Positive pole piece, secondary battery and electric device

Abstract

The invention relates to a positive pole piece, a secondary battery and an electric device. The positive pole piece is characterized by comprising a positive current collector and a positive material layer arranged on at least one surface of the positive current collector, and the positive material layer comprises a positive active material and a lithium supplement agent with coulombic efficiency less than or equal to 90%. According to the invention, the cycle life of the secondary battery can be effectively prolonged.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode sheet, a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, as the application scope of lithium-ion batteries has become more and more extensive, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As lithium-ion batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance. In addition, as the choice of positive electrode active materials is increasingly limited, introducing lithium supplements into the materials is one of the ways to improve the cycle performance.

[0004] However, the cycle performance of current lithium-ion batteries still needs to be further improved. Summary of the invention

[0005] The present application provides a positive electrode sheet that can effectively improve the cycle performance of a battery, as well as a secondary battery and an electrical device comprising the positive electrode sheet.

[0006] In a first aspect of the present application, a positive electrode plate is provided, comprising a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises a positive electrode active material and a lithium supplement, and the coulombic efficiency of the lithium supplement is ≤90%.

[0007] The positive electrode plate can effectively improve the cycle life of the secondary battery by using a lithium replenisher with low coulombic efficiency to replenish lithium. In addition, the test also found that the addition of a lithium replenisher with low coulombic efficiency can also reduce the early attenuation during the cycle.

[0008] In some embodiments, the coulombic efficiency of the lithium supplement is 70% to 90%; optionally, the coulombic efficiency of the lithium supplement is 75% to 85%. Reasonable control of the coulombic efficiency of the lithium supplement is conducive to further improving the cycle performance of the secondary battery.

[0009] In some embodiments, the upper limit of the working voltage range of the lithium supplement is denoted as P max , the lower limit is recorded as P min The upper limit of the working voltage range of the positive electrode active material is denoted as P` max , the lower limit is recorded as P` min , P max >P` max , P`max >P min ≥P` min In this way, during the working process of the secondary battery (the working voltage range is usually the working voltage range of the positive electrode active material), effective lithium replenishment can be achieved and the instability of the structure of the positive electrode active material can be reduced.

[0010] In some embodiments, the operating voltage range of the lithium supplement is 2V to 4.5V; the operating voltage range of the positive electrode active material is 2V to 4.1V.

[0011] In some embodiments, the lithium supplement includes one or more of ternary materials, lithium-rich lithium iron oxide, and lithium-rich lithium nickel oxide; optionally, the ternary material includes one or two of ternary NCM materials and ternary NCA materials. Using a suitable type of lithium supplement can further improve the cycle performance.

[0012] In some embodiments, the positive electrode active material includes one or both of lithium iron phosphate and lithium iron manganese phosphate.

[0013] In some embodiments, the mass percentage of the lithium supplement agent is 1% to 10% based on the mass in the positive electrode material layer; optionally, the mass percentage of the lithium supplement agent is 3% to 7%. Reasonable control of the proportion of the lithium supplement agent in the positive electrode material layer can further improve the cycle performance.

[0014] In some embodiments, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 85% to 90%.

[0015] A second aspect of the present application provides a secondary battery, comprising the positive electrode sheet described in the first aspect.

[0016] In some embodiments, the operating voltage of the secondary battery is P0, P` min ≤P0≤P` max ;

[0017] Among them, P` min Represents the lower limit of the working voltage range of the positive electrode active material in the positive electrode plate; P` max Indicates the upper limit of the working voltage range of the positive electrode active material in the positive electrode plate;

[0018] Optionally, the operating voltage of the secondary battery is 2V to 4.1V.

[0019] A third aspect of the present application provides an electrical device comprising at least one of the positive electrode sheet described in the first aspect and the secondary battery described in the second aspect.

[0020] 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

[0021] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the 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 of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0022] Figure 1 A schematic diagram of a battery cell according to an embodiment of the present application;

[0023] Figure 2 for Figure 1 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0024] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0025] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application;

[0026] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0027] Figure 6 A schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0028] Description of reference numerals:

[0029] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0030] Below, some embodiments of the positive electrode sheet, secondary battery and electrical 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 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.

[0031] The "range" disclosed in the present application can be defined in the form of a lower limit and an 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 boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and 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 a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 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 also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both 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 listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0032] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0035] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean 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 internal logic. If there is no special explanation, all steps of the present application can 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 also include step (c), indicating that step (c) can 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.

