Diaphragm, preparation method thereof and lithium battery

Abstract

The invention discloses a diaphragm and a preparation method thereof, and a lithium battery, the diaphragm comprises a base membrane, and also comprises an MXene coating arranged on one side of the base membrane along the thickness direction, and an alumina coating arranged on the other side of the base membrane along the thickness direction; wherein the MXene coating layer comprises MXene modified by metal single atoms, and the aluminum oxide coating layer comprises aluminum oxide. According to the diaphragm and the metal monatomic modified MXene, the transfer speed of lithium ions in the charging and discharging process of a lithium battery can be increased, so that the electrochemical reaction speed in the charging and discharging process is increased, the requirement of high-rate charging and discharging is met, and the cycle performance of the battery is improved; aluminum oxide can enhance the mechanical strength of the diaphragm and prevent negative lithium dendrites from puncturing the diaphragm, so that thermal runaway is avoided, and the safety of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a diaphragm and a preparation method thereof, and a lithium battery. Background Art

[0002] With the development of science and technology, lithium batteries are widely used in various portable electronic devices, electric vehicles and other fields due to their high energy density, long cycle life and environmental protection. Among them, lithium iron phosphate batteries have become a hot topic of research due to their high safety performance, low cost and environmental friendliness. However, the performance of lithium iron phosphate batteries is affected by many factors, such as positive and negative electrode materials, diaphragm materials, electrolytes, etc.

[0003] At present, the coating process for diaphragm modification is complicated and not suitable for large-scale production. Moreover, when the battery is charged and discharged at a high rate, the transmission speed of lithium ions is slow and cannot meet the requirements of high-rate charge and discharge. In addition, during the use of the battery, thermal runaway and other problems may occur due to the penetration of lithium dendrites, affecting the safety and cycle performance of the battery. Summary of the invention

[0004] The present invention is based on the inventor's discovery and understanding of the following facts and problems: The coating process of diaphragm modification is complicated. When the battery is charged and discharged at a high rate, the transmission speed of lithium ions is slow and cannot meet the requirements of high-rate charging and discharging. During the use of the battery, thermal runaway and other problems may occur due to the penetration of lithium dendrites, affecting the safety and cycle performance of the battery.

[0005] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, the embodiments of the present invention provide a diaphragm and a preparation method thereof, and a lithium battery. The MXene modified with a single metal atom can increase the transfer speed of lithium ions during the charging and discharging process of the lithium battery, thereby increasing the electrochemical reaction speed during the charging and discharging process, meeting the requirements of high-rate charging and discharging, and improving the cycle performance of the battery; aluminum oxide can enhance the mechanical strength of the diaphragm, prevent negative electrode lithium dendrites from piercing the diaphragm, thereby avoiding thermal runaway and improving the safety of the battery.

[0006] An embodiment of the present invention provides a diaphragm, including a base film, and also including a MXene coating arranged on one side of the base film along the thickness direction thereof, and an aluminum oxide coating arranged on the other side of the base film along the thickness direction thereof; wherein the MXene coating includes MXene modified with metal single atoms, and the aluminum oxide coating includes aluminum oxide.

[0007] Advantages and technical effects brought by the diaphragm of the embodiment of the present invention: MXene modified with metal single atoms can increase the transfer speed of lithium ions during the charging and discharging process of the lithium battery, thereby increasing the electrochemical reaction speed during the charging and discharging process, meeting the needs of high-rate charging and discharging, and improving the cycle performance of the battery; aluminum oxide can enhance the mechanical strength of the diaphragm, prevent negative electrode lithium dendrites from piercing the diaphragm, thereby avoiding thermal runaway and improving the safety of the battery.

[0008] In the embodiment of the present invention, MXene is a two-dimensional nano-layered material composed of transition metal carbon / nitride, which has excellent electrical conductivity, high specific surface area, high electrical conductivity, and has properties similar to graphene. The highly conductive and stable MXene material has a unique organ structure and a large specific surface area, which can significantly increase the transfer speed of lithium ions during the charge and discharge process.

