Negative electrode material and preparation method, negative electrode sheet, lithium ion battery and electric device

Abstract

The application discloses a negative electrode material and a preparation method thereof, a negative electrode sheet, a lithium ion battery and an electric device. The negative electrode material comprises: an inner core and a coating layer coated on the surface of the inner core; wherein the inner core comprises a silicon-based material, and the coating layer comprises a first coating layer, and the material of the first coating layer is an organic matter represented by the following formula; in the formula, the hydrogen atom in at least one of the three positions of A, B and C on the six-membered ring is replaced by a fluorine atom. The negative electrode material is beneficial to inhibiting the volume expansion of the silicon-based material, and in the first charging process of the battery, the fluorine atom in the organic matter is beneficial to forming a uniform and stable SEI film on the surface of the negative electrode material, thereby being beneficial to reducing the consumption of electrolyte and improving the safety of the battery, and the organic matter is also beneficial to improving the diffusion of lithium ions and prolonging the cycle life of the battery.

Description

Technical Field

[0001] The present invention generally relates to the field of new energy technology, and specifically relates to a negative electrode material and a preparation method thereof, a negative electrode plate, a lithium-ion battery and an electrical device. Background Art

[0002] Silicon-based negative electrode materials have a high theoretical specific capacity of up to 4200mAh / g, but the volume expansion of silicon-based negative electrode materials will be about 300% during the lithium insertion process. The large volume expansion will induce the destruction and pulverization of the silicon-based negative electrode structure, and the silicon surface will continuously produce a new SEI film (Solid Electrolyte Interface) with the electrolyte, consuming a large amount of active lithium, thereby causing the electrolyte to be exhausted. At the same time, the volume change will also cause the peeling between the silicon active particles and the current collector, affecting the electronic conductivity of the electrode, causing the battery capacity to decay rapidly, thus greatly limiting the practical application of silicon-based negative electrodes. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, it is desired to provide a negative electrode material and preparation method, a negative electrode plate, a lithium-ion battery and an electrical device. By using organic matter as the first coating layer, the volume expansion of the silicon-based material is suppressed, and during the first charging process of the battery, the fluorine atoms in the organic matter are conducive to forming a uniform and stable SEI film on the surface of the negative electrode material, thereby helping to reduce the consumption of the electrolyte and improve the safety of the battery. At the same time, the organic matter is also conducive to improving the diffusion of lithium ions and increasing the cycle life of the battery.

[0004] In a first aspect, the present invention provides a negative electrode material, comprising: a core and a coating layer coated on the surface of the core;

[0005] Wherein, the core comprises a silicon-based material, the coating layer comprises a first coating layer, and the material of the first coating layer is an organic substance represented by Formula I;

[0006]

[0007] In the formula, the hydrogen atom at at least one of the three positions A, B and C on the six-membered ring is replaced by a fluorine atom.

[0008] Alternatively, the hydrogen atoms at positions A and B in the six-membered ring are replaced by fluorine atoms.

[0009] As an optional solution, the hydrogen atom at the C position in the six-membered ring can be directly replaced by fluorine or by a fluoroalkyl group, wherein the fluoroalkyl group is a C1-C5 fluoroalkyl group.

[0010] As an optional solution, the thickness of the first cladding layer is 10 nm-200 nm.

[0011] As an optional solution, the coating layer further includes a second coating layer, the second coating layer is coated on the surface of the core, the first coating layer is arranged on a side of the second coating layer away from the core, and the second coating layer includes a conductive carbon material;

[0012] As an optional solution, the conductive carbon material includes at least one of soft carbon, hard carbon, and graphene.

[0013] As an optional solution, the thickness of the second cladding layer is 10 nm-300 nm.

[0014] As an optional solution, based on the weight of the negative electrode material, the weight percentage of the silicon-based material is 98%-99.8%.

[0015] As an optional solution, the particle size of the silicon-based material is 1 μm-30 μm.

[0016] As an optional solution, the silicon-based material includes at least one of a single silicon material, a silicon-oxygen composite material, a silicon-carbon composite material, and a silicon alloy material.

[0017] In a second aspect, the present invention provides a method for preparing the negative electrode material of the first aspect, comprising the following steps:

[0018] Materials for preparing the first coating layer:

[0019] The material of the first coating layer is coated on the silicon-based material to obtain the negative electrode material.

[0020] As an optional solution, the material for preparing the first coating layer includes:

[0021] 3,4-dihydroxybenzonitrile is oxidized to convert the hydroxyl group into a carbonyl group to obtain an oxidation product;

[0022] The oxidation product is subjected to F substitution to obtain an organic compound represented by Formula I, which is the material of the first coating layer.

[0023] As an optional solution, the first coating layer material is coated on the silicon-based material to obtain the negative electrode material, comprising:

[0024] The material of the first coating layer is coated on the silicon-based material by a high-temperature solid phase method to obtain the negative electrode material.

[0025] As an optional solution, in the process of coating the silicon-based material with the material of the first coating layer using a high-temperature solid phase method, the coating temperature is 500° C.-800° C.

[0026] As an optional solution, before coating the silicon-based material with the first coating layer material, the preparation method further comprises:

[0027] The silicon-based material and a gaseous carbon source are treated by a chemical vapor deposition method to obtain a silicon-based material coated by a second coating layer; wherein the gaseous carbon source includes acetylene or ethane.

