Silicon-based negative electrode material and preparation method thereof and lithium-ion battery

Abstract

The present application provides a silicon-based negative electrode material, the silicon-based negative electrode material comprises a core and a shell arranged outside the core, there is a gap between the core and the shell, the material of the core is Li x Si, 0≤x<4.4, the shell is made of lithium fluoride and titanium. The silicon-based negative electrode material has high electronic conductivity, small volume expansion effect, good cycle stability and excellent electrochemical performance. The application also provides a preparation method of the silicon-based negative electrode material and a lithium-ion battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to silicon-based negative electrode materials and preparation methods thereof, and lithium-ion batteries. Background Art

[0002] Existing silicon-based negative electrode materials have attracted widespread attention due to their very high theoretical specific capacity. However, silicon-based negative electrode materials undergo large volume changes during repeated charge and discharge, which may even cause the silicon-based negative electrode materials to shatter, affecting the performance of the silicon-based negative electrode materials, thus seriously restricting the application of silicon-based negative electrode materials. Summary of the invention

[0003] In view of this, the present application provides a silicon-based negative electrode material, a preparation method thereof, and a lithium-ion battery. The silicon-based negative electrode material has high electronic conductivity, small volume expansion effect, good cycle stability, and excellent electrochemical performance. The lithium-ion battery made from the silicon-based negative electrode material has high capacity and good cycle performance, which is conducive to its application.

[0004] In a first aspect, the present application provides a silicon-based negative electrode material, the silicon-based negative electrode material comprising a core and a shell arranged outside the core, a gap is formed between the core and the shell, and the material of the core is Li x Si, 0≤x<4.4, the material of the shell includes lithium fluoride and titanium.

[0005] Optionally, the volume of the voids accounts for 10%-60% of the sum of the volumes of the voids and the inner core.

[0006] Optionally, the porosity of the shell is less than 5%.

[0007] Optionally, the shell has a thickness of 3nm-500nm.

[0008] Optionally, the particle size of the inner core is 20nm-1000nm.

[0009] Optionally, the particle size of the silicon-based negative electrode material is 35nm-2.5μm.

[0010] In the silicon-based negative electrode material provided in the first aspect of the present application, by setting a gap between the inner core and the outer shell, the volume change of the silicon-based negative electrode material can be effectively coped with, the structural morphology can be maintained during the cycle, and the cycle stability can be enhanced; at the same time, the electronic conductivity of the outer shell of the silicon-based negative electrode material is excellent, which can improve the electrochemical performance of the silicon-based negative electrode material; in addition, the outer shell structure is tight, so that when the silicon-based negative electrode material is used in a lithium-ion battery, the consumption of electrolyte and lithium ions can be reduced, thereby improving the cycle performance of the battery.

[0011] In a second aspect, the present application also provides a method for preparing a silicon-based negative electrode material, comprising:

[0012] In Li z The surface of Si particles is coated with titanium tetrafluoride, and a silicon-based negative electrode material is obtained after heat treatment. The silicon-based negative electrode material includes a core and a shell arranged outside the core, and there is a gap between the core and the shell. The material of the core is Li x Si, the material of the shell includes lithium fluoride and titanium, wherein 0≤x<4.4, 0<z≤4.4, x<z.

[0013] Optionally, the Li z The surface of Si particles is coated with titanium tetrafluoride, and after heat treatment, a silicon-based negative electrode material is obtained, including:

[0014] The Li z The Si particles are placed in a first heating chamber, and the titanium tetrafluoride is placed in a second heating chamber, wherein the first heating chamber and the second heating chamber are connected;

[0015] Under a vacuum state, the first heating chamber and the second heating chamber are heated and kept warm for 20 min-2 h to obtain the silicon-based negative electrode material, wherein the heating temperature of the first heating chamber is 60°C-150°C, and the heating temperature of the second heating chamber is 200°C-400°C.

[0016] The preparation method of the silicon-based negative electrode material provided in the second aspect of the present application is simple, easy to operate, suitable for industrial production, and is conducive to the application of silicon-based negative electrode materials.

[0017] In a third aspect, the present application also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode, wherein the negative electrode comprises the silicon-based negative electrode material as described in the first aspect or the silicon-based negative electrode material prepared by the preparation method as described in the second aspect.

