A composite binder for a silicon negative electrode of a lithium battery, a silicon negative electrode sheet, and a lithium battery

Abstract

The present application relates to a kind of lithium battery silicon negative electrode composite binder, silicon negative pole piece and lithium battery, at least including A component, B component, C component and D component;Wherein, A component is acrylic multiblock copolymer, B component is low Tg's acrylic resin, C component is carbon nanotube, D component is tannic acid;With weight fraction, A component 100 parts, B component 1-30 parts, C component 1-10 parts, D component 1-50 parts.The present application improves the flexibility of electrode material, peel strength, reduces the electrochemical impedance of battery, prolongs the cycle life of battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a composite binder for a silicon negative electrode of a lithium battery, a silicon negative electrode pole piece and a lithium battery. BACKGROUND

[0002] Silicon materials are increasingly used as negative electrode materials of lithium batteries due to their high theoretical specific capacity, abundant reserves, controllable cost and the ability to improve the energy density of batteries.

[0003] However, when silicon materials are used as lithium battery negative electrodes, they store lithium ions by forming lithium-silicon alloys. Since silicon materials do not have a layered crystal structure, in the process of deintercalating lithium ions, Li 15 Si4 is converted into amorphous silicon, resulting in severe volume expansion and contraction and a large (280%) volume change.

[0004] At present, the components of silicon negative electrode materials are bonded together by a binder, and the mechanical strength is limited. When the binder cannot withstand the huge volume expansion of silicon during charging and discharging, the stress generated by the volume change of silicon materials in the cycle process will destroy the structure of the silicon negative electrode, causing the contact between the active material and the conductive agent to be disconnected and the conductive network to collapse, thereby affecting the cycle stability of the battery. Moreover, the volume expansion of the silicon negative electrode will also damage the solid electrolyte layer between the electrolyte and the pole piece. This process will consume a large amount of lithium ions and electrolyte, causing irreversible capacity loss and affecting the battery life.

[0005] Therefore, it is particularly important to develop a composite binder for a silicon negative electrode of a lithium battery, a silicon negative electrode pole piece and a lithium battery to improve the adhesion strength of the negative electrode material and the toughness of the electrode, improve the electrochemical kinetics of the battery, reduce the cycle cracking of the battery and improve the cycle life of the battery. SUMMARY

[0006] The application aims to overcome the defects in the prior art and provides a composite binder for a silicon negative electrode of a lithium battery, a silicon negative electrode pole piece and a lithium battery, which improves the flexibility and peel strength of the electrode material, reduces the electrochemical impedance of the battery and prolongs the cycle life of the battery.

[0007] To achieve the above-mentioned purpose, the technical solutions adopted by the application are as follows:

[0008] Technical solution one

[0009] The composite binder for a silicon negative electrode of a lithium battery comprises at least components A, B, C and D. Component A is an acrylic multi-copolymer, component B is a low-Tg acrylic resin, component C is a carbon nanotube and component D is a mononic acid.

[0010] The A component is 100 parts, the B component is 1-30 parts (such as 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, etc.), the C component is 1-10 parts (such as 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, etc.), and the D component is 1-50 parts (such as 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, etc.), all in terms of weight parts.

[0011] As a preferred technical solution, the acrylic multi-copolymer is a terpolymer of acrylonitrile, 2-acrylamide-2-phenyl ethanesulfonic acid and methacrylic acid.

[0012] As a preferred technical solution, the low-Tg acrylic resin has a Tg of -100℃ to 100℃ (such as -100℃, -90℃, -80℃, -70℃, -60℃, -50℃, -40℃, -30℃, -20℃, -10℃, 0℃, 10℃, 20℃, 10℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, etc.).

[0013] As a preferred technical solution, the low-Tg acrylic resin uses BT-9 resin, and the BT-9 resin has a Tg of 1℃. The use of BT-9 resin with a Tg of 1℃ has a better effect than other low-Tg acrylic resins.

[0014] As a preferred technical solution, the carbon nanotube is a single-walled carbon nanotube.

