A polymer lithium-ion battery and its preparation method

Abstract

The application relates to the technical field of polymer lithium ion batteries, in particular to a polymer lithium ion battery and a preparation method thereof. The polymer lithium ion battery comprises a positive electrode aluminum foil, a negative electrode graphite sheet and a polymer electrolyte; wherein the polymer electrolyte comprises 30-90 parts of a polymer matrix solution, 15-30 parts of a lithium salt, 10-20 parts of a plasticizer and 1-5 parts of a modified filler, and the polymer electrolyte is obtained by irradiating a polymer electrolyte precursor under ultraviolet light; the application provides the polymer lithium ion battery and the preparation method thereof, so as to solve the problems of low conductivity of a semi-solid electrolyte and obvious performance decline at low temperature in the related art.

Description

Technical Field

[0001] This application relates to the field of polymer lithium-ion battery technology, and in particular to a polymer lithium-ion battery and its preparation method. Background Technology

[0002] Lithium-ion batteries are secondary batteries that store and release energy by inserting / deintercalating lithium ions between the positive and negative electrodes. They are widely used in electric vehicles, energy storage and other fields.

[0003] Currently, most lithium-ion batteries are liquid batteries, which have the risks of electrolyte leakage, flammability, and explosion. Semi-solid batteries in related technologies introduce a small amount of liquid components or plasticizers to form "ion conduction channels" in a solid polymer matrix, balancing safety, conductivity, and processing performance. They eliminate the risk of liquid electrolyte leakage, have a high ignition point, and can reduce the probability of fires caused by overcharging and short circuits. At the same time, the electrolyte also functions as a separator, which can simplify the battery structure.

[0004] However, the contact area between semi-solid electrolytes and electrode materials is limited, and their conductivity at room temperature is lower than that of liquid electrolytes. In particular, their performance deteriorates significantly at low temperatures, affecting low-temperature battery life. Summary of the Invention

[0005] This application provides a polymer lithium-ion battery and its preparation method to solve the problems of low conductivity and significant performance degradation at low temperatures in the semi-solid electrolyte in related technologies.

[0006] In a first aspect, a polymer lithium-ion battery is provided, comprising:

[0007] Positive electrode aluminum foil, negative electrode graphite sheet, and polymer electrolyte;

[0008] The polymer electrolyte comprises 30-90 parts of polymer matrix solution, 15-30 parts of lithium salt, 10-20 parts of plasticizer and 1-5 parts of modified filler, and the polymer electrolyte is obtained by irradiating a polymer electrolyte precursor under ultraviolet light;

[0009] The method for preparing the modified filler includes:

[0010] Microcrystalline cellulose was dissolved in toluene at a mass-to-volume ratio of 1:20, dispersed, and then 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 75°C for 2 hours. After washing and drying, an intermediate was obtained. The mass of the 3-aminopropyltriethoxysilane was 40% of that of the microcrystalline cellulose.

[0011] The intermediate was reacted with methyl methacrylate and azobisisobutyronitrile for 3 hours to obtain the modified filler. The mass ratio of the intermediate to methyl methacrylate was 10:(2-5), and the mass of azobisisobutyronitrile was 1% of the total mass of the intermediate and methyl methacrylate.

[0012] Preferably, the method for preparing the polymer electrolyte includes the following steps:

[0013] At 50°C, lithium salt was added to the polymer matrix solution, followed by the addition of plasticizer and ultrasonic dispersion for 30 min. Then, modified filler was added and ultrasonic dispersion was carried out for 1 h to obtain the polymer electrolyte precursor.

[0014] The polymer electrolyte precursor was coated into a thin film of 50-80 μm, left to stand at room temperature for 2 hours, and then irradiated under ultraviolet light for 10 minutes to obtain the polymer electrolyte.

[0015] Preferably, the method for preparing the polymer matrix solution includes the following steps:

[0016] The polymer was mixed with N-methylpyrrolidone and magnetically stirred to obtain a homogeneous solution with a solid content of 30-40%.

[0017] Add adiponitrile and dicyandiamide to the homogeneous solution, heat to 70°C and introduce nitrogen gas, stir for 20 min, add azobisisobutyronitrile at 1% of the polymer mass, and simultaneously cool to 50°C and ultrasonically disperse for 1 h to obtain the polymer matrix solution.

[0018] The amount of adiponitrile added is 15% of the polymer mass, and the amount of dicyandiamide added is half of the adiponitrile.

