Negative electrode active material and preparation method thereof, negative electrode sheet, secondary battery, battery module, battery pack and electric device

Abstract

The present application provides a negative electrode active material including a core and a coating layer coating the core, wherein the core is graphite, the coating layer comprises at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to the graphite is (0.01-0.10):1.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion secondary batteries, and in particular to a negative electrode active material and a preparation method thereof, a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device. Background Art

[0002] In recent years, as the application scope of lithium-ion secondary batteries has become more and more extensive, lithium-ion secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As lithium-ion secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

[0003] As a negative electrode material, graphite has become the first choice for negative electrode active materials of commercial lithium-ion secondary batteries due to its low cost, convenient production, and actual capacity close to theoretical capacity. Usually used as negative electrode materials, including natural graphite and artificial graphite, but the defects on the surface of artificial graphite are usually more active, and it is easy to react with the electrolyte and consume active lithium; and the loss of active lithium ions will reduce the cycle performance of lithium-ion secondary batteries and damage the service life of lithium-ion secondary batteries. Therefore, the existing modification technology of artificial graphite still needs to be improved. Summary of the invention

[0004] Technical problem to be solved by the invention

[0005] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode active material, which has high hardness and small volume expansion in a highly lithium-embedded state, thereby being able to suppress the expansion of the negative electrode plate and extend the service life of the lithium-ion secondary battery.

[0006] Technical solutions to solve problems

[0007] In order to achieve the above-mentioned objectives, the present application provides a negative electrode active material and a preparation method thereof, a negative electrode plate, a secondary battery, a battery module, a battery pack and an electrical device.

[0008] The first aspect of the present application provides a negative electrode active material, comprising a core and a coating layer coating the core,

[0009] Among them, the core is graphite, the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to graphite is (0.01~0.10):1.

[0010] Therefore, the negative electrode active material of the present application has a core-shell structure, with graphite as the core and a coating layer on the surface of the core, the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to graphite is (0.01-0.10):1. The high hardness of the carbide in the above-mentioned coating layer can effectively inhibit the expansion volume of graphite when it is highly embedded with lithium electricity, reduce the rebound rate of the negative electrode plate, that is, reduce the expansion force inside the lithium-ion secondary battery, thereby reducing the probability of lithium precipitation, electrolyte shortage and other problems, and at the same time improve the cycle life of the lithium-ion secondary battery. It should be noted that the pole piece rebound rate is used to evaluate the degree of expansion of the pole piece in the thickness direction when the pole piece is 100% embedded with lithium, and the pole piece rebound rate satisfies the following formula:

[0011]

[0012] In any embodiment, the coating layer has a thickness of 10 to 500 nm, and optionally 20 to 200 nm. Thus, when the coating layer thickness of the negative electrode active material layer is within the above range, it has sufficient rigidity to suppress the expansion of graphite particles in a fully lithium-embedded state, and does not lose too much gram capacity, thereby ensuring the energy density of the lithium-ion secondary battery.

[0013] In any embodiment, the negative electrode active material has a Dv50 of 3 to 50 μm, and optionally 10 to 30 μm.

[0014] Therefore, the Dv50 of the negative electrode active material is selected in the above range, which can avoid the following situations: if the Dv50 of the negative electrode active material is too small, there will be too many fine particles, which may be difficult to evenly disperse in the slurry; on the contrary, it may cause too many scratches on the coated negative electrode sheet particles. At the same time, if the Dv50 is too large, it may increase the transmission path of lithium ions between the negative electrode active material particles, thereby causing the lithium insertion speed to be too slow. Therefore, from the perspective of ensuring the dynamic performance and processing performance of the negative electrode active material, the Dv50 of the negative electrode active material is selected in the above range.

[0015] In any embodiment, the tap density of the negative electrode active material is 0.8 to 1.5 g / cm 3 , optionally, 0.95 to 1.2 g / cm 3 The specific surface area of ​​the negative electrode active material is 0.6 to 4 m 2 / g, optionally, 0.9~2.5m 2 / g.

