Positive electrode lithium replenishment composite material having core-shell structure, preparation method therefor, and use thereof

Abstract

Provided in the present application are a positive electrode lithium replenishment composite material having a core-shell structure, a preparation method therefor and the use thereof. The positive electrode lithium replenishment composite material having a core-shell structure comprises a positive electrode lithium replenishment agent inner core material and a monomolecular coating layer that is coated on the surface of the positive electrode lithium replenishment agent inner core material, the material of the monomolecular coating layer comprising an amphiphilic compound, and the amphiphilic compound comprising a hydrophilic head and a hydrophobic tail. The present application regulates the composition and structure of the positive electrode lithium replenishment composite material, such that the formed coating layer has both good environmental stability and ion conduction performance, and especially, the formed monomolecular coating layer has the characteristics of being thin, dense and uniform, and is free of thickness changes due to morphologic changes in the positive electrode lithium replenishment agent material.

Description

A positive electrode lithium supplement composite material with a core-shell structure, a preparation method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium supplement materials, and particularly relates to a positive electrode lithium supplement composite material with a core-shell structure, a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries (LIBs) have the advantages of high energy density, low cost and long service life, and are a good carrier of clean energy (such as wind energy and solar energy), and thus can become an ideal power source in the field of electric vehicles. However, due to people's anxiety about the cruising range of vehicles, the market urgently needs LIBs that can provide higher energy density. Based on this, the addition of lithium supplement materials not only can solve the problem of low energy density of batteries, but also has a cost advantage in the development of lithium supplement materials. The current negative electrode lithium supplement technology has relatively harsh conditions and requires a very dry environment. Compared with the negative electrode lithium supplement technology, the positive electrode lithium supplement technology can mix the lithium supplement agent with the positive electrode material during the mixing stage, without the need for complex processes, and is convenient for industrial production.

[0003] However, the currently used positive electrode lithium supplement material has poor environmental stability during storage and processing, resulting in high processing cost of lithium ion batteries. Therefore, it is urgent to solve the problem of environmental stability of the positive electrode lithium supplement material to reduce the production cost of lithium ion batteries. For this purpose, the related technology discloses that the positive electrode lithium supplement material is coated with a hydrophobic layer, so as to further improve the environmental stability of the positive electrode lithium supplement material.

[0004] The technical means disclosed in the related technology is mostly to coat a physical barrier layer on the surface of the positive electrode lithium supplement material. After storage under environmental conditions, the positive electrode lithium supplement material is prone to react with water or carbon dioxide, resulting in capacity loss of the positive electrode material and increase of polarization in the battery, and finally failure, because the physical barrier layer has poor lithium ion conductivity and poor protection ability for the positive electrode material. In addition, the current coating technology usually uses high-temperature solid phase or atomic vapor deposition (ALD) for coating, so that the formed coating layer is thick, the process cost is high, and the thickness of the coating layer changes due to the change of the morphology of the positive electrode material, resulting in uneven thickness of the coating layer.

[0005] Therefore, in the field, there is an urgent need to develop a positive electrode lithium supplement composite material to solve the above problems. SUMMARY

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0007] The application provides a positive electrode lithium supplement composite material with a core-shell structure, a preparation method and application thereof. By adjusting the composition and structure of the positive electrode lithium supplement composite material, the formed coating layer has good environmental stability and ion conductivity, especially the formed monomolecular layer coating layer has the characteristics of thinness, compactness and uniformity, and will not change in thickness due to the change in morphology of the positive electrode lithium supplement material.

[0008] In a first aspect, the application provides a positive electrode lithium supplement composite material with a core-shell structure, which comprises a positive electrode lithium supplement core material and a monomolecular layer coating layer coated on the surface of the positive electrode lithium supplement core material.

[0009] The material of the monomolecular layer coating layer comprises an amphiphilic compound, the amphiphilic compound comprises a hydrophilic head and a hydrophobic tail, and the structural formula of the amphiphilic compound is shown as formula I: X-Y-Z formula I.

[0010] Among them, the structure of X contains any one or a combination of at least two of carboxylate group, sulfonate group, sulfate group or silane group;

[0011] Y is selected from at least one of a single bond, a hydrocarbon group or a nitrogen heterocycle;

[0012] Z is selected from at least one of a substituted or unsubstituted hydrocarbon group, a substituted or unsubstituted sulfur hydrocarbon group, or a substituted or unsubstituted aryl group.

