Positive pole piece, sodium ion secondary battery and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a positive pole piece, a sodium ion secondary battery and an electric device. The positive pole piece comprises a sodium supplementing agent and a positive active material, the sodium supplementing agent comprises NaqMnxMyO2, q is greater than or equal to 1 and less than or equal to 1.2, x is greater than or equal to 0.15 and less than 0.45, y is greater than 0, x + y is greater than or equal to 0.9 and less than or equal to 1, and M comprises transition metal elements; the Dv50 of the sodium supplement is less than the Dv50 of the positive electrode active material. The sodium supplementing agent NaqMnxMyO2 provided by the invention has relatively large structural instability, and sodium is easy to remove; the particle size of the sodium supplementing agent is smaller than that of the positive electrode active material, so that the sodium supplementing agent has higher reaction activity than the positive electrode active material, sodium ions can be preferentially removed to participate in electrochemical reaction than the positive electrode active material, and consumption of active sodium contained in the positive electrode active material in the early charging and discharging process of the battery is reduced; therefore, the structural damage condition of the positive active material is improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular to positive electrode sheets, sodium ion secondary batteries, and electrical devices. Background Art

[0002] Sodium-ion batteries have a similar working mechanism to lithium-ion batteries, and mainly realize the conversion of chemical energy and electrical energy through the deintercalation of sodium ions between the positive and negative electrodes. That is, during the charging process, the active material of the positive electrode releases sodium ions, and the sodium ions are embedded in the active material of the negative electrode after being transported by the electrolyte; during the discharge process, the sodium ions are released from the negative electrode active material and return to the positive electrode active material.

[0003] In practice, it is found that capacity decay and poor cycle performance are prone to occur during the charge and discharge process of sodium-ion batteries, which restricts the development of sodium-ion batteries. Summary of the invention

[0004] In view of the above problems, the present application provides a positive electrode plate, a sodium ion secondary battery, and an electrical device, which can solve the problem of poor cycle performance of sodium ion batteries.

[0005] In a first aspect, the present application provides a positive electrode plate, wherein the positive electrode plate comprises a sodium supplement and a positive electrode active material, wherein the sodium supplement comprises Na q Mn x M y O2, 1≤q≤1.2, 0.15≤x<0.45, y>0, 0.9≤x+y≤1, the M comprises a transition metal element; the Dv50 of the sodium supplement is less than the Dv50 of the positive electrode active material.

[0006] In the embodiment of the present application, Mn-based sodium oxide Na is added to the positive electrode plate. q Mn x M y O2 as a sodium supplement, Na q Mn x M y Mn in O2 includes unstable Mn 3+ , making Na q Mn x M y The structure of O2 is very unstable and it is easy to release sodium (Mn 3+ In this process, it can be converted into stable Mn 4+ ). Therefore, during the initial charge and discharge process of the battery, Na q Mn x M yO2 serves as an active sodium source consumed in forming a solid electrolyte interface film (SEI film), thereby reducing the consumption of active sodium contained in the positive electrode active material during the initial charge and discharge process of the battery, improving the structural damage of the positive electrode active material, and is beneficial to improving the cycle performance of the battery.

[0007] At the same time, generally, materials with small particle sizes have higher reactivity than materials with large particle sizes. In the embodiment of the present application, by setting the particle size of the sodium supplement agent to be smaller than the particle size of the positive electrode active material, the sodium supplement agent can have a higher reactivity than the positive electrode active material, and has faster kinetics during the early charge and discharge process of the battery, so it can preferentially release sodium ions than the positive electrode active material to provide for the formation of the SEI film, thereby further reducing the consumption of active sodium in the positive electrode active material and improving the cycle performance of the battery.

[0008] In some embodiments, 1≤q≤1.1. q may reflect the Na q Mn x M y The Na content in O2, setting q in these ranges not only makes Na q Mn x M y O2 provides sodium ions, reducing the consumption of active sodium contained in the positive electrode active material during the first cycle of charging, which is beneficial to increasing the capacity of the positive electrode sheet and improving the battery cycle performance; and it can make the sodium supplement have good structural stability after sodium removal.

[0009] In some embodiments, 0.2≤x≤0.44. x may reflect Na q Mn x M y Mn content in O2, Na q Mn x M y Mn in O2 includes unstable Mn 3+ , setting x in the above range can make Na q Mn x M y O2 contains enough Mn 3+ , making Na q Mn x M y The structure of O2 is relatively unstable and can easily release sodium, which is beneficial for achieving the effect of sodium supplementation. In addition, Mn has different valence states in different structures and can adapt to different Na contents. In other words, it can change its valence state to allow Na q Mn x M y Adding more Na to O2 will help increase the Na q Mn x M yThe Na content in O2 is beneficial to increase the capacity of the positive electrode and improve the battery cycle performance.

[0010] In some embodiments, 0.5≤y≤0.8. y reflects Na q Mn x M y The transition metal M content in O2. q Mn x M y O2 with an appropriate amount of M helps to increase Na q Mn x M y The structural stability after O2 desodiumization makes Na q Mn x M y O2 does not undergo serious structural collapse during the desodiumization process.

[0011] In some embodiments, the M includes one or more of Fe, Ni, Co, Cu, Al, Ti, and V. These transition metals contribute to increasing the Na q Mn x M y Structural stability after O2 desodiumization.

[0012] In some embodiments, the M comprises Fe and Ni, and the sodium supplement comprises Na q Mn x Ni y1 Fe y2 O2, 1≤q≤1.2, 0.15≤x<0.45, y1>0, y2>0, 0.9≤x+y1+y2≤1. The transition metal uses a combination of Ni and Fe to form a stable metal layer structure with Mn; and studies have shown that the combination of Ni and Fe is beneficial to improving the energy density of the material.

[0013] In some embodiments, the phase structure of the sodium supplement includes an O3 phase. + The sodium supplement in the embodiment of the present application includes an O3 phase, which is a phase structure with a high sodium content, and thus is conducive to providing a large amount of sodium in the sodium supplement.

[0014] In some embodiments, the Dv50 of the sodium supplement is 6% to 75% of the Dv50 of the positive electrode active material, and optionally 6% to 25%. Setting the particle size of the sodium supplement to be smaller than the particle size of the positive electrode active material can make the sodium supplement have a higher reaction activity than the positive electrode active material, and have faster kinetics during the first cycle of charging and the early cycle of the battery. Therefore, it can preferentially release sodium ions than the positive electrode active material to provide for the formation of the SEI film, thereby reducing the consumption of active sodium in the positive electrode active material and improving the cycle performance of the battery. At the same time, when there is a certain difference between the Dv50 of the sodium supplement and the Dv50 of the positive electrode active material, the battery can exhibit better cycle performance.

[0015] In some embodiments, the Dv50 of the sodium supplement is 0.5 μm to 6 μm, optionally 1 μm to 3 μm. At this particle size, the sodium supplement has a high specific surface area, high specific surface energy, and a short sodium transmission path, which is beneficial to improving its reaction activity and promoting sodium removal.

