A positive electrode active material, a method for preparing the same, and an application thereof

Abstract

A positive electrode active material, its preparation method, and its application are disclosed, relating to the field of battery materials technology. This positive electrode active material has a single-crystal structure and its general chemical formula is Na. x Ni y Mn z A (1‑y‑z) O2, 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, Al; the sodium interlayer spacing d of the positive electrode active material O‑Na‑O The interplanar spacing d of the (003) diffraction peak 003 The ratio R is 0.58-0.70. Polycrystalline material is mixed with deionized water in a certain proportion, stirred at a specific rate for a period of time, filtered, the filter cake is collected and dried to obtain single crystal material; then the single crystal material is mixed with sodium source and sintered, cooled to obtain positive electrode active material.

Description

A positive electrode active material and a preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a positive electrode active material and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries (SIBs) are considered as one of the main candidate technologies for large-scale energy storage applications due to their low cost, safety and environmental friendliness. The development of positive electrode active materials determines the final performance and commercialization process of sodium-ion batteries. Currently, the positive electrode active materials of sodium-ion batteries mainly include transition metal oxides, Prussian blue compounds, polyanion compounds and other organic compounds, etc. These different structural types of sodium storage positive electrode active materials have different sodium ion transport paths and barriers, resulting in different electrochemical performances of the positive electrode active materials.

[0003] The transition metal oxide can be represented as Na x TMO2, where TM is a transition metal element and x is the stoichiometric number of sodium. The transition metal oxide can be divided into layered metal oxides (TMOs, referred to as layered oxides) and tunnel structure oxides according to its crystal structure characteristics. The layered oxide positive electrode active material has a simple preparation method, high specific capacity, and diversity in composition, i.e., different types and proportions of elements can be used to replace the transition metal position, providing a large exploration space for basic research and industrial application. In addition, the structure of the layered oxide positive electrode active material is customizable, and through appropriate component adjustment and process adjustment, a layered oxide with a target structure can be prepared, which makes the layered oxide the most promising positive electrode active material for commercial application of sodium-ion batteries. During the full battery cycle, compared with polycrystalline layered oxide materials, single crystal materials have fewer particle cracks and surface areas, and higher compaction density, which is beneficial to increase the energy density and improve the conductivity of the electrode. However, the single crystal layered oxide material currently faces problems such as instability in air storage, high preparation difficulty and cost, and poor electrochemical performance, which seriously restricts the development of the commercialization process of sodium-ion batteries.

[0004] SUMMARY

[0005] The present application provides a positive electrode active material, which aims to at least solve one of the above problems to some extent.

[0006] In a first aspect, the present application provides a positive electrode active material, which has a single crystal structure and a chemical formula of Na x Ni y Mn z A (1-y-z)O2, wherein 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, Al; the sodium interlayer spacing d O-Na-O The ratio R of the (003) diffraction peak interplanar spacing d 003 is 0.58-0.70.

[0007] In an alternative embodiment, the d O-Na-O is

[0008] In an alternative embodiment, the d O-Na-O is

[0009] In an alternative embodiment, the d 003 is

[0010] In an alternative embodiment, the d 003 is

[0011] In an alternative embodiment, the R is 0.60-0.64.

[0012] In an alternative embodiment, 0.6≤x≤1.

[0013] In an alternative embodiment, 0.05≤y≤0.6.

[0014] In an alternative embodiment, 0.05≤z≤0.6.

[0015] In an alternative embodiment, the particle size Dv50 of the positive electrode active material is 7-15 μm.

[0016] In an alternative embodiment, the compaction density of the positive electrode active material under 3 tons of pressure is 3.2-3.4 g / cm 3 above.

[0017] In an alternative embodiment, the compaction density of the positive electrode active material under 3 tons of pressure is 3.4-3.5 g / cm 3 -3.5 g / cm 3 .

[0018] In a second aspect, the present application provides a preparation method of a positive electrode active material, comprising the following steps:

[0019] The polycrystalline material is mixed with deionized water at a mass ratio of 1:1-30, stirred at a speed of 200 r / min-1600 r / min for 0.1 min-10 min, filtered, the filter cake is collected, and dried to obtain a single crystal material; the chemical general formula of the polycrystalline material is Na x Ni y Mn z A (1-y-z) O2, wherein, 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, Al;

[0020] The single crystal material is mixed with a sodium source at a molar ratio of 1:0.01-0.1, and then sintering treatment is performed, and cooled to obtain a positive electrode active material.

[0021] In an alternative embodiment, the mass ratio of the polycrystalline material to deionized water is 1:5-25.

[0022] In an alternative embodiment, the speed is 600 r / min-1400 r / min.

[0023] In an alternative embodiment, the sintering treatment conditions include, increasing the temperature to 850℃-920℃ at a speed of 2℃ / min-3℃ / min and maintaining for 8h-14h.

[0024] In a third aspect, the application provides a positive electrode sheet, comprising:

[0025] A positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to the first aspect of the application or the positive electrode active material prepared by the preparation method according to the second aspect of the application.

[0026] In a fourth aspect, the application provides a secondary battery comprising the positive electrode sheet according to the third aspect of the application.

[0027] In a fifth aspect, the application provides an electric device comprising the secondary battery according to the fourth aspect of the application.

[0028] The technical scheme of the application has the following advantages:

[0029] The positive electrode active material provided by the application has a single crystal structure, and the chemical general formula is Na x Ni y Mn z A (1-y-z)O2, wherein, 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, Al; the sodium interlayer spacing d O-Na-O the ratio R of the interplanar spacing d of the (003) diffraction peak 003 is 0.58-0.70. By fine-tuning the contents of Na, Ni, Mn elements and doping a proper proportion of specific metal element A, while adjusting the sodium interlayer spacing d O-Na-O of the (003) diffraction peak 003 of the (003) diffraction peak is within the above range, the obtained positive electrode active material has a larger grain size and a higher compaction density, which is beneficial to improving the battery capacity.

[0030] Additional aspects and advantages of the embodiments will be described in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following description and accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings required to be used in the description of the specific embodiments or the prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0032] Figure 1 is an SEM image of the polycrystalline material prepared in Example 1 of the present application.

[0033] Figure 2 is an SEM image of the single-crystal material prepared in Example 1 of the present application.

[0034] Figure 3 is an SEM image of the positive electrode active material prepared in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof. Unless otherwise noted, the terms "plurality" and "a plurality" as used herein encompass both "multiple" and "two or more."

[0037] In the description of the embodiments of the present application, the meaning of "plurality" is two or more, unless explicitly and specifically defined otherwise.

[0038] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all directed to the same embodiment, or to a single alternative embodiment.

