Polymer lithium ion battery and preparation method thereof

Abstract

The invention 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 an anode aluminum foil sheet, a cathode 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; according to the polymer lithium ion battery and the preparation method thereof provided by the invention, the problems that the conductivity of a semi-solid electrolyte is relatively low and the performance of the semi-solid electrolyte is obviously reduced at a low temperature in the prior art are solved.

Description

Technical Field

[0001] The present application relates to the technical field of polymer lithium-ion batteries, and in particular to a polymer lithium-ion battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries are secondary batteries that store and release energy by embedding / de-embedding lithium ions between 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 risk of electrolyte leakage and flammability and explosion. The semi-solid batteries in related technologies introduce a small amount of liquid components or plasticizers to form "ion conduction channels" in the solid polymer matrix, balancing safety, conductivity and processing performance. There is no risk of liquid electrolyte leakage, and the ignition point is high, which can reduce the probability of fire caused by overcharging and short circuit. At the same time, the electrolyte also has the function of a diaphragm, which can simplify the battery structure.

[0004] However, the contact area between the semi-solid electrolyte and the electrode material is limited, and its conductivity at room temperature is lower than that of the liquid electrolyte. In particular, its performance decreases significantly at low temperatures, affecting low-temperature endurance. Summary of the Invention

[0005] The present application provides a polymer lithium-ion battery and a preparation method thereof, in order to solve the problem in the related art that the conductivity of the semi-solid electrolyte is low and the performance is significantly degraded at low temperatures.

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

[0009] The preparation method of the modified filler comprises:

[0010] Dissolve microcrystalline cellulose in toluene at a mass-to-volume ratio of 1:20, add 3-aminopropyltriethoxysilane after dispersion, reflux at 75°C for 2 hours, wash and dry to obtain an intermediate, wherein the mass of the 3-aminopropyltriethoxysilane is 40% of the microcrystalline cellulose;

[0011] The intermediate is reacted with methyl methacrylate and azobisisobutyronitrile for 3 hours to obtain a modified filler. 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.

[0012] Preferably, the preparation method of the polymer electrolyte comprises the following steps:

[0013] Adding lithium salt to the polymer matrix solution at 50° C., adding a plasticizer and then ultrasonically dispersing for 30 minutes, then adding a modified filler and ultrasonically dispersing for 1 hour to obtain the polymer electrolyte precursor;

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

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

[0016] The polymer is mixed with N-methylpyrrolidone and stirred magnetically 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, stir for 20 minutes, then add azobisisobutyronitrile (1% by weight of the polymer), cool to 50° C. and ultrasonically disperse for 1 hour to obtain a polymer matrix solution;

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

[0019] Preferably, the polymer includes 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, when adding a plasticizer, the following steps are included:

[0022] Ethylene carbonate and dimethyl carbonate were added in sequence, with the mass ratio of ethylene carbonate to dimethyl carbonate being 2:1.

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

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

[0025] The polymer electrolyte precursor is coated on the positive electrode aluminum foil by a slot coater to a thickness of 50 to 80 μm, and after standing for 30 minutes, it is cured under ultraviolet light for 8 to 12 minutes to form a polymer electrolyte layer on the positive electrode aluminum foil;

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

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

[0028] The present application provides a polymer lithium-ion battery and a preparation method thereof. The fiber structure of the modified filler can increase the specific surface area of ​​the electrolyte, and at the same time can adsorb polymer segments, hinder the formation of crystallization nuclei, inhibit the crystallization behavior of the polymer matrix at low temperatures, and reduce the problem of sudden increase in electrolyte viscosity at low temperatures; and the mechanical support of the modified filler can increase the puncture resistance of the electrolyte, which is also in line with the development trend of green batteries; dicyandiamide forms a chemically cross-linked network in the polymer matrix, thereby forming a three-dimensional through-hole ion transmission channel, which enhances the point-to-surface contact with the electrode active material and can reduce the loss of plasticizer. At the same time, the semi-solid electrolyte can avoid leakage of liquid electrolyte, thereby improving the safety of the battery in long-term circulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] Figure 1 This is a flow chart of the method for preparing a polymer lithium-ion battery provided in this application. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0032] See also Figure 1As shown, the present application provides a polymer lithium-ion battery and a preparation method thereof, which can solve the problems in the related art that the conductivity of the semi-solid electrolyte is low and the performance is significantly degraded at low temperatures.

