Soluble microspheres for controlling the gap between lithium battery separator and negative electrode sheet and a method for preparing the same

Abstract

The application discloses soluble microspheres for controlling the gap between a lithium battery diaphragm and a negative pole piece and a preparation method thereof, and belongs to the technical field of batteries. The soluble microspheres are composed of the following raw materials in parts by weight: a lithium supplement agent 20-30 parts, an acrylic ester 50-80 parts, a photoinitiator 0.5-3 parts and a compatible solvent 50-100 parts. The particle size of the soluble microspheres is controlled by a nozzle, the soluble microspheres are uniformly distributed on the diaphragm and the negative pole piece, the gap between the diaphragm and the negative pole piece can be controlled, the electrolyte impregnation degree and the conductivity are improved, and local lithium accumulation is avoided. The soluble microspheres can slowly dissolve and release the lithium supplement agent, supplement lithium loss during the first charge and discharge, and improve the battery capacity.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically a soluble microsphere for controlling the gap between the lithium battery separator and the negative electrode and its preparation method. Background Technology

[0002] Lithium-ion batteries face higher requirements for capacity and charge / discharge cycles during use. The porous structure of the separator provides a transport channel for lithium ions. Traditional coatings are prone to wrinkling and deformation when the separator is rolled up due to its own structural limitations, which can block the lithium ion exchange channels and reduce battery performance. The formation of a solid electrolyte interface film during the first charge / discharge cycle can also lead to lithium loss and affect the initial capacity of the battery. In addition, the expansion of the negative electrode and the precipitation of lithium dendrites during charge / discharge cycles can also squeeze or even puncture the separator, leading to safety issues.

[0003] Traditional separators are modified by multi-layer coating. For example, patent CN1325145A mentions a composite separator made of at least one ceramic composite layer and at least one polymer porous layer. However, this separator process is complex and prone to coating defects. The coating layer may block some micropores or increase the resistance to lithium ion migration. The weight and thickness increase, reducing the energy density of the battery. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a soluble microsphere for controlling the gap between the lithium battery separator and the negative electrode, and a method for preparing the same.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A soluble microsphere for controlling the gap between the separator and the negative electrode of a lithium battery, comprising, by weight, the following raw materials: 20-30 parts of lithium supplement, 50-80 parts of acrylate, 0.5-3 parts of photoinitiator, and 50-100 parts of solvent.

[0007] The method for preparing soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode includes the following steps:

[0008] 1) Preparation of precursor: Dissolve 20-30 parts of lithium supplement, 50-80 parts of acrylate and 0.5-3 parts of photoinitiator in 50-100 parts of solvent, stir at 25°C for 30 min to obtain a homogeneous and transparent precursor solution.

[0009] 2) Select a continuous phase;

[0010] 3) Ultraviolet polymerization: The precursor solution prepared in step 1) is loaded into a syringe, connected to a nozzle through a conduit, and the injection pump is started. The precursor solution forms discrete droplets in the continuous phase selected in step 2). The ultraviolet light wavelength is set to 365 nm, and the light power is 30~80 mW / cm². 2 Discrete droplets are irradiated with ultraviolet light for 10-30 seconds to obtain spherical microspheres;

[0011] 4) Post-processing: The spherical microspheres obtained in step 3) are washed with ethyl acetate 2-3 times, then washed with deionized water, and vacuum dried at 30-50℃ for 4-6 hours to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode.

[0012] The lithium supplement agent mentioned in step 1) is one or two of the following: lithium 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-allyl-3-methylimidazolium hexafluorophosphate, lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and lithium 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide.

[0013] The acrylate mentioned in step 1) is one or more of the following: methyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate, butyl methacrylate, hexafluorobutyl acrylate, polyethylene glycol monoacrylate, isobornyl methacrylate, lauryl methacrylate, dimethylaminoethyl methacrylate, polyethylene glycol diacrylate, and glycidyl methacrylate.

[0014] The photoinitiator mentioned in step 1) is one or two of TPO, Irgacure184 and Irgacure907.

[0015] The solvent mentioned in step 1) is one or two of ethyl acetate, ethanol, acetone, acrylic acid, methacrylic acid, polyethylene glycol monoacrylate and hydroxyethyl acrylate.

[0016] The continuous phase mentioned in step 2) is dimethyl silicone oil, phenylmethyl silicone oil, polymethylphenylsiloxane, methylchlorosilane, phenylchlorosilane or vinylchlorosilane.

