Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector; the negative electrode film layer is provided with a lithium supplementing part located on the edge of the negative electrode film layer, and the lithium supplementing part comprises metal lithium. The secondary battery can effectively inhibit edge lithium precipitation, and has high cycle performance and high energy density.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a secondary battery and an electrical device. Background Art

[0002] In recent years, with the increasingly wide application scope of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary batteries, higher requirements are put forward for their performance, especially the cycle performance.

[0003] Currently, in lithium-ion batteries, there is a problem that lithium deposition easily occurs at the edge of the negative electrode, which seriously affects the cycle life of lithium-ion batteries. The existing technology uses the method of spraying lithium powder or rolling lithium foil on the entire surface of the negative electrode film layer to supplement lithium, but this method not only reduces the energy density of the battery, has potential safety hazards, but also cannot fully suppress lithium deposition at the edge of the negative electrode, resulting in the influence on the cycle performance of the battery. Therefore, how to solve edge lithium deposition without damaging the energy density of the battery and ensuring safety has become an urgent technical problem to be solved. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a secondary battery with high energy density and high cycle performance, and an electrical device including the secondary battery.

[0005] To achieve the above purpose, the present application provides a secondary battery, including a negative electrode tab, the negative electrode tab including a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector; the negative electrode film layer has a lithium supplement portion located at the edge of the negative electrode film layer, and the lithium supplement portion includes metallic lithium. The secondary battery of the present application can effectively suppress edge lithium deposition and has high cycle performance and high energy density.

[0006] In some embodiments, the content of metallic lithium is 0.01% - 5% relative to the mass of the negative electrode film layer. By making the content of lithium metal within the above range, sufficient insertion sites can be provided for lithium ions from the positive electrode, and edge lithium deposition can be more effectively suppressed.

[0007] In some embodiments, the width of the negative electrode film layer is L1, and the width of the lithium supplement portion is L2, and L1 and L2 satisfy the following relationship: 0 < L2 ≤ 0.2L1. In some embodiments, 0 < L2 ≤ 0.1L1. By controlling L2 within the above range, it is more beneficial to improve the energy density and cycle performance of the secondary battery.

[0008] In some embodiments, on the width direction of the negative electrode film layer, lithium supplement parts are respectively provided at the edges on both sides of the negative electrode film layer. By respectively arranging lithium supplement parts at the edges on both sides of the negative electrode film layer, lithium deposition at the edges on both sides of the negative electrode film layer can be effectively inhibited.

[0009] In some embodiments, the widths of the lithium supplement parts located at the two side edges are L21 and L22 respectively, L21 and L22 are the same or different, and L1, L21, and L22 satisfy the following relationship: 0 < L21 ≤ 0.2L1, 0 < L22 ≤ 0.2L1. In some embodiments, 0 < L21 ≤ 0.1L1, 0 < L22 ≤ 0.1L1. By controlling L12 and L22 within the above ranges, it is more beneficial to improve the energy density and cycling performance of the secondary battery.

[0010] In some embodiments, the width of the lithium supplement part is 1 mm to 10 mm. By controlling the width of the lithium supplement part within the above range, more insertion sites can be provided at the negative electrode edge, and lithium deposition at the edge can be better inhibited.

[0011] In some embodiments, the lithium supplement part further includes a conductive carrier, and the metallic lithium exists inside the conductive carrier. Thus, the conductive carrier can protect the metallic lithium and reduce the risk of reaction between the metallic lithium and the negative electrode carbon material.

[0012] In some embodiments, the edge part of the secondary battery includes the edge of the negative electrode film layer and the edge of the positive electrode film layer facing the edge of the negative electrode film layer, the main body part of the secondary battery includes the main body of the negative electrode film layer and the main body of the positive electrode film layer facing the main body of the negative electrode film layer, and the CB value of the edge part of the secondary battery is greater than the CB value of the main body part of the secondary battery. By making the CB value of the edge part of the secondary battery greater than the CB value of the main body part of the secondary battery, it is beneficial to alleviate the lithium deposition problem caused by the COV (Covariance) fluctuation during the processing at the edge of the secondary battery, and can also alleviate the lithium deposition problem caused by insufficient kinetics at the edge of the secondary battery.

