Positive electrode slurry, lithium ion battery and electric device

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses positive electrode slurry, a lithium ion battery and an electric device. Wherein the positive electrode slurry comprises a positive electrode active material, a positive electrode conductive agent and a positive electrode binder, the positive electrode binder comprises a polyvinylidene fluoride-hexafluoropropylene copolymer and an in-situ free radical inhibitor, the polyvinylidene fluoride-hexafluoropropylene copolymer is prepared from 1, 1-difluoroethylene and hexafluoropropylene through a high-pressure emulsion polymerization method, and the in-situ free radical inhibitor is prepared from 1, 1-difluoropropylene and hexafluoropropylene through a high-pressure emulsion polymerization method. The in-situ free radical inhibitor is prepared from one or more of 2, 2, 6, 6-tetramethylpiperidine oxygen free radicals, butylated hydroxytoluene and tert-butylphenol. According to the invention, a water-based positive electrode binder system with anti-gelling capability is constructed, and a dual mechanism that PVDF-HFP and TEMPO synergistically regulate and control polymer chain segment crystallization behavior and free radical crosslinking reaction is realized. Therefore, the rebound of viscosity can be remarkably reduced, and the rate capability and cycle life of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a positive electrode slurry, a lithium ion battery and a power utilization device. BACKGROUND

[0002] Currently, high-nickel ternary positive electrode materials (for example, LiNi 0.9 Co 0.05 Mn 0.05 O2) are widely used in high-energy-density batteries due to their high capacity and high voltage platform. However, high-nickel ternary positive electrode materials with a Ni element content of more than 90% are usually accompanied by a high proportion of surface residual alkali (LiOH / Li2CO3). During the homogenizing slurry preparation process, the surface residual alkali forms a strong alkaline environment with a pH value of more than 11 with the solvent (for example, N-methyl pyrrolidone, NMP). Under this condition, the molecular chain of the polyvinylidene fluoride (PVDF) binder will undergo a dehydrofluorination reaction to form a carbon-carbon double bond (C=C) and further crosslink and gel, resulting in a significant increase in the viscosity of the positive electrode slurry. For example, the initial positive electrode slurry viscosity is about 4000 mPa·s, which rapidly rebounds to more than 20000 mPa·s within 2h, resulting in the loss of flowability of the positive electrode slurry, and ultimately leading to uneven coating thickness, loose electrode structure and even cracks.

[0003] In addition, after the gelation, the conductive agent in the related art cannot fully cover the surface of the active particles, the internal electron path of the electrode is broken, and the kinetic performance and cycle stability of the lithium ion battery are low. Even if oxalic acid or a weak acid is used for neutralization treatment in the related art, the pH value can only be reduced to less than 10, and the de-fluorination-crosslinking reaction in the PVDF still cannot be inhibited, and the introduction of impurity ions may have a negative impact on the quality of the subsequent SEI film.

[0004] 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

[0005] To facilitate an understanding of some aspects of the disclosed embodiments, a brief summary is given below. The summary is not an extensive overview of the embodiments and is not intended to identify key / critical elements of the embodiments or to delineate the scope of the embodiments, but to present some aspects of the embodiments in a simplified form as a prelude to the detailed description.

[0006] The positive electrode slurry, the lithium ion battery and the power utilization device provided by the embodiments of the present disclosure can significantly reduce the viscosity rebound of the positive electrode slurry, and improve the rate performance and cycle life of the lithium ion battery.

[0007] In some embodiments, the positive electrode slurry, including a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, is characterized in that the positive electrode binder includes a polyvinylidene-hexafluoropropylene copolymer and an in-situ radical inhibitor, wherein the polyvinylidene-hexafluoropropylene copolymer is prepared from 1,1-difluoroethylene and hexafluoropropylene by a high-pressure emulsion polymerization method, and the in-situ radical inhibitor includes one or more of 2,2,6,6-tetramethylpiperidinooxy radical, dibutylhydroxytoluene, and tert-butylphenol.

[0008] Optionally, in the Fourier transform infrared spectrogram corresponding to the polyvinylidene-hexafluoropropylene copolymer, there exists a characteristic peak at 764 cm -1 representing skeletal vibration of the α phase of polyvinylidene fluoride, a characteristic peak at 840 cm -1 representing skeletal vibration of the β phase of polyvinylidene fluoride, a characteristic peak at 1078 cm -1 representing stretching vibration of C-F bond, and a characteristic peak at 1180 cm -1 representing stretching vibration of CF2 group.

[0009] Optionally, the molecular weight of the polyvinylidene-hexafluoropropylene copolymer is 200,000 Da to 550,000 Da, and the molar content of hexafluoropropylene copolymer is 5% to 20%;

[0010] The β phase crystallinity of polyvinylidene fluoride is between 40% and 75%, and satisfies the following equation:

[0011]

[0012] wherein % (β) represents the percentage of the β phase, A α and A β represent the absorbance characteristic peak intensity at 764 cm -1 and 840 cm -1 in the Fourier transform infrared spectrogram corresponding to the polyvinylidene-hexafluoropropylene copolymer, respectively corresponding to the α phase content and the β phase content, K α and K β have absorption coefficients of 6.1 × 10 4 cm 2 / mol and 7.7 × 10 4 cm 2 / mol, respectively.

