Negative electrode material, secondary battery and electric device

Abstract

A negative electrode material, a secondary battery and an electric device. The negative electrode material comprises an inner core, a first shell layer and a second shell layer, wherein the first shell layer is arranged on the surface of the inner core, and the second shell layer is arranged on the surface of the first shell layer; the inner core comprises an active material, the first shell layer comprises a first polymer material, and the second shell layer comprises a conductive material, the first polymer material comprising at least one of a halogen, a hydroxyl, a carboxyl, aldehyde group, an amino, a thiol group, a carbonyl and an amido. The first shell layer comprising the first polymer material is firmly wound on the surface of the inner core, and can uniformly wind the conductive material on the surface thereof, such that expansion of the negative electrode material is effectively relieved, thereby inhibiting overexpansion of a negative electrode sheet, and in addition, after inner core particles are expanded and broken in a later period, a conductive network can still be maintained, and has better the cycling performance and lower expansion and a lower direct-current resistance.

Description

Negative electrode material, secondary battery and electrical equipment

[0001] This application claims priority to the Chinese patent invention filed with the China Patent Office on August 9, 2023, with application number "202311001219.9" and application name "A negative electrode material, secondary battery and electrical equipment", the entire content of which is incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of lithium-ion battery manufacturing, and in particular to a negative electrode material, a secondary battery, and an electrical device. Background Art

[0003] Currently, secondary batteries, especially lithium-ion batteries, have been widely used in various fields due to their many advantages such as long cycle life, high energy density, short charging time, small size, light weight, and no memory effect.

[0004] The theoretical capacity of lithium-ion batteries is closely related to the negative electrode material. Currently, lithium-ion batteries primarily use graphite as the negative electrode, but its theoretical specific capacity is only 372mAh / g. While silicon, tin, or their alloys have a maximum theoretical capacity of up to 4200mAh / g, silicon, tin, or their alloys experience a 150% to 300% volume change during charge and discharge, leading to separation of the negative electrode material from the substrate or contact separation between the negative electrode materials. The continuous rupture and repair of the SEI film consumes a large amount of active lithium, resulting in increased internal resistance and capacity decay, thus affecting the battery's cycle life.

[0005] Summary of the Invention

[0006] The technical problem to be solved by the present application is to provide a negative electrode material, a secondary battery and an electrical device to solve the problem that existing silicon, tin or their alloy negative electrode materials are prone to deformation of the pole piece due to volume change, which affects the battery cycle life.

[0007] In order to solve the above problems, this application is implemented through the following technical solutions:

[0008] The present application proposes a negative electrode material, wherein the negative electrode material includes a core, a first shell layer and a second shell layer, the first shell layer is arranged on the surface of the core, and the second shell layer is arranged on the surface of the first shell layer; the core includes an active material, the first shell layer includes a first polymer material, and the second shell layer includes a conductive material, and the first polymer material includes at least one of a halogen, a hydroxyl group, a carboxyl group, an aldehyde group, an amino group, a thiol group, a carbonyl group, and an amide group.

[0009] Furthermore, in the negative electrode material, the surface of the active material has active sites, and at least a portion of the first polymer material is grafted onto the surface of the active material.

[0010] Furthermore, in the negative electrode material, the active site comprises at least one of a carbonyl group, a hydroxyl group, a carboxyl group, an acyl chloride group, an azo group, and an epoxy group.

[0011] Furthermore, in the negative electrode material, the negative electrode material also includes a third shell layer, the third shell layer is arranged on the surface of the second shell layer, the third shell layer includes a second polymer material, and the second polymer material includes a dendritic polymer and / or a hyperbranched polymer.

[0012] Furthermore, in the negative electrode material, the second shell layer further includes a binder, the binder includes a linear polymer, and the first polymer material includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polydopamine, and polyacrylic acid embedded with a thiol group.

[0013] Furthermore, in the negative electrode material, the linear polymer, the dendritic polymer and the hyperbranched polymer are each independently selected from at least one of polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyimide, styrene-butadiene rubber, polystyrene, polypropylene alcohol and polyvinyl alcohol.

