Positive electrode active material and preparation method thereof, secondary battery, and electric device

Abstract

This application relates to a positive electrode active material, a preparation method thereof, a secondary battery, and an electrical device. The positive electrode active material comprises a ternary material and a coating layer coated on the surface of the ternary material. The coating layer comprises lithium iron phosphate coated with a carbon layer. The positive electrode active material exhibits excellent power performance.

Description

Technical Field

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

[0002] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. As lithium-ion batteries have achieved significant development, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0003] One approach to increasing the energy density of lithium-ion batteries is to use ultra-high nickel ternary materials (Ni content ≥ 95%) as the positive electrode active material. However, to maintain the nickel content, the cobalt content in the ternary material is usually reduced, which significantly reduces the power performance of the ultra-high nickel ternary material. Summary of the Invention

[0004] The present application provides a positive electrode active material and a preparation method thereof, a secondary battery, and an electrical device. The positive electrode active material has good power performance.

[0005] In a first aspect of the present application, a positive electrode active material is provided, comprising a ternary material and a coating layer coated on the surface of the ternary material, wherein the material of the coating layer comprises lithium iron phosphate having a carbon layer coated on the surface.

[0006] In some embodiments, the thickness of the carbon layer is 1 nm to 6 nm; optionally, the thickness of the carbon layer is 2 nm to 4 nm.

[0007] In some embodiments, the carbon residue of the carbon layer is 1% to 5%; optionally, the carbon residue of the carbon layer is 2% to 4%.

[0008] In some embodiments, the material of the carbon layer includes pyrolytic carbon.

[0009] In some embodiments, the average particle size of the lithium iron phosphate is 0.4 μm to 0.8 μm; optionally, the average particle size of the lithium iron phosphate is 0.4 μm to 0.6 μm.

[0010] In some embodiments, the mass ratio of the ternary material to the lithium iron phosphate having a carbon layer coated on the surface is (90-98): (10-2).

[0011] In some embodiments, the molar percentage of nickel in the ternary material is ≥80%; optionally, the molar percentage of nickel in the ternary material is ≥95%.

[0012] In some embodiments, the chemical formula of the ternary material is LiNi x Co y M 1-x-y O2, wherein x is 0.95 to 0.995, y is 0 to 0.05, and M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb.

[0013] In some embodiments, a passivation layer is further provided between the surface of the ternary material and the coating layer; optionally, the material of the passivation layer includes one or both of aluminum oxide and boron oxide.

[0014] The second aspect of the present application provides a method for preparing the positive electrode active material according to the first aspect, comprising the following steps:

[0015] The lithium iron phosphate with a carbon layer coated on the surface is coated on the surface of the ternary material to prepare the positive electrode active material.

[0016] In some embodiments, coating the lithium iron phosphate having a carbon layer coated on the surface of the ternary material comprises:

[0017] The ternary material is mixed with lithium iron phosphate having a carbon layer coated on the surface and a solvent to prepare a dispersion;

[0018] Drying the dispersion to prepare a powder material;

[0019] The powder material is sintered.

[0020] In some embodiments, the mixing conditions include: a stirring rate of 1000 to 3000 r / min and a stirring time of 0.5 h to 3 h.

[0021] In some embodiments, the drying method includes one or both of spray drying and oven drying;

[0022] Optionally, the spray drying conditions include: an atomization pressure of 1 MPa to 2 MPa, a spray hole diameter of 1 mm to 6 mm;

[0023] Optionally, the drying conditions include: a temperature of 75°C to 85°C.

[0024] In some embodiments, the sintering conditions include: a temperature of 180° C. to 300° C., and a sintering time of 40 min to 80 min.

[0025] In some embodiments, the method for preparing the lithium iron phosphate having a carbon layer coated on the surface is a carbon source method;

[0026] Optionally, the method for preparing the lithium iron phosphate having a carbon layer coated on the surface comprises the following steps:

[0027] mixing a carbon source, lithium iron phosphate and a solvent to prepare a dispersion;

[0028] sintering the dispersion to pyrolyze the carbon source and coat the surface of the lithium iron phosphate;

[0029] Optionally, the sintering conditions include: a temperature of 180° C. to 300° C. and a time of 40 min to 80 min;

[0030] Optionally, the solvent comprises N-methylpyrrolidone (NMP);

[0031] Optionally, the carbon source includes one or both of polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA).