[0016] In some embodiments, the Dv50 of the positive electrode active material is 6μm to 20μm, optionally 6μm to 10μm. At this particle size, the reaction activity of the positive electrode active material is lower than that of the sodium supplement, and it can slowly release sodium ions during the early charge and discharge process of the battery without preferentially releasing sodium ions, which can slow down the consumption of active sodium in the positive electrode active material. Moreover, the positive electrode active material and the sodium supplement are compounded with large and small particle sizes, and the small particle size sodium supplement can be filled between the large particle size positive electrode active materials, which is beneficial to increase the compaction density of the positive electrode sheet, thereby increasing the energy density of the positive electrode sheet.

[0017] In some embodiments, the mass ratio of the sodium supplement to the positive electrode active material is 1:(14-95), optionally 1:(18-46.5). The mass ratio of the sodium supplement to the positive electrode active material has an effect on the cycle performance of the sodium ion battery. At the above mass ratio, the sodium ion battery can exhibit excellent cycle performance.

[0018] In some embodiments, the mass content of the sodium supplement in the active layer of the positive electrode is 1% to 6%, and optionally 2% to 5%. Adding a small amount of the sodium supplement of the present application embodiment to the active layer of the positive electrode can effectively achieve the sodium supplement effect and improve the battery cycle performance.

[0019] In some embodiments, the positive electrode active material includes one or more of a layered oxide, a polyanion compound, and a Prussian blue compound; optionally, the layered oxide includes Na m M 1 z O2, 0.4≤m≤0.9, 0.9≤z≤1, the M 1Including transition metal elements. The positive electrode plate of the embodiment of the present application is suitable for various positive electrode active materials, and can improve the structural damage of these positive electrode active materials during the battery cycle process and improve the cycle performance of the battery.

[0020] In a second aspect, the present application provides a sodium ion secondary battery, wherein the sodium ion secondary battery comprises the positive electrode plate described in the first aspect.

[0021] The above-mentioned positive electrode plate contains a sodium supplement with a special structure, and the sodium supplement is combined with the positive electrode active material according to a specific particle size. After the positive electrode plate is applied to a sodium ion secondary battery, it is beneficial to improve the cycle performance of the sodium ion secondary battery.

[0022] In a third aspect, the present application provides an electrical device, which includes the sodium ion secondary battery described in the second aspect.

[0023] The sodium ion secondary battery disclosed in the embodiment of the present application can be used in electrical devices that use secondary batteries as power sources, or various energy storage systems that use batteries as energy storage elements, to provide electrical energy. The above-mentioned sodium ion secondary battery has good cycle performance. Therefore, the use of the above-mentioned sodium ion secondary battery can stably provide electrical energy for various electrical devices, thereby improving the user experience of various electrical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A schematic diagram of a secondary battery according to an embodiment of the present application;

[0026] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0027] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0028] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application;

[0029] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0030] Figure 6FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0031] Reference numerals:

[0032] Shell 01, cover plate 02, electrode assembly 03, battery cell 04, battery module 05, upper box body 06, lower box body 07. DETAILED DESCRIPTION

[0033] The following embodiments of the technical solution of the present application will be described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0035] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0036] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0038] In the description of the embodiments of the present application, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0039] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0040] The mass of the relevant components mentioned in the specification of the examples of this application can not only refer to the specific content of each component, but also represent the proportional relationship between the masses of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the specification of the examples of this application, it is within the scope disclosed in the specification of the examples of this application. Specifically, the mass described in the specification of the examples of this application can be mass units known in the chemical industry such as μg, mg, g, and kg.

[0041] Sodium-ion batteries have received extensive attention and research because their raw materials are abundant and widely distributed in nature. Similar to lithium-ion batteries, sodium-ion batteries mainly achieve the conversion of chemical energy into electrical energy through the intercalation and deintercalation of sodium ions between the positive and negative electrodes. That is, during the charging process, the active material of the positive electrode releases sodium ions, which are then embedded in the active material of the negative electrode after being transported by the electrolyte; during the discharging process, the sodium ions are released from the negative electrode active material and returned to the positive electrode active material.

[0042] However, in reality, not all sodium ions released from the positive electrode active material during the charging process can return to the positive electrode active material. For example, during the charging process, after the sodium ions released from the positive electrode active material reach the negative electrode active material, some of the sodium ions will form a solid electrolyte interface film (SEI film) on the surface of the negative electrode active material and cannot continue to participate in subsequent cycles; some sodium ions will be embedded in the negative electrode active material and cannot be released from the lattice of the negative electrode active material during the subsequent discharge process. These phenomena cause irreversible loss of sodium, which causes the battery capacity to decay and deteriorates the cycle performance of the sodium ion battery.

[0043] Researchers have developed a technical method for pre-sodiumization of the positive or negative electrode to solve the above problems. The pre-sodiumization method includes adding sodium powder or sodium foil to the positive or negative electrode by roller pressing or adsorption; or adding a pre-sodiumization reagent (sodium supplement) to the positive or negative electrode and the electrolyte to compensate for the lost sodium.

[0044] However, in practice, it is found that sodium powder or sodium foil has a strong reaction activity, has high requirements for the operating environment, and has potential safety issues. Most sodium supplements have limited sodium supplementation effects during the battery charging and discharging process. It is difficult to release sodium ions before the positive electrode active material during the charging and discharging process. Therefore, the positive electrode active material needs to provide sodium ions during the early charging and discharging process of the battery, which will also cause irreversible sodium loss in the positive electrode active material.

[0045] In view of the above problems, the embodiment of the present application adds a specific Mn-based sodium supplementing oxide as a sodium supplementing agent Na to the positive electrode plate. q Mn x M y O2, the sodium supplement contains unstable Mn 3+ , making Na q Mn x M y The structure of O2 is relatively unstable and easily releases sodium. The particle size of the sodium supplement is smaller than that of the positive electrode active material, so it has a higher reaction activity than the positive electrode active material and can release sodium ions preferentially to participate in the electrochemical reaction. Therefore, under the action of this sodium supplement, the consumption of active sodium contained in the positive electrode active material during the initial charge and discharge process of the battery can be reduced, the structural damage of the positive electrode active material can be improved, and the cycle performance of the battery can be improved.

[0046] The positive electrode plate containing the sodium supplement agent in the embodiment of the present application can be used to make a secondary battery, and can be further applied to various electrical devices.

[0047] The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0048]

Positive electrode

[0049] In a first aspect, the present application provides a positive electrode plate, the positive electrode plate comprising a sodium supplement and a positive electrode active material, the sodium supplement comprising Na q Mn x M y O2, 1≤q≤1.2, 0.15≤x<0.45, y>0, 0.9≤x+y≤1, M includes transition metal elements; Dv50 of the sodium supplement is less than Dv50 of the positive electrode active material.

[0050] The positive electrode active material is an important substance in the positive electrode sheet that participates in the electrochemical reaction of the battery and can serve as a medium for ion transport in the electrochemical reaction. In the positive electrode sheet of this article, the positive electrode active material refers to the positive electrode active material of the sodium ion battery. The sodium supplement contains Na q Mn x M y O2, the Na q Mn x M y The crystal form of O2 can be determined by X-ray diffraction, and the type of each element as well as the content and proportion of each element can be obtained in combination with an element analyzer, and then the subscripts q, x, and y of each element in the chemical formula can be obtained through conversion.

