Effect of overdischarge (overlithiation) on electrochemical properties of LiMn2O4 samples of different origin

Abstract

Overreaching certain minimum allowable voltage upon discharging a lithium-ion battery (overdischarge) leads to the insertion of an overstoichiometric amount of lithium into a cathode material and causes its degradation. Here we establish overdischarge tolerance margins for two samples of LiNi0.5Mn1.5O4, A commercial coarse-grained material by NEI reversibly inserts/releases ~ 0.37 gram equivalent of extra lithium ions in the 2.25–3.5 V region and ~ 0.75 gram equivalent of extra lithium ions in the 1.885–3.5 V region. It perfectly behaves in life tests (225 cycles) restoring its performance upon switching from a “non-standard” (2.25–5.0 V) to a “standard” (3.5–5.0 V) charge/discharge regime, in spite of a fast capacity fade within the widened voltage limit. A homemade fine-grained material does not tolerate even slightest overdischarge. It inserts/releases ~ 0.75 gram equivalent of extra lithium ions just in the 2.25–3.5 V region and quickly degrades either upon extending the voltage region to 1.885 V or in long-term cycling with switching from a “standard” to “non-standard” charge/discharge regime. Formation of Li1.375Ni0.5Mn1.5O4 and Li1.75Ni0.5Mn1.5O4 compounds upon overlithiation is explained by the transformation of the mother cubic $$ Fd\overline{3}m $$ structure to the rhombohedral $$ R\overline{3}m $$ structure with empty sites of proper multiplicity, which are able to accommodate 0.375 and 0.75 gram equivalents of extra Li+.