Sodium ion battery monomer, positive pole piece, preparation method of sodium ion battery monomer, preparation method of positive pole piece and related device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to a sodium ion battery monomer, a positive pole piece, a preparation method thereof and a related device. The sodium ion battery monomer comprises a positive pole piece, the positive pole piece comprises a positive active material and a solid electrolyte interface film at least combined on the surface of the positive active material, and the solid electrolyte interface film comprises one or more cations of Na < + >, Li < + >, K < + > and Ca < 2 + >. The solid electrolyte interface film combined on the surface of the positive electrode active material contains cations such as Na < + >, Li < + >, K < + > and Ca < 2 + >, and the cations can participate in electrochemical reaction of the sodium ion battery, so that reversible capacity is provided, capacity loss generated after the positive electrode active material is passivated is made up, and the cycle performance of the battery is improved. Meanwhile, the solid electrolyte interfacial film containing the cations is beneficial to reducing the impedance of the battery, so that the cycle performance of the battery is further improved.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to sodium ion battery cells and positive electrode sheets, as well as preparation methods and related devices thereof. Background Art

[0002] Batteries are the core of new energy vehicles and various electronic devices. With the development of technology, the market's requirements for battery performance are getting higher and higher. Long life is one of the basic requirements for batteries. However, during the battery cycle, due to various factors, the battery capacity usually decays quickly and the cycle performance deteriorates, which affects the battery life of various electrical devices and makes the user experience poor. Therefore, it is urgent to improve the cycle performance and extend the battery life. Summary of the invention

[0003] In view of the above problems, the present application provides a sodium ion battery cell and a positive electrode plate and a preparation method and related devices thereof, which can solve the problem of poor battery cycle performance.

[0004] In a first aspect, the present application provides a sodium ion battery cell, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode active material and a solid electrolyte interface membrane at least bonded to the surface of the positive electrode active material, the solid electrolyte interface membrane comprising Na + , Li + , K + , Ca 2+ One or more cations in a.

[0005] The solid electrolyte interface film bound to the surface of the positive electrode active material of the present application comprises Na + , Li + , K + , Ca 2+ These cations can participate in the electrochemical reaction of sodium ion batteries, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material by the solid electrolyte interface membrane, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane containing these cations has high ionic conductivity, which is conducive to reducing battery impedance, thereby further improving battery cycle performance.

[0006] In some embodiments, the solid electrolyte interface film comprises Na + , Li + , K + One or more cations in a.

[0007] These cations can participate well in electrochemical reactions, thereby compensating for the capacity loss caused by the passivation of the positive electrode active materials and improving the battery cycle performance.

[0008] In some embodiments, the mass content of the above cations contained in the solid electrolyte interface membrane in the positive electrode plate is 0.09% to 0.7%, and optionally 0.3% to 0.67%.

[0009] When the cations contained in the solid electrolyte interface membrane are in an appropriate content, they are conducive to fully exerting their active role, participating in electrochemical reactions, compensating for the capacity loss caused by the passivation of the positive electrode active material by the solid electrolyte interface membrane, and improving the battery cycle performance.

[0010] In a second aspect, the present application provides a method for preparing a sodium ion battery monomer, comprising:

[0011] An electrode assembly comprising a positive electrode sheet is prepared, wherein the positive electrode sheet comprises a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in

[0012] The electrode assembly is combined with the electrolyte and then subjected to a chemical formation treatment.

[0013] Sodium-ion battery cells are made by using positive electrode sheets containing specific additives. During the formation process, these additives can decompose Na + , Li + , K + , Ca 2+ One or more cations in the positive electrode participate in the formation of a solid electrolyte interface film on the surface of the positive electrode active material, so that the solid electrolyte interface film on the surface of the positive electrode active material contains Na + , Li + , K + , Ca 2+ One or more cations in Na + , Li + , K + , Ca 2+ The cations can participate in the electrochemical reaction of the sodium ion battery, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane has high ionic conductivity, which is conducive to reducing the battery impedance, thereby further improving the battery cycle performance.

[0014] In some embodiments, the additive includes one or more of nitrite and sulfite, and the cations in the nitrite and sulfite each independently include Na + , Li + , K + , Ca 2+ One or more of .

[0015] Na + , Li + , K + , Ca 2+ The nitrite and sulfite can decompose the corresponding cations during the charge and discharge process, participate in the electrochemical reaction, make up for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance.

[0016] In some embodiments, the sulfite includes one or more of potassium sulfite, potassium metabisulfite, sodium sulfite, sodium metabisulfite, calcium sulfite, and calcium metabisulfite.

[0017] In some embodiments, the nitrite includes one or more of lithium nitrite, potassium nitrite, sodium nitrite, and calcium nitrite.

[0018] These nitrites and sulfites can decompose corresponding cations during the battery charging process and participate in the formation of the solid electrolyte interface film on the surface of the positive electrode active material, which helps to reduce the consumption of sodium ions in the positive electrode active material, and participate in the electrochemical reaction to make up for the capacity loss caused by the passivation of the positive electrode active material and improve the battery cycle performance.

[0019] In some embodiments, the mass content of the additive in the active layer of the positive electrode sheet is 0.5% to 5%, and optionally 2% to 5%.

[0020] By controlling the content of additives within a certain range, a certain amount of cations can be formed in the solid electrolyte interface film on the surface of the positive electrode active material, which helps to improve the battery cycle performance; and the content of the positive electrode active material will not be too low, which is beneficial to reducing the loss of positive electrode capacity.

[0021] In some embodiments, the additive has a Dv50 of 2 μm to 75 μm, optionally 2 μm to 45 μm.

[0022] By reasonably setting the particle size of the additive, the additive can have a suitable specific surface area and shorten the diffusion path of cations and anions in the additive, which is beneficial to reduce the degree of electrode polarization during the charging and discharging process, and then promote the decomposition and film formation reaction of the additive during the battery charging and discharging process.

[0023] Moreover, after the additives are decomposed, pores will be left in the positive electrode sheet. By using additives with appropriate particle sizes, it is helpful to improve the increase in porosity of the positive electrode sheet due to the decomposition of the additives during the charge and discharge process, thereby improving the compaction density of the positive electrode sheet.

[0024] In some embodiments, the Dv50 of the positive electrode active material is 1 μm to 20 μm, optionally 4 μm to 10 μm.

[0025] The appropriate particle size of the positive electrode active material facilitates the processing of the positive electrode slurry and is also beneficial for bonding with the solid electrolyte interface membrane.

[0026] In some embodiments, the charging voltage range of the formation process includes 3V to 4.2V, and optionally includes 3V to 4V.

[0027] Within this voltage range, the additives in the positive electrode plate can effectively decompose the corresponding cations, participate in the formation of the solid electrolyte interface film, and improve the battery cycle performance.

[0028] In some embodiments, the charge rate in the formation step is 0.05C to 0.5C, and optionally 0.1C to 0.3C.

[0029] By carrying out the formation treatment at a low rate, the additives in the positive electrode plate can be decomposed into a film at a certain rate, which is beneficial to improving the uniformity of the solid electrolyte interface film on the surface of the positive electrode active material.

[0030] In a third aspect, the present application provides a positive electrode sheet, comprising a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in a.

[0031] By adding specific additives to the positive electrode sheet, after the positive electrode sheet is applied to the sodium ion battery monomer, these additives can decompose Na + , Li + , K + , Ca 2+ One or more cations in the positive electrode participate in the formation of a solid electrolyte interface film on the surface of the positive electrode active material particles, so that the solid electrolyte interface film contains Na + , Li + , K + , Ca 2+ One or more cations in Na + , Li + , K + , Ca 2+ The cations can participate in the electrochemical reaction of the sodium ion battery, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane has high ionic conductivity, which is conducive to reducing the battery impedance, thereby further improving the battery cycle performance.