[0051] Dv50 is a way of expressing the particle size of a material. For the particle size distribution of a material, it is usually expressed as the percentage of particles in different particle size ranges. There are many benchmarks for determining particle size distribution, such as number distribution, length distribution, area distribution, volume distribution, weight distribution, etc. Dv50 is a specific particle size distribution based on volume distribution, also known as median particle size, which refers to the particle size at which the cumulative distribution of particle volume is 50%, indicating that 50% of the particles have a diameter exceeding this value and 50% of the particles have a diameter below this value. The Dv50 of the particles can be obtained by referring to GB / T 19077-2016 / ISO 13320:2009 "Laser Diffraction Method for Particle Size Distribution". In the embodiments of the present application, the particle morphology of the sodium supplement and the positive electrode active material can be regular spheres, ellipsoids, polygons, or other irregular shapes. For spherical particles, their particle size is their diameter; for non-spherical or other irregularly shaped particles, their particle size is their equivalent diameter.

[0052] In the embodiment of the present application, Mn-based sodium oxide Na is added to the positive electrode plate. q Mn x M y O2 as a sodium supplement, Na q Mn x M y Mn in O2 includes unstable Mn 3+ , making Na q Mn x M y The structure of O2 is very unstable and it is easy to release sodium (Mn 3+ In this process, it can be converted into stable Mn 4+ ). Therefore, during the initial charge and discharge process of the battery, Na q Mn x M yO2 serves as an active sodium source consumed in forming a solid electrolyte interface film (SEI film), thereby reducing the consumption of active sodium contained in the positive electrode active material during the initial charge and discharge process of the battery, improving the structural damage of the positive electrode active material, and is beneficial to improving the cycle performance of the battery.

[0053] At the same time, generally, materials with small particle sizes have higher reactivity than materials with large particle sizes. In the embodiment of the present application, by setting the particle size of the sodium supplement agent to be smaller than the particle size of the positive electrode active material, the sodium supplement agent can have a higher reactivity than the positive electrode active material, and has faster kinetics during the early charge and discharge process of the battery, so it can preferentially release sodium ions than the positive electrode active material to provide for the formation of the SEI film, thereby further reducing the consumption of active sodium in the positive electrode active material and improving the cycle performance of the battery.

[0054] In some embodiments, 1≤q≤1.2, optionally, 1≤q≤1.1. For example, q can be any point value among 1.0, 1.1, 1.2 or a range of values ​​between any two. q can reflect Na q Mn x M y The Na content in O2, setting q in these ranges not only makes Na q Mn x M y O2 provides sodium ions, reducing the consumption of active sodium contained in the positive electrode active material during the initial charge and discharge process of the battery, which is beneficial to increasing the capacity of the positive electrode sheet and improving the battery cycle performance; and it can make the sodium supplement have good structural stability after sodium removal.

[0055] In some embodiments, 0.15≤x<0.45, optionally, 0.2≤x≤0.44. For example, x can be selected from any one of 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.44 or a range of values ​​between any two of them. x can reflect Na q Mn x M y Mn content in O2, Na q Mn x M y Mn in O2 includes unstable Mn 3+ , setting x in the above range can make Na q Mn x M y O2 contains enough Mn 3+ , making Na q Mn x M yThe structure of O2 is relatively unstable and can easily release sodium, which is beneficial for achieving the effect of sodium supplementation. In addition, Mn has different valence states in different structures and can adapt to different Na contents. In other words, it can change its valence state to allow Na q Mn x M y Adding more Na to O2 will help increase the Na q Mn x M y The Na content in O2 is beneficial to increase the capacity of the positive electrode and improve the battery cycle performance.

[0056] In some embodiments, y>0, optionally, 0.5≤y≤0.8. For example, y can be selected from any one of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or a range of values ​​between any two of them. q Mn x M y The transition metal M content in O2. q Mn x M y O2 with an appropriate amount of M helps to increase Na q Mn x M y The structural stability of O2 makes Na q Mn x M y O2 does not undergo serious structural collapse during the desodiumization process.

[0057] In some embodiments, M includes one or more of Fe, Ni, Co, Cu, Al, Ti, and V. Alternatively, M includes at least one of Fe and Ni. These transition metals contribute to increasing Na q Mn x M y Structural stability of O2.

[0058] In some embodiments, M includes Fe and Ni, and the sodium supplement includes Na q Mn x Ni y1 Fe y2 O2, 1≤q≤1.2, 0.15≤x<0.45, y1>0, y2>0, 0.9≤x+y1+y2≤1. The transition metal uses a combination of Ni and Fe to form a stable metal layer structure with Mn; and studies have shown that the combination of Ni and Fe is beneficial to improving the energy density of the material.

[0059] In some embodiments, y1>0, optionally, 0.3≤y1≤0.44, for example, y1 can be any point value of 0.3, 0.35, 0.4, 0.44 or a range value between any two of them. y2>0, optionally, 0.24≤y2≤0.34, for example, y2 can be any point value of 0.24, 0.25, 0.3, 0.34 or a range value between any two of them. Combining Ni and Fe in a certain ratio is conducive to better structural stability and energy density improvement.

[0060] In some embodiments, the phase structure of the sodium supplementing agent includes an O3 phase. q Mn x M y O2 is a layered oxide, which is composed of TO6 (in the present embodiment, T includes Mn and transition metal element M) layered structures. + Insertion and extraction between layers of TO6 stack. + The phase structure of layered oxides can be divided into O phase and P phase due to the different coordination environments. O represents Na + It is octahedral coordination, Na + Occupies octahedral sites; P represents Na + It is a prismatic coordination, Na + Occupies triangular prism points. In the crystal structure, Na + The TO6 structure is connected in an edge-sharing manner in the O phase and in a face-sharing and edge-sharing manner in the P phase.

[0061] According to the stacking order of the oxygen layers, the layered oxides can be further divided into P2 phase, O2 phase, P3 phase and O3 phase, where the stacking method of P2 is ABBA, the stacking method of O2 is ABAC (or ABCB), the stacking method of P3 is ABBCCA, and the stacking method of O3 is ABCABC. The numbers "2" and "3" represent the number of transition metal layers of different types of O stacking in each unit.

[0062] The phase structure can be obtained by X-ray diffraction analysis. For example, an X-ray powder diffractometer is used to test the sample to obtain the X-ray diffraction spectrum of the sample. The phase structure of the sample can be confirmed by comparing the XRD diffraction peaks in the X-ray diffraction spectrum with the standard card of the XRD analysis software.

[0063] In different phase structures, Na + The phase structure of the sodium supplement in the embodiment of the present application includes an O3 phase, which is a phase structure with a high sodium content, and thus is conducive to the sodium supplement providing a large amount of sodium.

[0064] In some embodiments, the Dv50 of the sodium supplement is 6% to 75% of the Dv50 of the positive electrode active material, and optionally 6% to 25%. For example, the Dv50 of the sodium supplement is 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% of the Dv50 of the positive electrode active material, or any range between two of them. Setting the particle size of the sodium supplement to be smaller than the particle size of the positive electrode active material can make the sodium supplement have a higher reaction activity than the positive electrode active material, and have faster kinetics during the first cycle of charging and the early cycle of the battery, so that it can preferentially release sodium ions than the positive electrode active material to provide for the formation of the SEI film, thereby reducing the consumption of active sodium in the positive electrode active material and improving the cycle performance of the battery. At the same time, when there is a certain difference between the sodium supplement Dv50 and the positive electrode active material Dv50, the battery can exhibit better cycle performance.

