A positive electrode sheet, a preparation method thereof, and a lithium-ion battery based thereon

Abstract

This proposal discloses a positive electrode sheet in the field of chemical energy storage batteries, comprising an active material, a binder, an organic solvent, and a conductive agent. The mass ratio of the active material to the organic solvent is 1:1.05-1.25, and the mass ratio of the active material, conductive agent, and binder is 72-96:4-6:4-6. This positive electrode sheet can significantly improve the power performance of lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of chemical energy storage batteries, and in particular relates to a positive electrode sheet, a preparation method thereof, and a lithium ion battery based thereon. Background Art

[0002] Lithium-ion batteries have the advantages of high voltage, high specific energy, and long cycle life. In recent years, they have been widely used in many fields such as consumer electronics, electric vehicles, and smart medical care. For lithium-ion batteries, power density and energy density are the two most important parameters affecting their practical application, and power density is a key factor in the application of fast-charging electric vehicles, high-power portable tools, and grid stability. The "Lithium-ion Battery Industry Standard Conditions" require: the power density of power-type battery cells ≥ 500W / kg, the power density of battery packs ≥ 350W / kg, the cycle life ≥ 1000 times, and the capacity retention rate ≥ 80%. However, in many application scenarios, such as electromagnetic catapults, laser weapons, etc., the power density requirements are much higher than these. Therefore, the need to develop high-power lithium-ion batteries that can be used in specific scenarios is extremely urgent.

[0003] The pole piece is the basis of lithium-ion battery preparation. The power density of lithium-ion battery can be improved by preparing high-performance pole pieces. Among them, the most effective means is to reduce the thickness of the battery pole piece, which can reduce the Li + The length of the electron transport path can be increased, and ion diffusion and conductivity can be increased, thereby greatly improving the power performance of the battery. However, currently, the preparation of high-power lithium-ion batteries is still mainly based on materials (such as patent CN1938883A) and processes (mainly formulations, such as CN101388449B). The lithium-ion batteries prepared by these methods can only discharge at a maximum of less than 50C, which cannot meet the requirements of aerospace, military and other applications.

[0004] Therefore, it is of positive significance to provide a positive electrode sheet for lithium-ion batteries with sufficient power density under ultra-high rate constant current discharge (150C) and ultra-high power pulse discharge (1000C). Summary of the Invention

[0005] The present invention aims to provide a positive electrode sheet and a preparation method thereof, so as to improve the power performance of a lithium-ion battery.

[0006] A positive electrode sheet in this solution includes an active material, a binder, an organic solvent and a conductive agent, wherein the mass ratio of the active material to the organic solvent is 1:1.05-1.25, and the mass ratio of the active material, the conductive agent and the binder is 72-96:4-6:4-6.

[0007] The beneficial effects of this solution are: the positive electrode sheet prepared using the above raw materials and their proportions has good conductivity and power performance.

[0008] Furthermore, the mass ratio of the active material, the conductive agent, and the binder is 90:5:5. With this ratio of binder, the coated electrode does not shed powder, has good density, and has excellent conductivity.

[0009] Furthermore, the active material is LiCoO2, LiMn2O4, LiFePO4, LiNi 1-x-y Co y Mn x O2 (NCM ternary material), LiNi 1-x-y Co y Al x O2 (NCA ternary material) and LiM x Mn 2-x O4 (M is a doping atom such as Fe, Co) is one of the positive electrode materials for lithium-ion batteries.

[0010] Furthermore, the binder is polyvinylidene fluoride (PVDF).

[0011] Furthermore, the organic solvent is N-methylpyrrolidone (NMP).

[0012] Furthermore, the conductive agent is at least one of carbon nanotubes (CNTs), superconducting carbon black (SP), conductive graphite (KS-6), Ketjen black (KB) and acetylene black. Selecting these materials as conductive agents can increase the conductivity of the electrode, which is beneficial to the discharge performance of the battery.

[0013] The present application also provides a method for preparing the positive electrode sheet, comprising the following steps:

[0014] Step 1: Prepare the active material, binder, organic solvent and conductive agent according to the ratio;

[0015] Step 2: Preparation of slurry: Add the active material and the conductive agent to the binder and mix them evenly, then add the organic solvent in batches to obtain a mixture. The organic solvent is added in batches at intervals of 1.5 to 2.5 hours. When the viscosity of the mixture reaches 2000 to 4000 mPa.s and the fineness reaches D50 ± 2 μm for the active material particles, a slurry is obtained.

