Positive electrode sheet for sodium ion battery, sodium ion battery and device

Abstract

A positive electrode sheet for a sodium ion battery, a sodium ion battery and a device. The positive electrode sheet comprises a positive electrode current collector, and a sodium supplementing layer and a positive electrode coating which are sequentially stacked on at least one side of the positive electrode current collector, wherein the sodium supplementing layer comprises a sodium supplementing agent (a sodium-rich transition metal oxide), and the positive electrode coating contains a positive electrode active material and a sacrificial positive electrode sodium supplement agent capable of decomposing to produce gas.

Description

Positive electrode sheet for sodium ion battery and sodium ion battery and device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on December 28, 2023, with application number 202311850171.9 and titled “Positive Electrode Sheet for Sodium Ion Batteries, Sodium Ion Batteries and Devices,” the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application belongs to the technical field of sodium ion batteries, and specifically relates to a positive electrode plate for a sodium ion battery and a sodium ion battery and device. Background Art

[0004] Sodium-ion batteries are a type of battery with a similar energy storage mechanism to lithium-ion batteries. Since the abundance of sodium in the earth's crust is much higher than that of lithium, the cost of sodium-ion batteries is much lower than that of lithium-ion batteries, making them more likely to meet the future demand for low-cost large-scale energy storage devices.

[0005] During the first charge of a sodium-ion battery, the formation of a solid electrolyte membrane (SEI membrane) on the surface of the negative electrode irreversibly consumes the active sodium ions released from the positive electrode, reducing the positive electrode capacity and energy density of the sodium-ion battery. Sodium supplementation for sodium-ion batteries can compensate for the irreversible consumption of active sodium ions by forming the negative electrode SEI membrane, thereby increasing the energy density of sodium-ion batteries and narrowing the gap in energy density with lithium-ion batteries. Sodium supplementation is generally divided into positive electrode sodium supplementation and negative electrode sodium supplementation. Positive electrode sodium supplementation has the greatest industrial application prospects due to its high safety and the fact that it does not require changes to existing battery preparation processes.

[0006] Positive electrode sodium replenishment typically involves directly mixing a positive electrode sodium replenisher (such as NaN3, Na2O2, Na2C2O4, Na5FeO4, Na2NiO2, or NaCrO2) with a high irreversible sodium removal capacity with the positive electrode active material. During the formation process of the sodium-ion battery, the positive electrode sodium replenisher decomposes at a certain potential to release active sodium ions, replenishing the battery with sodium. Existing positive electrode sodium replenishment solutions cannot achieve both high energy density and sustained discharge capability.

[0007] Therefore, it is necessary to develop a positive electrode sodium replenishment scheme that has a good sodium replenishment effect and does not affect the electrochemical performance of sodium-ion batteries after sodium replenishment.

[0008] Summary of the Invention

[0009] In view of this, the present application introduces a sacrificial positive electrode sodium supplement agent that can decompose and produce gas and a sodium-rich transition metal oxide into the positive electrode sheet for sodium ion batteries, and controls the reasonable distribution of the two, which can reduce the negative effects of using a single sodium supplement agent, so that the utilization rate of these two types of sodium supplement agents can be fully utilized and the battery energy density can be improved, without significantly increasing the battery impedance or reducing the continuous discharge capacity of the sodium ion battery.

[0010] Specifically, the first aspect of the present application provides a positive electrode sheet for a sodium ion battery, comprising a positive electrode current collector and a sodium supplement layer and a positive electrode coating 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 is arranged on the side of the sodium supplement layer away from the positive electrode current collector; the sodium supplement layer comprises a sodium-rich transition metal oxide; the positive electrode coating comprises a first sodium positive electrode active material and a sacrificial positive electrode sodium supplement agent that can decompose and produce gas.

[0011] In the above-mentioned positive electrode plate of the embodiment of the present application, the sodium-rich transition metal oxide and the sacrificial positive electrode sodium supplement are introduced at the same time, and their arrangement is reasonably distributed, so that the sodium supplement efficiency of the two types of sodium supplements can be improved. At the same time, the addition amount of the sacrificial positive electrode sodium supplement can be reduced to reduce the amount of gas generated by its decomposition, thereby reducing the damage to the microstructure of the positive electrode plate caused by the large amount of gas released and the resulting reduction in the volume energy density of the battery. It also avoids the problem of increased positive electrode liquid phase impedance caused by the sodium-rich transition metal oxide and other sodium supplements being distributed in the same layer as the first positive electrode active material, thereby improving the continuous discharge capability of the sodium ion battery. Therefore, the use of the above-mentioned positive electrode plate can produce a sodium ion battery with excellent comprehensive performance.

[0012] In some embodiments, the positive electrode coating comprises n layers of positive electrode sub-coatings, where n≥2, wherein the mass ratio of the sacrificial positive electrode sodium supplement to the first sodium positive electrode active material in each positive electrode sub-coating increases from the positive electrode current collector toward the sodium supplement layer;

[0013] Optionally, in a 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 first sodium positive electrode active material in each positive electrode sub-coating layer increases layer by layer.

[0014] In some embodiments, in the n-layer positive electrode coating, at least two adjacent layers satisfy: A m / (D m / D m-1 )-A m-1 ≥5%; among them, A m-1 A is the mass ratio of the sacrificial positive electrode sodium replenisher in the m-1th layer of positive electrode sub-coating to the total sacrificial positive electrode sodium replenisher in the positive electrode coating, mis the mass ratio of the sacrificial positive electrode sodium replenisher in the mth layer of positive electrode sub-coating to the total sacrificial positive electrode sodium replenisher in the positive electrode coating, D m-1 is the thickness of the m-1th layer of positive electrode coating, D m is the thickness of the mth positive electrode sub-coating layer, m is any integer from 2 to n; on the same side of the positive electrode current collector, the m-1th positive electrode sub-coating layer is closer to the positive electrode current collector than the mth positive electrode sub-coating layer;

[0015] Optionally, among the n layers of positive electrode coatings, any two adjacent layers of the positive electrode coatings satisfy: A m / (D m / D m-1 )-A m-1 ≥5%.

[0016] In some embodiments, in each of the positive electrode sub-coating layers, the mass proportion of the first sodium positive electrode active material is greater than 80%.

[0017] In some embodiments, in the positive electrode coating, the total mass of the sacrificial positive electrode sodium supplement is 0.5% to 10% of the total mass of the first sodium positive electrode active material.

[0018] In some embodiments, the sodium supplement layer comprises the following components in percentage by weight: 50% to 90% of a sodium-rich transition metal oxide, 0% to 40% of a second sodium positive electrode active material, 0.5% to 10% of a binder, and 0.5% to 10% of a conductive agent.

[0019] In some embodiments, the ratio of the sodium replenishing capacity provided by the sodium-rich transition metal oxide to the total sodium replenishing capacity provided by the sodium-rich transition metal oxide and the sacrificial positive electrode sodium replenishing agent is in the range of 10% to 90%;

[0020] Optionally, the ratio of the sodium replenishing capacity provided by the sodium-rich transition metal oxide to the total sodium replenishing capacity provided by the sodium-rich transition metal oxide and the sacrificial positive electrode sodium replenishing agent is in the range of 50% to 90%.

[0021] In some embodiments, the single-surface areal density of the positive electrode coating is greater than the single-surface areal density of the sodium supplement layer.

[0022] In some embodiments, the single-surface density of the sodium supplement layer is 1-20 g / m 2 The single surface density of the positive electrode coating is 50g / m 2 ~500g / m 2 .

[0023] In some embodiments, the chemical formula of the sodium-rich transition metal oxide is Na x MO y, wherein M may include one or more of Ni, Co, Fe, Mn, Cr, Cu, Mo, Ru, Ir, Sn and Nb; x is in the range of 1-6, and y is in the range of 1-4;

[0024] The sodium-rich transition metal oxide includes one or more of Na2FeO2, Na3FeO3, Na3FeO4, Na5FeO4, Na2NiO2, Na2CuO2, Na6MnO4 and Na6CoO4.

[0025] In some embodiments, the surface of the sodium-rich transition metal oxide further has a conductive coating layer.

[0026] In some embodiments, the sacrificial positive electrode sodium supplement is selected from one or more of sodium azide, sodium amide, sodium phosphide, sodium sulfide, sodium peroxide, sodium carbonate, sodium oxalate, sodium squarate, and sodium nitrite.

[0027] In some embodiments, the sodium-replenishing layer is in direct contact with the positive electrode current collector; and / or the positive electrode coating is in direct contact with the sodium-replenishing layer.

[0028] In a 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.

[0029] Due to the use of the above-mentioned positive electrode plate, the utilization rate of the two types of sodium supplements in the sodium ion battery is high, the total amount of reversible sodium in the battery is high, the energy density is high, and the battery impedance is low and the power performance is good.

