Sodium-ion battery cathode composite material, its preparation method and sodium-ion battery

Abstract

Embodiments of the present invention relate to the technical field of sodium-ion batteries, and specifically provide a composite cathode material for a sodium-ion battery, a preparation method thereof, and a sodium-ion battery. Among them, the composite cathode material for a sodium-ion battery includes a layered oxide and a Prussian blue material layer coated on the surface of the layered oxide, and the coating rate of the Prussian blue material layer on the layered oxide is between 25% and 45%; the layered oxide has a chemical formula shown in General Formula I, and the Prussian blue material layer has a chemical formula shown in General Formula II. The composite cathode material for a sodium-ion battery provided by the present invention is coated with a Prussian blue material layer on the surface of the layered oxide, effectively reducing the exposed area of the layered oxide, improving the stability of the composite cathode material for a sodium-ion battery. When assembled into a sodium-ion battery, the discharge specific capacity attenuation rate is relatively gentle, which can effectively improve the cycle performance of the sodium-ion battery and extend the service life of the sodium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a composite cathode material for a sodium-ion battery, a preparation method thereof, and a sodium-ion battery. Background Art

[0002] Sodium-ion batteries are considered to have great application prospects in electrochemical energy storage because of their lower raw material costs compared with lithium-ion batteries. The existing cathode materials for sodium-ion batteries are mainly layered oxides, which have characteristics such as high energy density. However, for sodium-ion batteries using layered oxides as the cathode active material, there is a problem of rapid decline in specific capacity during the cycling process, which also leads to a rapid decline in energy density, poor cycling performance, and poor rate performance. Summary of the Invention

[0003] The main purpose of the embodiments of the present invention is to provide a composite cathode material for a sodium-ion battery, aiming to solve the problems of rapid decline in specific capacity and rapid decline in energy density of the layered oxide cathode material of the existing sodium-ion battery.

[0004] In a first aspect, the embodiments of the present invention provide a composite cathode material for a sodium-ion battery, which includes a layered oxide and a Prussian blue material layer coated on the surface of the layered oxide, and the coating rate of the Prussian blue material layer on the layered oxide is between 25% and 45%;

[0005] Among them, the layered oxide has a chemical formula shown in General Formula I:

[0006] Na α MO 2-β X β (I);

[0007] M is selected from one or more of Ni, Mn, Fe, Co, Zn, Sn, Mg, Li, and Zr;

[0008] X is selected from one or more of Cl, F, and Br;

[0009] 0.4 < α < 1.2, 0 ≤ β < 0.2;

[0010] The Prussian blue material layer has a chemical formula shown in General Formula II:

[0011] A γ M1 δ [M2(CN)6]·θH2O (II);

[0012] A is Na or Li;

[0013] M1 is selected from one or more of Zn, Ni, Mn, Fe, Co, Ce, and Cu;

[0014] M2 is selected from one or more of Zn, Ni, Mn, Fe, Co, Cu, and Ce;

[0015] 0 < γ < 4, 0 < δ < 4, 0 ≤ θ < 8.

[0016] In some embodiments, the positive electrode composite material of the sodium ion battery further includes at least one of the features in items (1) to (4):

[0017] (1) The particle diameter of the layered oxide is 10 nm to 200 μm;

[0018] (2) The thickness of the Prussian blue material layer is 2 nm to 200 nm;

[0019] (3) The layered oxide includes NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Na 2 / 3 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Na 0.9 Ti 0.1 [Ni 1 / 3Co 1 / 3 Mn 1 / 3 0.9 O2, Na 0.8 [Ni 1 / 3 Co 1 / 3 Mn 1 / 3 0.8 Ti 0.1 Li 0.1 O2, Na 0.67 Ni 0.33 Mn 0.67 O2, Na 0.8 Li 0.1 Ni 0.23 Mn 0.67 O2, NaMg 0.2 Ni 0.1 Li 0.2 Mn 0.7 O2 and Na 0.67 (Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ) 0.8 Ti 0.1 Li 0.1 O 1.95 F 0.05 and at least one of them;

[0020] ​​(4) The Prussian blue material includes at least one of Na2Fe[Fe(CN)6], Na2Co[Fe(CN)6], Na2Fe[Co(CN)6], Na2Mn[Fe(CN)6]·H2O, Na2Ni[Fe(CN)6], Na2Mn[Mn(CN)6], NaV[Fe(CN)6], Na4[Fe(CN)6], Na 0.61 Fe[Fe(CN)6], Na 1.94 Mn 0.18 Co 0.17 Ni 0.03 Fe 0.62 [Fe(CN)6] 0.93 、Na 1.56 Fe[Fe(CN)6]·3.1H2O.

[0021] In some embodiments, the coating rate of the Prussian blue material layer on the layered oxide is 30.5%.

[0022] Compared with the prior art, the sodium ion battery positive composite material provided in the first aspect of the embodiments of the present invention includes a layered oxide and a Prussian blue material layer, and the Prussian blue material layer is coated on the surface of the layered oxide, thereby effectively reducing the exposed area of the layered oxide, improving the stability of the sodium ion battery positive composite material, and having a relatively gentle discharge specific capacity attenuation rate when assembled into a sodium ion battery, which can effectively improve the cycle performance of the sodium ion battery and extend the service life of the sodium ion battery.