[0028] As an optional solution, the silicon-based material is a silicon-carbon composite material, and before the silicon-carbon composite material is coated to obtain the negative electrode material, the preparation method further includes:

[0029] The carbon precursor is heat-treated to obtain a porous carbon matrix;

[0030] The porous carbon matrix and silane are treated by a chemical vapor deposition method to obtain the silicon-carbon composite material.

[0031] In a third aspect, the present application provides a negative electrode tab, which includes a current collector and the negative electrode material of the first aspect, and the negative electrode material is arranged on at least one side of the current collector.

[0032] In a fourth aspect, the present application provides a lithium ion battery, which includes the negative electrode tab of the third aspect.

[0033] In a fifth aspect, the present application provides an electrical equipment, which includes the battery of the fourth aspect, and the battery supplies power for the electrical equipment.

[0034] The negative electrode material provided by the present application includes a silicon-based material and a coating layer coated on the surface of the silicon-based material, and the coating layer includes a first coating layer, which is an organic matter. On one hand, during the first charging process of the battery, the fluorine atoms in the organic matter are detached, which is beneficial to form a uniform and stable SEI film on the surface of the negative electrode material, reduces the reaction between the electrolyte and the negative electrode material, and thus reduces the consumption of the electrolyte; and after the fluorine atoms in the organic matter are completely released, the organic matter is dissolved in the electrolyte, which is beneficial to inhibit the volatilization and combustion of the electrolyte, and thus is beneficial to improve the safety and cycle life of the battery; on the other hand, the existence of the organic coating layer can relieve and inhibit the material expansion caused by the volume change of the silicon-based material, avoid the detachment of the negative electrode material, and the existence of the cyano group in the organic matter can form a coordination bond or non-covalent bond with lithium ions in the electrolyte, and thus is beneficial to improve the diffusion efficiency of the lithium ions and improve the performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0035] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, read in conjunction with the accompanying drawings:

[0036] Figure 1 It is a scanning electron microscope photo of the negative electrode material of Example 1 of the present application. DETAILED DESCRIPTION

[0037] The present application will be further described in detail below with reference to the embodiments. It will be understood that the specific embodiments described herein are intended only to explain the relevant invention and are not intended to limit the invention. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application may be combined with each other. The present application will be described in detail below with reference to the embodiments.

[0038] At present, among the negative electrode materials of lithium-ion batteries, silicon-based materials have an energy density per weight that is about 10 times higher than that of graphite materials and an energy density per volume that is about 2-3 times higher than that of graphite materials. Depending on the reaction depth, silicon and lithium can generate different products, such as Li7Si3, Li13Si4, Li 22 Si5、Li 12 Si 17 、Li 4.4 Si, etc., in which lithium is embedded in silicon to form Li 4.4 Si alloy has a theoretical specific capacity of up to 4200mAh / g. However, silicon-based materials will undergo drastic volume expansion (up to 300%) and contraction during the lithium insertion and extraction reaction, which will lead to structural damage and pulverization of the electrode material. In addition, the silicon surface will continuously produce a new SEI film with the electrolyte, consuming a large amount of active lithium, thus leading to the exhaustion of the electrolyte. At the same time, the volume change will also lead to the peeling between the active particles and the current collector, affecting the electronic conductivity of the electrode and causing the battery capacity to decay rapidly. These negative effects have greatly limited the practical application of silicon negative electrodes.

[0039] Based on the above problems, on the first aspect, the embodiments of the present application provide a negative electrode material that can improve the problem of reduced battery performance and shortened service life caused by the volume change of silicon during the charge and discharge process of existing silicon-based negative electrode materials.

[0040] The embodiment of the present application provides a negative electrode material, comprising: a core and a coating layer coated on the surface of the core;

[0041] Wherein, the core comprises a silicon-based material, the coating layer comprises a first coating layer, and the material of the first coating layer is an organic substance represented by Formula I;

[0042]

[0043] In the formula, the hydrogen atom at at least one of the three positions A, B and C on the six-membered ring is replaced by a fluorine atom.

[0044] It should be noted that in formula I, the hydrogen atom in any one of the three positions A, B and C can be replaced by a fluorine atom; or, in formula I, the hydrogen atoms in positions A and B can each be replaced by a fluorine atom; or, in formula I, the hydrogen atoms in positions A and C can each be replaced by a fluorine atom; or, in formula I, the hydrogen atoms in positions B and C can each be replaced by a fluorine atom; or, in formula I, the hydrogen atoms in positions A, B and C can all be replaced by fluorine atoms.

[0045] In the negative electrode material of the embodiment of the present application, the first coating layer includes a plurality of fluorine atoms, and F cannot be completely released during the initial charging and discharging. The partially released F and Li in the electrolyte form uniform LiF. With the cycle of the charging and discharging process, the F atoms are completely released, the functional groups in the organic matter (DOBN) can be dissolved in the electrolyte, which can reduce the volatility and flammability of the electrolyte, improve the cycle life and safety life of the battery, and at the same time, the surface of the silicon-based material can alleviate the material expansion caused by the volume change of the silicon.

