Positive pole piece, preparation method thereof and lithium ion battery

Abstract

The invention provides a positive pole piece, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries. According to the positive pole piece, the carbon nano tube (O-CNT) subjected to ozone oxidation treatment is adopted as a conductive agent, after the carbon nano tube CNT is subjected to ozone oxidation treatment, functional groups such as carboxyl and hydroxyl are introduced to the surface of the carbon nano tube CNT, so that the surfaces of O-CNT particles are negatively charged, agglomeration of the O-CNT can be effectively inhibited under the action of electrostatic repulsive force, and the dispersion effect of the O-CNT in a dry-method positive pole is ensured; therefore, a uniform conductive network is formed in the positive pole piece, so that the conductivity of the positive pole piece is improved, and the internal resistance is reduced. The invention provides a preparation method of the positive pole piece, the positive pole piece is manufactured by adopting a dry-method electrode process, and due to the characteristics of the conductive agent O-CNT, the conductive agent O-CNT cannot be agglomerated even in the dry-method electrode preparation process, good dispersion can be realized, and the formation of a conductive network is facilitated.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] In recent years, lithium-ion batteries have garnered significant attention in fields such as electric vehicles and energy storage due to their superior performance and wide range of applications. Currently, most lithium-ion batteries are manufactured using a wet process, a simple and mature technology that is the choice of the vast majority of battery manufacturers. However, wet-process batteries require the use of N-methylpyrrolidone (NMP), which has potential hazards. Furthermore, solvents such as NMP or water can cause pores in the electrodes during the drying process, negatively impacting electrode uniformity and energy density.

[0003] Dry electrode manufacturing typically involves fiberizing polytetrafluoroethylene (PTFE) to form a film, eliminating the need for solvents. This saves on solvent drying and recovery processes, reducing equipment and production costs, and avoiding the formation of pores during solvent evaporation, offering significant advantages over wet processes. However, dry-process cathodes are generally thicker than wet-process cathodes, placing higher demands on the formation of the conductive network. Furthermore, the absence of solvents in the dry electrode preparation process makes particle dispersion difficult, and the smaller cathode particle size makes it challenging to uniformly mix traditional conductive agents such as conductive carbon black (SP); carbon nanotubes (CNTs) are prone to agglomeration, hindering the formation of the conductive network. These issues result in higher film resistance in dry-process cathodes, negatively impacting the rate capability and cycle life of the battery cell.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a positive electrode sheet, a method for preparing the same, and a lithium-ion battery, so as to improve at least one of the above-mentioned technical problems.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The primary objective of this invention is to provide a positive electrode sheet, comprising a current collector and a positive electrode film layer disposed on the surface of the current collector;

[0008] Based on the total mass of the positive electrode film layer as 100%, the positive electrode film layer comprises the following raw materials in the following mass fractions: 96-98% positive electrode active material, 1-2% binder and 1-2% conductive agent;

[0009] The conductive agent includes carbon nanotubes that have undergone ozone oxidation treatment.

[0010] Furthermore, based on the above technical solution of the present invention, the surface of the ozone-oxidized carbon nanotubes contains carboxyl groups and / or hydroxyl groups.

[0011] And / or, the atomic percentage of oxygen on the surface of the ozone-oxidized carbon nanotubes is 6-8 At%.

[0012] Furthermore, based on the above-mentioned technical solution of the present invention, the conductive agent also includes at least one of carbon black, graphene, or carbon fiber.

[0013] Furthermore, based on the above-described technical solution of the present invention, the adhesive includes polytetrafluoroethylene.

[0014] Furthermore, based on the above-mentioned technical solution of the present invention, the adhesive further includes a conductive polymer, which includes one or more of polyaniline, polypyrrole, and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate.

[0015] Furthermore, based on the above-mentioned technical solution of the present invention, the positive electrode active material includes one or more of nickel-cobalt-manganese ternary materials (NCM), nickel-cobalt-aluminum ternary materials (NCA), lithium iron phosphate, or lithium manganese iron phosphate.

[0016] The second objective of this invention is to provide a method for preparing the above-mentioned positive electrode sheet, comprising the following steps:

[0017] (a) The positive electrode active material and the conductive agent are initially mixed to obtain a mixture; the conductive agent includes carbon nanotubes treated with ozone oxidation.

