A kind of Na x M y (PO4)3 in-situ dispersion-distributed composite sodium ion active material and its preparation and application

Abstract

The present invention relates to the field of battery materials, and particularly to a preparation method of a composite sodium ion active material with in-situ dispersed NaxMy(PO4)3. A sodium source and a cathode precursor are mixed and sintered to obtain a sodium-containing cathode oxide active material substrate; the excess coefficient of the sodium source is 2-20 mol%; the residual sodium in the sodium-containing cathode oxide active material substrate is used as the sodium source, and an M source and a phosphorus source are prepared according to the stoichiometric ratio of NaxMy(PO4)3. Each raw material and an auxiliary agent are mixed and subjected to three-stage sintering to prepare a composite sodium ion active material with in-situ dispersed NaxMy(PO4)3. The present invention also relates to the material prepared by the above preparation method and its application in a battery. The method of the present invention can solve the problem of residual alkali, can obtain active materials with special components and structures, and has excellent performance.

Description

Technical Field

[0001] The present invention belongs to the field of battery materials, and particularly relates to the field of cathode materials for sodium-ion batteries. Background Art

[0002] Lithium-ion batteries have been widely used in industries such as mobile electronic devices, new energy vehicles, and grid energy storage. However, due to the relatively low lithium reserves in the earth's crust, the cost of lithium batteries is relatively high, which greatly limits the application of lithium-ion batteries in future energy storage systems. Therefore, it is crucial to find a new generation of electrochemical energy storage systems that can replace lithium-ion batteries. Sodium and lithium are elements in the same main group, and they have similar chemical properties and structures. However, compared with lithium, sodium has rich reserves, low cost, and higher safety for sodium-ion batteries. Therefore, sodium-ion batteries are considered to have important applications in fields such as low-speed new energy vehicles and static energy storage.

[0003] In recent years, materials researchers have carried out extensive research on cathode materials for sodium-ion batteries and developed cathode materials such as layered structure oxides, Prussian blue compounds, and polyanion compounds. Among them, the layered structure oxides have a relatively high specific capacity and many similarities with the cathode materials of currently mature lithium batteries in terms of synthesis and battery manufacturing. They are materials with the potential for commercial production of cathode materials for sodium-ion batteries. However, the layered structure oxides have poor storage stability in air and are prone to react with H2O, CO2, etc. in the environment to generate Na2CO3 and NaOH, which hinders the diffusion of sodium ions at the interface between the material and the electrolyte, increases the impedance between the interfaces of the material and the electrolyte, and easily causes the decline of the electrochemical performance of the battery. Therefore, this greatly limits the application of layered structure sodium cathode materials. Summary of the Invention

[0004] Aiming at the problem of unsatisfactory electrochemical performance of cathode materials for sodium-ion batteries, the first object of the present invention is to provide a preparation method of a composite sodium-ion active material with in-situ dispersed distribution of Na x M y (PO4)3 (the present invention is also referred to as the composite active material), aiming to prepare a cathode active material without residual alkali, with an in-situ dispersed distribution structure and excellent electrochemical performance.

[0005] The second object of the present invention is to provide the composite active material prepared by the above preparation method and its application in sodium-ion batteries.

[0006] The third object of the present invention is to provide a sodium-ion battery containing the composite active material and its cathode.

[0007] The preparation methods of existing cathode active materials often face the problem of residual alkali. To address this problem, the existing main approach is to reduce the excess coefficient of Na. However, this approach will affect the synthesis of the active material and is also difficult to essentially avoid the problem of residual alkali. Therefore, the present invention first proposes a solution idea of controllably transforming and restructuring the residual alkali. However, research has found that implementing this technical idea has great implementation difficulties, mainly because the distribution of residual alkali in the active material substrate is difficult to regulate, and the content of residual alkali in the substrate is relatively low, which will greatly affect the crystallization, embedding behavior, and embedding stability of the transformation product. Moreover, during the transformation of residual alkali, it is also easy to affect the phase structure of the active substrate, resulting in performance degradation. To solve this problem, the present invention provides the following solutions:

[0008] A method for preparing a composite sodium ion active material with in-situ dispersed distribution of Na x M y (PO4)3, comprising the following steps:

[0009] Step (1):

[0010] Mix and sinter a sodium source and a cathode precursor to obtain a sodium-containing cathode oxide active material substrate;

