CN114678533A - A cathode current collector and preparation method thereof, cathode sheet and preparation method thereof, and battery - Google Patents

Abstract

The invention relates to the technical field of batteries, in particular, to a positive electrode current collector and a preparation method thereof, a positive electrode sheet and a preparation method thereof, and a battery. The positive electrode current collector of the present invention includes aluminum foil or composite aluminum foil, and at least one surface of the positive electrode current collector is a corroded surface; the hardness of the corroded surface is less than 30Kg/mm ² ; the roughness of the corroded surface is an arithmetic mean height Sa The interface development area ratio Sdr is expressed as follows: Sa is 0.5 to 1.5 μm, and Sdr is 0.2 to 1.2. The positive electrode current collector of the present invention can not only ensure the high strength of the current collector, but also increase the contact area with the positive electrode active material, reduce the contact resistance, reduce the internal resistance of the battery, and improve the positive electrode active material by setting a specific corrosion surface. The adhesion between the aluminum foil and the aluminum foil improves the electrochemical performance and safety performance of the positive electrode sheet.

Description

A cathode current collector and preparation method thereof, cathode sheet and preparation method thereof, and battery

technical field

The present invention relates to the technical field of batteries, in particular, to a positive electrode current collector and a preparation method thereof, a positive electrode sheet and a preparation method thereof, and a battery.

Background technique

Lithium-ion batteries mainly include five parts: positive electrode, negative electrode, separator, electrolyte and packaging shell. The main function of the positive electrode of the lithium battery is to output current to the outside during discharge, and to embed the lithium ions migrated from the negative electrode to the inside; to receive current to the outside during charging, and to remove the lithium ions from the inside to migrate to the negative electrode. In order to ensure the electrochemical activity and low internal resistance of the positive electrode, it is necessary to roll and compact the electrode after coating and drying. In the coating process and rolling process, the aluminum foil as a carrier will bear a large force, so the existing aluminum foils are all high-strength aluminum foils in order to prevent the aluminum foil from breaking. The use of high hardness aluminium foil presents additional problems. Even after the active material and the high-strength aluminum foil are rolled, the aluminum foil is still difficult to deform, resulting in a small contact area between the active material and the aluminum foil, thereby significantly increasing the contact internal resistance.

The existing technical solution is to coat a carbon glue layer composed of conductive carbon and a binder on the high-strength aluminum foil to increase the contact between the active material and the aluminum foil, reduce the contact internal resistance, and improve the battery performance. However, this also brings the following problems: first, the carbon glue layer has a thickness, which increases the volume of the battery and reduces the energy density of the battery; secondly, the battery expands and contracts during the cycle of the lithium battery, and the battery sometimes works at a higher At high temperatures, this will lead to the possibility of this layer of carbon glue layer falling off.

In view of this, the present invention is proposed.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a positive electrode current collector to solve the problems of large contact internal resistance and poor adhesion in the prior art due to the small contact area between high-strength aluminum foil and positive electrode active material.

Another object of the present invention is to provide a method for preparing the cathode current collector, which is simple and efficient.

Another object of the present invention is to provide a positive electrode sheet, the contact area between the positive electrode active material and the positive electrode current collector is large, and the bonding force is good.

Another object of the present invention is to provide a method for preparing a positive electrode sheet, which is simple and efficient.

Another object of the present invention is to provide a battery with excellent electrochemical performance and safety performance.

In order to realize the above-mentioned purpose of the present invention, the following technical solutions are specially adopted:

A positive electrode current collector, the positive electrode current collector comprises aluminum foil or composite aluminum foil, and at least one side surface of the positive electrode current collector is a corroded surface;

The hardness of the corroded surface is less than 30Kg/mm ² ;

The roughness of the etched surface is represented by the arithmetic mean height Sa and the interface development area ratio Sdr: Sa is 0.5-1.5 μm, and Sdr is 0.2-1.2.

Preferably, the thickness of the positive electrode current collector is 5-16 μm.

Preferably, the aluminum foil includes H18 state aluminum foil.

Preferably, the composite aluminum foil includes a first aluminum foil and a second aluminum foil adhered to at least one surface of the first aluminum foil, and the first aluminum foil and the second aluminum foil are in H18 state respectively.

Preferably, the thickness of the first aluminum foil is 4-6 μm, and the thickness of the second aluminum foil is 5-7 μm.

