Novel binder, positive / negative electrode carbon-coated prime coat, preparation method and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a novel binder, a positive / negative electrode carbon-coated base coat, a preparation method and a lithium ion battery. The preparation method of the novel binder comprises the following steps: adding a chain transfer agent into an acrylic acid solution to obtain a first solution; heating the first solution to 70-90 DEG C, adding an initiator, carrying out constant-temperature reaction in an inert gas atmosphere for 2-4 hours, and adding an alcohol solution to obtain a second solution; the mass concentration of the acrylic acid solution is 10-30%, the mass concentration of the alcohol solution is 10-30%, the mass concentration of the acrylic acid solution is 10-30%, the mass concentration of the acrylic acid solution is 10-30%, the mass concentration of the alcohol solution is 10-30%, the mass concentration of the second solution is 70-90 DEG C, an initiator is added, a constant-temperature reaction is carried out for 2-4 h in an inert gas atmosphere, and a third solution is obtained; the chain transfer agent is isopropanol or dodecyl mercaptan, the alcohol is any one of C3-C8 alcohols, and the initiator is ammonium persulfate or potassium sulfate. When the positive / negative carbon-coated prime coat prepared by adopting the novel binder is applied to the lithium ion battery, the high-temperature storage performance, the cycle performance and the safety performance of the battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, in particular to a novel binder, a positive / negative electrode carbon-coated primer, a preparation method and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in electronic products in various fields. During the production and processing of lithium-ion batteries, in order to improve the performance of the electrodes, some conductive carbon-coated primers are coated on the current collectors of the positive and negative electrodes. At present, in the industry, the formula of the positive electrode carbon-coated primer contains the binder acrylic acid (PAA), mainly homopolymer, and there are problems such as difficult removal of moisture and poor adhesion; the formula of the negative electrode carbon-coated primer contains the binder styrene-butadiene (SBR) material, mainly copolymer, and there are problems such as large swelling, poor dispersion ability and poor adhesion. As a result, the high-temperature storage performance, cycle performance and safety performance of the produced lithium-ion batteries are reduced. Summary of the Invention

[0003] The technical problem to be solved in the embodiments of the present invention is to provide a novel binder, a positive / negative electrode carbon-coated primer, a preparation method and a lithium-ion battery to solve the problems of low high-temperature storage performance, cycle performance and installation performance of lithium-ion batteries in the prior art.

[0004] The present invention discloses a preparation method of a novel binder, comprising the following steps: adding a chain transfer agent to an acrylic acid solution to obtain a first solution;

[0005] Heating the first solution to 70°C - 90°C, introducing an inert gas into the first solution, adding an initiator, and carrying out a constant-temperature reaction for 2h - 4h in an inert gas atmosphere, and adding an alcohol solution to obtain a second solution;

[0006] Heating the second solution to 70°C - 90°C, adding an initiator, and carrying out a constant-temperature reaction for 2h - 4h in an inert gas atmosphere to obtain a third solution;

[0007] Cooling the third solution to room temperature, adjusting the pH value to 7 - 8, and performing devolatilization and purification to obtain the novel binder,

[0008] wherein, the mass concentration of the acrylic acid solution is 10% - 30%, and the mass concentration of the alcohol solution is 10% - 30%;

[0009] The chain transfer agent is isopropyl alcohol or dodecyl mercaptan, the alcohol is any one of C3 - C8 alcohols, and the initiator is ammonium persulfate or potassium sulfate.

[0010] Optionally, introducing an inert gas into the first solution for 20min - 40min.

[0011] Optionally, the step of adjusting the pH value to 7 - 8 includes:

[0012] A neutralizing agent is added to the third solution to adjust the pH value. The neutralizing agent is sodium hydroxide or lithium hydroxide.

[0013] The present invention also discloses a novel binder prepared by the above preparation method. The weight-average molecular weight of the novel binder is 300,000 - 350,000; the novel binder has a branched structure and has a polyacrylic acid homopolymer as the main chain.

[0014] The present invention also discloses a carbon-coated cathode primer, which includes a conductive agent, a dispersant, and the above-mentioned novel binder. Among them, the mass ratio of the conductive agent is 40% - 55%, the mass ratio of the dispersant is 5% - 10%, and the mass ratio of the novel binder is 35% - 50%;

[0015] The conductive agent is any one of carbon black, carbon nanotubes, nanofibrous carbon, and graphene, and the dispersant is any one of polyvinylpyrrolidone, polyethers, and polyesters.

[0016] Optionally, the solid content of the slurry of the carbon-coated cathode primer is 18% - 30%.

[0017] The present invention also discloses a carbon-coated anode primer, which includes a conductive agent, a dispersant, and the above-mentioned novel binder. Among them, the proportion of the conductive agent is 40 - 55%, the proportion of the dispersant is 5 - 10%, and the proportion of the novel binder is 35 - 50%;

[0018] The conductive agent is any one of carbon black, carbon nanotubes, nanofibrous carbon, and graphene, and the dispersant is any one of carboxymethyl cellulose and hydroxyethyl cellulose.

[0019] Optionally, the solid content of the slurry of the carbon-coated anode primer is 19% - 29%, and the particle size of the slurry of the carbon-coated anode primer is 4μm - 9.5μm.