[0039] "Ranges" disclosed herein are defined, described and covered, either explicitly or implicitly, with their lower and upper limits, given that a range is defined by selecting a lower limit and an upper limit, which delimit the particular range. Ranges defined in such a way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e. any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if minimum range values of 1 and 2 are listed, and if maximum range values of 3, 4 and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing all the individual numerical combinations of a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all the real numbers between "0-5" have been listed herein, "0-5" is just a shorthand way of indicating these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] In the description of the embodiments of the present application, the term "and / or", only describes an association relationship of associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in the text generally means that the front and rear associated objects have an "or" relationship.

[0041] The compaction density of the positive electrode active material is subject to the micro-morphology of the material, which includes the micro-morphology of the material and the primary and secondary particle size distribution. At present, single-crystal sodium battery layered oxides synthesized by a wet method can be obtained in a relatively ideal morphology by the following methods, for example, a high-temperature sintering method: heating the precursor to a very high temperature (several hundred degrees higher than the sintering temperature of the polycrystalline material) to promote grain growth, but this method will cause serious particle agglomeration and increase the production cost; for example, a molten salt synthesis method: mixing an extra sodium salt with the precursor to form a molten salt phase during calcination to promote dissolution and recrystallization, but this method requires an excess of sodium salt, resulting in excessive residual alkali, thereby affecting the subsequent electrochemical performance; for example, a fluxing element sintering method: mixing a large amount of fluxing elements during sintering to promote single crystal formation, which can reduce the sintering temperature of the single crystal and will not cause excessive residual alkali, but it limits the element regulation of the single crystal material, thereby negatively affecting the electrochemical performance of the material.

[0042] To solve the problems existing in the above-mentioned related technologies, according to a first aspect of the present application, the present application provides a positive electrode active material, the positive electrode active material has a single crystal structure, and its chemical general formula is Na x Ni y Mn z A (1-y-z) O2, wherein 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, and Al; the sodium interlayer spacing d O-Na-O of the positive electrode active material is 0.28-0.32 nm, and the ratio R of the interplanar spacing d 003 of the (003) diffraction peak to the interplanar spacing d O-Na-O of the (003) diffraction peak is 0.58-0.70.

[0043] Applicants have found that by finely adjusting the contents of Na, Ni, and Mn elements and doping a proper proportion of a specific metal element A, while adjusting the sodium interlayer spacing d O-Na-O of the material to be within the above range, the ratio R of the interplanar spacing d 003 of the (003) diffraction peak to the interplanar spacing d O-Na-O of the (003) diffraction peak, the positive electrode active material obtained thereby has a large grain size and a high compaction density, which is beneficial to improving the battery capacity. As an example, the ratio R of the interplanar spacing d 003 of the (003) diffraction peak to the interplanar spacing d O-Na-O of the (003) diffraction peak can be 0.58, 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, or within a range consisting of any of the above values.

[0044] As understood by those skilled in the art, the (003) crystal plane is almost full of transition metal ions (TM ion), and the interplanar spacing d 003That is, the TM-O-Na-O-TM spacing, therefore when d O-Na-O With d 003 When the ratio R is large, it can change the Na content in the crystalline material. + The stacking pattern promotes its transformation into a layered oxide P2-type stacked structure. However, when the R value is too large (R>0.7), it will lead to excessive hydrolysis of the material, resulting in a large amount of H3O. + Upon entering the sodium layer, the particles hydrolyze into flakes, resulting in extremely low compaction density; if the R value is too small (R < 0.58), the interlayer spacing of the sodium layers decreases, causing Na... + The transition to an O3-type stacked structure leads to a decrease in the material's compaction density. Introducing at least one metal element, such as Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, or Al, into the transition metal sites and / or sodium sites of the positive electrode active material can reduce the sodium interlayer spacing (d) during the hydrolysis of the polycrystalline material. O-Na-O Inhibit Na in aquatic environments + Excessive precipitation of the material regulates the degree of hydrolysis, thereby helping to form larger single-crystal primary particles and thus increasing the compaction density of the material.

[0045] X-ray diffraction (XRD) technology has wide applications in the detection of active materials for sodium-ion batteries. Through XRD analysis, the crystal structure type of the material and the occupancy and proportion of elements in the material can be determined. Those skilled in the art will understand that in the XRD pattern of active materials for cathodes, the interplanar spacing of the (003) diffraction peaks, also known as the interlayer spacing of the 003 crystal plane, is denoted as d. 003 The distance between a Na atom and the two adjacent O atoms is called the sodium interlayer spacing, denoted as d. O-Na-O The interplanar spacing d of the (003) diffraction peak of the positive electrode active material 003 and sodium interlayer spacing d O-Na-O All of these are well-known in the field. XRD patterns can be obtained using an X-ray diffractometer, and then the tested patterns can be refined using Highscore software combined with the Rietvald method to obtain d. 003 and d O-Na-O As an example, this application uses a Bruker D8 Advance X-ray diffractometer with CuKα rays as the radiation source. The scanning wavelength range of the 2θ angle is 10°-80°, and the scanning rate is 0.025° / s to obtain XRD patterns.

[0046] In one alternative implementation, the d O-Na-O for As an example, the sodium interlayer spacing d O-Na-O It can be It is equal to or falls within the range of any of the above values.

[0047] In an alternative embodiment, the d 003 For example, the d For example, the d 003 For example, the d For example, the d

[0048] In an alternative embodiment, the Na x For example, the d y For example, the d z For example, the d (1-y-z) For example, the d O-Na-O For example, the d 003 , and the ratio R can be adjusted to further improve the grain size and the tap density of the material. For example, the value of x can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or within a range formed by any of the above values; the value of y can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, or within a range formed by any of the above values; and the value of z can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, or within a range formed by any of the above values.

[0049] In an alternative embodiment, the particle size Dv50 of the positive electrode active material is 7-15 μm. A larger particle size is beneficial to improve the tap density of the positive electrode active material, but if the particle size is too large, it will be difficult to hydrolyze the polycrystalline particles into single-crystal particles while maintaining a certain Na content. For example, the particle size Dv50 of the positive electrode active material can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or within a range formed by any of the above values.

