Secondary battery and preparation method therefor, and electric apparatus

Abstract

A secondary battery and a preparation method therefor, and an electric apparatus. The secondary battery comprises a positive electrode plate, which positive electrode plate comprises a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and a material containing a chalcogen element. The secondary battery and an electric apparatus including the secondary battery have improved cycle performance and high-temperature storage performance.

Description

Secondary battery, preparation method thereof, and power-consuming device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310879812.7, filed on July 18, 2023, entitled “Secondary battery, method for preparing the same, and electrical device therefor,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of battery technology, and specifically relates to a secondary battery, a preparation method thereof, and an electrical device. Background Art

[0004] Secondary batteries, also known as rechargeable batteries, are batteries that can be repeatedly discharged and recharged for multiple uses. In recent years, as secondary batteries, particularly sodium-ion batteries, have become increasingly widely used, higher demands have been placed on their performance, particularly their cycle life.

[0005] Therefore, further improving the cycle performance and high-temperature storage performance of secondary batteries remains a technical problem that needs to be solved urgently.

[0006] Summary of the Invention

[0007] The purpose of this application is to provide a secondary battery and a preparation method thereof, which can improve the cycle performance and high-temperature storage performance of the secondary battery containing the same; the purpose of this application is also to provide an electrical device containing a secondary battery, which can obtain improved secondary battery cycle performance and high-temperature storage performance.

[0008] In a first aspect, an embodiment of the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer comprising a positive electrode active material and a material containing a chalcogen element.

[0009] According to an embodiment of the present application, the positive electrode film layer of the positive electrode plate in the secondary battery includes a material containing a chalcogen element, and the chalcogen element includes at least one of sulfur, selenium, or tellurium. On the one hand, the presence of the material containing a chalcogen element has been shown to reduce the residual alkali content of the positive electrode film layer during the preparation process, such as the content of Na2O and / or Na2CO3, thereby preventing the residual alkali from causing certain corrosion to the positive electrode plate containing the positive electrode film layer, forming electrolyte residues or producing other adverse electrochemical reactions, resulting in reduced conductivity of the positive electrode plate, thereby preventing the residual alkali in the secondary battery from generating electrolyte residues during the electrochemical cycle, or causing other adverse electrochemical reactions in the secondary battery, and improving the kinetic performance of the secondary battery containing the positive electrode plate on the basis of improving the conductivity of the positive electrode plate.

[0010] On the other hand, when the secondary battery is undergoing charge and discharge cycles, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer containing the sulfide element to form an in-situ coating layer on the surface of the positive electrode active material, which is equivalent to a protective film. It can reduce the contact interface between the electrolyte and the positive electrode active material, help to enhance the stability of the contact interface between the positive electrode active material and the electrolyte, reduce side reactions, and improve the battery's cycle performance and high-temperature storage performance.

[0011] In addition, when the secondary battery is formed, the Na2CO3 in the residual alkali of the positive electrode sheet forms CO2, which can be released together with other gases formed in the secondary battery formation process, thereby preventing the gas from being produced in the subsequent charge and discharge chemical cycle, and preventing it from affecting the structure of the secondary battery, causing bulging and other phenomena, and affecting the electrochemical performance of the secondary battery.

[0012] The material containing sulfide elements includes a reducing material containing sulfide elements, which is present in the positive electrode plate. During the formation or subsequent cycle of the secondary battery containing the positive electrode plate, the reducing material containing sulfide elements can be reduced and oxidized in the electrolyte to form a solid electrolyte membrane (SEI membrane) at the interface between the negative electrode plate and the electrolyte, such as a SEI membrane containing poly (ethylene oxide) (PEO)-type polymer and alkyl lithium sulfate (R-OSO2ONa) components. The SEI membrane has excellent elasticity and certain strength. The SEI membrane with strong toughness can allow a certain amount of volume change of the negative electrode plate during the charge and discharge process at the negative electrode plate-electrolyte interface, which is beneficial to protecting the structural stability of the battery cell, thereby improving the cycle performance and service life of the secondary battery; in addition, the SEI membrane with this component can quickly transport Na + The active ions included are beneficial to improving the power performance of secondary batteries, such as improving the ability of rapid charging and discharging.

[0013] In some optional embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the chalcogen element is less than or equal to 3%, and can be optionally 0.1%-2%.

[0014] According to an embodiment of the present application, the positive electrode film layer contains 0.01% to 3% by weight of a chalcogen, which includes at least one of sulfur, selenium, and tellurium. During the preparation of the positive electrode sheet, i.e., during the slurry stirring process, the chalcogen reacts with some residual alkali to form an intermediate product, which can effectively lower the pH of the slurry and alleviate or prevent the gelation of the slurry. Furthermore, the intermediate product further reacts with the residual alkali in the slurry, further preventing the occurrence of gelation, facilitating uniform stirring and proper coating of the slurry. This improves the overall performance of the positive electrode sheet, including uniformity, and contributes to the cycling and kinetic performance of the secondary battery containing the positive electrode sheet.

[0015] In some optional embodiments, the material containing chalcogen includes a simple substance containing chalcogen and / or a salt containing chalcogen.

[0016] According to the embodiment of the present application, the single substance of the sulfide element exists in the positive electrode plate as zero valence, and the salt of the sulfide element includes a salt with reducing properties. It can also include a salt with a positive divalent sulfide element. Due to its certain reducing properties, during the formation and / or circulation of the secondary battery, it reacts with the residual alkali in the positive electrode plate to form a protective film containing MO components (M includes at least one of Ni, Co, Mn, Fe and Cu), which is beneficial to improve the interface stability of the positive electrode active material with the electrolyte during subsequent cycles, reduce side reactions, and is beneficial to improve the cycle performance and high temperature storage performance of the secondary battery containing the positive electrode plate. In addition, the reaction of the single substance of the sulfide element with the residual alkali releases additional Na + Active ions including ions can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0017] In some optional embodiments, the salt containing a chalcogen element includes A2O32- or AO42-, wherein A represents a chalcogen element.

[0018] According to the embodiment of the present application, the salt of the sulfide element A is present in the positive electrode plate, which is beneficial to improving the uniformity of the components in the positive electrode film layer in the positive electrode plate, and is beneficial to reacting with the residual alkali in the positive electrode plate to generate a protective film containing MO components, which is beneficial to improving the interface stability between the positive electrode active material and the electrolyte during subsequent cycles, reducing side reactions, and is beneficial to improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0019] According to the embodiment of the present application, the salt containing the chalcogen element can be obtained by reacting the chalcogen element with the positive electrode active material, or can be directly added.

[0020] When a secondary battery comprising the positive electrode plate undergoes formation or electrochemical cycling, the positive electrode plate comprises a reducing material containing a chalcogen element, which can continue to react with the residual alkali in the positive electrode plate, thereby reducing the residual alkali content in the positive electrode active material and forming an artificial protective film. The protective film has very stable electrochemical stability, and its components include Na2SO4, etc., and is located on the surface of the positive electrode active material or exists alone. This is beneficial to improving the stability of the positive electrode active material in contact with the electrolyte during subsequent cycling, reducing side reactions, and is beneficial to improving the cycle performance and high-temperature storage performance of the secondary battery comprising the positive electrode plate.

[0021] In addition, the additional active ions including Na+ ions released by the reaction of the reducing salt containing sulfur elements with the residual alkali can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0022] In some optional embodiments, the valence state of the chalcogen element includes at least one of zero valence, positive divalent, positive tetravalent, and positive hexavalent; optionally, the valence state of the chalcogen element includes positive hexavalent and positive tetravalent.

[0023] When the secondary battery containing the positive electrode plate is formed and subsequently cycled, the single substance of the sulfide element contained in the positive electrode plate. The single substance of the sulfide element reacts with the residual alkali in the positive electrode plate to form a protective film containing MO components (M includes at least one of Ni, Co, Mn, Fe and Cu), which is beneficial to improving the interface stability of the positive electrode active material with the electrolyte during subsequent cycles, reducing side reactions, and improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate. In addition, the additional Na + Active ions including ions can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0024] In some optional embodiments, the ratio of the molar amount n2 of the hexavalent sulfide element in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide elements in the positive electrode film layer is (0.5-1):1, or optionally (0.7-1):1.

[0025] According to the embodiments of the present application, after the secondary battery is formed, the ratio of the molar amount n2 of the hexavalent sulfide element in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide elements in the positive electrode film layer is within the above range, indicating that the residual alkali such as Na2O and / or Na2CO3 in the positive electrode film layer including the above content is decomposed and consumed, forming a relatively stable salt containing the sulfide element, which is beneficial to the stability of the secondary battery.

[0026] In some alternative embodiments, the positive electrode active material comprises a layered transition metal oxide.

