Positive electrode active material and preparation method therefor, positive electrode slurry, positive electrode sheet, sodium-ion battery, and application thereof

Abstract

The present application relates to a positive electrode active material and a preparation method therefor, a positive electrode slurry, a positive electrode sheet, a sodium-ion battery, and an application thereof. The general formula of the positive electrode active material is NayZraTibZncNidFefMneMxO2, where M is one or more selected from V, Co, Al, Nb, Pb, Sb, and Mo; 0.01 ≤ a ≤ 0.05; 0.01 ≤ b ≤ 0.03; 0.01 ≤ c ≤ 0.03; 0 ≤ x ≤ 0.05; 0.7 ≤ y ≤ 0.85; 0 ≤ d ≤ 0.4; 0 ≤ f ≤ 0.4; 0 ≤ e ≤ 0.4; and a + b + c + d + e + f + x = 1. The positive electrode active material employs co-doping of Zr, Ti, and Zn and a synergistic multi-element effect to suppress phase transitions, increase the interlayer spacing of the positive electrode active material, and broaden sodium-ion diffusion channels, thereby enabling excellent cycling stability.

Description

Positive electrode active materials and their preparation methods, positive electrode slurry, positive electrode sheet, sodium-ion battery and its applications

[0001] Related applications

[0002] This application claims priority to Chinese Patent Application No. 2024119551620, filed on December 27, 2024, entitled "Positive Electrode Active Material and Preparation Method Thereof, Positive Electrode Slurry, Positive Electrode Sheet, Sodium-ion Battery and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of electrode materials technology, and in particular to a positive electrode active material and its preparation method, positive electrode slurry, positive electrode sheet, sodium-ion battery and its application. Background Technology

[0004] Lithium-ion batteries are widely used in all aspects of daily life. However, due to the scarcity and uneven distribution of lithium resources, people are forced to look for alternatives to lithium-ion batteries. Sodium-ion batteries have a similar working principle to lithium-ion batteries and are inexpensive and have readily available raw materials, so they have received widespread attention in recent years. However, sodium-ion batteries currently suffer from poor cycle stability, which greatly limits their application. Summary of the Invention

[0005] Therefore, it is necessary to provide a positive electrode active material that can improve cycle stability, its preparation method, positive electrode slurry, positive electrode sheet, sodium-ion battery, and its application.

[0006] One aspect of this application provides a positive electrode active material, the general formula of which is Na. y Zr a Ti b Zn c Ni d Fe f Mn e M x O2, where M is one or more of V, Co, Al, Nb, Pb, Sb and Mo, 0.01≤a≤0.05, 0.01≤b≤0.03, 0.01≤c≤0.03, 0≤x≤0.05, 0.7≤y≤0.85, 0≤d≤0.4, 0≤f≤0.4, 0≤e≤0.4, and a+b+c+d+e+f+x=1.

[0007] The aforementioned cathode active material utilizes Zr, Ti, and Zn co-doping, and the synergistic effect of multiple elements suppresses phase transitions. This prevents irreversible phase transitions or collapse of the crystal structure during sodium ion insertion and extraction, thereby improving the cycle stability of the cathode active material. Furthermore, the synergistic effect of these multiple elements increases the interlayer spacing of the cathode active material, widens the sodium ion diffusion channels, and further enhances the cycle stability, particularly exhibiting excellent cycle stability at high rates. Additionally, the synergistic effect of these multiple elements stabilizes the layered structure of the cathode active material, preventing changes in interlayer spacing and interlayer slippage. Moreover, this application incorporates various different metal elements into the cathode active material, resulting in a highly disordered distribution of these metal elements in the crystal lattice, forming a high-entropy structure. This further strengthens the crystal structure, further suppresses phase transitions, improves ion diffusion dynamics, increases battery capacity, and enhances the thermal stability of the cathode active material. The aforementioned cathode active material also has the advantages of being non-toxic, harmless, and easy to prepare.

[0008] In some embodiments, the positive electrode active material satisfies at least one of the following:

[0009] (1) The discharge plateau position of the positive electrode active material is 2.5V to 3.0V and / or 3.5V to 4.0V;

[0010] (2) The platform capacity of the positive electrode active material accounts for less than or equal to 50% of the total capacity;

[0011] (3) The plateau capacity of the positive electrode active material at a voltage of 3.5V to 4.0V accounts for less than or equal to 30% of the total capacity.

[0012] In some embodiments, the positive electrode active material is a layered oxide.

[0013] In some implementations, 0 <d≤0.4,0<f≤0.4,0<e≤0.4。

[0014] In some embodiments, the structural formula of the positive electrode active material includes

[0015] Na 0.85 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.33 Mn 0.35 O2, Na 0.82 Ti 0.02 Zn 0.01 Zr 0.02 Ni 0.25 Fe 0.33 Mn0.35 Sb 0.02 O2, Na 0.82 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.2 Fe 0.33 Mn 0.37 Al 0.03 O2, Na 0.8 Ti 0.03 Zn 0.02 Zr 0.02 Ni 0.23 Fe 0.33 Mn 0.35 Nb 0.02 O2, Na 0.75 Ti 0.01 Zn 0.03 Zr 0.05 Ni 0.25 Fe 0.31 Mn 0.35 O2 and Na 0.75 Ti 0.01 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.32 Mn 0.35 Sb 0.02 At least one of O2.

[0016] In some embodiments, the positive electrode active material comprises a sodium layer and a transition metal layer, wherein the interlayer spacing of the sodium layer is [missing information]. And / or, the interlayer spacing of the transition metal layer is

[0017] In some embodiments, the lattice parameter a of the positive electrode active material is And / or, the lattice parameter c is

[0018] In some embodiments, the median particle size D50 of the positive electrode active material is 5 μm to 10 μm.

[0019] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.4 m². 2 / g~0.8m 2 / g.

[0020] In some embodiments, the positive electrode active material satisfies at least one of the following conditions:

[0021] (1) The positive electrode active material is a P2 / O3 mixed phase structure;

[0022] (2) The mass content of the P2 phase in the positive electrode active material is 5% to 30%;

[0023] (3) The mass content of O3 phase in the positive electrode active material is 70% to 95%.

[0024] In some embodiments, the positive electrode active material satisfies at least one of the following conditions:

[0025] (1) The 2θ of the highest intensity peak in the XRD pattern is 14° to 16°;

[0026] (2) The 2θ of the second intensity peak in the XRD pattern is 40° to 45°;

[0027] (3) The peak half width at half maximum (FWHM) corresponding to the (003) crystal plane in the XRD pattern is 0.05°~0.5°.

