A sodium ion cathode material, its preparation method and composition

Abstract

The present invention provides a sodium ion cathode material, its preparation method and composition. The chemical formula of the sodium ion cathode material is NaxCayNiaFebMncTidTMeO2, where TM is at least one of the metal elements of Mg, Sr, Zr, Y, Al, La, Zn, Nb and necessarily includes Mg, 0.5 ≤ x ≤ 1.1, 0.01 ≤ y ≤ 0.1, 0.1 ≤ a ≤ 0.5, 0.05 ≤ b ≤ 0.3, 0.1 ≤ c ≤ 0.4, 0.01 ≤ d ≤ 0.3, 0.01 ≤ e ≤ 0.1, and the sodium ion cathode material is an O3-type sodium ion cathode material. In the sodium ion cathode material of the present invention, Ca2+ is doped at the sodium site and the molar ratio of sodium to calcium is controlled at the same time, and Ti and Mg are used as necessary doping elements at the transition metal site, which can make the O3-type sodium ion cathode material form a more stable crystal structure. After the working potential is increased to higher than 4.15V, the above O3-type sodium ion battery material takes into account both specific capacity and cycle stability and effectively increases the median discharge voltage.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and particularly to a sodium ion cathode material, a preparation method thereof, and a composition. Background Art

[0002] The chemical composition formula of the O3 layered oxide is NaxTMO2, (x≥0.8, TM is at least one of transition metal elements such as Ni, Fe, Mn, etc.). Taking NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as an example, it undergoes continuous O3-P3-O3' phase transitions at high cut-off voltages (>4.1V). Such multi-phase transitions can induce significant lattice distortions and volume strains, generating cracks and nano-voids inside the crystal, thereby leading to lattice oxygen reactions, metal layer slips, and interlayer cation mixing, which destroys the structural stability. The above problems result in the technical problem that it is difficult for the Na x TMO2 cathode material to coexist with high capacity and long cycle stability at high working voltages. In the prior art, the solutions to the above problems by means of transition metal ion doping and oxide coating are not yet satisfactory. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a sodium ion cathode material, a preparation method thereof, and a composition.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: a sodium ion cathode material, the chemical formula of the sodium ion cathode material is Na x Ca y Ni a Fe b Mn c Ti d TM e O2, wherein TM is at least one of metal elements of Mg, Sr, Zr, Y, Al, La, Zn, Nb and necessarily includes Mg, 0.5≤x≤1.1, 0.01≤y≤0.1, 0.1≤a≤0.5, 0.05≤b≤0.3, 0.1≤c≤0.4, 0.01≤d≤0.3, 0.01≤e≤0.1, and the sodium ion cathode material is an O3-type sodium ion cathode material.

[0005] During the process of the inventor's research on sodium-site doped O3-type sodium-ion cathode materials, it was found that a single sodium-site doped O3-type sodium-ion battery material was not sufficient to well improve the problems of high capacity and long cycle stability defects of O3-type sodium-ion cathode materials at high voltages. The inventor considered doping both the sodium site and the transition metal site of the O3-type sodium-ion cathode material, which is beneficial to improving the high capacity and long cycle stability of the O3-type sodium-ion battery material at high voltages, and found that doping Ca at the sodium site of the O3-type sodium-ion cathode material 2+ and doping elements such as Ti and Mg at the transition metal site, and taking Ti and Mg as necessary doping elements at the transition metal site. When the amount of doped elements is the same, doping Ca at the sodium site 2+ and simultaneously controlling the molar ratio of sodium and calcium, and taking Ti and Mg as necessary doping elements at the transition metal site, can make the O3-type sodium-ion cathode material form a more stable crystal structure. After the working potential is increased to higher than 4.15 V, the above O3-type sodium-ion battery material takes into account both specific capacity and cycle stability and effectively increases the median discharge voltage.

[0006] Preferably, TM is at least two of the metal elements Mg, Sr, La, Al, Y, and Nb and necessarily includes Mg.

