Positive electrode material, preparation method therefor, and sodium ion battery

Abstract

The present application provides a positive electrode material, a preparation method therefor, and a sodium ion battery. The positive electrode material comprises: an active substance matrix, and an aluminum magnesium silicate coating layer coated on the surface of the active substance matrix. The present application provides a positive electrode material, and the presence of an aluminum magnesium silicate coating layer can inhibit direct reaction of HF with NaOH / Na2Co3 on the surface of the matrix, such that the occurrence of gas production is further inhibited. In addition, the positive electrode material prepared in the present application can effectively inhibit high-pressure gas production by utilizing the characteristics of strong bond strength of the Al-O bond and strong bond strength of the Mg-O bond, without decreasing voltage, and can also maintain high capacity, and has good development potential.

Description

A positive electrode material, a preparation method thereof, and a sodium ion battery Technical Field

[0001] The embodiments of the present application relate to the field of battery technology, such as a positive electrode material and a preparation method thereof, and a sodium ion battery. Background Art

[0002] At present, most of the sodium ion battery cathode materials on the market are prone to O2 n- -The irreversible redox reaction of O2 leads to severe gas production under high pressure, causing bulging of the battery pack and affecting safety issues. In addition to the redox reaction that causes gas production under high pressure, the contact of residual sodium on the surface with fluorine additives in the electrolyte can also cause gas production.

[0003] Full batteries often use sodium hexafluorophosphate electrolytes containing fluorine additives. HF, a common decomposition product in fluorine-containing electrolytes, dissolves transition metal oxides, causing the layered structure to gradually collapse, ultimately leading to a decrease in cycle stability. To reduce gas production, most manufacturers currently choose to add ester additives to the commonly used sodium hexafluorophosphate electrolyte, which undoubtedly increases costs. Some use methods such as coating metal oxides such as boron oxide and zirconium oxide, but the effect is generally poor. Some choose to lower the cutoff voltage to suppress gas production, but this cannot achieve high voltage and will cause low capacity problems. Other manufacturers choose water washing or acid washing processes to reduce residual sodium, but water washing and acid washing can easily cause excessive dissolution of sodium ions, resulting in low capacity, and the combined drying and centrifugation increases costs.

[0004] Therefore, it is urgent to solve the problem of gas production under high voltage of sodium ion batteries, increase capacity and reduce costs.

[0005] Summary of the Invention

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

[0007] The embodiments of the present application provide a positive electrode material, a preparation method thereof, and a sodium ion battery.

[0008] In a first aspect, an embodiment of the present application provides a positive electrode material, which includes an active material matrix and a magnesium aluminum silicate coating layer coated on the surface of the active material matrix.

[0009] The present application provides a positive electrode material, in which the presence of a magnesium aluminum silicate coating layer can inhibit the direct reaction of HF with NaOH / Na2CO3 on the substrate surface, which further inhibits the occurrence of gas production; and the positive electrode material prepared in the present application can utilize the characteristics of strong Al-O bond strength and strong Mg-O bond strength without reducing the voltage, effectively inhibiting high-pressure gas production, while also maintaining high capacity, and has good development potential.

[0010] Preferably, the active material matrix comprises a layered oxide.

[0011] In this application, layered oxides are used to provide higher capacity and better reflect the advantages of energy density compared to polyphosphate and Prussian blue sodium cathode materials.

[0012] Preferably, the chemical formula of the layered oxide is Na m Ni x Fe y Mn 1-x-y-z Cu z O2, wherein 1.05≤m≤1.08, 0.2≤x≤0.4, 0.05≤y≤0.2, and 0.05≤z≤0.2. For example, m can be 1.05, 1.06, 1.07, or 1.08, for example, x can be 0.2, 0.25, 0.3, 0.35, or 0.4, for example, y can be 0.05, 0.07, 0.09, 0.1, 0.12, 0.15, 0.17, or 0.2, for example, and z can be 0.05, 0.07, 0.09, 0.1, 0.12, 0.15, 0.17, or 0.2, for example, but the values ​​are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0013] In the layered oxide of the present application, the ratio of the molar amount of the sodium source to the total molar amount of the nickel source, iron source, manganese source and copper source is 1.05-1.08. This parameter directly affects the sodium interlayer spacing. More sodium ions increase the attraction of O-Na-O, which reduces the sodium interlayer spacing. And part of the Mg in the magnesium aluminum silicate coating layer 2+ and Al 3+ Doping into the sodium layer creates stronger O-Mg-O and O-Al-O bonds, which in turn enhances the attraction between the two oxygen layers and reduces the distance between the sodium layers. The combination of these two factors ultimately reduces the distance between the sodium layers to a lower value. A smaller sodium interlayer distance inhibits the precipitation of free sodium ions, thereby reducing the formation of Na2CO3 and suppressing gas production.

[0014] Preferably, the sodium interlayer spacing of the layered oxide is For example it could be or However, it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In this application, the sodium interlayer distance (d Na+ ) is narrow, which is beneficial to inhibiting the precipitation of free sodium ions, reducing the formation of Na2CO3, and inhibiting the occurrence of gas production.