[0016] Step 3: Slurry selection: Select slurry with a density difference of ≤5% between the upper and lower layers;

[0017] Step 4: Use a coating machine to apply the selected slurry onto the current collector to obtain a wet electrode;

[0018] Step 5: The wet electrode sheet is dried and rolled to obtain a positive electrode sheet with a thickness of 25 to 30 μm.

[0019] The beneficial effects of this solution are: by preparing an ultra-thin positive electrode sheet with a thickness of 25-30 μm, it can not only reduce the amount of Li + Or the length of the path for electron transmission, and it can increase ion diffusion and conductivity; it can also increase the electrode / electrolyte contact area by increasing the number of pole pieces in the soft-pack battery, so that the battery can be discharged at an ultra-high rate, thereby preparing a high-power lithium-ion battery with excellent performance to meet the needs of high-power lithium-ion batteries in specific scenarios.

[0020] Furthermore, the drying temperature is 80-140° C. Adopting this temperature range can shorten the drying time of the positive electrode sheet while not causing negative effects such as oxidation and cracking on the positive electrode sheet.

[0021] Furthermore, the current collector is made of carbon-coated aluminum foil, which has a higher conductivity than ordinary aluminum foil and is more conducive to high-power discharge of the battery.

[0022] In addition to the above-mentioned positive electrode sheet, the present application also proposes a lithium-ion battery based on the above-mentioned positive electrode sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a picture showing the fineness of the slurry in the method for preparing a positive electrode sheet according to Example 1 of the present invention;

[0024] Figure 2 This is a picture of a positive electrode sheet prepared using the method for preparing a positive electrode sheet according to Example 1 of the present invention;

[0025] Figure 3 for Figure 2 Thickness detection picture of the positive electrode sheet;

[0026] Figure 4 1C discharge curves of soft-pack batteries assembled with positive electrode sheets prepared in Examples 1 and 2 of the present invention;

[0027] Figure 5 150C discharge curve of the pouch cell assembled with the positive electrode sheets prepared in Examples 1 and 2 of the present invention;

[0028] Figure 6 1000A pulse discharge curve of the positive electrode sheet assembled soft-pack battery prepared in Example 1 and Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The following is further described in detail through specific implementation methods:

[0030] Example 1: A method for preparing a positive electrode sheet, the specific production process is as follows:

[0031] Weigh 2.0 kg of LiCoO2 material (D 50 =9.6μm), 55.6g superconducting carbon black and 55.6g carbon nanotubes were added to 111.0g polyvinylidene fluoride (PVDF) and mixed evenly. Then, nitrogen methyl pyrrolidone (NMP) was added in three batches during the stirring process. 1500g nitrogen methyl pyrrolidone (NMP) was added for the first time. The interval between each addition was 1.5 to 2.5h, and a total of 2180g nitrogen methyl pyrrolidone (NMP) was added. During the stirring process, the viscosity of the slurry was tested to be 3258mPa·s and the fineness reached the active material particle size D50±2μm, indicating that the slurry fineness ( Figure 1 ) and viscosity meet the requirements, stirring is completed, and then the coating process is carried out. The sieved slurry is transferred to a fully automatic gap coating machine, using a 18μm thick carbon-coated aluminum foil, adjusting the coating and drying temperature to 100℃*105℃*100℃, and roller pressing (pressure of 30-60 tons) to obtain a 25μm thick ultra-thin positive electrode sheet (such as the attached Figure 2 、 Figure 3 ).

[0032] Example 2: A method for preparing a positive electrode sheet. The specific production process is as follows:

[0033] Weigh 2.5kg NCM811 material (D 50 =6.4μm), 70g superconducting carbon black, and 70g conductive graphite (KS-6) were added to 140.0g polyvinylidene fluoride (PVDF). Then, during stirring, nitrogen methyl pyrrolidone (NMP) was added in three batches, with 2000g of NMP added initially, and each addition was repeated for 1.5-2.5 hours, for a total of 2700g of NMP. During stirring, the slurry viscosity was tested to 2940mPa·s and the fineness reached D50±2μm for the active material particles, indicating that the slurry fineness and viscosity met the requirements. After stirring, the slurry was transferred to the coating process. The sieved slurry was transferred to a fully automatic gap coater using 12μm thick carbon-coated aluminum foil. The coating and drying temperatures were adjusted to 120℃*130℃*120℃. After roller pressing, an ultra-thin positive electrode sheet with a thickness of 28μm was obtained.

