Negative electrode material, negative electrode sheet, and battery

Abstract

The present application relates to the field of battery, in particular to a negative electrode material, a negative electrode sheet containing the negative electrode material and a battery containing the negative electrode material. The negative electrode material comprises a silicon-containing material, the silicon-containing material has a core-shell structure, the core of the core-shell structure comprises a silicon-based material, and the shell layer of the core-shell structure at least comprises elements F and P. The negative electrode material of the present application comprises a silicon-containing material with a core-shell structure, the shell layer of which can not only better alleviate the expansion and contraction of the core, but also has good compatibility with the electrolyte, thereby improving the initial efficiency and energy density of the battery.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more specifically to negative electrode materials, negative electrode sheets containing the negative electrode materials, and batteries containing the negative electrode materials. Background Technology

[0002] With the rapid development of lithium-ion battery technology, lithium-ion batteries are being used more and more widely in portable mobile electronic devices such as laptops and smartphones, and people's requirements for battery energy density are also getting higher and higher.

[0003] Currently, graphite-doped silicon anodes are the main method for improving battery energy density; however, silicon anodes have poor cycle performance. Typically, to improve the cycle performance of silicon anodes, the surface of the silicon anode material is coated, but this does not significantly improve cycle performance.

[0004] Therefore, it is very important to discover a battery that balances energy density and cycle performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a negative electrode material, a negative electrode sheet containing the negative electrode material, and a battery containing the negative electrode material. The negative electrode material of this invention comprises a coated silicon-based material. This coating layer not only adapts well to the expansion and contraction of the silicon-based material but also has good compatibility with the electrolyte, thereby improving the battery's initial efficiency and energy density.

[0006] In silicon-doped anodes, conventional coatings cannot adapt to the expansion and contraction of the silicon anode, leading to coating layer cracking. With continued cycling, the electrolyte continuously permeates through these cracks, reacting with the freshly exposed interface of the silicon anode material, ultimately causing its gradual failure. The inventors of this invention have discovered that coating the silicon anode with a shell comprising at least elements F and P can effectively isolate the electrolyte from contact with the silicon anode, thereby preventing the failure of the silicon anode material due to continuous electrolyte erosion.

[0007] The first aspect of the present invention provides a negative electrode material, the negative electrode material comprising a silicon-containing material having a core-shell structure, the core of the core-shell structure comprising a silicon-based material, and the shell of the core-shell structure comprising at least element F and element P.

[0008] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in the first aspect of the present invention.

[0009] A third aspect of the present invention provides a battery comprising the negative electrode material described in the first aspect of the present invention and / or the negative electrode sheet described in the second aspect of the present invention.

[0010] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: the negative electrode material of the present invention can effectively isolate the direct contact between the electrolyte and the silicon-containing negative electrode material, thereby avoiding the failure of the silicon-containing negative electrode material caused by direct exposure of the silicon-containing negative electrode material to the electrolyte, and thus effectively improving the cycle performance of the battery.

[0011] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0012] Figure 1 The image shown is a scanning electron microscope image of the silicon-containing material in Embodiment 1 of the present invention.

[0013] Figure 2 The image shown is an energy dispersive spectroscopy (EDS) diagram of the silicon-containing material in Example 1 of this invention. Detailed Implementation

[0014] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0015] The first aspect of the present invention provides a negative electrode material, which may include a silicon-containing material.

[0016] In this invention, the term "silicon-containing material" refers to silicon-based materials that have not undergone modification treatment or have undergone modification treatment. The modification treatment can be coating modification, doping modification, or simultaneous coating and doping modification.

[0017] In one example, the silicon-containing material is a silicon-based material that has been coated and modified.

[0018] In one example, the silicon-containing material has a core-shell structure, wherein the core of the core-shell structure comprises a silicon-based material, and the shell of the core-shell structure comprises at least element F and element P.

[0019] The inventors of this invention have discovered that when the shell layer includes at least element F and element P, the rate performance and cycle stability of the silicon-containing material are significantly improved.

[0020] like Figure 1 The image shown is a scanning electron microscope (SEM) image of a silicon-containing material according to an example of the present invention. As can be seen from the image, the silicon-containing material has a core-shell structure. Figure 2The figure shows an energy dispersive spectroscopy (EDS) analysis diagram of a silicon-containing material in an example of the present invention. As can be seen from the figure, the shell of the silicon-containing material includes elements F and P.