[0033] Example 1

[0034] The polymer lithium-ion battery provided in this embodiment has a preparation method comprising:

[0035] The polymer electrolyte precursor was coated on the positive electrode aluminum foil by a slot coater to a thickness of 60 μm, allowed to stand for 30 minutes, and then cured under ultraviolet light for 10 minutes to form a polymer electrolyte layer on the positive electrode aluminum foil;

[0036] The side of the positive electrode aluminum foil coated with the polymer electrolyte was overlapped with the negative electrode graphite sheet, and 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°C, 10 g of lithium hexafluorophosphate and 10 g of lithium bis(trifluoromethanesulfonyl imide) were added to 80 g of the polymer matrix solution, followed by 10 g of ethylene carbonate and 5 g of dimethyl carbonate. The mixture was ultrasonically dispersed for 30 min, and then 4 g of the modified filler was added and ultrasonically dispersed for 1 h to obtain a polymer electrolyte precursor.

[0039] The polymer electrolyte precursor was coated into a 60 μm thin film, allowed to stand at room temperature for 2 hours, and then irradiated under ultraviolet light for 10 minutes to obtain a polymer electrolyte.

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

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

[0042] 9 g of adiponitrile and 4.5 g of dicyandiamide were added to the homogeneous solution, the temperature was raised to 70° C. and nitrogen was introduced. After stirring for 20 min, 0.6 g of azobisisobutyronitrile was added. The temperature was lowered to 50° C. and ultrasonic dispersion was performed for 1 h to obtain a polymer matrix solution.

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

[0044] Dissolve 10 g of microcrystalline cellulose in 200 mL of toluene, add 4 g of 3-aminopropyltriethoxysilane after dispersion, reflux at 75 ° C for 2 h, wash and dry to obtain an intermediate;

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

[0046] Example 2

[0047] This embodiment differs from embodiment 1 in that the method for preparing the polymer matrix solution comprises the following steps:

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

[0049] 9 g of adiponitrile and 4.5 g of dicyandiamide were added to the homogeneous solution, the temperature was raised to 70° C. and nitrogen was introduced. After stirring for 20 min, 0.6 g of azobisisobutyronitrile was added. The temperature was lowered to 50° C. and ultrasonic dispersion was performed for 1 h to obtain a polymer matrix solution.

[0050] Example 3

[0051] This embodiment differs from embodiment 1 in that the method for preparing the polymer matrix solution comprises the following steps:

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

[0053] 9 g of adiponitrile and 4.5 g of dicyandiamide were added to the homogeneous solution, the temperature was raised to 70° C. and nitrogen was introduced. After stirring for 20 min, 0.6 g of azobisisobutyronitrile was added. The temperature was lowered to 50° C. and ultrasonic dispersion was performed for 1 h to obtain a polymer matrix solution.

[0054] Example 4

[0055] The polymer lithium-ion battery provided in this embodiment has a preparation method comprising:

[0056] The polymer electrolyte precursor was coated on the positive electrode aluminum foil by a slot coater to a thickness of 50 μm, allowed to stand for 30 minutes, and then cured under ultraviolet light for 8 minutes to form a polymer electrolyte layer on the positive electrode aluminum foil;

[0057] The side of the positive electrode aluminum foil coated with the polymer electrolyte was overlapped with the negative electrode graphite sheet, and 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°C, 20g of lithium hexafluorophosphate and 10g of lithium bis(trifluoromethanesulfonyl imide) were added to 60g of the polymer matrix solution, followed by the addition of 13.3g of ethylene carbonate and 6.7g of dimethyl carbonate, followed by ultrasonic dispersion for 30min. Then, 2g of the modified filler was added and ultrasonic dispersion was performed for 1h to obtain a polymer electrolyte precursor.