[0018] (b) The binder is mixed with the mixture, and then sheared and stirred at high speed to obtain the positive electrode powder;

[0019] (c) The positive electrode powder is rolled to obtain a positive electrode film;

[0020] (d) The positive electrode film is rolled onto the current collector and hot rolled to obtain the positive electrode sheet.

[0021] Furthermore, based on the above technical solution of the present invention, in step (a), the initial mixing speed is 2000-3000 rpm, and the initial mixing time is 10-30 s;

[0022] And / or, in step (b), the mixing speed is 500-3000 rpm and the mixing time is 1-2 min;

[0023] And / or, in step (b), the shearing and stirring speed is 2000-3000 rpm and the time is 1-3 min.

[0024] Furthermore, based on the above technical solution of the present invention, in step (c), the thickness of the positive electrode film is 50-60 μm;

[0025] And / or, in step (d), the temperature of the hot roller press is 100-160°C;

[0026] And / or, in step (d), the thickness of the positive electrode sheet is 60-80 μm.

[0027] The third objective of this invention is to provide a lithium-ion battery, including the positive electrode sheet provided by the first objective of this invention or the positive electrode sheet prepared by the preparation method provided by the second objective of this invention.

[0028] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0029] (1) This invention provides a positive electrode sheet using ozone-oxidized carbon nanotubes (O-CNTs) as a conductive agent. After ozone oxidation, functional groups such as carboxyl and hydroxyl groups are introduced on the surface of O-CNTs, making the surface of O-CNT particles negatively charged. Under the action of electrostatic repulsion, the aggregation of O-CNTs can be effectively inhibited, ensuring the dispersion effect of O-CNTs in the dry positive electrode, thereby forming a uniform conductive network in the positive electrode sheet, which is beneficial to improving the conductivity of the positive electrode sheet and reducing the internal resistance.

[0030] (2) The present invention provides a method for preparing the above-mentioned positive electrode sheet, which uses a dry electrode process to manufacture the positive electrode sheet. Among them, carbon nanotubes (O-CNT) treated with ozone oxidation are used as conductive agents. Taking advantage of the inherent properties of O-CNT, even if no solvent is added during the dry electrode preparation process, O-CNT will not agglomerate, and can achieve good dispersion, which is conducive to the formation of conductive network in the positive electrode sheet.

[0031] In addition, the materials required for this preparation method are widely available, the process is simple, and it has high practical value, showing significant advantages over wet methods.

[0032] (3) The present invention provides a lithium-ion battery comprising the above-mentioned positive electrode sheet. In view of the advantages of the above-mentioned positive electrode sheet, the lithium-ion battery made therefrom has good rate performance, cycle life and other properties. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0034] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0035] According to a first aspect of the present invention, a positive electrode sheet is provided, comprising a current collector and a positive electrode film layer disposed on the surface of the current collector;

[0036] Based on the total mass of the positive electrode film layer as 100%, the positive electrode film layer comprises the following raw materials in the following mass fractions: 96-98% positive electrode active material, 1-2% binder and 1-2% conductive agent;

[0037] The conductive agent includes carbon nanotubes that have undergone ozone oxidation treatment.

[0038] Unlike traditional conductive agents like carbon nanotubes, the positive electrode of this invention uses ozone-oxidized carbon nanotubes (O-CNTs) as the conductive agent. After ozone oxidation, the ozone reacts with the CNTs... 2 The carbon network undergoes a cycloaddition reaction to generate unstable primary ozonides, which then undergo ring-opening to form carboxyl and epoxy groups. During subsequent electrode fabrication, the epoxy groups hydrolyze with moisture in the air to produce hydroxyl groups. The carboxyl and hydroxyl functional groups on the O-CNT surface give the O-CNT particles a negative charge. Under the action of electrostatic repulsion, this effectively inhibits the aggregation of O-CNTs, ensuring their dispersion in the dry-process positive electrode. This results in the formation of a uniform conductive network within the positive electrode, which in turn contributes to improved conductivity and reduced internal resistance of the positive electrode.

[0039] In this positive electrode, there are further restrictions on the amount of each raw material used in the positive electrode film layer.

[0040] Typical, but not limited, mass fractions of conductive agents are 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, or 2%. Typical, but not limited, mass fractions of binders are 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, or 2%. Typical, but not limited, mass fractions of positive electrode active materials are 96%, 96.2%, 96.5%, 96.8%, 97%, 97.2%, 97.5%, 97.8%, or 98%.

