Negative electrode slurry and preparation method, negative electrode and lithium battery

Abstract

The present invention belongs to the field of lithium batteries, and specifically relates to a negative electrode slurry and preparation method, a negative electrode, and a lithium battery. The negative electrode slurry includes a negative electrode slurry body, which includes the following components by mass: 85-98 parts of active material, 0.5-6 parts of conductive agent, and 1.5-9 parts of binder. The present application improves the processing performance of the electrode during the coating process by adding a speed promoter to the negative electrode slurry and using a mixed glue system to increase the adhesion of the electrode. At the same time, a new coating process is used to ensure that the lower side has high adhesion with the negative electrode current collector and the negative electrode active material on the upper side has better conductivity, thereby improving the battery capacity and cycle performance.

Description

Technical Field

[0001] The present invention belongs to the field of lithium batteries, and in particular relates to a negative electrode slurry and a preparation method thereof, a negative electrode and a lithium battery. Background Art

[0002] At present, extreme climate conditions continue to occur, posing a great threat to human life and safety. my country's current carbon peak and carbon neutrality goals have strict requirements on carbon dioxide emissions. Lithium-ion batteries are environmentally friendly, and new energy vehicles are an effective way to replace fuel vehicles. Currently, traditional lithium-ion batteries have short cruising range, long charging time, and low temperature environments have a greater impact on cruising range.

[0003] Traditional negative electrode materials use conventional SBR and CMC composite as the binder of water-based negative electrodes. Although CMC has good dispersion in the negative electrode graphite slurry, the hydrophobicity of SBR will cause SBR to float during the negative electrode coating process, reducing the bonding force, resulting in a decrease in the electrical performance of the battery made from the negative electrode sheet, affecting battery safety. Summary of the Invention

[0004] The object of the present invention is to provide an electrode slurry and a preparation method thereof, a negative electrode and a lithium battery.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A negative electrode slurry comprises a negative electrode slurry main body, wherein the negative electrode slurry main body comprises the following components in parts by mass: 85-98 parts of active material, 0.5-6 parts of conductive agent, and 1.5-9 parts of binder.

[0007] Preferably, the active material comprises 76.96-96.2 parts by weight of the following components and 0-19.24 parts by weight of silicon; preferably, it comprises 76.96 parts by weight of the following components and 19.24 parts by weight of silicon.

[0008] Preferably, the binder comprises the following components by mass: 0.3-1 parts of CMC glue, 0-1.5 parts of PAA glue and 0.5-1.7 parts of SBR glue; preferably, the binder comprises the following components by mass: 1 part of CMC glue, 0.8 parts of PAA glue and 1 part of SBR glue.

[0009] Preferably, a speed aid is further included, and the mass ratio of the speed aid to the negative electrode slurry body is 0.4-1:100; preferably, the mass ratio of the speed aid to the negative electrode slurry body is 0.6:100.

[0010] Preferably, the speed-enhancing agent is one of 1,4-butanediol, ethylene carbonate, and N-methylpyrrolidone, or a mixture of at least two of them.

[0011] The present application also includes a method for preparing the negative electrode slurry, comprising the following steps: adding active material and conductive agent, then adding binder, adding water to adjust the viscosity to 1800-3000CP; controlling the solid content to 40-50%; and finally adding a speed enhancer.

[0012] The present invention also includes a negative electrode, which is prepared by the following method: coating the negative electrode slurry onto a negative electrode current collector; preferably, the negative electrode current collector is a double-glazed copper foil or a carbon-coated copper foil.