[0021] In this invention, the shell may include organic salts.

[0022] In this invention, the term "organic salt" has its conventional meaning in the art. The term "organic salt" refers to an ionic compound comprising an anion and a cation, wherein the anion and / or the cation comprises an organic functional group, such as 1-butyl-3-methylimidazolium hexafluorophosphate, 1-vinyl-3-ethylimidazolium hexafluorophosphate, 1-decyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethane sulfonate, 1-ethyl-3-methylimidazolium diethyl phosphate, and 1-ethyl-3-methylimidazolium dicyanamide.

[0023] The inventors of this invention have discovered that coating silicon-based materials with organic salts can further improve the stability of silicon-based materials in electrolytes, thereby effectively improving the problem of rapid cycle decay of silicon-based materials. The reason may be that the organic salts coated on the surface of silicon-based materials can better alleviate the expansion and contraction of silicon-based materials, and the organic salts have good stability in electrolytes (the organic salts have good compatibility with electrolytes). As silicon-based materials expand and contract, they can provide good protection for silicon-based materials, thereby avoiding failure caused by continuous reaction between the electrolyte and the fresh interface of the silicon-based materials.

[0024] In one instance, the organic salt comprises hexafluorophosphate ions.

[0025] The inventors of this invention have discovered that when the structure of the organic salt contains conjugated double bonds, the rate performance of the silicon-containing material can be further improved. This may be because the conjugated double bonds can form lithium-ion transport channels, thereby increasing the migration rate of lithium ions on the surface of the silicon-containing material and thus improving the rate performance.

[0026] In one example, the organic salt comprises the structure shown in Formula 1:

[0027]

[0028] Among them, R1 and R2 are each independently selected from C. 1-18 Hydrocarbon groups, such as C 1-18 Alkyl, C 1-18 alkenyl or C 1-18 Alkyne group.

[0029] In this invention, the term "C" 1-18 "With the conventional meaning in this field, the term "C" 1-18"" refers to the number of carbon atoms ranging from 1 to 18.

[0030] The imidazole groups in the organic salt can better adapt to the expansion and contraction of the silicon-based material, thereby avoiding failure caused by direct reaction between the electrolyte and the silicon-based material, and thus improving the electrochemical performance of the negative electrode material. Meanwhile, the structure shown in Formula 1 has good compatibility with the electrolyte and exhibits excellent stability in the electrolyte.

[0031] In one example, the organic salt comprises at least one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-vinyl-3-ethylimidazolium hexafluorophosphate, and 1-decyl-3-methylimidazolium hexafluorophosphate.

[0032] The inventors of this invention have discovered that when the sum of the masses of the elements F and P is greater than 50% of the total mass of the shell, the organic salt can form a quasi-artificial solid electrolyte membrane on the surface of the silicon-based material. This not only effectively protects the silicon-based material, but also allows the quasi-artificial solid electrolyte membrane to function as an SEI membrane, thereby improving the battery's initial efficiency and energy density.

[0033] In one instance, the ratio of the sum of the masses of element F and element P to the total mass of the shell is greater than 50%.

[0034] In one example, the organic salt comprises at least one of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-vinyl-3-ethylimidazolium hexafluorophosphate.

[0035] The aforementioned organic salts can form a quasi-artificial solid electrolyte membrane on the surface of silicon-based materials. This not only effectively protects the silicon-based materials, but also functions as an SEI membrane, improving the battery's initial efficiency and energy density.

[0036] In one example, the organic salt is a combination of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-vinyl-3-ethylimidazolium hexafluorophosphate.

[0037] The silicon-based material can be a silicon anode material conventionally used in the art, such as at least one selected from silicon, silicon-carbon, silicon-oxygen, and silicon alloys.

[0038] In one example, the silicon-based material is silicon-carbon.

[0039] In one example, the silicon-based material is silicon oxide.

[0040] In one example, the silicon-based material is SiO2. x (0 < x < 2).

[0041] The inventors of this invention have discovered that when the negative electrode material includes a carbon-based material, the expansion of the silicon-based material can be effectively suppressed, while the cycle performance of the battery using the silicon-based material can be improved.

[0042] In this invention, the negative electrode material may further include carbon-based materials.

[0043] The carbon-based material can be a carbon anode material conventionally used in the art, such as at least one selected from graphite, carbon nanotubes, graphene, soft carbon, hard carbon, and carbon black.

