Method for preparing pole piece by bidirectional rolling and pole piece

Abstract

The present invention belongs to the field of battery pole pieces, and specifically relates to a method for preparing pole pieces by bidirectional rolling and the pole piece. The preparation method comprises the following steps: 1) dispersing a conductive agent; 2) preparing a conductive adhesive; 3) dispersing an active substance; 4) diluting; 5) coating; 6) drying; 7) rolling: a cold pressing process is used for secondary bidirectional rolling, with a rolling speed of 5-15 m / min, a rolling pressure of 2-10 MPa, and a compaction density of 3.2-4.2 g / cm 3 The first rolling process achieves a compaction density of 80-90% of the total compaction density, which is considered forward rolling. The second rolling process compresses the electrode in the opposite direction to the final compaction density, completing the electrode production. The present invention uses a bidirectional rolling process to improve electrode orientation and prevent surface particle breakage.

Description

Technical Field

[0001] The present invention belongs to the field of battery pole pieces, and in particular relates to a method for preparing pole pieces by bidirectional rolling and the pole piece. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, environmental friendliness, and low self-discharge, and have broad application prospects. With the development of technology, people have increasingly higher requirements for the cycle life of lithium-ion batteries, so improving the cycle performance of batteries is particularly important.

[0003] Currently, electrode sheet rolling primarily utilizes a single-pass cold pressing process. This process, when subjected to rolling stress, orients the electrode sheet particles in one direction, resulting in an oblique arrangement of the particles on the foil surface. This hinders electrolyte infiltration and lithium ion insertion and extraction, impacting battery cycle performance. Therefore, the goal is to use forward and reverse bidirectional rolling to maximize the vertical alignment of the particles on the foil surface, thereby improving electrode sheet wettability and lithium ion insertion and extraction, and ultimately, battery cycle performance. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a pole piece by bidirectional rolling and a pole piece.

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

[0006] A method for preparing a pole piece by bidirectional rolling comprises the following steps:

[0007] 1) Conductive agent dispersion: Add the conductive agent, dispersant and a certain amount of solvent into a double planetary homogenizer and mix them at a low speed;

[0008] 2) Preparing a conductive adhesive: After step 1), a binder is added and dispersed to obtain a conductive adhesive;

[0009] 3) Dispersing the active material: adding the active material to the conductive adhesive obtained in step 2) and dispersing the active material; uniformly dispersing the PVDF binder, the conductive agent and the active material to form a slurry;

[0010] 4) Dilution: adding a solvent to the slurry obtained in step 3) to dilute the slurry, and controlling the slurry viscosity to be 6000-8000cp;

[0011] 5) Coating: Apply the above slurry evenly on the surface of the aluminum foil, with a single-sided coating density of 15-25 mg / cm 2 , double-sided density is 30-50mg / cm 2 ;

[0012] 6) Drying: Dry the evenly coated electrode;

[0013] 7) Roller pressing: Use cold pressing process for secondary bidirectional rolling, the rolling speed is 5-15m / min, the rolling pressure is 2-10MPa, and the compaction density is 3.2-4.2g / cm 3 ; The compaction density after the first rolling is 80-90% of the total compaction density, which is forward rolling; the second rolling presses the electrode in the opposite direction to the final compaction density to complete the electrode production.

[0014] The adhesive is prepared in the following manner: PVDF is dissolved in NMP with a solid content controlled at 5%-7%, and high-speed dispersion is performed at 1500-2500 rpm for 6-8 hours to obtain the adhesive.

[0015] The conductive agent in step 1) is: one of conductive graphite or Ketjen black; the dispersant is a synthetic rubber solution; the mass ratio of the conductive agent to the dispersant is: 1.3:1.

[0016] The active material in step 3) is a high-nickel ternary mixture, in which lithium nickel cobalt manganese oxide accounts for 97.4%, PVDF5130 accounts for 0.8%, and PVDF HSV900 accounts for 0.4%.

[0017] The specific process of step 1) is as follows: slow stirring speed is 7 rpm, and the dispersion time is 10 min; followed by high-speed mixing, slow stirring speed is 30 rpm, fast stirring speed is 500 rpm, and the dispersion time is 90 min.

[0018] The specific process of step 2) is as follows: the slow stirring speed is 15 rpm, the fast stirring speed is 2500 rpm, and the dispersion time is 90 min.

[0019] The specific process of step 3) is as follows: the speed of the slow stirring paddle is 30 rpm; the speed of the fast stirring paddle is 2500 rpm, and the dispersion time is 150 min.

[0020] The evenly coated electrode is continuously passed through a blower dryer, with a preferred drying speed of 5 m / min, a drying temperature of 110° C., and a fan frequency of 32 Hz.

[0021] The present invention also includes a pole piece obtained by the method for preparing a pole piece by bidirectional rolling.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention adopts a bidirectional rolling process, which can improve the orientation of the pole pieces and the problem of surface particle breakage; at the same time, combined with a special stirring process, a drying process and a suitable conductive material formula, it can ultimately improve the cycle performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Result diagram of capacity retention rate of the embodiment of the present invention and the comparative example;

[0025] Figure 2 The following are SEM images of the embodiments of the present invention and comparative examples. DETAILED DESCRIPTION

[0026] 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.