[0018] Optionally, the negative electrode includes a negative electrode current collector and a silicon-based negative electrode material layer disposed on the negative electrode current collector, and the silicon-based negative electrode material layer includes the silicon-based negative electrode material.

[0019] Furthermore, the silicon-based negative electrode material layer does not contain a conductive agent.

[0020] The lithium-ion battery provided in the third aspect of the present application has good cycle performance and excellent electrochemical performance, which is conducive to its application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the implementation modes of the present application, the drawings required for use in the implementation modes of the present application will be described below.

[0022] Figure 1A schematic diagram of the structure of a silicon-based negative electrode material provided in one embodiment of the present application.

[0023] Description of labels:

[0024] Core-11, shell-12, void-13, silicon-based negative electrode material-10. DETAILED DESCRIPTION

[0025] The following are preferred implementations of the present application. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application, and these improvements and modifications are also considered to be within the scope of protection of the present application.

[0026] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0027] See also Figure 1 , is a schematic diagram of the structure of a silicon-based negative electrode material 10 provided in one embodiment of the present application, wherein the silicon-based negative electrode material 10 comprises a core 11 and a shell 12 disposed outside the core 11, a gap 13 is formed between the core 11 and the shell 12, and the material of the core 11 is Li x Si, 0≤x<4.4, the material of the shell 12 includes lithium fluoride and titanium.

[0028] In the present application, there is a gap 13 between the core 11 and the shell 12, which can effectively alleviate the volume expansion effect of the silicon-based negative electrode material 10 during use, prevent the occurrence of pulverization of the core 11 during lithium insertion and extraction, maintain the long-term stability of the morphology of the silicon-based negative electrode material 10, and thus enhance the cycle performance; at the same time, the shell 12 contains metallic titanium, which improves the electronic conductivity and electronic network conduction capacity of the silicon-based negative electrode material 10; and the material of the shell 12 includes lithium fluoride and titanium, so that the shell structure is dense. In lithium-ion batteries, the shell 12 is equivalent to an artificial solid electrolyte interface film (SEI film), which blocks direct contact between the electrolyte and the core 11, reduces the consumption of electrolyte and lithium ions, and reduces the generation of SEI film, which is beneficial to improving the electrochemical performance of lithium-ion batteries.

[0029] In this application, the material of the core 11 is Li xSi, 0≤x<4.4. That is to say, when x is 0, the material of the core 11 is silicon material; when 0<x<4.4, the material of the core 11 is lithium silicon alloy material. In the present application, the core 11 can be silicon material, lithium silicon alloy material, or a mixed material of silicon material and lithium silicon alloy material. In one embodiment of the present application, x can be, but is not limited to, 0, 1.71, 2.33, 3.25, 3.75 or 4.4, etc.

[0030] In the embodiment of the present application, the mass fraction of the core 11 in the silicon-based negative electrode material 10 is 50%-85%. That is to say, the mass fraction of the core 11 in the entire silicon-based negative electrode material 10 is 50%-85%. Further, the mass fraction of the core 11 in the silicon-based negative electrode material 10 is 55%-80%. Further, the mass fraction of the core 11 in the silicon-based negative electrode material 10 is 60%-75%. Specifically, the mass fraction of the core 11 in the silicon-based negative electrode material 10 can be, but not limited to, 55%, 58%, 62%, 65%, 69%, 70%, 75%, 76%, 80%, 84%, 85%, 88% or 90%, etc. By setting the core 11 with the above mass proportion, the specific capacity of the silicon-based negative electrode material 10 is guaranteed, which is conducive to its application in lithium-ion batteries.

[0031] In the present application, the shape of the kernel 11 is not limited, and specifically can be but not limited to spherical, quasi-spherical, etc. In the embodiment of the present application, the particle size of the kernel 11 is 20nm-1000nm. It can be understood that when the material is quasi-spherical, the particle size is an equivalent particle size. Further, the particle size of the kernel 11 is 50nm-900nm. Further, the particle size of the kernel 11 is 100nm-800nm. Specifically, the particle size of the kernel 11 can be but not limited to 80nm, 130nm, 150nm, 170nm, 200nm, 300nm, 500nm, 650nm, 700nm, 820nm, 900nm or 970nm, etc. By setting the kernel 11 of the above-mentioned particle size, it is not only beneficial to ensure the specific capacity of the silicon-based negative electrode material 10, but also to alleviate the volume expansion effect to a certain extent, and enhance the cycle performance of the silicon-based negative electrode material 10.

