A metal-plated silicon-based material and a secondary battery

Abstract

The application discloses a metal plating layer coated silicon-based material and a secondary battery, and belongs to the technical field of lithium ion batteries. The silicon-based material comprises a silicon-based inner core structure, a metal plating layer structure and an ion adsorption layer structure; wherein the silicon-based inner core is located at the center of the silicon-based material; the metal plating layer structure is covered around the surface of the silicon-based inner core structure; and the ion adsorption layer structure is located at the outer layer of the metal plating layer and covers the surface of the entire silicon-based material. The metal plating layer coated silicon-based material can reduce the side reaction of the silicon material and the electrolyte contact, still maintains a good lithium precipitation window and cycle performance at a larger rate, thereby guaranteeing the cycle life and safety of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a metal coating coated silicon-based material and a secondary battery. BACKGROUND

[0002] Lithium ion batteries with high energy density and fast charging technology are widely used in digital products and power supplies. With the continuous upgrading of technology, the energy density of lithium ion batteries has reached its limit, and industrialized silicon negative materials are increasingly used in commercial lithium ion batteries.

[0003] Silicon is a relatively active element that can easily react with many compounds. Silicon reacts with oxygen within a few milliseconds to form a thin oxide film. It can also react with lithium ion battery electrolyte within a few milliseconds. During the expansion and contraction of silicon, the SEI forms cracks, leading to direct contact with the electrolyte, and new SEI is formed at these newly formed cracks. There is competition between the formation process of SEI and the direct chemical reaction of silicon / electrolyte, and the contribution of each process depends on their kinetics and the concentration of lithium ions at the silicon / electrolyte interface. Direct contact between silicon and electrolyte can produce side reactions, so a metal nanolayer deposited on the surface of silicon can reduce the generation of side reactions.

[0004] Therefore, it is necessary to develop a silicon-based material that can reduce the side reactions that occur when silicon material contacts with electrolyte and still maintain good lithium precipitation window cycling performance at a larger rate. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a metal coating coated silicon-based material that can reduce the side reactions that occur when silicon material contacts with electrolyte and still maintain good lithium precipitation window and cycling performance at a larger rate.

[0006] According to a first aspect of the present application, a metal coating coated silicon-based material is provided, the silicon-based material comprising a silicon-based core structure, a metal coating structure and an ion adsorption layer structure;

[0007] The silicon-based core is located at the center of the silicon-based material. The metal coating structure is wrapped around the surface of the silicon-based core structure. The ion adsorption layer structure is located on the outer layer of the metal coating and covers the surface of the entire silicon-based material.

[0008] The metal coating coated silicon-based material according to the first aspect of the present application has at least the following beneficial effects:

[0009] The metal-plated silicon-based material can isolate the electrolyte accumulated on the surface of the material outside the metal plating layer when the battery is subjected to large-rate charging, reduce the enrichment of ions on the surface of the negative silicon particles, alleviate the precipitation of lithium ions on the surface of the negative electrode sheet, thereby improving the fast-charging capability of silicon, maintaining a good lithium precipitation window at a larger rate, and solving the bottleneck of silicon use at a large rate.

[0010] The metal-plated silicon-based material has a metal plating layer and an ion adsorption layer on the surface. Since the silicon material itself is difficult to embed ions, the ion adsorption layer is more easily absorbed into the silicon material. The ion adsorption layer is mainly responsible for adsorbing and releasing lithium ions during charging and discharging, which can more effectively manage the migration of lithium ions between the anode and the cathode, thereby improving the charging and discharging efficiency and cycle life of the battery. The metal plating layer mainly plays a role in conducting electricity and structural support, which can enhance the electrical conductivity of the silicon-based material, thereby improving the charging and discharging efficiency of the battery. At the same time, the metal plating layer can also buffer the volume change of the silicon-based material to some extent during charging and discharging, reduce structural damage, and prolong the life of the battery.

