Lithium secondary batteries and nonaqueous electrolyte for use in the same
A lithium secondary battery comprising: a positive electrode and a negative electrode which each has a specific composition and specific properties; and a nonaqueous electrolyte which contains a cyclic siloxane compound represented by general formula (1), fluorosilane compound represented by general formula (2), compound represented by general formula (3), compound having an S—F bond in the molecule, nitric acid salt, nitrous acid salt, monofluorophosphoric acid salt, difluorophosphoric acid salt, acetic acid salt, or propionic acid salt in an amount of 10 ppm or more of the whole nonaqueous electrolyte. This lithium secondary battery has a high capacity, long life, and high output. [In general formula (1), R 1 and R 2 are an organic group having 1-12 carbon atoms and n is an integer of 3-10. In general formula (2), R 3 to R 5 are an organic group having 1-12 carbon atoms; x is an integer of 1-3; and p, q, and r each are an integer of 0-3, provided that 1≦p+q+r≦3. In general formula (3), R 6 to R 8 are an organic group having 1-12 carbon atoms and symbol A is a group constituted of H, C, N, O, F, S, Si, and/or P.]
1. A lithium secondary battery comprising: an electrode group comprising a positive electrode, a negative electrode, and a microporous film separator interposed between the electrodes; and a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt contained therein, the electrode group and the nonaqueous electrolyte being held in a battery case, and the positive electrode and the negative electrode each comprising a current collector and, formed thereon, an active-material layer comprising an active material capable of occluding/releasing a lithium ion,
wherein the nonaqueous electrolyte is a nonaqueous electrolyte comprising in an amount of 10 ppm or more of the whole nonaqueous electrolyte, of
lithium difluorophosphate; and
the positive electrode is any positive electrode selected from the group consisting of the following positive electrode [1] to positive electrode [5]:
positive electrode [1]: a positive electrode comprising a positive-electrode active material comprising manganese;
positive electrode [2]: a positive electrode comprising a positive-electrode active material having a composition represented by the following composition formula (4):
Li x Ni (1−y−z) Co y M z O 2 (4)
wherein M represents at least one element selected from the group consisting of Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≦1.2; y represents a number satisfying 0.05≦y≦0.5; and z represents a number satisfying 0.01≦z≦0.5;
positive electrode [3]: a positive electrode comprising a positive-electrode active material selected from the group consisting of the following (a) to (d):
(a) a positive-electrode active material having a BET specific surface area of from 0.4 m 2 /g to 2 m 2 /g,
(b) a positive-electrode active material having an average primary-particle diameter of from 0.1 μm to 2 μm,
(c) a positive-electrode active material having a median diameter d 50 of from 1 μm to 20 μm,
(d) a positive-electrode active material having a tap density of from 1.3 g/cm 3 to 2.7 g/cm 3 ;
positive electrode [4]: a positive electrode satisfying any requirement selected from the group consisting of the following (e) to (g):
(e) is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material, a conductive material, and a binder on a current collector, wherein the content of the conductive material in the positive-electrode active-material layer is in the range of from 6 % by mass to 20 % by mass,
(f) is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the positive-electrode active-material layer has a density in the range of from 1.7 g/cm 3 to 3.5 g/cm 3 ,
(g) is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the ratio of the thickness of the positive-electrode active-material layer to the thickness of the current collector, [i.e., the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector)], is in the range of from 1.6 to 20; and
positive electrode [5]: a positive electrode comprising two or more positive-electrode active materials differing in composition.
2. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] and the manganese-containing positive-electrode active material contained in the positive electrode [1] has a composition represented by the following composition formula (5):
Li x Mn (1−y) M 1 y O 2 (5)
wherein M 1 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≦1.2; and y represents a number satisfying 0.05≦y≦0.8.
3. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] and the manganese-containing positive-electrode active material contained in the positive electrode [1] has a composition represented by the following composition formula (6):
Li x Mn (1−y−z) Ni y M 2 z O 2 (6)
wherein M 2 represents at least one element selected from the group consisting of Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≦1.2; y represents a number satisfying 0.05≦y≦0.8; and z represents a number satisfying 0.01≦z≦0.5.
4. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] and the manganese-containing positive-electrode active material contained in the positive electrode [1] has a composition represented by the following composition formula (7):
Li x Mn (2−y) M 3 y O 4 (7)
wherein M 3 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≦1.2; and y represents a number satisfying 0.05≦y≦0.8.
5. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] and the manganese-containing positive-electrode active material contained in the positive electrode [1] has, adherent to the surface thereof, a substance having a composition different from that of the manganese-containing positive-electrode active material.
6. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] comprising the manganese-containing positive-electrode active material and positive electrode [1] further comprises a positive-electrode active material differing in composition from the manganese-containing positive-electrode active material.
7. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] comprising a current collector and, formed thereon, a positive-electrode active-material layer comprising the manganese-containing positive-electrode active material and a binder, the positive-electrode active-material layer having a density in the range of from 1.5 g/cm 3 to 3.5 g/cm 3 .
8. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [1] comprising a current collector and, formed thereon, a positive-electrode active-material layer comprising the manganese-containing positive-electrode active material and a binder, the thickness ratio between the current collector and the positive-electrode active-material layer which is represented by (thickness of the active-material layer on one side just before impregnation with the electrolyte)/(thickness of the current collector) being in the range of from 0.5 to 20.
9. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [2] and the positive-electrode active material contained in the positive electrode [2] comprises a core positive-electrode active material and, adherent to the surface thereof, a substance having a composition different from that of the core positive-electrode active material.
10. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [2] comprising the positive-electrode active material and positive electrode [2] further comprises a second positive-electrode active material differing in composition from the positive-electrode active material.
11. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [2] comprising a current collector and, formed thereon, a positive-electrode active-material layer comprising the positive-electrode active material and a binder, the positive-electrode active-material layer having a density in the range of from 1.5 g/cm 3 to 3.5 g/cm 3 .
12. The lithium secondary battery according to claim 1 , wherein the positive electrode is positive electrode [2] comprising a current collector and, formed thereon, a positive-electrode active-material layer comprising the positive-electrode active material and a binder, the value of (thickness of the positive-electrode active-material layer on one side just before impregnation with the electrolyte)/(thickness of the current collector) being in the range of from 0.5 to 20.
13. The lithium secondary battery according to claim 1 , which has any property selected from the group consisting of the following (1) to (3):
(1) the overall electrode area of the positive electrode is at least 20 times the surface area of the case of the secondary battery;
(2) the secondary battery has a direct-current resistance component of 20 milliohms (mΩ) or less; and
(3) the battery elements held in each battery case of the secondary battery have an electric capacity of 3 ampere-hours (Ah) or higher.