Positive electrode sheet, method for manufacturing the same, and battery

Abstract

The application relates to the technical field of sodium ion batteries, in particular to a positive electrode sheet, a preparation method thereof and a battery. The disclosed electrode sheet comprises a current collector and a first coating, a second coating and a third coating arranged on at least one side surface of the current collector in sequence in the thickness direction of the current collector. Specifically, the first coating is arranged on at least part of the at least one side surface of the current collector in the thickness direction, the first coating comprises a first active material, the first active material comprises an oxide, the second coating is arranged on the side of the first coating away from the current collector, the second coating comprises a functional material, the functional material comprises a nitride, and the third coating is arranged on the side of the second coating away from the current collector, the third coating comprises a second active material, and the second active material comprises a Prussian blue compound. The electrode sheet can well overcome the moisture generated by the Prussian blue compound during the cycle process, can avoid the generation of toxic substances, and can improve the cycle stability and safety performance of the battery.

Description

Technical Field

[0001] This application relates to the field of sodium-ion battery technology, specifically to a positive electrode sheet and its preparation method, and a battery. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries exhibit superior high and low temperature performance and higher safety. In recent years, Prussian blue compounds have been used as cathode materials in sodium-ion batteries. However, the use of Prussian blue compounds, due to the presence of water of crystallization and coordination water, can easily lead to a reduction in active sites and a decrease in reversible capacity, affecting the cycle stability of the battery. Furthermore, Prussian blue compounds are prone to hydrolysis under high temperature or humid environments, releasing highly toxic substances.

[0003] Therefore, it is of great significance to improve the capacity, cycle performance, and safety performance of Prussian blue sodium-ion batteries. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a positive electrode sheet and its preparation method, as well as a battery, which can effectively overcome the problem of Prussian blue compounds generating moisture during cycling, affecting the cycle stability of the battery; at the same time, it can also prevent the Prussian blue compounds on the positive electrode sheet from generating toxic substances, thus improving the safety performance of the battery.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] According to one aspect of the present invention, a positive electrode sheet is provided, comprising:

[0007] current collector;

[0008] A first coating is disposed on at least a portion of the surface on at least one side of the current collector in the thickness direction, the first coating comprising a first active material, the first active material comprising an oxide;

[0009] A second coating is disposed on the side of the first coating away from the current collector, and the second coating comprises a functional material, the functional material comprising a nitride;

[0010] A third coating is disposed on the side of the second coating away from the current collector, and the third coating includes a second active material, which includes a Prussian blue compound.

[0011] In some embodiments, the resistivity of the first coating is E, the resistivity of the second coating is F, and the resistivity of the third coating is G.

[0012] Wherein, E, F and G satisfy: G > 2F > E.

[0013] In some of these implementations, 7Ω·cm ≤ E ≤ 30Ω·cm.

[0014] In some of these implementations, 20Ω·cm ≤ F ≤ 50Ω·cm.

[0015] In some of these implementations, 140 Ω·cm ≤ G ≤ 150 Ω·cm.

[0016] In some embodiments, the median particle size D of the oxide in the first coating v50 Let X be the median particle size D of the Prussian blue compound in the third coating. v50 Y represents the median particle size D of the nitride. v50 Let Z be the sum of X and Y, where X > 1.3Y.

[0017] In some of these implementations, X satisfies: 8μm≤X≤15μm.

[0018] In some of these implementations, Y satisfies: 2μm≤Y≤6μm.

[0019] In some of these implementations, Z satisfies: 4μm≤Z≤8μm.

[0020] In some of these embodiments, the maximum thickness of the first coating is A, the maximum thickness of the second coating is B, and the thickness of the third coating is C, wherein A, B, and C satisfy: C ≥ 2A ≥ 6B.

[0021] In some of these implementations, A satisfies: 20μm≤A≤60μm.

[0022] In some of these implementations, B satisfies: 5μm≤B≤20μm.

[0023] In some of these implementations, C satisfies: 100μm≤C≤120μm.

[0024] In some embodiments, a tab is further provided on one side of the current collector in the width direction;

[0025] The thickness of the first coating increases gradually in the direction away from the tab; preferably, the thickness A1 of the first coating on the side closer to the tab is 0.

[0026] In some embodiments, the thickness of the second coating decreases gradually in a direction away from the tab.

[0027] In some embodiments, the oxide is a layered oxide with the chemical formula Na. x MO2, wherein x≤1, and M comprises at least one transition metal;

[0028] The transition metal includes at least one of Ni, Mn, Fe, Co, or Cu.

[0029] In some embodiments, the chemical formula of the Prussian blue compound is Na. x M1[M2(CN)6] y •zH2O, where 0<x≤2, 0.5≤y<1, 0<z≤20; M1 and M2 include any one of the same or different transition metals;

[0030] M1 includes any one of Fe, Mn, Cu, Ni or Co, and M2 includes any one of Fe, Mn, Cu, Ni or Co.

[0031] In some embodiments, the nitride is an inorganic nitride; the inorganic nitride includes at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, boron nitride, or silicon nitride.

[0032] According to another aspect of the present invention, the present invention also provides a method for preparing a positive electrode, comprising the following steps:

[0033] An oxide and a solvent are mixed to prepare a first slurry, and the first slurry is coated onto at least a portion of the surface of at least one side in the thickness direction of the current collector to form a first coating.

[0034] A second slurry is prepared by mixing a nitride and a solvent, and the second slurry is coated onto a first coating to form a second coating.

[0035] A third slurry is prepared by mixing a Prussian blue compound with a solvent, and the third slurry is coated onto a second coating to form a third coating.

[0036] The first slurry includes a first active material, which includes an oxide; the second slurry includes a functional material, which includes a nitride; and the third slurry includes a second active material, which includes a Prussian blue compound.

[0037] In some embodiments, the first slurry further includes a first binder and a first conductive agent, wherein the mass ratio of the oxide, the first conductive agent and the first binder is (90-94):(1-6):(2-4).