[0016] Therefore, from the perspective of ensuring the kinetic performance of the negative electrode active material, the above-mentioned specific surface area range is selected. The specific surface area of ​​the negative electrode active material is selected from the above-mentioned range to avoid the following situations: if the specific surface area of ​​the negative electrode active material is too small, the electrolyte has poor wettability to it, and the migration ability of active lithium ions between single particles is weak, which may lead to a slow lithium insertion rate; but if the specific surface area of ​​the negative electrode active material is too large, it may cause side reactions on the particle surface, consume a large amount of active lithium ions, and generate too much solid electrolyte interface film (SEI film), affecting its cycle performance. When the tap density of the negative electrode active material is within the above-mentioned range, the negative electrode active material particles can be in close contact with each other and can ensure sufficient infiltration of the electrolyte, shortening the diffusion path of active lithium ions between particles and improving its kinetic performance.

[0017] In any embodiment, the graphite is selected from at least one of artificial graphite and natural graphite. The above types of graphite are selected from the perspective of low cost and convenient processing.

[0018] The second aspect of the present application also provides a method for preparing a negative electrode active material:

[0019] A graphite precursor and a coating material containing at least one of a titanium precursor, a tungsten precursor, a chromium precursor, a boron precursor and a silicon precursor are uniformly mixed, maintained at a graphitization temperature of 2500 to 3500° C. for 10 to 60 hours to graphitize, and then cooled to room temperature to obtain a negative electrode active material.

[0020] Among them, the negative electrode active material includes a core and a coating layer covering the core, the core is graphite, and the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to the graphite is (0.01~0.10):1.

[0021] Therefore, the present application obtains the negative electrode active material by uniformly mixing the graphite precursor and the coating material containing at least one of the precursor containing titanium element, the precursor containing tungsten element, the precursor containing chromium element, the precursor containing boron element and the precursor containing silicon element, and then sintering in situ. The obtained negative electrode active material can effectively inhibit the expansion volume of graphite when highly embedded with lithium, reduce the rebound rate of the negative electrode plate, and reduce the expansion force inside the lithium-ion secondary battery, thereby reducing the probability of problems such as lithium precipitation and insufficient electrolyte, and at the same time increasing the service life of the lithium-ion secondary battery.

[0022] In addition, within the above-mentioned sintering temperature range and sintering time, the graphite precursor can form a carbide coating layer directly on the surface of the graphite particles in situ while being fully graphitized, which not only saves the extra energy consumption generated by the secondary coating of the conventional method, but also controls the thickness of the coating layer, and can play a role in inhibiting expansion in the case of low coating amounts.

[0023] In any embodiment, the graphite precursor is selected from at least one of anthracite, coke and needle coke, and the Dv50 of the graphite precursor is 8-25 μm. Therefore, from the perspective of economic cost and convenience, the above-mentioned substance with the above Dv50 is selected as the graphite precursor.

[0024] In any embodiment, the heating rate of the graphitization reaction is 5 to 20° C. / min, and / or the graphitization reaction is performed under an argon or helium atmosphere.

[0025] Therefore, when the heating rate of the graphitization reaction is within the above range, the graphite precursor can be heated uniformly, thereby obtaining graphite with a high degree of graphitization and fewer surface defects. In addition, the graphitization reaction under the above atmosphere can ensure that the graphite precursor will not react with oxygen.

[0026] In any embodiment, the coating material has a Dv50 of 0.2 to 10 μm.

[0027] Therefore, when the Dv50 of the coating material is within the above range, it can be fully mixed with the graphite precursor, and the obtained negative electrode active material has a uniform coating layer.

