Sodium-ion battery positive-electrode material, and preparation method therefor and precursor and application thereof

Abstract

Provided in the embodiments of the present application are a sodium-ion battery positive-electrode material, and a preparation method therefor and a precursor and application thereof. The sodium-ion battery positive-electrode material comprises a sodium-based metal oxide, wherein an X-ray diffraction spectrum of the material includes diffraction peaks of the following 12 crystal planes: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116) and (024), and the ratio of a peak area of a diffraction peak of the crystal plane (003) to the sum of peak areas of the diffraction peaks of the 12 crystal planes is less than 25%. The positive-electrode material that meets the above conditions has a high particle sphericity and a smoothly rounded structure, such that the material achieves a high compaction density and good dynamic performance, thereby facilitating an improvement in the energy density and rate performance of a sodium-ion battery.

Description

Sodium battery cathode material and its preparation method, precursor and application

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on February 29, 2024, with application number 202410234500.5 and application name “Sodium battery positive electrode materials, preparation methods, precursors and applications thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to the technical field of sodium ion batteries, and specifically to a sodium battery positive electrode material and a preparation method, precursor, and application thereof. Background Art

[0003] Since sodium resources are abundant and cheap on Earth, sodium-ion batteries have a low production cost and are expected to meet the low-cost demand for large-scale energy storage devices in the future. Among them, the cathode materials widely used in sodium-ion batteries are layered sodium-based transition metal oxides, but the apparent morphology of such materials is usually a flat sheet structure with a low compaction density, which leads to a low energy density of the sodium battery; and the thickness direction of the sheet structure of such materials is its electrochemically active surface, and the exposed area of ​​the active surface is small, resulting in poor kinetic performance of the material. Therefore, it is necessary to provide a sodium cathode material that can take into account both high compaction density and good kinetic performance. Summary of the Invention

[0004] In view of this, the present application provides a sodium-ion cathode material and a preparation method, a precursor and an application thereof, so that a sodium-ion battery using the sodium-ion cathode material can have both high energy density and rate performance.

[0005] Specifically, a first aspect of an embodiment of the present application provides a sodium-based positive electrode material, wherein the sodium-based positive electrode material includes a sodium-based metal oxide, and the X-ray diffraction spectrum of the sodium-based positive electrode material includes diffraction peaks of the following 12 crystal planes: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024), and the ratio of the peak area of ​​the diffraction peak of the (003) crystal plane to the sum of the peak areas of the diffraction peaks of the 12 crystal planes is less than 25%.

[0006] In the above-mentioned sodium battery positive electrode material, the area of ​​the inactive flat (003) crystal plane diffraction peak accounts for a low proportion, and the positive electrode material tends to be rounded particles with high sphericity, so that the exposure degree of its electrochemically active surface is increased and the kinetic performance can be improved. At the same time, its compaction density is high, which is conducive to the improvement of the energy density of the sodium battery; the uniformity of its sodium ion insertion and extraction is improved, which is conducive to improving the cycle performance of the sodium battery.

[0007] In some embodiments of the present application, the ratio of the diffraction peak area of ​​the (003) crystal plane to the sum of the diffraction peak areas of the 12 crystal planes is less than or equal to 23%. In this case, the sodium cathode material has a more rounded morphology and better kinetic performance.

[0008] In the embodiment of the present application, the ratio of the diffraction peak area of ​​the (003) crystal plane to the sum of the diffraction peak areas of the (012) crystal plane and the (110) crystal plane is less than 1.6. The ratio of the diffraction peak area of ​​the characteristic inactive crystal plane to the characteristic active crystal plane of the above-mentioned sodium cathode material is within this range, which can reflect that the orientation of the (003) crystal plane of the material is not high, the morphology structure is relatively rounded, which is more conducive to the deintercalation and extraction of sodium ions and has good electrochemical performance.

[0009] In the embodiment of the present application, the sodium cathode material is a single crystal or a quasi-single crystal particle.

[0010] In the embodiment of the present application, the average particle sphericity of the sodium cathode material is greater than or equal to 0.85. A higher average particle sphericity can reflect that the sodium cathode material is a particle with a rounded morphology, which increases the exposure of its electrochemically active surface and significantly improves its kinetic performance. At the same time, it can achieve denser packing and high compaction density, which is beneficial to the improvement of the energy density of the sodium battery. It also improves the uniformity of its ability to intercalate and deintercalate sodium ions, which is beneficial to improving the battery cycle performance.

[0011] In the embodiments of the present application, the sodium-ion cathode material has particles with a sphericity of less than 0.85 accounting for less than 30%. The low sphericity sodium-ion cathode material particles account for a relatively low proportion of the overall sodium-ion cathode material, thereby ensuring a high average particle sphericity, better kinetic performance, and a high compaction density.

[0012] In the embodiment of the present application, the aspect ratio of the particles having a sphericity of less than 0.85 is within a range of greater than 1 and less than 3. Even particles with relatively low sphericity still have a relatively small aspect ratio, which is much lower than the aspect ratio of conventional flat sheet materials. Their apparent morphology is relatively rounded, and their presence does not significantly affect the dynamic performance and compaction density of the positive electrode material.

[0013] In the embodiment of the present application, the average particle size of the sodium cathode material is within the range of 2 μm to 20 μm. This can avoid the average particle size of the cathode material being too large, which would lengthen the diffusion path of sodium ions and deteriorate the rate performance of the material, and can also avoid the average particle size of the cathode material being too small, which would result in a low compaction density of the material.

[0014] In an embodiment of the present application, the sodium-based cathode material further comprises a coating layer coated on the surface of the sodium-based metal oxide. The presence of the coating layer can improve the air stability and cycle stability of the sodium-based cathode material.

[0015] In an embodiment of the present application, the sodium cathode material has a compaction density of 3.1 g / mL or greater at 200 MPa. The sodium cathode material satisfies the aforementioned XRD spectrum characteristics, morphology and size characteristics of the present application, and has a relatively rounded apparent structure, which can achieve a higher compaction density and thus provide a sodium battery with high energy density.

[0016] A second aspect of an embodiment of the present application provides a sodium-based positive electrode material, wherein the sodium-based positive electrode material includes a sodium-based metal oxide, and the average particle sphericity of the sodium-based positive electrode material is greater than or equal to 0.85.

[0017] The higher average particle sphericity reflects that the above-mentioned sodium battery positive electrode material is a rounded particle with increased exposure of its electrochemically active surface and significantly improved kinetic performance. At the same time, it can achieve denser stacking and high compaction density, which is beneficial to the improvement of the energy density of sodium batteries. In addition, the uniformity of its ability to embed and deintercalate sodium ions is improved, which is beneficial to improving the battery cycle performance.

[0018] In the embodiment of the present application, the X-ray diffraction spectrum of the sodium cathode material includes diffraction peaks of the following 12 crystal planes: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024), and the ratio of the peak area of ​​the diffraction peak of the (003) crystal plane to the sum of the peak areas of the diffraction peaks of the 12 crystal planes is less than 25%.

[0019] In a third aspect, an embodiment of the present application provides a sodium-based cathode material precursor, wherein the sodium-based cathode material precursor comprises a sodium-based metal oxide precursor, wherein the internal porosity of the sodium-based cathode material precursor is greater than or equal to 10%, and / or the specific surface area of ​​the sodium-based cathode material precursor is greater than or equal to 25 m 2 / g.

[0020] When the positive electrode material precursor that meets the above requirements is calcined with a sodium source, the molten sodium source can easily enter the interior of the precursor and achieve uniform and rapid sodiumization, thereby inhibiting the excessive orientation of the flat (003) crystal plane in the obtained positive electrode material and making the positive electrode material have a higher sphericity.

[0021] In the embodiments of the present application, the sodium-ion cathode material precursor is a secondary particle, wherein the particle size of the secondary particles is in the range of 1-20 μm. The particle size of the sodium-ion cathode material precursor is within a suitable range to ensure that the cathode material formed after co-calcination with the sodium source has an appropriate particle size, thereby achieving a high compaction density and good rate performance.

[0022] A fourth aspect of the present application provides a method for preparing a sodium cathode material, comprising the following steps:

[0023] The sodium-based cathode material precursor described in the third aspect of the embodiment of the present application is mixed with a sodium source and calcined to obtain a sodium-based cathode material.

[0024] The positive electrode material is prepared by using a sodium battery positive electrode material precursor that meets the specific requirements of this application. The process is simple and easy to operate, and can ensure that the obtained positive electrode material can meet the XRD spectrum characteristic requirements and the average particle sphericity requirement of 0.85 or above as mentioned above in this application.

[0025] In the embodiment of the present application, the calcination temperature is 850° C.-1000° C., the calcination time is 6-30 hours; and the calcination atmosphere is an oxygen atmosphere or an air atmosphere.

[0026] In some embodiments of the present application, the calcination includes: first calcining at a first temperature for a first time, then cooling to a second temperature and calcining for a second time; wherein the first time is less than the second time. Such a calcination process is more conducive to producing a positive electrode material with a regular morphology and high crystallinity.

[0027] The fifth aspect of the embodiments of the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode material layer arranged on at least one side of the positive electrode collector, and the positive electrode material layer includes the sodium-based positive electrode material described in the first aspect or the second aspect of the embodiments of the present application, or includes the sodium-based positive electrode material prepared according to the preparation method described in the fourth aspect of the embodiments of the present application.

[0028] The compaction density of the above-mentioned sodium-ion positive electrode material is relatively high, which can make the compaction density of the positive electrode plate also relatively high, and the energy density of the sodium-ion battery relatively high. In addition, due to the good kinetic performance and high uniformity of the sodium-ion insertion and extraction of the above-mentioned sodium-ion positive electrode material, the positive electrode plate can be used to produce a sodium-ion battery with excellent rate performance and good cycle performance.

[0029] A fifth aspect of the present application provides a sodium-ion battery, comprising a negative electrode sheet and the positive electrode sheet described in the fifth aspect of the present application. The sodium-ion battery further comprises a separator and an electrolyte located between the positive electrode sheet and the negative electrode sheet. Because the sodium-ion battery utilizes the aforementioned sodium-ion cathode material, the sodium-ion battery can have a high energy density, good rate capability, and cycling stability.

