Bismuth silicate coated lithium ferric manganese phosphate material, preparation method thereof and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion battery materials, and discloses a bismuth silicate coated lithium ferric manganese phosphate material, a preparation method thereof and a lithium ion battery. The bismuth silicate coated lithium ferric manganese phosphate material comprises lithium ferric manganese phosphate and a coating layer coating at least part of the surface of the lithium ferric manganese phosphate, and the coating layer is made of bismuth silicate. Carrying out ball-milling mixing on the ferric manganese phosphate material, a lithium source, a carbon source and water to obtain mixed slurry; performing low-temperature spray drying on the mixed slurry to obtain a spray material; and carrying out wet mixing on a silicon source, a bismuth source and the spray material, carrying out high-temperature pyrolysis on the wet-mixed material in a spray pyrolysis furnace, and sintering to obtain the bismuth silicate coated lithium ferric manganese phosphate material. When the bismuth silicate coated lithium ferric manganese phosphate material is used as a positive electrode active material of a lithium ion battery, the high-temperature cycle performance of the battery can be improved while the high discharge capacity of the battery is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery materials, and in particular relates to the coating modification of lithium iron manganese phosphate. Background Art

[0002] There is a lot of room for technological upgrading of lithium iron manganese phosphate, and the market potential is constantly being stimulated. With the rapid development of new energy vehicles and energy storage systems, lithium iron manganese phosphate, as a high-performance, low-cost battery material, has achieved rapid growth in the global market size. Against this background, major manufacturers have increased their investment to improve the production capacity and technical level of lithium iron manganese phosphate.

[0003] Although lithium iron manganese phosphate materials have outstanding performance advantages, they also have obvious shortcomings. In order to achieve a higher discharge capacity of lithium iron manganese phosphate materials, it is necessary to reduce the primary particle size of the material, but small nanoparticles also bring a series of side effects, such as high water absorption and poor high-temperature cycle performance. Research and preparation of lithium iron manganese phosphate materials with high discharge capacity and excellent high-temperature cycle performance is the focus of major manufacturers. Summary of the invention

[0004] The first object of the present invention is to provide a bismuth silicate-coated lithium iron manganese phosphate material, so that the battery has a high discharge specific capacity and good high-temperature cycle performance. The second object of the present invention is to provide a method for preparing the bismuth silicate-coated lithium iron manganese phosphate material. The third object of the present invention is to provide a lithium ion battery.

[0005] To achieve the above objectives, the present invention provides the following specific technical solutions.

[0006] In a first aspect, the present invention provides a bismuth silicate-coated lithium iron manganese phosphate material, comprising lithium iron manganese phosphate and a coating layer coated on at least a portion of the surface of the lithium iron manganese phosphate, wherein the material of the coating layer is bismuth silicate.

[0007] In a second aspect, the present invention provides a method for preparing a bismuth silicate-coated lithium iron manganese phosphate material, comprising: ball-milling and mixing the iron manganese phosphate material, a lithium source, a carbon source, and water to obtain a mixed slurry; spray-drying the mixed slurry at low temperature to obtain a spray material; wet-mixing the silicon source, the bismuth source, and the spray material, and subjecting the wet-mixed material to high-temperature pyrolysis and sintering in a spray pyrolysis furnace to obtain a bismuth silicate-coated lithium iron manganese phosphate material.

[0008] In a third aspect, the present invention provides a lithium-ion battery comprising the aforementioned bismuth silicate-coated lithium iron manganese phosphate material.

[0009] The beneficial technical effects that can be achieved by one or more of the above technical solutions of the present invention will be reflected through the drawings, specific embodiments and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1This is the SEM image of the bismuth silicate-coated lithium iron manganese phosphate positive electrode material prepared in Example 1.

[0011] Figure 2 This is the high temperature cycle performance curve of lithium-ion batteries. DETAILED DESCRIPTION

[0012] The cost of lithium iron manganese phosphate material is relatively low, but it is difficult to achieve both the discharge specific capacity and high-temperature cycle performance of batteries using it as the positive electrode active material.

