High-entropy sodium ion P2 type positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a high-entropy sodium ion P2 type positive electrode material as well as a preparation method and application thereof. Compared with the prior art, the high-entropy sodium ion P2 type positive electrode material provided by the invention at least contains three doping elements, and when the ion radius of the doping element is close to the ion radius in the material body structure and the Fermi energy levels are different, the charge order of the transition metal layer can be eliminated; meanwhile, after doping, the proportion of Ni < 3 + > and Mn < 3 + > is reduced, and the Jahn-Teller effect of the material can be improved; in addition, the doped elements can improve ordered arrangement of Na < + > / vacancies, improve the diffusion rate of Na < + > and reduce migration activation energy; moreover, the doped elements can inhibit phase change, reduce interlayer spacing and material volume change, and enhance structural stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a high entropy sodium ion P2 type positive electrode material and a preparation method and application thereof. Background Art

[0002] As a beneficial supplement to lithium-ion battery technology, sodium-ion batteries have attracted much attention due to their abundant sodium resources, low cost and high safety. Similar to lithium-ion batteries, in sodium-ion battery systems, battery performance is mainly controlled by the positive electrode material, so the development of positive electrode materials is particularly critical.

[0003] At present, the widely studied positive electrode materials for sodium ion batteries mainly include layered oxides, polyanions and Prussian blue positive electrode materials. Among the layered oxide positive electrode materials, O3 and P2 are the main types. Among them, P2 layered oxide positive electrode materials have a lower sodium content and a larger interlayer spacing, so Na + The diffusion path is wider, showing better ion diffusion kinetics and air stability than the O3 structure. Therefore, theoretically speaking, P2-type materials have great application potential in long-cycle and high-rate scenarios. However, this structure has Na + / vacancies are arranged in an orderly manner, forming a new superlattice peak for Na in the bulk phase + Diffusion has an inhibitory effect, which is not conducive to capacity release; when the voltage is greater than 4.1V, a P2-O2 phase transition occurs, accompanied by stacking faults and large volume changes; in addition, due to Ni 3+ and Mn 3+ There is a lone electron on the energy level, and the Jahn-Teller effect under high voltage will destroy the degeneracy between the two g orbitals, resulting in lattice distortion. Summary of the invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a high-entropy sodium ion P2 type positive electrode material and a preparation method and application thereof, wherein the high-entropy sodium ion P2 type positive electrode material can ensure the capacity of the sodium ion positive electrode material and comprehensively improve the cycle stability and discharge medium-voltage stability of the sodium ion positive electrode material.

[0005] The present invention provides a high entropy sodium ion P2 type positive electrode material, wherein the structural formula of the high entropy sodium ion P2 type positive electrode material is Na x Ni y Ti a Mg b M c Mn zO2; wherein M includes one or more of Ca, Al, Sn, B, Fe, Zn and Zr; a+b+c+y+z=1.0; 0.6 <x<0.76;0.2<y<0.35;0.45<z<0.65;a> 0; b>0; c>0.

[0006] Preferably, 0.02≤a≤0.14; and / or, 0.01≤b≤0.08.

[0007] Preferably, 0.65≤x≤0.72; and / or, 0.25≤y≤0.3; and / or, 0.5≤z≤0.6; and / or, 0.05≤a≤0.14; and / or, 0.01≤c≤0.05.

[0008] Preferably, 0.68≤x≤0.72; and / or, 0.27≤y≤0.28; and / or, 0.54≤z≤0.56; and / or, 0.07≤a≤0.14; and / or, 0.01≤b≤0.07; and / or, 0.02≤c≤0.04.

[0009] Preferably, the high entropy sodium ion P2 type positive electrode material is a rounded single crystal particle without sharp corners;

[0010] And / or, the high entropy sodium ion P2 type positive electrode material D v50 2~12μm.

[0011] Preferably, the specific surface area of ​​the high entropy sodium ion P2 type positive electrode material is 0.4 to 1.2 m 2 ·g -1 .

