Nano cross-linked vulcanized polyacrylonitrile negative electrode material and battery application thereof

Abstract

The invention relates to a nano cross-linked vulcanized polyacrylonitrile negative electrode material and a battery application thereof. The preparation method of the nano cross-linked vulcanized polyacrylonitrile negative electrode material comprises the following steps: (1) mixing acrylonitrile, an initiator and a solvent, heating to react, and polymerizing acrylonitrile in situ to form nano polyacrylonitrile particles; (2) mixing the nano polyacrylonitrile particles obtained in the step (1) with a cross-linking agent to generate a cross-linking reaction to obtain nano cross-linked polyacrylonitrile particles; and (3) mixing and calcining the nano cross-linked polyacrylonitrile particles obtained in the step (2) and sulfur powder to obtain the nano cross-linked vulcanized polyacrylonitrile negative electrode material. The nanometer cross-linked sulfurized polyacrylonitrile negative electrode is wide in raw material source, low in preparation cost, high in specific capacity, excellent in rate capability, good in cycling stability, compatible with carbonic ester electrolyte commonly used by a lithium ion battery and the like; when the positive electrode material is matched with a lithium-rich manganese-based solid solution positive electrode material, the whole battery shows excellent energy / power density performance.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a nano-crosslinked sulfurized polyacrylonitrile negative electrode material and battery application thereof. Background Art

[0002] With the rapid development of electric vehicles, 3C consumer electronics, and electrochemical energy storage, people have put forward higher requirements for lithium-ion batteries, namely that batteries should not only have high energy density, but also high power density characteristics (i.e., fast charge and discharge capabilities). Currently, commercial lithium-ion battery negative electrode materials mainly use carbon materials such as graphite. However, the rapid charge and discharge capabilities of carbon materials are limited, which makes it difficult to further improve the power density of lithium-ion batteries.

[0003] Compared with carbon materials, lithium titanate (Li4Ti5O 12 Lithium titanate (LTO) anode materials offer significant advantages in rapid charge and discharge performance. This is due to the inherent three-dimensional lithium ion diffusion channels of LTO, which facilitate rapid lithium ion transport during charge and discharge reactions and provide high power density. Furthermore, LTO is a lithium insertion material with near-zero volume change, maintaining structural stability even during rapid charge and discharge, resulting in excellent negative electrode cycling performance. Therefore, LTO anodes have a definite market application in both electric vehicles and large-scale energy storage.

[0004] However, lithium titanate anode materials also have significant drawbacks. Their structure contains both lithium and titanium, two precious metals, making them expensive (~90,000 yuan / ton). The theoretical specific capacity of a lithium titanate anode is only 175 mAh / g, far lower than the capacity of a graphite anode (374 mAh / g). When paired with a cathode material (such as a layered oxide cathode), the energy density of a full lithium-ion battery is only 50-75 Wh / kg. In summary, achieving both high energy and high power density performance simultaneously based on existing lithium-ion battery technology remains a significant challenge.

[0005] Nano-sulfurized polyacrylonitrile is a new type of rate-sensitive negative electrode material. Compared to traditional rate-sensitive lithium titanate negative electrodes, the raw materials for sulfurized polyacrylonitrile are solely sulfur and acrylonitrile. It is composed of small molecules of sulfur chemically bonded to a polymer backbone. During the electrochemical conversion process, it offers a low voltage platform, high capacity, and strong rapid charge and discharge capabilities. It does not contain any precious metal elements and is inexpensive (≤30,000 yuan / ton). However, the nanoparticles often have excessive contact interfaces, which increases the electron transfer impedance on the negative electrode side and generates significant heat during rapid charge and discharge. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a nano-cross-linked sulfurized polyacrylonitrile negative electrode material and its battery application. The nano-cross-linked sulfurized polyacrylonitrile negative electrode raw material has a wide range of sources and low preparation cost. It has the advantages of high specific capacity, excellent rate performance, good cycle stability, and compatibility with carbonate electrolytes commonly used in lithium-ion batteries. When combined with a lithium-rich manganese-based solid solution positive electrode material, the full battery exhibits excellent energy / power density performance.

[0007] The technical solutions provided by the present invention are as follows:

[0008] The present invention discloses a method for preparing a nano-cross-linked sulfurized polyacrylonitrile negative electrode material, comprising the following steps:

[0009] (1) acrylonitrile, an initiator, and a solvent are mixed and heated to react, and acrylonitrile is in situ polymerized to form nano-polyacrylonitrile particles;

[0010] (2) mixing the nano-polyacrylonitrile particles obtained in step (1) with a cross-linking agent to undergo a cross-linking reaction to obtain nano-cross-linked polyacrylonitrile particles;

[0011] (3) The nano-cross-linked polyacrylonitrile particles obtained in step (2) are mixed with sulfur powder and calcined to obtain a nano-cross-linked sulfurized polyacrylonitrile negative electrode material.

