Preparation method and application of NaCrO2 single-crystal positive electrode material

Abstract

The invention belongs to the technical field of sodium ion batteries, relates to a preparation method and application of a NaCrO2 single-crystal positive electrode material, and particularly provides a large-size Cr2O3 single-crystal material and the NaCrO2 single-crystal positive electrode material which is prepared from the large-size Cr2O3 single-crystal material and has a long-range ordered structure, so that the direct conversion from single crystal to single crystal is realized, and the production cost is reduced. The problems of particle agglomeration, sodium salt volatilization, selection and cleaning of molten salt, tedious process and the like in the prior art (high-temperature roasting method, molten salt method and multi-step calcining method) of the transition metal layered oxide single crystal positive electrode material of the sodium ion battery are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and more specifically relates to a preparation method and application of a NaCrO2 single crystal positive electrode material. Background Art

[0002] Single crystal cathode materials can significantly improve the overall performance of batteries through their advantages in high mechanical strength, high compaction density, excellent electrochemical performance, thermal stability and air stability. However, existing single crystal cathode materials mainly use nano-sized small particle battery materials as precursors. After high temperature calcination, the crystal particles grow and the small particles grow into single crystal cathode materials. Since the raw materials are small particles, there are a large number of grain boundaries between the particles and the anisotropy of the lattice between the particles. It is impossible to obtain a perfect single crystal structure through high temperature treatment. Crystal defects caused by grain boundaries and anisotropy are inevitable. At present, the synthesis methods of single crystal cathode materials for sodium ion batteries mainly include the following:

[0003] 1. High-temperature sintering method: The growth of single crystals is promoted by increasing the sintering temperature, but the amount of lithium salt or sodium salt needs to be increased to compensate for the volatilization of lithium or sodium at high temperature;

[0004] 2. Molten salt method: Add low melting point fluxing salt to reduce the sintering temperature and accelerate ion transport and grain growth through liquid mass transfer;

[0005] 3. Multi-step calcination method: avoids the negative effects of one-step high-temperature sintering, such as grain agglomeration and impurity formation.

[0006] Although the above methods can prepare single-crystal positive electrode materials for sodium-ion batteries, the main problems they have include: the high-temperature sintering method has problems of particle agglomeration and sodium salt volatilization; the molten salt method has problems of molten salt screening and cleaning of single-crystal positive electrode materials; the multi-step calcination method has complex processes and high time costs.

[0007] Moreover, the above methods all convert polycrystalline or nano sodium ion battery positive electrode materials into single crystal positive electrode materials through subsequent heat treatment. However, due to the anisotropy of polycrystalline or nano sodium ion battery positive electrode material particles, it is inevitable that there are more lattice defects in the single crystal positive electrode materials prepared therefrom, which limits the formation of their long-range ordered structures. Summary of the Invention

[0008] The purpose of the present invention is to provide a preparation method and application of NaCrO2 single crystal positive electrode material, more specifically to provide a large-size Cr2O3 single crystal material, and a NaCrO2 single crystal positive electrode material prepared from the large-size Cr2O3 single crystal material, to achieve direct conversion from single crystal to single crystal, and to solve the problems of particle agglomeration and sodium salt volatilization, molten salt selection and cleaning, and complicated process existing in the existing technologies of transition metal layered oxide single crystal positive electrode materials for sodium ion batteries (high-temperature roasting method, molten salt method, multi-step calcination method).

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] One of the technical solutions of the present invention is to provide a method for preparing a large-sized Cr2O3 single crystal material, comprising the following steps:

[0011] The large-size Cr2O3 single crystal material is obtained by taking hexavalent chromium salt, alkaline reagent and reducing organic matter as raw materials through hydrothermal reaction and roasting.

[0012] Furthermore, the hexavalent chromium salt includes at least one of sodium chromate, sodium dichromate, potassium chromate, potassium dichromate, ammonium chromate and ammonium dichromate.

[0013] Furthermore, the alkaline reagent includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, sodium carbonate, potassium carbonate and urea.

[0014] Furthermore, the reducing organic matter includes at least one of carbon, glucose, starch, methanol, ethanol, acetic acid, citric acid and ascorbic acid.