[0013] Preferably, a double-layer coating process is used;

[0014] The negative electrode coating close to the negative electrode current collector is the inner coating, and the negative electrode coating far from the negative electrode current collector is the outer coating;

[0015] The inner layer slurry of the inner layer coating comprises the following components by weight: 65-75 parts of a conductive agent, 25-35 parts of a binder, and a solid content of the inner layer slurry of 15-20%; preferably, 70 parts of a conductive agent, 30 parts of a binder, and a solid content of the inner layer slurry of 18%; preferably, the inner layer slurry also includes 0.5-1 parts of a dispersant;

[0016] The outer layer slurry of the outer coating layer comprises the following components by weight: 75-85 parts of a conductive agent, 25-35 parts of a binder, and a solid content of the outer layer slurry of 20-30%; preferably, 80 parts of a conductive agent, 20 parts of a binder, and a solid content of the outer layer slurry of 25%; preferably, the outer layer slurry further comprises 1-2 parts of a dispersant;

[0017] Preferably, the conductive agent is a combination of SUPER-P, CNT carbon nanotubes, and graphene slurry, with a mass ratio of the three being 1:1:2;

[0018] Preferably, the dispersant is one or more of 2-methoxy-1-propyl acetate, alkali lignin, diblock copolymer and triblock copolymer;

[0019] Preferably, the thickness of the inner coating layer and the outer coating layer is 0.5-2 μm; the coating speed of the inner coating layer and the outer coating layer is 80-150 m / min, and the coating temperature of the inner coating layer and the outer coating layer is controlled at 80-130°C.

[0020] The present invention also includes a lithium ion battery, comprising the negative electrode and the positive electrode.

[0021] The positive electrode is prepared by the following method: coating the positive electrode slurry onto the positive electrode current collector; the positive electrode current collector is a carbon-coated aluminum foil;

[0022] Preferably, the positive electrode slurry comprises 85-98 parts of positive electrode active material, 0.5-6 parts of positive electrode conductive agent, and 1.5-9 parts of positive electrode binder; preferably, the positive electrode active material is lithium iron manganese phosphate, the positive electrode conductive agent is SP, and the binder is HSV900; preferably, the positive electrode slurry is prepared in the following manner: first add the positive electrode conductive agent and the positive electrode binder, and use 25r / 2500r / 80min to make a positive electrode conductive glue, then add the positive electrode active material, add NMP to adjust the viscosity, the viscosity is controlled at 5000-8000CP, and the solid content is controlled at 60-65%.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This application improves the electrode processing performance during the coating process by adding a accelerator to the negative electrode slurry and using a mixed glue system to increase the electrode adhesion. At the same time, a new coating process is used to make the lower side have high adhesion with the negative electrode current collector and the negative electrode active material on the upper side have better conductivity, thereby improving the battery capacity and cycle performance. The energy density of the lithium manganese iron phosphate and graphite system is increased to 220wh / kg, and it is expected to be used in the field of long-range power batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a coating method according to an embodiment of the present application;

[0026] Figure 2 This is a comparison chart of the bonding strength of the electrode after rolling with different schemes in Example 1 of this application;

[0027] Figure 3 This is a disassembly diagram of the negative electrode sheet of a fully charged battery after being rolled according to different schemes in Example 1 of the present application;

[0028] Figure 4 This is a comparison chart of the bonding strength of the electrode after rolling with different schemes in Example 2 of this application;

[0029] Figure 5 This is a disassembly diagram of the negative electrode sheet of a fully charged rolling battery according to different schemes in Example 2 of the present application;

[0030] Figure 6 This is a comparison chart of the bonding strength of the electrode after lamination with different schemes in Example 3 of this application;

[0031] Figure 7 This is a comparison chart of the bonding strength of the electrode after rolling with different schemes in Example 4 of this application;

[0032] Figure 8-9 This is a disassembly diagram of the negative electrode sheet of a fully charged battery after being rolled according to different schemes in Example 4 of the present application;

[0033] Figure 10This is a high-temperature cycle curve diagram of two battery cells in Example 4 of this application;

[0034] Figure 11 This is a diagram of the high and low temperature discharge capacity of two battery cells in Example 4 of this application;

[0035] Figure 12 This is a graph showing the discharge capacity retention rates of two battery cells at different rates in Example 4 of the present application;

[0036] Figure 13 This is an energy density diagram of two different battery cell solutions in Example 4 of this application. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and the best embodiments.