[0012] The present invention also provides a method for preparing the above-mentioned high entropy sodium ion P2 type positive electrode material, comprising the following steps:

[0013] A sodium source, a nickel source, a titanium source, a magnesium source, a M source and a manganese source are mixed and sintered by a solid phase sintering method to obtain a high entropy sodium ion P2 type positive electrode material.

[0014] Preferably, the nickel source is selected from one or more of nickel oxide, nickel chloride, nickel manganese oxide, nickel manganese hydroxide and nickel manganese chloride;

[0015] The manganese source is selected from one or more of manganese oxide, manganese chloride, nickel manganese oxide, nickel manganese hydroxide and nickel manganese chloride;

[0016] The sodium source is selected from one or more of sodium carbonate, sodium acetate, sodium oxalate and sodium hydroxide;

[0017] The titanium source is selected from one or more of titanium oxide, titanium phosphide, titanium hydroxide and titanium carbonate;

[0018] The iron source is selected from one or more of iron oxides, iron phosphides, iron hydroxides and iron carbonates;

[0019] The M source is selected from one or more of M oxides, M phosphides, M hydroxides and M carbonates.

[0020] Preferably, the calcination temperature is 900°C to 1030°C;

[0021] And / or, the heating rate of the calcination is 0.5 to 5°C / min;

[0022] And / or, the calcination time is 6 to 16 hours;

[0023] And / or, the calcining atmosphere is an oxygen-containing atmosphere.

[0024] The present invention also provides a sodium ion battery, comprising the above-mentioned high entropy sodium ion P2 type positive electrode material.

[0025] Compared with the prior art, the high entropy sodium ion P2 type positive electrode material provided by the present invention contains at least three doping elements. When the ion radius of the doping element is similar to the ion radius in the material body structure and the Fermi level is different, the charge order of the transition metal layer can be eliminated; at the same time, after doping, Ni 3+ , Mn 3+ The proportion of Na is reduced, which can improve the Jahn-Teller effect of the material; in addition, doping elements can improve the + / Orderly arrangement of vacancies, increasing Na + In summary, under the synergistic effect of three or more doping elements, the discharge medium voltage does not decay rapidly with the destruction of the layered structure caused by the phase change of the material, and has excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is the XRD pattern of the positive electrode material obtained in Example 2 of the present invention;

[0027] Figure 2 This is a SEM image of the positive electrode material obtained in Example 2 of the present invention;

[0028] Figure 3 The first charge and discharge curves of Example 2 and Comparative Examples 2 and 3 of the present invention are shown;

[0029] Figure 4 The discharge medium voltage retention rate curve diagram of Example 2 of the present invention and Comparative Example 1;

[0030] Figure 5It is a cycle retention rate curve diagram of Example 2 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention provides a high entropy sodium ion P2 type positive electrode material, wherein the structural formula of the high entropy sodium ion P2 type positive electrode material is Na x Ni y Ti a Mg b M c Mn z O2; wherein M includes one or more of Ca, Al, Sn, B, Fe, Zn and Zr; a+b+c+y+z=1.0; 0.6 <x<0.76;0.2<y<0.35;0.45<z<0.65;a> 0; b>0; c>0.

[0033] Optionally, x is 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or a range between any two of the above values.

[0034] x is the concentration of sodium ions in the high entropy sodium ion P2 type positive electrode material. Too high a sodium ion concentration will cause the positive electrode material to become a P2-O3 mixed structure; while too low a concentration may result in insufficient capacity and energy density of the material. In a specific embodiment provided by the present invention, preferably, 0.65≤x≤0.72; more preferably, 0.68≤x≤0.72. Under this preferred condition, the capacity of the positive electrode material can be guaranteed, and the doping elements can be used in conjunction to improve the cycle stability and discharge medium voltage of the material.

[0035] Optionally, y is 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, 0.30, 0.31, 0.32, 0.33, 0.34 or a range between any two of the above values.

[0036] y is the content of nickel ions in the high entropy sodium ion P2 type positive electrode material. In a specific embodiment provided by the present invention, preferably, 0.25≤y≤0.3; more preferably, 0.27≤y≤0.28. Under this preferred condition, it can cooperate with other metal doping elements to improve the cycle stability and discharge medium voltage of the material. Optionally, z is 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62, 0.63, 0.64 or the range between any two of the above values.