[0023] In the second aspect, the embodiments of the present invention further provide a preparation method of a sodium ion battery positive composite material, and the technical solution adopted is as follows:

[0024] A preparation method of a sodium ion battery positive composite material includes the following steps:

[0025] Mix the precursor and the first sodium source, and perform tabletting treatment to obtain a sheet material;

[0026] Calcine the sheet material at 500°C to 1100°C or 1200°C to obtain a layered oxide;

[0027] Dissolve the metal salt and the second sodium source in a solvent to obtain a mixed solution;

[0028] Put the layered oxide into the mixed solution, heat and keep warm so that the solute in the mixed solution deposits on the surface of the layered oxide to obtain a sodium ion battery positive composite material.

[0029] In some embodiments, the precursor includes at least one of M(OH)2 and M metal carbonate, where M is selected from one or more of Ni, Mn, Fe, Co, Zn, Sn, Mg, Li, and Zr;

[0030] The first sodium source is selected from at least one of sodium nitrate, sodium chlorate, and sodium sulfate.

[0031] In some embodiments, the molar ratio of the precursor to the first sodium source is 0.44 to 1.2.

[0032] In some embodiments, the metal salt includes at least one of the sulfate of M, the chlorate of M, the sulfate of M1, the chlorate of M1, and the cyanide of M2, where M1 is selected from one or more of Zn, Ni, Mn, Fe, Co, Ce, Cu, and V; M2 is selected from one or more of Zn, Ni, Mn, Fe, Co, Cu, and Ce;

[0033] The second sodium source is selected from at least one of sodium nitrate, sodium chlorate, and sodium sulfate.

[0034] In some embodiments, the molar ratio of the metal salt to the second sodium source is 0.5 to 4.0.

[0035] In some embodiments, the heating temperature is 450°C to 880°C, and the heat preservation time is 1 h to 72 h;

[0036] And / or, before the layered oxide is put into the mixed solution, it further includes the step of crushing the layered oxide into micro-nano scale powder;

[0037] And / or, ultrasonic conditions are applied during the heating and heat preservation treatment.

[0038] Compared with the prior art, the preparation method of the sodium ion battery positive composite material provided in the second aspect of the embodiments of the present invention has the characteristics of simple preparation process, and by using this method, a Prussian blue material layer can be effectively coated on the surface of the layered oxide, and the coating rate of the Prussian blue material layer on the surface of the layered oxide is between 25% and 45%, effectively reducing the exposed area of the layered oxide. When the obtained sodium ion battery positive composite material is assembled into a sodium ion battery, the discharge specific capacity attenuation rate is relatively mild, and the service life of the sodium ion battery can be effectively extended.

[0039] In the third aspect, the embodiments of the present invention further provide a sodium ion battery, including a positive electrode sheet and a negative electrode sheet, where the positive electrode sheet contains the above-mentioned sodium ion battery positive composite material, or the positive electrode sheet contains a sodium ion battery positive composite material prepared by using the preparation method of the above-mentioned sodium ion battery positive composite material.

[0040] Compared with the prior art, the sodium-ion battery provided in the third aspect of this embodiment contains the above-mentioned sodium-ion battery cathode composite material in the cathode sheet. Therefore, during use, the discharge specific capacity attenuation rate is relatively gentle, and it has relatively excellent cycling performance, which can effectively extend the service life of the sodium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 SEM diagram of the layered oxide material provided in Embodiment 1 of the present invention;

[0043] Figure 2 XRD diagrams of the layered oxide material provided in Embodiment 1 of the present invention and the sodium-ion battery cathode composite materials provided in Embodiments 2 to 6;

[0044] Figure 3 SEM spectrum of the sodium-ion battery cathode composite material provided in Embodiment 2 of the present invention;

[0045] Figure 4 TEM diagram of the sodium-ion battery composite material provided in Embodiment 2 of the present invention;

[0046] Figure 5 First charge-discharge curve of the sodium-ion battery assembled with the sodium-ion battery cathode composite material provided in Embodiment 2 of the present invention;

[0047] Figure 6 SEM diagram of the sodium-ion battery cathode composite material provided in Embodiment 4 of the present invention;

[0048] Figure 7 SEM diagram of the sodium-ion battery cathode composite material provided in Embodiment 5 of the present invention;

[0049] Figure 8 Cycling curves of the sodium-ion batteries provided in Embodiments 1, 2, 4, and 6 of the present invention;

[0050] Figure 9 Rate performance curves of the sodium-ion batteries provided in Embodiments 1, 2, 4, and 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0052] It should be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0053] An embodiment of the present invention provides a composite cathode material for a sodium-ion battery. The composite cathode material for a sodium-ion battery includes a layered oxide and a Prussian blue material layer coated on the surface of the layered oxide, and the coating rate of the Prussian blue material layer on the layered oxide is between 25% and 45%; wherein, the layered oxide has a chemical formula as shown in General Formula I, and the Prussian blue material layer is composed of a substance represented by a chemical formula as shown in General Formula II:

[0054] Na α MO 2-β X β (I);

[0055] A γ M1 δ [M2(CN)6]·θH2O (II);

[0056] Wherein, M is selected from one or more of Ni, Mn, Fe, Co, Zn, Sn, Mg, Li, Zr, and Ti;

[0057] X is selected from one or more of Cl, F, and Br;

[0058] 0.4 < α < 1.2, 0 ≤ β < 0.2;

[0059] A is Na or Li;

[0060] M1 is selected from one or more of Zn, Ni, Mn, Fe, Co, Ce, Cu, and V;

[0061] M2 is selected from one or more of Zn, Ni, Mn, Fe, Co, Cu, and Ce;

[0062] 0 < γ ≤ 4, 0 ≤ δ < 4, 0 ≤ θ < 8, 0 < μ ≤ 1.

