Secondary battery and preparation method therefor, and electric device

Abstract

The present application relates to a secondary battery and a preparation method therefor, and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet comprises a positive electrode film layer; the positive electrode film layer comprises a positive electrode active material and a positive electrode electrolyte interface film; and the positive electrode electrolyte interface film comprises Li2MO4, wherein M comprises chalcogens. The electrolyte comprises a solvent and a lithium salt, and further comprises at least one of a lithium metal chelate and an additive capable of being combined with lithium ions to form a chelate. The secondary battery of the present application has low DCR, and has good rate performance and cycle performance.

Description

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

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202311415282.7, filed on October 30, 2023, entitled “Secondary battery, preparation method thereof, and electrical device”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery, a preparation method thereof, and an electrical device. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0005] In recent years, as the application scope of secondary batteries has become increasingly wider, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in many fields such as power tools, electric bicycles, electric motorcycles and electric vehicles.

[0006] As secondary batteries have made great progress, higher requirements have been placed on the cycle performance and kinetic performance of secondary batteries. Therefore, seeking secondary batteries with better cycle performance and kinetic performance has become one of the key areas of focus for those skilled in the art.

[0007] Summary of the Invention

[0008] The present application is made in view of the above-mentioned problems, and one of its purposes is to provide a secondary battery having good cycle performance and kinetic performance.

[0009] In order to achieve the above-mentioned object, the first aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte;

[0010] The positive electrode sheet includes a positive electrode film layer, the positive electrode film layer includes a positive electrode active material and a positive electrode electrolyte interface film (CEI), and the positive electrode electrolyte interface film includes Li2MO4, wherein M includes a chalcogen element;

[0011] The electrolyte includes a solvent and a lithium salt, and further includes at least one of a lithium metal chelate and an additive capable of combining with lithium ions to form a chelate.

[0012] The positive electrode film layer of the secondary battery of the present application has a positive electrode electrolyte interface membrane, which includes Li2MO4, wherein M includes a chalcogen, and the Li2MO4 is obtained by the reaction of a chalcogen element and a residual lithium compound (RLCs) on the surface of the positive electrode active material; in this way, the residual lithium compound on the surface of the positive electrode active material is removed, and the electrochemical performance of the positive electrode electrolyte interface membrane containing Li2MO4 is stable, which can improve the first coulombic efficiency and storage performance of the secondary battery, especially the secondary battery using a high-nickel ternary positive electrode material, and can reduce the battery DCR, and improve the battery rate performance and cycle performance; the electrolyte of the secondary battery includes at least one of a lithium metal chelate and an additive that can combine with lithium ions to form a chelate, and the additive can form a chelate with lithium ions, inhibiting the chalcogen dissolved in the electrolyte from combining with lithium ions in the negative electrode of the battery to form a non-conductive chalcogen lithium compound, thereby further reducing the battery DCR and further improving the battery rate performance and cycle performance. The secondary battery of the present application has a high first coulombic efficiency, good cycle performance, kinetic performance and storage performance.

[0013] In any embodiment, the additive comprises one or more of an organic phosphonic acid, a phosphonate, and an oxalate. The use of such additives in the electrolyte can effectively chelate with lithium ions in the electrolyte, effectively alleviating the reaction of dissolved chalcogens in the electrolyte with lithium ions at the negative electrode to form non-conductive lithium chalcogenides, thereby effectively improving the cycling performance and kinetic performance of the secondary battery.

[0014] In any embodiment, the organic phosphonic acid comprises one or more of hydroxyethylidene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, and ethylenediamine tetramethylene phosphonic acid. The organic phosphonic acid additive has two symmetrical phosphorus-oxygen double bonds (P=O) in its molecule, which can better combine with lithium ions in the electrolyte to form a chelate.

[0015] In any embodiment, the phosphonate comprises one or more of diethyl hydroxyethylidene diphosphonate, dimethyl hydroxyethylidene diphosphonate, and dipropyl hydroxyethylidene diphosphonate. The phosphonate additive molecules also have two symmetrical phosphorus-oxygen double bonds (P=O), which can also better combine with lithium ions in the electrolyte to form a chelate.

[0016] In any embodiment, the oxalate comprises one or more of dimethyl oxalate, diethyl oxalate, dipropyl oxalate, and dibutyl oxalate. The oxalate additive has two symmetrical carbon-oxygen double bonds (C=O) in its molecule, which can better combine with lithium ions in the electrolyte to form a chelate.

[0017] In any embodiment, the lithium metal chelate comprises one or more of a chelate formed by a lithium ion and an organic phosphonic acid, a chelate formed by a lithium ion and a phosphonate, and a chelate formed by a lithium ion and an oxalate.

[0018] In any embodiment, the chalcogen element includes one or more of sulfur, selenium, and tellurium. Further, the chalcogen element is sulfur.

[0019] In any embodiment, the mass of Li2MO4 in the positive electrode electrolyte interface film is 0.1% to 4.5% of the mass of the positive electrode active material.

[0020] In any embodiment, the thickness of the cathode electrolyte interface film on the surface of the cathode active material is 5 nm to 20 nm. Alternatively, the thickness of the cathode electrolyte interface film is 5 nm to 10 nm.

[0021] In any embodiment, the positive electrode active material includes Li x Ni a Co b A c O2, wherein A includes at least one of Mn and Al, 0.2≤x≤1.2, 0.6≤a<1, 0<b≤0.2, and a+b+c=1. Thus, using a high-nickel ternary positive electrode material as the positive electrode active material can improve the energy density of the secondary battery.

[0022] In any embodiment, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, and lithium trifluoromethanesulfonate.

[0023] In any embodiment, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 1.5 mol / L.

[0024] In any embodiment, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.2 mol / L.

[0025] In any embodiment, the solvent includes one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and tetrahydrofuran.