[0030] In a third aspect, the present application provides a device comprising the sodium ion battery described in the second aspect of the present application, wherein the device comprises an electrical device or an energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a schematic structural diagram of a positive electrode plate provided in this application.

[0032] FIG2 is another structural schematic diagram of the positive electrode sheet provided in this application. Specific embodiments

[0033] The technical solutions of the embodiments of the present application will be described below with reference to the accompanying drawings.

[0034] Please refer to Figures 1 and 2 together. 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 supplement layer 20 and a positive electrode coating 30 stacked in sequence on at least one side of the positive electrode current collector 10, wherein the sodium supplement layer 20 includes a first sodium supplement, which is a sodium-rich transition metal oxide 201; the positive electrode coating 30 includes a sodium first positive electrode active material 302 and a second sodium supplement that can decompose and produce gas, which is a sacrificial positive electrode sodium supplement 301.

[0035] The above-mentioned positive electrode plate 100 contains both a sacrificial positive electrode sodium supplement 301 that can decompose and produce gas and a sodium-rich transition metal oxide sodium supplement 201. On the one hand, compared with the positive electrode plate containing only the sacrificial positive electrode sodium supplement 301, when the total amount of sodium supplement remains unchanged, the amount of sacrificial positive electrode sodium supplement 301 added to the positive electrode plate of the present application is lower, and the total amount of gas generated by its decomposition is also reduced accordingly, thereby reducing the damage to the microstructure of the positive electrode plate caused by a large amount of gas release and the resulting reduction in battery volume energy density; the sacrificial positive electrode sodium supplement 301 and the first positive electrode plate are added to the positive electrode plate 100. The positive electrode coating 30 of a sodium positive electrode active material is arranged on the surface of the positive electrode plate 100, away from the positive electrode current collector 10. The discharge path of the gas generated by its decomposition is shortened, which is more conducive to gas discharge. In this way, the battery polarization phenomenon is reduced during the decomposition process of the sacrificial positive electrode sodium supplement 301, and its decomposition ratio and sodium supplement effect are improved. Due to the reduction in battery polarization, the utilization rate of the sodium-rich transition metal oxide 201 sodium supplement can also be improved to a certain extent. At the same time, there is less gas remaining in the positive electrode plate 100, the battery impedance is also reduced, and the continuous discharge capability is improved.

[0036] On the other hand, the present application disposes the sodium-rich transition metal oxide 201, a positive electrode sodium supplement, in the sodium supplement layer 20 near the positive electrode current collector 10, and disposes a positive electrode coating 30 containing a sacrificial positive electrode sodium supplement 301 thereon. Firstly, compared to a positive electrode sheet whose sodium supplement material only contains the sodium-rich transition metal oxide 201, the sodium de-sodium potential of the sodium-rich transition metal oxide 201 in the present application does not gradually increase in the direction away from the positive electrode current collector 10, thereby ensuring its high sodium supplement efficiency. Secondly, compared to a positive electrode sheet whose sodium supplement material only contains the sodium-rich transition metal oxide 201, while the total sodium supplement capacity remains unchanged, the positive electrode of the present application introduces two types of positive electrode sodium supplements, and the amount of sodium-rich transition metal oxide 201 added is also reduced. Accordingly, the impact of the low positive electrode sheet compaction density caused by the poor particle size matching between the sodium-rich transition metal oxide 201 and the sodium positive electrode active material is also reduced, which is more conducive to improving the battery energy density. On the same side of the positive electrode current collector 10, the sodium-compensating layer 20 is closer to the positive electrode current collector 10 than the positive electrode coating 30. In some embodiments, the sodium-compensating layer 20 may be in direct contact with the positive electrode current collector 10; in some embodiments, the positive electrode coating 30 may be in direct contact with the sodium-compensating layer 20.

[0037] Therefore, in the above-mentioned positive electrode sheet of the embodiment of the present application, the above-mentioned two sodium supplements are arranged in layers as above, so that the sodium supplement efficiency of these two types of sodium supplements can be improved, the energy density of the sodium ion battery can be improved to a certain extent, and the impedance of the sodium ion battery can be reduced and the continuous discharge capability can be improved.

[0038] In some embodiments of the present application, the sodium-supplementing layer 20 may be in direct contact with the positive electrode current collector 10, and / or the positive electrode coating 30 may be in direct contact with the sodium-supplementing layer 20. It is understood that in other embodiments of the present application, another coating may be provided between the sodium-supplementing layer 20 and the positive electrode current collector 10. Another intermediate layer may also be provided between the positive electrode coating 30 and the sodium-supplementing layer 20.

[0039] In the present application, the sodium-rich transition metal oxide 201 is used as a positive electrode sodium supplement, which can release sodium ions during the formation and charging process of the sodium ion battery, with a theoretical gram capacity of about 300mAh / g to 700mAh / g, which far exceeds the positive electrode active materials currently used for sodium ion batteries. After the sodium ions are released, the structure of the sodium-rich transition metal oxide 201 undergoes irreversible changes, and a part of the main structure or desodium products will remain. In addition, compared with the sodium positive electrode active material, the sodium-rich transition metal oxide 201 has a poor ability to re-intercalate sodium ions. Within the working range of the sodium ion battery, the first sodium removal capacity of the sodium-rich transition metal oxide 201 is much higher than its first sodium insertion capacity, that is, its first coulombic efficiency is low (less than 30%), which is much lower than the first coulombic efficiency of the currently used sodium positive electrode active material.

[0040] In the embodiment of the present application, the chemical formula of the sodium-rich transition metal oxide 201 can be expressed as Na x MO y , where M may include, but is not limited to, one or more of Ni, Co, Fe, Mn, Cr, Cu, Mo, Ru, Ir, Sn, Nb, etc.; x is in the range of 1-6, and y is in the range of 1-4. Exemplarily, the sodium-rich transition metal oxide 201 may include one or more of Na2FeO2, Na3FeO3, Na3FeO4, Na5FeO4, Na2NiO2, Na2CuO2, Na6MnO4, Na6CoO4, etc., but is not limited thereto. The sodium-supplementing layer 20 may contain one or more sodium-rich transition metal oxides 201. In some embodiments of the present application, the surface of the sodium-rich transition metal oxide 201 may or may not have a conductive coating layer, preferably having a conductive coating layer.

[0041] In this application, the sacrificial cathode sodium supplement agent 301 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 sodium supplement effect. After the sacrificial cathode sodium supplement agent 301 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 agent 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 agent 301 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.

[0042] In the embodiments of this application, the first sodium cathode active material can include one or more of sodium transition metal oxides, sodium polyanion compounds, sodium prussian blue and its analogues, 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[[ID=​​​​​​​In the present application, the sodium-supplementing layer 20 may or may not contain a second sodium-based positive electrode active material. In embodiments of the present application, the sodium-supplementing layer 20 may include the following components in percentage by weight: 50% to 90% of a first positive electrode sodium-supplementing agent, 0% to 40% of a second sodium-based positive electrode active material, 0.5% to 10% of a first binder, and 0.5% to 10% of a first conductive agent. The selection range of the second sodium-based positive electrode active material can refer to the description of the first positive electrode active material in the positive electrode coating 30 previously described in this application. The first positive electrode active material in the positive electrode coating 30 and the second sodium-based positive electrode active material here can be the same or different materials. The first positive electrode sodium-supplementing agent has a greater percentage by weight than the second sodium-based positive electrode active material in the sodium-supplementing layer 20, which can provide a higher sodium-supplementing capacity for the sodium-supplementing layer 20 and improve the battery's energy density. The presence of an appropriate amount of the first binder can ensure the adhesion of the sodium-supplementing layer 20 to the positive electrode current collector 10, while the presence of an appropriate amount of the first conductive agent can help improve the electron conductivity of the sodium-supplementing layer 20. Specifically, the mass percentage of the first positive electrode sodium supplement agent in the sodium supplement layer 20 can be 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.

[0044] In some embodiments, the sodium-replenishing 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-replenishing layer 20 is zero. This avoids the problem of increased positive electrode liquid phase diffusion impedance and slower liquid phase sodium ion transport caused by direct mixing of the sodium-rich transition metal oxide 201 with the sodium positive electrode active material, thereby helping to reduce the impedance of the sodium-ion battery.

[0045] In some other embodiments of the present application, the sodium-replenishing 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%. The sodium-replenishing layer 20 contains an appropriate amount of the second sodium positive electrode active material, so that the sodium-replenishing layer 20 can also contribute to a certain capacity in the battery after formation.

