Polymer bonding microsphere, bonding microsphere dispersion liquid as well as preparation method and application of polymer bonding microsphere dispersion liquid

Abstract

The invention provides a polymer bonding microsphere, a bonding microsphere dispersion liquid and a preparation method and application thereof. The D50 particle size of the polymer bonding microspheres is 1-10 microns, the P value is less than or equal to 0.3, the glass transition temperature is 30-90 DEG C, the electrolyte swelling ratio is less than or equal to 150%, and the P value is equal to (sigma / d) 2 / [1 + (sigma / d) 2]; sigma is the standard deviation of the diameter of the polymer bonded microspheres, and d is the average diameter of the polymer bonded microspheres. The polymer bonding microspheres provided by the invention are good in particle size uniformity, the lithium battery diaphragm containing the polymer bonding microspheres is relatively high in bonding force with a positive plate and a negative plate, and a lithium battery containing the lithium battery diaphragm is low in internal resistance, good in cycling stability and good in bonding effect with the positive plate and the negative plate; the bonding microsphere dispersion liquid containing the polymer bonding microsphere has good stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery separators, and in particular relates to polymer bonded microspheres, a bonded microsphere dispersion, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery casing. The separator is a key internal component, separating the positive and negative electrodes and preventing contact and short circuits. Currently, separators used in lithium-ion batteries are typically polyolefin porous membranes, often coated with functional coatings to create composite separators. This improves heat resistance and adhesion, among other things, thereby enhancing lithium-ion battery performance. However, existing polymer binders in the art suffer from low bonding strength between the electrodes, resulting in poor performance in the resulting lithium-ion batteries, which needs further improvement.

[0003] Therefore, it is necessary to develop a polymer adhesive microsphere with good bonding effect with the positive and negative electrodes to improve the bonding effect and lithium-ion battery performance. Summary of the Invention

[0004] In response to the shortcomings of the prior art, the present invention provides a polymer-bonded microsphere dispersion, a preparation method, and applications thereof. The polymer-bonded microspheres exhibit good particle size uniformity, and a lithium battery separator containing the polymer-bonded microspheres exhibits high adhesion to positive and negative electrodes. A lithium battery containing the polymer-bonded microspheres exhibits low internal resistance, excellent cycle stability, and excellent adhesion to positive and negative electrodes. Furthermore, the polymer-bonded microsphere dispersion exhibits excellent stability.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides polymer-bonded microspheres, wherein the polymer-bonded microspheres have a D 50 The particle size is 1 to 10 μm (for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or 9 μm, etc.), the P value is ≤ 0.3 (for example, 0.03, 0.06, 0.09, 0.12, 0.15, 0.18, 0.21, 0.24 or 0.27, etc.), the glass transition temperature is 30 to 90° C. (for example, 40° C., 50° C., 60° C., 70° C. or 80° C., etc.), and the electrolyte swelling rate is ≤ 150% (for example, 20%, 40%, 60%, 80%, 100%, 120% or 140%, etc.), wherein the P value = (σ / d)2 / [1+(σ / d)2]; σ is the standard deviation of the diameter of the polymer-bonded microspheres, and d is the average diameter of the polymer-bonded microspheres.

[0007] In the present invention, the polymer adhesive microspheres have a P value of ≤0.3 and good particle size uniformity. On the one hand, the polymer adhesive microspheres with uniform particle size help increase the contact points between the polymer adhesive microspheres and the electrode, further improving the adhesion between the polymer adhesive microspheres and the electrode. On the other hand, the polymer adhesive microspheres with uniform particle size are monodispersed and uniformly distributed on the surface of the lithium battery separator, reducing the risk of substrate pore blockage, increasing the permeability of the lithium battery separator, ensuring the smooth shuttle of lithium ions between the pores of the lithium battery separator, reducing the internal resistance of the lithium battery, and further improving the electrochemical performance of the lithium battery. In addition, the polymer adhesive microspheres with uniform particle size can improve the thickness consistency of the prepared lithium battery separator. The battery cell design and manufacturing end is reflected in the fact that the battery cell process design is highly consistent with the actual height, reducing the design deviation caused by the excessive thickness of the lithium battery separator, improving the efficiency of the core preparation on the manufacturing end, significantly improving the yield rate, and reducing manufacturing costs.

[0008] In the present invention, the P value can be used to reflect the width and uniformity of the particle size distribution. A smaller P value indicates a narrower particle size distribution and more uniform size; a larger value indicates a wider particle size distribution and more uneven size. When the P value of the polymer-bonded microspheres is ≤0.3, the polymer-bonded microspheres have high particle size uniformity.

[0009] In a second aspect, the present invention provides a dispersion of bonded microspheres, the dispersion comprising the polymer bonded microspheres as described in the first aspect;

[0010] The raw materials for preparing the adhesive microsphere dispersion do not include a dispersant.

[0011] Preferably, the adhesive microsphere dispersion further comprises first main group metal ions.

[0012] Preferably, the concentration of the first main group metal ion is 0.001 to 1 g / L (eg, 0.05 g / L, 0.1 g / L, 0.3 g / L, 0.5 g / L, 0.7 g / L or 0.9 g / L, etc.), more preferably 0.01 to 0.5 g / L.

[0013] In the present invention, by controlling the concentration of the first main group metal ions in the adhesive microsphere dispersion within the range of 0.001 to 1 g / L, it is beneficial to the dispersion of the polymer adhesive microspheres on the one hand, and on the other hand, it is beneficial to reduce the OH in the system during battery application. - When the ions are controlled within a certain range, they are less likely to affect the activity of the electrode active materials, making the battery have better internal resistance and cycle performance.

[0014] Preferably, the mass percentage concentration of the polymer adhesive microspheres in the adhesive microsphere dispersion is 0.5% to 45% (eg, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, etc.).

[0015] It should be noted that in different application scenarios, those skilled in the art may use adhesive microsphere dispersions with different mass percentage concentrations as needed. However, when the mass percentage concentration of the polymer adhesive microspheres is too high, they are prone to agglomeration during the synthesis and storage process, resulting in an excessively wide particle size distribution, which increases the internal resistance of the battery and deteriorates the cycle when used in the battery. Controlling the mass percentage concentration of the polymer adhesive microspheres in the adhesive microsphere dispersion within the range of 0.5% to 45% is beneficial to simplifying the pulping steps in different scenarios, and at the same time, can enable the battery to have better cycle characteristics when used.

[0016] Preferably, the adhesive microsphere dispersion further comprises a dispersion medium.

[0017] Preferably, the dispersion medium comprises water.

[0018] Preferably, the water comprises deionized water.

