Battery Cell Foundations · Final exam

Final exam

Twenty questions across the whole course. Answer every question, then submit to see your score, which answers were right, and where to review the rest. Pass with 15 or more and you can print a statement of completion.

20 questions
15 of 20 to pass
About 20 min
Open book · unlimited attempts

Each question has one right answer unless it says “select every answer that applies”. Nothing you choose leaves this browser.

1 What does the separator let through? Both electrons and lithium ions Neither Electrons, but not lithium ions Lithium ions, but not electrons

2 While a cell is being charged, which electrode is the anode? Graphite is always the anode The negative electrode The positive electrode

3 Why is the negative current collector made of copper rather than aluminium? At the negative electrode’s low potential, aluminium would react with lithium; copper does not Copper conducts better, and the negative side carries more current Copper is cheaper and lighter

4 Pressing an electrode to a lower porosity mainly trades what for what? More energy per volume, for slower ion transport and less power More power, for less energy A higher cell voltage, for a shorter life

5 In a finished lithium-ion cell, where is the liquid electrolyte? Select every place.

Select every answer that applies.

Inside the copper and aluminium foils In the pores of the positive electrode In the pores of the negative electrode In the pores of the separator

6 A 50 Ah cell is discharged at 2C. What is the current? 52 A 25 A 100 A

7 What is the ideal duration of a full discharge at C/5? 0.2 hours 1 hour 5 hours

8 A 20 Ah LFP cell has a nominal voltage of 3.2 V. What is its nominal energy? 23.2 Wh 6.25 Wh 64 Wh

9 Why does a real cell often run for less than the ideal duration at high current? It reaches its lower voltage limit sooner, because of internal resistance and polarization The C-rate formula stops being exact at high current Its nominal capacity is defined differently at high current

10 Which production step builds the solid electrolyte interphase (SEI)? Formation Electrolyte filling End-of-line testing Calendering

11 Why is cell assembly done in a dry room? The electrolyte salt LiPF₆ reacts with water to form hydrofluoric acid To stop static electricity damaging the foils To keep dust away from the electrodes

12 Which property of an electrode does calendering set most directly? Its SEI thickness Its porosity and density Its coat weight, the active material per area

13 What is the main purpose of the aging step at the end of the line? To find cells with internal defects, whose open-circuit voltage falls faster than their neighbours’ To increase the cell’s capacity before shipping To dry out the last moisture

14 Moving to an all-solid-state cell, which conventional step disappears? Mixing Formation Electrolyte filling and wetting

15 Why does a sulfide solid-electrolyte line need a very dry or inert atmosphere? Sulfides react with moisture and release toxic hydrogen sulfide Only the lithium metal needs protection Sulfides catch fire in dry air at room temperature

16 Near room temperature, how much faster does a degradation reaction with an activation energy of about 50 kJ/mol run when the cell is 10 °C warmer? About ten times as fast About 10 % faster About twice as fast

17 An SEI film is 12 nm thick after one year. Under the same conditions, how thick is it after four years? Still 12 nm About 48 nm About 24 nm

18 Which operating condition most favours lithium plating? Fast charging at low temperature Slow discharge at room temperature Storage at high temperature

19 Under the same load current, a cell’s voltage now sags more than when it was new. Which effect is that? Self-discharge Impedance rise Capacity fade

20 By convention, at what remaining capacity is a cell said to have reached end of life? 80 % of its rated capacity When it can no longer be charged at all 50 % of its rated capacity

Final exam

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