Secondary battery, preparation method thereof and electric device

Abstract

The invention provides a secondary battery, a preparation method thereof and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector, and the positive film layer comprises a positive active material and a chalcogen-containing material. The secondary battery provided by the invention has improved cycle performance and high-temperature storage performance; the electrical device including the secondary battery can also obtain improved cycle performance and high-temperature storage performance of the secondary battery.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a secondary battery and a preparation method and an electrical device thereof. Background Art

[0002] Secondary batteries, also called rechargeable batteries, are batteries that can be repeatedly discharged and recharged and used multiple times. In recent years, as secondary batteries represented by sodium-ion batteries have been increasingly widely used, people have put forward higher requirements for their performance, especially cycle performance.

[0003] Therefore, further improving the cycle performance and high-temperature storage performance of secondary batteries remains a technical problem that needs to be solved urgently. Summary of the invention

[0004] The purpose of the present application is to provide a secondary battery and a method for preparing the same, which can improve the cycle performance and high-temperature storage performance of the secondary battery containing the same; the purpose of the present 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.

[0005] 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.

[0006] 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, and the chalcogen includes at least one of sulfur, selenium or tellurium. On the one hand, the presence of the material containing a chalcogen 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, to avoid 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 avoiding the residual alkali in the secondary battery from producing electrolyte residues during the electrochemical cycle, or 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.

[0007] On the other hand, when the secondary battery is undergoing a charge and discharge cycle, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer of the material 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.

[0008] 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, avoiding the production of the gas in the subsequent charge and discharge chemical cycle, avoiding it from affecting the structure of the secondary battery, causing bulging and other phenomena, and affecting the electrochemical performance of the secondary battery.

[0009] 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 process 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 interface of the negative electrode plate-electrolyte, which is beneficial to protect 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 transmit 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.

[0010] 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 may be 0.1%-2%.

[0011] According to an embodiment of the present application, the positive electrode film layer contains 0.01% to 3% by mass of chalcogens, and the chalcogens include at least one of sulfur, selenium, and tellurium. The chalcogens react with part of the residual alkali to form an intermediate product during the preparation of the positive electrode sheet, i.e., during the slurry stirring process, which can effectively reduce the pH of the slurry and alleviate or avoid the gelation of the slurry; in addition, the above intermediate product will further react with the residual alkali in the slurry 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 improving the comprehensive performance of the positive electrode sheet including uniformity, and is beneficial to the cycle performance and dynamic performance of the secondary battery containing the positive electrode sheet.

[0012] In some optional embodiments, the material containing a chalcogen element includes a simple substance containing a chalcogen element and / or a salt containing a chalcogen element.

[0013] 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 reducing salt. It may also include a salt of a positive divalent sulfide element. Due to its certain reducing property, during the formation and / or circulation of the secondary battery, it reacts with the residual alkali in the positive electrode plate to generate a protective film containing MO components (M includes at least one of Ni, Co, Mn, Fe and Cu), which is beneficial to improve the interfacial 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 + ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0014] In some optional embodiments, the salt containing chalcogen includes A2O3 2- or AO4 2- , wherein A represents a chalcogen element.

[0015] According to the embodiment of the present application, the salt of the sulfide element A exists 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 react 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.

[0016] According to the embodiment of the present application, the salt containing the chalcogen element can be obtained by reacting a single substance of the chalcogen element with the positive electrode active material, or can be directly added.

[0017] When the secondary battery including the positive electrode plate is formed or electrochemically cycled, the reducing material containing sulfide elements included in the positive electrode plate can continue to react with the residual alkali in the positive electrode plate, reduce the residual alkali content in the positive electrode active material, and form 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, 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 is beneficial to improve the cycle performance and high temperature storage performance of the secondary battery including the positive electrode plate;

[0018] In addition, the reducing sulfide-containing salt reacts with the residual alkali to release additional Na +ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0019] In some optional embodiments, 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.

[0020] 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 improve the interface stability between the positive electrode active material and the electrolyte during subsequent cycles, reduce side reactions, and improve the cycle performance and high temperature storage performance of the secondary battery containing the positive electrode plate. In addition, the single substance of the sulfide element reacts with the residual alkali to release additional Na + ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0021] In some optional embodiments, the ratio of the molar amount n2 of the hexavalent sulfide in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide in the positive electrode film layer is (0.5-1):1, or optionally (0.7-1):1.

[0022] 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, which forms a relatively stable salt containing the sulfide element, which is beneficial to the stability of the secondary battery.

[0023] In some alternative embodiments, the positive electrode active material includes a layered transition metal oxide.

[0024] In some optional embodiments, the layered transition metal oxide comprises a structural formula A 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.

[0025] 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 layered transition metal oxides result in a battery with a higher energy density. 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 prolongs the cycle life of the battery.

[0026] In some optional embodiments, the positive electrode active material includes a coating layer at least partially coated on the positive electrode active material, and the coating layer includes MO z , M includes one or more of Ni, Co, Mn, Fe and Cu, 0<z<2.

[0027] 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 can reduce the contact area between the positive electrode active material and the electrolyte.

[0028] In some optional embodiments, the coating layer has a thickness of 1 to 10 nm.