[0014] Furthermore, in the negative electrode material, the particle size Dv50 of the core is 0.01 to 10 μm; and / or

[0015] The thickness of the second shell layer is 5 to 250 nm; and / or

[0016] The thickness of the third shell layer is 5 to 150 nm.

[0017] Furthermore, in the negative electrode material, the active material includes at least one of a silicon-based active material and a tin-based active material.

[0018] Furthermore, in the negative electrode material, the silicon-based active material includes at least one of silicon carbon, single crystal silicon, silicon alloy, pre-lithiation silicon, and pre-magnesiation silicon.

[0019] Furthermore, in the negative electrode material, the conductive material includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; and / or

[0020] The conductive agent comprises carbon nanotubes with an aspect ratio of 500 to 10000:1.

[0021] The present application also proposes a secondary battery, which includes a negative electrode plate, wherein the negative electrode plate includes a negative electrode collector and a negative electrode active material layer disposed on the negative electrode collector, and the negative electrode active material layer includes the negative electrode material as described above.

[0022] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0023] The embodiments of the present application include the following advantages:

[0024] In an embodiment of the present application, the negative electrode material provided includes a core, a first shell layer, and a second shell layer, wherein the first shell layer is disposed on the surface of the core, and the second shell layer is disposed on the surface of the first shell layer, the core includes an active material, the first shell layer includes a first polymer material, and the second shell layer includes a conductive material, wherein the first polymer material includes at least one of a halogen, a hydroxyl group, a carboxyl group, an aldehyde group, an amino group, a thiol group, a carbonyl group, and an amide group. Among them, because the first polymer material includes polar groups such as halogen, hydroxyl group, carboxyl group, aldehyde group, amino group, thiol group, carbonyl group, and amide group, it can be firmly wrapped around the surface of the core, and the conductive material can be evenly wrapped around the surface, not only making the stress caused by particle expansion more uniform, but also making it possible to maintain a conductive network after the core particles expand and break in the later stage, its cycle performance is better, and the expansion and DC resistance are lower, thereby solving the problem that the negative electrode material is easily deformed due to volume change, affecting the battery cycle life.

[0025] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic structural diagram of a negative electrode material for a lithium-ion battery provided in an embodiment of the present application.

[0027] Explanation of reference numerals: 11 - inner core, 12 - first shell, 13 - second shell, 14 - third shell. Specific embodiments

[0028] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0029] The applicant of this application has discovered that in order to overcome the problem that the active material (especially silicon, tin or their alloy negative electrodes) is prone to deformation of the pole piece due to volume change, which affects the cycle life of the battery, carbon nanotubes or carbon black can be coated on the surface of the active material. However, it is difficult for carbon nanotubes or carbon black to be evenly coated on the surface of silicon, tin or their alloys, that is, it is difficult to fully exert the expansion inhibition and buffering effect of carbon nanotube winding, making it difficult to perform the performance of lithium-ion batteries. Reducing the silicon particle size can effectively reduce expansion, but the reduction of silicon particles leads to an increase in specific surface area, and silicon particles are prone to agglomeration during homogenization, which greatly reduces the application effect of this method. When the particles in the pole piece expand, they squeeze each other and cause the particles to break.

[0030] In order to solve the above problems, an embodiment of the present application provides a negative electrode material, as shown in Figure 1, the negative electrode material includes a core 11, a first shell 12 and a second shell 13, the first shell 12 is arranged on the surface of the core 11, and the second shell 13 is arranged on the surface of the first shell 12, the core 11 includes an active material, the first shell 12 includes a first polymer material, and the second shell 13 includes a conductive material, and the first polymer material includes at least one of a halogen, a hydroxyl group, a carboxyl group, an aldehyde group, an amino group, a thiol group, a carbonyl group, and an amide group.

