Negative pole piece, secondary battery, power utilization device, method and application

Abstract

The invention provides a negative pole piece, a secondary battery, a power utilization device, a method and application, a negative active material layer of the negative pole piece comprises lithium-loving nanoparticles, and the lithium-loving nanoparticles can be alloyed with lithium.

Description

Negative electrode sheet, secondary battery, power-consuming device, method and application Technical Field

[0001] The present application relates to the technical field of lithium-ion secondary batteries, and in particular to negative electrode sheets, secondary batteries, electrical devices, methods and applications. Background Art

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

[0003] Clean and portable production and lifestyles are increasingly becoming a common pursuit in society, and people are increasingly demanding portable electronic products, electric vehicles, and specialized electronic equipment with longer cycle life. However, the energy density of lithium-ion batteries using graphite as the negative electrode is increasingly unable to meet demand, while lithium metal batteries using lithium metal as the negative electrode suffer from severe lithium metal and electrolyte loss due to dendritic growth at the lithium metal negative electrode, resulting in less than ideal cycle life.

[0004] Summary of the Invention

[0005] In view of the above problems, the present application provides a negative electrode plate, a secondary battery, an electrical device, a method and an application. The negative electrode active material layer of the negative electrode plate includes lithium-philic nanoparticles, which can alloy with lithium, inhibit the reaction activity between the negative electrode material and the electrolyte, regulate the lithium deposition process, and effectively improve the cycle life of the negative electrode.

[0006] In a first aspect, the present application provides a negative electrode plate, which includes a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active substance and lithium-philic nanoparticles, and the lithium-philic nanoparticles can be alloyed with lithium.

[0007] Lithium-philic nanoparticles that can alloy with lithium are introduced into the negative active material layer of the negative electrode plate. The lithium-philic nanoparticles can provide a lower nucleation overpotential and induce lithium to be uniformly deposited inside the negative electrode plate. They can also reduce the lithium plating overpotential inside the plate and inhibit the reaction activity between the negative electrode material and the electrolyte, thereby effectively improving the cycle performance of the battery (such as cycle life).

[0008] In some embodiments, at least a portion of the lithium-philic nanoparticles are distributed on a portion of the surface of the negative electrode active material.

[0009] In the negative electrode plate, the negative electrode active material constitutes the negative electrode active skeleton. When at least a portion of the lithium-philic nanoparticles are distributed on a portion of the surface of the negative electrode active material, that is, lithium-philic nanoparticles capable of alloying with lithium are introduced on the surface of the negative electrode active skeleton, the lithium-philic nanoparticles can be alloyed with lithium and provide a lower nucleation overpotential. The lithium plating overpotential inside the plate can be reduced, and lithium can be induced to be uniformly deposited on the negative electrode active skeleton, thereby forming an artificial alloying interface, inhibiting the reaction activity between the negative electrode material and the electrolyte, and effectively improving the cycle life of the battery; in addition, the introduction of lithium-philic nanoparticles can also reduce the loss of lithium metal during the cycle and improve the coulombic efficiency after the first cycle.

[0010] On the other hand, the lithium-philic nanoparticles are covered on a part of the surface of the negative electrode active material, and the lithium-philic nanoparticles and the negative electrode active material together constitute a lithium-philic composite material. At this time, it can not only effectively exert the alloying effect of the lithium-philic nanoparticles, but also enable the negative electrode active material to effectively contact lithium ions, and give full play to the reversible deintercalation and deintercalation effect of the negative electrode active material on lithium ions, but also has little impact on the volume and weight of the negative electrode sheet, and can maintain a good energy density.

[0011] In some embodiments, the lithiophilic nanoparticles comprise a lithiophilic metal;

[0012] Optionally, the lithiophilic metal includes one or more metals from the following group: Ag, In, Mg, Zn, Au and Sn, and alloys of any of the foregoing metal elements.

[0013] In some embodiments, the lithiophilic metal comprises one or more metals from the group consisting of Ag, In, and Mg, and alloys of any of the foregoing metal elements; or

[0014] The lithiophilic metal includes one or more metals from the following group: Zn, Au and Sn, and alloys of any of the foregoing metal elements.

[0015] The lithiophilic metals introduced in this application are capable of alloying with lithium. Among them, Ag, In, Mg, and their alloys can form solid solutions with lithium and alloy, while Zn, Au, Sn, and their alloys can form intermetallic compounds with lithium and alloy. These easily alloyed lithiophilic materials can reduce the lithium plating overpotential within the electrode, reduce the reactivity between the negative electrode material and the electrolyte, effectively reduce lithium metal loss, and improve the coulombic efficiency and cycle life of the negative electrode after the first cycle. On the one hand, the lithiophilic nanoparticles can induce lithium metal deposition within the electrode, inhibiting expansion; on the other hand, the lithiophilic nanoparticles can regulate the uniform deposition of lithium metal and promote the formation of an artificial alloying interface. After the artificial alloying interface is formed, the spatial uniformity of the lithium deposition and stripping processes can be significantly improved, and the reactivity between the negative electrode material and the electrolyte can also be suppressed, thereby effectively reducing lithium metal loss and improving the coulombic efficiency (generally refers to the coulombic efficiency after the first cycle, unless otherwise specified) and cycle life of the negative electrode. Among them, lithium-philic nanoparticles (such as Ag) that can react with lithium to form a solid solution can exhibit high structural stability and excellent electrochemical performance; further, compared with lithium-philic nanoparticles (such as Au and Sn) that form intermetallic compounds with lithium, lithium-philic nanoparticles alloyed by forming a solid solution are not affected by lithium saturation and have better structural stability and cycle performance.

[0016] In some embodiments, the lithium-philic nanoparticles have a D n 50≤500nm;

[0017] Optionally, the D of the lithium-philic nanoparticles n 50 is selected from 10 nm to 300 nm;

[0018] Further optionally, the D of the lithium-philic nanoparticles n 50 is selected from 10 nm to 200 nm;

[0019] Further optionally, the D of the lithium-philic nanoparticles n 50 is selected from 10 nm to 100 nm;

[0020] Further optionally, the D of the lithium-philic nanoparticles n 50 is selected from 20 nm to 100 nm;

[0021] Alternatively, the Dn50 of the lithium-philic nanoparticles is selected from 5 nm to 320 nm;

[0022] Alternatively, the Dn50 of the lithium-philic nanoparticles is selected from 5 nm to 120 nm.

[0023] By rationally controlling the size of the lithiophilic nanoparticles, it is not only beneficial to obtain a more uniform lithiophilic coating, but also the contact area between the lithiophilic nanoparticles and lithium can be increased, thereby better promoting lithium alloying.

[0024] In some embodiments, the negative electrode active material layer includes an alloy formed by the lithium-philic nanoparticles and lithium.

[0025] When the negative electrode plate assembly of the first aspect is used to form a secondary battery, after the battery has been used for a period of time, an alloy formed by lithium-philic nanoparticles and lithium can be found in the negative electrode active material layer.

[0026] In some embodiments, the negative electrode active material layer includes a lithiophilic composite layer, wherein the lithiophilic composite layer is a structural layer in which the lithiophilic nanoparticles are distributed in a thickness direction of the negative electrode active material layer.

[0027] In some embodiments, the portion of the negative electrode active material distributed in the lithiophilic composite layer is recorded as the first negative electrode active material;

[0028] Wherein, the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material is ≤6%;

[0029] Optionally, the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material is selected from 1% to 5%.

[0030] In some embodiments, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥90%;

[0031] Optionally, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥92%;

[0032] Further optionally, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥94%;

[0033] Further optionally, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥95%.

[0034] In some embodiments, the thickness of the lithiophilic composite layer is selected from 5 μm to 150 μm;

[0035] Further optionally, the thickness of the lithiophilic composite layer is selected from 20 μm to 140 μm;

[0036] Further optionally, the thickness of the lithiophilic composite layer is selected from 20 μm to 120 μm;

[0037] Further optionally, the thickness of the lithiophilic composite layer is selected from 20 μm to 100 μm;

[0038] Alternatively, the thickness of the lithiophilic composite layer is selected from 10 μm to 150 μm;

[0039] Alternatively, the thickness of the lithiophilic composite layer is selected from 10 μm to 125 μm;

[0040] Alternatively, the thickness of the lithiophilic composite layer is selected from 10 μm to 100 μm.

[0041] By rationally controlling parameters such as the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material, the thickness of the lithium-philic composite layer (also referred to as the first active layer), and the sum of the mass percentages of the lithium-philic nanoparticles and the first negative electrode active material, the content of the lithium-philic nanoparticles in the negative electrode active material layer and the distribution of the lithium-philic nanoparticles in the negative electrode active material layer (which may include on the surface of the negative electrode active skeleton) can be rationally controlled. This effectively promotes alloying between the lithium-philic nanoparticles and lithium, and allows for better intercalation and deintercalation of lithium ions from the negative electrode active material. Increasing the content of the lithium-philic nanoparticles in the lithium-philic composite layer is beneficial to improving the uniform dispersion of the lithium-philic nanoparticles in the overall three-dimensional space of the lithium-philic composite layer.

[0042] In some embodiments, the first negative electrode active material includes a carbon-based material;

[0043] Optionally, the first negative electrode active material includes a graphite-like material;

[0044] Further optionally, the first negative electrode active material includes one or more of hard carbon and soft carbon;

[0045] Further optionally, the first negative electrode active material includes hard carbon.

[0046] In some embodiments, in the lithium-philic composite layer, the mass proportion of the graphite-like material in the first negative electrode active material is ≥50%;

[0047] Optionally, the mass proportion of the graphite-like material in the first negative electrode active material is selected from 80% to 100%;

[0048] Further optionally, the mass proportion of the graphite-like material in the first negative electrode active material is selected from 90% to 100%;

[0049] Further optionally, the mass proportion of the graphite-like material in the first negative electrode active material is selected from 95% to 100%;

[0050] Further optionally, the mass proportion of the graphite-like material in the first negative electrode active material is 100%.

[0051] When the negative electrode active material in the lithium-philic composite layer (referred to as the first negative electrode active material) adopts a carbon-based material containing a graphitized material (such as at least one of hard carbon and soft carbon), the graphite-like microcrystalline conductive structure can be used to provide a negative electrode lithium deposition skeleton body. During the charging process, the excess lithium ions in the positive electrode are deposited in the negative electrode active material layer (most of the lithium is embedded in the carbon-based host material, and a small amount of lithium can be deposited on the negative electrode active skeleton), so that the lithium and the negative electrode active skeleton material together form a composite negative electrode, reducing the expansion of the battery cell caused by lithium deposition on the surface of the electrode, and promoting the efficient use of metallic lithium. Using this composite negative electrode, the secondary battery can be given good cycle performance, rate performance and safety. Further reasonable control of the graphitized material to have a higher proportion will make the above effect more obvious.

[0052] In some embodiments, in the lithiophilic composite layer, the mass proportion of hard carbon in the first negative electrode active material is ≥50%;

[0053] Optionally, the mass proportion of hard carbon in the first negative electrode active material is selected from 80% to 100%;

[0054] Further optionally, the mass proportion of hard carbon in the first negative electrode active material is selected from 90% to 100%;

[0055] Further optionally, the mass proportion of hard carbon in the first negative electrode active material is selected from 95% to 100%;

[0056] Further optionally, the mass proportion of hard carbon in the first negative electrode active material is 100%.

[0057] Compared with graphite, hard carbon structures, which are difficult to completely graphitize at high temperatures (e.g., above 2800°C), have isotropic characteristics, a delithiation potential similar to graphite, and a higher specific capacity (e.g., 500-700 mAh / g). Furthermore, hard carbon has more layered wrinkles, which can provide more lithium storage sites. Furthermore, the larger interlayer spacing of hard carbon facilitates the rapid diffusion of lithium ions, which is beneficial for maintaining a high reversible capacity and achieving good battery cycle performance. This is beneficial for achieving a good balance between increasing the overall energy density of the battery cell and increasing cycle stability, and can also improve the battery's rate performance and safety. Further controlling the proportion of hard carbon in the first negative electrode active material of the lithiophilic composite layer is more beneficial for achieving a higher reversible capacity.

[0058] In some embodiments, the negative electrode plate includes a negative electrode current collector, and the negative electrode active material layer is disposed on at least one side of the negative electrode current collector;

[0059] The negative electrode active material layer further includes a second active layer, which is arranged on a side of the lithium-philic composite layer away from the negative electrode current collector. The second active layer includes a second negative electrode active material and does not include the lithium-philic nanoparticles.

[0060] On the basis that the lithium-philic nanoparticles in the lithium-philic composite layer (i.e., the first active layer) can alloy with lithium, a second active layer without lithium-philic nanoparticles is further provided on the side of the lithium-philic composite layer away from the negative electrode current collector. When the second active layer comes into contact with the electrolyte, it can form a denser solid electrolyte (SEI) film, which can induce the uniform deposition of lithium metal, reduce deposition expansion, and reduce lithium dendrites. The second active layer can also serve as a guiding layer to induce a portion of the precipitated lithium to precipitate uniformly and densely on the surface of the electrode, thereby improving the stability of the solid electrolyte interface (SEI) film. At this time, the negative electrode active material layer has a double-layer structure, and there is a synergistic induction deposition effect of lithium by the lithium-philic nanoparticles in the first active layer and the second active layer.

[0061] In some embodiments, the second negative electrode active material includes a graphite-like material;

[0062] Optionally, the second negative electrode active material includes soft carbon.

[0063] In some embodiments, in the second active layer, the mass proportion of soft carbon in the second negative electrode active material is ≥50%;

[0064] Optionally, the mass proportion of soft carbon in the second negative electrode active material is selected from 80% to 100%;

[0065] Further optionally, the mass proportion of soft carbon in the second negative electrode active material is selected from 90% to 100%;

[0066] Further optionally, the mass proportion of the soft carbon in the second negative electrode active material is selected from 95% to 100%;

[0067] Further optionally, the mass proportion of the soft carbon in the second negative electrode active material is 100%.

[0068] This application further proposes a double-layer coating structure design of "lower layer lithiation-philic + upper layer graphitized material". At this time, the negative electrode active material in the second active layer (that is, the second negative electrode active material) includes a graphitized material. When the second active layer contains hard carbon, it is conducive to achieving a higher reversible capacity. When the second active layer contains soft carbon, the degree of graphitization of the soft carbon is high and the microstructural defects are few. When the second active layer is in contact with the electrolyte, it can induce the uniform deposition of lithium metal to form a denser SEI film, reduce deposition expansion, and reduce lithium dendrites. When the proportion of soft carbon in the second negative electrode active material is high, it is more conducive to promoting the uniform deposition of lithium.

[0069] In some embodiments, the thickness of the second active layer is less than the thickness of the lithiophilic composite layer;

[0070] Optionally, the thickness of the second active layer is selected from 5 μm to 25 μm;

[0071] Further optionally, the thickness of the second active layer is selected from 10 μm to 20 μm;

[0072] Alternatively, the thickness of the second active layer is selected from 8 μm to 22 μm;

[0073] Alternatively, the thickness of the second active layer is selected from 8 μm to 12 μm.

[0074] In the present application, when the thickness of the second active layer is less than that of the first active layer (such as 5μm to 15μm, further such as about 10μm), it can not only induce the uniform deposition of lithium, but also reasonably adjust the transmission efficiency of lithium ions between the lithiophilic composite layer (first active layer) and the electrolyte. In addition, when the active material of the second negative electrode active material layer contains soft carbon, although the gram capacity of the soft carbon is relatively low (such as 150 to 200mAh / g), the second active layer can serve as a deposition inducing layer for the lithium deposition part, promoting the formation of a more complete SEI film, and utilizing the composite regulation of the lithium deposition process by the lithium-philic nanoparticles and the second active layer, the deposition of the lithium deposition part can be made more uniform and dense, which can effectively improve the coulombic efficiency and cycle life of the negative electrode; further regulating the second active layer to have a reasonable thickness can achieve a good balance between the overall energy density improvement and the cycle stability increase of the battery cell. If the second active layer is too thick, it may affect the conduction of lithium ions between the lithiophilic composite layer (first active layer) and the electrolyte.