[0038] In some embodiments, the second slurry further includes a second binder and a second conductive agent, wherein the mass ratio of the nitride, the second conductive agent and the second binder is (90-94): (1-6): (2-4).

[0039] In some embodiments, the third slurry further includes a third binder and a third conductive agent, wherein the mass ratio of the Prussian blue compound, the third conductive agent and the third binder is (90-94):(1-6):(2-4).

[0040] According to a third aspect of the present invention, the present invention also provides a battery comprising a positive electrode sheet according to any embodiment of the present invention;

[0041] And / or, the positive electrode sheet prepared by the preparation method of any embodiment of another aspect of the present invention.

[0042] Implementing the technical solution of the present invention has at least the following beneficial effects:

[0043] 1. In this invention, a first coating, a second coating, and a third coating are sequentially disposed on the surface of the current collector along its thickness direction. The oxide in the first coating has a high specific capacity, and the Prussian blue compound in the third coating has good stability. During battery cycling, the third coating can work synergistically with the first coating to prevent the oxide structure in the first coating from collapsing. At the same time, the second coating located between the first and third coatings contains a functional material nitride, which can absorb water during the cycling process of the Prussian blue compound. Its product is alkaline and can react with cyanide to form non-toxic cyanide. Cyanide can improve the interfacial stability of the cathode material, especially suppressing oxygen evolution under high voltage, reducing membrane yellowing, and improving battery cycle and safety performance.

[0044] 2. In a preferred embodiment of the present invention, the thickness of the first coating gradually increases in the direction away from the tab, and the thickness of the second coating gradually decreases in the direction away from the tab. In this way, at high rates, the temperature rise on the tab side is relatively high, which can further cover the oxides in the first coating and prevent structural collapse due to excessive temperature rise, thus ensuring that the battery has good rate performance, cycle performance and service life.

[0045] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0046] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0047] Figure 1The diagram shows the positive electrode structure provided by this invention. Figure 1 .

[0048] Figure 2 The diagram shows the positive electrode structure provided by this invention. Figure 2 .

[0049] Figure 3 The diagram shows the positive electrode structure provided by this invention. Figure 3 .

[0050] Figure 4 The diagram shows the positive electrode structure provided by this invention. Figure 4 .

[0051] Explanation of reference numerals in the attached figures:

[0052] 10 – Current collector; 20 – First coating; 30 – Second coating; 40 – Third coating; 50 – Tab.

[0053] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0054] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0055] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0058] Sodium-ion batteries are another type of energy storage battery with a similar working mechanism and battery structure to lithium-ion batteries. Sodium resources are far more abundant than lithium, and their price is low and stable. Furthermore, due to the easy availability and low price of sodium, and the fact that aluminum foil can be used as the negative electrode current collector in sodium batteries instead of copper foil as in lithium batteries, they have a significant potential price advantage. With ongoing research, the potential advantages of sodium-ion batteries are being continuously discovered, especially their excellent performance at high and low temperatures and their relatively high safety, laying a solid foundation for their application in energy storage and power fields. Cathode materials, as a key component for cost reduction in sodium-ion batteries, have received considerable attention in recent years. Among them, Prussian blue cathode materials, with their low cost, simple processing, and high safety, have attracted the favor of many researchers. However, Prussian blue sodium-ion batteries have the following problems:

[0059] Firstly, Prussian blue materials contain a certain amount of crystal water and coordination water. These water molecules occupy lattice vacancies, leading to a reduction in active sites and a decrease in reversible capacity. At the same time, water molecules may decompose during charging and discharging, generating gas and affecting battery safety and cycle stability.

[0060] Secondly, in high-temperature or humid environments, the cyano groups in Prussian blue will hydrolyze, releasing highly toxic cyanide, posing a safety hazard and limiting its large-scale application.

[0061] Third, Prussian blue materials have a low capacity. Currently, the market has increasingly higher requirements for their rate capability. Prussian blue materials have a low capacity at high rates and will amplify the disadvantages of the first two points. For example, the temperature rises at high rates, making it easier for cyanide to be generated. At the same time, the material crystallizes in the later stages of high-rate cycling, and coordination water is more likely to be released, which drastically reduces battery safety.

[0062] In view of the technical problems existing in the prior art, the present invention provides a positive electrode sheet and its preparation method, as well as a battery, which can effectively overcome the problem of Prussian blue compound generating moisture during cycling, affecting the cycle stability of the battery; at the same time, it can also avoid the generation of toxic substances by Prussian blue compound on the positive electrode sheet, thereby improving the safety performance of the battery.

[0063] The specific technical solution of the present invention is as follows:

[0064] [Positive electrode tablets]

[0065] refer to Figure 1 and Figure 2In some embodiments of the present invention, a positive electrode is provided, comprising: a current collector 10, and a first coating 20, a second coating 30, and a third coating 40 on the current collector 10; wherein the first coating 20 is disposed on at least a portion of the surface of at least one side in the thickness direction of the current collector 10, and the first coating 20 comprises a first active material, the first active material comprising an oxide; the second coating 30 is disposed on the side of the first coating 20 away from the current collector 10, and the second coating 30 comprises a functional material, the functional material comprising a nitride; the third coating 40 is disposed on the side of the second coating 30 away from the current collector 10, and the third coating 40 comprises a second active material, the second active material comprising a Prussian blue compound.

[0066] It is understood that the aforementioned "first coating 20 disposed on at least one surface of the current collector 10 along its thickness direction" means that the first coating 20 can be disposed on one surface of the current collector 10 along its own thickness direction, or on two surfaces of the current collector 10 along its own thickness direction. Here, "surface" can refer to the entire area of ​​the current collector 10 or only a portion of it. Similarly, the second coating 30 disposed on the surface of the first coating 20 away from the current collector 10 can refer to the entire area of ​​that surface or only a portion of it. Similarly, the third coating 40 disposed on the surface of the second coating 30 away from the current collector 10 can refer to the entire area of ​​that surface or only a portion of it. In this embodiment, the surface can be only a portion of the current collector 10, and the remaining portion of the current collector 10 can be used to connect the tab 50. This application does not impose any particular limitation on this, as long as the purpose of this application is achieved.