[0036] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., 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 including 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 not only includes a1, a2 and a3, but also includes other members". In the present 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.

[0037] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0038] Some traditional methods use ternary materials as lithium supplements to improve the cycle performance of secondary batteries. However, these methods usually supplement lithium at a higher working voltage. When the working voltage is higher than that of the positive electrode active material, the structural stability of the positive electrode active material will decrease, leading to deterioration of the cycle performance. In general, the cycle performance of secondary batteries has not been effectively improved.

[0039] Through research, the present application has found that by using a lithium replenisher with low coulombic efficiency for lithium replenishment, the lithium embedded in the negative electrode in each cycle is much greater than the lithium removed from the negative electrode, and the remaining lithium will remain in the negative electrode (which can be characterized by XRD), and the negative electrode plate will continue to be irreversibly replenished with lithium, achieving the effect of slow-release lithium replenishment, thereby effectively improving the cycle life of the secondary battery. In addition, the test also found that the addition of a lithium replenisher with low coulombic efficiency can also reduce the early attenuation during the cycle. In addition, since there is no need to use a high operating voltage, the problem of structural stability of the above-mentioned materials can be improved.

[0040] Based on this, some examples of the present application provide a positive electrode plate, including a positive electrode collector and a positive electrode material layer arranged on at least one surface of the positive electrode collector, the positive electrode material layer contains a positive electrode active material and a lithium supplement, and the coulombic efficiency of the lithium supplement is ≤90%.

[0041] Without limitation, the coulombic efficiency of a material can be determined by a reverse charge test.

[0042] In some examples, the coulombic efficiency of the lithium supplement is 70% to 90%. Reasonable control of the coulombic efficiency of the lithium supplement is conducive to further improving the cycle performance of the secondary battery. Specifically, the coulombic efficiency of the lithium supplement includes but is not limited to: 70%, 75%, 80%, 85%, 90% or a range between any two of the foregoing. Further, the coulombic efficiency of the lithium supplement is 75% to 85%.

[0043] In some examples, the upper limit of the working voltage range of the lithium supplement is denoted as P max , the lower limit is recorded as P min The upper limit of the working voltage range of the positive electrode active material is denoted as P` max , the lower limit is recorded as P` min , P max >P` max , P` max >P min ≥P` min In this way, during the working process of the secondary battery (the working voltage range is usually the working voltage range of the positive electrode active material), both effective lithium replenishment and reduced instability of the structure of the positive electrode active material can be achieved. Without limitation, the working voltage range of the material refers to the range from the starting voltage to the ending voltage under the optimal charge and discharge working conditions of the material, which can be determined by the charge and discharge curve of the material.

[0044] Furthermore, the operating voltage of the secondary battery containing the positive electrode plate is P0, P` min ≤P0≤P` maxOn the one hand, this can reduce the instability of the structure of the positive electrode active material. On the other hand, under this operating voltage, the lithium supplement will partially participate in the cycle, so as to release lithium in batches and slowly, further improving the cycle performance of the secondary battery. Without limitation, the operating voltage of a secondary battery refers to the voltage range of the battery during normal charge and discharge operation, which is usually the operating voltage range of the positive electrode active material and can be set manually.

[0045] In some of the examples, the operating voltage range of the lithium supplement is 2V to 4.5V; the operating voltage range of the positive electrode active material is 2V to 4.1V.

[0046] In some examples, the lithium supplement includes one or more of ternary materials, lithium-rich lithium iron oxide and lithium-rich lithium nickel oxide. The use of a suitable type of lithium supplement can further improve the cycle performance. In addition, the overall capacity of the positive electrode plate can be improved. Without limitation, the ternary material includes one or two of a ternary NCM material and a ternary NCA material. It can be understood that "lithium-rich" means that the molar content of lithium in the material molecular formula is greater than 1. For example, the molecular formula of lithium-rich lithium iron oxide is Li x FeO2, 1<x<2, the molecular formula of lithium-rich nickel oxide is Li x NiO2, 1<x<2. In addition, it can be understood that the coulombic efficiency of the material is also related to the material preparation process, so the same lithium supplement can present different coulombic efficiencies, and its more specific types, such as the brand of the ternary material, etc., may not be limited.