[0065] In some embodiments, the Dv50 of the sodium supplement is 0.5 μm to 6 μm, optionally 1 μm to 3 μm, for example, it can be any point value of 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm or any range value between two thereof. At this particle size, the sodium supplement has a high specific surface area, a high specific surface energy, and a short sodium transmission path, which is conducive to improving its reaction activity and promoting sodium removal.

[0066] In some embodiments, the mass ratio of the sodium supplement to the positive electrode active material is 1: (14-95), optionally 1: (18-46.5), for example, the mass ratio of the two can be 1: 14, 1: 20, 1: 25, 1: 30, 1: 35, 1: 40, 1: 45, 1: 50, 1: 55, 1: 60, 1: 65, 1: 70, 1: 75, 1: 80, 1: 85, 1: 90, 1: 95, any one point value or any range value between the two. The mass ratio of the sodium supplement to the positive electrode active material has an effect on the cycle performance of the sodium ion battery. At the above mass ratio, the sodium ion battery exhibits excellent cycle performance.

[0067] In some embodiments, the mass content of the sodium supplement in the active layer contained in the positive electrode plate is 1% to 6%, optionally 2% to 5%, for example, it can be any one of 1%, 2%, 3%, 4%, 5%, 6% or a range between any two. Adding a small amount of the sodium supplement of the embodiment of the present application to the active layer contained in the positive electrode plate can effectively achieve the sodium supplement effect and improve the battery cycle performance.

[0068] In some embodiments, the Dv50 of the positive electrode active material is 6μm to 20μm, optionally 6μm to 10μm, for example, it can be any point value of 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm or any range value between two of them. At this particle size, the reaction activity of the positive electrode active material is lower than that of the sodium supplement, and it can slowly release sodium ions during the early charge and discharge process of the battery without preferentially releasing sodium ions, thereby slowing down the consumption of active sodium in the positive electrode active material. Moreover, the positive electrode active material and the sodium supplement are compounded with large and small particle sizes, and the small particle size sodium supplement can be filled between the large particle size positive electrode active materials, which is beneficial to increase the compaction density of the positive electrode sheet, thereby increasing the energy density of the positive electrode sheet.

[0069] In some embodiments, the positive electrode active material may include one or more of a layered oxide, a polyanion compound, and a Prussian blue compound. For example, the layered oxide may include Na m M 1 z O2, 0.4≤m≤0.9, optionally 0.8≤m≤0.9; 0.9≤z≤1, M 1 Including transition metal elements. For example, m can be any point value among 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or any range value between two of them; z can be any point value among 0.9, 0.92, 0.94, 0.96, 0.98, 1 or any range value between two of them; M 1 Including one or more of Fe, Mn, Ni, Co, Cr, Sc, Ti, V, Cr, Cu, Zn. Optionally, the layered oxide may include Na m1 Mn z1 M z2 O2, 0.8≤m1≤0.9, 0.09<z1<0.45, 0.9≤z1+z2≤1. For example, the layered oxide may include Na 0.7 CoO2、Na 0.6 MnO2、Na 0.44 MnO2、Na 0.65 Mn 0.75 Ni 0.25 O2、Na 0.78 Ni 0.23 Mn 0.69 O2、Na 0.67 Mn 0.67 Ni 0.33 O2、Na 0.82 Mn 0.33 Ni 0.33 Fe 0.33 O2, etc.

[0070] Polyanionic compounds can be sodium ions, transition metal ions and tetrahedral (YO4) n- A class of compounds with anionic units; or, polyanionic compounds can be compounds with sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions, wherein the halogen includes one or more of F, Cl, and Br; or, the polyanion compound may be a compound having sodium ions, tetrahedral (YO4) n- Anion unit, polyhedral unit (ZO y ) n1+ and a class of compounds containing an optional halogen anion. Wherein the transition metal and Z can independently include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y includes one or more of P, S, and Si, and n represents (YO4) n- The valence state, n1 represents (ZO y ) n1+ For example, the polyanion compound may include one or more of phosphate, pyrophosphate, sulfate, and anion-doped compounds, such as one or more of olivine-type NaFePO4, Na2FeP2O7, NaFePO4F, Na3V2(PO4)3, and NaFeSO4.

[0071] Prussian blue compounds can be compounds having sodium ions, transition metal ions and cyanide ions (CN-), wherein the transition metal includes one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, Prussian blue compounds can include Na a M 2 b [M 3 c (CN)6] d , 0<a≤2, 0<b≤1, 0<c≤1, 0.8≤d≤1, M 2 、M 3 Each independently includes a transition metal element. For example, a can be any point value of 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2 or a range of values ​​between any two of them; b can be any point value of 0.2, 0.4, 0.6, 0.8, 1 or a range of values ​​between any two of them; c can be any point value of 0.2, 0.4, 0.6, 0.8, 1 or a range of values ​​between any two of them; d can be any point value of 0.8, 0.85, 0.9, 0.95, 1 or a range of values ​​between any two of them; M 2 、M 3It can include one or more of Ni, Cu, Fe, Mn, Co, and Zn independently. For example, Prussian blue compounds can include Na 0.61 Fe[Fe(CN)6] 0.94 , BR-FeHCF, Na 1.48 Ni[Fe(CN)6] 0.89 、NaNi 0.05 Mn 0.95 [Fe(CN)6] or more.

[0072] The positive electrode sheet of the embodiment of the present application is suitable for various positive electrode active materials, and can improve the structural damage of these positive electrode active materials during the battery cycle process, thereby improving the cycle performance of the battery.

[0073] In some embodiments, the mass content of the positive electrode active material in the active layer contained in the positive electrode sheet is 80% to 98%, for example, it can be any point value of 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98% or any range value between two of them. The positive electrode active material is the main substance participating in the electrochemical reaction in the positive electrode sheet and provides capacity. It can be understood that the high mass content of the positive electrode active material in the positive electrode active layer will be beneficial to improve the energy density of the positive electrode sheet.

[0074] In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm 3 ~4g / cm 3 , optionally 2.6 g / cm 3 ~3.3g / cm 3 , for example, it can be 2.5g / cm 3 , 2.6g / cm 3 , 2.8g / cm 3 , 3g / cm 3 、3.2g / cm 3 、3.4g / cm 3 , 3.5g / cm 3 、3.6g / cm 3 、3.8g / cm 3 , 4g / cm 3Any point value in or the range value between any two of them. The compaction density is the density of the product under a certain pressure. For the positive electrode sheet, its compaction density = surface density / (thickness of the positive electrode sheet after compaction - thickness of the current collector). The compaction density can refer to relevant standards, such as Appendix L "Test Method for Powder Compacted Density" in GB / T 24533-2019, and is obtained by testing with a compaction density meter. The compaction density has an impact on the energy density, electrolyte wetting performance, sodium ion transmission rate, etc. of the positive electrode sheet. The greater the compaction density, the higher the mass of the positive electrode active material and the sodium supplement per unit volume, which is beneficial to improve the energy density of the positive electrode sheet. At the same time, the compaction density also reflects the porosity of the electrode sheet. At a suitable porosity, the electrode sheet has good electrolyte wetting performance, which facilitates the transmission of sodium ions. The positive electrode sheet of the embodiment of the present application has a suitable compaction density, which is not only beneficial to improving the energy density of the electrode sheet, but also beneficial to improving the electrolyte wetting performance of the electrode sheet and accelerating the transmission of sodium ions.