[0013] The second aspect of the present application provides an electrical device, including the secondary battery of the first aspect of the present application. Description of the Drawings

[0014] Figure 1 is a top view of a negative electrode tab of an embodiment of the present application.

[0015] Description of the Reference Numerals:

[0016] 10 Negative electrode tab; 11 Negative electrode current collector; 12 Negative electrode film layer; 13, 131, 132 Lithium supplement parts. Detailed Embodiments

[0017] Hereinafter, embodiments of the secondary battery and the electrical device of the present application will be specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there are cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to avoid making the following description unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0018] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, 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, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation 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" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0019] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0020] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0021] If there is no special instruction, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art.

[0022] If there is no special instruction, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used test methods in the art. For example, they can be measured according to the test methods given in the present application.

[0023] In the present application, the term "active ion" refers to an ion that can intercalate and deintercalate between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0024] In the present application, the term "CB value" (cell balance) is the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area.

[0025] Currently, during the charging process of a secondary battery, due to uneven heat generation and heat dissipation in the battery, the temperature of the main body of the battery is higher than that of the edge. During the process of lithium ions transferring from the positive electrode to the negative electrode, the main body of the battery has better kinetics due to the higher temperature, resulting in lithium ions at the edge of the electrode being unable to be embedded into the negative electrode material in time due to insufficient kinetics and precipitating at the edge of the negative electrode. Therefore, lithium deposition is likely to occur at the edge of the negative electrode plate. Secondly, during the electrode processing, due to the existence of COV fluctuations, there are fluctuations in the thinning of the edge part of the electrode during coating, resulting in fluctuations in the CB value at the edge of the electrode during coating, and the CB value of the local edge part of the secondary battery is lower than that of the main body part of the secondary battery. During the cycling process, lithium deposition exists at the edge of the negative electrode plate.

[0026] In view of the above problems, there are reports proposing a method of spraying a lithium supplement layer on the entire surface of the negative electrode plate. However, the entire surface lithium supplement layer occupies too much space in the battery, resulting in a decrease in the energy density of the battery, and the processing is not safe and prone to explosion risks. In addition, there are also reports mentioning adding lithium supplement materials at the edge of the negative electrode. However, the present inventors have found that the above methods mentioned in the prior art are not sufficient in suppressing edge lithium deposition. In particular, although lithium metal has a high specific capacity, when a lithium sheet or lithium powder is added as a lithium supplement material on the surface of the graphite negative electrode material to form a battery for use, edge lithium deposition cannot be fully suppressed. The present inventors dissected the above battery and found that after injecting the electrolyte into the secondary battery, the lithium metal used as the lithium supplement material reacts with the negative electrode carbon material to generate LixCy compounds in the negative electrode plate, and fails to exist in the state of lithium metal. The generated LixCy compounds cannot provide an insertion site for the lithium ions extracted from the positive electrode as a lithium supplement material.

[0027] In view of this, the present application provides a secondary battery, which includes a negative electrode plate, as Figure 1 shown, the negative electrode plate 10 includes a negative electrode current collector 11 and a negative electrode film layer 12 provided on at least one surface of the negative electrode current collector 11. The negative electrode film layer 12 has a lithium supplement part 13 provided at the edge of the negative electrode film layer, and the lithium supplement part 13 includes metallic lithium.

[0028] The negative electrode film layer 12 includes a main body and an edge. In the present application, the term "edge" refers to the area formed by extending 1 mm to 10 mm inward from the outermost edge of the film layer. The term "main body" refers to the area between the two edges in the film layer.

[0029] In the secondary battery of the present application, in the presence of the electrolyte, lithium metal still exists in the form of metal at the edge of the negative electrode film layer and does not react with the negative electrode carbon material. Therefore, metallic lithium can receive lithium ions from the positive electrode, and the space in the negative electrode film layer that can accommodate the insertion of lithium ions increases, thereby suppressing the lithium deposition at the edge of the negative electrode plate and improving the cycling performance of the secondary battery. In addition, compared with the case where the lithium supplement layer is provided on the entire surface, the space occupied in the battery is greatly reduced, making the secondary battery have a high energy density.