[0028] A second aspect of this application provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0029] According to the stoichiometric molar ratio of the positive electrode active material, a sodium source, optional iron source, optional manganese source, optional nickel source, titanium source, zirconium source, zinc source and optional metal M source are dissolved in a solvent and blended to obtain a mixed solution.

[0030] The mixture was heated to obtain a mixed gel;

[0031] The mixed gel is dried to obtain the positive electrode active material.

[0032] In some embodiments, the method for preparing the positive electrode active material satisfies at least one of the following:

[0033] (1) The sodium source includes at least one of sodium dihydrogen carbonate, sodium carbonate, sodium acetate and sodium citrate;

[0034] (2) The iron source includes ferric nitrate;

[0035] (3) The manganese source includes at least one of manganese acetate and manganese nitrate;

[0036] (4) The nickel source includes at least one of nickel nitrate and nickel acetate;

[0037] (5) The titanium source includes at least one of titanium dioxide and titanium nitrate;

[0038] (6) The zirconium source includes at least one of zirconium oxide and zirconium nitrate;

[0039] (7) The zinc source includes at least one of zinc acetate and zinc nitrate;

[0040] (8) The metal M source is at least one of acetate, nitrate and oxide containing metal M;

[0041] (9) The complexing agent includes citric acid.

[0042] In some embodiments, the heating temperature of the heat treatment is 60°C to 110°C; and / or, the drying temperature of the drying treatment is 80°C to 130°C, and the drying time of the drying treatment is 5h to 15h.

[0043] In some embodiments, a calcination step is further included after the heat treatment, the calcination comprising the following steps:

[0044] The dried mixed gel was heated to 500℃~600℃ at a heating rate of 3℃ / min~8℃ / min and then calcined for 3h~7h.

[0045] The calcined mixed gel was heated to 850℃~950℃ at a heating rate of 3℃ / min~8℃ / min and then held at that temperature for 10h~15h to obtain the positive electrode active material.

[0046] A third aspect of this application provides a positive electrode slurry, comprising the positive electrode active material as described in the first aspect and the positive electrode active material prepared by the preparation method described in the second aspect.

[0047] In some embodiments, the positive electrode slurry includes the positive electrode material, a conductive agent, a binder, and a solvent.

[0048] In some embodiments, the positive electrode slurry satisfies at least one of the following conditions:

[0049] (1) The mass ratio of the positive electrode material, the conductive agent, and the binder is 0.8–0.9: 0.03–0.2: 0.03–0.2;

[0050] (2) The conductive agent includes at least one of Super P, graphene, carbon dots, CNT and Ketjen Black;

[0051] (3) The adhesive includes at least one of difluoroethylene, polyvinylidene fluoride and tetrafluoroethylene-hexafluoropropylene copolymer;

[0052] (4) The solid content of the positive electrode slurry is 50% to 60%.

[0053] A fourth aspect of this application provides a conductive coating comprising the positive electrode active material, conductive agent, and binder as described in the first aspect; or, the conductive coating is prepared using the positive electrode slurry as described in the third aspect.

[0054] A fifth aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive active layer, the positive active layer being disposed on at least one side of the positive current collector, the positive active layer comprising the positive active material as described in the first aspect; or the positive active layer being made from the positive slurry as described in the third aspect.

[0055] In some embodiments, the positive electrode sheet satisfies at least one of the following conditions:

[0056] (1) The thickness of the positive electrode sheet is 0.2 mm to 0.3 mm;

[0057] (2) The compaction density of the positive electrode sheet is 1.5 g / cm³. 3 ~3.0g / cm 3 .

[0058] A sixth aspect of this application provides a sodium-ion battery, including a positive electrode as described in the fifth aspect.

[0059] A seventh aspect of this application provides an electrical device including a sodium-ion battery as described in the sixth aspect. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the disclosed drawings without creative effort.

[0061] Figure 1 shows the capacity differential curve of the battery prepared in Example 1 within a voltage window of 2-4V.

[0062] Figure 2 shows the charge-discharge curves of the battery prepared in Example 1 at 1C within a 2-4V voltage window.

[0063] Figure 3 shows the capacity differential curve of the battery prepared in Example 2 within a voltage window of 2-4.2V.

[0064] Figure 4 shows the charge-discharge curves of the battery prepared in Example 2 within a voltage window of 2-4.2V.

[0065] Figure 5 shows the 2C cycle curve of the battery prepared in Example 3 under a voltage window of 2-4V.

[0066] Figure 6 shows the cycling curve of the battery prepared in Comparative Example 1 within a voltage window of 2-4V. Detailed Implementation

[0067] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0068] During charging, sodium ions are extracted from the positive electrode active material, migrate through the electrolyte to the negative electrode, and embed themselves in the negative electrode material. Simultaneously, electrons flow from the positive electrode to the negative electrode via the external circuit to maintain charge balance. During discharging, the process is reversed: sodium ions are extracted from the negative electrode, re-embedded in the positive electrode via the electrolyte, and electrons flow from the negative electrode to the positive electrode via the external circuit, thus forming an electric current to provide power to the external circuit. During cyclic charging and discharging, the electrode materials of sodium-ion batteries may undergo structural phase changes, particle breakage, or pulverization, leading to decreased interfacial stability between the electrode and the electrolyte and affecting cycle stability.

[0069] Based on this, one embodiment of this application provides a positive electrode active material, wherein the general formula of the positive electrode active material is Na. y Zr a Ti b Zn c Ni d Fe f Mn e M x O2, where M is one or more of V, Co, Al, Nb, Pb, Sb and Mo, 0.01≤a≤0.05, 0.01≤b≤0.03, 0.01≤c≤0.03, 0≤x≤0.05, 0.7≤y≤0.85, 0≤d≤0.4, 0≤f≤0.4, 0≤e≤0.4, and a+b+c+d+e+f+x=1.

