Patent ID: 6919141

Claim:
An electrochemical cell, which comprises: a) a negative electrode which intercalates with an alkali metal; b) a positive electrode comprising an electrode active material which intercalates with the alkali metal; c) a nonaqueous electrolyte activating the negative and the positive electrodes; d) a phosphate additive provided in the electrolyte, wherein the phosphate additive has the formula: (R 1 O)P(═O) (OR 2 ) (OR 3 ) with R 1 , R 2 and R 3 being the same or different, wherein at least one of the R groups contains: i) at least three carbon atoms and has a first structure of the type C(sp)-C(sp 3 ), wherein the C(sp 3 ) is directly connected to the —OPO— functional group; or ii) at least three carbon atoms and has a second structure of the type C(sp 2 )-C(sp 3 ), wherein the C(sp 3 ) is directly connected to the —OPO— functional group; and e) any remaining R group that is not i) or ii) is selected from the group consisting of hydrogen, saturated organic groups containing 1 to 13 carbon atoms, and unsaturated organic groups containing 2 to 13 carbon atoms.