CN116780003A

CN116780003A - Positive plate, method for determining uniform distribution of sodium supplementing particles and energy storage device

Info

Publication number: CN116780003A
Application number: CN202311051505.6A
Authority: CN
Inventors: 张国栋; 文佳琪; 龚琳辉
Original assignee: Shenzhen Haichen Energy Storage Control Technology Co ltd; Xiamen Hithium Energy Storage Technology Co Ltd
Current assignee: Shenzhen Haichen Energy Storage Technology Co ltd; Xiamen Hithium Energy Storage Technology Co Ltd
Priority date: 2023-08-21
Filing date: 2023-08-21
Publication date: 2023-09-19
Anticipated expiration: 2043-08-21
Also published as: CN116780003B

Abstract

The application discloses a positive plate, a method for determining uniform distribution of sodium supplementing particles and an energy storage device, and relates to the technical field of energy storage. The positive electrode sheet includes: a current collector and a coating, wherein the median particle size of the particles of the second sodium-containing compound in the coating is greater than the median particle size of the particles of the first sodium-containing compound; in the observed region of the coating, the number of particles of the second sodium-containing compound is not less than 2 and not more than 5, the inter-particle distances are all greater than 6 microns and less than 75 microns, the average orthographic projection area of the particles of the second sodium-containing compound is not less than 160 square microns and not more than 1600 square microns, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles is not more than 890 square microns. In the embodiment of the application, the supplementation of the active sodium is realized through the second sodium-containing compound, the particle number, the inter-particle distance and the orthographic projection area of the particles of the second sodium-containing compound in the observation area are limited, and the uniformity of the distribution of the second sodium-containing compound is ensured.

Description

Positive plate, method for determining uniform distribution of sodium supplementing particles and energy storage device

Technical Field

The application relates to the technical field of energy storage, in particular to a positive plate, a determination method for uniform distribution of sodium supplementing particles and an energy storage device.

Background

Secondary batteries, also called rechargeable batteries or secondary batteries, are batteries that can be used continuously by activating active materials by charging after the battery is discharged. The recyclable characteristic of the secondary battery gradually becomes a main power source of electric equipment, and as the demand of the secondary battery gradually increases, the performance requirements of people on all aspects of the secondary battery are also higher and higher, and particularly the energy density of the unit volume of the battery is required. Sodium ion batteries have been widely used in the fields of automobiles, energy sources, and the like in recent years because of their high energy density and high rate.

In the first charging process of the sodium ion battery, a solid electrolyte membrane formed on the surface of the negative electrode consumes part of active sodium to cause sodium loss of a positive electrode material, and the common graphite negative electrode consumes about 10% of sodium source in the first charging process; in addition, active sodium is continuously consumed in the continuous operation process of the sodium ion battery except the first charge and discharge process, so that capacity attenuation after circulation is caused. Therefore, how to supplement the consumption of active sodium is the key point of sodium-ion battery sodium-supplementing technology research.

Disclosure of Invention

The application mainly aims to provide a positive plate capable of realizing uniform replenishment of active sodium, a determination method for uniform sodium replenishment particle distribution and an energy storage device.

In order to achieve the purposes of the application, the application adopts the following technical scheme:

according to an aspect of the present application, there is provided a positive electrode sheet including: a current collector, and a coating on a surface of the current collector;

the coating comprises a first sodium-containing compound and a second sodium-containing compound in a particle shape, wherein the first sodium-containing compound is a positive electrode active material, the second sodium-containing compound is a nonmetallic sodium-containing compound, the sodium element content of the second sodium-containing compound is larger than that of the first sodium-containing compound, and the median particle diameter of the particles of the second sodium-containing compound is larger than that of the particles of the first sodium-containing compound;

the number of particles of the second sodium-containing compound is not less than 2 and not more than 5, and the inter-particle distances of the particles of the second sodium-containing compound are all greater than 6 microns and less than 75 microns, and the average area of the orthographic projection areas of the particles of the second sodium-containing compound is not less than 160 square microns and not more than 1600 square microns, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound is not more than 890 square microns, and the area of the observation area is not less than 6500 square microns and not more than 7000 square microns.

The inventors have found through a great deal of research that, when the positive electrode sheet includes a first sodium-containing compound as a positive electrode active material and a second sodium-containing compound as a sodium-supplementing material, the number of particles, the inter-particle distance, and the orthographic projection area of the particles of the second sodium-containing compound in the observation area all affect the sodium supplementing effect and the sodium precipitation condition of the energy storage device having the positive electrode sheet.

The inventor finds that when the coating is observed under the magnification of 1K by a scanning electron microscope, and the particle number of the second sodium-containing compound in the observation area on the coating is smaller than 2, the energy storage device with the positive plate is easy to influence the sodium supplementing effect due to the fact that the sodium supplementing particles (the particles of the second sodium-containing compound) in the observation area are fewer in the use process, and the content of sodium elements is lower; when the particle number of the second sodium-containing compound in the observation area on the coating is larger than 5, the energy storage device with the positive plate is easy to cause the phenomenon of sodium precipitation due to the fact that the sodium supplementing particles (the particles of the second sodium-containing compound) in the observation area are more, and the content of sodium element is larger.

The inventor also found that when the coating is observed under the magnification of 1K by a scanning electron microscope, when the inter-particle distance of the second sodium-containing compound in the observation area on the coating is smaller than 6 microns, the energy storage device with the positive plate is easy to cause sodium precipitation phenomenon due to more sodium element content because of more concentrated distribution of sodium supplementing particles (particles of the second sodium-containing compound) in the observation area in the use process; when the inter-particle distance of the second sodium-containing compound is greater than 75 micrometers, the energy storage device with the positive plate is easy to influence the sodium supplementing effect because sodium supplementing particles (particles of the second sodium-containing compound) are distributed and dispersed in the observation area in the use process, so that the content of sodium elements is low.

The inventor also found that when the average area of the orthographic projection area of the particles of the second sodium-containing compound in the observation area on the coating is smaller than 160 square micrometers when the coating is observed under the magnification of 1K by a scanning electron microscope, the energy storage device with the positive plate is easy to influence the sodium supplementing effect because the distribution of sodium supplementing particles (the particles of the second sodium-containing compound) in the observation area is more dispersed in the use process, so that the content of sodium elements is less; when the average area of the orthographic projection area of the particles of the second sodium-containing compound is larger than 1600 square micrometers, the energy storage device with the positive plate is easy to cause sodium precipitation phenomenon due to more sodium element content because of more concentrated distribution of sodium supplementing particles (the particles of the second sodium-containing compound) in the observation area in the use process.

The inventors have also found that when the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound in the observed area on the coating layer is greater than 890 square micrometers when the coating layer is observed under a magnification of 1K by a scanning electron microscope, the energy storage device with the positive plate is easy to cause a sodium precipitation phenomenon due to a larger difference in particle size of sodium supplementing particles (particles of the second sodium-containing compound) in the observed area, and to cause a smaller content of sodium element in the area where the maximum orthographic projection area is located, during use.

In view of the above, the inventors consider that, for the second sodium-containing compound included in the coating layer, it is necessary to define the number of particles of the second sodium-containing compound within the observation area to be not less than 2 and not more than 5, and the inter-particle distances of the second sodium-containing compound to be both more than 6 micrometers and less than 75 micrometers, and the average area of the orthographic projection areas of the particles of the second sodium-containing compound to be not less than 160 square micrometers and not more than 1600 square micrometers, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound to be not more than 890 square micrometers. Thus, the supplementation of active sodium is realized through the added second sodium-containing compound; and the uniformity of the distribution of the second sodium-containing compound in the coating is ensured by limiting the particle number, the particle spacing and the orthographic projection area of the second sodium-containing compound in the observation area, so that the sodium precipitation phenomenon is avoided while the sodium supplementing effect is ensured.

