Preparation method of NaCrO2 single crystal positive electrode material

Abstract

This invention discloses a method for preparing NaCrO2 single-crystal cathode material, belonging to the field of cathode material preparation technology. This invention proposes a novel method for preparing single-crystal cathode materials for high-performance sodium-ion batteries. First, large-size single-crystal Cr2O3 (1-30 μm) is used as raw material, mixed with a sodium source, and then subjected to a one-step high-temperature calcination to obtain NaCrO2 single-crystal cathode material. Furthermore, the NaCrO2 single-crystal cathode material prepared using this method has fewer single-crystal structural defects and exhibits a better long-range ordered layered structure.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of positive electrode material preparation, in particular to a preparation method of NaCrO2 single-crystal positive electrode material. BACKGROUND

[0002] Single-crystal positive electrode material has high mechanical strength, high compaction density, excellent electrochemical performance, thermal stability and air stability and many other advantages, and can significantly improve the overall performance of a battery. At present, the synthesis methods of single-crystal positive electrode material of a sodium ion battery mainly include the following: (1) high-temperature sintering method: single crystal growth is promoted by increasing the sintering temperature, the amount of lithium salt or sodium salt needs to be increased to compensate for the volatilization of lithium or sodium at high temperature, and the generated single crystal particles are prone to agglomeration; (2) molten salt method: low-melting-point fluxing salt is added to reduce the sintering temperature, and liquid mass transfer is used to speed up ion transmission and grain growth, but there are problems of screening of the molten salt and cleaning of the single-crystal positive electrode material; (3) multi-step calcination method: the negative effects of one-step high-temperature sintering, such as grain agglomeration and generation of impurities, can be avoided, but the process is complex and the time cost is high. And the above methods are all to convert polycrystalline sodium ion battery positive electrode material into single-crystal positive electrode material through subsequent heat treatment, but due to the anisotropy between the polycrystalline sodium ion battery positive electrode material particles, there are many lattice defects in the prepared single-crystal positive electrode material and the long-range ordered structure is limited. SUMMARY

[0003] The purpose of the present application is to provide a preparation method of NaCrO2 single-crystal positive electrode material to solve the problems existing in the prior art. The preparation method of the present application solves the problems existing in the preparation of single-crystal positive electrode material for sodium ion batteries, and realizes the simple and efficient preparation of single-crystal positive electrode material for sodium ion batteries.

[0004] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0005] One of the technical solutions of the present application: a preparation method of large-size single-crystal Cr2O3, comprising the following steps:

[0006] Mixing trivalent chromium salt and alkaline precipitant in the form of solution, constant temperature reaction, to obtain precipitate product trivalent chromium hydroxide;

[0007] Roasting the trivalent chromium hydroxide to obtain the large-size single-crystal Cr2O3.

[0008] Further, the trivalent chromium salt is a water-soluble trivalent chromium salt; the water-soluble trivalent chromium salt includes at least one of chromium chloride, chromium nitrate, chromium sulfate, chromium acetate, chromium citrate and potassium chromium sulfate;

[0009] The basic precipitant comprises at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate and potassium carbonate;

[0010] The temperature of the constant temperature reaction is 20-80 DEG C, and the time is 2-12h.

[0011] The temperature of the calcination is 1200 DEG C-1400, and the time is 2-24h.

[0012] Further, the diameter of the large-size single crystal Cr2O3 is 1-30 mu m.

[0013] The second technical scheme of the application is a large-size single crystal Cr2O3 prepared by the preparation method.

[0014] The third technical scheme of the application is an application of the large-size single crystal Cr2O3 in preparation of a sodium ion battery positive electrode material.

[0015] The fourth technical scheme of the application is a preparation method of a NaCrO2 single crystal positive electrode material, comprising the following steps:

[0016] The large-size single crystal Cr2O3 and a sodium source are mixed and then calcined to obtain the NaCrO2 single crystal positive electrode material.

