WO2023225843A1 - 隔膜及其制备方法、电化学装置和电子装置 - Google Patents

隔膜及其制备方法、电化学装置和电子装置 Download PDF

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WO2023225843A1
WO2023225843A1 PCT/CN2022/094669 CN2022094669W WO2023225843A1 WO 2023225843 A1 WO2023225843 A1 WO 2023225843A1 CN 2022094669 W CN2022094669 W CN 2022094669W WO 2023225843 A1 WO2023225843 A1 WO 2023225843A1
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cellulose
microcrystalline cellulose
cellulose composite
substrate
composite separator
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PCT/CN2022/094669
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English (en)
French (fr)
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陈嘉乐
夏恒涛
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宁德新能源科技有限公司
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Priority to PCT/CN2022/094669 priority Critical patent/WO2023225843A1/zh
Publication of WO2023225843A1 publication Critical patent/WO2023225843A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/44—Fibrous material

Definitions

  • the present application relates to the technical field of electrochemistry, and in particular to a separator and its preparation method, electrochemical device and electronic device.
  • Secondary batteries have the characteristics of large specific energy, high operating voltage, low self-discharge rate, small size, and light weight. They are widely used in various fields such as electrical energy storage, portable electronic devices, and electric vehicles. With the rapid development of electric vehicles and mobile electronic devices, people's demand for the performance of secondary batteries is also getting higher and higher.
  • separators in secondary batteries are polyethylene (PE) or polypropylene (PP) separators.
  • PE polyethylene
  • PP polypropylene
  • the above separators have poor thermal stability. That is, when the secondary battery is at a high ambient temperature, or due to short circuit or overcharge, When it heats up, the separator is prone to uneven shrinkage and rupture, which can lead to internal short circuit and thermal runaway.
  • PP or PE separators also have poor electrolyte wettability and liquid retention, which affects the safety performance of secondary batteries. , rate performance and cycle life will be adversely affected.
  • This application provides a separator, a preparation method thereof, an electrochemical device and an electronic device to improve the safety performance, rate performance and cycle life of the electrochemical device.
  • a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion batteries.
  • the first aspect of the present application provides a cellulose composite membrane, which includes a substrate and a microcrystalline cellulose layer located on at least one surface of the substrate and microcrystalline cellulose located in the pores of the substrate, so
  • the substrate includes polyethylene and/or polypropylene.
  • the base material includes polyethylene and/or polypropylene
  • the cellulose composite separator also includes microcrystalline cellulose (microcrystalline cellulose layer and microcrystalline cellulose in the pores of the base material), polyethylene And/or polypropylene and microcrystalline cellulose can exert a synergistic effect, making the cellulose composite separator have good thermal stability, electrolyte wettability and high-temperature closed-pore characteristics. Therefore, the electrochemical device using the cellulose composite separator of the present application can have good safety performance, rate performance and long cycle life.
  • the thickness of the microcrystalline cellulose layer is 2 ⁇ m to 20 ⁇ m, and the thickness of the substrate is 4 ⁇ m to 30 ⁇ m. Regulating the thickness of the microcrystalline cellulose layer and the thickness of the substrate within the above range is more conducive to improving the safety performance, rate performance, and energy density of the electrochemical device, and extending the cycle life of the electrochemical device.
  • the cellulose composite membrane has a porosity of 40% to 70%. In another embodiment of the present application, the cellulose composite membrane has a porosity of 45% to 60%. Regulating the porosity of the cellulose composite separator within the above range can enable the cellulose composite separator to have excellent ion transport capability and strength, which is more conducive to improving the rate performance of the electrochemical device and extending the cycle life of the electrochemical device.
  • the thermal shrinkage rate of the cellulose composite separator when heated at 120°C for 1 hour is 0% to 1.0%. In another embodiment of the present application, the thermal shrinkage rate of the cellulose composite separator when heated at 120° C. for 1 hour is 0.2% to 0.8%. In yet another embodiment of the present application, the thermal shrinkage rate of the cellulose composite separator when heated at 120° C. for 1 hour is 0.4% to 0.6%. It shows that the thermal shrinkage rate of the cellulose composite separator when heated at 120°C for 1 hour is low, and the cellulose composite separator has good thermal stability. This is more conducive to improving the safety performance of electrochemical devices.
  • the cellulose composite membrane has a liquid absorption rate of 100% to 240%. In another embodiment of the present application, the cellulose composite membrane has a liquid absorption rate of 120% to 200%. In yet another embodiment of the present application, the liquid absorption rate of the cellulose composite membrane is 140% to 180%. Regulating the liquid absorption rate of the cellulose composite separator within the above range is more conducive to improving the safety performance and rate performance of the electrochemical device and extending the cycle life of the electrochemical device.
  • the second aspect of this application provides a method for preparing a cellulose composite separator, which includes the following steps:
  • microcrystalline cellulose (2) The substrate is placed in a microcrystalline cellulose dispersion, and microcrystalline cellulose layers are independently induced and deposited on both surfaces of the substrate, and the microcrystalline cellulose layers are formed in the pores of the substrate. of microcrystalline cellulose; or,
  • the base material includes polyethylene and/or polypropylene.
  • the preparation method of the cellulose composite separator of the present application is simple and easy to operate, and can be widely used in industrial production.
  • polyethylene and/or polypropylene and microcrystalline cellulose can exert a synergistic effect, so that the cellulose composite separator has good thermal stability, electrolyte wettability and high temperature sealing. Pore properties. Therefore, the electrochemical device using the cellulose composite separator of the present application can have good safety performance, rate performance and long cycle life.
  • the deposition temperature of the induced deposition is 0°C to 60°C, and the deposition time is 10 min to 360 min. Regulating the deposition temperature and deposition time within the above range is more conducive to destroying the hydrogen bonds formed between microcrystalline cellulose and microcrystalline cellulose dispersion, inducing microcrystalline cellulose to precipitate and deposit on the substrate, and the preparation includes the substrate and The microcrystalline cellulose layer located on both surfaces of the substrate and the cellulose composite separator of microcrystalline cellulose located in the pores of the substrate are more conducive to improving the safety performance and rate performance of the electrochemical device and extending the cycle of the electrochemical device life.
  • the microcrystalline cellulose dispersion includes NaOH, urea, microcrystalline cellulose and water, based on the mass of the microcrystalline cellulose dispersion, the mass of the microcrystalline cellulose The percentage content is 1% to 4%. Regulating the mass percentage of microcrystalline cellulose within the above range is more conducive to the formation of the microcrystalline cellulose layer, which is more conducive to improving the safety performance and rate performance of the electrochemical device, and extending the cycle life of the electrochemical device.
  • the third aspect of the present application provides an electrochemical device, which includes the cellulose composite separator according to any one of the foregoing aspects; or includes the cellulose composite separator prepared by the preparation method according to any one of the foregoing aspects.
  • a fourth aspect of the present application provides an electronic device, which includes the electrochemical device described in any of the preceding aspects.
  • the present application provides a separator and its preparation method, electrochemical device and electronic device, in which the polyethylene and/or polypropylene and microcrystalline cellulose in the cellulose composite separator can exert a synergistic effect, so that the cellulose composite separator has Good thermal stability, electrolyte wettability and high temperature closed cell characteristics.
  • the cellulose composite separator of the present application is applied to an electrochemical device.
  • the electrochemical device is in a high-temperature environment or generates heat due to short circuit, overcharging, etc., the good thermal stability of the cellulose composite separator can reduce the occurrence of malfunctions.