[0015] Furthermore, the mass ratio of the hexavalent chromium salt, the alkaline reagent and the reducing organic matter is (15-25):(8-10):(3-9).

[0016] Furthermore, the temperature of the hydrothermal reaction is 200-280° C., and the time is 4-24 hours.

[0017] Furthermore, the calcination temperature is 1100-1400° C. and the calcination time is 2-24 hours.

[0018] The higher the hydrothermal temperature, the shorter the reaction time required, and the more thorough the reduction of hexavalent chromium to trivalent chromium hydroxide. The higher the high-temperature roasting temperature and the longer the high-temperature roasting time, the larger the size of the resulting large-sized Cr2O3 single crystal material.

[0019] Furthermore, after the hydrothermal reaction is completed, a purification step of the reaction product is also included.

[0020] Optionally, the purification step includes: after the hydrothermal reaction is completed, solid-liquid separation, washing the solid product until the pH value of the filtrate is neutral, and then drying.

[0021] The second technical solution of the present invention is to provide a large-size Cr2O3 single crystal material, which is prepared by the above-mentioned preparation method.

[0022] The large-size Cr2O3 single crystal material provided by the present invention has a size of 1 micron to 20 microns and a larger particle size, especially concentrated in a particle size of about 3 to 5 microns, laying a solid foundation for the subsequent preparation of high-performance sodium ion battery positive electrode materials.

[0023] The third technical solution of the present invention is to provide an application of the above-mentioned large-size Cr2O3 single crystal material in the preparation of positive electrode materials for sodium ion batteries.

[0024] The fourth technical solution of the present invention is to provide a method for preparing a NaCrO2 single crystal positive electrode material having a long-range ordered structure, the steps comprising:

[0025] The large-size Cr2O3 single crystal material is mixed with a sodium source and calcined to obtain the NaCrO2 single crystal positive electrode material with a long-range ordered structure.

[0026] Furthermore, the molar ratio of Cr to Na in the large-size Cr2O3 single crystal material and the sodium source is 1:1-1.05.

[0027] Furthermore, the sodium source includes at least one of NaOH, Na2CO3, NaHCO3, sodium acetate and sodium citrate.

[0028] Furthermore, the calcination temperature is not less than 700° C., and the calcination time is 5-12 hours.

[0029] Optionally, the calcination temperature is 800-1200°C.

[0030] The present invention uses large-sized single crystal Cr2O3 as a raw material, mixes it with a sodium source, and prepares a positive electrode material through a one-step calcination. By using an oxide of complete large-sized single crystal particles as a precursor, and mixing it with a Na source through a high-temperature process, active Na ions formed are gradually inserted into the crystal structure of the single crystal oxide, thereby maintaining the long-range ordered structure of the single crystal oxide precursor. This overcomes the problem in the prior art that a large number of crystal defects exist inside the particles as the particles grow from small to large, causing cracking inside the particles after multiple charges and discharges. This realizes direct conversion from single crystal to single crystal, and the obtained single crystal NaCrO2 positive electrode material has fewer single crystal structural defects and a better long-range ordered layered structure.

[0031] The fifth technical solution of the present invention: provides a NaCrO2 single crystal positive electrode material with a long-range ordered structure, and the NaCrO2 single crystal positive electrode material is prepared by the above-mentioned preparation method.

[0032] Technical solution six of the present invention: Provides an application of the above-mentioned NaCrO2 single crystal positive electrode material with a long-range ordered structure in the preparation of sodium ion batteries.

[0033] Technical solution seven of the present invention: Provides a sodium ion battery positive electrode, the active component of the sodium ion battery positive electrode includes the above-mentioned NaCrO2 single crystal positive electrode material with a long-range ordered structure.

[0034] Technical solution eight of the present invention: provides a sodium ion battery, including the above-mentioned sodium ion battery positive electrode.

[0035] The present invention discloses the following technical effects:

[0036] The size of the single crystal Cr2O3 prepared by the present invention can reach 1-20μm. The single crystal NaCrO2 positive electrode material prepared by the present invention has fewer single crystal structural defects and a better long-range ordered layered structure, which solves the problem in the prior art that a large number of crystal defects exist inside the particles as the particles grow from small to large, thereby causing cracking inside the particles after multiple charges and discharges. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 This is the SEM image of the large-sized Cr2O3 single crystal material prepared in Example 1.

