High-adhesion lithium ion battery diaphragm capable of pre-supplementing lithium and preparation method of high-adhesion lithium ion battery diaphragm

Abstract

The invention relates to the technical field of new energy, and discloses a high-adhesion lithium ion battery diaphragm capable of pre-supplementing lithium and a preparation method thereof.The high-adhesion lithium ion battery diaphragm is prepared from, by mass, 10%-20% of slurry including 70%-85% of a polyvinylidene fluoride-hexafluoropropylene copolymer, 10%-20% of a binder, 10%-20% of a binder, 1%-5% of a lubricant and 1%-5% of a lubricant; 5%-10% of a lithium pre-supplementing material; 2%-5% of a bonding enhancer; 3%-8% of a conductive filler; and 80%-90% of a solvent. The lithium pre-supplementing material is a nanoscale Li2S-Li3N compound, and the particle size range of the lithium pre-supplementing material is 50 nm to 200 nm. And the bonding reinforcing agent is a polydopamine coating. The conductive filler is a carbon nanotube, the diameter range of the conductive filler is 10-30 nm, and the length range of the conductive filler is 1-10 [mu] m. By selecting the Li2S-Li3N compound with a specific proportion as the lithium pre-supplementing material, the proportion of the Li2S-Li3N compound in the slurry is optimized, the lithium pre-supplementing capacity of the lithium ion battery diaphragm is improved, and experiments prove that the utilization rate of lithium in the first charging and discharging process of the battery is improved, the first coulombic efficiency is improved, and the battery is endowed with higher first discharging capacity.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion, and a preparation method thereof. Background Art

[0002] In today's society, with the rapid development of electronic devices and the gradual popularization of electric vehicles, the performance of lithium-ion batteries as core energy storage components has attracted more and more attention. Lithium-ion battery separators, as key isolation materials between the positive and negative electrodes of batteries, play a decisive role in the safety, stability and overall performance of batteries.

[0003] Traditional lithium-ion battery separators have obvious defects in pre-lithium replenishment technology. During the first charge and discharge process of the battery, lithium metal will be irreversibly consumed on the surface of the negative electrode to form a solid electrolyte interface film, namely SEI film, which leads to the loss of initial capacity of the battery and reduced energy density. In previous pre-lithium replenishment schemes, either the pre-lithium replenishment material is difficult to disperse evenly in the separator, resulting in uneven pre-lithium replenishment effects; or the pre-lithium replenishment material has poor compatibility with the separator matrix, and is easy to fall off or fail during the battery charge and discharge cycle, and cannot continuously and effectively replenish the lithium source for the battery, limiting the initial performance and long-term cycle stability of the battery.

[0004] Traditional technologies also face many challenges in terms of the bonding performance between the diaphragm and the electrode. Ordinary adhesives cannot form sufficiently strong chemical bonds or physical adsorption forces between the diaphragm and the electrode. During the battery charging and discharging process, due to the volume change of the electrode material and the erosion of the electrolyte, the interface between the diaphragm and the electrode is prone to separation. This not only increases the internal resistance of the battery, causing severe battery heating, but also affects the transmission efficiency of lithium ions between the electrode and the diaphragm, causing the battery's charge and discharge rate performance to decrease and the cycle life to shorten. In addition, traditional bonding processes are often too simple and cannot be optimized according to different electrode materials and diaphragm characteristics, making it difficult to meet the strict requirements of high-performance lithium-ion batteries for interface stability. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion and a preparation method thereof, which solves the problem that the lithium source cannot be continuously and effectively replenished for the battery, limiting the initial performance and long-term cycle stability of the battery.

[0006] To achieve the above objectives, the present invention is implemented by the following technical scheme: A lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion, comprising the following raw materials in percentage by mass:

[0007] 10% to 20% slurry, including: 70% to 85% polyvinylidene fluoride-hexafluoropropylene copolymer; 5% to 10% pre-supplemented lithium material; 2% to 5% adhesion enhancer; 3% to 8% conductive filler;

[0008] 80% to 90% solvent.