  • the cellulose composite separator will exert its good high-temperature closed-pore characteristics and promptly cut off the current channel inside the electrochemical device, further reducing the heat of the electrochemical device. Risk of loss of control;
  • the good electrolyte wettability of the cellulose composite separator can effectively adjust the internal resistance of the electrochemical device, improve the rate performance of the electrochemical device, and extend the cycle life of the electrochemical device. Therefore, the electrochemical device using the cellulose composite separator of the present application can have good safety performance, rate performance and long cycle life.
  • Figure 1 is a schematic diagram of the preparation process of a cellulose composite separator according to one embodiment of the present application
  • Figure 2 is a schematic diagram of the preparation process of a cellulose composite separator according to another embodiment of the present application.
  • a lithium ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium ion batteries.
  • a first aspect of the application provides a cellulose composite separator, which includes a base material and a microcrystalline cellulose layer located on at least one surface of the base material and microcrystalline cellulose located in the pores of the base material.
  • the base material includes polyethylene. and/or polypropylene.
  • the base material includes polyethylene and/or polypropylene
  • the cellulose composite separator also includes microcrystalline cellulose (microcrystalline cellulose layer and microcrystalline cellulose in the pores of the base material), polyethylene And/or polypropylene and microcrystalline cellulose can exert a synergistic effect, making the cellulose composite separator have good thermal stability, electrolyte wettability and high-temperature closed-pore characteristics.
  • the cellulose composite separator of the present application is applied to an electrochemical device.
  • the good thermal stability of the cellulose composite separator can reduce the occurrence of malfunctions. Risk of uniform shrinkage or membrane rupture; when the internal temperature of the electrochemical device rises above 130°C, the cellulose composite separator will exert its good high-temperature closed-pore characteristics and promptly cut off the current channel inside the electrochemical device, further reducing the heat of the electrochemical device.
  • the good electrolyte wettability of the cellulose composite separator can effectively adjust the internal resistance of the electrochemical device, improve the rate performance of the electrochemical device, and extend the cycle life of the electrochemical device. Therefore, the electrochemical device using the cellulose composite separator of the present application can have good safety performance, rate performance and long cycle life.
  • microcrystalline cellulose layer located on at least one surface of the substrate may be understood to mean that the microcrystalline cellulose layer is located on both surfaces of the substrate, or on any of the two surfaces of the substrate.
  • FIG. 1 shows a schematic cross-sectional structural diagram of a cellulose composite membrane in an embodiment of the present application.
  • the cellulose composite membrane includes a base material 10 As well as microcrystalline cellulose layers 30 located on both surfaces of the substrate 10 and microcrystalline cellulose 31 located in the pores (not shown) of the substrate 10 .
  • (f) in Figure 2 shows a schematic cross-sectional structural view of a cellulose composite membrane in another embodiment of the present application.
  • the cellulose composite membrane includes a base material 10 and a base material located on the base material 10.
  • the microcrystalline cellulose layer 30 can also be located on the second surface 102 of the substrate 10 .
  • the thickness Y of the microcrystalline cellulose layer 30 is 2 ⁇ m to 20 ⁇ m, and the thickness X of the substrate 10 is 4 ⁇ m to 30 ⁇ m.
  • the thickness Y of the microcrystalline cellulose layer 30 may be 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m, 10 ⁇ m, 13 ⁇ m, 16 ⁇ m, 20 ⁇ m, or any value between any two of the above numerical ranges.
  • the thickness Y of the microcrystalline cellulose layer 30 and the thickness thereby affecting the safety performance, rate performance and cycle life of the electrochemical device; the thickness Y of the microcrystalline cellulose layer 30 and the thickness X of the substrate 10 are too thick (for example, Y is greater than 20 ⁇ m,
  • the increase in ion transmission path and internal resistance will affect the rate performance of the electrochemical device, and the volume of the electrochemical device will increase accordingly, which will affect the volumetric energy density of the electrochemical device.
  • Regulating the thickness Y of the microcrystalline cellulose layer 30 and the thickness X of the substrate 10 within the above range is more conducive to improving the safety performance, rate performance, and energy density of the electrochemical device, and extending the cycle life of the electrochemical device.
  • the thickness Y of the microcrystalline cellulose layer refers to the thickness of a single microcrystalline cellulose layer located on one surface of the base material layer.
  • the cellulose composite membrane has a porosity ⁇ of 40% to 70%. In another embodiment of the present application, the cellulose composite membrane has a porosity of 45% to 60%.
  • the porosity ⁇ of the cellulose composite membrane can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any value between any two of the above numerical ranges.
  • the porosity ⁇ of the cellulose composite separator is too low (for example, less than 40%), and it is difficult for the electrolyte to infiltrate the cellulose composite separator, which affects the ion transmission capacity of the cellulose composite separator and increases the internal resistance of the electrochemical device; cellulose composite separator If the porosity ⁇ is too high (for example, higher than 70%), the cellulose composite separator becomes loose and its strength decreases, which affects the puncture resistance of the cellulose composite separator. Regulating the porosity ⁇ of the cellulose composite separator within the above range can make the cellulose composite separator have excellent ion transport capability and strength, which is more conducive to improving the rate performance of the electrochemical device and extending the cycle life of the electrochemical device.
  • the thermal shrinkage rate of the cellulose composite separator when heated at 120°C for 1 hour is 0% to 1.0%. In another embodiment of the present application, the thermal shrinkage rate of the cellulose composite separator when heated at 120° C. for 1 hour is 0.2% to 0.8%. In yet another embodiment of the present application, the thermal shrinkage rate of the cellulose composite separator when heated at 120° C. for 1 hour is 0.4% to 0.6%.
  • the thermal shrinkage rate of a cellulose composite separator heated at 120°C for 1 hour can be 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, or any value between any two of the above numerical ranges. It shows that the thermal shrinkage rate of the cellulose composite separator when heated at 120°C for 1 hour is low, and the cellulose composite separator has good thermal stability, which is more conducive to improving the safety performance of electrochemical devices.
  • the cellulose composite membrane has a liquid absorption rate of 100% to 240%. In another embodiment of the present application, the cellulose composite membrane has a liquid absorption rate of 120% to 200%. In yet another embodiment of the present application, the cellulose composite membrane has a liquid absorption rate of 140% to 180%.
  • the liquid absorption rate of the cellulose composite membrane can be 100%, 120%, 140%, 160%, 180%, 200%, 220%, 240% or any value between any two of the above numerical ranges.
  • the liquid absorption rate of the cellulose composite separator is too low (for example, less than 100%), and the electrolyte wettability and liquid retention of the cellulose composite separator are reduced, which will affect the ion transmission capacity of the cellulose composite separator and increase the electrochemical device's Internal resistance:
  • the liquid absorption rate of the cellulose composite membrane is too high (for example, higher than 240%), which increases the thickness of the cellulose composite membrane and lengthens the ion transmission path. Regulating the liquid absorption rate of the cellulose composite separator within the above range is more conducive to improving the safety performance and rate performance of the electrochemical device and extending the cycle life of the electrochemical device.
  • the second aspect of this application provides a method for preparing a cellulose composite separator, which includes the following steps:
  • the substrate is placed in the microcrystalline cellulose dispersion, and microcrystalline cellulose layers are independently induced and deposited on both surfaces of the substrate, and microcrystalline cellulose is formed in the pores of the substrate; or,
  • the base material includes polyethylene and/or polypropylene.
  • the preparation method of the cellulose composite separator of the present application is simple and easy to operate, and can be widely used in industrial production.
  • polyethylene and/or polypropylene and microcrystalline cellulose can exert a synergistic effect, so that the cellulose composite separator has good thermal stability, electrolyte wettability and high temperature sealing. Pore properties. Therefore, the electrochemical device using the cellulose composite separator of the present application can have good safety performance, rate performance and long cycle life.
  • the surface of the substrate can be modified by microwave plasma treatment.
