Negative electrode sheet, method for manufacturing the same, secondary battery, and power storage device

Abstract

The application provides a negative electrode sheet, which comprises a metal layer and a silicon interface layer located on at least one side of the metal layer, wherein the silicon interface layer comprises a material with a general formula of SiO x , wherein 0<=x<=2. The silicon interface layer has a higher negative electrode potential than the metal layer, can inhibit the formation and growth of dendrites, and is beneficial to the improvement of battery cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a negative electrode sheet, a preparation method, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, with the wide application of secondary batteries in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc., the market requirements for the performance of secondary batteries are also becoming higher and higher.

[0003] Compared with the commonly used negative electrode material graphite, metal negative electrodes (such as lithium metal) have lower potential and higher theoretical capacity, and are very potential negative electrode materials. SUMMARY

[0004] In view of the problems in the background art, the present application provides a negative electrode sheet, which aims to inhibit the formation of dendrites on the metal electrode and improve the cycle stability of the battery.

[0005] The first aspect of the present application provides a negative electrode sheet, comprising a metal layer and a silicon interface layer located on at least one side of the metal layer, the silicon interface layer comprising a material with a general formula of SiO x , wherein 0≤x≤2.

[0006] The silicon interface layer has a higher negative electrode potential than the metal layer, which can inhibit the growth of dendrites and improve the cycle performance of the battery.

[0007] In any embodiment, the silicon interface layer comprises a material with a general formula of SiO x , wherein 0

[0008] The silicon-oxygen material will be lithiated during the charge and discharge cycle, and can form a large amount of irreversible Li4SiO4. This substance has a Young's modulus as high as 8.81 Gpa, which can inhibit the growth of lithium dendrites through its high mechanical strength and improve the cycle stability of the battery. Moreover, the silicon-oxygen material also has a certain capacity, which can improve the capacity level of the battery while improving the cycle stability of the battery.

[0009] In any embodiment, the thickness of the silicon interface layer is 25 nm-1000 nm, which can be 50 nm-200 nm.

[0010] The thickness of the silicon interface layer is within a proper range, which can effectively protect the metal layer and inhibit the generation of dendrites, and can reduce the decline of the conductive performance of the negative electrode sheet, the increase of the resistance and the decline of the unit gram capacity of the battery caused by the over-thickness of the silicon interface layer, and can reduce the risk of brittle fracture of the negative electrode sheet caused by over-thickness, and improve the comprehensive performance of the battery.

[0011] In any embodiment, the oxygen content of the silicon interface layer near the metal layer is lower than that far from the metal layer in the thickness direction of the silicon interface layer. The oxygen content of the silicon interface layer near the metal layer is lower than that far from the metal layer in the thickness direction of the silicon interface layer, which is beneficial to the characteristics of different materials, and the comprehensive improvement of the cycle stability and capacity level of the battery.

[0012] In any embodiment, the silicon interface layer sequentially includes a silicon layer and a silicon-oxygen layer in the thickness direction of the silicon interface layer from near the metal layer to far from the metal layer, the silicon layer includes elemental silicon, and the silicon-oxygen layer includes a material with a general formula of SiO x , wherein 0 < x < 2.

[0013] The irreversible Li4SiO4 formed in the battery cycle process of the silicon-oxygen layer 622 can effectively solve the problem of large expansion rate of elemental silicon while inhibiting the growth of lithium dendrites, fully exerting the characteristics of high capacity of elemental silicon, so that the battery has high cycle performance and higher capacity level.

[0014] In any embodiment, the silicon interface layer sequentially includes a silicon-oxygen layer and a silicon dioxide layer in the thickness direction of the silicon interface layer from near the metal layer to far from the metal layer, the silicon-oxygen layer includes a material with a general formula of SiO x , wherein 0 < x < 2.

[0015] Compared with the silicon-oxygen material, the silicon dioxide layer can effectively inhibit the growth of lithium dendrites at a low thickness. The surface pore structure of the silicon-oxygen layer can be fully utilized by arranging the silicon dioxide layer on the silicon-oxygen layer. Compared with directly depositing the silicon dioxide layer on the metal layer, the surface pore structure of the silicon-oxygen layer can reduce the density of the silicon dioxide layer, inhibit the growth of dendrites, reduce the large decline of electrical conductivity caused by excessive density of the silicon dioxide layer, improve the cycle stability of the battery, and will not cause a large decline in the capacity level of the battery.

[0016] In any embodiment, the silicon interface layer sequentially includes a silicon layer, a silicon-oxygen layer and a silicon dioxide layer in the thickness direction of the silicon interface layer from near the metal layer to far from the metal layer, the silicon layer includes amorphous silicon, and the silicon-oxygen layer includes a material with a general formula of SiO x , wherein 0 < x < 2.

[0017] The superposition of the silicon layer, the silicon-oxygen layer and the silicon dioxide layer can give full play to the advantages of each layer, and realize the comprehensive improvement of the cycle stability and the capacity level of the battery through the mutual cooperation of each layer.

[0018] In any embodiment, in the thickness direction of the silicon interface layer from the position close to the metal layer to the position far from the metal layer, the silicon interface layer comprises SiOx1 layer, SiOx2 layer, …, SiOx n layer in sequence, wherein 0 < x1 < x2 < … < x n <2, n ≥ 2.

[0019] The silicon content of the silicon interface layer is high at the position close to the metal layer, which can give full play to the characteristics of high capacity of the material; the oxygen content is high at the position far from the metal layer, the negative electrode potential is increased, and the content of Li4SiO4 generated is increased, which is beneficial to inhibit the growth of dendrites.

[0020] In any embodiment, the negative electrode sheet satisfies at least one of the following conditions:

[0021] (i) the ratio of the thickness of the silicon layer to the thickness of the silicon-oxygen layer is 4-15;

[0022] (ii) the thickness of the silicon layer is 10 nm-100 nm;

[0023] (iii) the thickness of the silicon-oxygen layer is 25 nm-150 nm;

[0024] (iv) the thickness of the silicon dioxide layer is 1 nm-10 nm.

