Battery cell, preparation method thereof and lithium battery

Abstract

The invention provides a battery cell and a preparation method thereof and a lithium battery, the battery cell comprises a positive pole piece, a diaphragm, a negative pole piece and a porous film, the diaphragm is located between the positive pole piece and the negative pole piece, and the porous film is located between the negative pole piece and the diaphragm; the porous film is arranged between the negative pole piece and the diaphragm, and a large amount of space exists in the porous film and can be used as an accommodating space for depositing lithium ions, so that the volume expansion of the whole battery cell in the lithium metal charging and discharging process can be reduced. In addition, the porous film also has a certain effect of homogenizing the current density, and is beneficial to reducing the growth of dendritic crystals.

Description

Technical Field

[0001] This application relates to the field of lithium batteries, and more particularly to a battery cell, a method for preparing the same, and a lithium battery. Background Technology

[0002] Lithium metal batteries, due to their high energy density (theoretical specific capacity of 3860 mAh / g), are considered the core development direction of next-generation energy storage technology, especially with broad application prospects in wearable devices, drones, and other fields sensitive to size and weight. However, the dramatic volume expansion (theoretical expansion rate >300%) of lithium metal anodes caused by repeated lithium ion deposition / stripping during cycling has become a key bottleneck in their commercialization process.

[0003] In related technologies, the SEI film is used as a selective channel for lithium-ion transport, while electron transport can also be carried out, suppressing interfacial side reactions, thereby improving the charge and discharge efficiency and rate performance of the battery cell.

[0004] However, the modulus of the SEI film is usually greater than 10 GPa. When the lithium metal expands in volume, the high-modulus SEI film is prone to rupture during the expansion process, resulting in local current concentration and affecting the cycle stability of the cell during charging and discharging. Summary of the Invention

[0005] This application provides a battery cell, a method for preparing the same, and a lithium battery, aiming to improve the effective dissipation of expansion stress, thereby enhancing the cycle stability of the battery cell during the charging and discharging process.

[0006] To achieve the above objectives, in a first aspect, embodiments of this application provide a battery cell, the battery cell comprising a positive electrode, a separator, a negative electrode, and a porous film, wherein the separator is located between the positive electrode and the negative electrode, and the porous film is located between the negative electrode and the separator.

[0007] Optionally, in some embodiments of this application, the porous film includes a substrate and through holes disposed on the substrate; The porosity of the through holes on the substrate ranges from 70% to 90%.

[0008] Optionally, in some embodiments of this application, the aperture of the through hole ranges from 0.5 μm to 1000 μm.

[0009] Optionally, in some embodiments of this application, the aperture of the through hole ranges from 5 μm to 100 μm; Preferably, the diameter of the through hole ranges from 10 μm to 50 μm.

[0010] Optionally, in some embodiments of this application, the thickness of the porous film ranges from 2 μm to 50 μm; Preferably, the thickness of the porous film ranges from 5 μm to 15 μm.

[0011] Optionally, in some embodiments of this application, the porous film is an insulating porous film.

[0012] Optionally, in some embodiments of this application, the number of porous films is multiple, and the multiple porous films are arranged between the negative electrode sheet and the separator; wherein, the average pore size of the porous film closer to the negative electrode sheet is larger than the average pore size of the porous film closer to the separator.

[0013] Secondly, embodiments of this application provide a method for preparing a battery cell, which is used to prepare a battery cell as described above, the method including preparing a porous thin film; The porous thin film was prepared using the following method: The resin raw materials are dispersed in a solvent to obtain an initial mixed solution; A pore-forming agent was added to the initial mixed solution to prepare a precursor solution; The porous film is prepared by electrospinning the precursor solution.

[0014] Optionally, in some embodiments of this application, the resin raw material includes at least one selected from polyimide, polyvinylidene fluoride, polypropylene, and polyethylene; and / or The pore-forming agent includes at least one of sodium dodecyl sulfate, sodium chloride, potassium chloride, and tetraethoxysilane.

[0015] Optionally, in some embodiments of this application, the injection flow rate of the precursor solution in the electrospinning process is 0.05 mL / h to 1 mL / h.

[0016] Thirdly, embodiments of this application provide a lithium battery, which includes the cells as described above.

[0017] The battery cell in this embodiment includes a porous film located between the negative electrode and the separator. This porous film has a large amount of space, which can be used to deposit lithium ions, helping to reduce the volume expansion of the entire battery cell during lithium metal charging and discharging. In addition, the porous film also has a certain effect on homogenizing the current density, which helps to reduce dendrite growth. Attached Figure Description To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for preparing porous thin films in some embodiments of this application. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0020] During the charging and discharging process, lithium metal is deposited on the negative electrode side of the battery cell to form an SEI film. When the lithium metal expands in volume, the high-modulus SEI film is prone to rupture during the expansion process, resulting in local current concentration and affecting the cycle stability of the battery cell during the charging and discharging process.

