A polymer lithium-ion battery for low-temperature discharge and its preparation method

Abstract

This invention relates to the field of low-temperature lithium-ion battery technology, and discloses a polymer lithium-ion battery for low-temperature discharge and its preparation method, comprising the following steps: mixing lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black, stirring to obtain a positive electrode slurry; coating the positive electrode slurry onto an aluminum foil current collector, and rolling it using a roller press to obtain a positive electrode sheet; mixing a composite conductive agent, carboxymethyl cellulose, and acrylic resin, stirring to obtain a negative electrode slurry; coating the negative electrode slurry onto a copper foil current collector, and rolling it using a roller press to obtain a negative electrode sheet; uniformly winding a separator layer on the surface of the negative electrode sheet, and then winding it together with the positive electrode sheet to form a battery cell; placing the battery cell in a PET heat-shrink tubing, injecting electrolyte, sealing and curing to obtain a polymer lithium-ion battery. The negative electrode sheet formed by the composite conductive agent facilitates the insertion of lithium ions into the expanded graphite layers, improving the lithium-ion storage capacity and improving the discharge performance at low temperatures.

Description

Technical Field

[0001] This invention relates to the field of low-temperature lithium-ion battery technology, specifically to a polymer lithium-ion battery for low-temperature discharge and its preparation method. Background Technology

[0002] Compared to liquid lithium batteries, polymer lithium-ion batteries offer several significant advantages, including higher energy density, smaller size, ultra-thin design, lighter weight, and higher safety. They represent a new type of battery. In terms of shape, polymer lithium-ion batteries are ultra-thin, allowing them to be manufactured in any shape and capacity to meet product needs. Compared to liquid lithium-ion batteries, polymer lithium-ion batteries not only offer higher safety but also advantages such as thinness, arbitrary area, and arbitrary shape. The casing also utilizes a lighter aluminum-plastic composite film. However, the low-temperature discharge performance of existing polymer lithium batteries still needs improvement.

[0003] Graphite, as a negative electrode material for lithium-ion batteries, facilitates the insertion and extraction of lithium ions at low temperatures, resulting in good low-temperature discharge performance. This allows polymer lithium-ion batteries to have good discharge performance in low-temperature environments. However, the layered structure of graphite makes it easy for graphite negative electrode materials to stack, reducing the insertion and release of lithium ions and affecting the discharge performance of polymer lithium-ion batteries. Summary of the Invention

[0004] This invention provides a polymer lithium-ion battery for low-temperature discharge and its preparation method, which solves the problems of poor low-temperature discharge performance of polymer lithium batteries and the tendency of graphite materials to stack, which reduces the insertion and release of lithium ions.

[0005] The technical solution of this invention:

[0006] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0007] S1. Mix lithium cobalt oxide, polyvinylidene fluoride binder and carbon black, stir to obtain positive electrode slurry, coat the positive electrode slurry onto aluminum foil current collector, and roll it with a roller press to obtain positive electrode sheet;

[0008] S2. Mix the composite conductive agent, carboxymethyl cellulose and acrylic resin, stir to obtain a negative electrode slurry, coat the negative electrode slurry onto a copper foil current collector, and roll it using a roller press to obtain a negative electrode sheet;

[0009] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0010] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 60-80℃ for 2-3 hours to obtain a polymer lithium-ion battery.

[0011] The composite conductive agent is obtained by mixing polyethylene glycol fatty acid ester, expanded graphite and spinel lithium titanate microspheres;

[0012] The spinel lithium titanate microspheres are obtained by mixing and reacting nano-silica powder, coupling agent, spinel lithium titanate and polyacrylonitrile, followed by cyclization treatment.

[0013] Furthermore, the mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is (8-10):(1.5-2):(3-5).

[0014] Furthermore, the mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is (6-9):(1.2-1.5):(3-3.5).

[0015] Furthermore, the aluminum foil current collector has a thickness of 10-20 μm and a purity of 99-99.5%.

[0016] Furthermore, the copper foil current collector has a thickness of 12-16 μm and a purity of 99-99.5%.

[0017] Furthermore, the diaphragm is a glass fiber diaphragm with a thickness of 9-12 μm.

