Positive electrode sheet, sodium-ion secondary battery, and electric device

Abstract

The present application relates to the technical field of batteries, and in particular, relates to a positive electrode sheet, a sodium-ion secondary battery, and an electric device. The positive electrode sheet comprises a sodium-supplementing agent and a positive electrode active material, wherein the sodium-supplementing agent includes NaqMnxMyO2, where 1≤q≤1.2, 0.15≤x＜0.45, y＞0, 0.9≤x+y≤1, and M includes a transition metal element; and Dv50 of the sodium-supplementing agent is smaller than Dv50 of the positive electrode active material. The sodium-supplementing agent NaqMnxMyO2 of the present application has relatively high structural instability and is prone to releasing sodium; and the particle size of the sodium-supplementing agent is smaller than the particle size of the positive electrode active material, such that the sodium-supplementing agent has higher reaction activity than the positive electrode active material, and can preferentially, compared with the positive electrode active material, release sodium ions, so as to participate in an electrochemical reaction, which facilitates reducing the consumption of active sodium contained in the positive electrode active material during an early-stage charging and discharging process of a battery, thereby ameliorating structural damage of the positive electrode active material and improving the cycling performance of the battery.

Description

Positive electrode sheet, sodium ion secondary battery, power device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 16, 2023, with application number 202311531803.5 and invention name “Positive electrode sheet, sodium ion secondary battery, and electrical device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of battery technology, and in particular to a positive electrode sheet, a sodium ion secondary battery, and an electrical device. Background Art

[0003] Sodium-ion batteries operate under a similar mechanism to lithium-ion batteries, primarily converting chemical energy into electrical energy through the intercalation and deintercalation of sodium ions between the positive and negative electrodes. Specifically, during charging, the positive electrode's active material releases sodium ions, which are then transported through the electrolyte and intercalated into the negative electrode's active material. During discharge, the sodium ions are then released from the negative electrode's active material and returned to the positive electrode's active material.

[0004] In practice, it is found that capacity decay and poor cycle performance are prone to occur during the charging and discharging process of sodium-ion batteries, which restricts the development of sodium-ion batteries.

[0005] Application Contents

[0006] The purpose of the embodiments of the present application is to provide a positive electrode plate, a sodium ion secondary battery, and an electrical device, aiming to solve the problem of poor cycle performance of sodium ion batteries. Technical Solutions

[0007] The technical solution adopted in the embodiment of this application is:

[0008] In a first aspect, the present invention 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.

[0009] 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 Mn3+ , 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 early charge and discharge process of the battery, Na q Mn x M y O2 serves as an active sodium source consumed in forming the 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 helping to improve the cycle performance of the battery.

[0010] At the same time, generally, small-particle materials have higher reactivity than large-particle materials. 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. Therefore, it can preferentially release sodium ions compared to the positive electrode active material to form 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.

[0011] 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 can not only make 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 and improving the battery cycle performance; and it can also make the sodium supplement have good structural stability after de-sodiumization.

[0012] 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 yThe structure of O2 is relatively unstable and easily releases sodium, which is beneficial to achieve the effect of sodium supplementation. Moreover, Mn has different valence states in different structures and can adapt to different Na contents. In other words, it can change its own valence state to allow Na q Mn x M y Adding more Na to O2 will help increase Na q Mn x M y The Na content in O2 is beneficial to increasing the capacity of the positive electrode and improving the battery cycle performance.

[0013] 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 adding 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.

[0014] In some embodiments, the M comprises one or more of Fe, Ni, Co, Cu, Al, Ti, and V. These transition metals contribute to the improvement of Na q Mn x M y Structural stability after O2 desodiumization.

[0015] 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. A transition metal combination of Ni and Fe can form a stable metal layer structure with Mn; and research has shown that the Ni-Fe combination is beneficial for improving the energy density of the material.

[0016] In some embodiments, the phase structure of the sodium supplement comprises 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.

[0017] 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.

