A negative electrode slurry composition, a composite separator with a slow-release function, and a battery

Abstract

The application discloses a negative electrode slurry composition, a composite diaphragm with a slow-release function and a battery. The negative electrode slurry composition comprises an organic solvent and a binder and anhydrous metal nitrate dispersed in the organic solvent, the negative electrode slurry composition is coated on the side of a lithium ion battery negative electrode sheet away from a current collector or a diaphragm facing a negative electrode, and the binder is a polymer material capable of dissolving or dispersing or complexing the anhydrous metal nitrate. The metal nitrate in the application can be continuously released into an electrolyte, a protective SEI layer and a stable composite alloy are formed on the LMA, meanwhile, the volume expansion or shrinkage effect caused by lithium in the deposition / stripping process can be reduced, the desolvation process of lithium ions from a solvent shell molecule is accelerated, and in addition, the application shows excellent applicability to ether and ester electrolytes in the battery.

Description

Technical Field

[0001] This invention belongs to the field of membrane modification technology, and particularly relates to a negative electrode slurry composition, a composite membrane with slow-release function, and a battery. Background Technology

[0002] With the increasing global demand for clean energy, the development of new energy technologies, especially high-performance battery technologies, has become a research hotspot. Among various battery technologies, batteries using metals such as lithium, sodium, and zinc as anodes have attracted much attention due to their high theoretical specific capacity and low reduction potential, and are expected to significantly improve battery energy density. However, the high reactivity of these metals also brings significant challenges, especially the formation of dendrites on the surface of the metal anode. The continuous growth of these dendrites can not only penetrate the battery separator, causing short circuits and potential safety accidents, but also accelerate electrolyte consumption, reducing battery charge-discharge efficiency and lifespan. Therefore, solving the dendrite problem in metal anode batteries and improving battery safety and performance has become a key research focus.

[0003] While much research currently focuses on anode surface modification, uniform ion transport at the solid-liquid interface is equally crucial for preventing dendrite formation. Existing solutions, such as electrolyte additives or artificial solid electrolytes, are effective to some extent, but their high cost and complex preparation processes limit their commercial application. Therefore, finding a simple, low-cost, and environmentally friendly modification method is particularly important. In this regard, traditional polyolefin separators (such as polyethylene) used in lithium-ion batteries have shortcomings in lithium-ion and electrolyte affinity, pore distribution uniformity, and mechanical strength, all of which can lead to dendrite formation and battery short circuits. Therefore, modifying the battery separator is not only necessary. Given the positive role of lithium nitrate (LiNO3) in promoting the formation of a conductive and effective SEI film to protect LMAs, it is often used as an additive in ether-based electrolytes for lithium-sulfur batteries. This additive is beneficial for protecting the lithium metal anode because NO... 3- Ions promote the formation of conductive and efficient SEI films. However, the limited solubility of LiNO3 in electrolytes restricts its application. Furthermore, while batteries using Li-Mg alloys as anodes exhibit good performance, their high cost hinders commercialization. Summary of the Invention

[0004] The purpose of this invention is to provide a composite separator with a sustained-release function, which allows for low-cost modification of the separator and the formation of a protective SEI layer and a stable Li-Al alloy, thereby improving the kinetic performance of the battery.

[0005] To achieve the above objectives, in a first aspect, the present invention provides the application of a negative electrode slurry composition in the manufacture of a negative electrode sheet or separator for a lithium-ion battery. The negative electrode slurry composition comprises an organic solvent and a binder and an anhydrous metal nitrate dispersed in the organic solvent. The negative electrode slurry composition is coated on the side of the lithium-ion battery negative electrode sheet facing away from the current collector or the side of the separator facing the negative electrode. The binder is a polymer material capable of dissolving or dispersing anhydrous metal nitrate or capable of complexing with anhydrous metal nitrate.