[0038] Example 1: The positive electrode slurry adopts lithium iron manganese phosphate: conductive agent (SP): HSV900 = 96.5:1.5:2. The slurry is first added with SP and HSV900, and a conductive glue is prepared by 25r / 2500r / 80min. The lithium iron phosphate main material is subsequently added, and NMP is added to adjust the viscosity. The viscosity is controlled at 5000-8000CP and the solid content is controlled at 60-65%;

[0039] The negative electrode slurry uses graphite: silicon base: CMC: SBR: conductive agent (SP) = 96.2:0:1.1:1.7:1, 91.39:4.81:1.1:1.7:1, 86.58:9.62:1.1:1.7:1, 81.77:14.43:1.1:1.7:1, 76.96:19.24:1.1:1.7:1, and five ratio schemes are used for the negative electrode. The mass content of silicon base in the active material is 0%, 5% (4.81 / (91.39+4.81), and so on), 10%, 15%, and 20%. The solid content of the negative electrode is controlled at 43%, and the viscosity is adjusted to 1800-3000CP by adding water.

[0040] The specific preparation steps are as follows: graphite, silicon base and conductive agent SP are added first, and then slowly stirred for 15r / 15min. Then CMC glue is added in three times, each adding amount is 30%, and each stirring is 30r / 1000r / 90min. After the third addition of CMC, the viscosity is adjusted, and the solid content of the negative electrode is controlled at 43%. Water is added to adjust the viscosity to 1800-3000CP. Finally, SBR glue is added, and slowly stirred for 15r / 30min. Then vacuum is drawn and pressure is maintained for preparation.

[0041] like Figure 1As shown in a, the positive electrode preparation method is as follows: the positive electrode current collector uses carbon-coated aluminum foil, the thickness of the aluminum substrate is 15 μm, the coating of the positive electrode slurry on both sides is 1 μm each, the positive electrode adopts intermittent coating, the coating length of side A is 1088 mm, the coating length of side B is 950 mm, C is the short smooth foil area, the length is 56 mm, D is the long smooth foil area, the length is 194 mm, the extrusion coating method is adopted, and the positive electrode coating amount is 36, 38, 40, 42, and 44 mg / cm 2 The five schemes correspond to the negative electrode, the coating width is 228mm, and the pole piece compaction density is 2.45g / cm 3 ;

[0042] like Figure 1 As shown in b, the negative electrode preparation method is as follows: the negative electrode current collector uses double-glazed copper foil with a thickness of 8 μm, the negative electrode adopts interval coating of negative electrode slurry, and the coating speed is 20 m / min; the coating length of the E surface is 1096 mm, the coating length of the G surface is 976 mm, F is the short glazed foil area with a length of 38 mm, H is the long glazed foil area with a length of 158 mm, the negative electrode adopts single-layer coating, and the coating amount is 16.2 mg / cm 2 The coating width is 232mm, and two rollings are used; the density of the pole piece after one compaction is 1.5g / cm3, and the density after two rollings is 1.65g / cm3.

[0043] Comparison of the bonding strength of the five negative electrode sheets after rolling Figure 2 It shows that the electrode with 0% Si content has the highest bonding strength, which is 57.28gf (gf refers to the unit of force, which refers to the unit of gravity exerted on a substance with a mass of 1G, defined as 1 gram-force), and the electrode with 20% Si content has the lowest bonding strength of 30.16gf, indicating that as the silicon content increases, the electrode bonding strength gradually decreases.

[0044] Combine the positive electrode, negative electrode and other necessary components into a battery, and conduct battery charge and discharge tests. Use 0.5I1 (I1-1h rate discharge current, its value is equal to C1(A), the same below) for charge and discharge. The battery discharge capacity is 21Ah. The battery is charged to 4.0V at 0.5I1 and terminated at a constant voltage current of 0.05I1. The battery is fully charged and disassembled, and the electrodes are compared after fresh disassembly. Figure 3 In comparison, from the disassembled state of the fully charged battery electrodes, the electrodes with 0% silicon content have filamentous powder falling off at the R corner, while the electrodes with 20% silicon content have serious flaky powder falling off.