[0018] In some embodiments, the sodium supplement has a Dv50 of 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 and high specific surface energy, and a short sodium transport path, which is beneficial to improving its reaction activity and promoting sodium removal.

[0019] 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 in large and small particle sizes, and the small-particle sodium supplement can be filled between the large-particle 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.

[0020] 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 impact on the cycle performance of the sodium ion battery. At the above mass ratio, the sodium ion battery can exhibit excellent cycle performance.

[0021] In some embodiments, the sodium supplementing agent comprises 1% to 6% by weight of the active layer of the positive electrode, and optionally 2% to 5% by weight. Adding a small amount of the sodium supplementing agent of the present invention to the active layer of the positive electrode can effectively achieve a sodium supplementation effect and improve battery cycle performance.

[0022] 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 1The positive electrode sheet of the embodiment of the present application is applicable to 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.

[0023] In a second aspect, the present application provides a sodium ion secondary battery, which includes the positive electrode sheet described in the first aspect.

[0024] 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.

[0025] In a third aspect, the present application provides an electrical device, which includes the sodium ion secondary battery described in the second aspect.

[0026] The sodium-ion secondary batteries disclosed in the embodiments of this application can be used in electrical devices that use secondary batteries as power sources, or in various energy storage systems that use batteries as energy storage elements, to provide electrical energy. These sodium-ion secondary batteries have excellent cycle performance, and therefore, can stably provide electrical energy to various electrical devices, improving the user experience of these devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or exemplary technical descriptions. 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 any creative work.

[0028] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0029] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0030] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0031] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0032] FIG5 is an exploded view of the battery pack shown in FIG4 according to an embodiment of the present application;

[0033] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0034] The accompanying drawings in the specific implementation manner are as follows:

[0035] Shell 01, cover 02, electrode assembly 03, battery cell 04, battery module 05, upper box 06, lower box 07. DETAILED DESCRIPTION

[0036] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art 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" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0038] In the description of the embodiments of this application, the technical terms "first" and "second" are used only to distinguish different objects and should not be understood to indicate or imply relative importance or implicitly specify the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0039] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0040] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0041] 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.

[0042] 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. 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.

[0043] The masses of the relevant components mentioned in the examples of this application may 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 examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the masses described in the examples of this application may be mass units known in the chemical industry, such as μg, mg, g, and kg.

[0044] Sodium-ion batteries (SIBs) have garnered widespread attention and research due to the abundance and widespread distribution of raw materials in nature. Similar to lithium-ion batteries, SIBs primarily convert chemical energy into electrical energy through the intercalation and deintercalation of sodium ions between the positive and negative electrodes. Specifically, during charging, the positive electrode's active material releases sodium ions, which are then transported through the electrolyte and intercalated into the negative electrode's active material. During discharge, sodium ions are released from the negative electrode's active material and returned to the positive electrode's active material.

[0045] 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 crystal 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.

[0046] Researchers have developed a technique to pre-sodiumize the positive or negative electrode to address this issue. This involves adding sodium powder or foil to the positive or negative electrode via roller pressing or adsorption, or by adding a pre-sodiumizing agent (sodium supplement) to the positive or negative electrode or electrolyte to compensate for lost sodium.

[0047] However, in practice, it has been found that sodium powder or sodium foil are highly reactive, have high requirements for the operating environment, and pose potential safety issues. Furthermore, most sodium replenishers have limited sodium replenishment effects during the battery's charge and discharge process. They are unable to release sodium ions before the positive electrode active material during the charge and discharge process. Therefore, the positive electrode active material is required to provide sodium ions during the initial charge and discharge process, which can also cause irreversible sodium loss in the positive electrode active material.