[0019] In a third aspect, the present invention provides a method for preparing the adhesive microsphere dispersion according to the second aspect, the preparation method comprising the following steps:

[0020] (1) mixing an initiator, a dispersion medium, and a first mixed monomer, wherein the mass of the first mixed monomer is 1% to 30% (e.g., 3%, 6%, 9%, 12%, 15%, 18%, 21%, 24%, or 27%) based on the total mass of the initiator, the dispersion medium, and the first mixed monomer as 100%, and reacting to obtain a first dispersion;

[0021] (2) adding the second mixed monomer dropwise to the first dispersion prepared in step (1), reacting to obtain the adhesive microsphere dispersion;

[0022] The first mixed monomer and the second mixed monomer each independently include the following components in mass percentage: 40% to 95% (for example, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%) of hard monomers, 4% to 40% (for example, 5%, 10%, 15%, 20%, 25%, 30% or 35%) of soft monomers, 0.5% to 10% (for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%) of functional monomers and 0.5% to 10% (for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%) of cross-linking monomers.

[0023] In the present invention, no dispersant needs to be added during the preparation of the adhesive microsphere dispersion, which avoids the dispersant hindering the functional groups of the polymer adhesive microspheres from directly contacting the pole pieces, effectively improving the adhesion between the lithium battery separator and the positive and negative pole pieces.

[0024] In the present invention, in step (1), the weight of the first mixed monomer is 1% to 30%, based on the total weight of the initiator, dispersion medium, and first mixed monomer as 100%, which facilitates better control of the particle size and P value of the polymer particles. If the weight of the first mixed monomer is greater than 30%, it is likely to lead to the formation of agglomerates during the synthesis process, resulting in a large particle size and a wide distribution, which cannot meet application requirements.

[0025] In the prior art, the polymer particles prepared by suspension polymerization are relatively large, generally >50μm; the polymer particles prepared by emulsion polymerization are relatively small, generally <1μm; and the microsphere particles prepared by microsuspension polymerization can have a particle size distribution in the range of 1 to 50μm, but the size distribution of the prepared microsphere particles is uneven, and the P value is often greater than 0.3. In order to address the shortcomings of the prior art, the present invention adopts a dispersant-free aqueous precipitation polymerization method and a two-step addition of polymerization monomers to prepare D 50 The polymer adhesive microspheres have a particle size of 1 to 10 μm, a P value of ≤0.3, and good particle size uniformity. In the preparation method of the adhesive microsphere dispersion, in step (1), the monomer concentration of the reaction system is low, so that the reaction rate of the system is slow, and primary particles with uniform size and controllable particle size can be obtained. The particle size distribution of the primary particles is controlled to be 0.2 to 5 μm, and the P value is ≤0.05; in step (2), the second mixed monomer is gradually or continuously added dropwise, so that the reaction product of the second mixed monomer grows and precipitates uniformly on the surface of the primary particles, forming polymer adhesive microspheres with good size uniformity. 50 The particle size is controllable and adjustable in the range of 1 to 10 μm, and the P value is ≤ 0.3.

[0026] Preferably, based on the total mass of the initiator, the dispersion medium and the first mixed monomer being 100%, the mass of the first mixed monomer is 1% to 25%.

[0027] Preferably, after the reaction in step (2), a base containing a first main group metal ion is added to neutralize the mixture to a pH of 6 to 8, such as 6.2, 6.4, 6.6, 6.8, 7.0, 7.2, 7.4, 7.6 or 7.8.

[0028] Preferably, the base containing a first main group metal ion comprises lithium hydroxide.

[0029] Preferably, the reactions in step (1) and step (2) are carried out under a nitrogen atmosphere.

[0030] Preferably, the reaction temperature of step (1) and step (2) is independently 55 to 85°C, such as 60°C, 65°C, 70°C, 75°C or 80°C.

[0031] Preferably, the reaction time of step (1) and step (2) is independently 3 to 20 h, for example, 5 h, 7 h, 9 h, 11 h, 13 h, 15 h, 17 h or 19 h.

[0032] Preferably, the dripping time in step (2) is 6 to 20 hours, for example, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours or 18 hours.

[0033] Preferably, based on the total mass of the first mixed monomer and the second mixed monomer as 100%, the mass of the initiator is 0.2% to 10% (for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, etc.).

[0034] Preferably, based on the total mass of the first mixed monomer and the second mixed monomer as 100%, the mass of the second mixed monomer is 5% to 95% (for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, etc.).

[0035] Preferably, the functional monomer comprises a dispersing monomer.

[0036] Preferably, the functional monomer further includes a viscosity-increasing monomer.

[0037] The present invention adopts a dispersant-free aqueous precipitation polymerization method, with hard monomers, soft monomers, dispersing monomers and cross-linking monomers as reaction monomers, and can also add viscosity-increasing monomers to prepare polymer adhesive microspheres with uniform particle size, which have groups with bonding and dispersing functions on the surface. On the one hand, the interaction force between the polymer adhesive microspheres and the ceramic particles and the components in the electrode is improved, thereby improving the adhesion; on the other hand, the dispersion stability of the polymer adhesive microspheres in the adhesive microsphere dispersion is improved, forming a self-dispersing stable suspension, avoiding the problem of sedimentation and agglomeration after long-term standing, which is difficult to disperse and affects subsequent processing and use. The present invention improves the problem of low adhesion caused by the presence of dispersants or emulsifiers in traditional adhesive microsphere dispersions, which greatly hinders the interaction force between the surface groups of the polymer adhesive microspheres and the ceramic particles and the components in the electrode.

[0038] In the present invention, the viscosity-increasing monomer contains any one of a hydroxyl group, a carboxyl group, an epoxy group, an ester group or a silane group, and can increase the adhesion between the battery separator containing the polymer adhesive microspheres and the battery pole piece.

[0039] Preferably, the mass ratio of the dispersing monomer to the viscosity-increasing monomer is 1:10 to 5:1, for example, 1:8, 1:6, 1:4, 1:2, 1:1, 2:1, 3:1 or 4:1, and more preferably 1:5 to 4:1.

[0040] Preferably, the initiator includes any one or a combination of at least two of a persulfate initiator, a peroxide initiator, an azo initiator or a redox system initiator.

[0041] Preferably, the persulfate initiator comprises persulfate.

[0042] Preferably, the persulfate includes any one of sodium persulfate, potassium persulfate or ammonium persulfate, or a combination of at least two of them.

[0043] Preferably, the peroxide initiator includes any one of hydrogen peroxide, benzoyl peroxide or lauroyl peroxide, or a combination of at least two thereof.

[0044] Preferably, the azo initiator includes any one of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile or dimethyl azobisisobutyrate, or a combination of at least two thereof.

[0045] Preferably, the redox system initiator includes any one or a combination of at least two of persulfate-thiosulfate, azobisisobutylamidine hydrochloride (V-50 initiator), azobisisobutylimidazoline hydrochloride (VA-044 initiator), azobisisobutylimidazoline (VA061 initiator) or azobiscyanovaleric acid.

[0046] Preferably, the hard monomer includes any one or a combination of at least two of methyl methacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, vinyl acetate, styrene, methyl acrylate, butyl methacrylate, tert-butyl acrylate, 4-tert-butylcyclohexyl acrylate, isobornyl methacrylate, cyclohexyl methacrylate, dicyclopentenyl acrylate, stearic acid methacrylate, isobornyl acrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate or tetrahydrofurfuryl acrylate.

[0047] In the present invention, the glass transition temperature of the hard monomer is ≥0°C and ≤150°C.

