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

Abstract

The present application provides a negative electrode active material and a preparation method thereof, a negative electrode plate, a secondary battery and an electric device, wherein the negative electrode active material includes a core and a coating layer; the coating layer covers at least a portion of the surface of the core; the core is a silicon oxide compound, and the coating layer is mesoporous г‑Al2O3. The coating layer of the negative electrode active material of the present application absorbs moisture in the electrolyte, reduces the consumption of active lithium ions and the degree of battery swelling, improves the first coulomb efficiency, cycle capacity retention rate and rate capacity retention rate of the battery, and improves the stability and safety of the battery.

Description

Technical Field

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

[0002] In recent years, as the application scope of secondary batteries has become more and more extensive, 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 secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

[0003] The electrolyte of secondary batteries often contains trace amounts of water, which causes the battery to produce gases during formation, circulation, and high-temperature storage, including CO2, H2, CO, and hydrocarbons, causing battery swelling and reducing safety. At the same time, the presence of water promotes the generation of Li2O, which increases the consumption of active lithium ions, resulting in a decrease in the first coulomb efficiency of the battery, increased capacity attenuation during the battery cycle, and reduced cycle performance. Therefore, it is urgent to improve the safety, first coulomb efficiency, and cycle performance of the battery. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode active material and its preparation method, a negative electrode plate, a secondary battery and an electrical device to solve the problems of battery swelling and low safety caused by trace moisture in the electrolyte, and at the same time solve the problem that trace moisture leads to increased consumption of active lithium ions, thereby causing the first coulomb decrease and reduced cycle performance of the battery.

[0005] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode active material, including a core and a coating layer; the coating layer covers at least a portion of the surface of the core; the core is a silicon oxide compound, and the coating layer is mesoporous г-Al2O3.

[0006] Thus, the mesoporous г-Al2O3 coating layer in the above-mentioned negative electrode active material combines with the trace moisture in the electrolyte to generate AlOOH, thereby achieving the purpose of absorbing moisture, thereby reducing the consumption of active lithium ions and improving the initial coulombic efficiency and cycle capacity retention rate of the battery; moreover, the absorption of moisture by the mesoporous г-Al2O3 coating layer in the negative electrode active material reduces the gas production in the battery, reduces the degree of battery swelling, and improves the stability and safety of the battery; at the same time, the mesoporous г-Al2O3 coating layer in the negative electrode active material is conducive to the transmission of lithium ions, so that the battery exhibits excellent rate capacity retention performance.

[0007] In any embodiment, the pore size distribution of mesoporous г-Al2O3 is 5nm-50nm, and can be optionally 10nm-30nm. This pore size distribution is conducive to further improving the absorption of trace moisture by the coating layer, further reducing the consumption of active lithium ions, thereby improving the initial coulombic efficiency and cycle performance of the battery, and can further inhibit the swelling of the battery, and improve the safety and stability of the battery; the coating layer with this pore size distribution has good lithium ion transmission performance, high rate capacity retention rate, and is conducive to exerting the actual specific capacity of the core material.

[0008] In any embodiment, the coating layer has a thickness of 400nm-1100nm, and can be 500nm-1000nm. If the coating layer is too thick, it will occupy too much volume, which will easily lead to a decrease in the energy density and capacity of the battery; if the coating layer is too thin, it will not be able to effectively absorb the water in the battery, and will not be able to reduce the consumption of active lithium ions and the swelling of the battery, resulting in low initial coulombic efficiency, low cycle capacity retention, low safety and stability of the battery.

[0009] In any embodiment, the mass ratio of aluminum to silicon in the negative electrode active material is 1:6-6:1, and can be 1:5-5:1. As a result, the absorption of water in the battery by the mesoporous г-Al2O3 coating layer of the negative electrode active material is improved, the consumption of active lithium ions is further reduced, the first coulomb efficiency and cycle performance of the battery are further improved, and the swelling of the battery is reduced, and the safety and stability are further increased.

[0010] In any embodiment, the core is SiO x , wherein x is 1-2; optionally, x is 1.1-1.5. The negative electrode active material using the core is conducive to the battery maintaining a higher energy density and capacity.