[0025] In any embodiment, the metal layer comprises at least one of lithium metal, lithium alloy, sodium metal and sodium alloy.

[0026] In any embodiment, the silicon interface layer is prepared by at least one of chemical vapor deposition, atomic layer deposition, evaporation method and magnetron sputtering method.

[0027] The application provides a preparation method of a negative electrode sheet, which comprises: depositing a silicon interface layer on at least one side of a metal layer to prepare the negative electrode sheet, wherein the silicon interface layer comprises a material with a general formula of SiO x , wherein 0 ≤ x ≤ 2.

[0028] In any embodiment, the preparation method comprises: introducing a gas containing a silicon source or a mixed gas containing an oxygen source and a silicon source, and preparing a silicon interface layer by chemical vapor deposition; optionally, the oxygen source comprises N2O, and the silicon source comprises SiH4.

[0029] The silicon interface layer is prepared by chemical vapor deposition. The composition of the silicon interface layer can be adjusted by adjusting the flow rates of the oxygen source and the silicon source in real time, so that the formation of the battery has higher efficiency. Compared with other preparation methods, the flow rates of raw materials are controllable, and the composition and thickness of the silicon interface layer can be accurately controlled.

[0030] In any embodiment, the preparation method includes that the volume flow rate ratio M of the oxygen source to the silicon source is 0

[0031] In any embodiment, during the preparation of the silicon interface layer, the ratio M of the oxygen source to the silicon source is increased, so that the oxygen content of the silicon interface layer near the metal layer is lower than that far from the metal layer in the thickness direction of the silicon interface layer.

[0032] In any embodiment, the preparation method includes: introducing the silicon source for deposition; after a period of deposition, introducing the oxygen source and the silicon source for continuous deposition, wherein the volume flow rate ratio M of the oxygen source to the silicon source is 0

[0033] In any embodiment, the preparation method includes: introducing the oxygen source and the silicon source for deposition, wherein the volume flow rate ratio M of the oxygen source to the silicon source is 0

[0034] In any embodiment, the preparation method includes: introducing the silicon source for deposition; after a period of deposition, introducing the oxygen source and the silicon source for deposition, wherein the volume flow rate ratio M of the oxygen source to the silicon source is 0

[0035] In any embodiment, the preparation method includes: gradually increasing the volume flow rate ratio M of the oxygen source to the silicon source during the process of introducing the oxygen source and the silicon source for deposition.

[0036] The third aspect of the present application provides a secondary battery including the negative electrode tab of the first aspect or the negative electrode tab prepared by the preparation method of the second aspect.

[0037] In any embodiment, the secondary battery includes an electrolyte, and the silicon interface layer is located between the electrolyte and the metal layer.

[0038] The fourth aspect of the present application provides an electric device including the secondary battery of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a schematic diagram of a negative electrode tab according to an embodiment of the present application;

[0040] Figure 2 is a schematic view of a negative electrode tab of an embodiment of the present application;

[0041] Figure 3 is a schematic view of a negative electrode tab of an embodiment of the present application;

[0042] Figure 4 is a schematic view of a negative electrode tab of an embodiment of the present application;

[0043] Figure 5 is a schematic view of a negative electrode tab of an embodiment of the present application;

[0044] Figure 6 is a schematic view of a secondary battery of an embodiment of the present application;

[0045] Figure 7 is an exploded view of a secondary battery of an embodiment of the present application; Figure 6

[0046] Figure 8 is a schematic view of an electrical device of an embodiment of the present application.

[0047] Reference Signs:

[0048] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 sodium-ion battery; 51 housing; 52 electrode assembly; 53 cover plate; 6, 6-1, 6-2, 6-3, 6-4 negative electrode tab; 61 metal layer; 62, 62-1, 62-2, 62-3, 62-4 silicon interface layer; 621 silicon layer; 622 silicon-oxygen layer; 6221 SiO x1 layer; 6222 SiO x2 layer; 623 silicon dioxide layer. DETAILED DESCRIPTION

[0049] Hereinafter, embodiments of the negative electrode tab, the manufacturing method, the secondary battery, and the electrical device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there are cases where unnecessary detailed explanations are omitted. For example, there are cases where detailed explanations of matters that are well known, repeated explanations of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0050] ​The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges are also intended to include any and all sub-ranges of the range, i.e., all combinations of any two of the range limits, unless otherwise indicated. For example, a range of "1 to 10" is intended to include any number from 1 to 10, including the integers 1 and 10. Unless otherwise indicated, the use of "or" in the disclosed aspects herein is the inclusive, and not the exclusive use. Only the context, and not the number of times an item is used, can determine that it is the exclusive use. For example, the phrase "A uses B or C" means that A can use B, or A can use C, or A can use both B and C. Also, the use of the term "one" or "a" or "the" is intended to be singular as well as plural, unless only the singular form is used. For example, the phrase "one or more of A, B, and C" means that A, B, or C can be present, and that one of A, B, and C can be present, and that two of A, B, and C can be present, and that all of A, B, and C can be present.

[0051] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0052] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0053] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0054] Unless otherwise specified, "includes" and "comprises" mentioned in the present application are open-ended, and can also be closed. For example, "includes" and "comprises" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0055] 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". More specifically, 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).

[0056] Metal anodes are highly promising anode materials. Taking lithium metal as an example, it has the lowest voltage and a theoretical capacity of up to 3860 mAh / g, which is 10 times that of graphite anode materials. However, during cycling, metal anodes are prone to forming a large number of dendrites on the electrode surface, causing membrane puncture and resulting in direct contact and short circuit between the positive and negative electrodes, leading to serious safety accidents.

[0057] [Negative electrode plate]

[0058] Based on this, such as Figure 1 As shown, this application provides a negative electrode 6, including a metal layer 61 and a silicon interface layer 62 located on at least one side of the metal layer 61. The silicon interface layer 62 comprises silicon oxide (SiO₂). x The material is given by , where 0 ≤ x ≤ 2.

