Negative electrode active material, secondary battery containing the same, and electric device

Abstract

The present application relates to a negative electrode active material, a secondary battery and an electric device containing the same. Specifically, the negative electrode active material includes a main particle and a coating layer coated on at least a portion of the surface of the main particle; the main particle includes graphite, and the coating layer includes aluminum and manganese.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode active material, a secondary battery containing the negative electrode active material, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. However, as the application scope of secondary batteries becomes wider and wider, the performance of secondary batteries has also been severely challenged.

[0003] Research and development of negative electrode active materials with excellent performance is the key to improving the performance of secondary batteries. Most negative electrode active materials face problems such as large volume expansion and poor cycle stability. How to improve the volume expansion problem of negative electrode active materials while taking into account cycle stability is the current technical difficulty. Summary of the invention

[0004] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode active material, a main particle and a coating layer coated on at least a portion of the surface of the main particle; the main particle includes graphite, and the coating layer includes aluminum and manganese.

[0005] Therefore, the present application forms a coating layer containing aluminum and manganese elements on the surface of the graphite particles by adding Mn and Al elements to the main particles. The coating layer can play a similar role to the SEI film, and can make the SEI film formed on the graphite surface during the formation more compact and structurally more stable, thereby increasing the cycle stability and reducing the expansion problem of the graphite. At the same time, after the aluminum and manganese elements are added to the coating layer, the conductivity of the material is better, and the obtained negative electrode active material has excellent kinetic properties.

[0006] In any embodiment, the mass proportion of manganese in the negative electrode active material is less than or equal to 0.8%, and can be 0.5%-0.8%; and / or the mass proportion of aluminum in the negative electrode active material is less than or equal to 1.2%, and can be 0.5%-1.2%.

[0007] In any embodiment, the specific surface area of ​​the negative electrode active material is 1 g / m 2 -8g / m 2 , optional 2.5g / m 2 -4.5g / m 2 .

[0008] In any embodiment, the compaction density of the negative electrode active material at 2t is 1.6 g / m 3 -2g / m 3 , optional 1.8g / m 3-1.95g / m 3 .

[0009] In any embodiment, the volume average particle size Dv50 of the negative electrode active material is 10.0 μm-25.0 μm, and optionally 12.5 μm-14.5 μm.

[0010] In any embodiment, the graphitization degree of the negative electrode active material is 88%-94%, and optionally 89%-92%.

[0011] In any embodiment, the aluminum element is present in the form of Al2O3; and / or the manganese element is present in the form of MnO2.

[0012] In any embodiment, the graphite is selected from artificial graphite or natural graphite.

[0013] The second aspect of the present application also provides a method for preparing a negative electrode active material, comprising the following steps:

[0014] S1: providing graphite bulk particles;

[0015] S2: preparing a mixed solution of manganese salt and aluminum salt, adding the graphite body particles to the mixed solution, adjusting the mixed solution to be alkaline, and filtering and drying to obtain an intermediate material;

[0016] S3: sintering the intermediate material and screening to obtain the negative electrode active material;

[0017] The negative electrode active material comprises a main body particle and a coating layer coated on at least a portion of the surface of the main body particle, the main body particle comprises graphite, and the coating layer comprises aluminum and manganese.

[0018] Therefore, according to the preparation method provided in the present application, the negative electrode sheet provided in the first aspect of the present application can be obtained.

[0019] In any embodiment, the manganese salt includes one or more of manganese acetate, manganese oxalate, and manganese citrate, and can be selected from at least one of manganese acetate or manganese citrate; and / or the aluminum salt includes one or more of aluminum acetate, aluminum oxalate, and aluminum citrate, and can be selected from at least one of aluminum acetate or aluminum citrate.

[0020] In any embodiment, the sintering temperature of the sintering step in step S3 is 150° C.-450° C.; and / or the sintering time is 2-3 hours.

[0021] The third aspect of the present application provides a secondary battery, comprising the negative electrode plate of the first aspect of the present application or the negative electrode plate prepared according to the preparation method of the second aspect of the present application.

[0022] A fourth aspect of the present application provides a battery module, comprising the secondary battery provided in the third aspect of the present application.

