A high-rate lithium ion battery pole piece, a preparation method and application thereof

Abstract

The application provides a high-rate lithium ion battery pole piece and a preparation method thereof, and the composition comprises a porous current collector, a lithium-rich gel electrolyte and a gradient structure active material. The lithium-rich gel electrolyte is generated in situ at the pores of the porous current collector, the lithium salt concentration is greater than 3M, the gel electrolyte contains a high concentration of lithium ions, and the lithium ions can provide ions for the active material during charging and discharging, relieve local polarization of the current collector, realize ion and electron balance, and reduce the tortuosity of the active material by using twice coating to coat two particle sizes of the active material on the current collector. The battery pole piece provided by the application has low internal resistance and excellent rate performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a method for preparing a high-rate lithium-ion battery electrode and its application in batteries. Background Technology

[0002] Lithium-ion batteries possess a range of advantages, including high energy density, high voltage, low self-discharge, good cycle performance, and long lifespan. Currently, all batteries used in drones are lithium-ion batteries. With the development of the low-altitude economy, drone batteries face increasing demands for energy density, power performance, and safety, urgently requiring drone batteries with higher positive electrode active material loading and higher rate performance. Currently, high-load batteries exhibit high liquid-phase ion transport resistance, preventing them from operating at high rates. Common improvement measures include reducing the tortuosity of the positive electrode structure, shortening the ion transport distance, reducing concentration polarization, and improving the battery's rate performance. However, the active material near the current collector undergoes a rapid electron transfer process, resulting in a severe electron-ion exchange imbalance, limiting the improvement in battery rate performance.

[0003] Currently, lithium-ion batteries use porous aluminum foil as the positive electrode current collector. The three-dimensional porous aluminum foil is beneficial for the coating of the positive electrode material, while reducing the weight of the aluminum foil and increasing the energy density of the battery. However, this approach does not consider the problem of electron-ion exchange balance of the active material in the current collector and has not solved the problem of high-rate discharge of the battery. Summary of the Invention

[0004] To address the above problems, this invention generates an ion gel electrolyte in situ at the pores of a porous current collector, which provides lithium ions during battery discharge, achieving electron-ion exchange balance and improving the rate performance of lithium-ion batteries.

[0005] The primary objective of this invention is to provide a high-rate lithium-ion battery electrode.

[0006] The second objective of this invention is to provide a lithium-ion battery prepared using the electrode sheet of this application.

[0007] The third objective of this invention is to provide a method for preparing the electrode.

[0008] To achieve the objectives of this invention, the technical solution adopted is as follows:

[0009] A lithium-ion battery electrode includes a porous current collector, a gel electrolyte, and a porous active material layer attached to the surface of the current collector. The porous current collector is a porous metal foil, the ion gel electrolyte is an organic framework ion gel electrolyte, and the active material layer has a gradient structure, with the bottom layer consisting of small particles with a particle size <10μm (accounting for 40% of the thickness) and the top layer consisting of large particles with a particle size >15μm (accounting for 60% of the thickness).

[0010] Preferably, the thickness of the porous current collector is 15-20 μm, the micropore diameter is 100-150 μm, and the porosity is 25-30%.

[0011] Preferably, the tensile strength of the porous current collector is 140-180 MPa.

[0012] This invention generates an ion-gel electrolyte in situ at the pores of a porous current collector. A certain amount of lithium salt and conductive agent are added to a polymer monomer solution, and the mixture is stirred at room temperature for a certain time to obtain a uniform and transparent precursor solution. Then, a certain amount of plasticizer is added to the precursor solution, and finally, a trace amount of initiator is added, with continued stirring to obtain a uniform and transparent electrolyte precursor solution. The electrolyte precursor solution is then coated onto the porous current collector using a spatula, and the mixture is heated in an oven until gelation occurs, thus preparing a porous gel current collector. The gel electrolyte contains a high concentration of lithium ions, which can provide ions to the active material during charging and discharging, alleviating local polarization of the current collector and achieving ion-electron balance.

[0013] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a concentration ≥3M;

[0014] Preferably, the conductive agent is carbon nanotubes (CNTs).