[0013] After continuous research, the applicant provides a bismuth silicate-coated lithium iron manganese phosphate material, comprising lithium iron manganese phosphate and a coating layer coated on at least a portion of the surface of the lithium iron manganese phosphate, wherein the material of the coating layer is bismuth silicate.

[0014] The theoretical specific capacity of lithium iron manganese phosphate is 170 mA h / g, and the actual discharge specific capacity is only about 130 mA h / g. In addition, at high temperatures, the capacity retention rate of lithium iron manganese phosphate decays rapidly. In order to achieve a higher discharge specific capacity of lithium iron manganese phosphate materials, it is necessary to reduce the primary particle size of the material, but small nanoparticles also bring a series of side effects, such as high water absorption and poor high-temperature cycle performance. The study found that bismuth silicate has excellent melt properties, good fluidity, and high viscosity, so that it can be directly compounded on the surface of the primary particles during the high-temperature synthesis of lithium iron manganese phosphate primary particles; in addition, the high viscosity of bismuth silicate also enables it to fully bond to the surface of the primary particles of lithium iron manganese phosphate to form a primary particle complex, and it is not easy to agglomerate into secondary large particles at high temperature. Bismuth silicate is coated on the surface of lithium iron manganese phosphate material, with good interface contact, and the generated material is small in size and larger in specific surface area, thereby promoting more ion transport and charge storage. Furthermore, the researchers found that bismuth silicate coated on the surface of lithium iron manganese phosphate can effectively improve the high-temperature electrochemical properties of lithium iron manganese phosphate.

[0015] In some specific embodiments, the mass ratio of the bismuth silicate to the lithium iron manganese phosphate is 3.3-13.4:100.

[0016] In some specific embodiments, the particle size of the primary particles of the bismuth silicate-coated lithium iron manganese phosphate material is 80-150 nm.

[0017] In some specific embodiments, the bismuth silicate-coated lithium iron manganese phosphate material has a spherical or quasi-spherical morphology, and the particle size is 3-5 μm.

[0018] Furthermore, the present invention provides a method for preparing a bismuth silicate-coated lithium iron manganese phosphate material, comprising: The iron manganese phosphate material, lithium source, carbon source and water are ball-milled to obtain a mixed slurry; the mixed slurry is spray-dried at low temperature to obtain a spray material; the silicon source, bismuth source and spray material are wet-mixed, and the wet-mixed materials are pyrolyzed and sintered at high temperature in a spray pyrolysis furnace to obtain a bismuth silicate-coated lithium iron manganese phosphate material.

[0019] In some specific embodiments, the lithium source is one or more of lithium oxide, lithium hydroxide, and lithium carbonate; the carbon source is one or more of graphene, graphite, glucose, and carbon black; the silicon source is one or more of tetraethyl orthosilicate, tetramethyl silicate, and propane silicate; the bismuth source is one or more of bismuth nitrate and bismuth citrate.

[0020] In some specific embodiments, the molar ratio of the manganese iron phosphate material, the lithium in the lithium source, the carbon source, the silicon in the silicon source, and the bismuth in the bismuth source is 1: 2.05-2.08: 0.03-0.1: 0.02-0.08: 0.04-0.16. Under this molar ratio, the coating layer can be evenly coated on the surface of the primary particles without affecting the electrochemical capacity of the main body.

[0021] In some specific embodiments, the temperature of the low-temperature spray drying is 350-500° C., for example, 350° C., 400° C., 450° C., 500° C. It is further preferred that the spray flow rate of the low-temperature spray drying is 1-4 ml / min, and the pressure is 0.1-0.7 MPa, for example, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa.

[0022] In the present invention, low-temperature spray drying is used to evaporate and remove the surface moisture and structural water of the material, and the initial crystal structure of the lithium iron manganese phosphate precursor is formed.

[0023] In some specific embodiments, the temperature of the high temperature pyrolysis is 700-1000° C., and the time is 5-8 s.

