Text Exercise 4

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Li-ion batteries Exercise 1 – Li-ion battery voltage estimation A Li-ion battery with nominal capacity of 5 Ah operates at ambient temperature, supplying 3.6 V during discharge at SoC = 80% and C-rate = 1 h-1. Assuming that: • Tafel kinetics is valid for both electrodes • Ion and mass transfer effects in electrodes are negligible • Chemical activities of reactants are approximated to the value of SOC • Electrolyte resistance is equal to 0.02 Ω • Transfer coefficient of both electrodes during discharge is 0.5 Estimate the battery voltage at SoC = 20% and C-rate = 1. Exercise 2 – Li-ion batteries A Li-ion battery with a nominal capacity of 5 Ah operates at ambient temperature supplying 3.7 V during discharge at SoC 75% and C-rate = 1.5 h-1, and requiring 4.0 V during charge at SoC = 25% and C-rate = 1.5. Assuming that: • Tafel kinetics is valid for both electrodes • Ion and mass transfer effects in electrodes are negligible • Chemical activities of reactants are aproximated to the value of SOC • Electrolyte resistance is equal to 0.02 Ω • Transfer coefficient of both electrodes during discharge is 0.5 Calculate the number of batteries that are necessary to operate the cycle in figure with an overall efficiency higher than 90%, chose starting SoC and depict SoC variation in time.