Positive electrode sheet, its preparation method, secondary battery and electrical device

Abstract

This application relates to a positive electrode sheet, its preparation method, a secondary battery, and an electrical device. The positive electrode sheet includes a positive current collector, a positive active material layer disposed on at least one side of the positive current collector, and a lithium replenishment layer disposed on at least one side of the positive active material layer. The positive active material layer includes lithium iron phosphate, and the lithium replenishment layer includes a ternary material. The presence of a lithium replenishment layer containing a ternary material on at least one side of the positive active material layer of the aforementioned positive electrode sheet allows for irreversible lithium replenishment of the negative electrode sheet, effectively reducing lithium-ion loss in the positive active material layer during charge-discharge cycles, thereby delaying the capacity decay of the secondary battery and extending its cycle life.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode sheet, its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Lithium-ion batteries are a type of rechargeable battery widely used in electric vehicles, portable electronic products, aerospace, and other fields. Commercially available cathode materials mainly include ternary cathode materials, lithium cobalt oxide, and lithium iron phosphate. Among them, lithium iron phosphate has advantages such as low cost, low self-discharge rate, and high safety; however, the cycle life of lithium iron phosphate still needs to be improved. Summary of the Invention

[0003] Based on this, this application provides a positive electrode sheet, a method for preparing the same, a secondary battery, and an electrical device to extend the cycle life of a secondary battery containing the positive electrode sheet.

[0004] In a first aspect, this application provides a positive electrode sheet, which includes a positive current collector, a positive active material layer is disposed on at least one side of the positive current collector, a lithium supplement layer is disposed on at least one side of the positive active material layer, the positive active material layer includes lithium iron phosphate, and the lithium supplement layer includes a ternary material.

[0005] At least one side of the positive electrode active material layer in the above-mentioned positive electrode sheet is provided with a lithium replenishment layer. The positive electrode active material layer includes lithium iron phosphate, and the lithium replenishment layer includes ternary materials. By providing a lithium replenishment layer containing ternary materials, the amount of lithium ion loss of the positive electrode active material layer during charge and discharge cycles is effectively reduced, thereby reducing the early capacity decay of the secondary battery and extending the cycle life of the secondary battery.

[0006] In some embodiments, the lithium replenishment layer is disposed between the positive electrode current collector and the positive electrode active material layer. This further reduces the early capacity decay of the secondary battery and extends its cycle life. Furthermore, it improves the adhesion between the positive electrode active material layer and the lithium replenishment layer, thereby enhancing the adhesion and conductivity of the positive electrode sheet, reducing the DC internal resistance of the secondary battery, and improving its storage performance.

[0007] In some embodiments, the ternary material includes one or more of the following: ternary materials containing nickel, cobalt, and manganese, and ternary materials containing nickel, cobalt, and aluminum. This further reduces the early capacity decay of the secondary battery and extends its cycle life.

[0008] In some embodiments, the mass percentage of the ternary material to the lithium iron phosphate is 1%-10%, optionally 3%-5%. This further reduces the early capacity decay of the secondary battery and extends its cycle life.

[0009] In some embodiments, the single-sided thickness H2 of the lithium replenishment layer and the single-sided thickness H1 of the positive electrode active material layer satisfy the following condition: 5H2≤H1≤30H2. This further reduces the early capacity decay of the secondary battery and extends its cycle life. Optionally, the single-sided thickness H2 of the lithium replenishment layer and the single-sided thickness H1 of the positive electrode active material layer satisfy the following condition: 10H2≤H1≤15H2.

[0010] In some embodiments, the compaction density of the lithium replenishment layer is 3 g / cm³. 3 -3.8g / cm 3 This further reduces the early capacity decay of the secondary battery and extends its cycle life.

[0011] In some embodiments, the ternary material comprises 80%-97% by weight, based on the weight of the lithium replenishment layer. This further reduces the early capacity decay of the secondary battery and extends its cycle life.