[0048] Preferably, the soft monomer includes any one or a combination of at least two of ethyl acrylate, propyl acrylate, butyl acrylate, isooctyl acrylate, n-octyl acrylate, butyl methacrylate, hexyl acrylate, lauryl methacrylate, hexyl acrylate, heptyl acrylate, n-octyl methacrylate, isooctyl methacrylate, propoxylated nonylphenol acrylate, lauric acrylate, lauric methacrylate, isodecyl methacrylate, ethoxyethoxyethyl acrylate, 2-hydroxyethyl methacrylate phosphate, 2-ethylhexyl methacrylate or isodecyl acrylate.

[0049] In the present invention, the glass transition temperature of the soft monomer is ≥-80°C and <0°C.

[0050] In the present invention, the glass transition temperature of the final synthetic product can be regulated by selecting specific soft monomers and hard monomers and controlling their glass transition temperatures within a specific range.

[0051] Preferably, the dispersing monomer includes any one or a combination of at least two of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, acrylamide, hydroxymethyl acrylamide, N-vinyl pyrrolidone, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polyethylene glycol monomethacrylate, styrene sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, (meth)acrylic acid-2-sulfonic acid ethyl ester, stearic acid acrylate, polyethylene glycol diacrylate, polyethylene glycol or methoxy polyethylene glycol methacrylate.

[0052] Preferably, the polyethylene glycol dimethacrylate comprises polyethylene glycol (480) dimethacrylate.

[0053] In the present invention, the molecular weight of the polyethylene glycol molecule in the polyethylene glycol (480) dimethacrylate is 480.

[0054] Preferably, the viscosity-increasing monomer includes any one of ethyl acetoacetate methacrylate, glycidyl methacrylate, dimethylaminoethyl methacrylate, vinylsiloxane silane, vinyltriisopropoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltris(β-trimethoxyethoxysilane), hydroxyethyl acrylate, hydroxyethyl methacrylate, β-hydroxypropyl acrylate, β-hydroxypropyl methacrylate or phenyl glycidyl ether acrylate, or a combination of at least two thereof.

[0055] Preferably, the vinylsiloxane silane includes any one of vinyltrimethoxysilane, vinyltriethoxysilane or vinyltris(2-methoxyethoxy) or a combination of at least two thereof.

[0056] Preferably, the cross-linking monomer includes any one or a combination of at least two of divinylbenzene, ethylene glycol dimethacrylate, N-hydroxymethyl acrylamide, N-(isobutoxymethyl) acrylamide, acrylamide, diallyl phthalate, trimethylolpropane triacrylate, triallyl isocyanurate, allyl methacrylate, diacetone acrylamide, diethylene glycol diacrylate, N-ethyl acrylamide, N-(butoxymethyl) acrylamide or N-butyl acrylamide.

[0057] In a fourth aspect, the present invention provides a lithium battery separator coating slurry, which comprises any one of the polymer bonded microspheres described in the first aspect, the bonded microsphere dispersion described in the second aspect, or the bonded microsphere dispersion prepared by the preparation method described in the third aspect.

[0058] In a fifth aspect, the present invention provides a lithium battery separator, comprising a substrate and a coating coated on at least one side of the substrate, wherein the coating contains the polymer bonded microspheres as described in the first aspect or the coating is prepared from the lithium battery separator coating slurry as described in the fourth aspect.

[0059] Preferably, the substrate includes any one of a PP base film, a PE base film or a PP\PE composite film.

[0060] Preferably, the cold pressing bonding strength between the lithium battery separator and the positive electrode sheet or the negative electrode sheet is ≥1 N / m (for example, 1.5 N / m, 2 N / m, 2.5 N / m, 3 N / m or 3.5 N / m, etc.).

[0061] Preferably, the hot pressing bonding strength between the lithium battery separator and the positive electrode sheet or the negative electrode sheet is ≥5N / m (for example, 5.5N / m, 6N / m, 6.5N / m, 7N / m, 7.5N / m, 8N / m or 8.5N / m, etc.).

[0062] In a sixth aspect, the present invention provides a lithium battery, comprising the lithium battery separator as described in the fifth aspect.

[0063] Preferably, the lithium battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and the lithium battery separator as described in the fifth aspect.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The polymer bonded microspheres of the present invention have a D 50 The particle size is 1 to 10 μm, the P value is ≤0.3, the particle size uniformity is good, the lithium battery separator containing the polymer adhesive microspheres has high adhesion to the positive and negative electrode sheets whether at room temperature or under hot pressing, and the lithium battery containing the lithium battery separator has low internal resistance and good cycle stability; no dispersant needs to be added during the preparation process of the adhesive microsphere dispersion, the adhesive microsphere dispersion has good stability, and there is no obvious stratification and sedimentation after standing for one month, which is conducive to subsequent processing and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a SEM image of polymer-bonded microspheres in the bonded microsphere dispersion provided in Example 1;

[0067] Figure 2The particle size distribution diagram of the polymer bonded microspheres in the bonded microsphere dispersion provided in Example 1;

[0068] Figure 3 This is a schematic diagram of the structure of the lithium battery separator provided in Example 1, which is attached to the positive electrode sheet and the negative electrode sheet;

[0069] Among them, 1-polymer bonded microspheres; 2-ceramic particles; 3-positive electrode plate; 4-first coating layer; 5-substrate layer; 6-second coating layer; 7-negative electrode plate;

[0070] Figure 4 This is a particle size distribution diagram of polymer bonded microspheres in the bonded microsphere dispersion provided in Comparative Example 1;

[0071] Figure 5 This is the SEM image of the polymer bonded microspheres in the bonded microsphere dispersion provided in Comparative Example 1. DETAILED DESCRIPTION

[0072] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0073] Some of the components used in the following examples, comparative examples and performance tests are as follows.

[0074] Example 1

[0075] This embodiment provides a dispersion of adhesive microspheres, a lithium battery separator, and a lithium battery. The adhesive microsphere dispersion includes polymer adhesive microspheres.

[0076] The adhesive microsphere dispersion is prepared by the following method:

[0077] (1) Add 562 parts of dispersion medium (deionized water) and 1 part of initiator (sodium persulfate) into a reactor, stir evenly, add the first mixed monomer, flow nitrogen for 30 minutes, rotate at 400 rpm, heat to 70°C and react for 5 hours to obtain a first dispersion;

[0078] The first mixed monomer is a mixture of 67 parts of a hard monomer (acrylonitrile), 28 parts of a soft monomer (butyl acrylate), 3 parts of a dispersing monomer (acrylic acid) and 2 parts of a crosslinking monomer (divinylbenzene).

[0079] (2) The second mixed monomer was continuously added dropwise to the first dispersion prepared in step (1) for 8 hours, and the mixture was kept at 75° C. for 2 hours. A lithium hydroxide aqueous solution (the mass percentage of lithium hydroxide was 1%) was added to neutralize the mixture to a pH of 7 to obtain the bonded microsphere dispersion. The SEM image of the polymer bonded microspheres in the bonded microsphere dispersion is shown in FIG. Figure 1 As shown, the particle size distribution is Figure 2 shown.