[0013] In one aspect, the application coats the environment-sensitive positive electrode lithium supplement material by using an amphiphilic compound with a specific structure, wherein the hydrophilic head is combined with the surface basic group of the positive electrode lithium supplement material, and the hydrophobic tail faces the outside. Ultimately, a hydrophobic film with good chemical stability can be formed on the surface of the positive electrode lithium supplement material, thereby preventing water molecules and corrosive substances from directly contacting the positive electrode lithium supplement material, and improving the electrochemical stability and durability of the positive electrode lithium supplement composite material. Compared with the traditional solid-phase coated, it is thinner and more uniform, and therefore has higher conductivity. Specifically, the positive electrode lithium supplement composite material with a core-shell structure provided by the application has a residual alkali amount on the surface reduced by about 11.2% after being placed for 5 days compared with the uncoated positive electrode lithium supplement material.

[0014] On the other hand, compared with the traditional hydrophobic physical coating layer, the hydrophobic monomolecular layer coating layer formed by the application has the advantages of thinner thickness, uniform and dense distribution, better lithium ion conductivity, and lower interface transmission impedance on the surface of the coated positive electrode lithium supplement material due to the generation of inorganic salt components on the surface of the coating layer, and better electrochemical stability.

[0015] Preferably, the structure of X comprises a combination of silane-based groups and sulfonate groups, or a combination of carboxylate groups and sulfonate groups.

[0016] Preferably, Y is selected from a single bond or an alkyl group.

[0017] Preferably, Z is selected from at least one of a substituted or unsubstituted alkyl group, a substituted or unsubstituted thioalkyl group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, or a substituted or unsubstituted phenylsilane group.

[0018] Preferably, the substituted group comprises at least one of a halogen atom, a nitrogen heterocycle, an aryl group, or an alkyl group.

[0019] Preferably, the amphiphilic compound is selected from any one or a combination of at least two of polyphenylmethylsilane, phenyltris(trimethylsiloxy)silane, heptadecafluorodecyltrimethoxysilane, heptadecafluorodecyltriethoxysilane, pentadecafluorononyltrimethoxysilane, pentadecafluorononyltriethoxysilane, tridecafluorooctyltrimethoxysilane, or tridecafluorooctyltriethoxysilane.

[0020] Preferably, the amphiphilic compound is selected from any one or a combination of at least two of 3-fluorobenzene methane sulfonic acid, benzene sulfonic acid, 4-fluorobenzene sulfonic acid, dodecyl benzene sulfonic acid, undecyl benzene sulfonic acid, decyl benzene sulfonic acid, pentafluorobenzene sulfonic acid, perfluorohexyl sulfonic acid, sodium dodecyl sulfate, sodium tetradecyl sulfate, ammonium dodecyl sulfate, or sodium decyl sulfate.

[0021] Preferably, the amphiphilic compound is selected from any one or a combination of at least two of stearic acid, tryptophan, diphenylacetic acid, 2-[(difluoromethyl)thio]pyridine-3-carboxylic acid, or (2S,4R)-4-[(tert-butyldiphenylsilyl)oxy]pyrrolidine-2-carboxylic acid.

[0022] Preferably, when the amphiphilic compound comprises a combination of fluorosilane-based molecules and alkyl sulfonic acid molecules, the mass ratio of the fluorosilane-based molecules to the alkyl sulfonic acid molecules is (60-90):(10-40), preferably (65-85):(15-35), for example, it can be 60:40, 62:38, 65:35, 68:32, 70:30, 72:28, 75:25, 78:22, 80:20, 82:18, 85:15, 88:12, or 90:10, etc. By adjusting the mass ratio of fluorosilane-based molecules and alkyl sulfonic acid molecules, the positive electrode lithium supplement agent composite material has better hydrophobic effect and smaller polarization.

[0023] In the present application, by regulating the types of groups of the hydrophilic head and the hydrophobic tail of the amphiphilic compound, the hydrophilic head is combined with the basic groups on the surface of the positive lithium supplement agent material, so that the coating is more uniform, and the hydrophobic tail has a stronger hydrophobic effect.

[0024] Preferably, the chemical formula of the positive lithium supplement agent core material is Li a M x N 1-x O c , wherein 2≤a≤6, 0≤x≤1, and 1≤c≤6, and M includes Fe or Ni, and N includes at least one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn, or W.