[0013] Optionally, the mass percentage of the polyvinylidene-hexafluoropropylene copolymer and the in-situ radical inhibitor in the solid components of the positive electrode slurry as a whole is 0.5 wt% to 3.0 wt%.

[0014] Optionally, the positive electrode active material includes lithium nickel cobalt manganese oxide (LiNi xCo y Mn z M b O2) wherein 0.70≤x≤0.95, 0.1≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, element M comprises one or more of zirconium, tungsten, titanium, aluminum, strontium, boron and neodymium; the positive electrode conductive agent comprises carbon black and / or carbon nanotube.

[0015] Optionally, the viscosity rebound ratio of the positive electrode slurry within 12 hours at room temperature is less than 30%.

[0016] In some embodiments, the lithium ion battery comprises a positive electrode sheet composed of a positive electrode current collector and the positive electrode slurry as claimed in any one of claims 1 to 5 coated on at least one surface thereof, and the positive electrode sheet satisfies:

[0017] interface resistance R α is between 1.0 x 10 -2 and 4.0 x 10 -2 Ω·cm 2 .

[0018] 8.5 N / m≤peeling strength≤16.0 N / m.

[0019] Optionally, the consistency error of the coating thickness of the positive electrode slurry is less than ±1.5 μm, and the compaction density of the positive electrode slurry is between 3.5 g / cm 3 and 4.0 g / cm 3 .

[0020] Optionally, the lithium ion battery further 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 or 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.

[0021] Optionally, the discharge characteristics of the lithium ion battery are as follows: after the lithium ion battery at 100% charge rate is left to stand at 25℃ for 6 hours, the discharge capacity corresponding to the discharge to 2.5V at a rate of 0.1C is Q1; the discharge capacity corresponding to the discharge to 2.5V at a rate of 10C is Q2; and the retention rate of the discharge capacity Q2 / Q1≥70%.

[0022] Optionally, the capacity attenuation rate of the lithium ion battery is lower than 20% after 1000 cycles at a rate of 1C at 25℃.

[0023] In some embodiments, the power device includes a lithium ion battery as described herein.

[0024] The positive electrode slurry, the lithium ion battery and the power device provided by the embodiments of the present disclosure can achieve the following technical effects:

[0025] The present application adopts a composite strategy integrating structural design and chemical inhibition: first, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer is used to replace single polyvinylidene fluoride (PVDF), thereby reducing the crystallinity of the copolymer main chain. Second, by introducing in-situ free radical inhibitor (TEMPO), the crosslinking process induced by double bond is blocked. In this way, the present application constructs a water-based positive electrode binder system with anti-gelation ability, realizing the dual mechanism of PVDF-HFP and TEMPO synergistically regulating the crystallization behavior and free radical crosslinking reaction of polymer chain segments. Thus, the rebound of viscosity can be significantly reduced (2h rebound ratio < 50%, viscosity < 6000 mPa·s), and the rate performance and cycle life of the battery are improved.

[0026] The foregoing general description and the following description are merely exemplary and explanatory, and are not intended to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0027] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute a limitation on the embodiments, elements with the same reference numerals in the drawings are shown as similar elements, the drawings do not constitute a proportional limitation, and wherein:

[0028] Figure 1 is a structural schematic diagram of a lithium ion battery provided by the embodiments of the present disclosure;

[0029] Figure 2 is a structural schematic diagram of a battery roll core provided by the embodiments of the present disclosure;

[0030] Figure 3 is an unfolded schematic diagram of a battery roll core provided by the embodiments of the present disclosure;

[0031] Figure 4 is a Fourier transform infrared spectrogram corresponding to polyvinylidene fluoride-hexafluoropropylene copolymer provided by the embodiments of the present disclosure.

[0032] LIST OF REFERENCE NUMERALS

[0033] 1 - positive electrode end; 10 - battery roll core; 11 - positive electrode column; 12 - negative electrode end; 2 - shell; 3 - negative electrode sheet; 4 - separator; 5 - positive electrode sheet. DETAILED DESCRIPTION

[0034] 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 with reference to the accompanying drawings, which are only used for reference 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Unless otherwise specified, the term "a plurality of" means two or more.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In combination with Figure 1 As shown in the drawings, the present disclosure provides a lithium ion battery, which comprises a shell 2, the inside of which is used to accommodate a battery roll core, the top of which is a positive electrode end 1, the bottom of which is a negative electrode end 12, and a positive electrode column 11 is arranged on the positive electrode end 1. Specifically, Figure 2 The structural schematic diagram of the battery roll core in the present application is shown, Figure 3 The expanded schematic diagram of the battery roll core in the present application is shown. As shown in the drawings, Figure 3 The lithium ion battery further comprises a positive electrode sheet 5, a negative electrode sheet 3, a diaphragm 4 and an electrolyte, the positive electrode sheet 5, the negative electrode sheet 3 and the diaphragm 4 are stacked and then rolled to form a cylindrical battery roll core 10 as shown in the drawings, the initial rolling is the sheet end at the cylindrical axis, and the end of the rolling is the sheet end at the outer surface of the cylinder. Figure 2

[0043] Further, the positive electrode sheet 3 of the present application is composed of a positive electrode current collector and a positive electrode paste coated on at least one surface thereof, and the positive electrode sheet 3 of the present application satisfies: the interface resistance R α is between 1.0*10 -2 and 4.0*10 -2 Ω·cm 2 ; and the peeling strength is between 8.5N / m and 16.0N / m.

