Negative pole piece, secondary battery and electric device

Abstract

The invention relates to a negative pole piece, a secondary battery and an electric device, and belongs to the technical field of secondary batteries. The negative electrode plate provided by the invention comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer comprises graphite with a lamellar structure, and anions are embedded between at least part of adjacent graphite lamellas. The negative pole piece effectively improves the rate capability and the cycle life of the secondary battery.

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] Secondary batteries are widely used in electric vehicles and consumer electronics due to their outstanding features such as light weight, no pollution, and no memory effect. Negative electrode materials are an important component that determines the performance of secondary batteries. With the rapid growth and changes in the consumer market, especially the rapid development of electric vehicles, higher requirements are placed on the performance of secondary batteries. Graphite is a mainstream negative electrode material, and its poor rate performance makes it difficult to meet the needs of the fast charging market. Therefore, graphite negative electrode materials still need to be improved. Summary of the invention

[0004] Based on this, the present application provides a negative electrode plate, a secondary battery and an electrical device to improve the rate performance and cycle life of a secondary battery containing graphite.

[0005] In a first aspect of the present application, a negative electrode plate is provided, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer contains graphite with a lamellar structure, and anions are embedded between at least part of adjacent graphite lamellar layers.

[0006] By embedding anions between graphite sheets, the graphite sheets are stretched and the interlayer spacing of the graphite is increased, thereby reducing the resistance of active ions to embed into the graphite and the resistance to diffusion in the graphite, thereby improving the rate performance of secondary batteries containing graphite; the increase in the interlayer spacing of the graphite reduces the volume change of the graphite when the active ions are embedded in and de-embedded in the graphite, which can enhance the stability of the solid electrolyte interface film (SEI film) on the graphite surface and improve the cycle life of the secondary battery.

[0007] In some embodiments, the anion comprises PF6 - 、BF4 - TFSI-FSI - 、ODFB - PO2F2 - 、ClO4 - and NO3 - One or more of .

[0008] In some embodiments, the interlayer spacing of the graphite is d>0.336nm; optionally, 0.47nm≥d>0.336nm.

[0009] In some embodiments, the mass of the anions accounts for 0.1%-40% of the total mass of the graphite and the anions, and can be optionally 0.3%-30%.

[0010] In some embodiments, the volume average particle size Dv50 of the graphite is 4 μm-20 μm, and can be 6 μm-15 μm.

[0011] In some embodiments, the specific surface area of ​​the graphite is 0.8 m 2 / g-1.5m 2 / g.

[0012] In some embodiments, the graphite includes artificial graphite and natural graphite, and optionally includes artificial graphite.

[0013] A second aspect of the present application provides a secondary battery, comprising the negative electrode sheet described in the first aspect of the present application.

[0014] The secondary battery of the present application includes the negative electrode sheet provided in the first aspect of the present application, and thus has at least the same advantages as the negative electrode sheet.

[0015] In some embodiments, the secondary battery comprises a lithium-ion battery.

[0016] In some embodiments, the secondary battery further includes an electrolyte, and the electrolyte includes the anions.

[0017] A third aspect of the present application provides an electrical device, comprising the secondary battery described in the second aspect of the present application.

[0018] The electric device of the present application includes the secondary battery provided in the second aspect of the present application, and thus has at least the same advantages as the secondary battery.

[0019] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0021] Figure 1 The X-ray diffraction pattern of the negative electrode sheet and the negative electrode sheet intermediate according to one embodiment of the present application.

[0022] Figure 2 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0023] Figure 3 for Figure 2 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0024] Figure 4 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0025] Figure 5 A schematic diagram of a battery pack according to an embodiment of the present application.

[0026] Figure 6 for Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0027] Figure 7 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.

[0028] Description of reference numerals:

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

[0030] Below, some embodiments of the negative electrode plate, secondary battery and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0031] "Scope" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or excluding end values, and any end value can be included or not included independently, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are also listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are 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 for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

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

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

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

[0035] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0036] In the present application, in the open technical features or technical solutions described by the words "contain", "include", "comprise", etc., unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A not only includes a1, a2 and a3, but also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

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

[0038] As a power storage device, secondary batteries have great development potential and occupy a huge consumer market with their unique advantages. The negative electrode material is an important component that determines the performance of secondary batteries. Among them, graphite negative electrode materials have a theoretical specific capacity of 372mAh / g, and have many advantages such as low price, low voltage platform, wide source, non-toxic and harmless. However, its poor rate performance makes it difficult to meet the needs of the fast charging market.