[0045] Example 2: The difference between Example 2 and Example 1 is that the negative electrode slurry is different and the preparation process of the negative electrode is different; the negative electrode slurry adopts graphite: silicon base: CMC: PAA: SBR: SP = 96.2: 0: 1: 0.8: 1: 1, 91.39: 4.81: 1: 0.8: 1: 1, 86.58: 9.62: 1: 0.8: 1: 1, 81.77: 14.43: 1: 0.8: 1: 1, 76.96: 19.24: 1: 0.8: 1: 1, and the negative electrode adopts five ratio schemes, and the silicon base content is also 0%, 5%, 10%, 15%, and 20%. The negative electrode uses double-glazed copper foil with a thickness of 8μm. The coating speed can reach 25m / min. There is no bulging or cracking on the surface. The negative electrode is rolled twice. The density of the pole piece is 1.5g / cm3 after one compaction and 1.65g / cm3 after two compactions. 3 , the pole piece has good flexibility, no cracks or broken belts. The bonding strength test is carried out before and after the pole piece is rolled. Figure 4 The figure shows a comparison of the electrode bonding strength of the five negative electrode sheets after rolling. The electrode bonding strength of the five schemes of Example 2 is 79.8 gf for 0% Si and 50.8 gf for 20% Si, and the bonding strength of the Si negative electrode of each ratio is significantly improved compared with Scheme 1.

[0046] After aging, the battery is charged and discharged. The battery is charged to 4.0V at 0.5I1 and terminated at a constant voltage current of 0.05I1. The battery is then disassembled. Figure 5 As shown, the negative electrode of the battery cell with 0% Si is in good condition after disassembly, there is no powder falling off at the edge and bend of the electrode, and the electrode has good adhesion. The electrode of 20% Si has slight powder falling off.

[0047] Example 3: The difference between Example 3 and Example 2 is that a speed promoter is added; the negative electrode slurry uses graphite: silicon base: CMC: PAA: SBR: SP = 76.96:19.24:1:0.8:1:1, and the ratio of graphite: silicon base is 80:20;

[0048] In the negative electrode homogenization method, SBR glue and PAA glue are added in the last step of homogenization, and then the accelerator is added. The ratio of the accelerator 1,4-butanediol is 0.4%, 0.6%, 0.8% and 1% of the main material mass. After adding the accelerator, stir it, and then vacuum and pressure are maintained for coating; adding 0.4% of the accelerator can achieve a coating speed of 30m / min, and the negative electrode coating speed of the other four schemes can reach 38m / min. There are no drying marks and cracks on the pole pieces during the coating process of the four schemes, which improves the coating efficiency by 50% and reduces the impact of poor coating; at the same time, after the pole pieces are rolled, the bonding strength of the pole pieces of the four schemes is compared, as shown in the figure. Figure 6As shown in the figure, the addition of accelerator can further improve the bonding strength, especially the bonding strength of 0.6% accelerator is the highest, reaching 93.2gf. In summary, it can be seen that the performance is best when the amount of accelerator is controlled at 0.6%.

[0049] At the same time, the present application tested the addition of 0.6% of the speed-enhancing agent 1,4-butanediol at different silicon-based content ratios, such as graphite: silicon-based: CMC: PAA: SBR: SP = 96.2: 0: 1: 0.8: 1: 1, 91.39: 4.81: 1: 0.8: 1: 1, 86.58: 9.62: 1: 0.8: 1: 1, or 81.77: 14.43: 1: 0.8: 1: 1. The results showed that the addition of speed-enhancing agents at different silicon-based contents improved the bonding strength to varying degrees compared to not adding speed-enhancing agents.

[0050] Similarly, this application tested different ratios of active materials, conductive agents and binders, and added 0.6% of the speed-enhancing agent 1,4-butanediol, for example, active material: conductive agent: binder = 85:0.5:1.5, or active material: conductive agent: binder = 98:6:9, wherein the active material is a combination of graphite: silicon-based, and the ratio of the two is 76.96:19.24; the binder is: CMC:PAA:SBR = 1:0.8:1, and the conductive agent is SP. The results show that the addition of speed-enhancing agents to different ratios of active materials, conductive agents and binders is different from not adding speed-enhancing agents, and the addition of different types of speed-enhancing agents has different degrees of improvement in binding force; since a high silicon-based content is beneficial to improving battery performance, the negative electrode slurry adopts graphite: silicon-based: CMC:PAA:SBR:SP = 76.96:19.24:1:0.8:1:1 for subsequent experimental description.