[0011] The ion adsorption layer and the metal plating layer are used together in the present application. The ion adsorption layer can also prevent the metal plating layer from directly contacting the electrolyte, reduce unnecessary chemical reactions, and protect the internal structure of the battery. The metal plating layer and the ion adsorption layer work together to significantly improve the cycle life of the battery. The metal plating layer provides a stable structural foundation and excellent electrical conductivity, while the ion adsorption layer optimizes the migration process of lithium ions. The combination of the two layers enables the anode to better adapt to the volume change during the charging and discharging process, reduces structural damage, and thus improves the durability of the battery. The metal plating layer enhances the electrical conductivity and structural stability, while the ion adsorption layer optimizes the migration process of lithium ions. The combined action of the two layers significantly improves the performance of the battery.

[0012] According to some embodiments of the present application, the material of the silicon-based core structure includes at least one of silicon-oxygen particles, pre-lithiated silicon-oxygen particles, silicon nanowires, and silicon-carbon particles.

[0013] The use of silicon material can significantly improve the energy density of the system compared to graphite.

[0014] According to some embodiments of the present application, the metal plating layer structure contains at least one of copper, gold, silver, bismuth, osmium, rhodium, palladium, and platinum.

[0015] Preferably, the metal contained in the metal plating layer structure is copper.

[0016] According to some embodiments of the present application, the material of the ion adsorption layer structure comprises at least one of nano-etherified cellulose, nano-esterified cellulose, nano-cellulose, nano-grafted cellulose, and nano-metal skeleton composite.

[0017] According to some embodiments of the present application, the particle size of the silicon-based inner core structure is 5-20 μm.

[0018] According to some embodiments of the present application, the silicon-based content in the silicon-based material is 1-15 wt%.

[0019] Preferably, the silicon-based content in the silicon-based material is 2-8 wt%.

[0020] More preferably, the silicon-based content in the silicon-based material is 3 wt%.

[0021] According to some embodiments of the present application, the thickness of the metal plating layer structure is 2-20 nm.

[0022] Preferably, the thickness of the metal plating layer structure is 4-6 nm.

[0023] According to some embodiments of the present application, the thickness of the ion adsorption layer structure is 250-600 nm.

[0024] Preferably, the thickness of the ion adsorption layer structure is 250-400 nm.

[0025] According to some embodiments of the present application, the ion adsorption layer thickness (A) of the silicon-based material and the metal plating layer thickness (B) satisfy the relationship 60≥A / B≥40. For example, A / B can be 40, 50, or 60.

[0026] When A / B≥60, the ion adsorption layer is too thick, the tightness of the silicon outer coating is poor, and the structural stability is reduced; when A / B≤40, the metal plating layer is too thick, and the ion adsorption layer is relatively thin, and the safety is poor. Within the range of 60≥A / B≥40, the metal plating layer and the ion adsorption layer better synergize, and the electrochemical performance is better.

[0027] In addition to improving the cycle life, the anode of this composite structure can also bring other technical effects. For example, by optimizing the material of the ion adsorption layer, the energy density and power density of the battery can be improved. In addition, the combination of the metal plating layer and the ion adsorption layer can also improve the safety of the battery, reducing the risk of battery overheating or short circuit; by combining the metal plating layer and the ion adsorption layer, the anode design of this secondary battery not only improves the cycle life of the battery, but also can bring technical improvements in energy density, power density, and safety, etc.

[0028] According to some embodiments of the present application, the method for preparing the metal coating layer comprises the following steps: soaking the silicon-based inner core structure in a metal pretreatment solution, adding a plating solution, and obtaining the silicon-based material after the metal coating layer is prepared.

[0029] According to some embodiments of the present application, the specific surface area of the silicon-based material after the metal coating layer is prepared is 1.5-3.5 m 2 / g.

[0030] The greater the specific surface area of the silicon-based material is, the more adsorption sites are provided, which is conducive to forming a more uniform adsorption layer and enhancing the tightness of the coating.

[0031] According to some embodiments of the present application, the metal pretreatment solution comprises a silver nitrate solution and a hydrofluoric acid solution.

