Negative electrode slurry, negative electrode pole piece, preparation method of negative electrode pole piece and battery

Abstract

The invention provides negative electrode slurry, a negative electrode pole piece, a preparation method of the negative electrode pole piece and a battery, the negative electrode slurry comprises a negative electrode composition and a solvent, the negative electrode composition comprises a negative electrode active material, a binder, a silane coupling agent and a polyphenol compound, and the binder comprises at least one group of carboxyl, hydroxyl and amino. Through interaction between the silane coupling agent and the binder or the polyphenol compound, an organic-inorganic composite three-dimensional cross-linked structure is finally formed in the negative electrode plate, so that expansion of the negative electrode active material is inhibited, rebound of the negative electrode plate is further inhibited, the content of silicon in the negative electrode active material is further improved, and the service life of the negative electrode plate is prolonged. Therefore, the energy density of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode slurry, a negative electrode sheet, a method for preparing the same, and a battery. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in power banks, power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace and many other fields.

[0003] Silicon-based anode materials are currently the most promising anode materials, overcoming the low specific capacity of graphite and the relatively poor cycling and rate performance of silicon particles, while also possessing good safety and a wide range of raw material sources. However, the nearly 300% volume expansion rate of silicon-based anode materials during cycling makes their application difficult.

[0004] Therefore, how to reduce the volume expansion of silicon-based anode materials is an urgent problem to be solved. Summary of the Invention

[0005] This application provides a negative electrode slurry, a negative electrode sheet, a method for preparing the same, and a battery, aiming to suppress the volume expansion of silicon-based negative electrode materials and improve the cycle performance of the battery.

[0006] In a first aspect, this application provides a negative electrode slurry comprising a negative electrode composition and a solvent, wherein the negative electrode composition comprises a negative electrode active material, a binder, a silane coupling agent and a polyphenol compound, and the binder comprises at least one group selected from carboxyl, hydroxyl and amino groups.

[0007] Optionally, in the negative electrode composition, the mass content 'a' of the binder is 0.3%-5%.

[0008] Optionally, in the negative electrode composition, the mass content of the silane coupling agent is b, where 0.01% ≤ b ≤ 0.2a.

[0009] Optionally, in the negative electrode composition, the mass content of the polyphenol compound is c, where 0.1% ≤ c ≤ 0.5a.

[0010] Optionally, the adhesive includes at least one of polyacrylic acid, polyimide, and polyacrylamide.

[0011] Optionally, the silane coupling agent includes at least one of methoxysilane, mercaptosilane, and aminosilane.

[0012] Optionally, the polyphenolic compound includes at least one of chlorogenic acid, anthocyanins, isoflavones, catechins, quercetin, curcumin, cocoa polyphenols, tartrazine, rutin, and resveratrol.

[0013] Secondly, this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the negative electrode active material layer is formed from the negative electrode slurry as described in any of the above.

[0014] Thirdly, this application provides a method for preparing a negative electrode sheet, comprising the following steps: The negative electrode slurry is coated onto the negative electrode current collector, dried and rolled, and then heated at 120-320°C to obtain the negative electrode sheet.

[0015] Fourthly, this application provides a battery comprising the negative electrode sheet as described above, or comprising a negative electrode sheet prepared by the described preparation method.

[0016] In this application, the carboxyl, hydroxyl, or amino groups in the binder can undergo self-condensation or react with polyphenolic compounds to form a network structure, enhancing the interfacial bonding ability of the negative electrode sheet. Furthermore, the silane coupling agent undergoes hydrolysis in the solvent, further forming Si-O-Si bonds to construct an inorganic silicon-oxygen network in the negative electrode sheet. Simultaneously, the interaction between the silane coupling agent and the binder or polyphenolic compound ultimately forms an organic-inorganic composite three-dimensional cross-linked structure in the negative electrode sheet, thereby suppressing the expansion of the negative electrode active material, further suppressing the rebound of the negative electrode sheet, and further facilitating the increase of silicon content in the negative electrode active material, thereby improving the energy density of the battery. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] One embodiment of this application provides a negative electrode slurry, comprising a negative electrode composition and a solvent, wherein the negative electrode composition comprises a negative electrode active material, a binder, a silane coupling agent and a polyphenol compound, and the binder comprises at least one group selected from carboxyl, hydroxyl and amino groups.