[0050] Those skilled in the art will understand that higher compaction density allows for a larger contact area between sodium ions and the electrolyte in the positive electrode active material, increasing energy density. Furthermore, higher compaction density can reduce internal voids in the positive electrode active material, improving electrode conductivity and facilitating smoother electron and ion transport, thereby enhancing battery capacity and cycle performance. However, higher compaction density is not always better. Excessive compaction density results in smaller voids, preventing electrolyte penetration and leading to decreased electrode capacity. It also increases internal electrode stress, potentially causing structural damage and, in extreme cases, short circuits or explosions. Excessively high or low compaction densities can also cause structural changes and polarization in the positive electrode active material, affecting battery cycle performance. Therefore, this application addresses this issue by precisely controlling the content of Na, Ni, and Mn elements, and doping with appropriate proportions of other metal elements (A), while simultaneously adjusting the sodium interlayer spacing (d) of the material. O-Na-O The interplanar spacing d of the (003) diffraction peak 003 A ratio R between 0.58 and 0.70 yields a cathode active material with appropriate compaction density, which is beneficial for improving battery capacity, cycle performance, and safety. In some embodiments, the cathode active material of this application has a compaction density of 3.2 g / cm³ under 3 tons of pressure. 3 The above, for example, 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 It is equal to or falls within the range of any of the above values.

[0051] According to a second aspect of this application, a method for preparing a positive electrode active material is provided, comprising the following steps:

[0052] Polycrystalline material and deionized water were mixed at a mass ratio of 1:1-30, stirred at a speed of 200 r / min-1600 r / min for 0.1 min-10 min, filtered, the filter cake was collected, and dried to obtain single-crystal material; the general chemical formula of the polycrystalline material is Na. x Ni y Mn z A (1-y-z) O2, wherein 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-yz, and A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, and Al;

[0053] The single crystal material was mixed with a sodium source at a molar ratio of 1:0.01-0.1 and then sintered and cooled to obtain the positive electrode active material.

[0054] The present application takes advantage of the poor water stability of the polycrystalline material, mixes the polycrystalline material with water, so that the Na + dissolved in water will be precipitated, while the internal Na + cannot be completely precipitated due to the reduction of the sodium layer spacing, so that the polycrystalline material only undergoes moderate hydrolysis, forming single-crystal primary particles with a larger particle size, thereby facilitating the improvement of the compaction density of the positive active material. The applicant has found that the more water added and the faster the stirring speed, the faster the hydrolysis of the polycrystalline material, and more Na + will be precipitated in the same time; however, if the hydrolysis speed is too fast and the hydrolysis time is too long, the material will precipitate too much Na + , and the single-crystal particles formed thereby will have cracks, and if the hydrolysis speed is too slow and the hydrolysis time is too short, the material will still maintain a polycrystalline morphology and cannot obtain single-crystal particles, therefore, by controlling the water-to-material ratio, stirring speed and stirring time within the above ranges, the moderate hydrolysis of the polycrystalline material can be regulated, thereby obtaining single-crystal material with an ideal morphology. As an example, the mass ratio of polycrystalline material to deionized water can be 1:1, 1:3, 1:5, 1:7, 1:10, 1:15, 1:20, 1:25, 1:30, etc. or within a range consisting of any of the above values; the stirring speed can be, for example, 200 r / min, 400 r / min, 600 r / min, 800 r / min, 1000 r / min, 1200 r / min, 1400 r / min, 1600 r / min, etc. or within a range consisting of any of the above values; the stirring time can be, for example, 0.1 min, 1 min, 3 min, 5 min, 7 min, 10 min, etc. or within a range consisting of any of the above values. The applicant has found that during the hydrolysis of the polycrystalline material, the Na + on the surface and inside the material will also be precipitated to a certain extent, resulting in a decrease in sodium content, therefore, sodium needs to be supplemented after hydrolysis to avoid capacity loss. As an example, the molar ratio of single-crystal material to sodium source can be 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.1, etc. or within a range consisting of any of the above values; the sodium source is selected from at least one of sodium carbonate and sodium hydroxide.

[0055] Compared with the high-temperature sintering method, the preparation method of the present application has a low sintering temperature, thus being conducive to reducing the production cost. Compared with the molten salt synthesis method and the fluxing element sintering method, the present application does not need to add sodium salt or fluxing agent, which is not only conducive to cost control, but more importantly, does not affect the electrochemical performance of the material. Therefore, the preparation method of the present application can prepare a positive electrode active material with good electrochemical performance at a low cost, and since the positive electrode active material is prepared by polycrystalline hydrolysis, the present application can improve the defect of instability of the material in air to some extent, and the hydrolysis step can also remove part of the residual alkali on the surface of the material, which is conducive to improving the initial efficiency and cycle performance of the battery.

[0056] In an alternative embodiment, the conditions of the sintering treatment include heating to 850-920°C at a rate of 2-3°C / min and holding for 8-14h. The applicant has found that, after sodium supplementation, the single crystal material is sintered under the above conditions, which can convert the sodium-deficient phase formed on the surface of the material due to hydrolysis into a normal sodium ratio layered oxide, thus being more conducive to the repair of the material structure. If the heating rate is too fast, the sintering temperature is too high, or the sintering time is too long, it is not conducive to the repair of the layered structure or will cause a large amount of sodium loss, resulting in poor capacity or cycle performance of the material.

[0057] As understood by those skilled in the art, the Ni y Mn z (OH)2precursor can be prepared by coprecipitation, and then the precursor is mixed with a sodium source and an A salt and sintered to obtain a polycrystalline material with a chemical formula of Na x Ni y Mn z A (1-y-z) O2(wherein, 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, and A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, and Al), which is a conventional method for preparing layered oxide positive electrode active materials in the art. Of course, the above polycrystalline material can also be purchased through regular channels.

[0058] In some embodiments, the above polycrystalline material can be prepared by the following method:

[0059] 1) Precursor preparation: Dissolve a soluble nickel salt and a soluble manganese salt in deionized water to obtain a salt-containing solution, add it to a reactor, and simultaneously add a precipitating agent and a chelating agent to the reactor, stir, precipitate, and obtain a Ni y Mn z (OH)2precursor after post-treatment;

[0060] The soluble nickel salt is at least one of a sulfate salt, a chloride salt, and an acetate salt of nickel, the soluble manganese salt is at least one of a sulfate salt, a chloride salt, and an acetate salt of manganese, the molar ratio of nickel to manganese in the salt-containing solution is 0.3-2.5:1, the precipitant is at least one of sodium carbonate and sodium hydroxide, the chelating agent is at least one of ammonium bicarbonate, ammonium carbonate, and ammonia, and the molar ratio of the chelating agent to the total amount of metal elements (nickel and manganese) is 1-4:1.

