Negative pole piece, secondary battery and electric device

Abstract

The invention provides a negative pole piece, a secondary battery and an electric device. The negative pole piece comprises a negative current collector, and a first active layer and a second active layer which are positioned on at least one surface of the negative current collector, and the first active layer is positioned between the negative current collector and the second active layer; the first active layer comprises a first silicon-based material, the second active layer comprises a second silicon-based material, the sphericity degree of the first silicon-based material is larger than that of the second silicon-based material, and the sphericity degree of the first silicon-based material is larger than or equal to 0.6.

Description

Technical Field

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

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

[0003] In secondary batteries, the use of silicon-based materials can improve the energy density of the battery. However, after the battery is charged, the structural stability of the pole piece containing silicon-based materials is poor, which may reduce the cycle performance of the battery. Summary of the invention

[0004] The present application provides a negative electrode plate, comprising a negative electrode current collector, and a first active layer and a second active layer located on at least one surface of the negative electrode current collector, wherein the first active layer is located between the negative electrode current collector and the second active layer; the first active layer comprises a first silicon-based material, and the second active layer comprises a second silicon-based material, the sphericity of the first silicon-based material is greater than the sphericity of the second silicon-based material, and the sphericity of the first silicon-based material is ≥0.6.

[0005] In the above-mentioned negative electrode plate, by adapting the first silicon-based material and the second silicon-based material with appropriate sphericity, the stability of the negative electrode plate structure can be improved, thereby improving the cycle performance of the battery.

[0006] In some embodiments, the sphericity of the first silicon-based material is 0.6-1.

[0007] In some embodiments, the second silicon-based material has a sphericity of 0.3 to 0.8.

[0008] In some embodiments, the mass percentage of the first silicon-based material in the active material in the first active layer is less than the mass percentage of the second silicon-based material in the active material in the second active layer.

[0009] In some embodiments, the mass percentage of the first silicon-based material in the active material in the first active layer is ≤15%.

[0010] In some embodiments, the mass percentage of the second silicon-based material in the active material in the second active layer is 5% to 40%.

[0011] In some embodiments, Dv50 of the first silicon-based material ≤ Dv50 of the second silicon-based material.

[0012] In some embodiments, the Dv50 of the first silicon-based material is 4 μm to 8 μm.

[0013] In some embodiments, the Dv50 of the second silicon-based material is 6 μm to 10 μm.

[0014] In some embodiments, the specific surface area of ​​the first silicon-based material is less than or equal to the specific surface area of ​​the second silicon-based material.

[0015] In some embodiments, the specific surface area of ​​the first silicon-based material is 0.5 m 2 / g~2.5m 2 / g.

[0016] In some embodiments, the specific surface area of ​​the second silicon-based material is 1 m 2 / g~4m 2 / g.

[0017] In some embodiments, the thickness of the first active layer is greater than or equal to the thickness of the second active layer.

[0018] In some embodiments, the thickness of the first active layer is 20 μm to 40 μm.

[0019] In some embodiments, the second active layer has a thickness of 20 μm to 40 μm.

[0020] In some embodiments, the first silicon-based material contains oxygen.

[0021] In some embodiments, the mass percentage of oxygen in the first silicon-based material is 40% to 60%.

[0022] In some embodiments, the second silicon-based material includes oxygen.

[0023] In some embodiments, the mass percentage of oxygen in the second silicon-based material is ≤10%.

[0024] In some embodiments, the first silicon-based material comprises carbon.

[0025] In some embodiments, the mass percentage of carbon in the first silicon-based material is ≤8%.

[0026] In some embodiments, the second silicon-based material comprises carbon.

[0027] In some embodiments, the mass percentage of carbon element in the second silicon-based material is 40% to 60% of the mass of the second silicon-based material.

[0028] In some embodiments, the first silicon-based material contains a doping metal element; the doping metal element includes at least one of an alkali metal element and an alkaline earth metal element.

[0029] In some embodiments, the mass percentage of the doped metal element in the first silicon-based material is ≤10%.

[0030] In some embodiments, a surface of the first silicon-based material and / or a surface of the second silicon-based material is coated with a carbon coating layer.

[0031] In some embodiments, the carbon coating layer has a thickness of 10 nm to 300 nm.

[0032] In some embodiments, the first active layer further comprises a first graphite.

[0033] In some embodiments, the mass percentage of the first graphite in the active material in the first active layer is ≥ 85%.

[0034] In some embodiments, the second active layer further comprises a second graphite.