[0048] In order to solve 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. q Mn x M y O2, the sodium supplement contains unstable Mn 3+ , making Na q Mn x M y O2 has a highly unstable structure and is prone to releasing sodium. Furthermore, the sodium supplement has a smaller particle size than the positive electrode active material, resulting in a higher reactivity than the positive electrode active material, allowing it to preferentially release sodium ions to participate in electrochemical reactions. Therefore, this sodium supplement reduces the consumption of active sodium in the positive electrode active material during the initial charge and discharge phases of the battery, improves the structural damage to the positive electrode active material, and contributes to improved battery cycle performance.

[0049] 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 used in various electrical devices.

[0050] The present application will be further described below with reference to the following examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0051]

Positive electrode

[0052] In a first aspect, the present application provides a positive electrode plate, which 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, M includes a transition metal element; the Dv50 of the sodium supplement is less than the Dv50 of the positive electrode active material.

[0053] 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 transmission 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 types of elements, contents and proportions 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 by conversion.

[0054] 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 in the total amount. 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 "Particle Size Distribution Laser Diffraction Method". 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.

[0055] 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 early charge and discharge process of the battery, Na q Mn x M yO2 serves as an active sodium source consumed in forming the 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 helping to improve the cycle performance of the battery.

[0056] At the same time, generally, small-particle materials have higher reactivity than large-particle materials. 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. Therefore, it can preferentially release sodium ions compared to the positive electrode active material to form 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.

[0057] In some embodiments, 1≤q≤1.2, optionally, 1≤q≤1.1. For example, q can be any one of 1.0, 1.1, 1.2 or a range of values ​​between the two. q Mn x M y The Na content in O2, setting q in these ranges can not only make 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 and improving the battery cycle performance; and it can also make the sodium supplement have good structural stability after de-sodiumization.

[0058] 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 easily releases sodium, which is beneficial to achieve the effect of sodium supplementation. Moreover, Mn has different valence states in different structures and can adapt to different Na contents. In other words, it can change its own valence state to allow Na q Mn x M y Adding more Na to O2 will help increase Na q Mn x M y The Na content in O2 is beneficial to increasing the capacity of the positive electrode and improving the battery cycle performance.

[0059] 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 adding 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.

[0060] 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 the improvement of Na q Mn x M y Structural stability of O2.

[0061] 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. A transition metal combination of Ni and Fe can form a stable metal layer structure with Mn; and research has shown that the Ni-Fe combination is beneficial for improving the energy density of the material.

[0062] In some embodiments, y1>0, optionally, 0.3≤y1≤0.44, for example, y1 can be any value among 0.3, 0.35, 0.4, 0.44, or a range therebetween. y2>0, optionally, 0.24≤y2≤0.34, for example, y2 can be any value among 0.24, 0.25, 0.3, 0.34, or a range therebetween. Combining Ni and Fe in a certain ratio can enhance structural stability and improve energy density.

[0063] In some embodiments, the phase structure of the sodium supplement agent includes an O3 phase. q Mn x M y O2 is a layered oxide, which is composed of TO6 (in this embodiment, T includes Mn and transition metal elements M) layered structures. + Insertion and extraction between TO6 stacked layers. + 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 triangular prism coordination (Prismatic), 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 surface-sharing and edge-sharing manner in the P phase.

[0064] Based on the stacking order of the oxygen layers, layered oxides can be further divided into P2 phase, O2 phase, P3 phase, and O3 phase. The stacking pattern of P2 is ABBA, the stacking pattern of O2 is ABAC (or ABCB), the stacking pattern of P3 is ABBCCA, and the stacking pattern of O3 is ABCABC. The numbers "2" and "3" represent the number of transition metal layers stacked with different types of O in each unit cell.

[0065] Phase structure can be determined through X-ray diffraction analysis. For example, an X-ray powder diffractometer is used to analyze a sample to obtain an X-ray diffraction spectrum. The phase structure of the sample can be confirmed by comparing the XRD diffraction peaks in the spectrum with a standard chart in the XRD analysis software.

[0066] 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.

