Electrodes: Anode and Cathode Quiz

Electrodes (Anode and Cathode)

• Electrochemical cells consist of two electrodes with differing standard reaction potentials.
• The cathode absorbs electrons and has a more positive standard potential, while the anode loses electrons and has a more negative potential.
• Selection criteria for electrodes include the cathode’s need for high redox potential, specific capacity, and stability; the anode requires low redox potential, high specific capacity, and good conductivity.
• Cell potential is calculated as Ecell = Ecathode - Eanode; larger potential differences result in higher voltages.

Electrolytes

• Electrolytes can be liquid, solid, polymer, or hybrid, requiring high ionic conductivity and non-reactivity with electrodes.
• Traditional liquid electrolytes are low viscosity, high energy density, and operate between -40 °C and 60 °C, ensuring safety against flammability.
• Solid polymer electrolytes offer flexibility and stability but usually have low ionic conductivity.

Sodium-Ion Batteries

• Sodium-ion batteries present a cost-effective alternative to lithium-ion batteries, leveraging the abundance of sodium minerals.
• They are generally less energy-dense than lithium-ion batteries but suitable for stationary energy storage where cost-effectiveness is favored.
• Research is ongoing to overcome limitations and enhance their commercial viability.

Lead Acid Battery (Lead Accumulator)

• Constructed with lead grids maximizing electrode surface area; anode is spongy lead, and cathode is lead dioxide, both submerged in sulfuric acid electrolyte.
• The design allows the battery to function without separate compartments due to solid oxidizing and reducing agents kept apart by insulators.
• The battery functions as a wet cell, crucial for backup power applications due to its reliability during outages.

Discharging Reactions in Lead Acid Battery

• At the anode: lead oxidizes to produce lead ions and electrons.
• At the cathode: lead dioxide reduces and combines with hydrogen ions and electrons to form lead sulfate and water.
• Overall discharge reaction involves lead, lead dioxide, and sulfate ions forming lead sulfate and water.

Performance and Efficiency of Lead Acid Batteries

• Voltage efficiency approximates 80%, allowing for effective charge and discharge.
• Cycle longevity varies widely, with potential for over 2000 recharge cycles in sealed variants.
• Typical voltage output of a car battery is 12V, capable of delivering high current without damage.

Advantages and Disadvantages of Lead Acid Batteries

• Highly efficient with minimal internal self-discharge.
• Vulnerable to sulfation if left partially charged, risking damage.
• Heavy weight limits energy storage to weight ratio, averaging around 35 Wh/kg.
• Concentration of sulfuric acid decreases during discharge, affecting cell potential.

Nickel-Metal Hydride (NiMH) Batteries

• NiMH batteries are limited by lower voltage outputs compared to newer battery technologies, affecting compatibility.
• They find application in consumer electronics, medical devices, hybrid vehicles, and renewable energy storage.

Lithium-Ion (Li-Ion) Batteries

• Composed of lithium-carbide intercalates as anodes and transition metal oxides as cathodes, typically using lithium salts as electrolytes.
• Offers high energy density (150 Wh/kg) and long cycle life (400-1200 cycles).
• Engineered for safety, mitigating risks linked with lithium metal reactivity, and can charge quickly without fully depleting.

Limitations of Lithium-Ion Batteries

• Experience self-discharge rates around 10% monthly and poor charge retention.
• Higher production costs limit widespread accessibility.

Emerging Alternatives: Sodium-Ion Batteries

• Sodium-ion batteries leverage the abundant sodium element, posing a sustainable alternative to lithium-ion technologies.