lie at the heart of every BEV and are a critical component for all PHEVs.They represent a significant technological challenge for reasons that well explore later in this mini-course.

>> We can develop a set of broad baseline requirements for an EV battery:

>> It must handle high power input>> from charging and >> from regenerative braking>> It must have significant storage capacity>> for small BEV and PHEVs, between 4 and 30 kWh>> for larger BEVs, over 60 kWh

>> Today, these requirement are addressed with two dominant battery chemistries:>> Lithium Ion, Li-ion the dominant battery for BEVs>> Nickel metal hydrid, NiMH the common battery battery choice for PHEVs

But a number of other chemistries are in various stages of research and development. Well talk more about them in part 3 of this mini-course.

The challengeGasolines energy density13 kWh per kilogramover 100 times more energy density than a modern Li-ion battery!BUT electric propulsion is much more efficient than ICE80% for BEVs vs. 20% for ICEstore 1/4 the energy, get the same range

Regardless of the chemistry, battery requirements cannot be considered in a vacuum. The obvious competitor for EV batteries is the ICE vehicle energy storage mediumgasoline.>> Gasoline has an energy density of 13 kWh per kilogram>> over 100 times the energy density of a Li-ion battery>> BUT we have already learned that electric propulsion is much more efficient than ICE>> 80% for BEVs vs. 20% for ICEThe implication is that if EV batteries can >> store 1/4 the energy, they can achieve the same range as an ICE vehicle.The challenge is achieving that goal.

Battery BasicsBatteries are devices that convert stored chemical energy into useful electrical energy. U.S. DoEBatteries are built from cells that contain conducting material, called an electrolyte, and electrodes, and a separatorA cathode is a metal electrode that is negatively charged and is a source of electronsAn anode is an electrode and is a sink for electrons, that is, electrons flow into the anodeA separator is a permeable membrane that separates electrodes and allows electrons to flow between them

Source: Wikipedia

So everyone talks about batteries when they discuss EVs, but some folks really dont understand how a battery works. Lets take a simplified look.

The US DoE describes a battery this way: >> Batteries are devices that convert stored chemical energy into useful electrical energy.

>> Batteries are built from cells that contain specific componentsa conducting material, called an electrolyte, and electrodes, called cathodes and anodes, as well as one or more separators that are placed between the cathode and anode.

>> A cathode is an electrode that is negatively charged, and is a source of electrons; that is electrons flow out of the cathode toward the anode

>> An anode is an electrode and is a destination for electrons, that is, electrons flow into the anode, which is often depicted as having a positive charge

>> A separator is a permeable membrane that separates electrodes and allows electrons to flow between them

Battery BasicsCella complete batteryModulecells connected together as one addressable unitPacka set of modules that are organized so that they can be managed by a BMS

electrolyte, anode, cathode, separatormodulepack

All of the componentsthe electrolyte, the electrodes and separators are fabricated into a >> cell that is built individually and forms a complete battery>> cells are connected together as one addressable unit, called a module>> Finally, modules are organized into a pack so that they can be controlled by a battery management systemthe BMS.The BMS addresses a variety of operational concerns well consider in parts 2 and 3 of this mini-course.;

Building an EV BatteryComponent productionanodes, cathodes, electrolytes and separatorsCell productioncreating an individual cellModule productiongrouping the cells for control by an appropriate management subsystemPack assemblycombining modules with appropriate management subsystemsIntegration into the EV with appropriate hooks for a battery management system within the vehicle

EV Batteries are build using a production process that begins with basic components and ends with a complete EV battery. Lets consider the steps involved:

>> During component productionthe electrolyte, anodes, cathodes, and separators are built to the specification of the battery under consideration

>> Cell production creates an individual cella actual battery, that becomes the basic building block for the EV battery. An EV battery may contain many thousands of cells.

>> Module production groups the cells into a easily addressable subassemblies so that each can be controlled by with an appropriate management subsystem

>> Pack assembly combines modules with appropriate management subsystems to manage power, charging, and thermal issues

>> Integration places the pack into the EV with appropriate hooks for a battery management system within the vehicle

Battery CapacityCapacity is measured in kWhsmall: 4 - 15 kWhmoderate: 16 - 35 kWhlarge: >35 kWhWhy cant we build a higher capacity battery?

Chevy Volt battery: 17kWh

The capacity of the battery pack is directly proportional to the number of modules and the number of cells per module and depends on a variety of technology characteristics that well discuss in part 2.

>> As we learned in earlier EVU mini-courses, battery capacity is measured in kilowatt hours.

>> Small batteries are typically used in PHEVs and have a capacity in the neighborhood of 4 - 15 kWh. For example, the Prius plug-in PHEV has a 4.5kWh battery.

>> Moderately sized batteries are found in both PHEVs and some small BEV's and typically have a capacity between 16 and 35 kWh. For example, the Nissan Leaf BEV has a battery capacity of 24 kWh.

>> Large EV batteries remain relatively rare. Only the Tesla Model S offers battery sizes of 60 and 85 kWh.

The big questionsWhy is battery capacity is so low and

>> Why cant we build them bigger and better?

Well consider these questions in the next part of this EVU mini-course

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

OlharesRouletBeats d'Amor, track 12014-05-18T14:02:41118051.055OlharesRouletBeats d'Amor, track 12014-05-18T14:02:41118051.055