[0009] Preferably, the pre-lithium supplement material is a nanoscale Li2S-Li3N composite with a particle size ranging from 50nm to 200nm.

[0010] Preferably, the adhesion enhancer is a polydopamine coating.

[0011] Preferably, the conductive filler is a carbon nanotube with a diameter ranging from 10 nm to 30 nm and a length ranging from 1 μm to 10 μm.

[0012] Preferably, the solvent is N-methylpyrrolidone.

[0013] In addition, the present invention also provides a method for preparing a lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion, comprising the following steps:

[0014] Adding polyvinylidene fluoride-hexafluoropropylene copolymer into N-methylpyrrolidone solvent, stirring until completely dissolved, and adding pre-lithium supplement material, conductive filler and adhesion enhancer for ultrasonic dispersion;

[0015] Coating and self-polymerization, coating the mixed liquid on the substrate surface, using a scraper to control the thickness, and then immersing it in an alkaline solution;

[0016] Hot pressing molding, stacking the self-polymerized diaphragm and the electrode and hot pressing;

[0017] Vacuum drying: Place the hot-pressed diaphragm in a vacuum drying oven to remove residual solvent.

[0018] Preferably, the ultrasonic dispersion power is 200W to 400W, and the ultrasonic time is 30min to 60min.

[0019] Preferably, the pH of the self-polymerization alkaline solution is 8.5-9.0, the self-polymerization reaction time is 12h-24h, and the reaction temperature is 25°C-35°C.

[0020] Preferably, the hot pressing molding temperature is 70° C. to 90° C., the hot pressing pressure is 5 MPa to 10 MPa, and the hot pressing time is 5 min to 10 min.

[0021] Preferably, the vacuum drying temperature is 60°C to 80°C, the drying time is 12h to 24h, and the vacuum degree is -0.1MPa.

[0022] The invention provides a lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion and a preparation method thereof.

[0023] It has the following beneficial effects:

[0024] 1. The present invention selects a specific proportion of Li2S-Li3N composite as the pre-lithium replenishment material and optimizes its proportion in the slurry, so that the pre-lithium replenishment capacity of the lithium-ion battery separator is greatly improved. Experimental verification shows that the utilization rate of lithium in the first charge and discharge process of the battery is significantly improved, and the first coulomb efficiency is greatly improved, giving the battery a higher first discharge capacity.

[0025] 2. The present invention uses dopamine monomer as an adhesion enhancer, finely controls its dosage, and strictly controls the pH, temperature and duration of self-polymerization. The bonding strength between the diaphragm and the electrode is thus greatly enhanced. During battery use, the two are closely connected, eliminating the hidden danger of easy separation, fundamentally stabilizing the battery structure, and effectively reducing performance degradation caused by interface problems.

[0026] 3. The present invention rationally regulates the preparation process parameters such as the particle size of the Li2S-Li3N composite, the content of dopamine monomers, and the hot pressing pressure, so that the battery can still maintain the discharge capacity well in the test of long-term cycle charge and discharge. After multiple charge and discharge cycles, the battery capacity retention rate is considerable, which greatly extends the service life of the battery and reduces the cost of frequent battery replacement.

[0027] 4. The present invention optimizes the internal micro-environment of the battery by controlling key factors including NMP solvent content, CNT dosage, and self-polymerization temperature. The battery can output power stably at different charge and discharge rates, and the capacity retention rate is excellent. Whether the device is in low-power standby or high-energy fast operation, the battery equipped with the diaphragm can be stably adapted to meet diverse usage needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flow chart of the preparation of the lithium-ion battery separator. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Please see attached Figure 1 The embodiment of the present invention provides a lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion, comprising the following raw materials in percentage by mass:

[0031] 10% to 20% slurry, including: 70% to 85% polyvinylidene fluoride-hexafluoropropylene copolymer; 5% to 10% pre-supplemented lithium material; 2% to 5% adhesion enhancer; 3% to 8% conductive filler;

[0032] 80% to 90% solvent.