[0046] The negative electrode material of the embodiment of the present application solves the problems of reduced battery performance and shortened service life caused by the volume change of the existing silicon-based material. The negative electrode material of the embodiment of the present application sets a coating layer on the surface of the silicon-based material, and the coating layer includes a first coating layer, which is an organic matter. On the one hand, during the initial charging of the battery, the fluorine atoms in the organic matter are released, which is conducive to the formation of a uniform and stable SEI film on the surface of the negative electrode material, reduces the reaction between the electrolyte and the negative electrode material, and thus reduces the consumption of the electrolyte; and after the fluorine atoms in the organic matter are completely released, the organic matter is dissolved in the electrolyte, which is conducive to inhibiting the volatilization and combustion of the electrolyte, and thus is conducive to improving the safety and cycle life of the battery; on the other hand, the existence of the organic matter coating layer can alleviate and inhibit the material expansion caused by the volume change of the silicon-based material, avoid the shedding of the negative electrode material, and the existence of the cyan group in the organic matter can form a coordination bond or non-covalent bond with the lithium ions in the electrolyte, and thus is conducive to improving the diffusion efficiency of the lithium ions and improving the battery performance.

[0047] In some embodiments, when the hydrogen atoms in one or two of the three positions A, B and C in formula I are replaced by fluorine atoms, the hydrogen atoms in the remaining positions can remain unchanged, or at least one of the hydrogen atoms in the remaining positions can be replaced by other substituents; wherein the substituents can be but are not limited to cyan groups, low-molecular-weight fluorinated alkyl groups, etc.; if the hydrogen atoms in the three positions A, B and C are all replaced by fluorinated alkyl groups, alkyl lithium will be formed during the cycle process, which will sacrifice the material capacity. Therefore, in order to balance the cycle life and capacity of the battery, at least one of the hydrogen atoms in the three positions A, B and C on the six-membered ring is replaced by a fluorine atom.

[0048] In other embodiments, the hydrogen atoms at at least two of the three positions A, B, and C in Formula I may be substituted with fluoroalkyl groups, which is beneficial for improving the cycle performance of the battery.

[0049] As a practical approach, the hydrogen atoms at the A and B positions in the six-membered ring are substituted with fluorine atoms.

[0050] In this embodiment, the hydrogen atoms at positions A and B in the six-membered ring in Formula I serve as ortho positions to the cyano group. The hydrogen atoms at positions A and B are more active. After the hydrogen atoms at positions A and B are replaced by fluorine atoms, the fluorine atoms at positions A and B are more easily detached and released, which is beneficial to promoting the formation of the SEI film. At the same time, it is also beneficial to the dissolution of organic matter in the electrolyte, reducing the volatility and flammability of the electrolyte.

[0051] As an achievable manner, the hydrogen atom at the C position in the six-membered ring can be directly substituted by fluorine or by a fluoroalkyl group, wherein the fluoroalkyl group is a C1-C5 fluoroalkyl group.

[0052] It should be noted that a fluoroalkyl group refers to an alkyl group in which at least one hydrogen atom is replaced by a fluorine atom. The C1-C5 fluoroalkyl group may be, but is not limited to, a fluoromethyl group, a fluoroethyl group, a fluoro-n-propyl group, a fluoro-isopropyl group, a fluoro-n-butyl group, or a fluoro-pentyl group.

[0053] It can be understood that the hydrogen atoms at positions A and B in the six-membered ring are replaced by fluorine atoms, and the hydrogen atom at position C is directly replaced by a fluorine atom. In this way, the three hydrogen atoms on the six-membered ring are replaced by fluorine atoms. During the first charging of the battery, the fluorine atoms are more easily detached and released, forming a uniform and stable SEI film, which is beneficial to the dissolution of organic matter in the electrolyte, thereby reducing the volatility and flammability of the electrolyte.

[0054] In the six-membered ring, the hydrogen atoms at positions A and B are replaced by fluorine atoms, and the hydrogen atom at position C is replaced by a fluoroalkyl group. In this way, the fluoroalkyl group reduces the spatial structure of the six-membered ring, and the fluorine atom also increases the activity of the alkyl group, which is beneficial to the formation of SEI film at the negative electrode of the lithium-ion battery, protecting the solvent, reducing the consumption of electrolyte and active lithium, and thus improving the performance of the battery.

[0055] In some embodiments, the first cladding layer has a thickness of 10 nm to 200 nm.

[0056] In this embodiment, the thickness of the first coating layer is conducive to reliably suppressing the volume expansion of the silicon-based material, and is also conducive to ensuring the diffusion efficiency of lithium ions.

[0057] Specifically, the thickness of the first coating layer may be, but is not limited to, 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, or 200 nm. When the thickness of the first coating layer is less than 10 nm, the first coating layer is too thin to reliably suppress the volume expansion of the silicon-based material. When the thickness of the first coating layer is greater than 200 nm, the coating layer is too thick, which prolongs the lithium ion transmission path and reduces the lithium ion transmission efficiency.

[0058] As an achievable manner, the coating layer further includes a second coating layer, the second coating layer is coated on the surface of the core, the first coating layer is arranged on a side of the second coating layer away from the core, and the second coating layer includes a conductive carbon material;

[0059] In this embodiment, the second coating layer includes a conductive carbon material, which is mainly used to improve the conductivity of the silicon-based material on the one hand. On the other hand, the presence of the second coating layer further suppresses the volume expansion of the silicon-based material, avoids damage and pulverization of the electrode material, and ensures the structural integrity of the electrode material.

[0060] The first covering layer being arranged on the side of the second covering layer away from the core can be understood as the first covering layer covering the surface of the second covering layer, that is, the second covering layer is located between the core and the first covering layer.

[0061] In a preferred embodiment, the conductive carbon material includes at least one of soft carbon, hard carbon, and graphene.