[0016] Preferably, the c-axis lattice parameter of the layered oxide is For example it could be or etc., but are not limited to the listed values, and other values ​​not listed within this numerical range are also applicable. Preferably, the particle size D50 of the active material matrix is ​​6-12 μm, for example, it can be 6 μm, 8 μm, 10 μm or 12 μm, etc., but are not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0017] In the present application, when the particle size D50 of the active material matrix is ​​6-12 μm, the particles are not easily cracked after a long cycle, causing the electrolyte to corrode the interior of the particles and aggravate the side reaction.

[0018] Preferably, the chemical formula of the magnesium aluminum silicate coating is MgAl2(Si a O 2a+1 )4, where 1≤a≤2, a is a positive integer, and a can be 1 or 2, for example.

[0019] In this application, the chemical formula of the magnesium aluminum silicate coating is MgAl2(Si a O 2a+1 )4, a can be 1 or 2. Using this chemical formula, MgAl2(SiO3)4 or MgAl2(Si2O5)4 can be synthesized. When the molar ratio of Al, Mg, and Si is 2:1:4 or 2:1:8, the two coating layers formed can be used to coat the substrate material.

[0020] Preferably, the thickness of the magnesium aluminum silicate coating layer is 10-20 nm, for example, it can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0021] In this application, when the thickness of the magnesium aluminum silicate coating layer is 10-20nm, the comprehensive effect is excellent. If the thickness of the magnesium aluminum silicate coating layer is too small, the effect of inhibiting the generation of residual sodium will be reduced, the amount of Mg-O and Al-O will be small, and the effect of fixing O will be weakened; if the thickness of the magnesium aluminum silicate coating layer is too large, Mg 2+ and Al 3+If the amount of matrix material added is large, it will cause Mg 2+ and Al 3+ It not only penetrates into the Na layer, but also penetrates into the transition metal layer, thereby widening the distance between the sodium layers. In addition, the thicker coating layer will hinder the migration of sodium ions in and out, resulting in a decrease in capacity.

[0022] In a second aspect, an embodiment of the present application provides a method for preparing the positive electrode material according to the first aspect, the preparation method comprising:

[0023] (1) mixing a magnesium source, an aluminum source, a silica sol, and a solvent, and then heating the resulting mixture to obtain a magnesium aluminum silicate material;

[0024] (2) The magnesium aluminum silicate material and the active material are mixed and sintered to obtain the positive electrode material.

[0025] Preferably, the magnesium source in step (1) comprises at least one of magnesium acetate, magnesium nitrate, magnesium sulfate and magnesium oxide.

[0026] Preferably, the aluminum source in step (1) comprises at least one of aluminum acetate, aluminum nitrate, aluminum sulfate and aluminum oxide.

[0027] Preferably, the heating temperature in step (1) is 120-350°C, for example, it can be 120°C, 150°C, 200°C, 250°C, 300°C or 350°C, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0028] Preferably, the heating time in step (1) is 4-12 hours, for example, 4 hours, 6 hours, 8 hours, 10 hours or 12 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In the present application, the magnesium aluminum silicate material is suitably synthesized at a heating temperature of 120-350° C. and a heating time of 4-12 hours. If the temperature and time exceed the above ranges, the magnesium aluminum silicate material with impurities will be generated.

[0030] Preferably, the active material in step (2) comprises a layered oxide, the chemical formula of which is Na m Ni x Fe y Mn 1-x-y-z Cu zO2, wherein 1.05≤m≤1.08, 0.2≤x≤0.4, 0.05≤y≤0.2, and 0.05≤z≤0.2. For example, m can be 1.05, 1.06, 1.07, or 1.08, for example, x can be 0.2, 0.25, 0.3, 0.35, or 0.4, for example, y can be 0.05, 0.07, 0.09, 0.1, 0.12, 0.15, 0.17, or 0.2, for example, and z can be 0.05, 0.07, 0.09, 0.1, 0.12, 0.15, 0.17, or 0.2, for example, but the values ​​are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] Preferably, the preparation method of the layered oxide comprises: ball-milling a sodium source, a nickel source, an iron source, a manganese source and a copper source together, and calcining to obtain the layered oxide.

[0032] Preferably, the sodium source includes at least one of sodium carbonate, sodium acetate, sodium oxalate, sodium sulfate, sodium bicarbonate, sodium chloride and sodium nitrate.

[0033] Preferably, the nickel source includes at least one of nickel sulfate, nickel acetate tetrahydrate, nickel nitrate and nickel oxide.

[0034] Preferably, the iron source includes at least one of ferrous sulfate, ferrous oxide, ferrous oxide, ferric chloride and ferrous nitrate.

[0035] Preferably, the copper source includes at least one of copper sulfate, copper oxide, cuprous chloride and copper nitrate.