[0009] The single atoms in the metal single atom modified MXene show highly exposed active centers and maximized atomic utilization. The addition of single atoms not only directly introduces highly active sites, but also brings about the redistribution of the local electronic structure of MXene, thus showing good ionic conductivity. MXene has abundant vacancies, such as Ti3C2T x Ti vacancies may be ideal carriers for stabilizing and regulating single atoms, and the large specific surface area of ​​MXene can load more single atoms. Therefore, MXene modified with metal single atoms can combine high atomic utilization and excellent properties of MXene. MXene coating can make the diaphragm have better ionic conductivity, increase the transfer speed of lithium ions during the charging and discharging process of lithium batteries, thereby increasing the electrochemical reaction speed during the charging and discharging process, meeting the needs of high-rate charging and discharging, improving rate performance, and improving battery cycle performance.

[0010] In the embodiment of the present invention, the high mechanical strength aluminum oxide particles are evenly distributed on the other side of the diaphragm, which can effectively enhance the mechanical strength of the diaphragm and prevent the negative electrode lithium dendrites from piercing the diaphragm, thereby avoiding the occurrence of thermal runaway and other problems. In addition, the addition of aluminum oxide can also improve the heat resistance and flame retardancy of the diaphragm and improve the safety of the battery.

[0011] In some embodiments, in the metal single atom modified MXene, the metal single atom includes at least one of Ru, Ni, Cu, Co, and Mn;

[0012] And / or, the particle size of the metal single atom is 0.05-1 nm;

[0013] And / or, in the metal single atom modified MXene, the mass percentage of the metal single atom is 0.2-0.5wt%;

[0014] And / or, in the metal single atom modified MXene, the MXene comprises Ti3C2T x , Ti3C2, Ti4C3, V2C, Ta4C3T x or Nb2CT x At least one of;

[0015] And / or, the particle size of the metal single atom modified MXene is 100-500 nm.

[0016] In some embodiments, in the MXene coating, the mass percentage of the metal single atom-modified MXene is 65-95wt%;

[0017] And / or, the MXene coating further comprises a binder, and the mass percentage of the binder is 5-35wt%;

[0018] And / or, the thickness of the MXene coating is no greater than 10 μm.

[0019] In some embodiments, in the aluminum oxide coating, the particle size of the aluminum oxide is 200-300 nm;

[0020] And / or, in the aluminum oxide coating, the mass percentage of aluminum oxide is 65-95wt%.

[0021] In some embodiments, the aluminum oxide coating further includes a binder, and the mass percentage of the binder is 5-35wt%;

[0022] And / or, the thickness of the aluminum oxide coating is not greater than 10 μm.

[0023] In some embodiments, the base film includes at least one of polyethylene or polypropylene;

[0024] And / or, the base film has a thickness of 12-20 μm;

[0025] And / or, the separator has a thickness of 20-40 μm.

[0026] An embodiment of the present invention provides a method for preparing a diaphragm, comprising the following steps:

[0027] (1) coating a MXene slurry on one side of a base film along its thickness direction, drying, forming a MXene coating, and obtaining a base film coated on one side; the MXene slurry comprises MXene modified with a metal single atom;

[0028] (2) coating the base film coated on one side with an alumina slurry along the other side in the thickness direction thereof, drying the alumina slurry to form an alumina coating to obtain a diaphragm; wherein the alumina slurry comprises alumina.

[0029] In some embodiments, in step (1), in the MXene slurry, the mass percentage of the metal single atom modified MXene is 20-30wt%;

[0030] And / or, in the step (2), the mass percentage of the aluminum oxide in the aluminum oxide slurry is 20-30wt%.

[0031] An embodiment of the present invention provides a lithium battery, which includes a positive electrode, a negative electrode and a separator, and the separator is the separator described in the embodiment of the present invention or the separator prepared by the preparation method described in the embodiment of the present invention.

[0032] In the embodiments of the present invention, the rate performance, cycle performance and safety of the lithium battery are improved, the production process is simplified, the production cost is reduced, and the invention has high practical value and broad application prospects.