[0027] In some optional embodiments, the layered transition metal oxide comprises a structural formula of a Ni b Co c Mn f M d O eA transition metal oxide, wherein 0.5≤a≤1.2, 0≤b≤2, 0≤c≤2, 0≤f≤1, 0≤d≤1.5, 1≤e≤4, A includes one or more of Li and Na; M includes one or more of Ca, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B; optionally, b+c+d+f=1 or b+c+d+f=2; optionally, A also includes K.

[0028] According to the embodiments of the present application, the above-mentioned layered transition metal oxides generally have a higher active ion storage capacity. The above-mentioned types of layered transition metal oxides can embed and release more active ions, including sodium ions, thereby providing a higher battery capacity. This allows the battery to store more electrical energy and have a longer service life. The high capacity characteristics of the layered transition metal oxides result in the battery having a higher energy density. The layered transition metal oxides have a certain oxidizability, and the redox reaction that occurs therein is beneficial to the stability of the material structure, helps to reduce the structural changes and attenuation of the material, and thus extends the cycle life of the battery.

[0029] In some optional embodiments, the positive electrode active material includes a coating layer at least partially coated on the positive electrode active material, the coating layer comprising MO z , M includes one or more of Ni, Co, Mn, Fe and Cu, 0<z<2.

[0030] According to the embodiments of the present application, the coating layer on the surface of the positive electrode active material can maintain the stability of the positive electrode active material during the electrochemical cycle and reduce the contact area between the positive electrode active material and the electrolyte.

[0031] In some optional embodiments, the coating layer has a thickness of 1 to 10 nm.

[0032] According to the embodiments of the present application, the thickness of the coating layer is controlled within the above range, thereby improving the cycle performance of the secondary battery while reducing the contact area between the positive electrode active material and the electrolyte. A thinner protective film may not effectively prevent the electrolyte from contacting the positive electrode active material, while a thicker protective film restricts the transmission of ions and electrons, thereby reducing the electrochemical performance of the secondary battery.

[0033] In some optional embodiments, the positive electrode film layer includes sodium oxide. Optionally, the mass content of sodium oxide in the positive electrode film layer is ≤1000 ppm.

[0034] In some optional embodiments, the positive electrode film layer includes sodium carbonate, and the mass content of sodium carbonate in the positive electrode film layer is ≤2000 ppm.

[0035] According to an embodiment of the present application, the inclusion of the aforementioned content of Na2O and / or Na2CO3 in the positive electrode film layer contained in the secondary battery is beneficial for reducing the corrosion of the positive electrode sheet by the aforementioned Na2O and / or Na2CO3. The presence of Na2O and / or Na2CO3 in the positive electrode sheet may form electrolyte residues on the positive electrode sheet or produce other adverse electrochemical reactions, resulting in reduced conductivity of the positive electrode sheet. The inclusion of the aforementioned content of Na2O and / or Na2CO3 in the positive electrode film layer is beneficial for reducing electrolyte residues or other adverse electrochemical reactions, improving the conductivity of the positive electrode sheet, and improving the dynamic performance of the secondary battery containing the positive electrode sheet.

[0036] In addition, the CO2 generated by Na2CO3 in the positive electrode film layer can be released together with other gases formed during the secondary battery formation process. When the positive electrode active material of the secondary battery contains the above-mentioned content of Na2CO3 after formation, the generated gas will affect the structure of the secondary battery, causing bulging and other phenomena, thereby affecting the electrochemical performance of the secondary battery.

[0037] In some optional embodiments, the secondary battery is a sodium ion secondary battery.

[0038] In some optional embodiments, the positive electrode film layer includes a sodium supplement.

[0039] According to the embodiments of the present application, the material containing sulfide elements participates in the formation of the SEI film, consuming part of the active sodium. The composition includes a sodium supplement that can increase the capacity of the battery while supplementing the active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance and storage life.

[0040] In some optional embodiments, the sodium supplement includes one or more of sodium sulfide, sodium selenide, and sodium nitride.

[0041] According to the embodiments of the present application, materials containing sulfide elements can participate in the formation of SEI film, consuming part of the active sodium. The composition includes a sodium supplement that can increase the capacity of the battery while supplementing the active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance and storage life.

[0042] In a second aspect, an embodiment of the present application provides a method for preparing the secondary battery of the first aspect, comprising preparing a positive electrode sheet:

[0043] Preparing a positive electrode slurry: adding a mixture including a positive electrode active material and a material containing a chalcogen element into a solvent to form a slurry;

[0044] The positive electrode slurry is coated on at least one surface of the positive electrode current collector to form a positive electrode film layer.

[0045] According to an embodiment of the present application, the chalcogen element includes at least one of sulfur, selenium, and tellurium. As an example, the material containing the chalcogen element includes a simple substance of the chalcogen element. The simple substance of the chalcogen element can react with at least part of the residual alkali to form an intermediate product during the stirring process of the mixture for preparing the slurry, which can effectively reduce the pH of the slurry and alleviate or avoid the gelation phenomenon of the slurry; in addition, the above-mentioned intermediate product can further react with the residual alkali in the slurry in the subsequent process to further avoid the occurrence of the gelation phenomenon, which is beneficial to the uniform stirring of the slurry and the normal coating of the slurry, thereby facilitating the preparation of the composition containing the positive electrode active material and the simple substance of the chalcogen element into a positive electrode sheet, and improving the comprehensive performance of the positive electrode sheet including uniformity.

[0046] On the one hand, materials containing sulfide elements can reduce the residual alkali content of the positive electrode film layer during the preparation process, such as the content of Na2O and / or Na2CO3, to prevent the residual alkali from causing certain corrosion to the positive electrode plate containing the positive electrode film layer, forming electrolyte residues or producing other adverse electrochemical reactions, resulting in a decrease in the conductivity of the positive electrode plate, thereby preventing the residual alkali in the secondary battery from generating electrolyte residues during the electrochemical cycle, or causing other adverse electrochemical reactions in the secondary battery, and improving the kinetic performance of the secondary battery containing the positive electrode plate on the basis of improving the conductivity of the positive electrode plate.

[0047] On the other hand, when the secondary battery is undergoing charge and discharge cycles, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer containing the sulfide element to form an in-situ coating layer on the surface of the positive electrode active material, which is equivalent to a protective film. It can reduce the contact interface between the electrolyte and the positive electrode active material, help to enhance the stability of the contact interface between the positive electrode active material and the electrolyte, reduce side reactions, and improve the battery's cycle performance and high-temperature storage performance.

[0048] In some optional embodiments, the volume average particle size Dv50 of the material containing chalcogen is 50 nm-1000 nm, and optionally 100 nm-500 nm.

[0049] According to the embodiment of the present application, the volume average particle size Dv50 of the material containing chalcogen elements is within the above range, which is conducive to the dispersion of the chalcogen elements in the slurry and the reaction of the chalcogen elements with residual alkali, thereby avoiding gelation of the slurry.

[0050] In addition, the volume average particle size of the material containing sulfide elements in the positive electrode plate is within the above range. When the secondary battery containing the positive electrode plate is formed and subsequently cycled, it is beneficial to form a relatively uniform and appropriate volume coating layer for the positive electrode active material on the basis of protecting the structure of the positive electrode plate. The coating layer is beneficial to improving the interface stability between the positive electrode active material and the electrolyte during subsequent cycles, reducing side reactions, and improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0051] In some optional embodiments, the valence state of the chalcogen element includes at least one of zero valence, positive divalent valence, and positive hexavalent valence; optionally, the valence state of the chalcogen element includes zero valence and positive divalent valence.

[0052] According to an embodiment of the present application, the sulfide element in the above-mentioned valence state exists in the positive electrode plate, which is beneficial to improving the comprehensive electrochemical performance of the secondary battery containing the positive electrode plate when the secondary battery containing the positive electrode plate is formed and / or subsequently cycled.

[0053] In some optional embodiments, the ratio of the sum of the molar amounts n1 of zero-valent and divalent sulfide elements in the positive electrode film layer to the sum of the molar amounts n0 of zero-valent, divalent and hexavalent sulfide elements in the positive electrode film layer is (0.5-1):1, and can optionally be (0.8-1):1.

[0054] According to an embodiment of the present application, by controlling the sum of the molar amounts of zero-valent and divalent sulfide elements in the positive electrode film layer and the total molar amount of sulfide elements in the positive electrode film layer, the amount of the protective film in the positive electrode film layer can be controlled, thereby improving the overall performance of the secondary battery while protecting the positive electrode active material.

[0055] In some optional embodiments, the positive electrode slurry is prepared by adding a mixture including the positive electrode active material, the material containing the chalcogen element, and the sodium supplement agent into a solvent to form a slurry.