[0044] Among them, the positive electrode paste of the present application comprises polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer and in-situ free radical inhibitor (TEMPO), wherein the polyvinylidene fluoride-hexafluoropropylene copolymer is prepared by high-pressure emulsion polymerization method from 1,1-difluoroethylene and hexafluoropropylene. The in-situ free radical inhibitor includes one or more of 2,2,6,6-tetramethylpiperidyl oxyl radical, dibutyl hydroxytoluene, tertiary butyl phenol and phenyl ether inhibitor.

[0045] Optionally, in combination with Figure 4 As shown in the drawings, in the Fourier transform infrared spectrum of the polyvinylidene fluoride-hexafluoropropylene copolymer, there is a characteristic peak representing the skeletal vibration of the alpha phase of polyvinylidene fluoride at 764cm -1 , a characteristic peak representing the skeletal vibration of the beta phase of polyvinylidene fluoride at 840cm -1 , a characteristic peak representing the stretching vibration of C-F bond at 1078cm -1 , and a characteristic peak representing the stretching vibration of CF2 group at 1180cm -1 .

[0046] ​Optionally, the molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer of the present application is 200,000 Da to 550,000 Da, and the molar content of the hexafluoropropylene copolymer is 5% to 20%;

[0047] The β-phase crystallinity of polyvinylidene fluoride is between 40% and 75%, and satisfies the following equation:

[0048]

[0049] Among them, %(β) represents the percentage of β phase, A α and A β The Fourier transform infrared spectrum of polyvinylidene fluoride-hexafluoropropylene copolymer is 764 -1 840cm -1 The absorption characteristic peak intensity at , corresponds to the α phase content and β phase content, K α and K β The absorption coefficients are 6.1×10 4 cm 2 / mol and 7.7×10 4 cm 2 / mol.

[0050] Optionally, the mass percentage of the polyvinylidene fluoride-hexafluoropropylene copolymer and the in-situ free radical inhibitor in the solid components of the entire positive electrode slurry is 0.5 wt % to 3.0 wt %.

[0051] Optionally, the viscosity rebound ratio of the positive electrode slurry of the present application within 12 hours at room temperature is less than 30%.

[0052] Using the positive electrode slurry and lithium-ion battery provided by the embodiment of the present disclosure, a composite strategy integrating structural design and chemical inhibition is adopted: First, a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymer is used to replace a single polyvinylidene fluoride (PVDF), thereby reducing the crystallinity of the copolymer main chain. Secondly, an in-situ free radical inhibitor (TEMPO) is introduced to block the cross-linking process induced by the double bond. In this way, the present application constructs an aqueous positive electrode binder system with anti-gelation ability, realizing the dual mechanism of PVDF-HFP and TEMPO synergistically regulating the crystallization behavior of polymer chain segments and free radical cross-linking reactions. Thereby, the viscosity rebound can be significantly reduced (2h rebound ratio <50%, viscosity less than 6000mPa·s), and the battery rate performance and cycle life are improved.

[0053] In one embodiment of the present application, the positive electrode sheet of the present application further includes a positive electrode active material and a positive electrode conductive agent, wherein the positive electrode active material includes lithium nickel cobalt manganese oxide (LiNi x Co y Mn zM b O2) wherein, 0.70≤x≤0.95, 0.1≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, element M includes one or more of zirconium, tungsten, titanium, aluminum, strontium, boron and neodymium; the positive electrode conductive agent includes carbon black and / or carbon nanotubes.

[0054] Optionally, the lithium ion battery of the present application further comprises a negative electrode active material, a negative electrode binder and a negative electrode conductive agent, wherein the negative electrode active material of the present application comprises one or more of artificial graphite, natural graphite, soft carbon or hard carbon; the negative electrode conductive agent of the present application comprises one or more of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; the negative electrode binder of the present application comprises one or more of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and butadiene-styrene rubber.

[0055] Optionally, the discharge characteristics of the lithium ion battery of the present application are as follows: after the lithium ion battery with 100% charge rate is left at 25℃ for 6 hours, it is discharged to 2.5V at 0.1C rate, and the corresponding discharge capacity is Q1; the discharge capacity when discharged to 2.5V at 10C is Q2; the retention rate of discharge capacity Q2 / Q1≥70%.

[0056] Optionally, the capacity attenuation rate of the lithium ion battery is less than 20% after 1000 cycles at 1C rate at 25℃.

[0057] In addition, the present disclosure provides a power utilization device comprising the lithium ion battery as described in the present application.