[0032] The metal pretreatment solution is a mixed solution of silver nitrate and hydrofluoric acid, and the two of them cooperatively etch the silicon-based material, i.e., form a silicon nanowire array on the surface of the silicon-based particles, so that in the subsequent chemical copper plating layer process of heating and temperature rising, the silicon nanowire will be embedded into the chemical copper plating layer, improving the bonding force between the silicon and the metal coating layer, and effectively anchoring the metal coating layer on the surface of the silicon particles. The metal coating layer is divided into an etching stage of the silicon-based material by the two of silver nitrate and hydrofluoric acid and a chemical copper plating stage. By adjusting the concentration of the etchant, the etching of the silicon-based material is uniform and sufficient. Then, by controlling the preparation temperature and time of the chemical copper plating, the speed in the whole metal coating layer treatment process is stable. In addition, the construction of the ion adsorption layer makes the metal coating layer and the ion adsorption layer uniform and dense, and the combination with the silicon-based material is more tight, which is conducive to the continuity of the metal coating layer treatment, and then makes the coating uniform and dense.

[0033] According to some embodiments of the present application, the chemical plating solution in the chemical copper plating stage is selected from at least one of copper sulfate and copper nitrate.

[0034] According to some embodiments of the present application, the concentration of the silver nitrate solution is 0.01-0.03 mol / L.

[0035] Preferably, the concentration of the silver nitrate solution is 0.035-0.045 mol / L.

[0036] According to some embodiments of the present application, the concentration of the hydrofluoric acid solution is 2-6 mol / L.

[0037] Preferably, the concentration of the hydrofluoric acid solution is 3-5 mol / L.

[0038] According to some embodiments of the present application, the plating solution comprises at least one of a sulfate, a nitrate or an acetate of a metal.

[0039] According to some embodiments of the present application, the temperature for preparing the metal plating layer is 20-75℃.

[0040] Preferably, the temperature for preparing the metal plating layer is 25-50℃.

[0041] The suitable temperature can promote the reduction and deposition of metal ions to form a dense metal plating layer, which is conducive to the tight coating of the subsequent ion adsorption layer.

[0042] According to some embodiments of the present application, the time for preparing the metal plating layer is 10-30min.

[0043] Preferably, the time for preparing the metal plating layer is 15-25min.

[0044] According to some embodiments of the present application, the method for preparing the ion adsorption layer structure comprises the following steps:

[0045] The ion adsorption material solution is prepared, the silicon-based material containing the metal plating layer is dispersed in the ion adsorption layer material solution to obtain a dispersion liquid, and drying is performed to solidify the ion adsorption layer material to coat the surface of the silicon-based material containing the metal plating layer to form the ion adsorption layer structure.

[0046] According to the second aspect of the present application, a lithium ion battery negative electrode material is provided, which comprises a negative electrode active material, a conductive agent and a binder; the negative electrode active material is composed of the metal plating layer coated silicon-based material.

[0047] According to the third aspect of the present application, a secondary battery is provided, which comprises a separator film, an electrolyte, a positive electrode sheet and a negative electrode sheet.

[0048] The negative electrode sheet comprises the metal plating layer coated silicon-based material according to any one of claims 1-7.

[0049] The secondary battery according to the third aspect of the present application has at least the following beneficial effects:

[0050] The secondary battery according to the present application has high energy and fast charging, and has the characteristics of long cycle life.

[0051] According to some embodiments of the present application, the positive electrode material is selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiMnPO4, LiFePO4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.85 Co 0.15 Al 0.05 at least one of O2, LiNi

[0052] According to some embodiments of the present application, the positive current collector is an aluminum foil.

[0053] According to some embodiments of the present application, the negative current collector is a copper foil.

[0054] According to some embodiments of the present application, the separator film comprises at least one of polyethylene, polypropylene and polyvinylidene fluoride.

[0055] According to some embodiments of the present application, the separator film is disposed between the positive electrode tab and the negative electrode tab.

[0056] According to some embodiments of the present application, the electrolyte comprises an electrolyte salt, an organic solvent, a positive electrode film-forming additive, a negative electrode film-forming additive and a low-temperature additive.

[0057] In the present application, the specific types and compositions of the electrolyte salt, the organic solvent and the additives are not specifically limited.

