CN117133969A - Sodium ion battery monomer, preparation method thereof and related device - Google Patents

Sodium ion battery monomer, preparation method thereof and related device Download PDF

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Publication number
CN117133969A
CN117133969A CN202311380633.5A CN202311380633A CN117133969A CN 117133969 A CN117133969 A CN 117133969A CN 202311380633 A CN202311380633 A CN 202311380633A CN 117133969 A CN117133969 A CN 117133969A
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ion battery
lithium
sodium ion
sodium
electrolyte
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CN117133969B (en
Inventor
吴凯
陈佳华
李全国
唐正
叶永煌
许宝云
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/249—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders specially adapted for aircraft or vehicles, e.g. cars or trains
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The application belongs to the technical field of batteries, and particularly relates to a sodium ion battery monomer, a preparation method thereof and a related device. The sodium ion battery monomer comprises a negative electrode plate, wherein the negative electrode plate comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium elements; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm. According to the application, the lithium element is arranged in the solid electrolyte interface film, and the lithium element is controlled at a proper content, so that the loss of active sodium can be effectively reduced, meanwhile, the lithium ion transmission efficiency is good, and finally, the cycle life of the sodium ion battery can be effectively prolonged.

Description

Sodium ion battery monomer, preparation method thereof and related device
Technical Field
The application belongs to the technical field of batteries, and particularly relates to a sodium ion battery monomer, a preparation method thereof and a related device.
Background
Sodium ion batteries have a similar working principle to lithium ion batteries, and mainly rely on intercalation and deintercalation of sodium ions between a positive electrode and a negative electrode to realize interconversion of chemical energy and electric energy. Meanwhile, the sodium ion battery has the characteristics of rich raw material accumulation, wide distribution, low cost and the like, is widely focused and researched, and is expected to be applied to a bicycle and an energy storage system in the future.
Application scenes such as a two-wheel vehicle and an energy storage system require a long cycle life of the sodium ion battery. However, most sodium ion batteries often exhibit a short life during charge and discharge, and it is difficult to meet market demands.
Disclosure of Invention
In view of the above problems, the present application provides a sodium ion battery cell, a preparation method thereof, and a related device, which can solve the problem of short lifetime of a sodium ion battery.
In a first aspect, the present application provides a sodium ion battery cell comprising a negative electrode sheet comprising a solid electrolyte interface film comprising a lithium element; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm.
According to the embodiment of the application, the lithium element is introduced into the SEI film of the negative electrode plate of the sodium ion battery, so that the lithium-sodium mixed SEI film is formed. On the one hand, the presence of lithium element can reduce the sodium content in the SEI film, thereby reducing the consumption of active sodium; on the other hand, the solubility of the SEI film containing lithium is lower than that of a pure SEI film containing sodium, and the SEI film containing lithium has higher stability, so that the SEI film containing lithium and sodium has better stability, the repeated dissolution and reformation in the charge and discharge cycle process of a sodium ion battery are reduced, and the consumption of active sodium is further reduced.
Meanwhile, the content of lithium elements is controlled within a certain range, so that the lithium-sodium mixed SEI film has proper density, sodium ions can smoothly shuttle in the lithium-sodium mixed SEI film, and the lithium-sodium mixed SEI film has good sodium ion transmission efficiency.
Therefore, the embodiment of the application can effectively reduce the loss of active sodium by arranging the lithium element in the SEI film and controlling the lithium element to be in proper content, has good sodium ion transmission efficiency, and can finally effectively prolong the cycle life of the sodium ion battery.
In some embodiments, the lithium element accounts for 1-5 ppm of the mass content of the negative electrode plate. At this level, the sodium ion battery cell exhibits a very excellent cycle life.
In some embodiments, the lithium element is distributed in at least one position in the surface layer, the interior of the solid electrolyte interface film. The lithium element is distributed at any position in the SEI film, so that the stability of the SEI film can be improved, the loss of active sodium is reduced, the good sodium ion transmission efficiency is realized, and the cycle life of the sodium ion battery is prolonged.
In some embodiments, in the solid electrolyte interface film, the density of the surface layer is equal to or less than the density of the interior. The inner and outer compactness of SEI film influences the transmission condition of sodium ion, and then influences battery life. Therefore, the battery life can be improved by adjusting the density distribution of the SEI film. The density of the surface layer is smaller than or equal to that of the inside, and sodium ions can smoothly pass through the SEI film under the condition that the density of the surface layer is smaller than that of the inside, so that the service life of the battery is prolonged; further, in the case where the density of the surface layer is smaller than that of the inside, the battery can be made longer in life.
In a second aspect, the application provides a method for preparing a sodium ion battery cell, the sodium ion battery cell comprises a negative electrode piece, the negative electrode piece comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium element; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm;
the preparation method comprises the following steps:
preparing an electrode assembly comprising a positive electrode plate, injecting electrolyte into the electrode assembly, and performing formation treatment; wherein at least one of the electrolyte and the positive electrode sheet contains lithium element;
in the case where the electrolyte contains the lithium element, the lithium element accounts for more than 0 and less than or equal to 23ppm by mass in the electrolyte;
and under the condition that the positive electrode plate contains the lithium element, the mass content of the lithium element in the active layer contained in the positive electrode plate is more than 0 and less than or equal to 100ppm.
According to the embodiment of the application, the lithium element is added into at least one of the electrolyte and the positive electrode plate, and the content of the lithium element is controlled, so that the lithium element can participate in the formation of the SEI film in the single formation treatment of the sodium ion battery, and the lithium-sodium mixed SEI film with a certain lithium content is obtained, thereby being beneficial to prolonging the cycle life of the sodium ion battery.
Meanwhile, the preparation method is simple to operate and easy to industrialize by adding the required amount of lithium element into at least one of the electrolyte and the positive electrode plate on the basis of the traditional process.
In some embodiments, when the electrolyte contains the lithium element, the lithium element accounts for 2-10 ppm of the electrolyte by mass concentration.
In some embodiments, when the electrolyte contains the lithium element, the lithium element accounts for 4.5 to 10ppm by mass in the electrolyte.
In the case where lithium element is contained in the electrolyte of the sodium ion battery cell, the lithium content in the SEI film is related to the mass concentration of lithium element in the electrolyte. According to the embodiment of the application, the lithium element of the electrolyte is controlled at a certain concentration, so that the SEI film formed after formation treatment has the required content, and the cycle life of the sodium ion battery monomer is prolonged.
In some embodiments, when the positive electrode sheet contains the lithium element, the mass content of the lithium element in the active layer contained in the positive electrode sheet is 50-100 ppm.
In some embodiments, when the positive electrode sheet contains the lithium element, the mass content of the lithium element in the active layer contained in the positive electrode sheet is 70-100 ppm.
Under the condition that the positive electrode plate of the sodium ion battery monomer contains lithium element, the lithium content in the SEI film is related to the mass content of the lithium element in the positive electrode plate. According to the embodiment of the application, the lithium element of the positive electrode plate is controlled at a certain concentration, so that the SEI film formed after formation treatment has the required content, and the cycle life of the sodium ion battery monomer is prolonged.
In a third aspect, the present application provides another method for preparing a sodium ion battery cell, where the sodium ion battery cell includes a negative electrode piece, the negative electrode piece includes a solid electrolyte interface film, and the solid electrolyte interface film includes a lithium element; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm;
the preparation method comprises the following steps:
adding lithium element into the electrolyte of the sodium ion battery monomer subjected to the pre-formation treatment, wherein the mass concentration of the lithium element in the electrolyte is more than 0 and less than or equal to 23ppm;
and carrying out secondary formation treatment on the sodium ion battery monomer added with the lithium element.
An SEI film (mainly containing sodium compounds, which can be marked as an original SEI film) is formed in the sodium ion battery cell subjected to the pre-formation treatment. According to the embodiment of the application, lithium element is added into the electrolyte of the sodium ion battery monomer subjected to the pre-formation treatment, namely the electrolyte of the sodium ion battery monomer contains lithium element, and then the formation treatment is performed again. In the re-formation process, lithium element and sodium ions in the electrolyte are jointly involved in the formation of the SEI film, so that a lithium-sodium mixed SEI film is formed on at least one surface of the original SEI film. That is, the SEI film formed under the preparation method will have a double-layer structure or a sandwich structure. The lithium-sodium mixed SEI film performs surface protection on the original SEI film, so that dissolution of the original SEI film is reduced, and loss of active sodium is reduced. Meanwhile, due to the existence of lithium ions, the newly generated lithium-sodium mixed SEI film has lower sodium content than the original SEI film, so that the consumption of active sodium by the SEI film can be further reduced. In addition, the solubility of the SEI film containing lithium is lower than that of a pure SEI film containing sodium, so that the SEI film containing lithium has higher stability. Therefore, the lithium-sodium mixed SEI film has good stability, and the repeated dissolution and reformation conditions in the charge-discharge cycle process of the sodium ion battery are reduced, so that the consumption of active sodium is further reduced.
The concentration of lithium elements in the electrolyte is controlled, so that the formed lithium-sodium mixed SEI film has proper lithium content, proper compactness, and good sodium ion transmission efficiency, and sodium ions can smoothly shuttle in the lithium-sodium mixed SEI film.
Therefore, the embodiment of the application can effectively reduce the loss of active sodium by adding the lithium element into the sodium ion battery monomer subjected to the pre-formation treatment and controlling the lithium element to be in a proper content for the secondary formation treatment, has good sodium ion transmission efficiency, and can finally effectively prolong the cycle life of the sodium ion battery.
In some embodiments, the sodium ion battery cell comprises a positive electrode plate, the positive electrode plate contains lithium element, and the mass content of the lithium element contained in the positive electrode plate in the active layer contained in the positive electrode plate is more than 0 and less than or equal to 100ppm. By adding a certain amount of lithium element into the positive electrode plate, the lithium element can be participated in the electrolyte together to form a lithium-sodium mixed SEI film, and the lithium element can be further supplemented under the condition that the lithium element in the electrolyte is lost.
