EVT Battery Technology & Energy Storage 2 — Questions and Answers
Question 1: What is the primary cause of lithium plating in a lithium-ion battery cell?
- Charging at too high a temperature
- Charging at rates exceeding the anode's lithium insertion capacity (Correct answer)
- Excessive depth of discharge cycles
- High internal resistance from electrolyte degradation
Correct answer: Charging at rates exceeding the anode's lithium insertion capacity
Lithium plating occurs when the charging rate exceeds the anode's ability to intercalate lithium ions, causing metallic lithium to deposit on the anode surface.
Question 2: A battery management system (BMS) detects a single cell with a voltage of 2.8V while all other cells in the pack read 3.7V. What is the most likely diagnosis?
- Normal cell-to-cell variation within tolerance
- Cell undergoing thermal runaway
- Severely degraded or defective cell requiring pack inspection (Correct answer)
- BMS sensor fault only
Correct answer: Severely degraded or defective cell requiring pack inspection
A cell reading 2.8V while others read 3.7V indicates the cell is deeply discharged or failing, and the pack must be inspected to determine if the cell needs replacement.
Question 3: Which electrolyte property is most critical for preventing thermal runaway propagation between cells?
- High ionic conductivity
- Low vapor pressure and high flash point (Correct answer)
- Wide electrochemical stability window
- Low viscosity at cold temperatures
Correct answer: Low vapor pressure and high flash point
A low vapor pressure and high flash point electrolyte reduces the risk of ignition and slows thermal runaway propagation by limiting flammable vapor generation.
Question 4: What does the term 'C-rate' describe in battery technology?
- The temperature coefficient of the cell chemistry
- The charge or discharge current relative to the battery's capacity (Correct answer)
- The number of complete charge cycles before capacity falls to 80%
- The ratio of energy to power in watt-hours per watt
Correct answer: The charge or discharge current relative to the battery's capacity
C-rate expresses current as a multiple of battery capacity; a 1C rate fully charges or discharges a battery in one hour.
Question 5: In a nickel-metal hydride (NiMH) battery used in hybrid vehicles, what is the primary advantage over early lead-acid designs?
- Higher cell voltage of 3.6V per cell
- Greater specific energy and better cycle life (Correct answer)
- No need for thermal management
- Compatibility with fast DC charging infrastructure
Correct answer: Greater specific energy and better cycle life
NiMH batteries offer significantly higher specific energy and longer cycle life than lead-acid batteries, making them suitable for hybrid vehicle applications.
Question 6: Which condition will most rapidly accelerate capacity fade in a lithium-ion EV battery?
- Keeping the battery at 50% state of charge during storage
- Repeatedly charging to 100% and discharging to 0% at high temperatures (Correct answer)
- Using AC Level 2 charging exclusively
- Operating the vehicle in mild climates
Correct answer: Repeatedly charging to 100% and discharging to 0% at high temperatures
Repeated full charge/discharge cycles at elevated temperatures cause severe electrolyte decomposition, SEI layer growth, and active material degradation, rapidly accelerating capacity fade.
Question 7: What is the function of the solid electrolyte interphase (SEI) layer on a lithium-ion anode?
- It increases ionic conductivity between cathode and anode
- It acts as a protective passivation layer that prevents further electrolyte decomposition (Correct answer)
- It stores excess lithium to boost capacity
- It dissipates heat generated during fast charging
Correct answer: It acts as a protective passivation layer that prevents further electrolyte decomposition
The SEI layer forms during initial cycling and acts as a passivation film that prevents further electrolyte reduction while still allowing lithium ion transport.
EVT Battery Technology & Energy Storage 2
What is the primary cause of lithium plating in a lithium-ion battery cell?