Lithium secondary batteries

A lithium secondary battery comprising:

• a) a cathode comprising, as a cathode electroactive material, a lithium transition metal oxide represented by the following formula (I)
• Li[(2x+2)/(x+2)]Mn[2x/(x+2)]M[(2−2x)/(x+2)]O2 tm (I)
• wherein 0<x<1 and M is a combination of elements represented by a general formula (II)
• (NiaMnbCoc)1−dM′d (II)
• wherein a+b+c=1;
• 0≤c≤0.1;
• 0≤d≤0.1;
• and M′comprises at least one metal selected from the group consisting of Sc, Ti, V, Cr, Fe, Cu, Zn, Mg, Al, Sn, B, Ga, Sr, Ca, In, Si, Zr, La, P, Nb, and Ge;
• and
• b) a liquid electrolyte comprising at least one fluorinated acyclic carboxylic acid ester represented by the formula (III)
• R1-C(O)O-R2 (III)
• wherein R1 and R2 represent an alkyl group respectively;
• a sum of carbon atoms in R1 and R2 is from 2 to 7;
• and R1 does not contain fluorine, and R2 contains fluorine.