[0058] Other features and advantages of the present application will be set forth in the description that follows, and in part will become apparent from the description, or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0059] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0060] Figure 1 is a schematic diagram of a metal-coated silicon-based material structure according to the present application. DETAILED DESCRIPTION

[0061] Embodiments of the present application are described below in detail, identical or similar reference numerals are used throughout the description to denote identical or similar elements or elements having the same or similar functions. The embodiments described below are exemplary and are only used to explain the present application and cannot be understood as limiting the present application.

[0062] In the description of the present application, if there is a description to first, second, etc. is only for the purpose of distinguishing technical features, and can not be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the order of the indicated technical features.

[0063] In the description of the present application, it is understood that the orientation description, such as the orientation or position relationship indicated by up, down, etc. is based on the orientation or position relationship shown in the examples, only for the purpose of facilitating the description of the present application and simplifying the description, and is not intended to indicate or imply that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0064] The words "preferably", "more preferably" and the like in the present application refer to the embodiments of the present application which can provide certain beneficial effects in certain cases. However, other embodiments can also be preferred in the same or other cases. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present application.

[0065] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value. Further, when the range refers to an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0066] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of the present application.

[0067] The reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field, unless otherwise specified.

[0068] Example 1

[0069] The present embodiment provides a secondary battery, which is composed of a separator, an electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises a metal plated layer coated silicon-based material.

[0070] The secondary battery of the present embodiment is prepared by the following preparation method, specifically comprising the following steps:

[0071] 1) Positive electrode sheet: Active material LiCoO2, conductive agent acetylene black, conductive carbon nanotube, binder polyvinylidene fluoride (PVDF) are uniformly dispersed in N-methyl pyrrolidone solvent system in a weight ratio of 98.2:0.5:0.3:1.0, coated on an aluminum current collector, then cold pressed and slitted to obtain a positive electrode sheet.

[0072] 2) Negative electrode sheet: The negative electrode active material, conductive agent and binder are mixed in a weight ratio of 97.2:0.5:2.3 to prepare a negative electrode active material slurry, then cold pressed and slitted to obtain a negative electrode sheet. The content of silicon-based material in the negative electrode active material is 3%. The metal-coated silicon-based material meets the following design: the first part is pre-lithiated silicon oxide particles with a particle size of DV50=20 μm; the second part is a metal-coated copper layer with a thickness of 5 nm; and the third part is a nano-esterified cellulose material with an ion adsorption layer thickness of 250 nm. The chemical solution used for preparing the metal coating has a silver nitrate concentration of 0.035 mol / L and a hydrofluoric acid concentration of 3 mol / L, and the preparation temperature is 25°C and the preparation time is 15 min.

[0073] 3) Separation film: PE surface coated with ceramic mixture as a separation film.

[0074] 4) Electrolyte: Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a proportion of 1 mol / L to prepare an electrolyte.

[0075] 5) Battery preparation: The above positive electrode sheet, separation film, and negative electrode sheet are wound or stacked to make a bare cell, and then packaged and injected with electrolyte to make a finished lithium ion battery.

[0076] Example 2

[0077] The embodiment provides a secondary battery composed of a separation film, an electrolyte, a positive electrode sheet, and a negative electrode sheet, wherein the negative electrode sheet comprises a metal-coated silicon-based material.

[0078] The secondary battery of the embodiment is prepared by the following preparation method, specifically including the following steps:

[0079] 1) Positive electrode sheet: Active material LiCoO2, conductive agent acetylene black, conductive carbon nanotube, binder polyvinylidene fluoride (PVDF) are uniformly dispersed in N-methyl pyrrolidone solvent system in a weight ratio of 98.2:0.5:0.3:1.0, coated on an aluminum current collector, then cold pressed and slitted to obtain a positive electrode sheet.

