CN109950459A - Lithium-rich lithium ion battery diaphragm - Google Patents

Abstract

The invention relates to a lithium-rich lithium ion battery diaphragm, which is characterized in that a lithium-rich coating is arranged on at least one side of the diaphragm, and lithium salt contained in the lithium-rich coating can provide a stable lithium ion source for a battery in the using process. In the first charge-discharge process, lithium salt in the lithium-rich layer is dissolved in the electrolyte to release lithium ions, and the consumption of the lithium ions is supplemented when an SEI film is formed; meanwhile, an SEI film on the surface of the graphite cathode can be rapidly formed and reaches a stable state, the quality of the SEI film is improved, and the impedance of the SEI film is reduced; in the use process of the lithium ion battery, the lithium salt in the lithium-rich layer is gradually released, the concentration of the lithium salt in the electrolyte is maintained, and the cycle life of the battery is prolonged; the lithium exists in the lithium compound mode, so that potential safety hazards caused by using metal lithium are avoided, and the influence of harsh production conditions which are not beneficial to large-scale production is avoided.

Description

A lithium-rich lithium-ion battery separator

technical field

The invention belongs to the field of batteries, and in particular relates to a lithium-rich lithium ion battery separator.

Background technique

Lithium-ion batteries have become one of the most widely used secondary batteries due to their advantages of high voltage, high energy density and long cycle life. However, with the continuous development of miniaturization and long standby of portable electronic devices, as well as the activation of high-power and high-energy devices such as electric bicycles and electric vehicles, the energy density of lithium-ion batteries as energy storage power sources has become higher and higher. Require.

For the negative electrode sheet, some lithium will be consumed due to the formation of the solid electrolyte membrane (SEI film) during the first charging process of the battery, which will result in the loss of lithium in the positive electrode material, thereby reducing the capacity of the battery and causing the first efficiency. reduce. This is particularly evident in the negative electrode sheet with alloy materials (such as silicon alloy and tin alloy) as the active material.

In order to reduce the reduction of battery capacity due to the irreversible capacity of the battery during the first charging and discharging process, some solutions have been reported in some patent documents. For example, the Chinese patent application with publication number CN102916165A mentions that in an inert atmosphere, an organic lithium solution is sprayed or dripped on the surface of the negative electrode sheet, so that the lithium ions in the organic lithium solution are reduced to metallic lithium and embedded in the negative electrode sheet, and then Dry the negative sheet.

Another example is the Japanese patent application with the application number of JP1996027910, which uses the method of covering the surface of the negative electrode sheet with a metal lithium sheet, then winding it to form a battery, and then pouring an electrolyte to prepare a lithium ion battery. Although this method can also play the role of supplementing lithium, the amount of lithium that can be absorbed by the negative electrode sheet is far less than that provided by the metal lithium sheet, so it will cause uneven lithium insertion and lead to deformation of the electrode sheet. Lithium precipitation is also prone to occur.

Another example is the Chinese Patent Application Publication No. CN105932206A, where the metal lithium powder is covered on the separator through a binder, and then a ceramic layer is applied.

Although the above methods can play a role in supplementing lithium, the source of lithium supplementation is metal lithium in lithium supplementation, but due to the very strong activity of metal lithium, metal lithium powder is easy to contact with the external environment, causing potential safety hazards; and in practice In production applications, the requirements for equipment and environment are very strict, and large-scale production is difficult.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the present invention provides a lithium-rich lithium-ion battery separator, the lithium-rich layer of the separator can provide a stable source of lithium ions for the battery, and is environmentally friendly. The lithium in the lithium-rich layer exists in the form of a compound, which avoids the potential safety hazards caused by metal lithium powder and ensures production safety. The entire production process is simple and easy to achieve large-scale production. The content of lithium in the lithium-rich layer can be passed through the lithium-rich layer. The thickness and ratio of the battery can be adjusted, and the purpose of supplementing the battery with lithium can be achieved by a simple method.

