Positive plate, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a positive plate which comprises a positive current collector and a positive coating. Wherein the positive electrode current collector is treated through oxidation treatment equipment, so that the surface of the positive electrode current collector contains polar oxygen-containing functional groups, and the polar oxygen-containing functional groups comprise one or more of hydroxyl, carboxyl and carbonyl; the positive electrode coating comprises a positive electrode coating material coated on the surface of at least one side of the positive electrode current collector, and the positive electrode coating material comprises a positive electrode active substance, a positive electrode conductive agent and a modified binder; wherein the modified binder is a positive electrode binder subjected to laser defluorination treatment. On the premise of ensuring the structural stability, high rate performance, long cycle life and excellent energy utilization efficiency of the lithium ion battery can be realized. The invention also discloses a preparation method of the positive plate and a lithium ion battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and in particular to a positive electrode sheet, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] At present, with the wide application of lithium ion batteries in new energy vehicles, energy storage systems and portable electronic devices, the requirements for fast charging performance, low temperature adaptability and cycle life of lithium ion batteries continue to increase. Among them, the conductive connectivity, interface adhesion and compaction density of the electrode material system will affect the positive electrode performance of the lithium ion battery.

[0003] The electrode material system at the present stage generally uses polyvinylidene difluoride (PVDF) as a binder. PVDF has excellent chemical stability, heat resistance and film-forming property. However, its electrical conductivity is low. Therefore, in order to improve the electrical conductivity, a large amount of conductive carbon black or graphene is added to the electrode in the related technology to ensure the efficiency of electron transmission.

[0004] In the process of implementing the embodiments of the present disclosure, it is found that at least the following problems exist in the related technology:

[0005] The above-mentioned method can ensure the efficiency of electron transmission, but will affect the energy density and rate performance of the electrode, and will also increase the preparation cost. In addition, when the aluminum foil current collector is combined with the positive electrode slurry, it generally relies on intermolecular forces, and the interface is prone to problems such as insufficient adhesion strength or increased contact resistance. Especially under the conditions of high-rate charging and discharging and long cycle, active material peeling, interface resistance increase and other situations are prone to occur, thereby affecting the high-power output and cycle life of the battery.

[0006] It should be noted that the information disclosed in the above background section is only used to strengthen the understanding of the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0007] In order to have a basic understanding of some aspects of the disclosed embodiments, the following is a simple summary. The summary is not a general review, nor is it intended to determine the key / important components or delineate the scope of protection of these embodiments, but as a prelude to the detailed description below.

[0008] The embodiments of the present disclosure provide a positive electrode sheet, a preparation method thereof and a lithium ion battery, which can realize high-rate performance, long cycle life and excellent energy utilization efficiency of the lithium ion battery under the premise of ensuring structural stability.

[0009] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating. The positive electrode current collector is treated by an oxidation treatment device to provide a surface of the positive electrode current collector with polar oxygen-containing functional groups, including one or more of hydroxyl groups, carboxyl groups, and carbonyl groups; the positive electrode coating includes a positive electrode coating material coated on at least one side of the positive electrode current collector, the positive electrode coating material including a positive electrode active material, a positive electrode conductive agent, and a modified binder; wherein the modified binder is a positive electrode binder that has been subjected to laser defluorination treatment.

[0010] Optionally, the binder is defluorinated by a KrF excimer laser with a UV wavelength of 248 nm and an energy density of 200 mJ·cm -2 ~400mJ·cm -2 .

[0011] Optionally, the mass fraction of the modified binder is 0.5% to 2.5% of the total mass fraction of the positive electrode coating, and the positive electrode binder includes polyvinylidene fluoride or carboxylated polyvinylidene fluoride.

[0012] Optionally, in the infrared spectrum of the modified binder, at 844 cm -1 、1080cm -1 、1180cm -1 and 1400cm -1 There are characteristic peaks at 844cm -1 The characteristic peak at 1080cm corresponds to the composite characteristics of CH out-of-plane vibration and CH2 vibration; -1 The characteristic peak at 1180 cm corresponds to the stretching vibration of the C-F bond; -1 The characteristic peak at 1400 cm corresponds to the stretching vibration of the CF2 group; -1 The characteristic peak corresponds to CH2 vibration.

[0013] Alternatively, as the laser intensity increases, 1180 cm -1 The intensity of the characteristic peak at gradually decreases.

[0014] Optionally, in the infrared spectrum of the positive electrode current collector, at 500 cm -1 ~900cm -1 Between 1700cm -1 ~1750cm -1 Between and 3200cm -1 ~3400cm -1 There are characteristic peaks between them;

[0015] Among them, 500cm -1 ~900cm -1 The characteristic peaks at 1700 cm correspond to Al–O bending and stretching vibrations.-1 ~ 1750 cm -1 characteristic peak corresponding to the stretching vibration of the carbonyl group, 3200 cm -1 ~ 3400 cm -1 characteristic peak corresponding to the stretching vibration of the hydroxyl group.

[0016] Optionally, the positive electrode active material includes lithium nickel cobalt manganese oxide (LiNi x Co y Mn z M b O2); wherein, 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1; the element M includes one or more of Zr, W, Ti, Al, Sr, B and Nd.

[0017] Optionally, the positive electrode conductive agent includes carbon black and / or carbon nanotubes.

[0018] Optionally, the interface resistance R of the positive electrode sheet ranges from 1.1×10 -2 Ω·cm 2 ~ 2.0×10 -2 Ω·cm 2 .

[0019] Optionally, the compaction density P of the positive electrode sheet ranges from 3.5 g / cm -3 ~ 4.0 g / cm -3 .

[0020] Optionally, the peeling strength N of the positive electrode sheet ranges from 9.5 N / m to 20.0 N / m.

