Positive electrode active material, positive electrode sheet, secondary battery, and electric device

Abstract

Embodiments of the present application relate to a positive electrode active material, a positive electrode sheet, a secondary battery, and an electric device. The positive electrode active material includes a first active material and a second active material, the first active material includes a compound having a molecular formula of Li 1+x Fe 1‑y A y P 1‑z Q z O4 and a modified compound thereof, and the second active material includes a compound having a molecular formula of Li h Ni j Co k M1 d M2 e O f R g and a modified compound thereof. Embodiments of the present application can improve capacity development and cycle performance of a secondary battery.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and more specifically, to cathode active materials, cathode plates, secondary batteries, and electrical devices. Background Art

[0002] Secondary batteries have the advantages of reliable working performance, no pollution, no memory effect, etc., and are thus widely used. For example, with the increasing attention to environmental protection issues, new energy vehicles are becoming increasingly popular, and the demand for power secondary batteries will show explosive growth.

[0003] With the development of the new energy field, the requirements for battery performance are gradually increasing. How to further improve the capacity utilization and cycle performance of secondary batteries is an urgent problem to be solved today. Summary of the Invention

[0004] Embodiments of this application provide a cathode active material, a cathode plate, a secondary battery, and an electrical device. Embodiments of this application can improve the capacity utilization and cycle performance of secondary batteries.

[0005] In a first aspect, embodiments of this application propose a cathode active material. The cathode active material includes a first active material and a second active material. The first active material includes compounds with the molecular formula Li 1+x Fe 1-y A y P 1-z Q z O4 and their modified compounds, where 0 ≤ x < 1, 0 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.1, A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and Q includes one or more of B, Si, N, S, F, Cl, and Br; the second active material includes compounds with the molecular formula Li h Ni j Co k M1 d M2 e O f R g and their modified compounds, where 0.75 ≤ h ≤ 1.2, 0.38 < j < 1, 0.03 < k < 0.50, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 includes one or both of Mn or Al, M2 includes one or more of the group consisting of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Ba, Y, W, and Nb, and R includes one or more of the group consisting of N, F, S, and Cl.

[0006] Therefore, by specifically selecting polyanionic materials, when the first active material and the second active material satisfy the range of the above-mentioned molecular formula, the voltage plateau between the first active material and the second active material is relatively close, which is beneficial to jointly exert the capacity of both and improve the cycle performance of the secondary battery.

[0007] In some embodiments, a coin cell half-cell is formed by combining a positive electrode sheet containing the positive active material per unit area with a lithium sheet per unit area, and charged at a 0.1C rate to obtain a capacity-voltage derivative curve. The capacity-voltage derivative curve includes a first peak α and a second peak β. The unit of the first peak α is V, and the abscissa corresponding to the first peak α is v1. The unit of the second peak β is V, and the abscissa corresponding to the second peak β is v2. α-β≤0.25, v2<v1; optionally, 3.5<v1<4.0; and / or 3.3<v2<3.6.

[0008] Therefore, when the embodiments of this application satisfy the above-mentioned scope, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0009] In some embodiments, a coin cell half-cell is formed by combining a positive electrode sheet containing the first active material per unit area with a lithium sheet per unit area. The cell is charged at a 0.1C rate to obtain a first relationship curve between the state of charge (SOC) and its corresponding open-circuit voltage (OCV). The voltage plateau in the first relationship curve between 0% and 10% SOC is denoted as m, and its unit is V. A second relationship curve is also formed by combining a positive electrode sheet containing the second active material per unit area with a lithium sheet per unit area. The cell is charged at a 0.1C rate to obtain a second relationship curve between the state of charge (SOC) and its corresponding open-circuit voltage (OCV). The voltage plateau in the second relationship curve between 0% and 10% SOC is denoted as n, and its unit is V. Wherein, mn ≤ 0.15.

[0010] Therefore, when the embodiments of this application satisfy the above-mentioned scope, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0011] In some embodiments, the first active material satisfies at least one of the following conditions: (1) 0 ≤ x ≤ 0.3; (2) 0 ≤ y ≤ 0.7. Therefore, when the embodiments of this application satisfy the above ranges, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0012] In some embodiments, the first active substance satisfies at least one of the following conditions: (I) A includes one or more of Ti, V, Ni, Co and Mg; (II) Q includes one or more of B, Si, N and S.

[0013] Therefore, when the embodiments of this application satisfy the above-mentioned scope, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0014] In some embodiments, the first active substance includes LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 One or more of PO4 and LiFePO4.