[0007] Doping Ca at the sodium site of the O3-type sodium-ion cathode material 2+ and doping elements such as Ti and Mg at the transition metal site, and taking Ti and Mg as necessary doping elements at the transition metal site. When the amount of doped elements is the same, doping Ca at the sodium site 2+ and simultaneously controlling the molar ratio of sodium and calcium, and taking Ti and Mg as necessary doping elements at the transition metal site, and simultaneously doping Sr, Zr, Y, or Al in the transition metal layer, can make the O3-type sodium-ion battery material take into account both specific capacity and cycle stability, have better specific capacity and cycle stability while increasing the median discharge voltage.

[0008] Preferably, TM is two or three of Mg, Sr, and Y and necessarily includes Mg.

[0009] The above O3-type sodium-ion cathode material has better specific capacity and cycle stability while increasing the median discharge voltage.

[0010] Preferably, 0.8 ≤ x ≤ 1.1, 0.01 ≤ y ≤ 0.05, 0.25 ≤ a ≤ 0.50, 0.1 ≤ b ≤ 0.25, 0.2 ≤ c ≤ 0.35, 0.1 ≤ d ≤ 0.3, 0.02 ≤ e ≤ 0.05.

[0011] Preferably, 0.95 ≤ x ≤ 1.05, 0.02 ≤ y ≤ 0.03.

[0012] The above-mentioned O3-type sodium ion positive electrode material controls the molar ratio of sodium and calcium, which is beneficial to improving the specific capacity, cycle performance and discharge median voltage of the battery material.

[0013] Preferably, the method for preparing the sodium ion positive electrode material comprises the following steps:

[0014] Ni a Fe b Mn c Ti d After the (OH)2 precursor is fully mixed with the sodium source, calcium source and TM source in a stoichiometric ratio, it is calcined at 700-900°C for 1.5-2.5h, then continued to heat up to 900-1000°C for calcination for 10-14h, and then naturally cooled to obtain the sodium ion positive electrode material.

[0015] Preferably, the method comprises the following steps:

[0016] Ni a Fe b Mn c Ti d The (OH)2 precursor is fully mixed with the sodium source, calcium source, and TM source in a stoichiometric ratio, calcined at 700-900°C for 1.5-2.5h, then continued to heat to 900-1000°C for 10-14h, and then cooled naturally to obtain the sodium ion positive electrode material;

[0017] The sodium source is sodium carbonate, the calcium source is calcium carbonate or calcium oxide, and the TM source is the oxide or hydroxide of the corresponding element.

[0018] The present invention also provides a material composition for a sodium ion battery positive electrode, comprising 80 to 100 parts by weight of any of the above sodium ion positive electrode materials, 4 to 6 parts by weight of conductive carbon black, and 4 to 6 parts by weight of polyvinylidene fluoride.

[0019] The combination of the above-mentioned material composition for the sodium ion battery positive electrode can better exert the specific capacity and cycle performance of the sodium ion positive electrode material and improve the discharge median voltage.

[0020] The present invention also provides a battery positive electrode, comprising 80 to 100 parts by weight of any of the above sodium ion positive electrode materials, 4 to 6 parts by weight of conductive carbon black, and 4 to 6 parts by weight of polyvinylidene fluoride.

[0021] The beneficial effects of the present invention are as follows: the present invention provides a sodium ion positive electrode material and a preparation method and composition thereof, wherein the sodium ion positive electrode material of the present invention is doped with Ca 2+Meanwhile, controlling the molar ratio of sodium and calcium and using Ti and Mg as necessary doping elements at the transition metal sites can enable the O3-type sodium ion cathode material to form a more stable crystal structure. After the working potential is increased to above 4.15 V, the above O3-type sodium ion battery material takes into account both specific capacity and cycle stability and effectively increases the median discharge voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM diagram of a sodium ion cathode material according to an embodiment of the present invention.

[0023] Figure 2 XRD diagram of a sodium ion cathode material according to an embodiment of the present invention.