[0025] In the present application, the a may be, for example, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, or 6, etc.; the x may be, for example, 0, 0.2, 0.5, 0.8, or 1, etc.; and the c may be, for example, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, or 6, etc.

[0026] Preferably, the hydrophilic head is at least partially combined on the surface of the positive lithium supplement agent core material.

[0027] Preferably, the mass ratio of the material of the monomolecular layer coating layer to the positive lithium supplement agent core material is (0.001-0.05):1, preferably (0.005-0.03):1, which may be, for example, 0.001:1, 0.002:1, 0.005:1, 0.008:1, 0.01:1, 0.012:1, 0.015:1, 0.018:1, 0.02:1, 0.022:1, 0.025:1, 0.028:1, 0.03:1, 0.032:1, 0.035:1, 0.038:1, 0.04:1, 0.042:1, 0.045:1, 0.048:1, or 0.05:1, etc. In the present application, by regulating the mass ratio of the material of the monomolecular layer coating layer to the positive lithium supplement agent core material, the positive lithium supplement agent composite material has a better hydrophobic effect and a smaller polarization. If the content of the material of the monomolecular layer coating layer is higher, it will have a higher polarization, and vice versa.

[0028] In the present application, the thickness of the monomolecular layer coating layer is 2-10 nm, for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, etc.

[0029] In a second aspect, the present application provides a method for preparing the positive electrode lithium supplement composite material with core-shell structure according to the first aspect, the method comprising the following steps:

[0030] The amphiphilic compound is used to coat the positive electrode lithium supplement material by liquid phase method and / or gas phase method to obtain the positive electrode lithium supplement composite material with core-shell structure, wherein the amphiphilic compound comprises a hydrophilic head and a hydrophobic tail.

[0031] The present application uses a simple molecular self-assembly method for coating, and finally obtains an ultra-thin monomolecular layer coating layer, so it has high ion conductivity and uniformity, and the thickness will not change due to the change of the morphology of the material. In addition, the preparation method provided by the present application is simple to operate and easy to mass produce.

[0032] In the present application, the positive electrode lithium supplement material can be subjected to high temperature heating treatment (for example, 100-300°C) before the amphiphilic compound is used to coat the positive electrode lithium supplement material by liquid phase method and / or gas phase method, so as to remove the adsorbed moisture on the surface.

[0033] Preferably, the liquid phase method comprises mixing the amphiphilic compound, the positive electrode lithium supplement material and the solvent, and removing the solvent after reaction to obtain the positive electrode lithium supplement composite material with core-shell structure.

[0034] In the present application, the method for removing the solvent exemplarily comprises drying treatment, and the drying treatment mode comprises vacuum drying treatment or spray drying treatment, and the temperature of the spray drying treatment is 60-120°C, and the gas is dry air or inert atmosphere.

[0035] Further, the present application provides an exemplary preparation method of liquid phase method, which comprises the following steps:

[0036] Dissolving the amphiphilic compound in the solvent to form a solution;

[0037] Pouring the positive electrode lithium supplement material into the solution and stirring to make them fully contact and react, and the reaction time is 3h, after the reaction, using a suction filter bottle to perform suction filtration to remove the solvent and unreacted organic molecules;

[0038] According to the collected material, placing it in a vacuum oven under inert atmosphere, drying at 70°C for 2h, and the collected dry powder is the positive electrode lithium supplement composite material with core-shell structure.

[0039] In the present application, the solvent is exemplarily any one or a combination of two or more of N-methylpyrrolidone, ethanol, N,N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, or acetone, etc. The solvent used only needs to be capable of dissolving the above-mentioned amphiphilic compound and the positive electrode lithium supplement material, and the present application does not limit this.

[0040] Preferably, the gas phase method comprises placing the positive electrode lithium supplement material in a system containing the vapor of the amphiphilic compound, and forming the positive electrode lithium supplement composite material with a core-shell structure after cooling.

[0041] Further, the present application provides an exemplary gas phase method for preparation, which comprises the following steps:

[0042] The amphiphilic compound is placed at the bottom of a sealed container, and the positive electrode lithium supplement material powder is placed in the air above the amphiphilic compound;

[0043] The above-mentioned container is placed in an oven, the heating temperature is 120℃, and the heating time is 6h, so that the amphiphilic compound is heated and volatilized to spontaneously grow and form a monomolecular coating layer on the surface of the positive electrode lithium supplement material; after cooling to room temperature, the internal powder is stirred, and then heating, cooling and stirring are performed again, which is repeated 2-4 times to complete the coating, and the positive electrode lithium supplement composite material with a core-shell structure is collected.