[0035] In some embodiments, the second graphite accounts for 60% to 95% of the mass of the active material in the second active layer.

[0036] The present application also provides a secondary battery, comprising the negative electrode plate.

[0037] The present application also provides an electrical device, comprising at least one of the negative electrode plate and the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0039] Figure 1 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0040] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0041] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0042] Description of reference numerals:

[0043] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device.

[0044] In order to better describe and illustrate the embodiments and / or examples of the inventions disclosed herein, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered to limit the scope of the disclosed inventions, the embodiments and / or examples currently described, and any of the best modes of these inventions currently understood. DETAILED DESCRIPTION

[0045] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which the present application belongs. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0047] The "range" disclosed in the present application can be defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and any end value can be included or excluded independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0048] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0051] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] In this application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A includes not only a1, a2 and a3, but also other members".

[0053] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0054] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0055] An embodiment of the present application provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector, and a first active layer and a second active layer located on at least one surface of the negative electrode current collector, the first active layer is located between the negative electrode current collector and the second active layer; the first active layer includes a first silicon-based material, the second active layer includes a second silicon-based material, the sphericity of the first silicon-based material is greater than the sphericity of the second silicon-based material, and the sphericity of the first silicon-based material is ≥0.6.

[0056] In the negative electrode plate of the present embodiment, by adapting the first silicon-based material and the second silicon-based material with appropriate sphericity, the stability of the negative electrode plate structure can be improved, thereby improving the cycle performance of the battery.

[0057] It is understood that the sphericity in the present application represents the ratio of the shortest diameter to the longest diameter of a material. It can be tested by the following method: using a Malvern automatic image particle size analyzer to capture and process images of a certain number (≥20 particles) of dispersed particles, and then using image-guided Raman spectroscopy (MDRS) to accurately analyze the microstructure and morphology of the particles, obtain the longest diameter and the shortest diameter of all particles, calculate the ratio of the shortest diameter to the longest diameter of each particle, obtain the sphericity of each particle, and take the average of the sphericity of all particles as the average sphericity.

[0058] It can also be understood that, in the present application, the sphericity of the first silicon-based material refers to the average sphericity of the first silicon-based material, and the sphericity of the second silicon-based material refers to the average sphericity of the second silicon-based material.

[0059] In the present application, as some optional examples of the sphericity of the first silicon-based material, the sphericity of the first silicon-based material is 0.6 to 1. For example, the sphericity of the first silicon-based material is 0.6, 0.7, 0.8, 0.9 or 1, etc. When the sphericity of the first silicon-based material is too small, the sphericity of the first silicon-based material is poor. At this time, the first silicon-based material may show relatively sharp edges and corners, which may increase the risk of the first silicon-based material damaging the negative electrode current collector during the tableting process. In addition, when the sphericity of the first silicon-based material is too small, the shape of the first silicon-based material is relatively irregular, which may increase the risk of pulverization of the first silicon-based material during the tableting process, and may deteriorate the structural stability of the negative electrode sheet, thereby affecting the cycle performance of the battery.

[0060] In some embodiments, the sphericity of the second silicon-based material is 0.3 to 0.8. Optionally, the sphericity of the second silicon-based material is 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8, etc. If the sphericity of the second silicon-based material is too small, the shape of the second silicon-based material is relatively irregular, which may increase the risk of pulverization of the second silicon-based material during the tableting process, and may cause the structural stability of the negative electrode sheet to deteriorate, thereby affecting the cycle performance of the battery. If the sphericity of the second silicon-based material is too large, the increase in compaction density may be limited, thereby restricting the further improvement of the compaction density of the negative electrode sheet.

[0061] In some embodiments, the mass percentage of the first silicon-based material in the active material of the first active layer is ≤ the mass percentage of the second silicon-based material in the active material of the second active layer. This can effectively take into account both high energy density and low expansion rate, which is conducive to further maintaining high energy density and good cycle performance of the battery.

[0062] Optionally, the mass percentage of the first silicon-based material in the active material in the first active layer is ≤15%. If the mass percentage of the first silicon-based material in the active material in the first active layer is too small, the improvement in the battery energy density is limited. If the mass percentage of the first silicon-based material in the active material in the first active layer is too large, it may cause a large expansion problem and the battery cycle performance may be easily deteriorated. As some examples of the mass percentage of the first silicon-based material in the active material in the first active layer, the mass percentage of the first silicon-based material in the active material in the first active layer can be 1%, 2%, 5%, 8%, 10%, 12%, 15%, etc.