[0026] The second aspect of the present application provides a method for preparing the secondary battery of the first aspect of the present application, the method comprising the following steps:

[0027] Mixing a solvent, a positive electrode active material and a chalcogen element to form a slurry, coating the slurry on a positive electrode current collector, and drying to obtain a positive electrode sheet; and

[0028] Assembling the negative electrode sheet and the positive electrode sheet into a dry cell, and injecting electrolyte into the dry cell to obtain a secondary battery;

[0029] The electrolyte is composed of raw materials including a solvent, a lithium salt and an additive capable of combining with lithium ions to form a chelate.

[0030] The preparation method of the present application can remove residual lithium compounds such as Li2O and Li2CO3 on the surface of the positive electrode active material by adding a chalcogen element to the positive electrode slurry, and form an electrochemically stable Li2MO4 artificial CEI layer, which can improve the initial coulombic efficiency and storage performance of the secondary battery, reduce the battery DCR, and improve the battery's rate performance and cycle performance. By adding an additive that can combine with lithium ions to form a chelate complex in the electrolyte, it can improve the situation where the battery kinetics and cycle performance are reduced due to the combination of chalcogen ions dissolved in the electrolyte with lithium ions. As a result, the prepared secondary battery has a high initial coulombic efficiency, good cycle performance, kinetic performance, and storage performance.

[0031] In any embodiment, the mass of the chalcogen element in the slurry is 0.01% to 5% of the mass of the positive electrode active material. This effectively removes residual lithium compounds on the surface of the positive electrode active material while minimizing the negative impact on battery performance caused by excessive addition of the chalcogen element.

[0032] In any embodiment, the mass of the chalcogen element in the slurry is 0.35% to 1% of the mass of the positive electrode active material. This can effectively remove residual lithium compounds on the surface of the positive electrode active material while further reducing the adverse effects of the chalcogen element on battery performance.

[0033] In any embodiment, based on the total mass of the electrolyte, the mass fraction of the additive is 0.01% to 3%, thereby better improving the dynamic performance and cycle performance of the secondary battery.

[0034] In any embodiment, based on the total mass of the electrolyte, the mass fraction of the additive is 0.05% to 0.1%, thereby further improving the kinetic performance and cycle performance of the secondary battery.

[0035] In any embodiment, the positive electrode active material comprises a high nickel ternary positive electrode material, wherein the high nickel ternary positive electrode material comprises Li x Ni aCo b A c O2, wherein A is Mn or Al, 0.2≤x≤1.2, 0.6≤a<1, 0<b≤0.2, a+b+c=1.

[0036] In any embodiment, the surface of the positive electrode active material has residual lithium compounds, and the mass of the residual lithium compounds is 0.1% to 2.0% of the mass of the positive electrode active material.

[0037] A third aspect of the present application provides an electrical device comprising one or more of the secondary battery of the first aspect of the present application and the secondary battery prepared by the preparation method of the second aspect of the present application.

[0038] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0040] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0041] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0042] FIG3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0043] Description of reference numerals:

[0044] 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. DETAILED DESCRIPTION

[0045] Below, the secondary battery and its preparation method, and the embodiment of the electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0046] The "ranges" disclosed in this application can be defined in the form of lower limits and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. Ranges defined in this way can be inclusive or exclusive of the end values, any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are 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 also listed, the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise specified, the numerical range "a to b" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for a combination of these values. Furthermore, when a parameter is expressed as an integer greater than or equal to 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10," this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0047] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0048] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0050] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0051] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0052] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0053] Currently, due to the rapid development of secondary batteries, higher requirements have been placed on their cycle performance and kinetic performance. Therefore, the development of secondary batteries with excellent cycle performance and kinetic performance is one of the key areas of focus for those skilled in the art. In this regard, the present application provides a secondary battery that has improved cycle performance and kinetic performance by adjusting the composition of the positive electrode film layer and the composition of the electrolyte.

[0054] In some embodiments, the first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode film layer, the positive electrode film layer comprises a positive electrode active material and a positive electrode electrolyte interface film, the positive electrode electrolyte interface film comprises Li2MO4, wherein M comprises a sulfide element; the electrolyte comprises a solvent and a lithium salt, and also comprises at least one of a lithium metal chelate and an additive capable of combining with lithium ions to form a chelate.

[0055] In traditional secondary battery cathodes, cathode active materials, especially high-nickel ternary cathode materials, are widely used due to their high reversible capacity and low cost. However, residual lithium compounds (RLCs), such as Li2O and Li2CO3, may remain on the surface of these cathode active materials. This residue can have adverse effects during secondary battery use, resulting in low initial coulombic efficiency and poor storage performance.

[0056] The positive electrode film layer of the secondary battery of the present application comprises a positive electrode electrolyte interface film containing Li2MO4 formed by a chalcogen element and a residual lithium compound, wherein M comprises a chalcogen element; thus, the residual lithium compound on the surface of the positive electrode active material is removed, and the electrochemical performance of the positive electrode electrolyte interface film containing Li2MO4 is stable, which can improve the initial coulombic efficiency and storage performance of the secondary battery, especially the secondary battery using a high-nickel ternary positive electrode material, and can reduce the battery DCR, thereby improving the battery's rate performance and cycle performance. In addition, the present application adds an additive capable of combining with lithium ions to form a chelate complex in the electrolyte. The additive can form a chelate phase with the lithium ions in the electrolyte, making it more difficult for the chalcogen elements partially dissolved in the electrolyte to combine with the lithium ions in the electrolyte, thereby inhibiting the free chalcogen elements in the electrolyte from migrating to the negative electrode of the battery and forming a non-conductive chalcogen lithium compound with the lithium ions; thereby improving the degree of removal of the residual lithium compound on the surface of the positive electrode active material, and improving the situation where the battery dynamics and cycle performance are reduced due to the combination of the chalcogen elements dissolved in the electrolyte with the lithium ions. Therefore, the secondary battery has a higher first coulombic efficiency, better cycle performance, kinetic performance and storage performance.