[0046] In the present application, the positive electrode coating 30 can be a single layer (as shown in FIG1 ) or multiple layers (i.e., the number of layers is ≥ 2, as shown in FIG2 ). When the positive electrode coating 30 is a single layer (as shown in FIG1 ), the sacrificial positive electrode sodium supplement 301 can be uniformly dispersed in the first sodium positive electrode active material. When the positive electrode coating 30 is a multilayer, it can include n layers of positive electrode sub-coatings, where n is ≥ 2 and n is a positive integer (as shown in FIG2 ).

[0047] In the present application, the ratio of the sodium supplement capacity provided by the sodium-rich transition metal oxide 201 to the total sodium supplement capacity provided by the sodium-rich transition metal oxide 201 and the sacrificial positive electrode sodium supplement 301 in the positive electrode plate 100 is x, and the ratio of the sodium supplement capacity provided by the sacrificial positive electrode sodium supplement 301 to the total sodium supplement capacity provided by the sodium-rich transition metal oxide 201 and the sacrificial positive electrode sodium supplement 301 in the positive electrode plate 100 is 1-x. Wherein, x is in the range of 10%-90%, for example, specifically 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 85%, etc. Correspondingly, 1-x is also in the range of 10%-90%. By adjusting the sodium supplement capacity ratio of the two sodium supplements, different requirements of different batteries for energy density, power density, cycle life, etc. can be met. Preferably, x is in the range of 50%-90%, and correspondingly, 1-x is in the range of 10%-50%. In this case, the sodium replenishment capacity provided by the sodium-rich transition metal oxide 201 sodium replenisher is greater than the sodium replenishment capacity provided by the sacrificial positive electrode sodium replenisher 301. This can reduce the amount of sacrificial sodium replenisher used, thereby reducing the impact of the large amount of gas generated by the decomposition of the sacrificial sodium replenisher on the electrode microstructure. The sodium replenishment capacity provided by each sodium replenisher is equal to the product of its mass and its gram capacity. The gram capacity here is calculated based on the number of active sodium ions actually removed by each sodium replenisher during sodium replenishment, as is well known in the industry. For example, for Na5FeO4, its gram capacity corresponds to its theoretical gram capacity of 455mAh / g for removing 4 sodium ions; for Na6MnO4, its gram capacity corresponds to its theoretical gram capacity of 520mAh / g for removing 5 sodium ions; for Na2CO3, its gram capacity corresponds to its theoretical gram capacity of 505mAh / g for removing 2 sodium ions; and for Na2C2O4, its gram capacity corresponds to its theoretical gram capacity of 399mAh / g for removing 2 sodium ions.

[0048] In the embodiment of the present application, the positive electrode coating 30 includes the following components in percentage by weight: 80-99.5% of the first sodium positive electrode active material, 0.5-10% of the sacrificial positive electrode sodium supplement 301, 0.1-5% of the second conductive agent, 0.1-5% of the second binder, and 0-5% of the dispersant. The mass percentage 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. The second conductive agent and the first conductive agent are both commonly used conductive agents in the art, and the second conductive agent and the first conductive agent may be the same or different; the second binder and the first binder are both commonly used binders in the art, and the second binder and the first binder may be the same or different.

[0049] In some embodiments of the present application, in the positive electrode coating 30, the total mass of the sacrificial positive electrode sodium supplement 301 is 0.5-10% of the total mass of the first sodium positive electrode active material. Regardless of whether the positive electrode coating 30 is a single layer (as shown in FIG1 ) or multiple layers (i.e., the number of layers ≥ 2, as shown in FIG2 ), the range of this ratio is applicable. This parameter range helps to ensure that the sacrificial positive electrode sodium supplement 301 can provide an appropriately high sodium supplement capacity without producing too much gas. Specifically, the 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, the ratio is in the range of 1%-5%. This ensures that the second positive electrode sodium supplement replenishes the irreversible consumption of active sodium for the battery while not making the reversible capacity of the battery positive electrode too small or the positive electrode producing too much gas.

[0050] In some embodiments of the present application, when the positive electrode coating 30 includes n layers of positive electrode sub-coatings, the mass ratio of the sacrificial positive electrode sodium replenisher 301 to the first sodium positive electrode active material in each positive electrode sub-coating increases from the positive electrode current collector 10 toward the sodium replenishing layer 20 (i.e., the direction indicated by the arrow in FIG2 ). The mass of the first sodium positive electrode active material is the total mass of the sodium positive electrode active material in the positive electrode coating 30.

[0051] 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 recorded as L1, L2, ..., L n In this way, the surface of the positive electrode current collector 10 is sequentially provided with a sodium supplement layer 20, a first positive electrode sub-coating L1, a second positive electrode sub-coating L2, ..., an nth positive electrode sub-coating L n If the total mass ratio of the sacrificial positive electrode sodium supplement 301 in the first positive electrode sub-coating L1 to the sodium positive electrode active material in the positive electrode coating 30 is recorded as X1, the total mass ratio of the sacrificial positive electrode sodium supplement 301 in the second positive electrode sub-coating L2 to the sodium positive electrode active material in the positive electrode coating 30 is recorded as X2, ..., the total mass ratio of the nth positive electrode sub-coating L n The total mass ratio of the sacrificial positive electrode sodium supplement 301 to the sodium positive electrode active material in the positive electrode coating 30 is recorded as X n , then the above “increasing trend” can be expressed as: X1≤X2≤X3…≤X n , and X n >X1, X1≥0, for example, the above-mentioned "increasing trend" can be specifically: first increase - then remain unchanged - then increase, or first remain unchanged and then increase in sequence, or first remain unchanged - then increase - then remain unchanged - then increase, etc.; or a layer-by-layer increasing method (such as X1<X2<X3…<X n , X1≥0).

[0052] The present application controls the mass ratio of the sacrificial positive electrode sodium replenisher 301 to the first sodium positive electrode active material in each positive electrode sub-coating to increase 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 electrode sodium replenisher 301 in each positive electrode sub-coating close to the positive electrode current collector, which can reduce battery polarization and make the desodium potential of the sacrificial positive electrode sodium replenisher 301 in each positive electrode sub-coating basically consistent. As a result, the decomposition ratio and sodium replenishment efficiency of the sacrificial positive electrode sodium replenisher 301 in each positive electrode sub-coating are both high, and the reduction in battery polarization is also conducive to reducing the overall impedance of the battery and improving the sustainable discharge capacity of the battery. In addition, after the sacrificial positive electrode sodium replenisher 301 decomposes, the pores created by it in each positive electrode sub-coating can also form a gradient pore structure layer by layer. 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 or 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.

[0053] In some embodiments of the present application, when n layers of positive electrode sub-coatings are provided, the mass ratio of the sacrificial positive electrode sodium supplement 301 to the first sodium positive electrode active material in each positive electrode sub-coating increases layer by layer, from the positive electrode current collector 10 toward the sodium supplement layer 20. This facilitates smoother discharge of gases generated by the decomposition of the sacrificial positive electrode sodium supplement 301 in the positive electrode coating 30. After decomposition, the sacrificial positive electrode sodium supplement 301 imparts a pore structure to the positive electrode coating 30 in which the porosity increases in the direction of the arrow, further contributing to reduced battery impedance.

[0054] In some embodiments of the present application, in the n-layer positive electrode coating, at least two adjacent layers satisfy: A m / (D m / D m-1 )-A m-1 ≥5%; among them, A m-1 A is the mass ratio of the sacrificial positive electrode sodium replenisher 301 in the m-1th positive electrode sub-coating layer to the total sacrificial positive electrode sodium replenisher 301 in the positive electrode coating 30, m is the mass ratio of the sacrificial positive electrode sodium replenisher 301 in the mth layer of the positive electrode sub-coating to the total sacrificial positive electrode sodium replenisher 301 in the positive electrode coating 30, D m-1 is the thickness of the m-1th layer of positive electrode coating, D m is the thickness of the mth layer of positive electrode sub-coating, m is any integer from 2 to n; on the same side of the positive electrode current collector, the m-1th layer of positive electrode sub-coating is closer to the positive electrode current collector than the mth layer of positive electrode sub-coating. In this way, after the sacrificial positive electrode sodium supplement 301 decomposes, the porosity of at least two adjacent positive electrode sub-coatings can be clearly distinguished, which helps to reduce battery impedance and improve power performance. Furthermore, among the n layers of positive electrode sub-coatings, any two adjacent layers of positive electrode sub-coatings satisfy: A m / (Dm / D m-1 )-A m-1 ≥5%. In this way, after the battery is formed, 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 is more effective in reducing battery impedance and improving power performance. Optionally, A m / (D m / D m-1 )-A m-1 ≥10%, such as A m / (D m / D m-1 )-A m-1 Specifically, it is 10%, 15%, 20%, 25%, 30%, 40%, 50%, or 60%, etc.