[0036] Preferably, the manganese source includes at least one of manganese sulfate, manganese trioxide, manganese nitrate, manganese chloride and manganese acetate tetrahydrate.

[0037] Preferably, in the preparation method of the layered oxide, the ball milling rotation speed is 200-600 r / min, for example, it can be 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min or 600 r / min, etc., and the ball milling time is 4-8 h, for example, it can be 4 h, 5 h, 6 h, 7 h or 8 h, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] In the present application, in the preparation method of the layered oxide, a ball milling speed of 200-600 r / min and a ball milling time of 4-8 h are preferred. Within the above ranges, several substances can be uniformly mixed together.

[0039] Optionally, in the method for preparing the layered oxide, the mixer used for the ball milling includes at least one of a horizontal ball mill mixer, a planetary ball mill mixer, a three-dimensional mixer, a Kawada mixer and a plowshare mixer.

[0040] Preferably, in the preparation method of the layered oxide, the calcination temperature is 800-980°C, for example, it can be 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, 960°C or 980°C, etc., and the calcination time is 8-12h, for example, it can be 8h, 9h, 10h, 11h or 12h, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0041] In the present application, in the preparation method of the layered oxide, a calcination temperature of 800-980° C. and a calcination time of 8-12 h are preferred. Within the above ranges, a pure-phase layered oxide can be synthesized.

[0042] Preferably, in the method for preparing the layered oxide, a crushing step is performed after calcination. Optionally, the crushing method includes at least one of Chinese herbal medicine crushing, air flow mill crushing, mechanical mill crushing, grinding crushing, jaw crusher crushing, roller crushing, and sand mill crushing.

[0043] Preferably, the mixing method in step (2) includes ball milling and / or spraying.

[0044] In the present application, the mixing method is preferably ball milling and / or spraying, which can make the magnesium aluminum silicate material uniformly coated on the surface of the particles.

[0045] Preferably, the rotation speed of the ball milling of the magnesium aluminum silicate material and the active substance is 400-800 r / min, for example, it can be 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min or 800 r / min, etc., and the ball milling time of the magnesium aluminum silicate material and the active substance is 2-8 h, for example, it can be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h, etc., but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0046] In the present application, the rotation speed of the ball milling of the magnesium aluminum silicate material and the active substance is preferably 400-800 r / min, and the ball milling time is preferably 2-8 h. Within the above range, the magnesium aluminum silicate material can be evenly coated on the surface of the base material.

[0047] Optionally, the mixer used for ball milling the magnesium aluminum silicate material and the active substance includes at least one of a horizontal ball mill mixer, a planetary ball mill mixer, a three-dimensional mixer, a Kawada mixer and a plowshare mixer.

[0048] Preferably, the sintering temperature in step (2) is 600-750°C, for example, it can be 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 730°C or 750°C, and the sintering time is 4-8h, for example, it can be 4h, 5h, 6h, 7h or 8h, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0049] In this application, after the magnesium aluminum silicate material and the active material are mixed, the sintering temperature is preferably 600-750°C, and the sintering time is preferably 4-8h. Within the above range, the magnesium aluminum silicate material and the active material can react, and some Mg 2+ and Al 3+ Doped into the sodium layer, silicate ions form a sodium silicate coating layer on the surface of the active material.

[0050] Preferably, in step (2), a crushing step is performed after sintering. Optionally, the crushing method includes at least one of Chinese herbal medicine crushing, air flow mill crushing, mechanical mill crushing, grinding crushing, jaw crusher crushing, roller crushing and sand mill crushing.

[0051] As a preferred technical solution of the present application, the preparation method specifically comprises the following steps:

[0052] (I) ball milling a sodium source, a nickel source, an iron source, a manganese source, and a copper source at a rotation speed of 200-600 r / min for 4-8 hours, and then calcining at 800-980° C. for 8-12 hours to obtain a layered oxide having a chemical formula of Na m Ni x Fe y Mn 1-x-y-z Cu z O2, where 1.05≤m≤1.08, 0.2≤x≤0.4, 0.05≤y≤0.2, 0.05≤z≤0.2;

[0053] (II) adding a magnesium source, an aluminum source, and a silica sol into a reactor, then adding water into the reactor, heating the reactor at 120-350° C. for 4-12 hours, and sequentially performing solid-liquid separation, washing, and drying on the heated product to obtain a magnesium aluminum silicate material;

[0054] (III) The magnesium aluminum silicate material and the layered oxide are mixed and sintered to obtain the positive electrode material.

[0055] In this application, during the heating process of step (II), the pressure in the reactor is within a certain range, ranging from 5-10 MPa, for example, 5 MPa, 7 MPa, 8 MPa, or 10 MPa. The reactor is a high-temperature and high-pressure reactor. In step (III), the magnesium aluminum silicate material and the layered oxide are mixed as a dry blend.

[0056] In a third aspect, an embodiment of the present application provides a sodium ion battery, wherein the positive electrode of the sodium ion battery includes the positive electrode material described in the first aspect.

