Positive pole piece for sodium ion battery, sodium ion battery and device

Abstract

The invention provides a positive pole piece for a sodium ion battery, the sodium ion battery and a device. The positive pole piece comprises a positive current collector, a sodium supplementing layer and a positive coating, the sodium supplementing layer and the positive coating are sequentially stacked on at least one side of the positive current collector, and the sodium supplementing layer comprises a sodium supplementing agent sodium-rich transition metal oxide; and the positive electrode coating contains a positive electrode active material and a sacrificial positive electrode sodium supplementing agent which can be decomposed to generate gas. The two types of positive sodium supplements are introduced into the positive pole piece at the same time and are arranged in a layered manner, so that a plurality of problems caused by independent use of the two types of positive sodium supplements can be reduced, the energy density of the battery is improved, the impedance of the battery is not obviously increased, and the continuous discharge capacity of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium-ion batteries, and particularly to a positive electrode sheet for a sodium-ion battery, a sodium-ion battery, and a device. Background Art

[0002] A sodium-ion battery is a battery with a similar energy storage mechanism to a lithium-ion battery. Since the abundance of sodium in the earth's crust is much higher than that of lithium, the cost of a sodium-ion battery is much lower than that of a lithium-ion battery, making it more promising to meet the low-cost requirements for large-scale energy storage devices in the future.

[0003] During the first charging process of a sodium-ion battery, the formation of a solid electrolyte interface (SEI) film on the negative electrode surface irreversibly consumes a large amount of active sodium ions released from the positive electrode, reducing the specific capacity and energy density of the positive electrode of the sodium-ion battery. Sodium supplementation for the sodium-ion battery can compensate for the irreversible consumption of active sodium ions caused by the formation of the negative electrode SEI film, thereby improving the energy density of the sodium-ion battery and narrowing the gap in energy density between it and lithium batteries. Among them, the methods of sodium supplementation are generally divided into positive electrode sodium supplementation and negative electrode sodium supplementation, and positive electrode sodium supplementation has the most promising industrial application prospects due to its high safety and the need not to change the existing battery preparation process.

[0004] Among them, positive electrode sodium supplementation generally directly mixes a positive electrode sodium supplement agent with a high irreversible sodium deintercalation capacity (such as NaN3, Na2O2, Na2C2O4, Na5FeO4, Na2NiO2, NaCrO2, etc.) with the positive electrode active material. During the formation process of the sodium-ion battery, the positive electrode sodium supplement agent can decompose and release active sodium ions at a certain potential to supplement sodium for the battery. Existing positive electrode sodium supplementation schemes cannot take into account both the high energy density and the continuous discharge capacity of the battery.

[0005] Therefore, it is necessary to develop a positive electrode sodium supplementation scheme with good sodium supplementation effect and not affecting the subsequent electrochemical performance of the sodium-ion battery after sodium supplementation. Summary of the Invention

[0006] In view of this, the present application introduces a decomposable gas-producing sacrificial positive electrode sodium supplement agent and a sodium-rich transition metal oxide into the positive electrode sheet for a sodium-ion battery together, and controls their reasonable distribution, which can reduce the negative effects brought by using only one sodium supplement agent. While giving full play to the utilization rate of these two types of sodium supplement agents and improving the energy density of the battery, it does not significantly increase the battery impedance and reduce the continuous discharge capacity of the sodium-ion battery.

[0007] Specifically, the first aspect of the present application provides a positive electrode sheet for a sodium-ion battery, which includes a positive electrode current collector and a sodium supplement layer and a positive electrode coating layer stacked on at least one side of the positive electrode current collector. Among them, on the same side of the positive electrode current collector, the positive electrode coating layer is arranged on the side of the sodium supplement layer away from the positive electrode current collector; the sodium supplement layer includes a sodium supplement agent and a sodium-rich transition metal oxide; the positive electrode coating layer includes a sodium positive electrode active material and a sacrificial positive electrode sodium supplement agent that can decompose and generate gas.

[0008] In the above positive electrode sheet of the embodiment of the present application, by introducing a sodium-rich transition metal oxide and a sacrificial positive electrode sodium supplement agent at the same time and reasonably distributing their arrangements, the sodium supplement efficiency of the two types of sodium supplement agents can be improved. At the same time, the addition amount of the sacrificial positive electrode sodium supplement agent can be reduced, and the amount of gas generated by its decomposition can be reduced, thereby reducing the damage to the microstructure of the positive electrode sheet and reducing the deterioration of the battery volume energy density. It also avoids the problem of increased positive electrode liquid phase impedance caused by the same-layer distribution of sodium supplement agents such as sodium-rich transition metal oxides and positive electrode active materials, and improves the continuous discharge capacity of sodium-ion batteries. Therefore, a sodium-ion battery with excellent comprehensive performance can be prepared by using the above positive electrode sheet.

[0009] In the second aspect, the present application provides a sodium-ion battery, which includes the positive electrode sheet as described in the first aspect of the present application.

[0010] Due to the adoption of the above positive electrode sheet, the utilization rate of the two types of sodium supplement agents in the sodium-ion battery is high, the total reversible sodium amount of the battery is high, the energy density is improved, and at the same time, the battery impedance is low and the power performance is good.

[0011] In the third aspect, the present application provides a device including the sodium-ion battery described in the second aspect of the present application, and the device includes an electrical equipment or an energy storage system. Description of the Drawings

[0012] Figure 1 It is a schematic structural diagram of the positive electrode sheet provided by the present application.

[0013] Figure 2 It is another schematic structural diagram of the positive electrode sheet provided by the present application. Detailed Embodiments

[0014] Next, the technical solutions of the embodiments of the present application will be described with reference to the drawings.

[0015] Please refer to Figure 1 and Figure 2, an embodiment of the present application provides a positive electrode sheet 100 for a sodium-ion battery, which includes a positive electrode current collector 10 and a sodium supplementation layer 20 and a positive electrode coating layer 30 that are sequentially stacked on at least one side of the positive electrode current collector 10. Among them, the sodium supplementation layer 20 includes a first sodium supplementation agent, sodium-rich transition metal oxide 201; the positive electrode coating layer 30 includes a sodium positive electrode active material 302 and a sacrificial positive electrode sodium supplementation agent 301 that can decompose and generate gas.

[0016] In the above positive electrode sheet 100, both the sacrificial positive electrode sodium supplementation agent 301 that can decompose and generate gas and the sodium-rich transition metal oxide sodium supplementation agent 201 are contained. On the one hand, compared with the positive electrode sheet containing only the sacrificial positive electrode sodium supplementation agent, when the total sodium supplementation amount remains unchanged, the addition amount of the sacrificial positive electrode sodium supplementation agent in the positive electrode sheet of the present application is lower, and the total amount of gas generated by its decomposition also decreases accordingly, thereby reducing the damage to the microstructure of the positive electrode sheet caused by the release of a large amount of gas and the resulting reduction in the volumetric energy density of the battery; the positive electrode coating layer 30 containing the sacrificial positive electrode sodium supplementation agent and the sodium positive electrode active material is arranged on the surface of the positive electrode sheet 100, away from the positive electrode current collector 10, and the discharge path of the gas generated by its decomposition is shortened, which is more conducive to gas discharge. In this way, during its decomposition process, the battery polarization phenomenon is reduced, its decomposition ratio and sodium supplementation effect are improved. Due to the reduction of battery polarization, the utilization rate of the sodium-rich transition metal oxide sodium supplementation agent can also be improved to a certain extent. At the same time, there is less gas remaining in the positive electrode sheet 100, the battery impedance is reduced, and the continuous discharge capacity is improved.

[0017] On the other hand, in the present application, the sodium-rich transition metal oxide, which is a positive electrode sodium supplementation agent, is arranged in the sodium supplementation layer 20 close to the positive electrode current collector 10, and a positive electrode coating layer 30 containing a sacrificial positive electrode sodium supplementation agent is arranged thereon. First, compared with the positive electrode sheet whose sodium supplementation material only contains sodium-rich transition metal oxide, along the direction away from the positive electrode current collector 10, the sodium deintercalation potential of the sodium-rich transition metal oxide in the present application will not gradually increase, ensuring a relatively high sodium supplementation efficiency. Second, compared with the positive electrode sheet whose sodium supplementation material only contains sodium-rich transition metal oxide, when the total sodium supplementation capacity remains unchanged, two types of positive electrode sodium supplementation agents are introduced into the positive electrode of the present application, and the addition amount of the sodium-rich transition metal oxide is also reduced. Correspondingly, the influence of the low particle size matching degree between it and the sodium positive electrode active material on reducing the compaction density of the positive electrode sheet will also be reduced, which is more conducive to improving the energy density of the battery. On the same side of the positive electrode current collector 10, the sodium supplementation layer 20 is closer to the positive electrode current collector 10 than the positive electrode coating layer 30. In some embodiments, the sodium supplementation layer 20 can be in direct contact with the positive electrode current collector 10; in some embodiments, the positive electrode coating layer is in direct contact with the sodium supplementation layer 20.

[0018] Therefore, in the above-mentioned positive electrode sheet of the embodiment of the present application, by arranging the above two kinds of sodium supplementing agents for the positive electrode in layers as described above, the sodium supplementing efficiency of these two kinds of sodium supplementing agents can be improved, the energy density of the sodium ion battery can be increased to a certain extent, and at the same time, the impedance of the sodium ion battery can be reduced and the continuous discharge capacity can be improved.