[0039] Figure 2 This is the particle size distribution diagram of the large-sized Cr2O3 single crystal material prepared in Example 1.

[0040] Figure 3 This is the XRD pattern of the NaCrO2 single crystal positive electrode material with long-range ordered structure prepared in Example 1.

[0041] Figure 4 These are SEM images of the NaCrO2 single crystal positive electrode material with a long-range ordered structure prepared in Example 1 at different magnifications.

[0042] Figure 5 This is the SEM image of the Cr2O3 material prepared in Comparative Example 1.

[0043] Figure 6 This is the particle size distribution diagram of the Cr2O3 material prepared in Comparative Example 1.

[0044] Figure 7 This is the XRD pattern of the nano-NaCrO2 positive electrode material prepared in Comparative Example 1.

[0045] Figure 8 This is the SEM image of the nano-NaCrO2 positive electrode material prepared in Comparative Example 1.

[0046] Figure 9 The charge-discharge cycle performance of the sodium ion battery composed of the NaCrO2 single crystal positive electrode material obtained in Example 1 at 20C.

[0047] Figure 10 The cycling performance of the sodium ion battery composed of the nano-NaCrO2 positive electrode material obtained in Comparative Example 1 under 2C conditions.

[0048] Figure 11 The rate performance of the sodium ion battery composed of the NaCrO2 single crystal positive electrode material obtained in Example 1.

[0049] Figure 12 This is the rate performance of the sodium ion battery composed of the nano-NaCrO2 positive electrode material obtained in Comparative Example 1.

[0050] Figure 13 This is the SEM image of the NaCrO2 single crystal positive electrode material on the positive electrode after 1000 cycles at 20C in Example 1.

[0051] Figure 14 These are SEM images of Cr2O3 materials in Examples 2-4 and Comparative Examples 2-3, where a is Example 2, b is Example 3, c is Example 4, d is Comparative Example 2, and e is Comparative Example 3.

[0052] Figure 15 2-4 and comparative example 2-3, wherein a is embodiment 2, b is embodiment 3, c is embodiment 4, d is comparative example 2, and e is comparative example 3.

[0053] Figure 16 2-4 and comparative examples 2-3, wherein a is for example 2, b is for example 3, c is for example 4, d is for comparative example 2, and e is for comparative example 3.

[0054] Figure 17 These are SEM images of NaCrO2 materials in Examples 2-4 and Comparative Examples 2-3, where a is Example 2, b is Example 3, c is Example 4, d is Comparative Example 2, and e is Comparative Example 3.

[0055] Figure 18 The cycling performance of sodium ion batteries composed of the NaCrO2 positive electrode materials obtained in Examples 2-4 and Comparative Example 3 under charge and discharge conditions, wherein a is Example 2 at 20°C, b is Example 3 at 20°C, c is Example 4 at 10°C, and d is Comparative Example 3 at 10°C.

[0056] Figure 19 The rate performance of the sodium ion battery composed of the NaCrO2 positive electrode materials obtained in Examples 2-4 and Comparative Example 3, wherein a is Example 2, b is Example 3, c is Example 4, and d is Comparative Example 3. DETAILED DESCRIPTION

[0057] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0058] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0059] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0060] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0061] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0062] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0063] The raw materials and reagents used in the specific embodiments of the present invention are all commercially available products, and the purchase channels do not affect the realization of the technical effects.

[0064] Unless otherwise specified, the room temperature and normal temperature involved in the specific embodiments of the present invention refer to 20-30°C.

[0065] Example 1

[0066] The preparation steps of NaCrO2 single crystal cathode material with long-range ordered structure include:

[0067] S1. Mix 25 g of sodium chromate, 5 g of sodium carbonate, and 3 g of sodium hydroxide with water to form a 100 mL aqueous solution, and then add 8.1 g of citric acid monohydrate to obtain a mixed solution;

[0068] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 280° C., and hydrothermally reacted for 6 h. The mixture was then naturally cooled to room temperature. The solid product was washed to neutrality after filtration and dried to obtain an intermediate product.

