Negative pole piece and preparation method thereof, battery and power utilization device

Abstract

The invention discloses a negative pole piece, a preparation method of the negative pole piece, a battery and a power utilization device. The negative electrode active material layer is positioned on at least one side of the negative electrode current collector; the first protection layer is located on the side, away from the negative electrode current collector, of the negative electrode active material layer, the first protection layer is of a porous structure, the pore diameter of the porous structure ranges from 0.17 nm to 300 nm, and the electronic conductivity of the first protection layer at the temperature of 25 DEG C ranges from 2 * 10 <-10 > S / cm to 6 * 10 <-10 > S / cm. Therefore, when lithium dendrites are generated on the negative electrode side of the battery in the cyclic charging and discharging process, the lithium dendrites can be guided to grow between the negative electrode active material layer and the first protective layer through the arrangement of the first protective layer, so that the growth of the lithium dendrites on the surface of the negative electrode piece is inhibited.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular, to a negative electrode plate and a preparation method thereof, a battery, and an electrical device. Background Art

[0002] In recent years, with the development of lithium-ion battery technology, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and have been widely used in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. While lithium-ion batteries occupy a core position in power batteries, they also face great challenges. For example, in the middle and late stages of their service life, lithium-ion batteries have problems such as poor cycle performance, severe capacity attenuation, and thermal runaway. At present, there are still many problems to be solved in the application of batteries.

[0003] It should be noted that the above statements are only used to provide background technical information related to the present application and do not necessarily constitute prior art. Summary of the invention

[0004] In the first aspect of the present application, the present application proposes a negative electrode sheet, comprising: a negative electrode current collector; a negative electrode active material layer, the negative electrode active material layer is located on at least one side of the negative electrode current collector; a first protective layer, the first protective layer is located on the side of the negative electrode active material layer away from the negative electrode current collector, the first protective layer is a porous structure, the pore size of the porous structure is 0.17nm-300nm, and the electronic conductivity of the first protective layer at 25°C is 2×10 -10 S / cm-6×10 -10 S / cm. Thus, when lithium dendrites are generated on the negative electrode side of the battery during the cyclic charge and discharge process, the first protective layer can guide the lithium dendrites to grow between the negative electrode active material layer and the first protective layer, thereby inhibiting the growth of lithium dendrites on the surface of the negative electrode.

[0005] In any embodiment, the first protective layer includes a siloxane polymer, and optionally, the siloxane polymer includes at least one of vinyl-terminated polydimethylsiloxane, polydimethylsiloxane, polymethylphenylsiloxane, and polyphenylmethylsiloxane. Thus, the electronic conductivity and porosity of the first protective layer can be regulated by the siloxane oxide.

[0006] In any embodiment, the number average molecular weight of the siloxane polymer is 5000-200000; and / or the crystallinity of the siloxane polymer is 60%-82%. Thus, a first protective layer with suitable electronic conductivity and porosity can be obtained.

[0007] In any embodiment, the porosity of the first protective layer is 50%-60%, thereby facilitating lithium ions to pass through the first protective layer.

[0008] In any embodiment, the thickness of the first protective layer is 1 μm-25 μm. Thus, the first protective layer can guide lithium dendrites to grow between the negative electrode active material layer and the first protective layer, but is not easily pierced by lithium dendrites.

[0009] In any embodiment, the battery further comprises: a second protective layer, the second protective layer is located between the first protective layer and the negative electrode active material layer, and the second protective layer comprises at least one of metal iodide, 10-methylphenothiazine, thianthracene, and tetramethylpiperidinium oxide. Thus, the content of soluble lithium ions that can participate in the battery cycle charge and discharge can be effectively increased.

[0010] In any embodiment, the electronic conductivity of the second protective layer at 25° C. is 4.1×10 -6 S / cm-6.4×10 -2 S / cm.

[0011] In any embodiment, the thickness of the first protective layer is a, the thickness of the second protective layer is b, the units of a and b are both μm, a:b is (1:3)-(3:1), and a+b is 5μm-30μm. In this way, the growth of lithium dendrites on the surface of the negative electrode can be suppressed, and the lithium ions that have lost electrical connection with the current collector can be activated to participate in the cycle charge and discharge again.

[0012] In the second aspect of the present application, the present application proposes a method for preparing the aforementioned negative electrode sheet, comprising: forming a negative electrode active material slurry layer on at least one side of a negative electrode current collector; forming a first slurry layer on the side of the negative electrode active material slurry layer away from the negative electrode current collector to obtain a first electrode sheet; and drying the first electrode sheet to obtain the negative electrode sheet. Thus, the aforementioned negative electrode sheet can be prepared by a simple method.

[0013] In any embodiment, forming the first slurry layer includes: providing a first slurry, wherein the first slurry includes a siloxane polymer, a binder, and a dispersant, thereby forming a first protective layer with suitable porosity and conductivity.

[0014] In any embodiment, the mass of the siloxane polymer in the first slurry is m 1-1 , the mass of the binder in the first slurry is m 1-2 , the mass of the dispersant in the first slurry is m 1-3 , m 1-1 :m 1-2 is (8:1)-(12:1), m1-3 :(m 1-1 +m 1-2 )=(8:1)-(12:1). Thus, a first protective layer having suitable porosity and electronic conductivity can be obtained.

[0015] In any embodiment, the first slurry satisfies at least one of the following conditions: the binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; and the dispersant includes toluene. Thus, the bonding strength between the first protective layer and the negative electrode active material layer can be improved.

