Low-internal-resistance battery and preparation method thereof

Abstract

The invention discloses a low internal resistance battery and a preparation method thereof, the low internal resistance battery comprises an active substance, a conductive agent and a binder, the ratio of the active substance to the conductive agent to the binder is 90%-99%: 0.1%-5%: 1%-5%, the active substance is one of a positive electrode material and a negative electrode material, the positive electrode material is a ternary material, lithium iron phosphate and lithium manganese iron phosphate, and the negative electrode material is one of lithium iron phosphate and lithium manganese iron phosphate. The negative electrode material is graphite, silicon carbon and silica, the conductive agent is metal powder, the shape of the conductive agent is one or more of a linear shape, a sheet shape and a spherical shape, the material of the conductive agent can be one or more of copper, aluminum, silver, nickel and iron, and the binder is one or more of PTFE and PAA. According to the method, a dry electrode process is adopted, high-temperature baking of a pole piece for drying is not needed, the situation that the conductivity is reduced due to oxidation of a metal conductive agent is avoided, solvent homogenization is not needed, interface impedance caused by solvent residues is avoided, and meanwhile the problems of agglomeration and sedimentation of the metal conductive agent in the solvent are solved.

Description

Technical Field

[0001] The present invention relates to the field of new energy battery technology, and in particular to a low internal resistance battery and a preparation method thereof. By replacing a graphite conductive agent with a metal conductive agent and combining it with a dry electrode process, the electrode sheet resistance is significantly reduced and the battery rate performance is improved. Background Art

[0002] The internal resistance of lithium-ion batteries is a key factor affecting their rate performance, energy efficiency, and cycle life. Traditional lithium batteries typically use graphite-based conductive agents (such as carbon black and conductive graphite), but their conductivity is limited and can easily lead to increased polarization at high current densities. Furthermore, during the baking process of traditional wet electrode processes, metal conductive agents (such as copper powder and silver nanowires) are easily oxidized, forming an insulating layer that further increases interfacial resistance. Furthermore, metal conductive agents are poorly dispersed in the slurry and are prone to sedimentation and agglomeration.

[0003] While attempts have been made to improve electrical conductivity using metallic conductive agents, these efforts have been limited by oxidation issues, resulting in poor results in practical applications. Therefore, a method is urgently needed that can leverage the high electrical conductivity of metallic conductive agents while preventing their degradation due to oxidation. Summary of the Invention

[0004] The present invention provides a low-internal-resistance lithium battery and a preparation method thereof, which significantly reduces the electrode sheet resistance and improves the battery rate performance by replacing the graphite conductive agent with a metal conductive agent and combining it with a dry electrode process.

[0005] The present invention provides a low internal resistance battery, comprising an active material, a conductive agent, and a binder, wherein the ratio of the active material, the conductive agent, and the binder is: 90% to 99%: 0.1% to 5%: 1% to 5%; The active material is one of a positive electrode material and a negative electrode material, the positive electrode material is a ternary material, lithium iron phosphate and lithium manganese iron phosphate, and the negative electrode material is graphite, silicon carbon and silicon oxygen; The conductive agent is metal powder, which has a shape of one or more of wire, flake, and sphere, and its material can be one or more of copper, aluminum, silver, nickel, and iron; The binder is one or more of PTFE and PAA.

[0006] As a preferred solution of the present invention, the size of the metal conductive agent is 10nm~100um; The diameter of the spherical conductive agent: the diameter of the active material ranges from 1:10 to 1:300; The aspect ratio of the linear conductive agent ranges from 100:1 to 2000:1, with a typical diameter range of 10 to 50 nm and a length of 1 to 100 μm. The aspect ratio of the flake conductive agent is 100:1~1000:1, the thickness range is 10nm~100nm, and the lateral range is 1~100um.

[0007] As a preferred solution of the present invention, a three-dimensional network structure is constructed by compounding metal conductive agents of different shapes and sizes. The typical compounding ratio is sphere: wire: flake = 1~5:1~5:1~5.

[0008] As a preferred solution in the present invention, the material of the metal conductive agent is the same as that of the corresponding current collector, or the electrochemical window is similar. For example, when the positive electrode uses aluminum foil as the current collector, the conductive agent is also aluminum.

[0009] A method for preparing a low internal resistance battery adopts a dry electrode process, and the specific process is as follows: S1: Dry mixing: dry mix the active material, metal conductive agent and binder; S2: Hot pressing film formation: The mixture is pressed into a self-supporting electrode film by hot roller pressing; S3: Composite current collector: hot-press the electrode film and the conductive current collector.

[0010] As a preferred embodiment of the present invention, in S1, the active material and the metal conductive agent are first added and mixed for 5 to 30 minutes at a mixing speed of 50 to 500 rpm, and then PTFE (for example, 30% + 40% + 30%) is added in batches, each time with an interval of 10 to 30 minutes, and the shear rate is 1000 to 5000 rpm. At the same time, the temperature is controlled at 20 to 40°C by water cooling. In order to prevent oxidation, an inert gas protection can be used, and the inert gas can be one of nitrogen and argon.