[0055] For example, in some embodiments, when the thickness of each positive electrode coating is substantially the same (eg, D m / D m-1 =1), among n layers of positive electrode coating, any two adjacent layers of positive electrode coating satisfy: A m -A m-1 ≥5%, m is any integer from 2 to n. If the mass ratio of the sacrificial positive electrode sodium replenisher 301 in the first positive electrode sub-coating L1 to the total mass ratio of the sacrificial positive electrode sodium replenisher 301 in the positive electrode coating 30 is recorded as Y1, the mass ratio of the sacrificial positive electrode sodium replenisher 301 in the second positive electrode sub-coating L2 to the total mass ratio of the sacrificial positive electrode sodium replenisher 301 in the positive electrode coating 30 is recorded as Y2, ..., the mass ratio of the sacrificial positive electrode sodium replenisher 301 in the nth positive electrode sub-coating L n The mass ratio of the sacrificial positive electrode sodium supplement 301 to the total sacrificial positive electrode sodium supplement 301 in the positive electrode coating 30 is recorded 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%. Wherein, 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%.

[0056] In the embodiment of the present application, the mass proportion of the sodium positive electrode active material in each positive electrode sub-coating is more than 80%, for example, in the range of 80%-99.5%. This is more conducive to the higher reversible capacity provided by each positive electrode sub-coating, thereby ensuring that the reversible capacity of the overall positive electrode sheet is high. Taking the first positive electrode sub-coating L1 as an example, specifically, the ratio of the mass of the sodium positive electrode active material in the first positive electrode sub-coating L1 to the total mass of the first positive electrode sub-coating L1 is more than 80%, and can further be more than 90%.

[0057] In the present application, the single-sided areal density of each positive electrode material sub-layer can be equal or different. In some embodiments of the present application, the single-sided areal density of each positive electrode sub-coating layer is equal. This helps to ensure that their stacked structure is more stable.

[0058] In the present application, regardless of whether the positive electrode coating 30 is a single layer or multiple layers, the single-surface areal density of the positive electrode coating 30 is greater than the single-surface areal density of the sodium supplementation layer 20. The positive electrode coating 30 is the primary reversible capacity-providing layer of the battery, and its single-surface areal density is higher than that of the sodium supplementation layer 20, which helps ensure a high energy density and discharge capacity of the battery.

[0059] In the embodiment of the present application, the single surface density of the sodium supplement layer 20 can be 1g / m 2 ~50g / m 2 This can ensure that the sodium supplement capacity provided by the first positive electrode sodium supplement agent is appropriate to a certain extent, and ensure that the overall performance of the sodium ion battery is good. It will not cause the sodium supplement effect of the battery to be insignificant due to insufficient sodium supplement capacity of the first positive electrode sodium supplement agent, nor will it cause the sodium supplement amount of the sodium ion battery to exceed the reasonable level of the current battery design due to excessive addition of the first positive electrode sodium supplement agent. In some embodiments, the single surface density of the sodium supplement layer 20 is 1g / m 2 ~20g / m 2 , for example, 1.0 g / m 2 , 1.5g / m 2 , 2g / m 2 , 2.5g / m 2 3.0g / m 2 , 4.0g / m 2 , 5.0g / m 2 , 6.0g / m 2 , 7.0g / m 2 , 8.0g / m 2 , 9g / m 2 、10.0g / m 2 、15.0g / m 2 or 20.0g / m 2 This is more conducive to improving the utilization rate of the first positive electrode sodium supplement, and at the same time, the sodium ion battery has a higher positive electrode gram capacity and first coulombic efficiency.

[0060] In the embodiment of the present application, the single surface density of the positive electrode coating 30 can be 50g / m 2 ~500g / m 2 , for example, 60g / m 2 , 80g / m 2 , 100g / m 2 , 150g / m 2 , 200g / m 2 , 210g / m 2 , 220g / m 2 , 250g / m 2 , 300g / m 2 , 350g / m 2 , 400g / m 2 , 450g / m 2 The positive electrode coating 30 is in a higher range, which helps the sodium ion battery have a higher positive electrode capacity and ensures that the sacrificial sodium supplement agent provides a suitable sodium supplement capacity. In some embodiments, the single surface density of the positive electrode coating 30 is 100g / m 2 ~300g / m 2 .

[0061] In the present application, the thickness of the sodium-replenishing layer 20 is less than the thickness of the positive electrode coating 30. This is also conducive to ensuring that the energy density of the sodium-ion battery is high. In the embodiment of the present application, the thickness of the single side of the sodium-replenishing layer 20 can be in the range of 1μm to 50μm. In some embodiments, the thickness of the single side of the sodium-replenishing layer 20 is 1μm to 20μm, and can further be 1μm to 10μm, for example, specifically 1.0μm, 2.0μm, 3.0μm, 4.0μm, 5.0μm, 6.0μm, 7.0μm, 8.0μm or 9μm, etc. In this case, the thickness of the sodium-replenishing layer 20 containing the first positive electrode sodium-replenishing 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 production of the positive electrode during the first charging process of the sodium-ion battery is small and the battery impedance is low. In an embodiment of the present application, the single-sided thickness of the positive electrode coating 30 can be in the range of 25μm to 500μm, for example, 30μm, 50μm, 80μm, 100μm, 120μm, 150μm, 200μm, 220μm, 250μm, 300μm, 350μm, 400μm, or 450μm, etc.; in some embodiments, the single-sided thickness of the positive electrode coating 30 is 50μm to 250μm.

[0062] In the present application, in addition to the first positive electrode sodium supplement, the sodium supplement layer 20 may also contain a first binder and a first conductive agent. In addition to the first sodium positive electrode active material and the sacrificial positive electrode sodium supplement 301, the positive electrode coating 30 may also contain a second binder and a second conductive agent. Among them, each conductive agent can be independently 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 can be independently 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 30 may also contain a dispersant. Each dispersant may be selected from one or more of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), and the like.

[0063] The sodium replenishing layer 20 can be formed by coating a primer slurry containing a first positive electrode sodium replenishing agent and a solvent, followed by drying. The coating method can include, but is not limited to, a combination of one or more methods such as spin coating, brush coating, spray coating, dip coating, and blade coating. Similarly, the positive electrode coating layer 30 can be formed by coating a positive electrode slurry containing a first sodium positive electrode active material, a sacrificial positive electrode sodium replenishing agent 301, and a solvent, followed by drying.

[0064] The solvents contained in each slurry may be the same or different and may be independently selected from one or more of pyrrolidones (e.g., N-methylpyrrolidone (NMP), N-ethylpyrrolidone, etc.), cyclic ethers (e.g., tetrahydrofuran, methyltetrahydrofuran), dimethyl sulfoxide, ketones (e.g., acetone, butanone), lactones (e.g., butyrolactone, caprolactone), etc., but are not limited thereto. The solid content of each slurry is not particularly limited, as long as it can meet the fluidity and uniformity of the slurry coating. Generally, the solid content of the primer slurry can be 5% to 50%. The solid content of the positive electrode slurry is in the range of 50% to 70%.

[0065] Among them, when the positive electrode coating 30 is a layer, the positive electrode slurry is one type, and when the positive electrode coating 30 is a multi-layer, the type of positive electrode slurry used corresponds to the number of layers of the positive electrode coating 30. In addition, each layer of slurry can be applied simultaneously or sequentially, or applied on the coating formed by drying the previous slurry. Taking the positive electrode coating 30 as an example, a positive electrode slurry can be directly applied on the primer slurry (which can be applied simultaneously or sequentially), and then baked together to remove the solvent, and then rolled. If double-sided coating is required, the above operation can be repeated on the other side surface of the positive electrode current collector 10. Alternatively, the above primer slurry can be applied on one side surface of the positive electrode current collector 10 and dried to form the sodium supplement layer 20, and then the positive electrode slurry can be applied on the sodium supplement layer 20, and dried to form the positive electrode coating 30, and then rolled.

[0066] In the present application, the positive electrode current collector 10 may include, but is not limited to, aluminum foil, aluminum alloy foil, a polymer film coated with aluminum, or the aforementioned materials with a carbon coating on the surface. In some embodiments of the present application, the positive electrode current collector 10 is aluminum foil. In the present application, a stacked structure of a sodium-supplementing layer 20 and a positive electrode coating 30 may be formed on one surface of the positive electrode current collector 10 (as shown in Figures 1 and 2), or a stacked structure of a sodium-supplementing layer 20 and a positive electrode coating 30 may be formed on both opposite sides of the positive electrode current collector 10.

[0067] The embodiment of the present application further provides a sodium ion battery, which includes the positive electrode plate 100 described above in the embodiment of the present application.