[0080] The second mixed monomer is a mixture of 67 parts of a hard monomer (acrylonitrile), 28 parts of a soft monomer (butyl acrylate), 1.5 parts of a dispersing monomer (acrylic acid), 1.5 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 2 parts of a crosslinking monomer (divinylbenzene).

[0081] The lithium battery separator, such as Figure 3 As shown, it includes a first coating layer 4, a substrate layer 5 and a second coating layer 6 stacked in sequence, and the substrate layer 5 is a PE base film with a thickness of 7 μm.

[0082] The lithium battery separator is prepared by the following method: 500 parts of deionized water, 40 parts of sodium carboxymethyl cellulose dispersion (solid content of 0.4%), 10 parts of sodium polyacrylate dispersant (purchased from Lubrizol, molecular weight 4000), and 10 parts of styrene-butadiene aqueous solution (purchased from Japan Zeon Co., Ltd., BM-451B, solid content of 40%) are stirred at 800 rpm for 20 minutes, 120 parts of ceramic particles (aluminum oxide, particle size 0.4 μm) are added, and the mixture is stirred at a high speed of 1200 rpm for 30 minutes, and finally 60 parts of the above-mentioned adhesive microsphere dispersion are added, and the mixture is stirred at 800 rpm for 30 minutes to obtain a composite coating slurry; the composite coating slurry is evenly coated on both sides of the substrate layer by gravure roller coating, and the single-side coating amount is 0.35 g / m 2 , coating thickness 2 μm, drying, to obtain the lithium battery separator.

[0083] The lithium battery is prepared by the following method:

[0084] The positive electrode sheet, the above-mentioned lithium battery separator, and the negative electrode sheet are stacked in order, so that the lithium battery separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare battery cell, the electrode ears are welded to the bare battery cell, and the bare battery cell is transferred to an aluminum shell and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged lithium battery, which is then subjected to the steps of standing, hot and cold pressing, forming and shaping in sequence to obtain the lithium battery. The preparation method of the above-mentioned positive electrode sheet is as follows: nickel cobalt manganese (NCM) ternary material, conductive agent (carbon black), adhesive polyvinylidene fluoride (purchased from Arkema, HSV900) and N-methyl pyrrolidone are stirred and mixed in a weight ratio of 97.34:28.86:2.7:1.1 to obtain a positive electrode slurry, and then the positive electrode slurry is evenly coated on the positive electrode collector (aluminum foil), and then dried, cold pressed, and cut to obtain a positive electrode sheet; the preparation method of the above-mentioned negative electrode sheet is as follows: active material (artificial graphite), conductive agent (carbon black), adhesive styrene butadiene rubber (purchased from Japan Zeon Co., Ltd., BM-451B), thickening agent The electrolyte is prepared as follows: in an argon atmosphere glove box (H2O < 0.1ppm, O2 < 0.1ppm), ethylene carbonate (EC) and ethyl methyl carbonate are mixed in a volume ratio of 3 / 7, LIPF6 is added and stirred to dissolve, and the electrolyte is obtained. The mass percentage of LiPF6 in the electrolyte is 12.5%.

[0085] Examples 2 to 13

[0086] Examples 2 to 13 respectively provide a bonding microsphere dispersion, a lithium battery separator, and a lithium battery. The bonding microsphere dispersion includes polymer bonding microspheres. The difference between the bonding microsphere dispersion and Example 1 is only that the added raw materials and their contents are different, as shown in Tables 1 and 2 in parts by weight.

[0087] Table 1

[0088]

[0089]

[0090] In Table 1, “ / ” represents that the component was not added.

[0091] Table 2

[0092]

[0093]

[0094] In Table 2, “ / ” represents that the component was not added.

[0095] Example 14

[0096] This embodiment provides a dispersion of adhesive microspheres, a lithium battery separator, and a lithium battery. The only difference between this embodiment and embodiment 1 is that the dispersion of adhesive microspheres is prepared by the following method:

[0097] (1) Add 558 parts of the dispersion medium (deionized water) and 1 part of the initiator (azobisisobutyronitrile) into a reactor, stir evenly, add the first mixed monomer, flow nitrogen for 30 minutes, rotate at 400 rpm, heat to 85°C and react for 5 hours to obtain a first dispersion;

[0098] The first mixed monomer is a mixture of 33.5 parts of a hard monomer (acrylonitrile), 14 parts of a soft monomer (butyl acrylate), 1.5 parts of a dispersing monomer (acrylic acid) and 1 part of a crosslinking monomer (divinylbenzene).

[0099] (2) continuously adding the second mixed monomer to the first dispersion prepared in step (1) for 16 hours, keeping the mixture at 75° C. for 2 hours, and neutralizing the mixture with a lithium hydroxide aqueous solution (the mass percentage of lithium hydroxide is 1%) to a pH of 6.5 to obtain the adhesive microsphere dispersion;

[0100] The second mixed monomer is a mixture of 100.5 parts of a hard monomer (acrylonitrile), 42 parts of a soft monomer (butyl acrylate), 2.25 parts of a dispersing monomer (acrylic acid), 2.25 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 3 parts of a crosslinking monomer (divinylbenzene).

[0101] Other conditions are the same as in Example 1.

[0102] Example 15

[0103] This embodiment provides a separator-bonded microsphere particle dispersion, a lithium battery separator, and a lithium battery. The separator-bonded microsphere particle dispersion is prepared by the following method:

[0104] (1) Add 558 parts of dispersion medium (deionized water) and 1 part of initiator (sodium persulfate) into a reactor, stir evenly, add the first mixed monomer, pass nitrogen for 30 minutes, rotate at 400 rpm, heat to 55°C and react for 5 hours to obtain a first dispersion;

[0105] The first mixed monomer is a mixture of 100.5 parts of a hard monomer (acrylonitrile), 42 parts of a soft monomer (butyl acrylate), 4.5 parts of a dispersing monomer (acrylic acid) and 3 parts of a crosslinking monomer (divinylbenzene).

[0106] (2) continuously adding the second mixed monomer to the first dispersion prepared in step (1) for 6 hours, keeping the mixture at 70° C. for 2 hours, and neutralizing the mixture with a lithium hydroxide aqueous solution (the mass percentage of lithium hydroxide is 1%) to a pH of 7 to obtain the bonded microsphere particle dispersion;

[0107] The second mixed monomer is a mixture of 33.5 parts of a hard monomer (acrylonitrile), 14 parts of a soft monomer (butyl acrylate), 0.75 parts of a dispersing monomer (acrylic acid), 0.75 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 1 part of a crosslinking monomer (divinylbenzene).

[0108] Other conditions are the same as in Example 1.

[0109] Example 16

[0110] This embodiment provides a bonded microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between this embodiment and Example 1 is that no lithium hydroxide aqueous solution is added, and other conditions are the same as those in Example 1.

[0111] Example 17

[0112] This embodiment provides a bonding microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between this embodiment and embodiment 1 is that step (2) adds lithium hydroxide aqueous solution to a pH of 10 so that the concentration of lithium metal ions in the obtained bonding microsphere dispersion is 1.503 g / L. Other conditions are the same as those in embodiment 1.

