High-conductivity conjugated polymer modified positive electrode material, preparation method and lithium ion battery

Abstract

The invention discloses a high-conductivity conjugated polymer modified positive electrode material, a preparation method and a lithium ion battery. The high-conductivity conjugated polymer modified positive electrode material comprises a positive electrode active material and a high-conductivity conjugated polymer for compounding or coating the positive electrode active material, wherein the high-conductivity conjugated polymer is a polymer containing a donor-acceptor conjugated structure, a donor comprises phenazine and / or a phenazine derivative, and an acceptor comprises thianthrene and / or a thianthrene derivative. The high-conductivity conjugated polymer with a donor-acceptor conjugated structure is introduced into an inorganic positive electrode material system of a conventional lithium ion battery, so that the rate capability, the power density and the energy density of the battery are improved, and the output voltage polarization is reduced. In addition, the high-conductivity conjugated polymer can also improve the cycling stability of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a highly conductive conjugated polymer modified positive electrode material, a preparation method and a lithium ion battery. Background Art

[0002] With technological advancements, high-power lithium-ion batteries are increasingly being used in fields such as electric vehicles, mechanical equipment, drones, and aerospace. These applications require batteries capable of high-speed discharge, long-term continuous output, and instantaneous high-rate discharge. However, optimizing internal ion / electron transport and reducing output voltage polarization while balancing battery energy density and safety remain key challenges for high-power batteries.

[0003] The power density of lithium-ion batteries (LIBs) primarily depends on the ion and electron transport of the positive and negative electrode materials. Current strategies for the design and development of high-power batteries include: improving the ion / electron conductivity of electrodes and reducing battery internal resistance through nanosizing, constructing ion / electron channel networks, or gradient design; and improving the lithium ion transport kinetics between the electrolyte bulk and the solid electrolyte interface membrane by manipulating electrolyte solvents, lithium salts, or additive components. However, the high surface area of ​​​​nanostructured electrode materials can exacerbate side reactions between the electrode material and the electrolyte; constructing ion / electron channel networks increases the porosity of inactive materials or electrodes, reducing the battery's energy density; and high-kinetic electrolytes are constrained by the balance between electrochemical window and thermal stability, making it difficult for a single electrolyte component to simultaneously meet these requirements. In addition to these strategies, surface coating or direct composite coating of electrode materials can effectively enhance the kinetic performance of LIB electrodes. Carbon coating is generally considered the most effective method for improving the kinetic performance of electrode materials. However, as an inactive material, carbon lacks a structure for ion insertion / extraction, which reduces the overall energy density of the battery. Furthermore, the addition of carbon does not improve the ion transport properties of the electrode active material. When compounding with other electrochemically active electrode materials, it is necessary to comprehensively consider the reaction potential ranges of both.

[0004] Therefore, designing new high-kinetic electrode materials is of great significance for developing battery technologies that meet future high-power discharge requirements. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies and propose a highly conductive conjugated polymer modified positive electrode material, a preparation method and a lithium ion battery to solve the technical problem of excessively high output voltage polarization of high power batteries in the prior art.

[0006] In a first aspect, the present application provides a high-conductivity conjugated polymer modified positive electrode material, which comprises a positive electrode active material and a high-conductivity conjugated polymer that is compounded or coated on the positive electrode active material; wherein the high-conductivity conjugated polymer is a polymer containing a donor-acceptor conjugated structure, and the donor comprises phenazine and / or a phenazine derivative, and the acceptor comprises thianthrene and / or a thianthrene derivative.

[0007] In a second aspect, the present application provides a preparation method of a high-conductivity conjugated polymer modified positive electrode material, which comprises the following steps: providing a positive electrode active material and a high-conductivity conjugated polymer or a precursor monomer for preparing the high-conductivity conjugated polymer; modifying the positive electrode active material by using the high-conductivity conjugated polymer or the precursor monomer through direct compounding or in-situ polymerization coating to obtain the high-conductivity conjugated polymer modified positive electrode material.

[0008] In a third aspect, the present application provides a lithium ion battery comprising the high-conductivity conjugated polymer modified positive electrode material provided in the first aspect.

