CN115863528A - Negative electrode slurry for secondary battery and preparation method thereof - Google Patents
Negative electrode slurry for secondary battery and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a negative electrode slurry for a secondary battery and a preparation method thereof. The preparation method of the negative electrode slurry for the secondary battery comprises the following steps: 1) Diamine and dicarboxylic anhydride are used as raw materials to prepare a polyamide acid prepolymer solution with an amino end capping; 2) Uniformly mixing the amino-terminated polyamic acid prepolymer solution with a negative electrode active substance and a conductive agent, adding or not adding a polar solvent, and uniformly mixing to obtain a slurry precursor; 3) Adding ternary anhydride into the slurry precursor, and stirring for reaction to obtain the cathode slurry for the secondary battery; wherein the addition amount of the tribasic anhydride is 0.01 to 1.0mol percent of the dosage of the diamine in the step 1). When the cathode prepared by the cathode slurry is applied to a secondary battery, the first effect and the cycling stability of the secondary battery can be effectively improved.
Description
Technical Field
The invention relates to a secondary battery, in particular to a negative electrode slurry for the secondary battery and a preparation method thereof.
Background
Lithium ion secondary batteries characterized by small size and large capacity have been widely used as power sources for electronic devices such as mobile phones and notebook computers, and contribute to improving convenience of mobile IT devices. In recent years, large-scale applications such as power supplies for driving electric motorcycles and automobiles and storage batteries for smart grids have attracted attention. As the demand for lithium ion secondary batteries increases and they have been used in various fields, the batteries are required to have characteristics such as higher energy density, life characteristics capable of withstanding long-term use, and usability under a wide range of temperature conditions.
In all battery structures, the positive and negative electrode materials have the greatest influence on the capacity of the battery. The negative electrode material is widely commercially used graphite at present, the specific capacity of the graphite is close to the theoretical value of 372mAh/g, and the silicon-based negative electrode material has higher specific capacity which can reach 4200mAh/g and is considered to be the material which is most likely to replace the graphite. However, silicon-based materials undergo severe volume expansion and contraction (up to about 400% expansion) during the charging and discharging processes of batteries, so that the materials are very easy to crack, pulverize and peel, thereby causing capacity loss and battery failure.
The silicon-carbon composite negative electrode using carbon-coated silicon can reduce the volume effect of silicon, and on the basis, a bonding agent capable of being bonded with the copper foil and the silicon-carbon material is developed, so that the volume expansion effect of the negative electrode material can be relieved to a greater extent, and the cycle stability of the silicon-carbon negative electrode and the service life of a battery are improved.
In order to alleviate the disadvantages of the silicon-containing negative electrode such as volume expansion effect during charge and discharge, the prior art proposes to use a polyimide resin as a binder for the negative electrode active material. For example, patent publication No. CN114805804a discloses a preparation method of a polyimide adhesive, which comprises the following steps: (i) Performing polycondensation reaction on dicarboxylic anhydride and diamine containing common diamine and functional diamine in a polar solvent to obtain a linear polyamic acid solution, and then adding polyamine to perform reaction to obtain a branched cross-linked polyamic acid solution; (ii) Fully mixing and uniformly stirring a positive electrode active substance or a negative electrode active substance, a conductive agent, the branched cross-linked polyamic acid solution and a polar solvent to obtain electrode slurry; (iii) And uniformly coating the electrode slurry on a current collector, drying, rolling, and finally performing heat treatment to obtain the polyimide adhesive on the lithium ion battery electrode plate. The invention points out that the polyimide adhesive prepared by adopting functional diamine of strong polar group (at least one of hydroxyl group, carboxyl group, sulfonic acid group, trifluoromethyl and cyano group) has strong polarity, and the polyimide adhesive prepared by adding polyamine has a branched crosslinking structure; the polyimide adhesive with strong polarity and a branched crosslinking structure, which is obtained by adding functional diamine and polyamine, has strong hydrogen bond effect and bonding effect with an active material, so that the adhesive property among electrode material components is greatly enhanced, and the integrity of the electrode components is effectively ensured; meanwhile, a uniform and continuous protective coating is formed on the surface of the active material, so that the coating performance of the adhesive is greatly improved, and the stability of an electrode-electrolyte interface is effectively ensured. When the composite material is applied to a negative electrode, the composite material has better adhesiveness than a common PVDF system; when the lithium ion battery is applied to the anode, the capacity retention rate of the lithium ion battery is about 90% after 100 circles at 25 ℃; the negative electrode has no data record, and the physical property of the battery is effectively improved (better capacity retention rate). In general, the polyimide resin binder is not ideal for improving cycle stability, and the first coulombic efficiency of the battery after the binder is applied to a lithium ion secondary battery is not recorded. On the other hand, the applicant found that the addition of the polyamine before the size mixing in the above invention is very easy to cause the system to be gelled in case of high addition amount, which results in that the obtained polyamic acid solution cannot be used.