[0015] As a preferred technical solution, the tannic acid is a cypress tannic acid composed of a resorcinol type A ring.

[0016] Technical solution two:

[0017] A preparation method of the composite binder for the silicon negative electrode of the lithium battery comprises the following steps:

[0018] Step 1: 100 parts of the A component of the polymer binder is taken, and 1-30 parts of the B component is added thereto, and mechanical dispersion is performed to obtain a mixed glue solution;

[0019] Step 2: 1-10 parts of the C component is added to the mixed glue solution in step 1, mechanical dispersion is performed, and then the mixed sample is homogenized to obtain a composite glue solution;

[0020] Step 3: 1-50 parts of the D component is dissolved in water to prepare a tannic acid aqueous solution, and then the composite glue solution in step 2 is added to the tannic acid aqueous solution, and mechanical dispersion is performed to obtain a product.

[0021] As a preferred technical solution, in step 1, the mechanical dispersion is dispersed by a dispersing machine, the rotating speed of the mechanical dispersion is 1000 rpm, and the dispersion time is 30 min.

[0022] In step 2, the mechanical dispersion is dispersed by a dispersing machine, the rotating speed of the mechanical dispersion is 1000 rpm, and the dispersion time is 10 min.

[0023] In step 2, the homogenization is carried out by a high-pressure homogenizing dispersing machine, the flow rate of the high-pressure homogenizing dispersing machine is 0-500 L / h, the pressure is 0-1200 bar, and the homogenization time is 20-120 min.

[0024] In step 3, the mechanical dispersion is carried out by a dispersing machine, the rotating speed of the mechanical dispersion is 1000 rpm, and the dispersion time is 30 min.

[0025] Technical solution three:

[0026] A silicon negative pole piece contains the composite binder for the lithium battery silicon negative pole.

[0027] Technical solution four:

[0028] A lithium battery is provided with the silicon negative pole piece.

[0029] Compared with the prior art, the beneficial effects of the present application are that:

[0030] The present application adds low-Tg acrylic resin, single-walled carbon nanotubes and tannic acid to the acrylic multi-copolymer, wherein the single-walled carbon nanotubes are in a fibrous form and can form a continuous three-dimensional grid in the electrode material, the polyphenol hydroxyl groups of tannic acid can also form hydrogen bonds with the polypropylene segments in the binder, and a high-molecular crosslinked network structure is constructed by using hydrogen bonds, the network structures formed by the two are interpenetrated, the four components synergistically act, compared with the pure acrylic multi-copolymer as the binder, not only the conductivity of the binder is improved, but also the toughness of the binder and the electrode, the wettability of the electrode material to the binder, and the bonding strength of the binder are greatly improved, the cracking probability of the electrode sheet in the cyclic charging and discharging process is reduced, the peeling phenomenon caused by the volume change of the material in the electrode charging and discharging process is improved, the cycle life of the battery and the cycle stability of the electrode are improved. In addition, the carbon nanotubes can greatly improve the permeability of the electrolyte in the electrode material, and the polar structures such as phenolic hydroxyl groups and carbonyl groups of tannic acid can also improve the ion transfer effect of the lithium battery, thereby greatly reducing the electrochemical impedance of the lithium battery and improving the electrochemical performance.

[0031] The homogenization process is added in the application, solves the problem of poor dispersion caused by the agglomeration of carbon nanotubes under high-speed stirring in the traditional mechanical dispersion process, improves the dispersion effect of carbon nanotubes and low-Tg acrylic resin in the adhesive, and because of the introduction of the homogenization process, it not only makes it possible to replace the traditional technology of "adding carbon nanotubes in the form of carbon nanotube dispersion liquid into the adhesive" with "adding carbon nanotubes in the form of carbon nanotube solid directly into the adhesive", but also makes the adhesive can obtain uniform dispersion under high carbon nanotube addition amount. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 SEM morphology of the silicon negative electrode sheet material in Example 2 of the application;

[0033] Figure 2 SEM morphology of the silicon negative electrode sheet material in Comparative Example 4 of the application;

[0034] Figure 3 Electrochemical impedance spectrogram of the lithium battery in each example and comparative example of the application;

[0035] Figure 4 Capacity retention rate and charge-discharge cycle time relationship diagram of the lithium battery in each example and comparative example of the application. DETAILED DESCRIPTION

[0036] In the application,

[0037] Cotinus coggygria tannin: purchased from Shanghai Maikelin Biochemical Technology Co., Ltd.;

[0038] The chemical structural formula of Cotinus coggygria tannin is as follows:

[0039]

[0040] Single-walled carbon nanotubes: purchased from Aokehail Trade (Shenzhen) Co., Ltd.