[0015] In some embodiments, the second active material satisfies at least one of the following conditions: (a) 0.50 ≤ j < 1; optionally, 0.50 ≤ j ≤ 0.95; (b) M2 includes one or more of Mg, Ti, Ba, and Nb. Therefore, when the embodiments of this application satisfy the above ranges, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0016] In some embodiments, the second active material includes LiNi 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.70 Co 0.20 Mn 0.10 O2, LiNi 0.50 Co 0.30 Mn 0.20 O2, LiNi 0.60 Co 0.20 Mn 0.20 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2, LiNi 0.90 Co 0.05 Mn 0.05 One or more of O2.

[0017] In some embodiments, the mass percentage of the first active material is A% based on the mass of the positive electrode active material; the mass percentage of the second active material is B% based on the mass of the positive electrode active material, and the positive electrode active material satisfies: 1.5 ≤ A / B ≤ 9.0; optionally, 2.3 ≤ A / B ≤ 4.0. Further optionally, 60 ≤ A ≤ 90; even more optionally, 70 ≤ A ≤ 80; and / or 10 ≤ B ≤ 40; even more optionally, 20 ≤ B ≤ 30. Therefore, when the embodiments of this application satisfy the above ranges, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0018] In some embodiments, the first active material includes one or two of single-crystal particles and quasi-single-crystal particles; and / or the second active material includes one or more of single-crystal particles, quasi-single-crystal particles, and polycrystalline particles; optionally, the second active material includes polycrystalline particles.

[0019] Secondly, embodiments of this application provide a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising a positive electrode active material as described in any embodiment of the first aspect of this application.

[0020] Thirdly, embodiments of this application provide a secondary battery including a positive electrode as described in any embodiment of the second aspect of this application.

[0021] Fourthly, embodiments of this application provide an electrical device including a secondary battery as described in any embodiment of the third aspect of this application. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0024] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0025] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0026] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0027] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0028] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0029] Figure 7 This is a capacity-voltage derivative curve of the secondary battery in Embodiment 6 of this application.

[0030] The accompanying drawings may not be drawn to scale.

[0031] The reference numerals in the attached figures are explained below.

[0032] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module;

[0033] 5. Secondary battery; 51. Housing; 52. Electrode assembly;

[0034] 53. Cover plate;

[0035] 6. Electrical appliances. Detailed Implementation

[0036] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the positive electrode active material, positive electrode sheet, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions 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 fully understand this application and are not intended to limit the subject matter of the claims.

[0037] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, 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 specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0042] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0043] Positive electrode active materials include, but are not limited to, at least one of transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue-based materials. Because different positive electrode active materials have different properties, multiple different types of positive electrode active materials are often mixed to improve the overall performance of the secondary battery. However, due to significant differences between different types of active materials, such as differences in voltage plateaus, the capacity decay of some active materials is accelerated during charge and discharge, thus affecting the capacity utilization and cycle performance of the secondary battery.

[0044] To address the aforementioned problems, this application proposes a positive electrode active material comprising specific polyanionic materials and ternary materials, resulting in a closer similarity in their voltage platforms, thereby benefiting the capacity utilization and cycle performance of the secondary battery. The technical solution of this application's embodiments will be described below.

[0045] Positive electrode active material

[0046] In a first aspect, an embodiment of the present application provides a positive electrode active material, which includes a first active material and a second active material; the first active material includes a compound with the molecular formula Li 1+x Fe 1-y A y P 1-z Q z O4 and its modified compounds, where 0 ≤ x < 1, 0 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.1, A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and Q includes one or more of B, Si, N, S, F, Cl, and Br; the second active material includes a compound with the molecular formula Li h Ni j Co k M1 d M2 e O f R g and its modified compounds, where 0.75 ≤ h ≤ 1.2, 0.38 < j < 1, 0.03 < k < 0.50, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 includes one or both of Mn or Al, M2 includes one or more of the group consisting of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Ba, Y, W, and Nb, and R includes one or more of the group consisting of N, F, S, and Cl.

[0047] The first active material is a polyanion-type material. The polyanion-type material consists of a special framework structure formed by two-dimensional van der Waals bonds or a 3D framework. This structure is conducive to the insertion and extraction of metal ions such as lithium ions or sodium ions; and the polyanion-type material can not only rapidly conduct metal ions but also stabilize the redox potential of transition metals during charge and discharge. And due to the stability of the P-O bond in the polyanion-type material, the stability of oxygen in the lattice is significantly improved, thereby enhancing the stability of the polyanion-type material and being beneficial to increasing the stability of the positive electrode active material. When the polyanion-type material is used as the positive electrode active material in a secondary battery, the cycle performance of the secondary battery can be improved.

[0048] The second active material is a ternary material. There is a synergistic effect among nickel Ni, cobalt Co, M1 element, and M2 element. For example, the nickel element provides capacity for the second active material, the cobalt element improves the ionic conductivity of the second active material, and the M1 element and M2 element can improve the stability of the second active material. When the ternary material is used as the positive electrode active material in a secondary battery, the capacity, voltage platform, etc. of the secondary battery can be significantly improved.

