Phosphate-coated sodium ion battery positive electrode material, preparation method and application

Abstract

The invention belongs to the technical field of sodium ion layered oxide positive electrode materials, and relates to a phosphate-coated sodium ion battery positive electrode material, a preparation method and application, the positive electrode material comprises an O3-type main body material and a phosphate-coated material, the chemical formula of the O3-type main body material is NaxMnaMbO2, and the chemical formula of the phosphate-coated material is AnPO4; the preparation method comprises the following steps: mixing an O3 type main body material and a phosphate coating material to obtain a coating initial product; and sintering the mixed coating primary product powder to prepare the phosphate-coated sodium ion battery positive electrode material, the phosphate-coated sodium ion battery positive electrode material has excellent electrochemical performance, residual alkali on the surface of the material is obviously reduced after surface phosphate coating, and basic conditions are provided for industrial mass production of the phosphate-coated sodium ion battery positive electrode material; in addition, the preparation method of the phosphate-coated sodium ion battery positive electrode material provided by the invention has the characteristics of simple preparation mode, low cost, strong controllability and strong industrial implementation.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion layered oxide positive electrode materials, and relates to a phosphate-coated sodium ion battery positive electrode material, a preparation method and an application thereof. Background Art

[0002] With the widespread use of lithium-ion batteries, the scarcity of lithium resources cannot meet the growing demand for lithium, which has led to a continuous increase in the price of lithium resources. Therefore, it is urgent to explore alternatives to lithium-ion batteries. Sodium-ion batteries are considered to be a competitive alternative battery because their properties are similar to those of lithium-ion batteries and there are abundant Na resources in the earth's crust, which can greatly reduce costs. O3-type sodium-ion layered oxides have high theoretical capacity and high sodium content and are considered to be a promising cathode material. However, the actual capacity and cycle stability of O3-type layered oxide cathodes are still far below the actual requirements of energy storage devices. Therefore, it is necessary to improve the cycle performance of O3-type layered oxides.

[0003] So far, great efforts have been made to improve the cycle performance of transition metal oxides, such as nanostructure design, element doping or surface modification. In particular, surface coating is an important way to improve the cycle life of electrode materials. Surface coating not only maintains the stability of the material structure, but also prevents the formation of sodium carbonate or sodium bicarbonate on the surface of the material by absorbing little carbon dioxide and water. Carbon coating is also a common strategy to improve the electrochemical performance of electrode materials, but due to the poor mechanical properties of carbon, the cycle stability of carbon-coated layered oxides is only slightly improved. However, in the field of sodium-ion batteries, there are few studies on metal phosphate-modified layered oxide materials.

[0004] In the prior art, although surface coating technology has been widely popularized, the coating technology of phosphate system is mostly applied to the field of lithium-ion batteries; the current surface coating technology of sodium-ion batteries mostly adopts oxide system, such as titanium oxide, manganese oxide, etc. for surface coating, which can improve the cycle stability by reducing the interface reaction, but it will greatly hinder the sodium ion transmission channel, and the capacity will decrease to a certain extent; and the positive electrode material of sodium-ion battery coated with phosphate only exists in wet coating, and wet coating cannot be industrialized on a large scale. Therefore, a surface coating method of sodium-ion battery with simple preparation method, low cost, strong controllability and strong industrial feasibility is needed to solve the above problems. Summary of the invention

[0005] The technical solution adopted by the present invention to solve the technical problem is: a phosphate-coated sodium ion battery positive electrode material, the sodium ion battery positive electrode material comprises an O3 type main material and a phosphate coating material, the chemical formula of the O3 type main material is: Nax Mn a M b O 2 , where: 0.8 < x < 1, 0.2 < a < 0.8, 0 < b < 0.2, the element M includes one or more of Mg, Al, Ti, Fe, Co, Ni, Cu, Zn, Sr, Zr, and Sn; the chemical formula of the phosphate coating material is: A n PO 4 , where A includes one or more of Na, Zn, Al, Co, and Mn, 0 < n < 2; a nano-scale surface phosphate coating layer is formed by reacting the coating material with the residual alkali on the surface of the O3-type cathode material to reduce the residual alkali content of the cathode material itself and achieve excellent cycle stability; among them, A is the metal source in the final coating.

[0006] Preferably, the mass ratio of the O3-type host material to the phosphate coating material is 98% - 99.8%: 0.2% - 2%.

[0007] Preferably, the chemical formula of the O3-type host material is Na x Mn a M b O 2 in which, a + b = 1.

[0008] Preferably, the phosphoric acid source of the phosphate coating material is NH 4 H 2 PO 4 and / or (NH 4 ) 2 HPO 4 .