[0016] In any embodiment, the method further comprises: forming a second slurry layer on the side of the negative electrode active material slurry layer away from the negative electrode current collector; forming the first slurry layer on the side of the second slurry layer away from the negative electrode current collector, wherein forming the second slurry layer comprises: providing a second slurry, the second slurry comprises a redox intermediate, a binder, a conductive agent, and a dispersant, wherein the redox intermediate comprises at least one of metal iodide, 10-methyl phenothiazine, thianthrene, and tetramethyl piperidine oxide. Thus, a second protective layer with higher electronic conductivity can be obtained.

[0017] In any embodiment, the mass of the redox intermediate in the second slurry is m 2-1 , the mass of the binder in the second slurry is m 2-2 , the mass of the conductive agent in the second slurry is m 2-3 , the mass of the dispersant in the second slurry is m 2-4 , m 2-1 :m 2-2 :m 2-3 :m 2-4 The ratio of the ...

[0018] In any embodiment, the second slurry satisfies at least one of the following conditions: the binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; the conductive agent includes at least one of conductive carbon black, carbon nanotubes, Ketjen black, and acetylene black; and the dispersant includes water. Thus, the conductivity of the second protective layer and the degree of bonding with the adjacent film layer can be improved.

[0019] In any embodiment, the temperature of the drying process is 80° C.-150° C. Thus, the dispersant can be removed by the drying process to form a protective layer structure.

[0020] In the third aspect of the present application, the present application proposes a battery, comprising the aforementioned negative electrode sheet, or the negative electrode sheet prepared by the aforementioned method. Therefore, the battery has all the features and advantages of the aforementioned negative electrode sheet and the method for preparing the negative electrode sheet, which will not be described in detail here.

[0021] In any embodiment, the battery is a lithium ion battery.

[0022] In a fourth aspect of the present application, the present application proposes an electrical device, comprising the aforementioned battery. Therefore, the electrical device has all the features and advantages of the aforementioned battery, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0024] Figure 1 It is a schematic structural diagram of a negative electrode sheet according to one embodiment of the present application;

[0025] Figure 2 It is a schematic structural diagram of a negative electrode sheet according to another embodiment of the present application;

[0026] Figure 3 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0027] Figure 4 yes Figure 3 An exploded view of a battery cell according to an embodiment of the present application is shown;

[0028] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application;

[0029] Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0030] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0031] Figure 8 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application;

[0032] Fig. 9 is a scanning electron microscope image of the negative electrode sheet in Example 1 of the present application;

[0033] Fig.10 This is a scanning electron microscope image of the negative electrode sheet in Comparative Example 1 of the present application.

[0034] Description of reference numerals:

[0035] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell;

[0036] 51 housing; 52 electrode assembly; 53 top cover assembly;

[0037] 100: negative electrode current collector; 200: negative electrode active material layer; 310: first protective layer; 320: second protective layer. DETAILED DESCRIPTION

[0038] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0039] Unless otherwise defined, all technical and scientific terms used in this application have the same meanings as those commonly understood by technicians in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0040] The terms "including" and "having" in the specification and claims of the present application and any modifications thereof are open expressions, that is, including the contents specified in the present application but not excluding other contents.

[0041] " Scope " disclosed in the present application is 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 not including end values, and can be combined arbitrarily, that is, any lower limit can form a scope with any upper limit combination. 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 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 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 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.

[0042] In the description of this application, regardless of whether the words "about" or "approximately" are used, all the numbers disclosed herein are approximate values. The value of each number may differ by less than 10% or a reasonable difference considered by those skilled in the art, such as 1%, 2%, 3%, 4% or 5%.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0044] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0045] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. "First feature" and "second feature" may include one or more of the features.

[0046] In the description of the present application, "A and / or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for examples and may be any technical feature connected by "and / or" in the present application.

[0047] Lithium-ion batteries rely on the intercalation and deintercalation of lithium ions between the positive and negative electrodes to achieve charging and discharging. Specifically, when charging, lithium ions are deintercalated from the positive electrode, and then embedded in the negative electrode after passing through the electrolyte, and the negative electrode is in a lithium-rich state; when discharging, the opposite is true, lithium ions are deintercalated from the negative electrode, and then embedded in the positive electrode after passing through the electrolyte, and the positive electrode is in a lithium-rich state.

[0048] When a lithium-ion battery is charged at a high current, due to the influence of polarization and diffusion, metallic lithium is very easy to precipitate on the surface of the negative electrode active material layer to form dendrite-like lithium. The reversibility of the dendrite-like lithium is poor and it cannot participate in the embedding and de-embedding of lithium ions between the positive and negative electrodes. The subsequent precipitation and deposition of metallic lithium is limited by diffusion, and it is mainly deposited on the top of the dendrite-like lithium, making the growth of lithium dendrites appear tree-like. Small dendrites can pass through the micropores on the isolation membrane, causing a short circuit between the positive and negative electrodes of the battery, resulting in the risk of thermal runaway of the battery. In addition, the growth of lithium dendrites will also continuously destroy the solid electrolyte interface (SEI) on the surface of the negative electrode active material, causing the negative electrode active material to directly contact the electrolyte, and then continuously generate new solid electrolyte interface membranes, resulting in continuous consumption of the electrolyte, which significantly reduces the Coulomb efficiency and continuously loses the battery capacity.

[0049] Typically, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed 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 short circuits between the positive and negative electrodes, while allowing ions to pass through.

