Multifunctional binder for positive electrode of battery as well as preparation method and application of multifunctional binder

Abstract

The invention relates to the technical field of lithium battery positive electrode materials, in particular to a battery positive electrode multifunctional binder and a preparation method and application thereof. The multifunctional binder for the positive electrode of the battery comprises a lithium salt, 2-vinyl-1, 3-dioxolame and conductive carbon, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate and lithium bis (fluorosulfonyl) imide. The battery positive electrode multifunctional binder provided by the invention has good mechanical strength and bonding strength and excellent ion / electron conduction performance, a high-load positive electrode can be prepared based on the multifunctional binder, and a lithium battery assembled by the multifunctional binder can realize high energy density and stable circulation.

Description

Technical Field

[0001] This invention relates to the field of lithium battery cathode material technology, and in particular to a multifunctional binder for battery cathodes, its preparation method, and its application. Background Technology

[0002] As the core power carrier of the new energy revolution, lithium batteries have become a key breakthrough for achieving energy structure transformation through technological innovation. In recent years, although lithium-ion batteries have achieved industrialization breakthroughs in fields such as new energy vehicles and large-scale energy storage systems, the energy density of single cells under the existing system generally hovers in the range of 250~300Wh / kg, which is difficult to meet the increasing requirements for driving range and energy density of energy storage systems.

[0003] A key technological path to improving energy density lies in breakthroughs in cathode material systems, including increasing the areal loading of the cathode active material (>30 mg / cm³). 2 The most direct and effective solution is to use fluorine-based binders. However, the widely used polyvinylidene fluoride (PVDF) binder system, due to its inherent physicochemical properties, has become a key bottleneck restricting the development of high-capacity cathodes: firstly, the insufficient bonding strength of PVDF leads to structural delamination of thick electrodes; secondly, the interfacial compatibility between the fluorine-based framework and novel high-capacity cathode materials (such as lithium-rich manganese-based and high-nickel ternary materials) is poor; and thirdly, the electronic / ionic insulation properties of PVDF exacerbate the polarization effect of thick electrodes. This contradiction is particularly prominent in the development of next-generation batteries pursuing ultra-high energy density of 500Wh / kg. Currently, there is an urgent need to develop novel multifunctional binders that combine strong interfacial adhesion with excellent ion / electron conduction, breaking through the barriers to the engineering application of high-capacity electrodes and promoting a leap in the energy density of lithium batteries. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a multifunctional binder for battery cathodes, its preparation method, and its applications. The multifunctional binder for battery cathodes provided by this invention possesses excellent mechanical and adhesive strength, improving the adhesion between thick electrodes and current collectors and reducing the likelihood of peeling. Furthermore, this binder exhibits superior ion-conducting / electron-conducting properties, resolving issues such as discontinuous and slow lithium-ion transport within thick electrodes. Based on this multifunctional binder, a battery cathode with a loading capacity of not less than 50 mg·cm³ can be prepared. -2 The positive electrode of the lithium battery can achieve high energy density and stable cycling.

[0005] In a first aspect, the multifunctional binder for battery cathodes provided by this invention comprises a lithium salt, 2-vinyl-1,3-dioxolane (VDOL), and conductive carbon; the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), and lithium bis(fluorosulfonyl)imide (LiFSI). The multifunctional binder for battery cathodes provided by this invention is produced by in-situ polymerization of 2-vinyl-1,3-dioxolane (VDOL) monomers and the addition of lithium salt and conductive carbon. Through the interaction of lithium salt, VDOL, and conductive carbon, the binder significantly improves the lithium-ion transport rate, exhibiting excellent mechanical strength, bonding strength, and superior ion / electron conduction. Based on this binder, high-capacity cathodes can be prepared, and the assembled lithium batteries can achieve high energy density and stable cycling.

[0006] Preferably, the lithium salt is a first lithium salt and a second lithium salt in a mass ratio of 10~50:10~50; the first lithium salt is lithium hexafluorophosphate, and the second lithium salt is selected from one or more of lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), lithium difluorooxalateborate, and lithium bis(fluorosulfonyl)imide. By using a certain ratio of the first lithium salt (LiPF6) to interact with the second lithium salt, high ion conductivity and interfacial stability are complementary, further optimizing the ion transport efficiency and interfacial compatibility of the binder.