[0021] In some embodiments, the method for preparing the positive electrode sheet includes the following steps:

[0022] Preparation of the positive electrode current collector: cleaning the positive electrode current collector, and then placing it in an oxidation treatment device to cause the surface oxidation of the negative electrode current collector to react to generate polar oxygen-containing functional groups;

[0023] Preparation of the positive electrode coating material: configuring the positive electrode active material, the positive electrode conductive agent, the modified binder and the solvent into a mixed solution according to a preset ratio; wherein, the binder with a preset thickness is scanned multiple times by a laser under the protection of a protective gas to obtain the modified binder after defluorination;

[0024] Preparation of the positive electrode sheet: coating the positive electrode coating material on at least one side surface of the positive electrode current collector, and then drying and cold pressing to obtain the positive electrode sheet.

[0025] In some embodiments, the lithium ion battery, including a negative electrode sheet and the negative electrode sheet as described in the foregoing embodiments, the negative electrode sheet includes a negative electrode current collector and is coated with at least one negative electrode coating layer; the negative electrode coating layer includes a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; wherein the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon; the negative electrode conductive agent includes one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; and the negative electrode binder includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and butadiene-styrene rubber.

[0026] Optionally, the lithium ion battery further includes:

[0027] an electrolyte including a lithium salt, a solvent and an additive;

[0028] the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium difluorophosphate and lithium bis-trifluoromethylsulfonylimide;

[0029] the solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and methyl ethyl carbonate;

[0030] the additive includes one or more of fluoroethylene carbonate, bis-fluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate and vinyl carbonate.

[0031] Optionally, the capacity retention rate Q of the lithium ion battery at 25°C is R > 75%.

[0032] Optionally, the capacity attenuation rate Q of the lithium ion battery at 25°C after 1000 cycles at a rate of 1C is R ≤ 20%.

[0033] Optionally, the capacity ratio of the negative electrode sheet to the positive electrode sheet is 1.02-1.2.

[0034] The positive electrode sheet and the preparation method thereof, and the lithium ion battery provided by the embodiments of the present disclosure can achieve the following technical effects:

[0035] The application can make the surface of the positive current collector contain polar oxygen-containing functional groups by treating the positive current collector through an oxidation treatment device, thereby significantly enhancing the interfacial adhesion between the active material, the binder and the current collector compared with the untreated negative current collector. On this basis, the modified binder is a positive electrode binder treated by laser defluorination, so that the laser defluorination can break part of the C-F bonds of the positive electrode binder and form a carbon-rich conductive layer, thereby improving the conductivity of the binder and reducing its crystallinity. Therefore, by optimizing the interfacial adhesion of the positive current collector and the conductivity of the positive electrode binder, the multi-dimensional regulation of the interface resistance, the compaction density and the peeling strength of the positive plate can be realized, thereby improving the rate performance, the cycle stability and the compaction energy density of the battery.

[0036] The foregoing general description and the following description are only exemplary and explanatory, and are not intended to limit the application. BRIEF DESCRIPTION OF DRAWINGS

[0037] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are schematic and are not intended to be limiting of the embodiments, in which like reference numerals refer to like elements in the various figures and in which:

[0038] Figure 1 is a flowchart of a preparation method of a negative plate provided by an embodiment of the present disclosure;

[0039] Figure 2 is a structural diagram of a lithium ion battery provided by an embodiment of the present disclosure;

[0040] Figure 3 is a structural diagram of a lithium ion battery provided by an embodiment of the present disclosure;

[0041] Figure 4 is a structural diagram of a lithium ion battery provided by an embodiment of the present disclosure;

[0042] Figure 5 is an expanded diagram of a lithium ion battery provided by an embodiment of the present disclosure.

[0043] LIST OF REFERENCE NUMERALS

[0044] 1 - positive terminal; 10 - battery cell; 11 - positive pole; 12 - negative terminal; 2 - shell; 3 - negative plate; 4 - separator; 5 - positive plate. DETAILED DESCRIPTION

[0045] In order to enable a more detailed understanding of the features and technical content of the embodiments of the present disclosure, the implementation of the embodiments of the present disclosure is described in detail below, and the accompanying drawings are used for reference only and do not limit the embodiments of the present disclosure. In the following technical description, in order to facilitate explanation, a plurality of details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be simplified to facilitate the drawings.

[0046] The terms "first", "second", and the like in the specification and claims of the embodiments of the present disclosure and the above drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present disclosure described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0047] In the embodiments of the present disclosure, the terms "upper", "lower", "inner", "middle", "outer", "front", "back", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the embodiments of the present disclosure and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation. In addition, in addition to indicating the orientation or positional relationship, the above-mentioned terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain attachment relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0048] In addition, the terms "set", "connected", "fixed" should be broadly understood. For example, "connected" can be fixedly connected, detachably connected, or integrally configured; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0049] Unless otherwise specified, the term "a plurality of" means two or more.

[0050] In the embodiments of the present disclosure, the character " / " represents an "or" relationship between the objects before and after it. For example, A / B represents: A or B.

[0051] The term "and / or" is a description of the association between objects, which means that there can be three relationships. For example, A and / or B, which means: A or B, or, A and B, the three relationships.

[0052] It should be noted that the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0053] The positive electrode sheet provided by the embodiments of the present disclosure includes a positive electrode current collector and a positive electrode coating. The positive electrode current collector is processed by an oxidation treatment device to make the surface of the positive electrode current collector contain polar oxygen-containing functional groups, including one or more of hydroxyl, carboxyl and carbonyl. The positive electrode coating includes a positive electrode coating material coated on at least one side surface of the positive electrode current collector, and the positive electrode coating material includes a positive electrode active material, a positive electrode conductive agent and a modified binder. The modified binder is a positive electrode binder processed by laser defluorination.

[0054] By processing the positive electrode current collector by the oxidation treatment device, the surface of the positive electrode current collector contains polar oxygen-containing functional groups, which significantly enhances the interfacial adhesion between the active material and the binder and the current collector. On this basis, the modified binder is a positive electrode binder processed by laser defluorination, which can break part of the C-F bonds of the positive electrode binder and form a carbon-rich conductive layer, thereby improving the conductivity of the binder and reducing its crystallinity. Therefore, by optimizing the interfacial adhesion of the positive electrode current collector and the conductivity of the positive electrode binder, the multi-dimensional regulation of the interfacial resistance, the compaction density and the peeling strength of the positive electrode sheet can be realized, thereby improving the rate performance, the cycle stability and the compaction energy density of the battery.

