Units Practice Exam 1 Energy Storage (copy)

Capacity Units

Amp * hours (Ah)

If you integrate current over time, which unit does that yield?

Capacity

Q=∫Idt or Q=I×Δt

1 Amp*Hour = How many Coulombs?

3600 C

Definition of Capacity

Total amount of electrical charge a battery can store

Specific capacity units

Ah/kg

C/kg

Capacity density units

Ah/L

Energy Units

Watt*hours (Wh)

Capacity * Potential =

Energy

Specific Energy Units

Wh/kg

What is the definition of specific energy?

How much energy per unit mass

Energy Definition

The ability for a system to perform work

Energy density definition

How much energy per volume

Energy density units

Wh/L

Gibbs Free Energy Definition

The amount of energy in a system that is available to do work

Gibbs Free Energy Symbol

ΔG

Gibbs Free Energy Units

J (Joules) or Wh

∫V_cell * I_cell dt =

Gibbs Free Energy

Enthalpy Symbol

Δ𝐻

Enthalpy Definition

Total energy available to a system

Enthalpy Units

J (Joules) or sometimes MJ (megajoules)

entropy symbol

Δ𝑆

Entropy Units

J (Joules)

V_cell definition

Cell overall potential, represents voltage difference between cathode and anode

Calculate cell potential from anode and cathode potentials

V_cell = V_cathode - V_anode

Is voltage an intensive or extensive property? (Does it change when you change concentration, mass, etc.)?

Intensive property, does not change

Is capacity an intensive or extensive property? (Does it change when you change concentration, mass, etc.)?

Extensive property, it does change when you alter those things

What does TΔ𝑆 represent in Gibbs Free Energy Equation?

Thermodynamic penalty to the system

Nernst Equation

Delta G = -nFE

What does each variable (n, F, E) represent in Nernst Equation?

z= number of electrons transferred

F=Faraday’s Constant

E= cell potential

For a V vs C curve, what information can be extrapolated out?

• Can get Vcell

• Can get capacity

• Can get energy (by taking area under the curve)

• Can get Gibbs Free Energy from Nernst Equation

For a Tafel Plot, what can be extrapolated out?

• Vcell

• Power/Power Density ( Current * Voltage)

• Delta G from initial voltage (Nernst Equation)

What CANNOT be extrapolated from a Tafel Plot

Energy (no time)

Capacity (no time)

This is due to the fact that there was current is instantaneous (no time dimension)

What can be extrapolated from a Ragone Plot?

• Specific energy at different places

V_cell can be extrapolated from which of these options?

A. Voltage vs Capacity Curve

B. Tafel Polarization Plot

C. Ragone Plot

D. CV Plot

E. Cycle Life Curve

A. Voltage vs Capacity Curve

B. Tafel Polarization Plot

D. CV Plot

Capacity can be extrapolated from which of these options?

A. Voltage vs Capacity Curve

B. Tafel Polarization Plot

C. Ragone Plot

D. CV Plot

E. Cycle Life Curve

A. Voltage vs Capacity Curve

D. CV Plot (Can integrate peak area (I dt))

E. Cycle Life Curve - if y-axis is capacity

Energy can be extrapolated from which of these options?

A. Voltage vs Capacity Curve

B. Tafel Polarization Plot

C. Ragone Plot

D. CV Plot

E. Cycle Life Curve

A. Voltage vs Capacity Curve (area under curve)

C. Ragone Plot (if y-axis is energy)

D. CV Plot (integrate V * I dt)

Gibbs Free Energy can be extrapolated from which of these options?

A. Voltage vs Capacity Curve

B. Tafel Polarization Plot

C. Ragone Plot

D. CV Plot

E. Cycle Life Curve

A. Voltage vs Capacity Curve (at I=0)

B. Tafel Polarization Plot (at I=0)

D. CV Plot (by taking average of anode and cathode potential and dividing by 2)

Electrolyte in Li-ion battery

Organic solvent such as DME, PC, EC with lithium salt such as LiPF₆ dissolved in organic solvents

Electrolyte in Alkaline battery

KOH (potassium hydroxide)

Electrolyte in Lead-Acid battery

H₂SO₄ (sulfuric acid)

Water Electrolyte usable voltage

1.25-1.5 V

Lead-Acid Electrolyte usable voltage

~ 2.1 V

Organic LIB Electrolyte voltages

3.0-4.2 V

Solid State Electrolyte Voltages

4-4.8V

Alkaline/Zn-C Electrolyte Voltages

1.2-1.5V

From highest to lowest voltage stability windows, what electrolytes perform the best (and worst)?

1. Solid state electrolyte

2. Organic Liquid Electrolyte

3. Lead-Acid electrolyte

4. Alkaline Electrolyte

5. Water-Based Electrolyte

What are the axes of a Tafel Plot?

Y - Voltage

X - Current

What are the three regions on a Tafel plot?

1. Kinetic loss

2. Ohmic loss

3. Concentration Polarization loss

Kinetic Loss Tafel Plot

Comes from reaction overpotential, need to pay penalty to extract any reaction needed to drive electron movement

Ohmic Loss Tafel Plot

V=IR, simple charge transport resistance

Why is the Ohmic loss region linear on a Tafel Plot?

Due to it being governed by Ohm’s Law, and V=IR is directly linearly proportional to current I

Concentration Polarization Loss Tafel Plot

Current is pulling electrons so fast that the ions are not able to keep up with transport

voltage vs capacity curve axes

Y Axis - Voltage

X Axis - Capacity

Single-phase V vs C curve

Sloped downwards line

Dual-Phase V vs C curve

Flat portion and plateau

What information can be taken from a V vs C curve (in terms of area)?

Energy, is area under the curve