[0011] As a preferred embodiment of the present invention, in S2, the mixture is gradually rolled and sheared by 5 to 10 consecutive differential rollers to form a self-supporting electrode film with a thickness of 50 to 200 μm and a width that meets product requirements. The rolling pressure is 20 to 100 MPa, the temperature is 80 to 120°C, and the differential speed ratio is 10:3 to 10:7.

[0012] As a preferred solution of the present invention, in S3, the conductive current collector is preheated to 50-80° C., and then the self-supporting electrode film is pressed onto the conductive current collector at a pressing pressure of 5-20 MPa.

[0013] The conductive current collector is made of one of copper foil, aluminum foil, polymer composite copper foil, and polymer composite aluminum foil, with a thickness of 4 to 20 μm. In order to enhance the peel strength between the conductive current collector and the self-supporting electrode film, the surface of the conductive current collector can be corroded or coated with conductive glue to increase its surface adhesion.

[0014] The beneficial effects of the present invention are: 1. The conductivity of metal conductive agent far exceeds that of graphite conductive agent, which can effectively reduce the amount of conductive agent used and improve energy density; 2. Use metal conductive agents instead of traditional graphite conductive agents to reduce the resistivity of the electrode, reduce the internal resistance of the battery, and improve the rate performance; 3. Using conductive agents of different shapes and sizes, such as wire, sheet and sphere, can build an efficient conductive network and reduce the body resistance of the electrode; 4. The dry electrode process does not require high-temperature baking to dry the electrode, and will not cause oxidation of the metal conductive agent and reduce the conductive performance; 5. The dry electrode process does not require solvent for homogenization, avoiding the interface impedance caused by solvent residue and the agglomeration and sedimentation of the metal conductive agent in the solvent. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the SEM image of the graphite negative electrode dry process proposed in the present invention. DETAILED DESCRIPTION

[0016] The present invention will be further explained below with reference to specific embodiments. Example

[0017] refer to Figure 1 In this embodiment, a low internal resistance battery is proposed, comprising an active material, a conductive agent, and a binder, wherein the ratio of the active material, the conductive agent, and the binder is: 90% to 99%: 0.1% to 5%: 1% to 5%; The active material is one of a positive electrode material and a negative electrode material, the positive electrode material is a ternary material, lithium iron phosphate and lithium manganese iron phosphate, and the negative electrode material is graphite, silicon carbon and silicon oxygen; The conductive agent is metal powder, which has a shape of one or more of wire, flake, and sphere, and its material can be one or more of copper, aluminum, silver, nickel, and iron; The binder is one or more of PTFE and PAA.

[0018] In this embodiment, the size of the metal conductive agent is 10nm~100um; The diameter of the spherical conductive agent: the diameter of the active material ranges from 1:10 to 1:300; The aspect ratio of the linear conductive agent ranges from 100:1 to 2000:1, with a typical diameter range of 10 to 50 nm and a length of 1 to 100 μm. The aspect ratio of the flake conductive agent is 100:1~1000:1, the thickness range is 10nm~100nm, and the lateral range is 1~100um. Metal conductive agents of different shapes and sizes are compounded to construct a three-dimensional network structure. The typical compounding ratio is spherical: linear: flake = 1~5:1~5:1~5. The material of the metal conductive agent is the same as that of the corresponding current collector, or the electrochemical window is similar. For example, when aluminum foil is used as the current collector for the positive electrode, aluminum is also used as the conductive agent.

[0019] The present invention also proposes a method for preparing a low internal resistance battery, which adopts a dry electrode process, and the specific process is as follows: S1: Dry mixing: dry mix the active material, metal conductive agent and binder; S2: Hot pressing film formation: The mixture is pressed into a self-supporting electrode film by hot roller pressing; S3: Composite current collector: hot-press the electrode film and the conductive current collector.

[0020] In the S1, the active material and the metal conductive agent are first added and mixed for 5 to 30 minutes at a mixing speed of 50 to 500 rpm. Then, PTFE (for example, 30% + 40% + 30%) is added in batches, each time with an interval of 10 to 30 minutes, and the shear rate is 1000 to 5000 rpm. At the same time, the temperature is controlled at 20 to 40°C by water cooling. In order to prevent oxidation, an inert gas protection can be used. The inert gas can be one of nitrogen and argon.

[0021] In S2, the mixture is rolled and trimmed step by step through 5 to 10 consecutive differential rollers to form a self-supporting electrode film with a thickness of 50 to 200 μm and a width that meets product requirements. The rolling pressure is 20 to 100 MPa, the temperature is 80 to 120° C., and the differential speed ratio is 10:3 to 10:7.

[0022] In S3, the conductive current collector is preheated to 50-80° C., and then the self-supporting electrode film is pressed onto the conductive current collector at a pressing pressure of 5-20 MPa; The conductive current collector is made of one of copper foil, aluminum foil, polymer composite copper foil, and polymer composite aluminum foil, with a thickness of 4 to 20 μm. In order to enhance the peel strength between the conductive current collector and the self-supporting electrode film, the surface of the conductive current collector can be corroded or coated with conductive glue to increase its surface adhesion.