[0032] In a fourth aspect, the present application provides a method for preparing a positive electrode sheet, comprising:

[0033] Prepare a positive electrode slurry containing a positive electrode active material and an additive, wherein the additive contains Na + , Li + , K + , Ca 2+ One or more cations in

[0034] The positive electrode slurry is coated on the positive electrode current collector, and after drying and compacting, a positive electrode sheet is obtained.

[0035] By adding additives to the positive electrode slurry, these additives can decompose the corresponding cations during the charging process and participate in the formation of the solid electrolyte interface film on the surface of the positive electrode active material, which is beneficial to improve the battery cycle performance.

[0036] In a fifth aspect, the present application provides a battery module, comprising the sodium ion battery cell of the first aspect, or comprising the sodium ion battery cell prepared by the preparation method of the second aspect.

[0037] In a sixth aspect, the present application provides a battery pack comprising the battery module of the fifth aspect.

[0038] In the positive electrode sheet of the sodium ion battery cell of the embodiment of the present application, a special solid electrolyte interface film is combined on the surface of the positive electrode active material, which has excellent cycle performance and long life. Therefore, the battery module including the sodium ion battery cell and the battery pack including the battery module also show the characteristics of good cycle performance and long life.

[0039] In a seventh aspect, the present application provides an electrical device comprising at least one of the sodium ion battery cell of the first aspect, the battery module of the fifth aspect, and the battery pack of the sixth aspect.

[0040] The battery (sodium ion battery cell, battery module or battery pack) disclosed in the present application can be used in electrical devices that use batteries as power sources, or various energy storage systems that use batteries as energy storage elements, to provide electrical energy. The above-mentioned battery exhibits the advantage of long life, so after the battery is applied to various electrical devices, it is beneficial to extend the battery life of various electrical devices and improve the user experience of various electrical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 A schematic diagram of a battery cell according to an embodiment of the present application;

[0043] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0044] Figure 3 A schematic diagram of a battery module according to an embodiment of the present application;

[0045] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application;

[0046] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0047] Figure 6 A schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application.

[0048] Reference numerals:

[0049] 01-shell, 02-cover, 03-electrode assembly, 04-battery cell, 05-battery module, 06-upper box, 07-lower box. DETAILED DESCRIPTION

[0050] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0052] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0053] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0054] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0055] In the description of the embodiments of the present application, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple, respectively.

[0056] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0057] The mass of the relevant components mentioned in the specification of the examples of this application can not only refer to the specific content of each component, but also represent the proportional relationship between the masses of the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the specification of the examples of this application, it is within the scope disclosed in the specification of the examples of this application. Specifically, the mass described in the specification of the examples of this application can be mass units known in the chemical industry such as μg, mg, g, and kg.

[0058] Secondary batteries, such as sodium-ion batteries, usually include two electrodes, positive and negative. The active materials in the electrodes undergo electrochemical reactions during the battery cycle. For example, the positive electrode active material releases active metal ions during battery charging, and the active metal ions are then embedded in the negative electrode active material to form a complex with the negative electrode active material. These reactions can promote the conversion of electrical energy into chemical energy and affect various battery properties.

[0059] In sodium-ion batteries, the sodium ions released from positive electrode active materials, such as sodium ion oxide positive electrode active materials, during the cycle process can not only be reversibly deintercalated between the positive electrode active materials and the negative electrode active materials, but also some sodium ions participate in the formation of the solid electrolyte interface film on the electrode surface, so that these sodium ions can no longer be transmitted between the positive electrode and the negative electrode, resulting in active sodium loss. And the solid electrolyte interface film will repeatedly dissolve and regenerate during the battery charging and discharging process, resulting in continuous loss of active sodium. This phenomenon will cause capacity decay, thereby affecting the battery cycle life. At the same time, the positive electrode active material will undergo a phase change during the sodium removal process, which will lead to poor structural stability and expose too many crystal planes, resulting in high initial impedance and rapid impedance growth, thereby accelerating the cycle decay, further greatly deteriorating the battery cycle performance.

[0060] In order to improve the cycle performance of sodium-ion batteries, related technologies attempt to optimize the positive electrode active materials. For example, special elements are doped into the lattice structure of the positive electrode active materials to optimize the structure and composition of the positive electrode active materials. However, after element doping, some sodium ions in the positive electrode active materials continue to participate in the formation of the solid electrolyte interface film on the electrode surface, resulting in a serious loss of active sodium, and the improvement of the cycle performance of sodium-ion batteries is limited. Alternatively, by adding various additives to the electrolyte, but this method needs to consider the solubility and reactivity of the additives in the electrolyte. When the additives are not soluble, or the additives are difficult to react as required, or the additives have unnecessary side reactions, the battery cycle performance cannot be effectively improved.

[0061] In view of the above problems, the present invention adds Na into the solid electrolyte interface film on the surface of the positive electrode active material of the sodium ion battery monomer. + , Li + , K + , Ca 2+ The positive electrode active material can be passivated to a certain extent by removing the sodium ions from the positive electrode active material, thereby slowing down the loss of sodium ions in the positive electrode active material; and these cations can participate in the electrochemical reaction of the sodium ion battery, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane has high ionic conductivity, which is beneficial to reducing battery impedance and improving battery cycle performance.

[0062] The sodium ion battery cells with good cycle performance provided in the embodiments of the present application can be assembled into battery modules or battery packs, and can be further used to manufacture various electrical devices.

[0063] The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0064]

Sodium ion battery monomer

[0065] The first aspect of the present application provides a sodium ion battery cell, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode active material and a solid electrolyte interface membrane at least bonded to the surface of the positive electrode active material, the solid electrolyte interface membrane comprising Na + , Li + , K + , Ca 2+ One or more cations in a.

[0066] After the sodium-ion battery cell is charged and discharged, the positive electrode active material reacts with the electrolyte at the solid-liquid interface to form a passivation layer with solid electrolyte characteristics covering the surface of the positive electrode active material. The passivation layer is the solid electrolyte interface membrane. Among them, the positive electrode plate contains at least a solid electrolyte interface membrane bonded to the surface of the positive electrode active material, which means that part or all of the solid electrolyte interface membrane contained in the positive electrode plate is bonded to the surface of the positive electrode active material. The solid electrolyte interface membrane is bonded to the surface of the positive electrode active material, which means that the solid electrolyte interface membrane is in contact with the positive electrode active material and partially or completely covers the positive electrode active material. The field of electrochemistry has confirmed that the solid electrolyte interface membrane exists in the positive electrode plates of sodium-ion battery cells, and it has been determined that its distribution position is bonded to the surface of the positive electrode active material.

[0067] The ion composition in the solid electrolyte interface film can be qualitatively analyzed by X-ray photoelectron spectroscopy (XPS), specifically, the photoelectron spectrum (XPS spectrum) of the test sample can be used to obtain information about the sample surface or the inner layer at a certain distance from the surface. The binding energy of the photoelectrons excited by different elements has different values, and the binding energy of a given inner shell electron of a given element is also related to the chemical binding state of the element and its chemical environment. As the molecule in which the element is located is different, the photoelectron peak of the given inner shell electron will have a shift, that is, a chemical shift. Therefore, each element has its own characteristic peak in the XPS spectrum. The existence of the element and its chemical state (chemical environment, oxidation state) are determined based on the binding energy size, chemical shift, and peak intensity of the characteristic peak.

[0068] Since the solid electrolyte interface membrane is combined with the surface of the positive electrode active material, and the elemental composition of the solid electrolyte interface membrane is not exactly the same as that of the positive electrode active material, if the positive electrode sheet is etched during the XPS test, the XPS spectra corresponding to the solid electrolyte interface membrane and the positive electrode active material will be obtained successively. The elemental compositions of these XPS spectra are not exactly the same, so it can be analyzed that there is a layer of membrane combined with the surface of the positive electrode active material, and this layer of membrane contains Na + , Li + , K + , Ca 2+ One or more cations in a.