[0044] In one example, the carbon-based material is graphite.

[0045] In one instance, the graphite includes at least one of synthetic graphite and natural graphite.

[0046] The median particle size D50 of the core can be 5μm-15μm, for example, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm or 15μm.

[0047] The inventors of this invention have discovered that when the median particle size D50 of the core is within a certain range, the silicon-containing material exhibits optimal kinetic performance, exhibits fewer side reactions with the electrolyte, and is easier to handle during the coating process.

[0048] In one example, the median particle size D50 of the core is 6 μm-9 μm.

[0049] The median particle size D50 of the silicon-containing material can be 5.1μm-20μm, for example 5.1μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0050] The inventors of this invention have discovered that when the median particle size D50 of the silicon-containing material is within a certain range, the silicon-containing material exhibits optimal kinetic performance, exhibits fewer side reactions with the electrolyte, and is easier to handle during the coating process.

[0051] In one example, the median particle size D50 of the silicon-containing material is 7 μm-12 μm.

[0052] The thickness of the shell can be 0.1μm-5μm, for example 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm, 3μm, 4μm or 5μm.

[0053] The inventors of this invention have discovered that when the thickness of the shell is within a certain range, it can provide sufficient protection for the core without affecting the electrochemical performance of the battery.

[0054] In one example, the thickness of the shell is 1 μm-3 μm.

[0055] The mass ratio of the silicon-containing material to the carbon-based material can be 1:(0.25-99), for example, 1:0.25, 1:0.5, 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:99.

[0056] In one example, the mass ratio of the silicon-containing material to the carbon-based material is 1:(1-33).

[0057] In one example, the mass ratio of the silicon-containing material to the carbon-based material is 1:(2-19).

[0058] The mass ratio of the shell to the core can be 1:(10-100), for example, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95 or 1:100.

[0059] In one example, the mass ratio of the shell to the core is 1:(19-49).

[0060] The mass ratio of the organic salt to the silicon-based material can be 1:(10-100), for example, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, or 1:100.

[0061] In one example, the mass ratio of the organic salt to the silicon-based material is 1:(19-49).

[0062] The present invention also provides a method for preparing the silicon-containing material, the method comprising at least the following steps:

[0063] (1) Dissolve the organic salt in a solvent to obtain an organic salt solution;

[0064] (2) Mix the organic salt solution obtained in step (1) with the silicon-based material and heat until the solvent is completely evaporated.

[0065] In this invention, in step (1), the solvent includes at least one of deionized water and ethanol.

[0066] In this invention, step (2) further includes heating under continuous stirring.

[0067] In this invention, in step (2), the heating temperature is 50℃-100℃.

[0068] In this invention, the organic salt forms a coating layer on the surface of the silicon-based material. It is understood that the thickness of the coating layer is related to the amount of organic salt and silicon-based material fed into the material; when the amount of organic salt fed into the material is constant, the thickness of the coating layer is related to the heating time.

[0069] The method for preparing silicon-containing materials provided by the present invention involves dissolving an organic salt with a specific chemical structure in a solvent to form a liquid phase, thereby coating the surface of a silicon-based material to form a uniform coating layer. The method for preparing silicon-containing materials of the present invention can easily control the quality and thickness of the organic salt coating layer and ensure the uniformity of the organic salt coating layer.

[0070] The negative electrode material of the present invention includes a silicon-containing material and a carbon-based material. The silicon-containing material is a coated and modified silicon-based material. The coating layer of the silicon-based material can not only adapt well to the expansion and contraction of the silicon-based material, thereby avoiding failure caused by direct reaction between the electrolyte and the silicon-based material; but also the coating layer has good compatibility with the electrolyte and good stability in the electrolyte; furthermore, the coating layer can form a quasi-artificial solid electrolyte membrane on the surface of the silicon-based material. This quasi-artificial solid electrolyte membrane can act as an SEI membrane, improving the battery's initial efficiency and energy density.

[0071] A second aspect of the present invention provides a negative electrode sheet, the negative electrode sheet comprising the negative electrode material described in the first aspect of the present invention.

[0072] The negative electrode sheet includes a negative electrode current collector and a coating disposed on at least one side surface of the negative electrode current collector, the coating comprising the negative electrode material described in the first aspect of the present invention.