[0058] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0059] 1. Preparation method of positive electrode slurry:

[0060] The preparation of the positive electrode slurry adopts a dry pre-mixing process and a wet dispersion process by double planetary stirring paddles. The specific steps are as follows: first, according to the mass percentage (NCM811: SuperP: HCNT: PVDF-HFP: TEMPO = 96: 0.5: 1: 2: 0.5) ratio, accurately weigh each powder component (HCNT is oligo-wall carbon nanotube), and uniformly mix and slurry in a double planetary stirring kettle. The stirring speed is set to 40 rpm, and the stirring time is 30 minutes to ensure that the conductive agent and the binder are evenly coated on the surface of the active material. Then, a proper amount of NMP solvent is slowly added to control the solid content at 68±2wt%, and the low-speed-high-speed alternating mode is switched to. The slurry is stirred in stages: low speed 80 rpm for 30 minutes for preliminary wetting, and then high speed 3000 rpm for 2.5 hours to form a uniform slurry. The negative pressure in the kettle is maintained at -0.08 MPa throughout the stirring process to prevent air bubbles from being introduced, and the temperature is controlled at 25°C through the jacket. After stirring, the slurry is allowed to stand for degassing or vacuum degassing for 30 minutes to obtain a positive electrode slurry with stable viscosity, uniform dispersion, and suitable for coating.

[0061] 2. The method for making a positive electrode sheet comprises the following steps:

[0062] The above positive electrode slurry is uniformly coated on a 12.0 μm thick aluminum foil. After drying at 120°C for 1.5 hours, cold pressing, slitting, and cutting, a positive electrode sheet is obtained, and the tap density is 3.5 g / cm 3 .

[0063] The method for preparing PVDF-HFP comprises the following steps:

[0064] The PVDF-HFP copolymer is prepared by high-pressure emulsion polymerization. Vinylidene fluoride (VDF) and hexafluoropropylene (HFP) are introduced into a high-pressure reaction kettle in a certain molar ratio (such as 87.5:12.5). In the presence of deionized water and a surfactant (such as a fluorine surfactant), a free radical initiator (such as ammonium persulfate or an azo compound) is added, and the free radical emulsion copolymerization reaction is carried out at 60-90°C and 5-10 MPa. After polymerization, emulsion breaking, filtration, water washing, and drying, a PVDF-HFP powder with uniform particle size and excellent flexibility is obtained.

[0065] 3. The method for making a negative electrode comprises the following steps:

[0066] The negative electrode sheet comprises a negative electrode current collector copper foil and a negative electrode coating material coated on both sides of the copper foil. The negative electrode coating material comprises, by mass percentage, 96.0% of graphite, 1.5% of carbon nanotubes, 1.0% of thickening agent carboxymethyl cellulose sodium (CMC), and 1.5% of binder styrene-butadiene rubber (SBR). The above substances are added to deionized water to form the negative electrode coating material with a solid content of 40%. Then, the negative electrode coating material is coated on both sides of the negative electrode current collector (copper foil), and is subjected to drying and cold pressing to form the negative electrode sheet with a compacted density of 1.5 g / cm 3 ;

[0067] 4. Preparation of electrolyte solution:

[0068] Lithium salt lithium hexafluorophosphate (LiPF6), organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), first additive fluoroethylene carbonate (FEC), second additive vinyl sulfate (DTD), and third additive vinylene carbonate (VC)

[0069] The electrolyte solution is obtained by mixing the above substances in a mass ratio of 10.0:20.0:55.0:2.0:8.0:5.0.

[0070] 5. Separator:

[0071] A separator with high porosity is selected. The thickness of the base film PE in the separator is 9 μm, the thickness of the ceramic coating on both sides of the base film is 1.0 μm, and the thickness of the PVDF coating is 1.0 μm.

[0072] 6. Assembly of lithium ion battery:

[0073] The positive electrode sheet and the negative electrode sheet are respectively subjected to rolling and slitting, and are then wound together with the separator to obtain a 21700 cylindrical battery roll core. Subsequently, the battery roll core is welded with a connecting sheet, and is then loaded into a battery shell. After completing the processes of liquid injection, sealing, and formation, the lithium ion battery of Example 1 is obtained. The shell of the lithium ion battery is a cylinder with a size parameter of diameter: 21.0 mm and length: 70.0 mm.

[0074] Example 2

[0075] The difference between this example and Example 1 is that the molar ratio of VDF to HFP is 97.5:2.5, and the other conditions are the same as those in Example 1.

[0076] Example 3

[0077] The difference between this example and Example 1 is that the molar ratio of VDF to HFP is 95.0:5.0, and the other conditions are the same as those in Example 1.

[0078] Example 4

[0079] The difference between this embodiment and Example 1 is that the molar ratio of VDF to HFP is 90.0:10.0, and the others are the same as Example 1.

[0080] Example 5

[0081] The difference between this embodiment and Example 1 is that the molar ratio of VDF to HFP is 85.0:15.0, and the others are the same as Example 1.

[0082] Example 6

[0083] The difference between this embodiment and Example 1 is that the mass percentage of TEMPO added in the homogenization process is 5%, and the others are the same as Example 1.

[0084] Example 7

[0085] The difference between this embodiment and Example 1 is that the mass percentage of TEMPO added in the homogenization process is 10%, and the others are the same as Example 1.

[0086] Example 8

[0087] The difference between this embodiment and Example 1 is that the mass percentage of SuperP and HCNT added is 1% and 0.5%, i.e. SuperP:HCNT=2:1, and the others are the same as Example 1.