[0030] In some embodiments, the content of metallic lithium is 0.01% to 5% relative to the mass of the above-mentioned negative electrode film layer. For example, the content of metallic lithium is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 4%, 5% or a value between any two numerical values. Optionally, the content of metallic lithium is 0.1% to 2%. By making the content of lithium metal within the above range, sufficient insertion sites can be provided for lithium ions from the positive electrode, and lithium deposition at the edge can be more effectively suppressed.

[0031] In some embodiments, the width of the above-mentioned negative electrode film layer is L1, and the width of the above-mentioned lithium supplement part is L2. L1 and L2 satisfy the following relationship: 0 < L2 ≤ 0.2L1. For example, L2 is 0.005L1, 0.01L1, 0.015L1, 0.02L1, 0.025L1, 0.03L1, 0.035L1, 0.04L1, 0.045L1, 0.05L1, 0.055L1, 0.06L1, 0.065L1, 0.07L1, 0.075L1, 0.08L1, 0.085L1, 0.09L1, 0.095L1, 0.1L1, 0.11L1, 0.12L1, 0.13L1, 0.14L1, 0.15L1, 0.16L1, 0.17L1, 0.18L1, 0.19L1, 0.2L1 or a value between any two numerical values, but not limited thereto. When the width L1 of the negative electrode film layer is constant, the smaller the value of L2 / L1, the smaller the width L2 of the lithium supplement part. Preferably, L1 and L2 satisfy the following relationship: 0 < L2 ≤ 0.1L1. By controlling L2 within the above range, it is more beneficial to improve the energy density and cycling performance of the secondary battery.

[0032] In some embodiments, as Figure 1 shown, in the width direction of the above-mentioned negative electrode film layer 12, lithium supplement parts (131, 132) are respectively provided at the edges on both sides of the above-mentioned negative electrode film layer 12. The lithium supplement part 131 and the lithium supplement part 132 can effectively suppress lithium deposition at the edges on both sides of the negative electrode film layer 12.

[0033] In some embodiments, as Figure 1As shown, the widths of the lithium supplement parts on both sides located at the two side edges are L21 and L22 respectively. The widths L21 and L22 are the same or different, and L1, L21, and L22 satisfy the following relationship: 0 < L21 ≤ 0.2L1, 0 < L22 ≤ 0.2L1. In some embodiments, L1, L21, and L22 preferably satisfy the following relationship: 0 < L21 ≤ 0.1L1, 0 < L22 ≤ 0.1L1. For specific examples of L21 and L22, reference may be made to L2 above.

[0034] In some embodiments, the width of the above-mentioned lithium supplement part is 1 mm to 10 mm. For example, the width of the above-mentioned lithium supplement part is 1 mm, 2 mm, 3 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm, 4 mm, 4.2 mm, 4.4 mm, 4.6 mm, 4.8 mm, 5 mm, 5.2 mm, 5.4 mm, 5.6 mm, 5.8 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or a value within the range composed of any two values. Preferably, the width of the lithium supplement part is 3 mm to 6 mm. By controlling the width of the lithium supplement part within the above range, more infiltration sites can be provided at the negative electrode edge, and lithium deposition at the edge can be better inhibited.

[0035] In some embodiments, the above-mentioned lithium supplement part further includes a conductive carrier for carrying metallic lithium. For the conductive carrier, as long as it does not react with metallic lithium and can accommodate metallic lithium inside, there is no particular limitation. For example, carriers with a hollow structure capable of accommodating metallic lithium such as hollow carbon nanotubes and polymer conductive carriers can be used, and they can be in a strip structure or a tubular structure. As polymer conductive carriers, examples include: tubular polymer conductive carriers coated with titanium dioxide nanoparticles, hollow tubular nitrogen-doped conductive polymer aerogel materials, and tubular polymer conductive carriers coated with cobalt disulfide. By making metallic lithium exist inside the conductive carrier, metallic lithium can be protected, the risk of reaction between metallic lithium and the negative electrode carbon material can be reduced, and metallic lithium can fully play its role as a lithium supplement material.