[0069] The solid electrolyte interface film contains K + (or Li + , Ca 2+ ) as an example, the existence of the solid electrolyte interface film in the positive electrode sheet of the sodium ion battery monomer can be determined by the following method, and the solid electrolyte interface film contains K + :In a glove box, the sodium ion battery cell that has undergone an electrical cycle is disassembled, the positive electrode is cleaned and dried, and then transferred to the glove box for sample preparation, and then transferred to the XPS vacuum chamber for testing. During the XPS test, the sample surface is first tested to obtain the surface XPS spectrum (first XPS spectrum). + In this case, the first XPS spectrum will show K + The characteristic peaks of the positive electrode active material do not appear (for example, for the positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 O2, the characteristic peaks corresponding to Fe, Mn and Ni will not appear in the first XPS spectrum).

[0070] Then, under certain conditions (e.g., 2000 eV, with Ta2O5 target as standard), Ar + Ion etching is performed at a certain speed (e.g., 0.4 nm / s) in the depth direction of the sample at the same position of the sample, and an XPS spectrum is obtained after each etching distance. During the test, it can be found that after etching a certain distance, an nth XPS spectrum different from the first XPS spectrum can be obtained, and the nth XPS spectrum will have characteristic peaks unique to the positive electrode active material (e.g., for the positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 O2, the nth XPS spectrum will show characteristic peaks corresponding to Fe, Mn, and Ni, but not K + characteristic peaks.

[0071] According to the changes in the elemental composition in the XPS spectra during the entire XPS test process, it can be judged that the sample includes at least two layers with different chemical compositions, one of which is the positive electrode active material layer corresponding to the nth XPS spectrum, and on the surface of the positive electrode active material there is a film layer corresponding to the first XPS spectrum, namely, a solid electrolyte interface film, and the solid electrolyte interface film contains K + .

[0072] For solid electrolyte interface films containing Na + In the case of etching, the first XPS spectrum shows Na + The characteristic peaks of the nth XPS are not found, but the characteristic peaks unique to the positive electrode active material are not found. + characteristic peaks, but characteristic peaks unique to positive electrode active materials will also appear at the same time.

[0073] The solid electrolyte interface film bound to the surface of the positive electrode active material of the embodiment of the present application comprises Na + , Li + , K + , Ca 2+ These cations can participate in the electrochemical reaction of sodium ion batteries, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material by the solid electrolyte interface membrane, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane containing these cations has high ionic conductivity, which is conducive to reducing battery impedance, thereby further improving battery cycle performance.

[0074] In some embodiments, the solid electrolyte interface film comprises Na + , Li + , K + One or more cations in a.

[0075] These cations can participate well in electrochemical reactions, thereby compensating for the capacity loss caused by the passivation of the positive electrode active materials and improving the battery cycle performance.

[0076] In some embodiments, the mass content of the above-mentioned cations contained in the solid electrolyte interface membrane in the positive electrode plate is 0.09% to 0.7%, and optionally 0.3% to 0.67%, for example, it can be 0.09%, 0.1%, 0.12%, 0.15%, 0.2%, 0.22%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.67%, 0.7%, any one of the point values ​​or the range value between any two of them.

[0077] Since the solid electrolyte interface membrane is small and thin, and cannot be separated from the positive electrode sheet, it is inconvenient to directly measure the mass content of its cations in the solid electrolyte interface membrane. Therefore, the mass content of its cations in the positive electrode sheet can be used to reflect the amount of these cations. The mass content of cations in the positive electrode sheet can be obtained through ICP testing.

[0078] Specifically, for Li in the solid electrolyte interface film + , K + , Ca 2+ The active metal ions of the positive electrode active materials of sodium ion battery monomers are Na + , and usually does not contain Li + , K + , Ca 2+ Therefore, by disassembling the sodium ion battery monomer and dissolving its positive electrode (for example, aqua regia can be used for dissolution), an ICP test can be performed to obtain Li + , K + , Ca 2+ The mass content of cations in the positive electrode.

[0079] For the Na + , which can come from the positive electrode active material, or from other substances at the same time, such as certain additives. For an unknown positive electrode sheet (unknown sample), the positive electrode active material can be known based on XPS analysis, and the mass content m1 of the positive electrode active material in the unknown sample and the Na content in the unknown sample can be obtained through ICP testing. + The total mass content of a1; then prepare a positive electrode sheet containing only positive electrode active materials but no additives (blank control group), and control the mass content of the positive electrode active materials to be the same as that of the unknown sample (both m1). After charge and discharge cycles, test the Na + If a1 is greater than a2, it means that the Na + In addition to the positive electrode active material, it also comes from other substances, that is, the solid electrolyte interface film contains sodium ions from additives, so the difference between a1 and a2 is the Na ions from the additives. + quality content.

[0080] The cations contained in the solid electrolyte interface membrane at an appropriate content are conducive to fully exerting their active role to participate in the electrochemical reaction, making up for the capacity loss caused by the passivation of the positive electrode active material by the solid electrolyte interface membrane, and improving the battery cycle performance.

[0081] In some embodiments, the solid electrolyte interface film comprises NO3 - 、NO2- 、SO4 2- 、SO3 2- One or more anions, optionally including NO3 - and NO2 - The solid electrolyte interface membrane formed by the combination of these anions and cations has good ion conductivity, which is beneficial to reduce battery impedance and further improve battery cycle performance.

[0082]

Preparation of sodium-ion battery monomers

[0083] A second aspect of an embodiment of the present application provides a method for preparing a sodium ion battery monomer, comprising:

[0084] An electrode assembly comprising a positive electrode sheet is prepared, wherein the positive electrode sheet comprises a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in

[0085] The electrode assembly is combined with the electrolyte and then subjected to a chemical formation treatment.

[0086] The electrode assembly is an important component of a battery cell, and usually includes a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet, the separator, and the negative electrode sheet are arranged in sequence and stacked or wound to form an electrode assembly.

[0087] The electrode assembly and the electrolyte are combined by injecting a liquid electrolyte (electrolyte) into a housing containing the electrode assembly, or by stacking a solid electrolyte with the positive electrode sheet, separator, and negative electrode sheet in the electrode assembly in a certain order, and then fixing them by pressurizing or heating. After the battery cell containing the battery assembly and the electrolyte is packaged, a formation process is usually required, that is, charging the battery under a certain current. The function of formation is to activate the positive and negative active materials or other materials of the battery.

[0088] The present invention uses a positive electrode sheet containing specific additives to make a sodium ion battery cell. During the formation process, these additives decompose into Na + , Li + , K + , Ca 2+ One or more cations in the positive electrode participate in the formation of a solid electrolyte interface film on the surface of the positive electrode active material, so that the solid electrolyte interface film on the surface of the positive electrode active material contains Na + , Li + , K + , Ca 2+ One or more cations in Na +, Li + , K + , Ca 2+ The cations can participate in the electrochemical reaction of the sodium ion battery, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material by the solid electrolyte interface membrane, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane has high ionic conductivity, which is conducive to reducing the battery impedance, thereby further improving the battery cycle performance.

[0089] In some embodiments, the additive includes one or more of nitrite and sulfite, and the cations in the nitrite and sulfite independently include Na + , Li + , K + , Ca 2+ One or more of .

[0090] Na + , Li + , K + , Ca 2+ The nitrite and sulfite can decompose the corresponding cations during the charging process, participate in the electrochemical reaction, make up for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance.

[0091] The chemical reactions of these nitrites and sulfites decomposing into films during charging include:

[0092] 1) Nitrite

[0093] Step 1: XNO2→NO2↑+X + +e, or X(NO2)2→NO2↑+X 2+ +e;

[0094] Step 2: NO2 → NO3 - .

[0095] 2) Sulfites

[0096] Step 1: X2SO3 → SO3 2- +2X + +e, or XSO3→SO3 2- ↑+X 2+ +e;

[0097] Step 2: SO3 2- →SO4 2- .