[0073] The coating may also include additives commonly used in coatings, such as conductive agents and binders.

[0074] In one example, the coating includes the negative electrode material, the conductive agent, and the binder.

[0075] The conductive agent may include conductive agents conventionally used in the art, such as at least one selected from Super P, acetylene black, and Ketjen black.

[0076] The adhesive may include adhesives conventionally used in the art, for example, the adhesive is selected from at least one of sodium carboxymethyl cellulose, carboxymethyl cellulose, polyvinylidene fluoride and styrene-butadiene rubber.

[0077] Based on the total weight of the coating, the content of the negative electrode material can be 80-99% by weight (e.g., 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% by weight), the content of the conductive agent can be 0.5-10% by weight (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5% by weight), and the content of the binder can be 0.5-10% by weight (e.g., 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5% by weight).

[0078] In one example, based on the total weight of the coating, the content of the negative electrode material is 95-98.5% by weight, the content of the conductive agent is 0.5-2.5% by weight, and the content of the binder is 0.5-2.5% by weight.

[0079] In one example, based on the total weight of the coating, the content of the negative electrode material is 96-98% by weight, the content of the conductive agent is 1-2% by weight, and the content of the binder is 1-2% by weight.

[0080] A third aspect of the present invention provides a battery comprising the negative electrode material described in the first aspect of the present invention or the negative electrode sheet described in the second aspect of the present invention.

[0081] The components of the battery, excluding the negative electrode (e.g., positive electrode, separator, electrolyte, etc.), can all be conventional choices in the art.

[0082] In one example, the positive electrode includes a positive current collector and a positive active material layer coated on at least one side surface of the positive current collector, the positive active material layer including a positive active material.

[0083] The positive electrode active material can be a conventionally selected material in the art. For example, the positive electrode active material is selected from at least one of lithium cobalt oxide (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), lithium manganese phosphate (LMP), lithium vanadium phosphate (LVP), lithium manganese oxide (LMO), lithium nickel oxide, lithium nickel manganese oxide binary material, lithium-rich manganese-based material, and lithium manganese iron phosphate.

[0084] The positive electrode active material may also include doped and / or coated positive electrode active materials.

[0085] The batteries can all be assembled in accordance with conventional methods in the field.

[0086] The battery can be a liquid electrolyte battery, a semi-solid battery, or an all-solid battery.

[0087] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0088] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0089] The following examples illustrate the battery of the present invention.

[0090] Example 1

[0091] (1) Preparation of silicon-containing materials:

[0092] 0.3 g of 1-butyl-3-methylimidazolium hexafluorophosphate was dissolved in 10 ml of deionized water and stirred thoroughly to form a homogeneous aqueous solution. Then, 9.7 g of silica (median particle size D50 of 7 μm) was added and stirred at high speed (1200 r / min) to completely wet the silica in the homogeneous aqueous solution. The resulting mixture was heated in a water bath at 85 °C and stirred continuously until the solvent was completely evaporated. Then, it was placed in a vacuum drying oven at 100 °C and dried for 24 h to remove residual moisture. The thickness of the 1-butyl-3-methylimidazolium hexafluorophosphate coating layer was 2 μm.

[0093] (2) Preparation of negative electrode sheet:

[0094] The silicon-containing material obtained in step (1) is mixed with graphite, and then conductive carbon black and styrene-butadiene rubber are added. The mass ratio of silicon-containing material, graphite, conductive carbon black and styrene-butadiene rubber is 8.8:88.2:1:2. Deionized water is added and stirred. The mixture is then passed through a 200-mesh sieve to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry is coated onto copper foil using a transfer coating machine, dried at 120°C, and rolled to obtain a negative electrode sheet.

[0095] (3) Preparation of positive electrode sheet:

[0096] Lithium cobalt oxide, carbon nanotubes, acetylene black, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 96:1.2:1.5:1.3. N-methylpyrrolidone was then added and stirred. The mixture was then passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was coated onto aluminum foil using a coating machine, dried at 120°C, and then rolled to obtain a positive electrode sheet.

[0097] (4) Battery fabrication:

[0098] The negative electrode obtained in step (2), the positive electrode obtained in step (3), and the separator (polyethylene film) are wound together to form a core (width of 62 mm), packaged with aluminum-plastic film, baked to remove moisture, and then injected with electrolyte (1.0 mol / L LiPF6, FEC solvent is EC∶DEC∶EMC=2:1:2). After hot pressing, the battery cell is obtained.

