Battery Fundamentals & Electrochemistry Flashcards

What is the primary chemical composition of a typical lithium-ion battery electrolyte?

Answer: Lithium salt (e.g., LiPF₆) dissolved in organic carbonate solvents

Standard Li-ion electrolytes use lithium hexafluorophosphate (LiPF₆) dissolved in a mixture of organic carbonates such as ethylene carbonate and dimethyl carbonate.

Which of the following best describes the theoretical basis for Peukert's law?

Answer: Higher discharge currents cause disproportionately greater capacity loss due to kinetic and diffusion limitations

Peukert's law empirically captures that real capacity decreases at higher discharge rates because polarization and diffusion limitations remove more energy as heat rather than useful work.

In battery terminology, what is meant by 'calendar aging' as distinct from 'cycle aging'?

Answer: Degradation that occurs simply from time passing while the cell is stored, independent of cycling

Calendar aging refers to capacity and power fade that occurs due to storage over time (temperature, SOC level, humidity) without active cycling.

How does the concentration overpotential (diffusion overpotential) arise during high-rate battery discharge?

Answer: Lithium ion concentration gradients form within the electrolyte and electrode because supply cannot match demand

At high discharge rates, ion consumption outpaces diffusion, creating concentration gradients that reduce the effective electrochemical driving force and lower terminal voltage.

Which cathode material family is characterized by an olivine crystal structure with exceptional thermal stability?

Answer: LFP (LiFePO₄)

LiFePO₄ (LFP) has an olivine structure with strong P-O covalent bonds that prevent oxygen release, giving it superior thermal stability and safety compared to layered oxide cathodes.

What is the theoretical specific capacity of graphite as an anode material in lithium-ion batteries?

Answer: 372 mAh/g

Graphite's theoretical capacity is 372 mAh/g, based on the stoichiometric formation of LiC₆ where one lithium atom intercalates per six carbon atoms.

What condition is necessary for lithium metal plating to occur on a graphite anode during charging?

Answer: Anode potential drops below 0 V vs. Li/Li⁺ due to overpotential

Lithium plating occurs when local anode potential falls below 0 V vs. Li/Li⁺ — conditions that arise from fast charging, low temperatures, or an undersized anode — depositing metallic Li instead of intercalating it.