Method for optimizing cycle performance of battery, current collector and pole piece

Abstract

The invention discloses a method for optimizing the cycle performance of a battery, a current collector and a pole piece, diphenylmethane diisocyanate and nano crystalline cellulose are doped into conductive slurry, the mixture is uniformly mixed and then coated to a foil material to prepare the current collector, and the current collector is adopted to prepare the pole piece of the battery. According to the invention, trace nano crystalline cellulose and diphenylmethane diisocyanate are introduced into the conductive layer of the current collector, so that irreversible deformation of a pole piece after long-time charging and discharging of the battery can be prevented, and the influence of non-uniform density distribution of a conductive layer surface caused by agglomeration of particles in conductive slurry on the cycle performance of a battery end can be avoided; and the cycle performance of the battery is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for optimizing battery cycle performance, a current collector and a pole piece. Background Art

[0002] Today, energy storage and power batteries are developing rapidly, and along with it comes people's widespread recognition of electric vehicles. The competition among many battery factories has also become fierce, and companies are paying more and more attention to improving battery performance.

[0003] At present, companies are more focused on improving performance from the perspective of electrode active materials. For example, in terms of positive electrode materials, researchers prefer to use carbon coating methods to increase battery capacity, but there is no significant improvement in cycle performance. Cycle performance is as important to batteries as battery capacity. The capacity retention rate of cycle performance needs to ensure that the battery can still provide sufficient energy storage after a period of use, otherwise it will affect product performance and user experience. Therefore, how to improve cycle performance has become a problem that needs to be solved urgently. Summary of the invention

[0004] The purpose of the present invention is to provide a method for optimizing battery cycle performance, a current collector and a pole piece, and to improve the battery cycle performance by introducing a trace amount of nanocrystalline cellulose and diphenylmethane diisocyanate into the current collector conductive layer.

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

[0006] A first aspect of the present application provides a current collector for optimizing battery cycle performance, wherein a conductive layer is disposed on at least one surface of the current collector, and the conductive layer contains diphenylmethane diisocyanate and nanocrystalline cellulose.

[0007] The conductive layer of the current collector contains a conductive agent MXene.

[0008] The second aspect of the present application provides a method for optimizing battery cycle performance, wherein diphenylmethane diisocyanate and nanocrystalline cellulose are added to a conductive slurry, mixed evenly and coated on a foil to prepare a current collector, and the current collector is used to prepare a battery pole.

[0009] The specific method includes mixing a binder, a conductive agent, diphenylmethane diisocyanate and nanocrystalline cellulose in proportion with water to prepare a mixed conductive slurry that meets the solid content requirements, and evenly coating the mixed conductive slurry on a foil to prepare a current collector.

[0010] The conductive agent is Ti3C2T x; The binder is selected from at least one of polyacrylic acid, lithium polyacrylate, and sodium polyacrylate; the mass ratio of the binder to the conductive agent is in the range of 1-2:3-8.

[0011] Furthermore, the solid content of the mixed conductive paste is in the range of 7%-12%.

[0012] Furthermore, the mass proportion of the diphenylmethane diisocyanate in the mixed conductive paste is 3.0%-4.0%; the mass proportion of the nanocrystalline cellulose in the mixed conductive paste is 2.0%-3.0%.

[0013] Furthermore, the solid content of the nanocrystalline cellulose is 1.5%-2.0%.

[0014] Furthermore, the coating speed is controlled at 50-80 m / min, and the single-layer coating surface density is controlled at 0.3-2.0 g / m 2 .

[0015] The third aspect of the present application provides a battery electrode, which adopts the above-mentioned current collector for optimizing battery cycle performance, and an active material layer is provided on the surface of the current collector; preferably, the active material layer is a positive electrode active material layer; preferably, the positive electrode active material layer includes a lithium-based positive electrode material.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention coats a layer of conductive slurry on the current collector, and a trace amount of nanocrystalline cellulose (NCC) and diphenylmethane diisocyanate (MDI) are added to the conductive slurry as additives; NCC, as a kind of nanocellulose, can improve the toughness of the conductive layer, reduce the deformation of the pole piece after the battery is charged and discharged for a long time, and improve the cycle performance; the introduction of MDI can greatly reduce the van der Waals force between molecules and avoid the agglomeration of particles; NCC and MDI synergize to not only prevent the irreversible deformation of the pole piece after the battery is charged and discharged for a long time, but also avoid the influence of the uneven density distribution of the conductive layer surface caused by the agglomeration of particles in the conductive slurry on the cycle performance of the battery end, so that the cycle performance of the battery is significantly improved.

[0018] The present invention is particularly effective for carbon-coated current collectors using carbon-coated slurries to prepare conductive layers, such as MXene (Ti3C2T x ) is a carbon-coated current collector with a conductive agent; the introduction of MDI can graft and modify the functional groups on the surface of MXene and the binder, which not only makes it easy to disperse MXene, but also improves the compatibility with the polymer, thereby improving the cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1: Schematic diagram of the method flow of Example 1 of the present invention.