[0032] In some embodiments, the method for preparing the positive electrode active material further comprises the step of preparing a passivation layer between the surface of the ternary material and the coating layer;

[0033] Optionally, the step of preparing the passivation layer includes:

[0034] Mixing the ternary material with a passivating agent, and sintering the mixture in an oxygen atmosphere to form the passivation layer on the surface of the ternary material;

[0035] Further optionally, sintering in an oxygen atmosphere has one or more of the following characteristics:

[0036] (1) The oxygen flow rate is 3 to 10 L / min;

[0037] (2) The sintering temperature is 500℃~700℃ and the sintering time is 3h~8h.

[0038] In a third aspect of the present application, a positive electrode plate is provided, comprising a current collector and a positive electrode active layer stacked on a surface of the current collector, wherein the material of the positive electrode active layer comprises the positive electrode active material described in the first aspect.

[0039] In some embodiments, the positive electrode active layer has one or more of the following characteristics:

[0040] (1) Coating weight (CW) is 24 to 44 mg / cm 2 ;

[0041] (2) The thickness is 200 μm to 360 μm.

[0042] In a fourth aspect of the present application, a secondary battery is provided, comprising the positive electrode active material described in the first aspect or the positive electrode sheet described in the third aspect.

[0043] In a third aspect of the present application, the energy density of the secondary battery is provided to be 380 to 500 Wh / kg.

[0044] In a fifth aspect of the present application, an electrical device is provided, comprising the secondary battery described in the fourth aspect.

[0045] The above-mentioned positive electrode active material is first coated with a carbon layer on the surface of the lithium iron phosphate, and then the lithium iron phosphate with a carbon layer coated on the surface is coated on the surface of the ternary material. In this way, while effectively improving the power performance of the ternary material, the coating structure is relatively stable, thereby improving the cycle performance of the ternary material. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a schematic diagram of a secondary battery according to one embodiment of the present application;

[0047] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0048] Figure 3 A schematic diagram of a battery module according to an embodiment of the present application;

[0049] Figure 4 A schematic diagram of a battery pack according to an embodiment of the present application;

[0050] Figure 5 for Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0051] Figure 6 A schematic diagram of an electrical device using a secondary battery as a power source according to one embodiment of the present application;

[0052] Description of reference numerals:

[0053] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover; 6 power device;

[0054] Figure 7 This is an electron microscope image of the positive electrode active material prepared in Example 1. DETAILED DESCRIPTION

[0055] Below, the embodiments of the positive electrode active material and its preparation method, secondary battery, and electrical device of the present application are described in detail with appropriate reference to the drawings. However, there may be 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 description 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.

[0056] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0058] 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.

[0059] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating 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), indicating 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.

[0060] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0061] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0062] The traditional method of preparing ternary materials is carried out under oxygen-rich conditions, making it difficult to improve their power performance through carbon coating. In addition, there are methods to mix nano-lithium iron phosphate into ternary materials or coat ternary materials with lithium iron phosphate, but direct mixing will cause uneven dispersion of the slurry gel and agglomeration of nano-lithium iron phosphate, which will deteriorate interfacial ion transport. When applied to ultra-high nickel ternary materials, direct coating is prone to shedding of the coating layer due to the continuous expansion and contraction stress of the lattice during the cycle, thereby deteriorating battery performance.

[0063] Based on this, some examples of the present application provide a positive electrode active material, including a ternary material and a coating layer coated on the surface of the ternary material, wherein the material of the coating layer includes lithium iron phosphate having a carbon layer coated on the surface, and the material of the carbon layer includes pyrolytic carbon.

[0064] The above-mentioned positive electrode active material is first coated with a carbon layer on the surface of lithium iron phosphate, and then the lithium iron phosphate with the carbon layer coated on the surface is coated on the surface of the ternary material. In this way, while effectively improving the power performance of the ternary material, the coating structure is relatively stable, thereby improving the cycle performance of the ternary material. Without limitation, its possible principles include: (1) the thickness and morphology of the carbon layer on the surface of lithium iron phosphate are controllable, thereby enhancing the electronic conductivity and reaction activity of the surface of the ternary material; (2) during the discharge process, lithium iron phosphate has a platform at 3.2V that can exert its capacity before 1C. After 1C, it exists on the surface of the ternary material in the form of iron phosphate insulator. The surface heat generated heats the ternary material, so the mass transfer becomes faster, the number of reaction-activated molecules increases, and the power performance is improved.