[0099] Example 2

[0100] (1) Preparation of silicon-containing materials:

[0101] 0.2 g of 1-vinyl-3-ethylimidazolium hexafluorophosphate was dissolved in 10 ml of deionized water and stirred thoroughly to form a homogeneous aqueous solution. Then, 9.8 g of SiC (median particle size D50 of 6 μm) was added and stirred at high speed (1200 r / min) to completely immerse the SiC in the homogeneous aqueous solution. The resulting mixture was heated in a water bath at 85 °C and stirred continuously until the solvent was completely evaporated. Then, it was placed in a vacuum drying oven at 100 °C and dried for 24 h to remove residual moisture. The thickness of the 1-vinyl-3-ethylimidazolium hexafluorophosphate coating layer was 1 μm.

[0102] (2) Preparation of negative electrode sheet:

[0103] The silicon-containing material obtained in step (1) is mixed with graphite, and then conductive carbon black and styrene-butadiene rubber are added. The mass ratio of silicon-containing material, graphite, conductive carbon black and styrene-butadiene rubber is 32.3:64.7:1:2. Deionized water is added and stirred. The mixture is then passed through a 200-mesh sieve to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry is coated onto copper foil using a transfer coating machine, dried at 120°C, and rolled to obtain a negative electrode sheet.

[0104] (3) Preparation of positive electrode sheet:

[0105] Lithium cobalt oxide, carbon nanotubes, acetylene black, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 96:1.2:1.5:1.3. N-methylpyrrolidone was then added and stirred. The mixture was then passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was coated onto aluminum foil using a coating machine, dried at 120°C, and then rolled to obtain a positive electrode sheet.

[0106] (4) Battery fabrication:

[0107] The negative electrode obtained in step (2), the positive electrode obtained in step (3), and the separator (polyethylene film) are wound together to form a core (width of 62 mm), packaged with aluminum-plastic film, baked to remove moisture, and then injected with electrolyte (1.0 mol / L LiPF6, FEC solvent is EC∶DEC∶EMC=2:1:2). After hot pressing, the battery cell is obtained.

[0108] Example 3

[0109] (1) Preparation of silicon-containing materials:

[0110] A composition of 0.5 g of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-vinyl-3-ethylimidazolium hexafluorophosphate (with a mass ratio of 1:1) was dissolved in 10 ml of deionized water and stirred thoroughly to form a homogeneous aqueous solution. Then, 9.5 g of SiC (median particle size D50 of 9 μm) was added and stirred at high speed (1200 r / min) to completely immerse the SiC in the homogeneous aqueous solution. The resulting mixture was heated in a water bath at 85 °C and stirred continuously until the solvent was completely evaporated. Then, it was placed in a vacuum drying oven at 100 °C and dried for 24 h to remove residual moisture. The thickness of the coating layer of the composition of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-vinyl-3-ethylimidazolium hexafluorophosphate was 3 μm.

[0111] (2) Preparation of negative electrode sheet:

[0112] The silicon-containing material obtained in step (1) is mixed with graphite, and then conductive carbon black and styrene-butadiene rubber are added. The mass ratio of silicon-containing material, graphite, conductive carbon black and styrene-butadiene rubber is 4.8:92.2:1:2. Deionized water is added and stirred. The mixture is then passed through a 200-mesh sieve to obtain a negative electrode slurry with a solid content of 45wt%. The negative electrode slurry is coated onto copper foil using a transfer coating machine, dried at 120°C, and rolled to obtain a negative electrode sheet.

[0113] (3) Preparation of positive electrode sheet:

[0114] Lithium cobalt oxide, carbon nanotubes, acetylene black, and polyvinylidene fluoride were added to a mixing tank in a mass ratio of 96:1.2:1.5:1.3. N-methylpyrrolidone was then added and stirred. The mixture was then passed through a 200-mesh sieve to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was coated onto aluminum foil using a coating machine, dried at 120°C, and then rolled to obtain a positive electrode sheet.

[0115] (4) Battery fabrication:

[0116] The negative electrode obtained in step (2), the positive electrode obtained in step (3), and the separator (polyethylene film) are wound together to form a core (width of 62 mm), packaged with aluminum-plastic film, baked to remove moisture, and then injected with electrolyte (1.0 mol / L LiPF6, FEC solvent is EC∶DEC∶EMC=2:1:2). After hot pressing, the battery cell is obtained.