[0009] Compared with the prior art, the present application has the following beneficial effects: In the conventional inorganic positive electrode material system of a lithium ion battery, the present application introduces a high-conductivity conjugated polymer with a donor-acceptor conjugated structure through direct compounding or in-situ polymerization coating technology. The conjugated structure reduces the band gap, promotes charge transfer and electron delocalization, accelerates the transfer of electrons along the polymer main chain, further improves the electronic conductivity of the inorganic material in the coating layer / compounding layer, reduces the interface charge transfer resistance, improves the reaction kinetics of the inorganic positive electrode material during charging and discharging, improves the rate performance of the battery, and reduces the output voltage polarization. At the same time, the high-conductivity conjugated polymer has the reversibility of anion intercalation / deintercalation during charging and discharging, and its excellent rate performance and reversible electrochemical activity provide a solution for realizing a battery with high power density and high energy density. In addition, the high-conductivity conjugated polymer can also act as a physical barrier to reduce the corrosion of HF on the positive electrode, stabilize the positive electrode solid electrolyte interface film, and improve the cycle stability of the material. DETAILED DESCRIPTION

[0010] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0011] In a first aspect, the present application provides a high-conductivity conjugated polymer modified positive electrode material, which comprises a positive electrode active material and a high-conductivity conjugated polymer that is compounded or coated on the positive electrode active material.

[0012] In the present invention, the conjugated structure of the highly conductive conjugated polymer with a donor-acceptor conjugated structure reduces the band gap, promotes charge transfer and electron delocalization, accelerates the transfer of electrons along the polymer main chain, further improves the electronic conductivity of the inorganic material inside the coating layer / composite layer, reduces the interfacial charge transfer resistance, improves the reaction kinetics of the inorganic positive electrode material during the charge and discharge process, and improves the rate performance of the battery. At the same time, during the charge and discharge process, the highly conductive conjugated polymer has the reversibility of anion insertion / extraction, the platform voltage is greater than 3.2V, the additional reversible capacity is conducive to improving the energy density of the battery, and the rapid reaction kinetics helps to improve the rate performance of the battery. In addition, the highly conductive conjugated polymer can also serve as a physical barrier for the positive electrode material, inhibiting the corrosion of HF on the positive electrode, reducing the dissolution of high-valent metal ions, inhibiting the activation of lattice oxygen and stabilizing the positive electrode solid electrolyte interface layer, promoting the transmission of ions at the positive electrode / electrolyte interface, and improving the crystal structure stability of the material during the cycle.

[0013] In this embodiment, the highly conductive conjugated polymer is a polymer containing a donor-acceptor conjugated structure, wherein the donor includes phenazine and / or a phenazine derivative, and the acceptor includes thianthrene and / or a thianthrene derivative.

[0014] Specifically, the donor includes at least one of 5,10-dihydrophenazine, 1-methoxy-5,10-dihydrophenazine, and 2-acetyl-5,10-dihydrophenazine.

[0015] Specifically, the acceptor includes at least one of 2,7-dibromothianthrene and 2,7-dichlorothianthrene.

[0016] In this embodiment, the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese oxide, and layered lithium-rich manganese-based materials.

[0017] In this embodiment, the molar ratio of the highly conductive conjugated polymer to the positive electrode active material is (0.01-0.1):1, including but not limited to 0.01:1, 0.03:1, 0.05:1, 0.07:1, 0.1:1, etc.

[0018] In a second aspect, the present invention provides a method for preparing a highly conductive conjugated polymer modified positive electrode material, comprising the following steps: S1. Providing a positive electrode active material and a highly conductive conjugated polymer or a precursor monomer for preparing a highly conductive conjugated polymer; S2. Modify the positive electrode active material using a highly conductive conjugated polymer or precursor monomer by direct compounding or in-situ polymerization coating to obtain a highly conductive conjugated polymer-modified positive electrode material.

[0019] In the embodiment, the step of modifying the positive electrode active material by using the precursor monomer in the in-situ polymerization coating manner comprises: The positive electrode active material, the precursor monomer, and optionally the catalyst, the organic ligand, the base, and the first solvent are uniformly mixed and in-situ polymerized to obtain the high-conductivity conjugated polymer modified positive electrode material.

[0020] The precursor monomer comprises a monomer containing a donor structure and a monomer containing an acceptor structure, and the monomer containing the donor structure comprises phenazine and / or a phenazine derivative, and the monomer containing the acceptor structure comprises thianthrene and / or a thianthrene derivative.

[0021] Specifically, the molar ratio of the monomer containing the donor structure to the monomer containing the acceptor structure is 1: (0.8-1.2), preferably 1:1.

