Sodium-ion battery positive electrode material, preparation method thereof and sodium-ion battery

Abstract

The invention provides a sodium-ion battery positive electrode material, a preparation method thereof and a sodium-ion battery. The sodium-ion battery positive electrode material has a chemical formula as shown in a formula I: NaaNixMnyLimTinQqOrXs, wherein Q is one or more of Fe, Zr, K, Ti, Ca, Zn, W, Al, V, Bi, Sb, Cu, Mg, Co, Sn, La, Ce, Mo and Cr, X is one or more of F, Cl, Br and I, 0.8 < = a < = 1.2, 0 < x < = 1, 0 < y < = 1, 0 < = q < = 1, 0 < = s < = 0.2, x + y + m + n + q = 1, and 2r + s = 4; the sodium ion battery positive electrode material has single crystal morphology, and the single crystal surface has a stripe structure. The normal-temperature rate capability and the high-temperature cycle capacity retention ratio of the sodium ion battery positive electrode material at 2-4.2 V (vs Na / Na < + >) are obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a sodium ion battery positive electrode material, a preparation method thereof, and a sodium ion battery. Background Art

[0002] As human society's demand for renewable energy and electric vehicles grows, the development of more efficient and sustainable electrochemical energy storage technologies has become an important direction. Currently, lithium-ion batteries have become the mainstream energy storage solution in many fields such as electric vehicles and consumer electronics due to their high energy density, excellent power density and long cycle life. However, lithium mineral reserves are limited and concentrated in a few countries, which makes the supply of lithium resources vulnerable to geopolitical and market fluctuations. In addition, the mining and extraction process of lithium resources has a significant impact on the environment, increasing the environmental pressure of long-term use of lithium-ion batteries as the main energy storage technology.

[0003] In recent years, sodium-ion batteries (SIBs), citing their abundant sodium resources, widespread distribution, low cost, sustainable development, safety, stability, fast charging, and low-temperature performance, have been recognized as one of the best and most promising complements to lithium-ion batteries. Their potential in new energy vehicle power batteries and large-scale energy storage has drawn the attention of many battery companies to the development of SIB technology. SIBs have demonstrated potential as replacements for lead-acid batteries and, in some cases, lithium iron phosphate batteries, and are gradually finding application in A00-class electric vehicles, energy storage power stations, two-wheeled vehicles, and engineering equipment. Furthermore, the principles and processes of SIBs are similar to those of lithium-ion batteries. Compatible with existing lithium-ion equipment, SIBs and system designs can be modeled after SIBs, making SIB development relatively straightforward. The key lies in cathode material technology.

[0004] From the current industrialization perspective, layered oxide cathode materials for sodium-ion batteries have attracted widespread attention due to their simple synthesis methods, high theoretical specific capacity, and sufficient Na content. However, they still suffer from poor rate performance and cycle stability. Therefore, the development of high-performance layered oxide cathode materials is crucial. Summary of the Invention

[0005] The present invention provides a sodium ion battery positive electrode material, a preparation method thereof, and a sodium ion battery. The sodium ion battery positive electrode material of the present invention effectively improves its cycle stability and rate performance under high cut-off voltage and high current density.

[0006] The present invention provides a sodium ion battery positive electrode material having the chemical formula shown in Formula I:

[0007] Na a Ni x Mny Li m Ti n Q q O r X s Formula I;

[0008] wherein Q is one or more of Fe, Zr, K, Ti, Ca, Zn, W, Al, V, Bi, Sb, Cu, Mg, Co, Sn, La, Ce, Mo, and Cr, X is one or more of F, Cl, Br, and I, 0.8≤a≤1.2, 0<x≤1, 0<y≤1, 0≤q≤1, 0≤s≤0.2, x+y+m+n+q=1, and 2r+s=4;

[0009] The sodium ion battery positive electrode material has a single crystal morphology, and the surface of the single crystal has a striped structure.

[0010] Preferably, 0.1≤m<0.5, 0.1≤n≤0.2.

[0011] Preferably, 0.1≤m≤0.2, 0.1≤n≤0.2, 0.2≤m+n≤0.3.