[0057] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0058] Compared with the related art, the beneficial effects of the embodiments of the present application are:

[0059] The present invention provides a positive electrode material, which has the following advantages: (1) the distance between the sodium layers of the matrix material is narrow, d Na+ for It is beneficial to inhibit the precipitation of free sodium ions, reduce the formation of Na2CO3, and further inhibit the occurrence of gas production; (2) the silicate can react with the residual sodium on the surface of the substrate, thereby converting the residual sodium into sodium silicate, and then the sodium silicate reacts with HF, thereby inhibiting the direct reaction of HF with NaOH / Na2CO3 on the surface of the substrate to produce CO2, further inhibiting the occurrence of gas production; (3) without reducing the voltage, the strong bond strength of the Al-O bond and the strong bond strength of the Mg-O bond are utilized to effectively inhibit the precipitation of oxygen under high pressure and thus reduce gas production, while also maintaining high capacity.

[0060] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0062] FIG1 is a schematic structural diagram of the base material in the positive electrode material prepared in Example 1 of the present application.

[0063] FIG2 is a SEM image of the positive electrode material prepared in Example 1 of the present application.

[0064] FIG3 is a SEM image of the positive electrode material prepared in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0065] The technical solution of this application is further explained below through specific implementation methods.

[0066] Example 1

[0067] This embodiment provides a sodium layered oxide positive electrode material coated with aluminum magnesium silicate, the positive electrode material comprising an active material matrix and an aluminum magnesium silicate coating layer coated on the surface of the active material matrix;

[0068] Among them, the active material matrix is ​​a layered oxide, and its chemical formula is Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 O2, the sodium interlayer spacing of the layered oxide is As shown in FIG1 (Tm in the figure refers to transition metal), the c-axis lattice parameter of the layered oxide is The particle size D50 of the layered oxide is 6-12 μm;

[0069] The chemical formula of the magnesium aluminum silicate coating layer is MgAl2(SiO3)4, and the thickness of the coating layer is 15 nm.

[0070] This embodiment also provides a method for preparing the above-mentioned magnesium aluminum silicate-coated sodium layered oxide positive electrode material, comprising the following steps:

[0071] (1) Synthetic matrix material:

[0072] (a) Primary mixing: Sodium source, nickel source, iron source, manganese source, and copper source were weighed at a molar ratio of 1.07:0.3:0.1:0.5:0.1 and added to a mixing machine. Ball milling beads were added at a mass ratio of 2:1, and the mixture was ball milled at 400 rpm for 6 h.

[0073] The sodium source is sodium carbonate, the nickel source is nickel sulfate, the iron source is ferrous sulfate, the manganese source is manganese sulfate, and the copper source is copper sulfate.

[0074] (b) Primary sintering: The ball-milled mixture is compacted in a crucible and calcined at 880°C in air for 12 h. The mixture is then cooled to room temperature. The powder is removed, crushed, and passed through a 400-mesh sieve to obtain a sodium layered oxide cathode material matrix, i.e., a layered oxide matrix material.

[0075] (2) Synthetic magnesium aluminum silicate coating agent

[0076] (a) A magnesium source, an aluminum source, and a silica sol were added to a reactor in a molar ratio of 1:2:4, and pure water was added as a solvent. The reactor was then placed in an oven at 250°C for 6 hours. After cooling, the obtained sample was filtered, washed with water, and dried at 110°C for 3 hours to obtain a magnesium aluminum silicate coating agent.

[0077] Wherein, the magnesium source is magnesium acetate, the aluminum source is aluminum acetate, and the silica sol is a silicic acid aqueous solution;

[0078] (3) The layered oxide matrix material is added to the Kawada mixer, and the aluminum magnesium silicate coating agent is added to the Kawada mixer at the same time. The mixer is operated at a speed of 800 r / min for 2 hours to obtain a mixture; the mixture is packed into a crucible and compacted, kept warm in an air atmosphere at 680°C for 6 hours, and naturally cooled with the furnace. The powder is taken out, crushed, and passed through a 300-mesh sieve to obtain the aluminum magnesium silicate-coated sodium electrode layered oxide positive electrode material, as shown in Figure 2.

[0079] Example 2

[0080] This embodiment provides a sodium layered oxide positive electrode material coated with aluminum magnesium silicate, the positive electrode material comprising an active material matrix and an aluminum magnesium silicate coating layer coated on the surface of the active material matrix;

[0081] Among them, the active material matrix is ​​a layered oxide, and its chemical formula is Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 O2, the sodium interlayer spacing of the layered oxide is As shown in FIG1 (Tm in the figure refers to transition metal), the c-axis lattice parameter of the layered oxide is The particle size D50 of the layered oxide is 6-12 μm;

[0082] The chemical formula of the magnesium aluminum silicate coating layer is MgAl2(SiO3)4, and the thickness of the coating layer is 10 nm.

