Positive electrode composite material suitable for dry process, positive electrode plate, preparation method of positive electrode plate and lithium ion battery

Abstract

The embodiment of the invention provides a positive electrode composite material suitable for a dry process, a positive electrode plate, a preparation method and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The positive electrode composite material comprises the following components in percentage by mass: 90-97% of a positive electrode active material; 1% to 5% of a conductive agent; and 0.5% to 5% of a binder; wherein the positive electrode active material comprises spherical lithium iron phosphate; or the positive electrode active material comprises non-spherical lithium iron phosphate and a flow promoter, and the flow promoter comprises at least one of graphite, a carbon nanotube, a spherical ternary material, a spherical oxide and a spherical metal. According to the composite material disclosed by the embodiment of the invention, the positive electrode active material comprises the spherical lithium iron phosphate or the flow promoter, so that the flowability of the positive electrode active material is improved, and the composite material disclosed by the invention has a relatively good film forming effect.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a positive electrode composite material suitable for a dry process, a positive electrode sheet and a preparation method, and a lithium-ion battery. Background Art

[0002] Compared with wet electrodes, dry electrodes have simpler processes and higher flexibility, and are an environmentally friendly green process. However, it is still difficult to apply dry processes to positive electrodes. First, due to the characteristics of the positive electrode active material itself, there are problems such as difficulty in film formation, low strength, and poor consistency.

[0003] Olivine-type lithium iron phosphate has always attracted great attention as a positive electrode active material for lithium-ion batteries with good safety, low price and environmental friendliness. However, the lithium iron phosphate currently used as a positive electrode active material for lithium-ion batteries has the problem of being unable to form a film. In view of the problem that positive electrode composite materials including lithium iron phosphate or mainly lithium iron phosphate cannot form a film, relevant research has been conducted in the relevant technology. For example, CN114824280A and CN116190665A both prepared positive electrode composite materials including core layer components and shell layer components, but this method cannot achieve mass production, and there are problems such as unsatisfactory film strength and high cost. Summary of the invention

[0004] In view of this, the present application provides a positive electrode composite material, a positive electrode plate and a preparation method, and a lithium-ion battery suitable for a dry process, aiming to provide a positive electrode composite material with low cost and suitable for a dry process.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode composite material suitable for a dry process, and the composite material comprises, calculated by mass ratio:

[0006] Positive electrode active material 90% to 97%;

[0007] Conductive agent 1% to 5%; and

[0008] Binder 0.5% to 5%;

[0009] The positive electrode active material includes spherical lithium iron phosphate; or, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the flow aid includes at least one of graphite, carbon nanotubes, spherical ternary materials, spherical oxides, and spherical metals.

[0010] In some embodiments of the present application, the mass ratio of the flow aid to the positive electrode active material is 5% to 80%; and / or

[0011] The positive electrode active material includes spherical lithium iron phosphate, and the mass ratio of the spherical lithium iron phosphate to the positive electrode active material is 5% to 100%; and / or

[0012] The non-spherical lithium iron phosphate includes flaky lithium iron phosphate; and / or

[0013] The positive electrode active material includes the spherical lithium iron phosphate and the non-spherical lithium iron phosphate.

[0014] In some embodiments of the present application, the spherical ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; and / or

[0015] At least one of the spherical oxides silicon dioxide and aluminum oxide; and / or

[0016] The spherical metal includes at least one of lithium, nickel and cobalt; and / or

[0017] The conductive agent comprises at least one of carbon black, graphite, conductive polymer, and carbon nanotube; and / or

[0018] The binder is at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyethylene glycol and polysiloxane; and / or

[0019] The positive electrode active material comprises non-spherical lithium iron phosphate and a flow aid, wherein the mass ratio of the flow aid to the positive electrode active material is 5% to 25%; and / or

[0020] The mass ratio of the spherical lithium iron phosphate to the positive electrode active material is 20% to 95%.

