This invention employs a diamine electrolyte additive that enhances performance of lithium-ion batteries both at high and low temperatures, thereby minimizing the conventional performance gap across a wide temperature range, such as −30° C. to 60° C. At low temperatures, diamine additives can enhances cycling kinetics. At high temperatures, diamine additives can minimize capacity fading. In some variations, a lithium-ion battery electrolyte composition comprises a non-aqueous solvent, a lithium salt soluble in the non-aqueous solvent, and a diamine additive having the formula H2N—R—NH2, wherein R is an organic group such as (—CH2—)n, n=2-12.