[0088] Example 9

[0089] The difference between this embodiment and Example 1 is that the mass percentage of SuperP and HCNT added is 0.75% and 0.75%, i.e. SuperP:HCNT=1:1, and the others are the same as Example 1.

[0090] Example 10

[0091] The difference between this embodiment and Example 1 is that the mass percentage of SuperP and HCNT added is 0.25% and 1.25%, i.e. SuperP:HCNT=1:5, and the others are the same as Example 1.

[0092] Example 11

[0093] The difference between this embodiment and Example 1 is that the mass percentage of PVDF-HFP added in the homogenization process is 0.5%, and the others are the same as Example 1.

[0094] Example 12

[0095] The difference between this example and Example 1 is that the mass percentage of PVDF-HFP added in the homogenization process is 1.0%, and the others are the same as Example 1.

[0096] Example 13

[0097] The difference between this example and Example 1 is that the mass percentage of PVDF-HFP added in the homogenization process is 1.5%, and the others are the same as Example 1.

[0098] Example 14

[0099] The difference between this example and Example 1 is that the mass percentage of PVDF-HFP added in the homogenization process is 2.5%, and the others are the same as Example 1.

[0100] Example 15

[0101] The difference between this example and Example 1 is that the homogenization temperature is controlled at 15℃, and the others are the same as Example 1.

[0102] Example 16

[0103] The difference between this example and Example 1 is that the homogenization temperature is controlled at 20℃, and the others are the same as Example 1.

[0104] Example 17

[0105] The difference between this example and Example 1 is that the homogenization temperature is controlled at 30℃, and the others are the same as Example 1.

[0106] Example 18

[0107] The difference between this example and Example 1 is that the homogenization temperature is controlled at 40℃, and the others are the same as Example 1.

[0108] Comparative Example 1

[0109] The difference between this example and Example 1 is that PVDF is not copolymerized with HFP, and the others are the same as Example 1.

[0110] Comparative Example 2

[0111] The difference between this example and Example 1 is that TEMPO is not added in the homogenization process, and the others are the same as Example 1.

[0112] Test:

[0113] First, the lithium-ion battery is discharged at a constant current to 2.5 V to ensure it is in a safe state, reducing the risk of short-circuiting or thermal runaway during disassembly. Inside a glove box (protected by argon or other inert atmosphere), the battery is carefully disassembled, and the positive electrode tab of the cylindrical cell is removed. Using tweezers or appropriate tools, the tab is peeled off without damaging the active material layer. Next, the removed positive electrode tab is cut to an appropriate size and soaked in anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible byproducts. After removing the tab, the surface is gently wiped with a lint-free wipe, and then fresh DMC solution is replaced, repeating the soaking-wiping process three times to ensure that the tab surface is free of residual contaminants. Subsequently, the tab is rinsed with anhydrous ethanol and wiped again to further remove solvents and impurities. After completing the cleaning, the tab is left to dry in the glove box for 48 hours to ensure complete drying, preventing interference with subsequent tests due to solvent residues.

[0114] Method for testing the interfacial resistance of the positive electrode tab:

[0115] The interfacial resistance of the negative electrode tab is measured using the 46-probe method of the RM2610 resistance measurement system (45 probes arranged in a square matrix, with 1 probe as a ground probe). First, the negative electrode tab, which has been treated with dimethyl carbonate and vacuum-dried, is divided into 40 square cells to ensure the surface of the sample is flat. Next, the sample is placed on the testing device, and the pressure exerted by the probes is adjusted using a pressure gauge to ensure good contact between the probes and the sample, with a contact area of 0.01 cm 2 During the test, the outer 20 probes apply a constant current, causing the current to flow through the surface, interface, and current collector of the tab. At the same time, the middle 25 probes measure the voltage change in real time. Since the surface, interface, and current collector of the tab have significantly different resistances, the measured voltage will reflect these differences. Finally, the membrane resistance R1 is calculated according to Ohm's law and fitting analysis method. Subsequently, the same method is used to randomly select another 9 square cells on the above-mentioned tab for interfacial resistance measurement, with the values obtained being denoted as R2, R3, R4, R5, R6, R7, R8, R9, and R10, respectively. Finally, the average interfacial resistance Rα is obtained by calculating the arithmetic mean of these values, facilitating a comprehensive evaluation of the conductive properties and uniformity of the negative electrode tab.

[0116] Method for testing the compaction density of the positive electrode tab:

[0117] First, the positive electrode sheet after dimethyl carbonate rinsing treatment and vacuum drying is cut into 6 square samples of standard size (2.0 cm x 2.0 cm); then, the active material on the front and back of 3 of the square samples is rubbed off, and after being washed with ethanol and dried, the average mass M1 is calculated by weighing, and the average thickness L1 of the sample is measured using a screw micrometer; then, the mass of the other 3 square samples is weighed to obtain the average mass M2, and the average thickness L2 of the sample is measured, and the thickness of the sheet is calculated: L2-L1, unit: cm; and the compaction density of the sheet is calculated:

[0118] Unit: g / cm 3 .

