Liquid retaining agent and preparation method, lithium ion battery

Abstract

This application provides a liquid retainer, its preparation method, and a lithium-ion battery. The liquid retainer includes polymer I, the structural formula of which is shown in Formula I, wherein R1 and R2 are each independently selected from H, C1-C3 alkyl groups, and phenyl groups, and R1 and R2 are different; n = 5-49. Since the main effective component in the electrolyte of the battery is a small molecule ester compound, polymer I, as an oligomer rich in ester groups in its main chain, has a higher affinity for the small molecule ester compounds in the electrolyte and can effectively adsorb the electrolyte on its main chain. Using this liquid retainer as an auxiliary material for electrode materials can reduce electrolyte loss during battery cycling, improve the ionic conductivity of the electrode, and effectively improve the fast-charge cycle capability of the battery.

Description

Technical Field

[0001] This application belongs to the field of battery materials technology, specifically relating to a liquid retainer and its preparation method, and a lithium-ion battery. Background Technology

[0002] With the rapid development of mobile technologies such as portable consumer electronics and electric vehicles, a new trend has emerged in the power battery field: a focus on high-rate fast charging technology. High-rate fast charging refers to the ability of batteries to charge at a much faster speed, including 4C, 6C, and even higher charging rates.

[0003] The key to achieving high-rate fast charging lies in improving the charging capability of the battery's negative electrode. The rapid charging and discharging process relies on the insertion and extraction of lithium ions between the positive and negative electrodes. To achieve a better lithium-ion transport environment, the negative electrode needs to provide better conditions. However, if the electrolyte level of the electrode is insufficient, it can easily lead to capacity decay. Insufficient electrolyte level means that the electrode cannot provide enough liquid medium to support lithium-ion transport. This can cause problems in the battery during charging and discharging, such as reduced capacity or performance degradation.

[0004] How to increase the liquid retention of the electrode to enable the battery's cycle performance to meet the requirements of high-rate fast charging is a technical problem that needs to be solved. Summary of the Invention

[0005] This application provides a liquid retainer and its preparation method, as well as a lithium-ion battery, aiming to solve the problem that existing lithium-ion battery electrodes are prone to capacity decay during high-rate fast charging.

[0006] To address the aforementioned problems, the first embodiment of this application provides a liquid-retaining agent, comprising polymer I, wherein the structural formula of polymer I is shown in Formula I:

[0007]

[0008] R1 and R2 are each independently selected from H, C1-C3 alkyl groups and phenyl groups, and R1 and R2 are not the same;

[0009] n = 5 to 49.

[0010] In some embodiments, R1 is selected from H, and R2 is selected from phenyl.

[0011] In some embodiments, the molecular weight of polymer I is 1000 to 10000.

[0012] In some embodiments, the solid content of the liquid-retaining agent is 25% to 30%.

[0013] The second embodiment of this application provides a method for preparing a liquid-retaining agent, used to prepare the liquid-retaining agent in any of the above embodiments, comprising the following steps:

[0014] A first monomer and a second monomer are provided, a dehydrating agent is added, and the mixture is stirred to form a mixture;

[0015] The mixture is heated and pressurized to cause the first and second monomers to undergo a polymerization reaction, generating polymer I, and thus obtaining the liquid retaining agent;

[0016] The structural formula of the first monomer is shown in Formula II:

[0017]

[0018] The structural formula of the second monomer is shown in Formula III:

[0019]

[0020] R1 and R2 are each independently selected from H, C1-C3 alkyl groups and phenyl groups, and R1 and R2 are not the same.

[0021] In some embodiments, the mass ratio of the first monomer, the second monomer, and the dehydrating agent is 1-2:1-1:0.05-0.1.

[0022] In some embodiments, the dehydrating agent includes at least one of molecular sieve and anhydrous silica gel.

[0023] In some embodiments, the temperature of the stirring and mixing is 80–100°C.

[0024] In some embodiments, the polymerization reaction is carried out at a temperature of 110–130°C and a pressure of 0–200 Pa.

[0025] In some embodiments, after the step of polymerizing the first monomer and the second monomer to generate polymer I, the method further includes:

[0026] The polymer I was cooled to room temperature, dissolved in an organic solvent, and the insoluble matter was filtered out.

[0027] The organic solvent includes N-methylpyrrolidone (NMP).

[0028] The third embodiment of this application provides a lithium-ion battery, including an electrode, wherein the electrode includes the liquid retainer in any of the above embodiments or the liquid retainer prepared by the preparation method in any of the above embodiments.