In some embodiments, the charging rates in the pre-formation process and the re-formation process are respectively and independently 0.05-0.5 c.
In some embodiments, the charging rates in the pre-formation process and the re-formation process are respectively and independently 0.1-0.3 c.
And when the lithium ion battery is charged under a small multiplying power, lithium elements and sodium ions can slowly and orderly form a lithium-sodium mixed SEI film, and the formed lithium-sodium mixed SEI film has proper compactness.
In some embodiments, the charge rate in the re-formation process step is higher than the charge rate in the pre-formation process step. In general, the density of the SEI film decreases as the charging rate increases. According to the embodiment of the application, after the lithium element is added into the electrolyte, the electrolyte is charged at a higher multiplying power, so that a loose lithium-sodium mixed SEI film is formed on the surface of an original SEI film containing sodium, and the transmission efficiency of sodium ions in the SEI film is improved.
In a fourth aspect, the present application provides a battery module, including the sodium ion battery cell of the first aspect.
The sodium ion battery monomer has excellent cycle life due to the combination of the SEI film with specific lithium content on the negative electrode plate. Therefore, the battery module including the sodium ion battery cell also exhibits a long life.
In a fifth aspect, the present application provides a battery pack comprising the battery module of the fourth aspect.
Similar to the battery module, the battery pack also exhibits a long life.
In a sixth aspect, the present application further provides an electrical device, including the sodium ion battery cell of the first aspect, or including the battery module of the fourth aspect, or including the battery pack of the fifth aspect.
The sodium ion battery monomer, the battery module and the battery pack disclosed by the embodiment of the application can be used for an electric device which takes a battery as a power supply or various energy storage systems which take the battery as an energy storage element for providing electric energy. The battery has the advantage of long service life, and therefore, the battery is beneficial to improving the use experience of various electric devices after being applied to the various electric devices.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic view of the structure of different SEI films according to an embodiment of the present application;
fig. 2 is a schematic view of a battery cell according to an embodiment of the present application;
fig. 3 is an exploded view of a battery cell according to an embodiment of the present application shown in fig. 2;
fig. 4 is a schematic view of a battery module according to an embodiment of the present application;
FIG. 5 is a schematic view of a battery pack according to an embodiment of the present application;
fig. 6 is an exploded view of the battery pack of the embodiment of the present application shown in fig. 5;
fig. 7 is a schematic view of an electric device using a battery as a power source according to an embodiment of the present application.
Reference numerals:
a1-electrode material, a 2-SEI film containing sodium, b 2-SEI film containing lithium, and c 2-lithium-sodium mixed SEI film;
01-shell, 02-cover plate, 03-electrode assembly, 04-battery cell, 05-battery module, 06-upper box and 07-lower box.
Detailed Description
Embodiments of the technical scheme of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present application, and thus are merely examples, and are not intended to limit the scope of the present application.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having" and any variations thereof in the description of the application and the claims and the description of the drawings above are intended to cover a non-exclusive inclusion.
In the description of embodiments of the present application, the technical terms "first," "second," and the like are used merely to distinguish between different objects and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated, a particular order or a primary or secondary relationship. In the description of the embodiments of the present application, the meaning of "plurality" is two or more unless explicitly defined otherwise.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.
In the description of the embodiments of the present application, the term "and/or" is merely an association relationship describing an association object, and indicates that three relationships may exist, for example, a and/or B may indicate: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are an "or" relationship.
In the description of embodiments of the application, the term "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.
It should be understood that, in various embodiments of the present application, the sequence number of each process described above does not mean that the execution sequence of some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
The mass of the related components mentioned in the description of the embodiments of the present application may refer not only to the specific content of each component, but also to the proportional relationship between the mass of each component, so long as the content of the related component in the description of the embodiments of the present application is scaled up or down within the scope of the disclosure of the embodiments of the present application. Specifically, the mass described in the description of the embodiment of the application may be a mass unit known in the chemical industry field such as [ mu ] g, mg, g, kg.
Sodium ion batteries have a similar working principle to lithium ion batteries, and mainly rely on intercalation and deintercalation of sodium ions between a positive electrode and a negative electrode to realize interconversion of chemical energy and electric energy. Meanwhile, the sodium ion battery has the characteristics of rich raw material accumulation, wide distribution, low cost and the like, is widely focused and researched, and is expected to be applied to a bicycle and an energy storage system in the future.
Application scenes such as a two-wheel vehicle and an energy storage system require a long cycle life of the sodium ion battery. In the charge and discharge process of the sodium ion battery, sodium ions released from the positive electrode form a solid electrolyte membrane (SEI film) containing sodium at the negative electrode, as shown in a diagram in fig. 1, a1 in the diagram represents an electrode material, and a2 represents the SEI film containing sodium), and the SEI film has the characteristic of being relatively unstable. Specifically, the solubility of the SEI film containing sodium is stronger than that of the SEI film in a lithium ion battery, and is easily reformed after dissolution in a cyclic process, thereby continuously consuming active sodium in the positive electrode, further causing irreversible capacity loss and affecting the life.
Considering that the solubility of the lithium-containing SEI film in an electrolyte is low, if lithium ions are introduced into a sodium ion battery, the stability of the SEI film in the sodium ion battery is expected to be improved. However, since the radius of lithium ions is significantly reduced compared with that of sodium ions, the lithium-containing SEI film may exhibit a dense characteristic (as shown in b-chart in FIG. 1, in which a1 represents an electrode material and b2 represents the lithium-containing SEI film), so that sodium ions having a large radius of ions are difficult to transport, affecting the ion transport efficiency and thus the cycle life of the sodium ion battery.
Therefore, improvement of the SEI film of the sodium ion battery is required to reduce sodium loss during cycling and to increase ion transport efficiency to extend the cycle life of the sodium ion battery.
According to the embodiment of the application, the lithium element is introduced into the SEI film of the negative electrode plate of the sodium ion battery cell, and the lithium element in the SEI film is controlled to be in a certain content, so that the stability of the SEI film can be improved, sodium ions can smoothly shuttle in the SEI film, the good sodium ion transmission efficiency is achieved, and the cycle life of the sodium ion battery is prolonged.
In the preparation method of the sodium ion battery monomer, the lithium element with the required amount can be directly added into the electrolyte or the positive electrode plate, or the electrolyte which can provide the lithium element with the required amount can be secondarily injected in the process of forming the sodium ion battery monomer.
The sodium ion monomer with excellent cycle life provided by the embodiment of the application can be assembled into a battery module or a battery pack, and further can be applied to manufacturing various electric devices.
The application is further illustrated by the following examples. It is to be understood that these examples are illustrative of the present application and are not intended to limit the scope of the present application.
[ sodium ion Battery monomer ]
The first aspect of the embodiment of the application provides a sodium ion battery monomer, which comprises a negative electrode plate, wherein the negative electrode plate comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium elements; the mass content of lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm.
The battery cell, also called an electric core, is the most basic unit of the battery, and comprises an electrode assembly and electrolyte (specifically, electrolyte in the embodiment of the application), wherein the electrode assembly generally comprises a positive electrode plate, a negative electrode plate and a separation film. The positive pole piece and the negative pole piece are sequentially laminated, and an isolating film is arranged between the positive pole piece and the negative pole piece to play a role in isolation, so that the bare cell is obtained, and the bare cell can be obtained after lamination or after winding. And placing the bare cell in an outer package, injecting electrolyte, and packaging to obtain the battery cell.
The solid electrolyte interface film, also called SEI film, contained in the negative electrode plate is a passivation film layer with solid electrolyte property formed on the surface of the negative electrode plate. After the sodium ion battery monomer is charged, the active material in the pole piece and substances in the electrolyte react electrochemically, and a reaction product is deposited on the surface of the negative pole piece to form the SEI film. In general, an SEI film of a common sodium ion battery cell mainly contains a sodium element, and the SEI film of the embodiment of the present application contains a lithium element, and thus, the SEI film is a lithium-sodium mixed SEI film.
It can be understood that, for the lithium element in the SEI film, it exists mainly in the form of complex organic matters, inorganic matters formed by the reaction of the lithium element with the substances in the electrolyte, for example, it can be formed by the lithium element with the solvent, trace moisture, HF, etc. (CH 2 OCO 2 Li) 2 、LiCH 2 CH 2 OCO 2 Li、CH 3 OCO 2 Li、LiOH、Li 2 CO 3 One or more of LiF, etc., or other forms. The lithium element in the SEI film may exist in different forms in different electrolyte compositions.
The mass content of the lithium element in the embodiment of the application can be obtained by testing by an inductively coupled plasma spectrometer (ICP). The SEI film is typically thin and light (its mass is much lower than that of the negative electrode sheet, and the mass of the negative electrode sheet as a whole is almost negligible), and is difficult to separate from the negative electrode sheet. Therefore, the mass content of lithium element in the negative electrode plate can be obtained by ICP detection on the negative electrode plate, and the mass content is used for representing the lithium element content in the SEI film.
According to the embodiment of the application, the lithium element is introduced into the SEI film of the negative electrode plate of the sodium ion battery to form a lithium-sodium mixed SEI film (as shown in a graph c of FIG. 1, a1 in the graph represents an electrode material, and c2 in the graph represents the lithium-sodium mixed SEI film). On the one hand, the presence of lithium element can reduce the sodium content in the SEI film, thereby reducing the consumption of active sodium; on the other hand, the solubility of the SEI film containing lithium is lower than that of a pure SEI film containing sodium, and the SEI film containing lithium has higher stability, so that the SEI film containing lithium and sodium has better stability, the repeated dissolution and reformation in the charge and discharge cycle process of a sodium ion battery are reduced, and the consumption of active sodium is further reduced.
Meanwhile, the content of lithium elements is controlled within a certain range, so that the lithium-sodium mixed SEI film has proper density, sodium ions can smoothly shuttle in the lithium-sodium mixed SEI film, and the lithium-sodium mixed SEI film has good sodium ion transmission efficiency.