[0044] Further, the present application provides another exemplary gas phase method for preparation, which comprises the following steps:

[0045] The amphiphilic compound is placed in a sealed container, and the positive electrode lithium supplement material powder is placed in a porcelain boat, which is wrapped with an aluminum plastic film, and a small opening is made on the windward side of the aluminum plastic film;

[0046] In an inert atmosphere, the above-mentioned device is placed in a tube furnace, the heating temperature is 90℃, and the heating time is 5h, wherein the wind direction of the inert atmosphere is parallel to the horizontal plane of the device, so that the amphiphilic compound is heated and volatilized to spontaneously grow and form a coating layer on the surface of the material, and the positive electrode lithium supplement composite material with a core-shell structure is collected.

[0047] In a third aspect, the present application provides a positive electrode, which comprises a positive electrode active material and a lithium supplement material, and the lithium supplement material comprises the positive electrode lithium supplement composite material with a core-shell structure according to the first aspect.

[0048] Preferably, the mass percentage of the lithium supplementing material is 2wt.%-8wt.% based on 100% of the total mass of the positive electrode active material, for example, can be 2wt.%, 2.5wt.%, 3wt.%, 3.5wt.%, 4wt.%, 4.5wt.%, 5wt.%, 5.5wt.%, 6wt.%, 6.5wt.%, 7wt.%, 7.5wt.%, or 8wt.%, etc. In the present application, by adjusting the mass percentage of the lithium supplementing material, the prepared secondary battery has a longer cycle life.

[0049] In a fourth aspect, the present application provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the positive electrode according to the third aspect.

[0050] Compared with the related art, the present application has the following beneficial effects.

[0051] The present application provides a positive electrode lithium supplementing composite material with core-shell structure. On the one hand, the present application uses an amphiphilic compound with a specific structure to coat the environment-sensitive positive electrode lithium supplementing agent material, wherein the hydrophilic head combines with the surface basic group of the positive electrode lithium supplementing agent material, and the hydrophobic tail faces the outside. Finally, a hydrophobic film with good chemical stability can be formed on the surface of the positive electrode lithium supplementing agent material, so as to prevent water molecules and corrosive substances from directly contacting the positive electrode lithium supplementing agent material, and improve the electrochemical stability and durability of the positive electrode lithium supplementing composite material. Compared with the traditional solid-phase method, the coating is thinner and more uniform, and therefore has higher conductivity. Specifically, the positive electrode lithium supplementing composite material with core-shell structure provided by the present application has a surface residual alkali content reduced by about 11.2% after being placed for 5 days, compared with the uncoated positive electrode lithium supplementing agent material.

[0052] On the other hand, compared with the traditional hydrophobic physical coating layer, the hydrophobic monolayer coating layer formed by the present application has the advantages of thinner thickness, uniform distribution and densification. At the same time, it has better lithium ion conductivity itself, and because the inorganic salt component is generated on the surface of the coating layer, the interface transmission impedance of the surface of the coated positive electrode lithium supplementing agent material is reduced, and the electrochemical stability is better.

[0053] Other aspects can be apparent after reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0054] FIG. 1 is a preparation flowchart of the positive electrode lithium supplementing composite material with core-shell structure in Example 1;

[0055] FIG. 2 is an SEM image of the positive electrode lithium supplementing composite material with core-shell structure in Example 1;

[0056] Figure 3 is a flow chart of the preparation of the positive electrode lithium supplement composite material with core-shell structure in Example 2;

[0057] Figure 4 is a flow chart of the preparation of the positive electrode lithium supplement composite material with core-shell structure in Example 3;

[0058] Figure 5 is a comparison chart of the residual alkali content of the positive electrode lithium supplement composite material with core-shell structure provided by Example 1 and Comparative Example 1 in the present application;

[0059] Figure 6 is a comparison chart of the capacity retention of the first circle of the button half-cell assembled by the positive electrode lithium supplement composite material with core-shell structure provided by Example 1 and Comparative Example 1 in the present application. DETAILED DESCRIPTION

[0060] The technical solutions of the present application will be further described below by combining with the drawings and specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0061] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0062] The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0063] Example 1