  • the parameters during microwave plasma treatment are not particularly limited, as long as the purpose of this application can be achieved.
  • the power is 2KW to 6KW
  • the voltage is 100V to 300V
  • the time is 40s to 120s.
  • Figure 1 shows a schematic diagram of the preparation process of a cellulose composite separator according to an embodiment of the present application.
  • the substrate 10 shown in (a) in Figure 1 is prepared according to step (1) This method involves performing surface modification treatment in an air or oxygen atmosphere to increase polar sites 20 on the surface of the substrate 10 and the pore surface of the substrate as shown in (b) of Figure 1 .
  • the substrate 10 (containing the polar sites 20) shown in (b) of Figure 1 is placed in the microcrystalline cellulose dispersion, on both surfaces of the substrate 10
  • step (3) the composite material in Figure 1(c) is washed with water and vacuum dried to obtain the cellulose composite separator described in any of the above solutions.
  • FIG. 2 shows a schematic diagram of the preparation process of a cellulose composite separator according to another embodiment of the present application.
  • the substrate 10 shown in (d) in Figure 2 is processed according to the method of step (1).
  • Surface modification treatment is performed in an air or oxygen atmosphere to increase polar sites 20 on the surface of the substrate 10 and the surface of the substrate pores as shown in (e) of Figure 2 .
  • the microcrystalline cellulose dispersion is coated on the first surface 101 of the substrate 10 (containing the polar sites 20) shown in (e) of Figure 2.
  • the microcrystalline cellulose layer 30 shown in (f) in Figure 2 is formed on the first surface 101 of the base material 10, and the microcrystalline cellulose 31 located in the pores (not shown) of the base material 10 is formed.
  • the composite material in Figure 2(f) is washed with water and vacuum dried to obtain the cellulose composite separator described in any of the above solutions.
  • the microcrystalline cellulose dispersion can also be coated on the second surface 102 of the substrate 10 (containing the polar sites 20) shown in (e) of Figure 2.
  • the microcrystalline cellulose layer 30 is formed on the second surface 102 of the substrate 10 , and the microcrystalline cellulose 31 located in the pores of the substrate 10 is formed.
  • first surface and the second surface of the substrate can be understood as any one of the two surfaces of the substrate.
  • first and second is only for convenience of expression. It does not imply a limitation on both surfaces of the substrate.
  • the deposition temperature of induced deposition is 0°C to 60°C, and the deposition time is 10 min to 360 min.
  • the deposition temperature is 25°C to 60°C, and the deposition time is 10min to 30min.
  • the deposition temperature can be 0°C, 10°C, 20°C, 25°C, 30°C, 40°C, 45°C, 50°C, 60°C, or any value between any two of the above numerical ranges.
  • the deposition time can be 10min, 30min, 60min, 90min, 120min, 150min, 180min, 210min, 240min, 270min, 300min, 330min, 360min or any value between any two of the above numerical ranges.
  • the deposition temperature is too low (for example, below 0°C) or too high (for example, above 60°C), and the deposition time is too short (for example, less than 10 min) or too long (for example, longer than 360 min), which are not conducive to the formation of the microcrystalline cellulose layer.
  • Deposition, the thickness of the microcrystalline cellulose layer, the uniformity of deposition, and the porosity of the cellulose composite separator will all be affected.
  • Regulating the deposition temperature and deposition time within the above range is more conducive to destroying the hydrogen bonds formed between microcrystalline cellulose and microcrystalline cellulose dispersion, inducing microcrystalline cellulose to precipitate and deposit on the substrate, and the preparation includes the substrate and The microcrystalline cellulose layer located on both surfaces of the substrate and the cellulose composite separator of microcrystalline cellulose located in the pores of the substrate are more conducive to improving the safety performance and rate performance of the electrochemical device and extending the cycle of the electrochemical device life.
  • the microcrystalline cellulose dispersion includes NaOH, urea, microcrystalline cellulose and water
  • the mass percentage of microcrystalline cellulose is 1% based on the mass of the microcrystalline cellulose dispersion. to 4%.
  • the mass percentage of microcrystalline cellulose can be 1%, 2%, 3%, 4% or any value between any two of the above numerical ranges. Regulating the mass percentage of microcrystalline cellulose within the above range is more conducive to the formation of the microcrystalline cellulose layer, which is more conducive to improving the safety performance and rate performance of the electrochemical device, and extending the cycle life of the electrochemical device.
  • This application has no special restrictions on the quality of NaOH and urea in the microcrystalline cellulose dispersion, as long as the purpose of this application can be achieved.
  • the mass percentage of NaOH is 3% to 15%
  • the mass percentage of urea is 5% to 20%.
  • microcrystalline cellulose among the components of the microcrystalline cellulose dispersion is microcrystalline cellulose well known in the art.
  • the microcrystalline cellulose is a natural cellulose hydrolyzed granular product. Its main components are linear polysaccharides bonded with ⁇ -1,4-glucosidic bonds.
  • the particle size is 20 ⁇ m to 80 ⁇ m, and the ultimate degree of polymerization is 15 to 375. .
  • the microcrystalline cellulose is commercially available.
  • the preparation of microcrystalline cellulose dispersion includes the following steps: mix 3wt% to 15wt% NaOH, 5wt% to 20wt% urea and water to obtain a solution, cool the solution to -20°C to 0°C, and then add 1wt % to 4wt% of microcrystalline cellulose, stir until a colorless and transparent solution.
  • the above mass percentages are based on the total mass of the microcrystalline cellulose dispersion.
  • the third aspect of the present application provides an electrochemical device, which includes the cellulose composite separator according to any one of the foregoing aspects; or includes the cellulose composite separator prepared by the preparation method according to any one of the foregoing aspects. Therefore, the electrochemical device of the present application has good safety performance, rate performance and long cycle life.
  • the electrochemical device of this application also includes positive electrode pieces, negative electrode pieces, electrolyte, outer packaging, etc.
  • This application has no special restrictions on the positive electrode sheet, negative electrode sheet, electrolyte and outer packaging. It can be the positive electrode sheet, negative electrode sheet, electrolyte and outer packaging that are well known in the art, as long as the purpose of this application can be achieved.
  • the cellulose composite separator of the present application is located between the positive electrode piece and the negative electrode piece. It is used to separate the positive electrode piece and the negative electrode piece, prevent internal short circuit of the electrochemical device, allow electrolyte ions to pass freely, and complete the electrochemical charge and discharge process. .
  • the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion battery, a sodium ion battery, a lithium polymer secondary battery, a lithium ion polymer secondary battery, and the like.
  • the preparation process of the electrochemical device is well known to those skilled in the art, and the application is not particularly limited.
  • it may include but is not limited to the following steps: stacking the positive electrode sheet, the cellulose composite separator and the negative electrode sheet in order, and Winding, folding and other operations are performed as needed to obtain an electrode assembly with a wound structure, the electrode assembly is placed into a packaging case, the electrolyte is injected into the packaging case and sealed to obtain an electrochemical device; or, the positive electrode sheet, cellulose The composite separator and negative electrode plates are stacked in order, and then the four corners of the entire lamination structure are fixed with tape to obtain the electrode assembly of the lamination structure.
  • the electrode assembly is placed in the packaging shell, and the electrolyte is injected into the packaging shell and sealed. An electrochemical device is obtained.
  • overcurrent prevention components, guide plates, etc. can also be placed in the packaging case as needed to prevent pressure rise inside the electrochemical device and overcharge and discharge.
  • a fourth aspect of the present application provides an electronic device, which includes the electrochemical device described in any of the preceding aspects. Therefore, the electronic device of the present application has good safety performance, rate performance and long cycle life.
  • the electronic device of the present application is not particularly limited and may be used in any electronic device known in the art.