[0032] In the present application, there is a gap 13 between the core 11 and the shell 12, and the gap 13 is conducive to alleviating the volume expansion effect of the core 11 during use, and ensuring the structural stability and cycle performance of the silicon-based negative electrode material 10 during use.

[0033] In the embodiment of the present application, the volume of the void 13 accounts for 10%-60% of the total volume of the void 13 and the core 11. Further, the volume of the void 13 accounts for 15%-55% of the total volume of the void 13 and the core 11. Further, the volume of the void 13 accounts for 20%-50% of the total volume of the void 13 and the core 11. Specifically, the volume of the void 13 may be, but is not limited to, 12%, 15%, 17%, 20%, 23%, 25%, 28%, 30%, 35%, 40%, 45%, 54%, 59% or 60% of the total volume of the void 13 and the core 11. By setting the void 13 with the above volume proportion, it is beneficial to ensure that the volume expansion effect generated by the core 11 is alleviated, and the content of the core 11 can be increased, so as to ensure the cycle performance and specific capacity of the silicon-based negative electrode material 10.

[0034] In the present application, the material of the shell 12 includes lithium fluoride and titanium. The elastic modulus and shear modulus of lithium fluoride are relatively high. When the volume expansion of the core 11 exerts a force on the shell 12 or the shell 12 is subjected to an external force, the shell 12 undergoes a small deformation, thereby ensuring the structural stability of the silicon-based negative electrode material 10 and inhibiting the volume expansion effect of the core 11; and metallic titanium can improve the electronic conductivity of the silicon-based negative electrode material 10. In the embodiment of the present application, the molar ratio of lithium fluoride to titanium in the shell 12 is 4:1.

[0035] In the present application, the shell 12 is a dense structure, which is equivalent to an artificial SEI membrane, and can prevent the direct contact between the core 11 and the electrolyte, thereby reducing the consumption of lithium ions and reducing the production of the SEI membrane. In the embodiment of the present application, the porosity of the shell 12 is less than 5%. Further, the porosity of the shell 12 is less than 3%. Further, the porosity of the shell 12 is less than 2%. Specifically, the porosity of the shell 12 can be, but is not limited to, less than 4%, less than 1% or less than 0.5%, etc.

[0036] In the embodiment of the present application, the thickness of the shell 12 is 3nm-500nm. Further, the thickness of the shell 12 is 15nm-450nm. Further, the thickness of the shell 12 is 50nm-400nm. Specifically, the thickness of the shell 12 can be, but is not limited to, 5nm, 10nm, 60nm, 85nm, 90nm, 100nm, 135nm, 150nm, 180nm, 200nm, 250nm, 280nm, 300nm, 320nm, 370nm, 400nm, 420nm, 450nm, 475nm or 500nm, etc. By setting the shell 12 of the above thickness as the skeleton of the silicon-based negative electrode material 10, the stability of the structure of the silicon-based negative electrode material 10 is ensured. At the same time, the shell 12 of the above thickness can effectively improve the electronic conductivity, and will not increase its own impedance too much, which is more conducive to the improvement of the electrochemical performance of the silicon-based negative electrode material 10.

[0037] In an embodiment of the present application, the particle size of the silicon-based negative electrode material 10 is 35nm-2.5μm. Further, the particle size of the silicon-based negative electrode material 10 is 100nm-2μm. Further, the particle size of the silicon-based negative electrode material 10 is 300nm-1.5μm. Specifically, the particle size of the silicon-based negative electrode material 10 can be but is not limited to 50nm, 80nm, 100nm, 200nm, 250nm, 300nm, 400nm, 500nm, 750nm, 900nm, 1μm, 1.2μm, 1.5μm, 2μm, 2.3μm or 2.5μm, etc.

[0038] The present application also provides a method for preparing a silicon-based negative electrode material 10, comprising: z The surface of Si particles is coated with titanium tetrafluoride, and after heat treatment, a silicon-based negative electrode material is obtained. The silicon-based negative electrode material includes a core and a shell arranged outside the core, and there is a gap between the core and the shell. The material of the core is Li x Si, the material of the shell includes lithium fluoride and titanium, wherein 0≤x<4.4, 0<z≤4.4, x<z.