[0119] Test method for the peeling force of the positive electrode sheet:

[0120] The positive electrode sheet after dimethyl carbonate rinsing and drying under vacuum is cut into a standard size long strip sample (2 cm x 10 cm). The sample is fixed on a flat steel plate by double-sided tape, ensuring that the bonding area is in the center of the steel plate. Then, the protective film of the double-sided tape is removed, the long strip to be tested is bonded to the surface of the tape, and a pressure roller is used for uniform rolling to ensure that the sheet fully contacts and firmly bonds to the surface of the steel plate. At the end of the sheet that is not bonded, it is naturally folded to 180° and fixed to the clamp of the electronic tensile testing machine. The 180° peeling test is performed at a stretching speed of 100 mm / min, and the peeling force-displacement curve during the entire stretching process is recorded. The data at the stable stage where the force value fluctuates less than ±10% is selected, and the average value of the tension in this section is calculated. Finally, the average tension is divided by the width of the sheet to obtain the peeling strength per unit width, with the unit being N·m -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.

[0121] Test method for the 25°C rate discharge performance:

[0122] The battery is placed in a 25°C constant temperature box for 4 h and tested according to the following steps:

[0123] (1) Constant current and constant voltage charging to 3.65 V at 0.1C, with a cutoff current of 0.01C, and standing for 30 min;

[0124] (2) Constant current discharge to 2.5 V cutoff at 0.1C, with a capacity of Q1, and standing for 30 min;

[0125] (3) Constant current and constant voltage charging to 3.65 V at 0.1C, with a cutoff current of 0.01C, and standing for 30 min;

[0126] (4) Discharge at a constant current to 2.5V cut-off at 10C, the capacity is Q2, and stand for 30min;

[0127] The calculation method of 10C capacity retention rate is: Q2 / Q1x100.

[0128] Cycling performance test method:

[0129] Place the battery in a 25℃ constant temperature box for 4h and test according to the following steps:

[0130] First cycle constant current constant voltage charging: charge at a constant current of 0.1C to 4.2V, then change to constant voltage charging until the current decreases to 0.01C.

[0131] Stand for 10min after charging is completed.

[0132] Discharge at a constant current to 2.5V at a rate of 0.1C.

[0133] Repeat the above charging and discharging process: charge at a constant current to 4.2V at a rate of 1C. Stand for 30min again.

[0134] Discharge at a constant current to 2.5V at a rate of 1C.

[0135] Repeat the above charging and discharging process for a total of 1000 cycles.

[0136] Statistical discharge capacity Q1 and Q1000 of the battery after 1 cycle and 1000 cycles, and the capacity attenuation rate of the battery (Q1-Q1000) / Q1x100.

[0137] Table 1

[0138]

[0139] As shown in Table 1, from Comparative Example 1 to Example 5, it can be seen that when the HFP content gradually increases from 2.5 mol% to 12.5 mol%, the positive electrode interface resistance gradually decreases, the peeling strength increases, the viscosity rebound rate significantly decreases, the 10C rate retention rate and the cycle life significantly improve, and a continuous optimization trend is shown. However, when the HFP content is further increased to 15.0 mol%, some performances such as peeling strength and rate retention rate appear to fall back, and the overall performance shows a trend of “first optimization and then decline”. This phenomenon is due to the fact that HFP is a comonomer with high amorphousness, which can effectively reduce the crystallinity of the PVDF segment, improve the swelling and wetting behavior in the slurry. At a medium concentration (10-12.5 mol%), the flexible chain segment of HFP enhances the coating and contact effect of the binder on the positive electrode particles (such as NCM), improves the uniformity of the bonding interface and the continuity of the ion channel, and at the same time blocks the crosslinking tendency, maintains the stability of the slurry. However, when the HFP content is too high (≥15 mol%), the viscoelastic properties of the system decrease excessively, resulting in an increase in shrinkage during the drying process, causing the porosity of the film to increase and the adhesion to decrease, affecting the structure density, and the performance falls back.

[0140] Table 2

[0141]

[0142] As shown in Table 2, from Comparative Examples 1, 6 and 7, it can be seen that during the increase of the TEMPO addition amount from 0% to 0.08%, the electrode interface resistance rapidly decreases, the peeling strength and the rate capacity synchronously increase, and the viscosity rebound rate is effectively alleviated. However, when the TEMPO addition amount reaches 0.10%, some performances appear to fall back slightly, especially the peeling strength decreases slightly, and the interface resistance tends to be stable, indicating that there is an optimal addition window for TEMPO. This phenomenon is due to the fact that TEMPO inhibits the C–F bond rupture of PVDF in the alkaline environment through the free radical scavenging mechanism, and prevents the gelation crosslinking after the formation of the olefin structure of the chain segment. At a mass percentage of 0.08%, it is most effective to inhibit the polymerization-induced reaction, while the mechanical support ability of the PVDF-HFP segment is retained, realizing the best anti-gel efficiency and interface film forming quality. However, excessive TEMPO can destroy the film forming stability of PVDF, easily causing the polymer to phase separate or the electronic migration path to break, and thus some performances are weakened.