[0011] In any embodiment, the particle size of the core is 1 μm-20 μm, and can be 3 μm-10 μm. If the particle size is too small, the proportion of the core material in the negative electrode active material of equal volume is relatively reduced, resulting in a decrease in the energy density and capacity of the battery; if the particle size is too large, it is not conducive to the formation of the core-shell structure, and the coating layer is prone to incomplete coating.

[0012] The second aspect of the present application provides a method for preparing a negative electrode active material, comprising the following steps:

[0013] (1) mixing aluminum particles, silicon particles and water to obtain a mixture;

[0014] (2) reacting the mixture in a sealed environment at a high temperature to obtain a reaction product;

[0015] (3) Cooling, drying and calcining the reaction product to obtain a negative electrode active material.

[0016] Therefore, the mesoporous г-Al2O3 coating layer in the negative electrode active material prepared by the present application combines with the trace moisture in the electrolyte to generate AlOOH, thereby achieving the purpose of absorbing moisture, thereby reducing the consumption of active lithium ions and improving the initial coulombic efficiency and cycle capacity retention rate of the battery; moreover, the absorption of moisture by the mesoporous г-Al2O3 coating layer of the negative electrode active material reduces the gas production in the battery, reduces the degree of battery swelling, and improves the stability and safety of the battery; at the same time, the mesoporous г-Al2O3 coating layer in the negative electrode active material is conducive to the transmission of lithium ions, so that the battery exhibits excellent rate capacity retention performance.

[0017] In any embodiment, in step (1), during or after mixing, the pH value of the mixed system is adjusted to 5 to 7, for example, 6.

[0018] In any embodiment, in step (2), the high temperature is 120°C to 200°C, and can be optionally 160°C to 190°C, such as 180°C.

[0019] In any embodiment, in step (2), the reaction lasts for 1 to 6 hours, optionally 2 to 5 hours, for example 3 hours.

[0020] In any embodiment, in step (3), calcination is performed at 400° C. to 800° C. (eg, 600° C.) for 2 to 6 hours (optionally 3 to 5 hours).

[0021] In any embodiment, in step (3), calcination is carried out under the protection of an inert gas (such as argon).

[0022] In any embodiment, in step (3), during calcination, the temperature is raised to 400°C to 800°C (for example, 600°C) at a rate of 1°C / min to 5°C / min (for example, 3°C / min), and then maintained at this temperature for 2 to 6 hours (optionally 3 to 5 hours).

[0023] In any embodiment, in step (1), the mass ratio of aluminum particles to silicon particles is 1:6-6:1, and can be optionally 1:5-5:1.

[0024] In any embodiment, in step (1), both the aluminum particles and the silicon particles are nano-sized particles.

[0025] In any embodiment, in step (3), the reaction product is washed after cooling and before drying.

[0026] The negative electrode active material of the first aspect of the present application is prepared by the method of the second aspect of the present application.

[0027] 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 by the method of the second aspect of the present application. The negative electrode plate of the present application can absorb trace moisture in the battery, reduce the consumption of active lithium ions, improve the first coulomb efficiency and cycle capacity retention rate of the battery, reduce the degree of battery swelling, and improve the stability and safety of the battery.

[0028] The fourth aspect of the present application provides a secondary battery, comprising the negative electrode active material of the first aspect of the present application, the negative electrode active material prepared by the method of the second aspect of the present application, or the negative electrode plate of the third aspect of the present application.

[0029] A fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0031] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0032] Figure 3 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.

[0033] Figure 4 This is a SEM photograph of the negative electrode active material of Example 1 of the present application.

[0034] Figure 5 This is a TEM photograph of the negative electrode active material of Example 1 of the present application.

[0035] Figure 6 This is the XRD spectrum of the negative electrode active material of Example 1 of the present application.

[0036] Figure 7 This is the isothermal adsorption curve of the negative electrode active material of Example 1 of the present application.

[0037] Figure 8 This is a pore size distribution diagram of the negative electrode active material of Example 1 of the present application.

[0038] Description of reference numerals:

[0039] 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0040] Hereinafter, the negative electrode active material with a core-shell structure and its preparation method, negative electrode pole piece, secondary battery, battery module, battery pack and electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying 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.