[0067] As an example, the oxide in the first active material includes, but is not limited to, any one or more of inorganic oxides. Since oxides, as positive electrode active materials, have high specific capacity, they enable the battery to have high capacity. However, as positive electrode active materials, and disposed on the surface of the current collector, the structure of the oxide is prone to collapse and has poor stability under high rate or during cycling. Therefore, the Prussian blue compounds in the second active material of the third coating 40 have high rate performance and excellent stability, which can effectively ensure that the positive electrode has high specific capacity, good rate and cycle stability. The second coating 30, located between the first coating 20 and the third coating 40, includes functional materials, such as nitrides like boron nitride and silicon nitride. These functional materials can absorb moisture generated during cycling in the third coating 40, which contains Prussian blue compounds. The resulting product is alkaline and can react with cyanide to form non-toxic cyanide, which in turn improves the interfacial stability of the cathode material. Especially under high voltage conditions, it can effectively suppress oxygen evolution, reduce membrane yellowing, and thus improve battery cycle life and safety performance. It can also ensure the stability and safety of the battery during use.

[0068] In this embodiment, a first coating 20, a second coating 30, and a third coating 40 are sequentially arranged along the thickness direction away from the current collector 10. The first coating 20 includes a first active material containing oxides, which synergistically works with the third coating 40, which contains Prussian blue compounds, to improve the battery's rate capability, cycle performance, and capacity. The second coating 30, located in the middle and containing nitrides, effectively absorbs water generated by the Prussian blue compounds, further preventing the electrolysis of water during charging and discharging to produce gases (such as hydrogen and oxygen), thus affecting the battery's safety and cycle stability, and improving battery safety. Simultaneously, the nitrides in the second coating 30 absorb water molecules generated by the Prussian blue compounds in the third coating 40 during cycling and effectively prevent the cyano groups of the Prussian blue compounds in the third coating 40 from hydrolyzing and releasing highly toxic gases, making the battery safer and more environmentally friendly. In this embodiment, the positive electrode sheet has three coatings on the current collector 10 that can work together to improve battery capacity, rate capability, and cycle performance. At the same time, the three coatings can work together to effectively overcome the defects of a single coating, complement each other's strengths and weaknesses, and make the battery have excellent safety and improve the overall performance of the battery.

[0069] In some embodiments, the resistivity of the first coating 20 is E, the resistivity of the second coating 30 is F, and the resistivity of the third coating 40 is G; wherein, E, F, and G satisfy: G > 2F > E.

[0070] As an example, the film resistivity of the above-mentioned coating can be tested using the four-probe method, eddy current method, or electric field-potential method; this embodiment does not specifically limit this method. By ensuring that the film resistivity of the three coatings satisfies the above relationship—that is, in the thickness direction of the current collector 10, the film resistivity of the coating changes in a gradient from near to far from the current collector 10—with the first coating 20, second coating 30, and third coating 40 set as gradient resistivities, the polarization effect can be effectively reduced under high-rate cycling, thereby effectively improving the cycle life of the battery. If the above relationship is not satisfied, the polarization effect may be exacerbated under high-rate cycling, thus reducing the cycle life of the battery.

[0071] In some embodiments, 7Ω·cm ≤ E ≤ 30Ω·cm; exemplaryly, the diaphragm resistivity E can be any point value between any one or any two of 7Ω·cm, 8Ω·cm, 9Ω·cm, 10Ω·cm, 12Ω·cm, 15Ω·cm, 18Ω·cm, 20Ω·cm, 22Ω·cm, 24Ω·cm, 260Ω·cm, 280Ω·cm or 30Ω·cm.

[0072] In some embodiments, 20Ω·cm ≤ F ≤ 50Ω·cm; exemplaryly, the diaphragm resistivity F can be any point value between any one or any two of 20Ω·cm, 22Ω·cm, 25Ω·cm, 28Ω·cm, 30Ω·cm, 32Ω·cm, 35Ω·cm, 36Ω·cm, 38Ω·cm, 40Ω·cm, 42Ω·cm, 45Ω·cm, 46Ω·cm, 47Ω·cm, 48Ω·cm, 490Ω·cm, or 50Ω·cm.

[0073] In some embodiments, 140Ω·cm ≤ G ≤ 150Ω·cm; exemplaryly, the diaphragm resistivity G can be any point value between any one or any two of 140Ω·cm, 141Ω·m, 142Ω·cm, 143Ω·cm, 144Ω·cm, 145Ω·cm, 146Ω·cm, 147Ω·cm, 148Ω·cm, 149Ω·cm, 149.5Ω·cm, or 150Ω·cm.

[0074] In some embodiments, the median particle size D of the oxide in the first coating 20 v50 For X, the median particle size D of the Prussian blue compounds in the third coating 40 v50 Let Y be the median particle size D of the nitride. v50 Let Z be a integer, where X and Y satisfy: X > 1.3Y.

[0075] As an example, let X be the median particle size of the first active material oxide in the first coating 20, and Y be the median particle size of the second active material Prussian blue compound in the third coating 40. When X > 1.3Y, that is, when the positive electrode, negative electrode, separator, etc. are assembled into a battery, the Prussian blue compound positive electrode material particles closer to the negative electrode in the third coating 40 are smaller, which can ensure high-rate performance. The oxide particles closer to the current collector 10 in the first coating 20 are larger, which can ensure the overall capacity. At the same time, the first coating 20 is far from the negative electrode, which can alleviate the rapid volume expansion under high rate and ensure that the positive electrode has a certain structural stability. In other words, larger oxide particles result in higher structural stability during rapid expansion; if the oxide particles are smaller, the structural stability is lower, thus affecting the overall performance of the battery.

[0076] In some embodiments, X satisfies: 8μm≤X≤15μm; for example, X can be any point value between any one or any two of 8μm, 8.5μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0077] In some embodiments, Y satisfies: 2μm≤Y≤6μm; for example, Y can be any point value between any one or any two of 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm or 6μm.