[0031] Among them, because the first polymer material includes polar groups such as halogen, hydroxyl, carboxyl, aldehyde, amino, thiol, carbonyl, and amide, it can be firmly wrapped around the surface of the core, and the first polymer material can directly wrap the conductive material evenly around the surface, not only making the stress caused by particle expansion more uniform, but also making it possible to maintain a conductive network after the core particles expand and break in the later stage, its cycle performance is better, and the expansion and DC resistance are lower, thereby improving the problem that the negative electrode material is easily deformed due to volume change, affecting the cycle life of the battery. Furthermore, the above-mentioned groups possessed by the first polymer material can improve the suppression of the expansion rate of the core, reduce the battery expansion rate, and improve the cycle performance and cycle life of the battery. In some embodiments, the first polymer material comprises at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polydopamine, and polyacrylic acid embedded with a thiol group.

[0032] Optionally, in one embodiment, the active material has active sites on its surface, and at least a portion of the first polymer material is grafted onto the surface of the active material. In this embodiment, by surface-treating the active material with an oxidizing agent or the like, active sites are introduced onto its surface, facilitating the secure grafting of the first polymer material onto the surface, forming the first shell. This can enhance the first shell's ability to absorb stress during expansion of the active material, further reducing the active material's expansion rate. Energy spectrum analysis using a scanning electron microscope combined with infrared spectroscopy can identify the elements and groups on the surface of the negative electrode material core, thereby confirming the extent of grafting of the first polymer material onto the active material surface.

[0033] Alternatively, in one embodiment, the active material comprises at least one of a silicon-based active material and a tin-based active material. The active material has a high theoretical capacity and can improve the energy density of the battery. A first shell layer comprising a first polymer material and a second shell layer comprising a conductive material are sequentially formed on the surface of the active material. This not only makes the stress caused by particle expansion more uniform, but also allows the conductive network to be maintained after the core particles expand and break in the later stage. This results in better cycle performance, lower expansion and DC resistance, and can fully utilize the advantages of its high theoretical capacity. In some embodiments, the active material further comprises a carbonaceous material, wherein the carbonaceous material comprises at least one of graphite, hard carbon, or soft carbon.

[0034] Optionally, in a specific embodiment, the above-mentioned silicon-based active material includes at least one of silicon-carbon composite materials, single crystal silicon, silicon alloys, pre-lithiated silicon, and pre-magnesiumized silicon, wherein pre-lithiated silicon is a pre-lithiation treatment of silicon oxide materials (structural formula SiOx, 0<x≤2) to convert part of the silicon atoms into lithium silicate phase, and pre-magnesiumized silicon is a pre-magnesiumization treatment of silicon oxide materials to convert part of the silicon atoms into magnesium silicate phase, thereby improving the first coulombic efficiency of the battery.

[0035] Optionally, in a specific embodiment, the above-mentioned active sites can be at least one of hydroxyl, carboxyl, acyl chloride, azo, and epoxy groups, which are not only easy to form on the surface of active materials with relatively large expansion such as silicon-based and tin-based materials, but also can be effectively grafted with polar groups in the first polymer material.

[0036] Optionally, in one embodiment, the conductive material includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0037] Optionally, in a specific embodiment, the conductive material comprises carbon nanotubes with an aspect ratio of 500 to 10,000:1, which can fully utilize the carbon nanotube winding to inhibit expansion and provide buffering, thereby improving the performance of the lithium-ion battery. The aspect ratio of the carbon nanotubes can be 500:1, 800:1, 1200:1, 1800:1, 2500:1, 3600:1, 5500:1, 8000:1, 10,000:1, or any two of these. Optionally, in some embodiments, the conductive material is selected from carbon nanotubes with an aspect ratio of 1,000 to 5,000:1; alternatively, in some embodiments, the conductive material is selected from carbon nanotubes with an aspect ratio of 2,000 to 3,000:1; and alternatively, in some embodiments, the conductive material is selected from carbon nanotubes with an aspect ratio of 2,300 to 2,800:1.

[0038] Optionally, in one embodiment, the negative electrode material further includes a third shell layer 14, which is disposed on the surface of the second shell layer 13. The third shell layer 14 comprises a second polymer material selected from a dendrimer and / or a hyperbranched polymer. In this embodiment, by coating the surface of the second shell layer 13 with the third shell layer 14 formed of the second polymer material, the core and the conductive material can be further bound, thereby improving the stripping force. The mutual repulsion between the polymer materials can also be used to prevent the agglomeration of the negative electrode material, thereby improving the dispersion of the negative electrode material during the slurrying process.

