Preparation method of a polymer binder and its application in silicon negative electrode lithium battery

Abstract

The present invention belongs to the technical field of lithium batteries and relates to a preparation method of a polymer binder and its application in silicon negative electrode lithium batteries. The preparation method comprises: cross-linking polydopamine and polyureaurethane in an organic solvent, and then adding a metal ion solution to obtain a metal-coordinated PDA-X-BFPU binder; wherein the polyureaurethane has a dynamic covalent bond BO3 3‑ , -S-S- or -Se-Se-; the metal ion in the metal ion solution is Mg 2+ 、Co 3+ 、Al 3+ Cr 3+ 、Cu 2+ 、Fe 3+ 、Zn 2+ Compared with the prior art, the present invention improves the mechanical and electrochemical properties of the negative electrode material while avoiding the problems of low Coulomb efficiency and poor cycle life caused by the Si volume effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries and relates to a preparation method of a polymer binder and its application in silicon negative electrode lithium batteries. Background Art

[0002] Lithium-ion batteries (LIBs) have attracted widespread attention from researchers due to their high energy density, good safety, high voltage platform, strong adaptability to high and low temperatures, and good cycle performance. They are also one of the main batteries used in the electric vehicle field. Many studies have been conducted to improve the energy density of LIBs by developing high-capacity anode materials. Si is one of the most promising alloy materials with a capacity of 4200mAh g -1 Theoretical capacity and low working potential (~0.4V vs.Li / Li + ), which helps to avoid the formation of lithium dendrites. However, the low Coulombic efficiency and poor cycle life caused by the volume effect of Si severely limit the commercialization of Si-based anodes for LIBs. This can be improved by constructing nanostructured silicon, silicon / carbon composites, and exploring electrolyte additives such as fluoroethylene carbonate (FEC) and vinylene carbonate. In addition to the above strategies, designing new binders is also an effective method to enhance the adhesion to Si particles through hydrogen bonds and / or covalent bonds, thereby alleviating the huge volume change and maintaining the integrity of the Si negative electrode.

[0003] Currently, commonly used binders include polyacrylic acid (PAA), styrene-butadiene rubber / sodium carboxymethyl cellulose (SBR / CMC), and alginate (Alg). These binders are rich in hydroxyl (-OH) or carboxyl (-COOH) groups that can form hydrogen bonds with the surface of Si particles, thereby enhancing adhesion. At the same time, their strong polarity can also enhance the interfacial interaction between the Si negative electrode, current collector, and binder to a certain extent, thereby alleviating the huge volume change of silicon particles during the cycle and improving the battery cycle life. However, these single binders fail to show ideal mechanical properties and stable electrochemical properties during the lithium insertion and delithiation process of nano-scale Si particles. Therefore, it is very necessary to study and explore modified designs based on existing binders to improve the mechanical and electrochemical properties of negative electrode materials while avoiding the low Coulombic efficiency and poor cycle life problems caused by the Si volume effect.

