Negative electrode sheet and preparation method thereof

Abstract

The present application provides a negative electrode plate, which includes: a negative electrode active material layer; an inner layer film covering the negative electrode active material layer; and an outer layer film covering the inner layer film, wherein the negative electrode active material layer includes graphite, the inner layer film includes at least 10 monolayers of metal organic compounds, and the outer layer film includes at least 40 monolayers of organic polymers.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode and a preparation method thereof. Background Art

[0002] Lithium metal has the lowest electrode potential (lithium has the lowest electrode potential standard hydrogen electrode) and an ultra-high theoretical specific capacity (3860mAh electrode potential). -1 ), is an extremely attractive negative electrode material for the next generation of high energy density batteries. However, it has problems such as unlimited volume effect and lithium dendrites, resulting in low first coulombic efficiency, poor cycle performance and safety issues, which seriously restrict its practical application. Graphite, as the current mainstream commercial lithium secondary battery negative electrode material, has the advantages of small volume effect (volume change <10%), good cycle performance and low cost. However, its gram capacity has gradually approached the limit value and cannot meet people's actual needs for high specific energy and fast charging batteries.

[0003] Therefore, there is an urgent need in the art for a negative electrode plate that combines the advantages of high specific capacity of lithium metal and high stability of graphite, and can overcome the problems of volume effect and lithium dendrite growth during the cycle process to improve the specific capacity, safety and cycle stability of lithium secondary batteries. Summary of the invention

[0004] In view of the above problems, the purpose of the present application is to provide a negative electrode plate and a preparation method thereof, wherein the surface of the negative electrode plate is covered with a high mechanical strength, high flexibility and lithium-philic film. During the battery charging process, the lithium-philic film can guide the metallic lithium to uniformly nucleate and deposit at the interface of the inner film / negative electrode active material layer, forming a graphite / lithium metal composite negative electrode in situ, and realizing a mixed working mode of reversible insertion / deinsertion of lithium ions and deposition / stripping of metallic lithium, thereby improving the specific capacity of the negative electrode active material and the overall energy density of the secondary battery. In addition, due to its high mechanical strength and good flexibility, the film can also alleviate the volume effect of lithium metal while inhibiting the growth of lithium dendrites, maintain the stability of the negative electrode plate structure, and improve the cycle life and safety of the secondary battery. At the same time, using graphite as a carrier for lithium metal deposition also alleviates the volume effect of metallic lithium to a certain extent.

[0005] In a first aspect, the present application provides a negative electrode plate, the negative electrode plate comprising:

[0006] A negative electrode active material layer;

[0007] an inner layer film covering the negative electrode active material layer; and

[0008] an outer film covering the inner layer,

[0009] The negative electrode active material layer includes graphite, the inner layer film includes at least 10 monomolecular layers of metal organic compounds, and the outer layer film includes at least 40 monomolecular layers of organic polymers.

[0010] The inner film / outer film covering the surface of the negative electrode active material layer is a double-layer structure with uniform composition and structure and controllable structure, which can be prepared by molecular layer deposition. The outer film is composed of an organic polymer such as polyurea with electronic insulation and good flexibility, which can reduce the side reactions at the interface between the negative electrode active material and the electrolyte, and at the same time, alleviate the volume change of the negative electrode during the cycle, maintain the stability of the negative electrode structure, and improve the cycle life of the battery. The inner film is composed of a metal organic polymer such as Zincone with high mechanical strength and lithium affinity. The metal organic polymer contains lithium-philic metal sites such as zinc element, which can preferentially react with lithium ions to generate M-Li alloys, reduce the nucleation overpotential of lithium, and guide lithium to uniformly nucleate and deposit at the interface of the inner film / negative electrode active material layer. In addition, since the metal organic polymer has high mechanical strength, it is achieved to jointly suppress the formation of lithium dendrites from the nucleation and growth stages, avoid the generation of dead lithium, ensure the high safety of the battery and the reversible lithium ion insertion / extraction and deposition / stripping of metal lithium during the cycle.

[0011] In any embodiment, the monomolecular layer of the inner film is formed of one or more inner layer materials selected from zinc-based organic-inorganic composite thin films, aluminum-based organic-inorganic composite thin films, and titanium-based organic-inorganic composite thin films.

[0012] In any embodiment, the monomolecular layer of the inner film includes a metal element.

[0013] In any embodiment, the inner film comprises 10-60 monolayers, such as 15-50 monolayers, 20-45 monolayers or 25-35 monolayers.

[0014] Since the monomolecular layer containing the metal element has a relatively high electronic conductivity, if its thickness is too thick, lithium metal will be deposited in the inner film, which may affect the structural stability of the inner film / outer film.