[0021] The second aspect of the present application provides a dry method for preparing a positive electrode sheet, comprising the following steps:

[0022] Mixing a positive electrode active material, a conductive agent and a binder in a preset ratio to obtain a composite material;

[0023] The composite material is subjected to a fiberizing treatment to obtain a composite membrane;

[0024] Compounding the composite film with a current collector to obtain a positive electrode sheet;

[0025] The positive electrode active material includes spherical lithium iron phosphate; or, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the flow aid includes at least one of graphite, carbon nanotubes, spherical ternary materials, spherical oxides, and spherical metals.

[0026] In some embodiments of the present application, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid; the step of mixing the positive electrode active material, the conductive agent and the binder in a preset ratio includes:

[0027] The non-spherical lithium iron phosphate and the flow aid are mixed by a first process to obtain a first mixture;

[0028] Mixing the first mixture with the conductive agent through a second process to obtain a second mixture;

[0029] Mixing the second mixture with the binder through a third process to obtain the composite material;

[0030] Wherein, the mass ratio of the flow aid to the positive electrode active material is 5% to 80%.

[0031] In some embodiments of the present application, the first process includes a first stirring, and the rotation speed of the first stirring is 300 rpm to 600 rpm; and / or

[0032] The second process includes second stirring, and the rotation speed of the second stirring is 100 rpm to 1000 rpm.

[0033] In some embodiments of the present application, the step of fiberizing the composite material comprises:

[0034] The composite material is subjected to fiberization treatment by means of an airflow mixing high-speed mixer.

[0035] In some embodiments of the present application, the composite material comprises, by mass: 90% to 97% of positive electrode active material; 1% to 5% of conductive agent; and 0.5% to 5% of binder; and / or

[0036] The ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; and / or

[0037] The spherical oxide comprises at least one of spherical silicon dioxide and spherical aluminum oxide; and / or

[0038] The spherical metal includes at least one of spherical lithium, spherical nickel, and spherical cobalt.

[0039] A third aspect of the present application provides a positive electrode plate, which includes the positive electrode composite material and the positive electrode plate prepared by the above preparation method.

[0040] A fourth aspect of the present application provides a lithium-ion battery, comprising a positive electrode plate.

[0041] Beneficial effects:

[0042] In the composite material of the embodiment of the present application, since the positive electrode active material includes spherical lithium iron phosphate or a flow aid, the fluidity of the positive electrode active material is increased, thereby making the composite material in the present application have a better film-forming effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is a photo of the composite material in Comparative Example 1 after the film forming process;

[0045] Figure 2 This is a photo of the composite material in Example 1 after the film forming process;

[0046] Figure 3 is a graph showing the tensile strength test results of the dry electrode prepared in the embodiment of the present application;

[0047] Figure 4 This is a liquid absorption test result diagram of the dry electrode prepared in the embodiment of the present application;

[0048] Figure 5 is a resistance test result diagram of the dry electrode prepared in the embodiment of the present application;

[0049] Figure 6 It is a graph showing the cycle performance test results of the battery cell prepared in the embodiment of the present application. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0052] In this application, unless otherwise stated, directional words such as "upper" and "lower" generally refer to the upper and lower parts of the device in actual use or working state, specifically the drawing direction in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. In addition, in the description of this application, the term "including" means "including but not limited to". The terms first, second, third, etc. are used only as labels and do not impose numerical requirements or establish an order.

[0053] In this application, "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0054] In the present application, "at least one" means one or more, and "plurality" means two or more. "One or more", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0055] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0056] With the rapid development of modern society, economy and technology, the performance of traditional lithium-ion batteries can no longer meet the current energy needs. The rapidly developing electric vehicles, intelligent consumer electronic devices and other fields are in urgent need of lithium-ion batteries with higher energy density, long cycle life, low cost and high safety. In terms of positive and negative electrodes, the requirements for material performance are getting higher and higher, and higher requirements are also put forward for the preparation process of positive and negative electrode sheets.

[0057] The traditional production of batteries involves many steps, including mixing, stirring, coating, drying, compacting, rolling, slicing, laminating, vacuum drying, packaging, electrolyte filling, aging, etc. There are many steps and high energy consumption. At present, the dry electrode process has a short process, eliminating the slurry preparation, coating, drying and solvent recovery processes, and the equipment is highly integrated, the plant land is intensive, and the production material input is small, which plays a vital role in reducing the cost of battery cells in terms of site, equipment, energy, raw materials, etc.