[0069] S3, calcining the intermediate product at 1200° C. for 6 h, naturally cooling, washing, and drying to obtain a large-sized Cr2O3 single crystal material;

[0070] S4. The large-sized Cr2O3 single crystal material prepared in step S3 is mixed with sodium carbonate at a Cr:Na molar ratio of 1:1.05, and then calcined at 1100°C for 10 hours under an Ar atmosphere to obtain a NaCrO2 single crystal positive electrode material with a long-range ordered structure.

[0071] Example 2

[0072] The preparation steps of NaCrO2 single crystal cathode material with long-range ordered structure include:

[0073] S1. Mix 25 g of potassium chromate and 10 g of potassium carbonate with water to prepare 100 mL of aqueous solution, and then add 5.80 g of acetic acid to obtain a mixed solution;

[0074] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 260° C., and hydrothermally reacted for 12 h. The mixture was then naturally cooled to room temperature. The solid product was washed to neutrality after filtration and dried to obtain an intermediate product.

[0075] S3, calcining the intermediate product at 1300° C. for 4 h, naturally cooling, washing, and drying to obtain a large-sized Cr2O3 single crystal material;

[0076] S4. The large-sized Cr2O3 single crystal material prepared in step S3 is mixed with sodium hydroxide at a Cr:Na molar ratio of 1:1.05, and then calcined at 1000°C for 12 hours under an Ar atmosphere to obtain a NaCrO2 single crystal positive electrode material with a long-range ordered structure.

[0077] Example 3

[0078] The preparation steps of NaCrO2 single crystal cathode material with long-range ordered structure include:

[0079] S1. 15 g of sodium dichromate, 5 g of sodium carbonate, and 3 g of sodium hydroxide were mixed with water to form a 100 mL aqueous solution, and then 2.78 g of starch was added to obtain a mixed solution;

[0080] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 240° C., and hydrothermally reacted for 18 h. The mixture was then naturally cooled to room temperature. The solid product was washed to neutrality after filtration and dried to obtain an intermediate product.

[0081] S3, calcining the intermediate product at 1200° C. for 12 h, cooling naturally, washing, and drying to obtain a large-sized Cr2O3 single crystal material;

[0082] S4. The large-sized Cr2O3 single crystal material prepared in step S3 is mixed with sodium acetate at a Cr:Na molar ratio of 1:1.05, and then calcined at 900°C for 20 hours under an Ar atmosphere to obtain a NaCrO2 single crystal positive electrode material with a long-range ordered structure.

[0083] Example 4

[0084] The preparation steps of NaCrO2 single crystal cathode material with long-range ordered structure include:

[0085] S1. Mix 15 g of potassium dichromate and 7 g of potassium carbonate with water to prepare 100 mL of aqueous solution, and then add 4.59 g of glucose to obtain a mixed solution;

[0086] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 200° C., and hydrothermally reacted for 24 h. The mixture was then naturally cooled to room temperature. The solid product was washed to neutrality after filtration and dried to obtain an intermediate product.

[0087] S3, calcining the intermediate product at 1150° C. for 24 h, naturally cooling, washing, and drying to obtain a large-sized Cr2O3 single crystal material;

[0088] S4. The large-sized Cr2O3 single crystal material prepared in step S3 is mixed with sodium acetate at a Cr:Na molar ratio of 1:1.05, and then calcined at 800°C for 20 hours under an Ar atmosphere to obtain a NaCrO2 single crystal positive electrode material with a long-range ordered structure.

[0089] Comparative Example 1

[0090] The preparation steps of nano-scale NaCrO2 positive electrode material include:

[0091] S1. Mix 25 g of sodium chromate, 5 g of sodium carbonate, and 3 g of sodium hydroxide with water to form a 100 mL aqueous solution, and then add 8.1 g of citric acid monohydrate to obtain a mixed solution;

[0092] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 280° C., and hydrothermally reacted for 6 h. The mixture was then naturally cooled to room temperature. The solid product was washed to neutrality after filtration and dried to obtain an intermediate product.

[0093] S3, calcining the intermediate product at 800°C for 2h, cooling naturally, washing and drying to obtain nano-Cr2O3 material;

[0094] S4. The nano-Cr2O3 material prepared in step S3 is mixed with sodium carbonate at a Cr:Na molar ratio of 1:1.05, and then calcined at 1100°C for 10 hours under an Ar atmosphere to obtain a nano-scale NaCrO2 positive electrode material.