[0033] The pre-lithium supplement material is a nano-scale Li2S-Li3N composite with a particle size ranging from 50nm to 200nm.

[0034] The adhesion enhancer is a polydopamine coating.

[0035] The conductive filler is a carbon nanotube, and the diameter thereof ranges from 10 nm to 30 nm, and the length ranges from 1 μm to 10 μm.

[0036] The solvent is N-methylpyrrolidone.

[0037] In addition, the present invention also provides a method for preparing a lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion, comprising the following steps:

[0038] Adding polyvinylidene fluoride-hexafluoropropylene copolymer into N-methylpyrrolidone solvent, stirring until completely dissolved, and adding pre-lithium supplement material, conductive filler and adhesion enhancer for ultrasonic dispersion;

[0039] Coating and self-polymerization, coating the mixed liquid on the substrate surface, using a scraper to control the thickness, and then immersing it in an alkaline solution;

[0040] Hot pressing molding, stacking the self-polymerized diaphragm and the electrode and hot pressing;

[0041] Vacuum drying: Place the hot-pressed diaphragm in a vacuum drying oven to remove residual solvent.

[0042] The ultrasonic dispersion power is 200W to 400W, and the ultrasonic time is 30min to 60min.

[0043] The pH of the self-polymerization alkaline solution is 8.5-9.0, the self-polymerization reaction time is 12h-24h, and the reaction temperature is 25°C-35°C.

[0044] The hot pressing molding temperature is 70°C to 90°C, the hot pressing pressure is 5MPa to 10MPa, and the hot pressing time is 5min to 10min.

[0045] The vacuum drying temperature is 60℃~80℃, the drying time is 12h~24h, and the vacuum degree is -0.1MPa.

[0046] Example 1: Highly efficient pre-liquidation separator

[0047] Recipe composition:

[0048] Slurry:

[0049] Polyvinylidene fluoride-hexafluoropropylene copolymer: 75%

[0050] Li2S-Li3N composite: 8%

[0051] Dopamine monomer: 4%

[0052] Carbon nanotubes (CNT): 8%

[0053] N-methylpyrrolidone solvent: 85% (slurry content 15%)

[0054] Preparation steps:

[0055] Dissolving the polyvinylidene fluoride-hexafluoropropylene copolymer: add 75 g of the polyvinylidene fluoride-hexafluoropropylene copolymer into 425 g of N-methylpyrrolidone solvent and stir to dissolve.

[0056] Stirring speed: 400rpm.

[0057] Temperature: 55℃.

[0058] Time: 3h.

[0059] Adding Li2S-Li3N composite: add 8g Li2S-Li3N composite and disperse by ultrasonic.

[0060] Ultrasonic power: 300W.

[0061] Time: 45 minutes.

[0062] Add CNT: Add 8 g CNT and continue ultrasonic dispersion.

[0063] Ultrasonic power: 300W.

[0064] Time: 45 minutes.

[0065] Add dopamine monomer: add 4 g dopamine monomer and stir well.

[0066] Stirring speed: 250rpm.

[0067] Duration: 1.5h.

[0068] Coating and self-polymerization: The slurry was coated on a PET substrate with a thickness of 30 μm.

[0069] Coating speed: 8mm / s.

[0070] Immerse in alkaline solution with pH = 8.8 and react for 18 hours.

[0071] Temperature: 30℃.

[0072] Hot pressing: stacked with graphite negative electrode and hot pressed.

[0073] Temperature: 80℃.

[0074] Pressure: 8MPa.

[0075] Time: 8min.

[0076] Drying: vacuum drying, temperature 70℃, time 18h.