[0011] The excess coefficient of the sodium source is 2-20 mol%;

[0012] Step (2):

[0013] Use the residual sodium in the sodium-containing cathode oxide active material substrate as the sodium source, and prepare the M source and phosphorus source according to the stoichiometric ratio of Na x M y (PO4)3. Mix all raw materials and additives and perform three-stage sintering to prepare a composite sodium ion active material with in-situ dispersed distribution of Na x M y (PO4)3;

[0014] The M is at least one of V, Mn, Cr, Ti, and Zr; x + ny = 9, and n is the valence state of M;

[0015] The additive contains a boron source;

[0016] During the three-stage sintering process, the temperature of the first-stage sintering is 150-300 °C, the temperature of the second-stage sintering is 600-750 °C, and the temperature of the third-stage sintering is 800-1000 °C.

[0017] Regarding the problem of residual alkali, the present invention first proposes a solution idea of controllably transforming and restructuring it, and research has found that, innovatively, the residual alkali is transformed into Na x M y(PO4)3, combined with the joint control of a transformation aid and a three-stage calcination process, can achieve synergy, solve the problem of deterioration of the substrate during the transformation process. In addition, it can improve the crystallinity and phase purity of the transformation product, and can also induce the transformation product to be dispersed and in-situ distributed on the substrate, improving the chemical bonding stability between the transformation product and the substrate. The method described in the present invention can fundamentally solve the residual alkali problem and obtain a brand-new active material with excellent stability.

[0018] In the present invention, the sodium source is at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium bicarbonate, and sodium oxide.

[0019] In the present invention, the chemical formula of the cathode precursor is Ni a N b Mn(OH)2; where a≥0.5, a + b + c = 1, and N is at least one of Co, Fe, and Cu;

[0020] Preferably, the cathode precursor is at least one of Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.8 Fe 0.1 Mn 0.1 (OH)2, Ni 0.8 Cu 0.1 Mn 0.1 (OH)2.

[0021] In the present invention, the excess coefficient of Na refers to the excess percentage compared to the theoretical reaction molar amount. For example, the excess coefficient is (molar amount of Na - total molar amount of transition metals in the precursor) * 100%.

[0022] Preferably, the excess coefficient of Na in the sodium source is 6 - 12%.

[0023] In the present invention, in step (1), the sintering atmosphere is an oxygen-containing atmosphere; considering the processing cost, the oxygen-containing atmosphere is, for example, air.

[0024] Preferably, the sintering temperature is 600 - 1000 °C, preferably 750 - 850 °C;

[0025] Preferably, the sintering time is 6 - 15 hours.

[0026] In the present invention, innovatively, the residual alkali of the obtained active material is used as the only sodium source for subsequent treatment, and based on its content and the Na x M yStoichiometric ratio batching of (PO4)3 (in this batching process, no additional sodium source is introduced except for the residual alkali of the active material introducing the sodium source), further combined with the addition of additives, which is conducive to highly selectively converting the residual sodium into Na x M y The phase of (PO4)3, improving the purity, uniform dispersion distribution, and binding stability of the converted phase, reducing the impact of the conversion on the active material substrate, thereby effectively solving the residual alkali and preparing a material with high stability and high performance.

[0027] In the present invention, the M source is at least one of an oxide, carbonate, nitrate, and hydroxide of M metal;

[0028] Preferably, the phosphorus source is at least one of phosphoric acid, ammonium phosphate, monobasic ammonium phosphate, and dibasic ammonium phosphate;

[0029] Preferably, in the Na x M y (PO4)3, x is 2 to 5, preferably 3 to 4.

[0030] Preferably, the Na x M y (PO4)3 is at least one of Na3V2(PO4)3 and Na4MnCr(PO4)3.

[0031] In the present invention, the boron source is boric acid. The present invention innovatively uses the boron source as an additive, further combined with the idea of the present invention and the three-stage calcination process, which can achieve synergy and induce the formation of the Na x M y (PO4)3 phase, improving its dissemination stability and distribution uniformity, and improving its electrochemical performance.

[0032] Preferably, the boron source is 0.05 to 1% of the weight of the sodium-containing cathode oxide active material substrate, preferably 0.1 to 0.5%.

[0033] In the present invention, the atmosphere in the three-stage sintering stage is a protective atmosphere;

[0034] Preferably, the time for the first-stage calcination is 2 - 5 h;

[0035] Preferably, the time for the second-stage calcination is 3 - 6 h;

[0036] Preferably, the time for the third-stage calcination is 6 - 15.