[0075] In a second aspect, the present application provides a secondary battery comprising a positive electrode sheet, a separator and the negative electrode sheet described in the first aspect of the present application, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0076] The negative electrode plate of the first aspect of the present application is used to prepare a secondary battery, and the alloying of the lithium-philic nanoparticles and lithium in the lithium-philic composite layer can be utilized. On the one hand, after lithium alloying, the reaction activity between the negative electrode material and the electrolyte can be significantly reduced, thereby inducing the deposition of lithium metal inside and on the surface of the plate, reducing the high charging expansion problem caused by internal and surface lithium precipitation, and also reducing lithium metal loss, effectively improving the coulombic efficiency of the negative electrode and the battery cycle life.

[0077] In some embodiments, the CB value of the secondary battery is less than 1;

[0078] Optionally, the CB value of the secondary battery is selected from 0.1 to 0.9;

[0079] Optionally, the CB value of the secondary battery is selected from 0.15 to 0.9;

[0080] Among them, the side of the negative electrode sheet facing the positive electrode sheet includes the negative electrode active material layer, and the side of the positive electrode sheet facing the negative electrode sheet includes the positive electrode active material layer, and the CB value is the ratio of the capacity of the negative electrode active material layer and the positive electrode active material layer arranged relatively under the same area.

[0081] The present application also proposes a design of a low CB system lithiophilic modified negative electrode, which can take into account both high energy density and cycle stability. In the present application, for the design of a battery cell with a CB value of less than 1, the lithium-philic nanoparticles can alloy with lithium during the charging process to improve the stability of lithium metal, and can also induce lithium metal to be uniformly deposited inside the negative electrode pole piece (which may be included on the negative electrode active skeleton), so that lithium and the negative electrode active skeleton material together form a composite negative electrode, and achieve effective regulation of lithium deposition behavior, which can better achieve a good balance between the overall energy density improvement and the increase in cycle stability of the battery cell. When the CB value is less than 1, the lithium-philic nanoparticles in the negative electrode active material layer are used to allow a portion of the analyzed lithium metal to be uniformly deposited inside the negative electrode active material layer, reducing the expansion of the pole piece. When the surface of at least some of the negative electrode active materials is distributed with the aforementioned lithium-philic nanoparticles, the lithium-philic nanoparticles can induce lithium metal to be uniformly deposited on the negative electrode active skeleton, reducing the expansion of the pole piece. In addition, when the negative electrode is provided with the aforementioned second active layer, the second active layer can serve as a guiding layer to induce another part of the precipitated lithium to precipitate evenly and densely on the surface of the electrode. At this time, most of the lithium can be stored in the active material layer, and only a small part of the lithium is in the lithium metal precipitation state, and the lithium dendrite problem is significantly improved.

[0082] In some embodiments, the secondary battery is a lithium-ion secondary battery;

[0083] Furthermore, the positive electrode sheet contains a positive electrode active material;

[0084] Further optionally, the positive electrode active material includes a lithium ion material; wherein the lithium ion material includes one or more of the following substances: lithium-containing phosphate, lithium transition metal oxide, and a substance composed of any of the foregoing substances and a doping element;

[0085] Optionally, the positive electrode active material includes one or more of the following substances: lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, and a substance composed of any of the foregoing substances and doping elements;

[0086] The doping elements in any positive electrode active material independently include one or more transition metal elements and non-transition metal elements.

[0087] The active ions of lithium-ion secondary batteries include lithium ions. The negative electrode plate of the present application can use lithium-philic nanoparticles to regulate the lithium deposition process, inhibit the reaction activity between the negative electrode material and the electrolyte, reduce the loss of lithium metal during the cycle, and effectively improve the coulombic efficiency of the negative electrode and the battery cycle life.

[0088] In a third aspect, the present application provides an electrical device comprising at least one of the negative electrode sheet described in the first aspect of the present application and the secondary battery described in the second aspect of the present application.

[0089] An electrical device prepared using at least one of the negative electrode plate described in the first aspect of the present application and the secondary battery described in the second aspect of the present application can utilize the alloying of lithium-philic nanoparticles and lithium in the lithium-philic composite layer to inhibit the reaction activity between the negative electrode material and the electrolyte, regulate the lithium deposition process, effectively improve the coulombic efficiency of the negative electrode and the battery cycle life, and extend the service life of the electrical device.

[0090] In a fourth aspect, the present application provides a method for preparing a negative electrode sheet, comprising the following steps:

[0091] Preparing a first negative electrode slurry comprising a first negative electrode active material and lithium-philic nanoparticles; wherein the lithium-philic nanoparticles are as defined in the first aspect of the present application;

[0092] coating the first negative electrode slurry on at least one surface of a negative electrode substrate, drying the negative electrode slurry to form a lithiophilic composite layer, and preparing a lithiophilic substrate;

[0093] The lithiophilic substrate is cold pressed to prepare a negative electrode sheet; alternatively, a second negative electrode slurry containing a second negative electrode active material is coated on one surface of the lithiophilic substrate including the lithiophilic composite layer, dried, and cold pressed to form a second active layer to prepare a negative electrode sheet.

[0094] A dispersion containing lithiophilic nanoparticles is introduced into the negative electrode slurry, and the lithiophilic nanoparticles are uniformly dispersed in the negative electrode slurry. After further coating, drying and other processes, they can be assembled on the negative electrode substrate to form a lithiophilic composite layer. The lithiophilic composite layer can be directly used as the surface layer in contact with the electrolyte in the negative electrode sheet, and a second active layer (non-lithiophilic) can be further stacked to obtain the aforementioned "lower layer lithiophilic + upper layer non-lithiophilic" double-layer coating structure.

[0095] In some embodiments, the step of preparing the first negative electrode slurry comprises mixing the first negative electrode active material and a dispersion containing the lithium-philic nanoparticles; wherein the concentration of the lithium-philic nanoparticles in the dispersion is selected from 100 μg / L to 1000 μg / L;

[0096] Optionally, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 200 μg / L to 800 μg / L;

[0097] Optionally, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 400 μg / L to 500 μg / L.

[0098] By rationally controlling the concentration of lithium-philic nanoparticles in the dispersion, the distribution concentration of lithium-philic nanoparticles in the negative electrode slurry can be better adjusted, and then after coating and drying, a rational distribution inside the negative electrode active material layer (including on the surface of the negative electrode active skeleton) can be achieved, which can effectively induce uniform lithium deposition and the formation of an artificial alloying interface while maintaining a good lithium ion insertion / extraction rate.

[0099] In some embodiments, any one or more of the following characteristics are met:

[0100] The step of preparing the first negative electrode slurry further includes adding a conductive agent, a binder and a solvent;

[0101] The definition of the first negative electrode active material in the first negative electrode slurry is consistent with the definition of the first negative electrode active material in the lithiophilic composite layer in the first aspect of the present application;

[0102] The definition of the second negative electrode active material in the second negative electrode slurry is consistent with the second negative electrode active material in the second active layer in the first aspect of the present application;

[0103] The negative electrode plate is as defined in the first aspect of the present application.

[0104] The negative electrode sheet of the first aspect of the present application can be prepared by using the preparation method of the second aspect.

[0105] In some embodiments, the dispersion is prepared by a method comprising the following steps:

[0106] preparing a mixed solution containing a metal precursor, a reducing agent, and an optional dispersant; wherein the metal precursor comprises a salt precursor of the lithium-philic nanoparticles; and

[0107] The mixed solution is subjected to a reduction reaction to convert the salt-type precursor into the lithium-philic nanoparticles.

[0108] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0109] In order to better describe and illustrate the embodiments or examples of the applications disclosed herein, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered to limit the scope of the disclosed applications, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0110] FIG1 is a schematic structural diagram of a negative electrode active material layer in a negative electrode sheet in one embodiment of the present application;

[0111] FIG2 is a schematic diagram of the structure of a negative electrode plate in one embodiment of the present application, wherein the negative electrode active material layer of the negative electrode plate is a single-layer lithium-philic composite layer;

[0112] FIG3 is a schematic diagram of the structure of a negative electrode plate in one embodiment of the present application, wherein the negative electrode active material layer of the negative electrode plate has a double-layer structure, including a lithium-philic composite layer (also referred to as a first active layer) and a second active layer;

[0113] FIG4 is a scanning electron microscope (SEM) image of the side cross-section of the lithium deposition layer of Example 1 and Comparative Example 1 of the present application; wherein the left side is Comparative Example 1 and the right side is Example 1; “~18 μm” in Comparative Example 1 represents approximately 18 μm, and “~2 μm” in Example 1 represents approximately 2 μm;

[0114] FIG5 is a comparison chart of the expansion performance of the negative electrode sheets of Example 1 and Comparative Example 1 of the present application, wherein the vertical axis represents the thickness of the negative electrode sheet;

[0115] FIG6 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0116] FIG7 is an exploded view of the secondary battery of one embodiment of the present application shown in FIG6 ;

[0117] FIG8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present application.

[0118] Description of reference numerals:

[0119] 200, negative electrode active material layer; 201, lithiophilic active particles; 210, lithiophilic composite layer (also referred to as a first active layer); 220, second active layer; 100, negative electrode substrate; It is understood that in Figures 1-3, the shape, size, distribution density and distribution pattern of the lithiophilic active particles, the relative size and content of the negative electrode active material and the lithiophilic nanoparticles therein, and other parameters are schematic and non-restrictive, and these parameters in this application are not limited thereto;

[0120] 5, secondary battery; 51, shell; 52, electrode assembly; 53, cover plate; 6, electrical device;. DETAILED DESCRIPTION

[0121] Below, some embodiments of the negative electrode sheet, secondary battery, electrical device, method and application of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0122] The numerical value " range " disclosed in this 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 particular range. The scope limited in this way can include any one or two end values ​​or do not include any end value, and can be arbitrarily combined, that is, any lower limit can form a range 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 are listed, and if the maximum range values ​​3,4 and 5 are listed, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents an abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0123] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0124] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0125] Unless otherwise specified, the terms "having," "including," "containing," and "comprising" mentioned in this application can each independently represent an open or closed form. For example, "having," "including," "containing," and "comprising" can mean: other components not listed may also be included or included, or only the listed components may be included or included.

[0126] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B." Furthermore, the condition "A or B" is satisfied by any of the following conditions: 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).

[0127] In this application, "plurality", "multiple", "multiple times", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more than or equal to two.

[0128] As used herein, "combination thereof", "any combination thereof", "any combination thereof" and the like include all suitable combinations of any two or more of the listed items.

[0129] Herein, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the technical solution that can implement the present application.

[0130] Herein, the terms "preferred," "better," "more preferred," and "suitable" are used solely to describe preferred implementations or examples and should not be construed as limiting the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, each "preferred" term is considered independent unless otherwise specified and there are no contradictions or mutual constraints.

[0131] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate the differences in content between different technical solutions, but should not be understood as limiting the scope of protection of this application.

[0132] In this application, the terms "first," "second," "third," "fourth," etc. in "the first aspect," "the second aspect," "the third aspect," "the fourth aspect," etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor should they be understood as implicitly indicating the importance or quantity of the indicated technical features. Furthermore, "first," "second," "third," "fourth," etc. serve only as non-exhaustive enumeration and description, and should be understood not to constitute a closed-ended limitation on quantity.

[0133] In this application, the term "room temperature" or "normal temperature" generally refers to 4°C to 35°C, preferably 20°C ± 5°C. In some embodiments of this application, room temperature or normal temperature refers to 20°C to 30°C.

[0134] In this application, when referring to a data range, if the unit is only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, 3~5h or 3-5h both mean that the units of the left endpoint "3" and the right endpoint "5" are both hours.

[0135] The weights of the relevant components mentioned in the examples of this application may not only refer to the content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Furthermore, the weights mentioned in the examples of this application may be weight units commonly known in the chemical industry, such as μg, mg, g, and kg.

[0136] Regarding negative electrode active materials, traditional graphite materials offer advantages such as good conductivity and high first-cycle coulombic efficiency. However, graphite's gram capacity is relatively low (theoretical value is generally around 372mAh / g, but actual values ​​often fall short of this theoretical value), limiting the energy density of lithium-ion batteries. Furthermore, lithium diffusion between graphite layers restricts rate performance, preventing it from meeting the sustained high-current discharge capability required by large-scale power batteries. Compared to graphite materials, hard carbon has a higher gram capacity, but it suffers from drawbacks such as insufficient lithium storage space and low first-cycle coulombic efficiency, making it difficult to meet design requirements for high energy density (e.g., 400Wh / kg).

[0137] On the other hand, although the metal lithium negative electrode has an extremely high specific capacity (3860mAh / g) and an extremely low electrode potential (-3.04V, relative to the standard hydrogen electrode potential), the metal lithium negative electrode is accompanied by huge electrode volume changes, repeated growth of the SEI film and the formation of metal lithium dendrites during the charge and discharge process. The dendrite growth problem is very serious, and it is easy to quickly produce a large amount of dead lithium, which seriously limits the cycle life of the metal lithium battery. Therefore, the metal lithium negative electrode urgently needs to stably reduce the generation of dead lithium. These problems cause rapid attenuation of battery capacity and even internal short circuits.

[0138] Therefore, it is difficult to improve the cycle performance (such as cycle life) while meeting certain energy density requirements.

[0139] In response to the above-mentioned common technical problems, in the first aspect, the present application provides a negative electrode plate, which includes a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active substance and lithium-philic nanoparticles, and the lithium-philic nanoparticles can be alloyed with lithium.

[0140] In this application, unless otherwise specified, an electrode plate can be a positive electrode plate or a negative electrode plate, and the "active material" in the electrode plate refers to a substance that can reversibly embed and deintercalate lithium ions. Unless otherwise specified, "negative electrode active material" refers to a substance used in a negative electrode plate that can reversibly embed and deintercalate lithium ions; "positive electrode active material" refers to a substance used in a positive electrode plate that can reversibly embed and deintercalate lithium ions. When a secondary battery is charged, lithium ions are deintercalated from the positive electrode and embedded in the negative electrode through the electrolyte; when the secondary battery is discharged, lithium ions are deintercalated from the negative electrode and embedded in the positive electrode.

[0141] In this application, “negative electrode active substance” and “negative electrode active material” have the same meaning and can be used interchangeably; “positive electrode active substance” and “positive electrode active material” have the same meaning and can be used interchangeably.

[0142] In this application, unless otherwise specified, "active material layer" includes the positive electrode active material layer of the positive electrode sheet and the negative electrode active material layer of the negative electrode sheet. Depending on the specific circumstances, it can refer to either the positive electrode active material layer or the negative electrode active material layer. It is understood that the positive electrode active material layer contains a positive electrode active material, and the negative electrode active material layer contains a negative electrode active material.

[0143] In the present application, "lithiophilic nanoparticles" belong to lithiophilic substances, and refer to nanoparticles that can be alloyed with lithium; wherein, "lithiophilicity" refers to the property of being able to alloy with lithium; "lithiophilic substance" refers to a substance that can alloy with lithium, and a lithium-containing alloy can be obtained after alloying with lithium. The size of the lithiophilic nanoparticles can refer to the definition below. In the present application, the principle of alloying with lithium may include but is not limited to forming a solid solution with lithium and forming an intermetallic compound with lithium. In the present application, unless otherwise specified, the lithiophilic substance contains a lithiophilic metal element, wherein the metal element can be a metal element or a metal alloy. In the negative active material of the negative electrode plate, inter-particle agglomeration may or may not occur between the lithiophilic nanoparticles.

[0144] In the negative electrode active material layer of the negative electrode plate, lithium-philic nanoparticles that can alloy with lithium are introduced. The lithium-philic nanoparticles can provide a lower nucleation overpotential and induce lithium to be uniformly deposited inside the negative electrode plate. They can also reduce the lithium plating overpotential inside the plate and inhibit the reaction activity between the negative electrode material and the electrolyte, thereby effectively improving the cycle performance of the battery (such as cycle life).

[0145] In some embodiments, the lithium-philic nanoparticles in the negative electrode plate may be distributed on the surface of the negative electrode active material.

[0146] In this application, particles composed of negative electrode active materials having lithium-philic nanoparticles distributed on their surfaces may be referred to as "lithiophilic active particles." Unless otherwise specified, in the lithiophilic active particles, the lithium-philic nanoparticles are distributed on a portion of the surface of the negative electrode active material, allowing the negative electrode active material to effectively contact lithium ions.