[0012] In some embodiments, the ternary material comprises 90%-95% by weight, based on the weight of the lithium replenishment layer. This further reduces the early capacity decay of the secondary battery and extends its cycle life.

[0013] In some embodiments, the lithium replenishment layer further includes a conductive agent and a binder. This further improves the adhesion between the positive electrode active material layer and the lithium replenishment layer, thereby further improving the adhesion and conductivity of the positive electrode sheet, reducing the DC internal resistance of the secondary battery, and enhancing the storage performance of the secondary battery.

[0014] A second aspect of this application provides a method for preparing the positive electrode sheet described in the first aspect of this application, comprising the steps of forming the positive electrode active material layer and forming the lithium replenishment layer.

[0015] The positive electrode sheet prepared by the above preparation method has at least the same advantages as the positive electrode sheet described in the first aspect of this application. In addition, the above preparation method has the advantages of simple operation and easy large-scale production.

[0016] A third aspect of this application provides a secondary battery, including the positive electrode sheet described in the first aspect of this application or the positive electrode sheet prepared by the preparation method described in the second aspect of this application.

[0017] The aforementioned secondary battery has at least the same advantages as the positive electrode sheet described in the first aspect of this application.

[0018] In some embodiments, the operating voltage of the secondary battery is 2V-3.8V. This further reduces the early capacity decay of the secondary battery and extends its cycle life.

[0019] A fourth aspect of this application provides an electrical device including the secondary battery described in the third aspect of this application.

[0020] The aforementioned electrical device includes the secondary battery described in the third aspect of this application, and therefore has at least the same advantages as the secondary battery. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0022] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0023] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0024] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0025] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0026] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0029] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints 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 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps in this 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 it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0035] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0036] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0038] Lithium iron phosphate (LFP) has been widely used in energy storage due to its advantages such as low cost, low self-discharge rate, and high safety. Extending the cycle life of LFP can further promote its application in energy storage. The cycle life degradation of secondary batteries containing LFP is largely due to the loss of active lithium ions in the system. Therefore, this application provides a positive electrode sheet, which includes a positive current collector, a positive active material layer disposed on at least one side of the positive current collector, and a lithium replenishment layer disposed on at least one side of the positive active material layer. The positive active material layer includes LFP, and the lithium replenishment layer includes a ternary material. The presence of a lithium replenishment layer containing a ternary material on at least one side of the positive active material layer of the aforementioned positive electrode sheet allows for irreversible lithium replenishment of the negative electrode sheet, effectively reducing the lithium ion loss of the positive active material layer during charge-discharge cycles, thereby delaying the capacity degradation of the secondary battery and extending its cycle life.

[0039] Positive electrode sheet

[0040] One embodiment of this application provides a positive electrode sheet, including a positive current collector, a positive active material layer disposed on at least one side of the positive current collector, and a lithium supplement layer disposed on at least one side of the positive active material layer. The positive active material layer includes lithium iron phosphate, and the lithium supplement layer includes a ternary material.

[0041] In the above embodiments, since ternary materials experience faster cycle decay than lithium iron phosphate, the lithium replenishment layer can continuously provide irreversible lithium replenishment to the negative electrode during cyclic charging. That is, the irreversible capacity formed in the negative electrode and the lithium ions lost by the SEI film during cyclic charging are lithium ions from the lithium replenishment layer. This allows the lithium ions released from the positive electrode active material layer during cyclic charging to return to the positive electrode active material layer to the maximum extent during cyclic discharge. Furthermore, the lithium ions embedded in the lithium replenishment layer in the negative electrode can have a slow-release effect during subsequent cyclic discharge, effectively reducing the amount of lithium ions lost from the positive electrode active material layer during charge-discharge cycles. This, in turn, reduces the early capacity decay of the secondary battery and extends its cycle life. It should be noted that the lithium replenishment layer can be disposed between the positive electrode current collector and the positive electrode active material layer, or it can be disposed on the side of the positive electrode active material layer away from the positive electrode current collector. Of course, lithium replenishment layers can be disposed simultaneously between the positive electrode current collector and the positive electrode active material layer, and on the side of the positive electrode active material layer away from the positive electrode current collector. It is understandable that "the positive electrode active material layer includes lithium iron phosphate" means that the positive electrode active material layer contains lithium iron phosphate, and "the lithium replenishment layer includes ternary materials" means that the lithium replenishment layer contains ternary materials.