[0018] Furthermore, the inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 2-3 mm, and the outer diameter is 3-5 mm.

[0019] Furthermore, the electrolyte is prepared by mixing lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether and polyetheramine in a ratio of (1.6-2)g:(20-30)mL:(10-15)mL:(2-3)g:(2.5-3.5)g.

[0020] Furthermore, the composite conductive agent is prepared by the following steps:

[0021] A1. Add spinel lithium titanate to deionized water and ethanol, stir evenly, add coupling agent, stir until the reaction is complete, add nano silicon powder and hydrochloric acid, continue stirring until complete, filter, wash and dry to obtain modified spinel lithium titanate.

[0022] A2. Modified spinel lithium titanate and polyacrylonitrile are added to dimethylformamide, stirred evenly, heated to 150-155℃, and after stirring, washed and dried, placed in a muffle furnace and heat-treated at 200-230℃ for 1-3 hours, and cooled to room temperature to obtain spinel lithium titanate microspheres.

[0023] A3. Polyethylene glycol fatty acid esters and expanded graphite were added to deionized water, and after ultrasonic treatment, spinel lithium titanate microspheres were added. Ultrasonic treatment was continued, and the temperature was raised to 90-110℃. After stirring, the mixture was washed and dried to obtain a composite conductive agent.

[0024] Furthermore, during the A1 reaction process described above, the silanol groups generated by the hydrolysis of the coupling agent can be chemically bonded to the hydroxyl groups on the surface of the spinel lithium titanate, and the amino groups contained in the coupling agent can react with the amino groups on the surface of the nano-silicon powder, thereby coating the nano-silicon powder onto the surface of the spinel lithium titanate.

[0025] Furthermore, in the A2 reaction process described above, the modified spinel lithium titanate is dispersed in a solvent of polyacrylonitrile and dimethylformamide. At 150-155°C, the dimethylformamide evaporates, and then the polyacrylonitrile is coated onto the surface of the modified spinel lithium titanate. After the polyacrylonitrile is coated onto the surface of the modified spinel lithium titanate, it is heat-treated at 200°C, which causes the nitrile groups (-C≡N) in the polyacrylonitrile molecular chain to interact with adjacent groups and transform into a stable cyclic structure, thus obtaining spinel lithium titanate microspheres.

[0026] Furthermore, during the A3 reaction described above, polyethylene glycol fatty acid esters can enter the interlayer space of expanded graphite, thereby increasing the interlayer spacing of expanded graphite. Moreover, the hydroxyl groups carried on the polyethylene glycol fatty acid ester molecular chains can combine with spinel lithium titanate microspheres, allowing the spinel lithium titanate microspheres to enter the interlayer space of expanded graphite along with the polyethylene glycol fatty acid esters, forming a composite conductive agent.

[0027] Further, in step A1, the ratio of the amount of spinel lithium titanate, deionized water, ethanol, coupling agent, nano-silicon powder, and hydrochloric acid is (1-2)g:(15-25)mL:(45-55)mL:(0.3-0.6)g:(0.3-0.6)g:(0.1-0.3)mL.

[0028] Further, in step A2, the ratio of the modified spinel lithium titanate, polyacrylonitrile, and dimethylformamide is (2-3)g:(1-2)g:(25-35)mL.

[0029] Further, in step A3, the ratio of polyethylene glycol fatty acid ester, expanded graphite, deionized water, and spinel lithium titanate microspheres is (4-6) mL:(2-4) g:(80-120) mL:(1-1.4) g.

[0030] Furthermore, the coupling agent is γ-aminopropyltriethoxysilane.

[0031] Furthermore, the expanded graphite has a particle size of 1-3 μm.

[0032] Furthermore, the polyethylene glycol fatty acid ester is polyethylene glycol 400 monooleate.

[0033] Furthermore, the spinel lithium titanate has a particle size of 0.1-0.5 μm.

[0034] Furthermore, the particle size of the nano-silicon powder is 30-40 nm.

[0035] Furthermore, the degree of polymerization of polyacrylonitrile is 15,000-16,000.