[0037] The present invention also provides a composite sodium ion active material with in-situ dispersed distribution of Na x M y (PO4)3 prepared by the described preparation method.

[0038] The preparation method described in the present invention can endow the material with special composite phases and special in-situ composite characteristics, and the material prepared by the preparation method has excellent electrochemical performance.

[0039] For example, the composite sodium ion active material with in-situ dispersed distribution of Na x M y (PO4)3 in the present invention includes a sodium-containing cathode oxide active material substrate, and Na x M y (PO4)3 materials uniformly dispersed in situ in the form of dots on its surface; wherein, the molar ratio of Na in the substrate to Na x M y (PO4)3 materials is 1:0.02 - 0.2. Preferably, the sodium-containing cathode oxide active material substrate is a layered sodium-containing transition metal oxide, preferably NaNi a N b Mn c O2; wherein, a≥0.5, a + b + c = 1, and N is at least one of Co, Fe, and Cu; more preferably, it is at least one of NaNi 0.8 Co 0.1 Mn 0.1 O2, NaNi 0.8 Fe 0.1 Mn 0.1 O2, NaNi 0.8 Cu 0.1 Mn 0.1 O2. Preferably, the Na x M y (PO4)3 is at least one of Na3V2(PO4)3 and Na4MnCr(PO4)3.

[0040] The present invention also provides a positive electrode for a sodium ion battery, including a current collector and a positive electrode material compounded on its surface, and the positive electrode material contains the composite sodium ion active material with in-situ dispersed distribution of Na x M y (PO4)3 prepared by the preparation method described in the present invention;

[0041] Preferably, the positive electrode material further contains a binder and a conductive agent;

[0042] Preferably, in the positive electrode material, the content of the composite sodium ion active material with in-situ dispersed distribution of Na x M y (PO4)3 is 75 - 95 Wt.%.

[0043] The present invention also provides a sodium-ion battery, which is characterized by comprising the positive electrode described in the present invention.

[0044] In the present invention, based on existing means and theories, the battery and its components required for preparing the composite positive electrode material described in the present invention can be prepared.

[0045] Beneficial effects

[0046] Regarding the problem of residual alkali in the active material, the present invention innovatively proposes a solution idea of controllably converting it into Na x M y (PO4)3, and on the basis of this innovative idea, through the combined control of additives and a three-stage calcination process, it helps to further solve many problems faced in implementing this technical idea and can successfully prepare high-performance materials. Brief description of the drawings

[0047] Figure 1 It is a scanning electron microscope image of the sodium-ion positive electrode material obtained in Example 1 of the present invention; Detailed implementation manners

[0048] The technical solutions of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0049] Example 1

[0050] Step (1):

[0051] Using Na2CO3 as the lithium source and Ni 0.8 Co 0.1 Mn 0.1 (OH)2 as the precursor, mixing and proportioning are carried out according to the molar ratio of Na / (Ni + Co + Mn) = 1.08 (the excess coefficient is 8%), and sintering is carried out at 825 °C for 9 h in an oxygen atmosphere to obtain NaNi 0.8 Co 0.1 Mn 0.1 O2. The sodium content on the surface of the sintered material is tested by potentiometric titration, and the residual sodium content is obtained as 8000 ppm;

[0052] Step (2):

[0053] Weigh 1 kg of this cathode material and put it into a high-speed mixer. Weigh the required V2O3 and (NH4)3PO4 according to the stoichiometric ratio of Na3V2(PO4)3, and continue to add 2 g of boric acid into the high-speed mixer for dry high-speed mixing. The mixed material is placed in a closed atmosphere furnace, nitrogen is introduced, and sintered at 180 °C (T1) for 3 h, 750 °C (T2) for 5 h, and 800 °C (T3) for 10 h to obtain the sodium-ion cathode active material NaNi 0.8 Co 0.1 Mn 0.1 O2.

