A polyethylene separator for high-lithium-infiltration lithium batteries and a method of manufacturing the same

Abstract

The application discloses a polyethylene diaphragm for high-wetting lithium batteries and a preparation method thereof, and relates to the technical field of polyethylene diaphragms for lithium batteries. The polyethylene diaphragm for high-wetting lithium batteries comprises the following components in a mass ratio: 50-80 parts of a polyethylene base material, 5-20 parts of inorganic nano-particles, 1-5 parts of a surfactant, 10-30 parts of a pore-forming agent, 0.5-3 parts of a coupling agent and 1-2 parts of a stabilizer. Through the dynamic coordination network of the stabilizer and the synergistic effect of multiple components, the interface characteristics of the diaphragm and electrolyte are optimized, and more efficient lithium ion transmission is realized. The rigid stabilizer skeleton and the heteroatom bridging effect of the inorganic particles inhibit high-temperature shrinkage and stress deformation, and improve the reliability of the diaphragm under extreme working conditions. The space synergistic regulation of the pore-forming agent and the stabilizer forms uniform and interconnected micro-nano pores, and the mechanical strength and electrolyte wetting consistency are considered, so that the battery cycle life is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyethylene separator for lithium battery, and particularly relates to a high-wetting polyethylene separator for lithium battery and a preparation method thereof. BACKGROUND

[0002] With the booming development of new energy industry, lithium battery as an efficient and clean energy storage device, the demand in the field of electric vehicles, energy storage systems and consumer electronics is increasing. The performance of lithium battery not only depends on the electrode material, but also is closely related to the performance of the separator. As a key component of lithium battery, the separator mainly plays the role of isolating the positive and negative electrodes, preventing short circuit and providing transmission channel for lithium ions.

[0003] Currently, polyethylene separator is widely used due to its low cost, good mechanical properties and high chemical stability. However, there are some deficiencies in the prior art. First, the wettability of polyethylene separator is poor, which limits the transmission efficiency of lithium ions in the electrolyte, thereby affecting the charging and discharging speed and overall performance of the battery. Secondly, the thermal stability of the separator needs to be improved, when the battery works in high temperature environment or internal short circuit occurs, the separator is easy to shrink, leading to battery failure and even causing safety problems. In addition, the pore structure and size distribution of the separator are not ideal, which not only affects the consistency of lithium ion transmission, but also may lead to the shortening of the cycle life of the battery. In view of these problems, it is particularly urgent to develop a polyethylene separator for lithium battery with high wettability, high thermal stability and excellent pore structure. SUMMARY

[0004] The purpose of the present application is to solve the problems existing in the prior art, and to provide a polyethylene separator for lithium battery with high wettability, high thermal stability and excellent pore structure and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: a polyethylene separator for lithium battery with high wettability, characterized in that it comprises the following components by mass fraction: polyethylene base material 50-80 parts, inorganic nano-particles 5-20 parts, surfactant 1-5 parts, pore-forming agent 10-30 parts, coupling agent 0.5-3 parts, stabilizer 1-2 parts.

[0006] The stabilizer is a structure shown in formula 1:

[0007] Formula 1;

[0008] Z1 is selected from: -O-, -S-, -N(H)-, -C(CH3)(CH3)-.

[0009] Further, the inorganic nano-particles are at least one of silicon dioxide, aluminum oxide or barium titanate, and the particle size is 20-100 nm.

[0010] Further, the surface active agent is a fatty alcohol polyoxyethylene ether.

[0011] Further, the polyethylene substrate is a mixture of polypropylene and high-density polyethylene; the density of the high-density polyethylene is 0.941-0.960 g / cm 3 .

[0012] Further, the pore-forming agent is a mixture of polyethylene glycol and liquid paraffin in a mass ratio of 1: (1-3) parts.

[0013] Further, the coupling agent is trimethyl phosphate.

[0014] Further, the stabilizer is a compound represented by the following structure:

[0015] Stabilizer 1;

[0016] Stabilizer 2;

[0017] Stabilizer 3;

[0018] Stabilizer 4.

[0019] Further, the synthesis method of the stabilizer is:

[0020] ;

[0021] First step: raw material 1 and raw material 2 are subjected to a substitution reaction to synthesize intermediate 1;

[0022] Second step: intermediate 1 is subjected to boration to obtain intermediate 2;

[0023] Third step: intermediate 2 and raw material 3 are subjected to a Suzuki coupling reaction to synthesize the stabilizer.