[0019] In this embodiment, the carboxyl, hydroxyl, or amino groups in the binder can undergo self-condensation or react with polyphenolic compounds to form a network structure, enhancing the interfacial bonding ability of the negative electrode sheet. Additionally, the solvent includes water, and the silane coupling agent undergoes hydrolysis in the solvent, further forming Si-O-Si bonds to construct an inorganic silicon-oxygen network in the negative electrode sheet. Simultaneously, the interaction between the silane coupling agent and the binder or polyphenolic compound ultimately forms an organic-inorganic composite three-dimensional cross-linked network structure in the negative electrode sheet, thereby suppressing the expansion of the negative electrode active material, further suppressing the rebound of the negative electrode sheet, and further facilitating an increase in the silicon content of the negative electrode active material, thereby improving the energy density of the battery.

[0020] In one embodiment, the mass content 'a' of the binder in the negative electrode composition is 0.3%-5%. By adjusting the binder content, the viscosity of the negative electrode slurry and the peel strength of the negative electrode sheet are controlled.

[0021] Specifically, the mass content of the adhesive includes, but is not limited to, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%.

[0022] In one embodiment, the mass content of the silane coupling agent in the negative electrode composition is b, where 0.01% ≤ b ≤ 0.2a. By adjusting the content of the silane coupling agent to satisfy the above relationship, the density of the three-dimensional cross-linked network structure formed by the silane coupling agent, binder, and polyphenol compound is controlled, thereby better suppressing the expansion of the negative electrode active material.

[0023] In one embodiment, the mass content of the polyphenol compound in the negative electrode composition is c, where 0.1% ≤ c ≤ 0.5a. By adjusting the content of the polyphenol compound to satisfy the above relationship, the density of the three-dimensional cross-linked network structure formed by the silane coupling agent, binder, and polyphenol compound is controlled, thereby better suppressing the expansion of the negative electrode active material.

[0024] In one embodiment, the adhesive includes at least one of polyacrylic acid (PAA), polyimide (PI), and polyacrylamide (PAM).

[0025] In one embodiment, the silane coupling agent includes at least one of methoxysilane, mercaptosilane, and aminosilane.

[0026] Specifically, the silane coupling agent includes at least one of trimethylmethoxysilane, vinyltrimethoxysilane, mercaptopropyltriethoxysilane, (3-aminopropyl)triethoxysilane, and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. In the above silane coupling agent, the alkoxy groups hydrolyze in the negative electrode slurry, and some silanol groups further form Si-O-Si bonds, while the remaining silanol groups react with the binder or polyphenol compound to form covalent bonds.

[0027] In one embodiment, the polyphenolic compound includes at least one of chlorogenic acid, anthocyanins, isoflavones, catechins, quercetin, curcumin, cocoa polyphenols, tartrazine, rutin, and resveratrol.

[0028] In one embodiment, the negative electrode active material is a silicon-based negative electrode material.

[0029] An embodiment of this application also provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and the negative electrode active material layer is formed from the negative electrode slurry as described in any of the above claims.

[0030] In one embodiment, the negative electrode sheet satisfies at least one of the following conditions: The bonding strength of the negative electrode sheet ranges from 12 to 40 N / m; The cohesive strength ranges from 10 to 45 N / m; The porosity of the electrode sheets is 20%-60%; The tensile strength of the electrode is 150-500 MPa.

[0031] The electrode contact angle is 0-70°; The electrolyte absorption rate is 60-400 s / mL.

[0032] An embodiment of this application also provides a method for preparing a negative electrode sheet, comprising the following steps: The negative electrode slurry is coated onto the negative electrode current collector, dried and rolled, and then heated at 120-320°C to obtain the negative electrode sheet.

[0033] After drying and rolling, the negative electrode sheet is heated, causing the silane coupling agent, binder and polyphenol compound in the negative electrode slurry to react and form a three-dimensional cross-linked network structure.

[0034] In one embodiment, the negative electrode is heated for 1-8 hours, and the heating rate is 2-15°C / min.

[0035] In one embodiment, the negative electrode is heated under a protective atmosphere, which includes, but is not limited to, nitrogen, argon, or helium.

[0036] One embodiment of this application also provides a battery, including the negative electrode sheet as described above, or the negative electrode sheet prepared by the described preparation method. It should be noted that the battery can be a stacked, wound, or cylindrical battery.

[0037] In some embodiments, the battery further includes a separator and an electrolyte. The separator includes a base membrane, which includes at least one of PE separator, PP separator, non-woven separator, and PI separator.

