Positive electrode material of secondary battery

Abstract

The invention provides a secondary battery positive electrode material, and relates to the technical field of battery materials. The secondary battery positive electrode material comprises the following first raw material components: active particles, a conductive agent and a binder. The binder is obtained by reacting a second raw material component containing modified amino resin and an isocyanate curing agent. Rich ether bonds, ester bonds, urea bonds and other polar groups are introduced into the binder, the polarity of the binder is further improved while the effect of a polyurea material is exerted, and the obtained secondary battery has better electrical performance.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology and relates to a positive electrode material for secondary batteries. Background Technology

[0002] In secondary batteries (such as lithium-ion and sodium-ion batteries), the positive electrode binder is a key auxiliary material. Its function is to firmly bond the positive electrode active material, conductive agent, and other particles to the current collector (such as aluminum foil), while maintaining the integrity of the electrode structure and ensuring stable electrochemical performance during battery cycling. Existing positive electrode binders are mainly of two types: oil-based and water-based. The commonly used oil-based binder is polyvinylidene fluoride (PVDF), but it has drawbacks such as high cost, solvent dependence, strong hydrophobicity affecting electrolyte wetting, and insufficient flexibility. Water-based binders mainly suffer from insufficient long-lasting adhesion, affecting the lifespan of the secondary battery.

[0003] Therefore, the binders for the positive electrodes of existing secondary batteries urgently need further improvement. Summary of the Invention

[0004] Aspartic polyurea possesses excellent chemical resistance, high mechanical strength, and good weather resistance. This invention further optimizes the structure and molecular weight of the aspartic ester resin used in aspartic polyurea, improving its effectiveness as a binder for cathode materials. Based on this, this invention provides a cathode material for secondary batteries.

[0005] The technical solution of the present invention is as follows:

[0006] A secondary battery cathode material, comprising the following first raw material components A-1) to A-3):

[0007] A-1) Active particles;

[0008] A-2) Conductive agent;

[0009] A-3) Adhesive;

[0010] The adhesive is obtained by reacting a second raw material component comprising a modified amino resin and an isocyanate curing agent;

[0011] The modified amino resin is prepared by:

[0012] Prepolymers are obtained by reacting polymeric polyols with polyisocyanate compounds.

[0013] The prepolymer is then reacted with an amino compound to obtain the modified amino resin.

[0014] Preferably, the polymeric polyol is selected from one or a combination of two or more of polyether polyols and polyester polyols.

[0015] Preferably, the equivalent ratio of hydroxyl groups in the polymer polyol to NCO groups in the polyisocyanate compound is 1:1.2-2.

[0016] Preferably, the molecular weight of the polyisocyanate compound does not exceed 2000, and the average number of NCO groups in the structure of the polyisocyanate compound is 2-3.

[0017] Preferably, the equivalence ratio of the prepolymer to the amino compound is 1:1.1-2.

[0018] Preferably, the sum of the number of secondary amino groups and primary amino groups in the amino compound is 2, and the molecular weight of the amino compound does not exceed 10,000.

[0019] Preferably, the ratio of the sum of the molar numbers of secondary and primary amino groups in the modified amino resin to the molar number of NCO groups in the isocyanate curing agent is 0.8-1.2:1.

[0020] Preferably, the active particles account for no less than 70% of the weight of the positive electrode material of the secondary battery, and the active particles are selected from one or more combinations of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary materials, layered metal oxides, polyanionic compounds and Prussian blue and their analogues.

[0021] Preferably, the conductive agent accounts for 5-20% of the weight of the positive electrode material of the secondary battery, and the conductive agent is selected from one or a combination of two or more of carbon black, graphite, graphene, carbon nanotubes, fullerenes and conductive polymers.

[0022] Preferably, the second raw material component further comprises an organic solvent, wherein the organic solvent accounts for 10-90% of the weight of the second raw material component.

