Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte solution; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector and comprising a positive electrode active material; the positive electrode active material comprises an inner core of lithium iron phosphate material and a carbon shell layer at least partially covering the outer surface of the inner core; in the Raman spectrum of the positive electrode active material, a ratio Id / Ig of a peak intensity Id of D peak of a Raman shift within a range of 1350±50 cm-1 to a peak intensity Ig of G peak of a Raman shift within a range of 1580±50 cm-1 is 0.2-1.5; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector; and when the state of charge of the secondary battery is 100% or the voltage of the secondary battery is 3.65 V, a heat release amount Q of the negative electrode film layer in the electrolyte solution satisfies: 250 J / g≤Q≤600 J / g.

Description

Secondary battery and power consuming device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411389200.0, filed on September 30, 2024, entitled “Secondary battery and power consuming device”, which is incorporated by reference in its entirety into this application. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and a power consuming device. BACKGROUND

[0004] In recent years, secondary batteries are increasingly widely used in energy storage power supply systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. However, in the prior art, it is difficult to balance energy efficiency and overcharge safety for secondary batteries.

[0005] Therefore, it is necessary to provide a secondary battery that has both high energy efficiency and good overcharge safety. SUMMARY

[0006] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery and a power consuming device that have both high energy efficiency and good overcharge safety.

[0007] The inventors have found that the above-mentioned problems can be solved by using the technical solution of the present application.

[0008] A first aspect of the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte,

[0009] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and comprising a positive electrode active material, the positive electrode active material comprising a lithium iron phosphate-based material core and a carbon shell layer at least partially coated on the outer surface of the core, and in the Raman spectrum of the positive electrode active material, the peak intensity I of the D peak with a Raman shift in the range of 1350±50 cm -1 is less than 1 / 2 of the peak intensity I d of the G peak with a Raman shift in the range of 1580±50 cm -1 . g d g ​​0.2-1.5, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, and when the state of charge of the secondary battery is 100% or the voltage of the secondary battery is 3.65 V, the heat release Q of the negative electrode film layer in the electrolyte satisfies: 250 J / g≤Q≤600 J / g.

[0010] The secondary battery of the present application has both high energy efficiency and good overcharge safety.

[0011] In any embodiment, the I d / I g is 0.9-1.3.

[0012] When the I d / I g of the positive electrode active material is 0.9-1.3, the secondary battery of the present application has both high energy efficiency and good cycle performance.

[0013] In any embodiment, the I d / I g of the positive electrode active material is 0.3-1.1.

[0014] When the I d / I g of the positive electrode active material is 0.3-1.1, the secondary battery of the present application has low swelling force.

[0015] In any embodiment, the I d / I g of the positive electrode active material is 0.8-1.2.

[0016] When the I d / I g of the positive electrode active material is 0.8-1.2, the secondary battery of the present application has both high energy efficiency and good cycle performance.

[0017] In any embodiment, the carbon shell layer includes both amorphous carbon and graphene.

[0018] When the carbon shell layer includes both amorphous carbon and graphene, the secondary battery of the present application has both high energy efficiency and good cycle performance.

[0019] In any embodiment, the powder resistivity of the positive electrode active material under a pressure of 16 MPa is 0-30 Ω·cm.

[0020] When the powder resistivity of the positive electrode active material under a pressure of 16 MPa is 0-30 Ω·cm, the secondary battery of the present application has both high energy efficiency and good cycle performance.

[0021] In any embodiment, the lithium iron phosphate-based material includes a material represented by the following formula:

[0022] Li x Fe y M z PO4,

[0023] wherein 0.95 < x < 1.05, 0.96 < y < 1, 0 < z < 0.04,

[0024] M includes one or more of Ti, V, Mg, Zr, Y.

[0025] In any embodiment, the content of the element M is 0.02% to 0.3% based on the total weight of the positive electrode active material.

[0026] When the content of the element M is 0.02% to 0.3%, the secondary battery of the present application has higher energy efficiency and better cycle performance.