[0037] z is the content of manganese ions in the high entropy sodium ion P2 type positive electrode material. In a specific embodiment provided by the present invention, preferably, 0.5≤z≤0.6; more preferably, 0.54≤z≤0.56. Under this preferred condition, it can cooperate with other metal doping elements to improve the cycle stability and discharge medium voltage of the material.

[0038] Optionally, a is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a range between any two of the above values.

[0039] a is the content of titanium ions in the high entropy sodium ion P2 type positive electrode material. Titanium doping can enter the transition metal layer to make Ni 3+ and Mn 3+ The proportion decreases, improving the lattice distortion during charging and discharging of the material, forming the intermediate phase OP4, reducing the volume change, and effectively inhibiting the transformation of the P2 type material from the P2 phase to the O2 phase during the cycle, thereby enhancing the structural stability of the material and further improving the cycle performance of the battery. In a specific embodiment provided by the present invention, preferably, 0.02≤a≤0.14; more preferably, 0.05≤a≤0.14; and even more preferably, 0.07≤a≤0.14. Under this preferred condition, it can cooperate with other metal elements to improve the cycle stability and discharge medium voltage of the material.

[0040] Optionally, b is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a range between any two of the above values.

[0041] b is the content of magnesium ions in the high entropy sodium ion P2 type positive electrode material, and the inactive Mg 2+Entering the transition metal layer, allowing more Na + During charging, it stays in the prismatic position, inhibiting the slip and phase change of the transition metal layer, thereby stabilizing the overall charge balance of the compound and improving the cycle performance. Mg doping advances the phase change, and the Na + More, improve Na + / Vacancy order, improve the first charge capacity of the material. In a specific embodiment provided by the present invention, preferably, 0.01≤b≤0.08; more preferably, 0.01≤b≤0.07. Under this preferred condition, it can cooperate with other metal elements to improve the cycle stability and discharge medium voltage of the material.

[0042] c is the doping amount of the doping element M; optionally, c is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a range between any two of the above values.

[0043] In a specific embodiment provided by the present invention, preferably, 0.01≤c≤0.05; more preferably, 0.02≤c≤0.04.

[0044] In a specific embodiment provided by the present invention, the M is one or more of Ca, Al, Sn, B, Fe, Zn and Zr, preferably one or two of Ca, Al, Sn, B, Fe, Zn and Zr; when the M is a plurality of doping elements, the doping amounts of the plurality of doping elements may be the same or different, and there is no special restriction. In some embodiments provided by the present invention, when M is a plurality of doping elements, the doping amounts are preferably the same. Under the above preferred conditions, the material contains at least three doping elements, which can ensure the capacity of the sodium ion positive electrode material and synergistically improve the material's cycle stability and discharge medium voltage stability.

[0045] The high entropy sodium ion P2 type positive electrode material provided by the present invention contains doping elements Ti, Mg and M. 0.70 Ni 0.33 Mn 0.67 In the O2 structure, when the charging voltage is greater than 4.1V, some Ni 2+ Oxidized Ni 3+ , Ni 3+ and Mn 3+ It exhibits a strong Jahn-Teller effect and its structural stability deteriorates. 4+ Ionic radius 0.061nm and Ni 2+ (0.069nm) and Mn 3+(0.065nm) is close to that when Ti 4+ When the doping amount is between 0.04 and 0.14, a large amount of Ti 4+ Entering the transition metal layer makes Ni 3+ and Mn 3+ The proportion decreases, improving the lattice distortion during material charging and discharging, forming the intermediate phase OP4, and reducing volume change. Inactive Mg 2+ Entering the transition metal layer, allowing more Na + During charging, it stays in the prismatic position, inhibiting the slip and phase change of the transition metal layer, thereby stabilizing the overall charge balance of the compound and improving the cycle performance. Mg doping advances the phase change, and the Na + More, improve Na + / Vacancy order, improve the first charge capacity of the material. On the basis of Ti and Mg to ensure capacity and cycle, doping a third or more elements to further improve charge order, or adding a larger Ca 2+ , increasing the interlayer spacing of the sodium layers and further eliminating Na + / The influence of vacancy ordering improves the dynamic performance, and the strong bond energy of Ca-O also makes the structure more stable; adding high-valent Zr 4+ Can improve electronic conductivity, which is beneficial to Na + Under the synergistic effect of three or more doping elements, the discharge medium voltage does not decay rapidly with the destruction of the layered structure caused by the phase change of the material, and has excellent cycle stability.