[0023] The beneficial effects of this invention are as follows: This invention uses modified polyurea based on modified amino resin as a binder for the positive electrode of a secondary battery. It contains abundant polar functional groups such as -COC-, ester groups, and -NHCONH-. While aspartic polyurea possesses excellent mechanical properties and chemical corrosion resistance, its adhesion is further improved. This not only effectively suppresses the expansion problem caused by the positive electrode material during battery charging and discharging, but also effectively isolates the direct contact between the electrolyte and the active material, avoiding a series of side reactions, thereby improving the battery's cycle life. Furthermore, it can more quickly promote the conduction of metal ions during battery charging and discharging, improving charging and discharging efficiency. Moreover, the polar / non-polar structure can better disperse and coat the active particles and conductive agents, improving the dispersion uniformity and stability of the active particles and conductive agents in the binder. Therefore, the secondary battery of this invention has better rate performance, cycle performance, and other electrical properties. Detailed Implementation

[0024] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0025] This invention provides a secondary battery cathode material comprising the following first raw material components A-1) to A-3):

[0026] A-1) Active particles;

[0027] A-2) Conductive agent;

[0028] A-3) Adhesive;

[0029] The adhesive is obtained by reacting a second raw material component comprising a modified amino resin and an isocyanate curing agent;

[0030] The preparation method of modified amino resin is as follows:

[0031] Prepolymers are obtained by reacting polymeric polyols with polyisocyanate compounds.

[0032] The prepolymer is then reacted with an amino compound to obtain a modified amino resin.

[0033] This invention modifies an amino compound. A polymeric polyol is first reacted with a polyisocyanate compound to obtain a prepolymer containing NCO groups. The prepolymer is then reacted with an amino compound to obtain a modified amino resin with a larger molecular weight and abundant polar functional groups such as -COC-, ester groups, and -NHCONH-. This further improves the polarity of the aspartic polyurea adhesive and adjusts its polar / non-polar structure, resulting in the following advantages: ① The larger molecular weight and higher polarity further improve the adhesive's performance, resulting in better adhesion, mechanical properties, and chemical corrosion resistance. This effectively suppresses the negative effects of the positive electrode material on the battery during charging and discharging. The modified amino resin effectively addresses the expansion issue and isolates the electrolyte from direct contact with the active material, preventing a series of side reactions and thus improving the battery's cycle life. Secondly, increased polarity promotes faster metal ion conduction during battery charging and discharging, improving charging and discharging efficiency. Thirdly, the curing reaction of the modified amino resin and the adhesion of the counter electrode occur simultaneously during baking, allowing for more uniform adhesion of active particles and conductive agents to form a positive electrode composite material. Fourthly, the presence of polar / non-polar structures in the adhesive allows for better dispersion and coating of active particles and conductive agents, improving the uniformity and stability of their dispersion in the adhesive.

[0034] Therefore, the binder prepared based on modified amino resin improves the electrical performance of secondary batteries, especially the rate performance and cycle performance.

[0035] In some embodiments, the polymeric polyol is selected from one or a combination of two or more polyether polyols and polyester polyols. The polyether polyol can be polyethylene glycol (PEG), polypropylene glycol (PPG), PEG / PPG copolymer, polytetrahydrofuran ether diol (PTMEG), etc., and using polyether polyols can introduce -COC- ether bonds into the modified amino resin. The polyester polyol can be a conventional polyester diol formed by the condensation of polycarbonate diol, polycaprolactone diol, alkyl dicarboxylic acid, and alkyl diol, etc., and using polyester polyols can introduce ester bonds into the modified amino resin. Introducing ether and ester bonds into the modified amino resin can increase the polarity of the modified amino resin, thereby facilitating the conduction of metal ions in the battery and improving the charge-discharge efficiency. Furthermore, the higher polarity of the modified amino resin also helps to improve the adhesion of the adhesive to the current collector. The number-average molecular weight of the polymeric polyol is not particularly limited and can be 500-2000. The polymeric polyols of this invention are all commercially available.

[0036] In some embodiments, the equivalence ratio of hydroxyl groups in the polymeric polyol to NCO groups in the polyisocyanate compound is 1:1.2-2. For example, the equivalence ratio can be any value or any value between 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc. With an excess of NCO groups relative to hydroxyl groups, the resulting prepolymer has NCO group end groups, which can then react further with amino compounds.