[0041] "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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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).

[0047] [Secondary battery]

[0048] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can continue to be used by recharging the active materials after the battery is discharged.

[0049] Normally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. During the battery charging and discharging process, active ions (such as lithium ions) are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive electrode sheet and the negative electrode sheet, mainly to conduct active ions.

[0050] Negative electrode active material

[0051] One embodiment of the present application provides a negative electrode active material, including a core and a coating layer; the coating layer covers at least a portion of the surface of the core; the core is a silicon oxide compound, and the coating layer is mesoporous г-Al2O3.

[0052] Although the mechanism is not yet clear, the applicant unexpectedly discovered that: at present, trace amounts of water in the battery will decompose lithium hexafluorophosphate in the electrolyte to produce hydrogen fluoride, which further corrodes the lithium carbonate in the SEI film to generate irreversible lithium oxide and carbon dioxide. This process not only leads to an increase in the consumption of active lithium, but also causes the battery to swell due to the increase in internal gas, thereby reducing the battery's initial coulombic efficiency and cycle capacity retention rate, as well as reducing safety and stability. The present application achieves the purpose of absorbing moisture by combining the mesoporous г-Al2O3 coating layer in the negative electrode active material with trace moisture in the battery to generate AlOOH, thereby blocking the generation of hydrogen fluoride, thereby reducing the consumption of active lithium ions and improving the initial coulombic efficiency and cycle capacity retention rate of the battery; and, the absorption of moisture by the mesoporous г-Al2O3 coating layer in the negative electrode active material reduces the gas production in the battery, reduces the degree of battery swelling, and improves the stability and safety of the battery; at the same time, the mesoporous г-Al2O3 coating layer in the negative electrode active material is conducive to the transmission of lithium ions, so that the battery exhibits excellent rate capacity retention performance.

[0053] In some embodiments, the pore size distribution of mesoporous г-Al2O3 is 5nm-50nm, and can be 10nm-30nm, such as 10nm-20nm, 15nm-25nm, 20nm-30nm. This pore size distribution is conducive to further improving the absorption of trace moisture in the battery by the coating layer, further reducing the consumption of active lithium ions, thereby further improving the initial coulomb efficiency and cycle performance of the battery, and can also effectively inhibit the swelling of the battery, further improving the safety and stability of the battery; the coating layer with this pore size distribution has good lithium ion transmission performance, high rate capacity retention rate, and is conducive to exerting the actual specific capacity of the core material.

[0054] In some embodiments, the coating layer has a thickness of 400nm-1100nm, and can be optionally 500nm-1000nm. The coating layer of this thickness can effectively absorb moisture in the battery, reduce the consumption of active lithium ions and the swelling degree of the battery, thereby improving the first coulomb efficiency and cycle capacity retention rate of the battery, improving the safety and stability of the battery, and at the same time, the battery maintains a high energy density and capacity.

[0055] In some embodiments, the mass ratio of aluminum to silicon in the negative electrode active material is 1:6-6:1, and can be 1:5-5:1, such as 1:5.5, 1:5, 1:4, 1:3, 1:2, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 5.5:1. When the mass ratio of aluminum to silicon in the negative electrode active material is within the above range, the absorption of water in the battery by the mesoporous г-Al2O3 coating layer of the negative electrode active material is improved, the consumption of active lithium ions is further reduced, the first coulombic efficiency and cycle performance of the battery are further improved, and the swelling of the battery is reduced, and the safety and stability are further increased.

[0056] In some embodiments, the core is SiO x , wherein x is 1-2; optionally, x is 1.1-1.5, such as 1.1, 1.15, 1.2, 1.25, 1.3, 1.4. The negative electrode active material using the core is conducive to maintaining a higher energy density and capacity of the battery.

[0057] In some embodiments, the particle size of the core is 1 μm-20 μm, and can be 3 μm-10 μm. Using a core with this particle size range can ensure that the coating layer covers the core, which is conducive to the formation of a core-shell structure and ensures that the battery has a higher energy density and capacity.