[0113] Example 18

[0114] This embodiment provides a bonding microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between the embodiment 1 is that the 3 parts by weight of the dispersing monomer (acrylic acid) in step (1) is replaced with 0.5 parts by weight of the dispersing monomer (acrylic acid) and 2.5 parts by weight of the viscosity-increasing monomer (glycidyl methacrylate); the weight of the dispersing monomer (acrylic acid) in step (2) is adjusted to 0.5 parts, and the weight of the viscosity-increasing monomer (glycidyl methacrylate) is adjusted to 2.5 parts. The mass ratio of the dispersing monomer to the viscosity-increasing monomer is 1:5. The other conditions are the same as those in embodiment 1.

[0115] Example 19

[0116] This embodiment provides a bonding microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between the embodiment 1 and the embodiment 1 is that the 3 parts by weight of the dispersing monomer (acrylic acid) in step (1) is replaced with 2.4 parts by weight of the dispersing monomer (acrylic acid) and 0.6 parts by weight of the viscosity-increasing monomer (glycidyl methacrylate); the parts by weight of the dispersing monomer (acrylic acid) in step (2) are adjusted to 2.4 parts, and the parts by weight of the viscosity-increasing monomer (glycidyl methacrylate) are adjusted to 0.6 parts. The mass ratio of the dispersing monomer to the viscosity-increasing monomer is 4:1. The other conditions are the same as those in embodiment 1.

[0117] Comparative Example 1

[0118] This comparative example provides a bonded microsphere dispersion, a lithium battery separator, and a lithium battery. The difference between this comparative example and Example 1 is that the bonded microsphere dispersion is prepared by the following method:

[0119] 562 parts of a dispersion medium (deionized water) and 1 part of an initiator (sodium persulfate) were added to a reaction kettle, stirred evenly, and the mixed monomers were added. Nitrogen was passed through the reaction kettle for 30 minutes at a speed of 400 rpm, and the temperature was raised to 70° C. for reaction for 5 hours. A lithium hydroxide aqueous solution (lithium hydroxide having a mass percentage of 1%) was added to neutralize the mixture to a pH of 7 to obtain the adhesive microsphere dispersion.

[0120] The mixed monomer is a mixture of 134 parts of a hard monomer (acrylonitrile), 56 parts of a soft monomer (butyl acrylate), 4.5 parts of a dispersing monomer (acrylic acid), 1.5 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 4 parts of a crosslinking monomer (divinylbenzene).

[0121] Other conditions are the same as in Example 1.

[0122] Comparative Example 2

[0123] This comparative example provides a bonded microsphere dispersion, a lithium battery separator, and a lithium battery. The difference between this comparative example and Example 1 is that the weight portion of the dispersion medium (deionized water) is adjusted to 188 parts, and other conditions are the same as those in Example 1.

[0124] Comparative Example 3

[0125] This comparative example provides a bonded microsphere dispersion, a lithium battery separator and a lithium battery. The only difference between it and Example 1 is that the weight fraction of the hard monomer (acrylonitrile) in the first mixed monomer is adjusted to 35 parts, and the weight fraction of the soft monomer (butyl acrylate) is adjusted to 60 parts; the weight fraction of the hard monomer (acrylonitrile) in the second mixed monomer is adjusted to 35 parts, and the weight fraction of the soft monomer (butyl acrylate) is adjusted to 60 parts. Other conditions are the same as in Example 1.

[0126] Comparative Example 4

[0127] This comparative example provides a bonded microsphere dispersion, a lithium battery separator and a lithium battery. The only difference between it and Example 1 is that the weight fraction of the hard monomer (acrylonitrile) in the first mixed monomer is adjusted to 92 parts, and the weight fraction of the soft monomer (butyl acrylate) is adjusted to 3 parts; the weight fraction of the hard monomer (acrylonitrile) in the second mixed monomer is adjusted to 92 parts, and the weight fraction of the soft monomer (butyl acrylate) is adjusted to 3 parts. Other conditions are the same as in Example 1.

[0128] Comparative Example 5

[0129] This comparative example provides a bonded microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between the comparative example and Example 1 is that the weight fraction of the dispersing monomer (acrylic acid) in the first mixed monomer is adjusted to 0.40 parts. To ensure that the total mass of the first mixed monomer remains unchanged, the other components in the first mixed monomer are increased proportionally. The first mixed monomer is a mixture of 68.80 parts of a hard monomer (acrylonitrile), 28.75 parts of a soft monomer (butyl acrylate), 0.4 parts of a dispersing monomer (acrylic acid), and 2.05 parts of a cross-linking monomer (divinylbenzene).

[0130] The weight fraction of the dispersing monomer (acrylic acid) in the second mixed monomer is adjusted to 0.20 parts. In order to ensure that the total mass of the second mixed monomer remains unchanged, the other components in the second mixed monomer are increased proportionally. The second mixed monomer is a mixture of 67.88 parts of a hard monomer (acrylonitrile), 28.37 parts of a soft monomer (butyl acrylate), 0.20 parts of a dispersing monomer (acrylic acid), 1.52 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 2.03 parts of a cross-linking monomer (divinylbenzene).

[0131] Other conditions are the same as in Example 1.

[0132] Comparative Example 6

[0133] This comparative example provides a bonded microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between the comparative example and Example 1 is that the weight fraction of the dispersing monomer (acrylic acid) in the first mixed monomer is adjusted to 11 parts. To ensure that the total mass of the first mixed monomer remains unchanged, the other components in the first mixed monomer are reduced proportionally. The first mixed monomer is a mixture of 61.47 parts of a hard monomer (acrylonitrile), 25.69 parts of a soft monomer (butyl acrylate), 11.00 parts of a dispersing monomer (acrylic acid), and 1.84 parts of a cross-linking monomer (divinylbenzene).

[0134] The weight proportion of the dispersing monomer (acrylic acid) in the second mixed monomer is adjusted to 5.50 parts. To ensure that the total mass of the second mixed monomer remains unchanged, the other components in the second mixed monomer are reduced proportionally. The second mixed monomer is a mixture of 64.28 parts of a hard monomer (acrylonitrile), 26.86 parts of a soft monomer (butyl acrylate), 5.5 parts of a dispersing monomer (acrylic acid), 1.44 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 1.92 parts of a cross-linking monomer (divinylbenzene).

[0135] Other conditions are the same as in Example 1.

[0136] Comparative Example 7

[0137] This comparative example provides a bonded microsphere dispersion, a lithium battery separator, and a lithium battery. The only difference between the comparative example and Example 1 is that the weight fraction of the cross-linking monomer (divinylbenzene) in the first mixed monomer is adjusted to 0.40 parts. In order to ensure that the total mass of the first mixed monomer remains unchanged, the other components in the first mixed monomer are increased proportionally. The first mixed monomer is a mixture of 68.09 parts of a hard monomer (acrylonitrile), 28.46 parts of a soft monomer (butyl acrylate), 3.05 parts of a dispersing monomer (acrylic acid), and 0.40 parts of a cross-linking monomer (divinylbenzene).