[0006] The anhydrous metal nitrate is selected from at least one of Al(NO3)3·9H2O, Cu(NO3)2·6H2O, La(NO3)3·6H2O, Mg(NO3)2·6H2O, Fe(NO3)2·6H2O, Ca(NO3)2·4H2O, AgNO3, Bi(NO3)3, Ga(NO3)3, In(NO3)3, Zn(NO3)2, or Sn(NO3)2; the binder is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate, polyethylene oxide, polyvinyl alcohol, and polyamide; the organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, acetonitrile, acetone, ethanol, and methanol.

[0007] The mass ratio of the anhydrous metal nitrate to the binder is 1 to 3:1.

[0008] Secondly, the present invention provides a method for preparing the negative electrode slurry composition, comprising the following steps:

[0009] S1. Remove the water of crystallization of metal nitrates by heating them in a nitrogen dioxide gas atmosphere with a volume ratio of 5% to 20% and a heating environment of 200°C to 800°C;

[0010] S2. The anhydrous metal nitrates heated and dried in step 1 are mixed with the binder and dissolved in an organic solvent. After sonication and centrifugation, the supernatant is taken as the negative electrode slurry composition.

[0011] The anhydrous metal nitrate is selected from at least one of Al(NO3)3·9H2O, Cu(NO3)2·6H2O, La(NO3)3·6H2O, Mg(NO3)2·6H2O, Fe(NO3)2·6H2O, Ca(NO3)2·4H2O, AgNO3, Bi(NO3)3, Ga(NO3)3, In(NO3)3, Zn(NO3)2, or Sn(NO3)2; the binder is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate, polyethylene oxide, polyvinyl alcohol, and polyamide; the organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, acetonitrile, acetone, ethanol, and methanol.

[0012] The mass ratio of the anhydrous metal nitrate to the binder is 1 to 3:1.

[0013] In step S2, the sonication time is 1-2 hours and the centrifugation rate is 1500-2000 rpm; the volume of the supernatant taken in step S2 is 10 ml to 50 ml.

[0014] In the third and fourth aspects, the present invention provides a separator, wherein the side of the separator facing the negative electrode or the side of the lithium-ion battery negative electrode sheet facing the current collector is coated with the remaining material after drying of the negative electrode slurry composition of claim 1, wherein the thickness of the remaining material is 2 μm or less.

[0015] A lithium-ion battery negative electrode sheet, wherein the side of the separator facing the negative electrode or the side of the lithium-ion battery negative electrode sheet facing away from the current collector is coated with the remaining material after drying of the negative electrode slurry composition of claim 1, wherein the thickness of the remaining material is 2 μm or less.

[0016] The binder and organic solvent are polyvinylidene fluoride and N,N-dimethylformamide, respectively, with an anhydrous metal nitrate and polyvinylidene fluoride in a mass ratio of 1 to 3:1.

[0017] The separator is one of cellulose separator, polyolefin separator and ceramic separator. The side of the separator facing the positive electrode is coated with a modified layer. The modified layer is formed by drying a conductive agent and a binder dispersed in an organic solvent. The thickness of the modified layer is 2 μm or less. The conductive agent includes any one or a combination of at least two of graphite, carbon black, graphene, carbon nanotube conductive fibers, metal powder, conductive whiskers, conductive metal compounds or conductive polymers.

[0018] The conductive agent is Super-P, and the binder and dispersant are polyvinylidene fluoride and N-methylpyrrolidone, respectively. Super-P and polyvinylidene fluoride, by total weight, include 75% to 85% conductive carbon black and 15% to 25% polyvinylidene fluoride.

[0019] A lithium-ion battery includes a casing, a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode is the same as the lithium-ion battery negative electrode. A modified layer is coated on the side of the separator facing the positive electrode. The modified layer is formed by dispersing a conductive agent and a binder in an organic solvent and then drying them. The thickness of the modified layer is 2 μm or less. The conductive agent includes any one or a combination of at least two of the following: graphite, carbon black, graphene, carbon nanotube conductive fibers, metal powder, conductive whiskers, conductive metal compounds, or conductive polymers.