[0024] Figure 3 0.1C first charge-discharge curve of the sodium ion cathode material of Embodiment 1 of the present invention.

[0025] Figure 4 Cycle performance diagram of the sodium ion cathode material of Embodiment 1 of the present invention.

[0026] Figure 5 SEM diagram of a sodium ion cathode material according to an embodiment of the present invention.

[0027] Figure 6 XRD diagram of a sodium ion cathode material according to an embodiment of the present invention.

[0028] Figure 7 0.1C first charge-discharge curve of the sodium ion cathode material of Embodiment 3 of the present invention.

[0029] Figure 8 Cycle performance diagram of the sodium ion cathode material of Embodiment 3 of the present invention.

[0030] Figure 9 SEM diagram of a sodium ion cathode material according to a comparative example of the present invention.

[0031] Figure 10 XRD diagram of a sodium ion cathode material according to a comparative example of the present invention.

[0032] Figure 11 0.1C first charge-discharge curve of the sodium ion cathode material of Comparative Example 1 of the present invention.

[0033] Figure 12 Cycle performance diagram of the sodium ion cathode material of Comparative Example 1 of the present invention.

[0034] Figure 13 SEM diagram of a sodium ion cathode material according to Comparative Example 2 of the present invention.

[0035] Figure 14XRD pattern of a sodium ion cathode material for Comparative Example 2 of the present invention.

[0036] Figure 15 Initial charge-discharge curves at 0.1C of the sodium ion cathode material for Comparative Example 2 of the present invention.

[0037] Figure 16 Cycling performance graph of the sodium ion cathode material for Comparative Example 2 of the present invention. Detailed Description of the Invention

[0038] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0039] Example 1

[0040] As a sodium ion cathode material of an embodiment of the present invention, the chemical formula of the sodium ion cathode material is Na x Ca y Ni a Fe b Mn c Ti d TM e O2, where TM is Mg, x = 1.0, y = 0.02, a = 0.4, b = 0.15, c = 0.30, d = 0.15, e = 0.04, and the sodium ion cathode material is an O3-type sodium ion cathode material.

[0041] Mix Ni a Fe b Mn c Ti d (OH)2 precursor with a sodium source, a calcium source, and a TM source in a stoichiometric ratio in a high-efficiency mixer, then calcine in an air atmosphere at 800°C for 2 h, and then continue to heat up to 950°C and calcine for 12 h, and cool naturally to obtain the sodium ion cathode material of this example;

[0042] The sodium source is sodium carbonate, the calcium source is calcium carbonate, and the TM source is the oxide of the corresponding element.

[0043] Examples 2 to 6

[0044] As a sodium ion cathode material of an embodiment of the present invention, the only difference between this example and Example 1 is that there is a difference in TM, and the total content of TM in the material remains unchanged.

[0045] Example TM TM Element Ratio Example 2 Mg, Sr 1:1 Example 3 Mg, Y 1:1 Example 4 Mg, Sr, Nb 1:1:1 Example 5 Mg, Al 1:1 Example 6 Mg, La 1:1

[0046] Example 7

[0047] As a sodium ion cathode material of an embodiment of the present invention, the only difference between this example and Example 3 is that y = 0.01.

[0048] Example 8

[0049] As a sodium-ion cathode material according to an embodiment of the present invention, the only difference between this embodiment and Embodiment 3 is that y = 0.03.

[0050] Comparative Example 1

[0051] As a sodium-ion cathode material according to a comparative example of the present invention, the chemical formula of the sodium-ion cathode material is Na x Ni a Fe b Mn c Ti d TM e O2, wherein TM is Mg and Y, and the element ratio is 1:1, x = 1.0, a = 0.4, b = 0.15, c = 0.30, d = 0.15, e = 0.04, and the sodium-ion cathode material is an O3-type sodium-ion cathode material.