[0050] Based on this, in the present application, by setting a first protective layer with specific porosity and electronic conductivity on the surface of the negative electrode active material layer, the nanopores of the first protective layer can provide channels for lithium ions, so that lithium ions can migrate between the positive electrode active material and the negative electrode active material, thereby realizing the charge and discharge cycle of the battery; and because the conductivity of the first protective layer is poor, when the battery produces lithium dendrites under high current charging, the lithium dendrites tend to grow between the negative electrode active material layer and the first protective layer, thereby making it difficult for the lithium dendrites to directly contact the isolation membrane, and the extremely low electronic conductivity of the first protective layer will also make it impossible for the lithium dendrites to continue to grow in the direction of the isolation membrane, so that the first protective layer can effectively inhibit the growth of lithium dendrites and reduce the risk of short circuit between the positive electrode plate and the negative electrode plate due to lithium dendrites piercing the isolation membrane.

[0051] In the first aspect of the present application, the present application proposes a negative electrode plate, referring to Figure 1, comprising: a negative electrode current collector 100; a negative electrode active material layer 200, the negative electrode active material layer 200 is located on at least one side of the negative electrode current collector 100; a first protective layer 310, the first protective layer 310 is located on the side of the negative electrode active material layer 200 away from the negative electrode current collector 100, the first protective layer 310 is a porous structure, the pore size of the porous structure can be 0.17nm-300nm, and the electronic conductivity of the first protective layer 310 at 25°C can be 2×10 -10 S / cm-6×10 -10 When lithium dendrites are generated on the negative electrode side of the battery during the charge and discharge cycle, the first protective layer 310 can guide the lithium dendrites to grow between the negative electrode active material layer 200 and the first protective layer 310, thereby inhibiting the growth of lithium dendrites on the surface of the negative electrode.

[0052] Porous structure refers to a network structure composed of interconnected or closed pores. Porous materials have a large specific surface area, and substances with a size less than or equal to the pore size of the porous structure can migrate in the pores of the porous structure.

[0053] In some embodiments, when the pore size of the porous structure is 0.7nm-300nm, the pore size in the first protective layer is moderate, which helps lithium ions to pass through the first protective layer and contact with the negative electrode active material layer, thereby achieving lithium insertion. During the growth of lithium dendrites, since lithium dendrites tend to continue to grow toward the isolation membrane, when the pore size of the first protective layer is within the aforementioned range, it is not easy for lithium dendrites to pass through the pores of the first protective layer and continue to grow toward the isolation membrane, and finally pierce the isolation membrane to reach the positive electrode plate, resulting in a short circuit between the positive electrode plate and the negative electrode plate.

[0054] In some embodiments, when the electronic conductivity of the first protective layer 310 is 2×10 -10 S / cm-6×10 -10 S / cm, the first protective layer has a suitable electronic conductivity, which will neither cause lithium ions to be deposited on the surface of the first protective layer away from the negative electrode active material layer, thereby achieving the effect of guiding lithium ions between the first protective layer and the negative electrode active material layer, nor cause the resistance of the negative electrode plate to be too large due to the electronic conductivity being too low, thereby causing the internal resistance of the battery to be too large and the energy efficiency to decrease.

[0055] The "pore size" in this application has a well-known meaning in the art and can be measured using instruments and methods well-known in the art. As an example, the pore size of the first protective layer can be tested by the following method: mercury is pressed into a dry porous sample, the relationship between the volume of mercury infiltrated into the sample and the pressure is measured, and the pore size distribution of the sample is calculated based on the relationship.

[0056] The "electronic conductivity" in this application has a well-known meaning in the art and can be measured by instruments and methods well-known in the art. As an example, the electronic conductivity of the first protective layer can be tested by the following method: The electronic conductivity of the material can be determined by measuring its resistivity. At 25°C, according to the Ampere formula R=U / I, the resistance of the conductor is calculated by measuring the current passing through the conductor and the voltage drop through the conductor, and the geometric dimensions of the sample to be tested are measured, and then the conductivity is calculated by the formula.

[0057] In some embodiments, the first protective layer 310 may include a siloxane polymer. By using a siloxane polymer, the electronic conductivity and pore size of the first protective layer can be regulated. Specifically, because the electronic conductivity of the siloxane polymer is poor, and one of the necessary conditions for the formation of lithium dendrites is a large number of electrons, by utilizing the poor electronic conductivity of the siloxane polymer, the electron concentration in the first protective layer can be low, while the electron concentration in the adjacent negative electrode active material layer or the second protective layer is high, so that an electron concentration difference is formed between the first protective layer and the adjacent film layer, thereby making it difficult for lithium dendrites to grow on the surface of the first protective layer away from the negative electrode current collector; in addition, the siloxane polymer itself has good flexibility, and its internal pore structure can accommodate lithium dendrites, so that the lithium dendrites spread and grow along the internal pore path of the siloxane polymer, rather than growing directly toward the isolation membrane, and then piercing the isolation membrane.

[0058] In some embodiments, the siloxane polymer satisfies at least one of the following conditions: the siloxane polymer may include at least one of vinyl-terminated polydimethylsiloxane, polydimethylsiloxane, polymethylphenylsiloxane, and polyphenylmethylsiloxane.

[0059] In some embodiments, the number average molecular weight of the siloxane-based polymer may be 5,000-200,000.

[0060] The "number average molecular weight" in this application has a well-known meaning in the art and can be measured using instruments and methods well-known in the art. As an example, the number average molecular weight of a polymer can be obtained by gel permeation chromatography.