[0012] As a preferred technical solution, in step (1), the initiator is one or more of ammonium persulfate, sodium thiosulfate, azobisisobutyronitrile, and azobisisoheptylonitrile; the solvent is one or more of dimethyl sulfoxide, acetone, and water; the volume ratio of acrylonitrile to solvent is 1:1 to 10; the amount of initiator is 0.1 to 1 mg / mL; and the polymerization temperature is 30 to 100°C.

[0013] As a preferred technical solution, in step (2), the cross-linking agent is one or more of hydrazine hydrate, dicumyl peroxide, and benzoyl peroxide.

[0014] As a preferred technical solution, in step (3), the mixing ratio of nano-cross-linked polyacrylonitrile particles and sulfur powder is 1:0.5-10, the calcination temperature is 100-500° C., and the calcination time is 1-20 hours.

[0015] The invention also discloses a nano-cross-linked sulfurized polyacrylonitrile negative electrode material, which is prepared by adopting the preparation method.

[0016] The present invention also discloses a lithium ion battery, the preparation method of which is as follows:

[0017] The nano-cross-linked sulfurized polyacrylonitrile negative electrode material is mixed with a conductive agent, a binder, and a solvent to prepare a slurry, and then coated on an electrode to obtain a negative electrode;

[0018] A lithium-rich manganese-based solid solution positive electrode material is mixed with a conductive agent, a binder, and a solvent to prepare a slurry, which is then coated on an electrode to obtain a positive electrode. The chemical formula of the lithium-rich manganese-based solid solution is xLi2MnO3·(1-x)LiMO2, where M is a mixture of one or more metals selected from Ni, Co, and Mn, and 0.3≤x≤0.7.

[0019] Assemble the lithium-ion battery by combining the positive electrode sheet, separator, electrolyte and negative electrode sheet.

[0020] The beneficial effects of the present invention are:

[0021] The nano-sulfurized polyacrylonitrile negative electrode material of the present invention is widely available, has low production costs, and exhibits performance advantages such as high specific capacity, excellent rate performance, and good cycle stability. The present invention further crosslinks the nano-sulfurized polyacrylonitrile, resulting in a "neural network-like" structure. This facilitates rapid electron conduction, improving the rate characteristics and safety properties of the negative electrode. The network structure also enhances the structural stability of the material, inhibits volume expansion, and improves the material's cycle stability.

[0022] The present invention further discovered that when a nano-cross-linked sulfurized polyacrylonitrile negative electrode is paired with a lithium-rich manganese-based solid solution positive electrode, the assembled battery has an energy density of up to 263Wh / kg (calculated based on the active materials of the positive and negative electrodes), and a full battery power density of up to 2680W / kg at a 10C charge and discharge rate, which is much higher than the energy density and power density of existing lithium titanate batteries. The reason may be that during the first cycle of charging, the lithium-rich manganese-based positive electrode will irreversibly generate lithium oxide and dissolve; at this time, the excess lithium in the electrolyte can be used to activate the polyacrylonitrile negative electrode and form a stable SEI film structure, ensuring the stability of the negative electrode structure and extending the cycle life. In comparison, the traditional lithium titanate negative electrode cannot form a stable SEI film structure with the help of excess lithium, and is accompanied by severe gas production during the charge and discharge process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention provides the following drawings for illustration:

[0024] Figure 1 This is the SEM image of the nano-cross-linked vulcanized polyacrylonitrile in Example 1.

[0025] Figure 2 This is the charge and discharge curve of the (-) nano-cross-linked sulfurized polyacrylonitrile||lithium-rich manganese-based solid solution (+) full battery in Example 1.

[0026] Figure 3 This is the charge and discharge curve of the (-) lithium titanate|| lithium-rich manganese-based solid solution (+) full battery in Comparative Example 1.

[0027] Figure 4 This is the rate performance diagram of the (-) nano-cross-linked sulfurized polyacrylonitrile||lithium-rich manganese-based solid solution (+) full battery in Example 1.

[0028] Figure 5 This is the rate performance diagram of the (-) lithium titanate || lithium-rich manganese-based solid solution (+) full battery in Comparative Example 1.

[0029] Figure 6 This is a comparison chart of the long cycle curves of the two full batteries in Example 1 / Comparative Example 1. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention will be described in detail below in conjunction with the embodiments. The described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment provides a lithium-ion battery based on a nano-cross-linked sulfurized polyacrylonitrile negative electrode material, comprising the following steps:

[0033] (1) Acrylonitrile, azobisisobutyronitrile, and dimethyl sulfoxide were mixed and heated for reaction. The volume ratio of acrylonitrile to dimethyl sulfoxide was 1:10, the amount of azobisisobutyronitrile was 0.5 mg / mL, and the polymerization temperature was 70°C. Acrylonitrile was in situ polymerized to form nano-polyacrylonitrile particles.