[0029] According to the embodiments of the present application, the thickness of the coating layer is controlled within the above range, and the cycle performance of the secondary battery is improved under the premise of reducing the contact area between the positive electrode active material and the electrolyte. A thinner protective film may not effectively prevent the contact between the electrolyte and the positive electrode active material, and a thicker protective film limits the transmission of ions and electrons, reducing the electrochemical performance of the secondary battery.

[0030] 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.

[0031] 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 ≤2000ppm.

[0032] According to the embodiment of the present application, the inclusion of the above-mentioned content of Na2O and / or Na2CO3 in the positive electrode film layer contained in the secondary battery is conducive to reducing the corrosion of the above-mentioned Na2O and / or Na2CO3 on the positive electrode plate. The presence of Na2O and / or Na2CO3 in the positive electrode plate will form electrolyte residues on the positive electrode plate or produce other adverse electrochemical reactions, resulting in reduced conductivity of the positive electrode plate. The inclusion of the above-mentioned content of Na2O and / or Na2CO3 in the positive electrode film layer is conducive to reducing electrolyte residues or other adverse electrochemical reactions, improving the conductivity of the positive electrode plate, and improving the dynamic performance of the secondary battery containing the positive electrode plate.

[0033] In addition, the CO2 generated by Na2CO3 in the positive electrode film layer can be released together with other gases formed during the formation process of the secondary battery. 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.

[0034] In some optional embodiments, the secondary battery is a sodium ion secondary battery.

[0035] In some optional embodiments, the positive electrode film layer includes a sodium supplement.

[0036] 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 supplementer that can increase the capacity of the battery while replenishing the active sodium, further improving the battery's cycle life, including capacity retention rate and rate performance, kinetic performance and storage life.

[0037] In some optional embodiments, the sodium supplement includes one or more of sodium sulfide, sodium selenide, and sodium nitride.

[0038] According to the embodiments of the present application, the material containing sulfide elements can participate in the formation of SEI film, consuming part of the active sodium. The composition includes a sodium supplementer that can increase the capacity of the battery while replenishing the active sodium, further improving the battery's cycle life, including capacity retention rate and rate performance, kinetic performance and storage life.

[0039] In a second aspect, the present application provides a method for preparing the secondary battery of the first aspect, comprising preparing a positive electrode sheet:

[0040] 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;

[0041] The positive electrode slurry is coated on at least one surface of the positive electrode collector to form a positive electrode film layer.

[0042] 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 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.

[0043] 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 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.

[0044] On the other hand, when the secondary battery is undergoing a charge and discharge cycle, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer of the material 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.

[0045] 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.

[0046] 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 is conducive to the reaction of the chalcogen elements with residual alkali, thereby avoiding the gelation of the slurry.

[0047] 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 suitable 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 is beneficial to improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0048] 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.

[0049] According to an embodiment of the present application, the above-mentioned valence state of the sulfide element exists in the positive electrode plate, which is beneficial to improving the comprehensive electrochemical performance of the secondary battery including the positive electrode plate when the secondary battery including the positive electrode plate is formed and / or subsequently cycled.

[0050] In some optional embodiments, the ratio of the sum of the molar amounts n1 of zero-valent and divalent chalcogens in the positive electrode film layer to the sum of the molar amounts n0 of zero-valent, divalent and hexavalent chalcogens in the positive electrode film layer is (0.5-1):1, or optionally (0.8-1):1.

[0051] According to an embodiment of the present application, by controlling the sum of the molar amounts of zero-valent and divalent sulfur elements in the positive electrode film layer and the total molar amount of sulfur 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 comprehensive performance of the secondary battery while protecting the positive electrode active material.

[0052] In some optional embodiments, the positive electrode slurry is prepared by adding a mixture including a positive electrode active material, a material containing a chalcogen element, and a sodium supplementing agent into a solvent to form a slurry.

[0053] 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 supplementer that can increase the capacity of the battery while replenishing the active sodium, further improving the battery's cycle life, including capacity retention rate and rate performance, kinetic performance and storage life.

[0054] In some optional embodiments, 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 0.1%-2%. Adding a suitable amount of sodium supplement can increase the capacity of the battery while replenishing active sodium, and further improve the cycle life, kinetic performance and storage life of the battery including capacity retention rate and rate performance.

[0055] In some optional embodiments, the volume average particle size Dv50 of the sodium supplement is 1 μm to 5 μm.

[0056] 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.

[0057] 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).

[0058] According to the embodiments of the present application, the material containing sulfide elements reacts with the residual alkali in the slurry to generate an intermediate product, and part of the 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.

[0059] The mass ratio of the material containing sulfide elements to the sodium supplement agent is within the above range, which can avoid the excessive content of the material containing sulfide elements in the positive electrode film layer, affecting the capacity and kinetic performance of the positive electrode plate 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.

[0060] 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).

[0061] 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.