[0047] In some of the examples, the mass percentage of the lithium supplement agent is 1% to 10% based on the mass in the positive electrode active layer. Reasonable control of the proportion of the lithium supplement agent in the positive electrode material layer can further improve the cycle performance. At the same time, it can also facilitate the preparation process of the positive electrode pole piece and reduce the impact of the introduction of the lithium supplement agent on the characteristics of the positive electrode active material itself. Specifically, the mass percentage of the lithium supplement agent includes but is not limited to: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range between any two of the foregoing. Furthermore, the mass percentage of the lithium supplement agent is 3% to 7%.

[0048] In some examples, the mass percentage of the positive electrode active material is 85% to 90% based on the mass in the positive electrode active layer. Specifically, the mass percentage of the positive electrode active material includes but is not limited to: 85%, 86%, 87%, 88%, 89%, 90% or a range between any two of the foregoing.

[0049] In some other examples of the present application, a secondary battery is provided, comprising the positive electrode sheet as described above. The secondary battery has good cycle performance.

[0050] In some examples, the operating voltage of the secondary battery is P0, P` min ≤P0≤P` max ;

[0051] Among them, P` min Represents the lower limit of the working voltage range of the positive electrode active material in the positive electrode plate; P` max It represents the upper limit of the working voltage range of the positive electrode active material in the positive electrode sheet.

[0052] On the one hand, this can reduce the instability of the structure of the positive electrode active material. On the other hand, under this working voltage, the lithium supplement will partially participate in the cycle, achieving the release of lithium in batches and in a slow release, further improving the cycle performance.

[0053] In some of these examples, the operating voltage range of the lithium supplement is 2V to 4.5V;

[0054] In some of the examples, the working voltage range of the positive electrode active material is 2V to 4.1V.

[0055] In some of the examples, the operating voltage of the secondary battery is 2V to 4.1V.

[0056] In some other examples of the present application, an electrical device is provided, comprising at least one of the positive electrode plate described above and the secondary battery described above.

[0057] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0058] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0059] Positive electrode

[0060] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging 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 content of Li 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 content of Li in the positive electrode material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li 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 the new material obtained by appropriate modification on the basis of the listed positive electrode materials is also within the scope of the positive electrode material. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode material, and non-limiting examples include coating modification.

[0061] In the list of positive electrode materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0062] The positive electrode is as described above.

[0063] 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 material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0064] In some of the 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.

[0065] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries 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 (such as LiCoO2), 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 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 iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides 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 Co 0.2 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 0.15 Al 0.05 O2.

[0066] In some examples, the positive electrode active material includes one or both of lithium iron phosphate and lithium iron manganese phosphate.

[0067] In some of these embodiments, the positive electrode material layer may also 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.

[0068] In some embodiments, the positive electrode material layer may further 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.

[0069] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 to 25000 mPa·s. When the positive electrode slurry is applied, the coating unit surface density based on dry weight (excluding solvent) can be 15 to 35 mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0070] Negative electrode

[0071] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0072] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0073] In some of the 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. 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.

[0074] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, 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.

[0075] In some embodiments, the negative electrode active material layer may further 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).

[0076] In some embodiments, the negative electrode active material 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.

[0077] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0078] In some of the 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 collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode 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 10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75 to 220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0079] Electrolytes

[0080] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0081] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0082] In some of the embodiments, the electrolyte salt may include one or more of 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 difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0083] In some embodiments, the solvent may include 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), ethylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0084] In some embodiments, the electrolyte may further include additives, such as 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 or low temperature performance, etc.

[0085] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0086] Isolation film

[0087] 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 stability and mechanical stability can be selected.

[0088] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0089] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may be 12 to 20 μm.

[0090] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0091] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0092] 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, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0093] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0094] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0095] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 5 is a square structure as an example.

[0096] In some of these embodiments, reference Figure 2 , 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 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 form 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 actual needs.

[0097] The secondary battery may be a battery module 4 or a battery pack 1 .

[0098] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0099] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0100] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0101] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0102] Figure 4 and Figure 51 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0103] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0104] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0105] Figure 6 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0106] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0107] Example

[0108] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0109] Example 1

[0110] 1) Preparation of positive electrode

[0111] Lithium iron phosphate (LiFePO4), ternary NCM materials (LiNi 0.5 Co 0.2 Mn 0.3O2, Coulomb efficiency is 80%), binder polyvinylidene fluoride (PVDF), conductive carbon black are dispersed in solvent N-methylpyrrolidone in a weight ratio of 90%:5%:2%:3% and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is evenly coated on the double-side surface of the positive electrode current collector aluminum foil, and after drying at 120°C and cold pressing, a positive electrode sheet is obtained, wherein the coating amount per unit area on both sides is 0.27g / 1540.25mm 2 .