[0019] Preferably, the polymer comprises one or more of trimethylolpropane triacrylate, polyacrylonitrile, polyethylene oxide, and polyvinylidene fluoride.

[0020] Preferably, the polymer is a mixture of polyethylene oxide and polyvinylidene fluoride, wherein the mass ratio of polyethylene oxide to polyvinylidene fluoride is (1.5-3):1.

[0021] Preferably, the addition of the plasticizer includes the following steps:

[0022] Ethylene carbonate and dimethyl carbonate are added sequentially, wherein the mass ratio of ethylene carbonate to dimethyl carbonate is 2:1.

[0023] Preferably, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalato)borate.

[0024] In a second aspect, a method for preparing a polymer lithium-ion battery as described in any of the above-mentioned methods is provided, characterized in that it includes the following steps:

[0025] The polymer electrolyte precursor is coated onto the positive electrode aluminum foil with a thickness of 50-80 μm using a slit coater. After standing for 30 min, it is cured under ultraviolet light for 8-12 min to form a polymer electrolyte layer on the positive electrode aluminum foil.

[0026] The side of the positive electrode aluminum foil coated with polymer electrolyte is stacked with the negative electrode graphite sheet, and then hot-pressed at 80°C for 5 minutes to obtain a polymer lithium-ion battery.

[0027] The beneficial effects of the technical solution provided in this application include:

[0028] This application provides a polymer lithium-ion battery and its preparation method. The fibrous structure of the modified filler can increase the specific surface area of ​​the electrolyte and adsorb polymer segments, hindering the formation of crystal nuclei and suppressing the crystallization behavior of the polymer matrix at low temperatures, thus reducing the problem of a sudden increase in electrolyte viscosity at low temperatures. Moreover, the mechanical support of the modified filler can increase the puncture resistance of the electrolyte, which is in line with the development trend of green batteries. Dicyandiamide forms a chemical cross-linked network in the polymer matrix, thereby forming a three-dimensional through ion transport channel, which enhances the point-to-surface contact with the electrode active material and reduces the loss of plasticizer. At the same time, the semi-solid electrolyte can avoid the leakage of liquid electrolyte and improve the safety of the battery in long-term cycling. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A flowchart illustrating the preparation method of the polymer lithium-ion battery provided in this application. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] See Figure 1As shown, this application provides a polymer lithium-ion battery and its preparation method, which can solve the problems of low conductivity and significant performance degradation at low temperatures of semi-solid electrolytes in related technologies.

[0033] Example 1

[0034] The polymer lithium-ion battery provided in this embodiment is prepared by the following method:

[0035] The polymer electrolyte precursor was coated onto the positive electrode aluminum foil with a thickness of 60 μm using a slot coater. After standing for 30 min, it was cured under ultraviolet light for 10 min to form a polymer electrolyte layer on the positive electrode aluminum foil.

[0036] The side of the positive electrode aluminum foil coated with polymer electrolyte is stacked with the negative electrode graphite sheet, and then hot-pressed at 80°C for 5 minutes to obtain a polymer lithium-ion battery.

[0037] The preparation method of polymer electrolyte is as follows:

[0038] At 50℃, 10g of lithium hexafluorophosphate and 10g of lithium bis(trifluoromethanesulfonyl)imide were added to 80g of polymer matrix solution. Then, 10g of ethylene carbonate and 5g of dimethyl carbonate were added sequentially. The mixture was ultrasonically dispersed for 30min, and then 4g of modified filler was added. The mixture was ultrasonically dispersed for 1h to obtain the polymer electrolyte precursor.

[0039] The polymer electrolyte precursor was coated into a 60 μm film, left to stand at room temperature for 2 h, and then irradiated under ultraviolet light for 10 min to obtain the polymer electrolyte.

[0040] The preparation method of the polymer matrix solution is as follows:

[0041] 40g of polyethylene oxide, 20g of polyvinylidene fluoride and 170mL of N-methylpyrrolidone were mixed and magnetically stirred to obtain a homogeneous solution with a solid content of 35%.

[0042] Add 9g adiponitrile and 4.5g dicyandiamide to the homogeneous solution, heat to 70°C and purge with nitrogen, stir for 20 min, add 0.6g azobisisobutyronitrile, and simultaneously cool to 50°C. Disperse by ultrasonication for 1 h to obtain a polymer matrix solution.