Disclosure of Invention
The invention aims to provide a negative electrode slurry for a secondary battery and a preparation method thereof, wherein the negative electrode slurry can effectively improve the first coulombic efficiency (first effect) and the cycle stability of the secondary battery.
In order to solve the technical problems, the invention adopts the following technical scheme:
a preparation method of negative electrode slurry for a secondary battery comprises the following steps:
1) Diamine and dicarboxylic anhydride are used as raw materials to prepare a polyamide acid prepolymer solution with an amino end capping;
2) Uniformly mixing the amino-terminated polyamic acid prepolymer solution with a negative electrode active substance and a conductive agent, adding or not adding a polar solvent, and uniformly mixing to obtain a slurry precursor;
3) Adding ternary anhydride into the slurry precursor, and stirring for reaction to obtain the cathode slurry for the secondary battery; wherein the addition amount of the tribasic anhydride is 0.01 to 1.0mol percent of the dosage of the diamine in the step 1).
The negative electrode slurry is prepared by adding the tribasic anhydride to be crosslinked after size mixing to form a two-dimensional network-like surface structure which is completely coated on the surface of a negative electrode active material, and a polyamic acid molecular chain of the two-dimensional network-like surface structure is coated on a micro-nano porous silicon powder or porous silicon carbon composite active material body in a form similar to a whole planar network to form a cage-shaped structure; on the other hand, the molecular chain of the polyamic acid and/or the polyimide is chemically bonded with the surface active group of the silicon powder by covalent bond, hydrogen bond and the like to comprehensively form strong adhesive force. The comprehensive effects of the two aspects effectively inhibit the influence of cracks or micronization caused by repeated expansion and contraction of the volume of the silicon material in the charging and discharging processes, thereby greatly improving the cycle stability and the first effect (first coulomb efficiency) of the lithium ion battery.
In step 3) of the above preparation method, the triacid anhydride is preferably one or a combination of two or more selected from trimellitic anhydride, hexaazatrimellitic anhydride or benzo [ G, H, I ] perylene-1,2,4,5,10,11-hexacarboxylic anhydride, and more preferably hexaazatrimellitic anhydride containing N-heterocycle. The tribasic anhydride is preferably dissolved in a polar solvent and then added as a solution.
Applicants have found in tests that control of the amount of the tribasic anhydride added is critical and directly affects whether the resulting negative electrode slurry gels and the characteristics of the battery when applied to a lithium ion battery (e.g., first effect and suppression of volume expansion effect). The test results of the applicant show that when the addition amount of the ternary anhydride is controlled to be 0.05-0.5 mol% of the dosage of the diamine in the step 1), the obtained negative electrode slurry can obtain better first effect and cycle stability when applied to the negative electrode of the lithium ion battery. In a more preferred embodiment, the amount of the tribasic anhydride added is controlled to be 0.05 to 0.1mol% based on the amount of the diamine used in step 1).
In step 1) of the above preparation method, the diamine and the dicarboxylic anhydride are conventional aromatic diamine and aromatic dicarboxylic anhydride, and the polyamic acid prepolymer solution terminated with amino groups is prepared by a conventional method (such as in-situ polymerization), for example, the diamine and the dicarboxylic anhydride are placed in a polar aprotic solvent and subjected to polycondensation reaction. Wherein, the selection and the dosage of the polar aprotic solvent, the temperature and the time of the polycondensation reaction and the like are the same as those of the prior art. For example, the polar aprotic solvent may be any one or a combination of two or more of N, N-dimethylformamide, N-dimethylacetamide, N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, hexamethylphosphoric triamide, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, tetrahydrofuran, bis [2- (2-methoxyethoxy) ethyl ] ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethylurea, m-cresol, phenol, and γ -butyrolactone. Further preferred is N, N-dimethylacetamide, N-diethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone or γ -butyrolactone, and particularly preferred is N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone or γ -butyrolactone. The selection of other parameters is not described in detail here. In this step, the diamine is preferably used in an excess amount to the dicarboxylic anhydride based on the preparation of the polyamic acid prepolymer solution terminated with an amino group, and their molar ratio is preferably 1:0.94 to 0.99, particularly preferably 1:0.95 to 0.97. The applicant finds in experiments that the viscosity of the prepolymer solution system is proper in the range of 2000-80000 cp, and if the viscosity of the prepolymer solution system is too high, gelation is easily formed when the ternary anhydride is added.