[0033] In some embodiments, the MXene coating of the separator is adjacent to the positive electrode, and the alumina coating of the separator is adjacent to the negative electrode.

[0034] In some embodiments, the lithium battery is a lithium iron phosphate battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram of a diaphragm according to an embodiment of the present invention.

[0036] Figure 2 is the internal resistance of the soft-pack batteries of the embodiments of the present invention and the comparative example.

[0037] Figure 3 It is the 1C charge-discharge cycle capacity retention rate of the battery of the embodiment of the present invention and the comparative example at 25°C. DETAILED DESCRIPTION

[0038] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0039] like Figure 1 As shown, a diaphragm according to an embodiment of the present invention includes a base film, a MXene coating arranged on one side of the base film along its thickness direction, and an aluminum oxide coating arranged on the other side of the base film along its thickness direction; wherein the MXene coating includes MXene modified with metal single atoms, and the aluminum oxide coating includes aluminum oxide.

[0040] The diaphragm of the embodiment of the present invention, the MXene modified with metal single atoms can increase the transfer speed of lithium ions during the charging and discharging process of the lithium battery, thereby increasing the electrochemical reaction speed during the charging and discharging process, meeting the needs of high-rate charging and discharging, and improving the cycle performance of the battery; aluminum oxide can enhance the mechanical strength of the diaphragm, prevent negative electrode lithium dendrites from piercing the diaphragm, thereby avoiding thermal runaway and improving the safety of the battery.

[0041] In the embodiment of the present invention, MXene is a two-dimensional nano-layered material composed of transition metal carbon / nitride, which has excellent electrical conductivity, high specific surface area, high electrical conductivity, and has properties similar to graphene. The highly conductive and stable MXene material has a unique organ structure and a large specific surface area, which can significantly increase the transfer speed of lithium ions during the charge and discharge process.

[0042] The single atoms in the metal single atom modified MXene show highly exposed active centers and maximized atomic utilization. The addition of single atoms not only directly introduces highly active sites, but also brings about the redistribution of the local electronic structure of MXene, thus showing good ionic conductivity. MXene has abundant vacancies, such as Ti3C2T x Ti vacancies may be ideal carriers for stabilizing and regulating single atoms, and the large specific surface area of ​​MXene can load more single atoms. Therefore, MXene modified with metal single atoms can combine high atomic utilization and excellent properties of MXene. MXene coating can make the diaphragm have better ionic conductivity, increase the transfer speed of lithium ions during the charging and discharging process of lithium batteries, thereby increasing the electrochemical reaction speed during the charging and discharging process, meeting the needs of high-rate charging and discharging, improving rate performance, and improving battery cycle performance.

[0043] In the embodiment of the present invention, the high mechanical strength aluminum oxide particles are evenly distributed on the other side of the diaphragm, which can effectively enhance the mechanical strength of the diaphragm and prevent the negative electrode lithium dendrites from piercing the diaphragm, thereby avoiding the occurrence of thermal runaway and other problems. In addition, the addition of aluminum oxide can also improve the heat resistance and flame retardancy of the diaphragm and improve the safety of the battery.

[0044] In some embodiments, the MXene coating includes a metal single atom-modified MXene; optionally, in the metal single atom-modified MXene, the metal single atom is supported on the MXene;

[0045] Optionally, in the MXene modified with metal single atoms, the metal single atoms include at least one of Ru, Ni, Cu, Co, and Mn; Optionally, the particle size of the metal single atoms is 0.05-1 nm, specifically, for example, 0.05 nm, 0.1 nm, 0.5 nm, and 1 nm; Optionally, in the MXene modified with metal single atoms, the mass percentage of the metal single atoms is 0.2-0.5 wt%, specifically, for example, 0.2 wt%, 0.3 wt%, 0.38 wt%, 0.4 wt%, and 0.5 wt%. In the embodiment of the present invention, the MXene modified with metal single atoms can increase the transfer speed of lithium ions during the charging and discharging process of the lithium battery, thereby increasing the electrochemical reaction speed during the charging and discharging process, meeting the requirements of high-rate charging and discharging, improving the rate performance, and improving the cycle performance of the battery. By optimizing the type and content of metal single atoms in the MXene modified with metal single atoms, it is beneficial to further increase the transfer speed of lithium ions and reduce costs.