[0063] Optionally, the mass percentage of the second silicon-based material in the active material in the second active layer is 5% to 40%. Too small a mass percentage of the second silicon-based material in the active material in the second active layer may limit the effective improvement of the battery energy density. Too large a mass percentage of the second silicon-based material in the active material in the second active layer may cause a large expansion problem, and the battery cycle performance may be easily deteriorated. As some examples of the mass percentage of the second silicon-based material in the active material in the second active layer, the mass percentage of the second silicon-based material in the active material in the second active layer can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0064] In some embodiments, the first silicon-based material contains oxygen. Optionally, the mass percentage of oxygen in the first silicon-based material is 40% to 60%. Further optionally, the mass percentage of oxygen in the first silicon-based material is 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60%, etc. It is understandable that the first silicon-based material is selected from silicon-oxygen materials.

[0065] In some embodiments, the second silicon-based material contains oxygen. Optionally, the oxygen in the second silicon-based material accounts for ≤10% by mass of the second silicon-based material. Further optionally, the oxygen in the second silicon-based material accounts for ≤10%, ≤9%, ≤8%, ≤7%, ≤6%, ≤5%, ≤4%, ≤3%, ≤2% or 1% by mass of the second silicon-based material.

[0066] In some embodiments, the first silicon-based material and the second silicon-based material both contain oxygen, and the mass percentage of oxygen in the first silicon-based material is greater than the mass percentage of oxygen in the second silicon-based material. This can further reduce the expansion rate of the electrode and maintain the structural stability of the negative electrode during the charging process.

[0067] In some embodiments, the second silicon-based material does not contain oxygen, that is, the mass percentage of oxygen in the second material to the second silicon-based material is 0.

[0068] In some embodiments, the first silicon-based material contains carbon. Optionally, the mass percentage of carbon in the first silicon-based material is ≤8%. Further optionally, the mass percentage of carbon in the first silicon-based material is ≤7%, ≤6%, ≤5%, ≤4%, ≤3%, ≤2% or ≤1%, etc. It is understood that the first silicon-based material may not contain carbon.

[0069] In some embodiments, the second silicon-based material contains carbon. Optionally, the carbon in the second silicon-based material accounts for 40% to 60% of the mass percentage of the second silicon-based material. Further optionally, the carbon in the second silicon-based material accounts for 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60% of the mass percentage of the second silicon-based material. It is understood that the second silicon-based material is selected from a silicon-carbon composite.

[0070] In some embodiments, the first silicon-based material and the second silicon-based material both contain carbon, and the mass percentage of carbon in the first silicon-based material is less than the mass percentage of carbon in the second silicon-based material.

[0071] In some embodiments, the first silicon-based material is selected from silicon-oxygen materials. The second silicon-based material is selected from silicon-carbon composites.

[0072] In some embodiments, the silicon-oxygen material can be prepared by the following method:

[0073] S101: providing silicon and silicon dioxide, wherein the molar ratio of silicon to silicon dioxide is 1:1, to obtain a mixture. Optionally, metallic magnesium may also be added, the proportion of which accounts for 7% to 10% by mass of the mixture;

[0074] S102: Using a vapor deposition method, the mixed material in S101 is heated to 1100° C. to 1500° C. to form vapor, and then the vapor is cooled to 700° C. to 900° C. to form a deposit.

[0075] S103: crushing the sediment to obtain a crushed product of suitable particle size, adding the crushed material to a CVD rotary furnace, introducing an organic gas source, depositing at 600°C to 1000°C for 1h to 6h, sieving and removing magnetism, and obtaining a silicon-oxygen material. Optionally, the organic gas source includes a gaseous carbon source. Further optionally, the carbon source includes at least one of an alkane and an alkyne.

[0076] Further optionally, the silicon-oxygen material obtained in S103 may be subjected to a pre-lithiation treatment.

[0077] Further, optionally, the silicon-oxygen material may be subjected to post-coating treatment. Optionally, the post-coating may be inorganically coated with salts such as phosphates and / or silicates. The post-coating treatment may be liquid-phase coating.

[0078] In some embodiments, the silicon-carbon composite can be prepared by the following method:

[0079] S201: Provide a carbonaceous precursor. The carbonaceous precursor may be at least one of a biomass precursor and a resin precursor. Optionally, the biomass precursor may be at least one of coconut shell biomass and starch biomass.