Furthermore, the diamine is preferably an asymmetric diamine, and the dianhydride is preferably an asymmetric dianhydride, so that the first-effect and cycle stability characteristics of the lithium ion battery can be further optimized. Specifically, the asymmetric diamine may be any one or a combination of two or more selected from 3,4 '-diaminobenzanilide (3,4' -DABA), 3,4 '-diaminodiphenyl ether (3,4' -ODA), m-phenylenediamine (m-PDA), 3,4 '-diaminodiphenyl sulfone (3,4' -DDS), 3,4 '-diaminobiphenyl (3,4' -DAB), 3,4 '-diaminodiphenyl methane (3,4' -MDA), 3,4 '-diaminodiphenyl disulfide and 3,4' -diaminodiphenyl sulfide, and further preferably is 3,4'-DABA, 3,4' -ODA or 3,4 '-diaminodiphenyl sulfide, and particularly preferably is 3,4' -DABA. The asymmetric structural dianhydride may be any one or a combination of two or more selected from 2,3,3',4' -biphenyltetracarboxylic dianhydride (α -BPDA), 2,3,3',4' -benzophenonetetracarboxylic dianhydride (2,3,3 ',4' -BTDA), 2,3,3',4' -diphenylsulfonetetracarboxylic dianhydride (2,3,3 ',4' -DSDA), 2,3,3',4' -diphenylthioethertetracarboxylic dianhydride (2,3,3 ',4' -TDPA) and 2,3,3',4' -diphenylethertetracarboxylic dianhydride (α -ODPA), further preferably 2,3,3',4' -DSDA or 2,3,3',4' -TDPA, particularly preferably 2,3,3',4' -TDPA.
In step 2) of the preparation method, the negative electrode active material and the conductive agent are conventional choices in the prior art, and the negative electrode active material may preferably be a combination containing one or more of carbon, silicon and a silicon alloy, and more preferably is a porous silicon-carbon composite powder containing porous silicon powder or silicon alloy powder; for the conductive agent, conductive carbon black is generally used. The ratio of the amino-terminated polyamic acid prepolymer solution to the negative active substance to the conductive agent is also the same as that in the prior art, and in the application, the weight ratio of the amino-terminated polyamic acid prepolymer solution to the negative active substance to the conductive agent is preferably 15-2: 65-96: 20-2, wherein the amino-terminated polyamic acid prepolymer solution is calculated by the amount of solid components in the prepolymer solution.
The polar solvent involved in step 2) of the preparation method is a conventional solvent used in the prior art for preparing the negative electrode slurry, and may be specifically the same as the above-mentioned polar aprotic solvent used for preparing the polyamic acid prepolymer solution, and is preferably NMP and/or DMAc. The amount of the polar solvent used in this step is such that the viscosity of the obtained slurry precursor meets the requirement of easy coating, and the viscosity of the obtained slurry precursor is generally controlled to be 2000-10000 cp, preferably 4000-7000 cp. When the viscosity of the polyamide acid prepolymer solution prepared in the earlier stage and terminated by amino groups is lower, and the viscosity of the system is just in the limited range after the negative electrode active material and the conductive agent are added and uniformly stirred, no polar solvent needs to be added.
The invention also provides the negative electrode slurry for the secondary battery prepared by the method.