[0015] Preferably, the polymer monomer solution can be N,N-dimethylacrylamide (DMAA) or 1,3-dioxolane;

[0016] Preferably, the stirring time is 8 hours;

[0017] Preferably, the plasticizer is dimethyl carbonate (DMC).

[0018] Preferably, the initiator is azobisisobutyronitrile (AIBN).

[0019] This invention involves coating an active material onto a porous gel current collector. The active material is sieved multiple times according to a gradient to separate active particles with diameters >15μm and <10μm. A tortuous gradient positive electrode is prepared using a two-coating method. In this method, the smaller particle size active material is coated first, and after drying, the larger particle size active material is coated.

[0020] Preferably, the particle size of the small-diameter active material is <10μm. The active material, carbon nanotubes and PVDF are mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) is added to adjust the slurry to a suitable viscosity. Then, the slurry is coated on a porous current collector with gel electrolyte. The coating thickness is about 30μm. After coating, the slurry is dried in an oven. After drying, it is pressed for 5 minutes under a pressure of 10MPa using a roller press.

[0021] Preferably, after drying and pressing the small-particle-size active material, a large-particle-size active material (>15μm) is selected. The active material, carbon nanotubes, and PVDF are mixed in a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) is added to adjust the slurry to a suitable viscosity. Then, the slurry is coated onto a porous current collector with a gel electrolyte, with a coating thickness of about 35μm. After coating, it is dried in an oven. After drying, it is pressed for 5 minutes at a pressure of 10MPa using a roller press. A tortuous gradient electrode is thus prepared.

[0022] The battery electrode prepared by this invention has excellent ion transport performance, reduces the internal resistance of ion transport in the battery, and effectively improves the rate performance and energy density of the battery.

[0023] The battery electrode preparation method provided by this invention can be applied to various current collectors, including porous copper / aluminum foil and other porous and refined metal foils. The prepared porous battery electrode exhibits excellent electron-ion transport balance, improving the rate performance of the battery, allowing for further increases in the thickness of the battery active material, and enhancing the battery's energy density.

[0024] Compared with existing technologies, the advantages of the porous current collector preparation method and its application provided by this invention are as follows:

[0025] (1) The introduction of gel electrolyte can reduce the amount of liquid electrolyte used and improve the safety performance of the battery.

[0026] (2) The lithium-rich gel electrolyte can provide lithium ions to the active material near the current collector, which helps to eliminate the concentration polarization problem of the battery during high-rate discharge and improve the high-rate discharge capability of the battery.

[0027] (3) The double-coated electrode can reduce the ion transport distance and reduce the internal resistance of the battery, which is beneficial to the cycle stability of the battery. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the composition of high-rate battery electrodes;

[0029] Figure 2 Scanning electron microscope image of a porous metal current collector;

[0030] Figure 3 High-rate discharge curves for conventional batteries and batteries prepared using the high-rate current collector of this invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0032] In a first aspect, the present invention provides a method for preparing a lithium-rich porous current collector for lithium batteries.

[0033] A method for preparing a lithium-rich porous current collector for lithium batteries includes the following steps: LiTFSI and CNTs are added to an N,N-dimethylacrylamide (DMAA) monomer solution via in-situ polymerization. The solution is stirred at room temperature for a certain period to form a homogeneous and transparent precursor solution. Then, a certain amount of DMC plasticizer is added to the precursor solution. Finally, a trace amount of azobisisobutyronitrile (AIB) initiator is added, and stirring continues to obtain a homogeneous and transparent electrolyte precursor solution. The solution is then coated onto the surface of the porous current collector using a doctor blade and quickly transferred to a vacuum oven for in-situ polymerization.

[0034] Furthermore, the LiTFSI concentration is 3M and the CNT mass percentage is 10%.

[0035] Furthermore, the stirring time at room temperature is >8h.

[0036] Furthermore, the temperature of the vacuum oven is 60℃, and the heating time is 2 hours.

[0037] Furthermore, the porous current collector foil includes, but is not limited to, copper-based current collectors and aluminum-based current collectors.