[0030] A sixth aspect of the present application provides an electrical device, comprising an electrical component and a power supply component, wherein the power supply component supplies power to the electrical component, and the power supply component comprises the sodium-ion battery described in the fifth aspect of the present application. The electrical device comprises an electronic device or a powered mobile device.

[0031] By using the sodium ion battery provided in the embodiment of the present application to power the electrical equipment, the user experience and market competitiveness of the product can be improved.

[0032] A seventh aspect of the present application provides an energy storage system, comprising at least one battery pack, wherein the battery pack comprises a plurality of sodium-ion batteries as described in the fifth aspect of the present application. The sodium-ion batteries used in the energy storage system have high energy density, good rate performance, and cycle stability, thereby providing the energy storage system with superior energy storage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a schematic structural diagram of a positive electrode plate provided in an embodiment of the present application.

[0034] FIG2 is a schematic structural diagram of a sodium ion battery provided in an embodiment of the present application.

[0035] FIG3 is a schematic structural diagram of an electronic device provided in an embodiment of the present application.

[0036] FIG4 is a schematic structural diagram of a mobile device provided in an embodiment of the present application.

[0037] FIG5 is a schematic structural diagram of an energy storage system provided in an embodiment of the present application.

[0038] FIG6 summarizes cross-sectional scanning electron microscope (SEM) photos of the positive electrode material precursors prepared in Examples 1-2 and Comparative Examples 1-3 of the present application.

[0039] FIG7 summarizes the SEM photos of the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-3 of the present application.

[0040] FIG8 summarizes the particle sphericity test results of the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-3 of the present application.

[0041] FIG9 summarizes the XRD spectra of the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-3 of the present application.

[0042] FIG10 summarizes the powder compaction density curves of the positive electrode materials prepared in Examples 1-2 and Comparative Examples 1-3 of the present application.

[0043] FIG11 summarizes the first cycle charge and discharge curves of button-type sodium batteries assembled with the positive electrode materials of Examples 1-2 and Comparative Examples 1-3 of the present application.

[0044] FIG12 summarizes the rate performance test results of the button-type batteries of Example 2 and Comparative Examples 1 and 3.

[0045] FIG13 summarizes the test results of the constant current intermittent titration test of the button cells of Example 2 and Comparative Examples 1 and 3.

[0046] FIG14 summarizes the cycle performance test results of soft-pack sodium batteries assembled using the positive electrode materials of Examples 1-2 and Comparative Examples 1-3 of the present application. DETAILED DESCRIPTION

[0047] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0048] To address the problems of low compaction density and poor kinetic performance of sodium-based transition metal oxide positive electrode materials used in sodium batteries, an embodiment of the present application provides a sodium battery positive electrode material.

[0049] Specifically, an embodiment of the present application provides a sodium-based cathode material, which includes a sodium-based metal oxide. The XRD (X-Ray Diffraction) spectrum of the sodium-based cathode material contains at least the following 12 crystal plane diffraction peaks: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024), and the ratio of the peak area of ​​the diffraction peak of the (003) crystal plane to the sum of the peak areas of the diffraction peaks of the 12 crystal planes is less than 25%.

[0050] The (003) crystal plane is an inactive surface of a flat sheet of sodium-based metal oxide. The crystal plane is perpendicular to the thickness direction of the flat sheet of sodium-based metal oxide. The (003) crystal plane is also the surface with the largest exposed area. The diffraction peak area S of the (003) crystal plane in the XRD spectrum of the sodium-based metal oxide-containing sodium-based positive electrode material controlled by this application is (003) The sum of the peak areas of the 12 common crystal plane diffraction peaks (denoted as S a ) ratio is less than 25%, which can reflect that the orientation of the (003) crystal plane in the crystal structure of the positive electrode material is not high, the flat sheet structure is suppressed, and the sodium positive electrode material tends to be round particles with high sphericity. In this way, the exposure of the electrochemically active surface of the material is increased, so that the kinetic performance of the sodium positive electrode material can be significantly improved, which is beneficial to the improvement of the rate performance of the sodium battery. Moreover, the morphology of the round particles with high sphericity is regular, and it is easier to form dense packing between the particles. Therefore, the space utilization rate can be increased during rolling, thereby improving the compaction density of the material, thereby increasing the energy density of the sodium battery. In addition, the deintercalation and extraction of sodium ions (Na + ) has a better uniformity than the sheet structure, which avoids the formation of local excess Na in the material. +The area causes serious damage to the material structure, and thus the cycle performance of the sodium battery can be improved to a certain extent.

[0051] Therefore, the sodium cathode material that meets the above XRD spectrum requirements can take into account good kinetic performance, high compaction density and uniform Na insertion and extraction. + The ability enables the sodium battery using this sodium cathode material to have good rate performance, high energy density and good cycle performance.

[0052] The XRD spectrum of the material is represented by the horizontal axis of the 2θ angle (unit: °), and the vertical axis represents the relative intensity of the diffraction peak. Specifically, in the XRD spectrum of the sodium cathode material, within the diffraction angle 2θ range of 10°-90°, the following 12 crystal plane diffraction peaks are present simultaneously: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024). These 12 crystal plane diffraction peaks are common diffraction peaks of layered sodium-based metal oxides.

[0053] Among them, the diffraction angle 2θ of the above-mentioned (003) crystal plane diffraction peak is around 16.60°, the diffraction angle 2θ of the (006) crystal plane diffraction peak is around 33.57°, the diffraction angle 2θ of the (101) crystal plane diffraction peak is around 35.19°, the diffraction angle 2θ of the (012) crystal plane diffraction peak is around 36.50°, the diffraction angle 2θ of the (104) crystal plane diffraction peak is around 41.60°, the diffraction angle 2θ of the (107) crystal plane diffraction peak is around 53.48°, and the diffraction angle 2θ of the (108) crystal plane diffraction peak is around 54. Nearly, the diffraction angle 2θ of the (018) crystal plane diffraction peak is around 58.59°, the diffraction angle 2θ of the (110) crystal plane diffraction peak is around 62.24°, the diffraction angle 2θ of the (113) crystal plane diffraction peak is around 64.91°, the diffraction angle 2θ of the (1010) crystal plane diffraction peak is around 68.97°, the diffraction angle 2θ of the (116) crystal plane diffraction peak is around 72.59°, and the diffraction angle 2θ of the (024) crystal plane diffraction peak is around 77.66°.

[0054] It should be noted that, depending on the instrument model of the X-ray diffractometer or the state of the sample to be tested, the diffraction angles of the above-mentioned crystal plane diffraction peaks may have detection errors allowed in the art. These detection errors should also be included in the scope of protection required by this application. Therefore, in some embodiments of the present application, in the XRD spectrum of the sodium cathode material, the diffraction angles 2θ are 16.1°-17.1°, 33.07°-34.07°, 34.69°-35.69°, 36.05°-37.05°, 41.10°-42.10°, 53°-54°, ​​58.09°-59.09°, 61.74°-62.74°, 64.41°-6 Diffraction peaks appear at 5.41°, 68.47°-69.47°, 72.09°-73.09°, and 77.16°-78.16°, and the positions of these peaks correspond to the diffraction peaks of the following crystal planes: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024), respectively.

[0055] In addition, it should be noted that although the present application mentions that the XRD pattern of the above-mentioned sodium cathode material has diffraction peaks of the above-mentioned 12 crystal planes, it does not exclude that the XRD spectrum of the sodium cathode material does not have diffraction peaks of other crystal planes within the range of 2θ of 10°-90°, especially some peaks with weaker intensity. For example, in some embodiments, the XRD spectrum of the above-mentioned sodium cathode material also has a diffraction peak of the (015) crystal plane. Among them, the 2θ value corresponding to the (015) crystal plane diffraction peak is between the 2θ value corresponding to the (107) crystal plane diffraction peak and the 2θ value corresponding to the (104) crystal plane diffraction peak.

[0056] In some embodiments of the present application, the diffraction peak area S of the (003) crystal plane is (003) The sum of the peak areas of the diffraction peaks of the above 12 crystal planes S a The ratio can be less than or equal to 24%, or less than or equal to 23%, or less than or equal to 22%, or less than or equal to 21.5%, etc. In some embodiments, the ratio is less than or equal to 23%, and further less than or equal to 22%. In this case, the sodium cathode material has a more rounded morphology and better kinetic performance.

[0057] In the embodiment of the present application, in the XRD spectrum of the sodium positive electrode material, the diffraction peak area S of the (003) crystal plane is (003) The diffraction peak area S of (012) crystal plane (012) and the diffraction peak area S of (110) crystal plane (110) The ratio of its sum satisfies: S (003) / [S (012) +S(110) ]<1.6. Among them, (012) and (110) are the characteristic high-activity crystal planes of sodium-based metal oxides, and the control of S (003) The ratio of the diffraction peak area of ​​the inactive crystal plane to the active crystal plane is within the above range, which can reflect that the ratio of the diffraction peak area of ​​the inactive crystal plane to the active crystal plane of the material is within an appropriate range, which is conducive to ensuring that the preferred orientation of the (003) inactive crystal plane of the material is not high. The material has a relatively rounded structure rather than a sheet structure with a lateral size much larger than the thickness, which is more conducive to the deintercalation of sodium ions and has better electrochemical performance. Specifically, S (003) / [S (012) +S (110) ]≤1.5, or ≤1.4, or ≤1.3, etc. In some embodiments, S (003) / [S (012) +S (110) ] is in the range of [1.0, 1.5], and can further be in the range of [1.1, 1.4]. In this case, the sodium cathode material has both high sphericity and good kinetic properties, as well as good air stability and processability, and excellent cycle performance.

[0058] In the embodiment of the present application, in the XRD spectrum of the sodium positive electrode material, the diffraction peak area S of the (003) crystal plane is (003) The diffraction peak area S of (104) crystal plane (104) The ratio is less than 0.9. This helps to ensure that the (003) crystal plane of the sodium cathode material is not highly oriented. (003) / S (104) Less than or equal to 0.8, less than or equal to 0.75, less than or equal to 0.7, etc. In some embodiments, S (003) / S (104) Greater than or equal to 0.5, and further may be greater than or equal to 0.6, etc. In some embodiments, 0.6≤S (003) / S (104) ≤0.7. In this way, the sodium cathode material has high sphericity and electrochemical performance, while also taking into account the material's good air stability and processing characteristics.