[0061] When the number average molecular weight of the siloxane polymer is 5000-200000, the siloxane polymer has a suitable viscosity, which is convenient for preparing the slurry, and the obtained first protective layer has a suitable pore size.

[0062] In some embodiments, the siloxane-based polymer has a crystallinity of 60% to 82%.

[0063] As an example, the crystallinity of the siloxane-based polymer can be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81% or 82%.

[0064] When the crystallinity of the siloxane polymer is 60%-82%, the siloxane polymer has a suitable viscosity, which is convenient for preparing the slurry, and the obtained first protective layer has a suitable

[0065] The "crystallinity" in this application has a well-known meaning in the art and can be measured using instruments and methods well-known in the art. As an example, an XRD device can be used to compare the diffraction hardness of the measured material with a 100% crystalline sample (or a 100% amorphous sample) of the property to obtain the crystallinity range of the sample.

[0066] In some embodiments, the porosity of the first protective layer 310 may be 50%-60%.

[0067] As an example, the porosity of the first protective layer 310 may be 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%.

[0068] When the porosity of the first protective layer 310 is 50%-60%, the first protective layer not only facilitates the transfer of lithium ions, but also reduces the possibility of lithium dendrites penetrating the isolation membrane after penetrating the first protective layer.

[0069] The "porosity" in this application has a well-known meaning in the art and can be measured by instruments and methods well-known in the art. As an example, the porosity of the first protective layer can be tested and obtained by the following method: the pore volume is obtained according to the volume of BET nitrogen adsorption, and the porosity is calculated according to the pore volume and the apparent volume.

[0070] In some embodiments, the thickness of the first protection layer 310 may be 1 μm-25 μm.

[0071] As an example, the thickness of the first protection layer 310 may be 1 μm, 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 21 μm, 23 μm, or 25 μm.

[0072] When the thickness of the first protective layer 310 is 1 μm-25 μm, the first protective layer 310 can guide lithium dendrites to grow between the negative electrode active material layer 200 and the first protective layer 310 , but is not easily pierced by lithium dendrites.

[0073] The "thickness" in this application has a well-known meaning in the art and can be measured by instruments and methods well-known in the art. As an example, the thickness of the first protective layer can be tested by the following method: by preparing a sample of the cross section of the pole piece, the thickness value can be directly measured by a scanning electron microscope.

[0074] In some embodiments, during the growth of lithium dendrites, lithium dendrites are easily broken from the root, and the broken lithium ions cannot migrate to the surface of the negative electrode plate in time, and react with the solid electrolyte interface membrane to generate lithium-containing substances that cannot participate in subsequent charge and discharge cycles, such as Li2O, Li2O2, Li2CO3, Li2SO4, Li2S, LiOH and other electronically insulating inert substances, which will cover the surface of the negative electrode active material layer, resulting in a decrease in the coulombic efficiency of the battery and a serious attenuation of the capacity. Based on this, in the present application, by setting a second protective layer, the lithium ions that have lost electrical connection with the current collector can be reactivated so that they can participate in the battery's cyclic charge and discharge again.

[0075] In some embodiments, reference Figure 2 , further comprising: a second protective layer 320, the second protective layer 320 is located between the first protective layer 310 and the negative electrode active material layer 200, and the second protective layer 320 comprises at least one of metal iodide, 10-methylphenothiazine, thianthracene, and tetramethylpiperidinium oxide.

[0076] Metal iodides, 10-methyl phenothiazine, thianthrene, tetramethyl piperidine oxide, etc. can all be used as redox intermediates. Redox intermediates are substances in an intermediate state, which can be oxidized or reduced. Specifically, the redox intermediate becomes an oxidized redox intermediate after losing electrons, and the oxidized redox intermediate generates a reduced redox intermediate after gaining electrons, and the reduced redox intermediate can be converted into an oxidized redox intermediate after losing electrons, thereby realizing the mutual conversion of the redox intermediate between the oxidized state and the reduced state.

[0077] By adding redox intermediates, inert lithium-containing substances that cannot participate in subsequent charge and discharge cycles can be effectively activated. Specifically, during the charging process, the redox intermediates appear in an oxidized state, and the oxidized redox intermediates will spontaneously react with the inert lithium-containing substances to generate reduced redox intermediates and soluble lithium ions. After the reduced redox intermediates diffuse to the positive electrode side, they lose electrons and are oxidized to oxidized redox intermediates, and then diffuse to the negative electrode side again and can continue to participate in the activation of the inert lithium-containing substances.

[0078] Taking metal iodide as an example, during the charging process, the iodine ions in the metal iodide decompose and become oxidized iodine triions I3 -, oxidation state of iodine triion I3 - It will spontaneously react with inert lithium-containing substances to generate reduced iodide ions I - and soluble lithium ions, reduced iodide ions I - After diffusing to the positive electrode side, it loses electrons and is oxidized to iodine triion I3 - , thereby diffusing to the negative electrode side and continuing to participate in the activation of inert lithium-containing substances.

[0079] The redox potentials of 10-methylphenothiazine, 2,2,6,6-tetramethylpiperidinoxide, and thianthrene are all higher than that of the positive electrode active materials, and they can continuously participate in the activation of inert lithium-containing substances through the transition between their oxidation and reduction states.

[0080] In some embodiments, the electronic conductivity of the second protective layer 320 at 25° C. is 4.1×10 -6 S / cm-6.4×10 -2 S / cm.