[0080] 2) Negative electrode sheet: the negative electrode active material, the conductive agent, and the binder are mixed according to a weight ratio of 97.2:0.5:2.3 to obtain a negative electrode active material slurry, which is then cold-pressed and divided into strips to obtain a negative electrode sheet. The content of the silicon-based material in the negative electrode active material is 3%. The metal-coated silicon-based material satisfies the following design: the first part is pre-lithiated silicon-oxygen particles with a particle size of DV50=20 μm; the second part is a metal-coated copper layer with a thickness of 10 nm; and the third part is a nano-esterified cellulose material with an ion adsorption layer thickness of 400 nm. The chemical solution used for preparing the metal coating has a silver nitrate concentration of 0.035 mol / L and a hydrofluoric acid concentration of 5 mol / L, and the preparation temperature is 35°C and the preparation time is 20 min.

[0081] 3) Isolation film: a PE surface coated with a ceramic mixture is used as the isolation film.

[0082] 4) Electrolyte: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed according to a volume ratio of 1:1:4:4, and then a fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a proportion of 1 mol / L to prepare the electrolyte.

[0083] 5) Battery preparation: the above positive electrode sheet, isolation film, and negative electrode sheet are wound or laminated to make a bare cell, which is then packaged and injected with the electrolyte to make a finished lithium ion battery.

[0084] Example 3

[0085] The example provides a secondary battery composed of an isolation film, an electrolyte, a positive electrode sheet, and a negative electrode sheet, wherein the negative electrode sheet comprises a metal-coated silicon-based material.

[0086] The secondary battery of the example is prepared by the following preparation method, which specifically includes the following steps:

[0087] 1) Positive electrode sheet: the active material LiCoO2, the conductive agent acetylene black, the conductive carbon nanotube, and the binder polyvinylidene fluoride (PVDF) are uniformly dispersed in an N-methylpyrrolidone solvent system according to a weight ratio of 98.2:0.5:0.3:1.0, coated on an aluminum current collector, and then cold-pressed and divided into strips to obtain a positive electrode sheet.

[0088] 2) Negative electrode sheet: the negative electrode active material, the conductive agent, and the binder are mixed according to a weight ratio of 97.2:0.5:2.3 to obtain a negative electrode active material slurry, and then cold-pressed and slitted to obtain a negative electrode sheet. The content of the silicon-based material in the negative electrode active material is 3%. The metal coating coated silicon-based material meets the following design: the first part is silicon-carbon particles with a particle size of DV50=20 μm; the second part is a metal coating of platinum with a metal coating thickness of 5 nm; and the third part is a nano-esterified cellulose material with an ion adsorption layer thickness of 250 nm. The chemical solution used for preparing the metal coating has a silver nitrate concentration of 0.035 mol / L and a hydrofluoric acid concentration of 3 mol / L, the preparation temperature is 25°C, and the preparation time is 15 min.

[0089] 3) Isolation film: a PE surface coated with a ceramic mixture is used as an isolation film.

[0090] 4) Electrolyte: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed according to a volume ratio of 1:1:4:4, and then a fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent according to a proportion of 1 mol / L to prepare an electrolyte.

[0091] 5) Battery preparation: the above positive electrode sheet, isolation film, and negative electrode sheet are wound or laminated to make a bare cell, and then packaged and injected with an electrolyte to make a finished lithium ion battery.

[0092] Example 4

[0093] The embodiment provides a secondary battery composed of an isolation film, an electrolyte, a positive electrode sheet, and a negative electrode sheet, wherein the negative electrode sheet comprises a metal coating coated silicon-based material.

[0094] The secondary battery of the embodiment is prepared by the following preparation method, specifically including the following steps:

[0095] 1) Positive electrode sheet: the active material LiCoO2, the conductive agent acetylene black, the conductive carbon nanotube, and the binder polyvinylidene fluoride (PVDF) are uniformly dispersed in an N-methyl pyrrolidone solvent system according to a weight ratio of 98.2:0.5:0.3:1.0, coated on an aluminum current collector, and then cold-pressed and slitted to obtain a positive electrode sheet.