[0080] S202: Carbonizing the carbonaceous precursor in a nitrogen atmosphere at a temperature of 600° C. to 1000° C. for 2 h to 10 h to obtain porous carbon.

[0081] S203: The porous carbon is heated in an atmosphere containing a silicon source gas to deposit silicon element in the pores of the porous carbon to obtain a silicon-carbon composite.

[0082] Optionally, the silicon-carbon composite obtained in S203 may be subjected to carbon coating treatment.

[0083] It is understandable that silicon-oxygen materials and silicon-carbon composites can also be purchased from commercial channels.

[0084] In some embodiments, the first silicon-based material contains doped metal elements; the doped metal elements include at least one of alkali metal elements and alkaline earth metal elements. The introduction of doped metal elements can improve the initial efficiency of the battery. Optionally, the mass percentage of the doped metal elements in the first silicon-based material is ≤10%. Further optionally, the mass percentage of the doped metal elements in the first silicon-based material is ≤9%, ≤8%, ≤7%, ≤6%, ≤5%, ≤4%, ≤3%, ≤2% or ≤1%. It is understood that the alkali metal elements include at least one of lithium, sodium, potassium, rubidium and cesium. The alkaline earth metal elements include at least one of beryllium, magnesium, calcium, strontium and barium. Further optionally, the first silicon-based material includes pre-lithiation silicon-based materials and pre-magnesiation silicon-based materials.

[0085] In some embodiments, the surface of the first silicon-based material is coated with a carbon coating layer, and the coating layer has a thickness of 10nm to 300nm. Optionally, the thickness of the carbon coating layer on the surface of the first silicon-based material is 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, etc.

[0086] In some embodiments, the surface of the second silicon-based material is coated with a carbon coating layer, and the coating layer has a thickness of 10nm to 300nm. Optionally, the thickness of the carbon coating layer on the surface of the second silicon-based material is 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, etc.

[0087] In some embodiments, the first active layer further comprises a first graphite; optionally, the mass percentage of the first graphite in the active material in the first active layer is ≥ 85%. Optionally, the mass percentage of the first graphite in the active material in the first active layer is 85%, 88%, 90%, 92%, 95%, 98%, 99%, etc. Further optionally, the mass percentage of the first graphite in the active material in the first active layer is 85% to 99%.

[0088] In some embodiments, the second active layer further comprises a second graphite; optionally, the second graphite accounts for 60% to 95% of the mass percentage of the active material in the second active layer. Optionally, the second graphite accounts for 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc. of the mass percentage of the active material in the second active layer.

[0089] It can be understood that the first silicon-based material, the first graphite, the second silicon-based material, the second graphite, the oxygen element in the first silicon-based material, the carbon element in the first silicon-based material, the doped metal element in the first silicon-based material, the oxygen element in the second silicon-based material and the carbon element in the second silicon-based material can be detected by cross-section polishing (CP) of the negative electrode piece in combination with scanning electron microscopy (SEM), electrochemical dispersion spectroscopy (EDS) and inductively coupled plasma spectroscopy (ICP).

[0090] Another embodiment of the present application provides a secondary battery. The secondary battery includes the above-mentioned negative electrode plate.

[0091] Another embodiment of the present application provides an electric device, which includes at least one of the negative electrode sheet and the secondary battery.

[0092] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0093] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0094] Positive electrode

[0095] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0096] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0097] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0098] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333)、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.85 Co 0.15 Al 0.05 O2.

[0099] In some of these embodiments, the positive electrode active material layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0100] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000-25000mPa·s. When applying the positive electrode slurry, the coating unit area density based on dry weight (excluding solvent) can be 15-35 mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 to 3.6 g / cm 3 , can be selected as 3.3~3.5g / cm 3 .

[0102] Negative electrode

[0103] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0104] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0105] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0106] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0107] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0108] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0110] In some of the embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000-10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75-220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0111] Electrolytes

[0112] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0113] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0114] In some of the embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0115] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate One or more of fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0116] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0117] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0118] Isolation film

[0119] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0120] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0121] In some embodiments, the isolation film has a thickness of 6 to 40 μm, and may be 12 to 20 μm.

[0122] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0123] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0124] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0125] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0126] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0127] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The battery cell 1 is a square structure as an example.

[0128] In some of these embodiments, reference Figure 2, the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the battery cell 1 can be one or more, and those skilled in the art can select according to actual needs.

[0129] The secondary battery may be a battery module or a battery pack.