[0051] Example 4: The difference between Example 4 and Example 3 is that the negative electrode current collector uses carbon-coated copper foil, and the coating method is different; specifically, in this example, the thickness of the carbon-coated copper foil is 6+1+1 μm, and a micro-gravure roller coating process and a double-layer coating process are used;

[0052] Two slurries, the inner slurry close to the negative electrode current collector, includes a conductive agent, a binder, and a dispersant; the binder is the PAA modified binder (CMC:PAA:SBR=1:0.8:1) used in Example 3, and the conductive agent uses SUPER-P, CNT (carbon nanotube), and graphene slurry, with a mass ratio of 1:1:2; the coating dispersant is 2-methoxy-1-propyl acetate, with a content of 1%; the rest is the binder and the conductive agent, with a mass ratio of 3:7, using water as the solvent, the solid content is 18%, and the coating thickness is controlled to 0.6μm;

[0053] The outer layer slurry is far away from the current collector. The components of the conductive agent, binder and dispersant in the outer layer slurry are the same, and the content of the dispersant is also the same. The difference is that the mass ratio of the binder to the conductive agent is 2:8; water is used as the solvent, the solid content is 25%, and the coating thickness is controlled to be 0.4μm;

[0054] The coating speed of both layers of coating was 100 m / min. Both the upper and lower surfaces of the negative electrode current collector were coated with double layers, and the coating temperature was controlled at 120°C.

[0055] The two negative electrodes obtained in Example 4 were tested. Figure 7 The bonding strength of the double-glazed copper foil electrode is 90.8gf, and the bonding strength of the carbon-coated copper foil electrode is 120.6gf;

[0056] The batteries using the double-glazed copper foil and carbon-coated copper foil schemes were charged to 4.25V at 0.5I1, and the constant voltage charging current was terminated at 0.05I1. Then the batteries were disassembled. Figure 8 The picture above shows the electrode after being rolled using plain foil, and the picture below shows the electrode after being rolled using carbon-coated foil. Both types of electrode pieces do not lose powder after rolling.

[0057] Figure 9 In the above figure, a large number of flaky electrodes are peeled off at the bending position of the bare copper foil electrode. The active material and the copper foil have been separated and the bonding strength has deteriorated. Figure 9 The negative electrode sheet using carbon-coated copper foil in the figure below is in good condition, with no powder falling off after charging. This solution can prove that the carbon-coated copper foil has good adhesion to the negative electrode sheet, especially that the adhesion can remain stable after charging and discharging;

[0058] Figure 10-13 The cycle comparison diagram of double-glazed copper foil and carbon-coated copper foil, high and low temperature discharge capacity diagram, rate charge constant current ratio and energy density diagram are shown respectively.