[0077] Example 2: High Adhesion Separator

[0078] Recipe composition:

[0079] Slurry:

[0080] Polyvinylidene fluoride-hexafluoropropylene copolymer: 80%

[0081] Li2S-Li3N composite: 5%

[0082] Dopamine monomer: 5%

[0083] Carbon nanotubes (CNT): 5%

[0084] N-methylpyrrolidone solvent: 85% (slurry content 15%)

[0085] Preparation steps:

[0086] Dissolving the polyvinylidene fluoride-hexafluoropropylene copolymer: add 80 g of the polyvinylidene fluoride-hexafluoropropylene copolymer into 420 g of N-methylpyrrolidone solvent and stir to dissolve.

[0087] Stirring speed: 350rpm.

[0088] Temperature: 58℃.

[0089] Duration: 2.5h.

[0090] Adding Li2S-Li3N composite: add 5g Li2S-Li3N composite and disperse by ultrasonic.

[0091] Ultrasonic power: 250W.

[0092] Time: 50 minutes.

[0093] Add CNT: Add 5 g CNT and continue ultrasonic dispersion.

[0094] Ultrasonic power: 250W.

[0095] Time: 50 minutes.

[0096] Add dopamine monomer: add 5g dopamine monomer and stir evenly. Stirring speed: 220rpm.

[0097] Time: 1.8h.

[0098] Coating and self-polymerization: The slurry was coated on a PET substrate with a thickness of 25 μm.

[0099] Coating speed: 7mm / s.

[0100] Immerse in alkaline solution with pH = 8.7 and react for 20 hours.

[0101] Temperature: 28℃.

[0102] Hot pressing: stacked with graphite negative electrode and hot pressed.

[0103] Temperature: 75℃.

[0104] Pressure: 7MPa.

[0105] Time: 7 minutes.

[0106] Drying: vacuum drying, temperature 65℃, time 20h.

[0107] Example 3: Balanced Performance Diaphragm

[0108] Recipe composition:

[0109] Slurry:

[0110] Polyvinylidene fluoride-hexafluoropropylene copolymer: 78%

[0111] Li2S-Li3N composite: 7%

[0112] Dopamine monomer: 3%

[0113] Carbon nanotubes (CNT): 7%

[0114] N-methylpyrrolidone solvent: 85% (slurry content 15%)

[0115] Preparation steps:

[0116] Dissolving the polyvinylidene fluoride-hexafluoropropylene copolymer: Add 78 g of the polyvinylidene fluoride-hexafluoropropylene copolymer into 422 g of N-methylpyrrolidone solvent and stir to dissolve.

[0117] Stirring speed: 380rpm.

[0118] Temperature: 56℃.

[0119] Time: 2.8h.

[0120] Adding Li2S-Li3N composite: add 7g Li2S-Li3N composite and disperse by ultrasonic.

[0121] Ultrasonic power: 280W.

[0122] Time: 40 minutes.

[0123] Add CNT: Add 7 g CNT and continue ultrasonic dispersion.

[0124] Ultrasonic power: 280W.

[0125] Time: 40 minutes.

[0126] Add dopamine monomer: add 3g dopamine monomer and stir well.

[0127] Stirring speed: 230rpm.

[0128] Time: 1.6h.

[0129] Coating and self-polymerization: The slurry was coated on a PET substrate with a thickness of 28 μm.

[0130] Coating speed: 6mm / s.

[0131] Immerse in alkaline solution with pH = 8.6 and react for 16 hours.

[0132] Temperature: 32℃.

[0133] Hot pressing: stacked with graphite negative electrode and hot pressed.

[0134] Temperature: 85℃.

[0135] Pressure: 9MPa.

[0136] Time: 6 minutes.

[0137] Drying: vacuum drying, temperature 75℃, time 16h.

[0138] Example 4: Low-cost diaphragm

[0139] Recipe composition:

[0140] Polyvinylidene fluoride-hexafluoropropylene copolymer: 82%

[0141] Li2S-Li3N composite: 6%

[0142] Dopamine monomer: 2%

[0143] Carbon nanotubes (CNT): 5%

[0144] N-methylpyrrolidone solvent: 85% (slurry content 15%)

[0145] Preparation steps:

[0146] Dissolving the polyvinylidene fluoride-hexafluoropropylene copolymer: 82 g of the polyvinylidene fluoride-hexafluoropropylene copolymer was added to 418 g of N-methylpyrrolidone solvent and stirred to dissolve.

