Preparation method and application of lithium ion battery positive electrode slurry based on fluoride-free binder

Abstract

The invention discloses a preparation method and application of lithium ion battery positive electrode slurry based on a fluoride-free binder. The positive electrode material comprises the following components in parts by mass: 100 parts of a positive electrode active material, 0.5-5 parts of a fluoride-free binder, 2-5 parts of a conductive agent and the balance of a solvent N-methyl pyrrolidone NMP. The fluorine-free binder is composed of HNBR (hydrogenated nitrile butadiene rubber) and PAA (polyacrylic acid), and the molecular structure does not contain fluorine, so that on one hand, environmental pollution can be reduced; on the other hand, through composite use of PAA and HNBR, the problem of breakage of a pole piece when PAA is singly used as a positive electrode binder and the problem of poor stability of positive electrode paste when HNBR is singly used as the positive electrode binder can be solved; in addition, carboxyl in PAA can form a CEI film on the surface of the positive electrode to protect the electrode, cyano in HNBR can endow the binder with high chemical stability, and the cyclic stability of the battery can be improved by using PAA and HNBR at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy battery materials, and specifically relates to a preparation method and application of a lithium-ion battery positive electrode slurry based on a fluorine-free binder. Background Art

[0002] Currently, the primary binder used in lithium-ion battery cathode materials is polyvinylidene fluoride (PVDF), which offers stable performance and ease of processing. However, PVDF belongs to the PFAS (per- and polyfluoroalkyl substances) class, which has drawn widespread global attention due to its persistence, bioaccumulation, and potential toxicity. Furthermore, as market demands for battery performance continue to increase, the development of high-performance, high-voltage-resistant cathode binders is becoming increasingly urgent, creating an urgent need to find alternative materials to PVDF in lithium-ion batteries.

[0003] Currently, the predominantly non-PVDF binders on the market are aqueous binders, primarily used for lithium iron phosphate applications. Due to the presence of residual alkali on the surface of the NCM (ternary composite material), the pH value must be strictly controlled when applying the binder to an aqueous slurry. Excessively alkaline slurries can corrode aluminum foil after coating, creating numerous bubbles and damaging the foil surface. This can lead to uneven coating thickness and a significant decrease in the conductivity of the cathode sheet. This undoubtedly creates numerous challenges in the slurry preparation and production process.

[0004] Polyacrylic acid (PAA) is commonly used as a binder for water-based carbon-silicon anodes. The carboxyl groups on its surface react with active groups on the Si surface, thereby increasing the bonding strength between the anode active materials and reducing the volume expansion of the silicon anode, making it a popular choice. However, when PAA is used alone as an oily adhesive for positive electrodes, the coated electrode is brittle and exhibits low peel strength due to the strong hydrogen bonding between the carboxyl groups. This makes subsequent electrode processing difficult, the electrode easily cracks during cycling, and is difficult to use.

[0005] CN 112751036 A uses a combination of PAA and PVDF, and a composite current collector, which can increase the pass rate of the nail penetration test, while improving the bonding strength between the metal aluminum layer and the base film, and the electrode resistivity is relatively low.

[0006] In order to overcome the problem of electrode cracking, CN 119751739 A uses modified PAA in the positive electrode binder, which not only effectively prevents the electrode cracking, but also forms a double protective layer, forming a CEI film on the positive electrode surface to protect the electrode, thereby improving the cycle stability of the battery.

[0007] Hydrogenated nitrile rubber (HNBR) has excellent high and low temperature resistance and corrosion resistance. CN 119133455 A uses a blended positive electrode active material of lithium manganese iron phosphate and a high-nickel ternary layered oxide, combined with HNBR binder, conductive agent and solvent to prepare the positive electrode slurry. It is used in lithium-ion secondary batteries, and the battery has high energy density and high-voltage cycle stability.

[0008] CN 119170801 A uses an HNBR derivative as a first binder, an acrylonitrile derivative and a hydrogenated butadiene derivative as a second binder, and polyvinylidene fluoride and its derivatives or copolymers as a third binder in the preparation of positive electrodes for secondary lithium-ion batteries. This reduces or minimizes the use of polyvinylidene fluoride-based positive electrode binders, or can completely replace polyvinylidene fluoride-based positive electrode binders with hydrogenated nitrile rubber derivatives. Results show that this approach can increase the cycle life of rechargeable lithium batteries while increasing the adhesion of the positive electrode and reducing resistance.

