Sodium ion battery positive electrode material and preparation method thereof

Abstract

The present invention discloses a sodium ion battery positive electrode material and a preparation method thereof, wherein the positive electrode material comprises a core, a second coating layer and a first coating layer between the core and the second coating layer, wherein the chemical formula of the core is Na x Ni y Mn z M 1‑y‑z O2; M is a doping element, 0.5 < x ≤ 1, 0 < y ≤ 0.5, 0 < z ≤ 0.5; the material of the first coating layer includes at least one of dopamine and tannic acid; the material of the second coating layer includes at least one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-diethylenetriaminopropyltrimethoxysilane. The present invention produces a sodium ion battery positive electrode material with low residual alkali and high ion diffusion, which has the advantages of high rate, long cycle performance and storage stability.

Description

Technical Field

[0001] The present invention relates to the technical field of material preparation, and in particular to a sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] The demand for two-wheel electric and efficient grid-scale energy storage systems for renewable energy is growing. Sodium-ion batteries (SIBs) have become a promising candidate for energy storage systems due to their abundant sodium resources. The positive electrode material is one of the key components for sodium-ion batteries to achieve high energy density and long cycle life. Transition metal oxides are considered to be a very promising high-energy-density positive electrode material for sodium-ion batteries. The current synthesis process uses sodium salts and different metal salts through proportioning, mixing, and sintering to achieve the breaking of old chemical bonds and the formation of new chemical bonds to prepare new layered structure materials. However, layered sodium nickel manganese oxide is easily affected by moisture in the natural environment, which leads to the interfacial side reaction Na + / H3O + , aggravating the deterioration of the material. Harmful Na2CO3 / NaOH substances are precipitated on the surface of the particles, resulting in serious defluorination of the binder polyvinylidene fluoride (PVDF). The fluidity during the positive electrode slurrying process is poor, which aggravates the formation of jelly and cannot meet the coating requirements. In addition, the main components in the electrolyte, such as fluoroethylene carbonate (FEC) and sodium hexafluorophosphate (NaPF6), will decompose at the electrode-electrolyte interface during battery operation to form hydrogen fluoride (HF). The HF formed will actively attack transition metal (TM) ions to form TM fluoride, resulting in irreversible active mass loss of the positive electrode. At the same time, by-products continue to accumulate at the positive electrode-electrolyte interface, hindering the Na + and electron transfer, further causing internal impedance increase and capacity decay.

[0003] To address the above shortcomings, Chinese patent CN 108807069A discloses a method for reducing residual alkali on the surface of layered positive electrode materials for lithium-ion batteries. This method uses pure water and ethanol in a two-wash strategy to reduce the residual alkali on the surface. The resulting positive electrode material has a low residual alkali content. However, the lithium ion loss in the bulk of the layered material prepared by this method is serious, generating NiO with no electrochemical activity, which destroys the material structure and prevents the specific capacity and cycle performance from being fully utilized. In addition, Chinese patents CN 108807969 A and CN 110436531 A, etc., adopt a coating strategy to coat the material surface with a layer of passive oxide such as aluminum oxide, magnesium oxide, zinc oxide, titanium oxide, zirconium dioxide, tungsten oxide, etc. However, it is difficult to achieve a uniform network structure coating layer on the material surface using solid mixing and sol-gel coating techniques, and a typical island structure will appear. At the same time, most of the introduced oxides do not have the ability to conduct lithium / sodium ions, resulting in a reduction in the sodium ion diffusion rate of the positive electrode material after coating. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a sodium ion battery positive electrode material and a preparation method thereof, which can produce a sodium ion battery positive electrode material with low residual alkali and high ion diffusion, which has the advantages of high rate, long cycle performance and storage stability.

[0005] To achieve the above objectives, the present invention provides a sodium ion battery positive electrode material in a first aspect, comprising a core, a first coating layer and a second coating layer, wherein the first coating layer is located between the core and the second coating layer.

[0006] Among them, the core is a layered transition metal oxide material, and its chemical formula is Na x Ni y Mn z M 1-y-z O2; M is a doping element, 0.5<x≤1, 0<y≤0.5, 0<z≤0.5, and the values ​​of x, y, and z satisfy the charge balance of the chemical formula;

[0007] The material of the first coating layer includes at least one of dopamine and tannic acid;

[0008] The material of the second coating layer includes at least one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-diethylenetriaminopropyltrimethoxysilane.