Specifically, the lithium-rich lithium-ion battery separator includes a separator base film, and at least one side of the separator base film is coated with a lithium-rich coating;

The diaphragm base film is selected from polyolefin diaphragms;

Preferably, the polyolefin membrane is selected from any one of polyethylene (PE) membrane, polypropylene (PP) membrane and polyethylene-polypropylene composite membrane;

Preferably, the thickness of the diaphragm base film is 6-100 μm; most preferably, the thickness of the diaphragm base film is 9-30 μm;

The lithium-rich coating comprises lithium compounds, ceramic powders, polyacrylate compounds, and binders;

Preferably, the mass percentage of each component in the lithium-rich coating is as follows: 30-90% of lithium-containing compound, 0-40% of ceramic powder, 5-30% of polyacrylate compound, and 5-30% of binder ;

The lithium-containing compound is selected from one or more of lithium carbonate and lithium dioxalate borate, preferably lithium carbonate;

The ceramic powder is selected from aluminum oxide, silicon dioxide, titanium dioxide, tin dioxide, zinc oxide, calcium oxide, magnesium oxide, calcium carbonate, barium carbonate, barium sulfate, barium titanate, aluminum nitride, nitride one or more of magnesium;

The polyacrylate compound is selected from one or more of polymethyl methacrylate, polyethyl methacrylate, and polybutyl methacrylate;

The binder is selected from one or more of nitrile rubber, styrene butadiene rubber, and polyvinyl alcohol;

The thickness of the lithium-rich coating is 2-50 μm, preferably 2-8 μm;

Further, the preparation method of the lithium-rich lithium-ion battery separator comprises the following steps:

(1) Slurry preparation: Lithium-containing compound, ceramic powder, polyacrylate compound, and binder are added to the solvent, and mixed uniformly to obtain a mixture slurry;

(2) Coating the mixed slurry on the base film and drying at high temperature to obtain it.

The present invention has the following technical effects with respect to the prior art:

(1) The present invention aims at the deficiencies of the prior art. By arranging a lithium-rich coating on at least one side of the separator, the lithium salt contained in the lithium-rich coating can provide a stable source of lithium ions during use of the battery. During the first charge and discharge process, the lithium salt in the lithium-rich layer dissolves in the electrolyte to release lithium ions, which supplements the consumption of lithium ions during the formation of the SEI film; at the same time, the SEI film on the surface of the graphite negative electrode can be rapidly formed and reach a stable state. Improve the quality of the SEI film and reduce the impedance of the SEI film; during the use of the lithium-ion battery, the lithium salt in the lithium-rich layer is gradually released, maintaining the concentration of the lithium salt in the electrolyte, and improving the cycle life of the battery;

(2) Lithium in the lithium-rich coating of the present invention exists in the form of a lithium compound, which avoids the potential safety hazard brought by the use of metal lithium in the traditional lithium supplementation method, and the impact of harsh production conditions that are not conducive to large-scale production. The production process of the lithium-rich layer separator is simple, and it is friendly to the production environment, simple and convenient, and it is easy to realize mass production;

(3) The lithium-rich layer of the separator of the present invention can provide a stable source of lithium ions for the battery, and the entire manufacturing process is simple and easy to realize large-scale production. The content of lithium in the lithium-rich layer can be determined by the thickness of the lithium-rich layer and the ratio. The purpose of supplementing lithium to the battery is achieved by a simple method.

Description of drawings

1 is a schematic structural diagram of a lithium-ion battery separator containing a single-layer lithium-rich coating according to the present invention;

2 is a schematic structural diagram of a lithium-ion battery separator containing a double-layer lithium-rich coating according to the present invention;

101, the diaphragm base film; 102, the lithium-rich coating.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

As shown in FIG. 1 of the accompanying drawings, a lithium-rich lithium-ion battery separator includes a separator base film 101, the separator base film is a polypropylene (PP) separator, and the thickness of the separator base film 101 is 16 μm; One side of the membrane 101 is coated with a 4 μm thick lithium-rich coating 102 consisting of the following components:

Lithium carbonate powder (particle size is 5μm) 12g;

Aluminum oxide powder (particle size 5μm) 55g;

Polymethyl methacrylate (molecular weight is 60,000) 18g;

Nitrile rubber (acrylonitrile content is 15%) 15g;

The preparation method of the lithium-rich lithium-ion battery separator comprises the following steps:

(1) Preparation of mixed slurry: 32g of lithium carbonate powder, 35g of aluminum oxide powder, 18g of polymethyl methacrylate, and 15g of nitrile rubber were added to 100g of NMP solvent, and mixed evenly (using a high-speed disperser) get mixed slurry;

(2) Coat the mixed slurry on the PP film (using a gravure printing machine), and finally form a 4 μm lithium-rich coating on one side of the diaphragm base film, that is, obtain.

Further, adopt the separator of above-mentioned preparation, be assembled in the lithium ion battery that positive electrode material is ternary (523 type), negative electrode material artificial graphite, wherein electrolyte is: LiPF6/EC+DEC+DEC (volume ratio 1:1: 1), prepare 5Ah laminated soft pack battery.