[0078] In some embodiments, Z satisfies: 4μm≤Z≤8μm; as an example, Z can be any point value between any one or any two of 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm or 8μm.

[0079] In some embodiments, the maximum thickness of the first coating 20 is A, the maximum thickness of the second coating 30 is B, and the thickness of the third coating 40 is C, wherein A, B, and C satisfy: C≥2A≥6B.

[0080] As an example, in the thickness direction of the current collector 10, Figures 1-4 In the first direction, the thickness relationship between the three coatings satisfies the above formula, that is, the thickness of the third coating 40 is the largest. This ensures that the battery has a high capacity, as well as a better cycle rate and a better energy density; it can be understood that... Figures 1 to 4This is for illustrative purposes only and does not represent the actual thickness of each coating on the electrode sheet of this invention. The thickness of the third coating 40 is greater than the maximum thickness A of the first coating 20 and the maximum thickness B of the second coating 30. It can also be understood that the first coating 20 and the second coating 30 can be flat planes, uneven surfaces, or slopes with gradients changing in any direction. If the above relationship is not satisfied, for example, if the thickness of the second coating 30 is too thick, i.e., the content of nitride functional materials in the positive electrode sheet is too high, it will affect the overall energy density of the battery; while if the thickness of the first coating 20 in the positive electrode sheet is too thick, it will result in a higher proportion of oxides in the first active material of the positive electrode sheet, thus affecting the high-rate cycle life of the battery.

[0081] In some embodiments, A satisfies: 20μm≤A≤60μm; for example, A can be any point value between any one or any two of 20μm, 21μm, 22μm, 25μm, 28μm, 30μm, 32μm, 34μm, 36μm, 37μm, 38μm, 39μm, 40μm, 42μm, 45μm, 50μm, 55μm or 60μm.

[0082] In some embodiments, B satisfies: 5μm≤B≤20μm; as an example, B can be any point value between any one or any two of 5μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0083] In some embodiments, C satisfies: 100μm≤C≤120μm; for example, C can be any point value between any one or any two of 100μm, 101μm, 102μm, 103μm, 104μm, 105μm, 106μm, 107μm, 108μm, 109μm, 110μm, 112μm, 114μm, 116μm, 118μm or 120μm.

[0084] In some embodiments, in the width direction of the current collector 10, a tab 50 is also provided on one side of the current collector 10; the thickness of the first coating 20 increases gradually in the direction away from the tab 50; preferably, the thickness A1 of the first coating 20 near the tab 50 is 0.

[0085] refer to Figure 3 and Figure 4, in the second direction, i.e., the width direction of the current collector 10, a tab 50 is provided on either side of the current collector 10. The tab 50 and the current collector 10 can be connected by laser welding. Exemplarily, on one side close to the tab 50, the thickness of the first coating 20 is A1, and on the side far from the tab 50, the thickness of the first coating 20 is A2. Along the second direction away from the tab 50, the thickness gradient of the first coating 20 increases, that is, it changes in a gradient from A1 to A2, and A1 < A2. Since at high magnification, the temperature rise on the tab 50 side is relatively high, which has a certain adverse effect on the coating material on the current collector 10. For example, the first active material in the first coating 20, such as an oxide, may collapse due to excessive temperature. Through the above settings, the first active material in the first coating 20 can be well ensured to have a good structure, and the comprehensive performance of the battery is not affected. In a preferred embodiment, the thickness of the first coating 20 on the tab 50 side can be set to 0, that is, A1 = 0. In this way, it can be better ensured that when the temperature rise is too high, the first active material in the first coating 20 will not be affected and its structure will not collapse.

[0086] In some embodiments, the thickness of the second coating 30 decreases in a gradient along the direction away from the tab 50.

[0087] Reference Figure 4 , exemplarily, in the first direction, on the side close to the tab 50, the thickness of the second coating 30 is B1, and on the side far from the tab 50, the thickness of the second coating 30 is B2. Along the second direction away from the tab 50, the thickness gradient of the second coating 20 decreases, that is, it changes in a gradient from B1 to B2, and B1 > B2. Through the above settings, the thickness of the second coating 30 on the tab 50 side is relatively thick. It can be ensured that at high magnification, when the temperature rise on the tab 50 side is too high, the relatively thick second coating 30 can make the second active material in the third coating 40, such as a Prussian blue compound, less affected by temperature, thereby reducing the side reaction of the second active material in the third coating 40. That is to say, the second coating 30 on the tab 50 side is relatively thick, and in the thickness direction, less heat is transferred to the third coating 40, thus reducing the side reaction of the second active material, and the functional material in the second coating 30 is stable and will not be affected by excessive temperature, ensuring that the battery has good comprehensive performance.

[0088] In some embodiments, the oxide is a layered oxide, and the chemical formula of the layered oxide is Na x MO2, where x ≤ 1, and M includes at least one of transition metals; preferably, M includes at least one of Ni, Mn, Fe, Co, or Cu.

[0089] As an example, the oxide can preferably be a layered oxide, including but not limited to, NaNiO2, α-NaFeO2, Na 0.5 CoO2, Na0.8 CoO2, Na 0.6 One or more of CuO2.

[0090] In some embodiments, the chemical formula of Prussian blue compounds is Na. x M1[M2(CN)6] y • zH2O, wherein 0 < x ≤ 2, 0.5 ≤ y < 1, 0 < z ≤ 20; M1 and M2 include any one of the same or different transition metals; preferably, M1 includes any one of Fe, Mn, Cu, Ni or Co, and M2 includes any one of Fe, Mn, Cu, Ni or Co.

[0091] For example, Prussian blue compounds include, but are not limited to, Na. x Mn[Fe(CN)6] 0.8 • zH2O, Na x Co[Fe(CN)6] 0.7 • zH2O, Na x Ni[Fe(CN)6] 0.6 • zH2O, Na x Cu[Fe(CN)6] 0.5 • zH2O, Na x Fe[Cr(CN)6] 0.5 One or more of the following: •zH2O.