[0098] Where X + , X 2+It is the cation in nitrite and sulfite. The first step reaction of nitrite and sulfite in the charging process can decompose the corresponding cation.

[0099] In some embodiments, the sulfite includes one or more of potassium sulfite, potassium metabisulfite, sodium sulfite, sodium metabisulfite, calcium sulfite, and calcium metabisulfite.

[0100] In some embodiments, the nitrite includes one or more of lithium nitrite, potassium nitrite, sodium nitrite, and calcium nitrite, and may optionally include one or more of potassium nitrite, sodium nitrite, and calcium nitrite.

[0101] These nitrites and sulfites can decompose corresponding cations during battery charging and participate in the formation of a solid electrolyte interface film on the surface of the positive electrode active material, which helps to reduce the consumption of sodium ions in the positive electrode active material, participate in electrochemical reactions, compensate for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance.

[0102] In some embodiments, the mass content of the additive in the active layer contained in the positive electrode plate is 0.5% to 5%, optionally 2% to 5%, for example, it can be any point value among 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range value between any two of them.

[0103] The mass content of the additive in the active layer of the positive electrode can be calculated based on the raw materials used to prepare the positive electrode, or it can be obtained through ICP testing. By controlling the content of the additive within a certain range, a certain amount of cations can be formed in the solid electrolyte interface film on the surface of the positive electrode active material, which helps to improve the battery cycle performance; and the content of the positive electrode active material will not be too low, which is beneficial to reduce the loss of the positive electrode capacity.

[0104] In some embodiments, the Dv50 of the additive is 2μm to 75μm, optionally 2μm to 45μm, for example, it can be any point value among 2μm, 5μm, 10μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, or a range value between any two of them.

[0105] The particle size distribution of a material is usually expressed as the percentage of particles in different particle size ranges. There are many benchmarks for determining particle size distribution, such as number distribution, length distribution, area distribution, volume distribution, mass distribution, etc. Dv50 is a specific particle size distribution based on volume distribution, which refers to the particle size corresponding to 50% of the volume distribution. Dv50 can be measured by laser method.

[0106] By reasonably setting the particle size of the additive, the additive can have a suitable specific surface area and shorten the diffusion path of cations and anions in the additive, which is beneficial to reduce the degree of electrode polarization during the charging and discharging process, and then promote the decomposition and film formation reaction of the additive during the battery charging and discharging process.

[0107] Moreover, after the additives are decomposed, pores will be left in the positive electrode sheet. However, the embodiments of the present application use additives with suitable particle sizes to improve the increase in porosity of the positive electrode sheet due to the decomposition of the additives during the charge and discharge process, thereby improving the compaction density of the positive electrode sheet.

[0108] In some embodiments, the Dv50 of the positive electrode active material is 1 μm to 20 μm, optionally 4 μm to 10 μm, for example, it can be any point value among 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm or a range value between any two of them.

[0109] The appropriate particle size of the positive electrode active material facilitates the processing of the positive electrode slurry and is also beneficial for bonding with the solid electrolyte interface membrane.

[0110] It can be understood that in the positive electrode sheet, the positive electrode active material and the additive may be physically mixed.

[0111] In some embodiments, the charging voltage range of the formation treatment step includes 3V to 4.2V, and optionally includes 3V to 4V, for example, it can be a range value between any two of 3V, 3.2V, 3.4V, 3.6V, 3.8V, 4V, and 4.2V.

[0112] The formation treatment is to charge the battery at a certain current, and the voltage gradually increases during the charging process, that is, the formation treatment is carried out within a certain charging voltage range. The charging voltage range can be directly set on the equipment used for the formation treatment (such as a formation cabinet).

[0113] Within this charging voltage range, the additives in the positive electrode plate can effectively decompose the corresponding cations, participate in the formation of the solid electrolyte interface film, and improve the battery cycle performance.

[0114] It can be understood that in the charging voltage range of 3V to 4.2V, the charging cut-off voltage can be set to be close to 4.2V, for example, the cut-off voltage can be 3.8V to 4.2V.

[0115] In some embodiments, the charging rate in the formation treatment step is 0.05C to 0.5C, optionally 0.1C to 0.3C, for example, it can be any one of 0.05C, 0.1C, 0.15C, 0.2C or a range between any two of them.

[0116] The formation treatment includes the step of charging the sodium ion battery monomer. The speed of charging can be measured by the charging rate, which is the current intensity required for the battery to be charged to its rated capacity in a specified time. The charging rate can be directly set on the equipment used for the formation treatment (such as a formation cabinet). When the formation treatment is carried out at a low rate, the additives in the positive electrode plate can be decomposed into a film at a certain rate, which is conducive to improving the uniformity of the solid electrolyte interface film formed on the surface of the positive electrode active material.

[0117]

Positive electrode

[0118] The third aspect of the embodiment of the present application provides a positive electrode sheet, comprising a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in a.

[0119] By adding specific additives to the positive electrode sheet, after the positive electrode sheet is applied to the sodium ion battery monomer, these additives can decompose Na + , Li + , K + , Ca 2+ One or more cations in the positive electrode participate in the formation of the solid electrolyte interface film on the surface of the positive electrode active material, so that the solid electrolyte interface film contains Na + , Li + , K + , Ca 2+ One or more cations in Na + , Li + , K + , Ca 2+ The cations can participate in the electrochemical reaction of the sodium ion battery, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane has high ionic conductivity, which is conducive to reducing the battery impedance, thereby further improving the battery cycle performance.

[0120] Regarding the specific type selection, particle size, and mass content of the additive in the positive electrode plate, reference may be made to the content of the preparation method of the sodium ion battery monomer in the aforementioned second aspect.

[0121] In some embodiments, the positive electrode active material, that is, the sodium ion positive electrode active material, may include one or more of a layered oxide, a polyanion compound, and a Prussian blue compound. For example, the layered oxide may include Na x MO2, M = one or more of Fe, Mn, Ni, Co, Cr, Sc, Ti, V, Cr, Cu, Zn, 0.4≤x≤1, for example, NaFe 0.33 Mn 0.33 Ni 0.33 O2、NaFe 0.5 Ni 0.5 O2、Na 0.6 MnO2、Na 0.44 MnO2、Na 0.65 Mn 0.75 Ni 0.25 O2、NaNi 0.5 Mn 0.5 O2、Na 0.78 Ni 0.23 Mn 0.69 O2, NaVO2, NaFeO2, Na 0.7 CoO2, etc. The polyanion compounds may include one or more of phosphate, pyrophosphate, sulfate, anion doped, such as olivine NaFePO4, Na2FeP2O7, NaFePO4F, Na3V2(PO4)3, NaFeSO4. 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] or more.

[0122] The mass content of the positive electrode active material in the active layer of the positive electrode sheet is 90% to 95%, for example, it can be any point value of 90%, 91%, 92%, 93%, 94%, 95% or a range value between any two of them. It can be understood that setting the mass content of the positive electrode active material in the active layer of the positive electrode sheet at a higher level can improve the energy density of the sodium ion battery.

[0123] In some embodiments, the positive electrode sheet further includes a conductive agent, which is used to collect microcurrents between the positive electrode active materials and between the positive electrode active materials and the current collector to improve electronic conductivity, and the conductive agent can also promote the infiltration of the electrolyte into the positive electrode sheet.

[0124] The conductive agent may include one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene.

[0125] The mass content of the conductive agent in the active layer of the positive electrode plate is 1% to 5%, for example, it can be any point value among 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range value between any two of them, and can also be set to other contents as needed.

[0126] In some embodiments, the positive electrode sheet further includes a binder, which can improve the bonding strength between the various substances in the active layer of the positive electrode sheet and between the active layer of the positive electrode sheet and the positive electrode current collector.

[0127] The binder may include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber.

[0128] The mass content of the binder in the active layer of the positive electrode plate is 1% to 5%, for example, it can be any point value among 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range value between any two points, and can also be set to other contents as needed.