[0012] Preferably, the particle surface stripe coefficient G=E / F, where E is the number of surface stripes of a single crystal in the observation area, and F is the particle size of the single crystal, μm, and 0<G≤100.

[0013] The present invention provides a method for preparing the sodium ion battery positive electrode material as described above, comprising the following steps:

[0014] A sodium source, a nickel source, a manganese source, a lithium source, a titanium source, an optional metal Q source and an optional X source are mixed and subjected to high-temperature solid-phase sintering to obtain a sodium ion battery positive electrode material.

[0015] Preferably, the sodium source comprises one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium acetate, sodium nitrate, sodium nitrite, sodium sulfate and sodium oxalate;

[0016] The nickel source and manganese source are nickel-manganese compounds;

[0017] The lithium source includes one or more of lithium carbonate, oxide, hydroxide and fluoride;

[0018] The titanium source includes one or more of titanium carbonate, oxide, hydroxide and fluoride;

[0019] The metal Q source includes one or more of the carbonate, oxide, hydroxide and fluoride of metal Q;

[0020] The X source includes one or more of an X-containing inorganic salt compound, an X-containing inorganic acid compound, an X-containing element, and an X-containing organic compound.

[0021] Preferably, the sintering atmosphere for the high-temperature solid-phase sintering includes one or more of air, oxygen, nitrogen and argon.

[0022] Preferably, the holding temperature of the high-temperature solid-phase sintering is 900-1050° C., and the holding time of the high-temperature solid-phase sintering is 8-20 hours.

[0023] Preferably, the heating rate of the high-temperature solid-phase sintering is 0.01 to 10° C. / min, and the cooling rate is 0.01 to 10° C. / min.

[0024] The present invention provides a sodium ion battery, comprising the sodium ion battery positive electrode material described above or the sodium ion battery positive electrode material prepared by the method for preparing the sodium ion battery positive electrode material described above.

[0025] The present invention provides a sodium ion battery positive electrode material having a chemical formula shown in Formula I: Na a Ni x Mn y Li m Ti n Q q O r X s Formula I; wherein, Q is one or more of Fe, Zr, K, Ti, Ca, Zn, W, Al, V, Bi, Sb, Cu, Mg, Co, Sn, La, Ce, Mo, Cr, X is one or more of F, Cl, Br, I, 0.8≤a≤1.2, 0<x≤1, 0<y≤1, 0≤q≤1, 0≤s≤0.2, x+y+m+n+q=1, 2r+s=4; the sodium ion battery positive electrode material has a single crystal morphology, and the single crystal surface has a striped structure. The present invention increases the stability of the positive electrode material structure by forming a strong Li-O bond through Li substitution. The Ti element can increase the lattice spacing of the material, inhibit the irreversible multiple phase transitions in the high voltage region, and thus exhibit excellent high voltage stability. At the same time, the coordinated substitution of Li and Ti elements not only realizes the regulation of the internal crystal structure of the material, but also realizes the regulation of the striping of the single crystal surface. There are obvious morphological features under scanning electron microscope observation. This morphology is conducive to increasing the contact area between the single crystal and the electrolyte, which is beneficial to Na + Therefore, compared with the conventional sodium ion battery layered oxide positive electrode, the particle surface of the sodium ion battery positive electrode material in the present invention has a distinct stripe shape, and the synergistic effect of Li and Ti elements makes the material have a high capacity at 2-4.2V (vs Na / Na+ )’s room temperature rate performance and high temperature cycle capacity retention rate are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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 merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0027] Figure 1 The right figure is a SEM image of the sodium layered oxide positive electrode material prepared in Example 1 of the present invention, and the right figure is a schematic diagram for calculating the particle surface stripe coefficient G;

[0028] Figure 2 The right figure is a SEM image of the sodium layered oxide positive electrode material prepared in Example 2 of the present invention, and the right figure is a schematic diagram for calculating the particle surface stripe coefficient G;

[0029] Figure 3 This is a SEM image of the sodium layered oxide positive electrode material prepared in Comparative Example 5 of the present invention;