[0067] 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 any one of 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, and 75% of the Dv50 of the positive electrode active material, or a range of values ​​therebetween. Setting the particle size of the sodium supplement to be smaller than that of the positive electrode active material can make the sodium supplement have a higher reactivity than the positive electrode active material, and have faster kinetics during the first charge and early cycle of the battery. Therefore, the sodium supplement can preferentially release sodium ions than the positive electrode active material to form 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.

[0068] In some embodiments, the sodium supplement has a Dv50 of 0.5 μm to 6 μm, optionally 1 μm to 3 μm, for example, any one 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, and 6 μm, or a range of any two thereof. At this particle size, the sodium supplement has a high specific surface area and high specific surface energy, and the sodium transport path is short, which is beneficial to improving its reactivity and promoting sodium removal.

[0069] 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 any one of 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, or a range of values ​​between any two of them. The mass ratio of the sodium supplement to the positive electrode active material has an impact on the cycle performance of the sodium ion battery. At the above mass ratio, the sodium ion battery exhibits excellent cycle performance.

[0070] In some embodiments, the mass content of the sodium supplement in the active layer of the positive electrode is 1% to 6%, optionally 2% to 5%, for example, any one of 1%, 2%, 3%, 4%, 5%, and 6%, or a range therebetween. Adding a small amount of the sodium supplement of the present invention to the active layer of the positive electrode can effectively achieve sodium supplementation and improve battery cycle performance.

[0071] 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 a range of values ​​between any two. 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 in 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.

[0072] 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.

[0073] Polyanionic compounds can be sodium ions, transition metal ions and tetrahedral (YO4) n- Alternatively, the polyanion compound may be a compound having 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, polyhedron unit (ZO y ) n1+ and 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 types, such as one or more of olivine-type NaFePO4, Na2FeP2O7, NaFePO4F, Na3V2(PO4)3, and NaFeSO4.

[0074] Prussian blue compounds can be compounds containing 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 one of 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, or a range between any two of them; b can be any one of 0.2, 0.4, 0.6, 0.8, 1, or a range between any two of them; c can be any one of 0.2, 0.4, 0.6, 0.8, 1, or a range between any two of them; d can be any one of 0.8, 0.85, 0.9, 0.95, 1, or a range 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.

[0075] The positive electrode sheet of the embodiment of the present application is applicable to 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.

[0076] In some embodiments, the mass content of the positive electrode active material in the active layer of the positive electrode sheet is 80% to 98%, for example, any one of 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, or any range therebetween. The positive electrode active material is the primary substance involved in the electrochemical reaction in the positive electrode sheet, providing capacity. Therefore, a high mass content of the positive electrode active material in the positive electrode active layer will improve the energy density of the positive electrode sheet.

[0077] In some embodiments, the compacted 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 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, its compaction density = surface density / (thickness of the positive electrode after compaction - thickness of the current collector). The compaction density can refer to relevant standards, such as Appendix L "Test method for compaction density of powders" 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. The greater the compaction density, the higher the mass of the positive electrode active material and sodium supplement per unit volume, which is beneficial to improving the energy density of the positive electrode. At the same time, the compaction density also reflects the porosity of the electrode. At a suitable porosity, the electrode has good electrolyte wetting performance, which facilitates the transmission of sodium ions. The positive electrode 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, but also beneficial to improving the electrolyte wetting performance of the electrode and accelerating the transmission of sodium ions.

[0078] In addition, the positive electrode sheet usually also contains a conductive agent, a binder, and a positive electrode current collector. The conductive agent, the binder, the above-mentioned sodium supplement, and the positive electrode active material form the active layer of the positive electrode sheet, and the active layer is arranged on at least one surface of the positive electrode current collector. The conductive agent is used to collect microcurrents between the active materials and between the active materials and the positive electrode 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 sheet. The binder can improve the bonding strength between the various substances in the active layer and between the active layer and the positive electrode current collector. The positive electrode current collector is used to transmit electrons.

[0079] 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 one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of them, and can also be set to other contents as needed.

[0080] 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.