[0068] In the embodiment of the present application, the sodium ion battery further includes a positive electrode plate, and a separator and an electrolyte arranged between the negative electrode plate and the positive electrode plate.

[0069] The negative electrode sheet 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 third conductive agent, and a third binder. In the embodiments 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 microbeads, and silicon-carbon composite materials. The third conductive agent and the third binder are commonly used in the art.

[0070] The separator is used to separate the positive and negative electrode sheets, maintaining insulation and liquid retention between them. The separator, positive and negative electrode sheets together constitute the battery cell, which is housed in a battery casing and is soaked in the electrolyte contained in the casing. In some embodiments of the present application, the sodium-ion battery can be assembled by the following method: the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to form a cell; the cell is housed in a battery casing, and the electrolyte is injected, and the battery casing is sealed to produce a battery. The cell can be wound or laminated.

[0071] The separator can be any separator material used in batteries. For example, the separator may include, but is not limited to, single-layer PP (polypropylene) film, single-layer PE (polyethylene) film, double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and other polymer separators, or non-woven fabrics. The electrolyte includes an electrolyte salt and an organic solvent. The specific types and compositions of the electrolyte salt and organic solvent are conventional in the battery field and can be selected according to actual needs.

[0072] The embodiment of the present application also provides a device, which includes the above-mentioned sodium ion battery of the embodiment of the present application. Among them, the device can be an electric vehicle (such as a car, motorcycle, 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-mentioned 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-mentioned sodium ion battery has a long operating time and a fast charging speed.

[0073] The technical solution of the present application is further described below in conjunction with a number of specific embodiments.

[0074] Example 1

[0075] A positive electrode sheet for a sodium ion battery, the preparation method of which comprises:

[0076] The first positive electrode sodium supplement (specifically Na5FeO4 with a carbon coating layer on the surface, the mass proportion of the coating material is 3 wt%) is mixed with the binder PVDF, the conductive agent Super-P, and the solvent NMP in a mass ratio of 80:10:10:150, and stirred evenly to obtain a primer slurry with a solid content of 40.0 wt%. The primer slurry is coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm. The coating conditions are controlled to form a single-sided surface density of 8.4 g / m after drying. 2The sodium-filling layer has a thickness of 7±1 μm. The other side of the aluminum foil (which may be called the "reverse side") is then coated with the above-mentioned primer slurry and dried to obtain an aluminum foil with a double-sided sodium-filling layer.

[0077] The sodium cathode active material Na3V2(PO4)3 was mixed with a sacrificial sodium supplement agent Na2CO3, a binder PVDF, a conductive agent Super-P, a dispersant PVP, and a solvent NMP in different proportions to prepare two cathode coating slurries. The formula of the lower slurry coated close to the sodium supplement layer was: Na3V2(PO4)3: Na2CO3: PVDF: Super-P: PVP: NMP = 100: 2: 3: 2: 0.3: 68 , solid content is 61wt%, the formula of the upper slurry away from the sodium supplement layer is: Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP=100:4:3:2:0.3:70, with a solid content of 61wt%. The lower slurry and the upper slurry are simultaneously stacked and coated on the sodium supplement layer to form two positive electrode coatings with equal surface density after drying, and the sum of the single surface density of the two positive electrode coatings is 200g / m 2 Then, the lower and upper slurries are coated and dried on the reverse sodium replenishment layer to obtain a double-sided positive electrode sheet for use. In this positive electrode sheet, the ratio of the sodium replenishment capacity provided by the first positive sodium replenisher to that provided by the sacrificial sodium replenisher is 50%:50%.

[0078] Preparation of a sodium ion battery:

[0079] (1) Preparation of negative electrode sheet: The negative electrode active material spherical hard carbon, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) and water were 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 was coated on one side of the copper foil and dried to obtain a single-side surface density of 80 g / m 2 Then, the negative electrode slurry is coated on the reverse side of the copper foil and dried to obtain a double-sided negative electrode sheet.

[0080] (2) The positive electrode sheets and negative electrode sheets prepared above are rolled, slit, and die-cut, and then alternately stacked together with a separator (specifically a PP separator with a thickness of 14 μm) (so that the positive electrode sheets and the negative electrode sheets are separated by the separator) to form a sodium ion battery cell; then the cell is placed in a sodium ion battery shell (the battery shell size is 150*100*25 mm), and an electrolyte for a sodium ion battery is injected (the electrolyte is obtained by dissolving NaPF6 in a mixed solvent of EC:DEC:EMC (volume ratio is 1:1:1), and the concentration of NaPF6 is 1 M). The battery shell is sealed and an air bag is reserved. Then, after the process of infiltration, formation, aging, and volume separation, a sodium ion battery is prepared for subsequent electrochemical performance testing.

[0081] Example 2

[0082] The difference between Example 2 and Example 1 is that the positive electrode coating 30 is a single layer. The positive electrode coating 30 is prepared by coating and drying a positive electrode coating slurry having a solid content of 61 wt% with a mass ratio of Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP = 100:3:3:2:0.3:68. The single surface density of the positive electrode coating 30 is still 200 g / m 2 , with a thickness of 100μm.

[0083] According to the method described in Example 1, the positive electrode sheet of Example 2 was assembled into a sodium ion battery.

[0084] Example 3

[0085] A preparation method for a sodium ion battery positive electrode plate, which differs from Example 1 mainly in that the first positive electrode sodium supplement is replaced with Na6MnO4 with a carbon coating layer on the surface, and the mass proportion of the coating material is 2.5wt%. Among them, in the positive electrode plate prepared in Example 3, the single-surface density of the sodium supplement layer is 7.3g / m 2 , with a thickness of 6±1 μm; the ratio of the sodium replenishing capacity provided by the first positive electrode sodium replenishing agent and the sacrificial sodium replenishing agent is 50%:50%.

[0086] According to the method described in Example 1, the positive electrode sheet of Example 3 was assembled into a sodium ion battery.

[0087] Example 4

[0088] Preparation of a sodium ion battery positive electrode plate, which is different from Example 3 in that the positive electrode coating 30 is a single layer, and the single surface density is still 200g / m 2The positive electrode coating 30 is obtained by coating and drying a positive electrode coating slurry prepared with a mass ratio of Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP=100:3:3:2:0.3:69.

[0089] According to the method described in Example 1, the positive electrode sheet of Example 4 was assembled into a sodium ion battery.

[0090] Example 5

[0091] A preparation method for a positive electrode plate for a sodium-ion battery differs from Example 2 in that the sacrificial sodium supplement is replaced with Na2C2O4 instead of Na2CO3, and the positive electrode coating 30 is obtained by coating and drying a positive electrode coating slurry prepared in a mass ratio of Na3V2(PO4)3:Na2C2O4:PVDF:Super-P:PVP:NMP = 100:3.8:3:2:0.3:69. In the positive electrode coating 30 of the positive electrode plate prepared in Example 5, the ratio of the sodium supplement capacity provided by the first positive electrode sodium supplement to that provided by the sacrificial sodium supplement is 50%:50%.

[0092] According to the method described in Example 1, the positive electrode sheet of Example 5 was assembled into a sodium ion battery.

[0093] Example 6

[0094] A positive electrode plate for a sodium ion battery, which differs from Example 2 mainly in that the first positive electrode sodium supplement used is Na5FeO4 without a conductive coating layer on the surface.

[0095] According to the method described in Example 1, the positive electrode sheet of Example 6 was assembled into a sodium ion battery.

[0096] Example 7

[0097] The main difference between the positive electrode plate of Example 7 and Example 2 is that the sodium supplement layer also contains sodium positive electrode active material Na3V2(PO4)3.

[0098] The sodium supplement layer in Example 7 is obtained by coating and drying the primer slurry obtained by mixing the 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. The single-side density of the sodium supplement layer is 16.8g / m 2 The thickness of the single surface is 14±1μm. The positive electrode coating slurry with the same formula composition as Example 2 is coated on the above sodium supplement layer, and the single surface density is 193g / m 2 The positive electrode coating 30.

[0099] Repeat the above steps of forming the sodium supplement layer and the positive electrode coating 30 on the other side of the aluminum foil, followed by roll pressing to obtain a double-sided positive electrode sheet. In the positive electrode of Example 7, the sodium supplement capacity provided by the first positive electrode sodium supplement agent and the sacrificial sodium supplement agent still account for 50%:50%.

[0100] According to the method described in Example 1, the positive electrode sheet of Example 7 was assembled into a sodium ion battery.

[0101] Example 8

[0102] The main difference between Example 8 and Example 2 is that in the positive electrode plate of Example 8, the ratio of the sodium supplement capacity of the first positive electrode sodium supplement agent to that of the sacrificial sodium supplement agent is 66%:34%.