[0056] According to the embodiments of the present application, the material containing sulfide elements participates in the formation of the SEI film, consuming part of the active sodium. The composition includes a sodium supplement that can increase the capacity of the battery while supplementing the active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance and storage life.

[0057] In some optional embodiments, the sodium supplement accounts for less than or equal to 3% by weight of the total mass of the mixture, and may be 0.1% to 2%. Adding an appropriate amount of the sodium supplement can increase the capacity of the battery while replenishing active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance, and storage life.

[0058] In some optional embodiments, the volume average particle size Dv50 of the sodium supplement is 1 μm to 5 μm.

[0059] According to the embodiments of the present application, the volume average particle size Dv50 of the sodium supplement is within the above range, which is beneficial to protecting the structural stability of the positive electrode sheet, improving the porosity of the positive electrode sheet, and improving the dynamic performance of the positive electrode sheet.

[0060] In some optional embodiments, the mass ratio of the material containing chalcogen elements to the sodium supplement is 1:(0.5-5), and can be optionally 1:(0.5-3).

[0061] According to the embodiments of the present application, the material containing the chalcogen element reacts with the residual alkali in the slurry to generate an intermediate product, and some unreacted chalcogen element and the intermediate product participate in the formation of the SEI film, consuming a certain amount of active sodium. By controlling the mass ratio of the consumed active sodium and the sodium supplement within the above range, on the one hand, the chalcogen element can be effectively utilized and its role can be exerted, and on the other hand, the content of active sodium can be supplemented to increase the capacity of the battery, further improving the cycle life and storage life of the battery.

[0062] The mass ratio of the material containing chalcogen elements to the sodium supplement agent is within the above range, which can avoid the content of the material containing chalcogen elements in the positive electrode film layer being too high, affecting the capacity and kinetic performance of the positive electrode sheet containing the positive electrode film layer during the charge and discharge cycle of the secondary battery; if the content of the sodium supplement agent in the positive electrode film layer is too high, it can affect the performance, stability and safety of the secondary battery.

[0063] In some optional embodiments, the ratio of the volume average particle size Dv50 of the material containing chalcogen elements to the sodium supplement is 1:(1-5), and can be optionally 1:(1-2).

[0064] According to the embodiments of the present application, by controlling the ratio of the volume average particle size Dv50 of the material containing the sulfide element to the sodium supplement, it is beneficial to improve the uniformity of the positive electrode sheet containing the composition, which is beneficial to the cycle performance and kinetic performance of the secondary battery containing the positive electrode sheet.

[0065] In a fifth aspect, embodiments of the present application provide an electrical device comprising the secondary battery of the fourth aspect, thereby achieving improved cycle performance and high-temperature storage performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0067] FIG1( a ) shows the effect of the slurry of Example 10 of the present application, and FIG1( b ) shows the effect of the slurry of Comparative Example 1 of the present application;

[0068] FIG2 shows the viscosity change curves of the slurries of Comparative Example 1 and Example 10 of the present application over time;

[0069] FIG3 is a schematic diagram showing an embodiment of a secondary battery according to an embodiment of the present application;

[0070] FIG4 shows an exploded schematic diagram of the secondary battery shown in FIG3 according to an embodiment of the present application;

[0071] FIG5 is a schematic diagram showing an embodiment of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0072] In the accompanying drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0073] Below, the electrode assembly and its preparation method, secondary battery, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0074] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0075] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0076] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0077] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which indicates that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0078] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may indicate that other components not listed may also be included or that only the listed components are included.

[0079] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0080] Unless otherwise specified, the terms "connected" and "connection" in this application should be understood broadly. For example, they can refer to fixed connection, detachable connection, or integral connection; they can refer to direct connection, indirect connection through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0081] If not otherwise specified, in this application, the term "attach" refers to connection by adhesion, coating, etc.

[0082] Unless otherwise specified, in this application, the terms "first", "second", "third", "fourth", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0083] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be intercalated and extracted between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions, sodium ions, etc.

[0084] The term "several" used in this application refers to two or more (including two).

[0085] The secondary batteries mentioned in the embodiments of the present application may be lithium-ion batteries, sodium-ion batteries, lithium metal batteries, sodium metal batteries, etc., and the embodiments of the present application are not limited thereto.

[0086] A secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive and negative electrode sheets. The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector.

[0087] The positive electrode film layer includes positive electrode active materials, which mainly include layered transition metal oxide positive electrode materials, polyanion positive electrode materials, and Prussian blue positive electrode materials. Some of the positive electrode active materials in the positive electrode sheet give the positive electrode film layer a high alkalinity.

[0088] Taking the common secondary battery positive electrode slurry system as an example, the positive electrode film layer mainly includes positive electrode active material, polyvinylidene fluoride (PVDF), conductive carbon black (SP), and N-methylpyrrolidone (NMP). While PVDF provides strong bonding strength and electrochemical stability, it has poor alkali resistance. PVDF undergoes an elimination reaction in the presence of alkaline sodium ions to produce water, while NMP is a non-aqueous solvent. The double bonds generated by the PVDF elimination reaction cause cross-linking reactions between PVDF molecular chains, forming a gel. The oxidizing positive electrode active material readily reacts with CO2 and H2O in the air, forming NaOH and Na2CO3 on the material surface. As an example, residual alkali content and pH testing of the positive electrode film layer of the finished positive electrode sheet revealed that the residual NaOH content in the layered oxide positive electrode material was 2.37%, the Na2CO3 content was 2.10%, and the pH was 13.1.

[0089] As another example, the positive electrode film layer used in lithium secondary batteries uses lithium carbonate as a lithium source, and the residual LiOH and Li2CO3 content is generally less than 1%, and the pH is 8-11.

[0090] In comparison, sodium-ion materials are significantly more alkaline than lithium-ion materials. The presence of residual alkali on the surface of sodium-ion cathode materials not only degrades slurry processing but also significantly impacts the electrochemical performance of secondary batteries. For example, residual alkali on the surface of the cathode active material can lead to a series of side effects, such as low initial efficiency and degraded cycling and storage performance.

[0091] In view of this, the technical solution of the embodiment of the present application provides a secondary battery and a preparation method thereof, which can at least reduce the residual alkali content of the positive electrode film layer of the positive electrode sheet in the secondary battery and improve the cycle performance and high-temperature storage performance of the secondary battery.

[0092] secondary batteries

[0093] In a first aspect, an embodiment of the present application provides a secondary battery, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode collector and a positive electrode film layer arranged on at least one surface of the positive electrode collector, the positive electrode film layer comprising a positive electrode active material and a material containing a chalcogen element.

[0094] According to an embodiment of the present application, the positive electrode film layer of the positive electrode plate in the secondary battery includes a material containing a chalcogen element, and the chalcogen element includes at least one of sulfur, selenium, or tellurium. On the one hand, the material containing the chalcogen element indicates that when present, it has reduced the residual alkali content of the positive electrode film layer during the preparation process, such as the content of Na2O and / or Na2CO3, thereby preventing the residual alkali from causing certain corrosion to the positive electrode plate containing the positive electrode film layer, forming electrolyte residues or producing other adverse electrochemical reactions, resulting in reduced conductivity of the positive electrode plate, thereby preventing the residual alkali in the secondary battery from generating electrolyte residues during the electrochemical cycle, or causing other adverse electrochemical reactions in the secondary battery, and improving the kinetic performance of the secondary battery containing the positive electrode plate on the basis of improving the conductivity of the positive electrode plate.

[0095] On the other hand, when the secondary battery is undergoing charge and discharge cycles, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer containing the sulfide element to form an in-situ coating layer on the surface of the positive electrode active material, which is equivalent to a protective film. It can reduce the contact interface between the electrolyte and the positive electrode active material, help to enhance the stability of the contact interface between the positive electrode active material and the electrolyte, reduce side reactions, and improve the battery's cycle performance and high-temperature storage performance.

[0096] In addition, when the secondary battery is formed, the Na2CO3 in the residual alkali of the positive electrode sheet forms CO2, which can be released together with other gases formed in the secondary battery formation process, thereby preventing the gas from being produced in the subsequent charge and discharge chemical cycle, and preventing it from affecting the structure of the secondary battery, causing bulging and other phenomena, and affecting the electrochemical performance of the secondary battery.

