A sodium ion battery positive electrode material and preparation method thereof

Abstract

The present invention belongs to the field of electrochemical technology and discloses a sodium ion battery positive electrode material and a preparation method thereof. The positive electrode material has the general molecular formula of NaNi0.3Fe0.4‑m‑nMn0.3XmYnO2. The positive electrode material of the present invention is a ternary sodium ion battery positive electrode material of Ni, Fe, and Mn doped with a trace element X and coated with an element Y. Its precursor particles are flaky, and after a single sintering, the particles are spherical particles composed of crossed or overlapping flakes. The positive electrode after the second sintering is a uniform spherical particle with little fine powder and excellent processing performance. In addition, the doping and coating of the X and Y elements improve the stability of its crystal structure and significantly improve the cycle performance.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology and relates to a sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] Due to the depletion of lithium resources and insufficient abundance in the Earth's crust, the cost of lithium-ion batteries is increasing. Although sodium-ion batteries have lower energy density than lithium-ion batteries, their abundant sodium reserves and similar processing methods make them a useful supplement to lithium batteries.

[0003] The sodium cathode plays a decisive role in the electrochemical performance of the battery. Currently, the layered transition metal oxide NaxMeO2 (Me represents Ni, Co, Fe, Mn, etc.) has the highest theoretical specific capacity, which can reach 200mAh·g -1 . However, its structural stability is not as good as that of polyanionic compounds and Prussian blue materials. This is mainly because the Mn3+ in the system will bring about the Jahn-Teller effect, resulting in more phase changes during the charge and discharge process, and the continuous insertion and extraction of Na+ will gradually destroy the crystal structure, thereby greatly reducing the cycle performance. In order to take into account both capacity and stability, people have conducted research on how to improve the electrical performance of layered sodium. For example, in the Chinese patent CN112467119A, in order to bring into play the synergistic effect of different elements, Fe2O3, NiO, Co3O4, SnO2, and Ti2O are used as the main metals, and then Li2CO3 is added, and finally Na2CO3 is mixed and sintered to obtain a layered high-entropy sodium positive electrode material. However, its cost advantage over lithium battery preparation is not obvious, and the improvement in electrochemical performance is also relatively limited. For example, Chinese patent CN112234200 uses a combustion method to dope O3-type NaMn0.5Ni0.5O2 with specific trivalent metal cations (at least one of Y3+, La3+, Ac3+, Ca3+, or Sc3+) to suppress structural distortion during charge and discharge. However, the morphology and physicochemical properties of the precursor produced by this method are uncontrollable, and the particle uniformity and processing performance are unstable. Patent CN112374551A uses a liquid-phase synthesis method to prepare an M1-x-yFexMny(OH)2-type precursor (M is Ni2+, Ca2+, Mg2+, Zn2+, Co2+, Co3+, Ag+, etc.), and then obtains a relatively uniform layered oxide through calcination.

[0004] Among the numerous patent studies, few use the co-precipitation method to dope and coat sodium electrodes to improve material properties, and often the doping elements are synthesized or calcined as the main elements. The cost of some elements is not low, and the performance of small amounts of doping is not involved. Summary of the Invention

[0005] In order to solve the above problems, the present invention aims to provide a sodium ion battery positive electrode material and a preparation method thereof.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A sodium ion battery positive electrode material, the positive electrode material molecular formula is NaNi 0.3 Fe 0.4-m-n Mn 0.3 XmYnO2, wherein 0.02≤m+n≤0.08, X is one or more of Mg, Zr, Zn, Cr, V, and Nb, and Y is one or more of Cu, Al, Ti, Sn, and Li.

[0008] Furthermore, preferably, in terms of molar ratio, Ni:Fe:Mn:X:Y=3:3.4:3:0.4:0.2.

[0009] Based on a general inventive concept, the present application also provides a method for preparing a positive electrode material for a sodium ion battery, comprising the following steps:

[0010] Step 1: preparing a salt solution, wherein the salt solution includes a Ni, Fe, Mn ternary salt solution, an X salt solution, and a Y salt solution;

[0011] Step 2: preparing a precipitant, wherein the precipitant is sodium hydroxide solution or ammonium phosphate solution;

[0012] Step 3: preparing a complexing agent solution, wherein the complexing agent solution includes an ammonia solution, a sodium citrate solution and an EDTA-2Na solution;

[0013] Step 4: Pour pure water into the reactor, start stirring, raise the temperature to 45-65°C, and introduce nitrogen to form an inert atmosphere;

[0014] Step 5: adding a precipitant and at least one complexing agent solution to the reactor to adjust the pH value of the solution in the reactor to 10.5-11.5 and the total concentration of the complexing agent to 0.05-0.5 mol / L;