[0019] In some embodiments of the present application, the sodium supplementing layer 20 can be in direct contact with the positive electrode current collector 10, and / or the positive electrode coating 30 is in direct contact with the sodium supplementing layer 20. It can be understood that in some other embodiments of the present application, other coatings can also be provided between the sodium supplementing layer 20 and the positive electrode current collector 10. Other intermediate layers are also provided between the positive electrode coating 30 and the sodium supplementing layer 20.

[0020] In the present application, the sodium-rich transition metal oxide, as a kind of sodium supplementing agent for the positive electrode, can release sodium ions during the formation charging process of the sodium ion battery. Its theoretical specific capacity is about 300-700 mAh / g, far exceeding the positive electrode active materials currently used in sodium ion batteries. After the sodium ions are removed, the structure of the sodium-rich transition metal oxide undergoes an irreversible change, and a part of the main structure or sodium-depleted products will remain. In addition, compared with the sodium positive electrode active material, the ability of the sodium-rich transition metal oxide to intercalate sodium ions back is extremely poor. In the working range of the sodium ion battery, the first sodium-depletion capacity of the sodium-rich transition metal oxide is much lower than its first sodium-intercalation capacity, that is, its first Coulomb efficiency is relatively low (less than 30%), far lower than the first Coulomb efficiency of the sodium positive electrode active material.

[0021] In the embodiment of the present application, the chemical formula of the sodium-rich transition metal oxide can be expressed as Na x MO y , where M can include but is not limited to one or more of Ni, Co, Fe, Mn, Cr, Cu, Mo, Ru, Ir, Sn, Nb, etc.; x ranges from 1 to 6, and y ranges from 1 to 4. Exemplarily, the sodium-rich transition metal oxide can include one or more of Na2FeO2, Na3FeO3, Na3FeO4, Na5FeO4, Na2NiO2, Na2CuO2, Na6MnO4, Na6CoO4, etc., but is not limited thereto. Among them, the above-mentioned sodium supplementing layer 20 can contain one or more sodium-rich transition metal oxides. In some embodiments of the present application, the surface of the sodium-rich transition metal oxide can have or not have a conductive coating layer, and it is preferred to have a conductive coating layer.

[0022] In this application, the sacrificial cathode sodium supplement can decompose at a voltage higher than its sodium deintercalation potential, releasing active sodium ions and generating a large amount of gas to achieve the effect of sodium supplementation. After the sacrificial cathode sodium supplement decomposes, its main structure no longer exists, and it is impossible for sodium ions to intercalate back into it. Therefore, this type of sodium supplement only has a sodium deintercalation capacity and does not have a sodium intercalation capacity. In the embodiments of this application, the sacrificial cathode sodium supplement can be selected from one or more of sodium azide (NaN3), sodium amide (NaNH2), sodium phosphide (Na3P), sodium sulfide (Na2S), sodium peroxide (Na2O2), sodium carbonate (Na2CO3), sodium oxalate (Na2C2O4), sodium squarate (Na2C4O4), sodium nitrite (NaNO2), etc., but is not limited thereto.

[0023] In the embodiments of this application, the sodium cathode active material can include one or more of sodium transition metal oxides, sodium polyanion compounds, sodium prussian blue and its analogs, and sodium-containing organic compounds (such as Na2C6O6). Among them, the sodium transition metal oxides include, but are not limited to, sodium cobaltate (NaCoO2), sodium manganate (NaMnO2), sodium nickelate (NaNiO2), sodium ferrate (NaFeO2), sodium vanadate (NaVO2), Na(Fe x Mn 1-x )O2(0 < x < 1), Na(Ni x Mn 1-x )O2(0 < x < 1), Na 2 / 3 (Ni x Mn y Ti 1-x-y )O2(0 < x < 1, 0 < y < 1), etc. Among them, the sodium polyanion compounds include, but are not limited to, sodium vanadium phosphate (Na3V2(PO4)3), sodium fluorovanadate (NaVPO4F), sodium vanadium manganese phosphate, Na2FePO4F, Na3V2O2(PO4)2F, Na2Fe2(SO4)3, etc. It should be noted that these sodium cathode active materials can be undoped or doped and modified, and their surfaces can have a conductive coating or not have a conductive coating.

[0024] In this application, the sodium supplement layer 20 may or may not contain a sodium positive electrode active material. In the embodiments of this application, the sodium supplement layer 20 may include the following components in mass percentage: 50%-90% of a first positive electrode sodium supplement agent, 0-40% of a second sodium positive electrode active material, 0.5-10% of a binder, and 0.5-10% of a conductive agent. Among them, the selection range of the second sodium positive electrode active material can refer to the description of the positive electrode active material in the positive electrode coating 30 in the previous text of this application. The positive electrode active material in the positive electrode coating 30 and the second sodium positive electrode active material here can be the same or different materials. Among them, the mass percentage of the first positive electrode sodium supplement agent in the sodium supplement layer 20 is greater than that of the second sodium positive electrode active material, which can enable the sodium supplement layer 20 to provide a higher sodium supplement capacity and improve the battery energy density. The appropriate presence of the binder can ensure the adhesion of the sodium supplement layer 20 to the positive electrode current collector 10, and the appropriate presence of the conductive agent helps to improve the electron conduction ability of the sodium supplement layer 20. Specifically, the mass percentage of the first positive electrode sodium supplement agent in the sodium supplement layer 20 can be specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%, etc. The mass percentage of the binder or the conductive agent can independently be 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8% or 9%, etc.

[0025] In some embodiments, the sodium supplement layer 20 does not contain a sodium positive electrode active material. That is, the content of the second sodium positive electrode active material in the sodium supplement layer 20 is 0. This avoids the problems of increased positive electrode liquid-phase diffusion impedance and slowed liquid-phase transmission speed of sodium ions caused by the direct mixing of sodium-rich transition metal oxides and sodium positive electrode active materials, and thus helps to reduce the impedance of the sodium-ion battery.

[0026] In other embodiments of this application, the sodium supplement layer 20 contains a second sodium positive electrode active material, and its mass percentage can be 10-40%, for example, specifically 12%, 15%, 20%, 25%, 28%, 30%, 35% or 40%, etc. The appropriate amount of the second sodium positive electrode active material in the sodium supplement layer 20 can enable the sodium supplement layer 20 to also contribute a certain capacity in the formed battery.

[0027] In this application, the positive electrode coating 30 can be one layer (as shown in Figure 1 ), or it can be multiple layers (that is, the number of layers ≥ 2, as shown in Figure 2 ). When the positive electrode coating 30 is one layer (as shown in Figure 1 ), the sacrificial positive electrode sodium supplement agent can be evenly dispersed in the sodium positive electrode active material. When the positive electrode coating 30 is multiple layers, it can include n positive electrode sub-layers, n≥2 (as shown in Figure 2 ).

[0028] In this application, the proportion of the sodium compensation capacity provided by the sodium-rich transition metal oxide 201 in the total sodium compensation capacity provided by the sodium-rich transition metal oxide 201 and the sacrificial cathode sodium compensation agent 301 in the cathode electrode sheet 100 is x, and the proportion of the sodium compensation capacity provided by the sacrificial cathode sodium compensation agent 301 in the total sodium compensation capacity provided by the sodium-rich transition metal oxide 201 and the sacrificial cathode sodium compensation agent 301 in the cathode electrode sheet 100 is 1 - x. Among them, x ranges from 10% to 90%, for example, specifically 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 85%, etc. Correspondingly, 1 - x also ranges from 10% to 90%. By adjusting the proportion of the sodium compensation capacity of the two sodium compensation agents, different requirements of different batteries for energy density, power density, cycle life, etc. can be met. Preferably, x ranges from 50% to 90%, and correspondingly 1 - x ranges from 10% to 50%. In this case, the sodium compensation capacity provided by the sodium-rich transition metal oxide sodium compensation agent ≥ the sodium compensation capacity provided by the sacrificial cathode sodium compensation agent, which can reduce the dosage of the sacrificial sodium compensation agent, and further reduce the impact of a large amount of gas generated by the decomposition of the sacrificial sodium compensation agent on the microstructure of the electrode sheet. Among them, the sodium compensation capacity provided by each sodium compensation agent is equal to the product of its mass and its gram capacity. Here, the gram capacity is calculated according to the actual number of active sodium ions actually removed during sodium compensation of each sodium compensation agent known in the industry. For example, for Na5FeO4, its gram capacity corresponds to the theoretical gram capacity of 455 mAh / g when it removes 4 sodium ions; for Na6MnO4, its gram capacity corresponds to the theoretical gram capacity of 520 mAh / g when it removes 5 sodium ions; for Na2CO3, its gram capacity corresponds to the theoretical gram capacity of 505 mAh / g when it removes 2 sodium ions; for Na2C2O4, its gram capacity corresponds to the theoretical gram capacity of 399 mAh / g when it removes 2 sodium ions.

[0029] In the embodiments of this application, the positive electrode coating 30 includes the following components in mass percentage: 80 - 99.5% of the sodium positive electrode active material, 0.5 - 10% of the sacrificial cathode sodium compensation agent, 0.1 - 5% of the conductive agent, 0.1 - 5% of the binder, and 0 - 5% of the dispersant. Among them, the mass ratio of each component refers to the ratio of their total mass in the positive electrode coating 30 to the total mass of the positive electrode coating 30.

[0030] In some embodiments of this application, in the positive electrode coating 30, the total mass of the sacrificial cathode sodium compensation agent is 0.5 - 10% of the total mass of the sodium positive electrode active material. Whether the positive electrode coating 30 is one layer (as shown in Figure 1 ), or multiple layers (i.e., the number of layers ≥ 2, as shown in Figure 2As shown, the range of this ratio is applicable. This parameter range helps ensure that the sacrificial positive sodium supplement can provide an appropriately high sodium supplement capacity without excessive gas generation. Specifically, this ratio can be, for example, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, etc. In some embodiments, this ratio is in the range of 1% - 5%. This can ensure that while the second positive sodium supplement makes up for the irreversible consumption of active sodium in the battery, it does not make the reversible capacity of the battery positive electrode too small or the gas generation amount of the positive electrode too large.