[0036] In some embodiments, the polymer conductive carrier contains lithiophilic elements. As lithiophilic elements, at least one selected from boron (P), nitrogen (N), oxygen (O), phosphorus (P), fluorine (F), chlorine (Cl), and sulfur (S) is included. By adopting a polymer conductive carrier containing lithiophilic elements, it is beneficial for lithium ions to directly transport from the surface and inside of the polymer conductive carrier, reducing the lithium ion transport path and improving the charging speed of the battery.

[0037] In some embodiments, the main body slurry and the lithium supplement slurry are simultaneously coated on the current collector by a multi-nozzle coating device or by a plurality of coating devices, etc. to form a negative electrode film layer, which includes a main body portion and a lithium supplement portion (the lithium supplement portion forms the edge of the negative electrode). Additionally, after the negative electrode slurry is coated on the current collector to form a negative electrode film layer, the lithium supplement slurry can be coated on the edge of the negative electrode film layer, so as to form a lithium supplement portion on the upper surface of the edge of the above-mentioned negative electrode film layer, covering the edge of the above-mentioned negative electrode film layer. Additionally, the above-mentioned lithium supplement portion can also be arranged on the side surface of the edge of the above-mentioned negative electrode film layer, adjacent to the outermost edge of the negative electrode film layer; furthermore, the above-mentioned lithium supplement portion can also be arranged under the edge of the above-mentioned negative electrode film layer, with the edge covering the lithium supplement portion. Since the lithium supplement material in the lithium supplement portion has conductivity, this setting can reduce the usage amount of the bottom coating.

[0038] In some embodiments, the edge portion of the secondary battery of the present application includes the edge of the above-mentioned negative electrode film layer and the edge of the positive electrode film layer opposite to the edge of the above-mentioned negative electrode film layer, and the main body portion of the secondary battery includes the main body of the above-mentioned negative electrode film layer and the main body of the positive electrode film layer opposite to the main body of the above-mentioned negative electrode film layer. In the present application, the lithium supplement portion located at the edge of the negative electrode film layer contains lithium metal. Therefore, the CB value of the edge portion of the secondary battery is greater than the CB value of the main body portion of the secondary battery. Thereby, it is beneficial to alleviate the lithium deposition problem caused by the COV fluctuation during the processing of the edge of the secondary battery, and the increase in the edge CB value can improve the kinetics and improve the lithium deposition caused by insufficient kinetics at the edge of the secondary battery.

[0039] In some embodiments, the above-mentioned negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can 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 can be formed by forming a metal material (such as 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.).

[0040] In some embodiments, the negative electrode active material may be the negative electrode active material for batteries known in the art. 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. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0041] In some embodiments, the negative electrode film layer may further 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), carboxymethyl chitosan (CMCS), and polytetrafluoroethylene (PVDF).

[0042] In some embodiments, the negative electrode film layer may further 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.

[0043] In some embodiments, the negative electrode film layer may further optionally include other additives, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0044] In some embodiments, the negative electrode plate may be prepared in the following manner: the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after processes such as drying and cold pressing, a negative electrode film layer is formed. Then, a lithium metal-containing lithium supplementation slurry is coated on the edge of the negative electrode film layer to form a lithium supplementation part. Additionally, the coating area of the negative electrode film layer may be predetermined, and a lithium metal-containing lithium supplementation slurry is pre-coated at a position corresponding to the edge of the negative electrode film layer. After processes such as drying, a lithium supplementation part is formed, and then the above-mentioned negative electrode slurry is coated to form a negative electrode film layer.

[0045] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. The following will be described separately.

[0046] Under normal circumstances, a secondary battery cell includes a positive electrode plate, an electrolyte, a separator, and the above-mentioned negative electrode plate. During the charging and discharging process of the battery, active ions are inserted into and extracted from between the positive electrode plate and the negative electrode plate. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0047] Positive electrode plate

[0048] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.

[0049] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0050] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. 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 can be formed by forming a metal material (such as aluminum, aluminum 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.).