[0057] It is understood that the aforementioned additives may be added to the electrolyte during preparation. After addition, the additives will partially or completely combine with the lithium ions in the electrolyte, thereby forming the aforementioned lithium metal chelate. Therefore, the electrolyte of the secondary battery includes the lithium metal chelate and at least one of the aforementioned additives capable of combining with lithium ions to form a chelate.

[0058] In some embodiments, the additive capable of combining with lithium ions to form a chelate comprises one or more of an organic phosphonic acid, a phosphonate, and an oxalate. Correspondingly, the lithium metal chelate comprises one or more of a chelate formed between a lithium ion and an organic phosphonic acid, a chelate formed between a lithium ion and a phosphonate, and a chelate formed between a lithium ion and an oxalate.

[0059] Among the additives that have a chelating effect on lithium ions, those with phosphorus-oxygen double bonds (P=O) or carbon-oxygen double bonds (C=O) can form electron pairs, exhibit local electronegativity, and form ligands. Since lithium ions are positively charged and have empty orbitals in their outermost layer, the lithium ions with empty orbitals bind to the ligands with electron pairs through coordination bonds, thereby forming a chelate. The lithium ions and the chelating additives form a chelate phase, making it more difficult for the chalcogens dissolved in the electrolyte to bind to the lithium ions, thereby alleviating the migration of the chalcogens dissolved in the electrolyte to the negative electrode and combining with the lithium ions in the electrolyte to form insoluble Li2S.

[0060] It is understood that the additive capable of combining with lithium ions to form a chelate can be organic phosphonic acid, phosphonate or oxalate alone, or any two or more of the organic phosphonic acid, phosphonate and oxalate can be mixed and used.

[0061] In some embodiments, the organic phosphonic acid includes one or more of hydroxyethylidene diphosphonic acid, aminotrimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, and ethylenediamine tetramethylene phosphonic acid; the phosphonate includes one or more of diethyl hydroxyethylidene diphosphonate, dimethyl hydroxyethylidene diphosphonate, and dipropyl hydroxyethylidene diphosphonate; and the oxalate includes one or more of dimethyl oxalate, diethyl oxalate, dipropyl oxalate, and dibutyl oxalate. It will be understood that the organic phosphonic acid, phosphonate, and oxalate that are additives capable of combining with lithium ions to form a chelate can be, but are not limited to, the specific types listed above.

[0062] In some embodiments, the chalcogen element includes one or more of sulfur, selenium, and tellurium. In some specific embodiments, the chalcogen element is sulfur. It is understood that the chalcogen element in the positive electrode film layer can be any one of sulfur, selenium, and tellurium, or a combination of two or more of these elements.

[0063] In some embodiments, the mass of Li2MO4 in the positive electrode electrolyte interface film is 0.1% to 4.5% of the mass of the positive electrode active material. The thickness of the CEI layer attached to the surface of the positive electrode active material is 5nm to 20nm, and can be optionally 5nm to 10nm. It can be understood that the content of Li2MO4 in the CEI layer mainly depends on the content of residual lithium compounds on the surface of the positive electrode active material and the amount of chalcogen added to the positive electrode film layer. Similarly, the thickness of the CEI layer attached to the surface of the positive electrode active material also mainly depends on the content of residual lithium compounds on the surface of the positive electrode active material and the amount of chalcogen added to the positive electrode film layer.

[0064] It should be noted that most of the Li2MO4 artificial CEI layer in the positive electrode film layer will adhere to the surface of the positive electrode active material, and some CEI layers may exist alone in the positive electrode film layer.

[0065] In some embodiments, the positive electrode active material includes Li x Ni a Co b A c O2, where A is Mn or Al, 0.2 ≤ x ≤ 1.2, 0.6 ≤ a < 1, 0 < b ≤ 0.2, and a + b + c = 1. That is, the positive electrode active material uses a high-nickel ternary positive electrode material. This can enable a secondary battery with a higher energy density.

[0066] The second aspect of the present application provides a method for preparing the secondary battery of the first aspect of the present application, the method comprising the following steps:

[0067] Mixing a solvent, a positive electrode active material and a chalcogen element to form a slurry, coating the slurry on a positive electrode current collector, and drying to obtain a positive electrode sheet; and

[0068] Assembling the negative electrode sheet and the positive electrode sheet into a dry cell, and injecting electrolyte into the dry cell to obtain a secondary battery;

[0069] Among them, the components of the electrolyte include solvents, lithium salts and additives that can combine with lithium ions to form chelates.

[0070] The preparation method of the present application is to add a chalcogen element to the positive electrode film layer. These chalcogen elements have strong reducing properties and can react with the surface of the positive electrode active material to produce Li2M2O3. At the same time, some transition metal ions on the surface of the positive electrode active material are reduced to rock salt phase DO through "solid solution", where D is one or more transition metal elements such as Ni, Co, and Mn. Taking sulfur as an example, the equation for the reaction between the chalcogen element and the surface of the positive electrode active material is shown in the following formula (1): 4LiDO2+2S→4DO+Li2S2O3+Li2O (1)

[0071] The resulting rock salt phase DO can act as a barrier to alleviate the side reactions between the internal positive electrode active material and the electrolyte solvent. In addition, during the initial charging process, that is, the formation stage, Li2S2O3 can be electrochemically oxidized to Li2SO4, forming an electrochemically stable Li2SO4 artificial CEI (positive electrode electrolyte interface film) layer; at the same time, residual lithium compounds such as Li2O and Li2CO3 on the surface of the positive electrode active material are removed, and the generated CO2 can be released together with other gases formed during the formation process of the lithium-ion secondary battery. The reaction equations of Li2S2O3 with residual lithium compounds on the surface of the positive electrode active material are shown in the following equations (2) to (5): Li2S2O3+5Li2O-8e - →2Li2SO4+8Li + (2) Li2S2O3+Li2CO3-8e - →2Li2SO4+5CO2+8Li + (3) 2LiDO2+S+2Li2O-4e - →2DO+Li2SO4+4Li + (4) 2LiDO2+S+2Li2CO3-4e - →2DO+Li2SO4+2CO2+4Li + (5)

[0072] Therefore, the sulfide element in the positive electrode film layer can, on the one hand, reduce the positive electrode active material LiDO2 and form a DO protective layer on the surface of the positive electrode active material; on the other hand, it can remove residual lithium compounds such as Li2O and Li2CO3 on the surface of the positive electrode active material and form an electrochemically stable Li2SO4 artificial CEI layer, thereby improving the first coulombic efficiency and storage performance of secondary batteries, especially secondary batteries using high-nickel ternary positive electrode materials, and can reduce the DCR of secondary batteries and improve battery rate performance and cycle performance.

