Negative electrode slurry composition, composite diaphragm with slow release function and battery

Abstract

The invention 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 one side, opposite to a current collector, of a negative electrode plate of the lithium ion battery or on one side, facing a negative electrode, of a diaphragm, and the binder is a polymer material which can dissolve or disperse anhydrous metal nitrate or can be complexed with the anhydrous metal nitrate. The metal nitrate can be continuously released into the electrolyte, a protective SEI layer and a stable composite alloy are formed on the LMA, meanwhile, the volume expansion or shrinkage effect brought by lithium in the deposition / stripping process can be reduced, the desolvation process of lithium ions from solvent shell molecules is accelerated, and in addition, the performance of the lithium ion battery is improved. And excellent applicability of ether and ester electrolyte solutions is shown in the battery.

Description

Technical Field

[0001] The invention belongs to the technical field of diaphragm modification, and in particular relates to a negative electrode slurry composition, a composite diaphragm with a slow-release function, and a battery. Background Art

[0002] With the growing global demand for clean energy, the development of new energy technologies, especially high-performance battery technologies, has become a hot topic of research. Among the many battery technologies, batteries with metals such as lithium, sodium, and zinc as negative electrodes have attracted much attention due to their high theoretical specific capacity and low reduction potential, and are expected to significantly increase the energy density of batteries. However, the high activity of these metals also brings significant challenges, especially the formation of dendrites on the surface of metal negative electrodes. The continuous growth of these dendrites will not only penetrate the battery separator, causing short circuits and potential safety accidents, but also accelerate the consumption of electrolytes, reducing the battery's charge and discharge efficiency and life. Therefore, solving the dendrite problem in metal negative electrode batteries and improving battery safety and performance have become the focus of research.

[0003] Although many current studies focus on the modification of the negative electrode surface, uniform ion transport at the solid-liquid interface is equally critical for preventing dendrite formation. Some current solutions, such as electrolyte additives or artificial solid electrolytes, are effective to a certain extent, but the high cost and complex preparation process limit their commercial application. Therefore, it is particularly important to find a simple, low-cost and environmentally friendly modification method. In this regard, the polyolefin separators (such as polyethylene) used in traditional lithium-ion batteries have deficiencies in lithium ion and electrolyte affinity, pore distribution uniformity, and mechanical strength, all of which may lead to dendrite formation and battery short circuit. Therefore, it is not only necessary to modify the battery separator. In view of 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 to the ether electrolyte of lithium-sulfur batteries. This additive is beneficial to protect the lithium metal anode because NO 3- The ions promote the formation of conductive and efficient SEI films. However, the solubility of LiNO3 in the electrolyte is limited, which restricts its application. In addition, although batteries with Li-Mg alloy as anode show good performance, their high cost is not conducive to commercial promotion. Summary of the invention

[0004] The purpose of the present invention is to provide a composite diaphragm with a slow-release function, which can modify the diaphragm at low cost, form a protective SEI layer and a stable Li-Al alloy, and improve the dynamic performance of the battery.

[0005] In order to achieve the above-mentioned purpose, in a first aspect, the present invention provides an application of a negative electrode slurry composition in the preparation of a negative electrode sheet or a separator of a lithium ion battery, wherein the negative electrode slurry composition comprises an organic solvent and a binder and an anhydrous metal nitrate dispersed in the organic solvent, and the negative electrode slurry composition is coated on the side of the negative electrode sheet of the lithium ion battery facing away from the current collector or on the side of the separator facing the negative electrode, and the binder is a polymer material that can dissolve or disperse the anhydrous metal nitrate or can form a complex with the 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] In a second aspect, the present invention provides a method for preparing the negative electrode slurry composition, comprising the following steps:

[0009] S1. The metal nitrate is heated in a nitrogen dioxide gas atmosphere having a volume ratio concentration of 5% to 20% and a heating environment of 200 ℃ to 800 ℃ to remove crystal water;

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

[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] The ultrasonic time in step S2 is 1 h-2 h, and the centrifugal differential is 1500 r-2000 r; the volume range 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 negative electrode sheet of a lithium-ion battery facing away from the current collector is coated with the residual material after drying the negative electrode slurry composition of claim 1, and the thickness of the residual material is 2 μm or less.

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

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

[0017] The diaphragm is one of a cellulose diaphragm, a polyolefin diaphragm and a ceramic diaphragm, and a modified layer is coated on the side of the diaphragm facing the positive electrode, and the modified layer is formed after a conductive agent and a binder are dispersed in an organic solvent and dried, and the thickness of the modified layer is 2 μm or less; the conductive agent includes any one of graphite, carbon black, graphene, carbon nanotube conductive fiber, metal powder, conductive whisker, conductive metal compound or conductive polymer, or a combination of at least two of them.