[0058] Olivine-type lithium iron phosphate has always attracted great attention as a lithium-ion battery cathode active material with good safety, low price and environmental friendliness. However, the lithium iron phosphate currently used as a lithium-ion battery cathode active material is generally non-spherical (e.g., flaky lithium iron phosphate), which has the problem of being unable to form a film or having an unsatisfactory film strength.

[0059] In view of this, the first aspect of the embodiment of the present application provides a positive electrode composite material suitable for a dry process, and the positive electrode composite material comprises, calculated by mass ratio:

[0060] Positive electrode active material 90% to 97%;

[0061] Conductive agent 1% to 5%; and

[0062] Binder 0.5% to 5%;

[0063] The positive electrode active material includes spherical lithium iron phosphate; or, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the flow aid includes at least one of graphite, carbon nanotubes, spherical ternary materials, spherical oxides, and spherical metals.

[0064] In the composite material of the embodiment of the present application, since the positive electrode active material includes spherical lithium iron phosphate or a flow aid, the fluidity of the positive electrode active material is increased, so that the composite material in the present application has a better film-forming effect and can be suitable for preparing electrodes by dry process.

[0065] In some embodiments of the present application, the main component of the positive electrode active material is lithium iron phosphate, wherein the lithium iron phosphate can be spherical lithium iron phosphate and / or non-spherical lithium iron phosphate.

[0066] Specifically, the positive electrode active material may include only spherical lithium iron phosphate, that is, the mass ratio of spherical lithium iron phosphate to the positive electrode active material is 100%. In this embodiment, the positive electrode active material includes spherical lithium iron phosphate. Since spherical lithium iron phosphate has better fluidity than flaky lithium iron phosphate, the composite material in this application has a better film-forming effect. It should be noted that the preparation of spherical lithium iron phosphate does not belong to the main improvement point of this application and is not limited here. For example, non-spherical lithium iron phosphate can be obtained into spherical lithium iron phosphate by a coating treatment process.

[0067] In some embodiments of the present application, the positive electrode active material may include spherical lithium iron phosphate and non-spherical lithium iron phosphate (eg, flaky lithium iron phosphate), and the mass ratio of the spherical lithium iron phosphate to the positive electrode active material is 5% to 80%.

[0068] Exemplarily, the positive electrode active material includes spherical lithium iron phosphate and flaky lithium iron phosphate. Further, the positive electrode active material is composed of spherical lithium iron phosphate and flaky lithium iron phosphate, and the mass ratio of spherical lithium iron phosphate to the positive electrode active material is 5% to 80%, that is, the ratio of spherical lithium iron phosphate to the sum of the mass of spherical lithium iron phosphate and flaky lithium iron phosphate is 5% to 80%. In this embodiment, due to the low cost of raw materials of lithium iron phosphate, a certain proportion of spherical lithium iron phosphate and flaky lithium iron phosphate are compounded to improve the fluidity of the positive electrode active material, so that the positive electrode active material in the embodiment of the present application can be used for the preparation of electrodes by dry process, thereby solving the problem that non-spherical lithium iron phosphate cannot be used for the preparation of electrodes by dry process, which is conducive to reducing the preparation cost of the electrode. At the same time, compounding spherical lithium iron phosphate and flaky lithium iron phosphate is conducive to improving the tensile strength of the prepared electrode membrane.

[0069] Exemplarily, the mass ratio of the spherical lithium iron phosphate to the positive electrode active material is approximately 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% and any value between the foregoing two points.

[0070] In some embodiments of the present application, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the mass ratio of the flow aid to the positive electrode active material is 5% to 80%. Exemplarily, the mass ratio of the non-spherical lithium iron phosphate to the positive electrode active material is about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% and any value between the above two points.

