Positive pole piece, battery, battery pack and energy storage system

Abstract

The embodiment of the invention provides a positive pole piece, a battery, a battery pack and an energy storage system, relates to the technical field of batteries, and is used for improving the infiltration recovery capability of an electrolyte and prolonging the cycle life of the battery in a cycle process. The battery comprises a positive pole piece. The positive pole piece comprises a positive current collector and a positive active material layer. Along the first direction, the positive active material layer is arranged on the surface of the positive current collector. The positive active material layer comprises a first material layer and a second material layer, and the second material layer and the first material layer are arranged on the same surface of the positive current collector side by side in the second direction. The first substance layer includes a sodium-containing layered oxide. The second substance layer includes a polyanionic compound. Wherein the first direction is the thickness direction of the positive electrode current collector, and the second direction is perpendicular to the first direction.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a positive electrode sheet, a battery, a battery pack, and an energy storage system. Background Art

[0002] With the gradual application of lithium-ion batteries to electrical equipment and the energy storage field, the supply and demand problem of metallic lithium resources has become increasingly prominent. Since sodium resources are rich in reserves, widely distributed, and low in cost, sodium-ion batteries have attracted much attention in recent years.

[0003] However, during the cyclic charge and discharge process of sodium-ion batteries, it is easy for the electrolyte to have difficulty in restoring wetting to the positive electrode sheet due to battery swelling, which in turn affects the normal use of the battery and results in a short battery cycle life. Summary of the Invention

[0004] The purpose of the present application is to provide a positive electrode sheet, a battery, a battery pack, and an energy storage system, which are used to improve the ability of the electrolyte to restore wetting during the cycle and improve the cycle life of the battery.

[0005] In the first aspect of the embodiments of the present application, a battery is provided, which includes a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. Along a first direction, the positive electrode active material layer is disposed on the surface of the positive electrode current collector. And the positive electrode active material layer includes a first material layer and a second material layer, and the second material layer and the first material layer are arranged side by side along a second direction on the same surface of the positive electrode current collector. The first material layer includes a sodium-containing layered oxide. The second material layer includes a polyanion compound. Wherein, the first direction is the thickness direction of the positive electrode current collector, the second direction is perpendicular to the first direction, and the second direction can be the height direction of the battery. Exemplarily, along the first direction, a positive electrode active material layer is disposed on one surface of the positive electrode current collector; or, along the first direction, positive electrode active material layers are disposed on both surfaces of the positive electrode current collector.

[0006] The first material layer of the positive electrode active material layer includes a sodium-containing layered oxide. Among them, the sodium-containing layered oxide has a relatively high energy density, thereby ensuring that the capacity of the battery meets the requirements. During the cyclic charge and discharge process, the sodium-containing layered oxide has a large change in unit cell volume, resulting in stress concentration in some regions inside the particles of the positive electrode active material layer, which can cause particle breakage, and further cause the positive electrode sheet to expand. As the cycle progresses, the expansion force on the positive electrode sheet becomes larger and larger, making it difficult for the electrolyte to re-enter the pores of the positive electrode active material layer during the charge and discharge process, resulting in difficulty in the electrolyte restoring wetting of the positive electrode sheet. In the embodiments of the present application, the second material layer of the positive electrode active material layer includes a polyanion compound. During the charge and discharge process, the polyanion compound has a small change in unit cell volume, and the particle structure is stable, and it is not easy to produce the above-mentioned particle breakage phenomenon, so the expansion change is small. Supported by the large expansion of the first material layer, the influence of the expansion force on the second material layer is reduced, thereby ensuring that the electrolyte can fully wet the second material layer, ensuring the normal operation of the battery, and improving the battery cycle life.

[0007] In some embodiments of the present application, the first material layer further includes a polyanion compound, and the second material layer further includes a sodium-containing layered oxide. Among them, the mass fraction of the sodium-containing layered oxide in the first material layer is greater than the mass fraction of the sodium-containing layered oxide in the second material layer. The mass fraction of the polyanion compound in the first material layer is less than the mass fraction of the polyanion compound in the second material layer. Here, the mass fraction of the sodium-containing layered oxide in the first material layer is the percentage of the mass of the sodium-containing layered oxide in the first material layer in the total mass of the first material layer. The mass fraction of the sodium-containing layered oxide in the second material layer is the percentage of the mass of the sodium-containing layered oxide in the second material layer in the total mass of the second material layer. The mass fraction of the polyanion compound in the first material layer is the percentage of the mass of the polyanion compound in the first material layer in the total mass of the first material layer. The mass fraction of the polyanion compound in the second material layer is the percentage of the mass of the polyanion compound in the second material layer in the total mass of the second material layer.

[0008] During the charge-discharge cycle, after the positive electrode plate expands, it will affect the infiltration of the electrolyte into the positive active material layer. Moreover, the higher the mass fraction of the sodium-containing layered oxide, the higher the expansion rate of the positive electrode plate. Since the mass fraction of the sodium-containing layered oxide in the first material layer is greater than that in the second material layer, and the mass fraction of the polyanion compound in the first material layer is less than that in the second material layer. That is to say, the expansion rate of the first material layer is greater than that of the second material layer. Under the action of the external force generated by the structure such as the separator in contact with the positive electrode plate, because the first material layer expands more, the external force received by the first material layer is greater than that received by the second active material layer, resulting in a greater degree of reduction in the porosity of the first material layer, thereby making it difficult for the electrolyte to recover infiltration at the first material layer. While the external force received by the second material layer is smaller, and the porosity of the second material layer is basically unaffected or reduced less, thus ensuring the infiltration of the electrolyte into the second material layer and improving the cycle life of the battery. In addition, the material of the positive active material layer directly affects the capacity of the battery, and the energy density of the sodium-containing layered oxide is higher than that of the polyanion compound. The energy density of the battery is increased by the first material layer with a higher mass fraction of the sodium-containing layered oxide to ensure that the capacity of the battery meets the requirements in the early stage of the charge-discharge cycle.

[0009] In some embodiments of the present application, in the second direction, the width of the first material layer is less than or equal to the width of the second material layer. During the cyclic charge-discharge process, the expansion degree of the first material layer is greater than that of the second material layer, and the first material layer is more likely to cause difficulty in the electrolyte to recover infiltration due to excessive battery expansion force. However, the width of the first material layer in the embodiments of the present application is smaller, thereby reducing the influence of the first material layer on the battery cycle life.

