Lithium secondary battery
In order to enhance charge and discharge efficiency and to improve cycle characteristics by increasing a facing area between a positive electrode active material and a negative electrode active material, in a negative electrode for lithium secondary battery having a current collector and an active material layer carried on the current collector, the active material layer includes a plurality of columnar particles. The columnar particles include an element of silicon, and are tilted toward the normal direction of the current collector. Angle θ formed between the columnar particles and the normal direction of the current collector is preferably 10°≦θ<90°.
1. A negative electrode for a lithium secondary battery, including a current collector and an active material layer carried on said current collector,
said active material layer comprising a plurality of columnar particles,
said columnar particles comprising an element of silicon, and
said columnar particles being tilted from a direction perpendicular to a main flat surface of said current collector,
wherein all of said plurality of columnar particles are arranged with a substantially uniform pitch, and
wherein a porosity P of said active material layer is 10% to 70%.
2. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein an angle θ formed between said columnar particles and said normal direction of said current collector is 10° or more and less than 90°.
3. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein an area A of a portion in said current collector where said active material layer is carried, and an area B of an orthographic projection of said active material layer seen from said normal direction satisfy the relation:
A
-
B
A
×
100
≤
60.
4. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein said active material layer comprises at least one selected from the group consisting of a simple substance of silicon, a silicon alloy, a compound including silicon and oxygen, and a compound including silicon and nitrogen.
5. The negative electrode for a lithium secondary battery in accordance with claim 4 , wherein said silicon alloy is an alloy including silicon and a metal element M, and said metal element M does not form an alloy with lithium.
6. The negative electrode for a lithium secondary battery in accordance with claim 5 , wherein said metal element M is at least one selected from the group consisting of titanium, copper, and nickel.
7. The negative electrode for a lithium secondary battery in accordance with claim 4 , wherein said compound including silicon and oxygen comprises a composition represented by the general formula (I): SiO x , where θ<x<2.
8. A lithium ion secondary battery, comprising:
a positive electrode capable of absorbing and desorbing lithium ion,
the negative electrode in accordance with claim 1 ,
a separator disposed between said positive electrode and said negative electrode, and
an electrolyte having lithium ion conductivity.
9. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein said porosity is 30% to 60%.
10. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein each of the columnar particles has a different and separate starting point of growth.
11. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein the pitch is about 0.1 μm to about 200 μm.
12. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein said plurality of columnar particles are arranged in a substantially uniform direction with a substantially uniform angle of tilt.
13. The negative electrode for a lithium secondary battery in accordance with claim 1 , wherein said plurality of columnar particles have substantially straight sides along a direction extending from the current collector to an external surface of said electrode.