[0051] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can 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 lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2 (which can also be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be abbreviated as NCM523), LiNi 0.5 Co0.25 Mn 0.25 O2 (which can also be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2) and at least one of its modified compounds, etc. Examples of olivine-structured lithium-containing phosphates can include but are not limited to lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon.

[0052] During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0053] In the listing of the positive electrode active materials in this application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations.

[0054] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0055] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. 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.

[0056] In some embodiments, the positive electrode plate can be prepared in the following manner: Dispersing the components for preparing the positive electrode plate described above, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0057] Electrolyte

[0058] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0059] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0060] In some embodiments, the electrolyte salt can 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0061] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene 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.

[0062] In some embodiments, the electrolytic solution may optionally further include additives. For example, the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and can also include additives that can improve certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0063] Separator

[0064] In some embodiments, the battery cell further includes a separator. There is no particular limitation on the type of separator in this application, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0065] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0066] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0067] In some embodiments, a battery cell may include an outer package. The outer package may be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0068] In some embodiments, the outer package of the battery cell may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the battery cell may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be listed.

[0069] The present application has no particular limitation on the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape.

[0070] In some embodiments, the battery cells may be assembled into a battery module. The number of battery cells included in the battery module may be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery module.

[0071] In some embodiments, the above-mentioned battery module may further be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and those skilled in the art can select the specific number according to the application and capacity of the battery pack.

[0072] In addition, the present application also provides an electrical device. The electrical device includes the secondary battery provided by the present application. The secondary battery may be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0073] As the electrical device, a battery cell, a battery module, or a battery pack may be selected according to its usage requirements. As an example of the electrical device, a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. may be cited. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or a battery module may be adopted. As another example of the electrical device, a mobile phone, a tablet computer, a laptop, etc. may be cited. This device usually requires thinning, and a battery cell may be used as the power source.

[0074] Examples

[0075] The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those technologies or conditions not specified in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0076] Example 1

[0077] Preparation of negative electrode sheet

[0078] Step (a): Mix graphite (mass fraction 96.2 wt%), styrene-butadiene rubber SBR (mass fraction 2.5 wt%), conductive carbon black SP (mass fraction 1.3 wt%) with solvent N-methylpyrrolidone (NMP), and after stirring evenly, obtain Slurry 1.

[0079] Step (b): Mix graphite (mass fraction 96.15 wt%), styrene-butadiene rubber SBR (mass fraction 2.5 wt%), conductive carbon black SP (mass fraction 1.3 wt%), lithium supplement material (mass fraction 0.5 wt%) with solvent NMP, and after stirring evenly, obtain Slurry 2 (lithium supplement slurry).

[0080] Among them, the lithium supplement material is prepared as follows: Add metallic lithium to a silane solvent and heat up to 200 °C to obtain a solution containing molten metallic lithium. Next, add a hollow carbon nanotube conductive carrier (purchased from Tiannai Technology Co., Ltd.) to the silane solvent and stir evenly at 200 °C, then mix the solution containing molten metallic lithium with it, and continue to stir at 200 °C at 150 revolutions / min for 30 minutes until evenly mixed, then stop heating, wait until it cools to room temperature, collect the solid product and dry it in a vacuum box to obtain the lithium supplement material. The lithium metal content in this lithium supplement material is 10 wt%.

[0081] Step (c): Simultaneously coat the above-mentioned Slurry 1 and Slurry 2 on a copper foil current collector through a spraying device to form a negative electrode film layer with a total width (L1) of 50 mm, where Slurry 2 is coated on both sides of Slurry 1 to respectively form lithium supplement parts on both sides in the width direction of the negative electrode film layer, and the widths (L21, L22) are 5 mm respectively. With respect to the mass of the negative electrode film layer, the content of metallic lithium is 0.01 wt%.

[0082] Step (d): After processes such as drying and cold pressing, obtain a negative electrode sheet.