[0046] In a specific embodiment provided by the present invention, the high entropy sodium ion P2 type positive electrode material is a rounded single crystal particle without sharp corners.

[0047] In a specific embodiment provided by the present invention, the high entropy sodium ion P2 type positive electrode material D v50 2~12μm.

[0048] Optionally, the high entropy sodium ion P2 type positive electrode material D v50 It is 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or a range between any two of the above values.

[0049] In a specific embodiment provided by the present invention, the specific surface area of ​​the high entropy sodium ion P2 type positive electrode material is 0.4 to 1.2 m 2 ·g -1 .

[0050] Optionally, the specific surface area of ​​the high entropy sodium ion P2 type positive electrode material is 0.4m 2 ·g -1 、0.5m2 ·g -1 、0.6m 2 ·g -1 、0.7m 2 ·g -1 、0.8m 2 ·g -1 、0.9m 2 ·g -1 , 1.0m 2 ·g -1 、1.1m 2 ·g -1 , 1.2m 2 ·g -1 Or the range between any two of the above values.

[0051] The high entropy sodium ion P2 type positive electrode material provided by the present invention contains at least three doping elements. When the ion radius of the doping element is similar to the ion radius in the material body structure and the Fermi level is different, the charge order of the transition metal layer can be eliminated; at the same time, after doping, Ni 3+ , Mn 3+ The proportion of Na is reduced, which can improve the Jahn-Teller effect of the material. In addition, doping elements can improve the Na + / Vacancies are arranged in an orderly manner, increasing Na + In summary, under the synergistic effect of three or more doping elements, the discharge medium voltage does not decay rapidly with the destruction of the layered structure caused by the phase change of the material, and has excellent cycle stability.

[0052] The present invention also provides a method for preparing the above-mentioned high entropy sodium ion P2 type positive electrode material, comprising the following steps: mixing a sodium source, a nickel source, a titanium source, a magnesium source, an M source and a manganese source, and calcining by a solid phase sintering method to obtain the high entropy sodium ion P2 type positive electrode material.

[0053] The present invention has no particular limitation on the sources of all raw materials, and any raw materials available on the market can be used.

[0054] In a specific embodiment provided by the present invention, the nickel source is preferably one or more of nickel oxide, nickel chloride, nickel manganese oxide, nickel manganese hydroxide and nickel manganese chloride.

[0055] In a specific embodiment provided by the present invention, the manganese source is preferably one or more of manganese oxide, manganese chloride, nickel manganese oxide, nickel manganese hydroxide and nickel manganese chloride.

[0056] In a specific embodiment provided by the present invention, the sodium source is preferably one or more of sodium carbonate, sodium acetate, sodium oxalate and sodium hydroxide.

[0057] In a specific embodiment provided by the present invention, the titanium source is preferably one or more of titanium oxide, titanium phosphide, titanium hydroxide and titanium carbonate.

[0058] In a specific embodiment provided by the present invention, the iron source is preferably one or more of iron oxide, iron phosphide, iron hydroxide and iron carbonate.

[0059] In a specific embodiment provided by the present invention, the M source is preferably one or more of M oxide, M phosphide, M hydroxide and M carbonate.

[0060] Mix a sodium source, a nickel source, a titanium source, a magnesium source, an M source and a manganese source; the mixing method is a method well known to those skilled in the art and is not particularly limited. In the present invention, stirring is preferably used; the mixing speed is preferably 1000-2000rpm; optionally, the mixing speed is 1000rpm, 1100rpm, 1200rpm, 1300rpm, 1400rpm, 1500rpm, 1600rpm, 1700rpm, 1800rpm, 1900rpm, 2000rpm or a range between any two of the above values; the mixing time is preferably 5-60min; optionally, the mixing time is 5min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min or a range between any two of the above values; the mixing times may be once or multiple times. In order to mix evenly, the mixing times are preferably 2-4 times, more preferably 3 times.