[0059] The structure of the negative electrode sheet can be characterized by any method known in the art. As an example, the morphology of the ion-polished cross-section of the negative electrode sheet can be observed by scanning electron microscopy, and the material composition of the cross-section of the negative electrode sheet can be tested by energy dispersive spectroscopy.

[0060] In some embodiments, the metal layer 61 includes at least one of lithium metal, lithium alloy, sodium metal, and sodium alloy.

[0061] A lithium alloy is an alloy comprising lithium and at least one other metal. In some embodiments, the lithium content in the lithium alloy may be 90 wt% or higher, 95 wt% or higher, or 99 wt% or higher. For example, the lithium content in the lithium alloy may be 97 wt%, 97.5 wt%, 98 wt%, 98.5 wt%, 99.1 wt%, 99.3 wt%, 99.5 wt%, 99.7 wt%, or 99.9 wt%, etc. The lithium alloy may optionally include one or more of the following: lithium-copper alloy, lithium-indium alloy, lithium-zinc alloy, lithium-magnesium alloy, lithium-tin alloy, and lithium-silver alloy.

[0062] A sodium alloy is an alloy comprising sodium and at least one other metal. As a non-limiting example, a sodium alloy may be sodium with cesium, sodium with rubidium, or a mixture thereof.

[0063] In some embodiments, the silicon interface layer 62 comprises silicon, silicon dioxide, and a material of the general formula SiO2. xAt least one of the silicon-oxygen materials in the range of (0 < x < 2). It is understood that the above-mentioned materials can be located in the same layer or can be arranged in layers to form a silicon interface layer.

[0064] In some embodiments, the silicon interface layer 62 comprises silicon. In some embodiments, the silicon is amorphous silicon. Silicon has a higher electrode potential than lithium, which can reduce the probability of lithium dendrite formation by increasing the potential. Moreover, silicon has a larger negative electrode capacity than lithium, which can further improve the battery capacity.

[0065] In some embodiments, the silicon interface layer 62 comprises silicon of the general formula SiO x The silicon-oxygen material, where 0 < x < 2. In some embodiments, the silicon interface layer comprises a material of the general formula SiO. x The silicon-oxygen material, x can be selected as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or any value between them.

[0066] During charge-discharge cycles, silicon-oxygen materials undergo lithiation, forming a large amount of irreversible Li4SiO4. This material has a Young's modulus as high as 8.81 GPa, which can suppress the growth of lithium dendrites through its high mechanical strength, thereby improving the cycle stability of the battery. Moreover, silicon-oxygen materials also possess a certain capacity, which can improve the battery's capacity level while simultaneously enhancing its cycle stability.

[0067] In some embodiments, the silicon interface layer 62 comprises silicon of the general formula SiO x The silicon-oxygen material, where 0.7 < x < 1.5.

[0068] When the ratio of oxygen to silicon in silicon-oxygen materials is between 0.7 and 1.5, the materials possess both high specific capacity and low expansion rate, which is beneficial for further improving the cycle stability and capacity of the battery.

[0069] In some embodiments, the silicon interface layer 62 comprises silicon dioxide.

[0070] Silicon dioxide is a high-strength insulating material that provides almost no capacity. The Li4SiO4 generated during battery cycling is more dense and has higher mechanical strength. Compared with silicon-oxygen materials, it can more effectively suppress dendrite growth, stabilize the negative electrode structure, and improve the overall mechanical strength at low addition levels.

[0071] In summary, the silicon interface layer has a higher negative electrode potential than lithium metal, which can suppress the formation and growth of dendrites and improve the battery cycle performance.

[0072] In some embodiments, the thickness of the silicon interface layer 62 is 25nm-1000nm, and optionally 50nm-200nm.

[0073] In some embodiments, the thickness of the silicon interface layer 62 may be selected as 25nm, 50nm, 75nm, 100nm, 125nm, 150nm, 175nm, 200nm or any value thereof.

[0074] The thickness of the silicon interface layer 62 is within a suitable range, which can effectively protect the metal layer 61 and suppress the formation of dendrites. It can also reduce the decrease in conductivity, increase in resistance, and decrease in battery capacity caused by excessive thickness of the silicon interface layer 62. Furthermore, it can reduce the risk of brittle fracture of the negative electrode 6 due to excessive thickness and improve the overall performance of the battery.

[0075] In some embodiments, in the thickness direction of the silicon interface layer, the oxygen content of the silicon interface layer near the metal layer is lower than the oxygen content away from the metal layer.

[0076] The oxygen content at different locations in the silicon interface layer can be measured using a combination of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). For example, a cross-sectional image along the thickness direction of the electrode is obtained using an SEM, and the relative distribution of oxygen at different locations in the negative electrode is measured using the line scan, area scan, or point scan modules of the EDS, thereby determining the oxygen content at different locations in the negative electrode.

[0077] In the thickness direction of the silicon interface layer, the oxygen content near the metal layer is lower than that far from the metal layer, which is beneficial to leveraging the characteristics of different materials and achieving a comprehensive improvement in battery cycle stability and capacity.

[0078] In some implementations, such as Figure 2 As shown, in the negative electrode 6-1, in the silicon interface layer thickness direction from near the metal layer 61 to away from the metal layer 61, the silicon interface layer 62-1 sequentially includes a silicon layer 621 and a silicon oxide layer 622. The silicon layer 621 includes elemental silicon, and the silicon oxide layer 622 includes silicon oxide with the general formula SiO2. x The material is given by , where 0 < x < 2.

[0079] In some implementations, elemental silicon includes crystalline silicon and amorphous silicon.

[0080] Crystalline silicon includes monocrystalline silicon and polycrystalline silicon. The atomic arrangement of crystalline silicon is similar to that of diamond, forming a long-range ordered structure. Amorphous silicon is composed of atoms with short-range order and long-range disorder, and the bonding between atoms is very similar to that of crystalline silicon, forming a covalent random network structure.