[0009] The sodium ion battery positive electrode material of the present invention includes a core, a first coating layer and a second coating layer. The material of the first coating layer includes at least one of dopamine and tannic acid. Dopamine and / or tannic acid are coated on the surface of the core after mixing with a solvent, and the first coating layer is in situ grown on the surface of the core. On the one hand, the first coating layer is a polymer layer that can inhibit the formation of Na2CO3 / NaOH and prevent the corrosion of the electrolyte; on the other hand, the first coating layer introduces a functional group (-OH) that can provide abundant growth sites for the second coating layer to form a stable interface. The nitrogen introduced into the amide of the material of the second coating layer can reduce the anion / cation binding energy in the electrolyte, promote ion dissociation, increase the free ion concentration, help to increase the sodium ion transfer number, and promote the charge transfer process and reduce impedance. Through the combined action of the first coating layer and the second coating layer, the sodium ion battery positive electrode material of the present invention has good electronic conductivity, high rate performance, long cycle performance and storage stability.

[0010] In some embodiments, the M doping element is at least one of Li, Cu, Mg, Zn, Co, Al, Zr, Ti, Te, Sr, Al, B, Sn, Mo, Nb, Sb, and Nb. As an example, M can be Zr or W.

[0011] A second aspect of the present invention provides a method for preparing a positive electrode material for a sodium ion battery, comprising the steps of:

[0012] (1) mixing the material of the first coating layer with the first solvent, heating and stirring, to obtain a mixed material A;

[0013] (2) mixing the mixed material A with the layered transition metal oxide material, heating and stirring, then performing solid-liquid separation and drying to obtain material B;

[0014] (3) Mixing material B, the material of the second coating layer and the second solvent, heating and stirring, then performing solid-liquid separation, drying and sintering to obtain a sodium ion battery positive electrode material.

[0015] In some embodiments, in step (1), the first solvent is at least one of methanol, ethanol, propanol, butanediol, isopropanol, or tripropylene glycol.

[0016] In some embodiments, in step (1), the heating temperature is 30°C-100°C. As an example, the heating temperature may be, but is not limited to, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C.

[0017] In some embodiments, in step (1), the stirring time is 10 min-60 min, but not limited thereto.

[0018] In some embodiments, in step (2), the temperature of heating and stirring is 25°C-100°C. As an example, the temperature of heating and stirring may be but is not limited to 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C.

[0019] In some embodiments, the mass ratio of the material of the first coating layer to the first solvent is 1-15:100.

[0020] In some embodiments, the mass ratio of the mixture material A to the layered transition metal oxide material is 0.8-1.4:1-1.2.

[0021] In some embodiments, the mass ratio of material B, the material of the second coating layer, and the second solvent is 1-1.2:0.8-1.5:0.1-1.

[0022] In some embodiments, in step (2), the stirring time is 4 min-30 min, but not limited thereto.

[0023] In some embodiments, in step (2), the drying temperature is 60°C-150°C. As an example, the drying temperature may be, but is not limited to, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C.

[0024] In some embodiments, in step (2), the drying time is 4-10 hours, but not limited thereto.

[0025] In some embodiments, in step (2), the mass concentration of the solute in the mixed solution after mixing the mixed material A with the layered transition metal oxide material is 100-1000 g / L, but not limited thereto.

[0026] In some embodiments, in step (3), the second solvent is at least one of methanol, ethanol, propanol, butanediol, isopropanol, or tripropylene glycol.

[0027] In some embodiments, in step (3), the temperature of heating and stirring is 30°C-100°C. As an example, the temperature of heating and stirring may be, but is not limited to, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C.

[0028] In some embodiments, in step (3), the stirring time is 1 to 6 hours, but not limited thereto.

[0029] In some embodiments, in step (3), the drying temperature is 60°C-150°C. As an example, the drying temperature may be, but is not limited to, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or 150°C.

[0030] In some embodiments, in step (3), the drying time is 4-10 hours, but not limited thereto.

[0031] In some embodiments, in step (3), the mass concentration of the solute in the mixed solution after mixing material B, the material of the second coating layer and the second solvent is 100-800 g / L, but not limited thereto.

[0032] In some embodiments, in step (3), the sintering temperature is 400-700°C. As an example, the sintering temperature may be, but is not limited to, 400°C, 500°C, 600°C, or 700°C.