[0020] Or the diaphragm may be the diaphragm described above.

[0021] Beneficial effects: Compared with ordinary commercial separators, which have poor electrolyte wettability, poor thermal stability, low ionic conductivity, poor mechanical properties, and electrolyte depletion during the reaction process, this invention provides a composite separator with slow-release function. Super P can promote the reaction kinetics of the battery, and the metal nitrates in the modified layer can be continuously released into the electrolyte, forming a protective SEI layer and a stable alloy on LMA. At the same time, it can reduce the volume expansion or contraction effect of lithium during deposition / stripping, and accelerate the desolvation process of lithium ions from the solvent shell molecules. In addition, it exhibits excellent applicability to ether and ester electrolytes in the battery. Attached Figure Description

[0022] Figure 1 A comparison of the impedance diagrams of the sustained-release composite membrane of Example 1, Comparative Example 1, and Comparative Example 2 for the full cell.

[0023] Figure 2 This is a comparison chart of the long-cycle performance of the sustained-release composite separator of Example 1, Comparative Example 1, and Comparative Example 2 full cells at 1C rate.

[0024] Figure 3 The graph shows a comparison of the toroidal performance of the sustained-release composite separator of Example 1, Comparative Example 1, and Comparative Example 2 full cells at different rates.

[0025] Figure 4 The results of X-ray photoelectron spectroscopy (XPS) tests on the surface of the negative electrode after electrochemical cycle testing of Example 1 and Comparative Example 8 are shown. Detailed Implementation

[0026] The technical solution of the present invention will be described below through specific embodiments.

[0027] Example 1

[0028] A method for preparing a sustained-release composite membrane includes the following steps:

[0029] Step 1: Remove the water of crystallization of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) by heating in a nitrogen dioxide gas atmosphere with a volume ratio concentration of 5% to 20% at a temperature of 200℃ to 800℃ to obtain Al(NO3)3.

[0030] Step 2: Dissolve dried Al(NO3)3 and polyvinylidene fluoride (PVDF) in 100-200 ml of N,N-dimethylformamide (DMF) to prepare a slurry. The mass ratio of dried Al(NO3)3 to polyvinylidene fluoride (PVDF) is 1-3:1. Sonicate for two hours and then perform differential centrifugation at 1500-2000 rpm. Retain the supernatant obtained.

[0031] Step 3: Quantitatively measure 10-50 ml of the supernatant. Using vacuum filtration, uniformly load aluminum nitrate onto a polypropylene (PP) membrane, and after drying, obtain the AN@PP functionalized membrane.

[0032] Step 4: Add Super P and polyvinylidene fluoride (PVDF) to 50-100 ml of N-methylpyrrolidone (NMP) to prepare a solution with a Super P mass fraction of (75wt%-85wt%). Stir evenly to form a slurry. Use a scraper to coat the slurry onto the other side of PP@AN. After vacuum drying overnight, a sustained-release composite functionalized membrane is obtained.

[0033] Before use, all separators were cut into small discs (16 mm in diameter). The Al(NO3)3 slow-release layer faced the lithium anode in the lithium battery, and the Super P modified layer faced the other electrode in the battery. They were then combined with different battery electrodes to form half-cells, symmetrical cells, and full cells for electrochemical performance testing.

[0034] Example 2

[0035] Step 1: Remove the water of crystallization of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) by heating in an environment with a nitrogen dioxide concentration of 5%–20% by volume. Note: The heating temperature is 200℃–800℃ to obtain Mg(NO3)2;

[0036] Step 2: Dissolve dried Mg(NO3)2 and polyvinylidene fluoride (PVDF) in 100-200 ml of N,N-dimethylformamide (DMF) to prepare a slurry. The mass ratio of Mg(NO3)2 to PVDF is 1-3:1. Sonicate for two hours, then centrifuge using a differential centrifuge at 1500-2000 rpm. Retain the resulting supernatant.