[0073] However, the added chalcogen element in the positive electrode film may partially dissolve in the electrolyte to form ions. On the one hand, this may result in residual lithium compounds on the surface of the positive electrode active material that cannot be completely removed. On the other hand, the chalcogen element ions dissolved in the electrolyte will migrate to the negative electrode of the battery to form non-conductive chalcogen element lithium compounds, such as Li2S. These lithium compounds on the negative electrode surface will reduce the conductivity of the battery negative electrode, thereby deteriorating the kinetic performance of the negative electrode, increasing the battery's DCR, and reducing the battery's rate performance.

[0074] In this regard, the present application adds an additive that can combine with lithium ions to form a chelate in the electrolyte. The additive can form a chelate phase with the lithium ions in the electrolyte, making it more difficult for the sulfide elements dissolved in the electrolyte to combine with the lithium ions in the electrolyte, thereby inhibiting the migration of free sulfide ions in the electrolyte to the negative electrode of the battery, and inhibiting the dissolution of the sulfide element in the electrolyte, so that the sulfide element is more inclined to play a role in removing residual lithium compounds on the surface of the positive electrode active material at the positive electrode of the battery; thereby improving the degree of removal of residual lithium compounds on the surface of the positive electrode active material, improving the situation where the battery dynamics and cycle performance are reduced due to the combination of sulfide ions in the electrolyte with lithium ions, thereby further reducing the battery DCR and further improving the battery rate performance and cycle performance.

[0075] Specifically, the lithium ions in the electrolyte are mainly solvated lithium ions. After being released from the positive electrode, the lithium ions will undergo a solvation reaction with the electrolyte, undergo a desolvation reaction on the SEI film of the negative electrode, and then be embedded in the negative electrode active material. When the electrolyte does not contain additives that can combine with lithium ions to form chelates, a small number of lithium ions that have been desolvated and not embedded in the negative electrode active material will react with the free sulfide ions on the surface of the negative electrode SEI film to form insoluble lithium sulfide, thereby affecting battery performance. When an additive that can combine with lithium ions to form chelates is added to the electrolyte, a small number of lithium ions that have been desolvated and not embedded in the negative electrode active material will be chelated and fixed by the chelating additive, and will not react with the free sulfide ions on the surface of the negative electrode SEI film; thereby improving the battery's rate performance and kinetics.

[0076] In some embodiments, the chalcogen element includes one or more of sulfur, selenium, and tellurium. In some specific embodiments, the chalcogen element is sulfur. It is understood that the chalcogen element in the positive electrode film layer can be any one of sulfur, selenium, and tellurium, or a combination of two or more of the aforementioned elements.

[0077] In some embodiments, the mass of the elemental chalcogen in the positive electrode slurry is 0.01% to 5% of the mass of the positive electrode active material. The amount of elemental chalcogen in the positive electrode slurry within this range can effectively remove residual lithium compounds on the surface of the positive electrode active material and reduce the adverse effects of excessive chalcogen dissolution in the electrolyte on the performance of the secondary battery.

[0078] It will be understood that the mass of the chalcogen element can be, but is not limited to, 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.15%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.2%, 4.5%, 4.8%, and 5% of the mass of the positive electrode active material.

[0079] In some embodiments, the mass of the elemental chalcogen in the positive electrode slurry is 0.35% to 1% of the mass of the positive electrode active material. This effectively removes residual lithium compounds on the surface of the positive electrode active material while further mitigating the adverse effects of chalcogen dissolution in the electrolyte on secondary battery performance.

[0080] In some embodiments, based on the total mass of the electrolyte, the mass fraction of the additive capable of combining with lithium ions to form a chelate is 0.01% to 3%. Taking into account the effect of making the chelate additive have a better chelating Li and not affecting the performance of the battery cell, the amount of the additive is preferably limited to the above range. It is understood that the mass fraction of the additive capable of combining with lithium ions to form a chelate in the electrolyte can be but is not limited to 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%.

[0081] In some embodiments, the mass fraction of the additive capable of forming a chelate complex with lithium ions is 0.05% to 0.1% based on the total mass of the electrolyte, thereby further improving the cycle performance and rate performance of the secondary battery and reducing the battery DCR (direct current resistance).

[0082] In some embodiments, the positive electrode active material is a high nickel ternary positive electrode material, including Li x Ni a Co b A c O2, wherein A is Mn or Al, 0.2≤x≤1.2, 0.6≤a<1, 0<b≤0.2, a+b+c=1. In this way, the secondary battery can have a higher energy density.

[0083] In some embodiments, the mass fraction of residual lithium compounds on the surface of the positive electrode active material constituting the slurry is 0.1% to 2.0%. In other words, the positive electrode active material used to prepare the positive electrode slurry has a mass fraction of 0.1% to 2.0% of residual lithium on the surface.

[0084] In some embodiments, the solvent in the electrolyte can be selected from one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and tetrahydrofuran.

[0085] In some embodiments, the lithium salt in the electrolyte can be one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, and lithium trifluoromethanesulfonate. The concentration of the lithium salt in the electrolyte can be 0.5 mol / L to 1.5 mol / L, preferably 0.8 mol / L to 1.2 mol / L.

[0086] The third aspect of the present application further provides an electrical device, which includes one or more of the secondary battery of the first aspect of the present application and the secondary battery prepared by the preparation method of the second aspect of the present application.