[0027] In any embodiment, the content of the element M is 0.03% to 0.1% based on the total weight of the positive electrode active material.

[0028] When the content of the element M is 0.03% to 0.1%, the secondary battery of the present application has higher energy efficiency and better cycle performance.

[0029] The second aspect of the present application provides an electric device including the secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0031] FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0032] FIG. 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 1.

[0033] FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0034] FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0035] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4.

[0036] FIG. 6 is a schematic view of a power consuming device using the secondary battery as a power source according to an embodiment of the present application.

[0037] BRIEF DESCRIPTION OF DRAWINGS 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: secondary battery; 51: case; 52: electrode assembly; 53: cover plate. DETAILED DESCRIPTION

[0038] Hereinafter, embodiments of the secondary battery and the power consuming device according to the present application will be specifically described with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are well known and repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to sufficiently understand the present application, and are not intended to limit the subject matter recited in the claims.

[0039] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this manner can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing an arbitrarily selected combination of real numbers between "a" and "b", where "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing these combinations of numbers. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0041] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0042] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] If not specified otherwise, the terms "comprising" and "including" mentioned in the present application mean open-ended, and can also mean closed-ended. For example, the terms "comprising" and "including" can mean that other components not listed can also be included, or can mean that only the listed components are included.

[0044] If not specified otherwise, in the present 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 satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0045] In recent years, secondary batteries are increasingly widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. However, in the prior art, secondary batteries are difficult to balance in terms of energy efficiency and overcharge safety. Therefore, it is necessary to provide a secondary battery which has both high energy efficiency and good overcharge safety.

[0046] Based on this, the present application proposes a technical solution to solve the above technical problems.

[0047] The first aspect of the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte,

[0048] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and comprising a positive electrode active material, the positive electrode active material comprising a lithium iron phosphate-based material core and a carbon shell layer at least partially coated on the outer surface of the core, and in the Raman spectrum of the positive electrode active material, the ratio of the peak intensity I -1 of the D peak with a Raman shift in the range of 1350±50 cm d to the peak intensity I -1 of the G peak with a Raman shift in the range of 1580±50 cm g is greater than 0.9.d / I g The negative electrode sheet is 0.2-1.5, and includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector. When the state of charge of the secondary battery is 100% or the voltage of the secondary battery is 3.65V, the heat release Q of the negative electrode film layer in the electrolyte satisfies: 250J / g≤Q≤600J / g.

[0049] In this paper, the term "D peak" refers to the peak located at 1350±50 cm⁻¹ in Raman spectroscopy. -1 The peak corresponds to the characteristic peak of lattice defects in the carbon shell coating on the surface of the positive electrode active material.

[0050] In this paper, the term "G peak" refers to the peak located at 1350±50 cm⁻¹ in Raman spectroscopy. -1 The peak corresponds to the characteristic peak of the disordered structure in the carbon shell coating on the surface of the positive electrode active material.

[0051] In this article, the term "I" d "" refers to the peak intensity of peak D.

[0052] In this article, the term "I" g "" refers to the peak intensity of peak G.

[0053] In this article, the term "I" d / I g "" refers to the ratio of the intensity of the D peak to the intensity of the G peak, which is used to quantify the degree of graphitization of the positive electrode active material.

[0054] In this document, the term "graphitization degree" has the meaning known in the art, referring to the degree of graphitization of the carbon component, reflecting the integrity of the graphite crystal structure in the carbon-coated lithium iron phosphate of this application, especially in the carbon coating layer, that is, the degree of regularity of the arrangement of carbon atoms in the graphite structure.