Compared with the prior art, the invention is characterized in that:
1. in the invention, the three-component anhydride is added at the later stage of size mixing for crosslinking to form a quasi-two-dimensional reticular surface structure which is completely coated on the surface of a negative active material, and a polyamic acid molecular chain of the crosslinked reticular surface structure is coated on a micro-nano porous silicon powder or porous silicon carbon composite active material body in a form similar to a whole planar network to form a cage-shaped structure; on the other hand, the molecular chain of the polyamic acid and/or the polyimide is chemically bonded with the surface active group of the silicon powder by covalent bond, hydrogen bond and the like to comprehensively form strong adhesive force. The comprehensive effects of the two aspects effectively inhibit the influence of cracks or micronization caused by repeated expansion and contraction of the volume of the silicon material in the charging and discharging processes, thereby greatly improving the cycle stability and the first effect of the lithium ion battery.
2. Further, a polyimide structure formed by imidization of polyamic acid polymerized by asymmetric monomers has a high-degree amorphous phase, so that the lithium ion conductivity in a lithium battery system can be improved, namely lithium ions can rapidly migrate in the amorphous phase of a local loose chain segment in the polyimide structure, the binding agent is promoted to have good mechanical property, high room-temperature conductivity, a wide chemical stability window and the like, and the characteristics of the lithium ion battery such as cycle stability, first effect, high magnification and the like are further optimized.
3. The lithium battery characteristics (such as first effect, stable circulation and the like) can be further optimized by the cathode slurry prepared from the diamine containing the N asymmetric structure and the tribasic anhydride containing the N heterocyclic group.
4. The negative electrode slurry is used for preparing a negative electrode layer, and is further applied to a lithium ion battery, the first coulombic efficiency of the prepared battery is more than or equal to 90%, the circulation capacity retention rate of 200 cycles is more than or equal to 96%, and the Z-direction (thickness direction) expansion rate of the pole piece before and after 200 cycles is less than or equal to 56%.
Detailed Description
In order to better explain the technical solution of the present invention, the present invention is further described in detail with reference to the following examples, but the embodiments of the present invention are not limited thereto.
Example 1
1. Preparation of cathode slurry
1) 36.447g (0.182 mol) of aromatic diamine 4,4 '-diaminodiphenyl ether (4,4' -ODA) was dissolved in 510g of NMP under stirring at room temperature under nitrogen atmosphere, and then 53.018g (0.180 mol, divided into 3 portions) of aromatic dicarboxylic anhydride 3,3',3,4' -biphenyltetracarboxylic dianhydride (s-BPDA) was added in a total amount (molar ratio of diamine to dicarboxylic anhydride 1:0.99 Stirring for 24h to obtain a polyamic acid prepolymer solution terminated with amino groups (the solid content of the obtained polyamic acid prepolymer solution is about 15%, wherein the total solid content is about 90 g);
2) Taking 135g of the polyamic acid prepolymer solution (the total solid content is 15 g) with the amino end capping prepared in the step 1), 650g of negative active material (graphite 520g, nano-porous silicon powder (the specific surface area is 58.196 m) 2 G, average mesoporous diameter of about 26.9nm, the same applies below) 130g, graphite: nano porous silicon powder =8: 2) And 20.0g of a conductive agent (conductive carbon black), in which the active material: adhesive: conductive agent =65:15:20 (weight ratio), mixing uniformly, adding 1400g NMP, grinding the obtained mixture, blending and stirring to obtain a slurry precursor (the viscosity is about 6920 cp);
3) 8.742mg (0.031 mmol) of tribasic anhydride benzene hexaformic acid tribasic anhydride (the addition amount of the tribasic anhydride is equal to 0.01mol% of the amount of the diamine in the step 1) is added into the obtained slurry precursor, and the mixture is stirred and reacted for 6 hours, so that the cathode slurry is obtained.
2. Preparation of positive and negative electrodes of lithium battery
2.1 negative electrode
The negative electrode slurry prepared in the embodiment is uniformly coated on a copper foil, and the thickness of the solidified negative electrode slurry is controlled to be 38 microns +/-2.0 microns by adjusting the gap of a coating roller (scraper). And (3) placing the copper foil uniformly coated with the negative electrode slurry in an oven, heating for 1h at 80 ℃ under the conditions of flowing nitrogen and oxygen concentration lower than 18ppm, raising the temperature to 320 ℃ at the speed of 3.0 ℃/min, and preserving the temperature for 2.0h at 320 ℃ to obtain the pole piece for the negative electrode.