[0083] Preparation of secondary battery

[0084] The positive electrode plate is made of active material lithium iron phosphate (LiFePO4), conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 97:1:2. A polyethylene (PE) separator is used. After laminating the above-mentioned negative electrode plate, separator, and positive electrode plate, an electrolyte solution (composition: ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate as solvents, lithium hexafluorophosphate (LiPF6) as the lithium salt, and vinylene carbonate, fluoroethylene carbonate, ethylene sulfate, and lithium difluorooxalate borate as additives, and fully stirred until it is completely dissolved) is injected, and a secondary battery is assembled.

[0085] Examples 2 - 4

[0086] By adjusting the lithium metal content in the lithium supplement material and / or the content of the lithium supplement material in the negative electrode slurry, the content of metallic lithium in the negative electrode plate is as shown in Table 1 below. Except for this, the secondary battery is prepared in the same manner as in Example 1.

[0087] Examples 5 - 7

[0088] Using the same slurry 2 as in Example 2, the widths of L21 and L22 are changed so that L21 / L1 and L22 / L1 are as shown in Table 1 below, and the secondary battery is prepared in the same manner as in Example 2.

[0089] Comparative Example 1

[0090] Preparation of negative electrode sheet

[0091] Graphite (mass fraction of 96.2%), binder (mass fraction of 2.5%), conductive carbon black SP (mass fraction of 1.3%) are mixed with solvent NMP, and after stirring evenly, a negative electrode slurry is obtained. The negative electrode slurry is coated on a copper foil current collector to form a negative electrode film layer with a width (L1) of 50 mm. After drying and rolling the electrode plate, a lithium strip with a thickness of about 2 μm is laid on the entire surface of the electrode plate and compacted on the surface of the electrode plate. The mass ratio of the lithium strip to the total mass of the negative electrode film layer is 2%.

[0092] Except for this, the secondary battery is prepared in the same method as in Example 1.

[0093] Comparative Example 2

[0094] Preparation of negative electrode sheet

[0095] Graphite (mass fraction 96.2%), binder (mass fraction 2.5%), conductive carbon black SP (mass fraction 1.3%) were mixed with solvent NMP. After stirring evenly, a negative electrode slurry was obtained. The negative electrode slurry was coated on a copper foil current collector to form a negative electrode film layer with a width (L1) of 50 mm. The electrode was dried and rolled, and then lithium strips with widths (L21, L22) of 5 mm respectively (lithium strip thickness 6 μm) were laid on the surfaces of both edges in the width direction of the electrode, and pressed on the surface of the electrode to obtain a negative electrode sheet. The mass ratio of the lithium strip to the total mass of the negative electrode film layer was 2%.

[0096] In addition, a secondary battery was prepared by the same method as in Example 1.

[0097] <Performance Test>

[0098] (1) Lithium deposition at the negative electrode edge

[0099] The battery was disassembled, and the lithium deposition at the negative electrode edge was observed and judged according to the following method.

[0100] No lithium deposition: The edge part of the negative electrode sheet is yellowish-brown.

[0101] Slight lithium deposition: A white foggy substance covers the surface of the negative electrode sheet. Wiping off the white foggy substance on the surface reveals the yellowish-brown negative electrode sheet.

[0102] Severe lithium deposition: Grayish-black substances appear on the surface of the negative electrode sheet.

[0103] (2) Volume energy density of the secondary battery

[0104] Volume energy density of the secondary battery = Discharge capacity C0 of the secondary battery * Discharge plateau voltage (3.22 V) / Volume V0 of the secondary battery.

[0105] The secondary battery was charged at a constant current of 1 / 3C to 3.8 V at 25°C, then charged at a constant voltage to 0.05C, left standing for 30 min, and then discharged to 2.0 V. The capacity at this time was recorded as C0 by a battery capacity tester;

[0106] The volume of the battery was measured by the drainage method, that is, the secondary battery was placed in pure water, and the volume of the drained water was recorded as V0.

[0107] The discharge plateau voltage is the potential when the electrochemical reaction reaches equilibrium and is measured by a battery capacity tester.