[0055] Peak intensity I of D peak of positive electrode active material d Peak intensity I of G peak g The ratio I d / I g The lower the value, the higher the degree of graphitization of the positive electrode active material, meaning its structure is closer to the ideal graphite structure, its surface is smoother and more non-polar, and the overall hydrophobicity of the material is enhanced. Positive electrode active material I d / I gThe value within the appropriate range can reduce the water content of the positive active material, improve the positive electrode sheet processing process, reduce the water content in the positive electrode sheet, and the water content in the battery, thereby reducing the gas production of the battery and reducing the swelling force of the battery during the cycle process. In addition, as the graphitization degree of the lithium iron phosphate material increases, the conductivity of the lithium iron phosphate material also increases, which can reduce the overvoltage of the lithium iron phosphate material caused by insufficient conductivity during charging and discharging, and reduce the deformation degree of the positive active material and the expansion degree of the electrode sheet during the cycle, thereby improving the cycle performance of the battery; the enhanced conductivity also helps to reduce the interface impedance of the positive active material, reduce the electronic resistance and improve the internal resistance of the battery.

[0056] In the full charge state of the battery, the heat generation of the negative electrode film layer is limited within a certain range, which can reduce the heat generation of the battery and improve the overcharge performance.

[0057] The use of hydrophobic high-conductivity positive electrode sheets in combination with low-heat negative electrode sheets is conducive to improving energy efficiency while improving the safety performance of the battery, meeting the application requirements of the energy storage scene.

[0058] Therefore, the secondary battery of the present application has high energy efficiency and good overcharge safety.

[0059] I d / I g The measurement method can use any method known in the art, for example, referring to GB / T 40219-2021, the positive active material powder is pressed into a tablet, and a LabRAM HR Evolution laser micro-Raman spectrometer is used to test the tablet. Three points on the tablet are randomly selected for testing, and three sets of measurement values are obtained and averaged. Among them, a solid laser with a wavelength of 523 nm is used as the light source, the beam diameter is 1.2 μm, the power is 1 mW, the measurement mode is macro-Raman, and a CCD detector is used.

[0060] In some embodiments, the I d / I g may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or a range or value within the range composed of any two of the above values.

[0061] In some embodiments, the I d / I g is 0.9-1.3.

[0062] When the I d / I gWhen the I

[0063] In some embodiments, the I d / I g is 0.3-1.1.

[0064] When the I d / I g is 0.3-1.1, the secondary battery of the present application has a lower expansion force due to the strong hydrophobicity of the positive electrode active material.

[0065] In some embodiments, the I d / I g is 0.8-1.2.

[0066] When the I d / I g is 0.8-1.2, the secondary battery of the present application has a higher energy efficiency, better cycle performance and lower expansion force due to the high hydrophobicity, high electronic conductivity and high ionic conductivity of the positive electrode active material.

[0067] In some embodiments, the carbon shell layer comprises both amorphous carbon and graphene.

[0068] The lithium iron phosphate is coated with amorphous carbon and graphene, which can improve the electronic conductivity of the material, reduce the interface impedance of the positive electrode active material, reduce the electronic resistance and improve the battery internal resistance, improve the energy efficiency and cycle performance of the battery cell, thereby resulting in the secondary battery of the present application having a higher energy efficiency and better cycle performance.

[0069] In the preparation process of the lithium iron phosphate, the amorphous carbon and graphene can be coated simultaneously, or the amorphous carbon can be coated first and then the graphene can be coated.

[0070] In some embodiments, the powder resistivity of the positive electrode active material under a pressure of 16Mpa is 0-30Ω·cm.

[0071] When the powder resistivity of the positive electrode active material under a pressure of 16Mpa is 0-30Ω·cm, the battery internal resistance can be improved, the energy efficiency and cycle performance of the battery cell can be improved, thereby resulting in the secondary battery of the present application having a higher energy efficiency and better cycle performance.

[0072] In some embodiments, the lithium iron phosphate material comprises a material represented by the following formula:

[0073] Li x Fey M z PO4,

[0074] wherein, 0.95 < x < 1.05, 0.96 < y < 1, 0 < z < 0.04,

[0075] M comprises one or more of Ti, V, Mg, Zr, Y.

[0076] In some embodiments, the content of M element is 0.02%-0.3% calculated based on the total weight of the positive electrode active material. In some embodiments, the content of M element is 0.03%-0.1% calculated based on the total weight of the positive electrode active material.