[0033] In some embodiments, in step (3), the heating rate of the sintering temperature is 1-10° C. / min, but not limited thereto.

[0034] In some embodiments, in step (3), the sintering time is 4-10 hours.

[0035] The sodium ion battery positive electrode material and the preparation method thereof of the present invention have the following technical effects:

[0036] First, through a two-step method, a polymer layer is first grown in situ on the surface of the inner core as the first coating layer, which can inhibit the formation of Na2CO3 / NaOH and prevent the corrosion of the electrolyte. The polymer layer introduces functional groups (-OH), providing abundant growth sites for the second coating layer, forming a stable interface. Then, a second coating layer is grown in situ on the surface of the first coating layer. At the same time, the nitrogen in the amide introduced by the second coating layer can reduce the anion / cation binding energy in the electrolyte, promote ion dissociation, increase the free ion concentration, help increase the sodium ion transfer number, promote charge transfer, and reduce impedance.

[0037] Secondly, the present invention adopts a liquid phase in situ growth strategy and a two-step method to uniformly coat two coating layers on the surface of the O3 phase positive electrode material and perform functionalization to obtain a coated modified sodium ion battery positive electrode material, which can not only inhibit the side reactions between the positive electrode material and the electrolyte, and the positive electrode material and the air, but also the functional groups on the surface of the positive electrode material can bind the anions in the electrolyte, improve the migration of cations, and promote the charge transfer process, reduce impedance, and further improve the electronic conductivity of the positive electrode material, thereby improving the rate performance, cycle performance and storage stability of the sodium ion battery.

[0038] Third, the sodium hydroxide content on the surface of the sodium ion battery positive electrode material of the present invention is low, and it is a low-residual alkali sodium ion battery positive electrode material, which improves the processing performance of the material and also reduces the material's requirements for storage and use environment.

[0039] Fourthly, the sodium ion battery positive electrode material of the present invention has a high sodium ion diffusion coefficient, indicating that the sodium ion battery positive electrode material can reduce the anion / cation binding energy in the electrolyte, promote ion dissociation, and increase the free ion concentration, thereby obtaining a higher sodium ion diffusion coefficient, which can promote charge transfer, improve the electronic conductivity of the positive electrode material, and reduce impedance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of the positive electrode material of the sodium ion battery of the present invention.

[0041] Figure 2 This is the XRD test result diagram of the sodium ion battery positive electrode material of Example 1 of the present invention. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0043] like Figure 1 As shown, the positive electrode material of the sodium ion battery includes a core 10, a first coating layer 30 and a second coating layer 50, wherein the first coating layer 30 is between the core 10 and the second coating layer 50, that is, from the inside to the outside, the core 10, the first coating layer 30 and the second coating layer 50 are arranged in sequence. Among them, the core 10 is a layered transition metal oxide material, and its chemical formula is Na x Ni y Mn z M 1-y-z O2; M is a doping element, M is at least one of Li, Cu, Mg, Zn, Co, Al, Zr, Ti, Te, Sr, Al, B, Sn, Mo, Nb, Sb, and Nb; 0.5<x≤1, 0<y≤0.5, 0<z≤0.5, and the values ​​of x, y, and z satisfy the charge balance of the chemical formula; the material of the first coating layer 30 includes at least one of dopamine and tannic acid; the material of the second coating layer 50 includes at least one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-diethylenetriaminopropyltrimethoxysilane.

[0044] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0045] Example 1

[0046] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0047] (1) Weigh 20 g of dopamine and dissolve it in 400 mL of ethanol, stir it with magnetic stirring at 35°C for 20 minutes to obtain a mixture A;

[0048] (2) Add 400g of layered transition metal oxide positive electrode material Na into the mixture A. 0.9 Ni 0.4 Fe0.2 Mn 0.4 O2, magnetic stirring, speed of 100 rpm, temperature of 30 ° C, stirring time of 10 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 100 ° C for 6 h to obtain material B;

[0049] (3) Material B was added to 400 mL of ethanol, and 10 mL of 3-aminopropyltriethoxysilane (silane coupling agent KH-550) was added at the same time. The mixture was magnetically stirred at a speed of 200 rpm, a temperature of 80 ° C, and a stirring time of 3 h. The solution was then filtered and washed four times with ethanol. The filter cake was placed in a drying oven and dried at a temperature of 100 ° C for 6 h. It was then placed at a high temperature of 500 ° C for 5 h (heating rate of 3 ° C / min) to obtain a coated modified sodium ion battery positive electrode material.

