5. BATTERIES Notes in english

Rajasthan Polytechnic (BTER) March 13, 2025

 

5. BATTERIES

Batteries are an essential component of Electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs). They store electrical energy and provide power to the vehicle's electric motor. Let's explore each topic related to batteries in detail.

5.1 Overview of Batteries

A battery is a device that stores electrical energy in a chemical form and releases it as electrical energy when needed. In EVs, batteries power the electric motors, making them an essential component for the vehicle's functioning. The most commonly used batteries in electric vehicles today are Lithium-ion (Li-ion) batteries due to their high energy density, longer lifespan, and relatively lighter weight.

Key Points:

  • Energy Storage: A battery stores electrical energy in a chemical state and releases it when needed.
  • Types of Battery Chemistry: Different types of battery chemistries are used in EVs, including Lithium-ion (Li-ion), Nickel-Metal Hydride (NiMH), and Lead-acid batteries.
  • Voltage and Capacity: Batteries provide a specific voltage and have a storage capacity measured in kilowatt-hours (kWh), indicating how much energy it can store and release.

5.2 Battery Parameters

Battery parameters help in understanding a battery's performance, charging capacity, and efficiency. Some important parameters include:

  1. Voltage:

    • The voltage of a battery indicates the potential difference between its two terminals. EV batteries typically operate in a range from 300V to 800V depending on the vehicle’s design and power requirements.

  2. Capacity:

    • Battery capacity refers to the amount of charge a battery can store, typically measured in Ampere-hours (Ah) or kilowatt-hours (kWh). A higher capacity means a longer driving range for EVs.

  3. Energy Density:

    • Energy density refers to how much energy a battery can store per unit of weight or volume. High energy density means more energy stored in a smaller and lighter package, which is crucial for EVs to achieve long ranges.

  4. C-rate:

    • The C-rate indicates the rate at which a battery can be charged or discharged relative to its capacity. For example, a 1C rate means the battery will be fully charged or discharged in one hour.

  5. Cycle Life:

    • Cycle life refers to how many complete charge-discharge cycles a battery can go through before its capacity drops significantly. Lithium-ion batteries typically have a cycle life of around 1000-2000 cycles.

  6. State of Charge (SOC):

    • The SOC indicates how much charge is left in the battery, typically represented as a percentage. 100% SOC means a fully charged battery, and 0% SOC means it is empty.

  7. State of Health (SOH):

    • SOH is a measure of a battery's health and indicates how much capacity has been lost over time due to aging and usage.

5.3 Types of Batteries

Different types of batteries are used in EVs and HEVs, depending on their performance, energy density, cost, and lifespan. Some common types are:

  1. Lithium-Ion (Li-ion) Batteries:

    • Lithium-ion is the most commonly used battery chemistry in EVs due to its high energy density, long cycle life, and lightweight design.
    • Advantages: High energy density, long lifespan, lighter weight, and better efficiency.
    • Disadvantages: Expensive and sensitive to overcharging and high temperatures.

  2. Nickel-Metal Hydride (NiMH) Batteries:

    • These batteries were used in earlier hybrid electric vehicles (HEVs) like the Toyota Prius.
    • Advantages: Safer than Li-ion, longer cycle life, better performance at low temperatures.
    • Disadvantages: Lower energy density, larger size, and heavier than Li-ion batteries.

  3. Lead-Acid Batteries:

    • These are older, traditional batteries commonly used in combustion engine vehicles for starting purposes.
    • Advantages: Inexpensive and widely available.
    • Disadvantages: Low energy density, heavy weight, shorter lifespan, and less efficient.

  4. Solid-State Batteries:

    • An emerging technology that uses solid electrolytes instead of liquid electrolytes. They promise to offer higher energy densities and better safety.
    • Advantages: Higher efficiency, better safety, and longer lifespan.
    • Disadvantages: Currently expensive and not yet mass-produced.

5.4 Battery Charging

Charging an electric vehicle’s battery is the process of replenishing its energy storage. This is typically done through charging stations or home charging systems.