[0071] In some embodiments of the present application, the mass ratio of the flow aid to the positive electrode active material is 5% to 80%. Further, the mass ratio of the flow aid to the positive electrode active material is 5% to 20%. It can be understood that in this embodiment, the positive electrode active material is obtained by compounding non-spherical lithium iron phosphate and a flow aid, and the mass ratio of the flow aid to the positive electrode active material is 5% to 20%, thereby improving the fluidity of the non-spherical lithium iron phosphate, so that the non-spherical lithium iron phosphate main material in the embodiment of the present application can be used for the preparation of electrodes by dry process, which is conducive to further reducing the preparation cost of the electrode. It should be noted that the lithium iron phosphate currently used in lithium-ion batteries is generally flaky (i.e., flaky lithium iron phosphate) or columnar (i.e., columnar lithium iron phosphate). It is difficult to form a film of flaky nano-level lithium iron phosphate or columnar nano-level lithium iron phosphate, and the equipment requirements are high (the equipment procurement cost is high), which is not suitable for the preparation of electrodes by dry process. In the embodiment of the present application, a certain amount of flow aid and / or spherical lithium iron phosphate is added to non-spherical lithium iron phosphate (such as flake lithium iron phosphate, columnar lithium iron phosphate, etc.) to improve the fluidity of the positive electrode active material, so that the positive electrode active material in the embodiment of the present application can be used for preparing electrodes by a dry process, which is beneficial to reducing the preparation cost of the electrode.

[0072] Of course, in some embodiments of the present application, the positive electrode active material may also include spherical lithium iron phosphate and a flow aid. As another example, the positive electrode active material may also include non-spherical lithium iron phosphate (e.g., flaky lithium iron phosphate), spherical lithium iron phosphate, and a flow aid, wherein the sum of the mass of the spherical lithium iron phosphate and the flow aid to the mass ratio of the positive electrode active material is 5% to 80%.

[0073] In some embodiments of the present application, the graphite in the positive electrode active material includes at least one of natural flake graphite, artificial graphite, and expanded graphite.

[0074] In some embodiments of the present application, the ternary material includes at least one of lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide. The composite material in this embodiment can be applied to prepare electrodes by dry process and is beneficial to improve the tensile strength of the membrane.

[0075] In some embodiments of the present application, the spherical oxide includes at least one of spherical silicon dioxide (SiO2) and spherical aluminum oxide (Al2O3).

[0076] In some embodiments of the present application, the spherical metal includes at least one of spherical lithium (Li), spherical nickel (Ni), and spherical cobalt (Co).

[0077] In some embodiments of the present application, the conductive agent includes at least one of carbon black, conductive graphite, and conductive polymer. It should be noted that the selection of a specific type of conductive agent in this embodiment is beneficial to increasing the conductivity and uniformity of the composite material and further improving fluidity.

[0078] Specifically, the carbon black (SP) includes at least one of carbon fiber (VGCF) and carbon nanotube (CNT).

[0079] Specifically, the conductive graphite includes at least one of KS-6, KS-15, SFG-6, and SFG-15. Specifically, the conductive polymer includes polyaniline.

[0080] It should be noted that the inventors have found that in this embodiment, the liquid absorption of the positive electrode composite material can be improved by adding the above-mentioned specific conductive agent and flow aid to the positive electrode composite material.

[0081] In some embodiments of the present application, the binder includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), and polysiloxane.

[0082] In this embodiment, by selecting a conductive agent and a binder that are compatible with lithium iron phosphate, it is beneficial to improve the lubricity of lithium iron phosphate and improve the liquid absorption of the dry electrode.

[0083] In some embodiments of the present application, the binder includes polytetrafluoroethylene (PTFE), and at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), and polysiloxane. This embodiment reduces the PTFE content by compounding the binder, and the compounded binder can also increase the adhesion between the main material particles, thereby increasing the strength of the pole piece.

[0084] The second aspect of the present application provides a method for preparing a positive electrode sheet by a dry process, comprising the following steps:

[0085] S10: Mixing the positive electrode active material, the conductive agent and the binder in a preset ratio to obtain a composite material.

[0086] S20: performing fiberization treatment on the composite material to obtain a composite membrane.