[0042] As an example, the positive electrode current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer and / or lithium replenishment layer are disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0043] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0044] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0045] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0046] In some embodiments, a lithium replenishment layer is disposed between the positive electrode current collector and the positive electrode active material layer. In conventional positive electrode sheets, the positive electrode active material layer is in contact with the positive electrode current collector. Compared with conventional positive electrode sheets, the positive electrode sheet in this embodiment has a lithium replenishment layer disposed between the positive electrode active material layer and the positive electrode current collector. This reduces the early capacity decay during the cycling process of the secondary battery, extending the cycle life of the secondary battery. Furthermore, it improves the adhesion between the positive electrode active material layer and the lithium replenishment layer, thereby improving the adhesion and conductivity of the positive electrode sheet, reducing the DC internal resistance (DCR) of the secondary battery, and enhancing the storage performance of the secondary battery.

[0047] In some embodiments, the ternary material includes one or more of the following: ternary materials containing nickel, cobalt and manganese, and ternary materials containing nickel, cobalt and aluminum.

[0048] The aforementioned ternary materials containing nickel, cobalt, and manganese include, but are not limited to, lithium nickel cobalt manganese oxides. For example, lithium nickel cobalt manganese oxides can be: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 At least one of the following: nickel, cobalt, and aluminum. The aforementioned ternary materials containing nickel, cobalt, and aluminum include, but are not limited to, lithium nickel cobalt aluminum oxide, for example, LiNi... 0.85 Co 0.15 Al 0.05 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Al 0.2 O2, LiNi 0.5 Co 0.2 Al0.3 At least one of O2 and its modified compounds.

[0049] In some embodiments, the mass percentage of ternary material to lithium iron phosphate is 1%-10%. If the mass percentage of ternary material to lithium iron phosphate is too high, the capacity decay of the secondary battery is more severe due to the rapid degradation of the ternary material, resulting in a decreased cycle life. If the mass percentage of ternary material to lithium iron phosphate is too low, lithium ions released from the positive electrode active material layer during charge cycles may not return to the positive electrode active material layer during discharge cycles, leading to an insignificant lithium replenishment effect. Therefore, when the mass percentage of ternary material to lithium iron phosphate is within the above-mentioned range, the lithium ion loss of the positive electrode active material layer during charge-discharge cycles is further effectively reduced, thereby reducing the early capacity decay of the secondary battery and extending its cycle life. It is understood that the mass percentage of ternary material to lithium iron phosphate includes, but is not limited to: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. Optionally, the mass percentage of ternary material to lithium iron phosphate is 3%-5%.

[0050] In this application, the percentage of the mass of ternary material to the mass of lithium iron phosphate refers to the mass of ternary material / mass of lithium iron phosphate × 100%.

[0051] In some embodiments, the single-sided thickness H2 of the lithium replenishment layer and the single-sided thickness H1 of the positive electrode active material layer satisfy the following condition: 5H2≤H1≤30H2. When H1 is too thin relative to H2, the capacity decay of the secondary battery is more severe due to the faster degradation of the ternary material, resulting in a decreased cycle life. When H1 is too thick relative to H2, lithium ions released from the positive electrode active material layer during cyclic charging may not return to the positive electrode active material layer during cyclic discharging, leading to an insignificant lithium replenishment effect. Therefore, H1 and H2 satisfying the above conditions further reduce the early capacity decay of the secondary battery and extend its cycle life. Further, the single-sided thickness H2 of the lithium replenishment layer and the single-sided thickness H1 of the positive electrode active material layer satisfy the following condition: 10H2≤H1≤15H2. It can be understood that the single-sided thickness of the lithium replenishment layer refers to the thickness of the lithium replenishment layer located on the positive electrode current collector side, and the single-sided thickness of the positive electrode active material layer refers to the thickness of the positive electrode active material layer located on the positive electrode current collector side.