[0096] 2) Negative electrode sheet: the negative electrode active material, the conductive agent, and the binder are mixed in a weight ratio of 97.2:0.5:2.3 to prepare a negative electrode active material slurry, which is then cold-pressed and divided into strips to obtain a negative electrode sheet. The content of the silicon-based material in the negative electrode active material is 3%. The silicon-based material coated with a metal layer meets the following design: the first part is a silicon nanowire with a particle size of DV50=20 μm; the second part is a metal layer of platinum with a thickness of 10 nm; and the third part is a nanocellulose material with an ion adsorption layer thickness of 400 nm. The chemical solution used for preparing the metal layer has a silver nitrate concentration of 0.035 mol / L and a hydrofluoric acid concentration of 5 mol / L, and the preparation temperature is 35°C and the preparation time is 20 min.

[0097] 3) Separating film: a PE surface coated with a ceramic mixture is used as a separating film.

[0098] 4) Electrolyte: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a volume ratio of 1:1:4:4, and then a fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a proportion of 1 mol / L to prepare an electrolyte.

[0099] 5) Battery preparation: the above positive electrode sheet, separating film, and negative electrode sheet are wound or laminated to prepare a bare cell, which is then packaged and injected with an electrolyte to prepare a finished lithium ion battery.

[0100] Comparative Example 1

[0101] This comparative example provides a secondary battery composed of a separating film, an electrolyte, a positive electrode sheet, and a negative electrode sheet, wherein the negative electrode sheet includes a silicon-based material coated with a metal layer.

[0102] The difference between this comparative example and Example 1 is that the negative electrode sheet is different.

[0103] The negative electrode sheet of this comparative example includes the following preparation steps:

[0104] The negative electrode active material, the conductive agent, and the binder are mixed in a weight ratio of 97.2:0.5:2.3 to prepare a negative electrode active material slurry, which is then cold-pressed and divided into strips to obtain a negative electrode sheet. The content of the silicon-based material in the negative electrode active material is 3%. The silicon-based material meets the following design: the first part is a silicon nanowire; the second part is a metal layer of copper with a thickness of 15 nm; and the third part is a nanocellulose material with an ion adsorption layer thickness of 300 nm. The chemical solution used for preparing the metal layer has a silver nitrate concentration of 0.06 mol / L and a hydrofluoric acid concentration of 6 mol / L, and the preparation temperature is 45°C and the preparation time is 35 min.

[0105] Comparative Example 2

[0106] The comparative example provides a secondary battery composed of a separator, an electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises a metal plated layer coated silicon-based material.

[0107] The difference between the comparative example and Example 1 is that the negative electrode sheet is different.

[0108] The negative electrode sheet of the comparative example comprises the following preparation steps:

[0109] The negative electrode active material, the conductive agent and the binder are mixed in a weight ratio of 97.2:0.5:2.3 to prepare a negative electrode active material slurry, and then cold-pressed and slitted to obtain a negative electrode sheet. The content of the silicon-based material in the negative electrode active material is 3%. The silicon-based material satisfies the following design: the first part is a silicon nanowire; the second part is a metal plated layer of platinum, and the thickness of the metal plated layer is 40 nm; and the third part is a nanometer esterified cellulose material, wherein the thickness of the ion adsorption layer is 400 nm. The chemical solution used for preparing the metal plated layer has a silver nitrate concentration of 0.06 mol / L and a hydrofluoric acid concentration of 6 mol / L, the preparation temperature is 50°C, and the preparation time is 40 min.

[0110] Comparative Example 3

[0111] The comparative example provides a secondary battery composed of a separator, an electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-based material.

[0112] The difference between the comparative example and Example 1 is that the metal of the metal plated layer is nickel.

[0113] Comparative Example 4

[0114] The comparative example provides a secondary battery composed of a separator, an electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-based material.

[0115] The difference between the comparative example and Example 1 is that the ion adsorption layer is not included.

[0116] Comparative Example 5

[0117] The comparative example provides a secondary battery composed of a separator, an electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-based material.

[0118] The difference between the comparative example and Example 1 is that the metal plated layer is not performed.

[0119] Comparative Example 6

[0120] The comparative example provides a secondary battery composed of a separator, an electrolyte, a positive electrode sheet and a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-based material.

[0121] The difference from Example 1 is that the ion adsorption layer is adsorbed carbon fiber.