[0039] Graphite is a type of sp 2Anisotropic layered materials composed of hybrid carbon atoms work by intercalation mechanism. Under the reduction potential, active ions are embedded into the bulk phase from the edge of the graphite layer and diffuse to form intercalation compounds with carbon atoms. When the secondary battery is charged and discharged at a high rate, the diffusion rate of active ions in the electrolyte is much greater than the diffusion rate of active ions between graphite sheets. Active ions cannot be embedded in or de-embedded from the graphite layers in time, resulting in poor rate performance of graphite.

[0040] Based on the above technical problems, the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises graphite having a lamellar structure, and anions are embedded between at least some adjacent graphite lamellar layers. By embedding anions between graphite lamellar layers, the graphite lamellar layers are stretched open, the interlayer spacing of graphite is increased, the resistance of active ions to embedding into graphite and the resistance to diffusion in graphite are reduced, the embedding and de-embedding speed of active ions is increased, and the rate performance of secondary batteries containing graphite is improved. In addition, the interlayer spacing of graphite is increased, so that when active ions are embedded and de-embedded in graphite, the volume change of graphite is reduced, which is beneficial to enhance the stability of the SEI film on the graphite surface and improve the cycle life of the secondary battery.

[0041] Negative electrode

[0042] An embodiment of the present application provides a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, the negative electrode active material layer contains graphite with a lamellar structure, and anions are embedded between at least part of adjacent graphite lamellar layers.

[0043] In the above-mentioned embodiment, anions are embedded between graphite sheets to stretch the graphite sheets and increase the interlayer spacing of the graphite, thereby reducing the resistance of active ions to embed into the graphite and the resistance to diffusion in the graphite, thereby improving the rate performance of the secondary battery containing graphite; in addition, the interlayer spacing of the graphite is increased, so that when the active ions are embedded in and de-embedded in the graphite, the volume change of the graphite is reduced, thereby enhancing the stability of the SEI film on the graphite surface and improving the cycle life of the secondary battery.

[0044] After graphite is embedded with anions, the physical phase of graphite itself undergoes irreversible changes, the intensity of its 002 crystal plane decreases, the peak becomes wider, and a new characteristic peak appears in the X-ray diffraction spectrum. In addition, the following method can be used to detect the anions embedded between graphite sheets: discharge the battery to 2.5V, disassemble it, take out the negative electrode plate, soak the negative electrode plate with dimethyl carbonate 3 times, 15 minutes each time, wash and dry. Place the negative electrode plate in a Bruker D8 model XRD diffractometer and use a Cu target for testing; the test angle is 10°-70°. According to the angle 2θ measured by XRD and the Bragg equation 2dsinθ=nλ, the graphite interlayer spacing d is calculated; where n is the diffraction order and λ is the wavelength of the x-ray. If the calculated graphite interlayer spacing d>0.336nm, and a new characteristic peak appears in the obtained X-ray diffraction spectrum, it means that anions are embedded between the graphite sheets. Furthermore, the elemental species of the anions can be determined by inductively coupled plasma optical emission spectrometry (ICP-OES).

[0045] In the present application, since graphite includes a lamellar structure, "anions are embedded between at least some adjacent graphite lamellar layers" may mean that anions are embedded between all adjacent lamellar layers in the graphite, or only some adjacent lamellar layers in the graphite.

[0046] 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.

[0047] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. 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.

[0048] In some embodiments, the anion comprises PF6 - 、BF4 - TFSI - 、FSI - 、ODFB - PO2F2 - 、ClO4 - and NO3- One or more of the above. The embedding of the above-mentioned types of anions between graphite sheets can further improve the rate performance and cycle life of the secondary battery. The specific types of anions can be determined by measuring the components of the anions using an inductively coupled plasma optical emission spectrometer (ICP-OES) and / or an EDS spectrometer.

[0049] In some embodiments, the interlayer spacing d of graphite is greater than 0.336nm. The interlayer spacing of graphite is controlled within the above range, which can further improve the rate performance and cycle life of the secondary battery while taking into account the cost of the secondary battery. It is understood that the interlayer spacing d of graphite includes but is not limited to: 0.34nm, 0.35nm, 0.37nm, 0.39nm, 0.41nm, 0.43nm, 0.45nm, 0.47nm, 0.49nm, 0.51nm, etc. Further, 0.47nm≥d>0.336nm.