[0062] In a fifth aspect, the present application provides an electric device, comprising the secondary battery of the fourth aspect, to obtain improved cycle performance and high temperature storage performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order 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 implementation methods of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0064] Figure 1 (a) shows the effect of the slurry of Example 10 of the present application and Figure 1 (b) shows the effect of the slurry of Comparative Example 1 of the present application;

[0065] Figure 2 The viscosity variation curves of the slurries of Comparative Example 1 and Example 10 of the present application over time are shown;

[0066] Figure 3 A schematic diagram showing an implementation of a secondary battery according to an embodiment of the present application;

[0067] Figure 4 The embodiment of the present application is shown Figure 3 An exploded schematic diagram of a secondary battery is shown;

[0068] Figure 5 A schematic diagram showing an implementation of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0069] In the drawings, the drawings are not necessarily drawn to scale. DETAILED DESCRIPTION

[0070] 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 are 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 descriptions 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.

[0071] "Scope" disclosed in the present application is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The scope defined in this way can be inclusive or exclusive of end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following range can be fully expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, characterized in that a and b are all real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it 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.

[0072] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0073] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0074] 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 means 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 also include step (c), which means 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.

[0075] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, "include" and "comprising" may represent that other components not listed may also be included or only listed components may be included or only listed components may be included.

[0076] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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).

[0077] Unless otherwise specified, in this application, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0078] If not specifically stated otherwise, in this application, the term "attach" refers to connection by adhesion, coating or the like.

[0079] If not 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 and secondary relationship.

[0080] Unless otherwise specified, in this application, the term "active ions" refers to ions that can be inserted and removed back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions, sodium ions, etc.

[0081] The term "several" as used herein refers to two or more (including two).

[0082] The secondary battery mentioned in the embodiments of the present application may be a lithium ion battery, a sodium ion battery, a lithium metal battery, a sodium metal battery, etc., and the embodiments of the present application are not limited to this.

[0083] The secondary battery includes an electrode assembly and an electrolyte, wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. 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.

[0084] 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. Part of the positive electrode active materials in the positive electrode sheet makes the positive electrode film layer have a higher alkalinity.

[0085] Taking the common secondary battery positive electrode plate homogenization system as an example, the positive electrode film layer mainly includes positive electrode active materials, polyvinylidene fluoride PVDF, conductive carbon black SP, and N-methylpyrrolidone NMP. Among them, although PVDF can provide strong bonding strength and electrochemical stability, its alkali resistance is very poor; PVDF will undergo an elimination reaction to generate water under the action of alkaline sodium ion materials, and NMP is a non-aqueous solvent; the double bonds generated after the elimination reaction of PVDF cause cross-linking reactions between PVDF molecular chains to form a gel. The oxidizing positive electrode active material easily reacts with CO2 and H2O in the air, and NaOH and Na2CO3 will be formed on the surface of the material. As an example, the residual alkali content and pH test of the positive electrode film layer of the finished positive electrode plate found 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.

[0086] As another example, the positive electrode film layer for 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.

[0087] In comparison, the alkalinity of sodium ion materials is significantly stronger than that of lithium ion materials. In addition to deteriorating the slurry processing performance, the residual alkali on the surface of sodium ion positive electrode materials also has a great impact on the electrochemical performance of secondary batteries. For example, the residual alkali on the surface of positive electrode active materials brings a series of side effects, such as low initial efficiency, deteriorated cycle and storage performance, etc.

[0088] 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 plate in the secondary battery, and improve the cycle performance and high-temperature storage performance of the secondary battery.

[0089] Secondary battery

[0090] 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.

[0091] 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 a chalcogen element indicates that when it exists, 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, to avoid 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 avoiding the residual alkali in the secondary battery from producing electrolyte residues in the electrochemical cycle, or 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.

[0092] On the other hand, when the secondary battery is undergoing a charge and discharge cycle, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer of the material 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.

[0093] 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, avoiding the production of the gas in the subsequent charge and discharge chemical cycle, avoiding it from affecting the structure of the secondary battery, causing bulging and other phenomena, and affecting the electrochemical performance of the secondary battery.

[0094] 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 process 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 interface of the negative electrode plate-electrolyte, which is beneficial to protect 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 transmit Na +The active ions, including , are beneficial to improving the power performance of the secondary battery, such as improving the ability of rapid charge and discharge. In some optional embodiments, the secondary battery includes a solid electrolyte membrane located on the surface of the negative electrode plate, and the mass proportion of the sulfide element is less than or equal to 2% based on the total mass of the solid electrolyte membrane, and can be optionally 0.1%-1.5%.

[0095] 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. Optionally, a sodium ion battery may be used.

[0096] For example, the positive electrode current collector has two surfaces opposite to each other in the thickness direction thereof, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0097] 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 may be 0.1%-2%.

[0098] Optionally, the positive electrode film layer contains 0.01%, 0.05%, 0.1%, 0.15%, 0.20%,

[0099] 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%,

[0100] 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%,

[0101] 0.35%, 0.40%, 0.45%, 0.50%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%,

[0102] The chalcogen element may be any value between 2.5% and 3.0%, or in a composition range thereof.

[0103] According to an embodiment of the present application, the positive electrode film layer contains 0.01% to 3% by mass of chalcogens, and the chalcogens include at least one of sulfur, selenium, and tellurium. The chalcogens react with part of the residual alkali to form an intermediate product during the preparation of the positive electrode sheet, i.e., during the slurry stirring process, which can effectively reduce the pH of the slurry and alleviate or avoid the gelation of the slurry; in addition, the above intermediate product will further react with the residual alkali in the slurry 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 improving the comprehensive performance of the positive electrode sheet including uniformity, and is beneficial to the cycle performance and dynamic performance of the secondary battery containing the positive electrode sheet.