[0020] The present invention discloses a preparation method of a carbon-coated primer, which is characterized in that the method includes:

[0021] The dispersant and the conductive agent are placed in a stirring tank and stirred at a revolution speed of 18 - 22 rpm and a rotation speed of 1100 rpm to 1300 rpm for 25 min to 35 min;

[0022] Deionized water and the above-mentioned novel binder are added to the stirring tank, and stirred at a revolution speed of 18 - 22 rpm and a rotation speed of 2000 rpm to 2200 rpm for 110 min to 130 min.

[0023] The present invention also discloses a lithium-ion battery, which includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrode liquid; the positive electrode sheet includes a positive current collector and a positive primer coating provided on the surface of the positive current collector, or the negative electrode sheet includes a negative current collector and a negative primer coating provided on the surface of the negative current collector;

[0024] The positive primer coating uses the positive carbon-coated primer coating as described above; or, the negative primer coating uses the negative carbon-coated primer coating as described above;

[0025] Wherein, the peel strength between the positive carbon-coated primer coating and the positive current collector is 12-16 N / m, and the peel strength between the negative carbon-coated primer coating and the negative current collector is 8.5 N / m - 14 N / m.

[0026] Compared with the prior art, the beneficial effects of the novel binder, preparation method, positive carbon-coated primer coating, negative carbon-coated primer coating, and lithium-ion battery provided by the embodiments of the present invention are as follows: The novel binder of the present application introduces a hydrophobic (i.e., lipophilic) functional group ester chain. The ester functional group is lipophilic and the hydrophobicity is greatly enhanced. Applying the positive carbon-coated primer coating prepared with the novel binder on the positive current collector can reduce the water content of the positive electrode sheet while improving the peel strength between the positive carbon-coated primer coating and the positive current collector; at the same time, the lipophilic functional group ester chain has good affinity and adsorption with the conductive agent, and can improve the dispersion ability of the slurry during the preparation of the negative carbon-coated primer coating slurry. Applying the negative carbon-coated primer coating made with the novel binder on the negative electrode sheet can improve the peel strength between the negative carbon-coated primer coating and the negative current collector; finally, the positive / negative carbon-coated primer coatings prepared with this novel binder have good affinity with the electrolyte and can improve the lithium ion migration rate; in summary, applying the positive / negative carbon-coated primer coatings prepared with the binder of the carbon-coated primer coating of the present application on the positive and negative electrode sheets of the lithium ion can improve the high-temperature storage performance, cycle performance, and safety of the lithium-ion battery. Specific Embodiments

[0027] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. Now, with reference to the accompanying drawings, the preferred embodiments of the present invention will be described in detail.

[0028] The embodiments of the present invention provide a preparation method of a novel binder, including the following steps:

[0029] Dissolve acrylic monomers in water to obtain an acrylic acid solution, and control the mass concentration at 10%-30%, and the mass concentration can be 10%, 20%, 30%.

[0030] Add a chain transfer agent to obtain a first solution. The chain transfer agent is isopropyl alcohol or dodecyl mercaptan, which is used to control the molecular weight of the novel binder.

[0031] An inert gas is introduced into the first solution for 20 min - 40 min. The time can be 20 min, 30 min, or 40 min. This can remove the dissolved oxygen in the system, thereby preventing oxygen from inhibiting free radical polymerization. The inert gas can be nitrogen.

[0032] The first solution is heated to 70°C - 90°C. The temperature can be 70°C, 80°C, or 90°C. An initiator is added. The initiator can be ammonium persulfate or potassium sulfate (ammonium persulfate or potassium sulfate is added dropwise or all at once after being dissolved in water).

[0033] The reaction is carried out at a constant temperature for 2 h - 4 h. The time can be 2 h, 3 h, or 4 h. Stirring is maintained (200 rpm - 500 rpm) to ensure uniform heat transfer.

[0034] The reaction continues under an inert gas atmosphere until the monomer conversion rate > 90% (which can be monitored by titration or infrared). The weight-average molecular weight is controlled at 28 - 32W (tested by GPC). The inert gas can be nitrogen.

[0035] An alcohol solution is added, and the mass concentration is controlled at 10% - 30% to obtain the second solution. The alcohol is any one of C3 - C8 alcohols. For example, propanol (n-propanol, isopropanol), butanol (n-butanol, isobutanol, tert-butanol, 1-methylpropanol, 1,1-dimethylethanol), pentanol (1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol). The initiator is ammonium persulfate or potassium sulfate, and the mass concentration can be 10%, 20%, or 30%.

[0036] The second solution is heated to 70°C - 90°C. The temperature can be 70°C, 80°C, or 90°C. An initiator is added. The initiator can be ammonium persulfate or potassium sulfate (ammonium persulfate or potassium sulfate is added dropwise or all at once after being dissolved in water).

[0037] The reaction is carried out at a constant temperature for 2 h - 4 h. The time can be 2 h, 3 h, or 4 h. Stirring is maintained (200 rpm - 500 rpm) to ensure uniform heat transfer.

[0038] It is cooled to room temperature, and sodium hydroxide or lithium hydroxide is added dropwise to adjust the pH value to 7 - 8. After removing volatiles and purification, a novel binder is obtained.

[0039] The embodiments of the present invention also provide a novel binder prepared by the above preparation method. The weight-average molecular weight of the novel binder is 30W - 35W; the novel binder has a branched structure and has a polyacrylic acid homopolymer as the main chain.