[0020] Figure 2 : SEM image of the carbon-coated aluminum foil prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The above contents of the present invention are further described in detail below in the form of embodiments, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the above contents of the present invention belong to the scope of the present invention.

[0022] The experimental methods used in the following examples are all conventional methods unless otherwise specified, and the reagents, methods and equipment used are all conventional reagents, methods and equipment in the technical field unless otherwise specified.

[0023] The mixed conductive paste in the embodiment of the present invention is dried after being coated on the foil. The drying process can be carried out by drying in a vacuum environment at 90° C.-120° C. for 5-10 minutes.

[0024] The solution of the present invention can be used for lithium-ion batteries, sodium-ion batteries, etc. The present invention is described in detail below through a group of specific implementation schemes of lithium-ion batteries.

[0025] The following examples are based on MXene (Ti3C2T x ) is used as an example to introduce a carbon-coated current collector using a conductive agent. The carbon-coated layer contains diphenylmethane diisocyanate and nanocrystalline cellulose. The preparation process is as follows: diphenylmethane diisocyanate and nanocrystalline cellulose are added to the carbon-coated slurry, and the mixture is evenly mixed and then coated on the positive electrode foil to obtain the carbon-coated current collector. The carbon-coated current collector is then used to prepare the positive electrode sheet of the battery.

[0026] Embodiment 1:

[0027] 1. Preparation of Carbon Coating Slurry

[0028] The carbon coating layer binder is polyacrylic acid (PAA, solid content 25%), and the conductive agent is Ti3C2T x(Xianfeng Nano), in which a small amount of NCC material and MDI are added; the mass ratio of the binder to the conductive agent is 3:7, dissolved in water according to this ratio, stirred evenly, and a mixed carbon coating slurry with a solid content of 9% is prepared; the process steps are as follows: (1) PAA glue preparation: add water and PAA, rotate at 800rpm, and stir for 30min; (2) Conductive agent dispersion: add conductive agent, rotate at 2400rpm, and stir for 90min; (3) NCC and MDI introduction: add NCC and MDI, rotate at 1800rpm, and stir for 30min. Among them, the solid content of NCC is selected to be 1.5%-2.0%, the addition ratio is 2%-3% of the total slurry, and the addition ratio of MDI is 3%-3.5% of the total slurry.

[0029] 2. Preparation of carbon-coated aluminum foil:

[0030] The plain foil uses 13 micron aluminum foil, the carbon coating slurry uses the mixed carbon coating slurry prepared in the previous step, the coating speed is controlled at 65m / min, the drying temperature is controlled at 110℃, and the single-layer coating surface density is controlled at 1.0g / m 2 about.

[0031] 3. Preparation of positive electrode slurry:

[0032] LCO was selected as the positive electrode active material, PVDF (Kureha, KF1100) was selected as the binder, and Super P (Swiss Termeco) was selected as the conductive agent; the active material: binder: conductive agent = 95:2:3 were stirred and mixed, and after mixing evenly, coated on aluminum foil, and dried in a vacuum drying oven at 120°C for 12 hours to obtain a positive electrode sheet.

[0033] 4. Assembly of button batteries:

[0034] The button battery shell uses CR2032 model, the diaphragm uses 20um diaphragm, and the electrode uses the positive electrode with uniform coating in step 3. In a glove box filled with argon, assemble the button battery in the following order: battery shell - place positive electrode - drip electrolyte - place diaphragm - drip electrolyte - place lithium sheet - place gasket spring - battery shell.

[0035] 5.Button battery test:

[0036] The button battery was tested for charge and discharge cycles at 0.2C using a button battery charge and discharge tester (Wuhan Blue Electric, CT2001A) with a voltage range of 3.0-4.4V. The test results are shown in the table.

[0037] Embodiment 2:

[0038] The method is basically the same as Example 1, except that the solid content of NCC is 0.5%-1.0%;

[0039] Embodiment 3:

[0040] The method is basically the same as Example 1, except that the solid content of NCC is 1.0%-1.5%;

[0041] Embodiment 4:

[0042] The method is basically the same as Example 1, except that the solid content of NCC is 2.0%-2.5%;

[0043] Embodiment 5:

[0044] The method is basically the same as Example 1, except that the solid content of NCC is 2.5%-3.0%;

[0045] Embodiment 6:

[0046] The method is basically the same as Example 1, except that the addition ratio of MDI is 2.0%-2.5% of the total amount of the slurry;

[0047] Embodiment 7:

[0048] The method is basically the same as Example 1, except that: the addition ratio of MDI is 2.5%-3.0% of the total amount of the slurry;

[0049] Embodiment 8:

[0050] The method is basically the same as Example 1, except that: the addition ratio of MDI is 3.5%-4.0% of the total amount of the slurry;

[0051] Embodiment 9:

[0052] The method is basically the same as Example 1, except that the addition ratio of MDI is 4.0%-4.5% of the total amount of the slurry;

[0053] Comparative Example 1:

[0054] The method is substantially the same as Example 1, except that: no NCCI is added in step 1;

[0055] Comparative Example 2:

[0056] The method is basically the same as Example 1, except that: no MDI is added in step 1;

[0057] The test evaluation results of each embodiment are as follows:

[0058] serial number Capacity retention rate after 30 cycles Capacity retention after 50 cycles Capacity retention rate after 70 cycles Example 1 97.2％ 93.0％ 91.3％ Example 2 93.8％ 88.3％ 86.5％ Example 3 94.5％ 88.5％ 86.8％ Example 4 94.9％ 88.9％ 87.7％ Example 5 94.4％ 88.7％ 87.0％ Example 6 94.0％ 89.0％ 87.3％ Example 7 95.8％ 90.8％ 88.9％ Example 8 95.4％ 90.4％ 89.0％ Example 9 94.1％ 89.3％ 87.4％ Comparative Example 1 94.1％ 89.1％ 87.0％ Comparative Example 2 92.0％ 86.3％ 85.1％

[0059] The analysis of the embodiments and comparative examples is as follows:

[0060] The present invention uses NCC as a conductive layer additive, which can improve the toughness of the conductive layer and reduce the deformation of the pole piece after the battery is charged and discharged for a long time, so as to improve the cycle performance;

[0061] Furthermore, by introducing the synergistic effect of MDI and NCC, the van der Waals force between molecules can be greatly reduced, avoiding the uneven density distribution of the conductive layer caused by agglomeration between particles, and significantly improving the cycle performance of the battery.

[0062] The introduction of MDI can also graft and modify the functional groups on the surface of MXene and binder, which can significantly reduce the van der Waals forces between molecules. It not only makes it easy to disperse MXene, but also improves the compatibility with polymers and avoids agglomeration between particles, thereby improving the cycle stability of the battery.

[0063] Among them, controlling the solid content of NCC and the addition ratio of MDI has a significant effect on the achievement of technical effects.

[0064] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention and based on the technical essence of the present invention, may make any simple modifications, equivalent substitutions and improvements to the above embodiments, which are still within the protection scope of the technical solution of the present invention.

Claims

1. A current collector for optimizing battery cycle performance, characterized in that: A conductive layer is disposed on at least one surface of the current collector, and the conductive layer contains diphenylmethane diisocyanate and nanocrystalline cellulose.

2. The method for optimizing battery cycle performance according to claim 1, characterized in that: The conductive layer is a carbon-coated layer.

3. A method for optimizing battery cycle performance, characterized in that: Diphenylmethane diisocyanate and nanocrystalline cellulose are added to the conductive slurry, mixed evenly and then coated on the foil to prepare a current collector, and the current collector is used to prepare a battery pole piece.

4. The method for optimizing battery cycle performance according to claim 3, characterized in that: Its specific method The method comprises the following steps: uniformly mixing a binder, a conductive agent, diphenylmethane diisocyanate and nanocrystalline cellulose with water in a certain proportion to prepare a mixed conductive slurry meeting the solid content requirement; and uniformly coating the mixed conductive slurry on a foil to prepare a current collector.

5. The method for optimizing battery cycle performance according to claim 4, characterized in that: The mixed conductive paste is a mixed carbon-coated paste; the binder is selected from at least one of polyacrylic acid, lithium polyacrylate and sodium polyacrylate; the mass ratio of the binder to the conductive agent is in the range of 1-2:3-8.

6. The method for optimizing battery cycle performance according to claim 4, characterized in that: The solid content of the mixed conductive paste ranges from 7% to 12%.

7. The method for optimizing battery cycle performance according to claim 3, characterized in that: The mass proportion of the diphenylmethane diisocyanate in the mixed conductive paste is 3.0%-4.0%; the mass proportion of the nanocrystalline cellulose in the mixed conductive paste is 2.0%-3.0%.

8. The method for optimizing battery cycle performance according to claim 3, characterized in that: The solid content of the nano-crystalline cellulose is 1.5%-2.5%.

9. The method for optimizing battery cycle performance according to claim 3, characterized in that: The coating speed is controlled at 50-80 m / min, and the single-layer coating surface density is controlled at 0.3-2.0 g / m 2 .

10. A battery pole piece, characterized in that: The current collector for optimizing battery cycle performance according to claim 1 or 2 is used, and an active material layer is provided on the surface of the current collector; preferably, the active material layer is a positive electrode active material layer; preferably, the positive electrode active material layer includes a lithium-based positive electrode material.

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