[0104] According to an embodiment of the present application, the positive electrode film layer contains a material containing a chalcogen element with a mass content of 0.01% to 3%. The material containing a chalcogen element with a reducibility can be a single substance of the chalcogen element, or a reducible intermediate product (A2O3 2- ) exists in the positive electrode plate that has not undergone or has undergone a relatively small number of electrochemical cycles.

[0105] In some optional embodiments, the material containing a chalcogen element includes a simple substance containing a chalcogen element and / or a salt containing a chalcogen element.

[0106] 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 reducing salt. It may also include a salt of a positive divalent sulfide element. Due to its certain reducing property, during the formation and / or circulation of the secondary battery, it reacts with the residual alkali in the positive electrode plate to generate a protective film containing MO components (M includes at least one of Ni, Co, Mn, Fe and Cu), which is beneficial to improve the interfacial 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 + ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0107] In some optional embodiments, the salt containing chalcogen includes A2O3 2- or AO4 2- , wherein A represents a chalcogen element.

[0108] According to the embodiment of the present application, the salt of the sulfide element A exists 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 react 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.

[0109] According to the embodiment of the present application, the salt containing the chalcogen element can be obtained by reacting a single substance of the chalcogen element with the positive electrode active material, or can be directly added.

[0110] When the secondary battery including the positive electrode plate is formed or electrochemically cycled, the reducing material containing sulfide elements included in the positive electrode plate can continue to react with the residual alkali in the positive electrode plate, reduce the residual alkali content in the positive electrode active material, and form 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, 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 is beneficial to improve the cycle performance and high temperature storage performance of the secondary battery including the positive electrode plate;

[0111] In addition, the reducing sulfide-containing salt reacts with the residual alkali to release additional Na + ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0112] In some optional embodiments, 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.

[0113] In some optional embodiments, the positive electrode film layer contains 0.01% to 3% of divalent positive chalcogen element based on the total mass of the positive electrode film layer.

[0114] As an example, the reaction equation of the reaction between the reducing salt containing sulfide and the residual alkali is shown in equation (1):

[0115] Na2S2O3+ Na2CO3-8e - → 2 Na2SO4+5CO2+8Na + (1).

[0116] 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 improve the interface stability between the positive electrode active material and the electrolyte during subsequent cycles, reduce side reactions, and improve the cycle performance and high temperature storage performance of the secondary battery containing the positive electrode plate. In addition, the single substance of the sulfide element reacts with the residual alkali to release additional Na + ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0117] In some optional embodiments, the positive electrode film layer contains zero-valent and positive tetravalent chalcogen elements.

[0118] As an example, the reaction equation of the reaction between a single substance of a chalcogen element and a residual alkali is shown in equation (2):

[0119] 2NaMO2+S+2Na2CO3-4e - →2MO+ Na2SO4+2CO2+4Na + (2).

[0120] In some optional embodiments, the protective film including Na2SO4 is located on the surface of the MO component. The protective film of Na2SO4 located 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 is conducive to improving the cycle performance and high temperature storage performance of the secondary battery containing the positive electrode plate.

[0121] In some optional embodiments, the ratio of the molar amount n2 of the hexavalent sulfide in the positive electrode film layer to the sum of the molar amounts n0 of the zero-valent, tetravalent and hexavalent sulfide in the positive electrode film layer is (0.5-1):1, or optionally (0.7-1):1.

[0122] 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.

[0123] The method for detecting the molar ratio of sulfur elements in different valence states in the positive electrode plate includes: disassembling the secondary battery after charge and discharge to take the positive electrode plate, cutting the positive electrode plate into 1×1 cm size for sample preparation, and putting it into an X-ray photoelectron spectrometer for testing after sufficient drying, collecting and analyzing the data showing the energy spectrum peak position and intensity of sulfur elements in different valence states, and the peak area ratio of different valence states can be used as the valence state content ratio.

[0124] 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, which forms a relatively stable salt containing the sulfide element, which is beneficial to the stability of the secondary battery.

[0125] 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 a battery cell known in the art.

[0126] In some alternative embodiments, the positive electrode active material comprises a layered transition metal oxide.

[0127] In some optional embodiments, the layered transition metal oxide comprises a structural formula A 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

[0128] ≤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. 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.

[0129] 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 layered transition metal oxides result in a battery with a higher energy density. 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 prolongs the cycle life of the battery.

[0130] 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, a lithium-containing phosphate with an olivine structure, 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-containing phosphates with 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.

[0131] 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 f 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.

[0132] As an example, the positive electrode active material may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2(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.

[0133] 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.

[0134] As an example, the positive electrode active material may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2Ti 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 Xp M' q (PO4) r O x Y 3-x In the general formula X p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes a selection from H + , Li + 、Na + , K + and NH4 + One or more of, M' is a transition metal cation, which may be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which may be selected from one or more of F, Cl and Br.