Preferably, the hardness of the corroded surface is 15-28Kg/mm ² , and the roughness of the corroded surface is represented by the arithmetic mean height Sa and the interface development area ratio Sdr: Sa is 0.7-1.2 μm, Sdr is 0.5-1 .

The preparation method of the positive current collector comprises the following steps:

The surface of at least one side of the positive electrode current collector substrate is contacted with alkaline solution for corrosion treatment, and then washed; the positive electrode current collector substrate includes an aluminum foil substrate or a composite aluminum foil substrate.

Preferably, the thickness of the aluminum foil substrate is 7-20 μm.

Preferably, the preparation method of the composite aluminum foil substrate includes: coating at least one surface of a first aluminum foil substrate with a binder, and then thermally compounding it with a second aluminum foil substrate; the first aluminum foil substrate and the second aluminum foil substrate are in H18 state, respectively.

Preferably, the thickness of the first aluminum foil substrate is 5-7 μm, and the thickness of the second aluminum foil is 6-8 μm.

Preferably, the temperature of the thermal compounding is 90-100°C, and the pressure of the thermal compounding is 0.4-0.6 MPa.

Preferably, the thermal compound is allowed to stand for 140-160 hours, and then the corrosion treatment is performed.

Preferably, the lye solution includes sodium hydroxide solution.

Preferably, in the sodium hydroxide solution, the mass percentage of sodium hydroxide is 8% to 12%.

Preferably, the temperature of the etching treatment is 40-50°C, and the time of the etching treatment is 20-62 s.

A positive electrode sheet, comprising the positive electrode current collector, at least one surface of the positive electrode current collector has a plurality of depressions, the diameter of the depressions is 10-50 μm, and the depth is less than 10 μm.

A positive electrode active layer is provided on the side surface of the positive electrode current collector with the depression.

Preferably, the surface roughness of the depressions of the positive electrode current collector is expressed as an arithmetic mean height Sa and an interface development area ratio Sdr: Sa is 0.95-0.98 μm, and Sdr is 0.71-0.75.

Preferably, the positive electrode active layer comprises a positive electrode active material, a conductive agent and a binder, and the mass ratio of the positive electrode active material, the conductive agent and the binder is (95-97):(1.5-2.5):(1 ~2.5).

Preferably, the positive electrode active material includes lithium cobalt oxide and/or lithium iron phosphate.

Preferably, the particle size of the positive electrode active material is 0.5-10 μm, and the particle size of the conductive agent is 20 nm-1 μm.

Preferably, the compaction density of the positive electrode active layer is 4˜4.2 g/m ³ .

The preparation method of the positive electrode sheet comprises the following steps:

The mixed slurry of the positive electrode active material, the conductive agent, the binder and the solvent is coated on at least one surface of the positive electrode current collector, and is subjected to compaction treatment after drying.

Preferably, the pressure of the compaction treatment is 14.5-15.5 tons.

Preferably, the solid content of the mixed slurry is 64% to 70%.

Preferably, the mixed slurry is coated on at least one surface of the positive electrode current collector to form a slurry layer, and the areal density of the slurry layer is 185-195 g/m ² .

A battery includes the positive electrode sheet.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The positive electrode current collector of the present invention, by setting a specific corrosion surface, can not only ensure the high strength of the current collector, but also increase the contact area with the positive electrode active material, reduce the contact resistance, reduce the internal resistance of the battery, and at the same time can improve the positive electrode Adhesion between active substance and aluminum foil.

(2) The preparation method of the positive electrode current collector of the present invention is simple, feasible and efficient, and the surface of at least one side of the current collector can be corroded and cleaned by using an alkaline solution.

(3) In the positive electrode sheet of the present invention, the positive electrode current collector has multiple depressions of a specific size, the contact area between the positive electrode active material and the positive electrode current collector is larger, and the bonding force is better.

(4) The preparation method of the positive electrode sheet of the present invention is simple and efficient by coating the positive electrode slurry on at least one surface of the positive electrode current collector, drying and compacting it.

(5) The battery of the present invention has excellent electrochemical performance and safety performance.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings required in the description of the specific embodiments or the prior art. Obviously, the accompanying drawings in the following description The drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

1 is a cross-sectional SEM picture of a positive electrode sheet in Example 7 of the present invention;

2 is a SEM picture of the surface of the positive electrode current collector after the active material on the surface of the positive electrode sheet is removed in Example 7 of the present invention;

3 is a cross-sectional SEM picture of the positive electrode sheet in Comparative Example 1 of the present invention.