[0028] In any embodiment, the precursor of the titanium element is selected from at least one of Ti element, TiO2, TiO, Ti2O3 and TiH2; and / or, the precursor of the tungsten element is selected from at least one of W element, WO3, bis(cyclopentadiene)tungsten dihydride and bis(isopropylcyclopentadiene)tungsten dihydride; and / or, the precursor of the chromium element is selected from at least one of Cr element, Cr2O3 and CrO3; and / or, the precursor of the boron element is selected from at least one of B element and B2O3; and / or, the precursor of the silicon element is selected from at least one of Si, SiO and SiO2.

[0029] Therefore, the melting points of the titanium precursor, tungsten precursor, chromium precursor, boron precursor and silicon precursor selected in the present application are lower than the temperature of the graphitization reaction. After melting, they can be effectively coated on the graphite surface and react in situ to generate a carbide coating layer.

[0030] The third aspect of the present application provides a negative electrode plate, comprising the negative electrode active material of the first aspect of the present application or the negative electrode active material prepared according to the method of the second aspect of the present application.

[0031] The fourth aspect of the present application provides a secondary battery, comprising the negative electrode plate of the third aspect of the present application.

[0032] A fifth aspect of the present application provides a battery module, comprising the secondary battery of the fourth aspect of the present application.

[0033] The sixth aspect of the present application provides a battery pack, comprising the battery module of the fifth aspect of the present application.

[0034] The seventh aspect of the present application provides an electrical device comprising at least one selected from the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, or the battery pack of the sixth aspect of the present application.

[0035] Effects of the Invention

[0036] The present application provides a negative electrode active material having a core-shell structure, with graphite as the core, and a coating layer on the surface of the core, the coating layer comprising at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to the graphite is (0.01-0.10):1. The high hardness of the carbide in the above-mentioned coating layer can effectively inhibit the expansion volume of graphite when it is highly embedded with lithium, reduce the rebound rate of the negative electrode plate when it is fully embedded with lithium, and reduce the expansion force inside the lithium-ion secondary battery, thereby reducing the probability of problems such as lithium precipitation and insufficient electrolyte, and at the same time increasing the service life of the lithium-ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0038] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0039] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0040] Figure 4 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0041] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0042] Figure 6 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0043] Description of reference numerals:

[0044] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0045] Below, the negative electrode active material and its manufacturing method, negative electrode pole piece, secondary battery, battery module, battery pack and electric device of the present application are described in detail with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0046] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0048] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0049] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0050] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0051] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0052] Negative electrode active material

[0053] In one embodiment of the present application, the present application proposes a negative electrode active material, comprising a core and a coating layer coating the core, wherein the core is graphite, the coating layer comprises at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to the graphite is (0.01-0.10):1.

[0054] Although the mechanism is still unclear, the applicant unexpectedly discovered after research that the negative electrode active material of the present application has a core-shell structure, with graphite as the core and a coating layer on the surface of the core, the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to graphite is (0.01-0.10):1. The high hardness of the carbide in the above-mentioned coating layer can effectively inhibit the expansion volume of graphite when it is highly embedded with lithium, reduce the rebound rate of the negative electrode plate when it is fully embedded with lithium, that is, reduce the expansion force inside the lithium-ion secondary battery, thereby reducing the probability of lithium precipitation, insufficient electrolyte and other problems, and at the same time improve the cycle life of the lithium-ion secondary battery. It should be noted that the pole piece rebound rate is used to evaluate the degree of expansion of the pole piece in the thickness direction when the pole piece is 100% embedded with lithium, and the pole piece rebound rate satisfies the following formula:

[0055]

[0056] In some embodiments, the coating layer has a thickness of 10 to 500 nm, and optionally 20 to 200 nm. Thus, when the coating layer thickness of the negative electrode active material layer is within the above range, it can have sufficient rigidity to suppress the expansion of graphite particles in a fully lithium-embedded state, and will not lose too much gram capacity, thereby ensuring the energy density of the lithium-ion secondary battery.

[0057] In some embodiments, the negative electrode active material has a Dv50 of 3 to 50 μm, and optionally 10 to 30 μm.