[0024] A preparation method of a high-wetting lithium battery polyethylene diaphragm, comprising the following steps:

[0025] S1. The polyethylene substrate, inorganic nanoparticles, surface active agent, pore-forming agent, coupling agent and stabilizer are melt blended at 160-200°C to form a slurry;

[0026] S2. The slurry is extruded and then subjected to bidirectional stretching treatment, longitudinally stretched by 3-5 times and transversely stretched by 2-3 times to form a substrate film;

[0027] S3. The substrate film is soaked in a solvent at 60-80°C for 10-20 minutes, and then heat set at 90-100°C for 10-20 minutes to obtain a high-wetting lithium battery polyethylene diaphragm.

[0028] Further, the solvent in step S3 is at least one of xylene, acetone or isopropyl alcohol.

[0029] Further, the heat setting treatment in step S3 adopts a stepwise heating mode, first treated at 80-85 DEG C for 5-10 minutes, and then heated to 95-100 DEG C for 5-10 minutes.

[0030] From the rigid planar structure of the stabilizer mother nucleus, the mother nucleus of the stabilizer of formula 1 is a polycyclic fused aromatic hydrocarbon skeleton, and the planar conjugated structure has the effect of improving thermal stability. The conjugated pi electron system of the fused ring aromatic hydrocarbon can effectively disperse the internal thermal stress, block the free radical chain reaction, so that the separator maintains dimensional stability during processing at 160-200 DEG C and high temperature operation of the battery. The bridging effect of the heteroatom in the mother nucleus forms a dynamic coordination network at the Z1 site in the mother nucleus, and the oxygen / sulfur atom forms a hydrogen bond with the inorganic nanoparticles, so that the uniformity of the nanoparticle dispersion is improved. The nitrogen atom and the trimethyl phosphate coupling agent produce dipole-dipole interaction, and a three-dimensional cross-linked network is constructed, so that the porosity is stable.

[0031] In the multi-component synergistic system, the functions of each component are highly complementary and dynamically coupled: the polyethylene substrate constructs the basic mechanical network through the embedding effect of the crystalline region and the rigid skeleton of the stabilizer, the inorganic nanoparticles form a nano-reinforced phase through the bridging of the heteroatoms of the stabilizer, the surfactant and the stabilizer synergistically reduce the polymer-electrolyte interfacial tension, the pore-forming agent and the stabilizer maintain the stability of the pore structure together through the steric hindrance effect, and the coupling agent constructs a heat-responsive crosslinking point through dynamic coordination with the stabilizer. This multi-level synergy realizes the simultaneous improvement of material strength, wettability, pore connectivity and thermal stability, forming a "structure stability-interface optimization-pore regulation" three-in-one functional strengthening path.

[0032] Compared with the prior art, the beneficial effects of the present application are:

[0033] 1. The wettability and ion transport efficiency are significantly improved: through the dynamic coordination network of the stabilizer and the multi-component synergistic effect, the interface characteristics of the separator-electrolyte are optimized, and more efficient lithium ion transport is realized.

[0034] 2. Thermal stability and structural stability are enhanced: the rigid stabilizer skeleton and the heteroatom bridging effect of the inorganic particles inhibit high-temperature shrinkage and stress deformation, and improve the reliability of the separator under extreme working conditions.

[0035] 3. The uniformity and connectivity of the pore structure are improved: the pore-forming agent and the stabilizer form uniform and interconnected micro-nano pores through spatial synergistic regulation, which balances the mechanical strength and electrolyte wettability, and prolongs the cycle life of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1The synthesis method of the stabilizer described in the present application. DETAILED DESCRIPTION

[0037] The technical solutions of the present application will be clearly and completely described below with reference to the drawings in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present application.

[0038] Synthesis Example 1

[0039] Synthesis of stabilizer 1:

[0040] ;

[0041] First step, under nitrogen atmosphere, 20g of raw material 1 and 21.58g of aluminum chloride were sequentially added into the reaction system, 200g of dichloromethane was added, 17.54g of raw material 2 was slowly added at 0℃, the material was added at-20 to 10℃, and the reaction was carried out at room temperature for 8h. After the reaction was completed, the reaction liquid was slowly poured into 500ml of 0.1mol / L HCl at 0℃, stirred for 30min, and separated by standing. The organic phase was retained, the aqueous phase was washed with 50ml of dichloromethane for 3 times, the organic phases were combined, 100ml of 0.1mol / L sodium bicarbonate solution was added, stirred and shaken, the pH was adjusted to neutral, the organic phase was retained, dried with 20g of anhydrous magnesium sulfate, filtered, rotary evaporated, and oven dried to obtain 24.83g of intermediate 1. MS [MS+1]: 390.