Charging Methods:

  1. AC Charging (Alternating Current):

    • Level 1: Basic home charging using a standard 120V outlet (slow charging).
    • Level 2: A 240V outlet, typically found in homes and public charging stations, offering faster charging.

  2. DC Charging (Direct Current):

    • Level 3 (Fast Charging): Uses high-power DC charging stations to charge the battery rapidly. This is often found at highway rest stops and can charge a vehicle to 80% in about 30 minutes.

  3. Wireless Charging:

    • A newer technology that uses electromagnetic fields to transfer energy from a charging pad to the battery wirelessly. This is still in the research phase for many vehicles.

5.5 Alternative Novel Energy Sources

With the growing need for cleaner and more sustainable energy solutions, several alternative energy sources are being explored for EV and HEV applications. These include:

5.5.1 Solar Photovoltaic Cells:

  • Solar PV cells convert sunlight into electricity, which can be used to charge EVs either directly through a solar-powered charging station or by integrating solar panels into the vehicle itself.
  • Advantages: Renewable, reduces dependency on the grid, environmentally friendly.
  • Challenges: Solar energy is intermittent and depends on weather conditions, requiring efficient energy storage.

5.5.2 Fuel Cells:

  • Fuel cells convert hydrogen into electricity through a chemical process, emitting only water vapor as a byproduct. These can be used to power EVs in a process similar to battery-powered vehicles but with hydrogen as the fuel source.
  • Advantages: Zero emissions, fast refueling time.
  • Challenges: Expensive, hydrogen infrastructure is limited, and storage is a challenge.

5.5.3 Super Capacitors:

  • Super capacitors store energy electrostatically and can release energy very quickly. They are used for short bursts of high power, such as accelerating a vehicle.
  • Advantages: Very fast charging and discharging, longer cycle life.
  • Challenges: Lower energy density compared to batteries, limited storage capacity.

5.5.4 Flywheels:

  • Flywheels store energy in the form of rotational kinetic energy. They are used to provide bursts of power, such as during acceleration, and are integrated into some electric systems for short-term energy storage.
  • Advantages: Long lifespan, fast charging, and discharging.
  • Challenges: High cost, mechanical complexity, and large size.

5.6 Regenerative Braking in EVs

Regenerative braking is a technology used in electric vehicles and hybrid electric vehicles to recover some of the energy that would otherwise be lost as heat during braking. Instead of using conventional braking systems to slow down the vehicle, regenerative braking uses the electric motor to reverse its function, converting the kinetic energy of the vehicle back into electrical energy and storing it in the battery.

How Regenerative Braking Works:

  • Motor Reversal: When the driver applies the brakes, the electric motor works in reverse, acting as a generator.
  • Energy Conversion: Kinetic energy from the vehicle’s motion is converted into electrical energy.
  • Energy Storage: The converted energy is stored in the battery for later use, improving the vehicle's efficiency and increasing its driving range.

Benefits:

  • Increases Range: By recovering energy during braking, regenerative braking helps extend the range of the vehicle.
  • Reduces Wear on Brake Pads: Since the electric motor is doing most of the braking, it reduces the wear on traditional mechanical brake systems.
  • Environmentally Friendly: This system helps reduce energy consumption and increase overall vehicle efficiency.

Challenges:

  • Efficiency: The efficiency of regenerative braking is not 100%, and it is more effective at higher speeds.
  • Braking Feel: Some drivers may find the braking feel different from traditional brakes, as regenerative braking can feel less responsive or less consistent.

Summary

  • Batteries are essential for powering electric vehicles, with Lithium-ion batteries being the most common.
  • Battery parameters like capacity, voltage, and cycle life are crucial for understanding performance.
  • Different types of batteries include Li-ion, NiMH, and Lead-acid.
  • Battery charging can be done through AC charging, DC fast charging, and even wireless charging.
  • Alternative energy sources like solar cells, fuel cells, super capacitors, and flywheels are being explored for EVs.
  • Regenerative braking recovers energy during braking and stores it in the battery, increasing efficiency and range.
Rajasthan Polytechnic (BTER)

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