[0041] Si-C composite material containing Si and C (silicon-carbon negative electrode main material), silicon-based with a specific capacity of 600 mAh / g: purchased from Zhejiang Lianchen New Material Technology Co., Ltd.

[0042] PE / PP separator: purchased from Shanghai Enxin New Material Technology Co., Ltd.

[0043] In the application, the low-Tg acrylic resin is a commercial BT-9 resin, and the solid content of the low-Tg acrylic resin in the BT-9 resin is 40%.

[0044] BT-9 resin (Tg is 1℃): purchased from Evonik (China) Co., Ltd.

[0045] The adhesive polymer used in the present application is a terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid, and the preparation method is as follows:

[0046] Step a: 350 parts of pure water are added into a reaction kettle, stirring at 100 rpm, nitrogen is introduced at a flow rate of 2000 L / h, water-soluble oxygen is removed for 1.5 hours, then 55 parts of monomer acrylic acid, 5 parts of monomer N,N-diethyl acrylamide and 40 parts of monomer acrylonitrile are added, nitrogen is continuously introduced, and stirring is carried out for 3 hours to obtain a solution.

[0047] Step b: nitrogen is continuously introduced, the solution is heated to 55℃ at a heating rate of 1℃ / min, 0.5 parts of mass fraction (10%) initiator solution benzoyl peroxide is added, and the reaction is initiated for 10 hours to obtain a polymerization product.

[0048] Step c: the polymerization product is reduced to a vacuum degree lower than 0.1 MPa at 60℃ using a vacuum pump to remove residual monomers, and a polymerization product with a solid content of 40% is obtained.

[0049] Step d: 500g of the polymerization product with a solid content of 40% is neutralized to a pH of 7.5 at 50℃ using 3500g of lithium hydroxide aqueous solution to obtain a viscous adhesive polymer; the solid content of the prepared adhesive polymer is determined to be 5% for the terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid.

[0050] The present application is further described in detail in combination with the following examples.

[0051] In the following examples, the addition of the A component terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid is in the form of an adhesive polymer; the addition of the B component low-Tg acrylic resin is in the form of BT-9 resin; and the actual addition amount of the A component and the B component is calculated by the formula:

[0052] A component = adhesive polymer addition amount x A component solid content

[0053] B component = BT-9 resin addition amount x B component solid content

[0054] Example 1:

[0055] A composite adhesive for a silicon negative electrode of a lithium battery, and a preparation method thereof, the preparation method comprising the following steps:

[0056] Step 1, take 100 g of binder polymer (solid content of A component is 5%), add 0.625 g of BT-9 resin (solid content of B component is 40%) to it, mechanically disperse with a disperser at a speed of 1000 rpm for 30 min to obtain a mixed glue solution;

[0057] Step 2, add 0.1 g of single-walled carbon nanotubes to the mixed glue solution prepared in step 1, mechanically disperse with a disperser at a speed of 1000 rpm for 10 min, then homogenize the mixed sample with a high-pressure homogenizer, homogenize for 20 min to obtain a composite glue solution; the flow rate of the high-pressure homogenizer is 200 L / h, and the pressure is 200 bar;

[0058] Step 3, first, 10 g of wattle tannic acid solid is put into 90 g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%, then the composite glue solution prepared in step 2 is added to 2.63 g of the tannic acid aqueous solution with a mass concentration of 10%, and mechanically dispersed with a disperser at a speed of 1000 rpm for 30 min to obtain a composite binder for silicon negative electrode.