[0040] Among them, the conventional PAA binder uses acrylic acid as a monomer to form a linear binder, and the contact with the electrode (foil) material is linear contact. The novel binder in this embodiment has a branched structure (similar to a centipede shape) when the weight-average molecular weight is 300,000 - 350,000. The number of riveting points with the electrode (foil) material increases, and the peel strength is higher, which can ensure the firm adhesion between the electrode and the current collector (such as a conductive electrode plate), reduce the peeling and falling-off phenomena of the electrode material, and this helps to improve the stability of the battery during the cyclic charge and discharge process, improve the cycle stability and high-temperature storage performance of the battery, and extend the service life of the battery.

[0041] At the same time, using acrylic acid homopolymer as the main chain, mainly considering the material synthesis and preparation, it is basically an aqueous solution synthesis method. The acrylic acid monomer has strong polarity and good hydrophilicity, and is prone to homopolymerization reaction. After forming a homopolymer molecular chain, the intermolecular force increases, and the hydrophilicity gradually weakens, and the difficulty of grafting and introducing ester monomers decreases.

[0042] As a preferred scheme of this embodiment, the weight-average molecular weight of the binder for the carbon-coated bottom coating is 300,000 - 350,000. Among them, with the increase of the weight-average molecular weight in the preparation of the binder for the carbon-coated bottom coating, the copolymerization difficulty begins to increase; at the application end, if the molecular weight is too high, the material viscosity increases, resulting in a decrease in wettability and a poor dispersion ability of the slurry during mixing. Therefore, in this embodiment, the weight-average molecular weight of the binder for the carbon-coated bottom coating is limited to make it easier for acrylic acid and ester chains to copolymerize and not reduce the dispersion ability of the slurry during mixing.

[0043] The embodiment of the present application also discloses a preparation method for the carbon-coated bottom coating of the positive electrode. The method includes: placing a dispersant and a conductive agent in a stirring tank, stirring at a revolution speed of 18 - 22 rpm and a rotation speed of 1100 rpm to 1300 rpm for 25 min to 35 min; among them, the rotation speed can be 1100 rpm, 1200 rpm, 1300 rpm, and the stirring time can be 25 min, 30 min, 35 min.

[0044] Adding deionized water and the above-mentioned binder for the carbon-coated bottom coating into the stirring tank, stirring at a revolution speed of 18 - 22 rpm and a rotation speed of 2000 rpm to 2200 rpm for 110 min to 130 min; among them, the rotation speed can be 2000 rpm, 2100 rpm, 2200 rpm, and the stirring time can be 110 min, 120 min, 130 min.

[0045] Among them, the dispersant is any one of polyvinylpyrrolidone (PVP), polyethers, and polyesters, and the conductive agent is any one of carbon black, carbon nanotubes, nanofibrous carbon, and graphene.

[0046] When the binder for carbon-coated primer of this embodiment is used in the preparation of the positive electrode carbon-coated primer, the binder for carbon-coated primer can adapt to a relatively high rotation speed, improve the dispersion ability during the slurry mixing process, effectively disperse graphite particles evenly in the electrode, avoid particle agglomeration and accumulation, thereby improving the uniformity and stability of the electrode. This helps reduce the local resistance inside the electrode and improve the cycle performance and high-temperature storage performance of the battery.

[0047] This application also discloses a positive electrode carbon-coated primer, which includes a conductive agent, a dispersant, and the above-mentioned binder for carbon-coated primer. Among them, the proportion of the conductive agent is 40%-55%, the proportion of the dispersant is 5%-10%, and the proportion of the binder for carbon-coated primer is 35%-50%; the conductive agent is any one of carbon black, carbon nanotubes, nanofibrous carbon, and graphene, and the dispersant is any one of polyvinylpyrrolidone (PVP), polyethers, and polyesters.

[0048] Among them, the proportion of the conductive agent can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 55%; the proportion of the dispersant can be: 5%, 6%, 7%, 8%, 9%, 10%; the proportion of the binder can be 35%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%.

[0049] At the same time, this application also discloses a lithium-ion battery, which includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrode liquid; the positive electrode sheet includes a positive electrode current collector and a positive electrode primer provided on the surface of the positive electrode current collector. The positive electrode primer uses the above-mentioned positive electrode carbon-coated primer. When in use, the positive electrode primer is coated on the surface of the positive electrode current collector. Taking the soft-pack 406080 conventional design as an example, the positive electrode primer is evenly coated (the coating parameters are conventional conditions) on the positive electrode current collector according to the specifications, and after passing through the battery process (the process parameters are conventional conditions) and flowing through (rolling → winding → baking → injecting liquid → sealing the edge, forming, grading, etc.), a normal battery is prepared, and then short-term and long-term cycle tests are carried out.

[0050] This application embodiment also discloses a preparation method for a negative electrode carbon-coated primer. The method includes: placing the dispersant and the conductive agent in a stirring tank, stirring at a revolution speed of 18-22 rpm and a rotation speed of 1100-1300 rpm for 25-35 minutes; among them, the rotation speed can be 1100 rpm, 1200 rpm, 1300 rpm, and the stirring time can be 25 minutes, 30 minutes, 35 minutes.

[0051] Add deionized water and the above carbon-coated primer binder into a stirring tank, and stir for 110 to 130 minutes at an orbital speed of 18-22 rpm and an autorotation speed of 2000 to 2200 rpm; wherein the autorotation speed can be 2000 rpm, 2100 rpm, 2200 rpm, and the stirring time can be 110 minutes, 120 minutes, or 130 minutes.

