LiCoO2 crystallizes in a rhombohedral structure. Consider a situation where 50% lithium (Li) is extracted from the lattice. To keep the crystal electrically neutral, change in average oxidation state of Co is
LiCoO2 crystallises in a rhombohedral structure. Let at initial 100 atoms are present of both Li and Co and after 50%Li is extracted only 50 atoms of Li is remaining. But total charge on the crystal is converted so cobalt have to increase its oxidation state. So, 100Li+100Co‌‌=400 50Li+100Co*‌‌=400 100Co⋆‌‌=350 Co*‌‌=3.5 So, after extraction of 50%Li atom new oxidation state of Co to 3.5. Change in oxidation state = final oxidation state - initial oxidation state =3.5−3 Change in average oxidation state of Co=0.5 of of change in average oxidation state of Co=‌
0.5
3
×100=16.66% (increases) Hence, the correct option is (b).