[0061] After mixing, a solid phase sintering method is used to calcine to obtain a high entropy sodium ion P2 type positive electrode material; the calcination temperature is preferably 900°C to 1030°C; optionally, the calcination temperature is 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, 990°C, 1000°C, 1010°C, 1020°C, 1030°C or a range between any two of the above values; the calcination heating rate is preferably 0.5 to 5°C / min; optionally, the calcination heating rate is 0 .5℃ / min, 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min or the range between any two of the above values; the calcination time is preferably 6-16h; optionally, the calcination time is 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h or the range between any two of the above values; the calcination atmosphere is preferably an oxygen-containing atmosphere, more preferably air; after calcination, it is preferably cooled naturally to obtain a high entropy sodium ion P2 type positive electrode material.

[0062] The present invention also provides a sodium ion battery, comprising the above-mentioned high entropy sodium ion P2 type positive electrode material.

[0063] In a specific embodiment provided by the present invention, the sodium ion battery includes a positive electrode; the positive electrode includes a positive electrode collector and a positive electrode active layer arranged on at least one surface of the positive electrode collector; the positive electrode collector can be a positive electrode collector well known to those skilled in the art, without special restrictions, and is preferably aluminum foil in the present invention; the positive electrode active layer includes the above-mentioned high entropy sodium ion P2 type positive electrode material; the mass of the high entropy sodium ion P2 type positive electrode material is preferably 85% to 95% of the mass of the positive electrode active layer; optionally, the mass of the high entropy sodium ion P2 type positive electrode material is 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or a range between any two of the above values ​​of the mass of the positive electrode active layer; the positive electrode active layer preferably also includes a positive electrode conductive agent and a positive electrode binder; the positive electrode conductive The mass of the agent is preferably 1% to 10% of the mass of the positive electrode active layer; optionally, the mass of the positive electrode conductive agent is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the mass of the positive electrode active layer or the range between any two of the above values; the positive electrode conductive agent can be a positive electrode conductive agent well known to those skilled in the art, without any special restrictions, and is preferably carbon black and / or carbon nanotubes in the present invention; the positive electrode binder is preferably 1% to 10% of the mass of the positive electrode active layer; optionally, the mass of the positive electrode binder is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or the range between any two of the above values; the positive electrode binder can be a positive electrode binder well known to those skilled in the art, without any special restrictions, and is preferably polyvinylidene fluoride (PVDF) in the present invention.

[0064] In a specific embodiment provided by the present invention, the sodium ion battery further comprises a negative electrode; the negative electrode can be any negative electrode well known to those skilled in the art without any special limitation, and in the present invention, a metal sodium sheet is preferred.

[0065] In a specific embodiment provided by the present invention, the sodium ion battery further includes a separator.

[0066] In order to further illustrate the present invention, a high entropy sodium ion P2 type positive electrode material, a preparation method and an application thereof provided by the present invention are described in detail below in combination with embodiments.

[0067] The reagents used in the following examples are all commercially available.

[0068] Example 1

[0069] 1.1 Preparation of positive electrode material Na 0.69 Ni 0.28 Ti 0.11 Mg 0.03 Al 0.02 Mn0.56 O2

[0070] Weigh Na2CO3, Ni 0.33 Mn 0.67 The remaining raw materials were weighed in a ratio of TiO2:Mg(OH)2:Al2O3=0.11:0.03:0.01, and mixed in a 5L high-speed mixer at a mixing speed of 1200rpm for 15min. After mixing three times, the resulting mixture was placed in an air atmosphere box furnace and kept at 980℃ for 10h before being cooled naturally to obtain Ti, Mg, and Al co-doped Na 0.69 Ni 0.28 Ti 0.11 Mg 0.03 Al 0.02 Mn 0.56 O2.