[0061] 2) adding the precursor, the A salt, and the sodium source prepared in step 1) into a ball mill, then adding a certain amount of deionized water for ultrasonic-assisted ball milling, drying after ball milling for a period of time to obtain a mixture, sintering the mixture, and then cooling to room temperature to obtain a polycrystalline material;

[0062] The A salt is at least one of a sulfate salt, a chloride salt, and an acetate salt of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, and Al, the ratio of the A salt to the total molar amount of nickel and manganese in the precursor is 0.01-9:1, the sodium source is at least one of sodium carbonate and sodium hydroxide, the ratio of the sodium source to the total molar amount of nickel and manganese in the precursor is 0.9-1:1, the concentration of the sodium source solution in the ball mill is 0.2-2 mol / L, the ultrasonic frequency of the ultrasonic-assisted ball mill is 10-50 kHz, and the stirring rod rotation speed is 200-800 r / min; the sintering conditions include: an air gas flow rate of 1.5-3 L / min, a heating rate of 2-3 ℃ / min to 650-750 ℃, a holding time of 4-7 h, a second heating to 850-900 ℃, and a holding time of 8-12 h; and the cooling rate is 100-150 ℃ / h.

[0063] According to a third aspect of the present application, the present application provides a positive electrode tab, which comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to the first aspect of the present application or the positive electrode active material prepared by the preparation method according to the second aspect of the present application.

[0064] As can be understood by those skilled in the art, the positive electrode tab of the present application has the advantages of high compaction density, which is beneficial to improving the capacity, cycle performance, and safety of the battery.

[0065] According to a fourth aspect of the present application, the present application provides a secondary battery comprising the positive electrode tab according to the third aspect of the present application.

[0066] As can be understood by those skilled in the art, the secondary battery of the present application has the advantages of large capacity, good cycle performance, and high safety.

[0067] The following describes a sodium-ion secondary battery according to the present application.

[0068] [Positive electrode sheet]

[0069] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material.

[0070] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0071] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. As a metal foil, for example, an aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0072] In the present application, the positive electrode active material is a compound capable of reversibly intercalating and deintercalating Na + As an example, the positive electrode active material includes a transition metal oxide, a polyanion compound, a Prussian blue analog, etc.

[0073] In some embodiments, the positive electrode active material is a transition metal oxide, and the positive electrode active material layer in the positive electrode sheet according to the present application is not limited to other positive electrode active materials other than the layered oxide provided in the present application. As an example, Na x MO2 or Na y M2O4 (where M is a transition metal, 0≤x≤1, 0≤y≤2) indicates a sodium-containing composite oxide, a spinel-like oxide, a layered metal chalcogenide, an olivine structure, etc. For example, sodium cobalt oxides such as NaCoO2, sodium manganese oxides such as NaMn2O4, sodium nickel oxides such as NaNiO2, sodium titanium oxides such as NaTiO2, Na 4 / 3 Ti 5 / 3 O4, sodium manganese nickel composite oxides, sodium manganese nickel cobalt composite oxides; materials having an olivine-type crystal structure such as NaMPO4 (M = Fe, Mn, Ni), etc.

[0074] In some embodiments, the positive electrode active material is optionally a sodium-containing composite oxide having a layered structure or a spinel-like structure, such as NaCoO2, NaMn2O4, NaNi1 / 2 Mn 1 / 2 O2, etc. represented by NaNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, NaNi 0.6 Mn 0.2 Co 0.2 O2, etc. represented by NaNi 1-x-y-z Co x Al y Mg z O2(wherein, 0≤x≤1, 0≤y≤0.1, 0≤z≤0.1, 0≤1-x-y-z≤1), etc. containing sodium complex oxides. Further, the containing sodium complex oxides in which a part of the constituent elements is substituted by Ge, Ti, Zr, Mg, Al, Mo, Sn, etc. additive elements are also included in the scope of the present application.

[0075] In some embodiments, optionally, the positive active material is a polyanionic compound. As an example, the polyanionic compound can be a compound having sodium ions, transition metal ions, and tetrahedral (YO4) n- anion units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; and n represents the valence of (YO4) n- . The polyanionic compound can also be a compound having sodium ions, transition metal ions, tetrahedral (YO4) n- anion units, and halogen anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, n represents the valence of (YO4) n- ; and the halogen can be at least one of F, Cl, or Br. The polyanionic compound can also be a compound having sodium ions, tetrahedral (YO4) n- anion units, polyhedral (ZO y ) m+ m anions. Y can be at least one of P, S, and Si, n represents the valence of (YO4) n- ; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents the valence of (ZO y m+ ​valence; the halogen can be at least one of F, CI, and Br. The polyanionic compound is, for example, NaFePO4, Na3V2(PO4)3, NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1) at least one.

[0076] In some embodiments, the positive active material is optionally a Prussian blue analog. As an example, the Prussian blue analog can be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN - ) in the compound. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The Prussian blue analog is, for example, Na a Me b Me' c (CN)6, where Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0

[0077] In some embodiments, the positive active material layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0078] In some embodiments, the binder is optionally 0.1-3.5%, optionally 0.5-2.5%, of the total weight of the positive active material layer.

[0079] In some embodiments, the positive active material layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0080] In some embodiments, the conductive agent is optionally 0.05-5%, optionally 0.5-3%, of the total weight of the positive active material layer.

[0081] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and subjecting to processes such as drying, cold pressing, etc. to obtain the positive electrode sheet.

[0082] [Negative electrode sheet]

[0083] In the sodium-ion battery, the negative electrode sheet generally comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material.

[0084] The negative electrode sheet can also only comprise a negative electrode current collector, i.e. does not contain a negative electrode active material. The negative electrode sheet can also comprise a pre-deposited metal phase on the negative electrode current collector. The negative electrode current collector can be made of a conventional metal foil, a carbon-coated metal foil or a porous metal plate, etc. As an example, the negative electrode current collector can be made of a copper foil or an aluminum foil.

[0085] The specific type of the negative electrode active material is not limited, and any active material known in the art that can be used in the negative electrode of a sodium-ion battery can be used, and a person skilled in the art can select according to actual needs. As an example, the negative electrode active material can include but is not limited to one or more of sodium metal, a carbon material, an alloy material, a transition metal oxide and / or sulfide, a phosphorus-based material, and a titanate material. Specifically, the carbon material can include one or more of hard carbon, soft carbon, amorphous carbon, and nanostructured carbon material; the alloy material can include an alloy material formed by one or more of Si, Ge, Sn, Pb, and Sb; the transition metal oxide and sulfide can have a general formula of M x N y , wherein M includes one or more of Fe, Co, Ni, Mn, Sn, Mo, Sb, and V, and N includes O or S; the phosphorus-based material can include one or more of red phosphorus, white phosphorus, and black phosphorus; and the titanate material can include one or more of Na2Ti3O7, Na2Ti6O 13 , Na4Ti5O 12 , Li4Ti5O 12 , and NaTi2(PO4)3. These materials can be obtained through commercial channels.

[0086] The negative electrode active material layer can also optionally include a binder and a conductive agent, wherein the conductive agent is used to improve the conductivity of the negative electrode active material layer, and the binder is used to firmly bond the negative electrode active material and the conductive agent to the negative electrode current collector. The type of the conductive agent and the binder is not specifically limited in the present application, and can be selected according to actual needs.