[0052] The dispersant is any one of sodium carboxymethyl cellulose (CMC) and hydroxyethyl cellulose, and the conductive agent is any one of carbon black, carbon tube, nanocarbon fiber and graphene.

[0053] In the process of preparing the negative electrode carbon primer by using the novel binder of this embodiment, the binder of the carbon primer can adapt to a higher rotation speed, improve the dispersibility during the slurry mixing process, and effectively disperse the graphite particles evenly in the electrode to avoid particle agglomeration and accumulation, thereby improving the uniformity and stability of the electrode. This helps to reduce the local resistance inside the electrode and improve the cycle performance and high temperature storage performance of the battery.

[0054] The present application also discloses a negative electrode carbon coating, including a conductive agent, a dispersant and the above-mentioned carbon coating binder, wherein the conductive agent accounts for 40%-55%, the dispersant accounts for 5%-10%, and the binder of the carbon coating accounts for 35%-50%; the conductive agent is any one of carbon black, carbon tube, nano carbon fiber, and graphene, and the dispersant is any one of sodium carboxymethyl cellulose (CMC) and hydroxyethyl cellulose. Among them, the conductive agent accounts for 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 55%; the dispersant accounts for 5%, 6%, 7%, 8%, 9%, 10%; the binder accounts for 35%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%.

[0055] At the same time, the application also discloses a lithium-ion battery, including a positive electrode sheet, a separator, a negative electrode sheet and an electrode liquid; the negative electrode sheet includes a negative electrode collector and a negative electrode primer arranged on the surface of the negative electrode collector, the negative electrode primer adopts the above-mentioned negative electrode carbon coating primer, and the negative electrode primer is coated on the surface of the negative electrode collector when in use. Taking the conventional design of soft package 406080 as an example, the negative electrode primer is evenly coated on the negative electrode collector according to specifications (coating parameters are conventional conditions), and a normal battery is prepared through a battery process (process parameters are conventional conditions) (rolling → winding → baking → liquid injection → edge sealing, formation, capacity division, etc.), and then short-term and long-term cycle tests are carried out.

[0056] A specific implementation method is given below.

[0057] New Binder and Its Preparation

[0058] Example 1:

[0059] Preparation method of the new binder: Add a chain transfer agent (isopropyl alcohol) to an acrylic acid solution (monomer mass concentration 20%) to obtain a first solution. Heat the first solution to 80°C, introduce nitrogen into the first solution for 30 min, and add an initiator (ammonium persulfate). React at a constant temperature (80°C) for 3 h under nitrogen conditions (to obtain a linear acrylic acid homopolymer); add an alcohol solution (n-pentanol, alcohol mass concentration 20%) to obtain a second solution (branched structure acrylic acid copolymer); add an initiator (ammonium persulfate) to the second solution and react at a constant temperature (80°C) for 3 h under nitrogen conditions to obtain a third solution. Cool the third solution to room temperature (25°C), add a neutralizing agent (sodium hydroxide) to the third solution, adjust the pH value to 7.5, and then remove volatile components and purify to obtain the new binder. Among them, the weight-average molecular weight of the new binder prepared in this example is 330,000.

[0060] Example 2:

[0061] Preparation method of the new binder: Add a chain transfer agent (isopropyl alcohol) to an acrylic acid solution (monomer mass concentration 10%) to obtain a first solution. Heat the first solution to 90°C, introduce nitrogen into the first solution for 40 min, and add an initiator (ammonium persulfate). React at a constant temperature (90°C) for 2 h under nitrogen conditions (to obtain a linear acrylic acid homopolymer); add an alcohol solution (n-octanol, alcohol mass concentration 20%) to obtain a second solution (branched structure acrylic acid copolymer); add an initiator (ammonium persulfate) to the second solution and react at a constant temperature (90°C) for 2 h under nitrogen conditions to obtain a third solution. Cool the third solution to room temperature (25°C), add a neutralizing agent (lithium hydroxide) to the third solution, adjust the pH value to 7, and then remove volatile components and purify to obtain the new binder. Among them, the weight-average molecular weight of the new binder prepared in this example is 300,000.

[0062] Example 3:

[0063] The preparation method of the novel adhesive is as follows: a chain transfer agent (dodecyl mercaptan) is added to an acrylic acid solution (monomer mass concentration of 30%) to obtain a first solution, the first solution is heated to 70°C, nitrogen is introduced into the first solution for 20 minutes, and an initiator (potassium sulfate) is added, and the mixture is reacted at a constant temperature (70°C) for 4 hours under nitrogen conditions (to obtain a straight-chain acrylic acid homopolymer); an alcohol (n-propanol, alcohol mass concentration of 20%) solution is added to obtain a second solution (branched acrylic acid copolymer); an initiator (potassium sulfate) is added to the second solution, and the mixture is reacted at a constant temperature (70°C) for 4 hours under nitrogen conditions to obtain a third solution, the third solution is cooled to room temperature (25°C), a neutralizer (sodium hydroxide) is added to the third solution, the pH value is adjusted to 8, and then the novel adhesive is obtained by devolatilization and purification, wherein the weight average molecular weight of the novel adhesive prepared in this embodiment is 35W.

[0064] Positive electrode carbon coating and its preparation

[0065] Embodiment 1

[0066] The novel adhesive of Example 1 was used.