[0147] Stirring speed: 320rpm.

[0148] Temperature: 52℃.

[0149] Time: 2.2h.

[0150] Adding Li2S-Li3N composite: add 6g Li2S-Li3N composite and disperse by ultrasonic.

[0151] Ultrasonic power: 220W.

[0152] Time: 35 minutes.

[0153] Add CNT: Add 5 g CNT and continue ultrasonic dispersion.

[0154] Ultrasonic power: 220W.

[0155] Time: 35 minutes.

[0156] Add dopamine monomer: add 2 g dopamine monomer and stir well.

[0157] Stirring speed: 210rpm.

[0158] Time: 1.2h.

[0159] Coating and self-polymerization: The slurry was coated on a PET substrate with a thickness of 22 μm.

[0160] Coating speed: 5mm / s.

[0161] Immerse in alkaline solution with pH = 8.5 and react for 14 hours.

[0162] Temperature: 26℃.

[0163] Hot pressing: stacked with graphite negative electrode and hot pressed.

[0164] Temperature: 70℃.

[0165] Pressure: 6MPa.

[0166] Time: 5 minutes.

[0167] Drying and cutting: vacuum drying, temperature 60℃, time 14h.

[0168] Comparative experiment

[0169] Comparative Example 1: Adjusting the amount of raw materials (corresponding to Example 1)

[0170] Formula adjustment: reduce the Li2S-Li3N complex from 8% to 4% and increase the dopamine monomer from 4% to 6%.

[0171] Preparation steps: A lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion is prepared according to the method of Example 1, wherein the hot pressing temperature is reduced from 80°C to 60°C.

[0172] Comparative Example 2: Shortened self-polymerization time (corresponding to Example 2)

[0173] Formula adjustment: Increase the polyvinylidene fluoride-hexafluoropropylene copolymer from 80% to 85%, and reduce the CNT from 5% to 3%.

[0174] Preparation steps: A lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion is prepared according to the method of Example 2, wherein the self-polymerization time is shortened from 20 hours to 10 hours.

[0175] Comparative Example 3: Changing the distribution of pre-supplemented lithium materials (corresponding to Example 3)

[0176] Formula adjustment: Increase the particle size of Li2S-Li3N composite from 50-200nm to 300-500nm, and reduce the dopamine monomer from 3% to 1%.

[0177] Preparation steps: A lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion is prepared according to the method of Example 3, wherein the hot pressing pressure is increased from 9 MPa to 12 MPa.

[0178] Comparative Example 4: Coating Parameter Change (Corresponding to Example 4)

[0179] Formulation adjustment: N-methylpyrrolidone solvent was increased from 5% to 10% (solid content was reduced from 15% to 10%), and CNT was increased from 5% to 10%.

[0180] Preparation steps: A lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion is prepared according to the method of Example 4, wherein the self-polymerization temperature is increased from 26°C to 40°C.

[0181] Comparative experiment

[0182] Experiment 1: Verification of the effect of pre-supplementation with lithium

[0183] Experimental samples: finished lithium-ion battery separators of Example 1 and Comparative Example 1

[0184] Experimental method: Assemble button half-cell (diaphragm + graphite anode + lithium sheet), the electrolyte is 1MLiPF6inEC / DMC;

[0185] The blue power test system performs the first charge and discharge (0.1C);

[0186] Calculate the first coulombic efficiency: first discharge capacity / first charge capacity × 100%.