[0009] The present invention also discloses a preparation method of a phosphate-coated sodium-ion battery cathode material, and the preparation method is used to prepare the above-mentioned phosphate-coated sodium-ion battery cathode material. The preparation method includes:

[0010] Step 1, mixing the O3-type host material and the phosphate coating material to obtain a preliminary coating product;

[0011] Step 2, sintering the mixed preliminary coating product powder to obtain a phosphate-coated sodium-ion battery cathode material.

[0012] Preferably, in step 1, the phosphate coating material is any one of diammonium hydrogen phosphate and ammonium dihydrogen phosphate or one or more of the oxides containing element A, and the mixing method is dry ball milling. The rotation speed of the ball milling is 350 - 500 rpm, and the mixing time of the ball milling is 1 - 2 h.

[0013] Preferably, in step 2, the sintering temperature is 300-750°C, and the heating rate is 1-5°C min -1 The sintering time is 4 to 8 hours, and the sintering atmosphere is air or oxygen atmosphere.

[0014] The present invention also discloses an application of a phosphate-coated sodium ion battery positive electrode material. The application adopts the above-mentioned phosphate-coated sodium ion battery positive electrode material. The sodium ion battery positive electrode material is used to prepare a sodium ion battery positive electrode sheet. The sodium ion battery positive electrode sheet is prepared by dissolving the sodium ion battery positive electrode material, a conductive agent and a binder in a solvent to obtain a slurry, coating the slurry on the surface of a current collector and then drying it.

[0015] Preferably, the sodium ion battery positive electrode plate is used to prepare a sodium ion battery.

[0016] The beneficial effects of the present invention are:

[0017] 1. The phosphate-coated sodium ion battery positive electrode material of the present invention forms a nano-scale surface phosphate coating layer by reacting the coating with the residual alkali on the surface of the O3 type positive electrode material, so as to reduce the residual alkali content of the positive electrode material itself and achieve excellent cycle stability.

[0018] 2. The preparation method of the phosphate-coated sodium ion battery positive electrode material of the present invention is simple, efficient, low-cost, and highly controllable, which is conducive to large-scale industrial production.

[0019] 3. The phosphate-coated sodium ion battery positive electrode material of the present invention has the characteristics of good cycle stability, and the discharge specific capacity in the voltage range of 2.0 to 4.2 V reaches 150 to 160 mAh g -1 After 100 cycles at a current density of 1C, the capacity retention rate of the sodium ion battery reached 80% to 86%.

[0020] 4. The sodium ion battery of the present invention provides a new idea for improving the cycle stability of the positive electrode material of the sodium ion battery by surface coating, and provides the possibility for the commercialization of the surface-coated sodium ion positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a phosphate-coated sodium ion battery positive electrode material, preparation method and application of the present invention. Example 1 is a sodium ion battery cycle performance curve at 1C;

[0022] Figure 2 is a cycle performance curve of the sodium ion battery of Example 2 of the present invention at 1C;

[0023] Figure 3 This is a cycle performance curve of the sodium ion battery of Example 3 of the present invention at 1C;

[0024] Figure 4 This is a cycle performance curve of the sodium ion battery of Comparative Example 1 of the present invention at 1C;

[0025] Figure 5 This is a cycle performance curve of the sodium ion battery of Comparative Example 2 of the present invention at 1C. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] refer to Figures 1 to 5 The positive electrode material of the sodium ion battery of this embodiment reacts with the residual alkali on the surface of the coating and the O3 type positive electrode material to generate a nano-scale surface phosphate coating layer, so as to reduce the residual alkali content of the positive electrode material itself and achieve excellent cycle stability. The positive electrode material can be obtained by mixing the coated O3 type positive electrode material and the coating and then sintering. It is simple, efficient, and low-cost, which is conducive to large-scale industrial production. The sodium ion battery obtained with the positive electrode material has the characteristics of good cycle stability, thereby completing this embodiment.

[0028] The present embodiment is further described below through specific examples.