[0055] Optionally, the binder is defluorinated by a KrF excimer laser, the wavelength of the ultraviolet light is 248 nm, and the energy density is 200 mJ·cm -2 ~ 400 mJ·cm -2 .

[0056] Optionally, the mass fraction of the modified binder is 0.5% to 2.5% of the total mass fraction of the positive electrode coating, and the positive electrode binder includes polyvinylidene fluoride or carboxylated polyvinylidene fluoride.

[0057] In this embodiment, the defluorination of the binder by the KrF excimer laser means that the ultraviolet light of 248 nm wavelength of the KrF excimer laser can break part of the C-F bonds of the positive electrode binder. Here, the wavelength of the ultraviolet light of the KrF excimer laser can be calculated according to the energy and wavelength equation:

[0058] E(eV) = 1240 / λ

[0059] Wherein, λ is the wavelength of the ultraviolet light, and E is the energy of the photon.

[0060] That is, 1240 / 248 = 5.0 eV, while the C-F bond energy is close to 5.0 eV.

[0061] Therefore, part of the C-F bond is broken by the ultraviolet light of 248 nm wavelength, and carbonization occurs to form a carbon-rich conductive layer.

[0062] Optionally, in combination with Figure 2 As shown in the infrared spectrum of the modified binder, there are characteristic peaks at 844 cm -1 , 1080 cm -1 , 1180 cm -1 , and 1400 cm -1 ; wherein the characteristic peak at 844 cm -1 corresponds to the CH out-of-plane vibration and CH2 vibration composite characteristics; the characteristic peak at 1080 cm -1 corresponds to the stretching vibration of the C-F bond; the characteristic peak at 1180 cm -1 corresponds to the stretching vibration of the CF2 group; and the characteristic peak at 1400 cm -1 corresponds to the CH2 vibration.

[0063] Optionally, as the laser intensity increases, the characteristic peak intensity at 1180 cm -1 gradually decreases.

[0064] Optionally, in the infrared spectrum of the positive current collector, there are characteristic peaks between 500 cm -1 and 900 cm -1 , between 1700 cm -1 and 1750 cm -1 , and between 3200 cm -1 and 3400 cm -1 ; wherein the characteristic peak between 500 cm -1 and 900 cm -1 corresponds to the Al-O bending and stretching vibration, the characteristic peak between 1700 cm -1 and 1750 cm -1 corresponds to the carbonyl stretching vibration, and the characteristic peak between 3200 cm -1 and 3400 cm -1 corresponds to the stretching vibration of the hydroxyl group.

[0065] Optionally, the positive active material includes lithium nickel cobalt manganese oxide (LiNi x Co y Mn z M bO2); wherein, 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1; the element M includes one or more of Zr, W, Ti, Al, Sr, B and Nd.

[0066] Optionally, the positive electrode conductive agent includes carbon black and / or carbon nanotubes.

[0067] Optionally, the interface resistance R of the positive electrode sheet ranges from 1.1×10 -2 Ω·cm 2 ~2.0×10 -2 Ω·cm 2 .

[0068] Optionally, the compaction density P of the positive electrode sheet ranges from 3.5g / cm -3 ~4.0g / cm -3 .

[0069] Optionally, the peeling strength N of the positive electrode sheet ranges from 9.5N / m to 20.0N / m.

[0070] In combination with Figure 1 the drawings, the embodiments of the present disclosure also provide a preparation method of a positive electrode sheet, including the following steps:

[0071] Preparation of a negative electrode coating material:

[0072] S101, preparation of a positive electrode current collector: cleaning the positive electrode current collector, and then placing it in an oxidation treatment device to make the surface of the negative electrode current collector react to generate polar oxygen-containing functional groups.

[0073] In an embodiment, the positive electrode current collector can use an aluminum foil with a thickness of 15μm. The aluminum foil is sequentially cleaned by ultrasonic oil removal, deionized water and ethanol, and then dried with nitrogen. The treated and nitrogen-dried aluminum foil is placed in a UV / ozone treatment device for treatment for 5min; wherein the wavelength of the ultraviolet light is 254nm, the power is 100W, the ozone concentration is 30ppm, and the temperature is 25℃.

[0074] In this way, O2 in the air is converted into O3 by high-energy UV induction, and active oxygen atoms are formed by cracking. The active oxygen reacts with the surface of the aluminum foil to generate polar oxygen-containing functional groups such as hydroxyl (–OH) and carboxyl (–COOH).

[0075] S102, preparation of a positive electrode coating material: the positive electrode active material, the positive electrode conductive agent, the modified binder and the solvent are configured into a mixed solution according to a preset ratio; wherein the binder with a preset thickness is scanned multiple times by a laser under the protection of a protective gas to obtain a modified binder after defluorination.

[0076] In the embodiment, the positive electrode active material, the positive electrode conductive agent, the modified binder and the solvent are mixed uniformly in the N-methyl pyrrolidone solvent system according to a preset weight ratio of 96:2:2.

[0077] In the embodiment, the PVDF powder is laid on a high-temperature-resistant carrier with a laying thickness of 1 mm, and is irradiated by a KrF excimer laser under nitrogen protection at an energy density of 300 mJ·cm -2 The laser is scanned for 10 times to obtain the modified binder after defluorination, wherein the laser wavelength is 248 nm, the pulse width is 15 ns, and the laser frequency is 10 Hz.

[0078] S103, preparing a negative electrode sheet: coating the negative electrode coating material on at least one side surface of the negative electrode current collector, drying and cold-pressing to obtain the negative electrode sheet.

[0079] The lithium ion battery provided by the embodiment of the present disclosure comprises the negative electrode sheet and the negative electrode sheet in the foregoing embodiment, and the negative electrode sheet comprises a negative electrode current collector and at least one negative electrode coating; the negative electrode coating comprises a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; the negative electrode active material comprises one or more of artificial graphite, natural graphite, soft carbon and hard carbon; the negative electrode conductive agent comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; and the negative electrode binder comprises one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and butadiene-styrene rubber.

