Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive film layer arranged on the surface of the positive current collector, the positive film layer comprises a positive active material, the positive active material comprises a lithium iron phosphate material doped with an element M and an element Q, M comprises one or more of Mn, Ni, Co, Cr, Cu, Bi and Sb, and Q comprises one or more of F, N and Cl.

Description

Technical Field

[0001] The present application relates to the technical field of lithium batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] In recent years, as the application scope of lithium-ion batteries has become increasingly wider, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] The improvement of secondary battery energy density often comes at the expense of rate performance and cycle stability. How to simultaneously improve the energy density, rate performance and cycle stability of secondary batteries is a technical problem that urgently needs to be solved in this field. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and an object of the present application is to provide a secondary battery and an electric device.

[0005] A first aspect of the present application provides a secondary battery, which includes a positive electrode plate, the positive electrode plate includes a positive electrode collector and a positive electrode film layer arranged on the surface of the positive electrode collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium iron phosphate material doped with M elements and Q elements, wherein M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0006] The Q element doped in the positive electrode active material can replace the oxygen on the oxygen site in lithium iron phosphate to distort the unit cell, expand the unit cell volume, expand the migration channel of lithium ions, and improve the rate performance of the secondary battery; the negative ions of the doped M element have high electronegativity and strong ability to attract electrons, making Fe 2+ / Fe 3+ The redox potential of the secondary battery is increased, which improves the voltage platform of the secondary battery, and increases the discharge medium voltage and energy density of the secondary battery. The positive electrode active material is doped with M element and Q element at the same time to achieve the simultaneous improvement of the energy density and rate performance of the secondary battery.

[0007] In any embodiment, the composition of the positive electrode active material includes:

[0008] LiFe 1-x M x PO y Q z ,

[0009] Among them, 0 < x ≤ 0.1, 3.85 ≤ y ≤ 4, 0 ≤ z ≤ 0.05; M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0010] In any embodiment, M includes Mn; Q includes F.

[0011] The different coordination charges between the anions of element Q and the anions of element O will lead to inequivalent substitution, increasing the lattice instability and sacrificing the cycle stability of the secondary battery; when element M includes Mn and element N includes F, Mn doping causes the Jahn-Teller effect to occur during charge and discharge of the positive electrode active material, resulting in two Mn-O bonds being elongated, making P 5+ and F - 's coordination structure more stable, while improving the energy density and fast charging performance of the secondary battery, simultaneously improving the cycle stability of the secondary battery. The Jahn-Teller effect also shortens the four Mn-O bonds of MnO6 2- and elongates the Fe-O bond, making the redox potential of Fe 2+ / Fe 3+ increase. At the same time, the F element at the oxygen site can further increase the strength of the Mn-O-F bond through its strong electronegativity, further enhancing the electrochemical potential of the positive electrode active material, and further playing the role of improving the voltage platform and increasing the energy density through the synergistic effect of Mn and F.

[0012] In any embodiment, 0.005 ≤ x ≤ 0.05, 0.001 ≤ z ≤ 0.01.

[0013] When x and y of the positive electrode active material are within the above ranges, the energy density, cycle stability, and rate performance of the secondary battery can be balanced.

[0014] In any embodiment, the positive electrode active material further includes carbon element, and based on the total mass of the positive electrode active material, the mass content of the carbon element is 1.05% - 1.35%.

[0015] The positive electrode active material with a carbon content within the above range has a low powder resistivity, which is beneficial to improving the rate performance of the secondary battery.

[0016] In any embodiment, the unit cell parameters of the positive electrode active material satisfy:

[0017]

[0018] This lithium iron phosphate positive electrode active material has a large unit cell parameter b, which is beneficial to expanding the lithium ion transport channels and improving the rate performance.

[0019] In any embodiment, the unit cell volume V of the positive electrode active material is:

[0020] The lithium iron phosphate positive electrode active material has a large unit cell volume V, which is beneficial to the expansion of lithium ion transmission channels and the improvement of rate performance.