[0030] Figure 4 This is an SEM image of the sodium layered oxide positive electrode material prepared in Comparative Example 6 of the present invention. DETAILED DESCRIPTION

[0031] The present invention provides a sodium ion battery positive electrode material having the chemical formula shown in Formula I:

[0032] Na a Ni x Mn y Li m Ti n Q q O r X s Formula I;

[0033] wherein Q is one or more of Fe, Zr, K, Ti, Ca, Zn, W, Al, V, Bi, Sb, Cu, Mg, Co, Sn, La, Ce, Mo, and Cr, X is one or more of F, Cl, Br, and I, 0.8≤a≤1.2, 0<x≤1, 0<y≤1, 0≤s≤0.2, 0≤q≤1, x+y+m+n+q=1, and 2r+s=4;

[0034] The sodium ion battery positive electrode material has a single crystal morphology, and the surface of the single crystal has a striped structure.

[0035] In the present invention, 0.8≤a≤1.2, preferably, 0.9≤a≤1.1, such as a is 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, preferably with any of the above values ​​as the upper or lower limit; 0<x≤1, such as x is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, preferably with any of the above values ​​as the upper limit Or the range value of the lower limit; 0<y≤1, such as y is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, preferably the range value with any of the above values ​​as the upper or lower limit; 0≤q≤1, preferably, 0<q≤1, such as q is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, preferably the range value with any of the above values ​​as the upper or lower limit.

[0036] In the present invention, 0.1≤m<0.5, preferably, 0.1≤m≤0.2, such as m is 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, preferably a range value with the above arbitrary numerical value as the upper or lower limit; 0.1≤n≤0.2, preferably, 0.11≤n≤0.18, such as n is 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, preferably a range value with the above arbitrary numerical value as the upper or lower limit. Within the preferred range of the above m and n values, a striped structure is generated on the surface of the positive electrode material particles, and the rate electrical performance is excellent.

[0037] In the present invention, the sodium ion battery positive electrode material has a single crystal morphology, and the surface of the single crystal has a stripe structure, which is beneficial to increase the contact area between the single crystal and the electrolyte, thereby improving the Na + The rapid transmission performance of the material is improved, thereby improving the capacity of the material at high rates. In the present invention, the fringe coefficient of the particle surface is G = E / F, where E is the number of surface fringes of a single crystal in the observation area, and F is the particle size of the corresponding single crystal in μm. The particle surface fringe coefficient G represents the number of surface fringes of a single crystal per unit size, in μm. -1 , 0<G≤100, preferably, 0<G≤50, more preferably, 1.6≤G≤10.

[0038] The present invention also provides a method for preparing the above-mentioned sodium ion battery positive electrode material, comprising the following steps:

[0039] A sodium source, a nickel source, a manganese source, a lithium source, a titanium source, an optional metal Q source and an optional X source are mixed and subjected to high-temperature solid-phase sintering to obtain a sodium ion battery positive electrode material.

[0040] In the present invention, the sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium acetate, sodium nitrate, sodium nitrite, sodium sulfate and sodium oxalate; the nickel source and manganese source are nickel-manganese compounds, and the nickel-manganese compounds are compounds containing both nickel and manganese, preferably one or more of nickel-manganese oxides, hydroxides and carbonates; the lithium source includes one or more of lithium carbonates, oxides, hydroxides and fluorides; the titanium source includes one or more of titanium carbonates, oxides, hydroxides and fluorides; the metal Q source includes one or more of metal Q carbonates, oxides, hydroxides and fluorides, and the metal Q is preferably Fe, Zr, K, Ti, Ca, Z The X source preferably includes one or more of an inorganic salt compound containing X, an inorganic acid compound containing X, a simple substance containing X, and an organic compound containing X, such as an ammonium salt of X (such as one or more of NH4F, NH4Cl, NH4Br, and NH4I), an alkali metal salt of X (such as one or more of NaCl, NaF, NaBr, KCl, KF, and KBr), an inorganic acid of X (such as one or more of HCl, HBr, HI, and HF), F2, I2, Cl2, Br2, and one or more of C1-C10 halogenated hydrocarbons.