[0143] Table 3

[0144]

[0145] As shown in Table 3, comparative examples 1, 8 to 10, keeping the total content of carbon black conductive agent Super P + hierarchical carbon nanotubes at 1.5%, gradually increasing the mass percentage of HCNT to 1.0%, the interface resistance is significantly reduced, the peel strength and rate performance are improved, which reflects the advantage of the construction of continuous conductive network of carbon nanotubes. But continue to improve the mass percentage of HCNT (to 1.25%), the slurry dispersion decreases, the peel strength and 10C capacity begin to decrease, showing a turning point of "enhancement - oversaturation". This phenomenon is attributed to the fact that Super P provides a point-like conductive bridge structure, while HCNT provides a continuous long-path conductive network, and the two together form a three-dimensional electronic channel. When the ratio of HCNT and Super is 2:1, the optimal composite conductive skeleton is formed, making the transmission path of electrons in the electrode short and efficient. However, when the content of HCNT is too high, due to its high aspect ratio and high surface area characteristics, it is easy to compete with PVDF for adsorption, resulting in a decrease in the coating rate of the binder, while the surface tension of the slurry increases, the slurry rebound rate increases, and the film uniformity decreases, causing the interface structure to be unstable, resulting in a decrease in the rate performance and cycle performance of the lithium battery.

[0146] Table 4

[0147]

[0148] As shown in Table 4, comparative examples 1, 11 to 14, with the mass fraction of PVDF-HFP increasing from 0.5% to 2.0%, the electrode showed a trend of lower interface resistance and viscosity rebound, higher adhesion, rate performance and cycle performance. But when the content increased to 2.5%, some performances such as peel strength and 10C rate performance decreased, indicating that there is an optimal addition range. The phenomenon is attributed to the fact that PVDF-HFP has film-forming, flexibility and adhesion, which plays a triple role in the system: first, through its block structure, it improves the continuity of the film, making the active material and the conductive framework form a dense connection; second, relying on the amorphous segment of HFP, it enhances the wetting and dispersion behavior of the binder, and builds a stable three-dimensional network structure; third, it provides built-in flexibility, effectively releasing internal stress during drying and compaction, and improving the integrity of the electrode. In the low content area <1.5%, the network structure provided by PVDF-HFP is weak, and the proportion of free-flowing particles in the system is high, so the binder is not enough to coat all the positive electrode particles and conductive agents, resulting in more bridging between particles, and the viscosity rebound is obvious. In the 1.5% to 2.0% addition range, PVDF-HFP fully realizes the synergistic optimization of particle bridging, carbon agent network coating and electrode flexibility enhancement, resulting in the lowest interface resistance, the strongest peel strength and the optimal rate capability. But when the addition amount exceeds 2.0% (such as 2.5%), the polymer film thickness increases significantly, the local ion transport path is blocked, the viscosity rises, the coating uniformity decreases, and the compaction difficulty increases, eventually leading to the double decline of interface ion conductivity and mechanical strength, forming a performance "inflection point".

[0149] Table 5

[0150]

[0151] As shown in Table 5, comparative examples 1, 15 to 18, with the dispersion temperature increasing from 10°C to 25°C, the swelling efficiency of PVDF-HFP and the dispersion performance of carbon material improved significantly, and various performances were optimized simultaneously. But when the temperature increased from 25°C to 40°C, the slurry system appeared a slight cross-linking induction, the peel strength and interface resistance deteriorated slightly, indicating that there is an optimal dispersion temperature window. The phenomenon is attributed to the fact that the dispersion temperature affects the thermal motion of the polymer chain segment and the surface depolymerization degree of the carbon conductive agent. At 25°C, the swelling speed of the polymer chain segment and the carbon network shaping reach a good balance, which is beneficial to the uniform distribution of energy in the slurry. But when the temperature exceeds 30°C, the activity of the oxygen functional groups on the surface of the carbon material increases, which is easy to react with the binder to induce cross-linking of the chain segment, and the surface tension of the system decreases, which affects the coating uniformity and drying rate, finally causing structural non-uniformity and performance fluctuation.

[0152] Table 6

[0153]

[0154] As shown in Table 6, compared with Comparative Example 1 and Comparative Examples 1 and 2, it can be seen that PVDF not copolymerizing HFP and not adding TEMPO in the homogenization process will cause the interface resistance to increase significantly, the slurry viscosity to rebound significantly, and the electrode peeling strength to decrease significantly, thereby causing the rate discharge performance and the cycle performance to decrease significantly. The phenomenon is attributed to the fact that the lack of HFP copolymerization segment will cause the overall crystallinity of PVDF to be high, the segment flexibility to be insufficient, the inter-particle adhesion to be insufficient, and the interface ion channel to lack continuity, which will easily induce the electron and ion transmission channel to break; the lack of TEMPO addition will cause the PVDF main chain to undergo defluorination reaction in the alkaline environment, the C-F bond to break to form an unsaturated olefin structure, crosslinking gelation to be induced, and the slurry internal friction to increase, the interface structure to be damaged, and the electrode film to be cracked and peeled after drying.

[0155] In summary, the present application realizes the synergistic improvement of the positive electrode slurry system in the conductivity, the adhesion strength, the interface stability, and the anti-gelation performance by introducing the HFP copolymerization structure to regulate the PVDF crystallinity, combining the TEMPO free radical stabilizer to inhibit the segment crosslinking in the alkaline system, and optimizing the ratio of SuperP and HCNT, the PVDF-HFP content, and the dispersion temperature. The experimental results show that the suitable formula and process window can significantly reduce the electrode interface resistance and the viscosity rebound rate, improve the rate retention rate and the cycle stability, and provide a bonding solution that can be popularized industrially for the high-performance lithium battery positive electrode slurry preparation process.

