CN111653732A - A positive electrode material, positive electrode sheet and lithium ion battery - Google Patents

Abstract

In order to overcome the problems of insufficient compaction density and safety performance in the existing high-nickel ternary positive electrode materials of lithium ion batteries, the present invention provides a positive electrode material, including a positive electrode active material, and the positive electrode active material includes secondary spheres mixed with each other. Type nickel-cobalt-manganese ternary material and single crystal nickel-cobalt-manganese ternary material, the molar ratio of the secondary spherical nickel-cobalt-manganese ternary material and the single-crystal nickel-cobalt-manganese ternary material is 1:1～ 9:1. At the same time, the present invention also discloses a positive electrode plate and a lithium ion battery comprising the above positive electrode material. The positive electrode material provided by the invention not only ensures the advantages of high gram capacity of the nickel-cobalt-manganese ternary material, but also has good structural stability, improves the disadvantages of the nickel-cobalt-manganese ternary material being easily broken and has a low thermal decomposition temperature, and has higher thermal conductivity. Stability, high compaction density.

Description

A positive electrode material, positive electrode sheet and lithium ion battery

technical field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a positive electrode material, a positive electrode pole piece and a lithium ion battery.

Background technique

A lithium-ion battery is a secondary battery that relies on the migration of lithium ions between positive and negative electrodes. As an efficient energy storage device, lithium-ion batteries are widely used in consumer electronic equipment, new energy vehicles, energy storage and other fields. At present, the most studied cathode materials for lithium-ion batteries include lithium cobalt oxide, lithium nickel cobalt manganate ternary material, nickel cobalt lithium aluminate ternary material, lithium manganate, lithium iron phosphate, etc.

In the field of new energy vehicle power batteries, lithium iron phosphate and ternary materials are the most widely used. Among them, lithium iron phosphate has the advantages of high safety and long cycle life, but its shortcomings such as low gram capacity, low conductivity, and poor low temperature performance limit its application in the field of new energy passenger vehicles. At this stage, ternary materials (including nickel cobalt lithium manganate and nickel cobalt lithium aluminate) are widely used in new energy passenger vehicle power batteries.

With the continuous improvement of battery energy density requirements, the content of nickel in the ternary materials used also increases. In ternary materials, the increase of nickel content can effectively improve the gram capacity of the material, but at the same time, it brings disadvantages such as poor safety, poor structural stability, and poor cycle life. In addition, in order to meet the demand for volumetric energy density of power cells, the compaction density of cathode materials in lithium-ion batteries is also increasing.

In order to improve the structural stability, safety, and compaction performance of high-nickel ternary materials, the existing high-nickel materials are mixed with other types of positive electrode materials, or high-nickel ternary materials of different particle sizes. To a certain extent, many deficiencies in the application process of high-nickel ternary materials are improved.

In the existing technical solutions, the mixed use solutions based on high-nickel cathode materials can be divided into two categories:

(1) Mixing with materials with better safety (lithium manganate, lithium iron phosphate, etc.) The theoretical gram capacity of lithium manganate and lithium iron phosphate is low. Using this technical solution will reduce the energy density of the original ternary material system.

(2) Mixing with secondary spherical ternary material with small particle size, for example, in patent CN 103904310, mixing nickel-cobalt lithium manganate materials with two particle sizes can improve the compaction density of the material to a certain extent, but There is no obvious improvement in safety; if a high-nickel ternary material with a small particle size is used for mixing, it will aggravate the side reaction between the material and the electrolyte, and deteriorate the safety of the cell.

SUMMARY OF THE INVENTION

Aiming at the problems of insufficient compaction density and safety performance of existing high-nickel ternary positive electrode materials for lithium ion batteries, the present invention provides a positive electrode material, a positive electrode piece and a lithium ion battery.

The technical scheme adopted by the present invention to solve the above-mentioned technical problems is as follows:

In one aspect, the present invention provides a positive electrode material, including a positive electrode active material, the positive electrode active material includes a secondary spherical nickel-cobalt-manganese ternary material and a single-crystal nickel-cobalt-manganese ternary material mixed with each other, the two The molar ratio of the sub-spherical nickel-cobalt-manganese ternary material to the single-crystal nickel-cobalt-manganese ternary material is 1:1-9:1.

According to the positive electrode material provided by the present invention, the secondary spherical nickel-cobalt-manganese ternary material and the single-crystal nickel-cobalt-manganese ternary material are mixed and used. There is a synergistic effect between the material and the single-crystal nickel-cobalt-manganese ternary material with single crystal morphology. The positive active material obtained by blending not only ensures the advantages of high gram capacity of the nickel-cobalt-manganese ternary material, but also has good structural stability. , which improves the disadvantages of the nickel-cobalt-manganese ternary material being easily broken and the thermal decomposition temperature is low, and has higher thermal stability and higher compaction density.