[0138] The weight fraction of the dispersing monomer (acrylic acid) in the second mixed monomer is adjusted to 0.40 parts. In order to ensure that the total mass of the second mixed monomer remains unchanged, the other components in the second mixed monomer are increased proportionally. The second mixed monomer is a mixture of 68.09 parts of a hard monomer (acrylonitrile), 28.46 parts of a soft monomer (butyl acrylate), 1.52 parts of a dispersing monomer (acrylic acid), 1.52 parts of a viscosity-increasing monomer (glycidyl methacrylate) and 0.40 parts of a cross-linking monomer (divinylbenzene).

[0139] Other conditions are the same as in Example 1.

[0140] Comparative Example 8

[0141] This comparative example provides a bonding microsphere dispersion, a lithium battery separator, and a lithium battery. The difference between this comparative example and Example 1 is that step (1) in the preparation method of the bonding microsphere dispersion is adjusted as follows:

[0142] (1) 558 parts of a dispersion medium (deionized water), 1 part of a dispersant (PVA1788, molecular weight 74800), and 1 part of an initiator (sodium persulfate) were added to a reactor, stirred evenly, and the first mixed monomer was added. Nitrogen was passed through the reactor for 30 minutes at a speed of 400 rpm, and the temperature was raised to 70°C for reaction for 5 hours to obtain a first dispersion liquid.

[0143] The first mixed monomer is a mixture of 67 parts of a hard monomer (acrylonitrile), 28 parts of a soft monomer (butyl acrylate), 3 parts of a dispersing monomer (acrylic acid) and 2 parts of a crosslinking monomer (divinylbenzene).

[0144] Other conditions are the same as in Example 1.

[0145] Performance Testing

[0146] The following tests were performed on the adhesive microsphere dispersions provided in Examples 1-15 and Comparative Examples 1-8.

[0147] (1) Glass transition temperature (Tg): The adhesive microsphere dispersion was made into a thin film and dried to constant weight. The glass transition temperature was measured using a differential scanning calorimeter.

[0148] (2)D 50 Particle size: 0.1 ml of a 25% solids dispersion of polymeric ...

[0149] (3) Field Emission Scanning Electron Microscope (SEM) Test: 1 ml of a 25% solids polymer microsphere dispersion was added to 40 ml of deionized water and dispersed under ultrasonic vibration for 20 min. The dispersion was then dropped onto a clean silicon wafer using a disposable pipette and vacuum dried for at least 3 h. The wafer was then placed on a sample stage for testing. At the same time, 50 particles were collected to measure particle size. The P value was calculated from the 50 particle size data: P value = (σ / d)² / [1+(σ / d)²], where σ is the standard deviation of the diameter of the polymer microspheres and d is the average diameter of the polymer microspheres.

[0150] (4) Swelling rate: The adhesive microsphere dispersion was made into a film and dried to constant weight, cut into circular slices with a diameter of 20 mm, and the weight was recorded as W0. The film was immersed in an electrolyte (composed of ethylene carbonate, ethyl methyl carbonate, and LiPF6, with a volume ratio of ethylene carbonate and ethyl methyl carbonate of 3 / 7, and the mass percentage of LiPF6 in the electrolyte was 12.5%). After 24 hours, the film was taken out, the electrolyte on the surface was wiped dry, and the film was weighed and recorded as W1. Swelling rate = (W1-W0) / W0×100%.

[0151] (4) Stability: Place the adhesive microsphere dispersion at 25°C for 1 month and observe whether there is stratification and sedimentation.

[0152] The test results are shown in Table 3.

[0153] The lithium battery separators provided in Examples 1-15 and Comparative Examples 1-8 were subjected to the following tests.

[0154] (1) Air permeability: According to the method of GB / T 36363-2018, the air permeability tester EG01-55-1MR is used for the measurement. The principle of the pressure difference method is as follows: in an environment with a humidity of 40RH% and a temperature of 25℃, the sample to be tested is placed between the upper and lower test chambers and clamped and sealed. According to the sample under a pressure difference of 1.21kPa, the sample passes through 6.45cm 2 The time required for 100ml of gas to pass through an area is used to test the Gurley value. The average value of 10 data points is taken for each sample to obtain the air permeability.

[0155] (2) Ionic conductivity: The lithium battery membrane was assembled into a stainless steel-to-stainless steel button symmetrical battery. The electrolyte consisted of ethylene carbonate, ethyl methyl carbonate, and LiPF6. The volume ratio of ethylene carbonate to ethyl methyl carbonate was 3 / 7. The mass percentage of LiPF6 in the electrolyte was 12.5%. The sealed button symmetrical battery was subjected to EIS test. The EIS test parameters were set. The test parameters were consistent with those of conventional symmetrical batteries, with a frequency of 1 Hz to 500 kHz. The ionic conductivity of the lithium battery membrane was then calculated according to the formula: ionic conductivity = L / RA. Wherein L is the thickness of the lithium battery membrane (in cm), R is the resistance of the lithium battery membrane (in mΩ), and A is the area of the electrode (in cm). 2 ), which is the actual effective contact area between stainless steel and lithium battery separator.

[0156] (3) Cold pressure bonding strength and hot pressure bonding strength:

[0157] Cold pressing preparation: The positive electrode sheet provided in Preparation Example 1 or the negative electrode sheet provided in Preparation Example 2 is pressed together with the lithium battery separator at room temperature (25°C) with a pressing pressure of 7 MPa and a pressing time of 15 seconds to obtain a cold pressed electrode sheet.

[0158] Hot pressing preparation: The positive electrode sheet provided in Preparation Example 1 or the negative electrode sheet provided in Preparation Example 2 was pressed together with the lithium battery separator at 70°C, with a pressing pressure of 3 MPa and a pressing time of 3 seconds to obtain a hot pressed electrode sheet.

[0159] Adhesion test with positive and negative electrodes: The test is conducted in accordance with the national standard GB / T 2790-1995 "Adhesive 180° Peel Strength Test Method". The specific test process is as follows: a special double-sided tape with a width of 20mm and a length of 100mm is attached to a steel plate. Then, a 30mm wide and 100mm long cold-pressed electrode or hot-pressed electrode pattern is cut with a blade. One side of the positive electrode or negative electrode is attached to the double-sided tape. A paper tape with a width of the same width as the cold-pressed electrode or hot-pressed electrode pattern and a length of 250mm is inserted under the lithium battery separator and fixed with wrinkle glue.

[0160] Turn on the Sansi tensile testing machine (sensitivity is 1N), the indicator light will light up, adjust the limit block to the appropriate position, and fix the end of the steel plate without the electrode pattern with the lower clamp. Fold the paper tape upwards and fix it with the upper clamp. Use the "up" and "down" buttons on the manual controller included with the tensile testing machine to adjust the position of the upper clamp. Then perform the test and read the value. The force when the positive or negative electrode sheet and the lithium battery separator are peeled off and the force is divided by the width of the special double-sided tape to represent the bonding strength between the positive or negative electrode sheet and the lithium battery separator.