[0081] The irreversible Li4SiO4 formed by the silicon oxide layer 622 during battery cycling not only inhibits lithium dendrite growth but also effectively solves the problem of high expansion rate of elemental silicon, giving full play to the high capacity characteristics of elemental silicon, so that the battery has a higher capacity level while having high cycle performance.

[0082] In some implementations, such as Figure 3 As shown, in the negative electrode 6-2, in the silicon interface layer thickness direction from near the metal layer 61 to away from the metal layer 61, the silicon interface layer 62-2 sequentially includes a silicon oxide layer 622 and a silicon dioxide layer 623. The silicon oxide layer 622 includes silicon oxide with the general formula SiO2. x The material is given by , where 0 < x < 2.

[0083] In some embodiments, the silicon dioxide layer 623 comprises silicon dioxide.

[0084] Compared to silicon-oxygen materials, the silicon dioxide layer 623 can effectively suppress lithium dendrite growth even at a low thickness. Depositing the silicon dioxide layer 623 on the silicon-oxygen layer 622 allows full utilization of the surface porosity of the silicon-oxygen layer 622. Compared to directly depositing the silicon dioxide layer 623 on the metal layer 61, the surface porosity of the silicon-oxygen layer 622 allows for a decrease in the density of the silicon dioxide layer 623. This suppresses dendrite growth while reducing the significant decrease in conductivity caused by excessive density of the silicon dioxide layer 623, thus improving battery cycle stability without causing a significant drop in battery capacity.

[0085] In some implementations, such as Figure 4 As shown, in the negative electrode 6-3, in the silicon interface layer thickness direction from near the metal layer 61 to away from the metal layer 61, the silicon interface layer 62-3 sequentially includes a silicon layer 621, a silicon oxide layer 622, and a silicon dioxide layer 623. The silicon layer 621 includes elemental silicon, and the silicon oxide layer 622 includes silicon dioxide of the general formula SiO2. x The material is given by , where 0 < x < 2.

[0086] The stacked arrangement of silicon layer 621, silicon oxide layer 622 and silicon dioxide layer 623 can not only give full play to the advantages of each layer, but also achieve a comprehensive improvement in battery cycle stability and capacity level through the mutual cooperation of each layer.

[0087] In some embodiments, the silicon interface layer 62 sequentially comprises a SiOx1 layer, a SiOx2 layer, ..., a SiOx layer in the direction of thickness from near the metal layer 61 to away from the metal layer 61. n Layers, where 0 < x1 < x2 < ... < x n<2, n≥2. It can be understood that the oxygen content in the silicon-oxygen material can be continuously changed or increased in stages. The silicon interface layer 62 has a high silicon content near the metal layer 61, which can fully utilize the high capacity characteristics of the material; and has a high oxygen content away from the metal layer 61, which increases the negative electrode potential and the content of Li4SiO4 generated, thereby helping to inhibit the growth of dendrites.

[0088] In some embodiments, as shown in FIG. 6A, the silicon interface layer 62-4 in the negative electrode tab 6-4 includes, in order from the position close to the metal layer 61 to the position away from the metal layer 61, a silicon layer 621, a SiOx1 layer 6221, a SiOx2 layer 6222, and a silicon dioxide layer 623, the silicon layer 621 includes elemental silicon, and 0 < x1 < x2 < 2. Figure 5 In some embodiments, the ratio of the thickness of the silicon layer to the thickness of the silicon-oxygen layer is 4-15.

[0089] In some embodiments, the ratio of the thickness of the silicon layer to the thickness of the silicon-oxygen layer is selected from 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or any value therebetween.

[0090] Controlling the ratio of the thickness of the silicon layer to the thickness of the silicon-oxygen layer within the above range can improve the capacity of the battery while inhibiting the growth of lithium dendrites and the expansion of the silicon material through the high modulus of the silicon-oxygen layer, and at the same time improve the cycle stability and electrochemical performance of the battery.

[0091] In some embodiments, the thickness of the silicon layer is 10 nm-100 nm.

[0092] In some embodiments, the thickness of the silicon layer is selected from 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any value therebetween.

[0093] Controlling the thickness of the silicon layer within this range can fully utilize the high capacity characteristics of elemental silicon and reduce the negative impact of the expansion of elemental silicon on the cycle performance of the battery.

[0094] In some embodiments, the thickness of the silicon-oxygen layer is 25 nm-150 nm.

[0095] In some embodiments, the thickness of the silicon-oxygen layer is selected from 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or any value therebetween.

[0096] In some embodiments, the thickness of the silicon-oxygen layer is selected from 25 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, or any value therebetween.

[0097] Controlling the thickness of the silicon oxide layer in this range can effectively suppress dendrites without sacrificing capacity and without causing too much negative impact on the conduction of lithium ions in the negative electrode sheet.

[0098] In some embodiments, the thickness of the silicon oxide layer is 1 nm-10 nm.

[0099] In some embodiments, the thickness of the silicon oxide layer is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any value therebetween.

[0100] Controlling the thickness of the silicon oxide layer in this range can effectively suppress dendrites without sacrificing capacity and without causing too much negative impact on the conduction of lithium ions in the negative electrode sheet.

[0101] In some embodiments, the silicon interface layer is prepared by at least one of a chemical vapor deposition method, an atomic layer deposition method, an evaporation method, and a magnetron sputtering method.

[0102] The chemical vapor deposition method is a chemical vapor reaction growth method. Under different temperature fields and different vacuum degrees, the compound or elemental reaction source gas containing the elements constituting the thin film material is introduced into the reaction chamber containing the metal layer, and the decomposition, desorption, and combination reactions are carried out at the interface between the metal layer and the gas phase to generate new solid substances and deposit them on the surface of the metal layer to form a uniform thin film. By controlling the reaction temperature, reaction source gas composition, concentration, pressure, and other parameters, the organization structure and composition of the thin film can be easily controlled, the mechanical properties and chemical properties can be changed, and the performance requirements of the electrode sheet under different conditions can be met. The chemical vapor deposition method includes but is not limited to electron cyclotron resonance microwave, plasma chemical vapor deposition, hot wire plasma chemical vapor deposition, and radio frequency plasma chemical vapor deposition.