[0059] It should be noted that, when the sodium-based cathode material 100 only includes sodium-based metal oxide, the XRD spectrum characteristics of the above sodium-based cathode material are the XRD spectrum characteristics of the sodium-based metal oxide.

[0060] In this application, the sodium-based metal oxide refers to an oxide including sodium element and metal element. Among them, the metal element at least includes a transition metal element, that is, the metal element is a transition metal element, or includes a transition metal element and a main group metal element. It should be noted that although the sodium-based metal oxide includes sodium element, metal element and oxygen element, it does not exclude the inclusion of other elements. For example, in some cases, the oxide can also contain non-metal elements.

[0061] In an embodiment of this application, the chemical formula of the sodium-based metal oxide can include Na x M a D b O y , where 0.5 ≤ x ≤ 1.2, 1.8 ≤ y ≤ 2.2, 0 < a ≤ 1, 0 ≤ b < 1, M is a metal element, and M at least includes one transition metal element, D is a non-metal element. The elements in the chemical formula satisfy charge balance. Exemplarily, M includes one or more of V (vanadium), Fe (iron), Cr (chromium), Mn (manganese), Co (cobalt), Ni (nickel), Cu (copper), Ti (titanium), Zn (zinc), Zr (zirconium), Mo (molybdenum), Nb (niobium), Li (lithium), K (potassium), Al (aluminum), Mg (magnesium), Ca (calcium), Sr (strontium), Sn (tin), Sb (antimony), etc., but is not limited thereto. In some embodiments, M at least includes at least one of V, Fe, Cr, Mn, Co, Ni, Cu. The D can include at least one of F (fluorine), B (boron), P (phosphorus), Si (silicon), C (carbon), N (nitrogen), etc., but is not limited thereto. Among them, the value of x can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 or 1.1, etc. y can be 1.85, 1.9, 2.0, 2.1, 2.2, etc. In some embodiments, the chemical formula of the sodium-based metal oxide includes Na x MO y . Where when M includes multiple metal elements, the sum of the subscripts of each metal element can be 1. The elements satisfy charge balance.

[0062] In some embodiments of the present application, the above-mentioned sodium-based positive electrode material may further include a coating layer coated on the surface of the sodium-based metal oxide. In this case, the sodium-based positive electrode material may include a core and a coating layer coated on the surface of the core, and the core includes a sodium-based metal oxide, wherein the coating layer may completely coat the surface of the core, or may only coat a portion of the surface of the core. When the XRD characteristics of the sodium-based metal oxide meet the above conditions, the presence of the coating layer may further enhance the air stability and cycle stability of the overall sodium-based positive electrode material. In the embodiment of the present application, the material of the coating layer may include one or more of oxides, fluorides, and phosphates, but is not limited thereto. The thickness of the coating layer may be in the range of 1 nm to 100 nm.

[0063] In the embodiment of the present application, the sodium cathode material is a single crystal or quasi-single crystal particle. Compared with polycrystalline sodium cathode materials, single crystal or quasi-single crystal sodium cathode materials have a higher degree of crystallinity, a more stable bulk structure, and better cycle performance.

[0064] In the embodiments of the present application, the sodium cathode material is in the form of spherical or quasi-spherical particles. That is, the sodium cathode material can be in the form of spherical or quasi-single crystal or quasi-single crystal particles. The spherical or quasi-spherical morphology can result in a higher compaction density and better kinetic performance for the sodium cathode material.

[0065] In the embodiment of the present application, the average particle sphericity of the sodium-electrode positive electrode material is greater than or equal to 0.85. Wherein, the "average particle sphericity" is the average value of the sphericity of multiple sodium-electrode positive electrode material particles. For example, the area equivalent sphericity of a single particle (equal to the ratio of the area equivalent radius d1 of the particle to the perimeter equivalent radius d2 of the particle) can be obtained from a two-dimensional SEM photograph containing multiple (such as more than 50) sodium-electrode positive electrode material particles; based on this, the average value of the sphericity of multiple sodium-electrode positive electrode material particles is calculated. Wherein, d1 can be calculated based on the projected area S of a single particle, and d2 can be calculated based on the perimeter L of the projected outline of the particle: S=πd l 2 ; L = 2πd2. For another example, the volume equivalent sphericity of a single sodium cathode material particle (equal to the ratio of the volume equivalent radius d3 of the particle to its surface area equivalent radius d4) can be obtained from a three-dimensional SEM photograph containing multiple (e.g., more than 50) sodium cathode material particles, and the average sphericity of the multiple sodium cathode material particles can be calculated based on this. Wherein, d3 can be calculated based on the volume V of the particle, and d4 can be calculated based on the surface area S' of the particle: V = 4πd l 3 / 3; S'=πd4 2It is understood that the average particle sphericity of the sodium cathode material is less than or equal to 1.0. That is, the average particle sphericity of the sodium cathode material is within the range of 0.85-1.0. The closer the particle sphericity is to 1, the closer the particle morphology is to a standard sphere.

[0066] The higher average particle sphericity can reflect that the sodium cathode material in this application is a rounded particle rather than a flat sheet structure. The exposure of its electrochemically active surface is increased, and the kinetic performance can be significantly improved, which is conducive to improving the rate performance of the sodium battery. The rounded sodium cathode material particles are more likely to form a dense stack, and the compaction density of the material is higher, which can increase the energy density of the sodium battery. In addition, the deintercalation and extraction of sodium ions (Na + ) also has a certain improvement in uniformity compared to sheet structures, which can further improve the cycling performance of sodium batteries. Specifically, the above average particle sphericity is ≥0.85, ≥0.86, ≥0.87, ≥0.88, ≥0.90, ≥0.92, ≥0.95, etc.

[0067] In the embodiment of the present application, in the sodium-based positive electrode material, the number of sodium-based positive electrode material particles with a particle sphericity of less than 0.85 accounts for less than 30%. The number of sodium-based positive electrode material particles with low sphericity accounts for a low proportion in the overall sodium-based positive electrode material, thereby ensuring that the average particle sphericity of the material is high, the dynamic performance is better, and the compaction density is high. In some embodiments, the number ratio can be less than or equal to 25%, less than or equal to 20%, less than or equal to 15%, less than or equal to 10%, less than or equal to 8%, less than or equal to 6%, less than or equal to 5%, etc.

[0068] In the embodiment of the present application, the particle width-to-thickness ratio of the sodium battery positive electrode material with a particle sphericity of less than 0.85 is within the range of greater than 1 and less than 3. Even for particles with relatively low sphericity, the width-to-thickness ratio is still relatively small, much lower than the width-to-thickness ratio of conventional flat sheet materials, its apparent morphology is relatively rounded, and its kinetic performance is still relatively high. The presence of such particles in the overall positive electrode material will not affect the kinetic performance and compaction density of the positive electrode material too much. Among them, "width-to-thickness ratio" refers to the ratio of the maximum lateral dimension of the particle to its thickness. The maximum lateral dimension of particles with a sphericity of less than 0.85 is greater than the thickness. Among them, "maximum lateral dimension" can specifically refer to the distance between the two largest points on the cross section perpendicular to the thickness direction. For example, when the cross section is a polygon, the maximum lateral dimension can be the diameter of the circumscribed circle of the polygon. The above-mentioned width-to-thickness ratio can be obtained from a scanning electron microscope photograph of the material. In some embodiments, the aspect ratio of the sodium battery positive electrode material particles having a particle sphericity of less than 0.85 may be less than or equal to 2.8, less than or equal to 2.5, less than or equal to 2.2, less than or equal to 2.0, less than or equal to 1.8, less than or equal to 1.5, less than or equal to 1.4, etc.

[0069] In some embodiments of the present application, the particle sphericity of each sodium cathode material particle is greater than or equal to 0.85.

[0070] In the embodiment of the present application, the average particle size of the sodium-based positive electrode material is in the range of 2μm-20μm. That is, the average particle size of the aforementioned single crystal or single-crystal-like particles is 2μm-20μm. Controlling the average particle size of the sodium-based positive electrode material with a single crystal or single-crystal-like structure within the above range can not only avoid the average particle size of the positive electrode material being too large, which will lengthen the diffusion path of sodium ions and deteriorate the rate performance of the material, but also avoid the low compaction density of the material due to the average particle size of the positive electrode material being too small. Specifically, the average particle size can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or 19μm, etc. The average particle size can be obtained from a scanning electron microscope photograph of the sodium-based positive electrode material.

[0071] In the embodiment of the present application, the compaction density of the sodium positive electrode material at 200MPa is above 3.1g / mL, for example, in the range of 3.2-4.0g / mL. Based on the control of the XRD characteristics of the aforementioned sodium-based transition metal oxides in the embodiment of the present application, the sphericity of the sodium positive electrode material can be high, and its compaction density is correspondingly high, thereby increasing the active material loading of the battery negative electrode sheet and improving the energy density of the battery. Specifically, the compaction density of the sodium positive electrode material at 200MPa can be 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45g / mL, etc. Among them, the above-mentioned compaction density can be measured by a powder compaction density meter when testing the powdered sodium positive electrode material, and the compaction density read from the equipment under a pressure of 200MPa. In addition, it should be noted that when the sodium positive electrode material has or does not have a coating layer, its compaction density can meet the above requirements.

[0072] The present application also provides a sodium cathode material, comprising a sodium-based metal oxide, wherein the average particle sphericity of the sodium cathode material is greater than or equal to 0.85. The definition of "average particle sphericity" can be found in the previous description of this application and will not be repeated here.

[0073] The average particle sphericity of the sodium cathode material of the present application is relatively high, which can reflect that the material particles are rounded rather than flat sheet-like. The exposure degree of the electrochemical active surface of the material is increased, and the kinetic performance can be significantly improved, which is conducive to improving the rate performance of the sodium battery. The rounded sodium cathode material particles are more likely to form dense packing, and the compaction density of the material is higher, thereby increasing the energy density of the sodium battery. In addition, the deintercalation and extraction of sodium ions (Na + ) also has a certain improvement in uniformity compared to sheet structures, which can further improve the cycling performance of sodium batteries. Specifically, the above average particle sphericity is ≥0.85, ≥0.86, ≥0.87, ≥0.88, ≥0.90, ≥0.92, ≥0.95, etc.

