Electric Vehicle Battery Systems

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Electric Vehicle Battery Systems

• 1 ELECTRIC VEHICLE BATTERIES
• 2 ELECTRIC VEHICLE BATTERY EFFICIENCY
• 3 ELECTRIC VEHICLE BATTERY CAPACITY
• 4 ELECTRIC VEHICLE BATTERY CHARGING
• 5 ELECTRIC VEHICLE BATTERY FAST CHARGING
• 6 LECTRIC VEHICLE BATTERY DISCHARGING
• 7 ELECTRIC VEHICLE BATTERY PERFORMANCE
• 8 TESTING AND COMPUTER-BASED

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1 ELECTRIC VEHICLE BATTERIES
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Road vehicles - pollution

• Road vehicles emit significant air-borne
  pollution
• 18 of America's suspended particulates,
• 27 of the volatile organic compounds,
• 28 of Pb,
• 32 of nitrogen oxides,
• 62 of CO.
• Vehicles also release 25 of America's
  energy-related CO2, the principle greenhouse
  gas.

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• technological revolutions of 20th century
• - Electrification,
• - automotive transportation
• energy markets
• - electrical generation 34
• - transportation consumes 27
• nation's electricity coal and natural gas
  provide more than 65 of the energy
• Renewable energy less than 2 of the energy used
• oil consumption
• - transportation (cars, trucks, and buses)
  more than 2/3,
• - Aircraft 14,
• - ships and locomotives 5.

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Difficulty of electric cars

• development of electric cars1900-1920
• the weight of these vehicles,
• long recharging time,
• poor durability of electric barriers
• 1 pound of gasoline 100 pounds of Pb-acid
  batteries.
• Refueling required only minutes,
• delivery with relatively cheap and easy.

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ELECTRIC VEHICLE OPERATION

• Because power/torque curves for electric motors
  are much broader than those for internal
  combustion (IC) engines, the acceleration of EV
  can be much quicker.
• regenerative braking
• operate very quietly
• handling and operation of EVs internal
  combustion counterparts.

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Electric Vehicle Components

• an electric motor,
• an electronic control module (ECM),
• a traction battery, a battery management system,
  a smart battery charger, a cabling system, a
  regenerative braking system,
• a vehicle body, a frame, EV fluids for cooling,
  braking, etc.,
• and lubricants.

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Electronic Drive Systems

• An EV is propelled by an electric motor.
• The traction motor is controlled by an electronic
  control module.
• The controller takes a signal from the vehicle's
  accelerator pedal and controls the electric
  energy provided to the motor, causing the torque
  to turn the wheels.
• types of electric drive systems alternating
  current (AC) and direct current (DC).
• In the past, DC motors were commonly used for
  variable-speed applications.
• AC motors are now more widely used for these
  applications.

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• DC motors are easier to control and are less
  expensive, but they are often larger and heavier
  than AC motors.
• AC motors and controllers usually have a higher
  efficiency over a large operational range, but,
  due to complex electronics, the ECMs are more
  expensive.
• Today, both AC and DC technologies can be found
  in commercial automobiles.

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BATTERY BASICS

• A battery cell consists of five major components
  
• (1) electrodesanode and cathode
• (2) separators
• (3) terminals
• (4) electrolyte and
• (5) a case or enclosure.
• Battery cells are grouped together into a single
  mechanical and electrical unit called a battery
  module.

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Electrolyte

• can be a liquid, gel, or solid material.
  lead-acid (Pb-acid), nickel-cadmium (NiCd), and
  others have used a liquid electrolyte.
• either be acidic or alkaline, depending on the
  type of battery.
• advanced batteries a gel, paste, or resin.
• Pb-acid, NiMH, and Lithium (Li)-ion batteries.
• Lithium-polymer batterieshave a solid
  electrolyte

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BATTERY BASICS

• When an electrical load such as a motor is
  connected to the battery terminals, an electric
  circuit is completed, and current is passed
  through the motor, generating the torque.
• the battery delivers its stored energy from a
  charged to a discharged state.
• If the electrical load is replaced by an external
  power source that reverses the flow of the
  current through the battery, the battery can be
  charged.
• This process is used to reform the electrodes to
  their original chemical state, or full charge.

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INTRODUCTION TO ELECTRIC VEHICLE BATTERIES

• EV development 1900s, 1970s, 1990s, 2007
• U.S. Advanced Battery Consortium (USABC) to
  accelerate the development of advanced batteries
  for use in EV design.
• The USABC has established battery performance
  goals intended to make EVs competitive with
  conventional IC engine vehicles in performance,
  price, and range.
• technological development for EV batteries will
  emphasize advanced Pb-acid, NiMH batteries,
  Li-ion, and lithium-polymer batteries.

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INTRODUCTION TO ELECTRIC VEHICLE BATTERIES

• salient features of the traction battery
• - one charge to provide a long range or
  mileage
• - stable power with deep discharge
  characteristics to allow for acceleration and
  ascending power capability of the EV
• - Long cycle life with maintenance free and
  high safety mechanisms built into the battery
• - Wide acceptance as a recyclable battery
  from the environmental standpoint

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The Pb-Acid Battery

• flooded lead-acid batteries(????) requires
  maintenance by periodic replenishment of
  distilled water, service lives of up to 20 years,
  specific gravity1.215
• valve regulated lead-acid (VRLA) battery(?????)
  recombination factor efficiency is 95 to 99,
  specific gravity1.3, lowest internal resistance,
  
• Two types of VRLA traction batteries are
  available commercially, the absorbed glass mat
  (AGM) battery(?????????) and the gel technology
  battery(?????) .