[0015] In any embodiment, among the monomolecular layers of the inner layer film, 1 to 15, for example, 1 to 10 or 2 to 6 monomolecular layers comprise the metal element.

[0016] In any embodiment, the metal element is selected from one or more of Zn, Al, and Ti.

[0017] Metal elements M such as Zn, Al, Ti, etc. can form M-Li alloys with metallic lithium to reduce the nucleation overpotential of lithium.

[0018] In any embodiment, the monomolecular layer of the outer film is formed by an organic polymer; optionally, the organic polymer is selected from one or more of polyurea, polyurethane, and polyamide.

[0019] In any embodiment, the ratio of the number of monolayers of the outer layer film to the number of monolayers of the inner layer film is (2-5):1.

[0020] In the present application, the outer film includes an organic polymer such as polyurea, which has high electronic insulation and inhibits the internal deposition of metallic lithium in the inner film / outer film. The inner film includes a metal organic polymer, and the metal organic polymer optionally contains a portion of a metal element, so the inner film may have a certain conductivity. In order to avoid the deposition of metallic lithium inside the inner film, the thickness of the inner film may be optionally reduced so that the metallic lithium is deposited at the interface of the inner film / negative electrode active material layer. In addition, in addition to having a lithium-philic effect, the inner film also has higher mechanical strength and rigidity than the outer film, which can effectively inhibit the growth of lithium dendrites.

[0021] The second aspect of the present application provides a method for preparing the negative electrode sheet of the present application, comprising the following steps:

[0022] S1. Preparing a negative electrode active material layer;

[0023] S2. In step S1, the negative electrode active material layer is covered with the inner layer film by molecular layer deposition;

[0024] S3. In step S2, the negative electrode active material layer covering the inner layer film is covered with an outer layer film by the molecular layer deposition method,

[0025] The negative electrode active material layer includes graphite, the inner layer film includes at least 10 monomolecular layers of metal organic compounds, and the outer layer film includes at least 40 monomolecular layers of organic polymers.

[0026] Molecular layer deposition is a technology for preparing organic polymer and organic-inorganic hybrid films. It can deposit a single molecular layer in each cycle and has good process repeatability, film thickness and composition controllability and conformality. The deposition principle is: by alternately introducing multiple reaction gases (or steam) into the reactor in the form of gas pulses, the adsorbed molecules (such as hydroxyl or amino groups) left on the substrate surface undergo chemical adsorption and reaction to form a thin film. Since the reactants participating in each reaction are limited to the molecules chemically adsorbed on the substrate surface, this makes molecular layer deposition have self-limiting growth characteristics.

[0027] In any embodiment, in the step S2, the process of depositing a monomolecular layer of the inner film includes: placing the negative electrode active material layer described in step S1 as a substrate in a molecular layer deposition reaction chamber (S2-1); alternately pulsing a metal precursor gas (or vapor) and one or more organic precursor gases (or vapors) into the reaction chamber to react with the substrate surface or the monomolecular layer on the substrate surface to generate a monomolecular layer by chemical adsorption (S2-2); optionally, pulsing free radicals of a reducing agent into the reaction chamber to reduce the metal ions on the substrate surface (S2-3).

[0028] In any embodiment, in the step S3, the process of depositing a monomolecular layer of the outer film includes: using the negative electrode active material layer covering the inner film obtained in the step S2 as a substrate, alternately pulsing one or more of the organic polymer precursor gases (or vapors) into the reaction chamber, and relying on chemical adsorption to react with the substrate surface or the monomolecular layer on the substrate surface to generate a monomolecular layer (S3);.

[0029] In any embodiment, in the step S2, the reduction reaction in the step (S2-3) may be placed before and / or after the pulse of the organic precursor in the step (S2-2).

[0030] In any embodiment, the metal precursor is selected from one or more of diethylzinc, trimethylaluminum, and titanium tetrachloride; or, the organic precursor is selected from one or more of ethylene glycol, glycerol, and hydroquinone; or, the free radical of the reducing agent is derived from at least one of hydrogen or ammonia.

[0031] In any embodiment, in the step S2, the reduction reaction in the step (S2-3) may be placed before and / or after the pulse of the organic precursor in the step (S2-2).

[0032] In any embodiment, in step S3, the organic polymer precursor is selected from one or more of ethylene glycol, ethylenediamine, 1,4-phenylene diisocyanate, glycerol, and hydroquinone.

[0033] The third aspect of the present application also provides a secondary battery, a battery module or an ion battery pack, wherein the secondary battery, the battery module or the battery pack comprises the negative electrode plate described in the present application.

[0034] The fourth aspect of the present application also provides an electrical device, which includes at least one of the secondary battery, battery module or battery pack described in the present application, and the secondary battery, battery module or battery pack provides electrical energy to the electrical device.