[0087] The secondary battery and the electric device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0088] Unless otherwise specified, the components, material types, or contents of the batteries mentioned are applicable to both lithium-ion secondary batteries and sodium-ion secondary batteries.

[0089] In one embodiment of the present application, a secondary battery is provided.

[0090] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0091] Positive electrode

[0092] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

[0093] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0095] In some embodiments, the positive electrode active material may include a positive electrode active material for a battery known in the art.

[0096] As a non-limiting example, the positive electrode active material of the lithium-ion secondary battery may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, 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 and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, 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 manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc.; Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.1 Al 0.05 O2.

[0097] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0098] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0099] As non-limiting examples, the positive electrode active material of a sodium ion secondary battery may include one or more of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries may also be used.

[0100] As an optional technical solution of the present application, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1.

[0101] As an optional technical solution of the present application, the polyanionic compound can be a compound having sodium ions, transition metal ions and tetrahedral (YO4) n-A class of compounds with anionic units. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; Y can be one or more of P, S and Si; n represents (YO4) n- valence.

[0102] Polyanionic compounds can also be sodium ions, transition metal ions, tetrahedral (YO4) n- A class of compounds containing anion units and halogen anions. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be one or more of P, S, and Si, and n represents (YO4) n- valence state; the halogen can be one or more of F, Cl and Br.

[0103] Polyanionic compounds can also be sodium ions, tetrahedral (YO4) n- Anion unit, polyhedron unit (ZO y ) m+ and an optional halogen anion. Y can be one or more of P, S and Si, and n represents (YO4) n- valence state; Z represents a transition metal, which can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce; m represents (ZO y ) m+ valence state; the halogen can be one or more of F, Cl and Br.

[0104] Polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y One or more of (0≤y≤1).

[0105] Prussian blue compounds can be sodium ions, transition metal ions and cyanide ions (CN - ) compounds. The transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Prussian blue compounds are, for example, Na a Me b Me' c (CN)6, wherein Me and Me' are each independently one or more of Ni, Cu, Fe, Mn, Co and Zn, 0<a≤2, 0<b<1, 0<c<1.

[0106] The weight ratio of the positive electrode active material in the positive electrode film layer is 80 to 100 weight percent based on the total weight of the positive electrode film layer.

[0107] In some embodiments, the positive electrode film layer may further optionally include a binder. As a non-limiting example, the 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 acrylate resin. The weight ratio of the binder in the positive electrode film layer is 0 to 20 weight%, based on the total weight of the positive electrode film layer.

[0108] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0 to 20% by weight, based on the total weight of the positive electrode film layer.

[0109] Negative electrode

[0110] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0111] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0112] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. Among them, in the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0113] In some embodiments, the negative electrode active material may be a negative electrode active material for batteries known in the art.

[0114] As a non-limiting example, the negative electrode active material of the lithium-ion secondary battery may include one or more of the following materials: artificial graphite, natural 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 oxides, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0115] As a non-limiting example, the negative active material of the sodium ion secondary battery is generally a hard carbon material, a two-dimensional metal carbide or a nitride. Preferably, the negative active material of the sodium ion secondary battery is generally a hard carbon material.

[0116] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0117] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0119] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 to 10000 mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 to 220 g / m 2 The compaction density of the negative electrode can be 1.0g / cm 3 ~1.8g / cm 3 .

[0120] electrolytes

[0121] The electrolyte conducts ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0122] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0123] In some embodiments, the electrolyte salt of the lithium ion secondary battery may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0124] In some embodiments, the solvent may include one or more of fluoroethylene carbonate (FEC), 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), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0125] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0126] Isolation film

[0127] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0128] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0129] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may optionally be 12 μm to 20 μm.

[0130] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0131] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0132] 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 shell, such as a pouch-type soft shell. The material of the soft shell can be plastic. Further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0133] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0134] In this application, unless otherwise specified, "secondary battery" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode, a negative electrode, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrodes. The electrolyte plays the role of conducting active ions between the positive and negative electrodes.

[0135] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 having a square structure as an example.

[0136] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0137] In some embodiments, the battery cells 5 can be assembled into a battery module. The number of battery cells 5 contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0138] In the battery module, the plurality of battery cells 5 can be arranged in sequence along the length of the battery module. Of course, they can also be arranged in any other manner. Furthermore, the plurality of battery cells 5 can be fixed by fasteners.

[0139] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0140] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0141] A battery pack may include a battery box and multiple battery modules disposed within the box. The battery box comprises an upper case and a lower case. The upper case can be placed over the lower case to form an enclosed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0142] In addition, the present application also provides an electric device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as 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., but is not limited thereto.

[0143] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0144] FIG3 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0145] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0146] The following are some examples.

[0147] In order to make the technical problems, technical solutions and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0148] If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. All reagents or instruments used without specifying the manufacturer are commercially available conventional products.

[0149] 1. Implementation

[0150] Example 1:

[0151] 1) Preparation of positive electrode sheet

[0152] (1) Dispersing sulfur in an organic solvent, N-methylpyrrolidone (NMP), stirring at a speed of 400 to 1000 r / s for 0.5 h to fully dissolve the sulfur, and preparing a sulfur solution with a concentration of 1 mol / L;

[0153] (2) The positive electrode active material ternary lithium, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methylpyrrolidone (NMP) in a mass ratio of 97:1:1, and stirred evenly to obtain a positive electrode slurry; wherein the positive electrode active material is a nickel-rich layered oxide positive electrode material, and its molecular formula is LiNi 0.8 Co 0.1 Mn 0.1 O2;

[0154] (3) adding the sulfur element solution prepared in step (1) to the positive electrode slurry prepared in step (2), and mixing them uniformly to obtain a positive electrode slurry containing sulfur element; wherein the stirring speed is maintained at 400 rpm to 1000 rpm, and the stirring time is 0.5 h to 6 h;

[0155] (4) coating the positive electrode slurry prepared in step (3) on the positive electrode current collector aluminum foil;

[0156] (5) The coated current collector obtained in step (4) was placed in an oven and dried at 90°C, followed by cold pressing and slitting to obtain a positive electrode sheet. The mass of the chalcogen element in the positive electrode film layer was 0.35% of the mass of the nickel-rich layered oxide positive electrode material, and the surface density of the positive electrode film layer was 0.290g / 1540.25mm 2 The thickness of the positive electrode film layer on one side of the current collector is 66μm.