[0070] The aforementioned cathode active material utilizes Zr, Ti, and Zn co-doping, and the synergistic effect of multiple elements suppresses phase transitions. This prevents irreversible phase transitions or collapse of the crystal structure during sodium ion insertion and extraction, thereby improving the cycle stability of the cathode active material. Furthermore, the synergistic effect of these multiple elements increases the interlayer spacing of the cathode active material, widens the sodium ion diffusion channels, and further enhances the cycle stability, particularly exhibiting excellent cycle stability at high rates. Additionally, the synergistic effect of these multiple elements stabilizes the layered structure of the cathode active material, preventing changes in interlayer spacing and interlayer slippage. Moreover, this application incorporates various different metal elements into the cathode active material, resulting in a highly disordered distribution of these metal elements in the crystal lattice, forming a high-entropy structure. This further strengthens the crystal structure, further suppresses phase transitions, improves ion diffusion dynamics, increases battery capacity, and enhances the thermal stability of the cathode active material. The aforementioned cathode active material also has the advantages of being non-toxic, harmless, and easy to prepare.

[0071] As an example, 'a' can be 0.01, 0.02, 0.03, 0.04, and 0.05, or it can be any two of the above values ​​used as endpoints. 'a' is preferably between 0.02 and 0.03.

[0072] As an example, b can be 0.01, 0.02, and 0.03, or it can be any two of the above point values ​​within the range of endpoints. b is preferably 0.01 to 0.02.

[0073] c can be 0.01, 0.02, or 0.03, or any two of the above values ​​as endpoints. c is preferably 0.02.

[0074] x can be 0, 0.01, 0.02, 0.03, 0.04, and 0.05, or any two of the above values ​​as endpoints. x is preferably 0.02 to 0.04.

[0075] y can be 0.7, 0.75, 0.8, 0.82, 0.83, and 0.85, or any two of the above values ​​as endpoints. y is preferably between 0.75 and 0.83.

[0076] d can be 0, 0.1, 0.2, 0.3, 0.4, or any two of the above values ​​as endpoints. d is preferably between 0.2 and 0.33.

[0077] f can be 0, 0.1, 0.2, 0.3, 0.4, or any two of the above values ​​as endpoints. f is preferably between 0.25 and 0.33.

[0078] e can be 0, 0.1, 0.2, 0.3, 0.4, or any two of the above values ​​as endpoints. e is preferably 0.3 to 0.37.

[0079] M preferably contains Nb, Sb, and Al.

[0080] In some implementations, 0 <d≤0.4,0<f≤0.4,0<e≤0.4。

[0081] In some embodiments, the structural formula of the positive electrode active material includes Na. 0.85 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.33 Mn 0.35 O2, Na 0.82 Ti 0.02 Zn 0.01 Zr 0.02 Ni 0.25 Fe 0.33 Mn 0.35 Sb 0.02 O2, Na 0.82 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.2 Fe 0.33 Mn 0.37 Al 0.03 O2, Na 0.8 Ti 0.03 Zn 0.02 Zr 0.02 Ni 0.23 Fe 0.33 Mn 0.35 Nb 0.02 O2, Na 0.75 Ti 0.01 Zn 0.03 Zr 0.05 Ni 0.25 Fe 0.31 Mn 0.35 O2 and Na 0.75 Ti 0.01 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.32 Mn 0.35 Sb 0.02 At least one of O2.

[0082] In some embodiments, the discharge plateau of the positive electrode active material is located at 2.5V–3.0V and / or 3.5V–4.0V. The positive electrode active material has fewer plateaus, with only one or two, resulting in fewer phase transitions and improved cycle stability.

[0083] In some embodiments, the platform capacity of the positive electrode active material accounts for less than or equal to 50% of the total capacity. A low platform capacity ratio of the positive electrode active material indicates a smaller phase transition and higher stability.

[0084] Furthermore, the platform capacity of the positive electrode active material accounts for 20% to 50% of the total capacity.

[0085] Furthermore, the plateau capacity of the positive electrode active material accounts for 20% to 40% of the total capacity. Within this range, the plateau capacity further reduces phase transition and improves the cycle stability of the positive electrode active material.

[0086] In some embodiments, the positive electrode active material has a platform capacity of less than or equal to 30% of the total capacity at a voltage of 3.5V to 4.0V.

[0087] Furthermore, the positive electrode active material has a plateau capacity accounting for 20% to 30% of the total capacity at a voltage of 3.5V to 4.0V.

[0088] In some embodiments, the plateau capacity of the positive electrode active material accounts for less than or equal to 50% of the total capacity, and the plateau capacity of the positive electrode active material at a voltage of 3.5V to 4.0V accounts for less than or equal to 30% of the total capacity. The low plateau capacity ratio of the positive electrode active material, especially at high voltage, reduces phase transition and thus improves cycle stability.

[0089] In some embodiments, the discharge plateau positions of the positive electrode active material are 2.5V–3.0V and 3.5V–4.0V, the plateau capacity of the positive electrode active material accounts for less than or equal to 50% of the total capacity, and the plateau capacity at 3.5V–4.0V accounts for less than or equal to 30% of the total capacity. The positive electrode active material has few charge / discharge plateaus, a low plateau capacity ratio, and minimal phase transitions, thereby improving cycle stability.

[0090] In some embodiments, the positive electrode active material is a layered oxide.

[0091] The aforementioned cathode active material utilizes Zr, Ti, and Zn co-doping to form a high-entropy sodium ion layered oxide. The synergistic effect of multiple elements suppresses phase transitions, making the crystal structure of the high-entropy sodium ion layered oxide less prone to irreversible phase transitions or collapse during sodium ion insertion and extraction, thereby improving the cycle stability of the cathode active material. In addition, the synergistic effect of the aforementioned multiple elements increases the interlayer spacing of the high-entropy sodium ion layered oxide, widens the sodium ion diffusion channels, and further improves the cycle stability of the cathode active material, enabling it to exhibit excellent cycle stability under high-rate conditions.

[0092] In some embodiments, the positive electrode active material comprises a sodium layer and a transition metal layer, wherein the interlayer spacing of the sodium layer is [missing information].

[0093] As an example, the interlayer spacing of the sodium layer can be and It can also be within the range formed by any two of the above point values ​​as endpoints. The interlayer spacing of the sodium layer is preferably...

[0094] Understandably, the layered structure of the positive electrode active material is composed of transition metal layers and sodium layers arranged crosswise along the c-axis direction; the transition metal layers are formed by interconnected MO6 octahedral units sharing edges, while sodium ions are located between the transition metal layers.

[0095] In some embodiments, the positive electrode active material comprises a sodium layer and a transition metal layer, wherein the interlayer spacing of the transition metal layer is [missing information].