[0075] In addition, the positive electrode plate usually also includes a conductive agent, a binder, and a positive current collector. The conductive agent, the binder, the above-mentioned sodium supplement, and the positive active material form the active layer of the positive electrode plate, and the active layer is arranged on at least one surface of the positive current collector. The conductive agent is used to collect microcurrents between the active materials and between the active materials and the positive current collector to improve the electronic conductivity. At the same time, the conductive agent can also promote the infiltration of the electrolyte into the positive electrode plate. The binder can increase the bonding strength between the substances in the active layer and between the active layer and the positive current collector. The positive current collector is used to transmit electrons.

[0076] Optionally, the mass content of the conductive agent in the active layer contained in the positive electrode plate is 0.5% to 5%, optionally 1% to 5%, for example, any point value among 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range value between any two of them, and can also be set to other contents as needed.

[0077] The conductive agent may include, but is not limited to, one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0078] Optionally, the mass content of the binder in the active layer contained in the positive electrode plate is 0.5% to 5%, optionally 1% to 7%, for example, any point value among 0.5%, 1%, 2%, 3%, 4%, 5% or a range value between any two of them, and can also be set to other contents as needed.

[0079] The binder may include, but is not limited to, one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0080] In the embodiment of the present application, the positive electrode current collector may include but is not limited to a metal current collector, a carbon current collector, a conductive resin current collector, a composite current collector of metal and resin, etc., more specifically, aluminum, copper, nickel, titanium, iron and their respective alloys, stainless steel, carbon fiber, carbon nanotube (CNT), graphite, etc. Optionally, the positive electrode current collector includes aluminum.

[0081]

Preparation method of positive electrode sheet

[0082] The positive electrode sheet of the embodiment of the present application can be prepared by the following preparation method, including:

[0083] Prepare a positive electrode slurry containing a sodium supplement and a positive electrode active material, apply the positive electrode slurry on at least one surface of a current collector, and obtain a positive electrode sheet after drying and compacting;

[0084] Sodium supplements contain Na q Mn x M y O2, 1≤q≤1.2, 0.15≤x<0.45, y>0, 0.9≤x+y≤1, M includes transition metal elements; Dv50 of the sodium supplement is less than Dv50 of the positive electrode active material.

[0085] By adding Na q Mn x M y O2, and Dv50 is less than the sodium supplement of the positive electrode active material. On the one hand, Na q Mn x M y Due to the structural instability of O2, it is used as an active sodium source consumed in the formation of a solid electrolyte interface film, thereby reducing the consumption of active sodium contained in the positive electrode active material during the first cycle of charging, improving the structural damage of the positive electrode active material, and is beneficial to improving the cycle performance of the battery; on the other hand, small-particle sodium supplements have higher reaction activity than large-particle positive electrode active materials, and have faster kinetics during the first cycle of charging and the early cycle of the battery. Therefore, they can release sodium ions preferentially compared to the positive electrode active material to provide for the formation of the SEI film, further reducing the consumption of active sodium in the positive electrode active material and improving the cycle performance of the battery.

[0086] More specifically, the positive electrode sheet can be made as follows:

[0087] The sodium supplement agent, the positive electrode active material, the conductive agent, the binder (optionally, a thickener or other additives may be added as needed) and the solvent are mixed to obtain a positive electrode slurry;

[0088] The positive electrode slurry is coated on at least one surface of the current collector, and after drying and compacting, a positive electrode sheet is obtained.

[0089] The solvent may include but is not limited to N-methylpyrrolidone (NMP). The compaction method may include one or more of hot pressing and cold pressing. The pressure used in the compaction step may be determined according to the target compaction density.

[0090] In addition, the sodium supplement in the embodiment of the present application can be prepared by a solid phase method or other methods. For example, the sodium supplement can be prepared by referring to the following method:

[0091] According to Na q Mn x M y The atomic ratio of O2 is determined by calcining the Na source, Mn source and M source together.

[0092] By using the solid phase method, various raw materials are calcined together to obtain Na q Mn x M y O2, the preparation method is simple and suitable for large-scale production.

[0093] Wherein, the temperature of calcination treatment is 600 ℃~1200 ℃, for example, it may include but not limited to any one of 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃ or any range between two values. The holding time at the temperature of calcination treatment is 5h~24h, for example, it may include but not limited to any one of 5h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h or any range between two values. The temperature of calcination treatment and the holding time at this temperature can be directly set and controlled on the calcination equipment, such as muffle furnace. At the appropriate calcination temperature and time, each raw material can be fully melted, mixed and reacted to form a composite metal oxide of Na, Mn and M.

[0094] The above calcination treatment step can be carried out in air or oxygen atmosphere.

[0095] Before the calcination step, a step of mixing the Na source, the Mn source and the M source may be included. The mixing method includes but is not limited to one or more of mechanical stirring, grinding and ball milling to fully mix the raw materials and reduce the particle size of the materials.

[0096] After the calcination step, a crushing step may be further included to allow the sodium supplementer to have a desired particle size.

[0097] In the preparation method of the sodium supplement, the Na source, the Mn source and the M source can be selected independently from their respective soluble compounds or insoluble compounds. For example, the specific types of each raw material can be selected from the following compounds:

[0098] The Na source includes but is not limited to one or more of Na2CO3, NaHCO3, NaOH, Na2O2 and other sodium salts;

[0099] The Mn source includes but is not limited to one or more of Mn2O3, Mn3O4, MnO, and MnO2;

[0100] The M source includes, but is not limited to, one or more of an oxide containing M, a hydroxide containing M, a carbonate containing M, and a bicarbonate containing M.

[0101]

Sodium ion secondary battery

[0102] The positive electrode sheet containing the specific sodium supplement can be used to make a sodium ion secondary battery (hereinafter referred to as a secondary battery).

[0103] A second aspect of an embodiment of the present application provides a secondary battery, which includes the positive electrode plate of the first aspect.

[0104] According to different packaging forms, secondary batteries are divided into battery cells, battery modules, and battery packs. The secondary battery of the embodiment of the present application may include one or more of the battery cells, battery modules, and battery packs.

[0105] The positive electrode plate contains a sodium supplement with a special structure, and the sodium supplement is combined with the positive electrode active material according to a specific particle size. After the positive electrode plate is applied to a secondary battery, it is beneficial to improve the cycle performance of the secondary battery.

[0106] Generally, a secondary battery also includes a negative electrode plate, an electrolyte, a separator, an outer package or other components. The components of a secondary battery are described below.

