Bulk phase coating and surface coating co-modified positive electrode material and preparation method thereof, positive electrode plate and sodium ion battery

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a bulk phase coating and surface coating co-modified positive electrode material, a preparation method thereof, a positive plate and a sodium ion battery. The general formula of the bulk phase coating and surface coating co-modified positive electrode material is Na < x > Cu Ni Mn < c > Ti < d > O < 2 > (at) M < alpha > Q < beta > B < gamma >, m is a bulk phase coating element capable of being inserted into the sodium layer, and alpha is the ratio of the molar weight of the M element to the total molar weight of copper, nickel, manganese and titanium elements; q is an element which is subjected to bulk phase coating and surface coating at the same time, and the valence of Q is greater than or equal to + 5; beta is the ratio of the molar weight of the Q element to the total molar weight of copper, nickel, manganese and titanium elements; b is a surface coating element, and gamma is the ratio of the molar weight of the element B to the total molar weight of copper, nickel, manganese and titanium. According to the invention, through the combined action of bulk phase and surface coating, the cycling stability of the positive electrode material in a voltage range of 2.0-4.30 V can be effectively improved on the premise of ensuring high energy density.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and in particular, to a cathode material jointly modified by bulk coating and surface coating, a preparation method thereof, a cathode sheet, and a sodium-ion battery. Background Art

[0002] Sodium-ion layered transition metal oxide cathode materials have the advantages of relatively high specific capacity, simple preparation, high tap density, and adjustable voltage range. In order to improve the energy density of the cathode material of sodium-ion batteries, the charging cut-off voltage is increased to 4.30 V or higher, thereby releasing more capacity.

[0003] However, at high voltages, sodium-ion layered transition metal oxide cathode materials tend to undergo irreversible phase transitions, and at the same time, the decomposition of the electrolyte is accelerated, which in turn leads to a rapid decay of the electrochemical performance. Therefore, it is difficult to balance the two indicators of high energy density and long cycle life.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a cathode material jointly modified by bulk coating and surface coating. The present invention uses the bulk coating of element M that can insert into the sodium layer and the high-valence element Q to stabilize the layered transition metal oxide structure; and uses the surface coating of the high-valence element Q and boron element to reduce the exposure of the internal layered transition metal oxide to the electrolyte contact, thereby reducing the occurrence of interfacial side reactions. At the same time, the coupling effect of the high-valence element Q, boron element and the surface of the cathode material is used to stabilize the material interface; through the combined action of bulk coating and surface coating, the cycle stability of the cathode material in the high voltage range of 2.0 V to 4.30 V can be effectively improved on the premise of ensuring high energy density.

[0006] The second object of the present invention is to provide a preparation method of a cathode material jointly modified by bulk coating and surface coating. The combined action of bulk coating and surface coating can effectively improve the cycle stability of the cathode material in the high voltage range of 2.0 V to 4.30 V on the premise of ensuring high energy density, and the preparation method has the advantages of simple operation, short process, and suitability for large-scale production.

[0007] The third object of the present invention is to provide a cathode sheet. The battery prepared with this cathode sheet can balance high energy density and long cycle life at high voltages.

[0008] The fourth object of the present invention is to provide a sodium-ion battery, which balances high energy density and long cycle life in the high voltage range of 2.0 V to 4.30 V.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] The present invention first provides a cathode material modified by both bulk coating and surface coating. The general formula of the cathode material is Na x Cu a Ni b Mn c Ti d O2@M α Q β B γ ; wherein, Na x Cu a Ni b Mn c Ti d O2 is a layered transition metal oxide substrate, 0.88 ≤ x < 1.02, 0.07 ≤ a ≤ 0.13, 0.37 ≤ b ≤ 0.43, 0.37 ≤ c ≤ 0.43, 0.07 ≤ d ≤ 0.13, and a + b + c + d = 1; M is a bulk coating element capable of inserting into the sodium layer, α is the molar ratio of the M element to the total molar amount of the copper, nickel, manganese, and titanium elements; Q is a high-valence element that undergoes both bulk coating and surface coating, and the valence of Q is not less than +5; β is the molar ratio of the Q element to the total molar amount of the copper, nickel, manganese, and titanium elements; B is a surface coating element, and γ is the molar ratio of the B element to the total molar amount of the copper, nickel, manganese, and titanium elements.

[0011] Further, the M includes at least one of Ca, Zn, Mg, and K elements.

[0012] Further, the Q includes at least one of Mo, Nb, Ta, and W elements.

[0013] Further, 0.0001 < α < 0.01.

[0014] Further, 0.0001 < β < 0.01.

[0015] Further, 0.0001 < γ < 0.02.

[0016] Further, the pH value of the solution obtained by dissolving 2 g of the cathode material in 40 mL of water at 25°C is 11.7 - 12.5.

[0017] Further, the specific surface area of the cathode material is ≤ 0.50 m 2 / g.

[0018] Further, the tap density of the cathode material is ≥ 1.8 g / cm 3 .

[0019] Further, the carbon element content in the cathode material is ≤ 1500 ppm.

[0020] The present invention further provides a method for preparing the cathode material co-modified by the above-mentioned bulk coating and surface coating, comprising the following steps: mixing a nickel-copper-manganese oxide precursor, a sodium source and a titanium source, and then calcining to obtain a layered transition oxide substrate with the chemical formula Na x Cu a Ni b Mn c Ti d O2; wherein, 0.88 ≤ x < 1.02, 0.07 ≤ a ≤ 0.13, 0.37 ≤ b ≤ 0.43, 0.37 ≤ c ≤ 0.43, 0.07 ≤ d ≤ 0.13, and a + b + c + d = 1; mixing the layered transition oxide substrate with an M source, a Q source and a B source, and then sintering to obtain the cathode material co-modified by the bulk coating and surface coating; wherein, M in the M source is a bulk coating element capable of inserting into the sodium layer; Q in the Q source is a high-valence element that simultaneously performs bulk coating and surface coating, and the valence of Q is not less than +5; B in the B source is a surface coating element.

