Secondary battery and electric device

Abstract

The application provides a secondary battery (4) and an electric device. The secondary battery (4) comprises a positive electrode sheet and a negative electrode sheet. The total capacity of the positive electrode sheet is P, and the total capacity of the negative electrode sheet is N. N / P<1 is satisfied. The negative electrode sheet comprises a current collector and a first negative electrode active layer, an insulating material layer and a second negative electrode active layer arranged on the surface of the current collector in sequence. The secondary battery (4) has high energy density and excellent cycle performance.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to a secondary battery and an electrical device. Background Technology

[0002] Secondary batteries are increasingly widely used due to their cleanliness and renewability. Secondary batteries, such as lithium-ion batteries, are mainly composed of five parts: positive electrode, negative electrode, separator, electrolyte, and shell. They mainly rely on the movement of lithium ions between the positive and negative electrodes to generate electrical energy. During charging, lithium ions or sodium ions are extracted from the positive electrode and inserted into the negative electrode through the electrolyte. The reverse is true during discharging.

[0003] In recent years, with the rapid development of the new energy industry, people's demand for new energy transportation tools such as electric vehicles and electric bicycles has been increasing, and their performance requirements have also been getting higher and higher. Secondary batteries are an important power source for electric vehicles. Therefore, people's requirements for the energy density and cycle performance of secondary batteries are also getting higher and higher.

[0004] As demand increases, the energy density and cycle performance of traditional rechargeable batteries are increasingly unable to meet people's needs and require further improvement. Summary of the Invention

[0005] In view of the above problems, this application provides a secondary battery and an electrical device, which has both high energy density and excellent cycle performance.

[0006] To achieve the above objectives, the first aspect of this application provides a secondary battery, which includes a positive electrode and a negative electrode, wherein the total capacity of the positive electrode is P and the total capacity of the negative electrode is N, and N and P satisfy: N / P < 1.

[0007] The negative electrode sheet includes a current collector and a first negative electrode active layer, an insulating material layer, and a second negative electrode active layer sequentially disposed on the surface of the current collector.

[0008] In the aforementioned secondary battery, on the one hand, the total capacity of the positive and negative electrodes is designed and controlled to ensure N / P < 1, so that the amount of lithium ions in the positive electrode is much greater than the amount of lithium ions that the positive electrode can hold. During charging, some of the excess lithium ions will deposit on the negative electrode in the form of lithium metal, thereby forming a lithium metal complex with the negative electrode active material on the negative electrode. The formation of the lithium metal complex can improve the energy density of the secondary battery. On the other hand, some excess lithium ions will form lithium dendrites when deposited on the surface of the negative electrode, causing a short circuit problem. By sequentially setting a first negative electrode active layer, an insulating material layer, and a second negative electrode active layer on the current collector surface of the negative electrode, lithium dendrites can be deposited between the insulating material layer and the current collector interface. The second negative electrode active layer absorbs and covers the lithium dendrites that pierce through the insulating material layer, preventing the formation of lithium dendrites on the surface of the negative electrode, which could then pierce the separator and cause a short circuit. Thus, the secondary battery has both high energy density and excellent cycle performance.

[0009] In any embodiment of this application, the thickness of the insulating material layer is L1 μm, the thickness of the second negative electrode active layer is L2 μm, and L1 and L2 satisfy: L1=-16×N / P+17.5, 0.01≤L2 / L1.

[0010] The thickness of the insulating material layer is determined by the N / P ratio. When the N / P ratio is low, there are more excess lithium ions, resulting in thicker lithium dendrites deposited on the negative electrode. Therefore, the thickness of the insulating material layer must be increased. Simultaneously, the thickness ratio of the insulating material layer to the second negative electrode active layer is controlled to ensure good ion transport while preventing the formation of lithium dendrites on the negative electrode surface, which could puncture the separator and cause a short circuit. This allows the secondary battery to possess both high energy density and excellent cycle performance.

[0011] In any embodiment of this application, 0.01 ≤ L2 / L l ≤0.1;

[0012] Optionally, 0.03 ≤ L2 / L1 ≤ 0.08.

[0013] In any embodiment of this application, the thickness of the insulating material layer is 0.2 μm to 15 μm;

[0014] Optionally, the thickness of the insulating material layer is 3.1 μm to 7.9 μm.

[0015] In any embodiment of this application, the thickness of the first negative electrode active layer is 10 μm to 300 μm;

[0016] Optionally, the thickness of the first negative electrode active layer is 60 μm to 200 μm.

[0017] In any embodiment of this application, the components of the second negative electrode active layer include a lithium-philic material.

[0018] During the cycle of a secondary battery, lithium dendrites deposit and accumulate between the insulating material layer and the current collector interface. When they accumulate to a certain extent, they will pierce the insulating material layer and embed into the second negative electrode active layer. On the one hand, the second negative electrode active layer further coats the lithium dendrites, preventing them from piercing the separator. On the other hand, the lithium-loving material in the second negative electrode active layer can further combine with the lithium dendrites embedded in the second negative electrode active layer, thereby absorbing the lithium dendrites and preventing further diffusion of lithium dendrites, thus achieving passivation.

[0019] In any embodiment of this application, lithium metal is used as the reference electrode, and the overpotential of the lithiophilic material is no greater than 0.03V.

[0020] In any embodiment of this application, the lithiophilic material is selected from one or more of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, Mg and their oxides, sulfides, fluorides, nitrides, chlorides and carbides.

