Precursor and preparation method and application thereof

Abstract

The present invention belongs to the field of sodium ion battery materials and discloses a precursor and a preparation method and application thereof. The preparation method of the precursor comprises: mixing Ni x Fe y Mn z (OH)2 and sodium hexafluorophosphate are mixed to obtain a mixed powder, the mixed powder is calcined at 180-250°C in an inert atmosphere, and cooled to obtain the precursor; wherein 0.2≤x≤0.5, 0.2≤y≤0.4, 0.1≤z≤0.6, x+y+z=1. The precursor is modified by sodium hexafluorophosphate, and then mixed with sodium and calcined to obtain a positive electrode material with excellent cycle stability.

Description

Technical Field

[0001] The invention belongs to the field of sodium ion battery materials, and specifically relates to a precursor and a preparation method and application thereof. Background Art

[0002] Sodium, the main element in sodium-ion batteries, is abundant on Earth, and one of its raw materials, sodium carbonate, is inexpensive, so it is very likely to replace lithium-ion batteries in the near future.

[0003] In the existing technology, researchers have found that as the number of cycles of the single-crystal layered oxide positive electrode material of the sodium-ion battery increases, the transition metal ions on its surface will dissolve, causing the side reactions of the electrolyte to intensify, which in turn causes the electrolyte to gradually decompose and be exhausted, affecting the battery's cycle performance. Summary of the invention

[0004] In view of the defects and shortcomings of the prior art, in the first aspect, the present invention provides a method for preparing a precursor; in the second aspect, the present invention provides a precursor; in the third aspect, the present invention provides a method for preparing a positive electrode material; in the fourth aspect, the present invention provides a positive electrode material; in the fifth aspect, the present invention provides a battery.

[0005] In a first aspect, the present invention provides a method for preparing a precursor, comprising: mixing Ni x Fe y Mn z (OH) 2 and sodium hexafluorophosphate to obtain a mixed powder, calcining the mixed powder at 180-250° C. in an inert atmosphere, and cooling to obtain the precursor; wherein 0.2≤x≤0.5, 0.2≤y≤0.4, 0.1≤z≤0.6, and x+y+z=1.

[0006] Preferably, Ni x Fe y Mn z (OH) 2 The mass ratio of sodium hexafluorophosphate to sodium hexafluorophosphate is 1:0.5%~2%.

[0007] Preferably, the calcination time is 2 to 5 hours.

[0008] Preferably, Ni x Fe y Mn z (OH) 2 The D50 is 3.5~5.5μm.

[0009] Preferably, the gas providing the inert atmosphere is any one or both of argon and nitrogen.

[0010] In a second aspect, the present invention provides a precursor material prepared by the above preparation method.

[0011] In a third aspect, the present invention provides a method for preparing a positive electrode material, comprising: mixing a precursor material prepared by the above preparation method and a sodium source, and calcining to obtain the positive electrode material.

[0012] Preferably, the sodium source is any one or more of sodium carbonate, sodium oxalate and sodium acetate.

[0013] Preferably, the molar ratio of the precursor to the sodium in the sodium source is 1:1-1.2.

[0014] Preferably, the calcination temperature is 700-1000° C. and the calcination time is 12-24 hours.

[0015] In a fourth aspect, the present invention provides a positive electrode material prepared by the above preparation method.

[0016] In a fifth aspect, the present invention provides a battery, comprising the positive electrode material prepared by the above preparation method or the above positive electrode material.

[0017] Compared with the prior art, the present invention has the following obvious beneficial effects: The precursor is modified by sodium hexafluorophosphate and then mixed with sodium and calcined to obtain a positive electrode material with excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a SEM image of the positive electrode material prepared in Example 1; Figure 2 This is an EDS surface scan of the positive electrode material prepared in Example 1; Figure 3 It is a schematic diagram of the cycle performance of a battery assembled with the positive electrode materials prepared in Examples 1 to 3 and Comparative Example 1. DETAILED DESCRIPTION

[0019] The present invention provides the following specific technical solutions.