[0129] In some embodiments, the positive electrode plate further comprises a dispersant. An exemplary dispersant includes carboxymethyl cellulose (CMC). The mass content of the dispersant in the active layer of the positive electrode plate can be set to 0.5% to 5%, optionally 1% to 5%, including but not limited to any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any range between the two.

[0130] In some embodiments, the positive electrode plate further comprises a positive current collector. The positive current collector is used to transmit electrons, and the active layer of the positive electrode plate comprising components such as positive active material, additives, conductive agent, binder, etc. is disposed on at least one side of the positive current collector, and optionally on both sides of the current collector.

[0131] The positive electrode current collector may include, but is not limited to, a metal current collector, a carbon current collector, a conductive resin current collector, a composite current collector of metal and resin, and more specifically, aluminum, copper, nickel, titanium, iron, and their respective alloys, stainless steel, carbon fiber, carbon nanotube (CNT), graphite, etc. Optionally, the positive electrode current collector includes aluminum.

[0132] The thickness of the positive electrode current collector may be 3 μm to 20 μm, and may be optionally 10 μm to 15 μm, for example, any one of 3 μm, 5 μm, 10 μm, 15 μm, and 20 μm, or a range between any two of them.

[0133] In some embodiments, the porosity of the positive electrode sheet is 40% to 60%, optionally 50% to 60%, for example, it can be any one of 40%, 45%, 50%, 55%, 60% or a range between any two of the values. The porosity of the positive electrode sheet can be calculated by using the apparent volume and true volume of the positive electrode sheet, that is, porosity = (V0-V) / V*100%, where V0 is the apparent volume of the positive electrode sheet, and V is the true volume of the positive electrode sheet. The positive electrode sheet of the embodiment of the present application has a higher porosity, which can provide a channel for the entry and exit of sodium ions and cations in the solid electrolyte interface membrane, thereby improving the ion conduction efficiency.

[0134] In some embodiments, the compaction density of the positive electrode sheet is 2 g / cm 3 ~4g / cm 3 , optionally 3g / cm 3 ~3.5g / cm 3 , for example, it can be 2g / cm 3 , 2.2g / cm 3 , 2.4g / cm 3 , 2.6g / cm 3 , 2.8g / cm 3 , 3g / cm 3 、3.2g / cm 3 、3.4g / cm 3 、3.6g / cm 3 、3.8g / cm 3 , 4g / cm 3 Any point value or the range between any two point values. The compaction density of the positive electrode sheet can be obtained by using a compaction density meter and referring to relevant standards such as GB / T 24533-2019. A higher compaction density is conducive to improving the capacity of the positive electrode sheet.

[0135]

Preparation of positive electrode

[0136] A fourth aspect of the present application provides a method for preparing a positive electrode sheet, comprising:

[0137] Prepare a positive electrode slurry containing a positive electrode active material and an additive, wherein the additive contains Na + , Li + , K + , Ca 2+ One or more cations in

[0138] The positive electrode slurry is coated on the positive electrode current collector, and is dried and compacted to obtain a positive electrode sheet.

[0139] Among them, the specific type selection, particle size, and mass content of the above-mentioned additives in the positive electrode plate can refer to the content of the preparation method of the sodium ion battery monomer in the second aspect mentioned above.

[0140] By adding additives to the positive electrode slurry, these additives can decompose the corresponding cations during the charging process and participate in the formation of the solid electrolyte interface film on the surface of the positive electrode active material, which is beneficial to improve the battery cycle performance.

[0141] It can be understood that the sodium ion battery cell of the first aspect of the embodiment of the present application includes not only a positive electrode sheet, but also a negative electrode sheet, an electrolyte, a separator, an outer packaging and other components. For more detailed technical features of these components, please refer to the following:

[0142] 1. Negative electrode

[0143] The sodium ion battery cell also includes a negative electrode sheet, which is usually isolated from the positive electrode sheet. The negative electrode sheet 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, a conductive agent, a binder, etc.

[0144] The negative electrode current collector may include but is not limited to metal or composite current collectors. For example, as the metal, sodium, sodium alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. may be used.

[0145] The composite current collector may include a composite material of a polymer material and a metal, wherein the polymer material may include but is not limited to polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc., and the metal may include but is not limited to sodium, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0146] The thickness of the negative electrode current collector may be 3 μm to 15 μm, for example, any one of 3 μm, 5 μm, 8 μm, 10 μm, and 15 μm, or a range between any two of them.

[0147] In the case where the negative electrode plate includes a negative electrode active layer, the negative electrode active material in the negative electrode active layer may include but is not limited to a mixture or composite material formed by any one or more of carbon-based materials, alloy materials, titanium-based materials, and sodium metal. Among them, carbon-based materials include but are not limited to one or more of graphite, soft carbon, hard carbon, carbon microspheres, and carbon fibers; alloy materials include but are not limited to one or more of sodium-tin alloy, sodium-germanium alloy, and sodium-antimony alloy; titanium-based materials include but are not limited to one or more of titanium dioxide, titanate, and titanium phosphate.

[0148] The mass content of the negative electrode active material in the negative electrode active layer can be set to 85% to 98%, optionally to 95% to 98%, for example, any one of 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or a range between any two of them.

[0149] Conductive agents include one or more of acetylene black (SP), carbon nanotubes, conductive carbon black (super-P), Ketjen black, carbon fiber, and graphene. Binders include, but are not limited to, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, polyimide, polytetrafluoroethylene, polybutyl acrylate, polyacrylonitrile, carboxymethyl cellulose, carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, polyvinyl alcohol, sodium alginate, cyclodextrin, styrene-butadiene rubber, vinyl acetate resin, acrylic resin, and chlorinated rubber. The negative electrode active layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC).

[0150] The mass contents of the conductive agent, binder and thickener in the negative electrode active layer can be independently set to 0.5% to 5%, for example, any one of 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of them.

[0151] 2. Electrolytes

[0152] The sodium ion battery cell further includes an electrolyte, for example, the electrolyte may be an electrolyte solution including an electrolyte sodium salt and a solvent.

[0153] Among them, the electrolyte sodium salt may include one or more of sodium hexafluorophosphate (NaPF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaOTf), sodium fluoride (NaF), sodium nitrate (NaNO3), sodium difluorooxalatoborate (NaDFOB), sodium tetrafluoroborate (NaBF4), and sodium perchlorate (NaClO4).

[0154] The concentration of electrolyte sodium salt in the electrolyte can be set to 0.1mol / L~1.5mol / L, optionally 0.8mol / L~1.2mol / L, for example, it can be any one of 0.1mol / L, 0.2mol / L, 0.6mol / L, 0.8mol / L, 1mol / L, 1.2mol / L, 1.5mol / L or a range between any two of the values.

[0155] The solvent includes one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl ether (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, 2,2,2,2-trifluoroethyl ether, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, trifluoroethyl methyl carbonate (FEMC), dioxolane (DOL), acetonitrile (AN), fluorobenzene, triethyl phosphate (TEP), sulfolane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfoxide, and N,N-dimethylacetamide.

[0156] 3. Isolation film

[0157] The sodium ion battery cell also includes a separator, which is arranged between the positive electrode and the negative electrode to separate the positive and negative electrodes. The separator prevents electrons in the battery from passing freely, preventing short circuits between the electrodes, but allows ions in the electrolyte to pass freely between the positive electrode and the negative electrode.

[0158] The isolation membrane can be a porous structure isolation membrane with electrochemical stability and mechanical stability, such as a single-layer or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0159] 4. Outer packaging

[0160] The sodium ion battery cell may include an outer packaging, which may be used to encapsulate an electrode assembly including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0161] The outer packaging of the sodium ion battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.; or a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0162] The outer packaging shape of the sodium ion battery cell can be cylindrical, square or other arbitrary shapes. For example, Figure 1 The sodium ion battery cell is shown as an example, with the outer packaging shape being a square structure.

