Amorphous (lithium) niobium sulfide or (lithium) titanium niobium sulfide
The sulfide of the present invention comprises an amorphous (lithium) niobium sulfide having an average composition represented by formula (1): Li k1 NbS n1 (wherein 0≤k1≤5; 3≤n1≤10; and when n1≥3.5, k1≤0.5), or an amorphous (lithium) titanium niobium sulfide having an average composition represented by formula (2): Li k2 Ti 1-m2 Nb m2 S n2 (wherein 0≤k2≤5; 0<m2<1; 2≤n2≤10; and when n2≥3.5, k2≤1.5). The sulfide of the present invention is a material that is useful as a cathode active material for lithium batteries, such as lithium primary batteries, lithium secondary batteries, and lithium ion secondary batteries, and has a high charge-discharge capacity, high electrical conductivity, and excellent charge-discharge performance.
1. A sulfide comprising an amorphous (lithium) niobium sulfide having an average composition represented by formula (1):
Li k1 NbS n1
wherein 0≤k1≤1.5; 3.5≤n1≤10, or
an amorphous (lithium) titanium niobium sulfide having an average composition represented by formula (2):
Li k2 Ti 1-m2 Nb m2 S n2
wherein the formula (2) satisfies (i) or (ii) below,
(i) 0≤k2≤5; 0<m2<1; and 3≤n2≤3.5, or
(ii) 0□k2□□□5; 0<m2<1; and 3.5□n2□10.
2. The sulfide according to claim 1 , wherein the sulfide has an impurity concentration of not more than 2 wt. %.
3. A sulfide comprising an amorphous sulfide having an average composition represented by a formula:
Li k3 Ti 1-m3 Nb m3 S n3
wherein 0≤k3≤1.5; 0<m3≤1; 3.5≤n3≤10,
the sulfide having an impurity concentration of not more than 2 wt. %.
4. The sulfide according to claim 1 , wherein the amorphous (lithium) niobium sulfide or the amorphous (lithium) titanium niobium sulfide is present as a matrix, and the sulfide further comprises a crystalline metal sulfide that is present in the matrix.
5. The sulfide according to claim 1 , wherein in an X-ray diffraction diagram obtained using CuKα radiation, the sulfide has a half-width of 0.3° or more at diffraction angles 2θ=15.0±0.5°, 15.5±0.5°, and 23.0±0.5°, or has no diffraction peaks at diffraction angles 2θ=15.0±0.5°, 15.5±0.5°, and 23.0±0.5°.
6. The sulfide according to claim 1 , wherein the sulfide contains no crystallites, or has an average crystallite size of 5 nm or less.
7. A sulfide comprising:
an amorphous (lithium) niobium sulfide or an amorphous (lithium) titanium niobium sulfide as a matrix; and
a crystalline metal sulfide or carbon that is present in the matrix,
wherein the sulfide has an average composition represented by a formula:
Li k4 Ti 1-m4 Nb m4 S n4 C x
wherein 0≤k4≤1.5; 0<m4≤1; 3.5n4≤10; 0≤x≤10.
8. The sulfide according to claim 7 , wherein in an X-ray diffraction diagram obtained using CuKα radiation, the amorphous (lithium) niobium sulfide or amorphous (lithium) titanium niobium sulfide has a half-width of 0.3° or more at diffraction angles 2θ=15.0±0.5°, 15.5±0.5°, and 23.0±0.5°, or has no diffraction peaks at diffraction angles 2θ=15.0±0.5°, 15.5±0.5°, and 23.0±0.5°.
9. The sulfide according to claim 7 , wherein the amorphous (lithium) niobium sulfide or amorphous (lithium) titanium niobium sulfide contains no crystallites, or has an average crystallite size of 5 nm or less.
10. A method for producing the sulfide according to claim 1 comprising mechanically milling a starting material, wherein the starting material comprises a niobium-containing material and a sulfur-containing material.
11. The method according to claim 10 , wherein the starting material comprises at least one of crystalline niobium sulfide, amorphous (lithium) niobium sulfide, and amorphous (lithium) titanium niobium sulfide.
12. The method according to claim 11 , wherein the starting material further comprises sulfur.
13. The method according to claim 10 , wherein the starting material further comprises at least one of a titanium-containing material, a lithium-containing material, and a carbonaceous material.
14. The method according to claim 13 , wherein the titanium-containing material is titanium sulfide, and the lithium-containing material is lithium sulfide.
15. A charge-discharge product of the sulfide according to claim 1 .
16. A cathode active material for lithium batteries comprising the sulfide according to claim 1 .
17. An electrode for lithium batteries comprising the cathode active material for lithium batteries according to claim 16 .
18. The electrode for lithium batteries according to claim 17 , wherein the electrode is a cathode for lithium batteries.
19. A lithium battery comprising the electrode for lithium batteries according to claim 17 .
20. The lithium battery according to claim 19 , wherein the lithium battery is a non-aqueous electrolyte battery or an all-solid-state battery.