[0035] By covering the surface of the negative electrode active material layer with a lithium-philic inner layer film and / or outer layer film, metallic lithium is guided to uniformly nucleate and deposit at the interface of the inner layer film / negative electrode active material layer during the battery charging process, and a graphite / lithium metal composite negative electrode is formed in situ, realizing a hybrid working mode of reversible insertion / deinsertion of lithium ions and deposition / stripping of metallic lithium, thereby improving the specific capacity of the negative electrode active material and the overall energy density of the battery.

[0036] The negative electrode plate of the present application can inhibit the growth of lithium dendrites and alleviate the unlimited volume effect of lithium metal. The inner layer and / or outer layer covering the surface of the negative electrode active material layer has high mechanical strength and good flexibility, which can inhibit the growth of lithium dendrites while alleviating the volume effect of lithium metal, maintain the stability of the negative electrode plate structure, and improve the cycle life and safety of the battery. At the same time, using the negative electrode active material layer as a carrier for lithium metal deposition also alleviates the volume effect of the metal lithium layer on the surface of the negative electrode plate to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of a negative electrode sheet according to an embodiment of the present application is described.

[0038] Figure 2 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0039] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0040] Figure 4 It is a schematic diagram of a battery module according to one embodiment of the present application.

[0041] Figure 5 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0042] Figure 6 yes Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0043] Figure 7 Schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0044] Description of reference numerals:

[0045] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; current collector 01; negative electrode active material layer 02; inner film 03; outer film 04. DETAILED DESCRIPTION

[0046] "Scope" disclosed herein is defined in the form of lower limit and 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 boundary of a particular range. The scope defined in this way can be including end values ​​or not including end values, and can be arbitrarily combined, 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 particular 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 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] In this application, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined with each other to form a new technical solution.

[0048] In this application, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0049] In the present application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0050] In this application, unless otherwise specified, the terms "include" and "comprising" mentioned herein may be open-ended or closed-ended. For example, the terms "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0051] In the description of this article, it should be noted that, unless otherwise specified, "above" and "below" are inclusive of the number itself, and "several" in "one or several" means two or more.

[0052] In the description herein, unless otherwise specified, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0053] Herein, unless otherwise specified, percentage (%) or part refers to percentage by weight or part by weight relative to the composition.

[0054] Herein, if there is no contrary description, the sum of the contents of the various components in the composition is 100%.

[0055] Herein, if there is no contrary description, the sum of the parts of each component in the composition may be 100 parts by weight.

[0056] In this context, unless otherwise specified, "a combination thereof" means a multi-component mixture of the elements described, for example a mixture of two, three, four and up to the maximum possible multi-component mixture.

[0057] If not specifically stated, the terms "a" or "an" used in the present specification means "at least one".

[0058] Herein, unless otherwise stated, all reactions are carried out at normal temperature and pressure.

[0059] Negative electrode

[0060] On one hand, the present application provides a negative electrode plate, the negative electrode plate comprising:

[0061] A negative electrode active material layer;

[0062] an inner layer film covering the negative electrode active material layer; and

[0063] an outer film covering the inner layer,

[0064] The negative electrode active material layer includes graphite, the inner layer film includes at least 10 monomolecular layers of metal organic compounds, and the outer layer film includes at least 40 monomolecular layers of organic polymers.

[0065] In the present application, the negative electrode active material layer may be a graphite negative electrode active material layer commonly used in the field of lithium-ion batteries. The negative electrode active material layer is commercially available. In one embodiment, the negative electrode active material layer comprises negative electrode active material graphite, a conductive agent, a binder and / or a current collector, etc. Optionally, the graphite is selected from one or more of natural graphite, artificial graphite, etc. In one embodiment, the negative electrode active material layer comprises graphite and conductive carbon black. In another embodiment, the negative electrode active material layer comprises graphite, conductive carbon black and styrene-butadiene rubber (SBR). In another embodiment, the negative electrode active material layer comprises graphite, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose (CMC).

[0066] In the present application, the monolayer of the inner film is formed by one or more inner layer materials selected from materials such as Zincone (zinc-based organic-inorganic composite film), Alucone (aluminum-based organic-inorganic composite film), Titanicone (titanium-based organic-inorganic composite film), etc. For example, the monolayer can be obtained by reacting a metal precursor, an organic precursor containing two or more functional groups (such as diols (phenols), polyols, dicarboxylic acids, etc.) and an optional reducing agent radical (such as hydrogen radicals, ammonia radicals, etc.) alternately pulsed to a substrate. Zincone monolayer can be obtained by the reaction of zinc precursor (such as diethyl zinc) and organic precursor (such as ethylene glycol, hydroquinone, etc.) and optional reducing agent free radical (such as hydrogen free radical); Alucone monolayer can be obtained by the reaction of aluminum precursor (such as trimethyl aluminum) and organic precursor (such as ethylene glycol, hydroquinone, etc.) and optional reducing agent free radical (such as hydrogen free radical); Titanicone monolayer can be obtained by the reaction of titanium precursor (such as titanium tetrachloride) and organic precursor (such as ethylene glycol, glycerol, etc.) and optional reducing agent free radical (such as hydrogen free radical).