[0021] In any embodiment, the Fe-O bond length L1 of the positive electrode active material satisfies: The PO bond length L2 of the positive electrode active material satisfies: 1.533

[0022]

[0023] Compared with pure lithium iron phosphate material, the positive electrode active material has a longer Fe-O bond length L1, which is beneficial to Fe 2 + / Fe 3 +The increase in redox potential improves the discharge potential of the positive electrode active material and increases the energy density of the secondary battery.

[0024] In any embodiment, the powder compaction density of the positive electrode active material satisfies: 2.509 g / cm 3 -2.571g / cm 3 .

[0025] The positive electrode active material has a high powder compaction density, which is beneficial to further improve the energy density of the secondary battery.

[0026] In any embodiment, the particle distribution size D50 of the positive electrode active material satisfies: 0.79 um-1.35 um.

[0027] The positive electrode active material with a particle distribution size D50 within the above range has a suitable grain size, which is beneficial to the balance between rate performance and energy density of the secondary battery.

[0028] In any embodiment, the discharge gram capacity of the positive electrode active material at a discharge rate of 0.1C is greater than or equal to 158 mAh / g.

[0029] The positive electrode active material has high discharge capacity and is beneficial to improving the energy density of the secondary battery.

[0030] In any embodiment, the discharge intermediate voltage of the secondary battery at a discharge rate of 0.1C is 3.396V-4.036V.

[0031] The secondary battery has a high discharge medium voltage, which is beneficial to further improve the energy density of the secondary battery.

[0032] A second aspect of the present application provides an electric device, the electric device comprising the secondary battery of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0034] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0035] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0036] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0037] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0038] Figure 6 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0039] Description of reference numerals:

[0040] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0041] Below, the embodiments of the secondary battery and the electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying 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 structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following 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.

[0042] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0044] 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.

[0045] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0046] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0047] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0048] As a positive electrode active material, lithium iron phosphate has the advantages of low cost, high safety, and long cycle life. However, pure lithium iron phosphate has low electronic conductivity (10 -9 cm·s -1 ), low ionic conductivity (10 -13 ~10 - 16 cm 2 ·s -1 ), low discharge medium voltage and other deficiencies. Discharge medium voltage refers to the voltage when the battery capacity is discharged to a certain extent during the use of lithium batteries. It is usually defined as the voltage when the battery discharge capacity reaches about 50% of the rated capacity. Low discharge medium voltage will lead to low energy density of secondary batteries; low electronic conductivity and low ion conductivity will lead to low electron and ion transmission speed of secondary batteries, and it is difficult to improve the rate performance of secondary batteries.

[0049] [Positive electrode active material]

[0050] Based on this, the present application proposes a positive electrode active material, which comprises a lithium iron phosphate material doped with M elements and Q elements, wherein M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0051] The Q element doped in the positive electrode active material can replace the oxygen on the oxygen site in lithium iron phosphate to distort the unit cell, expand the unit cell volume, expand the migration channel of lithium ions, and improve the rate performance of the secondary battery; while the negative ions of the doped M element have high electronegativity and strong ability to attract electrons, making Fe 2+ / Fe 3+ The redox potential of the secondary battery is increased, which improves the voltage platform of the secondary battery, and increases the discharge medium voltage and energy density of the secondary battery. The positive electrode active material is doped with M element and Q element at the same time to achieve the simultaneous improvement of the energy density and rate performance of the secondary battery.

[0052] In some embodiments, the composition of the positive electrode active material includes:

[0053] LiFe 1-x M x PO y Q z ,

[0054] Among them, 0 < x ≤ 0.1, 3.85 ≤ y ≤ 4, 0 ≤ z ≤ 0.05; M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

[0055] In some embodiments, x can be optionally selected as one of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or the numerical range between any two of them.

[0056] In some embodiments, y can be optionally selected as one of 3.85, 3.86, 3.87, 3.88, 3.89, 3.90, 3.91, 3.92, 3.93, 3.94, 3.95, 3.96, 3.97, 3.98, 3.99, 4 or the numerical range between any two of them.