[0097] The material containing sulfide elements includes a reducing material containing sulfide elements, which is present in the positive electrode plate. During the formation or subsequent cycle of the secondary battery containing the positive electrode plate, the reducing material containing sulfide elements can be reduced and oxidized in the electrolyte to form a solid electrolyte membrane (SEI membrane) at the interface between the negative electrode plate and the electrolyte, such as a SEI membrane containing poly (ethylene oxide) (PEO)-type polymer and alkyl lithium sulfate (R-OSO2ONa) components. The SEI membrane has excellent elasticity and certain strength. The SEI membrane with strong toughness can allow a certain amount of volume change of the negative electrode plate during the charge and discharge process at the negative electrode plate-electrolyte interface, which is beneficial to protecting the structural stability of the battery cell, thereby improving the cycle performance and service life of the secondary battery; in addition, the SEI membrane with this component can quickly transport Na +Active ions, including sulfide, are beneficial for improving the power performance of the secondary battery, such as improving the ability to quickly charge and discharge. In some optional embodiments, the secondary battery includes a solid electrolyte membrane located on the surface of the negative electrode plate. Based on the total mass of the solid electrolyte membrane, the mass proportion of chalcogen elements is less than or equal to 2%, and can be 0.1%-1.5%.

[0098] The present application has no particular limitation on the type of secondary battery. For example, the secondary battery may be a lithium-ion battery, a sodium-ion battery, etc. A sodium-ion battery may be selected.

[0099] For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0100] In some optional embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the chalcogen element is less than or equal to 3%, and can be optionally 0.1%-2%.

[0101] Optionally, the positive electrode film layer contains a chalcogen element with a mass content of 0.01%, 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0% or any other range of its composition.

[0102] According to an embodiment of the present application, the positive electrode film layer contains 0.01% to 3% by weight of a chalcogen, which includes at least one of sulfur, selenium, and tellurium. During the preparation of the positive electrode sheet, i.e., during the slurry stirring process, the chalcogen reacts with some residual alkali to form an intermediate product, which can effectively lower the pH of the slurry and alleviate or prevent the gelation of the slurry. Furthermore, the intermediate product further reacts with the residual alkali in the slurry, further preventing the occurrence of gelation, facilitating uniform stirring and proper coating of the slurry. This improves the overall performance of the positive electrode sheet, including uniformity, and contributes to the cycling and kinetic performance of the secondary battery containing the positive electrode sheet.

[0103] According to an embodiment of the present application, the positive electrode film layer contains a reducing chalcogen-containing material with a mass content of 0.01% to 3%. The reducing chalcogen-containing material can be a simple substance of the chalcogen, or a reducing intermediate product (A2O3 2-) exists in the positive electrode sheet that has not undergone or has undergone a relatively small number of electrochemical cycles.

[0104] In some optional embodiments, the material containing chalcogen includes a simple substance containing chalcogen and / or a salt containing chalcogen.

[0105] According to the embodiment of the present application, the single substance of the sulfide element exists in the positive electrode plate as zero valence, and the salt of the sulfide element includes a salt with reducing properties. It can also include a salt with a positive divalent sulfide element. Due to its certain reducing properties, during the formation and / or circulation of the secondary battery, it reacts with the residual alkali in the positive electrode plate to form a protective film containing MO components (M includes at least one of Ni, Co, Mn, Fe and Cu), which is beneficial to improve the interface stability of the positive electrode active material with the electrolyte during subsequent cycles, reduce side reactions, and is beneficial to improve the cycle performance and high temperature storage performance of the secondary battery containing the positive electrode plate. In addition, the reaction of the single substance of the sulfide element with the residual alkali releases additional Na + Active ions including ions can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0106] In some optional embodiments, the salt containing a chalcogen element includes A2O32- or AO42-, wherein A represents a chalcogen element.

[0107] According to the embodiment of the present application, the salt of the sulfide element A is present in the positive electrode plate, which is beneficial to improving the uniformity of the components in the positive electrode film layer in the positive electrode plate, and is beneficial to reacting with the residual alkali in the positive electrode plate to generate a protective film containing MO components, which is beneficial to improving the interface stability between the positive electrode active material and the electrolyte during subsequent cycles, reducing side reactions, and is beneficial to improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0108] According to the embodiment of the present application, the salt containing the chalcogen element can be obtained by reacting the chalcogen element with the positive electrode active material, or can be directly added.

[0109] When a secondary battery comprising the positive electrode plate undergoes formation or electrochemical cycling, the positive electrode plate comprises a reducing material containing a chalcogen element, which can continue to react with the residual alkali in the positive electrode plate, thereby reducing the residual alkali content in the positive electrode active material and forming an artificial protective film. The protective film has very stable electrochemical stability, and its components include Na2SO4, etc., and is located on the surface of the positive electrode active material or exists alone. This is beneficial to improving the stability of the positive electrode active material in contact with the electrolyte during subsequent cycling, reducing side reactions, and is beneficial to improving the cycle performance and high-temperature storage performance of the secondary battery comprising the positive electrode plate.

[0110] In addition, the additional active ions including Na+ ions released by the reaction of the reducing salt containing sulfur elements with the residual alkali can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0111] In some optional embodiments, the valence state of the chalcogen element includes at least one of zero valence, positive divalent, positive tetravalent, and positive hexavalent; optionally, the valence state of the chalcogen element includes positive hexavalent and positive tetravalent.

[0112] In some optional embodiments, the positive electrode film layer contains 0.01% to 3% of a divalent positive chalcogen element based on the total mass of the positive electrode film layer.

[0113] As an example, the reaction equation of the reaction between a reducing salt containing a sulfide element and a residual alkali is shown in equation (1): Na2S2O3+Na2CO3-8e - →2Na2SO4+5CO2+8Na + (1).

[0114] When the secondary battery containing the positive electrode plate is formed and subsequently cycled, the single substance of the sulfide element contained in the positive electrode plate. The single substance of the sulfide element reacts with the residual alkali in the positive electrode plate to form a protective film containing MO components (M includes at least one of Ni, Co, Mn, Fe and Cu), which is beneficial to improving the interface stability of the positive electrode active material with the electrolyte during subsequent cycles, reducing side reactions, and improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate. In addition, the additional active ions including Na+ ions released by the reaction of the single substance of the sulfide element with the residual alkali can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0115] In some optional embodiments, the positive electrode film layer contains zero-valent and positive tetravalent chalcogen elements.

[0116] As an example, the reaction equation of the reaction between a single chalcogen element and a residual alkali is shown in equation (2): 2NaMO2+S+2Na2CO3-4e - →2MO+Na2SO4+2CO2+4Na + (2).

[0117] In some optional embodiments, a protective film comprising Na2SO4 is located on the surface of the MO component. The presence of a protective film comprising Na2SO4 on the surface of the MO component can further improve the stability of the positive electrode active material in contact with the electrolyte during subsequent cycles, reduce side reactions, and improve the cycling performance and high-temperature storage performance of a secondary battery containing the positive electrode sheet.

[0118] In some optional embodiments, the ratio of the molar amount n2 of the hexavalent sulfide element in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide elements in the positive electrode film layer is (0.5-1):1, or optionally (0.7-1):1.

[0119] Optionally, after the secondary battery is formed, the ratio of the molar amount n2 of the hexavalent sulfide element in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide elements in the positive electrode film layer can be any value or its composition range among 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1.

[0120] The method for detecting the molar ratio of sulfide elements in different valence states in the positive electrode plate includes: disassembling the secondary battery after charge and discharge to obtain the positive electrode plate, cutting the positive electrode plate into 1×1 cm size for sample preparation, and placing it in an X-ray photoelectron spectrometer for testing after sufficient drying, collecting data showing the energy spectrum peak position and intensity of sulfide elements in different valence states, and analyzing them. The peak area ratio of different valence states can be used as the valence state content ratio.

[0121] According to the embodiments of the present application, after the secondary battery is formed, the ratio of the molar amount n2 of the hexavalent sulfide element in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide elements in the positive electrode film layer is within the above range, indicating that the residual alkali such as Na2O and / or Na2CO3 in the positive electrode film layer including the above content is decomposed and consumed, forming a relatively stable salt containing the sulfide element, which is beneficial to the stability of the secondary battery.

[0122] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for battery cells known in the art.

[0123] In some alternative embodiments, the positive electrode active material comprises a layered transition metal oxide.

[0124] In some optional embodiments, the layered transition metal oxide comprises a structural formula of a Ni b Co c Mn f M d O eA transition metal oxide, wherein 0.5≤a≤1.2, 0≤b≤2, 0≤c≤2, 0≤f≤1, 0≤d≤1.5, 1≤e≤4, A comprises one or more of Li and Na; M comprises one or more of Ca, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B; optionally, b+c+d+f=1 or b+c+d+f=2; optionally, A further comprises K. In some optional embodiments, a+2b+2c+2f+2d-2e=0 or a+2b+2c+4f+2d-2e=0 or a+2b+2c+3f+2d-2e=0.