[0130] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0131] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0132] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0133] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0134] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0135] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0136] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0137] Figure 3 The power consumption device 2 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0138] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0139] Example

[0140] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0141] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0142] The preparation method of the secondary battery is as follows:

[0143] (1) Preparation of negative electrode sheet.

[0144] The first graphite, the first silicon-based material, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are mixed, deionized water is added, and the mixture is vacuum stirred to obtain a first slurry with a solid content of 49%.

[0145] The second graphite, the second silicon-based material, the conductive agent acetylene black, the thickener sodium carboxymethyl cellulose, and the binder styrene-butadiene rubber are mixed, deionized water is added, and the mixture is stirred in vacuum to obtain a second slurry with a solid content of 49%.

[0146] The first slurry was coated on the current collector copper foil and dried at 85°C to form the first active layer on the current collector. The second slurry was then coated on the first active layer and dried at 85°C, followed by cold pressing, trimming, striping, cutting, and finally drying at 120°C under vacuum for 12 hours to obtain the negative electrode sheet.

[0147] (2) Preparation of positive electrode sheets.

[0148] The positive electrode active material NCM, the binder polyvinylidene fluoride, and the conductive agent acetylene black were mixed in a ratio of 97:2:1, and then the solvent N-methylpyrrolidone (NMP) was added and stirred to form a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, dried, and cold pressed to obtain a positive electrode sheet.

[0149] (3) Preparation of electrolyte.

[0150] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed evenly in a volume ratio of 20:20:60 as an organic solvent, and then LiPF6 is dissolved in the above organic solvent, and fluoroethylene carbonate (FEC) is added. The concentration of LiPF6 in the electrolyte is 1 mol / L, and the mass percentage of FEC is 5wt%.

[0151] (4) The isolation membrane is Celgard 2400 isolation membrane.

[0152] (5) The negative electrode sheet, the separator, and the positive electrode sheet are stacked and wound in order to obtain a wound battery cell. The battery cell design capacity is 4.5Ah. The battery cell is placed in an outer square aluminum shell, dried, and then injected with electrolyte. After packaging, standing, formation, aging, secondary packaging, capacity, and other processes, a secondary battery is obtained.

[0153] The compositions of the negative electrode sheets in the examples and comparative examples are shown in Table 1.

[0154] Test Case

[0155] (1) Test the energy density of the battery: At 25°C, the prepared battery was fully discharged at 1C, then fully charged at 1C, and fully discharged at 1C, and the actual discharge energy at this time was recorded. At 25°C, the effective length, width, and thickness of the battery cell in the 1C fully charged state were tested, and the effective volume V was calculated; the ratio of the battery 1C actual discharge energy D to the effective volume V of the battery cell is the actual energy density E of the battery, E = D / V, where D is in Wh and V is in L.

[0156] (2) Electrode structure stability test: The obtained battery is fully charged at 1C, and the negative electrode is disassembled to obtain the negative electrode. The large surface is folded horizontally, and the folding line is rolled once with a 1kg standard roller. The folding and rolling operations are repeated three times to confirm the light transmission or fracture at the fold of the electrode. It is divided into four levels according to the severity: 1. Fracture: the electrode is disconnected; 2. Severe light transmission: >5 light transmission points; 3. Slight light transmission: 1 to 5 light transmission points; 4. No light transmission.

[0157] (3) Battery cycle performance test: The prepared battery was subjected to a 0.5C / 1C cycle test at 25°C, and the number of cycles at which the battery decayed to 80% was obtained, which corresponds to the battery cycle performance.

[0158] (4) Negative electrode expansion rate test: Fully charge the fresh battery cell at 0.33C / 0.33C after formation, disassemble it in a drying room to obtain the negative electrode, measure the thickness of the electrode in the fully charged state, and calculate the expansion rate by comparing it with the cold pressed thickness of the electrode. Expansion rate = (thickness of the negative electrode in the fully charged state - thickness of the negative electrode after cold pressing) / thickness of the negative electrode after cold pressing × 100%.