[0021] Further, the M source includes at least one of a Ca source, a Zn source, a Mg source and a K source.

[0022] Further, the Ca source includes at least one of CaCO3, CaO, CaO2, Ca(OH)2, CaF2 and CaSO4.

[0023] Further, the Zn source includes at least one of ZnO, Zn(OH)2, ZnS, ZnCl2 and ZnSO4.

[0024] Further, the Mg source includes at least one of MgO, Mg(OH)2, MgCl2 and MgCO3.

[0025] Further, the K source includes at least one of K2CO3, KOH and KF.

[0026] Further, the B source includes at least one of B2O3 and H3BO3.

[0027] Further, the Q source includes at least one of MoO3, Nb2O5, Ta2O5 and WO3.

[0028] Further, the ratio α of the molar amount of element M in the M source to the total molar amount of copper, nickel, manganese and titanium elements in the layered transition oxide substrate satisfies 0.0001 < α < 0.01.

[0029] Further, the ratio β of the molar amount of element Q in the Q source to the total molar amount of copper, nickel, manganese and titanium elements in the layered transition oxide substrate satisfies 0.0001 < β < 0.01.

[0030] Further, the ratio γ of the molar amount of element B in the B source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < γ < 0.02.

[0031] Further, the calcination temperature is 900 - 1000 °C, and the holding time for calcination is 15 - 24 h.

[0032] Further, the sintering temperature is 900 - 1000 °C, and the holding time for sintering is 12 - 24 h.

[0033] Further, the method for preparing the nickel - copper - manganese oxide precursor includes: mixing a nickel - manganese - copper mixed salt solution with a carbonate solution and performing a coprecipitation reaction to obtain a nickel - manganese - copper carbonate precursor; calcining the nickel - manganese - copper carbonate precursor to obtain the nickel - copper - manganese oxide precursor.

[0034] Further, the particle size Dv50 of the nickel - manganese - copper carbonate precursor is 3 - 15 μm.

[0035] Further, the reaction temperature of the coprecipitation reaction is 40 - 70 °C, and the reaction pH is 7 - 10.

[0036] The present invention also provides a positive electrode sheet, which includes the positive electrode material modified by the above - mentioned bulk coating and surface coating.

[0037] The present invention further provides a sodium - ion battery, which includes the above - mentioned positive electrode sheet.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The high - performance sodium - ion battery positive electrode material modified by the above - mentioned bulk coating and surface coating provided by the present invention uses the bulk coating of element M that can insert into the sodium layer and the high - valence element Q to stabilize the layered transition oxide structure; and uses the surface coating of the high - valence element Q and boron element to reduce the exposure of the internal layered transition oxide to the electrolyte contact, thereby reducing the occurrence of interfacial side reactions. At the same time, the coupling effect of the high - valence element, boron element, and the surface of the positive electrode material is used to stabilize the material interface; through the combined action of bulk coating and surface coating, it can effectively improve the cycle stability of the positive electrode material in the high - voltage range of 2.0 V - 4.30 V while ensuring a high energy density.

[0040] (2) The high - performance sodium - ion battery positive electrode material modified by the above - mentioned bulk coating and surface coating provided by the present invention has a low pH, a low specific surface area, a high tap density, and a low carbon element content. Description of the Drawings

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 SEM image of the cathode material co-modified by bulk coating and surface coating prepared in Example 1 provided by the present invention;

[0043] Figure 2 0.1C first-cycle charge-discharge curves of the battery composed of the cathode materials of Example 1 and Comparative Example 1 provided by the present invention;

[0044] Figure 3 1C cycle retention curves of the battery composed of the cathode materials of Example 1 and Comparative Example 1 provided by the present invention. Specific Embodiments

[0045] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0046] If there is no special description, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on the quantity.

[0047] If there is no special description, "including" and "comprising" mentioned in the present invention mean open-ended, and can also be closed-ended. For example, the said "including" and "comprising" can mean that other components not listed can also be included, or only the listed components can be included.

[0048] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or more.

[0049] In a first aspect, the present invention provides a high-performance cathode material for a sodium-ion battery with co-modification of bulk coating and surface coating. The general formula of the cathode material with co-modification of bulk coating and surface coating is Na x Cu a Ni b Mn c Ti d O2@M α Q β B γ .

[0050] Among them, Na x Cu a Ni b Mn c Ti d O2 is a layered transition oxide substrate, 0.88 ≤ x < 1.02, 0.07 ≤ a ≤ 0.13, 0.37 ≤ b ≤ 0.43, 0.37 ≤ c ≤ 0.43, 0.07 ≤ d ≤ 0.13, and a + b + c + d = 1. Among them, x includes, but is not limited to, any point value among 0.88, 0.89, 0.90, 0.92, 0.93, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02 or the range value between any two of them; a includes, but is not limited to, any point value among 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13 or the range value between any two of them; b includes, but is not limited to, any point value among 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43 or the range value between any two of them; c includes, but is not limited to, any point value among 0.37, 0.38, 0.39, 0.40, 0.41, 0.42, 0.43 or the range value between any two of them; d includes, but is not limited to, any point value among 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13 or the range value between any two of them. This substrate is a copper-nickel-manganese-titanium layered transition oxide substrate, in which the contents of copper and titanium are both about 10%, and the nickel element content is about 40%. This ratio has a smooth first charge-discharge curve and a high capacity at a voltage of 2.0 - 4.30V.

[0051] That is, the cathode material with co-modification of bulk coating and surface coating includes a chemical formula of Na x Cu a Ni b Mn cTi d a matrix material of O2, and a coating layer containing elements M, Q, and B, the coating layer coating the matrix material.