[0147] In one embodiment shown in FIG1 , the negative electrode active material layer 200 of the negative electrode sheet includes lithiophilic active particles 201. It should be understood that the shape, size, distribution density, and distribution pattern of the lithiophilic active particles in FIG1 , as well as the relative sizes and contents of the negative electrode active material and lithiophilic nanoparticles therein, are illustrative and non-limiting.

[0148] In some embodiments, at least a portion of the lithiophilic nanoparticles are distributed on a portion of the surface of the negative electrode active material. In this case, at least a portion of the negative electrode active material is lithiophilically modified and exists in the form of lithiophilic active particles.

[0149] In the negative electrode plate, the negative electrode active material constitutes the negative electrode active skeleton. When at least a portion of the lithium-philic nanoparticles are distributed on a portion of the surface of the negative electrode active material, that is, lithium-philic nanoparticles capable of alloying with lithium are introduced on the surface of the negative electrode active skeleton, the lithium-philic nanoparticles can be alloyed with lithium and provide a lower nucleation overpotential. The lithium plating overpotential inside the plate can be reduced, and lithium can be induced to be uniformly deposited on the negative electrode active skeleton, thereby forming an artificial alloying interface, inhibiting the reaction activity between the negative electrode material and the electrolyte, and effectively improving the cycle life of the battery; in addition, the introduction of lithium-philic nanoparticles can also reduce the loss of lithium metal during the cycle and improve the coulombic efficiency after the first cycle.

[0150] In this application, unless otherwise specified, "first-cycle coulombic efficiency" refers to the ratio of the discharge capacity to the charge capacity of a lithium-ion battery in the first charge and discharge cycle, which can be numerically equal to the percentage obtained by dividing the discharge capacity by the charge capacity.

[0151] In this application, unless explicitly stated as "first-cycle coulombic efficiency," all references to "coulombic efficiency" refer to the coulombic efficiency of the cycling process after the first cycle, unless otherwise specified. Generally speaking, the higher the coulombic efficiency in the cycling process after the first cycle, the longer the cycle life, and accordingly, the higher the number of cycles completed before the capacity decays to a specific value. Similarly, the longer the cycle life or the more cycles completed before the capacity decays to a specific value, the higher the coulombic efficiency is generally.

[0152] On the other hand, the lithium-philic nanoparticles are covered on a part of the surface of the negative electrode active material to form a lithium-philic composite material. At this time, the lithium-philic nanoparticles can effectively exert their alloying effect and other functions, and the negative electrode active material can effectively contact lithium ions, fully exerting the reversible deintercalation and deintercalation effect of the negative electrode active material on lithium ions, and the impact on the volume and weight of the negative electrode plate is small, so that a good energy density can be maintained.

[0153] In this application, unless otherwise specified, "negative electrode active skeleton" refers to a three-dimensional structure containing negative electrode active material and having internal interconnected pores. In some embodiments, the material component of the negative electrode active skeleton contains a carbon-based material, which can be a carbon-based material, or a composite material composed of a carbon-based material and a non-carbon-based material, such as a carbon-silicon composite material. The weight proportion of the carbon-based material in the negative electrode active skeleton can be ≥50%, and can also be selected from the ranges of 50% to 100%, 55% to 100%, 60% to 100%, 70% to 100%, 80% to 100%, 90% to 100%, etc., and can also be selected from any one of the following percentages or a numerical interval consisting of any two percentages: 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc. When the weight proportion of the carbon-based material in the negative electrode active skeleton is 100%, it means that the negative electrode active skeleton is completely composed of carbon-based material. The carbon-based materials that can be used for the negative electrode plates of the present application may include one or more of graphite (further including artificial graphite and natural graphite), soft carbon and hard carbon. The non-carbon-based materials that can be used for the negative electrode plates of the present application may include, but are not limited to, carbon-based materials. The silicon-based material may be selected from one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites and silicon alloys. The present application is not limited to the materials or substances listed above, and other traditional materials or substances that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials or substances may be used alone or in combination of two or more. For example, a combination of hard carbon and soft carbon, a combination of hard carbon and graphite, a combination of hard carbon and silicon-based materials, etc.

[0154] In the present application, unless otherwise specified, a "lithiophilic composite material" is a composite material comprising a negative electrode active material and lithium-philic nanoparticles. It will be understood that the material comprising the aforementioned lithiophilic active particles is within the scope of the lithiophilic composite material of the present application. The active structural layer containing the lithiophilic composite material in the negative electrode active material layer corresponds to the "lithiophilic composite layer", which is also referred to as the "first active layer" in the present application. The "negative electrode active material" in the lithiophilic composite layer is also referred to as the first negative electrode active material. In the present application, the first negative electrode active material may include a carbon-based material (optionally, it may be a carbon-based material), and non-limiting examples may include one or more of hard carbon, soft carbon, etc. Due to the alloying effect between the lithium-philic nanoparticles and lithium, lithium can be uniformly deposited on the surface of the negative electrode active skeleton to form an artificial alloying interface, and the artificial alloying interface also allows reversible delithiation and dealloying, so that this part of the negative electrode active material layer has the dual advantages of high cycle stability of the carbon-based negative electrode and high energy density of the lithium metal negative electrode. In addition, the alloying effect of lithium-philic nanoparticles and their ability to induce uniform deposition of lithium inside the electrode can reduce the expansion of the battery cell, reduce the generation of lithium dendrites and thus avoid the breakage of dendrites to form dead lithium. It can also reduce the loss of lithium metal during the cycle, improve coulombic efficiency and extend the cycle life.

[0155] In some embodiments, the lithiophilic nanoparticles comprise a lithiophilic metal.

[0156] In this application, unless otherwise specified, "lithiophilic metal" refers to a metal having lithiophilicity, which may be a single metal or an alloy.

[0157] In some embodiments, the lithiophilic metal includes one or more metals selected from the group consisting of Ag, In, Mg, Zn, Au, and Sn, and alloys of any of the foregoing metal elements.

[0158] In some embodiments, the lithiophilic metal includes one or more metals selected from the group consisting of Ag, In, and Mg, and alloys of any of the foregoing metal elements.

[0159] In some other embodiments, the lithiophilic metal includes one or more metals from the group consisting of Zn, Au, and Sn, and alloys of any of the foregoing metal elements.

[0160] The lithiophilic metals introduced in this application can alloy with lithium, among which Ag, In, Mg, and their alloys can form solid solutions with lithium and alloy, and Zn, Au, Sn, and their alloys can form intermetallic compounds with lithium and alloy. Such lithiophilic substances that are easy to alloy can reduce the lithium plating overpotential inside the electrode, reduce the reactivity between the negative electrode material and the electrolyte, effectively reduce lithium metal loss, and improve the coulombic efficiency and cycle life of the negative electrode. On the one hand, the lithiophilic nanoparticles can induce lithium metal to deposit inside the electrode and inhibit expansion; on the other hand, the lithiophilic nanoparticles can regulate the uniform deposition of lithium metal and promote the formation of an artificial alloying interface. After the artificial alloying interface is formed, the spatial uniformity of the lithium deposition and stripping processes can be significantly improved, and the reactivity between the negative electrode material and the electrolyte can also be inhibited, thereby effectively improving the coulombic efficiency of the negative electrode and the cycle life of the battery. Among them, lithium-philic nanoparticles (such as Ag) that can react with lithium to form a solid solution can exhibit high structural stability and excellent electrochemical performance; further, compared with lithium-philic nanoparticles (such as Au and Sn) that form intermetallic compounds with lithium, lithium-philic nanoparticles alloyed by forming a solid solution are not affected by lithium saturation and have better structural stability and cycle performance.

[0161] In some embodiments, the lithium-philic nanoparticles have a D n 50≤500nm, can also meet D n 50≤400nm, and can further meet D n 50≤350nm, furthermore, it can also meet D n 50≤300nm, furthermore, it can also meet D n 50≤250nm, furthermore, D n 50≤200nm, furthermore, it can also meet D n 50≤150nm, can also meet D n 50≤120nm, can also meet D n 50≤100nm, can also meet D n 50≤40nm; On the other hand, the D of the lithium-philic nanoparticles n 50 may satisfy ≥5nm, may satisfy ≥10nm, may further satisfy ≥15nm, and may further satisfy ≥20nm. n50 can also be selected from any of the following sizes: 5nm, 6nm, 8nm, 10nm, 12nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, 110nm, 120nm, 125nm, 150nm, 200nm, 220nm, 250nm, 300nm, 320nm, 350nm, 400nm, etc., and can also be selected from the interval consisting of any two of the above sizes, for example, D n 50 can also be selected from 5nm to 500nm, 5nm to 450nm, 5nm to 400nm, 5nm to 320nm, 5nm to 300nm, 5nm to 250nm, 5nm to 200nm, 5nm to 150nm, 5nm to 120nm, 5nm to 100nm, 10nm to 500nm, 10nm to 450nm, 10nm to 400nm, 10nm to 300nm, 10nm to 250nm , 10nm~200nm, 10nm~150nm, 10nm~120nm, 10nm~100nm, 10nm~40nm, 20nm~500nm, 20nm~450nm, 20nm~400nm, 20nm~300nm, 20nm~250nm, 20nm~200nm, 20nm~250nm, 20nm~120nm, 20nm~100nm, etc. any appropriate range.

[0162] In this application, unless otherwise stated, D n 50 refers to the particle size corresponding to when the cumulative number distribution percentage of the particle mixture reaches 50%. This parameter indicates that the particle size of 50% of the particles is less than or equal to D n 50, and 50% of the particles have a particle size larger than D n 50. Those skilled in the art will understand that n 50, and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer and LS-909 laser particle size analyzer (Europe and America) produced by Malvern Instruments Ltd., UK. In addition, it should be noted that the D n 50" refers to the size of a single particle that has not agglomerated or a single particle unit in a multi-particle agglomerate.

[0163] By rationally controlling the size of the lithiophilic nanoparticles, it is not only beneficial to obtain a more uniform lithiophilic coating, but also the contact area between the lithiophilic nanoparticles and lithium can be increased, better promoting lithium alloying. As the particle size increases, the number of lithiophilic sites formed decreases when depositing the same mass of lithiophilic nanoparticles. When the particle size of the lithiophilic nanoparticles is larger (e.g., greater than 500nm), the deposition uniformity of the carbon-based active framework may be increased.

[0164] In some embodiments, the negative electrode active material layer includes an alloy formed by the lithium-philic nanoparticles and lithium.

[0165] When a secondary battery is assembled using the negative electrode assembly of the first aspect, after a period of use, an alloy formed between the lithium-philic nanoparticles and lithium may be found in the negative electrode active material layer. This alloy can be detected and identified using common elemental analysis methods for metals and their alloys in the art (e.g., XRD analysis of the alloy phase composition). Furthermore, the morphology and elemental composition of the lithium-philic alloy can be detected using a scanning electron microscope (SEM) and its accompanying energy dispersive spectrometer (EDS).

[0166] In some embodiments, the negative electrode active material layer includes a lithiophilic composite layer.

[0167] In the present application, unless otherwise specified, "lithiophilic composite layer" refers to a structural layer in which lithium-philic nanoparticles are distributed in the thickness direction of the negative electrode active material layer. It will be understood that the lithium-philic composite layer contains the aforementioned lithium-philic composite material. The distribution of lithium-philic nanoparticles in the lithium-philic composite layer can be uniform or non-uniform. When the lithium-philic nanoparticles are non-uniformly distributed in the lithium-philic composite layer, for example, a change in distribution concentration is allowed in at least one direction of the longitudinal direction (thickness direction of the electrode piece) and the transverse direction (direction parallel to the surface of the electrode piece). In some preferred examples, for a given thickness position, the lithium-philic nanoparticles are basically uniformly distributed along the transverse direction of the negative electrode piece, that is, at a given thickness position, there is no significant difference in the distribution concentration along the transverse direction (for example, there is no significant difference at the p<0.05 level).

[0168] Figures 1, 2, and 3 each provide an example of a lithiophilic composite layer. In these three examples, the lithiophilic composite layer includes lithiophilic active particles, and therefore includes lithiophilic nanoparticles distributed on the surface of the negative electrode active material. It should be understood that the size, content, shape, distribution, and other parameters of the lithiophilic nanoparticles in Figures 1-3 are illustrative and non-limiting.

[0169] In this application, unless otherwise specified, the portion of the negative electrode active material distributed in the lithiophilic composite layer is referred to as the “first negative electrode active material”.

[0170] In some embodiments, the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material is ≤6%. The mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material can also be selected from any one of the following percentages or a range consisting of any two of the following percentages: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. In some preferred embodiments, the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material is selected from 1% to 5%.

[0171] In some embodiments, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥ 90%. The sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer can also be selected from any one of the following percentages or an interval consisting of any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc. In some embodiments, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥ 92%. In other embodiments, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥ 94%. In other embodiments, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥ 95%.

[0172] In some embodiments, the thickness of the lithiophilic composite layer is selected from 5 μm to 150 μm. The thickness of the lithiophilic composite layer can also be selected from any one of the following thicknesses or an interval consisting of any two of the following thicknesses: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm, 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 110 μm, 115 μm, 120 μm, 125 μm, 130 μm, 140 μm, etc. In some embodiments, the thickness of the lithiophilic composite layer can be selected from any of the following ranges: 5 μm to 150 μm, 5 μm to 140 μm, 5 μm to 125 μm, 5 μm to 120 μm, 5 μm to 100 μm, 5 μm to 80 μm, 6 μm to 125 μm, 10 μm to 150 μm, 10 μm to 140 μm, 10 μm to 12 5μm, 10μm~120μm, 10μm~100μm, 10μm~80μm, 20μm~150μm, 20μm~140μm, 20μm~12 5μm, 20μm~120μm, 20μm~100μm, 20μm~80μm, 40μm~60μm, 45μm~55μm, 48μm~52μm.

[0173] In the present application, samples can be taken at different thickness positions of the negative electrode active material layer, and the presence of lithiophilic substances can be detected using element detection related methods, so as to obtain the average thickness of the lithiophilic substance distribution area through statistical analysis, and this average thickness is used as the "thickness of the lithiophilic composite layer."

[0174] By rationally controlling parameters such as the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material, the thickness of the lithium-philic composite layer (also referred to as the first active layer), and the sum of the mass percentages of the lithium-philic nanoparticles and the first negative electrode active material, the content of the lithium-philic nanoparticles in the negative electrode active material layer and the distribution of the lithium-philic nanoparticles in the negative electrode active material layer (which may include on the surface of the negative electrode active skeleton) can be rationally controlled, thereby effectively promoting alloying between the lithium-philic nanoparticles and lithium and enabling better insertion and extraction of lithium ions from the negative electrode active material. As the content of the lithium-philic nanoparticles in the lithium-philic composite layer increases, the uniform dispersion of the lithium-philic nanoparticles in the overall three-dimensional space of the lithium-philic composite layer is improved.

[0175] In some embodiments, the first negative electrode active material includes a carbon-based material. The carbon-based material may include a graphitized material, and the graphitized material may include one or more of hard carbon and soft carbon. In some embodiments, the first negative electrode active material includes a graphitized material. In some embodiments, the first negative electrode active material includes one or more of hard carbon and soft carbon. In some embodiments, the first negative electrode active material includes hard carbon. In other embodiments, the first negative electrode active material includes soft carbon.

[0176] In some embodiments, in the lithiophilic composite layer, the mass proportion of the graphite-like material in the first negative electrode active material is ≥50%, ≥60%, ≥70%, ≥80%, ≥90%, ≥92%, ≥94%, ≥95%, ≥96%, ≥97%, ≥98%, or ≥99%. Furthermore, the mass proportion of the graphite-like material in the first negative electrode active material can also be selected from any one of the following percentages: 50%, 60%, 70%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc., and can also be selected from a numerical range consisting of any two of the above percentages, such as 80% to 100%, 90% to 100%, 92% to 100%, 94% to 100%, 95% to 100%, 96% to 100%, 97% to 100%, 98% to 100%, 99% to 100%, etc. In some embodiments, the mass proportion of the graphite-like material in the first negative electrode active material is 100%. In this case, the first negative electrode active material is a graphite-like material.