[0010] In some embodiments of the present application, the positive active material layer further includes a third material layer. The third material layer and the first material layer are disposed on the same surface of the positive active material layer, and the second material layer is located between the first material layer and the third material layer. The mass fraction of the sodium-containing layered oxide in the third material layer is greater than the mass fraction of the sodium-containing layered oxide in the second material layer. Wherein, the mass fraction of the sodium-containing layered oxide in the third material layer is the percentage of the mass of the sodium-containing layered oxide in the third material layer in the total mass of the third material layer. At this time, the expansion degrees generated by the first material layer and the third material layer are both greater than that of the second material layer. In the first direction, both the expanded first material layer and the third material layer protrude from the second material layer. Supported by the larger expansion of the first material layer and the third material layer, the external force received by the second material layer located between the first material layer and the third material layer is further reduced, ensuring that the degree of reduction in the porosity of the second material layer is small, thereby ensuring that the electrolyte can fully infiltrate the second material layer, ensuring the normal operation of the battery, and improving the battery cycle life.

[0011] In some embodiments of the present application, in the second direction, the width of the second material layer is greater than or equal to the sum of the widths of the first material layer and the third material layer. During the cyclic charge and discharge process, the degree of expansion of both the first material layer and the third material layer is greater than that of the second material layer. The first material layer and the third material layer are more likely to cause difficulty in the restoration of electrolyte infiltration due to excessive battery expansion force. However, the total width of the first material layer and the third material layer in the embodiments of the present application is small, thereby reducing the influence of the first material layer and the third material layer on the battery cycle life.

[0012] In some other embodiments of the present application, the positive electrode active material layer further includes a third material layer. The third material layer and the first material layer are disposed on the same surface, and the first material layer is located between the second material layer and the third material layer. The third material layer includes a sodium-containing layered oxide and a polyanion compound. Among them, the mass fraction of the sodium-containing layered oxide in the third material layer is less than the mass fraction of the sodium-containing layered oxide in the first material layer. At this time, the degree of expansion generated by the first material layer is greater than that of the second material layer and the third material layer. In the first direction, the expanded first material layer protrudes from the second material layer and the third material layer. Supported by the relatively large expansion of the first material layer, the influence of the expansion force on the second material layer and the third material layer is reduced, ensuring that the degree of reduction in the porosity of the second material layer and the third material layer is small, thereby ensuring that the electrolyte can fully infiltrate the second material layer and the third material layer, ensuring the normal operation of the battery, and improving the battery cycle life.

[0013] In some embodiments of the present application, in the second direction, the sum of the widths of the second material layer and the third material layer is greater than or equal to the width of the first material layer. During the cyclic charge and discharge process, the degree of expansion of the first material layer is greater than that of the second material layer and the third material layer. The first material layer is more likely to cause difficulty in the restoration of electrolyte infiltration due to excessive battery expansion force. However, the width of the first material layer in the embodiments of the present application is small, thereby reducing the influence of the first material layer on the battery cycle life.

[0014] In some embodiments of the present application, the surface density d1 of the first material layer and the surface density d2 of the second material layer satisfy: 1 < d1 / d2 ≤ 2. Among them, the surface density d1 of the first material layer is equal to the ratio of the weight m1 of the first material layer to the projected area S1 of the first material layer on the surface of the positive electrode current collector facing the first material layer (i.e., d1 = m1 / S1); the surface density d2 of the second material layer is equal to the ratio of the weight m2 of the second material layer to the projected area S2 of the second material layer on the surface of the positive electrode current collector facing the second material layer (i.e., d2 = m2 / S2).

[0015] When d1 / d2 > 1, the weight of the first material layer per unit area is greater than that of the second material layer. Furthermore, it can further ensure that the material weight per unit volume of the first material layer is greater than that of the second material layer per unit volume. When a relatively high energy density is provided by the first material layer, it can ensure that the energy density of the battery meets the requirements, and at the same time, the energy density required to be provided by the second material layer can be reduced. Therefore, the mass fraction of the sodium-containing layered oxide in the second material layer can be reduced, thereby reducing the swelling of the second material layer and the external force received by the second material layer. In addition, the areal density of the second material layer is relatively low and the porosity is relatively high, which further ensures that the electrolyte can re-wet the second material layer. It is ensured that during the cyclic charge and discharge process, when the porosity of the first material layer electrode sheet decreases and it becomes difficult for the electrolyte to re-wet at the first material layer, the electrolyte can still re-wet the second material layer that is less affected by the swelling force and has a higher porosity, ensuring the normal operation of the battery and improving the battery cycle life.

[0016] In addition, during the production and preparation process of the positive electrode active material layer, after the materials of the first material layer and the second material layer are coated on the surface of the positive electrode current collector, the first material layer and the second material layer are simultaneously roll-pressed. When the ratio of the areal density A1 of the first material layer after the preset roll pressing to the areal density A2 of the second material layer is greater than 2 (i.e., A1 / A2 > 2), the material thickness that needs to be coated before roll pressing of the first material layer is greater than that of the first material layer. During the roll pressing process, when the compaction degree of the first material layer reaches the roll pressing limit, the thickness of the first material layer may still be higher than the thickness of the first material layer before roll pressing. At this time, effective roll pressing of the second material layer cannot be performed, and thus the structural stability of the second material layer cannot be ensured. When d1 / d2 ≤ 2, it is ensured that during the roll pressing process, the first material layer and the second material layer can be roll-pressed simultaneously, ensuring the structural stability of the first material layer and the second material layer.

[0017] In some embodiments of the present application, 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 ; and / or, 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 . Exemplarily, 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 ; or, 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 ; or, 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 , and 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 . When D1 ≥ 1.5 g / cm 3or D2≥1.5 g / cm 3 When, during the production and preparation of the positive electrode active material layer, after rolling the first material layer or the second material layer, it is possible to ensure a relatively high material content per unit volume, thereby ensuring a relatively high energy density of the battery. When D1≤3.7 g / cm 3 or D2≤3.7 g / cm 3 it is ensured that the porosity of the first material layer or the second material layer is not too small, so that the electrolyte can infiltrate the first material layer and the second material layer through the pores of the first material layer and the second material layer.

[0018] In some embodiments of the present application, the sodium-containing layered oxide includes Na α (M x Mn y )O2; wherein, M includes at least one of Ni, Fe, Cu, Mg, Al, Co, Ti, Ca, and Zn; and / or, the polyanion compound includes at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7; wherein, N includes at least one of Fe, V, Mn, Co, Ti, Zr, and Ni. Exemplarily, the sodium-containing layered oxide includes Na α (M x Mn y )O2. Alternatively, the polyanion compound includes at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7. Or, the sodium-containing layered oxide includes Na α (M x Mn y )O2; and the polyanion compound includes at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7.