[0096] As an example, the interlayer spacing of the transition metal layer can be and It can also be within the range formed by any two of the above point values ​​as endpoints. The interlayer spacing of the transition metal layer is preferably...

[0097] In some embodiments, the positive electrode active material comprises a sodium layer and a transition metal layer, wherein the interlayer spacing of the sodium layer is [missing information]. And / or, the interlayer spacing of the transition metal layer is The positive electrode active material can maintain structural stability under this interlayer spacing and is not prone to irreversible phase transition. At the same time, it is also conducive to sodium ion diffusion, which further improves the cycle stability of the positive electrode active material under high rate conditions and extends the cycle life.

[0098] In some embodiments, XRD tests are performed on the positive electrode active material, and data refinement is performed using GSAS software to obtain the interlayer spacing of the sodium layer and the interlayer spacing of the transition metal layer.

[0099] In some embodiments, the lattice parameter a of the positive electrode active material is In some embodiments, the lattice parameter c of the positive electrode active material is:

[0100] In some embodiments, the lattice parameter a of the positive electrode active material is The lattice parameter c of the positive electrode active material is: Positive electrode active materials with this cell edge length characteristic are more conducive to sodium ion diffusion, thereby further improving the battery's capacity, cycle stability, and rate performance.

[0101] In some embodiments, the median particle size D50 of the positive electrode active material is 5 μm to 15 μm.

[0102] As an example, the median particle size of the positive electrode active material can be 5μm, 5.5μm, 5.9μm, 6μm, 6.3μm, 6.5μm, 7μm, 7.2μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 9.6μm, 10μm, 11μm, 12μm, 13μm, 14μm, and 15μm, or it can be within the range formed by any two of the above point values ​​as end values.

[0103] Furthermore, the median particle size D50 of the positive electrode active material is 5 μm to 10 μm. At this median particle size, the diffusion path of sodium ions in the active material is shortened, accelerating the diffusion rate and resulting in higher battery charge-discharge efficiency. Moreover, at this median particle size, the volume change of the positive electrode active material during charge-discharge is relatively uniform, reducing particle breakage, pulverization, and structural damage caused by volume expansion and contraction, thereby further improving cycle stability and extending service life.

[0104] Furthermore, the median particle size of the positive electrode active material is 5 μm to 8.0 μm. Batteries with this median particle size exhibit higher capacity retention after 300 cycles.

[0105] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g~0.8m 2 / g.

[0106] As an example, the specific surface area of ​​the positive electrode active material can be 0.2 m². 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g and 0.8m 2 / g can also be any two of the above point values ​​as endpoints within the range.

[0107] The specific surface area of ​​the positive electrode active material is preferably 0.4 m². 2 / g~0.8m 2 / g.

[0108] At this specific surface area, the number of active sites on the surface of the positive electrode active material increases, and the exchange interface between the electrode and the electrolyte increases, making the transport of sodium ions easier and faster, thereby further improving the charge and discharge efficiency and rate performance of the battery. Moreover, at this specific surface area, the utilization rate of the positive electrode active material can be improved, the battery capacity can be increased, and the cycle stability can be further improved.

[0109] The specific surface area of ​​the positive electrode active material is preferably 0.5 m². 2 / g~0.6m 2 / g. At this specific surface area, the battery retains a higher capacity after 300 cycles.

[0110] In some embodiments, the positive electrode active material exhibits a plate-like polycrystalline morphology.

[0111] In some embodiments, the positive electrode active material is a P2 / O3 mixed-phase structure. The P2 / O3 mixed-phase structure retains the interlayer channels of the P2 phase that facilitate sodium ion diffusion, while also possessing the structural stability of the O3 phase, enabling the material to better balance lithium ion diffusion and structural stability during charging and discharging.

[0112] In some embodiments, the mass content of the P2 phase in the positive electrode active material is 5% to 30%. Preferably, the mass content of the P2 phase in the positive electrode active material is 10% to 25%.

[0113] In some embodiments, the O3 phase in the positive electrode active material has a mass content of 70% to 95%. Preferably, the O3 phase content in the positive electrode active material is 75% to 90%.

[0114] In some embodiments, the mass content of the P2 phase in the positive electrode active material is 5% to 30%, and the mass content of the O3 phase in the positive electrode active material is 70% to 95%. The positive electrode active material structure with these mass content ratios of P2 and O3 phases effectively balances the diffusion of sodium ions with structural stability, further enhancing the cycle stability of the positive electrode active material.

[0115] In some embodiments, the positive electrode active material has a 2θ of 14° to 16° as the peak intensity in its XRD pattern.

[0116] In some embodiments, the positive electrode active material has a 2θ of 40° to 45° in the intensity of the second peak in the XRD pattern.

[0117] In some embodiments, the peak half-width of the (003) crystal plane in the XRD pattern of the positive electrode active material is 0.05° to 0.5°.

[0118] A second aspect of this application provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0119] According to the stoichiometric molar ratio of the positive electrode active material, a sodium source, optional iron source, optional manganese source, optional nickel source, titanium source, zirconium source, zinc source and optional metal M source are dissolved in a solvent and blended to obtain a mixed solution.

[0120] The mixture was heated to obtain a mixed gel;

[0121] The mixed gel is dried to obtain the positive electrode active material.

[0122] Understandably, the "optional" in "optional iron source," "optional manganese source," "optional nickel source," and "optional metal M source" means that they can be added or not, depending on the general formula Na. y Zr a Ti b Zn c Ni d Fe f Mn e M x If the corresponding index in O2 is 0, then it is not added.

[0123] The above preparation method adopts a sol-gel mixing method, which makes the raw materials fully mixed, resulting in a more uniform and orderly distribution of metals, forming a high-entropy material. This makes it less likely for the positive electrode active material to undergo phase separation or form intermetallic compounds, thereby improving the capacitance and cycle stability of the positive electrode active material.

[0124] In some embodiments, the sodium source includes at least one of sodium dihydrogen carbonate, sodium carbonate, sodium acetate, and sodium citrate.

[0125] In some embodiments, the iron source includes ferric nitrate.

[0126] In some embodiments, the manganese source includes at least one of manganese acetate and manganese nitrate.

[0127] In some embodiments, the nickel source includes at least one of nickel nitrate and nickel acetate.

[0128] In some embodiments, the titanium source includes at least one of titanium dioxide and titanium nitrate.

[0129] In some embodiments, the zirconium source includes at least one of zirconium oxide and zirconium nitrate.