[0107] 1. Negative electrode

[0108] In a secondary battery, the negative electrode plate is usually isolated from the positive electrode plate (usually by a separator). The negative electrode plate includes a negative electrode current collector and optionally a negative electrode active layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active layer contains a negative electrode active material.

[0109] The negative electrode current collector may include but is not limited to a metal or a composite current collector. For example, as the metal, sodium, sodium alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. may be used. In the case of using sodium or sodium alloy as the negative electrode current collector, since sodium or sodium alloy itself can also be used as a negative electrode active material, the negative electrode plate may not contain a negative electrode active layer, and sodium or sodium alloy is both a current collector and a negative electrode active material.

[0110] The composite current collector may include a composite material of a polymer material and a metal, wherein the polymer material may include but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc., and the metal may include but is not limited to sodium, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy. The composite current collector may be obtained by mixing a polymer material and a metal, or may be coated on at least one side of the polymer material by electroplating, coating or other methods.

[0111] In the case where the negative electrode plate includes a negative electrode active layer, the negative electrode active material in the negative electrode active layer may include but is not limited to a mixture or composite material formed by any one or more of carbon-based materials, alloy materials, titanium-based materials, and sodium metal. Among them, carbon-based materials include but are not limited to one or more of graphite, soft carbon, hard carbon, carbon microspheres, and carbon fibers; alloy materials include but are not limited to one or more of sodium-tin alloy, sodium-germanium alloy, and sodium-antimony alloy; titanium-based materials include but are not limited to one or more of titanium dioxide, titanate, and titanium phosphate.

[0112] The mass content of the negative electrode active material in the negative electrode active layer can be set to 85% to 98%, such as 95% to 98%, for example, any one of 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or a range between any two of them.

[0113] The negative electrode active layer may also include one or more of a conductive agent and a binder. The conductive agent is used to collect microcurrents between active materials and between active materials and current collectors to improve electronic conductivity. The conductive agent can also promote the infiltration of electrolyte into the negative electrode sheet. The binder can improve the bonding strength between the various substances in the active layer and between the active layer and the current collector.

[0114] The mass content of the conductive agent in the negative electrode active layer can be set to 0.5% to 10%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range between any two of them, and can also be set to other contents as needed.

[0115] The conductive agent includes one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0116] The mass content of the binder in the negative electrode active layer is 0.5% to 10%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range between any two of them, and can also be set to other contents as needed.

[0117] The binder includes, but is not limited to, one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0118] The negative electrode active layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). The mass content of the thickener in the positive electrode active layer may be set to 0.5% to 5%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any range between two of them.

[0119] When the current collector is the negative electrode active material, the current collector can be cut into pieces to form a negative electrode sheet.

[0120] In the case where the negative electrode sheet includes a negative electrode active layer, the negative electrode active material can be coated on at least one side of the current collector by physical vapor deposition, chemical vapor deposition, electroplating, etc. Alternatively, the negative electrode sheet can be formed by processes such as slurrying, coating, drying, and compacting. For example, the negative electrode active material, the conductive agent, the binder (optionally, other additives can be added as needed) are mixed with a solvent to obtain a negative electrode slurry; the negative electrode slurry is coated on the current collector, dried, and compacted to obtain a negative electrode sheet. The solvent may include, but is not limited to, N-methylpyrrolidone (NMP). The compaction method may include one or more of hot pressing and cold pressing. The pressure used in the compaction step can be determined according to the target compaction density.

[0121] 2. Electrolytes

[0122] The secondary battery also includes an electrolyte solution, and the positive electrode plate and the negative electrode plate are in contact with the electrolyte independently. The electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate. The electrolyte can be liquid, gel or all-solid.

[0123] For example, the electrolyte may be an electrolyte solution including an electrolyte sodium salt and a solvent.

[0124] The electrolyte sodium salt includes one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, sodium sulfide, sodium chloride, sodium fluoride, sodium sulfate, sodium carbonate, sodium phosphate, sodium nitrate, sodium difluorooxalatoborate, sodium pyrophosphate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, trisodium citrate, sodium metaborate, sodium borate, sodium molybdate, sodium tungstate, sodium bromide, sodium nitrite, sodium iodate, sodium iodide, sodium silicate, sodium ligninsulfonate, sodium oxalate, sodium aluminate, sodium methanesulfonate, sodium acetate, sodium dichromate, sodium hexafluoroarsenate, sodium tetrafluoroborate, sodium perchlorate, and sodium trifluoromethanesulfonylimide.

[0125] The solvent includes one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl ether (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, 2,2,2,2-trifluoroethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, trifluoroethyl methyl carbonate (FEMC), dioxolane (DOL), acetonitrile (AN), fluorobenzene, triethyl phosphate (TEP), sulfolane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfoxide, and N,N-dimethylacetamide.

[0126] The electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high or low temperature performance of the secondary battery, and the like.

[0127] 3. Isolation film

[0128] The secondary battery also includes a separator, which is arranged between the positive electrode and the negative electrode to separate the positive and negative electrodes. The separator prevents electrons in the secondary battery from passing freely, preventing short circuits between the electrodes, but allows ions in the electrolyte to pass freely between the positive electrode and the negative electrode.

[0129] The isolation membrane can be a porous structure isolation membrane with electrochemical stability and mechanical stability, such as a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0130] 4. Outer packaging

[0131] The secondary battery may include an outer package that can be used to package an electrode assembly including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0132] The outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.; or a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0133] The outer packaging shape of the secondary battery can be cylindrical, square or other arbitrary shapes. For example, Figure 1 As an example, the secondary battery has a square outer package shape.

[0134] Reference Figure 2 The outer package may include a shell 01 and a cover plate 02. The shell 01 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 01 has an opening connected to the receiving cavity, and the cover plate 02 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 03 through a winding process or a lamination process. One or more electrode assemblies 03 are encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 03.

[0135] 5.Battery cells, battery modules, battery packs

[0136] The secondary battery of the embodiment of the present application includes one or more of a battery cell, a battery module, and a battery pack.

[0137] According to the different packaging forms, secondary batteries can be divided into battery cells, battery modules, and battery packs. Among them, the battery cell is the most basic unit of the secondary battery, including an electrode assembly and an electrolyte. The electrode assembly usually includes a positive electrode sheet, a negative electrode sheet, a lithium supplement electrode, and a separator. The positive electrode sheets and the negative electrode sheets are alternately stacked, and a separator is set between the positive electrode sheets and the negative electrode sheets to play an isolation role, to obtain a bare cell, or a bare cell after winding. The bare cell is placed in an outer package, injected with electrolyte, and packaged to obtain a battery cell.

[0138] One or more battery cells are integrated to form a battery module, which can provide higher voltage and capacity, and have output with specific functions. One or more battery modules are installed in the battery box, and a battery management system is usually added to form a battery pack. The battery pack is usually a product provided to users. Alternatively, one or more battery cells can be directly installed in the box to form a battery pack.

[0139] refer to Figure 3, which is an example of a battery module. In the battery module, multiple battery cells 04 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other way. Further, the multiple battery cells 04 can be fixed by fasteners.

[0140] Optionally, the battery module may further include a housing having a receiving space, and a plurality of battery cells 04 are received in the receiving space.

