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Ch.20 - Electrochemistry
Brown - Chemistry: The Central Science 15th Edition
Brown15th EditionChemistry: The Central ScienceISBN: 9780137542970Non è quello che usi tu?Cambia libro di testo
Capitolo 20, Problema 84b

Li-ion batteries used in automobiles typically use a LiMn2O4 cathode in place of the LiCoO2 cathode found in most Li-ion batteries. (b) Which material has a higher percentage of lithium? Does this help to explain why batteries made with LiMn2O4 cathodes deliver less power on discharging?

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insert step 1> Calculate the molar mass of LiMn_2O_4 by adding the atomic masses of lithium (Li), manganese (Mn), and oxygen (O).
insert step 2> Calculate the molar mass of LiCoO_2 by adding the atomic masses of lithium (Li), cobalt (Co), and oxygen (O).
insert step 3> Determine the percentage of lithium in LiMn_2O_4 by dividing the atomic mass of lithium by the molar mass of LiMn_2O_4 and multiplying by 100.
insert step 4> Determine the percentage of lithium in LiCoO_2 by dividing the atomic mass of lithium by the molar mass of LiCoO_2 and multiplying by 100.
insert step 5> Compare the percentages of lithium in both compounds to determine which has a higher percentage of lithium, and discuss how this relates to the power delivery of the batteries.

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Lithium Content in Cathodes

The lithium content in a cathode material is crucial for determining the energy capacity and performance of a lithium-ion battery. LiMn2O4 contains less lithium per formula unit compared to LiCoO2, which affects the overall energy density of the battery. Understanding the stoichiometry of these compounds helps in evaluating their efficiency and power delivery.
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Battery Power Delivery

The power delivery of a battery is influenced by its internal resistance and the rate at which lithium ions can move between the anode and cathode. LiMn2O4, while being more stable and safer, has a lower conductivity compared to LiCoO2, which can lead to reduced power output during discharge. This relationship between material properties and performance is essential for battery design.
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Electrochemical Properties of Cathode Materials

The electrochemical properties of cathode materials, such as voltage, capacity, and stability, play a significant role in battery performance. LiCoO2 typically offers higher voltage and energy density, making it suitable for applications requiring high power. In contrast, LiMn2O4, while safer and more environmentally friendly, may sacrifice some of these properties, leading to lower power delivery.
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In some applications nickel–cadmium batteries have been replaced by nickel–zinc batteries. The overall cell reaction for this relatively new battery is: 2 H2O(l) + 2 NiO(OH)(s) + Zn(s) → 2 Ni(OH)2(s) + Zn(OH)2(s) (c) A single nickel–cadmium cell has a voltage of 1.30 V. Based on the difference in the standard reduction potentials of Cd2+ and Zn2+, what voltage would you estimate a nickel–zinc battery will produce? (d) Would you expect the specific energy density of a nickel–zinc battery to be higher or lower than that of a nickel–cadmium battery?

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In some applications nickel–cadmium batteries have been replaced by nickel–zinc batteries. The overall cell reaction for this relatively new battery is: 2 H2O(l) + 2 NiO(OH)(s) + Zn(s) → 2 Ni(OH)2(s) + Zn(OH)2(s) (b) What is the anode half-reaction?

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Li-ion batteries used in automobiles typically use a LiMn2O4 cathode in place of the LiCoO2 cathode found in most Li-ion batteries. (a) Calculate the mass percent lithium in each electrode material.

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(a) Which reaction is spontaneous in the hydrogen fuel cell: hydrogen gas plus oxygen gas makes water, or water makes hydrogen gas plus oxygen gas?

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Li-ion batteries used in automobiles typically use a LiMn2O4 cathode in place of the LiCoO2 cathode found in most Li-ion batteries. (c) In a battery that uses a LiCoO2 cathode, approximately 50% of the lithium migrates from the cathode to the anode on charging. In a battery that uses a LiMn2O4 cathode, what fraction of the lithium in LiMn2O4 would need to migrate out of the cathode to deliver the same amount of lithium to the graphite anode?

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