[0017] The nozzle orifice diameter described in step 3) is 10~50μm.

[0018] The flow rate ratio of the precursor solution to the continuous phase in step 3) is 1:10.

[0019] The soluble microspheres used to control the gap between the lithium battery separator and the negative electrode sheet, as described in step 4), have a particle size of 5~50μm.

[0020] In step 3), the photoinitiator in the discrete droplets decomposes under ultraviolet light to generate free radicals, which initiate a chain polymerization reaction of acrylate in the precursor solution, and the droplets gradually solidify into spherical microspheres.

[0021] The present invention has the following advantages over the prior art:

[0022] The soluble microspheres of this invention, used to control the gap between the lithium battery separator and the negative electrode, are prepared using droplet photocuring technology. They can be uniformly fixed onto the separator by electrostatic adsorption or vacuum coating to construct an effective ion transport channel. By controlling the proportion and size of the microspheres in the separator, the pore size of the separator and the gap between it and the negative electrode can be controlled, thereby improving ion conductivity. The microspheres are embedded in the separator rather than tightly cross-linked, which can reduce the internal stress generated in the separator during production and use, avoid coating wrinkling and deformation that blocks the lithium ion exchange channels, and ensure the normal migration of lithium ions between the positive and negative electrodes.

[0023] The present invention relates to soluble microspheres for controlling the gap between the separator and the negative electrode in lithium batteries. The acrylic copolymer shell of the soluble microspheres can be oxidized in the electrolyte into small molecule products such as carboxylic acid and CO2, releasing the lithium-ion core and replenishing the lithium loss caused by the formation of the solid electrolyte interface film during the first charge-discharge cycle, thereby increasing the battery capacity. At the same time, after the microspheres dissolve, they form a gap between the separator and the negative electrode, providing space for the negative electrode material to swell and preventing the negative electrode from squeezing and puncturing the separator.

[0024] The soluble microspheres of this invention, used to control the gap between the lithium battery separator and the negative electrode, have low coating quality per unit area, thus improving battery capacity. The coating process is compatible with existing production lines, requiring no adjustment to the electrode process, and is highly compatible and applicable to existing production lines. At the same time, it provides some ideas for the research and development of solid-state batteries. Attached Figure Description

[0025] Figure 1 This is a process route diagram for preparing soluble microspheres used in the present invention to control the gap between the lithium battery separator and the negative electrode sheet;

[0026] Figure 2 This is a chemical structural diagram of the soluble microspheres prepared in Example 1 of the present invention. Detailed Implementation

[0027] To better understand the technical solution of the present invention, the following detailed embodiments further illustrate the above-mentioned content of the present invention. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following examples. All technologies implemented based on the above-mentioned content of the present invention fall within the scope of the present invention.

[0028] Example 1: 20 kg of lithium supplement 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 12 kg of ethyl acrylate, 12 kg of butyl acrylate, 46 kg of methyl methacrylate, and 0.5 kg of photoinitiator TOP were dissolved in 50 kg of ethyl acetate and stirred at 25°C for 30 min to obtain a homogeneous and transparent precursor solution; Figure 1 As shown, the prepared precursor solution was loaded into a syringe, connected to a nozzle via a tubing, and the injection pump was started. The precursor solution formed discrete droplets in the continuous phase dimethyl silicone oil, with a flow rate ratio of precursor solution to continuous phase of 1:10. The ultraviolet light wavelength was set to 365 nm, and the optical power was 30 mW / cm². 2 Discrete droplets were irradiated under ultraviolet light for 10 s to obtain spherical microspheres. The obtained spherical microspheres were washed three times with ethyl acetate, then three times with deionized water, and vacuum dried at 40 °C for 12 h to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode. The chemical structural formula of the soluble microspheres is as follows: Figure 2 As shown.

[0029] In Example 2, 25 kg of lithium 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, 15 kg of methyl acrylate, 60 kg of butyl methacrylate, and 0.5 kg of photoinitiator TOP were dissolved in 60 kg of ethyl acetate and stirred at 25°C for 30 min to obtain a homogeneous and transparent precursor solution. The prepared precursor solution was loaded into a syringe, and a nozzle was connected through a conduit. The syringe pump was started, and the precursor solution formed discrete droplets in the continuous phase phenylchlorosilane. The flow rate ratio of the precursor solution to the continuous phase was 1:10. The ultraviolet light wavelength was set to 365 nm, and the optical power was 40 mW / cm². 2 Discrete droplets were irradiated under ultraviolet light for 15 s to obtain spherical microspheres. The obtained spherical microspheres were washed three times with ethyl acetate and then three times with deionized water. They were then vacuum dried at 40 °C for 12 h to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode.