[0052] It can be understood that bulk-phase coating means that the coating elements can diffuse into the interior of the material at high temperature to form gradient doping, that is, the concentration of the bulk-phase coating elements is lower closer to the interior of the material, rather than simply on the surface of the particles. Surface coating, on the other hand, forms a coating layer on the surface of the material and does not penetrate into the interior of the material.

[0053] It can be understood that the coating elements in the coating layer mainly exist in the form of oxides.

[0054] M is a bulk-phase coating element that can insert into the sodium layer, and α is the ratio of the molar amount of element M to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate (or the positive electrode material).

[0055] Q is a high-valence element that simultaneously performs bulk-phase coating and surface coating, and the valence of Q is not less than +5; β is the ratio of the molar amount of element Q to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate (or the positive electrode material).

[0056] For example, the valence of Q is +5 or +6.

[0057] Among them, both M and Q are metal elements.

[0058] B is a surface coating element, and γ is the ratio of the molar amount of element B to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate (or the positive electrode material).

[0059] The present invention uses the bulk-phase coating of element M that can insert into the sodium layer and high-valence element Q to stabilize the structure of the layered transition oxide; and uses the surface coating of high-valence element Q and boron element to reduce the exposure of the internal layered transition oxide to the electrolyte, thereby reducing the occurrence of interfacial side reactions. At the same time, the coupling effect of high-valence element Q, boron element, and the surface of the positive electrode material is used to stabilize the material interface; through the combined action of bulk-phase coating and surface coating, the cycle stability of the positive electrode material in the high-voltage range of 2.0V to 4.30V can be effectively improved while ensuring high energy density.

[0060] In some specific embodiments, M includes at least one of Ca, Zn, Mg, and K elements; two, three, or four of them can also be selected.

[0061] In some specific embodiments, Q includes at least one of Mo, Nb, Ta, and W elements, and two, three, or four of them can also be selected.

[0062] In some specific embodiments, 0.0001 < α < 0.01; wherein, α includes, but is not limited to, any point value of 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01 or the range value between any two of them.

[0063] In some specific embodiments, 0.0001 < β < 0.01; wherein, β includes, but is not limited to, any point value of 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01 or the range value between any two of them.

[0064] In some specific embodiments, 0.0001 < γ < 0.02. Wherein, γ includes, but is not limited to, any point value of 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0008, 0.001, 0.003, 0.005, 0.006, 0.008, 0.010, 0.012, 0.013, 0.015, 0.016, 0.018, 0.02 or the range value between any two of them.

[0065] In some specific embodiments, the pH value of the solution obtained by dissolving 2 g of the positive electrode material in 40 mL of water at 25°C is 11.7 to 12.5, including, but not limited to, any point value of 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5 or the range value between any two of them.

[0066] In some specific embodiments, the specific surface area (BET) of the positive electrode material ≤ 0.50 m 2 / g; including, but not limited to, 0.25 m 2 / g, 0.28 m 2 / g, 0.30 m 2 / g, 0.32 m 2 / g, 0.33 m 2 / g, 0.34 m 2 / g, 0.35 m 2 / g, 0.36 m 2 / g, 0.38 m 2 / g, 0.40m 2 / g, 0.43m 2 / g, 0.45m 2 / g, 0.50m 2 / g, or any range between them. If BET is greater than 0.5m 2 / g, more contact with the electrolyte, the corresponding increase in side reactions will lead to a rapid decay of cycle performance.

[0067] In some specific embodiments, the tap density (TD) of the positive electrode material is ≥1.8 g / cm 3 ; Including but not limited to 1.8g / cm 3 , 1.85g / cm 3 , 1.9g / cm 3 , 1.95g / cm 3 , 2.0g / cm 3 , 2.05g / cm 3 , 2.1g / cm 3 , 2.15g / cm 3 , 2.2g / cm 3 Any point value or any range value between the two. Improving the compaction is beneficial to increase the compaction density at the cell end.

[0068] In some specific embodiments, the carbon content in the positive electrode material is ≤1500ppm, including but not limited to any point value of 800ppm, 900ppm, 950ppm, 1000ppm, 1050ppm, 1100ppm, 1150ppm, 1200ppm, 1250ppm, 1300ppm, 1400ppm, 1500ppm or any range value between two thereof. The carbon content is related to many factors, such as sodium matching, sintering temperature, time and sintering atmosphere, etc. In the sodium positive electrode, the carbon content in the carbon content is generally in the form of sodium carbonate or sodium bicarbonate. If the carbon content is high, it is unfavorable to the material during the material cycle, so the carbon content of the material should be controlled.

[0069] In a second aspect, the present invention provides a method for preparing the positive electrode material modified by bulk coating and surface coating, comprising the following steps:

[0070] The nickel-copper-manganese oxide precursor, the sodium source and the titanium source are mixed and calcined, and then pulverized after cooling to obtain a product with the chemical formula Na x Cu a Ni b Mn c Ti d Layered transition oxide substrate of O2.

[0071] Chemical formula: Na x Cu a Ni b Mn c Ti d In O₂, 0.88 ≤ x < 1.02, 0.07 ≤ a ≤ 0.13, 0.37 ≤ b ≤ 0.43, 0.37 ≤ c ≤ 0.43, 0.07 ≤ d ≤ 0.13, and a + b + c + d = 1.

[0072] Furthermore, the layered transition metal oxide substrate is mixed with an M source, a Q source, and a B source, then sintered, and pulverized after cooling to obtain the cathode material co-modified by bulk coating and surface coating.

[0073] Among them, M in the M source is an element for bulk coating that can be inserted into the sodium layer; Q in the Q source is a high-valence element for both bulk coating and surface coating, where the valence of Q is not less than +5; B in the B source is an element for surface coating.