[0057] In some embodiments, z can be optionally selected as one of 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05 or the numerical range between any two of them.

[0058] The composition of the positive electrode active material can be tested by phase analysis methods such as X-ray diffraction method in combination with component analysis methods such as inductively coupled plasma emission spectrometry.

[0059] In some embodiments, M includes Mn; Q includes F.

[0060] The different coordination charges of the anions of Q element and the anions of O element will lead to inequivalent substitution, increasing the lattice instability and sacrificing the cycle stability of the secondary battery; when the M element includes Mn and the N element includes F, Mn doping causes the Jahn-Teller effect to occur during the charge and discharge of the positive electrode active material, resulting in two Mn-O bonds being elongated, making P 5+ and F - The coordination structure is more stable, while improving the energy density and fast charging performance of the secondary battery, simultaneously improving the cycle stability of the secondary battery. The Jahn-Teller effect also shortens the four Mn-O bonds of MnO6 2- and elongates the Fe-O bond, making the redox potential of Fe 2+ / Fe 3+ increase, and at the same time, the F element at the oxygen site can further increase the strength of the Mn-O-F bond through strong electronegativity, further enhancing the electrochemical potential of the positive electrode active material, and further playing the role of improving the voltage platform and increasing the energy density through the synergistic effect of Mn and F.

[0061] In some embodiments, 0.005≤x≤0.05, 0.001≤z≤0.01.

[0062] When x and y of the positive electrode active material are within the above range, the energy density, cycle stability and rate performance of the secondary battery can be taken into consideration.

[0063] In some embodiments, the positive electrode active material further includes carbon element, and the mass content of the carbon element is 1.05%-1.35% based on the total mass of the positive electrode active material.

[0064] In some embodiments, based on the total mass of the positive electrode active material, the mass content of carbon element may be 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35% or any range therebetween.

[0065] Based on the total mass of the positive electrode active material, the mass content of the carbon element can be tested by any known method in the art. As an example, the carbon content is tested by infrared absorption method after combustion in a high-frequency induction furnace. The specific testing process is based on the standard GB / T20123-2006 / ISO 15350:2000 "Determination of total carbon and sulfur content of steel - infrared absorption method after combustion in a high-frequency induction furnace", and is conveniently measured using a carbon and sulfur analyzer, such as Dekai HCS infrared carbon and sulfur analyzer, for carbon content testing.

[0066] The positive electrode active material with a carbon content within the above range has a lower powder resistivity, which is beneficial to improving the rate performance of the secondary battery.

[0067] In some embodiments, the unit cell parameters of the positive electrode active material satisfy:

[0068]

[0069] In some embodiments, a can be selected from

[0070]

[0071] Any one of them or the numerical range between any two of them.

[0072] In some embodiments, b may be selected from

[0073] Any one of them or the numerical range between any two of them.

[0074] In some embodiments, c can be selected from Any one of them or the numerical range between any two of them.

[0075] LiFePO4 has an olivine structure and is an orthorhombic Pnma space group. There are 4 LiFePO4 units in each unit cell. In the LiFePO4 crystal structure, O atoms are arranged in a slightly distorted hexagonal close-packed pattern, phosphorus atoms are at the 4c ​​position of the oxygen tetrahedron, and Fe atoms and Li atoms are at the 4c ​​and 4a positions of the oxygen octahedron, respectively. On the bc plane, the FeO6 octahedrons are connected by common points. One FeO6 octahedron shares edges with two LiO6 and one PO4 tetrahedron, and Li + A continuous straight chain sharing the same corner or edge is formed at the 4a position, and a continuous straight chain of Li+ parallel to the c-axis can form a two-dimensional diffusion motion along the c-axis and can be freely released or embedded.

[0076] The unit cell parameters refer to the length of the smallest repeating unit in the a, b, and c directions of the crystal, and can be tested by any known method in the art. As an example, they can be tested and calculated by X-ray diffraction. Specifically, the American X'pert PRO X-ray powder diffractometer is used for testing and EXPGUI software is used for calculation.