[0017] Under the action of high temperature, the sodium source forms active sodium oxide, which gradually embeds into the crystal lattice of the chromium sesquioxide under the induction of the long-range ordered single crystal structure of the large-size single crystal chromium sesquioxide, and finally forms an ordered structure to form a sodium chromite single crystal.

[0018] Further, the sodium source comprises at least one of NaOH, Na2CO3, NaHCO3, sodium acetate and sodium citrate.

[0019] The molar ratio of Cr in the large-size single crystal Cr2O3 to Na in the sodium source is 1:(1-1.05).

[0020] The temperature of the calcination is 700 DEG C-1200, and the time is 2-24h.

[0021] The fifth technical scheme of the application is a NaCrO2 single crystal positive electrode material prepared by the preparation method.

[0022] The sixth technical scheme of the application is an application of the NaCrO2 single crystal positive electrode material in preparation of a sodium ion battery.

[0023] The seventh technical scheme of the application is a method for reducing internal defects of a NaCrO2 single crystal positive electrode material, comprising the following steps:

[0024] The large-size single crystal Cr2O3 and a sodium source are mixed and then calcined to obtain the NaCrO2 single crystal positive electrode material.

[0025] Further, the sodium source includes at least one of NaOH, Na2CO3, NaHCO3, sodium acetate and sodium citrate;

[0026] The molar ratio of Cr in the large-size single crystal Cr2O3 and Na in the sodium source is 1:(1-1.05);

[0027] The temperature of the calcination is 700-1200℃, and the time is 2-24h.

[0028] The technical principle and the overcome technical problem of the large-size chromium trioxide for preparing NaCrO2 single crystal positive electrode material (i.e. single crystal NaCrO2 positive electrode material) are as follows:

[0029] The technical principle of the existing single crystal positive electrode material is mainly to take the nanometer size battery material as a precursor, and realize the crystal particle growth through high temperature calcination. The main defects are that, in the process of growing the nanometer size raw material into single crystal positive electrode material, a large number of crystal boundaries and anisotropy of the crystal lattice between the particles exist due to the small particle size of the raw material, so that a perfect single crystal structure cannot be obtained through high temperature treatment, and the prepared single crystal positive electrode material has crystal defects.

[0030] The present application takes the complete large-size single crystal particle oxide (chromium trioxide) as a precursor, mixes with a sodium source, and then forms active Na ions gradually inserted into the crystal structure of the single crystal particle oxide through a high temperature process, so that the long-range ordered structure of the single crystal particle oxide is maintained, and the problem of cracking in the particle interior after multiple charge and discharge due to a large number of crystal defects in the particle interior caused by the increase of the particle size is overcome.

[0031] The present application has the following technical effects:

[0032] (1) The preparation method of the large-size single crystal Cr2O3 is simple, and the size of the prepared single crystal Cr2O3 is 1-30μm.

[0033] (2) The preparation method of the NaCrO2 single crystal positive electrode material is simple and efficient, realizes the direct conversion from single crystal to single crystal, and avoids the problems existing in the high temperature sintering method, the molten salt method and the multi-step calcination method.

[0034] (3) The present application proposes a new method for preparing a single crystal positive electrode material for high-performance sodium ion batteries, which first takes large-size single crystal Cr2O3 as a raw material (the size is 1-30μm), mixes with a sodium source, and then obtains single crystal NaCrO2 positive electrode material through one-step high temperature calcination. And the single crystal NaCrO2 positive electrode material prepared by the method of the present application has less single crystal structure defects and has a better long-range ordered layered structure. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the accompanying drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

[0036] Figure 1 SEM image of the monocrystalline chromium trioxide prepared in Example 1 (500 times magnification);

[0037] Figure 2 SEM image of the monocrystalline chromium trioxide prepared in Example 1 (500 times magnification);

[0038] Figure 3 SEM image of the monocrystalline NaCrO2 cathode material prepared in Example 1 (500 times magnification);

[0039] Figure 4 SEM image of the monocrystalline NaCrO2 cathode material prepared in Example 1 (5000 times magnification);

[0040] Figure 5 SEM image of the monocrystalline NaCrO2 cathode material prepared in Example 1 (130000 times magnification);

[0041] Figure 6 Cycle performance of the sodium ion battery assembled with the monocrystalline NaCrO2 cathode material prepared in Example 1 under 10C condition;

[0042] Figure 7 Rate performance of the sodium ion battery assembled with the monocrystalline NaCrO2 cathode material prepared in Example 1.