[0067] In the process of forming the monolayer, if a reducing agent radical (such as a hydrogen radical) is used, the monolayer may include a metal element. Preferably, the monolayer consists of a metal element.

[0068] Preferably, the monolayer of the inner film comprises a Zincone monolayer.

[0069] The inner layer film may cover (eg, completely cover) the surface of the negative electrode active material layer, or directly cover (eg, completely cover) the surface of the negative electrode active material layer.

[0070] The inner layer film comprises at least 10 monolayers, and optionally, the inner layer film comprises 10-60 monolayers. In one embodiment, the inner layer film comprises 15-50 monolayers, such as 20-45 monolayers, 25-35 monolayers.

[0071] In the monolayer of the inner film, optionally, there are 1-15 monolayers including a metal element, for example, 1-10 monolayers including a metal element, or 2-6 monolayers including a metal element. The monolayers including a metal element may be randomly distributed in the monolayer of the inner film. For example, the monolayers including a metal element are continuously distributed, or the monolayers including a metal element are continuously distributed near the negative electrode active material layer. Optionally, the monolayers including a metal element contact the surface of the negative electrode active material layer.

[0072] In one embodiment, the monolayer containing the metal element is located at the bottom of the inner film (i.e., close to the surface of the negative electrode active material layer). The metal ions in the sedimentary layer near the bottom of the inner film are reduced, which is beneficial to capture lithium ions to form M-Li alloy during battery charging, thereby promoting uniform nucleation and deposition of lithium at the interface of the inner film / negative electrode active material layer.

[0073] Optionally, the ratio of the monolayer containing the metal element to the total number of monolayers in the inner film is 1:(6-16), for example 1:(6-12). Since the monolayer containing the metal element has a relatively high electronic conductivity, if the thickness is too thick, lithium metal will be deposited in the inner film, which may affect the structural stability of the inner film / outer film.

[0074] Optionally, a metal single substance M such as Zn, Al, Ti, etc. can form an M-Li alloy with metallic lithium to reduce the nucleation overpotential of lithium.

[0075] In the present application, the monomolecular layer of the outer film is formed by an organic polymer. The organic polymer is selected from one or more organic polymers such as polyurea, polyurethane, polyamide, etc. Optionally, the organic polymer is polyurea.

[0076] In the present application, the inner film / outer film covering the surface of the negative electrode active material layer is a double-layer structure with uniform and controllable composition and structure, and is prepared by molecular layer deposition. The outer film is made of an organic polymer such as polyurea with electronic insulation and good flexibility, which can reduce the side reactions occurring at the interface between the negative electrode active material layer and the electrolyte. At the same time, it can alleviate the volume change of the negative electrode active material during the cycle, maintain the structural stability of the negative electrode plate, and improve the cycle life of the battery. The inner film is made of a metal organic compound such as Zincone with high mechanical strength and lithium affinity. The metal organic compound contains lithium-philic metal sites such as zinc. The metal site can preferentially react with lithium ions to generate M-Li alloys, reduce the nucleation overpotential of lithium, and guide lithium to uniformly nucleate and deposit at the interface of the inner film / negative electrode active material layer. In addition, since the metal organic compound has high mechanical strength, it can jointly inhibit the formation of lithium dendrites from the nucleation and growth stages, avoid the separation of lithium dendrites and current collector to form dead lithium that loses electrochemical activity, prevent battery capacity decay, ensure high battery safety and reversible lithium ion insertion / extraction and deposition / stripping of metallic lithium during the cycle process.

[0077] In one embodiment, the total thickness of the inner layer film and the outer layer film is between 1-100 nm, and can be optionally between 5-50 nm.

[0078] In one embodiment, the ratio of the number of monolayers of the outer layer and the inner layer is (2-5):1. The outer film described in the present application includes an organic polymer such as polyurea, which has a high electronic insulation and inhibits the deposition of metallic lithium inside the outer layer of SEI. However, the inner film includes a metal organic compound, and the organic compound contains some metal elements, so the inner film has a certain conductivity. In order to avoid lithium deposition inside the inner film, it is optional to reduce the thickness of the inner film so that lithium is deposited at the interface of the inner film / negative electrode active material layer. However, considering that the inner film has higher mechanical strength and rigidity than the outer layer in addition to its lithium-philic effect, it can effectively inhibit the growth of lithium dendrites, so the inner layer needs to have a certain thickness.