[0021] In any embodiment of this application, the secondary battery satisfies at least one of the following conditions a to b:

[0022] a. In the second negative electrode active layer, the mass percentage of the lithiophilic material is 0.2% to 5%;

[0023] Optionally, in the second negative electrode active layer, the mass percentage of the lithiophilic material is 0.3% to 3%;

[0024] b. The overpotential of the second negative electrode active layer is 0 to 0.3V.

[0025] In any embodiment of this application, the overpotential of the first negative electrode active layer is 0.1V to 0.6V.

[0026] In any embodiment of this application, the components of the first negative electrode active layer and the second negative electrode active layer both include a negative electrode active material and metallic lithium, wherein the metallic lithium is loaded on the surface of the negative electrode active material.

[0027] In any embodiment of this application, the positive electrode sheet includes a current collector and a positive electrode active layer loaded on the surface of the current collector. The positive electrode active layer is composed of a lithium-ion positive electrode active material, and the metallic lithium is derived from lithium ions in the lithium-ion positive electrode active material contained in the positive electrode sheet.

[0028] In any embodiment of this application, the secondary battery satisfies at least one of the following conditions c to d:

[0029] c. In the first negative electrode active layer, the proportion of the negative electrode active material is 80% to 98%;

[0030] d. In the second negative electrode active layer, the proportion of the negative electrode active material is 80% to 98%.

[0031] In any embodiment of this application, the negative electrode active material includes at least one of the following: mesophase carbon microspheres, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, magnesium-based materials, tin-based materials, and iron-based materials.

[0032] In any embodiment of this application, the components of the insulating material layer include insulating material and adhesive.

[0033] In any embodiment of this application, the insulating material includes at least one of organic insulating materials and inorganic insulating materials. The inorganic insulating material is selected from at least one of alumina, silicon oxide, zinc oxide, iron oxide, copper oxide, titanium oxide, mica, asbestos, marble, and ceramics. The organic insulating material is selected from at least one of natural rubber, styrene-butadiene rubber, cis-butadiene rubber, and isoprene rubber.

[0034] A second aspect of this application provides an electrical device, which includes the secondary battery of the first aspect of this application.

[0035] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0036] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0037] Figure 1 This is a schematic diagram of one embodiment of a secondary battery.

[0038] Figure 2 yes Figure 1 The exploded diagram.

[0039] Figure 3 This is a schematic diagram of one embodiment of the battery pack.

[0040] Figure 4 yes Figure 3 The exploded diagram.

[0041] Figure 5 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Secondary battery; 41. Housing; 42. Electrode assembly; 43. Cover plate; 5. Electrical device. Detailed Implementation

[0044] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0046] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0047] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0048] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0049] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0050] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0051] In this description, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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). Unless otherwise stated, the terms used in this application have their commonly known meanings as understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0052] As described in the background section, with increasing demands, the energy density and cycle performance of traditional rechargeable batteries are increasingly unable to meet people's needs. In rechargeable batteries such as lithium-ion batteries, the capacity balance between the negative electrode (NE) and the positive electrode (PE) is considered a critical point. Generally, if the positive electrode is overloaded, excess lithium ions released from the positive electrode during charging will precipitate on the surface of the negative electrode, forming lithium dendrites, which can easily cause internal short circuits in the battery, thus affecting battery safety performance. Furthermore, the formation of lithium dendrites can puncture the separator, causing short circuits and leading to safety accidents. Therefore, in traditional technologies, to avoid lithium deposition and achieve good safety, the negative electrode generally needs to be overloaded, that is, the total capacity ratio N / P value of the corresponding areas of the negative and positive electrode sheets is controlled to be greater than 1.

[0053] However, the technicians of this application discovered during the actual production and R&D process of batteries that when the total capacity ratio N / P value within the corresponding area of ​​the positive and negative electrodes is greater than 1, the improvement of energy density and cycle performance of secondary batteries such as lithium-ion batteries is limited, and it is difficult to meet people's increasingly higher demands for energy density and cycle performance of secondary batteries.

[0054] Based on this, after extensive research and experimentation, the engineers of this application have found a new approach and broken the constraints of traditional technology by controlling N / P < 1 and designing the structure of the negative electrode to achieve high energy density while avoiding the formation of lithium dendrites, thus enabling the secondary battery to have both high energy density and excellent cycle performance.

[0055] One embodiment of this application provides a secondary battery, which includes a positive electrode and a negative electrode. The total capacity of the positive electrode is P, and the total capacity of the negative electrode is N. N and P satisfy: N / P < 1.

[0056] The negative electrode sheet includes a current collector and a first negative electrode active layer, an insulating material layer, and a second negative electrode active layer sequentially disposed on the surface of the current collector.

[0057] In the aforementioned secondary battery, on the one hand, the total capacity of the positive and negative electrodes is designed and controlled to ensure N / P < 1, so that the amount of lithium ions in the positive electrode is much greater than the amount of lithium ions that the positive electrode can hold. During charging, some of the excess lithium ions will deposit on the negative electrode in the form of lithium metal, thereby forming a lithium metal complex with the negative electrode active material on the negative electrode. The formation of the lithium metal complex can improve the energy density of the secondary battery. On the other hand, some excess lithium ions will form lithium dendrites when deposited on the surface of the negative electrode, causing a short circuit problem. By sequentially setting a first negative electrode active layer, an insulating material layer, and a second negative electrode active layer on the current collector surface of the negative electrode, lithium dendrites can be deposited between the insulating material layer and the current collector interface. The second negative electrode active layer absorbs and covers the lithium dendrites that pierce through the insulating material layer, preventing the formation of lithium dendrites on the surface of the negative electrode, which could then pierce the separator and cause a short circuit. Thus, the secondary battery has both high energy density and excellent cycle performance.