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

[0019] A lithium ion battery, comprising a housing, a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet is the negative electrode sheet of the lithium ion battery, and a modified layer is coated on the side of the separator facing the positive electrode, wherein the modified layer is formed by drying a conductive agent and a binder dispersed in an organic solvent, and the thickness of the modified layer is 2 μm or less; the conductive agent comprises any one of graphite, carbon black, graphene, carbon nanotube conductive fiber, metal powder, conductive whisker, conductive metal compound or conductive polymer, or a combination of at least two thereof;

[0020] Or the diaphragm is the diaphragm described.

[0021] Beneficial effects: Compared with common commercial diaphragms, which have poor electrolyte wettability, poor thermal stability, low ion conductivity, poor mechanical properties, and electrolyte depletion during the reaction process, the present invention provides a composite diaphragm with a sustained release function. Super P can promote the reaction kinetics of the battery. The metal nitrate in the modified layer can be continuously released into the electrolyte to form a protective SEI layer and a stable alloy on the LMA. At the same time, the volume expansion or contraction effect brought about by lithium during the deposition / stripping process can be reduced, and the desolvation process of lithium ions from the solvent shell molecules is accelerated. In addition, it shows excellent applicability to ether and ester electrolytes in batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Comparison of the full-cell impedance diagrams of the sustained-release composite diaphragm of Example 1, Comparative Example 1, and Comparative Example 2;

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

[0024] Figure 3 It is a comparison chart of the ring performance of the sustained-release composite diaphragm of Example 1, Comparative Example 1 and the full battery of Comparative Example 2 at different rates;

[0025] Figure 4 The X-ray photoelectron spectroscopy (XPS) test results of the negative electrode surface after the electrochemical test cycle performance of Example 1 and Comparative Example 8. DETAILED DESCRIPTION

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

[0027] Example 1

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

[0029] Step 1, heating in a nitrogen dioxide gas atmosphere with a volume ratio concentration of 5% to 20% to remove the crystal water of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), the heating temperature is 200°C to 800°C, and Al(NO3)3 is obtained;

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

[0031] Step 3: quantitatively measure the volume of the supernatant to 10-50 ml. Through vacuum filtration, aluminum nitrate is uniformly loaded on the polypropylene (PP) membrane, and after drying, an AN@PP functionalized membrane is obtained.

[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 on the other side of PP@AN, and vacuum dry overnight to obtain a sustained-release composite functionalized diaphragm.

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

[0034] Example 2

[0035] Step 1: Heat in an environment with a volume ratio concentration of 5% to 20% nitrogen dioxide to remove crystal water of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O). Note: The heating temperature is 200°C to 800°C to obtain Mg(NO3)2;

[0036] Step 2: Dissolve the dried Mg(NO3)2 and polyvinylidene fluoride (PVDF) in 100-200 ml N,N-dimethylformamide (DMF) to prepare a slurry, wherein the mass ratio of Mg(NO3)2 to polyvinylidene fluoride (PVDF) is 1-3:1. Ultrasonicate for two hours, perform differential centrifugation in a centrifuge, and perform differential centrifugation in a centrifuge at 1500-2000 r, and retain the obtained supernatant.

[0037] Step 3: quantitatively measure the supernatant to a volume of 10 to 50 ml. Through vacuum filtration, magnesium nitrate is uniformly loaded on a polypropylene membrane (PP), and after drying, a 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 on the other side of PP@AN, and vacuum dry overnight to obtain a sustained-release composite functionalized diaphragm.

[0039] Example 3

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

[0041] Example 4

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

[0043] Comparative Example 1

[0044] Comparative Example 1 is based on Example 1. The difference between Comparative Example 1 and Example 1 is that: Comparative Example 1 uses polypropylene (PP) diaphragm without other treatment, and the diaphragm is cut into small discs (diameter 16 mm) before use. It is 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 uses the composite diaphragm prepared with halides in other reports as a reference, and the preparation steps are as follows: immerse the polypropylene (PP) diaphragm in a mixed solution composed of zinc chloride and PVDF, the concentration of the zinc chloride solution is 1 mg / ml, and the concentration of the PVDF solution is 2 mg / ml. After immersion for 8 hours, roll pressing is then performed. The rolled diaphragm is then left to stand for 12 hours without being disturbed to obtain a modified diaphragm, which is placed in a 60°C oven for standby use. The modified diaphragm is then combined with different battery electrodes, assembled into half-cells, symmetrical cells and full cells for electrochemical performance testing.