[0039] In the implementation manner of the present application, z is set to 2<z≤4.4. Specifically, Li z Si may include Li 1.71 Si, Li 2.33 Si, Li 3.25 Si, Li 3.75 Si, Li 4.4 At least one of Si, etc.

[0040] In the implementation mode of the present application, in Li z The surface of Si particles is coated with titanium tetrafluoride, and after heat treatment, a silicon-based negative electrode material is obtained, including: z Si particles are placed in the first heating chamber, and titanium tetrafluoride is placed in the second heating chamber. The first heating chamber and the second heating chamber are connected. Under vacuum conditions, the first heating chamber and the second heating chamber are heated and kept warm for 20min-2h to obtain silicon-based negative electrode materials, wherein the heating temperature of the first heating chamber is 60℃-150℃, and the heating temperature of the second heating chamber is 200℃-400℃. In this process, the second heating chamber is heated to sublime titanium tetrafluoride, which enters the first heating chamber and is coated on the Li z Si particle surface; while the first heating chamber heats Li z Si particles make Li z Lithium removal from Si particles z The titanium tetrafluoride on the surface of the Si particles reacts to generate lithium fluoride and titanium to form the outer shell 12, and due to the removal of lithium, Li zThe Si particle volume becomes smaller, so that the generated shell 12 is closely connected to the smaller Li z The gaps 13 are formed between Si particles, and after heat treatment, the volume of Li z The Si particles become the core 11. Under the above heating conditions, Li z Lithium in Si particles can be easily released to react with silicon materials to ensure that the gaps of appropriate size are obtained. z While the surface of Si particles is coated with titanium tetrafluoride, titanium tetrafluoride is also reacting with lithium, and the two processes are carried out simultaneously. Optionally, the heating rate of the first heating chamber and the second heating chamber is 1°C / min-20°C / min. Specifically, the heating rates of the first heating chamber and the second heating chamber are respectively selected from 1°C / min, 3°C / min, 5°C / min, 7°C / min, 10°C / min, 12°C / min, 15°C / min or 18°C / min. In one embodiment, Li z Si particles and titanium tetrafluoride were placed in two sample slots respectively, and then placed in two different but interconnected heating chambers. Under vacuum, the heating chamber where titanium tetrafluoride was located was heated to 200°C. z The heating chamber where the Si particles are located is heated to 80°C and kept warm for 20min-2h to obtain the silicon-based negative electrode material. z The sample tank of Si particles has a stirring function. Further, the stirring speed is less than 10 rpm. This is more conducive to forming a shell 12 with a uniform distribution of materials.

[0041] In one embodiment of the present application, the shell 12 is made of lithium fluoride and titanium. That is, in the above preparation process, titanium tetrafluoride is completely reacted and no residue remains. In another embodiment of the present application, the shell 12 is made of lithium fluoride, titanium and titanium tetrafluoride, wherein the mass content of titanium tetrafluoride is less than 5%. That is, a small amount of titanium tetrafluoride remains in the above preparation process.

[0042] In the embodiment of the present application, the preparation of the silicon-based negative electrode material 10 is carried out under a protective gas. Specifically, the protective gas includes at least one of nitrogen, helium, hydrogen, etc.

[0043] The relevant parameters and functions of the silicon-based negative electrode material 10 prepared by the preparation method of the present application are as described above and will not be repeated here.

[0044] The preparation method of the silicon-based negative electrode material 10 provided in the present application is simple, easy to operate, suitable for industrial production, and is conducive to the application of the silicon-based negative electrode material 10.

[0045] The present application also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode, wherein the negative electrode comprises the silicon-based negative electrode material 10 in any of the above embodiments.

[0046] In the embodiment of the present application, the negative electrode includes a negative electrode current collector and a silicon-based negative electrode material layer disposed on the negative electrode current collector, and the silicon-based negative electrode material layer includes a silicon-based negative electrode material 10. Specifically, the thickness of the silicon-based negative electrode material layer may be, but is not limited to, 5 μm-50 μm.