[0052] Comparative Example 2

[0053] As a sodium-ion cathode material according to a comparative example of the present invention, the chemical formula of the sodium-ion cathode material is Na x Ca y Ni a Fe b Mn c Ti d TM e O2, wherein TM is Y and Al, and the element ratio is 1:1, x = 1.0, y = 0.02, a = 0.4, b = 0.15, c = 0.30, d = 0.15, e = 0.04, and the sodium-ion cathode material is an O3-type sodium-ion cathode material.

[0054] Comparative Example 3

[0055] As a sodium-ion cathode material according to a comparative example of the present invention, the chemical formula of the sodium-ion cathode material is Na x Ca y Ni a Fe b Mn c Ti d TM e O2, wherein TM is Y and Nb, and the element ratio is 1:1, x = 1.0, y = 0.02, a = 0.4, b = 0.15, c = 0.30, d = 0.15, e = 0.04, and the sodium-ion cathode material is an O3-type sodium-ion cathode material.

[0056] Comparative Example 4

[0057] As a sodium ion cathode material of the comparative example of the present invention, the chemical formula of the sodium ion cathode material is Na x Ca y Ni a Fe b Mn c Ti d TM e O2, where TM is Zr and Nb, the element ratio is 1:1, x = 1.0, y = 0.02, a = 0.4, b = 0.15, c = 0.30, d = 0.15, e = 0.04, and the sodium ion cathode material is an O3-type sodium ion cathode material.

[0058] Experimental method

[0059] I. Material characterization

[0060] 1. As Figure 1 is the SEM image of the sodium ion cathode material of Example 1 of the present invention.

[0061] 2. As Figure 2 is the XRD image of the sodium ion cathode material of Example 1 of the present invention.

[0062] 3. As Figure 5 is the SEM image of the sodium ion cathode material of Example 3 of the present invention.

[0063] 4. As Figure 6 is the XRD image of the sodium ion cathode material of Example 3 of the present invention.

[0064] 5. As Figure 9 is the SEM image of the sodium ion cathode material of Comparative Example 1 of the present invention.

[0065] 6. As Figure 10 is the XRD image of the sodium ion cathode material of Comparative Example 1 of the present invention.

[0066] 7. As Figure 13 is the SEM image of the sodium ion cathode material of Comparative Example 2 of the present invention.

[0067] 8. As Figure 14 is the XRD image of the sodium ion cathode material of Comparative Example 2 of the present invention.

[0068] From Figure 1 、 Figure 2 、 Figure 5 、 Figure 6 、 Figure 9 、 Figure 10 、 Figure 13 、 Figure 14 it can be seen that by doping Ca at the sodium site in the present invention 2+Meanwhile, control the molar ratio of sodium and calcium, and use Ti and Mg as necessary doping elements for the transition metal sites, so as to form a more stable crystal structure for the O3-type sodium-ion cathode material.

[0069] II. Battery performance detection method

[0070] Testing method: Take the cathode materials obtained in Examples 1-8 and Comparative Examples 1-4 as active substances, mix them according to the mass ratio of active substance: conductive agent (Super P): binder (PVDF) of 90:5:5, add an appropriate amount of solvent NMP to adjust the solid content, stir into a slurry by a pulper, coat it on an aluminum foil, and dry the electrode sheet in an oven at 110 °C for 4 hours after coating. Use a sodium sheet as the anode, a glass fiber as the separator, and 1M NaPF6 (solvent EC: DEC = 1:1 Vol%) as the electrolyte, and assemble a button cell in a glove box. The battery is tested within the voltage range of 2.0-4.15V. After two weeks of activation at 0.1C, the rate performance is tested at 0.2C and 0.5C for one week each, and then the 1C 50-week cycle performance test is carried out.