[0023] The fifth aspect of the present application provides a battery pack, comprising the battery module provided in the fourth aspect of the present application.

[0024] A sixth aspect of the present application provides an electrical device comprising at least one of the secondary battery of the third aspect, the battery module of the fourth aspect, or the battery pack of the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a scanning electron microscope image of one embodiment of the present application.

[0026] Figure 2 is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0027] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0028] Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

[0029] Figure 5 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0030] Figure 6 yes Figure 5 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0031] Figure 7 Schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0032] Description of reference numerals:

[0033] 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

[0034] Below, the embodiments of the separator, positive electrode sheet, negative electrode sheet, electrolyte, secondary battery, battery module, battery pack and power device of the present application are specifically disclosed 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 structures 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.

[0035] "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.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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).

[0041] [Secondary battery]

[0042] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged. Usually, secondary batteries include positive electrode sheets, negative electrode sheets, separators and electrolytes. During the battery charging and discharging process, active ions (such as lithium ions) are embedded and released back and forth between the positive electrode sheets and the negative electrode sheets. The separator is arranged between the positive electrode sheets and the negative electrode sheets, and its main function is to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. The electrolyte is between the positive electrode sheets and the negative electrode sheets, and its main function is to conduct active ions.

[0043] [Negative electrode active material]

[0044] One embodiment of the present application provides a negative electrode active material, including a main particle and a coating layer coated on at least a portion of the surface of the main particle; the main particle includes graphite, and the coating layer includes aluminum and manganese.

[0045] Therefore, the present application adds Mn and Al elements to the main particles to form a coating on the surface of the graphite particles to obtain a new type of negative electrode active material. Figure 1 From the scanning electron microscope image, we can see that there is a partial coating layer on the graphite surface. This coating layer can play a similar role to the SEI film and can make the SEI film formed on the graphite surface more compact and structurally stable during the formation, thereby increasing the cycle stability and reducing the expansion problem of graphite. At the same time, the coating layer containing Mn and Al elements has good conductivity, which makes the kinetic performance of the obtained negative electrode active material more excellent.

[0046] In some embodiments, the mass proportion of manganese in the negative electrode active material is less than or equal to 0.8%, and can be optionally 0.5%-0.8%.

[0047] In some embodiments, the mass proportion of aluminum in the negative electrode active material is less than or equal to 1.2%, and can be optionally 0.5%-1.2%.

[0048] In the present application, adding a suitable amount of manganese and / or aluminum can make the coating layer of moderate thickness and better structure, further improving the cycle performance of the battery.

[0049] In some embodiments, the specific surface area of ​​the negative electrode active material is 1 g / m 2 -8g / m 2 , optional 2.5g / m 2 -4.5g / m 2 When the specific surface area of ​​the negative electrode active material provided in the present application satisfies the above relationship, it is beneficial to the transmission of active ions and further improves the rate performance of the battery.

[0050] In some embodiments, the compaction density of the negative electrode active material at 2t is 1.6 g / m 3 -2g / m 3 , optional 1.8g / m 3 -1.95g / m 3 When the compaction density of the negative electrode active material provided in the present application at 2t satisfies the above range, it is beneficial to reduce the expansion of the negative electrode active material and further improve the cycle performance of the battery.

[0051] In some embodiments, the volume average particle size Dv50 of the negative electrode active material is 10.0 μm-25.0 μm, and can be 12.5 μm-14.5 μm. Negative electrode active materials with suitable particle sizes are easy to disperse in a solvent (eg, deionized water) to form negative electrode slurry.

[0052] In some embodiments, the graphitization degree of the negative electrode active material is 88%-94%, and can be 89%-92%. The negative electrode active material provided in the present application has a larger interlayer spacing than conventional graphite, and such a structure is conducive to the deintercalation of lithium ions during the charge and discharge process. During the cycle process, the structure is more stable, which is more conducive to improving the cycle stability of the battery.

[0053] In some embodiments, the aluminum element exists in the form of Al2O3; and / or the manganese element exists in the form of MnO2. The coating layer in the form of oxide is denser and has a more stable structure, which is more conducive to reducing the expansion problem.