[0015] Step 6: According to the co-precipitation reaction requirements, the salt solution, precipitant and complexing agent are uniformly introduced into the reactor at flow rates set in proportion;

[0016] Step 7: When the reaction is carried out for 30-50 hours, the feeding is stopped, the stirring speed is reduced, and the constant temperature is maintained for 2 hours; then the stirring is restored to the original speed and the Y salt solution, complexing agent solution, and precipitant are introduced into the reactor at a certain flow rate; when the coating amount of the Y salt solution meets the design requirements, the feeding is stopped and the stirring speed is reduced for aging;

[0017] Step 8: The aged slurry is subjected to solid-liquid separation, and the solid precipitate is processed to obtain precursor particles;

[0018] Step 9: Use a high-efficiency mixer to evenly mix the precursor and Na2CO3 in a ratio of 1:1-1:1.07;

[0019] Step 10: The mixed materials are placed in an atmosphere sintering furnace for primary sintering. The heating rate during the primary sintering is 2-4°C / min, the air flow rate is 300-1000L / h, and the temperature is kept at 700-850°C for 10-15h. After cooling to room temperature, the materials are taken out for grinding, gas breaking, and screening.

[0020] Step 11: The undersize material obtained in step 10 is subjected to secondary sintering. The undersize material is placed in an atmosphere sintering furnace, the heating rate is set to 2-4°C / min, the air flow rate is 300-1000L / h, and it is kept at 750-900°C for 10-15h; after cooling to room temperature, it is taken out for grinding, gas breaking, and screening to obtain the finished product.

[0021] Furthermore, preferably, the ternary salt solution is 1.8-2 mol / L sulfate, and the X salt and the Y salt are 0.1-1 mol / L sulfate or chloride, respectively.

[0022] Furthermore, preferably, in step 2, the concentration of the sodium hydroxide solution is 4-10 mol / L, and the concentration of the ammonium phosphate solution is 1.5-2.5 mol / L.

[0023] Furthermore, preferably, in step three, the concentration of the ammonia solution is 4-10 mol / L, the concentration of the sodium citrate solution is 1-3 mol / L, and the concentration of the EDTA-2Na solution is 0.1-0.3 mol / L.

[0024] Furthermore, preferably, in step 4, the stirring speed is 600-900 rpm; and in step 7, the reduced stirring speed is 300-600 rpm.

[0025] Furthermore, preferably, in step eight, the solid precipitate obtained by solid-liquid separation is washed, dried, and sieved.

[0026] Based on a general inventive concept, the present application also provides a sodium ion battery in which a positive electrode is made of the above-mentioned positive electrode material, or a positive electrode material prepared by the above-mentioned preparation method.

[0027] Compared with the prior art, the present invention has the following advantages and positive effects:

[0028] 1. No cobalt, little nickel, only a small amount of doping and coating elements, all raw materials can be soluble salts, not necessarily nano-oxides, and the raw material cost is low;

[0029] 2. The precursor and cathode material are uniform spherical particles with less fine powder and easy processing, which increases the raw material yield and reduces the processing cost;

[0030] 3. Doping and coating are completed in the precursor synthesis stage, the doping is more uniform, the coating is more complete, the electrochemical properties of the material are effectively improved, and at least one sintering process can be reduced;

[0031] 4. The present invention is based on low cost, with capacity and cycle performance as the goal, and uses co-precipitation method and two-stage sintering as means to prepare a positive electrode material with low raw material and processing costs and good cycle performance.

[0032] The cathode material of the present invention is a ternary sodium-ion battery cathode material composed of Ni, Fe, and Mn, doped with trace elements X (one or more of Mg, Zr, Zn, Cr, V, and Nb) and coated with elements Y (one or more of Cu, Al, Ti, Sn, and Li). The precursor primary particles are flaky, while the secondary particles are quasi-spherical particles composed of intersecting or overlapping flaky particles. The sintered product is uniform, quasi-spherical, with minimal fines and excellent processing properties. The doping and coating enhance the stability of the crystal structure, significantly improving cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is an electron microscope image of the precursor of Example 1 of the present invention;

[0035] Figure 2 This is an electron microscope image of the material after primary sintering in Example 1 of the present invention;

[0036] Figure 3 This is an electron microscope image of the material after secondary sintering in Example 1 of the present invention;

[0037] Figure 4 This is a rate test cycle diagram of Example 1 of the present invention;

[0038] Figure 5 This is an electron microscope image of the material after secondary sintering in Example 2 of the present invention;

[0039] Figure 6 This is a rate test cycle diagram of Example 2 of the present invention;