[0007] Preferably, the mass ratio of lithium hexafluorophosphate to conductive carbon is 10~20:10~20; the mass ratio of the second lithium salt to conductive carbon is also 10~20:10~20. Optimizing the mass ratio of lithium hexafluorophosphate, the second lithium salt, and conductive carbon to form a synergistic network helps reduce the polarization effect of thick electrodes and further improves the ion / electron conduction effect of high-load cathode sheets.

[0008] Preferably, the mass ratio of lithium hexafluorophosphate, 2-vinyl-1,3-dioxolane, the second lithium salt, and conductive carbon is 10~50:10~80:10~50:10~50. Through the synergistic effect of the specific proportions of lithium salts, VDOL, and conductive carbon, the multifunctional binder for the battery cathode possesses excellent mechanical strength, bonding performance, and ion / electron conduction capabilities, enabling better high-load thick cathodes (>50 mg / cm³). 2 The preparation of ) can improve battery energy density and cycle stability.

[0009] Further preferably, the mass ratio of lithium hexafluorophosphate, 2-vinyl-1,3-dioxolane, the second lithium salt, and conductive carbon is 10~20:60~80:10~20:10~20, more preferably 10:70:10:10. The preferred ratio yields the best results.

[0010] Further preferably, the conductive carbon is selected from one or more of Ketjen black, super P, VGCF, CNTs, and graphene. The selection of conductive carbons such as Ketjen black and VGCF is beneficial for further improving the electron transport efficiency of the thick electrode.

[0011] Secondly, this invention provides a method for preparing the aforementioned multifunctional binder for battery cathodes, comprising mixing and stirring lithium salt, 2-vinyl-1,3-dioxolane, and conductive carbon, allowing it to stand, and then drying to obtain the multifunctional binder for battery cathodes; preferably, the method comprises mixing and stirring lithium hexafluorophosphate and 2-vinyl-1,3-dioxolane, adding a second lithium salt and conductive carbon, stirring, allowing it to stand, and then drying. This invention features a simple process. Through the mixing, stirring, and drying of the above-mentioned raw materials, it ensures better interaction and dispersion of the components, promotes the in-situ polymerization of VDOL to form a continuous polymer skeleton, and improves the overall performance of the multifunctional binder for battery cathodes.

[0012] Preferably, the stirring time is 2 to 60 minutes; and / or the standing time is 1 to 24 hours; and / or the drying temperature is 60 to 160°C.

[0013] Further preferred methods include mixing lithium hexafluorophosphate and 2-vinyl-1,3-dioxolane and stirring for 2 to 20 minutes, adding a second lithium salt and conductive carbon, stirring for 2 to 40 minutes, allowing it to stand, and then drying.

[0014] Further optimization involves mixing lithium hexafluorophosphate and 2-vinyl-1,3-dioxolane and stirring for 10-20 minutes, adding a second lithium salt and conductive carbon, stirring for 20-40 minutes, then allowing it to stand for 1-12 hours, and finally vacuum drying at 60-80°C for 6-12 hours. The optimized process yields better results.

[0015] Thirdly, the present invention provides the application of the above-mentioned multifunctional battery cathode binder or the multifunctional battery cathode binder obtained by the above preparation method in the cathode of a lithium battery.

[0016] Fourthly, the present invention provides a lithium battery positive electrode, which includes the above-mentioned multifunctional battery positive electrode binder or the multifunctional battery positive electrode binder obtained by the above-mentioned preparation method.

[0017] The multifunctional binder for battery cathodes provided by this invention can achieve a loading capacity greater than 50 mg·cm³. -2 The positive electrode of a lithium battery, such as 60 mg·cm⁻¹ -2 70mg·cm -2 80mg·cm -2 90mg·cm -2 100mg·cm -2 wait.

[0018] Preferably, the preparation of the lithium battery cathode includes: mixing a multifunctional binder, a high-nickel ternary active material (such as NCM811) and a conductive additive (such as Super P) with an organic solvent (such as NMP) in a ratio (such as a mass ratio of 5~10:80~90:5~10), then coating the mixture onto a current collector (such as carbon-coated aluminum foil), drying it under vacuum, and then cutting it.

[0019] Fifthly, the present invention also provides a lithium battery comprising the above-described lithium battery positive electrode.