Therefore, the embodiment of the application can effectively reduce the loss of active sodium by arranging the lithium element in the SEI film and controlling the lithium element to be in proper content, has good sodium ion transmission efficiency, and can finally effectively prolong the cycle life of the sodium ion battery.
In some embodiments, the lithium element accounts for 1-5 ppm, optionally 3-5 ppm, of the mass content of the negative electrode piece. For example, the mass content may be any one of the point values or a range between any two of the point values of 0.5ppm, 1ppm, 1.5ppm, 2ppm, 2.5ppm, 3ppm, 3.5ppm, 4ppm, 4.5ppm, 5ppm, 6ppm, 7ppm, 8ppm, 9ppm, 10ppm, 11ppm, 12ppm, 12.5 ppm. At this level, the sodium ion battery cell exhibits a very excellent cycle life.
In some embodiments, lithium elements are distributed in at least one position in the surface layer, the inside of the SEI film.
The surface layer of the SEI film is the outermost layer of the SEI film contacting with the outside, and generally, the region in the thickness range of 0-40% from outside to inside, alternatively 0-20% in the thickness range can be regarded as the surface layer. The region outside the surface layer may then be regarded as the inside of the SEI film. The distribution position of the lithium element can be determined by means of a scanning electron microscope spectroscopy technology. The lithium element is distributed at any position in the SEI film, so that the stability of the SEI film can be improved, the loss of active sodium is reduced, the good sodium ion transmission efficiency is realized, and the cycle life of the sodium ion battery is prolonged.
In some embodiments, the SEI film has a surface layer having a density less than or equal to the density of the interior, optionally the surface layer has a density less than the density of the interior.
The compactness refers to the tightness degree of substances and structures. The density of the SEI film surface layer can be equal to or less than the density of the inside, that is, the structure of the surface layer is the same as the tightness of the inside, or the structure of the surface layer is more loose than the inside. And the density relationship between the surface layer and the inside of the SEI film can be obtained by carrying out electron microscope observation on the section of the negative electrode plate in the thickness direction of the SEI film.
The inner and outer compactness of SEI film influences the transmission condition of sodium ion, and then influences battery life. Therefore, the battery life can be improved by adjusting the density distribution of the SEI film. The density of the surface layer is smaller than or equal to that of the inside, and sodium ions can smoothly pass through the SEI film under the condition that the density of the surface layer is smaller than that of the inside, so that the service life of the battery is prolonged; further, in the case where the density of the surface layer is smaller than that of the inside, the battery can be made longer in life.
The film layer with high density can be obtained by charging under low multiplying power, and the density is reduced along with the increase of the charging multiplying power. Therefore, in actual operation, the surface layer and the interior of the SEI film may have different densities by adjusting the charging rate in the formation process for forming the SEI film, for example, charging may be performed at a low rate and then at a high rate.
For more detailed technical features of the various groups of parts in the sodium-ion battery cell, reference may be made to the following:
1. electrolyte composition
The sodium ion battery cell contains electrolyte, and particularly can adopt solid electrolyte or electrolyte solution. Wherein the electrolyte may include an electrolyte sodium salt and a solvent.
Wherein the electrolyte sodium salt may include sodium hexafluorophosphate (NaPF 6 ) Sodium bis (fluorosulfonyl imide) (NaFSI), sodium trifluoromethane sulfonate (NaOTf), sodium sulfide (Na) 2 S), sodium chloride (NaCl), sodium fluoride (NaF), sodium sulfate (Na) 2 SO 4 ) Sodium carbonate (Na) 2 CO 3 ) Sodium phosphate (Na) 3 PO 4 ) Sodium nitrate (NaNO) 3 ) Sodium difluorooxalato borate (NaDFOB), sodium pyrophosphate (Na 4 P 2 O 7 ) Sodium Dodecyl Benzene Sulfonate (SDBS), sodium Dodecyl Sulfate (SDS), trisodium citrate, sodium metaborate (NaBO) 2 ) Sodium borate (Na) 2 B 4 O 7 ) Sodium molybdate (Na) 2 MoO 4 ) Sodium tungstate (Na) 2 WO 4 ) Sodium bromide (NaBr), sodium nitrite (NaNO) 2 ) Sodium iodate (NaIO) 3 ) Sodium iodide (NaI), sodium silicate (Na) 2 SiO 3 ) Sodium lignin sulfonate, sodium oxalate (Na 2 C 2 O 4 ) Sodium metaaluminate (NaAlO) 2 ) Sodium methylsulfonate, sodium acetate (CH) 3 COONa), sodium dichromate (Na 2 Cr 2 O 7 ) Sodium hexafluoroarsenate (NaAsF) 6 ) Sodium tetrafluoroborate (NaBF) 4 ) Sodium perchlorate (NaClO) 4 ) One or more of the following.
The mass content of the electrolyte sodium salt in the electrolyte may be set to 500 to 2000ppm, alternatively 800 to 1200ppm, for example, any one point value or a range between any two point values of 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1200ppm, 1400ppm, 1600ppm, 1800ppm, 2000 ppm.
The solvent may include one or more of Ethylene Carbonate (EC), ethylmethyl carbonate (EMC), dimethyl ether (DME), diethyleneglycol dimethyl ether, diethyleneglycol diethyl ether, tetraethyleneglycol dimethyl ether, 2, 2, 2-trifluoroethyl ether, ethyleneglycol diethyl ether, triethyleneglycol dimethyl ether, methyltrifluoroethyl carbonate (FEMC), dioxolane (DOL), acetonitrile (AN), fluorobenzene, triethylphosphate (TEP), sulfolane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethylsulfoxide, N dimethylacetamide.
The electrolyte may also include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.
The electrolyte may be configured as follows: and (3) dissolving the electrolyte sodium salt in a solvent in a protective atmosphere (such as argon, nitrogen and helium), and uniformly stirring.
2. Positive electrode plate
The sodium ion battery cell comprises a positive pole piece. For the sodium ion battery monomer, the active layer contained in the positive electrode plate comprises a positive electrode active material, a conductive agent and a binder, and optionally one or more of a thickening agent and a sodium supplementing additive; meanwhile, the positive electrode sheet generally further includes a current collector.
The positive electrode active materials are key substances which participate in chemical reaction of the battery in the positive electrode plate, the conductive agent is used for collecting micro-current between the positive electrode active materials and the current collector, so that the electronic conductivity is improved, and meanwhile, the conductive agent can also promote the infiltration of the electrolyte to the positive electrode plate. The binding agent can improve the bonding strength between substances in the active layer contained in the positive electrode plate and between the active layer contained in the positive electrode plate and the current collector. The thickener is beneficial to improving the viscosity degree of the positive electrode slurry and improving the processing performance of the positive electrode slurry. The sodium supplementing additive can remove sodium ions in the electrochemical reaction, supplement sodium ions lost by the positive electrode active material in the charging and discharging processes of the battery, improve the capacity of the battery and prolong the service life of the battery. The current collector is used for transporting electrons.
2.1. Positive electrode active material
The positive electrode active material may include one or more of layered oxides, polyanion-based compounds, and prussian blue-based compounds. For example, the layered oxide may include Na x MO 2 M= Fe, mn, ni, co, cr, sc, ti, V, cr, cu, zn and combinations thereof, 0.4.ltoreq.xLess than or equal to 1, e.g. NaVO 2 、NaFeO 2 、Na 0.7 CoO 2 、NaNi 1/3 Fe 1/3 Mn 1/3 O 2 、NaFe 0.5 Ni 0.5 O 2 、Na 0.6 MnO 2 、Na 0.44 MnO 2 、Na 0.65 Mn 0.75 Ni 0.25 O 2 、NaNi 0.5 Mn 0.5 O 2 、Na 0.78 Ni 0.23 Mn 0.69 O 2 、Na 0.67 Mn 0.67 Ni 0.33 O 2 Etc. The polyanionic compound may include one or more of phosphate, pyrophosphate, sulfate type, and anion doped type, such as olivine type NaFePO 4 、Na 2 FeP 2 O 7 、NaFePO 4 F、Na 3 V 2 (PO 4 ) 3 、NaFeSO 4 One or more of the following. Prussian blue compounds may 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 ]One or more of the following.
The mass content of the positive electrode active material in the active layer contained in the positive electrode sheet is 50% -98%, optionally 80% -95%, and for example, any one point value or a range value between any two points of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98% can be included. It can be appreciated that setting the mass content of the positive electrode active material in the active layer contained in the positive electrode sheet at a higher level can increase the energy density of the sodium ion battery.
2.2. Conductive agent
The conductive agent may include one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), ketjen black, carbon fibers, graphene.
The mass content of the conductive agent in the active layer contained in the positive electrode sheet is 0.5% -10%, optionally 1% -7%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a range between any two, and may be set to other content as required.
2.3. Adhesive agent
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 salt, polyacrylic acid, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, chlorinated rubber.
The mass content of the binder in the active layer contained in the positive electrode sheet is 0.5% to 15%, optionally 1% to 7%, for example, any one point value or a range value between any two points of 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or other contents may be set as required.
2.4. Thickener, sodium supplement additive
Exemplary thickeners include carboxymethyl cellulose (CMC). The mass content of the thickener in the active layer contained in the positive electrode sheet may be set to 0.5% -5%, optionally 1% -5%, including but not limited to any one point value or a range value between any two of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.
Exemplary sodium supplement additives include one or more of transition metal sodium salts, sodium azide, squaraine sodium salts, prussian blue sodium salts. The mass content of the sodium supplement additive in the positive electrode active layer may be set to be 0.1% -20%, for example, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or a range between any two.
2.5. Current collector
The active layer contained in the positive electrode plate is arranged on at least one side of the current collector, and optionally arranged on two sides of the current collector. The current collector may include, but is not limited to, a metal current collector, a carbon current collector, a conductive resin current collector, a metal and resin composite current collector, etc., more specifically, for example, aluminum, copper, nickel, titanium, iron, and their respective alloys, stainless steel, carbon fiber, carbon Nanotubes (CNT), graphite, etc. Optionally, the current collector comprises aluminum.