[0009] Although the above-mentioned and other patents apply HNBR as a lithium-ion positive electrode binder, the range of HNBR structures used is very wide. Different structures and unsaturations have huge differences in the slurry state and the high-voltage resistance of the battery. The use of group-modified HNBR and other modified binder components not only increases production costs, but also has uncertain effects on various battery properties. When HNBR that has not been modified by the group is used alone as a positive electrode binder, the slurry settles severely and the viscosity changes rapidly, making it difficult to apply a uniform electrode, resulting in difficulties in subsequent production and processing.

[0010] Because HNBR is elastic, it can improve the flexibility of the electrode, while the interaction between the carboxyl groups in PAA and the crosslinking between chains can improve the sedimentation of the slurry and help the slurry disperse evenly. Therefore, when the two are mixed, they can simultaneously improve the flexibility of the positive electrode and the stability of the positive electrode slurry, while forming a CEI film to protect the positive electrode and improve the cycle performance of the battery. Compared with electrode sheets using PVDF alone, the electrode sheets are more flexible and have better high-voltage resistance. At the same time, the composite binder composition is completely fluorine-free, which has broad prospects and important significance in expanding the use and application of positive electrode binders. Summary of the Invention

[0011] The purpose of the present invention is to provide a composite fluorine-free binder, a preparation method and application of a lithium-ion battery positive electrode slurry, to solve the problems of environmental pollution and biological toxicity caused by the current reliance on PVDF as a positive electrode binder in the field of lithium-ion batteries, and at the same time improve the high-voltage performance and cycle performance of lithium-ion batteries.

[0012] To achieve the above object, the technical solution adopted by the present invention is as follows: a lithium-ion battery positive electrode slurry based on a fluorine-free binder, the slurry having a solid content of 50-75 wt%, by weight, comprising the following components and their mass parts:

[0013] 100 parts of positive electrode active material, 0.5-5 parts of fluorine-free binder, 2-5 parts of conductive agent, and the rest is solvent N-methylpyrrolidone (NMP);

[0014] In the above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder, the positive electrode active material may be a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). The lithiated intercalation compound may use one or more types (or species) of composite oxides of lithium combined with cobalt, manganese, nickel, aluminum, iron, and phosphorus;

[0015] The above-mentioned composite oxide may include lithium cobalt oxide, lithium manganate oxide, lithium iron phosphate compounds, ternary layered oxides or combinations thereof;

[0016] As an example, the molecular formula of the ternary layered oxide may be LiNi a Co b Mn 1-a-b O2, wherein 0.3≤a<1, 0<b≤0.3, and a+b<1.

[0017] The above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder comprises hydrogenated nitrile rubber (HNBR) and polyacrylic acid (PAA), wherein the content of hydrogenated nitrile rubber in the fluorine-free binder is 50-90 wt%, and the rest is polyacrylic acid, with a content of 10-50 wt%.

[0018] Furthermore, it is preferred that the content of hydrogenated nitrile rubber in the fluorine-free binder is 60-70 wt%, and the content of polyacrylic acid is 30-40 wt%, by weight;

[0019] The above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder, wherein the hydrogenated nitrile rubber in the fluorine-free binder has an acrylonitrile content of 20 to 45 wt%, an unsaturation degree of 0.1 to 5%, a Mooney viscosity of 30 to 70 ML (1+4) at 100° C., and a molecular weight of 80,000 to 500,000;

[0020] Furthermore, it is preferred that the acrylonitrile content in the hydrogenated nitrile rubber is 32-38 wt%, by weight, the unsaturation is ≤1%, the Mooney viscosity is 60-70 ML(1+4)100°C, and the molecular weight is between 350,000 and 450,000;

[0021] The above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder, wherein the molecular weight of the polyacrylic acid in the fluorine-free binder is between 100,000 and 1,000,000;

[0022] Furthermore, the molecular weight of the polyacrylic acid is preferably between 500,000 and 1,000,000;

[0023] The above-mentioned lithium ion positive electrode slurry based on a fluorine-free binder, wherein the polyacrylic acid in the fluorine-free binder can be polyacrylic acid prepared by homopolymerization of acrylic acid monomer, or modified polyacrylic acid prepared by copolymerization of acrylic acid and a modifying monomer; in the modified polyacrylic acid, the acrylic acid content is 70-95 wt%, and the modifying monomer content is 5-30 wt%, by weight;