[0063] The positive electrode composite material of the sodium-ion battery provided by the embodiment of the present invention can effectively improve the stability of the material due to the coating of a Prussian blue material layer on the surface of the layered oxide. When assembled into a sodium-ion battery, the attenuation rate of the specific capacity of the battery becomes mild, improving the cycle stability and rate performance of the sodium-ion battery, which is beneficial to improving the service life of the sodium-ion battery, and at the same time, it can have high rate characteristics.

[0064] In some embodiments, the Prussian blue material layer is coated on the surface of the layered oxide, and the coating rate of the Prussian blue material layer on the surface of the layered oxide is positively correlated with the material stability of the positive electrode composite material of the sodium-ion battery. The higher the coating rate, the smaller the exposed area of the surface of the layered oxide, which is more conducive to isolating the layered oxide from the outside world, thereby effectively improving the stability of the layered oxide and reducing the contact area with the electrolyte. In some embodiments, the coating rate of the Prussian blue material layer can be obtained by adjusting the preparation process of the positive electrode composite material of the sodium-ion battery.

[0065] In some embodiments, the particle diameter of the layered oxide is 10 nm to 200 μm. If the particle diameter of the layered oxide is too large, it will increase the coating difficulty of the Prussian blue material layer, and there will be coating layer stress after coating, and the coating layer is easy to break, which is not conducive to obtaining a high coating rate and is also not conducive to obtaining a stable coating layer. In some embodiments, the thickness of the Prussian blue material layer is 2 to 200 nm. In some embodiments, the Prussian blue material layer is uniformly coated on the surface of the layered oxide, and the D50 of the thickness of the Prussian blue material layer is between 50 nm and 100 nm. It should be noted that the conventional definition of D50 is the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. In the embodiment of the present invention, D50 is used to define the thickness corresponding to when the cumulative thickness distribution percentage of the Prussian blue material layer coated on the surface of the layered oxide reaches 50%.

[0066] In some embodiments, the layered oxide includes NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Na 2 / 3 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Na 0.9 Ti 0.1 [Ni 1 / 3 Co 1 / 3 Mn 1 / 3 0.9 O2, Na 0.8 [Ni 1 / 3 Co 1 / 3 Mn 1 / 3 0.8 Ti 0.1 Li​​0.1 O2, Na 0.67 Ni 0.33 Mn 0.67 O2, Na 0.8 Li 0.1 Ni 0.23 Mn 0.67 O2, NaMg 0.2 Ni 0.1 Li 0.2 Mn 0.7 O2 and Na 0.67 (Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ) 0.8 Ti 0.1 Li 0.1 O 1.95 F 0.05 At least one of; the materials constituting the Prussian blue layer include Na2Fe[Fe(CN)6], Na2Co[Fe(CN)6], Na2Fe[Co(CN)6], Na2Mn[Fe(CN)6]·H2O, Na2Ni[Fe(CN)6], Na2Mn[Mn(CN)6], NaV[Fe(CN)6], Na4[Fe(CN)6], Na 0.61 Fe[Fe(CN)6], Na 1.94 Mn 0.18 Co 0.17 Ni 0.03 Fe 0.62 [Fe(CN)6] 0.93 , Na 1.56 Fe[Fe(CN)6]·3.1H2O.

[0067] Based on the sodium ion battery cathode composite material provided above, an embodiment of the present invention also provides a preparation method for the sodium ion battery cathode composite material.

[0068] Specifically, the sodium ion battery cathode composite material can be prepared according to the following steps:

[0069] S01. Mix the precursor and the first sodium source, and perform tablet pressing to obtain a sheet material.

[0070] In step S01, the precursor includes at least one of M(OH)2 and M metal carbonates, where M is selected from one or more of Ni, Mn, Fe, Co, Zn, Sn, Mg, Li, and Zr; the first sodium source is selected from at least one of sodium nitrate, sodium chlorate, and sodium sulfate.

[0071] In some embodiments, the molar ratio of the precursor to the first sodium source is 0.44 to 1.2.

[0072] In some embodiments, the tabletting process can be carried out as follows: the powder is loaded into a cylindrical mold, and a pressure of 5 to 3000 MPa is applied.

[0073] S02: Calcinate the lamellar material under the condition of 500 °C to 1100 °C or 1200 °C to obtain a layered oxide.

[0074] In step S02, during the calcination treatment, the calcination treatment can be carried out in an air atmosphere.

[0075] S03: Dissolve the metal salt and the second sodium source in a solvent to obtain a mixed solution.

[0076] In step S03, the metal salt includes at least one of the sulfate of M, the chlorate of M, the sulfate of M1, the chlorate of M1, and the cyanide of M2. M1 is selected from one or more of Zn, Ni, Mn, Fe, Co, Ce, Cu, and V; M2 is selected from one or more of Zn, Ni, Mn, Fe, Co, Cu, and Ce; the second sodium source is selected from at least one of sodium nitrate, sodium chlorate, and sodium sulfate.

[0077] In some embodiments, the molar ratio of the metal salt to the second sodium source is 1:2.

[0078] In some embodiments, the solvent is selected from deionized water.