[0036] The present invention has the following beneficial effects:

[0037] (1) In the technical solution of the present invention, spinel lithium titanate has a lot of lithium ion binding sites, which is conducive to the insertion and diffusion of lithium ions and improves the charge and discharge performance of lithium ion batteries. The nano silicon powder is coated on the surface of spinel lithium titanate. On the one hand, the nano silicon powder has a high energy storage capacity, which can significantly improve the energy density of polymer lithium ion batteries and increase the low-temperature discharge performance of lithium ion batteries. Moreover, the shape stability of nano silicon powder avoids the volume expansion and contraction of expanded graphite during charge and discharge, which affects the performance of polymer lithium ion batteries. On the other hand, the combination of nano silicon powder and inorganic spinel lithium titanate has a stronger lithium storage capacity, which can significantly improve the discharge performance of batteries at low temperatures.

[0038] (2) In the technical solution of the present invention, polyacrylonitrile is coated on the surface of modified spinel lithium titanate. After cyclization, spinel lithium titanate microspheres are formed, which can improve the lithium ion transport rate, improve conductivity, and avoid the shedding of nano-silicon powder. After polyacrylonitrile is coated on the surface of modified spinel lithium titanate, after cyclization treatment, the nitrile group (-C≡N) in the polyacrylonitrile molecular chain interacts with the adjacent group and transforms into a stable cyclic structure, which increases the rigidity, stability and elasticity of the molecule, can accommodate volume expansion, avoid the electrode material from being crushed at low temperature, and improve the discharge performance at low temperature.

[0039] (3) In the technical solution of the present invention, the expanded graphite has a porous structure and a high specific surface area. There are a large number of micropores and channels inside, which is beneficial to the embedding and transport of lithium-ion batteries. The spinel lithium titanate microspheres enter the interlayer of expanded graphite along with polyethylene glycol fatty acid esters to form a composite conductive agent. On the one hand, it can expand the interlayer spacing of expanded graphite, which is beneficial to the embedding of lithium ions into the interlayer of expanded graphite and improve the lithium ion storage capacity. On the other hand, the spinel lithium titanate microspheres can effectively shorten the diffusion path of lithium ions and effectively prevent the re-stacking of expanded graphite sheets, thereby maximizing the intercalation sites of lithium ions and improving the discharge performance at low temperature.

[0040] (4) In the technical solution of the present invention, the epoxy groups contained in the polypropylene glycol diglycidyl ether in the electrolyte can polymerize with the amine groups of the polyetheramine to form a polymer electrolyte. The polymer electrolyte does not contain residual initiators, which is beneficial to improve lithium-ion conduction, effectively reduce the internal resistance of the battery, and improve the discharge performance at low temperature. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0042] The raw materials used in the embodiments of this invention are shown below, and all reagents used are analytical grade.

[0043] The coupling agent is γ-aminopropyltriethoxysilane.

[0044] The expanded graphite has a particle size of 2.5 μm.

[0045] The polyethylene glycol fatty acid ester is polyethylene glycol 400 monooleate.

[0046] The spinel lithium titanate has a particle size of 0.4 μm.

[0047] The particle size of the nano-silicon powder is 40nm.

[0048] The degree of polymerization of polyacrylonitrile is 15000.

[0049] The polyvinylidene fluoride adhesive was purchased from Shanghai Heyiyuan Plastic Raw Materials Co., Ltd.

[0050] Acrylic resin, CAS number 9003-01-4, purity 99%, purchased from Zhengzhou Aikem Chemical Co., Ltd.

[0051] Example 1

[0052] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0053] S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 8:1.5:3; the rolling density is 2 g / cm³. 3 .

[0054] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 6:1.2:3; the rolling density is 1 g / cm³. 3 .

[0055] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0056] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 60°C for 2 hours to obtain a polymer lithium-ion battery.

[0057] The aluminum foil current collector has a thickness of 10μm and a purity of 99%.

[0058] The copper foil current collector has a thickness of 12μm and a purity of 99%.

[0059] The diaphragm is a glass fiber diaphragm with a thickness of 9 μm.

[0060] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 2mm, and the outer diameter is 3mm.