[0041] In the present invention, the amounts of the sodium source, nickel source, manganese source, lithium source, titanium source, metal Q source and X source can be mixed according to the stoichiometric ratio in Formula I, and the present invention will not be repeated here.

[0042] In the present invention, the sintering atmosphere of the high-temperature solid-phase sintering preferably includes one or more of air, oxygen, nitrogen and argon, and the holding temperature of the high-temperature solid-phase sintering is preferably 900-1050°C, more preferably 950-1000°C, such as 900°C, 920°C, 950°C, 980°C, 1000°C, 1020°C, 1050°C, preferably a range value with any of the above values ​​as the upper or lower limit; within this sintering range, a striped structure can be formed on the surface of the particles, and the holding time of the high-temperature solid-phase sintering is 8-20 hours, more preferably 12-18 hours.

[0043] In the present invention, the heating rate of the high temperature solid phase sintering is preferably 0.01 to 10 ° C / min, more preferably 0.1 to 8 ° C / min, such as 0.01 ° C / min, 0.05 ° C / min, 0.1 ° C / min, 0.5 ° C / min, 1 ° C / min, 2 ° C / min, 3 ° C / min, 4 ° C / min, 5 ° C / min, 6 ° C / min, 7 ° C / min, 8 ° C / min, 9 ° C / min, 10 ° C / min, preferably with any of the above values ​​as the upper or lower limit of the range value, the high temperature solid phase sintering After the junction insulation is completed, the temperature is lowered to room temperature at a certain cooling rate. The cooling rate is preferably 0.01-10°C / min, more preferably 0.1-8°C / min, such as 0.01°C / min, 0.05°C / min, 0.1°C / min, 0.5°C / min, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, preferably a range value with any of the above values ​​as the upper or lower limit.

[0044] The present invention also provides a sodium ion battery, comprising the sodium ion battery positive electrode material described above, the sodium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, the positive electrode comprising a positive electrode current collector and a positive electrode active layer composited on at least one surface of the positive electrode current collector, the positive electrode current collector is preferably a carbon-coated aluminum foil, the positive electrode active layer comprises the sodium ion battery positive electrode material described above, a conductive agent and a binder, the conductive agent is preferably carbon black (Super P), the binder is preferably polyvinylidene fluoride (PVDF) and / or polytetrafluoroethylene (PTFE), the mass ratio of the sodium ion battery positive electrode material, the conductive agent and the binder is preferably (89-92): (4-6): (4-6), specifically, in one embodiment of the present invention, the mass ratio of the sodium ion battery positive electrode material, the conductive agent and the binder is 90:5:5; the negative electrode is preferably a sodium sheet, the electrolyte preferably includes a sodium salt, an additive and a solvent, the sodium salt is preferably NaPF6, the concentration of the sodium salt is preferably 1-1.5 mol / L, the additive is preferably fluoroethylene carbonate (FEC), the volume fraction of the additive in the electrolyte is 5-8%, and the solvent preferably includes ethylene carbonate (PC); the separator is preferably polyethylene (PE).

[0045] The present invention provides a sodium ion battery positive electrode material having a chemical formula shown in Formula I: Na a Ni x Mn y Li m Ti n Q q O r X sFormula I; wherein, Q is one or more of Fe, Zr, K, Ti, Ca, Zn, W, Al, V, Bi, Sb, Cu, Mg, Co, Sn, La, Ce, Mo, Cr, X is one or more of F, Cl, Br, I, 0.8≤a≤1.2, 0<x≤1, 0<y≤1, 0≤q≤1, x+y+m+n+q=1, 2r+s=4; the sodium ion battery positive electrode material has a single crystal morphology, and the single crystal surface has a striped structure. The present invention increases the stability of the positive electrode material structure by forming a strong Li-O bond through Li substitution. The Ti element can increase the lattice spacing of the material, inhibit the irreversible multiple phase transitions in the high voltage region, and thus exhibit excellent high voltage stability. At the same time, the coordinated substitution of Li and Ti elements not only realizes the regulation of the internal crystal structure of the material, but also realizes the regulation of the striping of the single crystal surface. There are obvious morphological features under scanning electron microscope observation. This morphology is conducive to increasing the contact area between the single crystal and the electrolyte, which is beneficial to Na + Therefore, compared with the conventional sodium ion battery layered oxide positive electrode, the particle surface of the sodium ion battery positive electrode material in the present invention has a distinct stripe shape, and the synergistic effect of Li and Ti elements makes the material have a high capacity at 2-4.2V (vs Na / Na + )’s room temperature rate performance and high temperature cycle capacity retention rate are significantly improved.