[0087] As an example, the conductive agent can include one or more of super-p carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] As an example, the binder can include one or more of styrene butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0089] The negative active material layer can further optionally include a thickening agent, such as carboxymethyl cellulose (CMC). However, the present application is not limited thereto, and other materials that can be used as a thickening agent for a sodium-ion battery negative electrode sheet can also be used.

[0090] [Separator]

[0091] As the separator described above, the present application is not particularly limited, and any known porous structure separator having electrochemical stability and mechanical stability can be used according to the actual needs, and for example, can be a single layer or a multi-layer film including one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0092] [Electrolyte]

[0093] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The electrolyte can include an electrolyte salt and a solvent.

[0094] As an example, the electrolyte sodium salt includes at least one of sodium hexafluorophosphate, sodium difluoro oxalate borate, sodium tetrafluoroborate, sodium bisoxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethylsulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0095] As an example, the solvent can include one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), dimethoxyethane (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, diethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, tetrahydrofuran, methyl tetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, tetrahydropyran, methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0096] In some embodiments, the electrolyte further comprises an additive. For example, the additive can comprise a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that improves certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high-temperature performance of the battery, or an additive that improves low-temperature performance of the battery.

[0097] The sodium-ion solid-state electrolyte can be any of various sodium-ion solid-state electrolytes commonly used in the art.

[0098] In some embodiments, the sodium-ion solid-state electrolyte comprises, but is not limited to: NASICON type: Na(1+x9+2y5)Zr (2-y5) M y5 P (3-x9) Si x9 O 12 , 0≤x9≤3, 0≤y5≤1, M comprises at least one of Zn, Mg, Ca; Na-β-Alumina type: Na2O·2Al2O3 or Na2O·3Al2O3, etc.; Na (3+x10) M y6 A (1-y6) Q (4-z6) T z6 type, where -1 < x10 < 2, 0≤y6≤1, 0≤z6≤2, M comprises at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A comprises at least one of P, As, Sb, Bi, Q comprises at least one of S, Se, T comprises at least one of F, Cl, Br, I; Na (11+x11) M (2-y7) A (1+y7) Q (12-z7) T z7 type, where -1 < x11 < 1, 0≤y7≤2, 0≤z7≤2, M comprises at least one of B, Al, In, Si, Ge, Sn, Ti, W, Mo, A comprises P, As, Sb, Bi; Q = at least one of S, Se, T comprises at least one of F, Cl, Br, I; Anti-perovskite type Na3OX, X comprises at least one of Cl, Br, I, BH4.

[0099] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to make an electrode assembly through a roll-pressing process or a stacking process.

[0100] In some embodiments, the sodium-ion battery can comprise an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0101] In some embodiments, the outer package of the sodium-ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the sodium-ion battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0102] The shape of the sodium-ion battery according to the present application is not particularly limited, and the sodium-ion battery can be cylindrical, square, or any other shape.

[0103] In some embodiments, the sodium-ion battery can be assembled into a battery module, and the number of sodium-ion batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0104] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0105] According to a fifth aspect of the present application, the present application provides a power consuming device comprising the secondary battery according to the fourth aspect of the present application.

[0106] In some embodiments, the above-mentioned power consuming device can also include a battery module or a battery pack assembled from the above-mentioned secondary battery. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include but is not limited to a mobile device (e.g., a mobile phone, a notebook computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0107] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the demand of the power consuming device. As an example of the power consuming device, a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. can be used, and in order to meet the demand of the power consuming device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0108] As another example of the device, a mobile phone, a tablet computer, a notebook computer, etc. can be used. The device usually requires thin and light, and a sodium-ion battery can be used as a power source.

[0109] The present application will be further described in detail below in conjunction with specific examples, which cannot be understood as limiting the scope of the present application.

[0110] Example 1

[0111] The preparation method of the positive electrode active material provided by the embodiment comprises the following steps:

[0112] Nickel sulfate and manganese sulfate are dissolved in deionized water in a molar ratio of 8:9 to obtain a salt-containing solution with a nickel and manganese molar concentration of 1.0 mol / L, which is pumped into a continuous stirred tank reactor, and a precipitating agent 2.0 mol / L NaOH aqueous solution and a chelating agent 10.0 mol / L ammonia are added into the reactor respectively, the pumping rate is set to a molar ratio of ammonia to total transition metal of 3:1, the stirring rate is 1000 rpm, then the pH is controlled at 11.0-11.2 by adjusting the pumping rate of the NaOH aqueous solution, and after stirring for 192 h, the spherical precipitate is filtered, washed with water for 3 times, and dried at 85℃ for 12 h to obtain a precursor Ni 0.47 Mn 0.53 (OH)2.

[0113] The precursor is placed in an ultrasonic-assisted ball mill, 20 stainless steel ball milling media with a diameter of 4 mm are added, then a Na2CO3 aqueous solution (molar concentration 2 mol / L), ferrous chloride, magnesium chloride and calcium chloride are added, the molar ratio of the precursor to the added Na2CO3 is 1:0.495, and the molar ratio of ferrous chloride, magnesium chloride, calcium chloride to nickel and manganese elements in the precursor is 28:3:1:32:36; the ultrasonic frequency of the ball mill is 45 kHz, the stirring rod speed is 300 r / min, ultrasonic ball milling is performed for 1 hour, and after filtration, the mixture is dried at 105℃ for 8 h to obtain a mixture uniformly loaded with Fe, Mg, Ca and sodium sources.

[0114] The mixture is subjected to high-temperature sintering in an air atmosphere (gas flow rate is 2.5 L / min), heated to 750℃ at a rate of 3℃ / min, kept for 7 h, then heated to 900℃ at a rate of 3℃ / min, kept for 12 h, and finally cooled to room temperature at a cooling rate of 150℃ / h to obtain a polycrystalline material, and the SEM thereof is shown in FIG. 1.

[0115] The polycrystalline material is placed in a beaker, deionized water is added, the mass ratio of the polycrystalline material to the deionized water is 1:20, the stirring rod speed is 1000 r / min, and the stirring time is 2 min, the hydrolyzed material is filtered and dried, the drying temperature is 110℃, and the drying time is 8 h to obtain a single crystal material with a particle size Dv50 of 13.2 μm, and the SEM thereof is shown in FIG. 2.

[0116] The single crystal material and sodium carbonate are added into a ball mill in a molar ratio of 1:0.02 for dry ball milling at a ball milling rate of 800 r / min for 30 min to obtain a mixture, and then the mixture is subjected to sintering treatment in an air atmosphere at a gas flow rate of 2 L / min, and then heated to 900 ℃ at a rate of 3 ℃ / min, and then kept for 8 h, and then cooled to room temperature at a rate of 150 ℃ / h to obtain the positive electrode active material.