[0046] In some embodiments, the MXene coating includes metal single atom-modified MXene;

[0047] Optionally, in the metal single atom modified MXene, the MXene includes Ti3C2T x , Ti3C2, Ti4C3, V2C, Ta4C3T x or Nb2CT x At least one of; optionally, T includes at least one of -OH, -O, -F, -Cl;

[0048] Optionally, the thickness of the MXene is 1-2 nm, specifically, for example, 1 nm, 1.2 nm, 1.5 nm, 1.7 nm, 2 nm;

[0049] Optionally, the particle size of the metal single atom modified MXene is 100-500 nm, specifically, for example, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm.

[0050] In the embodiments of the present invention, MXene is beneficial to improving the rate performance of the battery and enhancing the cycle performance of the battery.

[0051] In some embodiments, there is no particular limitation on the preparation method of metal single atom-modified MXene or MXene, and it can be prepared by conventional methods in the art, for example,

[0052] Optionally, the preparation method of the metal single atom modified MXene comprises: dispersing MXene in a solvent, ultrasonicating under an inert atmosphere, then adding a metal salt to react, washing, and drying to obtain the metal single atom modified MXene; optionally, testing the content of the metal single atom in the MXene by ICP-OES; optionally, the salt comprises at least one of RuCl3·xH2O, NiCl2·6H2O, CuCl2·2H2O, CoCl2·6H2O or MnCl2·4H2O;

[0053] In a specific embodiment, the preparation method of the metal single atom modified MXene includes: dispersing 100 mg of MXene in 100 mL of deionized water, and ultrasonicating for 30 minutes under a N2 atmosphere, and then adding 2 mg of metal salt and magnetically stirring for 6 hours, and after centrifugation, washing the precipitate with ultrapure water for 3 times, and freeze-drying to obtain the metal single atom modified MXene;

[0054] Optionally, the preparation method of MXene includes: adding MAX powder to HF solution for reaction, and washing and drying after the reaction to obtain MXene powder;

[0055] In a specific embodiment, the preparation method of MXene includes: slowly adding MAX powder to 30 ml of HF solution, then stirring at 60°C for 24 hours, washing the reaction solution with deionized water several times until the pH value reaches 6, and drying the sediment in a vacuum oven at 50°C for 8 hours to obtain MXene powder.

[0056] In some embodiments, in the MXene coating, the mass percentage of the metal single atom modified MXene is 65-95wt%, specifically, for example, 65wt%, 70wt%, 80wt%, 90wt%, 95wt%.

[0057] In some embodiments, the MXene coating further includes a binder; optionally, the binder includes PVDF; the mass percentage of the binder is 5-35wt%, specifically, for example, 5wt%, 10wt%, 20wt%, 30wt%, 35wt%.

[0058] In some embodiments, the thickness of the MXene coating is not more than 10 μm, specifically, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm. In the embodiment of the present invention, the thickness of the MXene coating is not more than 10 μm, which is beneficial to increase the transfer speed of lithium ions inside the battery. If the coating is too thick, the internal resistance of the battery will increase, and if the coating is too thin, the improvement effect on the diaphragm will be poor.

[0059] In some embodiments, in the aluminum oxide coating, the particle size of the aluminum oxide is 200-300 nm, specifically, for example, 200 nm, 250 nm, 300 nm; and / or, in the aluminum oxide coating, the mass percentage of the aluminum oxide is 65-95 wt%, specifically, for example, 65 wt%, 70 wt%, 80 wt%, 90 wt%, 95 wt%. In the embodiments of the present invention, it is beneficial to enhance the mechanical strength of the diaphragm, prevent the negative electrode lithium dendrites from piercing the diaphragm, and thus avoid the occurrence of problems such as thermal runaway.

[0060] In some embodiments, the aluminum oxide coating further includes a binder; optionally, the binder includes PVDF; the mass percentage of the binder is 5-35wt%, specifically, for example, 5wt%, 10wt%, 20wt%, 30wt%, 35wt%.