[0074] The preparation method of the cathode material co-modified by bulk coating and surface coating provided by the present invention, through the combined action of bulk coating and surface coating, can effectively improve the cycling stability of the cathode material in the high voltage range of 2.0 V to 4.30 V while ensuring a high energy density.

[0075] Moreover, this preparation method has the advantages of simple operation, short process, and suitability for batch production.

[0076] In some specific embodiments, the M source includes at least one of a Ca source, a Zn source, a Mg source, and a K source; two, three, or four of them can also be selected.

[0077] In some specific embodiments, the Ca source includes Ca-containing compounds.

[0078] As an example, the Ca-containing compounds include but are not limited to at least one of CaCO₃, CaO, CaO₂, Ca(OH)₂, CaF₂, and CaSO₄.

[0079] In some specific embodiments, the Zn source includes Zn-containing compounds.

[0080] As an example, the Zn-containing compounds include but are not limited to at least one of ZnO, Zn(OH)₂, ZnS, ZnCl₂, and ZnSO₄.

[0081] In some specific embodiments, the Mg source includes Mg-containing compounds.

[0082] As an example, the Mg-containing compounds include but are not limited to at least one of MgO, Mg(OH)₂, MgCl₂, and MgCO₃.

[0083] In some specific embodiments, the K source includes a K-containing compound.

[0084] As an example, the K-containing compound includes at least one of K2CO3, KOH, and KF.

[0085] In some specific embodiments, the B source includes at least one of B2O3 and H3BO3.

[0086] In some specific embodiments, the Q source includes at least one of a Mo source, a Nb source, a Ta source, and a W source; two, three, or four of them can also be selected.

[0087] In some specific embodiments, the Mo source includes MoO3. Among them, the Mo element is +6 valence.

[0088] In some specific embodiments, the Nb source includes Nb2O5. Among them, the Nb element is +5 valence.

[0089] In some specific embodiments, the Ta source includes Ta2O5. Among them, the Ta element is +5 valence.

[0090] In some specific embodiments, the W source includes WO3. Among them, the W element is +6 valence.

[0091] In some specific embodiments, the sodium source includes a Na-containing compound, such as sodium carbonate, but is not limited thereto.

[0092] In some specific embodiments, the titanium source includes a Ti-containing compound, such as titanium dioxide, but is not limited thereto.

[0093] In some specific embodiments, the ratio α of the molar amount of the M element in the M source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < α < 0.01.

[0094] In some specific embodiments, the ratio β of the molar amount of the Q element in the Q source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < β < 0.01.

[0095] In some specific embodiments, the ratio γ of the molar amount of the B element in the B source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < γ < 0.02.

[0096] In some specific embodiments, the calcination temperature is 900 to 1000 °C, including but not limited to the point values of any one of 900 °C, 920 °C, 930 °C, 950 °C, 980 °C, 1000 °C or the range values between any two of them; the heat preservation time of the calcination is 15 to 24 h, including but not limited to the point values of any one of 15 h, 16 h, 18 h, 20 h, 22 h, 24 h or the range values between any two of them.

[0097] In some specific embodiments, the calcination is carried out in an air atmosphere and / or an oxygen atmosphere.

[0098] In some specific embodiments, the sintering temperature is 900 to 1000 °C, including but not limited to the point values of any one of 900 °C, 920 °C, 930 °C, 950 °C, 980 °C, 1000 °C or the range values between any two of them; the heat preservation time of the sintering is 12 to 24 h, including but not limited to the point values of any one of 12 h, 15 h, 16 h, 18 h, 20 h, 22 h, 24 h or the range values between any two of them.

[0099] In some specific embodiments, the sintering is carried out in an air atmosphere and / or an oxygen atmosphere.

[0100] In some specific embodiments, the method for preparing the nickel copper manganese oxide precursor includes: mixing a nickel manganese copper mixed salt solution and a carbonate solution and carrying out a coprecipitation reaction, and after the coprecipitation reaction is completed, separating the solid from the liquid to obtain a spherical and / or spherical nickel manganese copper carbonate precursor; then roasting the nickel manganese copper carbonate precursor and cooling to obtain the nickel copper manganese oxide precursor.

[0101] Among them, the nickel manganese copper mixed salt solution refers to a mixed aqueous solution containing nickel element, manganese element and copper element. The carbonate solution refers to an aqueous solution containing carbonate ions.

[0102] In some specific embodiments, the nickel manganese copper mixed salt solution and the carbonate solution are added to a reaction kettle containing a bottom liquid to carry out the coprecipitation reaction.

[0103] In some specific embodiments, the coprecipitation reaction is carried out until the particle size Dv50 of the nickel manganese copper carbonate precursor is 3 to 15 μm; including but not limited to the point values of any one of 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm or the range values between any two of them.

[0104] In some specific embodiments, the reaction temperature of the coprecipitation reaction is 40 to 70 °C, including but not limited to any point value among 40 °C, 45 °C, 50 °C, 55 °C, 60 °C, 65 °C, 70 °C or the range value between any two of them.

[0105] In some specific embodiments, the reaction pH of the coprecipitation reaction is 7 to 10, including but not limited to any point value among 7, 7.5, 8, 8.5, 9, 9.5, 10 or the range value between any two of them.

[0106] In some specific embodiments, the reaction time of the coprecipitation reaction is 40 to 130 h, including but not limited to any point value among 40 h, 50 h, 60 h, 80 h, 100 h, 110 h, 130 h or the range value between any two of them.

[0107] In some specific embodiments, during the coprecipitation reaction, stirring is carried out at a speed of 400 to 1200 rpm. Among them, the stirring speed includes but not limited to any point value among 400 rpm, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm or the range value between any two of them.

[0108] In some specific embodiments, the nickel-manganese-copper mixed salt solution further includes a dispersant, such as sodium dodecyl sulfate.