[0058] Method for preparing negative electrode active material

[0059] One embodiment of the present application provides a method for preparing a negative electrode active material, comprising the following steps:

[0060] (1) mixing aluminum particles, silicon particles and water to obtain a mixture;

[0061] (2) reacting the mixture in a sealed environment at a high temperature to obtain a reaction product;

[0062] (3) Cooling, drying and calcining the reaction product to obtain a negative electrode active material.

[0063] Therefore, the mesoporous г-Al2O3 coating layer in the negative electrode active material prepared by the present application combines with the trace moisture in the battery to generate AlOOH, thereby achieving the purpose of absorbing moisture, thereby reducing the consumption of active lithium ions and improving the initial coulombic efficiency and cycle capacity retention rate of the battery; moreover, the absorption of moisture by the mesoporous г-Al2O3 coating layer of the negative electrode active material reduces the gas production in the battery, reduces the degree of battery swelling, and improves the stability and safety of the battery; at the same time, the mesoporous г-Al2O3 coating layer in the negative electrode active material is conducive to the transmission of lithium ions, so that the battery exhibits excellent rate capacity retention performance.

[0064] In some embodiments, in step (1), during or after the mixing, the pH value of the mixed system is adjusted to 5 to 7, for example, 6. A suitable pH value is conducive to forming a structure in which a mesoporous г-Al2O3 coating layer covers a silicon oxide core.

[0065] In some embodiments, in step (2), the high temperature is 120°C to 200°C, and can be optionally 160°C to 190°C, for example 180°C.

[0066] In some embodiments, in step (2), the reaction lasts for 1 to 6 hours, optionally 2 to 5 hours, for example 3 hours.

[0067] In some embodiments, in step (3), calcination is performed at 400° C. to 800° C. (eg, 600° C.) for 2 to 6 hours (optionally 3 to 5 hours).

[0068] In some embodiments, in step (3), calcination is performed under the protection of an inert gas (such as argon).

[0069] In some embodiments, in step (1), the mass ratio of aluminum particles to silicon particles is 1:6-6:1, and can be optionally 1:5-5:1, for example, 1:5.5, 1:5, 1:4, 1:3, 1:2, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 5.5:1.

[0070] By adopting the above-mentioned reaction conditions, calcination conditions and raw material ratio, a negative electrode active material with a core-shell structure can be prepared, wherein the core is a silicon oxide compound and the coating layer is a mesoporous г-Al2O3; wherein the coating layer material can absorb moisture in the battery, reduce the consumption of active lithium ions, improve the battery's first coulombic efficiency and cycle capacity retention rate, reduce battery swelling, and the mesoporous г-Al2O3 coating layer is conducive to the transmission of lithium ions, thereby improving the battery's rate capacity retention performance.

[0071] In some embodiments, in step (3), during calcination, the temperature is raised to 400°C to 800°C (e.g., 600°C) at a rate of 1°C / min to 5°C / min (e.g., 3°C / min), and then maintained at this temperature for 2 to 6 hours (optionally 3 to 5 hours). This calcination condition is conducive to forming a core of SiO x (x is 1-2), and the coating layer is a negative electrode active material of mesoporous г-Al2O3.

[0072] In some embodiments, in step (1), the mass of water is 100 to 160 times the sum of the masses of the aluminum particles and the silicon particles.

[0073] In some embodiments, in step (1), both the aluminum particles and the silicon particles are nano-sized particles.

[0074] In some embodiments, in step (3), the reaction product is washed after cooling and before drying. The washing process can maintain the purity of the reaction product, avoid the occurrence of side reactions in subsequent drying and calcining processes, and improve the purity of the negative electrode active material.

[0075] In some embodiments, in step (3), water and ethanol are used for washing multiple times.

[0076] In some embodiments, in step (1), the mixing is performed under ultrasonic conditions.

[0077] In some embodiments, in step (1), during or after the mixing, an acid solution is used to adjust the pH value of the mixed system; at least one selected from hydrochloric acid solution, acetic acid solution and sulfuric acid solution can be used.

[0078] In some embodiments, in step (2), the reaction is carried out in a sealed autoclave.

[0079] In some embodiments, in step (3), cooling is natural cooling.

[0080] In some embodiments, in step (3), drying is performed in a vacuum environment.