[0052] In some embodiments, the compaction density of the lithium replenishment layer is 3 g / cm³. 3 -3.8g / cm 3Controlling the compaction density of the lithium replenishment layer within the aforementioned range can reduce the internal resistance of the secondary battery, decrease polarization loss, and further extend the cycle life of the secondary battery. It is understood that the compaction density of the lithium replenishment layer includes, but is not limited to, 3 g / cm³. 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 .

[0053] In some embodiments, the weight fraction of the ternary material is 80%-97%, based on the weight of the lithium replenishment layer. Controlling the weight fraction of the ternary material in the lithium replenishment layer within the above range further reduces early capacity decay during secondary battery cycling and extends the cycle life of the secondary battery. It is understood that the weight fraction of the ternary material includes, but is not limited to: 80%, 82%, 85%, 87%, 90%, 92%, 95%, and 97%. The weight fraction of the ternary material can be selected as 90%-95%, based on the weight of the lithium replenishment layer.

[0054] In some embodiments, the lithium replenishment layer further includes a conductive agent and a binder. The conductive agent and binder in the lithium replenishment layer further improve the adhesion between the positive electrode active material layer and the lithium replenishment layer, thereby further improving the adhesion and conductivity of the positive electrode sheet, reducing the DC internal resistance (DCR) of the secondary battery, and improving the storage performance of the secondary battery. The mass ratio of the ternary material, conductive agent, and binder in the lithium replenishment layer can be, for example, 80:8:12, 85:6:9, 90:4:6, or 95:2:3. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0055] Another embodiment of this application provides a method for preparing the above-mentioned positive electrode sheet, including the steps of forming a positive active material layer and forming a lithium replenishment layer.

[0056] The positive electrode sheet prepared by the above preparation method has at least the same advantages as the positive electrode sheet mentioned above. In addition, the above preparation method has the advantages of simple operation and easy large-scale production.

[0057] In some embodiments, the positive electrode sheet can be prepared by dispersing lithium iron phosphate, a conductive agent, a binder, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a lithium replenishing slurry; coating the lithium replenishing slurry onto the positive current collector and drying it to form a lithium replenishing layer; dispersing lithium iron phosphate, a conductive agent, a binder, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the side of the lithium replenishing layer away from the positive current collector, and then drying, cold pressing, and other processes to obtain the positive electrode sheet.

[0058] In other embodiments, the positive electrode sheet can be prepared by dispersing lithium iron phosphate, a conductive agent, a binder, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a lithium replenishing slurry; coating the lithium replenishing slurry onto a positive current collector and drying it to form a lithium replenishing layer; dispersing lithium iron phosphate, a conductive agent, a binder, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the side of the lithium replenishing layer away from the positive current collector and drying it to form a positive active material layer; coating the lithium replenishing slurry onto the side of the positive active material layer away from the positive current collector, and then drying and cold pressing the coating to obtain the positive electrode sheet.

[0059] In other embodiments, the positive electrode sheet can be prepared by dispersing lithium iron phosphate, a conductive agent, a binder, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector and drying it to form a positive electrode active material layer; dispersing lithium iron phosphate, a conductive agent, a binder, and any other components in a solvent (e.g., N-methylpyrrolidone) to form a lithium replenishing slurry; coating the lithium replenishing slurry onto the side of the positive electrode active material layer away from the positive electrode current collector, and then drying, cold pressing, and other processes to obtain the positive electrode sheet.