[0049] Combining polyanionic and ternary materials offers a solution. Polyanionic materials exhibit better thermochemical stability, while ternary materials offer higher capacity. This combination can improve the capacity of the secondary battery while maintaining its reliability. However, there are significant differences in the voltage platforms of conventional polyanionic and ternary materials. During charge and discharge, voltage and rate performance can vary considerably. In particular, the actual rate capability of the ternary material in the hybrid system is higher than that of the overall secondary battery. Therefore, prolonged cycling tests on the mixed positive electrode active material can lead to rapid capacity decay of the ternary material, thus affecting the capacity utilization and cycle performance of the secondary battery.

[0050] In this embodiment, by specifically selecting polyanionic materials, when the first active material and the second active material meet the range of the above-mentioned molecular formula, the voltage plateau between the first active material and the second active material is relatively close, which is beneficial to jointly exert the capacity of both and improve the cycle performance of the secondary battery.

[0051] In the embodiments of this application, the compound can be modified, and the modified compound can be a doping modification and / or surface coating modification of the above-mentioned compound material.

[0052] The embodiments of this application can further improve the capacity utilization and cycle performance of the secondary battery when the positive electrode active material further meets one or more of the following conditions.

[0053] In some embodiments, a coin cell half-cell is formed by combining a positive electrode sheet containing the positive active material per unit area with a lithium sheet per unit area, and charged at a 0.1C rate to obtain a capacity-voltage derivative curve dQ / dV-V graph. The capacity-voltage derivative curve graph includes a first peak α and a second peak β. The first peak α is in V, and the abscissa corresponding to the first peak α is v1. The second peak β is in V, and the abscissa corresponding to the second peak β is v2, where α-β≤0.25 and v2<v1.

[0054] Optionally, 3.5 < v1 < 4.0. For example, v1 can be 3.6, 3.7, 3.8, 3.9 or a range of any two of the above values.

[0055] Optionally, 3.3 < v2 < 3.6. For example, v2 can be 3.35, 3.40, 3.42, 3.45, 3.50, 3.53, 3.55, 3.58 or a range of any two of the above values.

[0056] In this embodiment, the capacity-voltage curve can be obtained by the following steps: a coin cell half-cell is formed by combining a positive electrode sheet containing the positive electrode active material per unit area with a lithium sheet per unit area, and charged at a 0.1C rate to obtain the voltage value and the capacity value corresponding to the voltage value; for each adjacent data, the Δcapacity / Δvoltage value is calculated as the corresponding dQ / dV value; with voltage as the abscissa and dQ / dV as the ordinate, the dQ / dV-V curve is obtained.

[0057] In some embodiments, a positive electrode sheet containing the first active material per unit area is combined with a lithium sheet per unit area to form a coin cell half battery, which is charged at a rate of 0.1C to obtain a first relationship curve between the state of charge (SOC) and its corresponding open-circuit voltage (OCV). The voltage plateau in the first relationship curve between 0% and 10% SOC is denoted as a, and its unit is V.

[0058] A coin cell half-cell is formed by combining a positive electrode sheet containing the second active material per unit area with a lithium sheet per unit area. The cell is charged at a rate of 0.1C to obtain a second relationship curve between the state of charge (SOC) and its corresponding open-circuit voltage (OCV). The voltage plateau in the second relationship curve between 0% and 10% SOC is denoted as b, and its unit is V.

[0059] Where ab≤0.15.

[0060] The first relationship curve is plotted with the state of charge (SOC) on the x-axis and the open-circuit voltage (OCV) on the y-axis. The second relationship curve is plotted with the state of charge (SOC) on the x-axis and the open-circuit voltage (OCV) on the y-axis.

[0061] When a and b satisfy the above relationship, it indicates that the voltage plateaus of the first and second active materials are not significantly different. When the positive electrode active material composed of the two materials is subjected to cycle testing, it will not cause excessive loss of one of the active materials, thereby improving the capacity utilization and cycle performance of the secondary battery.

[0062] The embodiments of this application can further improve the capacity utilization and cycle performance of secondary batteries by further selecting the first active material and the second active material.

[0063] In some implementations, the first active substance satisfies: 0 ≤ x ≤ 0.3.

[0064] In some implementations, the first active substance satisfies: 0 ≤ y ≤ 0.7.

[0065] In some embodiments, the first active substance satisfies the following condition: A includes one or more of Ti, V, Ni, Co, and Mg.

[0066] In some embodiments, the first active material satisfies the following condition: Q includes one or more of B, Si, N, and S.