[0054] In some embodiments, the bulk graphite particles are selected from artificial graphite or natural graphite. The bulk graphite particles can be homemade or commercially available, or can be recycled graphite material obtained by recycling the negative electrode plate.

[0055] [Method for preparing negative electrode active material]

[0056] One embodiment of the present application provides a method for preparing a negative electrode active material, comprising the following steps:

[0057] S1: providing graphite bulk particles;

[0058] S2: preparing a mixed solution of manganese salt and aluminum salt, adding the graphite body particles to the mixed solution, adjusting the mixed solution to be alkaline, and filtering and drying to obtain an intermediate material;

[0059] S3: sintering the intermediate material and screening to obtain the negative electrode active material;

[0060] The negative electrode active material comprises a main body particle and a coating layer coated on at least a portion of the surface of the main body particle, the main body particle comprises graphite, and the coating layer comprises aluminum and manganese.

[0061] In some embodiments, the manganese salt includes one or more of manganese acetate, manganese oxalate, and manganese citrate, and can be at least one of manganese acetate or manganese citrate.

[0062] In some embodiments, the aluminum salt includes one or more of aluminum acetate, aluminum oxalate, and aluminum citrate, and can be selected from at least one of aluminum acetate and aluminum citrate.

[0063] Although the mechanism is not clear, the inventors unexpectedly found that the preferred manganese acetate, manganese citrate, aluminum acetate, and aluminum citrate are more conducive to the synthesis of the coating layer, and the formed coating layer is more dense and stable.

[0064] In some embodiments, the amount of manganese salt added is 0.03 mol-0.08 mol per 120 g of graphite.

[0065] In some embodiments, the amount of aluminum salt added is 0.03 mol-0.12 mol per 120 g of graphite.

[0066] In some embodiments, a 0.1 mol / L NaOH solution is added to the mixed solution to adjust the mixed solution to be alkaline. Under alkaline conditions, the added manganese element and aluminum element can be attached to the intermediate material, which is convenient for the next step of preparation. In addition, the inventors found that when the pH of the mixed solution is adjusted to ≥ 10.5, the morphology of the formed coating layer is better and the cycle performance of the secondary battery obtained is better.

[0067] In some embodiments, the sintering temperature in the sintering step in step S3 is 150°C-450°C.

[0068] In some embodiments, the sintering time of the sintering step in step S3 is 2-3 hours.

[0069] The inventors have found that by adjusting the pH and controlling the sintering temperature and time, the prepared coating layer can include two oxides, Al2O3 and MnO2.

[0070] In some embodiments, when the graphite bulk particles are artificial graphite, the following preparation steps may be included:

[0071] 1. Providing a carbon precursor, optionally, the carbon precursor is selected from at least one of polyvinyl butyral, asphalt, furfural resin, epoxy resin or phenolic resin;

[0072] 2. The carbon precursor is subjected to conventional crushing, shaping and granulation steps in the art to obtain an intermediate;

[0073] 3. Place in a graphitization furnace (such as an Acheson graphitization furnace) for high-temperature graphitization treatment at 2750°C-3250°C to obtain artificial graphite particles.

[0074] In some embodiments, when the graphite body particles are natural graphite, conventional processing steps in the art may be used.

[0075] In some embodiments, when the graphite bulk particles are made of recycled graphite materials, obtaining the bulk particles includes the following recycling steps:

[0076] 1. Remove the negative electrode sheets from the recycled batteries, mechanically crush the removed negative electrode sheets, and then pickle, wash and dry them to obtain a crude product;

[0077] 2. Sintering the crude product at a certain temperature (eg, 500° C.-700° C.) for a certain time (eg, 1-3 h) to obtain graphite bulk particles.

[0078] The above method is used to remove impurities such as the binder through sintering to obtain relatively pure graphite particles.

[0079] [Negative electrode]

[0080] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0081] 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.

[0082] 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.).

[0083] In some embodiments, the negative electrode active material may also include other types of negative electrode active materials for batteries known in the art. For example, the negative electrode active material may also include graphite materials, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. different from those provided in the present application. The silicon-based material may 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 may 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 that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0084] 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).

[0085] 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.

[0086] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0087] 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.

[0088] [Positive electrode]

[0089] 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.

[0090] 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.

[0091] 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.).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] [Electrolytes]

[0097] 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.