[0081] Optionally, the mass content of the binder in the active layer contained in the positive electrode sheet is 0.5% to 5%, optionally 1% to 7%, for example, any one of 0.5%, 1%, 2%, 3%, 4%, 5% or a range between any two of them, and can also be set to other contents as needed.

[0082] 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, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0083] In the embodiments 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, and more specifically, aluminum, copper, nickel, titanium, iron, and their respective alloys, stainless steel, carbon fiber, carbon nanotubes (CNTs), graphite, etc. Optionally, the positive electrode current collector includes aluminum.

[0084]

Preparation method of positive electrode sheet

[0085] The positive electrode sheet of the embodiment of the present application can be prepared by the following preparation method, including:

[0086] 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;

[0087] 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 a transition metal element; the Dv50 of the sodium supplement is less than the Dv50 of the positive electrode active material.

[0088] 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 for the formation of the 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.

[0089] More specifically, the positive electrode sheet can be made as follows:

[0090] Mixing the sodium supplement, the positive electrode active material, the conductive agent, the binder (optionally, a thickener or other additives may be added as needed) with a solvent to obtain a positive electrode slurry;

[0091] The positive electrode slurry is coated on at least one surface of the current collector, dried and compacted to obtain a positive electrode sheet.

[0092] 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.

[0093] 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:

[0094] According to Na q Mn x M y The atomic ratio of O2 is adjusted by calcining the Na source, Mn source and M source together.

[0095] By adopting 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.

[0096] Wherein, the calcination temperature is 600°C to 1200°C, for example, including but not limited to any one of 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, and 1200°C, or a range between any two thereof. The holding time at the calcination temperature is 5h to 24h, for example, including but not limited to any one of 5h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, and 24h, or a range between any two thereof. The calcination temperature and the holding time at the temperature can be directly set and controlled on a calcination device, such as a muffle furnace. At the appropriate calcination temperature and time, the raw materials can be fully melt-mixed and reacted to form a composite metal oxide of Na, Mn, and M.

[0097] The calcination step can be carried out in air or oxygen atmosphere.

[0098] 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.

[0099] After the calcination step, a crushing step may be further included to allow the sodium supplementer to have a desired particle size.

[0100] In the preparation method of the sodium supplement, the Na source, the Mn source, and the M source can be independently selected from soluble compounds or insoluble compounds. For example, the specific types of the raw materials can be selected from the following compounds:

[0101] The Na source includes but is not limited to one or more of Na2CO3, NaHCO3, NaOH, Na2O2 and other sodium salts;

[0102] The Mn source includes but is not limited to one or more of Mn2O3, Mn3O4, MnO, and MnO2;

[0103] The M source includes, but is not limited to, one or more of an M-containing oxide, an M-containing hydroxide, an M-containing carbonate, and an M-containing bicarbonate.

[0104] Sodium-ion secondary battery

[0105] The positive electrode sheet containing the specific sodium supplement can be used to make sodium ion secondary batteries (hereinafter referred to as secondary batteries).

[0106] A second aspect of an embodiment of the present application provides a secondary battery, which includes the positive electrode sheet according to the first aspect.

[0107] According to different packaging forms, secondary batteries are divided into battery cells, battery modules, and battery packs. The secondary batteries of the embodiments of the present application may include one or more of the battery cells, battery modules, and battery packs.

[0108] 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 secondary battery, it is beneficial to improve the cycle performance of the secondary battery.

[0109] Typically, a secondary battery also includes a negative electrode plate, an electrolyte, a separator, an outer packaging, or other components. The following describes the components of a secondary battery.

[0110] 1. Negative electrode

[0111] In a secondary battery, the negative electrode plate is usually separated from the positive electrode plate (usually separated by a separator). The negative electrode plate includes a negative electrode current collector and optionally includes a negative electrode active layer disposed on at least one side of the negative electrode current collector, the negative electrode active layer containing a negative electrode active material.