[0087] S30: Compounding the composite film with a current collector to obtain a positive electrode sheet.

[0088] The positive electrode active material includes spherical lithium iron phosphate; or, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the flow aid includes at least one of graphite, spherical ternary materials, spherical oxides, and spherical metals.

[0089] In the embodiment of the present application, spherical lithium iron phosphate and / or a flow aid are added to the positive electrode active material, thereby increasing the fluidity of the positive electrode active material, thereby making the positive electrode composite material in the present application have a better film-forming effect and can be suitable for preparing positive electrode sheets by a dry process.

[0090] In some embodiments of the present application, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid; the step of mixing the positive electrode active material, the conductive agent and the binder in a preset ratio includes:

[0091] S11: Mixing the non-spherical lithium iron phosphate and the flow aid in a preset ratio through a first process to obtain a first mixture, wherein the mass ratio of the flow aid to the positive electrode active material is 5% to 80%.

[0092] Specifically, a flow aid and non-spherical lithium iron phosphate are added to a mixing device, and mixed by a first process to obtain a uniformly mixed first mixture. Exemplarily, the first process includes a first stirring, and the rotation speed of the first stirring is 300 rpm to 600 rpm. In this embodiment, the stirring speed of the first stirring is relatively low, which is conducive to improving the dispersion effect of the flow aid and non-spherical lithium iron phosphate.

[0093] Specifically, the mass ratio of the flow aid to the positive electrode active material is approximately 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% and any value between the foregoing two points.

[0094] S12: Mixing the first mixture with the conductive agent through a second process to obtain a second mixture.

[0095] Specifically, a conductive agent of a preset mass is added to the first mixture, and mixed by a second process to obtain a uniformly mixed second mixture. Exemplarily, the second process includes a second stirring. For example, the second stirring includes high-speed stirring and low-speed stirring, and the second stirring time is 30 minutes. Among them, the stirring speed of the high-speed stirring is 900rpm to 1000rpm, and the high-speed stirring time is 15 minutes. The stirring speed of the low-speed stirring is 300rpm to 600rpm, and the stirring time of the low-speed stirring is 15 minutes.

[0096] S13: mixing the second mixture with the binder through a third process to obtain the composite material.

[0097] Specifically, a preset mass of binder is added to the mixed powder of lithium iron phosphate and conductive agent, and mixed by a third process to obtain a uniformly mixed composite material. Exemplarily, the third process includes a third stirring. For example, the stirring speed of the third stirring is 300 rpm to 600 rpm, and the stirring time is 10 minutes.

[0098] In some embodiments of the present application, step S20 includes: fiberizing the composite material by a high-speed shearing machine.

[0099] It should be noted that the positive electrode composite material in the present application forms a self-supporting film after step S20. The self-supporting film in the present application refers to a film that can be picked up independently without relying on a substrate (such as a foil) and will not break.

[0100] In some embodiments of the present application, step S30 includes: compounding the composite film prepared in step S20 on two opposite surfaces of the current collector.

[0101] Specifically, the self-supporting film is composited with the current collector by a double-roll device. For example, the current collector is a foil material, and the self-supporting film and the foil material are composited under the conditions of a roller temperature of 120° C. and a pressure of 10 t (ton).

[0102] In some embodiments of the present application, the composite material includes: 90% to 97% of positive electrode active material; 1% to 5% of conductive agent; and 0.5% to 5% of binder.

[0103] In some embodiments of the present application, the ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0104] In some embodiments of the present application, the spherical oxide includes at least one of spherical silicon dioxide (SiO2) and spherical aluminum oxide (Al2O3).

[0105] In some embodiments of the present application, the spherical metal includes at least one of spherical lithium (Li), spherical nickel (Ni), and spherical cobalt (Co).

[0106] In some embodiments of the present application, the conductive agent includes at least one of carbon black, graphite, and a conductive polymer.

[0107] Specifically, the carbon black includes at least one of SP, VGCF, and CNT.

[0108] Specifically, the graphite includes at least one of KS-6, KS-15, SFG-6, and SFG-15.