[0061] The electrolyte is a mixture of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 1.6g:20mL:10mL:2g:2.5g.

[0062] The composite conductive agent is prepared by the following steps:

[0063] A1. Add 1g of spinel lithium titanate to 15mL of deionized water and 45mL of ethanol, stir well, add 0.3g of γ-aminopropyltriethoxysilane, stir and react at 50℃ for 10min, add 0.3g of nano-silicon powder and 0.1mL of 36% hydrochloric acid, continue stirring and reacting for 10min, filter, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain modified spinel lithium titanate;

[0064] A2. Add 2g of modified spinel lithium titanate and 1g of polyacrylonitrile to 25mL of dimethylformamide, stir evenly, heat to 150℃, stir until dimethylformamide evaporates, wash 3 times with deionized water, dry in an oven at 70℃ for 10min, place in a muffle furnace, pass argon gas at a rate of 1.5L / min, heat treat at 200℃ for 2h, cool to room temperature, and obtain spinel lithium titanate microspheres;

[0065] A3. Add 4 mL of polyethylene glycol 400 monooleate and 5 g of expanded graphite to 80 mL of deionized water, sonicate at 250 W and 40 kHz for 30 min, add 1 g of spinel lithium titanate microspheres, continue sonication for 30 min, heat to 100 °C, stir until solvent evaporates, wash 3 times with deionized water, and dry in a 70 °C oven for 10 min to obtain the composite conductive agent.

[0066] Example 2

[0067] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following steps: S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 9:1.8:4; the rolling density is 2.5 g / cm³. 3 .

[0068] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 8:1.3:3.3; the rolling density is 1.3 g / cm³. 3 .

[0069] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0070] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 70°C for 2.5 hours to obtain a polymer lithium-ion battery.

[0071] The aluminum foil current collector has a thickness of 15μm and a purity of 99.3%.

[0072] The copper foil current collector has a thickness of 14μm and a purity of 99.3%.

[0073] The diaphragm is a glass fiber diaphragm with a thickness of 10 μm.

[0074] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 2.5 mm, and the outer diameter is 4 mm.

[0075] The electrolyte is a mixture of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 1.8g:25mL:13mL:2.5g:3g.

[0076] The composite conductive agent is prepared by the following steps:

[0077] A1. Add 1.5g of spinel lithium titanate to 20mL of deionized water and 50mL of ethanol, stir well, add 0.5g of γ-aminopropyltriethoxysilane, stir and react at 50℃ for 10min, add 0.5g of nano-silicon powder and 0.2mL of 36% hydrochloric acid, continue stirring and reacting for 10min, filter, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain modified spinel lithium titanate;

[0078] A2. Add 2.5g of modified spinel lithium titanate and 1.5g of polyacrylonitrile to 30mL of dimethylformamide, stir evenly, heat to 153℃, stir until dimethylformamide evaporates, wash 3 times with deionized water, dry in an oven at 70℃ for 10min, place in a muffle furnace, pass argon gas at a rate of 1.5L / min, heat treat at 220℃ for 2h, cool to room temperature, and obtain spinel lithium titanate microspheres;

[0079] A3. Add 5 mL of polyethylene glycol 400 monooleate and 3 g of expanded graphite to 100 mL of deionized water, sonicate at 250 W and 40 kHz for 30 min, add 1.2 g of spinel lithium titanate microspheres, continue sonication for 30 min, heat to 100 °C, stir until solvent evaporates, wash 3 times with deionized water, and dry in a 70 °C oven for 10 min to obtain the composite conductive agent.

[0080] Example 3

[0081] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0082] S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 10:2:5; the rolling density is 3 g / cm³. 3 .

[0083] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 9:1.5:3.5; the rolling density is 1.5 g / cm³. 3 .

[0084] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0085] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 80°C for 3 hours to obtain a polymer lithium-ion battery.

[0086] The aluminum foil current collector has a thickness of 20μm and a purity of 99.5%.

[0087] The copper foil current collector has a thickness of 16μm and a purity of 99.5%.

[0088] The diaphragm is a glass fiber diaphragm with a thickness of 12 μm.