[0081] As an example, the electronic conductivity of the second protective layer can be tested by referring to the testing method of the electronic conductivity of the first protective layer, which will not be described in detail here.

[0082] In some embodiments, reference Figure 2 The thickness of the first protective layer 310 is a, the thickness of the second protective layer 320 is b, the units of a and b are both μm, a:b can be (1:3)-(3:1), and a+b can be 5μm-30μm.

[0083] As an example, a:b may be (1:3)-(3:1), for example, a:b may be 1:3, 1:2, 2:3, 1:1, 3:2, 2:1 or 3:1.

[0084] Through the combined effect of the first protective layer and the second protective layer, the growth of lithium dendrites on the surface of the negative electrode can be suppressed, and the lithium ions that have lost electrical connection with the current collector can be activated so that they can participate in the cycle charge and discharge again.

[0085] When a:b is (1:3)-(3:1), the thickness of the first protective layer and the second protective layer is moderate, and the long-term accumulated lithium dendrites are not easy to pierce the first protective layer, and then pierce the diaphragm to cause short circuit, etc.; the second protective layer can also effectively activate lithium ions that have lost electrical connection with the current collector.

[0086] As an example, the thickness of the second protective layer can be tested by referring to the test method for the thickness of the first protective layer, which will not be described in detail here.

[0087] As an example, the negative electrode current collector 100 has two surfaces facing each other in its own thickness direction, and the negative electrode active material layer 200 is disposed on any one or both of the two facing surfaces of the negative electrode current collector 100 .

[0088] In some embodiments, the negative electrode current collector 100 may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials include at least one 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 can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0090] In some embodiments, the negative electrode active material layer 200 may further include a binder. The binder includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0091] In some embodiments, the negative electrode active material layer 200 may further include a conductive agent, which includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0092] In some embodiments, the negative electrode active material layer 200 may further include other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0093] In a second aspect of the present application, the present application proposes a method for preparing the aforementioned negative electrode sheet, comprising:

[0094] S10: Forming a negative electrode active material slurry layer on at least one side of the negative electrode current collector

[0095] In some embodiments, in this step, a negative electrode active material slurry layer is formed on at least one side of the negative electrode current collector, and the negative electrode active material layer can be obtained after drying.

[0096] As an example, the negative electrode active material layer can be prepared in the following manner: the components for preparing the negative electrode active material layer, such as the negative electrode active material, the conductive agent, the binder and any other components (such as additives) are dispersed in a solvent (such as deionized water) to form a negative electrode active material slurry; the negative electrode active material slurry is coated on the negative electrode current collector 100, and after drying, cold pressing and other processes, the negative electrode active material layer can be obtained.

[0097] In some embodiments, the selection of the negative electrode current collector, the negative electrode active material, the conductive agent, the binder, and the auxiliary agent can refer to the aforementioned embodiments and will not be described in detail herein.

[0098] S20: forming a first slurry layer on the side of the negative electrode active material slurry layer away from the negative electrode current collector

[0099] In some embodiments, a first slurry layer is formed in this step to obtain a first electrode sheet. At this time, the first electrode sheet includes a negative electrode active material slurry layer on the surface of at least one side of the negative electrode current collector, and a first slurry layer located on the side of the negative electrode active material slurry layer away from the negative electrode current collector. By drying the first electrode sheet, the negative electrode active material layer and the first protective layer stacked on the surface of at least one side of the negative electrode current collector can be obtained.

[0100] In some embodiments, forming the first slurry layer includes: providing a first slurry, wherein the first slurry includes a siloxane polymer, a binder, and a dispersant.

[0101] By adding a dispersant to the first slurry, the dispersibility of the siloxane polymer in the first slurry can be improved, and the flocculation and sedimentation of the siloxane polymer in the first slurry can be reduced. By adding a binder, the bonding strength between the first protective layer and the negative electrode active material layer can be improved, and the shedding can be reduced.

[0102] In some embodiments, the mass of the siloxane polymer in the first slurry is m 1-1 , the mass of the binder in the first slurry is m 1-2 , the mass of the dispersant in the first slurry is m 1-3 , m 1-1 :m 1-2 is (8:1)-(12:1), m 1-3 :(m 1-1 +m 1-2 )=(8:1)-(12:1).

[0103] In some embodiments, the binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; and the dispersant includes toluene.

[0104] In some embodiments, further comprising:

[0105] S21: forming a second slurry layer on the side of the negative electrode active material slurry layer away from the negative electrode current collector

[0106] In some embodiments, forming the second slurry layer includes: providing a second slurry, wherein the second slurry includes a redox intermediate, a binder, a conductive agent, and a dispersant. Metal iodides, 10-methylphenothiazine, thianthracene, tetramethylpiperidinium oxide, etc. can be used as redox intermediates.

[0107] By adding a dispersant to the second slurry, the dispersibility of the redox intermediates in the second slurry can be improved; by adding a binder to the second slurry, the bonding strength between the second protective layer and the negative electrode active material layer and the first protective layer can be improved; by adding a conductive agent to the second slurry, the second protective layer can have a higher electronic conductivity, which is more conducive to the deposition of lithium on the surface of the second protective layer, and is also conducive to the activation of lithium ions that have lost electrical connection with the current collector by the redox intermediates in the second protective layer.

[0108] In some embodiments, the mass of the redox intermediate in the second slurry is m 2-1 , the mass of the binder in the second slurry is m 2-2 , the mass of the conductive agent in the second slurry is m 2-3 , the mass of the dispersant in the second slurry is m 2-4 , m 2-1 :m 2-2 :m 2-3 :m 2-4 It is (40-60):(0.5-1.3):(20-40):(8-15).