[0034] (2) mixing the nano-polyacrylonitrile particles obtained in step (1) with hydrazine hydrate to undergo a cross-linking reaction to obtain nano-cross-linked polyacrylonitrile particles;

[0035] (3) mixing the nano-cross-linked polyacrylonitrile particles obtained in step (2) with sulfur powder in a ratio of 1:4, and then calcining at a temperature of 350° C. for 6 h to obtain a nano-cross-linked sulfurized polyacrylonitrile negative electrode material;

[0036] (4) The nano-cross-linked sulfide polyacrylonitrile negative electrode material obtained in step (3) is uniformly mixed with acetylene black and sodium carboxymethyl cellulose in a ratio of 8:1:1, and then an appropriate amount of deionized water is added and stirred to obtain a negative electrode active material slurry, which is then coated on the electrode to obtain a negative electrode sheet;

[0037] The lithium-rich manganese-based solid solution positive electrode material is uniformly mixed with acetylene black and polyvinylidene fluoride at a ratio of 9:0.5:0.5, the chemical formula of the lithium-rich manganese-based solid solution is 0.5Li2MnO3·0.5LiMO2, then an appropriate amount of N-methyl pyrrolidone is added and stirred uniformly to obtain a positive electrode active material slurry, and then coated on the pole piece to obtain a positive electrode pole piece;

[0038] The above pole piece is placed in a vacuum oven and baked at 120°C for 12h, and the vacuum is continuously drawn, and the water content of the positive and negative pole pieces is controlled to be <200ppm;

[0039] (5) After the baked pole piece is cut, the battery is assembled in the order of positive pole piece, separator, electrolyte and negative pole piece.

[0040] Comparative Example 1

[0041] (1) The lithium titanate negative electrode material is uniformly mixed with acetylene black and sodium carboxymethyl cellulose at a ratio of 8:1:1, then an appropriate amount of deionized water is added and stirred uniformly to obtain a negative electrode active material slurry, and then coated on the pole piece to obtain a negative electrode pole piece;

[0042] The lithium-rich manganese-based solid solution positive electrode material is uniformly mixed with acetylene black and polyvinylidene fluoride at a ratio of 9:0.5:0.5, the chemical formula of the lithium-rich manganese-based solid solution is 0.5Li2MnO3·0.5LiMO2, then an appropriate amount of N-methyl pyrrolidone is added and stirred uniformly to obtain a positive electrode active material slurry, and then coated on the pole piece to obtain a positive electrode pole piece;

[0043] The above pole piece is placed in a vacuum oven and baked at 120°C for 12h, and the vacuum is continuously drawn, and the water content of the positive and negative pole pieces is controlled to be <200ppm;

[0044] (2) After the baked pole piece is cut, the battery is assembled in the order of positive pole piece, separator, electrolyte and negative pole piece.

[0045] Figure 1 For the SEM picture of the nano-crosslinked sulfided polyacrylonitrile in Example 1, it can be found that after crosslinking, there is a crosslinking network that is intertwined with each other, and this crosslinked and intertwined network structure is in a "neural network-like" structure, which helps the rapid conduction of electrons, improves the rate characteristics and safety properties of the negative electrode side, and at the same time, the network structure also enhances the structural stability of the material, inhibits volume expansion, and improves the cycle stability of the material.

[0046] Figure 2Figure 2 shows the charge and discharge curves of the full cell (-) nano-cross-linked sulfide polyacrylonitrile || lithium-rich manganese-based solid solution (+) in Example 1. The test results show that the discharge specific capacity of the full cell in Example 1 at current densities of 0.2, 0.5, 1C, 2C, 5C, 6C, and 10C is 332.5, 320.9, 304.6, 277.7, 233.1, 220.1, and 192.3 mAh / g, respectively (calculated based on the total mass of the positive and negative electrode active materials).

[0047] Figure 3 The charge and discharge curves for the (-) lithium titanate || lithium-rich manganese-based solid solution (+) full cell in Comparative Example 1 are shown. Test results show that the discharge specific capacities of the full cell in Comparative Example 1 at current densities of 0.2, 0.5, 1C, 2C, 5C, 6C, and 10C are 97.2, 90.2, 82.1, 70.8, 50.7, 46.6, and 36.2 mAh / g, respectively (calculated based on the total mass of the positive and negative electrode active materials). These results confirm that the full cell assembled in Example 1, using a lithium-rich manganese-based positive electrode material as the positive electrode and nano-cross-linked sulfurized polyacrylonitrile particles as the negative electrode, exhibits excellent charge and discharge performance.

