Negative electrode for lithium-ion secondary battery

1 . A negative electrode for a lithium-ion secondary battery, comprising:

a negative electrode current collector, and

a negative electrode active material layer, wherein the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector,

the negative electrode active material layer including:

a lower layer portion facing the at least one surface of the negative electrode current collector and comprising a first negative electrode active material that includes a first graphite and a first conductive material, and

an upper layer portion disposed on a top of the lower layer portion and comprising:

a second negative electrode active material that includes a second graphite and silicon oxide, wherein the upper layer portion comprises the second graphite and silicon oxide at a weight ratio range of from 70:30 to 90:10, and

a second conductive material, wherein the second conductive material comprises (i) graphene, or (ii) a linear conductive material comprising single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or both, or (iii) a combination of (i) and (ii),

wherein the silicon oxide has a particle diameter, D 50 , of 3-10 μm, and

wherein the silicon oxide has a sphericity, s, satisfying 0.4≤s<0.8.

2 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the lower layer portion comprises the first graphite in an amount of 90 wt % or more based on 100 wt % of the first negative electrode active material present in the lower layer portion.

3 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the silicon oxide comprises at least one compound represented by Chemical Formula 1:

SiO x   [Chemical Formula 1]

wherein x is equal to or more than 0 and less than 2.

4 . The negative electrode for a lithium-ion secondary battery according to claim 3 , wherein x is 0.5-1.5.

5 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the silicon oxide comprises a metal including at least one selected from Li, Mg, and Al, and the metal is distributed on surface of silicon oxide particles, inside of the silicon oxide particles, or on the surface and inside of the silicon oxide particles.

6 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the linear conductive material comprises single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs).

7 . A lithium-ion secondary battery comprising the negative electrode as defined in claim 1 .

8 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the linear conductive material comprises single-walled carbon nanotubes (SWCNTs).

9 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the linear conductive material comprises multi-walled carbon nanotubes (MWCNTs).

10 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the sphericity is calculated according to Formula 1:

Sphericity

=

4

⁢

Area

π

⁢

Dmax

2

[

Formula

⁢

1

]

where Area and Dmax values are determined by using scanning electron microscopy,

where Area is an area of a silicon oxide particle, and

where Dmax is a maximum diameter of the silicon oxide particle.

11 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the first graphite includes an artificial graphite and a natural graphite, and

wherein the artificial graphite has an average particle diameter of 8-30 μm.

12 . The negative electrode for a lithium-ion secondary battery according to claim 11 , wherein the natural graphite has a particle diameter of 5-30 μm.

13 . The negative electrode for a lithium-ion secondary battery according to claim 12 wherein the artificial graphite, before mixed with the natural graphite to form the first graphite, has a tap density of 0.7-1.1 g/cc.

14 . The negative electrode for a lithium-ion secondary battery according to claim 11 , wherein the first graphite includes an artificial graphite and a natural graphite in a ratio of 5:5 by weight.

15 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the lower layer portion comprises the first graphite in an amount of 95 wt % or more based on 100 wt % of the first negative electrode active material present in the lower layer portion.

16 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the first conductive material includes carbon black.

17 . The negative electrode for a lithium-ion secondary battery according to claim 16 , wherein the first conductive material is present in the lower layer portion.

18 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the second graphite includes artificial graphite that has an average particle diameter of 8-30 μm.

19 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the upper layer portion comprises the second negative electrode active material in an amount of 90 wt % or more based on 100 wt % of the upper layer portion.

20 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the upper layer portion comprises the second negative electrode active material in an amount of 96.5 wt % or more based on 100 wt % of the upper layer portion.

21 . The negative electrode for a lithium-ion secondary battery according to claim 1 , wherein the silicon oxide has a sphericity in a range of 0.4 to 0.6.