[0037] In some embodiments, the molecular weight of the polyisocyanate compound does not exceed 2000, and the average number of NCO groups in the polyisocyanate compound structure is 2-3. For example, the polyisocyanate compound can be a diisocyanate monomer such as HDI, IPDI, HMDI, TDI, MDI, PDI, NDI, TXDI, XDI, or CHDI; it can also be a trimer of the above diisocyanate monomers, such as HDI trimer or IPDI trimer; or it can be an adduct of the above diisocyanate monomers with a diol compound (such as a polyether diol or a polyester diol). Further, the molecular weight of the polyisocyanate compound does not exceed 500.

[0038] In some embodiments, the equivalence ratio of the prepolymer to the amino compound is 1:1.1-2. For example, the equivalence ratio can be any value or any value between 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc. The equivalence ratio of the prepolymer to the amino compound refers to the equivalence ratio of the NCO groups in the prepolymer to the primary / secondary amino groups in the amino compound.

[0039] In some embodiments, the sum of the number of secondary and primary amino groups in the amino compound is 2, and the molecular weight of the amino compound does not exceed 10,000. For example, the amino compound can be aspartic acid ester resin, 4,4'-bis-sec-butylaminodiphenylmethane, 4,4'-bis-sec-butylaminodicyclohexylmethane, 4,4'-methylenediphenylamine, 4,4'-methylenedicyclohexylamine, etc. The amino compound is preferably aspartic acid ester resin. Aspartic polyurethane contains ester groups and may also contain ether bonds, which can bring more ester groups and ether bonds to the adhesive, improving the polarity of the adhesive. The structure of the aspartic acid ester resin can be shown in formula (1) below.

[0040]

[0041] R1 can be a divalent organic group with a molecular weight not exceeding 5000 that is reactive with the NCO group at 100℃, and R2 and R3 can be C1-C4 alkyl groups, respectively. Aspartic acid ester resins can be obtained directly from the market, such as F420 resin, F520 resin, F220 resin, F421 resin, F330 resin, F2850 resin, and F221 resin from Feiyang Junyan Company.

[0042] In some embodiments, the ratio of the sum of the molar numbers of secondary and primary amino groups in the modified amino resin to the molar number of NCO groups in the isocyanate curing agent is 0.8-1.2:1. For example, the ratio can be any value or any value between 0.8:1, 0.9:1, 0.95:1, 0.98:1, 1:1, 1.02:1, 1.05:1, 1.1:1, 1.2:1, etc., without any particular limitation.

[0043] In some embodiments, the active particles constitute at least 70% of the weight of the cathode material in the secondary battery. The active particles are selected from one or more combinations of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary materials, layered metal oxides, polyanionic compounds, and Prussian blue and its analogues. For example, the weight percentage of the active particles in the cathode material of the secondary battery may be 70%, 72%, 75%, 78%, 80%, 82%, 85%, etc.

[0044] In some embodiments, the conductive agent accounts for 5-20% of the weight of the positive electrode material of the secondary battery. The conductive agent is selected from one or a combination of two or more of carbon black, graphite, graphene, carbon nanotubes, fullerenes, and conductive polymers. For example, the weight percentage of the conductive agent in the positive electrode material of the secondary battery may be 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc.

[0045] The weight percentage of binder in the positive electrode material of secondary batteries can be 3-20%, such as 3%, 5%, 7%, 10%, 12%, 15%, 18%, 20%, etc.

[0046] In some embodiments, the second raw material component further comprises an organic solvent, wherein the organic solvent accounts for 10-90% by weight in the second raw material component. The organic solvent may be N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), etc.

[0047] The preparation method of the secondary battery positive electrode material of the present invention is not particularly limited. One method is as follows: active particles and conductive agents are added to a modified amino resin solution, and the active particles and conductive agents are well dispersed in the modified amino resin solution by high-speed mechanical stirring or grinding. Then, an isocyanate curing agent is added, and the mixture is stirred and mixed evenly to obtain a secondary battery positive electrode material mixed solution. In use, the secondary battery positive electrode material mixed solution is directly coated onto a current collector and cured by heating. The thickness of the cured positive electrode material can be 10-300 μm.

[0048] The technical solution of the present invention will be further described and explained below with reference to various preparation examples and embodiments. Unless otherwise specified, the parts mentioned in the following preparation examples and embodiments are parts by weight.