[0163] Reference Figure 2The outer package may include a shell 01 and a cover plate 02. The shell 01 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 01 has an opening connected to the receiving cavity, and the cover plate 02 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 03 through a winding process or a lamination process. One or more electrode assemblies 03 are encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 03.

[0164]

Battery module, battery pack

[0165] A fifth aspect of an embodiment of the present application provides a related device, which is a battery module, including the sodium ion battery cell of the first aspect above, or a sodium ion battery cell prepared by the preparation method of the second aspect above.

[0166] A sixth aspect of an embodiment of the present application provides a related device, which is a battery pack, including the battery module of the fifth aspect mentioned above.

[0167] One or more battery cells are integrated to form a battery module, which can provide higher voltage and capacity, and have specific functional output. One or more battery modules are installed in a battery box, and a battery management system is usually added to form a battery pack. The battery pack is usually a product provided to users.

[0168] refer to Figure 3 , which is an example of a battery module. In the battery module, multiple battery cells 04 can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other way. Further, the multiple battery cells 04 can be fixed by fasteners.

[0169] Optionally, the battery module may further include a housing having a receiving space, and a plurality of battery cells 04 are received in the receiving space.

[0170] refer to Figure 4 and Figure 5 , which is used as an example of a battery pack. The battery pack may include a battery box and a plurality of battery modules 05 disposed in the battery box. The battery box includes an upper box body 06 and a lower box body 07, and the upper box body 06 can be covered on the lower box body 07 to form a closed space for accommodating the battery module 05. The plurality of battery modules 05 can be arranged in the battery box in any manner.

[0171] In the positive electrode sheet of the sodium ion battery cell of the embodiment of the present application, a special solid electrolyte interface film is combined on the surface of the positive electrode active material, which has excellent cycle performance and long life. Therefore, the battery module including the sodium ion battery cell and the battery pack including the battery module also show the characteristics of good cycle performance and long life.

[0172]

Electrical devices

[0173] The embodiment of the present application also provides another related device, which is an electrical device, and the electrical device includes at least one of the sodium ion battery cell of the first aspect, the battery module of the fifth aspect, and the battery pack of the sixth aspect.

[0174] The battery (sodium ion battery cell, battery module or battery pack) disclosed in the embodiment of the present application can be used in an electrical device using the battery as a power source, or in various energy storage systems using the battery as an energy storage element, to provide electrical energy. The above-mentioned battery exhibits the advantage of long life, so after the battery is applied to various electrical devices, it is beneficial to extend the battery life of various electrical devices and improve the user experience of various electrical devices.

[0175] The electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, the electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and the spacecraft may include airplanes, rockets, space shuttles and spacecraft, etc. As the electrical devices, the battery cells, battery modules or battery packs in the battery may be selected according to their usage requirements.

[0176] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the battery, a battery pack or a battery module can be used.

[0177] The following detailed description of the embodiments of the present application is given. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be obtained commercially.

[0178] [Example 1 to Example 6, Comparative Example 1, Comparative Example 2]

[0179] Example 1

[0180] This embodiment provides a sodium ion battery cell, and the preparation method thereof comprises the following steps:

[0181] (1) Preparation of positive electrode sheet

[0182] Aluminum foil with a thickness of 12 μm was used as the positive electrode current collector.

[0183] The Dv50 of the positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 O2, sodium nitrite with a Dv50 of 45 μm, carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder are fully stirred and mixed in a proper amount of solvent N-methylpyrrolidone NMP at a mass ratio of 93:2:3:2 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a compaction density of 3.1 g / cm is obtained. 3 The invention relates to a positive electrode sheet having a porosity of 45% and a mass content of sodium nitrite in the positive electrode active layer of 2%.

[0184] (2) Negative electrode

[0185] A copper foil with a thickness of 8 μm was used as the negative electrode.

[0186] (3) Isolation film

[0187] A porous polyethylene (PE) film is used as the isolation membrane.

[0188] (4) Preparation of electrolyte

[0189] In an environment where the water content is less than 10 ppm, non-aqueous organic solvents ethylene carbonate EC and diethyl carbonate DMC are mixed in a volume ratio of 1:1 to obtain a mixed solvent, and then sodium hexafluorophosphate and the mixed solvent are mixed to prepare an electrolyte with a sodium hexafluorophosphate concentration of 1 mol / L.

[0190] (5) Preparation of sodium ion battery monomers

[0191] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then the electrode assembly is obtained through a stacking process; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a sodium ion battery cell is obtained.

[0192] The formation process includes: placing the sodium ion battery monomer in a formation cabinet for charging, charging from 3.1V to a cut-off voltage of 3.8-4.2V at a rate of 0.33C at 25°C, and completing the formation of the sodium ion battery monomer.

[0193] Example 2

[0194] This embodiment provides a sodium ion battery cell, which differs from Embodiment 1 only in that the additive sodium nitrite is replaced by an equal mass of potassium nitrite.

[0195] Example 3

[0196] This embodiment provides a sodium ion battery cell, which differs from Embodiment 1 only in that the additive sodium nitrite is replaced by an equal mass of calcium nitrite.

[0197] Example 4

[0198] This embodiment provides a sodium ion battery cell, which differs from Embodiment 1 only in that the additive sodium nitrite is replaced with an equal mass of lithium nitrite.

[0199] Example 5

[0200] This embodiment provides a sodium ion battery cell, which differs from Embodiment 1 only in that the additive sodium nitrite is replaced by an equal mass of sodium sulfite.

[0201] Example 6

[0202] This embodiment provides a sodium ion battery cell, which differs from Embodiment 1 only in that the additive sodium nitrite is replaced by an equal mass of potassium sulfite.

[0203] Comparative Example 1

[0204] This comparative example provides a sodium ion battery cell, which is different from Example 1 in that the positive electrode sheet does not contain additives, NaFe 0.33 Mn 0.33 Ni 0.33 The mass content of O2 in the positive electrode active layer is adaptively increased to 95%.

[0205] Comparative Example 2

[0206] This comparative example provides a sodium ion battery cell, which is different from Example 1 in that the positive electrode sheet does not contain additives, NaFe 0.33 Mn 0.33 Ni 0.33 The mass content in the positive electrode active layer is adaptively increased to 95%; at the same time, the electrolyte contains a saturated amount of sodium nitrite (sodium nitrite is poorly soluble in the electrolyte, so the saturated concentration of sodium nitrite in the electrolyte is extremely low).

[0207] After formation, according to the working mechanism of the sodium ion battery monomer, a solid electrolyte interface film is formed on the surface of the positive electrode active material of the positive electrode plate in the sodium ion battery monomers of each embodiment and comparative example. The sodium ion battery monomer was disassembled, and the disassembled positive electrode plates were subjected to XPS and ICP analysis. It was found that the chemical composition and / or mass content of the solid electrolyte interface film of Examples 1 to 6 were different from those of Comparative Example 1, and the solid electrolyte membranes of Examples 1 and 5 contained a higher mass content of Na than that of Comparative Example 1. + , the solid electrolyte interface films of Examples 2 to 4 and 6 showed K+ , Ca 2+ , Li + The chemical composition of the solid electrolyte interface membrane in each embodiment and the mass content of the relevant cations in the solid electrolyte interface membrane in the positive electrode sheet are shown in Table 1 below.

[0208] Combined with the preparation method of sodium ion battery monomer, it can be inferred that: due to the Na + The source is only the positive electrode active material and the additive, then the solid electrolyte interface membrane of Example 1 and Example 5 increases the Na + The K in the solid electrolyte interface membranes of Examples 2 to 4 and 6 should be derived from the added additives sodium nitrite and sodium sulfite respectively; + , Ca 2 , Li + The only source of cations is additives. Therefore, the newly added cations in the solid electrolyte interface membranes of Examples 2 to 4 and 6 compared with Comparative Example 1 should be derived from the added additives potassium nitrite, calcium nitrite, lithium nitrite and potassium sulfite. + , K + , Ca 2+ , Li + The cations of nitrite and sulfite in the positive electrode plate can be contained in the solid electrolyte interface film on the surface of the positive electrode active material of the positive electrode plate. The solid electrolyte interface film is usually formed on the surface of the positive electrode active material after the active ions in the positive electrode plate participate in the electrochemical reaction. Therefore, it can be inferred that the Na in the additive + , K + , Ca 2+ , Li + Isotropic cations also participate in the electrochemical reactions of sodium-ion battery cells.