[0089] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 3mm and the outer diameter is 5mm.

[0090] The electrolyte is composed of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 2g:30mL:15mL:3g:3.5g.

[0091] The composite conductive agent is prepared by the following steps:

[0092] A1. Add 2g of spinel lithium titanate to 25mL of deionized water and 55mL of ethanol, stir well, add 0.6g of γ-aminopropyltriethoxysilane, stir and react at 50℃ for 10min, add 0.6g of nano-silicon powder and 0.3mL of 36% hydrochloric acid, continue stirring and reacting for 10min, filter, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain modified spinel lithium titanate;

[0093] A2. Add 3g of modified spinel lithium titanate and 2g of polyacrylonitrile to 35mL of dimethylformamide, stir evenly, heat to 155℃, stir until dimethylformamide evaporates, wash 3 times with deionized water, dry in an oven at 70℃ for 10min, place in a muffle furnace, pass argon gas at a rate of 1.5L / min, heat treat at 230℃ for 3h, cool to room temperature, and obtain spinel lithium titanate microspheres;

[0094] A3. Add 6 mL of polyethylene glycol 400 monooleate and 4 g of expanded graphite to 120 mL of deionized water, sonicate at 250 W and 40 kHz for 30 min, add 1.4 g of spinel lithium titanate microspheres, continue sonication for 30 min, heat to 110 °C and stir until the solvent evaporates, wash 3 times with deionized water, and dry in an oven at 70 °C for 10 min to obtain the composite conductive agent.

[0095] Comparative Example 1

[0096] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0097] S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 10:2:5; the rolling density is 3 g / cm³. 3 .

[0098] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 9:1.5:3.5; the rolling density is 1.5 g / cm³. 3 .

[0099] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0100] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 80°C for 3 hours to obtain a polymer lithium-ion battery.

[0101] The aluminum foil current collector has a thickness of 20μm and a purity of 99.5%.

[0102] The copper foil current collector has a thickness of 16μm and a purity of 99.5%.

[0103] The diaphragm is a glass fiber diaphragm with a thickness of 12 μm.

[0104] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 3mm and the outer diameter is 5mm.

[0105] The electrolyte is composed of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 2g:30mL:15mL:3g:3.5g.

[0106] The composite conductive agent is prepared by the following steps:

[0107] A1. Add 3g of spinel lithium titanate and 2g of polyacrylonitrile to 35mL of dimethylformamide, stir evenly, heat to 155℃, stir until dimethylformamide evaporates, wash 3 times with deionized water, dry in an oven at 70℃ for 10min, place in a muffle furnace, pass argon gas at a rate of 1.5L / min, heat treat at 230℃ for 3h, cool to room temperature, and obtain spinel lithium titanate microspheres;

[0108] A2. Add 6 mL of polyethylene glycol 400 monooleate and 4 g of expanded graphite to 120 mL of deionized water, sonicate at 250 W and 40 kHz for 30 min, add 1.4 g of spinel lithium titanate microspheres, continue sonication for 30 min, heat to 110 °C and stir until the solvent evaporates, wash 3 times with deionized water, and dry in an oven at 70 °C for 10 min to obtain the composite conductive agent.

[0109] Comparative Example 2

[0110] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0111] S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 10:2:5; the rolling density is 3 g / cm³. 3 .

[0112] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 9:1.5:3.5; the rolling density is 1.5 g / cm³. 3 .

[0113] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0114] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 80°C for 3 hours to obtain a polymer lithium-ion battery.

[0115] The aluminum foil current collector has a thickness of 20μm and a purity of 99.5%.

[0116] The copper foil current collector has a thickness of 16μm and a purity of 99.5%.

[0117] The diaphragm is a glass fiber diaphragm with a thickness of 12 μm.

[0118] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 3mm and the outer diameter is 5mm.

[0119] The electrolyte is composed of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 2g:30mL:15mL:3g:3.5g.