[0079] S04: Put the layered oxide into the mixed solution, heat and keep warm, so that the solute in the mixed solution deposits on the surface of the layered oxide to obtain a composite cathode material for a sodium-ion battery.

[0080] In step S04, before putting the layered oxide into the mixed solution, it further includes the step of crushing the layered oxide into micro-nano scale powder. In some embodiments, the particle size of the micro-nano scale powder is 20 nm to 500 μm. In some embodiments, a crushing device such as a planetary ball mill is used to crush the layered oxide so that the layered oxide becomes a micro-nano scale powder. When ball milling with a ball mill, the ball milling speed is 200 r / min to 1000 r / min.

[0081] In some embodiments, after putting the layered oxide into the mixed solution, stir first to make the materials mix evenly, which is beneficial to uniform dispersion and uniform precipitation.

[0082] In some embodiments, the heating temperature is 450°C to 880°C. That is, after the layered oxide is put into the mixed solution, the reaction system is heated to 450°C to 880°C, and then kept at 450°C to 880°C for 1 h to 72 h. By extending the holding time, it is beneficial to improve the coating rate.

[0083] In some embodiments, an ultrasonic condition is also included during the heating and holding processes. Through the ultrasonic wave, a uniform Prussian blue material layer is formed on the surface of the layered oxide, improving the coating uniformity of the Prussian blue material layer and being beneficial to improving the coating rate, so that the coating rate reaches more than 80%. In some embodiments, when applying the ultrasonic condition, the frequency of the ultrasonic wave is between 20 kHz and 120 kHz. The ultrasonic wave within this frequency range can effectively inhibit the aggregation of Prussian blue crystal nuclei during the deposition process, being beneficial to the uniform dispersion of Prussian blue crystal nuclei on the surface of the layered oxide, thereby obtaining a uniform coating layer and effectively improving the coating rate. In some embodiments, the mixed solution is continuously added after heating, making the metal salt and the second sodium source in the reaction system in excess to improve the coating rate.

[0084] In some embodiments, after the deposition step of step (4), it also includes washing, filtering, and drying with deionized water, etc., to obtain a dry composite cathode material for sodium-ion batteries.

[0085] Based on the above composite cathode material for sodium-ion batteries and the preparation method of the composite cathode material for sodium-ion batteries, the embodiments of the present invention also provide a sodium-ion battery.

[0086] Specifically, the sodium-ion battery includes a positive electrode sheet and a negative electrode sheet. Among them, the positive electrode sheet contains the above-mentioned sodium-ion battery positive composite material, or the positive electrode sheet contains the sodium-ion battery positive composite material prepared by using the preparation method of the above-mentioned sodium-ion battery positive composite material. In some embodiments, the positive electrode sheet of the sodium-ion battery includes a positive electrode current collector and a positive electrode active layer stacked on the surface of the positive electrode current collector. The positive electrode active layer includes a positive electrode conductive agent, a positive electrode binder, and the above-mentioned sodium-ion battery positive composite material. Among them, the mass content of the sodium-ion battery positive composite material in the above active layer is more than 60%. The positive electrode current collector, the positive electrode conductive agent, and the positive electrode binder are common materials in the field of secondary batteries, so they will not be elaborated here. In some embodiments, the negative electrode active material in the negative electrode sheet can be any one of sodium metal, hard carbon, or soft carbon. In some embodiments, the sodium-ion battery further includes a separator or a solid electrolyte layer, and the separator or the solid electrolyte layer is used to separate the positive electrode sheet and the negative electrode sheet to prevent short circuit between the positive electrode sheet and the negative electrode sheet. The separator or the solid electrolyte layer is a well-known material in the field of secondary batteries, so it will not be elaborated here. The sodium-ion battery further includes an electrolyte. For example, the electrolyte can be a 0.4-1.5 M solution of sodium perchlorate (NaClO4) or sodium hexafluorophosphate (NaPF6) in propylene carbonate (PC) / fluoroethylene carbonate (FEC) (the volume ratio of PC to FEC is 95:5). Of course, the solvent of the electrolyte can also be a mixed solution of ethylene carbonate (EC) and PC in a volume ratio of 1:1.

[0087] To better illustrate the solution of the present invention, the following will be further explained through multiple specific examples.

[0088] Example 1

[0089] A preparation method of a layered oxide for a sodium-ion battery includes the following steps:

[0090] The NiCoMn carbonate precursor is uniformly mixed with sodium carbonate in a molar ratio of 1:1. Subsequently, the mixture is pressed into a cylindrical sheet material under a pressure of 400 MPa. The cylindrical sheet material is calcined at 1200 °C for 12 hours and then taken out and ground into powder to obtain the first sample.

[0091] The first sample obtained in Example 1 was analyzed for its morphology using a scanning electron microscope (SEM), an X-ray polycrystalline diffractometer (XRD), and an inductively coupled plasma spectroscopy (ICP-OES) instrument. The results are as Figure 1 、 Figure 2 and Table 1 show.

[0092] From Figure 1 it can be seen that there are no abnormal particles and no impurities on the surface.