[0040] Figure 7 This is an electron microscope image of the material after secondary sintering in Comparative Example 1 of the present invention;

[0041] Figure 8 This is a rate test cycle diagram of Comparative Example 1 of the present invention;

[0042] Figure 9 This is an electron microscope image of the material after secondary sintering in Comparative Example 2 of the present invention;

[0043] Figure 10 This is a 2-fold test cycle diagram for the comparative example of the present invention. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0045] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the devices or components referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance. In addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or it can be internal communication between two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0046] Example 1

[0047] A method for preparing a positive electrode material for a sodium ion battery, wherein the positive electrode material has a molecular formula of NaNi0.3Fe0.4-m-nMn0.3XmYnO2, wherein 0.02≤m+n≤0.08, comprises the following steps:

[0048] Step 1: Weigh the salt raw materials according to the molar ratio of Ni:Fe:Mn:X:Y=3:3.4:3:0.4:0.2;

[0049] Use pure water to prepare Ni, Fe, and Mn ternary salt solutions of nickel sulfate, manganese sulfate, and ferrous sulfate with a total concentration of 2 mol / L, a mixed salt solution of zirconium oxychloride and magnesium sulfate with a total concentration of 0.5 mol / L as salt X, and a mixed salt solution of titanium tetrachloride and lithium sulfate with a total concentration of 0.5 mol / L as salt Y;

[0050] Step 2: preparing a precipitant, wherein the precipitant is 8 mol / L sodium hydroxide solution and 2 mol / L ammonium phosphate solution;

[0051] Step 3: Prepare a complexing agent solution, which includes a 4 mol / L ammonia solution and a 2 mol / L sodium citrate solution.

[0052] Step 4: Pour 40% of the volume of pure water into the reactor, start stirring at 850 rpm, raise the temperature to 55°C, and then blow 99.99% pure nitrogen gas into the reactor;

[0053] Step 5: After nitrogen gas is bubbled for 2 hours, sodium hydroxide precipitant, ammonia solution, and sodium citrate solution are added to the reactor to adjust the pH value of the solution system in the reactor to 11.0±0.1, the concentration of ammonia solution to 0.1 mol / L, and the concentration of sodium citrate solution to 0.05 mol / L;

[0054] Step 6: Set the flow rate of the ternary salt solution to 4 L / h and the flow rate of the X salt solution to 1.02 L / h according to the proportional requirements; set the flow rate of the complexing agent ammonia solution according to the growth requirements to maintain the ammonia concentration in the reactor at 2-3 g / L; set the flow rate of the complexing agent sodium citrate solution to maintain the concentration in the reactor at 0.05-0.1 mol / L; set the flow rate of the precipitant to maintain the pH of the reactor at 10.8-11.0; use a metering pump to evenly pump the above solutions into the reactor for co-precipitation synthesis reaction, and use a thickener to discharge the mother liquor during the reaction;

[0055] Step 7: When the reaction is carried out for 40 hours, the feeding is stopped, the stirring speed is reduced to 600 rpm, and the constant temperature is maintained for 2 hours; then the stirring speed is restored to the original speed of 850 rpm, and the Y salt solution is introduced at a flow rate of 2L / h, the chelating agent solution is stopped, and the precipitant is changed to ammonium phosphate solution to maintain the ammonia value in the reactor at 6-8g / L; when the coating amount of the Y salt solution meets the design requirements, the feeding is stopped, and the stirring speed is reduced to 600 rpm for aging;

[0056] Step 8: The aged slurry is subjected to solid-liquid separation, and the solid precipitate is washed, dried, and sieved to obtain a precursor; the electron microscope image of the precursor is as follows: Figure 1 As shown;

[0057] Step 9: The precursor particles and Na2CO3 are placed in a mixer at a ratio of 1:1.05 and mixed evenly;

[0058] Step 10: The mixed material is placed in a sagger, and the sagger is placed in an atmosphere sintering furnace for a single sintering. The heating rate during the single sintering is 3°C / min, the air flow rate is 1000L / h, and the material is kept at 750°C for 12h. After cooling to room temperature, the material is taken out for grinding, gas breaking, and screening. The electron microscope image of the material after the single sintering is as follows: Figure 2 As shown;

[0059] Step 11: The undersize material obtained in step 10 is subjected to secondary sintering. The undersize material is placed in an atmosphere sintering furnace, the heating rate is set to 2-4℃ / min, the air flow rate is 1000L / h, and the temperature is kept at 800℃ for 12 hours; after cooling to room temperature, it is taken out for grinding, gas breaking, and screening to obtain the finished product. The electron microscope image of the material after secondary sintering is as follows Figure 3 shown.