[0058] In any embodiment of this application, the thickness of the insulating material layer is L1μm, the thickness of the second negative electrode active layer is L2μm, and L1 and L2 satisfy: L1=-16×N / P+17.5, 0.01≤L2 / L1.

[0059] After extensive and creative experiments, and through analysis, the engineers of this application have determined that the thickness of the insulating material layer should be determined based on the N / P ratio. When the N / P ratio is low, there are more excess lithium ions, resulting in thicker lithium dendrites deposited on the negative electrode. Therefore, the thickness of the insulating material layer should be increased. Simultaneously, the thickness ratio of the insulating material layer to the second negative electrode active layer should be controlled to ensure good ion transport while preventing the formation of lithium dendrites on the surface of the negative electrode, which could puncture the separator and cause a short circuit. This allows the secondary battery to possess both high energy density and excellent cycle performance.

[0060] In any embodiment of this application, L1 and L2 satisfy: 0.01≤L2 / L1≤0.1.

[0061] Preferably, L1 and L2 satisfy: 0.03≤L2 / L1≤0.08.

[0062] In the above "0.01≤L2 / L1≤0.1", the value of L2 / L1 includes the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples of L2 / L1 include, but are not limited to, the point values ​​in the embodiments and: 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0063] In any embodiment of this application, the thickness of the above-mentioned insulating material layer is 0.2 μm to 15 μm.

[0064] Optionally, the thickness of the above-mentioned insulating material layer is 3.1 μm to 7.9 μm.

[0065] The range "0.2μm to 15μm" includes the minimum and maximum values ​​within this range, as well as every value between these two values. Specific examples include, but are not limited to, the point values ​​in the embodiments and: 0.2μm, 0.3μm, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm m, 6.5μm, 7μm, 7.1μm, 7.2μm, 7.3μm, μm, 7.5μm, 7.7μm, 7.8μm, 7.9μm, 8μm, 8.5μm, 9μm , 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 4μm, 14.5μm, 15μm.

[0066] In any embodiment of this application, the thickness of the first negative electrode active layer is 10 μm to 300 μm.

[0067] In any embodiment of this application, the thickness of the first negative electrode active layer is 60 μm to 200 μm.

[0068] In any embodiment of this application, the components of the second negative electrode active layer include a lithium-philic material.

[0069] During the cycle of a secondary battery, lithium dendrites deposit and accumulate between the insulating material layer and the current collector interface. When they accumulate to a certain extent, they will pierce the insulating material layer and embed into the second negative electrode active layer. On the one hand, the second negative electrode active layer further coats the lithium dendrites, preventing them from piercing the separator. On the other hand, the lithium-loving material in the second negative electrode active layer can further combine with the lithium dendrites embedded in the second negative electrode active layer, thereby absorbing the lithium dendrites and preventing further diffusion of lithium dendrites, thus achieving passivation.

[0070] In any embodiment of this application, lithium metal is used as the reference electrode, and the overpotential of the lithiophilic material is no greater than 0.03V.

[0071] Specifically, the overpotential of the aforementioned lithiophilic material was tested using a three-electrode electrochemical cell, with the lithiophilic material as the working electrode. 0.5 FePO4 was used as the reference electrode, and lithium metal was used as the counter electrode.

[0072] The specific testing method is as follows:

[0073] At 10μA cm- 2 Lithium metal was deposited on the working electrode using a current density. The voltage of the working electrode relative to Li metal (Li / Li+) was plotted on the ordinate, and the capacity on the abscissa. As the capacity increased, the voltage initially decreased and then leveled off. During this process, if the curve had no inflection point or the absolute value of the voltage on the ordinate corresponding to the inflection point was ≤0.03V, it indicated that the material under test had lithium affinity.

[0074] In any embodiment of this application, the lithiophilic material is selected from one or more of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, Mg and their oxides, sulfides, fluorides, nitrides, chlorides and carbides.

[0075] In any embodiment of this application, the mass percentage of the lithiophilic material in the second negative electrode active layer is 0.2% to 5%.

[0076] In any embodiment of this application, the mass percentage of the lithiophilic material in the second negative electrode active layer is 0.3% to 3%.

[0077] In any embodiment of this application, lithium metal is used as the reference electrode, and the overpotential of the second negative electrode active layer is 0 to 0.3V.

[0078] In any embodiment of this application, lithium metal is used as the reference electrode, and the overpotential of the first negative electrode active layer is 0.1V to 0.6V.

[0079] The overpotential of the second or first negative electrode active layer was tested using a three-electrode electrochemical cell, with the second or first negative electrode active layer as the working electrode. 0.5 FePO4 was used as the reference electrode, and lithium metal was used as the counter electrode. The specific testing method is as follows:

[0080] At 10μA cm -2The current density is used to deposit metallic lithium on the working electrode. The voltage of the working electrode relative to Li metal (Li / Li+) is plotted on the ordinate, and the capacity on the abscissa. As the capacity increases, the voltage first decreases and then levels off. During this process, the absolute value of the voltage on the ordinate corresponding to the inflection point of the curve is the overpotential.