[0112] 2) Preparation of negative electrode sheet

[0113] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the adhesive styrene butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on both sides of the copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then super-cold pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides is 0.17g / 1540.25mm 2 .

[0114] 3) Isolation film

[0115] A 12μm thick polypropylene isolation film was selected.

[0116] 4) Preparation of electrolyte

[0117] The organic solvent is a mixed solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20:60. In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt LiPF6 is dissolved in the organic solvent and mixed evenly to obtain an electrolyte. The concentration of the lithium salt is 1 mol / L.

[0118] 5) Preparation of batteries

[0119] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role. Then, they are wound into a square bare battery cell, loaded with aluminum-plastic film, and then baked at 80°C to remove water. After that, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0120] The secondary batteries of Examples 2 to 15 are prepared in a similar manner to that of Example 1, but the coulombic efficiency, type, mass percentage of the lithium replenisher or the type of positive electrode active material used in the positive electrode plates are different, as shown in Table 1 below.

[0121] The preparation method of the secondary battery of Comparative Example 1 is similar to that of the secondary battery of Example 1, the main difference being that no lithium supplementing agent is added.

[0122] The preparation method of the secondary battery of Comparative Example 2 is similar to that of the secondary battery of Example 1, with the main difference being that the coulombic efficiency of the lithium supplement agent used is 95%.

[0123] Table 1

[0124]

[0125]

[0126] Test example:

[0127] The effect of lithium supplementation is verified by cycle testing as follows:

[0128] Cycle performance: At 25°C, charge at a constant current rate of 0.5C to the upper limit of the secondary battery working voltage in Table 1, then charge at a constant voltage to 0.05C, let stand for 10 minutes, then discharge at a current of 0.5C to 2.5V, then discharge at a current of 0.1C to the lower limit of the secondary battery working voltage in Table 1. Stop the test when the battery cell cycles to 80% SOH and record the number of cycles. At the same time, record the fading value of the first 500 cycles to characterize the effect of reducing the early attenuation.

[0129] The test results are shown in Table 2 below:

[0130] Table 2

[0131]

[0132]

[0133] It can be seen from the examples and comparative examples 1 to 2 that the present application introduces a lithium supplement with a low coulombic efficiency, which can significantly improve the cycle performance of the secondary battery and also reduce the early attenuation during the cycle.

[0134] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0135] 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 exerting the same effect within the scope of 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.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises a positive electrode active material and a lithium supplement, and the coulombic efficiency of the lithium supplement is ≤90%.

2. The positive electrode sheet according to claim 1, characterized in that: The coulombic efficiency of the lithium supplement is 70% to 90%; Optionally, the coulombic efficiency of the lithium supplement is 75% to 85%.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The upper limit of the working voltage range of the lithium supplement is denoted as P max , the lower limit is recorded as P min The upper limit of the working voltage range of the positive electrode active material is denoted as P` max , the lower limit is recorded as P` min , P max >P` max , P` max >P min ≥P` min .

4. The positive electrode sheet according to claim 3, characterized in that: The working voltage range of the lithium supplement is 2V to 4.5V; the working voltage range of the positive electrode active material is 2V to 4.1V.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The lithium supplement comprises one or more of ternary materials, lithium-rich lithium iron oxide and lithium-rich lithium nickel oxide; Optionally, the ternary material includes one or both of a ternary NCM material and a ternary NCA material.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The positive electrode active material includes one or both of lithium iron phosphate and lithium iron manganese phosphate.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The mass percentage of the lithium supplement agent is 1% to 10% based on the mass in the positive electrode material layer; Optionally, the mass percentage of the lithium supplement is 3% to 7%; Optionally, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 85% to 90%.

8. A secondary battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that: The operating voltage of the secondary battery is P0, P` min ≤P0≤P` max ; Among them, P` min Represents the lower limit of the working voltage range of the positive electrode active material in the positive electrode plate; P` max Indicates the upper limit of the working voltage range of the positive electrode active material in the positive electrode plate; Optionally, the operating voltage of the secondary battery is 2V to 4.1V.

10. An electrical device, characterized in that: The invention comprises at least one of the positive electrode sheet according to any one of claims 1 to 7 and the secondary battery according to claim 9.

Images