[0141] refer to Figure 4 and Figure 5 , which is used as an example of a battery pack. The battery pack may include a battery box and a plurality of battery modules 05 disposed in the battery box. The battery box includes an upper box body 06 and a lower box body 07, and the upper box body 06 can be covered on the lower box body 07 to form a closed space for accommodating the battery modules 05. The plurality of battery modules 05 can be arranged in the battery box in any manner.

[0142]

Electrical devices

[0143] An embodiment of the present application further provides an electrical device, which includes the secondary battery mentioned above.

[0144] The secondary battery disclosed in the embodiment of the present application can be used in electrical devices that use the secondary battery as a power source, or various energy storage systems that use the secondary battery as an energy storage element, to provide electrical energy. The secondary battery has good cycle performance, so the use of the secondary battery can stably provide electrical energy to various electrical devices, improving the user experience of various electrical devices.

[0145] The electric device may include but is not limited to mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, the electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and the spacecraft may include airplanes, rockets, space shuttles and spacecraft, etc. As the electric device, a battery cell, a battery module or a battery pack in a secondary battery may be selected according to its use requirements.

[0146] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0147] The following detailed description of the embodiments of the present application is given. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

[0148] Example 1

[0149]

Positive electrode

[0150] This embodiment provides a positive electrode plate, the active layer of which contains a sodium supplement Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2 and positive electrode active material Na 0.82 Mn 0.33 Ni 0.33 Fe 0.33 O2. Among them, the Dv50 of the sodium supplement is 2 μm, and the mass content of the sodium supplement in the active layer is 3%; the Dv50 of the positive electrode active material is 8 μm, and the mass content of the positive electrode active material in the active layer is 92% (the mass ratio of the sodium supplement to the positive electrode active material = 3:92 = 1:30.7).

[0151] The method for preparing the positive electrode sheet comprises the following steps:

[0152] The positive electrode active material, sodium supplement, binder (polyvinylidene fluoride, PVDF) and conductive agent (conductive carbon) were fully stirred and mixed in a solvent (N-methylpyrrolidone, NMP) to obtain a positive electrode slurry. The mass ratio of the positive electrode active material, sodium supplement, binder and conductive agent was 92:3:2:3. The positive electrode slurry was coated on the current collector (aluminum foil), dried and cold pressed to obtain a compaction density of 3g / cm 3 The positive electrode.

[0153] Sodium-ion battery

[0154] In this embodiment, the positive electrode sheet is used to assemble a sodium ion battery. The sodium ion battery comprises the positive electrode sheet, a negative electrode sheet, a separator, an electrolyte, and the like.

[0155] (1) Electrolyte

[0156] 1 mol / L NaPF6 solution was used as the electrolyte, and the solvents included: ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate FEC = 47.5:47.5:5 (volume ratio).

[0157] (2) Negative electrode

[0158] The negative electrode active material (hard carbon), conductive agent (conductive carbon), and binder (carboxymethyl cellulose, CMC) are fully stirred and mixed in deionized water to obtain a negative electrode slurry. The mass ratio of the negative electrode active material, conductive agent, and binder is 95:2:3. The negative electrode slurry is coated on the current collector (copper foil), dried, and cold pressed to obtain a negative electrode sheet.

[0159] (3) Isolation film

[0160] Glass fiber film is used as the isolation membrane.

[0161] (4) Sodium ion battery

[0162] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and the electrode assembly is formed after winding. The electrode assembly is placed in a packaging shell, and after adding electrolyte, it is sealed, formed and left to stand.

[0163] Example 2

[0164] The difference between this embodiment and embodiment 1 is that the sodium supplement Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2 replaced by Na 1.2 Mn 0.2 Ni 0.44 Fe 0.34 O2.

[0165] Example 3

[0166] The difference between this embodiment and embodiment 1 is that the sodium supplement Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2 replaced by NaMn 0.44 Ni 0.3 Fe 0.24 O2.

[0167] Example 4

[0168] The difference between this embodiment and embodiment 1 is that the Dv50 of the sodium supplement is 0.5 μm.

[0169] Example 5

[0170] The difference between this embodiment and embodiment 1 is that the Dv50 of the sodium supplement is 6 μm.

[0171] Example 6

[0172] The difference between this embodiment and embodiment 1 is that in the positive electrode plate, the total mass content of the sodium supplement and the positive electrode active material in the active layer is kept unchanged, and the mass content of the sodium supplement in the active layer is set to 1% (the mass ratio of the sodium supplement to the positive electrode active material = 1:94).

[0173] Example 7

[0174] The difference between this embodiment and embodiment 1 is that in the positive electrode plate, the total mass content of the sodium supplement agent and the positive electrode active material in the active layer is kept unchanged, and the mass content of the sodium supplement agent in the active layer is set to 2% (the mass ratio of the sodium supplement agent to the positive electrode active material = 2:93 = 1:46.5).

[0175] Example 8

[0176] The difference between this embodiment and embodiment 1 is that in the positive electrode plate, the total mass content of the sodium supplement agent and the positive electrode active material in the active layer is kept unchanged, and the mass content of the sodium supplement agent in the active layer is set to 5% (the mass ratio of the sodium supplement agent to the positive electrode active material = 5:90 = 1:18).

[0177] Example 9

[0178] The difference between this embodiment and embodiment 1 is that in the positive electrode plate, the total mass content of the sodium supplement agent and the positive electrode active material in the active layer is kept unchanged, and the mass content of the sodium supplement agent in the active layer is set to 6% (the mass ratio of the sodium supplement agent to the positive electrode active material = 6:89 = 1:14.8).

[0179] Comparative Example 1

[0180] The difference between this comparative example and Example 1 is that the positive electrode plate does not contain a sodium supplement.

[0181] Comparative Example 2

[0182] The difference between this comparative example and Example 1 is that the sodium supplement Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2 replaced by Na 0.7 Mn 0.09 Ni 0.6 Fe 0.24 O2.

[0183] Comparative Example 3

[0184] The difference between this comparative example and Example 1 is that the sodium supplement Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2 replaced by Na 1.1 Mn 0.5 Ni0.3 Fe 0.19 O2.

[0185] Comparative Example 4

[0186] The difference between this embodiment and embodiment 1 is that the Dv50 of the sodium supplement is 10 μm.

[0187] The capacity, initial efficiency, and cycle performance of the sodium ion batteries of the embodiments and comparative examples were tested, and the results are shown in Tables 1 to 3 below.

[0188] Table 1. Electrochemical performance test results using different sodium supplements

[0189] (Sodium supplement Dv50 = 2 μm, positive electrode active material Dv50 = 8 μm, mass ratio of sodium supplement to positive electrode active material = 1:30.7)

[0190]

[0191] Table 1 shows that compared with the case where no sodium supplement is added to the positive electrode plate (Comparative Example 1), Examples 1 to 3 add 3% (mass ratio of sodium supplement to positive electrode active material = 1:30.7) of Na with Dv50 = 2 μm to the active layer of the positive electrode plate. 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2、Na 1.2 Mn 0.2 Ni 0.44 Fe 0.34 O2、NaMn 0.44 Ni 0.3 Fe 0.24 O2, as a sodium supplement, can make the sodium ion battery show good cycle performance. After 300 cycles, the capacity retention rate is as high as 86.8% to 89.2%; at the same time, the sodium ion battery also shows a high first efficiency. The test data shows that the addition of a suitable sodium supplement to the positive electrode plate can well realize the sodium supplement function, reduce the sodium loss of the positive electrode active material during the first cycle of charge and discharge (manifested as a high first efficiency), and is beneficial to improve the battery cycle performance. Moreover, it can be seen from the comparison that after adding a suitable sodium supplement to the positive electrode plate in Examples 1 to 3, the discharge capacity and first efficiency of the sodium ion battery are similar to those without the addition of the sodium supplement, and even improved, reflecting that these sodium supplements will not cause a decrease in the capacity and first efficiency of the sodium ion battery.

