Electric Vehicle University - 210a EV BATTERY TECHNOLOGY
THE CENTRAL QUESTION ...
Since the battery is pivotal to my EV, what are the core issues that will allow me to understand battery technology?
A discussion of battery components and fabrication approach, the reasons that building higher capacity batteries are constrained by geometry and technological factors, the key characteristics to assess when comparing battery chemistries, and new battery tech that may lead to significant improvements in those characteristics. To obtain a copy of the EVU study guide for this and other available EVU courses, please complete the form on this page.
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 we’ll 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. We’ll talk more about them in part 3 of this mini-course.
Regardless of the chemistry, battery requirements cannot be considered in a vacuum. The obvious competitor for EV batteries is the ICE vehicle energy storage medium—gasoline. >> 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 ICE The 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.
So … everyone talks about batteries when they discuss EVs, but some folks really don’t understand how a battery works. Let’s 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 components— a 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
All of the components—the 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 system—the BMS. The BMS addresses a variety of operational concerns we’ll consider in parts 2 and 3 of this mini-course.;
EV Batteries are build using a production process that begins with basic components and ends with a complete EV battery. Let’s consider the steps involved:
>> During component production—the electrolyte, anodes, cathodes, and separators are built to the specification of the battery under consideration
>> Cell production creates an individual cell—a 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
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 we’ll 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 questions—Why is battery capacity is so low and …
>> Why can’t we build them bigger and better?
We’ll consider these questions in the next part of this EVU mini-course
Electric Vehicle University - 210a EV BATTERY TECHNOLOGY
This course is presented as part of
Evannex University—a free, open
learning environment that presents
concise, video-based mini-courses for
those who have interest in electric
vehicles (EVs) …
handle high power (up to 100 kW) input
from regenerative braking
have significant storage capacity
small EV, between 4 and 30 kWh
larger BEVs, over 60 kWh
two major battery chemistries
Lithium Ion, Li-ion
Nickel metal hydrid, NiMH
Gasoline’s energy density—13 kWh per kilogram
over 100 times more energy density than a modern
BUT … electric propulsion is much more efficient than
80% for BEVs vs. 20% for ICE
store 1/4 the energy, get the same range
“Batteries are devices that convert stored chemical
energy into useful electrical energy.” U.S. DoE
Batteries are built from cells that contain conducting
material, called an electrolyte, and electrodes, and a
A cathode is a metal electrode that is negatively
charged and is a source of electrons
An anode is an electrode and is a sink for electrons,
that is, electrons flow into the anode
A separator is a permeable membrane that separates
electrodes and allows electrons to flow between
Cell—a complete battery
together as one addressable
Pack—a set of modules that
are organized so that they
can be managed by a BMS
Building an EV Battery
Component production—anodes, cathodes, electrolytes and
Cell production—creating an individual cell
Module production—grouping the cells for control by an
appropriate management subsystem
Pack assembly—combining modules with appropriate management
Integration into the EV with appropriate hooks for a battery
management system within the vehicle
Capacity is measured in kWh
small: 4 - 15 kWh
moderate: 16 - 35 kWh
large: >35 kWh
Why can’t we build a higher
Chevy Volt battery: 17kWh
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