[0029] This application provides a liquid retainer comprising polymer I, the structural formula of which is shown in Formula I, wherein R1 and R2 are each independently selected from H, C1-C3 alkyl groups, and phenyl groups, and R1 and R2 are different; n = 5-49. Since the main effective components in the battery electrolyte are small molecule ester compounds, polymer I, as an oligomer rich in ester groups in its main chain, has a higher affinity for small molecule ester compounds in the electrolyte and can effectively adsorb the electrolyte on its main chain. Using this liquid retainer as an auxiliary material for electrode materials can reduce electrolyte loss during battery cycling, improve the ionic conductivity of the electrode, and effectively enhance the fast-charging cycle capability of the battery. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection, an indirect connection through an intermediate medium, or an indirect connection through a pipe or conduit; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0032] The first embodiment of this application provides a liquid retainer, comprising polymer I, the structural formula of polymer I being shown in Formula I:

[0033]

[0034] R1 and R2 are each independently selected from H, C1-C3 alkyl groups and phenyl groups, and R1 and R2 are not the same;

[0035] n = 5 to 49.

[0036] The main active components in the battery electrolyte are small-molecule ester compounds. Polymer I, as an oligomer rich in ester groups in its main chain, has a higher affinity for small-molecule ester compounds in the electrolyte and can effectively adsorb the electrolyte onto its main chain. Using this electrolyte retainer as an auxiliary material for electrode materials can reduce electrolyte loss during battery cycling, improve the ionic conductivity of the electrode, and effectively enhance the battery's fast-charge cycle capability. Furthermore, Polymer I can be obtained by the dehydration polymerization of two α-hydroxycarboxylic acids. The polymerization process requires no catalyst or initiator, is simple to implement, and facilitates large-scale promotion.

[0037] In some embodiments, R1 is selected from H, and R2 is selected from phenyl.

[0038] The presence of phenyl side chains can provide additional adsorption sites for graphite, which can improve the dispersion level of polymer I. The ester main chain can increase the interaction force with small ester molecules, which is more conducive to the adsorption of electrolyte by polymer I. The alkyl side chain of appropriate length can ensure the stability of polyester while avoiding the large steric hindrance caused by long alkyl chains, thus avoiding the reduction of diffusion rate and adsorption capacity of small ester molecules in polyester oligomers.

[0039] In some embodiments, the molecular weight of polymer I is 1000 to 10000.

[0040] In this application, molecular weight refers to the weight-average molecular weight of the polymer. It is understood that the molecular weight of polymer I can be any value or a range between any two of the following: 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000. When the molecular weight of polymer I meets the above-mentioned range, polymer I can possess good strength and polarity.

[0041] In some embodiments, the solid content of the liquid retainer is 25% to 30%.

[0042] It is understandable that the solid content of the liquid retainer can be any value or a range between any two of 25%, 26%, 27%, 28%, 29%, and 30%. When the solid content of the liquid retainer meets the above range, it ensures that the effective components in the liquid retainer can cover all parts of the electrode, ensuring the liquid retention capacity of the electrode, while also giving the liquid retainer a relatively ideal viscosity, so that it has good bonding strength on the electrode surface.

[0043] The second embodiment of this application provides a method for preparing a liquid-retaining agent, used to prepare the liquid-retaining agent in any of the above embodiments, comprising the following steps:

[0044] A first monomer and a second monomer are provided, a dehydrating agent is added, and the mixture is stirred to form a mixture;

[0045] The mixture is heated and pressurized to cause the first and second monomers to undergo a polymerization reaction, generating polymer I, which yields the liquid retainer.

[0046] The structural formula of the first monomer is shown in Formula II:

[0047]

[0048] The structural formula of the second monomer is shown in Formula III:

[0049]

[0050] R1 and R2 are each independently selected from H, C1-C3 alkyl groups and phenyl groups, and R1 and R2 are not the same.

[0051] The first and second monomers, being two types of α-hydroxycarboxylic acids, can undergo dehydration condensation to form polyester oligomers rich in ester groups in the main chain. They have a higher affinity for small molecule ester compounds in the electrolyte and can effectively adsorb the electrolyte on the main chain. During the polymerization process, no catalyst, initiator, or end-capping is required, making the process simple. Since the condensation reaction is reversible, the use of a dehydrating agent as an auxiliary agent can effectively remove the water content in the reaction system in a timely manner during the reaction, allowing the reaction to proceed in the forward direction.

[0052] In some embodiments, R1 is selected from H, R2 is selected from phenyl, and the mass ratio of the first monomer, the second monomer, and the dehydrating agent is 1-2:1-2:0.05-0.01.

[0053] When the mass ratio of the first monomer and the second monomer meets the above-mentioned range, it can ensure that the phenyl groups in the polymer I formed by polycondensation have a reasonable percentage. This can provide additional adsorption sites for graphite and improve the dispersion level of polymer I, while avoiding the large steric hindrance caused by excessive side chains and preventing the diffusion rate and adsorption capacity of small ester molecules in polyester oligomers from decreasing.