[0024] During the high-temperature pyrolysis process, a high-temperature chemical reaction occurs, which can achieve high-temperature structural strengthening of the lithium iron manganese phosphate precursor and form lithium iron manganese phosphate crystals with a stable structure; in addition, the silicon source and the bismuth source can achieve a high-temperature composite reaction to generate bismuth silicate and coat the surface of the lithium iron manganese phosphate crystals.

[0025] The method further selects high-temperature pyrolysis in a spray pyrolysis furnace, and utilizes the advantages of the spray pyrolysis furnace to obtain a product with uniform morphology, uniform particle size and uniform bismuth silicate coating.

[0026] In some specific embodiments, the sintering temperature is 700-900°C, and the sintering time is 0.5-2h. Since the spray pyrolysis time is extremely short, only a few seconds, the nanometer-scale or micrometer-scale powder formed by spray pyrolysis can only be regarded as the precursor of the lithium iron manganese phosphate lithium material (also as the crystal nucleus), and further sintering treatment is required to obtain the lithium iron manganese phosphate material with a complete crystalline structure. During the sintering process, the structure of the precursor (crystal nucleus) is further optimized and continuously aggregated and connected to form secondary particles with a certain particle size range. The sintering temperature is similar to the range of the pyrolysis temperature. If the temperature is too high, the bismuth silicate material in the formed lithium iron manganese phosphate composite material melts and flows on the surface of the particles, affecting the distribution uniformity of bismuth silicate. If the temperature is too low, the formation of secondary particles is incomplete, and it is easy to form lithium iron manganese phosphate positive electrode materials with inconsistent particle sizes. The longer the sintering time, the easier it is to form overly large secondary particles, thereby reducing the specific surface area of ​​lithium iron manganese phosphate. The shorter the sintering time, the inability to fully achieve the generation of secondary particles, affecting the particle size uniformity of the final product.

[0027] In addition, the present invention provides a lithium ion battery, comprising the aforementioned bismuth silicate-coated lithium iron manganese phosphate material. The lithium ion battery using the bismuth silicate-coated lithium iron manganese phosphate material as the positive electrode active material has high discharge specific capacity and excellent high temperature cycle performance.

[0028] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0029] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0030] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0031] Preparation Example Dissolve 0.15 mol manganese acetate and 0.15 mol ferrous acetate in 100 ml of deionized water to form a metal salt solution, and dissolve 0.2 mol (NH4)2HPO4 in 50 ml of deionized water to form a phosphate solution. Add the phosphate solution to the metal salt solution and stir continuously. After fully reacting for 18 hours, ferrous manganese phosphate precipitate is obtained. After washing with water, washing with alcohol, and drying, ferrous manganese phosphate material is obtained.

[0032] Example 1 0.15 mol of the manganese iron phosphate material prepared in the preparation example, 0.154 mol of Li2O, and 7.5 mmol of graphene were dispersed in 200 ml of deionized water and ball-milled for 4 hours to obtain a mixed slurry.

[0033] The mixed slurry was spray dried at low temperature at a temperature of 450° C., a flow rate of 3 ml / min, and a pressure of 0.4 MPa to obtain a lithium iron manganese phosphate precursor spray material. The lithium iron manganese phosphate precursor spray material, 5 mmol tetraethyl orthosilicate, and 10 mmol bismuth nitrate were dispersed in 200 ml of deionized water for wet mixing to obtain a wet mixed material.

[0034] The temperature of the spray pyrolysis furnace was adjusted to 830° C. The wet mixed material was transferred into the spray pyrolysis furnace through a conveying device and pyrolyzed for 6 seconds to obtain a pyrolysis material.

[0035] The bismuth silicate-coated lithium iron manganese phosphate positive electrode material can be prepared by sintering the pyrolysis material at 850°C for 1 hour in a nitrogen atmosphere.