[0081] [Negative electrode]

[0082] The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises the above-mentioned negative electrode active material or the negative electrode active material prepared by the above-mentioned method.

[0083] 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.

[0084] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a 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.).

[0085] In some embodiments, the above-mentioned negative electrode active material or the negative electrode active material prepared by the above-mentioned method can also be used in combination with negative electrode active materials for batteries known in the art. As an example, negative electrode active materials for batteries known in the art may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials known in the art that can be used as negative electrode active materials for batteries can also be used.

[0086] In some embodiments, the negative electrode film layer may further include a binder. As an example, 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).

[0087] In some embodiments, the negative electrode film layer may further include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0089] 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.

[0090] [Positive electrode]

[0091] The positive electrode sheet generally 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.

[0092] 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.

[0093] 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.).

[0094] 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 )、LiNi 0.5 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 0.05O2) 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.

[0095] In some embodiments, the positive electrode film layer may also 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.

[0096] In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0097] 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.

[0098] [Electrolytes]

[0099] 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.

[0100] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0101] 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.

[0102] 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.

[0103] In some embodiments, the electrolyte may further include additives. As examples, the additives may include 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.

[0104] [Isolation film]

[0105] 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.

[0106] 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.

[0107] 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.

[0108] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0109] 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.

[0110] 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.

[0111] In some embodiments, reference Figure 2, the outer package 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.

[0112] 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.

[0113] 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.

[0114] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can 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.

[0115] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0116] Figure 3 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.

[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] 1. Preparation of negative electrode active material: 0.2 g aluminum nanopowder and 0.1 g silicon nanopowder were dispersed in 40 ml deionized water, the pH value was adjusted to 6 with hydrochloric acid, and ultrasonic treatment was performed to obtain a mixture; the mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and sealed, reacted at 180°C for 3 h, cooled naturally, centrifuged and washed several times with deionized water and ethanol, dried under vacuum, and then heated to 600°C at a heating rate of 3°C / min under argon protection, and calcined at 600°C for 4 h to obtain a negative electrode active material, whose SEM photo is shown as follows: Figure 4 shown.

[0121] 2. Preparation of negative electrode sheets: Add negative electrode active material, conductive agent carbon black, and binder polyacrylic acid into solvent deionized water in a weight ratio of 7:1.5:1.5, mix well and prepare negative electrode slurry; evenly coat the negative electrode slurry on the negative electrode collector copper foil once or multiple times, and obtain negative electrode sheets after drying, cold pressing and slitting.

[0122] 3. Preparation of positive electrode sheets: dissolve lithium iron phosphate (LiFePO4) material, conductive agent carbon black, and sodium cellulose in a weight ratio of 8:1:1 in solvent N-methylpyrrolidone (NMP), stir and mix evenly to obtain positive electrode slurry; then evenly coat the positive electrode slurry on the positive electrode collector aluminum foil, and then dry, cold press, and cut to obtain positive electrode sheets.

[0123] 4. Isolation film: polypropylene film.

[0124] 5. Preparation of electrolyte: In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), mix organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, add 12.5% ​​(W / W) LiPF6 lithium salt and dissolve it in the organic solvent, and stir evenly.

[0125] 6. Preparation of secondary batteries: stack and wind the above-mentioned positive electrode sheets, separators, and negative electrode sheets in order to obtain an electrode assembly; place the electrode assembly in an outer package, add the above-prepared electrolyte, and obtain a secondary battery after packaging, standing, formation, aging and other processes.

[0126] Examples 2-7 and Comparative Examples 1-3

[0127] The secondary battery preparation methods of Examples 2-7 and Comparative Examples 1-3 are similar to those of Example 1, but the parameters of the negative electrode active materials are adjusted. The different parameters are detailed in Table 1.

[0128] (1) Determination of the SiO content of the core material in the negative electrode active materials of Examples 1-7 and Comparative Examples 1-3 xThe x value of .

[0129] Determination method: Weigh a certain mass of dry negative electrode active material (mass is recorded as W), put it into a thermogravimetric / differential thermal analyzer, heat it from room temperature to 1200℃ in air atmosphere, and record the mass increase (ΔW, the mass increase is due to SiO x Completely oxidized to SiO2), combined with the mass ratio of Al and Si elements in the raw material (z), the SiO x The molar mass of SiO x The x value in .