[0095] Comparative Example 2

[0096] The preparation steps of NaCrO2 single crystal positive electrode material include:

[0097] S1. Mix 25 g of sodium chromate, 5 g of sodium carbonate, and 3 g of sodium hydroxide with water to form a 100 mL aqueous solution, and then add 8.1 g of citric acid monohydrate to obtain a mixed solution;

[0098] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 280° C., and hydrothermally reacted for 6 h. The mixture was then naturally cooled to room temperature. The solid product was washed to neutrality after filtration and dried to obtain an intermediate product.

[0099] S3, calcining the intermediate product at 1200°C for 6 hours, naturally cooling, washing, and drying to obtain a large-sized Cr2O3 material;

[0100] S4. The large-sized Cr2O3 single crystal material prepared in step S3 is mixed with sodium carbonate at a Cr:Na molar ratio of 1:1.05, and then calcined at 700°C for 10 hours under an Ar atmosphere to obtain a NaCrO2 single crystal positive electrode material. At this time, the product contains unreacted raw materials Cr2O3 and Na2CO3.

[0101] Comparative Example 3

[0102] The preparation steps of NaCrO2 single crystal positive electrode material include:

[0103] S1. Mix 25 g of sodium chromate, 5 g of sodium carbonate, and 3 g of sodium hydroxide with water to form a 100 mL aqueous solution, and then add 5.4 g of citric acid monohydrate to obtain a mixed solution;

[0104] S2. The mixed solution was transferred to a 200 mL stainless steel high-temperature reactor, heated to 280°C, and hydrothermally reacted for 6 h, then naturally cooled to room temperature. After filtration, the solid product was washed to neutrality and dried to obtain an intermediate product. Unreacted hexavalent ions were present in the mother liquor.

[0105] S3, calcining the intermediate product at 1200°C for 6 hours, naturally cooling, washing, and drying to obtain a large-sized Cr2O3 material;

[0106] S4. The large-sized Cr2O3 single crystal material prepared in step S3 is mixed with sodium carbonate at a Cr:Na molar ratio of 1:1.05, and then calcined at 1100°C for 10 hours in an Ar atmosphere to obtain a NaCrO2 single crystal positive electrode material.

[0107] Test example

[0108] Figure 1 This is the SEM image of the large-sized Cr2O3 single crystal material prepared in Example 1.

[0109] Figure 2 This is the particle size distribution diagram of the large-sized Cr2O3 single crystal material prepared in Example 1.

[0110] Depend on Figure 1 and Figure 2 It can be seen that the size of the large-sized Cr2O3 single crystal material prepared by the present invention reaches the micron level. The particle size of the large-sized chromium oxide single crystal material shown in the picture is above 1.5 microns and is a monodisperse particle.

[0111] Figure 3 The XRD pattern of the NaCrO2 single crystal cathode material with long-range ordered structure prepared in Example 1 is shown in FIG. Figure 3 It can be seen that the obtained NaCrO2 positive electrode material is NaCrO2 with very high purity and no impurities are present.

[0112] Figure 4 The SEM images of the NaCrO2 single crystal cathode material with long-range ordered structure prepared in Example 1 at different magnifications are shown. Figure 4 The resulting NaCrO2 single crystals have a similar particle size to the large-sized Cr2O3 single crystals from the raw material, indicating monodispersity. The interior of the resulting NaCrO2 single crystals is composed of ordered layers, indicating long-range order.

[0113] Figure 5 This is the SEM image of the Cr2O3 material prepared in Comparative Example 1.

[0114] Figure 6This is the particle size distribution diagram of the Cr2O3 material prepared in Comparative Example 1.

[0115] Depend on Figure 5 and Figure 6 It can be seen that the size of the nano-Cr2O3 material prepared in the comparative example is nanoscale. The particle size of the nano-material shown in the picture is about 50 to 200 nm, and it is a monodisperse particle.

[0116] Figure 7 This is the XRD pattern of the nano-NaCrO2 positive electrode material prepared in Comparative Example 1.

[0117] Depend on Figure 7 It can be seen that, similar to Example 1, the obtained NaCrO2 positive electrode material is NaCrO2 with very high purity and no impurities are present.