[0019] The sodium-containing layered oxide has a relatively high energy density. When using this sodium-containing layered oxide, it is possible to ensure that the battery has a relatively high capacity. In addition, the particle structure of the polyanion compound is stable and the expansion change is small, so that the porosity of the second material layer is relatively large, the electrolyte can fully infiltrate the second material layer, ensuring the normal operation of the battery and improving the battery cycle life.

[0020] In the second aspect of the embodiments of the present application, a positive electrode sheet is provided. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. Along a first direction, the positive electrode active material layer is disposed on the surface of the positive electrode current collector. And the positive electrode active material layer includes a first material layer and a second material layer, and the second material layer and the first material layer are arranged side by side along a second direction on the same surface of the positive electrode current collector. The first material layer includes a sodium-containing layered oxide. The second material layer includes a polyanion compound. Wherein, the first direction is the thickness direction of the positive electrode current collector, and the second direction is perpendicular to the first direction. The above positive electrode sheet has the same technical effects as the positive electrode sheet in the battery provided in the foregoing embodiments, and will not be elaborated herein.

[0021] In the third aspect of the embodiments of the present application, a battery pack is provided. The battery pack includes a plurality of batteries as described in the foregoing embodiments, and the plurality of batteries are connected in series or in parallel. A relatively high voltage and capacity are provided by the plurality of batteries. In addition, the above battery pack has the same technical effects as the battery provided in the foregoing embodiments, and will not be elaborated herein.

[0022] In the fourth aspect of the embodiments of the present application, an energy storage system is provided. The energy storage system includes a power converter and at least one battery pack as described in the foregoing embodiments. The power converter is configured to perform power conversion on the voltage output by the battery pack and then output it to the power grid or a load, and / or perform power conversion on the voltage output by an external power source and then output it to the battery pack. Exemplarily, the power converter is configured to perform power conversion on the voltage output by the battery pack and then output it to the power grid. Or, the power converter is configured to perform power conversion on the voltage output by the battery pack and then output it to the load. Or, the power converter is configured to perform power conversion on the voltage output by the external power source and then output it to the battery pack. Or, the power converter is configured to perform power conversion on the voltage output by the battery pack and then output it to the power grid or a load, and at the same time, the power converter is further configured to perform power conversion on the voltage output by the external power source and then output it to the battery pack. In addition, the above energy storage system has the same technical effects as the battery provided in the foregoing embodiments, and will not be elaborated herein. Description of the Drawings

[0023] Figure 1 is a schematic structural diagram of an energy storage system provided by an embodiment of the present application;

[0024] Figure 2 is a schematic structural diagram of another energy storage system provided by an embodiment of the present application;

[0025] Figure 3 is an exploded view of a battery pack provided by an embodiment of the present application;

[0026] Figure 4 is an exploded view of a battery provided by an embodiment of the present application;

[0027] Figure 5 is Figure 4 a sectional view in the A1 - A2 direction;

[0028] Figure 6 is Figure 4 another sectional view in the A1 - A2 direction;

[0029] Figure 7 is Figure 4 yet another sectional view in the A1 - A2 direction;

[0030] Figure 8 is a schematic structural view of a positive electrode plate provided by an embodiment of the present application;

[0031] Figure 9 is Figure 8 a sectional view in the B1 - B2 direction;

[0032] Figure 10 is a sectional view of another positive electrode plate provided by an embodiment of the present application;

[0033] Figure 11 is Figure 10 a sectional view of the positive electrode active material layer of the positive electrode plate shown after expansion;

[0034] Figure 12 is a sectional view of yet another positive electrode plate provided by an embodiment of the present application;

[0035] Figure 13 is Figure 12 a sectional view of the positive electrode active material layer of the positive electrode plate shown after expansion.

[0036] Reference numerals:

[0037] 100 - energy storage system; 01 - battery pack; 02 - power converter; 03 - power grid; 04 - load; 05 - photovoltaic module; 10 - battery; 20 - box body; 30 - box cover; 11 - positive electrode plate; 12 - negative electrode plate; 13 - housing; 14 - cover body; 15 - positive electrode terminal; 16 - separator; 111 - positive electrode current collector; 112 - positive electrode active material layer; 1121 - first material layer; 1122 - second material layer; 1123 - third material layer; 113 - positive electrode tab. Detailed implementation manners

[0038] Next, the technical solutions in the embodiments of the present application will be described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments.

[0039] Hereinafter, terms such as "first", "second", "third", etc. are only used for convenience of description and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0040] In this application, unless otherwise clearly specified and defined, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed mechanical connection, a detachable mechanical connection, or integrated; or, "connection" can be a direct connection, or an indirect connection through an intermediate medium; or, "connection" can also be an electrical connection.

[0041] In the embodiments of this application, words such as "exemplarily", "for example", etc. are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "exemplarily", "for example" in the embodiments of this application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplarily", "for example" is intended to present relevant concepts in a specific manner.

[0042] In the drawings of the embodiments of this application, components are represented by guiding lines with arrows; parts are only represented by guiding lines.

[0043] The embodiments of this application provide an energy storage system 100. As Figure 1 or Figure 2 shown, the energy storage system 100 may include a battery pack 01 and a power converter 02 electrically connected to the battery pack 01. The power converter 02 is configured to perform power conversion on the voltage output by the battery pack and then output it to the power grid 03 or the load 04, and / or perform power conversion on the voltage output by an external power source and then output it to the battery pack 01. Exemplarily, the power converter 02 is configured to perform power conversion on the voltage output by the battery pack 01 and then output it to the power grid 03. Or, the power converter 02 is configured to perform power conversion on the voltage output by the battery pack 01 and then output it to the load 04. Or, the power converter 02 is configured to perform power conversion on the voltage output by an external power source and then output it to the battery pack 01. Or, the power converter 02 is configured to perform power conversion on the voltage output by the battery pack 01 and then output it to the power grid 03 or the load 04, and at the same time, the power converter 02 is also configured to perform power conversion on the voltage output by an external power source and then output it to the battery pack 01.

[0044] For example, the above energy storage system 100 can be a photovoltaic system, a wind power generation system, a hydroelectric power generation system, a geothermal power generation system, a new energy vehicle, etc.

[0045] Hereinafter, the above energy storage system 100 is taken as an example of a photovoltaic system for illustration. AsFigure 1 As shown, the photovoltaic system may further include a photovoltaic module 05. The photovoltaic module 05 converts solar energy into electrical energy and sends it to the battery pack 01 for storage. In addition, after the battery pack 01 performs power conversion on the voltage through the power converter 02, it is directly transmitted to the load 04 or transmitted to the load 04 through the power grid 03 to provide electrical energy for the operation of the load 04.