[0059] A silicon negative electrode sheet, the preparation method thereof comprises the following steps:

[0060] Step a, mix Si-C composite material (silicon-based with a specific capacity of 600 mAh / g), conductive carbon black, and the binder for silicon negative electrode, then add deionized water, disperse uniformly, and pass through a 100 mesh sieve to prepare a silicon negative electrode slurry with a total solid content of 45%; in the silicon negative electrode slurry, the silicon negative electrode material accounts for 95.5 wt% of the total solid content, the conductive carbon black accounts for 2.0 wt% of the total solid content, and the binder for silicon negative electrode accounts for 2.5 wt% of the total solid content in terms of solid content;

[0061] Step b, coat the silicon negative electrode slurry on a 10 μm thick copper foil as a current collector, then put it into a drying oven at 120°C for 5 minutes, naturally cool to room temperature in the oven, and calender to obtain a silicon negative electrode sheet under a unit length load of 10 x 10 4 N / m.

[0062] A lithium battery, the preparation method thereof is as follows:

[0063] Take the silicon negative electrode sheet as the negative electrode, take lithium nickel cobalt manganese oxide NCM523 as the positive electrode, take a mixed solvent of ethylene carbonate EC, methyl ethylene carbonate EMC, and diethyl carbonate DEC in a mass ratio of 3:2:5, containing 1M LiPF6, as the electrolyte, take PE / PP separator as the separator, and make P383450 lithium battery.

[0064] Example 2:

[0065] A composite binder for a silicon negative electrode of a lithium battery, a preparation method thereof comprising the following steps:

[0066] Step 1, take 100g of binder polymer (solid content of A component is 5%), add 0.625g of BT-9 resin (solid content of B component is 40%) to it, mechanically disperse with a disperser at a speed of 1000rpm for 30min to obtain a mixed glue solution;

[0067] Step 2, add 0.1g of carbon nanotubes to the mixed glue solution prepared in step 1, mechanically disperse with a disperser at a speed of 1000rpm for 10min, then homogenize the mixed sample with a high-pressure homogenizer, homogenize for 20min to obtain a composite glue solution; the flow rate of the high-pressure homogenizer is 200L / h, and the pressure is 400bar;

[0068] Step 3, first, put 10g of solid cypress tannic acid into 90g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%, then add the composite glue solution prepared in step 2 to 5.56g of the tannic acid aqueous solution with a mass concentration of 10%, mechanically disperse with a disperser at a speed of 1000rpm for 30min to obtain a composite binder for a silicon negative electrode.

[0069] A silicon negative electrode sheet, a preparation method thereof: same as example 1.

[0070] A lithium battery, a preparation method thereof: same as example 1.

[0071] Example 3:

[0072] A composite binder for a silicon negative electrode of a lithium battery, a preparation method thereof comprising the following steps:

[0073] Step 1, take 100g of binder polymer (solid content of A component is 5%), add 0.625g of BT-9 resin (solid content of B component is 40%) to it, mechanically disperse with a disperser at a speed of 1000rpm for 30min to obtain a mixed glue solution;

[0074] Step 2, add 0.1g of carbon nanotubes to the mixed glue solution prepared in step 1, mechanically disperse with a disperser at a speed of 1000rpm for 10min, then homogenize the mixed sample with a high-pressure homogenizer, homogenize for 20min to obtain a composite glue solution, the flow rate of the high-pressure homogenizer is 200L / h, and the pressure is 600bar;

[0075] Step 3, first, 10 g of solid tannic acid of wisteria was put into 90 g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%, and then the composite glue solution prepared in step 2 was added to 8.82 g of the tannic acid aqueous solution with a mass concentration of 10%, and a disperser was used to mechanically disperse at a speed of 1000 rpm for 30 min, to obtain the composite binder for the silicon negative electrode.

[0076] A silicon negative electrode sheet, and a preparation method thereof.

[0077] A lithium battery, and a preparation method thereof.

[0078] Example 4

[0079] A composite binder for a silicon negative electrode of a lithium battery, and a preparation method thereof.