[0024] The above-mentioned lithium-ion positive electrode slurry based on a fluorine-free binder, the modified monomer may be one or more of methyl acrylate, methyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, 2-ethylhexyl acrylate, vinyl acetate, butyl acrylate, ethyl acrylate and the like;

[0025] In the above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder, the conductive agent may be one or more of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.;

[0026] Furthermore, the conductive agent is preferably one or more of carbon black, acetylene black, and carbon nanotubes;

[0027] The preparation method of the above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder is as follows:

[0028] (1) Cut the hydrogenated nitrile rubber solid into small pieces, mix it with acrylic acid powder, and dissolve it in N-methylpyrrolidone as a solvent at a stirring speed of 700-1200 rpm and a temperature of 50-75°C for 6-10 h to obtain a uniform mixture;

[0029] (2) Add a conductive agent to the above mixture and continue mixing at a speed of 600-800 rpm for 60-120 min;

[0030] (3) Adding the positive electrode active material to the above mixture, continuing to mix at a speed of 800-1200 rpm for 120-180 min, and mixing to obtain a lithium-ion battery positive electrode slurry based on a fluorine-free binder.

[0031] The above-mentioned lithium-ion battery positive electrode slurry based on a fluorine-free binder has a rotational viscosity between 1000 and 10000 mPa·s;

[0032] Furthermore, the lithium-ion battery positive electrode slurry based on the fluorine-free binder has a rotational viscosity of 3000-4000 mPa·s;

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The lithium-ion battery positive electrode slurry based on a fluorine-free binder provided by the technical solution of the present invention does not contain fluorine. Existing positive electrode binders generally contain PVDF and its derivatives. PVDF belongs to the PFAS (per- and polyfluoroalkyl substances) class of substances, which are difficult to degrade in nature and are persistent, bioaccumulative, and potentially toxic.

[0035] 2. The fluorine-free binder-based lithium-ion battery cathode slurry provided by the technical solution of the present invention can significantly improve the problem of electrode fracture caused by polyacrylic acid (PAA)-based binders when used alone in the cathode. The polyacrylic acid (PAA) in the binder component is rich in carboxyl groups and can form a CEI film on the positive electrode, protecting the electrode and improving the stability of the battery cycle. The hydrogenated nitrile rubber (HNBR) in the binder component is rich in cyano groups and can enhance the high-voltage performance of the electrode. The combination of the two not only makes the electrode elastic, but also improves the sedimentation problem of the slurry when hydrogenated nitrile rubber (HNBR) is used alone.

[0036] 3. The lithium-ion battery positive electrode slurry based on the fluorine-free binder provided by the technical solution of the present invention does not require the introduction of other functional groups into the binder structure for modification. However, the performance of the binder can be further enhanced by introducing other functional groups. Under the general trend of reducing costs and increasing efficiency in the new energy field, it can effectively reduce raw material and R&D costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Cycling curves of button batteries prepared with the positive electrode slurries described in Example 3 and Comparative Example 3. DETAILED DESCRIPTION

[0038] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0039] The present invention is described in detail below with reference to the following examples. The raw materials used in the examples and comparative examples are all commercially available and are not particularly limited in the present invention.

[0040] Example 1 Lithium-ion cathode slurry based on fluorine-free binder

[0041] (1) Take 2 parts of fluorine-free adhesive, including 1.5 parts of hydrogenated nitrile rubber (acrylonitrile content of 34%, unsaturation ≤5%, molecular weight of 300,000), cut into small pieces and place them in a 250 mL beaker, then add 0.5 parts of homopolymerized polyacrylic acid powder (molecular weight of 700,000) and 40 parts of N-methylpyrrolidone, stir at 70 °C for 8 h to completely dissolve it, and obtain a mixed adhesive solution.

[0042] (2) Add 2 parts of conductive agent KS-6 to the above mixed glue in batches, use a stirring speed of 700 rpm, and stir for 60 minutes to evenly disperse the conductive agent in the glue to prepare a conductive glue.

[0043] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 1000 rpm for 180 min to obtain a positive electrode slurry with a rotational viscosity of 4460 mPa·s.