[0064] The present embodiment provides a positive electrode lithium supplement composite material with core-shell structure, which comprises Li2Ni 0.8 Cu 0.2 O2 positive electrode lithium supplement agent core material and a monolayer coating layer coated on the surface of the Li2Ni 0.8 Cu 0.2 O2 positive electrode lithium supplement agent core material; the material of the monolayer coating layer comprises an amphiphilic compound, and the amphiphilic compound comprises perfluorohexyl sulfonic acid. Among them, the mass ratio of the amphiphilic compound and the Li2Ni 0.8 Cu 0.2 O2 positive electrode lithium supplement agent core material is 0.025:1.

[0065] The present embodiment also provides a method for preparing the positive electrode lithium supplement composite material with core-shell structure as described above, as shown in Figure 1, the method comprises the following steps:

[0066] Dissolve 0.01 g of commercially available perfluorohexyl sulfonic acid in 10 g of N-methyl pyrrolidone to obtain an N-methyl pyrrolidone solution with a mass concentration of 0.1 wt.%. Dissolve 2 g of Li2Ni 0.8 Cu 0.2The O2 cathode lithium supplement agent material (particle size of 2-10 μm) is added into a 0.1 wt.% mass concentration of N-methylpyrrolidone solution of perfluorohexyl sulfonic acid. After stirring for 3 h at a speed of 500 r / min by a magnetic stirrer, the solution is filtered by a suction filter bottle, and the solution is filtered out. The excess perfluorohexyl sulfonic acid is washed away by continuously washing the suction filter bottle with N-methylpyrrolidone. The powder thus prepared is collected and placed in a vacuum oven for vacuum drying at 70 °C for 1 h to obtain the cathode lithium supplement composite material with a core-shell structure.

[0067] The cathode lithium supplement composite material with a core-shell structure prepared in this example is shown in FIG. 2.

[0068] Example 2

[0069] This example provides a cathode lithium supplement composite material with a core-shell structure, which includes Li2Ni 0.7 Cu 0.3 O2 cathode lithium supplement agent core material and a monolayer coating layer coated on the surface of the Li2Ni 0.7 Cu 0.3 O2 cathode lithium supplement agent core material. The material of the monolayer coating layer includes an amphiphilic compound, and the amphiphilic compound includes perfluorohexyl sulfonic acid. The mass ratio of the amphiphilic compound to the Li2Ni 0.7 Cu 0.3 O2 cathode lithium supplement agent core material is 0.005:1.

[0070] This example also provides a method for preparing the cathode lithium supplement composite material with a core-shell structure, and the method includes the following steps:

[0071] 0.1 g of commercially available perfluorohexyl sulfonic acid is placed at the bottom of the device shown in FIG. 3, 2 g of Li2Ni 0.7 Cu 0.3 O2 cathode lithium supplement agent material (particle size of 2-10 μm) is placed above the amphiphilic compound. The above container is placed in an oven, heated at a temperature of 120 °C for 6 h, so that the amphiphilic compound is volatilized by heat to spontaneously grow and form a monolayer coating layer on the surface of the cathode lithium supplement agent material. After cooling to room temperature, the internal powder is stirred, and then heating, cooling and stirring are repeated for 2-4 times to complete the coating to obtain the cathode lithium supplement composite material with a core-shell structure.

[0072] Example 3

[0073] This example provides a cathode lithium supplement composite material with a core-shell structure, which includes Li2Ni 0.6 Cu 0.4 O2 cathode lithium supplement agent core material and a monolayer coating layer coated on the surface of the Li2Ni 0.6 Cu 0.4O2 positive electrode lithium supplement agent core material surface monolayer coating layer; the material of the monolayer coating layer comprises an amphiphilic compound, and the amphiphilic compound comprises perfluorohexyl sulfonic acid. 0.6 Cu 0.4 The mass ratio of the O2 positive electrode lithium supplement agent core material is 0.03:1.