[0023] The specific implementation process is as follows: The NCM811 positive electrode material, aluminum nanospheres: aluminum nanowires: aluminum nanosheets = 3:1.5:1.5, and PTFE were dry-mixed at a ratio of 96.2%:1.8%:2% at a shear rate of 4000 rpm; after continuous hot pressing with 8 rollers, the film was compounded with 13um aluminum foil to make a positive electrode sheet with a sheet resistivity of 3.2Ω·cm.

[0024] The silicon-carbon negative electrode material, copper nanospheres: copper nanowires: copper nanosheets = 4:1:1, and PTFE were dry-mixed in a ratio of 96.5%:1.5%:2% at a shear rate of 3000 rpm; after continuous hot pressing with 8 rollers, the film was compounded with 6um copper foil to make a negative electrode sheet. The electrode sheet resistivity was tested using a Hioki RM2610 electrode sheet resistivity meter and the result was 0.15Ω·cm.

[0025] After the prepared positive and negative electrode sheets are wound and assembled into a 4695 full-tab battery, the internal resistance of the battery is 0.35mΩ.

[0026] Typical comparison examples are as follows: The same formula is used, but the metal conductive agent is replaced with a graphite conductive agent (such as SP, CNTS, graphene), and wet coating + baking (positive electrode 120℃, negative electrode 100℃) is used. The resistivity of the prepared positive / negative electrode sheets is 5.3Ω·cm / 0.35Ω·cm respectively, and the internal resistance of the 4695 full-tab battery is 1.2mΩ.

[0027] It can be seen from the embodiments and comparative examples that when using metal conductive agents and dry electrodes to make batteries with the same internal resistance, the amount of conductive agent can be reduced by more than 50%; when using the same amount of conductive agent, the internal resistance of the battery can be reduced by more than 50%.

[0028] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A low internal resistance battery, characterized in that: The active material, the conductive agent and the binder are included in a ratio of 90% to 99%: 0.1% to 5%: 1% to 5%; The active material is one of a positive electrode material and a negative electrode material, the positive electrode material is a ternary material, lithium iron phosphate and lithium manganese iron phosphate, and the negative electrode material is graphite, silicon carbon and silicon oxygen; The conductive agent is metal powder, and its shape is one or more of wire, flake, and spherical; The binder is one or more of PTFE and PAA.

2. A low internal resistance battery according to claim 1, characterized in that: The size of the metal conductive agent is 10nm~100um; The diameter of the spherical conductive agent: the diameter of the active material ranges from 1:10 to 1:300; The aspect ratio of the linear conductive agent ranges from 100:1 to 2000:1, with a typical diameter range of 10 to 50 nm and a length of 1 to 100 μm. The aspect ratio of the flake conductive agent is 100:1~1000:1, the thickness range is 10nm~100nm, and the lateral range is 1~100um.

3. A low internal resistance battery according to claim 1, characterized in that: A three-dimensional network structure is constructed by compounding metal conductive agents of different shapes and sizes. The typical compounding ratio is spherical: linear: flake = 1~5:1~5:1~5.

4. A low internal resistance battery according to claim 1, characterized in that: The material of the metal conductive agent is the same as that of the corresponding current collector, and the electrochemical window is similar.

5. A method for preparing a low internal resistance battery, characterized in that: The preparation method adopts dry electrode technology, and its specific process is as follows: S1: Dry mixing: dry mix the active material, metal conductive agent and binder; S2: Hot pressing film formation: The mixture is pressed into a self-supporting electrode film by hot roller pressing; S3: Composite current collector: hot-press the electrode film and the conductive current collector.

6. The method for preparing a low internal resistance battery according to claim 5, characterized in that: In the S1, the active material and the metal conductive agent are first added and mixed for 5 to 30 minutes at a mixing speed of 50 to 500 rpm. Then, PTFE (for example, 30% + 40% + 30%) is added in batches, each time with an interval of 10 to 30 minutes, and the shear rate is 1000 to 5000 rpm. At the same time, the temperature is controlled at 20 to 40°C by water cooling. In order to prevent oxidation, an inert gas protection can be used. The inert gas can be one of nitrogen and argon.

7. The method for preparing a low internal resistance battery according to claim 5, characterized in that: In S2, the mixture is rolled and trimmed step by step through 5 to 10 consecutive differential rollers to form a self-supporting electrode film with a thickness of 50 to 200 μm and a width that meets product requirements. The rolling pressure is 20 to 100 MPa, the temperature is 80 to 120° C., and the differential speed ratio is 10:3 to 10:

7.

8. The method for preparing a low internal resistance battery according to claim 5, characterized in that: In the above-mentioned S3, the conductive current collector is preheated to 50-80° C., and then the self-supporting electrode film is pressed onto the conductive current collector at a pressing pressure of 5-20 MPa.

9. The method for preparing a low internal resistance battery according to claim 8, characterized in that: The conductive current collector is made of one of copper foil, aluminum foil, polymer composite copper foil, and polymer composite aluminum foil, and has a thickness of 4 to 20 μm.

10. The method for preparing a low internal resistance battery according to claim 8, characterized in that: The surface of the conductive current collector is coated with conductive glue.

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