[0029] Embodiment 1:

[0030] (1) Weigh diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 and alumina Al 2 O 3 In an agate mortar, hand grind for 5 minutes and then mix the mixed powder with the corresponding mass of uncoated positive electrode material Na 0.98 Mn 0.328 Ni 0.328 Fe 0.164 Cu 0.02 Cu 0.02 Zn 0.04 Li 0.02 Ti 0.08 Co 0.03 O 2 Add it into a plastic ball mill jar, add zirconium dioxide ball mill beads, and ball mill at 480 rpm for 1 h to obtain a precursor powder;

[0031] The precursor powder was spread on a porcelain boat, placed in a muffle furnace, and heated at 3°C ​​min at room temperature (25°C) in an air atmosphere.-1 The heating rate was raised to 300℃ and sintered for 4h, and then -1 The heating rate was raised to 750°C and sintered for 4 hours; then the mixture was naturally cooled to room temperature in an air atmosphere to obtain a phosphate-coated sodium ion battery positive electrode material;

[0032] (2) The positive electrode material obtained in step (1), Super-P and polyvinylidene fluoride in a mass ratio of 8:1:1 are mixed, and N-methylpyrrolidone solvent (NMP) is added and mixed evenly to form a slurry, and the slurry is coated on an aluminum foil using a scraper, and dried in a blast oven until the NMP is completely volatilized, and then placed in a vacuum oven at 80° C. for 10 h to be punched into a sodium ion battery positive electrode sheet with a diameter of 10 mm;

[0033] (3) The positive electrode prepared in step (2) was assembled with a sodium metal sheet with a diameter of 12 mm to form a sodium ion battery. The electrolyte consisted of 1 mol L -1 NaClO 4 , 1 mol L -1 Propylene carbonate (PC) and 5wt.% (NaClO 4 The CR2032 button-type sodium ion battery was assembled in a glove box with an argon atmosphere.

[0034] The prepared sodium ion battery was subjected to constant current charge and discharge curve performance test in the test voltage range of 2–4.2 V. -1 ) and the prepared sodium ion battery was cycled 100 times at 1C rate. The cycle performance is shown in Figure 1 As shown, it can be seen that after 100 cycles, the capacity retention rate reaches 85.8%;

[0035] Embodiment 2:

[0036] (1) According to the stoichiometric ratio, diammonium hydrogen phosphate and aluminum oxide were weighed in an agate mortar, and the mixed powder and the corresponding mass of uncoated cathode material were added to a plastic ball mill, and zirconium dioxide ball milling beads were added. The mixture was ball milled at 480 rpm for 1 h to obtain a precursor powder;

[0037] The precursor powder was spread on a porcelain boat, placed in a muffle furnace, and heated at 3°C ​​min at room temperature (25°C) in an air atmosphere. -1 The heating rate is raised to 750°C and sintered for 6 hours; then the mixture is naturally cooled to room temperature in an air atmosphere to obtain a phosphate-coated sodium ion battery positive electrode material;

[0038] (2) The positive electrode material obtained in step (1), Super-P and polyvinylidene fluoride in a mass ratio of 8:1:1 are mixed, and N-methylpyrrolidone solvent (NMP) is added and mixed evenly to form a slurry, and the slurry is coated on an aluminum foil using a scraper, and dried in a blast oven until the NMP is completely volatilized, and then placed in a vacuum oven at 80° C. for 10 h to be punched into a sodium ion battery positive electrode sheet with a diameter of 10 mm;

[0039] (3) The positive electrode prepared in step (2) was assembled with a sodium metal sheet with a diameter of 12 mm to form a sodium ion battery. The electrolyte consisted of 1 mol L -1 NaClO 4 , 1 mol L -1 Propylene carbonate (PC) and 5wt.% (NaClO 4 The CR2032 button-type sodium ion battery was assembled in a glove box with an argon atmosphere.

[0040] The prepared sodium ion battery was subjected to constant current charge and discharge curve performance test in the test voltage range of 2–4.2 V. -1 ) and the prepared sodium ion battery was cycled 100 times at 1C rate. The cycle performance is shown in Figure 2 As shown, it can be seen that after 100 cycles, the capacity retention rate reaches 81.3%;

[0041] Embodiment 3:

[0042] (1) According to the stoichiometric ratio, diammonium hydrogen phosphate and zinc oxide were weighed in an agate mortar, and the mixed powder and the corresponding mass of uncoated cathode material were added to a plastic ball mill, and zirconium dioxide ball milling beads were added. The mixture was ball milled at 480 rpm for 1 h to obtain a precursor powder;

[0043] The precursor powder was spread on a porcelain boat, placed in a muffle furnace, and heated at 3°C ​​min at room temperature (25°C) in an air atmosphere. -1 The heating rate is raised to 750°C and sintered for 6 hours; then the mixture is naturally cooled to room temperature in an air atmosphere to obtain a phosphate-coated sodium ion battery positive electrode material;