[0108] (3) Capacity retention rate of the secondary battery after 5000 cycles at 25°C

[0109] At 25 °C, the secondary battery is charged at a constant current of 1C to 3.8V, allowed to stand for 30 minutes, and then discharged at a constant current of 1C to 2.0V. This is a cycle of charge and discharge. Record the discharge capacity at this time as D0, which is the initial capacity of the secondary battery. The secondary battery is subjected to 5000 cycles of charge and discharge tests according to the above method. Record the discharge capacity at 1000 cycles as D1. The capacity retention rate of the secondary battery after 5000 cycles at 25 °C is D 1 / D0 * 100%.

[0110] Table 1

[0111]

[0112] As can be seen from the results in Table 1, compared with Comparative Example 1, in the secondary batteries of Examples 1-7, the edge portion of the negative electrode sheet contains metallic lithium, which can effectively inhibit the lithium deposition at the edge of the negative electrode sheet, improving the cycle performance and energy density of the secondary battery. By comparing Example 3 with Comparative Example 2, it shows that when the width of the lithium supplement portion of the negative electrode film layer is the same and the content of metallic lithium added to the negative electrode film layer is the same (2%) during the preparation of the negative electrode sheet, compared with Comparative Example 2, the cycle performance and energy density of the secondary battery of Example 3 are both improved.

[0113] After completely discharging the secondary batteries of Comparative Examples 1 and 2, the negative electrode sheets are disassembled. The negative electrode sheets are subjected to spectroscopic tests using a Bruker nuclear magnetic resonance spectrometer, and no signal from metallic lithium is seen. It can be seen that there is no metallic lithium in the negative electrode sheets of Comparative Examples 1 and 2. The metallic lithium added as a lithium supplement material reacts with the negative electrode carbon material to form LiC6 and cannot provide an insertion site for the lithium ions deintercalated from the positive electrode as a lithium supplement material. Therefore, the lithium deposition at the edge of the negative electrode film layer in Comparative Examples 1 and 2 is serious, the capacity retention rate is small after 5000 cycles, and the cycle life of the secondary battery is short.

[0114] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical scope of this application are included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, including a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative electrode film layer provided on at least one surface of the negative current collector; the negative electrode film layer has a lithium supplement portion located at the edge of the negative electrode film layer, and the lithium supplement portion includes metallic lithium.

2. The secondary battery according to claim 1, wherein, The content of the metallic lithium is 0.01% to 5% relative to the mass of the negative electrode film layer.

3. The secondary battery according to claim 1 or 2, characterized in that, The width of the negative electrode film layer is L1, and the width of the lithium supplement portion is L2. L1 and L2 satisfy the following relationship: 0 < L2 ≤ 0.2L1.

4. The secondary battery according to claim 3, wherein L1 and L2 satisfy the following relationship: 0 < L2 ≤ 0.1L1.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, In the width direction of the negative electrode film layer, the lithium supplement portions are respectively provided at the edges on both sides of the negative electrode film layer.

6. The secondary battery according to claim 5, characterized in that, The widths of the lithium supplement portions located at the two side edges are L21 and L22 respectively. L21 and L22 are the same or different, and L1, L21, and L22 satisfy the following relationship: 0 < L21 ≤ 0.2L1, 0 < L22 ≤ 0.2L1.

7. The secondary battery according to claim 6, characterized in that, L1, L21, and L22 satisfy the following relationship: 0 < L21 ≤ 0.1L1, 0 < L22 ≤ 0.1L1.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The width of the lithium supplement portion is 1 mm to 10 mm.

9. The secondary battery according to any one of claims 1-8, characterized in that, The lithium supplement portion further includes a conductive carrier, and the metallic lithium exists inside the conductive carrier.

10. The secondary battery according to any one of claims 1-9, characterized in that the edge portion of the secondary battery includes the edge of the negative electrode film layer and the edge of the positive electrode film layer facing the edge of the negative electrode film layer, the main body portion of the secondary battery includes the main body of the negative electrode film layer and the main body of the positive electrode film layer facing the main body of the negative electrode film layer, the CB value of the edge portion of the secondary battery is greater than the CB value of the main body portion of the secondary battery.

11. An electrical device, characterized in that, including the secondary battery according to any one of claims 1 to 10.

Images