[0157] 2) Preparation of negative electrode sheet

[0158] The negative electrode active material graphite, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC) and binder styrene butadiene rubber (SBR) are dissolved in deionized water at a mass ratio of 96:1:2:1, mixed evenly and prepared into a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil once or multiple times and dried at 90°C, cold pressed and cut to obtain the negative electrode sheet. The surface density of the negative electrode film layer is 0.181g / 1540.25mm 2 The thickness of the negative electrode film layer on one side of the current collector is 75μm.

[0159] 3) Isolation film

[0160] A polyethylene film with a thickness of 12 μm was used as the separator.

[0161] 4) Electrolyte

[0162] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, LiPF6 lithium salt was added and dissolved in the organic solvent to prepare a 1 mol / L LiPF6 electrolyte, and 0.05% of hydroxyethylidene diphosphonic acid (chelating additive) relative to the weight of the electrolyte was added to the 1 mol / L LiPF6 electrolyte and stirred to obtain an electrolyte.

[0163] 5) Battery assembly

[0164] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as an insulator. The sheets are then wound, the tabs welded, and placed in an aluminum shell. The cells are then baked at 105°C to remove moisture. Electrolyte is then injected and sealed to produce an uncharged secondary battery cell. The uncharged cells then undergo a series of processes, including resting, hot and cold pressing, formation, shaping, and capacity testing, to produce lithium-ion secondary battery cells. After the formation process, a positive-electrolyte interface film containing Li2MO4 forms within the positive electrode film layer.

[0165] Example 2:

[0166] This embodiment is basically the same as embodiment 1, except that the content of hydroxyethylidene diphosphonic acid, an additive capable of forming a chelate with lithium ions, in the electrolyte is different. The content of hydroxyethylidene diphosphonic acid in the electrolyte of the secondary battery of this embodiment is 0.01%.

[0167] Example 3:

[0168] This embodiment is basically the same as embodiment 1, except that the content of hydroxyethylidene diphosphonic acid, an additive capable of forming a chelate with lithium ions, in the electrolyte is different. The content of hydroxyethylidene diphosphonic acid in the electrolyte of the secondary battery of this embodiment is 0.1%.

[0169] Example 4:

[0170] This embodiment is basically the same as embodiment 1, except that the content of hydroxyethylidene diphosphonic acid, an additive capable of forming a chelate with lithium ions, in the electrolyte is different. The content of hydroxyethylidene diphosphonic acid in the electrolyte of the secondary battery of this embodiment is 3%.

[0171] Example 5:

[0172] This embodiment is basically the same as embodiment 1, except that the content of hydroxyethylidene diphosphonic acid, an additive capable of forming a chelate with lithium ions, in the electrolyte is different. The content of hydroxyethylidene diphosphonic acid in the electrolyte of the secondary battery of this embodiment is 5%.

[0173] Example 6:

[0174] This embodiment is substantially the same as embodiment 3, with the only difference being that the type of additive in the electrolyte that can form a chelate with lithium ions is different. The additive in the electrolyte of the secondary battery of this embodiment is dimethyl oxalate.

[0175] Example 7:

[0176] This embodiment is substantially the same as embodiment 3, with the only difference being that the type of additive in the electrolyte that can form a chelate with lithium ions is different. The additive in the electrolyte of the secondary battery of this embodiment is diethyl oxalate.

[0177] Example 8:

[0178] This embodiment is basically the same as embodiment 3, except that the type of additive in the electrolyte that can form a chelate with lithium ions is different. The additive in the electrolyte of the secondary battery of this embodiment is diethyl hydroxyethylidene diphosphonate.

[0179] Example 9:

[0180] This embodiment is substantially the same as embodiment 3, with the only difference being the content of the chalcogen element in the positive electrode film layer. In this embodiment, the mass of the chalcogen element in the positive electrode film layer is 0.01% of the mass of the nickel-rich layered oxide positive electrode material.

[0181] Example 10:

[0182] This embodiment is substantially the same as embodiment 3, with the only difference being the content of the chalcogen element in the positive electrode film layer. In this embodiment, the mass of the chalcogen element in the positive electrode film layer is 1.00% of the mass of the nickel-rich layered oxide positive electrode material.

[0183] Example 11:

[0184] This embodiment is basically the same as embodiment 3, except that the content of the chalcogen element in the positive electrode film is different. In this embodiment, the mass of the chalcogen element in the positive electrode film is 2.00% of the mass of the nickel-rich layered oxide positive electrode material.

[0185] Example 12:

[0186] This embodiment is substantially the same as embodiment 3, with the only difference being the content of the chalcogen element in the positive electrode film layer. In this embodiment, the mass of the chalcogen element in the positive electrode film layer is 4.00% of the mass of the nickel-rich layered oxide positive electrode material.

[0187] Example 13:

[0188] This embodiment is basically the same as embodiment 3, except that the content of the chalcogen element in the positive electrode film is different. In this embodiment, the mass of the chalcogen element in the positive electrode film is 5.00% of the mass of the nickel-rich layered oxide positive electrode material.

[0189] Example 14:

[0190] This embodiment is substantially the same as embodiment 3, with the only difference being that the type of the chalcogen element in the positive electrode film layer is different. In this embodiment, the chalcogen element in the positive electrode film layer is selenium.

[0191] Example 15:

[0192] This embodiment is substantially the same as embodiment 3, with the only difference being the type of the chalcogen element in the positive electrode film layer. In this embodiment, the chalcogen element in the positive electrode film layer is tellurium.

[0193] 2. Comparative Example

[0194] Comparative Example 1:

[0195] This comparative example is substantially the same as Example 1, except that no additive capable of combining with lithium ions to form a chelate is added to the electrolyte.