[0044] Example 2 Lithium-ion cathode slurry based on fluorine-free binder

[0045] (1) Take 1.5 parts of fluorine-free adhesive, including 1 part of hydrogenated nitrile rubber (acrylonitrile content of 36%, unsaturation of 0.1%, molecular weight of 340,000), cut it into small pieces and place it in a 250 mL beaker, then add 0.5 parts of homopolymerized polyacrylic acid powder (molecular weight of 1,000,000) and 43 parts of N-methylpyrrolidone, stir at 65 °C for 6 h to completely dissolve it, and obtain a mixed adhesive solution.

[0046] (2) Add 2.5 parts of conductive agent, including 1.5 parts of Li-435 and 1 part of KS-6, to the above mixed glue in batches, use a stirring speed of 700 rpm, and stir for 60 minutes to uniformly disperse the conductive agent in the glue to prepare a conductive glue.

[0047] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 900 rpm for 150 min to obtain a positive electrode slurry with a rotational viscosity of 3200 mPa·s.

[0048] Example 3 Lithium-ion cathode slurry based on fluorine-free binder

[0049] (1) Take 1.7 parts of fluorine-free adhesive, including 1.13 parts of hydrogenated nitrile rubber (acrylonitrile content of 36%, unsaturation ≤1%, molecular weight of 340,000), cut into small pieces and place them in a 250 mL beaker, then add 0.57 parts of homopolymerized polyacrylic acid powder (molecular weight of 1,000,000) and 48 parts of N-methylpyrrolidone, stir at 65 °C for 6 h to completely dissolve it, and obtain a mixed adhesive solution.

[0050] (2) 3.3 parts of a conductive agent, including 2 parts of Li-435 and 1.3 parts of KS-6, were added to the mixed adhesive solution in batches. The mixture was stirred at a stirring speed of 700 rpm for 80 min to uniformly disperse the conductive agent in the adhesive solution to obtain a conductive adhesive solution.

[0051] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 900 rpm for 135 min to obtain a positive electrode slurry with a rotational viscosity of 3760 mPa·s.

[0052] Example 4 Lithium-ion cathode slurry based on fluorine-free binder

[0053] (1) Take 0.5 parts of fluorine-free adhesive, including 0.3 parts of hydrogenated nitrile rubber (acrylonitrile content of 45%, unsaturation ≤1%, molecular weight of 500000), cut into small pieces and place them in a 250 mL beaker, then add 0.2 parts of homopolymerized polyacrylic acid powder (molecular weight of 100000) and 40 parts of N-methylpyrrolidone, stir at 50 °C for 6 h to completely dissolve it, and obtain a mixed adhesive solution.

[0054] (2) Add 2 parts of conductive agent, including 0.5 parts of CNT and 1.5 parts of Li-435, to the above mixed glue in batches. Stir at a stirring speed of 600 rpm for 80 minutes to uniformly disperse the conductive agent in the glue to obtain a conductive glue.

[0055] (3) 100 parts of NCM811 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 800 rpm for 120 min to obtain a positive electrode slurry with a rotational viscosity of 3420 mPa·s.

[0056] Example 5 Lithium-ion cathode slurry based on fluorine-free binder

[0057] (1) Take 5 parts of fluorine-free adhesive, including 3.5 parts of hydrogenated nitrile rubber (acrylonitrile content of 20%, unsaturation ≤1%, molecular weight of 80,000), cut into small pieces and place them in a 250 mL beaker. Then add 1.5 parts of homopolymerized polyacrylic acid powder (molecular weight of 500,000) and 60 parts of N-methylpyrrolidone. Stir at 75 °C for 10 h to completely dissolve it to obtain a mixed adhesive solution.

[0058] (2) Add 5 parts of conductive agent, including 3 parts of Li-435 and 2 parts of KS-6, to the mixed glue in batches. Stir at a stirring speed of 800 rpm for 120 minutes to uniformly disperse the conductive agent in the glue to obtain a conductive glue.

[0059] (3) 100 parts of NCM811 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 1200 rpm for 180 min to obtain a positive electrode slurry with a rotational viscosity of 5780 mPa·s.

