(a) Which ion is smaller, Co3+ or Co4+?
(b) In a lithium ion battery that is discharging to power a device, for every Li+ that inserts into the lithium cobalt oxide electrode, a Co4+ ion must be reduced to a Co3+ ion in order to balance charge. Using the CRC Handbook of Chemistry and Physics or other standard reference, find the ionic radii of Li+, Co3+, and Co4+. Order these ions from smallest to largest.
(c) Will the lithium cobalt electrode expand or contract as lithium ions are inserted?
(d) Lithium is not nearly as abundant as sodium. If sodium ion batteries were developed that function as lithium ion ones, do you think "sodium cobalt oxide" would still work as the electrode material? Explain.
(e) If you don't think cobalt would work as the redox-active partner ion in the sodium version of the electrode, suggest an alternative metal ion and explain your reasoning.