[0062] The conductive carbon material in this embodiment has readily available raw materials and is easy to prepare, and can reliably improve the conductivity of silicon-based materials.

[0063] As an achievable manner, the thickness of the second cladding layer is 10 nm-300 nm.

[0064] The thickness of the second coating layer in this embodiment is conducive to reliably improving the conductivity of the silicon-based material while reliably suppressing the volume expansion of the silicon-based material and avoiding damage and pulverization of the electrode material.

[0065] Specifically, the thickness of the second coating layer may be, but is not limited to, 10 nm, 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, or 300 nm. When the thickness of the second coating layer is less than 10 nm, the conductivity of the silicon-based material cannot be effectively improved, resulting in poor conductivity of the entire negative electrode material. When the thickness of the second coating layer is greater than 300 nm, the thickness of the second coating layer is relatively large, and combined with the thickness of the first coating layer, the thickness of the entire negative electrode material is relatively large, which affects the transmission of lithium ions.

[0066] In some embodiments, based on the weight of the negative electrode material, the weight percentage of the silicon-based material is 98%-99.8%.

[0067] The weight percentage of the silicon-based material in this embodiment is conducive to ensuring that the entire negative electrode material has a higher specific capacity, while ensuring that the coating layer can reliably coat the silicon-based material, inhibiting the volume expansion of the silicon-based material, and thus ensuring that the negative electrode material has a good cycle life.

[0068] Specifically, the weight percentage of the silicon-based material may be, but is not limited to, 98%, 98.2%, 98.5%, 99%, 99.2%, 99.5%, or 99.8%. When the weight percentage of the silicon-based material is less than 98%, the amount of silicon-based material is less, resulting in poor battery performance of the negative electrode material. When the weight percentage of the silicon-based material is greater than 99.8%, the amount of silicon-based material is greater, and the volume expansion of the silicon-based material may not be reliably suppressed, resulting in structural damage and pulverization of the electrode material. Furthermore, the negative electrode material may have poor conductivity, thereby affecting battery performance.

[0069] As an optional solution, the particle size of the silicon-based material is 1 μm-30 μm.

[0070] The particle size of the silicon-based material of this embodiment is conducive to ensuring that the negative electrode material has a higher specific capacity, which not only controls the cost but also ensures the stability of the formed coating layer structure, thereby further facilitating the suppression of the volume expansion of the silicon-based material during the charge and discharge process.

[0071] Specifically, the particle size of the silicon-based material can be but is not limited to 1μm, 5μm, 10μm, 15μm, 20μm, 25μm or 30μm, etc.; when the particle size of the silicon-based material is greater than 30μm, the particle size of the silicon-based material is too large, which may cause the formed coating layer structure to be unstable. During the charging and discharging process, the coating layer cannot effectively suppress the volume expansion of silicon and the particle size is large, which will result in a longer lithium ion transmission path, affecting the capacity and rate performance of the material; when the particle size of the silicon-based material is less than 1μm, the particle size of the silicon-based material is too small, the particles are easy to agglomerate, affecting the cycle performance and the cost is too high.

[0072] In some embodiments, the silicon-based material includes at least one of a single silicon material, a silicon-oxygen composite material, a silicon-carbon composite material, and a silicon alloy material.

[0073] In summary, the negative electrode material of the present application is provided with a coating layer on the surface of the silicon-based material, and the coating layer includes a first coating layer, and the first coating layer is an organic matter. On the one hand, during the first charging process of the battery, the fluorine atoms in the organic matter fall off, which is conducive to the formation of a uniform and stable SEI film on the surface of the negative electrode material, reducing the reaction between the electrolyte and the negative electrode material, thereby reducing the consumption of the electrolyte; and after the fluorine atoms on the organic matter are completely shed and released, the organic matter dissolves in the electrolyte, which is conducive to inhibiting the volatilization and combustion of the electrolyte, thereby helping to improve the safety and cycle life of the battery; on the other hand, the presence of the organic coating layer can alleviate and inhibit the material expansion caused by the volume change of the silicon-based material, avoid the shedding of the negative electrode material, and the presence of the cyanide group in the organic matter can form a coordination bond with the lithium ions in the electrolyte or undergo non-covalent bond interactions, thereby helping to improve the diffusion efficiency of lithium ions and improve battery performance;

[0074] In addition, the coating layer also includes a second coating layer. The second coating layer is beneficial to improving the conductivity of the negative electrode material while further suppressing the volume expansion of the silicon-based material, avoiding damage and pulverization of the electrode material, ensuring the structural integrity of the electrode material, and thus helping the negative electrode material to have good battery performance.

[0075] In a second aspect, the present invention provides a method for preparing the negative electrode material of the first aspect, comprising the following steps:

[0076] S1. Materials for preparing the first coating layer:

[0077] S2. Coating the silicon-based material with the material of the first coating layer to obtain a negative electrode material.

[0078] In the embodiment of the present application, the silicon-based material and the material in Formula I are subjected to high temperature treatment, so that a coating layer is reliably formed on the surface of the silicon-based material. During the charge and discharge process of the battery, the F released in the coating layer can form a uniform LiF with the Li in the electrolyte, which is coated on the surface of the particles, helping to form a stable and uniform SEI film, thereby preventing the negative electrode material from further contacting the electrolyte to produce side reactions, and the functional groups in the organic matter (DOBN) can be dissolved in the electrolyte, which can reduce the volatility and flammability of the electrolyte, and improve the cycle life and safety life of the battery; and the presence of the cyanide group can form coordination bonds with lithium ions or undergo non-covalent interactions, thereby improving lithium ion diffusion and improving the cycle life.