According to an embodiment of the present application, the orthographic projection area of the particles of the second sodium-containing compound in the observation area refers to an area of an edge surrounding area of orthographic projection of the particles of the second sodium-containing compound.

According to an embodiment of the present application, the orthographic projection area of the particles of the second sodium-containing compound in the observation area refers to a circle area of a minimum circumcircle of orthographic projections of the particles of the second sodium-containing compound.

According to an embodiment of the present application, the orthographic projection area of the particles of the second sodium-containing compound in the observation area refers to a circle area of a largest inscribed circle of orthographic projections of the particles of the second sodium-containing compound.

According to an embodiment of the present application, the orthographic projection area of the particles of the second sodium-containing compound in the observation area refers to a sum of areas of a plurality of spliced patterns included in orthographic projections of the particles of the second sodium-containing compound.

According to an embodiment of the present application, the particles of the second sodium-containing compound have a median particle diameter of not less than 10 μm.

In embodiments of the present application, the differentiation of the particles of the first sodium-containing compound from the particles of the second sodium-containing compound within the observation region is facilitated by defining a minimum median particle diameter of the particles of the second sodium-containing compound.

According to an embodiment of the application, the particles of the second sodium-containing compound have a median particle diameter of not more than 20 μm.

In the embodiment of the application, the maximum median particle diameter of the particles of the second sodium-containing compound is limited, so that the situation that the spacing between the particles of the second sodium-containing compound in the coating is large due to the large particles of the second sodium-containing compound when preparing the positive electrode slurry, and the concentration of sodium element content is relatively high due to the large particles of the second sodium-containing compound is avoided, and therefore, the phenomenon of sodium precipitation is avoided while sodium supplementation is realized for the energy storage device with the positive electrode plate.

According to an embodiment of the present application, the observation area is rectangular, and the long side is 100 micrometers, and the wide side is 67.2 micrometers.

According to an embodiment of the present application, the second sodium-containing compound has a formula of: naxUyVzTw, wherein x ranges from 1 to 5, y, z and w ranges from 0 to 10, and at least one of y, z and w is not 0,U and V, T is one of elements C, O, N, F, S, P, si, H, cl.

According to an embodiment of the present application, the second sodium-containing compound is at least one of an inorganic sodium-containing additive and an organic sodium-containing additive of Na2CO3, na2O, na O2, na3N, na3F, na3P, na C4O4, na2C3O3, na2C5O5, na2C6O 6.

According to an aspect of the present application, there is provided a method for determining uniform distribution of sodium compensating particles, the method comprising:

step one: providing a positive plate, wherein the positive plate comprises a coating, and the coating comprises a granular first sodium-containing compound and a granular second sodium-containing compound, wherein the first sodium-containing compound is a positive electrode active material, and the second sodium-containing compound is a nonmetallic sodium supplementing material;

step two: adjusting a scanning electron microscope to 1K magnification, accelerating voltage to 5kV, and observing the positive plate by adopting the scanning electron microscope to obtain an electron microscope image in an observation area, wherein the observation area comprises complete particles of the second sodium-containing compound, and the area of the observation area is not less than 6500 square micrometers and not more than 7000 square micrometers;

Step three: determining the number of particles and the plurality of inter-particle distances of the second sodium-containing compound in the electron microscopy image, and the orthographic projection area of each particle of the second sodium-containing compound;

step four: determining the average area of the particles of the second sodium-containing compound in the electron microscopy image according to the orthographic projection area of each particle of the second sodium-containing compound;

step five: and determining that sodium compensating particles are uniformly distributed in the coating of the positive electrode sheet when the number of particles of the second sodium-containing compound is not less than 2 and not more than 5, and the inter-particle distances of the particles of the second sodium-containing compound are all greater than 6 microns and less than 75 microns, the average area of the particles of the second sodium-containing compound is not less than 160 square microns and not more than 1600 square microns, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound is not more than 890 square microns.

In the embodiment of the application, an electron microscope is used for determining an electron microscope image of an observation area on a coating of a positive plate, and then the particle number and the particle spacing of a second sodium-containing compound in the observation area and the absolute value of the difference value between the average area, the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound are determined according to the electron microscope image, so as to determine whether the particles of the second sodium-containing compound are uniformly distributed in the coating, further determine the sodium supplementing effect of the second sodium-containing compound on the positive plate, and simultaneously avoid the situation of sodium precipitation in the local area of the positive plate.

According to an embodiment of the present application, in the third step, determining an orthographic projection area of each particle of the second sodium-containing compound in the electron microscope image includes:

determining the area of the edge surrounding area of the orthographic projection of the particles of the second sodium-containing compound, or determining the circle area of the minimum circumscribed circle of the orthographic projection of the particles of the second sodium-containing compound, or determining the circle area of the maximum inscribed circle of the orthographic projection of the particles of the second sodium-containing compound; or determining the sum of the areas of the plurality of mosaic patterns comprised by the orthographic projection of the particles of the second sodium-containing compound.

According to an aspect of the present application, there is provided an energy storage device comprising:

a housing including a receiving chamber having an opening;

the electrode assembly is accommodated in the accommodating cavity and comprises a positive plate, a negative plate and a diaphragm which are arranged in a stacked manner, wherein the positive plate is the positive plate in the aspect;

and an end cap unit sealing the opening of the accommodating chamber.

In an embodiment of the present application, for the energy storage device including the positive plate according to the above aspect, the capacity attenuation of the energy storage device can be reduced under the condition of having enough active sodium, so as to reduce the problem of circulating water jump of the energy storage device, and prolong the service life of the energy storage device.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application as claimed.

Drawings

The above and other features and advantages of the present application will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

Fig. 1 is a schematic cross-sectional structure of an energy storage device according to an exemplary embodiment.

Fig. 2 is a schematic cross-sectional structure of an electrode assembly according to an exemplary embodiment.

Fig. 3 is a schematic cross-sectional structure of a positive electrode sheet according to an exemplary embodiment.

Fig. 4 is an electron micrograph showing an orthographic projected area of second sodium-containing compound particles within an observation region according to an exemplary embodiment.

Fig. 5 is an electron micrograph showing another orthographic projected area of second sodium-containing compound particles within an observation region according to an exemplary embodiment.

Fig. 6 is a binarized electron microscope image of the observation area shown in fig. 4.

Fig. 7 is a graph illustrating capacity retention of an energy storage device according to an example embodiment.

Fig. 8 is a flow chart illustrating a method of determining a uniform pair of sodium compensating particle distribution according to an exemplary embodiment.

Wherein reference numerals are as follows:

100. an energy storage device;

10. a housing; 20. an electrode assembly; 30. an end cap unit;

11. a receiving chamber;

21. a positive plate; 22. a negative electrode sheet; 23. a diaphragm;

31. a cover plate; 32. an electrode terminal;

211. a current collector; 212. a coating;

na1, a first sodium-containing compound; na2, a second sodium-containing compound.

Detailed Description

Example embodiments will now be described more fully with reference to the accompanying drawings. However, the exemplary embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and thus detailed descriptions thereof will be omitted.