[0074] In the embodiment of the present application, the XRD spectrum of the sodium cathode material contains at least the following 12 diffraction peaks of the crystal plane: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), (024). Furthermore, the diffraction peak area S of the (003) crystal plane is (003) The ratio of the peak area of ​​the (003) crystal plane diffraction peak to the sum of the peak areas of the 12 crystal planes is less than 25%. The low proportion of the peak area of ​​the (003) crystal plane diffraction peak can also reflect that the orientation of the (003) crystal plane in the crystal structure of the sodium cathode material is not high, the flat flaky structure is suppressed, and the material tends to be rounded particles with high sphericity, thereby having good rate performance and high compaction density.

[0075] The structural characteristics, XRD spectrum characteristics and performance descriptions of the sodium cathode materials described above are all applicable to the sodium cathode materials herein and will not be described in detail here.

[0076] The present application also provides a sodium cathode material precursor, which can be mixed with a sodium source and then calcined to obtain the sodium cathode material of the present application. The sodium cathode material precursor comprises a sodium-based metal oxide precursor, wherein the internal porosity of the sodium cathode material precursor is greater than or equal to 10%, and / or the specific surface area of ​​the sodium cathode material precursor is greater than or equal to 25m 2 / g.

[0077] The internal porosity of the precursor material can be determined from a cross-sectional SEM image. Specifically, it refers to the ratio of the area of ​​the pores (usually the pores are dark and the material is light) to the area of ​​the entire cross-section in the cross-sectional SEM image. The specific surface area of ​​the precursor material can be measured using the nitrogen adsorption method (also known as the "BET method"), and the precursor used for the test can be a solid powder.

[0078] Unlike conventional sodium-based cathode material precursors, which are compact structures with small specific surface areas, the sodium-based cathode material precursors of the present application have large internal porosity and / or specific surface area, and a loose internal structure. During the calcination of the precursor and the sodium source, the molten sodium source is more likely to enter the interior of the precursor and achieve uniform and rapid sodiumization. The exterior of the precursor material will not be exposed to the molten sodium salt environment for a long time and will not form excessive flat (003) crystal planes. This shortens the crystallization phase formation time of the precursor material and the sodium source, reduces the exposure of the flat (003) crystal planes in the formed cathode material, and suppresses the probability of presenting a flat sheet structure. Therefore, the morphology of the resulting cathode material will present a spherical or quasi-spherical rounded structure, and the peak area of ​​the (003) crystal plane diffraction peak in its XRD spectrum is low, which can be less than 25%.

[0079] In an embodiment of the present application, the sodium-electric cathode material precursor is a secondary particle. That is, the sodium-electric cathode material precursor is a polycrystalline particle, which is formed by stacking a plurality of primary particles. The sodium-electric cathode material precursor is generally a spherical or quasi-spherical particle. In an embodiment of the present application, the particle size of the secondary particles is in the range of 1 μm-20 μm. The particle size of the sodium-electric cathode material precursor is in a suitable range, which is conducive to ensuring that the cathode material formed after co-calcination with the sodium source has a suitable particle size, so as to take into account high compaction density, good rate performance, etc. For example, the particle size of the secondary particles can be specifically 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, etc. In some embodiments, the particle size of the secondary particles may be in the range of 3 μm to 15 μm, and further in the range of 5 μm to 10 μm.

[0080] The sodium-based metal oxide precursor is used to calcine with a sodium source to form a sodium-based metal oxide. It is understood that the sodium-based metal oxide precursor does not contain sodium and can be thermally decomposed into a sodium-free metal oxide. In the embodiment of the present application, the sodium-based metal oxide precursor includes a hydroxide, carbonate, or oxyhydroxide corresponding to the sodium-free metal oxide. In some embodiments, the sodium-based metal oxide precursor is a hydroxide, and its chemical formula can be expressed as M a D b (OH)2. In some other embodiments, the sodium-based metal oxide precursor is a carbonate, and its chemical formula can be expressed as M a D b In some other embodiments, the sodium-based metal oxide precursor is an oxyhydroxide, an exemplary chemical formula of which can be expressed as M a D b O(OH).

[0081] The sodium-ion positive electrode material precursor can be prepared by mixing raw materials for forming the sodium-ion positive electrode material precursor and then coprecipitating the precursor. The precursor meeting the requirements of the present application can be prepared by adjusting the technical parameters during the preparation of the sodium-ion positive electrode material precursor.

[0082] Taking the positive electrode material precursor as a hydroxide as an example, its preparation method may include: preparing a metal salt solution for forming the precursor, mixing the metal salt solution with a precipitant (specifically an alkali, such as sodium hydroxide) and a complexing agent (such as ammonia water, disodium ethylenediaminetetraacetic acid, etc.), and obtaining a precursor-metal element-containing hydroxide by coprecipitation reaction. Among them, the precursors with different particle sizes and different pore structures can be obtained by adjusting the reaction temperature, reaction time, reaction pH, stirring speed, and the addition rate of each raw material that affect the coprecipitation growth of the positive electrode material precursor. In addition, the growth of the precursor (or "coprecipitation reaction") can be carried out in one step or multiple steps, and multiple steps are preferred in order to better regulate the internal pore structure of the precursor. In some embodiments of the present application, a precipitant and a precipitant can be added to the metal salt solution. After the coprecipitation reaction, after the precursor particles of a certain target particle size are grown, at least one of the reaction temperature, reaction pH, stirring speed, etc. is adjusted to change the coprecipitation reaction conditions to continue to grow the precursor particles. This is more conducive to the preparation of a positive electrode material precursor with a loose structure, high internal porosity, and a large specific surface area. The coprecipitation reaction conditions can be changed once or multiple times, and the coprecipitation reaction conditions can be changed each time after the precursor particles reach the target particle size.

[0083] The present invention also provides a method for preparing the above-mentioned sodium cathode material, which comprises the following steps:

[0084] The sodium cathode material precursor of the embodiment of the present application is mixed with a sodium source and calcined to obtain a sodium cathode material.

[0085] The sodium cathode material of the embodiment of the present application is prepared by mixing the specific sodium cathode material precursor provided by the embodiment of the present application with a sodium source and then sintering. The obtained cathode material has a rounded structure with high sphericity, high compaction density, and high Na + The dynamic performance is good.

[0086] In the present application, the sodium source is used to provide sodium ions to form the positive electrode material of the sodium battery system. The sodium source can be a sodium salt, for example, one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, etc. The sodium positive electrode material precursor meets the requirements of the above-mentioned application, for example, its internal porosity is greater than or equal to 10%, and / or its specific surface area is greater than or equal to 25m 2 / g, so that it can form a positive electrode material with a round structure after calcination with a sodium source.

[0087] In an embodiment of the present application, the calcination temperature may be 850°C-1200°C, for example, specifically 860°C, 880°C, 900°C, 920°C, 950°C, 980°C, 990°C, 1000°C, 1100°C, or 1150°C. In an embodiment of the present application, the calcination time may be 6-30 hours, for example, specifically 8 hours, 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 24 hours, 28 hours, etc. Wherein, the calcination atmosphere is an oxygen-containing atmosphere (for example, specifically an air atmosphere or an oxygen atmosphere) so that the precursor in the form of the hydroxide, carbonate, or oxyhydroxide decomposes into an oxide. In addition, before the calcination, pre-calcination may be performed to remove water, impurities, etc. from the mixture containing the precursor and the sodium source. It is understandable that the pre-calcination temperature is lower than the calcination temperature.

[0088] In the present application, the calcination can be performed in one stage or in two or more stages. In some embodiments of the present application, the calcination is performed in two stages, first calcining at a first temperature for a first time, then lowering the temperature to a second temperature and calcining for a second time. It is understood that the first temperature is higher than the second temperature. Both the first and second temperatures are within the range of 850°C-1200°C. The first time can be shorter than the second time. Short sintering at a higher temperature allows for rapid nucleation, allowing the positive electrode material particles to grow, while long sintering at a relatively lower second temperature can provide a shaping effect, resulting in a more regular morphology of the positive electrode material particles. The first temperature can be within the range of 900-1200°C, and the second temperature can be within the range of 850-1000°C. The first time can be within the range of 2-10 hours, for example, 4 hours, 5 hours, 6 hours, 8 hours, etc.; the second time can be within the range of 8-24 hours, for example, 10 hours, 12 hours, 16 hours, 18 hours, 20 hours, etc. In some embodiments, the mixture containing the above-mentioned precursor and the sodium source is pre-sintered, then heated to a first sintering temperature of 950° C. and sintered for 6 hours, and then cooled to a second sintering temperature of 900° C. and sintered for 18 hours.

[0089] In some embodiments of the present application, when the sodium-based cathode material precursor is mixed with a sodium source, a doping element source may be introduced to achieve mixing of the cathode material precursor with the sodium source and the doping element source, so as to form a sodium-based cathode material containing the doping element after calcination.

[0090] The preparation method of the above-mentioned sodium cathode material provided in the embodiment of the present application has a simple process, is easy to operate, is suitable for large-scale production, and can produce a sodium cathode material that meets the requirements of the above-mentioned application.

[0091] It should be noted that after the mixed positive electrode material precursor and sodium source are calcined as described above, a sodium-based metal oxide having the XRD spectrum characteristics that meet the requirements of this application is mainly prepared. When the desired sodium-based positive electrode material also includes a coating layer, the operation of constructing the coating layer can be performed after the above-mentioned calcination step. Among them, the coating layer can be constructed by mixing the sodium-based metal oxide with the coating layer material or the raw materials of the synthetic coating layer material. The construction method of the coating layer includes but is not limited to a solid phase method or a liquid phase method. For example, the solid phase method can be a mechanical stirring method, a solid phase high-energy ball milling method, a mechanical fusion method, etc., and the liquid phase method can be one or more of a sol-gel method, a co-precipitation coating method, a hydrothermal / solvothermal coating method, a liquid phase high-energy ball milling method, a coating method, and a spray drying coating method. Generally, when the liquid phase method is adopted, heat treatment is required after the mixing to promote the formation of the coating layer material, enhance the binding force between it and the sodium-based metal oxide, etc.

[0092] The embodiment of the present application also provides a positive electrode plate for a sodium battery, which includes the sodium battery positive electrode material described above in the embodiment of the present application.