[0047] Comparative Example 3

[0048] Comparative Example 3 is a reference to a composite diaphragm prepared by ceramic coating in other reports. The preparation steps are as follows: 1g of porous aluminum oxide powder, 0.3g of polyvinylidene fluoride (PVDF) and 7.5g of N-methylpyrrolidone (NMP) are mixed evenly to obtain a ceramic coating slurry; the ceramic coating slurry is evenly coated on one side of a polypropylene (PP) diaphragm by a coater, and vacuum dried at 80°C to form a coated ceramic composite diaphragm. Afterwards, the modified diaphragm is combined with different battery electrodes, assembled into half-cells, symmetrical cells and full cells for electrochemical performance tests. Electrochemical performance test.

[0049] Comparative Example 4

[0050] The experimental steps are the same as those of Comparative Example 2, except that the polypropylene diaphragm (PP) is replaced with a ceramic diaphragm, and other conditions remain unchanged.

[0051] Comparative Example 5

[0052] The experimental steps are the same as those of Comparative Example 3, except that the polypropylene diaphragm (PP) is replaced with a ceramic diaphragm, and other conditions remain unchanged.

[0053] Comparative Example 6

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

[0055] Comparative Example 7

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

[0057] Comparative Example 8

[0058] The experimental steps are the same as those in Example 1, except that step 4 is not adopted and other conditions remain unchanged.

[0059] Example 9

[0060] Steps 1 to 2 of Example 1 are used to prepare a negative electrode slurry composition, and the negative electrode slurry composition is coated on the side of the negative electrode sheet of the lithium ion battery facing away from the current collector according to the method of step 3 in Example 1. The method of step 4 of Example is used to add Super P and polyvinylidene fluoride (PVDF) to 50 to 100 ml of N-methylpyrrolidone (NMP) to prepare a solution with a mass fraction of Super P of (75wt% to 85wt%), and the slurry is uniformly stirred to form a slurry, and the slurry is applied to the side of the polypropylene diaphragm (PP) facing the positive electrode sheet using a scraper, and the functionalized diaphragm is obtained after vacuum drying overnight. The functionalized diaphragm and the negative electrode sheet of the lithium ion battery coated with the negative electrode slurry composition, the positive electrode and the electrolyte are respectively assembled into lithium ion batteries in an argon atmosphere glove box.

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

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

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

[0064] The preparation method of the 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 dispersed in polymethylpyrrolidone (NMP), then placed in a homogenizer for 20 minutes to obtain a uniform slurry, and the slurry is scraped onto aluminum foil with a preparation device, placed in a vacuum drying oven at 80°C and dried for 12 hours, and the positive electrode sheet is cut into small discs (diameter 12 mm) before use.

[0065] The above assembled battery was subjected to electrochemical impedance spectroscopy (EIS) test. The Nyquist curve is as follows Figure 1 As shown, the charge transfer impedance Rct of the battery in Example 1 is much lower than that in Comparative Example 1 and Comparative Example 2, which means that the Li+ transport resistance through the interface membrane is reduced and the Al 3+ The release of Li promotes the formation of Li-Al alloy. +The migration is faster, achieving high-speed and uniform transportation of lithium ion flux.

[0066] The long cycle performance of 2.8~4.3V was tested under the condition of 1C rate, 1C=200mAhg -1 , the amount of NCM811 active substance is 25mg, Figure 2 The cycle performance of Example 1, Comparative Example 1 and Comparative Example 2 at 1C rate. Figure 2 As shown, after the first three cycles were activated at 0.1C, the first cycle of Example 1 had 196.5 mAhg -1 The discharge capacity of the first cycle is 188.3 mAhg. -1 The discharge capacity of the battery is 185.3 mAh g after 100 cycles. -1 However, after 100 cycles, the battery capacity retention rate is only 41%. At the same time, there is currently no composite diaphragm that can be used with high surface loading (22mg cm -2 ) after 100 cycles of long cycle test of ternary material NCM811, the capacity retention rate can reach 85%. Even if the composite diaphragm in which the Al element is introduced on the diaphragm by ceramic coating in Comparative Example 3 is used, according to relevant reports: under low surface loading and 0.5C low rate conditions, the ternary material NCM532 is used as the positive electrode, and the capacity retention rate after 100 cycles is about 85%, and when NCM532 is used as the positive electrode, the battery discharge specific capacity is low, and the energy density is much less than NCM811. The use of the sustained-release composite diaphragm of the present invention can achieve such a high discharge specific capacity and capacity retention rate, which is attributed to the fact that Super P in the composite diaphragm can promote the reaction kinetics of the battery, promote the formation of the CEI film of the NCM811 positive electrode material, make the lithium ions transport evenly, and play a role in homogenizing the lithium flow.