[0192] In contrast, when the elements in the sodium supplement agent used have an inappropriate ratio, for example, q and x in Comparative Example 2 are too small, that is, the ratio of Na to Mn is too small, and x in Comparative Example 3 is too large, that is, the ratio of Mn is too large, it cannot achieve the effect of sodium supplementation during the charge and discharge process of the sodium ion battery, and the cycle performance of the sodium ion battery is significantly deteriorated compared with Examples 1 to 3.

[0193] Table 2. Electrochemical performance test results of different sodium supplement particle sizes (the chemical formula of the sodium supplement is Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2, the mass ratio of sodium supplement to positive electrode active material = 1: 30.7)

[0195]

[0196] Example 1, Example 4, Example 5 and Comparative Example 4 use sodium supplements with different Dv50 in the positive electrode plate, so that the sodium ion battery exhibits different cycle performance. Combined with the Dv50 of the positive active material, it can be seen that when the Dv50 of the sodium supplement is less than the Dv50 of the positive active material (Example 1, Example 4, Example 5), the capacity retention rate of the sodium ion battery after 300 cycles is high; and when the Dv50 of the sodium supplement is greater than the Dv50 of the positive active material (Comparative Example 4), the capacity retention rate of the sodium ion battery after 300 cycles is reduced. This may be because when the Dv50 of the sodium supplement is less than the Dv50 of the positive active material, the sodium supplement with a small particle size has a higher reaction activity during the charge and discharge process, and the sodium ions it provides preferentially participate in the formation of the SEI film and other electrochemical reactions that will consume active sodium, thereby reducing the loss of active sodium in the positive active material, so that the sodium ion battery exhibits excellent cycle performance.

[0197] At the same time, when there is a certain difference between the sodium supplement Dv50 and the positive electrode active material Dv50, for example, when the sodium supplement Dv50 is 6.25% to 75% of the positive electrode active material Dv50, the capacity retention rate of the sodium ion battery after 300 cycles is above 82.7%; and when the sodium supplement Dv50 is 25% of the positive electrode active material Dv50, the capacity retention rate of the sodium ion battery is higher than other cases.

[0198] In addition, the test results show that under different sodium supplements Dv50, sodium ion batteries have higher discharge capacity and first efficiency, reflecting that these sodium supplements will not cause a decrease in the capacity and first efficiency of sodium ion batteries.

[0199] Table 3. Electrochemical performance test results at different sodium supplement dosages

[0200] (The chemical formula of sodium supplement is Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2, Dv50 = 2 μm; positive electrode active material

[0201] Dv50=8μm)

[0202]

[0203] The test results show that the amount of sodium supplement has an impact on the cycle performance of sodium ion batteries. When the mass ratio of sodium supplement to positive electrode active material is in the range of 1:(14.8-94), as the mass ratio of sodium supplement increases, the capacity retention rate of sodium ion batteries after 300 cycles increases first and then decreases; among them, when the mass ratio of sodium supplement to positive electrode active material is 1:(18-46.5), the capacity retention rate after 300 cycles is higher than other cases. Therefore, sodium ion batteries can exhibit better cycle performance by adjusting the mass ratio of sodium supplement to positive electrode active material.

[0204] Appendix: The specific test methods for the above-mentioned various properties are as follows:

[0205] (1)Dv50

[0206] Referring to GB / T 19077-2016 / ISO 13320:2009 “Particle size distribution by laser diffraction method”, Dv50 was obtained by using a laser particle size analyzer.

[0207] (2) Compacted density

[0208] Refer to Appendix L "Test method for compaction density of powders" in GB / T 24533-2019 and obtain the result by testing with a compaction density meter.

[0209] (3) Capacity, initial efficiency, and capacity retention rate

[0210] At 25°C, let the sodium ion battery stand for 30 minutes; then charge it to 4.0V at a constant current of 0.33C, then charge it to 0.05C at a constant voltage of 4.0V; then let it stand for 30 minutes; discharge it to 2V at a constant current of 0.33C, and then let it stand for 30 minutes. This is a cycle of charge and discharge. Record the charge capacity C during the first cycle of charge and discharge 10 and discharge capacity C 20 , the first effect is calculated using the formula: first effect = C 20 / C 10 ×100%.

[0211] The sodium ion battery is cycled for 300 cycles according to the above steps, and the discharge capacity C at this time is recorded. 21The capacity retention rate after 300 cycles (capacity retention rate = C 21 / C 20 ×100%).

[0212] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode plate comprises a sodium supplement and a positive electrode active material, wherein the sodium supplement comprises Na q Mn x M y O2, 1≤q≤1.2, 0.15≤x<0.45, y>0, 0.9≤x+y≤1, the M comprises a transition metal element; the Dv50 of the sodium supplement is less than the Dv50 of the positive electrode active material.

2. The positive electrode sheet according to claim 1, characterized in that: 1≤q≤1.1。 3. The positive electrode sheet according to claim 1 or 2, characterized in that: 0.2≤x≤0.44。 4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: 0.5≤y≤0.8。 5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The M includes one or more of Fe, Ni, Co, Cu, Al, Ti, and V.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The M includes Fe and Ni, and the sodium supplement includes Na q Mn x Ni y1 Fe y2 O2; 1≤q≤1.2, 0.15≤x<0.45, y1>0, y2>0, 0.9≤x+y1+y2≤1.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The phase structure of the sodium supplement includes an O3 phase.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: The Dv50 of the sodium supplement is 6% to 75% of the Dv50 of the positive electrode active material, and optionally 6% to 25%.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The Dv50 of the sodium supplement is 0.5 to 6 μm, and optionally 1 to 3 μm.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The Dv50 of the positive electrode active material is 6 to 20 μm, and optionally 6 to 10 μm.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The mass ratio of the sodium supplement to the positive electrode active material is 1:(14-94), and optionally 1:(18-46.5).

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The mass content of the sodium supplement in the active layer of the positive electrode plate is 1% to 6%, and optionally 2% to 5%.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The positive electrode active material includes one or more of a layered oxide, a polyanion compound, and a Prussian blue compound; optionally, the layered oxide includes Na m M 1 z O2, 0.4≤m≤0.9, 0.9≤z≤1, the M 1 Including transition metal elements.

14. A sodium ion secondary battery, characterized in that: The battery comprises the positive electrode sheet according to any one of claims 1 to 13.

15. An electrical device, characterized in that: The electrical device comprises the sodium ion secondary battery according to claim 14.

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