Detailed ways

The embodiments of the present invention will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If the specific conditions are not indicated in the examples, it is carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used without the manufacturer's indication are conventional products that can be obtained from the market.

According to one aspect of the present invention, the present invention relates to a positive electrode current collector, the positive electrode current collector comprises aluminum foil or composite aluminum foil, and at least one side surface of the positive electrode current collector is a corrosion surface;

The hardness of the corroded surface is less than 30Kg/mm ² ;

The roughness of the etched surface is represented by the arithmetic mean height Sa and the interface development area ratio Sdr: Sa is 0.5-1.5 μm, and Sdr is 0.2-1.2.

The positive electrode current collector of the present invention can increase the contact area with the positive electrode active material, reduce the contact resistance, and reduce the internal resistance of the battery by providing a specific corrosion surface while ensuring the strength of the current collector, and can improve the positive electrode active material and the aluminum foil. adhesion between.

In one embodiment, Sa includes, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm.

In one embodiment, Sdr includes, but is not limited to, 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, or 1.2.

In one embodiment, the hardness of the corroded surface includes but is not limited to 5Kg/mm ² , 7Kg/mm ² , 10Kg/mm ² , 11Kg/mm ² , 12Kg/mm ² , 13Kg/mm ² , 14Kg/mm ² , 15Kg/mm ² , 16Kg/mm ² , 17Kg/mm ² , 18Kg/mm ² , 20Kg/mm ² , 21Kg/mm ² , 22Kg/mm ² , 23Kg/mm ² , 24Kg/mm ² , 25Kg/mm ² , 26Kg/mm ² , 27Kg/mm ² , 28Kg/mm ² or 29Kg/mm ² . In the present invention, by setting the surface hardness of the positive electrode current collector to be less than or equal to 30Kg/mm ² , the hardness of the current collector can not only be ensured, the belt will not be broken in the later stage of rolling, and deformation will occur at the same time, thereby increasing the contact area with the positive electrode active material.

In one embodiment, the thickness of the positive electrode current collector is 5-16 μm. In one embodiment, the thickness of the positive electrode current collector includes but is not limited to 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15μm or 16.5μm.

In one embodiment, the composite aluminum foil includes a first aluminum foil and a second aluminum foil adhered to at least one surface of the first aluminum foil, and the first aluminum foil and the second aluminum foil are in H18 state respectively. In an embodiment, the thickness of the first aluminum foil is 4-6 μm, and the thickness of the second aluminum foil is 5-7 μm. In an embodiment, the thickness of the first aluminum foil includes but is not limited to 4.1 μm μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5 μm, 5.1 μm, 5.1 μm, 5.3 μm, 5.5 μm, 5.6 μm, 5.8 μm or 5.9 μm. In one embodiment, the thickness of the second aluminum foil includes, but is not limited to, 5.2 μm, 5.5 μm, 5.6 μm, 5.9 μm, 6 μm, 6.2 μm, 6.5 μm, 6.7 μm or 6.9 μm.

In one embodiment, the hardness of the corroded surface is 15-28Kg/mm ² , and the roughness of the corroded surface is expressed by the arithmetic mean height Sa and the interface expansion area ratio Sdr: Sa is 0.7-1.2 μm, Sdr is 0.5 to 1.

According to another aspect of the present invention, the present invention also relates to the preparation method of the positive electrode current collector, comprising the following steps:

The surface of at least one side of the positive electrode current collector substrate is contacted with alkaline solution for corrosion treatment, and then washed; the positive electrode current collector substrate includes an aluminum foil substrate or a composite aluminum foil substrate.

The lye reacts chemically with aluminum to form metaaluminate and hydrogen. During this process, the surface of the aluminum foil will corrode, and hydrogen embrittlement will occur, which greatly reduces the hardness of the surface of the aluminum foil. Based on this mechanism, the present invention uses alkaline solution to etch at least one surface of the substrate of the positive electrode current collector, thereby forming a corroded surface and reducing the surface hardness of the positive electrode current collector. This method is simple and easy to implement.