Example 2

As shown in FIG. 2 of the accompanying drawings, a lithium-rich lithium-ion battery separator includes a separator base film 101, the separator base film is a polyethylene (PE) separator, and the thickness of the separator base film is 20 μm; Both sides of 101 are respectively coated with a 2 μm thick lithium-rich coating 102, and the lithium-rich coating 102 is composed of the following components:

Lithium carbonate powder (particle size is 5μm) 18g;

Aluminum oxide powder (particle size 5μm) 40g;

Polymethyl methacrylate (molecular weight is 60,000) 15g;

Nitrile rubber (27% acrylonitrile) 27g;

The preparation method of the lithium-rich lithium-ion battery separator comprises the following steps:

(1) Preparation of mixed slurry: Add 58g of lithium carbonate powder, 20g of aluminum oxide powder, 10g of polymethyl methacrylate, and 12g of nitrile rubber into 100g of NMP solvent, and mix them evenly (using a high-speed disperser) get mixed slurry;

(2) Coat the mixed slurry on the PE film (using a gravure printing machine), and finally form a 2 μm lithium-rich layer on both sides of the base film.

Further, adopt the separator prepared above; be assembled in the lithium ion battery that the positive electrode material is ternary (523 type), and the negative electrode material artificial graphite, wherein the electrolyte is: LiPF6/EC+DEC+DEC (volume ratio 1:1: 1), prepare 5Ah laminated soft pack battery.

Example 3

As shown in FIG. 2 of the accompanying drawings, a lithium-rich lithium-ion battery separator includes a separator base film 101, the separator base film is a polyethylene (PE) separator, and the thickness of the separator base film is 20 μm; Both sides of 101 are respectively coated with a 2 μm thick lithium-rich coating 102, and the lithium-rich coating 102 is composed of the following components:

Lithium carbonate powder (particle size is 5μm) 10g;

Aluminum oxide powder (particle size 5μm) 60g;

Polymethyl methacrylate (molecular weight is 60,000) 20g;

Nitrile rubber (acrylonitrile content is 10%) 10g;

The preparation method of the lithium-rich lithium-ion battery separator comprises the following steps:

(1) Preparation of mixed slurry: 70g of lithium carbonate powder, 10g of aluminum oxide powder, 7g of polymethyl methacrylate, and 13g of nitrile rubber were added to 100g of NMP solvent, and mixed evenly (using a high-speed disperser) get mixed slurry;

(2) Coat the mixed slurry on the PE film (using a gravure printing machine), and finally form a 2 μm lithium-rich layer on both sides of the base film.

Further, adopt the separator prepared above; be assembled in the lithium ion battery that the positive electrode material is ternary (523 type), and the negative electrode material artificial graphite, wherein the electrolyte is: LiPF6/EC+DEC+DEC (volume ratio 1:1: 1), prepare 5Ah laminated soft pack battery.

Comparative Example 1

A lithium ion battery diaphragm, comprising a diaphragm base film 101, the diaphragm base film is a polypropylene (PP) diaphragm, and the thickness of the diaphragm base film 101 is 16 μm;

Further, using the above-mentioned separator, it is assembled in a lithium ion battery whose positive electrode material is ternary (523 type) and negative electrode material artificial graphite, wherein the electrolyte is: LiPF6/EC+DEC+DEC (volume ratio 1:1:1) , to prepare 5Ah laminated soft pack battery.

Comparative Example 2

A lithium ion battery diaphragm, comprising a diaphragm base film 101, the diaphragm base film is a polypropylene (PE) diaphragm, and the thickness of the diaphragm base film 101 is 20 μm;

Further, using the above-mentioned separator, it is assembled in a lithium ion battery whose positive electrode material is ternary (523 type) and negative electrode material artificial graphite, wherein the electrolyte is: LiPF6/EC+DEC+DEC (volume ratio 1:1:1) , to prepare 5Ah laminated soft pack battery.

Verification example

The lithium ion batteries in Example 1-3 and Comparative Example 1-2 were taken for cycle performance test (1.0C/1.0C rate, temperature 25±3°C).

(1) First charge and discharge efficiency test

Charge the battery with a constant current of 0.1C to 3.4V, then charge the battery with a constant current of 0.2C to 3.95V to form the battery, and then charge the battery with a constant current and voltage of 0.2C to 4.2V after pumping and sealing, and the cut-off current is 0.02C. The total charge capacity is then discharged to 3.0V at 0.2C to obtain the discharge capacity, discharge efficiency=discharge capacity/total charge capacity*100%.