[0074] The embodiment also provides a method for preparing the positive electrode lithium supplement composite material with the core-shell structure, and the method comprises the following steps:

[0075] 0.1 g of commercially available perfluorohexyl sulfonic acid is placed in a sealed container as shown in FIG. 4, 2 g of Li2Ni 0.6 Cu 0.4 The O2 positive electrode lithium supplement agent material (with a particle size of 2-10 μm) is placed in a porcelain boat, and the porcelain boat is wrapped with an aluminum plastic film, and a small opening is formed in the aluminum plastic film in the upwind direction; the device is placed in a tube furnace in a nitrogen atmosphere, the heating temperature is 90 ℃, and the heating time is 5 h, wherein the wind direction of the nitrogen atmosphere is parallel to the horizontal plane of the device, so that the amphiphilic compound is heated and volatilized, and a coating layer is spontaneously formed on the surface of the material to obtain the positive electrode lithium supplement composite material with the core-shell structure.

[0076] Example 4

[0077] The embodiment differs from example 1 in that the amphiphilic compound is replaced by an equal amount of dodecyl benzene sulfonic acid, and the other conditions are the same as those in example 1.

[0078] Example 5

[0079] The embodiment differs from example 1 in that the amphiphilic compound is replaced by an equal amount of dodecyl benzene sulfonic acid, and the other conditions are the same as those in example 1.

[0080] Example 6

[0081] The embodiment differs from example 1 in that the amphiphilic compound is replaced by an equal amount of dodecyl benzene sulfonic acid, and the other conditions are the same as those in example 1.

[0082] Example 7

[0083] The embodiment differs from example 6 in that the amphiphilic compound is replaced by an equal amount of dodecyl benzene sulfonic acid, and the other conditions are the same as those in example 6.

[0084] Example 8

[0085] The embodiment differs from example 6 in that the mass ratio of heptadecafluorodecyltrimethoxysilane and dodecylbenzenesulfonic acid is 50:50, and the others are the same as example 6.

[0086] Comparative example 1

[0087] The present comparative example provides a Li2Ni 0.8 Cu 0.2 O2 positive electrode lithium supplement material.

[0088] Comparative example 2

[0089] The present comparative example differs from example 1 in that the material of the coating layer is replaced by an equal amount of carbon material, and the others are the same as example 1.

[0090] Comparative example 3

[0091] The present comparative example differs from example 1 in that the material of the coating layer is replaced by an equal amount of dodecylbenzene, and the others are the same as example 1.

[0092] Test conditions

[0093] The positive electrode lithium supplement composite materials provided by examples 1 to 8 and comparative examples 1 to 3 are tested, and the test method is as follows:

[0094] The positive electrode lithium supplement composite materials (initial state and after storage in air environment for 5 days) provided by examples and comparative examples, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1, and N-methyl pyrrolidone (NMP) is used as a solvent for homogenate coating to make a positive electrode sheet. The prepared positive electrode sheet is assembled with a lithium metal electrode, a polypropylene (PP) separator and an electrolyte to obtain a 2032 type button cell for cycle performance test, wherein the cycle test conditions are: 0.1C rate cycle for 3 cycles (1C=500mAh·g -1 , and the charge and discharge cut-off voltage is 2-4.5V.

[0095] The positive electrode lithium supplement composite materials provided by examples and comparative examples are stored in air environment for 5 days, and added to LiNi 0.8 Co 0.1 Mn 0.1 O2 in an amount of 3wt.% (based on the total mass of 100% of LiNi 0.8 Co 0.1 Mn 0.1O2(NCM811) and then mixed with conductive carbon black and polyvinylidene fluoride binder to make a positive electrode sheet. A graphite is used as a negative active material to make a negative electrode sheet, and a full battery is assembled according to the N / P ratio of 1.04 to test the cycle performance, wherein the cycle test conditions are: 0.1C rate for 3 cycles, and then 0.5C rate (1C = 200mAh·g -1 , and the charge and discharge cut-off voltage is 3-4.3V.

[0096] The test results are shown in Table 1:

[0097] Table 1

[0098] As can be seen from Table 1, according to Examples 1-3 and Comparative Example 1, using the same amphiphilic compound but different preparation methods, both can obtain a positive electrode lithium supplement composite material with high environmental stability and high ion conductivity, further indicating that the present application provides a technical solution with low process requirements and improved electrochemical performance of lithium ion batteries.