[0050] In the present application, anions may be embedded between all adjacent graphite sheets, or only between some adjacent graphite sheets. Therefore, the interlayer spacing of graphite may be completely equal, partially unequal, or completely unequal. "The interlayer spacing of graphite d>0.336nm" can be understood as the maximum interlayer spacing of graphite d>0.336nm.

[0051] In some embodiments, the mass of anions accounts for 0.1%-40% of the total mass of graphite and anions. The mass of anions accounts for the percentage of the total mass of graphite and anions within the above range, which can further improve the rate performance and cycle life of the secondary battery. It is understandable that the mass of anions accounts for the percentage of the total mass of graphite and anions, including but not limited to: 0.1%, 0.2%, 0.3%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 35%, 40%. Further, the mass of anions accounts for the percentage of the total mass of graphite and anions, which can be selected as 0.3%-30%.

[0052] In some embodiments, graphite has a diffraction peak between 18° and 22° in the X-ray diffraction spectrum. After the graphite is embedded with anions, the physical phase of the graphite itself undergoes an irreversible change, the intensity of its 002 crystal plane decreases, the peak becomes wider, and a new characteristic peak appears between 18° and 22° in the X-ray diffraction spectrum. Figure 1 PF6 anions are embedded in the graphite layers of the negative electrode. - , the graphite layers in the negative electrode intermediate are not embedded with anions PF6 - ; Compared with the negative electrode intermediate, the 002 crystal plane intensity in the X-ray diffraction pattern of the negative electrode is reduced, the peak becomes wider, and a new characteristic peak appears between 18° and 22°.

[0053] In some embodiments, the volume average particle size Dv50 of graphite is 4μm-20μm. The volume average particle size Dv50 of graphite is controlled within the above range, which can further improve the rate performance and cycle performance of the secondary battery. It can be understood that the volume average particle size Dv50 of graphite includes but is not limited to: 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm, 17μm, 18μm, 20μm. The volume average particle size Dv50 of graphite can be selected as 6μm-15μm.

[0054] In some embodiments, the specific surface area of ​​graphite is 0.8 m 2 / g-1.5m 2 / g. The specific surface area of ​​graphite is controlled within the above range, which can further improve the rate performance and cycle performance of the secondary battery. It can be understood that the specific surface area of ​​graphite includes but is not limited to: 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g.

[0055] In the present application, the volume average particle size Dv50 of graphite is the same or substantially the same as the volume average particle size Dv50 of the graphite raw material, and the specific surface area of ​​graphite is the same or substantially the same as the specific surface area of ​​the graphite raw material. The graphite raw material refers to graphite without anions embedded therein.

[0056] In some embodiments, the graphite includes artificial graphite and natural graphite. Artificial graphite may be optionally included.

[0057] In some embodiments, in addition to graphite, the negative electrode active material in the negative electrode active material layer may also use other negative electrode active materials for batteries known in the art. As a non-limiting example, in addition to graphite, the negative electrode active material may also include one or more of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials 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.

[0058] 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).

[0059] 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.

[0060] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0061] Another embodiment of the present application provides a method for preparing the above-mentioned negative electrode sheet, comprising the following steps:

[0062] Preparing a negative electrode active material layer on at least one surface of a negative electrode current collector to obtain a negative electrode sheet intermediate;

[0063] The negative electrode sheet intermediate is charged in an electrolyte containing the above anions to obtain a negative electrode sheet.

[0064] In some embodiments, the step of charging the negative electrode sheet intermediate in the first electrolyte containing the above-mentioned anions to obtain the negative electrode sheet includes:

[0065] Assembling the negative electrode intermediate, the separator and the positive electrode, and then baking and injecting the electrolyte containing the above anions to form a battery, wherein the separator is arranged between the negative electrode intermediate and the positive electrode;

[0066] Charging the battery so that the anions in the electrolyte containing the anions are embedded in the negative electrode plate intermediate;

[0067] Disassemble the charged battery to obtain the negative electrode;

[0068] Or include:

[0069] Assembling the negative electrode intermediate, the separator and the positive electrode, and then baking and injecting the electrolyte containing the above anions to form a battery, wherein the separator is arranged between the negative electrode intermediate and the positive electrode;

[0070] A third electrode is provided, and the negative electrode sheet intermediate is charged by the third electrode, so that the anions in the electrolyte containing the above anions are embedded in the negative electrode sheet intermediate to obtain the negative electrode sheet.