[0067] The NCM811 full battery with ceramic composite diaphragm and cellulose composite diaphragm was tested in the same way as above. The capacity retention rate after 100 cycles in the voltage range of 2.8-4.3V and 1C condition is shown in Table 2 and Table 3:

[0068] The cycle performance of 2.8-4.3V was tested under different rate conditions. The amount of NCM811 active material was 25mg. Figure 3 The cycle performance of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at different rates can be clearly seen from the figure. 3-The introduction of Super P promotes the reaction kinetics of the battery, and even at a high current density, it still maintains a high discharge capacity. The halide composite diaphragm prepared in Comparative Example 2, even if the diaphragm slightly improves the discharge capacity in the initial stage of the battery, when it undergoes a high current density cycle, the capacity is improved to a certain extent compared with the unmodified polyolefin diaphragm in Comparative Example 1, but the effect is not significant, and even after being subjected to a high current density, the cycle performance is difficult to recover. The ceramic coating composite diaphragm prepared in Comparative Example 3 has a high discharge capacity under the initial low rate conditions, and even under 2C conditions, the discharge capacity has not declined significantly. However, under 5C high rate conditions, although the ceramic coating composite diaphragm also introduces Al elements, the battery performance is not stable, and the discharge capacity is low. When it is subsequently restored to the low rate conditions, the discharge capacity has a significant attenuation. It can be seen that the introduction of Al elements has a certain improvement in battery performance, but it is still difficult to withstand high current density. The composite diaphragm with a sustained release function in Example 1 can continuously provide NO3 for the electrolyte system. - , which can form a nitride-rich electrolyte interface film (SEI) on the surface of the lithium negative electrode, NO3 - It can react with Li and be reduced to Li3N and LiNxOy by lithium, which constitute the main components of the SEI film, so that the SEI film of the lithium negative electrode is continuously repaired during the cycle process. Li3N can provide high ionic conductivity and cooperate with Super P on the other side of the composite diaphragm to promote the reaction kinetics of the battery, thereby realizing the cycle life of the lithium metal battery.

[0069] At the same time, the NCM811 full batteries assembled in Example 1 and Comparative Example 8 were disassembled after 100 cycles, and the surfaces of the negative electrode plates of the two cycles were tested by X-ray photoelectron spectroscopy (XPS). The results of the N1s characteristic peak obtained by fitting are as follows: Figure 4 As shown: Li3N and LiNxOy can be clearly observed in Example 1, while only PF6 - , and the anion PF6 - The content is significantly higher than that in Example 1, indicating that the composite membrane in Example 1 cooperates with the Super P on the other side to promote the reaction kinetics of the battery and also promotes the desolvation effect of lithium ions. - It will preferentially enter the inner side of the solvent sheath and react with Li to be reduced to Li3N and LiNxOy by lithium. XPS characterization results and electrochemical tests show that NO3 － The reduction constructs a nitrogen-containing SEI interface, which contributes to high-performance lithium metal batteries.

[0070] Table 1

[0071]

[0072] From the data in Table 1, it can be seen that the free Al 3+ and Mg 2+ After reacting with Li, Li-Al and Li-Mg alloys are generated and attached to the surface of lithium metal, which prevents lithium metal from being consumed by electrolyte, resulting in loss of active lithium and consumption of electrolyte. At the same time, the modified diaphragm has a certain mechanical strength, which can inhibit lithium dendrites from piercing the diaphragm and causing internal short circuit of the battery. At the same time, the aluminum element in Example 1 is a lithium-philic element, which can provide a certain deposition site for lithium ions and promote the uniform deposition of lithium. At the same time, it is found that the composite diaphragm obtained by filtration in Example 1 and Example 2 has a greater surface density of the loaded material while taking into account the thinner thickness of the diaphragm, which proves that while ensuring that the porosity and pore size distribution of the diaphragm are not damaged, the diaphragm is given a sustained release function. The various indicators of the modified diaphragm are also significantly improved.