[0177] Traditional graphite-based negative electrode materials cannot meet the continuous high-current discharge capacity required by large-scale power batteries due to the limitations of Li-ion transmission channels caused by their lamellar structure. Traditional metal lithium negative electrodes are accompanied by huge changes in electrode volume during the charge and discharge process, repeated growth of solid electrolyte interface (SEI) films and the formation of metal lithium dendrites. The dendrite growth problem is very serious. These problems cause rapid battery capacity decay, low Coulomb efficiency and safety hazards caused by internal short circuits. Traditional hard carbon materials have a higher gram capacity than graphite. However, hard carbon materials have insufficient lithium storage space and still cannot meet the design requirements of high energy density (such as 400Wh / kg) battery cells.

[0178] In the present application, when the negative electrode active material (denoted as the first negative electrode active material) in the lithiophilic composite layer adopts a carbon-based material containing a graphitized material (such as at least one of hard carbon and soft carbon), the graphite-like microcrystalline conductive structure can be used to provide a negative electrode lithium precipitation skeleton body. During the charging process, excess lithium ions in the positive electrode are deposited in the negative electrode active material layer (most of the lithium is embedded in the carbon-based host material, and a small amount of lithium can be deposited on the negative electrode active skeleton), so that lithium and the negative electrode active skeleton material form a composite negative electrode together, reducing the expansion of the battery cell caused by lithium precipitation on the surface of the pole piece, and promoting the efficient use of metallic lithium. By using this composite negative electrode, the secondary battery can be given good cycle performance, rate performance and safety. Further reasonable control of the graphitized material to have a higher proportion will make the above effects more obvious.

[0179] In some embodiments, the graphite-like material comprises hard carbon, and in this case, the first negative electrode active material comprises hard carbon. In some embodiments, the hard carbon comprises one or more of pyrolytic carbon and carbon black (such as acetylene carbon).

[0180] In some embodiments, in the lithium-philic composite layer, the mass proportion of hard carbon in the first negative electrode active material is ≥50%, and can be greater than 60%, and can also be ≥70%, and can also be ≥80%, and can also be ≥90%, and can also be ≥92%, and can also be ≥94%, and can also be ≥95%, and can also be ≥96%, and can also be ≥97%, and can also be ≥98%, and can also be ≥99%; Further, in the lithium-philic composite layer, the mass proportion of hard carbon in the first negative electrode active material can also be selected from the following Any of the above percentages: 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc., can also be selected from a numerical range consisting of any two of the above percentages, such as 80% to 100%, 90% to 100%, 92% to 100%, 94% to 100%, 95% to 100%, 96% to 100%, 97% to 100%, 98% to 100%, 99% to 100%, etc. In some embodiments, in the lithiophilic composite layer, the mass proportion of hard carbon in the first negative electrode active material is 100%. In this case, the first negative electrode active material is hard carbon.

[0181] Compared with graphite, hard carbon structures, which are difficult to completely graphitize at high temperatures (e.g., above 2800°C), have isotropic characteristics and a similar delithiation potential to graphite and a higher specific capacity (e.g., 500mAh / g to 700mAh / g). In addition, hard carbon has more layered wrinkles, which can provide more lithium storage sites. The larger interlayer spacing of hard carbon facilitates the rapid diffusion of lithium ions, which is beneficial for maintaining a high reversible capacity and achieving good battery cycle performance, rate performance, and safety. Further controlling the proportion of hard carbon in the first negative electrode active material of the lithiophilic composite layer is more beneficial for achieving a higher reversible capacity.

[0182] The carbon layer spacing of traditional graphite materials is only 0.34nm, which greatly limits its ability to store and transmit lithium ions. At the same time, during the charging and discharging process, the surface structure of the graphite electrode becomes more disordered, and the exposed graphite surface reacts with the electrolyte to continuously produce the SEI film, thereby further reducing the reversible capacity.

[0183] In some embodiments, hard carbon having the following structural characteristics can be selected to induce uniform lithium deposition and reduce lithium dendrites: the average pore size of the internal nanopores can be less than 50 nm, preferably 0.1 nm to 5 nm; the specific surface area can be selected from 0.5 to 50 m 2 / g, preferably 2 to 5 m 2 / g; the interlayer spacing of the carbon spheres can be higher than 0.7nm, preferably 0.77 to 2nm, and the tap density can be selected from 0.8 to 1.2g / cm 3 , can be further selected from 0.9 to 1.0 g / cm 3 Wherein, "tap density" has a well-known meaning in the art.

[0184] In some embodiments, the negative electrode plate includes a negative electrode current collector, and the negative electrode active material layer is disposed on at least one side of the negative electrode current collector;

[0185] The negative electrode active material layer further includes a second active layer, which is arranged on a side of the lithium-philic composite layer away from the negative electrode current collector. The second active layer includes a second negative electrode active material and does not include the lithium-philic nanoparticles.

[0186] On the basis that the lithium-philic nanoparticles in the lithium-philic composite layer (i.e., the first active layer) can alloy with lithium, a second active layer without lithium-philic nanoparticles is further provided on the side of the lithium-philic composite layer away from the negative electrode current collector. When the second active layer comes into contact with the electrolyte, it can form a denser solid electrolyte (SEI) film, which can induce the uniform deposition of lithium metal, reduce deposition expansion, and reduce lithium dendrites. The second active layer can also serve as a guiding layer to induce a portion of the precipitated lithium to precipitate uniformly and densely on the surface of the electrode, thereby improving the stability of the solid electrolyte interface (SEI) film. At this time, the negative electrode active material layer has a double-layer structure, and there is a synergistic induction deposition effect of lithium by the lithium-philic nanoparticles in the first active layer and the second active layer.

[0187] In some embodiments, the second negative electrode active material in the second active layer includes a graphite-like material. In some embodiments, the second negative electrode active material in the second active layer includes soft carbon. In some embodiments, the soft carbon includes one or more of coke, carbon fiber, and nanocarbon. In some embodiments, the second negative electrode active material in the second active layer includes hard carbon.

[0188] In some embodiments, in the second active layer, the mass proportion of soft carbon in the second negative electrode active material is ≥50%, ≥60%, ≥70%, ≥80%, ≥90%, ≥92%, ≥94%, ≥95%, ≥96%, ≥97%, ≥98%, or ≥99%. Furthermore, in the second active layer, the mass proportion of soft carbon in the second negative electrode active material can also be selected from any one of the following percentages: 50%, 60%, 70%, 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc., and can also be selected from a numerical range consisting of any two of the above percentages, such as 80%-100%, 90%-100%, 92%-100%, 94%-100%, 95%-100%, 96%-100%, 97%-100%, 98%-100%, 99%-100%, etc. In some embodiments, in the second active layer, the mass proportion of soft carbon in the second negative electrode active material is 100%. In this case, the second negative electrode active material in the second active layer is soft carbon.

[0189] This application also proposes a double-layer coating structure design of "lower layer lithiation-philic + upper layer graphitized material". At this time, the negative electrode active material in the second active layer (that is, the second negative electrode active material) includes a graphitized material. When the second active layer contains hard carbon, it is conducive to achieving a higher reversible capacity. When the second active layer contains soft carbon, the degree of graphitization of the soft carbon is high and the microstructural defects are few. When the second active layer is in contact with the electrolyte, it can induce the uniform deposition of lithium metal to form a denser SEI film, reduce deposition expansion, and reduce lithium dendrites. When the proportion in the second negative electrode active material is high, it is more conducive to promoting the uniform deposition of lithium and the formation of a dense SEI film.

[0190] In some embodiments, the thickness of the second active layer is less than the thickness of the lithiophilic composite layer.

[0191] In some embodiments, the thickness of the second active layer is selected from 5μm to 25μm, and can also be selected from any of the following thicknesses: 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 20μm, etc., and can also be selected from the interval consisting of any two of the foregoing thicknesses. For example, in some embodiments, the thickness of the second active layer is selected from 8μm to 12μm, 8μm to 22μm, 5μm to 20μm, 8μm to 20μm, 10μm to 20μm.

[0192] In the present application, when the thickness of the second active layer is less than that of the first active layer (such as 5μm to 15μm, and further such as about 10μm), it can not only induce the uniform deposition of lithium, but also reasonably adjust the transmission efficiency of lithium ions between the lithiophilic composite layer (first active layer) and the electrolyte. In addition, when the active material of the second negative electrode active material layer contains soft carbon, although the gram capacity of the soft carbon is relatively low, the second active layer can serve as a deposition inducing layer for the lithium deposition part, promoting the formation of a more complete SEI film, and utilizing the composite regulation of the lithium deposition process by the lithium-philic nanoparticles and the second active layer, the deposition of the lithium deposition part can be made more uniform and dense, which can effectively improve the coulombic efficiency and cycle life of the negative electrode; further regulating the second active layer to have a reasonable thickness can achieve a good balance between the overall energy density improvement and the cycle stability increase of the battery cell. If the second active layer is too thick, it may affect the conduction of lithium ions between the lithiophilic composite layer (first active layer) and the electrolyte.

[0193] The negative electrode sheet of the first aspect of the present application includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector. Furthermore, at least one of the negative electrode film layers includes the aforementioned negative electrode active material layer, and any of the negative electrode active material layers contains a negative electrode active substance.

[0194] The negative electrode active material in at least one of the negative electrode active material layers includes the aforementioned first negative electrode active material and the optional second negative electrode active material (when the negative electrode sheet includes a second active layer, the corresponding negative electrode active material layer includes the second negative electrode active material).

[0195] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0196] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to each other in the thickness direction of the negative electrode current collector. Furthermore, the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector. As a non-limiting example, when a negative electrode film layer is disposed on both sides of the negative electrode current collector, the negative electrode film layers on both sides may be the same or different. As a non-limiting example, when a negative electrode active material layer is disposed on both sides of the negative electrode current collector, the negative electrode active material layers on both sides may be the same or different.

[0197] In this application, unless otherwise specified, “disposed on at least one surface of the current collector” means disposed on at least one side of the current collector in the thickness direction of the current collector, and either side may be independently in direct contact with the current collector or not.

[0198] As a non-limiting example, the aforementioned negative electrode active material layer is disposed on at least one side of the negative electrode current collector. In some embodiments, the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector, and may be disposed on one surface of the negative electrode current collector or on both surfaces of the negative electrode current collector. In some embodiments, at least one of the negative electrode active material layers is in direct contact with the negative electrode current collector. In this case, the negative electrode active material layer is in direct contact with at least one surface (one or both surfaces) of the negative electrode current collector.

[0199] In one embodiment shown in FIG2 , the negative electrode sheet includes a negative electrode substrate 100 (e.g., a negative electrode current collector, or a substrate including a negative electrode current collector), and a lithiophilic composite layer 210 located on a single surface of the negative electrode substrate 100. The lithiophilic composite layer 210 includes lithiophilic active particles 201. The negative electrode active material layer has a single-layer structure, with the lithiophilic composite layer serving as the negative electrode active material layer.

[0200] In one embodiment shown in FIG3 , the negative electrode sheet includes a negative electrode substrate 100 (e.g., a negative electrode current collector, or a substrate including a negative electrode current collector), a lithiophilic composite layer 210 located on a single surface of the negative electrode substrate 100, and a second active layer 220 located on a surface of the lithiophilic composite layer 210 facing away from the negative electrode substrate. The lithiophilic composite layer 210 includes lithiophilic active particles 201. The negative electrode active material layer has a double-layer structure, consisting of a lithiophilic composite layer and a second active layer.

[0201] In the application, unless otherwise specified, "negative electrode substrate" refers to a substrate that can be used to apply negative electrode slurry. In some non-limiting examples, the negative electrode substrate includes a negative electrode current collector. In some non-limiting examples, the negative electrode substrate is a negative electrode current collector.

[0202] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0203] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0204] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0205] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC)).

[0206] In some embodiments, the negative electrode sheet can be prepared by the following method: the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the lithium-philic nanoparticle dispersion (preferably the lithium-philic nanoparticle colloidal solution), the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side surface of the negative electrode substrate (such as the negative electrode current collector) (which can be on a single surface or on two surfaces), and after drying, compacting (which can be done by cold pressing) and other processes, the negative electrode sheet can be obtained.

[0207] In this application, unless otherwise specified, "dispersion liquid" refers to a mixed liquid formed by stably dispersing solid particles in a liquid phase.

[0208] In this application, unless otherwise specified, "colloid liquid" refers to a liquid colloid that includes two different phases: a liquid continuous phase and a dispersed phase composed of tiny (non-limiting example, less than or equal to 1000 nm) solid particles or droplets.

[0209] As used herein, “lithiophilic nanoparticle dispersion” refers to a dispersion containing lithiophilic nanoparticles.

[0210] As used in this application, the “lithiophilic nanoparticle colloid solution” refers to a colloid solution containing lithium-philic nanoparticles, wherein the dispersed phase of the colloid solution is composed of lithium-philic nanoparticles (solid particles). In other words, the “lithiophilic nanoparticle colloid solution” refers to a colloid solution wherein the dispersed phase is composed of lithium-philic nanoparticles.

[0211] In this application, the D of the lithiophilic nanoparticles n50 can be less than 1000nm, and non-limiting examples such as less than 500nm can also refer to the above definition. The particle size parameters (such as average particle size, volume cumulative distribution particle size, number cumulative distribution particle size, particle size distribution range, etc.) of the lithium-philic nanoparticles in the "lithium-philic nanoparticle dispersion" and "lithium-philic nanoparticle colloid" can be obtained by testing using a laser particle size analyzer. For example, a Mastersizer 2000E laser particle size analyzer or an LS-909 laser particle size analyzer (Europe and America) of Malvern Instruments Co., Ltd. of the United Kingdom can be used. Wherein, "volume cumulative distribution particle size" refers to the particle size corresponding to the cumulative volume distribution percentage of the material when it reaches a certain percentage, which can be obtained from the volume cumulative distribution curve of the material particle size. If there is no other explanation, the volume cumulative distribution curve is accumulated from zero on the small particle size side. In addition, "number cumulative distribution particle size" refers to the particle size corresponding to the cumulative number distribution percentage of the material when it reaches a certain percentage, which can be obtained from the number cumulative distribution curve of the material particle size. If there is no other explanation, the number cumulative distribution curve is accumulated from zero on the small particle size side. Taking the volume cumulative distribution particle size as an example to further illustrate: In the context of this application, the volume cumulative distribution particle size D v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material, which refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches N%. The particle size is less than or equal to D v The volume percentage of N is N%. v 99.D v 50. D v 10 as an example, D v 99 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 99%; D v 50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%; D v 10 refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching 10%; further, D v For example, 50 means that the particle size of 50% of the material volume is less than or equal to D v 50, and 50% of the volume of the material has a particle size larger than D v 50;D v For example, 99 means that the particle size of 99% of the material volume is less than or equal to D v 99, and the particle size of 1% of the material volume is larger than D v Those skilled in the art can understand the meaning of average particle size and volume cumulative distribution particle size, and can use instruments and methods known in the art to measure them.

[0212] In the inventors' experimental research, some experimental examples used hard carbon as the first negative electrode active material, and the lithium-ion secondary batteries prepared had a long cycle life (correspondingly, the coulombic efficiency after the first cycle would also be high), low pole piece expansion, and the lithium dendrite problem was significantly improved. The reasons are speculated to be as follows: having a high gram capacity allows most of the lithium to be embedded in the hard carbon host material, reducing the reaction loss of lithium metal and electrolyte caused by exposure to the electrolyte, and allowing a small amount of lithium to precipitate on the surface of the carbon host material, which can reduce the loss of lithium metal during the cycle and improve the coulombic efficiency of the cycle after the first cycle. Including but not limited to Examples 1-12, 21-24.

[0213] In some other experimental examples, the first negative electrode active material uses a composite material (e.g., a combination of hard carbon and soft carbon, a combination of hard carbon and graphite, or a combination of hard carbon and a silicon-based material) including hard carbon (the mass proportion of hard carbon in the first negative electrode active material satisfies ≥50%, selected from 50% to 100%, including 50%, 80%, 90%, 95%, etc.). These examples also have long cycle life, low electrode expansion, and significantly improved lithium dendrite problems. These examples include but are not limited to Examples 13-15.

[0214] In some experimental examples, lithium-ion secondary batteries fabricated using a combination of Ag and Au lithiophilic nanoparticles exhibited long cycle life (and, correspondingly, high coulombic efficiency after the first cycle), low electrode expansion, and significantly improved lithium dendrite resistance. In this case, the lithium alloying mechanism includes both solid solution formation and intermetallic compound formation with lithium.