[0061] In some embodiments, the thickness of the aluminum oxide coating is not higher than 10 μm, specifically, for example, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm; optionally, the thickness of the aluminum oxide coating is the same as or different from the thickness of the MXene coating. In the embodiment of the present invention, the thickness of the aluminum oxide coating is not higher than 10 μm, which is beneficial to enhance the mechanical strength of the diaphragm. If the coating is too thick, the internal resistance of the battery will increase, and if the coating is too thin, the improvement effect on the diaphragm will be poor.

[0062] In some embodiments, the base film includes at least one of polyethylene (PE) or polypropylene (PP); and / or the thickness of the base film is 12-20 μm, specifically, for example, 12 μm, 15 μm, 17 μm, 20 μm; and / or the thickness of the diaphragm is 20-40 μm, specifically, for example, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm.

[0063] A method for preparing a diaphragm according to an embodiment of the present invention comprises the following steps:

[0064] (1) coating a MXene slurry on one side of a base film along its thickness direction, drying, forming a MXene coating, and obtaining a base film coated on one side; the MXene slurry comprises MXene modified with metal single atoms;

[0065] (2) coating the base film coated on one side with an alumina slurry along the other side in the thickness direction thereof, drying the alumina slurry to form an alumina coating to obtain a diaphragm; wherein the alumina slurry comprises alumina.

[0066] In some embodiments, in step (1), in the MXene slurry, the mass percentage of the metal single atom modified MXene is 20-30wt%, specifically, for example, 20wt%, 25wt%, 30wt%.

[0067] In some embodiments, in step (1), the MXene slurry further includes a binder, and the mass percentage of the binder is 5-20wt%, specifically, for example, 5wt%, 10wt%, 15wt%, 20wt%.

[0068] In some embodiments, in step (1), the MXene slurry includes a solvent; optionally, the mass percentage of the solvent is 50-75wt%, specifically, for example, 50wt%, 60wt%, 70wt%, 75wt%; the solvent includes NMP.

[0069] In some embodiments, in step (1), metal single atom-modified MXene, a binder, and a solvent are mixed to obtain a MXene slurry.

[0070] In some embodiments, in step (1), the coating is sprayed; optionally, the spraying speed is 3-10 mm / s, specifically, for example, 3 mm / s, 5 mm / s, 8 mm / s, 10 mm / s. In the embodiment of the present invention, the MXene slurry is sprayed on one side of the diaphragm by spraying. Compared with other methods, such as electrodeposition, sol-gel method, etc., the operation is simpler, the cost is relatively low, and it is more suitable for large-scale production.

[0071] In some embodiments, in the step (1), MXene slurry is coated on one side of the base film along its thickness direction and dried; optionally, the drying is carried out by oven drying; optionally, the drying temperature is 50-80°C, specifically, for example, 50°C, 60°C, 70°C, 80°C, and the drying time is 4-12h, specifically, for example, 4h, 6h, 8h, 10h, 12h.

[0072] In some embodiments, in step (2), in the alumina slurry, the mass percentage of alumina is 20-30wt%, specifically, for example, 20wt%, 25wt%, 30wt%.

[0073] In some embodiments, in step (2), the alumina slurry further includes a binder, and the mass percentage of the binder is 5-20wt%, specifically, for example, 5wt%, 10wt%, 15wt%, 20wt%.

[0074] In some embodiments, in step (2), the alumina slurry includes a solvent; optionally, the mass percentage of the solvent is 50-75wt%, specifically, for example, 50wt%, 60wt%, 70wt%, 75wt%; the solvent includes NMP.

[0075] In some embodiments, in step (2), alumina, a binder and a solvent are mixed to obtain alumina slurry.

[0076] In some embodiments, in step (2), the coating is sprayed; optionally, the spraying speed is 3-10 mm / s, specifically, for example, 3 mm / s, 5 mm / s, 8 mm / s, 10 mm / s; optionally, the spraying speeds in steps (1) and (2) are the same or different. In the embodiment of the present invention, the alumina slurry is sprayed on the other side of the diaphragm by spraying. Compared with other methods, such as electrodeposition, sol-gel method, etc., the operation is simpler, the cost is relatively low, and it is more suitable for large-scale production.