[0047] In the embodiment of the present application, the silicon-based negative electrode material layer does not contain a conductive agent. Since the shell 12 contains metallic titanium, the electronic conductivity of the silicon-based negative electrode material 10 is improved. Therefore, a conductive base may not be added to the silicon-based negative electrode material layer, so that the silicon-based negative electrode material layer can include a silicon-based negative electrode material 10 with a large content and electrochemical activity, thereby making the capacity of the negative electrode larger and the energy density of the lithium-ion battery higher. It is understandable that in order to further improve the electronic conductivity, a conductive agent can also be added to the silicon-based negative electrode material layer.

[0048] In an embodiment of the present application, the silicon-based negative electrode material layer also includes at least one of the binders. Among them, the binder helps to firmly fix the silicon-based negative electrode material layer on the negative electrode current collector and make the silicon-based negative electrode material layer have a certain elasticity. In one embodiment of the present application, the binder may include but is not limited to polythiophene, polypyrrole, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyacrylamide, ethylene-propylene-diene copolymer resin, styrene butadiene rubber, polybutadiene, fluororubber, polyvinyl pyrrolidone, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, carboxypropyl cellulose, ethyl cellulose, polyethylene oxide, sodium carboxymethyl cellulose and styrene-butadiene rubber. In another embodiment of the present application, the mass percentage of the binder in the silicon-based negative electrode material layer is 0.01%-10%. Specifically, the mass percentage of the binder in the silicon-based negative electrode material layer may be, but is not limited to, 0.05%-9.5%, 0.1%-9%, 1%-8.5% or 2.5%-7%.

[0049] In the embodiment of the present application, the positive electrode may include a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, wherein the positive electrode material layer may include a positive electrode active material, a conductive agent, and a positive electrode binder.

[0050] In the embodiment of the present application, the positive electrode active material includes one or more of oxide type, sulfide type, polyanion type and composites of the above materials. In one embodiment of the present application, the oxide type positive electrode active material may include but is not limited to TiO2, Cr3O8, V2O5, MnO2, NiO, WO3, LiMn2O4, Li2CuO2, LiCom Ni 1-m O2(0≤m≤1), LiCo a Ni 1-a-b Al b O2(0≤a≤1,0≤b≤1), LiFe c Mn d G e O4 (G is selected from at least one of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn and Mo, 0≤c≤1, 0≤d≤1, 0≤e≤1, c+d+e=1), Li 1+f L 1－g－h H g R h O2 (L, H and R are independently selected from at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S and B, and L, H and R are different elements, and -0.1≤f≤0.2, 0≤g≤1, 0≤h≤1, 0≤g+h≤1) etc. Specifically, the oxide-type positive electrode active material may be, but is not limited to, one or more of LiCoO2, LiNiO2, LiMn2O4. In another embodiment of the present application, the sulfide-type positive electrode active material may include TiS2, V2S3, FeS, FeS2, WS2, LiJS i (J is selected from at least one of Ti, Fe, Ni, Cu and Mo, 1≤i≤2.5), etc. In another embodiment of the present application, the polyanionic positive electrode active material may specifically include at least one of LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3 and LiVPO4F.

[0051] In the embodiment of the present application, the particle size of the positive electrode active material is 100 nm-500 μm. Specifically, the particle size of the positive electrode active material may be, but is not limited to, 100 nm-100 μm, 100 nm-50 μm or 500 nm-50 μm.

[0052] In the present application, there is no particular restriction on the positive electrode binder in the positive electrode material layer, for example, it can be at least one of fluorine-containing resin, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, etc. There is no particular restriction on the conductive agent in the positive electrode material layer, and conventional materials available in the art can be used, such as at least one of conductive carbon black (such as acetylene black, Ketjen black), carbon nanotubes, carbon fibers and graphite. In one embodiment of the present application, the mass percentage content of the positive electrode binder in the positive electrode material layer is 0.01%-10%. Specifically, the mass percentage content of the positive electrode binder in the positive electrode material layer can be, but is not limited to, 0.015%-8%, 0.02%-7%, 0.02%-5% or 0.05%-4.5%, etc. In another embodiment of the present application, the mass percentage content of the conductive agent in the positive electrode material layer is 0.1%-20%. Specifically, the mass percentage of the conductive agent in the positive electrode material layer may be, but is not limited to, 0.5%-18%, 1%-15%, 1%-10% or 3%-8.5%.