[0077] The lithium iron phosphate positive electrode active material has a larger unit cell parameter b, which is beneficial to the expansion of lithium ion transmission channels and the improvement of rate performance.

[0078] In some embodiments, the unit cell volume of the positive electrode active material is: 290.718

[0079]

[0080] In some embodiments, the unit cell volume of the positive electrode active material may be selected to be

[0081] Any one of them or the numerical range between any two of them.

[0082] The unit cell volume of the positive electrode active material refers to the volume of the unit cell determined by its unit cell parameters, which can be tested by any known method in the art. For example, it can be tested by X-ray diffraction method and calculated by EXPGUI software.

[0083] The lithium iron phosphate positive electrode active material has a large unit cell volume V, which is beneficial to the expansion of lithium ion transmission channels and the improvement of rate performance.

[0084] In some embodiments, the Fe-O bond length L1 of the positive electrode active material satisfies: The PO bond length L2 of the positive electrode active material satisfies: 1.533

[0085]

[0086] In some embodiments, the Fe-O bond length L1 of the positive electrode active material can be selected as

[0087] Or any range of values ​​in between.

[0088] In some embodiments, the PO bond length L2 of the positive electrode active material satisfies: 1.533

[0089]

[0090] Or any range of values ​​in between.

[0091] The Fe—O bond length L1 and the PO bond length L2 of the positive electrode active material can be tested by any known method in the art. As an example, they can be tested by X-ray diffraction and calculated by EXPGUI software.

[0092] Compared with pure lithium iron phosphate material, the positive electrode active material has a longer Fe-O bond length L1, which is beneficial to Fe 2+ / Fe 3+ The increase in redox potential improves the discharge potential of the positive electrode active material and increases the energy density of the secondary battery.

[0093] In some embodiments, the powder compaction density of the positive electrode active material under a pressure of 3t satisfies: 2.509 g / cm 3 -2.571g / cm 3 .

[0094] The powder compaction density of the positive electrode active material under a pressure of 3t can be tested by any known method in the art. As an example, 1g of the positive electrode active material is weighed and added to a cylindrical mold, and the cross-sectional area of ​​the circular hole of the mold is S. A pressure of 3t is applied to the powder in the mold, and the pressure is maintained for 30s, and the thickness of the powder is recorded as t. Then the powder compaction density ρ of the positive electrode active material can be calculated by the following formula: ρ = m / (S×t).

[0095] In some embodiments, the powder compaction density of the positive electrode active material under a pressure of 3t can be 2.509 g / cm 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.53g / cm 3 , 2.54g / cm 3 , 2.55g / cm 3 , 2.56g / cm3 , 2.571g / cm 3 Or any range of values ​​in between.

[0096] The positive electrode active material has a high powder compaction density, which is beneficial to further improve the energy density of the secondary battery.

[0097] In some embodiments, the particle distribution size D50 of the positive electrode active material satisfies: 0.79 um-1.35 um.

[0098] D50 refers to the particle size corresponding to when the cumulative particle size distribution percentage of the positive electrode active material reaches 50%, which can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer with reference to GB / T 19077-2016 particle size distribution laser diffraction method. The test instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0099] In some embodiments, the particle distribution size D50 of the positive electrode active material can be selected as 0.79um, 0.85um, 0.9um, 0.95um, 1.0um, 1.05um, 1.1um, 1.15um, 1.16um, 1.17um, 1.18um, 1.19um, 1.2um, 1.21um, 1.22um, 1.23um, 1.24um, 1.25um, 1.3um, 1.35um or any numerical range therebetween.

[0100] The positive electrode active material with a particle distribution size D50 within the above range has a suitable grain size, which is beneficial to the balance between rate performance and energy density of the secondary battery.

[0101] In some embodiments, the positive electrode active material has a discharge capacity of greater than or equal to 158 mAh / g at a discharge rate of 0.1C.