In one embodiment, the thickness of the aluminum foil substrate is 7-20 μm. In one embodiment, the thickness of the aluminum foil substrate includes, but is not limited to, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 19.5 μm.

In an embodiment, the preparation method of the composite aluminum foil substrate includes: coating at least one surface of the first aluminum foil substrate with an adhesive, and then thermally compounding it with the second aluminum foil substrate; the first aluminum foil substrate is thermally compounded; An aluminum foil substrate and the second aluminum foil substrate are in H18 state respectively. In one embodiment, the thickness of the first aluminum foil base material is 5-7 μm, and the thickness of the second aluminum foil is 6-8 μm. The thickness of the first aluminum foil substrate includes, but is not limited to, 5.2 μm, 5.5 μm, 6 μm, 6.2 μm, 6.5 μm, 6.7 μm or 6.9 μm. The thickness of the second aluminum foil includes, but is not limited to, 6.2 μm, 6.5 μm, 6.7 μm, 7 μm, 7.2 μm, 7.5 μm, 7.7 μm or 7.9 μm.

In one embodiment, the temperature of the thermal compounding is 90-100° C., and the pressure of the thermal compounding is 0.4-0.6 MPa. In one embodiment, the temperature of the thermal compounding includes, but is not limited to, 91°C, 92°C, 93°C, 94°C, 95°C, 96°C, 97°C, 98°C, or 99°C. The pressure of the thermal compounding includes, but is not limited to, 0.42 MPa, 0.45 MPa, 0.47 MPa, 0.5 MPa or 0.55 MPa.

In one embodiment, after the thermal compounding, it is allowed to stand for 140-160 hours, and then the etching treatment is performed. In one embodiment, the standing time after thermal compounding includes but is not limited to 141h, 142h, 143h, 144h, 145h, 146h, 147h, 148h, 149h, 150h, 151h, 152h, 153h, 154h, 155h, 156h or 159h.

In one embodiment, the lye comprises sodium hydroxide solution.

In one embodiment, in the sodium hydroxide solution, the mass percentage of sodium hydroxide is 8% to 12%. The mass percentage of sodium hydroxide includes, but is not limited to, 8.2%, 8.5%, 8.6%, 8.8%, 9%, 9.5%, 10%, 10.5%, 11% or 11.5%.

In one embodiment, the temperature of the etching treatment is 40-50° C., and the time of the etching treatment is 20-62 s. The temperature of the etching treatment includes, but is not limited to, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C or 49°C. The time of the etching treatment is 20s, 22s, 25s, 27s, 30s, 31s, 33s, 35s, 37s, 40s, 42s, 45s, 46s, 48s, 50s, 53s, 55s, 57s, 59s or 60s.

In the present invention, the corrosion surface with the required hardness and roughness can be obtained by using the alkali solution with the appropriate concentration and temperature to treat the corrosive surface for the appropriate time.

According to another aspect of the present invention, the present invention also relates to a positive electrode sheet, comprising the positive electrode current collector, at least one surface of the positive electrode current collector has a plurality of depressions, and the diameter of the depressions is 10-50 μm , the depth is less than 10μm;

A positive electrode active layer is provided on the side surface of the positive electrode current collector with the depression.

The positive electrode sheet of the present invention can increase the contact area between the positive electrode active material and the positive electrode current collector, and reduce the internal resistance of the battery; multiple concave structures form a mosaic effect, the combination is firmer, and the bonding force between the positive electrode active material and the positive electrode current collector is improved. .

In one embodiment, the diameter of the recess includes, but is not limited to, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 27 μm, 30 μm, 32μm, 35μm, 37μm, 40μm, 42μm, 45μm, 46μm or 48μm. The depth of the recess includes, but is not limited to, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9μm or 9.5μm.

In one embodiment, the surface roughness of the positive electrode current collector with the depressions is expressed as the arithmetic mean height Sa and the interface expansion area ratio Sdr: Sa is 0.95-0.98 μm, and Sdr is 0.71-0.75.

In one embodiment, the arithmetic mean height Sa includes, but is not limited to, 0.951 μm, 0.955 μm, 0.958 μm, 0.959 μm, 0.96 μm, 0.965 μm, 0.968 μm, 0.97 μm, 0.972 μm, 0.975 μm, 0.977 μm, or 0.98 μm . The interface developed area ratio Sdr is 0.71, 0.712, 0.715, 0.717, 0.72, 0.723, 0.725, 0.727, 0.729, 0.73, 0.732, 0.735, 0.737, 0.74, 0.742, 0.745, 0.748 or 0.75.