[0130] In some embodiments, the zinc source includes at least one of zinc acetate and zinc nitrate.

[0131] In some embodiments, the metal M source is at least one of an acetate, nitrate, and oxide containing metal M.

[0132] In some embodiments, the complexing agent includes citric acid.

[0133] In some embodiments, the heating temperature of the heat treatment is 60°C to 110°C. Preferably, the heating temperature of the heat treatment is 80°C to 100°C.

[0134] In some embodiments, the drying temperature of the drying process is 80°C to 130°C, and the drying time is 5 hours to 15 hours. Preferably, the drying temperature is 90°C to 120°C, and the drying time is 10 hours to 12 hours.

[0135] In some embodiments, a calcination step is further included after the heat treatment, the calcination comprising the following steps:

[0136] The dried mixed gel was heated to 500℃~600℃ at a heating rate of 3℃ / min~8℃ / min and then calcined for 3h~7h.

[0137] The calcined mixed gel was heated to 850℃~950℃ at a heating rate of 3℃ / min~8℃ / min and then held at that temperature for 10h~15h to obtain the positive electrode active material.

[0138] In some embodiments, the drying temperature is 90℃~120℃, and the drying time is 10h~12h. Then, the dried mixed gel is heated to 500℃~600℃ at a heating rate of 3℃ / min~8℃ / min and calcined for 3h~7h. Next, the calcined mixed gel is heated to 900℃~950℃ at a heating rate of 3℃ / min~8℃ / min and held at this temperature for 10h~15h to obtain the positive electrode active material. The positive electrode active material prepared under these temperature conditions has a more stable structure, better electrochemical performance, and a higher capacity retention rate in the corresponding battery.

[0139] In some of these implementations, according to Na y Zr a Ti b Zn c Ni d Fe f Mn e M x In the stoichiometric ratio of O2, sodium, iron, manganese, nickel, titanium, zirconium, zinc and metal M sources are added, along with a complexing agent. The mixture is dissolved in a solvent and stirred at room temperature for 0.5 hours to fully mix. Then, it is transferred to an oil bath for stirring and heating. The solvent is evaporated to obtain a mixed gel. The mixed gel is then transferred to an oven to dry overnight, ground, and then transferred to a muffle furnace for calcination.

[0140] A third aspect of this application provides a positive electrode slurry, comprising the positive electrode active material as described in the first aspect and the positive electrode active material prepared by the preparation method described in the second aspect.

[0141] In some embodiments, the positive electrode slurry includes the positive electrode active material, a conductive agent, a binder, and a solvent.

[0142] Furthermore, the solvent can be NMP (N-methyl-2-pyrrolidone).

[0143] In some embodiments, the mass ratio of the positive electrode material, the conductive agent, and the binder is 0.8–0.9: 0.03–0.2: 0.03–0.2.

[0144] In some embodiments, the solid content of the positive electrode slurry is 50% to 60%.

[0145] In some embodiments, the conductive agent includes at least one of Super P, graphene, carbon dots, CNTs, and Ketjen black. Super P is small-particle conductive carbon black; CNTs are carbon nanotubes.

[0146] In some embodiments, the adhesive includes at least one of difluoroethylene, polyvinylidene fluoride, and tetrafluoroethylene-hexafluoropropylene copolymer.

[0147] In some embodiments, the positive electrode slurry is prepared by mixing the positive electrode active material, conductive agent and binder uniformly in a solvent.

[0148] A fourth aspect of this application provides a conductive coating comprising the positive electrode active material, conductive agent, and binder as described in the first aspect; or, the conductive coating is prepared using the positive electrode slurry as described in the third aspect.

[0149] A fifth aspect of this application provides a positive electrode sheet, comprising a positive current collector and a positive active layer, the positive active layer being disposed on at least one side of the positive current collector, the positive active layer comprising the positive active material as described in the first aspect; or the positive active layer being made from the positive slurry as described in the third aspect.

[0150] In some embodiments, the positive electrode sheet is prepared by uniformly coating a positive electrode slurry onto at least one side of a positive electrode current collector, drying it to form a positive electrode active layer, and thus obtaining a positive electrode sheet.

[0151] In some embodiments, the mass percentage of the positive electrode material in the positive electrode active layer is 80% to 90%.

[0152] In some embodiments, the mass percentage of the conductive agent in the positive electrode active layer is 3% to 20%.

[0153] In some embodiments, the binder content in the positive electrode active layer is 3% to 20% by mass.

[0154] Furthermore, the drying temperature is 80℃~130℃, and the drying time is 5h~13h.

[0155] Furthermore, the positive current collector uses aluminum foil.

[0156] Furthermore, the drying equipment uses an oven.

[0157] In some embodiments, the areal density of the positive electrode active layer on one side is 2 mg / cm³. 2 ~8mg / cm 2 .

[0158] In some embodiments, the thickness of the positive electrode sheet is 0.2 mm to 0.3 mm. This thickness refers to the overall thickness of the positive electrode sheet encompassing the positive active layer and the positive current collector.

[0159] In some embodiments, the compaction density of the positive electrode sheet is 1.5 g / cm³. 3 ~3.0g / cm 3 .

[0160] A fifth aspect of this application provides a sodium-ion battery, including a positive electrode as described in the fourth aspect.

[0161] Sodium-ion batteries also include a negative electrode, which is arranged opposite to the positive electrode.

[0162] Furthermore, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector.

[0163] Copper foil can be used as the negative electrode current collector.

[0164] The negative electrode active layer includes negative electrode active material, binder and conductive agent.

[0165] Furthermore, in the negative electrode active layer, the mass percentage of the negative electrode active material is 90% to 96%.

[0166] Furthermore, in the negative electrode active layer, the mass percentage of the binder is 0.1% to 6%.

[0167] Furthermore, the mass percentage of the conductive agent in the negative electrode active layer is 1% to 8%.

[0168] In some embodiments, the negative electrode active material may be at least one of hard carbon, soft carbon, sodium titanate, and antimony trisulfide.

[0169] In some embodiments, the binder in the negative electrode active layer may be at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, and polyamide.

[0170] In some embodiments, the conductive agent in the negative electrode active layer may be at least one of conductive carbon black, Ketjen black, acetylene black, and graphene.

[0171] In some embodiments, the sodium-ion battery also includes an electrolyte, which comprises an electrolyte salt and a solvent.