Optionally, the positive electrode active material is composed of a secondary spherical nickel-cobalt-manganese ternary material and a single-crystal nickel-cobalt-manganese ternary material mixed with each other.

Optionally, the particle size range of the secondary spherical nickel-cobalt-manganese ternary material is D50=9 μm˜12 μm, and the particle size range of the single crystal nickel-cobalt-manganese ternary material is D50=3.5 μm˜6.5 μm.

Optionally, the molecular formula of the secondary spherical nickel-cobalt-manganese ternary material is LiNi _x 'Co _y 'Mn _1-x ' _-y 'O ₂ , wherein 0.6≤x'<1, 0<y'≤ 0.2.

Optionally, the molecular formula of the single crystal nickel-cobalt-manganese ternary material is LiNi _x "Co _y " Mn _1-x " _-y "O ₂ , wherein 0.6≤x"<1, 0<y"≤0.2 .

Optionally, the positive electrode material further includes a positive electrode conductive agent, and the positive electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black, acetylene black, graphene and graphite.

Optionally, the positive electrode material further includes a positive electrode binder, and the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylic acid, and polyimide. kind.

In another aspect, the present invention provides a positive electrode sheet, comprising a positive electrode current collector and the above-mentioned positive electrode material, and the positive electrode material is attached to the positive electrode current collector.

In another aspect, the present invention provides a lithium ion battery, including an electrolyte, a negative electrode piece, and the above-mentioned positive electrode piece.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The embodiment of the present invention discloses a positive electrode material, including a positive electrode active material, and the positive electrode active material includes a secondary spherical nickel-cobalt-manganese ternary material and a single-crystal nickel-cobalt-manganese ternary material mixed with each other, and the secondary The molar ratio of the spherical nickel-cobalt-manganese ternary material and the single-crystal nickel-cobalt-manganese ternary material is 1:1-9:1.

In the positive electrode material, the secondary spherical nickel-cobalt-manganese ternary material and the single-crystal nickel-cobalt-manganese ternary material are mixed and used. Based on a large number of experiments, the inventor found that the secondary spherical nickel-cobalt-manganese ternary material and The single-crystal nickel-cobalt-manganese ternary materials with single-crystal morphology have synergistic effects. The positive active material obtained by blending not only ensures the advantages of high gram capacity of nickel-cobalt-manganese ternary materials, but also has good structural stability and improves the The disadvantages of the nickel-cobalt-manganese ternary material are easily broken and the thermal decomposition temperature is low, and it has higher thermal stability and higher compaction density.

In some embodiments, the positive electrode active material is composed of a secondary spherical nickel-cobalt-manganese ternary material and a single-crystal nickel-cobalt-manganese ternary material mixed with each other.

In some embodiments, the particle size range of the secondary spherical nickel-cobalt-manganese ternary material is D50=9 μm˜12 μm, and the particle size range of the single crystal nickel-cobalt-manganese ternary material is D50=3.5 μm～6.5 μm .

By adjusting the particle size distribution of the secondary spherical nickel-cobalt-manganese ternary material and the single-crystal nickel-cobalt-manganese ternary material, the single-crystal nickel-cobalt-manganese ternary material with small particle size can be filled in the secondary material with large particle size. In the gaps between the spherical nickel-cobalt-manganese ternary material particles, the compaction density of the positive electrode active material is further improved, and the bond between the secondary spherical nickel-cobalt-manganese ternary material and the single-crystal nickel-cobalt-manganese ternary material is guaranteed. Good electrical contact.

In some embodiments, the molecular formula of the secondary spherical nickel-cobalt-manganese ternary material is LiNi _x' Co _y' Mn _1-x'-y' O ₂ , wherein 0.6≤x'<1, 0<y '≤0.2.

In some embodiments, the molecular formula of the single crystal nickel-cobalt-manganese ternary material is LiNi _{x "} Co _y" Mn _1-x"-y" O ₂ , wherein 0.6≤x"<1, 0<y" ≤0.2.

In some embodiments, the positive electrode material further includes a positive electrode conductive agent, and the positive electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black, acetylene black, graphene, and graphite.

In a more preferred embodiment, the positive electrode conductive agent is selected from conductive carbon black super-P and multi-walled CNT.

The positive electrode conductive agent is used to improve the electrical conductivity between positive electrode active materials.

In some embodiments, the positive electrode material further includes a positive electrode binder, and the positive electrode binder includes one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylic acid, and polyimide or more.

In a more preferred embodiment, the positive electrode binder is selected from polyvinylidene fluoride (PVDF).