2.6. Preparation of positive electrode plate
In the embodiment of the application, the positive electrode plate can be prepared according to the following method:
dispersing a positive electrode active material, a conductive agent, and a binder (other components may be added as necessary) in a solvent (e.g., N-methylpyrrolidone NMP) to obtain a positive electrode slurry; and (3) coating the positive electrode slurry on a current collector, and drying and compacting to obtain the positive electrode plate.
3. Negative pole piece
The sodium ion battery cell includes a negative electrode sheet, which is typically isolated from a positive electrode sheet. The negative electrode tab 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 including a negative electrode active material. The SEI film may be attached to the surface of the anode active layer.
Wherein the negative electrode current collector may include, but is not limited to, a metal or a composite current collector. For example, as the metal, sodium, a sodium alloy, copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, or the like can be used. In the case of using sodium or a sodium alloy as the negative electrode current collector, since sodium or a sodium alloy itself may also be used as the negative electrode active material, the negative electrode tab may not contain a negative electrode active layer, and sodium or a sodium alloy is both the current collector and the negative electrode active material.
The composite current collector may include a composite material of a polymer material including, but not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc., and a metal including, but not limited to, sodium, copper alloy, nickel alloy, titanium alloy, silver alloy. The composite current collector may be obtained by blending a polymer material with a metal, or may be coated on at least one side of the polymer material by electroplating, coating or other means.
In the case where the negative electrode tab 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 mixed or composite material formed of any one or more of a carbon-based material, an alloy material, a titanium-based material, and a sodium metal. Wherein the carbon-based material includes, but is not limited to, one or more of graphite, soft carbon, hard carbon, carbon microspheres, carbon fibers; alloy materials include, but are not limited to, one or more of sodium tin alloy, sodium germanium alloy, sodium antimony alloy; titanium-based materials include, but are not limited to, one or more of titanium dioxide, titanates, titanophosphate.
The mass content of the anode active material in the anode active layer may be set to 85% to 98%, alternatively 95% to 98%, for example, any one point value or a range value between any two of 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%.
The anode active layer may further include one or more of a conductive agent and a binder. The conductive agent is used for collecting micro-current between the active materials and the current collector, so that the electronic conductivity is improved, and meanwhile, the conductive agent can also promote the infiltration of the electrolyte to the negative electrode plate. The binder can then increase the bond strength between the substances in the active layer and between the active layer and the current collector.
The mass content of the conductive agent in the anode active layer may be set to 0.5% to 10%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or any range between any two, and may be set to other content as required.
The conductive agent comprises one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), ketjen black, carbon fiber and graphene.
The mass content of the binder in the anode active layer is 0.5% to 10%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a range between any two, and may be set to other content as required.
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 salt, polyacrylic acid, polyacrylate, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, chlorinated rubber.
The anode 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 any one point value or a range value between any two of 0.5% -5%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.
4. Isolation film
The sodium ion battery monomer also comprises an isolating film, and the isolating film is arranged between the positive pole piece and the negative pole piece and can separate the positive pole from the negative pole. The isolating film can prevent the electrons in the battery from passing through freely and prevent the electrodes from being in short circuit, but can allow the ions in the electrolyte to pass through freely between the positive electrode plate and the negative electrode plate.
The separator may be any known porous separator having electrochemical stability and mechanical stability, such as a single-layer or multi-layer film of one or more of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).
5. External packing
The sodium ion battery cell may include an outer package. The outer package can be used for packaging an electrode assembly comprising a positive electrode plate, a negative electrode plate and a separation film, and electrolyte.
The outer package of the sodium ion battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like; but may also be a flexible bag, such as a bag-type flexible bag. The soft bag can be made of plastics such as polypropylene, polybutylene terephthalate, polybutylene succinate and the like.
The outer package shape of the sodium ion battery cell can be cylindrical, square or any other shape. For example, fig. 2 shows a sodium ion battery cell with a square outer package as an example.
Referring to fig. 3, the outer package may include a housing 01 and a cover 02. The casing 01 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a containing cavity. The housing 01 has an opening communicating with the accommodation chamber, and the cover plate 02 can be provided to cover the opening to close the accommodation chamber. The positive electrode sheet, the negative electrode sheet and the separator may be formed into the electrode assembly 03 through a winding process or a lamination process. One or more electrode assemblies 03 are enclosed in the receiving chamber. The electrolyte is impregnated in the electrode assembly 03.
[ method for preparing sodium ion Battery monomer ]
The second aspect of the embodiment of the application provides a preparation method of a sodium ion battery monomer, which comprises a negative electrode plate, wherein the negative electrode plate comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium element; the mass content of lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm;
the preparation method comprises the following steps:
preparing an electrode assembly comprising a positive electrode plate, injecting electrolyte into the electrode assembly, and performing formation treatment; wherein at least one of the electrolyte and the positive electrode sheet contains lithium element;
in the case that the electrolyte contains lithium element, the lithium element accounts for more than 0 mass concentration and less than or equal to 23ppm in the electrolyte;
when the positive electrode sheet contains lithium element, the mass content of the lithium element in the active layer contained in the positive electrode sheet is more than 0 and less than or equal to 100ppm.
Among them, formation is one of important processes in the preparation of a battery. After packaging a battery module (cell) including a positive electrode, a negative electrode, and a separator, and an electrolyte (electrolyte in the embodiment of the present application), a formation process, that is, charging and discharging the battery at a certain current, is generally performed. The formation function is to activate the positive and negative active materials inside the electrode and form an SEI film on the surface of the electrode (such as a negative electrode).
According to the embodiment of the application, the lithium element is added into at least one of the electrolyte and the positive electrode plate, and the content of the lithium element is controlled, so that the lithium element can participate in the formation of the SEI film in the single formation treatment of the sodium ion battery, and the lithium-sodium mixed SEI film with a certain lithium content is formed, thereby being beneficial to prolonging the cycle life of the sodium ion battery.
Meanwhile, the preparation method is simple to operate and easy to industrialize by adding the required amount of lithium element into at least one of the electrolyte and the positive electrode plate on the basis of the traditional process.
In some embodiments, where the electrolyte contains lithium, the lithium may be present in the electrolyte at a mass concentration of 2 to 10ppm, alternatively 4.5 to 10ppm, for example, at any one point value or in a range between any two point values of 1ppm, 1.5ppm, 2ppm, 2.3ppm, 2.5ppm, 3ppm, 3.5ppm, 4ppm, 4.5ppm, 4.6ppm, 5ppm, 5.5ppm, 6ppm, 6.5ppm, 7ppm, 7.5ppm, 8ppm, 8.8ppm, 9ppm, 9.2ppm, 9.5ppm, 10ppm, 15ppm, 20ppm, 23 ppm. In the process of preparing the sodium ion battery monomer, the concentration of lithium element in the electrolyte can be determined according to the mass of the lithium compound added when preparing the electrolyte; alternatively, the concentration of lithium element in the electrolyte may be measured spectrophotometrically. Research shows that in the case that the electrolyte of the sodium ion battery monomer contains lithium element, the lithium content in the SEI film is related to the mass concentration of the lithium element in the electrolyte. According to the embodiment of the application, the lithium element of the electrolyte is controlled at a certain concentration, so that the SEI film formed after formation treatment has the required content, and the cycle life of the sodium ion battery monomer is prolonged.
In some embodiments, when the positive electrode sheet contains lithium, the mass content of the lithium element in the active layer contained in the positive electrode sheet is 50 to 100ppm, optionally 70 to 100ppm, and for example, may be any one point value or a range between any two point values of 10ppm, 20ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, and 100 ppm. In the process of preparing the sodium ion battery monomer, the content of lithium element in the positive electrode plate can be determined according to the mass of the lithium compound added in the process of preparing the positive electrode plate; alternatively, the measurement may be performed by spectrophotometry, SEM-EDS, ICP, or the like. Under the condition that the positive electrode plate of the sodium ion battery monomer contains lithium element, the lithium content in the SEI film is related to the mass content of the lithium element in the positive electrode plate. According to the embodiment of the application, the lithium element of the positive electrode plate is controlled at a certain concentration, so that the SEI film formed after formation treatment has the required content, and the cycle life of the sodium ion battery monomer is prolonged.
In some embodiments, the positive electrode sheet contains lithium elements, which are distributed in an active layer contained in the positive electrode sheet, and/or which are attached to the surface of the positive electrode sheet. The lithium element is distributed in an active layer contained in the positive electrode plate, namely, the lithium element is taken as a component part of the active layer; the lithium element is attached to the surface of the positive electrode plate, namely the surface of the positive electrode plate is coated with a film containing the lithium element, namely the positive electrode plate sequentially comprises a current collector, an active layer and a film containing the lithium element from inside to outside. Lithium elements are added into the positive electrode plate, and lithium ions can be provided by the lithium elements under different distribution forms so as to form a lithium-sodium mixed SEI film. Also, the lithium-sodium mixed SEI film generally tends to be formed on the surface of the negative electrode, and thus the addition of lithium element in the positive electrode sheet can reduce the coverage of the electrode, especially the surface of the negative electrode. Meanwhile, the distribution mode of the lithium element in the positive electrode plate has little influence on the adhesiveness inside the active layer and the adhesiveness between the active layer and the current collector of the positive electrode plate, so that after the lithium element is added into the positive electrode plate, the positive electrode plate can still keep good adhesiveness, thereby being beneficial to keeping good electrochemical performance.
In some embodiments, the lithium element of at least one of the electrolyte and the positive electrode sheet is derived from a lithium compound including lithium hexafluorophosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium perchlorate (LiClO) 4 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium bis (fluorosulfonyl) imide (LiLSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTf), lithium difluorooxalato borate (LiDFOB), lithium bis (oxalato) borate (LiBOB), lithium difluorophosphate (LiPO) 2 F 2 ) Lithium difluorooxalate phosphate (LiDFOP), lithium tetrafluorooxalate phosphate (LiTFOP), lithium carbonate (Li) 2 CO 3 ) One or more of lithium hydroxide (LiOH), lithium chloride (LiCl). These lithium compounds can provide lithium element for at least one of the electrolyte and the positive electrode sheet, and thus participate in the formation of the SEI film.