[0093] From Figure 2It can be seen that the obtained material only has diffraction peaks of P2-type layered oxides. Combining Figure 1 and Figure 2 it can be seen that the obtained material is a layered oxide, and its chemical formula is NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0094] Taking the obtained first sample group as the positive electrode active material, it is mixed according to the mass ratio of positive electrode active material: binder (PVDF): positive electrode conductive agent = 8:1:1 to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, vacuum dried, and then cut and pressed. Using a sodium sheet as the negative electrode and an electrolyte of 0.5 M NaPF6 (the solvent is a mixed solution of PC and FEC with a volume ratio of 95:5), a sodium-ion battery is assembled. After standing for 24 h and measuring the stable voltage, within the voltage range of 2.0 V to 4.5 V, charge-discharge tests are carried out respectively according to the charge-discharge conditions of 0.1 C and 0.5 C rates, as shown in Table 1, Figure 8 and Figure 9 as shown. At a rate of 0.1 C (low rate), the discharge specific capacity is 191 mAh / g -1 ; at a rate of 0.5 C (high rate), the discharge specific capacity is 72 mAh / g -1 , and the specific capacity retention rate under the high-rate discharge condition is 37.6% relative to the low rate, and the specific capacity retention rate is only 29.5% after 50 cycles under the condition of 0.5 C.

[0095] Example 2

[0096] A preparation method of a positive electrode composite material for a sodium-ion battery includes the following steps:

[0097] Mix the NiCoMn carbonate precursor and sodium carbonate evenly according to a molar ratio of 1:1, and then place the mixture under a pressure of 400 MPa and press it into a cylindrical sheet material. Place the cylindrical sheet material under the condition of 1200 °C and calcine it for 12 hours, and then take it out and grind it into a powder. The chemical formula of the obtained powdery material is NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0098] After mixing the powdery material and Na4Fe(CN)6 according to a mass ratio of 9:5, disperse it in deionized water, then add ferric chloride with an equal molar mass ratio to Na4Fe(CN)6, keep it warm at 140 °C for 40 hours and then take it out, filter it, and wash it with deionized water 3 times. After drying at 120 °C for 24 hours, in NaNi 1 / 3 Co 1 / 3 Mn 1 / 3A coating layer is formed on the O2 surface to obtain the second sample.

[0099] The second sample was analyzed by X-ray diffraction (XRD), and the results are as Figure 2 shown. It can be seen from Figure 2 that the material contains both the diffraction peaks of the layered oxide and the diffraction peaks of Prussian blue, and the chemical formula of Prussian blue is Na2Fe[Fe(CN)6].

[0100] The morphology of the second sample obtained in Example 2 was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and inductively coupled plasma spectrometer (ICP-OES), and the results are as Figure 3 , Figure 4 and Table 1 shown.

[0101] It can be seen from Figure 3 that it is hardly visible that the obtained material has a layered structure, while it can be seen from Figure 4 that the second sample includes two materials, where the left part is Prussian blue material and the honeycomb material on the right part is layered oxide. Combining Figure 3 and Figure 4 it can be determined that there is a coating layer on the surface of the obtained second sample material. According to the ICP analysis results, the coating rate of the Prussian blue material layer is 45.5%, which proves that the coating has been successfully achieved and it is difficult to see the morphology of the internal particles from the surface.

[0102] The obtained second sample group was used as the positive electrode active material, and mixed according to the ratio of positive electrode active material: binder (PVDF): positive electrode conductive agent = 8:1:1 to obtain the positive electrode slurry. The positive electrode slurry was coated on the surface of the aluminum foil, dried in vacuum, and cut and pressed. Using a sodium sheet as the negative electrode and an electrolyte of 0.5 M NaPF6 (the solvent is a mixed solution of PC and FEC with a volume ratio of 95:5), a sodium-ion battery was assembled. In the voltage range of 2.0 V to 4.5 V, charge and discharge tests were carried out respectively under the charge and discharge conditions of 0.1 C and 0.5 C to obtain the cycle curves, and the results are shown in Table 1, Figure 8 and Figure 9 shown.

[0103] According to Table 1, Figure 8 and Figure 9 , it can be known that at a rate of 0.1 C, the initial discharge specific capacity is 167 mAhg -1 ; at a rate of 0.5 C, the discharge specific capacity is 108 mAhg -1 , and the specific capacity retention rate under high-rate discharge conditions is 64.7% relative to low rate. It can be seen that under high-rate charge and discharge conditions, the specific capacity retention rate is higher after coating the Prussian blue material layer than before coating the Prussian blue material layer.

[0104] From Figure 8 It can be seen that under the charge-discharge conditions of 0.5C, the specific capacity retention rate of the electrode material is 80.9% after 50 cycles, with a relatively gentle specific capacity decay rate, and it has a higher specific capacity retention rate than the electrode material without the Prussian blue material layer coated. The specific capacity retention rate of the electrode material without the Prussian blue material coated is only 29.5% after 50 cycles.

[0105] Example 3

[0106] A preparation method of a positive electrode composite material for a sodium-ion battery, comprising the following steps:

[0107] Mix the NiCoMn carbonate precursor and sodium carbonate evenly according to a molar ratio of 0.59:1, and then place it under a pressure of 15 MPa and press it into a cylindrical sheet material. Place the cylindrical sheet material under the condition of 900 °C and calcine it for 24 hours, and then take it out and grind it into powder. The chemical formula of the obtained powder material is Na 2 / 3 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0108] Mix the obtained powder material and Na4Fe(CN)6 according to a mass ratio of 9:3.5, disperse it in deionized water, and then add a mixture of ferric chloride and cobalt chloride with an equal molar mass ratio to Na4Fe(CN)6, where the molar ratio of ferric chloride to cobalt chloride is 1:1. Then keep it warm at 140 °C for 20 hours, take it out and filter, wash it with deionized water 3 times, dry it at 120 °C for 24 hours, and form a coating layer on the surface of Na 2 / 3 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2 to obtain the third sample.