[0022] The present application does not limit the types of catalyst, organic ligand, base, and first solvent, and a person skilled in the art can select them according to the actual situation. In some specific embodiments of the present application, the catalyst is palladium acetate, palladium nitrate, etc., the organic ligand is 2-dicyclohexylphosphine-2', 4', 6'-triisopropyl biphenyl, etc., the base is sodium tert-butoxide or potassium tert-butoxide, etc., and the first solvent is toluene or p-xylene, etc.

[0023] The present application does not limit the amount of catalyst, organic ligand, base, and first solvent, and a person skilled in the art can select them according to the actual situation. In some specific embodiments of the present application, the molar ratio of the monomer containing the donor structure to the catalyst, the organic ligand, and the base is 1: (0.1-0.2): (0.15-0.3): (2-3); and the amount ratio of the monomer containing the donor structure to the first solvent is 1 mol: (25-30) L.

[0024] In the embodiment, the temperature of the in-situ polymerization is 120-140℃, and the time of the in-situ polymerization is 36-60h.

[0025] In the embodiment, the in-situ polymerization is carried out under the condition of a protective atmosphere and stirring. The present application does not limit the type of the protective atmosphere, and a person skilled in the art can select it according to the actual situation. For example, the protective atmosphere can be argon, etc.

[0026] In the embodiment, after the in-situ polymerization reaction is completed, the method further comprises: adding a quenching agent to the reaction system to carry out a quenching reaction, and then cooling, filtering, washing, and purifying to obtain the high-conductivity conjugated polymer modified positive electrode material.

[0027] The quenching agent is bromobenzene. By adding bromobenzene, the present application can quench the above reaction and promote the dissolution of the catalyst and the ligand, which is convenient for subsequent filtration removal.

[0028] The quenching reaction is performed for 2-8 hours.

[0029] The washing is performed by using dichloromethane, methanol, tetrahydrofuran and water.

[0030] The purification is performed by uniformly dispersing the washed product into dichloromethane, filtering, and then putting it into a Soxhlet extractor, and using methanol, triethylamine, tetrahydrofuran and dichloromethane for purification, respectively.

[0031] In the embodiment, the step of modifying the positive active material by using the high-conductivity conjugated polymer through direct compounding comprises: The high-conductivity conjugated polymer and the positive active material are uniformly mixed to obtain the high-conductivity conjugated polymer modified positive material.

[0032] In the present application, the direct compounding process can be performed alone or in the wet homogenization process of the positive electrode preparation. In order to simplify the process, in some preferred embodiments of the present application, the direct compounding process is performed in the wet homogenization process of the positive electrode preparation. The specific steps comprise uniformly mixing the high-conductivity conjugated polymer, the positive active material, the conductive agent, the binder and the second solvent, and then drying to obtain the high-conductivity conjugated polymer modified positive electrode.

[0033] The present application does not limit the specific types and amounts of the conductive agent, the binder and the second solvent, and the person skilled in the art can select them according to the actual situation. In some specific embodiments of the present application, the conductive agent can be conductive carbon black or acetylene black, the binder can be vinylidene fluoride, and the second solvent can be N-methyl pyrrolidone.

[0034] In a third aspect, the present application provides a lithium ion battery comprising the high-conductivity conjugated polymer modified positive material provided by the first aspect of the present application.

[0035] Example 1 (1) Preparation of lithium cobaltate material coated with high-conductivity conjugated polymer in-situ polymerization 5,10-dihydrophenazine (1.5 mmol) and 2,7-dibromothianthrene (1.5 mmol), catalyst palladium acetate (0.15 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropyl biphenyl (0.3 mmol), sodium tert-butoxide (3.75 mmol) and lithium cobaltate (30 mmol) were added into 40 mL of p-xylene. Under argon protection, first stirred at 120°C for 24 h, then stirred at 140°C for 24 h. 0.5 mL of bromobenzene was added to the reaction mixture and stirred for another 5 h. It was cooled to room temperature, filtered to obtain the reaction product, and washed with a large amount of dichloromethane, methanol, tetrahydrofuran and water, filtered, then the obtained solid part was dispersed in dichloromethane by grinding and ultrasonic, filtered and put into a Soxhlet extractor, purified with methanol, triethylamine, tetrahydrofuran, dichloromethane respectively, and finally obtained a high-conductivity polymer in-situ polymerization coated lithium cobaltate material with phenazine-thianthrene conjugated structure. In this composite material, the molar ratio of high-conductivity conjugated polymer and lithium cobaltate material is 0.05:1.