In an embodiment, the positive electrode active layer includes a positive electrode active material, a conductive agent and a binder, and the mass ratio of the positive electrode active material, the conductive agent and the binder is (95-97): (1.5-2.5 ): (1～2.5).

In one embodiment, the mass ratio of the positive electrode active material, the conductive agent and the binder is 95:2.5:2.5, 96:2:2 or 97:1.5:1.5.

In one embodiment, the positive electrode active material includes lithium cobalt oxide and/or lithium iron phosphate.

In one embodiment, the particle size of the positive electrode active material is 0.5-10 μm, and the particle size of the conductive agent is 20 nm-1 μm. In one embodiment, the particle size of the positive electrode active material includes, but is not limited to, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, μm, 5 μm, 6 μm, 7 μm, 8 μm , 9μm, 10μm. The particle size of the conductive agent may be 20 nm, 50 nm, 100 nm, 500 nm, 800 nm or 1 μm.

In one embodiment, the conductive agent includes conductive carbon black.

In one embodiment, the binder comprises PVDF (polyvinylidene fluoride). For example PVDF HSV900.

In one embodiment, the compaction density of the positive electrode active layer is 4˜4.2 g/m ³ . The compaction density of the positive active layer includes, but is not limited to, 4.1 g/m ³ , 4.12 g/m ³ , 4.15 g/m ³ , and 4.17 g/m ³ .

According to another aspect of the present invention, the present invention also relates to the preparation method of the positive electrode sheet, comprising the following steps:

The mixed slurry of the positive electrode active material, the conductive agent, the binder and the solvent is coated on at least one surface of the positive electrode current collector, and is subjected to compaction treatment after drying.

The preparation method of the positive electrode sheet of the present invention is simple and easy to implement. During the compaction process, due to the reduction of the surface hardness of the positive electrode current collector, the positive electrode active material will squeeze the aluminum foil and cause the aluminum foil to deform, forming a depression with a diameter of 10-50 μm and a depth of less than 10 μm; thus increasing the contact between the positive electrode active material and the positive electrode current collector area.

In one embodiment, the pressure of the compaction process is 14.5-15.5 tons. The pressure of the compaction process includes, but is not limited to, 14.2 tons, 14.5 tons, 14.7 tons, 15 tons, 15.2 tons, or 15.4 tons.

In one embodiment, the solid content of the mixed slurry is 64%-70%. The solids content of the mixed slurry includes, but is not limited to, 65%, 66%, 67%, 68% or 69%.

In one embodiment, the solvent includes N-methylpyrrolidone.

In one embodiment, the mixed slurry is coated on at least one surface of the positive electrode current collector to form a slurry layer, and the areal density of the slurry layer is 185-195 g/m ² . The areal density of the slurry layer includes, but is not limited to, 186 g/m ² , 187 g/m ² , 188 g/m ² , 190 g/m ² , 192 g/m ² , 193 g/m ² or 194 g/m ² .

In one embodiment, the drying temperature is 95-105° C., and the drying time is 3.5-4.5 h. In one embodiment, the drying temperature includes, but is not limited to, 96°C, 97°C, 98°C, 99°C, 100°C, 101°C, or 103°C. The drying time includes but is not limited to 3.7h, 4h or 4.3h.

According to one aspect of the present invention, the present invention also relates to a battery, including the positive electrode sheet.

The battery of the invention has excellent electrochemical performance and high safety performance.

The present invention will be further explained below in conjunction with specific examples and comparative examples.

In one embodiment, the lithium cobaltate is selected from GEM Corporation.

In one embodiment, the conductive carbon black Super P is selected from the company Timcal.

In one embodiment, PVDF HSV900 is selected from Arkema.

In one embodiment, the adhesive WB888 glue is selected from Wuxi Yuke Company.

In one embodiment, the lithium iron phosphate is selected from Defang Nano.

The following is further explained and explained in conjunction with specific embodiments and comparative examples.

Example 1

A preparation method of a positive electrode current collector, comprising the following steps:

Use 14μm H18 aluminum foil as the base material, soak in sodium hydroxide solution for 25s, wherein the solute mass content in the sodium hydroxide solution is 10%, and the temperature of the sodium hydroxide solution is 45 ℃; then quickly take out and rinse with distilled water clean.