[0209] At the same time, the performance of each sodium ion battery cell was tested, and the test results are shown in Table 1.

[0210] [Table 1]

[0211]

[0212] Note: 1) In the table, X a+ represents the cation corresponding to the additive in the solid electrolyte interface film, and a is 1 or 2. For example, for Example 1, X represents Na + In Example 2, X represents K + .

[0213] 2) In Examples 1 and 6, the Na+ The mass content in the positive electrode refers to the Na corresponding to the additive. + The mass content (c0) in the positive electrode sheet, that is, the Na + The mass content in the positive electrode sheet does not include the NaFe from the positive electrode active material 0.33 Mn 0.33 Ni 0.33 O2Na + The mass content in the positive electrode.

[0214] 3) "Battery cell capacity" refers to the initial discharge capacity of a sodium ion battery cell. "Battery cell capacity increase ratio" refers to the percentage of the ratio to the battery cell capacity of comparative example 1. For example, the battery cell capacity increase ratio of Example 1 = battery cell capacity of Example 1 / battery cell capacity of comparative example 1 * 100%; the battery cell capacity increase ratio of Example 2 = battery cell capacity of Example 2 / battery cell capacity of comparative example 1 * 100%.

[0215] The test results show that compared with Comparative Example 1, the sodium ion battery cells of Examples 1 to 6 have lower DCR (DCR is reduced by 69% to 83%); the cell capacity is increased; the capacity retention rate after 1000 cycles is higher, reaching 83% and above, and the battery life is extended. Combined with the chemical composition of the solid electrolyte interface membrane of Examples 1 to 6, it can be seen that the solid electrolyte interface membrane increases the Na + , or the solid electrolyte interface film contains Li + , K + , Ca 2+ The cations can participate in the electrochemical reaction of sodium ion batteries, provide reversible capacity, make up for the capacity loss caused by the passivation of the positive electrode active material by the solid electrolyte interface membrane, and improve the battery cycle performance. At the same time, the solid electrolyte interface membrane containing these cations is conducive to reducing the battery impedance, thereby further improving the battery cycle performance.

[0216] In addition, the test found that there was no significant difference in the chemical composition and mass content of related ions of the solid electrolyte interface membranes of Comparative Example 1 and Comparative Example 2. At the same time, Comparative Example 2 shows that the addition of sodium nitrite as an additive to the electrolyte has no effect on the performance of the sodium ion battery. This may be due to: on the one hand, the sodium nitrite additive in Comparative Example 2 is poorly soluble in the electrolyte in an organic environment and has a very low content; on the other hand, the sodium nitrite additive cannot decompose the corresponding cations in the electrolyte, and thus cannot participate in the film formation on the surface of the positive electrode active material, that is, it cannot increase the Na in the solid electrolyte interface membrane. + The content ultimately cannot make up for the capacity loss caused by the passivation of the positive electrode active material.

[0217] [Example 7 to Example 10]

[0218] Example 7

[0219] This embodiment provides a sodium ion battery cell, which differs from the embodiment 1 only in that: in the preparation step of the positive electrode sheet, the mass content of sodium nitrite in the positive electrode active layer is 0.5%; at the same time, the positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 The mass content of O2 in the positive electrode active layer is adaptively adjusted to 94.5%.

[0220] Example 8

[0221] This embodiment provides a sodium ion battery cell, which differs from the embodiment 1 only in that: in the preparation step of the positive electrode sheet, the mass content of sodium nitrite in the positive electrode active layer is 1%; at the same time, NaFe 0.33 Mn 0.33 Ni 0.33 The mass content of O2 in the positive electrode active layer is adaptively adjusted to 94%.

[0222] Example 9

[0223] This embodiment provides a sodium ion battery cell, which differs from the embodiment 1 only in that: in the preparation step of the positive electrode sheet, the mass content of sodium nitrite in the positive electrode active layer is 3%; at the same time, NaFe 0.33 Mn 0.33 Ni 0.33 The mass content of O2 in the positive electrode active layer is adaptively adjusted to 92%.

[0224] Example 10

[0225] This embodiment provides a sodium ion battery cell, which differs from the embodiment 1 only in that: in the preparation step of the positive electrode sheet, the mass content of sodium nitrite in the positive electrode active layer is 5%; at the same time, NaFe 0.33 Mn 0.33 Ni 0.33 The mass content of O2 in the positive electrode active layer is adaptively adjusted to 90%.

[0226] In Examples 7 to 10, the mass content of cations corresponding to the additives in the solid electrolyte interface film formed on the surface of the positive electrode active material in the positive electrode sheet, and the performance test results of the sodium ion battery monomer are shown in Table 2 below.

[0227] [Table 2]

[0228]

[0229] Table 2 shows that as the mass content of sodium nitrite in the positive electrode increases during the preparation process, the Na + The mass content of the positive electrode also increases, which further reflects that the Na in sodium nitrite + Participated in the formation of the solid electrolyte interface film. And in Example 1 and Example 7~

[0230] Under the conditions of Example 10, the sodium ion battery has a lower DCR, a higher cell capacity and a higher capacity retention rate than that of Comparative Example 1, and as the Na + As the mass content of the positive electrode increases, the capacity of the battery increases accordingly, which also shows that the Na in sodium nitrite + It can participate in the electrochemical reaction of sodium-ion batteries and provide reversible capacity.

[0231] [Example 11 to Example 14]

[0232] Embodiment 11

[0233] This embodiment provides a sodium ion battery cell, which is different from the embodiment 1 only in that in the preparation step of the positive electrode plate, the Dv50 of the sodium nitrite used is 2 μm.

[0234] Example 12

[0235] This embodiment provides a sodium ion battery cell, which is different from the embodiment 1 only in that in the preparation step of the positive electrode plate, the Dv50 of the sodium nitrite used is 10 μm.

[0236] Embodiment 13

[0237] This embodiment provides a sodium ion battery cell, which is different from the embodiment 1 only in that in the preparation step of the positive electrode plate, the Dv50 of the sodium nitrite used is 30 μm.

[0238] Embodiment 14

[0239] This embodiment provides a sodium ion battery cell, which is different from the embodiment 1 only in that in the preparation step of the positive electrode plate, the Dv50 of the sodium nitrite used is 75 μm.

[0240] In Examples 11 to 14, the porosity of the positive electrode sheet before and after formation, and the performance test results of the sodium ion battery cell are shown in Table 3 below.

[0241] [Table 3]

[0242]

[0243]

[0244] Table 3 shows that after the formation, the porosity of the positive electrode sheet increases. Moreover, the larger the particle size of sodium nitrite, the greater the porosity of the positive electrode sheet after the formation. This indirectly reflects that the sodium nitrite in the positive electrode sheet decomposes during the formation process, resulting in more pores in the positive electrode sheet. At the same time, when the added sodium nitrite Dv50 is in the range of 2 to 75 μm, the DCR of the sodium ion battery can be effectively reduced and the capacity retention rate of the sodium ion battery can be improved.

[0245] [Test method]

[0246] The test methods for each item of each embodiment and comparative example in Table 1 to Table 3 are as follows:

[0247] (1) Qualitative and quantitative analysis of solid electrolyte interface films

[0248] 1) After disassembling the battery cells in the glove box, take out the positive electrode sheets, clean them with DMC, dry them, and cut them into 1540.25mm in a vacuum glove box. 2 The circular pole piece samples were sent for XPS for qualitative analysis.