[0031] In some embodiments of the present application, when the positive electrode coating 30 includes n positive electrode sub - coatings, in the direction from the positive electrode current collector 10 to the sodium supplement layer 20 (i.e., Figure 2 the direction indicated by the arrow in), the mass ratio of the sacrificial positive sodium supplement to the sodium - positive electrode active material in each positive electrode sub - coating shows an increasing trend.

[0032] In the direction from the positive electrode current collector 10 to the sodium supplement layer 20, each sub - coating of the positive electrode coating 30 can be sequentially denoted as L1, L2…L n . In this way, the surface of the positive electrode current collector 10 is sequentially provided with the sodium supplement layer 20, the first positive electrode sub - coating L1, the second positive electrode sub - coating L2,…, the nth positive electrode sub - coating L n . If the mass ratio of the sacrificial positive sodium supplement to the sodium - positive electrode active material in the first positive electrode sub - coating L1 is denoted as X1, the mass ratio of the sacrificial positive sodium supplement to the sodium - positive electrode active material in the second positive electrode sub - coating L2 is denoted as X2,…, and the mass ratio of the sacrificial positive sodium supplement to the sodium - positive electrode active material in the nth positive electrode sub - coating L n is denoted as X n , then the above - mentioned "showing an increasing trend" can be expressed as: X1≤X2≤X3…≤X n , and X n >X1, X1≥0. Exemplarily, the above - mentioned "showing an increasing trend" can specifically be: first increasing - then remaining unchanged - then increasing again, or first remaining unchanged and then increasing sequentially, or first remaining unchanged - then increasing - then remaining unchanged - then increasing, etc., non - sequential increasing ways; or a way of increasing layer by layer sequentially (such as X1<X2<X3…<X n , X1≥0).

[0033] In the present application, the mass ratio of the sacrificial positive sodium supplement agent to the sodium positive active material in each positive electrode sub - coating shows an increasing trend in the direction away from the positive electrode current collector 10. This is more conducive to the smooth discharge of the gas generated by the decomposition of the sacrificial positive sodium supplement agent in each positive electrode sub - coating close to the positive electrode current collector. This can reduce battery polarization and make the sodium - removal potential of the sacrificial positive sodium supplement agent in each positive electrode sub - coating basically the same. Furthermore, the decomposition ratio and sodium - supplement efficiency of the sacrificial positive sodium supplement agent in each positive electrode sub - coating are relatively high, and the reduction of battery polarization is also beneficial to reducing the overall impedance of the battery and improving the sustainable discharge capacity of the battery. In addition, after the decomposition of the sacrificial positive sodium supplement agent, the pores created by it in each positive electrode sub - coating can gradually form a gradient pore structure. This gradient pore structure helps to increase the overall porosity of the positive electrode sheet and reduce the pore tortuosity without significantly increasing the volume of the positive electrode sheet and without significantly reducing the volume energy density of the battery, further reducing the overall impedance of the battery and improving the power performance of the battery.

[0034] In some embodiments of the present application, in the case of n positive electrode sub - coatings, in the direction from the positive electrode current collector 10 to the sodium - supplement layer 20, the mass ratio of the sacrificial positive sodium supplement agent to the sodium positive active material in each positive electrode sub - coating increases layer by layer in sequence. This is conducive to the more smooth discharge of the gas generated by the decomposition of the sacrificial positive sodium supplement agent in the positive electrode coating 30, and endows the positive electrode coating 30 with a pore structure in which the porosity increases in sequence along the arrow direction after its decomposition, which is more conducive to reducing the battery impedance.

[0035] In some embodiments of the present application, among the n positive electrode sub - coatings, at least two adjacent layers satisfy: A m / (D m / D m-1 ) - A m-1 ≥5%; where A m-1 is the mass ratio of the sacrificial positive sodium supplement agent in the (m - 1)th positive electrode sub - coating to the total sacrificial positive sodium supplement agent in the positive electrode coating, A m is the mass ratio of the sacrificial positive sodium supplement agent in the mth positive electrode sub - coating to the total sacrificial positive sodium supplement agent in the positive electrode coating, D m-1 is the thickness of the (m - 1)th positive electrode sub - coating, D m is the thickness of the mth positive electrode sub - coating, and m is any integer from 2 to n; on the same side of the positive electrode current collector, the (m - 1)th positive electrode sub - coating is closer to the positive electrode current collector than the mth positive electrode sub - coating. In this way, after the decomposition of the sacrificial positive sodium supplement agent, the porosities of at least two adjacent positive electrode sub - coatings can be significantly distinguished, which helps to reduce the battery impedance and improve the power performance. Further, among the n positive electrode sub - coatings, any two adjacent positive electrode sub - coatings satisfy: A m / (D m / D m-1 ) - A m-1≥5%. After the battery formation, the porosity formed in the positive electrode coating 30 increases layer by layer in the direction away from the positive electrode current collector 10, which has a better effect on reducing the battery impedance and improving the power performance. Optionally, A m / (D m / D m-1 )-A m-1 ≥10%, for example A m / (D m / D m-1 )-A m-1 Specifically 10%, 15%, 20%, 25%, 30%, 40%, 50%, or 60%, etc.

[0036] Exemplarily, in some embodiments, when the thicknesses of the positive electrode sub-layers are substantially the same (such as D m / D m-1 =1), among the n positive electrode sub-layers, any two adjacent positive electrode sub-layers satisfy: A m -A m-1 ≥5%, where m is any integer from 2 to n. If the mass ratio of the sacrificial positive electrode sodium supplement in the first positive electrode sub-layer L1 to all the sacrificial positive electrode sodium supplements in the positive electrode coating 30 is denoted as Y1, the mass ratio of the sacrificial positive electrode sodium supplement in the second positive electrode sub-layer L2 to all the sacrificial positive electrode sodium supplements in the positive electrode coating 30 is denoted as Y2,..., and the mass ratio of the sacrificial positive electrode sodium supplement in the nth positive electrode sub-layer L n to all the sacrificial positive electrode sodium supplements in the positive electrode coating 30 is denoted as Y n , if D m / D m-1 =1, then |Y2 - Y1|, |Y3 - Y2|,..., |Y n -Y n-1 | are all ≥5%, preferably ≥10%. Among them, Y1 can be greater than or equal to 0. In some embodiments, when n = 2, Y1 = 20%, Y2 = 80%; or Y1 = 30%, Y2 = 70%; or Y1 = 40%, Y2 = 60%; or Y1 = 45%, Y2 = 55%. When n = 3, Y1 = 23%, Y2 = 33%, Y3 = 44%; or Y1 = 20%, Y2 = 30%, Y3 = 50%; or Y1 = 10%, Y2 = 30%, Y3 = 60%.

[0037] In the embodiments of the present application, the mass ratio of the sodium positive electrode active material in each positive electrode coating is more than 80%, for example, in the range of 80%-99.5%. This is more conducive to each positive electrode coating providing a relatively high reversible capacity, and thus ensuring a relatively high reversible capacity of the overall positive electrode sheet. Taking the first positive electrode coating L1 as an example, specifically, the ratio of the mass of the sodium positive electrode active material in the first positive electrode coating L1 to the total mass of the first positive electrode coating L1 is more than 80%, and further can be more than 90%.

[0038] In the present application, the single-sided surface density of each positive electrode material sub-layer can be equal or unequal. In some embodiments of the present application, the single-sided surface density of each positive electrode coating is equal. This is more helpful to ensure that their laminated structure is more stable.

[0039] In the present application, whether the above-mentioned positive electrode coating 30 is one layer or multiple layers, the single-sided surface density of the positive electrode coating 30 is greater than that of the sodium supplement layer 20. The positive electrode coating 30 is the main reversible capacity providing layer of the battery, and its single-sided surface density is higher than that of the sodium supplement layer 20, which is beneficial to ensuring a relatively high energy density and discharge capacity of the battery.

[0040] In the embodiments of the present application, the single-sided surface density of the sodium supplement layer 20 can be 1-50 g / m 2 , which can ensure to a certain extent that the sodium supplement capacity provided by the first positive electrode sodium supplement agent is appropriate, and ensure that the comprehensive performance of the sodium ion battery is good. It will neither cause the sodium supplement effect on the battery to be not obvious due to the insufficient sodium supplement capacity of the first positive electrode sodium supplement agent, nor cause the sodium supplement amount of the sodium ion battery to exceed the reasonable level of the current battery design due to the excessive addition amount of the first positive electrode sodium supplement agent. In some embodiments, the single-sided surface density of the sodium supplement layer 20 is 1-20 g / m 2 , for example, specifically 1.0 g / m 2 , 1.5 g / m 2 , 2 g / m 2 , 2.5 g / m 2 , 3.0 g / m 2 , 4.0 g / m 2 , 5.0 g / m 2 , 6.0 g / m 2 , 7.0 g / m 2 , 8.0 g / m 2 , 9 g / m 2 , 10.0 g / m 2 , 15.0 g / m 2 or 20.0 g / m 2 etc. This is more helpful to improve the utilization rate of the first positive electrode sodium supplement agent, and at the same time, the sodium ion battery has a relatively high positive electrode specific capacity and first Coulomb efficiency.