[0081] In any embodiment of this application, the components of the first negative electrode active layer and the second negative electrode active layer both include a negative electrode active material and lithium metal, with the lithium metal loaded on the surface of the negative electrode active material.

[0082] Lithium metal is loaded onto the surface of the negative electrode active material to form lithium metal composite lithium, which is beneficial to improve the energy density of the secondary battery. The energy density of the above secondary battery can reach 300Wh / kg to 600Wh / kg, or even higher.

[0083] In any embodiment of this application, the proportion of negative electrode active material in the first negative electrode active layer is 80% to 99%.

[0084] In any embodiment of this application, the proportion of negative electrode active material in the first negative electrode active layer is 88% to 98%.

[0085] In any embodiment of this application, the proportion of negative electrode active material in the second negative electrode active layer is 80% to 99%.

[0086] In any embodiment of this application, the proportion of negative electrode active material in the second negative electrode active layer is 88% to 98%.

[0087] In any embodiment of this application, the aforementioned negative electrode active material includes at least one of the following: mesophase carbon microspheres, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, magnesium-based materials, and iron-based materials.

[0088] Specific examples of the above-mentioned anode active materials include, but are not limited to, at least one of the following: interphase carbon microspheres, natural graphite, artificial graphite, graphene, glassy carbon, carbon nanotubes, carbon fibers, hard carbon, soft carbon, iron oxide, tin oxide, silicon oxide, magnesium oxide, and silicon-carbon composites.

[0089] In any embodiment of this application, the components of both the first negative electrode active layer and the second negative electrode active layer further include a binder.

[0090] In any embodiment of this application, the proportion of binder in the first negative electrode active layer is 0.5% to 10%.

[0091] In any embodiment of this application, the proportion of binder in the first negative electrode active layer is 1% to 4%.

[0092] In any embodiment of this application, the proportion of binder in the second negative electrode active layer is 0.5% to 10%.

[0093] In any embodiment of this application, the proportion of binder in the second negative electrode active layer is 1% to 4%.

[0094] In any embodiment of this application, the components of the first negative electrode active layer further include a conductive agent.

[0095] In any embodiment of this application, the proportion of conductive agent in the first negative electrode active layer is 0.1% to 10%.

[0096] In any embodiment of this application, the proportion of the conductive agent in the first negative electrode active layer is 0.3% to 3%.

[0097] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0099] Furthermore, the components of the first and second active layers may also include a thickener. For example, the thickener may be sodium carboxymethyl cellulose (CMC-Na).

[0100] In any embodiment of this application, the positive electrode sheet includes a current collector and a positive electrode active layer loaded on the surface of the current collector. The positive electrode active layer includes a lithium-ion positive electrode active material, wherein the lithium metal is derived from the lithium ions in the lithium-ion positive electrode active material contained in the positive electrode sheet.

[0101] It is understandable that in the above-mentioned secondary battery, if N / P < 1 is controlled, during the charging process, lithium ions contained in the positive electrode active material in the positive electrode active layer on the positive electrode sheet are released. However, the amount of lithium ions in the positive electrode sheet is much greater than the amount of lithium ions that the positive electrode sheet can hold. Some of the excess lithium ions will be deposited on the negative electrode sheet in the form of lithium metal, thereby forming lithium metal composite lithium with the negative electrode active material on the negative electrode sheet, thus improving the energy density of the secondary battery.

[0102] It should be noted that charging and discharging can be performed during the battery formation stage so that the negative electrode of the secondary battery already has negative electrode active material and lithium metal forming a lithium metal composite. This lithium metal composite can also be formed during subsequent use.

[0103] In any embodiment of this application, the mass percentage of lithium-ion positive electrode active material in the positive electrode active layer is 80% to 98%.

[0104] The aforementioned lithium-ion cathode active material can be any lithium-ion cathode active material known in the art for use in secondary batteries.

[0105] As an example, lithium-ion cathode active materials may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery cathode active materials may also be used. These cathode 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, NCM ternary materials and lithium cobalt oxides (such as LiC). o O2), 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), lithium nickel cobalt manganese oxide (such as LiNi), 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0. 25Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, abbreviated as LFP), lithium manganese phosphate (such as LiMnPO4), and lithium manganese iron phosphate.

[0106] In any embodiment of this application, the molecular formula of the active material in the first coated particles and / or the second coated particles is: LiFe x Mn (1-x) PO4, where x takes any number from 0 to 1.

[0107] It is understandable that when x is 0, LiFe x Mn (1-x) PO4 is LiMnPO4, which is lithium manganese phosphate. When x is 1, LiFePO4 is LiFePO4, which is lithium iron phosphate.

[0108] The general structural formula of NCM ternary materials is LiNi x1 Co y1 Mn z1 O2, x1, y1, z1 take any number from 0 to 1, and x1+y1+z1=1.

[0109] In any embodiment of this application, the positive electrode active layer further comprises a positive electrode binder and a positive electrode conductive agent, wherein the positive electrode binder accounts for 0.5% to 10% of the positive electrode active layer by mass; optionally, the positive electrode binder accounts for 1% to 4% of the positive electrode active layer by mass.

[0110] Optionally, the positive electrode conductive agent accounts for 0.1% to 8% of the mass of the positive electrode active layer.