[0067] Preparation method of positive electrode carbon coating primer: take 10% dispersant (PVP) and 40% conductive agent (carbon black), put them in a stirring tank, stir for 30 minutes at an orbital speed of 20 rpm and an autorotation speed of 1200 rpm, add deionized water and 50% of the new binder of the present invention into the stirring tank, stir for 120 minutes at an orbital speed of 20 rpm and an autorotation speed of 2100 rpm to obtain a positive electrode carbon coating primer slurry.

[0068] Embodiment 2 ':

[0069] The difference from Example 1' is that in the positive electrode carbon coating primer preparation method, the proportion of the new binder is 45%, the proportion of the conductive agent (carbon black) is 45%, and the other conditions remain unchanged to obtain the positive electrode carbon coating primer slurry.

[0070] Embodiment 3 ':

[0071] The difference from Example 1' is that in the positive electrode carbon coating primer preparation method, the proportion of the new binder is 40%, the proportion of the conductive agent (carbon black) is 50%, and the other conditions remain unchanged to obtain the positive electrode carbon coating primer slurry.

[0072] Embodiment 4 ':

[0073] The difference from Example 1' is that in the positive electrode carbon coating primer preparation method, the proportion of the new binder is 35%, the proportion of the conductive agent (carbon black) is 55%, and the other conditions remain unchanged to obtain the positive electrode carbon coating primer slurry.

[0074] Example 5':

[0075] The difference from Example 1' is that in the positive electrode carbon coating primer preparation method, the new binder accounts for 43%, the conductive agent (carbon black) accounts for 50%, the dispersant (PVP) accounts for 7%, and the other conditions remain unchanged to obtain a positive electrode carbon coating primer slurry.

[0076] Embodiment 6 ':

[0077] The difference from Example 1' is that in the positive electrode carbon coating primer preparation method, the proportion of the new binder is 45%, the proportion of the conductive agent (carbon black) is 50%, the proportion of the dispersant (PVP) is 5%, and the other conditions remain unchanged to obtain the positive electrode carbon coating primer slurry.

[0078] Example 7':

[0079] The difference from Example 1' is that the new adhesive prepared in Example 2 is used to obtain the positive electrode carbon coating primer slurry.

[0080] Embodiment 8 ':

[0081] The difference from Example 1' is that the new adhesive prepared in Example 3 is used to obtain the positive electrode carbon coating primer slurry.

[0082] Embodiment 9 ':

[0083] The difference from Example 1' is that the conductive agent is carbon tube, and the dispersant is polyether (polycaprolactone-polyphosphate) to obtain the positive electrode carbon coating slurry.

[0084] Embodiment 10 ':

[0085] The difference from Example 1' is that the conductive agent is nano-carbon fiber, and the dispersant is polyester (polyester-type hyperdispersant: a hyperdispersant formed by the reaction of terminal carboxyl polyester and polyamine and alcohol amine substances, with -C-NH- or -C-0- as a bridge group and amine as an anchoring group) to obtain a positive electrode carbon coating slurry.

[0086] Embodiment 11 ':

[0087] The difference from Example 1' is that the conductive agent is graphene, and the dispersant is polyvinyl pyrrolidone (PVP), to obtain the positive electrode carbon-coated primer slurry.

[0088] Embodiment 12 ':

[0089] The difference from Example 1' is that the dispersant (PVP) and the conductive agent (carbon black) are placed in a stirring tank and stirred for 25 minutes at an orbital speed of 18 rpm and an autorotation speed of 1100 rpm, deionized water and the new binder of the present invention are added to the stirring tank, and stirred for 110 minutes at an orbital speed of 18 rpm and an autorotation speed of 2000 rpm to obtain the positive electrode carbon coating primer slurry.

[0090] Example 13':

[0091] The difference from Example 1' is that the dispersant (PVP) and the conductive agent (carbon black) are placed in a stirring tank and stirred for 35 min at a revolution speed of 22 rpm and a rotation speed of 1300 rpm. Deionized water and the novel binder of the present invention are added to the stirring tank and stirred for 130 min at a revolution speed of 22 rpm and a rotation speed of 2200 rpm to obtain the positive electrode carbon-coated primer slurry.

[0092] Comparative Example 1':

[0093] The difference between this comparative example and Example 1' is that in the preparation method of the positive electrode carbon-coated primer, the type of the binder is a conventional PAA binder, and the other conditions remain unchanged, to obtain the positive electrode carbon-coated primer slurry.

[0094] For the positive electrode carbon-coated primers prepared in Examples 1' to 11' and Comparative Example 1', the solid content of their slurries was measured. The positive electrode carbon-coated primer slurries prepared in the above examples and comparative examples were made into batteries, and the peel strength and the moisture content of the positive electrode current collector and the positive electrode carbon-coated primer were measured. At the same time, the internal resistance of the battery, the 3C rate discharge, the cycle capacity retention rate at 45°C 2C @ 400 cycles, and the thickness change rate during storage at 60°C @ 35 d were measured. Among them, the preparation method of the battery is as follows:

[0095] Positive electrode plate:

[0096] The positive electrode carbon-coated primer slurry was coated on the positive electrode current collector aluminum foil and dried at 90°C. Lithium cobaltate, conductive agent Super-P, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 98:0.5:0.5:1 in the solvent N-methylpyrrolidone (NMP) and stirred for 6 h in a vacuum mixer until the system was homogeneous to obtain the positive electrode slurry. The positive electrode slurry was coated on the positive electrode carbon-coated primer on the aluminum foil, dried at 90°C, and then cold-pressed, sliced, and slit according to the design to obtain the positive electrode plate.