[0156] The above description and drawings sufficiently illustrate embodiments of the present disclosure to enable one skilled in the art to practice them. Other embodiments can include structural and other changes. The embodiments are merely representative of the possible variations. Individual components and functions are optional unless specifically required, and the order of operations can be changed. Parts and features of some embodiments can be included or replace parts and features of other embodiments. The embodiments of the present disclosure are not limited to the structures that have been described above and shown in the drawings, and can be variously modified and changed without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A positive electrode slurry comprising a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, characterized by, The positive electrode binder comprises a polyvinylidene fluoride-hexafluoropropylene copolymer and an in-situ radical inhibitor, wherein the polyvinylidene fluoride-hexafluoropropylene copolymer is prepared by high-pressure emulsion polymerization of 1,1-difluoroethylene and hexafluoropropylene, and the in-situ radical inhibitor comprises one or more of 2,2,6,6-tetramethylpiperidinooxy radical, dibutylhydroxytoluene and tert-butyl phenol.

2. The positive electrode slurry according to claim 1, characterized by, In the Fourier transform infrared spectrum of the polyvinylidene fluoride-hexafluoropropylene copolymer, a characteristic peak representing skeletal vibration of the α phase of the polyvinylidene fluoride exists at 764 cm -1 -1, a characteristic peak representing skeletal vibration of the β phase of the polyvinylidene fluoride exists at 840 cm -1 -1, a characteristic peak representing skeletal vibration of the β phase of the polyvinylidene fluoride exists at 840 cm -1 -1, a characteristic peak representing skeletal vibration of the β phase of the polyvinylidene fluoride exists at 840 cm -1 -1, a characteristic peak representing skeletal vibration of the β phase of the polyvinylidene fluoride exists at 840 cm 3. The positive electrode slurry according to claim 2, characterized by, The molecular weight of the polyvinylidene fluoride-hexafluoropropylene copolymer is 200,000 Da to 550,000 Da, and the molar content of the hexafluoropropylene copolymer is 5% to 20%; The β-phase crystallinity of the polyvinylidene fluoride is between 40% and 75%, and satisfies the following equation: Among them, %(β) represents the percentage of β phase, A α and A β The Fourier transform infrared spectrum of polyvinylidene fluoride-hexafluoropropylene copolymer is 764 -1 840cm -1 The absorption characteristic peak intensities at , respectively corresponding to the α phase content and β phase content, K α and K β The absorption coefficients are 6.1×10 4 cm 2 / mol and 7.7×10 4 cm 2 / mol.

4. The positive electrode slurry according to claim 1, wherein The mass percentage of the polyvinylidene fluoride-hexafluoropropylene copolymer and the in-situ radical inhibitor in the solid components of the positive electrode slurry as a whole is 0.5wt% to 3.0wt%.

5. The positive electrode slurry of claim 1, wherein The positive active material includes lithium nickel cobalt manganese oxide (LiNi x Co y Mn z M b O2) wherein, 0.70≤x≤0.95, 0.1≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, the element M comprises one or more of zirconium, tungsten, titanium, aluminum, strontium, boron and neodymium; the positive electrode conductive agent comprises carbon black and / or carbon nanotubes.

6. The positive electrode slurry according to any one of claims 1 to 5, characterized in that, The viscosity rebound ratio of the positive electrode slurry within 12 hours at room temperature is less than 30%.

7. A lithium-ion battery, characterized by The positive electrode pole piece is composed of a positive electrode current collector and the positive electrode slurry as claimed in any one of claims 1 to 5 coated on at least one surface thereof, and the positive electrode pole piece satisfies: Interface resistance R α between 1.0 x 10 -2 and 4.0 x 10 -2 Ω-cm 2 ; 8.5 N / m≤peeling strength≤16.0 N / m.

8. The lithium-ion battery of claim 7, wherein, The consistency error of the coating thickness of the positive electrode slurry is less than ±1.5 μm, and the compaction density of the positive electrode slurry is between 3.5 g / cm 3 ~ 4.0 g / cm 3 .

9. The lithium-ion battery of claim 7, wherein, The negative electrode active material comprises one or more of artificial graphite, natural graphite, soft carbon or 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.

10. The lithium-ion battery of claim 7, wherein, The discharge characteristics of the lithium ion battery are as follows: after the lithium ion battery with a 100% charge rate is left to stand at 25°C for 6 hours, the discharge capacity is Q1 when discharged at a rate of 0.1C to 2.5V, and the discharge capacity is Q2 when discharged at a rate of 10C to 2.5V; the retention rate of the discharge capacity Q2 / Q1 is ≥70%.

11. The lithium-ion battery according to any one of claims 7 to 10, characterized in that, The capacity attenuation rate of the lithium ion battery is less than 20% after 1000 cycles at a rate of 1C at 25°C.

12. An electrical device, characterized by The lithium ion battery as claimed in any one of claims 7 to 11 is included.

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