[0111] The positive electrode binder can be any type of binder commonly used in the art. As examples, the positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene-butadiene rubber, butadiene acrylate rubber, polypyrrole, polyaniline, epoxy resin, and guar gum.

[0112] As an example, the positive electrode conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] The current collectors in the aforementioned positive and negative electrode plates can be current collectors for secondary batteries that are known in the art.

[0114] The current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (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.).

[0115] In any embodiment of this application, the components of the insulating material layer include insulating material and adhesive.

[0116] In any embodiment of this application, the mass percentage of insulating material in the insulating material layer is 20% to 95%; optionally, preferably, the mass percentage of insulating material in the insulating material layer is 50% to 75%.

[0117] Furthermore, the insulating material layer is composed of a mixture of insulating material and adhesive.

[0118] The aforementioned adhesive may be a known secondary battery adhesive, including at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, sodium carboxymethyl cellulose, hydroxypropyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, diacetyl cellulose, polyacrylic acid, sodium alginate, styrene-butadiene rubber, butadiene acrylate rubber, polypyrrole, polyaniline, epoxy resin, and guar gum.

[0119] In any embodiment of this application, the insulating material includes at least one of inorganic insulating materials and organic insulating materials. Inorganic insulating materials include at least one of alumina, silicon oxide, zinc oxide, iron oxide, copper oxide, titanium oxide, mica, asbestos, marble, and ceramics; organic insulating materials can be selected from various insulating resins, such as natural rubber, styrene-butadiene rubber, cis-butadiene rubber, and isoprene rubber.

[0120] In any embodiment of this application, the insulating material includes at least one of alumina and styrene-butadiene rubber.

[0121] In any embodiment of this application, the secondary battery further includes a separator membrane disposed between the positive electrode and the negative electrode.

[0122] In any embodiment of this application, the secondary battery further includes an electrolyte.

[0123] The positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process. The electrolyte acts as a conductor of ions between the positive and negative electrodes.

[0124] The electrolyte may include an electrolyte salt and a solvent. As an example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0125] As an example, the solvents mentioned above may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0126] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0127] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0128] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. It can also be a separator with a boehmite coating, comprising a porous substrate and a boehmite coating loaded on the surface of the porous substrate. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0129] In some embodiments, the secondary battery of this application is a lithium-ion battery.

[0130] The preparation of the above-mentioned secondary battery includes the following steps S10 to S30.

[0131] Step S10: Provide a positive electrode and a separator, the total capacity of the positive electrode being P.

[0132] Step S20: A first negative electrode active layer, an insulating material layer, and a second negative electrode active layer are sequentially formed on the surface of the current collector to obtain a negative electrode sheet with a total capacity of N; wherein, N / P is controlled to be less than 1.

[0133] It is understandable that by designing the total capacity polarity of the positive and negative electrodes to control their ratio, the design can be based on the following calculation formula:

[0134] N = Anode material specific capacity × areal density × mass percentage of anode active material × anode sheet size

[0135] P = Cathode material specific capacity × areal density × mass percentage of cathode active material × cathode sheet size

[0136] The mass percentage of the negative electrode active material refers to the mass percentage of the negative electrode active material in the negative electrode active layer, and the mass percentage of the positive electrode active material refers to the mass percentage of the positive electrode active material in the positive electrode active layer. The size of the negative electrode sheet refers to the area of ​​the negative electrode sheet loaded with the negative electrode active layer. Similarly, the size of the positive electrode sheet refers to the area of ​​the positive electrode sheet loaded with the positive electrode active layer.

[0137] Furthermore, the negative electrode sheet of this application includes a first negative electrode active layer and a second negative electrode active layer. According to the above-mentioned capacity calculation formula for the negative electrode sheet, the capacities N1 and N2 corresponding to the first negative electrode active layer and the second negative electrode active layer are calculated respectively. Then, the total capacity of the negative electrode sheet is N = N1 + N2.

[0138] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode active material, positive electrode conductive agent, positive electrode binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0139] In step S20, the thickness of the insulating material layer is L1μm; the thickness of the second negative electrode active layer is L2μm; and L1 is controlled to be -16×N / P+17.5, and 0.01≤L2 / L1.

[0140] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, negative electrode conductive agent, negative electrode binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a first negative electrode slurry, and forming an insulating slurry and a second negative electrode slurry respectively according to the same steps; coating the first negative electrode slurry onto the negative electrode current collector and drying it, then coating it with a cold insulating slurry and drying it, and finally coating it with the second negative electrode slurry. After drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0141] Secondary batteries can be prepared using conventional methods in the art, such as sequentially winding (or stacking) a positive electrode, a separator, and a negative electrode, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining an electrode assembly. The electrode assembly is then placed in an outer package, infused with electrolyte, and sealed to obtain the secondary battery. The embodiments of this application do not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0142] The aforementioned secondary battery also includes a casing for packaging the positive electrode, negative electrode, separator, and electrolyte.

[0143] In any embodiment of this application, the outer shell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. It can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 4.

[0145] In some embodiments, refer to Figure 2 The outer casing may include a housing 41 and a cover plate 43. The housing 41 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 41 has an opening communicating with the receiving cavity, and the cover plate 43 can be placed over the opening to close the receiving cavity.