[0030] In Example 3, 27 kg of lithium 1-ethyl-3-methylimidazolium difluoromethanesulfonylimide, 15 kg of hydroxyethyl acrylate, 13 kg of isobornyl methacrylate, 42 parts of lauryl methacrylate, and 1 kg of photoinitiator Irgacure 184 were dissolved in 90 kg of acrylic acid and stirred at 25°C for 30 min to obtain a homogeneous and transparent precursor solution. The prepared precursor solution was loaded into a syringe, and a nozzle was connected through a conduit. The syringe pump was started, and the precursor solution formed discrete droplets in the continuous phase methylchlorosilane. The flow rate ratio of the precursor solution to the continuous phase was 1:10. The ultraviolet light wavelength was set to 365 nm, and the optical power was 50 mW / cm². 2Discrete droplets were irradiated under ultraviolet light for 20 s to obtain spherical microspheres. The obtained spherical microspheres were washed three times with ethyl acetate and then three times with deionized water. They were then vacuum dried at 40 °C for 12 h to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode.

[0031] In Example 4, 29 kg of lithium supplement 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 20 kg of hexafluorobutyl acrylate, 50 kg of glycidyl methacrylate, and 2 kg of photoinitiator Irgacure 184 were dissolved in 95 kg of polyethylene glycol monoacrylate. The solution was stirred at 25°C for 30 min to obtain a homogeneous and transparent precursor solution. The prepared precursor solution was loaded into a syringe, and a nozzle was connected through a conduit. The syringe pump was started, and the precursor solution formed discrete droplets in the continuous phase vinylchlorosilane. The flow rate ratio of the precursor solution to the continuous phase was 1:10. The ultraviolet light wavelength was set to 365 nm, and the optical power was 60 mW / cm². 2 Discrete droplets were irradiated under ultraviolet light for 25 s to obtain spherical microspheres. The obtained spherical microspheres were washed three times with ethyl acetate and then three times with deionized water. They were then vacuum dried at 40 °C for 12 h to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode.

[0032] In Example 5, 30 kg of lithium supplementer 1-allyl-3-methylimidazolium hexafluorophosphate, 30 kg of polyethylene glycol monoacrylate, 50 kg of methyl methacrylate, and 3 kg of photoinitiator Irgacure907 were dissolved in 100 kg of hydroxyethyl acrylate and stirred at 25°C for 30 min to obtain a homogeneous and transparent precursor solution. The prepared precursor solution was loaded into a syringe, and a nozzle was connected through a conduit. The syringe pump was started, and the precursor solution formed discrete droplets in the continuous phase polymethylphenylsiloxane. The flow rate ratio of the precursor solution to the continuous phase was 1:10. The ultraviolet light wavelength was set to 365 nm, and the optical power was 80 mW / cm². 2 Discrete droplets were irradiated under ultraviolet light for 30 s to obtain spherical microspheres. The obtained spherical microspheres were washed three times with ethyl acetate and then three times with deionized water. They were then vacuum dried at 40 °C for 12 h to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode.

[0033] Emulsion polymerization was employed, in which 30 kg of lithium supplement 1-allyl-3-methylimidazolium hexafluorophosphate, 30 kg of polyethylene glycol monoacrylate, and 50 kg of methyl methacrylate were dissolved in ethyl acetate, and a polymer solution was prepared under the catalysis of 2 kg of photoinitiator Irgacure 184. The polymer solution was slowly added dropwise (1-2 drops / s) to chloroform under vigorous stirring (600 rpm) to form droplets, and emulsified using a high-shear disperser for 30 min to obtain an emulsion. The chloroform was evaporated by stirring at room temperature, and the mixture was vacuum dried at 40 °C for 12 h. The resulting spherical microspheres were washed three times with ethyl acetate, then three times with deionized water, and vacuum dried at 40 °C for 12 h to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode.