[0049] Preparation Examples 1-4: Preparation of Modified Amino Resins

[0050] Preparation Example 1

[0051] Under dry nitrogen protection, 108.06 g of IPDI was added to a container, the temperature was raised to 80 °C, and 416.67 g of 330N polyether (hydroxyl value 33.66 mg KOH / g) was added dropwise. After reacting for 2 hours, the NCO content was measured to be reduced to 5.7 wt%, the reaction was stopped, and the product was recorded as isocyanate prepolymer 1.

[0052] Add 82.90g of F420 resin and 877.24g of NMP to a container, heat to 40°C, and add 68.88g of the above isocyanate prepolymer 1 dropwise. After the addition is complete, continue to react at 40°C for 6 hours to obtain a modified amino resin 1 solution with an amino equivalent of 5000.

[0053] Preparation Example 2

[0054] The difference between this preparation example and Preparation Example 1 is that in Preparation Example 1, the amount of isocyanate prepolymer 1 was adjusted from 68.88 g to 139.50 g to obtain a modified amino resin 2 solution with an amino equivalent of 10000. The remaining steps remained unchanged.

[0055] Preparation Example 3

[0056] Add 30.85g of 4,4'-bis-sec-butylaminodiphenylmethane and 844.65g of NMP to a container, heat to 40°C, and add 76.30g of the above isocyanate prepolymer 1 dropwise. After the addition is complete, continue the reaction at 40°C for 6 hours to obtain a modified amino resin 3 solution with an amino equivalent of 10000.

[0057] Preparation Example 4

[0058] Under dry nitrogen protection, 262.50 g of HMDI was added to a container, the temperature was raised to 80 °C, and 500.00 g of propylene glycol oxalate polyester polyol (hydroxyl value: 112.2 mg KOH / g) was added dropwise. After reacting for 2 hours, the NCO content was measured to be reduced to 5.5 wt%, and the reaction was stopped. The product was recorded as isocyanate prepolymer 2.

[0059] 20.23 g of dimethylthiotoluene diamine and 791.96 g of DMF were added to a container, the temperature was raised to 40 °C, and 76.30 g of the above isocyanate prepolymer 2 was added dropwise. After the addition was complete, the reaction was continued at 40 °C for 6 hours to obtain a modified amino resin 4 solution with an amino equivalent of 10000.

[0060] Example 1

[0061] The weight ratio of lithium iron phosphate, Super P and binder is 8:1:1, where the binder is the effective weight excluding organic solvents.

[0062] The adhesive is composed of modified amino resin and isocyanate curing agent (HT-600) in a molar ratio of amino to NCO groups of 1:1.05.

[0063] Lithium iron phosphate and conductive carbon were mixed with Super P and then ground and dispersed evenly. The modified amino resin 1 solution of Preparation Example 1 was added and dispersed evenly. Then, isocyanate curing agent was added and stirred and mixed evenly. The mixture was coated onto the current collector and heated in a vacuum oven at 80°C for 12 hours to evaporate the solvent and cure, thus obtaining the positive electrode material.

[0064] Example 2

[0065] The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the weight ratio of lithium iron phosphate, Super P, and binder was adjusted from 8:1:1 to 85:12:3. The remaining steps remain unchanged.

[0066] Example 3

[0067] The difference between this embodiment and Embodiment 1 is that in Embodiment 1, the weight ratio of lithium iron phosphate, Super P, and binder was adjusted from 8:1:1 to 7:1:2. The remaining steps remain unchanged.

[0068] Example 4

[0069] The difference between this embodiment and Example 1 is that in Example 1, the modified amino resin 1 solution of Preparation Example 1 was replaced with the modified amino resin 2 solution of Preparation Example 2 by weight equal amounts of modified amino resin. The remaining steps remain unchanged.

[0070] Example 5

[0071] The difference between this embodiment and Example 1 is that in Example 1, the modified amino resin 1 solution of Preparation Example 1 was replaced with the modified amino resin 3 solution of Preparation Example 3 by weight of the modified amino resin. The remaining steps remain unchanged.

[0072] Example 6

[0073] The difference between this embodiment and Example 1 is that in Example 1, the modified amino resin 1 solution of Preparation Example 1 was replaced with the modified amino resin 4 solution of Preparation Example 4 by weight of the modified amino resin. The remaining steps remain unchanged.