[0146] The positive electrode, negative electrode, and separator can be formed into electrode assembly 42 by a winding or stacking process. Electrode assembly 42 is encapsulated within a receiving cavity. Electrolyte is immersed in electrode assembly 42. The battery 4 can contain one or more electrode assemblies 42, which can be adjusted according to requirements.

[0147] This application also provides an electrical device that includes the aforementioned secondary battery.

[0148] Furthermore, in the aforementioned electrical device, the secondary battery can exist in the form of a single battery cell, or it can be further assembled into a battery pack.

[0149] Figure 3 and Figure 4 Here is an example of a battery pack 1. The battery pack 1 includes a battery box and one or more secondary batteries 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 being able to cover the lower box 3 and form a closed space for the secondary batteries 4.

[0150] Multiple secondary batteries 4 can be arranged in the battery box in any way.

[0151] The aforementioned secondary batteries or battery packs assembled from them can be used as power sources for electrical devices or as energy storage units for electrical devices.

[0152] The aforementioned electrical devices may include, but are not limited to, 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.

[0153] Figure 5 This is an example of an electrical device 5. This electrical device 5 can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device 5, a battery pack can be used.

[0154] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use batteries as their power source.

[0155] The present invention will now be described with reference to specific embodiments. However, the present invention is not limited to the embodiments described below. It should be understood that the appended claims summarize the scope of the present invention. Under the guidance of the inventive concept, those skilled in the art should realize that any changes made to the various embodiments of the present invention will be covered by the spirit and scope of the claims of the present invention.

[0156] The following are specific examples. Specific Implementation

[0158] Example 1

[0159] (1) Preparation of positive electrode

[0160] Cobalt-manganese (NCM) ternary materials (LiNi) 0.8 Mn 0.1 Co0.1 O2), conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:2. N-methylpyrrolidone is added and the mixture is stirred for 6 hours to obtain a positive electrode slurry. The slurry is then uniformly coated onto the surface of a 13μm thick aluminum foil, dried, cold-pressed to form a positive electrode active layer, and then slit to obtain a positive electrode sheet.

[0161] (2) Preparation of negative electrode

[0162] Artificial graphite (the first active material), carbon black (the conductive agent), styrene-butadiene rubber (SBR) (the binder), and sodium carboxymethyl cellulose (CMC) (the thickener) were added to deionized water at a weight ratio of 97:0.5:1.25:1.25 and mixed and stirred for 6 hours to obtain the first negative electrode slurry. This slurry was then uniformly coated onto a 6 μm thick copper foil of the negative electrode current collector and dried to form the first negative electrode active layer, the thickness of which is denoted as L0. Please refer to Table 1 for details.

[0163] Polyvinylidene fluoride and Al2O3 were mixed in a weight ratio of 1:1, and N-methylpyrrolidone was added. The mixture was stirred for 06 hours to obtain an insulating slurry. The insulating slurry was then uniformly coated on the surface of the first negative electrode active layer and dried to form an insulating material layer with a thickness denoted as L1. See Table 1 for details.

[0164] The second active material graphite, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 1:0.5:0.5, added to deionized water, and stirred for 6 hours to obtain the second negative electrode slurry. This slurry is then uniformly coated onto the surface of the insulating material sheet and dried to form the second negative electrode active layer, the thickness of which is denoted as L2.

[0165] The total capacity N of the negative electrode and the total capacity P of the positive electrode can be calculated according to the following formula. For specific N / P values, please refer to Table 1.

[0166] N = Anode active material specific capacity × areal density × anode percentage × anode sheet size

[0167] P = Cathode active material specific capacity × areal density × cathode percentage × cathode sheet size

[0168] The mass percentage of the negative electrode active material refers to the mass percentage of the negative electrode active material in the negative electrode active layer, and the mass percentage of the positive electrode active material refers to the mass percentage of the positive electrode active material in the positive electrode active layer. The size of the negative electrode sheet refers to the area of ​​the negative electrode sheet loaded with the negative electrode active layer. Similarly, the size of the positive electrode sheet refers to the area of ​​the positive electrode sheet loaded with the positive electrode active layer.

[0169] The aforementioned negative electrode sheet includes a first negative electrode active layer and a second negative electrode active layer. According to the capacity calculation formula of the aforementioned negative electrode sheet, the capacities N1 and N2 corresponding to the first negative electrode active layer and the second negative electrode active layer are calculated respectively. Then, the total capacity of the negative electrode sheet is N = N1 + N2.

[0170] The thickness of each layer on the electrode can be tested using methods known in the art, specifically through a profilometer test method: the probe of the profilometer gently glides across the sample surface with a very small force, and the micron or even nanometer-level undulations on the sample surface are amplified millions of times by the sensor connected to the probe, and then converted into electronic signals, input into computer software, and finally displayed in the form of digital and graphical data.

[0171] (3) Preparation of electrolyte

[0172] LiPF6 was dissolved in a mixed solvent to prepare an electrolyte with a concentration of 1 mol / L. The mixed solvent was prepared by mixing ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1.

[0173] (4) Preparation of the separating membrane

[0174] Conventional polypropylene (PP) film is used as the separator.