[0058] Therefore, the Dv50 of the negative electrode active material is selected in the above range, which can avoid the following situations: if the Dv50 of the negative electrode active material is too small, there will be too many fine particles, which may be difficult to evenly disperse in the slurry; on the contrary, it may cause too many scratches on the coated negative electrode sheet particles. At the same time, if the Dv50 is too large, it may increase the transmission path of lithium ions between the negative electrode active material particles, thereby causing the lithium insertion speed to be too slow. Therefore, from the perspective of taking into account the dynamic performance and processing performance of the negative electrode active material, the Dv50 of the negative electrode active material is selected in the above range.

[0059] In some embodiments, the tap density of the negative electrode active material is 0.8 to 1.5 g / cm 3 , optionally, 0.95 to 1.2 g / cm 3 ; The specific surface area of ​​the negative electrode active material is 0.6 to 4 m 2 / g, optionally, 0.9~2.5m 2 / g.

[0060] Therefore, from the perspective of improving the kinetic performance of the negative electrode active material, the above-mentioned specific surface area range is selected, so as to avoid the following problems: if the specific surface area of ​​the negative electrode active material is too small, the electrolyte has poor wettability to it, and the migration ability of active lithium ions between individual particles is weak, which may lead to a slow lithium insertion rate; but if the specific surface area of ​​the negative electrode active material is too large, it may cause side reactions on the particle surface, consume a large amount of active lithium ions to generate too much solid electrolyte interface film (SEI film), and affect its cycle performance. When the tap density of the negative electrode active material is within the above range, the negative electrode active material particles can be in close contact with each other and fully wetted by the electrolyte, shortening the diffusion path of active lithium ions between particles and improving the kinetic performance of the negative electrode active material.

[0061] In some embodiments, the graphite is selected from at least one of artificial graphite and natural graphite. The above types of graphite are selected from the perspective of low cost and convenient processing.

[0062] Method for preparing negative electrode active material

[0063] In one embodiment of the present application, the present application also provides a method for preparing a negative electrode active material:

[0064] A graphite precursor and a coating material containing at least one of a titanium precursor, a tungsten precursor, a chromium precursor, a boron precursor and a silicon precursor are uniformly mixed, maintained at a graphitization temperature of 2500 to 3500° C. for 10 to 60 hours to graphitize, and then cooled to room temperature to obtain a negative electrode active material.

[0065] Among them, the negative electrode active material includes a core and a coating layer covering the core, the core is graphite, and the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2), boron carbide (B4C) and silicon carbide (SiC), and the weight ratio of the coating layer to the graphite is (0.01~0.10):1.

[0066] Therefore, the present application uniformly mixes a graphite precursor and a coating material containing at least one of a titanium precursor, a tungsten precursor, a chromium precursor, a boron precursor, and a silicon precursor, and then sinters them in situ to obtain a negative electrode active material. The obtained negative electrode active material can effectively inhibit the expansion volume of graphite when highly lithium is embedded, reduce the rebound rate of the negative electrode plate, and reduce the expansion force inside the lithium-ion secondary battery, thereby reducing the probability of problems such as lithium precipitation and insufficient electrolyte, and at the same time increasing the service life of the lithium-ion secondary battery.

[0067] In some embodiments, the graphite precursor is selected from at least one of anthracite, coke and needle coke, and the Dv50 of the graphite precursor is 8-25 μm. Therefore, from the perspective of economic cost and convenience, the above-mentioned substance with the above Dv50 is selected as the graphite precursor.

[0068] In some embodiments, the heating rate of the graphitization reaction is 5-20° C. / min, and / or the graphitization reaction is performed under an argon or helium atmosphere.

[0069] Therefore, when the heating rate of the graphitization reaction is within the above range, the graphite precursor can be heated uniformly, thereby obtaining graphite with a high degree of graphitization and fewer surface defects. In addition, the graphitization reaction under the above atmosphere can ensure that the graphite precursor will not react with oxygen.