[0172] As an example, a 1M NaClO4EC:DEC ratio of 1:1 is used, meaning that the concentration of the electrolyte salt in the mixed solvent of EC and DEC is 1M, and the volume ratio of EC to DEC is 1:1.

[0173] A sixth aspect of this application provides an electrical device comprising a sodium-ion battery as described in the fifth aspect.

[0174] Electrical devices include, but are not limited to, watches, wireless earphones, digital products, smart cards, remote controls, automotive parts, and electronic products.

[0175] The following are specific examples.

[0176] Example 1

[0177] This embodiment provides a positive electrode active material with the structural formula Na. 0.85 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.33 Mn 0.35 O2.

[0178] The preparation method of the positive electrode active material in this embodiment is as follows: sodium acetate is used as the sodium source, titanium dioxide as the titanium source, zinc acetate as the zinc source, zirconium nitrate as the zirconium source, nickel acetate and manganese acetate as the nickel and manganese sources respectively, and ferric nitrate as the iron source. These are added to deionized water according to stoichiometric ratios, with citric acid as the complexing agent. The mixture is heated in an 80°C water bath until the deionized water is completely evaporated. It is then transferred to a 120°C oven for drying for 12 hours. After grinding, it is transferred to a muffle furnace and sintered at 500°C for 5 hours and then at 930°C for 12 hours, with a heating rate of 5°C / min. After calcination, Na is obtained. 0.85 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.33 Mn 0.35 O2 black powder.

[0179] The positive electrode preparation method in this embodiment is as follows: The above-mentioned positive electrode active material, conductive agent Super P, and binder PVDF are weighed in a mass ratio of 8:1:1. The PVDF is pre-prepared as a 4% (w / w) NMP solution. The positive electrode active material, Super P, and PVDF are mixed to obtain a positive electrode slurry. A small amount of NMP is added to achieve a solid content of 55%. The positive electrode slurry is then uniformly coated onto aluminum foil, with an areal density of 3.0 mg / cm³. 2 After drying and cold pressing, the positive electrode sheet is obtained.

[0180] Example 2

[0181] This embodiment provides a positive electrode active material with the structural formula Na. 0.8 Ti 0.03 Zn 0.02 Zr 0.02 Ni 0.23 Fe 0.33 Mn 0.35 Nb 0.02 O2.

[0182] The preparation method of the positive electrode active material in this embodiment is as follows: sodium acetate is used as the sodium source, titanium dioxide as the titanium source, zinc acetate as the zinc source, zirconium nitrate as the zirconium source, nickel acetate and manganese acetate as the nickel and manganese sources respectively, ferric nitrate as the iron source, and niobium pentoxide as the niobium source. These are added to deionized water according to the stoichiometric ratio, with citric acid as the complexing agent. The mixture is heated in an oil bath at 100°C until the deionized water is completely evaporated. It is then transferred to a 90°C oven for drying for 12 hours. After grinding, it is transferred to a muffle furnace and sintered at 600°C for 3 hours and then at 950°C for 10 hours, with a heating rate of 5°C / min. After calcination, Na is obtained. 0.8 Ti 0.03 Zn 0.02 Zr 0.02Ni 0.23 Fe 0.33 Mn 0.35 Nb 0.02 O2 black powder.

[0183] The positive electrode preparation method in this embodiment is as follows: The above-mentioned positive electrode active material, conductive agent acetylene black, and binder PVDF are weighed according to a mass ratio of 9:0.5:0.5. The PVDF is pre-prepared as a 4% (w / w) NMP solution. The positive electrode active material, acetylene black, and PVDF are mixed to obtain a positive electrode slurry. A small amount of NMP is added to achieve a solid content of 55%. The positive electrode slurry is then uniformly coated onto aluminum foil, with an areal density of 3.0 mg / cm³. 2 After drying and cold pressing, the positive electrode sheet is obtained.

[0184] Example 3

[0185] This embodiment provides a positive electrode active material with the structural formula Na. 0.75 Ti 0.01 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.32 Mn 0.35 Sb 0.02 O2.

[0186] The preparation method of the positive electrode active material in this embodiment is as follows: sodium acetate is used as the sodium source, titanium nitrate as the titanium source, zinc acetate as the zinc source, zirconium nitrate as the zirconium source, nickel nitrate and manganese nitrate as the nickel and manganese sources respectively, ferric nitrate as the iron source, and antimony trioxide as the antimony source. These are added to deionized water according to the stoichiometric ratio, with citric acid as the complexing agent. The mixture is heated in an oil bath at 100°C until the deionized water is completely evaporated. It is then transferred to a 100°C oven for drying for 10 hours. After grinding, it is transferred to a muffle furnace and sintered at 500°C for 5 hours and then at 900°C for 15 hours, with a heating rate of 5°C / min. After calcination, Na is obtained. 0.75 Ti 0.01 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.32 Mn 0.35 Sb 0.02 O2 black powder.

[0187] The positive electrode preparation method in this embodiment is as follows: The above-mentioned positive electrode active material, conductive agent Super P, and binder PVDF are weighed according to a mass ratio of 0.85:0.15:0.05. The PVDF is pre-prepared as a 4% (w / w) NMP solution. The positive electrode active material, Super P, and PVDF are mixed to obtain a positive electrode slurry. A small amount of NMP is added to achieve a solid content of 55%. The positive electrode slurry is then uniformly coated onto aluminum foil, with an areal density of 3.0 mg / cm³. 2 After drying and cold pressing, the positive electrode sheet is obtained.

[0188] Example 4

[0189] Example 4 is basically the same as Example 1, except that the median particle size D50 of the cathode material is 15 μm. It was prepared using the same proportions and sintering method as Example 1, and with a precursor material having a particle size D50 of 12 μm or larger.

[0190] Example 5

[0191] Example 5 is basically the same as Example 1, except that the specific surface area of ​​the positive electrode material is 0.25 m². 2 / g. Increasing the sintering temperature to 1000℃ and extending the sintering time to 20h results in larger grains and a reduced specific surface area.

[0192] Comparative Example 1

[0193] Comparative Example 1 provides a positive electrode active material with the structural formula NaNi. 0.5 Mn 0.5 O2.