[0098] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] [Isolation film]

[0103] 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.

[0104] 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.

[0105] 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.

[0106] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0107] 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.

[0108] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 2 The secondary battery 5 is a square structure as an example.

[0109] In some embodiments, reference Figure 3, 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.

[0110] 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.

[0111] Figure 4 4 is an example of a battery module. Figure 4 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.

[0112] 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.

[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] Figure 5 and Figure 6 1 is a battery pack 1 as an example. Figure 5 and Figure 6 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.

[0115] 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.

[0116] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0117] Figure 7 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.

[0118] [Example]

[0119] 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.

[0120] It is well known in the art that the recycled graphite particles will cause a significant decrease in battery performance when reused. Therefore, this application takes the recycled graphite particles as raw materials as an example and provides the following examples to verify the relevant performance of the negative electrode active material provided by this application. However, the solution of this application is not limited thereto.

[0121] Example 1

[0122] Preparation of negative electrode active materials

[0123] The negative electrode sheets are removed from the recycled batteries, and the negative electrode sheets are mechanically crushed, and then pickled, washed with water, and dried to obtain a crude product; the crude product is sintered at 600°C under nitrogen protection for 2 hours to obtain artificial graphite bulk particles; a mixed salt solution of aluminum citrate and manganese citrate is prepared, and the artificial graphite bulk particles are added to the mixed salt solution, and an intermediate is obtained by suction filtration and drying, the pH is adjusted to 10.5, and the mixture is sintered at 350°C in an air atmosphere for 3 hours, and the negative electrode active material is obtained by sieving through a 200-mesh sieve, wherein the negative electrode active material contains a coating layer and the coating layer contains manganese and aluminum elements, and the mass proportion of aluminum and manganese elements in the coating layer is 0.65wt%; and the aluminum element exists in the form of Al2O3; and the manganese element exists in the form of MnO2.

[0124] Preparation of negative electrode

[0125] The negative electrode active material, conductive agent, acetylene black, thickener CMC, and binder SBR prepared above are mixed in a mass ratio of 96.4:1:1.2:1.4, deionized water solvent is added, and the mixture is stirred under the action of a vacuum mixer until the system becomes uniform to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed and cut to obtain a negative electrode sheet.

[0126] Preparation of positive electrode

[0127] The positive electrode active material NCM523, the conductive agent acetylene black, and the binder PVDF are mixed in a mass ratio of 96:2:2, and the solvent NMP is added. The mixture is stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying, and then cold pressed and cut to obtain a positive electrode sheet.

[0128] Preparation of electrolyte

[0129] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0130] Isolation film

[0131] A polyethylene film is used as the isolation film.

[0132] Preparation of secondary batteries

[0133] The positive electrode sheet, isolation film and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, and after drying, the electrolyte is injected, and a secondary battery is obtained through vacuum packaging, standing, forming, shaping and other processes.

[0134] Embodiment 2-5

[0135] Except for adjusting the sintering temperature to that shown in parameter table 1, the other steps of embodiments 2-5 are the same as those of embodiment 1.

[0136] Embodiment 6-13

[0137] Except for adjusting the addition amounts of aluminum and manganese elements to those shown in parameter table 1, the other steps of Examples 6-13 are the same as those of Example 1.

[0138] Comparative Example 1-2

[0139] Except for adjusting the addition amounts of aluminum and manganese elements to those shown in parameter table 1, the other steps of comparative examples 1-3 are the same as those of example 1.

[0140] Comparative Example 3

[0141] Except that the negative electrode active material is replaced with the artificial graphite particles prepared in Example 1, other steps of Comparative Example 3 are the same as those of Example 1.

[0142] The preparation parameters of Examples 1-13 and Comparative Examples 1-3 prepared according to the above method are shown in Table 1.

[0143] Table 1: Preparation parameters of Examples 1-13 and Comparative Examples 1-3

[0144]

[0145]

[0146] Material Testing

[0147] (1) Morphology test

[0148] The morphology of the negative electrode active material can be tested by methods known in the art. For example, the negative electrode active material is adhered to a conductive adhesive, and the morphology of the particles is tested using a scanning electron microscope & energy dispersive spectrometer (such as Sigma 300). The test can refer to JY / T010-1996.