[0041] The preparation method of ozone-oxidized carbon nanotubes (O-CNTs) is not limited. As an optional embodiment of the technical solution of the present invention, the preparation method of ozone-oxidized carbon nanotubes (O-CNTs) is as follows: CNTs are oxidized by exposing them to a high concentration of ozone atmosphere to obtain ozone-oxidized carbon nanotubes (O-CNTs).

[0042] As an optional embodiment of the technical solution of this invention, the surface of ozone-oxidized carbon nanotubes (O-CNTs) mainly contains carboxyl groups and / or hydroxyl groups. These specific groups give the O-CNT particles a negative charge on their surface, effectively inhibiting O-CNT aggregation under electrostatic repulsion. This allows for good dispersion of O-CNTs in the positive electrode, facilitating the formation of a conductive network within the positive electrode, enhancing its conductivity, and reducing the film resistance of the dry-process positive electrode. This also improves the rate capability, cycle life, and other performance characteristics of the battery cell. It should be noted that after ozone oxidation, the surface of carbon nanotubes may contain not only carboxyl groups and / or hydroxyl groups but also other groups. However, this invention primarily utilizes carboxyl groups and / or hydroxyl groups to give the O-CNT particles a negative charge, thereby promoting uniform dispersion of the O-CNT particles.

[0043] As an optional embodiment of the technical solution of the present invention, the atomic percentage of oxygen on the surface of the ozone-oxidized carbon nanotubes (O-CNTs) is controlled at 6 to 8 At%, for example, 6 At%, 6.5 At%, 7 At%, 7.5 At%, or 8 At. Too low an oxygen atomic percentage on the O-CNT surface will reduce the dispersion effect of O-CNTs, while too high an oxygen atomic percentage will reduce the conductivity of O-CNTs. Therefore, it is best to limit the oxygen atomic percentage to the above-mentioned range.

[0044] In this invention, besides using O-CNT as a conductive agent, other types of conductive materials in the art can also be compounded with O-CNT. As an optional embodiment of the technical solution of this invention, the conductive agent further includes at least one of carbon black, graphene, or carbon fiber.

[0045] As an optional embodiment of the technical solution of the present invention, the binder includes polytetrafluoroethylene (PTFE). Using PTFE as a binder mainly utilizes the fiberization of PTFE under shear force, and then uses it to dry-process the positive electrode sheet with the positive electrode active material and conductive agent.

[0046] In addition to polytetrafluoroethylene, the adhesive also includes a conductive polymer. As an optional embodiment of the technical solution of this invention, the conductive polymer includes one or more of polyaniline (CAS No.: 5612-44-2), polypyrrole (CAS No.: 30604-81-0), and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (CAS No.: 155090-83-8).

[0047] The aforementioned conductive polymers can act as binders together with PTFE, reducing the amount of PTFE used. Simultaneously, the conductive polymers coat the surface of the positive electrode active material, improving the conductivity of the positive electrode. However, the electronic conductivity of the conductive polymers is limited; therefore, using them in conjunction with O-CNTs can further form a long-range conductive network, significantly improving the conductivity of the positive electrode.

[0048] When the binder includes both polytetrafluoroethylene (PTFE) and a conductive polymer, the mass ratio between PTFE and the conductive polymer can be optimized. As an optional embodiment of the present invention, the mass ratio of PTFE to the conductive polymer is 1:(1-3), for example, 1:1, 1:1.5, 1:2, 1:2.5, or 1:3. When the mass proportion of the conductive polymer in the binder is too small, its effect on improving the conductivity of the positive electrode is not significant; when the mass proportion of the conductive polymer in the binder is too large, it may affect the PTFE fiberization effect and adversely affect cycle performance.

[0049] As an optional embodiment of the technical solution of the present invention, the positive electrode active material includes one or more of the following: NCM ternary materials (e.g., NCM811, NCM622, 9-series ternary materials), NCA ternary materials, lithium iron phosphate, or lithium manganese iron phosphate.

[0050] According to a second aspect of the present invention, a method for preparing the above-mentioned positive electrode sheet is also provided, comprising the following steps:

[0051] (a) The positive electrode active material and the conductive agent are initially mixed to obtain a mixture; the conductive agent includes carbon nanotubes (O-CNT) treated with ozone oxidation.