[0020] In a first aspect, the present invention provides a method for preparing a precursor, comprising: mixing Ni x Fe y Mn z (OH) 2 and sodium hexafluorophosphate to obtain a mixed powder, calcining the mixed powder at 180-250° C. in an inert atmosphere, and cooling to obtain the precursor; wherein 0.2≤x≤0.5, 0.2≤y≤0.4, 0.1≤z≤0.6, and x+y+z=1.

[0021] The precursor was modified by sodium hexafluorophosphate and then mixed with sodium for calcination to obtain a positive electrode material with excellent cycle stability. On the one hand, the addition of fluorine and phosphorus elements can change the binding energy of oxygen, enhance the binding energy of transition metals and oxygen, and promote Na + diffusion; secondly, fluorophosphorus surface modification helps to form a stable SEI layer on the electrode surface, reduce the decomposition of the electrolyte, inhibit the occurrence of side reactions, and help improve the cycle stability and safety of the battery; thirdly, surface modification can also optimize the structure of the electrode material, improve the structural stability, reduce the phase change during the charge and discharge process, and further enhance the cycle stability of the battery.

[0022] Preferably, Ni x Fe y Mn z (OH) 2 The mass ratio of sodium hexafluorophosphate to sodium hexafluorophosphate is 1:0.5%~2%.

[0023] Preferably, the calcination time is 2 to 5 hours.

[0024] Preferably, Ni x Fe y Mn z (OH) 2 The D50 is 3.5~5.5μm.

[0025] In the actual production process, the D50 of the precursor is preferably 3.5~5.5μm, which can reduce the possibility of cracking of the precursor in subsequent processes.

[0026] Preferably, the gas providing the inert atmosphere is any one or both of argon and nitrogen.

[0027] In a second aspect, the present invention provides a precursor material prepared by the above preparation method.

[0028] In a third aspect, the present invention provides a method for preparing a positive electrode material, comprising: mixing a precursor material prepared by the above preparation method and a sodium source, and calcining to obtain the positive electrode material.

[0029] Preferably, the sodium source is any one or more of sodium carbonate, sodium oxalate and sodium acetate.

[0030] Preferably, the molar ratio of the precursor to the sodium in the sodium source is 1:1-1.2.

[0031] Preferably, the calcination temperature is 700-1000° C. and the calcination time is 12-24 hours.

[0032] After research, the inventors found that the calcination temperature is preferably 700~1000℃. If the calcination temperature is too low, it will easily lead to incomplete crystal structure of the formed material and insufficient grain growth, affecting the electrochemical properties of the material; if the calcination temperature is too high, overburning may occur, the material's lattice is distorted, the grains grow excessively, and even the material may change phase, thereby affecting the structural stability and cycle performance of the positive electrode material.

[0033] In a fourth aspect, the present invention provides a positive electrode material prepared by the above preparation method.

[0034] In a fifth aspect, the present invention provides a battery, comprising the positive electrode material prepared by the above preparation method or the above positive electrode material.

[0035] In order to make the technical problems, technical solutions and technical advantages to be solved by the present invention more clear, they will be described in detail below with reference to specific examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0036] Unless otherwise defined, all 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.

[0037] 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.

[0038] Embodiment 1: A method for preparing a positive electrode material comprises the following steps: Step 1, Mixing Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH) 2 and sodium hexafluorophosphate to obtain a mixed powder, Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH) 2 The mass ratio of sodium hexafluorophosphate to sodium hexafluorophosphate is 1:0.01, and the mixed powder is calcined at 200°C for 2.5 hours under argon and cooled to obtain a coated modified precursor.

[0039] Step 2: Take 2.0 g of the precursor prepared in step 1 and 1.20 g of sodium carbonate, mix them evenly, calcine them at 850° C. for 16 h, and cool them to obtain the positive electrode material.

[0040] Figure 1 is a SEM image of the positive electrode material obtained in Example 1. Figure 1 It can be seen that the primary particles of the positive electrode material are flake-shaped, and the secondary particles are spherical.

[0041] Figure 2 This is the EDS surface scan of the positive electrode material prepared in Example 1. Figure 2 It can be seen that the distribution trends of sodium, nickel, iron, manganese, fluorine and phosphorus in the positive electrode materials are basically the same, which proves that the fluorine and phosphorus elements are successfully coated on the surface of the positive electrode material.