[0037] Step 3: Quantitatively measure 10-50 ml of the supernatant. Magnesium nitrate is uniformly loaded onto a polypropylene membrane (PP) using vacuum filtration, and after drying, the MN@PP functionalized membrane is obtained.

[0038] Step 4: Add Super P and polyvinylidene fluoride (PVDF) to 50-100 ml of N-methylpyrrolidone (NMP) to prepare a solution with a Super P mass fraction of (75wt%-85wt%). Stir evenly to form a slurry. Use a scraper to coat the slurry onto the other side of PP@AN. After vacuum drying overnight, a slow-release composite functionalized membrane is obtained.

[0039] Example 3

[0040] The experimental procedure was the same as in Example 1, except that the polypropylene diaphragm (PP) was replaced with a ceramic diaphragm, while other conditions remained unchanged.

[0041] Example 4

[0042] The experimental procedure was the same as in Example 1, except that the polypropylene membrane (PP) was replaced with a cellulose membrane, while other conditions remained unchanged.

[0043] Comparative Example 1

[0044] Comparative Example 1 is based on Example 1, but differs from Example 1 in that it uses a polypropylene (PP) membrane without any other treatment. Before use, the membrane is cut into small discs (16 mm in diameter). It is then combined with different battery electrodes to form half-cells, symmetrical cells, and full cells for electrochemical performance testing.

[0045] Comparative Example 2

[0046] Comparative Example 2 used a composite membrane prepared with halides as a reference in other reports. The preparation steps were as follows: A polypropylene (PP) membrane was immersed in a mixture of zinc chloride and PVDF, with a zinc chloride solution concentration of 1 mg / ml and a PVDF solution concentration of 2 mg / ml. After immersion for 8 hours, it was rolled. The rolled membrane was then left to stand undisturbed for 12 hours to obtain a modified membrane, which was then placed in a 60°C oven for later use. The modified membrane was then combined with different battery electrodes to form half-cells, symmetrical cells, and full cells for electrochemical performance testing.

[0047] Comparative Example 3

[0048] Comparative Example 3 used composite separators prepared with ceramic coating as a reference in other reports. The preparation steps were as follows: 1g of porous alumina powder, 0.3g of polyvinylidene fluoride (PVDF), and 7.5g of N-methylpyrrolidone (NMP) were mixed evenly to obtain a ceramic coating slurry. The ceramic coating slurry was uniformly coated onto one side of a polypropylene (PP) separator using a coating machine and vacuum dried at 80℃ to form a coated ceramic composite separator. The modified separator was then combined with different battery electrodes to form half-cells, symmetrical cells, and full cells for electrochemical performance testing. Electrochemical performance testing.

[0049] Comparative Example 4

[0050] The experimental procedure was the same as that of Comparative Example 2, except that the polypropylene diaphragm (PP) was replaced with a ceramic diaphragm, while other conditions remained unchanged.

[0051] Comparative Example 5

[0052] The experimental procedure was the same as that of Comparative Example 3, except that the polypropylene diaphragm (PP) was replaced with a ceramic diaphragm, while other conditions remained unchanged.

[0053] Comparative Example 6

[0054] The experimental procedure was the same as that of Comparative Example 2, except that the polypropylene membrane (PP) was replaced with a cellulose membrane, while other conditions remained unchanged.

[0055] Comparative Example 7

[0056] The experimental procedure was the same as that of Comparative Example 3, except that the polypropylene membrane (PP) was replaced with a cellulose membrane, while other conditions remained unchanged.

[0057] Comparative Example 8

[0058] The experimental procedure was the same as in Example 1, except that step 4 was not used, and other conditions remained unchanged.