[0039] Optionally, in some embodiments, the second polymer material may further include a linear polymer.

[0040] Optionally, in one embodiment, the second shell layer further comprises a binder selected from a linear polymer. Adding a linear polymer as a binder to the second shell layer facilitates uniform dispersion of the conductive material, while using a dendrimer and / or a hyperbranched polymer in the third shell layer can reduce entanglement between chain molecules, lower the viscosity of the negative electrode slurry, increase the solid content, and improve the peeling force.

[0041] The linear polymer, dendrimer and hyperbranched polymer are each independently selected from at least one of polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyimide, styrene-butadiene rubber, polystyrene, polypropylene glycol and polyvinyl alcohol.

[0042] Alternatively, in one embodiment, the particle size Dv50 of the core is 0.01 to 10 μm, for example, 0.01 μm, 1 μm, 2.5 μm, 3.8 μm, 4.3 μm, 5.9 μm, 7.0 μm, 8.2 μm, or 10 μm, or any two thereof. Alternatively, in some embodiments, the particle size Dv50 of the core is 0.5 to 8 μm.

[0043] Optionally, in some embodiments, the particle size Dv50 of the core is 2-5 μm.

[0044] Optionally, in one embodiment, the thickness of the second shell layer is 5 to 250 nm, for example, it can be a range of one or any two of 5 nm, 40 nm, 50 nm, 80 nm, 130 nm, 180 nm, 220 nm, and 250 nm; in some embodiments, the thickness of the second shell layer is 10 to 200 nm; in some embodiments, the thickness of the second shell layer is 50 to 150 nm; in some embodiments, the thickness of the second shell layer is 80 to 100 nm.

[0045] Optionally, in one embodiment, the thickness of the third shell layer is 5 to 150 nm, for example, it can be a range of one or any two of 5 nm, 30 nm, 50 nm, 80 nm, 100 nm, 120 nm, and 150 nm; in some embodiments, the thickness of the third shell layer is 10 to 120 nm; in some embodiments, the thickness of the third shell layer is 50 to 100 nm; in some embodiments, the thickness of the third shell layer is 70 to 80 nm.

[0046] In some embodiments, the thickness of the first shell layer is 5 to 80 nm, for example, 5 nm, 10 nm, 20 nm, 45 nm, 60 nm, or 80 nm. A first shell layer with a suitable thickness can ensure that the first shell layer constrains the core and reduces core expansion.

[0047] The present application also proposes a secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode material as described above. The secondary battery comprises a lithium-ion secondary battery.

[0048] In the secondary battery provided in the embodiment of the present application, the negative electrode plate also includes a conductive agent and a binder; optionally, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes a carboxymethyl cellulose-based binder and a resin binder.

[0049] Optionally, in one embodiment, the carboxymethyl cellulose-based binder includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based binder includes one or more of styrene rubber, polyacrylic acid, and polyacrylonitrile.

[0050] In some embodiments, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of a negative electrode current collector such as copper foil; and after baking, rolling, cutting and other processes, the negative electrode sheet can be obtained.

[0051] In some embodiments, the surface density of the negative electrode active material layer is 0.007 to 0.013 g / cm 2 .

[0052] In some embodiments, the compaction density of the negative electrode sheet is 1.3 to 1.9 g / cm 3 .

[0053] The secondary battery provided in the embodiment of the present application further includes a positive electrode plate, a separator and an electrolyte.

[0054] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, which may include a lithium ion transition metal oxide, a ternary positive electrode material, or the like. The lithium ion transition metal oxide may include at least one of lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate. The ternary positive electrode material may specifically be a high-nickel layered ternary positive electrode material.

[0055] Optionally, in one embodiment, the positive electrode plate further includes a conductive agent, and the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0056] In some embodiments, the positive electrode sheet is prepared as follows: the components for preparing the positive electrode sheet, such as the positive electrode active material including the above-mentioned positive electrode material, the binder and the conductive agent are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector such as aluminum foil; after drying, rolling, die-cutting and other processes, the positive electrode sheet can be obtained.