[0103] The atomic layer deposition method is a method that can deposit substances in the form of a monatomic film on the surface of a substrate layer by layer.

[0104] The evaporation method refers to a method of heating the raw material in the evaporation container to be formed into a thin film, so that the atoms or molecules are vaporized and escaped from the surface to form a vapor flow, which is incident on the surface of the deposition material to condense and form a solid thin film.

[0105] The magnetron sputtering method is a direct current diode sputtering method performed under the control of a magnetic field, which is a physical film coating method.

[0106] The second aspect of the present application provides a preparation method of a negative electrode sheet, which comprises: depositing a silicon interface layer on at least one side of a metal layer to prepare a negative electrode sheet, the silicon interface layer comprising a material with a general formula of SiO x , wherein 0≤x≤2.

[0107] In some embodiments, the preparation method comprises: introducing a gas containing a silicon source or a mixed gas containing an oxygen source and a silicon source, and depositing a silicon interface layer by chemical vapor deposition; optionally, the oxygen source comprises N2O, and the silicon source comprises SiH4.

[0108] In some embodiments, only the silicon source is introduced during the preparation of the silicon interface layer, and the volume flow ratio M of the oxygen source to the silicon source is 0, so as to prepare a silicon layer.

[0109] In some embodiments, the volume flow ratio M of the oxygen source to the silicon source introduced is 0 x , and the silicon-oxygen layer comprises a material of a general formula of SiOx, wherein 0

[0110] In some embodiments, the volume flow ratio M of the oxygen source to the silicon source introduced is greater than 20, so as to prepare a silicon dioxide layer.

[0111] The silicon interface layer is prepared by the chemical vapor deposition method, the composition of the silicon interface layer can be adjusted by adjusting the gas flow of the oxygen source and the silicon source at any time, so that the formation of the battery has higher efficiency. Compared with other preparation methods, the flow of raw materials is controllable, and the composition and thickness of the silicon interface layer can be accurately controlled.

[0112] In some embodiments, the preparation method comprises: the volume flow ratio M of the oxygen source to the silicon source introduced is 0

[0113] In some embodiments, the volume flow ratio M of the oxygen source to the silicon source introduced during the preparation of the silicon interface layer is increased, so that the oxygen content of the silicon interface layer close to the metal layer is lower than the oxygen content of the silicon interface layer far from the metal layer in the thickness direction of the silicon interface layer.

[0114] It can be understood that the volume flow ratio M of the oxygen source to the silicon source can be continuously increased to deposit a silicon interface layer with continuously changing composition; or the volume flow ratio M of the oxygen source to the silicon source can be increased in stages, so that a material with a certain fixed composition has a certain thickness.

[0115] In some embodiments, the preparation method comprises: introducing a silicon source for deposition; introducing an oxygen source and a silicon source for deposition after a period of deposition, wherein the volume flow ratio M of the oxygen source to the silicon source is 0

[0116] In some embodiments, the preparation method comprises: introducing an oxygen source and a silicon source for deposition, wherein the volume flow ratio M of the oxygen source to the silicon source is 0

[0117] In some embodiments, the preparation method comprises: introducing a silicon source for deposition; after a period of deposition, introducing an oxygen source and a silicon source for deposition, wherein the volume flow ratio M of the oxygen source and the silicon source is 0 < M < 20; after a period of deposition, increasing the volume flow ratio M of the oxygen source and the silicon source to more than 20 for deposition.

[0118] In some embodiments, during the process of introducing the oxygen source and the silicon source for deposition, the volume flow ratio M of the oxygen source and the silicon source is gradually increased to prepare a plurality of SiOx layers with different x values. x layer.

[0119] The chemical vapor deposition method can realize efficient preparation of silicon interface layers with different buffer potentials in one step, reduce the probability of dendrite generation by increasing the negative electrode potential, further inhibit the growth of dendrites by adjusting the mechanical strength of the silicon interface layer, and simultaneously deposit high-capacity negative electrode materials, thereby improving the cycle performance of the battery while considering the electrochemical performance of the battery.

[0120] [Positive electrode sheet]

[0121] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material of the first aspect of the present application.

[0122] For example, the positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is arranged on any one or both of the two opposite surfaces of the positive electrode current collector.

[0123] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0124] In some embodiments, the positive active material can employ a positive active material for a battery known in the art. As an example, the positive active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material for a battery can also be used. These positive active materials can be used alone only one kind, or two or more kinds in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also can be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and a modified compound thereof, etc. Examples of the lithium-containing phosphate of an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4(also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0125] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one 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.

[0126] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and then drying, cold-pressing, or the like to obtain the positive electrode tab.

[0128] [Electrolyte]

[0129] The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab. The type of electrolyte is not particularly limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0130] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0131] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0132] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0133] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive that improves certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high-temperature or low-temperature performance of the battery, and the like.

[0134] [Separator]

[0135] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly limited in the present application and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0136] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, without particular limitation.

[0137] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly through a winding process or a stacking process.

[0138] The second aspect of the present application provides a secondary battery comprising the negative electrode tab of any of the embodiments, and / or the negative electrode tab prepared by the preparation method of any of the embodiments.

[0139] In some embodiments, the secondary battery comprises an electrolyte, and the silicon interface layer is located between the electrolyte and the metal layer.

[0140] In some embodiments, the secondary battery can comprise an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0141] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0142] The present application does not have particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. For example, Figure 6 is a square structure of the secondary battery 5 as an example.