[0060] The polymer electrolyte precursor was coated into a 50 μm thin film, allowed to stand at room temperature for 2 hours, and then irradiated under ultraviolet light for 8 minutes to obtain a polymer electrolyte.

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

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

[0063] 9 g of adiponitrile and 4.5 g of dicyandiamide were added to the homogeneous solution, the temperature was raised to 70° C. and nitrogen was introduced. After stirring for 20 min, 0.6 g of azobisisobutyronitrile was added. The temperature was lowered to 50° C. and ultrasonic dispersion was performed for 1 h to obtain a polymer matrix solution.

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

[0065] 5 g of microcrystalline cellulose was dissolved in 100 mL of toluene, and 2 g of 3-aminopropyltriethoxysilane was added after dispersion. The mixture was refluxed at 75 ° C for 2 h, and then washed and dried to obtain an intermediate.

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

[0067] Example 5

[0068] The polymer lithium-ion battery provided in this embodiment has a preparation method comprising:

[0069] The polymer electrolyte precursor was coated on the positive electrode aluminum foil by a slot coater to a thickness of 80 μm, allowed to stand for 30 minutes, and then cured under ultraviolet light for 12 minutes to form a polymer electrolyte layer on the positive electrode aluminum foil;

[0070] The side of the positive electrode aluminum foil coated with the polymer electrolyte was overlapped with the negative electrode graphite sheet, and 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°C, 25g of lithium hexafluorophosphate and 5g of lithium bis(oxalatoborate) were added to 90g of the polymer matrix solution, followed by the addition of 13.3g of ethylene carbonate and 6.7g of dimethyl carbonate, followed by ultrasonic dispersion for 30min. 5g of the modified filler was then added and ultrasonic dispersion was performed for 1h to obtain a polymer electrolyte precursor.

[0073] The polymer electrolyte precursor was coated into a thin film of 80 μm, allowed to stand at room temperature for 2 hours, and then irradiated under ultraviolet light for 12 minutes to obtain a polymer electrolyte.

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

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

[0076] 9 g of adiponitrile and 4.5 g of dicyandiamide were added to the homogeneous solution, the temperature was raised to 70° C. and nitrogen was introduced. After stirring for 20 min, 0.6 g of azobisisobutyronitrile was added. The temperature was lowered to 50° C. and ultrasonic dispersion was performed for 1 h to obtain a polymer matrix solution.

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

[0078] Dissolve 10 g of microcrystalline cellulose in 200 mL of toluene, add 4 g of 3-aminopropyltriethoxysilane after dispersion, reflux at 75 ° C for 2 h, wash and dry to obtain an intermediate;

[0079] 6 g of the intermediate was reacted with 3 g of methyl methacrylate and 0.09 g of azobisisobutyronitrile for 3 h to obtain a modified filler.

[0080] Example 6

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

[0082] Comparative Example 1

[0083] This comparative example is different from Example 1 in that no modified filler is added to the polymer electrolyte.

[0084] Comparative Example 2

[0085] This comparative example differs from Example 1 in that 4 g of the modified filler in the polymer electrolyte is replaced with 4 g of microcrystalline cellulose.

[0086] Comparative Example 3

[0087] This comparative example is different from Example 1 in 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 the conductivity at room temperature (25° C.) and low temperature (-20° C. and -40° C.) was tested.

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

[0091] Table 1

[0092]

[0093] From Table 1, it can be seen that the mixed polymer matrix and modified filler in Example 1 improve the ion channel, and the modified filler and plasticizer can still maintain a certain ion migration ability in collaboration at low temperatures. From Example 2, compared with Example 1 using a polymer matrix of pure PEO, at room temperature (25°C), the conductivity is relatively high due to better dissociation of lithium salts. However, below -20°C, the crystallization area in the polymer electrolyte increases, ion transmission is hindered, and the conductivity is relatively low.

[0094] From 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 the viscosity of the system and an increase in the ion migration resistance. At the same time, the amount of modified filler used is reduced, the supporting structure is insufficient at low temperatures, and the conductivity decreases significantly.

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

[0096] In Comparative Example 1 in which no modified filler was added, the electrical conductivity was slightly low due to the absence of the modified filler.