[0109] In some embodiments, the binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid; the conductive agent includes at least one of conductive carbon black, carbon nanotubes, Ketjen black, and acetylene black; and the dispersant includes water. Thus, the electronic conductivity of the second protective layer and the degree of bonding with the adjacent film layer can be improved.

[0110] In some embodiments, after forming the second slurry layer, a first slurry layer is formed on the side of the second slurry layer away from the negative electrode current collector to obtain a first electrode sheet. At this time, the first electrode sheet includes a negative electrode active material slurry layer on the surface of at least one side of the negative electrode current collector, a second slurry layer located on the side of the negative electrode active material slurry layer away from the negative electrode current collector, and a first slurry layer located on the side of the second slurry layer away from the negative electrode active material slurry layer. By drying the first electrode sheet, the negative electrode active material layer, the second protective layer, and the first protective layer stacked on the surface of at least one side of the negative electrode current collector can be obtained.

[0111] S30: Drying the first pole piece

[0112] In some embodiments, in this step, the first electrode sheet is dried to obtain the negative electrode sheet. The drying process can remove or remove as much as possible the dispersant and other substances in the slurry, thereby improving the structural stability and energy density of the film layer.

[0113] In some embodiments, the drying process may be performed at a temperature of 80°C to 150°C.

[0114] As an example, the temperature of the drying process may be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C.

[0115] In the third aspect of the present application, the present application proposes a battery, comprising the aforementioned negative electrode sheet, or the negative electrode sheet prepared by the aforementioned method. Therefore, the battery has all the features and advantages of the aforementioned negative electrode sheet and the method for preparing the negative electrode sheet, which will not be described in detail here.

[0116] The battery of the present application includes a battery cell form, a battery module form and a battery pack form.

[0117] Typically, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active 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 of the battery from short-circuiting, while allowing ions to pass through.

[0118] In some embodiments, the battery may be a lithium-ion battery.

[0119] [Positive electrode]

[0120] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material of the first aspect of the present application.

[0121] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0122] 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 and a metal layer formed on at least one side of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] In some embodiments, when the battery is a lithium ion battery, the positive electrode active material may be a positive electrode active material for lithium ion batteries known in the art.

[0124] As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other 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. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 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 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds. Examples of lithium-containing phosphates with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, and a composite material of lithium manganese iron phosphate and carbon. The modified compounds of the above materials may be doping modification and / or surface coating modification of the materials.

[0125] The battery will be accompanied by Li deintercalation and consumption during the charge and discharge process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle.

[0126] In the list of positive electrode active materials in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0127] In some embodiments, the positive electrode active material layer may further optionally include a binder.

[0128] As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0129] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent.

[0130] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0131] 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 (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0132] [Electrolytes]

[0133] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0134] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0135] In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0136] In some embodiments, the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0137] 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.

[0138] [Isolation film]

[0139] In some embodiments, the battery cell 5 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.

[0140] In some embodiments, the material of the isolation membrane includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can 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 can be the same or different, without particular limitation.

[0141] 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.

[0142] In some embodiments, the battery may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0143] In some embodiments, the outer packaging of the battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] The present application has no particular limitation on the shape of the battery, which may be cylindrical, square or any other shape. Figure 3 The battery cell 5 is a square structure as an example.

[0145] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a top cover assembly 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 top cover assembly 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 can be one or more, and those skilled in the art can select according to specific actual needs.

[0146] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0147] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of battery cells 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 may be fixed by fasteners.

[0148] Optionally, the battery module 4 may further include a housing having a receiving space, and a plurality of battery cells are received in the receiving space.

[0149] In some embodiments, the battery modules or battery cells mentioned above may also be assembled into a battery pack. The number of battery modules or battery cells contained in the battery pack may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0150] Figure 6 and Figure 71 is a battery pack 1 as an example. Figure 6 and Figure 7 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.

[0151] In a fourth aspect of the present application, the present application proposes an electrical device, comprising the aforementioned battery. Therefore, the electrical device has all the features and advantages of the aforementioned battery, which will not be described in detail here.

[0152] In some embodiments, the electrical device includes at least one of the batteries, battery modules, and battery packs provided in the present application. The battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0153] As an electrical device, a battery, a battery module or a battery pack can be selected according to its usage requirements.

[0154] Figure 8 The power consumption device 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. In order to meet the high power and high energy density requirements of the power consumption device for the battery, a battery pack or a battery module can be used.

[0155] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery may be used as a power source.

[0156] The scheme of the present application is described below by specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this area or the product instructions are used. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be obtained commercially.

[0157] Example 1

[0158] Preparation of the first slurry: polydimethylsiloxane (number average molecular weight of 100,000, crystallinity of 75%) and binder styrene butadiene rubber are mixed in a weight ratio of 10:1, and the bubbles are removed by vacuum treatment, and then diluted with dispersant toluene and stirred for 60 minutes, and the weight ratio of toluene to the mixture of polydimethylsiloxane and styrene butadiene rubber is 10:1.

[0159] Preparation of the second slurry: dry-mix the redox intermediate tin iodide and the conductive agent carbon black, then add the binder styrene-butadiene rubber, the binder sodium carboxymethyl cellulose and water and continue mixing, wherein the mass ratio of tin iodide, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose is 55.35:10:22.2:12.45, and adjust the viscosity by adding water and slowly stir and ship, so that the viscosity of the second slurry is 7000mPa·s-2000mPa·s.