[0071] 1.2 Preparation of sodium ion button cells

[0072] (1) The positive electrode material, conductive carbon nanotubes, and polyvinylidene fluoride (PVDF) obtained in 1.1 were weighed in a mass ratio of 90:5:5, and an appropriate amount of NN-dimethylpyrrolidone was added and ground for 15 minutes to obtain a positive electrode slurry.

[0073] (2) The positive electrode slurry was evenly coated on the surface of the aluminum foil, placed in a vacuum drying oven for drying, and rolled to form a positive electrode active layer (surface density 12 mg / cm 2 , compacted density 3.0mg / cm 2 ), and then cut the positive electrode active layer into a 10mm positive electrode sheet.

[0074] (3) After the positive electrode sheet, glass fiber separator, and metal sodium negative electrode sheet are assembled, the electrode assembly is placed in the outer packaging, and 1 mol / L NaPF6 electrolyte (solvent EC:DMC:DEC=1:1:1) is slowly introduced to assemble a CR2032 button-type sodium ion battery in a glove box.

[0075] Button cell battery test:

[0076] First time: 25℃, voltage window 2.2~4.25V(vs Na + / Na), 0.1C; cycle: 45℃, 2.2~4.25V, 1.0C cycle for 50 cycles (1C=120mA / g).

[0077] In the voltage window of 2.2-4.25V, the material has a 0.1C first charge capacity of 118.9mAh / g, a discharge medium voltage of 3.553V, a cycle retention rate of 97.5% for 50 cycles at 45°C, and a discharge medium voltage retention rate of 99.1%.

[0078] Example 2: Preparation of positive electrode material Na 0.72 Ni 0.28 Ti 0.10 Mg 0.04 Fe 0.02 Mn 0.56 O2

[0079] The preparation process is the same as that of Example 1, except that the remaining raw materials are weighed in a ratio of TiO2:Mg(OH)2:Fe2O3=0.10:0.04:0.01, and Ti, Mg, and Fe co-doped Na 0.72 Ni 0.28 Ti 0.10 Mg 0.04 Fe 0.02 Mn 0.56 O2.

[0080] The positive electrode material obtained in Example 2 was analyzed by X-ray diffraction, and its XRD pattern was obtained as follows: Figure 1 As shown. Figure 1 It can be seen that the doping elements do not change the crystal structure of the material, which is still a pure P2 phase.

[0081] The positive electrode material obtained in Example 2 was analyzed using a scanning electron microscope, and its SEM image was obtained as follows: Figure 2 As shown. Figure 2 It can be seen that the microscopic morphology of the positive electrode material is rounded block-shaped small single crystals with uniform particle distribution.

[0082] According to the steps in Example 1, a button cell was prepared and its performance was tested, and the results were as follows: in the voltage window of 2.2-4.25V, the 0.1C first charge capacity was 118.4mAh / g, the discharge medium voltage was 3.562V, the cycle retention rate was 98.6% after 50 cycles at 45°C, and the discharge medium voltage retention rate was 99.9%.

[0083] Example 3: Positive electrode material Na 0.71 Ni 0.27 Ti 0.14 Mg 0.01 Zr 0.02 Mn 0.56 O2

[0084] The preparation process is consistent with that of Example 1, the main difference being that the remaining raw materials are weighed in a ratio of TiO2:Mg(OH)2:ZrO=0.14:0.01:0.02, and Ti, Mg, and Zr co-doped Na 0.71 Ni 0.27 Ti 0.14 Mg 0.01 Zr 0.02 Mn 0.56 O2.

[0085] According to the steps in Example 1, a button cell was prepared and its performance was tested, and the results were as follows: in the voltage window of 2.2-4.25V, the 0.1C first charge capacity was 117.9mAh / g, the discharge medium voltage was 3.571V, the cycle retention rate was 97.8% after 50 cycles at 45°C, and the discharge medium voltage retention rate was 99.3%.

[0086] Example 4: Positive electrode material Na 0.68 Ni 0.27 Ti 0.07 Mg 0.07 Ca 0.02 Al 0.02 Mn 0.55 O2

[0087] The preparation process is consistent with that of Example 1, the main difference being that the additives are weighed in a ratio of TiO2:Mg(OH)2:CaCO3:Al2O3=0.07:0.07:0.02:0.01, and Ti, Mg, Ca, and Al co-doped Na 0.68 Ni 0.27 Ti 0.07 Mg 0.07 Ca 0.02 Al 0.02 Mn 0.55 O2.