[0036] Figure 1 This is a SEM image of the bismuth silicate-coated lithium iron manganese phosphate positive electrode material prepared in Example 1. It can be seen that the positive electrode material is a secondary spherical particle formed by the polymerization of the primary nanosheets, and the size of the primary nanosheets is uniform. The secondary particles formed by the polymerization of the primary particles are the final product morphology, which is spherical or quasi-spherical. The size of the primary particles is about 80~150nm, and the size of the secondary spherical particles is 3~5μm.

[0037] Comparative Example 1 0.15 mol of the manganese iron phosphate material prepared in the preparation example, 0.154 mol of Li2O, and 7.5 mmol of graphene were dispersed in 200 ml of deionized water and ball-milled for 4 hours to obtain a mixed slurry.

[0038] The mixed slurry was subjected to low-temperature spray drying at a temperature of 450° C., a flow rate of 40 rpm, and a pressure of 0.4 MPa to obtain a lithium iron manganese phosphate precursor spray material.

[0039] The spray material can be sintered at 850°C for 1 hour in a nitrogen atmosphere to prepare the lithium iron manganese phosphate positive electrode material.

[0040] Example 2 0.15 mol of the manganese iron phosphate material prepared in the preparation example, 0.3075 mol of LiOH and 4.5 mmol of graphite were dispersed in 200 ml of deionized water and ball-milled for 4 hours to obtain a mixed slurry.

[0041] The mixed slurry was spray dried at low temperature at a temperature of 350° C., a flow rate of 1 ml / min, and a pressure of 0.7 MPa to obtain a lithium iron manganese phosphate precursor spray material. The lithium iron manganese phosphate precursor spray material, 2 mmol tetramethyl orthosilicate, and 4 mmol bismuth citrate were dispersed in 200 ml of deionized water for wet mixing to obtain a wet mixed material.

[0042] The temperature of the spray pyrolysis furnace was adjusted to 700° C. The wet mixed material was transferred into the spray pyrolysis furnace through a conveying device and pyrolyzed for 8 seconds to obtain a pyrolysis material.

[0043] The bismuth silicate-coated lithium iron manganese phosphate positive electrode material can be prepared by sintering the pyrolysis material at 900°C for 0.5h in a nitrogen atmosphere.

[0044] Example 3 0.15 mol of the iron manganese phosphate material prepared in the preparation example, 0.156 mol of Li2CO3, and 15 mmol of graphite were dispersed in 200 ml of deionized water and ball-milled for 4 hours to obtain a mixed slurry.

[0045] The mixed slurry was spray dried at low temperature at a temperature of 500° C., a flow rate of 4 ml / min, and a pressure of 0.1 MPa to obtain a lithium iron manganese phosphate precursor spray material. The lithium iron manganese phosphate precursor spray material, 8 mmol tetraethyl orthosilicate, and 16 mmol bismuth nitrate were dispersed in 200 ml of deionized water for wet mixing to obtain a wet mixed material.

[0046] The temperature of the spray pyrolysis furnace was adjusted to 1000° C. The wet mixed material was transferred into the spray pyrolysis furnace through a conveying device and pyrolyzed for 5 seconds to obtain a pyrolysis material.

[0047] The bismuth silicate-coated lithium iron manganese phosphate positive electrode material can be prepared by sintering the pyrolysis material at 700°C for 2 hours in a nitrogen atmosphere.

[0048] The positive electrode materials prepared in Examples 1 to 3 and Comparative Example 1 were assembled into batteries by the following method: The positive electrode materials prepared in Examples 1 to 3 and Comparative Example 1 were used as positive electrode active materials, and mixed with conductive agent acetylene black (AB) and binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was used as solvent. The mixture was placed in a small beaker and stirred at a speed of 800 r / min for 2 hours to obtain a slurry. The slurry was coated on the current collector aluminum foil using an automatic coating machine, placed flat on tempered glass and transferred to a vacuum drying oven at 85°C for 4 hours, punched into a pole piece with a diameter of 12 mm, and then dried at 105°C in a vacuum drying oven for 4 hours. The pole piece was placed in a glove box filled with argon atmosphere with a water content and oxygen content of less than 0.1 ppm for 4 hours to reduce the moisture adsorbed by the pole piece during the transfer process, and then assembled into a CR2032 button battery in the glove box. The battery uses a pure metal lithium sheet with a diameter of 16 mm and a thickness of 0.5 mm as the negative electrode, and a porous polyethylene membrane of model Celgard2300 with a diameter of 18 mm as the separator.