[0065] In addition, based on the experimental research of the inventors, it can be preliminarily considered that the above-mentioned positive electrode active material also has the following advantages:

[0066] (1) The surface resistance and charge transfer resistance of the ternary material after the above coating are both low, and the side reaction between the surface of the ternary material and the electrolyte can be significantly reduced, reducing the phase transition process on the surface; the phosphate in the lithium iron phosphate is preferentially adsorbed on the transition metal site, stabilizing the transition metal ions and oxygen ions on the surface, even at high voltage (≥4.6Vv.Li / Li + ), and also against conventional electrolytes such as those containing ethylene carbonate;

[0067] (2) Ternary materials, especially ultra-high nickel ternary materials, have poor surface stability and serious lithium-nickel mixing under high voltage, which deteriorates the electrochemical performance. After the above coating, the interface stability of the material can be improved, thereby improving the safety performance of the material, such as reducing the thermal runaway temperature;

[0068] (3) Ternary materials, especially ultra-high nickel ternary materials, have low compaction density and are prone to overpressure cracking and brittleness problems during the compaction process. After the above coating, the slip effect of the coating layer can reduce the overpressure cracking and brittleness problems during the compaction process;

[0069] (4) Ternary materials, especially ultra-high nickel ternary materials, may experience particle cracks and breakage during cycling due to stress accumulation and release, resulting in loss of electrical contact. After the above coating, the presence of the coating layer can at least achieve point contact, reducing attenuation.

[0070] (5) Compared with the traditional method of directly mixing conductive carbon, the above-mentioned coating method through the carbon layer can also avoid the agglomeration of conductive carbon, uniformly disperse it on the surface of the ternary material, thereby improving the electronic transport properties of the material, reducing the membrane resistance of the electrode, and improving power.

[0071] In some examples, the thickness of the carbon layer is 1nm to 6nm. Reasonable control of the thickness of the carbon layer can, on the one hand, achieve rapid electron transport on the surface of the ternary material, and on the other hand, optimize the stability of the structure and improve the power performance and cycle performance of the material. Specifically, the thickness of the carbon layer includes but is not limited to: 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm or a range formed by any two of the foregoing values. Furthermore, the thickness of the carbon layer is 2nm to 4nm.

[0072] In some examples, the carbon residue of the carbon layer is 1% to 5%. It can be understood that "carbon residue" refers to the percentage of elemental carbon based on the total mass of the carbon layer. Reasonable control of the carbon residue of the carbon layer can improve electron conduction, thereby reducing the direct current resistance (DCR) and improving power performance. Specifically, the carbon residue of the carbon layer includes but is not limited to: 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or the range formed by any two of the foregoing values. Furthermore, the carbon residue of the carbon layer is 2% to 4%.

[0073] In some examples, the material of the carbon layer includes pyrolytic carbon.

[0074] In some examples, the average particle size of the lithium iron phosphate is 0.4 μm to 0.8 μm. Reasonable control of the average particle size of the lithium iron phosphate can further improve power performance and cycle performance. Specifically, the average particle size of the lithium iron phosphate includes but is not limited to: 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or a range formed by any two of the foregoing values. Furthermore, the carbon residue of the carbon layer is 0.4 μm to 0.6 μm.

[0075] In some examples, the mass ratio of the ternary material to the lithium iron phosphate having a carbon layer coated on the surface is (90-98):(10-2). Specifically, the mass ratio of the ternary material to the lithium iron phosphate having a carbon layer coated on the surface includes but is not limited to: 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2, or a range formed by any two of the foregoing values.

[0076] In some examples, the molar percentage of nickel in the ternary material is ≥80%. Furthermore, the molar percentage of nickel in the ternary material is ≥95%. The use of high-nickel or ultra-high-nickel ternary materials can further increase the energy density of lithium-ion batteries. The above coating scheme is applicable to high-nickel or ultra-high-nickel ternary materials, improving their power performance and cycle performance.

[0077] Without limitation, the chemical formula of the ternary material is LiNi x Co y M 1-x-y O2, wherein x is 0.95 to 0.995, y is 0 to 0.05, and M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb.

[0078] In some examples, a passivation layer is provided between the surface of the ternary material and the coating layer. This passivation layer can relatively completely coat the surface of the ternary material, filling the gaps in the coating of the lithium iron phosphate, and further reducing the contact between the ternary material and the electrolyte during cycling.

[0079] Furthermore, the material of the passivation layer includes one or both of aluminum oxide and boron oxide.

[0080] In some examples, the positive electrode active material has a gram capacity of 238 to 250 mAh / g.