In the case where the electrolyte contains a lithium element, the corresponding lithium compound may be selected to have good solubility in the electrolyte, and specifically, lithium salts among the above-mentioned various lithium compounds may be selected. For example, in the electrolyte, the lithium compound may include lithium hexafluorophosphate (LiPF 6 ) Lithium tetrafluoroborate (LiBF) 4 ) Lithium perchlorate (LiClO) 4 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium bis (fluorosulfonyl) imide (LiLSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTf), bis (LiOTf)Lithium fluoxalate borate (LiDFOB), lithium bisoxalato borate (LiBOB), lithium difluorophosphate (LiPO) 2 F 2 ) One or more lithium salts of lithium difluorooxalato phosphate (LiDFOP), lithium tetrafluorooxalato phosphate (LiTFOP).
In the case of the positive electrode sheet containing lithium element, the solubility requirement for the lithium compound is low in terms of selection of the lithium compound. Meanwhile, in consideration of compatibility of the lithium compound with other components in the positive electrode sheet, the lithium compound may include lithium carbonate (Li 2 CO 3 ) Lithium salts such as lithium chloride (LiCl) may include lithium hydroxide (LiOH).
In the case where the lithium element is contained in the electrolyte, the mass concentration of the lithium compound in the electrolyte may be set to a range of 500ppm or less, optionally 50 to 200ppm, and still optionally 100 to 200ppm, and for example, may be in a range of 10ppm, 15ppm, 20ppm, 23ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 150ppm, 200ppm, 250ppm, 300ppm, 350ppm, 400ppm, 450ppm, 500ppm, or any one point value or any two point values.
When the positive electrode sheet contains a lithium element, the mass content of the lithium compound in the active layer contained in the positive electrode sheet may be set to a range of 0.06% or more, optionally 0.02% to 0.06%, and may be, for example, any one point value or a range between any two point values of 0.005%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, 0.055%, and 0.06%.
In some embodiments, the charging rate in the formation processing step is 0.05 to 0.5C, optionally 0.1 to 0.3C, for example, the charging rate may be any one point value or a range value between any two of 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, 0.35C, 0.4C, 0.45C, and 0.5C.
Typically, the formation process steps include: and charging the sodium ion battery cell to a cut-off voltage. The charging speed can be measured by the charging rate, i.e. the current intensity required by the battery to charge to its rated capacity at a specified time. The charge magnification and the discharge magnification may be directly set on an apparatus for formation processing (for example, a formation tank). And when the lithium ion battery is charged under a small multiplying power, lithium elements and sodium ions in the electrolyte can slowly and orderly form a lithium-sodium mixed SEI film, and the formed lithium-sodium mixed SEI film has proper compactness.
In the manufacturing method of the second aspect, the step of manufacturing the electrode assembly including the positive electrode tab may include: and sequentially laminating or winding the positive electrode plate, the isolating film and the negative electrode plate to form the electrode assembly. Other possible methods may also be employed to prepare the electrode assembly.
The third aspect of the embodiment of the application provides another preparation method of a sodium ion battery monomer, wherein the sodium ion battery monomer comprises a negative electrode plate, the negative electrode plate comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium element; the mass content of lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm;
the preparation method comprises the following steps:
adding lithium element into the electrolyte of the sodium ion battery monomer subjected to the pre-formation treatment, wherein the mass concentration of the lithium element in the electrolyte is more than 0 and less than or equal to 23ppm;
and carrying out secondary formation treatment on the sodium ion battery monomer added with the lithium element.
An SEI film (mainly containing sodium compounds, which can be marked as an original SEI film) is formed in the sodium ion battery cell subjected to the pre-formation treatment. According to the embodiment of the application, lithium element is added into the electrolyte of the sodium ion battery monomer subjected to the pre-formation treatment, namely the electrolyte of the sodium ion battery monomer contains lithium element, and then the formation treatment is performed again. In the re-formation process, lithium element and sodium ions in the electrolyte are jointly involved in the formation of the SEI film, so that a lithium-sodium mixed SEI film is formed on at least one surface of the original SEI film. That is, the SEI film formed under the preparation method will have a double-layer structure or a sandwich structure. The lithium-sodium mixed SEI film performs surface protection on the original SEI film, so that dissolution of the original SEI film is reduced, and loss of active sodium is reduced. Meanwhile, due to the existence of lithium ions, the newly generated lithium-sodium mixed SEI film has lower sodium content than the original SEI film, so that the consumption of active sodium by the SEI film can be further reduced. In addition, the solubility of the SEI film containing lithium is lower than that of a pure SEI film containing sodium, so that the SEI film containing lithium has higher stability. Therefore, the lithium-sodium mixed SEI film has good stability, and the repeated dissolution and reformation conditions in the charge-discharge cycle process of the sodium ion battery are reduced, so that the consumption of active sodium is further reduced.
In combination with the control of the concentration of lithium element in the electrolyte (regarding the detailed content setting of lithium element in the electrolyte of the sodium ion battery monomer, reference may be made to the preparation method of the second aspect, which is not repeated herein), the formed lithium-sodium mixed SEI film may have a suitable lithium content, exhibit a suitable density, and enable sodium ions to smoothly shuttle in the lithium-sodium mixed SEI film, thereby having a good sodium ion transmission efficiency.
Therefore, the embodiment of the application can effectively reduce the loss of active sodium by adding the lithium element into the sodium ion battery monomer subjected to the pre-formation treatment and controlling the lithium element to be in a proper content for the secondary formation treatment, has good sodium ion transmission efficiency, and can finally effectively prolong the cycle life of the sodium ion battery.
In some embodiments, the sodium ion battery cell comprises a positive electrode sheet, the positive electrode sheet contains lithium element, and the mass content of the lithium element contained in the positive electrode sheet in the active layer contained in the positive electrode sheet is more than 0 and less than or equal to 100ppm. Regarding the content setting of lithium element in the positive electrode sheet, reference may be made to the preparation method of the second aspect, and details thereof will not be repeated here. By adding a certain amount of lithium element into the positive electrode plate, the lithium element can be participated in the electrolyte together to form a lithium-sodium mixed SEI film, and the lithium element can be further supplemented under the condition that the lithium element in the electrolyte is lost.
In some embodiments, the charging rates in the pre-formation treatment and the re-formation treatment steps are respectively and independently 0.05-0.5C, optionally 0.1-0.3C, for example, the charging rate may be any one point value or a range value between any two points of 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, 0.35C, 0.4C, 0.45C and 0.5C. And when the lithium ion battery is charged under a small multiplying power, lithium elements and sodium ions can slowly and orderly form a lithium-sodium mixed SEI film, and the formed lithium-sodium mixed SEI film has proper compactness.
It will be appreciated that the charge rates employed in the pre-formation process and the re-formation process steps may be the same or different. Optionally, the charge rate in the re-formation processing step is higher than the charge rate in the pre-formation processing step. For example, the charging rate in the pre-formation treatment step is 0.05 to 0.2C, optionally 0.05 to 0.1C; the charging rate in the re-formation treatment step is 0.3-0.5C, optionally 0.3-0.4C. In general, the density of the SEI film decreases as the charging rate increases. After adding lithium element into electrolyte, charging is carried out by adopting a higher multiplying power, which is beneficial to forming a loose lithium-sodium mixed SEI film on the surface of an original SEI film containing sodium, thereby improving the transmission efficiency of sodium ions in the SEI film.
In some embodiments, the discharge rates in the pre-formation treatment and the re-formation treatment steps are each independently 0.05 to 0.5C, optionally 0.1 to 0.3C, for example, the discharge rate may be any one point value or a range value between any two of 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C, 0.35C, 0.4C, 0.45C, 0.5C. The discharge multiplying power in the steps of the pre-formation treatment and the re-formation treatment can be the same or different; meanwhile, the discharge rate in the pre-formation process may be the same as or different from the charge rate in this step. Similarly, the discharge rate in the reforming process may be the same as or different from the charge rate in this step.
In some embodiments, the manner of adding the lithium element includes: and injecting the electrolyte containing lithium into the sodium ion battery cell subjected to the pretreatment.
Specifically, before the pre-formation treatment, the sodium ion battery monomer comprises a first electrolyte; after the sodium ion battery monomer is subjected to pre-formation treatment, injecting a second electrolyte containing lithium element, and mixing the second electrolyte with the first electrolyte to obtain a third electrolyte; the mass concentration of lithium element in the third electrolyte is greater than 0 and less than or equal to 23ppm.
Wherein the lithium element in the second electrolyte may be provided by adding a lithium compound to the second electrolyte, and the mass concentration of the lithium compound in the second electrolyte may be set to be between 0 and 5000ppm (excluding 0), for example, any one point value or a range between any two point values of 50ppm, 100ppm, 150ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm, 3000ppm, 3500ppm, 4000ppm, 4500ppm, 5000 ppm. The second electrolyte and the first electrolyte are mixed in a certain proportion, so that the mass concentration of lithium element in the third electrolyte is more than 0 and less than or equal to 23ppm, for example, the volume of the second electrolyte can be set to be 5% -60% of the third electrolyte, alternatively 10% -15%, for example, any one point value or any range between any two point values of 5%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% and 60%.
Meanwhile, the first electrolyte may not contain lithium element. Further, other components of the first electrolyte and the second electrolyte and their concentrations may be the same or different except for the lithium element (or lithium compound). In order to maintain consistency of the electrolytes, the first electrolyte is identical to the second electrolyte in terms of other components and concentrations except for lithium element (or lithium compound). For example, the first electrolyte and the second electrolyte each include an electrolyte sodium salt and a solvent, and optionally also include additives such as a negative electrode film-forming additive, a positive electrode film-forming additive, and the like. The electrolyte sodium salt, its concentration, the solvent type, etc. may be referred to as the sodium ion battery cell of the first aspect, and will not be described herein.