[0135] The modified compounds of the above-mentioned positive electrode active materials may be the ones that undergo doping modification and / or surface coating modification on the positive electrode active materials.

[0136] In some optional embodiments, the positive electrode active material includes a coating layer at least partially coated on the positive electrode active material, and the coating layer includes MO z , M includes one or more of Ni, Co, Mn, Fe and Cu, 0<z<2.

[0137] As an example, MO z Including any one or more of NiO, CoO, MnO, Fe2O3, and CuO.

[0138] 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 can reduce the contact area between the positive electrode active material and the electrolyte.

[0139] In some optional embodiments, the coating layer has a thickness of 1 to 10 nm.

[0140] According to the embodiments of the present application, the thickness of the coating layer is controlled within the above range, and the cycle performance of the secondary battery is improved under the premise of reducing the contact area between the positive electrode active material and the electrolyte. A thinner protective film may not effectively prevent the contact between the electrolyte and the positive electrode active material, and a thicker protective film limits the transmission of ions and electrons, reducing the electrochemical performance of the secondary battery.

[0141] 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.

[0142] 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 ≤2000ppm.

[0143] According to the embodiment of the present application, the inclusion of the above-mentioned content of Na2O and / or Na2CO3 in the positive electrode film layer contained in the secondary battery is conducive to reducing the corrosion of the above-mentioned Na2O and / or Na2CO3 on the positive electrode plate. The presence of Na2O and / or Na2CO3 in the positive electrode plate will form electrolyte residues on the positive electrode plate or produce other adverse electrochemical reactions, resulting in reduced conductivity of the positive electrode plate. The inclusion of the above-mentioned content of Na2O and / or Na2CO3 in the positive electrode film layer is conducive to reducing electrolyte residues or other adverse electrochemical reactions, improving the conductivity of the positive electrode plate, and improving the dynamic performance of the secondary battery containing the positive electrode plate.

[0144] In addition, the CO2 generated by Na2CO3 in the positive electrode film layer can be released together with other gases formed during the formation process of the secondary battery. 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, and affecting the electrochemical performance of the secondary battery.

[0145] As an example, the above-mentioned method for detecting Na2O and / or Na2CO3 includes disassembling a secondary battery that undergoes a charge-discharge chemical cycle, taking out a positive electrode plate, scraping powder, and then using an acid-base titration test to confirm the content of Na2O and Na2CO3 respectively. The detection can be performed when the number of charge-discharge cycles of the secondary battery is less than or equal to 100 times.

[0146] In some optional embodiments, the secondary battery is a sodium ion secondary battery.

[0147] In some optional embodiments, the positive electrode film layer includes a sodium supplement.

[0148] 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 supplementer that can increase the capacity of the battery while replenishing the active sodium, further improving the battery's cycle life, including capacity retention rate and rate performance, kinetic performance and storage life.

[0149] In some optional embodiments, the sodium supplement includes one or more of sodium sulfide, sodium selenide, or sodium nitride.

[0150] According to the embodiments of the present application, the material containing sulfide elements can participate in the formation of SEI film, consuming part of the active sodium. The composition includes a sodium supplementer that can increase the capacity of the battery while replenishing the active sodium, further improving the battery's cycle life, including capacity retention rate and rate performance, kinetic performance and storage life.

[0151] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application has no particular restrictions on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0152] In some embodiments, the positive electrode film layer may further include a positive electrode binder. The present application has no particular restrictions on 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.

[0153] 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).

[0154] [Negative electrode]

[0155] 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 to this.

[0156] 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 opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0157] 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 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.

[0158] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present application has no particular restrictions on the type of the negative electrode conductive agent. As an 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.

[0159] In some embodiments, the negative electrode film layer may further include a negative electrode binder. The present application has no particular restrictions on the type of negative electrode binder. As an example, the negative electrode binder may include 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). One or more.

[0160] In some embodiments, the negative electrode film layer may further include other additives. As an example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC-Na), a PTC thermistor material, and the like.

[0161] 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, a 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).

[0162] The negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0163] The negative electrode plate does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate of the present application may also 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 also include a protective film covering the surface of the negative electrode film layer.

[0164] When the battery cell is a lithium metal battery cell, the negative electrode plate may not include negative electrode active materials capable of extracting and embedding 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 three-dimensional skeleton layer, such as foam copper (or copper alloy), foam nickel (or nickel alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, etc.

[0165] When the battery cell is a sodium metal battery cell, the negative electrode plate may not include negative electrode active materials capable of extracting and embedding 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 foam copper (or copper alloy), foam nickel (or nickel alloy), foam aluminum (or aluminum alloy), copper (or copper alloy) mesh, nickel (or nickel alloy) mesh, aluminum (or aluminum alloy) mesh, etc.

[0166] [Electrolytes]

[0167] In some embodiments, the secondary battery includes an electrolyte. The electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).

[0168] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0169] 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 difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate phosphate) (LiDFOP), lithium tetrafluorooxalate phosphate (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.

[0170] 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), cyclopentane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).

[0171] In some embodiments, the electrolyte may also optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and 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.

[0172] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0173] 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.

[0174] The present application has no particular limitation on the shape of the secondary battery, which may be a flat body, a rectangular parallelepiped or other shapes. Figure 3 The secondary battery 5 is a rectangular parallelepiped structure as an example.