[0073] Table 2

[0074]

[0075] Table 3

[0076]

[0077] As shown in Table 2 and Table 3, the cycle performance of the slow-release composite membrane of the embodiment is significantly better than that of the comparative example. The above results show that the use of the slow-release composite membrane can continuously supply NO 3- , which promotes the formation of conductive and efficient SEI film and plays a positive role in protecting LMAs.

[0078] It should be understood that the above description of the preferred embodiment is relatively detailed and cannot be regarded as limiting the scope of patent protection of the present invention. Under the enlightenment of the present invention, ordinary technicians in this field can also make substitutions or modifications without departing from the scope of protection of the claims of the present invention, which all fall within the scope of protection of the present invention. The scope of protection requested for the present invention shall be based on the attached claims.

Claims

1. Application of a negative electrode slurry composition in making a negative electrode sheet or a separator for a lithium ion battery, characterized in that: The negative electrode slurry composition includes an organic solvent, a binder and an anhydrous metal nitrate dispersed in the organic solvent. The negative electrode slurry composition is coated on the side of the negative electrode sheet of the lithium ion battery facing away from the current collector or the side of the separator facing the negative electrode. The binder is a polymer material that can dissolve or disperse the anhydrous metal nitrate or can form a complex with the anhydrous metal nitrate.

2. The use according to claim 1, characterized in that: 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.

3. The use according to claim 1, characterized in that: The mass ratio of the anhydrous metal nitrate to the binder is 1 to 3:

1.

4. A method for preparing a negative electrode slurry composition, characterized in that: The following steps are involved: S1. The metal nitrate is heated in a nitrogen dioxide gas atmosphere having a volume ratio concentration of 5% to 20% and a heating environment of 200°C to 800°C to remove crystal water; S2. The anhydrous metal nitrate and the binder after heating and drying in step 1 are mixed and dissolved in an organic solvent, and the supernatant is taken as the negative electrode slurry composition after ultrasonication and centrifugation; 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; The mass ratio of the anhydrous metal nitrate to the binder is 1 to 3:

1.

5. The preparation method according to claim 4, characterized in that: The ultrasonic time in step S2 is 1 h-2 h, and the centrifugal differential is 1500 r-2000 r; the volume range of the supernatant taken in step S2 is 10 ml to 50 ml.

6. A separator or a negative electrode sheet for a lithium-ion battery, characterized in that: The side of the separator facing the negative electrode or the side of the negative electrode sheet of the lithium ion battery facing away from the current collector is coated with the residual material after drying the negative electrode slurry composition of claim 1, and the thickness of the residual material is 2 μm or less. The side of the separator facing the negative electrode or the side of the negative electrode sheet of the lithium ion battery facing away from the current collector is coated with the residual material after drying the negative electrode slurry composition of claim 1, and the thickness of the residual material is 2 μm or less.

7. The separator according to claim 6 or the negative electrode sheet of a lithium-ion battery according to claim 7, characterized in that: The binder and the organic solvent are polyvinylidene fluoride and N,N-dimethylformamide respectively, and the mass ratio of anhydrous metal nitrate to polyvinylidene fluoride is 1-3:

1.

8. The diaphragm according to claim 6, characterized in that The diaphragm is one of a cellulose diaphragm, a polyolefin diaphragm and a ceramic diaphragm, and a modified layer is coated on the side of the diaphragm facing the positive electrode, and the modified layer is formed after a conductive agent and a binder are dispersed in an organic solvent and dried, and the thickness of the modified layer is 2 μm or less; the conductive agent includes any one of graphite, carbon black, graphene, carbon nanotube conductive fiber, metal powder, conductive whisker, conductive metal compound or conductive polymer, or a combination of at least two of them.

9. The diaphragm according to claim 8, characterized in that The conductive agent is Super-P, the binder and the dispersant are polyvinylidene fluoride and N-methylpyrrolidone respectively, and the total weight of Super-P and polyvinylidene fluoride includes 75% to 85% of conductive carbon black and 15% to 25% of polyvinylidene fluoride.

10. A lithium ion battery, characterized in that: The invention comprises a shell, a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet is the negative electrode sheet of the lithium ion battery according to claim 6, and a modified layer is coated on the side of the separator facing the positive electrode, wherein the modified layer is formed by drying a conductive agent and a binder dispersed in an organic solvent, and the thickness of the modified layer is 2 μm or less; the conductive agent comprises any one of graphite, carbon black, graphene, carbon nanotube conductive fiber, metal powder, conductive whisker, conductive metal compound or conductive polymer, or a combination of at least two thereof; Or the diaphragm is the diaphragm according to claim 6 or 8.

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