[0102] The discharge capacity in grams of the positive electrode active material at a discharge rate of 0.1C can be tested by methods known in the art. As an example, the secondary battery is placed in a 25°C oven, left to stand for 2 hours, and then subjected to a charge and discharge test. The charge and discharge process is as follows: charge to 3.65V at a constant current of 0.1C, continue constant voltage charging until the charging current is less than 0.05C, then cut off; pause for 5 minutes; discharge to 2.0V at a constant current of 0.1C; pause for 5 minutes. The discharge capacity in grams of the positive electrode active material at a discharge rate of 0.1C is calculated by dividing the capacity released by the secondary battery from full charge (3.65V) to full discharge (2.0V) by the mass of the positive electrode active material.

[0103] In some embodiments, the discharge gram capacity of the positive electrode active material at a discharge rate of 0.1C may be selected as 158 mAh / g, 158.5 mAh / g, 159 mAh / g, 159.5 mAh / g, 160 mAh / g, 160.5 mAh / g, 161 mAh / g, 161.5 mAh / g, 162 mAh / g or any range therebetween.

[0104] The positive electrode active material has high discharge capacity and is beneficial to improving the energy density of the secondary battery.

[0105] In some embodiments, the discharge intermediate voltage of the secondary battery at a 0.1C discharge rate is 3.396V-4.036V.

[0106] The discharge medium voltage of a secondary battery at a 0.1C discharge rate can be tested by any known method in the art. As an example, the secondary battery is placed in a 25°C oven, left to stand for 2 hours, and then subjected to a charge and discharge test. A charge and discharge process is as follows: 0.1C constant current charging to 3.65V, constant voltage charging is continued until the charging current is less than 0.05C, then the charging current is cut off; pause for 5 minutes; 0.1C constant current discharge to 2.0V; pause for 5 minutes. The potential at which the discharge capacity is 70mAh / g is taken as the discharge medium voltage.

[0107] In some embodiments, the discharge intermediate voltage of the secondary battery at a 0.1C discharge rate may be selected as 3.396V, 3.398V, 3.400V, 3.402V, 3.404V, 3.406V, 3.408V, 3.41V, 3.412V, 3.414V, 3.416V, 3.418V, 3.42V, 3.43V, 3.44V, 3.45V, 3.46V, 3.47V, 3.48V, 3.5V, 3.6V, 3.7V, 3.8V, 3.9V, 4.0V, 4.01V, 4.02V, 4.03V, 4.036V or any range of values ​​therebetween.

[0108] The secondary battery has a high discharge medium voltage, which is beneficial to further improve the energy density of the secondary battery.

[0109] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0110] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0111] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0113] [Negative electrode]

[0114] In some embodiments, the secondary battery further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0115] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0116] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0117] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery 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.

[0118] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0119] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0120] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0121] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0122] [Electrolytes]

[0123] In some embodiments, the secondary battery further includes an electrolyte. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0124] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0125] 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.

[0126] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0127] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0128] [Isolation film]

[0129] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0130] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0131] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0132] A third aspect of the present application provides an electric device, wherein the electric device comprises the secondary battery according to the second aspect.

[0133] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0134] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0135] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0136] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0137] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0138] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0139] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0140] 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.

[0141] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0142] Figure 4 and Figure 5 1 is a battery pack 1 as an example. Figure 4 and Figure 5The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0143] In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0144] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0145] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0146] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0147] Example

[0148] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0149] Example 1

[0150] (1) Preparation of positive electrode active materials

[0151] The raw materials are iron phosphate, lithium carbonate, manganese nitrate, carbon source and lithium fluoride, and the raw materials are added in a proportion and sequence such that the molecular formula of the finished product is lithium iron phosphate. The carbon source is glucose, sucrose and polyethylene glycol PEG with a weight average molecular weight of 2000-4000.

[0152] The raw materials are sequentially added into solvent water for wet grinding to obtain a mixed slurry; the obtained mixed slurry is spray dried, and then the dried product is placed in a roller furnace and sintered at 750°C in an air-tight state for 28 hours, and then naturally cooled to a material temperature of less than 80°C and discharged to obtain a calcined material; the calcined material is crushed, screened, and demagnetized to obtain a positive electrode active material.