[0120] The composite conductive agent is prepared by the following steps:

[0121] A1. Add 2g of spinel lithium titanate to 25mL of deionized water and 55mL of ethanol, stir well, add 0.6g of γ-aminopropyltriethoxysilane, stir and react at 50℃ for 10min, add 0.6g of nano-silicon powder and 0.3mL of 36% hydrochloric acid, continue stirring and reacting for 10min, filter, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain modified spinel lithium titanate;

[0122] A2. Add 6 mL of polyethylene glycol 400 monooleate and 4 g of expanded graphite to 120 mL of deionized water, sonicate at 250 W and 40 kHz for 30 min, add 1.4 g of modified spinel lithium titanate, continue sonication for 30 min, heat to 110 °C and stir until the solvent evaporates, wash 3 times with deionized water, and dry in an oven at 70 °C for 10 min to obtain the composite conductive agent.

[0123] Comparative Example 3

[0124] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0125] S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 10:2:5; the rolling density is 3 g / cm³. 3 .

[0126] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 9:1.5:3.5; the rolling density is 1.5 g / cm³. 3 .

[0127] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0128] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 80°C for 3 hours to obtain a polymer lithium-ion battery.

[0129] The aluminum foil current collector has a thickness of 20μm and a purity of 99.5%.

[0130] The copper foil current collector has a thickness of 16μm and a purity of 99.5%.

[0131] The diaphragm is a glass fiber diaphragm with a thickness of 9-12 μm.

[0132] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 3mm and the outer diameter is 5mm.

[0133] The electrolyte is composed of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 2g:30mL:15mL:3g:3.5g.

[0134] The composite conductive agent is prepared by the following steps:

[0135] A1. Add 2g of spinel lithium titanate to 25mL of deionized water and 55mL of ethanol, stir well, add 0.6g of γ-aminopropyltriethoxysilane, stir and react at 50℃ for 10min, add 0.6g of nano-silicon powder and 0.3mL of 36% hydrochloric acid, continue stirring and reacting for 10min, filter, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain modified spinel lithium titanate;

[0136] A2. Add 3g of modified spinel lithium titanate and 2g of polyacrylonitrile to 35mL of dimethylformamide, stir evenly, heat to 155℃, stir until dimethylformamide evaporates, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain spinel lithium titanate microspheres.

[0137] A3. Add 6 mL of polyethylene glycol 400 monooleate and 4 g of expanded graphite to 120 mL of deionized water, sonicate at 250 W and 40 kHz for 30 min, add 1.4 g of spinel lithium titanate microspheres, continue sonication for 30 min, heat to 110 °C and stir until the solvent evaporates, wash 3 times with deionized water, and dry in an oven at 70 °C for 10 min to obtain the composite conductive agent.

[0138] Comparative Example 4

[0139] A method for preparing a polymer lithium-ion battery for low-temperature discharge includes the following preparation steps:

[0140] S1. Lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black are mixed and stirred at 250 r / min for 40 min to obtain a positive electrode slurry. The positive electrode slurry is coated onto an aluminum foil current collector and rolled using a roller press to obtain a positive electrode sheet. The mass ratio of lithium cobalt oxide, polyvinylidene fluoride binder, and carbon black is 10:2:5; the rolling density is 3 g / cm³. 3 .

[0141] S2. The composite conductive agent, carboxymethyl cellulose, and acrylic resin are mixed and stirred at 250 r / min for 40 min to obtain a negative electrode slurry. The negative electrode slurry is coated onto a copper foil current collector and rolled using a roller press to obtain a negative electrode sheet. The mass ratio of the composite conductive agent, carboxymethyl cellulose, and acrylic resin is 9:1.5:3.5; the rolling density is 1.5 g / cm³. 3 .

[0142] S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell;

[0143] S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 80°C for 3 hours to obtain a polymer lithium-ion battery.

[0144] The aluminum foil current collector has a thickness of 20μm and a purity of 99.5%.

[0145] The copper foil current collector has a thickness of 16μm and a purity of 99.5%.

[0146] The diaphragm is a glass fiber diaphragm with a thickness of 9-12 μm.

[0147] The inner diameter of the PET (polyethylene terephthalate) heat shrink tubing is 3mm and the outer diameter is 5mm.

[0148] The electrolyte is composed of lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether, and polyetheramine in a ratio of 2g:30mL:15mL:3g:3.5g.