[0057] The electrolyte conducts ions between the positive and negative electrodes and can be liquid, gel, or solid. In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent, wherein the electrolyte salt is a lithium salt.

[0058] In practical applications, the negative electrode sheet, the positive electrode sheet and the separator are wound to obtain a core, the core is packaged to obtain a dry cell, and the dry cell is baked and then injected with liquid, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0059] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0060] For the above-mentioned secondary battery embodiments and electrical equipment embodiments, their negative electrode plates include a negative electrode active material layer, and the above-mentioned negative electrode active material layer includes the above-mentioned negative electrode material, and can achieve the same technical effects. To avoid repetition, they will not be described here. For relevant details, please refer to the partial description of the negative electrode material embodiment.

[0061] In order to make the application purpose, technical solutions and beneficial effects of this application clearer, the present application is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate this application and are not used to limit the scope of this application.

[0062] The present application is described in detail below through examples.

[0063] Test method:

[0064] (1) Shell thickness test:

[0065] The material was frozen in liquid nitrogen and then sliced, and the thickness of the outer layer of the material was visually tested using electron microscopy.

[0066] (2) 25℃ cycle test:

[0067] At 25°C, the lithium-ion battery is charged and discharged at 1C / 1C in the voltage range of 2.5-4.2V until the capacity of the lithium-ion battery is less than 80% of the initial capacity. The number of cycles of the lithium-ion battery is recorded to characterize the cycle performance of the battery. The unit is cycle.

[0068] (3)DCR test:

[0069] At 25°C, discharge the lithium-ion battery at 0.5C to 2.5V, then charge it to 4.2V at a constant current of 0.5C, charge it to a cutoff current of 0.05C at a constant voltage, and then discharge it to 2.5V at 0.5C. Note the discharge capacity at this time as C0. Then fully charge it at 0.5C0, discharge it for 60 minutes to 50% SOC, and finally test DCR using 4C DC 10S.

[0070] (4) Test of battery negative electrode expansion rate:

[0071] 1. Take the negative electrode sheet before winding, use a vernier caliper to measure the thickness of the negative electrode sheet at different positions, and take the average thickness as the initial thickness H0 of the negative electrode sheet.

[0072] 2. Perform a cycle test on the battery at 25°C. After 500 cycles, disassemble the battery and use a vernier caliper to measure the thickness of the negative electrode at different positions after the cycle. Take the average thickness as the final thickness value H1 of the negative electrode. The expansion rate of the negative electrode = 100% * (H1-H0) / H0.

[0073] Example 1

[0074] (1) Preparation of negative electrode materials:

[0075] a. Weigh 10 kg of nano-silicon material (particle size of 15 nm) and place it in a container. Then add 20 L of 30% hydrogen peroxide to the container, then add 30 L of concentrated sulfuric acid and ultrasonically vibrate for 100 minutes to allow it to react fully. After the reaction is completed, filter out the liquid and then ultrasonically clean it with deionized water, and dry it to obtain the hydroxylated silicon material;

[0076] b. Add 10 kg of hydroxylated silicon material to a reactor containing 50 L of SOCl2 (thionyl chloride) and 100 L of carbon tetrachloride, heat to 55 ° C, stir magnetically for 8 hours, distill off carbon tetrachloride under reduced pressure, heat to 60 ° C, evacuate, remove residual SOCl2, and dry to obtain a surface acyl chloride silicon material;

[0077] c. Add 10 kg of the acyl chloride silicon material to a reactor containing 100 L of tetrahydrofuran and 20 kg of lithium carboxymethyl cellulose with a solid content of 1.2%, heat to 60° C., magnetically stir for 1 hour, and reflux in an oil bath at 100° C. for 5 hours. After the reaction, repeatedly rinse with deionized water to obtain a first silicon material having a first shell layer, and test its grafting rate;

