Positive-electrode active material for secondary cell, and method for manufacturing same

1. A positive-electrode active material for a secondary cell, comprising a compound particle represented by the following formula (A):

LiFe a Mn b M 1 c PO 4   (A)

wherein in formula (A), M 1 represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd; and a, b and c represent numbers satisfying 0.01≤a≤0.99, 0.01≤v≤0.99, and 0≤c≤0.3, a and b are not simultaneously 0, and 2a+2b+(valence of M 1 )×c=2 is satisfied; and

carbon,

wherein the carbon is derived from a cellulose nanofiber and is supported on the compound particle,

wherein an amount of the carbon derived from the cellulose nanofiber and supported on the compound particle is from 0.3 to 6 mass %, and

the positive-electrode active material is a product obtained by pyrolyzing a granule S comprising the compound particle and the cellulose nanofiber and having a particle size (D 50 value) of 1 to 15 μm.

2. The positive-electrode active material for a secondary cell according to claim 1 , wherein, in a Raman spectrum, an intensity ratio (G/D) of D band and G band is 0.5 to 1.8; an intensity ratio (PO 4 /G) of a peak attributed to PO 4 3− and G band; and G band is 0.01 to 0.10 and no radial breathing mode (RBM) peak is present.

3. The positive-electrode active material for a secondary cell according to claim 1 , wherein the granule S is a granulated material of an oxide, wherein the oxide is a product of a synthetic reaction of a lithium compound or a sodium compound, a phosphoric acid compound or a silicic acid compound and a metal salt comprising at least an iron compound or a manganese compound, and the cellulose nanofiber.

4. A method for manufacturing a positive-electrode active material for a secondary cell, comprising a compound particle represented by the following formula (A):

LiFe a Mn b M 1 c PO 4   (A)

wherein in formula (A), M 1 represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd; and a, b and c represent numbers satisfying 0.01≤a≤0.99, 0.01≤v≤0.99, and 0≤c≤0.3, a and b are not simultaneously 0, and 2a+2b+(valence of M 1 )×c=2 is satisfied; and

carbon,

wherein the carbon is derived from a cellulose nanofiber and is supported on the compound particle,

wherein an amount of the carbon derived from the cellulose nanofiber and supported on the compound particle is from 0.3 to 6 mass %, and

the positive-electrode active material is a product obtained by pyrolyzing a granule S comprising the compound particle and the cellulose nanofiber and having a particle size (D 50 value) of 1 to 15 μm,

the method comprising: (I′) mixing slurry Q comprising an oxide obtained by a synthetic reaction with slurry R comprising a cellulose nanofiber, to obtain slurry S,

(II′) subjecting the slurry S obtained to spray drying to obtain granule S having a particle size (D 50 value) of 1 to 15 μm, and

(III′) pyrolyzing the granule S obtained under a reducing atmosphere or an inert atmosphere.

5. The method for manufacturing a positive-electrode active material for a secondary cell according to claim 4 , wherein in the mixing (I′), the content of a cellulose nanofiber relative to 100 parts by mass of an oxide in slurry S is 0.3 to 6.4 parts by mass in terms of carbon atom.

6. The positive-electrode active material for a secondary cell according to claim 1 , wherein the positive-electrode active material is a product obtained by the method comprising:

(I′) mixing slurry Q comprising an oxide obtained by a synthetic reaction with slurry R comprising the cellulose nanofiber, to obtain slurry S,

(II′) subjecting the slurry S obtained to spray drying to obtain granule S having the particle size (D 50 value) of 1 to 15 μm, and

(III′) pyrolyzing the granule S obtained under a reducing atmosphere or an inert atmosphere.

7. The positive-electrode active material for a secondary cell according to claim 1 , wherein the compound particle is selected from the group consisting of LiFe 0.2 Mn 0.8 PO 4 , LiFe 0.1 Mn 0.8 Mg 0.1 PO 4 , LiFe 0.1 Mn 0.8 Zr 0.05 PO 4 , LiFe 0.3 Mn 0.7 PO 4 , LiFe 0.3 Mn 0.7 PO 4 , and LiFe 0.9 Mn 0.1 PO 4 .

8. The positive-electrode active material for a secondary cell according to claim 1 , wherein the compound particle is selected from the group consisting of LiFe 0.1 Mn 0.8 Mg 0.1 PO 4 , LiFe 0.1 Mn 0.8 Zr 0.3 Mn 0.7 PO 4 , LiFe 0.3 Mn 0.7 PO 4 , LiFe 0.3 Mn 0.7 PO 4 , and LiFe 0.9 Mn 0.1 PO 4.