[0175] In some embodiments, Figure 4 As shown, the outer packaging may include a shell 51 and a cover plate 53. Among them, 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 receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving 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 receiving cavity. The electrolyte is infiltrated 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.

[0176] Method for preparing a secondary battery

[0177] In a second aspect, the present application provides a method for preparing the secondary battery of the first aspect, comprising preparing a positive electrode sheet:

[0178] 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;

[0179] The positive electrode slurry is coated on at least one surface of the positive electrode collector to form a positive electrode film layer.

[0180] In the related art, the slurry contains positive electrode active materials with certain oxidizability. In the process of preparing positive electrode sheets, especially in the process of preparing 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. It is not intended to be limited to any theory or explanation. If not treated, this type of residual alkali present in the slurry will lead to a more serious gelation phenomenon. Such a gelation phenomenon will cause particle agglomeration, 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 positive electrode sheet with better quality.

[0181] The material containing chalcogen can be understood as a material having reducing properties that contains chalcogen and can react with an alkali.

[0182] 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 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.

[0183] On the other hand, when the secondary battery is undergoing a charge and discharge cycle, it can not only ensure the initial coulombic efficiency of the secondary battery, but also enable the positive electrode film layer of the material 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.

[0184] 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 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] The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry usually includes a positive electrode active material, an optional conductive agent, an optional binder and any other components dispersed in a solvent and stirred uniformly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0186] In some optional embodiments, the mixture contains 0.01% to 5% of a single substance of chalcogen based on the total mass of the mixture.

[0187] Optionally, the mixture for the positive electrode sheet contains 0.01%, 0.05%, 0.1%, 0.15%, 0.20%,

[0188] 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%,

[0189] 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%,

[0190] A single substance of chalcogen element in any value selected from 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.

[0191] According to the embodiment of the present application, according to the embodiment of the present application, the mixture can be understood as the part of the slurry for the positive electrode plate that does not contain the solvent. The sulfide element includes at least one of sulfur, selenium, and tellurium. The simple substance of the sulfide 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 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 sulfide element into a positive electrode plate, and improving the comprehensive performance of the positive electrode plate including uniformity.

[0192] In some optional embodiments, the mixture includes 0.1% to 2% by mass of a single substance of chalcogen.

[0193] According to the embodiment of the present application, the mixture includes the above-mentioned mass content of the single substance of the sulfide 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 it and the electrolyte during the charge and discharge process of the secondary battery, 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.

[0194] According to the embodiments of the present application, the amount of the 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 plate 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 the 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 deteriorate the impedance and increase the polarization, thereby reducing the capacity of the secondary battery.

[0195] 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 50nm-1000nm, and optionally 100nm-500nm.

[0196] 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 is conducive to the reaction of the chalcogen elements with residual alkali, thereby avoiding the gelation of the slurry.

[0197] 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 suitable 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 is beneficial to improving the cycle performance and high-temperature storage performance of the secondary battery containing the positive electrode plate.

[0198] Volume average particle size D v 50 is a well-known meaning in the art, which indicates the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be measured by instruments and methods well-known in the art. For example, it can be conveniently measured by a laser particle size analyzer with reference to GB / T19077-2016 particle size distribution laser diffraction method, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.

[0199] 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.

[0200] As an example, the reaction between a single substance of a chalcogen element and a positive electrode active material can be as shown in formula (3):

[0201] 4NaMO2+2S→4MO+Na2S2O3+Na2O(3), wherein M includes at least one of Ni, Co, and Mn.

[0202] According to an embodiment of the present application, the above-mentioned valence state of the sulfide element exists in the positive electrode plate, which is beneficial to improving the comprehensive electrochemical performance of the secondary battery including the positive electrode plate when the secondary battery including the positive electrode plate is formed and / or subsequently cycled.

[0203] In some optional embodiments, the ratio of the sum of the molar amounts n1 of zero-valent and divalent chalcogens in the positive electrode film layer to the sum of the molar amounts n0 of zero-valent, divalent and hexavalent chalcogens in the positive electrode film layer is (0.5-1):1, or optionally (0.8-1):1.

[0204] Optionally, the ratio of the sum of the molar amounts n1 of zero-valent and divalent chalcogens in the positive electrode film layer to the sum of the molar amounts n0 of zero-valent, divalent and hexavalent chalcogens in the positive electrode film layer can be any value or composition range of 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1.

[0205] According to an embodiment of the present application, by controlling the sum of the molar amounts of zero-valent and divalent sulfur elements in the positive electrode film layer and the total molar amount of sulfur 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 comprehensive performance of the secondary battery while protecting the positive electrode active material.

[0206] In some optional embodiments, the positive electrode slurry is prepared by adding a mixture including a positive electrode active material, a material containing a chalcogen element, and a sodium supplementing agent into a solvent to form a slurry.

[0207] 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 supplementer that can increase the capacity of the battery while replenishing the active sodium, further improving the battery's cycle life, including capacity retention rate and rate performance, kinetic performance and storage life.

[0208] 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.