[0175] (5) Preparation of lithium-ion batteries

[0176] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0177] (6) The performance of the prepared lithium-ion battery is tested, including the following:

[0178] 1. Energy density testing of lithium-ion batteries

[0179] At 25℃, the lithium-ion battery was charged at a constant current rate of 0.33C to a voltage of 4.25V, and then charged at a constant voltage of 4.25V to a current of 0.05C. At this point, the lithium-ion battery was fully charged. After resting for 5 minutes, it was discharged at a constant current rate of 0.33C to a voltage of 2.8V, and then rested for another 5 minutes. The capacity and voltage plateau of the lithium-ion battery during the constant current discharge at a rate of 0.33C were recorded. Finally, the mass of the lithium-ion battery was measured.

[0180] The energy density of a secondary battery (Wh / kg) = (capacity of lithium-ion battery at 0.33C constant current discharge rate × voltage plateau of lithium-ion battery at 0.33C constant current discharge rate) / mass of lithium-ion battery.

[0181] 2. Cycle life test of lithium-ion batteries at 25℃

[0182] At 25℃, the battery was charged at a constant current of 1C to 4.25V, then switched to constant voltage charging. Charging was stopped when the charging current dropped to 0.05C. Then, the battery was discharged at a constant current of 1C to 2.8V. The number of cycles at this point was 1. The charge-discharge cycle was repeated until the battery capacity dropped to 80% of the initial capacity. The number of cycles at this point was taken as the 25℃ cycle life of the secondary battery.

[0183] Please see Table 1 for the specific results.

[0184] Example 2

[0185] Example 2 is basically the same as Example 1, except that in step (2) during the preparation of the negative electrode, the active material graphite in the second negative electrode slurry is replaced with graphene, and the total capacity N of the negative electrode is kept the same as in Example 1.

[0186] The remaining steps are the same as in Example 1. Please see Table 1 for specific parameters and test results.

[0187] Example 3

[0188] Example 2 is basically the same as Example 1, except that in step (2) during the preparation of the negative electrode, the active material graphite in the second negative electrode slurry is replaced with magnesium oxide, and the total capacity N of the negative electrode is kept the same as in Example 1.

[0189] The remaining steps are the same as in Example 1. Please see Table 1 for specific parameters and test results.

[0190] Example 4

[0191] Example 3 is basically the same as Example 1, except that in step (2) during the preparation of the negative electrode, the active material graphite in the first negative electrode slurry is replaced with silicon oxide, L0 is adjusted, and the total capacity N of the negative electrode is kept the same as in Example 2.

[0192] The remaining steps are the same as in Example 2. Please see Table 1 for specific parameters and test results.

[0193] Example 5

[0194] Example 5 is basically the same as Example 1, except that in step (2) during the preparation of the negative electrode sheet, the active material graphite in the first negative electrode slurry is replaced with iron oxide, Al2O3 in the insulating slurry is replaced with an equal mass of styrene-butadiene rubber, polyvinylidene fluoride is replaced with sodium carboxymethyl cellulose, and the total capacity N of the negative electrode sheet is kept the same as in Example 2.

[0195] The remaining steps are the same as in Example 2. Please see Table 1 for specific parameters and test results.

[0196] Example 6

[0197] Example 6 is basically the same as Example 1, except that in step (2) during the preparation of the negative electrode, Al2O3 in the insulating slurry is replaced with a mixture of Al2O3 and styrene-butadiene rubber of equal mass, wherein the mass ratio of Al2O3 to styrene-butadiene rubber is 1:1, polyvinylidene fluoride is replaced with sodium carboxymethyl cellulose, and the total capacity N of the negative electrode is kept the same as in Example 2.

[0198] The remaining steps are the same as in Example 2. Please see Table 1 for specific parameters and test results.

[0199] Examples 7-9

[0200] Examples 7 to 9 are basically the same as Example 1, except that: in step (2) during the preparation of the negative electrode sheet, the total capacity N of the negative electrode sheet is changed by adjusting the amount of negative active material added in the first active slurry, thereby changing the N / P value and correspondingly changing the values ​​of L1 and L2. Please see Table 1 for details.

[0201] The remaining steps are the same as in Example 2. Please see Table 1 for specific parameters and test results.

[0202] Examples 10-13

[0203] Examples 10-13 are basically the same as Example 2, except that: in step (2) during the preparation of the negative electrode, the thickness of the second negative electrode active layer is adjusted, while ensuring that the capacity N of the negative electrode is basically the same as that of Example 2. Please see Table 1 for details.

[0204] The remaining steps are the same as in Example 1. Please see Table 1 for specific parameters and test results.

[0205] Example 14

[0206] Example 14 is basically the same as Example 2, except that in step (2) during the preparation of the negative electrode, the second active material graphene, the lithiophilic material ZnO, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:3:0.5:0.5, added to deionized water, and mixed and stirred for 6 hours to obtain the second negative electrode slurry. At the same time, the capacity N of the negative electrode is basically the same as that of Example 2. Please see Table 1 for details.

[0207] The remaining steps are the same as in Example 1. Please see Table 1 for specific parameters and test results.

[0208] Comparative Example 1

[0209] Comparative Example 1 is basically the same as Example 2, except that in step (2) during the preparation of the negative electrode sheet, only the first negative electrode active layer is formed, and the N / P value in the lithium-ion battery is controlled to be 0.6.

[0210] The remaining steps are the same as in Example 2. Please see Table 1 for specific parameters and test results.

[0211] Comparative Example 2

[0212] Comparative Example 2 is basically the same as Example 4, except that in the preparation process of the negative electrode sheet in step (2), only the first negative electrode active layer is formed, and the N / P value in the lithium-ion battery is controlled to be 0.6.