[0109] Specifically, the conductive polymer includes polyaniline.

[0110] In some embodiments of the present application, the binder is at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyethylene glycol, and polysiloxane.

[0111] A third aspect of the present application provides a positive electrode plate, which includes the positive electrode composite material or is prepared by the above-mentioned preparation method.

[0112] Specifically, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on the surface of the positive electrode current collector. The positive electrode active layer includes the positive electrode composite material mentioned above.

[0113] A fourth aspect of the present application provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode plate.

[0114] Example 1

[0115] According to the preset ratio, a mixture of LFP (flaky lithium iron phosphate) and spherical LFP (spherical lithium iron phosphate) is stirred and dispersed by a mixing device to obtain a first mixture. The stirring speed is 600rpm and the stirring time is 20min. Then add a conductive agent (SP) to the first mixture, first rotate at a high speed of 1000rpm for 15min, and then rotate at a low speed of 300rpm for 15min to obtain a second mixture. Then add polytetrafluoroethylene (PTFE) to the second mixture, stir at a speed of 600rpm, stir and mix for 15min to obtain a third mixture. Calculated by mass ratio, in the third mixture, LFP: spherical LFP: SP: PTFE = 75:20:2:3.

[0116] 500g of the third mixed material was taken and sheared at high speed by a high-speed shearing machine for 3 minutes, and then formed into a self-supporting film at 100°C. The self-supporting film and the foil were then composited by a double-roll device at a roller temperature of 120°C and a pressure of 10t to obtain a dry electrode (i.e., a positive electrode sheet).

[0117] Example 2

[0118] According to the preset ratio, the mixture of LFP (lithium iron phosphate flakes) and NCM811 is stirred and dispersed by a mixing device to obtain the first mixture. The stirring speed is 600rpm and the stirring time is 20min. Then add the conductive agent (SP) to the first mixture, first rotate at a high speed of 1000rpm for 15min, and then rotate at a low speed of 300rpm for 15min to obtain the second mixture. Then add polytetrafluoroethylene (PTFE) to the second mixture, stir at a speed of 600rpm, stir and mix for 15min to obtain the third mixture. Calculated by mass ratio, in the third mixture, LFP:NCM811:SP:PTFE=75:20:2:3.

[0119] 500g of the third mixed material was taken and sheared at high speed by a high-speed shearing machine for 3 minutes, and then formed into a self-supporting film at 100°C. The self-supporting film was then composited with the foil material by a double-roll device at a roller temperature of 120°C and a pressure of 10t to obtain a dry electrode.

[0120] Example 3

[0121] According to the preset ratio, the mixture of LFP (lithium iron phosphate) and CNT is stirred and dispersed by a mixing device to obtain a first mixture. The stirring speed is 600rpm and the stirring time is 20min. Then add a conductive agent (SP) to the first mixture, first rotate at a high speed of 1000rpm for 15min, and then rotate at a low speed of 300rpm for 15min to obtain a second mixture. Then add polytetrafluoroethylene (PTFE) to the second mixture, stir at a speed of 600rpm, stir and mix for 15min to obtain a third mixture. Calculated by mass ratio, in the third mixture, LFP:CNT:SP:PTFE=90:5:2:3.

[0122] 500g of the third mixed material was taken and sheared at high speed by a high-speed shearing machine for 3 minutes, and then formed into a self-supporting film at 100°C. The self-supporting film was then composited with the foil material by a double-roll device at a roller temperature of 120°C and a pressure of 10t to obtain a dry electrode.

[0123] Example 4

[0124] Take a certain amount of spherical LFP (spherical lithium iron phosphate) and stir and disperse it through a mixing device to obtain a first mixture. The stirring speed is 600rpm and the stirring time is 20min. Then add a conductive agent (SP) to the first mixture, first rotate at a high speed of 1000rpm for 15min, and then rotate at a low speed of 300rpm for 15min to obtain a second mixture. Then add polytetrafluoroethylene (PTFE) to the second mixture, stir at a speed of 600rpm, stir and mix for 15min to obtain a third mixture. Calculated by mass ratio, in the third mixture, spherical LFP: SP: PTFE = 95:2:3.