[0046] Next, the above energy storage system 100 will be described by taking a new energy vehicle as an example. As Figure 2 shown, the load 04 of the new energy vehicle may include any electrical device for functions such as starting, driving, or navigation of the new energy vehicle. The battery pack 01 provides electrical energy for the load 04, and the power converter 02 is used to perform power conversion on the voltage output by the battery pack 01 and then output it to the load 04 to meet the power consumption requirements of the new energy vehicle.

[0047] The above embodiments, such as Figure 1 or Figure 2 shown, are all described by taking the energy storage system 100 including 1 battery pack 01 and 1 power converter 02 as an example. In other embodiments of the present application, the numbers of the battery pack 01 and the power converter 02 may also be other numbers.

[0048] In the above embodiments, the battery pack 01 in the energy storage system 100, as Figure 3 shown, may include a plurality of batteries 10. The plurality of batteries 10 can be connected in series or in parallel along the X direction and the Y direction. A relatively high voltage and capacity are provided by the plurality of batteries 10. Or, in some other embodiments of the present application, the plurality of batteries 10 can be connected in series or in parallel along the Z direction.

[0049] Continuing as Figure 3 shown, the above battery pack 01 may further include a box body 20 and a box cover 30. For the convenience of description, it is taken as an example that the short side extension direction of the side of the box body 20 facing away from the box cover 30 is the X direction, the long side extension direction is the Y direction, and the direction of the box body 20 facing the box cover 30 is the Z direction. The box body 20 and the box cover 30 are connected, the battery 10 is arranged in the box body 20, and the box body 20 and the box cover 30 limit and protect the battery 10.

[0050] Or, in some other embodiments of the present application, the above battery pack 01 may also be composed of one battery 10.

[0051] The following is a detailed example description of the structure of the above battery 10. As Figure 4 shown, the battery 10 may include a positive electrode plate 11 and a negative electrode plate 12. Through the chemical reactions occurring on the positive electrode plate 11 and the negative electrode plate 12, and at the same time the movement of sodium ions between the positive electrode plate 11 and the negative electrode plate 12, the mutual conversion between chemical energy and electrical energy is finally realized.

[0052] Continue as Figure 4 shown, the battery 10 may further include a housing 13, a cover 14, and an electrolyte (not shown in the figure). The positive electrode plate 11, the negative electrode plate 12, and the electrolyte are all disposed within the housing 13. The cover 14 and the housing 13 are sealingly connected. The housing 13 is used to accommodate the positive electrode plate 11, the negative electrode plate 12, and the electrolyte. The cover 14 isolates the interior of the housing 13 from the exterior of the housing 13 to prevent the leakage of the electrolyte.

[0053] Furthermore, as Figure 5 , Figure 6 or Figure 7 shown, the battery 10 (as Figure 4 shown) may further include a separator 16. The separator 16 is disposed between the positive electrode plate 11 and the negative electrode plate 12 to prevent the short circuit of the positive electrode plate 11 and the negative electrode plate 12, and at the same time allows sodium ions to pass through. After the positive electrode plate 11, the negative electrode plate 12, and the separator 16 are integrated into one body, it may be a winding arrangement as Figure 5 or Figure 6 shown, or it may be a stacking arrangement as Figure 7 shown. The embodiments of the present application do not make any limitations.

[0054] The structure of the above positive electrode plate 11 will be further described in detail by way of examples. As Figure 8 and Figure 9 shown, for the sake of convenience of description, the Y direction is taken as the first direction and the Z direction is taken as the second direction as an example. The positive electrode plate 11 may include a positive current collector 111 and a positive active material layer 112. The positive current collector 111 may include a surface a and a surface b disposed opposite to each other along the first direction Y. Among them, the first direction Y is the thickness direction of the positive current collector 111. The positive active material layer 112 is coated on the surface a and the surface b respectively.

[0055] The above as Figure 9The material of the positive electrode current collector 111 shown may include a positive electrode metal foil or a positive electrode composite material. Among them, the positive electrode metal foil may include aluminum foil, nickel foil, etc. The positive electrode composite material may include a polymer material base layer and a metal layer located on at least one side of the polymer material base layer. The polymer material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The metal layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. The above-mentioned positive electrode metal foil and positive electrode composite material have good conductivity, thereby ensuring that the current can flow smoothly in the positive electrode current collector 111.

[0056] During the charge and discharge process of the battery cycle, sodium ions need to be cyclically embedded in and out of the positive active material layer 112 of the positive electrode plate 11. During the charge and discharge process of the cycle, the unit cell volume in the positive active material layer 112 changes. In the related art, the active material material of the positive active material layer 112 generally adopts sodium-containing layered oxides. During the charge and discharge process of the sodium-containing layered oxide, the unit cell volume changes greatly, causing stress concentration in some areas inside the particles of the positive active material layer 112, which will cause the particles to break and cause the positive electrode plate 11 to expand and increase. As the cycle progresses, the expansion force on the positive electrode plate 11 becomes greater and greater, which makes it difficult for the electrolyte to re-enter the pores of the positive active material layer 112 during the charge and discharge process of the plate, making it difficult for the electrolyte to resume infiltration of the positive electrode plate 11. This affects the normal use of the battery and shortens the battery cycle life.

[0057] To solve the above problem, continue as Figure 8 and Figure 9As shown, the positive electrode active material layer 112 may include a first material layer 1121 and a second material layer 1122. The second material layer 1122 and the first material layer 1121 are arranged side by side along the second direction Z on the same surface of the positive electrode current collector 112. The second direction Z is perpendicular to the first direction Y. The second direction Z may be the height direction of the battery, that is, the extending direction of the positive electrode current collector 112 toward the positive electrode tab 113. The first material layer 1121 may include a sodium-containing layered oxide. The sodium-containing layered oxide has a relatively high energy density, thereby ensuring that the capacity of the battery meets the requirements. The second material layer 1122 may further include a polyanion compound. During the charge and discharge process, the unit cell volume of the polyanion compound changes little, the particle structure is stable, and particle breakage is not likely to occur. Therefore, the expansion change of the polyanion compound is small. That is to say, the expansion change of the second material layer 1122 is relatively small. Supported by the relatively large expansion of the first material layer 1121, the influence of the expansion force on the second material layer 1122 is reduced, thereby ensuring that the electrolyte can fully infiltrate the second material layer 1122, ensuring the normal operation of the battery, and improving the battery cycle life.