[0187] Experimental data:

[0188] Table 1:

[0189]

[0190] Experimental summary:

[0191] In this experiment, button-type half-cells were assembled, the first charge and discharge were performed using a blue power test system, and the first coulombic efficiency was calculated to verify the pre-lithium replenishment effect of the lithium-ion battery diaphragm in Example 1 and Comparative Example 1. From the experimental data, the first coulombic efficiency of Example 1 was as high as 87.5%, while that of Comparative Example 1 was only 70.97%, which shows that the specific raw material formula and preparation process in Example 1 make the pre-lithium replenishment effect of the diaphragm more significant, and can more effectively improve the utilization rate of lithium during the first charge and discharge of the battery, thereby providing the battery with a higher first discharge capacity. In comparison, due to the reduced amount of Li2S-Li3N composite and the lower hot pressing temperature, the pre-lithium replenishment effect of Comparative Example 1 is negatively affected, and the first coulombic efficiency is low.

[0192] Experiment 2: Verification of interface bonding strength

[0193] Experimental samples: finished lithium-ion battery separators of Example 2 and Comparative Example 2

[0194] Experimental method: The separator was laminated with the graphite negative electrode and cut into 25 mm × 100 mm samples;

[0195] Use a universal tensile testing machine to test the 180° peel strength (tensile speed 50 mm / min);

[0196] The peak peel strength was recorded.

[0197] Experimental data:

[0198] Table 2:

[0199] sample Peel strength peak (N / cm) Example 2 12 Comparative Example 2 7

[0200] Experimental summary: In this experiment, the diaphragms of Example 2 and Comparative Example 2 were laminated to the graphite negative electrode to form specimens, and the 180° peel strength was tested using a universal tensile machine to verify the interfacial bonding strength between the diaphragm and the electrode. The experimental results showed that the peak peel strength of Example 2 reached 12 N / cm, while that of Comparative Example 2 was only 7 N / cm, which fully demonstrated that the formula and preparation process of Example 2, especially the specific polyvinylidene fluoride-hexafluoropropylene copolymer content, dopamine monomer dosage and self-polymerization time, effectively enhanced the bonding effect between the diaphragm and the electrode. The interfacial bonding strength of Comparative Example 2 decreased due to the increased polyvinylidene fluoride-hexafluoropropylene copolymer content, decreased CNT content and shortened self-polymerization time. During the use of the battery, the diaphragm and the electrode may be more easily separated, affecting the battery performance.

[0201] Experiment 3: Cyclic stability verification

[0202] Experimental samples: finished lithium-ion battery separators of Example 3 and Comparative Example 3

[0203] Experimental method: Assemble the full battery (diaphragm + graphite negative electrode + LiCoO2 positive electrode), the electrolyte is 1MLiPF6inEC / DMC;

[0204] The blue power test system performs 500 cycles of charge and discharge (1C);

[0205] The first and 500th discharge capacities were recorded, and the capacity retention rate was calculated.

[0206] Experimental data:

[0207] Table 3:

[0208]

[0209]

[0210] Experimental summary: In this experiment, a full battery was assembled, and 500 cycles of charge and discharge were performed using a blue power test system. The first and 500th discharge capacities were recorded and the capacity retention rate was calculated to verify the cycle stability of the lithium-ion battery separators of Example 3 and Comparative Example 3. The capacity retention rate of Example 3 was 85.19%, while that of Comparative Example 3 was only 65.38%, which shows that the separator of Example 3 can better maintain the discharge capacity of the battery in multiple charge and discharge cycles under the synergistic effect of factors such as suitable Li2S-Li3N composite particle size, dopamine monomer content, and hot pressing pressure in formula and preparation process, and has good cycle stability. In Comparative Example 3, due to the increased particle size of the Li2S-Li3N composite, the reduced dopamine monomer content, and the increased hot pressing pressure, the performance of the separator decays faster during the cycle, resulting in a lower capacity retention rate, which affects the long-term performance of the battery.

[0211] Experiment 4: Rate performance verification

[0212] Experimental samples: finished lithium-ion battery separators of Example 4 and Comparative Example 4

[0213] Experimental method: Assemble the full battery (diaphragm + graphite negative electrode + LiCoO2 positive electrode);

[0214] The Blue Electric test system was charged and discharged at 0.2C, 0.5C, 1C, and 2C rates, with each rate cycled 5 times;

[0215] The discharge capacity at different rates was recorded and the capacity retention rate was calculated (based on the 0.2C capacity).