  • the electronic device may include, but is not limited to, a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a stereo headset , VCR, LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, power-assisted bicycle, bicycle , lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • a ten thousandth thickness gauge to measure the thickness Y of the microcrystalline cellulose layer.
  • the thickness of the microcrystalline cellulose layer Y (T-X)/2, where X is the thickness of the substrate.
  • the gas displacement method is used to test the porosity ⁇ of the cellulose composite separator.
  • the porosity ⁇ (V-V0)/V ⁇ 100%, and the pore volume is V-V0, where V0 is the true volume of the tested sample and V is the measured sample. Measure the total volume of the sample.
  • the testing equipment is a fully automatic true density tester (AccuPyc II 1340), and the test gas is helium.
  • Microcrystalline cellulose located in the pores of the substrate;
  • the deposition temperature of induced deposition is 25°C and the deposition time is 10 minutes;
  • the microcrystalline cellulose dispersion includes: 7wt% NaOH, 12wt% urea, 1.5wt% microcrystalline cellulose and 79.5wt% water.
  • the temperature of the microcrystalline cellulose dispersion is -12°C.
  • step (3) Wash the composite material prepared in step (2) with water and dry it in vacuum to obtain a cellulose composite separator.
  • the positive electrode sheet, cellulose composite separator, and negative electrode sheet prepared above are stacked in order, so that the cellulose composite separator is between the positive and negative electrodes for isolation, and the electrode assembly is obtained by winding.
  • the electrode assembly is placed in the outer packaging, the prepared electrolyte is injected and packaged, and the lithium-ion battery is obtained through processes such as formation, degassing, and trimming.
  • Example 1 Except for adjusting relevant preparation parameters according to Table 1, the rest is the same as Example 1. Among them, when the mass percentage of microcrystalline cellulose increases, the mass percentage of water decreases, and the mass percentage of NaOH and urea remains unchanged, so that the mass percentage of NaOH, urea, microcrystalline cellulose and water The sum of the masses is 100%.
  • Comparative Example 1 uses a PE base material with a thickness of 5 ⁇ m and a porosity of 37% as the separator.
  • the cellulose composite separator of the present application has larger porosity, smaller transverse and longitudinal thermal shrinkage, and lower absorption.
  • the liquid rate is higher, and the cellulose composite separator of the present application is applied to lithium-ion batteries.
  • the lithium-ion batteries have higher overcharge safety test pass rate and cycle life, and have good discharge capacity. It shows that the safety performance and rate performance of lithium-ion batteries using the cellulose composite separator of the present application can be improved, and the cycle life can be extended.
  • the mass percentage of microcrystalline cellulose in the microcrystalline cellulose dispersion usually affects the safety performance, rate performance and cycle life of lithium-ion batteries. It can be seen from Examples 1 to 3 that a lithium-ion battery with a mass percentage of microcrystalline cellulose within the scope of the present application has good safety performance, rate performance, and long cycle life.
  • the deposition time of induced deposition usually also affects the safety performance, rate performance and cycle life of lithium-ion batteries. It can be seen from Example 3 to Example 6 and Example 10 that the lithium-ion battery with a deposition time within the scope of the present application has good safety performance, rate performance, and long cycle life.