[0159] Table 1

[0160]

[0161] It is understood that in Table 1, "silicon oxygen" refers to silicon oxygen materials, and "silicon carbon" refers to silicon carbon composites. In Table 1, the unit of Dv50 is μm. The unit of specific surface area is m 2 / g. The unit of the thickness of the first active layer is μm. The unit of the thickness of the second active layer is μm. The unit of the thickness of the carbon coating layer is nm. The unit of the battery energy density is Wh / L. The unit of the battery cycle performance is cycle. The mass percentage of the first silicon-based material represents the mass percentage of the first silicon-based material in the active material of the first active layer. The mass percentage of the first graphite represents the mass percentage of the first graphite in the active material of the first active layer. The mass percentage of the second silicon-based material represents the mass percentage of the second silicon-based material in the active material of the first active layer. The mass percentage of the second graphite represents the mass percentage of the second graphite in the active material of the second active layer.

[0162] It can be seen from Table 1 that when the negative electrode plate contains silicon-based materials, the energy density of the battery is higher. When the sphericity of the first silicon-based material is greater than the sphericity of the second silicon-based material, the structural stability of the negative electrode plate is better, and the battery has better cycle performance. When the sphericity of the first silicon-based material is less than the sphericity of the second silicon-based material, the structural stability of the negative electrode plate is poor, and the cycle performance of the battery is also correspondingly poor.

[0163] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0164] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A negative electrode plate, characterized in that: It includes a negative electrode current collector, and a first active layer and a second active layer located on at least one surface of the negative electrode current collector, wherein the first active layer is located between the negative electrode current collector and the second active layer; the first active layer comprises a first silicon-based material, and the second active layer comprises a second silicon-based material, the sphericity of the first silicon-based material is greater than the sphericity of the second silicon-based material, and the sphericity of the first silicon-based material is ≥0.

6.

2. The negative electrode sheet according to claim 1, characterized in that: The sphericity of the first silicon-based material is 0.6 to 1; and / or, The sphericity of the second silicon-based material is 0.3-0.

8.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The mass percentage of the first silicon-based material in the active material of the first active layer is ≤ the mass percentage of the second silicon-based material in the active material of the second active layer; Optionally, the mass percentage of the first silicon-based material in the active material in the first active layer is ≤15%; Optionally, the mass percentage of the second silicon-based material in the active material in the second active layer is 5% to 40%.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The Dv50 of the first silicon-based material is ≤ the Dv50 of the second silicon-based material; Optionally, the Dv50 of the first silicon-based material is 4 μm to 8 μm; Optionally, the Dv50 of the second silicon-based material is 6 μm to 10 μm.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The specific surface area of ​​the first silicon-based material is less than or equal to the specific surface area of ​​the second silicon-based material; Optionally, the specific surface area of ​​the first silicon-based material is 0.5 m 2 / g~2.5m 2 / g; Optionally, the specific surface area of ​​the second silicon-based material is 1 m 2 / g~4m 2 / g.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The thickness of the first active layer is greater than or equal to the thickness of the second active layer; Optionally, the thickness of the first active layer is 20 μm to 40 μm; Optionally, the second active layer has a thickness of 20 μm to 40 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The first silicon-based material contains oxygen; Optionally, the mass percentage of oxygen element in the first silicon-based material is 40% to 60% of the first silicon-based material.

8. The negative electrode sheet according to any one of claims 1 to 7, characterized in that: The second silicon-based material contains oxygen; Optionally, the mass percentage of oxygen in the second silicon-based material is ≤10%.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that: The first silicon-based material contains carbon; Optionally, the mass percentage of carbon element in the first silicon-based material is ≤8%.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that: The second silicon-based material contains carbon; Optionally, the mass percentage of carbon element in the second silicon-based material is 40% to 60% of the mass of the second silicon-based material.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that: The first silicon-based material contains a doped metal element; the doped metal element includes at least one of an alkali metal element and an alkaline earth metal element; Optionally, the mass percentage of the doped metal element in the first silicon-based material is ≤10%.

12. The negative electrode sheet according to any one of claims 1 to 11, characterized in that: The surface of the first silicon-based material and / or the surface of the second silicon-based material is coated with a carbon coating layer; Optionally, the carbon coating layer has a thickness of 10 nm to 300 nm.

13. The negative electrode sheet according to any one of claims 1 to 12, characterized in that: The first active layer further comprises a first graphite; optionally, the first graphite accounts for ≥85% of the mass percentage of the active material in the first active layer; and / or, The second active layer further comprises a second graphite; optionally, the second graphite accounts for 60% to 95% of the mass percentage of the active material in the second active layer.

14. A secondary battery, characterized in that: The invention comprises the negative electrode sheet according to any one of claims 1 to 13.

15. An electrical device, characterized in that: The invention comprises at least one of the negative electrode sheet according to any one of claims 1 to 13 and the secondary battery according to claim 14.

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