[0004] Chinese patent CN115472842A discloses a binder, a preparation method thereof, and a secondary battery. The binder includes sodium alginate, polyetherthiourea, and metal ions. The sodium alginate coordinates with the metal ions and forms a double network structure with the polyetherthiourea. The binder of the present application has good mechanical properties and stable rheological properties and can achieve rapid self-healing at room temperature. The battery using this binder has good cycle stability and excellent rate performance. However, under the impact of high current, the structure of the binder is damaged, making it impossible to limit the volume expansion of silicon particles, resulting in poor cycle stability. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a polymer binder and its application in silicon negative electrode lithium batteries, so as to improve the mechanical properties and electrochemical properties of the negative electrode material while avoiding the low coulombic efficiency and poor cycle life problems caused by the Si volume effect.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] In the present invention, polydopamine (PDA) can form hydrogen bonds with hydroxyl groups on the silicon surface due to its abundant hydroxyl groups in the catechol functional groups, thereby enhancing the binding force between the PDA and the current collector. Polyureaurethane (BFPU) is an elastomer composed of a hard segment (isocyanate and chain extender) and a soft segment (polyethylene glycol), which has excellent mechanical properties, corrosion resistance and wear resistance. The two can be cross-linked through hydrogen bonds to obtain a PDA-X-BFPU adhesive, and on this basis, polyvalent metal ions (X n+ ) forms metal coordination bonds with the catechol groups in PDA and the urea groups in BFPU, thereby forming a room-temperature self-healing adhesive with a high-strength cross-linked network that synergizes dynamic covalent bonds and dynamic non-covalent bonds. Among them, the dynamic covalent bonds are provided by the chain extender, while the non-covalent bonds include hydrogen bonds and metal coordination bonds. This binder system can form more hydrogen bonds between silicon and the current collector, increase contact with silicon, improve the adhesion between Si particles and the current collector, and can better adapt to the volume expansion of Si particles, thereby enhancing the cycling stability of the electrode.

[0008] A first aspect of the present invention provides a method for preparing a polymer binder, comprising: performing a cross-linking reaction between polydopamine and polyureaurethane in an organic solvent, and then adding a metal ion solution to obtain a metal-coordinated PDA-X-BFPU binder;

[0009] Wherein, the polyureaurethane has dynamic non-covalent H bond and dynamic covalent bond BO3 3 - , -SS- or -Se-Se-;

[0010] The metal ion in the metal ion solution is Mg2+ 、Co 3+ 、Al 3+ Cr 3+ 、Cu 2+ 、Fe 3+ 、Zn 2+ One or more combinations of .

[0011] Furthermore, the preparation method of the polyureaurethane comprises:

[0012] Polyethylene glycol, isophorone diisocyanate, and dibutyltin dilaurate are heated to react to obtain a polyureaurethane prepolymer; and the polyureaurethane prepolymer is mixed with a chain extender to react to obtain polyureaurethane;

[0013] Wherein, the chain extender is one or more combinations of boric acid, bis(4-hydroxyphenyl)disulfide or selenocystamine hydrochloride.

[0014] Furthermore, the molar ratio of polyethylene glycol, isophorone diisocyanate, and dibutyltin dilaurate is 1000-1500:3000-5000:3-5;

[0015] The reaction temperature of the heating reaction is 75-120°C;

[0016] The dosage of the chain extender is 1-1.2 mol / mol polyethylene glycol.

[0017] Furthermore, the feed ratio of the polydopamine, polyureaurethane and metal ion solution is (4-6) g: (4-6) g: (100-120) mL; the concentration of the metal ion solution is 0.5-2 mol / L;

[0018] Furthermore, the cross-linking reaction is carried out at room temperature, and the reaction time is preferably 10 to 24 hours; after adding the metal ion solution, stirring is continued for 10 to 24 hours to obtain the metal-coordinated PDA-X-BFPU adhesive.

[0019] Furthermore, the preparation method of polydopamine comprises: adding dopamine to a tris hydrochloric acid solution, controlling the pH value between 7 and 9, and stirring thoroughly to obtain polydopamine.

[0020] An application of a polymer binder comprises using the polymer binder to prepare a silicon negative electrode of a lithium battery.

[0021] Furthermore, the preparation method of the silicon negative electrode includes: mixing silicon powder, a conductive agent, a polymer binder, and a solvent, coating the mixture on a negative electrode current collector, and forming the mixture to obtain a lithium battery silicon negative electrode.

[0022] Furthermore, the feeding ratio of the silicon powder, the conductive agent, the polymer binder and the solvent is (6-8) g: (1-2) g: (1-2) g: (30-40) mL.

[0023] Furthermore, the silicon powder is nano silicon powder with an average particle size of 80 to 120 nm.

[0024] Furthermore, the conductive agent is conductive carbon black.

[0025] Furthermore, the positive electrode of the lithium battery is a lithium iron phosphate (LFP) positive electrode or a nickel cobalt manganese (NCM) positive electrode.