[0034] The soluble microspheres prepared in Examples 1-5 and the comparative example for controlling the gap between the lithium battery separator and the negative electrode were used as separators, and the following tests were performed:

[0035] Porosity: P=(1-(M / V) / ρ)×100%, where P is porosity, M is sample mass, V is sample volume, and ρ is sample density;

[0036] Average aperture size: observed directly using a scanning electron microscope (SEM);

[0037] Ionic conductivity: σ = d / (R × S), where σ is the membrane conductivity, d is the average membrane thickness, R is the ionic resistance, and S is the effective area of ​​the membrane. The detection results are shown in Table 1.

[0038] Table 1 Comparison of the performance of membranes containing soluble microspheres

[0039]

[0040] As shown in Table 1, when the soluble microspheres prepared in this invention for controlling the gap between the lithium battery separator and the negative electrode are present in the separator, the porosity and ionic conductivity of the separator are significantly better than those of commonly used separators. Compared with the emulsion polymerization method of Comparative Example 1, the preparation method of this invention is simple to operate and the particle size is controllable. The soluble microspheres prepared in this invention for controlling the gap between the lithium battery separator and the negative electrode form a gap after dissolving in the electrolyte, avoiding the expansion, compression, and puncture of the separator by the negative electrode. The soluble microspheres can control the pore size of the separator, avoiding excessively high local current density that leads to polarization concentration.

[0041] The soluble microspheres prepared by this invention for controlling the gap between the lithium battery separator and the negative electrode can also compensate for the lithium loss caused by the formation of a solid electrolyte interface film during the first charge and discharge of the lithium battery, effectively replenishing lithium ions and improving battery capacity. This approach can also provide some ideas for the research of solid-state batteries.

[0042] While the specific embodiments of the present invention have been described above, they are not intended to limit the scope of protection of the present invention. Based on the technical solutions of the present invention, various modifications or variations that can be made by those skilled in the art without creative effort are still within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium battery separator, characterized in that: Includes the following steps: 1) Preparation of precursor: Dissolve 20-30 parts of lithium supplement, 50-80 parts of acrylate and 0.5-3 parts of photoinitiator in 50-100 parts of solvent, stir at 25°C for 30 min to obtain a homogeneous and transparent precursor solution. 2) Select a continuous phase; 3) Ultraviolet polymerization: The precursor solution prepared in step 1) is loaded into a syringe, connected to a nozzle via a conduit, and the injection pump is started. The precursor solution forms discrete droplets in the continuous phase selected in step 2). The ultraviolet light wavelength is set to 365 nm, and the light power is 30~80 mW / cm². 2 Discrete droplets are irradiated with ultraviolet light for 10-30 seconds to obtain spherical microspheres; 4) Post-processing: The spherical microspheres obtained in step 3) are washed with ethyl acetate 2-3 times, then washed with deionized water, and vacuum dried at 30-50℃ for 4-6 hours to obtain soluble microspheres for controlling the gap between the lithium battery separator and the negative electrode. The prepared soluble microspheres are uniformly fixed on the separator by electrostatic adsorption or vacuum coating to obtain the lithium battery separator.

2. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The lithium supplement agent mentioned in step 1) is one or two of the following: lithium 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-allyl-3-methylimidazolium hexafluorophosphate, lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, lithium 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and lithium 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide.

3. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The acrylate mentioned in step 1) is one or more of the following: methyl methacrylate, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, butyl acrylate, butyl methacrylate, hexafluorobutyl acrylate, polyethylene glycol monoacrylate, isobornyl methacrylate, lauryl methacrylate, dimethylaminoethyl methacrylate, polyethylene glycol diacrylate, and glycidyl methacrylate.

4. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The photoinitiator mentioned in step 1) is one or two of TPO, Irgacure184 and Irgacure907.

5. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The solvent mentioned in step 1) is one or two of ethyl acetate, ethanol, acetone, acrylic acid, methacrylic acid, polyethylene glycol monoacrylate and hydroxyethyl acrylate.

6. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The continuous phase mentioned in step 2) is dimethyl silicone oil, phenylmethyl silicone oil, polymethylphenylsiloxane, methylchlorosilane, phenylchlorosilane or vinylchlorosilane.

7. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The nozzle orifice diameter described in step 3) is 10~50μm.

8. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The flow rate ratio of the precursor solution to the continuous phase in step 3) is 1:

10.

9. The method for preparing a lithium battery separator as described in claim 1, characterized in that: The soluble microspheres used to control the gap between the lithium battery separator and the negative electrode sheet, as described in step 4), have a particle size of 5~50μm.

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