[0118] Figure 8 This is the SEM image of the nano-NaCrO2 positive electrode material prepared in Comparative Example 1.

[0119] Depend on Figure 8 It can be seen that the particle size of the obtained nano-NaCrO2 single crystal material is slightly smaller than that of the raw material nano-Cr2O3 material, and is monodisperse, but does not show long-range ordered layers.

[0120] The NaCrO2 cathode materials prepared in Examples 1-4 and Comparative Examples 1-3 are prepared into sodium ion batteries, comprising the following steps:

[0121] The positive electrode materials, NaCrO2, polyvinylidene fluoride (PVDF), and acetylene black, were ground and mixed in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added and the mixture was shaken at 1500 rpm in an oscillating ball mill for 30 minutes to form a slurry, which was then evenly coated on aluminum foil. The coated electrode was dried in a vacuum oven at 60°C for 2 hours, then heated to 120°C and dried for 10 hours. After drying, the electrode was cut into 12 mm diameter discs. The mass of the active material in the electrode was 1.5-2.5 mg cm -3 A sodium metal sheet was used as the counter electrode, a glass fiber (GF / D) as the separator, and a 1.0 M sodium perchlorate (NaClO4) solution as the electrolyte. CR2025 button-type cells were assembled in an argon-filled glove box (water and oxygen contents were both less than 0.01 ppm). The assembled half-cell was left to rest for 12 hours.

[0122] Cyclic performance test, the specific steps include:

[0123] The blue battery test system was used for constant current charge and discharge, with a voltage range of 2.0-3.6V (relative to Na + / Na), the test temperature is 25 ° C, where 1C = 120mA g-1 . Carry out cycle performance test.

[0124] Figure 9 The charge-discharge cycle performance of the sodium ion battery composed of the NaCrO2 single crystal positive electrode material obtained in Example 1 at 20C.

[0125] Depend on Figure 9 It can be seen that the capacity retention rate of the obtained NaCrO2 single crystal positive electrode material is above 80% after 1000 cycles of charge and discharge at 20C, showing extremely high cycle stability.

[0126] Figure 10 The cycling performance of the sodium ion battery composed of the nano-NaCrO2 positive electrode material obtained in Comparative Example 1 under 2C conditions is shown in the figure. As can be seen from the figure, the capacity retention rate is less than 60% after 600 cycles.

[0127] Rate performance test, the specific steps include:

[0128] The blue battery test system was used for constant current charge and discharge, with a voltage range of 2.0-3.6V (relative to Na + / Na), the test temperature is 25 ° C, where 1C = 120mA g -1 . Carry out rate performance test.

[0129] Figure 11 The figure shows the rate performance of the sodium-ion battery composed of the NaCrO2 single crystal positive electrode material obtained in Example 1. As can be seen from the figure, the capacity retention rate of the NaCrO2 single crystal positive electrode material is still above 80% under the 50C rate condition, showing excellent rate performance.

[0130] Figure 12 The figure shows the rate performance of the sodium ion battery composed of the nano-NaCrO2 positive electrode material obtained in Comparative Example 1. As can be seen from the figure, the capacity of nano-NaCrO2 decays rapidly under the rate condition greater than 5C, and the rate performance is poor.

[0131] Depend on Figures 9-12 It can be seen that the cycle stability and rate performance of the sodium ion battery prepared in Comparative Example 1 are significantly different from the electrochemical performance of the sodium ion battery composed of the NaCrO2 single crystal positive electrode material obtained in Example 1 of the present invention.

[0132] Figure 13 This is an SEM image of the NaCrO2 single crystal positive electrode material on the positive electrode of Example 1 after 1000 cycles at 20C. It can be seen from the figure that the NaCrO2 single crystal positive electrode material shows good integrity and no obvious cracking, further indicating that the structural stability of the NaCrO2 single crystal positive electrode material prepared by the present invention is good.

[0133] The accompanying drawings related to other embodiments and comparative examples are as follows:

[0134] Figure 14 These are SEM images of Cr2O3 materials in Examples 2-4 and Comparative Examples 2-3, where a is Example 2, b is Example 3, c is Example 4, d is Comparative Example 2, and e is Comparative Example 3.