[0020] The beneficial effects of this invention are at least as follows: This invention possesses excellent comprehensive properties such as bonding performance, high ionic / electronic conductivity, and interfacial stability. The binder prepared by VDOL in-situ polymerization enhances bonding performance through the interaction of CH groups, making it suitable for high-load, thick electrodes where the electrode sheet is less prone to peeling and delamination. Simultaneously, the rational ratio of raw materials, including lithium salt and conductive carbon, increases the number of groups available for lithium ion bonding, significantly improving ionic conductivity. The added conductive carbon further promotes the ion / electron transport performance of the high-load, thick electrode. The bonding of this binder with the cathode material improves the mechanical strength of the electrode sheet, effectively resisting lithium dendrite penetration and enhancing battery safety, while also effectively improving the interfacial contact between the electrolyte and the electrode, reducing interfacial transport impedance, and increasing the efficiency of lithium ion transport at the interface. Lithium batteries made with this multifunctional cathode binder possessing the above-mentioned excellent properties exhibit superior energy density and cycle stability. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The images show the infrared (left) and thermogravimetric (right) images of the multifunctional binder and the monomer VDOL on the positive electrode of the battery in this embodiment of the invention.

[0023] Figure 2 The images show the peel strength of the positive electrode sheet in Embodiment 1 and Comparative Example 1 of the present invention.

[0024] Figure 3 The diagram shows the constant current charge-discharge test results of the batteries assembled in Embodiment 1 and Comparative Example 1 of the present invention.

[0025] Figure 4 These are bending test diagrams of the positive electrode sheet in Embodiment 2 and Comparative Example 2 of the present invention.

[0026] Figure 5 The images show the constant current charge-discharge test results of the positive electrode coin cells prepared in Example 2 and Comparative Example 2 of this invention.

[0027] Figure 6 The images show constant current charge-discharge test results of the high-load positive electrode coin cells prepared in Example 3 and Comparative Example 2 of this invention.

[0028] Figure 7 The figures show the constant current intermittent titration test results of the high-load positive electrode coin cells prepared in Examples 2 and 3 of this invention.

[0029] Figure 8 The electrochemical impedance spectroscopy results are shown for the high-load positive electrode coin cells prepared in Example 4 and Comparative Example 1 of this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0031] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0032] Unless otherwise specified, the techniques or conditions described in the embodiments of this invention shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Devices, instruments, reagents, etc., without specified manufacturers, are all conventional products that can be purchased through legitimate channels. All experimental reagents and raw materials involved are commercially available products, and all reagents are analytical grade products.

[0033] Example 1 This embodiment provides a multifunctional binder for battery positive electrodes, using LiPF6, VDOL, LiTFSI, and Ketjen Black as raw materials, with a mass ratio of 10:70:10:10. The specific steps of its preparation method are as follows: In a glove box, 10 mg of LiPF6 powder is added to 70 mg of 2-vinyl-1,3-dioxolane solution and stirred for 10 min. Then, 10 mg of LiTFSI powder and 10 mg of Ketjen Black are added, and the mixture is stirred for 20 min. After standing for 1 h, the mixture is dried under vacuum at 60°C for 12 h to obtain the multifunctional binder for battery positive electrodes.

[0034] The multifunctional binder for the positive electrode provided in this embodiment is mixed with NCM811 and super P in a mass ratio of 5:90:5, and NMP solvent is added. After mixing evenly, the mixture is coated onto carbon-coated aluminum foil to prepare a positive electrode sheet. The electrode sheet is vacuum dried at 80°C for 12 hours and then cut into circular pieces with a diameter of 12 mm. The pieces are then assembled into an NCM811||Li button cell (CR2032 mold) in a glove box for subsequent testing.

[0035] Example 2 The preparation method of this embodiment is the same as that of Example 1, except that LiTFSI powder is replaced with LiFSI, Ketjen Black is replaced with VGCF, and the mass ratio of battery positive electrode multifunctional binder, NCM811 and super P is changed from 5:90:5 to 10:80:10.

[0036] Example 3 The raw materials are LiPF6, VDOL, and VGCF in a mass ratio of 10:70:20. The specific steps of the preparation method are as follows: In a glove box, 10 mg of LiPF6 powder is added to 70 mg of 2-vinyl-1,3-dioxolane solution and stirred for 10 min. Then, 20 mg of VGCF is added and stirred for 30 min. After standing for 1 h, the mixture is dried under vacuum at 60°C for 12 h to obtain the multifunctional binder for the battery positive electrode. The preparation method of the positive electrode sheet is the same as in Example 2.