[0078] d. Dispersing the first silicon material in linear polyacrylic acid (average molecular weight 3 million), carbon nanotubes (single-walled CNT powder), a dispersant (sodium cellulose CMC2200), and a surfactant (Ashland K30) with stirring and dispersing, adjusting the viscosity of the mixture with deionized water, and then spray-granulating the mixture to obtain a second silicon material having a second shell layer, and measuring the thickness of the second shell layer; wherein the aspect ratio of the carbon nanotubes is 1000:1, the evaporation water rate of the spray dryer is 780 mL / min, the inlet temperature is 170° C. to 180° C., and the outlet temperature is 120° C. to 130° C.;

[0079] e. The second silicon material, dendritic polyacrylic acid, and surfactant (Ashland K30) obtained in the previous step were stirred and dispersed with deionized water to adjust the viscosity of the mixture, and then the mixture was spray granulated to obtain a negative electrode material having a third shell layer, and the thickness of the third shell layer was measured; wherein the evaporation water rate of the spray dryer was 780 mL / min, the inlet temperature was 170°C to 180°C, and the outlet temperature was 120°C to 130°C to prepare the negative electrode material of the present application.

[0080] (2) Preparation of negative electrode sheet

[0081] a. Homogenate:

[0082] The negative electrode material, carbon black, graphite and binder (Indile LA136D) were placed in a planetary mixer at a mass ratio of 10.6:0.5:86.4:2.5 and homogenized for 2 h. Appropriate deionized water was added to adjust the viscosity to 7000-8000 mPa.s to obtain a negative electrode slurry;

[0083] b. Coating:

[0084] The negative electrode slurry is coated on the negative electrode current collector copper foil using a dedicated transfer coating device. The thickness of the copper foil is 8 μm. The gap coating is performed on both sides of the copper foil. The coated electrode sheet is dried to obtain the negative electrode sheet. The coating weight of the negative electrode sheet is 0.0082 g / cm 2 .

[0085] c. Roller pressing:

[0086] The above pole pieces are passed through a roller mill and compacted to a density of 1.6 g / cm 3 , that is, a negative electrode sheet that can be used for subsequent battery production is obtained.

[0087] (4) Preparation of positive electrode sheet

[0088] 97 parts by mass of ternary material (NCM 811), 3 parts of conductive carbon black, and 0.5 parts of carbon nanotubes were dry-mixed to obtain a dry blend, and then 1.5 parts of polyvinylidene fluoride was added to the dry blend, and mixed to obtain a positive electrode slurry;

[0089] The positive electrode slurry is coated on aluminum foil by extrusion coating, dried at high temperature, and then rolled and die-cut to obtain a positive electrode sheet.

[0090] (5) Preparation of lithium-ion batteries

[0091] The prepared positive electrode sheet, negative electrode sheet and separator are wound into a core using a winding machine, which is then encapsulated with aluminum-plastic film. After being baked under vacuum for 48 hours to remove moisture, a lithium salt electrolyte is injected, and the battery is then formed and capacity-divided to prepare a lithium-ion battery.

[0092] Example 2

[0093] The difference between Example 2 and Example 1 is that in the step (c) of preparing the negative electrode material, 10 kg of silicon chloride material is added to a reactor containing 100 L of tetrahydrofuran and 20 kg of sodium carboxymethyl cellulose.

[0094] Example 3

[0095] The difference between Example 3 and Example 1 is that in the step (c) of preparing the negative electrode material, 10 kg of silicon chloride material is added to a reactor containing 100 L of tetrahydrofuran and 20 kg of sodium alginate.

[0096] Example 4

[0097] The difference between Example 4 and Example 1 is that in the step (c) of preparing the negative electrode material, 10 kg of silicon chloride material is added to a reaction kettle containing 100 L of tetrahydrofuran and 20 kg of polydopamine.

[0098] Example 5

[0099] The difference between Example 5 and Example 1 is that in the step (c) of preparing the negative electrode material, 10 kg of silicon chloride material is added to a reaction kettle containing 100 L of tetrahydrofuran and 20 kg of polyacrylic acid embedded with thiol groups.

[0100] Example 6

[0101] The difference between Example 6 and Example 1 is that in the preparation step (b) of the negative electrode material, SOCl2 and carbon tetrachloride are replaced by succinic anhydride and silane coupling agent to form a surface carboxylated silicon material.