[0070] In some embodiments, the coating material has a Dv50 of 0.2 to 10 μm.

[0071] Therefore, when the Dv50 of the coating material is within the above range, it can be fully mixed with the graphite precursor, and the obtained negative electrode active material has a uniform coating layer.

[0072] In some embodiments, the precursor of the titanium element is selected from at least one of Ti element, TiO2, TiO, Ti2O3 and TiH2; and / or, the precursor of the tungsten element is selected from at least one of W element, WO3, bis(cyclopentadiene)tungsten dihydride and bis(isopropylcyclopentadiene)tungsten dihydride; and / or, the precursor of the chromium element is selected from at least one of Cr element, Cr2O3 and CrO3; and / or, the precursor of the boron element is selected from at least one of B element and B2O3; and / or, the precursor of the silicon element is selected from at least one of Si, SiO and SiO2.

[0073] Therefore, the melting points of the titanium precursor, tungsten precursor, chromium precursor, boron precursor and silicon precursor selected in the present application are lower than the temperature of the graphitization reaction. After melting, they can be effectively coated on the graphite surface and react in situ to generate a carbide coating layer.

[0074] It should be noted that the average volume distribution particle size Dv50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 50%. In the present application, the volume average particle size Dv50 of the negative electrode active material can be measured by laser diffraction particle size analysis. For example, with reference to the standard GB / T 19077-2016, a laser particle size analyzer (such as MalvernMaster Size 3000) is used for measurement.

[0075] In addition, the secondary battery, battery module, battery pack, and electric device of the present application will be described below with reference to the drawings as appropriate.

[0076] In one embodiment of the present application, a secondary battery is provided.

[0077] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0078] [Positive electrode]

[0079] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0080] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0081] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0083] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0084] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0086] [Negative electrode]

[0087] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes the negative electrode active material of the first aspect of the present application.

[0088] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0089] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0090] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0091] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0092] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0093] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0094] [Electrolytes]

[0095] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0096] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0097] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0098] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0099] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0100] [Isolation film]

[0101] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0102] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0103] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0104] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0105] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0106] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0107] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0108] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0109] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0110] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0111] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0112] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0113] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0114] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0115] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0116] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0117] Example

[0118] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0119] Example 1

[0120] The graphite precursor and the precursor containing titanium element as the coating raw material are uniformly mixed by ball milling, placed in a graphite furnace, maintained at a graphitization temperature of 2700° C. for 30 hours to graphitize them, and then cooled to room temperature to obtain a negative electrode active material.

[0121] Among them, the graphite precursor is coal-based needle coke, and its Dv50 is 15 μm; the precursor containing titanium element is Ti single substance powder, and its Dv50 is 1.2 μm; the feed ratio: graphite precursor: coating raw material = 1:0.028 (wt:wt); the heating rate is 10°C / min.

[0122] Example 2

[0123] Except for the ratio of graphite precursor: coating raw material = 1:0.045 (wt:wt), other conditions are the same as those in Example 1.

[0124] Example 3

[0125] Except that the graphitization temperature is 3500°C; the coating raw material is W single substance powder, whose Dv50=1.0μm; and the graphite precursor: coating raw material=1:0.025 (wt:wt), the other conditions are the same as those in Example 1.

[0126] Example 4

[0127] Except that the graphitization temperature is 2800°C; the coating raw material is Cr single substance powder, whose Dv50=1.3μm; and the graphite precursor: coating raw material=1:0.025 (wt:wt), the other conditions are the same as Example 1.

[0128] Example 5

[0129] Except that the graphitization temperature is 2800°C; the coating raw material is Si single substance powder, whose Dv50=0.8μm; and the graphite precursor: coating raw material=1:0.025 (wt:wt), the other conditions are the same as Example 1.

[0130] Example 6

[0131] Except that the graphitization temperature is 2500°C; the coating raw material is TiH2, whose Dv50=1.1μm; and the graphite precursor: coating raw material=1:0.03 (wt:wt), the other conditions are the same as Example 1.