[0122] Comparative Example 7

[0123] The present comparative example provides a secondary battery composed of a separator, an electrolyte, a positive electrode sheet, and a negative electrode sheet, wherein the negative electrode sheet includes a silicon-based material.

[0124] The difference from Example 1 is that the metal plating layer has a thickness of 25 nm and the ion adsorption layer has a thickness of 600 nm.

[0125] Test Example

[0126] The secondary batteries described in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to performance tests.

[0127] The rate window was measured as a standard in which lithium precipitation was not observed after 20 cycles of charging at 2.0 C, 2.2 C, 2.4 C, 2.6 C, 2.8 C, 3.0 C, 3.2 C, and then charging at a rate of 1.5 C to a cutoff voltage.

[0128] The cycle retention rate was the percentage of the remaining capacity of the battery cell after 800 cycles of charging at 2.8 C and then charging at a rate of 1.8 C to a cutoff voltage, with respect to the initial capacity.

[0129] The swelling rate was the percentage of the difference between the thickness of the battery cell after 100 cycles of charging at 2.8 C and then charging at a rate of 1.8 C to a cutoff voltage, with respect to the initial thickness.

[0130] The power density was calculated using the formula: battery capacity * voltage platform / cell size (cell length * width * thickness). The cycle life in this document refers to the number of cycles of the battery cell when the capacity retention rate is less than 60% after the battery is cycled.

[0131] The most significant test for safety performance testing is the thermal shock test: thermal shock refers to taking three battery cells in an oven at a certain temperature for a certain period of time, and the battery cells do not explode, catch fire, or have broken tabs to pass. In this document, the thermal shock condition is to fully charge the battery cells to 100% SOC at 0.5 C constant current and constant voltage, and then maintain 132°C for 60 minutes. The passing condition is that the battery cells have a good appearance, no electrolyte leakage, explosion, or fire. If three battery cells meet the conditions, it is 3 / 3 pass.

[0132] Table 1 Performance parameters of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 7

[0133]

[0134] According to the above test results, the secondary batteries of the embodiments 1-4 of the application have good cycle retention rate and low expansion rate; the embodiments 1 and 2 of the application are compared with the embodiments 3 and 4, the metal plating layer of the embodiments 1-2 is preferably copper, under the plating layer thickness defined in the application, the rate window and cycle retention rate are the best, which significantly improves the electrical performance of the lithium ion battery. The silver nitrate concentration and the hydrofluoric acid concentration in the comparative example 1 and the comparative example 2 are not within the range of the application, the battery appears lithium precipitation and rapid cycle capacity decay under the condition of large rate charge and discharge, the reason is that the influence factors of each stage of the metal plating layer are superimposed, the etching force of the silver nitrate and the hydrofluoric acid on the silicon nanowire is too large, the nanowire array is too dense, the latter has a long preparation temperature and time, which accelerates the chemical copper plating rate, the whole process changes nonlinearly, reduces the continuity of the chemical copper plating treatment, and causes the weak bonding force between the silicon substrate and the chemical plating layer, so that the lithium precipitation and rapid cycle capacity decay occur under the condition of large rate charge and discharge. According to the experimental results of the comparative examples 4-5, the silicon-based core structure, the metal plating layer structure and the ion adsorption layer structure of the metal plating layer coated material have a synergistic effect, and still maintain a good lithium precipitation window and cycle performance under a larger rate; if only the ion adsorption layer in the comparative example 5, the contact between the ion adsorption layer and the silicon is not as close as the contact between the silicon and the metal plating layer, and there is also a small part of the silicon in contact with the electrolyte, which produces more gas and has poor heat box. According to the comparative examples 6 and 7, the cycle capacity retention rate of the materials with other ion adsorption layer structures and parameters outside the limited range is very poor.