[0079] Method for preparing negative electrode sheet

[0080] On the other hand, the present application provides a method for preparing the negative electrode sheet of the present application, comprising the following steps:

[0081] S1. Preparing a negative electrode active material layer;

[0082] S2. In step S1, the negative electrode active material layer is covered with the inner layer film by molecular layer deposition;

[0083] S3. In step S2, the negative electrode active material layer covering the inner layer film is covered with an outer layer film by the molecular layer deposition method,

[0084] The negative electrode active material layer includes graphite, the inner layer film includes at least 10 monomolecular layers of metal organic compounds, and the outer layer film includes at least 40 monomolecular layers of organic polymers.

[0085] Optionally, in step S1, the negative electrode active material layer may be prepared by mixing graphite, a conductive agent and a binder as a negative electrode active material and coating the mixture on the surface of a current collector, and drying the mixture to form the negative electrode active material layer.

[0086] Optionally, in step S2, the process of depositing a monomolecular layer of the inner film includes: placing the negative electrode active material layer described in step S1 as a substrate in a molecular layer deposition reaction chamber (S2-1); alternately pulsing a metal precursor gas (or vapor) and one or more organic precursor gases (or vapors) into the reaction chamber to react with the substrate surface or the monomolecular layer on the substrate surface to generate a monomolecular layer by chemical adsorption (S2-2); optionally, pulsing free radicals of a reducing agent into the reaction chamber to reduce the metal ions on the substrate surface (S2-3).

[0087] Optionally, in the step S3, the process of depositing a monomolecular layer of the outer film includes: using the negative electrode active material layer covering the inner film obtained in the step S2 as a substrate, alternately pulsing one or more organic polymer precursor gases (or vapors) into the reaction chamber, and relying on chemical adsorption to react with the substrate surface or the monomolecular layer on the substrate surface to generate a monomolecular layer (S3);.

[0088] Optionally, in step S2, the metal precursor is selected from one or more of diethylzinc, trimethylaluminum, and titanium tetrachloride.

[0089] Optionally, in step S2, the organic precursor is selected from one or more of ethylene glycol, glycerol, and hydroquinone.

[0090] Optionally, in step S2, the free radicals of the reducing agent are derived from at least one of hydrogen or ammonia. Optionally, the free radicals of the reducing agent can be generated by applying a voltage difference to a gas (eg, at least one of hydrogen or ammonia) through an electrode.

[0091] Optionally, in the step S2, the pulse sequence and the number of pulses of the metal-containing precursor and the organic precursor in the step (S2-2) can be adjusted to achieve regulation of the composition and structure of the inner layer film.

[0092] Optionally, in the step S2, the thickness of the inner layer film can be regulated by controlling the number of times the metal-containing precursor and the organic precursor are pulsed in the step (S2-2), wherein each pulse of the metal precursor or the organic precursor is considered to deposit a monolayer.

[0093] Optionally, in the step S2, the reduction reaction in the step (S2-3) may be placed before and / or after the pulsing of the organic precursor in the step (S2-2).

[0094] Optionally, in step S3, the organic polymer precursor is selected from one or more of ethylene glycol, ethylenediamine, 1,4-phenylene diisocyanate, glycerol, and hydroquinone to form an organic polymer monolayer. The organic polymer includes but is not limited to one or more of polyurea, polyurethane, and polyamide.

[0095] Molecular layer deposition (MLD) principle: Molecular layer deposition is a technology for preparing organic polymer and organic-inorganic hybrid films. It can deposit a single molecular layer in each cycle and has good process repeatability, film thickness and composition controllability and conformality. The deposition principle is: by alternately introducing multiple reaction gases (or steam) into the reactor in the form of gas pulses, the adsorbed molecules (such as hydroxyl or amino groups) left on the surface of the substrate are chemically adsorbed and reacted to form a thin film. Since the reactants participating in each reaction are limited to the molecules chemically adsorbed on the surface of the substrate, this makes molecular layer deposition have self-limiting growth characteristics.

[0096] Another aspect of the present application provides a secondary battery, a battery module or a battery pack, wherein the secondary battery, the battery module or the battery pack comprises the negative electrode plate described in the present application.

[0097] In another aspect, the present application provides an electric device, which includes at least one of the secondary battery, battery module or battery pack described in the present application, and the secondary battery, battery module or battery pack provides electric energy to the electric device. The electric device includes but is not limited to mobile digital devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0098] Figure 1 A schematic diagram of a negative electrode sheet according to an embodiment of the present application is described. A negative electrode sheet with uniform and controllable lithium plating is composed of a current collector 01, a negative electrode active material layer 02, an inner film 03 and an outer film 04 which are distributed in sequence.