[0077] In some embodiments, in the step (2), an alumina slurry is coated on the other side of the base film coated on one side in the thickness direction and dried; optionally, the drying is performed by oven drying; optionally, the drying temperature is 50-80°C, specifically, for example, 50°C, 60°C, 70°C, 80°C, and the drying time is 4-12h, specifically, for example, 4h, 6h, 8h, 10h, 12h.

[0078] A lithium battery according to an embodiment of the present invention comprises a positive electrode, a negative electrode and a separator, and the separator is the separator described in the embodiment of the present invention or the separator prepared by the preparation method described in the embodiment of the present invention.

[0079] In the embodiments of the present invention, the rate performance, cycle performance and safety of the lithium battery are improved, the production process is simplified, the production cost is reduced, and the invention has high practical value and broad application prospects.

[0080] In some embodiments, the MXene coating of the diaphragm is adjacent to the positive electrode, and the alumina coating of the diaphragm is adjacent to the negative electrode; that is, the MXene coating of the diaphragm faces the positive electrode, and the alumina coating faces the negative electrode. In the embodiment of the present invention, the MXene coating faces the positive electrode and the alumina coating faces the negative electrode because lithium dendrites are formed at the negative electrode, and the function of the alumina coating is to enhance the mechanical strength of the diaphragm and prevent the dendrites of the negative electrode from piercing the diaphragm; the MXene coating is mainly used to enhance the transfer speed of lithium ions during charging and discharging, reduce the internal resistance of the battery, and improve the cycle performance; the alumina coating and the MXene coating are separately coated on both sides of the diaphragm to better and more targetedly exert the performance of the material itself.

[0081] In some embodiments, the positive electrode includes a positive electrode active material, and the positive electrode active material includes LiFePO4; optionally, the lithium battery is a lithium iron phosphate battery.

[0082] In some embodiments, the lithium battery further includes an electrolyte; the electrolyte includes a lithium salt, optionally, the lithium salt includes LiPF6, and the concentration of the lithium salt is 1M; the electrolyte includes a solvent, optionally, the solvent includes at least one of ethylene carbonate (EC) and dimethyl carbonate (DMC); optionally, the solvent includes ethylene carbonate and dimethyl carbonate, and the volume ratio of ethylene carbonate to dimethyl carbonate is 1:1.

[0083] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0084] Embodiment 1:

[0085] A method for preparing a lithium iron phosphate battery comprises the following steps:

[0086] 1. Preparation of diaphragm:

[0087] (1) Cut the PP diaphragm (thickness 12 μm) into 50 mm*50 mm to obtain the base film. x , particle size 300nm, Ru content of 0.38wt%) and binder PVDF in a mass ratio of 8:2, mixed with solvent NMP to prepare MXene slurry, the mass percentage of single-atom Ru-modified MXene material in the MXene slurry is 25wt%.

[0088] The MXene slurry was sprayed onto one side of the base membrane, and the spraying speed was controlled to 5 mm / s to ensure that the single-atom Ru-modified MXene could be evenly distributed on the diaphragm. After spraying, it was dried at 60 °C for 4 hours to form a MXene coating with a thickness of 8 μm, thereby obtaining a single-side coated base membrane.

[0089] (2) Alumina powder (particle size 200-300 nm) and binder PVDF are mixed with solvent NMP in a mass ratio of 8:2 to prepare an alumina slurry, and the mass percentage of alumina in the slurry is 25 wt %.

[0090] Alumina slurry was evenly sprayed on the other side of the base film at a spraying speed of 5 mm / s. The sprayed diaphragm was dried at 60° C. for 4 hours to form an alumina coating with a thickness of 8 μm to obtain a diaphragm.