2.2 Positive electrode
Ternary positive electrode (NCM 523) active material: polyvinylidene fluoride: the conductive carbon black is 95:2:3, adding a solvent NMP to adjust the system to a proper viscosity (6000 +/-500 cp), placing the mixture in a three-roll grinder to grind for 3 hours and dispersing at a high speed for 2 hours to obtain the anode slurry. Coating the positive electrode slurry on an aluminum foil by using a scraper, adjusting the gap of a coating roller (scraper) to control the thickness of the cured positive electrode slurry to be 110 mu m +/-3.0 mu m, placing the coated aluminum foil in an oven, and preserving the heat for 2.2h at 120 ℃ under the condition of air circulation to obtain the pole piece for the positive electrode.
3. Preparation of the Battery
In order to reduce the gap between the active materials, the negative pole piece and the positive pole piece of the lithium battery are properly rolled by a rolling machine. And cutting the rolled negative plate and positive plate into round pieces with the diameter of 14mm by using a punching machine. In an argon glove box (H) 2 O＜0.01ppm O 2 Less than 0.01 ppm) assembling a CR2032 button cell, sequentially assembling a negative electrode shell, a negative electrode sheet, a diaphragm, a positive electrode sheet, foamed nickel, a spring sheet and a positive electrode shell, and respectively dropwise adding about 1mL of electrolyte at two ends of the diaphragm, wherein the electrolyte is 1.0mol/LLIPF 6 Dissolving in mixed solution of EC and DMC (EC: DMC =1:1, volume ratio), placing the assembled battery in a sealing machine for packaging, wherein the packaging pressure is 75MPa, and carrying out corresponding electrochemical performance test after standing for 24 h.
4. Measurement of Charge and discharge characteristics
The battery groups manufactured by the method are subjected to a cyclic charge-discharge characteristic test, the battery is subjected to a charge and discharge test and a cyclic test at 25 ℃, the test adopts a 0.2C current charge-discharge test, the voltage window is 0.005-1.5V, and the electric quantity flowing from the start to the end of charge or discharge is defined as the charge capacity or the discharge capacity.
The charge and discharge efficiency after the first 200 cycles [ wherein charge and discharge efficiency = (discharge capacity/charge capacity) × 100% ] was tested.
And calculating the expansion rate of the negative plate according to the thickness of the active material of the plate before charging and discharging and the thickness of the active material of the plate after 200 cycles by taking the thickness of the scanning electron microscope sectional view of the negative plate of the battery before charging and discharging and after 200 cycles as a reference. Measuring the initial thickness H of the negative pole piece 0 Measuring the thickness H of the cathode after 200 cycles 200 And according to the formula (thickness direction Z), the expansion rate = (H) 200 -H 0 )/H 0 * And calculating the expansion rate of the pole piece by 100 percent.
The test results are: the first coulombic efficiency is about 90%, the capacity retention rate after 200 cycles is about 96%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 56%.
Comparative examples 1 to 1
The difference from example 1 is only that: when preparing the negative electrode slurry, the step 3) is omitted, namely, the slurry precursor prepared in the step 2) is used as the negative electrode slurry to prepare the negative electrode.
The test results are: the initial coulombic efficiency is about 76%, the capacity retention rate after 200 cycles is about 79%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 128%.
Comparative examples 1 to 2
The difference from example 1 is only that: in the preparation of the negative electrode slurry, the ternary anhydride is added before the negative electrode active material and the conductive agent are added. The specific operation is as follows:
1) Same as step 1) of example 1;
2) Taking 135g of the polyamic acid prepolymer solution (the total solid content is 15 g) which is prepared in the step 1) and is end-capped by amino, mixing 8.742mg (0.031 mmol) of tribasic anhydride benzene hexaformic acid tribasic anhydride (the addition of the tribasic anhydride is equal to 0.01mol percent of the usage of diamine in the step 1), and stirring for reaction for 6 hours;
3) 650g of negative active material (graphite 520g and nano-porous silicon powder (the specific surface area is about 58.196 m) are added into the feed liquid obtained in the step 2) 2 (ii) g, mesoporeAverage pore diameter of about 26.9nm, the same applies below) 130g, graphite: nano porous silicon powder =8: 2) And 20.0g of a conductive agent (conductive carbon black), in which the active material: adhesive: conductive agent =65:15:20 (weight ratio), mixing evenly, adding 1400g NMP, grinding the mixture, blending and stirring to obtain the cathode slurry.