[0081] Some examples of the present application also provide a method for preparing the positive electrode active material as described above, comprising the following steps:

[0082] The lithium iron phosphate with a carbon layer coated on the surface is coated on the surface of the ternary material to prepare the positive electrode active material.

[0083] In some examples, coating the lithium iron phosphate having a carbon layer coated on the surface of the ternary material includes:

[0084] The ternary material is mixed with lithium iron phosphate having a carbon layer coated on the surface and a solvent to prepare a dispersion;

[0085] Drying the dispersion to prepare a powder material;

[0086] The powder material is sintered.

[0087] By combining drying and sintering, a close bond between the ternary material and the lithium iron phosphate having a carbon layer coated on the surface can be achieved, thereby improving the cycle stability of the material.

[0088] In some examples, the mixing conditions include: a stirring rate of 1000 to 3000 r / min and a stirring time of 0.5 h to 3 h.

[0089] Without limitation, the drying method includes one or both of spray drying and oven drying. Further, the drying method is spray drying.

[0090] In some of the examples, the spray drying conditions include: an atomization pressure of 1 MPa to 2 MPa, and a spray hole diameter of 1 mm to 6 mm.

[0091] In some examples, the drying conditions include a temperature of 75° C. to 85° C.

[0092] In some examples, the sintering conditions include: a temperature of 180° C. to 300° C., and a sintering time of 40 min to 80 min.

[0093] In some examples, the method for preparing the lithium iron phosphate having a carbon layer coated on the surface is a carbon source method.

[0094] Furthermore, the method for preparing the lithium iron phosphate having a carbon layer coated on the surface comprises the following steps:

[0095] mixing a carbon source, lithium iron phosphate and a solvent to prepare a dispersion;

[0096] The dispersion is sintered to pyrolyze the carbon source and coat the surface of the lithium iron phosphate.

[0097] Without limitation, the sintering conditions include: a temperature of 180° C. to 300° C. and a sintering time of 40 min to 80 min.

[0098] Without limitation, the solvent includes N-methylpyrrolidone (NMP).

[0099] Without limitation, the carbon source includes one or both of polyacrylonitrile (PAN) and polymethyl methacrylate (PMMA).

[0100] In some examples, the method for preparing the positive electrode active material further includes the step of preparing a passivation layer between the surface of the ternary material and the coating layer.

[0101] Without limitation, the step of preparing the passivation layer includes: mixing the ternary material with a passivating agent, sintering the mixture in an oxygen atmosphere, and forming the passivation layer on the surface of the ternary material.

[0102] Optionally, during the sintering process in an oxygen atmosphere, the flow rate of oxygen is 3 to 10 L / min.

[0103] Optionally, during the sintering process in an oxygen atmosphere, the sintering temperature is 500° C. to 700° C., and the sintering time is 3 h to 8 h.

[0104] Other examples of the present application further provide a positive electrode plate, comprising a current collector and a positive electrode active layer stacked on the surface of the current collector, wherein the material of the positive electrode active layer comprises the positive electrode active material as described above.

[0105] In some examples, the positive electrode active layer has one or more of the following characteristics:

[0106] (1) Coating weight (CW) is 24 to 44 mg / cm 2 ;

[0107] (2) The thickness is 200 μm to 360 μm.

[0108] Another approach to improving the energy density of lithium-ion batteries is to increase the coating weight of the active material layer in the positive electrode sheet to create a thicker positive electrode sheet. However, this increases the distance electrons need to travel within the sheet and degrades the conductive network. The aforementioned coating solution is suitable for thicker positive electrode sheets, improving their electronic conductivity and reducing the sheet resistance, thereby enhancing power performance.

[0109] Other examples of the present application further provide a secondary battery, comprising the positive electrode active material or positive electrode sheet as described above.

[0110] In some examples, the energy density of the secondary battery is 380 to 500 Wh / kg. Based on the above coating scheme, it is possible to simultaneously use ultra-high nickel ternary materials and thick positive electrode designs to prepare high energy density batteries.

[0111] Other examples of the present application further provide an electric device including the secondary battery as described above.

[0112] The secondary battery, battery module, battery pack, and electric device of the present application are described below with reference to the accompanying drawings as appropriate.

[0113] In one embodiment of the present application, a secondary battery is provided.

[0114] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0115] Positive electrode

[0116] The positive electrode is as described above.

[0117] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0118] 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 layer and a metal layer formed on at least one surface of the polymer material base layer. 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 made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0120] In some embodiments, the positive electrode active material 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.