[0079] In some embodiments, step S1, preparing the material of the first coating layer, comprises:

[0080] 3,4-dihydroxybenzonitrile is oxidized to convert the hydroxyl group into a carbonyl group to obtain an oxidation product;

[0081] The oxidation product is subjected to F substitution to obtain an organic compound represented by Formula I, i.e., the material of the first coating layer;

[0082] The oxidation treatment process may be to react 3,4-dihydroxybenzonitrile with a strong oxidant (such as but not limited to hydrogen peroxide); under the action of the strong oxidant, the hydroxyl group is oxidatively dehydrogenated to a carbonyl group;

[0083] The oxidation product can be subjected to F substitution by light irradiation, and the number of substituted hydrogen atoms can be controlled by controlling the reaction conditions (such as but not limited to the reaction temperature, reaction time, etc.); for example, the oxidation product is reacted with fluorooxytrifluoromethane under light to obtain the organic compound represented by Formula I.

[0084] In some embodiments, step S2, coating the silicon-based material with the material of the first coating layer to obtain the negative electrode material, comprises:

[0085] The material of the first coating layer is coated on the silicon-based material by a high-temperature solid phase method to obtain the negative electrode material.

[0086] Among them, the high-temperature solid-phase method can be understood as the generation of composite products through processes such as contact, reaction, nucleation, and crystal growth between solid interfaces at high temperatures.

[0087] As an achievable manner, in the process of coating the silicon-based material with the material of the first coating layer using a high-temperature solid phase method, the coating temperature is 500° C.-800° C.

[0088] Specifically, the temperature of the coating treatment can be but is not limited to 500°C, 600°C, 700°C or 800°C; when the temperature of the coating treatment is lower than 500°C, reliable coating of the silicon-based material may not be guaranteed; when the temperature of the coating treatment is higher than 800°C, the structure of the negative electrode material may collapse and be damaged.

[0089] The temperature of the coating treatment in the embodiment of the present application is conducive to reliably forming a coating layer on the surface of the silicon-based material, thereby reliably alleviating the volume change of the silicon-based material.

[0090] In some embodiments, before coating the silicon-based material with the first coating layer material, the preparation method further comprises:

[0091] The silicon-based material and the gaseous carbon source are processed by chemical vapor deposition to obtain the silicon-based material coated with the second coating layer; wherein the gaseous carbon source includes acetylene or ethane.

[0092] In this embodiment, it is beneficial to form a conductive carbon material coating layer on the surface of the silicon-based material, thereby improving the conductivity of the negative electrode material and alleviating the volume change of the silicon-based material.

[0093] In some embodiments, the silicon-based material is a silicon-carbon composite material. Before coating the silicon-carbon composite material to obtain the negative electrode material, the preparation method further comprises:

[0094] heat-treating the carbon precursor to obtain a porous carbon matrix;

[0095] The porous carbon matrix and silane are treated by chemical vapor deposition to obtain a silicon-carbon composite material.

[0096] It is understood that the carbon precursor includes at least one of coal tar, coal pitch, petroleum pitch, phenolic resin, epoxy resin, furan resin, furfuryl alcohol resin, polyacrylonitrile, and sugar organic matter.

[0097] This embodiment is conducive to reliably obtaining a silicon-carbon composite material, thereby ensuring that the negative electrode material has a high specific capacity while having good conductive properties.

[0098] In a third aspect, the present invention provides a negative electrode plate comprising a current collector and the negative electrode material of the first aspect, wherein the negative electrode material is disposed on at least one side of the current collector.

[0099] It is understood that the negative electrode material can be disposed on the surface of the current collector by any method, such as but not limited to dry / wet coating, spraying, electrospinning or chemical vapor deposition.

[0100] The current collector may be copper foil or aluminum foil. In a preferred embodiment, the current collector of the negative electrode is usually copper foil.

[0101] The negative electrode material may be provided on one surface or both surfaces of the current collector, which is not specifically limited in the embodiments of the present application.

[0102] It is understood that the negative electrode plates of the embodiments of the present application have all the characteristics and advantages of the above-mentioned negative electrode materials. In short, the negative electrode plates of the embodiments of the present application have excellent battery performance.

[0103] In a fourth aspect, the present invention provides a battery comprising the negative electrode sheet according to the third aspect.

[0104] Therefore, the battery has all the features and advantages of the negative electrode sheet mentioned above, which will not be repeated here. In general, the battery has good capacity performance, safety and excellent cycle performance.

[0105] It is understandable that the battery can be a lithium-ion battery, a solid oxide battery, etc., and the embodiments of the present application do not specifically limit this.

[0106] In a fifth aspect, the present invention provides an electrical device comprising the battery according to the fourth aspect, wherein the battery supplies power to the electrical device.

[0107] Therefore, the electrical device has all the features and advantages of the battery described above, which will not be described in detail here.

[0108] Specifically, the electrical device may be an electric vehicle, a hybrid vehicle, or an intelligent terminal device (such as but not limited to a mobile phone).