[0083] This embodiment also provides a method for preparing the above-mentioned magnesium aluminum silicate-coated sodium layered oxide positive electrode material, comprising the following steps:

[0084] (1) Synthetic matrix material:

[0085] The base material was synthesized using the same method as in Example 1;

[0086] (2) Synthetic magnesium aluminum silicate coating agent

[0087] (a) adding a magnesium source, an aluminum source, and silica sol into a reactor at a molar ratio of 1:2:4, and adding pure water as a solvent, then placing the reactor in an oven at 120°C for 12 hours. After cooling, the obtained sample was filtered, washed with water, and dried at 110°C for 3 hours to obtain a magnesium aluminum silicate coating agent;

[0088] Wherein, the magnesium source is magnesium acetate, the aluminum source is aluminum acetate, and the silica sol is a silicic acid aqueous solution;

[0089] (3) Adding the layered oxide matrix material to the Kawada mixer, and at the same time adding the aluminum magnesium silicate coating agent to the Kawada mixer, and running the mixer at a speed of 600 r / min for 5 hours to obtain a mixture; the mixture is packed into a crucible and compacted, kept warm in an air atmosphere at 600°C for 8 hours, and naturally cooled with the furnace, and the powder is taken out, crushed, and passed through a 300-mesh sieve to obtain the aluminum magnesium silicate-coated sodium electrode layered oxide positive electrode material.

[0090] Example 3

[0091] This embodiment provides a sodium layered oxide positive electrode material coated with aluminum magnesium silicate, the positive electrode material comprising an active material matrix and an aluminum magnesium silicate coating layer coated on the surface of the active material matrix;

[0092] Among them, the active material matrix is ​​a layered oxide, and its chemical formula is Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 O2, the sodium interlayer spacing of the layered oxide is As shown in FIG1 (Tm in the figure refers to transition metal), the c-axis lattice parameter of the layered oxide is The particle size D50 of the layered oxide is 6-12 μm;

[0093] The chemical formula of the magnesium aluminum silicate coating layer is MgAl2(SiO3)4, and the thickness of the coating layer is 20 nm.

[0094] This embodiment also provides a method for preparing the above-mentioned magnesium aluminum silicate-coated sodium layered oxide positive electrode material, comprising the following steps:

[0095] (1) Synthetic matrix material:

[0096] The base material was synthesized using the same method as in Example 1;

[0097] (2) Synthetic magnesium aluminum silicate coating agent

[0098] (a) A magnesium source, an aluminum source, and a silica sol were added to a reactor in a molar ratio of 1:2:4, and pure water was added as a solvent. The reactor was then placed in an oven at 350°C for 4 hours. After cooling, the obtained sample was filtered, washed with water, and dried at 110°C for 3 hours to obtain a magnesium aluminum silicate coating agent.

[0099] The magnesium source is magnesium nitrate, the aluminum source is aluminum nitrate, and the silica sol is a silicic acid aqueous solution;

[0100] (3) Adding the layered oxide matrix material to the Kawada mixer, and at the same time adding the aluminum magnesium silicate coating agent to the Kawada mixer, running at a speed of 400 r / min for 8 hours to obtain a mixture; the mixture is packed into a crucible and compacted, kept warm in an air atmosphere at 750°C for 4 hours, and naturally cooled with the furnace, and the powder is taken out, crushed, and passed through a 300-mesh sieve to obtain the aluminum magnesium silicate-coated sodium electrode layered oxide positive electrode material.

[0101] Example 4

[0102] The difference between this embodiment and embodiment 1 is that the chemical formula of the magnesium aluminum silicate coating layer is adjusted to MgAl2(Si2O5)4 by adjusting the molar ratio of the magnesium source, the aluminum source and the silica sol.

[0103] The rest of the preparation methods and parameters remained the same as in Example 1.

[0104] Example 5

[0105] The difference between this embodiment and embodiment 1 is that the thickness of the magnesium aluminum silicate coating layer is 5 nm by adjusting the amount of the magnesium aluminum silicate coating agent added.

[0106] The rest of the preparation methods and parameters remained the same as in Example 1.

[0107] Example 6

[0108] The difference between this embodiment and embodiment 1 is that the thickness of the magnesium aluminum silicate coating layer is 25 nm by adjusting the amount of the magnesium aluminum silicate coating agent added.

[0109] The rest of the preparation methods and parameters remained the same as in Example 1.

[0110] Comparative Example 1

[0111] This comparative example provides an alumina-coated sodium layered oxide positive electrode material, the positive electrode material comprising an active material matrix and an alumina coating layer coated on the surface of the active material matrix;

[0112] The active material matrix is ​​consistent with that in Example 1; and the thickness of the aluminum oxide coating layer is 15 nm.