[0215] In the inventors' experimental research, some experimental examples using soft carbon as the first negative electrode active material showed extended cycle life, reduced electrode expansion, and significant improvement in the lithium dendrite problem compared to soft carbon negative electrodes without the introduction of lithium-philic nanoparticles. This includes but is not limited to Example 16.

[0216] In the experimental research of the inventors, some experimental examples used hard carbon as the first negative electrode active material and soft carbon as the second negative electrode active material, all of which had a long cycle life (correspondingly, the coulombic efficiency after the first cycle would also be high), low pole piece expansion and the lithium dendrite problem was significantly improved. The reasons are speculated to be as follows: they all have a high gram capacity, which allows most of the lithium to be embedded in the hard carbon host material, and another part of the lithium is induced by the lithium-philic substance to precipitate inside the pole piece to reduce the cycle expansion change rate, and soft carbon as the negative electrode active material can induce the remaining lithium to precipitate more uniformly and densely on the pole piece surface, so that the lithium metal dendrites are significantly reduced. Including but not limited to Example 1, Example 17, and Example 18.

[0217] In a second aspect, the present application provides a secondary battery comprising a positive electrode sheet, a separator and the negative electrode sheet described in the first aspect of the present application, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

[0218] In the present application, a secondary battery comprises a positive electrode sheet, the negative electrode sheet described in the first aspect of the present application, an electrolyte, and a separator. During the battery's charge and discharge process, lithium ions are intercalated and released back and forth between the positive and negative electrode sheets. The electrolyte conducts lithium ions between the positive and negative electrode sheets. The separator is disposed between the positive and negative electrode sheets, primarily preventing a short circuit between the positive and negative electrodes while allowing lithium ions to pass through.

[0219] The negative electrode plate of the first aspect of the present application is used to prepare a secondary battery, and the alloying of the lithium-philic nanoparticles and lithium in the lithium-philic composite layer can be utilized. On the one hand, after lithium alloying, the reaction activity between the negative electrode material and the electrolyte can be significantly reduced, thereby inducing the deposition of lithium metal inside and on the surface of the plate, reducing the high charging expansion problem caused by internal and surface lithium precipitation, and also reducing lithium metal loss, effectively improving the coulombic efficiency of the negative electrode and the battery cycle life.

[0220] In some embodiments, the CB value of the secondary battery is less than 1; wherein, the side of the negative electrode sheet facing the positive electrode sheet includes the negative electrode active material layer, and the side of the positive electrode sheet facing the negative electrode sheet includes the positive electrode active material layer, and the CB value is the ratio of the capacity of the negative electrode active material layer and the positive electrode active material layer arranged relatively under the same area (the formation loss is supplemented by the amount of lithium replenished after experimental confirmation, and the actual measured value may have a slight deviation).

[0221] In some embodiments, the CB value of the secondary battery may satisfy 0.1≤CB<1, and may further satisfy 0.15≤CB<1. Furthermore, in some embodiments, the CB value of the secondary battery may be selected from any of the following values: 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, etc., and may be selected from an interval consisting of any two of the aforementioned values.

[0222] In some embodiments, the CB value of the secondary battery can be selected from any one of the following ranges: 0.1-0.9, 0.1-0.8, 0.1-0.75, 0.1-0.7, 0.15-0.9, 0.15-0.8, 0.15-0.75, 0.15-0.7, 0.3-0.9, 0.3-0.6, 0.2-0.8, 0.2-0.9, 0.6-0.75, 0.3-0.7, 0.3-0.8, 0.4-0.8, 0.5-0.7, etc.

[0223] In the present application, the "CB (Cell Balance) value" is the ratio of the surface capacity of the negative electrode to the surface capacity of the positive electrode, which is numerically equal to the ratio of the capacity of the negative electrode sheet to the capacity of the positive electrode sheet under the same area. In the present application, "surface capacity" has a well-known meaning, which refers to the ratio of the electrode capacity to the electrode area. In a low CB value system, a portion of the lithium is embedded in the carbon material in the form of lithiate, and another portion of the lithium may be precipitated onto the surface of the electrode in the form of lithium metal due to the saturation of the lithium storage space inside the carbon-based material, thereby ensuring the cycle life. In the present application, the CB value can be obtained based on half-cell tests made from the positive electrode sheet and the negative electrode sheet. The method of preparing half-cells is known to those skilled in the art. When testing the CB value of a battery, the following method can be used: for the capacity of the positive electrode plate in the battery to be tested, the positive electrode sets a charge and discharge cut-off voltage (such as 2.0~4.3V, further such as 2.0~3.65V or 2.8~4.3V) for lithium and a small current cycle of 0.1C, and the positive electrode capacity can be calibrated according to the data of the first cycle (or a specific number of cycles); for the capacity of the negative electrode plate in the battery to be tested, the charge and discharge cut-off voltage (0-2V) for lithium can be set and a small current cycle can be used to calibrate the negative electrode capacity according to the corresponding first cycle data (or a specific number of cycles).

[0224] The present application also proposes a design of a low CB system lithiophilic modified negative electrode, which can take into account both high energy density and cycle stability. In the present application, for the design of a battery cell with a CB value of less than 1, the lithium-philic nanoparticles can alloy with lithium during the charging process to improve the stability of lithium metal, and can also induce lithium metal to be uniformly deposited inside the negative electrode pole piece (which may be included on the negative electrode active skeleton), so that lithium and the negative electrode active skeleton material together form a composite negative electrode, and achieve effective regulation of lithium deposition behavior, which can better achieve a good balance between the overall energy density improvement and the increase in cycle stability of the battery cell. When the CB value is less than 1, the lithium-philic nanoparticles in the negative electrode active material layer are used to allow a portion of the analyzed lithium metal to be uniformly deposited inside the active material layer, reducing the expansion of the pole piece. When the surface of at least some of the negative electrode active materials is distributed with the aforementioned lithium-philic nanoparticles, the lithium-philic nanoparticles can induce lithium metal to be uniformly deposited on the negative electrode active skeleton, reducing the expansion of the pole piece. In addition, when the negative electrode plate is provided with the aforementioned second active layer, the second active layer can serve as a guiding layer to induce another portion of the precipitated lithium to precipitate evenly and densely on the surface of the plate. At this time, most of the lithium can be stored in the active material layer, and only a small portion of the lithium is in the lithium metal precipitation state.

[0225] In some embodiments, the negative electrode capacity can be increased to 500 mAh / g to 700 mAh / g by designing the CB value of the battery cell.

[0226] Positive electrode

[0227] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. At least one of the positive electrode film layers includes a positive electrode active material layer, and any of the positive electrode active material layers contains a positive electrode active substance. Therefore, the positive electrode sheet contains a positive electrode active substance.

[0228] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction. Furthermore, the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector.

[0229] 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 surface 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.).

[0230] In the present application, the secondary battery may be a lithium-ion battery, i.e., a lithium-ion secondary battery, wherein the positive electrode active material comprises a lithium-ion material (non-limiting examples include lithium-containing phosphates, lithium transition metal oxides, and modifications of any of the foregoing).

[0231] In some embodiments, the positive electrode plate contains a positive electrode active material; the positive electrode active material includes a lithium ion material; further, the lithium ion material includes one or more of the following substances: lithium-containing phosphates (such as lithium-containing phosphates with an olivine structure), lithium transition metal oxides, and substances composed of any of the foregoing substances and doping elements.

[0232] In some embodiments, the positive electrode active material includes one or more of the following substances: lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, as well as a substance composed of any of the foregoing substances and doping elements.

[0233] In this application, unless otherwise specified, the doping elements in any positive electrode active material independently include one or more transition metal elements and non-transition metal elements. The active ions of lithium-ion secondary batteries include lithium ions. The negative electrode plate of this application can utilize a lithiophilic metal to regulate the lithium deposition process, inhibit the reactivity between the negative electrode material and the electrolyte, reduce lithium metal loss during the cycle, and effectively improve the coulombic efficiency of the negative electrode and the battery cycle life.

[0234] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As a non-limiting example, the positive electrode active material may include one or more 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 or substances that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, non-limiting 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, etc. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of 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, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0235] In some embodiments, the positive electrode film layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0236] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0237] In some embodiments, the positive electrode sheet can be prepared by the following method: 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 at least one side surface of the positive electrode collector (it can be a single surface or two surfaces), and after drying, compacting (cold pressing can be used), etc., the positive electrode sheet can be obtained.

[0238] electrolytes

[0239] The electrolyte conducts active ions (lithium ions) between the positive electrode and the negative electrode.

[0240] In some embodiments, the electrolyte is a liquid electrolyte, that is, an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent. In a lithium-ion secondary battery, the electrolyte salt may include an electrolyte lithium salt.

[0241] In some embodiments, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate (LiBOB), lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0242] In some embodiments, the electrolyte lithium salt may include one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonyl imide), LiTFSI (lithium bistrifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium bisoxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate) and LiTFOP (lithium tetrafluorooxalatophosphate), and further, may include one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiBOB (lithium bisoxalatoborate), LiDFOB (lithium difluorooxalatoborate), LiTFSI (lithium bistrifluoromethanesulfonyl imide) and LiFSI (lithium bisfluorosulfonyl imide).

[0243] In some embodiments, the solvent in the electrolyte is an organic solvent. In some embodiments, the organic solvent in the electrolyte may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), 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.

[0244] In some embodiments, one or more organic solvents that are conducive to the reversible deposition and stripping of lithium on the negative electrode active skeleton can be selected. Furthermore, the organic solvent can be an ester or an ether.

[0245] The above-mentioned ester solvents may include one or more of carbonates and halogenated carbonates, such as, as non-limiting examples, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), 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) and one or more of the fluorinated compounds of any of the foregoing; further, it may include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC) and trifluoromethylethyl carbonate (TFMEC).

[0246] In some embodiments, the electrolyte may further include additives. For example, the additives may include 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, and additives that improve battery high or low temperature performance.

[0247] In some embodiments, the additive may include one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), methylene methanedisulfonate (MMDS), 1-propylene-1,3-sultone (PST), vinyl sulfite (ES), propylene sulfite (PS), vinyl sulfate (DTD), succinonitrile (SN), adiponitrile (ADN), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB) and anisole.

[0248] In some embodiments, the electrolyte filling coefficient of a single battery cell is ≥2.4 g / Ah, and may preferably be 2.4 to 3.2 g / Ah.

[0249] Isolation film

[0250] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0251] In some embodiments, the material of the separator can be selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. 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.

[0252] Electrode assembly, secondary battery

[0253] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0254] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0255] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0256] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG6 shows a secondary battery 5 with a square structure as an example.

[0257] In some embodiments, referring to Figure 7, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film can be formed into 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 secondary battery 5 can be one or more, and those skilled in the art can select according to actual needs.

[0258] In a third aspect, the present application provides an electrical device comprising at least one of the negative electrode sheet described in the first aspect of the present application and the secondary battery described in the second aspect of the present application.

[0259] An electrical device prepared using at least one of the negative electrode plate described in the first aspect of the present application and the secondary battery described in the second aspect of the present application can utilize the alloying of lithium-philic nanoparticles and lithium in the lithium-philic composite layer to inhibit the reaction activity between the negative electrode material and the electrolyte, regulate the lithium deposition process, effectively improve the coulombic efficiency of the negative electrode and the battery cycle life, and extend the service life of the electrical device.

[0260] The secondary battery described in the second aspect of the present application 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, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, and the like. Examples of mobile devices include, but are not limited to, mobile phones and laptop computers; examples of electric vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0261] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0262] Fig. 8 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.

[0263] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0264] In a fourth aspect, the present application provides a method for preparing a negative electrode sheet, which can be used to prepare the negative electrode sheet described in the first aspect of the present application.

[0265] In some embodiments, a method for preparing a negative electrode sheet is provided, comprising the following steps:

[0266] S100: preparing a first negative electrode slurry comprising a first negative electrode active material and lithium-philic nanoparticles; wherein the lithium-philic nanoparticles are as defined in the first aspect of the present application;

[0267] S300: coating the first negative electrode slurry on at least one surface of a negative electrode substrate, drying to form a lithiophilic composite layer, and preparing a lithiophilic substrate;

[0268] S500: cold pressing the lithiophilic substrate to prepare a negative electrode plate; alternatively, coating a second negative electrode slurry containing a second negative electrode active material on one surface of the lithiophilic substrate including the lithiophilic composite layer, drying, and cold pressing to form a second active layer to prepare a negative electrode plate.

[0269] The definition of "negative electrode substrate" can be found in the first aspect of this application and refers to a substrate that can be used to apply the negative electrode slurry. In some non-limiting examples, the negative electrode substrate includes a negative electrode current collector. In some non-limiting examples, the negative electrode substrate is a negative electrode current collector.

[0270] A dispersion containing lithium-philic nanoparticles is introduced into the negative electrode slurry, and the lithium-philic nanoparticles are uniformly dispersed in the negative electrode slurry. After further coating, drying and other processes, the particles can be assembled onto a negative electrode substrate (such as a negative electrode current collector, and also a substrate including a negative electrode current collector) to form a lithium-philic composite layer. The lithium-philic composite layer can be directly used as the surface layer in contact with the electrolyte in the negative electrode sheet, and a second active layer (non-lithiophilic) can be further stacked to obtain the aforementioned "lower layer lithium-philic + upper layer non-lithiophilic" double-layer coating structure, such as a "lithiophilic composite layer + second active layer" double-layer structure.

[0271] In some embodiments, the step of preparing the first negative electrode slurry includes mixing the first negative electrode active material and a dispersion containing the lithium-philic nanoparticles. Further, in some embodiments, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 100μg / L to 1000μg / L. The concentration of the lithium-philic nanoparticles in the dispersion can also be selected from any of the following concentrations: 100μg / L, 150μg / L, 200μg / L, 250μg / L, 300μg / L, 350μg / L, 400μg / L, 450μg / L, 500μg / L, 520μg / L, 540μg / L, 545μg / L, 550μg / L, 560μg / L, 580μg / L, 600μg / L, 700μg / L, 750μg / L, 800μg / L, 850μg / L, 900μg / L, 950μg / L, 1000μg / L, etc., and can also be selected from the interval consisting of any two of the above concentrations, for example, 200μg / L~800μg / L, 400μg / L~800μg / L, 400μg / L~600μg / L, 400μg / L~500μg / L, 500μg / L~600μg / L, 520μg / L~580μg / L, etc.

[0272] In the present application, the “dispersion liquid containing lithiophilic nanoparticles” may be referred to as lithiophilic nanoparticle dispersion liquid.

[0273] In some embodiments, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 200 μg / L to 800 μg / L.

[0274] In some embodiments, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 400 μg / L to 500 μg / L.

[0275] By rationally controlling the concentration of lithium-philic nanoparticles in the dispersion, the distribution concentration of lithium-philic nanoparticles in the negative electrode slurry can be better adjusted, and then after coating and drying, a rational distribution inside the negative electrode active material layer (including on the surface of the negative electrode active skeleton) can be achieved, which can effectively induce uniform lithium deposition and the formation of an artificial alloying interface while maintaining a good lithium ion insertion / extraction rate.

[0276] In some embodiments, any one or more of the following features are met (which can be any suitable combination of multiple features in the following group):

[0277] The step of preparing the first negative electrode slurry further includes adding a conductive agent, a binder and a solvent;

[0278] The definition of the first negative electrode active material in the first negative electrode slurry is consistent with the definition of the first negative electrode active material in the lithiophilic composite layer in the first aspect of the present application;

[0279] The definition of the second negative electrode active material in the second negative electrode slurry is consistent with the second negative electrode active material in the second active layer in the first aspect of the present application;

[0280] The negative electrode plate is as defined in the first aspect of the present application.

[0281] In some embodiments, the first negative electrode active material in the first negative electrode slurry is defined as the first negative electrode active material in the lithiophilic composite layer described in the first aspect of the present application. For example, the first negative electrode active material includes a graphitized material. Furthermore, the first negative electrode active material may include one or more of hard carbon and soft carbon. Furthermore, the first negative electrode active material may include hard carbon. Furthermore, the hard carbon may include one or more of pyrolytic carbon and carbon black.