[0109] The present invention is described below by means of specific examples. It should be noted that the following specific examples are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0110] Example 1

[0111] Preparation of negative electrode sheet:

[0112] Step 1: 3,4-dihydroxybenzonitrile (structural formula: ) is dissolved in ethanol and hydrogen peroxide is added to oxidize the hydroxyl functional group to a carbonyl group to obtain DOBN Then, F substitution was carried out by light irradiation (the specific process is as follows: DOBN and trichlorofluoromethane were added to a reaction flask with a magnetic stirrer and a reflux condenser, the temperature was cooled to -78°C with liquid nitrogen, and high-pressure mercury lamp was used for irradiation. Fluorooxytrifluoromethane gas was introduced within 1 hour, and the reaction was stirred at -78°C for 30 minutes, and then the temperature was slowly raised to room temperature and stirred for 1 hour to obtain

[0113] Step 2: placing the asphalt in a muffle furnace and maintaining it at a temperature of approximately 1000° C. for 18 hours in an inert gas atmosphere to carbonize it to obtain a porous carbon material matrix;

[0114] Step 3: placing the porous carbon material substrate in a chamber of a chemical vapor deposition (CVD) device, raising the temperature to 400° C., introducing silane gas, and causing the silane to enter the pores of the porous carbon material substrate and further thermally decompose it to obtain a silicon-carbon composite material having silicon deposited in the porous carbon, wherein the D50 of the silicon-carbon composite material is 13.2 μm;

[0115] Step 4: placing the silicon-carbon composite material in a chamber of a CVD device, using acetylene as a carbon source, heating to 700° C., introducing acetylene at a gas flow rate of 2 L / min, and reacting for 1 h to form a second coating layer on the surface of the silicon-carbon composite material. The thickness of the second coating layer is 100 nm.

[0116] Step 5: The silicon-carbon composite material with the second coating layer obtained in step 4 and the silicon-carbon composite material in step 1 The mixture was added into a stirring tank at a mass ratio of 0.99:0.01, stirred for 5 hours, and then sintered at 700°C for 10 hours under a nitrogen atmosphere to form a first coating layer on the surface of the second coating layer. The thickness of the first coating layer was 100 nm, and a double-layer coated silicon-carbon composite particle negative electrode material was finally obtained. The weight proportion of the silicon-carbon composite material in the negative electrode material was about 99%;

[0117] like Figure 1 As shown, the negative electrode material prepared in Example 1 has an obvious coating layer, and the white granular dots are the coating that has not been burned in. If the temperature is further increased, the formation of the internal carbon material will be affected. If the amount of the coating layer added is slightly changed, the effect is not significant. If the amount of the coating layer added is greatly reduced, the improvement effect will be affected. The material in this state has the best effect.

[0118] Step 6: Mix the negative electrode material with the conductive agent CNT, the binder CMC and SBR in deionized water to make a slurry, apply the negative electrode slurry on the copper foil with a coating thickness of 100 μm, dry and cut to obtain the negative electrode sheet.

[0119] Preparation of lithium batteries:

[0120] The above-mentioned negative electrode sheet, lithium sheet, separator, and electrolyte were assembled into a button battery in a glove box for capacity, initial efficiency, and cycle tests.

[0121] Example 2

[0122] The difference between this embodiment and embodiment 1 is that only the first coating layer is formed on the surface of the silicon-carbon composite material, that is, this embodiment does not include step 4, and step 5 directly forms the silicon-carbon composite material obtained in step 3 and the silicon-carbon composite material obtained in step 1. The silicon-carbon composite material was added into a stirring tank in a mass ratio of 0.99:0.01, stirred for 5 hours, and then sintered at 700°C for 10 hours under a N2 atmosphere to form a first coating layer on the surface of the silicon-carbon composite material, and finally a negative electrode material of silicon-carbon composite particles coated with the first coating layer was obtained.

[0123] Example 3

[0124] The difference between this embodiment and embodiment 1 is that the organic matter obtained in this embodiment is

[0125] The preparation method of the organic compound is to add catalyst PdCl2, alkali Na2CO 3、 After nitrogen substitution three times, NaF and DOBN were injected with DMF (dimethylformamide) and heated at 90°C for 6 h. The mixture was then diluted with ethyl acetate, washed three times with water, and dried over anhydrous Na2SO4. The organic solution was concentrated under reduced pressure and finally separated and purified using a silica gel column (petroleum ether:ethyl acetate = 100:1).

[0126] Example 4

[0127] The difference between this embodiment and embodiment 1 is that the organic matter obtained in this embodiment is The preparation method of the organic compound comprises the following steps: adding a catalyst PdCl2, a base Na2CO3, NaF and DOBN to a reaction tube, replacing the reaction mixture with nitrogen three times, injecting DMF, and heating the mixture at 110°C for 8 hours; diluting the mixture with ethyl acetate, washing the mixture with water three times, and drying the mixture with anhydrous Na2SO4; concentrating the organic solution under reduced pressure, and finally separating and purifying the mixture with a silica gel column (petroleum ether:ethyl acetate = 100:1);

[0128] Example 5

[0129] The difference between this embodiment and embodiment 1 is that the organic matter obtained in this embodiment is The preparation method of the organic compound comprises the following steps: adding the sample obtained in Example 3 and a catalyst AlCl3 into a reaction tube, then introducing methane gas, reacting for 5 hours, adding a catalyst PdCl2, a base Na2CO3 and NaF into the reaction tube, replacing the gas with nitrogen three times, injecting DMF, and heating at 110°C for 8 hours; then diluting with ethyl acetate, washing with water three times, and drying with anhydrous Na2SO4, concentrating the organic solution under reduced pressure, and finally separating and purifying the solution using a silica gel column (petroleum ether:ethyl acetate = 100:1);