[0071] In the above embodiment, two methods can be used to prepare the negative electrode sheet. The first method is to assemble the negative electrode sheet into a battery, pre-embed the negative electrode sheet intermediate with anions, disassemble the battery, and take out the negative electrode sheet; after the negative electrode sheet is assembled into a battery again, the rate performance and cycle performance of the battery are improved. The first method is a method of non-in-situ embedding of anions. The second method is to charge the negative electrode sheet intermediate through the third electrode (i.e., charging the negative electrode sheet intermediate in a three-electrode system). The electrolyte contains the above anions, so the negative electrode sheet intermediate can be embedded with the above anions in situ to form a negative electrode sheet. This method does not require disassembly and reassembly of the battery, which is conducive to mass production.

[0072] In some embodiments, the charging potential is 2 V to 4.9 V, and the charging current is 0.01 C to 3 C. The percentage of the mass of anions to the total mass of graphite and anions can be controlled by adjusting the charging potential and the charging current.

[0073] In some embodiments, the step of preparing a negative electrode active material layer on at least one surface of a negative electrode current collector to obtain a negative electrode sheet intermediate includes: disposing a negative electrode slurry containing a graphite raw material on at least one surface of the negative electrode current collector to obtain a negative electrode sheet intermediate. "Graphite raw material" refers to graphite without anions embedded therein.

[0074] In some embodiments, the negative electrode sheet intermediate can be prepared in the following manner: the above-mentioned components for preparing the negative electrode sheet intermediate, 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 intermediate 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%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s-10000mPa·s. When the negative electrode slurry is coated, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 -220g / m 2 The compaction density of the negative electrode intermediate can be 1.0g / cm 3 -1.8g / cm 3 .

[0075] Yet another embodiment of the present application provides a secondary battery, comprising the above-mentioned negative electrode plate.

[0076] In some embodiments, the secondary battery comprises a lithium-ion battery.

[0077] In some embodiments, the secondary battery further comprises an electrolyte, and the electrolyte comprises anions. If the electrolyte comprises the anions, the anions can be in-situ embedded in the graphite layers in the electrolyte, and the process is more convenient.

[0078] Yet another embodiment of the present application provides an electrical device, comprising the secondary battery described above.

[0079] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0080] 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.

[0081] Positive electrode

[0082] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material.

[0083] 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.

[0084] 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.

[0085] As the Li content in the positive electrode active material changes, how to define the subscript of Li in the general formula:

[0086] For ternary materials:

[0087] Li x (Ni a Co b Mnc ) 1-d M d O 2-y A y , x is 0.2-1.2;

[0088] Li x A a (Ni a Co b Mn c ) 1-d M d O 2-y A y , x+a is 0.2-1.2;

[0089] For lithium manganese iron phosphate materials:

[0090] 1)Li a Mn 1-y B y P 1-z C z O 4-n D n , a is 0-1.1;

[0091] 2)Li a A x Mn 1-y B y P 1-z C z O 4-n D n , a+x is 0-1.1;

[0092] The above definition of x includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2V-5V).

[0093] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charging and discharging process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the enumeration of positive electrode active materials in this application, unless otherwise specified, the content of Li is the initial state of the material. The positive electrode active material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the content of Li in the positive electrode active material contained in the plate usually changes. Among them, the content of Li can be measured by molar content, but is not limited to this. Regarding "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that the new material obtained by appropriate modification on the basis of the listed positive electrode active materials is also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to the acceptable modification method for the positive electrode active material, and non-limiting examples include coating modification.

[0094] In the list of positive electrode active materials in this application, the content of oxygen (O) is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. Among them, the content of O can be measured by molar content, but is not limited to this.

[0095] In some embodiments, the positive electrode active material may adopt 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.

[0096] In some 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.

[0097] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some 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%-80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s-25000mPa·s. When applying the positive electrode slurry, the coating unit surface density based on dry weight (excluding solvent) can be 15 mg / cm 2 -35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 -3.6g / cm 3 , optional 3.3g / cm 3 -3.5g / cm 3 .

[0099] Negative electrode

[0100] The negative electrode sheet of the above embodiment of the present application is adopted.

[0101] Electrolytes

[0102] 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.

[0103] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0104] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Isolation film

[0109] 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.

[0110] 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.