[0125] 500g of the third mixed material was taken and sheared at high speed by a high-speed shearing machine for 3 minutes, and then formed into a self-supporting film at 100°C. The self-supporting film was then composited with the foil material by a double-roll device at a roller temperature of 120°C and a pressure of 10t to obtain a dry electrode.

[0126] Comparative Example 1

[0127] Take a certain amount of LFP (lithium iron phosphate flakes) and stir and disperse it through a mixing device to obtain the first mixture. The stirring speed is 600rpm and the stirring time is 20min. Then add a conductive agent (SP) to the first mixture, first rotate at a high speed of 1000rpm for 15min, and then rotate at a low speed of 300rpm for 15min to obtain the second mixture. Then add polytetrafluoroethylene (PTFE) to the second mixture, stir at a speed of 600rpm, stir and mix for 15min to obtain the third mixture. Calculated by mass ratio, in the third mixture, LFP:SP:PTFE=95:2:3.

[0128] 500 g of the third mixed material was taken and high-speed sheared by a high-speed shearing machine for 3 minutes, and then formed into a film at 100° C., but no self-supporting film could be obtained.

[0129] Application Example 1 to Application Example 4

[0130] The battery cell to be tested is assembled from the negative electrode sheet (graphite negative electrode), the diaphragm (ceramic diaphragm), the electrolyte and the positive electrode sheet prepared in Examples 1 to 4.

[0131] Experimental testing

[0132] Liquid absorption test: After the membrane is composited with the current collector, the compaction density of the positive electrode membrane is 2.6g / cm 3 , use a dropper to drop 2μL of electrolyte at different positions of the positive electrode, and record the time it takes for the electrolyte to fully penetrate.

[0133] Tensile strength test of dry electrode membrane: After film formation, cut the membrane into 20mm*50mm pieces and test them with a universal tensile tester.

[0134] Membrane resistance test: After forming the membrane, use a two-probe tester to test the resistance of different locations on the membrane. The voltage is 0.402V

[0135] Cycle performance test: Preparation of soft-pack battery cells, the compaction density of the positive electrode film is 2.6g / cm 3 , the compaction density of the negative electrode film is 1.4g / cm 3 . Under 25℃ environment, the battery cell is cycled at 0.5C.

[0136] Table 1

[0137]

[0138] The compositions and proportions of the composite materials in Examples 1 to 4 and Comparative Example 1 are shown in Table 1. Figure 1 This is a real photo of the composite material in Comparative Example 1 after being processed by the film-forming process. It is impossible to prepare a self-supporting film, and LFP has the problem of difficulty in dry film formation or inability to form a film. Figure 2 The composite material in Example 1 is a real photo after being processed by the film forming process, which can obtain a self-supporting film. The composite materials in Examples 2 to 4 can also obtain a self-supporting film after the film forming process, and the positive electrode composite materials in the embodiments of the present application have a good film forming effect.

[0139] Figure 3 The tensile strength test results of the dry electrodes (i.e., positive electrode sheets) prepared in Examples 1 to 4 are as follows: Figure 4 It can be seen that the dry electrode prepared from the positive electrode composite material in the embodiment of the present application has higher mechanical properties. In addition, compared with the positive electrode active main material being all spherical LFP (Example 4), the positive electrode active main material using non-spherical LFP mixed with a flow aid or spherical LFP (Examples 1 to 3) is conducive to further improving the mechanical strength.

[0140] Figure 4 The liquid absorption test results of the dry electrodes prepared in Examples 1 to 4 show that the dry membrane blended with CNT and flaky LFP has better liquid absorption, and the positive electrode composite material in the examples of the present application has a higher liquid absorption.

[0141] Figure 5 The resistance test results of the dry electrodes prepared in Examples 1 to 4 show that the resistance of the membrane mixed with CNT and flaky LFP is lower, and the dry electrodes prepared from the positive electrode composite materials in the examples of the present application have lower resistance.