[0036] (2) Electrode preparation, battery assembly and performance test The modified lithium cobaltate active material described above, a conductive agent (acetylene black), and a binder (polyvinylidene fluoride) were mixed uniformly in a mass ratio of 8:1:1, a solvent N-methyl pyrrolidone was added to prepare a positive electrode slurry, coated on an aluminum current collector, vacuum dried to obtain a positive electrode sheet; in an argon atmosphere glove box, a graphite negative electrode, a separator, the positive electrode described above, and a commercial ester electrolyte (1M LiPF6EC / DMC) were sequentially assembled to complete the assembly of a button cell 2032; based on a blue cell test system, 0.1C charging to 4.5V, 0.1C discharging to 3.0V, 0.1C charging to 4.5V again, then discharging to 3.0V at a rate of 25C, and observing the obtained discharge specific capacity value and discharge polarization voltage difference (25C and 0.1C difference).

[0037] Example 2 The difference between this example and example 1 is that the positive electrode material modification in this example is carried out by direct compounding. The steps are as follows: first, based on the synthesis method of example 1, no lithium cobaltate is added in the synthesis process of high-conductivity conjugated polymer with phenazine-thianthrene conjugated structure, pure high-conductivity conjugated polymer with phenazine-thianthrene conjugated structure is obtained first, then in the preparation process of the positive electrode, the high-conductivity conjugated polymer with phenazine-thianthrene conjugated structure is mixed uniformly with lithium cobaltate at a molar ratio of 0.05:1, and then a conductive agent, an adhesive and a solvent are added to prepare a slurry to coat and prepare an electrode. The other battery assembly and test methods remain the same as example 1.

[0038] Example 3 The difference between this embodiment and embodiment 1 is that, in the preparation process of the lithium cobalt oxide material coated in-situ with the high-conductivity conjugated polymer having phenazine-thiophene conjugated structure, the amount of lithium cobalt oxide added is adjusted to 150 mmol, and finally the molar ratio of the high-conductivity conjugated polymer to the lithium cobalt oxide material in the composite material is 0.01:1.

[0039] Example 4 The difference between this embodiment and embodiment 1 is that, in the preparation process of the lithium cobalt oxide material coated in-situ with the high-conductivity conjugated polymer having phenazine-thiophene conjugated structure, the amount of lithium cobalt oxide added is adjusted to 150 mmol, and finally the molar ratio of the high-conductivity conjugated polymer to the lithium cobalt oxide material in the composite material is 0.01:1.

[0040] Comparative Example 1 The lithium cobalt oxide material coated with the high-conductivity conjugated polymer having phenazine-thiophene conjugated structure in embodiment 1 is heat-treated under an inactive atmosphere (argon), and the heat-treatment temperature is 600°C and the heat-treatment time is 24 h, to obtain a carbon-coated lithium cobalt oxide material. The carbon-coated lithium cobalt oxide material is subjected to positive electrode preparation, battery assembly and performance testing; the method is the same as the battery preparation and testing process described in embodiment 1.

[0041] The discharge data of the above-mentioned examples and comparative examples are analyzed and compared, and the test results are shown in Table 1.

[0042] Table 1

[0043] As can be seen from Table 1, compared with comparative example 1, the battery made of the high-conductivity conjugated polymer modified positive electrode material of the application has higher discharge specific capacity, better rate performance and lower discharge voltage difference, which shows that the high-conductivity conjugated polymer modified positive electrode material of the application has more obvious advantages compared with the carbon-coated positive electrode material.

[0044] Compared with embodiment 2, the battery made of the high-conductivity conjugated polymer modified positive electrode material of embodiment 1 of the application has higher discharge specific capacity, better rate performance and lower discharge voltage difference, which shows that the high-conductivity conjugated polymer modified positive electrode material made by the in-situ polymerization coating method of the application has more obvious advantages compared with the direct composite method.

[0045] Compared with embodiments 3 and 4, the battery made of the high-conductivity conjugated polymer modified positive electrode material of embodiment 1 of the application has higher discharge specific capacity, better rate performance and lower discharge voltage difference, which shows that too high or too low ratio of the high-conductivity conjugated polymer to the positive electrode active material is not conducive to obtaining the optimal performance.

[0046] The above description of the specific embodiments of the present application is not intended to limit the scope of the present application. Any other corresponding changes and modifications made according to the technical concept of the present application should be included in the scope of protection of the claims of the present application.