Embodiments of the present application provide an energy storage device 100, where the energy storage device 100 may be, but is not limited to, a single battery, a battery module, a battery pack, a battery system, etc. The unit cell may be a sodium ion secondary battery, a sodium sulfur battery, or the like, and the unit cell may be a cylinder, a flat body, a rectangular parallelepiped, or the like, which is not limited in the embodiment of the present application.

Next, the energy storage device 100 is explained in detail using the energy storage device 100 as a cylindrical unit cell as an example.

Fig. 1 illustrates a schematic structure of an energy storage device 100 according to an embodiment of the present application. As shown in fig. 1, the energy storage device 100 includes a case 10, an electrode assembly 20, and an end cap unit 30, the case 10 including a receiving chamber 11 having an opening; the electrode assembly 20 is accommodated in the accommodating chamber; the end cap unit 30 seals the opening of the accommodation chamber 11.

Wherein the housing 10 may have a cylindrical structure with one end opened, and the energy storage device 100 includes an end cap unit 30 to be capable of sealing one opening of the housing 10; of course, the housing 10 may have a cylindrical structure with two open ends, and the energy storage device 100 may include one end cap unit 30 and one end cap, or include two end cap units 30, so that two openings of the housing 10 can be sealed.

As shown in fig. 1, the end cap unit 30 includes a cover plate 31 and an electrode terminal 32, the electrode terminal 32 is disposed on the cover plate 31 in a penetrating manner, one end of the electrode terminal 32 is connected to one tab of the electrode assembly 20, and the other end of the electrode terminal is exposed out of the casing 10 to serve as an output end of the energy storage device 100; the cover plate 31 may further be provided with an explosion-proof valve for discharging the gas in the accommodating cavity 11 to improve the safety of the energy storage device 100, and/or a liquid injection hole for injecting the electrolyte into the accommodating cavity 11 of the energy storage device 100.

As shown in fig. 2, the electrode assembly 20 includes a positive electrode sheet 21, a negative electrode sheet 22, and a separator 23 stacked together, and the separator 23 is located between the positive electrode sheet 21 and the negative electrode sheet 22, and both ends of the positive electrode sheet 21 and the negative electrode sheet 22 in the axial direction of the electrode assembly 20 have tabs to form positive and negative electrode tabs of the electrode assembly 20. The positive electrode tab and the negative electrode tab are positioned at different ends of the electrode assembly 20, and one of the positive electrode tab and the negative electrode tab is connected to the electrode terminal 32 included in the cap unit 30 while the other is connected to the bottom of the case 10, so that the output of the electric power of the electrode assembly 20 is achieved through the electrode terminal 32 of the cap unit 30 and the bottom of the case 10.

It should be noted that, the energy storage device 100 further includes a metal adaptor, and the connection between one tab of the electrode assembly 20 and one electrode terminal 32 of the end cap unit 30 can be achieved through one metal adaptor, and the connection between the other tab of the electrode assembly 20 and the bottom of the casing 10 can be achieved through the other metal adaptor, so as to ensure the output of the electric energy of the electrode assembly 20. The two metal adapters may have the same or different structures.

During the use of the energy storage device 100, particularly during the first use, a solid electrolyte interface film is formed on the surface of the negative electrode sheet 22 of the electrode assembly 20 to cause consumption of active sodium of the energy storage device 100, and during the subsequent use of the energy storage device 100, consumption of active sodium is caused for various reasons, thereby causing capacity degradation of the energy storage device 100 and causing a problem of circulating water jump. Therefore, the embodiment of the application provides the positive plate 21 for realizing the active sodium supplement and avoiding the phenomenon of sodium precipitation at the same time, so as to reduce the capacity attenuation of the energy storage device 100, further reduce the problem of circulating water jump of the energy storage device 100, and prolong the cycle life of the energy storage device 100.

The positive electrode sheet 21 according to the present application will be explained in detail.

Fig. 3 illustrates a schematic cross-sectional structure of a positive electrode sheet 21 according to an embodiment of the present application. As shown in fig. 3, the positive electrode sheet 21 includes: a current collector 211, and a coating 212 on the surface of the current collector 211.

The positive electrode sheet 21 may have a coating 212 on one surface of the current collector 211, or may have a coating 212 on both surfaces of the current collector 211. Compared with the case where the surface of one side of the current collector 211 is provided with the coating 212, the case where the surfaces of both sides of the current collector 211 are provided with the coating 212 can effectively increase the content of active sodium in the unit area of the positive electrode sheet 21, so that the specific capacity of the energy storage device 100 including the positive electrode sheet 21 can be effectively increased, and meanwhile, the weight of the energy storage device 100 can be reduced because the amount of the current collector 211 is reduced.

The coating 212 on the surface of the current collector 211 includes a granular first sodium-containing compound Na1 and a second sodium-containing compound Na2, where the first sodium-containing compound Na1 is a positive electrode active material, the second sodium-containing compound Na2 is a nonmetallic sodium-containing compound, and the sodium element content of the second sodium-containing compound Na2 is greater than the sodium element content of the first sodium-containing compound Na1, that is, the sodium element mass ratio of the second sodium-containing compound Na2 is greater than the sodium element mass ratio of the first sodium-containing compound Na1, so that the active sodium is supplemented by the added second sodium-containing compound Na 2.

Wherein, the mass ratio of sodium element of the first sodium-containing compound Na1 is less than or equal to 20%, and the mass ratio of sodium element of the second sodium-containing compound Na2 is more than 20%, so that the sodium supplementing effect of the positive plate 21 is achieved by adding the second sodium-containing compound Na2. At this time, when the positive electrode slurry corresponding to the coating layer 212 is manufactured, the mass ratio of the first sodium-containing compound Na1 and the mass ratio of the second sodium-containing compound Na2 in the coating layer 212 according to the related art can be redistributed to realize the sodium supplementation of the positive electrode sheet 21 through the sodium element more than the first sodium-containing compound Na1 in the second sodium-containing compound Na2, and meanwhile, the adjustment of the mass ratio of other components included in the coating layer 212 is avoided, so that the configuration process of the positive electrode slurry is simplified.

Wherein, prior to redistribution, the coating 212 includes a particulate first sodium-containing compound Na1 and does not include a second sodium-containing compound Na2; after redistribution, the coating 212 includes both the first sodium-containing compound Na1 and the second sodium-containing compound Na2 in particulate form. In addition, the mass ratio of the first sodium-containing compound Na1 before redistribution is equal to the sum of the mass ratio of the first sodium-containing compound Na1 after redistribution and the mass ratio of the second sodium-containing compound Na2. Illustratively, the mass ratio of the first sodium-containing compound Na1 in the pre-redistribution coating 212 is 0.88, the mass ratio of the first sodium-containing compound Na1 in the post-redistribution coating 212 is 0.72, and the mass ratio of the second sodium-containing compound Na2 is 0.16.

The first sodium-containing compound Na1 is a positive electrode active material, and specifically may be at least one of a polyanion compound, a transition metal oxide, or prussian blue, and an organic compound containing sodium. Thus, the selection criteria for the first sodium-containing compound Na1 can be reduced to reduce the cost of the coating 212 when selecting a cathode material with a smaller unit price; in addition, the first sodium-containing compound Na1 may also be constituted by a plurality of types of positive electrode active materials to improve the electrical properties of the positive electrode sheet 21 by the cooperation of the plurality of types of positive electrode materials.