[ Battery Module, battery pack ]
The embodiment of the application also provides a related device of the sodium ion battery monomer, which comprises a battery module and a battery pack.
An embodiment of the present application provides a battery module, including the above sodium ion battery cell.
A fifth aspect of the embodiment of the present application provides a battery pack, including the above battery module.
The battery module is formed by integrating one or more battery cells, and can provide higher voltage and capacity and output with specific functions. One or more battery modules are mounted in a case of a battery, and a battery management system or the like is generally added to form a battery pack. The battery pack is typically a product provided to the user.
Referring to fig. 4, there is shown an exemplary battery module. In the battery module, the plurality of battery cells 04 may be sequentially arranged along the length direction of the battery module. Of course, the arrangement may be performed in any other way. The plurality of battery cells 04 may be further fixed by fasteners.
Alternatively, the battery module may further include a case having an accommodating space in which the plurality of battery cells 04 are accommodated.
Reference is made to fig. 5 and 6, which are battery packs as one example. A battery case and a plurality of battery modules 05 disposed in the battery case may be included in the battery pack. The battery box includes an upper box body 06 and a lower box body 07, and the upper box body 06 can be covered on the lower box body 07 and forms a closed space for accommodating the battery module 05. The plurality of battery modules 05 may be arranged in the battery case in any manner.
The sodium ion battery monomer has excellent cycle life due to the combination of the SEI film with specific lithium content on the negative electrode plate. Therefore, the battery module or the battery pack including the sodium ion battery cell also exhibits a long life.
[ electric device ]
The embodiment of the application also provides another related device of the sodium ion battery monomer, which is an electric device.
The embodiment of the application also provides an electric device, which comprises the sodium ion battery monomer, the battery module or the battery pack.
The sodium ion battery monomer, the battery module and the battery pack disclosed by the embodiment of the application can be used for an electric device which takes a battery as a power supply or various energy storage systems which take the battery as an energy storage element for providing electric energy. The battery has the advantage of long service life, and therefore, the battery is beneficial to improving the use experience of various electric devices after being applied to the various electric devices.
The powered device may include, but is not limited to, a cell phone, tablet, notebook computer, electric toy, electric tool, battery car, electric car, ship, spacecraft, and the like. Among them, the electric toy may include fixed or mobile electric toys, such as game machines, electric car toys, electric ship toys, electric plane toys, and the like, and the spacecraft may include planes, rockets, space planes, and spacecraft, and the like. As the electricity consumption device, a battery cell, a battery module, or a battery pack in the battery may be selected according to the use requirement thereof.
Fig. 7 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or the like. In order to meet the requirements of the electric device for high power and high energy density of the battery, a battery pack or a battery module may be used.
Embodiments of the present application are described in detail below. The following examples are illustrative only and are not to be construed as limiting the application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
Examples A1 to A4 and comparative examples A1 to A4
Example A1
The present embodiment provides a sodium ion battery cell, wherein the electrolyte contains lithium salt LiPF 6 . Specifically, each component of the sodium ion battery monomer and the assembly method are as follows:
(1) Electrolyte solution
Lithium salt LiPF was charged in an argon atmosphere glove box 6 And sodium salt NaPF 6 Dissolved in carbonate solvent [ ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate fec=47.5: 47.5:5 (body)Product ratio]Uniformly stirring to obtain LiPF 6 Concentration by mass of 50ppm, naPF 6 Electrolyte with mass concentration of 1000 ppm.
(2) Positive electrode plate
The positive electrode active material (Na 0.67 Mn 0.67 Ni 0.33 O 2 ) And (3) fully stirring and uniformly mixing the conductive agent (conductive carbon) and the binder (polyvinylidene fluoride, PVDF) in the solvent (N-methylpyrrolidone, NMP) to obtain the positive electrode slurry. Wherein the mass ratio of the positive electrode active material, the solvent, the conductive agent and the binder is 95:100:2:3. and (3) coating the positive electrode slurry on a current collector (aluminum foil), and drying and cold pressing to obtain a positive electrode plate.
(3) Negative pole piece
And (3) fully stirring and uniformly mixing the anode active material (hard carbon), the conductive agent (conductive carbon) and the binder (carboxymethyl cellulose (CMC)) in deionized water to obtain anode slurry. Wherein the mass ratio of the anode active material to deionized water to the conductive agent to the binder is 95:100:2:3. and (3) coating the negative electrode slurry on a current collector (copper foil), and drying and cold pressing to obtain a negative electrode plate.
(4) Isolation film
The glass fiber film is used as a separation film.
(5) Sodium ion battery cell
And stacking the positive electrode plate, the glass fiber film and the negative electrode plate in sequence, winding to form an electrode assembly, loading the electrode assembly into a packaging shell, adding electrolyte, sealing, forming and standing. The formation process comprises the following steps: placing the sodium ion battery monomer in a formation cabinet, and charging to cut-off voltage of 4.0V at 25 ℃ under the multiplying power of 0.1C; then discharging to the lower limit voltage of 1.5V under the multiplying power of 0.1C to finish the formation of the sodium ion battery monomer.
Example A2
The present embodiment provides a sodium ion battery cell, which is different from embodiment A1 in that: liPF in electrolyte 6 The mass concentration was 100ppm.
Example A3
The present embodiment provides a sodium ionThe battery cell differs from example A1 in that: liPF in electrolyte 6 The mass concentration was 200ppm.
Example A4
The present embodiment provides a sodium ion battery cell, which is different from embodiment A1 in that: liPF in electrolyte 6 The mass concentration was 500ppm.
Comparative example A1
This comparative example provides a sodium ion battery cell, which differs from example A1 in that: liPF in electrolyte 6 The mass concentration is 0, i.e. no LiPF is added into the electrolyte 6 。
Comparative example A2
This comparative example provides a sodium ion battery cell, which differs from example A1 in that: liPF in electrolyte 6 The mass concentration was 600ppm.
Comparative example A3
This comparative example provides a sodium ion battery cell, which differs from example A1 in that: liPF in electrolyte 6 The mass concentration was 700ppm.
Comparative example A4
This comparative example provides a sodium ion battery cell, which differs from example A1 in that: liPF in electrolyte 6 The mass concentration was 800ppm.
[ lithium content and cycle life ]
After formation, SEI films are formed on the surfaces of the negative electrode plates of the sodium ion battery cells in examples A1 to A4 and comparative examples A1 to A4, namely, the negative electrode plates comprise solid electrolyte interface films. Dismantling the fully-placed sodium ion battery monomer, soaking and cleaning the negative electrode plate by using a dimethyl carbonate (DMC) solvent to remove impurities, drying, and quantitatively measuring the lithium element in the negative electrode plate by using an ICP method, wherein the specific flow is as follows: scraping the film powder of the negative electrode plate, putting the powder into 10mL of prepared concentrated nitric acid to start digestion, transferring the powder into a 100mL volumetric flask to fix the volume, taking out the solution, and detecting in an ICP spectrometer to obtain the mass content of lithium element in the negative electrode plate, namely the mass content of lithium element in the negative electrode plate. The lithium elements in the negative electrode plate after the formation are all detected from the SEI film, so that the mass content of the lithium elements in the negative electrode plate after the formation can be used for reflecting the mass content of the lithium elements in the SEI film. The results are shown in Table 1 below.
Meanwhile, the cycle life of the sodium ion battery cells of examples A1 to A4 and comparative examples A1 to A4 were tested. The testing method comprises the following steps:
at 25 ℃, the sodium ion battery monomer is charged to 4.0V at a constant current of 0.1C multiplying power, then is charged to 0.05C at a constant voltage of 4.0V, then is left stand for 5min, is discharged to 1.5V at a constant current of 0.1C multiplying power, and is left stand for 5min, wherein the discharge capacity of the sodium ion battery monomer is recorded as the discharge capacity (initial discharge capacity) of the 1 st cycle of the sodium ion battery monomer in a cycle of charging and discharging process. And (3) continuously carrying out cyclic charge and discharge test on the sodium ion battery monomer according to the method until the discharge capacity is reduced to 80% of the initial discharge capacity, and recording the cycle number, namely the cycle life of the sodium ion battery monomer.
The relevant lithium content and the corresponding cycle life test results of the sodium ion battery cells of examples A1 to A4 and comparative examples A1 to A4 are shown in the following table.
In Table 1, "lithium element mass concentration in electrolyte" is based on LiPF 6 The mass concentration of the individual lithium element in the electrolyte obtained after the mass concentration conversion. "cycle life change rate" means that the sodium ion battery cell is free of LiPF in the electrolyte 6 Cycle life change rate in the case of (comparative example A1).
Table 1 shows that comparative example A1 uses no LiPF added 6 After 1000 cycles, the discharge capacity of the assembled sodium ion battery monomer is attenuated to 80% of the initial discharge capacity. Examples A1 to A4 were prepared by adding a certain amount of LiPF to an electrolyte 6 The cycle life of the sodium ion battery monomer can be effectively prolonged. This is mainly due to LiPF 6 Can provide lithium ions which are co-located on the surface of the negative electrode plate together with sodium ions in the electrolyte in the formation processThe lithium-sodium mixed SEI film is generated, so that the stability of the SEI film can be improved, and the loss of active sodium can be reduced; and the lithium-sodium mixed SEI film has a proper content of lithium element (characterized by the mass content of lithium element in a negative electrode plate in table 1), shows proper compactness and can be used for rapid transmission of sodium ions.
However, liPF in electrolyte 6 In the case of an excessively high concentration, for example, comparative examples A2 to A4, the cycle life of the sodium ion battery cell is not increased and decreased. The lithium-sodium mixed SEI film is mainly characterized in that the content of lithium element in the formed lithium-sodium mixed SEI film is too high, the structure is too compact, and sodium ions with large ionic radius are difficult to transmit.
Therefore, by forming an SEI film with a certain lithium content on the negative electrode plate, the cycle life of the sodium ion battery cell can be effectively prolonged.