[0080] The specific structure of the positive electrode sheet refers to the above-mentioned embodiment, and since the lithium ion battery adopts all the technical solutions of all the above-mentioned embodiments, it at least has all the technical effects brought by the technical solutions of the above-mentioned embodiments, which will not be described here.

[0081] Optionally, the lithium ion battery further comprises an electrolyte comprising a lithium salt, a solvent and an additive.

[0082] The lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium difluoro oxalate borate and lithium bistrifluoromethylsulfonylimide.

[0083] The solvent comprises one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and methyl ethyl carbonate.

[0084] The additive comprises one or more of fluoroethylene carbonate, bisfluoroethylene carbonate, ethylene sulfate, ethylene sulfite, vinylene carbonate and vinyl carbonate.

[0085] Optionally, the discharge characteristics of the lithium-ion battery are as follows: after the lithium-ion battery with a 100% charge rate is left at 25°C for 6 hours, it is discharged to 2.5V at a rate of 0.1C, and the corresponding discharge capacity is Q1; the discharge capacity to 2.5V at a rate of 10C is Q2; wherein Q2 / Q1 is the capacity retention rate Q of the lithium-ion battery discharge. R , and the capacity retention rate Q of the lithium ion battery discharge R >75%.

[0086] Optionally, after a lithium-ion battery is cycled for 1000 cycles at a rate of 1C at 25°C, its capacity decay rate Q R ≤20%.

[0087] Optionally, the capacity ratio of the negative electrode sheet to the positive electrode sheet is 1.02 to 1.2.

[0088] In the embodiment of the present disclosure, the lithium-ion battery further includes a shell, and the positive electrode sheet and the negative electrode sheet are encapsulated in the shell. Figures 3 to 5 As shown, the lithium-ion battery specifically includes a cylindrical shell 2, the interior of which is used to accommodate the battery cell, wherein the top is the positive terminal 1, the bottom is the negative terminal 12, and the positive terminal 1 is provided with a positive column 11. Specifically, Figure 3 and Figure 4 shows a schematic structural diagram of the lithium-ion battery in this application, Figure 5 FIG1 shows a schematic diagram of the lithium-ion battery in the present application. Figure 5 As shown in the stacking, then winding to form Figure 3 The cylindrical battery cell 10 shown has the electrode end at the cylinder axis at the beginning of winding and at the outer surface of the cylinder at the end of winding. The positive electrode sheet 5 comprises a strip of positive electrode foil, a positive electrode coating applied to the surface of the positive electrode foil strip, and a first hollow foil region. The negative electrode sheet 3 comprises a strip of negative electrode foil, a negative electrode coating applied to the surface of the negative electrode foil strip, and a second hollow foil region. The first and second hollow foil regions are perpendicular to the winding direction and are formed by flattening or cutting and stacking to form the top and bottom end faces of the lithium-ion battery.

[0089] On this basis, an embodiment of the present disclosure provides a method for preparing a lithium-ion battery, comprising:

[0090] Preparation of positive electrode sheet: Mix the positive electrode coating materials, apply them on both sides of the aluminum foil, dry and cold press to obtain the positive electrode sheet;

[0091] Preparation of negative electrode sheet: Mix the negative electrode coating material, apply it on both sides of the copper foil, dry it and cold press it to obtain the negative electrode sheet;

[0092] Preparation of battery cells: The positive and negative electrode sheets are rolled and slit, and then wound together with the separator to obtain battery cells;

[0093] Assembling the lithium ion battery: welding the tab of the lithium ion battery with the electric connection sheet, loading into the battery shell, performing the electrolyte injection, sealing and formation process, to obtain the lithium ion battery.

[0094] In addition, the disclosure provides a power supply device, which comprises the lithium ion battery for providing power as described in the present application.

[0095] The present application is further explained and described in the following examples.

[0096] Example 1

[0097] The present example 1 provides a preparation method of a lithium ion battery as follows:

[0098] Preparation of the positive electrode sheet: selecting positive active material (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black, carbon nanotube and laser modified polyvinylidene fluoride (PVDF) and mixing them uniformly in N-methyl pyrrolidone solvent system at a mass ratio of 96:1:1:2, to form a stable positive electrode slurry; then the positive electrode slurry is coated on the 12μm thick aluminum foil treated by oxidation, and after drying, cold pressing, slitting and cutting, a positive electrode sheet with a compacted density of 3.62g / cm 3 is obtained. The D 50 of the positive active material NMC811 is 8.5μm; the parameters of the KrF excimer laser include: energy density of 300mJ·cm -2 , laser wavelength of 248nm, pulse width of 15ns, and laser frequency of 10Hz; the positive current collector is placed in the ultraviolet / ozone treatment device for 5min; the ultraviolet wavelength is 254nm, the power is 100W, the ozone concentration is 30ppm, and the temperature is 25℃.

[0099] Preparation of the negative electrode sheet: selecting graphite, carbon nanotube, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) and mixing them at a mass ratio of 96:1.5:1:1.5, and stirring in deionized water to form a stable negative electrode slurry with a solid content of 40%; then the negative electrode coating material is coated on both sides of the copper foil, and after drying and cold pressing, a negative electrode sheet with a compacted density of 1.5g / cm 3 is obtained.

[0100] Preparation of electrolyte: lithium salt lithium hexafluorophosphate (LiPF6), organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), first type of additive fluoroethylene carbonate (FEC), second additive ethylene sulfate (DTD) and third type of additive vinylene carbonate (VC); mixed in a ratio of 10:20:55:2:8:5 to obtain the electrolyte.

[0101] Preparation of separator: a high porosity separator is selected, the thickness of the base film polyethylene (PE) in the separator is 9 μm, the thickness of the ceramic coating on both sides of the base film is 1 μm, and the thickness of the polyvinylidene fluoride (PVDF) coating is 1 μm.

[0102] Assembling lithium ion battery: by rolling and slitting the positive and negative electrode sheets respectively, and then winding them together with the separator, a cylindrical battery roll core is obtained, then the battery roll core is welded with the electrical connection sheet, and then the battery is assembled into the shell. After completing the liquid injection, sealing and formation process, the lithium ion battery of the present embodiment is obtained, and the shell of the lithium ion battery is a cylinder with a size parameter of diameter: 46.0 mm, length 80.0 mm.