[0054] Example 2

[0055] Using Na2CO3 as the lithium source and Ni 0.8 Fe 0.1 Mn 0.1 (OH)2 as the precursor, mix and proportion according to the molar ratio of Na / (Ni + Fe + Mn) = 1.12 (the excess coefficient is 12%), and sinter at 865 °C for 10 h in an oxygen atmosphere to obtain NaNi 0.8 Fe 0.1 Mn 0.1 O2. The sodium content on the surface of the first-fired material is tested by potentiometric titration, and the residual sodium content is obtained as 12000 ppm. Weigh 1 kg of this cathode material and put it into a high-speed mixer. Weigh the required MnO, Cr2O3, (NH4)3PO4 according to the stoichiometric ratio of Na4MnC r (PO4)3, and 3 g of boric acid, add them into the high-speed mixer for dry high-speed mixing. The mixed material is placed in a closed atmosphere furnace, nitrogen is introduced, sintered at 200 °C for 2 h, 730 °C for 4 h, and 830 °C for 12 h to obtain the sodium-ion cathode active material NaNi r (PO4)3 0.8 Fe 0.1 Mn 0.1 O2.

[0056] Example 3

[0057] Using NaHCO3 as the lithium source and Ni 0.8 Cu 0.1 Mn 0.1 (OH)2 as the precursor, mix and proportion according to the molar ratio of Na / (Ni + Cu + Mn) = 1.06 (the excess coefficient is 6%), and sinter at 885 °C for 8 h in an oxygen atmosphere to obtain NaNi 0.8 Cu 0.1 Mn 0.1O2, a burning material was tested for sodium content on its surface by potentiometric titration, and the residual sodium content was 6000ppm. 1kg of this positive electrode material was weighed and put into a high-pressure mixer. According to Na4MnC r The required MnO, Cr2O3, (NH4)3PO4 and 4g of boric acid were weighed in a stoichiometric ratio of (PO4)3, and added into a high-speed mixer for dry high-speed mixing. The mixed materials were placed in a closed atmosphere furnace, nitrogen was introduced, and sintered at 250℃ for 3h, 700℃ for 5h, and 850℃ for 15h to obtain a surface-coated Na4MnC r (PO4)3 sodium ion positive electrode active material NaNi 0.8 Cu 0.1 Mn 0.1 O2.

[0058] Comparative Example 1

[0059] Compared with Example 1, the only difference is that the processing of step 2 is not performed, and other operations and parameters are the same as Example 1.

[0060] Comparative Example 2

[0061] Compared with Example 1, the only difference is that in step 2, the ingredients are prepared according to the stoichiometric ratio of the Na3VO4 phase, and no phosphorus source is added. Other operations and parameters are the same as in Example 1.

[0062] Comparative Example 3

[0063] Compared with Example 1, the only difference is that in step 2, the ingredients are prepared according to the stoichiometric ratio of the Na3PO4 phase, and no vanadium source is added. Other operations and parameters are the same as in Example 1.

[0064] Comparative Example 4

[0065] Compared with Example 1, the only difference is that in step 2, the required MgO and (NH4)3PO4 are weighed according to the stoichiometric ratio of Na3Mg3(PO4)3, and the other operations and parameters are the same as those in Example 1.

[0066] Comparative Example 5

[0067] Compared with Example 1, the only difference is that in step 2, boric acid is not added, and other operations and parameters are the same as in Example 1.

[0068] Comparative Example 6

[0069] Compared with Example 1, the only difference is that in step 2, CaF2 is used instead of boric acid, and other operations and parameters are the same as in Example 1.

[0070] Compared with Example 1, the only difference is that in step 2, the three-stage gradient sintering treatment is not performed, but only the heat preservation treatment is performed at the temperature of T3. Other operations and parameters are the same as those in Example 1.

[0071] Comparative Example 8 (Comparative case of in-situ preparation without using residual alkali)

[0072] Compared with Example 1, the difference is only that after the treatment in step (1), the material is washed to remove the residual alkali, and then step 2 is carried out. And in step 2, the same molar amount of residual alkali as in Example 1 is provided by sodium carbonate, and other operations and parameters are the same as those in Example 1.

[0073] The sodium-ion positive electrode active materials of the examples and comparative examples were mixed with acetylene black and polyvinylidene fluoride (PVDF) in a mass ratio of 80:15:5 in a beaker, ground into a slurry after adding a small amount of NMP, and then the slurry was uniformly coated on an aluminum foil with a coater with a thickness of 120 μm, placed in a vacuum drying oven and kept at 100 °C for 8 h, and then punched into a positive electrode sheet with a diameter of 15 mm for use. An organic solution of 1.2 M NaPF6 in ethylene carbonate was used as the electrolyte, and a sodium metal sheet was used as the negative electrode, and it was assembled into a CR2032 coin cell in a glove box filled with Ar. The performance of the battery was tested with a battery tester of BlueTEC, and the test voltage was 2.5 - 4.2 V.