[0052] (b) After mixing the binder with the mixture, high-speed shearing and stirring are performed to obtain the positive electrode powder;

[0053] (c) The positive electrode powder is rolled to obtain a positive electrode film;

[0054] (d) The positive electrode film is rolled onto the current collector and hot rolled to obtain the positive electrode sheet.

[0055] This invention employs a dry electrode process to manufacture the positive electrode sheet, in which O-CNT is used as a conductive agent. Since O-CNT is carbon nanotube CNT treated with ozone oxidation, its surface contains a certain amount of carboxyl and / or hydroxyl groups. These groups can make the surface of O-CNT particles negatively charged. Under the action of electrostatic repulsion, the aggregation of O-CNT can be effectively inhibited, so as to achieve good dispersion of the conductive agent in the positive electrode sheet, which is conducive to the formation of the conductive network in the positive electrode sheet.

[0056] In addition, the materials required for this preparation method are widely available, the process is simple, and it has high practical value, showing significant advantages over wet methods.

[0057] As an optional embodiment of the technical solution of the present invention, in step (a), the initial mixing speed is 2000-3000 rpm, for example, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm or 3000 rpm, and the initial mixing time is 10-30s, for example, 10s, 20s or 30s.

[0058] As an optional embodiment of the technical solution of the present invention, in step (b), the mixing speed is 500-3000 rpm, for example, 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm or 3000 rpm, and the mixing time is 1-2 min, for example, 1 min, 1.5 min or 2 min.

[0059] As an optional embodiment of the technical solution of the present invention, in step (b), the rotation speed of shearing and stirring is 2000-3000 rpm, such as 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm or 3000 rpm, and the time is 1-3 min, such as 1 min, 1.5 min, 2 min, 2.5 min or 3 min.

[0060] As an optional embodiment of the technical solution of the present invention, in step (c), the thickness of the positive electrode film is 50-60 μm, for example, 50 μm, 52 μm, 54 μm, 55 μm, 56 μm, 58 μm or 60 μm.

[0061] As an optional embodiment of the technical solution of the present invention, in step (d), the temperature of the hot roller pressing is 100-160℃, for example, 100℃, 120℃, 140℃, 150℃ or 160℃.

[0062] As an optional embodiment of the technical solution of the present invention, in step (d), the thickness of the positive electrode sheet is 60-80μm, for example, 60μm, 65μm, 70μm, 75μm or 80μm.

[0063] According to a third aspect of the present invention, a lithium-ion battery is also provided, comprising a positive electrode sheet provided in the first aspect of the present invention or a positive electrode sheet prepared by the preparation method provided in the second aspect of the present invention.

[0064] Given the advantages of the aforementioned positive electrode, lithium-ion batteries made from it have excellent rate performance and cycle life.

[0065] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The raw materials used in the following embodiments and comparative examples are described as follows: polyaniline (CAS No.: 5612-44-2, molecular weight 10000-50000); poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (CAS No.: 155090-83-8, molecular weight 150000-180000);

[0066] Ozone-oxidized carbon nanotubes were prepared by the following method: CNTs were placed in a closed space, and ozone was introduced at a rate of 0.8 L / min under 0.08 MPa. After treatment at room temperature for 2 hours, O-CNTs with a surface oxygen atom percentage of about 6-8 At% (which can be detected by testing instruments) were obtained.

[0067] Example 1

[0068] This embodiment provides a positive electrode sheet, including a current collector aluminum foil and a positive electrode film layer disposed on the surface of the current collector aluminum foil (thickness of 14μm);

[0069] Based on the total mass of the positive electrode film layer as 100%, the positive electrode film layer comprises the following raw materials in the following mass fractions: 97% positive electrode active material, 1% binder and 2% conductive agent;

[0070] The positive electrode active material is NCM811, and the binder is PTFE. The conductive agent is ozone-oxidized carbon nanotubes (O-CNTs) with an oxygen atom percentage of approximately 6-8% on their surface.

[0071] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0072] (a) 97g of positive electrode active material NCM811 and 2g of conductive agent O-CNT were initially mixed at 2000rpm for 30s to obtain a mixture;

[0073] (b) Add 1g of binder PTFE to the mixture in step (a), mix evenly at low speed of 500rpm for 1min, and then shear and stir at high speed of 3000rpm for 2min to fiberize PTFE and obtain positive electrode powder.