[0102] Example 7

[0103] The difference between Example 7 and Example 1 is that in the preparation step (b) of the negative electrode material, the material in step (a) is first added to toluene, and then the silane coupling agent KH570 is added and refluxed for 8 hours, and then DMSO (dimethyl sulfoxide), ACVA (azobiscyanovaleric acid), and lutidine are added to the container, protected by nitrogen, and reacted for 4 hours at a temperature of 55°C to form a surface azo silicon material.

[0104] Example 8

[0105] The difference between Example 8 and Example 1 is that in the preparation step (b) of the negative electrode material, SOCl2 and carbon tetrachloride are replaced by a silane coupling agent and methyl methacrylate glycidyl ester to form a surface epoxy silicon material.

[0106] Example 9

[0107] The difference between Example 9 and Example 1 is that step (b) is not included in the preparation of the negative electrode material, and in step (c), 10 kg of hydroxylated silicon material is directly added to a reactor containing 100 L of tetrahydrofuran and 20 kg of lithium carboxymethyl cellulose to form a surface hydroxylated silicon material.

[0108] Example 10

[0109] The difference between Example 10 and Example 1 is that in the step (e) of preparing the negative electrode material, the dendritic polyacrylic acid is replaced by a hyperbranched polyacrylic acid.

[0110] Example 11

[0111] The difference between Example 11 and Example 1 is that in the step (d) of preparing the negative electrode material, the dendritic polyacrylic acid is replaced by a dendritic styrene-butadiene rubber.

[0112] Example 12

[0113] The difference between Example 12 and Example 1 is that in the step (d) of preparing the negative electrode material, the linear polyacrylic acid is replaced by linear polyimide.

[0114] Example 13

[0115] The difference between Example 13 and Example 1 is that in the step (d) of preparing the negative electrode material, carbon nanotubes with an aspect ratio of 500:1 are used.

[0116] Example 14

[0117] The difference between Example 14 and Example 1 is that in the step (d) of preparing the negative electrode material, carbon nanotubes with an aspect ratio of 10000:1 are used.

[0118] Example 15

[0119] The difference between Example 15 and Example 1 is that in the step (d) of preparing the negative electrode material, the carbon nanotubes are replaced with conductive carbon black.

[0120] Example 16

[0121] The difference between Example 16 and Example 1 is that in the step (d) of preparing the negative electrode material, the carbon nanotubes are replaced by graphene.

[0122] Example 17

[0123] The difference between Example 17 and Example 1 is that in the step (a) of preparing the negative electrode material, nano-silicon with a Dv50 of 10 nm is used.

[0124] Example 18

[0125] The difference between Example 18 and Example 1 is that in the step (a) of preparing the negative electrode material, nano-silicon with a Dv50 of 10000 nm is used.

[0126] Example 19

[0127] The difference between Example 19 and Example 1 is that in the step (d) of preparing the negative electrode material, the spray outlet pressure is adjusted (so that the thickness of the second shell layer is 120 nm).

[0128] Example 20

[0129] The difference between Example 20 and Example 1 is that in the step (d) of preparing the negative electrode material, the spray outlet pressure is adjusted (so that the thickness of the second shell layer is 250 nm).

[0130] Examples 21 to 23

[0131] The difference between Examples 21 to 23 and Example 1 is that in the steps (d) and (e) of preparing the negative electrode material, the spray outlet pressure is adjusted to adjust the thickness of the second shell layer and the third shell layer.

[0132] Example 24

[0133] The difference between Example 24 and Example 1 is that in the preparation of the negative electrode material, nano-silicon is replaced by nano-tin.

[0134] Example 25

[0135] The difference between Example 24 and Example 1 is that step e is not included in the preparation of the negative electrode material.

[0136] Comparative Example 1

[0137] The difference between Comparative Example 1 and Example 1 is that the surface of the nano-silicon is not coated.

[0138] The components and parameters of the negative electrode sheets in each embodiment and comparative example are shown in Table 1.

[0139] Table 1

[0140] The batteries prepared in each embodiment were subjected to a 25°C cycle test, a DCR test, and an expansion rate test of the negative electrode plate. The test data are shown in Table 2.