[0043] Figure 8 SEM image of the nanometer chromium trioxide prepared in Comparative Example 1 (50000 times magnification);

[0044] Figure 9 SEM image of the nanometer NaCrO2 cathode material prepared in Comparative Example 1 (50000 times magnification);

[0045] Figure 10 Cycle performance of the sodium ion battery prepared with the nanometer NaCrO2 cathode material prepared in Comparative Example 1 under 2C condition;

[0046] Figure 11 Rate performance of the sodium ion battery prepared with the nanometer NaCrO2 cathode material prepared in Comparative Example 1. DETAILED DESCRIPTION

[0047] Various exemplary embodiments of the present application will now be described in detail, which should be considered to be non-limiting examples of the application, and are understood to be illustrative of certain aspects, features and embodiments of the present application.

[0048] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. Additionally, for a range of values of a parameter, unless otherwise stated, the inclusion of either extremity of the range is to be understood as if both are stated. For example, "from 1 to 10" should be interpreted as meaning "from 1 to 10 as well as 1 to 10".

[0049] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe in further detail the methods and / or materials associated with the documents. In the case of conflict between the present specification and any document incorporated by reference, the present specification will control.

[0050] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. The specification and examples are illustrative only.

[0051] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps.

[0052] It should be noted that the present application does not describe in detail the conventional operation means in the art, and is not the focus of the present application.

[0053] Example 1

[0054] A preparation method of a NaCrO2 single crystal positive electrode material:

[0055] (1) 26.6 g of CrCl3-6H2O was dissolved in 200 mL of water to prepare a trivalent chromium solution;

[0056] 14.4 g of NaOH was dissolved in 50 mL of water to prepare a basic solution.

[0057] (2) The trivalent chromium solution was added into a 500 mL reaction tank, and the basic solution was added dropwise into the reaction tank under stirring to react with Cr in the solution;3+ After the precipitation reaction is carried out and the alkaline solution is added dropwise, the mixture is kept at 50°C for 6 hours to obtain a solid-liquid mixture.

[0058] (3) Filter the solid-liquid mixture slurry, wash it thoroughly with secondary water until the pH of the filtrate is neutral, and then dry the filter cake in an oven to obtain trivalent chromium hydroxide powder.

[0059] (4) The trivalent chromium hydroxide powder was calcined at 1300℃ for 6 hours, cooled naturally, washed and dried to obtain single crystal chromium trioxide.

[0060] (5) Mix single-crystal chromium trioxide and Na2CO3 at a Cr:Na molar ratio of 1:1.05, and then calcine at 1100℃ for 10h under Ar atmosphere to obtain single-crystal NaCrO2 cathode material.

[0061] SEM image (500x magnification) of the single-crystal chromium trioxide prepared in Example 1 is shown below. Figure 1 SEM image (500x magnification) of the single-crystal chromium trioxide prepared in Example 1 is shown below. Figure 2 The SEM image (500x magnification) of the single-crystal NaCrO2 cathode material prepared in Example 1 is shown below. Figure 3 The SEM image (magnified 5000x) of the single-crystal NaCrO2 cathode material prepared in Example 1 is shown below. Figure 4 The SEM image (magnified 130,000 times) of the single-crystal NaCrO2 cathode material prepared in Example 1 is shown below. Figure 5 .

[0062] from Figures 1-2 As can be seen from the data, the particle size of most of the single-crystal chromium trioxide prepared in Example 1 is above 1 micrometer, which is large and monodisperse.