Example 2

A preparation method of a positive electrode current collector, except that the H18 state aluminum foil is soaked in a sodium hydroxide solution for 20s, other conditions are the same as in Example 1.

Example 3

A preparation method of a positive electrode current collector, except that the H18 state aluminum foil is soaked in a sodium hydroxide solution for 40s, other conditions are the same as those in Example 1.

Example 4

A preparation method of a positive electrode current collector, comprising the following steps:

(a) Preparation of composite aluminum foil: Coating adhesive on 5 μm H18 aluminum foil and drying, the adhesive layer after drying is 1.5 μm, and the adhesive is WB888 glue; Thermal compounding, the compounding temperature is 95°C, the compounding pressure is 0.5MPa, and the standing time after compounding is 150 hours;

(b) Surface corrosion of composite aluminum foil: soak the composite aluminum foil obtained in step (a) in a sodium hydroxide solution for 60s, wherein the mass content of the sodium hydroxide solution is 10%, and the temperature is 45 ° C; then quickly take out distilled water Rinse well.

Example 5

A preparation method of a positive electrode current collector, except that the composite aluminum foil is soaked in a sodium hydroxide solution for 20s, other conditions are the same as in Example 2.

Example 6

A preparation method of a positive electrode current collector, except that the composite aluminum foil is soaked in a sodium hydroxide solution for 40s, other conditions are the same as those in Example 2.

Example 7

A method for preparing a positive electrode sheet, comprising the following steps:

(a) Add the positive electrode active material, conductive agent and binder to N-methylpyrrolidone in a mass ratio of 96:2:2, and stir to form a positive electrode slurry. The solid content of the slurry is 65%, and the positive electrode active The material is lithium cobalt oxide, the conductive agent is conductive carbon black Super P, and the binder is PVDF HSV900;

(b) uniformly coating the positive electrode slurry obtained in step (a) on one surface of the positive electrode current collector in Example 1, with an areal density of 190 g/m ² , and vacuum-drying it at 100° C. for 4 hours. The other side surface of the anode is coated with the above-mentioned positive electrode slurry and vacuum dried; the above-mentioned dried positive electrode sheet is rolled with a pressure of 15 tons, and the compacted density after rolling is 4.1 g/m ³ .

The cross-sectional SEM picture of the positive electrode sheet in this example is shown in FIG. 1 . The SEM picture of the surface of the positive electrode current collector after the active material on the surface of the positive electrode sheet in this embodiment is removed is shown in FIG. 2 .

Example 8

A preparation method of a positive electrode sheet, except that the positive electrode current collector obtained in Example 2 is used, other conditions are the same as those in Example 7.

Example 9

A preparation method of a positive electrode sheet, except that the positive electrode current collector obtained in Example 3 is used, other conditions are the same as those in Example 7.

Example 10

A preparation method of a positive electrode sheet, except that the positive electrode current collector obtained in Example 4 is used, other conditions are the same as those in Example 7.

Example 11

A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 5 is used, other conditions are the same as those in Example 7.

Example 12

A method for preparing a positive electrode sheet, except that the positive electrode current collector obtained in Example 6 is used, other conditions are the same as those in Example 7.

Example 13

A preparation method of a positive electrode sheet, except that the positive electrode active material is lithium iron phosphate, the coating surface density is 200g/m ² , and the density after rolling is 2.40g/m ³ , and other conditions are the same as in Example 7.

Example 14

A preparation method of a positive electrode sheet, except that the positive electrode active material is lithium iron phosphate, the coating surface density is 200g/m ² , and the density after rolling is 2.40g/m ³ , and other conditions are the same as those in Example 10.

Example 15

A preparation method of a positive electrode sheet, except that the H18 state aluminum foil is subjected to single-sided corrosion treatment; the obtained corrosion surface is coated with slurry, and other conditions are the same as those in Example 7.

Comparative Example 1

A positive electrode current collector is 12μm H18 state aluminum foil.

A method for preparing a positive electrode sheet, except that the above-mentioned 12 μm H18 state aluminum foil is directly used as the current collector, other conditions are the same as those in Example 7.

The cross-sectional SEM picture of the positive electrode sheet in this comparative example is shown in FIG. 3 .