[0149] The composite conductive agent is prepared by the following steps:

[0150] A1. Add 2g of spinel lithium titanate to 25mL of deionized water and 55mL of ethanol, stir well, add 0.6g of γ-aminopropyltriethoxysilane, stir and react at 50℃ for 10min, add 0.6g of nano-silicon powder and 0.3mL of 36% hydrochloric acid, continue stirring and reacting for 10min, filter, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain modified spinel lithium titanate;

[0151] A2. Add 3g of modified spinel lithium titanate and 2g of polyacrylonitrile to 35mL of dimethylformamide, stir evenly, heat to 155℃, stir until dimethylformamide evaporates, wash 3 times with deionized water, dry in an oven at 70℃ for 10min, place in a muffle furnace, pass argon gas at a rate of 1.5L / min, heat treat at 230℃ for 3h, cool to room temperature, and obtain spinel lithium titanate microspheres;

[0152] A3. Add 4g of expanded graphite to 120mL of deionized water, sonicate at 250W and 40kHz for 30min, add 1.4g of spinel lithium titanate microspheres, continue sonication for 30min, heat to 110℃ and stir until the solvent evaporates, wash 3 times with deionized water, and dry in an oven at 70℃ for 10min to obtain the composite conductive agent.

[0153] The performance of the polymer lithium-ion batteries treated in Examples 1-3 and Comparative Examples 1-4 was then tested.

[0154] The polymer lithium-ion battery is fully charged to 4.2V at room temperature using a 0.5C current.

[0155] Low-temperature discharge performance testing: After the polymer lithium-ion battery was fully charged to 4.2V at room temperature using a 0.5C current, the fully charged battery was placed in environments of -20℃, -40℃, and -60℃ respectively, and discharged to 3V at 0.5C. After 500 charge-discharge cycles, the battery capacity retention and discharge efficiency were recorded. The results are shown in Table 1 below.

[0156] Table 1 Performance testing of polymer lithium-ion batteries after treatment in Examples 1-3 and Comparative Examples 1-6

[0157]

[0158]

[0159] As shown in Table 1, the polymer lithium-ion batteries prepared in Examples 1-3 exhibit good low-temperature discharge performance. In Comparative Example 1, when the modified spinel lithium titanate was replaced with a composite conductive agent prepared from spinel lithium titanate, the low-temperature discharge performance of the polymer lithium-ion battery decreased. This demonstrates that coating the surface of spinel lithium titanate with nano-silicon powder increases the low-temperature discharge performance of the battery, and the shape stability of the nano-silicon powder prevents the volume expansion and contraction of the expanded graphite during charging and discharging.

[0160] In Comparative Example 2, the spinel lithium titanate microspheres were replaced with a composite conductive agent prepared from modified spinel lithium titanate for the production of polymer lithium-ion batteries. The low-temperature discharge performance of the polymer lithium-ion batteries decreased, demonstrating that polyacrylonitrile coated on the surface of modified spinel lithium titanate and cyclized to form spinel lithium titanate microspheres can improve the lithium-ion transport rate, increase conductivity, prevent the shedding of nano-silicon powder, and improve the discharge performance at low temperatures.

[0161] In Comparative Example 3, the composite conductive agent prepared by polyacrylonitrile without cyclization treatment was used to produce polymer lithium-ion batteries. Its low-temperature discharge performance decreased, indicating that after polyacrylonitrile was coated on the surface of modified spinel lithium titanate and then cyclized, the nitrile groups (-C≡N) in the polyacrylonitrile molecular chain interacted with adjacent groups, transforming into a stable cyclic structure. This increased the rigidity, stability, and elasticity of the molecule, allowing it to accommodate volume expansion, preventing the electrode material from pulverizing at low temperatures, and improving the discharge performance at low temperatures.

[0162] In Comparative Example 4, the composite conductive agent prepared without the addition of polyethylene glycol 400 monooleate was used to produce polymer lithium-ion batteries. Its low-temperature discharge performance decreased, which proves that the spinel lithium titanate microspheres, along with polyethylene glycol fatty acid esters, enter the interlayer of expanded graphite, thereby increasing the interlayer spacing of expanded graphite and improving the lithium-ion storage capacity. Furthermore, the spinel lithium titanate microspheres can effectively shorten the diffusion path of lithium ions and improve the discharge performance at low temperatures.