[0080] Step 1, 100 g of a binder polymer (solid content of component A is 5%) was taken, 3.75 g of BT-9 resin (solid content of component B is 40%) was added, a disperser was used to mechanically disperse at a speed of 1000 rpm for 30 min, to obtain a mixed glue solution;

[0081] Step 2, 0.5 g of carbon nanotubes was added to the mixed glue solution prepared in step 1, a disperser was used to mechanically disperse at a speed of 1000 rpm for 10 min, and then the mixed sample was homogenized by using a high-pressure homogenizer, and the homogenization treatment was performed for 20 min, to obtain a composite glue solution; the flow rate of the high-pressure homogenizer was 200 L / h, and the pressure was 400 bar;

[0082] Step 3, first, 10 g of solid tannic acid of wisteria was put into 90 g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%, and then the composite glue solution prepared in step 2 was added to 25 g of the tannic acid aqueous solution with a mass concentration of 10%, and a disperser was used to mechanically disperse at a speed of 1000 rpm for 30 min, to obtain the composite binder for the silicon negative electrode.

[0083] A silicon negative electrode sheet, and a preparation method thereof.

[0084] A lithium battery, and a preparation method thereof.

[0085] Example 5:

[0086] A composite binder for a silicon negative electrode of a lithium battery, and a preparation method thereof.

[0087] Step 1, take 100g of binder polymer (solid content of A component is 5%), add 1.875g of BT-9 resin (solid content of B component is 40%) to it, mechanically disperse with a disperser at a speed of 1000 rpm for 30 min to obtain a mixed glue solution;

[0088] Step 2, add 0.25g of carbon nanotubes to the mixed glue solution prepared in step 1, mechanically disperse with a disperser at a speed of 1000 rpm for 10 min, then homogenize the mixed sample with a high-pressure homogenizer, homogenize for 20 min to obtain a composite glue solution; the flow rate of the high-pressure homogenizer is 200 L / h, and the pressure is 400 bar;

[0089] Step 3, first, put 10g of wattle tannic acid solid into 90g of deionized water to prepare a tannic acid water dispersion with a mass concentration of 10%, then add the composite glue solution prepared in step 2 to 12.5g of the tannic acid water dispersion with a mass concentration of 10%, mechanically disperse with a disperser at a speed of 1000 rpm for 30 min to obtain a composite binder for a silicon negative electrode.

[0090] A silicon negative electrode sheet, the preparation method of which is as follows:

[0091] A lithium battery, the preparation method of which is as follows:

[0092] Example 6:

[0093] A composite binder for a lithium battery silicon negative electrode, the preparation method thereof comprises the following steps:

[0094] Step 1, take 100g of binder polymer (solid content of A component is 5%), add 0.125g of BT-9 resin (solid content of B component is 40%) to it, mechanically disperse with a disperser at a speed of 1000 rpm for 30 min to obtain a mixed glue solution;

[0095] Step 2, add 0.05g of carbon nanotubes to the mixed glue solution prepared in step 1, mechanically disperse with a disperser at a speed of 1000 rpm for 10 min, then homogenize the mixed sample with a high-pressure homogenizer, homogenize for 20 min to obtain a composite glue solution; the flow rate of the high-pressure homogenizer is 200 L / h, and the pressure is 400 bar;

[0096] Step 3, first, put 10g of wattle tannic acid solid into 90g of deionized water to prepare a tannic acid water dispersion with a mass concentration of 10%, then add the composite glue solution prepared in step 2 to 0.5g of the tannic acid water dispersion with a mass concentration of 10%, mechanically disperse with a disperser at a speed of 1000 rpm for 30 min to obtain a composite binder for a silicon negative electrode.

[0097] A silicon negative electrode tab, the preparation method of which is as follows: same as Example 1.

[0098] A lithium battery, the preparation method of which is as follows: same as Example 1.