[0093] Referring to Figure 1, the positive electrode sheet 100 provided in an embodiment of the present application includes a positive electrode current collector 101 and a positive electrode material layer 102 disposed on the positive electrode current collector 101. The positive electrode material layer 102 includes the above-mentioned sodium-ion positive electrode material described in the embodiment of the present application. The above-mentioned sodium-ion positive electrode material serves as the positive electrode active material of the positive electrode sheet 100. The positive electrode material layer 102 is disposed on one surface or on two opposite surfaces of the positive electrode current collector 101. In the embodiment of the present application, the positive electrode material layer 102 may further include a binder, a conductive agent, etc.

[0094] Among them, the positive electrode current collector 101, binder, and conductive agent are conventional choices in the field of sodium batteries. For example, the positive electrode current collector can be aluminum foil, carbon-coated aluminum foil, aluminum-plated polymer film, etc. The binder can specifically include but is not limited to polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyacrylamide (PAM), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR) and sodium alginate, etc. One or more. The conductive agent can specifically include but is not limited to one or more of acetylene black, Ketjen black, Super P conductive carbon black, graphite, graphene, carbon nanotubes, carbon fiber, amorphous carbon, etc. In some embodiments, the positive electrode material layer 102 may also include other positive electrode active materials different from the above-mentioned sodium positive electrode materials.

[0095] Referring to Figure 2, Figure 2 is a schematic diagram of the structure of a sodium ion battery provided in an embodiment of the present application. The sodium ion battery 200 includes a positive electrode 21, a negative electrode 22, an electrolyte 23, a diaphragm 24, and corresponding connecting accessories and circuits. Among them, the diaphragm 24 is arranged between the positive electrode 21 and the negative electrode 22, and the positive electrode 21, the negative electrode 22, and the diaphragm 24 are immersed in the electrolyte 23. Among them, the positive electrode 21 includes the positive electrode sheet 100 described above in the embodiment of the present application, which also correspondingly includes the above-mentioned sodium positive electrode material provided in the embodiment of the present application.

[0096] For sodium ion batteries, it is through sodium ions (Na + ) between the positive electrode 21 and the negative electrode 22 to achieve energy storage and release. The electrolyte 23 is Na + The carrier is transferred between the positive electrode 21 and the negative electrode 22. The ion-conducting but electronically insulating separator 24 is used to separate the positive electrode 21 from the negative electrode 22 to prevent short circuit. + It escapes from the positive electrode 21 and migrates to the negative electrode 22 through the electrolyte 23 and the separator 24 to achieve the storage of electrical energy. + The negative electrode active material is released from the negative electrode 22 and migrates back to the positive electrode 21 through the electrolyte 23 and the separator 24 to perform external work, that is, release electrical energy to the power load connected to the sodium ion battery 200.

[0097] The positive and negative active materials are the main parts of the sodium ion battery that perform the energy storage function, and determine the energy density, cycle performance and safety performance of the battery. After determining the battery negative electrode material system, the capacity of the positive electrode active material is crucial to the improvement of the energy density of the entire battery. The positive electrode 21 of the sodium ion battery 200 in the embodiment of the present application uses the above-mentioned sodium positive electrode material provided in the embodiment of the present application, and the above-mentioned sodium positive electrode material has good dynamic performance, high compaction density, and can evenly deintercalate Na + , which enables the sodium ion battery 200 to have good rate performance, high energy density and good cycle performance.

[0098] The sodium ion battery 200 shown in FIG2 is a liquid battery, which uses an electrolyte as a liquid electrolyte. It is understood that in other embodiments of the present application, the sodium ion battery can also be a solid / semi-solid battery, which includes a positive electrode, a negative electrode, and a solid / semi-solid electrolyte layer located therebetween.

[0099] The sodium-ion batteries provided in the embodiments of the present application can be used as batteries for consumer electronic devices, power batteries for mobile devices such as electric vehicles, and can also be applied to energy storage systems. Consumer electronic devices may include, but are not limited to, mobile phones, tablet computers, laptop computers, and wearable electronic devices.

[0100] The present application also provides an electrical device that uses the sodium ion battery described above to power it. The electrical device may include an electronic device or a mobile device (such as an electric vehicle). The electrical device includes an electrical component and a power supply component, the power supply component providing power to the electrical component, and the power supply component includes the sodium ion battery described above in the present application.

[0101] In the implementation manner of this application, the electronic device can be a mobile phone, a tablet computer, a laptop computer, a wearable device (such as a smart watch, a smart bracelet, smart glasses, etc.), an augmented reality (AR) device, a virtual reality (VR) device, a television, a digital camera, a vehicle-mounted device and other electronic products, and this application does not limit this.

[0102] In some embodiments, referring to FIG3 , an embodiment of the present application provides an electronic device 300. The electronic device 300 includes a housing 301 and a circuit board assembly (not shown in FIG3 ) and a battery 302 housed in the housing 301. The battery 302 can power the electronic device 300, and the battery 302 includes the sodium ion battery 200 described above in the embodiment of the present application. The battery 302 is electrically connected to the circuit board and can power the circuit board assembly. The circuit board assembly can be one of the electrical components of the electronic device 300. In some embodiments, the housing 301 may include a front cover assembled on the front side of the electronic device and a rear shell assembled on the rear side, and the battery 302 may be fixed on the inside of the rear shell. The electronic device 300 shown in FIG3 may specifically be a mobile phone, etc.

[0103] In some other embodiments, referring to FIG. 4 , an embodiment of the present application provides a mobile device 400. Mobile device 400 can be any movable device used for loading, transporting, assembling, disassembling, security, etc., such as various types of vehicles, including but not limited to electric cars, electric buses, electric trucks, electric motorcycles, electric bicycles, etc. In this embodiment, mobile device 400 is specifically an electric car.

[0104] Specifically, the mobile device 400 may include a body 401, a mobile component 402 (for example, a wheel), and a drive component. The drive component includes a motor 403 and a battery system 404. The battery system 404 includes the above-mentioned sodium ion battery 200 provided in the embodiment of the present application. The battery system 404 is housed in the body 401 (for example, under the chassis of the vehicle) and is electrically connected to the motor 403. It can supply power to the motor 403, and the motor 403 then provides power to drive the mobile component 402 to move. The motor 403 is one of the electrical components of the mobile device 400. The battery system 404 may be a battery pack, which includes a plurality of the above-mentioned sodium ion batteries 200. The plurality of sodium ion batteries may be connected in series and parallel to form a battery pack, and at least one battery module and a battery management system may be packaged to form a battery pack.

[0105] The embodiment of the present application further provides an energy storage system, which includes a plurality of the sodium ion batteries 200 described above according to the embodiment of the present application.

[0106] 5 , the energy storage system 500 includes one or more battery packs 501 ( FIG. 5 is an example of two battery packs 501 ), and a battery management system 502 electrically connected to each battery pack 501 , wherein each battery pack 501 includes a plurality of the sodium ion batteries 200 described above according to an embodiment of the present application. The battery pack 501 may be a module composed of a plurality of sodium ion batteries 200 connected in series and parallel. The battery management system 502 may be used to monitor the status information of each sodium ion battery 200 in the battery pack 501 , adjust the voltage and temperature of the battery pack, and implement charge and discharge protection and other functions. The battery pack 501 and the battery management system 502 may be packaged to form a battery pack. The energy storage system 500 shown in FIG. 5 may be an electric vehicle energy storage system, a data center short-term backup power system, a site energy backup power system, an intelligent photovoltaic energy storage power station, and the like.

[0107] The embodiments of the present application are further described below with reference to a number of embodiments.

[0108] Example 1

[0109] A sodium ion battery cathode material precursor, whose chemical formula is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, its internal porosity is 15.76%, and its specific surface area is 29.86m 2 / g. The synthesis of the precursor comprises the following steps:

[0110] (1-1) preparing a nickel-iron-manganese metal salt solution: dissolving nickel sulfate, ferrous sulfate, and manganese sulfate in water at a molar ratio of Ni, Fe, and Mn of 1:1:1 to prepare a nickel-iron-manganese metal salt solution, wherein the total concentration of metal ions is 2 mol / L;

[0111] (1-2) preparing an aqueous ammonia solution with a molar concentration of 7.0 mol / L and an aqueous sodium hydroxide solution with a concentration of 10.0 mol / L;

[0112] (1-3) Deionized water was added to the reactor, and then the prepared ammonia solution and sodium hydroxide solution were added to the reactor. The temperature was adjusted to 60° C., the pH value was 11.6, the concentration of ammonia in the reactor was 10 g / L, the stirring speed was 500 rpm, and the metal salt solution prepared in the above (1-1) was added under stirring to co-precipitate the growth precursor material.

[0113] (1-4) After the precursor particles grow to a particle size of 2 μm, the temperature is maintained at 60° C., the pH value is changed to 10.0, the ammonia concentration is changed to 7.5 g / L, the stirring speed is changed to 450 rpm, and the ammonia solution and sodium hydroxide solution prepared in (1-2) and the nickel-iron-manganese metal salt solution prepared in (1-1) are slowly injected again;

[0114] (1-5) After the precursor particles grow to a size of 4-5 μm, slowly inject the prepared ammonia solution and sodium hydroxide solution, maintain the temperature at 60°C and pH at 10.0, change the stirring speed to 400 rpm, and continue aging and stirring for 12 h;

[0115] (1-6) After aging is completed and the sample is completely precipitated, the supernatant is removed and the resulting precipitate is washed with a 1.0 mol / L sodium hydroxide solution at 50°C for 1 h, followed by water washing 5 times, each washing for 1 h.

[0116] (1-7) The washed sample was dried in an oven at 120° C. for about 24 h, and the dried sample was sieved using a 500-mesh sieve to obtain a precursor sample.

[0117] A sodium cathode material with the chemical formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the synthesis of the sodium cathode material comprises the following steps:

[0118] (2-1) The cathode material precursor Ni prepared above 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 and sodium carbonate (Na2CO3) are fully mixed to obtain a mixture, wherein the sodium carbonate is added in a molar ratio of 1:1 between the transition metal (including Ni, Fe, and Mn) in the precursor and the sodium in the sodium carbonate;

[0119] (2-2) The mixture in (2-1) was calcined in a muffle furnace, first at 950°C for 6 hours, then cooled to 900°C for 18 hours in a pure oxygen atmosphere, and then naturally cooled after calcination.