[0103] The preparation of the positive electrode plate of Example 8 includes:

[0104] The primer slurry with the same formulation as Example 2 (ie, the same as Example 1) was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, the single-side surface density was 11.0 g / m 2 , a sodium supplement layer with a thickness of 9±1μm on one side;

[0105] The sodium positive electrode active material Na3V2(PO4)3 was 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 100:2:3:2:0.3:68 to prepare a positive electrode slurry. The positive electrode slurry was coated on the sodium supplement layer and dried to obtain a single-side surface density of 200g / m 2 A positive electrode coating 30;

[0106] Then, the above-mentioned operation of forming the sodium supplement layer and the positive electrode coating 30 is repeated on the other side of the aluminum foil, and then roll-pressing is performed to obtain a positive electrode sheet.

[0107] According to the method described in Example 1, the positive electrode sheets of Example 8 were assembled into a sodium ion battery.

[0108] Example 9

[0109] The main difference between Example 9 and Example 2 is that in the positive electrode sheet of Example 9, the ratio of the sodium supplement capacity of the first sodium supplement agent to that of the sacrificial sodium supplement agent is 90%:10%.

[0110] The preparation of the positive electrode plate of Example 9 includes:

[0111] The primer slurry with the same formulation as Example 2 was coated on one side of the positive electrode current collector aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 15.0 g / m 2, a sodium-filling layer with a thickness of 12±1 μm on one side; and then the sodium-filling layer is also formed on the reverse side of the aluminum foil;

[0112] The sodium positive electrode active material Na3V2(PO4)3 was 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 100:0.6:3:2:0.3:68 to obtain a positive electrode slurry with a solid content of 61wt%. The positive electrode slurry was coated on the sodium supplement layer and baked to form a single-side surface density of 200g / m 2 then, the positive electrode slurry is coated and dried on the reverse side of the sodium replenishing layer to obtain a double-sided positive electrode sheet to be used.

[0113] According to the method described in Example 1, the positive electrode sheets of Example 9 were assembled into a sodium ion battery.

[0114] Example 10

[0115] The main difference between Example 10 and Example 2 is that in the positive electrode coating 30 of the positive electrode plate of Example 10, the total mass of the sacrificial sodium supplement is 1% of the total mass of the sodium positive electrode active material; in the positive electrode coating 30, the ratio of the sodium supplement capacity of the first positive electrode sodium supplement to that of the sacrificial sodium supplement is approximately 83%:17%.

[0116] The preparation of the positive electrode plate in Example 10 includes:

[0117] The primer slurry with the same formula as Example 2 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 13.8 g / m 2 , a sodium-filling layer with a thickness of 11±1 μm on one side; and then forming the sodium-filling layer on the reverse side of the aluminum foil;

[0118] 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 dried to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0119] According to the method described in Example 1, the positive electrode sheet of Example 10 was assembled into a sodium ion battery.

[0120] Example 11

[0121] The main difference between Example 11 and Example 2 is that in the positive electrode plate of Example 10, the ratio of the sodium supplement capacity of the first positive electrode sodium supplement agent to that of the sacrificial sodium supplement agent is 30%:70%.

[0122] The method for preparing the positive electrode sheet in Example 11 includes:

[0123] The primer slurry with the same formula as Example 2 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 5.0 g / m 2 , a sodium-filling layer with a thickness of 4±1 μm on one side; and then forming the sodium-filling layer on the reverse side of the aluminum foil;

[0124] The sodium positive electrode active material Na3V2(PO4)3 was 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 slurry. The positive electrode slurry was coated on the sodium supplement layer and dried to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0125] According to the method described in Example 1, the positive electrode sheet of Example 11 was assembled into a sodium ion battery.

[0126] Example 12

[0127] The main difference between Example 12 and Example 2 is that in the positive electrode coating 30 of the positive electrode plate of Example 12, the total mass of the sacrificial sodium supplement is 5% of the total mass of the sodium positive electrode active material; in the positive electrode coating 30, the ratio of the sodium supplement capacity of the first positive electrode sodium supplement to that of the sacrificial sodium supplement is approximately 16%:84%.

[0128] The preparation of the positive electrode plate of Example 12 includes:

[0129] The primer slurry with the same formula as Example 2 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 2.7 g / m 2 , a sodium-filling layer with a thickness of 2 μm on one side; and then forming such a sodium-filling layer on the reverse side of the aluminum foil;

[0130] 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 slurry; the positive electrode slurry is coated on the sodium supplement layer and dried to form a single-side surface density of 200g / m 2The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0131] According to the method described in Example 1, the positive electrode sheet of Example 12 was assembled into a sodium ion battery.

[0132] Example 13

[0133] The main difference between Example 13 and Example 2 is that in the positive electrode sheet of Example 11, the ratio of the sodium supplement capacity of the first sodium supplement agent to that of the sacrificial sodium supplement agent is 5%:95%.

[0134] The preparation of the positive electrode plate of Example 13 includes:

[0135] The primer slurry with the same formulation as Example 2 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm and a surface density of 0.9 g / m 2 , the thickness of one side is 1 μm; then the sodium supplement layer is also formed on the reverse side of the aluminum foil;

[0136] The sodium positive electrode active material Na3V2(PO4)3 was 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 100:5.7:3:2:0.3:68 to obtain a positive electrode slurry. The positive electrode slurry was coated on the sodium supplement layer and dried to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0137] According to the method described in Example 1, the positive electrode sheet of Example 13 was assembled into a sodium ion battery.

[0138] Example 14

[0139] The main difference between Example 14 and Example 2 is that in the positive electrode coating 30 of Example 14, the total mass of the sacrificial sodium supplement is 10% of the total mass of the sodium positive electrode active material. In the positive electrode coating 30, the sodium supplement capacity ratio of the first positive electrode sodium supplement to the sacrificial sodium supplement is approximately 3.5%:96.5%.

[0140] The preparation of the positive electrode sheet includes:

[0141] The primer slurry with the same formula as Example 2 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 1.0 g / m 2 , a sodium-filling layer with a thickness of 1 μm on one side; and then forming such a sodium-filling layer on the reverse side of the aluminum foil;

[0142] The sodium positive electrode active material Na3V2(PO4)3 was 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 100:10:3:2:0.3:68 to prepare a positive electrode slurry. The positive electrode slurry was coated on the sodium supplement layer and dried to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0143] According to the method described in Example 1, the positive electrode sheet of Example 14 was assembled into a sodium ion battery.

[0144] Example 15

[0145] The main difference between Example 15 and Example 2 is that in the positive electrode sheet of Example 15, the ratio of the sodium supplement capacity of the first sodium supplement agent to that of the sacrificial sodium supplement agent is 95%:5%.

[0146] The preparation of the positive electrode plate of Example 15 includes:

[0147] The primer slurry with the same formula as Example 2 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 16.0 g / m 2 , a sodium-filling layer with a thickness of 13±1 μm on one side; and then forming the sodium-filling layer on the reverse side of the aluminum foil;

[0148] The sodium positive electrode active material Na3V2(PO4)3 was 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 100:0.3:3:2:0.3:68 to obtain a positive electrode slurry. The positive electrode slurry was coated on the above-mentioned sodium supplement layer and dried to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0149] According to the method described in Example 1, the positive electrode sheet of Example 15 was assembled into a sodium ion battery.

[0150] Example 16

[0151] The main difference between Example 16 and Example 2 is that in the positive electrode coating 30 of Example 16, the total mass of the sacrificial sodium supplement is 0.2% of the total mass of the sodium positive electrode active material. In the positive electrode coating 30, the sodium supplement capacity ratio of the first positive electrode sodium supplement to the sacrificial sodium supplement is approximately 96.6%:3.4%.

[0152] The preparation of the positive electrode sheet includes: coating the primer slurry with the same formula as Example 2 on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and drying it to form a single-side surface density of 16.0 g / m 2 , a sodium-filling layer with a thickness of 13±1 μm on one side; and then forming such a sodium-filling layer on the reverse side of the aluminum foil;

[0153] The sodium positive electrode active material Na3V2(PO4)3 was 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 100:0.2:3:2:0.3:68 to prepare a positive electrode slurry. The positive electrode slurry was coated on the sodium supplement layer and dried to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is formed, and then the positive electrode slurry is coated and dried on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used.

[0154] According to the method described in Example 1, the positive electrode sheet of Example 16 was assembled into a sodium ion battery.

[0155] Example 17

[0156] The main difference between the positive electrode plate of Example 17 and Example 1 is that the difference in mass ratio between the sacrificial positive electrode sodium replenisher 301 in the upper and lower positive electrode sub-coatings and the total sacrificial positive electrode sodium replenisher 301 is 50%.