[0194] Comparative Example 1: The preparation method of the positive electrode active material is as follows: Sodium acetate is used as the sodium source, and nickel nitrate and manganese nitrate are used as the nickel and manganese sources, respectively. They are added to deionized water according to the stoichiometric ratio. Citric acid is used as the complexing agent. The mixture is heated in an oil bath at 100°C until the deionized water is completely evaporated. It is then transferred to an oven at 100°C and dried for 10 hours. After grinding, it is transferred to a muffle furnace and sintered at 500°C for 5 hours and then at 900°C for 15 hours. The heating rate is 5°C / min. After calcination, NaNi is obtained. 0.5 Mn 0.5 O2 black powder.

[0195] The preparation method of the positive electrode sheet of Comparative Example 1 is as follows: The positive active material, conductive agent Super P, and binder PVDF prepared in Comparative Example 1 are weighed in a mass ratio of 8:1:1. The PVDF is pre-prepared as a 4% (w / w) NMP solution. The positive active material, Super P, and PVDF are mixed to obtain a positive electrode slurry. A small amount of NMP is added to achieve a solid content of 55%. The positive electrode slurry is then uniformly coated onto aluminum foil, with an areal density of 3.0 mg / cm³. 2 After drying and cold pressing, the positive electrode sheet is obtained.

[0196] Comparative Example 2

[0197] Comparative Example 2 is basically the same as Example 1, except that the zirconium source is omitted in the preparation of the positive electrode active material.

[0198] Comparative Example 3

[0199] Comparative Example 3 is basically the same as Example 1, except that the titanium source is omitted in the preparation of the positive electrode active material.

[0200] Comparative Example 4

[0201] Comparative Example 4 is basically the same as Example 1, except that the zinc source is omitted in the preparation of the positive electrode active material.

[0202] The physicochemical and electrical properties of the positive electrode active materials prepared in Examples 1-5 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1 below. The positive electrode sheets prepared in Examples 1-5 and Comparative Examples 1-4 were assembled with a sodium metal negative electrode to create 2032 type button half-cells. After the assembled button cells were left to stand for 12 hours, they were transferred to a LAND tester for performance testing. Charge-discharge cycle tests were performed at voltage windows of 2-4V and 2-4.2V. Capacitance differential curves were plotted using the second charge-discharge curve, or the cells were activated once and then transferred to an electrochemical workstation for CV (capacitance-voltage) testing. The test results are shown in Table 2 below.

[0203] The test conditions or standards for each performance test item are as follows:

[0204] Specific surface area: The specific surface area is calculated using the BET equation by measuring the amount of adsorption under different relative pressures. The BET method typically uses nitrogen as the adsorbate, and physical adsorption occurs at liquid nitrogen temperature. The specific surface area is calculated by measuring the adsorption isotherm.

[0205] Specific capacity at 0.2C:

[0206] a. Let stand for 2 minutes;

[0207] b. Constant current discharge: Discharge to the limit voltage with a current of 0.2C (calculated according to the theoretical capacity);

[0208] c. Let stand for 10 minutes;

[0209] d. Constant current and constant voltage charging: current 0.2C, charging to the cutoff voltage, cutoff current 0.05C;

[0210] e. Let stand for 10 minutes;

[0211] f. Constant current discharge: Current 0.2C, discharge to the limiting voltage;

[0212] The gc~f cycle repeats 3 times;

[0213] h. Take the average discharge capacity of the three steps f as the battery capacity.

[0214] 2C specific capacity:

[0215] a. Let stand for 2 minutes;

[0216] b. Constant current discharge: Discharge to the limit voltage with a current of 0.2C (calculated according to the theoretical capacity);

[0217] c. Let stand for 10 minutes;

[0218] d. Constant current and constant voltage charging: current 2C, charging to the cutoff voltage, cutoff current 0.05C;

[0219] e. Let stand for 10 minutes;

[0220] f. Constant current discharge: Discharge at a current of 2C until the limiting voltage is reached;

[0221] The gc~f cycle repeats 3 times;

[0222] h. Take the average discharge capacity of the three steps f as the battery capacity.

[0223] Table 1

[0224] Table 2

[0225] As can be seen from Tables 1 and 2 above, the positive electrode active materials of Examples 1 to 5 utilize the synergistic effect of multiple elements to suppress phase transitions, and the high-entropy structure formed by multiple metal elements in the crystal lattice further strengthens the crystal structure and further suppresses phase transitions, resulting in a capacity retention rate of up to 99.8% after 300 cycles and improving cycle stability. However, as can be seen from Comparative Examples 1 to 4, the lack of any of the metal elements Zr, Ti, and Zn cannot achieve the technical effect of this application.

[0226] The capacity differential curve of the battery prepared in Example 1 within the 2-4V voltage window is shown in Figure 1, with a plateau capacity voltage range of 2.6V to 2.9V and a discharge plateau position of 2.82V. The charge-discharge curve of the battery prepared in Example 1 within the 2-4V voltage window at 1C is shown in Figure 2. The capacity differential curve of the battery prepared in Example 2 within the 2-4.2V voltage window is shown in Figure 3, with a plateau capacity voltage range of 3.5V to 4.0V and a discharge plateau position of 3.68V. The charge-discharge curve of the battery prepared in Example 2 within the 2-4.2V voltage window is shown in Figure 4, with a discharge capacity of approximately 40mAh / g in the 3.5V to 4.0V voltage range. The 2C cycle curve of the battery prepared in Example 3 within the 2-4V voltage window is shown in Figure 5. The cycle curve of the battery prepared in Comparative Example 1 within the 2-4V voltage window is shown in Figure 6. Figures 5 and 6 show that the cycle stability of the battery prepared using the positive electrode active material of this application is significantly improved.

[0227] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0228] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode active material having the general formula Na y Zr a Ti b Zn c Ni d Fe f Mn e M x O2, where, M is one or more of V, Co, Al, Nb, Pb, Sb and Mo, 0.01≤a≤0.05, 0.01≤b≤0.03, 0.01≤c≤0.03, 0≤x≤0.05, 0.7≤y≤0.85, 0≤d≤0.4, 0≤f≤0.4, 0≤e≤0.4, and a+b+c+d+e+f+x=1.

2. The positive electrode active material according to claim 1, wherein Meet at least one of the following: (1) The discharge plateau position of the positive electrode active material is 2.5V to 3.0V and / or 3.5V to 4.0V; (2) The platform capacity of the positive electrode active material accounts for less than or equal to 50% of the total capacity; (3) The plateau capacity of the positive electrode active material at a voltage of 3.5V to 4.0V accounts for less than or equal to 30% of the total capacity.

3. The positive electrode active material according to any one of claims 1 to 2, wherein The positive electrode active material is a layered oxide.