[0120] (2-3) The powder obtained after cooling in (2-2) is crushed, sieved, demagnetized and vacuum packaged to obtain the sodium cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0121] A preparation method for a positive electrode sheet: the above-mentioned sodium battery positive electrode material, binder polyvinylidene fluoride (PVDF), and conductive agent super P are added to N-methylpyrrolidone (NMP) in a mass ratio of 94:3:3, and the mixture is thoroughly stirred and mixed to obtain a slurry. The slurry is coated on an aluminum foil current collector, dried, cold pressed, and cut to obtain a positive electrode sheet.

[0122] Preparation of a button-type sodium ion battery: The prepared positive electrode sheet and sodium sheet, electrolyte (the electrolyte contains NaClO4 with a concentration of 1 mol / L) and a separator are made into a 2032 button-type battery.

[0123] Example 2

[0124] A sodium ion battery cathode material precursor, whose chemical formula is Ni 0.32 Fe 0.32 Mn 0.32 Cu 0.04 (OH)2, its internal porosity is 16.99% and its specific surface area is 30.52m 2 / g. The synthesis of the precursor comprises the following steps:

[0125] (1-1) preparing a nickel-iron-manganese-copper metal salt solution: dissolving nickel sulfate, ferrous sulfate, manganese sulfate, and copper sulfate in water at a molar ratio of Ni, Fe, Mn, and Cu of 32:32:32:4 to prepare a nickel-iron-manganese-copper metal salt solution having a total metal ion concentration of 2 mol / L;

[0126] (1-2) preparing a 0.3 mol / L aqueous solution of disodium edetate and a 10.0 mol / L aqueous solution of sodium hydroxide;

[0127] (1-3) Deionized water was added to the reaction kettle, and then the prepared disodium EDTA solution and sodium hydroxide aqueous solution were added to the reaction kettle. The temperature was adjusted to 50° C., the pH value was 11.5, the concentration of disodium EDTA in the reaction kettle was 0.05 mol / L, the stirring speed was 500 rpm, and the metal salt solution prepared in the above (1-1) was added under stirring to grow precursor particles.

[0128] (1-4) After the precursor particles grow to a particle size of 2-3 μm, the temperature is increased to 55° C., the pH value is changed to 10.5, the concentration of disodium EDTA is kept constant, the stirring speed is 450 rpm, and the disodium EDTA solution and sodium hydroxide aqueous solution prepared in (1-2) and the nickel, iron, manganese and copper metal salt solution prepared in (1-1) are slowly injected again;

[0129] (1-5) After the precursor particles grow to a size of 5-6 μm, slowly inject the prepared disodium EDTA solution and sodium hydroxide aqueous solution, maintain the temperature at 55 °C and pH 10.5, change the stirring speed to 400 rpm, and continue aging and stirring for 12 h;

[0130] (1-6) After aging is completed and the sample is completely precipitated, the supernatant is removed and the resulting precipitate is washed with a 1.0 mol / L sodium hydroxide solution at 50°C for 1 h, followed by water washing 5 times, each washing for 1 h.

[0131] (1-7) The washed sample was dried in an oven at 120°C for 24 h. The dried sample was sieved using a 500-mesh sieve to obtain a precursor sample.

[0132] Synthesis of sodium battery cathode material NaNi 0.32 Fe 0.32 Mn 0.32 Cu 0.04 O2: According to the method described in Example 1, the positive electrode material precursor Ni prepared above 0.32 Fe 0.32 Mn 0.32 Cu 0.04 (OH)2 is mixed with sodium carbonate and calcined to prepare the positive electrode material.

[0133] Referring to the method described in Example 1, the above-mentioned positive electrode material NaNi 0.32 Fe 0.32 Mn 0.32 Cu 0.04 O2 is used to prepare positive electrode sheets and sodium ion batteries.

[0134] Example 3

[0135] A sodium ion battery cathode material precursor, whose chemical formula is Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 CO3, with an internal porosity of 15.4% and a specific surface area of ​​27.56m 2 / g. The synthesis of the precursor comprises the following steps:

[0136] (1-1) preparing a nickel-iron-manganese metal salt solution: dissolving nickel sulfate, ferrous sulfate, and manganese sulfate in water at a molar ratio of Ni, Fe, and Mn of 1:1:1 to prepare a nickel-iron-manganese metal salt solution having a total metal ion concentration of 2 mol / L;

[0137] (1-2) preparing a 0.3 mol / L aqueous solution of ammonium sulfate (as a complexing agent) and a 2.0 mol / L aqueous solution of sodium carbonate (as a precipitant);

[0138] (1-3) Deionized water was added to the reactor, followed by an aqueous ammonium sulfate solution, maintaining the concentration of ammonium sulfate in the reactor at 12 g / L. The pH value was adjusted to 8.0 with aqueous ammonia, the temperature was adjusted to 60° C., and the stirring speed was adjusted to 700 rpm.

[0139] (1-4) Slowly inject the nickel-iron-manganese metal salt solution prepared in (1-1) and the ammonium sulfate aqueous solution and sodium carbonate aqueous solution prepared in (1-2) into the reactor, maintaining the temperature at 60° C., the pH value at 8.0, and the stirring speed at 700 rpm;

[0140] (1-5) After the precursor particles grow to a particle size of 4 μm, the temperature is maintained at 60° C., the stirring speed is adjusted to 450 rpm, and the ammonium sulfate aqueous solution and sodium carbonate aqueous solution prepared in (1-2) and the nickel, iron and manganese metal salt solution prepared in (1-1) are slowly injected again;

[0141] (1-6) After the precursor particles grow to a particle size of 8-10 μm, stop feeding, adjust the stirring speed to 400 rpm, and continue aging and stirring for 12 h;

[0142] (1-7) After aging is completed and the sample is completely precipitated, the supernatant is removed and the resulting precipitate is washed with a 0.5 mol / L sodium hydroxide solution at 50°C for 1 h, followed by water washing 5 times, each washing for 1 h.

[0143] (1-8) The washed sample was dried in an oven at 120 °C for 24 h. The dried sample was sieved using a 400-mesh sieve to obtain a precursor sample.

[0144] Synthesis of sodium battery cathode material NaNi 1 / 3 Fe1 / 3 Mn 1 / 3 O2: According to the method described in Example 1, the positive electrode material precursor Ni prepared above 1 / 3 Fe 1 / 3 Mn 1 / 3 CO3 is mixed with sodium carbonate and calcined to prepare the positive electrode material.

[0145] Referring to the method described in Example 1, the above-mentioned positive electrode material was used to prepare a positive electrode sheet and a sodium ion battery.

[0146] Comparative Example 1

[0147] A sodium ion battery cathode material precursor Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, its specific surface area is 6.69m 2 / g, and the internal porosity is 2.39%. The synthesis of the precursor includes the following steps:

[0148] (1-1) preparing a nickel-iron-manganese metal salt solution: dissolving nickel sulfate, ferrous sulfate, and manganese sulfate in water at a molar ratio of Ni, Fe, and Mn of 1:1:1 to prepare a nickel-iron-manganese metal salt solution having a total metal ion concentration of 2 mol / L;

[0149] (1-2) preparing a 7.0 mol / L ammonia aqueous solution and a 10.0 mol / L sodium hydroxide aqueous solution;

[0150] (1-3) Deionized water was added to the reactor, and then the prepared ammonia solution and sodium hydroxide solution were added to the reactor. The temperature was adjusted to 40°C, the pH value was 11.7, the concentration of ammonia solution in the reactor was 9 g / L, and the stirring speed was 500 rpm. The metal salt solution prepared in (1-1) was added under stirring to grow precursor particles.

[0151] (1-4) After the precursor particles grow to a particle size of 2 μm, the temperature is increased to 70° C., the pH value is changed to 10.4, the ammonia concentration is changed to 8.2 g / L, the stirring speed is changed to 450 rpm, and the ammonia solution and sodium hydroxide solution prepared in (1-2) and the nickel-iron-manganese metal salt solution prepared in (1-1) are slowly injected again;

[0152] (1-5) After the precursor particles grow to a size of 4-5 μm, slowly inject the prepared ammonia solution and sodium hydroxide solution, maintain the temperature at 70°C and pH 10.4, change the stirring speed to 400 rpm, and continue aging and stirring for 12 hours;

[0153] (1-6) After aging is completed and the sample is completely precipitated, the supernatant is removed and the resulting precipitate is washed with a 1.0 mol / L sodium hydroxide solution at 50°C for 1 h, followed by five water washes, each for 1 h.

[0154] (1-7) The washed sample was dried in an oven at 120°C for about 24 h, and the dried sample was sieved using a 500-mesh sieve to obtain a precursor sample.

[0155] Synthesis of sodium battery cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2: According to the method described in Example 1, the positive electrode material precursor Ni prepared in Comparative Example 1 is used. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 was used to prepare the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0156] Referring to the method described in Example 1, the positive electrode material NaNi of Comparative Example 1 was used. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used to prepare positive electrode sheets and sodium ion batteries.

[0157] Comparative Example 2

[0158] A sodium ion battery cathode material precursor Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2, its specific surface area is 14.62m 2 / g, and the internal porosity is 8.27%. The synthesis of the precursor includes the following steps:

[0159] (1-1) preparing a nickel-iron-manganese metal salt solution: dissolving nickel sulfate, ferrous sulfate, and manganese sulfate in water at a molar ratio of Ni, Fe, and Mn of 1:1:1 to prepare a nickel-iron-manganese metal salt solution having a total metal ion concentration of 2 mol / L;

[0160] (1-2) preparing a 7.0 mol / L ammonia aqueous solution and a 10.0 mol / L sodium hydroxide aqueous solution;

[0161] (1-3) Deionized water was added to the reactor, and then the prepared ammonia solution and sodium hydroxide solution were added to the reactor. The temperature was adjusted to 40°C, the pH value was 11.6, the concentration of ammonia solution in the reactor was 10 g / L, and the stirring speed was 500 rpm. The metal salt solution prepared in (1-1) was added under stirring to grow precursor particles.

[0162] (1-4) After the precursor particles grow to a particle size of 2.5 μm, the temperature is increased to 62° C., the pH value is changed to 9.9, the ammonia concentration is changed to 8.6 g / L, the stirring speed is changed to 450 rpm, and the ammonia solution and sodium hydroxide solution prepared in (1-2) and the nickel-iron-manganese metal salt solution prepared in (1-1) are slowly injected again;

[0163] (1-5) After the precursor particles grow to a size of 4 μm, slowly inject the prepared ammonia solution and sodium hydroxide solution, maintain the temperature at 62 °C and pH 9.9, change the stirring speed to 400 rpm, and continue aging and stirring for 12 h;

[0164] (1-6) After aging is completed and the sample is completely precipitated, the supernatant is removed and the resulting precipitate is washed with a 1.0 mol / L sodium hydroxide solution at 50°C for 1 h, followed by five water washes, each for 1 h.