The test results are shown in Table 1 below:

Table 1 The first charge-discharge efficiency of lithium-ion batteries

project first charge and discharge efficiency Example 1 91.2% Example 2 91.6% Example 3 91.5% Comparative Example 1 87.4% Comparative Example 2 88.8%

(2) Battery DC internal resistance test

a) Standard charging of lithium-ion batteries with 0.2C5A constant current and 4.2V voltage limiting;

b) Discharge to 10% DOD with 0.2C5A constant current;

c) Charge the battery with constant current with high current (usually 1C5A);

d) Repeat steps a) to c), increasing the depth of discharge by 10% each time until the depth of discharge is 90%;

e) Discharge at a constant current of 0.2C5A to a final voltage of 2.5V to fully discharge the battery.

The test results are shown in Table 2 below:

Table 2 Lithium-ion battery cycle performance

project Cycling performance (500 cycle retention rate) Battery DC internal resistance (mΩ) Example 1 90.2% 4.3 Example 2 92.6% 3.8 Example 3 89.5% 4.8 Comparative Example 1 85.4% 5.5 Comparative Example 2 87.8% 5.1

It can be seen from the above Table 1 and Table 2 that the cycle performance and DC internal resistance rate of the lithium-ion battery with the lithium-rich lithium-ion battery separator prepared in Example 1-3 of the present invention are significantly better than those prepared in Comparative Example 1-2. The resulting lithium-ion battery does not contain a lithium-rich coated lithium-ion battery separator.

The reason is that the SEI film formed in the lithium battery consumes lithium ions during the cycle, which increases the internal resistance of the battery and reduces the lithium ion transmission rate, while the lithium-rich layer on the surface of the lithium-rich layer separator is released in time to supplement the charge and discharge of the lithium battery. The process consumes lithium ions and improves the cycle performance of the battery.

In the present invention, the lithium-rich separator is provided with a lithium-rich layer on one or both sides of the base film. On the one hand, the stability of the SEI film during the formation of the lithium ion battery can be improved, the resistance of the SEI film can be reduced, and the lithium lost during the formation of the SEI film can be supplemented. On the other hand, during the cycle, the electrolyte composition is stabilized, the consumed lithium is replenished, and the battery cycle life is improved.

Claims (10)

1. a kind of lithium ion battery separator of richness lithium, including diaphragm basement membrane, which is characterized in that at least the one of the diaphragm basement membrane Side is coated with rich lithium coating, and lithium-containing compound, ceramic powder, polyacrylacid ester compounds are contained in the richness lithium coating and are glued Mixture.

2. the lithium ion battery separator of richness lithium according to claim 1, which is characterized in that the lithium-containing compound is selected from carbon One of sour lithium, dioxalic acid lithium borate are a variety of.

3. the lithium ion battery separator of richness lithium according to claim 1, which is characterized in that the ceramic powder is selected from three oxygen Change two aluminium, silica, titanium dioxide, stannic oxide, zinc oxide, calcium oxide, magnesia, calcium carbonate, barium carbonate, barium sulfate, One of barium titanate, aluminium nitride, magnesium nitride are a variety of.

4. the lithium ion battery separator of richness lithium according to claim 1, which is characterized in that the polyacrylate chemical combination Object is selected from one of polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate or a variety of.

5. the lithium ion battery separator of richness lithium according to claim 1, which is characterized in that the binder is selected from butyronitrile rubber One of glue, butadiene-styrene rubber, polyvinyl alcohol are a variety of.

6. the lithium ion battery separator of richness lithium according to claim 1, which is characterized in that the diaphragm basement membrane is selected from polyene Hydro carbons diaphragm, with a thickness of 6-100 μm, preferably 9-30 μm.

7. the lithium ion battery separator of richness lithium according to claim 6, which is characterized in that the polyolefins diaphragm is selected from Any one in polyethylene diagrams, polypropylene diaphragm and polyethylene-polypropylene composite membrane.

8. the lithium ion battery separator of richness lithium according to claim 1, which is characterized in that each ingredient in the richness lithium coating Mass percent is as follows: lithium-containing compound 30-90%, ceramic powder 0-40%, polyacrylacid ester compounds 5-30%, bonding Agent 5-30%.

9. it is according to claim 1 richness lithium lithium ion battery separator, which is characterized in that it is described richness lithium coating with a thickness of 2-50μm。

10. the lithium ion battery separator of richness lithium according to claim 9, which is characterized in that the thickness of the richness lithium coating It is 2-8 μm.