[0092] In some embodiments, the nitride is an inorganic nitride; preferably, the inorganic nitride includes, but is not limited to, one or more of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, boron nitride, or silicon nitride.

[0093] [Preparation method of positive electrode plate]

[0094] In some embodiments of the present invention, a method for preparing a positive electrode sheet is provided, comprising the following steps:

[0095] S101. Mix oxide and solvent to prepare a first slurry, and apply the first slurry to at least a portion of the surface on at least one side of the current collector in the thickness direction to form a first coating.

[0096] S102. The nitride and solvent are mixed to prepare a second slurry, and the second slurry is coated onto the first coating to form a second coating.

[0097] S103. A third slurry is prepared by mixing a Prussian blue compound with a solvent, and the third slurry is coated onto a second coating layer to form a third coating layer; wherein, the first slurry includes a first active material, the first active material includes an oxide, the second slurry includes a functional material, the functional material includes a nitride, and the third slurry includes a second active material, the second active material includes a Prussian blue compound.

[0098] Exemplarily, the first slurry includes a first active material, such as an oxide, preferably a layered oxide, in any of the above embodiments; the second slurry includes a functional material, such as a nitride, in any of the above embodiments; and the third slurry includes a second active material, such as a Prussian blue compound, in any of the above embodiments. Solvents include, but are not limited to, N-methylpyrrolidone (NMP), toluene, acetone, etc. It is understood that when preparing the first slurry, techniques such as ball milling can be used to grind the oxide, thereby effectively controlling the median particle size Dv50 of the first active material in the first slurry. This allows for effective control of the overall performance of the positive electrode and the battery, achieving the technical effects achieved by the electrode in any of the above embodiments.

[0099] In some embodiments, the first slurry further includes a first binder and a first conductive agent, wherein the mass ratio of the oxide, the first conductive agent and the first binder is (90-94):(1-6):(2-4).

[0100] As an example, the mass ratio of oxide, first binder and first conductive agent in the first slurry can be any one of 90:1:2, 90:6:4, 92:1:1, 90:3:3, 94:6:4 or 94:1:2 or any ratio within any of the above ranges; by controlling the mass ratio between the components in the first slurry, the content of the first active material in the formed first coating can be well controlled, thereby effectively controlling the overall performance of the subsequently produced positive electrode sheet.

[0101] In some embodiments, the second slurry further includes a second binder and a second conductive agent, wherein the mass ratio of the nitride, the second conductive agent, and the second binder is (90–94):(1–6):(2–4). Exemplarily, the mass ratio of the nitride, the second conductive agent, and the second binder can be any one of 90:1:2, 90:6:4, 90:4:3, 92:1:2, 94:1:2, 94:6:4, or 94:3:3.5, or any ratio within any of the above ranges.

[0102] In some embodiments, the third slurry further includes a third binder and a third conductive agent, wherein the mass ratio of the Prussian blue compound, the third conductive agent, and the third binder is (90–94):(1–6):(2–4). Exemplarily, the mass ratio of the Prussian blue compound, the second conductive agent, and the second binder can be any one of 90:1:2, 90:6:4, 90:2:3.2, 92:1:2, 94:1:2, 94:6:4, or 94:5:3, or any ratio within any of the above ranges.

[0103] Optionally, the first conductive agent includes one or more of Super P, acetylene black, Ketjen black, conductive graphite, and carbon black; the second conductive agent includes one or more of Super P, acetylene black, Ketjen black, conductive graphite, and carbon black; and the third conductive agent includes one or more of Super P, acetylene black, Ketjen black, conductive graphite, and carbon black. The first binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylates, and polyacrylic acid binders; the second binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylates, and polyacrylic acid binders; and the third binder includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylates, and polyacrylic acid binders.

[0104] Optionally, the current collector 10 in the positive electrode can be made of metal materials such as aluminum, copper, nickel, stainless steel, or nickel-plated steel, or it can be a foil material with a surface coating layer. This coating layer has one or more functions such as improving conductivity, improving adhesion, improving safety, reducing DCR, and increasing lithium-ion conductivity. For example, it can be a carbon coating layer, a carbon coating + graphene / conductive carbon nanotube / boehmite or alumina, or a solid electrolyte coating. Of course, in other embodiments, a composite current collector can also be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on a polymer material substrate such as polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, etc.

[0105] [Battery]

[0106] In some embodiments of the present invention, a battery is also provided, comprising: the positive electrode sheet in any of the above embodiments;

[0107] In some embodiments, the battery includes a positive electrode sheet prepared by the method for preparing the positive electrode sheet in any of the above embodiments.

[0108] The battery also includes an electrolyte, a separator, and a battery casing. That is, the battery may include the positive electrode, negative electrode, separator, electrolyte, and battery casing as described in any of the above embodiments, with the positive electrode, negative electrode, separator, and electrolyte all disposed within the battery casing. Battery structures include, but are not limited to, blade batteries, prismatic hard-case batteries, or cylindrical hard-case batteries.

[0109] The diaphragm used in this embodiment is a diaphragm used in the art and is not particularly limited herein. All solvents and substances in this invention are commercially available.

[0110] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0111] The present application will be described in detail below with reference to the accompanying drawings and examples. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0112] Example 1

[0113] S11: Weigh out layered oxides NaFeO2, SP (conductive carbon black), and PVDF (polyvinylidene fluoride) in a mass ratio of 90:6:4. Add NMP at a mass ratio of NaFeO2 to N-methylpyrrolidone (NMP) of 1:2, disperse at high speed, and mix evenly to obtain the first slurry; wherein, layered oxide D v50 It is 10μm.

[0114] S12: Weigh aluminum nitride, SP, and PVDF according to a mass ratio of 90:5:5. Add NMP according to a mass ratio of aluminum nitride to N-methylpyrrolidone (NMP) of 1:2. Disperse at high speed and mix evenly to obtain the second slurry; wherein, the D of aluminum nitride... v50 It is 6μm.