[0026] Compared with the prior art, the present invention has the following characteristics:

[0027] 1) Urea hydrogen bond and strong metal coordination bond (urea-X n+ ) as a non-covalent sacrificial bond, forming multi-level energy dissipation and multi-time scale dissociation-bonding, which simultaneously improves the toughness and self-repair performance of the material; and introducing BO3 on the BFPU main chain through different chain extenders 3 - One or two of the three room temperature dynamic covalent bonds, -SS-, -Se-Se-, ensure the self-healing performance of the material without reducing the mechanical strength of the material, solving the disadvantage of low strength of existing room temperature self-healing elastomers;

[0028] 2) The phenolic hydroxyl groups in polydopamine (PDA) form hydrogen bonds with the urea groups in polyureaurethane (BFPU), and on this basis, multivalent metal ions (X n+ ) forms a metal coordination bond with the catechol group in PDA and the urea group in BFPU, thereby forming a metal complex with a dynamic covalent bond (BO3 3- A room-temperature self-healing adhesive with a high-strength cross-linked network that works synergistically with (-SS-, -Se-Se-) and non-covalent bonds (hydrogen bonds, metal coordination bonds). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Comparison of the average peeling force of silicon negative electrodes prepared with different binders in Examples 1-9;

[0030] Figure 2 Comparison of elongation before and after the adhesive breaks in Example 1;

[0031] Figure 3 Comparison of half-cell cyclic voltammograms in Examples 1-3;

[0032] Figure 4 Comparison of half-cell cyclic voltammograms in Examples 4-6;

[0033] Figure 5 Comparison of half-cell cyclic voltammograms in Examples 7-9;

[0034] Figure 6 Comparison of half-cell rate performance in Examples 1-3;

[0035] Figure 7 Comparison of half-cell rate performance in Examples 4-6;

[0036] Figure 8 Comparison of half-cell rate performance in Examples 7-9;

[0037] Figure 9 The long cycle performance of the half-cell at high current density in Example 1;

[0038] Figure 10 Comparison of the LFP full-cell rate performance in Examples 1, 4, and 7;

[0039] Figure 11 Comparison of the cycling performance of LFP full batteries in Examples 2, 5, and 8;

[0040] Figure 12 Comparison of the rate performance of NCM811 full cells in Examples 2, 5, and 8;

[0041] Figure 13 Comparison of the full battery cycle performance of NCM811 in Examples 3, 6, and 9. DETAILED DESCRIPTION

[0042] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are implemented based on the above technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following embodiments.

[0043] Example 1:

[0044] A method for preparing a metal-coordinated polydopamine-polyureaurethane polymer binder comprises the following steps:

[0045] S1: Preparation of polyureaurethane

[0046] 0.01 mol of polyethylene glycol was placed in a flask and heated to 110°C to dry for 2.5 hours. Then, 0.04 mol of isophorone diisocyanate and 0.04 mmol of dibutyltin dilaurate were added to the flask and the reaction was maintained at 75°C for 2 hours to obtain a polyureaurethane prepolymer. Finally, 0.01 mol of a chain extender was added to the flask and the temperature was maintained for 1.5 hours to obtain the polyureaurethane product.

[0047] S2: Preparation of polydopamine

[0048] Add 2 g of dopamine to 25 mL of tris hydrochloric acid solution and control the pH to about 8. Stir thoroughly until it is completely dissolved to obtain a dark yellow solution, which is the polydopamine solution.

[0049] S3: Preparation of Metal-Coordinated Polydopamine-Polyureaurethane Polymer Binders

[0050] 0.05 g of polydopamine and 0.05 g of polyureaurethane were dissolved in 2 mL of dimethylpyrrolidone solvent and stirred at room temperature for 12 hours to obtain a homogeneous solution. 1 mL of a 1 mol / L aqueous solution of metal ions was then added to the solution and stirred for another 12 hours to form a homogeneous solution, which is the metal-coordinated polydopamine-polyureaurethane polymer binder.