[0125] According to the embodiments of the present application, the above-mentioned layered transition metal oxides generally have a higher active ion storage capacity. The above-mentioned types of layered transition metal oxides can embed and release more active ions, including sodium ions, thereby providing a higher battery capacity. This allows the battery to store more electrical energy and have a longer service life. The high capacity characteristics of the layered transition metal oxides result in the battery having a higher energy density. The layered transition metal oxides have a certain oxidizability, and the redox reaction that occurs therein is beneficial to the stability of the material structure, helps to reduce the structural changes and attenuation of the material, and thus extends the cycle life of the battery.

[0126] For example, when the battery cell is a lithium-ion battery cell or a lithium metal battery cell, the positive electrode active material may include one or more of a lithium transition metal oxide, an olivine-structured lithium-containing phosphate, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphates containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials may also be used.

[0127] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e A fA lithium transition metal oxide. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0128] As an example, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2.

[0129] When the secondary battery is a sodium ion battery cell or a sodium metal battery cell, the positive electrode active material may include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0130] As an example, the positive electrode active material may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and general formula X p M' q (PO4) r O x Y 3-x One or more materials. p M' q (PO4) rO x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes H + 、Li + 、Na + , K + and NH4 + One or more of, M' is a transition metal cation, which can be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which can be selected from one or more of F, Cl and Br.

[0131] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0132] In some optional embodiments, the positive electrode active material includes a coating layer at least partially coated on the positive electrode active material, the coating layer comprising MO z , M includes one or more of Ni, Co, Mn, Fe and Cu, 0<z<2.

[0133] As an example, MO z Including any one or more of NiO, CoO, MnO, Fe2O3, and CuO.

[0134] According to the embodiments of the present application, the coating layer on the surface of the positive electrode active material can maintain the stability of the positive electrode active material during the electrochemical cycle and reduce the contact area between the positive electrode active material and the electrolyte.

[0135] In some optional embodiments, the coating layer has a thickness of 1 to 10 nm.

[0136] According to the embodiments of the present application, the thickness of the coating layer is controlled within the above range, thereby improving the cycle performance of the secondary battery while reducing the contact area between the positive electrode active material and the electrolyte. A thinner protective film may not effectively prevent the electrolyte from contacting the positive electrode active material, while a thicker protective film restricts the transmission of ions and electrons, thereby reducing the electrochemical performance of the secondary battery.

[0137] In some optional embodiments, the positive electrode film layer includes sodium oxide. Optionally, the mass content of sodium oxide in the positive electrode film layer is ≤1000 ppm.

[0138] In some optional embodiments, the positive electrode film layer includes sodium carbonate, and the mass content of sodium carbonate in the positive electrode film layer is ≤2000 ppm.

[0139] According to an embodiment of the present application, the inclusion of the aforementioned content of Na2O and / or Na2CO3 in the positive electrode film layer contained in the secondary battery is beneficial for reducing the corrosion of the positive electrode sheet by the aforementioned Na2O and / or Na2CO3. The presence of Na2O and / or Na2CO3 in the positive electrode sheet may form electrolyte residues on the positive electrode sheet or produce other adverse electrochemical reactions, resulting in reduced conductivity of the positive electrode sheet. The inclusion of the aforementioned content of Na2O and / or Na2CO3 in the positive electrode film layer is beneficial for reducing electrolyte residues or other adverse electrochemical reactions, improving the conductivity of the positive electrode sheet, and improving the dynamic performance of the secondary battery containing the positive electrode sheet.

[0140] In addition, the CO2 generated by Na2CO3 in the positive electrode film layer can be released together with other gases formed during the secondary battery formation process. When the positive electrode active material of the secondary battery contains the above-mentioned content of Na2CO3 after formation, the generated gas will affect the structure of the secondary battery, causing bulging and other phenomena, affecting the electrochemical performance of the secondary battery.

[0141] As an example, the above-mentioned method for detecting Na2O and / or Na2CO3 includes disassembling a secondary battery undergoing chemical charge and discharge cycles, removing the positive electrode, scraping the powder, and then using an acid-base titration test to confirm the Na2O and Na2CO3 contents, respectively. Testing can be performed when the secondary battery has undergone 100 or fewer charge and discharge cycles.

[0142] In some optional embodiments, the secondary battery is a sodium ion secondary battery.

[0143] In some optional embodiments, the positive electrode film layer includes a sodium supplement.

[0144] According to the embodiments of the present application, the material containing sulfide elements participates in the formation of the SEI film, consuming part of the active sodium. The composition includes a sodium supplement that can increase the capacity of the battery while supplementing the active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance and storage life.

[0145] In some optional embodiments, the sodium supplement includes one or more of sodium sulfide, sodium selenide, or sodium nitride.

[0146] According to the embodiments of the present application, materials containing sulfide elements can participate in the formation of SEI film, consuming part of the active sodium. The composition includes a sodium supplement that can increase the capacity of the battery while supplementing the active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance and storage life.

[0147] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. This application does not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0149] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0150] [Negative electrode]

[0151] The specific composition and structure of the negative electrode plate can be selected according to the type of battery cell, and the embodiments of the present application are not limited thereto.

[0152] For example, when the battery cell is a lithium-ion battery cell or a sodium-ion battery cell, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces that are opposed in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0153] The negative electrode active material is a material that can extract and embed active ions (such as lithium ions, sodium ions, etc.), and the negative electrode active material can adopt materials well known in the art. As an example, the negative electrode active material includes but is not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite and silicon alloy materials. Tin-based materials may include one or more of elemental tin, tin oxide and tin alloy materials. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials may also be used.

[0154] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. For example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0155] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0156] In some embodiments, the negative electrode film layer may optionally include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC-Na), a PTC thermistor material, and the like.

[0157] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0158] The negative electrode film layer is typically formed by coating the negative electrode slurry onto the negative electrode current collector, drying it, and cold pressing it. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0159] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate of the present application may further include a protective film covering the surface of the negative electrode film layer.

[0160] When the battery cell is a lithium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a lithium plate or a lithium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam-like three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0161] When the battery cell is a sodium metal battery cell, the negative electrode plate may not include a negative electrode active material capable of extracting and inserting active ions. For example, in some embodiments, the negative electrode plate may include a sodium plate or a sodium alloy plate; in other embodiments, the negative electrode plate includes a mesh or foam three-dimensional skeleton layer, such as copper foam (or copper alloy), nickel foam (or nickel alloy), aluminum foam (or aluminum alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, aluminum (or aluminum alloy) mesh, etc.

[0162] [Electrolytes]

[0163] In some embodiments, a secondary battery includes an electrolyte. The electrolyte conducts active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte may be selected based on needs. For example, the electrolyte may be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte solution).

[0164] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0165] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. For example, the electrolyte salt includes one or more selected from lithium salts for lithium ion batteries and sodium salts for sodium ion batteries. As an example, the lithium salt includes one or more selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorooxalatophosphate (LiTFOP). As an example, the sodium salt includes one or more selected from NaPF6, NaClO4, NaBCl4, NaCF3SO3, NaTFSI, NaFSI, NaBF4, NaBOB, NaAsF6, NaClO4, and Na(CH3)C6H4SO3. The sodium salt can be selected from one or more of the following.

[0166] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0167] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0168] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0169] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0170] The present application has no particular limitation on the shape of the secondary battery, which can be a flat body, a rectangular parallelepiped, or other shapes. FIG3 shows a secondary battery 5 with a rectangular parallelepiped structure as an example.

[0171] In some embodiments, as shown in Figure 4, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate together form a accommodating cavity. The shell 51 has an opening connected to the accommodating cavity, and the cover plate 53 is used to cover the opening to close the accommodating cavity. The electrode assembly 52 of the first aspect of the embodiment of the present application or the electrode assembly 52 prepared by the method according to the second aspect of the embodiment of the present application is encapsulated in the accommodating cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be adjusted according to demand.

[0172] Method for preparing a secondary battery

[0173] In a second aspect, an embodiment of the present application provides a method for preparing the secondary battery of the first aspect, comprising preparing a positive electrode sheet:

[0174] Preparing a positive electrode slurry: adding a mixture including a positive electrode active material and a material containing a chalcogen element into a solvent to form a slurry;

[0175] The positive electrode slurry is coated on at least one surface of the positive electrode current collector to form a positive electrode film layer.

[0176] In the related art, the slurry contains positive electrode active materials with a certain degree of oxidizability. In the process of preparing positive electrode sheets, especially in the process of preparing the slurry for forming positive electrode sheets, in addition to the positive electrode active materials, many alkaline substances will also remain in the slurry: NaOH and Na2CO3 are found in the slurry of positive electrode active materials containing sodium ions, and the slurry is alkaline; LiOH and Li2CO3 are found in the slurry of positive electrode active materials containing lithium ions. Without intending to be limited by any theory or explanation, if such residual alkali present in the slurry is not treated, it will lead to a more serious gelation phenomenon. Such a gelation phenomenon will cause the particles to agglomerate, making it impossible to evenly stir the positive electrode active material, and the slurry in the gel state cannot be coated normally, and it is impossible to prepare a high-quality positive electrode sheet.