[0161] The test results are shown in Table 4.

[0162] The following performance tests were performed on lithium batteries assembled from the lithium battery separators provided in Examples 1-19 and Comparative Examples 1-8.

[0163] (1) Battery DC resistance (DCR) test: At 25°C, charge the lithium battery at a constant current of 1 / 3C to 4.35V, then charge it at a constant voltage of 4.35V to a current of 0.05C. After standing for 5 minutes, record the voltage V1. Then discharge it at 4C for 30 seconds, record the voltage V2, and then calculate the internal resistance of the battery after the first cycle (V2-V1) / 4C, which is recorded as DCR1.

[0164] (2) Battery capacity retention test: At 25°C, charge the lithium battery at a constant current of 1 / 3C to 4.35V, then charge it at a constant voltage of 4.35V to a current of 0.05C for 5 minutes, and then discharge it at 1 / 3C to 2.8V. The obtained capacity is recorded as the initial capacity C0. Repeat the above steps for the same lithium battery and record the discharge capacity C0 of the battery after the nth cycle. n , then the battery capacity retention rate P after each cycle n =C n / C0×100%, and the battery capacity retention rate after 500 cycles was obtained.

[0165] The test results are shown in Table 4 below.

[0166] Table 3

[0167]

[0168] Table 4

[0169]

[0170]

[0171] It can be seen from the contents of Tables 3 and 4 that the polymer adhesive microspheres provided in Examples 1-19 have good particle size uniformity, and the lithium battery separator containing the polymer adhesive microspheres has high adhesion to the positive and negative electrode sheets both at room temperature and under hot pressing; the adhesive microsphere dispersion has no obvious stratification and sedimentation after standing for 1 month, and has good stability, which is conducive to subsequent processing and use.

[0172] Compared with Example 1, if the lithium hydroxide aqueous solution is not added (Example 16), the internal resistance of the prepared lithium battery performance increases slightly and the battery capacity retention rate decreases slightly.

[0173] Compared with Example 1, if the concentration of lithium metal ions in the adhesive microsphere dispersion is too high (Example 17), the performance of the prepared lithium battery is reduced.

[0174] Compared with Example 1, if the one-step method is used to add the mixed monomer (Comparative Example 1) to prepare the bonded microsphere dispersion, the polymer bonded microspheres have a P value greater than 0.3, a wide particle size distribution, and poor stability. The SEM image is as follows: Figure 4 As shown in the particle size distribution diagram Figure 5 As shown in the figure, the air permeability, adhesion and lithium battery performance of the prepared lithium battery separator are all reduced. This is because the particle size uniformity is poor, only the larger particles contact and adhere to the electrode, and there are fewer bonding sites, which significantly reduces the adhesion to the electrode. In addition, smaller particles easily cause the pore structure of the substrate in the lithium battery separator to be blocked.

[0175] Compared with Example 1, if the total mass of the initiator, dispersion medium and first mixed monomer is 100%, the mass of the first mixed monomer is too high (Comparative Example 2), then the P value of the polymer bonded microspheres in the prepared polymer bonded microsphere dispersion is greater than 0.3, the particle size distribution becomes wider, the stability is poor, and the permeability, adhesion and lithium battery performance of the prepared lithium battery separator are reduced.

[0176] Compared with Example 1, if the weight fraction of the hard monomer (acrylonitrile) is too low and the weight fraction of the soft monomer (butyl acrylate) is too high (Comparative Example 3), the glass transition temperature of the prepared polymer bonded microspheres is lower than 30°C, and the adhesion performance is excellent, but the internal resistance of the prepared lithium battery separator increases significantly, and the cycle performance of the lithium battery decreases rapidly. This is because the glass transition temperature of the polymer bonded microspheres is low. After being compressed, the polymer bonded microspheres are easily deformed and blocked, resulting in the obstruction of the shuttle of lithium ions between the positive and negative electrodes and the deterioration of the electrochemical performance; if the weight fraction of the hard monomer (acrylonitrile) is too high and the weight fraction of the soft monomer (butyl acrylate) is too low (Comparative Example 4), the glass transition temperature of the prepared polymer bonded microspheres is higher than 90°C, and the adhesion to the positive and negative electrodes is significantly reduced, resulting in easy powder loss, and the adhesion effect with the positive and negative electrodes in the electrolyte state deteriorates, the internal resistance of the prepared lithium battery increases, and the cycle performance of the lithium battery deteriorates. It can be seen that the performance of the lithium battery produced when the glass transition temperature of the polymer bonded microspheres is within the range of 30 to 90°C is better.

[0177] Compared with Example 1, if the weight fraction of the functional monomer is too low (Comparative Example 5), the particle size of the prepared polymer bonded microspheres is larger, which will cause the coated lithium battery separator to be too thick, making it difficult to put the lithium battery into the shell and reducing the core yield. In addition, the energy density of the lithium battery is reduced, and the gap between the positive and negative electrodes during the lithium battery cycle is too large, resulting in the interruption of lithium ion shuttle in the electrolyte and deterioration of the lithium battery cycle performance. If the weight fraction of the functional monomer is too high (Comparative Example 6), the particle size of the prepared polymer bonded microspheres is smaller, and the cycle performance of the prepared lithium battery is deteriorated. This is because when the polymer bonded microspheres are less than 1 μm, the Gurley value increases, the permeability of the lithium battery separator deteriorates, the ionic conductivity decreases, and the shuttle of lithium ions between the positive and negative electrodes is hindered, indicating that the polymer bonded microspheres seriously block the pore structure of the substrate, resulting in deterioration of the lithium battery electrical performance. Therefore, when the polymer bonded microspheres are in the range of 1 to 10 μm, the performance of the prepared lithium battery separator and lithium battery is better.

[0178] Compared to Example 1, if the weight fraction of the crosslinking monomer (divinylbenzene) is too low (Comparative Example 7), the swelling rate of the resulting polymer-bonded microspheres exceeds 200%, increasing the internal resistance of the resulting lithium battery and deteriorating its cycling performance. This is because when the polymer-bonded microspheres have a high swelling rate in the electrolyte, they expand more in the electrolyte state, weakening the adhesion between the lithium battery separator and the positive and negative electrodes, increasing the gap between the positive and negative electrodes, and extending the lithium ion transmission distance. This increases the internal resistance of the lithium battery and deteriorates its cycling performance.

[0179] Compared with Example 1, if a dispersant is added (Comparative Example 8), the adhesion to the positive and negative electrodes is significantly reduced. This is because the introduction of the dispersant hinders the interaction between the polar groups in the polymer adhesive microspheres and the components of the positive and negative electrodes, thereby significantly reducing the adhesion between them.

[0180] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A polymer bonded microsphere, characterized in that: The D 50 The particle size is 1 to 10 μm, the P value is ≤0.3, the glass transition temperature is 30 to 90° C., and the electrolyte swelling rate is ≤150%, wherein the P value = (σ / d)2 / [1+(σ / d)2]; σ is the standard deviation of the diameter of the polymer bonded microspheres, and d is the average diameter of the polymer bonded microspheres.