[0063] from Figures 3-5 As can be seen from the data, the particle size of the single-crystal NaCrO2 cathode material prepared in Example 1 is similar to that of single-crystal chromium trioxide particles. The particles are large and monodisperse, and the particles are divided into long-range ordered layered structures.

[0064] Example 2

[0065] A method for preparing NaCrO2 single-crystal cathode material:

[0066] (1) Dissolve 25g Cr2(SO4)3·6H2O in 200mL of water to prepare a trivalent chromium solution;

[0067] Prepare an alkaline solution by dissolving 20.2g of KOH in 50mL of water.

[0068] (2) Add the trivalent chromium solution to a 500 mL reaction vessel. Under stirring, add the alkaline solution dropwise to the reaction vessel to react with the chromium in the solution. 3+ After the precipitation reaction is carried out and the alkaline solution is added dropwise, the mixture is kept at 30°C for 12 hours to obtain a solid-liquid mixture.

[0069] (3) Filter the solid-liquid mixture slurry, wash it thoroughly with secondary water until the pH of the filtrate is neutral, and then dry the filter cake in an oven to obtain trivalent chromium hydroxide powder.

[0070] (4) The trivalent chromium hydroxide powder was calcined at 1350℃ for 4 hours, naturally cooled, washed and dried to obtain single crystal chromium trioxide with a size of 2-30 μm.

[0071] (5) Mix single-crystal chromium trioxide with NaOH at a Cr:Na molar ratio of 1:1.05, and then calcine at 1000℃ for 12h under Ar atmosphere to obtain single-crystal NaCrO2 cathode material with a size of 2-30μm.

[0072] Example 3

[0073] A method for preparing NaCrO2 single-crystal cathode material:

[0074] (1) Dissolve 40g Cr(NO3)3·9H2O in 200mL of water to prepare a trivalent chromium solution;

[0075] An alkaline solution was prepared by dissolving 14.4 g of NaOH in 50 mL of water.

[0076] (2) Add the trivalent chromium solution to a 500 mL reaction vessel. Under stirring, add the alkaline solution dropwise to the reaction vessel to react with the chromium in the solution. 3+ After the precipitation reaction is carried out and the alkaline solution is added dropwise, the mixture is kept at 30°C for 12 hours to obtain a solid-liquid mixture.

[0077] (3) Filter the solid-liquid mixture slurry, wash it thoroughly with secondary water until the pH of the filtrate is neutral, and then dry the filter cake in an oven to obtain trivalent chromium hydroxide powder.

[0078] (4) The trivalent chromium hydroxide powder was calcined at 1200℃ for 24h, naturally cooled, washed and dried to obtain single crystal chromium trioxide with a size of 1~15μm.

[0079] (5) Mix single-crystal chromium trioxide and sodium acetate at a Cr:Na molar ratio of 1:1.05, and then calcine at 900℃ for 20h under Ar atmosphere to obtain single-crystal NaCrO2 cathode material with a size of 1~15μm.

[0080] Example 4

[0081] A method for preparing NaCrO2 single-crystal cathode material:

[0082] (1) Dissolve 50g KCr(SO4)2·12H2O in 200mL of water to prepare a trivalent chromium solution;

[0083] Prepare an alkaline solution by dissolving 20.2g of KOH in 50mL of water.

[0084] (2) Add the trivalent chromium solution to a 500 mL reaction vessel. Under stirring, add the alkaline solution dropwise to the reaction vessel to react with the chromium in the solution. 3+ After the precipitation reaction is carried out and the alkaline solution is added dropwise, the mixture is kept at 30°C for 12 hours to obtain a solid-liquid mixture.

[0085] (3) The solid-liquid mixture slurry is filtered and washed thoroughly with secondary water until the pH of the filtrate is neutral. Then the filter cake is dried in an oven to obtain trivalent chromium hydroxide powder.

[0086] (4) The trivalent chromium hydroxide powder was calcined at 1250℃ for 18h, naturally cooled, washed and dried to obtain single crystal chromium trioxide with a size of 2 to 20 μm.