[0177] The material containing chalcogen elements may be understood as a reducing material containing chalcogen elements and capable of reacting with an alkali.

[0178] On the one hand, materials containing sulfide elements can reduce the residual alkali content of the positive electrode film layer during the preparation process, such as the content of Na2O and / or Na2CO3, to prevent the residual alkali from causing certain corrosion to the positive electrode plate containing the positive electrode film layer, forming electrolyte residues or producing other adverse electrochemical reactions, resulting in a decrease in the conductivity of the positive electrode plate, thereby preventing the residual alkali in the secondary battery from generating electrolyte residues during the electrochemical cycle, or causing other adverse electrochemical reactions in the secondary battery, and improving the kinetic performance of the secondary battery containing the positive electrode plate on the basis of improving the conductivity of the positive electrode plate.

[0179] On the other hand, when the secondary battery is undergoing charge and discharge cycles, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer containing the sulfide element to form an in-situ coating layer on the surface of the positive electrode active material, which is equivalent to a protective film. It can reduce the contact interface between the electrolyte and the positive electrode active material, help to enhance the stability of the contact interface between the positive electrode active material and the electrolyte, reduce side reactions, and improve the battery's cycle performance and high-temperature storage performance.

[0180] According to an embodiment of the present application, the chalcogen element includes at least one of sulfur, selenium, and tellurium. As an example, the material containing the chalcogen element includes a simple substance of the chalcogen element. The simple substance of the chalcogen element can react with at least part of the residual alkali to form an intermediate product during the mixing and stirring process of the composition for preparing the slurry, which can effectively reduce the pH of the slurry and alleviate or avoid the gelation phenomenon of the slurry; in addition, the above-mentioned intermediate product can further react with the residual alkali in the slurry in the subsequent process to further avoid the occurrence of the gelation phenomenon, which is beneficial to the uniform stirring of the slurry and the normal coating of the slurry, thereby facilitating the preparation of the composition containing the positive electrode active material and the simple substance of the chalcogen element into a positive electrode sheet, and improving the comprehensive performance of the positive electrode sheet including uniformity.

[0181] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry typically comprises a positive electrode active material, an optional conductive agent, an optional binder, and any other components dispersed in a solvent and stirred until uniformly mixed. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0182] In some optional embodiments, the mixture comprises 0.01% to 5% of a single substance of chalcogen based on the total mass of the mixture.

[0183] Optionally, the mixture for the positive electrode sheet contains 0.01%, 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 0. A single substance of a chalcogen element having any numerical value selected from the group consisting of 10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%, or a composition range thereof.

[0184] According to the embodiments of the present application, the mixture can be understood as the portion of the slurry for the positive electrode sheet that does not contain a solvent. The chalcogen element includes at least one of sulfur, selenium, and tellurium. The simple substance of the chalcogen element can react with at least part of the residual alkali to form an intermediate product during the mixing and stirring process of the composition for preparing the slurry, which can effectively reduce the pH of the slurry and alleviate or avoid the gelation phenomenon of the slurry; in addition, the above-mentioned intermediate product can further react with the residual alkali in the slurry in the subsequent process to further avoid the occurrence of the gelation phenomenon, which is beneficial to the uniform stirring of the slurry and the normal coating of the slurry, thereby facilitating the preparation of the composition containing the positive active material and the simple substance of the chalcogen element into a positive electrode sheet, and improving the comprehensive performance of the positive electrode sheet including uniformity.

[0185] In some optional embodiments, the mixture includes 0.1% to 2% by mass of a single chalcogen element.

[0186] According to an embodiment of the present application, the mixture includes the above-mentioned mass content of the single substance of the chalcogen element, which is beneficial to maintaining the uniformity of the slurry, avoiding aggregation in the slurry, and facilitating the slurry coating to form the positive electrode plate; the positive electrode plate containing the mixture is beneficial to improving the interface stability between the positive electrode plate and the electrolyte during the charge and discharge process of the secondary battery, reducing side reactions, and improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0187] According to the embodiments of the present application, the amount of sulfide element added to the mixture is too high. During the charge and discharge cycle of the secondary battery containing the mixture, the unreacted sulfide element in the positive electrode is not conducive to the impedance and kinetic performance of the secondary battery, and too much unreacted sulfide element affects the capacity of the active material and the cycle stability; if the amount of sulfide element added to the mixture is too low, the residual alkali in the slurry will not react completely, and the remaining residual alkali will worsen the impedance and increase polarization, thereby reducing the capacity of the secondary battery.

[0188] In some embodiments, the mixture may include a binder and / or a conductive agent. In some optional embodiments, the volume average particle size Dv50 of the material containing chalcogen is 50 nm-1000 nm, optionally 100 nm-500 nm.

[0189] According to the embodiment of the present application, the volume average particle size Dv50 of the material containing chalcogen elements is within the above range, which is conducive to the dispersion of the chalcogen elements in the slurry and the reaction of the chalcogen elements with residual alkali, thereby avoiding gelation of the slurry.

[0190] In addition, the volume average particle size of the material containing sulfide elements in the positive electrode plate is within the above range. When the secondary battery containing the positive electrode plate is formed and subsequently cycled, it is beneficial to form a relatively uniform and appropriate volume coating layer for the positive electrode active material on the basis of protecting the structure of the positive electrode plate. The coating layer is beneficial to improving the interface stability between the positive electrode active material and the electrolyte during subsequent cycles, reducing side reactions, and improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0191] Volume average particle size D v The term "50" is generally known in the art and represents the particle size corresponding to the 50% cumulative volume distribution percentage of the material. This can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution - Laser Diffraction Method.

[0192] In some optional embodiments, the valence state of the chalcogen element includes at least one of zero valence, positive divalent valence, and positive hexavalent valence; optionally, the valence state of the chalcogen element includes zero valence and positive divalent valence.

[0193] As an example, the reaction between a single substance of a chalcogen element and a positive electrode active material can be shown as formula (3):

[0194] 4NaMO2+2S→4MO+Na2S2O3+Na2O(3), wherein M includes at least one of Ni, Co, and Mn.

[0195] According to an embodiment of the present application, the sulfide element in the above-mentioned valence state exists in the positive electrode plate, which is beneficial to improving the comprehensive electrochemical performance of the secondary battery containing the positive electrode plate when the secondary battery containing the positive electrode plate is formed and / or subsequently cycled.

[0196] In some optional embodiments, the ratio of the sum of the molar amounts n1 of zero-valent and divalent sulfide elements in the positive electrode film layer to the sum of the molar amounts n0 of zero-valent, divalent and hexavalent sulfide elements in the positive electrode film layer is (0.5-1):1, and can optionally be (0.8-1):1.

[0197] Optionally, the ratio of the sum of the molar amounts n1 of the zero-valent and divalent chalcogens in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, divalent, and hexavalent chalcogens in the positive electrode film layer can be 0.5:1, 0.6:1,

[0198] Any value or composition range thereof among 0.7:1, 0.8:1, 0.9:1, 1.0:1.

[0199] According to an embodiment of the present application, by controlling the sum of the molar amounts of zero-valent and divalent sulfide elements in the positive electrode film layer and the total molar amount of sulfide elements in the positive electrode film layer, the amount of the protective film in the positive electrode film layer can be controlled, thereby improving the overall performance of the secondary battery while protecting the positive electrode active material.

[0200] In some optional embodiments, the positive electrode slurry is prepared by adding a mixture including the positive electrode active material, the material containing the chalcogen element, and the sodium supplement agent into a solvent to form a slurry.

[0201] According to the embodiments of the present application, the material containing sulfide elements participates in the formation of the SEI film, consuming part of the active sodium. The composition includes a sodium supplement that can increase the capacity of the battery while supplementing the active sodium, further improving the battery's cycle life, including capacity retention and rate performance, dynamic performance and storage life.

[0202] In some optional embodiments, the mixture comprises 0.05% to 3% by weight of the sodium supplement, optionally 0.1% to 2% by weight of the sodium supplement, based on the total weight of the mixture.

[0203] Optionally, the composition for the positive electrode sheet contains 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0% of any value or range of its composition of a sodium supplement.

[0204] According to an embodiment of the present application, in a secondary battery containing the mixture, the mixture in the positive electrode plate contains the sodium supplement with the above-mentioned mass fraction, which is beneficial to replenishing the active sodium ions consumed in the secondary battery and is beneficial to the electrochemical performance of the secondary battery.

[0205] In some optional embodiments, the volume average particle size Dv50 of the sodium supplement is 1 μm to 5 μm.