[0042] Second step, under nitrogen atmosphere, 24.83g of intermediate 1 and 500ml of super dry tetrahydrofuran were sequentially added into the reaction system, cooled to-70℃, and 4.31g of n-butyllithium was slowly added. After the addition was completed, it was stirred for 1h, 17.91g of triisopropyl borate was added dropwise, and after the addition was completed, it was naturally raised to room temperature and reacted overnight. The solvent was rotary evaporated to obtain 16.91g of intermediate 2. MS [MS+1]: 357.

[0043] Third step, under nitrogen atmosphere, 16.91g of intermediate 2, 17.93g of raw material 3 and 19.69g of anhydrous potassium carbonate were sequentially added into the reaction system, a mixed solution of toluene, ethanol and water (volume ratio 2:1:1) was added, replaced twice with nitrogen, 1.65g of tetrakis(triphenylphosphine)palladium was added into the system under nitrogen protection, replaced twice with nitrogen, heated to 75℃ and refluxed for 10h. The heating was turned off, cooled to room temperature, and separated by standing. The aqueous phase was extracted with ethyl acetate twice, the organic phases were combined, washed with water three times, rotary evaporated, and column chromatographed with a mixture of petroleum ether and dichloromethane as eluent to obtain 20.01g of stabilizer. MS [MS+1]: 589.

[0044] Synthesis Example 2-Synthesis Example 4

[0045] The compounds synthesized in Synthesis Example 2-Synthesis Example 4 were synthesized according to the preparation method of Synthesis Example 1, with the raw material 1 being replaced, and the rest being the same as Synthesis Example 1. The specific structure of raw material 1, the structure of stabilizer, and MS [MS+1] data are shown in the following table.

[0046]

[0047] Example 1

[0048] A preparation method of a high-wettability polyethylene separator for lithium batteries is as follows:

[0049] Raw material ratio (mass parts): polyethylene base material: high-density polyethylene 60 parts and polypropylene 20 parts, a total of 80 parts; inorganic nanoparticles: silicon dioxide 15 parts; surfactant: fatty alcohol polyoxyethylene ether 3 parts; pore-forming agent: polyethylene glycol 10 parts and liquid paraffin 20 parts; coupling agent: trimethyl phosphate 2 parts; stabilizer: stabilizer 1.5 parts prepared by Synthesis Example 1.

[0050] The preparation method comprises the following steps:

[0051] S1. The polyethylene base material, inorganic nanoparticles, surfactant, pore-forming agent, coupling agent, and stabilizer are added to a twin-screw extruder, and melt blended at 180°C for 30 minutes to form a uniform slurry.

[0052] S2. The slurry is extruded and cast into a film through a slit die, with a casting temperature of 185°C. The base film is bidirectionally stretched: 4 times in the longitudinal direction and 2.5 times in the transverse direction, to form a base film with a thickness of 20 μm.

[0053] S3. The base film is immersed in 70°C isopropanol for 15 minutes to elute the residual pore-forming agent. Heat setting treatment: first at 83°C for 8 minutes, then at 98°C for 10 minutes, to obtain a high-wettability polyethylene separator for lithium batteries.

[0054] Example 2-Example 4

[0055] According to the preparation method in Example 1, the stabilizer therein is replaced by the stabilizers synthesized in Synthesis Example 2-Synthesis Example 4 in turn, and the rest remains unchanged.

[0056] Comparative Example 1

[0057] According to the preparation method in Example 1, the stabilizer therein is replaced by Comparative Compound 1, and the rest remains unchanged.

[0058] Comparative Compound 1: .

[0059] Comparative Example 2

[0060] Referring to the preparation method in Comparative Example 1, the stabilizer therein is replaced by Comparative Compound 2, and the rest remains unchanged.

[0061] Comparative Compound 2: .

[0062] Comparative Example 3

[0063] Referring to the preparation method in Comparative Example 1, the stabilizer therein is not added, and the rest remains unchanged.