[0060] Example 6 Lithium-ion cathode slurry based on fluorine-free binder

[0061] (1) Take 1.7 parts of fluorine-free adhesive, including 1.13 parts of hydrogenated nitrile rubber (acrylonitrile content of 36%, unsaturation ≤1%, molecular weight of 80,000), cut into small pieces and place in a 250 mL beaker, then add 0.57 parts of modified polyacrylic acid powder (molecular weight of 1,000,000, acrylic acid content of 70 wt%, methyl methacrylate content of 30 wt%, by weight), and then add 55 parts of N-methylpyrrolidone, stir at 65 °C for 6 h to completely dissolve it, and obtain a mixed adhesive solution.

[0062] (2) 3.3 parts of a conductive agent, including 2 parts of Li-435, 1 part of KS-6, and 0.3 parts of CNT, were added to the mixed glue in batches. The mixture was stirred at a stirring speed of 700 rpm for 80 min to uniformly disperse the conductive agent in the glue to obtain a conductive glue.

[0063] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 900 rpm for 135 min to obtain a positive electrode slurry with a rotational viscosity of 3420 mPa·s.

[0064] Example 7 Lithium Ion Cathode Slurry Based on Fluorine-Free Binder

[0065] (1) Take 1.7 parts of fluorine-free adhesive, including 1.13 parts of hydrogenated nitrile rubber (acrylonitrile content of 36%, unsaturation ≤1%, molecular weight of 80,000), cut into small pieces and place in a 250 mL beaker, then add 0.57 parts of modified polyacrylic acid powder (molecular weight of 1,000,000, acrylic acid content of 95 wt%, methyl acrylate content of 5 wt%, by weight), and then add 47.8 parts of N-methylpyrrolidone, stir at 65 °C for 6 h to completely dissolve it, and obtain a mixed adhesive solution.

[0066] (2) Three parts of a conductive agent, including two parts of KS-6 and one part of Li-435, were added to the mixed adhesive solution in batches. The mixture was stirred at a stirring speed of 700 rpm for 80 min to uniformly disperse the conductive agent in the adhesive solution to obtain a conductive adhesive solution.

[0067] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 800 rpm for 120 min to obtain a positive electrode slurry with a rotational viscosity of 3660 mPa·s.

[0068] Comparative Example 1: Lithium Ion Cathode Slurry Based on Polyacrylic Acid

[0069] (1) Take 1.7 parts of homopolymerized polyacrylic acid (molecular weight 550,000), place it in a 250 mL beaker, add 34 parts of N-methylpyrrolidone, and stir at room temperature at a stirring speed of 600 rpm for 6 h to obtain a clear and transparent glue solution.

[0070] (2) Add 2 parts of conductive agent Li-435 to the above glue solution in batches, and stir at a stirring speed of 700 rpm for 60 minutes to uniformly disperse the conductive agent in the glue solution to obtain a conductive glue solution.

[0071] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 900 rpm for 150 min to obtain a positive electrode slurry with a rotational viscosity of 2800 mPa·S.

[0072] Comparative Example 2 Lithium Ion Cathode Slurry Based on Hydrogenated Nitrile-Butadiene Rubber

[0073] (1) Take 1.1 parts of hydrogenated nitrile rubber (acrylonitrile content 36%, unsaturation ≤ 1%, molecular weight 340000), place it in a 250 mL beaker, add 30 parts of N-methylpyrrolidone, and stir at room temperature at a stirring speed of 600 rpm for 8 h to obtain a transparent rubber solution.

[0074] (2) 2.5 parts of a conductive agent, including 1.5 parts of Li-435 and 1 part of KS-6, were added to the above-mentioned adhesive solution in batches, and stirred at a stirring speed of 800 rpm for 90 min to uniformly disperse the conductive agent in the adhesive solution to obtain a conductive adhesive solution.

[0075] (3) 100 parts of NCM523 were added to the conductive adhesive prepared above in batches, and the mixture was stirred at a stirring speed of 1000 rpm for 180 min to obtain a positive electrode slurry with a rotational viscosity of 5670 mPa·s.

[0076] Comparative Example 3: Lithium Ion Cathode Slurry Based on Polyvinylidene Fluoride

[0077] (1) Take 1.7 parts of polyvinylidene fluoride, place it in a 250 mL beaker, add 24 parts of N-methylpyrrolidone, and stir at room temperature at a stirring speed of 600 rpm for 5 h to obtain a clear and transparent glue solution.