[0103] Example 2

[0104] Example 2 provides a kind of lithium ion battery, and the difference between the present embodiment and example 1 is that the energy density of KrF excimer laser is 200 mJ·cm -2 . The others are the same as example 1.

[0105] Example 3

[0106] Example 3 provides a kind of lithium ion battery, and the difference between the present embodiment and example 1 is that the energy density of KrF excimer laser is 250 mJ·cm -2 . The others are the same as example 1.

[0107] Example 4

[0108] Example 4 provides a kind of lithium ion battery, and the difference between the present embodiment and example 1 is that the energy density of KrF excimer laser is 350 mJ·cm -2 . The others are the same as example 1.

[0109] Example 5

[0110] Example 5 provides a kind of lithium ion battery, and the difference between the present embodiment and example 1 is that the energy density of KrF excimer laser is 400 mJ·cm -2 . The others are the same as example 1.

[0111] Example 6

[0112] Example 6 provides a lithium-ion battery. The difference between this example and Example 1 is that the laser frequency of the KrF excimer laser is 1.0 Hz. All other aspects are the same as Example 1.

[0113] Example 7

[0114] Example 7 provides a lithium-ion battery. The difference between this example and Example 1 is that the laser frequency of the KrF excimer laser is 5.0 Hz. All other aspects are the same as Example 1.

[0115] Example 8

[0116] Example 8 provides a lithium-ion battery. The difference between this example and Example 1 is that the laser frequency of the KrF excimer laser is 20.0 Hz. All other aspects are the same as Example 1.

[0117] Example 9

[0118] Example 9 provides a lithium-ion battery. The difference between this example and Example 1 is that the laser frequency of the KrF excimer laser is 40.0 Hz. All other aspects are the same as Example 1.

[0119] Example 10

[0120] Example 10 provides a lithium-ion battery. This example differs from Example 1 in that the positive electrode current collector is placed in a UV / ozone treatment device for 1 minute. All other aspects are the same as Example 1.

[0121] Example 11

[0122] Example 11 provides a lithium-ion battery. This example differs from Example 1 in that the positive electrode current collector is placed in a UV / ozone treatment device for 2 minutes. All other aspects are the same as Example 1.

[0123] Example 12

[0124] Example 12 provides a lithium-ion battery. This example differs from Example 1 in that the positive electrode current collector is placed in a UV / ozone treatment device for 10 minutes. All other steps are the same as in Example 1.

[0125] Example 13

[0126] Example 13 provides a lithium-ion battery. This example differs from Example 1 in that the positive electrode current collector is placed in a UV / ozone treatment device for 15 minutes. All other steps are the same as in Example 1.

[0127] Example 14

[0128] Example 14 provides a lithium ion battery, this example is different from example 1 in that the mass fraction of laser modified polyvinylidene fluoride is 1%. The others are the same as example 1.

[0129] Example 15

[0130] Example 15 provides a lithium ion battery, this example is different from example 1 in that the mass fraction of laser modified polyvinylidene fluoride is 1.5%. The others are the same as example 1.

[0131] Example 16

[0132] Example 16 provides a lithium ion battery, this example is different from example 1 in that the mass fraction of laser modified polyvinylidene fluoride is 2.5%. The others are the same as example 1.

[0133] Example 17

[0134] Example 17 provides a lithium ion battery, this example is different from example 1 in that the D50 of the added positive electrode active material NMC811 is 2.5μm. The others are the same as example 1. 50

[0135] Example 18

[0136] Example 18 provides a lithium ion battery, this example is different from example 1 in that the D50 of the added positive electrode active material NMC811 is 15.8μm. The others are the same as example 1. 50

[0137] Comparative example 1

[0138] Comparative example 1 provides a lithium ion battery, this comparative example is different from example 1 in that the polyvinylidene fluoride is not laser modified, and the others are the same as example 1.

[0139] Comparative example 2

[0140] Comparative example 2 provides a lithium ion battery, this comparative example is different from example 1 in that the positive electrode current collector is not oxidized, and the others are the same as example 1.

[0141] The lithium ion batteries of example 1 to example 18, and comparative example 1 and comparative example 2 are tested correspondingly.

[0142] ​​Discharge the lithium-ion battery at a constant current to 2.5 V; here, ensure that the lithium-ion battery is in a safe state to reduce the risk of short circuit or thermal runaway during disassembly. Disassemble the battery in a glove box, and take out the positive plate of the cylindrical cell; wherein the glove box is a pure argon gas environment or other inert gas environment. Use tweezers or suitable tools to peel off the positive plate, avoiding damage to the active material layer.

[0143] Cut the removed positive plate to an appropriate size and soak it in a solution of anhydrous dimethyl carbonate (DMC) for 30 min; to dissolve and remove residual electrolyte and possible by-products. Take out the plate and wipe the surface of the plate with a dust-free wipe, then replace the anhydrous dimethyl carbonate (DMC) solution and repeat the soaking and wiping process three times; to ensure that the surface of the plate is free of residual contaminants.

[0144] Use anhydrous ethanol to rinse the plate and wipe it again to further remove solvents and impurities.

[0145] After completing the cleaning, place the positive plate in the glove box for 48 h to ensure that the plate is completely dry to prevent subsequent tests from being disturbed by solvent residues. After drying, use a plastic spatula or blade to scrape the positive active material, while ensuring that the collected powder is not contaminated. Transfer the scraped powder to a centrifuge tube containing anhydrous ethanol and ultrasonically disperse it in an ultrasonic cleaner for 30 min to further remove possible residual electrolyte, binder and impurities.

[0146] After ultrasonic treatment, centrifuge the sample at 5000 rpm for 2 min, remove the supernatant, and redisperse the powder with anhydrous ethanol, then ultrasonically disperse it in an ultrasonic cleaner for 10 min, followed by centrifugation again, repeating the process three times to ensure the purity of the powder sample.