[0206] Optionally, the volume average particle size Dv50 of the sodium supplement is any value among 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or a composition range thereof.

[0207] According to the embodiments of the present application, the volume average particle size Dv50 of the sodium supplement is within the above range, which is beneficial to protecting the structural stability of the positive electrode sheet, improving the porosity of the positive electrode sheet, and improving the dynamic performance of the positive electrode sheet.

[0208] In some optional embodiments, the mass ratio of the material containing chalcogen elements to the sodium supplement is 1:(0.5-5), and can be optionally 1:(0.5-3).

[0209] Optionally, the mass ratio of the material containing chalcogen elements to the sodium supplement can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, Any value or a range thereof among 1:2.7, 1:2.8, 1:2.9, 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, 1:4.9, 1:5.0.

[0210] According to the embodiments of the present application, the material containing the sulfide element reacts with the residual alkali in the slurry to generate an intermediate product, and some unreacted sulfide element and the intermediate product participate in the formation of the SEI film, consuming a certain amount of active sodium. By controlling the mass ratio of the consumed active sodium and the sodium supplement within the above range, on the one hand, the sulfide element can be effectively utilized and its role can be exerted, and on the other hand, the content of active sodium can be supplemented to increase the capacity of the battery, further improving the cycle life and storage life of the battery.

[0211] The mass ratio of the material containing chalcogen elements to the sodium supplement agent is within the above range, which can avoid the content of the material containing chalcogen elements in the positive electrode film layer being too high, affecting the capacity and kinetic performance of the positive electrode sheet containing the positive electrode film layer during the charge and discharge cycle of the secondary battery; if the content of the sodium supplement agent in the positive electrode film layer is too high, it can affect the performance, stability and safety of the secondary battery.

[0212] In some optional embodiments, the ratio of the volume average particle size Dv50 of the material containing chalcogen elements to the sodium supplement is 1:(1-5), and can be optionally 1:(1-2).

[0213] Optionally, the ratio of the volume average particle size Dv50 of the material containing chalcogen elements to the sodium supplement can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8 , 1:2.9, 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, 1:4.9, 1:5.0, or any range thereof.

[0214] According to the embodiments of the present application, by controlling the ratio of the volume average particle size Dv50 of the material containing the sulfide element to the sodium supplement, it is beneficial to improve the uniformity of the positive electrode sheet containing the composition, which is beneficial to the cycle performance and kinetic performance of the secondary battery containing the positive electrode sheet.

[0215] [Preparation method]

[0216] The method for preparing the battery of the present application is well known. The method for preparing the secondary battery of the present application is well known and includes at least the step of preparing the electrode assembly according to the second aspect of the embodiment of the present application. In some embodiments, the electrode assembly can be placed in an outer packaging, dried, and then injected with electrolyte. The secondary battery is obtained through vacuum packaging, static standing, formation, and shaping.

[0217] In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a secondary battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process. The electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After packaging, standing, forming, shaping and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel, or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel, or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0218] In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0219] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of secondary batteries are accommodated in the accommodation space.

[0220] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0221] Electrical devices

[0222] In a third aspect, an embodiment of the present application provides an electrical device, comprising the secondary battery of the first aspect and the secondary battery prepared by the method of the second aspect.

[0223] The electric device of the present application includes a secondary battery, and thus has at least the advantages corresponding to the secondary battery.

[0224] Secondary batteries can be used as power sources or energy storage units for electrical devices. These devices include, but are not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0225] Figure 5 is a schematic diagram of an exemplary electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module may be used.

[0226] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0227] Example

[0228] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0229] Example 1

[0230] Preparation of positive electrode

[0231] O3-type layered oxide NaFe 2 / 3 Mn 1 / 6 Co 1 / 6O2, nano-sulfur, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotubes (CNT) were stirred and mixed at a rotation speed of 400 to 1000 r / s in a weight ratio of 88.5:0.5:4.7:3.3:3.0, and then wetted, kneaded, and dispersed to obtain the positive electrode slurry. The slurry mixture is shown in Figure 1. Compared with the positive electrode slurry without the addition of nano-sulfur (Figure 1b), the positive electrode slurry of this embodiment (Figure 1a) has better fluidity and more stable viscosity (Figure 2), and no gelation occurs.

[0232] The prepared slurry is then coated on aluminum foil and dried, cold pressed, and cut to obtain the positive electrode sheet of Example 1.

[0233] Preparation of negative electrode sheet

[0234] The active material hard carbon, the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are dry-mixed in a weight ratio of 97.2:0.8:0.8:1.2, and then deionized water is added and mixed to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector aluminum foil, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

[0235] Preparation of electrolyte

[0236] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), the organic solvent ethylene carbonate (EC) / ethyl methyl carbonate (EMC) was mixed in a volume ratio of 4:6, 12.5% ​​NaPF6 sodium salt was added and dissolved in the organic solvent, and stirred evenly to obtain the electrolyte of Example 1.

[0237] Preparation of isolation membrane

[0238] Polyethylene film is used as the isolation film.

[0239] Preparation of sodium ion secondary batteries

[0240] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets, and then wound to obtain a bare battery cell; the bare battery cell is placed in the battery outer packaging, and then the electrolyte is injected, packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of the lithium-ion battery, wherein the lithium-ion battery has a thickness of 4.2 mm, a width of 32 mm, and a length of 82 mm.

[0241] Examples 2 to 9: The preparation method is similar to that of Example 1, except that the content and type of the chalcogen element in the composition or the positive electrode sheet are adjusted. The relevant parameters in the preparation steps are detailed in Table 1.

[0242] Examples 10-18: The preparation method is similar to that of Example 1, except that an additional sodium supplement is added to the composition or the positive electrode sheet to form an O3-type layered oxide NaFe 2 / 3 Mn 1 / 6 Co 1 / 6 O2, nano sulfur, sodium sulfide, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), carbon nanotubes (CNT) are stirred and mixed at a speed of 400 to 1000 r / s in a weight ratio of 88:0.5:0.5:4.7:3.3:3.0, and then wetted, kneaded and dispersed to obtain the result. The slurry mixing effect of the positive electrode slurry is shown in Figure 1. The positive electrode slurry of this embodiment (Figure a in Figure 1) is better than the positive electrode slurry of Comparative Example 1 (Figure b in Figure 1) without the addition of nano sulfur. Compared with Comparative Example 1, Example 10 has better fluidity and more stable viscosity (as shown in Figure 2), and no gel phenomenon occurs.

[0243] The prepared slurry was then coated on aluminum foil and dried, cold pressed, and cut to obtain the positive electrode sheet of Example 1, as shown in Table 1. The content of the sodium supplement in the positive electrode active layer is shown in Table 1.

[0244] Examples 19-20:

[0245] The preparation method is similar to that of Example 10, except that the type of sodium supplement is different. See Table 1 for details.

[0246] Examples 21 to 23:

[0247] The preparation method is similar to that of Example 10, except that the ratio of the volume average particle diameter Dv50 of the elemental chalcogen element and the sodium supplement is different. See Table 1 for details.

[0248] Comparative Example 1

[0249] The difference between this comparative example and Example 1 is that: Preparation of the positive electrode sheet:

[0250] Layered oxide NaFe 2 / 3 Mn 1 / 6 Co 1 / 6 O2, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and carbon nanotubes (CNT) are fully stirred and mixed in a weight ratio of 89:4.7:3.3:3 to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet of the comparative example.

[0251] Test section

[0252] 1) Detection method of chalcogen content in the positive electrode film layer:

[0253] First, the positive electrode is digested with aqua regia, a digestion reagent made by mixing concentrated nitric acid (HNO3) and concentrated hydrochloric acid (HCl) in a 1:1 volume ratio. Digestion methods include plate digestion, acid digestion, or microwave digestion (high temperature and pressure, approximately 200°C). The digested solution is then collected and placed in an inductively coupled plasma spectrometer for testing, which can quantitatively measure the chalcogen content.

[0254] 2) The 0.33C capacity retention rate test method is as follows: At 25°C, the sodium ion battery is charged at a constant current of 0.33C to 4.25V, then charged at a constant voltage of 4.25V until the current is less than 0.05C, and then discharged at a constant current of 0.33C to 3.0V. This charge and discharge process is repeated in this way, and the capacity retention rate of the sodium ion battery after 100 cycles is calculated.

[0255] 3) Capacity retention rate (%) of the sodium ion battery after 100 cycles at 25°C = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100%.

[0256] 4) Test method for 60°C storage capacity retention rate:

[0257] The battery capacity recovery rate test process is as follows: before storage, at 25°C, the battery corresponding to Implementation 1 was charged to 4.25V at a constant current of 1 / 3C, then charged to 0.05C at a constant voltage of 4.25V, left for 30 minutes, and then discharged to 2.8V at 1 / 3C. The obtained capacity was recorded as the initial capacity C0. After storage at 60°C for 100 days, the battery temperature was cooled to room temperature and the above steps were repeated. The measured capacity was recorded as Cr. The battery capacity recovery rate after storage for 50 days is H=Cr / C0*100%.