[0117] Example 4

[0118] This set of examples illustrates the impact of changes in the mass ratio of organic salts to silicon-based materials.

[0119] This set of embodiments is based on Embodiment 1, except that the mass ratio of the organic salt to the silicon-based material is changed. Specifically:

[0120] In Example 4a, 1g of 1-butyl-3-methylimidazolium hexafluorophosphate was dissolved in 10ml of deionized water and stirred thoroughly to form a homogeneous aqueous solution. Then, 10g of silica was added. The thickness of the 1-butyl-3-methylimidazolium hexafluorophosphate coating layer was 4.5μm.

[0121] In Example 4b, 0.1 g of 1-butyl-3-methylimidazolium hexafluorophosphate was dissolved in 10 ml of deionized water and stirred thoroughly to form a homogeneous aqueous solution. Then, 9 g of silicon dioxide was added. The thickness of the 1-butyl-3-methylimidazolium hexafluorophosphate coating layer was 1 μm.

[0122] Example 5

[0123] This set of examples illustrates the impact of changes in the mass ratio of silicon-containing materials to carbon-based materials.

[0124] This set of embodiments is based on Embodiment 1, except that the mass ratio of silicon-containing material to carbon-based material is changed. Specifically:

[0125] In Example 5a, the mass ratio of silicon-containing material, graphite, conductive carbon black, and styrene-butadiene rubber was 48.5:48.5:1:2.

[0126] In Example 5b, the mass ratio of silicon-containing material, graphite, conductive carbon black, and styrene-butadiene rubber was 2.9:94.1:1:2.

[0127] In Example 5c, the mass ratio of silicon-containing material, graphite, conductive carbon black, and styrene-butadiene rubber is 1.1:95.9:1:2 (silicon-containing material).

[0128] Example 6

[0129] This set of examples is used to demonstrate the impact of changes in the material included in the shell.

[0130] This set of embodiments is based on Embodiment 1, except that the 1-butyl-3-methylimidazolium hexafluorophosphate is changed. Specifically:

[0131] In Example 6a, 1-butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal mass of 1-decyl-3-methylimidazolium hexafluorophosphate;

[0132] Example 6b, 1-Butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal mass of 1-Butyl-3-methylimidazolium tetrafluoroborate;

[0133] In Example 6c, 1-butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal mass of 1-ethyl-3-methylimidazolium diethylphosphate.

[0134] Comparative Example 1

[0135] The experiment was carried out in accordance with Example 1, except that 1-butyl-3-methylimidazolium hexafluorophosphate was not added; that is, in this comparative example, silicon suboxide was the silicon-containing material.

[0136] Comparative Example 2

[0137] The procedure was carried out in accordance with Example 1, except that 1-butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal mass of fluoroethylene carbonate.

[0138] Comparative Example 3

[0139] The procedure was carried out in accordance with Example 1, except that 1-butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal mass of ethylene carbonate.

[0140] Comparative Example 4

[0141] The procedure was carried out in accordance with Example 1, except that 1-butyl-3-methylimidazolium hexafluorophosphate was replaced with an equal mass of vinylene carbonate.

[0142] Test case

[0143] (1) Scanning electron microscope image of silicon-containing materials:

[0144] The negative electrode obtained in step (2) of Example 1 was analyzed by scanning electron microscopy. The specific operation steps are as follows: The negative electrode was cut with argon ions using a Leica EM TIC3X ion beam cutting and polishing instrument. The cut cross section was observed by scanning electron microscopy.

[0145] like Figure 1 The image shown is a scanning electron microscope image of a silicon-containing material. It can be seen from the image that 1-butyl-3-methylimidazolium hexafluorophosphate is uniformly coated on the surface of silicon suboxide, forming a uniform and continuous coating layer.

[0146] (2) Energy dispersive spectroscopy analysis of silicon-containing materials:

[0147] The silicon-containing material obtained in step (1) of Example 1 was subjected to EDS energy dispersive spectroscopy analysis. Figure 2 The image shows the energy dispersive spectroscopy (EDS) analysis of the silicon-containing material. It can be clearly seen from the image that the coating layer formed by organic salts on the surface of silicon particles is visible. The unique coating layer formed by 1-butyl-3-methylimidazolium hexafluorophosphate contains F and P elements.