2. A dispersion of bonded microspheres, characterized in that: The adhesive microsphere dispersion comprises the polymer adhesive microspheres as claimed in claim 1; The raw materials for preparing the adhesive microsphere dispersion do not include a dispersant.

3. The adhesive microsphere dispersion according to claim 2, characterized in that: The adhesive microsphere dispersion further includes a first main group metal ion; Preferably, the concentration of the first main group metal ion is 0.001 to 1 g / L; Preferably, the mass percentage concentration of polymer adhesive microspheres in the adhesive microsphere dispersion is 0.5% to 45%; Preferably, the adhesive microsphere dispersion further comprises a dispersion medium; Preferably, the dispersion medium comprises water.

4. A method for preparing a dispersion of bonded microspheres according to claim 2 or 3, characterized in that: The preparation method comprises the following steps: (1) mixing an initiator, a dispersion medium, and a first mixed monomer, wherein the mass of the first mixed monomer is 1% to 30% based on the total mass of the initiator, the dispersion medium, and the first mixed monomer as 100%, and reacting to obtain a first dispersion; (2) adding the second mixed monomer dropwise to the first dispersion prepared in step (1), reacting to obtain the adhesive microsphere dispersion; The first mixed monomer and the second mixed monomer each independently include the following components by mass percentage: 40% to 95% of hard monomer, 4% to 40% of soft monomer, 0.5% to 10% of functional monomer and 0.5% to 10% of cross-linking monomer.

5. The preparation method according to claim 4, characterized in that After the reaction in step (2), a base containing a first main group metal ion is added to neutralize the mixture to a pH of 6 to 8; Preferably, the base containing a first main group metal ion comprises lithium hydroxide; Preferably, the reactions in step (1) and step (2) are carried out under a nitrogen atmosphere; Preferably, the reaction temperature in step (1) and step (2) is independently 55 to 85°C; Preferably, the reaction time of step (1) and step (2) is independently 3 to 20 hours; Preferably, the dripping time in step (2) is 6 to 20 hours; Preferably, based on the total mass of the first mixed monomer and the second mixed monomer being 100%, the mass of the initiator is 0.2% to 10%; Preferably, based on the total mass of the first mixed monomer and the second mixed monomer being 100%, the mass of the second mixed monomer is 5% to 95%.

6. The preparation method according to claim 4 or 5, characterized in that The functional monomers include dispersing monomers; Preferably, the functional monomer further comprises a viscosity-increasing monomer; Preferably, the mass ratio of the dispersing monomer to the viscosity-increasing monomer is 1:10 to 5:

1.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The initiator includes any one or a combination of at least two of a persulfate initiator, a peroxide initiator, an azo initiator or a redox system initiator; Preferably, the persulfate initiator comprises persulfate; Preferably, the persulfate comprises any one of sodium persulfate, potassium persulfate or ammonium persulfate, or a combination of at least two thereof; Preferably, the peroxide initiator comprises any one of hydrogen peroxide, benzoyl peroxide or lauroyl peroxide, or a combination of at least two thereof; Preferably, the azo initiator includes any one or a combination of at least two of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile or dimethyl azobisisobutyrate; Preferably, the redox system initiator comprises any one of persulfate-thiosulfate, azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobisisobutylimidazoline or azobiscyanovaleric acid, or a combination of at least two thereof; Preferably, the hard monomer comprises any one or a combination of at least two of methyl methacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, vinyl acetate, styrene, methyl acrylate, butyl methacrylate, tert-butyl acrylate, 4-tert-butylcyclohexyl acrylate, isobornyl methacrylate, cyclohexyl methacrylate, dicyclopentenyl acrylate, stearic acid methacrylate, isobornyl acrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, 2-phenoxyethyl methacrylate, isobornyl methacrylate or tetrahydrofurfuryl acrylate; Preferably, the soft monomer comprises any one or a combination of at least two of ethyl acrylate, propyl acrylate, butyl acrylate, isooctyl acrylate, n-octyl acrylate, butyl methacrylate, hexyl acrylate, lauryl methacrylate, hexyl acrylate, heptyl acrylate, n-octyl methacrylate, isooctyl methacrylate, propoxylated nonylphenol acrylate, lauric acrylate, lauric methacrylate, isodecyl methacrylate, ethoxyethoxyethyl acrylate, 2-hydroxyethyl methacrylate phosphate, 2-ethylhexyl methacrylate or isodecyl acrylate; Preferably, the dispersing monomer comprises any one or a combination of at least two of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, acrylamide, hydroxymethyl acrylamide, N-vinyl pyrrolidone, polyethylene glycol dimethacrylate, polypropylene glycol diacrylate, polyethylene glycol monomethacrylate, styrenesulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, (meth)acrylic acid-2-sulfonic acid ethyl ester, stearic acid acrylate, polyethylene glycol diacrylate, polyethylene glycol or methoxy polyethylene glycol methacrylate; Preferably, the viscosity-increasing monomer includes any one or a combination of at least two of ethyl acetoacetate methacrylate, glycidyl methacrylate, dimethylaminoethyl methacrylate, vinylsiloxane silane, vinyltriisopropoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltris(β-trimethoxyethoxysilane), hydroxyethyl acrylate, hydroxyethyl methacrylate, β-hydroxypropyl acrylate, β-hydroxypropyl methacrylate or phenyl glycidyl ether acrylate; Preferably, the cross-linking monomer includes any one or a combination of at least two of divinylbenzene, ethylene glycol dimethacrylate, N-hydroxymethyl acrylamide, N-(isobutoxymethyl) acrylamide, acrylamide, diallyl phthalate, trimethylolpropane triacrylate, triallyl isocyanurate, allyl methacrylate, diacetone acrylamide, diethylene glycol diacrylate, N-ethyl acrylamide, N-(butoxymethyl) acrylamide or N-butyl acrylamide.

8. A lithium battery separator coating slurry, characterized in that: The lithium battery separator coating slurry comprises any one of the polymer bonded microspheres according to claim 1, the bonded microsphere dispersion according to claim 2 or 3, or the bonded microsphere dispersion prepared by the preparation method according to any one of claims 4 to 7.

9. A lithium battery separator, characterized in that: The lithium battery separator comprises a substrate and a coating coated on at least one side of the substrate, wherein the coating comprises the polymer bonded microspheres according to claim 1 or the coating is prepared from the lithium battery separator coating slurry according to claim 8; Preferably, the substrate comprises any one of a PP base film, a PE base film or a PP\PE composite film; Preferably, the cold pressing bonding strength between the lithium battery separator and the positive electrode sheet or the negative electrode sheet is ≥1 N / m (for example, 1.5 N / m, 2 N / m, 2.5 N / m, 3 N / m or 3.5 N / m, etc.); Preferably, the hot pressing bonding strength between the lithium battery separator and the positive electrode sheet or the negative electrode sheet is ≥5N / m (for example, 5.5N / m, 6N / m, 6.5N / m, 7N / m, 7.5N / m, 8N / m or 8.5N / m, etc.).

10. A lithium battery, characterized in that: The lithium battery comprises the lithium battery separator according to claim 9.

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