Wherein the molecular formula of the polyanion compound is NaxMy (Xaob) zZw, M is one of elements Ti, V, cr, mn, fe, co, ni, ca, mg, al, nb and the like, X is one of elements Si, S, P, as, B, mo, W, ge, and Z is element F or OH radical ion; such as polyanionic compounds: na3V2 (PO 4) 3, na2FeP2O7. The molecular formula of the transition metal oxide is NaxMO2, M is a transition metal atom, and particularly one of elements Ti, V, cr, mn, fe, co, ni, cu, ca, mg, al, nb, wherein x is more than 0 and less than or equal to 1; for example, the transition metal oxide is NaxFeO2, naxNiO2, naxCoO2, naxMnO2, naxVO2, naxCrO2 (x.ltoreq.1). Prussian blue has a molecular formula of NaxM [ Fe (CN) 6]y.nH2O, M is one of elements Ni, fe, mn, co, cu, zn, 1<x is less than or equal to 2,0< y is less than or equal to 1, and 0< n is less than 15; for example, prussian blue is NaxFeFe (CN) 6, naxMnFe (CN) 6, naxCoFe (CN) 6, naxNiFe (CN) 6 (x.ltoreq.2).

In addition, for the first sodium-containing compound Na1 of different types, in order to achieve a better sodium supplementing effect, the sodium element mass ratio of the second sodium-containing compound Na2 is also different. The mass ratio of sodium element in the second sodium-containing compound Na2 is more than 20% for the case that the first sodium-containing compound Na1 is a polyanion compound or Prussian blue, and the mass ratio of sodium element in the second sodium-containing compound Na2 is more than 23% for the case that the first sodium-containing compound Na1 is a transition metal oxide.

Wherein the second sodium-containing compound Na2 is a nonmetallic sodium-containing compound. Optionally, the molecular formula of the second sodium-containing compound Na2 is NaxUyVzTw, where x ranges from 0.5 to 5, y, z, and w all ranges from 0 to 10, and at least one of y, z, and w is not 0,U and V, T is one of the elements C, O, N, F, S, P, si, H, cl. Illustratively, the second sodium-containing compound Na2 is at least one of an inorganic sodium-containing additive and an organic sodium-containing additive such as Na2CO3, na2O, na O2, na3N, na3F, na3P, na C4O4, na2C3O3, na2C5O5, na2C6O6, and the like.

In an embodiment of the present application, in order to ensure uniformity of the distribution of the second sodium-containing compound Na2 in the coating layer 212, an observation area of the coating layer 212 is generally used as a reference, and an observation area of the coating layer 212 is an area that can be observed in a window area of a scanning electron microscope when the surface or the tangential surface of the coating layer 212 is observed by the scanning electron microscope. For example, the visible area of the coating 212 when viewed on a surface or cut surface is measured by a scanning electron microscope of the type zeiss sigma300 at a working distance of not less than 3.0 mm and not more than 6.0 mm at a magnification of 1K.

The observation area is an area of the coating 212 that is not less than 6500 square micrometers and not more than 7000 square micrometers, that is, the area of the observation area is not less than 6500 square micrometers and not more than 7000 square micrometers. Illustratively, the working distance is 3.0 millimeters, 3.5 millimeters, 4.0 millimeters, 4.5 millimeters, 5.0 millimeters, 5.5 millimeters, 6.0 millimeters, and the like. The area of the observation region is 6500 square micrometers, 6600 square micrometers, 6720 square micrometers, 6800 square micrometers, 6900 square micrometers, 7000 square micrometers, or the like.

The shape of the observation area may be a positive direction, a rectangle, or a circle, but may also be an ellipse, etc., depending on the shape of the window area of the scanning electron microscope used in the observation. Illustratively, taking the shape of the observation region as a rectangle, and the area of the observation region as 6720 square microns as an example, the observation region may be a rectangular region with a long side of 100 microns and a short side of 67.2 microns on the surface or cut-out of the coating 212.

In some embodiments, the uniformity of the distribution of the particles of the second sodium-containing compound Na2 in the coating 212 may be characterized by the number of particles and inter-particle distances of the second sodium-containing compound Na2 within the observation region of the coating 212, as well as the orthographic projected area of the particles of the second sodium-containing compound Na 2.

Wherein, as the inventors have studied earnestly, it is found that when the number of particles of the second sodium-containing compound Na2 is not less than 2 and not more than 5, and the inter-particle distances of the particles of the second sodium-containing compound Na2 are all more than 6 micrometers and less than 75 micrometers, the average area of the orthographic projection areas of the particles of the second sodium-containing compound Na2 is not less than 160 square micrometers and not more than 1600 square micrometers, and the absolute value of the maximum difference in orthographic projection areas (the difference between the maximum orthographic projection area and the minimum orthographic projection area) of the particles of the second sodium-containing compound Na2 is not more than 890 square micrometers, it can be determined that the particles of the second sodium-containing compound Na2 are uniformly distributed in the coating 212.

In this way, by defining the number of particles and the inter-particle distance of the second sodium-containing compound Na2 in the observed area on the coating layer 212 and the absolute value of the difference between the average area of the orthographic projection area and the maximum area of the particles of the second sodium-containing compound Na2, the uniformity of the distribution of the particles of the second sodium-containing compound Na2 in the coating layer 212 is ensured, so that the sodium supplementing effect of the second sodium-containing compound Na2 on the positive electrode sheet 21 is ensured, and meanwhile, excessive sodium element supplementation caused by the aggregation of the particles of the second sodium-containing compound Na2 in the local area of the positive electrode sheet 21 is avoided, namely, the sodium element content in the whole area of the positive electrode sheet 21 is ensured to be substantially the same.

Wherein the number of particles of the second sodium-containing compound Na2 in the observation region is equal for a plurality of observation regions on the coating 212, and the number of particles of the second sodium-containing compound Na2 in each observation region may be 2, 3, 4, or 5. Illustratively, as shown in the electron microscopy images of the observation area of fig. 4 or 5, the coating 212 has 2 particles (particles A1, A2, respectively) of the second sodium-containing compound Na2 within the observation area.

Wherein for a plurality of inter-particle distances of the second sodium-containing compound Na2 within the observation region, the observation region has, for example, 4 particles of the second sodium-containing compound Na2, there are 6 inter-particle distances at this time, and are 10 microns, 20 microns, 28 microns, 44 microns, 57 microns, 68 microns, respectively.

Further, in order to more accurately analyze the uniformity of the particle distribution of the second sodium-containing compound Na2 by the inter-particle distance of the second sodium-containing compound Na2, it is also possible to determine whether the inter-particle distance of the second sodium-containing compound Na2 is greater than the ratio of 30 micrometers to the number of particles and less than the ratio of 150 micrometers to the number of particles. Illustratively, the number of particles of the second sodium-containing compound Na2 in the observation region is 4, at which time it is determined whether the inter-particle distances of the 4 particles are each greater than a ratio of 7.5 microns and less than 37.5 microns.

Wherein the average area of the orthographic projection area for the particles of the second sodium-containing compound Na2 within the observation region may be 160 square micrometers, 210 square micrometers, 530 square micrometers, 790 micrometers, 1030 micrometers, 1340 micrometers, 1600 square micrometers, or the like.

Wherein, for the maximum difference in orthographic projection area of the particles of the second sodium-containing compound Na2 in the observation area, for example, the maximum orthographic projection area of the particles of the second sodium-containing compound Na2 in the observation area is 1340 square micrometers, and the minimum orthographic projection area is 530 square micrometers, and at this time, the maximum difference in orthographic projection area of the particles of the second sodium-containing compound Na2 is 810 square micrometers (less than 890 square micrometers).