[0143] In some embodiments, referring to Figure 7 , the outer package can comprise a shell 51 and a cover plate 53. The shell 51 can comprise 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 communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be used to form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of the electrode assembly 52 contained in the secondary battery 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0144] In addition, the application also provides a power utilization device, which comprises at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0145] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0146] Figure 8 The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. as an example.

[0147] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0148] Embodiment

[0149] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by purchase.

[0150] I. Preparation method

[0151] Embodiment 1

[0152] 1) Preparation of the positive electrode tab

[0153] The positive electrode active material lithium nickel cobalt manganese oxide, the binder polyvinylidene fluoride (PVDF), and the conductive agent conductive carbon black (Super-P) are mixed uniformly in N-methyl pyrrolidone (NMP) solvent at a mass ratio of 96%:2%:2% to prepare a positive electrode slurry. The positive electrode slurry is coated on the surface of an aluminum foil according to the positive electrode active material unit area mass requirement by using an extrusion coating machine and dried, and then the coated tab is subjected to cold pressing treatment by a cold press machine to prepare a final positive electrode tab. The areal density of the positive electrode film layer is 0.224 g / 1540.25 mm 2 .

[0154] 2) Preparation of the negative electrode tab

[0155] A silicon interface layer was prepared on a 20-μm-thick lithium metal layer by plasma-enhanced chemical vapor deposition (PECVD) to serve as the negative electrode sheet.

[0156] Chemical vapor deposition was performed on the lithium metal layer by introducing Ar, SiH4, and N2O, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 1.25 min, the thickness was 25 nm, and the deposited layer was a silicon-oxygen layer containing SiOx with x being 1.

[0157] 3) Preparation of electrolyte

[0158] In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) were mixed in a mass ratio of EC:PC:DMC = 3:3:3, and then LiPF6 was added to the mixed organic solvent. After stirring uniformly, an electrolyte was obtained, wherein the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0159] 4) Separator

[0160] A polyethylene film (PE separator) was used as the separator.

[0161] 5) Preparation of battery

[0162] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator being between the positive and negative electrodes to play a separating role, and were wound to obtain a bare cell. The bare cell was placed in an outer package, injected with the prepared electrolyte, and packaged to obtain a lithium ion battery.

[0163] The preparation method of Example 2 was similar to that of Example 1, except that the preparation method of the negative electrode sheet in Example 2 was as follows:

[0164] Chemical vapor deposition was performed on the lithium metal layer by introducing Ar, SiH4, and N2O, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 2.5 min, the thickness was 50 nm, and the deposited layer was a silicon-oxygen layer containing SiOx with x being 1.

[0165] The preparation method of Example 3 was similar to that of Example 1, except that the preparation method of the negative electrode sheet in Example 3 was as follows:

[0166] Chemical vapor deposition was performed on the lithium metal layer by introducing Ar, SiH4, and N2O, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 7.5 min, the thickness was 150 nm, and the deposited layer was a silicon-oxygen layer containing SiOx with x being 1.

[0167] The preparation method of Example 4 was similar to that of Example 1, except that the preparation method of the negative electrode sheet in Example 4 was as follows:

[0168] A silicon interface layer was prepared on a 20-um-thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) as a negative electrode tab.

[0169] Ar, SiH4, N2O were introduced to deposit on the lithium metal layer, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 10 min, and the thickness was 200 nm.

[0170] The preparation method of Example 5 was similar to that of Example 1, except that the preparation method of the negative electrode tab in Example 5 was as follows:

[0171] A silicon interface layer was prepared on a 20-um-thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) as a negative electrode tab.

[0172] Ar, SiH4, N2O were introduced to deposit on the lithium metal layer, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 50 min, and the thickness was 1000 nm.

[0173] The preparation method of Example 6 was similar to that of Example 1, except that the preparation method of the negative electrode tab in Example 6 was as follows:

[0174] A silicon interface layer was prepared on a 20-um-thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) as a negative electrode tab.

[0175] Ar, SiH4, N2O were introduced to deposit on the lithium metal layer, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 50 min, and the thickness was 1000 nm.

[0176] The preparation method of Example 7 was similar to that of Example 1, except that the preparation method of the negative electrode tab in Example 7 was as follows:

[0177] A silicon interface layer was prepared on a 20-um-thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) as a negative electrode tab.

[0178] Ar, SiH4, N2O were introduced to deposit on the lithium metal layer, wherein the volume flow ratio of N2O to SiH4 was 1:2, the deposition time was 50 min, and the thickness was 1000 nm.

[0179] The volume of N2O was increased, so that the gas flow ratio of N2O to SiH4 was 20:1, the deposition time was 0.5 min, and the thickness was 5 nm. The deposit included silicon dioxide.

[0180] The preparation method of Example 8 is similar to that of Example 1, except that the preparation method of the negative electrode sheet in Example 8 is as follows:

[0181] A silicon interface layer is prepared on a 20-μm-thick lithium metal layer by using a plasma-enhanced chemical vapor deposition (PECVD) technique, and used as the negative electrode sheet.

[0182] In the initial deposition stage, only SiH4 and Ar are introduced, and amorphous Si film is directly deposited on the lithium metal negative electrode by dissociation of SiH4 in high vacuum by plasma, with a deposition time of 1 min and a thickness of 10 nm;

[0183] Ar, SiH4 and N2O are introduced for deposition on the lithium metal layer, with a volume flow ratio of N2O to SiH4 of 1:2, a deposition time of 7.5 min, and a thickness of 150 nm. The deposited SiO x The material is SiO2, and the value of x is 1.

[0184] The volume flow ratio of N2O to SiH4 is increased to 20:1, the deposition time is 0.5 min, the deposited layer is a silicon dioxide layer, and the deposition thickness is 5 nm.

[0185] The preparation method of Example 9 is similar to that of Example 1, except that the preparation method of the negative electrode sheet in Example 9 is as follows:

[0186] A silicon interface layer is prepared on a 20-μm-thick lithium metal layer by using a plasma-enhanced chemical vapor deposition (PECVD) technique, and used as the negative electrode sheet.