[0113] This comparative example also provides a method for preparing the above-mentioned alumina-coated sodium layered oxide positive electrode material, comprising the following steps:

[0114] (1) The preparation method of the synthetic matrix material is consistent with that in Example 1;

[0115] (2) Adding the layered oxide matrix material to the Kawada mixer, and adding the alumina powder to the Kawada mixer at the same time, and running the mixer at a speed of 800 r / min for 2 hours to obtain a mixture; the mixture is packed into a crucible and compacted, and kept warm in an air atmosphere at 680°C for 6 hours, and naturally cooled with the furnace, and the powder is taken out, crushed, and passed through a 300-mesh sieve to obtain the alumina-coated sodium layered oxide positive electrode material.

[0116] Comparative Example 2

[0117] This comparative example provides a magnesium oxide-coated sodium layered oxide positive electrode material, the positive electrode material comprising an active material matrix and a magnesium oxide coating layer coated on the surface of the active material matrix;

[0118] The active material matrix is ​​consistent with that in Example 1; and the thickness of the magnesium oxide coating layer is 15 nm.

[0119] This comparative example also provides a method for preparing the above-mentioned magnesium oxide-coated sodium layered oxide positive electrode material, comprising the following steps:

[0120] (1) The preparation method of the synthetic matrix material is consistent with that in Example 1;

[0121] (2) adding the layered oxide matrix material to the Kawada mixer, and adding the magnesium oxide powder to the Kawada mixer at the same time, and running the mixer at a speed of 800 r / min for 2 hours to obtain a mixture; the mixture is packed into a crucible and compacted, kept warm in an air atmosphere at 680°C for 6 hours, and naturally cooled with the furnace, and the powder is taken out, crushed, and passed through a 300-mesh sieve to obtain the magnesium oxide-coated sodium layered oxide positive electrode material.

[0122] Comparative Example 3

[0123] This comparative example provides a silicon dioxide-coated sodium layered oxide positive electrode material, the positive electrode material comprising an active material matrix and a silicon dioxide coating layer coated on the surface of the active material matrix;

[0124] The active material matrix is ​​consistent with that in Example 1; and the thickness of the silicon dioxide coating layer is 15 nm.

[0125] This comparative example also provides a method for preparing the above-mentioned silicon dioxide-coated sodium layered oxide positive electrode material, comprising the following steps:

[0126] (1) The preparation method of the synthetic matrix material is consistent with that in Example 1;

[0127] (2) adding the layered oxide matrix material to the Kawada mixer, and simultaneously adding the silica powder to the Kawada mixer, and running the mixer at a speed of 800 r / min for 2 h to obtain a mixture; the mixture is packed into a crucible and compacted, kept warm in an air atmosphere at 680° C. for 6 h, and naturally cooled with the furnace, and the powder is taken out, crushed, and passed through a 300-mesh sieve to obtain the silica-coated sodium layered oxide positive electrode material.

[0128] Comparative Example 4

[0129] The difference between this comparative example and Example 1 is that the coating of magnesium aluminum silicate is not performed, that is, step (2) is replaced by the following steps:

[0130] The base material was added into the crucible and compacted and marked, and then heated to 750℃ in air atmosphere and kept for 6h. After cooling naturally, Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 O2 material is crushed by air flow mill to obtain Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 The finished O2 product is shown in Figure 3.

[0131] The rest of the preparation methods and parameters remained the same as in Example 1.

[0132] Comparative Example 5

[0133] The difference between this comparative example and comparative example 4 is that Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 After the O2 product is finished, a water washing step is also carried out, which specifically includes:

[0134] Will Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 The O2 finished product is added to the water-washed axe, and ultrapure ice water with a temperature close to 0°C is added according to the water-to-material ratio of 0.8. The speed is set to 100r / min and stirred for 60s. Then the material in the water-washed axe and water are added to the centrifuge and centrifuged at a speed of 150r / min for 20min to obtain the water-separated material; the material is placed in an oven at 120°C for drying to obtain the washed Na 1.07 Ni 0.3 Fe0.1 Mn 0.5 Cu 0.1 O2 finished product.

[0135] The rest of the preparation methods and parameters remained the same as those in Comparative Example 4.

[0136] Comparative Example 6

[0137] The difference between this comparative example and comparative example 4 is that Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 After the O2 product is finished, the pickling step is also carried out, which specifically includes:

[0138] (i) Weighing a certain amount of ultrapure water at a water-to-material ratio of 0.8, adding 1 wt% acetic acid to the ultrapure water; setting the stirrer speed to 800 rpm, stirring for 30 minutes to obtain a uniform acetic acid solution, and then adding ice cubes to cool the solution to 0°C;

[0139] (ii) Put Na 1.07 Ni 0.3 Fe 0.1 Mn 0.5 Cu 0.1 The O2 finished product is added to the water-washed axe, and the acetic acid solution is added according to the water-to-material ratio of 0.8; the speed is set to 100r / min, the stirring paddle is turned on, and after stirring for 60s, the material in the water-washed axe and water are added to the centrifuge, and centrifuged at a speed of 150r / min for 20min to obtain the material separated from the acetic acid solution; the material is placed in an oven at 120℃ for drying to obtain the acid-washed NaNi 0.3 Fe 0.1 Mn 0.5 Cu 0.1 O2 finished product.