[0043] The preparation method of the modified filler is as follows:

[0044] 10g of microcrystalline cellulose was dissolved in 200mL of toluene, dispersed, and then 4g of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 75℃ for 2h, and after washing and drying, an intermediate was obtained.

[0045] 5g of intermediate was reacted with 2g of methyl methacrylate and 0.07g of azobisisobutyronitrile for 3h to obtain the modified filler.

[0046] Example 2

[0047] The difference between this embodiment and Example 1 is that the preparation method of the polymer matrix solution includes the following steps:

[0048] 60g of polyethylene oxide was mixed with 200mL of N-methylpyrrolidone and magnetically stirred to obtain a homogeneous solution with a solid content of 30%.

[0049] Add 9g adiponitrile and 4.5g dicyandiamide to the homogeneous solution, heat to 70°C and purge with nitrogen, stir for 20 min, add 0.6g azobisisobutyronitrile, and simultaneously cool to 50°C. Disperse by ultrasonication for 1 h to obtain a polymer matrix solution.

[0050] Example 3

[0051] The difference between this embodiment and Example 1 is that the preparation method of the polymer matrix solution includes the following steps:

[0052] 45g of polyethylene oxide, 15g of polyvinylidene fluoride and 150mL of N-methylpyrrolidone were mixed and magnetically stirred to obtain a homogeneous solution with a solid content of 40%.

[0053] Add 9g adiponitrile and 4.5g dicyandiamide to the homogeneous solution, heat to 70°C and purge with nitrogen, stir for 20 min, add 0.6g azobisisobutyronitrile, and simultaneously cool to 50°C. Disperse by ultrasonication for 1 h to obtain a polymer matrix solution.

[0054] Example 4

[0055] The polymer lithium-ion battery provided in this embodiment is prepared by the following method:

[0056] The polymer electrolyte precursor was coated onto the positive electrode aluminum foil with a thickness of 50 μm using a slot coater. After standing for 30 min, it was cured under ultraviolet light for 8 min to form a polymer electrolyte layer on the positive electrode aluminum foil.

[0057] The side of the positive electrode aluminum foil coated with polymer electrolyte is stacked with the negative electrode graphite sheet, and then hot-pressed at 80°C for 5 minutes to obtain a polymer lithium-ion battery.

[0058] The preparation method of polymer electrolyte is as follows:

[0059] At 50℃, 20g of lithium hexafluorophosphate and 10g of lithium bis(trifluoromethanesulfonyl)imide were added to 60g of polymer matrix solution. Then, 13.3g of ethylene carbonate and 6.7g of dimethyl carbonate were added sequentially, and the mixture was ultrasonically dispersed for 30min. Finally, 2g of modified filler was added, and the mixture was ultrasonically dispersed for 1h to obtain the polymer electrolyte precursor.

[0060] The polymer electrolyte precursor was coated into a 50 μm film, left to stand at room temperature for 2 h, and then irradiated under ultraviolet light for 8 min to obtain the polymer electrolyte.

[0061] The preparation method of the polymer matrix solution is as follows:

[0062] 36g of polyethylene oxide, 24g of polyvinylidene fluoride and 200mL of N-methylpyrrolidone were mixed and magnetically stirred to obtain a homogeneous solution with a solid content of 30%.

[0063] Add 9g adiponitrile and 4.5g dicyandiamide to the homogeneous solution, heat to 70°C and purge with nitrogen, stir for 20 min, add 0.6g azobisisobutyronitrile, and simultaneously cool to 50°C. Disperse by ultrasonication for 1 h to obtain a polymer matrix solution.

[0064] The preparation method of the modified filler is as follows:

[0065] 5g of microcrystalline cellulose was dissolved in 100mL of toluene, dispersed, and then 2g of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 75℃ for 2h, and after washing and drying, an intermediate was obtained.

[0066] 2.5g of the intermediate was reacted with 0.5g of methyl methacrylate and 0.03g of azobisisobutyronitrile for 3 hours to obtain the modified filler.

[0067] Example 5

[0068] The polymer lithium-ion battery provided in this embodiment is prepared by the following method:

[0069] The polymer electrolyte precursor was coated onto the positive electrode aluminum foil with a thickness of 80 μm using a slot coater. After standing for 30 min, it was cured under ultraviolet light for 12 min to form a polymer electrolyte layer on the positive electrode aluminum foil.