[0115] S13: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73 Fe[Fe(CN)6] • 3,8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the third slurry; Prussian blue D v50 It is 3μm.

[0116] S14: Set the parameters of the coating machine to make the coating thickness 50μm, and uniformly coat the first slurry onto the aluminum foil (current collector). After the coating is completed, the electrode is dried at 110℃ for 3 hours to obtain the first electrode. The thickness of the first coating at A2 is 50μm and the thickness at A1 is 0μm.

[0117] S15: The second slurry is uniformly coated on the first electrode and dried to obtain the second electrode. The thickness of the second coating at B1 is 15μm and the thickness at B2 is 5μm.

[0118] S16: The third slurry is uniformly coated on the second electrode and dried at 110°C for 4 hours to obtain the positive electrode. The thickness C of the third coating is 110 μm.

[0119] The resistivity of the first coating is 10 Ω·cm, the resistivity of the second coating is 25 Ω·cm, and the resistivity of the third coating is 150 Ω·cm.

[0120] Example 2

[0121] S21: Layered oxides NaFeO2, SP, and PVDF are weighed out in a mass ratio of 90:6:4. NMP is added in a mass ratio of NaFeO2 to N-methylpyrrolidone (NMP) of 1:2. The mixture is then dispersed at high speed and thoroughly mixed to obtain the first slurry. Layered oxides D v50 It is 10μm.

[0122] S22: Weigh silicon nitride, SP, and PVDF according to a mass ratio of 90:5:5. Add NMP according to a mass ratio of aluminum nitride to N-methylpyrrolidone (NMP) of 1:2. Disperse at high speed and mix evenly to obtain the second slurry; wherein, the D of silicon nitride... v50 It is 5μm.

[0123] S23: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73 Fe[Fe(CN)6] • 3,8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the third slurry; Prussian blue D v50 It is 3μm.

[0124] S24: Set the coating machine parameters to make the coating thickness 50μm, and uniformly coat the first slurry onto the aluminum foil. After the coating is completed, the electrode is dried at 110℃ for 3 hours to obtain the first electrode. The thickness of the first coating at A2 is 50μm and the thickness at A1 is 0μm.

[0125] S25: The second slurry is uniformly coated on the first electrode and dried to obtain the second electrode. The thickness of the second coating at B1 is 15μm and the thickness at B2 is 5μm.

[0126] S26: The third slurry is uniformly coated on the second electrode and dried at 110°C for 4 hours to obtain the positive electrode. The thickness C of the third coating is 110 μm.

[0127] The resistivity of the first coating is 10 Ω·cm, the resistivity of the second coating is 25 Ω·cm, and the resistivity of the third coating is 150 Ω·cm.

[0128] Example 3

[0129] S31: Layered oxides NaFeO2, SP, and PVDF are weighed out in a mass ratio of 90:6:4. NMP is added in a mass ratio of NaFeO2 to N-methylpyrrolidone (NMP) of 1:2. The mixture is then dispersed at high speed and thoroughly mixed to obtain the first slurry. Layered oxides D v50 It is 9μm.

[0130] S32: Weigh aluminum nitride, SP, and PVDF according to a mass ratio of 90:5:5. Add NMP according to a mass ratio of aluminum nitride to N-methylpyrrolidone (NMP) of 1:2. Disperse at high speed and mix evenly to obtain the second slurry; wherein, the D of aluminum nitride... v50 It is 6μm.

[0131] S33: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73 Fe[Fe(CN)6] • 3,8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the third slurry; Prussian blue D v50 It is 6μm.

[0132] S34: Set the coating machine parameters to make the coating thickness 50μm, and uniformly coat the first slurry onto the aluminum foil. After the coating is completed, the electrode is dried at 110℃ for 3 hours to obtain the first electrode. The thickness of the first coating at A2 is 50μm and the thickness at A1 is 0μm.

[0133] S35: The second slurry is uniformly coated on the first electrode and dried to obtain the second electrode. The thickness of the second coating at B1 is 15μm and the thickness at B2 is 5μm.

[0134] S36: The third slurry is uniformly coated on the second electrode and dried at 110°C for 4 hours to obtain the positive electrode. The thickness C of the third coating is 110 μm.

[0135] The resistivity of the first coating is 7 Ω·cm, the resistivity of the second coating is 20 Ω·cm, and the resistivity of the third coating is 140 Ω·cm.

[0136] Example 4

[0137] S41: Layered oxides NaFeO2, SP, and PVDF are weighed out in a mass ratio of 90:6:4. NMP is added in a mass ratio of NaFeO2 to N-methylpyrrolidone (NMP) of 1:2. The mixture is then dispersed at high speed and thoroughly mixed to obtain the first slurry. Layered oxides D v50 It is 11μm.

[0138] S42: Weigh aluminum nitride, SP, and PVDF according to a mass ratio of 90:5:5. Add NMP according to a mass ratio of aluminum nitride to N-methylpyrrolidone (NMP) of 1:2. Disperse at high speed and mix evenly to obtain the second slurry; wherein, the D of aluminum nitride... v50 It is 6μm.

[0139] S43: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73 Fe[Fe(CN)6] • 3,8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the third slurry; Prussian blue D v50 It is 3μm.

[0140] S44: Set the coating machine parameters to make the coating thickness 50μm, and uniformly coat the first slurry onto the aluminum foil. After the coating is completed, the electrode is dried at 110℃ for 3 hours to obtain the first electrode. The thickness of the first coating at A2 is 50μm and the thickness at A1 is 0μm.

[0141] S45: The second slurry is uniformly coated on the first electrode and dried to obtain the second electrode. The thickness of the second coating at B1 is 15μm and the thickness at B2 is 5μm.

[0142] S46: The third slurry is uniformly coated on the second electrode and dried at 110°C for 4 hours to obtain the positive electrode. The thickness C of the third coating is 110 μm.

[0143] The resistivity of the first coating is 30 Ω·cm, the resistivity of the second coating is 50 Ω·cm, and the resistivity of the third coating is 150 Ω·cm.