[0209] Optionally, the composition for the positive electrode sheet comprises 0.05%, 0.1%, 0.15%, 0.20%, 0.25%,

[0210] 0.30%, 0.35%, 0.40%, 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%,

[0211] 0.80%, 0.85%, 0.90%, 0.95%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%,

[0212] A sodium supplement having any numerical value or composition range among 0.40%, 0.45%, 0.50%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%.

[0213] 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 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.

[0214] In some optional embodiments, the volume average particle size Dv50 of the sodium supplement is 1 μm to 5 μm.

[0215] 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.

[0216] 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.

[0217] 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).

[0218] 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.

[0219] According to the embodiments of the present application, the material containing sulfide elements reacts with the residual alkali in the slurry to generate an intermediate product, and part of the 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.

[0220] The mass ratio of the material containing sulfide elements to the sodium supplement agent is within the above range, which can avoid the excessive content of the material containing sulfide elements in the positive electrode film layer, affecting the capacity and kinetic performance of the positive electrode plate 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.

[0221] 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).

[0222] 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 , any value or its composition range among 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.

[0223] 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.

[0224] [Preparation method]

[0225] The preparation method of the battery of the present application is well known. The preparation method of the secondary battery of the present application is well known, and the method at least includes the step of preparing the electrode assembly of the second aspect of the embodiment of the present application. In some embodiments, the electrode assembly can be placed in an outer package, and after drying, an electrolyte can be injected, and a secondary battery can be obtained through vacuum packaging, standing, forming, shaping and other processes.

[0226] In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery cell. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. 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 mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel or in mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0227] 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.

[0228] 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.

[0229] 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.

[0230] Electrical devices

[0231] 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.

[0232] The electric device of the present application includes a secondary battery, and thus has at least the advantages corresponding to the secondary battery.

[0233] Secondary batteries can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices may be, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0234] Figure 5 Schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

[0235] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0236] Example

[0237] The following examples describe the disclosure of the present application in more detail, and these examples are only for illustrative purposes, as it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on 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, and the instruments used in the examples are commercially available.

[0238] Example 1

[0239] Preparation of positive electrode

[0240] O3-type layered oxide NaFe 2 / 3 Mn 1 / 6 Co 1 / 6 O2, nano sulfur, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), carbon nanotube (CNT) are stirred and mixed at a weight ratio of 88.5:0.5:4.7:3.3:3.0 at a speed of 400-1000r / s, and then wetted, kneaded and dispersed to obtain the positive electrode slurry. Figure 1 As shown. The positive electrode slurry of this embodiment ( Figure 1 a), relative to the positive electrode slurry without adding nano sulfur element ( Figure 1 b), its fluidity is better and viscosity is more stable ( Figure 2 ), no gelation phenomenon occurred.

[0241] The prepared slurry is then coated on an aluminum foil and dried, cold pressed, and cut to obtain the positive electrode sheet of Example 1.

[0242] Preparation of negative electrode

[0243] Active material hard carbon, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dry-mixed evenly in a weight ratio of 97.2:0.8:0.8:1.2, and then deionized water is added and mixed evenly 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.

[0244] Preparation of electrolyte

[0245] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), organic solvents ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were 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.

[0246] Preparation of isolation membrane

[0247] A polyethylene film is used as the isolation film.

[0248] Preparation of sodium ion secondary batteries

[0249] The prepared positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, with the isolation film placed between the positive and negative electrode sheets, and then wound to obtain a bare battery cell; the bare battery cell is placed in a battery outer package, and then injected with electrolyte, packaged, allowed to stand, formed, shaped, and capacity tested to complete the preparation of a 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.

[0250] Examples 2 to 9: The preparation method is similar to that of Example 1, except that the content and type of the single substance 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.

[0251] Examples 10 to 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 nanotube (CNT) are stirred and mixed at a speed of 400-1000r / 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 positive electrode slurry. Figure 1 As shown. The positive electrode slurry of this embodiment ( Figure 1 Figure a), relative to the positive electrode slurry of Comparative Example 1 without adding nano sulfur element ( Figure 1 (b), Example 10 has better fluidity and more stable viscosity than Comparative Example 1 (e.g. Figure 2 ), and no gelation occurred.

[0252] The prepared slurry was then coated on an aluminum foil, 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.

[0253] Embodiments 19-20:

[0254] The preparation method is similar to that of Example 10, except that the type of sodium supplement is different. See Table 1 for details.

[0255] Embodiments 21 to 23:

[0256] The preparation method is similar to that of Example 10, except that the ratio of the volume average particle diameter Dv50 of the simple substance of the chalcogen element and the sodium supplement is different. See Table 1 for details.

[0257] Comparative Example 1

[0258] The difference between this comparative example and Example 1 is that: Preparation of the positive electrode sheet:

[0259] 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 a positive electrode sheet of the comparative example.

[0260] Test Section

[0261] 1) Detection method of chalcogen content in positive electrode film layer:

[0262] First, the positive electrode is digested with a digestion reagent: aqua regia prepared by mixing concentrated nitric acid (HNO3) and concentrated hydrochloric acid (HCl) in a volume ratio of 1:1. The digestion method can be plate / acid digestion / microwave digestion (high temperature and high pressure are about 200°C). Then the digested solution is collected and put into an inductively coupled plasma spectrometer for testing, and the chalcogen content can be quantitatively measured.