[0053] In the embodiment of the present application, the above-mentioned negative electrode current collector and positive electrode current collector are independently selected from metal foil or alloy foil. Among them, the metal foil includes copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold or silver foil, and the alloy foil includes stainless steel, or an alloy containing at least one element of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold and silver. For example, the negative electrode current collector can be specifically aluminum foil, and the positive electrode current collector can be specifically copper foil. The thickness and surface roughness of the negative electrode current collector and the positive electrode current collector in this application can be adjusted according to actual needs.

[0054] In the present application, there is no particular limitation on the electrolyte, which is a solution containing lithium ions, for example, the solute in the electrolyte includes at least one of LiPF6, LiClO4, LiBF4, and LiAsF6, and the solvent may be, but not limited to, ethylene carbonate, dimethyl carbonate, and the like. Further, additives may be added to the electrolyte to improve the performance of the lithium-ion battery. Specifically, the additives may be, but not limited to, anisole, carbodiimide compounds, sodium imidazole rings, biphenyls, carbazoles, and the like.

[0055] In the present application, there is no particular restriction on the material of the diaphragm, which may be, but is not limited to, a polymer diaphragm, such as a polyolefin diaphragm, a polyimide diaphragm, etc. The surface of the polymer diaphragm may also be coated with ceramic particles or a polymer coating.

[0056] In an embodiment of the present application, a method for preparing a lithium ion battery is also provided, comprising:

[0057] S201: preparing a negative electrode: mixing the silicon-based negative electrode material 10 with a first solvent, and adding at least one of the binders to obtain a negative electrode mixed slurry; coating the negative electrode mixed slurry on a negative electrode current collector, and obtaining a negative electrode after drying and pressing.

[0058] S202: preparing a positive electrode: mixing a positive electrode active material, a conductive agent, a positive electrode binder and a second solvent evenly to obtain a positive electrode mixed slurry; coating the positive electrode mixed slurry on a positive electrode current collector, drying and pressing to obtain a positive electrode.

[0059] S203: Assemble the positive electrode, the separator and the negative electrode, and inject the electrolyte to obtain a lithium-ion battery.

[0060] In the embodiment of the present application, the first solvent, the second solvent and the third solvent are independently selected from at least one of water, ethanol, toluene, xylene, anisole, acetonitrile, heptane, decane, ethyl acetate, ethyl propionate, butyl butyrate, N-methylpyrrolidone, acetone, etc. The amount of each solvent can generally be 50wt%-400wt% of the mass of dry materials in the corresponding mixed slurry.

[0061] In the embodiment of the present application, the tabletting may be, but is not limited to, roller pressed at 0-5 MPa.

[0062] In the embodiment of the present application, the temperature of the hot pressing treatment may be but is not limited to about 100°C, and the hot pressing treatment time may be but is not limited to 0.5h-3h; the isostatic pressing pressure may be but is not limited to above 100MPa, for example, the pressure is 100MPa-300MPa; the isostatic pressing treatment time may be but is not limited to 3min-10min.

[0063] In the embodiment of the present application, S203 includes: a lithium-ion battery can be made by winding or stacking the battery cells into lithium-ion battery cells, and the battery cells are sealed in a battery metal shell to obtain a lithium-ion battery, and then the lithium-ion battery is obtained after liquid injection, aging, formation, and capacity separation.

[0064] The lithium-ion battery provided in the present application, because it contains the above-mentioned silicon-based negative electrode material 10, has high battery capacity and good cycle performance, which is beneficial to its application.

[0065] The present application is further described below with reference to a number of embodiments.

[0066] Example 1

[0067] A preparation method for a lithium ion battery, comprising:

[0068] (1) Preparation of negative electrode

[0069] Under protective atmosphere, 1000g Li1.71 Si negative electrode material (particle size about 50nm) and 200g TiF4 were placed in two different sample slots, and the two sample slots were placed in two different sealed heating chambers (heating chamber volume>2.5L). The two sealed heating chambers were connected to each other, and Li 1.71 The Si sample tank has a stirring function. Use a vacuum pump to extract the gas to ensure the vacuum state in the heating chamber. Under slow stirring (<10rpm), heat up at a rate of 5℃ / min. The heating chamber containing titanium tetrafluoride is heated to 200℃, and Li 1.71 The heating chamber of Si is heated to 80°C and kept warm for 40 minutes to obtain a silicon-based negative electrode material, which is then taken out after natural cooling. The silicon-based negative electrode material includes a core and an outer shell, with a gap between the core and the outer shell. The core is silicon particles, and the outer shell is made of lithium fluoride and titanium.