[0196] Comparative Example 2:

[0197] This comparative example is substantially the same as Example 1, except that no additive capable of combining with lithium ions to form a chelate is added to the electrolyte, and no chalcogen element is added to the positive electrode film layer.

[0198] 3. Test Method

[0199] 1) 25℃ DCR ​​test

[0200] At 25°C, the prepared secondary battery was charged at a constant current of 1 / 3C to 4.25V, and then charged at a constant voltage of 4.25V to a current of 0.05C. After standing for 30 minutes, the voltage U1 was recorded; then it was discharged at 1 / 3C for 30 seconds, and the voltage U2 was recorded; then the internal resistance DCR of the secondary battery before storage was calculated based on the formula (U2-U1) / 1 / 3C.

[0201] 2) Rate performance test

[0202] At 25°C, the lithium-ion secondary battery is first charged to 4.25V at a constant current of 0.33C; further charged at a constant voltage of 4.25V to a current of 0.05C, and left for 30 minutes; then the lithium-ion secondary battery is discharged to 2.8V at a constant current of 0.3C, and the discharge capacity this time is recorded as Cap1, that is, the 0.33C initial capacity (mAh); then the above 0.33C charging step is repeated, left for 30 minutes, and then the lithium-ion battery is discharged to 2.8V at a constant current of 0.5C, and the discharge capacity this time is recorded as Cap2. 0.5C capacity retention rate (%) M1 = [Cap2 / Cap1] × 100%.

[0203] Repeat the above 0.33C charging step again and let it sit for 30 minutes; then discharge the lithium-ion battery to 2.8V at a constant current of 1C. The discharge capacity this time is recorded as Cap3, and the 1C capacity retention rate (%) M2 = [Cap3 / Cap1] × 100%.

[0204] 3) 0.33C cycle capacity retention test

[0205] At 25°C, the lithium-ion secondary battery is first charged to 4.25V at a constant current of 0.33C, and then charged to a current of 0.05C at a constant voltage of 4.25V and left for 30 minutes; then the lithium-ion secondary battery is discharged to 2.8V at a constant current of 0.33C. This is a charge and discharge cycle process; the discharge capacity this time is the discharge capacity of the first cycle, recorded as Cap4. The lithium-ion secondary battery is subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity of the 100th cycle is taken and recorded as Cap5. The capacity retention rate (%) of the lithium-ion secondary battery after 100 cycles is M3 = [Cap5 / Cap4] × 100%. The larger the M3 value, the smaller the capacity loss of the battery and the better the cycle performance.

[0206] 4) 1C cycle capacity retention test

[0207] At 25°C, first charge the lithium-ion battery to 4.25V at a constant current of 1C; further charge at a constant voltage of 4.25V to a current of 0.05C and leave it for 30 minutes; then discharge the lithium-ion battery to 2.8V at a constant current of 1C. This is a charge and discharge cycle process; the discharge capacity this time is the discharge capacity of the first cycle, recorded as Cap6. The lithium-ion battery is subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity of the 100th cycle is taken and recorded as Cap7. The capacity retention rate (%) of the lithium-ion battery after 100 cycles is M4 = [Cap7 / Cap6] × 100%. The larger the M4 value, the smaller the capacity loss of the battery and the better the cycle performance.

[0208] 5) First Coulombic efficiency test

[0209] At 25°C, the lithium-ion battery after injection is subjected to the first formation charge. The lithium-ion battery is charged to 4.25V at a constant current of 0.3C, and further charged at a constant voltage of 4.25V to a current of 0.05C. The first charge capacity is recorded and recorded as Cap8. The lithium-ion battery is then discharged to 2.8V at a constant current of 0.3C, and the first discharge capacity is recorded and recorded as Cap9. The first coulombic efficiency (%) of the lithium-ion battery is M5 = [Cap9 / Cap8] × 100%. The larger the M5 value, the better the reversibility of the battery and the better the kinetic performance.

[0210] 6) Storage capacity retention test

[0211] At 25°C, the lithium-ion battery is first charged to 4.25V at a constant current of 0.3C, then charged to a current of 0.05C at a constant voltage of 4.25V, and then discharged to 2.8V at a constant current of 0.3C. This is a charge and discharge cycle process. The discharge capacity this time is the discharge capacity before the first storage, recorded as Cap10. The battery is then charged to 4.25V according to the above method and placed in a constant temperature box at 60°C for 60 days. After 60 days, the battery is taken out and cooled to 25°C, and a charge and discharge test is performed in the above manner. The discharge capacity this time is the discharge capacity after 60 days of storage, recorded as Cap11. The capacity retention rate (%) of the lithium-ion battery stored at 60°C for 60 days is M6 = [Cap11 / Cap10] × 100%. The larger the M6 ​​value, the smaller the battery capacity loss and the better the improvement effect.

[0212] The parameters and performance test results of the secondary batteries of the above-mentioned embodiments and comparative examples of the present application are shown in Tables 1 and 2. In Tables 1 and 2, "S" represents an embodiment, such as S1 represents embodiment 1, S2 represents embodiment 2, and so on; similarly, "D" represents a comparative example, such as D1 represents comparative example 1, and D2 represents comparative example 2.

[0213] Table 1

[0214] Table 2

[0215] From the data in Table 1 and Table 2, we can see that:

[0216] In each embodiment of the present application, a chalcogen element is added to the positive electrode slurry, and an additive that can combine with lithium ions to form a chelate is added to the electrolyte. The secondary battery formed has a lower DCR, better rate performance, better cycle performance, higher first coulombic efficiency and better storage performance.

[0217] Among them, by comparing Examples 1 to 5, it can be seen that by controlling the amount of the additive capable of combining with lithium ions to form a chelate in the electrolyte within the range of 0.05% to 3%, the rate performance, cycle performance, first coulombic efficiency and storage performance of the secondary battery can be further improved, and the DCR of the secondary battery can be further reduced; by controlling the amount of the additive in the electrolyte within the range of 0.05% to 0.1%, the rate performance, cycle performance, first coulombic efficiency and storage performance of the secondary battery can be further improved, and the DCR of the secondary battery can be further reduced.