[0147] Collect the precipitate and transfer it to a vacuum drying oven, dry at a temperature of 80°C for 12 h to ensure complete removal of residual solvents, and pack the dried powder into a sealed bag or sealed sample box, immediately remove it from the glove box, and quickly test the active material particle D 50 .

[0148] The present embodiment provides a test method for an active material particle D 50 , comprising the following steps:

[0149] Spread a small amount of sample powder evenly on the conductive tape;

[0150] Take clear particle images of at least 5 different areas under a scanning electron microscope (SEM), and import the particle images through ImageJ software or Nano Measure software;

[0151] After the calibration of the ruler, the projected diameters of more than 200 particles are measured manually or automatically, the data are arranged in ascending order and the cumulative distribution curve is plotted, and the particle size value corresponding to the cumulative percentage of 50% is taken as D50. 50 .

[0152] Among them, the interference data of obvious agglomerates need to be excluded to ensure accuracy.

[0153] The embodiment also provides a test method for the interfacial resistance of the positive electrode sheet. An RM2610 resistance test system is used to measure the film resistance of the negative electrode sheet. Among them, 45 probes of the resistance test system are arranged in a square matrix form, and one probe is used as a grounding probe.

[0154] The test method comprises the following steps:

[0155] The positive electrode sheet subjected to the dimethyl carbonate rinsing treatment and vacuum drying is divided into 40 square cells to ensure the flatness of the test sample surface;

[0156] The test sample is placed on the test device, and the pressure applied by the probes is adjusted using a pressure gauge to ensure good contact between the probes and the test sample, and the contact area is 0.01 cm 2 .

[0157] During the test, the 20 outer probes apply a constant current to make the current flow through the surface, interface and positive electrode current collector of the positive electrode sheet, and the 25 middle probes measure the voltage change in real time. Since the surface, interface and current collector of the electrode sheet have obviously different resistances, the measured voltage will reflect these differences. The film resistance R1 is calculated according to the Ohm's law and the fitting analysis method.

[0158] The same method is used to randomly select another 9 square cells on the above-mentioned electrode sheet for interfacial resistance measurement, and the obtained resistance values are respectively denoted as R2, R3, R4, R5, R6, R7, R8, R9, and R 10 The average film resistance R of the actually tested positive electrode sheet is obtained by calculating the average value of the above-mentioned resistance values, R = (R1+R2+R3+R4+R5+R6+R7+R8+R9+R 10 ) / 10. In order to comprehensively evaluate the conductive characteristics and uniformity of the positive electrode sheet.

[0159] The embodiment also provides a test method for the peeling force of the positive electrode sheet, comprising the following steps:

[0160] The positive electrode sheet subjected to the dimethyl carbonate rinsing treatment and vacuum drying is cut into 6 square samples of a standard size, and the length is 2 cm and the width is 2 cm;

[0161] Fix the test sample on a flat steel plate using double-sided tape, ensuring that the tape is applied to the center area of the steel plate;

[0162] Then remove the protective film of the double-sided tape, apply the test sample to the double-sided tape, and use a roller to evenly roll the test sample to ensure good adhesion;

[0163] Subsequently, tear off the unattached end, bend the torn test sample naturally upwards, and clamp it in the upper clamp of the tensile testing machine for a 180° peeling test at a stretching speed of 100 mm / min. Record the peeling force-displacement curve during the entire stretching process, select data at the stable stage where the force value fluctuates less than ±10%, and calculate the average value of the tensile force in this section;

[0164] Divide the average tensile force by the width of the pole piece to obtain the peeling strength per unit width, with units of Nm -1 To improve the reliability of the test, at least 3 tests should be performed on different sample positions, and the average value is taken as the final peeling strength.

[0165] The present embodiment also provides a method for testing the compaction density of a positive electrode sheet, comprising the following steps:

[0166] Cut the positive electrode sheet treated with dimethyl carbonate rinsing and vacuum dried into 6 square samples of standard size, with a length of 2 cm and a width of 2 cm;

[0167] Scrape off the active material on the front and back of 3 square samples, rinse with ethanol, then dry, weigh and calculate the average mass M1, and at the same time, use a screw micrometer to measure the average thickness L1 of the sample;

[0168] Weigh the mass of the other 3 square samples and calculate the average mass M2, and at the same time, use a screw micrometer to measure the average thickness L2 of the sample;

[0169] Calculate the compaction density of the pole piece by the formula

[0170] The present embodiment also provides a method for testing the rate capability of a lithium ion battery. The lithium ion battery is discharged to 2.5V and placed in a thermostat at a temperature of 25℃ for 4h, and the test is performed according to the following steps:

[0171] Under the condition of 0.1C charging rate, charge to 3.65V at constant current and constant voltage, with a cutoff current of 0.01C, and stand for 30min;

[0172] Under the condition of 0.1C discharging rate, discharge to 2.5V at constant current, with a capacity of Q1, and stand for 30min;

[0173] ​Charge at 0.1C to 3.65V with constant current and constant voltage, and cut off current is 0.01C, and stand for 30min;

[0174] Discharge at 10C to 2.5V cut off, and the capacity is recorded as Q2, and stand for 30min.

[0175] Here, the 10C capacity retention rate Q of the lithium ion battery is calculated by Q1 and Q2 R , wherein Q R = Q2 / Q1 x 100%.

[0176] The present embodiment also provides a test method for the cycle performance of a lithium ion battery. The lithium ion battery is placed in a thermostat at 25℃ for 4h, and the test is carried out according to the following steps:

[0177] First circle charging step: charge at 0.1C to 4.2V with constant current, and then change to constant voltage charging until the current decreases to 0.01C; stand for 10min after charging is completed.

[0178] First circle discharging step: discharge at 0.1C to 2.5V.

[0179] Cycle charging and discharging process: charge at 1C to 4.2V with constant current; stand for 30min again. Discharge at 1C to 2.5V with constant current.

[0180] Repeat the cycle charging and discharging process for a total of 1000 circles. The discharge capacity Q1 and Q of the battery after 1 circle and 1000 circles of cycle are recorded. 1000 Calculate the capacity attenuation rate Q of the lithium ion battery C , Q C = (Q1-Q 1000 ) / Q1 x 100%.