[0059] Example 9

[0060] Following steps 1 and 2 of Example 1, a negative electrode slurry composition was prepared. This composition was then coated onto the side of the lithium-ion battery negative electrode sheet facing away from the current collector, as described in step 3 of Example 1. Following step 4 of Example 1, Super P and polyvinylidene fluoride (PVDF) were added to 50-100 ml of N-methylpyrrolidone (NMP) to prepare a solution with a Super P mass fraction of 75 wt%-85 wt%. The solution was stirred uniformly to form a slurry. The slurry was then coated onto the side of a polypropylene separator (PP) facing the positive electrode sheet using a spatula. After vacuum drying overnight, a functionalized separator was obtained. Using the functionalized separator, the negative electrode sheet coated with the negative electrode slurry composition, the positive electrode, and the electrolyte, lithium-ion batteries were assembled separately in an argon-atmospheric glove box.

[0061] The polypropylene composite separators prepared in Examples 1, 2, 1, 2 and 3, NCM811 as the positive electrode, lithium metal as the negative electrode, and 1M LiPF6 EC / DEC (volume ratio 1:1) as the electrolyte were assembled into NCM811 batteries in an argon atmosphere glove box.

[0062] The ceramic composite separators prepared in Examples 3, 4, and 5, NCM811 as the positive electrode, lithium metal as the negative electrode, and 1M LiPF6 EC / DEC (volume ratio 1:1) as the electrolyte were assembled into NCM811 batteries in an argon atmosphere glove box.

[0063] The cellulose composite membranes prepared in Examples 4, 6, and 7, NCM811 as the positive electrode, lithium metal as the negative electrode, and 1M LiPF6 EC / DEC (volume ratio 1:1) as the electrolyte were assembled into NCM811 batteries in an argon atmosphere glove box.

[0064] The preparation method of NCM811 positive electrode sheet is as follows: nickel cobalt manganese (NCM), SuperP (conductive carbon black), and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 8:1:1, ground evenly, and then dispersed in polymethylpyrrolidone (NMP). After homogenization in a homogenizer for 20 minutes, a uniform slurry is obtained. The slurry is then coated onto aluminum foil using a preparation tool and dried in an 80℃ vacuum drying oven for 12 hours. Before use, the positive electrode sheet is cut into small discs (12 mm in diameter).

[0065] The assembled battery was subjected to electrochemical impedance spectroscopy (EIS) testing. The Nyquist curve is shown below. Figure 1 As shown, the charge transfer impedance Rct of the battery in Example 1 is much lower than that in Comparative Examples 1 and 2, which means that the Li+ transport resistance through the interface film is reduced, and Al 3+ The release of [Li] promoted the formation of Li-Al alloys. +Migration is faster, enabling high-speed, uniform transport of lithium ions.

[0066] Long-term cycling performance of 2.8–4.3V was tested at a 1C rate (1C = 200 mAh g). -1 The amount of active substance in NCM811 is 25 mg. Figure 2 The cycling performance of Example 1, Comparative Example 1, and Comparative Example 2 at a 1C rate. For example... Figure 2 As shown, after activation at 0.1C for the first three cycles, the first cycle of Example 1 has a capacity of 196.5 mAh g. -1 The discharge specific capacity was [value missing], and the capacity retention rate after 100 cycles was 85%. Comparative Example 1 showed a discharge specific capacity of 188.3 mAh g / L in the first cycle. -1 The discharge specific capacity was high, but after 100 cycles, the battery capacity retention was only 9%. Comparative Example 2 had a discharge specific capacity of 185.3 mAh g in the first cycle. -1 The battery exhibits a high discharge specific capacity, yet its capacity retention is only 41% after 100 cycles. Furthermore, currently no composite separator can be paired with a high areal loading (22mg / cm³). -2 After 100 cycles of long-term cycling testing, the ternary material NCM811 retains 85% of its capacity. Even when using the composite separator described in Comparative Example 3, which incorporates Al elements through a ceramic coating, reports indicate that under low areal loading and low rate (0.5C) conditions, using ternary material NCM532 as the cathode results in approximately 85% capacity retention after 100 cycles. Furthermore, the battery discharge specific capacity and energy density using NCM532 as the cathode are significantly lower than those of NCM811. The high discharge specific capacity and capacity retention achieved using the slow-release composite separator of this invention are attributed to the fact that Super P in the composite separator promotes battery reaction kinetics, facilitates the formation of the CEI film on the NCM811 cathode material, and ensures uniform lithium-ion transport, thus homogenizing the lithium flow.