[0099] As can be seen from Examples 1 and Examples 4-5, Example 4 has the same hydrophilic head group as Example 1, but the hydrophobic tail is a full alkyl chain; and Example 5 has a similar hydrophobic tail group to Example 1, but the hydrophilic head group is a silane group; the hydrophobicity of the full alkyl chain hydrophobic tail in Example 4 is worse than that of the perfluoroalkyl chain hydrophobic tail in Example 1, and the lithium ion diffusion coefficient of the silane hydrophilic head group in Example 5 is not as good as that of the sulfonic acid hydrophilic head group in Example 1, so the comprehensive performance of the lithium ion batteries assembled by the two is decreased. Therefore, it can be known that the preferred tail group with strong hydrophobicity and the head group with high lithium ion diffusion coefficient can be beneficial to improve the environmental stability and cycle performance of the lithium ion battery.

[0100] As can be seen from Examples 1 and Examples 6-7, the present application combines the amphiphilic compounds with different preferred types of hydrophilic head groups and hydrophobic tail groups, which can be more compact and have stronger ion conductivity compared to using a single type of amphiphilic compound for coating, so that the comprehensive performance of the lithium ion battery is higher.

[0101] It can be seen from Examples 6-7 and Example 8 that the mass ratio of heptadecafluorodecyltrimethoxysilane and dodecylbenzenesulfonic acid used in Example 8 is not within the preferred range of the present application, so that the positive electrode lithium supplement material has poor hydrophobic effect and high polarization, thereby the comprehensive performance of the lithium ion battery prepared is reduced, further indicating that the mass ratio of the fluorine-containing silane type molecule and the alkyl sulfonic acid type molecule is controlled within the preferred range, which is beneficial to improve the environmental stability of the coating layer and the cycle performance of the lithium ion battery prepared.

[0102] It can be seen from Example 1 and Comparative Example 1 that the Li2Ni 0.8 Cu 0.2 O2positive electrode lithium supplement material, as shown in FIG. 5, the residual alkali amount of the positive electrode lithium supplement material modified by the specific type of monomolecular layer coating layer provided by the present application is obviously reduced; and as shown in FIG. 6, the first cycle capacity retention rate of the button half-cell obtained after the powder is placed for 5 days is obviously improved, proving that the positive electrode lithium supplement composite material provided by the present application has strong hydrophobic ability and good environmental stability. It can be seen that the present application uses amphiphilic compounds to self-assemble and coat the positive electrode lithium supplement material, and then adds it to the battery system, so that the lithium ion battery obtained has better cycle performance.

[0103] It can be seen from Example 1 and Comparative Example 2 that the conventional carbon material is used as the coating layer in Comparative Example 2, and the environmental stability cannot achieve all the technical effects of the present application; it can be seen that the present application uses a tail group with strong hydrophobicity as a modified interface, so that the positive electrode lithium supplement composite material powder has excellent hydrophobic performance, and further makes the lithium ion battery have better cycle performance.

[0104] It can be seen from Example 1 and Comparative Example 3 that Comparative Example 3 only uses dodecylbenzene with hydrophobic function for modification, and the physical adsorption between dodecylbenzene and the surface of the positive electrode lithium supplement material is only physical adsorption. Although it has a certain hydrophobic effect, it cannot guarantee good ion conduction characteristics, further indicating that the present application uses a specific type of amphiphilic compound as a coating source, which can ensure that it has good environmental stability while also having high ion superconductivity, so that the lithium ion battery obtained has a longer cycle life.

[0105] The applicant declares that the above examples are used to illustrate the process of the present application, but the present application is not limited to the above process steps, that is, it does not mean that the present application must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement of the present application, equivalent replacement of the materials selected by the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A positive electrode lithium supplement composite material with a core-shell structure, comprising a positive electrode lithium supplement agent inner core material and a monolayer coating layer coated on the surface of the positive electrode lithium supplement agent inner core material; the material of the monolayer coating layer comprises an amphiphilic compound, the amphiphilic compound comprises a hydrophilic head and a hydrophobic tail, and the structural formula of the amphiphilic compound is shown as formula I: X-Y-Z formula I; wherein the structure of X comprises any one or a combination of at least two of a carboxylate group, a sulfonate group, a sulfate group or a silane group; Y is selected from at least one of a single bond, a hydrocarbon group or a nitrogen heterocycle; Z is selected from at least one of a substituted or unsubstituted hydrocarbon group, a substituted or unsubstituted sulfur hydrocarbon group, or a substituted or unsubstituted aromatic group.

2. The positive electrode lithium supplementing composite material with core-shell structure according to claim 1, wherein, the structure of X comprises a combination of a silane group and a sulfonate group, or a combination of a carboxylate group and a sulfonate group.