[0117] Example 2

[0118] The preparation method of the positive electrode active material provided in the embodiment comprises the following steps:

[0119] Nickel sulfate and manganese sulfate are dissolved in deionized water in a molar ratio of 0.5:1 to obtain a salt-containing solution with nickel and manganese molar concentrations of 0.67 mol / L and 1.33 mol / L, respectively, which is pumped into a continuous stirred tank reactor, and a precipitant 2.0 mol / L NaOH aqueous solution and a chelating agent 10.0 mol / L ammonia water are added into the reactor at the same time, the pumping rate is set to be 3:1 of the molar ratio of ammonia to the total amount of transition metals, and the stirring rate is 1000 rpm, then the pH is controlled at 11.0-11.2 by adjusting the pumping rate of the NaOH aqueous solution, and after stirring for 160 h, the spherical precipitate is filtered, washed with water for 3 times, and then dried at 85 ℃ for 12 h to obtain a precursor Ni 0.33 Mn 0.67 (OH)2.

[0120] The precursor is placed into an ultrasonic-assisted ball mill, 20 stainless steel ball milling media with a diameter of 4 mm are added, and then a Na2CO3 aqueous solution (molar concentration 1.75 mol / L), ferrous chloride, magnesium chloride and copper chloride are added, the molar ratio of the precursor to the added Na2CO3 is 1:0.435, and the molar ratio of ferrous chloride, magnesium chloride, copper chloride to nickel and manganese in the precursor is 32:3:5:20:40; the ultrasonic frequency of the ball mill is 45 kHz, the stirring rod rotating speed is 300 r / min, ultrasonic ball milling is performed for 1 h, and then the mixture is filtered and dried at 105 ℃ for 8 h to obtain a mixture uniformly loaded with Fe, Mg, Cu and sodium sources.

[0121] The mixture is subjected to high-temperature sintering in an air atmosphere (gas flow rate 2.5 L / min), heated to 750 ℃ at a rate of 3 ℃ / min, kept for 7 h, then heated to 900 ℃ at a rate of 3 ℃ / min, kept for 12 h, and finally cooled to room temperature at a rate of 150 ℃ / h to obtain a polycrystalline material.

[0122] The polycrystalline material is placed in a beaker, deionized water is added, the mass ratio of the polycrystalline material to the deionized water is 1:18, the stirring rod rotation speed is 1000 r / min, the stirring time is 1 min, the hydrolyzed material is filtered and dried, the drying temperature is 110°C, the drying time is 8 h, and the single crystal material is obtained, and the particle size Dv50 of the single crystal material is 10.1 μm.

[0123] The single crystal material and sodium carbonate are added to a ball mill in a molar ratio of 1:0.02 for dry ball milling, the ball milling rate is 800 r / min, the ball milling time is 30 min, and the mixture is obtained, and then the mixture is subjected to sintering treatment, the gas flow rate of the sintering atmosphere air is 2 L / min, the temperature is raised to 900°C at a rate of 3°C / min, and the temperature is kept for 8 h, and then the temperature is cooled to room temperature at a rate of 150°C / h, and the positive electrode active material is obtained.

[0124] Example 3

[0125] The preparation method of the positive electrode active material provided in this embodiment comprises the following steps:

[0126] Nickel sulfate and manganese sulfate are dissolved in deionized water in a molar ratio of 5:6 to obtain a salt-containing solution with nickel and manganese molar concentrations of 1.2 mol / L and 0.8 mol / L, respectively, which is pumped into a continuous stirred tank reactor, and a precipitating agent 2.0 mol / L NaOH aqueous solution and a chelating agent 10.0 mol / L ammonia are added to the reactor at the same time, the pumping rate is set to a molar ratio of 3:1 of ammonia to the total amount of transition metals, the stirring rate is 1000 rpm, then the pH is controlled at 11.0-11.2 by adjusting the pumping rate of the NaOH aqueous solution, and after stirring for 120 h, the spherical precipitate is filtered, washed with water for 3 times, and dried at 85°C for 12 h to obtain a precursor Ni 0.455 Mn 0.545 (OH)2.

[0127] The precursor is placed in an ultrasonic-assisted ball mill, 20 stainless steel ball milling media with a diameter of 4 mm are added, then a Na2CO3 aqueous solution (molar concentration 1.93 mol / L), ferrous chloride, zinc chloride and aluminum chloride are added, the molar ratio of the precursor to the added Na2CO3 is 1:0.48, and the molar ratio of ferrous chloride, zinc chloride, aluminum chloride to nickel and manganese elements in the precursor material is 20:5:9:30:36. The ultrasonic frequency of the ball mill is 45 kHz, the stirring rod rotation speed is 300 r / min, the ultrasonic ball milling time is 1 h, and the mixture uniformly loaded with Fe, Zn, Al and sodium sources is obtained after filtration and drying at 105°C for 8 h.

[0128] The mixture is subjected to high-temperature sintering, the sintering atmosphere is air (the gas flow rate is 2.5 L / min), the temperature is raised to 750°C at a rate of 3°C / min, and the temperature is maintained for 7 h, then the temperature is raised to 900°C at a rate of 3°C / min, and the temperature is maintained for 12 h, and finally the temperature is cooled to room temperature at a rate of 150°C / h, to obtain a polycrystalline material.

[0129] The polycrystalline material is placed in a beaker, deionized water is added, the mass ratio of the polycrystalline material to the deionized water is 1:15, the stirring rod rotates at a speed of 1000 r / min, and the stirring time is 1 min, the hydrolyzed material is filtered and dried, the drying temperature is 110°C, and the drying time is 8 h, to obtain a single-crystal material with a particle size Dv50 of 8 μm.

[0130] The single-crystal material and sodium carbonate are added to a ball mill in a molar ratio of 1:0.02 for dry ball milling, the ball milling rate is 800 r / min, and the ball milling time is 30 min, to obtain a mixture, and then the mixture is subjected to sintering treatment, the sintering atmosphere is air with a gas flow rate of 2 L / min, the temperature is raised to 900°C at a rate of 3°C / min, and the temperature is maintained for 8 h, and then the temperature is cooled to room temperature at a rate of 150°C / h, to obtain a positive electrode active material.

[0131] Example 4

[0132] The same method as in Example 3 is used to prepare a positive electrode active material, except that in the hydrolysis step of the polycrystalline material, the mass ratio of the polycrystalline material to the deionized water is controlled to be 1:25, the stirring rod rotates at a speed of 600 r / min, and the stirring time is 3 min.