[0087] (5) Mix single-crystal chromium trioxide and sodium citrate at a Cr:Na molar ratio of 1:1.05, and then calcine at 800℃ for 24h under an Ar atmosphere to obtain a single-crystal NaCrO2 cathode material with a size of 2-20μm.

[0088] Example of effect 1

[0089] The single-crystal NaCrO2 cathode material prepared in Example 1 was assembled into a sodium-ion battery. The specific preparation steps are as follows:

[0090] Monocrystalline NaCrO2 cathode material, polyvinylidene fluoride (PVDF), and acetylene black were ground and mixed uniformly in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added, and the mixture was shaken at 1500 rpm for 30 minutes in a vibrating ball mill to form a slurry. This slurry was then uniformly coated onto aluminum foil. The coated electrode was dried in a vacuum drying oven at 60℃ for 2 hours, followed by drying at 120℃ for 10 hours. After drying, the electrode was cut into 12 mm diameter discs. The mass of the active material (i.e., monocrystalline NaCrO2 cathode material) was 1.5–2.5 mg / cm³. -3A sodium metal sheet was used as the counter electrode, glass fiber (GF / D) as the separator, and a 1.0M sodium perchlorate (NaClO4) solution as the electrolyte. The CR2025 coin cell was assembled in an argon-filled glove box (water and oxygen content both less than 0.01 ppm). The assembled half-cells were allowed to stand for 12 hours.

[0091] Cyclic performance testing, the specific steps include:

[0092] A constant current charge-discharge test was performed using a Blue Battery testing system, with a voltage range of 2.0-3.6V (relative to Na). + / Na), the test temperature was 25℃, where 1C=120mAg -1 Perform cyclic performance testing.

[0093] The circulation performance was tested at 10°C, and the results are shown below. Figure 6 The rate performance of the sodium-ion battery was measured, and the results are shown in [the table below]. Figure 7 .

[0094] from Figure 6 As can be seen from the data, the single-crystal NaCrO2 cathode material prepared in Example 1 retains more than 80% of its capacity after 1000 charge-discharge cycles at 10C, demonstrating extremely high cycle stability.

[0095] from Figure 7 As can be seen from the data, the single-crystal NaCrO2 cathode material prepared in Example 1 still retains more than 80% of its capacity under a 40C rate condition, exhibiting excellent rate performance.

[0096] Comparative Example 1

[0097] Preparation method of nanoscale NaCrO2 cathode material:

[0098] (1) Dissolve 26.6g CrCl3·6H2O in 200mL of water to prepare a trivalent chromium solution;

[0099] An alkaline solution was prepared by dissolving 14.4 g of NaOH in 50 mL of water.

[0100] (2) Add the trivalent chromium solution to a 500 mL reaction vessel. Under stirring, add the alkaline solution dropwise to the reaction vessel to react with the chromium in the solution. 3+ After the precipitation reaction is carried out and the alkaline solution is added dropwise, the mixture is kept at 50°C for 6 hours to obtain a solid-liquid mixture.

[0101] (3) Filter the solid-liquid mixture slurry, wash it thoroughly with secondary water until the pH of the filtrate is neutral, and then dry the filter cake in an oven to obtain trivalent chromium hydroxide powder.

[0102] (4) The trivalent chromium hydroxide powder was calcined at 900℃ for 2 hours, cooled naturally, washed and dried to obtain nano chromium trioxide.

[0103] (5) Nano-chromium trioxide and Na2CO3 were mixed at a Cr:Na molar ratio of 1:1.05, and then calcined at 1100℃ for 10h under Ar atmosphere to obtain nano-sized NaCrO2 cathode material.

[0104] SEM image (50,000x magnification) of the nano-chromium trioxide prepared in Comparative Example 1 is shown below. Figure 8 SEM image (magnified 50,000 times) of the nanoscale NaCrO2 cathode material prepared in Comparative Example 1 is shown below. Figure 9 .

