Investigation of the high-voltage Li[Ni
0.5鈥?i>xMn
1.5+x]O
4 (
x = 0, 0.05, 0.08) spinels prepared at temperatures of
T 鈮?900 掳C and given different thermal treatments has shown that the solubility limit for oxygen vacancies in the disor
dered spinel phase is small at 600 掳C. With
x = 0, long-range or
dering of Ni
2+ and Mn
4+ and elimination of all oxygen vacancies occurs after an anneal at 700 掳C. Above 700 掳C, a reversible transition from spinel to rock-salt is initiated, to accommodate oxygen loss. A sample quenched from 900 掳C into liquid nitrogen traps some rock-salt second phase; the volume fraction of rock-salt phase decreases with oxygen uptake to 600 掳C. However, upon slow coo
ling (1 掳C min
鈥?) from 900 掳C, the particles have time to eliminate most of the rock-salt phase by 700 掳C; upon further coo
ling below 700 掳C, the spinel phase and the oxygen gain are retained. However, the spinel phase retains oxygen vacancies and attendant Mn
3+ with only short-range or
der of Ni and Mn. The rock-salt phase lowers sharply the electrochemical capacity of the quenched sample; but retention of Mn
3+ in the slow-cooled sample improves the electrochemical performance relative to that of an oxygen-stoichiometric spinel formed by annea
ling at 700 掳C. The Mn-rich Li[Ni
0.45Mn
1.55]O
4 sample annealed at 700 掳C exhibits a segregation of a long-range-or
dered spinel phase and a Ni-deficient spinel phase having a larger fraction near the particle surface. Removal of the Ni
4+/Ni
2+ redox reactions from the surface stabilizes the electrochemical performance at 55 掳C, but the problem of Mn
2+ dissolution resulting from surface disproportionation of Mn
3+ to Mn
2+ and Mn
4+ remains.
Keywords:
Li-ion battery; spinel to rock-salt transition; high-voltage cathode; der%E2%88%92disorder&qsSearchArea=searchText">order鈭抎isorder