[0051] The chain extender type and metal ion type are shown in Table 1.

[0052] Table 1 Types of chain extenders and metal ions corresponding to Examples 1-9

[0053]

[0054] Example 2: Electrode Preparation

[0055] (1) Preparation of silicon-based negative electrode sheets:

[0056] After being fully dried in a vacuum drying oven, 0.8g of nano-silicon powder (average particle size 100nm), 0.1g of conductive carbon black, and 0.1g of one of the 9 binders in Example 1 were weighed, placed in a quartz mortar and ground thoroughly, and transferred to a glass container. 3.5mL of dimethylpyrrolidone was added to the glass container and stirred to form a uniform electrode slurry. The stirred electrode slurry was evenly coated on a clean copper foil (negative current collector) using a four-sided preparation device and placed in a vacuum oven to fully dry to obtain a silicon-based negative electrode sheet with a thickness of 75μm.

[0057] (2) Preparation of positive electrode sheet:

[0058] (2.1) Preparation of binary positive electrode lithium iron phosphate (LFP) positive electrode sheet:

[0059] After thorough drying in a vacuum oven, 0.8g of LiFePO4, 0.1g of conductive carbon black, and 0.1g of PVDF binder were weighed and ground thoroughly in a quartz mortar. The mixture was then transferred to a glass container. 3.5mL of dimethylpyrrolidone was added to the glass container and stirred to form a uniform electrode slurry. The electrode slurry was then evenly coated onto aluminum foil (the positive electrode current collector) using a four-sided preparation device and thoroughly dried in a vacuum oven to obtain a 75μm thick LFP positive electrode sheet.

[0060] (2.2) Preparation of ternary positive electrode nickel-cobalt-manganese (NCM) positive electrode sheet:

[0061] After being fully dried in a vacuum drying oven, 0.8 g of LiNi 0.8 Co 0.1 Mn0.1 x O2, 0.1g of conductive carbon black, and 0.1g of PVDF binder were thoroughly ground in a quartz mortar and transferred to a glass container. 3.5mL of dimethylpyrrolidone was added to the glass container and stirred to form a uniform electrode slurry. The electrode slurry was then evenly coated onto aluminum foil (the positive electrode current collector) using a four-sided preparation device and thoroughly dried in a vacuum oven to produce a 75μm thick NCM positive electrode sheet.

[0062] Example 3: Battery Assembly

[0063] (1) Assembly of button half-cell:

[0064] The silicon-based negative electrode sheet prepared in Example 2 was cut into discs with a diameter of 9 mm using a slicer, weighed and recorded, and then assembled into a C2025 button cell in a glove box (i.e., a lithium-ion battery was assembled in the order of positive electrode shell-positive electrode sheet-diaphragm-negative electrode sheet-gasket-spring sheet-negative electrode shell). Celgard 2400 polypropylene was used as the separator; a lithium sheet was used as the counter electrode.

[0065] (2) Assembly of full battery:

[0066] (2.1) Lithium iron phosphate (LFP) full battery

[0067] The silicon-based negative electrode sheet prepared in Example 1 with a diameter of 12 mm was used as the negative electrode, and the lithium sheet was used as the counter electrode. A C2025 button cell was assembled in the above manner. After assembly, the battery was left for 6 hours to allow the electrolyte to fully penetrate the electrode sheet. The electrode sheet was then pre-lithiated: the half-cell was discharged at a constant current (1.5 mA) for 5 hours. Finally, the half-cell was disassembled in a glove box, and the pre-lithiated electrode sheet was taken out as the negative electrode of the full cell; the lithium iron phosphate electrode sheet was used as the positive electrode, and the full cell was assembled (i.e., the lithium-ion battery was assembled in the order of positive electrode shell-positive electrode sheet-diaphragm-negative electrode sheet-gasket-spring sheet-negative electrode shell).