[0144] Example 5

[0145] S51: Layered oxides NaFeO2, SP, and PVDF are weighed out in a mass ratio of 90:6:4. NMP is added in a mass ratio of NaFeO2 to N-methylpyrrolidone (NMP) of 1:2. The mixture is then dispersed at high speed and thoroughly mixed to obtain the first slurry. Layered oxides D v50 It is 10μm.

[0146] S52: Weigh aluminum nitride, SP, and PVDF according to a mass ratio of 90:5:5. Add NMP according to a mass ratio of aluminum nitride to N-methylpyrrolidone (NMP) of 1:2. Disperse at high speed and mix evenly to obtain the second slurry; wherein, the D of aluminum nitride... v50 It is 6μm.

[0147] S53: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73 Fe[Fe(CN)6] • 3,8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the third slurry; Prussian blue D v50 It is 3μm;

[0148] S54: Set the coating machine parameters to make the coating thickness 50μm, and uniformly coat the first slurry onto the aluminum foil. After the coating is completed, the electrode is dried at 110℃ for 3 hours to obtain the first electrode. The thickness of the first coating at A2 is 60μm and the thickness at A1 is 0μm.

[0149] S55: The second slurry is uniformly coated on the first electrode and dried to obtain the second electrode. The thickness of the second coating at B1 is 20μm and the thickness at B2 is 5μm.

[0150] S56: The third slurry is uniformly coated on the second electrode and dried at 110°C for 4 hours to obtain the positive electrode. The thickness C of the third coating is 110 μm.

[0151] The resistivity of the first coating film is 10 Ω·cm, the resistivity of the second coating film is 25 Ω·cm, and the resistivity of the third coating film is 150 Ω·cm.

[0152] Example 6

[0153] S61: Layered oxides NaFeO2, SP, and PVDF were weighed out in a mass ratio of 90:6:4. NMP was added at a mass ratio of NaFeO2 to N-methylpyrrolidone (NMP) of 1:2. The mixture was then dispersed at high speed and thoroughly mixed to obtain the first slurry. Layered oxides D v50 It is 11μm.

[0154] S62: Weigh aluminum nitride, SP, and PVDF according to a mass ratio of 90:5:5. Add NMP according to a mass ratio of aluminum nitride to N-methylpyrrolidone (NMP) of 1:2. Disperse at high speed and mix evenly to obtain the second slurry; wherein, the D of aluminum nitride... v50 It is 6μm.

[0155] S63: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73 Fe[Fe(CN)6] • 3,8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the third slurry; Prussian blue D v50 It is 4μm.

[0156] S64: Set the coating machine parameters to make the coating thickness 50μm, and uniformly coat the first slurry onto the aluminum foil. After the coating is completed, the electrode is dried at 110℃ for 3 hours to obtain the first electrode. The thickness A of the first coating is 50μm.

[0157] S65: The second slurry is uniformly coated on the first electrode and dried to obtain the second electrode. The thickness B of the second coating is 5 μm.

[0158] S66: The third slurry is uniformly coated on the second electrode and dried at 110°C for 4 hours to obtain the positive electrode. The thickness C of the third coating is 110 μm.

[0159] The resistivity of the first coating is 8 Ω·cm, the resistivity of the second coating is 20 Ω·cm, and the resistivity of the third coating is 145 Ω·cm.

[0160] Comparative Example 1

[0161] S91: Weigh out Prussian blue analogue Na in a mass ratio of 90:6:4. 1.73 Fe[Fe(CN)6] •3.8H2O, SP and PVDF, according to the Prussian blue analogue Na 1.73Fe[Fe(CN)6]•3.8H2O and NMP were added in a mass ratio of 1:2.2, and NMP was dispersed at high speed and mixed evenly to obtain the second slurry.

[0162] S93: Set the coating machine parameters to make the coating thickness 110μm, and uniformly coat the positive electrode slurry onto the aluminum foil. After the coating is completed, the electrode is dried at 110℃ for 2 hours to obtain the positive electrode.

[0163] The resistivity of the Prussian blue film is 150 Ω·cm.

[0164] Test case

[0165] 1. Battery manufacturing

[0166] (1) Preparation of positive electrode sheet: The positive electrode sheets obtained in the examples and comparative examples were rolled and pressed, and the positive electrode sheets were punched into positive electrode sheets with a diameter of φ14mm using a punching machine.

[0167] (2) Preparation of negative electrode sheet: The negative electrode hard carbon material, conductive carbon black, and binder PVDF are mixed with solvent NMP in a ratio of 8:1:1 to prepare a negative electrode slurry. The negative electrode slurry is uniformly coated on copper foil in a certain ratio and vacuum dried at 80°C. The negative electrode sheet is then rolled and punched into a negative electrode sheet with a diameter of φ16mm using a punching machine.

[0168] (3) The diaphragm is Whatman GF / D glass fiber; the electrolyte is a 1 mol / L NaPF6 diethylene glycol dimethyl ether solution.

[0169] Battery fabrication: The full cell was assembled in the following order: positive electrode shell, positive electrode sheet, separator, negative electrode sheet, nickel foam, and negative electrode shell. The assembled full cell was held with insulated tweezers and placed on a sealing machine for sealing. Finally, the sealed full cell was left to stand for 24 hours to allow the electrolyte to fully wet the electrode materials before electrochemical testing.

[0170] 2. Testing Methods

[0171] (1) First-cycle capacity test: Sodium-ion batteries prepared in the example and comparative examples were tested for first-cycle capacity under the following conditions: 25°C, 0.2C rate, charging cut-off voltage of 4.8 V, and discharging cut-off voltage of 2.0 V.

[0172] (2) 2C / 1C cycle life test: Sodium-ion batteries prepared in the examples and comparative examples were tested under the following conditions: 0.2 C rate, 4.8 V charging cut-off voltage, and 2.0 V discharging cut-off voltage at 25°C. Then, 2C / 1C cycle test was conducted at 25°C (4.8 V charging cut-off voltage and 2.0 V discharging cut-off voltage).