[0112] The negative electrode current collector may include, but is not limited to, a metal or composite current collector. For example, the metal may include sodium, sodium alloys, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, silver alloys, etc. When sodium or a sodium alloy is used as the negative electrode current collector, since the sodium or sodium alloy itself can also serve as the negative electrode active material, the negative electrode plate may not contain a negative electrode active layer. The sodium or sodium alloy serves as both the current collector and the negative electrode active material.

[0113] The composite current collector may include a composite material of a polymer and a metal. The polymer 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 alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The composite current collector may be obtained by blending the polymer and the metal, or may be coated on at least one side of the polymer by electroplating, coating, or other methods.

[0114] 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 of any one or more of a carbon-based material, an alloy material, a titanium-based material, and sodium metal. 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; and titanium-based materials include, but are not limited to, one or more of titanium dioxide, titanates, and titanium phosphates.

[0115] 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.

[0116] 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 the active materials and between the active materials and the current collector, improving electronic conductivity. It also promotes electrolyte wetting of the negative electrode. The binder improves the bonding strength between the various substances in the active layer and between the active layer and the current collector.

[0117] 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.

[0118] The conductive agent includes one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0119] 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.

[0120] 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, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0121] 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%, for example, any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, or a range therebetween.

[0122] In the case where the current collector is the negative electrode active material, the current collector can be cut into pieces to form negative electrode sheets.

[0123] 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.

[0124] 2. Electrolytes

[0125] Secondary batteries also contain an electrolyte, which is independently in contact with the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The electrolyte can be liquid, gel, or solid.

[0126] For example, the electrolyte may be an electrolyte solution including an electrolyte sodium salt and a solvent.

[0127] 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 lauryl 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 trifluoromethanesulfonyl imide.

[0128] 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.

[0129] The electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain properties of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, and additives that improve the high or low temperature performance of the secondary battery.

[0130] 3. Isolation film

[0131] Secondary batteries also include a separator, which is placed between the positive and negative electrodes to separate them. This separator blocks electrons from flowing freely within the secondary battery, preventing short circuits between the electrodes, but allows ions in the electrolyte to flow freely between the positive and negative electrodes.

[0132] 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).

[0133] 4. Outer packaging

[0134] The secondary battery may include an outer packaging that can be used to encapsulate an electrode assembly including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0135] The outer packaging of secondary batteries can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell, or a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0136] The outer package of the secondary battery can be cylindrical, square or any other shape. For example, FIG1 shows a secondary battery with a square outer package as an example.

[0137] Referring to Figure 2 , the outer packaging may include a housing 01 and a cover plate 02 . Housing 01 may include a base plate and side plates connected thereto, which together form a housing cavity. Housing 01 has an opening communicating with the housing cavity, and cover plate 02 can be positioned over the opening to seal the housing cavity. The positive electrode sheet, negative electrode sheet, and separator may be wound or laminated to form an electrode assembly 03 . One or more electrode assemblies 03 are encapsulated within the housing cavity. Electrolyte is impregnated within electrode assembly 03 .

[0138] 5.Battery cells, battery modules, and battery packs

[0139] 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.

[0140] 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 the electrode assembly and the electrolyte. The electrode assembly usually includes a positive electrode sheet, a negative electrode sheet, a lithium supplement electrode, and a separator. The positive and negative electrode sheets are alternately stacked, and a separator is set between the positive and negative electrode sheets to play an isolating role to obtain a bare cell, or a bare cell can be obtained after winding. The bare cell is placed in the outer packaging, injected with electrolyte, and packaged to obtain a battery cell.

[0141] One or more battery cells are combined to form a battery module, which can provide higher voltage and capacity, with a specific functional output. One or more battery modules are installed in a battery housing, often with a battery management system, to form a battery pack. This battery pack is typically provided to the user. Alternatively, one or more battery cells can be directly installed in a housing to form a battery pack.