[0067] Similar to the steps described above, the capacity retention of NCM811 full cells with ceramic composite membranes and cellulose composite membranes after 100 cycles under a voltage range of 2.8–4.3V and a 1C condition was tested. The results are shown in Tables 2 and 3.

[0068] Cyclic performance was tested at different rate conditions from 2.8 to 4.3 V, with 25 mg of NCM811 active material. Figure 3 The figures show the cycling performance of Examples 1, 2, Comparative Example 1, and Comparative Example 2 at different expansion rates. It is clear from the figures that Examples 1 and 2 show improved performance due to the reduced NO content in the sustained-release composite membrane. 3-The introduction of Al and Super P promote the battery's reaction kinetics, maintaining a high discharge specific capacity even at high current densities. In contrast, the halide composite separator prepared in Comparative Example 2, while offering a slight improvement in discharge specific capacity initially, only shows a slight increase in capacity compared to the unmodified polyolefin separator in Comparative Example 1 after high current density cycling, though the effect is not significant. Furthermore, the cycling performance is difficult to recover after high current density cycling. The ceramic-coated composite separator prepared in Comparative Example 3 exhibits high discharge specific capacity under initial low-rate conditions, even showing no significant decline at 2C. However, at 5C high-rate conditions, despite the introduction of Al, the battery performance is unstable, and the discharge specific capacity is low, with a significant decrease upon returning to low-rate conditions. It is evident that the introduction of Al improves battery performance to some extent, but it is still difficult to withstand high current densities. The composite separator with slow-release function in Example 1 can continuously provide NO3- to the electrolyte system. - It can form a nitrogen-rich electrolyte interphase (SEI) film on the lithium anode surface, NO3 - It can react with Li to be reduced to Li3N and LiNxOy, which are the main components of the SEI film. This allows the lithium anode SEI film to be continuously repaired during cycling. Li3N can provide high ionic conductivity and, together with Super P on the other side of the composite separator, promotes the reaction kinetics of the battery, thereby achieving the cycle life of lithium metal batteries.

[0069] Simultaneously, the NCM811 full cells assembled in Example 1 and Comparative Example 8 were disassembled after 100 cycles. X-ray photoelectron spectroscopy (XPS) was performed on the surface of the negative electrode after both cycles. The fitted N1s characteristic peak results are as follows: Figure 4 As shown: Li3N and LiNxOy can be clearly observed in Example 1, while only PF6 is observed in Comparative Example 8. - And the anion PF6 - The content was significantly higher than in Example 1, indicating that in Example 1, the composite separator, in conjunction with the Super P on the other side, promoted the battery's reaction kinetics and also promoted the lithium-ion desolvation effect. - It preferentially enters the inner side of the solvent sheath and reacts with Li to be reduced to Li3N and LiNxOy. XPS characterization results and electrochemical tests show that NO3 － The reduction process constructs a nitrogen-containing SEI interface, which contributes to high-performance lithium metal batteries.

[0070] Table 1

[0071]

[0072] As can be seen from the data in Table 1, the composite membranes prepared in Examples 1 and 2 respectively provide free Al 3+ and Mg 2+ After reacting with Li, Li-Al and Li-Mg alloy phases are formed and adhere to the lithium metal surface, preventing the lithium metal from being consumed by the electrolyte, thus avoiding the loss of active lithium and electrolyte consumption. Simultaneously, the modified membrane possesses a certain mechanical strength, which can inhibit lithium dendrites from piercing the membrane and causing internal short circuits in the battery. Furthermore, aluminum in Example 1 is a lithiophilic element, providing deposition sites for lithium ions and promoting uniform lithium deposition. It was also found that the composite membranes obtained by vacuum filtration in Examples 1 and 2 have a higher areal density of the loaded material while maintaining a thinner membrane thickness, demonstrating that the membrane's porosity and pore size distribution are not damaged while simultaneously imparting a slow-release function. The various properties of the modified membrane are also significantly improved.