[0078] (2) 3.3 parts of a conductive agent, including 2 parts of Li-435 and 1.3 parts of KS-6, were added to the above-mentioned adhesive solution in batches, and stirred at a stirring speed of 700 rpm for 60 min to uniformly disperse the conductive agent in the adhesive solution to obtain a conductive adhesive solution.

[0079] (3) 100 parts of NCM523 were added to the conductive glue prepared above in batches, and then 1 part of polyvinyl pyrrolidone (PVP) was added as a dispersant. The mixture was stirred at a stirring speed of 900 rpm for 120 min to prepare a positive electrode slurry with a rotational viscosity of 2820 mPa·s.

[0080] Application Example 1: Performance of electrodes made from lithium-ion cathode slurry based on fluorine-free binder

[0081] The positive electrode slurries prepared in Examples 1-7 and Comparative Examples 1-3 were respectively coated on aluminum foil, dried, and rolled into electrodes. The prepared positive electrode electrodes were cut into 8×2.5 cm strips, and the strip electrodes were pasted on a plexiglass plate. One end of the strip electrode was attached to the electrode plate using 3M transparent tape. The other ends of the plexiglass plate and the 3M transparent tape were respectively fixed to the upper and lower clamps of a universal tensile testing machine, and a 90° peel strength test was performed on the electrode plate at a tensile rate of 10 mm / min. The prepared positive electrode sheets were cut into small discs with a diameter of about 20 mm, and a disc resistance test was performed. The results are shown in Table 1.

[0082] Table 1 90° peel strength and wafer resistance of electrode

[0083] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 90° peeling / (N / m) 17.8 20.8 25.4 16.8 40.2 33.5 27.8 4.2 29.1 25.5 Chip resistance / Ω 0.70 0.79 0.62 0.43 0.85 0.74 0.65 0.83 0.96 0.64

[0084] As can be seen from Table 1, compared with the positive electrode slurry prepared using only PAA in Comparative Example 1, the electrode sheets coated using the positive electrode slurries prepared using Examples 1-7 have higher peel strength and better flexibility, which is beneficial to the processing of the electrode sheets; compared with the positive electrode slurry prepared using only HNBR in Comparative Example 2, the electrode sheets coated using Examples 1-7 have lower internal resistance, which is beneficial to improving the rate performance of the battery; compared with the electrode sheets prepared using PVDF in Comparative Example 3, the peel strength and wafer resistance of the electrode sheets coated using Examples 1-7 are relatively close, and the composite of HNBR and PAA can replace PVDF in the positive electrode slurry.

[0085] Application Example 2: Viscosity of Lithium-ion Cathode Slurry Based on Fluorine-free Binder

[0086] At room temperature, a rotational viscometer was used to measure the changes in the rotational viscosity of the positive electrode slurries prepared in Examples 1-7 and Comparative Examples 1-3 after standing for different periods of time. A No. 4 rotor was used at a speed of 30 r / min. The results are shown in Table 2.

[0087] Table 2 Viscosity of slurry at different standing times

[0088] Time rotation viscosity 0 h 0.5 h 1 h 2 h 4 h 8 h 24h Example 1 4460 4860 5020 4980 5120 5280 5560 Example 2 3200 3460 3380 3480 3520 3460 3880 Example 3 3760 3640 3920 3860 3720 4020 4260 Example 4 3420 3440 3380 3340 3420 3480 3600 Example 5 5780 5820 5800 5900 6000 6020 6540 Example 6 3420 3560 3600 3780 3860 4020 4420 Example 7 3660 3680 3720 3740 3800 3880 4160 Comparative Example 1 2800 2820 2780 2960 3020 2840 3140 Comparative Example 2 5670 6400 6880 7160 6960 7420 13200 Comparative Example 3 2820 3400 3240 3140 3350 3160 2579

[0089] As can be seen from Table 2, the viscosity of the positive electrode slurry prepared using only HNBR in Comparative Example 2 changed greatly after standing for 24 hours, which is not conducive to subsequent processing. However, the viscosity of the positive electrode slurries prepared in Examples 1-7 changed little after standing for 24 hours, which is conducive to subsequent processing.