[0070] 940g of silicon-based negative electrode material (94%) and 60g of adhesive SBR rubber (6%) were added to 1000mL of toluene solvent, and then stirred in a mixer to form a stable and uniform negative electrode slurry. The negative electrode slurry was uniformly and intermittently coated on copper foil (copper foil width 160mm, thickness 16μm), then dried at 373K, and cut into lithium battery negative electrodes with a size of 480mm (length) × 45mm (width) after roller pressing. The scanning electron microscope (SEM) results of the sample cut by focused ion beam (FIB) showed that the particle size of silicon particles in the silicon-based negative electrode material was about 80nm, the thickness of the shell was 10nm, and the average particle size of the silicon-based negative electrode material was about 120nm.

[0071] (2) Preparation of positive electrode

[0072] 930g LiCoO2 positive electrode material (93%), 30g binder PVDF (3%), 20g acetylene black (2%), 20g conductive agent carbon fiber (2%) were added to 1500g N-methylpyrrolidone solvent, and then stirred in a vacuum mixer to form a stable and uniform positive electrode slurry. The positive electrode slurry was uniformly and intermittently coated on the two opposite surfaces of aluminum foil (aluminum foil width 160mm, thickness 16μm), then dried at 393K, pressed by a roller press, and cut into lithium battery positive electrodes with a size of 480mm (length) × 45mm (width).

[0073] (3) Production of lithium-ion batteries

[0074] The positive electrode, negative electrode and polypropylene separator with a thickness of 20 μm are wound into a square lithium-ion battery cell, and the cell is sealed in a square battery aluminum shell of 5 mm×34 mm×50 mm to make a 053450 type lithium-ion battery. The lithium-ion battery is then obtained after liquid injection, aging, formation and capacity separation.

[0075] Example 2

[0076] A preparation of a lithium ion battery, which is substantially the same as Example 1, except that Li 1.71 Si negative electrode material changes to Li 4.4 Si negative electrode material, the core of the obtained silicon-based negative electrode material is Li 3.75 Si particles; LiCoO2 positive electrode material is changed to TiS2 positive electrode material, and the rest of the steps remain unchanged. The scanning electron microscopy (SEM) results of the sample cut by focused ion beam (FIB) show that Li 3.75 The particle size of Si particles is about 75nm, the thickness of the shell is 10nm, and the average particle size of the silicon-based negative electrode material is about 120nm.

[0077] Example 3

[0078] A preparation of a lithium ion battery, which is substantially the same as Example 1, except that 1000 g Li 1.71 Si negative electrode material (particle size about 50nm), 200g TiF4, but 1000g Li 1.71 Si negative electrode material (particle size of about 30nm), 150g TiF4, the scanning electron microscope (SEM) results of the sample after focused ion beam cutting (FIB) showed that the particle size of silicon particles in the silicon-based negative electrode material was about 17nm, the thickness of the shell was 2nm, and the average particle size of the silicon-based negative electrode material was about 30nm.

[0079] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided:

[0080] Comparative Example 1

[0081] A preparation of a lithium ion battery, which is different from Example 1 in that 940 g of silicon particles are used to replace the silicon-based negative electrode material in Example 1, and the other steps remain unchanged.

[0082] Comparative Example 2

[0083] A preparation of a lithium ion battery, which differs from Example 2 in that 940 g of Li 3.75 Si particles replace the silicon-based negative electrode material in Example 1, and the other steps remain unchanged.

[0084] Comparative Example 3

[0085] A preparation of a lithium ion battery, which is different from Example 1 in that the specific operation of step (1) is as follows: 1000 g of Si and 240 g of sucrose are placed together in 1000 mL of deionized water and stirred evenly, and then heated to 100° C. during stirring, and after the water evaporates, the solid is taken out and heated to 300° C. under an inert atmosphere to obtain a carbon-coated silicon negative electrode material, and the carbon-coated silicon negative electrode material is used to replace the silicon-based negative electrode material in Example 1, and the other steps remain unchanged.