[0068] (2.2) Nickel-cobalt-manganese (NCM811) full battery

[0069] A C2025 button cell was assembled using the 12mm diameter silicon-based negative electrode sheet prepared in Example 1 as the negative electrode and a lithium sheet as the counter electrode in the manner described above. After assembly, the cells were left standing for 6 hours to allow the electrolyte to fully infiltrate the electrode sheet. The electrode sheet was then pre-lithiated: the half-cell was discharged at a constant current (1.5mA) for 5 hours. The pre-lithiated electrode sheet was then removed and used as the negative electrode of the full cell. A full cell was assembled using the nickel-cobalt-manganese electrode sheet as the positive electrode (i.e., the lithium-ion battery was assembled in the order of positive electrode shell - positive electrode sheet - diaphragm - negative electrode sheet - gasket - spring sheet - negative electrode shell).

[0070] Performance testing:

[0071] 1. Metal-coordinated polydopamine-polyureaurethane polymer binder

[0072] (1) Peeling performance:

[0073] The peeling performance of the prepared metal-coordinated polydopamine-polyureaurethane polymer binder was tested using a universal materials testing instrument. A constant 180° peel test was performed at a rate of 20 mm / min. The adhesion of the binder to the silicon surface significantly affects the electrochemical performance of the electrode.

[0074] The results are as follows Figure 1 As shown, Figure 1 The figure shows a comparison of the average peeling force of the silicon negative electrodes prepared with different binders in Examples 1-9, which proves that the selection of different chain extenders or metal ions will have a certain impact on the bonding performance of the electrode.

[0075] (2) Self-repair performance:

[0076] The tensile properties of the prepared metal-coordinated polydopamine-polyureaurethane polymer adhesive were tested using a universal materials testing instrument. A 20 mm wide and 60 mm long strip of sample was cut in half with a sharp glass knife and the two cut surfaces were butted together to ensure the cuts matched as closely as possible. After being squeezed with the fingers for 10 seconds, the sample was left to heal naturally under ambient conditions. The tensile strength of the spliced sample was then remeasured after different healing times.

[0077] The results are as follows Figure 2 As shown, Figure 2 Stress-strain tests conducted on the original sample of the adhesive in Example 1 and the adhesive sample cut into two parts and recovered for 1 hour showed that the adhesive system has a strong self-healing ability, with a recovery efficiency of up to 90% within 1 hour.

[0078] 2. Button half-cell

[0079] (1) The cycling performance of the metal-coordinated polydopamine-polyureaurethane polymer binder was studied by constant current charge and discharge tests. A lithium symmetric battery was used at 0.1 mA / cm-2 Tested at a current density of .

[0080] Figure 3-5 The cyclic voltammetry comparison diagrams of silicon negative electrodes prepared with binders coordinated with different metal ions in Examples 1-9 and a binder without added metal ions (blank) respectively prove that metal coordination has a positive effect on the reversibility inside the battery, and that different metal ions will produce different effects.

[0081] (2) The important electrochemical properties of the electrodes, such as cycle life, rate capability, discharge capacity, and coulombic efficiency, were studied through charge and discharge tests. All batteries were subjected to constant current charge and discharge cycle tests at room temperature.

[0082] Figure 6-8 The performance comparison diagrams of rate tests of silicon negative electrodes prepared with binders coordinated with different metal ions in Examples 1-9 respectively show that different metal coordinations correspond to different rate performances, and the comparison results are consistent with the above cyclic voltammograms.

[0083] Figure 9 The long cycle test of the silicon negative electrode prepared with the binder in Example 1 at 1C shows that the binder has good cycle performance even at high current density.

[0084] 3. Full battery

[0085] The charge-discharge tests were conducted to investigate important electrochemical properties of the electrodes, including cycle life, rate capability, discharge capacity, and coulombic efficiency. All batteries were tested under constant current at room temperature.