[0050] Figure 2 The XRD pattern of the sodium ion battery cathode material prepared in Example 1 is shown. Figure 2 It can be seen that the XRD pattern shows that the positive electrode material of the sodium ion battery is O3 phase and is well crystallized.

[0051] Example 2

[0052] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0053] (1) Weigh 20 g of dopamine and dissolve it in 400 mL of ethanol, stir it with magnetic stirring at 35°C for 20 minutes to obtain a mixture A;

[0054] (2) Add 400g of layered transition metal oxide positive electrode material Na into the mixture A. 0.9 Ni 0.4 Fe 0.2 Mn 0.4 O2, magnetic stirring, speed of 100 rpm, temperature of 30 ° C, stirring time of 10 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 100 ° C for 6 h to obtain material B;

[0055] (3) Material B was added to 400 mL of ethanol, and 40 mL of 3-aminopropyltriethoxysilane was added at the same time. The mixture was magnetically stirred at a speed of 200 rpm, a temperature of 80 ° C, and a stirring time of 3 h. The solution was then filtered and washed four times with ethanol. The filter cake was placed in a drying oven and dried at a temperature of 100 ° C for 6 h. It was then placed at a high temperature of 500 ° C for 5 h (heating rate of 3 ° C / min) to obtain a coated modified sodium ion battery positive electrode material.

[0056] Example 3

[0057] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0058] (1) Weigh 20 g of dopamine and dissolve it in 400 mL of ethanol, stir it with magnetic stirring at 35°C for 20 minutes to obtain a mixture A;

[0059] (2) Add 400g of layered transition metal oxide positive electrode material Na into the mixture A. 0.9 Ni 0.4 Fe 0.2 Mn 0.4 O2, magnetic stirring, speed of 100 rpm, temperature of 30 ° C, stirring time of 10 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 100 ° C for 6 h to obtain material B;

[0060] (3) Material B was added to 400 mL of ethanol, and 70 mL of 3-aminopropyltriethoxysilane was added at the same time. The mixture was magnetically stirred at a speed of 200 rpm, a temperature of 80 ° C, and a stirring time of 3 h. The solution was then filtered and washed four times with ethanol. The filter cake was placed in a drying oven and dried at a temperature of 100 ° C for 6 h. It was then placed at a high temperature of 500 ° C for 5 h (heating rate of 3 ° C / min) to obtain a coated modified sodium ion battery positive electrode material.

[0061] Example 4

[0062] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0063] (1) Weigh 20 g of dopamine and dissolve it in 400 mL of ethanol, stir it with magnetic stirring at 35°C for 20 minutes to obtain a mixture A;

[0064] (2) Add 400g of layered transition metal oxide positive electrode material Na into the mixture A. 0.9 Ni 0.4 Fe 0.2 Mn 0.4 O2, magnetic stirring, speed of 100 rpm, temperature of 30 ° C, stirring time of 10 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 100 ° C for 6 h to obtain material B;

[0065] (3) Material B was added to 400 mL of ethanol, and 100 mL of 3-aminopropyltriethoxysilane was added at the same time. The mixture was magnetically stirred at a speed of 200 rpm, a temperature of 80 ° C, and a stirring time of 3 h. The solution was then filtered and washed four times with ethanol. The filter cake was placed in a drying oven and dried at a temperature of 100 ° C for 6 h. It was then placed at a high temperature of 500 ° C for 5 h (heating rate of 3 ° C / min) to obtain a coated modified sodium ion battery positive electrode material.

[0066] Example 5

[0067] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0068] (1) 10 g of tannic acid was weighed and dissolved in 400 mL of isopropanol, with magnetic stirring at 40° C. for 15 minutes to obtain a mixture A;

[0069] (2) Add 400g of layered transition metal oxide positive electrode material NaNi into the mixture A. 0.3 Fe 0.2 Mn 0.4 Cu 0.1 O2, magnetic stirring, speed of 100 rpm, temperature of 40 ° C, stirring time of 15 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 120 ° C for 5 h to obtain material B;

[0070] (3) Material B was added to 400 mL of isopropanol, and 100 mL of N-2-aminoethyl-3-aminopropylmethyldiethoxysilane was added at the same time. The mixture was magnetically stirred at a speed of 200 rpm, a temperature of 60 ° C, and a stirring time of 5 h. The solution was then filtered and washed four times with ethanol. The filter cake was placed in a drying oven and dried at a temperature of 120 ° C for 6 h. It was then placed at a high temperature of 600 ° C for 4 h to obtain a coated modified sodium ion battery positive electrode material.