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• The negative and the positive plates are pasted
  with an active materiallead oxide (PbO2) and
  sometimes lead sulphate (PbSO4). The active
  material provides a large surface area for
  storing electrochemical energy.
• The electrolyte solution is a combination of
  sulphuric acid (H2SO4) and distilled water.
• During the charge phase, water in the electrolyte
  solution is broken down by electrolysis. Oxygen
  evolves at the positive plates and hydrogen
  evolves at the negative plates.
• The evolution of hydrogen and oxygen results in
  up to 30 recombination
• In the VRLA battery, the efficiency is 95 to 99.

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The NiMH Battery

• A strong growth of the rechargeable battery
  consumer appliance market for laptop computers,
  mobile phones, and camcorders
• 1950s - Ni-Cd battery
• mid-1980s - NiMH battery
• for the smaller size NiMH battery, the higher
  energy density 8-8.5 g/cm3(AB5 alloys ) 5-7
  g/cm3(AB2 alloys )

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Li-ion Battery

• lithium is the metal with the highest negative
  potential and lowest atomic weight
• provide EVs with the greatest performance
  characteristics in terms of acceleration and
  range.
• charge and discharge faster than Pb-acid and NiMH
  batteries.
• typically 40 smaller and weigh half than NiMH
• These batteries have an open circuit voltage
  (OCV) of approximately 4.1V at full charge.

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Li-ion Battery

• Overcharging of Li-ion batteries will cause
  damage in the form of electrode or electrolyte
  decomposition.
• The development of advanced battery management
  systems is a key to ensuring that lithium-ion
  batteries operate safely, during normal operation
  as well as in the event of vehicle accidents.
• Li-ion battery charging systems must be capable
  of working with the battery management systems to
  ensure that overcharging does not occur.
• the Li-ion is an environmentally friendly battery
  in comparison with nickel-based batteries, which
  use NiMH battery chemistry.

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Li-ion Battery

• Commercialization of these Li-ion batteries
  1960s-1970s
• solid-state Li-ion battery 1995
• The first Li-ion cells for EV applications were
  based on the LiCoO2 (lithium-cobalt-oxide)
  cathode and demonstrated a capacity of 30Ahr.
• 60Ahr battery cells are now available and capable
  of providing a specific energy of 115 Whr/kg.
• Table 1-2 Development of Li-ion battery systems.

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The Li-Polymer Battery

• design challenges associated with kinetics of the
  battery electrodes, the ability of the cathode
  and anode to absorb and release lithium ions, has
  resulted in lower specific power and limited
  cycle life for lithium-polymer batteries.
• considered as solid-state batteries
• The polymers can conduct ions at temperatures
  above about 60C (140F),
• can be formed in any size or shape

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FUEL CELL TECHNOLOGY

• battery, chemical energy is stored in the
  electrode,
• fuel cell, the energy is stored outside the
  electrodes. Thus there is no physical limit to
  the amount of fuel stored.
• Water electricity ? 2H2 02
• 2H2 02 ?2H20 electricity
• Anode H2 ? M12H 2e-
• Cathode 02 4H 4 e - ? 2H2O

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Table 1-3 Comparison between electrolytes
fuel-cell electrolytes
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FUEL CELL TECHNOLOGY

• Fuel oxidant ? H20 other products
  electricity
• The open circuit voltage (OCV) is 1.25 V,
• As soon as the current flows through the cell
  with a load connected to the terminals, fuel cell
  voltage drops, and the efficiency of the fuel
  cell drops.
• current density of 0.8-1.2A/cm2 is possible from
  a single fuel cell within the range of 0.55-0.75
  V.
• connected in series or parallel to form a fuel
  cell battery stack
• practical efficiency of 50 to 60 higher than the
  25 to 35 for the heat engine.

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FUEL CELL TECHNOLOGY

• power density of 0.3 to 0.35 kW/L
• Most thermal combustion engines have power
  densities of approximately 1 kW/L,
• IC engine powertrain costs range between 20/kW
  to 30/kW

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FUEL CELL TECHNOLOGY

• The compressed hydrogen tank size required to
  contain 6.8kg of hydrogen for a 3-L, 1,500-kg
  vehicle with a driving range of 560km is 340L at
  25MPa, and 160L at 52MPa.
• A typical gas tank volume for such a vehicle is
  70 L.
• Thus the limited energy storage capacity of
  hydrogen and the lack of an infrastructure to
  supply it makes it necessary to develop a process
  to extract hydrogen from gasoline.

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CHOICE OF A BATTERY TYPE FOR ELECTRIC VEHICLES

• Li-ion batteries are capable of storing up to
  three times more energy per unit weight and
  volume than the conventional Pb-acid and NiMH
  batteries.
• Because of the high-energy characteristics,
  Li-ion batteries find wide-spread applications
  including aerospace, EV, and hybrid EV designs.
• The self-discharge rate of the solid-state Li-ion
  battery is fairly low5 of the capacity per
  month, compared to the 15 for the VRLA battery
  and 25 for NiMH battery.

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CHOICE OF A BATTERY TYPE FOR ELECTRIC VEHICLES

• memory effect
• - Li-ion battery no
• - the NiMH and the VRLA battery yes
• the cycle life typically drops to 80 of the
  rated capacity at the C-rate (one hour charge
  followed by a one hour discharge)
• - NiMH 500 cycles
• - Li-ion 1,200 cycles
• mass-produced at less than a 1 per Whr solid
  Li-ion batteries, NiMH battery

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characteristics of the Li-ion battery are
favorable for EV

• High gravimetric and volumetric energy densities
• Ambient temperature operation
• Long life cycle (See Figure 1-1)
• Good pulse power density

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Table 1-5 Developing Li-ion battery chemistry
and characteristics.
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next generation design efforts

• to further extend the battery service life to 10
  years
• to cut the battery costs significantly

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END