[0034] The specific implementation process is as follows: the positive electrode sheets prepared in Example 1 and Example 2 are used to assemble soft-pack batteries. The specific process is as follows: the positive electrode sheets are cut into a certain size through a mold, and then stacked through a semi-automatic stacking machine to prepare a battery cell; after the battery cell is welded with the pole ears, packaged, injected with liquid, and aged, it is formed. After the formation is completed, the capacity and power test can be carried out.

[0035] The 1C discharge of the positive electrode sheets assembled with the soft pack batteries prepared in Example 1 and Example 2 was tested (the discharge current was set to 1A and the voltage range was 4.4-2.2V). The discharge curves are shown in the attached figure. Figure 4 As shown in the attached Figure 4 It can be seen that the discharge capacity of the positive electrode sheet-assembled soft-pack batteries prepared in Example 1 and Example 2 at a 1C rate is both around 1 Ah.

[0036] The 150C discharge of the positive electrode sheet assembled soft pack battery prepared in Example 1 and Example 2 was tested (the discharge current was set to 150A and the voltage range was 4.4-2.2V). The discharge curve is shown in the attached figure. Figure 5 As shown in the attached Figure 5 It can be seen that the discharge capacity of the positive electrode sheet assembled soft-pack batteries prepared in Example 1 and Example 2 is more than 80% of the 1C discharge capacity, indicating that the rate performance of this battery is very excellent, far higher than the 50C constant current discharge level of high-power lithium-ion batteries on the market.

[0037] The 1000A pulse discharge of the positive electrode sheets assembled into soft-pack batteries prepared in Example 1 and Example 2 was tested. The pulse test procedure was as follows: discharge current 1000A, discharge time 20ms, interval time 100ms, repeated 5 cycles. The 1000A pulse discharge diagram is shown in the attached figure. Figure 6 As shown in the attached Figure 6 It can be seen that the 1000A pulse specific power of the soft-pack battery assembled with the positive electrode sheets prepared in Example 1 and Example 2 can reach more than 85kW / kg.

[0038] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises an active material, a binder, an organic solvent and a conductive agent, wherein the mass ratio of the active material to the organic solvent is 1:1.05-1.25, and the mass ratio of the active material, the conductive agent and the binder is 72-96:4-6:4-6; the positive electrode sheet is prepared by the following method: Step 1: Prepare the active material, binder, organic solvent and conductive agent according to the ratio; Step 2: Preparation of slurry: Add the active material and the conductive agent to the binder and mix them evenly, then add the organic solvent in batches to obtain a mixture. The organic solvent is added in batches at intervals of 1.5 to 2.5 hours. When the viscosity of the mixture reaches 2000 to 4000 mPa.s and the fineness reaches D50 ± 2 μm for the active material particles, a slurry is obtained. Step 3: Slurry selection: Select slurry with a density difference of ≤5% between the upper and lower layers; Step 4: Use a coating machine to apply the selected slurry onto the current collector to obtain a wet electrode; Step 5: The wet electrode sheet is dried and rolled to obtain a positive electrode sheet with a thickness of 25 to 30 μm.

2. The positive electrode sheet according to claim 1, wherein: The mass ratio of the active material, the conductive agent and the binder is 90:5:

5.

3. The positive electrode sheet according to claim 2, characterized in that: The active material is LiCoO2, LiMn2O4, LiFePO4, LiNi 1-x-y Co y Mn x O2、LiNi 1-x-y Co y Al x O2 and LiM x Mn 2-x One of O4, LiM x Mn 2-x M in O4 is Fe or Co.

4. The positive electrode sheet according to claim 3, characterized in that: The binder is polyvinylidene fluoride.

5. The positive electrode sheet according to claim 4, characterized in that: The organic solvent is N-methylpyrrolidone.

6. The positive electrode sheet according to claim 5, characterized in that: The conductive agent is at least one of carbon nanotubes (CNTs), superconducting carbon black (SP), conductive graphite (KS-6), Ketjen black (KB) and acetylene black.

7. The positive electrode sheet according to claim 6, characterized in that: The drying temperature is 80-140°C.

8. The positive electrode sheet according to claim 7, characterized in that: The current collector is made of carbon-coated aluminum foil.

9. A lithium-ion battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 8.

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