[0165] (1-7) The washed sample was dried in an oven at 120 °C for about 24 h, and the dried sample was sieved using a 500-mesh sieve to obtain a precursor sample.

[0166] Synthesis of sodium battery cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2: According to the method described in Example 1, the positive electrode material precursor Ni prepared in Comparative Example 2 is used. 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)2 was used to prepare the positive electrode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0167] Referring to the method described in Example 1, the positive electrode material NaNi of Comparative Example 2 was used. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used to prepare positive electrode sheets and sodium ion batteries.

[0168] Comparative Example 3

[0169] A sodium ion battery cathode material precursor Ni0.32 Fe 0.32 Mn 0.32 Ca 0.04 (OH)2, its specific surface area is 17.18m 2 / g, and the internal porosity is 5.06%. The synthesis of the precursor includes the following steps:

[0170] (1-1) preparing a nickel-iron-manganese-calcium metal salt solution: dissolving nickel sulfate, ferrous sulfate, manganese sulfate, and calcium nitrate in water at a molar ratio of Ni:Fe:Mn:Ca of 32:32:32:4 to prepare a nickel-iron-manganese-calcium metal salt solution having a total metal ion concentration of 2 mol / L;

[0171] (1-2) preparing a 7.0 mol / L ammonia aqueous solution and a 10.0 mol / L sodium hydroxide aqueous solution;

[0172] (1-3) Deionized water was added to the reaction kettle, and then the prepared ammonia solution and sodium hydroxide solution were added to the reaction kettle. The temperature was adjusted to 40°C, the pH value was 11.7, the ammonia concentration was 9.5 g / L, and the stirring speed was 500 rpm. The metal salt solution prepared in (1-1) was added under stirring to grow precursor particles.

[0173] (1-4) After the precursor particles grow to a particle size of 2.5 μm, the temperature is maintained constant, the pH value is changed to 10.5, the ammonia concentration is changed to 7.0 g / L, the stirring speed is changed to 450 rpm, and the ammonia solution and sodium hydroxide solution prepared in (1-2) and the nickel, iron, manganese and calcium metal salt solution prepared in (1-1) are slowly injected again;

[0174] (1-5) After the precursor particles grow to a size of 5 μm, slowly inject the prepared ammonia solution and sodium hydroxide solution, maintain the temperature at 53 °C, change the pH value to 10.0, and stir at 400 rpm, and continue aging and stirring for 12 h;

[0175] (1-6) After aging is completed and the sample is completely precipitated, the supernatant is removed and the resulting precipitate is washed with a 1.0 mol / L sodium hydroxide solution at 50°C for 1 h, followed by five water washes, each for 1 h.

[0176] (1-7) The washed sample was dried in an oven at 120 °C for about 24 h, and the dried sample was sieved using a 500-mesh sieve to obtain a precursor sample.

[0177] Synthesis of sodium battery cathode material NaNi 0.32 Fe 0.32 Mn 0.32 Ca0.04 O2: According to the method described in Example 1, the positive electrode material precursor NaNi prepared in Comparative Example 3 is used. 0.32 Fe 0.32 Mn 0.32 Ca 0.04 (OH)2 was used to prepare the positive electrode material.

[0178] Referring to the method described in Example 1, the positive electrode material NaNi of Comparative Example 3 was used. 0.32 Fe 0.32 Mn 0.32 Ca 0.04 O2 is used to prepare positive electrode sheets and sodium ion batteries.

[0179] The cathode material precursors prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to cross-sectional SEM testing. The resulting cross-sectional SEM photographs are summarized in Figure 6 (the dark areas in the figure represent pores, and the light areas represent material areas). The internal porosity of each cathode precursor was determined based on these cross-sectional SEM photographs, and the results are summarized in Table 1 below. In addition, the specific surface area of ​​each cathode precursor powder was tested using nitrogen adsorption, and the relevant results are also summarized in Table 1 below.

[0180] Table 1 Test results of various cathode material precursors

[0181] It can be seen from Table 1 that the internal porosity and specific surface area of ​​the positive electrode material precursors of Examples 1-2 are significantly higher than those of Comparative Examples 1-3. The high internal porosity and high specific surface area of ​​the precursors can make it easier for sodium salt to penetrate into the interior of the precursor during sintering with the precursor, thereby making the morphology and structure of the obtained positive electrode material more rounded and the single crystal effect better.

[0182] The positive electrode materials obtained in Examples 1-2 and Comparative Examples 1-3 were tested using a scanning electron microscope, and the resulting SEM photographs are shown in Figure 7. It can be seen from Figure 7 that the positive electrode materials of Examples 1-2 exhibit obvious roundness and high sphericity of single crystal material characteristics, while the positive electrode materials of Comparative Examples 1-3 all exhibit obvious flat sheet structures, wherein the positive electrode materials of Comparative Examples 1 and 3 are single crystal or quasi-single crystal structures, while the positive electrode material of Comparative Example 2 is a particle with a polycrystalline structure. It can also be seen from Figure 7 that the average particle size D50 of the positive electrode material in Example 1 of the present application is 2 μm, the D50 of the positive electrode materials of Example 2, Comparative Example 1, and Comparative Example 3 are all 5 μm, and the D50 of the positive electrode material of Comparative Example 2 is 3 μm.

[0183] From the SEM photographs of the positive electrode materials of Examples 1-2 and Comparative Examples 1-3, more than 50 positive electrode material particles were taken to calculate the sphericity of each particle. The resulting distribution diagram is shown in Figure 8. In Figure 8, the abscissa is the inverse of the particle sphericity, and the ordinate is the number of particles. It can be seen from Figure 8 that the average values ​​of the circumference equivalent radius d2 / area equivalent radius d1 of the positive electrode material particles of Examples 1-2 are 1.10 and 1.13, respectively; while the average values ​​of d2 / d1 of the positive electrode material particles of Comparative Examples 1-3 are 1.31, 1.35, and 1.25, respectively. According to the definition of average particle sphericity above, it can be seen that the average particle sphericity of the positive electrode material particles of Examples 1-2 is 0.9091 and 0.8849, respectively, both greater than 0.85, while the average particle sphericity of the positive electrode material particles of Comparative Examples 1-3 is 0.7633, 0.7407, and 0.8, respectively, all significantly lower than the average particle sphericity of the positive electrode materials of Examples 1-3. It can be seen that the positive electrode material particles in the embodiment of the present application have a high degree of roundness in morphology.

[0184] In addition, it can be seen from Figure 8 that among the 58 sodium-ion positive electrode material particles selected in Example 1, the number of particles with a sphericity less than 0.85 accounts for only 5.2%, and among the 56 sodium-ion positive electrode material particles selected in Example 2, the number of particles with a sphericity less than 0.85 accounts for about 13%. It can be seen that the number of sodium-ion positive electrode material particles with low sphericity accounts for a low proportion, which is conducive to ensuring that the average particle sphericity of the positive electrode material is high, and thus is conducive to improving the dynamic properties and compaction density of the material.

[0185] The positive electrode materials obtained in Examples 1-2 and Comparative Examples 1-3 were tested using an XRD (X-ray Diffraction) instrument, and the resulting XRD spectra are shown in FIG9 . As can be seen from FIG9 , the positive electrode materials obtained in Examples 1-2 and Comparative Examples 1-3 all have characteristic diffraction peaks of the following 13 crystal planes: (003), (006), (101), (012), (104), (015), (107), (018), (110), (113), (1010), (116), and (024). If the sum of the peak areas of the above 13 diffraction peaks in each XRD spectrum is S all The peak area of ​​the (003) crystal plane diffraction peak is recorded as S (003) The sum of the areas of the other 12 crystal plane diffraction peaks except (015) is recorded as S a , then the peak area of ​​each crystal plane diffraction peak is compared with S all The ratio of S (003) With S a The ratio of S (003) / [S (012) +S (110) ] are summarized in Table 2 below.

[0186] Table 2 Summary of XRD spectra of various cathode materials

[0187] From Table 1, we can see that in the XRD spectrum of the positive electrode material of Example 1-2, S (003) / S a The values ​​are 21.42% and 21.51%, respectively, which are all less than 25%; while the S of the positive electrode materials of Comparative Examples 1-3 (003) / S a The values ​​are all greater than 25%. This reflects that the positive electrode materials of the present application examples are round particles with high sphericity. In addition, the S (003) / [S (012) +S (110) ] are lower than those in Comparative Examples 1-3. (003) / [S (012) +S (110) ] are all less than 1.6, which also reflects that the orientation degree of the (003) crystal plane in the positive electrode material of the embodiment of the present application is not high, and the positive electrode material is a round particle with high sphericity.

[0188] The positive electrode materials of Examples 1-2 and Comparative Examples 1-3 were respectively tested for compaction density in a powder compaction density meter, and the test results are shown in Figure 10. Among them, the compaction density values ​​of each powder material under a pressure of 200MPa are summarized in Table 3 below. In addition, button-type sodium batteries assembled with the positive electrode materials of Examples 1-2 and Comparative Examples 1-3 were also subjected to charge and discharge tests, wherein the voltage range of the charge and discharge tests was 2.0-4.0V, the first cycle charge and discharge rate was 0.1C, and the electrochemical curve of the first cycle is shown in Figure 11. The charge specific capacity of each button-type sodium battery during the first charge and discharge process, the median voltage during the charging process, and the battery energy density calculated therefrom are summarized in Table 3 below. Among them, battery energy density = compaction density of positive electrode material × first charge specific capacity × median voltage.

[0189] Table 3 Summary of the compaction density and electrochemical performance of each cathode material

[0190] It can be seen from Table 3 that the compaction density of the positive electrode material powder of Examples 1-2 is relatively high, reaching 3.21g / mL and 3.42g / mL respectively, which may be related to the fact that the positive electrode materials of the embodiments of the present application have the above-mentioned higher sphericity and rounded structure. However, the positive electrode materials of Comparative Examples 1-3 are flat structures, which easily produce obvious gaps during the compaction test. Therefore, the compaction density of the positive electrode material powder of the comparative example is significantly lower, and none of them exceeds 3.10g / mL. In addition, because the compaction density of the positive electrode material of the embodiment of the present application is relatively high, the battery energy density calculated based on this is also relatively high, at above 1450Wh / L, which is much higher than the energy density of the button batteries of Comparative Examples 1-3. The energy density of these three does not exceed 1350Wh / L.