[0073] Table 2

[0074]

[0075] Table 3

[0076]

[0077] As shown in Tables 2 and 3, the cycling performance of the sustained-release composite membrane in the examples is significantly better than that in the comparative examples. These results demonstrate that using the sustained-release composite membrane allows for a continuous supply of NO... 3- This promotes the formation of conductive and efficient SEI films, and plays a positive role in protecting LMAs.

[0078] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for preparing a diaphragm, characterized in that, Includes the following steps: S1. Remove the water of crystallization of metal nitrates by heating them in a nitrogen dioxide gas atmosphere with a volume ratio of 5% to 20% and a heating environment of 200°C to 800°C; S2. The anhydrous metal nitrates heated and dried in step 1 are mixed with the binder and dissolved in an organic solvent. After sonication and centrifugation, the supernatant is taken as the negative electrode slurry composition. S3. The supernatant is coated onto the side of the diaphragm facing the negative electrode by vacuum filtration and dried to obtain the diaphragm; The metal nitrate is selected from at least one of Al(NO3)3·9H2O, Cu(NO3)2·6H2O, La(NO3)3·6H2O, Mg(NO3)2·6H2O, Fe(NO3)2·6H2O, Ca(NO3)2·4H2O, AgNO3, Bi(NO3)3, Ga(NO3)3, In(NO3)3, Zn(NO3)2 or Sn(NO3)2; The adhesive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, carboxymethyl cellulose, sodium carboxymethyl cellulose, sodium alginate, polyethylene oxide, polyvinyl alcohol, and polyamide. The organic solvent is selected from one or more of dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, acetonitrile, acetone, ethanol, and methanol; The mass ratio of the anhydrous metal nitrate to the binder is 1 to 3:

1.

2. The preparation method according to claim 1, characterized in that, In step S2, the ultrasonic time is 1-2 hours and the centrifugation speed is 1500-2000 rpm; the volume of the supernatant taken in step S2 is 10 ml to 50 ml.

3. The diaphragm prepared by the method according to claim 1, characterized in that, The side of the diaphragm facing the negative electrode is coated with the remaining material after the negative electrode slurry composition has been dried, and the thickness of the remaining material is 2 μm or less.

4. The diaphragm as described in claim 3, characterized in that, The binder and organic solvent are polyvinylidene fluoride and N,N-dimethylformamide, respectively, and the mass ratio of anhydrous metal nitrate to polyvinylidene fluoride is 1 to 3:

1.

5. The diaphragm according to claim 4, characterized in that, The separator is one of cellulose separator, polyolefin separator and ceramic separator. The side of the separator facing the positive electrode is coated with a modified layer. The modified layer is formed by drying a conductive agent and a binder dispersed in an organic solvent. The thickness of the modified layer is 2 μm or less. The conductive agent includes any one or a combination of at least two of graphite, carbon black, graphene, carbon nanotube conductive fibers, metal powder, conductive whiskers, conductive metal compounds or conductive polymers.

6. The diaphragm according to claim 5, characterized in that, The conductive agent in the modified layer is Super-P, and the binder and organic solvent are polyvinylidene fluoride and N-methylpyrrolidone, respectively. Super-P and polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone to prepare a solution with a Super-P mass fraction of 75wt% to 85wt%.

7. A lithium-ion battery, characterized in that, The device includes a shell, a positive electrode, a negative electrode, an electrolyte, and a separator. The side of the separator facing the positive electrode is coated with a modified layer, which is formed by drying a conductive agent and a binder dispersed in an organic solvent. The thickness of the modified layer is 2 μm or less. The conductive agent includes any one or a combination of at least two of graphite, carbon black, graphene, carbon nanotube conductive fibers, metal powder, conductive whiskers, conductive metal compounds, or conductive polymers. The separator is the separator according to any one of claims 3-6.

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