ADDITIVE FOR POSITIVE ELECTRODES OF LITHIUM SECONDARY BATTERIES, AND POSITIVE ELECTRODE FOR LITHIUM SECONDARY BATTERIES
Provided are an additive for positive electrodes, which is capable of increasing the output of a lithium secondary battery and is capable of maintaining cycle characteristics even during high-speed charge and discharge; and a positive electrode for lithium secondary batteries. The additive for positive electrodes of lithium secondary batteries, which contains, as an essential constituent, a substituted polythiophene that has a repeating unit, which is obtained by substituting a hydrogen atom in the 3-position and/or in the 4-position of a thiophene ring with at least one group that is selected from the group consisting of a perfloroalkylalkoxy group, a perfloroalkoxy group, a perfloroalkoxyalkyl group and an alkyl group substituted with the perfloroalkylalkoxy group, as at least a part of a thiophene repeating group.
1 . An additive for positive electrodes of a lithium secondary battery comprising a substituted polythiophene (P), as an essential component, having thiophene repeating units (D) where a hydrogen atom(s) at the 3-position and/or the 4-position of a thiophene ring is/are substituted at least one group (f) selected from a group consisting of groups (f1) through (f4) represented by the following formulae (1) through (4) respectively, as a portion of the thiophene repeating units:
—OR 1 —R 2 (1)
[wherein: R 1 represents a C 1-6 alkylene group; and R 2 represents a C 1-15 perfluoroalkyl group);
—O—R 3 (2)
[wherein R 3 represents a C 1-15 perfluoroalkyl group];
—R 4 —O—R 5 (3)
[wherein: R 4 represents a straight or branched C 1-6 alkylene group; and R 5 represents C 1-15 perfluoroalkyl group]; and
—R 6 —OR 7 —R 8 (4)
[wherein: R 6 represents a straight or branched C 1-6 alkylene; R 7 represents a C 1-6 alkylene group; and R 8 represents a C 1-15 perfluoroalkyl group].
2 . The additive according to claim 1 , wherein
the thiophene repeating unit (D) is at least one type of repeating unit selected from a group consisting of repeating units (D1) through (D4) represented by the following general formulae (5) through (8), respectively:
3 . The additive according to claim 1 , wherein
the repeating unit (D) is a repeating unit substituted by at least one type of group selected from a group constituting 2,2,2,-trifluoroethoxy group, 2,2,3,3,3-pentafluoropropoxy group, 2,2,3,3,4,4,4-heptafluorobutoxy group, 2,2,3,3,4,4,5,5,5-nonafluoropentoxy group, 3,3,3-trifluoro-1-propoxy group, 4,4,4-trifluoro-1-butoxy group and 5,5,5-trifluoro-1-pentoxy group.
4 . The additive according to claim 1 , wherein
a content of the repeating unit (D) is 50 to 100 molar percentages based upon weight of the substituted polythiophene (P).
5 . The additive according to claim 1 , wherein
a group represented by the following general formula is bound at the 3-position or the 4-position of one or more thiophene rings in the substituted polythiophene (P):
—SO 3 − M + (9)
[wherein, M + is an alkali metal cation or proton].
6 . The additive according to claim 1 , wherein
regioregularity defined by the percentage of head-to-tail-head-to-tail bonds of the substituted polythiophene (P) is 90% or higher.
7 . The additive according to claim 1 , further comprising polyvinylidene fluoride and/or polytetrafluoroethylene.
8 . The additive according to claim 1 , further comprising carboxymethylcellulose.
9 . Positive electrodes for a lithium secondary battery, comprising the additive according to claim 1 , an active material (B) and a collector (C).
10 . A lithium secondary battery using positive electrodes comprising the additive according to claim 1 .