[0041] In the embodiments of the present application, the single-sided surface density of the positive electrode coating 30 can be 50-500 g / m 2 , for example, specifically 60 g / m 2 , 80 g / m 2 , 100 g / m 2 , 150 g / m 2 , 200 g / m 2 , 210 g / m 2 , 220 g / m 2 , 250 g / m 2 , 300 g / m 2 , 350 g / m 2 , 400 g / m 2 , 450 g / m 2 etc. In a relatively high range, the positive electrode coating helps the sodium-ion battery to have a relatively high positive electrode specific capacity per gram and ensures that the sacrificial sodium supplement agent provides an appropriate sodium supplement capacity. In some embodiments, the single-sided surface density of the positive electrode coating 30 is 100-300 g / m 2 .

[0042] In the present application, the thickness of the sodium supplement layer 20 is less than the thickness of the positive electrode coating 30. This is also beneficial to ensuring a relatively high energy density of the sodium-ion battery. In the embodiments of the present application, the single-sided thickness of the sodium supplement layer 20 can be in the range of 1-50 μm. In some embodiments, the single-sided thickness of the sodium supplement layer 20 is 1-20 μm, and further can be 1-10 μm. For example, specifically 1.0 μm, 2.0 μm, 3.0 μm, 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm or 9 μm, etc. In this case, the thickness of the sodium supplement layer 20 containing the first positive electrode sodium supplement agent is appropriate, the total discharge capacity of the sodium-ion battery is high, the energy density is high, and at the same time, the gas generation amount at the positive electrode during the first charging process of the sodium-ion battery is small and the battery impedance is low. In the embodiments of the present application, the single-sided thickness of the positive electrode coating 30 can be in the range of 25-500 μm. For example, specifically 30 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, 200 μm, 220 μm, 250 μm, 300 μm, 350 μm, 400 μm, or 450 μm, etc.; in some embodiments, the single-sided thickness of the positive electrode coating 30 is 50-250 μm.

[0043] In this application, in addition to the above-mentioned first positive electrode sodium supplement agent, the sodium supplement layer 20 may further contain a binder and a conductive agent. In addition to the sodium positive electrode active material and the sacrificial positive electrode sodium supplement agent, the positive electrode coating layer 30 may further contain a binder and a conductive agent. Among them, each conductive agent may independently be selected from one or more of conductive carbon black (such as acetylene black, Ketjen black, Super-P, 350G carbon black, etc.), carbon nanotubes (single-walled carbon nanotubes or multi-walled carbon nanotubes), graphene, carbon fiber, ordered mesoporous carbon, etc. Each binder may independently be selected from one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyolefins (such as polyethylene (PE), polypropylene (PP)), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyimide (PI), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), sodium alginate (SA), gelatin, etc., but is not limited thereto. In some embodiments, the sodium supplement layer 20 and the positive electrode coating layer 30 may further contain a dispersant. Each dispersant may be selected from one or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), etc.

[0044] Among them, the sodium supplement layer 20 can be formed by coating and drying a bottom coating slurry containing the first positive electrode sodium supplement agent and a solvent. The coating method may include, but is not limited to, a combination of one or more methods such as spin coating, brush coating, spray coating, dip coating, doctor blade coating, etc. Similarly, the positive electrode coating layer 30 can be formed by coating and drying a positive electrode slurry containing a sodium positive electrode active material, a sacrificial positive electrode sodium supplement agent, and a solvent.

[0045] The solvents contained in each slurry may be the same or different, and may independently be selected from one or more of pyrrolidone-based (such as N-methylpyrrolidone (NMP), N-ethylpyrrolidone, etc.), cyclic ethers (such as tetrahydrofuran, methyltetrahydrofuran), etc., dimethyl sulfoxide, ketones (such as acetone, methyl ethyl ketone), lactones (such as butyrolactone, caprolactone), etc., but is not limited thereto. There is no special limitation on the solid content of each slurry, as long as it can meet the fluidity and uniformity of the slurry coating. Generally, the solid content of the bottom coating slurry may be 5-50%. The solid content of the positive electrode slurry is in the range of 50%-70%.

[0046] Among them, when the positive electrode coating 30 is a single layer, there is one type of positive electrode slurry. When the positive electrode coating 30 is multiple layers, the types of positive electrode slurries used correspond to the number of layers of the positive electrode coating 30. In addition, each layer of slurry can be coated simultaneously or sequentially, or coated on the coating formed by drying the previous slurry. Taking the positive electrode coating 30 being a single layer as an example, one type of positive electrode slurry can be directly coated on the base coating slurry (it can be coated simultaneously or sequentially), and then baked together to remove the solvent, followed by rolling. If double-sided coating is required, the above operations can be repeated on the other surface of the positive electrode current collector 10. Alternatively, the base coating slurry can be coated on one surface of the positive electrode current collector 10 and dried to form the sodium supplement layer 20, then the positive electrode slurry can be coated on the sodium supplement layer 20 and dried to form the positive electrode coating 30, and then rolling is carried out.

[0047] In the present application, the positive electrode current collector 10 can include but is not limited to aluminum foil, aluminum alloy foil, polymer film material plated with metal aluminum, or the aforementioned materials with carbon coating on the surface, etc. In some embodiments of the present application, the positive electrode current collector 10 is aluminum foil. In the present application, a laminated structure of the sodium supplement layer 20 and the positive electrode coating 30 can be formed on one surface of the positive electrode current collector 10 (as shown in Figure 1 and Figure 2 ), or a laminated structure of the sodium supplement layer 20 and the positive electrode coating 30 can be formed on both opposite surfaces of the positive electrode current collector 10.

[0048] The embodiment of the present application also provides a sodium ion battery, which includes the positive electrode plate 100 of the embodiment of the present application described above.

[0049] In the embodiment of the present application, the sodium ion battery further includes a positive electrode plate, and a separator and an electrolyte disposed between the negative electrode plate and the positive electrode plate.

[0050] Among them, the negative electrode plate generally includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer generally contains a negative electrode active material, a conductive agent, and a binder. In the embodiment of the present application, the negative electrode active material for the sodium ion battery can be selected from one or more of hard carbon, soft carbon, graphite, mesophase carbon microspheres, silicon-carbon composite materials, etc.

[0051] Among them, the separator is used to separate the positive electrode plate and the negative electrode plate, maintaining the insulation and liquid retention characteristics between the two; the separator, together with the positive electrode plate and the negative electrode plate, constitutes the battery core, and the core is accommodated in the battery case and is wetted by the electrolyte contained in the case. In some embodiments of the present application, the sodium ion battery can be assembled by the following method: the positive electrode plate, the separator, and the negative electrode plate are stacked in sequence to form a core; the core is accommodated in the battery case, and the electrolyte is injected, and then the battery case is sealed to obtain the battery. Among them, the core can be a wound type or a stacked type.

[0052] Among them, any separator material in the battery can be used for the separator. Exemplarily, the separator may include, but is not limited to, polymer separators such as single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer film PP / PE, double-layer film PP / PP, and triple-layer PP / PE / PP, or non-woven fabric, etc. The electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and the organic solvent are all conventional selections in the battery field and can be selected according to actual needs.

[0053] The embodiment of the present application also provides a device, which includes the above sodium-ion battery of the embodiment of the present application. Among them, the device can be an electric vehicle (such as a car, a motorcycle, a bicycle, etc.), an electric toy, a 3C product (such as a mobile phone, a laptop, a tablet computer, a pen-input computer, an e-book player, a wearable device, etc.) and other electrical equipment; it can also be an energy storage system. The energy storage system may include a plurality of the above sodium-ion batteries and a battery management system. The energy storage system can also supply power to electrical equipment. Among them, the electrical equipment powered by the above sodium-ion battery has a long running time and a fast charging speed.

[0054] The technical solution of the present application will be further described below in conjunction with a plurality of specific embodiments.

[0055] Example 1

[0056] A positive electrode sheet for a sodium-ion battery, and its preparation method includes:

[0057] Mix a first positive electrode sodium supplement agent (specifically Na5FeO4 with a carbon coating layer on the surface, and the mass ratio of the coating layer material is 3wt%) with a binder PVDF, a conductive agent Super-P, and a solvent NMP at a mass ratio of 80:10:10:150, and stir evenly to obtain a bottom coating slurry with a solid content of 40.0wt%. Coat the bottom coating slurry on the surface of a positive electrode current collector - aluminum foil with a thickness of 13μm, and control the coating conditions to form a sodium supplement layer with a single-sided surface density of 8.4g / m 2 after drying, and its thickness is 7±1μm. Then, on the other side of the aluminum foil (which can be called the "reverse side"), the reverse coating and drying of the above bottom coating slurry are carried out again to obtain an aluminum foil with sodium supplement layers on both sides.

[0058] The sodium positive electrode active material Na3V2(PO4)3, the sacrificial sodium supplement agent Na2CO3, the binder PVDF, the conductive agent Super-P, the dispersant PVP, and the solvent NMP are formulated into two slurries for the positive electrode sub-coatings in different proportions. Among them, the formulation of the lower slurry coated closer to the sodium supplement layer is: Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP = 100:2:3:2:0.3:68, and the solid content is 61 wt%. The formulation of the upper slurry coated farther from the sodium supplement layer is: Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP = 100:4:3:2:0.3:70, and the solid content is 61 wt%. The lower slurry and the upper slurry are simultaneously laminated and coated on the sodium supplement layer to form two positive electrode sub-coatings with equal areal densities after drying, and the sum of the single-sided areal densities of the two positive electrode sub-coatings is 200 g / m 2 , and then, the above-mentioned lower slurry and upper slurry are coated and dried on the sodium supplement layer on the reverse side to obtain a double-sided positive electrode sheet for use. Among them, in this positive electrode sheet, the ratio of the sodium supplement capacity provided by the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is 50%:50%.