[0058] On this basis, continue as Figure 9 As shown, in some embodiments of the present application, the first material layer 1121 further includes a polyanion compound, and the second material layer 1122 further includes a sodium-containing layered oxide. Among them, the mass fraction of the sodium-containing layered oxide in the first material layer 1121 is greater than the mass fraction of the sodium-containing layered oxide in the second material layer 1122. The mass fraction of the polyanion compound in the first material layer 1121 is less than the mass fraction of the polyanion compound in the second material layer 1122. Among them, the mass fraction of the sodium-containing layered oxide in the first material layer 1121 is the percentage of the mass of the sodium-containing layered oxide in the first material layer 1121 accounting for the total mass of the first material layer 1121. The mass fraction of the sodium-containing layered oxide in the second material layer 1122 is the percentage of the mass of the sodium-containing layered oxide in the second material layer 1122 accounting for the total mass of the second material layer 1122. The mass fraction of the polyanion compound in the first material layer 1121 is the percentage of the mass of the polyanion compound in the first material layer 1121 accounting for the total mass of the first material layer 1121. The mass fraction of the polyanion compound in the second material layer 1122 is the percentage of the mass of the polyanion compound in the second material layer 1122 accounting for the total mass of the second material layer 1122. The first material layer 1121 and the second material layer 1122 can be distinguished by observing the electron microscope image of the positive electrode active material layer 112 and the distribution of characteristic elements in the material of the positive electrode active material layer 112.

[0059] During the cyclic charge and discharge process, after the positive electrode plate 11 expands, it will affect the wetting of the electrolyte on the positive active material layer 112. The degree of change in the unit cell volume of the sodium-containing layered oxide is greater than that of the polyanion compound. The sodium-containing layered oxide is more likely to experience stress concentration in some regions inside the particles, resulting in particle breakage, and further increasing the expansion of the positive electrode plate 11. The higher the mass fraction of the sodium-containing layered oxide, the higher the expansion rate of the positive electrode plate 11. Because the mass fraction of the sodium-containing layered oxide in the first material layer 1121 is greater than that in the second material layer 1122, and the mass fraction of the polyanion compound in the first material layer 1121 is less than that in the second material layer 1122. That is to say, the expansion rate of the first material layer 1121 is greater than that of the second material layer 1122. Under the action of the external force generated by the diaphragm 16 (such as Figure 5 shown) and other structures in contact with the positive electrode plate 11, the external force received by the first material layer 1121 is greater than that received by the second active material layer. Under the action of the external force, the first material layer 1121 is squeezed, resulting in a decrease in the porosity of the first material layer 1121, thereby making it difficult for the electrolyte to resume wetting at the first material layer 1121. However, the external force received by the second material layer 1122 is smaller, and the porosity of the second material layer 1122 is basically unaffected or decreased less, thereby ensuring the wetting of the electrolyte on the second material layer 1122 and improving the cycle life of the battery. In addition, the energy density of the sodium-containing layered oxide is higher than that of the polyanion compound. That is to say, when the content of the sodium-containing layered oxide in the material of the positive active material layer 112 is relatively high, it can provide a higher energy density for the battery. The energy density of the battery is increased by the first material layer 1121 with a relatively high mass fraction of the sodium-containing layered oxide to ensure that the capacity of the battery meets the requirements in the early stage of the charge and discharge cycle.

[0060] Continuing as Figure 9 shown, in the second direction, the width L1 of the first material layer 1121 is less than or equal to the width L2 of the second material layer 1122, that is, L1≤L2. During the cyclic charge and discharge process, the degree of expansion of the first material layer 1121 is greater than that of the second material layer 1122. The first material layer 1121 is more likely to cause difficulty in the electrolyte resuming wetting due to excessive battery expansion force. In the embodiment of the present application, the width of the first material layer 1122 is smaller, thereby reducing the influence of the first material layer 1121 on the battery cycle life.

[0061] In some embodiments of the present application, such as Figure 10As shown, the positive electrode active material layer 112 may further include a third material layer 1123. The third material layer 1123 and the first material layer 1121 are disposed on the same surface of the positive electrode active material layer 112, and the second material layer 1122 is located between the first material layer 1121 and the third material layer 1123. The third material layer 1123 may include a sodium-containing layered oxide and a polyanion compound. The mass fraction of the sodium-containing layered oxide in the third material layer 1123 is greater than that of the sodium-containing layered oxide in the second material layer 1122. Herein, the mass fraction of the sodium-containing layered oxide in the third material layer 1123 is the percentage of the mass of the sodium-containing layered oxide in the third material layer 1123 to the total mass of the third material layer 1123. At this time, the swelling degrees of both the first material layer 1121 and the third material layer 1123 are greater than that of the second material layer 1122. In the later stage of the charge and discharge cycle of the battery, after the positive electrode active material layer 112 swells, as Figure 11 shown, in the first direction Y, both the swollen first material layer 1121 and the third material layer 1123 protrude from the second material layer 1122. Supported by the larger swelling of the first material layer 1121 and the third material layer 1123, the external force applied to the second material layer 1122 is further reduced, thereby ensuring that the electrolyte can fully wet the second material layer 1122, ensuring the normal operation of the battery, and improving the battery cycle life. In addition, since the first material layer 1121 and the third material layer 1123 are respectively located on both sides of the second material layer 1122, after the first material layer 1121 abuts against other structures such as the separator 16 on the side of the positive electrode active material layer 112 away from the positive electrode current collector 111, the first material layer 1121 and the third material layer 1123 that protrude from the second material layer 1122 can reduce the difference in the swelling degree change at both ends of the positive electrode plate 11 in the second direction Z, and even do not generate inclination, thereby avoiding excessive inclination of the positive electrode plate 11, resulting in Figure 4 shown) at the bottom inner wall of the housing 13, preventing the positive electrode active material layer 112 from being damaged due to stress concentration.

[0062] On this basis, continue as Figure 10As shown, in the second direction Z, the width L2 of the second material layer 1122 is greater than or equal to the sum of the width L1 of the first material layer 1121 and the width L3 of the third material layer 1123, that is, L2≥L1 + L3. During the charging and discharging cycles, the degree of expansion of both the first material layer 1121 and the third material layer 1123 is greater than that of the second material layer 1122. The first material layer 1121 and the third material layer 1123 are more likely to cause difficulties in the restoration of electrolyte infiltration due to excessive battery expansion force. However, the total width of the first material layer 1121 and the third material layer 1123 in the embodiments of the present application is smaller, thereby reducing the influence of the first material layer 1121 and the third material layer 1123 on the battery cycle life.