[0070] The side of the positive electrode aluminum foil coated with polymer electrolyte is stacked with the negative electrode graphite sheet, and then hot-pressed at 80°C for 5 minutes to obtain a polymer lithium-ion battery.

[0071] The preparation method of polymer electrolyte is as follows:

[0072] At 50℃, 25g of lithium hexafluorophosphate and 5g of lithium bis(oxalato)borate were added to 90g of polymer matrix solution. Then, 13.3g of ethylene carbonate and 6.7g of dimethyl carbonate were added sequentially, and the mixture was ultrasonically dispersed for 30min. Finally, 5g of modified filler was added, and the mixture was ultrasonically dispersed for 1h to obtain the polymer electrolyte precursor.

[0073] The polymer electrolyte precursor was coated into an 80 μm film, left to stand at room temperature for 2 h, and then irradiated under ultraviolet light for 12 min to obtain the polymer electrolyte.

[0074] The preparation method of the polymer matrix solution is as follows:

[0075] 60g of trimethylolpropane triacrylate was mixed with 200mL of N-methylpyrrolidone and magnetically stirred to obtain a homogeneous solution with a solid content of 30%.

[0076] Add 9g adiponitrile and 4.5g dicyandiamide to the homogeneous solution, heat to 70°C and purge with nitrogen, stir for 20 min, add 0.6g azobisisobutyronitrile, and simultaneously cool to 50°C. Disperse by ultrasonication for 1 h to obtain a polymer matrix solution.

[0077] The preparation method of the modified filler is as follows:

[0078] 10g of microcrystalline cellulose was dissolved in 200mL of toluene, dispersed, and then 4g of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 75℃ for 2h, and after washing and drying, an intermediate was obtained.

[0079] The modified filler was obtained by reacting 6g of the intermediate with 3g of methyl methacrylate and 0.09g of azobisisobutyronitrile for 3h.

[0080] Example 6

[0081] The difference between this embodiment and Example 5 is that, in the preparation of the polymer matrix solution, 60g of trimethylolpropane triacrylate is replaced with a mixture of 40g of trimethylolpropane triacrylate and 20g of polyacrylonitrile.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that no modified filler is added to the polymer electrolyte.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 1 is that 4g of modified filler in the polymer electrolyte was replaced with 4g of microcrystalline cellulose.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 1 is that adiponitrile and dicyandiamide are not added in the preparation of the polymer matrix solution.

[0088] The polymer lithium-ion batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 3 were tested.

[0089] First, the conductivity of the prepared polymer electrolyte was tested, specifically at room temperature (25℃) and low temperatures (-20℃ and -40℃).

[0090] The test was performed using AC impedance spectroscopy at a frequency of 10. -2 ~10 6 The test results are shown in Table 1, with a frequency of Hz and an amplitude of 10mV.

[0091] Table 1

[0092]

[0093] As shown in Table 1, the mixed polymer matrix and modified filler in Example 1 improved the ion channels, and the modified filler and plasticizer could still maintain a certain ion migration ability at low temperature. Compared with Example 1, which used a pure PEO polymer matrix, Example 2 had a relatively high conductivity at room temperature (25°C) due to better lithium salt dissociation. However, below -20°C, the polymer electrolyte had an increased number of crystalline regions, which hindered ion transport and resulted in a relatively low conductivity.

[0094] As seen in Example 4, the amount of lithium salt added is greater, but the solid content of the polymer matrix is ​​reduced, resulting in a decrease in system viscosity and an increase in ion migration resistance. At the same time, the amount of modified filler is reduced, the support structure is insufficient at low temperatures, and the electrical conductivity decreases significantly.

[0095] The polymer matrix trimethylolpropane triacrylate in Example 5 lacks polar groups, resulting in poor lithium salt dissociation. Especially at low temperatures, the cross-linked structure restricts ion migration, leading to a significant decrease in conductivity (significantly lower in Examples 1-6). In Example 6, compared to Example 5, 20g of polyacrylonitrile was added. The polar cyano groups promoted lithium salt dissociation, improving ion transport to some extent, and the conductivity was slightly higher than in Example 5.

[0096] In Comparative Example 1, which did not contain modified filler, the electrical conductivity was slightly lower due to the absence of modified filler.