[0038] Secondly, the present invention provides a two-step coating method for active substances.

[0039] Furthermore, the active material with a particle size of <10μm is coated for the first time. It is mixed with CNT and PVDF in a mass ratio of 8:1:1 to form a paste. An appropriate amount of N-methylpyrrolidone (NMP) is added to adjust the slurry to a suitable viscosity. Then, it is coated on a porous current collector with gel electrolyte. The coating thickness is about 30μm. After coating, it is dried in an oven. After drying, it is pressed for 5 minutes under a pressure of 10MPa using a roller press.

[0040] Furthermore, the active material with a particle size of <10μm for the second coating is mixed with CNT and PVDF in a mass ratio of 8:1:1 to form a paste. An appropriate amount of N-methylpyrrolidone (NMP) is added to adjust the slurry to a suitable viscosity. The paste is then coated on a porous current collector with gel electrolyte, with a coating thickness of about 35μm. After coating, the paste is dried in an oven. After drying, it is pressed for 5 minutes at a pressure of 10MPa using a roller press.

[0041] Example 1:

[0042] This embodiment provides a method for preparing a lithium-rich gel porous current collector that enables low-temperature, high-power discharge of lithium-ion batteries, such as... Figure 1 As shown, the method includes the following steps.

[0043] 3 mol / L LiTFSI lithium salt and 10% (w / w) carbon nanotube (CNT) conductive agent were added to an N,N-dimethylacrylamide (DMAA) polymer monomer solution and stirred at room temperature for 8 hours to obtain a homogeneous and transparent precursor solution. 10% (w / w) dimethyl carbonate (DMC) was added to the precursor solution as a plasticizer, and stirring continued until homogeneous. Finally, 0.1% (w / w) azobisisobutyronitrile (AIBN) was added as an initiator, and stirring continued until a homogeneous and transparent electrolyte precursor solution was obtained. The electrolyte precursor solution was uniformly coated onto a porous aluminum foil with a thickness of 20 μm and a pore size of 100 μm using a doctor blade. The foil was then heated to 120°C in an oven and maintained for 2 hours to form an ionogel electrolyte, thus producing a porous gel current collector.

[0044] A positive electrode active material with a particle size of 7-10 μm was selected and mixed with carbon nanotubes and PVDF at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added to adjust the mixture into a suitable coating slurry. The slurry was uniformly coated onto a porous gel current collector to a thickness of 30 μm, and then dried in an oven at 80°C for 2 hours. After drying, the material was pressed using a roller press under a pressure of 10 MPa for 5 minutes.

[0045] A positive electrode active material with a particle size of 15-18 μm was selected and mixed with carbon nanotubes and PVDF at a mass ratio of 8:1:1, with an appropriate amount of NMP added to adjust the slurry. The slurry was uniformly coated onto the current collector already coated with large-particle active material, with a coating thickness of 35 μm, and then placed in an oven at 80°C for 2 hours to dry. After drying, it was pressed again using a roller press at a pressure of 10 MPa for 5 minutes to obtain a porous active material layer with a gradient structure.

[0046] The prepared high-rate lithium-ion battery electrodes are assembled into batteries and their performance is tested.

[0047] Example 2:

[0048] This embodiment provides a battery electrode structure with gradient active materials, and a method for preparing lithium-rich gel porous current collectors that enables low-temperature, high-power discharge of lithium-ion batteries, such as... Figure 1 As shown, the method includes the following steps.

[0049] A positive electrode active material with a particle size of 7-10 μm was selected and mixed with carbon nanotubes and PVDF at a mass ratio of 8:1:1. An appropriate amount of N-methylpyrrolidone (NMP) was added to adjust the mixture into a suitable coating slurry. The slurry was uniformly coated onto an aluminum foil current collector with a current collector thickness of 20 μm and a coating thickness of 30 μm. The coated material was then dried in an oven at 80°C for 2 hours. After drying, the material was pressed using a roller press under a pressure of 10 MPa for 5 minutes.

