BMS Battery Fundamentals & Electrochemistry 2 — Questions and Answers
Question 1: What is the Nernst equation used to calculate in electrochemistry?
- Maximum charge capacity of a cell
- Equilibrium cell potential at non-standard conditions (Correct answer)
- Internal resistance as a function of temperature
- Self-discharge rate over time
Correct answer: Equilibrium cell potential at non-standard conditions
The Nernst equation relates the equilibrium cell potential to the standard electrode potential, temperature, and the concentrations of reactants and products.
Question 2: Which phenomenon describes the gradual loss of lithium inventory due to irreversible side reactions at the anode?
- Electrode delamination
- Lithium plating
- Loss of lithium inventory (LLI) (Correct answer)
- Electrolyte oxidation
Correct answer: Loss of lithium inventory (LLI)
Loss of lithium inventory (LLI) refers to lithium that becomes electrochemically inactive due to SEI growth, lithium plating, or other side reactions, reducing capacity.
Question 3: A galvanic cell has a positive standard cell potential (E°cell > 0). What does this indicate?
- The reaction is non-spontaneous and requires external energy
- The reaction is spontaneous and produces electrical energy (Correct answer)
- The cell is in equilibrium with no net current flow
- The anode potential is higher than the cathode potential
Correct answer: The reaction is spontaneous and produces electrical energy
A positive E°cell means the Gibbs free energy change (ΔG) is negative, confirming the electrochemical reaction proceeds spontaneously.
Question 4: In a lithium-ion cell, what role does the separator play?
- It stores lithium ions during the charge cycle
- It conducts electrons between electrodes to complete the circuit
- It prevents electronic contact between electrodes while allowing ionic transport (Correct answer)
- It catalyzes the oxidation reaction at the cathode
Correct answer: It prevents electronic contact between electrodes while allowing ionic transport
The separator is an electrically insulating but ionically permeable membrane that prevents short circuits while enabling lithium-ion flow between anode and cathode.
Question 5: What is the primary cause of voltage hysteresis observed during charge and discharge of a battery?
- Differences in electrolyte viscosity at high and low currents
- Polarization effects including ohmic, activation, and concentration losses (Correct answer)
- Thermal runaway onset at high state of charge
- Separator porosity variations under compression
Correct answer: Polarization effects including ohmic, activation, and concentration losses
Voltage hysteresis arises from polarization losses — ohmic resistance, activation overpotential, and concentration overpotential — causing charge voltage to be higher and discharge voltage to be lower than OCV.
Question 6: Which electrochemical technique applies a small AC signal across a range of frequencies to characterize battery internal impedance?
- Cyclic voltammetry (CV)
- Electrochemical impedance spectroscopy (EIS) (Correct answer)
- Galvanostatic intermittent titration technique (GITT)
- Potentiostatic hold
Correct answer: Electrochemical impedance spectroscopy (EIS)
EIS applies sinusoidal voltage or current perturbations at multiple frequencies to separate and quantify ohmic, charge-transfer, and diffusion impedance components.
Question 7: How does increasing C-rate generally affect the usable capacity of a lithium-ion battery?
- Usable capacity increases due to higher reaction kinetics
- Usable capacity remains constant regardless of C-rate
- Usable capacity decreases because polarization losses cause earlier voltage cutoff (Correct answer)
- Usable capacity increases at low temperatures but decreases at room temperature
Correct answer: Usable capacity decreases because polarization losses cause earlier voltage cutoff
At higher C-rates, increased polarization losses cause the terminal voltage to reach the cutoff threshold sooner, reducing the amount of capacity that can be extracted.
BMS Battery Fundamentals & Electrochemistry 2
What is the Nernst equation used to calculate in electrochemistry?