[0135] The above embodiments of the application are described in detail, but the application is not limited to the above embodiments, and various changes can be made within the knowledge range of ordinary skilled persons in the art without departing from the purpose of the application. In addition, the embodiments of the application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A metal-coated silicon-based material, characterized in that, The silicon-based material comprises a silicon-based inner core structure, a metal plating layer structure, and an ion adsorption layer structure. The silicon-based inner core structure is located at the center of the silicon-based material, the metal plating layer structure is wrapped around the surface of the silicon-based inner core structure, and the ion adsorption layer structure is located at the outer layer of the metal plating layer and covers the surface of the entire silicon-based material. The metal plating layer structure contains at least one of copper or platinum, the ion adsorption layer structure contains at least one of nano-etherified cellulose, nano-esterified cellulose, nano-cellulose, or nano-grafted cellulose, the thickness of the metal plating layer structure is 2-20 nm, the thickness of the ion adsorption layer structure is 250-600 nm, and the ratio of the thickness A of the ion adsorption layer to the thickness B of the metal plating layer is 60≥A / B≥40.

2. The metal-coated silicon-based material of claim 1, wherein, The silicon-based inner core structure contains at least one of silicon oxide particles, pre-lithiated silicon oxide particles, silicon nanowires, or silicon-carbon particles.

3. The metal-coated silicon-based material of claim 1, wherein The Dv50 particle size of the material in the silicon-based inner core structure is 5-50 μm.

4. The metal-coated silicon-based material of claim 1, wherein, The method for preparing the metal plating layer structure comprises the following steps: immersing the silicon-based inner core structure in a metal pretreatment solution, etching a nano-array on the surface of the silicon-based particles, and adding a plating solution to obtain a silicon-based material with a metal plating layer.

5. The metal-coated silicon-based material of claim 4, wherein the metal coating is a metal selected from the group consisting of aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, iron, zinc, tin, lead, and alloys thereof. The method for preparing the ion adsorption layer structure comprises the following steps: dispersing the silicon-based material with a metal plating layer in a material solution of the ion adsorption layer to obtain a dispersion liquid, and drying to solidify the ion adsorption layer material and coat the surface of the silicon-based material with a metal plating layer to form an ion adsorption layer structure.

6. The metal-coated silicon-based material of claim 4, wherein the metal coating is a metal selected from the group consisting of aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, iron, zinc, tin, lead, and alloys thereof. The specific surface area of the silicon-based material after the metal plating is 1.5-3.5 m 2 / g.

7. The metal-coated silicon-based material of claim 4, wherein the metal coating is a metal selected from the group consisting of aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, iron, zinc, tin, lead, and alloys thereof. The metal pretreatment solution comprises a silver nitrate solution and a hydrofluoric acid solution.

8. The metal-coated silicon-based material of claim 7, wherein the metal coating is a metal selected from the group consisting of aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, iron, zinc, tin, lead, and alloys thereof. The concentration of the silver nitrate solution is 0.035-0.045 mol / L.

9. The metal-coated silicon-based material of claim 7, wherein the metal coating is a metal selected from the group consisting of aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, iron, zinc, tin, lead, and alloys thereof. The concentration of the hydrofluoric acid solution is 2-6 mol / L.

10. The metal-coated silicon-based material of claim 5, wherein, The plating solution contains at least one of a metal sulfate, a metal nitrate, or a metal acetate.

11. The metal-coated silicon-based material of claim 4, wherein the metal coating is a metal selected from the group consisting of aluminum, copper, silver, gold, platinum, palladium, nickel, cobalt, iron, zinc, tin, lead, and alloys thereof. The temperature for preparing the metal plating layer is 20-75°C.

12. The metal-coated silicon-based material of claim 5, wherein, The time for preparing the metal plating layer is 10-30 min.

13. A lithium-ion battery anode material, characterized in that, The lithium ion battery negative electrode material comprises a negative electrode active material, a conductive agent, and a binder. The negative electrode active material comprises the metal plating layer-coated silicon-based material according to any one of claims 1-12.

14. The lithium-ion battery anode material of claim 13, wherein, The content of the metal plating layer-coated silicon-based material in the negative electrode active material is 1wt%-15wt%.

15. A secondary battery characterized by comprising: The secondary battery comprises a separator, an electrolyte, a positive electrode sheet, and a negative electrode sheet. The negative electrode sheet comprises the metal plating layer-coated silicon-based material according to any one of claims 1-12.

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