In addition, the orthographic projection area of the particles of the second sodium compound Na2 in the observation area may be an area surrounded by edges of orthographic projections of the particles of the second sodium compound Na 2; the circular area of the largest inscribed circle that can be orthographic projection of the particles of the second sodium-containing compound Na2 as shown in fig. 4; the circle area of the smallest circumscribed circle that may be the orthographic projection of the particles of the second sodium-containing compound Na2 as shown in fig. 5; of course, it is also possible to be the sum of the areas of the plurality of mosaic patterns comprised by the orthographic projection of the particles of the second sodium compound Na 2.

Alternatively, the area of the area surrounded by the edge of the orthographic projection of the second sodium compound Na2 particle is determined according to a straight-line relational expression corresponding to the edge of the orthographic projection of the particle according to a pre-established rectangular coordinate system, and the area surrounded by the edge of the orthographic projection of the particle is determined according to a plurality of straight-line relational expressions by means of fixed integration (refer to the related art for specific). For the sum of the areas of the plurality of spliced patterns included in the orthographic projection of the particles of the second sodium-containing compound Na2, optionally, dividing the orthographic projection of the particles into a plurality of rectangles with the same size according to a pre-established rectangular coordinate system and a plurality of straight lines parallel to the horizontal axis and the vertical axis, and determining the sum of the areas of the plurality of rectangles according to the number of rectangles and the size of the rectangles to obtain the orthographic projection area of the particles of the second sodium-containing compound Na 2.

The orthographic projections described above are projections in a direction perpendicular to the surface or tangential plane of the coating layer 212, and since the particles of the second sodium-containing compound Na2 are small, the area where the orthographic projections are located cannot be confirmed, and therefore, the area surrounded by the edges of the particles of the second sodium-containing compound Na2 on the electron microscopic image can be defined as the orthographic projection area of the particles of the second sodium-containing compound Na 2. In addition, for the edges of the particles of the second sodium-containing compound Na2 in the observation region, for example, after obtaining an electron micrograph (a position in which the particles of the second sodium-containing compound Na2 are marked in the electron micrograph) as shown in fig. 4, the obtained electron micrograph is subjected to binarization processing (for example, the gray value may be set to 170) to obtain a binarized electron micrograph (a black region surrounded by the edges of the particles of the second sodium-containing compound Na2 is highlighted in the electron micrograph, and is embodied as an orthographic projection of the particles of the second sodium-containing compound Na 2) as shown in fig. 6.

For example, for the particles A1 and A2 having the second sodium compound Na2 in the binarized electron microscope image of the observation area shown in fig. 6, the diameter of the smallest circumcircle of the edge of the particle A1 is 14.68 micrometers, the diameter of the smallest circumcircle of the edge of the particle A2 is 16.53 micrometers, the orthographic projection area of the corresponding particle A1 is 169.17 square micrometers, the orthographic projection area of the particle A2 is 214.49 square micrometers, and the planar area of the orthographic projection area of the second sodium compound Na2 in the observation area is the orthographic projection area of the particle A1, and the average value of the orthographic projection areas of the particle A2 is 191.83 square micrometers.

In the embodiment of the present application, since the median particle diameter of the particles of the second sodium-containing compound Na2 is larger than that of the particles of the first sodium-containing compound Na1, the particles of the first sodium-containing compound Na1 and the particles of the second sodium-containing compound Na2 can be distinguished by the size of the particles in the observation area when the coating 212 of the positive electrode sheet 21 is observed by a scanning electron microscope. In this way, the particles of the second sodium-containing compound Na2 in the electron micrograph can be more intuitively distinguished for the electron micrograph of the observation region obtained by the scanning electron microscope.

Alternatively, since the median particle diameter of the particles of the first sodium-containing compound Na1 is typically around 6 microns (e.g., 5 microns, 6 microns, 7 microns), the median particle diameter of the particles of the second sodium-containing compound Na2 may be set to be not less than 10 microns, thereby facilitating the differentiation of the particles of the first sodium-containing compound Na1 from the particles of the second sodium-containing compound Na2 within the observation region by defining the minimum median particle diameter of the particles of the second sodium-containing compound Na 2. Illustratively, the particles of the second sodium-containing compound Na2 have a median particle diameter of 10 microns, 12 microns, 14 microns, 16 microns, 18 microns, etc.

Further, the median particle diameter of the particles of the second sodium-containing compound Na2 may be set to be not more than 20 micrometers, so that by defining the maximum median particle diameter of the particles of the second sodium-containing compound Na2, the situation that the inter-particle spacing of the second sodium-containing compound Na2 in the coating layer 212 is large due to the large particles of the second sodium-containing compound Na2 and the concentration of sodium element due to the large particles of the second sodium-containing compound Na2 is avoided when the positive electrode slurry is prepared. In this way, the energy storage device 100 having the positive electrode sheet 21 is not likely to cause sodium precipitation while sodium is being replenished.

In the embodiment of the present application, the electron microscope images were obtained by a scanning electron microscope under conditions of a 1K magnification and an acceleration voltage of 5.0 kV.

In an embodiment of the present application, the coating 212 on the surface of the current collector 211 includes at least a conductive agent, a dispersing agent, a binder, and a solvent in addition to the first sodium-containing compound Na1 and the second sodium-containing compound Na 2. The components (conductive agent, binder, dispersant, solvent, first sodium-containing compound Na1, second sodium-containing compound Na 2) included in the coating layer 212 may form a positive electrode slurry by means of high-speed stirring while ensuring uniformity of distribution of particles of the first sodium-containing compound Na1, the second sodium-containing compound Na2 in the positive electrode slurry, and further coating the positive electrode slurry on at least one side surface of the current collector 211, so that the coating layer 212 is formed on the surface of the current collector 211 after drying, so that the particles of the first sodium-containing compound Na1, the second sodium-containing compound Na2 are uniformly distributed in the coating layer 212.

Due to the uniformity of the distribution of the particles of the first sodium-containing compound Na1 and the second sodium-containing compound Na2 in the coating 212, the sodium supplementing effect of the second sodium-containing compound Na2 on the positive plate 21 is ensured, and meanwhile excessive sodium element supplementation in a local area caused by aggregation of the particles of the second sodium-containing compound Na2 in the local area of the positive plate 21 is avoided, namely, the sodium element content in the whole area of the positive plate 21 is ensured to be basically the same. Thus, for the energy storage device 100 with the positive plate 21, the active sodium supplement is realized, the phenomenon of sodium precipitation caused by overlarge content of sodium element in a local area of the positive plate 21 is avoided, the capacity attenuation problem of the energy storage device 100 is reduced, the circulating water jump problem of the energy storage device 100 is further reduced, and the circulating life of the energy storage device 100 is prolonged.

The method for manufacturing the positive plate 21 comprising the coating 212 comprises the following steps:

(1) Uniformly mixing and dispersing the conductive agent, the binder and the first part of solvent at the temperature of more than 0 ℃ and less than 35 ℃ of the dew point to obtain first slurry;

(2) Uniformly mixing and dispersing the dispersing agent, the first sodium-containing compound Na1 particles, the second sodium-containing compound Na2 particles and the second part of solvent to obtain second slurry;

(3) Mixing and stirring the first slurry and the second slurry to obtain positive electrode slurry, wherein the viscosity of the positive electrode slurry is 4000 millipascals/second-20000 millipascals/second, and the solid content is 35% -70%;

(4) The obtained positive electrode slurry was coated on the surface of the current collector 211, and dried, rolled and rinsed to obtain a positive electrode sheet 21.