[0099] Figure 2 It is a schematic diagram of a secondary battery 5 according to an embodiment of the present application. Figure 3 yes Figure 2 The exploded view of a secondary battery according to an embodiment of the present application is shown in FIG. The secondary battery 5 includes a housing 51 , an electrode assembly 52 and a top cover assembly 53 . Figure 4 Schematic diagram of a battery module 4 according to an embodiment of the present application. The battery module 4 includes a plurality of secondary batteries 5 . Figure 5 It is a schematic diagram of a battery pack 1 according to an embodiment of the present application. Figure 6 yes Figure 5 The exploded view of a battery pack 1 according to an embodiment of the present application is shown. The battery pack 1 includes a plurality of battery modules 4, an upper box 2 and a lower box 3. Figure 7 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0100] In the following, the influence of the negative electrode plate manufactured according to the implementation mode of the present application on the performance of the electrochemical device is characterized based on specific examples, but it should be pointed out in particular that the scope of protection of the present application is limited by the claims and is not limited to the above specific implementation modes.

[0101] Example

[0102] Example 1

[0103] See also Figure 1 , a negative electrode sheet with uniform and controllable lithium plating, which is composed of a current collector 01, a negative electrode active material layer 02, an inner film 03 and a highly flexible outer film 04 distributed in sequence. The preparation method is as follows:

[0104] 1. Preparation of negative electrode active material layer

[0105] The negative electrode active material graphite, the conductive agent carbon black, the binder styrene butadiene rubber (SBR) and the thickener carboxymethyl cellulose (CMC) in a mass ratio of 96:1:1.5:1.5 were mixed with solvent water to form a slurry, which was coated on a copper foil and dried at 90°C to obtain a negative electrode active material layer.

[0106] 2. Inner membrane

[0107] (1) The negative electrode active material layer obtained in step 1 is placed as a substrate in a molecular layer deposition (MLD) reaction chamber. (2) Diethyl zinc (DEZ) and ethylene glycol (EG) are used as metal precursors and organic precursors, respectively, and their temperatures are controlled at 25°C and 85°C, respectively. Hydrogen radicals are used as a reducing agent, nitrogen is used as a carrier gas and a cleaning gas for transporting precursor gases, the reaction chamber temperature is controlled at 135°C, and the vacuum is maintained at 500mTorr. (3) The deposition process of the inner layer film is as follows: the precursor gas is pulsed into the reaction chamber alternately according to the following time and sequence: (a) 0.05s / 50s / 0.05s / 50s / 0.5s / 50s (DEZ pulse / purge / EG pulse / purge / reducing agent free radical pulse / purge), and the MLD process is repeated 5 times; (b) 0.05s / 50s / 0.05s / 50s (DEZ pulse / purge / EG pulse / purge), and the MLD process is repeated 10 times to obtain a negative electrode active material layer covered with an inner layer film (30 molecular deposition layers).

[0108] 3. [Outer membrane]

[0109] (1) The negative electrode active material layer covering the inner layer obtained in step 2 is used as the substrate; (2) Ethylene diamine (ED) and 1,4-phenylene diisocyanate (PDIC) are used as two organic precursors, and their temperatures are controlled at 25°C and 90°C respectively. Nitrogen is used as the carrier gas and cleaning gas for transporting the precursor gas. The temperature of the reaction chamber is controlled at 80°C, and the vacuum degree is maintained at 800mTorr. (3) The deposition process of the outer layer is: 0.1s / 50s / 1s / 50s (ED pulse / purge / PDIC pulse / purge). The MLD process is repeated 45 times, and finally a negative electrode sheet covering 30 inner monolayers + 90 outer monolayers is obtained, wherein 5 inner layers are deposited layers containing Zn element.

[0110] 4. Preparation of button cell

[0111] The negative electrode sheet, Celgard 2400 separator, NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) The positive electrodes were assembled in sequence and injected with 1 mol / L LiPF 6 (EC (ethylene carbonate): DMC (dimethyl carbonate): DEC (diethyl carbonate) = 1:1:1) electrolyte was used to make a button cell, in which the N / P ratio of graphite and NCM523 positive electrode was 0.82.

[0112] The button cell was left at room temperature for 12 hours, then cycled at 0.1C / 0.1C for 3 cycles at 25°C, and then cycled at 0.2C / 0.5C for 300 cycles, with a charge and discharge window of 3.0V-4.3V. Finally, the battery surface capacity after 10 cycles at 0.2C / 0.5C and the battery capacity retention rate after 300 cycles were measured.

[0113] Example 2

[0114] The steps are basically the same as those in Example 1, except that the number of MLD cycles in step (b) of the deposition process of the inner film in step 2 is changed to 25, and the number of MLD cycles in the deposition process of the outer film in step 3 is changed to 90, so as to obtain a negative electrode sheet with 60 inner monolayers + 180 outer monolayers, wherein 5 of the inner layers are monolayers containing Zn element.