[0191] In order to verify that the kinetic performance of the sodium-based positive electrode material provided in the embodiments of the present application is good, button batteries made of the positive electrode materials of Example 2, Comparative Example 1, and Comparative Example 3, whose particle sizes are similar, are subjected to rate tests and GITT (Galvanostatic Intermittent Titration Technique) tests to eliminate the influence of the difference in particle radius on the results. Among them, the test results of rate performance are shown in Figure 12, and the test results of GITT are shown in Figure 13. It can be clearly seen from Figure 12 that the capacity retention rate of the button battery made of the positive electrode material of Example 2 at high rate is significantly better than that of Comparative Example 1 and Comparative Example 3, and it can be seen from Figure 13 that the diffusion coefficient of the positive electrode material of Example 2 during the charge and discharge process is significantly higher than that of Comparative Example 1 and Comparative Example 3. This may be mainly because the exposure degree of the active surface of the rounded single crystal particles with high sphericity is increased, which can significantly improve the kinetic performance of the layered positive electrode material, thereby improving the rate performance of the battery.

[0192] Next, the improvement in the cycle performance of the sodium-based positive electrode material provided in the embodiments of the present application is discussed. First, the sodium-based positive electrode material of each embodiment or comparative example is prepared into a soft-pack sodium-ion battery, and the specific preparation steps include: adding the above-mentioned sodium-based positive electrode material and binder polyvinylidene fluoride (PVDF), conductive agent super P, conductive agent carbon nanotube CNT, and oxalic acid to the solvent N-methylpyrrolidone (NMP) in a mass ratio of 96:1:0.5:0.5, and stirring and mixing them to obtain a mixed slurry, which is coated on both sides of an aluminum foil current collector, and dried, cold pressed, and cut to obtain a positive electrode sheet. At the same time, hard carbon is used as the negative electrode active material, and is stirred evenly with binder CMC, SBR, and conductive agent Super P to prepare a negative electrode slurry, which is coated on an aluminum foil current collector, and dried, cold pressed, and cut to obtain a negative electrode sheet. The positive electrode sheet, diaphragm, and negative electrode sheet are stacked in a laminated manner to obtain a bare battery cell, and encapsulated with an aluminum-plastic film to obtain a soft-pack battery.

[0193] Then, the soft-pack sodium battery assembled with the positive electrode materials of Examples 1-2 and Comparative Examples 1-3 was subjected to electrochemical testing, wherein the voltage range of the electrochemical test was 2.0-3.95V, the cycle rate was 1C, and for every 50 cycles of charge and discharge at 1C, a cycle of charge and discharge at a rate of 0.1C was performed to recover the capacity. The cycle performance test results of each soft-pack sodium battery are summarized in Figure 14. It can be seen from Figure 14 that the cycle performance of the fully packed sodium battery of Example 1-2 is better than that of Comparative Examples 1-3. This may be due to the higher sphericity of the particles of the positive electrode material of Example 1-2, which can deintercalate Na during the battery cycle. + The uniformity of the material is improved, which can avoid local excessive Na removal in the material. + The formation of the region. + The formation of the region will cause serious damage to the material structure, resulting in a decrease in its cycle performance. + The uniformity is improved, and thus its cycle stability is improved.

[0194] The above merely represents several exemplary embodiments of the present application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art would be able to make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

[0195] In the description of this application, unless otherwise specified, the meaning of "multiple (kinds)" refers to greater than or equal to two (kinds). "At least one (kind)" refers to one (kind) or more (kinds). "At least one of the following (kinds)" or similar expressions refers to any combination of these items, including any combination of single (individual) or plural (individual) items. For example, "at least one (individual) of a, b, or c", or "at least one (individual) of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0196] In addition, the numerical range represented by "-" in this application refers to the range including the numerical values ​​recorded before and after "-" as the minimum and maximum values, respectively. In this application, expressions about parameter ranges, such as "greater than or equal to (≥)", "less than or equal to (≤)", "above...", and "below..." all include the number itself. The numerical values ​​and numerical ranges involved in the embodiments of this application are approximate values. Due to the influence of manufacturing process / testing method, etc., there may be a certain range of errors, which can be considered negligible by those skilled in the art.

Claims

1. A sodium cathode material, characterized in that The sodium-based positive electrode material includes a sodium-based metal oxide. The X-ray diffraction spectrum of the sodium-based positive electrode material includes diffraction peaks of the following 12 crystal planes: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024). The ratio of the peak area of ​​the diffraction peak of the (003) crystal plane to the sum of the peak areas of the diffraction peaks of the 12 crystal planes is less than 25%.

2. The sodium cathode material according to claim 1, wherein The ratio of the peak area of ​​the diffraction peak of the (003) crystal plane to the sum of the peak areas of the diffraction peaks of the 12 crystal planes is less than or equal to 23%.

3. The sodium cathode material according to claim 1 or 2, wherein The ratio of the diffraction peak area of ​​the (003) crystal plane to the sum of the diffraction peak areas of the (012) crystal plane and the (110) crystal plane is less than 1.

6.

4. The sodium cathode material according to any one of claims 1 to 3, wherein The sodium battery positive electrode material is single crystal or single crystal-like particles.

5. The sodium cathode material according to any one of claims 1 to 4, characterized in that The sodium cathode material is in the form of spherical or quasi-spherical particles.

6. The sodium cathode material according to any one of claims 1 to 5, characterized in that The average particle sphericity of the sodium-ion positive electrode material is greater than or equal to 0.

85.

7. The sodium cathode material according to claim 6, wherein In the sodium battery positive electrode material, the number of particles with a sphericity of less than 0.85 accounts for less than 30%.

8. The sodium cathode material according to claim 7, wherein The aspect ratio of the particles having a sphericity of less than 0.85 is within a range of greater than 1 and less than 3.

9. The sodium battery cathode material according to any one of claims 1 to 8, characterized in that The average particle size of the sodium cathode material is in the range of 2 μm to 20 μm.

10. The sodium cathode material according to any one of claims 1 to 9, characterized in that The chemical formula of the sodium-based metal oxide includes Na x M a D b O y , where 0.5 ≤ x ≤ 1.2, 1.8 ≤ y ≤ 2.2, 0 < a ≤ 1, 0 ≤ b < 1, A is a metal element, and A includes at least one transition metal element, and D is a non-metal element.

11. The sodium cathode material according to claim 10, wherein The A includes one or more of V, Fe, Cr, Mn, Co, Ni, Cu, Ti, Zn, Zr, Mo, Nb, Li, K, Al, Mg, Ca, Sr, Sn, and Sb; and the D includes at least one of F, B, P, Si, C, and N.

12. The sodium battery cathode material according to any one of claims 1 to 11, characterized in that The sodium-based positive electrode material further includes a coating layer coated on the surface of the sodium-based metal oxide.

13. The sodium battery cathode material according to any one of claims 1 to 12, wherein: The compaction density of the sodium cathode material at 200 MPa is above 3.1 g / mL.

14. A sodium cathode material, characterized in that The sodium-based positive electrode material includes a sodium-based metal oxide, and the average particle sphericity of the sodium-based positive electrode material is greater than or equal to 0.

85.

15. The sodium cathode material according to claim 14, wherein The X-ray diffraction spectrum of the sodium cathode material includes diffraction peaks of the following 12 crystal planes: (003), (006), (101), (012), (104), (107), (018), (110), (113), (1010), (116), and (024), and the ratio of the peak area of ​​the diffraction peak of the (003) crystal plane to the sum of the peak areas of the diffraction peaks of the 12 crystal planes is less than 25%.

16. The sodium cathode material according to claim 14 or 15, characterized in that The sodium battery positive electrode material is a single crystal or quasi-single crystal particle.

17. A sodium cathode material precursor, characterized in that: The sodium-based cathode material precursor comprises a sodium-based metal oxide precursor, wherein the internal porosity of the sodium-based cathode material precursor is greater than or equal to 10%, and / or the specific surface area of ​​the sodium-based cathode material precursor is greater than or equal to 25 m 2 / g.

18. The sodium cathode material precursor according to claim 17, characterized in that The sodium cathode material precursor is a secondary particle; wherein the particle size of the secondary particle is in the range of 1-20 μm.

19. The sodium cathode material precursor according to claim 17 or 18, characterized in that The sodium-based metal oxide precursor includes hydroxide, carbonate, or oxyhydroxide.

20. A method for preparing a sodium cathode material, characterized in that: The following steps are involved: The sodium-based cathode material precursor according to any one of claims 17 to 19 is mixed with a sodium source and calcined to obtain the sodium-based cathode material.

21. The preparation method according to claim 20, characterized in that The calcination temperature is 850° C.-1200° C., the calcination time is 6-30 hours; and the calcination atmosphere is an oxygen atmosphere or an air atmosphere.

22. The preparation method according to claim 21, wherein The calcination includes: first calcining at a first temperature for a first time, then lowering the temperature to a second temperature, and calcining for a second time; wherein the first time is shorter than the second time.

23. A positive electrode plate, characterized in that: The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer arranged on at least one side of the positive electrode current collector, and the positive electrode material layer includes the sodium-based positive electrode material according to any one of claims 1 to 13, or the sodium-based positive electrode material according to any one of claims 14 to 16, or the sodium-based positive electrode material obtained by the preparation method according to any one of claims 20 to 21.

24. A sodium ion battery, characterized in that: The sodium ion battery includes a negative electrode plate and a positive electrode plate as claimed in claim 23, and the sodium ion battery also includes a separator and an electrolyte located between the positive electrode plate and the negative electrode plate.

25. An electrical device, characterized in that: The electrical equipment includes an electrical component and a power supply component, the power supply component supplies power to the electrical component, and the power supply component includes the sodium ion battery as described in claim 24.

26. The electrical equipment according to claim 25, characterized in that: The electrical equipment includes electronic equipment or a power-moving device.

27. An energy storage system, characterized in that: The energy storage system includes at least one battery pack, and the battery pack includes a plurality of sodium ion batteries as claimed in claim 24.

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