[0071]

[0072]

[0073] Figure 3 This is the 0.1C first charge-discharge curve of the sodium-ion cathode material of Example 1 of the present invention. Figure 4 This is the cycle performance graph of the sodium-ion cathode material of Example 1 of the present invention. Figure 7 This is the 0.1C first charge-discharge curve of the sodium-ion cathode material of Example 3 of the present invention. Figure 8 This is the cycle performance graph of the sodium-ion cathode material of Example 3 of the present invention. Figure 11 This is the 0.1C first charge-discharge curve of the sodium-ion cathode material of Comparative Example 1 of the present invention. Figure 12 This is the cycle performance graph of the sodium-ion cathode material of Comparative Example 1 of the present invention. Figure 15 This is the 0.1C first charge-discharge curve of the sodium-ion cathode material of Comparative Example 2 of the present invention. Figure 16 This is the cycle performance graph of the sodium-ion cathode material of Comparative Example 2 of the present invention.

[0074] From Figure 3 、 4 、7, 8, 11, 12, 15, 16 and Table 1, it can be seen that Ca is doped at the sodium site in the sodium-ion cathode material of the present invention 2+Meanwhile, controlling the molar ratio of sodium and calcium and using Ti and Mg as necessary doping elements for the transition metal sites can enable the O3-type sodium ion cathode material to form a more stable crystal structure. After the working potential is increased to higher than 4.15 V, the above O3-type sodium ion battery material takes into account both specific capacity and cycle stability and effectively increases the median discharge voltage.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A sodium ion positive electrode material, characterized in that The chemical formula of the sodium ion positive electrode material is Na x Ca y Ni a Fe b Mn c Ti d TM e O2, wherein TM is at least two of the metal elements Mg, Sr, La, Y, and Nb and must contain Mg, 0.5≤x≤1.1, 0.01≤y≤0.1, 0.1≤a≤0.5, 0.05≤b≤0.3, 0.1≤c≤0.4, 0.01≤d≤0.3, 0.01≤e≤0.1, and the sodium ion positive electrode material is an O3 type sodium ion positive electrode material.

2. The sodium ion positive electrode material according to claim 1, characterized in that TM is two or three of Mg, Sr, and Y and necessarily contains Mg.

3. The sodium ion positive electrode material according to claim 1, characterized in that 0.8≤x≤1.1,0.01≤y≤0.05,0.25≤a≤0.50,0.1≤b≤0.25,0.2≤c≤0.35,0.1≤d≤0.3,0.02≤e≤0.05。 4. The sodium ion positive electrode material according to claim 1, characterized in that 0.95≤x≤1.05, 0.02≤y≤0.

03.

5. The sodium ion positive electrode material according to claim 1, characterized in that The preparation method of the sodium ion positive electrode material comprises the following steps: Ni a Fe b Mn c After the Tid(OH)2 precursor is fully mixed with the sodium source, calcium source and TM source in a stoichiometric ratio, it is calcined at 700~900℃ in an air atmosphere for 1.5~2.5h, then the temperature is continued to be raised to 900℃~1000℃ and calcined for 10~14h, and then the temperature is naturally cooled to obtain the sodium ion positive electrode material.

6. The method for preparing the sodium ion positive electrode material according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: Ni a Fe b Mn c The Tid(OH)2 precursor is fully mixed with a sodium source, a calcium source, and a TM source in a stoichiometric ratio, and then calcined at 700-900°C for 1.5-2.5 hours, and then further heated to 900-1000°C for 10-14 hours, and then cooled naturally to obtain the sodium ion positive electrode material; The sodium source is sodium carbonate, the calcium source is calcium carbonate or calcium oxide, and the TM source is the oxide or hydroxide of the corresponding element.

7. A material composition for a sodium ion battery positive electrode, characterized in that: The invention comprises 80 to 100 parts by weight of the sodium ion positive electrode material according to any one of claims 1 to 5, 4 to 6 parts by weight of conductive carbon black, and 4 to 6 parts by weight of polyvinylidene fluoride.

8. A battery positive electrode, characterized in that: The invention comprises 80 to 100 parts by weight of the sodium ion positive electrode material according to any one of claims 1 to 6, 4 to 6 parts by weight of conductive carbon black, and 4 to 6 parts by weight of polyvinylidene fluoride.

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