[0130]

[0131] Where W is the mass of the dry negative electrode active material, M SiO2 is the molar mass of silicon dioxide, M Al is the molar mass of aluminum, z is the mass ratio of Al and Si elements, ΔW is the mass increase, M Si is the molar mass of silicon, M Al2O3 is the molar mass of aluminum oxide.

[0132] (2) TEM analysis was performed on the negative electrode active materials of Examples 1-7 and Comparative Examples 1-3. The core SiO x The particle size and coating thickness of the negative electrode active material of Example 1 are shown in the TEM image. Figure 5 As shown, it can be concluded that the core SiO x The particle size is 3μm-10μm, and the coating layer thickness is 500nm-1000nm.

[0133] (3) Determine the XRD spectra of the negative electrode active materials of Examples 1-7 and Comparative Examples 1-3, and determine the material of the coating layer by comparing with the standard spectra; wherein the XRD spectrum of the negative electrode active material of Example 1 is as follows: Figure 6 shown.

[0134] (4) According to the national standard GB / T21650-2008 "Mercury Intrusion Pore Size Distribution and Porosity of Solid Materials by Gas Adsorption Method Part 2: Analysis of Mesopores and Macropores by Gas Adsorption Method", the pore size distribution of the negative electrode active materials of Examples 1-7 and Comparative Examples 1-3 was calculated by the BJH method, where: Figure 7 is the isothermal adsorption curve of the negative electrode active material of Example 1, Figure 8 This is the pore size distribution diagram of the negative electrode active material of Example 1.

[0135] The above results are shown in Table 1.

[0136] Table 1: Parameter results of Examples 1-7 and Comparative Examples 1-3

[0137]

[0138]

[0139] * 0.2 g aluminum nanopowder and 0.1 g silicon nanopowder were dispersed in 40 ml deionized water, ultrasonically treated to obtain a mixture, centrifuged and washed several times with deionized water and ethanol, dried under vacuum, and then heated to 600 °C at a heating rate of 3 °C / min under argon protection and normal pressure, and calcined at 600 °C for 4 h to obtain the negative electrode active material, and non-mesoporous ordinary alumina-coated SiO x Negative electrode material.

[0140] #0.2g aluminum nanopowder and 0.1g silicon nanopowder were dispersed in 40ml deionized water, adjusted to pH 6 with hydrochloric acid, ultrasonically treated, reacted at 180℃ for 3h under normal pressure and air atmosphere, cooled naturally, centrifuged and washed several times with deionized water and ethanol, dried under vacuum, and then heated to 600℃ at a heating rate of 3℃ / min under argon protection, and calcined at 600℃ for 4h to obtain non-mesoporous г-Al2O3-coated SiO x Negative polarity material.

[0141] Battery Test

[0142] The secondary batteries of Examples 1-7 and Comparative Examples 1-3 were tested as follows.

[0143] (1) Room temperature capacity performance: The first charge and discharge is performed at 25°C. Constant current and constant voltage charging is performed at a charging current of 0.33C until the upper limit voltage is 2.00V. Then, constant current discharge is performed at a discharge current of 0.33C until the final voltage is 0.05V. The discharge capacity value is recorded as the capacity C at room temperature. n .

[0144] (2) Room temperature cycle performance: The battery was charged and discharged for the first time at 25°C. Constant current and constant voltage charging was performed at a charging current of 0.33C until the upper limit voltage was 2.00V. Then, constant current discharge was performed at a discharge current of 1C until the final voltage was 0.05V. The discharge capacity of the first cycle was recorded. The battery was then cycled N times according to the above operation. Finally, the discharge capacity of the Nth cycle was recorded. The cycle capacity retention rate was calculated according to the following formula. The number of cycles N in this test was 1000 times.