[0258] 5) Test method for the first coulombic efficiency:

[0259] The injected cell is charged to 3.9V at 0.1C on a forming machine, and the formed capacity is recorded as C1; the formed cell is then placed on a blue electric charger and discharged machine and charged to 4.25V at 0.33C, and the charge capacity at this time is recorded as C2; finally, it is discharged to 2.8V at 0.33C, and the discharge capacity at this time is D1. The first coulombic efficiency of the cell is calculated as D1 / (C1+C2)*100%.

[0260] 6) Fast charging performance (10%-80% SOC fast charging time)

[0261] The 10%-80% SOC charging time test procedure is as follows: At 25°C, the batteries in the examples and comparative examples were charged from 10% SOC to 80% SOC at a step-by-step rate of 1.0C / 0.8C / 0.5C / 0.33C. The charging time until lithium plating does not occur at the negative electrode is the battery's fast charge time at that point. A shorter fast charge time indicates better fast charge performance.

[0262] 7) Test method for molar ratio of different valence states of chalcogens:

[0263] After charging and discharging, the secondary battery is disassembled to take out the positive electrode sheet, cut the positive electrode sheet into 1×1 cm size for sample preparation, and after being fully dried, put it into the X-ray photoelectron spectrometer for testing. The data showing the energy spectrum peak position and intensity of different valence states of the sulfur element are collected and analyzed. The peak area ratio of different valence states can be used as the valence state content ratio.

[0264] From the test results in Table 1, it can be seen that when the sulfur element is within the above range, it can react with the sulfide in the slurry to avoid the gelation of the slurry. The positive electrode sheet contains a reducing intermediate product containing sulfur elements, which continues to react with the residual alkali in the positive electrode sheet, reducing the residual alkali content in the positive electrode active material while forming an artificial protective film. The protective film has a very stable electrochemical stability. Its components include Na2SO4, etc., which is located on the surface of the positive electrode active material or exists alone, which is beneficial to improve the stability of the positive electrode active material in contact with the electrolyte in the subsequent cycle process, reduce side reactions, and improve the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode sheet; in addition, the intermediate product reacts with the residual alkali to release additional Na + Active ions including ions can be used to compensate for the loss of active ions caused by the formation of SEI, thereby increasing the content of active ions in the secondary battery, which is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0265] As shown in Table 1, compared with Comparative Example 1, the addition of a single chalcogen element to the composition of Examples 1-9 generates a protective film on the positive electrode sheet during secondary battery formation, improving the stability of the positive electrode active material and facilitating improved capacity retention and high-temperature storage performance of the secondary battery. This also enhances the charge and discharge performance of the secondary battery.

[0266] As shown in Table 1, in Examples 10-20, compared with Comparative Example 1, the compositions contain a simple substance of chalcogen element and a sodium supplement. During the formation of the secondary battery, a protective film is formed on the positive electrode sheet, which improves the stability of the positive electrode active material and is beneficial to improving the capacity retention rate and high-temperature storage performance of the secondary battery. The presence of the sodium supplement replenishes the active sodium ions consumed in the formation of the SEI film by the simple substance of the chalcogen element, thereby improving the initial coulombic efficiency and the charge and discharge performance of the secondary battery.

[0267] According to Table 1, compared with Example 10, Examples 21-23 have different ratios of the average particle size Dv50 of the chalcogen element and the sodium supplement, which have a certain impact on the charge and discharge performance of the secondary battery, the capacity retention rate of the secondary battery, and the high-temperature storage performance.

[0268] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical idea and performing the same function are all included in the technical scope of the present application. In addition, without departing from the scope of the subject matter of the present application, other methods of constructing the embodiments by applying various modifications that can be conceived by those skilled in the art and combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises a positive electrode active material and a material containing a chalcogen element.

2. The secondary battery according to claim 1, wherein Based on the total mass of the positive electrode film layer, the mass proportion of the chalcogen element is less than or equal to 3%, and can be optionally 0.1%-2%.

3. The positive electrode sheet according to claim 1 or 2, wherein: The chalcogen element includes at least one of sulfur, selenium or tellurium.

4. The secondary battery according to any one of claims 1 to 3, wherein: The material containing chalcogen element includes a simple substance containing chalcogen element and / or a salt containing chalcogen element.

5. The secondary battery according to claim 4, wherein The salt containing chalcogen includes A2O3 2- or AO4 2- , wherein A represents the chalcogen element.

6. The secondary battery according to any one of claims 1 to 5, wherein: The valence state of the chalcogen element includes at least one of zero valence, divalent valence, tetravalent valence and hexavalent valence; optionally, the valence state of the chalcogen element includes hexavalent valence and tetravalent valence.

7. The secondary battery according to claim 6, wherein The ratio of the molar amount n2 of the hexavalent sulfide element in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide elements in the positive electrode film layer is (0.5-1):1, and can be optionally (0.7-1):

1.

8. The secondary battery according to any one of claims 1 to 7, wherein: The positive electrode active material includes a layered transition metal oxide; Optionally, the layered transition metal oxide comprises a structural formula of a Ni b Co c Mn f M d O e A transition metal oxide, wherein 0.5≤a≤1.2, 0≤b≤2, 0≤c≤2, 0≤f≤1, 0≤d≤1.5, 1≤e≤4, A includes one or more of Li and Na; M includes one or more of Ca, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B; optionally, b+c+d+f=1 or b+c+d+f=2.

9. The secondary battery according to claim 1 or 8, wherein: The positive electrode active material includes a coating layer at least partially coated on the positive electrode active material, and optionally, the coating layer includes MO z , M includes one or more of Ni, Co, Mn, Fe and Cu, 0<z<2.

10. The secondary battery according to claim 9, wherein The coating layer has a thickness of 1 to 10 nm.

11. The secondary battery according to any one of claims 1 to 10, wherein: The positive electrode film layer includes sodium oxide, and optionally, the mass content of the sodium oxide in the positive electrode film layer is ≤1000ppm; and / or, The positive electrode film layer includes sodium carbonate, and the mass content of the sodium carbonate in the positive electrode film layer is ≤2000ppm.

12. The secondary battery according to claims 1 to 11, wherein: The secondary battery is a sodium ion secondary battery.

13. The secondary battery according to any one of claims 1 to 12, wherein: The positive electrode film layer includes a sodium supplement.

14. The secondary battery according to claims 1 to 13, wherein: The sodium supplement includes one or more of sodium sulfide, sodium selenide and sodium nitride.

15. A method for preparing a secondary battery according to claims 1 to 14, wherein: Including preparation of positive electrode sheet: Preparing positive electrode slurry: adding a mixture including a positive electrode active material and a material containing a chalcogen element into a solvent to form a slurry; The positive electrode slurry is coated on at least one surface of a positive electrode current collector to form a positive electrode film layer.

16. The method according to claim 15, wherein: The mixture contains 0.01% to 5% of a simple substance of a chalcogen element based on the total mass of the mixture; and / or, The volume average particle size Dv50 of the material containing chalcogen is 50nm-1000nm, and can be optionally 100nm-500nm.

17. The method according to claim 15 or 16, wherein: The valence state of the chalcogen element includes at least one of zero valence, positive divalent valence and positive hexavalent valence; optionally, the valence state of the chalcogen element includes zero valence and positive divalent valence; Optionally, the ratio of the sum of the molar amounts n1 of the zero-valent and divalent sulfide elements in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, divalent and hexavalent sulfide elements in the positive electrode film layer is (0.5-1):1, or optionally (0.8-1):

1.

18. The method according to any one of claims 15 to 17, wherein: The preparation of the positive electrode slurry comprises: adding a mixture including a positive electrode active material, a material containing a chalcogen element and a sodium supplement agent into a solvent to form a slurry; Optionally, the volume average particle size Dv50 of the sodium supplement is 1 μm to 5 μm; Optionally, based on the total mass of the mixture, the mass proportion of the sodium supplement is less than or equal to 3%, and can be optionally 0.1%-2%.

19. The method according to claim 18, wherein: The mass ratio of the material containing chalcogen elements to the sodium supplement is 1:(0.5-5), and can be optionally 1:(0.5-3); and / or, The ratio of the volume average particle size Dv50 of the material containing chalcogen elements to the sodium supplement is 1:(1-5), and can be optionally 1:(1-2).

20. An electrical device, wherein: A secondary battery comprising the secondary battery described in any one of claims 1 to 14 and a secondary battery prepared by the method described in any one of claims 15 to 19.

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