[0091] 2. Preparation of batteries:

[0092] The separator was assembled into a battery, with the MXene coating facing the positive electrode and the alumina coating facing the negative electrode. LiFePO4 was selected as the positive electrode material, and the mass ratio of LiFePO4: conductive carbon black SP: PVDF in the positive electrode was 97:2:1. Graphite was used as the negative electrode material, and ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1M LiPF6 (volume ratio of 1:1) were selected as the electrolyte to obtain a lithium iron phosphate battery.

[0093] Example 2

[0094] The preparation method is the same as that in Example 1, except that the thickness of the MXene coating and the alumina coating are both 6 μm.

[0095] Example 3

[0096] The preparation method is the same as that of Example 1, except that the thickness of the MXene coating and the alumina coating are both 10 μm.

[0097] Comparative Example 1

[0098] The preparation method is the same as that of Example 1, except that step 1 is omitted and a 50 mm*50 mm PP diaphragm is directly used as the diaphragm in step 2.

[0099] Comparative Example 2

[0100] The preparation method is the same as that of Example 1, except that step (1) is omitted, that is, the diaphragm is only provided with an aluminum oxide coating.

[0101] Comparative Example 3

[0102] The preparation method is the same as that of Example 1, except that MXene material (Ti3C2T x ) replaces the single-atom Ru-modified MXene material, that is, unmodified MXene is used in the MXene coating; step (2) is omitted, that is, no alumina coating is provided.

[0103] Comparative Example 4

[0104] The preparation method is the same as that of Example 1, except that step (2) is omitted, that is, the diaphragm is not provided with an aluminum oxide coating, but only with a MXene coating containing single-atom Ru-modified MXene.

[0105] Table 1

[0106]

[0107] It can be seen from Table 1 that, relative to Example 2, the thickness of the MXene coating in Example 1 increases and the surface resistance of the diaphragm decreases. This is because the MXene modified with metal single atoms has excellent electrical conductivity, high specific surface area and high electrical conductivity, which can significantly reduce the surface resistance of the diaphragm and increase the speed at which lithium ions pass through the diaphragm during charging and discharging, thereby improving the cycle performance and rate performance of the battery.

[0108] Compared with Example 1, the surface resistance slightly increased when the thickness of the MXene coating and the alumina coating was 10 μm in Example 3. Due to the increase in the thickness of the alumina coating, the separator in Example 3 has good mechanical strength and thermal conductivity, the thermal shrinkage of the separator is reduced, and the puncture strength is increased.

[0109] Compared with Example 1, the thermal shrinkage rate of the uncoated diaphragm in Comparative Example 1 is higher, which is not conducive to maintaining the stability of the diaphragm size during the heating process of the battery cell. When the temperature is high, the diaphragm is reduced in size, and the positive and negative electrodes may contact and cause a short circuit.

[0110] Compared with Comparative Example 3, the surface resistance of Comparative Example 4 is reduced. This is because the addition of metal single atoms introduces more active sites, which can better improve the ionic conductivity of the diaphragm. Therefore, the MXene coating modified with metal single atoms in Comparative Example 4 can better improve the transfer rate of lithium ions during charging and discharging.

[0111] By comparing Examples 1-3 and Comparative Examples 1-4, it can be seen that the MXene coating can improve the electrical conductivity and reduce the surface resistance of the diaphragm; the alumina coating can reduce the thermal shrinkage of the diaphragm and enhance the puncture strength, thereby improving the safety performance of the battery.

[0112] Figure 2 The internal resistance diagram of the soft pack battery of the embodiment and the comparative example. Figure 2 It can be seen that the internal resistance of the battery using the separators of Comparative Examples 3 and 4 is relatively small, followed by Examples 1-3, and the largest internal resistance is Comparative Example 2. This is because the MXene coating is conductive, which can improve the conductivity and reduce the internal resistance of the battery. With the addition of the alumina coating, the internal resistance of the battery increases, so the resistance of Examples 1-3 is slightly larger than that of Comparative Examples 3 and 4. In Examples 1-3, as the thickness of the coating increases, the internal resistance of the soft-pack battery does not change much.