[0121] In some embodiments, the positive electrode sheet can be prepared by the following method: 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.

[0122] Negative electrode

[0123] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0124] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0125] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. 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 base layer (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0126] In some of the embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material 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 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.

[0127] In some embodiments, the negative electrode active material layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0128] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0130] In some embodiments, the negative electrode sheet can be prepared by the following method: 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.

[0131] electrolytes

[0132] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0133] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0134] 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.

[0135] 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, methylpropyl carbonate, ethylpropyl 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, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0136] In some embodiments, the electrolyte may optionally include additives. For example, 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, and additives that improve battery high or low temperature performance.

[0137] Isolation film

[0138] 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 and mechanical stability can be selected.

[0139] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0140] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0141] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0142] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0143] The present application has no particular restrictions on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, Figure 1 The secondary battery 5 is a square structure as an example.

[0144] In some of these embodiments, reference Figure 2 The outer packaging may include a shell 51 and a cover plate 53. 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 impregnated 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.

[0145] In some embodiments, secondary batteries may be assembled into a battery module. The battery module may contain one or more secondary batteries. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0146] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length of the battery module 4. Of course, they may also be arranged in any other manner. The plurality of secondary batteries 5 may further be fixed by fasteners.

[0147] 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.

[0148] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. The specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0149] Figure 4 and Figure 5 The battery pack 1 is used as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple 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 an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner in the battery box.

[0150] In addition, the present application also provides an electrical device, which includes at least one of the secondary batteries, battery modules, or battery packs provided in the present application. The secondary batteries, battery modules, or battery packs can be used as power sources for the electrical device, or as energy storage units for the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptop computers, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0151] As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0152] Figure 6 The power consumption device 6 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 power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module can be used.

[0153] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0154] Example

[0155] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0156] Preparation Example 1

[0157] This embodiment is a method for preparing a positive electrode active material, and the steps are as follows:

[0158] (1) Preparation of ultra-high nickel ternary materials:

[0159] The ultra-high nickel ternary precursor was mixed with lithium hydroxide, a dopant Zr(OH)4, and calcined at 750°C for 13 hours to prepare an ultra-high nickel ternary material Li with a nickel content of 98%. 0.98 Ni 0.98 Co 0.015 Mn 0.005 O2;

[0160] (2) Preparation of passivation layer:

[0161] The ultra-high nickel ternary material of step (1) is washed with water, the solid-liquid ratio (mass ratio) of the material to water is 0.5:1, the washing time is 5 minutes, and a powder is obtained after filtering and vacuum drying; the powder is mixed with a coating agent (aluminum oxide) to obtain a mixture, and the content of the coating agent in the mixture is 1500ppm; the mixture is distributed in a sintering container sagger according to a porosity of 50%, and then sent to an atmosphere furnace, the volume of the mixture accounts for 15% of the sagger capacity, and is sintered in an oxygen atmosphere, the oxygen flow rate is 5L / min, the heating rate during sintering is 2°C / min, the holding temperature during sintering is 600°C, the time is 5h, and the mixture is cooled with the furnace in an oxygen atmosphere;

[0162] (3) Preparation of lithium iron phosphate with carbon layer coating (C@LFP):

[0163] A carbon source (PAN) and lithium iron phosphate (average particle size of 0.6 μm) were dispersed in a solvent (NMP) at a mass ratio of 5:97 to prepare a dispersion.

[0164] The dispersion was sintered at a temperature of 180° C. for 60 minutes to pyrolyze the carbon source and coat the surface of the lithium iron phosphate to form a carbon layer with a thickness of 1.5 nm and a carbon residue of 3%.

[0165] (4) Coating

[0166] 950 g of the ternary material prepared in step (2) was mixed with a C@LFP dispersion with a mass fraction of 5% (including 50 g of C@LFP, 5 g of surfactant PVP, and a solvent of NMP), and a high-speed disperser was used with a stirring rate of 2000 r / min and a stirring time of 1 hour to obtain a dispersion in which LFP was evenly dispersed and coated; the dispersion was spray-dried with an atomization pressure of 1.5 MPa and a spray hole diameter of 3 mm to prepare a powder material; the powder material was sintered in protective gas Ar gas at a temperature of 200° C. for 60 minutes to obtain a C@LFP-coated ultra-high nickel ternary material.

[0167] The electron microscope image of the positive electrode active material of Preparation Example 1 is as follows: Figure 7 As shown, it can be seen that the surface of the ternary material is coated with C@LFP material.