[0046] To further illustrate the present invention, a sodium ion battery positive electrode material, a preparation method thereof, and a sodium ion battery provided by the present invention are described in detail below in conjunction with examples, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.8:0.05:0.1 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0049] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.4 Mn 0.4 Li 0.1 Ti 0.1 O2. Among them, a=1, x=0.4, y=0.4, m=0.1, n=0.1, m+n=0.2, q=0, s=0, G=3.93~8.05.

[0050] Example 2

[0051] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.7:0.05:0.2 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0052] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.35 Mn 0.35 Li 0.1 Ti 0.2 O2. Among them, a=1, x=0.35, y=0.35, m=0.1, n=0.2, m+n=0.3, q=0, s=0, G=2.09~4.56.

[0053] Example 3

[0054] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3, TiO2 and MgO were mixed in a molar ratio of 0.5:0.7:0.05:0.15:0.05 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0055] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.35 Mn 0.35 Li 0.1 Ti 0.15 Mg 0.05 O2. Among them, a=1, x=0.35, y=0.35, m=0.1, n=0.15, m+n=0.25, q=0.05, s=0, G=3.24~5.23.

[0056] Example 4

[0057] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3, TiO2 and Fe2O3 were mixed in a molar ratio of 0.5:0.7:0.05:0.15:0.025 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0058] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.35 Mn 0.35 Li 0.1 Ti 0.15 Fe 0.05 O2. Among them, a=1, x=0.35, y=0.35, m=0.1, n=0.15, m+n=0.25, q=0.05, s=0, G=1.89~3.22.

[0059] Example 5

[0060] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3, TiO2 and Al2O3 were mixed in a molar ratio of 0.5:0.7:0.05:0.15:0.025 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0061] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.35 Mn 0.35 Li 0.1 Ti 0.15 Al 0.05 O2. Among them, a=1, x=0.35, y=0.35, m=0.1, n=0.15, m+n=0.25, q=0.05, s=0, G=3.11~6.27.

[0062] Example 6

[0063] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3, TiO2 and NH4F were mixed in a molar ratio of 0.5:0.7:0.05:0.2:0.1 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0064] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.35 Mn 0.35 Li 0.1 Ti 0.2 O1.95 F 0.1 . Among them, a=1, x=0.35, y=0.35, m=0.1, n=0.2, m+n=0.3, q=0, s=0.1, G=1.77~3.46.

[0065] The structures of the sodium layered oxide cathode materials prepared in Example 1 and Example 2 were characterized using a scanning electron microscope. Figures 1 and 2 As shown by Figure 1 and Figure 2 It can be seen that the particle surfaces of the positive electrode materials prepared in Example 1 and Example 2 have obvious stripe structures.

[0066] Comparative Example 1

[0067] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2 and TiO2 were mixed in a molar ratio of 0.5:0.7:0.3 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0068] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted, particle-free, surface-striped sodium ion battery cathode material. 0.35 Mn 0.35 Ti 0.3 O2. Among them, a=1, x=0.35, y=0.35, m=0, n=0.3, m+n=0.3, q=0, s=0, G=0.

[0069] Comparative Example 2

[0070] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.7:0.125:0.05 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0071] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted, particle-free, surface-striped sodium ion battery cathode material. 0.35 Mn 0.35 Li 0.25 Ti 0.05 O2. Among them, a=1, x=0.35, y=0.35, m=0.25, n=0.05, m+n=0.3, q=0, s=0, G=0.