[0042] Comparative Example 1: A method for preparing a positive electrode material comprises the following steps: Step 2, take 2.0gNi 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH) 2 Mix evenly with 1.20g of sodium carbonate, calcine at 850℃ for 16h, and cool to obtain the positive electrode material.

[0043] Embodiment 2: Step 1, Mixing Ni 0.3 Fe 0.3 Mn 0.4 (OH) 2 and sodium hexafluorophosphate to obtain a mixed powder, Ni x Fe y Mn z (OH) 2 The mass ratio of sodium hexafluorophosphate to sodium hexafluorophosphate is 1:0.005, and the mixed powder is calcined at 180°C for 2 hours in an inert atmosphere and cooled to obtain a coated modified precursor.

[0044] Step 2: Take 2.0 g of the precursor prepared in step 1 and 1.18 g of sodium carbonate, mix them evenly, calcine them at 700° C. for 12 h, and cool them to obtain the positive electrode material.

[0045] Embodiment 3: Step 1, Mixing Ni 0.2 Fe 0.3 Mn 0.5 (OH) 2 and sodium hexafluorophosphate to obtain a mixed powder, Ni x Fe y Mn z (OH) 2 The mass ratio of sodium hexafluorophosphate to sodium hexafluorophosphate is 1:0.02, and the mixed powder is calcined at 250°C for 5 hours in an inert atmosphere and cooled to obtain a coated modified precursor.

[0046] Step 2: Take 2.0 g of the precursor prepared in step 1 and 1.42 g of sodium carbonate, mix them evenly, calcine them at 1000° C. for 24 h, and cool them to obtain the positive electrode material.

[0047] The positive electrode materials prepared in Examples 1 to 3 and Comparative Example 1 were mixed with acetylene black and polyvinylidene fluoride in a mass ratio of 8:1:1, and then added into N-methylpyrrolidone to form a slurry. The slurry was coated on aluminum foil and dried to obtain a positive electrode sheet. Metal sodium was used as the negative electrode, Whatman GF / D was used as the separator, and 1M NaClO 4 In DMC:EC=1∶1 Vol% with 5%FEC as electrolyte, button cells were assembled in a glove box, and the battery was cycled for 50 cycles at a voltage of 2~4V and 0.5C. The cycle performance was as follows Figure 3 shown.

[0048] Depend on Figure 3 It can be seen that by comparing the cycle performance of the battery assembled from the positive electrode materials prepared in Example 1 and Comparative Example 1, it can be proved that the battery assembled from the positive electrode material provided by the present invention has more excellent cycle performance.

[0049] The embodiments described above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a precursor, characterized in that: include: Mixed Ni x Fe y Mn z (OH)2 and sodium hexafluorophosphate are used to obtain a mixed powder, and the mixed powder is calcined at 180-250°C in an inert atmosphere and cooled to obtain the precursor; wherein 0.2≤x≤0.5, 0.2≤y≤0.4, 0.1≤z≤0.6, and x+y+z=1.

2. The method for preparing a precursor according to claim 1, characterized in that: Ni x Fe y Mn z The mass ratio of (OH)2 and sodium hexafluorophosphate is 1:0.5%~2%.

3. The method for preparing a precursor according to claim 1, characterized in that: The calcination time is 2~5h.

4. The method for preparing a precursor according to claim 1, characterized in that: Ni x Fe y Mn z The D50 of (OH)2 is 3.5~5.5μm.

5. A precursor material, characterized in that Prepared by the preparation method according to any one of claims 1 to 4.

6. A method for preparing a positive electrode material, characterized in that: include: The precursor material prepared by the preparation method according to any one of claims 1 to 4 and a sodium source are mixed and calcined to obtain the product.

7. The method for preparing the positive electrode material according to claim 6, characterized in that: The sodium source is any one or more of sodium carbonate, sodium oxalate and sodium acetate; the molar ratio of the precursor to the sodium in the sodium source is 1:1-1.

2.

8. The method for preparing the positive electrode material according to claim 6, characterized in that: The calcination temperature is 700~1000℃ and the calcination time is 12~24h.

9. A positive electrode material, characterized in that: Prepared by the preparation method according to any one of claims 6 to 8.

10. A battery comprising the positive electrode material prepared by the preparation method according to any one of claims 6 to 8 or the positive electrode material according to claim 9.

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