[0097] Negative electrode plate:

[0098] Artificial graphite, thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 98:1:1, and deionized water was added. The negative electrode slurry was obtained under the action of a vacuum mixer for 5 h. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil; the copper foil was dried at 85°C, and then cold-pressed, sliced, and slit to obtain the negative electrode plate:

[0099] Separator: A 7-μm base film (PE material) is sufficient

[0100] Electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed evenly according to a mass ratio of 1:1:1, and 2% fluoroethylene carbonate (FEC) was added. After dissolving and stirring thoroughly, lithium salt LiPF6 was added and mixed evenly to obtain the electrolyte. Among them, the concentration of LiPF6 was 1.05 mol / L;

[0101] Preparation of the battery:

[0102] The positive electrode, separator, and negative electrode were wound into a core, the tabs were welded, and it was placed in an aluminum-plastic film. The core was vacuum baked at 85 °C for 12 h, and the moisture was controlled at ≤300 ppm; the electrolyte was injected, and after vacuum packaging, standing, formation, shaping, capacity testing and other processes, the battery was obtained.

[0103] The partial preparation condition parameters and test results of Examples 1' to 11' and Comparative Example 1' are listed in Table 1.

[0104] Table 1 Preparation condition parameters and test results of the carbon-coated bottom coating of the positive electrode.

[0105]

[0106]

[0107] It can be seen from the content recorded in Table 1 that for the carbon-coated bottom coating of the positive electrode in Examples 1' to 6' of this application, the novel binder of this example was used. Compared with Comparative Example 1' using the conventional PAA binder, the solid content of the slurry increased, the peel strength between the positive current collector and the carbon-coated bottom coating of the positive electrode increased, the moisture content of the electrode sheet decreased. Applying it to the positive electrode sheet of a lithium-ion battery can reduce the internal resistance of the battery, the 3C rate discharge increases by about 2%, the capacity retention rate at 45 °C increases by about 5%, and the thickness change rate during storage at 60 °C for 35 days decreases by about 3%; it shows that compared with the conventional PAA binder, the carbon-coated bottom coating of the positive electrode obtained by using the novel binder has significantly improved the high-temperature storage, cycle performance, and safety performance of the lithium-ion battery when applied to the lithium-ion battery.

[0108] Carbon-coated bottom coating of the negative electrode and its preparation

[0109] Example 1”

[0110] The novel binder of Example 1 was used.

[0111] Preparation method of negative electrode carbon coating primer: take 10% dispersant (hydroxyethyl cellulose) and 40% conductive agent (carbon tube), put them in a stirring tank, stir for 35 minutes at an orbital speed of 18 rpm and an autorotation speed of 1100 rpm, add deionized water and 50% of the new binder of the present invention into the stirring tank, stir for 110 minutes at an orbital speed of 18 rpm and an autorotation speed of 2200 rpm to obtain the negative electrode carbon coating primer slurry.

[0112] Example 2":

[0113] Preparation method of negative electrode carbon coating primer: take 10% dispersant (CMC) and 40% conductive agent (carbon black), put them in a stirring tank, stir for 30 minutes at an orbital speed of 20 rpm and an autorotation speed of 1200 rpm, add deionized water and 50% of the new binder of the present invention into the stirring tank, stir for 120 minutes at an orbital speed of 20 rpm and an autorotation speed of 2100 rpm to obtain the negative electrode carbon coating primer slurry.

[0114] Example 8":

[0115] Preparation method of negative electrode carbon coating primer: take 10% dispersant (CMC) and 40% conductive agent (nano carbon fiber), put them in a stirring tank, stir for 25 minutes at an orbital speed of 22 rpm and an autorotation speed of 1300 rpm, add deionized water and 50% of the new binder of the present invention into the stirring tank, stir for 130 minutes at an orbital speed of 22 rpm and an autorotation speed of 2000 rpm to obtain the negative electrode carbon coating primer slurry.

[0116] Example 9":

[0117] Preparation method of negative electrode carbon coating primer: take 10% dispersant (CMC) and 40% conductive agent (graphene), put them in a stirring tank, stir for 30 minutes at an orbital speed of 20 rpm and an autorotation speed of 1200 rpm, add deionized water and 50% of the new binder of the present invention into the stirring tank, stir for 120 minutes at an orbital speed of 20 rpm and an autorotation speed of 2100 rpm to obtain the negative electrode carbon coating primer slurry.

[0118] Example 3":

[0119] The difference from Example 2 is that in the preparation method of the negative electrode carbon coating primer, the proportion of the new binder is 45%, the proportion of the conductive agent (carbon black) is 45%, the proportion of the dispersant (CMC) is 10%, and the other conditions remain unchanged to obtain the negative electrode carbon coating primer slurry.

[0120] Example 4":

[0121] The difference from “Example 2” is that in the preparation method of the negative electrode carbon-coated primer, the proportion of the new binder is 40%, the proportion of the conductive agent (carbon black) is 50%, and the proportion of the dispersant (CMC) is 10%, and the remaining conditions remain unchanged, obtaining the negative electrode carbon-coated primer slurry.

[0122] Example 5:

[0123] The difference from “Example 2” is that in the preparation method of the negative electrode carbon-coated primer, the proportion of the new binder is 35%, the proportion of the conductive agent (carbon black) is 55%, and the proportion of the dispersant (CMC) is 10%, and the remaining conditions remain unchanged, obtaining the negative electrode carbon-coated primer slurry.