[0072] Comparative Example 3

[0073] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.4:0.15:0.3 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0074] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted, particle-free, surface-striped sodium ion battery cathode material. 0.2 Mn 0.2 Li 0.3 Ti 0.3 O2. Among them, a=1, x=0.2, y=0.2, m=0.3, n=0.3, m+n=0.6, q=0, s=0, G=0.

[0075] Comparative Example 4:

[0076] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.4:0.05:0.5 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0077] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 980°C for 14 h at a heating rate of 1°C / min to obtain NaNi, a Ti-substituted sodium ion battery cathode material with particle surface stripes. 0.2 Mn 0.2 Li 0.1 Ti 0.5 O2. Among them, a=1, x=0.2, y=0.2, m=0.1, n=0.5, m+n=0.6, q=0, s=0, G=0.64~1.53.

[0078] Comparative Example 5

[0079] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.8:0.05:0.1 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0080] The uniform mixture was placed in an air atmosphere box furnace and calcined at a heating rate of 1 ° C / min and a temperature of 800 ° C for 14 h to obtain Ti-substituted, particle-free, surface-striped sodium ion battery positive electrode material NaNi 0.4 Mn 0.4 Li 0.1 Ti 0.1 O2. Among them, a=1, x=0.4, y=0.4, m=0.1, n=0.1, m+n=0.2, q=0, s=0, G=0.

[0081] Comparative Example 6

[0082] Na2CO3 and Ni 0.5 Mn 0.5 (OH)2, Li2CO3 and TiO2 were mixed in a molar ratio of 0.5:0.8:0.05:0.1 by a high-speed mixer at a speed of 1700 rpm for 20 minutes four times to obtain a uniform mixture.

[0083] The uniform mixture was placed in an air atmosphere box furnace and calcined at a temperature of 1 ° C / min and 1200 ° C for 14 h to obtain Ti-substituted, particle-free, surface-striped sodium ion battery positive electrode material NaNi 0.4 Mn 0.4 Li 0.1 Ti 0.1 O2. Among them, a=1, x=0.4, y=0.4, m=0.1, n=0.1, m+n=0.2, q=0, s=0, G=0.

[0084] The structures of the sodium layered oxide cathode materials prepared in Comparative Examples 5 and 6 were characterized using a scanning electron microscope. Figures 3 and 4 As shown. Figure 3 and Figure 4 It can be seen that the sintering temperature of Comparative Example 5 is too low, and the positive electrode material prepared cannot form a single crystal. Although the particles of the positive electrode material prepared in Comparative Example 6 form a partial single crystal structure, the surface of the single crystal does not have a striped structure, indicating that the sintering temperature has a direct impact on the formation of the striped structure.

[0085] The particle edge stripe coefficients of the sodium layered oxide positive electrode materials prepared in Examples 1 to 2 and Comparative Examples 1 to 6 were calculated, and the results are shown in Table 1.

[0086] Table 1 Stripe coefficient G of sodium layered oxide positive electrode materials prepared in Examples and Comparative Examples

[0087]

[0088] The positive electrode materials prepared in the examples and comparative examples were assembled into button cells. The positive electrode sheets of the button cells were prepared in a mass ratio of positive electrode material: conductive agent: PVDF = 90:5:5, and the negative electrode was a sodium sheet. The test conditions included: CR2032, 0.1C, 2-4.2V, vs. Na + / Na, the assembled button battery was charged and discharged at a constant current of 0.5C in the voltage range of 2V to 4.2V for 50 cycles at a constant temperature of 45℃. The test results are shown in Table 2.

[0089] Table 2 Performance data of the positive electrode material assembled batteries prepared in Examples and Comparative Examples

[0090]

[0091] As shown in Table 2, in Comparative Example 1, without Li doping, the Ti element cannot exert a synergistic effect. In Examples 1 to 6, based on the simultaneous presence of Li and Ti, the introduction of the Q element or halogen X does not change the fundamental nature of the surface stripes of the material, but rather causes fluctuations in the particle surface stripe coefficient to a certain extent, which is beneficial to improving the material's rate performance and cycling stability.