[0133] Example 5

[0134] The same method as in Example 3 is used to prepare a positive electrode active material, except that in the hydrolysis step of the polycrystalline material, the mass ratio of the polycrystalline material to the deionized water is controlled to be 1:30, the stirring rod rotates at a speed of 1400 r / min, and the stirring time is 8 min.

[0135] Example 6

[0136] The same method as in Example 3 is used to prepare a positive electrode active material, except that in the hydrolysis step of the polycrystalline material, the mass ratio of the polycrystalline material to the deionized water is controlled to be 1:5, the stirring rod rotates at a speed of 1600 r / min, and the stirring time is 5 min.

[0137] Example 7

[0138] The same method as in Example 3 is used to prepare a positive electrode active material, except that in the hydrolysis step of the polycrystalline material, the mass ratio of the polycrystalline material to the deionized water is controlled to be 1:1, the stirring rod rotates at a speed of 200 r / min, and the stirring time is 10 min.

[0139] Example 8

[0140] The positive electrode active material was prepared by the same method as in Example 3, with the only difference being that the molar ratio of the single crystal material to sodium carbonate was controlled to be 1:0.1 in the sodium supplementing and resintering step of the single crystal material.

[0141] Example 9

[0142] The positive electrode active material was prepared by the same method as in Example 3, with the only difference being that the mixture of the single crystal material and sodium carbonate was heated to 850°C at a rate of 2°C / min and kept for 14 h in the sodium supplementing and resintering step of the single crystal material.

[0143] Example 10

[0144] The positive electrode active material was prepared by the method of Example 3, with the only difference being the stoichiometric ratio of the elements (see Table 1) and the doping element being Ti and Co.

[0145] Example 11

[0146] The positive electrode active material was prepared by the method of Example 3, with the only difference being the stoichiometric ratio of the elements (see Table 1) and the doping element being Zr.

[0147] Comparative Example 1

[0148] The method for preparing the positive electrode active material provided in this comparative example includes the following steps:

[0149] The precursor Ni 0.5 Mn 0.5 (OH)2was prepared by the method of Example 1.

[0150] The precursor was placed in an ultrasonic-assisted ball mill, 20 stainless steel ball milling media with a diameter of 4 mm were added, and then an aqueous Na2CO3 solution (molar concentration 2 mol / L) was added, the molar ratio of the precursor to the added Na2CO3 being 1:0.495. The ultrasonic frequency of the ball mill was 45 kHz, the stirring rod rotation speed was 300 r / min, ultrasonic ball milling was performed for 1 h, and after filtration, the mixture was dried at 105°C for 8 h to obtain a mixture uniformly loaded with a sodium source.

[0151] High-temperature sintering was performed on the mixture, the sintering atmosphere was air (gas flow rate 2.5 L / min), the temperature was raised to 750°C at a rate of 3°C / min, kept for 7 h, then raised to 900°C at a rate of 3°C / min, kept for 12 h, and finally cooled to room temperature at a rate of 150°C / h, to obtain a polycrystalline material.

[0152] The polycrystalline material is placed in a beaker, deionized water is added, the mass ratio of the polycrystalline material to the deionized water is 1:20, the stirring rod rotation speed is 1000 r / min, the stirring time is 2 min, the hydrolyzed material is filtered and dried, the drying temperature is 110°C, the drying time is 8 h, and the single crystal material is obtained.

[0153] The single crystal material and sodium carbonate are added to a ball mill in a molar ratio of 1:0.02 for dry ball milling, the ball milling rate is 800 r / min, the ball milling time is 30 min, the mixture is obtained, and then the mixture is subjected to sintering treatment, the sintering atmosphere is air, the gas flow rate is 2 L / min, the temperature is raised to 900°C at a rate of 3°C / min, and the temperature is kept for 8 h, and then the temperature is cooled to room temperature at a rate of 150°C / h, and the positive electrode active material is obtained, and the SEM image is shown in FIG. 3.

[0154] As can be seen from FIG. 3, the material cannot maintain the single crystal morphology of the primary particles, which indicates that without the doping of the metal element A, the polycrystalline material will be completely decomposed in the hydrolysis step, and due to the Na + In the hydrolysis step, a large amount of material is lost, so the chemical formula is Na 0.65 Ni 0.5 Mn 0.5 O2.

[0155] Comparative Example 2

[0156] The preparation method of the positive electrode active material provided in the present comparative example is exactly the same as the preparation method of the polycrystalline material in Example 2, that is, the difference between the present comparative example and Example 2 is only that the hydrolysis of the polycrystalline material and the sodium supplementing and sintering of the single crystal material are omitted.

[0157] Comparative Example 3

[0158] The preparation method of the positive electrode active material provided in the present comparative example is exactly the same as the preparation method of the single crystal material in Example 2, that is, the difference between the present comparative example and Example 2 is only that the sodium supplementing and sintering of the single crystal material is omitted.

[0159] Comparative Example 4

[0160] The positive electrode active material is prepared by the same method as in Example 3, and the only difference is that the mass ratio of the polycrystalline material to the deionized water in the hydrolysis step of the polycrystalline material is controlled to be 1:32.

[0161] Comparative Example 5

[0162] The positive electrode active material is prepared by the same method as in Example 3, and the only difference is that the mass ratio of the polycrystalline material to the deionized water in the hydrolysis step of the polycrystalline material is controlled to be 1:0.9.

[0163] Comparative Example 6

[0164] The positive electrode active material was prepared by the same method as in Example 3, with the only difference being that the stirring speed was controlled at 100 r / min in the hydrolysis step of the polycrystalline material.

[0165] Comparative Example 7

[0166] The positive electrode active material was prepared by the same method as in Example 3, with the only difference being that the stirring speed was controlled at 1800 r / min in the hydrolysis step of the polycrystalline material.

[0167] Comparative Example 8

[0168] The positive electrode active material was prepared by the same method as in Example 3, with the only difference being that the stirring (hydrolysis) time was controlled at 12 min in the hydrolysis step of the polycrystalline material.

[0169] Comparative Example 9

[0170] The positive electrode active material was prepared by the method of Example 3, with the only difference being that the stoichiometric ratio of each element (see Table 1) and the doping element was Sr.

[0171] Test Example

[0172] 1. XRD Test

[0173] The positive electrode active material prepared in the above examples or comparative examples was tested by an XRD diffractometer of model Bruker D8 Advance. The XRD pattern after testing was refined by Highscore software in combination with the Rietvald method, and the specific refinement method was as follows: first, Default and automatic fitting were performed, and then the material phase card was imported, and the inserted phase, peak type, pattern parameters, structure parameters, etc. were refined and analyzed by manual refinement, and the lattice parameters a, c, vZ(O) and (003) diffraction peak position and peak intensity were recorded, and then the material was generally refined to obtain d 003 and d O-Na-O . The results are shown in Table 1.