[0142] Referring to Figure 3, which illustrates an exemplary battery module, multiple battery cells 04 may be arranged sequentially along the length of the module. Alternatively, they may be arranged in any other manner. Furthermore, the multiple battery cells 04 may be secured together using fasteners.

[0143] Optionally, the battery module may further include a housing having a receiving space, and the plurality of battery cells 04 are received in the receiving space.

[0144] Refer to Figures 4 and 5, which illustrate an example battery pack. The battery pack may include a battery box and multiple battery modules 05 disposed within the battery box. The battery box comprises an upper box body 06 and a lower box body 07. The upper box body 06 can be placed over the lower box body 07 to form an enclosed space for accommodating the battery modules 05. The multiple battery modules 05 can be arranged in any manner within the battery box.

[0145]

Electrical devices

[0146] An embodiment of the present application further provides an electrical device, which includes the above-mentioned secondary battery.

[0147] The secondary batteries disclosed in the embodiments of this application can be used in electrical devices that use the secondary battery as a power source, or in various energy storage systems that use the secondary battery as an energy storage element, to provide electrical energy. These secondary batteries have excellent cycle performance, and therefore, can stably provide electrical energy to various electrical devices, improving the user experience of these devices.

[0148] Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, and the like. Electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft. The electrical devices may be selected from secondary batteries, including single cells, battery modules, or battery packs, depending on their intended use.

[0149] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0150] The following embodiments of the present application are described in detail. 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. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0151] Example 1

[0152]

Positive electrode

[0153] 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. 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).

[0154] The method for preparing the positive electrode sheet comprises the following steps:

[0155] The positive electrode active material, sodium supplement, binder (polyvinylidene fluoride, PVDF) and conductive agent (conductive carbon) were thoroughly 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 a current collector (aluminum foil), dried and cold pressed to obtain a compaction density of 3g / cm 3 The positive electrode.

[0156] Sodium-ion battery

[0157] 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.

[0158] (1) Electrolyte

[0159] 1 mol / L NaPF6 solution was used as the electrolyte, and the solvent included: ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate FEC = 47.5:47.5:5 (volume ratio).

[0160] (2) Negative electrode

[0161] The negative electrode active material (hard carbon), conductive agent (conductive carbon), and binder (carboxymethyl cellulose, CMC) are thoroughly stirred and mixed in deionized water to form 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 then coated onto a current collector (copper foil), dried, and cold-pressed to form a negative electrode sheet.

[0162] (3) Isolation film

[0163] Glass fiber film is used as the isolation membrane.

[0164] (4) Sodium ion batteries

[0165] The positive electrode sheet, separator and negative electrode sheet are stacked in order and wound to form an electrode assembly. The electrode assembly is placed in a packaging shell, and after adding electrolyte, it is sealed, formed and allowed to stand.

[0166] Example 2

[0167] 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 is replaced by Na 1.2 Mn 0.2 Ni 0.44 Fe 0.34 O2.

[0168] Example 3

[0169] 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 is replaced by NaMn 0.44 Ni 0.3 Fe 0.24 O2.

[0170] Example 4

[0171] The difference between this embodiment and embodiment 1 is that the Dv50 of the sodium supplement is 0.5 μm.

[0172] Example 5

[0173] The difference between this embodiment and embodiment 1 is that the Dv50 of the sodium supplement is 6 μm.

[0174] Example 6

[0175] The difference between this embodiment and embodiment 1 is that: in the positive electrode sheet, 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 1% (the mass ratio of the sodium supplement agent to the positive electrode active material = 1:94).

[0176] Example 7

[0177] The difference between this embodiment and embodiment 1 is that: in the positive electrode sheet, 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% (mass ratio of sodium supplement agent to positive electrode active material = 2:93 = 1:46.5).

[0178] Example 8

[0179] The difference between this embodiment and embodiment 1 is that: in the positive electrode sheet, 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% (mass ratio of sodium supplement agent to positive electrode active material = 5:90 = 1:18).