[0282] In some embodiments, the second negative electrode active material in the second negative electrode slurry is defined as the second negative electrode active material in the second active layer in the first aspect of this application. For example, the second negative electrode active material in the second active layer may include a graphite-like material. Furthermore, the second negative electrode active material in the second active layer may include soft carbon. Furthermore, optionally, the soft carbon may include one or more of coke, carbon fiber, and nanocarbon.

[0283] In some embodiments, the negative electrode sheet is as defined in any embodiment of the first aspect of the present application. The negative electrode sheet of the first aspect of the present application can be prepared using the preparation method of the second aspect.

[0284] In some embodiments, the lithium-philic nanoparticle dispersion is prepared by a method comprising the following steps:

[0285] preparing a mixed solution containing a metal precursor, a reducing agent, and an optional dispersant; wherein the metal precursor comprises a salt precursor of the lithium-philic nanoparticles; and

[0286] The mixed solution is subjected to a reduction reaction to convert the salt-type precursor into the lithium-philic nanoparticles.

[0287] In some preparation methods, the preparation method of the negative electrode sheet satisfies any one or more of the following characteristics (which can be any suitable combination of multiple characteristics in the following group):

[0288] The concentration of the salt precursor (such as silver precursor) in the mixed solution is selected from 1 μM to 20 μM; optionally, the concentration of the salt precursor in the mixed solution is selected from 2 μM to 10 μM;

[0289] The mass volume concentration of the reducing agent in the mixed solution is selected from 0.10% to 0.30% (w / v); optionally, the mass volume concentration of the reducing agent in the mixed solution is selected from 0.15% to 0.26% (w / v); optionally, the mass volume concentration of the reducing agent in the mixed solution is selected from 0.20% to 0.26% (w / v);

[0290] The reducing agent includes one or more of sodium citrate, hydrazine hydrate, sodium hypophosphite, carboxymethyl cellulose and its sodium salt (such as sodium carboxymethyl cellulose), glucose, gluconic acid and its sodium salt, formaldehyde, sodium borohydride, ascorbic acid and hydrogen peroxide; alternatively, the reducing agent includes one or more of sodium citrate, hydrazine hydrate, sodium hypophosphite, sodium carboxymethyl cellulose, glucose, formaldehyde, sodium borohydride, ascorbic acid and hydrogen peroxide;

[0291] The dispersant includes one or more of polyethylene glycol, polyvinyl pyrrolidone (PVP), aniline and formaldehyde sulfonic acid.

[0292] For those skilled in the art, when the chemical composition of the metal nanoparticles is known, the corresponding dispersion (such as a colloidal liquid) can be prepared by conventional methods in the art, wherein parameters such as the type of precursor, the type and amount of the reducing agent, and the type and amount of the dispersant can be selected according to the concentration and particle size requirements of the lithium-philic nanoparticle dispersion. For different lithium-philic metals, the types of precursors and reducing agents required may be different. By adjusting parameters such as the concentration of the precursor, the reducing power of the reducing agent, and the amount of the reducing agent, the particle size of the metal particles generated by the reduction can be regulated. In addition, when the target concentration or target particle size of the lithium-philic nanoparticle dispersion is different, different dispersants can be selected to maintain the uniform dispersion of the generated lithium-philic nanoparticles in the dispersion. The "lithium-philic nanoparticle dispersion" used in this application can be directly purchased from the market, or can be obtained by making a dispersion from commercially available nanoparticles, or can be prepared with reference to existing preparation methods in the art. For example, to obtain a nano silver dispersion, a soluble silver salt (such as silver nitrate) can be used as a precursor, and further, one or more reducing agents can be selected from carboxymethyl cellulose and its sodium salt (such as sodium carboxymethyl cellulose), glucose, gluconic acid and its sodium salt, formaldehyde, sodium borohydride, ascorbic acid, hydrogen peroxide, etc. For example, to obtain a nano gold dispersion, a soluble gold salt (such as chloroauric acid) can be used as a precursor, and further, a reducing agent such as sodium citrate can be selected. Taking the preparation of nano gold colloid as an example, the more reducing agent (such as citric acid) is used, the smaller the diameter of the colloidal gold particles, and conversely, the less reducing agent is used, the larger the diameter of the colloidal gold particles; however, if the diameter of the nanoparticles is too small (such as less than 5nm, or less than 10nm), they are prone to agglomeration and are not easy to exist stably for a long time.

[0293] The lithium-philic nanoparticles described herein are produced by reducing a salt precursor of the lithium-philic nanoparticles using a reducing agent. A suitable dispersant can also be introduced into the reaction system to prepare a uniform dispersion of the lithium-philic nanoparticles. By properly controlling various preparation parameters, including but not limited to the type and amount of the precursor, the type and amount of the reducing agent, and the type of dispersant, the size of the lithium-philic nanoparticles and their concentration in the dispersion can be controlled, thereby better controlling the uniform distribution of the lithium-philic nanoparticles on the surface of the negative electrode active skeleton.

[0294] Some reducing agents can also act as dispersants, which can reduce the precursor while preventing the generated nanoparticles from settling.

[0295] When the reducing agent or dispersant contains polar groups (such as carboxyl, hydroxyl and halogen groups, etc.), it can provide more abundant lithium ion adsorption sites, which is more conducive to achieving uniform lithium ion deposition flux. Furthermore, the smooth and flat lithium alloying interface and uniform surface stress distribution can stabilize the SEI film, thereby effectively reducing the consumption of active lithium metal and electrolyte. The lithiophilic coating and polar groups can work synergistically to reduce the lithium deposition overpotential inside the electrode, more effectively guide the uniform lithium deposition inside the skeleton, and avoid the formation of dead lithium. Among them, carboxymethyl cellulose and its sodium salt, glucose, gluconic acid and its sodium salt all contain hydroxyl groups. Carboxymethyl cellulose and gluconic acid contain carboxyl groups.

[0296] In some embodiments, the reducing agent comprises sodium carboxymethylcellulose.

[0297] In the preparation method of the present invention, a suitable type of dispersant can be selected according to the reducing agent system.

[0298] In some embodiments, the dispersant includes one or more of polyethylene glycol, polyvinyl pyrrolidone (PVP), aniline, and formaldehyde sulfonic acid.

[0299] In some embodiments, the dispersant includes polyvinylpyrrolidone (PVP); further, the reducing agent includes sodium carboxymethylcellulose.

[0300] Sodium carboxymethyl cellulose is safe, environmentally friendly and low-cost. In the negative electrode slurry containing hard carbon powder, it can stably increase the slurry viscosity and prevent the slurry from settling. It contains rich -COO - The functional group can form good adhesion with the negative electrode current collector (such as metal foil) and has conductivity.

[0301] Using PVP as a dispersant has two advantages. On the one hand, the long molecular chains of PVP can coat the surface of lithium-philic nanoparticles to prevent the agglomeration of the formed nanoparticles. On the other hand, PVP molecules can selectively attach to specific crystal planes, making the growth rate of these crystal planes slower than that of other crystal planes, thereby controlling the micromorphology of the generated nanoparticles.

[0302] In other embodiments, the present application further provides a method for preparing a negative electrode sheet, which comprises the following steps:

[0303] S200: Providing a carbon-based negative electrode plate; wherein the carbon-based negative electrode plate comprises a negative electrode substrate and a carbon-based active material layer located on at least one side of the negative electrode substrate; the carbon-based active material layer comprises the aforementioned carbon-based active substance;

[0304] S400: infiltrating the aforementioned lithium-philic nanoparticle dispersion from the surface of the carbon-based active material layer toward the negative electrode substrate, drying, and converting at least a portion of the carbon-based active material layer into a lithium-philic material layer (a lithium-philic composite that has not been cold-pressed, referred to as a first structural layer) to obtain a lithium-philic substrate;

[0305] S500: As described above, the lithiophilic substrate is cold pressed to prepare a negative electrode sheet; alternatively, a second negative electrode slurry containing a second negative electrode active material is applied to a surface of the lithiophilic substrate including the lithiophilic composite layer, dried, and cold pressed to form a second active layer (at this point, the first structural layer is converted into a cold-pressed lithiophilic composite layer) to prepare a negative electrode sheet.

[0306] An in-situ deposition method can be used to form a coating containing lithium-philic nanoparticles on the surface of the negative electrode active skeleton, thereby converting a portion of the negative electrode active material layer into a lithium-philic composite layer. This can improve the utilization rate of lithium through alloying of lithium-philic nanoparticles with lithium, reduce lithium metal loss during the cycle, and effectively improve the coulombic efficiency of the negative electrode and the battery cycle life.

[0307] In some embodiments, in step S400, the aforementioned lithiophilic nanoparticle dispersion is infiltrated from the surface of the carbon-based active material layer toward the negative electrode substrate by one or more of the following methods: drop coating, dipping, wire rod coating, and doctor blade coating, so that the lithiophilic nanoparticle dispersion is fully infiltrated into the non-lithiophilic carbon-based active material layer. Furthermore, a non-limiting example of a drying method is to allow the mixture to stand in a vacuum oven at 80°C for a period of time (e.g., ≥3 hours) until trace water is removed.

[0308] In a fifth aspect, the present invention provides the use of the negative electrode sheet described in the first aspect of the present invention in preparing a lithium-ion secondary battery. For details, please refer to the method for using the negative electrode slurry in the first aspect of the present invention and the method for assembling a secondary battery using the negative electrode sheet in the second aspect of the present invention.

[0309] Below, some embodiments of the present application are described. The embodiment described below is exemplary, is only used to explain the present application, and cannot be construed as limiting the present application. In the embodiment, if no technology or conditions are indicated, it is carried out according to the description above, or according to the technology or conditions described in the document in this area or according to the product specification. Reagents used or instruments that are not indicated by the manufacturer are conventional products that can be obtained commercially, or can be synthesized in a conventional manner by commercially available products.

[0310] In the following examples and comparative examples, room temperature and normal temperature each independently refer to 20°C to 30°C, and further, may be 25°C.

[0311] In the following examples, unless otherwise specified, CMC refers to sodium carboxymethyl cellulose (CAS No.: 9004-32-4).

[0312] In the following examples, unless otherwise specified, wt% represents the percentage by mass.

[0313] Raw material preparation: dispersion containing lithium-philic nanoparticles (lithiphilic nanoparticle dispersion)

[0314] The dispersion containing lithium-philic nanoparticles can be purchased commercially, or prepared by using commercially available nanoparticles to make a dispersion. It can also be prepared by the following method: using a precursor of the lithium-philic nanoparticles and a reducing agent to carry out a reduction reaction, and depending on the stability of the reduction reaction system, a suitable dispersant can be added to enable the lithium-philic nanoparticles generated by the reduction reaction to form a stable dispersion.

[0315] By referring to the type of lithiophilic substance, the predetermined concentration of the lithiophilic nanoparticle dispersion, and the predetermined particle size shown in Table 1, the type and amount of raw materials, such as the precursor, reducing agent, and dispersant, for the lithiophilic nanoparticles, as well as appropriate reaction conditions, can be selected to prepare a dispersion containing the target lithiophilic nanoparticles. Dispersions containing lithiophilic nanoparticles of different chemical compositions can be mixed to prepare a dispersion containing two or more types of lithiophilic nanoparticles. The dispersion can be tested for particle size using a laser particle size analyzer to confirm whether the nanoparticle size falls within the predetermined range.

[0316] The lithium-philic nanoparticle dispersions SL01 to SL09 were prepared in the aforementioned manner, see Table 1.

[0317] The following provides a detailed preparation method using the preparation of nanosilver dispersion and nanogold dispersion as non-limiting examples. In addition, commercially available nanotin powder (particle size of about 50 nm) and nanozinc powder (particle size of 20-50 nm) are used to prepare the dispersion. In this application, the size of the particles can be expressed as "grain size". For the particles to be measured, the diameter of a sphere of the same material can be used as the equivalent particle size of the measured particles.

[0318] Dispersion SL01. Lithium-philic nanoparticles are Ag

[0319] At room temperature, 32 mL of 0.2% (w / v) CMC aqueous solution was stirred for 15 min, 16 mL of 0.5 mM AgNO3 aqueous solution was added dropwise, and stirring was continued for 10 min to stabilize the system. Then, 480 μL of 0.1 M glucose aqueous solution and 2.4 mL of 0.1 M NaOH aqueous solution were added, and the mixed solution was adjusted to pH = 12. The mixture was heated in a water bath at 60 ° C for 30 min to obtain a nanosilver dispersion. n 50 is about 50nm.

[0320] Dispersion SL01a. The method is basically the same as SL01, except that the particle size of the nanosilver particles is changed by adjusting the amount of CMC. n 50Nanosilver dispersion of approximately 10 nm. See Table 1.

[0321] Dispersion SL01b. The method is basically the same as SL01, except that the particle size of the nanosilver particles is changed by adjusting the amount of CMC. n 50 Nanosilver dispersion of approximately 100 nm. See Table 1.

[0322] Dispersion SL01c. The method is basically the same as SL01, except that the particle size of the nanosilver particles is changed by adjusting the amount of CMC. n 50 Nanosilver dispersion of approximately 200 nm. See Table 1.

[0323] Dispersion SL02. Lithium-philic nanoparticles are Au

[0324] 100 mL of a 0.01 wt% chloroauric acid aqueous solution was heated to boiling, and then 100 mL of a 1 wt% chloroauric acid solution was rapidly added and heated to boiling. Then, 4 mL of a 1 wt% sodium citrate solution was rapidly added. At this point, the solution immediately turned blue. Heating was continued until the solution changed from blue to a transparent orange-red color. The heating time was about 7 to 10 minutes. A nanogold dispersion was prepared (see Table 1).

[0325] Dispersion SL03. The lithiophilic nanoparticles are Sn. The concentration and particle size of the nanotin dispersion are shown in Table 1.

[0326] Dispersion SL04. The lithiophilic nanoparticles are Zn. The concentration and particle size of the nano-zinc dispersion are shown in Table 1.

[0327] Dispersion SL05. Lithium-philic nanoparticles containing two elements (two alloying mechanisms: solid solution + intermetallic compound)

[0328] Equal volumes of dispersion SL01 and dispersion SL02 are mixed to obtain a composite dispersion SL05 containing two types of lithium-philic nanoparticles, nano-Ag and nano-Au.

[0329] The preparation method of dispersion SL06 is basically the same as that of dispersion SL01, except that no glucose is added.

[0330] Dispersions SL07-SL09. The lithium-philic nanoparticles are Mg. The concentration and particle size of the nano-Mg dispersions are shown in Table 1.

[0331] Solution CT01 (control 1, reducing agent solvent). A reducing agent solution with the same final concentration as SL01 was prepared. The differences from the dispersion of SL01 were that no precursor of the lithiophilic nanoparticles was added, the silver nitrate aqueous solution was replaced with an equal mass of water, and NaOH was still used to adjust the pH.

[0332] Solution CT02 (control 2, silver nitrate solution). A silver nitrate solution with the same final concentration as SL01 was prepared. The difference from the dispersion of SL01 was that no reducing agent was added, and no reduction reaction was performed. The CMC aqueous solution and the glucose aqueous solution were replaced with equal masses of water, and NaOH was still used to adjust the pH.

[0333] Particle size D n 50 test method:

[0334] Sample processing: The sample can be diluted and placed in a quartz bottle for measurement.

[0335] Equipment model: Malvern 2000 Laser Particle Sizer, Reference Standard Procedure: GB / T19077-2016 / ISO 13320:2009. Detailed test procedure: Take an appropriate amount of the sample to be tested (ensure the sample concentration is 8% to 12% obscuration), add 20 mL of anhydrous ethanol, and sonicate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, measure the sample according to GB / T19077-2016 / ISO 13320:2009. To prevent agglomeration during the drying process from affecting the particle size measurement, the sample was washed and moistened for dispersion testing.

[0336] Table 1. Preparation and testing parameters of dispersions containing lithiophilic nanoparticles

[0337]

[0338] Example 1. The negative electrode active material layer has a double-layer structure, including a lithium-philic composite layer (first active layer) and a second active layer.