[0059] Preparation of a sodium-ion battery:

[0060] (1) Preparation of the negative electrode sheet: The negative electrode active material spherical hard carbon, the conductive carbon black Super-P, the binder styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and water are mixed in a mass ratio of 100:1:1.5:1.5:150 to prepare a negative electrode slurry with a solid content of 41%. The negative electrode slurry is coated on one surface of the copper foil, and after drying, a negative electrode active material layer with a single-sided areal density of 80 g / m 2 is obtained. Then, the above-mentioned negative electrode slurry is coated and dried on the reverse side of the copper foil to obtain a double-sided negative electrode sheet.

[0061] (2) After the positive electrode sheet and the negative electrode sheet prepared above are roll-pressed, slit, and die-cut, they are alternately laminated with a separator (specifically, a PP separator with a thickness of 14 μm) (separating the positive electrode sheet and the negative electrode sheet by the separator) to form a battery core for a sodium-ion battery; then the battery core is placed in a sodium-ion battery housing (the size of the battery housing is 150*100*25 mm), and a sodium-ion battery electrolyte is injected (this electrolyte is obtained by dissolving NaPF6 in a mixed solvent of EC:DEC:EMC (volume ratio 1:1:1), and the concentration of NaPF6 is 1 M). The battery housing is sealed and an air bag is reserved, and then through processes such as infiltration, formation, aging, and grading, a sodium-ion battery is prepared for subsequent electrochemical performance testing.

[0062] Example 2

[0063] Example 2 is different from Example 1 in that: the positive electrode coating is a single layer, and this positive electrode coating is obtained by coating and drying a positive electrode coating slurry prepared according to a mass ratio of Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP = 100:3:3:2:0.3:68 with a solid content of 61 wt%. The single-sided areal density of this positive electrode coating is still 200 g / m 2 , and the thickness is 100 μm.

[0064] According to the method described in Example 1, the positive electrode sheet of Example 2 was assembled into a sodium-ion battery.

[0065] Example 3

[0066] The preparation of a positive electrode sheet for a sodium-ion battery is mainly different from that of Example 1 in that: the first positive electrode sodium supplement agent is replaced with Na6MnO4 with a carbon coating layer on its surface, and the mass ratio of the coating layer material is 2.5 wt%. Among them, in the positive electrode sheet prepared in Example 3, the single-sided areal density of the sodium supplement layer is 7.3 g / m 2 , and the thickness is 6 ± 1 μm; the ratio of the sodium supplement capacity provided by the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is 50%:50%.

[0067] According to the method described in Example 1, the positive electrode sheet of Example 3 was assembled into a sodium-ion battery.

[0068] Example 4

[0069] The preparation of a positive electrode sheet for a sodium-ion battery is mainly different from that of Example 3 in that: the positive electrode coating is a single layer, and the single-sided areal density is still 200 g / m 2 , and this positive electrode coating is obtained by coating and drying a positive electrode coating slurry prepared according to a mass ratio of Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP = 100:3:3:2:0.3:69.

[0070] According to the method described in Example 1, the positive electrode sheet of Example 4 was assembled into a sodium-ion battery.

[0071] Example 5

[0072] The preparation of a positive electrode sheet for a sodium-ion battery, the main difference from Example 2 being that: the sacrificial sodium supplement agent is replaced from Na2CO3 to Na2C2O4, and the positive electrode coating is obtained by coating and drying a positive electrode coating slurry prepared according to a mass ratio of Na3V2(PO4)3:Na2C2O4:PVDF:Super-P:PVP:NMP = 100:3.8:3:2:0.3:69. Among them, in the positive electrode coating of the positive electrode sheet prepared in Example 5, the ratio of the sodium supplement capacity provided by the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is 50%:50%.

[0073] According to the method described in Example 1, the positive electrode sheet of Example 5 was assembled into a sodium-ion battery.

[0074] Example 6

[0075] A positive electrode sheet for a sodium-ion battery, the main difference from Example 2 being that: the first positive electrode sodium supplement agent used is Na5FeO4 without a conductive coating layer on its surface.

[0076] According to the method described in Example 1, the positive electrode sheet of Example 6 was assembled into a sodium-ion battery.

[0077] Example 7

[0078] The main difference between the positive electrode sheet of Example 7 and Example 2 is that: the sodium supplement layer further contains the sodium positive electrode active material Na3V2(PO4)3.

[0079] Among them, the sodium supplement layer in Example 7 was obtained by coating and drying a bottom coating slurry obtained by mixing the above first positive electrode sodium supplement agent with Na3V2(PO4)3, binder PVDF, conductive agent Super-P, and solvent NMP in a mass ratio of 40:40:10:10:150. And the single-sided surface density of this sodium supplement layer is 16.8 g / m 2 , and the single-sided thickness is 14 ± 1 μm. The positive electrode coating slurry with the same formulation as in Example 2 was coated on the above sodium supplement layer and dried to form a positive electrode coating with a single-sided surface density of 193 g / m 2 .

[0080] On the other side of the aluminum foil, the above operations of forming the sodium supplement layer and the positive electrode coating were repeated, and then roll pressing was performed to obtain a double-sided positive electrode sheet. Among them, in the positive electrode of Example 7, the ratio of the sodium supplement capacity provided by the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent still accounts for 50%:50%.

[0081] According to the method described in Example 1, the positive electrode sheet of Example 7 was assembled into a sodium-ion battery.

[0082] Example 8

[0083] The main difference between Example 8 and Example 2 is that in the positive electrode sheet of Example 8, the ratio of the sodium compensation capacity of the first positive sodium compensator to that of the sacrificial sodium compensator is 66%:34%.

[0084] The preparation of the positive electrode sheet of Example 8 includes:

[0085] Coat the undercoat slurry with the same formulation as in Example 2 (i.e., the same as in Example 1) on the surface of the positive current collector - aluminum foil with a thickness of 13 μm, and after drying, obtain a sodium compensation layer with a single-sided areal density of 11.0 g / m 2 and a single-sided thickness of 9 ± 1 μm;

[0086] Mix the sodium positive electrode active material Na3V2(PO4)3 with the sacrificial sodium compensator Na2CO3, binder PVDF, conductive agent Super-P, dispersant PVP, and solvent NMP in a mass ratio of 100:2:3:2:0.3:68 to prepare a positive electrode slurry. Coat the positive electrode slurry on the sodium compensation layer, and after drying, obtain a positive electrode coating with a single-sided areal density of 200 g / m 2 ;

[0087] Then, repeat the above operations of forming the sodium compensation layer and the positive electrode coating on the other side of the aluminum foil, and then perform rolling to obtain the positive electrode sheet.

[0088] According to the method described in Example 1, assemble the positive electrode sheet of Example 8 into a sodium ion battery.

[0089] Example 9

[0090] The main difference between Example 9 and Example 2 is that in the positive electrode sheet of Example 9, the ratio of the sodium compensation capacity of the first sodium compensator to that of the sacrificial sodium compensator is 90%:10%.

[0091] The preparation of the positive electrode sheet of Example 9 includes:

[0092] Coat the undercoat slurry with the same formulation as in Example 2 on one side surface of the positive current collector - aluminum foil with a thickness of 13 μm, and after drying, form a sodium compensation layer with a single-sided areal density of 15.0 g / m 2 , and a single-sided thickness of 12 ± 1 μm; then form the same sodium compensation layer on the reverse side of the aluminum foil;

[0093] Mix the sodium positive electrode active material Na3V2(PO4)3 with the sacrificial sodium compensator Na2CO3, binder PVDF, conductive agent Super-P, dispersant PVP, and solvent NMP in a mass ratio of 100:0.6:3:2:0.3:68 to prepare a positive electrode slurry with a solid content of 61 wt%. Coat the positive electrode slurry on the sodium compensation layer, and after baking, form a positive electrode coating with a single-sided areal density of 200 g / m 2The positive electrode coating; then, the positive electrode slurry is coated and dried on the sodium supplement layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0094] According to the method described in Example 1, the positive electrode sheet of Example 9 is assembled into a sodium-ion battery.

[0095] Example 10

[0096] The main difference between Example 10 and Example 2 is that in the positive electrode coating of the positive electrode sheet of Example 10, the total mass of the sacrificial sodium supplement agent is 1% of the total mass of the sodium positive electrode active material; in this positive electrode coating, the sodium supplement capacity ratio of the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is about 83%:17%.

[0097] The preparation of the positive electrode sheet of Example 10 includes:

[0098] The undercoat slurry with the same formulation as in Example 2 is coated on the surface of a positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a sodium supplement layer with a single-sided areal density of 13.8 g / m 2 and a single-sided thickness of 11 ± 1 μm is formed; then, the same sodium supplement layer is also formed on the reverse side of the aluminum foil;

[0099] The sodium positive electrode active material Na3V2(PO4)3, the sacrificial sodium supplement agent Na2CO3, the binder PVDF, the conductive agent Super-P, the dispersant PVP, and the solvent NMP are configured into a positive electrode slurry in a ratio of 100:1:3:2:0.3:68. The positive electrode slurry is coated on the sodium supplement layer, and after drying, a positive electrode coating with a single-sided areal density of 200 g / m 2 is formed. Then, the positive electrode slurry is coated and dried on the sodium supplement layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0100] According to the method described in Example 1, the positive electrode sheet of Example 10 is assembled into a sodium-ion battery.

[0101] Example 11

[0102] The main difference between Example 11 and Example 2 is that in the positive electrode sheet of Example 10, the sodium supplement capacity ratio of the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is 30%:70%.