[0163] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0164] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for preparing a polymer lithium-ion battery for low-temperature discharge, characterized in that, The preparation steps include the following: S1. Mix lithium cobalt oxide, polyvinylidene fluoride binder and carbon black, stir to obtain positive electrode slurry, coat the positive electrode slurry onto aluminum foil current collector, and roll it with a roller press to obtain positive electrode sheet; S2. Mix the composite conductive agent, carboxymethyl cellulose and acrylic resin, stir to obtain a negative electrode slurry, coat the negative electrode slurry onto a copper foil current collector, and roll it using a roller press to obtain a negative electrode sheet; S3. After uniformly winding a separator on the surface of the negative electrode, it is then wound together with the positive electrode to form a battery cell; S4. Place the battery cell in a PET heat shrink tubing, inject electrolyte, seal it, and cure it at 60-80℃ for 2-3 hours to obtain a polymer lithium-ion battery. The composite conductive agent is obtained by mixing polyethylene glycol fatty acid ester, expanded graphite and spinel lithium titanate microspheres; The spinel lithium titanate microspheres are obtained by mixing and reacting nano-silica powder, coupling agent, spinel lithium titanate and polyacrylonitrile, followed by cyclization treatment.

2. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 1, characterized in that, The composite conductive agent is prepared by the following steps: A1. Add spinel lithium titanate to deionized water and ethanol, stir evenly, add coupling agent, stir until the reaction is complete, add nano silicon powder and hydrochloric acid, continue stirring until complete, filter, wash and dry to obtain modified spinel lithium titanate. A2. Modified spinel lithium titanate and polyacrylonitrile are added to dimethylformamide, stirred evenly, heated to 150-155℃, and after stirring, washed and dried, placed in a muffle furnace and heat-treated at 200-230℃ for 1-3 hours, and cooled to room temperature to obtain spinel lithium titanate microspheres. A3. Polyethylene glycol fatty acid esters and expanded graphite were added to deionized water, and after ultrasonic treatment, spinel lithium titanate microspheres were added. Ultrasonic treatment was continued, and the temperature was raised to 90-110℃. After stirring, the mixture was washed and dried to obtain a composite conductive agent.

3. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 2, characterized in that, In step A1, the ratio of the amount of spinel lithium titanate, deionized water, ethanol, coupling agent, nano-silicon powder, and hydrochloric acid is (1-2)g:(15-25)mL:(45-55)mL:(0.3-0.6)g:(0.3-0.6)g:(0.1-0.3)mL.

4. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 2, characterized in that, In step A2, the ratio of modified spinel lithium titanate, polyacrylonitrile, and dimethylformamide is (2-3)g:(1-2)g:(25-35)mL.

5. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 2, characterized in that, In step A3, the ratio of polyethylene glycol fatty acid ester, expanded graphite, deionized water, and spinel lithium titanate microspheres is (4-6) mL:(2-4) g:(80-120) mL:(1-1.4) g.

6. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 1, characterized in that, The aluminum foil current collector has a thickness of 10-20 μm and a purity of 99-99.5%; the copper foil current collector has a thickness of 12-16 μm and a purity of 99-99.5%.

7. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 1, characterized in that, The diaphragm is a glass fiber diaphragm with a thickness of 9-12 μm; the PET heat shrink tubing has an inner diameter of 2-3 mm and an outer diameter of 3-5 mm.

8. The method for preparing a polymer lithium-ion battery for low-temperature discharge according to claim 1, characterized in that, The electrolyte is prepared by mixing lithium hexafluorophosphate, ethyl methyl carbonate, vinylene carbonate, polypropylene glycol diglycidyl ether and polyetheramine in a ratio of (1.6-2)g:(20-30)mL:(10-15)mL:(2-3)g:(2.5-3.5)g.

9. A polymer lithium-ion battery prepared by the preparation method according to any one of claims 1-8.

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