[0168] The preparation methods of the C@LFP-coated ultra-high nickel ternary materials of Preparation Examples 2 to 11 are the same as those of Preparation Example 1, except that the parameters such as the thickness of the carbon layer in the C@LFP, the carbon residue in the carbon layer in the C@LFP, the average particle size of the lithium iron phosphate, and the mass ratio of the ternary material prepared in step (2) to the C@LFP prepared in step (3) are different. For details, see Table 1.

[0169] The preparation method of the material of Comparative Example 1 is the same as that of Example 1, except that no carbon layer is provided. The preparation steps are as follows:

[0170] (1) Preparation of ultra-high nickel ternary material: same as in Example 1;

[0171] (2) Preparation of passivation layer: same as in Example 1;

[0172] (3) Coating:

[0173] 950 g of the ternary material prepared in step (2) was mixed with a 5% by mass LFP dispersion (including 50 g of LFP, 5 g of surfactant PVP, and a solvent of NMP), and a high-speed disperser was used at a stirring rate of 2000 r / min and a stirring time of 1 hour to obtain an LFP-coated dispersion; the dispersion was spray-dried with an atomization pressure of 1.5 MPa and a spray hole diameter of 3 mm to prepare a powder material; the powder material was sintered in protective gas Ar gas at a temperature of 200° C. for 60 minutes to obtain an LFP-coated ultra-high nickel ternary material.

[0174] The preparation method of the material of Comparative Example 2 is the same as that of Example 1, except that the ternary material is directly mixed with LFP without coating. The preparation steps are as follows:

[0175] (1) Preparation of ultra-high nickel ternary material: same as in Example 1;

[0176] (2) Preparation of passivation layer: same as in Example 1;

[0177] (3) Mixing: 950 g of the ternary material prepared in step (2) was mixed with 50 g of LFP to obtain an LFP-blended ultra-high nickel ternary material.

[0178] Table 1

[0179]

[0180]

[0181] Example 1

[0182] This embodiment is a method for preparing a lithium-ion battery, and the steps are as follows:

[0183] 1) Preparation of positive electrode sheet

[0184] The C@LFP-coated ultra-high nickel ternary material prepared in Example 1, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) were dispersed in a solvent N-methylpyrrolidone at a mass ratio of 97%:1%:2% and mixed and stirred for 3 hours to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil with a coating mass of 43 mg / cm 2 After drying, cold pressing and cutting, the positive electrode sheet is obtained, and the thickness of the positive electrode active layer is 300μm.

[0185] 2) Preparation of negative electrode sheet

[0186] The negative electrode active material is doped with artificial graphite of silicon-based composite material (doping mass percentage is 60%), conductive agent carbon black, carbon nanotubes (CNT), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) in a mass ratio of 94.5%: 1%: 0.375%: 2.8%: 1.325%. Deionized water is added and the mixture is stirred for 3 hours to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on a copper foil. After drying, cold pressing, and slitting, a negative electrode sheet is obtained, and its coating mass per unit area is 0.17g / 1540.25mm 2 .

[0187] 3) Isolation film

[0188] A polypropylene film is used as the base film, and its surface is coated with 1CCS with a thickness of 1 micron and PCS with a thickness of 1 micron.

[0189] 4) Preparation of electrolyte

[0190] LiPF6 / LIFSI (mass ratio of 7:3) was dissolved in a solvent mixture of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and FEC in a volume ratio of 1:1:1:1 to prepare an electrolyte with a concentration of 1 mol / L.

[0191] 5) Battery Preparation

[0192] The positive electrode sheet, separator, and negative electrode sheet are wound in sequence to obtain a bare cell; the bare cell is placed in a packaging shell, dried, and then injected with electrolyte, and a lithium-ion battery is obtained through vacuum packaging, standing, forming, shaping, and other processes.

[0193] The lithium ion batteries of Examples 2 to 11 and Comparative Examples 1 to 2 were prepared in a similar manner to the lithium ion battery of Example 1, but used the positive electrode active materials of the corresponding preparation examples.