[0037] Example 4 This embodiment provides a multifunctional binder for battery positive electrodes, using LiPF6, VDOL, LiBOB, and graphene as raw materials, with a mass ratio of LiPF6, VDOL, LiBOB, and graphene of 10:65:15:5. The specific preparation steps are as follows: In a glove box, 10 mg of LiPF6 powder is added to 65 mg of 2-vinyl-1,3-dioxolane solution and stirred for 10 min. Then, 15 mg of LiBOB powder and 5 mg of graphene are added, stirred for 10 min, allowed to stand for 1 h, and dried under vacuum at 60°C for 12 h to obtain the multifunctional binder for battery positive electrodes. The preparation method for the positive electrode sheet is the same as in Example 1.

[0038] Comparative Example 1 The method is the same as in Example 1, except that the multifunctional binder for the positive electrode of the battery in Example 1 is replaced with PVDF.

[0039] Comparative Example 2 The same method as in Example 2 is used, except that the multifunctional binder for the positive electrode of the battery in Example 2 is replaced with PVDF.

[0040] The above embodiments and comparative examples were subjected to performance tests: 1. Testing Method (1) The multifunctional binder for the positive electrode of the battery in Example 1 and the monomer VDOL were characterized by infrared and thermogravimetric analysis.

[0041] (2) Peel strength performance test was performed on the positive electrode sheets of Example 1 and Comparative Example 1.

[0042] (3) The positive electrode sheets of Example 1 and Comparative Example 1 were subjected to bending tests. Each electrode sheet was bent 50 times and the crack condition was observed.

[0043] (4) The button cells prepared by Example 1 and Comparative Example 1 were subjected to constant current charge-discharge test at a rate of 1C (1C=200mAh / g) in the Newway test software.

[0044] (5) The positive electrode coin cells prepared by Example 2 and Comparative Example 2 were subjected to constant current charge-discharge test at a rate of 0.1C (1C=200mAh / g) in the Newway test software.

[0045] (6) The button cells prepared in Examples 3 and 2 were subjected to constant current charge-discharge tests at a rate of 1C (1C=200mAh / g) in the Xinwei test software.

[0046] (7) The button cells prepared by Example 3 and Comparative Example 2 were subjected to constant current intermittent titration tests in the Xinwei test software.

[0047] (8) The coin cells prepared by Example 4 and Comparative Example 1 were subjected to impedance testing in the Newway test software.

[0048] 2. Test Results like Figure 1 As shown, a comparison was made before and after the preparation of the multifunctional binder for the battery cathode in Example 1. In the Fourier transform infrared (FT-IR) spectrum, the VDOL monomer was at 3083 cm⁻¹. -1 The peak at 1729 cm⁻¹ corresponds to the =CH in the vinyl group; this peak disappears after polymerization, indicating that double bond breaking has occurred. Furthermore, the peak at 1729 cm⁻¹... -1The new peak at the point corresponds to C=O, indicating that a large number of C=O groups were introduced into the long chain of the multifunctional binder for the battery cathode after polymerization; the thermogravimetric (TG) curve results show that the decomposition temperature of the multifunctional binder for the battery cathode is about 220℃, which is much higher than the initial decomposition temperature of VDOL (79℃).

[0049] like Figure 2 As shown, the positive electrode sheet obtained in Example 1 has better peel strength, proving that the active material is more tightly bonded to the current collector and is less prone to delamination.

[0050] like Figure 3 As shown, the NCM811||Li coin cell assembled in Example 1 can stably cycle 100 times at 1C rate with a capacity retention of 74.9% and an initial discharge capacity of 179 mAh / g. In contrast, the NCM811||Li coin cell assembled in Comparative Example 1 exhibits significant capacity decay, with a capacity retention of only 63.7% after 100 cycles and an initial discharge capacity of 173 mAh / g. This demonstrates that the multifunctional binder on the positive electrode of this invention can promote ion / electron transport and contribute to cycle stability.

[0051] like Figure 4 As shown, Example 2 can prepare a loading capacity of 60 mg·cm³. -2 The positive electrode sheet prepared in Comparative Example 2 is not easily cracked when bent, while the high-load electrode sheet prepared in Comparative Example 2 is easily cracked.