  • the deposition temperature that induces deposition usually also affects the safety performance, rate performance, and cycle life of lithium-ion batteries. It can be seen from Example 3, Example 7 to Example 10 that the lithium-ion battery with a deposition temperature within the range of the present application has good safety performance, rate performance, and long cycle life.
  • the composition of the substrate also generally affects the safety performance, rate performance and cycle life of lithium-ion batteries. It can be seen from Example 3, Example 11 and Example 12 that a lithium-ion battery with a base material composition within the scope of the present application has good safety performance, rate performance, and long cycle life.
  • the thickness of the substrate also generally affects the safety performance, rate performance and cycle life of lithium-ion batteries. It can be seen from Example 3, Example 13 and Example 14 that a lithium-ion battery with a base material thickness within the scope of the present application has good safety performance, rate performance, and long cycle life.

Abstract

本申请提供的一种隔膜及其制备方法、电化学装置和电子装置，其中，纤维素复合隔膜包括基材以及位于所述基材的至少一个表面上的微晶纤维素层和位于所述基材孔隙中的微晶纤维素，所述基材包括聚乙烯和/或聚丙烯。该纤维素复合隔膜中，基材包括聚乙烯和/或聚丙烯，且纤维素复合隔膜中同时包括微晶纤维素(微晶纤维素层以及基材孔隙中的微晶纤维素)，聚乙烯和/或聚丙烯与微晶纤维素能够发挥协同作用，使得纤维素复合隔膜具有良好的热稳定性、电解液浸润性和高温闭孔特性。由此，应用本申请纤维素复合隔膜的电化学装置能够具有良好的安全性能、倍率性能和较长的循环寿命。

Description

隔膜及其制备方法、电化学装置和电子装置 技术领域
本申请涉及电化学技术领域，特别是涉及一种隔膜及其制备方法、电化学装置和电子装置。
背景技术
二次电池具有比能量大、工作电压高、自放电率低、体积小、重量轻等特点，广泛应用于电能储存、便携式电子设备和电动汽车等各个领域。随着电动汽车和可移动电子设备的高速发展，人们对二次电池的性能需求也越来越高。
二次电池中常用的隔膜为聚乙烯(PE)或聚丙烯(PP)隔膜，但是上述隔膜存在热稳定性较差的问题，即当二次电池处于高的环境温度，或因短路、过充等导致自身发热时易出现隔膜不均匀收缩、破膜，进而发生内部短路和热失控，同时，PP或PE隔膜对电解液的浸润性和保液性也较差，对二次电池的安全性能、倍率性能和循环寿命带来不利影响。
发明内容
本申请提供了隔膜及其制备方法、电化学装置和电子装置，用以提升电化学装置的安全性能、倍率性能和循环寿命。
需要说明的是，本申请的发明内容中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
本申请第一方面提供了一种纤维素复合隔膜，其包括基材以及位于所述基材的至少一个表面上的微晶纤维素层和位于所述基材孔隙中的微晶纤维素，所述基材包括聚乙烯和/或聚丙烯。该纤维素复合隔膜中，基材包括聚乙烯和/或聚丙烯，且纤维素复合隔膜中同时包括微晶纤维素(微晶纤维素层以及基材孔隙中的微晶纤维素)，聚乙烯和/或聚丙烯与微晶纤维素能够发挥协同作用，使得纤维素复合隔膜具有良好的热稳定性、电解液浸润性和高温闭孔特性。由此，应用本申请纤维素复合隔膜的电化学装置能够具有良好的安全性能、倍率性能和较长的循环寿命。
在本申请的一种实施方案中，所述微晶纤维素层的厚度为2μm至20μm，所述基材的厚度为4μm至30μm。将微晶纤维素层的厚度和基材的厚度调控在上述范围内，更利于提升电化学装置的安全性能、倍率性能、能量密度，延长电化学装置的循环寿命。
在本申请的一种实施方案中，所述纤维素复合隔膜的孔隙率为40％至70％。在本申请 的另一种实施方案中，所述纤维素复合隔膜的孔隙率为45％至60％。将纤维素复合隔膜的孔隙率调控在上述范围内，能够使纤维素复合隔膜具有优良的离子传输能力和强度，从而更利于提升电化学装置的倍率性能、延长电化学装置的循环寿命。
在本申请的一种实施方案中，所述纤维素复合隔膜在120℃加热1h的热收缩率为0％至1.0％。在本申请的另一种实施方案中，所述纤维素复合隔膜在120℃加热1h的热收缩率为0.2％至0.8％。在本申请的再一种实施方案中，所述纤维素复合隔膜在120℃加热1h的热收缩率为0.4％至0.6％。表明纤维素复合隔膜在120℃加热1h的热收缩率较低，纤维素复合隔膜具有良好的热稳定性。从而更利于提升电化学装置的安全性能。
在本申请的一种实施方案中，所述纤维素复合隔膜的吸液率为100％至240％。在本申请的另一种实施方案中，所述纤维素复合隔膜的吸液率为120％至200％。在本申请的再一种实施方案中，所述纤维素复合隔膜的吸液率为140％至180％。将纤维素复合隔膜的吸液率调控在上述范围内，更利于提升电化学装置的安全性能和倍率性能、延长电化学装置的循环寿命。
本申请第二方面提供了一种纤维素复合隔膜的制备方法，其包括以下步骤：
(1)在空气或氧气气氛中对基材进行表面改性处理；
(2)将所述基材置于微晶纤维素分散液中，在所述基材的两个表面上各自独立地经诱导沉积形成微晶纤维素层，并形成位于所述基材孔隙中的微晶纤维素；或者，
(2’)将微晶纤维素分散液涂覆于所述基材的第一表面，在所述基材的第一表面上形成微晶纤维素层，并形成位于所述基材孔隙中的微晶纤维素；
(3)水洗，真空干燥，得到前述任一方案所述的纤维素复合隔膜；
其中，所述基材包括聚乙烯和/或聚丙烯。
本申请的纤维素复合隔膜的制备方法，简单易操作，能够广泛应用于工业生产中。通过本申请的制备方法制得的纤维素复合隔膜，聚乙烯和/或聚丙烯与微晶纤维素能够发挥协同作用，使得纤维素复合隔膜具有良好的热稳定性、电解液浸润性和高温闭孔特性。由此，应用本申请纤维素复合隔膜的电化学装置能够具有良好的安全性能、倍率性能和较长的循环寿命。
在本申请的一种实施方案中，步骤(2)中，所述诱导沉积的沉积温度为0℃至60℃、沉积时间为10min至360min。将沉积温度和沉积时间调控在上述范围内，更利于破坏微晶纤维素与微晶纤维素分散液形成的氢键，诱导微晶纤维素析出并沉积在基材上，制得包括 基材以及位于基材的两个表面的微晶纤维素层和位于基材孔隙中的微晶纤维素的纤维素复合隔膜，从而更利于提升电化学装置的安全性能和倍率性能，延长电化学装置的循环寿命。
在本申请的一种实施方案中，所述微晶纤维素分散液包括NaOH、尿素、微晶纤维素和水，基于所述微晶纤维素分散液的质量，所述微晶纤维素的质量百分含量为1％至4％。将微晶纤维素的质量百分含量调控在上述范围内，更利于微晶纤维素层的形成，从而更利于提升电化学装置的安全性能和倍率性能，延长电化学装置的循环寿命。
本申请第三方面提供了一种电化学装置，其包括前述任一方案所述的纤维素复合隔膜；或，包括前述任一方案所述的制备方法所制备得到的纤维素复合隔膜。
本申请第四方面提供了一种电子装置，其包括前述任一方案所述的电化学装置。
本申请的有益效果：