4. The positive electrode active material according to any one of claims 1 to 3, wherein 0 <d≤0.4,0<f≤0.4,0<e≤0.4。 5. The positive electrode active material according to any one of claims 1 to 4, wherein The structural formula of the positive electrode active material includes Na. 0.85 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.33 Mn 0.35 O2, Na 0.82 Ti 0.02 Zn 0.01 Zr 0.02 Ni 0.25 Fe 0.33 Mn 0.35 Sb 0.02 O2, Na 0.82 Ti 0.02 Zn 0.02 Zr 0.03 Ni 0.2 Fe 0.33 Mn 0.37 Al 0.03 O2, Na 0.8 Ti 0.03 Zn 0.02 Zr 0.02 Ni 0.23 Fe 0.33 Mn 0.35 Nb 0.02 O2, Na 0.75 Ti 0.01 Zn 0.03 Zr 0.05 Ni 0.25 Fe 0.31 Mn 0.35 O2 and Na 0.75 Ti 0.01 Zn 0.02 Zr 0.03 Ni 0.25 Fe 0.32 Mn 0.35 Sb 0.02 At least one of O2.

6. The positive electrode active material according to any one of claims 1 to 5, wherein, The positive electrode active material comprises a sodium layer and a transition metal layer, wherein the interlayer spacing of the sodium layer is [missing information]. And / or, the interlayer spacing of the transition metal layer is 7. The positive electrode active material according to any one of claims 1 to 6, wherein, The lattice parameter a of the positive electrode active material is And / or, the lattice parameter c of the positive electrode active material is 8. The positive electrode active material according to any one of claims 1 to 7, wherein, The median particle size D50 of the positive electrode active material is 5 μm to 10 μm.

9. The positive electrode active material according to any one of claims 1 to 8, wherein The specific surface area of ​​the positive electrode active material is 0.4 m². 2 / g~0.8m 2 / g.

10. The positive electrode active material according to any one of claims 1 to 9, wherein The positive electrode active material satisfies at least one of the following conditions: (1) The positive electrode active material is a P2 / O3 mixed phase structure; (2) The mass content of the P2 phase in the positive electrode active material is 5% to 30%; (3) The mass content of O3 phase in the positive electrode active material is 70% to 95%.

11. The positive electrode active material according to any one of claims 1 to 10, wherein, The positive electrode active material satisfies at least one of the following conditions: (1) The 2θ of the highest intensity peak in the XRD pattern is 14° to 16°; (2) The 2θ of the second intensity peak in the XRD pattern is 40° to 45°; (3) The peak half width at half maximum (FWHM) corresponding to the (003) crystal plane in the XRD pattern is 0.05°~0.5°.

12. A method for preparing the positive electrode active material according to any one of claims 1 to 11, comprising the following steps: According to the stoichiometric molar ratio of the positive electrode active material, a sodium source, optional iron source, optional manganese source, optional nickel source, titanium source, zirconium source, zinc source and optional metal M source are dissolved in a solvent and blended to obtain a mixed solution. The mixture was heated to obtain a mixed gel; The mixed gel is dried to obtain the positive electrode active material.

13. The method for preparing the positive electrode active material according to claim 12, wherein, Meet at least one of the following: (1) The sodium source includes at least one of sodium dihydrogen carbonate, sodium carbonate, sodium acetate and sodium citrate; (2) The iron source includes ferric nitrate; (3) The manganese source includes at least one of manganese acetate and manganese nitrate; (4) The nickel source includes at least one of nickel nitrate and nickel acetate; (5) The titanium source includes at least one of titanium dioxide and titanium nitrate; (6) The zirconium source includes at least one of zirconium oxide and zirconium nitrate; (7) The zinc source includes at least one of zinc acetate and zinc nitrate; (8) The metal M source is at least one of acetate, nitrate and oxide containing metal M; (9) The complexing agent includes citric acid.

14. The method for preparing the positive electrode active material according to any one of claims 12-13, wherein, The heating temperature of the heat treatment is 60℃~110℃; and / or the drying temperature of the drying treatment is 80℃~130℃, and the drying time of the drying treatment is 5h~15h.

15. The method for preparing the positive electrode active material according to any one of claims 12 to 14, wherein, The heat treatment is followed by a calcination step, which includes the following steps: The dried mixed gel was heated to 500℃~600℃ at a heating rate of 3℃ / min~8℃ / min and then calcined for 3h~7h. The calcined mixed gel was heated to 850℃~950℃ at a heating rate of 3℃ / min~8℃ / min and then held at that temperature for 10h~15h to obtain the positive electrode active material.

16. A positive electrode slurry, comprising the positive electrode active material as described in any one of claims 1 to 11 and the positive electrode active material prepared by the preparation method as described in any one of claims 12 to 15.

17. The positive electrode slurry of claim 16, wherein, The positive electrode slurry includes the positive electrode material, conductive agent, binder, and solvent.

18. The positive electrode slurry according to any one of claims 16-17, wherein, At least one of the following conditions must be met: (1) The mass ratio of the positive electrode material, the conductive agent, and the binder is 0.8–0.9: 0.03–0.2: 0.03–0.2; (2) The conductive agent includes at least one of Super P, graphene, carbon dots, CNT and Ketjen Black; (3) The adhesive includes at least one of difluoroethylene, polyvinylidene fluoride and tetrafluoroethylene-hexafluoropropylene copolymer; (4) The solid content of the positive electrode slurry is 50% to 60%.

19. A conductive coating, wherein the components of the conductive coating include the positive electrode active material, conductive agent and binder as described in any one of claims 1 to 11; or, the conductive coating is prepared using the positive electrode slurry as described in any one of claims 16 to 18.

20. A positive electrode sheet, comprising a positive current collector and a positive active layer, wherein the positive active layer is disposed on at least one side of the positive current collector, and the positive active layer comprises the positive active material as described in any one of claims 1 to 11; or the positive active layer is made using the positive slurry as described in any one of claims 16 to 18.

21. The positive electrode sheet of claim 20, wherein At least one of the following conditions must be met: (1) The thickness of the positive electrode sheet is 0.2 mm to 0.3 mm; (2) the compacted density of the positive electrode plate is 1.5 g / cm 3 ~ 3.0 g / cm 3 .

22. A sodium-ion battery, comprising a positive electrode as described in any one of claims 20 to 21.

23. An electrical device comprising a sodium-ion battery as described in claim 22.

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