[0090] Application Example 3 Cycling Performance of Batteries Prepared with Lithium-Ion Cathode Slurry Based on Fluorine-Free Binder

[0091] The positive electrode sheets prepared in Example 3 and Comparative Example 3 were cut into small discs with a diameter of approximately 10 mm using a cutting machine as the positive electrode. A metal lithium sheet was used as the negative electrode. A mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1 containing 1 M lithium hexafluorophosphate was used as the electrolyte. A 20 μm polypropylene (PP) was used as the separator. A button-type lithium-ion battery was assembled in an argon glove box with a water pressure and an oxygen pressure of less than 0.01 ppm. The assembled button-type lithium-ion battery was cycled 0.5 C / 1 C at a voltage of 2.5-4.5 V. The results are shown in FIG. Figure 1 As shown. Figure 1 It can be seen that after 300 cycles, the capacity retention rate of the button half-cell made using Example 3 is better than that of the button half-cell made using the traditional binder PVDF. The battery capacity decays more slowly and has better cycle stability, which shows good application value.

[0092] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the embodiments described herein. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A lithium-ion battery positive electrode slurry based on a fluorine-free binder, characterized in that: It includes the following components, calculated by mass: 100 parts of positive electrode active material, 0.5-5 parts of fluorine-free binder, 2-5 parts of conductive agent, and the rest is solvent N-methylpyrrolidone, the fluorine-free binder contains hydrogenated nitrile rubber and polyacrylic acid; the content of hydrogenated nitrile rubber in the fluorine-free binder is 50-90 wt%, and the rest is polyacrylic acid, with a content of 10-50 wt%; in the fluorine-free binder, the acrylonitrile content of the hydrogenated nitrile rubber is 20-45 wt%, the unsaturation is 0.1-5%, the Mooney viscosity is 30-70 ML (1+4) 100 ° C, and the molecular weight is between 80000 and 500000; the molecular weight of the polyacrylic acid in the fluorine-free binder is between 100000 and 1000000; the polyacrylic acid in the fluorine-free binder is polyacrylic acid prepared by homopolymerization of acrylic acid monomer, or modified polyacrylic acid prepared by copolymerization of acrylic acid and modified monomer; in the modified polyacrylic acid, the acrylic acid content is 70-95 wt%, and the content of the modified monomer is 5-30 wt%, by weight; the modified monomer is one or more of acrylate compounds such as methyl acrylate, methyl methacrylate, hydroxyethyl methacrylate, glycidyl methacrylate, 2-ethylhexyl acrylate, vinyl acetate, butyl acrylate, and ethyl acrylate.

2. The positive electrode slurry for lithium-ion batteries based on a fluorine-free binder according to claim 1, characterized in that: The positive electrode active material is a compound capable of intercalating and deintercalating lithium, and the compound capable of intercalating and deintercalating lithium is a composite oxide of lithium and one or more of cobalt, manganese, nickel, aluminum, iron, and phosphorus.

3. The positive electrode slurry for lithium-ion batteries based on a fluorine-free binder according to claim 2, characterized in that: The composite oxide is one or more of lithium cobalt oxide, lithium manganate oxide, lithium iron phosphate compound, and ternary layered oxide; The molecular formula of the ternary layered oxide is LiNi a Co b Mn 1-a-b O2, wherein 0.3≤a<1, 0<b≤0.3, and a+b<1.

4. The positive electrode slurry for lithium-ion batteries based on a fluorine-free binder according to claim 1, characterized in that: The conductive agent is one or more of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.

5. The method for preparing a positive electrode slurry for a lithium-ion battery based on a fluorine-free binder according to any one of claims 1 to 4, characterized in that: Here’s how: (1) Cut the hydrogenated nitrile rubber solid into small pieces, mix it with polyacrylic acid powder, and dissolve it in N-methylpyrrolidone as a solvent at a stirring speed of 700-1200 rpm and a temperature of 50-75°C for 6-10 h to obtain a uniform mixture; (2) Add a conductive agent to the above mixture and continue mixing at a speed of 600-800 rpm for 60-120 min; (3) Adding the positive electrode active material to the above mixture, continuing to mix at a speed of 800-1200 rpm for 120-180 min, and mixing to obtain a lithium-ion battery positive electrode slurry based on a fluorine-free binder.

6. The method for preparing a positive electrode slurry for a lithium-ion battery based on a fluorine-free binder according to claim 5, wherein: The rotational viscosity of the positive electrode slurry is between 1000 and 10000 mPa·S.

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