[0109] Perform XRD analysis on the third sample, and the results are as Figure 2 shown.

[0110] From Figure 2 It can be seen that there are diffraction peaks of layered oxides and diffraction peaks of a small amount of other materials, and the chemical formula of the other materials is Na2Co[Fe(CN)6].

[0111] Example 4

[0112] A preparation method of a positive electrode composite material for a sodium-ion battery, comprising the following steps:

[0113] Mix the NiCoMn carbonate precursor, titanium oxide, and sodium carbonate evenly at a molar ratio of 0.9:0.1:0.9. Then, place it under a pressure of 200 MPa and press it into a cylindrical sheet material. After placing the cylindrical sheet material in a calcination condition of 1100 °C for 12 hours, take it out and grind it into a powder. The chemical formula of the obtained powder material is Na 0.9 Ti 0.1 [Ni 1 / 3Co 1 / 3 Mn 1 / 3 0.9 O2.

[0114] Mix the powder material and Na4Co(CN)6 at a mass ratio of 9:3.5. Then, disperse it in deionized water, add an iron sulfate solution with an equal molar mass ratio to Na4Co(CN)6, and then keep it warm at 140 °C for 20 hours. After taking it out, filtering, and washing it with deionized water 3 times, and drying it at 120 °C for 24 hours, a coating layer is formed on the surface of Na 0.9 Ti 0.1 [Ni 1 / 3 Co 1 / 3 Mn 1 / 3 0.9 O2. The coating layer is Na2Fe[Co(CN)6], and the fourth sample can be obtained.

[0115] Perform XRD analysis, inductively coupled plasma spectroscopy (ICP-OES) analysis, and SEM scanning on the fourth sample. The results are as Figure 2 , Figure 6 shown.

[0116] It can be seen from Figure 2 that the material mainly contains diffraction peaks of layered oxides, and at the same time has a small number of diffraction peaks of other materials. It can be seen from Figure 6 that the third sample has two different morphologies and particle sizes. Part of it is layered, and part or all of the layered material is coated with non-layered material. According to the morphology of the layered oxide, it can be confirmed that the layered morphology material in this example is the layered oxide, and the coating layer on the surface of the layered oxide is the Prussian blue material layer. It shows that the material obtained in this example is mainly layered oxide, and the coating result is shown in Table 1, and the coating rate is 30.5%.

[0117] Combined with Figure 6 and Figure 3 it can also be seen that in the sodium-ion battery cathode composite material obtained in this example, the coating rate of the Prussian blue material layer is lower than that of the sodium-ion battery cathode composite material obtained in Example 2.

[0118] ​​The obtained fourth sample group was used as the positive electrode active material and mixed in a ratio of positive electrode active material: binder (PVDF): positive electrode conductive agent = 8:1:1 by mass to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil, dried in vacuum, and then cut and pressed. A sodium sheet was used as the negative electrode, and the electrolyte was 0.5 M NaPF6 (the solvent was a mixed solution of PC and FEC in a volume ratio of 95:5). A sodium-ion battery was assembled and charged and discharged under charge and discharge conditions at a rate of 0.5C within a voltage range of 2.0V to 4.5V to obtain a cycle curve. The results are shown in Table 1, Figure 8 and Figure 9 as shown below.

[0119] From Table 1, Figure 8 and Figure 9 it can be seen that at a rate of 0.1C, the initial discharge specific capacity is 165 mAh g -1 ; at a rate of 0.5C, the discharge specific capacity is 103 mAh g -1 , and the specific capacity retention rate under high-rate discharge conditions is 62% compared to low rates.

[0120] It can also be seen from Figure 8 that under the charge and discharge conditions of 0.5C, the specific capacity retention rate of the electrode material is 80% after 50 cycles, showing a relatively gentle specific capacity decay rate.

[0121] Example 5

[0122] A method for preparing a positive electrode composite material for a sodium-ion battery, comprising the following steps:

[0123] The NiCoMn carbonate precursor was uniformly mixed with titanium oxide, lithium carbonate, and sodium carbonate in a molar ratio of 0.8:0.1:0.1:0.8, and then placed under a pressure of 200 MPa and pressed into a cylindrical sheet material. The cylindrical sheet material was calcined at 1100°C for 12 hours, taken out and ground into a powder. The chemical formula of the obtained powder material is Na 0.8 [Ni 1 / 3 Co 1 / 3 Mn 1 / 3 0.8 Ti 0.1 Li 0.1 O2.

[0124] ​Mix the powder with Na4Fe(CN)6 in a mass ratio of 9:3, disperse it in deionized water, then add manganese chloride with an equal molar mass ratio to Na4Fe(CN)6, keep it at 140 °C for 15 hours, then take it out, filter it, and wash the filter with deionized water 3 times, and dry it at 100 °C for 12 hours to form a coating layer, and the coating layer is Na2Mn[Fe(CN)6]·H2O, then the fifth sample can be obtained.

[0125] Perform XRD analysis, SEM scanning and inductively coupled plasma spectroscopy (ICP-OES) analysis on the fifth sample respectively, and the results are as shown in Figure 2 、 Figure 7 and Table 1 respectively.