[0339] 1.1. Preparation of positive electrode

[0340] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent acetylene black, and binder PVDF were mixed in a mass ratio of 96:2:2, and solvent N-methylpyrrolidone (NMP) was added and stirred until the system became uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on a positive electrode current collector aluminum foil with a thickness of 12 μm. The positive electrode surface capacity was 3.5 mAh cm -2 After drying at room temperature, transfer to a 50°C oven and continue drying for 5 hours. Cut into corresponding sizes and set aside.

[0341] 1.2. Preparation of negative electrode sheet

[0342] A double-layer coating composite structure is adopted, and the negative electrode active material layer includes a first active layer and a second active layer.

[0343] (1) Negative electrode slurry

[0344] Active material hard carbon, conductive agent carbon black, styrene acrylic binder S D-3 , 0.5% (w / v) and an additive, sodium carboxymethyl cellulose (CMC), are dissolved in a deionized water solvent in a weight ratio of 95.5:1:3.1:0.4, and the mixture is uniformly mixed to prepare a negative electrode slurry;

[0345] (2) Lithiophilic modification: Add 3% by weight of a lithium-philic nanoparticle dispersion (nanosilver dispersion) to the negative electrode slurry and continue mixing until uniform. Stirring is performed while adding the lithium-philic nanoparticle dispersion. This yields the first negative electrode slurry.

[0346] (3) Prepare a negative electrode substrate including a carbon-based active material layer.

[0347] The first negative electrode slurry is evenly coated on the single side surface of the negative electrode current collector copper foil with a single-side coating thickness of 100 μm. After drying, a lithium-philic composite layer (ie, the first active layer) is formed to obtain a negative electrode substrate A with a preset CB value (CB value of 0.6 in this example).

[0348] (4) Referring to the manufacturing process of step (3), a second negative electrode slurry is coated on the first active layer side of the negative electrode substrate A (the second negative electrode slurry is the negative electrode slurry prepared in step (1)), dried, and a second active layer is formed on the first active layer. The composite negative electrode sheet is obtained by cold pressing and cutting.

[0349] The single-side capacity of the negative electrode plate is determined according to the preset surface capacity and the preset CB value of the positive electrode plate.

[0350] 1.3. Isolation film

[0351] Polyethylene (PE) film is used as the separator, and the surface of the separator is covered with CCS (Ceramic Composite Separator) ceramic coating on both sides.

[0352] Among them, CCS ceramic coating refers to nano-alumina Al2O3 coating.

[0353] 1.4. Electrolyte

[0354] Lithium salt LiPF6 (lithium hexafluorophosphate) is added to a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 35:65, and the mixture is mixed evenly to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte is 1 mol / L.

[0355] 1.5. Assembly of secondary batteries

[0356] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The bare cell is then welded to the tabs and secured in an aluminum-plastic film. 0.4g of electrolyte (the cell filling coefficient meets 2.4-3.2g / Ah) is injected into one end of the film and heat-sealed to produce an uncharged dry cell. The uncharged dry cell then undergoes a series of processes, including resting, hot and cold pressing, shaping, and capacity testing, to produce a lithium-ion secondary battery.

[0357] Examples 2 to 24 and Comparative Examples 1 to 11 were prepared by referring to the preparation method of Example 1 and the parameter settings in Tables 1, 2 and 3 to prepare negative electrode sheets and lithium-ion secondary batteries.

[0358] Example 2. The negative electrode active material layer is a single-layer structure. The method is basically the same as that of Example 1, except that step (4) of the negative electrode plate preparation process is omitted, that is, the second active layer is not provided, and the negative electrode substrate prepared in step (3) is used as the negative electrode plate for assembling a secondary battery.

[0359] Examples 3-5. Monolayer Structure: Adjusting the Particle Size of Lithiophilic Nanoparticles. The method was essentially the same as in Example 2, except that nanosilver dispersions with varying particle sizes were used. Examples 3-5 used dispersions SL01a, SL01b, and SL01c, respectively.

[0360] Examples 6-7. Single-layer structure, adjusting the amount of lithium-philic nanoparticles in the first negative electrode slurry. The method is essentially the same as that of Example 2, except that the amount of lithium-philic nanoparticles used in preparing the negative electrode sheets relative to the first negative electrode active material is different (1 wt% and 5 wt% for Examples 6-8, respectively).

[0361] Examples 8-10: Single-layer Structures, Varying the Type of Lithophilic Nanoparticles and the Thickness of the First Active Layer. The method was essentially the same as that of Example 2, except that different types of lithiophilic nanoparticle dispersions containing different lithiophilic substances were used. Examples 8-10 used dispersions SL02, SL03, and SL04, respectively, with the lithiophilic substances Au, Sn, and Zn. Examples 9-10 also varied the thickness of the single-layer coating of the first negative electrode slurry.

[0362] Example 11: Single-layer structure, lithiophilic nanoparticles containing two lithiophilic metals, and varying the thickness of the first active layer. The method was essentially the same as Example 2, except that the lithiophilic nanoparticles contained two lithiophilic materials, Ag and Au, and the dispersion SL05 was used, and the thickness of the first active layer was varied.

[0363] Example 12: Single-layer structure, adjusting the reducing agent type to achieve control of nanosilver particle size. The method was essentially the same as in Example 2, except that the lithium-philic nanoparticle dispersion SL06 was used, and the nanosilver particle size was different from that in SL01. Furthermore, when preparing this dispersion SL06, glucose was omitted as the reducing agent compared to SL01.

[0364] Examples 13-15. Single-layer structure, adjusting the type and CB value of the first negative electrode active material. The method is essentially the same as that of Example 12, except that the negative electrode active materials in the lithiophilic composite layer are different and the CB values ​​are different. Examples 13-15 respectively use a combination of hard carbon + graphite (Example 13), a combination of hard carbon + soft carbon (Example 15), and a combination of hard carbon + silicon (Example 15).

[0365] Example 16: Single-layer structure, first negative electrode active material uses soft carbon. The method is essentially the same as Example 12, except that the negative electrode active material in the lithiophilic composite layer is different, resulting in a different CB value. Example 16 uses soft carbon as the first negative electrode active material.

[0366] Example 17. Double-layer structure. The method is essentially the same as that of Example 12, except that a second active layer is added. Compared to Example 1, the difference is that the particle size of the lithium-philic nanoparticles is adjusted.

[0367] Example 18. Double-layer structure, adjusting the thickness of the second active layer. The method is basically the same as that of Example 17, except that the thickness of the second active layer is different.

[0368] Example 19: Dual-layer structure, changing the type of the second negative electrode active material. The method is essentially the same as that of Example 17, except that the negative electrode active material in the second active layer is replaced with hard carbon. In this case, the first negative electrode active material remains hard carbon.

[0369] Example 20: Dual-layer structure, changing the types of the first and second negative electrode active materials. The method is essentially the same as that of Example 17, except that the negative electrode active material in the first active layer is replaced with soft carbon, and the negative electrode active material in the second active layer is replaced with hard carbon.

[0370] Examples 21-23. Single-layer structures, varying the type of lithiophilic nanoparticles and the thickness of the lithiophilic composite layer. The method was essentially the same as that used in Example 2, except that different types of lithiophilic nanoparticle dispersions were used, the amounts of lithiophilic nanoparticles varied, and the thickness of the lithiophilic composite layer was varied. Furthermore, Examples 21 and 23 varied the particle size of the lithiophilic nanoparticles. Examples 21-23 used dispersions SL07, SL08, and SL09, respectively, and magnesium powders of varying particle sizes.

[0371] Example 24. Single-layer structure based on different CB values ​​The method is basically the same as that of Example 12, except that the CB value is 0.9 and the thickness of the first active layer is 150 μm.

[0372] Comparative Examples 1-3. Omitting the Lithiophilic Modification Step. Methods substantially identical to those of Examples 1, 2, and 16 were employed, with the exception that the Lithiophilic Modification step, i.e., step (3) in preparing the negative electrode sheet, was omitted, and no dispersion containing the Lithiophilic nanoparticles was added to the negative electrode slurry.

[0373] Comparative Example 4: Omitting the precursor of the lithium-philic nanoparticles and using a reducing agent solution. A method substantially the same as Example 2 was used, except that the lithium-philic nanoparticle dispersion SL01 was replaced with the control solution CT01, wherein CT01 contained CMC and glucose.

[0374] Comparative Example 5: Omitting the reducing agent and using silver nitrate solution: The method is basically the same as that of Example 2, except that blank solution CT02 (silver nitrate aqueous solution) is used instead of the lithiophilic nanoparticle dispersion SL01.

[0375] Comparative Examples 6-11. The lithiation step was omitted relative to Examples 6-8 and 18-20, and the dispersion containing the corresponding lithiation-affinity nanoparticles was not added to the negative electrode slurry.

[0376] Table 2. Preparation parameters of negative electrode sheet

[0377]

[0378] In Table 2, “ / ” indicates that the material is not added or does not exist. In the first negative electrode active material of Examples 13-15, the two materials are calculated by mass ratio, and “1:1” indicates that the mass ratio is 1:1.

[0379] Parameter and performance test analysis

[0380] 1. Lithium deposition morphology on the surface of the negative electrode

[0381] The CP-SEM test process for lithium deposition on the electrode surface is as follows: at 25°C, the secondary battery to be tested (full battery) is charged to 3.8V at a constant current of 1 / 3C, and the first cycle of fully charged battery cells is disassembled in a dry room or glove box to obtain the negative electrode for lithium deposition, and the residual lithium salt crystals on the surface of the electrode are rinsed with the main solvent of the electrolyte of the full battery mentioned above, and a 1cm×2cm area in the center of the negative electrode is taken and transferred in a vacuum transfer device or an inert atmosphere protection environment, and a cross-section is made at low temperature in an argon ion beam milling (CP) device. After cutting, it is attached to the cross-section sample stage with conductive tape and transferred to the vacuum chamber of a scanning electron microscope (SEM) for sample observation.

[0382] SEM test parameters: instrument model (Zeiss, Sigma 300), accelerating voltage 1.00 kV, magnification 10000, working distance 4.0 mm, ETD (SE) mode selected.

[0383] 2. Battery parameter and performance test

[0384] (1) Secondary battery CB value

[0385] The CB value of a secondary battery is equal to the ratio of the negative electrode surface capacity to the positive electrode surface capacity.

[0386] The negative electrode areal capacity is measured using the following method: A number (at least six) of small discs of negative electrode sheets are cut and the area A1 of each disc is calculated. A low current cycle with a cutoff voltage (0-2V) for lithium charge and discharge is then set. The negative electrode capacity is calibrated based on the corresponding 100 cycles of testing, resulting in the negative electrode sheet capacity C1. The areal capacity of the negative electrode sheet sample is C1 / A1. The average CB value of the multiple parallel samples is taken and recorded as the CB value of the negative electrode sheet.

[0387] Unless otherwise stated, the positive electrode surface capacity in each embodiment and comparative example is set to 3.5 mAh cm -2 .

[0388] For example, the negative electrode surface capacity of Example 1 is 2.1 mAh·cm -2 The positive electrode surface capacity is 3.5 mAh cm -2 The ratio is 0.6, that is, the CB value is 0.6.

[0389] (2) Battery cell energy density test

[0390] At the discharge platform (3.7V for NCM811 / Li), the ratio is calculated by multiplying the first-cycle discharge capacity (Ah) by the discharge voltage z and dividing it by the cell mass. In other words, energy density = first-cycle discharge capacity (Ah) × discharge platform (3.7V) / cell mass (M).

[0391] The test conditions are as follows: charge to 4.3V at 0.33C standard at room temperature, charge to 0.05C at 4.3V constant voltage, let it stand for 10 minutes, and then discharge to 2.8V at 0.33C (the discharge platform of NCM811 / Li is 3.7V). The discharge capacity (Ah) of the first week is recorded, the mass of the battery cell (M, in kg) is weighed, and the energy density of the battery cell is calculated.

[0392] (3) Battery cycle performance test

[0393] The charge and discharge cycle test was carried out using an electrochemical workstation. The prepared lithium-ion battery was charged and discharged at 1.5 mA cm at 25 °C. 2 The battery was charged at a constant current of 4.3 V and then at a constant voltage of 4.3 V until the current dropped to 0.3 mA cm -2 ; then 1.5mA·cm -2 The battery is discharged at a constant current to 2.8 V. The resulting capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery and record the discharge capacity C0 of the battery after the nth cycle. n , then the battery capacity retention rate P after each cycle n =C n / C0×100%(n is the number of cycles), with P1, P2...P n (When P n The curve of full battery capacity retention rate and cycle number is obtained by taking the cut-off point equal to or less than 60% as the ordinate and the corresponding cycle number as the abscissa.

[0394] The test results can be found in Table 3 under “Number of cycles (capacity decay to 60%)”, which can also be recorded as n 60％ .

[0395] For different battery samples, the "Coulombic efficiency after the first cycle" is positively correlated with the number of cycles when the capacity decays to the same percentage. The more cycles, the higher the corresponding Coulombic efficiency.

[0396] (4) Observation of the surface of the negative electrode

[0397] The secondary battery after 100 cycles in the above-mentioned "Battery Capacity Retention Test" was disassembled, and the surface morphology of the metal lithium negative electrode was observed under a metallographic optical microscope (Axio Observer Z1M) at a magnification of 1000 times to observe whether lithium dendrites were generated.

[0398] (5) Battery in-situ expansion test

[0399] The battery in-situ expansion test process is as follows: at 25°C, place the secondary battery to be tested (full battery) in the middle of the expansion force sensor of the in-situ expansion tester, set a preload of 100N, let it stand for 5 minutes, and record the initial thickness d0 of the battery cell. Charge it to 4.3V at a constant current of 1 / 3C, then charge it at a constant voltage of 4.3V to a current of 0.05C, let it stand for 5 minutes, and then discharge it to 2.8V at 1 / 3C. During the charge and discharge cycle, record the thickness change of the battery cell under constant pressure in situ. After completion, make a curve with time as the horizontal axis and the corresponding thickness change as the vertical axis. The thickness of the battery cell after n cycles (n is a positive integer) is recorded as d n .

[0400] The in-situ expansion rate of the cell during n cycles is equal to (d n -d0) / d0×100%. The “cell in-situ expansion rate” in Table 3 corresponds to 100 cycles.

[0401] (6) First week Coulomb efficiency test

[0402] The prepared lithium-ion battery was charged at 1.5 mA cm at 25 °C. -2 The battery was charged at a constant current of 4.3 V and then at a constant voltage of 4.3 V until the current dropped to 0.3 mA cm -2 , get the first week charge capacity (Cc1); then at 1.5mA·cm -2 The battery was discharged at a constant current to 2.0V to obtain the first-cycle discharge capacity (Cd1). The first-cycle efficiency of the lithium-ion battery was calculated using the following formula: First-cycle Coulombic efficiency of a lithium-ion battery = First-cycle discharge capacity (Cd1) / First-cycle charge capacity (Cc1). The test results are shown in Table 3 below.

[0403] The percentage of the first-cycle discharge capacity to the first-cycle charge capacity is the first-cycle coulombic efficiency.

[0404] Test results

[0405] The cross-sectional morphologies of the negative electrode sheets of Example 1 and Comparative Example 1 are shown in Figure 4. It can be seen that Comparative Example 1 exhibits severe lithium dendrite growth and a loose and porous cross-sectional morphology, while Example 1 exhibits uniform and dense lithium metal deposition, indicating that the nanoparticles employed have a significant effect in inducing lithium deposition.

[0406] The results of the in-situ expansion tests of the full-cells for Example 1 and Comparative Example 1 are shown in Figure 5. It can be seen that the expanded thickness of Comparative Example 1 is significantly greater than that of Example 1. During discharge, the expanded thickness of Example 1 decreases significantly (approximately approaching the thickness before charge), indicating that irreversible expansion is minimal and that lithium returns to the positive electrode material during discharge, while the irreversible expansion of Comparative Example 1 increases significantly after discharge. Figure 5 also clearly shows that the lithium deposited in Example 1 is more uniform and dense, presumably because the lithiophilic species can alloy with lithium, inducing some lithium precipitation within the electrode. The lithium deposited in Comparative Example 1 is loose and porous, with a thickness (18 μm) significantly greater than that of Example 1 (2 μm).