[0038] The electrolyte includes organic solvents, lithium salts, and additives. The solvents include, but are not limited to, PC (propylene carbonate), EC (ethylene carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), DEC (diethyl carbonate), and DME (ethylene glycol dimethyl ether).

[0039] Lithium salts include, but are not limited to, lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroantimonyate (LiSbF6), lithium bis(trifluoromethanesulfonate imide) (LiTFSI or LiN(SO2CF2)2), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiFSI or LiN(SO2CF3)2), lithium perchlorate (LiClO4), lithium iodide (LiI), and lithium bis(fluorosulfonyl)imide magnesium (Li2Mg(N(SO2CF3)2)2).

[0040] The present application will be further illustrated by the following examples.

[0041] Example 1 This embodiment illustrates the negative electrode slurry, negative electrode sheet, preparation method thereof, and battery disclosed in this application, and includes the following operational steps: 1. Negative electrode slurry The following mixtures were prepared: silicon carbon, dispersant CMC, binder PAA, silane coupling agent (3-aminopropyl), triethoxysilane, conductive agent CNT, and polyphenol compound isoflavone, and stirred for 15 minutes. Then, water was added to adjust the solid content to 45%, and the mixture was dispersed again for 60 minutes to obtain the negative electrode slurry.

[0042] 2. Preparation of negative electrode sheet The negative electrode slurry is coated onto the copper foil current collector, dried and rolled, and then placed in an argon atmosphere with a gas flow rate of 0.5 mL / min. The temperature is increased at a rate of 5 °C / min, and the temperature is raised to 300 °C for 3 hours. Then the temperature is lowered to obtain the negative electrode sheet.

[0043] 3. Preparation of the positive electrode sheet NCM911, CNT, Super-P, and PVDF binder are mixed in a mass ratio of 96.7:0.5:1.1:1.7. The mixture is thoroughly stirred in NMP solvent to form a uniform positive electrode slurry. This slurry is coated onto at least one side of the positive electrode current collector aluminum foil, and after drying, rolling, and die-cutting, a satisfactory positive electrode sheet is obtained.

[0044] 4. Preparation of electrolyte Electrolyte for liquid batteries: Lithium salt LiPF6 is dissolved in organic solvent EC-DMC (ethylene carbonate-dimethyl carbonate, 1:1 volume ratio) to obtain a liquid electrolyte at a concentration of 1M.

[0045] 5. Battery manufacturing The negative electrode, separator, and positive electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, one end of the negative electrode, separator, and positive electrode is wound around the separator to form a core. The wound core is then placed in a pre-formed aluminum-plastic film bag. The electrolyte prepared above is injected into the baked and dried battery cell. After vacuum sealing, settling, and formation processes, the battery is obtained.

[0046] Example 2-16 Examples 2-16 illustrate the negative electrode slurry, negative electrode sheet and its preparation method, and battery disclosed in this application, including most of the operation steps in Example 1 above, except that the parameters in Table 1 are used.

[0047] Comparative Examples 1-5 Comparative Examples 1-5 are used to illustrate the negative electrode slurry, negative electrode sheet and its preparation method, and battery disclosed in this application, including most of the operation steps in Example 1, the difference being that the parameters in Table 1 are used.

[0048] Table 1 Performance testing I. The following performance tests were performed on the negative electrode sheets and batteries prepared in the above embodiments and comparative examples: 1. The adhesive strength, or peel strength, of the negative electrode sheet: 1) Stick the double-sided tape onto the steel plate. The steel plate dimensions are (150mm long, 25mm wide, and 1mm thick). 2) Cut the electrode sheet into 20mm * 100mm pieces and attach them to the other side of the double-sided tape; 3) Place the above electrode assembly on a tensile testing machine, peel the electrode at 90°, set the parameters, start the test, and take the readings.

[0049] 2. Cohesive force of the negative electrode: 1) Prepare samples following the same procedure as described above for testing adhesive electrodes; 2) After sample preparation, the green adhesive is then bonded to the surface of the electrode sheet; 3) Place the electrode assembly on the tensile testing machine, peel the green adhesive at a 90° angle, set the parameters, start the test, and take the readings.

[0050] 3. Tensile strength of the negative electrode sheet: 1) Place the electrode plates directly at both ends of the high-speed rail tensile testing machine; 2) Stretch the electrode until it breaks and take a reading.

