Electrolyte for lithium secondary batteries with improved low temperature performance and lithium secondary battery including the same

Patent metadata

Field	Value
Publication number	US-2017288257-A1
Application number	US-201515509661-A
Country	US
Kind code	A1
Filing date	Dec 2, 2015
Priority date	Dec 2, 2014
Publication date	Oct 5, 2017
Grant date	—

Abstract

Disclosed are an electrolyte for lithium secondary batteries including 10 to 50% by weight of a cyclic carbonate compound, and 50 to 90% by weight of a linear ester compound, based on the total weight of a non-aqueous solvent, wherein a content of ethyl propionate of the linear ester compound is 20 to 60% by weight, based on the total weight of the non-aqueous solvent, and a lithium secondary battery including the electrolyte and exhibiting superior low-temperature characteristics.

First claim

1 . An electrolyte for lithium secondary batteries comprising an aqueous solvent and a lithium salt,
wherein the electrolyte comprises: 10 to 50% by weight of a cyclic carbonate compound; and 50 to 90% by weight of a linear ester compound, based on the total weight of the non-aqueous solvent, and a content of ethyl propionate of the linear ester compound is 20 to 60% by weight, based on the total weight of the non-aqueous solvent.

2 . The electrolyte according to claim 1 , wherein the cyclic carbonate compound comprises at least one selected from the group consisting of ethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, fluoroethylene carbonate and vinylene carbonate.

3 . The electrolyte according to claim 2 , wherein the cyclic carbonate compound comprises ethylene carbonate.

4 . The electrolyte according to claim 1 , wherein the linear ester compound comprises ethyl propionate and further comprises at least one selected from the group consisting of methyl propionate, propyl propionate and butyl propionate.

5 . The electrolyte according to claim 4 , wherein the linear ester compound is a mixture of ethyl propionate and propyl propionate.

6 . The electrolyte according to claim 5 , wherein the electrolyte comprises 20 to 40% by weight of ethyl propionate and 20 to 60% by weight of propyl propionate, based on the total weight of the non-aqueous solvent.

7 . The electrolyte according to claim 5 , wherein the electrolyte comprises 25 to 35% by weight of ethyl propionate (EP) and 30 to 40% by weight of propyl propionate (PP), based on the total weight of the non-aqueous solvent.

8 . The electrolyte according to claim 1 , wherein, the electrolyte comprises 20 to 40% by weight of the cyclic carbonate compound and 60 to 80% by weight of the linear ester compound, based on the total weight of the non-aqueous solvent.

9 . The electrolyte according to claim 1 , wherein the electrolyte has an ionic conductivity at −10° C. equal to or higher than 5.5 mS/cm and equal to or lower than 6.5 mS/cm and a viscosity at −10° C. equal to or higher than 4.5 cP and equal to or lower than 5.9 cP.

10 . The electrolyte according to claim 1 , wherein, the electrolyte has an ionic conductivity at −10° C. equal to or higher than 5.5 mS/cm and equal to or lower than 6.0 mS/cm and a viscosity at −10° C. equal to or higher than 5.0 cP and equal to or lower than 5.9 cP.

11 . A lithium secondary battery comprising:
the electrolyte according to claim 1 ; a positive electrode; a negative electrode; and a polymer membrane, wherein an electrode assembly having a structure in which the polymer membrane is interposed between the positive electrode and the negative electrode is impregnated with the electrolyte and accommodated in a battery case.

12 . The lithium secondary battery according to claim 11 , wherein the positive electrode comprises, as a positive electrode active material, at least one selected from the group consisting of a compound represented by the following Formula 1 and a compound represented by the following Formula 2:
Li x MO 2-z A z   (1)
Li a M′(PO 4-c )X c   (2)
wherein 0.9≦x≦1.2, 0≦z<0.2, 0.5≦a≦1.5, 0≦c≦0.1; M comprises at least one element selected from the group consisting of Co, Ni, Mn, Al, Mg, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; M′ comprises at least one element selected from the group consisting of Fe, Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, and Ga; A comprises at least one anion with a charge of −1 or −2; and X comprises at least one element selected from F, S and N.

13 . The lithium secondary battery according to claim 12 , wherein the compound represented by Formula 1 is represented by the following Formula 3 and the compound represented by Formula 2 is represented by the following Formula 4:
Li x Co y M 1-y O 2-z A z   (3)
Li a Fe 1-b M′ b (PO 4-c )X c   (4)
wherein 0.9≦x≦1.2, 0<y≦1, 0≦z<0.2, 0.5≦a≦1.5, 0≦b≦0.5, 0≦c≦0.1; M comprises at least one element selected from the group consisting of Ni, Mn, Al, Mg, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi; M′ comprises at least one element selected from the group consisting of Mn, Co, Ni, Cu, Zn, Mg, Cr, V, Mo, Ti, Al, Nb, B, and Ga; A comprises at least one anion with a charge of −1 or −2; and X comprises at least one element selected from F, S and N.

14 . The lithium secondary battery according to claim 13 , wherein the compound represented by Formula 3 is LCoO 2 and the compound represented by Formula 4 is LiFePO 4 .

15 . The lithium secondary battery according to claim 12 , wherein the positive electrode active material comprises the compound of Formula 1 and the compound of Formula 2, and a weight mix ratio of the compound of Formula 1 and the compound of Formula 2 is 60:40 to 99:1.

16 . The lithium secondary battery according to claim 15 , wherein the weight mix ratio of the compound of Formula 1 and the compound of Formula 2 is 70:30 to 99:1.

17 . The lithium secondary battery according to claim 11 , wherein the negative electrode comprises, as a negative electrode active material, a carbon-based material.

18 . A battery pack comprising the lithium secondary battery according to claim 11 as a unit battery.

19 . A device comprising the battery pack according to claim 18 .

20 . The device according to claim 19 , wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a system for storing power.

Assignees

• Lg Chemical Ltd

Inventors

• Kil Eun Hye
• Lee Jin Kyu
• Kim Ki Tae
• Yun Hyung Ku
• Han Hyeaeun

Classifications

• C07D317/36 Primary

  Alkylene carbonates; Substituted alkylene carbonates · CPC title

• C07C69/22

  having three or more carbon atoms in the acid moiety · CPC title

• H01M10/0566

  Liquid materials · CPC title

• H01M4/364

  as mixtures · CPC title

• H01M2300/0037

  Mixture of solvents · CPC title