CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Chinese Patent Application No. 201810720748.7, filed on Jun. 29, 2018, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The invention belongs to the technical field of energy storage devices, particularly refers to a negative electrode plate, a preparation method thereof and an electrochemical device.

BACKGROUND

Electrochemical device, which can convert chemical energy into electric energy, has advantages including stable voltage and current, reliable performance, simple structure and being easy to carry. It has become the main power source for various consumer electronic products and electric products, and is widely used in all aspects of production and life of mankind. In recent years, the market has placed increasing demands on the cycle performance and safety performance of electrochemical devices.

However, in the existing electrochemical devices, there are many side reactions between electrolyte and negative electrode interface during cycle process, which cause decomposition of electrolyte and gas production, thereby deteriorating safety performance of electrochemical devices and continuously consuming electrolyte cation on negative electrode. Irreversible capacity of the electrochemical device is continuously increased, resulting in rapid decay of cycle life. Moreover, the poor transmission performance of electrolyte cation in negative electrode also causes the formation of metal dendrites on the negative electrode interface, which easily induces short circuit in the electrochemical device and further deteriorates safety performance of electrochemical device.

SUMMARY

The application provides a negative electrode plate, a preparation method thereof and an electrochemical device, to improve safety performance and cycle performance of electrochemical device.

The first aspect of the application provides a negative electrode plate, comprising: a negative current collector; a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer comprising opposite first surface and second surface, wherein the first surface is disposed away from the negative current collector; and an inorganic dielectric layer disposed on the first surface of the negative active material layer; the inorganic dielectric layer comprises first dielectric layer and second dielectric layer; wherein the first dielectric layer is located on an outer surface of the negative active material layer and has a thickness T1of 30 nm≤T1≤1000 nm; the second dielectric layer is located on an inner wall of at least a portion of pores inside the negative active material layer and has a thickness T2of 0 nm<T2≤500 nm; the second dielectric layer extends in the thickness direction from the first surface to the second surface; and extension depth H and thickness T1of the first dielectric layer satisfy: 0.5≤H/T1≤5.

The second aspect of the application provides a method for preparation of a negative electrode plate comprising the steps of: disposing a negative active material layer on at least one surface of a negative current collector, wherein the negative active material layer comprises opposite first surface and second surface, and the first surface is disposed away from the negative current collector; disposing an inorganic dielectric layer on the first surface of the negative active material layer by vapor deposition; wherein the inorganic dielectric layer comprises first dielectric layer and second dielectric layer; the first dielectric layer is located on an outer surface of the negative active material layer and has a thickness T1of 30 nm≤T1≤1000 nm; the second dielectric layer is located on an inner wall of at least a portion of pores inside the negative active material layer and has a thickness T2of 0 nm<T2≤500 nm; and the second dielectric layer extends in the thickness direction from the first surface to the second surface; and extension depth H and the thickness T1of the first dielectric layer satisfy: 0.5≤H/T1≤5.

The third aspect of the application provides an electrochemical device, comprising a positive electrode plate, a negative electrode plate, a separator and a electrolyte, wherein the negative electrode plate is the negative electrode plate according to the first aspect of the application.

As compared with the existing prior art, the application has at least the following beneficial effects:

By disposing a first dielectric layer on an outer surface of the negative active material layer, disposing a second dielectric layer on an inner wall of at least a portion of pores inside the negative active material layer, using the second dielectric layer extending in the thickness direction from the first surface to the second surface, and using an extension depth H and a thickness T1of the first dielectric layer satisfying 0.5≤H/T1≤5, the negative electrode plate provided by the application can stabilize negative electrode interface, and reduce side reactions between electrolyte and negative electrode interface, inhibit gas production, avoid an increase in irreversible capacity, improve wetting and retention of electrolyte on the negative electrode plate and improve ion permeability of negative electrode plate. The negative electrode plate of the application can also improve the kinetic performance of the electrochemical device, inhibit the precipitation of the reduced metal of electrolyte cation on the negative electrode, and avoid short circuit in electrochemical device. Therefore, the electrochemical device has simultaneously excellent safety performance and cycle performance, and the improved high temperature performance.

In addition, the negative electrode plate of the application can ensure electron migration performance, and can significantly inhibit the increase of Direct Current Resistance (DCR) during cycle and storage process of electrochemical device, thereby reducing thermal effects, reducing polarization, and improving rate performance.