[0109] In some specific embodiments, the calcination temperature is 550 to 750 °C, including but not limited to any point value among 550 °C, 580 °C, 600 °C, 610 °C, 630 °C, 650 °C, 680 °C, 700 °C, 720 °C, 750 °C or the range value between any two of them; the holding time of the calcination is 5 to 12 h, including but not limited to any point value among 5 h, 6 h, 8 h, 10 h, 12 h or the range value between any two of them.

[0110] In some specific embodiments, the calcination is carried out in an air atmosphere and / or an oxygen atmosphere.

[0111] In a third aspect, the present invention provides a positive electrode sheet, including the cathode material jointly modified by the bulk coating and the surface coating.

[0112] The battery prepared by using this positive electrode sheet can take into account high energy density and long cycle life at high voltage.

[0113] Optionally, the positive electrode sheet further includes at least one of a binder and a conductive agent (i.e., a conductive additive), and the present invention does not limit this.

[0114] As an example, the binder may be one or more of polyolefins, fluorine-containing resins, polypropylene resins, and rubbers, but is not limited thereto.

[0115] The conductive agent may be one or more of carbon nanotubes, acetylene black, conductive carbon black, conductive graphite, carbon fiber, and graphene, but is not limited thereto.

[0116] The amount of the binder added may be any amount commonly used in the art, for example, the mass of the binder accounts for a percentage of less than or equal to 10 wt % of the sum of the mass of the positive electrode material, the binder and the conductive agent.

[0117] The amount of the conductive agent added may be any amount commonly used in the art, for example, the mass of the conductive agent accounts for a percentage of the sum of the mass of the positive electrode material, the binder and the conductive agent that is less than or equal to 10 wt %.

[0118] Furthermore, the current collector in the positive electrode sheet includes aluminum foil.

[0119] In a fourth aspect, the present invention provides a sodium ion battery comprising the positive electrode sheet.

[0120] This sodium-ion battery combines high energy density and long cycle life in the high voltage range of 2.0V to 4.30V.

[0121] Optionally, the sodium ion battery further includes a negative electrode sheet, a separator and an electrolyte, which is not limited in the present invention.

[0122] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0123] Example 1

[0124] The positive electrode material Na modified by bulk coating and surface coating provided in this embodiment 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Ca 0.002 B 0.005 Mo 0.003 The preparation method comprises the following steps:

[0125] (1) Weigh the raw materials of nickel sulfate, copper sulfate and manganese sulfate according to the molar ratio of Ni, Cu, and Mn metal elements of 0.427:0.112:0.461, and dissolve them in pure water to prepare a mixed metal salt solution with a total molar concentration of metal elements (i.e., the sum of the molar concentrations of Ni element, Cu element and Mn element) of 2 mol / L. Add sodium dodecyl sulfate as a dispersant to the mixed metal salt solution, and transfer it to a jacketed reactor. Stir continuously under the heat preservation condition of 50 °C, and the stirring speed is 900 r / min. Then use a peristaltic pump to dropwise add a Na2CO3 solution with a molar concentration of 4 mol·L -1 as a precipitant, control the pH of the coprecipitation reaction process at 7.6, and carry out the coprecipitation reaction until the particle size Dv50 is 4.5 μm and SPAN (span of particle size distribution) < 0.8. After that, it is filtered by suction, washed with hot water, and dried to obtain a spherical nickel-manganese-copper carbonate precursor. Place the above nickel-manganese-copper carbonate precursor in an atmosphere furnace, introduce dry compressed air, heat it from room temperature to 610 °C at a heating rate of 5 °C / min and calcine for 6 h, and obtain a nickel-copper-manganese oxide precursor after cooling.

[0126] (2) Weigh 3000 g of the above nickel-copper-manganese oxide precursor, 2168.61 g of sodium carbonate and 378.84 g of titanium dioxide, and use a high-speed mixer to mix the three at high speed until there are no obvious white spots visually to obtain a mixed material. Load the mixed material into a crucible of 330 mm × 330 mm × 100 mm, with a loading amount of 3.0 kg, and calcine in a box-type atmosphere furnace at an air flow rate of 25 L / min at 920 °C for 18 h. After the calcined material is cooled, it is crushed by a jet mill to obtain a layered transition oxide substrate Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2.

[0127] (3) According to the ratio in the target general formula, weigh 3000 g of the layered transition oxide substrate, 5.43 g of CaCO3, 4.72 g of B2O3 and 11.72 g of MoO3 and mix them evenly using a high-speed mixer. Then load the evenly mixed material into a crucible of 330 mm × 330 mm × 100 mm, with a loading amount of 3.0 kg, and sinter in a box-type atmosphere furnace at an air flow rate of 25 L / min at 900 °C for 15 h. Then it is crushed by a jet mill to obtain a cathode material modified by both bulk coating and surface coating.

[0128] As Figure 1 shown is the SEM image of the cathode material modified by both bulk coating and surface coating prepared in this example.

[0129] Example 2

[0130] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Ca 0.002 B 0.005 Mo 0.006 co-modified by bulk coating and surface coating is basically the same as that in Example 1, except that in step (3), the mass of MoO3 is replaced by 23.44 g.

[0131] Example 3

[0132] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Zn 0.002 B 0.005 Mo 0.003 co-modified by bulk coating and surface coating is basically the same as that in Example 1, except that in step (3), 5.43 g of CaCO3 is replaced by 4.42 g of ZnO2.

[0133] Example 4

[0134] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Zn 0.002 B 0.005 Nb 0.003 co-modified by bulk coating and surface coating is basically the same as that in Example 1, except that in step (3), 5.43 g of CaCO3 is replaced by 4.42 g of ZnO2, and 11.72 g of MoO3 is replaced by 10.83 g of Nb2O5.