[0044] (2) The positive electrode material obtained in step (1), Super-P and polyvinylidene fluoride in a mass ratio of 8:1:1 are mixed, and N-methylpyrrolidone solvent (NMP) is added and mixed evenly to form a slurry, and the slurry is coated on an aluminum foil using a scraper, and dried in a blast oven until the NMP is completely volatilized, and then placed in a vacuum oven at 80° C. for 10 h to be punched into a sodium ion battery positive electrode sheet with a diameter of 10 mm;

[0045] (3) The positive electrode prepared in step (2) was assembled with a sodium metal sheet with a diameter of 12 mm to form a sodium ion battery. The electrolyte consisted of 1 mol L -1 NaClO 4 , 1 mol L -1 Propylene carbonate (PC) and 5wt.% (NaClO 4 The CR2032 button-type sodium ion battery was assembled in a glove box with an argon atmosphere.

[0046] The prepared sodium ion battery was subjected to constant current charge and discharge curve performance test in the test voltage range of 2–4.2 V. -1 ) and the prepared sodium ion battery was cycled 100 times at 1C rate. The cycle performance is shown in Figure 3 As shown, it can be seen that after 100 cycles, the capacity retention rate reaches 80.8%;

[0047] Comparative Example:

[0048] Comparative Example 1:

[0049] (1) hand-grinding the uncoated positive electrode material for 5 minutes to obtain an uncoated positive electrode material for a sodium ion battery;

[0050] (2) The positive electrode material obtained in step (1), Super-P and polyvinylidene fluoride in a mass ratio of 8:1:1 are mixed, and N-methylpyrrolidone solvent (NMP) is added and mixed evenly to form a slurry, and the slurry is coated on an aluminum foil using a scraper, and dried in a blast oven until the NMP is completely volatilized, and then placed in a vacuum oven at 80° C. for 10 h to be punched into a sodium ion battery positive electrode sheet with a diameter of 10 mm;

[0051] (3) The positive electrode prepared in step (2) was assembled with a sodium metal sheet with a diameter of 12 mm to form a sodium ion battery. The electrolyte consisted of 1 mol L -1 NaClO 4 , 1 mol L -1 Propylene carbonate (PC) and 5wt.% (NaClO 4The CR2032 button-type sodium ion battery was assembled in a glove box with an argon atmosphere.

[0052] The prepared sodium ion battery was subjected to constant current charge and discharge curve performance test in the test voltage range of 2–4.2 V. -1 ) and the prepared sodium ion battery was cycled 100 times at 1C rate. The cycle performance is shown in Figure 4 As shown, it can be seen that after 100 cycles, the capacity retention rate reaches 76.8%;

[0053] Comparative Example 2:

[0054] (1) The uncoated cathode material was hand-milled for 5 minutes and then added to a plastic ball mill, zirconium dioxide ball milling beads were added, and the ball milling was carried out at a speed of 480 rpm for 1 hour to obtain a precursor powder;

[0055] The precursor powder was spread on a porcelain boat, placed in a muffle furnace, and heated at 3°C ​​min at room temperature (25°C) in an air atmosphere. -1 The heating rate is raised to 750°C and sintered for 6 hours; then the mixture is naturally cooled to room temperature in an air atmosphere to obtain a re-fired uncoated sodium ion battery positive electrode material;

[0056] (2) The positive electrode material obtained in step (1), Super-P and polyvinylidene fluoride in a mass ratio of 8:1:1 are mixed, and N-methylpyrrolidone solvent (NMP) is added and mixed evenly to form a slurry, and the slurry is coated on an aluminum foil using a scraper, and dried in a blast oven until the NMP is completely volatilized, and then placed in a vacuum oven at 80° C. for 10 h to be punched into a sodium ion battery positive electrode sheet with a diameter of 10 mm;

[0057] (3) The positive electrode prepared in step (2) was assembled with a sodium metal sheet with a diameter of 12 mm to form a sodium ion battery. The electrolyte consisted of 1 mol L -1 NaClO 4 , 1 mol L -1 Propylene carbonate (PC) and 5wt.% (NaClO 4 The CR2032 button-type sodium ion battery was assembled in a glove box with an argon atmosphere.

[0058] The prepared sodium ion battery was subjected to constant current charge and discharge curve performance test in the test voltage range of 2–4.2 V. -1 ) and the prepared sodium ion battery was cycled 100 times at 1C rate. The cycle performance is shown in Figure 5 As shown, it can be seen that after 100 cycles, the capacity retention rate reaches 78.1%;

[0059] The sodium ion batteries prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were compared in terms of 0.2C charge specific capacity, 0.2C discharge specific capacity, 1C discharge specific capacity, and 1C capacity retention rate (100 cycles). The results are shown in Table 1.