[0060] Another embodiment of this application provides a secondary battery, including the above-described positive electrode sheet or the positive electrode sheet prepared by the above-described preparation method.

[0061] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0062] In some embodiments, the operating voltage of the secondary battery is 2V-3.8V. Ternary materials typically operate at 2.8V-4.25V, while lithium iron phosphate (LFP) has a maximum operating voltage of 3.8V. Because the operating voltage ranges of ternary materials and LFP differ, using them simultaneously can easily lead to overcharging of LFP, causing structural damage and affecting the cycle performance of the LFP-containing secondary battery. In this embodiment, the operating voltage of the secondary battery is set to 2V-3.8V, allowing the ternary material to operate within this voltage range. This does not affect the structure of the LFP in the positive electrode active material layer and also enables irreversible lithium replenishment to the negative electrode, thereby further reducing the early capacity decay of the secondary battery and extending its cycle life.

[0063] Negative electrode sheet

[0064] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material.

[0065] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0066] 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 substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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.

[0068] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one 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).

[0069] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0071] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0072] electrolytes

[0073] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0074] In some embodiments, the electrolyte is an electrolyte solution. This electrolyte solution includes an electrolyte salt and a solvent.

[0075] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0076] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0077] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0078] Separating membrane

[0079] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0080] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven 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.

[0081] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0082] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0083] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0084] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0085] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0086] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0087] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0088] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0089] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0090] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0091] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack 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, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0092] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0093] Figure 6Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0094] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0095] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0096] Example 1

[0097] (1) Preparation of positive electrode sheet

[0098] (1.1) Ternary material LiNi 0.5 Mn 0.3 Co 0.2 O2, polyvinylidene fluoride (PVDF), and conductive carbon black are mixed in a weight ratio of 90:4:6. N-methylpyrrolidone (NMP) solvent is added and the mixture is stirred thoroughly to obtain a lithium replenishing slurry. The slurry is then coated on both surfaces of an aluminum foil and dried in an oven at 120°C for 30 minutes. The thickness of the lithium replenishing layer on one side is 10 μm.

[0099] (1.2) Lithium iron phosphate (LiFePO4), polyvinylidene fluoride, and conductive carbon black were mixed in a weight ratio of 96:2:2. N-methylpyrrolidone solvent was added, and the mixture was thoroughly stirred to obtain a positive electrode slurry. The positive electrode slurry was coated onto a lithium replenishment layer, with a single-sided thickness of 150 μm. The positive electrode was then dried and cold-pressed to form a positive electrode sheet. The compaction density of the positive electrode active material layer was 2.65 g / cm³. 3 The compaction density of the lithium replenishment layer is 3.5 g / cm³. 3 ;

[0100] (2) Preparation of negative electrode sheet

[0101] Artificial graphite, conductive carbon black, and styrene-butadiene rubber (SBR) were mixed in a weight ratio of 96:2:2, and deionized water was added as a solvent. The mixture was thoroughly stirred to obtain a negative electrode slurry, which was then coated onto both surfaces of a copper foil. After drying and cold pressing, the negative electrode sheet was formed. The compaction density of the negative electrode active material layer was 1.45 g / cm³. 3 ;

[0102] (3) Assembling lithium-ion batteries

[0103] The aforementioned positive and negative electrode sheets are matched with a 12μm thick PE separator and wound to form a lithium-ion battery cell. The cell is then encapsulated in a metal casing to form a lithium-ion battery. After drying, it is injected with an electrolyte consisting of 1M LiPF6 and solvents DMC:EC:EMC = 1:1:1 Vol%. After the electrolyte has fully entered the cell, formation and capacity testing are performed.