[0135] Figure 15 2-4 and comparative example 2-3, wherein a is embodiment 2, b is embodiment 3, c is embodiment 4, d is comparative example 2, and e is comparative example 3.

[0136] Figure 16 The XRD patterns of NaCr2O3 materials in Examples 2-4 and Comparative Examples 2-3 are shown, where a is Example 2, b is Example 3, c is Example 4, d is Comparative Example 2, and e is Comparative Example 3. As can be seen from the figure, there are mixed peaks in d, indicating that there are unreacted substances.

[0137] Figure 17 The SEM images of NaCrO2 materials in Examples 2-4 and Comparative Examples 2-3 are shown, where a is Example 2, b is Example 3, c is Example 4, d is Comparative Example 2, and e is Comparative Example 3. As can be seen from the figure, there is unreacted material in d.

[0138] Figure 18 The cycling performance of sodium ion batteries composed of the NaCrO2 positive electrode materials obtained in Examples 2-4 and Comparative Example 3 under charge and discharge conditions, wherein a is Example 2 at 20°C, b is Example 3 at 20°C, c is Example 4 at 10°C, and d is Comparative Example 3 at 10°C.

[0139] Figure 19 The rate performance of the sodium ion battery composed of the NaCrO2 positive electrode materials obtained in Examples 2-4 and Comparative Example 3, wherein a is Example 2, b is Example 3, c is Example 4, and d is Comparative Example 3.

[0140] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0141] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing large-sized Cr2O3 single crystal material, characterized in that the steps include: The large-size Cr2O3 single crystal material is obtained by taking hexavalent chromium salt, alkaline reagent and reducing organic matter as raw materials through hydrothermal reaction and roasting.

2. The preparation method according to claim 1, wherein The hexavalent chromium salt includes at least one of sodium chromate, sodium dichromate, potassium chromate, potassium dichromate, ammonium chromate and ammonium dichromate; and / or, the alkaline reagent comprises at least one of sodium hydroxide, potassium hydroxide, aqueous ammonia, sodium carbonate, potassium carbonate and urea; and / or, the reducing organic matter comprises at least one of carbon, glucose, starch, methanol, ethanol, acetic acid, citric acid and ascorbic acid; And / or, the mass ratio of the hexavalent chromium salt, the alkaline reagent and the reducing organic matter is (15-25):(8-10):(3-9); And / or, the hydrothermal reaction temperature is 200-280° C. and the time is 4-24 h; And / or, the calcination temperature is 1100-1400° C. and the calcination time is 2-24 hours; And / or, after the hydrothermal reaction is completed, a purification step of the reaction product is further included.

3. A large-size Cr2O3 single crystal material, characterized in that: The large-size Cr2O3 single crystal material is prepared by the preparation method described in claim 1 or 2.

4. Use of the large-sized Cr2O3 single crystal material according to claim 3 in the preparation of positive electrode materials for sodium ion batteries.

5. A method for preparing a NaCrO2 single crystal cathode material having a long-range ordered structure, characterized in that the steps include: The large-size Cr2O3 single crystal material according to claim 3 is mixed with a sodium source and calcined to obtain the NaCrO2 single crystal positive electrode material having a long-range ordered structure.

6. The preparation method according to claim 5, wherein The molar ratio of Cr to Na in the large-sized Cr2O3 single crystal material and the sodium source is 1:1-1.05; and / or, the sodium source comprises at least one of NaOH, Na2CO3, NaHCO3, sodium acetate and sodium citrate; And / or, the calcination temperature is not less than 700° C. and the calcination time is 5-12 hours.

7. A NaCrO2 single crystal cathode material having a long-range ordered structure, characterized in that: The NaCrO2 single crystal positive electrode material is prepared by the preparation method described in claim 5 or 6.

8. Use of the NaCrO2 single crystal positive electrode material with a long-range ordered structure according to claim 7 in the preparation of a sodium ion battery.

9. A sodium ion battery positive electrode, characterized in that The active component of the sodium ion battery positive electrode includes the NaCrO2 single crystal positive electrode material with a long-range ordered structure as claimed in claim 7.

10. A sodium ion battery, characterized in that: Including the sodium ion battery positive electrode according to claim 9.

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