[0174] 2. Button Cell Test

[0175] The positive electrode active material prepared in the above examples or comparative examples was mixed with the conductive additive carbon black and the polyvinylidene fluoride binder in a mass ratio of 70:20:10 to form a slurry, which was then uniformly coated on an aluminum foil, and then placed in a vacuum oven at 80°C for drying for 12 h to obtain a working electrode with a diameter of 10 mm and an active material loading of 2.5 mg / cm 2 -3.0 mg / cm 2Finally, the button cell was assembled, the button cell model was CR2032, the charge-discharge tester for testing the battery performance was Wuhan Lan electric CT2001A, the test conditions were as follows: the nominal specific capacity was 130 mAh / g, the test voltage was 2V-4V, the first circle was 0.2C charge-discharge, then the cycle was connected, the cycle was 0.5C charge-discharge, the cycle number was 50, and the test results were shown in Table 2.

[0176] The first discharge efficiency = the first circle 0.2C discharge capacity / 0.2C charge capacity.

[0177] The capacity retention rate = the discharge capacity after cycle under the condition of 0.5C charge-discharge / the first circle 0.5C discharge capacity.

[0178] 3, The compaction density test

[0179] The powder compaction density tester was used, and the test pressure was 3T.

[0180] 4, Particle size test

[0181] The particle size Dv50 was determined by referring to the standard GB / T19077-2016 / ISO 13320:2009, and a laser particle size analyzer (Malvern Master Size 2000) was used.

[0182] Table 1 Chemical formula and structure parameters of the positive electrode active material

[0183] Table 2 Button cell performance

[0184] It can be seen from Table 1 and Table 2 that the particle size of examples 1-11 is large (7-15 μm) and the R value is in the range of 0.58-0.70, which makes the positive electrode active material of examples 1-11 have a high compaction density, and the battery using the material of examples 1-11 also has a high capacity. At the same time, due to the hydrolysis step, part of the residual alkali on the surface of the material is removed, so that the battery has a high first efficiency and cycle retention rate.

[0185] Compared with example 1, the R value of the material of comparative example 1 is larger, the polycrystalline particles are hydrolyzed into small flaky particles, which results in a significantly lower compaction density. This shows that, by introducing suitable doping elements, the application can control the precipitation degree of Na + in the material, thereby skillfully using the hydrolysis method to prepare single-crystal sodium battery layered oxides with large grain size, thereby improving the compaction density of the material.

[0186] Compared to Example 2, the R value of the material in Comparative Example 2 is lower, resulting in a decrease in compaction density. However, the R value of the material in Comparative Example 3 remains basically unchanged, so the compaction density of Comparative Example 3 is the same as that in Example 2. This indicates that by controlling the degree of hydrolysis of polycrystalline materials, this application can obtain monocrystalline sodium-based layered oxides with larger grain sizes. However, the hydrolysis step will lose some sodium, and sodium needs to be replenished and reheated to ensure that the battery has a high capacity.

[0187] Compared to Example 3, Comparative Examples 4, 7, and 8 exhibit excessively high hydrolysis levels and large R values, resulting in the hydrolysis of polycrystalline particles into tiny flake-like particles and a significant decrease in compaction density. Conversely, Comparative Examples 5 and 6 show excessively low hydrolysis levels and small R values, leading to a significant reduction in compaction density. As can be seen from the above comparative examples, this application, by controlling the hydrolysis conditions of polycrystalline materials (water-to-material ratio, hydrolysis stirring speed, and hydrolysis time), can produce single-crystal sodium-ion layered oxides with larger grain sizes, thereby significantly improving the compaction density of the material.

[0188] The larger R value of the material in Comparative Example 9 resulted in a significant decrease in compaction density. This indicates that only specific doping elements can reduce the sodium interlayer spacing, thereby improving the compaction density of the material.

[0189] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A positive electrode active material, characterized by, The positive electrode active material has a single crystal structure and its general chemical formula is Na. x Ni y Mn z A (1-y-z) O2, wherein 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-yz, and A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, and Al; the sodium interlayer spacing d of the positive electrode active material is... O-Na-O The interplanar spacing d of the (003) diffraction peak 003 The ratio R is 0.58-0.

70.

2. The positive electrode active material according to claim 1, characterized by The d O-Na-O To And / or, the d 003 To 3. The positive electrode active material according to claim 2, characterized by The d O-Na-O To And / or, the d 003 To 4. The positive electrode active material according to any one of claims 1 to 3, characterized by, The R is 0.60-0.64; and / or, 0.6≤x≤1, and / or, 0.05≤y≤0.6, and / or, 0.05≤z≤0.

6.

5. The positive electrode active material according to any one of claims 1 to 3, characterized by, The particle size Dv50 of the positive electrode active material is 7-15 μm; and / or the positive electrode active material has a compaction density of 3.2 g / cm3 under a pressure of 3 tons 3 The above.

6. The positive electrode active material according to claim 5, characterized by The positive electrode active material has a compaction density of 3.4 g / cm 3 - 3.5 g / cm 3 .

7. A method for producing a positive electrode active material, characterized by, The method comprises the following steps: The polycrystalline material is mixed with deionized water at a mass ratio of 1:1-30, stirred at a speed of 200 r / min-1600 r / min for 0.1 min-10 min, filtered, the filter cake is collected, and dried to obtain a single crystal material; the chemical general formula of the polycrystalline material is Na x Ni y Mn z A (1-y-z) O2, wherein, 0.5≤x≤1, 0.01≤y≤0.7, 0.01≤z≤0.7, 0<1-y-z, A is selected from at least one of Mg, Ca, Ti, Zr, Fe, Co, Cu, Zn, Al. The single crystal material is mixed with a sodium source at a molar ratio of 1:0.01-0.1, and then sintering treatment is performed, and the mixture is cooled to obtain the positive electrode active material.

8. The method for producing a positive electrode active material according to claim 7, characterized by, The mass ratio of the polycrystalline material to deionized water is 1:5-25; And / or, the rotation speed is 600-1400 r / min; And / or, the sintering treatment is performed at a temperature of 850-920 ℃ and a holding time of 8-14 h at a temperature increasing rate of 2-3 ℃ / min.

9. A positive electrode sheet characterized by comprising: The method comprises the following steps: The positive electrode current collector and the positive electrode active material layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1-6 or the positive electrode active material prepared by the method according to any one of claims 7-8.

10. A secondary battery characterized by comprising: The positive electrode sheet according to claim 9.

11. An electrical device, characterized by The secondary battery according to claim 10.

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