[0104] Example 2-14

[0105] The basic structure is the same as in Example 1, except that the composition, single-sided thickness, and compaction density of the lithium replenishment layer in step (1.1), the composition, single-sided thickness, compaction density of the positive electrode active material layer, and the working voltage of the secondary battery in step (1.2) are different from those in Example 1.

[0106] Comparative Example 1

[0107] The process is basically the same as in Example 1, except that step (1.1) is not performed, and in step (1.2), the positive electrode slurry is coated on both surfaces of the aluminum foil.

[0108] Comparative Example 2

[0109] Basically the same as Example 1, except that the method for preparing the positive electrode sheet is different from that in Example 1;

[0110] The positive electrode sheet of this comparative example was prepared according to the following method: ternary material LiNi 0.5 Mn 0.3 Co 0.2 O2, lithium iron phosphate, polyvinylidene fluoride, and conductive carbon black are mixed in a weight ratio of 5:90:2:3. N-methylpyrrolidone solvent is added, and the mixture is thoroughly stirred to obtain a positive electrode slurry. This slurry is then coated onto both surfaces of an aluminum foil, with a single-sided thickness of 160 μm for the positive electrode active material layer. After drying and cold pressing, the slurry is formed into a positive electrode sheet with a compacted density of 2.65 g / cm³. 3 .

[0111] Comparative Example 3

[0112] The process is basically the same as in Example 1, except that step (1.1) is not performed, and in step (1.2), the positive electrode slurry is coated on both surfaces of the aluminum foil; the operating voltage range of the lithium-ion battery is 2-4V.

[0113] Comparative Example 4

[0114] Basically the same as Example 1, except that the method for preparing the positive electrode sheet is different from that in Example 1;

[0115] The positive electrode sheet of this comparative example was prepared according to the following method: ternary material LiNi0.5 Mn 0.3 Co 0.2 O2, lithium iron phosphate, polyvinylidene fluoride, and conductive carbon black are mixed in a weight ratio of 5:90:2:3. N-methylpyrrolidone solvent is added, and the mixture is thoroughly stirred to obtain a positive electrode slurry. This slurry is then coated onto both surfaces of an aluminum foil, with a single-sided thickness of 160 μm for the positive electrode active material layer. After drying and cold pressing, the slurry is formed into a positive electrode sheet with a compacted density of 2.65 g / cm³. 3 The operating voltage range of lithium-ion batteries is 2-4V.

[0116] The product parameters of the lithium-ion batteries obtained in each embodiment and comparative example are shown in Table 1.

[0117] Table 1 Product parameters for each embodiment and comparative example.

[0118]

[0119]

[0120]

[0121] Performance testing

[0122] (1) Test method for adhesion

[0123] Take the electrode to be tested, and cut a sample with a width of 30mm and a length of 100mm-160mm using a blade. Attach it to the steel plate with special double-sided adhesive, test side down. Then, roll it three times in the same direction using a pressure roller. Insert a paper strip with the same width as the electrode under the electrode and fix it in place. Fix the steel plate and paper strip to the tensile testing machine using clamps. Pull the paper strip upwards at a speed of 50mm / min until the displacement is greater than 70mm. Record the tensile test machine reading at this point as the adhesion force between the active material layer or lithium supplement layer and the current collector.

[0124] (2) Test method for DC internal resistance

[0125] At room temperature, charge the lithium-ion battery at a 1 / 3C rate to the upper limit of the working voltage (3.8V or 4V), which is 100% SOC. Then discharge the lithium-ion battery to 50% SOC, let it stand for 5 minutes, and then discharge it at a 4C rate for 10 seconds to obtain the DC internal resistance DCR of the lithium-ion battery at 50% SOC at room temperature.

[0126] (3) Storage performance testing methods

[0127] At 25°C, lithium-ion batteries were stored in a constant temperature chamber for 365 days. The battery capacity was measured every 30 days. After storage, the batteries were charged at a constant current rate of 0.5C to the upper limit of the working voltage (3.8V or 4V), then charged at a constant voltage rate to 0.05C, then discharged at a current rate of 0.5C to 2.5V, and then discharged at a current rate of 0.1C to 2.0V. The ratio of the capacity at this point to the initial capacity was recorded.