[0059] Comparing the current recycling of double-glazed copper foil and carbon-coated copper foil, Figure 10 The results show that the double-light copper foil battery cell has a 2C cycle rate of 800 times at 45°C @ 75.37%, and the carbon-coated copper foil battery cell has a cycle rate of 800 times @ 78.60%, which is a year-on-year increase of 3.23%. Figure 11 In the comparison of high and low temperature battery discharge performance, the discharge capacity of carbon-coated copper foil at -20℃ is increased by more than 10%. Figure 12 In terms of rate charge and discharge performance, the 4.5C constant current charge ratio of carbon-coated copper foil is more than 9% higher, and the 4.5C constant current discharge capacity is increased by more than 7.5%. It can be seen that the performance of carbon-coated copper foil in cycling, high and low temperature, and rate charge and discharge has been significantly improved. Figure 13 As shown, by using lithium manganese iron phosphate and graphite silicon-based systems, the energy density of the carbon-coated copper foil battery cell can be increased to 225wh / kg, and is expected to be used in high-energy-density power batteries.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A negative electrode, characterized in that The negative electrode slurry is applied to the negative electrode current collector; The negative electrode slurry comprises a negative electrode slurry main body, which comprises the following components by weight: 85-98 parts of active material, 0.5-6 parts of conductive agent, and 1.5-9 parts of binder; the slurry solvent is water; The active material comprises the following components by weight: 76.96-96.2 parts of graphite and 0-19.24 parts of silicon-based; The binder comprises the following components by weight: 0.3-1 parts of CMC adhesive, 0-1.5 parts of PAA adhesive and 0.5-1.7 parts of SBR adhesive; The negative electrode slurry further includes a speed promoter, and the mass ratio of the speed promoter to the negative electrode slurry body is (0.4-1):100; the speed promoter is one of 1,4-butanediol, ethylene carbonate, and N-methylpyrrolidone, or a mixture of at least two thereof; The negative electrode adopts a double-layer coating process; the negative electrode coating close to the negative electrode current collector is the inner coating, and the negative electrode coating away from the negative electrode current collector is the outer coating; The inner layer slurry of the inner layer coating comprises the following components by weight: 65-75 parts of a conductive agent, 25-35 parts of a binder, and a solid content of the inner layer slurry of 15-20%; the inner layer slurry also comprises 0.5-1 parts of a dispersant; The outer layer slurry of the outer coating layer includes the following components by weight: 75-85 parts of a conductive agent, 25-35 parts of a binder, and a solid content of the outer layer slurry of 20-30%; the outer layer slurry also includes 1-2 parts of a dispersant; The dispersant is one or more of 2-methoxy-1-propyl acetate, alkali lignin, diblock copolymer and triblock copolymer.

2. The negative electrode according to claim 1, characterized in that The active material includes 76.96 parts of graphite and 19.24 parts of silicon.

3. The negative electrode according to claim 1, characterized in that The adhesive comprises the following components by weight: 1 part of CMC glue, 0.8 part of PAA glue and 1 part of SBR glue.

4. The negative electrode according to claim 1, characterized in that The mass ratio of the accelerator to the negative electrode slurry is 0.6:

100.

5. The negative electrode according to claim 1, characterized in that The negative electrode current collector is a double-glazed copper foil or a carbon-coated copper foil.

6. The negative electrode according to any one of claims 1 to 5, characterized in that The preparation method of the negative electrode slurry comprises the following steps: adding active material and conductive agent, then adding binder, adding water to adjust the viscosity to be controlled at 1800-3000CP; controlling the solid content to be 40-50%; and finally adding speed enhancer.

7. The negative electrode according to claim 1, characterized in that The inner layer slurry of the inner layer coating includes 70 parts of a conductive agent and 30 parts of a binder, and the solid content of the inner layer slurry is 18%.

8. The negative electrode according to claim 7, characterized in that The conductive agent is a combination of SUPER-P, CNT carbon nanotubes, and graphene slurry, with the mass ratio of the three being 1:1:2; The thickness of the inner coating layer and the outer coating layer is 0.5-2 μm; the coating speed of the inner coating layer and the outer coating layer is 80-150 m / min; the coating temperature of the inner coating layer and the outer coating layer is 80-130°C.

9. A lithium-ion battery, characterized in that: The invention comprises the negative electrode and the positive electrode according to any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that The positive electrode is prepared by the following method: coating the positive electrode slurry onto the positive electrode current collector; the positive electrode current collector is a carbon-coated aluminum foil; The positive electrode slurry comprises 85-98 parts of positive electrode active material, 0.5-6 parts of positive electrode conductive agent, and 1.5-9 parts of positive electrode binder.

11. The lithium-ion battery according to claim 10, wherein: The positive electrode active material is lithium iron manganese phosphate, the positive electrode conductive agent is SP, and the binder is HSV900; the positive electrode slurry is prepared by the following method: first add the positive electrode conductive agent and the positive electrode binder, use 25r / 2500r / 80min to make a positive electrode conductive glue, then add the positive electrode active material, add NMP to adjust the viscosity, the viscosity is controlled at 5000-8000CP, and the solid content is controlled at 60-65%.

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