[0407] Examples 1 to 23 all have a lithiophilic substance uniformly dispersed in the first active layer, which can induce lithium deposition inside the electrode. Compared with the corresponding comparative examples without the introduction of lithium, while maintaining a relatively high energy density, the number of cycles attenuated to a certain percentage (such as 60%) is significantly extended, and the cycle life is significantly improved (so the coulombic efficiency after the first cycle is also significantly improved). In addition, the expansion of the electrode is significantly reduced, and the problem of lithium dendrites is significantly improved. For example, Example 1 is relative to Comparative Example 1, Example 2 is relative to Comparative Examples 2, 4, and 5, Example 16 is relative to Comparative Example 3, Examples 8-9 are relative to Comparative Examples 6-8, and Examples 18-20 are relative to Comparative Examples 9-11. Example 24 can achieve a significant extension of the cycle life and a significant reduction in electrode expansion while meeting a certain energy density.

[0408] Table 3.

[0409]

[0410] In Table 3, "cell energy density" is a preset value; the value obtained using the test method in Section 2(2) of the aforementioned "Parameter and Performance Test Analysis" deviates slightly from the preset value, but the fluctuation is not large. The fluctuation range between the preset value and the measured value of Examples 1-23 and Comparative Examples 1-11 is within the range of ±2Wh / kg. In addition, the preset value is mainly designed based on the lithiophilic composite layer (i.e., the first active layer).

[0411] Take Comparative Example 1 as an example. No lithium-philic nanoparticles are added to the first negative electrode slurry of Comparative Example 1. Compared with Example 1, when the negative electrode active material layer has a double-layer structure, the cycle performance of Comparative Example 1 is significantly worse, the pole piece expansion is significantly increased, and the lithium dendrite problem is serious. The reasons are speculated to be as follows: in the absence of lithium-philic substances, lithium metal exceeding the CB value will be precipitated on the surface of the pole piece. This part of lithium is prone to dendrite growth. Despite the induction effect of the second active substance, it will still be exposed to the electrolyte, resulting in a large amount of lithium loss. The volume expansion increases significantly during the cycle, and the degree of dendrite growth increases as the cycle progresses.

[0412] Take Comparative Example 2 as an example. No lithium-philic nanoparticles were added to the first negative electrode slurry of Comparative Example 2. Compared with Example 2, when the negative electrode active material layer had a single-layer structure, the cycle performance of Comparative Example 2 was significantly worse, the electrode expansion increased significantly, and the lithium dendrite problem was serious. The reasons are speculated to be as follows: in the absence of lithium-philic substances, lithium metal exceeding the CB value will precipitate on the surface of the electrode and be exposed to the electrolyte, causing a large amount of lithium loss. Moreover, due to the severe growth of these lithium dendrites, the volume expansion increased significantly during the cycle.

[0413] Take Comparative Example 3 as an example. No lithium-philic nanoparticles were added to the first negative electrode slurry of Comparative Example 3. Compared with Example 16, when the lithium-philic composite layer used soft carbon as the first negative electrode active material, the cycle performance of Comparative Example 3 was significantly worse, the pole piece expansion increased significantly, and the lithium dendrite problem was serious. The reasons are speculated to be as follows: Due to the low specific capacity of soft carbon, most of the lithium was precipitated outside the host material. Although soft carbon as a base layer can induce the precipitated lithium metal to deposit more uniformly and densely, there is still a large amount of lithium metal exposed to the electrolyte, resulting in the loss of lithium metal and electrolyte, thus causing a sharp deterioration in the cycle performance, a high volume expansion rate of the battery cell, and severe dendrite growth during the cycle.

[0414] Take Comparative Example 4 as an example. In Comparative Example 4, the first negative electrode slurry is prepared by using the dispersion CT01 in which the nano-lithiophilic particle precursor is omitted, which is equivalent to adding a reducing agent solution to the negative electrode slurry. The reducing agents are CMC and glucose. Compared with Example 2, when the negative electrode active material layer has a single-layer structure, the cycle performance of Comparative Example 4 is significantly worse, the pole piece expansion is significantly increased, and the lithium dendrite problem is serious. The reasons are speculated to be as follows: in the absence of a lithium-philic substance, lithium metal exceeding the CB value will precipitate on the pole piece surface. This part of lithium will be exposed to the electrolyte, causing a large amount of lithium loss and easy dendrite growth. The volume expansion increases significantly during the cycle. As the cycle progresses, the degree of dendrite growth is significantly aggravated, and the cycle life deteriorates sharply.

[0415] Take Comparative Example 5 as an example. In Comparative Example 5, the first negative electrode slurry is prepared by using the dispersion CT02 in which the reducing agent is omitted, which is equivalent to adding a silver nitrate solution to the negative electrode slurry. Compared with Example 2, when the negative electrode active material layer has a single-layer structure, the cycle performance of Comparative Example 5 is significantly worse, the pole piece expansion is significantly increased, and the lithium dendrite problem is serious. The reasons are speculated to be as follows: the silver nitrate solution cannot be reduced, and it is very easy to react with the CMC in the negative electrode slurry during the mixing process in the negative electrode slurry to agglomerate. After the battery cell is made, in the absence of lithium-philic substances, lithium metal exceeding the CB value will precipitate on the surface of the pole piece. This part of lithium will be exposed to the electrolyte, causing a large amount of lithium loss and easy dendrite growth. The volume expansion increases significantly during the cycle. As the cycle progresses, the degree of dendrite growth is significantly aggravated, and the cycle life deteriorates sharply.

[0416] It should be noted that for other applicable types of lithium-philic nanoparticles, when preparing the negative electrode active material layer of the negative electrode plate, the corresponding dispersion is not added to the first negative electrode slurry to obtain a lithium-ion secondary battery (including but not limited to Example 24 using different CB value designs, Examples 21-23 using nano-magnesium particles as lithium-philic nanoparticles, and Example 11 using Ag+Au mixed particles as lithium-philic nanoparticles), that is, when the lithium-philic nanoparticles described in this application are not introduced into the negative electrode active material layer, according to a large number of experimental explorations by the inventors of this application, the experimental results also found that the cycle life is reduced (the number of cycles that decay to a certain percentage (such as 60%) is reduced, and the coulombic efficiency after the first cycle is also reduced), and the expansion of the plate increases, and the lithium dendrite problem is aggravated.

[0417] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0418] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and within the scope of the technical solution of the present application, embodiments that have substantially the same structure as the technical idea and exert the same effect are all included in the technical scope of the present application. The above-mentioned embodiments only express several embodiments of the present application, and their descriptions are relatively detailed, but they cannot be understood as limiting the scope of the patent. In addition, without departing from the scope of the subject matter of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of constructing by combining some of the constituent elements in the embodiments are also included in the scope of the present application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several modifications and improvements can be made, which all fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be based on the attached claims, and the description and drawings may be used to explain the content of the claims.

Claims

1. A negative electrode sheet comprising a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active substance and lithium-philic nanoparticles, wherein the lithium-philic nanoparticles are capable of alloying with lithium.

2. The negative electrode sheet according to claim 1, wherein: At least a portion of the lithium-philic nanoparticles are distributed on a portion of the surface of the negative electrode active material.

3. The negative electrode sheet according to claim 1 or 2, wherein: The lithiophilic nanoparticles comprise a lithiophilic metal; Optionally, the lithiophilic metal includes one or more metals from the following group: Ag, In, Mg, Zn, Au and Sn, and alloys of any of the foregoing metal elements.

4. The negative electrode sheet according to claim 3, wherein: The lithiophilic metal includes one or more metals in the following group: Ag, In and Mg, and alloys of any of the foregoing metal elements; or The lithiophilic metal includes one or more metals from the following group: Zn, Au and Sn, and alloys of any of the foregoing metal elements.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The lithium-philic nanoparticles n 50≤500nm; Optionally, the D of the lithium-philic nanoparticles n 50 is selected from 10 nm to 300 nm; Further optionally, the D of the lithium-philic nanoparticles n 50 is selected from 10 nm to 200 nm; Further optionally, the D of the lithium-philic nanoparticles n 50 is selected from 10 nm to 100 nm; Further optionally, the D of the lithium-philic nanoparticles n 50 is selected from 20 nm to 100 nm; Alternatively, the lithium-philic nanoparticles have a D n 50 is selected from 5 nm to 320 nm; Alternatively, the lithium-philic nanoparticles have a D n 50 is selected from 5nm to 120nm.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The negative electrode active material layer includes an alloy formed by the lithium-philic nanoparticles and lithium.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The negative electrode active material layer includes a lithiophilic composite layer, which is a structural layer in which the lithiophilic nanoparticles are distributed in the thickness direction of the negative electrode active material layer.

8. The negative electrode sheet according to claim 7, wherein: The portion of the negative electrode active material distributed in the lithiophilic composite layer is recorded as the first negative electrode active material; Wherein, the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material is ≤6%; Optionally, the mass percentage of the lithium-philic nanoparticles relative to the first negative electrode active material is selected from 1% to 5%.

9. The negative electrode sheet according to claim 8, wherein: The sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥90%; Optionally, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥92%; Further optionally, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥94%; Further optionally, the sum of the mass proportions of the lithium-philic nanoparticles and the first negative electrode active material in the lithium-philic composite layer is ≥95%.

10. The negative electrode sheet according to any one of claims 7 to 9, wherein: The thickness of the lithium-philic composite layer is selected from 5 μm to 150 μm; Optionally, the thickness of the lithiophilic composite layer is selected from 20 μm to 140 μm; Further optionally, the thickness of the lithiophilic composite layer is selected from 20 μm to 120 μm; Further optionally, the thickness of the lithiophilic composite layer is selected from 20 μm to 100 μm; Alternatively, the thickness of the lithiophilic composite layer is selected from 10 μm to 150 μm; Alternatively, the thickness of the lithiophilic composite layer is selected from 10 μm to 125 μm; Alternatively, the thickness of the lithiophilic composite layer is selected from 10 μm to 100 μm.

11. The negative electrode sheet according to any one of claims 8 to 10, wherein: The first negative electrode active material includes a carbon-based material; Optionally, the first negative electrode active material includes a graphite-like material; Further optionally, the first negative electrode active material includes one or more of hard carbon and soft carbon; Further optionally, the first negative electrode active material includes hard carbon.

12. The negative electrode sheet according to claim 11, wherein: In the lithium-philic composite layer, the mass proportion of the graphite-like material in the first negative electrode active material is ≥50%; Optionally, the mass proportion of the graphite-like material in the first negative electrode active material is selected from 80% to 100%; Optionally, the mass proportion of the graphite-like material in the first negative electrode active material is selected from 90% to 100%; Optionally, the mass proportion of the graphite-like material in the first negative electrode active material is selected from 95% to 100%; Optionally, the mass proportion of the graphite-like material in the first negative electrode active material is 100%.

13. The negative electrode sheet according to claim 11 or 12, wherein: In the lithium-philic composite layer, the mass proportion of hard carbon in the first negative electrode active material is ≥50%; Optionally, the mass proportion of hard carbon in the first negative electrode active material is selected from 80% to 100%; Further optionally, the mass proportion of hard carbon in the first negative electrode active material is selected from 90% to 100%; Further optionally, the mass proportion of hard carbon in the first negative electrode active material is selected from 95% to 100%; Further optionally, the mass proportion of hard carbon in the first negative electrode active material is 100%.

14. The negative electrode sheet according to any one of claims 7 to 13, wherein: The negative electrode plate includes a negative electrode current collector, and the negative electrode active material layer is disposed on at least one side of the negative electrode current collector; The negative electrode active material layer further includes a second active layer, which is arranged on a side of the lithium-philic composite layer away from the negative electrode current collector. The second active layer includes a second negative electrode active material and does not include the lithium-philic nanoparticles.

15. The negative electrode sheet according to claim 14, wherein: The second negative electrode active material includes a graphite-like material; Optionally, the second negative electrode active material includes soft carbon.

16. The negative electrode sheet according to claim 15, wherein: In the second active layer, the mass proportion of soft carbon in the second negative electrode active material is ≥50%; Optionally, the mass proportion of soft carbon in the second negative electrode active material is selected from 80% to 100%; Further optionally, the mass proportion of soft carbon in the second negative electrode active material is selected from 90% to 100%; Further optionally, the mass proportion of the soft carbon in the second negative electrode active material is selected from 95% to 100%; Further optionally, the mass proportion of the soft carbon in the second negative electrode active material is 100%.

17. The negative electrode sheet according to any one of claims 14 to 16, wherein: The thickness of the second active layer is less than the thickness of the lithium-philic composite layer; Optionally, the thickness of the second active layer is selected from 5 μm to 25 μm; Further optionally, the thickness of the second active layer is selected from 10 μm to 20 μm; Alternatively, the thickness of the second active layer is selected from 8 μm to 22 μm; Alternatively, the thickness of the second active layer is selected from 8 μm to 12 μm.

18. A secondary battery comprising a positive electrode sheet, a separator, and the negative electrode sheet according to any one of claims 1 to 17, wherein: The separator is located between the positive electrode sheet and the negative electrode sheet.

19. The secondary battery according to claim 18, wherein The CB value of the secondary battery is less than 1; Optionally, the CB value of the secondary battery is selected from 0.1 to 0.9; Optionally, the CB value of the secondary battery is selected from 0.15 to 0.9; Among them, the side of the negative electrode sheet facing the positive electrode sheet includes the negative electrode active material layer, and the side of the positive electrode sheet facing the negative electrode sheet includes the positive electrode active material layer, and the CB value is the ratio of the capacity of the negative electrode active material layer and the positive electrode active material layer arranged relatively under the same area.

20. The secondary battery according to claim 18 or 19, wherein The secondary battery is a lithium-ion secondary battery; Furthermore, the positive electrode sheet contains a positive electrode active material; Optionally, the positive electrode active material includes a lithium ion material; wherein the lithium ion material includes one or more of the following substances: lithium-containing phosphate, lithium transition metal oxide, and a substance composed of any of the foregoing substances and a doping element; Further optionally, the positive electrode active material includes one or more of the following substances: lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, and a substance composed of any of the foregoing substances and doping elements; The doping elements in any positive electrode active material independently include one or more transition metal elements and non-transition metal elements.

21. An electrical device comprising at least one of the negative electrode sheet according to any one of claims 1 to 17 and the secondary battery according to any one of claims 18 to 20.

22. A method for preparing a negative electrode sheet, comprising the following steps: A first negative electrode slurry comprising a first negative electrode active material and lithium-philic nanoparticles is prepared; wherein, The lithium-philic nanoparticles are as defined in any one of claims 1, 3 to 5; coating the first negative electrode slurry on at least one surface of a negative electrode substrate, drying the negative electrode slurry to form a lithiophilic composite layer, and preparing a lithiophilic substrate; The lithiophilic substrate is cold pressed to prepare a negative electrode sheet; alternatively, a second negative electrode slurry containing a second negative electrode active material is coated on one surface of the lithiophilic substrate including the lithiophilic composite layer, dried, and cold pressed to form a second active layer to prepare a negative electrode sheet.

23. The preparation method according to claim 22, wherein The step of preparing the first negative electrode slurry comprises mixing the first negative electrode active material and a dispersion containing the lithium-philic nanoparticles; wherein the concentration of the lithium-philic nanoparticles in the dispersion is selected from 100 μg / L to 1000 μg / L; Optionally, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 200 μg / L to 800 μg / L; Further optionally, the concentration of the lithium-philic nanoparticles in the dispersion is selected from 400 μg / L to 500 μg / L.

24. The preparation method according to claim 22 or 23, wherein Satisfy any one or more of the following characteristics: The step of preparing the first negative electrode slurry further includes adding a conductive agent, a binder and a solvent; The definition of the first negative electrode active material in the first negative electrode slurry is consistent with the definition of the first negative electrode active material in the lithium-philic composite layer in claim 8 or 11; The definition of the second negative electrode active material in the second negative electrode slurry is consistent with the definition of the second negative electrode active material in the second active layer in claim 14 or 15; The negative electrode plate is defined in any one of claims 1 to 17.

25. The preparation method according to claim 23 or 24, wherein The dispersion is prepared by a method comprising the following steps: preparing a mixed solution containing a metal precursor, a reducing agent, and an optional dispersant; wherein the metal precursor comprises a salt precursor of the lithium-philic nanoparticles; and The mixed solution is subjected to a reduction reaction to convert the salt-type precursor into the lithium-philic nanoparticles.

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