The positive electrode binder is used to bind the positive electrode active material to ensure the stability of the positive electrode material.

Another embodiment of the present invention provides a positive electrode sheet, including a positive electrode current collector and the above-mentioned positive electrode material, and the positive electrode material is attached to the positive electrode current collector.

The positive electrode material is obtained by coating the positive electrode slurry and drying it. The positive electrode slurry includes the components of the positive electrode material and a solvent for dispersing the components of the positive electrode material. The solvent can be selected from an organic solvent. Yes, the solvent can be N-methylpyrrolidone.

The positive electrode current collector can adopt various metal materials with good conductivity.

In a more preferred embodiment, the positive electrode current collector is aluminum foil.

Another embodiment of the present invention provides a lithium ion battery, including an electrolyte, a negative pole piece, and the above-mentioned positive pole piece.

In some embodiments, the lithium-ion battery further includes a separator located between the negative pole piece and the positive pole piece.

The separator can be an existing polyolefin separator. The polyolefin separator is a general separator for lithium ion batteries, including polypropylene (PP) separator, polyethylene (PE) separator, and PE/PP/PE three-layer separator.

In some embodiments, the negative electrode sheet is a negative electrode current collector and a negative electrode material layer, and the negative electrode material layer covers the negative electrode current collector.

The negative electrode current collector can be made of various metal materials with good electrical conductivity.

In a more preferred embodiment, the negative electrode current collector is copper foil.

The negative electrode material layer includes a negative electrode active material, a negative electrode conductive agent and a negative electrode binder.

The negative electrode active material may be prepared from one or more of carbon materials, metal alloys, lithium-containing oxides and silicon-containing materials.

The negative electrode conductive agent includes one or more of carbon nanotubes, conductive carbon black, acetylene black, graphene and graphite.

The negative electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylic acid and polyimide.

The present invention will be further illustrated by the following examples.

Example 1

This embodiment is used to illustrate the positive electrode material, the positive electrode sheet, the lithium ion battery and the preparation method thereof disclosed in the present invention, and includes the following operation steps:

(1) Preparation of positive electrode sheet

The positive active material is secondary spherical LiNi _0.8 Co _0.1 Mn _0.1 O ₂ with D50=10.5 μm and single crystal LiNi _0.83 Co _0.12 Mn _0.05 O ₂ with D50=5.0 μm mixed uniformly in a ratio of 7:3, and the mixed powder was measured. The compacted density of the material was 3.48 g/cm ³ . Mix the powder with conductive carbon black super-P, multi-walled CNT, and binder PVDF in a mass fraction of 96.5:1.0:0.8:1.7, add an appropriate amount of N-methylpyrrolidone (NMP), and disperse it in a high-speed disperser to the viscosity It is 3000-6000mPa·S, and the positive electrode slurry is obtained. The above-mentioned positive electrode slurry was uniformly coated on an aluminum foil current collector with a thickness of 14 μm, and a positive electrode pole piece was obtained after drying, rolling and slitting.

(2) Preparation of negative pole piece

The negative active material is artificial graphite, conductive agent super-P, adhesive styrene-butadiene rubber (SBR), and sodium carboxymethylcellulose (CMC) in a mass ratio of 95.2:1.5:2.0:1.3. Mix uniformly, and add deionized water. , dispersed in a high-speed disperser to a viscosity of 2500-4500 mPa·S to obtain a negative electrode slurry. The above negative electrode slurry is uniformly coated on a copper foil current collector with a thickness of 8 μm, and a negative electrode pole piece is obtained after drying, rolling and slitting.

(3) Preparation of lithium ion battery

Put the positive and negative pole pieces on the winding machine respectively, separate the positive and negative pole pieces with a separator, prepare the bare cell by winding, make a packaging bag with aluminum-plastic film composite material, and put the bare cell into the packaging After being packaged in the bag, a dry cell is obtained, and the dry cell is subjected to processes such as baking, liquid injection, sealing, standing, forming, degassing, packaging, and capacity separation to obtain a lithium-ion battery.

Example 2

This example is used to illustrate the positive electrode material, positive electrode piece, lithium ion battery and preparation method thereof disclosed in the present invention, including most of the operation steps in Example 1, and the differences are:

In the preparation of the positive pole piece:

The positive electrode active material is the secondary spherical LiNi _0.83 Co _0.12 Mn _0.05 O ₂ with D50=11.3 μm and the single crystal LiNi _0.83 Co _0.12 Mn _0.05 O ₂ with D50=4.8 μm mixed uniformly in the ratio of 8:2, and the mixed powder was measured. The compacted density of the material was 3.51 g/cm ³ .

