Positive electrode material and secondary battery

1 . A positive electrode material for secondary batteries, the positive electrode material comprising:

a Li-rich transition metal oxide having a lithium-to-oxygen atomic ratio: Li/O of 0.8 or more; and

a dicarboxylic acid and/or an anhydride of the dicarboxylic acid,

wherein the anhydride of the dicarboxylic acid has 3 to 6 carbonyl carbon atoms,

wherein the positive electrode material has a surface at least partially covered with a coating containing lithium, oxygen, and carbon, and

wherein the positive electrode material further comprises a binder including polyvinylidene fluoride (PVdF).

2 . The positive electrode material according to claim 1 , wherein

the Li-rich transition metal oxide is a first composite oxide represented by a general formula (1): Li x1 M 1 A 1 2 , where 1.5≤x1≤2.3, and belonging to a space group Immm,

M 1 including at least one selected from the group consisting of Ni, Co, Mn, Cu, and Fe,

A 1 including at least oxygen,

A 1 having an oxygen content of 85 atom % or more.

3 . The positive electrode material according to claim 2 , wherein

the first composite oxide is represented by a general formula (1a): Li x1 M 1A 1-x2 M 1B x2 O 2-y A 2 y , where 0≤x2≤0.5, 0≤y≤0.3, and at least one of x2 and y not being 0,

M 1A being at least one selected from the group consisting of Ni, Co, Mn, Cu, and Fe,

M 1B including at least one selected from the group consisting of Al, Mg, Sc, Ti, Cr, V, Zn, Ga, Zr, Mo, Nb, Ta, and W,

A 2 including at least one selected from the group consisting of F, Cl, Br, S, and P.

4 . The positive electrode material according to claim 1 , wherein

the Li-rich transition metal oxide is a second composite oxide represented by a general formula (2): Li x3 M 2 O z , where 4≤x3≤7 and 3.5≤z≤5, and belonging to a space group Pbca,

M 2 including at least one selected from the group consisting of Ni, Co, Mn, Cu, and Fe.

5 . The positive electrode material according to claim 1 , further comprising a third composite oxide belonging to a space group R-3m, wherein

the third composite oxide is represented by a general formula: Li x4 M 3 O 2 , where 0.8≤x4≤1.2,

M 3 including at least one selected from the group consisting of Co, Mn, Cu, Fe, and Cr.

6 . The positive electrode material according to claim 5 , wherein a ratio of the Li-rich transition metal oxide to a total of the Li-rich transition metal oxide and the third composite oxide is 0.3 to 20 mass %.

7 . The positive electrode material according to claim 5 , wherein a half width w of a diffraction peak corresponding to the (101) plane of the Li-rich transition metal oxide is 10 times or more as large as a half width of a highest intensity diffraction peak of the third composite oxide.

8 . The positive electrode material according to claim 1 , wherein the dicarboxylic acid has 3 to 6 carbon atoms.

9 . The positive electrode material according to claim 8 , wherein the dicarboxylic acid includes malonic acid.

10 . The positive electrode material according to claim 1 , wherein the anhydride of the dicarboxylic acid further includes a maleic anhydride, glutaric anhydride, and/or succinic anhydride.

11 . A secondary battery, comprising:

a positive electrode; a negative electrode; and an electrolyte,

the positive electrode having a positive electrode material layer,

the positive electrode material layer including the positive electrode material according to claim 1 .

12 . The secondary battery according to claim 11 , wherein the dicarboxylic acid and/or the anhydride of the dicarboxylic acid is contained in a proportion of 0.1 to 10 mass % in the positive electrode material layer.

13 . The secondary battery according to claim 11 , wherein

the negative electrode includes a negative electrode active material,

the negative electrode active material includes an alloy-based material, and

the alloy-based material contains at least one element selected from the group consisting of Si, Sn, Ga, and In.

14 . The secondary battery according to claim 11 , wherein

the positive electrode material partially has an amorphous structure mainly composed of LiM 4 O 2 , a transition metal oxide mainly composed of one selected from the group consisting of LiFeO 2 , CoO and MnO, and/or a transition metal oxide mainly composed of a composite of at least two selected from the group consisting of LiFeO 2 , CoO, and MnO,

M 4 including at least one selected from the group consisting of Ni, Co, Mn, Cu and Fe.

15 . The secondary battery according to claim 11 , wherein, at a 4.3 V charged state, metal lithium is deposited on the negative electrode.

16 . The secondary battery according to claim 11 , wherein the positive electrode material has a surface at least partially covered with a coating containing lithium, oxygen, and carbon.

17 . A positive electrode material for secondary batteries, the positive electrode material comprising:

a Li-rich transition metal oxide having a lithium-to-oxygen atomic ratio: Li/O of 0.8 or more; and

a dicarboxylic acid and/or an anhydride of the dicarboxylic acid,

wherein the positive electrode material is a positive electrode active material powder, a positive electrode material mixture, a slurry of a positive electrode material mixture, or a positive electrode material layer, which is free of an electrolyte,

wherein the positive electrode material partially has an amorphous structure mainly composed of LiM 4 O 2 , a transition metal oxide mainly composed of one selected from the group consisting of LiFeO 2 , CoO and MnO, and/or a transition metal oxide mainly composed of a composite of at least two selected from the group consisting of LiFeO 2 , CoO, and MnO,

M 4 including at least one selected from the group consisting of Ni, Co, Mn, Cu and Fe,

wherein the positive electrode material has a surface at least partially covered with a coating containing lithium, oxygen, and carbon, and

wherein the positive electrode material further comprises a binder including polyvinylidene fluoride (PVdF).

18 . The positive electrode material according to claim 17 , wherein a half width w of a diffraction peak corresponding to the (101) plane of the Li-rich transition metal oxide obtained by X-ray diffractometry satisfies w>1.5°.

19 . A positive electrode material for secondary batteries, the positive electrode material comprising:

a Li-rich transition metal oxide having a lithium-to-oxygen atomic ratio: Li/O of 0.8 or more; and

a dicarboxylic acid and/or an anhydride of the dicarboxylic acid,

wherein the positive electrode material is a positive electrode active material powder, a positive electrode material mixture, a slurry of a positive electrode material mixture, or a positive electrode material layer, which is free of an electrolyte,

wherein the positive electrode material has a surface at least partially covered with a coating containing lithium, oxygen, and carbon, and

wherein the positive electrode material further comprises a binder including polyvinylidene fluoride (PVdF).