[0099] Comparative Example 1

[0100] A composite binder for a lithium battery silicon negative electrode, the preparation method of which comprises the following steps:

[0101] Step 1, take 100 g of binder polymer (solid content of component A is 5%), add 0.625 g of BT-9 resin (solid content of component B is 40%) to it, mechanically disperse with a disperser at a speed of 1000 rpm for 30 min to obtain a mixed glue solution;

[0102] Step 2, add 0.1 g of carbon nanotubes to the mixed glue solution prepared in step 1, mechanically disperse with a disperser at a speed of 1000 rpm for 10 min, and then homogenize the mixed sample with a high-pressure homogenizer, homogenize for 20 min to obtain a composite binder for a lithium battery silicon negative electrode;

[0103] The flow rate of the high-pressure homogenizer is 200 L / h, and the pressure is 400 bar.

[0104] A silicon negative electrode tab, the preparation method of which is as follows: same as Example 1.

[0105] A lithium battery, the preparation method of which is as follows: same as Example 1.

[0106] Comparative Example 2

[0107] A binder for a lithium battery silicon negative electrode, which uses a binder polymer containing a terpolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid and methacrylic acid, and the solid content is 5%.

[0108] A silicon negative electrode tab, the preparation method of which comprises the following steps:

[0109] Step a, mix Si-C composite material (silicon-based with specific capacity of 600 mAh / g), conductive carbon black and the binder for a silicon negative electrode, add deionized water, disperse uniformly, and then pass through a 100-mesh sieve to obtain a silicon negative electrode slurry with a total solid content of 45%; in the silicon negative electrode slurry, the silicon negative electrode material accounts for 95.5 wt% of the total solid content, the conductive carbon black accounts for 2.0 wt% of the total solid content, and the binder for a silicon negative electrode accounts for 2.5 wt% of the total solid content in terms of solid content;

[0110] Step b, coat the silicon negative electrode slurry on a 10 μm thick copper foil as a current collector, then put it into a 120°C drying oven for 5 minutes, and then naturally cool it in the oven to room temperature, and then cut it into a size of 10 x 104 The silicon negative electrode sheet is obtained by calendering with a unit length load of 0.5-1.5 N / m.

[0111] A lithium battery is prepared by the following method:

[0112] The silicon negative electrode sheet is used as a negative electrode, lithium nickel cobalt manganese oxide NCM523 is used as a positive electrode, a mixed solvent of ethylene carbonate EC, methyl ethylene carbonate EMC and diethyl carbonate DEC in a mass ratio of 3:2:5 is used as an electrolyte, 1M LiPF6 is contained in the electrolyte, and PE / PP separator is used as a separator to make a P383450 lithium battery.

[0113] Comparative Example 3

[0114] A composite binder for a silicon negative electrode of a lithium battery is prepared by the following method:

[0115] Step 1: 100g of a binder polymer (solid content of the A component is 5%) is taken, 0.625g of BT-9 resin (solid content of the B component is 40%) is added, and mechanical dispersion is carried out at a speed of 1000rpm for 30min using a disperser to obtain a composite binder for a silicon negative electrode of a lithium battery.

[0116] A silicon negative electrode sheet is prepared by the method of Comparative Example 2.

[0117] A lithium battery is prepared by the method of Comparative Example 2.

[0118] Comparative Example 4

[0119] A composite binder for a silicon negative electrode of a lithium battery is prepared by the following method:

[0120] Step 1: 100g of a binder polymer (solid content of the A component is 5%) is taken, 0.625g of BT-9 resin (solid content of the B component is 40%) is added, and mechanical dispersion is carried out at a speed of 1000rpm for 30min using a disperser to obtain a mixed glue solution.

[0121] Step 2: 0.1g of carbon nanotubes is added to the mixed glue solution prepared in Step 1, and mechanical dispersion is carried out at a speed of 1000rpm for 10min using a disperser to obtain a mixed sample.

[0122] Step 3: First, 10g of solid Chinese schima tannic acid is put into 90g of deionized water to prepare a tannic acid aqueous solution with a mass concentration of 10%, then 5.56g of the tannic acid aqueous solution with a mass concentration of 10% is added to the mixed sample prepared in Step 2, and mechanical dispersion is carried out at a speed of 1000rpm for 30min using a disperser to obtain a composite binder for a silicon negative electrode.