[0051] 4. Negative electrode contact angle: 1) Place the electrolyte in a contact angle tester. The electrolyte is lithium salt LiPF6 dissolved in organic solvent EC-DMC (ethylene carbonate-dimethyl carbonate, 1:1 volume ratio), and the lithium salt concentration is 1M. 2) Select the negative electrode as the test substrate; 3) The test begins when the electrolyte is dripped onto the electrode surface.

[0052] 5. Electrolyte absorption rate of the negative electrode: 1) Drop the above-mentioned electrolyte onto the surface of the electrode; 2) Observe the time from when the electrolyte comes into contact with the electrode surface until it dries completely.

[0053] 6. Cell expansion rate: 1) After the battery cell leaves the factory, the initial thickness H1 is the 50% SOC group at the set capacity; 2) The speed positioning H2 after the battery cell has undergone 100 cycles and is fully charged; 3) Expansion rate = [(H2-H1) / H1]*100%. 7. Cyclic Performance Test: At 25℃, the cell is fully charged to 4.2V at 0.5C with a cutoff current of 0.05C, then discharged to 3.0V at 1C for 300 cycles. Calculate the battery's cycle capacity retention rate.

[0054] The test results are shown in Table 2.

[0055] Table 2 As shown in Table 2, when the negative electrode slurry contains binder, silane coupling agent and polyphenol compound at the same time, the negative electrode sheet after baking and heating will eventually form an organic-inorganic composite three-dimensional cross-linked structure, thereby inhibiting the expansion of the negative electrode active material and further inhibiting the rebound of the negative electrode sheet.

[0056] The test results of Examples 1-5 show that when the binder content in the negative electrode composition is 0.3%-5%, the negative electrode sheet has good peel strength and capacity retention. The test results of Examples 1 and 6-8 show that when the content of the silane coupling agent decreases, the contact angle of the negative electrode sheet increases, the electrolyte water absorption rate decreases, and the wettability of the electrode sheet decreases; when the content of the silane coupling agent increases, the contact angle of the negative electrode sheet decreases, the electrolyte water absorption rate increases, and the wettability of the electrode sheet increases.

[0057] As can be seen from the test results of Examples 1 and 9-11, when the content of polyphenolic compounds decreases, the contact angle of the negative electrode increases, the water absorption rate of the electrolyte decreases, and the wettability of the electrode decreases; when the content of polyphenolic compounds increases, the contact angle of the negative electrode decreases, the water absorption rate of the electrolyte increases, and the wettability of the electrode increases.

[0058] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A negative electrode slurry, characterized by, A negative electrode composition including a negative electrode active material, a binder including at least one group of a carboxyl group, a hydroxyl group, and an amino group, a silane coupling agent, and a polyphenol compound, and a solvent.

2. The negative electrode slurry of claim 1, wherein The mass content of the binder in the negative electrode composition is a, and 0.3% ≤ a ≤ 5%.

3. The negative electrode slurry of claim 2, wherein The mass content of the silane coupling agent in the negative electrode composition is b, and 0.01% ≤ b ≤ 0.2a.

4. The negative electrode slurry of claim 2, wherein The mass content of the polyphenol compound in the negative electrode composition is c, and 0.1% ≤ c ≤ 0.5a.

5. The negative electrode slurry of claim 1, wherein the carbon-based material is selected from the group consisting of carbon black, carbon nanotubes, carbon nanofibers, and combinations thereof. The binder includes at least one of polyacrylic acid, polyimide, and polyacrylamide.

6. The negative electrode slurry of claim 1, wherein The silane coupling agent includes at least one of methoxysilane, mercaptosilane, and aminosilane.

7. The negative electrode slurry of claim 1, wherein the carbon-based material is selected from the group consisting of carbon black, carbon nanotubes, carbon nanofibers, and combinations thereof. The polyphenol compound includes at least one of chlorogenic acid, anthocyanin, isoflavone, catechin, quercetin, curcumin, cocoa polyphenol, flavoxate, rutin, and resveratrol.

8. A negative electrode sheet characterized by comprising: A negative electrode including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer being formed from the negative electrode slurry of any one of claims 1-7.

9. The method for producing a negative electrode sheet according to claim 8, wherein The method includes the steps of: The negative electrode slurry of any one of claims 1-7 is coated on a negative electrode current collector, dried, rolled, and then heated at 120-320°C to obtain the negative electrode tab.

10. A battery, characterized by The negative electrode tab of claim 8, or the negative electrode tab prepared by the preparation method of claim 9.

Images