The test results are: the initial coulombic efficiency is about 88 percent, the capacity retention rate after 200 cycles is about 93 percent, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 95 percent.
Comparative examples 1 to 3
The difference from example 1 is only that: in preparing the anode slurry, the amount of the tribasic anhydride added in step 3) was equivalent to 1.05mol% of the amount of the diamine used in step 1).
The obtained negative electrode slurry has gel points, cannot be normally coated and used, and then cannot be used for preparing a negative electrode, so that the test of the battery characteristics cannot be carried out.
Example 2
The difference from example 1 is only that: in the step 3), the adding amount of the tribasic anhydride, the mellitic acid and the tribasic anhydride is changed to 0.875g (3.035 mmol) (the adding amount of the tribasic anhydride is equal to 1.0mol percent of the using amount of the diamine in the step 1)), and the stirring reaction is changed to 8 hours.
The test results are: the initial coulombic efficiency is about 92%, the capacity retention rate after 200 cycles is about 97%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 55%.
Comparative example 2-1
The difference from example 2 is only that: in the preparation of the negative electrode slurry, the ternary anhydride is added before the negative electrode active material and the conductive agent are added. The specific operation is as follows:
1) Same as step 1) of example 2;
2) Taking 135g of the polyamic acid prepolymer solution (the total solid content is 15 g) which is prepared by the step 1) and is end-capped by amino, mixing with 0.875g (3.035 mmol) of tribasic anhydride benzene hexacarboxylic acid tribasic anhydride (the addition of the tribasic anhydride is equal to 1.0mol percent of the dosage of the diamine in the step 1), and stirring for reaction for 8 hours. The polyamic acid solution obtained in the step has a gel point, and cannot be used for preparing the negative electrode slurry in the next step.
Example 3
1) Under the conditions of nitrogen atmosphere and room temperature, 34.132g (0.170 mol) of asymmetric structure diamine 3,4 '-diaminodiphenyl ether (3,4' -ODA) is stirred and dissolved in 704g of DMAc, and then 53.621g (0.164 mol) of asymmetric structure dianhydride 2,3,3',4' -diphenyl sulfide tetracarboxylic dianhydride (2,3,3 ',4' -TDPA) is added in 1 portion (the molar ratio of diamine to dianhydride is 1:0.94 Stirring for 12h to obtain a polyamic acid prepolymer solution terminated with amino groups (the solid content of the obtained polyamic acid prepolymer solution is about 12%, wherein the total solid content is about 96 g);
2) Taking 84.0g of the polyamide acid prepolymer solution (total solid content: 15.0 g) end-capped with anhydride group prepared in step 1), 80.0g of negative electrode active material (graphite 40g, nano-porous silicon powder 40g, graphite: nano porous silicon powder =5: 5) And 10.0g of a conductive agent (conductive carbon black), in which the active material: adhesive: conductive agent =80:10:10 (weight ratio), mixing uniformly, adding about 185g DMAc, grinding the obtained mixture, blending and stirring to obtain a slurry precursor (the viscosity is about 4080 cp);
3) And (3) adding 0.04g (0.139 mmol) of tribasic anhydride benzene hexacarboxylic acid tribasic anhydride (the addition amount of the tribasic anhydride is equal to 0.5mol% of the dosage of the diamine in the step 1) into the obtained slurry precursor, and stirring for reacting for 6 hours to obtain the cathode slurry.
The preparation of the positive and negative electrodes of the lithium battery, the preparation of the battery, and the charge and discharge characteristics test were the same as in example 1.
The test results are: the initial coulombic efficiency is about 95%, the capacity retention rate after 200 cycles is about 98%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 52%.