[0111] In some embodiments, the isolation film has a thickness of 6 μm-40 μm, and optionally 12 μm-20 μm.

[0112] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0113] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0114] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0115] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0116] 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.

[0117] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 2 The battery cell 5 is a square structure as an example.

[0118] In some embodiments, reference Figure 3, the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0119] The secondary battery may be a battery module 4 or a battery pack 1 .

[0120] 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.

[0121] Figure 4 4 is an example of a battery module. Figure 4 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0122] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0123] In some embodiments, the battery modules described above may also be assembled into a battery pack. The number of battery modules contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0124] Figure 5 and Figure 6 1 is a battery pack 1 as an example. Figure 5 and Figure 6 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0125] 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.

[0126] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0127] Figure 7 The power consumption device 6 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0128] 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.

[0129] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If the techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used that do not specify the manufacturer are all conventional products that can be obtained commercially.

[0130] Example 1

[0131] (1) Preparation of positive electrode sheet

[0132] The positive electrode active material lithium iron phosphate, the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2.5:1.5, and the solvent N-methylpyrrolidone was added, and the mixture was fully stirred to obtain a positive electrode slurry, which was then coated on both surfaces of the positive electrode current collector aluminum foil. The coating weight of the positive electrode slurry was 0.300 g / 1540.25 mm 2 (measured by weight excluding solvent), and then dried and cold pressed to obtain a positive electrode sheet.

[0133] (2) Preparation of negative electrode sheet

[0134] (2.1) The negative electrode active material graphite raw material, the conductive agent acetylene black, and the binder (SBR and CMC) were mixed in a weight ratio of 96:2:1.6:0.4, and the solvent deionized water was added. The mixture was stirred and mixed to obtain a negative electrode slurry, which was then coated on both surfaces of the negative electrode current collector copper foil. The coating weight of the negative electrode slurry was 0.137 g / 1540.25 mm 2 (based on weight excluding solvent), drying and cold pressing to obtain a negative electrode intermediate; wherein the graphite raw material is artificial graphite;

[0135] (2.2) Assemble the negative electrode intermediate, PE isolation film and lithium sheet, then bake and inject an electrolyte containing LiPF6 to form a battery, wherein the isolation film is arranged between the negative electrode intermediate and the lithium sheet; adjust the charging potential of the battery to 2.0V-4.8V, and the charging current to 0.1C (0.05mA). After charging is completed, disassemble the battery to obtain the negative electrode sheet.

[0136] (3) Preparation of electrolyte

[0137] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, DMC, etc. are mixed in a specific proportion and then the fully dried lithium salt LiPF6 is dissolved in the above mixed organic solvent. After stirring evenly, an electrolyte is obtained in which the concentration of LiPF6 is 1 mol / L.

[0138] (4) Isolation film

[0139] A polyethylene porous membrane was used as the isolation membrane.

[0140] (5) Preparation of secondary batteries

[0141] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play a role of isolation, and then stacked to obtain a bare cell. The bare cell is placed in an aluminum shell, injected with a prepared electrolyte and packaged to obtain a lithium-ion secondary battery.

[0142] The secondary batteries of Examples 2-17 and the secondary batteries of Comparative Example 1 are prepared in a similar manner to the secondary battery of Example 1, but use the negative electrode sheets prepared in the corresponding Examples or Comparative Examples. The product parameters of Examples 1-17 and Comparative Example 1 are shown in Table 1.

[0143] Performance Testing

[0144] (1) Specific surface area test of graphite raw materials

[0145] The specific surface area of ​​the graphite raw material is tested by nitrogen adsorption and desorption method. For example, a specific surface area analyzer (Tri star II) can be used to measure the BET specific surface area of ​​the material, referring to GB / T 19587-2004 standard.

[0146] (2) Volume average particle size Dv50 test of graphite raw materials

[0147] Dv50 refers to the particle size corresponding to 50% in the volume distribution. As an example, Dv50 can be conveniently measured by referring to GB / T19077-2016 particle size distribution laser diffraction method using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK.

[0148] (3) Test on the percentage of the mass of anions to the total mass of graphite and anions

[0149] The mass of the anions is determined by an inductively coupled plasma optical emission spectrometer (ICP-OES) based on the characteristic elements of the anions. The total mass of the graphite and the anions can be weighed using a high-precision balance, thereby calculating the percentage of the mass of the anions in the total mass of the graphite and the anions.