[0105] Example 2

[0106] The nanoscale NaCrO2 cathode material prepared in Comparative Example 1 was assembled into a sodium-ion battery. The specific preparation steps are as follows:

[0107] Nanoscale NaCrO2 cathode material, polyvinylidene fluoride (PVDF), and acetylene black were ground and mixed uniformly in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added, and the mixture was shaken at 1500 rpm for 30 minutes in a vibrating ball mill to prepare a slurry. This slurry was then uniformly coated onto aluminum foil. The coated electrode was dried in a vacuum drying oven at 60℃ for 2 hours, followed by drying at 120℃ for 10 hours. After drying, the electrode was cut into 12 mm diameter discs. The mass of the active material (i.e., nanoscale NaCrO2 cathode material) was 1.5–2.5 mg / cm³. -3 A sodium metal sheet was used as the counter electrode, glass fiber (GF / D) as the separator, and a 1.0M sodium perchlorate solution (NaClO4) as the electrolyte. The CR2025 coin cell was assembled in an argon-filled glove box (water and oxygen content both less than 0.01 ppm). The assembled half-cells were allowed to stand for 12 hours.

[0108] Cyclic performance testing, the specific steps include:

[0109] A constant current charge-discharge test was performed using a Blue Battery testing system, with a voltage range of 2.0-3.6V (relative to Na). + / Na), the test temperature was 25℃, where 1C=120mAg -1 Perform cyclic performance testing.

[0110] The circulation performance was tested under 2C conditions, and the results are shown below. Figure 10 The rate performance of the sodium-ion battery was measured, and the results are shown in [the table below]. Figure 11 .

[0111] fromFigures 10-11 As can be seen, the cycle stability and rate performance of the nanoscale NaCrO2 cathode material prepared in Comparative Example 1 are significantly lower than those of the single-crystal NaCrO2 cathode material prepared in Example 1.

[0112] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a large-sized single crystal Cr203, characterized by, The method comprises the following steps: mixing a trivalent chromium salt and an alkaline precipitant in the form of a solution, constant temperature reaction, to obtain a precipitate product trivalent chromium hydroxide; roasting the trivalent chromium hydroxide to obtain the large-size single crystal Cr2O3; the trivalent chromium salt is a water-soluble trivalent chromium salt; the alkaline precipitant comprises at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate and potassium carbonate; the constant temperature reaction is carried out at a temperature of 20-80℃; the roasting is carried out at a temperature of 1200-1400℃ for 2-24h.

2. The production method according to claim 1, characterized by, The large-size single crystal Cr2O3 has a diameter of 1-30μm.

3. A large-size single crystal Cr2O3 prepared by the preparation method of claim 1 or 2.

4. Application of the large-size single crystal Cr2O3 of claim 3 in preparation of a sodium ion battery positive electrode material.

5. A method for preparing NaCrO2 single crystal cathode material, characterized in that, The method comprises the following steps: mixing the large-size single crystal Cr2O3 of claim 3 and a sodium source, and then roasting to obtain the NaCrO2 single crystal positive electrode material; the sodium source comprises at least one of NaOH, Na2CO3, NaHCO3, sodium acetate and sodium citrate; the molar ratio of Cr in the large-size single crystal Cr2O3 to Na in the sodium source is 1:(1-1.05); the roasting is carried out at a temperature of 700-1200℃ for 2-24h.

6. A NaCrO2 single crystal positive electrode material prepared by the preparation method of claim 5.

7. Application of the NaCrO2 single crystal positive electrode material of claim 6 in preparation of a sodium ion battery.

8. A method for reducing internal defects of NaCrO2 single crystal cathode material, characterized in that, The method comprises the following steps: mixing the large-size single crystal Cr2O3 of claim 3 and a sodium source, and then roasting to obtain the NaCrO2 single crystal positive electrode material; the sodium source comprises at least one of NaOH, Na2CO3, NaHCO3, sodium acetate and sodium citrate; the molar ratio of Cr in the large-size single crystal Cr2O3 to Na in the sodium source is 1:(1-1.05); the roasting is carried out at a temperature of 700-1200℃ for 2-24h.

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