[0160] Negative electrode active material slurry: The negative electrode active material graphite, the conductive agent carbon black, the binder styrene-butadiene rubber, and the thickener sodium hydroxymethyl cellulose are dissolved in the solvent deionized water at a weight ratio of 97.2:0.8:0.8:1.2, and the negative electrode active material slurry is prepared after being mixed evenly.

[0161] Preparation of negative electrode sheet: Coat the negative electrode active material slurry on the negative electrode current collector copper foil, with a single-side weight of 0.175g / 1540.25mm 2 ; The second slurry layer is coated on the side of the negative electrode active material slurry layer away from the negative electrode current collector, and the first slurry layer is coated on the side of the second slurry layer away from the negative electrode active material slurry layer. The total weight of the first slurry layer and the second slurry layer on one side is 0.02g / 1540.25mm 2 To obtain the first pole piece, wherein the thickness ratio of the first protective layer to the second protective layer is 1:2, the total thickness of the first protective layer and the second protective layer is 15 μm, and the first pole piece is dried at a temperature of 100° C., and then cold pressed and cut to obtain the negative pole piece.

[0162] Preparation of positive electrode sheet: Using methyl pyrrolidone (NMP) as solvent, the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent carbon nanotubes, and binder PVDF are mixed in a mass ratio of 97:2:1 to prepare positive electrode slurry. The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil (double-sided coating, single-sided weight is 0.131g / 1540.25mm 2 ), and after sufficient drying, cold pressing and slitting, the positive electrode sheet is obtained.

[0163] Preparation of the battery: Add LiPF6 to a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 at room temperature to obtain a 1M LiPF6 solution as the electrolyte. Using Celgard 2300 as a separator, stack and wind the positive and negative electrode sheets prepared above in a low-humidity constant temperature room in the order of "positive electrode sheet-separator-negative electrode sheet", then fill with electrolyte and assemble the battery.

[0164] Example 2

[0165] Example 2 is consistent with Example 1, except that the second slurry layer is not coated, and the thickness of the first protective layer is 15 μm.

[0166] Embodiment 3-6

[0167] Examples 3-6 are consistent with Example 1, except that in Example 3, the total thickness of the first protective layer and the second protective layer is 6 μm; in Example 4, the total thickness of the first protective layer and the second protective layer is 12 μm; in Example 5, the total thickness of the first protective layer and the second protective layer is 18 μm; in Example 6, the total thickness of the first protective layer and the second protective layer is 27 μm.

[0168] Examples 7-10

[0169] Examples 7-10 are consistent with Example 1, except that in Example 7, the thickness ratio of the first protective layer to the second protective layer is 3:1; in Example 8, the thickness ratio of the first protective layer to the second protective layer is 2:1; in Example 9, the thickness ratio of the first protective layer to the second protective layer is 1:1; in Example 7, the thickness ratio of the first protective layer to the second protective layer is 1:3.

[0170] Examples 11-16

[0171] Examples 11-16 are consistent with Example 1, except that the number average molecular weight of polydimethylsiloxane in Example 11 is 100,000; the number average molecular weight of polydimethylsiloxane in Example 12 is 90,000; the number average molecular weight of polydimethylsiloxane in Example 13 is 50,000; the number average molecular weight of polydimethylsiloxane in Example 14 is 12,000; the number average molecular weight of polydimethylsiloxane in Example 15 is 8,000; and the number average molecular weight of polydimethylsiloxane in Example 16 is 5,000.

[0172] Comparative Example 1

[0173] Comparative Example 1 is consistent with Example 1, except that the coating of the first slurry layer and the second slurry layer is not performed.

[0174] Comparative Example 2

[0175] Comparative Example 2 is consistent with Example 2, except that the number average molecular weight of polydimethylsiloxane is 250,000.

[0176] Comparative Example 3

[0177] Comparative Example 3 is consistent with Example 2, except that the number average molecular weight of polydimethylsiloxane is 3000.

[0178] Comparative Example 4

[0179] Comparative Example 4 is consistent with Example 2, except that the crystallinity of the polydimethylsiloxane is 50%.

[0180] Comparative Example 5

[0181] Comparative Example 5 is consistent with Example 2, except that the crystallinity of the polydimethylsiloxane is 85%.

[0182] Test Section

[0183] 1. Cycle capacity retention rate

[0184] At 25°C, charge the battery at a constant current of 1 / 3C to 4.4V, then charge at a constant voltage of 4.4V to a current of 0.05C, let stand for 5 minutes, and then discharge at 1 / 3C to 2.5V. The measured capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery, and record the discharge capacity C of the battery after the nth cycle. n , then the battery capacity retention rate after n cycles is P n =C n / C0×100%, for example, the capacity retention rate of the battery after 500 cycles (n=500) is P 500 .

[0185] 2. Scanning electron microscope (SEM) of negative electrode

[0186] After 500cls of cycling, the battery is charged at 1 / 3C constant current to 4.4V, and then charged at 4.4V constant voltage to a current of 0.1C. At this time, the battery is fully charged. (NCM 811 The voltage window is 2.5V-4.4V). The battery is disassembled and the fully charged negative electrode is taken out. The lithium dendrites on the surface of the negative electrode facing the isolation membrane are observed using a scanning electron microscope.

[0187] 3. Thickness of protective layer

[0188] By preparing a sample of the electrode cross section, the thickness value can be directly measured using a scanning electron microscope.