[0113] Figure 3 The capacity retention rate of the soft-pack battery of the embodiment and the comparative example at 1C charge and discharge cycle at 25°C is shown in FIG. Figure 3It can be seen that Example 1 has the highest capacity retention rate, followed by Example 3 and Example 2. Comparative Examples 3 and 4 show that both the MXene coating alone and the MXene coating modified by metal single atoms can improve the capacity retention rate of the battery to a certain extent. Since the addition of metal single atoms introduces more active sites, the ionic conductivity of the diaphragm can be better improved. Therefore, the MXene coating modified by metal single atoms in Comparative Example 4 can better improve the transfer rate of lithium ions during charging and discharging. The capacity retention rate of Comparative Example 4 is slightly higher than that of Comparative Example 3. Since the diaphragm of Comparative Example 2 is only modified by the aluminum oxide coating, the internal resistance of the battery is increased to a certain extent, which hinders the transfer rate of lithium ions during charging and discharging, and is not conducive to the cycle and capacity retention of the battery. Therefore, the capacity retention rate of Comparative Example 2 is slightly lower than that of Comparative Example 1.

[0114] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0115] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that: It includes a base film, a MXene coating arranged on one side of the base film along the thickness direction thereof, and an aluminum oxide coating arranged on the other side of the base film along the thickness direction thereof; wherein the MXene coating includes MXene modified with metal single atoms, and the aluminum oxide coating includes aluminum oxide.

2. The diaphragm according to claim 1, characterized in that In the metal single atom modified MXene, the metal single atom includes at least one of Ru, Ni, Cu, Co, and Mn; And / or, the particle size of the metal single atom is 0.05-1 nm; And / or, in the metal single atom modified MXene, the mass percentage of the metal single atom is 0.2-0.5wt%; And / or, in the metal single atom modified MXene, the MXene comprises Ti3C2T x , Ti3C2, Ti4C3, V2C, Ta4C3T x or Nb2CT x At least one of; And / or, the particle size of the metal single atom modified MXene is 100-500 nm.

3. The diaphragm according to claim 1, characterized in that In the MXene coating, the mass percentage of the metal single atom-modified MXene is 65-95wt%; And / or, the MXene coating further comprises a binder, and the mass percentage of the binder is 5-35wt%; And / or, the thickness of the MXene coating is no greater than 10 μm.

4. The diaphragm according to claim 1, characterized in that In the aluminum oxide coating, the particle size of the aluminum oxide is 200-300 nm; And / or, in the aluminum oxide coating, the mass percentage of aluminum oxide is 65-95wt%.

5. The diaphragm according to claim 1, characterized in that The aluminum oxide coating also includes a binder, and the mass percentage of the binder is 5-35wt%; And / or, the thickness of the aluminum oxide coating is not greater than 10 μm.

6. The diaphragm according to claim 1, characterized in that The base film comprises at least one of polyethylene or polypropylene; And / or, the base film has a thickness of 12-20 μm; And / or, the separator has a thickness of 20-40 μm.

7. A method for preparing the diaphragm according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) coating a MXene slurry on one side of a base film along its thickness direction, drying, forming a MXene coating, and obtaining a base film coated on one side; the MXene slurry comprises MXene modified with metal single atoms; (2) coating the base film coated on one side with an alumina slurry along the other side in the thickness direction thereof, drying the alumina slurry to form an alumina coating to obtain a diaphragm; wherein the alumina slurry comprises alumina.

8. The method for preparing a diaphragm according to claim 7, characterized in that: In the step (1), in the MXene slurry, the mass percentage of the metal single atom modified MXene is 20-30wt%; And / or, in the step (2), the mass percentage of the aluminum oxide in the aluminum oxide slurry is 20-30wt%.

9. A lithium battery, characterized in that: The lithium battery comprises a positive electrode, a negative electrode and a separator, wherein the separator is the separator according to any one of claims 1 to 6 or the separator prepared by the preparation method according to claim 7 or 8.

10. The lithium battery according to claim 9, characterized in that: The MXene coating of the separator is adjacent to the positive electrode, and the alumina coating of the separator is adjacent to the negative electrode; And / or, the lithium battery is a lithium iron phosphate battery.

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