[0092] When there is no Li, the material has no surface streaks G=0, and the high voltage stability and rate of the material are significantly reduced (Comparative Example 1). When Li and Ti are co-doped and Ti is relatively low, the material has no surface streaks G=0, and the high voltage stability of the material is better but the rate is not good (Comparative Example 2). When Li and Ti are co-doped and Li is relatively high, the material has no surface streaks G=0, and the high voltage stability of the material is better but the rate is poor (Comparative Example 3). When Li and Ti are co-doped and Ti is relatively high, the material has surface streaks, and the rate of the material is relatively good but the cycle is poor (Comparative Example 4).

[0093] Temperature has a significant impact on the material's single crystals and surface striations. At temperatures too low (800°C), single crystals cannot form, the particle surface striation coefficient is meaningless, and the material exhibits poor rate performance and cycling stability (Comparative Example 5). At temperatures too high (1200°C), single crystals can form, but the particle surface striations disappear. While the material exhibits improved stability compared to temperatures too low, it still exhibits poor rate performance (Comparative Example 6).

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A sodium ion battery cathode material having the chemical formula shown in Formula I: Na a Ni x Mn y Li m Ti n Q q O r X s Formula I; in, Q is one or more of Fe, Zr, K, Ti, Ca, Zn, W, Al, V, Bi, Sb, Cu, Mg, Co, Sn, La, Ce, Mo, and Cr; X is one or more of F, Cl, Br, and I; 0.8≤a≤1.2, 0<x≤1, 0<y≤1, 0≤q≤1, 0≤s≤0.2, x+y+m+n+q=1, and 2r+s=4; The sodium ion battery positive electrode material has a single crystal morphology, and the surface of the single crystal has a striped structure.

2. The sodium ion battery positive electrode material according to claim 1, characterized in that 0.1≤m<0.5, 0.1≤n≤0.

2.

3. The sodium ion battery positive electrode material according to claim 2, characterized in that 0.1≤m≤0.2, 0.1≤n≤0.2, 0.2≤m+n≤0.

3.

4. The sodium ion battery cathode material according to claim 1, characterized in that The particle surface stripe coefficient G=E / F, where E is the number of surface stripes of a single crystal in the observation area, and F is the particle size of the single crystal, μm, 0<G≤100.

5. The method for preparing the positive electrode material for sodium ion batteries according to claim 1, comprising the following steps: A sodium source, a nickel source, a manganese source, a lithium source, a titanium source, an optional metal Q source and an optional X source are mixed and subjected to high-temperature solid-phase sintering to obtain a sodium ion battery positive electrode material.

6. The preparation method according to claim 5, characterized in that The sodium source includes one or more of sodium carbonate, sodium hydroxide, sodium bicarbonate, sodium acetate, sodium nitrate, sodium nitrite, sodium sulfate and sodium oxalate; The nickel source and manganese source are nickel-manganese compounds; The lithium source includes one or more of lithium carbonate, oxide, hydroxide and fluoride; The titanium source includes one or more of titanium carbonate, oxide, hydroxide and fluoride; The metal Q source includes one or more of the carbonate, oxide, hydroxide and fluoride of metal Q; The X source includes one or more of an X-containing inorganic salt compound, an X-containing inorganic acid compound, an X-containing element, and an X-containing organic compound.

7. The preparation method according to claim 5, characterized in that The sintering atmosphere for the high-temperature solid-phase sintering includes one or more of air, oxygen, nitrogen and argon.

8. The preparation method according to claim 5, characterized in that The holding temperature of the high-temperature solid-phase sintering is 900-1050° C., and the holding time of the high-temperature solid-phase sintering is 8-20 hours.

9. The preparation method according to claim 8, characterized in that The high-temperature solid-phase sintering has a heating rate of 0.01 to 10° C. / min and a cooling rate of 0.01 to 10° C. / min.

10. A sodium ion battery, characterized in that: The invention relates to a sodium ion battery positive electrode material according to any one of claims 1 to 4 or a sodium ion battery positive electrode material prepared by the preparation method of the sodium ion battery positive electrode material according to any one of claims 5 to 9.

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