[0071] Example 6

[0072] (1) Weigh 20 g of tannic acid and dissolve it in 400 mL of isopropanol, stir magnetically at 40° C. for 15 minutes to obtain a mixture A;

[0073] (2) Add 400g of layered transition metal oxide positive electrode material NaLi to the mixture A 0.1 Ni 0.3 Fe 0.2 Mn 0.4O2, magnetic stirring, speed of 100 rpm, temperature of 50 ° C, stirring time of 10 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 120 ° C for 4 h to obtain material B;

[0074] (3) Material B was added to 400 mL of isopropanol, and 70 mL of 3-aminopropyltrimethoxysilane was added at the same time. The mixture was magnetically stirred at a speed of 200 rpm, a temperature of 50 ° C, and a stirring time of 5 h. The solution was then filtered and washed four times with ethanol. The filter cake was placed in a drying oven to dry at a temperature of 120 ° C for 6 h, and then placed at a high temperature of 700 ° C for 4 h (heating rate of 3 ° C / min) to obtain a coated modified sodium ion battery positive electrode material.

[0075] Comparative Example 1

[0076] The comparative example directly uses the layered transition metal oxide positive electrode material Na 0.9 Ni 0.4 Fe 0.2 Mn 0.4 O2 as the cathode material for sodium-ion batteries.

[0077] Comparative Example 2

[0078] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0079] (1) Weigh 20 g of dopamine and dissolve it in 400 mL of ethanol, stir it with magnetic stirring at 35°C for 20 minutes to obtain a mixture A;

[0080] (2) Add 400g of layered transition metal oxide positive electrode material Na into the mixture A. 0.9 Ni 0.4 Fe 0.2 Mn 0.4 O2, magnetic stirring, speed of 100 rpm, temperature of 30 ° C, stirring time of 10 min, then filter the solution and wash four times with ethanol, the filter cake is placed in a drying oven to dry at a temperature of 100 ° C for 6 hours, and then placed at a high temperature of 500 ° C for 5 hours (heating rate of 3 ° C / min), time 5 hours to obtain a coated modified sodium ion battery positive electrode material.

[0081] The electrochemical performance of the sodium ion battery positive electrode materials of Examples 1 to 6 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0082] Electrochemical performance test: The sodium ion battery positive electrode material is mixed with conductive carbon black and polyvinylidene fluoride binder in a mass ratio of 99:0.5:0.5, and an appropriate amount of N-methylpyrrolidone solution is added until a slurry is formed in a dry environment at room temperature; the prepared slurry is evenly coated on the aluminum foil of the current collector, and after initial drying, it is compacted and cut into circular electrodes with a diameter of 12 mm; the circular electrodes are dried at 120°C under vacuum conditions for 12 hours and then transferred to a glove box for use.

[0083] Assembled in an argon-filled glove box, the CR2032 button-shaped battery used sodium metal as the counter electrode, glass fiber as the separator, and a 1 mol / L NaPF6 solution in ethylene carbonate (EC) / dimethyl carbonate (DMC) (volume ratio 1:1) as the electrolyte. Charge and discharge tests were conducted in constant current mode at 0.1C / 0.1C within a voltage window of 2.0V-4.0V to obtain the initial discharge specific capacity. The test results are shown in Table 1 below.

[0084] Sodium hydroxide (NaOH) content test: Weigh 2 g of the sodium ion battery positive electrode material obtained in Examples 1-6 and Comparative Examples 1-2, respectively, add 30 mL of deionized water, place on a magnetic stirrer and stir for 30 minutes, then use a Buchner funnel to reduce pressure and filter to obtain the filtrate. The content of sodium hydroxide (NaOH) in the residual alkali on the surface of the layered positive electrode material is tested by a potentiometric titrator.