[0126] From Figure 2 it can be seen that there are diffraction peaks of P2-type layered oxide and Prussian blue material in the obtained material.

[0127] From Figure 7 it can be seen that the surface of the layered oxide is almost bare, and there is a small amount of non-layered oxide material on the surface of the layered oxide, and these non-layered oxide materials are the Prussian blue material layer, that is, Na2Mn[Fe(CN)6]·H2O. From this, it can be seen that the coating rate is relatively low. Combining Figure 7 and Figure 6 it can be seen that the coating rate of the Prussian blue material layer in Example 5 is lower than that in Example 4.

[0128] Combining Figure 7 、 Figure 6 and Figure 3 it can be seen that the holding and standing time has an impact on the coating rate. The longer the holding and standing time, the higher the coating rate and the better the coating effect.

[0129] Example 6

[0130] A preparation method of a composite cathode material for a sodium-ion battery, comprising the following steps:

[0131] Uniformly mix the NiCoMn carbonate precursor with titanium oxide, lithium carbonate, sodium carbonate, and sodium fluoride in a molar ratio of 0.8:0.1:0.1:0.62:0.05, and then press it into a cylindrical sheet material under a pressure of 200 MPa. Place the cylindrical sheet material in a furnace at 1100 °C and calcine it for 12 hours, then take it out and grind it into a powder. The chemical formula of the obtained powder material is: Na 0.67 (Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ) 0.8 Ti 0.1 Li 0.1 O0.95 F 0.05 。

[0132] Mix the powdery material with Na4Fe(CN)6 in a mass ratio of 9:2, disperse it in deionized water, then add nickel chloride with an equimolar mass ratio to Na4Fe(CN)6, keep it warm at 140 °C for 20 hours, take it out, filter it, and wash the filter with deionized water 3 times, dry it at 120 °C for 24 hours to obtain a coating layer, and the coating layer is Na2Ni[Fe(CN)6], then the sixth sample can be obtained.

[0133] Perform XRD analysis and inductively coupled plasma spectroscopy (ICP-OES) analysis on the sixth sample, and the results are as Figure 2 shown in Table 1.

[0134] From Figure 2 it can be seen that the material mainly contains diffraction peaks of layered materials, and it can also be seen that the sixth sample includes layered oxide Na 0.67 (Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ) 0.8 Ti 0.1 Li 0.1 O 0.95 F 0.05 and a Prussian blue material layer Na2Ni[Fe(CN)6] coated on the surface of the layered oxide. As shown in Table 1, the coating rate is 24.8%.

[0135] Take the obtained sixth sample group as the positive electrode active material, mix it according to the mass ratio of positive electrode active material: binder (PVDF): positive electrode conductive agent = 8:1:1 to obtain a positive electrode slurry. Coat the positive electrode slurry on the surface of aluminum foil, dry it in vacuum, and then cut and press it. Use a sodium sheet as the negative electrode and an electrolyte of 0.5 M NaPF6 (the solvent is a mixed solution of PC and FEC with a volume ratio of 95:5) to assemble a sodium-ion battery. In the voltage range of 2.0 V to 4.5 V, perform charge and discharge tests according to the charge and discharge conditions at a rate of 0.5 C to obtain a cycle curve. The results are shown in Table 1, Figure 8 and Figure 9 shown.

[0136] From Table 1, Figure 8 and Figure 9 it can be known that at a rate of 0.1 C, the initial discharge specific capacity is 162 mAhg -1 ; at a rate of 0.5 C, the discharge specific capacity is 93 mAhg -1 , and the specific capacity retention rate under high-rate discharge conditions is 57% relative to low rate.

[0137] FromFigure 8 It can also be seen that under the charge-discharge conditions of 0.5C, the specific capacity retention rate of the electrode material is 68.2% after 50 cycles, and it has a relatively gentle specific capacity decay rate.

[0138] Table 1 Coating rate and cycling performance of each example

[0139]

[0140] According to Table 1, Figure 8 and Figure 9 It can also be seen that after forming a Prussian blue material coating layer on the surface of the layered oxide and using it as the positive electrode active material, the cycling performance and rate performance of the sodium-ion battery can be effectively improved, thereby improving the cycle service life of the sodium-ion battery. And before a certain value of the coating rate of the Prussian blue material layer, with the increase of the coating rate, the cycling performance and rate performance gradually increase. However, after exceeding a certain coating rate, when the coating rate is further increased, the cycling performance and rate performance show a downward trend. Thus, it can be seen that the coating rate of the Prussian blue material on the layered oxide is more suitable at 25% - 45%, and when the coating rate is 30.5%, the cycling performance and rate performance are more excellent than those at 25% or 45%.

[0141] From the above Examples 1 to 6, it can be seen that the positive electrode composite material of the sodium-ion battery prepared in the embodiments of the present invention can effectively isolate the layered oxide from the outside world after coating the Prussian blue material layer on the surface of the layered oxide, improve the stability of the composite material. Therefore, when the composite material is assembled into a sodium-ion battery as the positive electrode active material, it is beneficial to delay the specific capacity decay rate of the sodium-ion battery, improve the cycling performance and rate performance, and effectively extend the service life of the sodium-ion battery.