[0086] Study the cycle life and rate performance of full-battery LFP electrodes through charge and discharge tests Full-battery testing

[0087] Figure 10 The figure shows a comparison of the rate performance of LFP full batteries prepared with different binders in Examples 1, 4, and 7, all of which have good rate performance.

[0088] Figure 11 This is a comparison chart of the cycle performance of LFP full batteries prepared with different binders in Examples 2, 5, and 8 at 0.5C, all of which have good cycle performance.

[0089] The cycle life and rate performance of the full battery NCM811 electrode are tested by charge and discharge.

[0090] Figure 12 The figure shows a comparison of the rate performance of NCM811 full batteries prepared with different binders in Examples 2, 5, and 8, all of which have good rate performance.

[0091] Figure 13The figure shows a comparison of the cycling performance of NCM811 full batteries prepared with different binders in Examples 3, 6, and 9 at 0.5C, all of which have good cycling performance.

[0092] The above description of the embodiments is intended to facilitate understanding and use of the 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 above-described embodiments. 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 method for preparing a polymer binder, characterized in that: include: Polydopamine and polyureaurethane are cross-linked in an organic solvent, and then a metal ion solution is added and mixed to obtain a metal-coordinated PDA-X-BFPU adhesive; Wherein, the polyureaurethane has a dynamic covalent bond BO3 3- , -SS- or -Se-Se-; The metal ion in the metal ion solution is Mg 2+ 、Co 3+ 、Al 3+ Cr 3+ 、Cu 2+ 、Fe 3+ 、Zn 2+ One or more combinations of .

2. The method for preparing a polymer binder according to claim 1, wherein: The preparation method of the polyureaurethane comprises: Polyethylene glycol, isophorone diisocyanate, and dibutyltin dilaurate are heated to react to obtain a polyureaurethane prepolymer; and the polyureaurethane prepolymer is mixed with a chain extender to react to obtain polyureaurethane; Wherein, the chain extender is one or more combinations of boric acid, bis(4-hydroxyphenyl) disulfide or selenocystamine hydrochloride.

3. The method for preparing a polymer binder according to claim 2, wherein: The molar ratio of polyethylene glycol, isophorone diisocyanate, and dibutyltin dilaurate is 1000-1500:3000-5000:3-5; The reaction temperature of the heating reaction is 75~120℃; The amount of the chain extender is 1-1.2 mol / 1 mol of polyethylene glycol.

4. The method for preparing a polymer binder according to claim 1, wherein: The feeding ratio of the polydopamine, polyureaurethane and metal ion solution is (4-6) g: (4-6) g: (100-120) mL; The concentration of the metal ion solution is 0.5~2 mol / L; The cross-linking reaction is carried out at room temperature for 10 to 24 hours. After the metal ion solution is added, stirring is continued for 10 to 24 hours to obtain the metal-coordinated PDA-X-BFPU adhesive.

5. Use of a polymer binder prepared by the method according to any one of claims 1 to 4, characterized in that: The polymer binder is used for preparing the silicon negative electrode of the lithium battery.

6. The use of a polymer binder according to claim 5, characterized in that: The preparation method of the silicon negative electrode comprises: mixing silicon powder, a conductive agent, a polymer binder and a solvent, coating the mixture on a negative electrode current collector, and forming the mixture to obtain a lithium battery silicon negative electrode.

7. The use of a polymer binder according to claim 6, characterized in that: The feeding ratio of the silicon powder, the conductive agent, the polymer binder and the solvent is (6-8) g: (1-2) g: (1-2) g: (30-40) mL.

8. The use of a polymer binder according to claim 6, characterized in that: The silicon powder is nano silicon powder with an average particle size of 80-120 nm.

9. The use of a polymer binder according to claim 6, characterized in that: The conductive agent is conductive carbon black.

10. The use of a polymer binder according to claim 5, characterized in that: The positive electrode of the lithium battery is a lithium iron phosphate positive electrode or a nickel cobalt manganese positive electrode.

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