[0088] According to the steps in Example 1, a button cell was prepared and its performance was tested, and the results were as follows: in the voltage window of 2.2-4.25V, the 0.1C first charge capacity was 117.3mAh / g, the discharge medium voltage was 3.549V, the cycle retention rate was 97.0% after 50 cycles at 45°C, and the discharge medium voltage retention rate was 98.8%.

[0089] Comparative Example 1: Positive Electrode Material Na 0.67 Ni 0.29 Ti 0.10 Mg 0.04 Mn 0.57 O2

[0090] The preparation process is the same as that of Example 1, the main difference being that the additives are weighed according to TiO2:MgO=0.10:0.04, and Ti and Mg co-doped Na 0.67 Ni 0.29 Ti 0.10 Mg 0.04 Mn 0.57 O2 was used as comparative example 1.

[0091] According to the steps in Example 1, a button cell was prepared and its performance was tested, and the results were as follows: in the voltage window of 2.2-4.25V, the 0.1C first charge capacity was 115.2mAh / g, the discharge medium voltage was 3.523V, the cycle retention rate was 95.8% after 50 cycles at 45°C, and the discharge medium voltage retention rate was 97.3%.

[0092] Comparative Example 2: Positive Electrode Material Na 0.74 Ni 0.32 Mg 0.04 Fe 0.02 Mn 0.62 O2

[0093] The preparation process is the same as that of Example 1, the main difference being that the additives are weighed according to Mg(OH)2:Fe2O3=0.04:0.01, and Mg and Fe co-doped Na 0.74 Ni 0.32 Mg 0.04 Fe 0.02 Mn 0.62 O2 was used as comparative example 2.

[0094] According to the steps in Example 1, a button cell was prepared and its performance was tested, and the results were as follows: in the voltage window of 2.2-4.25V, the 0.1C first charge capacity was 126.1mAh / g, the discharge medium voltage was 3.499V, the cycle retention rate was 88.7% after 50 cycles at 45°C, and the discharge medium voltage retention rate was 90.1%.

[0095] Comparative Example 3: Positive Electrode Material Na 0.69 Ni 0.30 Ti 0.10 Ca 0.02 Mn 0.58 O2

[0096] The preparation process is the same as that of Example 1, except that the additives are weighed according to TiO2:CaCO3=0.10:0.02, and Ti and Ca co-doped Na 0.69 Ni 0.30 Ti 0.10 Ca 0.02 Mn 0.58 O2 was used as comparative example 3.

[0097] According to the steps in Example 1, a button cell was prepared and its performance was tested, and the results were as follows: in the voltage window of 2.2-4.25V, the 0.1C first charge capacity was 103.8mAh / g, the discharge medium voltage was 3.502V, the cycle retention rate was 91.1% after 50 cycles at 45°C, and the discharge medium voltage retention rate was 94.2%.

[0098] The sodium ion battery positive electrode materials obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were made into sodium ion button batteries according to the above method and relevant characterization tests were carried out. The test results are shown in Table 1; the first charge and discharge curves of Example 2 and Comparative Examples 2 and 3 are shown in Figure 3 The discharge voltage retention rate curves of Example 2 and Comparative Example 1 are shown as follows: Figure 4 As shown; the cycle retention rate curves of Example 2 and Comparative Example 1 are obtained as shown Figure 5 shown.

[0099] Table 1 Summary of electrochemical performance

[0100]

[0101] Depend on Figure 3 It can be seen that there are multiple step-like platforms in the charge and discharge curve of comparative example 2, indicating that the phase change process is complicated and the cycle stability is poor; the charge and discharge curve of comparative example 3 is smoother, but the gram capacity of the first charge is too low; compared with the following embodiment 2, the charge and discharge curve is smoother and has a higher gram capacity.

[0102] Depend on Figure 4 It can be seen that the discharge medium voltage of Example 2 is higher at 3.562V and has no decay after 50 cycles; the discharge medium voltage of Comparative Example 1 is 3.523V, and the retention rate is 97.3% after 50 cycles.