[0049] After the battery was assembled, it was aged for 12 h, then activated for 2 cycles at a voltage of 2.5~4.5 V and a current density of 0.1 C at 45 ° C, and then cycled for 100 cycles at a current density of 1 C.

[0050] Test results such as Figure 2 As shown. Figure 2 It can be seen that the bismuth silicate-coated lithium iron manganese phosphate material enables the lithium-ion battery to have very excellent high-temperature cycle performance. When the uncoated lithium iron manganese phosphate material is applied to the lithium-ion battery, the capacity of the lithium-ion battery decays very quickly during the high-temperature cycle process.

[0051] In addition, analysis Figure 2 The ordinate represents the discharge specific capacity of the lithium-ion battery. It is found that the bismuth silicate-coated lithium iron manganese phosphate material makes the discharge specific capacity of the lithium-ion battery higher than that of the uncoated lithium iron manganese phosphate material.

[0052] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A bismuth silicate-coated lithium iron manganese phosphate material, characterized in that: It comprises lithium iron manganese phosphate and a coating layer coated on at least a part of the surface of the lithium iron manganese phosphate, wherein the material of the coating layer is bismuth silicate.

2. The bismuth silicate-coated lithium iron manganese phosphate material according to claim 1, characterized in that: The mass ratio of the bismuth silicate to the lithium iron manganese phosphate is 3.3-13.4:

100.

3. The bismuth silicate-coated lithium iron manganese phosphate material according to claim 1, characterized in that: The primary particles of the bismuth silicate-coated lithium iron manganese phosphate material have a particle size of 80-150 nm; the bismuth silicate-coated lithium iron manganese phosphate material has a spherical or quasi-spherical morphology, and the particle size is 3-5 μm.

4. A method for preparing a bismuth silicate-coated lithium iron manganese phosphate material, characterized in that: include: The iron manganese phosphate material, lithium source, carbon source and water are ball-milled to obtain a mixed slurry; the mixed slurry is spray-dried at low temperature to obtain a spray material; the silicon source, bismuth source and spray material are wet-mixed, and the wet-mixed materials are pyrolyzed and sintered at high temperature in a spray pyrolysis furnace to obtain a bismuth silicate-coated lithium iron manganese phosphate material.

5. The preparation method according to claim 4, characterized in that: The lithium source is one or more of lithium oxide, lithium hydroxide, and lithium carbonate; the carbon source is one or more of graphene, graphite, glucose, and carbon black; the silicon source is one or more of tetraethyl orthosilicate, tetramethyl silicate, and propane silicate; the bismuth source is one or more of bismuth nitrate and bismuth citrate.

6. The preparation method according to claim 4 or 5, characterized in that: The molar ratio of the iron manganese phosphate material, the lithium in the lithium source, the carbon source, the silicon in the silicon source, and the bismuth in the bismuth source is 1:2.05-2.08:0.03-0.1:0.02-0.08:0.04-0.

16.

7. The preparation method according to claim 4 or 5, characterized in that: The temperature of the low-temperature spray drying is 350-500° C., the spray flow rate is 1-4 ml / min, and the pressure is 0.1-0.7 MPa.

8. The preparation method according to claim 4 or 5, characterized in that: The temperature of the high temperature pyrolysis is 700-1000° C., and the time is 5-8 seconds.

9. The preparation method according to claim 4 or 5, characterized in that: The sintering temperature is 700-900° C., and the sintering time is 0.5-2 h.

10. A lithium ion battery, characterized in that: It includes the bismuth silicate-coated lithium iron manganese phosphate material as described in any one of claims 1 to 3 or the bismuth silicate-coated lithium iron manganese phosphate material prepared by the preparation method as described in any one of claims 4 to 9.

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