The conductive agent may be at least one of conductive carbon black, conductive graphite, graphene, carbon nanotubes, carbon fibers and the like, the binder may be at least one of styrene-butadiene rubber, polyvinylidene fluoride, polyvinyl alcohol, polyvinyl acrylic acid, polystyrene acid ester, polytetrafluoroethylene and the like, and the solvent may be at least one of deionized water, N-methylpyrrolidone and the like.

In the above steps, the median particle diameter of the particles of the first sodium-containing compound Na1 is 5 micrometers, the median particle diameter of the particles of the second sodium-containing compound Na2 is 15 micrometers, the total content X of the first sodium-containing compound Na1 and the second sodium-containing compound Na2 in the positive electrode slurry is 30-68%, the content a of the first sodium-containing compound Na1 is 20-67%, and the content b of the second sodium-containing compound Na2 is X-a. Illustratively, the total content X of the first sodium-containing compound Na1 and the second sodium-containing compound Na2 in the positive electrode slurry is 50%, the content a of the first sodium-containing compound Na1 is 28%, and the content b of the second sodium-containing compound Na2 is 22%.

In the steps, the stirring speeds of the first slurry, the second slurry and the positive electrode slurry are respectively 500-2000 rpm, 500-5000 rpm and 1000-5000 rpm, so that the uniformity of the dispersion of each component in each slurry, particularly the uniformity of the dispersion of the first sodium-containing compound Na1 and the second sodium-containing compound Na2 in the positive electrode slurry, is ensured. For example, the stirring speeds for the first slurry were 500 rpm, 1000 rpm, 1500 rpm, 2000 rpm, 500 rpm, 2000 rpm, and 5000 rpm for the second slurry, and 1000 rpm, 3000 rpm, 5000 rpm for the positive slurry.

In the above steps, the drying temperature of the positive electrode slurry coated on the surface of the current collector 211 is kept at 60 ℃ to 130 ℃ and the duration is 2 hours to 20 hours; the pressure value of the dried positive electrode slurry is 10 kilonewtons to 200 kilonewtons when the positive electrode slurry is rolled. Illustratively, the drying temperature of the positive electrode slurry is 60 degrees celsius, 80 degrees celsius, 110 degrees celsius, 130 degrees celsius, the duration of the drying temperature is 2 hours, 8 hours, 14 hours, 20 hours, and the pressure value of rolling after drying is 10 kilonewtons, 60 kilonewtons, 110 kilonewtons, 160 kilonewtons, 200 kilonewtons.

Comparative example 1: in combination with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 5800 mpa/s and a solid content of 58% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 6 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirring tank at a humidity of 15% rh or less, and then coating the positive electrode slurry on the surface of the current collector 211 at a drying temperature of 120 ℃ for a drying time period of 4 hours, and a rolling pressure value of 30 kN. And then observing the positive electrode comparison sample piece 1 through a scanning electron microscope under the conditions of 1K magnification and 5kV pair of acceleration voltage to obtain the particle number of the second sodium-containing compound Na2 in the observation area as 0. For the energy storage device 100 with the positive electrode comparative sample, the capacity retention rate for 100 cycles was only 81.9%, and no sodium precipitation occurred.

Example 1: in combination with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 6000 mpa/s and a solid content of 59% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 5.3 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 13.6 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then the positive electrode slurry was applied to the surface of the current collector 211 at a drying temperature of 110 ℃ for 15 hours and a rolling pressure value of 20 kN. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the sample wafer 1 of the positive electrode example is observed by a scanning electron microscope, the number of particles of the second sodium-containing compound Na2 in an observation area with the area of 6600 square micrometers is 5, the inter-particle distances among the particles of the 5 second sodium-containing compounds are all larger than 6 micrometers and smaller than 75 micrometers, the average area of the orthographic projection areas of the particles of the 5 second sodium-containing compounds is 1480.3 square micrometers, and the absolute value of the maximum difference value of the orthographic projection areas is 689.4 square micrometers. For the energy storage device 100 having this positive electrode example sample sheet 1, the capacity retention rate for 100 cycles was 91.2%, and no sodium precipitation phenomenon occurred.

Example 2: in combination with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 6300 mpa/s and a solid content of 60% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 5.6 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 14.6 μm), a 3% conductive agent (conductive carbon black), a 2% binder (polyvinylidene fluoride), and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, then coating the positive electrode slurry on the surface of the current collector 211, and drying at 80 ℃ for 20 hours, and a rolling pressure value of 50 kN. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the sample wafer 2 of the positive electrode example is observed through a scanning electron microscope, the particle number of the second sodium-containing compound Na2 in the observed area with the area of 6600 square micrometers is 2, the inter-particle distance between the 2 particles of the second sodium-containing compound is 54 micrometers, the average area of the orthographic projection areas of the 2 particles is 500.7 square micrometers, and the absolute value of the maximum difference value of the orthographic projection areas is 361.4 square micrometers. For the energy storage device 100 having this positive electrode example sample sheet 2, the capacity retention rate for 100 cycles was 91.1%, and no sodium precipitation phenomenon occurred.

Example 3: in connection with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 6700 mpa/s and a solid content of 60.5% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 6.8 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 14.2 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then applying the positive electrode slurry to the surface of the current collector 211 at a drying temperature of 110 ℃ for a drying time period of 12 hours, and a pressure value of 60kN in a roll-press sample. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the positive electrode sample wafer 3 is observed through a scanning electron microscope, the number of particles of the second sodium-containing compound Na2 in an observation area with the area of 6600 square micrometers is 4, the inter-particle distances among the particles of the 4 second sodium-containing compounds are all larger than 6 micrometers and smaller than 75 micrometers, the average area of orthographic projection areas of the particles of the 4 second sodium-containing compounds is 160 square micrometers, and the absolute value of the maximum difference value of the orthographic projection areas is 37.4 square micrometers. For the energy storage device 100 having this positive electrode example sample sheet 3, the capacity retention rate for 100 cycles was 90.2%, and no sodium precipitation phenomenon occurred.

Example 4: in combination with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 6800 mpa/s and a solid content of 61% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 5.3 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 18.2 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then the positive electrode slurry was applied to the surface of the current collector 211 at a drying temperature of 115 ℃ for a drying time of 12 hours, and a pressure value of 70kN by rolling. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the positive electrode sample wafer 4 is observed through a scanning electron microscope, the number of particles of the second sodium-containing compound Na2 in an observation area with the area of 6600 square micrometers is 3, the inter-particle distances among the particles of the 3 second sodium-containing compounds are all larger than 6 micrometers and smaller than 75 micrometers, the average area of orthographic projection areas of the particles of the 3 second sodium-containing compounds is 1600 square micrometers, and the absolute value of the maximum difference value of the orthographic projection areas is 788.5 square micrometers. For the energy storage device 100 having this positive electrode example sample sheet 4, the capacity retention rate for 100 cycles was 90.0%, and no sodium precipitation phenomenon occurred.

Example 5: in connection with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 6870 mpa/s and a solid content of 61.3% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 6.7 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 17.8 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then the positive electrode slurry was applied to the surface of the current collector 211 at a drying temperature of 125 ℃ for a drying time period of 7 hours, and a pressure value of 80kN in a roll-press sample. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the sample wafer 5 of the positive electrode example is observed by a scanning electron microscope, the particle number of the second sodium-containing compound Na2 in the observed area with the area of 6600 square micrometers is 1, and the average area of the orthographic projection area of 1 particle is 143.2 square micrometers (no difference value between the inter-particle distance and the orthographic projection area exists). For the energy storage device 100 having this positive electrode example sample sheet 5, the capacity retention rate for 100 cycles was 89.9%, and no sodium precipitation phenomenon occurred.

