Lithium-ion secondary battery

1. A lithium-ion secondary battery comprising:

a positive electrode current collector;

a positive electrode active material layer retained on the positive electrode current collector and containing positive electrode active material particles;

a negative electrode current collector; and

a negative electrode active material layer retained on the negative electrode current collector and containing negative electrode active material particles comprising a graphite material,

the positive electrode active material particles being in the form of secondary particles in which a plurality of primary particles having an elongated shape are aggregated;

the positive electrode active material particles being perforated hollow particles each comprising:

a shell portion comprising a layered lithium-transition metal oxide;

a hollow portion formed inside the shell portion; and

a through-hole penetrating through the shell portion,

wherein:

the proportion of the hollow portion is equal to or greater than 20% of the apparent cross-sectional area of the positive electrode active material particle,

the positive electrode active material layer has a density A of 1.80 g/cm 3 ≦A≦2.35 g/cm 3 ; and

the negative electrode active material layer has a density B of 0.95 g/cm 3 ≦B≦1.25g/cm 3 .

2. The lithium-ion secondary battery according to claim 1 , wherein, when the thickness of the shell portion at an arbitrary position within an inner surface of the shell portion is defined by the minimum distance from the arbitrary position within the inner surface of the shell portion to an outer surface of the shell portion in an arbitrary cross section of the positive electrode active material layer, the thickness of the shell portion is less than or equal to 3.0 μm in average of the positive electrode active material layer.

3. The lithium-ion secondary battery according to claim 1 , wherein the thickness of the shell portion is equal to or greater than 0.1 μm.

4. The lithium-ion secondary battery according to claim 1 , wherein the primary particles have a major axis length of less than or equal to 0.8 μm in average of the positive electrode active material layer.

5. The lithium-ion secondary battery according to claim 4 , wherein the primary particles have a major axis length of equal to or greater than 0.2 μm.

6. The lithium-ion secondary battery according to claim 1 , wherein the through-hole has an aperture width of from 0.01 μm to 2.0 μm in average of the positive electrode active material layer.

7. The lithium-ion secondary battery according to claim 1 , wherein the lithium-transition metal oxide contains at least one metal element selected from the group consisting of Ni, Co, and Mn.

8. The lithium-ion secondary battery according to claim 1 , wherein the lithium-transition metal oxide contains Ni, Co, and Mn.

9. The lithium-ion secondary battery according to claim 8 , wherein:

the lithium-transition metal oxide is Li 1+x Ni y Co z Mn (1−y−z) M γ O 2 , where:

0≦x≦0.2, 0.1<y<0.9, 0.1<z<0.4, and 0≦γ≦0.03; and

M is at least one additive selected from the group consisting of Zr, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B, and F.

10. The lithium-ion secondary battery according to claim 7 , wherein the lithium-transition metal oxide contains W, and the W content m MA is from 0.05 mole % to 2 mole % when the total number m MT of moles of Ni, Co, and Mn is set at 100 mole % expressed in mole percentage.

11. The lithium-ion secondary battery according to claim 1 , wherein: the positive electrode active material layer further comprises a conductive agent and PVDF in addition to the positive electrode active material particles; and the positive electrode active material particles is contained in an amount of from 86 mass % to 94 mass %, the conductive agent is contained in an amount of from 6 mass % to 10 mass %, and the PVDF is contained in an amount of from 1 mass % to 4 mass %.

12. The lithium-ion secondary battery according to claim 1 , wherein the negative electrode active material layer contains the negative electrode active material particles in an amount of from 97 mass % to 99 mass %.

13. The lithium-ion secondary battery according to claim 1 , wherein the positive electrode active material particles are manufactured by a method comprising the steps of:

producing a source hydroxide by supplying ammonium ions to an aqueous solution of a transition metal compound to precipitate particles of a transition metal hydroxide from the aqueous solution, the aqueous solution containing at least one of the transition metal elements constituting the lithium-transition metal oxide;

mixing the transition metal hydroxide with a lithium compound to prepare an unsintered mixture; and

sintering the mixture to obtain the active material particles.