[0263] 2) The test method for 0.33C capacity retention rate is: at 25°C, charge the sodium ion battery to 4.25V at 0.33C constant current, then charge at 4.25V constant voltage until the current is less than 0.05C, and then discharge the sodium ion battery to 3.0V at 0.33C constant current. This is a charge and discharge process. Repeat the charging and discharging process in this way, and calculate the capacity retention rate of the sodium ion battery after 100 cycles.

[0264] 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%.

[0265] 4) Test method for 60℃ storage capacity retention rate:

[0266] The battery capacity recovery rate test process is as follows: before storage, at 25°C, the battery corresponding to implementation 1 is 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 is recorded as the initial capacity C0. After storage at 60°C for 100 days, the battery temperature is cooled to room temperature, and the above steps are repeated. The measured capacity is recorded as Cr, and the battery capacity recovery rate after storage for 50 days is H=Cr / C0*100%.

[0267] 5) Test method for the first coulombic efficiency:

[0268] The injected battery cell is charged to 3.9V at 0.1C current on a formation machine, and the formation capacity at this time is recorded as C1; the formed battery cell is then placed on a blue electric charger and discharger, and charged to 4.25V at 0.33C current, and the charging capacity at this time is recorded as C2; finally, it is discharged to 2.8V at 0.33C current, and the discharge capacity at this time is D1, and the first coulombic efficiency of the battery cell is calculated as D1 / (C1+C2)*100%.

[0269] 6) Fast charging performance (10%-80% SOC fast charging time)

[0270] The test process of 10%-80% SOC charging time is as follows: at 25°C, the batteries in the embodiment and comparative example are charged from 10% SOC to 80% SOC at 1.0C / 0.8C / 0.5C / 0.33C step by step. The charging time when no lithium deposition occurs at the negative electrode is the fast charging time of the battery at this time. The shorter the fast charging time, the better the fast charging performance of the battery.

[0271] 7) Testing method for molar ratio of different valence states of chalcogens:

[0272] After charging and discharging, the secondary battery is disassembled to take out the positive electrode sheet, and the positive electrode sheet is cut into 1×1cm size for sample preparation. After being fully dried, it is put into the X-ray photoelectron spectrometer for testing, and the data showing the energy spectrum peak position and intensity of different valence states of sulfur elements are collected and analyzed. The peak area ratio of different valence states can be used as the valence state content ratio.

[0273] From the test results in Table 1, it can be seen that when the single substance of sulfide is within the above range, it can react with the participants in the slurry to avoid gelation of the slurry. The positive electrode plate contains a reducing intermediate product containing sulfide elements, which continues to react with the residual alkali in the positive electrode plate, 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, and its components include Na2SO4, etc. It 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 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 intermediate product reacts with the residual alkali to release additional Na + ions can be used to compensate for the loss of active ions caused by the formation of SEI, which increases the content of active ions in the secondary battery and is beneficial to increasing the energy density, energy storage capacity, power performance and cycle life of the secondary battery.

[0274] According to Table 1, compared with Comparative Example 1, in Examples 1-9, a single substance of chalcogen element is added to the composition, and a protective film is formed on the positive electrode sheet during the formation of the secondary battery, which improves the stability of the positive electrode active material, is beneficial to improving the capacity retention rate and high-temperature storage performance of the secondary battery, and also improves the charge and discharge performance of the secondary battery.

[0275] According to Table 1, in Examples 10-20, compared with Comparative Example 1, the compositions contain a single substance of chalcogen elements and a sodium supplement, and a protective film is formed on the positive electrode sheet during the formation of the secondary battery, thereby improving the stability of the positive electrode active material and facilitating the improvement of 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 single substance of the chalcogen elements, thereby improving the initial coulombic efficiency and the charge and discharge performance of the secondary battery.

[0276] According to Table 1, compared with Example 10, Examples 21-23 have different ratios of the average particle size Dv50 of the single substance of the sulfide element and the sodium supplement, which have a certain influence on the charge and discharge performance of the secondary battery, the capacity retention rate of the secondary battery, and the high-temperature storage performance.

[0277] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and playing the same role within the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

[0278]

[0279]

[0280]

Claims

1. A secondary battery, comprising a positive electrode plate, characterized in that: The positive electrode sheet includes 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 includes a positive electrode active material and a material containing a chalcogen element.

2. The secondary battery according to claim 1, characterized in that: 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, characterized in that: 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, characterized in that: The material containing chalcogen includes a simple substance containing chalcogen and / or a salt containing chalcogen.

5. The secondary battery according to claim 4, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: The positive electrode active material includes a coating layer at least partially coated on the positive electrode active material. 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, characterized in that: The coating layer has a thickness of 1 to 10 nm.

11. The secondary battery according to any one of claims 1 to 10, characterized in that: 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, characterized in that: The secondary battery is a sodium ion secondary battery.

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

14. The secondary battery according to claims 1 to 13, characterized in that: 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, characterized in that: Including the 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, characterized in that 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, characterized in that 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, characterized in that: 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 supplementing 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, characterized in that The mass ratio of the material containing chalcogen 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, characterized in that: 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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