[0103] Depend on Figure 5 It can be seen that the cycle retention rate of comparative example 1 is 95.8% for 50 weeks and the downward trend has not slowed down, and the cycle retention rate of embodiment 2 is 98.6% for 50 weeks and tends to be flat subsequently.

[0104] Figures 3 to 5 The superiority of the coexistence of Ti and Mg and then doping with other M proposed in the present invention is verified. The comparative examples of only Ti and M or Mg and M are not as good as Examples 1 to 4, indicating that when Ti and Mg are within the doping range of the present invention, any regulation of the ratio of the two and M can show higher cycle stability and lower discharge mid-voltage decay.

[0105] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high entropy sodium ion P2 type positive electrode material, characterized in that: The structural formula of the high entropy sodium ion P2 type positive electrode material is Na x Ni y Ti a Mg b M c Mn z O2; wherein M includes one or more of Ca, Al, Sn, B, Fe, Zn and Zr; a+b+c+y+z=1.0; 0.6 <x<0.76;0.2<y<0.35;0.45<z<0.65;a> 0; b>0; c>0.

2. The high entropy sodium ion P2 type positive electrode material according to claim 1, characterized in that 0.02≤a≤0.14; and / or, 0.01≤b≤0.

08.

3. The high entropy sodium ion P2 type positive electrode material according to claim 1, characterized in that 0.65≤x≤0.72; and / or, 0.25≤y≤0.3; and / or, 0.5≤z≤0.6; and / or, 0.05≤a≤0.14; and / or, 0.01≤c≤0.

05.

4. The high entropy sodium ion P2 type positive electrode material according to claim 1, characterized in that 0.68≤x≤0.72; and / or, 0.27≤y≤0.28; and / or, 0.54≤z≤0.56; and / or, 0.07≤a≤0.14; and / or, 0.01≤b≤0.07; and / or, 0.02≤c≤0.

04.

5. The high entropy sodium ion P2 type positive electrode material according to any one of claims 1 to 4, characterized in that: The high entropy sodium ion P2 type positive electrode material is a rounded single crystal particle without sharp corners; And / or, the high entropy sodium ion P2 type positive electrode material D v50 2~12μm.

6. The high entropy sodium ion P2 type positive electrode material according to any one of claims 1 to 5, characterized in that: The specific surface area of ​​the high entropy sodium ion P2 type positive electrode material is 0.4 to 1.2 m 2 ·g -1 .

7. A method for preparing the high entropy sodium ion P2 type positive electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: A sodium source, a nickel source, a titanium source, a magnesium source, a M source and a manganese source are mixed and sintered by a solid phase sintering method to obtain a high entropy sodium ion P2 type positive electrode material.

8. The preparation method according to claim 7, characterized in that: The nickel source is selected from one or more of nickel oxide, nickel chloride, nickel manganese oxide, nickel manganese hydroxide and nickel manganese chloride; The manganese source is selected from one or more of manganese oxide, manganese chloride, nickel manganese oxide, nickel manganese hydroxide and nickel manganese chloride; The sodium source is selected from one or more of sodium carbonate, sodium acetate, sodium oxalate and sodium hydroxide; The titanium source is selected from one or more of titanium oxide, titanium phosphide, titanium hydroxide and titanium carbonate; The iron source is selected from one or more of iron oxides, iron phosphides, iron hydroxides and iron carbonates; The M source is selected from one or more of M oxides, M phosphides, M hydroxides and M carbonates.

9. The preparation method according to claim 7, characterized in that: The calcination temperature is 900°C to 1030°C; And / or, the heating rate of the calcination is 0.5 to 5°C / min; And / or, the calcination time is 6 to 16 hours; And / or, the calcining atmosphere is an oxygen-containing atmosphere.

10. A sodium ion battery, characterized in that: It comprises the high entropy sodium ion P2 type positive electrode material as described in any one of claims 1 to 6 or the high entropy sodium ion P2 type positive electrode material prepared by the preparation method as described in any one of claims 7 to 9.

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