[0249] Specifically, during the XPS test, the sample surface is first tested to obtain the XPS spectrum of the surface (the first XPS spectrum). The first XPS spectrum of the circular pole piece corresponding to each embodiment will show X a+ (Na + , K + , Li + , Ca 2+ The characteristic peaks of one or more of the positive electrode active materials NaFe 0.33 Mn 0.33 Ni 0.33 Characteristic peaks corresponding to Fe, Mn, and Ni in O2.

[0250] Then, at 2000 eV, Ar + The same position of the sample was ion-etched in the depth direction, with Ta2O5 target as the standard sample, and the etching rate was 0.4nm / s. An XPS spectrum was obtained after each etching distance. During the test, it was found that after etching a certain distance, the nth XPS spectrum different from the first XPS spectrum could be obtained. The positive electrode active material NaFe 0.33 Mn 0.33 Ni 0.33 The characteristic peaks corresponding to Fe, Mn, and Ni in O2 may show Na + The characteristic peak of K + , Li + , Ca 2+ characteristic peaks.

[0251] According to the changes in the elemental composition in the XPS spectra during the entire XPS test process, it can be judged that the sample includes at least two layers with different chemical compositions, one of which is the positive electrode active material layer corresponding to the nth XPS spectrum, and on the surface of the positive electrode active material there is a film layer corresponding to the first XPS spectrum, namely, a solid electrolyte interface film, and the solid electrolyte interface film contains Na + , K + , Li + , Ca 2+ One or more cations in a.

[0252] 2) In addition, take the dried positive circular electrode, scrape off all the active layer powder of the circular electrode, weigh it, dissolve the powder with aqua regia, and send it to ICP for quantitative analysis.

[0253] For the example, the cation contained in the additive is K + , Li + , Ca 2+ In the case of + , Li + , Ca 2+ The mass content in the positive electrode.

[0254] For the example, the cation contained in the additive is Na + In the case of the above, the total mass content c1 in the positive electrode sheet can be obtained by ICP test, and the Na content in the positive electrode sheet can be obtained by testing the blank control group (i.e., comparative example 1 without additives). + The total mass content c2, then the Na in the solid electrolyte interface film from the additive + The mass content of the positive electrode sheet is c0=c1-c2.

[0255] (2)DCR

[0256] At 25°C, charge at 0.33C rate to 4.2V, let stand for 5min, discharge at 1C rate to 1.5V, let stand for 15min, charge at 0.33C rate to 4.2V, discharge at 0.33C rate to 50% SOC, let stand for 30min, record voltage V1, pulse discharge at 4C(I) rate for 30s, record voltage V2 after pulse discharge.

[0257] The DCR is calculated according to the formula: DCR = (static end voltage V1 - pulse discharge voltage V2) / pulse current I.

[0258] (3) Battery cell capacity improvement ratio and cycle performance (capacity retention rate)

[0259] At 25°C, the sodium ion battery monomer is charged at a constant current of 0.33C to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of 1C, then left to stand for 5 minutes, discharged at a constant current of 0.33C to a voltage of 1.5V, and then left to stand for 5 minutes. This is a cycle of charge and discharge. The discharge capacity of this time is recorded as the discharge capacity (initial discharge capacity) of the first cycle of the sodium ion battery monomer. Set the initial discharge capacity of Comparative Example 1 to A, and the initial discharge capacity of each embodiment to B, then the battery capacity improvement ratio of each embodiment = (B / A)*100%.

[0260] The sodium ion battery monomer is cycled for 1000 cycles according to the above method, and the discharge capacity after 1000 cycles is recorded to obtain the corresponding capacity retention rate. Capacity retention rate = discharge capacity after 1000 cycles / initial discharge capacity*100%.

[0261] (4) Porosity of positive electrode sheet

[0262] Cut the positive electrode into 20 circular double-sided electrodes with a diameter of 14 mm, record the total weight and total thickness of the 20 circular double-sided electrodes, and calculate the volume density. Put the 20 circular double-sided electrodes into the sample cup of the true density porosity tester, use helium replacement, and combine Archimedes' law and Bohr's law to obtain the true volume of the 20 circular double-sided electrodes, and then calculate the true density. Porosity = (1-volume density / true density)*100%.

[0263] (5)Dv50

[0264] Take an appropriate amount of the sample to be tested, add 20 mL of deionized water to disperse it, and then measure the sample using a Malvern 3000 (MasterSizer 3000) laser particle size analyzer according to GB / T19077-2016 / ISO 13320:2009 standard.

[0265] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A sodium ion battery cell, characterized in that: The invention comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material and a solid electrolyte interface film at least combined with the surface of the positive electrode active material, wherein the solid electrolyte interface film comprises Na + , Li + , K + , Ca 2+ One or more cations in a.

2. The sodium ion battery cell according to claim 1, characterized in that: The solid electrolyte interface film comprises Na + , Li + , K + One or more cations in a.

3. The sodium ion battery monomer according to claim 1 or 2, characterized in that: The mass content of the cation in the positive electrode plate is 0.09% to 0.7%, and optionally 0.3% to 0.67%.

4. A method for preparing a sodium ion battery monomer, characterized in that: include: An electrode assembly comprising a positive electrode sheet is prepared, wherein the positive electrode sheet comprises a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in The electrode assembly is combined with an electrolyte and then subjected to a chemical formation treatment.

5. The method for preparing a sodium ion battery monomer according to claim 4, characterized in that: The additive includes one or more of nitrite and sulfite, and the cations in the nitrite and the sulfite independently include Na + , Li + , K + , Ca 2+ One or more of .

6. The method for preparing a sodium ion battery monomer according to claim 5, characterized in that: The sulfite includes one or more of potassium sulfite, potassium pyrosulfite, sodium sulfite, sodium pyrosulfite, calcium sulfite, and calcium pyrosulfite.

7. The method for preparing a sodium ion battery monomer according to claim 5 or 6, characterized in that: The nitrite includes one or more of lithium nitrite, potassium nitrite, sodium nitrite and calcium nitrite.

8. The method for preparing a sodium ion battery monomer according to any one of claims 4 to 7, characterized in that: The mass content of the additive in the active layer of the positive electrode plate is 0.5% to 5%, and optionally 2% to 5%.

9. The method for preparing a sodium ion battery monomer according to any one of claims 4 to 8, characterized in that: The Dv50 of the additive is 2 μm to 75 μm, and optionally 2 μm to 45 μm.

10. The method for preparing a sodium ion battery monomer according to any one of claims 4 to 9, characterized in that: The Dv50 of the positive electrode active material is 1 μm to 20 μm, and optionally 4 μm to 10 μm.

11. The method for preparing a sodium ion battery monomer according to any one of claims 4 to 10, characterized in that: The charging voltage range of the formation treatment step includes 3V to 4.2V, and optionally includes 3V to 4V.

12. The method for preparing a sodium ion battery monomer according to any one of claims 4 to 11, characterized in that: The charging rate in the formation treatment step is 0.05C to 0.5C, and optionally 0.1C to 0.3C.

13. A positive electrode plate for a sodium ion battery, characterized in that: The invention comprises a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in a.

14. A method for preparing a positive electrode sheet for a sodium ion battery, characterized in that: include: Prepare a positive electrode slurry comprising a positive electrode active material and an additive, wherein the additive comprises Na + , Li + , K + , Ca 2+ One or more cations in The positive electrode slurry is coated on the positive electrode current collector, and then dried and compacted to obtain a positive electrode sheet.

15. A battery module, characterized in that: The invention comprises a sodium ion battery monomer as claimed in any one of claims 1 to 3, or a sodium ion battery monomer prepared by the preparation method as claimed in any one of claims 4 to 12.

16. A battery pack, characterized in that: Comprising the battery module as claimed in claim 15.

17. An electrical device, characterized in that: It comprises at least one of the sodium ion battery cell according to any one of claims 1 to 3, the battery module according to claim 15, and the battery pack according to claim 16.

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