本申请提供的一种隔膜及其制备方法、电化学装置和电子装置，其中，纤维素复合隔膜中的聚乙烯和/或聚丙烯与微晶纤维素能够发挥协同作用，使得纤维素复合隔膜具有良好的热稳定性、电解液浸润性和高温闭孔特性。这样，将本申请的纤维素复合隔膜应用于电化学装置中，电化学装置处于高温环境，或因短路、过充等导致自身发热时，纤维素复合隔膜良好的热稳定性能够降低其出现不均匀收缩或破膜的风险；电化学装置内部温度升高至130℃以上时，纤维素复合隔膜将发挥其良好的高温闭孔特性，及时切断电化学装置内部电流通道，进一步降低电化学装置热失控的风险；纤维素复合隔膜良好的电解液浸润性能够有效调整电化学装置的内阻、提升电化学装置的倍率性能、延长电化学装置的循环寿命。由此，应用本申请纤维素复合隔膜的电化学装置能够具有良好的安全性能、倍率性能和较长的循环寿命。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面对实施例中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，本领域普通技术人员来讲还可以根据这些附图获得其他的附图。
图1为本申请一种实施方案的纤维素复合隔膜的制备过程示意图；
图2为本申请另一种实施方案的纤维素复合隔膜的制备过程示意图。
附图标记的说明：
10基材；20活性位点；30微晶纤维素层；31微晶纤维素；101第一表面；102第二表面。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本发明进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。本领域普通技术人员基于本申请中的实施例所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
本申请第一方面提供了一种纤维素复合隔膜，其包括基材以及位于基材的至少一个表面上的微晶纤维素层和位于基材孔隙中的微晶纤维素，基材包括聚乙烯和/或聚丙烯。该纤维素复合隔膜中，基材包括聚乙烯和/或聚丙烯，且纤维素复合隔膜中同时包括微晶纤维素(微晶纤维素层以及基材孔隙中的微晶纤维素)，聚乙烯和/或聚丙烯与微晶纤维素能够发挥协同作用，使得纤维素复合隔膜具有良好的热稳定性、电解液浸润性和高温闭孔特性。这样，将本申请的纤维素复合隔膜应用于电化学装置中，电化学装置处于高温环境，或因短路、过充等导致自身发热时，纤维素复合隔膜良好的热稳定性能够降低其出现不均匀收缩或破膜的风险；电化学装置内部温度升高至130℃以上时，纤维素复合隔膜将发挥其良好的高温闭孔特性，及时切断电化学装置内部电流通道，进一步降低电化学装置热失控的风险；纤维素复合隔膜良好的电解液浸润性能够有效调整电化学装置的内阻、提升电化学装置的倍率性能、延长电化学装置的循环寿命。由此，应用本申请纤维素复合隔膜的电化学装置能够具有良好的安全性能、倍率性能和较长的循环寿命。
在本申请中，上述“位于基材的至少一个表面上的微晶纤维素层”可以理解为微晶纤维素层位于基材的两个表面上，或位于基材的两个表面中的任一表面上。示例性地，图1中的(c)示出了本申请一种实施方案中的纤维素复合隔膜的剖面结构示意图，如图1中的(c)所示，纤维素复合隔膜包括基材10以及位于基材10的两个表面上的微晶纤维素层30和位于基材10孔隙(未图示)中的微晶纤维素31。图2中的(f)示出了本申请另一种实施方案中的纤维素复合隔膜的剖面结构示意图，如图2中的(f)所示，纤维素复合隔膜包括基材10以及位于基材10的第一表面101上的微晶纤维素层30和位于基材10孔隙(未图示)中的微晶纤维素31。当然，微晶纤维素层30也可以位于基材10的第二表面102上。
在本申请的一种实施方案中，参见图1中的(c)，微晶纤维素层30的厚度Y为2μm至20μm，基材10的厚度X为4μm至30μm。例如，微晶纤维素层30的厚度Y可以为2μm、 3μm、4μm、5μm、6μm、7μm、8μm、9μm、10μm、13μm、16μm、20μm或上述任两个数值范围间的任一数值。基材层10的厚度X可以为4μm、8μm、12μm、16μm、20μm、25μm、30μm或上述任两个数值范围间的任一数值。微晶纤维素层30的厚度Y和基材10的厚度X过薄(例如，Y小于2μm、X小于4μm)，将影响纤维素复合隔膜的热稳定性、电解液浸润性和高温闭孔特性，进而影响电化学装置的安全性能、倍率性能和循环寿命；微晶纤维素层30的厚度Y和基材10的厚度X过厚(例如，Y大于20μm、X大于30μm)，电化学装置内部离子传输路径增长，内阻增大，将影响电化学装置的倍率性能，并且电化学装置的体积随之增大，将影响电化学装置的体积能量密度。将微晶纤维素层30的厚度Y和基材10的厚度X调控在上述范围内，更利于提升电化学装置的安全性能、倍率性能、能量密度，延长电化学装置的循环寿命。需要说明，在本申请中，微晶纤维素层的厚度Y是指位于基材层的一个表面上的单层微晶纤维素层的厚度。
在本申请的一种实施方案中，纤维素复合隔膜的孔隙率α为40％至70％。在本申请的另一种实施方案中，所述纤维素复合隔膜的孔隙率为45％至60％。例如，纤维素复合隔膜的孔隙率α可以为40％、45％、50％、55％、60％、65％、70％或上述任两个数值范围间的任一数值。纤维素复合隔膜的孔隙率α过低(例如低于40％)，电解液难以浸润纤维素复合隔膜，影响纤维素复合隔膜的离子传输能力，增大电化学装置的内阻；纤维素复合隔膜的孔隙率α过高(例如高于70％)，纤维素复合隔膜变得疏松，强度下降，影响影响纤维素复合隔膜的抗穿刺性能。将纤维素复合隔膜的孔隙率α调控在上述范围内，能够使纤维素复合隔膜具有优良的离子传输能力和强度，从而更利于提升电化学装置的倍率性能、延长电化学装置的循环寿命。
在本申请的一种实施方案中，纤维素复合隔膜在120℃加热1h的热收缩率为0％至1.0％。在本申请的另一种实施方案中，所述纤维素复合隔膜在120℃加热1h的热收缩率为0.2％至0.8％。在本申请的再一种实施方案中，所述纤维素复合隔膜在120℃加热1h的热收缩率为0.4％至0.6％。例如，纤维素复合隔膜在120℃加热1h的热收缩率可以为0％、0.2％、0.4％、0.6％、0.8％、1.0％或上述任两个数值范围间的任一数值。表明纤维素复合隔膜在120℃加热1h的热收缩率较低，纤维素复合隔膜具有良好的热稳定性，从而更利于提升电化学装置的安全性能。
在本申请的一种实施方案中，纤维素复合隔膜的吸液率为100％至240％。在本申请的另一种实施方案中，所述纤维素复合隔膜的吸液率为120％至200％。在本申请的再一种实 施方案中，所述纤维素复合隔膜的吸液率为140％至180％。例如，纤维素复合隔膜的吸液率可以为100％、120％、140％、160％、180％、200％、220％、240％或上述任两个数值范围间的任一数值。纤维素复合隔膜的吸液率过低(例如低于100％)，纤维素复合隔膜的电解液浸润性和保液性下降，将影响纤维素复合隔膜的离子传输能力，增大电化学装置的内阻；纤维素复合隔膜的吸液率过高(例如高于240％)，使得纤维素复合隔膜的厚度增加，离子传输路径变长。将纤维素复合隔膜的吸液率调控在上述范围内，更利于提升电化学装置的安全性能和倍率性能、延长电化学装置的循环寿命。
本申请第二方面提供了一种纤维素复合隔膜的制备方法，其包括以下步骤：
(1)在空气或氧气气氛中对基材进行表面改性处理；
(2)将基材置于微晶纤维素分散液中，在基材的两个表面上各自独立地经诱导沉积形成微晶纤维素层，并形成位于基材孔隙中的微晶纤维素；或者，
(2’)将微晶纤维素分散液涂覆于基材的第一表面过滤，在基材的第一表面上形成微晶纤维素层，并形成位于基材孔隙中的微晶纤维素；
(3)水洗，真空干燥，得到前述任一方案所述的纤维素复合隔膜；
其中，基材包括聚乙烯和/或聚丙烯。
本申请的纤维素复合隔膜的制备方法，简单易操作，能够广泛应用于工业生产中。通过本申请的制备方法制得的纤维素复合隔膜，聚乙烯和/或聚丙烯与微晶纤维素能够发挥协同作用，使得纤维素复合隔膜具有良好的热稳定性、电解液浸润性和高温闭孔特性。由此，应用本申请纤维素复合隔膜的电化学装置能够具有良好的安全性能、倍率性能和较长的循环寿命。
在本申请中，对上述步骤(1)中的基材表面改性处理的方法没有特别限制，只要能够实现本申请目的即可。例如，可以通过微波等离子体处理的方法对基材进行表面改性处理。其中，微波等离子体处理时的参数没有特别限制，只要能够实现本申请目的即可。例如，功率为2KW至6KW、电压为100V至300V、时间为40s至120s。通过对基材进行表面改性处理，经表面改性处理后，基材表面和基材孔隙表面将引入COO-、C＝O、C-O-C等极性含氧基团，形成极性位点，以利于步骤(2)或步骤(2’)中微晶纤维素在基材上的附着，进一步形成微晶纤维素层和位于基材孔隙中的微晶纤维素。
示例性地，图1示出了本申请一种实施方案的纤维素复合隔膜的制备过程示意图，如图1所示，将图1中的(a)示出的基材10按照步骤(1)的方法，在空气或氧气气氛中进 行表面改性处理，使基材10表面和基材孔隙表面增加如图1中的(b)示出的极性位点20。然后按照步骤(2)的方法，将图1中的(b)示出的基材10(含极性位点20)置于微晶纤维素分散液中，在基材10的两个表面上各自独立地经诱导沉积形成图1中的(c)示出的微晶纤维素层30，并形成位于基材10孔隙(未图示)中的微晶纤维素31。最后按照步骤(3)的方法，将图1(c)中的复合材料经水洗，真空干燥，即得到前述任一方案所述的纤维素复合隔膜。