[0077] The conductivity of lithium iron phosphate is relatively low. Doping metal elements can increase the free electron concentration in the lithium iron phosphate lattice, reduce the transport barrier of lithium ions, improve the diffusion rate of lithium ions, and improve the rate performance of the battery. It can also effectively improve the structural stability of the positive electrode active material, so that the secondary battery has high energy efficiency and good cycle performance.

[0078] In some embodiments, the content of M element is 0, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or a range or a value in the range formed by any two of the above values, calculated based on the total weight of the positive electrode active material.

[0079] The positive electrode active material can be prepared by a method commonly used in the art. In some embodiments, the preparation method of the positive electrode active material comprises the following steps: mixing a lithium source, an iron source, a phosphorus source, an M source and a carbon source according to a proportion, sintering, thereby obtaining a positive electrode active material comprising a lithium iron phosphate material core and a carbon shell layer at least partially coated on the outer surface of the core.

[0080] In some embodiments, the lithium source comprises one or more of Li2CO3, LiH2PO4, Li3PO4.

[0081] In some embodiments, the iron source comprises one or more of FeSO4, FePO4, FeCl2, FeC2O4, Fe2O3.

[0082] In some embodiments, the phosphorus source comprises one or more of NH4H2PO4, H3PO4.

[0083] In some embodiments, the M source comprises one or more of metal salts, metal oxides, and metal organic compounds containing Nb, Ti, V, W, Mn elements.

[0084] In some embodiments, the carbon source comprises one or more of glucose, sucrose, starch, polyethylene glycol, phenol formaldehyde, carbon black, graphite, carbon nanotube, tannic acid, sodium dodecyl benzene sulfonate, alkyl glucoside, polyaniline, fructose, disodium ethylenediaminetetraacetate, polyvinylpyrrolidone, lecithin.

[0085] In some embodiments, the sintering temperature is 500-900℃, for example 600℃; the sintering time at the sintering temperature is 8-20h, for example 16h.

[0086] In some embodiments, the sintering temperature is 500℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, or a range between any two of the above values or a value within the range.

[0087] In some embodiments, the sintering time is 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, or a range between any two of the above values or a value within the range.

[0088] A second aspect of the present application provides a power consuming device comprising the secondary battery of the first aspect of the present application.

[0089] In addition, the secondary battery and the power consuming device of the present application are described below with appropriate reference to the accompanying drawings.

[0090] In one embodiment of the present application, a secondary battery is provided.

[0091] Generally, a secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted into and extracted from the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and functions to prevent short circuiting between the positive electrode and the negative electrode, while allowing ions to pass through.

[0092] [Positive electrode sheet]

[0093] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material.

[0094] By way of example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0095] In some embodiments, the positive current collector can employ a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be employed. The composite current collector can 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 can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0096] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can 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 acrylic ester resin.

[0097] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some embodiments, the positive electrode tab can be prepared by dispersing the above-described components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, coating the positive electrode slurry on the positive electrode current collector, and subjecting the same to a drying, cold-pressing, or the like process to obtain the positive electrode tab.

[0099] [Negative electrode tab]

[0100] The negative electrode tab includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0101] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative current collector.

[0102] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be employed. The composite current collector can 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 can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0103] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0104] In some embodiments, the negative film layer can further optionally include a binder. The binder can 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).

[0105] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0107] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-described components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector; and drying, cold-pressing, and the like to obtain the negative electrode sheet.

[0108] [Electrolyte]

[0109] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be liquid, gel, or all-solid.

[0110] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0111] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalato borate, lithium di-oxalato borate, lithium difluoro di-oxalato phosphate, and lithium tetrafluoro oxalato phosphate.

[0112] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0113] In some embodiments, the electrolyte solution can optionally further include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0114] [Separator]

[0115] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly limited in the present application and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0116] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0117] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly through a winding process or a stacking process.