[0153] (2) Preparation of positive electrode sheet

[0154] The above-mentioned positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are mixed in a mass ratio of 96.5:2.0:1.5, and then N-methylpyrrolidone (NMP) solvent is added to form a uniform positive electrode slurry; the slurry is coated on a carbon-coated aluminum foil with a thickness of 13 μm, and the coating surface density is 26 mg / cm2. After drying, cold pressing, and slitting, the positive electrode sheet of the present application is obtained.

[0155] (3) Preparation of negative electrode sheet

[0156] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the adhesive styrene butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97:1:1:1, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on a copper foil with a thickness of 8 μm; after drying, the negative electrode sheet is obtained by cold pressing and slitting to obtain a negative electrode sheet.

[0157] (4) Isolation film

[0158] A 12μm thick polypropylene isolation film was selected.

[0159] (5) Electrolyte

[0160] The solvents ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed in a mass ratio of 30:70, LiPF6 is added, and after it is completely dissolved, vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are added. After mixing evenly, an electrolyte with a LiPF6 concentration of 1 mol / L and a mass content of VC and FEC of 3% respectively is obtained.

[0161] (6) Assembly of secondary batteries

[0162] The positive electrode sheet and the negative electrode sheet are placed in a high-temperature oven at 110°C and baked for 7 hours to remove moisture from the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order so that the isolation film is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. After winding into a square bare battery cell, an aluminum-plastic film is inserted, and the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a lithium-ion battery is obtained.

[0163] The preparation methods of the secondary batteries of Examples 2 to 7 and Comparative Examples 1-4 are similar to those of the secondary battery of Example 1, except that the input ratio of the manganese source and the fluorine source during the preparation of the positive electrode active material is adjusted, so that the molar ratio of the manganese element, the fluorine element and the lithium element in the final prepared product is adjusted. The specific product parameters are shown in Table 1.

[0164] In Example 3 and Comparative Example 3, a nickel source, nickel nitrate, was also added during the feeding stage.

[0165] The preparation method of Example 7 is basically the same as that of Example 1, except that the sintering temperature is adjusted to 770°C.

[0166] Table 1

[0167]

[0168]

[0169] 2. Battery performance test

[0170] 1.0.1C battery gram capacity test method

[0171] Place the lithium-ion battery in a 25℃ oven, let it stand for 2 hours, and then perform a charge and discharge test. The charge and discharge process is as follows: charge to 3.65V at 0.1C constant current, continue constant voltage charging until the charging current is less than 0.05C, then stop; pause for 5 minutes; discharge to 2.0V at 0.1C constant current; pause for 5 minutes. The above is a charge and discharge of the battery.

[0172] Battery gram capacity = discharge capacity of secondary battery / mass of positive electrode active material.

[0173] 2. Discharge medium voltage test

[0174] The lithium-ion batteries of the embodiment and the comparative example were placed in a 25°C oven and left to stand for 2 hours, and then subjected to charge and discharge tests. The charge and discharge process was as follows: 0.1C constant current charging to 3.65V, constant voltage charging continued until the charging current was less than 0.05C, then cut off; paused for 5 minutes; 0.1C constant current discharge to 2.0V; paused for 5 minutes. The potential when the discharge gram capacity was 70mAh / g was taken as the discharge medium voltage.

[0175] 3. Energy density test

[0176] Place the lithium-ion battery in a 25℃ oven, let it stand for 2 hours, and then perform a charge and discharge test. The charge and discharge process is as follows: 1C constant current charge to 3.65V, continue constant voltage charge until the charging current is less than 0.05C, then cut off; pause for 5 minutes; 1C constant current discharge to 2.0V; pause for 5 minutes. The above is a charge and discharge of the battery.

[0177] Cell mass energy density (Wh / kg) = (capacity of the third discharge during the cycle × discharge platform) / mass of positive electrode active material.