[0180] Example 9

[0181] The difference between this embodiment and embodiment 1 is that: in the positive electrode sheet, 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% (mass ratio of sodium supplement agent to positive electrode active material = 6:89 = 1:14.8).

[0182] Comparative Example 1

[0183] The difference between this comparative example and Example 1 is that the positive electrode plate does not contain a sodium supplement.

[0184] Comparative Example 2

[0185] 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 is replaced by Na 0.7 Mn 0.09 Ni 0.6 Fe 0.24 O2.

[0186] Comparative Example 3

[0187] 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 is replaced by Na 1.1 Mn 0.5 Ni0.3 Fe 0.19 O2.

[0188] Comparative Example 4

[0189] The difference between this embodiment and embodiment 1 is that the Dv50 of the sodium supplement is 10 μm.

[0190] 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.

[0191] Table 1. Electrochemical performance test results using different sodium supplements (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)

[0192] Table 1 shows that compared with the case where no sodium supplement was added to the positive electrode sheet (Comparative Example 1), Examples 1 to 3 added 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 sheet. 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 improving 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.

[0193] In contrast, when the elements in the sodium supplement agent used have an inappropriate ratio, for example, in Comparative Example 2, q and x are too small, that is, the ratio of Na to Mn is too small, and in Comparative Example 3, x 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.

[0194] Table 2. Electrochemical performance test results of different sodium supplement particle sizes (the chemical formula of sodium supplement is Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2, mass ratio of sodium supplement to positive electrode active material = 1:30.7)

[0195] Example 1, Example 4, Example 5 and Comparative Example 4 used sodium supplements with different Dv50 in the positive electrode sheet, so that the sodium ion battery exhibited different cycle performance. Combined with the Dv50 of the positive electrode active material, it can be seen that when the Dv50 of the sodium supplement is less than the Dv50 of the positive electrode 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 electrode 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 electrode active material, the small particle size sodium supplement 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 electrode active material, so that the sodium ion battery exhibits excellent cycle performance.

[0196] At the same time, when there is a certain difference between the sodium supplement agent Dv50 and the positive electrode active material Dv50, for example, when the sodium supplement agent 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 agent Dv50 is 25% of the positive electrode active material Dv50, the capacity retention rate of the sodium ion battery is higher than other cases.

[0197] 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.

[0198] Table 3. Electrochemical performance test results under different sodium supplementation dosages (the chemical formula of sodium supplementation is Na 1.1 Mn 0.44 Ni 0.3 Fe 0.24 O2, Dv50 = 2 μm; positive electrode active material Dv50 = 8 μm)

[0199] 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 within the range of 1: (14.8-94), as the mass ratio of sodium supplement increases, the capacity retention rate of the sodium-ion battery after 300 cycles first increases 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 that in other cases. Therefore, sodium-ion batteries can exhibit better cycle performance by adjusting the mass ratio of sodium supplement to positive electrode active material.

[0200] Appendix: The specific test methods for the above-mentioned various properties are as follows:

[0201] (1)Dv50

[0202] Referring to GB / T 19077-2016 / ISO 13320:2009 “Particle size distribution by laser diffraction method”, Dv50 was obtained using a laser particle size analyzer.

[0203] (2) Compacted density

[0204] Refer to Appendix L "Test method for compaction density of powders" in GB / T 24533-2019 and obtain the result using a compaction density meter.

[0205] (3) Capacity, initial efficiency, and capacity retention rate

[0206] At 25°C, let the sodium ion battery rest for 30 minutes; then charge it at a constant current of 0.33C to 4.0V, then charge it at a constant voltage of 4.0V to a current of 0.05C; then let it rest for 30 minutes; then discharge it at a constant current of 0.33C to 2V, and then let it rest for another 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%.

[0207] The sodium ion battery is cycled for 300 cycles according to the above steps, and the discharge capacity C at this time is recorded. 21 The capacity retention rate after 300 cycles (capacity retention rate = C 21 / C 20 ×100%).

[0208] 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions 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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