[0130] Example 6

[0131] The difference between this embodiment and embodiment 1 is that, in the reaction conditions of step 4 of this embodiment, acetylene is introduced, the gas flow rate is 5 L / min, the reaction time is 2 h, and a second coating layer is formed on the surface of the silicon-carbon composite material, and the thickness of the second coating layer is 300 nm;

[0132] Example 7

[0133] This embodiment differs from embodiment 1 in that acetylene is introduced into the reaction conditions of step 4 of this embodiment, the gas flow rate is 0.5 L / min, the reaction time is 0.5 h, and a second coating layer is formed on the surface of the silicon-carbon composite material, and the thickness of the second coating layer is 10 nm;

[0134] Example 8

[0135] This embodiment differs from embodiment 1 in that acetylene is introduced into the reaction conditions of step 4 of this embodiment, the gas flow rate is 0.1 L / min, the reaction time is 0.5 h, and a second coating layer is formed on the surface of the silicon-carbon composite material, and the thickness of the second coating layer is 5 nm;

[0136] Example 9

[0137] The difference between this embodiment and embodiment 1 is that, in the reaction conditions of step 4 of this embodiment, acetylene is introduced, the gas flow rate is 10 L / min, the reaction time is 4 h, and a second coating layer is formed on the surface of the silicon-carbon composite material, and the thickness of the second coating layer is 400 nm;

[0138] Example 10

[0139] The difference between this embodiment and embodiment 1 is that the reaction conditions in step 5 of this embodiment are added to the stirring tank at a mass ratio of 0.98:0.02, stirred for 5 hours, and then sintered at 700°C for 15 hours under N2 atmosphere to form a first coating layer on the surface of the second coating layer. The thickness of the first coating layer is 200 nm.

[0140] Example 11

[0141] The difference between this embodiment and embodiment 1 is that, in the reaction conditions of step 5 of this embodiment, the reaction mixture is added to the stirring tank at a mass ratio of 0.998:0.002, stirred for 5 hours, and then sintered at 700°C for 5 hours under a N2 atmosphere to form a first coating layer on the surface of the second coating layer. The thickness of the first coating layer is 10 nm.

[0142] Example 12

[0143] The difference between this embodiment and embodiment 1 is that the reaction conditions in step 5 of this embodiment are added to the stirring tank at a mass ratio of 0.999:0.001, stirred for 5 hours, and then sintered at 700°C for 2 hours under N2 atmosphere to form a first coating layer on the surface of the second coating layer. The thickness of the first coating layer is 5 nm.

[0144] Example 13

[0145] The difference between this embodiment and embodiment 1 is that, in the reaction conditions of step 5 of this embodiment, the mass ratio of 0.90:0.1 is added to the stirring tank, stirred for 5 hours, and then sintered at 700°C for 15 hours under N2 atmosphere to form a first coating layer on the surface of the second coating layer. The thickness of the first coating layer is 300 nm.

[0146] Comparative Example 1

[0147] The difference between this comparative example and Example 1 is that the negative electrode material in this comparative example directly adopts the silicon-carbon material obtained in steps 2 and 3;

[0148] Comparative Example 2

[0149] The difference between this comparative example and Example 1 is that the negative electrode material in this comparative example is a silicon-carbon composite material coated with a second coating layer, that is, the preparation process of the negative electrode plate does not include steps 1 and 5;

[0150] Comparative Example 3

[0151] The difference between the present comparative example and Example 1 is that the DOBN in the present comparative example is not subjected to fluorine substitution.

[0152] The performance test process of the battery and the test results are described below:

[0153] (1) Coulombic efficiency test

[0154] The button cells prepared in the above examples and comparative examples were subjected to charge-discharge at a voltage range of 0.005-1.5 V in the form of first discharge and then charge at a rate of 0.1 C, and were cycled for 3 times. The discharge capacity of the first cycle was recorded as the gravimetric capacity of the negative electrode material. The charge capacity of the first cycle / the discharge capacity of the first cycle was recorded as the initial efficiency of the negative electrode material.

[0155] (2) Battery cycle performance test

[0156] In an inert gas glove box with water and oxygen content less than 0.1 ppm, it was assembled into a negative electrode / electrolyte / lithium metal button cell. The charge-discharge cycle test was carried out at a current density of 0.2 C, and was cycled for 100 cycles. The capacity retention rate was calculated.

[0157] The results of the battery tests of Examples 1-13 and Comparative Examples 1-3 according to the above process and method are shown in Table 1:

[0158] Table 1 Test results of Examples 1-13 and Comparative Examples 1-3

[0159]

[0160]

[0161] According to the results shown in Table 1:

[0162] From the results of Examples 1-13 and Comparative Examples 1-3, it can be seen that by providing a coating layer on the surface of the silicon-based material, the coating layer includes a first coating layer, and the first coating layer is an organic matter. During the first charging of the battery, the fluorine atoms of the first coating layer fall off, which is beneficial to form a uniform and stable SEI film on the surface of the negative electrode material, reduces the reaction between the electrolyte and the negative electrode material, inhibits the volume expansion of the silicon-based material, ensures the structural stability of the material, and improves the cycle performance; the second coating layer is a conductive carbon material, which can improve the conductivity of the silicon-based material and improve the rate performance. Moreover, the carbon material can buffer the volume change caused by the expansion of the silicon-based material. When both coating layers exist, the cycle performance can be guaranteed to the maximum extent on the premise of maintaining the capacity. When the coating layer is small, it cannot inhibit the expansion, improve the conductivity, and stabilize the SEI. When the coating layer is thick, it will affect the diffusion of lithium ions, and thus reduce the battery performance.