[0145] Cycle capacity retention rate = 100% × (discharge capacity at the Nth cycle / discharge capacity at the first cycle)

[0146] (3) Rate performance: For the first charge and discharge at 25°C, constant current and constant voltage charging was performed at a charging current of 1 / 3C until the upper limit voltage was 2.00V. Then, constant current discharge was performed at discharge currents of 1 / 3C, 1C, and 3C, respectively, until the final voltage was 0.05V, and the discharge capacities were recorded. Taking the discharge capacity at a discharge current of 1 / 3C as 100%, the percentages of the discharge capacities at discharge currents of 1C and 3C relative to the discharge capacity at a discharge current of 1 / 3C were calculated, respectively, and recorded as the rate capacity retention percentage.

[0147] The above results are shown in Table 2.

[0148] Table 2: Performance test results of secondary batteries of Examples 1-7 and Comparative Examples 1-3

[0149]

[0150] As shown in Table 2, compared with Comparative Examples 1-3, the room temperature capacity, room temperature capacity retention rate and rate capacity retention rate of the secondary battery of the present application are significantly improved, which shows that the mesoporous г-Al2O3 coating layer of the negative electrode active material of the present application has a strong ability to bind to the water in the electrolyte, blocking the generation of hydrogen fluoride, reducing the consumption of active lithium ions, and significantly improving the room temperature capacity and capacity retention rate. At the same time, the coating layer structure will not hinder the transmission of lithium ions, showing excellent rate capacity retention performance. However, the negative electrode active material of Comparative Example 1 does not have a coating layer and cannot absorb water in the electrolyte, so that the active lithium ions are consumed in large quantities, resulting in poor room temperature capacity, capacity retention rate and rate capacity retention performance of the battery; the coating layer of the negative electrode active material of Comparative Examples 2-3 has a weak ability to absorb water and has an obstructive effect on the transmission of lithium ions, resulting in low room temperature capacity, capacity retention rate and rate capacity retention performance of the battery.

[0151] 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, comprising a core and a coating layer; The coating layer covers at least a portion of the surface of the core; The core is a silicon oxide compound, the coating layer is a mesoporous г-Al2O3, and the pore size of the mesoporous г-Al2O3 is distributed in the range of 5nm-50nm; The mass ratio of aluminum element to silicon element in the negative electrode active material is 1:6-6:

1.

2. The negative electrode active material according to claim 1, wherein The pore size of the mesoporous г-Al2O3 is distributed in the range of 10nm-30nm.

3. The negative electrode active material according to claim 1, wherein The coating layer has a thickness of 400nm-1100nm.

4. The negative electrode active material according to claim 1, wherein The coating layer has a thickness of 500nm-1000nm.

5. The negative electrode active material according to claim 1, wherein The core is SiO x , where x is 1-2.

6. The negative electrode active material according to any one of claims 1 to 5, wherein The particle size of the core is 1 μm-20 μm.

7. A method for preparing the negative electrode active material according to any one of claims 1 to 6, comprising the following steps: (1) mixing aluminum particles, silicon particles and water to obtain a mixture; wherein: The mass ratio of the aluminum particles to the silicon particles is 1:6-6:1; (2) reacting the mixture in a sealed environment at 120° C. to 200° C. for 1 to 6 hours to obtain a reaction product; (3) Cooling and drying the reaction product, and calcining it at 400° C. to 800° C. for 2 to 6 hours under the protection of an inert gas to obtain a negative electrode active material.

8. The method according to claim 7, wherein: In step (1), during or after the mixing, the pH value of the mixed system is adjusted to 5-7.

9. The method according to claim 7, wherein: In step (3), during calcination, the temperature is raised to 400°C to 800°C at a rate of 1°C / min to 5°C / min, and then maintained at this temperature for 2 to 6 hours.

10. The method according to claim 7, wherein: In step (1), the aluminum particles and the silicon particles are both nano-scale particles.

11. The method according to any one of claims 7 to 10, wherein: In step (3), after cooling and before drying, the cooled reaction product is washed. 12 . A negative electrode sheet, comprising the negative electrode active material according to claim 1 or the negative electrode active material prepared by the method according to claim 7 . 13 . A secondary battery comprising the negative electrode active material according to claim 1 , the negative electrode active material prepared by the method according to claim 7 , or the negative electrode sheet according to claim 12 .

14. An electrical device comprising the secondary battery according to claim 13.

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