Comparative Example 2

A positive electrode current collector is prepared according to step (a) of Example 3.

A method for preparing a positive electrode sheet, except that the positive electrode current collector in this embodiment is used, other conditions are the same as those in Embodiment 7.

Comparative Example 3

A method for preparing a positive electrode sheet, except that the positive electrode active material is lithium iron phosphate, and other conditions are the same as those of Comparative Example 2.

Experimental example

1. Hardness test

The positive electrode current collectors obtained in Example 1, Example 4 and Comparative Examples 1-2 were tested for thickness, Vickers hardness and surface roughness. The test results are shown in Table 1.

Roughness test: According to ISO 25178, the surface properties of the cathode current collector were tested by using the Keyence shape measurement laser microscope VK-X3000 to test the arithmetic mean height Sa and the interface development area ratio Sdr. Among them, the interface development area ratio Sdr indicates how much the development area of the defined area increases relative to the total area of the defined area, and the Sdr of a completely flat surface is 0. If the surface is tilted, the Sdr will become larger.

Sa=1/A·∫ _A ∫|Z(x,y)|dxdy.

Table 1 Thickness, hardness and roughness test results of cathode current collectors

It can be seen from Table 1 that the present invention can give the positive electrode current collector a surface with specific hardness and roughness by using alkaline solution to corrode the positive electrode current collector and limit the specific corrosion conditions, which is conducive to the deformation of the slurry compaction in the later stage, and improves the compatibility with the positive electrode current collector. The contact area of the positive active material improves the bonding force and reduces the internal resistance of the battery. The current collectors of Comparative Example 1 and Comparative Example 2 have not been corroded by alkali solution, and the hardness of the surface is relatively high. The contact area is very small, which will significantly increase the contact internal resistance.

2. Test of peeling force of positive electrode sheet

The positive electrode sheets obtained in Example 7, Example 10, Example 13, Comparative Example 2 and Comparative Example 3 were tested for peeling force, and the specific method was the same as the patent application with the application number of CN201811570558.8. The test results are shown in Table 2.

Table 2 Test results of the peeling force of the positive electrode sheet

Examples and Comparative Examples Peeling force (N/cm) Example 7 28.4 Example 10 24.5 Example 13 22.3 Comparative Example 2 14.6 Comparative Example 3 13.5

It can be seen from Table 2 that the method of the present invention obtains a positive electrode sheet. During the rolling process, the positive electrode active material will squeeze the surface of the positive electrode current collector to deform, forming a mosaic effect, thereby improving the viscosity of the positive electrode active material and the current collector. knot force. The peeling force between the positive active material of the present invention and the current collector is above 22 N/cm, while that of Comparative Example 2 is 14.6 N/cm, and Comparative Example 3 is 13.5 N/cm, which is far lower than the peeling force of the embodiment of the present invention.

3. Test of surface roughness of positive electrode

The positive electrode sheets obtained in Example 7, Example 10, Example 13, Example 14, Comparative Example 2, and Comparative Example 3 were soaked in N-methylpyrrolidone, respectively, and the surface material was eluted; SEM observation was performed to measure the surface Sag size. The arithmetic mean height Sa and interface development area ratio Sdr of the surface of the cathode current collector after removing the cathode active layer on the surface were respectively tested. The results are shown in Table 3.

Table 3 Test results of the peeling force of the positive electrode sheet

It can be seen from Table 3 that the method of the present invention makes the surface of the positive electrode current collector form depressions, increases the contact area with the positive electrode active material, and improves the bonding force.

Fourth, the composite solvent immersion test

The positive plates obtained in Examples 7-14 and Comparative Examples 1-3 were soaked in a composite solvent respectively, and ultrasonically treated for 15 min to observe the shedding of the active material layer; wherein, the composite solvent was EC (ethylene carbonate), PC (carbonic acid) propylene ester) and DMC (dimethyl carbonate), the mass ratio of EC:PC:DMC is 1:1:3.

The results show that the positive electrode sheet of the embodiment of the present invention does not fall off after being soaked in the composite solvent. On the other hand, the positive electrode sheets of Comparative Examples 1 to 3 all experienced peeling of the positive electrode active layer.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand: It is still possible to modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present invention. range.