[0163] It should be noted that the discharge gram capacity of Comparative Example 2 and Comparative Example 3 is not much different from that of the examples, which may be due to inconsistent capacity release caused by the process of assembling the battery or preparing the electrode sheet; but the initial efficiency and capacity retention of Comparative Example 2 and Comparative Example 3 are greatly different from those of the examples, mainly because Comparative Example 2 does not perform organic coating, and Comparative Example 3 does not perform F substitution on the organic coating layer. Since the organic coating layer has a great influence on the initial efficiency and cycle performance of the battery, and the negative electrode is discharged (i.e., the negative electrode is embedded with lithium) first during the discharge of the negative electrode, the lithium sheet is delithiated, and the discharge gram capacity is only related to the active sites of the negative electrode, and the coating layer does not affect this discharge gram capacity. During the discharge process, an SEI film is formed on the negative electrode, and when the negative electrode is delithiated during charging, the coating layer of the negative electrode will affect the SEI film, thereby affecting the charging capacity and the initial efficiency. Therefore, the presence or absence of the organic coating layer has little effect on the initial discharge capacity, but has a great influence on the initial efficiency and cycle. Therefore, it is further illustrated that the organic coating layer of the present application is beneficial to improve the initial efficiency and cycle performance of the battery.

[0164] The above description is merely the preferred embodiments of the present application and the explanation of the applied technical principles. It should be understood by those skilled in the art that the scope of the application involved in the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features can be replaced with the technical features disclosed in the present application (but not limited to) having similar functions to form technical solutions.

Claims

1. A negative electrode material, characterized in that include: A core and a coating layer coated on the surface of the core; Wherein, the core comprises a silicon-based material, the coating layer comprises a first coating layer, and the material of the first coating layer is an organic compound represented by Formula I; Formula I In the formula, the hydrogen atom at at least one of the three positions A, B and C on the six-membered ring is replaced by a fluorine atom.

2. The negative electrode material according to claim 1, characterized in that The hydrogen atoms at positions A and B in the six-membered ring are replaced by fluorine atoms.

3. The negative electrode material according to claim 2, characterized in that The hydrogen atom at the C position in the six-membered ring can be directly substituted by fluorine or by a fluoroalkyl group, wherein the fluoroalkyl group is a C1-C5 fluoroalkyl group.

4. The negative electrode material according to claim 1, characterized in that The thickness of the first coating layer is 10 nm-200 nm.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that The coating layer further includes a second coating layer, the second coating layer is coated on the surface of the core, the first coating layer is arranged on a side of the second coating layer away from the core, and the second coating layer includes a conductive carbon material.

6. The negative electrode material according to claim 5, characterized in that The conductive carbon material includes at least one of soft carbon, hard carbon and graphene.

7. The negative electrode material according to claim 5, characterized in that The thickness of the second coating layer is 10 nm to 300 nm.

8. The negative electrode material according to claim 5, characterized in that Based on the weight of the negative electrode material, the weight percentage of the silicon-based material is 98%-99.8%.

9. The negative electrode material according to claim 5, characterized in that The particle size of the silicon-based material is 1 μm-30 μm.

10. The method for preparing a negative electrode material according to any one of claims 1 to 9, characterized in that: The process includes the following: Materials for preparing the first coating layer: The negative electrode material is obtained by coating the silicon-based material with the first coating layer material.

11. The preparation method according to claim 10, characterized in that: The material for preparing the first coating layer includes: 3,4-dihydroxybenzonitrile is oxidized to convert the hydroxyl group into a carbonyl group to obtain an oxidation product; The oxidation product is subjected to F substitution to obtain an organic compound represented by Formula I, which is the material of the first coating layer.

12. The preparation method according to claim 10, characterized in that The method of coating the silicon-based material with the first coating layer material to obtain the negative electrode material comprises: The material of the first coating layer is used to coat the silicon-based material by a high-temperature solid-phase method to obtain the negative electrode material.

13. The preparation method according to claim 12, characterized in that The coating treatment temperature is 500°C-800°C.

14. The preparation method according to claim 12, characterized in that Before coating the silicon-based material with the first coating layer material, the preparation method further comprises: The silicon-based material and a gaseous carbon source are processed by chemical vapor deposition to obtain a silicon-based material coated with a second coating layer; wherein the gaseous carbon source includes acetylene or ethane.

15. The preparation method according to claim 12, characterized in that The silicon-based material is a silicon-carbon composite material. Before coating the silicon-carbon composite material to obtain the negative electrode material, the preparation method further includes: heat-treating the carbon precursor to obtain a porous carbon matrix; The porous carbon matrix and silane are treated by chemical vapor deposition to obtain the silicon-carbon composite material.

16. A negative electrode plate, characterized in that: The invention comprises a current collector and the negative electrode material according to any one of claims 1 to 9, wherein the negative electrode material is arranged on at least one side of the current collector.

17. A lithium ion battery, characterized in that: Including the negative electrode sheet according to claim 16.

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