[0052] like Figure 5 As shown, the first-cycle discharge specific capacity of Example 2 at 0.1C rate is 205mAh / g, while the first-cycle discharge specific capacity of Comparative Example 2 is only 200mAh / g. According to the calculation, the energy density of the soft-pack battery assembled with the positive electrode sheet of Example 2 can reach 450Wh / kg, which shows the promoting effect of the multifunctional binder of the positive electrode of the present invention on energy density.

[0053] like Figure 6 As shown, the electrode loading in both Example 3 and Comparative Example 2 was 40 mg / cm³. 2 Around 0.5C, in cycling, Example 3 maintained a capacity retention of 93.0% after 50 cycles, while Comparative Example 2 maintained a capacity retention of only 73.9% after 50 cycles. Although Example 3 did not have a second lithium salt compared to Example 2, the binder performance of Example 3 was still better than that of the PVDF binder in Comparative Example 2. The excellent performance of the multifunctional binder for the positive electrode of the present invention in high-load thick electrodes can promote ion / electron transport and contribute to cycle stability.

[0054] like Figure 7 As shown, the coin cells assembled in Examples 3 and 2 were subjected to constant current intermittent titration tests. The results showed that the ion diffusion coefficient of Example 2 was greater, indicating that the addition of the second lithium salt promoted ion transport.

[0055] like Figure 8 As shown, the coin cells assembled in Example 4 and Comparative Example 1 were subjected to electrochemical impedance spectroscopy. The results showed that Example 4 had a lower impedance, indicating that the multifunctional binder can accelerate charge transfer on the electrode surface and result in higher electrode reactivity.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-functional binder for a battery cathode, characterized by comprising: The lithium salt, the 2-vinyl-1,3-dioxolane and the conductive carbon; the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bisfluorosulfonylimide.

2. The battery cathode multifunctional binder of claim 1, wherein, The lithium salt is a first lithium salt and a second lithium salt with a mass ratio of 10-50:10-50; the first lithium salt is lithium hexafluorophosphate, and the second lithium salt is selected from one or more of lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bisfluorosulfonylimide.

3. The battery cathode multifunctional binder of claim 2, wherein, The mass ratio of the lithium hexafluorophosphate and the conductive carbon is 10-20:10-20; the mass ratio of the second lithium salt and the conductive carbon is 10-20:10-20.

4. The battery cathode multifunctional binder of claim 3, wherein, The mass ratio of the lithium hexafluorophosphate, the 2-vinyl-1,3-dioxolane, the second lithium salt and the conductive carbon is 10-50:10-80:10-50:10-50.

5. The multi-functional binder for battery cathode according to any one of claims 1 to 4, characterized by, The conductive carbon is selected from one or more of Ketjen black, super P, VGCF, CNTs, and graphene.

6. The method of producing the multifunctional binder for the positive electrode of the battery according to any one of claims 1 to 5, characterized by, The method comprises mixing, stirring, standing and drying a lithium salt, a 2-vinyl-1,3-dioxolane and a conductive carbon to obtain a battery positive electrode multifunctional binder.

7. The production method according to claim 6, characterized by, The method comprises mixing and stirring lithium hexafluorophosphate and 2-vinyl-1,3-dioxolane, adding a second lithium salt and a conductive carbon, stirring, standing, and then drying; and / or, the stirring time is 2-60 min; and / or, the standing time is 1-24 h; and / or, the drying temperature is 60-160℃.

8. Use of the battery positive electrode multifunctional binder of any one of claims 1-5 or the battery positive electrode multifunctional binder prepared by the method of claim 6 or 7 in a lithium battery positive electrode.

9. A lithium battery cathode, characterized by, The method comprises using the battery positive electrode multifunctional binder of any one of claims 1-5 or the battery positive electrode multifunctional binder prepared by the method of claim 6 or 7.

10. A lithium battery, characterized by, The lithium battery positive electrode comprises the battery positive electrode multifunctional binder of any one of claims 1-5 or the battery positive electrode multifunctional binder prepared by the method of claim 6 or 7. The lithium battery positive electrode comprises the battery positive electrode multifunctional binder of any one of claims 1-5 or the battery positive electrode multifunctional binder prepared by the method of claim 6 or 7.

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