[0097] In Comparative Example 2, no modified filler was used; instead, microcrystalline cellulose was used. While it could serve as a physical filler, it could not form ion transport sites. Furthermore, the unmodified microcrystalline cellulose had poor dispersibility and was hydrophilic, leading to agglomeration that could destroy the electrolyte, resulting in lower conductivity than Comparative Example 1. This is because, although no modified filler or microcrystalline cellulose was added to the polymer in Comparative Example 1, the polymer matrix solution was more homogeneous, allowing lithium ions to migrate directly through chain segment movement and lithium salt dissociation. Therefore, the conductivity of Comparative Example 1 was higher than that of Comparative Example 2 at low temperatures.

[0098] Comparative Example 3, which did not contain adiponitrile or dicyandiamide, had a conductivity at 25°C that was not much different from that of Example 1. However, the polymer electrolyte obtained in Comparative Example 3 had poor stability at low temperatures (-20°C and -40°C), and the ion migration pathways were easily broken, resulting in a greater decrease in conductivity than that in Example 1.

[0099] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A polymer lithium-ion battery, characterized in that, It comprises: Positive aluminum foil, negative graphite sheet and polymer electrolyte; The polymer electrolyte comprises 30-90 parts of polymer matrix solution, 15-30 parts of lithium salt, 10-20 parts of plasticizer and 1-5 parts of modified filler, and the polymer electrolyte is obtained by irradiating the polymer electrolyte precursor under ultraviolet light; The preparation method of the modified filler comprises: Dissolve microcrystalline cellulose in toluene at a mass-volume ratio of 1:20, add 3-aminopropyl triethoxysilane after dispersion, reflux at 75℃ for 2h, and then clean and dry to obtain the intermediate, the mass of 3-aminopropyl triethoxysilane is 40% of the mass of microcrystalline cellulose; After reacting the intermediate with methyl methacrylate and azobisisobutyronitrile for 3h, the modified filler is obtained, the mass ratio of the intermediate to methyl methacrylate is 10:(2-5), and the mass of azobisisobutyronitrile is 1% of the total mass of the intermediate and methyl methacrylate.

2. The polymer lithium ion battery of claim 1, wherein: The preparation method of the polymer electrolyte comprises the following steps: At 50℃, add lithium salt to the polymer matrix solution, add plasticizer and ultrasonic dispersion for 30min, then add modified filler and ultrasonic dispersion for 1h to obtain the polymer electrolyte precursor; Coat the polymer electrolyte precursor into a film with a thickness of 50-80μm, stand still at room temperature for 2h, and then irradiate under ultraviolet light for 10min to obtain the polymer electrolyte.

3. The polymer lithium ion battery of claim 1 or 2, wherein: The preparation method of the polymer matrix solution comprises the following steps: Mix the polymer with N-methyl pyrrolidone and magnetically stir to obtain a homogeneous solution with a solid content of 30-40%; Add adiponitrile and dicyandiamide to the homogeneous solution, heat to 70℃ and introduce nitrogen, stir for 20min, then add azobisisobutyronitrile with a mass of 1% of the mass of the polymer, and at the same time, cool to 50℃, ultrasonic dispersion for 1h to obtain the polymer matrix solution; The amount of adiponitrile added is 15% of the mass of the polymer, and the amount of dicyandiamide added is half of the amount of adiponitrile.

4. The polymer lithium ion battery of claim 3, wherein: The polymer comprises one or more of trimethylolpropane triacrylate, polyacrylonitrile, polyethylene oxide, and polyvinylidene fluoride.

5. The polymer lithium ion battery of claim 3 or 4, wherein: The polymer is a mixture of polyethylene oxide and polyvinylidene fluoride, and the mass ratio of polyethylene oxide to polyvinylidene fluoride is (1.5-3):

1.

6. The polymer lithium ion battery of claim 2, wherein: When adding the plasticizer, the following steps are included: Add ethylene carbonate and dimethyl carbonate in sequence, and the mass ratio of ethylene carbonate to dimethyl carbonate is 2:

1.

7. The polymer lithium ion battery of claim 1, wherein: The lithium salt comprises one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalato)borate.

8. A method of producing a polymer lithium ion battery as claimed in any one of claims 1 to 7, characterized in that It comprises the following steps: The polymer electrolyte precursor is coated on the positive aluminum foil by a slot coater to a thickness of 50-80 μm, and then cured under ultraviolet light for 8-12 min after standing for 30 min, to form a polymer electrolyte layer on the positive aluminum foil; The positive aluminum foil coated with the polymer electrolyte is laminated with the negative graphite sheet, and then hot-pressed at 80 ℃ for 5 min to obtain a polymer lithium ion battery.

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