[0027] Example 1: Formula: active material lithium nickel cobalt manganese oxide S900 accounts for 97.4%, PVDF5130 accounts for 0.8%, PVDFHSV900 accounts for 0.4%, conductive agent Ab05 accounts for 0.5%, conductive agent ECP accounts for 0.8%, and dispersant BM720H accounts for 0.1%;

[0028] Preparation of binder: Dissolve a certain proportion of PVDF in NMP, control the solid content to 6%, and disperse it at a high speed of 2500 rpm for 6 hours. The appearance is transparent and free of impurities.

[0029] 1) Conductive agent dispersion: Add the conductive agent, dispersant and a certain amount of solvent into a double planetary homogenizer and mix them at low speed, with a slow stirring speed of 7 rpm and a dispersion time of 10 minutes; then mix them at high speed, with a slow stirring speed of 30 rpm and a fast stirring speed of 500 rpm and a dispersion time of 90 minutes.

[0030] 2) Preparation of conductive adhesive: After completing step 1 above, add binder and disperse at high speed, with a slow stirring speed of 15 rpm and a fast stirring speed of 2500 rpm, for 90 minutes;

[0031] 3) Disperse the active substance: Add the active substance to the slurry in step 2 and disperse it at high speed to evenly disperse the PVDF binder, conductive agent and dispersant in the slurry. The speed of the slow stirring paddle is 30 rpm; the speed of the fast stirring paddle is 2500 rpm, and the dispersion time is 150 minutes.

[0032] 4) Dilution: Add solvent to the slurry for dilution, control the speed at 2500 rpm, and disperse for 20 minutes to adjust the slurry viscosity. Preferably, the slurry viscosity in this step is controlled at 6700 cp;

[0033] 5) Coating: The slurry is evenly coated on the surface of the aluminum foil. The preferred single-sided coating density is 24.64 mg / cm 2 , double-sided density is 49.28mg / cm 2 ;

[0034] 6) Drying: The evenly coated electrode is continuously passed through a blower dryer at a drying speed of 5 m / min, a drying temperature of 110°C, and a fan frequency of 32 Hz;

[0035] 7) Rolling: Rolling adopts cold pressing process, the rolling speed is 10m / min, the first rolling density is 89% of the total compaction density, which is positive rolling, and the second rolling presses the electrode in the opposite direction to the final compaction density to complete the electrode production.

[0036] Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that only forward rolling is performed in step 7), and the first rolling compaction density is 89% of the total compaction density, which is forward rolling. The second rolling presses the electrode in the same direction to the final compaction density to complete the electrode production.

[0037] The obtained electrode was tested: it was paired with a graphite negative electrode to make an 18650 model battery for cycle performance testing. The negative electrode sheet formula of the graphite negative electrode is: graphite accounts for 89.65%, silicon oxide accounts for 7.8%, single-walled carbon nanotubes account for 0.1%, sodium carboxymethyl cellulose accounts for 0.95%, and SBR accounts for 1.5%; Figure 1 The test results show that the capacity retention rate of the same-direction rolling (Comparative Example 1) after 270 cycles is 85%, and the capacity retention rate of the opposite-direction rolling is 92%. The opposite-direction rolling (Example 1) has a more obvious advantage. Figure 2 middle Figure 2 a, 2b are SEM images of rolling in the same direction; Figure 2 c and 2d are SEM images of the anisotropic rolling process. The results show that the particles of the pole piece rolled in the same direction are severely broken, while the particles of the anisotropic rolling process are more complete and can maintain a good structure.

[0038] 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 method for preparing pole pieces by bidirectional rolling, characterized in that: The steps include: 1) Conductive agent dispersion: Add the conductive agent, dispersant and a certain amount of solvent into a double planetary homogenizer and mix them at a low speed. The mass ratio of conductive agent to dispersant is 1.3:

1. 2) Preparing a conductive adhesive: After step 1), a binder is added and dispersed to obtain a conductive adhesive; 3) Dispersing the active material: adding the active material to the conductive adhesive obtained in step 2) and dispersing it; The PVDF binder, conductive agent and active material are evenly dispersed to form a slurry; the active material is lithium nickel cobalt manganese oxide, of which lithium nickel cobalt manganese oxide accounts for 97.4%, PVDF 5130 accounts for 0.8%, and PVDF HSV900 accounts for 0.4%; 4) Dilution: adding a solvent to the slurry obtained in step 3) to dilute the slurry, and controlling the slurry viscosity to be 6000-8000cp; 5) Coating: Evenly apply the above slurry on the surface of the aluminum foil, with a single-sided coating density of 15-25 mg / cm² and a double-sided coating density of 30-50 mg / cm²; 6) Drying: Dry the evenly coated electrode; 7) Rolling: The cold pressing process is used for secondary bidirectional rolling, with a rolling speed of 5-15m / min, a rolling pressure of 2-10MPa, and a compaction density of 3.2-4.2g / cm³; the compaction density after the first rolling is 80-90% of the total compaction density, which is forward rolling; the second rolling presses the electrode in the opposite direction to the final compaction density to complete the electrode production.

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