[0103] The preparation method of the positive electrode sheet of Example 11 includes:

[0104] The undercoat slurry with the same formulation as in Example 2 is coated on the surface of a positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a sodium supplement layer with a single-sided areal density of 5.0 g / m 2 and a single-sided thickness of 4 ± 1 μm is formed; then, the same sodium supplement layer is also formed on the reverse side of the aluminum foil;

[0105] The sodium positive electrode active material Na3V2(PO4)3 is mixed with a sacrificial sodium supplement agent Na2CO3, a binder PVDF, a conductive agent Super-P, a dispersant PVP, and a solvent NMP in a mass ratio of 100:4.1:3:2:0.3:68 to prepare a positive electrode paste. The positive electrode paste is coated on the sodium supplement layer and dried to form a positive electrode coating with a single-sided surface density of 200 g / m 2 Then, the positive electrode paste is coated and dried on the sodium supplement layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0106] According to the method described in Example 1, the positive electrode sheet of Example 11 is assembled into a sodium ion battery.

[0107] Example 12

[0108] The main difference between Example 12 and Example 2 is that in the positive electrode coating of the positive electrode sheet in Example 12, the total mass of the sacrificial sodium supplement agent is 5% of the total mass of the sodium positive electrode active material; in this positive electrode coating, the sodium supplement capacity ratio of the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is about 16%:84%.

[0109] The preparation of the positive electrode sheet in Example 12 includes:

[0110] The bottom coating paste with the same formula as in Example 2 is coated on the surface of a positive electrode current collector - aluminum foil with a thickness of 13 μm and dried to form a sodium supplement layer with a single-sided surface density of 2.7 g / m 2 and a single-sided thickness of 2 μm; then, such a sodium supplement layer is also formed on the reverse side of the aluminum foil;

[0111] The sodium positive electrode active material Na3V2(PO4)3 is mixed with a sacrificial sodium supplement agent Na2CO3, a binder PVDF, a conductive agent Super-P, a dispersant PVP, and a solvent NMP in a mass ratio of 100:5:3:2:0.3:68 to obtain a positive electrode paste; the positive electrode paste is coated on the sodium supplement layer and dried to form a positive electrode coating with a single-sided surface density of 200 g / m 2 Then, the above positive electrode paste is coated and dried on the sodium supplement layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0112] According to the method described in Example 1, the positive electrode sheet of Example 12 is assembled into a sodium ion battery.

[0113] Example 13

[0114] The main difference between Example 13 and Example 2 is that in the positive electrode sheet of Example 11, the sodium supplement capacity ratio of the first sodium supplement agent to the sacrificial sodium supplement agent is 5%:95%.

[0115] The preparation of the positive electrode sheet in Example 13 includes:

[0116] The formulation was coated on the surface of a positive current collector - aluminum foil with a thickness of 13 μm as the undercoat slurry in Example 2, with a surface density of 0.9 g / m 2 , and the single-sided thickness was 1 μm; then, such a sodium compensation layer was also formed on the reverse side of the aluminum foil;

[0117] The sodium positive electrode active material Na3V2(PO4)3 was mixed with a sacrificial sodium compensating agent Na2CO3, a binder PVDF, a conductive agent Super-P, a dispersant PVP, and a solvent NMP in a mass ratio of 100:5.7:3:2:0.3:68 to obtain a positive electrode slurry. The positive electrode slurry was coated on the sodium compensation layer and dried to form a positive electrode coating with a single-sided surface density of 200 g / m 2 . Then, the positive electrode slurry was coated and dried on the sodium compensation layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0118] According to the method described in Example 1, the positive electrode sheet of Example 13 was assembled into a sodium-ion battery.

[0119] Example 14

[0120] The main difference between Example 14 and Example 2 is that in the positive electrode coating of the positive electrode sheet in Example 14, the total mass of the sacrificial sodium compensating agent is 10% of the total mass of the sodium positive electrode active material. In this positive electrode coating, the ratio of the sodium compensation capacity of the first positive electrode sodium compensating agent to the sacrificial sodium compensating agent is approximately 3.5%:96.5%.

[0121] The preparation of this positive electrode sheet includes:

[0122] The undercoat slurry with the same formulation as in Example 2 was coated on the surface of a positive current collector - aluminum foil with a thickness of 13 μm, and after drying, a sodium compensation layer with a single-sided surface density of 1.0 g / m 2 and a single-sided thickness of 1 μm was formed; then, such a sodium compensation layer was also formed on the reverse side of the aluminum foil;

[0123] The sodium positive electrode active material Na3V2(PO4)3 was mixed with a sacrificial sodium compensating agent Na2CO3, a binder PVDF, a conductive agent Super-P, a dispersant PVP, and a solvent NMP in a mass ratio of 100:10:3:2:0.3:68 to prepare a positive electrode slurry. The positive electrode slurry was coated on the sodium compensation layer and dried to form a positive electrode coating with a single-sided surface density of 200 g / m 2 . Then, the above positive electrode slurry was coated and dried on the sodium compensation layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0124] According to the method described in Example 1, the positive electrode sheet of Example 14 was assembled into a sodium-ion battery.

[0125] Example 15

[0126] The main difference between Example 15 and Example 2 is that in the positive electrode sheet of Example 15, the ratio of the sodium compensation capacity of the first sodium compensator to that of the sacrificial sodium compensator is 95%:5%.

[0127] The preparation of the positive electrode sheet of Example 15 includes:

[0128] Coat the undercoat slurry with the same formulation as in Example 2 on the surface of a positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, form a sodium compensation layer with a single-sided areal density of 16.0 g / m 2 and a single-sided thickness of 13 ± 1 μm; then form such a sodium compensation layer on the reverse side of the aluminum foil;

[0129] Mix the sodium positive electrode active material Na3V2(PO4)3 with the sacrificial sodium compensator Na2CO3, binder PVDF, conductive agent Super-P, dispersant PVP, and solvent NMP in a mass ratio of 100:0.3:3:2:0.3:68 to obtain a positive electrode slurry. Coat this positive electrode slurry on the above sodium compensation layer, and after drying, form a positive electrode coating with a single-sided areal density of 200 g / m 2 Then, coat and dry this positive electrode slurry on the sodium compensation layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0130] According to the method described in Example 1, assemble the positive electrode sheet of Example 15 into a sodium-ion battery.

[0131] Example 16

[0132] The main difference between Example 16 and Example 2 is that in the positive electrode coating of the positive electrode sheet of Example 16, the total mass of the sacrificial sodium compensator is 0.2% of the total mass of the sodium positive electrode active material. In this positive electrode coating, the ratio of the sodium compensation capacity of the first positive electrode sodium compensator to that of the sacrificial sodium compensator is approximately 96.6%:3.4%.

[0133] The preparation of this positive electrode sheet includes: Coat the undercoat slurry with the same formulation as in Example 2 on the surface of a positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, form a sodium compensation layer with a single-sided areal density of 16.0 g / m 2 and a single-sided thickness of 13 ± 1 μm; then form such a sodium compensation layer on the reverse side of this aluminum foil;

[0134] Mix the sodium positive electrode active material Na3V2(PO4)3 with the sacrificial sodium compensator Na2CO3, binder PVDF, conductive agent Super-P, dispersant PVP, and solvent NMP in a mass ratio of 100:0.2:3:2:0.3:68 to prepare a positive electrode slurry. Coat this positive electrode slurry on the sodium compensation layer, and after drying, form a positive electrode coating with a single-sided areal density of 200 g / m 2The positive electrode coating, and then, the above-mentioned positive electrode slurry is coated and dried on the sodium supplement layer on the reverse side to obtain a double-sided positive electrode sheet for use.

[0135] According to the method described in Example 1, the positive electrode sheet of Example 16 is assembled into a sodium-ion battery.

[0136] Example 17

[0137] The main difference between the positive electrode sheet of Example 17 and that of Example 1 is that: the difference in the mass ratio between the sacrificial positive electrode sodium supplement agent in the upper and lower positive electrode sub-coatings and all the sacrificial positive electrode sodium supplement agents is 50%.

[0138] Among them, when preparing the positive electrode sheet of Example 17, the formula of the lower positive electrode slurry coated close to the sodium supplement layer is: Na3V2(PO4)3: Na2CO3: PVDF: Super-P: PVP: NMP = 100: 1: 3: 2: 0.3: 68; the formula of the upper positive electrode slurry coated far from the sodium supplement layer is: Na3V2(PO4)3: Na2CO3: PVDF: Super-P: PVP: NMP = 100: 3: 3: 2: 0.3: 70. In addition, in the positive electrode sheet of Example 17, the single-sided surface density of the positive electrode coating is 300 g / m 2 ; the ratio of the sodium supplement capacity of the first positive electrode sodium supplement agent to the sacrificial sodium supplement agent is still about 50%: 50%.

[0139] According to the method described in Example 1, the positive electrode sheet of Example 17 is assembled into a sodium-ion battery.

[0140] Example 18

[0141] The main difference between the positive electrode sheet of Example 18 and that of Example 1 is that: the first positive electrode sub-coating close to the current collector does not contain the sacrificial positive electrode sodium supplement agent; the second positive electrode sub-coating far from the current collector contains both the sodium-containing positive electrode active material and the sacrificial positive electrode sodium supplement agent.