[0115] Example 3

[0116] The steps are basically the same as those in Example 1, except that the number of MLD cycles in step (b) of the deposition process of the inner layer film in step 2 is changed to 40, and the number of MLD cycles in the deposition process of the outer layer of the artificial SEI film in step 3 is changed to 135, and a negative electrode plate with 90 inner monolayers + 270 outer monolayers can be obtained, wherein 5 of the inner layers are monolayers containing Zn element.

[0117] Comparative Example 1

[0118] The steps are basically the same as those in Example 1, except that step 2 is deleted and the number of MLD cycles in the deposition process of the outer film in step 3 is changed to 60, so that a negative electrode sheet coated with an artificial SEI film (120 outer molecular deposition layers) can be obtained.

[0119] Example 4

[0120] The steps are basically the same as those in Example 1, except that the number of MLD cycles in step (b) of the deposition process of the inner film in step 2 is changed to 35, and the number of MLD cycles in the deposition process of the outer film in step 3 is changed to 20, so as to obtain a negative electrode sheet with 70 inner monolayers + 40 outer monolayers, wherein 5 inner layers are deposited layers containing Zn element.

[0121] Example 5

[0122] The steps are basically the same as those in Example 1, except that the number of MLD cycles in steps (a) and (b) of the deposition process of the inner layer film in step 2 is changed to 10 and 5 respectively, to obtain a negative electrode sheet with 30 inner monolayers + 90 outer monolayers, wherein 10 of the inner layers are deposited layers containing Zn alone.

[0123] Example 6

[0124] The steps are basically the same as those in Example 1, except that step (a) of the inner film deposition process in step 2 is deleted, and the number of MLD cycles in step (b) is changed to 15, to obtain a negative electrode plate with an inner layer of 30 monolayers and an outer layer of 90 monolayers of a Zn-free deposition layer.

[0125] Comparative Example 2

[0126] The difference from Example 1 is that steps 2 and 3 of covering the surface of the negative electrode active material layer with the inner layer film and the outer layer film in Example 1 are omitted.

[0127]

Battery test calculation

[0128] 1. Battery surface capacity

[0129] Battery surface capacity = Cn*positive electrode coating surface density*positive electrode active material ratio, where Cn is the discharge capacity in grams after n cycles.

[0130] 2. Battery capacity retention rate

[0131] The battery capacity retention rate Pn = Cn / C0*100%, where C0 is the initial reversible discharge capacity and Cn is the discharge capacity in grams after n cycles.

[0132] 3. N / P ratio

[0133] N / P ratio = negative electrode capacity per unit area / positive electrode capacity per unit area = negative electrode active material gram capacity * negative electrode surface density * negative electrode active material ratio / (positive electrode active material gram capacity * positive electrode surface density * positive electrode active material ratio).

[0134] The test results are listed in Table 1 below.

[0135]

[0136]

[0137] The comparison results of Examples 1-3 show that: as the number of deposited layers increases, the surface capacity of the battery gradually decreases and the cycle performance decreases. The comparison results of Example 1 and Comparative Example 1 show that the inner film with lithium affinity and high mechanical strength is conducive to promoting the uniform deposition of metallic lithium at the inner film / negative electrode active material layer interface, inhibiting the formation of lithium dendrites, thereby improving the cycle stability of the battery. The comparison results of Examples 1 and 4 and 5 show that if the proportion of the inner film is too high or the proportion of the metal single layer in the inner film is too high, lithium metal will be deposited in the inner film, destroying the inner film / outer film structure and affecting the battery cycle stability.

[0138] The comparison results of Example 1 and Example 6 show that the monomolecular layer including the metal element helps to achieve uniform deposition of lithium metal on the graphite surface, thereby better inhibiting the generation of lithium dendrites and improving the safety and cycle performance of the battery. The comparison results of Example 1 and Comparative Example 2 show that the inner layer film / outer layer film on the surface of the negative electrode active material layer is conducive to inhibiting lithium dendrites and preventing the separation of lithium dendrites and current collectors to form dead lithium that loses electrochemical activity, thereby improving the cycle stability of the battery.

Claims

1. A negative electrode plate, characterized in that: include: A negative electrode active material layer; an inner layer film covering the negative electrode active material layer; and an outer layer film covering the inner layer film, The negative electrode active material layer includes graphite, the inner layer film includes at least 10 monomolecular layers of metal organic compounds, and the outer layer film includes at least 40 monomolecular layers of organic polymers.

2. The negative electrode sheet according to claim 1, characterized in that: The monomolecular layer of the inner film is formed by one or more inner layer materials selected from zinc-based organic-inorganic composite thin films, aluminum-based organic-inorganic composite thin films, and titanium-based organic-inorganic composite thin films.

