CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2017-0071647, filed on Jun. 8, 2017 and Korean Patent Application No. 10-2018-0065929 filed on Jun. 8, 2018, the disclosures of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a negative electrode, a secondary battery including the same, and a method of preparing the negative electrode, and particularly, to a negative electrode, which includes a current collector; a negative electrode active material layer disposed on the current collector; a first layer disposed on the negative electrode active material layer and including Li; and a second layer disposed on the first layer and including an inorganic material, wherein a loading amount of the first layer may satisfy Equation 1 below.
0.65×(x1−y1)<loading amount of the first layer<0.95×(x1−y1)  [Equation 1]

In Equation 1, x1is a charge loading amount of the negative electrode active material layer, and y1is a discharge loading amount of the negative electrode active material layer. Units of the loading amount of the first layer, the charge loading amount and the discharge loading amount are mAh/cm2, the charge loading amount and the discharge loading amount are capacities per unit area measured in a half-cell which includes a lithium metal electrode and an electrode including the negative electrode active material layer, wherein the charge loading amount is a capacity per unit area of the half-cell when a charging current decreases to 0.005C after the half-cell being charged at a constant current (CC) until a potential difference of the electrode including the negative electrode active material layer with respect to the lithium metal electrode becomes 0.005V, and then charged at a constant voltage (CV), and the discharge loading amount is a difference between the capacity per unit area of the half-cell and the charge loading amount when a potential difference of the electrode including the negative electrode active material with respect to the lithium metal electrode while the half-cell is discharged at a constant current becomes 1.5V.

BACKGROUND ART

A dramatic increase in the use of fossil fuels results in an increasing demand for the use of alternative energy or clean energy, and as part of this, the most actively researched fields are fields of power generation and electricity storage using an electrochemical reaction.

Today, a representative example of an electrochemical device using such electrochemical energy may be a secondary battery including the same, and the scope of the application thereof is gradually expanding. In recent years, according to the increase in technological development and demands for portable devices such as portable computers, mobile phones, cameras, etc., the demand for secondary batteries as an energy source is dramatically increasing, various studies have been made on lithium secondary batteries with high energy density, that is, high capacity, have been conducted, and the batteries have been commercialized and widely used.

Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte and a separator. Wherein, the negative electrode includes a current collector and a negative electrode active material, which may be disposed on the current collector. To increase an energy density of the negative electrode, although a variety of negative electrode active materials such as silicon, etc., are used, there are problems of a decreased capacity of the battery and a deterioration of the lifespan property, due to a high irreversible capacity.

To solve this, there was an attempt to solve the problem of irreversible capacity by applying lithium to the negative electrode active material layer (Chinese Unexamined Patent Application Publication No. 102916165). However, when a separate layer consisting of lithium is disposed on a negative electrode active material layer through such techniques, the high reactivity of lithium leads to the formation of a native oxide film, which cannot smoothly resolve the problem of irreversible capacity. In addition, when a layer containing lithium is formed through solution spraying, which is one of the above-mentioned techniques, the layer becomes excessively thick, and non-uniform.

Accordingly, there are demands for a method of preparing a negative electrode and a negative electrode, which can smoothly resolve the problem of irreversible capacity by preventing the generation of the native oxide film and easily control a loading amount of the layer containing lithium.

PRIOR ART LITERATURE

Patent Literature

(Patent Literature 1) Chinese Unexamined Patent Application Publication No. 102916165

DISCLOSURE

Technical Problem

To attain the present invention, the present invention is directed to providing a method of preparing a negative electrode and a negative electrode, which can smoothly resolve the problem of irreversible capacity by preventing the generation of the native oxide film and easily control a loading amount of the layer containing lithium.

Technical Solution

According to an exemplary embodiment of the present invention, there is provided a negative electrode, which includes a current collector; a negative electrode active material layer disposed on the current collector; a first layer disposed on the negative electrode active material layer and containing Li; and a second layer disposed on the first layer and containing an inorganic material, wherein a loading amount of the first layer satisfies Equation 1 below.
0.65×(x1−y1)<loading amount of the first layer<0.95×(x1−y1)  [Equation 1]

In Equation 1, x1is a charge loading amount of the negative electrode active material layer, and y1is a discharge loading amount of the negative electrode active material layer. Units of the loading amount of the first layer, the charge loading amount and the discharge loading amount are mAh/cm2, the charge loading amount and the discharge loading amount are capacities per unit area measured in a half-cell which includes a lithium metal electrode and an electrode including the negative electrode active material layer, wherein the charge loading amount is a capacity per unit area of the half-cell when a charging current decreases to 0.005C after the half-cell being charged at a constant current (CC) until a potential difference of the electrode including the negative electrode active material layer with respect to the lithium metal electrode becomes 0.005V, and then charged at a constant voltage (CV), and the discharge loading amount is a difference between the capacity per unit area of the half-cell and the charge loading amount when a potential difference of the electrode including the negative electrode active material with respect to the lithium metal electrode while the half-cell is discharged at a constant current becomes 1.5V. A method of preparing a negative electrode, which includes disposing a negative electrode active material layer on a current collector, vapor-depositing a first layer containing Li on the negative electrode active material layer using a Li-containing raw material as a source, and disposing a second layer containing an inorganic material on the first layer, is provided.

Advantageous Effects

According to a method of preparing a negative electrode according to an exemplary embodiment of the present invention, a second layer containing an inorganic material is formed on a first layer containing lithium, and thus a problem of irreversible capacity can be smoothly resolved by preventing the generation of a native oxide film formed through oxidation of the lithium during the process. In addition, since the first layer is formed by vacuum deposition, a loading amount of the first layer is easy to control and thus a content and lifespan of the negative electrode can be improved. Moreover, the lithium oxidation can be further more prevented by the second layer, and when the negative electrode is used together with the separator, thermal resistance of the separator can be improved, and thus stability of a battery can be increased.