[0060] Example 2

[0061] A method for preparing a positive electrode material for a sodium ion battery, wherein the positive electrode material has a molecular formula of NaNi0.3Fe0.4-m-nMn0.3XmYnO2, wherein 0.02≤m+n≤0.08, comprises the following steps:

[0062] Step 1: Weigh the salt raw materials according to the molar ratio of Ni:Fe:Mn:X:Y=3:3.96:3:0.2:0.2;

[0063] Use pure water to prepare a ternary salt solution of Ni, Fe, and Mn (nickel sulfate, manganese sulfate, and ferrous sulfate) with a total concentration of 2 mol / L, a salt solution X (zirconium oxychloride and magnesium sulfate) with a total concentration of 0.5 mol / L, and a salt solution Y (titanium tetrachloride and lithium sulfate) with a total concentration of 0.5 mol / L.

[0064] The other steps 2 to 11 are the same as those in Example 1.

[0065] The electron microscope image of the material after secondary sintering in this embodiment is as follows Figure 5 shown.

[0066] Comparative Example 1

[0067] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0068] Step 1: Weigh the salt raw material according to the molar ratio of Ni:Fe:Mn=3:4:3;

[0069] Prepare a ternary salt solution of nickel sulfate, manganese sulfate, and ferrous sulfate with a total concentration of 2 mol / L using pure water;

[0070] Step 2: preparing a precipitant, wherein the precipitant is 8 mol / L sodium hydroxide solution;

[0071] Step 3: Prepare a complexing agent solution, which includes a 4 mol / L ammonia solution and a 2 mol / L sodium citrate solution.

[0072] Step 4: Pour 40% of the volume of pure water into the reactor, start stirring at 850 rpm, raise the temperature to 55°C, and then blow 99.99% pure nitrogen gas into the reactor;

[0073] Step 5: After nitrogen is bubbled for 2 hours, sodium hydroxide precipitant, ammonia solution, and sodium citrate solution are added to the reactor to adjust the pH value of the solution system in the reactor to 10.8-11.0, the concentration of ammonia solution to 0.1 mol / L, and the concentration of sodium citrate solution to 0.05 mol / L;

[0074] Step 6: Set the ternary salt solution at 4 L / h according to the proportional requirements; set the flow rate of the complexing agent ammonia solution according to the growth requirements to maintain the ammonia concentration in the reactor at 2-3 g / L; set the flow rate of the complexing agent sodium citrate solution to maintain the concentration in the reactor at 0.05-0.1 mol / L; set the flow rate of the precipitant to maintain the pH of the reactor at 10.8-11.0; use a metering pump to evenly pump the above solution into the reactor for co-precipitation synthesis reaction, and use a thickener to discharge the mother liquor during the reaction;

[0075] Step 7: When the reaction is carried out for 40 hours, the feeding is stopped, the stirring speed is reduced to 600 rpm, and the constant temperature is maintained for 2 hours for aging;

[0076] Step 8: The aged slurry is subjected to solid-liquid separation, and the solid precipitate is washed, dried, and sieved to obtain a precursor;

[0077] Other steps 9 to 11 are the same as those in Example 1.

[0078] The electron microscope image of the material after secondary sintering in this comparative example is as follows Figure 7 shown.

[0079] Comparative Example 2

[0080] Sintering preparation is carried out according to the proportions of Example 1, and a certain mass of nano-scale or micron-scale Na2CO3, NiO, Fe2O3, Mn2O3, MgO, and ZrO2 are placed in a ball mill and mixed in proportion. After mixing evenly, the mixture is placed in an atmosphere furnace and kept warm at 750°C for 12 hours; after cooling, the mixture is crushed and sieved; and then a second-stage sintering is carried out at 800°C and kept warm for 12 hours.

[0081] After crushing and screening the secondary sintered material, TiO2 and Li2CO3 were added in the proportions described in Example 1 and thoroughly mixed in a mixer. The material was then placed in an atmosphere furnace at 400°C for 12 hours. After cooling, it was crushed and screened.

[0082] The electron microscope image of the material after secondary sintering in this comparative example is as follows Figure 9 shown.