[0149] (2) Specific surface area test

[0150] The specific surface area of ​​the negative electrode active material is a well-known meaning in the art and can be tested by methods known in the art. For example, it can be tested by nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017 and calculated by BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by Tri-Star 3020 specific surface area pore size analysis tester of Micromeritics, USA.

[0151] (3) Compaction density test

[0152] Take a certain amount of powder and put it in a special compaction mold, then put the mold on the compaction density instrument and set the pressure to 2 tons. The thickness of the powder (thickness after pressure relief) can be read on the equipment, and the compaction density can be calculated through ρ=m / v.

[0153] (4) Particle size test

[0154] The Dv50 of the negative electrode active material is well known in the art and can be measured by methods known in the art, for example, by referring to the standard GB / T 19077.1-2016 and using a laser particle size analyzer (such as Malvern Master Size 3000).

[0155] The physical meaning of Dv50 is as follows: it refers to the particle size corresponding to when the cumulative volume distribution percentage of the negative electrode active material reaches 50%.

[0156] (5) Graphitization degree

[0157] The degree of graphitization of the negative electrode active material is well known in the art and can be tested by methods known in the art. For example, an X-ray diffractometer (such as Bruker D8 Discover) can be used, and the test can refer to JIS K 0131-1996, JB / T 4220-2011 and GB / T 24533-2019. Specifically, the size of d002 is first measured, and then the degree of graphitization is calculated according to the formula G=(0.344-d002) / (0.344-0.3354)×100%, where d002 is the interlayer spacing in the graphite crystal structure expressed in nanometers (nm). In the X-ray diffraction analysis test, a copper target can be used as the anode target, and CuKα rays can be used as the radiation source, and the ray wavelength is The scanning 2θ angle range is 20° to 80°, and the scanning rate can be 4° / min.

[0158] The above tests were performed on Examples 1-13 and Comparative Examples 1-3, and the product parameters are shown in Table 2.

[0159] Table 2: Product parameters of Examples 1-13 and Comparative Examples 1-3

[0160]

[0161]

[0162] Electrochemical performance test

[0163] (1) Gram capacity and initial effect test

[0164] After the obtained secondary battery was left to stand for 12 hours, it was charged to 3.4V with a current of 0.05C, left to stand for 10 minutes, charged to 3.75V with a current of 0.1C, left to stand for 10 minutes, charged to 4.25V with a current of 0.33C, left to stand for 10 minutes, charged to 0.05C with a voltage of 4.25V, and the charging capacity was recorded; then, it was discharged to 2.8V with a current of 0.33C, left to stand for 10 minutes, and then discharged to 2.8V with a current of 0.05C, and the discharge capacity was recorded. The ratio of the discharge capacity to the mass of graphite is the gram capacity of the graphite; the ratio of the discharge capacity to the charge capacity is the first efficiency of the graphite.

[0165] (2) Cycle test

[0166] At 25° C., the secondary batteries prepared in the examples and comparative examples were charged at a 1C rate and discharged at a 1C rate, and full charge and discharge cycle tests were performed until the capacity of the battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0167] (3) Expansion rate test

[0168] The thickness h1 of the negative electrode sheet before winding is measured and recorded. When the lithium-ion battery is prepared, the lithium-ion battery is fully charged at 1C, and then the battery is disassembled to obtain the fully charged negative electrode sheet, and its thickness h2 is measured and recorded. The full charge expansion rate of the negative electrode sheet of the lithium-ion battery is (h2-h1) / h1.

[0169] (4) Capacity retention test

[0170] At 25°C, the lithium ion batteries prepared in the embodiments and comparative examples were first charged at a rate of 0.33C and then discharged at rates of 0.33C / 2C / 3C, respectively, and the discharge capacity at each rate was recorded. The ratio of the discharge capacity at 0.33C to the discharge capacity at 0.33C was the capacity retention rate; the batteries were discharged at a rate of 0.33C and then charged at rates of 0.33C / 2C / 3C, respectively, and the charge capacity at each rate was recorded. The ratio of the charge capacity at 0.33C to the charge capacity at 0.33C was the capacity retention rate.