[0064] Comparative Example 4

[0065] Referring to the preparation method in Comparative Example 1, the raw material ratio (mass parts) is changed to: polyethylene substrate: high-density polyethylene 65 parts and polypropylene 20 parts, a total of 85 parts; inorganic nanoparticles: silicon dioxide 20 parts; surfactant: fatty alcohol polyoxyethylene ether 3 parts; pore-forming agent: polyethylene glycol 10 parts and liquid paraffin 20 parts; coupling agent: trimethyl phosphate 2 parts; stabilizer: stabilizer 1.5 parts prepared in Synthetic Example 1, and the rest remains unchanged.

[0066] Performance test:

[0067] 1. Porosity test: The porosity of the separator is determined by the mercury intrusion method (GB / T21650.1-2008). The sample is placed in the mercury porosimeter, the pressure range is 0.1-400 MPa, and the percentage of pore volume to total volume is calculated.

[0068] 2. Liquid absorption rate test: The separator is cut into a 5 cm x 5 cm sample and soaked in 1 mol / L LiPF6 / EC: DMC (volume ratio 1:1) electrolyte for 30 minutes. After taking out, the surface liquid is wiped dry, and the liquid absorption rate is calculated: liquid absorption rate (%) = [(W2-W1) / W1] x 100%, where W1 is the dry membrane mass, and W2 is the wet membrane mass.

[0069] 3. Ion conductivity test: The separator is assembled into a symmetrical battery (stainless steel electrode), and the ion conductivity is tested by electrochemical impedance spectroscopy (EIS) with a frequency range of 0.1 Hz-100 kHz. The calculation formula is: σ = d / (R x A) (d is the thickness of the separator, R is the bulk resistance, and A is the electrode area).

[0070]

[0071] The examples are significantly better than the comparative examples, in which the stabilizers containing specific heteroatom structures (Examples 1-4) exhibit simultaneous improvement in pore connectivity, electrolyte wettability and ion transport efficiency, and the performance varies in a gradient with the type and steric hindrance of the heteroatoms in the stabilizer molecules. In the comparative examples, the absence or structural change of the stabilizer (Comparative Examples 1-3) leads to a significant decrease in porosity, liquid absorption rate and conductivity, and the imbalance of inorganic-substrate ratio (Comparative Example 4) further aggravates the performance deterioration, indicating that the multi-component synergistic effect and the dynamic coordination network of the stabilizer play a decisive role in the performance of the separator.

[0072] While embodiments of the present application have been shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A polyethylene separator for high-impregnation lithium batteries, characterized by, The composition comprises the following components by mass fraction: polyethylene base material 50-80 parts, inorganic nanoparticles 5-20 parts, surfactant 1-5 parts, pore-forming agent 10-30 parts, coupling agent 0.5-3 parts, and stabilizer 1-2 parts. The stabilizer is a structure shown in formula 1: Formula 1; Z1 is selected from -O-, -S-, -N(H)-, and -C(CH3)(CH3)-. The preparation method of the polyethylene separator for high-wetting lithium batteries comprises the following steps: S1. Melting and blending the polyethylene base material, inorganic nanoparticles, surfactant, pore-forming agent, coupling agent, and stabilizer at 160-200°C to form a slurry; S2. After extrusion and casting, the slurry is subjected to bidirectional stretching treatment, longitudinally stretched by 3-5 times, and transversely stretched by 2-3 times to form a base film; S3. The base film is soaked in a solvent at 60-80°C for 10-20 minutes, and then heat set at 90-100°C for 10-20 minutes to obtain a polyethylene separator for high-wetting lithium batteries.

2. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized by, The inorganic nanoparticles are at least one of silicon dioxide, aluminum oxide, or barium titanate, and have a particle size of 20-100 nm.

3. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized in that, The surfactant is a fatty alcohol polyoxyethylene ether.

4. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized by, The polyethylene substrate is a mixture of polypropylene and high density polyethylene; the high density polyethylene has a density of 0.941 to 0.960 g / cm 3 .

5. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized in that, The pore-forming agent is a mixture of polyethylene glycol and liquid paraffin, with a mass ratio of 1:(1-3) parts.

6. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized in that, The coupling agent is trimethyl phosphate.

7. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized in that, The solvent in step S3 is at least one of xylene, acetone, or isopropyl alcohol.

8. The high-wettability polyethylene separator for lithium batteries according to claim 1, characterized in that, The heat setting treatment in step S3 adopts a stepwise heating mode, first treated at 80-85°C for 5-10 minutes, and then heated to 95-100°C for 5-10 minutes.

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