[0083] Experimental testing

[0084] Take the finished positive electrode materials in Examples 1 and 2, Comparative Examples 1 and 2, and mix them with PVDF glue, SP powder conductive agent and a certain amount of NMP dispersant in a homogenizer to form an active substance. The prepared active material slurry is coated on aluminum foil, dried and cut into positive electrode sheets with a diameter of 12 mm. Then, glass fiber is used as a diaphragm, a mixture of DMC, EMC, EC, NaPF6 and FEC in a certain molar ratio is used as the electrolyte, and a sodium sheet with a diameter of 14 mm is used as the negative electrode to produce a 2032 type button battery. The prepared button battery is placed in a blue electricity test system for electrochemical testing, and the charge and discharge voltage is selected to be 2.0-4.0V, the rate is 0.1-2C, and the test temperature is 25°C. The 2-rate test cycle diagrams of Example 1, Example 2, Comparative Example 1 and Comparative Example 2 are shown as follows. Figure 4 、 6 , 8, and 10.

[0085] Table 1:

[0086]

[0087] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work, any modifications, equivalent substitutions, improvements, etc. made should be included in the scope of protection of the present invention.

Claims

1. A sodium ion battery cathode material, characterized in that: The general formula of the positive electrode material is NaNi 0.3 Fe 0.4-m- n Mn 0.3 X m Y n O2, wherein 0.02≤m+n≤0.08, X is one or more of Mg, Zr, Zn, Cr, V, and Nb, and Y is one or more of Cu, Al, Ti, Sn, and Li; In terms of molar ratio, Ni:Fe:Mn:X:Y=3:3.4:3:0.4:0.2; The method for preparing the sodium ion battery positive electrode material comprises the following steps: Step 1: preparing a salt solution, wherein the salt solution includes a Ni, Fe, Mn ternary salt solution, an X salt solution, and a Y salt solution; Step 2: preparing a precipitant, wherein the precipitant is sodium hydroxide solution or ammonium phosphate solution; Step 3: preparing a complexing agent solution, wherein the complexing agent solution includes an ammonia solution, a sodium citrate solution and an EDTA-2Na solution; Step 4: Pour pure water into the reactor, start stirring, raise the temperature to 45-65°C, and introduce nitrogen to form an inert atmosphere; Step 5: adding a precipitant and at least one complexing agent solution to the reactor to adjust the pH value of the solution in the reactor to 10.5-11.5 and the total concentration of the complexing agent to 0.05-0.5 mol / L; Step 6: According to the co-precipitation reaction requirements, the Ni, Fe, Mn ternary salt solution, X salt solution, precipitant and complexing agent are uniformly introduced into the reactor at a set flow rate; Step 7: When the reaction is carried out for 30-50 hours, the feeding is stopped, the stirring speed is reduced, and the constant temperature is maintained for 2 hours; then the stirring is restored to the original speed and the Y salt solution, complexing agent solution, and precipitant are introduced into the reactor at a certain flow rate; when the coating amount of the Y salt solution meets the design requirements, the feeding is stopped and the stirring speed is reduced for aging; Step 8: The aged slurry is subjected to solid-liquid separation to form a filter cake, which is then processed into precursor particles; Step 9: Evenly mix the precursor and Na2CO3 in a high-efficiency mixer at a ratio of 1:1-1:1.07; The mixed materials in step 10 and step 9 are placed in an atmosphere sintering furnace for primary sintering, with a heating rate of 2-4°C / min, an air flow rate of 300-1000L / h, and a temperature of 700-850°C for 10-15h; after cooling to room temperature, the materials are taken out for grinding, gas crushing, and screening; Step 11: The undersize material obtained in step 10 is subjected to secondary sintering. The undersize material is placed in an atmosphere sintering furnace, the heating rate is set to 2-4°C / min, the air flow rate is 300-1000L / h, and it is kept at 750-900°C for 10-15h; after cooling to room temperature, it is taken out for grinding, gas breaking, and screening to obtain the finished product.

2. A sodium ion battery positive electrode material according to claim 1, characterized in that: The ternary salt solution is 1.8-2 mol / L sulfate, and the X salt and the Y salt are 0.1-1 mol / L sulfate or chloride respectively.

3. A sodium ion battery positive electrode material according to claim 1, characterized in that: In step 2, the concentration of the sodium hydroxide solution is 4-10 mol / L, and the concentration of the ammonium phosphate is 1.5-2.5 mol / L.

4. A sodium ion battery positive electrode material according to claim 1, characterized in that: In step 3, the concentration of the ammonia solution is 4-10 mol / L, the concentration of the sodium citrate solution is 1-3 mol / L, and the concentration of the EDTA-2Na solution is 0.1-0.3 mol / L.

5. The sodium ion battery cathode material according to claim 1, wherein: In step 4, the stirring speed is 600-900 rpm; in step 7, the stirring speed is reduced to 300-600 rpm.

6. A sodium ion battery cathode material according to claim 1, characterized in that: In step eight, the solid precipitate obtained by solid-liquid separation is washed, dried, and sieved.

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