[0141] Table 2

[0142] As can be seen from the above data, the use of the negative electrode material of the present application can effectively suppress the expansion rate of the negative electrode plate, reduce the DC internal resistance of the battery, and improve the battery cycle performance. The reason is that the first polymer material and the conductive material are coated on the surface of the active material, which can make the first polymer material firmly wrapped around the surface of the core, and the conductive material can be evenly wrapped around the surface. This not only makes the stress caused by particle expansion more uniform, but also allows the conductive network to be maintained after the core particles expand and break in the later stage. Its cycle performance is better and the expansion and DC resistance are lower. This solves the problem that existing silicon, tin or their alloy-based negative electrode materials are prone to deformation of the plate due to volume change, affecting the battery cycle life and rate performance.

[0143] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the claims are intended to include the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0144] The above is a detailed introduction to a negative electrode material, a secondary battery and an electrical device provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, according to the ideas of the present application, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A negative electrode material, wherein: The negative electrode material comprises a core, a first shell layer and a second shell layer, wherein the first shell layer is arranged on the surface of the core, and the second shell layer is arranged on the surface of the first shell layer; The inner core includes an active material, the first shell layer includes a first polymer material, the second shell layer includes a conductive material, and the first polymer material includes at least one of halogen, hydroxyl, carboxyl, aldehyde, amino, thiol, carbonyl, and amide.

2. The negative electrode material according to claim 1, wherein The surface of the active material has active sites, and at least a portion of the first polymer material is grafted onto the surface of the active material.

3. The negative electrode material according to claim 2, wherein The active site comprises at least one of a carbonyl group, a hydroxyl group, a carboxyl group, an acyl chloride group, an azo group, and an epoxy group.

4. The negative electrode material according to claim 1, wherein The negative electrode material further includes a third shell layer, which is disposed on the surface of the second shell layer. The third shell layer includes a second polymer material, which includes a dendritic polymer and / or a hyperbranched polymer.

5. The negative electrode material according to claim 4, wherein The second polymer material also includes a linear polymer.

6. The negative electrode material according to claim 4, wherein The second shell layer further comprises a binder, wherein the binder comprises a linear polymer, and the first polymer material comprises at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polydopamine, and polyacrylic acid embedded with a thiol group.

7. The negative electrode material according to claim 6, wherein The linear polymer, the dendritic polymer and the hyperbranched polymer are each independently selected from at least one of polyacrylic acid, polyacrylonitrile, polymethyl methacrylate, polyimide, styrene-butadiene rubber, polystyrene, polypropylene alcohol and polyvinyl alcohol.

8. The negative electrode material according to claim 4, wherein The particle size Dv50 of the core is 0.01 to 10 μm; and / or The thickness of the second shell layer is 5 to 250 nm; and / or The thickness of the third shell layer is 5 to 150 nm.

9. The negative electrode material according to any one of claims 1 to 8, wherein The thickness of the first shell layer is 5-80 nm.

10. The negative electrode material according to claim 1, wherein The active material includes at least one of a silicon-based active material and a tin-based active material.

11. The negative electrode material according to claim 10, wherein The silicon-based active material includes at least one of silicon carbon, single crystal silicon, silicon alloy, pre-lithiation silicon, and pre-magnesiation silicon.

12. The negative electrode material according to claim 10, wherein The active material further includes a carbonaceous material, and the carbonaceous material includes at least one of graphite, hard carbon or soft carbon.

13. The negative electrode material according to claim 1, wherein The conductive material includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; And / or, the conductive material comprises carbon nanotubes with an aspect ratio of 500 to 10000:

1.

14. A secondary battery, comprising a negative electrode plate, wherein: The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer comprises the negative electrode material according to any one of claims 1 to 13.

15. The secondary battery according to claim 14, wherein The negative electrode plate also includes a conductive agent and a binder.

16. The secondary battery according to claim 15, wherein The conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes a carboxymethyl cellulose-based binder and a resin-based binder.

17. An electrical device, wherein: The secondary battery comprises the secondary battery according to any one of claims 14 to 16, wherein the secondary battery is used as a power supply for the electrical device.

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