[0063] Alternatively, in some other embodiments of the present application, as Figure 12 shown, the positive electrode active material layer 112 may further include a third material layer 1123. The third material layer 1123 and the first material layer 1121 are disposed on the same surface of the positive electrode active material layer 112, and the first material layer 1121 is located between the second material layer 1122 and the third material layer 1123. The third material layer 1123 may include a sodium-containing layered oxide and a polyanion compound. Among them, the mass fraction of the sodium-containing layered oxide in the third material layer 1123 is less than the mass fraction of the sodium-containing layered oxide in the first material layer 1121. At this time, the degree of expansion generated by the first material layer 1121 is greater than that of the second material layer 1122 and the third material layer 1123. In the later stage of the battery charge and discharge cycle, after the positive electrode active material layer 112 expands, as Figure 13 shown, in the first direction Y, the expanded first material layer 1121 protrudes from the second material layer 1122 and the third material layer 1123. With the support of the larger expansion of the first material layer 1121, the external forces on the second material layer 1122 and the third material layer 1123 are reduced, thereby ensuring that the electrolyte can fully infiltrate the second material layer 1122 and the third material layer 1123, and further improving the battery cycle life. In addition, the difference in the degree of expansion between the second material layer 1122 and the third material layer 1123 is small. The inclination degree caused by the difference in the degree of expansion at both ends of the positive electrode plate 11 in the second direction Z is reduced, or even no inclination occurs, thereby avoiding a large stress concentration at the contact between the positive electrode plate 11 and the bottom inner wall of the housing 13 (as Figure 4 shown), and preventing the positive electrode active material layer 112 from being damaged due to stress concentration.

[0064] On this basis, continue as Figure 12As shown, in the second direction Z, the sum of the width L2 of the second material layer 1122 and the width L3 of the third material layer 1123 is greater than or equal to the width L1 of the first material layer 1121, that is, L2 + L3 ≥ L1. During the charging and discharging cycle, the degree of expansion of the first material layer 1121 is greater than that of the second material layer 1122 and the third material layer 1123. The first material layer 1121 is more likely to cause difficulty in the restoration of electrolyte infiltration due to excessive battery expansion force. However, the width of the first material layer 1121 in the embodiment of the present application is smaller, thereby reducing the influence of the first material layer 1121 on the battery cycle life.

[0065] In addition, in some other embodiments of the present application, such as Figure 9 shown, the first material layer 1121 may not include a polyanion compound; such as Figure 9 shown, the second material layer 1122 may not include a sodium-containing layered oxide. At this time, a higher proportion of sodium-containing layered oxide can be provided in the first material layer 1121, and a higher proportion of polyanion compound can be provided in the second material layer 1122. In this way, while ensuring that the energy density of the battery meets the requirements, it is further ensured that the porosity of the second material layer 1122 is basically not affected or reduced to a small extent, thereby ensuring the infiltration of the electrolyte into the second material layer 1122 and improving the cycle life of the battery.

[0066] On this basis, such as Figure 10 shown, the third material layer 1123 may also not include a polyanion compound. At this time, a higher proportion of sodium-containing layered oxide can be provided in the third material layer 1123 to further ensure that the energy density of the battery meets the requirements. In addition, the beneficial effects of the third material layer 1123 in this embodiment are the same as those of the third material layer 1123 in the embodiment shown in Figure 10 above, and will not be elaborated here.

[0067] Or, such as Figure 12 shown, the third material layer 1123 may also not include a polyanion compound. The beneficial effects of the third material layer 1123 in this embodiment are the same as those of the third material layer 1123 in the embodiment shown in Figure 12 above, and will not be elaborated here.

[0068] In any of the above embodiments such as Figure 9 , Figure 10 and Figure 12 shown, it is taken as an example that the positive electrode active material layer 112 is coated on both the surface a and the surface b of the positive electrode current collector 111, so as to improve the overall energy density of the battery. In other embodiments of the present application, the positive electrode active material layer 112 may be coated only on the surface a or the surface b of the positive electrode current collector 111 to reduce the thickness of the positive electrode plate 11, and thus reduce the volume of the positive electrode plate 11.

[0069] Furthermore, such asFigure 9 , Figure 10 and Figure 12 In any of the embodiments shown, the first material layer 1121 and the second material layer 1122 may also include a positive electrode binder. By bonding the positive electrode binder to the positive electrode current collector 111, the connection stability between the first material layer 1121 and the second material layer 1122 and the positive electrode current collector 111 is ensured. Exemplarily, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. The above positive electrode binder has good bonding performance, ensuring firm bonding between the first material layer 1121 and the second material layer 1122 and the positive electrode current collector 111.

[0070] Continuing as in Figure 10 or Figure 12 In the embodiments shown, the third material layer 1123 may also include a positive electrode binder. Thereby ensuring the connection stability between the third material layer 1123 and the positive electrode current collector 111.

[0071] In addition, as in Figure 9 , Figure 10 and Figure 12 In any of the embodiments shown, the first material layer 1121 and the second material layer 1122 may also include a positive electrode conductive agent. The conductivity of the first material layer 1121 and the second material layer 1122 is improved by the positive electrode conductive agent. Exemplarily, the positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The above positive electrode conductive agent has good conductivity and good chemical stability, ensuring the conductivity of the first material layer 1121 and the second material layer 1122 while increasing the service life of the first material layer 1121 and the second material layer 1122.

[0072] Continuing as in Figure 10 or Figure 12 In the embodiments shown, the third material layer 1123 may also include a positive electrode conductive agent. The conductivity of the third material layer 1123 is improved by the positive electrode conductive agent.

[0073] Furthermore, as in Figure 9 , Figure 10 and Figure 12In any of the embodiments shown, the areal density of the first material layer 1121 may be d1, and the areal density of the second material layer 1122 may be d2; wherein, 1 < d1 / d2 ≤ 2. Among them, the areal density d1 of the first material layer 1121 is equal to the ratio of the weight m1 of the first material layer 1121 to the projected area S1 of the first material layer 1121 on the surface of the positive electrode current collector 111 facing the first material layer 1121 (i.e., d1 = m1 / S1); the areal density d2 of the second material layer 1122 is equal to the ratio of the weight m2 of the second material layer 1122 to the projected area S2 of the second material layer 1122 on the surface of the positive electrode current collector 111 facing the second material layer 1122 (i.e., d2 = m2 / S2).