[0142] Figure 6 The cycle performance test results of the batteries prepared in Application Example 1 to Application Example 4 show that the capacity retention rate of the battery cell mixed with CNT is slightly higher, and the overall difference is not large. The batteries prepared in the examples of the present application have good cycle performance.

[0143] The technical solutions provided by the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A positive electrode composite material suitable for a dry process, characterized in that: Calculated by mass ratio, the composite material comprises: Positive electrode active material 90% to 97%; Conductive agent 1% to 5%; and Binder 0.5% to 5%; The positive electrode active material includes spherical lithium iron phosphate; or, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the flow aid includes at least one of graphite, carbon nanotubes, spherical ternary materials, spherical oxides, and spherical metals.

2. The positive electrode composite material according to claim 1, characterized in that The mass ratio of the flow aid to the positive electrode active material is 5% to 80%; and / or The positive electrode active material includes spherical lithium iron phosphate, and the mass ratio of the spherical lithium iron phosphate to the positive electrode active material is 5% to 100%; and / or The non-spherical lithium iron phosphate includes flaky lithium iron phosphate; and / or The positive electrode active material includes the spherical lithium iron phosphate and the non-spherical lithium iron phosphate.

3. The positive electrode composite material according to claim 1 or 2, characterized in that: The spherical ternary material comprises at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; and / or The spherical oxide comprises at least one of spherical silicon dioxide and spherical aluminum oxide; and / or The spherical metal includes at least one of spherical lithium, spherical nickel, and spherical cobalt; and / or The positive electrode active material comprises non-spherical lithium iron phosphate and a flow aid, wherein the mass ratio of the flow aid to the positive electrode active material is 5% to 25%; and / or The mass ratio of the spherical lithium iron phosphate to the positive electrode active material is 20% to 95%; and / or The conductive agent comprises at least one of carbon black, graphite, and a conductive polymer; and / or The binder is at least one of polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, polyethylene glycol and polysiloxane.

4. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the positive electrode composite material according to any one of claims 1 to 3.

5. A dry method for preparing a positive electrode sheet, characterized in that: The following steps are involved: Mixing a positive electrode active material, a conductive agent and a binder in a preset ratio to obtain a composite material; The composite material is subjected to a fiberizing treatment to obtain a composite membrane; Compounding the composite film with a current collector to obtain a positive electrode sheet; The positive electrode active material includes spherical lithium iron phosphate; or, the positive electrode active material includes non-spherical lithium iron phosphate and a flow aid, and the flow aid includes at least one of graphite, carbon nanotubes, spherical ternary materials, spherical oxides, and spherical metals.

6. The preparation method according to claim 5, characterized in that: The positive electrode active material comprises non-spherical lithium iron phosphate and a flow aid; the step of mixing the positive electrode active material, the conductive agent and the binder in a preset ratio comprises: The non-spherical lithium iron phosphate and the flow aid are mixed by a first process to obtain a first mixture; Mixing the first mixture with the conductive agent through a second process to obtain a second mixture; Mixing the second mixture with the binder through a third process to obtain the composite material; Wherein, the mass ratio of the flow aid to the positive electrode active material is 5% to 80%.

7. The preparation method according to claim 6, characterized in that: The first process includes first stirring, wherein the rotation speed of the first stirring is 300 rpm to 600 rpm; and / or The second process includes second stirring, and the rotation speed of the second stirring is 100 rpm to 1000 rpm.

8. The preparation method according to claim 5, characterized in that: The step of fiberizing the composite material comprises: The composite material is subjected to fiberization treatment by a high-speed shearing machine.

9. The preparation method according to claim 5 or 6, characterized in that: The composite material comprises, by mass: 90% to 97% of a positive electrode active material; 1% to 5% of a conductive agent; and 0.5% to 5% of a binder; and / or The ternary material includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide; and / or The spherical oxide comprises at least one of spherical silicon dioxide and spherical aluminum oxide; and / or The spherical metal includes at least one of spherical lithium, spherical nickel and spherical cobalt.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet according to claim 4 or the positive electrode sheet obtained by the preparation method according to any one of claims 5 to 9.

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