[0074] (c) The positive electrode powder is rolled to obtain a positive electrode film with a thickness of 60 μm;

[0075] (d) The positive electrode film is then rolled onto the current collector aluminum foil and then hot rolled at 150°C to obtain a positive electrode sheet with a thickness of 74±2μm.

[0076] Example 2

[0077] This embodiment provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 1% O-CNT and 1% conductive carbon black SP by mass, the other raw material composition is the same as in Example 1.

[0078] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the conductive agent in step (a) of Example 1 is changed from 2g O-CNT to 1g O-CNT and 1g conductive carbon black SP.

[0079] Example 3

[0080] This embodiment provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 1% O-CNT and 1% carbon fiber VGCF by mass, and the other raw material composition is the same as in Example 1.

[0081] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the conductive agent in step (a) of Example 1 is changed from 2g O-CNT to 1g O-CNT and 1g carbon fiber VGCF.

[0082] Example 4

[0083] This embodiment provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 1.5% O-CNT by mass, and the binder is changed from 1% PTFE by mass to 1.5% PTFE by mass. The composition of the remaining raw materials is the same as in Example 1.

[0084] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the conductive agent in step (a) is changed from 2g O-CNT to 1.5g O-CNT and the binder in step (b) is changed from 1g PTFE to 1.5g PTFE.

[0085] Example 5

[0086] This embodiment provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 1% O-CNT by mass, and the binder is changed from 1% PTFE by mass to 2% PTFE by mass. The composition of the remaining raw materials is the same as in Example 1.

[0087] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the conductive agent in step (a) is changed from 2g O-CNT to 1g O-CNT and the binder in step (b) is changed from 1g PTFE to 2g PTFE.

[0088] Example 6

[0089] This embodiment provides a positive electrode sheet, except that the binder in Example 1 is changed from 1% PTFE by mass to 0.5% PTFE and 0.5% polyaniline by mass, and the composition of other raw materials is the same as in Example 1.

[0090] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the binder in step (b) of Example 1 is changed from 1g PTFE to 0.5g PTFE and 0.5g polyaniline.

[0091] Example 7

[0092] This embodiment provides a positive electrode sheet, except that the binder in Example 1 is changed from 1% PTFE by mass to 0.5% PTFE and 0.5% poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate by mass, and the other raw material composition is the same as in Example 1.

[0093] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the binder in step (b) of Example 1 is changed from 1g PTFE to 0.5g PTFE and 0.5g poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate.

[0094] Example 8

[0095] This embodiment provides a positive electrode sheet, including a current collector aluminum foil and a positive electrode film layer disposed on the surface of the current collector aluminum foil (thickness of 14μm);

[0096] Based on the total mass of the positive electrode film layer as 100%, the positive electrode film layer comprises the following raw materials in the following mass fractions: 97% positive electrode active material, 2% binder and 1% conductive agent;

[0097] The positive electrode active material is NCM811, the binder is PTFE and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate with a mass ratio of 1:3, and the conductive agent is ozone-oxidized carbon nanotubes (O-CNTs) with an oxygen atom percentage of about 6-8% on their surface.

[0098] The preparation method of the positive electrode sheet in this embodiment includes the following steps:

[0099] (a) 97g of positive electrode active material NCM811 and 1g of conductive agent O-CNT were initially mixed at 2000rpm for 30s to obtain a mixture;

[0100] (b) Add 0.5g of binder PTFE and 1.5g of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate to the mixture in step (a), mix evenly at low speed of 500rpm for 2min, and then shear and stir at high speed of 2000rpm for 3min to fiberize PTFE and obtain positive electrode powder.

[0101] (c) The positive electrode powder is rolled to obtain a positive electrode film with a thickness of 60 μm;

[0102] (d) The positive electrode film is then rolled onto the current collector aluminum foil and then hot rolled at 140°C to obtain a positive electrode sheet with a thickness of 74±2μm.

[0103] Comparative Example 1

[0104] This comparative example provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 2% conductive carbon black SP by mass, and the other raw material composition is the same as in Example 1.