[0118] In some embodiments, the secondary battery can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0119] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0120] The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square, or any other shape. For example, FIG. 1 is a secondary battery 5 of a square structure as an example.

[0121] In some embodiments, referring to FIG. 2, the outer package can include a shell 51 and a cover plate 53. The shell 51 can 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 communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged 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, which can be selected by a person skilled in the art according to specific actual needs.

[0122] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0123] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0124] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0125] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0126] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0127] In addition, the application also provides a power utilization device comprising at least one of the secondary battery, the battery module, or the battery pack provided by the application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, and can also be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0128] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0129] FIG. 6 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0130] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0131] Embodiment

[0132] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0133] I. Preparation method

[0134] Embodiment 1

[0135] 1) Preparation of the positive electrode sheet

[0136] 0.1 mol of lithium carbonate, 0.198 mol of ferrous oxalate, 0.2 mol of ammonium dihydrogen phosphate powder, 0.001 mol of tetrabutyl titanate, 0.015 mol of glucose, and 0.1 g of graphene powder were uniformly dispersed in 50 ml of anhydrous ethanol, and ball-milled at a rotation number of 400 r / min for 12 h. The ball-milled powder was dried to obtain a mixed precursor powder. Then, the precursor powder was placed in a sintering furnace, an inert atmosphere was introduced, and the temperature was increased to 600 ℃ at a heating rate of 2 ℃ / min, and the temperature was maintained for 14 h to obtain a lithium iron phosphate positive electrode material. It was determined that the I d / Ig 1.1, which has a powder resistivity of 12.0 Ω-cm under a pressure of 16 MPa.

[0137] The lithium iron phosphate positive electrode active material prepared above, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97:1:2, a solvent N-methyl pyrrolidone is added, and stirring is performed to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on both sides of a positive electrode current collector aluminum foil, and drying, cold pressing, and slitting are performed to obtain a positive electrode tab. The single-side coating amount of the positive electrode film layer is 21.7 mg / cm 2 .

[0138] 2) Preparation of a negative electrode tab

[0139] The negative electrode active material graphite, the thickening agent sodium carboxymethyl cellulose, the binder styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 95:2:2:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on both sides of a copper foil, and drying, cold pressing, and slitting are performed to obtain a negative electrode tab. The single-side coating amount of the negative electrode film layer is 9.7 mg / cm 2 .

[0140] 3) Preparation of an electrolyte

[0141] Under an argon atmosphere with a water content of less than 10 ppm, 2,2-difluoroethyl acetate, ethylene carbonate (EC), and methyl ethyl carbonate (EMC) are mixed in a mass ratio of 3:3:4 to obtain an organic solvent, and then LiPF6 is dissolved in the organic solvent at a concentration of 1.0 mol / L to prepare an electrolyte.

[0142] 4) Separating film

[0143] A 9-μm-thick polypropylene film is selected as the separating film.

[0144] 5) Preparation of a secondary battery

[0145] The positive electrode tab, the separating film, and the negative electrode tab are stacked in sequence, with the separating film between the positive electrode tab and the negative electrode tab to play a separating role, and then the electrode assembly is obtained by winding; the electrode assembly is placed in an outer package, electrolyte is injected after drying, and the secondary battery is obtained by performing processes such as vacuum packaging, standing, formation, and shaping.

[0146] Example 2-9 and Comparative Examples 1-2 differ from Example 1 mainly as shown in Table 1.

[0147] II. Test methods

[0148] 1. Graphitization degree I of a positive electrode active material d / I g Test

[0149] Referring to GB / T 40219-2021, the positive active material powder is pressed into a tablet, and the tablet is tested by a LabRAM HR Evolution laser micro-Raman spectrometer. Three points on the tablet are randomly selected for testing, and three sets of measurement values are obtained and averaged. Among them, a solid laser with a wavelength of 523 nm is used as a light source, the beam diameter is 1.2 μm, the power is 1 mW, the measurement mode is macro-Raman, and a CCD detector is used.