Claims (10)

1. The positive current collector is characterized by comprising an aluminum foil or a composite aluminum foil, wherein at least one side surface of the positive current collector is a corrosion surface;

the hardness of the corroded surface is less than 30Kg/mm²；

The roughness of the etched surface is expressed as an arithmetic average height Sa and an interface development area ratio Sdr: sa is 0.5-1.5 μm, Sdr is 0.2-1.2.

2. The positive electrode current collector according to claim 1, wherein the positive electrode current collector has a thickness of 5 to 16 μm;

preferably, the aluminum foil comprises H18 state aluminum foil;

preferably, the composite aluminum foil comprises a first aluminum foil and a second aluminum foil adhered to at least one side surface of the first aluminum foil, and the first aluminum foil and the second aluminum foil are respectively in an H18 state;

preferably, the thickness of the first aluminum foil is 4-6 μm, and the thickness of the second aluminum foil is 5-7 μm;

preferably, the hardness of the corroded surface is 15-28 Kg/mm²The roughness of the etched surface is expressed as an arithmetic average height Sa and an interface spread area ratio Sdr: sa is 0.7 to 1.2 μm, and Sdr is 0.5 to 1.

3. The method for preparing a positive electrode current collector according to claim 1 or 2, comprising the steps of:

contacting at least one side surface of the positive current collector substrate with alkali liquor for corrosion treatment, and then washing; the positive current collector substrate comprises an aluminum foil substrate or a composite aluminum foil substrate.

4. The method for preparing the positive electrode current collector according to claim 3, wherein the aluminum foil substrate has a thickness of 7 to 20 μm;

preferably, the preparation method of the composite aluminum foil substrate comprises the following steps: coating a binder on at least one side surface of the first aluminum foil substrate, and thermally compounding the first aluminum foil substrate and the second aluminum foil substrate; the first aluminum foil substrate and the second aluminum foil substrate are in an H18 state respectively;

preferably, the thickness of the first aluminum foil substrate is 5-7 μm, and the thickness of the second aluminum foil is 6-8 μm;

preferably, the temperature of the thermal compounding is 90-100 ℃, and the pressure of the thermal compounding is 0.4-0.6 MPa;

preferably, the heat compounding is performed, then the still standing is performed for 140-160 h, and then the corrosion treatment is performed.

5. The method for preparing a positive electrode current collector according to claim 3, wherein the alkali solution comprises a sodium hydroxide solution;

preferably, in the sodium hydroxide solution, the mass percent of sodium hydroxide is 8% -12%;

preferably, the temperature of the corrosion treatment is 40-50 ℃, and the time of the corrosion treatment is 20-62 s.

6. A positive electrode sheet, comprising the positive electrode current collector of claim 1 or 2, wherein at least one side surface of the positive electrode current collector has a plurality of depressions, the depressions have a diameter of 10 to 50 μm and a depth of less than 10 μm;

and a positive active layer is arranged on the surface of one side of the positive current collector with the recess.

7. The positive electrode sheet according to claim 6, wherein the surface roughness of the recesses of the positive electrode current collector is expressed as an arithmetic average height Sa and an interfacial development area ratio Sdr: sa is 0.95-0.98 mu m, and Sdr is 0.71-0.75;

preferably, the positive electrode active layer comprises a positive electrode active material, a conductive agent and a binder, and the mass ratio of the positive electrode active material to the conductive agent to the binder is (95-97): (1.5-2.5): (1-2.5);

preferably, the positive electrode active material includes lithium cobaltate and/or lithium iron phosphate;

preferably, the particle size of the positive electrode active material is 0.5-10 μm, and the particle size of the conductive agent is 20 nm-1 μm;

preferably, the compacted density of the positive active layer is 4-4.2 g/m³。

8. The method for producing a positive electrode sheet according to claim 6 or 7, characterized by comprising the steps of:

and coating the mixed slurry of the positive electrode active material, the conductive agent, the binder and the solvent on at least one side surface of the positive electrode current collector, and performing compaction treatment after drying.

9. The method for producing a positive electrode sheet according to claim 8, wherein the pressure of the compacting treatment is 14.5 to 15.5 tons;

preferably, the solid content of the mixed slurry is 64-70%;

preferably, the mixed slurry is coated on at least one side surface of the positive electrode current collector to form slurryA material layer, wherein the surface density of the slurry layer is 185-195 g/m²。

10. A battery comprising the positive electrode sheet according to claim 6 or 7.

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