[0050] A positive electrode active material with a particle size of 15-18 μm was selected and mixed with carbon nanotubes and PVDF at a mass ratio of 8:1:1, with an appropriate amount of NMP added to adjust the slurry. The slurry was uniformly coated onto the current collector already coated with large-particle active material, with a coating thickness of 35 μm, and then placed in an oven at 80°C for 2 hours to dry. After drying, it was pressed again using a roller press at a pressure of 10 MPa for 5 minutes to obtain a porous active material layer with a gradient structure.

[0051] The prepared electrodes are assembled into batteries for performance testing.

[0052] Example 3

[0053] This embodiment provides a method for preparing a conventional electrode, such as... Figure 1 As shown, the method includes the following steps.

[0054] The positive electrode active material was not sieved. It was mixed with carbon nanotubes and PVDF at a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) was added to adjust it into a suitable coating slurry. The slurry was uniformly coated onto an aluminum foil current collector with a current collector thickness of 20 μm and a coating thickness of 65 μm. Then, it was placed in an oven and dried at 80°C for 2 hours. After drying, it was pressed using a roller press at a pressure of 10 MPa for 5 minutes.

[0055] The prepared electrodes are assembled into batteries for performance testing.

[0056] Table 1

[0057]

Claims

1. A high-rate lithium-ion battery positive electrode, characterized in that, include: A porous current collector, wherein the porous current collector is a porous aluminum foil or copper foil, having a porosity of 25-30%, a pore size of 100-150 μm, and a thickness of 15-20 μm; An ion gel electrolyte filling the pores of the porous current collector, the ion gel electrolyte comprising a lithium salt, a conductive agent, a polymer monomer, a plasticizer and an initiator, wherein the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) with a concentration of 3M or higher; A gradient structure active material layer is attached to the surface of the porous current collector. The active material layer includes a bottom layer and an upper layer. The bottom layer is composed of active materials with a particle size of <10μm, and the upper layer is composed of active materials with a particle size of >15μm. The thickness ratio of the bottom layer to the upper layer is 40%:60%.

2. The lithium-ion battery positive electrode sheet according to claim 1, characterized in that, The tensile strength of the porous current collector is 140-180 MPa.

3. The lithium-ion battery positive electrode sheet according to claim 1, characterized in that, The conductive agent is carbon nanotubes (CNTs), the polymer monomer is selected from N,N-dimethylacrylamide (DMAA) or 1,3-dioxolane, the plasticizer is dimethyl carbonate (DMC), and the initiator is azobisisobutyronitrile (AIBN).

4. A lithium-ion battery, characterized in that, It includes the high-rate lithium-ion battery positive electrode sheet as described in any one of claims 1-3.

5. A method for preparing the high-rate lithium-ion battery positive electrode sheet according to claim 1, characterized in that, Includes the following steps: Step 1: Preparation of porous gel current collector a. Add lithium salt and conductive agent to the polymer monomer solution and stir to form a precursor solution; b. Add plasticizer to the precursor solution, mix well, and then add initiator to obtain electrolyte precursor solution; c. Coat the surface of the porous current collector with the electrolyte precursor solution, and heat to initiate an in-situ polymerization reaction to form an ion gel electrolyte that fills the pores; Step 2: Coating of the gradient active material layer d. Mix small particulate active material with a particle size <10μm with conductive agent and binder at a mass ratio of 8:1:1, add solvent to make slurry, coat the surface of the porous gel current collector in step one, and dry and roll to form the bottom layer; e. Mix large-particle active materials with a particle size >15μm with conductive agents and binders at a mass ratio of 8:1:1, add solvent to make a slurry, coat it on the bottom surface, and dry and roll it to form the top layer, thus obtaining a gradient structure active material layer.

6. The preparation method according to claim 5, characterized in that, The stirring time in step a is more than 8 hours, and the heating temperature in step c is 60-120℃ for 2 hours.

7. The preparation method according to claim 5, characterized in that, The rolling pressure in steps d and e is 10 MPa, and the rolling time is 5 minutes; the thickness of the bottom coating is 30 μm, and the thickness of the top coating is 35 μm.

8. The preparation method according to claim 5, characterized in that, The adhesive is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP).

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