[0123] A silicon negative electrode sheet is prepared by the method of Example 1.

[0124] A lithium battery, a preparation method thereof: same as example 1.

[0125] Example 1:

[0126] The glass transition temperature of the adhesive prepared in each example and comparative example was determined, the peeling strength and the film resistance of the electrode tab prepared in each example and comparative example were tested, the electrochemical performance of the lithium battery prepared in examples 1-3 and comparative examples 1-3 was tested, in addition, the SEM morphology scanning of the electrode material on the electrode tab prepared in example 2 and comparative example 4 was performed.

[0127] 1. The determination method of the glass transition temperature: after the adhesive was vacuum dried into a solid at 40 DEG C, the determination was performed according to GB / T 19466.2 plastics-differential scanning calorimetry (DSC) part 2: determination of glass transition temperature, and the results are shown in table 1.

[0128] 2. The test of the peeling strength: the electrode tab was cut into a long strip of 20 cm x 2.5 cm, a steel plate with a thickness of 1 mm was adhered to the current collector side with double-sided tape, a transparent tape was pasted to the coating layer side, a tensile testing machine was used to peel off at a speed of 100 mm / min in the direction of 180 DEG, and the peeling stress was determined, and the test results are shown in table 1.

[0129] 3. The test method of the film resistance: the test was performed by using the ACCFILM film resistance test system, and the test was performed according to the operation process of the equipment manufacturer, and the results are shown in table 1.

[0130] Test steps:

[0131] 1) Turn on the power switches of the computer, the resistance module and the ACCFILM test mechanism and other parts;

[0132] 2) Turn on the gas source switch of the ACCFILM test mechanism;

[0133] 3) Dip a small amount of "ACCFILM probe special scrubbing agent" on a piece of test paper, and wipe the upper and lower probes to ensure that there is no foreign matter on the surface of the probes and keep them clean and bright;

[0134] 4) Turn the probe clutch switch to the closed state, and rotate the pressure size adjustment switch to adjust the pressure value to the target value (default is 0.3t);

[0135] 5) Double-click to open the computer desktop film resistance test software "ACCFILM";

[0136] 6) Click the communication connection key on the left side of the upper software interface, at this time, the resistance, voltage, pressure, etc. display window on the left side of the software interface displays the corresponding real-time data, indicating that the communication connection is successful; if it is not automatically connected, select the connection setting in "instrument setting" to perform manual connection operation.

[0137] 7) Input group name and sample thickness (measured by screw micrometer) and other data;

[0138] 9) Click the "test start" button, that is, the system completes the test condition equipment and has the ability to start the test; (single point mode; resistance: test-100-3100Ω; the test area is "154.025mm 2 )

[0139] 10) Turn the probe clutch switch, so that the upper and lower probes are in the disconnected state, at this time, the software interface measurement state indication bar will display "measurement not started" synchronously;

[0140] 11) Place the sample (electrode sheet) to be measured on the lower probe, and turn the probe clutch switch again, at this time, the software interface measurement state indication bar will display "measurement in progress" synchronously; when the measurement data is displayed in the "data display interface" data record table, it indicates the end of the single measurement process, and the measurement state indication bar will display "measurement has ended" synchronously;

[0141] 12) Save the data.

[0142] 4, The electrode material on the electrode sheet was subjected to SEM morphology scanning: see Figures 1-4 ;

[0143] 5, The test method of cycle performance: the lithium battery was subjected to charge-discharge cycle at 0.5C in the voltage range of 2.5-4.2V at 25℃, the first coulomb efficiency and the coulomb efficiency after 50 cycles and the capacity retention rate were tested by constant current method, the capacity retention rate obtained after 55 weeks of charge-discharge cycle is shown in Figure 4 , and the EIS result is shown in Figure 3 .

