Lithium ion secondary battery and method for manufacturing the same
A lithium ion secondary battery includes a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode contains, as a positive electrode active material, a lithium-containing transition metal compound that belongs to space group Fd3-m and that contains lithium and transition metal M (M represents Mo, or Mo and at least one selected from the group consisting of Mn, Co, Ni, W, and V), a molar ratio of the lithium to the transition metal M is 2.7 or more and 3.3 or less, and a ratio of a mass of the lithium-containing transition metal compound to a total mass of the positive electrode active material in the positive electrode is 0.8 or more.
1. A lithium ion secondary battery comprising:
a positive electrode containing one or more positive electrode active materials;
a negative electrode;
a separator disposed between the positive electrode and the negative electrode; and
a non-aqueous electrolyte,
wherein the one or more positive electrode active materials include a lithium-containing transition metal compound that contains lithium and transition metal M, where M represents Mo, or Mo and at least one selected from the group consisting of Mn, Co, Ni, W, and V, a crystal structure of the lithium-containing transition metal compound belonging to space group Fd3-m,
a molar ratio of the lithium to the transition metal M in the lithium-containing transition metal compound is 2.7 or more and 3.3 or less, and
a ratio of a mass of the lithium-containing transition metal compound to a total mass of the one or more positive electrode active materials in the positive electrode is 0.8 or more.
2. The lithium ion secondary battery according to claim 1 , wherein the lithium-containing transition metal compound is Li α M β O γ , where 2.7β≤α≤3.3β, 1.8≤β≤2.2, 6.4≤γ≤7.6.
3. The lithium ion secondary battery according to claim 1 , wherein the lithium-containing transition metal compound is Li 6 M 2 O 7 .
4. The lithium ion secondary battery according to claim 2 , wherein the lithium-containing transition metal compound is Li α Mo β-x Me x O γ , where 0≤x≤1.5, Me represents at least one selected from the group consisting of Mn, Co, Ni, W, and V.
5. The lithium ion secondary battery according to claim 4 , wherein the lithium-containing transition metal compound is Li 6 Mo 2-x Me x O 7 , where 0≤x≤1.5.
6. The lithium ion secondary battery according to claim 2 , wherein the positive electrode contains a plurality of positive electrode active materials.
7. The lithium ion secondary battery according to claim 6 , wherein the plurality of positive electrode active materials further include at least one additional lithium-containing transition metal compound which can insert therein and release therefrom lithium ions reversibly.
8. The lithium ion secondary battery according to claim 7 , wherein the at least one additional lithium-containing transition metal compound is at least one selected from the group consisting of Li 2 MeO 3 , LiMeO 2 , Li 4 MeO 5 , Li 2 MeO 4 , and LiMe 2 O 4 , where Me represents at least one selected from the group consisting of Mo, Mn, Co, Ni, Fe, W, Cr, and V.
9. The lithium ion secondary battery according to claim 1 , wherein the lithium-containing transition metal compound maintains the crystal structure belonging to space group Fd3-m after charge and discharge.
10. The lithium ion secondary battery according to claim 1 , wherein the non-aqueous electrolyte contains at least one fluorine solvent selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate.
11. A method for manufacturing a lithium ion secondary battery, the method comprising:
preparing a positive electrode, a negative electrode containing lithium, and a separator; and
assembling the positive electrode, the separator, and the negative electrode such that the separator is disposed between the positive electrode and the negative electrode,
wherein the positive electrode contains, as a positive electrode active material, a lithium-containing transition metal compound that belongs to space group Fd3-m and that contains lithium and transition metal M (M represents Mo, or Mo and at least one selected from the group consisting of Mn, Co, Ni, W, and V),
a molar ratio of the lithium to the transition metal M is 2.7 or more and 3.3 or less,
a ratio of a mass of the lithium-containing transition metal compound to a total positive-electrode-active-material mass in the positive electrode is 0.8 or more.
12. The method according to claim 11 , wherein the lithium-containing transition metal compound is Li α M β O γ (2.7β≤α≤3.3β, 1.8≤β≤2.2, 6.4≤γ≤7.6).
13. The method according to claim 11 , wherein the lithium-containing transition metal compound is Li 6 M 2 O 7 .
14. The method according to claim 12 , wherein the lithium-containing transition metal compound is Li α Mo β-x Me x O γ (0≤x≤1.5, Me represents at least one selected from the group consisting of Mn, Co, Ni, W, and V).
15. The method according to claim 14 , wherein the positive electrode active material is Li 6 Mo 2-x Me x O 7 (0≤x≤1.5).
16. The lithium ion secondary battery according to claim 1 , wherein the one or more positive electrode active materials contain substantially only the lithium-containing transition metal compound.
17. The lithium ion secondary battery according to claim 1 , wherein the lithium-containing transition metal compound exists as a plurality of particles.
18. The lithium ion secondary battery according to claim 17 , wherein an average value of primary particles of the lithium-containing transition metal compound is within a range of 50 nm to 500 nm.
19. The lithium ion secondary battery according to claim 17 , wherein the positive electrode further contains a conductive agent that partially covering surfaces of the plurality of particles.