[0048] Figure 4 This is a rate performance diagram for the full cell (-) nano-cross-linked sulfide polyacrylonitrile || lithium-rich manganese-based solid solution (+) in Example 1. The test results show that the full cell of Example 1 has excellent rate performance, high energy density, and high power density. At a charge and discharge current density of 0.2C, its energy density is 263Wh / kg (calculated based on the positive and negative electrode active materials), and at a charge and discharge current density of 10C, its power density is 2680W / kg. The data results are shown in the following table:

[0049]

[0050] Figure 5 This is the rate performance diagram of the full battery (-) lithium titanate || lithium-rich manganese-based solid solution (+) in Comparative Example 1. The data results are shown in the following table:

[0051]

[0052] The energy density of a full battery with nano-cross-linked sulfurized polyacrylonitrile as the negative electrode is higher than that of a lithium titanate battery (204Wh / kg) at a charge and discharge current density of 0.2C. Furthermore, its power density (2680W / kg) at a charge and discharge current density of 10C is also higher than that of a full lithium titanate battery (1740W / kg) at a charge and discharge current density of 10C. Therefore, a full battery assembled with a lithium-rich manganese-based solid solution as the positive electrode and nano-cross-linked sulfurized polyacrylonitrile particles as the negative electrode has a high energy density and excellent power density.

[0053] Figure 6 The long cycle curves of the two full cells in Example 1 / Comparative Example 1 are compared. It can be found that the full cell prepared in Example 1 has a discharge specific capacity of 276.2 mAh / g after 200 cycles at a current density of 1C, a capacity retention of 91%, and a capacity decay of only 0.00047% per cycle, showing good cycle stability.

[0054] The above examples are only used to illustrate the preferred embodiments of the present application, but not to limit the concept and protection scope of the present application. Any modification, equivalent replacement and improvement within the concept and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing a nano-cross-linked sulfurized polyacrylonitrile negative electrode material, characterized by: The following steps are involved: (1) acrylonitrile, an initiator, and a solvent are mixed and heated to react, and acrylonitrile is in situ polymerized to form nano-polyacrylonitrile particles; (2) mixing the nano-polyacrylonitrile particles obtained in step (1) with a cross-linking agent to undergo a cross-linking reaction to obtain nano-cross-linked polyacrylonitrile particles; (3) mixing the nano-cross-linked polyacrylonitrile particles obtained in step (2) with sulfur powder and calcining them to obtain a nano-cross-linked sulfurized polyacrylonitrile negative electrode material.

2. The method for preparing a nano-cross-linked sulfurized polyacrylonitrile negative electrode material according to claim 1, characterized in that: In the step (1), the initiator is one or more of ammonium persulfate, sodium thiosulfate, azobisisobutyronitrile, and azobisisoheptylonitrile; the solvent is one or more of dimethyl sulfoxide, acetone, and water; the volume ratio of acrylonitrile to the solvent is 1:1 to 10; the amount of the initiator is 0.1 to 1 mg / mL; and the polymerization temperature is 30 to 100°C.

3. The method for preparing a nano-cross-linked sulfurized polyacrylonitrile negative electrode material according to claim 1, characterized in that: In the step (2), the cross-linking agent is one or more of hydrazine hydrate, dicumyl peroxide, and benzoyl peroxide.

4. The method for preparing a nano-cross-linked sulfurized polyacrylonitrile negative electrode material according to claim 1, characterized in that: In the step (3), the mixing ratio of the nano-cross-linked polyacrylonitrile particles and the sulfur powder is 1:0.5-10, the calcination temperature is 100-500° C., and the calcination time is 1-20 hours.

5. A nano-cross-linked sulfurized polyacrylonitrile negative electrode material, characterized by: The preparation method is described in any one of claims 1 to 4.

6. A lithium-ion battery, characterized in that: Its preparation method is: The nano-cross-linked sulfurized polyacrylonitrile negative electrode material according to claim 5 is mixed with a conductive agent, a binder, and a solvent to prepare a slurry, and then coated on an electrode to obtain a negative electrode; A lithium-rich manganese-based solid solution positive electrode material is mixed with a conductive agent, a binder, and a solvent to prepare a slurry, which is then coated on an electrode to obtain a positive electrode. The chemical formula of the lithium-rich manganese-based solid solution is xLi2MnO3·(1-x)LiMO2, where M is a mixture of one or more metals selected from Ni, Co, and Mn, and 0.3≤x≤0.

7. Assemble the lithium-ion battery by combining the positive electrode sheet, separator, electrolyte and negative electrode sheet.

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