Comparative example 3-1
1. Preparation of cathode slurry
1) 63.399g (0.293 mol) of asymmetric diamine 3,4 '-diaminodiphenyl ether (3,4' -ODA) is stirred and dissolved in 840g DMAC under the condition of nitrogen atmosphere and room temperature, then 96.601g (0.296 mol) of asymmetric diamine 2,3,3',4' -diphenyl sulfide tetracarboxylic dianhydride (2,3,3 ',4' -TDPA) is added in a total amount of 3 times (the molar ratio of diamine to diamine is 0.99: 1) Stirring for 24h to obtain polyamide acid prepolymer solution terminated by anhydride group (the solid content of the obtained polyamide acid prepolymer solution is about 16%, wherein the total solid content is about 160 g);
2) Taking 37.5g of the polyamide acid prepolymer solution end-capped with anhydride groups prepared in step 1) (the total solid content is 6.0 g), and 90.0g of negative electrode active material (45 g of graphite, 45g of nano-porous silicon powder, graphite: nano porous silicon powder =5: 5) And 4.0g of a conductive agent (conductive carbon black), in which the active material: adhesive: conductive agent =90:6:4 (weight ratio), uniformly mixing, adding about 150g of NMP, grinding the obtained mixture, blending and stirring to obtain a slurry precursor (the viscosity is about 10000 cp);
3) 1,3,5-Triaminobenzene (TAB) triamine (the dosage of the triamine is 0.1mol percent of the total molar weight of the dibasic anhydride, the diamine and the triamine) is added into the obtained slurry precursor, and the mixture is stirred and reacted for 3 hours to obtain the cathode slurry.
The preparation of the positive and negative electrodes of the lithium battery, the preparation of the battery and the charge and discharge characteristics test were the same as in example 1.
The test results are: the first coulombic efficiency is about 84%, the capacity retention rate after 200 cycles is about 88%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 89%.
Comparative examples 3 to 2
The difference from comparative example 3 is only that: when the cathode slurry is prepared, the adding amount of the triamine 1,3,5-Triaminobenzene (TAB) in the step 3) is changed to be 2mol% of the total molar amount of the dicarboxylic anhydride, the diamine and the triamine, the reaction is carried out, the obtained branched crosslinking type polyamic acid solution is gelatinized, and the cathode cannot be further prepared normally.
Example 4
1. Preparation of cathode slurry
1) 88.681g (0.391 mol) of asymmetric diamine 3,4 '-diaminobenzanilide (3,4' -DABA) was dissolved in 984g of NMP under stirring at room temperature under nitrogen atmosphere, and then 123.5g (0.379 mol) of asymmetric diamine 2,3,3',4' -diphenylsulfide tetracarboxylic dianhydride (2,3,3 ',4' -TDPA) was added in 3 portions (molar ratio of diamine to dicarboxylic anhydride: 1:0.97 Stirring for 22h to obtain a polyamic acid prepolymer solution terminated with amino groups (the solid content of the obtained polyamic acid prepolymer solution is about 18%, wherein the total solid content is about 216 g);
2) Taking 33.5g of the polyamic acid prepolymer solution end-capped with an anhydride group prepared in step 1) (total solid content 6.0 g), 90.0g of a negative electrode active material (54 g of graphite, 36g of nanoporous silicon powder, graphite: nano porous silicon powder =6: 4) And 4.0g of a conductive agent (conductive carbon black), in which the active material: adhesive: conductive agent =90:6:4 (weight ratio), uniformly mixing, adding about 120g of NMP, grinding the obtained mixture, blending and stirring to obtain a slurry precursor (the viscosity is about 10130 cp);
3) And (3) adding 0.025g (0.05 mmol) of ternary anhydride hexaazatrimellitic acid anhydride (the addition amount of the ternary anhydride is equal to 0.5mol% of the amount of the diamine in the step 1) into the obtained slurry precursor, and stirring for reaction for 4 hours to obtain the cathode slurry.
The preparation of the positive and negative electrodes of the lithium battery, the preparation of the battery and the charge and discharge characteristics test were the same as in example 1.
The test results are: the initial coulombic efficiency is about 96%, the capacity retention rate after 200 cycles is about 98%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 50%.
Example 5
The only difference from example 4 is that: in the preparation of the negative electrode slurry, the amount of the trianhydride hexaazatriphenylhexacarboxylic anhydride added in step 3) is equivalent to 0.05mol% of the amount of the diamine used in step 1).
The test results are: the initial coulombic efficiency is about 96%, the capacity retention rate after 200 cycles is about 98%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 51%.
