Negative electrode for lithium secondary battery, method for producing same, and lithium secondary battery comprising such negative electrode for lithium secondary battery

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

a current collector;

a negative-electrode active material body supported by the current collector, the negative-electrode active material body having a chemical composition represented as SiO x (0.1≦x≦1.2)

a covering layer formed on the negative-electrode active material body, the covering layer being composed of silicon dioxide; and

an expansion buffer layer formed between the negative-electrode active material body and the covering layer, the expansion buffer layer having a chemical composition represented as SiO y (x<y<2),

wherein the covering layer has a thickness which is greater than 1 nm and no more than 10 nm.

2. The negative electrode for a lithium secondary battery of claim 1 , wherein an oxygen concentration along a depth direction of the expansion buffer layer increases from the negative-electrode active material body toward the covering layer.

3. The negative electrode for a lithium secondary battery of claim 2 , wherein a molar ratio of an oxygen amount with respect to a silicon amount along the depth direction of the expansion buffer layer is the aforementioned x at an interface between the expansion buffer layer and the negative-electrode active material body, and 2 at an interface between the expansion buffer layer and the covering layer.

4. The negative electrode for a lithium secondary battery of claim 1 , wherein the negative-electrode active material body comprises a plurality of active material particles formed on the current collector.

5. The negative electrode for a lithium secondary battery of claim 4 , wherein the active material particles grow along a generally normal direction to the current collector.

6. The negative electrode for a lithium secondary battery of claim 4 , wherein a growth direction of the active material particles is tilted with respect to the normal direction to the current collector.

7. The negative electrode for a lithium secondary battery of claim 6 , wherein the active material particles have a plurality of portions with different growth directions, each growth direction being tilted with respect to the normal direction to the current collector.

8. The negative electrode for a lithium secondary battery of claim 6 , wherein,

the current collector has a plurality of bumps on a surface thereof; and

each of the plurality of active material particles is formed on a corresponding bump.

9. A lithium-ion secondary battery comprising:

a positive electrode capable of occluding and releasing lithium ions;

the negative electrode for a lithium secondary battery of claim 1 ;

a separator disposed between the positive electrode and the negative electrode for a lithium secondary battery; and

an electrolyte having lithium-ion conductivity.

10. A method of producing a negative electrode for a lithium-ion secondary battery, comprising:

(A) a step of providing a current collector;

(B) a step of forming a negative-electrode active material body on the current collector by supplying oxygen and silicon onto a surface of the current collector, said negative-electrode active material body having a chemical composition represented as SiO x (0.1≦x≦1.2); and

(C) a step of forming, on the negative-electrode active material body, a layer having a higher mole fraction of oxygen than does the negative-electrode active material body, step (C) including:

a step of forming a covering layer composed of silicon dioxide, said covering layer having a thickness which is greater than 1 nm and no more than 10 nm; and

a step of forming an expansion buffer layer between the negative-electrode active material body and the covering layer, the expansion buffer layer having a chemical composition represented as SiO y (x<y<2).