[0142] The preparation of the positive electrode sheet of Example 18 includes:

[0143] (1) Coating the bottom coating slurry with the same formula as in Example 1 on the surface of a positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, forming a sodium supplement layer with a single-sided surface density of 8.4 g / m 2 and a single-sided thickness of 7 ± 1 μm; then forming such a sodium supplement layer on the reverse side of the aluminum foil;

[0144] (2) A positive electrode coating including two sub - coatings is formed on the above - mentioned sodium - supplementing layer. Among them, the slurry formula corresponding to the first positive electrode sub - coating close to the sodium - supplementing layer is: Na3V2(PO4)3:PVDF:Super - P:PVP:NMP = 100:3:2:0.3:68; the slurry formula corresponding to the second positive electrode sub - coating far from the sodium - supplementing layer is: Na3V2(PO4)3:Na2CO3:PVDF:Super - P:PVP:NMP = 100:6.3:3:2:0.3:70.

[0145] (3) The above - mentioned positive electrode coating is formed on the sodium - supplementing layer on the reverse side to obtain a double - sided positive electrode sheet for use. Among them, in the positive electrode sheet of Example 18, the single - side surface density of the positive electrode coating is 200 g / m 2 ; the ratio of the sodium - supplementing capacity of the first positive electrode sodium - supplementing agent to the sacrificial sodium - supplementing agent is still 50%:50%.

[0146] According to the method described in Example 1, the positive electrode sheet of Example 18 is assembled into a sodium - ion battery.

[0147] Example 19

[0148] The main difference between the positive electrode sheet of Example 19 and that of Example 2 is that the sodium - positive electrode active material in the positive electrode coating is replaced from Na3V2(PO4)3 with Na[Ni 0.25 Fe 0.5 Mn 0.25 O2.

[0149] According to the method described in Example 1, the positive electrode sheet of Example 19 is assembled into a sodium - ion battery.

[0150] To highlight the beneficial effects of this application, Comparative Examples 1 - 4 are also set in this application.

[0151] Comparative Example 1

[0152] The preparation of a non - sodium - supplementing positive electrode sheet includes: mixing Na3V2(PO4)3, PVDF, Super - P, PVP, and NMP in a mass ratio of 100:3:2:0.3:69 to prepare a positive electrode coating slurry, directly coating the slurry on the aluminum foil, and after drying, forming a positive electrode coating with a single - side surface density still of 200 g / m 2 ; then coating the positive electrode coating slurry on the other side of the aluminum foil and drying to obtain a double - sided positive electrode sheet.

[0153] According to the method described in Example 1, the positive electrode sheet of Comparative Example 1 is assembled into a sodium - ion battery.

[0154] Comparative Example 2

[0155] A positive electrode plate, which is different from that of Example 2 in that: a mixed layer containing a first positive electrode sodium supplement and a sodium positive electrode active material is directly provided on the aluminum foil.

[0156] Preparation of the positive electrode plate of Comparative Example 2 includes: mixing Na3V2(PO4)3, a first positive electrode sodium supplement (the same as in Example 2, Na5FeO4 with a conductive carbon coating layer on the surface), PVDF, Super-P, PVP, and NMP in a mass ratio of 100:3:3:2:0.3:69 to prepare a positive electrode coating slurry; directly coating the positive electrode slurry on the aluminum foil, controlling the single-sided surface density of the coating to still be 200 g / m 2 , and forming a positive electrode coating after baking; then coating the positive electrode coating slurry on the other side of the aluminum foil and baking to obtain a double-sided positive electrode plate.

[0157] According to the method described in Example 1, the positive electrode plate of Comparative Example 2 is assembled into a sodium ion battery.

[0158] Comparative Example 3

[0159] A positive electrode plate, which is different from that of Example 2 in that: a mixed layer containing a sacrificial sodium supplement and a sodium positive electrode active material is directly provided on the aluminum foil.

[0160] The preparation of the positive electrode plate includes: mixing Na3V2(PO4)3, the sacrificial sodium supplement Na2CO3, PVDF, Super-P, PVP, and NMP in a mass ratio of 100:3:3:2:0.3:69 to prepare a positive electrode coating slurry, directly coating the slurry on the aluminum foil, and forming a positive electrode coating with a single-sided surface density of still 200 g / m after baking 2 ; then coating the positive electrode coating slurry on the other side of the aluminum foil and baking to obtain a double-sided positive electrode plate.

[0161] According to the method described in Example 1, the positive electrode plate of Comparative Example 3 is assembled into a sodium ion battery.

[0162] Comparative Example 4

[0163] A positive electrode plate, the main difference from that of Example 2 is that: a mixed layer containing a first positive electrode sodium supplement, a sacrificial sodium supplement and a sodium positive electrode active material is directly provided on the aluminum foil.

[0164] The preparation of the positive electrode plate of Comparative Example 4 includes: mixing Na3V2(PO4)3, Na5FeO4, Na2CO3, PVDF, Super-P, PVP, and NMP in a mass ratio of 100:3:3:3:2:0.3:69 to prepare a positive electrode coating slurry; directly coating the positive electrode slurry on the aluminum foil, and forming a positive electrode coating with a single-sided surface density of still 200 g / m after baking 2The positive electrode coating; then the positive electrode coating slurry is coated on the other side of the aluminum foil and baked to obtain a double-sided positive electrode sheet.

[0165] According to the method described in Example 1, the positive electrode sheet of Comparative Example 4 is assembled into a sodium-ion battery.

[0166] Comparative Example 5

[0167] A positive electrode sheet, which is different from that of Example 2 in that: a sodium supplement layer containing a first positive electrode sodium supplement agent is provided on the aluminum foil, and a positive electrode coating without a sacrificial sodium supplement agent is provided on the sodium supplement layer.

[0168] The preparation of a positive electrode sheet, which is different from that of Example 2 in that: a positive electrode coating slurry prepared by mixing Na3V2(PO4)3, PVDF, Super-P, PVP, and NMP in a mass ratio of 100:3:2:0.3:69 is coated on the sodium supplement layer, and the remaining steps are the same as those in Example 1.

[0169] According to the method described in Example 1, the positive electrode sheet of Comparative Example 5 is assembled into a sodium-ion battery.

[0170] Comparative Example 6

[0171] A positive electrode sheet, which is different from that of Example 2 in that: the positions of the positive electrode coating and the sodium supplement layer in Example 2 are reversed. That is, the positive electrode coating containing the sacrificial sodium supplement agent in Example 2 is directly in contact with the aluminum foil, and a sodium supplement layer containing a first positive electrode sodium supplement agent is provided on the positive electrode coating (the sodium supplement layer has the same composition as the sodium supplement layer in Example 2).

[0172] According to the method described in Example 1, the positive electrode of Comparative Example 6 is assembled into a sodium-ion battery.

[0173] Comparative Example 7

[0174] The preparation of a positive electrode, which is different from that of Comparative Example 1 in that: the sodium positive electrode active material is replaced from Na3V2(PO4)3 to Na[Ni 0.25 Fe 0.5 Mn 0.25 O2.

[0175] The preparation method of this positive electrode includes: mixing the sodium positive electrode active material Na[Ni 0.25 Fe 0.5 Mn 0.25 O2, PVDF, Super-P, PVP, and NMP in a mass ratio of 100:3:2:0.3:68, and preparing a positive electrode coating slurry; directly coating the slurry on the aluminum foil, and after baking, forming a single-sided surface density still of 200 g / m 2The positive electrode coating; then, the positive electrode coating slurry is coated on the other side of the aluminum foil and baked to obtain a double-sided positive electrode sheet.

[0176] According to the method described in Example 1, the positive electrode sheets of Comparative Example 7 are assembled into sodium-ion batteries.

[0177] To strongly support the beneficial effects brought by the technical solutions of this application, the sodium-ion batteries of the above-mentioned various examples or comparative examples are respectively subjected to the following performance tests:

[0178] a. Positive electrode specific capacity test: At room temperature (25 ± 3 °C), the above-mentioned various sodium-ion batteries are charged at a constant current and constant voltage of 1 / 3C to the upper limit voltage of 4.3V (C is the battery capacity) for formation, and the first charging capacity (i.e., the charging capacity during formation) is recorded. Then, it is discharged at 1 / 3C for the first time to the lower limit voltage of 2.0V, and the first discharge capacity (unit: mAh) and the average discharge voltage are recorded. Then, the positive electrode specific capacity = the first discharge capacity / the total mass of the positive electrode active material; the volume energy density of the battery = the first discharge capacity × the average discharge voltage / the battery volume.

[0179] b. Cycle performance test: At room temperature (25 ± 3 °C), the above-mentioned formed sodium-ion batteries are charged at a constant current and constant voltage of 1 / 3C to the upper limit voltage of 3.8V, and then discharged at 1 / 3C to the lower limit voltage of 2.0V. The above charging and discharging steps are repeated 500 times, and the capacity retention rate after 500 cycles is recorded. Among them, the capacity retention rate after 500 cycles = the discharge capacity of the 500th cycle / the discharge capacity of the first discharge after formation.

[0180] c. Battery DC internal resistance (DCIR) test: At room temperature (25 ± 3 °C), the above-mentioned formed sodium-ion batteries are charged at a constant current of 1 / 3C to the upper limit voltage of 3.8V, and then discharged at 1 / 3C to the lower limit voltage of 2.0V. After cycling 3 times, then at room temperature, it is charged at a constant current of 1 / 3C to 50% SOC, and the battery voltage after standing for 1 hour is recorded as V1; then it is discharged at 1.5C for 30s, and the battery voltage after the discharge is recorded as V2. Among them, DCIR = (V1 - V2) / 1.5C.

[0181] d. Utilization rate test of sodium supplementing material:

[0182] Non-sodium-supplementing batteries corresponding to the sodium-supplementing batteries of the examples and some comparative examples of this application are fabricated (wherein, Examples 1 - 19 and Comparative Examples 2 - 7 are sodium-supplementing batteries, Comparative Example 1 is the non-sodium-supplementing battery corresponding to Examples 1 - 18 and Comparative Examples 2 - 6, and Comparative Example 7 is the non-sodium-supplementing battery corresponding to Example 19).