[0054] In some embodiments, the dehydrating agent includes at least one of molecular sieve and dehydrating silica gel, wherein the molecular sieve includes commercially available 3A grade molecular sieve and 4A grade molecular sieve; the dehydrating agent is further preferably 4A grade molecular sieve and dehydrating silica gel, mixed in a 1:1 mass ratio.

[0055] Molecular sieves possess a highly ordered pore structure, providing numerous adsorption sites and thus exhibiting high adsorption capacity. However, they are sensitive to humidity, and their adsorption capacity may decrease at high humidity levels. Dehydrated silica gel has a high hygroscopic capacity, capable of absorbing moisture from the surrounding environment and maintaining relative dryness. However, compared to molecular sieves, dehydrated silica gel has a lower adsorption capacity and cannot handle high concentrations of humidity. Using a mixture of 4A-grade molecular sieves and dehydrated silica gel as a dehydrating agent ensures that the dehydrating agent maintains ideal hygroscopic capacity throughout the entire reaction process.

[0056] In some embodiments, the mixing temperature is 80–100°C.

[0057] It is understood that the mixing temperature (unit: °C) can be any value or a range between any two of 80, 85, 90, 95, and 100. When the mixing temperature meets the above range, it can ensure that a condensation reaction occurs between the first and second monomers.

[0058] In some embodiments, the polymerization reaction temperature is 110–130°C and the reaction pressure is 0–200 Pa.

[0059] It is understandable that the reaction temperature (unit: °C) of the polymerization reaction can be any value or any range between two of 110, 115, 120, 125, and 130 °C, and the reaction pressure (unit: Pa) can be any value or any range between two of 10, 20, 40, 60, 80, 120, 140, 160, 180, and 200 Pa. The polyester dehydration condensation reaction requires a relatively large negative pressure to ensure that the dehydration rate is greater than the reaction rate. When the reaction temperature and reaction pressure meet the above-mentioned ranges, it can ensure that the polymerization reaction proceeds in the forward direction.

[0060] In some embodiments, after the step of polymerizing the first monomer and the second monomer to generate polymer I, the method further includes:

[0061] Polymer I was cooled to room temperature, dissolved in an organic solvent, and the insoluble matter was filtered out.

[0062] The organic solvents include NMP.

[0063] By dissolving polymer I in an organic solvent and filtering out insoluble matter, the content of effective components in the liquid retainer can be increased, thereby further enhancing the liquid retainer's liquid retention capacity.

[0064] The third embodiment of this application provides a lithium-ion battery, including an electrode sheet, which includes the liquid retainer in any of the above embodiments or the liquid retainer prepared by the preparation method in any of the above embodiments.

[0065] The following description, in conjunction with specific embodiments, illustrates the liquid-retaining agent and its preparation method, as well as the lithium-ion battery provided in this application:

[0066] Example 1

[0067] Example 1 provides a liquid retainer and a negative electrode sheet, which are prepared through the following steps:

[0068] Glycolic acid and mandelic acid monomers were provided, mixed with 5% by mass of 4A grade molecular sieve and 5% by mass of silica gel, and stirred with a screw impeller at 80°C. The mixture was dehydrated and condensed at 120°C under a pressure of 100Pa to form polymer I, denoted as PMGA. The reaction time was controlled at 1 hour. After cooling to room temperature and depressurization, NMP was added and ultrasonically dissolved for 30 minutes. The insoluble matter was removed by filtration. The product was tested and found to have a solid content of 25%, thus obtaining a liquid retainer.

[0069] The positive and negative electrode sheets were prepared according to the following formulas: positive electrode: 96.1% NCM811 + 2% carbon black + 0.7% carbon nanotubes + 1% PVDF + 0.2% PMGA; negative electrode: 96.4% graphite + 0.5% carbon black + 1.4% CMC + 1.5% SBR + 0.2% PMGA. The specific steps are as follows:

[0070] Add PVDF and NMP to a dual planetary mixer, mix at medium speed, and disperse for 3 hours.

[0071] Add the PVDF adhesive and SP to a dual planetary mixer and disperse at medium speed for 1 hour. Add NCM811 in two batches, followed by NMP, and disperse at high speed for 2 hours each time. Add 0.2% PMGA and disperse at medium speed for 30 minutes. After completion, add an appropriate amount of NMP to adjust the viscosity of the slurry to a suitable range for coating.

[0072] The positive electrode sheet is obtained by coating one or both sides of aluminum foil or carbon-coated aluminum foil by transfer coating or extrusion coating, and then baking in an oven at 105°C for 2 minutes.

[0073] Add CMC and deionized water to a dual planetary mixer and mix at medium speed for 1 hour.

[0074] CMC adhesive and 0.5% SP were added to a dual planetary mixer and dispersed at medium speed for 2 hours. Then, 4C graphite was added in two batches, along with an appropriate amount of deionized water. The mixture was dispersed at high speed for 3 hours. SBR and PMGA were added and stirred at low speed for 0.5 hours. Finally, an appropriate amount of deionized water was added to adjust the viscosity of the slurry to a suitable range for coating.

