Hollow fiber membrane as well as preparation method and application thereof

Abstract

The invention provides a hollow fiber membrane as well as a preparation method and application thereof, and relates to the technical field of lithium ion batteries. The preparation method of the hollow fiber membrane comprises the following steps: S1, heating and stirring a polymer A and a solvent to obtain a mixture A; heating and stirring the polymer B and a solvent to obtain a mixture B; s2, heating and stirring the mixture A and the mixture B to obtain a spinning solution; s3, performing wet spinning on the spinning solution to obtain the hollow fiber membrane. The hollow fiber membrane has relatively high liquid absorption and storage capabilities, so that lithium ion transmission in the charging and discharging process of the battery is facilitated, and the pre-lithium effect is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a hollow fiber membrane and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries have the characteristics of high energy density, good cycle life and safety performance, and are widely used in industrial fields such as mobile phones, automobiles, and aerospace. However, when lithium-ion batteries are charged and discharged for the first time, they will consume lithium ions from the positive electrode to form a SEI film, resulting in low initial coulombic efficiency and irreversible capacity loss. Therefore, in order to ensure the initial coulombic efficiency, capacity and cycle stability of the battery, it is necessary to replenish lithium externally to make up for the lithium source consumed by the formation of the SEI film during the first charge.

[0003] Common negative electrode lithium replenishment technologies include physical contact pre-lithiation and electrochemical pre-lithiation. Physical contact pre-lithiation is to directly contact lithium powder or lithium sheets with the negative electrode. This method realizes spontaneous lithium insertion of active materials in the form of internal short circuit, making lithium insertion more uniform. However, both lithium sheets and lithium powder have extremely high reactivity and environmental sensitivity, which can easily lead to safety risks. Electrochemical pre-lithiation is to short-circuit the lithium-copper composite sheet with the negative electrode. Due to the potential difference between the negative electrode and lithium, metallic lithium will be converted into lithium ions in the form of electrical corrosion and embedded in the surface of the negative electrode. However, the lithium ions in this method are embedded from the edge to the middle, the embedding speed is relatively slow, and the lithium insertion is not uniform enough. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a hollow fiber membrane and a preparation method and application thereof.

[0005] The present invention provides a method for preparing a hollow fiber membrane, comprising the following steps:

[0006] S1, heating and stirring polymer A and a solvent to obtain a mixture A; heating and stirring polymer B and a solvent to obtain a mixture B;

[0007] S2, heating and stirring the mixture A and the mixture B to obtain a spinning solution;

[0008] S3. The spinning solution is subjected to wet spinning to obtain a hollow fiber membrane.

[0009] The present invention prepares a hollow fiber membrane by wet spinning. The hollow fiber membrane has a cavity structure, has a high porosity and liquid absorption and storage capacity, and is conducive to the lithium ion transmission during the battery charging and discharging process after being infiltrated with electrolyte. At the same time, the hollow fiber membrane can be used as a medium to delay the direct reaction between the negative electrode active material and metallic lithium, reducing safety risks.

[0010] Preferably, in S1, the solvent is selected from one or more of DMF, DMAC, NMP, anisole and DMSO.

[0011] Preferably, in S1, polymer A and polymer B are independently selected from one or more of PAN, PMMA and PVDF.

[0012] By selecting the type of polymer, it helps to control the physical properties of the hollow fiber membrane, such as toughness and high temperature resistance.

[0013] Preferably, in the S1, the mass ratio of polymer A to polymer B is (10-90):(10-90).

[0014] Preferably, in the above S1, the step of drying polymer A and polymer B before heating and stirring them includes drying polymer A and polymer B at a temperature of 35-50° C. for 12-24 hours, and the moisture content after drying is 50-500 ppm.

[0015] Preferably, in S1 and S2, the heating temperature is 50-80° C. and the stirring time is 12-24 h.

[0016] By controlling the heating temperature and stirring time within a certain range, the polymer can be dissolved more fully and the film can be formed more uniformly.

[0017] Preferably, in S2, the total mass of polymer A and polymer B in the spinning solution accounts for 10%-30% of the mass of the spinning solution; the total mass of the solvent in the spinning solution accounts for 70%-90% of the mass of the spinning solution.