Examples B1 to B3 and comparative examples B1 to B4
Example B1
The present embodiment provides a sodium ion battery cell, in which lithium salt-containing LiPF is injected during the formation of the battery cell 6 Is used as an electrolyte. Specifically, each component of the sodium ion battery monomer and the assembly method are as follows:
(1) Electrolyte solution
Electrolyte 1: sodium salt NaPF was taken in an argon atmosphere glove box 6 Dissolved in carbonate solvent [ ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate fec=47.5: 47.5:5 (volume ratio)]Uniformly stirring to obtain NaPF 6 Electrolyte 1 with a mass concentration of 1000 ppm.
Electrolyte 2: lithium salt LiPF was charged in an argon atmosphere glove box 6 And sodium salt NaPF 6 Dissolved in carbonate solvent [ ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate fec=47.5: 47.5:5 (volume ratio)]Uniformly stirring to obtain LiPF 6 500ppm by mass of NaPF 6 Electrolyte 2 with a mass concentration of 1000 ppm.
(2) Positive electrode plate
The positive electrode active material (Na 0.67 Mn 0.67 Ni 0.33 O 2 ）、And (3) fully stirring and uniformly mixing the conductive agent (conductive carbon) and the binder (polyvinylidene fluoride, PVDF) in a solvent (N-methylpyrrolidone, NMP) to obtain the anode slurry. Wherein the mass ratio of the positive electrode active material, the solvent, the conductive agent and the binder is 95:100:2:3. and (3) coating the positive electrode slurry on a current collector (aluminum foil), and drying and cold pressing to obtain a positive electrode plate.
(3) Negative pole piece
And (3) fully stirring and uniformly mixing the anode active material (hard carbon), the conductive agent (conductive carbon) and the binder (carboxymethyl cellulose (CMC)) in deionized water to obtain anode slurry. Wherein the mass ratio of the anode active material to deionized water to the conductive agent to the binder is 95:100:2:3. and (3) coating the negative electrode slurry on a current collector (copper foil), and drying and cold pressing to obtain a negative electrode plate.
(4) Isolation film
The glass fiber film is used as a separation film.
(5) Sodium ion battery cell
The positive electrode sheet, the glass fiber film and the negative electrode sheet are sequentially stacked, an electrode assembly is formed after winding, the electrode assembly is arranged in a packaging shell, an electrolyte 1 is added, then the packaging shell is sealed, and then primary formation (pre-formation) is carried out. The first formation process comprises the following steps: placing the sodium ion battery monomer in a formation cabinet, and charging to cut-off voltage of 4V at 25 ℃ under the multiplying power of 0.1C; then discharging to the lower limit voltage of 1.5V under the multiplying power of 0.1C to finish the first formation of the sodium ion battery cell.
After the first formation is completed, the electrolyte 2 is injected into the sodium ion battery cell and then sealed again, wherein the volume of the electrolyte 2 added is 10% of the total electrolyte (all electrolyte contained in the sodium ion battery cell after the electrolyte 2 is injected), so that the LiPF in the total electrolyte 6 The mass concentration was 50ppm. Then, a second chemical conversion is performed. The second chemical conversion process comprises the following steps: and placing the sodium ion battery monomer in a formation cabinet, charging to 4.0V at the rate of 0.3C at the temperature of 25 ℃, and discharging to the lower limit voltage of 1.5V at the rate of 0.3C to complete secondary formation.
Example B2
The present embodiment provides a sodium ion battery cell, which is different from embodiment B1 in that: liPF in electrolyte 2 6 The mass concentration is 1000ppm. Thus, after the first formation is completed and electrolyte 2 is injected, liPF is contained in the entire electrolyte of the sodium ion battery cell 6 The mass concentration was 100ppm.
Example B3
The present embodiment provides a sodium ion battery cell, which is different from embodiment B1 in that: liPF in electrolyte 2 6 The mass concentration was 2000ppm. Thus, after the first formation is completed and electrolyte 2 is injected, liPF is contained in the entire electrolyte of the sodium ion battery cell 6 The mass concentration was 200ppm.
Comparative example B1
This comparative example provides a sodium ion battery cell, which differs from example B1 in that: after the end of the first formation, the electrolyte 2 was not injected, while the second formation was not performed. Thus, liPF in the bulk electrolyte of sodium ion battery cells 6 The mass concentration is 0.
Comparative example B2
This comparative example provides a sodium ion battery cell, which differs from example B1 in that: liPF in electrolyte 2 6 The mass concentration is 0, i.e. electrolyte 2 does not contain LiPF 6 。
Comparative example B3
This comparative example provides a sodium ion battery cell, which differs from example B3 in that: after the first formation, the volume of the electrolyte 2 added was 30% of the total electrolyte. Thus, after the first formation is completed and electrolyte 2 is injected, liPF is contained in the entire electrolyte of the sodium ion battery cell 6 The mass concentration was 600ppm.
Comparative example B4
This comparative example provides a sodium ion battery cell, which differs from example B3 in that: after the first formation, the volume of the electrolyte 2 added was 40% of the total electrolyte. Thus, after the first formation is completed and electrolyte 2 is injected, liPF is contained in the entire electrolyte of the sodium ion battery cell 6 The mass concentration was 800ppm.
[ lithium content and cycle life ]
The mass content of lithium element in the negative electrode sheet and the cycle life of the sodium ion battery cells of examples B1 to B3 and comparative examples B1 to B4 were tested by the same test method as examples A1 to A4 after the sodium ion battery cells were secondarily formed, and the results are shown in the following table.
In Table 2, "after injection of electrolyte 2, the mass concentration of lithium element in the whole electrolyte" is based on the LiPF of the whole electrolyte after injection of electrolyte 2 6 Mass concentration, the mass concentration of the individual lithium element in the electrolyte obtained after conversion. "cycle life change rate" refers to the cycle life change rate of the sodium ion battery unit body in comparison with the case where the electrolyte 2 (comparative example B1) is not injected.
Table 2 reflects that no LiPF was used 6 Is subjected to primary formation (comparative example B1), or is injected after the first formation without LiPF 6 And then carrying out secondary formation (comparative example B2), wherein the SEI film formed on the surface of the negative electrode plate does not contain lithium elements, and the cycle life of the sodium ion battery monomer is only 1000 circles. In the embodiment B1 to the embodiment B3, after the first formation, a liquid containing a constant concentration of LiPF is injected 6 The electrolyte 2 of the (2) can effectively prolong the cycle life of the sodium ion battery monomer; and within a certain range, with LiPF in electrolyte 6 The concentration is increased, and the cycle life is prolonged. Similarly to examples A1 to A3, examples B1 to B3 show a long life mainly due to LiPF in the electrolyte 6 The provided lithium ion and sodium ion together generate a lithium-sodium mixed SEI film with certain lithium element content on the surface of the negative electrode plate, the lithium-sodium mixed SEI film has proper compactness, sodium ions can be rapidly transmitted, meanwhile, the stability of the SEI film is improved, and the loss of active sodium is reduced. At the same time, the same LiPF as in Table 1 6 By re-injecting the LiPF-containing solution after the first formation, compared with the case of concentration 6 Electrolyte 2 of (2), sodium ion battery cellCan be extended to a greater extent, mainly due to the reinjection of LiPF-containing materials through the first formation 6 The electrolyte 2 is charged by adopting a higher multiplying power than the first formation, the surface layer density of the formed lithium-sodium mixed SEI film is lower than the inner density, the transmission of sodium ions in the charging and discharging process is facilitated, and the cycle life of the sodium ion battery monomer is prolonged.
However, in the case where the mass content of the lithium element in the negative electrode sheet is excessively high, for example, comparative examples B3 and B4, the cycle life of the sodium ion battery cell is deteriorated.
Examples C1 to C3, comparative examples C1 to C4
Example C1
The embodiment provides a sodium ion battery monomer, wherein a positive electrode plate contains lithium salt lithium carbonate. Specifically, each component of the sodium ion battery monomer and the assembly method are as follows:
(1) Electrolyte solution
Sodium salt NaPF was taken in an argon atmosphere glove box 6 Dissolved in carbonate solvent [ ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate fec=47.5: 47.5:5 (volume ratio) ]Uniformly stirring to obtain NaPF 6 Electrolyte with a mass content of 1000 ppm.
(2) Positive electrode plate
The positive electrode active material (Na 0.67 Mn 0.67 Ni 0.33 O 2 ) The lithium salt (lithium carbonate), the conductive agent (conductive carbon) and the binder (polyvinylidene fluoride, PVDF) are fully stirred and uniformly mixed in the solvent (N-methyl pyrrolidone, NMP) to obtain the anode slurry. Wherein the mass ratio of positive electrode active material to lithium carbonate, solvent, conductive agent and binder is 95:100:2:3, and controlling the mass content of lithium element in the active layer contained in the positive electrode plate to be 50ppm (0.005%). And (3) coating the positive electrode slurry on a current collector (aluminum foil), and drying and cold pressing to obtain a positive electrode plate.
(3) Negative pole piece
And (3) fully stirring and uniformly mixing the anode active material (hard carbon), the conductive agent (conductive carbon) and the binder (carboxymethyl cellulose (CMC)) in deionized water to obtain anode slurry. Wherein the mass ratio of the anode active material to deionized water to the conductive agent to the binder is 95:100:2:3. and (3) coating the negative electrode slurry on a current collector (copper foil), and drying and cold pressing to obtain a negative electrode plate.
(4) Isolation film
The glass fiber film is used as a separation film.
(5) Sodium ion battery cell
And stacking the positive electrode plate, the glass fiber film and the negative electrode plate in sequence, winding to form an electrode assembly, loading the electrode assembly into a packaging shell, adding electrolyte, sealing, forming and standing. The formation process comprises the following steps: placing the sodium ion battery monomer in a formation cabinet, and charging to cut-off voltage of 4.0V at 25 ℃ under the multiplying power of 0.1C; then discharging to the lower limit voltage of 1.5V under the multiplying power of 0.1C to finish the formation of the sodium ion battery monomer.