[0181] After the above tests are carried out on the examples 1 to 18, and the comparative examples 1 and 2, the corresponding interface resistance, peeling strength, compaction density, 10C capacity retention rate and 1000 circle cycle capacity attenuation rate are obtained. The relevant data are shown in Tables 1 to 6 as follows:

[0182]

[0183] Table 1

[0184] In Table 1, by comparing examples 1 to 5, it can be seen that the positive plate of example 1 has the lowest interface resistance, the highest peeling strength, the highest compaction density, and the corresponding lithium battery presents the best rate discharge performance and cycle stability. Among them, the energy density deviating from the laser is 300mJ·cm -2The lithium ion battery of the embodiment has a downward trend in both kinetic performance and sequential stability.

[0185] The main reason is that moderate laser energy density can form a continuous and dense carbon-rich conductive layer on the surface of PVDF, significantly improve the electronic transmission ability of the binder and promote the interface bonding, improve the kinetic performance and interface cycle stability. At the same time, laser treatment can selectively break the C-F bond, reduce the crystallinity of PVDF, and increase the amorphous segment, so that PVDF is more flexible and deformed, and can better penetrate between the positive electrode particles to improve the compaction surface density.

[0186] However, when the laser energy density is too high, local ablation or non-uniform carbonization may occur on the surface of PVDF, resulting in fracture or hardening of the conductive layer, which in turn blocks the electron channel and weakens the interface adhesion, ultimately leading to overall performance degradation.

[0187]

[0188] Table 2

[0189] In Table 2, by comparing Example 1 and Examples 6 to 9, it can be seen that when the laser frequency of the KrF excimer laser is below 10 Hz, the obtained electrode sheet has the lowest interface resistance and the highest peeling strength, and the 10C rate discharge and cycle retention rate are also optimal. Among them, too low (1 Hz) or too high (≥20 Hz) frequency will cause performance degradation.

[0190] Here, the laser frequency as the number of pulses per unit time plays a decisive role in the carbonization rate of PVDF and the uniformity of the carbon layer. Among them, 10 Hz is the critical balance point for considering heat affected zone control and surface carbonization efficiency, which can realize local carbonization uniformity, dense and continuous carbon layer. If the frequency is too low, it will result in insufficient energy accumulation and discontinuous carbon layer; if the frequency is too high, the carbonization layer will have ablation holes or structure expansion due to heat accumulation and non-uniformity of light and heat, resulting in a decrease in conductivity and adhesion. Ultimately, the performance is degraded in multiple dimensions such as electronic conduction, mechanical connection and structure compaction.

[0191]

[0192] Table 3

[0193] In Table 3, by comparing Example 1 and Examples 10 to 13, it can be seen that the processing time of the positive electrode current collector in the ultraviolet / ozone treatment device also affects the performance of the electrode sheet. Among them, after being treated in the ultraviolet / ozone treatment device for 5 min, the electrode sheet shows the lowest interface resistance and the highest peeling strength, and the corresponding lithium ion battery shows the highest discharge rate performance and cycle stability.

[0194] The main reason is that the UV / O3 treatment device can introduce abundant carboxyl groups (-COOH) and hydroxyl groups (-OH) on the surface of aluminum, which can form stable hydrogen bonds or dipole-dipole interactions with the carbon-rich layer on the surface of the laser-modified PVDF, significantly improving the adhesion and electronic continuity between the current collector and the slurry interface.

[0195] However, when the processing time is too short, the functional groups are not enough; and when it is too long, a dense amorphous oxide layer may be formed, which destroys the interface matching, increases the contact resistance and weakens the adhesion, thereby affecting the rate performance and cycle performance.

[0196]

[0197] Table 4

[0198] In Table 4, by comparing Example 1 and Examples 14-16, it can be seen that as the mass fraction of modified PVDF added in the pole piece increases from 0.5% to 2.0%, the interface resistance of the pole piece gradually decreases, the peel strength significantly improves, and the rate discharge performance and cycle performance simultaneously increase; when the mass fraction of PVDF is further increased from 2.0% to 2.5%, some performance indicators fall. This trend shows that under the premise of laser modification, the optimal amount of PVDF should be controlled at about 2.0%. At this concentration, the binder can form a continuous conductive bonding network between the active materials, which helps to reduce the resistance of the pole piece.

[0199] However, if the mass fraction of PVDF is too low, the bonding network is discontinuous, and the pole piece structure is easy to crack; on the contrary, if the mass fraction of PVDF is too high, not only the electron insulation area increases, but also the conductive path is blocked, thereby affecting the rate and cycle performance, and even leading to the decrease of the energy density of lithium batteries.

[0200]

[0201] Table 5

[0202] In Table 5, by comparing Example 1, Example 17 and Example 18, it can be seen that the D 50 When the particle size is 8.5 μm, the comprehensive performance is best, the interface resistance is lowest, the peel strength reaches the peak, and the 10C rate and long cycle stability are also optimal. When the particle size is too small (D 50 When the particle size is too large (D 50 When the particle size is too large (D

[0203] The main reason is that the particle size has a synergistic regulation effect on the packing structure, uniformity of distribution and specific surface area of the slurry: a moderate particle size helps to form a uniform and dense packing body with low porosity and large contact area, which is beneficial to the formation of continuous electron channels and effective bonding network.

[0204] However, too small particle size increases the surface area, which easily adsorbs more binder, leading to local accumulation, poor rheological properties of the slurry, and increased interface side reactions and interface polarization; too large particles have large lithium ion solid-phase diffusion, which further affects the rate discharge and long-term stability.

[0205]

[0206] Table 6

[0207] In Table 6, by comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that PVDF without KrF laser treatment and the positive current collector without oxidation treatment will cause a significant increase in interface resistance and a significant decrease in electrode peel strength, which further leads to a significant decrease in rate discharge performance and cycle performance.

[0208] Here, PVDF without KrF excimer laser modification is a high-crystallinity electrically insulating polymer with extremely low conductivity, which limits the continuity of the overall electrode conductive path, causing an increase in interface resistance and polarization, and thus limiting the rate performance and cycle performance.