[0124] Example 6:

[0125] The difference from “Example 2” is that in the preparation method of the negative electrode carbon-coated primer, the proportion of the new binder is 43%, the proportion of the conductive agent (carbon black) is 50%, and the proportion of the dispersant (CMC) is 7%, and the remaining conditions remain unchanged, obtaining the negative electrode carbon-coated primer slurry.

[0126] Example 7:

[0127] The difference from “Example 2” is that in the preparation method of the negative electrode carbon-coated primer, the proportion of the new binder is 45%, the proportion of the conductive agent (carbon black) is 50%, and the proportion of the dispersant (CMC) is 5%, and the remaining conditions remain unchanged, obtaining the negative electrode carbon-coated primer slurry.

[0128] Example 10:

[0129] The difference from “Example 2” is that the new binder prepared in Example 2 is used to obtain the negative electrode carbon-coated primer slurry.

[0130] Example 11:

[0131] The difference from “Example 2” is that the new binder prepared in Example 3 is used to obtain the negative electrode carbon-coated primer slurry.

[0132] Example 12:

[0133] The difference from “Example 2” is that the dispersant (CMC) and the conductive agent (carbon black) are taken and placed in a stirring tank, stirred at a revolution speed of 18 rpm and a rotation speed of 1100 rpm for 25 minutes, deionized water and the new binder of the present invention are added to the stirring tank, and stirred at a revolution speed of 18 rpm and a rotation speed of 2000 rpm for 110 minutes to obtain the negative electrode carbon-coated primer slurry.

[0134] Example 13:

[0135] The difference from “Example 2” is that a dispersant (CMC) and a conductive agent (carbon black) are taken and placed in a stirring tank, stirred at a speed of 22 rpm for the revolution speed and 1300 rpm for the rotation speed for 35 min, deionized water and the novel binder of the present invention are added into the stirring tank, and stirred at a speed of 22 rpm for the revolution speed and 2200 rpm for the rotation speed for 130 min to obtain the negative electrode carbon-coated primer slurry.

[0136] “Comparative Example 1”:

[0137] Preparation method of conventional negative electrode carbon-coated primer:

[0138] Take 10% of the dispersant (CMC) and 40% of the conductive agent (carbon black), place them in a stirring tank, stir at a speed of 20 rpm for the revolution speed and 1200 rpm for the rotation speed for 30 min, then adjust the speed, stir at a speed of 20 rpm for the revolution speed and 2100 rpm for the rotation speed for 120 min, and then add 50% of conventional SBR, stir at 10 rpm for the revolution speed for 30 min to obtain the negative electrode carbon-coated primer slurry.

[0139] “Comparative Example 2”:

[0140] The difference between this comparative example and “Example 2” is that in the preparation method of the negative electrode carbon-coated primer, the type of the binder is a conventional SBR binder. (The conventional SBR binder is in the form of emulsion globules, cannot be sheared at high speed, is prone to demulsification, and cannot adapt to a relatively high rotation speed, resulting in the scrapping of the slurry and inability to coat.)

[0141] For the negative electrode carbon-coated primers prepared in “Example 1” to “Example 9” and Comparative Example 1, measure their slurry solid content and slurry particle size. Prepare the negative electrode carbon-coated primer slurries prepared in the above examples and comparative examples into batteries, and measure the peel strength between the negative electrode carbon-coated primer and the negative electrode current collector. At the same time, measure the internal resistance of the battery, 3C rate discharge, 45 °C 2C @ 400-cycle capacity retention rate, and 60 °C @ 35-day storage thickness change rate.

[0142] Among them, the preparation method of the battery is as follows:

[0143] Positive electrode plate:

[0144] Lithium cobaltate, conductive agent Super-P, carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 98:0.5:0.5:1 in a solvent N-methylpyrrolidone (NMP), and stirred in a vacuum mixer for 6 h until the system is uniform to obtain a positive electrode slurry. Coat the positive electrode slurry on a positive electrode current collector aluminum foil, dry the aluminum foil at 90 °C, and then perform cold pressing, cutting, and slitting according to the design to obtain a positive electrode plate.

[0145] Negative electrode plate:

[0146] Apply the negative electrode carbon-coated primer slurry onto the negative electrode current collector copper foil and dry it at 85°C. Mix artificial graphite, thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in a weight ratio of 98:1:1, add deionized water, and obtain the negative electrode slurry under the action of a vacuum mixer for 5 hours. Uniformly coat the negative electrode slurry on the carbon-coated primer of the copper foil, dry it at 85°C, and then obtain the negative electrode plate after cold pressing, slicing, and slitting:

[0147] Separator: A 7μm base film is sufficient (PE material)

[0148] Electrolyte: In a dry argon atmosphere glove box, mix ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) in a mass ratio of 1:1:1, add 2% fluoroethylene carbonate (FEC), dissolve and stir well, then add the lithium salt LiPF6 and mix evenly to obtain the electrolyte. Among them, the concentration of LiPF6 is 1.05 mol / L;

[0149] Preparation of the battery:

[0150] Wind the positive electrode, separator, and negative electrode into a core, weld the electrode tabs, place them in an aluminum-plastic film, bake the core in a vacuum at 85°C for 12 hours, and control the moisture content to ≤300 ppm; inject the electrolyte, and obtain the battery through processes such as vacuum packaging, standing, formation, shaping, and capacity testing.