[0135] Example 5

[0136] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Zn 0.002 B 0.005 Ta 0.003The preparation method is basically the same as that of Example 1, except that in step (3), 5.43 g of CaCO3 is replaced with 4.42 g of ZnO2, and 11.72 g of MoO3 is replaced with 18 g of Ta2O5.

[0137] Example 6

[0138] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Zn 0.002 B 0.005 W 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), 5.43 g of CaCO3 is replaced with 4.42 g of ZnO2, and 11.72 g of MoO3 is replaced with 18.89 g of WO3.

[0139] Example 7

[0140] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Mg 0.002 B 0.005 Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), 5.43 g of CaCO3 is replaced with 3.17 g of Mg(OH)2.

[0141] Example 8

[0142] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@K 0.002 B 0.005 Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), 5.43 g of CaCO3 is replaced with 3.75 g of K2CO3.

[0143] Example 9

[0144] The preparation method of the cathode material Na 0.96 Ni 0.38 Cu0.11 Mn 0.4 0Ti 0.11 O2@Ca 0.005 B 0.005 Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), the mass of CaCO3 is replaced with 13.57 g.

[0145] Example 10

[0146] The cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Ca 0.002 B 0.01 Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), the mass of B2O3 is replaced with 9.34 g.

[0147] Example 11

[0148] The cathode material Na 0.96 Ni 0.43 Cu 0.07 Mn 0.3 7Ti 0.13 O2@Ca 0.002 B 0.005 Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (1), the raw materials are weighed according to the molar ratio of Ni, Cu, and Mn metal elements of 0.478:0.078:0.411 to prepare the nickel copper manganese oxide precursor, and in step (2), the layered transition oxide substrate Na 0.96 Ni 0.43 Cu 0.07 Mn 0.37 Ti 0.13 O2 is prepared for use in step (3) to make the cathode material.

[0149] Example 12

[0150] The cathode material Na 0.96 Ni 0.40 Cu 0.10 Mn 0.4 0Ti 0.10 O2@Ca 0.002 B 0.005 Mo 0.003The preparation method is basically the same as that of Example 1, except that: in step (1), each raw material is weighed according to the molar ratio of Ni, Cu, and Mn metal elements of 0.444:0.111:0.444 to obtain a nickel copper manganese oxide precursor, and in step (2), the layered transition oxide substrate Na 0.96 Ni 0.40 Cu 0.10 Mn 0.40 Ti 0.10 O2 is used in step (3) to make the positive electrode material.

[0151] Example 13

[0152] The positive electrode material Na 0.88 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Ca 0.002 B 0.005 Mo 0.003 prepared in this example with co-modification of bulk coating and surface coating has a preparation method basically the same as that of Example 1, except that: in step (2), the mass of sodium carbonate (1987.89 g) is adaptively adjusted according to the target chemical formula ratio.

[0153] Example 14

[0154] The positive electrode material Na 1.02 Ni 0.38 Cu 0.11 Mn 0.4 0Ti 0.11 O2@Ca 0.002 B 0.005 Mo 0.003 prepared in this example with co-modification of bulk coating and surface coating has a preparation method basically the same as that of Example 1, except that: in step (2), the mass of sodium carbonate (2304.15 g) is adaptively adjusted according to the target chemical formula ratio.

[0155] Example 15

[0156] The positive electrode material Na 0.96 Ni 0.38 Cu 0.09 Mn 0.4 3Ti 0.10 O2@Ca 0.002 B 0.005 Mo 0.003The preparation method is basically the same as that of Example 1, with the differences being: in step (1), the raw materials are weighed according to the molar ratio of Ni, Cu, and Mn metal elements of 0.427:0.101:0.483 to obtain the nickel copper manganese oxide precursor, and in step (2), when mixing at high speed, the mass of sodium carbonate is adjusted to 2186.28 g and the mass of titanium dioxide is adjusted to 381.93 g.

[0157] Example 16

[0158] The cathode material Na 0.96 Ni 0.40 Cu 0.11 Mn 0.4 2Ti 0.07 O2@Ca 0.002 B 0.005 Mo 0.003 The preparation method is basically the same as that of Example 1, with the differences being: in step (1), the raw materials are weighed according to the molar ratio of Ni, Cu, and Mn metal elements of 0.449:0.124:0.472 to obtain the nickel copper manganese oxide precursor, and in step (2), when mixing at high speed, the mass of sodium carbonate is adjusted to 2010.52 g and the mass of titanium dioxide is adjusted to 223.51 g.

[0159] Comparative Example 1

[0160] The cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2 (without bulk coating and surface coating) is prepared in the same way as in Example 1, except that in step (3), CaCO3, B2O3, and MoO3 are not added.

[0161] Comparative Example 2

[0162] The cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2@Ca 0.02 is prepared in the same way as in Example 1, except that in step (3), B2O3 and MoO3 are not added, and the mass of CaCO3 is replaced with 54.3 g.

[0163] Comparative Example 3

[0164] The cathode material Na 0.96 Ni 0.38 Cu 0.11 Mn0.40 Ti 0.11 O2@B 0.05 The preparation method is basically the same as that of Example 1, except that in step (3), CaCO3 and MoO3 are not added, and the mass of B2O3 is replaced with 94.46 g.

[0165] Comparative Example 4

[0166] The positive electrode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2@Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), CaCO3 and B2O3 are not added.

[0167] Comparative Example 5

[0168] The positive electrode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2@Ca 0.002 B 0.005 Mo 0.01 The preparation method is basically the same as that of Example 1, except that in step (3), the mass of MoO3 is replaced with 39.09 g.

[0169] Comparative Example 6

[0170] The positive electrode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2@Ca 0.002 B 0.02 Mo 0.003 The preparation method is basically the same as that of Example 1, except that in step (3), the mass of B2O3 is replaced with 37.78 g.