[0194] Test example:

[0195] (1) Energy density:

[0196] 1) The discharge energy measurement of the battery cell is as follows:

[0197] Let the battery cell stand at 25℃ for 2 hours to ensure the temperature of the battery cell is 25℃;

[0198] After charging the battery cell to the charge cut-off voltage at 0.1C at 25°C, continue constant voltage charging at the charge cut-off voltage until the current reaches 0.05C, and then charge is cut off (where C represents the rated capacity of the battery cell);

[0199] Let the battery cells stand at 25°C for 1 hour;

[0200] At 25°C, discharge the battery cells at 0.1C to the discharge cut-off voltage, and record the total discharge capacity C0 of the battery cells, and the total discharge energy E0;

[0201] 2) Battery cell weight measurement: Place the battery cell on an electronic balance until the weight stabilizes, and read the battery cell weight value M0;

[0202] 3) Energy density calculation: Battery cell discharge energy E0 / battery cell weight M0 is the energy density of the battery cell;

[0203] (2) Power performance:

[0204] 1) Let the battery cell stand for 10 minutes at a temperature of 25°C;

[0205] 2) Discharge at 0.33C0 constant current to 0.6C0 at 25°C, let stand for 10 minutes, and adjust the SOC to 40%;

[0206] 3) Let the battery cell stand for 30 minutes at a temperature of 25°C;

[0207] 4) Discharge at 5C0 constant current for 120s at 25°C, let stand for 1min, and jump to the next step directly after triggering the protection voltage;

[0208] 5) Let the battery cell stand for 30 minutes at a temperature of 25°C.

[0209] (3) Cycle performance:

[0210] The voltage calibration method is as follows:

[0211] 1) Leave the battery cell at 25°C for 2 hours to ensure the temperature of the battery cell is 25°C;

[0212] 2) Charge the battery cells to 4.25V at 0.33C0 at 25°C, and charge at 4.25V constant voltage to a current of 0.05C0;

[0213] 3) Let stand for 1 hour;

[0214] 4) Discharge at 0.33C0 to 0.95C0 at 25°C and record the voltage V1 at this time;

[0215] 5) Let stand for 5 minutes;

[0216] 6) Discharge to 2.0V at 0.33C0 at 25°C;

[0217] 7) Let stand for 5 minutes;

[0218] 8) Charge the battery cell at 0.33C0 to 0.97C0 at 25°C and record the voltage V2 at this time;

[0219] 9) Let stand for 2 hours.

[0220] The cycle test process is as follows:

[0221] 1) Leave the battery cell at 25°C for 2 hours to ensure the temperature of the battery cell is 25°C;

[0222] 2) Charge the battery cells to voltage V2 at 0.33C0 at 25°C;

[0223] 3) Let stand for 0.5h;

[0224] 4) Discharge the battery cell at 0.33C0 at 25°C to voltage V1, and record the capacity at this point as Cn;

[0225] 5) Let stand for 0.5h;

[0226] 6) Repeat steps 2 to 5 until the number of cycles n reaches 100 cls.

[0227] The test results are shown in Table 2 below:

[0228] Table 2

[0229] Battery energy density (Wh / kg) Power performance Cycle performance / cycle Example 1 406 160S 1200 Example 2 406 170S 1400 Example 3 405 140S 1000 Example 4 408 162S 1150 Example 5 407 168S 1380 Example 6 404 165S 1360 Example 7 402 150S 1250 Example 8 403 167S 1180 Example 9 401 153S 1120 Example 10 393 172S 1380 Example 11 407 168S 1360 Comparative Example 1 392 138S 800 Comparative Example 2 392 136S 900

[0230] It can be seen from Table 2 that, compared with the comparative example, the positive electrode active material of the embodiment has better power performance and cycle performance.

[0231] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized in that It comprises a ternary material and a coating layer coated on the surface of the ternary material, wherein the coating layer comprises lithium iron phosphate having a carbon layer coated on the surface; A passivation layer is further provided between the surface of the ternary material and the coating layer, and the material of the passivation layer includes one or both of aluminum oxide and boron oxide.

2. The positive electrode active material according to claim 1, characterized in that The thickness of the carbon layer is 1 nm to 6 nm.

3. The positive electrode active material according to claim 2, characterized in that The thickness of the carbon layer is 2nm~4nm.

4. The positive electrode active material according to claim 1, characterized in that The carbon residue in the carbon layer is 1% to 5%.

5. The positive electrode active material according to claim 4, characterized in that The carbon residue in the carbon layer is 2% to 4%.

6. The positive electrode active material according to claim 1, characterized in that The material of the carbon layer includes pyrolytic carbon.

7. The positive electrode active material according to claim 1, characterized in that The average particle size of the lithium iron phosphate is 0.4 μm to 0.8 μm.