Example C2
The present embodiment provides a sodium ion battery cell, which is different from embodiment C1 in that: the total amount of the positive electrode active material and the lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 70ppm (0.007%).
Example C3
The present embodiment provides a sodium ion battery cell, which is different from embodiment C1 in that: the total amount of the positive electrode active material and the lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 100ppm (0.01%).
Comparative example C1
This comparative example provides a sodium ion battery cell, which differs from example 1 in that: the positive electrode sheet does not contain lithium carbonate.
Comparative example C2
This comparative example provides a sodium ion battery cell, which differs from example 1 in that: the total amount of the positive electrode active material and the lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 150ppm (0.015%).
Comparative example C3
This comparative example provides a sodium ion battery cell, which differs from example 1 in that: the total amount of the positive electrode active material and the lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 170ppm (0.017%).
Comparative example C4
This comparative example provides a sodium ion battery cell, which differs from example 1 in that: the total amount of the positive electrode active material and the lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 200ppm (0.020%).
[ lithium content and cycle life ]
The mass content of lithium element in the negative electrode plate and the cycle life of the sodium ion battery cells of examples C1 to C3 and comparative examples C1 to C4 were tested by the same test method as in examples A1 to A4, and the results are shown in the following table.
In table 3, "cycle life change rate" refers to the cycle life change rate of the sodium ion battery unit cell without lithium carbonate in the positive electrode sheet (comparative example C1).
As can be seen from table 3, in the embodiments C1 to C3, after a certain amount of lithium carbonate is added into the positive electrode plate of the sodium ion battery monomer, an SEI film with a certain mass content of lithium element can be formed on the surface of the negative electrode plate, which can effectively prolong the cycle life of the sodium ion battery monomer; and in a certain range, the cycle life is prolonged along with the increase of the mass content of lithium element in the negative electrode plate. However, when the mass content of lithium element in the negative electrode sheet is too high, the cycle life of the sodium ion battery cell is reduced as compared with the case where the lithium element is not contained (comparative examples C2 to C4).
Example D1 to example D3, comparative example D1
Example D1
The embodiment provides a sodium ion battery monomer, wherein both electrolyte and positive electrode plate contain lithium salt. Specifically, each component of the sodium ion battery monomer and the assembly method are as follows:
(1) Electrolyte solution
Lithium salt LiPF was charged in an argon atmosphere glove box 6 And sodium salt NaPF 6 Dissolved in carbonate solvent [ ethylene carbonate EC: propylene carbonate PC: fluoroethylene carbonate fec=47.5: 47.5:5 (volume ratio)]Uniformly stirring to obtain LiPF 6 Concentration by mass of 50ppm, naPF 6 Electrolyte with mass concentration of 1000 ppm.
(2) Positive electrode plate
The positive electrode active material (Na 0.67 Mn 0.67 Ni 0.33 O 2 ) The lithium salt (lithium carbonate), the conductive agent (conductive carbon) and the binder (polyvinylidene fluoride, PVDF) are fully stirred and uniformly mixed in the solvent (N-methyl pyrrolidone, NMP) to obtain the anode slurry. Wherein the mass ratio of positive electrode active material to lithium carbonate, solvent, conductive agent and binder is 95:100:2:3, and controlling the mass content of lithium element in the active layer contained in the positive electrode plate to be 50ppm (0.005%). And (3) coating the positive electrode slurry on a current collector (aluminum foil), and drying and cold pressing to obtain a positive electrode plate.
(3) Negative pole piece
And (3) fully stirring and uniformly mixing the anode active material (hard carbon), the conductive agent (conductive carbon) and the binder (carboxymethyl cellulose (CMC)) in deionized water to obtain anode slurry. Wherein the mass ratio of the anode active material to deionized water to the conductive agent to the binder is 95:100:2:3. and (3) coating the negative electrode slurry on a current collector (copper foil), and drying and cold pressing to obtain a negative electrode plate.
(4) Isolation film
The glass fiber film is used as a separation film.
(5) Sodium ion battery cell
And stacking the positive electrode plate, the glass fiber film and the negative electrode plate in sequence, winding to form an electrode assembly, loading the electrode assembly into a packaging shell, adding electrolyte, sealing, forming and standing. The formation process comprises the following steps: placing the sodium ion battery monomer in a formation cabinet, and charging to cut-off voltage of 4.0V at 25 ℃ under the multiplying power of 0.1C; then discharging to the lower limit voltage of 1.5V under the multiplying power of 0.1C to finish the formation of the sodium ion battery monomer.
Example D2
The present embodiment provides a sodium ion battery cell, which is different from embodiment D1 in that: liPF in electrolyte 6 The mass concentration is 100ppm; meanwhile, in the positive electrode plate, the total amount of the positive electrode active material and lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 70ppm (0.007%).
Example D3
The present embodiment provides a sodium ion battery cell, which is different from embodiment D1 in that: liPF in electrolyte 6 The mass concentration is 200ppm; meanwhile, in the positive electrode plate, the total amount of the positive electrode active material and lithium carbonate is kept unchanged, and the mass content of lithium element in an active layer contained in the positive electrode plate is 80ppm (0.008%).
Comparative example D1
This comparative example provides a sodium ion battery cell, which differs from example D1 in that: liPF in electrolyte 6 The mass concentration is 0, i.e. no LiPF is added into the electrolyte 6 The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, the positive plate does not contain lithium carbonate.
[ lithium content and cycle life ]
The lithium element mass content in the negative electrode sheet and the cycle life of the sodium ion battery cells of examples D1 to D3 and comparative example D1 were tested by the same test method as in examples A1 to A3, and the test results are shown in the following table.
In table 4, "cycle life change rate" refers to the cycle life change rate of the sodium ion battery cell relative to comparative example D1.
As can be seen from Table 4, by adding an appropriate amount of LiPF to the electrolyte 6 At the same time, a positive pole piece is doped withAnd the quantitative carbonate can form an SEI film with certain mass content of lithium elements on the surface of the negative electrode plate, so that the cycle life of the sodium ion battery monomer can be prolonged.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the application has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the application, and are intended to be included within the scope of the appended claims and description. In particular, the technical features mentioned in the respective embodiments may be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions falling within the scope of the claims.

Claims (17)

1. A sodium ion battery cell, comprising a negative electrode sheet comprising a solid electrolyte interface film comprising a lithium element; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm.
2. The sodium ion battery cell according to claim 1, wherein the lithium element accounts for 1-5 ppm of the mass content of the negative electrode plate.
3. The sodium ion battery cell according to claim 1 or 2, wherein the lithium element is distributed in at least one position of a surface layer and an inside of the solid electrolyte interface film.
4. A sodium ion battery cell according to claim 3, wherein the density of the surface layer in the solid electrolyte interface film is equal to or less than the density of the interior.
5. The preparation method of the sodium ion battery monomer is characterized in that the sodium ion battery monomer comprises a negative electrode plate, wherein the negative electrode plate comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium element; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm;
the preparation method comprises the following steps:
preparing an electrode assembly comprising a positive electrode plate, injecting electrolyte into the electrode assembly, and performing formation treatment; wherein at least one of the electrolyte and the positive electrode sheet contains lithium element;
in the case where the electrolyte contains the lithium element, the lithium element accounts for more than 0 and less than or equal to 23ppm by mass in the electrolyte;
And under the condition that the positive electrode plate contains the lithium element, the mass content of the lithium element in the active layer contained in the positive electrode plate is more than 0 and less than or equal to 100ppm.
6. The method for producing a sodium ion battery cell according to claim 5, wherein, when the electrolyte contains the lithium element, the lithium element occupies 2 to 10ppm by mass in the electrolyte.
7. The method for producing a sodium ion battery cell according to claim 5 or 6, wherein, when the electrolyte contains the lithium element, the lithium element occupies 4.5 to 10ppm by mass in the electrolyte.
8. The method for producing a sodium ion battery cell according to claim 5, wherein, when the positive electrode sheet contains the lithium element, the mass content of the lithium element in the active layer contained in the positive electrode sheet is 50 to 100ppm.
9. The method for producing a sodium ion battery cell according to claim 5 or 8, wherein, when the positive electrode sheet contains the lithium element, the mass content of the lithium element in the active layer contained in the positive electrode sheet is 70 to 100ppm.
10. The preparation method of the sodium ion battery monomer is characterized in that the sodium ion battery monomer comprises a negative electrode plate, wherein the negative electrode plate comprises a solid electrolyte interface film, and the solid electrolyte interface film contains lithium element; the mass content of the lithium element in the negative electrode plate is more than 0 and less than or equal to 12.5ppm;
The preparation method comprises the following steps:
adding lithium element into the electrolyte of the sodium ion battery monomer subjected to the pre-formation treatment, wherein the mass concentration of the lithium element in the electrolyte is more than 0 and less than or equal to 23ppm;
and carrying out secondary formation treatment on the sodium ion battery monomer added with the lithium element.
11. The method for preparing a sodium ion battery cell according to claim 10, wherein the sodium ion battery cell comprises a positive electrode plate, the positive electrode plate contains lithium elements, and the mass content of the lithium elements contained in the positive electrode plate in the active layer contained in the positive electrode plate is more than 0 and less than or equal to 100ppm.
12. The method for preparing a sodium ion battery cell according to claim 10, wherein the charging rates in the pre-formation treatment and the re-formation treatment are respectively and independently 0.05-0.5 ℃.
13. The method according to claim 12, wherein the charging rates in the pre-formation treatment and the re-formation treatment are respectively and independently 0.1 to 0.3c.
14. The method of producing a sodium ion battery cell according to claim 12 or 13, wherein the charge rate in the reforming process step is higher than the charge rate in the pre-reforming process step.
15. A battery module comprising the sodium-ion battery cell of any one of claims 1 to 4.
16. A battery pack comprising the battery module of claim 15.
17. An electrical device comprising a sodium ion battery cell according to any one of claims 1 to 4, or comprising a battery module according to claim 15, or comprising a battery pack according to claim 16.
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