[0075] The negative electrode sheet is obtained by coating one or both sides of copper foil or carbon-coated copper foil by transfer coating or extrusion coating, and then baking in an oven at a temperature of 50-80℃ for 2 minutes.

[0076] Example 2:

[0077] The operating steps are the same as in Example 1.

[0078] The cathode formulation was modified to: 96.3% NCM811 + 2% carbon black + 0.7% carbon nanotubes + 1% PVDF.

[0079] Example 3:

[0080] The operating steps are the same as in Example 1.

[0081] The negative electrode formulation was modified to: 96.6% graphite + 0.5% carbon black + 1.4% CMC + 1.5% SBR.

[0082] Comparative Example 1:

[0083] The operating steps are the same as in Example 1.

[0084] The positive and negative electrode formulations have been modified as follows: positive electrode formulation: 96.1% NCM811 + 2% carbon black + 0.7% carbon nanotubes + 1% PVDF + 0.2% polyacrylate liquid retainer; negative electrode formulation: 96.4% graphite + 0.5% carbon black + 1.4% CMC + 1.5% SBR + 0.2% polyacrylate liquid retainer.

[0085] Comparative Example 2:

[0086] The operating steps are the same as in Example 1, except that 0.2% PMGA is removed from both the positive and negative electrode formulations, and 0.2% of the main material is added.

[0087] Cyclic performance tests were performed on the examples and comparative examples, and the results are shown in Table 1.

[0088] Table 1

[0089]

[0090] As can be seen from Table 1:

[0091] Example 1, in which both positive and negative electrodes were added with a liquid retainer containing polymer I (PMGA), showed a significant improvement in charge-discharge retention rate and cycle capability under a 4C charging regime compared to Comparative Example 2. It was also significantly better than Comparative Example 1, in which both positive and negative electrodes were added with an equal amount of branched ester polyacrylate liquid retainer.

[0092] Example 2, in which PMGA was added to the positive electrode, showed a better improvement in fast charging capability than Example 3, in which PMGA was added to the negative electrode. However, regardless of whether PMGA was added only to the positive electrode or only to the negative electrode, its performance in charge-discharge retention rate and cycle capability was better than that of Comparative Example 1 and Comparative Example 2. This shows that using PMGA as a liquid retainer component can improve the electrical performance of the electrode.

[0093] The above provides a detailed description of a liquid retainer and its preparation method, as well as a lithium-ion battery, provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of this application. 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. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A lithium-ion battery, comprising battery electrodes and an electrolyte, wherein the battery electrodes include a liquid retainer, and the electrolyte contains at least an ester compound, characterized in that, The liquid-retaining agent includes polymer I, and the structural formula of polymer I is shown in Formula I: Formula I; R1 and R2 are each independently selected from H, C1~C3 alkyl and phenyl, and R1 and R2 are not the same; n=5~49。 2. A lithium-ion battery according to claim 1, characterized in that, R1 is selected from H, and R2 is selected from phenyl.

3. A lithium-ion battery according to claim 1, characterized in that, The molecular weight of polymer I is 1000~10000.

4. A lithium-ion battery according to claim 1, characterized in that, The solid content of the liquid retaining agent is 25%~30%.

5. A lithium-ion battery according to claim 1, characterized in that, The preparation method of the liquid-retaining agent includes the following steps: A first monomer and a second monomer are provided, a dehydrating agent is added, and the mixture is stirred to form a mixture; The mixture is heated and pressurized to cause the first and second monomers to undergo a polymerization reaction, generating polymer I, and thus obtaining the liquid retaining agent; The structural formula of the first monomer is shown in Formula II: Formula II; The structural formula of the second monomer is shown in Formula III: Formula III; R1 and R2 are each independently selected from H, C1~C3 alkyl and phenyl, and R1 and R2 are not the same.

6. A lithium-ion battery according to claim 5, characterized in that, The mass ratio of the first monomer, the second monomer, and the dehydrating agent is 1~2:1~2:0.05~0.

1.

7. A lithium-ion battery according to claim 5, characterized in that, The dehydrating agent includes at least one of molecular sieve and anhydrous silica gel.

8. A lithium-ion battery according to claim 5, characterized in that, The mixing temperature is 80~100℃; and / or, The polymerization reaction is carried out at a temperature of 110~130℃ and a pressure of 0~200Pa.

9. A lithium-ion battery according to claim 5, characterized in that, After the step of polymerizing the first monomer and the second monomer to generate polymer I, the process further includes: The polymer I was cooled to room temperature, dissolved in an organic solvent, and the insoluble matter was filtered out. The organic solvent includes N-methylpyrrolidone.

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