[0074] When d1 / d2 > 1, that is to say, the weight of the first material layer 1121 per unit area is greater than that of the second material layer 1122. And the mass fraction of the sodium-containing layered oxide in the first material layer 1121 is greater than that of the sodium-containing layered oxide in the second material layer 1122, and the energy density of the sodium-containing layered oxide is relatively high. When the areal density of the first material layer 1121 is relatively high and the mass fraction of the sodium-containing layered oxide is also relatively high, the energy density of the battery can be further improved. When the first material layer 1121 provides a relatively high energy density, the energy density of the battery can be ensured to meet the requirements, and at the same time, the energy density required to be provided by the second material layer 1122 can be reduced. Therefore, the mass fraction of the sodium-containing layered oxide in the second material layer 1122 can be further reduced, thereby reducing the swelling of the second material layer 1122 and the external force received by the second material layer 1122. In addition, when d1 / d2 > 1, the porosity in the second material layer 1122 is higher than that in the first material layer 1121, and the electrolyte is more likely to enter the pores in the second material layer 1122 to achieve wetting of the second material layer 1122. In this way, during the charge and discharge cycle process, when the porosity of the first material layer 1121 electrode decreases and it becomes difficult to restore wetting of the electrolyte at the first material layer 1121, the electrolyte can still wet the second material layer 1122 with a smaller swelling force and a higher porosity, ensuring the normal operation of the battery and improving the battery cycle life.

[0075] In addition, during the production process of the positive electrode active material layer 112, after the materials of the first material layer 1121 and the second material layer 1122 are coated on the surface of the positive electrode current collector 111, the first material layer 1121 and the second material layer 1122 are simultaneously roll-pressed. When the ratio of the surface density A1 of the first material layer 1121 after the preset roll-pressing to the surface density A2 of the second material layer 1122 is greater than 2 (i.e., A1 / A2 > 2), the thickness of the material to be coated on the first material layer 1121 before roll-pressing is greater than that of the first material layer 1121. During the roll-pressing process, when the compaction degree of the first material layer 1121 reaches the roll-pressing limit, the thickness of the first material layer 1121 may still be higher than the thickness of the first material layer 1121 before roll-pressing. At this time, effective roll-pressing of the second material layer 1122 cannot be performed, and thus the structural stability of the second material layer 1122 cannot be guaranteed. When d1 / d2 ≤ 2, it is ensured that during the roll-pressing process, the first material layer 1121 and the second material layer 1122 can be roll-pressed simultaneously, and the structural stability of the first material layer 1121 and the second material layer 1122 is guaranteed.

[0076] In some embodiments of the present application, as Figure 10 shown, the surface density of the third material layer 1123 can be d3; wherein, 1 < d3 / d2 ≤ 2. Among them, the surface density d3 of the third material layer 1123 is equal to the ratio of the weight m3 of the third material layer 1123 to the projected area S3 of the third material layer 1123 on the surface of the positive electrode current collector 111 facing the third material layer 1123 (i.e., d3 = m3 / S3). Similarly, at this time, the weight of the third material layer 1123 provided per unit area on the surface a or the surface b is also greater than the weight of the second material layer 1122, thereby improving the energy density of the battery. At the same time, it is ensured that during the roll-pressing process, the second material layer 1122 and the third material layer 1123 can be roll-pressed simultaneously, and the structural stability of the second material layer 1122 and the third material layer 1123 is guaranteed.

[0077] In other embodiments of the present application, as Figure 12 shown, the surface density of the third material layer 1123 can be d3; wherein, 1 < d3 / d2 ≤ 2. Similarly, at this time, the weight of the third material layer 1123 provided per unit area on the surface a or the surface b is less than the weight of the first material layer 1121, and the porosity in the third material layer 1123 is higher than that in the first material layer 1121. The electrolyte can more easily enter the pores in the third material layer 1123 to achieve the infiltration of the third material layer 1123. At the same time, it is ensured that during the roll-pressing process, the first material layer 1121 and the third material layer 1123 can be roll-pressed simultaneously, and the structural stability of the first material layer 1121 and the third material layer 1123 is guaranteed.

[0078] As Figure 9 、 Figure 10and Figure 12 In any of the embodiments shown, 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 ; and / or, 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 . Exemplarily, 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 ; or, 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 ; or again, 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 , and 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 . Again exemplarily, the density D1 of the first material layer 1121 can be 1.5 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 2 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3.1 g / cm 3 , 3.3 g / cm 3 , 3.5 g / cm 3 , 3.7 g / cm 3 , etc. Again exemplarily, the density D2 of the second material layer 1122 can be 1.5 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 2 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3.1 g / cm 3 , 3.3 g / cm 3 , 3.5 g / cm 3 , 3.7 g / cm 3 , etc.

[0079] When D1 < 1.5 g / cm 3 or D2 < 1.5 g / cm 3When the material content per unit volume of the first material layer 1121 or the second material layer 1122 is low, the energy density of the battery is low and cannot meet the capacity requirements of the battery.

[0080] When D1 > 3.7 g / cm 3 or D2 > 3.7 g / cm 3 the porosity of the first material layer 1121 or the second material layer 1122 is small. Especially after the unit cells of the first material layer 1121 or the second material layer 1122 expand, it is easy to cause difficulty in the electrolyte infiltrating the first material layer 1121 or the second material layer 1122, and the battery cycle life is short.

[0081] When 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 ; or, 1.5 g / cm 3 ≤ D2 ≤ 3.7 g / cm 3 during the production and preparation of the positive electrode active material layer 112, after rolling the first material layer 1121 or the second material layer 1122, it can ensure a high material content per unit volume, thereby ensuring a high energy density of the battery. At the same time, it ensures that the porosity of the first material layer 1121 or the second material layer 1122 is not too small, so as to ensure that the electrolyte can infiltrate the first material layer 1121 and the second material layer 1122 through the pores of the first material layer 1121 and the second material layer 1122, avoiding difficult electrolyte infiltration, and thus improving the battery cycle life.

[0082] Such as Figure 10 and Figure 12 In any of the embodiments shown, 1.5 g / cm 3 ≤ D3 ≤ 3.7 g / cm 3 . Exemplarily, the density D3 of the third material layer 1123 can be 1.5 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 2 g / cm 3 , 2.2 g / cm 3 , 2.4 g / cm 3 , 2.6 g / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3.1 g / cm 3 , 3.3 g / cm 3 , 3.5 g / cm 3 , 3.7 g / cm 3Similarly, in the production process of the positive electrode active material layer 112, after rolling the third material layer 1123, it is possible to ensure a high material content per unit volume, thereby ensuring a high energy density of the battery. At the same time, it is ensured that the porosity of the third material layer 1123 is not too small, so that the electrolyte can infiltrate the third material layer 1123 through the pores of the third material layer 1123, avoiding difficult electrolyte infiltration, and thus improving the battery cycle life.