Example 6: in combination with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 7200 mpa/s and a solid content of 62% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 5.4 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 15.6 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then the positive electrode slurry was applied to the surface of the current collector 211 at a drying temperature of 70 ℃ for a drying time period of 24 hours, and a rolling pressure value of 30 kN. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the sample wafer 6 of the positive electrode example is observed by a scanning electron microscope, so that the particle number of the second sodium-containing compound Na2 in the observed area with the area of 6600 square micrometers is 1, and the orthographic projection area of 1 particle is 1420.6 square micrometers (no difference value between the particle spacing and the orthographic projection area exists). For the energy storage device 100 having this positive electrode example sample sheet 6, the capacity retention rate for 100 cycles was 87.6%, and no sodium precipitation phenomenon occurred.

Example 7: in connection with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 7400 mpa/s and a solid content of 62.7% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 7 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 14.0 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then applying the positive electrode slurry to the surface of the current collector 211 at a drying temperature of 90 ℃ for 18 hours and a rolling pressure value of 100 kN. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the positive electrode sample wafer 7 is observed through a scanning electron microscope, the number of particles of the second sodium-containing compound Na2 in an observation area with the area of 6600 square microns is 6, inter-particle distances smaller than 6 microns exist among the particles of the 6 second sodium-containing compounds, the average area of the orthographic projection areas of the 6 particles is 1340.6 square microns, and the absolute value of the maximum difference value of the orthographic projection areas is 549.2 square microns. For the energy storage device 100 having this positive electrode example sample sheet 7, the capacity retention rate of 100 cycles was 85.8%, and a sodium precipitation phenomenon occurred.

Example 8: in connection with the above-described method for producing the positive electrode sheet 21, a positive electrode slurry having a viscosity of 7800 mpa/s and a solid content of 64% was obtained by stirring a first sodium-containing compound Na1 (chemical formula: na0.97ni0.34fe0.31mn0.35o2, median particle diameter: 5 μm), a second sodium-containing compound Na2 (chemical formula: na2NiO2, median particle diameter: 16.0 μm), a conductive agent (conductive carbon black) having a content of 3%, a binder (polyvinylidene fluoride) having a content of 2%, and a solvent (N-methylpyrrolidone) in a stirred tank at a humidity of 15% rh or less, and then the positive electrode slurry was applied to the surface of the current collector 211 at a drying temperature of 105 ℃ for a drying time period of 16 hours, and a rolling pressure value of 120kN, to obtain a positive electrode sample sheet 8. Then, under the conditions of 1K magnification and 5kV pair of acceleration voltage, the positive electrode sample wafer 8 is observed through a scanning electron microscope, the number of particles of the second sodium-containing compound Na2 in an observation area with the area of 6600 square microns is 6, inter-particle distances smaller than 6 microns exist among the particles of the 6 second sodium-containing compounds, the average area of the orthographic projection areas of the 6 particles is 1800.6 square microns, and the absolute value of the maximum difference value of the orthographic projection areas is 924.37 square microns. For the energy storage device 100 having this positive electrode example sample sheet 8, the capacity retention rate of 100 cycles was 83.8%, and a sodium precipitation phenomenon occurred.

For the energy storage device 100 including the positive electrode sheet 21 manufactured in the above comparative example 1 and examples 1 to 8, respectively, physical parameters of the particles of the second sodium-containing compound Na2 in the positive electrode sheet 21, and specific charge capacity, specific discharge capacity, and lithium evolution of the energy storage device 100 when the energy storage device 100 is used are shown in the following table.

As is clear from the above-described comparative example 1 and examples 1 to 8, when the number of particles of the second sodium-containing compound Na2 in the observation area is not less than 2 and not more than 5, and the inter-particle distances of the second sodium-containing compound Na2 are all more than 6 micrometers and less than 75 micrometers, the average area of the orthographic projection areas of the particles of the second sodium-containing compound Na2 is not less than 160 square micrometers and not more than 1600 square micrometers, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound Na2 is not more than 890 square micrometers, the particles representing the second sodium-containing compound Na2 are uniformly distributed in the coating layer 212, and the energy storage device 100 having the positive electrode sheet 21 satisfying this condition has a high capacity retention after 100 cycles, and does not show the sodium precipitation phenomenon.

Fig. 7 shows a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to the comparative example, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 1, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 2, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 3, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 4, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 5, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 6, a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 7, and a graph of the 25℃ -1C capacity retention rate of the energy storage device 100 according to example 8. As can be seen from the above, compared with the comparative example, when the second sodium-containing compound Na2 is added to the coating layer 212 of the positive electrode sheet 21 to supplement sodium, the number of particles of the second sodium-containing compound Na2 in the observation area is not less than 2 and not more than 5, the inter-particle distances of the second sodium-containing compound Na2 are all more than 6 micrometers and less than 75 micrometers, the average area of the orthographic projection area of the particles of the second sodium-containing compound Na2 in the observation area is not less than 160 square micrometers and not more than 1600 micrometers, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound Na2 is not more than 890 square micrometers, the energy storage device 100 according to the embodiments 1 to 4 has a better capacity retention rate.

In the energy storage device 100 of the above comparative example and example, the method for determining whether sodium precipitation occurs is as follows: charging the energy storage device 100 from an initial temperature T0 (e.g., -20 degrees celsius) to a temperature increase Δt (not less than 5 degrees celsius) at a charging rate of 0.3-5C to bring the temperature to a target temperature T1; continuously charging the energy storage device 100 from the target temperature T1 to 80% of SOC at a charging rate of 0.5-5C, and disassembling each energy storage device 100 charged to 80% of SOC to observe whether sodium is separated from the interface of the negative electrode plate.

The embodiment of the application also provides a determination method for uniform distribution of sodium supplementing particles. As shown in fig. 8, the method includes the following steps.

Step one: the positive plate comprises a coating, and the coating comprises a granular first sodium-containing compound and a granular second sodium-containing compound, wherein the first sodium-containing compound is a positive electrode active material, and the second sodium-containing compound is a nonmetallic sodium supplementing material.

Step two: and adjusting a scanning electron microscope to 1K magnification, enabling the accelerating voltage to be 5kV, observing the positive plate by adopting the scanning electron microscope to obtain an electron microscope image in an observation area, wherein the observation area comprises complete particles of the second sodium-containing compound, and the area of the observation area is not smaller than 6500 square micrometers and not larger than 7000 square micrometers.

Step three: the number of particles and the plurality of inter-particle distances of the second sodium-containing compound, and the orthographic projected area of each of the particles of the second sodium-containing compound, are determined in an electron micrograph.

Step four: the average area of the particles of the second sodium-containing compound in the electron microscopy image is determined from the orthographic projected area of each particle of the second sodium-containing compound.

Step five: and determining that the sodium compensating particles are uniformly distributed in the coating of the positive plate when the number of particles of the second sodium-containing compound is not less than 2 and not more than 5, and the distances among the particles of the second sodium-containing compound are all more than 6 microns and less than 75 microns, the average area of the particles of the second sodium-containing compound is not less than 160 square microns and not more than 1600 square microns, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound Na2 is not more than 890 square microns.