3. The negative electrode sheet as claimed in claim 1 or 2, characterized in that: The monomolecular layer of the inner film includes a metal element.

4. The negative electrode sheet according to claim 1, characterized in that: The inner layer membrane includes 10-60 monolayers.

5. The negative electrode sheet according to claim 4, characterized in that: The inner layer membrane includes 15-50 monolayers.

6. The negative electrode sheet according to claim 5, characterized in that: The inner membrane includes 20-45 monolayers.

7. The negative electrode sheet according to claim 6, characterized in that: The inner membrane includes 25-35 monolayers.

8. The negative electrode sheet according to claim 3, characterized in that: Among the monomolecular layers of the inner film, 1 to 15 monomolecular layers include the metal element.

9. The negative electrode sheet according to claim 8, characterized in that: Among the monomolecular layers of the inner film, 1 to 10 monomolecular layers include the metal element.

10. The negative electrode sheet according to claim 9, characterized in that: Among the monomolecular layers of the inner film, 2 to 6 monomolecular layers include the metal element.

11. The negative electrode sheet according to claim 3, characterized in that: The metal element is selected from one or more of Zn, Al and Ti.

12. The negative electrode sheet according to claim 1, characterized in that: The monomolecular layer of the outer film is formed of an organic polymer.

13. The negative electrode sheet according to claim 12, characterized in that: The organic polymer is selected from one or more of polyurea, polyurethane and polyamide.

14. The negative electrode sheet according to claim 1, characterized in that: The ratio of the number of monomolecular layers of the outer layer membrane to that of the inner layer membrane is (2-5):

1.

15. A method for preparing the negative electrode sheet according to any one of claims 1 to 14, characterized in that: The steps include: S1. Preparing a negative electrode active material layer; S2. In step S1, the negative electrode active material layer is covered with the inner layer film by molecular layer deposition; S3. In step S2, the negative electrode active material layer covering the inner layer film is covered with an outer layer film by the molecular layer deposition method, The negative electrode active material layer includes graphite, the inner layer film includes at least 10 monomolecular layers of metal organic compounds, and the outer layer film includes at least 40 monomolecular layers of organic polymers.

16. The method according to claim 15, characterized in that In the step S2, the process of depositing a monomolecular layer of the inner layer film includes: S2-1. The negative electrode active material layer described in step S1 is placed as a substrate in a molecular layer deposition reaction chamber; S2-2. Alternately pulse metal precursor gas or vapor and one or more organic precursor gases or vapors into the reaction chamber, and rely on chemical adsorption to react with the substrate surface or the monomolecular layer on the substrate surface to form a monomolecular layer.

17. The method according to claim 16, characterized in that In the step S2, the process of depositing a monomolecular layer of the inner film further comprises: S2-3. Pulsing free radicals of a reducing agent into the reaction chamber to reduce metal ions on the surface of the substrate.

18. The method according to claim 17, characterized in that In the step S2, the reduction reaction in the step S2-3 is placed before and / or after the pulse of the organic precursor in the step S2-2.

19. The method according to claim 15, characterized in that In the step S3, the process of depositing a monomolecular layer of the outer film includes: using the negative electrode active material layer covering the inner film obtained in the step S2 as a substrate, alternately pulsing one or more organic polymer precursor gases or vapors into the reaction chamber, and relying on chemical adsorption to react with the substrate surface or the monomolecular layer on the substrate surface to generate a monomolecular layer.

20. The method of claim 16, wherein: The metal precursor is selected from one or more of diethyl zinc, trimethyl aluminum, and titanium tetrachloride; or, the organic precursor is selected from one or more of ethylene glycol, glycerol, and hydroquinone.

21. The method of claim 17, wherein: The free radicals of the reducing agent are derived from at least one of hydrogen or ammonia.

22. The method of claim 19, wherein: In the step S3, the organic polymer precursor is selected from one or more of ethylene glycol, ethylenediamine, 1,4-phenylene diisocyanate, glycerol, and hydroquinone.

23. A secondary battery, characterized in that: The secondary battery comprises the negative electrode sheet according to any one of claims 1 to 14 or the negative electrode sheet prepared by the method according to any one of claims 15 to 22.

24. A battery module, characterized in that: The battery module comprises the negative electrode sheet according to any one of claims 1 to 14 or the negative electrode sheet prepared by the method according to any one of claims 15 to 22.

25. A battery pack, characterized in that: The battery pack comprises the negative electrode sheet according to any one of claims 1 to 14 or the negative electrode sheet prepared by the method according to any one of claims 15 to 22. 26 . An electrical device comprising the secondary battery of claim 23 , the battery module of claim 24 , or the battery pack of claim 25 , wherein the secondary battery, the battery module, or the battery pack provides electrical energy to the electrical device.

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