[0083] Furthermore, in any of the embodiments shown in Figure 9 , Figure 10 and Figure 12 , the sodium-containing layered oxide may include Na α (M x Mn y )O2; and / or, the polyanion compound may include at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7. Exemplarily, the sodium-containing layered oxide includes Na α (M x Mn y )O2. Alternatively, the polyanion compound includes at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7. Or, the sodium-containing layered oxide includes Na α (M x Mn y )O2; and the polyanion compound includes at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7. Wherein, in any of the above embodiments, M may include at least one of Ni, Fe, Cu, Mg, Al, Co, Ti, Ca, and Zn; in any of the above embodiments, N may include at least one of Fe, V, Mn, Co, Ti, Zr, and Ni.

[0084] Na α (M x Mn y )O2 has a high energy density. When using the above sodium-containing layered oxide, it is possible to ensure that the battery has a high capacity. In addition, the particle structures of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7 are stable and have small expansion changes, thereby ensuring a large porosity of the second material layer 1122, and the electrolyte can fully infiltrate the second material layer 1122, ensuring the normal operation of the battery and improving the battery cycle life.

[0085] In addition, in Figure 9 , Figure 10 and Figure 12In any of the embodiments shown, the positive electrode tab 11 further includes a positive electrode terminal 113. One end of the positive electrode terminal 113 is connected to the positive electrode current collector 111, and the other end of the positive electrode terminal 113 is connected to the positive electrode terminal 15 (as Figure 4 shown). The positive electrode current collector 111 is electrically connected to the positive electrode terminal 15 through the positive electrode terminal 113. Exemplarily, the positive electrode terminal 113 and the positive electrode current collector 111 may be an integral structural member. During the production process, the positive electrode terminal 113 and the positive electrode current collector 111 can be integrally formed. At this time, the connection between the positive electrode terminal 113 and the positive electrode current collector 111 is relatively stable, avoiding the situation that the positive electrode current collector 111 cannot transfer current to the positive electrode terminal 15 due to the separation of the positive electrode terminal 113 and the positive electrode current collector 111.

[0086] In the above embodiments, such as Figure 9 , Figure 10 and Figure 12 shown, the positive electrode tab 11 only includes one positive electrode terminal 113. In other embodiments of the present application, the positive electrode tab 11 may further include two positive electrode terminals 113 disposed on both sides of the positive electrode current collector 111 along the second direction Z.

[0087] In the above, such as Figure 9 , Figure 10 and Figure 12 shown, the material of the positive electrode terminal 113 may also include a positive electrode metal foil or a positive electrode composite material. The above positive electrode metal foil and positive electrode composite current collector have good electrical conductivity, thus ensuring that current can flow smoothly in the positive electrode terminal 113.

[0088] The above is only the specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any change or replacement within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claimed rights.

Claims

1. A battery, characterized in that, It includes a positive electrode plate, and the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer. Along the first direction, the positive electrode active material layer is disposed on the surface of the positive electrode current collector; The positive electrode active material layer includes a first material layer and a second material layer. The second material layer and the first material layer are arranged side by side along the second direction on the same surface of the positive electrode current collector. The first material layer includes a sodium-containing layered oxide, and the second material layer includes a polyanion compound. Wherein, the first direction is the thickness direction of the positive electrode current collector, and the second direction is perpendicular to the first direction.

2. The battery according to claim 1, characterized in that, The first material layer further includes a polyanion compound, and the second material layer further includes a sodium-containing layered oxide; The mass fraction of the sodium-containing layered oxide in the first material layer is greater than the mass fraction of the sodium-containing layered oxide in the second material layer, and the mass fraction of the polyanion compound in the first material layer is less than the mass fraction of the polyanion compound in the second material layer.

3. The battery according to claim 2, wherein, In the second direction, the width of the first material layer is less than or equal to the width of the second material layer.

4. The battery according to claim 2, characterized in that The positive electrode active material layer further includes a third material layer. The third material layer and the first material layer are disposed on the same surface, and the second material layer is located between the first material layer and the third material layer; The third material layer includes a sodium-containing layered oxide and a polyanion compound, and the mass fraction of the sodium-containing layered oxide in the third material layer is greater than the mass fraction of the sodium-containing layered oxide in the second material layer.

5. The battery according to claim 4, wherein, In the second direction, the width of the second material layer is greater than or equal to the sum of the widths of the first material layer and the third material layer.

6. The battery according to claim 2, characterized in that, The positive electrode active material layer further includes a third material layer. The third material layer and the first material layer are disposed on the same surface, and the first material layer is located between the second material layer and the third material layer; The third material layer includes a sodium-containing layered oxide and a polyanion compound, and the mass fraction of the sodium-containing layered oxide in the third material layer is less than the mass fraction of the sodium-containing layered oxide in the first material layer.

7. The battery according to claim 6, characterized in that, In the second direction, the sum of the widths of the second material layer and the third material layer is greater than or equal to the width of the first material layer.

8. The battery according to claim 2, characterized in that, The surface density d1 of the first material layer and the surface density d2 of the second material layer satisfy: 1 < d1 / d2 ≤ 2.

9. The battery according to any one of claims 1-8, characterized in that, The density D1 of the first material layer satisfies: 1.5 g / cm 3 ≤ D1 ≤ 3.7 g / cm 3 ; and / or, the density D2 of the second material layer satisfies: 1.5 g / cm 3 ≤D2≤3.7 g / cm 3 .

10. The battery according to any one of claims 1-8, characterized in that, The sodium-containing layered oxide includes Na α (M x Mn y )O2; wherein, M includes at least one of Ni, Fe, Cu, Mg, Al, Co, Ti, Ca and Zn; And / or, the polyanion compound includes at least one of Na4N2(PO4)2P2O7, Na3N2(PO4)3, and Na2NP2O7; wherein, N includes at least one of Fe, V, Mn, Co, Ti, Zr, and Ni.

11. A positive electrode sheet, characterized in that, It includes a positive electrode current collector and a positive electrode active material layer. Along the first direction, the positive electrode active material layer is disposed on the surface of the positive electrode current collector; The positive electrode active material layer includes a first material layer and a second material layer. The second material layer and the first material layer are arranged side by side in a second direction on the same surface of the positive electrode current collector. The first material layer includes a sodium-containing layered oxide, and the second material layer includes a polyanion compound. Wherein, the first direction is the thickness direction of the positive electrode current collector, and the second direction is perpendicular to the first direction.

12. A battery pack, characterized in that, The battery pack includes a plurality of batteries as described in any one of claims 1-10, and the plurality of batteries are connected in series or in parallel.

13. An energy storage system, characterized in that, The energy storage system includes a power converter and at least one battery pack as described in claim 12; the power converter is configured to perform power conversion on the voltage output by the battery pack and then output it to the power grid or the load, and / or perform power conversion on the voltage output by an external power source and then output it to the battery pack.

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