Claims

1. A highly conductive conjugated polymer modified positive electrode material, characterized in that: It comprises a positive electrode active material and a highly conductive conjugated polymer compounded with or coated with the positive electrode active material; wherein, The highly conductive conjugated polymer is a polymer containing a donor-acceptor conjugated structure, wherein the donor includes phenazine and / or a phenazine derivative, and the acceptor includes thianthrene and / or a thianthrene derivative.

2. The highly conductive conjugated polymer modified positive electrode material according to claim 1, characterized in that: The donor includes at least one of 5,10-dihydrophenazine, 1-methoxy-5,10-dihydrophenazine, and 2-acetyl-5,10-dihydrophenazine; the acceptor includes at least one of 2,7-dibromothianthrene and 2,7-dichlorothianthrene.

3. The highly conductive conjugated polymer modified positive electrode material according to claim 1, characterized in that: The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, ternary nickel cobalt manganese oxide, and layered lithium-rich manganese-based materials.

4. The highly conductive conjugated polymer modified positive electrode material according to claim 1, characterized in that: The molar ratio of the highly conductive conjugated polymer to the positive electrode active material is (0.01-0.1):

1.

5. A method for preparing a highly conductive conjugated polymer modified positive electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Providing a positive electrode active material and a highly conductive conjugated polymer or a precursor monomer for preparing the highly conductive conjugated polymer; The positive electrode active material is modified by using the highly conductive conjugated polymer or the precursor monomer in a direct composite or in-situ polymerization coating manner to obtain a highly conductive conjugated polymer-modified positive electrode material.

6. The method for preparing a highly conductive conjugated polymer modified positive electrode material according to claim 5, characterized in that: The step of modifying the positive electrode active material by using the precursor monomer in an in-situ polymerization coating manner includes: The positive electrode active material, the precursor monomer, and optionally the catalyst, the organic ligand, the base, and the first solvent are uniformly mixed and in-situ polymerized to obtain a highly conductive conjugated polymer modified positive electrode material.

7. The method for preparing a highly conductive conjugated polymer modified positive electrode material according to claim 6, characterized in that: The precursor monomers include monomers containing donor structures and monomers containing acceptor structures, and the monomers containing donor structures include phenazine and / or phenazine derivatives, and the monomers containing acceptor structures include thianthrene and / or thianthrene derivatives; The catalyst is at least one of palladium acetate and palladium nitrate; The organic ligand is at least one of 2-dicyclohexylphosphine-2',4',6'-triisopropylbiphenyl; The base is at least one of sodium tert-butoxide or potassium tert-butoxide; The first solvent is at least one of toluene or p-xylene; The molar ratio of the monomer containing the donor structure to the monomer containing the acceptor structure is 1:(0.8-1.2); The molar ratio of the monomer containing the donor structure to the catalyst, the organic ligand, and the base is 1: (0.1-0.2): (0.15-0.3): (2-3); The ratio of the monomer containing the donor structure to the first solvent is 1 mol: (25-30) L; The temperature of the in-situ polymerization is 120-140° C., and the time of the in-situ polymerization is 36-60 hours; The in-situ polymerization is carried out under a protective atmosphere and stirring conditions.

8. The method for preparing a highly conductive conjugated polymer modified positive electrode material according to claim 7, wherein: After the in-situ polymerization reaction is completed, the method further comprises: A quenching agent is added to the reaction system to quench the reaction, followed by cooling, filtering, washing, and purification to obtain a highly conductive conjugated polymer modified cathode material; wherein, The quenching agent is bromobenzene; The quenching reaction time is 2 to 8 hours; The washing method is: washing with dichloromethane, methanol, tetrahydrofuran and water; The purification method is as follows: the washed product is evenly dispersed in dichloromethane, filtered and then placed in a Soxhlet extractor, and purified using methanol, triethylamine, tetrahydrofuran and dichloromethane respectively.

9. The method for preparing a highly conductive conjugated polymer modified positive electrode material according to claim 5, wherein: The step of modifying the positive electrode active material by using the highly conductive conjugated polymer in a direct composite manner comprises: The highly conductive conjugated polymer and the positive electrode active material are uniformly mixed to obtain a highly conductive conjugated polymer modified positive electrode material.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the highly conductive conjugated polymer-modified positive electrode material according to any one of claims 1 to 4.

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