[0150] 2. Heat release test of negative electrode film layer

[0151] A fully charged cell (the state of charge of the secondary battery is 100% or the voltage of the secondary battery is 3.65V) is disassembled in a glove box, and an appropriate amount of negative electrode sheet is taken out. The negative electrode sheet is placed in DMC solvent for 2 min, the residual electrolyte is washed off, and then dried for 8 h. The negative electrode film layer on the sheet is scraped off.

[0152] Ethylene carbonate and methyl ethyl carbonate are mixed in a volume ratio of 3:7, and LiPF6 is added to the mixture to form an electrolyte. The concentration of LiPF6 is 1 mol / L.

[0153] The heat release Q of the negative electrode film layer is measured by differential scanning calorimetry. The mass ratio of the negative electrode film layer and the electrolyte is 0.78:1, and the temperature is raised from 30°C to 450°C at a rate of 5°C / min.

[0154] 3. Powder resistivity test

[0155] Referring to the standard GB / T 30835-2014, the resistivity tester is used for testing, and the resistivity value under the pressure of 16 MPa is recorded.

[0156] 4. Cell energy efficiency test

[0157] At 25°C and normal pressure, the prepared secondary battery is discharged at 0.5P constant power to 2.5V, and then charged to 3.65V at 0.5P constant power. The charging energy E1 at this time is recorded, and the battery is placed for 30 min. Then discharged to 2.5V at 0.5P constant power, the discharge energy E2 at this time is recorded. The energy efficiency of the cell at 0.5P rate is E2 / E1*100%.

[0158] 5. Cell cycle life and expansion force test method

[0159] Install the secondary cell mounting clamp and the pressure sensor, the initial clamp force is 3000N, and the pressure sensor monitors the external pressure of the cell large surface (length x height). At 45℃, the cell is tested for charge-discharge cycling on a charge-discharge instrument, with a cycle rate of 0.5P (i.e. the charge rate and discharge rate are both 0.5P), the charge voltage is 2.5V to 3.65V, and the capacity and maximum pressure value of each cycle during cycling are recorded. The maximum pressure value at the 1000th cycle is the swelling force (N) at the 1000th cycle.

[0160] The capacity retention rate of 45℃ cycling is: the capacity retention rate after the 1000th cycle = (the discharge capacity after the 1000th cycle / the discharge capacity of the first cycle) x 100%.

[0161] 6. Overcharged cell large surface maximum temperature test

[0162] The overcharge test is carried out according to the overcharge test standard in GBT 36276-2023, and the maximum temperature of the large surface of the overcharge test cell is recorded.

[0163] 7. Content of M element

[0164] The content of M element is tested by ICP.

[0165] 8. Carbon shell layer composition

[0166] The carbon layer morphology on the surface of the positive electrode material is observed by transmission electron microscope, and the composition of the carbon shell layer can be determined by combining the interlayer spacing of the carbon shell layer. The interlayer spacing of amorphous carbon is larger than that of graphene. If two different thicknesses of interlayer spacing are observed, it indicates that there are two carbon compositions.

[0167] III. Analysis of test results of each embodiment and comparative example

[0168] The secondary batteries of each embodiment and comparative example are prepared according to the above method, and each parameter is measured. The related parameters of the positive electrode active material and the negative electrode sheet are shown in Table 1, and the performance test results of the secondary batteries are shown in Table 2.

[0169] Table 1: Related parameters of positive electrode active material and negative electrode sheet

[0170] Table 2: Performance test results of secondary batteries

[0171] Based on the above results, it can be seen that the secondary batteries in Examples 1-9 all include a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector and including a positive electrode active material. The positive electrode active material includes a lithium iron phosphate core and a carbon shell layer at least partially covering the outer surface of the core. In the Raman spectrum of the positive electrode active material, the Raman shift is within 1350±50 cm⁻¹. -1 Peak intensity I of D peak within the range d With Raman displacement at 1580±50cm -1 Peak intensity I of G peak within the range g The ratio I d / I g The negative electrode sheet is 0.2-1.5, and includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector. When the state of charge of the secondary battery is 100% or the voltage of the secondary battery is 3.65V, the heat release Q of the negative electrode film layer in the electrolyte satisfies: 250J / g≤Q≤600J / g.