[0171] Comparative Example 7

[0172] The positive electrode material Na 0.96 Ni 0.38 Cu 0.11 Mn 0.40 Ti 0.11 O2@Ba 0.005 Zr 0.005The preparation method is basically the same as that of Example 1, except that in step (3), B2O3 is not added, CaCO3 is replaced by BaO, MoO3 is replaced by ZrO2, and the masses of BaO and ZrO2 are adjusted adaptively according to the ratios in the target general formula.

[0173] The specific surface area (BET), tapped density (TD), carbon element content of the positive electrode materials prepared in each example and each comparative example, and the pH of the aqueous solution of the positive electrode material were tested respectively, and the results are shown in Table 1.

[0174] Among them, the specific surface area test method is as follows: Use the Belsorp BSD-660S dynamic adsorption specific surface area analyzer; Test method: Pretreatment: Weigh 5.000 ± 0.01 g of the material and degas it at 150 °C for 60 min; Adsorbent: Nitrogen.

[0175] The pH test method is as follows: Use the Mettler Toledo FE-28 pH meter, Test method: Weigh 2 g of the sample, dissolve it in 40 ml of pure water at 25 °C, stir for 10 min, let it stand for 5 min, and then test the pH value of the solution.

[0176] The carbon content test method is as follows: Use the high-frequency infrared carbon and sulfur analyzer CS-2800G, adopt the high-frequency infrared absorption method, place the test sample in a high-frequency induction furnace, pass in oxygen to make it burn completely, the carbon element is converted into CO and a small amount of CO, the CO gas enters the infrared absorption cell, the infrared light of a specific wavelength (such as 4.26 μm) is absorbed by the CO molecule, the absorption intensity is linearly related to the concentration, and the carbon content is calculated by detecting the light intensity attenuation value, and the sensitivity can reach 0.001%.

[0177] Table 1 BET, TD, carbon element content of each positive electrode material and pH of the aqueous solution of the positive electrode material

[0178]

[0179]

[0180] It can be seen from Table 1 that compared with each comparative example, the positive electrode materials prepared in each example have a higher tapped density, which is beneficial to improving the compaction density of the battery, and then improving the energy density of the battery.

[0181] At the same time, the positive electrode materials prepared in each example have an appropriate pH value, an appropriate specific surface area and a low carbon content.

[0182] Further, the cathode materials prepared in each example and each comparative example were used as active substances, and were mixed according to a mass ratio of active substance:SP:PVDF of 90:5:5. Then, NMP was added thereto to prepare a viscous glue solution, which was coated on an aluminum foil and baked in a vacuum drying oven at 120 °C for 12 h to obtain a cathode electrode sheet. Subsequently, a sodium metal sheet was used as the counter electrode, a glass fiber (Waterman) was used as the separator, and 1 mol / L NaPF6 in EC / DMC = 1:1 (Alfa) was used as the electrolyte, and 2032 coin cells were assembled in an Ar-protected glove box. Then, the electrochemical performance of each coin cell was tested respectively: the cell was tested within a voltage range of 2.0 - 4.30 V, activated at 0.1C for three weeks, cycled at 1C for 100 weeks, and the 0.1C first-week discharge specific capacity, charge specific capacity, and first Coulombic efficiency (referred to as the first efficiency for short), the 1C first-week discharge specific capacity, and the discharge specific capacity retention rate after 1C cycling for 100 weeks were recorded.

[0183] Table 2 Electrochemical performance results of each cell

[0184]

[0185]

[0186] Figure 2 The 0.1C first-week charge-discharge curve of the cell composed of the cathode materials of Example 1 and Comparative Example 1.

[0187] Figure 3 The 1C cycle retention rate curve of the cell composed of the cathode materials of Example 1 and Comparative Example 1.

[0188] As can be seen from Table 2, the cathode materials prepared in each example have excellent cycling performance, which is significantly higher than that of each comparative example. This shows that the structural stability of the high-performance sodium-ion cathode materials with bulk and surface coating co-modification provided in each example of the present invention is significantly better than that of each comparative example, and can effectively inhibit the side reaction between the cathode material and the electrolyte at high voltage, thereby improving the cycling performance of the prepared cell. Among them, the higher the 1C capacity, the better the rate performance of the material. The 1C capacity of the modified material is high, and the 1C 100th cycle retention rate is high, indicating that the modified material not only does not have a significant decrease in rate performance, but also has a significant improvement in cycling performance, that is, the interfacial side reaction is less.

[0189] Among them, comparing Examples 1 - 10 with Comparative Example 1, through the effects of bulk and surface coating of the substrate, on the basis of ensuring the first charge, first discharge, and 1C first discharge of the material, the cycling performance of the material can be significantly improved, that is, through bulk and surface coating, the side reaction between the substrate and the electrolyte can be effectively inhibited and the cycling performance of the cathode material can be improved.

[0190] Comparing Example 1 with Example 13, a decrease in sodium coordination number will lead to a decrease in the first charge of the material. However, the cycling performance of the material after bulk and surface coating is still excellent. The main reason for the decrease in the first charge of the material caused by the decrease in sodium coordination number is that when the coordination number decreases, the binding of sodium ions to the surrounding lattice may become loose or defective, resulting in an irreversible phase change or collapse of the material structure after sodium ions are removed during the first charging process. In order to suppress this irreversible phase change or collapse, the cathode material will spontaneously limit the subsequent removal of sodium ions, which ultimately leads to a decrease in the first charge capacity.

[0191] Comparing Example 1 with Example 14, an increase in sodium coordination number will lead to an increase in the first charge of the material, but the first efficiency will correspondingly decrease, and the carbon content will correspondingly increase. However, the cycling performance of the material after bulk and surface coating is still excellent compared to Comparative Example 1.