[0021] In view of this, embodiments of this application provide a battery cell, a method for preparing the same, and a lithium battery.

[0022] In a first aspect, this application provides a battery cell that may include a positive electrode, a separator, a negative electrode, and a porous film, wherein the separator is located between the positive electrode and the negative electrode, and the porous film is located between the negative electrode and the separator.

[0023] By adopting the above scheme, a porous film is formed between the negative electrode and the separator. The porous film has a large amount of space, which can be used to deposit lithium ions, helping to reduce the volume expansion of the entire cell during lithium metal charging and discharging. In addition, the porous film also has a certain effect on homogenizing the current density, reducing the current concentration effect, thereby helping to reduce dendrite growth.

[0024] It should be noted that the battery cell consists of a positive electrode, a separator, and a negative electrode. This part of the structure is the same as that of a conventional battery cell. The innovation of this application embodiment is that a porous film is added between the separator and the negative electrode, which helps to reduce the subsequent expansion of the battery cell and improve the cycle performance and rate performance of the battery cell.

[0025] In some embodiments of this application, the porous film includes a substrate and through holes disposed on the substrate; wherein the porosity of the through holes on the substrate ranges from 70% to 90%.

[0026] By adopting the above scheme, the porosity of the through holes on the substrate ranges from 70% to 90%, indicating that there are more through holes on the porous film, which helps to provide space for lithium metal deposition.

[0027] In some embodiments of this application, the aperture of the through hole can range from 0.5 μm to 1000 μm. Exemplarily, the aperture of the through hole can be 0.5 μm, 1 μm, 10 μm, 50 μm, 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, or any value between two adjacent values ​​mentioned above.

[0028] In some embodiments of this application, the aperture of the through-hole can range from 5 μm to 100 μm. Further, the aperture of the through-hole can range from 10 μm to 50 μm. Exemplarily, the aperture of the through-hole can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or any value between two adjacent values.

[0029] By adopting the above scheme, the vias with moderate pore size help to improve the uniformity of lithium metal deposition. If the pore size is too small, lithium metal will have difficulty entering the pores of the porous film, thus losing its buffering effect; if the space is too large, the current homogenization effect will not be obvious, and the suppression effect of lithium dendrites will be poor.

[0030] In some embodiments of this application, the thickness of the porous film can range from 2 μm to 50 μm. Further, the thickness of the porous film can range from 5 μm to 15 μm. Exemplarily, the thickness of the porous film can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or any value between two adjacent values ​​mentioned above.

[0031] By adopting the above-mentioned approach, porous films with an appropriate thickness range can help improve the cycle performance of the battery cell and reduce its degradation. If the thickness is too large, it will lead to an increase in side reactions in the battery cell, resulting in a decrease in the cycle performance and an excessively rapid decline in battery life. If the thickness is too small, the pores of the porous film will be filled too early, failing to buffer subsequent expansion.

[0032] In summary, the porous film of this application embodiment has the following beneficial effects through the synergistic design of pore size and thickness: 1) Spatial buffer: The pore structure of the porous film can accommodate the initial deposition of lithium metal and inhibit the formation of lithium dendrites. The porous film also has a certain effect of homogenizing current density and reducing the growth of lithium dendrites; 2) Densification guidance: During the charging process of the battery cell, in the initial stage of charging, lithium metal is deposited inside the porous film. At this time, since it is not under pressure, it tends to grow vertically. When the lithium metal deposition reaches the film thickness (at this time, there is still a lot of space in the porous film), it begins to be subjected to external pressure. The lithium metal begins to preferentially fill the pores in the porous film. That is, when the deposition thickness exceeds the thickness of the porous film, the external pressure forces the lithium ions to grow laterally and achieve densification, reducing subsequent expansion.

[0033] In some embodiments of this application, the porous film is an insulating porous film.

[0034] By adopting the above scheme, the presence of the insulating porous film helps to increase the path length and difficulty of lithium dendrite growth, making it difficult for them to penetrate the separator, thereby effectively inhibiting the growth of lithium dendrites. Moreover, the insulating porous film can play a certain stabilizing role in the transport of lithium ions, making the transport more uniform and stable, avoiding local overcharging and over-discharging caused by the non-uniformity of lithium ion transport, and improving the cycle stability and capacity retention of the battery.

[0035] In some embodiments of this application, there are multiple porous films located between the negative electrode and the separator; wherein the average pore size of the porous film closer to the negative electrode is larger than the average pore size of the porous film closer to the separator.