[0128] (4) Cyclic performance testing methods

[0129] The effect of lithium replenishment can be verified by cycling tests of lithium-ion batteries. The cycling test conditions are as follows: at 25°C, charge at a constant current rate of 0.5C to the upper limit of the working voltage (3.8V or 4V), then charge at a constant voltage rate 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 2.0V, until the discharge capacity of the lithium-ion battery decays to 80% of the initial capacity, and record the number of cycles at this time.

[0130] Table 2 Performance parameters of the positive electrode and lithium-ion battery for each embodiment and comparative example.

[0131]

[0132] Analysis of Tables 1 and 2, and comparison of Examples 1-10, Examples 12-14, and Comparative Examples 1-2, shows that the secondary batteries prepared in Examples 1-10 have significantly lower DC internal resistance and a higher number of cycles to 80% of their initial capacity. Comparison of Example 11 and Comparative Examples 3-4 shows that the secondary batteries prepared in Example 11 have significantly lower DC internal resistance and a higher number of cycles to 80% of their initial capacity. This indicates that the provision of a lithium replenishment layer on at least one side of the positive electrode active material layer in Examples 1-14 extends the cycle life of the secondary batteries while reducing their DC internal resistance.

[0133] As can be seen from Examples 1, 9-10 and Comparative Examples 1-2, the lithium replenishment layer disposed between the positive electrode current collector and the positive electrode active material layer improves the adhesion between it and the current collector, while reducing the DC internal resistance of the secondary battery.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A secondary battery characterized by comprising: The secondary battery comprises a positive electrode tab, the positive electrode tab comprises a positive electrode current collector, at least one side of the positive electrode current collector is provided with a positive electrode active material layer, at least one side of the positive electrode active material layer is provided with a lithium supplement layer, the positive electrode active material layer comprises lithium iron phosphate, the lithium supplement layer comprises a ternary material, the percentage of the mass of the ternary material to the mass of the lithium iron phosphate is 1%-10%, and the working voltage of the secondary battery is 2V-3.8V.

2. The secondary battery according to claim 1, characterized by The lithium supplement layer is arranged between the positive electrode current collector and the positive electrode active material layer.

3. The secondary battery according to claim 1, characterized by The ternary material comprises one or more of a ternary material containing nickel elements, cobalt elements and manganese elements and a ternary material containing nickel elements, cobalt elements and aluminum elements.

4. The secondary battery according to any one of claims 1 to 3, characterized by The percentage of the mass of the ternary material to the mass of the lithium iron phosphate is 1%-7.5%.

5. The secondary battery according to any one of claims 1 to 3, characterized by The percentage of the mass of the ternary material to the mass of the lithium iron phosphate is 3%-5%.

6. The secondary battery according to any one of claims 1 to 3, characterized by The one-side thickness H2 of the lithium supplement layer and the one-side thickness H1 of the positive electrode active material layer satisfy the following condition: 5H2≤H1≤30H2.

7. The secondary battery according to claim 6, characterized by 10H2≤H1≤15H2.

8. The secondary battery according to any one of claims 1 to 3, characterized by The compaction density of the lithium supplement layer is 3 g / cm 3 - 3.8 g / cm 3 .

9. The secondary battery according to claim 1, characterized by The weight fraction of the ternary material is 80%-97% based on the weight of the lithium supplement layer.

10. The secondary battery according to claim 1, characterized by The weight fraction of the ternary material is 90%-95% based on the weight of the lithium supplement layer.

11. The secondary battery according to any one of claims 1, 9 and 10, characterized by The lithium supplement layer further comprises a conductive agent and a binder.

12. An electrical device, characterized by The secondary battery of any one of claims 1-11.

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