BMS Battery Fundamentals & Electrochemistry 3 — Questions and Answers
Question 1: What is the definition of Coulombic efficiency (CE) in a battery cycle?
- Ratio of energy delivered on discharge to energy consumed on charge
- Ratio of charge extracted on discharge to charge input on charge (Correct answer)
- Ratio of cell capacity at end of life to initial capacity
- Ratio of open-circuit voltage to terminal voltage under load
Correct answer: Ratio of charge extracted on discharge to charge input on charge
Coulombic efficiency is the ratio of discharge capacity to charge capacity in a given cycle, reflecting how much charge is lost to side reactions.
Question 2: Which factor most significantly reduces ionic conductivity of a liquid electrolyte at low temperatures?
- Increased electrode surface area
- Higher viscosity reducing ion mobility (Correct answer)
- Elevated internal pressure in the cell
- Faster SEI film formation kinetics
Correct answer: Higher viscosity reducing ion mobility
At low temperatures, electrolyte viscosity increases substantially, slowing ionic mobility and reducing the electrolyte's ability to conduct lithium ions efficiently.
Question 3: In a lead-acid battery, what is the active material at the positive electrode during discharge?
- Lead (Pb)
- Lead sulfate (PbSO₄)
- Lead dioxide (PbO₂) (Correct answer)
- Sulfuric acid (H₂SO₄)
Correct answer: Lead dioxide (PbO₂)
During discharge, PbO₂ at the positive electrode is reduced to PbSO₄ as it reacts with sulfate ions from the electrolyte.
Question 4: What does the term 'intercalation' mean in the context of lithium-ion batteries?
- The chemical dissolution of electrode material into the electrolyte
- The insertion of lithium ions into the layered host structure of an electrode without destroying it (Correct answer)
- The precipitation of lithium metal on the anode surface
- The formation of gas bubbles within the electrolyte during charging
Correct answer: The insertion of lithium ions into the layered host structure of an electrode without destroying it
Intercalation is the reversible insertion of guest ions (Li⁺) into the interstitial spaces of a host crystal lattice, enabling repeated charge-discharge cycling.
Question 5: What is the standard reduction potential reference electrode used in aqueous electrochemistry?
- Saturated calomel electrode (SCE)
- Silver/silver chloride electrode (Ag/AgCl)
- Standard hydrogen electrode (SHE) (Correct answer)
- Copper/copper sulfate electrode
Correct answer: Standard hydrogen electrode (SHE)
The Standard Hydrogen Electrode (SHE) is defined as 0.00 V and serves as the universal reference against which all other electrode potentials are measured.
Question 6: Which aging mechanism is primarily responsible for capacity fade in NMC cathode materials at elevated voltages?
- Lithium plating on the anode
- Transition metal dissolution and cathode structural degradation (Correct answer)
- Separator pore blockage by lithium deposits
- Anode graphite exfoliation
Correct answer: Transition metal dissolution and cathode structural degradation
At high voltages, NMC cathodes undergo transition metal (Mn, Ni, Co) dissolution into the electrolyte and phase transformations, causing structural degradation and capacity loss.
Question 7: What is the relationship between a battery's energy density and power density, often visualized on a Ragone plot?
- Higher power density always yields higher energy density in all chemistries
- Energy density and power density are generally inversely related — high power comes at the cost of lower energy (Correct answer)
- Both increase together as cell temperature rises above 45°C
- They are independent parameters with no correlation
Correct answer: Energy density and power density are generally inversely related — high power comes at the cost of lower energy
The Ragone plot shows that devices optimized for high power (like supercapacitors) sacrifice energy density, while high-energy devices (like batteries) deliver lower peak power.
BMS Battery Fundamentals & Electrochemistry 3
What is the definition of Coulombic efficiency (CE) in a battery cycle?