[0171] The above tests were performed on Examples 1-13 and Comparative Examples 1-3, and the performance test results are shown in Table 3.

[0172] Table 3: Performance test results of Examples 1-13 and Comparative Examples 1-3

[0173]

[0174] According to the above results, due to the addition of manganese source and aluminum source, a coating layer containing manganese (in the form of MnO2) and aluminum (in the form of Al2O3) is formed on the surface of the bulk graphite particles in Examples 1-13, achieving good electrochemical performance. The first efficiency, number of cycles, and capacity retention rate of the battery are all improved in the examples, while the expansion rate of the battery when fully charged is reduced, and the cycle stability of the secondary battery is enhanced.

[0175] In contrast, in Comparative Examples 1-3, when the graphite particles were coated with one of the coating layers containing manganese (in the form of MnO2) and aluminum (in the form of Al2O3) or not coated, the secondary batteries obtained did not achieve good results in all aspects and had poor cycle stability.

[0176] 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 bulk particle and a coating layer coated on at least a portion of the surface of the bulk particle; The bulk particles include graphite, and the coating layer includes aluminum and manganese elements, The mass proportion of manganese in the negative electrode active material is 0.5%-0.8%. The mass proportion of aluminum element in the negative electrode active material is 0.5%-1.2%.

2. The negative electrode active material according to claim 1, characterized in that The specific surface area of ​​the negative electrode active material is 1 g / m 2 -8g / m 2 .

3. The negative electrode active material according to claim 2, characterized in that: The specific surface area of ​​the negative electrode active material is 2.5 g / m 2 -4.5g / m 2 .

4. The negative electrode active material according to claim 1, characterized in that The compaction density of the negative electrode active material at 2t is 1.6 g / m 3 -2g / m 3 .

5. The negative electrode active material according to claim 4, characterized in that The compaction density of the negative electrode active material at 2t is 1.8 g / m 3 -1.95g / m 3 .

6. The negative electrode active material according to claim 1, characterized in that The volume average particle size Dv50 of the negative electrode active material is 10.0 μm-25.0 μm.

7. The negative electrode active material according to claim 6, characterized in that: The volume average particle size Dv50 of the negative electrode active material is 12.5 μm-14.5 μm.

8. The negative electrode active material according to claim 1, characterized in that The graphitization degree of the negative electrode active material is 88%-94%.

9. The negative electrode active material according to claim 8, characterized in that The graphitization degree of the negative electrode active material is 89%-92%.

10. The negative electrode active material according to any one of claims 1 to 9, characterized in that: The aluminum element exists in the form of Al2O3; and / or the manganese element exists in the form of MnO2.

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

12. A method for preparing a negative electrode active material, comprising the following steps: S1: providing graphite bulk particles; S2: preparing a mixed solution of manganese salt and aluminum salt, adding the graphite body particles to the mixed solution, adjusting the mixed solution to be alkaline, and filtering and drying to obtain an intermediate material; S3: sintering the intermediate material and screening to obtain the negative electrode active material; in, The negative electrode active material comprises a main body particle and a coating layer coated on at least a portion of the surface of the main body particle, the main body particle comprises graphite, and the coating layer comprises aluminum and manganese elements, The mass proportion of manganese in the negative electrode active material is 0.5%-0.8%. The mass proportion of aluminum element in the negative electrode active material is 0.5%-1.2%.

13. The preparation method according to claim 12, characterized in that: The manganese salt includes one or more of manganese acetate, manganese oxalate and manganese citrate; and / or, The aluminum salt includes one or more of aluminum acetate, aluminum oxalate, and aluminum citrate.

14. The preparation method according to claim 13, characterized in that: The manganese salt is at least one of manganese acetate or manganese citrate; and / or, The aluminum salt is at least one of aluminum acetate or aluminum citrate.

15. The preparation method according to any one of claims 12 to 14, characterized in that: The sintering temperature of the sintering step in step S3 is 150° C.-450° C.; and / or, The sintering time is 2-3h. 16 . A secondary battery comprising the negative electrode active material according to claim 1 or the negative electrode active material prepared by the preparation method according to claim 12 .

17. An electrical device, characterized in that: A secondary battery selected from the group consisting of:

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