[0172] As can be seen from the comparison between Examples 1-9 and Comparative Examples 1-2, the secondary batteries of this application have both high energy efficiency and good overcharge safety.

[0173] A comparison of Examples 1-3 and Example 4 shows that when the positive electrode active material I... d / I g When the value is 0.9-1.3, the secondary battery of this application embodiment has high energy efficiency and good cycle performance.

[0174] A comparison of Examples 1-2 and 4 with Example 3 shows that when the positive electrode active material I... d / I g When the value is 0.3-1.1, the secondary battery of this application embodiment has a low expansion force.

[0175] A comparison of Examples 1-2 and Examples 3-4 shows that when the positive electrode active material I... d / I g When the coefficient of performance is 0.8-1.2, the secondary battery of this application embodiment has high energy efficiency, good cycle performance and low expansion force.

[0176] As can be seen from the comparison between Examples 1, 8-9 and Example 7, when the content of element M is 0.02%-0.3% (calculated based on the total weight of the positive electrode active material), the secondary battery of this application embodiment has high energy efficiency and good cycle performance.

[0177] From the comparison of Example 1, 8 and Example 7, 9, it can be seen that when the content of M element is 0.03%-0.1% (calculated based on the total weight of the positive active material), the secondary battery of the present application has higher energy efficiency and better cycle performance.

[0178] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exerting the same effects within the scope of the technical solution of the present application are all included in the technical scope of the present application. Furthermore, within the scope of the gist of the present application, various modifications that can be thought of by those skilled in the art are applied to the embodiments, and other modes constructed by combining part of the constituent elements of the embodiments are also included in the scope of the present application.

Claims

A secondary battery characterized by The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, The positive electrode tab includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector and including a positive electrode active material, the positive electrode active material including a lithium iron phosphate-based material core and a carbon shell layer at least partially coated on an outer surface of the core, in a Raman spectrum of the positive electrode active material, a peak intensity I of a D peak with a Raman shift in a range of 1350±50 cm -1 -1.5 d and a peak intensity I of a G peak with a Raman shift in a range of 1580±50 cm -1 -1.5 g are in a ratio I d / I g of 0.2-1.5, The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, and the heat release Q of the negative electrode film layer in the electrolyte satisfies 250J / g≤Q≤600J / g when the state of charge of the secondary battery is 100% or the voltage of the secondary battery is 3.65V. The secondary battery according to claim 1, characterized in that I of the positive electrode active material is 0.9-1.

3. d / I g 0.9-1.

3. The secondary battery according to claim 1, characterized in that I of the positive electrode active material is 0.3-1.

1. d / I g 0.3-1.

1. The secondary battery according to any one of claims 1 to 3, characterized in that, I of the positive electrode active material is 0.8-1.

2. d / I g 0.8-1.

2. The secondary battery according to any one of claims 1 to 4, characterized in that, The carbon shell layer comprises both amorphous carbon and graphene. The secondary battery according to any one of claims 1 to 5, characterized in that, The powder resistivity of the positive electrode active material under a pressure of 16Mpa is 0-30Ω·cm. The secondary battery according to any one of claims 1 to 6, characterized in that, The lithium iron phosphate-based material comprises a material represented by the following formula: Li x Fe y M z PO4, wherein 0.95 < x < 1.05, 0.96 < y ≤ 1, 0 ≤ z < 0.04, M comprises one or more of Ti, V, Mg, Zr and Y. The secondary battery according to claim 7, characterized in that The content of the M element is 0.02%-0.3% calculated based on the total weight of the positive electrode active material. The secondary battery according to claim 7, characterized in that The content of the M element is 0.03%-0.1% calculated based on the total weight of the positive electrode active material. An electric power utilization device characterized by comprising: The secondary battery according to any one of claims 1 to 9.

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