LITHIUM SECONDARY BATTERY POSITIVE ELECTRODE AND LITHIUM SECONDARY BATTERY
A lithium secondary battery positive electrode of the present invention includes a positive electrode material mixture layer containing a positive electrode active material, a conductivity enhancing agent and a binder on one or both sides of a current collector, and the positive electrode active material contains a lithium-containing composite oxide represented by the general compositional formula: Li 1+x MO 2 , where x is in a range of −0.15≦x≦0.15 and M represents an element group of three or more elements including at least Ni, Co and Mn. The binder contains a tetrafluoroethylene-vinylidene fluoride copolymer (P(TFE-VDF)) and polyvinylidene fluoride (PVDF). The total content of the binder in the positive electrode material mixture layer is 1 to 4 mass %, and the ratio of the P(TFE-VDF) is 10 mass % or more, when the total of the P(TFE-VDF) and the PVDF is taken as 100 mass %.
1 . A lithium secondary battery positive electrode comprising a positive electrode material mixture layer containing a positive electrode active material, a conductivity enhancing agent and a binder on one or both sides of a current collector,
wherein the positive electrode active material contains a lithium-containing composite oxide represented by the general compositional formula:
Li 1+x MO 2 ,
where x is in a range of −0.15≦x≦0.15 and M represents an element group of three or more elements including at least Ni, Co and Mn,
the ratios of Ni, Co and Mn to the total elements constituting M satisfy 50≦a≦90, 5≦b≦30, 5≦c≦30, and 10≦b+c≦50 where the ratios of Ni, Co and Mn are represented by a, b and c, respectively, in units of mol %,
the binder contains a tetrafluoroethylene-vinylidene fluoride copolymer and polyvinylidene fluoride,
the total content of the binder in the positive electrode material mixture layer is 1 to 4 mass %, and
the ratio of the tetrafluoroethylene-vinylidene fluoride copolymer is 10 mass % or more, when the total of the tetrafluoroethylene-vinylidene fluoride copolymer and the polyvinylidene fluoride is taken as 100 mass %.
2 . The lithium secondary battery positive electrode according to claim 1 , wherein the ratio of the tetrafluoroethylene-vinylidene fluoride copolymer is 30 mass % or less, when the total of the tetrafluoroethylene-vinylidene fluoride copolymer and the polyvinylidene fluoride is taken as 100 mass %.
3 . The lithium secondary battery positive electrode according to claim 1 , wherein the positive electrode material mixture layer has a density of 3.2 g/cm 3 or more.
4 . The lithium secondary battery positive electrode according to claim 1 , wherein the positive electrode material mixture layer has a density of 3.8 g/cm 3 or less.
5 . The lithium secondary battery positive electrode according to claim 1 , wherein the average valence A of Ni in the whole lithium-containing composite oxide is 2.2 to 2.9, and the valence B of Ni on the surface of particles of the lithium-containing composite oxide satisfies the relationship: B<A.
6 . The lithium secondary battery positive electrode according to claim 1 , wherein the average valence C of Co in the whole lithium-containing composite oxide is 2.5 to 3.2, and the valence D of Co on the surface of particles of the lithium-containing composite oxide satisfies the relationship: D<C.
7 . The lithium secondary battery positive electrode according to claim 1 , wherein the average valence of Mn in the whole lithium-containing composite oxide is 3.5 to 4.2.
8 . The lithium secondary battery positive electrode according to claim 1 , wherein the ratio b of Co and the ratio c of Mn satisfy the relationship: b>c.
9 . The lithium secondary battery positive electrode according to claim 1 , wherein the ratio b of Co and the ratio c of Mn satisfy the relationship: b≦c.
10 . The lithium secondary battery positive electrode according to claim 1 , wherein the lithium-containing composite oxide is represented by the general compositional formula: Li 1+x Ni 1−d−e Co d Mn e O 2 , and −0.15≦x≦0.15, 0.05≦d≦0.3, 0.05≦e≦0.3 and 0.1≦d+e≦0.5.
11 . A lithium secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
wherein the positive electrode, the negative electrode and the separator form a wound electrode assembly,
the positive electrode comprises a positive electrode material mixture layer containing a positive electrode active material, a conductivity enhancing agent and a binder on one or both sides of a current collector,
the positive electrode active material contains a lithium-containing composite oxide represented by the general compositional formula:
Li 1+x MO 2 ,
where x is in a range of −0.15≦x≦0.15 and M represents an element group of three or more elements including at least Ni, Co and Mn,
the ratios of Ni, Co and Mn to the total elements constituting M satisfy 50≦a≦90, 5≦b≦30, 5≦c≦30, and 10≦b+c≦50 where the ratios of Ni, Co and Mn are represented by a, b and c, respectively, in units of mol %,
the binder contains a tetrafluoroethylene-vinylidene fluoride copolymer and polyvinylidene fluoride,
the total content of the binder in the positive electrode material mixture layer is 1 to 4 mass %, and
the ratio of the tetrafluoroethylene-vinylidene fluoride copolymer is 10 mass % or more, when the total of the tetrafluoroethylene-vinylidene fluoride copolymer and the polyvinylidene fluoride is taken as 100 mass %.
12 . The lithium secondary battery according to claim 11 , wherein the ratio of the tetrafluoroethylene-vinylidene fluoride copolymer is 30 mass % or less, when the total of the tetrafluoroethylene-vinylidene fluoride copolymer and the polyvinylidene fluoride is taken as 100 mass %.
13 . The lithium secondary battery according to claim 11 , wherein the positive electrode material mixture layer has a density of 3.2 g/cm 3 or more.
14 . The lithium secondary battery according to claim 11 , wherein the positive electrode material mixture layer has a density of 3.8 g/cm 3 or less.
15 . The lithium secondary battery according to claim 11 , wherein the average valence A of Ni in the whole lithium-containing composite oxide is 2.2 to 2.9, and the valence B of Ni on the surface of particles of the lithium-containing composite oxide satisfies the relationship: B<A.
16 . The lithium secondary battery according to claim 11 , wherein the average valence C of Co in the whole lithium-containing composite oxide is 2.5 to 3.2, and the valence D of Co on the surface of particles of the lithium-containing composite oxide satisfies the relationship: D<C.
17 . The lithium secondary battery according to claim 11 , wherein the average valence of Mn in the whole lithium-containing composite oxide is 3.5 to 4.2.
18 . The lithium secondary battery according to claim 11 , wherein the ratio b of Co and the ratio c of Mn satisfy the relationship: b>c.
19 . The lithium secondary battery according to claim 11 , wherein the ratio b of Co and the ratio c of Mn satisfy the relationship: b≦c.
20 . The lithium secondary battery according to claim 11 , wherein the lithium-containing composite oxide is represented by the general compositional formula: Li 1+x Ni 1−d−e Co d Mn e O 2 , and −0.15≦x≦0.15, 0.05≦d≦0.3, 0.05≦e≦0.3 and 0.1≦d+e≦0.5.