[0142] The above is only the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A composite cathode material for a sodium-ion battery, characterized in that, The positive composite material of the sodium-ion battery includes a layered oxide and a Prussian blue material layer coated on the surface of the layered oxide. The coating rate of the Prussian blue material layer on the layered oxide is between 25% and 45%, and the particle diameter of the layered oxide is 10 nm to 200 μm; Among them, the layered oxide has a chemical formula shown in General Formula I: Na α MO 2-β X β (I); M is selected from one or more of Ni, Mn, Fe, Co, Zn, Sn, Mg, Li, Zr, and Ti; X is selected from one or more of Cl, F, and Br; 0.4<α<1.2，0≤β<0.2； The Prussian blue material layer has a chemical formula shown in General Formula II: A γ M1 δ [M2(CN)6] μ ·θH2O(II); A is Na or Li; M1 is selected from one or more of Zn, Ni, Mn, Fe, Co, Ce, Cu, and V; M2 is selected from one or more of Zn, Ni, Mn, Fe, Co, Cu, and Ce; 0 < γ ≤ 4, 0 ≤ δ < 4, 0 ≤ θ < 8, 0 < μ ≤ 1.

2. The positive electrode composite material of the sodium ion battery according to claim 1, wherein The positive composite material of the sodium-ion battery further includes at least one of the features in items (2) to (4): (2) The thickness of the Prussian blue material layer is 2 nm to 200 nm; (3) The layered oxide includes NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Na 2 / 3 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Na 0.9 Ti 0.1 [Ni 1 / 3 Co 1 / 3Mn 1 / 3 0.9 O2, Na 0.8 [Ni 1 / 3 Co 1 / 3 Mn 1 / 3 0.8 Ti 0.1 Li 0.1 O2, Na 0.67 Ni 0.33 Mn 0.67 O2, Na 0.8 Li 0.1 Ni 0.23 Mn 0.67 O2, NaMg 0.2 Ni 0.1 Li 0.2 Mn 0.7 O2 and Na 0.67 (Ni 1 / 3 Mn 1 / 3 Co 1 / 3 ) 0.8 Ti 0.1 Li 0.1 O 1.95 F 0.05 at least one of;​​ (4) The Prussian blue material layer includes at least one of Na2Fe[Fe(CN)6], Na2Co[Fe(CN)6], Na2Fe[Co(CN)6], Na2Mn[Fe(CN)6]·H2O, Na2Ni[Fe(CN)6], Na2Mn[Mn(CN)6], NaV[Fe(CN)6], Na4[Fe(CN)6], Na 0.61 Fe[Fe(CN)6], Na 1.94 Mn 0.18 Co 0.17 Ni 0.03 Fe 0.62 [Fe(CN)6] 0.93 、Na 1.56 Fe[Fe(CN)6]·3.1H2O.

3. The positive electrode composite material of the sodium ion battery according to claim 1 or 2, characterized in that The coating rate of the Prussian blue material layer on the layered oxide is 30.5%.

4. A method for preparing a positive electrode composite material of a sodium ion battery according to any one of claims 1 to 3, characterized in that, Including the following steps: Mix the precursor and the first sodium source, and perform tablet pressing treatment to obtain a sheet material; Calcine the sheet material at 500 °C to 1100 °C or 1200 °C to obtain a layered oxide; Dissolve the metal salt and the second sodium source in a solvent to obtain a mixed solution; Put the layered oxide into the mixed solution, heat and keep warm, so that the solute in the mixed solution deposits on the surface of the layered oxide to obtain the positive composite material of the sodium-ion battery.

5. The preparation method of the composite cathode material for a sodium-ion battery according to claim 4, characterized in that, The precursor includes at least one of M(OH)2 and M metal carbonates, where M is selected from one or more of Ni, Mn, Fe, Co, Zn, Sn, Mg, Li, Zr, and Ti; The first sodium source is selected from at least one of sodium nitrate, sodium chlorate, sodium sulfate, sodium carbonate, and sodium fluoride.

6. The preparation method of the composite cathode material for a sodium ion battery according to any one of claims 4 or 5, characterized in that, The molar ratio of the precursor to the first sodium source is (0.44 to 1.2):

1.

7. The preparation method of the positive electrode composite material for a sodium ion battery according to any one of claims 4 or 5, characterized in that The metal salt includes at least one of the sulfate of M1 and the chloride of M1 and the cyanide of M2. M1 is selected from one or more of Zn, Ni, Mn, Fe, Co, Ce, Cu, and V; M2 is selected from one or more of Zn, Ni, Mn, Fe, Co, Cu, and Ce; The second sodium source is selected from at least one of sodium nitrate, sodium chlorate, and sodium sulfate.

8. The preparation method of the sodium ion battery cathode composite material according to any one of claims 4 or 5, characterized in that, The molar ratio of the metal salt to the second sodium source is (0.5 to 4.0):

1.

9. The preparation method of the composite cathode material for a sodium-ion battery according to any one of claims 4 or 5, characterized in that The heating temperature is 450 °C to 880 °C, and the heat preservation time is 1 h to 72 h; And / or, before putting the layered oxide into the mixed solution, it further includes the step of crushing the layered oxide into micro-nano powders with a particle size range of 20 nm to 500 μm; And / or, ultrasonic conditions are applied during the heating and heat preservation.

10. A sodium-ion battery, comprising a positive electrode sheet and a negative electrode sheet, characterized in that, The positive electrode sheet contains the sodium-ion battery positive electrode composite material described in any one of claims 1 to 3, or the positive electrode sheet contains the sodium-ion battery positive electrode composite material prepared by using the preparation method of the sodium-ion battery positive electrode composite material described in any one of claims 4 to 9.

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