[0213] The remaining steps are the same as in Example 4. Please see Table 1 for specific parameters and test results.

[0214] Comparative Example 3

[0215] Comparative Example 3 is basically the same as Example 5, except that in step (2) during the preparation of the negative electrode sheet, only the first negative electrode active layer is formed, and the N / P value in the lithium-ion battery is controlled to be 0.6.

[0216] The remaining steps are the same as in Example 5. Please see Table 1 for specific parameters and test results.

[0217] Comparative Example 4

[0218] Comparative Example 4 is basically the same as Example 2, except that: in the preparation process of the negative electrode sheet in step (2), no second negative electrode active layer is formed, and the N / P value of the lithium-ion battery is the same as that in Example 2.

[0219] The remaining steps are the same as in Example 2. Please see Table 1 for specific parameters and test results.

[0220] Please refer to Table 1 for the relevant parameters and test results in each embodiment and comparative example.

[0221] Table 1

[0222]

[0223]

[0224] In this context, " / " indicates that the structure or substance does not exist.

[0225] As can be seen from the data in Table 1, the secondary battery prepared according to the technology of this application has both high energy density and excellent cycle performance.

[0226] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode and a negative electrode. The total capacity of the positive electrode is P, and the total capacity of the negative electrode is N. N and P satisfy: N / P<1. The negative electrode sheet includes a current collector and a first negative electrode active layer, an insulating material layer, and a second negative electrode active layer sequentially disposed on the surface of the current collector. The second negative electrode active layer comprises a lithium-loving material and a negative electrode active material.

2. The secondary battery as described in claim 1, characterized in that, The thickness of the insulating material layer is L1, in μm, and the thickness of the second negative electrode active layer is L2, in μm. L1 and L2 satisfy: L1 = -16×N / P + 17.5, 0.01 ≤ L2 / L1.

3. The secondary battery as described in claim 2, characterized in that, L1 and L2 satisfy: 0.01≤L2 / L1≤0.

1.

4. The secondary battery as described in claim 3, characterized in that, L1 and L2 satisfy: 0.03≤L2 / L1≤0.

08.

5. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the insulating material layer is 0.2 μm to 15 μm.

6. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the insulating material layer is 3.1 μm to 7.9 μm.

7. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the first negative electrode active layer is 10μm~300μm.

8. The secondary battery according to any one of claims 1 to 4, characterized in that, The thickness of the first negative electrode active layer is 60μm~200μm.

9. The secondary battery according to any one of claims 1 to 4, characterized in that, Using lithium metal as a reference electrode, the overpotential of the lithiophilic material is no greater than 0.03V.

10. The secondary battery according to any one of claims 1 to 4, characterized in that, The lithiophilic material is selected from one or more of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, Mg and their oxides, sulfides, fluorides, nitrides, chlorides and carbides.

11. The secondary battery according to any one of claims 1 to 4, characterized in that, The secondary battery satisfies at least one of the following conditions a to b: a. In the second negative electrode active layer, the mass percentage of the lithiophilic material is 0.2% to 5%; b. Using lithium metal as the reference electrode, the overpotential of the second negative electrode active layer is 0~0.3V.

12. The secondary battery as described in claim 11, characterized in that, In the second negative electrode active layer, the mass percentage of the lithiophilic material is 0.3% to 3%.

13. The secondary battery according to any one of claims 1 to 4, characterized in that, Using lithium metal as the reference electrode, the overpotential of the first negative electrode active layer is 0.1 V to 0.6 V.

14. The secondary battery according to any one of claims 1 to 4, characterized in that, The first negative electrode active layer comprises a negative electrode active material and lithium metal, and the second negative electrode active layer comprises lithium metal, wherein the lithium metal is loaded on the surface of the negative electrode active material.

15. The secondary battery as described in claim 14, characterized in that, The positive electrode includes a current collector and a positive electrode active layer loaded on the surface of the current collector. The positive electrode active layer is composed of lithium-ion positive electrode active material, and the metallic lithium is derived from lithium ions in the lithium-ion positive electrode active material contained in the positive electrode.

16. The secondary battery according to any one of claims 14, characterized in that, The secondary battery satisfies at least one of the following conditions c to d: c. In the first negative electrode active layer, the proportion of the negative electrode active material is 80%~98%; d. In the second negative electrode active layer, the proportion of the negative electrode active material is 80%~98%.

17. The secondary battery as described in any one of claims 14, characterized in that, The negative electrode active material includes at least one of the following: mesophase carbon microspheres, graphite, glassy carbon, carbon nanotubes, carbon-carbon composite materials, carbon fibers, hard carbon, soft carbon, silicon-based materials, tin-based materials, and iron-based materials.

18. The secondary battery according to any one of claims 1 to 4, characterized in that, The insulating material layer comprises insulating material and adhesive.

19. The secondary battery as described in claim 18, characterized in that, The insulating material includes at least one of organic insulating materials and inorganic insulating materials. The inorganic insulating material is selected from at least one of alumina, silicon oxide, zinc oxide, iron oxide, copper oxide, titanium oxide, mica, asbestos, marble, and ceramics. The organic insulating material is selected from at least one of natural rubber, styrene-butadiene rubber, cis-butadiene rubber, and isoprene rubber.

20. An electrical appliance, characterized in that, The electrical device includes a secondary battery as described in any one of claims 1 to 19.

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