[0189] 4. Aperture of protective layer

[0190] The pore volume was obtained from the volume of BET nitrogen adsorption, and the porosity was calculated from the pore volume and apparent volume.

[0191] 5. Electronic conductivity of the protective layer

[0192] At 25°C, according to the Ampere formula R=U / I, the resistance of the conductor is calculated by measuring the current passing through the conductor and the voltage drop through the conductor, and the geometric dimensions of the sample to be tested are measured, and then the conductivity is calculated by the formula.

[0193] The test results are shown in Table 1:

[0194] Table 1

[0195]

[0196]

[0197] See also Fig. 9 It can be seen that the provision of the first protective layer and the second protective layer can effectively alleviate the growth of lithium dendrites on the surface of the negative electrode plate and improve the cycle performance of the battery. Fig.10 It can be seen that long lithium dendrites appear on the surface of the negative electrode plate without a protective layer, which poses a risk of piercing the isolation membrane and causing a short circuit between the positive electrode plate and the negative electrode plate.

[0198] 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: include: Anode current collector; A negative electrode active material layer, the negative electrode active material layer is located on at least one side of the negative electrode current collector; The first protective layer is located on the side of the negative electrode active material layer away from the negative electrode current collector, the first protective layer is a porous structure, the pore size of the porous structure is 0.17nm-300nm, and the electronic conductivity of the first protective layer at 25°C is 2×10 -10 S / cm-6×10 -10 S / cm.

2. The negative electrode sheet according to claim 1, characterized in that: The first protective layer includes a siloxane polymer; Optionally, the siloxane polymer includes at least one of vinyl-terminated polydimethylsiloxane, polydimethylsiloxane, polymethylphenylsiloxane and polyphenylmethylsiloxane.

3. The negative electrode sheet according to claim 2, characterized in that: The number average molecular weight of the siloxane polymer is 5000-200000; and / or the crystallinity of the siloxane polymer is 60%-82%.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The porosity of the first protective layer is 50%-60%.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The thickness of the first protective layer is 1 μm-25 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: Further including: The second protective layer is located between the first protective layer and the negative electrode active material layer, and the second protective layer includes at least one of metal iodide, 10-methylphenothiazine, thianthracene, and tetramethylpiperidinium oxide.

7. The negative electrode sheet according to claim 6, characterized in that: The electronic conductivity of the second protective layer at 25°C is 4.1×10 -6 S / cm–6.4×10 -2 S / cm.

8. The negative electrode sheet according to claim 6 or 7, characterized in that: The thickness of the first protective layer is a, the thickness of the second protective layer is b, the units of a and b are both μm, a:b is (1:3)-(3:1), and a+b is 5μm-30μm.

9. A method for preparing the negative electrode sheet according to any one of claims 1 to 8, characterized in that: include: forming a negative electrode active material slurry layer on at least one side of the negative electrode current collector; forming a first slurry layer on a side of the negative electrode active material slurry layer away from the negative electrode current collector to obtain a first electrode sheet; The first electrode sheet is dried to obtain the negative electrode sheet.

10. The method according to claim 9, characterized in that Forming the first slurry layer includes: A first slurry is provided, wherein the first slurry includes a siloxane polymer, a binder, and a dispersant.

11. The method according to claim 10, characterized in that The mass of the siloxane polymer in the first slurry is m 1-1 , the mass of the binder in the first slurry is m 1-2 , the mass of the dispersant in the first slurry is m 1-3 , m 1-1 :m 1-2 is (8:1)-(12:1), m 1-3 :(m 1-1 +m 1-2 )=(8:1)-(12:1).

12. The method according to claim 10 or 11, characterized in that: The first slurry satisfies at least one of the following conditions: The binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber and polyacrylic acid; The dispersant includes toluene.

13. The method according to any one of claims 9 to 12, characterized in that: Further including: forming a second slurry layer on a side of the negative electrode active material slurry layer away from the negative electrode current collector; forming the first slurry layer on a side of the second slurry layer away from the negative electrode current collector, Wherein, forming the second slurry layer comprises: providing a second slurry, wherein the second slurry comprises a redox intermediate, a binder, a conductive agent, and a dispersant, wherein the redox intermediate comprises at least one of metal iodide, 10-methylphenothiazine, thianthracene, and tetramethylpiperidinium oxide.

14. The method according to claim 13, characterized in that The mass of the redox intermediate in the second slurry is m 2-1 , the mass of the binder in the second slurry is m 2-2 , the mass of the conductive agent in the second slurry is m 2-3 , the mass of the dispersant in the second slurry is m 2-4 , m 2-1 :m 2-2 :m 2-3 :m 2-4 It is (40-60):(0.5-1.3):(20-40):(8-15).

15. The method according to claim 13 or 14, characterized in that The second slurry satisfies at least one of the following conditions: The binder includes at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber and polyacrylic acid; The conductive agent includes at least one of conductive carbon black, carbon nanotubes, Ketjen black, and acetylene black; The dispersant includes water.

16. The method according to any one of claims 9 to 15, characterized in that: The temperature of the drying process is 80°C-150°C.

17. A battery, characterized in that: A negative electrode sheet comprising the negative electrode sheet as described in any one of claims 1 to 8, or a negative electrode sheet prepared by the method as described in any one of claims 9 to 16.

18. The battery according to claim 17, characterized in that The battery is a lithium-ion battery.

19. An electrical device, characterized in that: A battery comprising the battery of claim 17 or 18.

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