[0018] Controlling the quality of the polymer and solvent within a certain range helps to control the strength of the hollow fiber membrane.

[0019] Preferably, in said S3, the spinning nozzle in the wet spinning process comprises a liquid outlet, a tail liquid inlet, a side liquid inlet, and an inner cavity.

[0020] Preferably, in S3, the wet spinning comprises: injecting the spinning solution and the pore-forming agent separately and then extruding them, and solidifying and forming them in a coagulation bath to obtain a hollow fiber membrane.

[0021] Hollow fiber membranes are obtained through wet spinning. On the one hand, wet spinning has low costs and water can be selected as a coagulation bath or pore-forming agent. On the other hand, it is widely used in industrial applications and there are currently no technical barriers.

[0022] More preferably, in the S3, the wet spinning includes: placing the spinning solution in a syringe A connected to the liquid inlet at the tail of the spinning nozzle, placing the pore-forming agent in a syringe B connected to the liquid inlet at the side end of the spinning nozzle, the pore-forming agent is used to form the inner wall of the hollow fiber membrane, and the spinning solution is solidified and formed as the outer wall in a coagulation bath to finally obtain a hollow fiber membrane.

[0023] More preferably, the pore-forming agent is selected from one or more of DMF, DMAC, dilute hydrochloric acid, dilute sulfuric acid, and water.

[0024] The pore size can be controlled by selecting different pore formers.

[0025] More preferably, the concentration of DMF and DMAC is 1%-10%; the concentration of dilute hydrochloric acid and dilute sulfuric acid is 0.01%-0.1%.

[0026] More preferably, the coagulation bath is water.

[0027] More preferably, the injection speed of the syringe is controlled by controlling a peristaltic pump, and the speed of the peristaltic pump is 1-50 mL / min.

[0028] Controlling the speed of the peristaltic pump within a certain range helps to control the inner and outer diameters of the hollow fiber membrane.

[0029] More preferably, the liquid outlet of the spinning nozzle is in a flat U-shaped shape, with an inner circle length of 10 cm and a width of 1 mm, and an outer circle length of 12 cm and a width of 2 mm.

[0030] The present invention also provides a hollow fiber membrane prepared by the above preparation method.

[0031] A hollow fiber membrane or an application of the hollow fiber membrane prepared by the above preparation method in a lithium ion battery.

[0032] A method for preparing a lithium ion battery comprises the following steps:

[0033] A lithium sheet is placed in the above-mentioned hollow fiber membrane cavity and cold pressed to obtain a hollow fiber membrane containing a lithium sheet; the hollow fiber membrane containing a lithium sheet, the negative electrode, and the hollow fiber membrane containing a lithium sheet are stacked to form a unit body A; the diaphragm, the unit body A, the diaphragm, the positive electrode, the diaphragm, the unit body A, and the diaphragm are stacked in a Z shape to form a unit body B; the unit body B is assembled with an electrolyte to obtain a lithium-ion battery.

[0034] The lithium sheet is placed in the cavity of the hollow fiber membrane, and after cold pressing, a hollow fiber membrane containing lithium sheets is formed. On the one hand, hollow fiber membranes are widely used in industry and have low costs; on the other hand, hollow fiber membranes have high liquid absorption and storage capabilities. After being infiltrated with electrolyte, they are conducive to the transmission of lithium ions during the battery charging and discharging process. The presence of the hollow fiber membrane also makes the reaction in the pre-lithiation process more peaceful. The assembled pre-lithiation battery cell can enhance the pre-lithiation effect and reduce safety risks.

[0035] Preferably, the number of the unit cells B is 10-100.

[0036] Preferably, the thickness of the lithium sheet is 3-100 μm.

[0037] Preferably, the extended length of the hollow fiber membrane of the lithium-containing sheet is no more than 2 cm, and the thickness of the hollow fiber membrane of the lithium-containing sheet is 10-1000 μm.

[0038] Preferably, the thickness of the diaphragm is 5 μm-10 μm.

[0039] Preferably, the active material of the negative electrode is selected from one or more of graphite, silicon oxide, and silicon carbon.