[0132] Example 7

[0133] Except that the graphitization temperature is 2800°C; the coating raw material is TiO2, whose Dv50 is 1.5μm; and the graphite precursor: coating raw material = 1:0.055 (wt:wt), the other conditions are the same as those in Example 1.

[0134] Comparative Example 1

[0135] The graphite precursor was placed in a graphite furnace, maintained at a graphitization temperature of 2700° C. for 30 hours to be graphitized, and then cooled to room temperature to obtain a negative electrode active material.

[0136] The graphite precursor is coal-based needle coke, and its Dv50 is 15 μm; the heating rate is 10° C. / min.

[0137] Comparative Example 2

[0138] Except for the ratio of graphite precursor: coating raw material = 1:0.005 (wt:wt), other conditions are the same as those in Example 1.

[0139] Comparative Example 3

[0140] Except for the ratio of graphite precursor: coating raw material = 1:0.167 (wt:wt), other conditions are the same as those in Example 1.

[0141] The relevant parameters of the negative electrode active materials of Examples 1 to 7 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0142] Table 1: Parameter results of Examples 1 to 7 and Comparative Examples 1 to 3

[0143]

[0144] In addition, the negative electrode active materials obtained in the above Examples 1 to 7 and Comparative Examples 1 to 3 were respectively prepared into button-type batteries as shown below, and performance tests were performed. The test results are shown in Table 2 below.

[0145] (1) Preparation of button cells

[0146] The negative electrode active materials in the above-mentioned embodiments and comparative examples are dissolved in deionized water with the conductive agent carbon black (SP), the thickener sodium carboxymethyl cellulose (CMC) and the adhesive styrene polybutadiene rubber (SBR) at a ratio of 90:2:3:5, and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is coated on a copper foil, dried and cold pressed to obtain a negative electrode sheet. A lithium sheet is used as a counter electrode, and an electrolyte of 1M LiPF6 dissolved in a volume ratio of 1:1 ethylene carbonate (EC): diethyl carbonate (DEC) is added, and a button battery is assembled in a button box.

[0147] (2) Initial gram capacity test and pole piece rebound rate test of button cell

[0148] Each button cell prepared above was first discharged to 0.005V at 0.1C, and the capacity at this time was the lithium insertion capacity, recorded as C0; after standing for 5 minutes, it was charged to 2V at 0.1C, and the capacity at this time was the initial lithium removal capacity, recorded as D0, and the first efficiency was D0 / C0*100%. The tested lithium removal capacity value (i.e., C0) was divided by the mass of the negative electrode active material in the button cell, which was the initial gram capacity of the negative electrode active material.

[0149] After the gram capacity test is completed, the button cells are discharged at 0.1C to 0.005V, the negative electrode sheets are disassembled and taken out, and the thickness of the negative electrode sheets is measured using a micrometer. The rebound rate of the sheet when fully embedded with lithium is calculated according to the following formula:

[0150]

[0151] Table 2: Performance test results of Examples 1 to 7 and Comparative Examples 1 to 3

[0152]

[0153] According to the above results, the negative electrode active materials in Examples 1 to 7 have a core-shell structure, with graphite as the core and hard carbide as the coating layer. The mass ratio of the coating layer to the core is moderate, so that the volume expansion of the electrode sheet using the negative electrode active material in the fully lithium-intercalated state is suppressed without damaging the gram capacity of the negative electrode active material.

[0154] In contrast, Comparative Examples 1 and 2 did not achieve effective improvement in suppressing the volume expansion of the negative electrode sheet in the fully lithium-embedded state. Although Comparative Example 3 effectively suppressed the volume expansion of the negative electrode sheet, the coating layer of the negative electrode active material had too high a content and had no electrochemical activity to lithium ions. Therefore, the gram capacity of the negative electrode active material was greatly lost, which would affect the energy density of the secondary battery using the negative electrode active material.