[0085] Sodium ion diffusion coefficient test method: Assemble half-cells of the sodium ion battery cathode materials obtained in Examples 1-6 and Comparative Examples 1-2, and obtain cyclic voltammetry curves at 0.1, 0.3, 0.5, 0.7, and 1 mV / s. The corresponding diffusion coefficient can be calculated according to the following formula: where ip is the peak current value; n is the number of electrons participating in 1 mol of reaction, which is 1 in this case; A is the contact area between the electrode and the electrolyte, which is the area of ​​the electrode plate 64mm in this case. 2 , D is the apparent diffusion coefficient; C is the molar concentration of sodium ions in the electrode; ν is the scanning speed.

[0086]

[0087] Table 1 Test results

[0088]

[0089] As can be seen from the results in Table 1, compared with Comparative Examples 1 to 2, the content of sodium hydroxide on the surface of the coated and modified sodium ion battery positive electrode material obtained in Examples 1-6 is significantly reduced, and the measured pH value is also significantly reduced, which improves the processing performance of the material and also reduces the material's requirements for storage and use environment. At the same time, the sodium ion battery positive electrode material of the present invention has a high sodium ion diffusion coefficient, indicating that the sodium ion battery positive electrode material can reduce the anion / cation binding energy in the electrolyte, promote ion dissociation, and increase the free ion concentration, thereby obtaining a higher sodium ion diffusion coefficient, which can promote charge transfer, improve the electronic conductivity of the positive electrode material, and reduce impedance, thereby improving the rate performance, cycle performance and storage stability of the sodium ion battery.

[0090] In addition, it can be seen from the test results in Table 1 that the coated modified sodium ion battery positive electrode material of the present invention has good first discharge specific capacity and first charge and discharge efficiency.

[0091] It can also be seen from the experimental data of Examples 1-4 that as the amount of the material used in the second coating layer increases from a small amount to a large amount, the performance first increases and then gradually decreases. It can be seen that the amount of the material used in the second coating layer affects the performance of the positive electrode material of the sodium ion battery, mainly because the amount of the material used in the second coating layer affects the thickness of the second coating layer of the positive electrode material. As can be seen from Table 1, if the amount of the material used in the second coating layer is too low, it will affect the uniformity of the second coating layer. Although the sodium ion diffusion coefficient is slightly improved, the cycle performance will be reduced, affecting its cycle life. If the amount is too high, the increase in thickness will affect the insertion and extraction of sodium ions, affecting the rate performance.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A sodium ion battery cathode material, characterized in that: It includes a core, a first coating layer and a second coating layer, wherein the first coating layer is between the core and the second coating layer. Wherein, the core is a layered transition metal oxide material, and its chemical formula is Na x Ni y Mn z M 1-y-z O2; M is a doping element, 0.5<x≤1, 0<y≤0.5, 0<z≤0.5, and the values ​​of x, y, and z satisfy the charge balance of the chemical formula; The material of the first coating layer includes at least one of dopamine and tannic acid; The material of the second coating layer includes at least one of 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-aminoethyl-3-aminopropylmethyldiethoxysilane, N-2-aminoethyl-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-diethylenetriaminopropyltrimethoxysilane.

2. The sodium ion battery positive electrode material according to claim 1, characterized in that The doping element is at least one of Li, Cu, Mg, Zn, Co, Al, Zr, Ti, Te, Sr, Al, B, Sn, Mo, Nb, Sb, and Nb.

3. The method for preparing a positive electrode material for a sodium ion battery according to any one of claims 1 to 2, wherein: Including steps: (1) mixing the material of the first coating layer with the first solvent, heating and stirring, to obtain a mixed material A; (2) mixing the mixed material A with a layered transition metal oxide material, heating and stirring, then performing solid-liquid separation, and drying to obtain material B; (3) mixing the material B, the material of the second coating layer and the second solvent, heating and stirring, then performing solid-liquid separation, drying and sintering to obtain a sodium ion battery positive electrode material.

4. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (1), the first solvent is at least one of methanol, ethanol, propanol, butanediol, isopropanol or tripropylene glycol.

5. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (2), the drying temperature is 60°C-150°C.

6. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (3), the second solvent is at least one of methanol, ethanol, propanol, butanediol, isopropanol or tripropylene glycol.

7. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (3), the drying temperature is 60°C-150°C.

8. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (3), the sintering temperature is 400-700°C.

9. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (3), the temperature of heating and stirring is 30°C-100°C.

10. The method for preparing a positive electrode material for a sodium ion battery according to claim 3, wherein: In step (2), the temperature of heating and stirring is 25°C-100°C.

Images