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Battery and energy materials

Check cathode and anode materials for lithium-ion batteries and theoretical capacity calculations, layered, spinel and olivine structures, solid electrolytes, fuel cells, band gaps for solar cells, and the ZT of thermoelectric materials with multiple-choice questions.

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Battery and energy materials: key points

In lithium-ion batteries, Li⁺ shuttles between the crystals of the positive and negative electrodes during charge and discharge. Cathodes include layered rock salt LiCoO₂, spinel LiMn₂O₄ and olivine LiFePO₄, and the structure determines the dimensionality of the Li⁺ pathways, the voltage and the safety. The theoretical capacity of an electrode is Q = nF/(3.6M) mAh/g. Research is also advancing on all-solid-state batteries, which replace the liquid electrolyte with a solid electrolyte.

In fuel cells, whether the electrolyte conducts protons or oxide ions determines the operating temperature, and the theoretical emf of the hydrogen–oxygen reaction is about 1.23 V. The efficiency limit of solar cells is set by the balance between light transmission and thermalization losses, governed by the band gap of the absorber. The performance of thermoelectric materials is expressed by ZT = S²σT/κ, calling for materials that conduct electricity but not heat.

All Battery and energy materials questions (12)
  1. When a lithium-ion battery (graphite anode, LiCoO₂ cathode) discharges, which correctly describes the movement of lithium ions and electrons?
  2. Which correctly pairs lithium-ion battery cathode materials with their crystal structures?
  3. When a graphite anode is fully lithiated, it becomes LiC₆. Which value is closest to the theoretical capacity of graphite (per mass of graphite)? Take the atomic mass of carbon as 12.01, the Faraday constant as 96485 C/mol and 1 mAh = 3.6 C.
  4. For the olivine cathode material LiFePO₄, assuming all the lithium is extracted and reinserted via the Fe²⁺/Fe³⁺ reaction, which value is closest to the theoretical capacity? Take the formula weight of LiFePO₄ as 157.8 g/mol, the Faraday constant as 96485 C/mol and 1 mAh = 3.6 C.
  5. Which is a characteristic of the olivine LiFePO₄ cathode?
  6. Which statement about silicon (Si) as an anode material is correct?
  7. Which statement about sulfide solid electrolytes used in all-solid-state batteries is correct?
  8. Which statement about the electrolyte of a polymer electrolyte fuel cell (PEFC, also called a PEM fuel cell) is correct?
  9. The standard Gibbs energy change of the reaction forming liquid water from hydrogen and oxygen, H₂ + 1/2 O₂ → H₂O(l), is −237 kJ/mol at 25 °C. Which value is closest to the theoretical emf of a fuel cell using this reaction? Take the Faraday constant as 96485 C/mol.
  10. For a single-junction solar cell, there is an optimum band gap of the absorber semiconductor that maximizes the theoretical efficiency (about 1.1–1.4 eV under terrestrial sunlight). Which is the correct reason?
  11. A thermoelectric material at 300 K has a Seebeck coefficient of 200 µV/K, an electrical conductivity of 1.0×10⁵ S/m and a thermal conductivity of 1.5 W/(m·K). Which value is closest to the dimensionless figure of merit ZT = S²σT/κ?
  12. Which is a correct strategy for increasing the thermoelectric figure of merit ZT?

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