[0074] Comparative Example 1

[0075] The difference between this comparative example and Example 1 is that in Example 1, the modified amino resin 1 solution prepared in Example 1 was replaced with a combination of F420 resin and NMP by weight of the resin. The remaining steps remained unchanged.

[0076] Comparative Example 2

[0077] The difference between this comparative example and Example 1 is that in Example 1, the modified amino resin 1 solution prepared in Example 1 was replaced with a combination of aspartic acid ester resin and NMP by weight of the resin. The remaining steps remained unchanged.

[0078] The preparation method of aspartic acid ester resin solution is as follows: under nitrogen protection, Huntsman ED-2003 is added to the reaction vessel, and diethyl maleate is added dropwise at room temperature. After the addition is completed, the temperature is raised to 80℃ and reacted for 160 hours to obtain aspartic acid resin.

[0079] The positive electrode material was cut into positive electrode sheets with a diameter of 12 mm. The batteries were assembled in the following order: negative electrode shell, nickel mesh, lithium metal sheet, electrolyte (1 mol / L NaPF6@(EC / DEC+5% FEC)), positive electrode sheet, and positive electrode shell. The discharge capacity of the batteries was tested at current densities of 0.2C, 1.0C, 3.0C, and 5.0C. After 300 charge-discharge cycles at 3.0C, the capacity retention rate was tested, and the rate capability and cycle performance were compared. The results are shown in Table 1 below.

[0080] Table 1

[0081]

[0082] As can be seen from the results in Table 1 above, the secondary battery prepared by the cathode material of the present invention has good electrical performance, high rate capability and good cycle performance. This indicates that the binder used in the cathode material of the present invention has good adhesion, good ionic conductivity and good electrolyte resistance. This is mainly due to the structure of the modified amino resin used in the binder of the present invention.

[0083] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A positive electrode material for a secondary battery, characterized in that, It contains the following first raw material components A-1) to A-3): A-1) Active particles; A-2) Conductive agent; A-3) Adhesive; The adhesive is obtained by reacting a second raw material component comprising a modified amino resin and an isocyanate curing agent; The modified amino resin is prepared by: Prepolymers are obtained by reacting polymeric polyols with polyisocyanate compounds. The prepolymer is then reacted with an amino compound to obtain the modified amino resin.

2. The secondary battery cathode material according to claim 1, characterized in that, The polymer polyol is selected from one or a combination of two or more of polyether polyols and polyester polyols.

3. The secondary battery cathode material according to claim 1, characterized in that, The equivalent ratio of hydroxyl groups in the polymer polyol to NCO groups in the polyisocyanate compound is 1:1.2-2.

4. The secondary battery cathode material according to claim 1, characterized in that, The molecular weight of the polyisocyanate compound does not exceed 2000, and the average number of NCO groups in the structure of the polyisocyanate compound is 2-3.

5. The secondary battery cathode material according to claim 1, characterized in that, The equivalence ratio of the prepolymer to the amino compound is 1:1.1-2.

6. The secondary battery cathode material according to claim 1, characterized in that, The amino compound has a total number of 2 secondary amino groups and 2 primary amino groups, and the molecular weight of the amino compound does not exceed 10,000.

7. The secondary battery cathode material according to claim 1, characterized in that, The ratio of the sum of the molar numbers of secondary and primary amino groups in the modified amino resin to the molar number of NCO groups in the isocyanate curing agent is 0.8-1.2:

1.

8. The secondary battery cathode material according to claim 1, characterized in that, The active particles account for no less than 70% of the weight of the positive electrode material of the secondary battery, and the active particles are selected from one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, ternary materials, layered metal oxides, polyanionic compounds and Prussian blue and their analogues.

9. The secondary battery cathode material according to claim 1, characterized in that, The conductive agent accounts for 5-20% of the weight of the positive electrode material of the secondary battery, and the conductive agent is selected from one or a combination of two or more of carbon black, graphite, graphene, carbon nanotubes, fullerene and conductive polymers.

10. The secondary battery cathode material according to claim 1, characterized in that, The second raw material component further includes an organic solvent, wherein the organic solvent accounts for 10-90% of the weight of the second raw material component.

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