[0187] In the initial deposition stage, only SiH4 and Ar are introduced, and amorphous Si film is directly deposited on the lithium metal negative electrode by dissociation of SiH4 in high vacuum by plasma, with a deposition time of 1 min and a thickness of 10 nm;

[0188] Ar, SiH4 and N2O are introduced for deposition, with a volume flow ratio of N2O to SiH4 of 1:2 for 1 min. The volume flow of N2O is increased, so that the volume flow ratio of N2O to SiH4 is 2:1 for 1 min, 5:1 for 1 min, 8:1 for 1 min, 11:1 for 1 min, 14:1 for 1 min, 17:1 for 1 min, and 18:1 for 0.5 min.

[0189] Increase the flow rate of N2O so that the ratio of N2O to SiH4 is 20:1, and the deposition time is 0.5 min.

[0190] The preparation method of Example 10 is similar to that of Example 1, except that in Example 10, the preparation method of the negative electrode sheet is as follows:

[0191] A silicon interface layer is prepared on a 20-μm-thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) technology, and used as the negative electrode sheet.

[0192] Ar, SiH4, and N2O are introduced for deposition, wherein the ratio of N2O to SiH4 is 1:2, the deposition time is 2.5 min, a 50-nm-thick SiOx film is prepared on the upper base, and x is 1;

[0193] The flow rate of N2O is increased so that the ratio of N2O to SiH4 is greater than 20:1, and the deposition time is 0.5 min, to ensure that the generated substance is SiO2, and a 5-nm-thick SiO2 film is deposited on the outermost layer.

[0194] The preparation method of Example 11 is similar to that of Example 1, except that in Example 11, the preparation method of the negative electrode sheet is as follows:

[0195] A silicon interface layer is prepared on a 20-μm-thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) technology, and used as the negative electrode sheet.

[0196] In the initial deposition stage, only SiH4 and Ar are introduced, and amorphous Si film is directly deposited on the lithium metal negative electrode by dissociation of SiH4 in high vacuum through plasma, the deposition time is 10 min, and the thickness is 100 nm;

[0197] Ar, SiH4, and N2O are introduced for deposition on the lithium metal layer, wherein the ratio of N2O to SiH4 is 1:2, the deposition time is 2.5 min, the thickness is 50 nm, and the deposited SiO x material, and x is 1;

[0198] The flow rate of N2O is increased so that the ratio of N2O to SiH4 is 20:1, the deposition time is 0.5 min, the deposited layer is a silicon dioxide layer, and the deposition thickness is 5 nm.

[0199] The preparation method of Example 12 is similar to that of Example 1, except that in Example 12, the preparation method of the negative electrode sheet is as follows:

[0200] A silicon interface layer was prepared on a 20µm thick lithium metal layer using plasma-enhanced chemical vapor deposition (PECVD) to serve as the negative electrode.

[0201] In the initial deposition stage, only SiH4 and Ar are introduced. The amorphous Si film is directly deposited on the lithium metal anode by the dissociation of SiH4 by plasma in high vacuum. The deposition time is 10 min and the thickness is 100 nm.

[0202] Ar, SiH4, and N2O were introduced to deposit a lithium metal layer, with a N2O to SiH4 gas flow rate ratio of 1:2, a deposition time of 2.5 min, and a thickness of 50 nm. The deposited SiO2... x Material, x value is 1.

[0203] Comparative Example 1

[0204] In Comparative Example 1, a lithium metal layer was used as the negative electrode, and other aspects were the same as in Example 1. The specific capacity of the negative electrode in this battery was 3860 mAh / g.

[0205] II. Testing Methods

[0206] 1) Capacity retention during ambient temperature cycling

[0207] At 25°C, the lithium-ion secondary battery was first charged at a constant current of 1C (the current value required to completely discharge the theoretical capacity within 1 hour) to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After resting for 5 minutes, the lithium-ion secondary battery was discharged at a constant current of 1C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to multiple charge-discharge cycles using the above method, and the discharge capacity of the 500th cycle was measured.

[0208] The capacity retention rate of a lithium secondary battery after 500 cycles = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%.

[0209] 2) Negative electrode potential

[0210] The test method for the negative electrode potential is referenced in CN115825765A. A brief test method includes:

[0211] Prepare a reference electrode.

[0212] The copper wire was soaked in concentrated sulfuric acid for 50 minutes, then rinsed three times with deionized water, and finally rinsed three times with ethanol and dried to remove the oxide layer on the surface of the copper wire. The oxide layer was then observed under a CCD to determine if it had been completely removed. If not, the process was repeated until the oxide layer was completely removed. The diameter of the copper wire was approximately 6 micrometers (μm).

[0213] Preparation of three electrodes

[0214] The materials prepared in the above steps are assembled into a stacked battery in the following order: positive electrode, separator, negative electrode, separator, reference electrode, separator, and positive electrode.

[0215] Lithium plating of the reference electrode

[0216] Connect the positive electrode of the battery to the reference electrode and charge the battery with a current of 20 microamps (μA) for two hours to deposit lithium on the side of the reference electrode closest to the positive electrode. Similarly, connect the negative electrode of the battery to the reference electrode and charge the battery with a current of 20 μA for two hours to deposit lithium on the side of the reference electrode closest to the negative electrode. The entire lithium plating process is now complete.

[0217] Verification of three electrodes

[0218] Use a multimeter to measure the positive and negative electrode voltages V1, the positive electrode voltage V2 and the reference electrode voltage V3. If V1 = V2 + V3, the three electrodes of the cell are normal and the next test can be performed. Otherwise, the three electrodes should be remade.

[0219] Monitor the first potential of the negative electrode and the second potential of the reference electrode.