3. The positive electrode lithium supplementing composite material with core-shell structure according to claim 1 or 2, wherein, Y is selected from a single bond or an alkyl group.

4. The positive electrode lithium supplementing composite material with core-shell structure according to any one of claims 1-3, wherein, Z is selected from at least one of a substituted or unsubstituted alkyl group, a substituted or unsubstituted sulfur alkyl group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, or a substituted or unsubstituted phenyl silane group; preferably, the substituted group comprises at least one of a halogen atom, a nitrogen heterocycle, an aromatic group or an alkyl group.

5. The positive electrode lithium supplementing composite material having a core-shell structure according to any one of claims 1 to 4, wherein, the amphiphilic compound is selected from any one or a combination of at least two of a polyphenylmethyl silane, a phenyl tris (trimethylsiloxy) silane, a heptadecafluorodecyl trimethoxysilane, a heptadecafluorodecyl triethoxysilane, a pentadecafluorononyl trimethoxysilane, a pentadecafluorononyl triethoxysilane, a tridecafluorooctyl trimethoxysilane or a tridecafluorooctyl triethoxysilane; preferably, the amphiphilic compound is selected from any one or a combination of at least two of a 3-fluorobenzene methane sulfonic acid, a benzene sulfonic acid, a 4-fluorobenzene sulfonic acid, a dodecyl benzene sulfonic acid, an undecyl benzene sulfonic acid, a decyl benzene sulfonic acid, a pentafluorobenzene sulfonic acid, a perfluorohexyl sulfonic acid, a dodecyl sodium sulfate, a tetradecyl sodium sulfate, a dodecyl ammonium sulfate or a decyl sodium sulfate; preferably, the amphiphilic compound is selected from any one or a combination of at least two of a stearic acid, a tryptophan, a diphenyl acetic acid, a 2-[(difluoromethyl) sulfanyl] pyridine-3-carboxylic acid or a (2S, 4R)-4-[(tert-butyldiphenylsilyl) oxy] pyrrolidine-2-carboxylic acid.

6. The positive electrode lithium supplementing composite material with core-shell structure according to claim 5, wherein, when the amphiphilic compound comprises a combination of a fluorine-containing silane molecule and an alkyl sulfonic acid molecule, the mass ratio of the fluorine-containing silane molecule to the alkyl sulfonic acid molecule is (60-90) : (10-40), preferably (65-85) : (15-35).

7. The positive-electrode lithium supplementing composite material with a core-shell structure according to any one of claims 1-6, wherein, The chemical formula of the positive electrode lithium supplementing agent core material is Li a M x N 1-x O c , wherein 2≤a≤6, 0≤x≤1, 1≤c≤6, and M includes Fe or Ni, and N includes at least one of Mg, Al, Si, Ca, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Sn or W. preferably, the hydrophilic head is at least partially combined on the surface of the positive electrode lithium supplement agent inner core material.

8. The positive-electrode lithium supplementing composite material with a core-shell structure according to any one of claims 1-7, wherein, the mass ratio of the material of the monolayer coating layer to the positive electrode lithium supplement agent inner core material is (0.001-0.05) : 1, preferably (0.005-0.03) :

1. 9.A method for preparing the positive electrode lithium supplement composite material with a core-shell structure according to any one of claims 1-8, comprising the following steps: The amphiphilic compound is used to coat the positive electrode lithium supplement material by liquid phase method and / or gas phase method to obtain the positive electrode lithium supplement composite material with core-shell structure, wherein the amphiphilic compound comprises a hydrophilic head and a hydrophobic tail.

10. The method of claim 9, wherein, The liquid phase method comprises mixing the amphiphilic compound, the positive electrode lithium supplement material and a solvent, and removing the solvent after reaction to obtain the positive electrode lithium supplement composite material with core-shell structure.

11. The method of claim 9 or 10, wherein, The gas phase method comprises placing the positive electrode lithium supplement material in a system containing the amphiphilic compound vapor, and forming the positive electrode lithium supplement composite material with core-shell structure after cooling.

12. A positive electrode comprising a positive electrode active material and a lithium supplement material, wherein the lithium supplement material comprises the positive electrode lithium supplement composite material with core-shell structure according to any one of claims 1-8. Preferably, the mass percentage of the lithium supplement material is 2wt.%-8wt.% based on the total mass of the positive electrode active material being 100%.

13. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the positive electrode according to claim 12.

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