[0036] By adopting the above scheme, since lithium metal is deposited on the negative electrode side, the pore size of the porous film near the negative electrode sheet is larger, which helps to provide a larger space for lithium ion deposition, thereby reducing the volume expansion of the cell during charging and discharging.

[0037] Secondly, this application provides a method for preparing a battery cell, for preparing the aforementioned battery cell, with reference to... Figure 1 The preparation method includes the preparation of porous thin films; The porous thin film was prepared using the following method: S100. Disperse the resin raw materials in a solvent to obtain an initial mixed solution; S200. Add a pore-forming agent to the initial mixed solution to obtain a precursor solution; S300. The precursor solution is electrospinned to obtain the porous film.

[0038] By adopting the above scheme, the porous film of this application embodiment is formed by electrospinning. Adding a pore-forming agent can create pores on the porous film, thereby realizing the preparation of a porous film with densely distributed pores. The porous film prepared by the above method has the characteristic of high pore uniformity.

[0039] In some embodiments of this application, the resin raw material may include at least one of polyimide, polyvinylidene fluoride, polypropylene, and polyethylene.

[0040] By adopting the above scheme, polyimide has a wide operating temperature range and maintains good mechanical properties and chemical stability even at high temperatures; polyvinylidene fluoride has good chemical corrosion resistance, excellent electrical insulation properties, and good mechanical properties; polypropylene is lightweight and has high tensile strength, flexural modulus, and impact strength; polyethylene has a stable chemical structure, good flexibility and impact resistance, and can deform under external impact without easily breaking. Different types of resin raw materials are selected according to different application requirements.

[0041] In some embodiments of this application, the pore-forming agent may include at least one of sodium dodecyl sulfate, sodium chloride, potassium chloride, and tetraethoxysilane.

[0042] By adopting the above scheme, sodium dodecyl sulfate, sodium chloride, potassium chloride, and tetraethoxysilane have a regulating effect on the formation and distribution of pores; moreover, sodium chloride and potassium chloride, as inorganic pore-forming agents, play a role in controlling porosity and pore size.

[0043] Thirdly, embodiments of this application provide a lithium battery, which includes the cells as described above.

[0044] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0045] Example 1 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 1 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed of the rotating collector was set to 1200r / min to obtain a porous film with a thickness of 3μm and a pore size of 5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0046] Example 2 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 1 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed of the rotating collector was set to 700r / min to obtain a porous film with a thickness of 5μm and a pore size of 5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0047] Example 3 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 1 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed of the rotating collector was set to 500r / min to obtain a porous film with a thickness of 10μm and a pore size of 5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain a battery cell with a capacity of 20Ah.

[0048] Example 4 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 1 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed of the rotating collector was set to 400r / min to obtain a porous film with a thickness of 15μm and a pore size of 5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0049] Example 5 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 1 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed of the rotating collector was set to 250r / min to obtain a porous film with a thickness of 20μm and a pore size of 5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0050] Example 6 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 1 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed was set to 200r / min to obtain a porous film with a thickness of 25μm and a pore size of 5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0051] Example 7 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 22 wt%. The precursor solution was loaded into a 10mL syringe and a 23G needle (0.33mm inner diameter) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 0.5um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0052] Example 8 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 20 wt%. The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 1µm. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0053] Example 9 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 3um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0054] Example 10 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 3 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 10um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0055] Example 11 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 5 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 1mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 30um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0056] Example 12 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 5 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 0.8mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 50um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0057] Example 13 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 5 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (0.33mm inner diameter) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 0.6mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 100um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0058] Example 14 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 5 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 0.4mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 200um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0059] Example 15 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 5 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 0.2mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 500um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0060] Example 16 A battery cell is prepared using the following steps: Preparation of porous thin films: Dimethylformamide (DMF) and dimethylacetamide (DMAc) were mixed at a volume ratio of 1:1 as a solvent. Polyimide (PI) was added to the solvent and magnetically stirred at 60°C for 6 hours until completely dissolved. The mixture was then allowed to stand for 12 hours to remove bubbles, resulting in a preliminary mixed solution with a concentration of 15 wt%. Add 5 wt% sodium dodecyl sulfate to the preliminary mixed solution and sonicate for 30 minutes to obtain the precursor solution; The precursor solution was loaded into a 10mL syringe and a 23G needle (inner diameter 0.33mm) was installed. The voltage was adjusted to 20kV, the receiving distance was set to 30cm, the flow rate of the syringe pump was controlled at 0.05mL / h, the spinning time was set to 2h, and the rotation speed was set to 800r / min to obtain a porous film with a thickness of 5μm and a pore size of 1000um. Cell manufacturing: The porous film was placed in a vacuum oven and preheated at 60°C for 2 hours to obtain a dried porous film. According to the NCM811 positive electrode (area capacity 3.5mAh / cm²) 2 The aluminum foil current collector, separator, dried porous film and lithium metal anode (50μm) are stacked in sequence with an interlayer alignment accuracy of ±0.3mm. After stacking, a pressure of 1MPa is applied to the stack core and held for 10min. The stack is then packed into an aluminum-plastic film and injected with ether electrolyte (1.5g / Ah). After vacuum sealing, it is left to stand for 48h to obtain the battery cell.