[0074] Table 1 Chemical property results of each case

[0075]

[0076] It can be seen from the results in Table 1 that after the sodium-ion positive electrode material prepared by the method described in the present invention is made into a sodium-ion battery, the first discharge specific capacity at 1C, the charge-discharge cycle at 1C, and the capacity retention rate after 100 cycles of charge-discharge at 5C are all improved.

[0077] Obviously, the above examples are only for clearly illustrating the examples and are not intended to limit the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A Na x M y (PO4)3 in-situ dispersion-distributed composite sodium ion active material preparation method, characterized in that the steps Including: Step (1): Mix and sinter a sodium source and a cathode precursor to obtain a sodium-containing cathode oxide active material substrate; The excess coefficient of the sodium source is 6-12 mol%; The chemical formula of the positive electrode precursor is Ni a N b Mn(OH)2; where a≥0.5, a + b + c = 1, and N is at least one of Co, Fe, and Cu; Step (2): Using the residual sodium in the sodium-containing cathode oxide active material substrate as a sodium source, and preparing the M source and phosphorus source according to the stoichiometric ratio of Na x M y (PO4)3, mixing each raw material and additive, and performing three-stage sintering to obtain a composite sodium ion active material with in-situ dispersed Na x M y (PO4)3; The described Na x M y (PO4)3 is at least one of Na3V2(PO4)3 and Na4MnCr(PO4)3; The additive contains a boron source; During the three-stage sintering process, the temperature of the first-stage sintering is 150-300 °C, the temperature of the second-stage sintering is 600-750 °C, and the temperature of the third-stage sintering is 800-1000 °C.

2. The preparation method according to claim 1, characterized in that, The sodium source is at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium bicarbonate, and sodium oxide.

3. The preparation method according to claim 1, characterized in that, The described cathode precursor is Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.8 Fe 0.1 Mn 0.1 (OH)2, Ni 0.8 Cu 0.1 Mn 0.1 (OH)2, or at least one of them.

4. The preparation method according to claim 1, wherein In step (1), the sintering atmosphere is an oxygen-containing atmosphere.

5. The preparation method according to claim 1, wherein, The sintering temperature is 600-1000 °C.

6. The preparation method according to claim 1, characterized in that, The sintering time is 6-15 hours.

7. The preparation method according to claim 1, characterized in that, The M source is at least one of an oxide, carbonate, nitrate, and hydroxide of M metal.

8. The preparation method according to claim 1, characterized in that, The phosphorus source is at least one of phosphoric acid, ammonium phosphate, monoammonium hydrogen phosphate, and diammonium hydrogen phosphate.

9. The preparation method according to claim 1, characterized in that, The boron source is boric acid.

10. The preparation method according to claim 1, characterized in that, The boron source is 0.05-1% of the weight of the sodium-containing cathode oxide active material substrate.

11. The preparation method according to claim 1, characterized in that, The atmosphere in the three-stage sintering stage is a protective atmosphere.

12. The preparation method according to claim 1, characterized in that, The roasting time of the first stage is 2-5 h; The roasting time of the second stage is 3-6 h; The roasting time of the third stage is 6-15.

13. A composite sodium ion active material with in-situ dispersed and distributed Na x M y (PO4)3 14. A positive electrode of a sodium-ion battery, comprising a current collector and a positive electrode material composite on its surface, characterized in that, The positive electrode material contains a composite sodium ion active material in which Na x M y (PO4)3 is in-situ diffusely distributed, which is prepared by the preparation method according to any one of claims 1 to 12.

15. The positive electrode of the sodium-ion battery according to claim 14, comprising a current collector and a positive electrode material compounded on its surface, characterized in that, The cathode material further includes a binder and a conductive agent.

16. The positive electrode of the sodium ion battery according to claim 15, comprising a current collector and a positive electrode material compounded on its surface, characterized in that, In the positive electrode material described, the Na x M y (PO4)3 in-situ dispersion distribution of the composite sodium ion active material content is 75 to 95 Wt.%.

17. A sodium-ion battery, characterized in that, Including the cathode according to any one of claims 14-16.

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