[0148] (3) Specific capacity test

[0149] The silicon-containing materials prepared in the examples and comparative examples were added to conductive carbon black and styrene-butadiene rubber, wherein the mass ratio of silicon-containing materials, conductive carbon black and styrene-butadiene rubber was 97:1:2. Deionized water was added and stirred, and then passed through a 200-mesh sieve to obtain a negative electrode slurry with a solid content of 45wt%. The above negative electrode slurry was coated onto copper foil using a transfer coating machine, dried at 120°C, and rolled to obtain a negative electrode sheet. Lithium half-cell tests were conducted, and the specific test methods are as follows: constant current discharge at 0.05C to 5mV, standing for 10min, constant current discharge at 0.025C to 5mV; constant current charging at 0.05C to 1.5V. The test results are recorded in Table 1.

[0150] (4) Capacity retention test

[0151] The batteries prepared in the examples and comparative examples were subjected to 1C / 1C cycle tests at a test temperature of 25°C, and the test results are recorded in Table 1.

[0152] (5) Energy density test

[0153] The batteries prepared in the examples and comparative examples were tested at 25°C under 0.5C constant current constant voltage charging / 0.2C discharging conditions to measure the battery discharge capacity. The energy density was calculated as discharge capacity × average voltage / (thickness × width × height). The test results are recorded in Table 1.

[0154] Table 1

[0155] Specific capacity (mAh / g) 500T capacity retention rate (%) Energy density (Wh / L) Example 1 1732 87.11 735 Example 2 1844 85.44 740 Example 3 1564 88.86 721 Example 4a 1421 88.79 715 Example 4b 1856 83.78 745 Example 5a 1732 79.54 803 Example 5b 1732 88.45 703 Example 5c 1732 90.67 692 Example 6a 1740 85.23 734 Example 6b 1734 83.63 735 Example 6c 1722 82.65 732 Comparative Example 1 1785 77.56 737 Comparative Example 2 1730 78.21 733 Comparative Example 3 1731 79.23 734 Comparative Example 4 1730 78.34 733

[0156] As can be seen from Table 1, the battery prepared by the negative electrode material of the present invention, compared with the comparative example, has a significantly improved 500T capacity retention rate while maintaining a high energy density.

[0157] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a silicon-containing material, the silicon-containing material has a core-shell structure, the core of the core-shell structure includes a silicon-based material, and the shell of the core-shell structure includes at least element F and element P; The ratio of the sum of the masses of element F and element P to the total mass of the shell is greater than 50%; The thickness of the shell layer is 0.1 μm-5 μm; The shell layer comprises an organic salt, which includes hexafluorophosphate ions; the organic salt comprises the structure shown in Formula 1: Formula 1, R1 and R2 are each independently selected from C1-18 alkyl, C1-18 alkenyl, or C1-18 alkynyl.

2. The negative electrode material according to claim 1, wherein, The organic salt includes at least one of 1-butyl-3-methylimidazolium hexafluorophosphate, 1-vinyl-3-ethylimidazolium hexafluorophosphate, and 1-decyl-3-methylimidazolium hexafluorophosphate.

3. The negative electrode material according to claim 2, wherein the organic salt comprises at least one of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-vinyl-3-ethylimidazolium hexafluorophosphate.

4. The negative electrode material according to claim 1, wherein, The silicon-based material is selected from at least one of silicon, silicon-carbon, silicon-oxygen, and silicon alloys; And / or, the negative electrode material further includes a carbon-based material; And / or, the carbon-based material is selected from at least one of graphite, carbon nanotubes, graphene, soft carbon, hard carbon, and carbon black.

5. The negative electrode material according to claim 1, wherein, The median particle size D50 of the silicon-containing material is 5.1 μm-20 μm; And / or; the median particle size D50 of the core is 5μm-15μm.

6. The negative electrode material according to claim 4, wherein, The mass ratio of the silicon-containing material to the carbon-based material is 1:(0.25-99). And / or, the mass ratio of the shell to the core is 1:(10-100). And / or, the mass ratio of the organic salt to the silicon-based material is 1:(10-100).

7. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode material according to any one of claims 1-6.

8. A battery, characterized in that, The battery comprises the negative electrode material according to any one of claims 1-6 or the negative electrode sheet according to claim 7.

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