[0183] At room temperature (25 ± 3 °C), each of the above batteries is first charged at a constant current and constant voltage of 1 / 3C to the upper limit voltage of 4.3V for formation, and then discharged at 1 / 3C to the lower limit voltage of 2.0V. The discharge capacity of each sodium-supplemented battery is denoted as C1, and the discharge capacity of the non-sodium-supplemented battery corresponding to each sodium-supplemented battery is denoted as C2. Then, the utilization rate of the sodium-supplemented material = (C1 - C2) / (the mass of each sodium-supplemented material × the specific capacity of the corresponding sodium-supplemented material). Here, the specific capacity of each sodium-supplemented material is calculated according to the number of active sodium ions actually removed during sodium supplementation by each sodium-supplementing agent known in the industry.

[0184] The relevant test results are summarized in Table 1 below.

[0185] Table 1

[0186]

[0187]

[0188] From the comparison between Example 2 and Comparative Examples 1-6 in Table 1, it can be known that when the battery positive electrode does not contain a sodium-supplementing agent (Comparative Example 1), both the specific capacity and the volume energy density of the battery positive electrode are relatively low, and the DCIR value is relatively high. When the positive electrode only contains one type of positive electrode sodium-supplementing agent (such as Comparative Examples 2, 3, 5), or the positive electrode contains two types of positive electrode sodium-supplementing agents but they are not distributed as in Example 1 of the present application in Comparative Examples 4 and 6 (the sum of the sodium-supplementing capacities provided by the sodium-supplementing agents in the positive electrode sheets of Comparative Examples 2-6 is close to that of Example 2), although it can improve the specific capacity and volume energy density of the battery positive electrode to a certain extent compared with Comparative Example 1, the effect of reducing the DCIR value of the battery is not obvious, and the impedance of the DCIR value of the battery is still relatively high (which can reflect the poor power performance of the battery), and at the same time, the utilization rate of the sodium-supplementing agent is not high. In Example 2 of the present application, the first positive electrode sodium-supplementing agent (i.e., sodium-rich transition metal oxide) and the sacrificial sodium-supplementing agent are simultaneously used in the positive electrode of the sodium-ion battery and are arranged in the manner required by the present application, which can significantly improve the utilization rate of these two sodium-supplementing agents, reduce the DCIR value of the battery, and at the same time increase the specific capacity and volume energy density of the positive electrode of the sodium-ion battery. Example 1, whose only difference from Example 2 lies in that the positive electrode coating has two layers, also has a similar effect and the effect is even better than that of Example 1. Similar above phenomena can also be known from the comparison between Comparative Example 7 and Example 19. The sodium-supplemented ion batteries provided by other examples of the present application also have the advantages of high utilization rate of the sodium-supplementing material, low DCIR value of the battery, high specific capacity of the battery positive electrode, high volume energy density of the battery, and good cycle performance.

[0189] In addition, from the comparison between Examples 2 and 8-16, it can be learned that when the proportion of the sodium supplementation capacity provided by the first positive electrode sodium supplement agent is between 10% and 90%, the comprehensive performance of the sodium-ion battery is relatively excellent, the DCIR value of the battery is lower, the utilization rate of the sodium supplementation material is higher, the specific capacity of the positive electrode is higher, and when the proportion of the sodium supplementation capacity provided by the first positive electrode sodium supplement agent is within the range of 50% to 90%, the comprehensive performance of the sodium-ion battery is even more excellent. In addition, in the positive electrode coating, when the mass ratio of the sacrificial positive electrode sodium supplement agent to the sodium positive electrode active material is greater than 0.3% (for example, within the range of 0.5% to 10%), it is more conducive to improving the utilization rate of the sodium supplementation material, the specific capacity of the positive electrode, etc., and when the mass ratio is between 1% and 5%, the comprehensive effect of the battery is better.

[0190] In addition, from the comparison between Example 2 and Example 6, it can be learned that when other parameters of the battery positive electrode are the same, when the surface of the first positive electrode sodium supplement agent is provided with a conductive coating layer, it is more conducive to improving the specific capacity of the battery positive electrode, the utilization rate of the sodium supplementation material, etc.

[0191] The above-described embodiments merely represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A positive electrode sheet for a sodium-ion battery, characterized in that, The positive electrode sheet includes a positive electrode current collector and a sodium supplement layer and a positive electrode coating layer stacked on at least one side of the positive electrode current collector. Wherein, on the same side of the positive electrode current collector, the positive electrode coating layer is arranged on the side of the sodium supplement layer away from the positive electrode current collector; the sodium supplement layer includes a sodium-rich transition metal oxide; the positive electrode coating layer includes a sodium positive electrode active material and a sacrificial positive electrode sodium supplement agent that can decompose and generate gas.

2. The positive electrode sheet according to claim 1, wherein The positive electrode coating layer includes n positive electrode sub-coating layers, n≥2. Wherein, in the direction from the positive electrode current collector to the sodium supplement layer, the mass ratio of the sacrificial positive electrode sodium supplement agent to the sodium positive electrode active material in each positive electrode sub-coating layer shows an increasing trend. Optionally, in the direction from the positive electrode current collector to the sodium supplement layer, the mass ratio of the sacrificial positive electrode sodium supplement agent to the sodium positive electrode active material in each positive electrode sub-coating layer increases layer by layer in sequence.

3. The positive electrode sheet according to claim 2, characterized in that, Among the n-layer positive electrode sub-coatings, the following condition is satisfied between at least two adjacent layers: A m / (D m / D m-1 ) - A m-1 ≥5%; where A m-1 is the mass ratio of the sacrificial positive electrode sodium supplement in the (m - 1)-th layer of the positive electrode sub-coating to the total sacrificial positive electrode sodium supplement in the positive electrode coating, and A m is the mass ratio of the sacrificial positive electrode sodium supplement in the m-th layer of the positive electrode sub-coating to the total sacrificial positive electrode sodium supplement in the positive electrode coating, D m-1 is the thickness of the (m - 1)-th layer of the positive electrode sub-coating, D m is the thickness of the m-th layer of the positive electrode sub-coating, and m is any integer from 2 to n; on the same side of the positive electrode current collector, the (m - 1)-th layer of the positive electrode sub-coating is closer to the positive electrode current collector than the m-th layer of the positive electrode sub-coating; Optionally, among the n-layer positive electrode sub-coatings, any two adjacent positive electrode sub-coatings satisfy: A m / (D m / D m-1 )-A m-1 ≥5%.

4. The positive electrode sheet according to claim 2 or 3, characterized in that, In each positive electrode sub-coating layer, the mass proportion of the sodium positive electrode active material is more than 80%.

5. The positive electrode sheet according to any one of claims 1-4, characterized in that, In the positive electrode coating layer, the total mass of the sacrificial positive electrode sodium supplement agent is 0.5-10% of the total mass of the sodium positive electrode active material.

6. The positive electrode sheet according to any one of claims 1-5, characterized in that, The sodium supplement layer includes the following components in mass percentage: 50%-90% of sodium-rich transition metal oxide, 0-40% of the second sodium positive electrode active material, 0.5-10% of binder, 0.5-10% of conductive agent.

7. The positive electrode sheet according to any one of claims 1-6, characterized in that, The proportion of the sodium supplement capacity provided by the sodium-rich transition metal oxide in the total sodium supplement capacity provided by the sodium-rich transition metal oxide and the sacrificial positive electrode sodium supplement agent is in the range of 10%-90%. Optionally, the proportion of the sodium supplement capacity provided by the sodium-rich transition metal oxide in the total sodium supplement capacity provided by the sodium-rich transition metal oxide and the sacrificial positive electrode sodium supplement agent is in the range of 50%-90%.

8. The positive electrode sheet according to any one of claims 1-7, characterized in that, The single-sided surface density of the positive electrode coating layer is greater than the single-sided surface density of the sodium supplement layer.

9. The positive electrode sheet according to claim 8, wherein The single-sided areal density of the sodium supplement layer is 1-20 g / m 2 ; the single-sided areal density of the positive electrode coating is 50-500 g / m 2 .

10. The positive electrode sheet according to any one of claims 1-9, characterized in that, The chemical formula of the sodium-rich transition metal oxide is Na x MO y , where M may include one or more of Ni, Co, Fe, Mn, Cr, Cu, Mo, Ru, Ir, Sn, and Nb; x ranges from 1 to 6, and y ranges from 1 to 4; Optionally, the sodium-rich transition metal oxide includes one or more of Na2FeO2, Na3FeO3, Na3FeO4, Na5FeO4, Na2NiO2, Na2CuO2, Na6MnO4 and Na6CoO4.

11. The positive electrode sheet according to any one of claims 1-10, characterized in that, The surface of the sodium-rich transition metal oxide also has a conductive coating layer.

12. The positive electrode sheet according to any one of claims 1-11, characterized in that, The sacrificial positive electrode sodium supplement agent is selected from one or more of sodium azide, sodium amide, sodium phosphide, sodium sulfide, sodium peroxide, sodium carbonate, sodium oxalate, sodium squarate, sodium nitrite.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that, The sodium supplement layer is in direct contact with the positive electrode current collector; and / or the positive electrode coating layer is in direct contact with the sodium supplement layer.

14. A sodium-ion battery, characterized in that, Including the positive electrode sheet according to any one of claims 1-13.

15. An apparatus including the sodium ion battery according to claim 14, the apparatus including an electrical device or an energy storage system.

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