[0218] By comparing Example 3 and Examples 9 to 13, it can be seen that controlling the amount of chalcogen element added to the positive electrode slurry to 0.35% to 1% of the mass of the positive electrode active material can further improve the rate performance, cycle performance, first coulombic efficiency and storage performance of the secondary battery, and further reduce the DCR of the secondary battery.

[0219] It can be seen from Comparative Example 2 that when no additive capable of combining with lithium ions to form a chelate is added to the electrolyte, and no sulfide element is added to the positive electrode film layer, the DCR of the secondary battery is high, and the rate performance, cycle performance, first coulombic efficiency and storage performance of the secondary battery are all poor.

[0220] As can be seen from Comparative Example 1, which only adds a chalcogen element to the positive electrode slurry without adding an additive capable of forming a chelate with lithium ions to the electrolyte, the secondary battery of Comparative Example 1 has a higher DCR than the aforementioned examples, while the secondary battery's rate performance, cycle performance, initial coulombic efficiency, and storage performance are all poor. However, because Comparative Example 1 adds a chalcogen element to the positive electrode slurry, it can form a positive electrode electrolyte interface film containing Li2MO4. The secondary battery's DCR is lower than that of Comparative Example 2, while its rate performance, cycle performance, initial coulombic efficiency, and storage performance are all superior to those of Comparative Example 2.

[0221] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0222] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; The positive electrode sheet includes a positive electrode film layer, the positive electrode film layer includes a positive electrode active material and a positive electrode electrolyte interface film, and the positive electrode electrolyte interface film includes Li2MO4, wherein M includes a chalcogen element; The electrolyte includes a solvent and a lithium salt, and also includes at least one of a lithium metal chelate and an additive capable of combining with lithium ions to form a chelate.

2. The secondary battery according to claim 1, wherein The additive includes one or more of organic phosphonic acid, phosphonate and oxalate.

3. The secondary battery according to claim 2, wherein: The organic phosphonic acid includes one or more of hydroxyethylidene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid and ethylenediamine tetramethylene phosphonic acid.

4. The secondary battery according to claim 2 or 3, wherein: The phosphonate includes one or more of diethyl hydroxyethylidene diphosphonate, dimethyl hydroxyethylidene diphosphonate and dipropyl hydroxyethylidene diphosphonate.

5. The secondary battery according to any one of claims 2 to 4, wherein The oxalate ester includes one or more of dimethyl oxalate, diethyl oxalate, dipropyl oxalate and dibutyl oxalate.

6. The secondary battery according to any one of claims 1 to 5, wherein The lithium metal chelate includes one or more of a chelate formed by lithium ions and organic phosphonic acid, a chelate formed by lithium ions and phosphonic acid ester, and a chelate formed by lithium ions and oxalic acid ester.

7. The secondary battery according to any one of claims 1 to 6, wherein The chalcogen element includes one or more of sulfur, selenium and tellurium.

8. The secondary battery according to any one of claims 1 to 7, wherein The mass of Li2MO4 in the positive electrode electrolyte interface film is 0.1% to 4.5% of the mass of the positive electrode active material.

9. The secondary battery according to any one of claims 1 to 8, wherein The thickness of the positive electrode electrolyte interface film on the surface of the positive electrode active material is 5 nm to 20 nm.

10. The secondary battery according to any one of claims 1 to 9, wherein The thickness of the positive electrode electrolyte interface film on the surface of the positive electrode active material is 5 nm to 10 nm.

11. The secondary battery according to any one of claims 1 to 10, wherein The positive electrode active material includes Li x Ni a Co b A c O2, wherein A includes at least one of Mn and Al, 0.2≤x≤1.2, 0.6≤a<1, 0<b≤0.2, a+b+c=1.

12. The secondary battery according to any one of claims 1 to 11, wherein The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, and lithium trifluoromethanesulfonate.

13. The secondary battery according to any one of claims 1 to 12, wherein The concentration of the lithium salt in the electrolyte is 0.5 mol / L to 1.5 mol / L.

14. The secondary battery according to any one of claims 1 to 13, wherein The concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.2 mol / L.

15. The secondary battery according to any one of claims 1 to 14, wherein The solvent includes one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and tetrahydrofuran.

16. A method for preparing a secondary battery according to any one of claims 1 to 15, comprising the following steps: Mixing a solvent, a positive electrode active material and a chalcogen element to form a slurry, coating the slurry on a positive electrode current collector, and drying to obtain a positive electrode sheet; and Assembling the negative electrode sheet and the positive electrode sheet into a dry cell, and injecting electrolyte into the dry cell to obtain a secondary battery; in, The electrolyte comprises raw materials including a solvent, a lithium salt and an additive capable of combining with lithium ions to form a chelate.

17. The method for preparing a secondary battery according to claim 16, wherein: The mass of the chalcogen element in the slurry is 0.01% to 5% of the mass of the positive electrode active material.

18. The method for preparing a secondary battery according to claim 16 or 17, wherein: The mass of the chalcogen element in the slurry is 0.35% to 1% of the mass of the positive electrode active material.

19. The method for preparing a secondary battery according to any one of claims 16 to 18, wherein: Based on the total mass of the electrolyte, the mass fraction of the additive is 0.01% to 3%.

20. The method for preparing a secondary battery according to any one of claims 16 to 19, wherein: Based on the total mass of the electrolyte, the mass fraction of the additive is 0.05% to 0.1%.

21. The method for preparing a secondary battery according to any one of claims 16 to 20, wherein: The surface of the positive electrode active material has residual lithium compounds, and the mass of the residual lithium compounds is 0.1% to 2.0% of the mass of the positive electrode active material.

22. An electrical device comprising one or more of the secondary battery according to any one of claims 1 to 15 and the secondary battery prepared by the preparation method according to any one of claims 16 to 21.

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