Phosphate additives for nonaqueous electrolyte rechargeable electrochemical cells

An electrochemical cell, which comprises:

• a) a negative electrode which intercalates with lithium;
• b) a positive electrode comprising an electrode active material and which intercalates with lithium;
• c) an electrolyte solution activating the anode and the cathode, the electrolyte including a carbonate mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), wherein with the negative electrode deintercalated with the alkali metal and the positive electrode intercalated with the alkali metal before being activated with the electrolyte, the dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate are in an essentially equilibrated molar mixture as determined by the graph of:
• 4
• d) wherein from a beginning molar ratio of z(DMC) and 1-z(DEC) entered on the abscissa of the graph and then moving up the y-intersect to curve 10 as the equilibrated molar percentage of DMC, curve 12 as the equilibrated molar percentage of EMC and curve 14 as the equilibrated molar percentage of DEC in the equilibrated molar mixture;
• d) a phosphate additive provided in the electrolyte, wherein the phosphate additive has the formula:
• (R1O)P(═O)(OR2)(OR3) and wherein R1, R2 and R3 are the same or different, wherein at least one, but not all three, of the R groups is at least one of the group consisting of:
• i) hydrogen;
• ii) one that contains contains at least three carbon atoms and has a first structure of the type C(sp)-C(sp3), wherein the C(Sp3) is directly connected to the —OPO— functional group;
• and
• iii) one that contains contains at least three carbon atoms and has a second structure of the type C(sp2)-C(sp3), wherein the C(Sp3) is directly connected to the —OPO— functional group;
• and
• e) wherein from a beginning molar mixture of DMC and DEC solvents in a ratio of a% of DMC and 1-a% of DEC entered on the abscissa of the graph and then from the a(DMC)% point moving up the y-intersect to determine the equilibrated molar mixture by intersecting curve 10 to get the equilibrated molar percentage of DMC, intersecting curve 12 to get the equilibrated molar percentage of EMC and intersecting curve 14 to get the equilibrated molar percentage of DEC;
• and
• f) wherein the cell is repeatedly cyclable between a discharged and a charged state with the dimethyl carbonate, the ethyl methyl carbonate and the diethyl carbonate remaining in the equilibrated molar mixture and wherein in the equilibrated molar mixture, the rate at which ethyl methyl carbonate is producible from dimethyl carbonate and diethyl carbonate by an ester exchange reaction is essentially equal to the rate at which ethyl methyl carbonate is disproportionable into dimethyl carbonate and diethyl carbonate such that the equilibrated molar mixture of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate essentially does not change as the cell discharges.

An electrochemical cell, which comprises:

• a) an anode of a carbonaceous material capable of intercalating lithium;
• b) a cathode comprising lithium cobalt oxide;
• and
• c) a nonaqueous electrolyte activating the anode and the cathode, the nonaqueous electrolyte comprising a phosphate additive, wherein the phosphate additive has the formula:
• (R1O)P(═O)(OR2)(OR3) and wherein R1, R2 and R3 are the same or different, wherein at least one, but not all three, of the R groups is at least one of the group consisting of:
• i) hydrogen;
• ii) one that contains contains at least three carbon atoms and has a first structure of the type C(sp)-C(Sp3), wherein the C(sp3) is directly connected to the —OPO— functional group;
• and
• iii) one that contains contains at least three carbon atoms and has a second structure of the type C(Sp2)-C (Sp3), wherein the C(sp3) is directly connected to the —OPO— functional group.

A method for providing an electrochemical cell, comprising the steps of:

• a) providing a negative electrode which intercalates with an alkali metal;
• b) providing a positive electrode comprising an electrode active material which intercalates with the alkali metal;
• c) activating the negative and positive electrodes with a nonaqueous electrolyte;
• and
• d) providing a phosphate additive in the electrolyte, wherein the phosphate additive has the formula:
• (R1O)P(═O)(OR2)(OR3) and wherein R1, R2 and R3 are the same or different, wherein at least one, but not all three, of the R groups is at least one of the group consisting of:
• i) hydrogen;
• ii) one that contains contains at least three carbon atoms and has a first structure of the type C(sp)-C(sp3), wherein the C(Sp3) is directly connected to the —OPO— functional group;
• and
• iii) one that contains contains at least three carbon atoms and has a second structure of the type C(sp2)-C(Sp3 ), wherein the C(sp3) is directly connected to the —OPO— functional group.