8. The positive electrode active material according to claim 7, characterized in that The average particle size of the lithium iron phosphate is 0.4 μm to 0.6 μm.

9. The positive electrode active material according to claim 1, characterized in that The mass ratio of the ternary material to the lithium iron phosphate with a carbon layer coated on the surface is (90-98): (10-2).

10. The positive electrode active material according to claim 1, characterized in that The molar percentage of nickel in the ternary material is ≥80%.

11. The positive electrode active material according to claim 10, characterized in that The molar percentage of nickel in the ternary material is ≥95%.

12. The positive electrode active material according to claim 10, characterized in that The chemical formula of the ternary material is LiNi x Co y M 1-x-y O2, wherein x is 0.95-0.995, y is 0-0.05, and M includes one or more of Mn, Al, B, Zr, Sr, Y, Sb, W, Ti, Mg and Nb.

13. The method for preparing a positive electrode active material according to any one of claims 1 to 12, characterized in that: The steps include: Coating the lithium iron phosphate having a carbon layer coated on the surface of the ternary material to prepare the positive electrode active material; The method further includes a step of preparing a passivation layer between the surface of the ternary material and the coating layer; the material of the passivation layer includes one or both of aluminum oxide and boron oxide.

14. The method for preparing a positive electrode active material according to claim 13, wherein: Coating the lithium iron phosphate having a carbon layer coated on the surface of the ternary material comprises: The ternary material is mixed with lithium iron phosphate having a carbon layer coated on the surface and a solvent to prepare a dispersion; Drying the dispersion to prepare a powder material; The powder material is sintered.

15. The method for preparing a positive electrode active material according to claim 14, characterized in that: The mixing conditions include: a stirring rate of 1000-3000 r / min and a stirring time of 0.5 h-3 h.

16. The method for preparing a positive electrode active material according to claim 14, wherein: The drying method includes one or both of spray drying and oven drying.

17. The method for preparing a positive electrode active material according to claim 16, wherein: The conditions for spray drying include: atomization pressure 1Mpa~2Mpa, and spray hole diameter 1mm~6mm.

18. The method for preparing a positive electrode active material according to claim 16, wherein: The drying conditions include: temperature of 75℃~85℃.

19. The method for preparing a positive electrode active material according to any one of claims 14 to 18, wherein: The sintering conditions include: temperature of 180°C to 300°C and time of 40min to 80min.

20. The method for preparing a positive electrode active material according to any one of claims 13 to 18, characterized in that: The method for preparing the lithium iron phosphate with a carbon layer coated on the surface is a carbon source method.

21. The method for preparing a positive electrode active material according to claim 20, wherein: The method for preparing the lithium iron phosphate having a carbon layer coated on the surface comprises the following steps: mixing a carbon source, lithium iron phosphate and a solvent to prepare a dispersion; The dispersion is sintered to pyrolyze the carbon source and coat the surface of the lithium iron phosphate.

22. The method for preparing a positive electrode active material according to claim 21, wherein: The sintering conditions include: a temperature of 180°C to 300°C and a time of 40 min to 80 min; and / or, The solvent includes N-methylpyrrolidone; and / or, The carbon source includes one or both of polyacrylonitrile and polymethyl methacrylate.

23. The method for preparing a positive electrode active material according to any one of claims 13 to 18, characterized in that: The steps of preparing the passivation layer include: The ternary material is mixed with a passivating agent and sintered in an oxygen atmosphere to form the passivation layer on the surface of the ternary material.

24. The method for preparing a positive electrode active material according to claim 23, wherein: Sintering in an oxygen atmosphere has one or more of the following characteristics: (1) The oxygen flow rate is 3~10L / min; (2) The sintering temperature is 500℃~700℃ and the sintering time is 3h~8h.

25. A positive electrode plate, characterized in that: The invention comprises a current collector and a positive electrode active layer stacked on the surface of the current collector, wherein the material of the positive electrode active layer comprises the positive electrode active material according to any one of claims 1 to 12.

26. The positive electrode sheet according to claim 25, characterized in that: The positive electrode active layer has one or more of the following characteristics: (1) Coating weight is 24~44mg / cm 2 ; (2) Thickness is 200μm~360μm.

27. A secondary battery, characterized in that: The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 12 or the positive electrode sheet according to any one of claims 25 to 26.

28. The secondary battery according to claim 27, characterized in that The energy density of the secondary battery is 380-500Wh / kg.

29. An electrical device, characterized in that: Includes the secondary battery according to claim 27 or 28.

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