图2示出了本申请另一种实施方案的纤维素复合隔膜的制备过程示意图，如图2所示，将图2中的(d)示出的基材10按照步骤(1)的方法，在空气或氧气气氛中进行表面改性处理，使基材10表面和基材孔隙表面增加如图2中的(e)示出的极性位点20。然后按照步骤(2’)的方法，将微晶纤维素分散液涂覆于图2中的(e)示出的基材10(含极性位点20)的第一表面101，在基材10的第一表面101上形成图2中的(f)示出的微晶纤维素层30，并形成位于基材10孔隙(未图示)中的微晶纤维素31。最后按照步骤(3)的方法，将图2(f)中的复合材料经水洗，真空干燥，即得到前述任一方案所述的纤维素复合隔膜。当然，在步骤(2’)中，也可以将微晶纤维素分散液涂覆于图2中的(e)示出的基材10(含极性位点20)的第二表面102，在基材10的第二表面102上形成微晶纤维素层30，并形成位于基材10孔隙中的微晶纤维素31。可以理解，本申请中，基材的第一表面和第二表面，均可以理解为基材两个表面中的任一表面，“第一”和“第二”的使用，仅仅为了方便表述，并不表示对基材两个表面的限定。
在本申请的一种实施方案中，步骤(2)中，诱导沉积的沉积温度为0℃至60℃、沉积时间为10min至360min。优选地，沉积温度为25℃至60℃、沉积时间为10min至30min。例如，沉积温度可以为0℃、10℃、20℃、25℃、30℃、40℃、45℃、50℃、60℃或上述任两个数值范围间的任一数值。例如，沉积时间可以为10min、30min、60min、90min、120min、150min、180min、210min、240min、270min、300min、330min、360min或上述任两个数值范围间的任一数值。沉积温度过低(例如低于0℃)或过高(例如高于60℃)、沉积时间过短(例如短于10min)或过长(例如长于360min)，均不利于微晶纤维素层的沉积，微晶纤维素层的厚度、沉积均匀程度以及纤维素复合隔膜的孔隙率等均将受到影响。将沉积温度和沉积时间调控在上述范围内，更利于破坏微晶纤维素与微晶纤维素分散液形成的氢键，诱导微晶纤维素析出并沉积在基材上，制得包括基材以及位于基材的两个表面的微晶纤维素层和位于基材孔隙中的微晶纤维素的纤维素复合隔膜，从而更利于提升电化学装置的安 全性能和倍率性能，延长电化学装置的循环寿命。
在本申请的一种实施方案中，微晶纤维素分散液包括NaOH、尿素、微晶纤维素和水，基于微晶纤维素分散液的质量，微晶纤维素的质量百分含量为1％至4％。例如，微晶纤维素的质量百分含量可以为1％、2％、3％、4％或上述任两个数值范围间的任一数值。将微晶纤维素的质量百分含量调控在上述范围内，更利于微晶纤维素层的形成，从而更利于提升电化学装置的安全性能和倍率性能，延长电化学装置的循环寿命。
本申请对NaOH和尿素在微晶纤维素分散液中的质量没有特别限制，只要能够实现本申请目的即可。例如，基于微晶纤维素分散液的质量，NaOH的质量百分含量为3％至15％，尿素的质量百分含量为5％至20％。
在本申请中，微晶纤维素分散液的组成成分中的微晶纤维素，为本领域公知的微晶纤维素。该微晶纤维素为天然纤维素水解颗粒产物，主要成分为以β-1,4-葡萄糖苷键结合的直链式多糖类物质，颗粒大小为20μm至80μm，极限聚合度为15至375。该微晶纤维素可以通过市售获得。
本申请对微晶纤维素分散液的制备方法没有特别限制，只要能够实现本申请目的即可。例如，微晶纤维素分散液的制备包括以下步骤：将3wt％至15wt％的NaOH、5wt％至20wt％的尿素和水混合得到溶液，将溶液冷却至-20℃至0℃，再加入1wt％至4wt％的微晶纤维素，搅拌至无色透明溶液即可。以上质量百分数均基于微晶纤维素分散液的总质量。
本申请第三方面提供了一种电化学装置，其包括前述任一方案所述的纤维素复合隔膜；或，包括前述任一方案所述的制备方法所制备得到的纤维素复合隔膜。因此，本申请的电化学装置具有良好的安全性能、倍率性能和较长的循环寿命。
本申请的电化学装置还包括正极极片、负极极片、电解液和外包装等。本申请对正极极片、负极极片、电解液和外包装没有特别限制，可以为本领域公知的正极极片、负极极片、电解液和外包装，只要能够实现本申请目的即可。
本申请的纤维素复合隔膜位于正极极片和负极极片之间，用以分隔正极极片和负极极片，防止电化学装置内部短路，允许电解质离子自由通过，完成电化学充放电过程的作用。
本申请对电化学装置的种类没有特别限制，其可以包括发生电化学反应的各种装置。在一些实施例中，电化学装置可以包括但不限于：锂金属二次电池、锂离子电池、钠离子电池、锂聚合物二次电池或锂离子聚合物二次电池等。
电化学装置的制备过程为本领域技术人员所熟知的，本申请没有特别的限制，例如， 可以包括但不限于以下步骤：将正极极片、纤维素复合隔膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入包装壳内，将电解液注入包装壳并封口，得到电化学装置；或者，将正极极片、纤维素复合隔膜和负极极片按顺序堆叠，然后用胶带将整个叠片结构的四个角固定好得到叠片结构的电极组件，将电极组件置入包装壳内，将电解液注入包装壳并封口，得到电化学装置。此外，也可以根据需要将防过电流元件、导板等置于包装壳中，从而防止电化学装置内部的压力上升、过充放电。
本申请第四方面提供了一种电子装置，其包括前述任一方案所述的电化学装置。因此，本申请的电子装置具有良好的安全性能、倍率性能和较长的循环寿命。
本申请的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，所述电子装置可以包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。
测试方法和设备：
微晶纤维素层的厚度Y的测试：
使用万分测厚仪测量微晶纤维素层的厚度Y。首先用冲切机完成2片100mm×100mm纤维素复合隔膜的冲切。然后用万分测厚仪分别测量每片纤维素复合隔膜的4个角位及中心位置厚度，一共获得10个厚度数据，计算平均值T。微晶纤维素层的厚度Y＝(T-X)/2，其中X是基材厚度。
纤维素复合隔膜的孔隙率α的测试：
采用气体置换法测试纤维素复合隔膜的孔隙率α，孔隙率α＝(V-V0)/V×100％，孔体积为V-V0，其中，V0为被测样品的真实体积，V为被测样品的总体积。测试设备为全自动真密度测试仪(AccuPyc Ⅱ 1340)，测试气体为氦气。
热收缩率的测试：
沿各实施例和对比例的隔膜的横向(TD)和纵向(MD)方向取大于或等于30mm×30mm的样品各5片，测量样品的实际尺寸，然后把样品夹在两片A4纸中间，待烘箱温度稳定后，将样品放入烘箱中，120℃加热1h后取出，测量加热后的尺寸并计算收缩率s，收缩率s＝(L0-L)/L0×100％，其中，L0为TD或MD方向的初始长度，L为加热后的长度。5片样品热收缩的平均值即为其热收缩率。
吸液率的测试：
裁100mm×100mm大小的各实施例和对比例的隔膜5片，称量质量，把每片隔膜浸于对应实施例和对比例的电解液中10min，取出样品，用滤纸吸干表面的电解液，再次称量质量，计算浸电解液后质量增加的百分数，即为吸液率a，a＝(W-W0)/W0×100％，其中，W0是隔膜样品的初始质量，W是隔膜样品吸收了电解液后的质量。5片隔膜吸液率的平均值即为其吸液率。
过充安全性能测试：
取各实施例和对比例的锂离子电池5颗，在25±3℃环境下0.2C放电至3.0V，接着以0.5C电流进行过充电，当电压达到6V后停止充电，等待锂离子电池温度恢复到室温±10℃后即为测试结束。若锂离子电池未发生起火和爆炸则认为该锂离子电池通过测试。测试结果表示为通过率n/m，其中m为测试锂离子电池总数，n为通过测试的锂离子电池数。
倍率放电性能测试：
取各实施例和对比例的锂离子电池5颗，在25±3℃环境下进行满充后的放电容量测试。放电倍率依次为0.2C、0.5C、1C、2C。以0.2C放电容量为基准计算各倍率下的相对放电容量。取5颗锂离子电池的平均值作为测量值。
循环寿命测试：
取各实施例和对比例的锂离子电池5颗，在25±3℃环境下以0.7C恒流充电至4.4V，再以4.4V恒压充电至0.05C，然后以0.5C恒流放电至3.0V，此为一个充放电循环，按照上述充放电循环进行测试。以锂离子电池容量衰退至原容量的80％所需的循环圈数作为该锂离子电池循环寿命。取5颗锂离子电池的平均值作为测量值。
实施例1
<纤维素复合隔膜的制备>
(1)在常压空气气氛中对厚度X＝5μm、孔隙率37％的PE基材通过微波等离子处理的 方法进行表面改性处理；其中，微波等离子体处理的功率为4KW、电压为200V、时间为80s。
