Energy Storage Systems for EVs

Questions and Answers

What is the practical capacity of a battery primarily defined by?

Internal resistance

Battery lifespan

Constant discharge current characteristics (correct)

Temperature fluctuations

How does the magnitude of discharge current affect the capacity of a battery?

Higher discharge currents increase capacity

Discharge current does not impact capacity

Lower discharge currents decrease capacity

Higher discharge currents decrease capacity (correct)

What is the nominal capacity of a battery given at a 1C-rate indicative of?

Discharging the battery in 1 hour (correct)

A reduction of total energy

Optimal temperature during operation

Charging the battery in 1 hour

If a battery has a practical capacity of 100 Ah, what would its discharge rate be when discharged over 10 hours?

10 A Signup and view all the answers

What happens to the charge time of a battery as the charge rate increases?

Charge time decreases Signup and view all the answers

What does not affect the announced capacity of a battery?

The physical size of the battery Signup and view all the answers

If a battery's practical capacity increases from 42 Ah at a 10-hour discharge to 46 Ah at a 20-hour discharge, what does this imply?

Longer discharge times allow for higher capacity Signup and view all the answers

What is the formula to calculate discharge rate?

Discharge rate = Capacity / Time Signup and view all the answers

What is NOT a requirement of an energy storage system for electric vehicles?

Maintenance required Signup and view all the answers

What is the primary function of a galvanic cell during its operation?

Converting chemical energy into electric energy Signup and view all the answers

Which characteristic is essential for the operational efficiency of an energy storage system?

High energy density Signup and view all the answers

What happens to nickel oxyhydroxide during the discharge of a nickel-cadmium cell?

It reduces to nickel hydroxide. Signup and view all the answers

Which active material is used in the charged negative plate of a nickel-cadmium cell?

Cadmium metal Signup and view all the answers

What happens during the charging process of an electrochemical cell?

Electric energy is converted to chemical energy Signup and view all the answers

Which of the following statements about the life cycle of a battery is true?

Cycle life is linked to discharge capabilities Signup and view all the answers

What is the primary reason the practical capacity of a battery is lower than its theoretical capacity?

Incomplete discharge of energized materials Signup and view all the answers

Which feature is NOT described as a requirement for an energy storage system for EVs?

Easy to refill Signup and view all the answers

What is the Faraday constant used to represent?

Charge carried by one mole of electrons Signup and view all the answers

What type of cell is primarily associated with charging processes?

Electrolytic cell Signup and view all the answers

What is the net reaction in the potassium hydroxide electrolyte during the discharge of a nickel-cadmium cell?

Cd + 2NiOOH + 2H2O Signup and view all the answers

What charge does 1 A carry in terms of Coulombs over 1 second?

1 C Signup and view all the answers

Which property ensures the safety of an energy storage system during operation?

Sealed and leak proof design Signup and view all the answers

During the discharge process, what happens to cadmium metal?

It oxidizes to cadmium hydroxide and releases electrons. Signup and view all the answers

What is the voltage associated with the net reaction of a nickel-cadmium battery during discharge?

1.299 V Signup and view all the answers

What is the rated continuous power of a battery?

Maximum power for prolonged discharge intervals Signup and view all the answers

How can the energy of an electrochemical cell be improved?

By increasing the voltage Signup and view all the answers

Which factor influences the specific power of a battery the most?

The load connected to the battery Signup and view all the answers

What does power density refer to in a battery?

The power of the battery per unit volume Signup and view all the answers

What must be minimized to improve the power of an electrochemical cell?

Voltage drop with increased current Signup and view all the answers

How does specific energy differ from specific power in a battery context?

Specific energy indicates capacity; specific power indicates loading Signup and view all the answers

What is the primary condition needed for enhancing the energy of an electrochemical cell?

Increased amount of active material Signup and view all the answers

Which statement regarding energy and power conditions for a cell is correct?

Energy and power conditions are completely opposed to each other Signup and view all the answers

What is the primary characteristic illustrated by a Ragone Plot?

Energy density as a function of power density Signup and view all the answers

At which point in a Ragone Plot can high specific energy be delivered but at low power output?

Point B Signup and view all the answers

What defines Coulombic efficiency in electrochemical cells?

The charge transferred during discharging to charging Signup and view all the answers

Which efficiency metric is primarily concerned with energy transfer in electrochemical cells?

Energy Efficiency Signup and view all the answers

What is a possible consequence of operating a cell at high power output from an energy optimized configuration?

Increased polarization and large losses Signup and view all the answers

Why may energy optimized cells lead to larger losses under high power conditions?

Because it compromises energy density for power density Signup and view all the answers

What are the two main types of efficiency metrics used for electrochemical cells?

Coulombic Efficiency and Energy Efficiency Signup and view all the answers

What is another term used for Coulombic efficiency?

Amphour efficiency Signup and view all the answers

Study Notes

Energy Storage System Requirements for EVs

Must be portable, compact, and lightweight.
Should have low initial cost and provide continuous electric supply.
High energy storage per unit mass and volume is essential.
Efficiency and wide operational temperature range are critical.
Should exhibit long inactive shelf life and operational life.
Constructed to be sealed, leak-proof, and rugged against abuse.
Safety during use, high cycle life, and maintenance-free operation are required.

Electrochemical Cell Overview

Fundamental unit of a battery; converts chemical energy to electric energy during discharge and vice versa during charging.
Two main types: electrolytic cells (charging) and galvanic cells (discharging).
Performance is influenced by the materials used within the cell.

Battery Performance Parameters

Capacity (QT): Theoretical measure based on chemical reactions; example with nickel-cadmium cells shows discharge processes with specific voltages (e.g., 1.299 V).
Practical Capacity (QP): Actual charge released during a complete battery discharge, typically lower than theoretical due to practical limitations.
High discharge rates can lead to reduced battery capacity; smaller discharge currents yield higher capacities.

Discharge and Charge Rates

Discharge rate calculates the current based on the battery's rated capacity and total discharge time.
Charge rate (C-rate) defines how quickly a cell can accept charge; presented as a factor of the battery's capacity (1C charges in 1 hour).

Power and Specific Power

Maximum power output is crucial during quick discharges in EVs; rated continuous power defines safe prolonged discharge limits.
Specific power relates to electrical power per kg of battery mass; typical lead-acid batteries offer around 280 W/kg.
Power density refers to power capacity relative to volume (W/L).

Energy and Power Relationships

Energy of a cell improves by increasing voltage and active material quantity.
Power enhancement occurs by minimizing voltage drops and reducing ohmic and kinetic constraints, potentially by using thinner electrodes.
Cells can be optimized either for energy or power, affecting overall efficiency and performance.

Ragone Plot

Illustrates the tradeoff between energy density and power density logarithmically.
Point A on the plot represents high specific power but limited specific energy, while Point B represents high specific energy at lower power output.
Used to compare battery technologies and performance characteristics relevant to automotive applications.

Efficiency Metrics

Performance metrics include:
- Coulombic Efficiency: Ratio of charge discharged to charge charged, indicating efficiency in charge transfer.
- Energy Efficiency: Measures overall energy conversion effectiveness, characterized by energy retention relative to energy input.

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Description

This quiz focuses on the requirements for energy storage systems specifically designed for electric vehicles (EVs). Explore essential features such as efficiency, cost, and operational capabilities to understand what makes these systems effective for modern transportation.