[0151] The specific preparation conditions and related properties of the above negative electrode carbon-coated primer slurry are referred to Table 2.

[0152] Table 2 Preparation condition parameters and performance test results of the negative electrode carbon-coated primer

[0153]

[0154]

[0155] It can be seen from Table 2 that:

[0156] After introducing the binder of the carbon-coated primer of the present invention, the solid content of the slurry is significantly increased, and the dispersibility of the slurry is improved; after the negative electrode dressing layer is coated and roll-pressed, the peel strength between the negative electrode current collector and the carbon-coated primer of the negative electrode is increased. It shows that compared with the conventional SBR binder, the new binder in this embodiment has advantages in both slurry dispersion and electrode plate peel strength.

[0157] After introducing the binder of the carbon-coated primer of the present invention, the resistance of the battery is reduced, the 3C rate discharge performance is improved, and the high-temperature cycle and high-temperature storage performance are improved.

[0158] At the same time, in this application, only by using the new binder can the carbon-coated primer of the positive electrode and the carbon-coated primer of the negative electrode be prepared, which is convenient to use and improves the production efficiency of lithium-ion batteries.

[0159] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features can be equivalently replaced; and all such modifications and replacements should fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a novel binder, characterized in that, It includes the following steps: Add a chain transfer agent to an acrylic acid solution to obtain a first solution; Heat the first solution to 70°C - 90°C, introduce an inert gas into the first solution, add an initiator, and react at a constant temperature for 2h - 4h under an inert gas atmosphere, then add an alcohol solution to obtain a second solution; Heat the second solution to 70°C - 90°C, add an initiator, and react at a constant temperature for 2h - 4h under an inert gas atmosphere to obtain a third solution; Cool the third solution to room temperature, adjust the pH value to 7 - 8, and remove volatile components and purify to obtain a novel binder; Wherein, the mass concentration of the acrylic acid solution is 10% - 30%, and the mass concentration of the alcohol solution is 10% - 30%; The chain transfer agent is isopropyl alcohol or dodecyl mercaptan, the alcohol is any one of C3 - C8 alcohols, and the initiator is ammonium persulfate or potassium sulfate.

2. The preparation method of the novel binder according to claim 1, wherein, Introduce an inert gas into the first solution for 20min - 40min.

3. The preparation method of the novel binder according to claim 1, characterized in that, The step of adjusting the pH value to 7 - 8 includes: Add a neutralizing agent to the third solution to adjust the pH value, and the neutralizing agent is sodium hydroxide or lithium hydroxide.

4. A novel binder, characterized in that, Obtained by using the preparation method according to any one of claims 1 to 3, the weight - average molecular weight of the novel binder is 30W - 35W; the novel binder has a branched structure and has a main chain of acrylic acid homopolymer.

5. A positive electrode carbon-coated primer, characterized in that, It includes a conductive agent, a dispersant, and the novel binder according to claim 4, wherein the mass ratio of the conductive agent is 40% - 55%, the mass ratio of the dispersant is 5% - 10%, and the mass ratio of the novel binder is 35% - 50%; The conductive agent is any one of carbon black, carbon nanotubes, nanofibrous carbon, graphene, and the dispersant is any one of polyvinylpyrrolidone, polyethers, polyesters.

6. The carbon-coated anode primer according to claim 5, characterized in that, The solid content of the slurry for the positive electrode carbon - coated undercoat is 18% - 30%.

7. A negative electrode carbon-coated primer, characterized in that, It includes a conductive agent, a dispersant, and the novel binder according to claim 4, wherein the mass ratio of the conductive agent is 40% - 55%, the mass ratio of the dispersant is 5% - 10%, and the mass ratio of the novel binder is 35% - 50%; The conductive agent is any one of carbon black, carbon nanotubes, nanofibrous carbon, graphene, and the dispersant is any one of carboxymethyl cellulose, hydroxyethyl cellulose.

8. The carbon-coated undercoat for the negative electrode according to claim 7, characterized in that, The solid content of the slurry for the negative electrode carbon - coated undercoat is 19% - 29%, and the particle size of the slurry for the negative electrode carbon - coated undercoat is 4μm - 9.5μm.

9. A preparation method of a carbon-coated primer, characterized in that, It includes the following steps: Place the dispersant and the conductive agent in a stirring tank, stir at a revolution speed of 18 - 22rpm and a rotation speed of 1100rpm to 1300rpm for 25min to 35min; Add deionized water and the novel binder according to any one of claims 1 to 4 to the stirring tank, and stir at a revolution speed of 18 - 22rpm and a rotation speed of 2000rpm to 2200rpm for 110min to 130min.

10. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, a separator, a negative electrode sheet and an electrode liquid; the positive electrode sheet includes a positive electrode current collector and a positive electrode undercoat provided on the surface of the positive electrode current collector, or the negative electrode sheet includes a negative electrode current collector and a negative electrode undercoat provided on the surface of the negative electrode current collector; The positive electrode undercoat uses the positive electrode carbon-coated undercoat according to any one of claims 5 to 6; or, the negative electrode undercoat uses the negative electrode carbon-coated undercoat according to any one of claims 7 to 8; Wherein, the peeling strength between the positive electrode carbon-coated undercoat and the positive electrode current collector is 12 N / m to 16 N / m, and the peeling strength between the negative electrode carbon-coated undercoat and the negative electrode current collector is 8.5 N / m to 14 N / m.

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