[0140] The rest of the preparation methods and parameters remained the same as those in Comparative Example 4.

[0141] Performance Testing

[0142] The base materials and cathode materials prepared in the above examples and comparative examples were tested, including:

[0143] (1) Matrix material interlayer spacing test

[0144] The XRD data of the sample can be obtained by X-ray diffraction test, and the measured XRD data can be refined by Fullprof software to R WPData below 6% is trustworthy. Read the c value from the SUM file of the refined data; obtain the refined Cif file from the refined data, import the refined Cif file into Vesta software, and use Vesta to measure the distance between Na1 and O1 to obtain d(Na1-O1); w(Na1-O1) = d(Na1-O1) / c to obtain w(Na1-O1); d(003) = c / 3 to obtain d(003); d(Tm) = c*w(Na1-O1) - d(003) / 2 to obtain d(Tm), the transition metal layer spacing; d(Na1-O1) = d(003) / 2 to obtain d(003) / 3. + )=d(003)-d(Tm) can be obtained as d(Na + ), d(Na + ) can also be expressed as d Na + , that is, the sodium interlayer distance.

[0145] (2) Residual alkali content test of positive electrode materials

[0146] Take 1g of positive electrode material for each sample and dissolve it in 100mL of ultrapure water in a conical flask; after stirring for 30min in a closed conical flask, immediately filter and obtain the filtrate. Take 5mL of the filtrate from each sample and use 0.05mol / L standard hydrochloric acid solution to titrate the residual alkali (Na2CO3+NaOH) content on the sample surface on a potentiometric titrator.

[0147] (3) Battery performance test

[0148] The positive electrode materials prepared in the above examples and comparative examples, Super P, and PVDF were added to a mortar and mixed in a mass ratio of 8:1:1. After coating, the mixture was dried to obtain a positive electrode sheet. The positive electrode sheet, glass fiber separator, and sodium sheet were used to form a sodium ion battery, in which the electrolyte contained 1 mol / L NaClO4 and the solvent was ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. Each sodium ion battery was tested, including:

[0149] (1) Capacity test

[0150] The assembled battery was left to stand for 12 h to allow the electrolyte to fully contact the electrode and separator. 1C was set to 150 mAh / g, and the battery was charged at a constant current rate of 0.1 C to 4.2 V, then charged at a constant voltage rate until the current was less than 0.05 mA, and then discharged at a constant current to 1.5 V to obtain the first-cycle discharge specific capacity.

[0151] (2) Capacity retention test

[0152] Let the assembled battery rest for 2 hours, then charge it at a constant current rate of 0.1C to 4.2V, then charge it at a constant voltage rate until the current is less than 0.05mA, and then discharge it at a constant current rate to 1.5V. After activating it twice, charge it at a constant current rate of 1C to 4.2V, then charge it at a constant voltage rate until the current is less than 0.05mA, and then discharge it at a constant current rate to 1.5V. Record the discharge capacity D1. Repeat this charge and discharge method for 50 cycles, and record the discharge capacity D2 at the 50th discharge.

[0153] The capacity retention rate is calculated as follows: capacity retention rate = D2 / D1×100%.

[0154] (3) Inflation rate test

[0155] The formed battery was placed at 25°C for 2 h, charged at a constant current rate of 0.5C to 4.2V, and then charged at a constant voltage to a current of 0.03C. The battery volume V1 was measured. The battery was stored at 60°C for 14 days, and the battery volume V2 was measured. The inflation rate = (V2-V1) / V1×100%.

[0156] The test results are shown in Table 1.

[0157] Table 1

[0158] analyze:

[0159] It can be seen from the data results of Examples 1-3 that the positive electrode material provided in this application can effectively inhibit the precipitation of free sodium ions, reduce the formation of Na2CO3, and inhibit the occurrence of gas production, while also maintaining high capacity and having excellent electrochemical properties.

[0160] The data from Examples 1 and 4 show that a MgAl2(SiO3)4 coating layer forms when the molar ratio of Al, Mg, and Si is 2:1:4, while a MgAl2(Si2O5)4 coating layer forms when the molar ratio of Al, Mg, and Si is 2:1:8. Both coatings can be used to coat substrate materials, and the resulting positive electrode materials exhibit excellent electrochemical performance.

[0161] From the data results of Example 1 and Example 5-6, it can be seen that if the thickness of the magnesium aluminum silicate coating layer is too small, the effect of inhibiting the generation of residual sodium will be reduced, the amount of Mg-O and Al-O will be small, and the effect of fixing O will be weakened; if the thickness of the magnesium aluminum silicate coating layer is too large, Mg will be 2+ and Al 3+ If the amount of matrix material added is large, it will cause Mg 2+ and Al 3+ It not only penetrates into the Na layer, but also penetrates into the transition metal layer, thereby widening the distance between the sodium layers. In addition, the thicker coating layer will hinder the migration of sodium ions in and out, resulting in a decrease in capacity.