[0178] 4. Cyclic stability test

[0179] The lithium-ion battery was placed in a 60°C oven and left to stand for 2 hours before the charge and discharge test. The process of a charge and discharge cycle is as follows: 1C constant current charging to 3.65V, and then constant voltage charging until the charging current is less than 0.05C and then cut off; pause for 5 minutes; 1C constant current discharge to 2.5V; pause for 5 minutes. The above is a charge and discharge cycle of the battery, which is repeated continuously. After 2000 cycles, the ratio of the battery discharge capacity to the first cycle discharge capacity is calculated as the cycle capacity retention rate.

[0180] 5. Rate performance test

[0181] The lithium-ion battery was placed in a 25°C oven, left to stand for 3 minutes, and then subjected to charge and discharge tests. The charge and discharge process is as follows: 0.1C constant current charging to 3.65V, and then constant voltage charging until the charging current is less than 0.05C and then cut off; pause for 5 minutes; 0.1C constant current discharge to 2.0V; pause for 5 minutes, and record the discharge capacity as C1; subsequently adjust the charge and discharge rate to 1C, 5C, and 10C, respectively, record the discharge capacity of 1C as C2, and the discharge capacity of 10C as C3, and use C2 / C1 to characterize the rate performance of the battery at a 1C discharge rate, and use C3 / C1 to characterize the rate performance of the battery at a 10C discharge rate.

[0182] III. Analysis of test results of various embodiments and comparative examples

[0183] The batteries of the embodiments and comparative examples were prepared according to the above method, and various performance parameters were measured. The results are shown in Table 2 below.

[0184] Table 2

[0185]

[0186] Table 3

[0187]

[0188] The XRD test results show that the positive electrode active material in the present application is a lithium iron phosphate phase with an olivine structure, and the positive electrode active material in the embodiment is doped with M elements and Q elements at the same time, wherein M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl. Compared with the material in the comparative example, the positive electrode active material in the embodiment has a large unit cell volume, Fe-O bond length L1, and powder compaction density, which is conducive to the simultaneous improvement of the discharge medium voltage, energy density, and rate performance of the secondary battery.

[0189] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A secondary battery, characterized in that: The secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on the surface of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, the positive electrode active material contains a lithium iron phosphate material doped with M element and Q element, where M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

2. The secondary battery according to claim 1, characterized in that: The composition of the positive electrode active material includes: LiFe 1-x M x PO y Q z , where 0 < x ≤ 0.1, 3.85 ≤ y ≤ 4, 0 ≤ z ≤ 0.05; M includes one or more of Mn, Ni, Co, Cr, Cu, Bi, and Sb, and Q includes one or more of F, N, and Cl.

3. The secondary battery according to claim 1, wherein M includes Mn; Q includes F.

4. The secondary battery according to claim 1, wherein 0.005 ≤ x ≤ 0.05, 0.001 ≤ z ≤ 0.

01.

5. The secondary battery according to claim 1, wherein The positive electrode active material further includes carbon element, and based on the total mass of the positive electrode active material, the mass content of the carbon element is 1.05% - 1.35%.

6. The secondary battery according to any one of claims 1 to 5, characterized in that: The positive electrode active material satisfies at least one of the following conditions: (1) The unit cell parameters of the positive electrode active material satisfy: (2) The unit cell volume V of the positive electrode active material is: (3) The Fe-O bond length L1 of the positive electrode active material satisfies: The PO bond length L2 of the positive electrode active material satisfies:

7. The secondary battery according to any one of claims 1 to 5, characterized in that: The positive electrode active material satisfies at least one of the following conditions: (1) The powder compaction density of the positive electrode active material meets the following requirements: 2.509 g / cm 3 -2.571g / cm 3 ; (2) The particle size distribution D50 of the positive electrode active material satisfies: 0.79um - 1.35um; (3) The discharge capacity per gram of the positive electrode active material at a discharge rate of 0.1C is greater than or equal to 158 mAh / g.

8. The secondary battery according to any one of claims 1 to 5, characterized in that: The discharge mid-voltage of the secondary battery at a discharge rate of 0.1C is 3.396V - 4.036V.

9. An electrical device, characterized in that: The electrical device includes the secondary battery according to any one of claims 1 to 8.

Images