[0150] (4) Test of graphite interlayer spacing d

[0151] The secondary battery was discharged to 2.5V, disassembled, and the negative electrode was taken out. The negative electrode was soaked in dimethyl carbonate for 3 times, 15 minutes each time, and then washed and dried. The negative electrode was placed in a Bruker D8 XRD diffractometer and tested with a Cu target; the test angle was 10°-70°. According to the angle 2θ measured by XRD and the Bragg equation 2dsinθ=nλ, the graphite layer spacing d was calculated; where n is the diffraction order and λ is the x-ray wavelength.

[0152] (5) Capacity retention test

[0153] At room temperature, the secondary battery is charged to the upper limit voltage at a rate of 0.33C, and then discharged to the lower limit voltage at 0.33C and 1C respectively. The discharge capacity at a rate of 0.33C is used as the nominal capacity reference group, and the capacity retention rate of the lithium-ion battery discharged at a rate of 1C is calculated, which is the 1C capacity retention rate.

[0154] At room temperature, the secondary battery is charged to the upper limit voltage at 0.33C rate, and then discharged to the lower limit voltage at 0.33C and 2C respectively. The discharge capacity at 0.33C rate is used as the nominal capacity reference group, and the capacity retention rate of the lithium-ion battery discharged at 2C rate is calculated, which is the 2C capacity retention rate.

[0155] At room temperature, the discharge capacity of the secondary battery prepared in Comparative Example 1 at a rate of 0.33C is recorded as C0, and the discharge capacity of the secondary batteries prepared in Examples 1-17 at a rate of 0.33C is recorded as C nThe calculation method of 0.33C-base of the secondary battery prepared in Examples 1-17 is as follows: (C n -C0) / C0×100%.

[0156] (6) Cycle life test

[0157] At 25°C, charge the secondary battery to 3.65V at a rate of 0.5C, then charge at a constant voltage until the current is less than 0.05C, and then discharge to 2.5V at a rate of 1C. Perform a cycle test in this full charge and discharge form until the discharge capacity of the lithium-ion battery decays to 80% of the initial capacity. Record the number of cycles at this time, which is the cycle life.

[0158] The performance of the secondary batteries of Examples 1-17 and Comparative Example 1 is shown in Table 2.

[0159] Table 1

[0160]

[0161] Table 2

[0162]

[0163]

[0164] It can be seen from Table 1 and Table 2 that anions are embedded between the graphite flakes of Examples 1-17, the interlayer spacing of the graphite of Examples 1-17 is larger than the interlayer spacing of the graphite of Comparative Example 1, and the 2C capacity retention rate and cycle life of the secondary batteries of Examples 1-17 are significantly improved relative to the secondary battery of Comparative Example 1, indicating that the anions embedded between the graphite flakes of Examples 1-17 effectively improve the rate performance and cycle life of the secondary batteries.

[0165] The above description of various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced to each other, and for the sake of brevity, they will not be repeated herein.

[0166] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: The negative electrode plate 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 graphite having a sheet structure, and anions are embedded between at least some adjacent graphite sheets.

2. The negative electrode sheet according to claim 1, characterized in that: The anion includes PF6 - 、BF4 - TFSI-FSI - 、ODFB-、PO2F2 - 、ClO4 - and NO3 - One or more of .

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The interlayer spacing of the graphite is d>0.336nm; optionally, 0.47nm≥d>0.336nm.

4. The negative electrode sheet according to claim 1 or 2, characterized in that: The mass of the anions accounts for 0.1%-40% of the total mass of the graphite and the anions, and can be optionally 0.3%-30%.

5. The negative electrode sheet according to claim 1 or 2, characterized in that: The volume average particle size Dv50 of the graphite is 4 μm-20 μm, and can be optionally 6 μm-15 μm.

6. The negative electrode sheet according to claim 1 or 2, characterized in that: The specific surface area of ​​the graphite is 0.8 m 2 / g-1.5m 2 / g.

7. The negative electrode sheet according to claim 1 or 2, characterized in that: The graphite includes artificial graphite and natural graphite, and optionally includes artificial graphite.

8. A secondary battery, characterized in that: A negative electrode sheet comprising any one of claims 1 to 7; Optionally, the secondary battery comprises a lithium-ion battery.

9. The secondary battery according to claim 8, characterized in that: The secondary battery further includes an electrolyte solution containing the anions.

10. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 8 to 9.

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