[0173] (3) Yellowing of the separator and damage of layered oxide particles after 200 cycles: After 200 cycles, the battery was disassembled to observe the yellowing of the separator. The positive electrode was obtained after disassembly, and SEM tests were performed on the front and cross-section to check the particle damage.

[0174] (4) Membrane resistivity test: The electrode is punched into a small disc and placed between the two electrodes of the membrane resistivity meter. The test pressure (8 MPa) is set on the MRMS software, and the test is started to obtain the membrane resistivity. The test results are shown in Table 1 and Table 2.

[0175] Table 1. Test results of particle size and diaphragm resistivity:

[0176]

[0177] As can be seen from Table 1, the film resistivity of each coating of the electrode in the embodiments of the present invention satisfies the above-mentioned relationship.

[0178] Table 2. Initial charge / discharge capacity, coulombic efficiency, 2C / 1C cycle life, diaphragm yellowing after 200 cycles, and particle breakage:

[0179]

[0180] As can be seen, compared with the comparative example, the battery in this embodiment of the invention has a higher discharge specific capacity and a longer cycle life. The breakage of the first active material particles in the first coating is extremely slight. The separator does not turn yellow, indicating that the Prussian blue compound in the third coating has not undergone hydrolysis. Under high voltage, it inhibits oxygen evolution, reduces separator yellowing, and enables the battery to have higher cycle and safety performance.

[0181] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0182] In the above embodiments, the descriptions of each embodiment have their own emphasis. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments. The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0183] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0184] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0185] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0186] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A positive electrode plate, characterized in that, include: current collector; A first coating is disposed on at least a portion of the surface on at least one side of the current collector in the thickness direction, the first coating comprising a first active material, the first active material comprising an oxide; A second coating is disposed on the side of the first coating away from the current collector, and the second coating comprises a functional material, the functional material comprising a nitride; A third coating is disposed on the side of the second coating away from the current collector, and the third coating includes a second active material, which includes a Prussian blue compound.

2. The positive electrode sheet according to claim 1, characterized in that, The resistivity of the first coating is E, the resistivity of the second coating is F, and the resistivity of the third coating is G. Wherein, E, F and G satisfy: G > 2F > E.

3. The positive electrode sheet according to claim 2, characterized in that, Satisfying at least one of features (1) to (3): (1) 7Ω·cm≤E≤30Ω·cm; (2) 20Ω·cm≤F≤50Ω·cm; (3) 140Ω·cm≤G≤150Ω·cm.

4. The positive electrode sheet according to claim 1, characterized in that, The median particle size D of the oxide in the first coating v50 Let X be the median particle size D of the Prussian blue compound in the third coating. v50 Y represents the median particle size D of the nitride. v50 Z; Wherein, X, Y and Z satisfy at least one of features (1) to (4): (1) X>1.3Y; (2) 8μm≤X≤15μm; (3) 2μm≤Y≤6μm; (4) 4μm≤Z≤8μm.

5. The positive electrode sheet according to claim 4, characterized in that, The maximum thickness of the first coating is A, the maximum thickness of the second coating is B, and the thickness of the third coating is C; Wherein, A, B and C satisfy at least one of features (1) to (4): (1) C≥2A≥6B; (2) 20μm≤A≤60μm; (3) 5μm≤B≤20μm; (4) 100μm≤C≤120μm.

6. The positive electrode sheet according to claim 1, characterized in that, In the width direction of the current collector, one side of the current collector is also provided with an electrode tab; The thickness of the first coating increases gradually in the direction away from the tab; And / or, the thickness of the second coating decreases gradually in a direction away from the tab.

7. The positive electrode sheet according to claim 6, characterized in that, The thickness of the first coating near the tab is A1, where A1 = 0.

8. The positive electrode sheet according to claim 1, characterized in that, Satisfying at least one of features (1) to (3): (1) The oxide is a layered oxide, and the chemical formula of the layered oxide is Na. x MO2, wherein x≤1, and M comprises at least one transition metal; The transition metal includes at least one of Ni, Mn, Fe, Co, or Cu; (2) The chemical formula of the Prussian blue compound is Na x M1[M2(CN)6] y • zH2O, where 0 < x ≤ 2, 0.5 ≤ y < 1, 0 < z ≤ 20; M1 and M2 include any one of the same or different transition metals; M1 includes any one of Fe, Mn, Cu, Ni or Co, and M2 includes any one of Fe, Mn, Cu, Ni or Co; (3) The nitride is an inorganic nitride; the inorganic nitride includes at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, boron nitride or silicon nitride.

9. A method for preparing a positive electrode sheet as described in any one of claims 1 to 8, characterized in that, Includes the following steps: An oxide and a solvent are mixed to prepare a first slurry, and the first slurry is coated onto at least a portion of the surface of at least one side in the thickness direction of the current collector to form a first coating. A second slurry is prepared by mixing a nitride and a solvent, and the second slurry is coated onto a first coating to form a second coating. A third slurry is prepared by mixing a Prussian blue compound with a solvent, and the third slurry is coated onto a second coating to form a third coating. The first slurry includes a first active material, which includes an oxide; the second slurry includes a functional material, which includes a nitride; and the third slurry includes a second active material, which includes a Prussian blue compound.

10. The method for preparing the positive electrode sheet according to claim 9, characterized in that, Satisfying at least one of features (1) to (3): (1) The first slurry further includes a first binder and a first conductive agent, wherein the mass ratio of the oxide, the first conductive agent and the first binder is (90-94):(1-6):(2-4); (2) The second slurry also includes a second binder and a second conductive agent, wherein the mass ratio of the nitride, the second conductive agent and the second binder is (90-94): (1-6): (2-4); (3) The third slurry also includes a third binder and a third conductive agent, and the mass ratio of the Prussian blue compound, the third conductive agent and the third binder is (90-94):(1-6):(2-4).

11. A battery, characterized in that, include: The positive electrode sheet according to any one of claims 1 to 8; And / or, the positive electrode sheet prepared by the method of preparation of the positive electrode sheet according to claim 9 or 10.

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