(2)将步骤(1)得到的基材置于微晶纤维素分散液中，在基材的两个表面上各自独立地经诱导沉积形成厚度均为Y＝2μm的微晶纤维素层和位于基材孔隙中的微晶纤维素；其中，
诱导沉积的沉积温度为25℃、沉积时间为10min；
微晶纤维素分散液包括：7wt％的NaOH、12wt％的尿素、1.5wt％的微晶纤维素和79.5wt％的水。微晶纤维素分散液的温度为-12℃。
(3)将步骤(2)制得的复合材料水洗，真空干燥，即得到纤维素复合隔膜。
<正极极片的制备>
将正极活性材料LiCoO 2、导电炭黑、聚偏氟乙烯(PVDF)按质量比为97.6:1.2:1.2混合，然后加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成固含量为75wt％的正极浆料，并搅拌均匀。将正极浆料均匀涂布在厚度为10μm的铝箔的一个表面上，90℃条件下烘干，得到正极活性材料层厚度为100μm的正极极片，然后在该正极极片的另一个表面上重复以上步骤，得到双面涂布有正极活性材料层的正极极片。将正极极片冷压、裁切成规格为74mm×867mm的片材待用。
<负极极片的制备>
将负极活性材料人造石墨、羧甲基纤维素钠、丁苯橡胶按质量比97.7:1.1:1.2混合，然后加入去离子水作为溶剂，调配成固含量为70wt％的负极浆料，并搅拌均匀，将负极浆料均匀涂布在厚度为6μm的铜箔的一个表面上，110℃条件下烘干，得到涂层厚度为150μm的单面涂布负极活性材料层的负极极片，然后在该负极极片的另一个表面上重复以上涂布步骤，得到双面涂布有负极活性材料层的负极极片。将负极极片冷压、裁切成规格为76mm×851mm的片材待用。
<电解液的制备>
在干燥氩气气氛中，将有机溶剂碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)按照质量比30:40:30混合，然后向有机溶剂中加入LiPF 6溶解并混合均匀，得到电解液。其中，LiPF 6在电解液中的摩尔浓度为1.05mol/L。
<锂离子电池的制备>
将上述制备的正极极片、纤维素复合隔膜、负极极片按顺序叠好，使纤维素复合隔膜 处于正负极中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装中，注入配好的电解液并封装，经过化成，脱气，切边等工艺流程得到锂离子电池。
实施例2至实施例14
除了按照表1调整相关制备参数以外，其余与实施例1相同。其中，微晶纤维素的质量百分含量增大时，水的质量百分含量随之减小，NaOH和尿素的质量百分含量不变，以使NaOH、尿素、微晶纤维素和水的质量之和为100％。
对比例1
除了选用厚度X＝5μm、孔隙率37％的PE基材作为隔膜，替换微晶纤维素隔膜以外，其余与实施例1相同。
各实施例和对比例的制备参数如表1所示、性能参数如表2所示。
表1
Figure PCTCN2022094669-appb-000001
注：表1中的“\”表示无对应参数；对比例1选用厚度5μm、孔隙率37％的PE基材作为隔膜。
表2
Figure PCTCN2022094669-appb-000002
从实施例1至实施例14和对比例1相比可以看出，相较于对比例1的隔膜，本申请的纤维素复合隔膜孔隙率更大、横向和纵向的热收缩率更小、吸液率更高，将本申请的纤维素复合隔膜应用于锂离子电池中，锂离子电池具有更高的过充电安全测试通过率和循环寿命，且具有良好的放电容量。表明应用本申请的纤维素复合隔膜的锂离子电池的安全性能和倍率性能得以提升，循环寿命得到延长。
微晶纤维素在微晶纤维素分散液中的质量百分含量通常也会影响锂离子电池的安全性能、倍率性能和循环寿命。从实施例1至实施例3可以看出，选用微晶纤维素的质量百分含量在本申请范围内的锂离子电池，具有良好的安全性能和倍率性能、较长的循环寿命。
在基材表面形成微晶纤维素层时，诱导沉积的沉积时间通常也会影响锂离子电池的安全性能、倍率性能和循环寿命。从实施例3至实施例6、实施例10可以看出，选用沉积时间在本申请范围内的锂离子电池，具有良好的安全性能和倍率性能、较长的循环寿命。
在基材表面形成微晶纤维素层时，诱导沉积的沉积温度通常也会影响锂离子电池的安全性能、倍率性能和循环寿命。从实施例3、实施例7至实施例10可以看出，选用沉积温度在本申请范围内的锂离子电池，具有良好的安全性能和倍率性能、较长的循环寿命。
基材的成分通常也会影响锂离子电池的安全性能、倍率性能和循环寿命。从实施例3、 实施例11和实施例12可以看出，选用基材的成分在本申请范围内的锂离子电池，具有良好的安全性能和倍率性能、较长的循环寿命。
基材的厚度通常也会影响锂离子电池的安全性能、倍率性能和循环寿命。从实施例3、实施例13和实施例14可以看出，选用基材的厚度在本申请范围内的锂离子电池，具有良好的安全性能和倍率性能、较长的循环寿命。
需要说明的是，在本文中，诸如“第一”和“第二”等之类的关系术语仅仅用来将一个实体与另一个实体区分开来，而不一定要求或者暗示这些实体之间存在任何这种实际的关系或者顺序。而且，术语“包括”、“包含”或者其任何其它变体意在涵盖非排他性的包含，从而使得包括一系列要素的物品或者设备不仅包括那些要素，而且还包括没有明确列出的其它要素，或者是还包括为这种物品或者设备所固有的要素。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (15)

  1. 一种纤维素复合隔膜，其特征在于，包括基材以及位于所述基材的至少一个表面上的微晶纤维素层和位于所述基材孔隙中的微晶纤维素，所述基材包括聚乙烯和/或聚丙烯。
  2. 根据权利要求1所述的纤维素复合隔膜，其中，所述微晶纤维素层的厚度为2μm至20μm，所述基材的厚度为4μm至30μm。
  3. 根据权利要求1所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜的孔隙率为40％至70％。
  4. 根据权利要求3所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜的孔隙率为45％至60％。
  5. 根据权利要求1所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜在120℃加热1h的热收缩率为0％至1.0％。
  6. 根据权利要求5所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜在120℃加热1h的热收缩率为0.2％至0.8％。
  7. 根据权利要求6所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜在120℃加热1h的热收缩率为0.4％至0.6％。
  8. 根据权利要求1所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜的吸液率为100％至240％。
  9. 根据权利要求8所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜的吸液率为120％至200％。
  10. 根据权利要求9所述的纤维素复合隔膜，其特征在于，所述纤维素复合隔膜的吸液率为140％至180％。
  11. 一种纤维素复合隔膜的制备方法，其特征在于，包括以下步骤：
    (1)在空气或氧气气氛中对基材进行表面改性处理；
    (2)将所述基材置于微晶纤维素分散液中，在所述基材的两个表面上各自独立地经诱导沉积形成微晶纤维素层，并形成位于所述基材孔隙中的微晶纤维素；或者，
    (2’)将微晶纤维素分散液涂覆于所述基材的第一表面，在所述基材的第一表面上形成微晶纤维素层，并形成位于所述基材孔隙中的微晶纤维素；
    (3)水洗，真空干燥，得到权利要求1至10中任一项所述的纤维素复合隔膜；
    其中，所述基材包括聚乙烯和/或聚丙烯。
  12. 根据权利要求11所述的制备方法，其特征在于，步骤(2)中，所述诱导沉积的沉积温度为0℃至60℃、沉积时间为10min至360min。
  13. 根据权利要求11所述的制备方法，其特征在于，所述微晶纤维素分散液包括NaOH、尿素、微晶纤维素和水，基于所述微晶纤维素分散液的质量，所述微晶纤维素的质量百分含量为1％至4％。
  14. 一种电化学装置，其特征在于，包括权利要求1至10中任一项所述的纤维素复合隔膜；或，包括权利要求11至13中任一项的制备方法所制备得到的纤维素复合隔膜。
  15. 一种电子装置，其特征在于，包括权利要求14所述的电化学装置。
PCT/CN2022/094669 2022-05-24 2022-05-24 隔膜及其制备方法、电化学装置和电子装置 WO2023225843A1 (zh)

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