[0216] Experimental data:

[0217] Table 4:

[0218]

[0219]

[0220] Experimental summary: In this experiment, a full battery was assembled, and the Blue Electric test system was used to charge and discharge at different rates, and the capacity retention rate at different rates was calculated. The rate performance of the lithium-ion battery separator of Example 4 and Comparative Example 4 was verified. The experimental data showed that the capacity retention rate of Example 4 at different rates was relatively high, such as 91.67% at 0.5C, 83.33% at 1C, and 70.83% at 2C; while the capacity retention rate of Comparative Example 4 at the same rate was lower, such as 82.61% at 0.5C, 69.57% at 1C, and 5 2.17%, which indicates that the diaphragm formula and preparation process of Example 4, such as the specific N-methylpyrrolidone solvent content, CNT dosage and self-polymerization temperature, can better maintain the discharge capacity of the battery at different charge and discharge rates and has good rate performance. In Comparative Example 4, due to the increased N-methylpyrrolidone solvent content, the increased CNT content and the increased self-polymerization temperature, the internal ion transport and electrode reaction of the battery are hindered to a certain extent when the diaphragm is charged and discharged at a high rate, thereby reducing the capacity retention rate and affecting the performance of the battery at different rates.

[0221] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion, characterized in that: The following raw materials are included in percentage by mass: 10% to 20% slurry, including: 70% to 85% polyvinylidene fluoride-hexafluoropropylene copolymer; 5% to 10% pre-supplemented lithium material; 2% to 5% adhesion enhancer; 3% to 8% conductive filler; 80% to 90% solvent.

2. A lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 1, characterized in that: The pre-lithium supplement material is a nano-scale Li2S-Li3N composite with a particle size ranging from 50nm to 200nm.

3. The lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 1, characterized in that: The adhesion enhancer is a polydopamine coating.

4. The lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 1, characterized in that: The conductive filler is a carbon nanotube with a diameter ranging from 10 nm to 30 nm and a length ranging from 1 μm to 10 μm.

5. The lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 1, characterized in that: The solvent is N-methylpyrrolidone.

6. A method for preparing a lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion, used for preparing a lithium-ion battery separator that can be pre-supplemented with lithium and has high adhesion as described in claims 1-5, characterized in that: The following steps are involved: Adding polyvinylidene fluoride-hexafluoropropylene copolymer into N-methylpyrrolidone solvent, stirring until completely dissolved, and adding pre-lithium supplement material, conductive filler and adhesion enhancer for ultrasonic dispersion; Coating and self-polymerization, coating the mixed liquid on the substrate surface, using a scraper to control the thickness, and then immersing it in an alkaline solution; Hot pressing molding, stacking the self-polymerized diaphragm and the electrode and hot pressing; Vacuum drying: Place the hot-pressed diaphragm in a vacuum drying oven to remove residual solvent.

7. The method for preparing a lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 6, characterized in that: The ultrasonic dispersion power is 200W to 400W, and the ultrasonic time is 30min to 60min.

8. The method for preparing a lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 6, characterized in that: The pH of the self-polymerization alkaline solution is 8.5-9.0, the self-polymerization reaction time is 12h-24h, and the reaction temperature is 25°C-35°C.

9. The method for preparing a lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 6, characterized in that: The hot pressing molding temperature is 70° C. to 90° C., the hot pressing pressure is 5 MPa to 10 MPa, and the hot pressing time is 5 min to 10 min.

10. The method for preparing a lithium-ion battery separator capable of pre-supplementing lithium and having high adhesion according to claim 6, characterized in that: The vacuum drying temperature is 60° C. to 80° C., the drying time is 12 h to 24 h, and the vacuum degree is -0.1 MPa.

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