[0040] The beneficial effects of the present invention are:

[0041] The present invention prepares a hollow fiber membrane by wet spinning. The hollow fiber membrane has a cavity structure and has a high porosity and liquid absorption and storage capacity. A lithium sheet is placed in the cavity of the hollow fiber membrane and, after cold pressing, a lithium-containing hollow fiber membrane is formed, which is beneficial to the lithium ion transmission during the battery charging and discharging process, makes the reaction in the pre-lithium process more peaceful, and enhances the pre-lithium effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of the spinning proposed in the present invention, 1-injector A, 2-peristaltic pump A, 3-injector B, 4-peristaltic pump B, 5-tail liquid inlet of the spinning nozzle, 6-side liquid inlet of the spinning nozzle, 7-liquid outlet of the spinning nozzle, 8-inner cavity of the spinning nozzle.

[0043] Figure 2 Schematic diagram of the cross section of a hollow fiber membrane containing a lithium sheet, 9-hollow fiber membrane, 10-lithium sheet. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is described in detail through specific embodiments.

[0045] Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial sources.

[0046] Example 1

[0047] A method for preparing a lithium ion battery comprises the following steps:

[0048] S1. Weigh 30 g of PAN powder and place it in an oven to dry for 24 h, pour the dried PAN powder into 70 g of DMF solution, and heat and stir at 60 ° C for 12 h to obtain mixture A; weigh 10 g of PMMA powder and place it in an oven to dry for 24 h, pour the dried PMMA powder into 90 g of DMF solution, and heat and stir at 60 ° C for 24 h to obtain mixture B;

[0049] S2, heating and stirring 100 g of mixture A and 10 g of mixture B at 80° C. for 12 h, cooling to room temperature, and obtaining a spinning solution;

[0050] S3, the spinning solution was placed in syringe A and connected to the liquid inlet at the tail of the spinning nozzle, the pump speed of peristaltic pump A was 15mL / min, 1% DMF solution was placed in syringe B and connected to the liquid inlet at the side of the spinning nozzle, the pump speed of peristaltic pump B was 5mL / min, and the spinning was placed in water for 24h. The obtained hollow fiber membrane was 12cm long and 2mm wide, and the inner circle was 10cm long and 1mm wide;

[0051] S4, after the hollow fiber membrane is fully dried, a 100 μm lithium sheet is placed in the hollow fiber membrane cavity, and it is cold pressed with a roller press at a pressure of 100 kg to obtain a hollow fiber membrane containing a lithium sheet;

[0052] S5. The hollow fiber membrane containing lithium sheet, the negative electrode sheet, and the hollow fiber membrane containing lithium sheet are formed into a unit A. The diaphragm, the unit A, the diaphragm, the positive electrode, the diaphragm, the unit A, and the diaphragm are stacked in a Z shape to form a unit B. 55 units B are combined to obtain a lithium-ion battery.

[0053] Example 2

[0054] The only difference between this embodiment and embodiment 1 is that the preparation of mixture B in S1 is different. The preparation of mixture B includes weighing 10 g of PAN powder and placing it in an oven to dry for 24 hours, pouring the dried PAN powder into 90 g of DMF solution, and heating and stirring at 60° C. for 12 hours to obtain mixture B. The rest of the preparation method is consistent with that of embodiment 1.

[0055] Example 3

[0056] The only difference between this embodiment and embodiment 1 is that the preparation of mixture B in S1 is different. The preparation of mixture B includes weighing 10 g of PVDF powder and placing it in an oven to dry for 24 hours, pouring the dried PVDF powder into 90 g of NMP solution, and heating and stirring at 60°C for 24 hours to obtain mixture B. The rest of the preparation method is consistent with that of embodiment 1.

[0057] Example 4

[0058] The only difference between this embodiment and embodiment 1 is that the solution in syringe B in S3 is replaced by water instead of 1% DMF solution, and the rest of the preparation method is consistent with that in embodiment 1.

[0059] Example 5

[0060] The only difference between this embodiment and embodiment 1 is that the solution in syringe B in S3 is replaced by 0.05% hydrochloric acid solution instead of 1% DMF solution, and the rest of the preparation method is consistent with embodiment 1.