Example 3

This example is used to illustrate the positive electrode material, positive electrode piece, lithium ion battery and preparation method thereof disclosed in the present invention, including most of the operation steps in Example 1, and the differences are:

In the preparation of the positive pole piece:

The positive active material is the secondary spherical LiNi _0.6 Co _0.2 Mn _0.2 O ₂ with D50=9.8 μm and the single-crystal LiNi _0.6 Co _0.2 Mn _0.2 O ₂ with D50=6.0 μm mixed uniformly in a ratio of 9:1, and the mixed powder was measured. The compacted density of the material was 3.45 g/cm ³ .

Comparative Example 1

This comparative example is used to compare and illustrate the positive electrode material, the positive electrode sheet, the lithium ion battery and the preparation method thereof disclosed in the present invention, including most of the operation steps in Example 1, and the differences are:

In the preparation of the positive pole piece:

The positive electrode active material was secondary spherical LiNi _0.8 Co _0.1 Mn _0.1 O ₂ with D50=10.5 μm, and the measured powder compacted density was 3.31 g/cm ³ .

Comparative Example 2

This comparative example is used to compare and illustrate the positive electrode material, the positive electrode sheet, the lithium ion battery and the preparation method thereof disclosed in the present invention, including most of the operation steps in Example 1, and the differences are:

In the preparation of the positive pole piece:

The positive electrode active material was secondary spherical LiNi _0.6 Co _0.2 Mn _0.2 O ₂ with D50=9.8 μm, and the measured compact density of the mixed powder was 3.29 g/cm ³ .

Performance Testing

The following performance tests were performed on the positive electrode pieces prepared in the above-mentioned Examples 1 to 3 and Comparative Examples 1 and 2:

Positive pole piece thermal stability test (DSC)

Step 1: Assemble the positive electrode to be tested into a button battery, charge and discharge at 0.1C for one cycle (3.0-4.3V, cut-off current 0.05C), and then charge at 0.1C to 4.3V (cut-off current 0.05C);

The second step: disassemble the button battery in the glove box, soak the pole piece in DMC; after drying, scrape the positive electrode material from the pole piece, take a sample of 3-5mg, transfer it to a stainless steel pressure crucible, and drop 3μL of electrolyte , conduct DSC test. 25-400°C, scanning speed 10°C/min.

The obtained test results are filled in Table 1.

Table 1

From the test results of Examples 1 to 3 and Comparative Examples 1 and 2 in Table 1, it can be seen that the positive electrode material provided by the present invention has higher compaction density, especially, the positive electrode material has better thermal stability, It is beneficial to improve the safety performance of lithium-ion batteries.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (9)

1. The positive electrode material is characterized by comprising a positive electrode active material, wherein the positive electrode active material comprises a secondary spherical nickel-cobalt-manganese ternary material and a single crystal type nickel-cobalt-manganese ternary material which are mixed with each other, and the molar ratio of the secondary spherical nickel-cobalt-manganese ternary material to the single crystal type nickel-cobalt-manganese ternary material is 1: 1-9: 1.

2. The positive electrode material according to claim 1, wherein the positive electrode active material is composed of a quadratic spherical nickel-cobalt-manganese ternary material and a single crystal type nickel-cobalt-manganese ternary material mixed with each other.

3. The positive electrode material according to claim 1 or 2, wherein the secondary spherical nickel-cobalt-manganese ternary material has a particle size range D50 ═ 9 μm to 12 μm, and the single crystal nickel-cobalt-manganese ternary material has a particle size range D50 ═ 3.5 μm to 6.5 μm.

4. The cathode material according to claim 1, wherein the molecular formula of the secondary spherical nickel-cobalt-manganese ternary material is LiNi_x＇Co_y＇Mn_1-x＇-y＇O₂Wherein x 'is more than or equal to 0.6 and less than 1, and y' is more than 0 and less than or equal to 0.2.

5. The positive electrode material as claimed in claim 1, wherein the single crystal type nickel-cobalt-manganese ternary materialMolecular formula is LiNi_x＂Co_y＂Mn_1-x＂-y＂O₂Wherein x is more than or equal to 0.6 and less than 1, and y is more than 0 and less than or equal to 0.2.

6. The lithium ion battery cathode material according to claim 1, further comprising a cathode conductive agent, wherein the cathode conductive agent comprises one or more of carbon nanotubes, conductive carbon black, acetylene black, graphene and graphite.

7. The positive electrode material of the lithium ion battery of claim 1, further comprising a positive electrode binder, wherein the positive electrode binder comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylic acid, and polyimide.

8. A positive electrode plate, comprising a positive electrode current collector and the positive electrode material according to any one of claims 1 to 7, wherein the positive electrode material is attached to the positive electrode current collector.

9. A lithium ion battery comprising an electrolyte, a negative electrode tab, and the positive electrode tab of claim 8.