[0061] Comparative Example 1 One type of battery cell differs from Example 1 in that it lacks a porous film. The battery cell is made of a positive electrode, a separator, and a negative electrode.

[0062] Performance testing: At 25℃, the battery was charged to 3.7V with a constant current of 0.05C, to 4.0V with a constant current of 0.1C, and to 4.4V with a constant current of 0.2C. Then, it was charged at a constant voltage of 4.4V until the cutoff current was 0.05C. The battery was then discharged to 2.8V with a constant current of 0.1C. After three cycles, the cycle performance and expansion rate were tested. The test results are shown in Table 1.

[0063] The test results are shown in Table 1: Table 1

[0064] Compared with Examples 1 to 6, the pore size of the porous film is kept constant at 5 μm, and the thickness of the porous film is increased. The thickness of the insulating film corresponds to the size of the lithium storage space. According to Table 1, the larger the thickness, the smaller the relative expansion rate. However, excessive thickness will lead to loose lithium metal deposition and violent side reactions, resulting in a decrease in cycle life. Therefore, the reasonable range of thickness is 5 to 25 μm.

[0065] Compared with Examples 7-16, keeping the thickness of the porous film constant at 5 μm, the pore size of the porous film was changed. As shown in Table 1, when the pore size is too small, lithium metal cannot be deposited into the pores and cannot play a spatial buffering role. When the pore size is too large, the uniformity of lithium metal deposition will be poor.

[0066] The battery cell, its preparation method, and lithium battery provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electric cell, characterized in that, the electric cell comprises a positive electrode sheet, a separator, a negative electrode sheet, and a porous film, the separator is located between the positive electrode sheet and the negative electrode sheet, and the porous film is located between the negative electrode sheet and the separator.

2. The electric cell according to claim 1, characterized in that, the porous film comprises a base body and through-holes arranged on the base body; wherein the porosity of the through-holes on the base body ranges from 70% to 90%.

3. The electric cell according to claim 2, characterized in that, the pore size of the through-holes ranges from 0.5 μm to 1000 μm.

4. The electric cell according to claim 3, characterized in that, the pore size of the through-holes ranges from 5 μm to 100 μm; preferably, the pore size of the through-holes ranges from 10 μm to 50 μm.

5. The electric cell according to any one of claims 1 to 4, characterized in that, the thickness of the porous film ranges from 2 μm to 50 μm; preferably, the thickness of the porous film ranges from 5 μm to 15 μm.

6. The electric cell according to any one of claims 1 to 5, characterized in that, the porous film is an insulating porous film; and / or the porous film comprises at least one of a polyimide film, a polyvinylidene fluoride film, a polypropylene film, and a polyethylene film.

7. The electric cell according to any one of claims 1 to 6, characterized in that, the number of the porous films is plural, and the plural porous films are arranged between the negative electrode sheet and the separator; wherein the average pore size of the porous films close to the negative electrode sheet is greater than the average pore size of the porous films close to the separator.

8. A method of making an electrochemical cell, characterized by, a method for preparing the electric cell according to any one of claims 1 to 7, the method comprising preparing a porous film; the porous film is prepared by the following method: dispersing a resin-based raw material in a solvent to obtain an initial mixed solution; adding a pore-forming agent to the initial mixed solution to obtain a precursor solution; the precursor solution is prepared by an electrospinning process.

9. The method for preparing the electric cell according to claim 8, characterized in that, the resin-based raw material comprises at least one of a polyimide, a polyvinylidene fluoride, a polypropylene, and a polyethylene; and / or the pore-forming agent comprises at least one of sodium dodecyl sulfate, sodium chloride, potassium chloride, and tetraethoxysilane.

10. The method for preparing the electric cell according to claim 8, characterized in that, in the electrospinning process, the injection flow rate of the precursor solution is 0.05 mL / h to 1 mL / h.

11. A lithium battery, characterized in that, the lithium battery comprises the electric cell according to any one of claims 1 to 7.

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