[0157] When preparing the positive electrode sheet of Example 17, the formula of the lower positive electrode slurry coated near 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 away 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-side surface density of the positive electrode coating 30 is 300g / m 2 ; The ratio of the sodium replenishing capacity of the first positive electrode sodium replenishing agent to the sacrificial sodium replenishing agent is still about 50%:50%.

[0158] According to the method described in Example 1, the positive electrode sheet of Example 17 was assembled into a sodium ion battery.

[0159] Example 18

[0160] The main difference between the positive electrode sheet of Example 18 and Example 1 is that the first positive electrode sub-coating close to the current collector does not contain the sacrificial positive electrode sodium supplement 301; the second positive electrode sub-coating away from the current collector contains both sodium positive electrode active material and sacrificial positive electrode sodium supplement 301.

[0161] Example 18 Preparation of a positive electrode plate, comprising:

[0162] (1) The primer slurry with the same formulation as Example 1 was coated on the surface of the positive electrode current collector - aluminum foil with a thickness of 13 μm, and after drying, a single-side surface density of 8.4 g / m 2 , a sodium-filling layer with a thickness of 7±1 μm on one side; and then forming such a sodium-filling layer on the reverse side of the aluminum foil;

[0163] (2) A positive electrode coating 30 including two sub-coatings is formed on the above-mentioned sodium supplement layer: wherein the slurry formula corresponding to the first positive electrode sub-coating close to the sodium supplement 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 away from the sodium supplement layer is: Na3V2(PO4)3:Na2CO3:PVDF:Super-P:PVP:NMP=100:6.3:3:2:0.3:70.

[0164] (3) The above-mentioned positive electrode coating 30 is formed on the reverse sodium supplement layer to obtain a double-sided positive electrode sheet to be used. In the positive electrode sheet of Example 18, the single-side surface density of the positive electrode coating 30 is 200 g / m 2 ; The ratio of the sodium replenishing capacity of the first positive electrode sodium replenishing agent to the sacrificial sodium replenishing agent is still 50%:50%.

[0165] According to the method described in Example 1, the positive electrode sheet of Example 18 was assembled into a sodium ion battery.

[0166] Example 19

[0167] The main difference between the positive electrode sheet of Example 19 and Example 2 is that the sodium positive electrode active material in the positive electrode coating 30 is replaced from Na3V2(PO4)3 to Na[Ni 0.25 Fe 0.5 Mn 0.25 ]O2.

[0168] According to the method described in Example 1, the positive electrode sheet of Example 19 was assembled into a sodium ion battery.

[0169] In order to highlight the beneficial effects of the present application, the present application also provides the following comparative examples 1-4.

[0170] Comparative Example 1

[0171] A preparation method for a non-sodium-supplemented positive electrode comprises: 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 aluminum foil, and drying the slurry to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is then applied to the other side of the aluminum foil and dried to obtain a double-sided positive electrode sheet.

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

[0173] Comparative Example 2

[0174] A positive electrode plate, which differs from 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.

[0175] Comparative Example 2 Preparation of the positive electrode sheet, comprising: mixing Na3V2(PO4)3, a first positive electrode sodium supplement (the same as 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 aluminum foil, controlling the single-sided surface density of the coating to be still 200g / m 2 , and after baking, a positive electrode coating 30 is formed; 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 sheet of Comparative Example 2 was assembled into a sodium ion battery.

[0177] Comparative Example 3

[0178] A positive electrode plate, which differs from 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.

[0179] The preparation of the positive electrode plate includes: mixing Na3V2(PO4)3, 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 aluminum foil, and baking to form a single-side surface density of 200g / m 2 The positive electrode coating 30 is then applied to the other side of the aluminum foil, and baked to obtain a double-sided positive electrode sheet.

[0180] According to the method described in Example 1, the positive electrode sheets of Comparative Example 3 were assembled into a sodium ion battery.

[0181] Comparative Example 4

[0182] A positive electrode plate, which differs from Example 2 mainly in 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.

[0183] Comparative Example 4 Preparation of the positive electrode sheet, comprising: 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 aluminum foil, and baking the resulting single-sided surface density to still be 200g / m 2 The positive electrode coating 30 is then applied to the other side of the aluminum foil, and baked to obtain a double-sided positive electrode sheet.

[0184] According to the method described in Example 1, the positive electrode sheet of Comparative Example 4 was assembled into a sodium ion battery.

[0185] Comparative Example 5

[0186] A positive electrode plate, which differs from Example 2 in that: a sodium supplement layer containing a first positive electrode sodium supplement is provided on the aluminum foil, and a positive electrode coating 30 without a sacrificial sodium supplement is provided on the sodium supplement layer.

[0187] A preparation method for a positive electrode plate, which differs from 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 consistent with Example 1.

[0188] According to the method described in Example 1, the positive electrode sheet of Comparative Example 5 was assembled into a sodium ion battery.

[0189] Comparative Example 6

[0190] A positive electrode sheet differs from Example 2 in that the positions of the positive electrode coating 30 and the sodium-supplementing layer in Example 2 are reversed. That is, the positive electrode coating 30 containing the sacrificial sodium-supplementing agent in Example 2 is directly in contact with the aluminum foil, and a sodium-supplementing layer containing the first positive electrode sodium-supplementing agent is provided on the positive electrode coating 30 (the sodium-supplementing layer has the same composition as the sodium-supplementing layer in Example 2).

[0191] According to the method described in Example 1, the positive electrode of Comparative Example 6 was assembled into a sodium ion battery.

[0192] Comparative Example 7

[0193] A preparation method of a positive electrode, which is different from the comparative example 1 in that the sodium positive electrode active material is replaced by Na3V2(PO4)3 0.25 Fe 0.5 Mn 0.25 ]O2.

[0194] The preparation method of the positive electrode comprises: preparing a sodium positive electrode active material Na[Ni 0.25 Fe 0.5 Mn 0.25 ]O2, PVDF, Super-P, PVP, and NMP were mixed in a mass ratio of 100:3:2:0.3:68 to prepare a positive electrode coating slurry; the slurry was directly coated on aluminum foil, and after baking, the single-sided surface density was still 200g / m 2 The positive electrode coating 30 is then applied to the other side of the aluminum foil, and baked to obtain a double-sided positive electrode sheet.

[0195] According to the method described in Example 1, the positive electrode sheet of Comparative Example 7 was assembled into a sodium ion battery.

[0196] In order to strongly support the beneficial effects brought about by the technical solution of the present application, the sodium ion batteries of the above embodiments or comparative examples were subjected to the following performance tests:

[0197] a. Positive Electrode Gram Capacity Test: At room temperature (25±3°C), charge each of the aforementioned sodium-ion batteries at a constant current and constant voltage of 1 / 3C to an upper voltage limit of 4.3V (C represents the battery capacity) for formation. Record the initial charge capacity (i.e., the charge capacity during formation). Then, discharge the battery at a 1 / 3C charge to a lower voltage limit of 2.0V. Record the initial discharge capacity (in mAh) and the average discharge voltage. Positive electrode gram capacity = initial discharge capacity / total mass of positive electrode active material; battery volume energy density = initial discharge capacity × average discharge voltage / battery volume.

[0198] b. Cycling Performance Test: At room temperature (25±3°C), charge each of the above-mentioned sodium-ion batteries at a constant current and constant voltage of 1 / 3C to an upper voltage of 3.8V, and then discharge at a constant current and constant voltage of 1 / 3C to a lower voltage of 2.0V. Repeat the above charge and discharge steps 500 times, and record the capacity retention rate after 500 cycles. Wherein, the capacity retention rate after 500 cycles = the discharge capacity at the 500th cycle / the discharge capacity at the first discharge after formation.

[0199] c. Battery Direct Current Internal Resistance (DCIR) Test: Each of the sodium-ion batteries formed above was charged at a constant current of 1 / 3C to an upper voltage limit of 3.8V at room temperature (25±3°C), and then discharged at 1 / 3C to a lower voltage limit of 2.0V. After three cycles, the battery was again charged at a constant current of 1 / 3C at room temperature to 50% SOC. The battery voltage after standing for 1 hour was recorded as V1. The battery was then discharged at 1.5C for 30s, and the battery voltage after the discharge was recorded as V2. Wherein, DCIR = (V1-V2) / 1.5C.

[0200] d. Utilization rate test of sodium supplement materials:

[0201] Non-sodium-supplemented batteries corresponding to the sodium-supplemented batteries of the embodiments and some comparative examples of the present application were prepared (wherein, embodiments 1-19 and comparative examples 2-7 are all sodium-supplemented batteries, comparative example 1 is the non-sodium-supplemented battery corresponding to embodiments 1-18 and comparative examples 2-6, and comparative example 7 is the non-sodium-supplemented battery corresponding to embodiment 19).