[0086] Performance Testing

[0087] The battery cycle life test of the lithium-ion batteries obtained in the above embodiments and comparative examples is carried out as follows: 20 lithium-ion battery samples prepared in each embodiment and comparative example are taken, and each battery is subjected to a charge and discharge cycle test at a rate of 0.1C at 298±1K on a LAND CT2001C secondary battery performance testing device.

[0088] The test steps are as follows: leave for 10 minutes; charge at constant voltage until 4.25V / 0.05C is reached; leave for 10 minutes; discharge at constant current until 3V is reached, which is one cycle. The discharge capacity of the first cycle is recorded (when TiS2 is used as the positive electrode, the upper and lower limits of the voltage are 3V / 0.05C and 1V, respectively, and the other conditions are the same). Repeat the above cycle steps. When the battery capacity is lower than 80% of the initial discharge capacity during the cycle, the cycle is terminated. The number of cycles at the end of the cycle is the cycle life of the battery. The average value is taken for each group. The results are shown in Table 1.

[0089] Table 1 Cycle life test data of each group of samples

[0090]

[0091]

[0092] It can be seen from Table 1 that the lithium ion batteries prepared in Comparative Examples 1-3 have average discharge capacity and poor cycle life, which cannot meet the application requirements of lithium ion batteries; compared with the comparative examples, the performance discharge capacity and cycle life of the lithium ion batteries provided in the embodiments of the present application are greatly improved, and the electrochemical performance is excellent, which is conducive to its widespread use.

[0093] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A silicon-based negative electrode material, characterized in that: The silicon-based negative electrode material comprises a core and a shell arranged outside the core, a gap is formed between the core and the shell, and the core is made of Li x Si, 0≤x<4.4, the material of the shell includes lithium fluoride and titanium; The preparation of the silicon-based negative electrode material comprises: In Li z The surface of Si particles is coated with titanium tetrafluoride, and after heat treatment, a silicon-based negative electrode material is obtained, wherein 0<z≤4.4, x<z.

2. The silicon-based negative electrode material according to claim 1, characterized in that: The volume of the voids accounts for 10%-60% of the sum of the volumes of the voids and the core.

3. The silicon-based negative electrode material according to claim 1, characterized in that: The porosity of the shell is less than 5%.

4. The silicon-based negative electrode material according to claim 1, characterized in that: The thickness of the shell is 3nm-500nm.

5. The silicon-based negative electrode material according to claim 1, characterized in that: The particle size of the core is 20nm-1000nm.

6. The silicon-based negative electrode material according to claim 1, characterized in that: The particle size of the silicon-based negative electrode material is 35nm-2.5μm.

7. A method for preparing a silicon-based negative electrode material, characterized in that: include: In Li z The surface of Si particles is coated with titanium tetrafluoride, and a silicon-based negative electrode material is obtained after heat treatment. The silicon-based negative electrode material includes a core and a shell arranged outside the core, and there is a gap between the core and the shell. The material of the core is Li x Si, the material of the shell includes lithium fluoride and titanium, wherein 0≤x<4.4, 0<z≤4.4, x<z.

8. The preparation method according to claim 7, characterized in that: As stated in Li z The surface of Si particles is coated with titanium tetrafluoride, and after heat treatment, a silicon-based negative electrode material is obtained, including: The Li z The Si particles are placed in a first heating chamber, and the titanium tetrafluoride is placed in a second heating chamber, wherein the first heating chamber and the second heating chamber are connected; Under a vacuum state, the first heating chamber and the second heating chamber are heated and kept warm for 20 min-2 h to obtain the silicon-based negative electrode material, wherein the heating temperature of the first heating chamber is 60°C-150°C, and the heating temperature of the second heating chamber is 200°C-400°C.

9. A lithium ion battery, characterized in that: It comprises a positive electrode, a negative electrode, an electrolyte and a separator located between the positive electrode and the negative electrode, wherein the negative electrode comprises the silicon-based negative electrode material as described in any one of claims 1 to 6 or the silicon-based negative electrode material prepared by the preparation method as described in any one of claims 7 to 8.

10. The lithium ion battery according to claim 9, characterized in that The negative electrode includes a negative electrode current collector and a silicon-based negative electrode material layer disposed on the negative electrode current collector. The silicon-based negative electrode material layer includes the silicon-based negative electrode material, and the silicon-based negative electrode material layer does not contain a conductive agent.

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