In the embodiment of the application, an electron microscope is used for determining an electron microscope image of an observation area on a coating of the positive plate, and then the particle number of the second sodium-containing compound in the observation area and the average area of the orthographic projection area of the particles of the second sodium-containing compound are determined according to the electron microscope image, so as to determine whether the particles of the second sodium-containing compound are uniformly distributed in the coating, further determine the sodium supplementing effect of the second sodium-containing compound on the positive plate, and simultaneously avoid the situation of sodium precipitation in a local area of the positive plate.

In the first step, the positive electrode sheet may be manufactured by the manufacturing method described in the above embodiment.

In the second step, the type of the scanning electron microscope may be zeiss sigma300, but may be any other type as long as particles in the observed area on the coating of the positive electrode sheet can be clearly observed. For other types of scanning electron microscopes, the magnification and the accelerating voltage of the type of scanning electron microscope can be slightly adjusted in order to ensure that the obtained electron microscope images can clearly distinguish particle types due to the difference of the structural parameters of the electron microscope.

In the third step, before determining the number of particles and the inter-particle distance of the second sodium-containing compound in the electron microscope image, and the orthographic projection area of each particle of the second sodium-containing compound, the particles of the first sodium-containing compound and the particles of the second sodium-containing compound may be distinguished according to the size of each particle in the electron microscope image, and further determined according to the distinguished particles of the second sodium-containing compound.

Wherein determining the orthographic projection area of each particle of the second sodium-containing compound in the electron micrograph comprises: determining the area of the edge surrounding area of the orthographic projection of the particles of the second sodium-containing compound, or determining the circle area of the minimum circumscribed circle of the orthographic projection of the particles of the second sodium-containing compound, or determining the circle area of the maximum inscribed circle of the orthographic projection of the particles of the second sodium-containing compound; or determining the sum of the areas of the plurality of mosaic patterns comprised by the orthographic projection of the particles of the second sodium-containing compound. The embodiments of the present application will be described with reference to the above embodiments, and will not be repeated.

In embodiments of the present application, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; the term "plurality" means two or more, unless expressly defined otherwise. The terms "mounted," "connected," "secured," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; "coupled" may be directly coupled or indirectly coupled through intermediaries. The specific meaning of the above terms in the embodiments of the present application will be understood by those skilled in the art according to specific circumstances.

In the description of the embodiments of the present application, it should be understood that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "rear", etc. are based on the directions or positional relationships shown in the drawings, are merely for convenience of describing the embodiments of the present application and to simplify the description, and do not indicate or imply that the devices or units referred to must have a specific direction, be configured and operated in a specific direction, and thus should not be construed as limiting the embodiments of the present application.

In the description of the present specification, the terms "one embodiment," "some embodiments," "particular embodiments," and the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of implementations of the application. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above is only a preferred example of the embodiment of the present application and is not intended to limit the embodiment of the present application, and various modifications and variations of the embodiment of the present application will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present application should be included in the protection scope of the embodiments of the present application.

Claims

1. A positive electrode sheet (21), characterized by comprising: a current collector (211), and a coating (212) on the surface of the current collector (211);

the coating (212) includes a particulate first sodium-containing compound (Na 1) and a second sodium-containing compound (Na 2), the first sodium-containing compound (Na 1) being a positive electrode active material, the second sodium-containing compound (Na 2) being a non-metallic sodium-containing compound, the sodium element content of the second sodium-containing compound (Na 2) being greater than the sodium element content of the first sodium-containing compound (Na 1), and the median particle size of the particles of the second sodium-containing compound (Na 2) being greater than the median particle size of the particles of the first sodium-containing compound (Na 1);

The number of particles of the second sodium-containing compound (Na 2) is not less than 2 and not more than 5, and the inter-particle distances of the particles of the second sodium-containing compound (Na 2) are each greater than 6 microns and less than 75 microns, the average area of the orthographic projection areas of the particles of the second sodium-containing compound (Na 2) is not less than 160 square microns and not more than 1600 square microns, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound (Na 2) is not more than 890 square microns, and the area of the observation area is not less than 6500 square microns and not more than 7000 square microns.

2. Positive electrode sheet (21) according to claim 1, characterized in that the orthographic projection area of the particles of the second sodium-containing compound (Na 2) in the observation area refers to the area of the edge-surrounding area of orthographic projection of the particles of the second sodium-containing compound (Na 2).

3. Positive electrode sheet (21) according to claim 1, characterized in that the orthographic projection area of the particles of the second sodium-containing compound (Na 2) in the observation area refers to the circle area of the smallest circumscribed circle of orthographic projection of the particles of the second sodium-containing compound (Na 2).

4. Positive electrode sheet (21) according to claim 1, characterized in that the orthographic projection area of the particles of the second sodium-containing compound (Na 2) in the observation area refers to the circular area of the largest inscribed circle of orthographic projections of the particles of the second sodium-containing compound (Na 2).

5. Positive electrode sheet (21) according to claim 1, characterized in that the orthographic projection area of the particles of the second sodium-containing compound (Na 2) in the observation area refers to the sum of the areas of the plurality of mosaic patterns comprised by orthographic projections of the particles of the second sodium-containing compound (Na 2).

6. Positive electrode sheet (21) according to any one of claims 1 to 5, wherein the particles of the second sodium-containing compound (Na 2) have a median particle diameter of not less than 10 μm.

7. The positive electrode sheet (21) as set forth in claim 6, characterized in that the particles of the second sodium-containing compound (Na 2) have a median particle diameter of not more than 20 μm.

8. The positive electrode sheet (21) as claimed in any one of claims 1 to 5, characterized in that the viewing area is rectangular and has a long side of 100 micrometers and a broad side of 67.2 micrometers.

9. The positive electrode sheet (21) of claim 1, wherein the second sodium-containing compound (Na 2) has the formula: naxUyVzTw, wherein x ranges from 1 to 5, y, z and w ranges from 0 to 10, and at least one of y, z and w is not 0,U and V, T is one of elements C, O, N, F, S, P, si, H, cl.

10. The positive electrode sheet (21) of claim 9 wherein the second sodium-containing compound (Na 2) is at least one of Na2CO3, na2O, na2O2, na3N, na3F, na3P, na C4O4, na2C3O3, na2C5O5, na2C6O6 inorganic and organic sodium-containing additives.

11. A method for determining uniform distribution of sodium compensating particles, the method comprising:

step five: and determining that sodium compensating particles are uniformly distributed in the coating of the positive electrode sheet when the number of particles of the second sodium-containing compound is not less than 2 and not more than 5, and the distances among the plurality of particles of the second sodium-containing compound (Na 2) are all greater than 6 microns and less than 75 microns, the average area of the particles of the second sodium-containing compound is not less than 160 square microns and not more than 1600 square microns, and the absolute value of the difference between the maximum orthographic projection area and the minimum orthographic projection area of the particles of the second sodium-containing compound (Na 2) is not more than 890 square microns.

12. The method of claim 11, wherein in step three, determining the orthographic projection area of each particle of the second sodium-containing compound in the electron micrograph comprises:

13. An energy storage device (100), comprising:

a housing (10) comprising a receiving chamber (11) having an opening;

an electrode assembly (20) accommodated in the accommodating cavity (11) and comprising a positive plate (21), a negative plate (22) and a separator (23) which are stacked, wherein the positive plate (21) is the positive plate (21) according to any one of claims 1 to 10;

an end cap unit (30) seals the opening of the accommodation chamber (11).