[0162] It can be seen from the data results of Example 1 and Comparative Examples 1-3 that if aluminum oxide, magnesium oxide or silicon dioxide is coated on the surface of the sodium layered oxide positive electrode material, the synergistic effect of the three ions is not achieved. Mg-O and Al-O alone or sodium silicate coating on the surface cannot significantly reduce the residual alkali and inhibit gas production.

[0163] It can be seen from the data results of Example 1 and Comparative Example 4 that if the sodium layered oxide positive electrode material is not coated, the gas production will be very large and the residual sodium precipitated on the surface will also be relatively high, resulting in a decrease in the capacity retention rate.

[0164] From the data results of Comparative Examples 4 and 5-6, it can be seen that if NaNi 0.3 Fe 0.1 Mn 0.5 Cu 0.1 If the finished O2 product is acid-washed or water-washed, a large amount of sodium ions will migrate out and dissolve in water or be filtered out by acid. Although the residual alkali content is low, the material itself contains fewer sodium ions, which greatly reduces the capacity.

[0165] The applicant declares that the above is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Technical personnel in the relevant technical field should understand that any changes or substitutions that can be easily thought of by technical personnel in the relevant technical field within the technical scope disclosed in this application fall within the protection scope and disclosure scope of this application.

Claims

1. A positive electrode material, wherein: The positive electrode material comprises an active material matrix and a magnesium aluminum silicate coating layer coated on the surface of the active material matrix.

2. The positive electrode material according to claim 1, wherein The active material matrix includes a layered oxide.

3. The positive electrode material according to claim 2, wherein The chemical formula of the layered oxide is Na m Ni x Fe y Mn 1-x-y-z Cu z O2, where 1.05≤m≤1.08, 0.2≤x≤0.4, 0.05≤y≤0.2, 0.05≤z≤0.

2.

4. The positive electrode material according to claim 2 or 3, wherein The sodium interlayer spacing of the layered oxide is 5. The positive electrode material according to any one of claims 2 to 4, wherein The particle size D50 of the active material matrix is ​​6-12 μm.

6. The positive electrode material according to any one of claims 1 to 5, wherein The chemical formula of the magnesium aluminum silicate coating layer is MgAl2(Si a O 2a+1 )4, where 1≤a≤2 and a is a positive integer.

7. The positive electrode material according to any one of claims 1 to 5, wherein The thickness of the magnesium aluminum silicate coating layer is 10-20 nm.

8. A method for preparing the positive electrode material according to any one of claims 1 to 7, comprising: (1) mixing a magnesium source, an aluminum source, a silica sol and a solvent, and then heating the obtained mixture to obtain a magnesium aluminum silicate material; (2) The magnesium aluminum silicate material and the active material are mixed and sintered to obtain the positive electrode material.

9. The preparation method according to claim 8, wherein: The heating temperature in step (1) is 120-350° C. The heating time in step (1) is 4-12 hours.

10. The preparation method according to claim 8 or 9, wherein: The active material in step (2) includes layered oxides, and the preparation method of the layered oxides includes: ball-milling a sodium source, a nickel source, an iron source, a manganese source and a copper source together, and calcining to obtain the layered oxides.

11. The preparation method according to claim 10, wherein: In the preparation method of the layered oxide, the rotation speed of the ball mill is 200-600 r / min, and the time of the ball mill is 4-8 h.

12. The preparation method according to claim 10 or 11, wherein: The calcination temperature is 800-980° C., and the calcination time is 8-12 hours.

13. The preparation method according to any one of claims 8 to 12, wherein: The mixing method in step (2) includes ball milling and / or spraying; The rotation speed of the ball milling of the magnesium aluminum silicate material and the active substance is 400-800 r / min, and the ball milling time of the magnesium aluminum silicate material and the active substance is 2-8 hours; The sintering temperature in step (2) is 600-750° C., and the sintering time is 4-8 hours.

14. The preparation method according to any one of claims 8 to 13, wherein: The preparation method specifically comprises the following steps: (I) ball milling a sodium source, a nickel source, an iron source, a manganese source and a copper source at a rotation speed of 200-600 r / min for 4-8 hours, and then calcining at 800-980° C. for 8-12 hours to obtain a layered oxide, wherein the chemical formula of the layered oxide is Na m Ni x Fe y Mn 1-x-y-z Cu z O2, where 1.05≤m≤1.08, 0.2≤x≤0.4, 0.05≤y≤0.2, 0.05≤z≤0.2; (II) adding a magnesium source, an aluminum source and a silica sol into a reaction kettle, then adding water into the reaction kettle, and then heating the reaction kettle at 120-350° C. for 4-12 hours, and sequentially performing solid-liquid separation, washing and drying on the heated product to obtain a magnesium aluminum silicate material; (III) The magnesium aluminum silicate material and the layered oxide are mixed and sintered to obtain the positive electrode material.

15. A sodium ion battery, wherein: The positive electrode of the sodium ion battery comprises the positive electrode material according to any one of claims 1 to 7.

Images