[0202] At room temperature (25±3°C), each of the above-mentioned batteries was first charged at a constant current and constant voltage rate of 1 / 3C to an upper voltage limit of 4.3V for formation, and then discharged at a constant current and constant voltage rate of 1 / 3C to a lower voltage limit of 2.0V. The discharge capacity of each sodium-supplemented battery was recorded as C1, and the discharge capacity of the non-sodium-supplemented battery corresponding to each sodium-supplemented battery was recorded as C2. The utilization rate of the sodium-supplementing material = (C1-C2) / (mass of each sodium-supplementing material × gram capacity of the corresponding sodium-supplementing material). The gram capacity of each sodium-supplementing material here is calculated based on the number of active sodium ions actually removed by each sodium-supplementing agent during sodium supplementation, as is known in the industry.

[0203] The relevant test results are summarized in Table 1 below.

[0204] Table 1

[0205] From the comparison of Example 2 and Comparative Examples 1-6 in Table 1, it can be seen that when the positive electrode of the battery does not contain a sodium supplement (Comparative Example 1), the positive electrode gram capacity and volume energy density of the battery are both low, and the DCIR value is high. However, the positive electrode contains only one type of positive electrode sodium supplement (such as Comparative Examples 2, 3, and 5), or the positive electrode contains two types of positive electrode sodium supplements but they are not distributed like in Example 1 of the present application, such as Comparative Examples 4 and 6 (the sum of the sodium supplement capacity provided by the sodium supplement in the positive electrode sheets of Comparative Examples 2-6 is close to that of Example 2). Although compared with Comparative Example 1, the positive electrode gram capacity and volume energy density of the battery can be improved to a certain extent, the effect of reducing the DCIR value of the battery is not obvious, and the DCIR value impedance of the battery is still high (which can reflect the poor power performance of the battery), and the utilization rate of the sodium supplement is not high. In Example 2 of the present application, a first positive electrode sodium supplement (i.e., a sodium-rich transition metal oxide 201) and a sacrificial sodium supplement are simultaneously used in the positive electrode of the sodium ion battery, and they are arranged in the manner required by the present application, which can significantly improve the utilization rate of the two sodium supplements, reduce the DCIR value of the battery, and at the same time improve the positive electrode gram capacity and volume energy density of the sodium ion battery. The only difference from Example 2 is that Example 1, in which the positive electrode coating 30 is two layers, also has a similar effect, and the effect is even better than that of Example 1. Similar phenomena can also be seen from the comparison between Comparative Example 7 and Example 19. The sodium ion batteries provided by other embodiments of the present application also have the advantages of taking into account the high utilization rate of sodium supplement materials, low DCIR value of the battery, high positive electrode gram capacity of the battery, high volume energy density of the battery, and good cycle performance.

[0206] In addition, from the comparison between Examples 2 and 8-16, it can be seen that when the sodium supplement capacity provided by the first positive electrode sodium supplement agent accounts for 10-90%, the overall performance of the sodium ion battery is better, the battery DCIR value is lower, the utilization rate of the sodium supplement material is higher, and the positive electrode specific capacity is higher. When the sodium supplement capacity provided by the first positive electrode sodium supplement agent accounts for 50-90%, the overall performance of the sodium ion battery is even better. In addition, in the positive electrode coating 30, when the mass ratio of the sacrificial positive electrode sodium supplement agent 301 to the sodium positive electrode active material is greater than 0.3% (for example, in the range of 0.5-10%), it is more conducive to improving the utilization rate of the sodium supplement material and the positive electrode specific capacity. When this mass ratio is 1-5%, the overall effect of the battery is better.

[0207] In addition, from the comparison between Example 2 and Example 6, it can be seen that when other parameters of the battery positive electrode are the same, when the surface of the first positive electrode sodium supplement agent has a conductive coating layer, it is more conducive to improving the battery positive electrode capacity, the utilization rate of the sodium supplement material, etc.

[0208] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A positive electrode sheet for a sodium-ion battery, the positive electrode sheet comprising a positive electrode current collector and a sodium supplement layer and a positive electrode coating (30) laminated on at least one side of the positive electrode current collector, wherein, On the same side of the positive current collector, the positive electrode coating (30) is disposed on the side of the sodium supplement layer away from the positive current collector; the sodium supplement layer includes a sodium-rich transition metal oxide (201); the positive electrode coating (30) includes a first sodium positive electrode active material and a sacrificial positive electrode sodium supplement agent (301) that can decompose and generate gas.

2. The positive electrode sheet according to claim 1, wherein, The positive electrode coating (30) includes n positive electrode sub-layers, n≥2. Wherein, in the direction from the positive current collector to the sodium supplement layer, the mass ratio of the sacrificial positive electrode sodium supplement agent (301) to the first sodium positive electrode active material in each positive electrode sub-layer shows an increasing trend; Optionally, in the direction from the positive current collector to the sodium supplement layer, the mass ratio of the sacrificial positive electrode sodium supplement agent (301) to the first sodium positive electrode active material in each positive electrode sub-layer increases layer by layer in sequence.

3. The positive electrode sheet according to claim 2, wherein, Among the n-layer 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 (301) in the (m - 1)-th layer of the positive electrode sub-coating to the total sacrificial positive sodium supplement agent (301) in the positive electrode coating (30), and A m is the mass ratio of the sacrificial positive sodium supplement agent (301) in the m-th layer of the positive electrode sub-coating to the total sacrificial positive sodium supplement agent (301) in the positive electrode coating (30), 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, in the n-layer positive electrode coating, any two adjacent layers of the positive electrode coating satisfy: A m / (D m / D m-1 )-A m-1 ≥ 5%.

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

5. The positive electrode sheet according to any one of claims 1-4, wherein, In the positive electrode coating (30), the total mass of the sacrificial positive electrode sodium supplement agent (301) is 0.5% - 10% of the total mass of the first sodium positive electrode active material.

6. The positive electrode sheet according to any one of claims 1-5, wherein, The sodium supplement layer includes the following components in mass percentage: 50% - 90% of sodium-rich transition metal oxide (201), 0 - 40% of a second sodium positive electrode active material, 0.5% - 10% of a binder, and 0.5% - 10% of a conductive agent.

7. The positive electrode sheet according to any one of claims 1-6, wherein, The mass percentage of the first positive electrode sodium supplement agent in the sodium supplement layer is greater than that of the second sodium positive electrode active material.

8. The positive electrode sheet according to any one of claims 1-7, wherein, The proportion of the sodium supplement capacity provided by the sodium-rich transition metal oxide (201) in the total sodium supplement capacity provided by the sodium-rich transition metal oxide (201) and the sacrificial positive electrode sodium supplement agent (301) is in the range of 10% - 90%; Optionally, the proportion of the sodium supplement capacity provided by the sodium-rich transition metal oxide (201) in the total sodium supplement capacity provided by the sodium-rich transition metal oxide (201) and the sacrificial positive electrode sodium supplement agent (301) is in the range of 50% - 90%.

9. The positive electrode sheet according to any one of claims 1-8, wherein, The single-sided surface density of the positive electrode coating (30) is greater than the single-sided surface density of the sodium supplement layer.

10. The positive electrode sheet according to claim 9, 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 (30) is 50 g / m 2 ~500 g / m 2 .

11. The positive electrode sheet according to any one of claims 1-10, wherein, The chemical formula of the sodium-rich transition metal oxide (201) 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; The sodium-rich transition metal oxide (201) includes one or more of Na2FeO2, Na3FeO3, Na3FeO4, Na5FeO4, Na2NiO2, Na2CuO2, Na6MnO4, and Na6CoO4.

12. The positive electrode sheet according to any one of claims 1-11, wherein, The surface of the sodium-rich transition metal oxide (201) also has a conductive coating layer.

13. The positive electrode sheet according to any one of claims 1-12, wherein, The sacrificial positive electrode sodium supplement agent (301) is selected from one or more of sodium azide, sodium amide, sodium phosphide, sodium sulfide, sodium peroxide, sodium carbonate, sodium oxalate, sodium squarate, and sodium nitrite.

14. The positive electrode sheet according to any one of claims 1-13, wherein, The sodium supplement layer is in direct contact with the positive current collector; and / or the positive electrode coating (30) is in direct contact with the sodium supplement layer.

15. The positive electrode sheet according to any one of claims 1-14, wherein, The sodium supplement layer does not contain a sodium positive electrode active material.

16. A sodium ion battery, comprising a positive electrode sheet according to any one of claims 1 - 15.

17. A device comprising the sodium ion battery according to claim 16, the device comprising an electrical device or an energy storage system.

Images