Example 6
1. Preparation of cathode slurry
1) 53.778g (0.269 mol) of asymmetric diamine 3,4 '-diaminodiphenyl ether (3,4' -ODA) was dissolved in 850g of NMP under stirring at room temperature in a nitrogen atmosphere, and then 91.412g (0.256 mol) of asymmetric dianhydride 2,3,3',4' -diphenylsulfone tetracarboxylic dianhydride (2,3,3 ',4' -DSDA) was added in a total amount of 91.412g (1 divided addition) (molar ratio of diamine to dianhydride was 1:0.95 Stirring for 12h to obtain a polyamic acid prepolymer solution terminated with amino groups (the solid content of the obtained polyamic acid prepolymer solution is about 15%, wherein the total solid content is about 150 g);
2) Taking 40g of the anhydride group-terminated polyamic acid prepolymer solution prepared in step 1) (6.0 g of the total solid content), 88.0g of a negative electrode active material (44 g of graphite, 44g of nanoporous silicon powder, graphite: nano porous silicon powder =5: 5) And 6.0g of a conductive agent (conductive carbon black), in which the active material: adhesive: conductive agent =88:6:6 (weight ratio), uniformly mixing, adding 224g of NMP, grinding the obtained mixture, blending and stirring to obtain a slurry precursor (the viscosity is about 2926 cp);
3) Adding a DMF solution containing 0.039g (0.086 mmol) of hexaazatrimellitic anhydride into the obtained slurry precursor (formed by dissolving 0.039g of hexaazatrimellitic anhydride in 10g of DMF, wherein the addition amount of the hexaazatrimellitic anhydride is equal to 0.8mol% of the dosage of the diamine in the step 1), and stirring for reaction for 7.5h to obtain the cathode slurry.
The preparation of the positive and negative electrodes of the lithium battery, the preparation of the battery, and the charge and discharge characteristics test were the same as in example 1.
The test results are as follows: the first coulombic efficiency is about 95%, the capacity retention rate after 200 cycles is about 98%, and the Z-direction (thickness direction) expansion rate of the pole piece after 200 cycles is about 52%.
Claims (10)
1. A preparation method of negative electrode slurry for a secondary battery comprises the following steps:
1) Diamine and dicarboxylic anhydride are used as raw materials to prepare a polyamide acid prepolymer solution with an amino end capping;
2) Uniformly mixing the amino-terminated polyamic acid prepolymer solution with a negative electrode active substance and a conductive agent, adding or not adding a polar solvent, and uniformly mixing to obtain a slurry precursor;
3) Adding ternary anhydride into the slurry precursor, and stirring for reaction to obtain the cathode slurry for the secondary battery; wherein the addition amount of the tribasic anhydride is 0.01 to 1.0mol percent of the dosage of the diamine in the step 1).
2. The method according to claim 1, wherein in step 3), the triacid anhydride is one or a combination of two or more selected from trimellitic anhydride, hexaazatrimellitic anhydride, or benzo [ G, H, I ] perylene-1,2,4,5,10,11-hexacarboxylic anhydride.
3. The process according to claim 1, wherein in the step 3), the tribasic anhydride is hexaazatrimellitic anhydride.
4. The method according to claim 1, wherein the amount of the tribasic anhydride added in step 3) is 0.05 to 0.5mol% based on the amount of the diamine used in step 1).
5. The method according to claim 1, wherein the amount of the tribasic anhydride added in step 3) is 0.05 to 0.1mol% based on the amount of the diamine used in step 1).
6. The method according to any one of claims 1 to 5, wherein in the step 1), the diamine is an asymmetric diamine.
7. The method according to claim 6, wherein the unsymmetrical diamine is one or a combination of two or more selected from 3,4' -diaminobenzanilide, 3,4' -diaminodiphenyl ether, m-phenylenediamine, 3,4' -diaminodiphenyl sulfone, 3,4' -diaminobiphenyl, 3,4' -diaminodiphenyl methane, 3,4' -diaminodiphenyl disulfide and 3,4' -diaminodiphenyl sulfide.
8. The process according to any one of claims 1 to 5, wherein in the step 1), the dibasic anhydride is an asymmetric structure dibasic anhydride.
9. The method according to claim 8, wherein the asymmetric structure dicarboxylic anhydride is one or a combination of two or more selected from 2,3,3',4' -biphenyltetracarboxylic dianhydride, 2,3,3',4' -benzophenonetetracarboxylic dianhydride, 2,3,3',4' -diphenylsulfonetetracarboxylic dianhydride, 2,3,3',4' -diphenylsulfide tetracarboxylic dianhydride, and 2,3,3',4' -diphenylethertetracarboxylic dianhydride.
10. The negative electrode slurry for a secondary battery prepared by the method according to any one of claims 1 to 9.
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