[0097] Comparative Example 2 uses no modified filler and instead uses microcrystalline cellulose. This can function as a physical filler, but it cannot form ion transport sites. Furthermore, unmodified microcrystalline cellulose has poor dispersibility and is hydrophilic, so its aggregation can destroy the electrolyte, resulting in lower conductivity than Comparative Example 1. This is because, although the polymer in Comparative Example 1 lacks modified fillers and microcrystalline cellulose, the polymer matrix solution is relatively uniform, allowing lithium ions to migrate directly through chain segment motion and lithium salt dissociation. Therefore, the conductivity of Comparative Example 1 is higher than that of Comparative Example 2 at low temperatures.

[0098] The conductivity of Comparative Example 3, in which no adiponitrile or dicyandiamide was added, was not much different from that of Example 1 at 25°C. However, the polymer electrolyte obtained in Comparative Example 3 had poor stability at low temperatures (-20°C and -40°C), the ion migration path was easily broken, and the decrease in conductivity was greater than that in Example 1.

[0099] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present 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 the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A polymer lithium-ion battery, characterized in that: It includes: Positive electrode aluminum foil, negative electrode graphite sheet and polymer electrolyte; The polymer electrolyte comprises 30 to 90 parts of a polymer matrix solution, 15 to 30 parts of a lithium salt, 10 to 20 parts of a plasticizer, and 1 to 5 parts of a modified filler, and the polymer electrolyte is obtained by irradiating a polymer electrolyte precursor under ultraviolet light; The preparation method of the modified filler comprises: Dissolve microcrystalline cellulose in toluene at a mass-to-volume ratio of 1:20, add 3-aminopropyltriethoxysilane after dispersion, reflux at 75°C for 2 hours, wash and dry to obtain an intermediate, wherein the mass of the 3-aminopropyltriethoxysilane is 40% of the microcrystalline cellulose; The intermediate is reacted with methyl methacrylate and azobisisobutyronitrile for 3 hours to obtain a modified filler. 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 according to claim 1, wherein: The preparation method of the polymer electrolyte comprises the following steps: Adding lithium salt to the polymer matrix solution at 50° C., adding a plasticizer and then ultrasonically dispersing for 30 minutes, then adding a modified filler and ultrasonically dispersing for 1 hour to obtain the polymer electrolyte precursor; The polymer electrolyte precursor is coated into a thin film of 50 to 80 μm, left to stand at room temperature for 2 hours, and then irradiated under ultraviolet light for 10 minutes to obtain a polymer electrolyte.

3. The polymer lithium-ion battery according to claim 1 or 2, wherein: The preparation method of the polymer matrix solution comprises the following steps: The polymer is mixed with N-methylpyrrolidone and stirred magnetically to obtain a homogeneous solution with a solid content of 30-40%; Add adiponitrile and dicyandiamide to the homogeneous solution, heat to 70° C. and introduce nitrogen, stir for 20 minutes, then add azobisisobutyronitrile (1% by weight of the polymer), cool to 50° C. and ultrasonically disperse for 1 hour to obtain a 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 mass of adiponitrile.

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

5. The polymer lithium-ion battery according to claim 3 or 4, wherein: 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.

6. The polymer lithium-ion battery according to claim 2, wherein: When adding plasticizer, the following steps are included: Ethylene carbonate and dimethyl carbonate were added in sequence, with the mass ratio of ethylene carbonate to dimethyl carbonate being 2:

1.

7. The polymer lithium-ion battery according to claim 1, wherein: The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, and lithium bis(oxalatoborate).

8. A method for preparing a polymer lithium-ion battery according to any one of claims 1 to 7, characterized in that: It includes the following steps: The polymer electrolyte precursor is coated on the positive electrode aluminum foil by a slot coater to a thickness of 50 to 80 μm, and after standing for 30 minutes, it is cured under ultraviolet light for 8 to 12 minutes to form a polymer electrolyte layer on the positive electrode aluminum foil; The side of the positive electrode aluminum foil coated with the polymer electrolyte was overlapped with the negative electrode graphite sheet, and hot pressed at 80° C. for 5 minutes to obtain a polymer lithium-ion battery.

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