[0060]

[0061] Table 1

[0062] The residual alkali contents of the sodium ion batteries prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were compared, and the results are shown in Table 2.

[0063] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 <![CDATA[W(OH - )]]> 0.0032 0.0283 0.0007 0.0431 0.0387 <![CDATA[W(CO 3 2- )]]> 1.0312 1.0721 1.2134 1.3214 1.2531

[0064] Table 2

[0065] Combined with the above chart, it can be concluded that the phosphate-coated sodium ion battery positive electrode material provided in this embodiment has the characteristics of good cycle stability, and the discharge specific capacity in the voltage range of 2.0 to 4.2 V reaches 150 to 160 mAh g -1 After 100 cycles at a current density of 1C, the capacity retention rate of the sodium ion battery reached 80% to 86%.

[0066] It can be seen from Table 1 that the phosphate-coated sodium ion battery positive electrode materials in Example 1, Example 2, and Example 3 have higher capacity and cycle stability, while the uncoated Comparative Examples 1 and 2 have poor cycle stability.

[0067] It can be seen from Table 2 that the phosphate-coated sodium ion battery positive electrode materials in Example 1, Example 2, and Example 3 have lower residual alkalinity values, which is consistent with their excellent electrochemical properties.

[0068] In summary, the phosphate-coated sodium ion battery positive electrode material of the present invention has excellent electrochemical properties. After the surface phosphate coating is performed, the residual alkali on the surface of the material is significantly reduced, providing basic conditions for its large-scale industrial production. In addition, the preparation method of the phosphate-coated sodium ion battery positive electrode material provided by the present invention has the characteristics of simple preparation method, low cost, strong controllability and strong industrial feasibility.

[0069] It should be emphasized that the above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A phosphate-coated sodium ion battery cathode material, It is characterized in that The positive electrode material of the sodium-ion battery includes an O3-type host material and a phosphate coating material. The chemical formula of the O3-type host material is: Na x Mn a M b O 2 , where: 0.8 < x < 1, 0.2 < a < 0.8, 0 < b < 0.2, and the element M includes one or more of Mg, Al, Ti, Fe, Co, Ni, Cu, Zn, Sr, Zr, and Sn; the chemical formula of the phosphate coating material is: A n PO 4 , where A includes one or more of Na, Zn, Al, Co, and Mn, and 0 < n < 2.

2. A phosphate-coated sodium ion battery positive electrode material according to claim 1, It is characterized in that The mass ratio of the O3 type main material to the phosphate coating material is 98% to 99.8%: 0.2% to 2%.

3. A phosphate-coated sodium ion battery positive electrode material according to claim 1, It is characterized in that The phosphate source of the phosphate coating material is NH 4 H 2 PO 4 and or (NH 4 ) 2 HPO 4 .

4. A method for preparing a phosphate-coated sodium ion battery positive electrode material, It is characterized in that The preparation method is used to prepare the phosphate-coated sodium ion battery positive electrode material according to any one of claims 1 to 3, and the preparation method comprises: Step 1, mixing an O3-type main material and a phosphate coating material to obtain a coated primary product; Step 2: sintering the mixed coated primary product powder to obtain a phosphate-coated sodium ion battery positive electrode material.

5. The method for preparing a phosphate-coated sodium ion battery positive electrode material according to claim 4, It is characterized in that In step 1, the phosphate coating material is any one of diammonium hydrogen phosphate and ammonium dihydrogen phosphate or one or more oxides containing element A, and the mixing method is dry ball milling mixing. The rotation speed of the ball milling mixing is 350 to 500 rpm, and the mixing time of the ball milling mixing is 1 to 2 hours.

6. The method for preparing a phosphate-coated sodium ion battery positive electrode material according to claim 4, It is characterized in that In step 2, the sintering temperature is 300-750°C, and the heating rate is 1-5°C min -1 The sintering time is 4 to 8 hours, and the sintering atmosphere is air or oxygen atmosphere.

7. Application of a phosphate-coated sodium ion battery cathode material, It is characterized in that The application adopts the phosphate-coated sodium ion battery positive electrode material according to any one of claims 1 to 3, and the sodium ion battery positive electrode material is used to prepare a sodium ion battery positive electrode plate. The sodium ion battery positive electrode plate is prepared by dissolving the sodium ion battery positive electrode material, a conductive agent and a binder in a solvent to obtain a slurry, and coating the slurry on the surface of a current collector and then drying it.

8. Use of a phosphate-coated sodium ion battery positive electrode material according to claim 7, It is characterized in that The sodium ion battery positive electrode plate is used for preparing a sodium ion battery.

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