[0061] Example 6

[0062] The only difference between this embodiment and embodiment 1 is that the thickness of the lithium sheet in S4 is 5 μm, and the rest of the preparation method is the same as that of embodiment 1.

[0063] Example 7

[0064] The only difference between this embodiment and embodiment 1 is that the lithium sheet in S4 is replaced by a porous lithium foil with a pore size of 100 μm, and the rest of the preparation method is consistent with that of embodiment 1.

[0065] Comparative Example 1

[0066] A method for preparing a lithium ion battery comprises the following steps: stacking a separator, a negative electrode, a separator, a positive electrode, a separator, a negative electrode and a separator in a Z-shape to form a unit body B, and combining 55 unit bodies B to obtain a lithium ion battery.

[0067] The prepared lithium-ion battery was subjected to a 200-cycle capacity retention test, and the lithium-ion battery was disassembled and analyzed for the negative electrode after 200 cycles. The test results are shown in Table 1.

[0068] Table 1

[0069]

[0070] It can be seen from the data in Table 1 that the lithium-ion battery prepared by the present invention has a high cycle capacity retention rate. The hollow fiber membrane prepared by mixing PAN+PAN polymer is relatively loose after compounding, resulting in bubbles at the negative electrode interface during the pre-lithiation process, and the pole piece is more severely mottled; the polymer is PAN+PVDF or PAN+PMMA mixed with better effect. In addition, in terms of pore-forming agents, water and dilute hydrochloric acid have poor effects, because large pores are generated during pore formation, resulting in uneven pre-lithiation.

[0071] like Figure 1 As shown, Figure 1 The spinning schematic diagram proposed by the present invention is as follows: Figure 2Schematic diagram of the cross section of a hollow fiber membrane containing lithium sheets.

[0072] In summary, the lithium-ion battery provided by the present invention has a high cycle capacity retention rate, and the interface of the negative electrode sheet of the lithium-ion battery disassembled after 200 cycles is good.

[0073] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a hollow fiber membrane, characterized in that: The following steps are involved: S1, heating and stirring polymer A and a solvent to obtain a mixture A; heating and stirring polymer B and a solvent to obtain a mixture B; S2, heating and stirring the mixture A and the mixture B to obtain a spinning solution; S3. The spinning solution is subjected to wet spinning to obtain a hollow fiber membrane.

2. The preparation method according to claim 1, characterized in that: In S1, polymer A and polymer B are independently selected from one or more of PAN, PMMA and PVDF.

3. The preparation method according to claim 1, characterized in that: In the above-mentioned S1 and S2, the heating temperature is 50-80°C and the stirring time is 12-24h.

4. The preparation method according to claim 1, characterized in that: In the above-mentioned S2, the total mass of polymer A and polymer B in the spinning solution accounts for 10%-30% of the mass of the spinning solution; the total mass of the solvent in the spinning solution accounts for 70%-90% of the mass of the spinning solution.

5. The preparation method according to claim 1, characterized in that: In the above-mentioned S3, the wet spinning comprises: injecting the spinning solution and the pore-forming agent respectively, and then extruding them, and solidifying and forming them in a coagulation bath to obtain a hollow fiber membrane.

6. The preparation method according to claim 5, characterized in that: The pore-forming agent is selected from one or more of DMF, DMAC, dilute hydrochloric acid, dilute sulfuric acid and water.

7. A hollow fiber membrane, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 6.

8. A lithium ion battery, characterized in that: The hollow fiber membrane comprises the hollow fiber membrane according to claim 7 or is prepared by the preparation method according to any one of claims 1 to 6.

9. A method for preparing a lithium ion battery according to claim 8, characterized in that: The following steps are involved: Putting a lithium sheet into the hollow fiber membrane cavity and cold pressing it to obtain a hollow fiber membrane containing a lithium sheet; The hollow fiber membrane containing lithium sheets, the negative electrode, and the hollow fiber membrane containing lithium sheets are stacked to form a unit body A; the diaphragm, the unit body A, the diaphragm, the positive electrode, the diaphragm, the unit body A, and the diaphragm are stacked in a Z shape to form a unit body B; the unit body B is assembled with the electrolyte to obtain a lithium-ion battery.

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