[0192] At the same time, compared with each comparative example, the capacity and first efficiency of Example 1 are both higher. This shows that for the cathode material provided by the present invention, by simultaneously using element M that can be inserted into the sodium layer, high-valence element Q, and boron element, through the combined action of bulk coating and surface coating, the two indicators of high energy density and long cycle life can be balanced.

[0193] In addition, by comparing Example 1 with Comparative Example 7, it can be seen that not any coating element can achieve the effect of balancing high energy density and long cycle life.

[0194] Although the present invention has been illustrated and described with specific embodiments, it should be realized that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A cathode material modified by both bulk coating and surface coating, characterized in that, The general formula of the positive electrode material is Na x Cu a Ni b Mn c Ti d O2@M α Q β B γ ; Among them, Na x Cu a Ni b Mn c Ti d O2 is a layered transition oxide substrate, 0.88 ≤ x < 1.02, 0.07 ≤ a ≤ 0.13, 0.37 ≤ b ≤ 0.43, 0.37 ≤ c ≤ 0.43, 0.07 ≤ d ≤ 0.13, and a + b + c + d = 1; M is a bulk coating element capable of inserting into the sodium layer, and α is the ratio of the molar amount of element M to the total molar amount of copper, nickel, manganese, and titanium elements; Q is a high-valence element for both bulk coating and surface coating, and the valence of Q is not less than +5; β is the ratio of the molar amount of element Q to the total molar amount of copper, nickel, manganese, and titanium elements; B is a surface coating element, and γ is the ratio of the molar amount of element B to the total molar amount of copper, nickel, manganese, and titanium elements.

2. The cathode material co-modified by bulk coating and surface coating according to claim 1, characterized in that, At least one of the following conditions is satisfied: (1) The M includes at least one of Ca, Zn, Mg, and K elements; (2) The Q includes at least one of Mo, Nb, Ta, and W elements; (3)0.0001<α<0.01； (4)0.0001<β<0.01； (5) 0.0001 < γ < 0.

02.

3. The cathode material jointly modified by bulk coating and surface coating according to claim 1, characterized in that, At least one of the following conditions is satisfied: (1) The pH value of the solution obtained by dissolving 2 g of the positive electrode material in 40 mL of water at 25 °C is 11.7 - 12.5; (2) The specific surface area of the positive electrode material ≤ 0.50 m 2 / g; (3) The tap density of the positive electrode material is ≥ 1.8 g / cm 3 ; (4) The carbon element content in the positive electrode material ≤ 1500 ppm.

4. The preparation method of the cathode material co-modified by bulk coating and surface coating according to any one of claims 1 to 3, characterized in that, It includes the following steps: Mix a nickel copper manganese oxide precursor, a sodium source, and a titanium source and then calcine them to obtain a layered transition oxide substrate with the chemical formula Na x Cu a Ni b Mn c Ti d O2; wherein, 0.88 ≤ x < 1.02, 0.07 ≤ a ≤ 0.13, 0.37 ≤ b ≤ 0.43, 0.37 ≤ c ≤ 0.43, 0.07 ≤ d ≤ 0.13, and a + b + c + d = 1; Mix the layered transition oxide substrate with the M source, Q source, and B source and then sinter to obtain the positive electrode material jointly modified by bulk coating and surface coating; wherein, M in the M source is a bulk coating element capable of inserting into the sodium layer; Q in the Q source is a high-valence element for both bulk coating and surface coating, and the valence of Q is not less than +5; B in the B source is a surface coating element.

5. The preparation method of the cathode material co-modified by bulk coating and surface coating according to claim 4, wherein, The M source includes at least one of a Ca source, a Zn source, a Mg source, and a K source; Preferably, the Ca source includes at least one of CaCO3, CaO, CaO2, Ca(OH)2, CaF2, and CaSO4; Preferably, the Zn source includes at least one of ZnO, Zn(OH)2, ZnS, ZnCl2, and ZnSO4; Preferably, the Mg source includes at least one of MgO, Mg(OH)2, MgCl2, and MgCO3; Preferably, the K source includes at least one of K2CO3, KOH, and KF.

6. The preparation method of the cathode material jointly modified by bulk coating and surface coating according to claim 4, characterized in that The B source includes at least one of B2O3 and H3BO3; And / or, the Q source includes at least one of MoO3, Nb2O5, Ta2O5, and WO3.

7. The preparation method of the cathode material co-modified by bulk coating and surface coating according to claim 4, wherein, At least one of the following conditions is satisfied: (1) The ratio α of the molar amount of element M in the M source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < α < 0.01; (2) The ratio β of the molar amount of element Q in the Q source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < β < 0.01; (3) The ratio γ of the molar amount of element B in the B source to the total molar amount of copper, nickel, manganese, and titanium elements in the layered transition oxide substrate satisfies 0.0001 < γ < 0.02; (4) The calcination temperature is 900 - 1000 °C, and the calcination holding time is 15 - 24 h; (5) The sintering temperature is 900 - 1000 °C, and the sintering holding time is 12 - 24 h.

8. The preparation method of the cathode material co-modified by bulk coating and surface coating according to claim 4, characterized in that, The preparation method of the nickel copper manganese oxide precursor includes: mixing a nickel manganese copper mixed salt solution and a carbonate solution and carrying out a coprecipitation reaction to obtain a nickel manganese copper carbonate precursor; calcining the nickel manganese copper carbonate precursor to obtain the nickel copper manganese oxide precursor; Preferably, the particle size Dv50 of the nickel manganese copper carbonate precursor is 3 to 15 μm; Preferably, the reaction temperature of the coprecipitation reaction is 40 to 70 °C, and the reaction pH is 7 to 10.

9. A positive electrode sheet, characterized in that, It includes a cathode material co-modified by bulk coating and surface coating as described in any one of claims 1 to 3.

10. A sodium-ion battery, characterized in that, It includes a cathode sheet as described in claim 9.

Images