[0220] During the charging and discharging process of the battery, the first potential of the negative electrode and the second potential of the reference electrode are monitored. At 25 degrees Celsius (°C), the cell is charged to 4.2V at a constant current of 1 / 3C, left to rest for 5 minutes, and then discharged to 2.8V at 1 / 3C. During this process, the first potential of the negative electrode and the second potential of the reference electrode are detected in real time, thereby realizing real-time monitoring of the negative electrode potential of the cell.

[0221] 3) Negative electrode specific capacity test

[0222] The prepared lithium metal anode was punched to a 14mm sheet in a glove box. The water and oxygen content in the glove box was less than 0.5ppm. A CR2025 positive electrode shell was used to assemble coin cells. After the successfully assembled coin cells were allowed to stand for 24 hours, a Newway testing platform was used, with the charge / discharge voltage range set to 2.5V-4.2V and the test temperature controlled at 25℃. The theoretical specific capacity was set to 3860mAh / g. Then, the cells were discharged at 0.05C to 2.5V, allowed to stand for 5 minutes, charged at 0.05C to 4.2V, and then charged at a constant voltage until the current cutoff was 0.01C. After standing for 30 minutes, the cells were discharged at 0.05C to 2.5V. The capacity at this step is the battery capacity. Dividing this capacity by the mass of the anode active material gives the specific capacity of the anode.

[0223] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0224] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 1 below.

[0225] Table 1

[0226]

[0227] As can be seen from Examples 1-5, when the thickness of the silicon interface layer is 25nm–1000nm, lithium metal has a higher negative electrode potential, which can suppress dendrite growth and further improve the cycle stability of the battery. When the thickness of the silicon interface layer is 50nm–200nm, the battery simultaneously exhibits high cycle stability and specific capacity.

[0228] As can be seen from the comparison of Examples 3, 8-9 and Examples 2, 10-12, in the thickness direction of the silicon interface layer, the oxygen content of the silicon interface layer near the metal layer is lower than that far from the metal layer. Compared with the silicon interface layer containing a single component, it can further optimize the overall performance of the battery, including cycle stability and specific capacity.

[0229] As can be seen from the comparison between Example 9 and Example 8, the gradual change in the content of the silicon oxide layer can further improve the cycle stability and specific capacity of the battery.

[0230] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode sheet, characterized in that, Includes a metal layer and a silicon interface layer located on at least one side of the metal layer. Along the thickness direction of the silicon interface layer from near the metal layer to away from the metal layer, the silicon interface layer sequentially comprises a silicon layer, a silicon oxide layer, and a silicon dioxide layer. The silicon layer comprises amorphous silicon, and the silicon oxide layer comprises silicon dioxide of the general formula SiO. x The material, where 0 < x < 2; The thickness of the silicon interface layer is greater than or equal to 25 nm and less than 1000 nm; The metal layer includes at least one of lithium metal and lithium alloy.

2. The negative electrode sheet according to claim 1, characterized in that, The silicon oxide layer comprises SiO₂. x The material is given by the expression , where 0.7 < x < 1.

5.

3. The negative electrode sheet according to claim 2, characterized in that, The thickness of the silicon interface layer is 50 nm-200 nm.

4. The negative electrode sheet according to claim 3, characterized in that, In the thickness direction of the silicon interface layer, the oxygen content of the silicon interface layer near the metal layer is lower than the oxygen content away from the metal layer.

5. The negative electrode sheet according to claim 4, characterized in that, Along the thickness direction of the silicon oxide layer from near the metal layer to far away from the metal layer, the silicon oxide layer sequentially includes a SiOx1 layer, a SiOx2 layer, ..., a SiOx layer. n Layers, where 0 < x1 < x2 < ... < x n <2, n≥2.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The negative electrode sheet satisfies at least one of the following conditions: (i) The thickness of the silicon layer is 10nm-100nm; (ii) The thickness of the silicon oxide layer is 25nm-150nm; (iii) The thickness of the silicon dioxide layer is 1nm-10nm.

7. The negative electrode sheet according to claim 6, characterized in that, The silicon interface layer is prepared by at least one of chemical vapor deposition, atomic layer deposition, vapor deposition, and magnetron sputtering.

8. A method for preparing a negative electrode sheet according to claim 1, characterized in that, The preparation method includes: depositing a silicon interface layer on at least one side of the metal layer to prepare the negative electrode sheet, wherein the silicon interface layer comprises SiO₂. x The material is given by , where 0 ≤ x ≤ 2.

9. The preparation method according to claim 8, characterized in that, The preparation method includes: The silicon interface layer is prepared by chemical vapor deposition by introducing a gas containing a silicon source or a mixture of a gas containing an oxygen source and a silicon source.

10. The preparation method according to claim 9, characterized in that, The oxygen source includes N2O, and the silicon source includes SiH4.

11. The preparation method according to claim 10, characterized in that, The preparation method includes: The volumetric flow rate ratio M of the oxygen source and the silicon source is 0 < M < 20, and the silicon interface layer comprises a material with the general formula SiOx, where 0 < x < 2.

12. The preparation method according to claim 11, characterized in that, The preparation method includes: Deposition is performed by introducing the silicon source; After deposition for a period of time, the oxygen source and the silicon source are introduced to continue deposition, wherein the volumetric flow rate ratio M of the oxygen source and the silicon source is 0 < M < 20. After deposition for a period of time, the ratio M of the oxygen source and the silicon source is increased to not less than 20 for deposition.

13. The preparation method according to any one of claims 9 to 12, characterized in that, The preparation method includes: During the deposition process involving the introduction of the oxygen source and the silicon source, the volumetric flow rate ratio M of the oxygen source and the silicon source is gradually increased.

14. A secondary battery, characterized in that, Includes the negative electrode sheet according to any one of claims 1 to 7, and / or the negative electrode sheet prepared by the preparation method according to any one of claims 8 to 13.

15. The secondary battery according to claim 14, characterized in that, The secondary battery includes an electrolyte, and the silicon interface layer is located between the electrolyte and the metal layer.

16. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 14 or 15.

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