[0209] The positive current collector surface without oxidation treatment has a natural passivation oxide layer, which is inert and not liquid, and lacks polar functional groups, and cannot form effective hydrogen bonds or dipole interactions with PVDF binder or active particles, relying only on mechanical contact and intermolecular forces to maintain interface stability, resulting in weak interface adhesion, large contact resistance, and easy debonding and performance degradation under high rate or long cycle.

[0210] In summary, the present application processes the positive current collector by an oxidation treatment device, which can make the surface of the positive current collector contain polar oxygen-containing functional groups, significantly enhancing the interface adhesion between the active material and the binder and the current collector. On this basis, the modified binder is a positive electrode binder treated by laser defluorination, which can break part of the C-F bonds in the positive electrode binder and form a carbon-rich conductive layer, thereby improving the conductivity of the binder and reducing its crystallinity. Therefore, by optimizing the interface adhesion of the positive current collector and the conductivity of the positive electrode binder, the interface resistance, the compaction density and the peel strength of the positive electrode sheet can be multi-dimensionally regulated, thereby improving the rate performance, cycle stability and compaction energy density of the battery.

[0211] The above description and drawings suffice to fully enable one skilled in the art to practice the embodiments of the present disclosure. Other embodiments can include structural and other changes. The embodiments are merely representative of possible variations. Individual components and functions are optional unless explicitly required, and the order of operations can be varied. Portions and features of some embodiments can be included in, or substituted for, portions and features of other embodiments. The embodiments of the present disclosure are not limited to the structures described above and shown in the drawings, and can be varied in a variety of ways. The scope of the present disclosure is limited only by the claims that follow.

Claims

1. A positive electrode sheet, characterized in that: include: A positive electrode current collector is treated by an oxidation treatment device so that the surface of the positive electrode current collector contains polar oxygen-containing functional groups, including one or more of hydroxyl groups, carboxyl groups and carbonyl groups; The positive electrode coating comprises a positive electrode coating material coated on at least one side of the positive electrode current collector, wherein the positive electrode coating material comprises a positive electrode active material, a positive electrode conductor and a modified binder; wherein the modified binder is a positive electrode binder treated by laser defluorination.

2. The positive electrode sheet according to claim 1, characterized in that The binder was defluorinated by a KrF excimer laser with an ultraviolet wavelength of 248 nm and an energy density of 200 mJ·cm -2 ~400mJ·cm -2 .

3. The positive electrode sheet according to claim 1, characterized in that The mass fraction of the modified binder is 0.5% to 2.5% of the total mass fraction of the positive electrode coating, and the positive electrode binder includes polyvinylidene fluoride or carboxylated polyvinylidene fluoride.

4. The positive electrode sheet according to claim 1, characterized in that In the infrared spectrum of the modified binder, at 844 cm -1 , 1080cm -1 、1180cm -1 and 1400cm -1 There are characteristic peaks at 844cm -1 The characteristic peak at 1080cm corresponds to the composite characteristics of CH out-of-plane vibration and CH2 vibration; -1 The characteristic peak at 1180 cm corresponds to the stretching vibration of the C-F bond; -1 The characteristic peak at 1400 cm corresponds to the stretching vibration of the CF2 group; -1 The characteristic peak corresponds to CH2 vibration.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: In the infrared spectrum of the positive electrode current collector, at 500 cm -1 ~900cm -1 Between 1700cm -1 ~1750cm -1 Between and 3200cm -1 ~3400cm -1 There are characteristic peaks between them; among them, 500cm -1 ~900cm -1 The characteristic peaks at 1700 cm correspond to Al–O bending and stretching vibrations. -1 ~1750cm -1 The characteristic peak at 3200 cm corresponds to the carbonyl stretching vibration. -1 ~3400cm -1 The characteristic peak corresponds to the stretching vibration of hydroxyl groups.

6. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The interface resistance R of the positive electrode sheet is in the range of 1.1×10 -2 Ω·cm 2 ~2.0×10 -2 Ω·cm 2 .

7. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The compaction density P of the positive electrode sheet is in the range of 3.5 g / cm -3 ~4.0g / cm -3 .

8. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The peel strength N of the positive electrode sheet ranges from 9.5 N / m to 20.0 N / m.

9. A method for preparing a positive electrode sheet according to any one of claims 1 to 4, characterized in that: The following steps are involved: Preparation of positive electrode current collector: Clean the positive electrode current collector and then place it in an oxidation treatment device to cause surface oxidation reaction of the negative electrode current collector to generate polar oxygen-containing functional groups; Preparation of positive electrode coating material: A positive electrode active material, a positive electrode conductive agent, a modified binder and a solvent are configured into a mixed solution according to a preset ratio; wherein the binder of a preset thickness is scanned multiple times by a laser under the protection of a protective gas to obtain a defluorinated modified binder; Preparation of positive electrode sheet: coating the positive electrode coating material on at least one side of the positive electrode current collector, drying and cold pressing to obtain the positive electrode sheet.

10. A lithium ion battery, characterized in that: It comprises a negative electrode sheet and a positive electrode sheet as claimed in any one of claims 1 to 8, wherein the negative electrode sheet comprises a negative electrode current collector and is coated with at least one layer of negative electrode coating; the negative electrode coating comprises a negative electrode active material, a negative electrode binder and a negative electrode conductive agent; wherein the negative electrode active material comprises one or more of artificial graphite, natural graphite, soft carbon and hard carbon; the negative electrode conductive agent comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; the negative electrode binder comprises one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber.

11. The lithium-ion battery according to claim 10, wherein: Also includes: electrolyte, including lithium salts, solvents, and additives; The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide; The solvent comprises one or more of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate; The additive includes one or more of fluoroethylene carbonate, bisfluoroethylene carbonate, vinyl sulfate, vinyl sulfite, vinylene carbonate and vinyl carbonate.

12. The lithium-ion battery according to claim 10, wherein: At 25°C, the capacity retention rate Q of the lithium-ion battery discharged R >75%.

13. The lithium-ion battery according to claim 10, characterized in that After the lithium-ion battery is cycled for 1000 cycles at 1C rate at 25°C, its capacity decay rate Q C ≤20%.

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