[0155] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode active material, characterized in that: comprising a core and a coating layer coating the core, Wherein, the inner core is graphite, the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2) and boron carbide (B4C), and the weight ratio of the coating layer to the graphite is (0.01-0.10):

1.

2. The negative electrode active material according to claim 1, characterized in that The coating layer has a thickness of 10 to 500 nm.

3. The negative electrode active material according to claim 1, characterized in that The coating layer has a thickness of 20 to 200 nm.

4. The negative electrode active material according to any one of claims 1 to 3, characterized in that: The negative electrode active material has a Dv50 of 3 to 50 μm.

5. The negative electrode active material according to any one of claims 1 to 3, characterized in that: The negative electrode active material has a Dv50 of 10 to 30 μm.

6. The negative electrode active material according to any one of claims 1 to 3, characterized in that: The tap density of the negative electrode active material is 0.8 to 1.5 g / cm 3 , The specific surface area of ​​the negative electrode active material is 0.6 to 4 m 2 / g.

7. The negative electrode active material according to claim 6, characterized in that: The tap density of the negative electrode active material is 0.95 to 1.2 g / cm 3 .

8. The negative electrode active material according to claim 6, characterized in that The specific surface area of ​​the negative electrode active material is 0.9 to 2.5 m 2 / g.

9. The negative electrode active material according to any one of claims 1 to 3, characterized in that: The graphite is selected from at least one of artificial graphite and natural graphite.

10. A method for preparing a negative electrode active material, characterized in that: A graphite precursor and at least one coating material selected from a titanium precursor, a tungsten precursor, a chromium precursor and a boron precursor are uniformly mixed, graphitized at a graphitization temperature of 2500 to 3500° C. for 10 to 60 hours, and then cooled to room temperature to obtain a negative electrode active material. Among them, the negative electrode active material includes a core and a coating layer coating the core, the core is graphite, the coating layer contains at least one of titanium carbide (TiC), tungsten carbide (WC), chromium carbide (Cr3C2) and boron carbide (B4C), and the weight ratio of the coating layer to the graphite is (0.01-0.10):

1.

11. The method for preparing the negative electrode active material according to claim 10, characterized in that: The graphite precursor is selected from at least one of anthracite, coke and needle coke, The Dv50 of the graphite precursor is 8-25 μm.

12. The method for preparing the negative electrode active material according to claim 10, characterized in that: The heating rate of the graphitization reaction is 5-20° C. / min, and / or the graphitization reaction is carried out in an argon or helium atmosphere.

13. The method for preparing a negative electrode active material according to any one of claims 10 to 12, characterized in that: The coating material has a Dv50 of 0.2 to 10 μm.

14. The method for preparing a negative electrode active material according to any one of claims 10 to 12, characterized in that: The precursor containing titanium element is selected from at least one of Ti element, TiO2, TiO, Ti2O3 and TiH2; and / or, The precursor of the tungsten element is selected from at least one of W element, WO3, bis(cyclopentadiene)tungsten dihydride and bis(isopropylcyclopentadiene)tungsten dihydride; and / or, The precursor of the chromium element is selected from at least one of Cr element, Cr2O3 and CrO3; and / or, The precursor of the boron element is selected from at least one of single substance B and B2O3.

15. A negative electrode plate, characterized in that: The invention comprises the negative electrode active material according to any one of claims 1 to 9 and the negative electrode active material prepared by the method for preparing the negative electrode active material according to any one of claims 10 to 14.

16. A secondary battery, characterized in that: Includes the negative electrode sheet as described in claim 15.

17. A battery module, characterized in that: Includes the secondary battery as claimed in claim 16.

18. A battery pack, characterized in that: Comprising the battery module as claimed in claim 17.

19. An electrical device, characterized in that: The battery comprises at least one selected from the secondary battery of claim 16, the battery module of claim 17, or the battery pack of claim 18.

Images