[0144] Table 1

[0145]

[0146]

[0147] As can be seen from the data in Table 1: 1) The peel strength of Examples 1-3 with added tannic acid is significantly improved compared to Comparative Example 1 without added tannic acid; 2) The glass transition temperature of Examples 1-3 and Comparative Examples 1 and 3 with added BT-9 is significantly lower than that of Comparative Example 2 without added BT-9, indicating a significant increase in the flexibility of the electrode material; 3) The film resistance of Examples 1-3 and Comparative Example 1 with added single-walled carbon nanotubes is significantly reduced compared to Comparative Examples 2-3 without added single-walled carbon nanotubes, indicating that the addition of single-walled carbon nanotubes in this invention reduces the internal resistance of the electrode film; 4) The comparison between Example 2 and Comparative Example 4 shows that the introduction of the homogenization process after adding single-walled carbon nanotubes allows for better dispersion of the single-walled carbon nanotubes, thereby effectively reducing the internal resistance of the electrode film.

[0148] Depend on Figures 1-2 As can be seen from the above, the silicon anode electrode prepared by this invention is shown in the figure. Figure 1 This allows for the uniform network distribution of single-walled carbon nanotubes on and between silicon particles, while the silicon anode electrode prepared in Comparative Example 4 shows... Figure 2 Single-walled carbon nanotubes are distributed in bundles and clusters on the surface of silicon materials.

[0149] Depend on Figure 3 It can be seen that: 1) In Examples 1-3, where a composite binder containing tannic acid, carbon nanotubes, and BT-9 was added to the polypropylene binder, the electrochemical impedance spectroscopy (EIS) of the battery was significantly improved, indicating that the composite binder of the present invention is more conducive to ion transfer in the electrochemical process. 2) From the comparison of Comparative Example 1 with added single-walled carbon nanotubes, Comparative Example 3 without added single-walled carbon nanotubes, and Comparative Example 2 without added single-walled carbon nanotubes and BT-9, it can be seen that the addition of carbon nanotubes alone can also improve the electrochemical impedance spectroscopy (EIS) of the battery to a certain extent.

[0150] Depend on Figure 4 As can be seen, the cycle stability of the composite binders containing tannic acid, carbon nanotubes and BT-9 added to the polypropylene binder in Examples 1-3 was significantly improved. Among them, Example 2 had the best cycle stability, while Comparative Example 2 had the worst cycle stability.

[0151] The embodiments described above are merely preferred embodiments of the present invention, and not an exhaustive list of all possible implementations of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A composite binder for a silicon anode of a lithium battery, characterized by, At least comprising A component, B component, C component and D component; wherein, the A component is acrylic multi-copolymer, the B component is low Tg acrylic resin, the C component is carbon nanotube, and the D component is tannic acid; In terms of weight parts, 100 parts of A component, 1-30 parts of B component, 1-10 parts of C component and 1-50 parts of D component; The acrylic multi-copolymer is a terpolymer of acrylonitrile, 2-acrylamide-2-phenylsulfonic acid and methacrylic acid; The Tg of the low Tg acrylic resin is -100℃ to 1℃; The tannic acid is cypress tannic acid consisting of resorcinol type A ring.

2. The composite binder for lithium battery silicon negative electrode according to claim 1, characterized in that, The carbon nanotube is single-walled carbon nanotube.

3. A method of preparing a composite binder for a silicon anode of a lithium battery according to any one of claims 1-2, characterized in that, Comprising the following steps: Step 1, taking 100 parts of the A component in the polymer binder by weight parts, adding 1-30 parts of the B component to it, mechanically dispersing to prepare a mixed glue solution; Step 2, adding 1-10 parts of the C component to the mixed glue solution in step 1, mechanically dispersing after homogenizing the mixed sample to obtain a composite glue solution; Step 3, dissolving 1-50 parts of the D component in water to prepare a tannic acid aqueous solution, then adding the composite glue solution in step 2 to the tannic acid aqueous solution, mechanically dispersing to obtain a composite binder for lithium battery silicon negative electrode.

4. A silicon negative electrode sheet characterized by Containing the composite binder for lithium battery silicon negative electrode according to any one of claims 1-2.

5. A lithium battery, characterized by Provided with the silicon negative electrode sheet according to claim 4.

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