[0105] The preparation method of the positive electrode sheet in this comparative example is the same as that in Example 1, except that the conductive agent in step (a) of Example 1 is changed from 2g O-CNT to 2g conductive carbon black SP.

[0106] Comparative Example 2

[0107] This comparative example provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 2% carbon nanotube CNT (without ozone oxidation treatment), and the other raw material composition is the same as in Example 1.

[0108] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the conductive agent in step (a) of Example 1 is changed from 2g O-CNT to 2g carbon nanotube CNT.

[0109] Comparative Example 3

[0110] This comparative example provides a positive electrode sheet, except that the conductive agent in Example 1 is changed from 2% O-CNT by mass to 2% VGCF by mass, and the other raw material composition is the same as in Example 1.

[0111] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the conductive agent in step (a) of Example 1 is changed from 2g O-CNT to 2g VGCF.

[0112] Comparative Example 4

[0113] This comparative example provides a positive electrode sheet, including a current collector aluminum foil and a positive electrode film layer disposed on the surface of the current collector aluminum foil (thickness of 14 μm);

[0114] Based on the total mass of the positive electrode film layer as 100%, the positive electrode film layer comprises the following raw materials in the following mass fractions: 97% positive electrode active material, 1% binder and 2% conductive agent;

[0115] The positive electrode active material is NCM811, and the binder is PVDF. The conductive agent is ozone-oxidized carbon nanotubes (O-CNTs) with an oxygen atom percentage of approximately 6-8% on their surface.

[0116] The preparation method of the positive electrode sheet in this comparative example includes the following steps:

[0117] (a) Add 97g of positive electrode active material NCM811, 1g of binder PVDF, and 2g of conductive agent O-CNT to solvent NMP, and adjust the viscosity to 4000±1000mpa·s to obtain positive electrode slurry;

[0118] (b) The above positive electrode slurry is coated, rolled, and cut into sheets to obtain a positive electrode sheet with a total thickness of 74±2μm.

[0119] Comparative Example 5

[0120] This comparative example provides a positive electrode sheet, except that the conductive agent in Comparative Example 4 is changed from 2% O-CNT by mass to 2% CNT by mass, and the composition of other raw materials is the same as that in Comparative Example 4.

[0121] The preparation method of the positive electrode sheet in this comparative example is the same as that in comparative example 4, except that the conductive agent in step (a) of comparative example 4 is changed from 2g O-CNT to 2g CNT.

[0122] To further illustrate the technical effects of the above embodiments and comparative examples, the following experimental examples are provided.

[0123] Experimental Example 1

[0124] The membrane resistance of the positive electrode sheets prepared in each embodiment and comparative example was tested: the membrane resistance was measured under a pressure of 20 MPa, and the specific results are shown in Table 1.

[0125] The positive electrode sheets prepared in each embodiment and comparative example are assembled into a battery. The specific steps are as follows:

[0126] A button cell is assembled from a positive electrode, a separator, and lithium metal. The separator is a PE membrane, and the electrolyte is 1 mol / L lithium hexafluorophosphate dissolved in a solvent with a volume ratio of EC:DMC:EMC of 2:4:4. The amount of electrolyte added is 1.5 g / Ah.

[0127] The performance of the batteries assembled from the positive electrode sheets of each embodiment and comparative example was tested, as follows:

[0128] (1) Cycle life: The number of cycles from 0.1C charge / 0.1C discharge until the capacity retention rate drops to 80%.

[0129] (2) 25℃ DCIR: Let I0 be the current corresponding to 0.1C and I1 be the current corresponding to 1C. Place the fresh battery cell that has not undergone electrical performance testing in a constant temperature chamber at 25℃ for more than 1 hour, charge it to 4.2V with constant current and constant voltage with current I0; let it stand for 10 minutes; discharge it with constant current I0 for 5 hours, and record the voltage at the moment of discharge as U0. Then discharge it with constant current I1 for 1 second, and record the voltage at the moment of discharge as U1.

[0130] The formula for calculating DCIR at 25℃ is: DCIR=(U1-U0) / (I1-I0).

[0131] The specific test results are shown in Table 1.

[0132] Table 1

[0133]

[0134]

[0135] As can be seen from the data in Table 1, using O-CNT as a conductive agent can effectively reduce the battery's internal resistance. Furthermore, the combined use of O-CNT and conductive polymers not only further strengthens the conductive network but also ensures interparticle contact during cycling, thus improving cycle performance.

[0136] Furthermore, comparing the data from Example 1 and Comparative Example 2, as well as Comparative Example 4 and Comparative Example 5, it can be seen that the positive electrode sheet prepared by dry method using O-CNT as a conductive agent (Example 1) and the battery assembled from it are basically equivalent in performance to the positive electrode sheet prepared by wet method using O-CNT as a conductive agent (Comparative Example 4) and the battery assembled from it. That is, the dry method of electrode preparation can achieve the same effect as the wet method of O-CNT electrode preparation. However, the dry method saves the solvent drying and recovery process, reducing equipment investment and production costs by about 25%, showing a significant cost advantage. Meanwhile, comparing the data from Comparative Example 4 and Comparative Example 5, it can be seen that since CNTs do not have a problem of uneven dispersion in the wet method of electrode preparation, even ozone oxidation treatment of CNTs does not significantly improve their dispersion in the wet preparation process; on the contrary, the conductivity of CNTs may even slightly decrease due to ozone oxidation treatment. CNTs commonly exhibit uneven dispersion in dry electrode fabrication. Ozone oxidation significantly improves their dispersibility during dry electrode fabrication, resulting in positive electrode sheets prepared by dry methods that achieve performance comparable to those prepared by wet methods. Furthermore, since dry electrode fabrication eliminates the need for solvent drying and recovery, it offers advantages over wet methods in terms of cost and overall product performance.

[0137] Comparing Examples 1, 6, 7, and 8 with Comparative Example 4, it is evident that adding a small amount of conductive polymer can further reduce the resistance of the dry electrode and improve cycle performance, achieving the same performance as the conventional wet process. However, increasing the amount of conductive polymer added, while still reducing resistance, may affect the PTFE fiberization effect and negatively impact cycle performance.

[0138] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode film layer disposed on the surface of the current collector; Based on the total mass of the positive electrode film layer as 100%, the positive electrode film layer comprises the following raw materials in the following mass fractions: 96-98% positive electrode active material, 1-2% binder and 1-2% conductive agent; The conductive agent includes carbon nanotubes that have undergone ozone oxidation treatment.

2. The positive electrode sheet according to claim 1, characterized in that, The surface of the ozone-oxidized carbon nanotubes contains carboxyl groups and / or hydroxyl groups; And / or, the percentage of oxygen atoms on the surface of the ozone-oxidized carbon nanotubes is 6-8 At%.

3. The positive electrode sheet according to claim 1, characterized in that, The conductive agent also includes at least one of carbon black, graphene, or carbon fiber.

4. The positive electrode sheet according to claim 1, characterized in that, The adhesive includes polytetrafluoroethylene.

5. The positive electrode sheet according to claim 4, characterized in that, The adhesive further includes a conductive polymer, which includes one or more of polyaniline, polypyrrole, and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The positive electrode active material includes one or more of nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, or lithium manganese iron phosphate.

7. The method for preparing the positive electrode sheet according to any one of claims 1-6, characterized in that, Includes the following steps: (a) The positive electrode active material and the conductive agent are initially mixed to obtain a mixture; the conductive agent includes carbon nanotubes treated with ozone oxidation. (b) The binder is mixed with the mixture, and then sheared and stirred at high speed to obtain the positive electrode powder; (c) The positive electrode powder is rolled to obtain a positive electrode film; (d) The positive electrode film is rolled onto the current collector and hot rolled to obtain the positive electrode sheet.

8. The method for preparing the positive electrode sheet according to claim 7, characterized in that, In step (a), the initial mixing speed is 2000-3000 rpm, and the initial mixing time is 10-30 s; And / or, in step (b), the mixing speed is 500-3000 rpm and the mixing time is 1-2 min; And / or, in step (b), the shearing and stirring speed is 2000-3000 rpm and the time is 1-3 min.

9. The method for preparing the positive electrode sheet according to claim 7, characterized in that, In step (c), the thickness of the positive electrode film is 50-60 μm; And / or, in step (d), the temperature of the hot roller press is 100-160°C; And / or, in step (d), the thickness of the positive electrode sheet is 60-80 μm.

10. A lithium-ion battery, characterized in that, This includes the positive electrode sheet as described in any one of claims 1-6 or the positive electrode sheet prepared by the preparation method described in claims 7-9.

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