[0067] For example, the first active substance includes LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 One or more of PO4 and LiFePO4.

[0068] To further improve the conductivity of the first active material, in some embodiments, the first active material includes a modified compound, specifically a coating modification, that is, a conductive layer can be coated on the surface of the particles, and the material of the conductive layer can include one or more of carbon, phosphate, and pyrophosphate.

[0069] In some implementations, the second active substance satisfies: 0.50 ≤ j < 1.

[0070] In some implementations, the second active substance satisfies: 0.50≤j≤0.95.

[0071] In some embodiments, the second active substance satisfies the following condition: M2 includes one or more of Mg, Ti, Ba and Nb.

[0072] For example, the second active material includes LiNi 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.70 Co 0.20 Mn 0.10 O2, LiNi 0.50 Co 0.30 Mn 0.20 O2, LiNi 0.60 Co 0.20 Mn 0.20 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2, LiNi 0.90 Co 0.05 Mn 0.05 One or more of O2.

[0073] In this application, the types of the first and second active substances can be detected using conventional methods and equipment in the art, such as phase analysis using X-ray diffraction (XRD) and / or confirmation of chemical elements and their proportions using inductively coupled plasma emission spectrometer (ICP).

[0074] The embodiments of this application can further improve the capacity utilization and cycle performance of the secondary battery when the positive electrode active material further meets one or more of the following conditions.

[0075] In some embodiments, the mass percentage of the first active material is A% based on the mass of the positive electrode active material; the mass percentage of the second active material is B% based on the mass of the positive electrode active material, and the positive electrode active material satisfies: 1.5 ≤ A / B ≤ 9.0; optionally, 2.3 ≤ A / B ≤ 4.0. For example, A / B can be 1.5, 1.8, 2.0, 2.3, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 9.0, or a range consisting of any two of the above values.

[0076] When the ratio of the mass percentage of the first active material to the mass percentage of the second active material is within the above range, the first and second active materials can fully exert their synergistic effect, improving the capacity utilization and cycle performance of the secondary battery.

[0077] In some embodiments, 60 ≤ A ≤ 90; alternatively, 70 ≤ A ≤ 80. Exemplarily, the mass percentage of the first active substance is 60, 65, 70, 75, 80, 85, 90, or a range consisting of any two of the above values.

[0078] In some embodiments, 10 ≤ B ≤ 40; alternatively, 20 ≤ B ≤ 30. For example, the mass percentage of the second active substance is 10, 15, 20, 25, 30, 35, 40, or a range consisting of any two of the above values.

[0079] In the embodiments of this application, the contents of the first active substance and the second active substance can be detected using conventional methods and equipment in the art. For example, the phase can be confirmed by X-ray diffraction (XRD), and the elemental ratio can be determined by inductively coupled plasma atomic emission spectrometry (ICP). 5-100 mg of sample is weighed and digested using concentrated nitric acid as the digestion reagent. The contents of the first and second active substances (elemental content / mass percentage of the element in the additive) are calculated based on the measured elemental contents.

[0080] When the morphology of the positive electrode active material is specifically selected in the embodiments of this application, the capacity utilization and cycle performance of the secondary battery can be further improved.

[0081] In some embodiments, the first active material includes one or both of single-crystal particles and single-crystal-like particles.

[0082] In some embodiments, the second active material is one or more of single-crystal particles, quasi-single-crystal particles, and polycrystalline particles; optionally, the second active material includes polycrystalline particles.

[0083] Polycrystalline particles are secondary spherical particles formed by the agglomeration of multiple primary particles. Therefore, the lithium-ion transport path is shorter, the rate performance is better, and in the hybrid system, the capacity is less likely to deteriorate when subjected to a higher rate.

[0084] In the embodiments of this application, the morphology of the first and second active substances can be confirmed by scanning with a scanning electron microscope (SEM); for example, a JSM-5610LV scanning electron microscope from FEI Corporation, USA, is used to observe the morphology and structure after vacuum sputtering gold onto the sample. And / or a transmission electron microscope (TEM) is used to confirm the fine structure.

[0085] Positive electrode sheet

[0086] Secondly, embodiments of this application also provide a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0087] In the embodiments of this application, the positive electrode film layer includes the positive electrode active material as described in any embodiment of the first aspect of this application.

[0088] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose particular limitations on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the positive electrode film layer, the mass percentage content of the positive electrode conductive agent is ≤5 wt%.

[0089] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose particular limitations on the type of positive electrode binder. As an example, the positive electrode binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is ≤5 wt% based on the total weight of the positive electrode film layer.

[0090] In some embodiments, the positive current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymeric material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0091] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0092] Secondary batteries

[0093] Thirdly, the embodiments of this application also provide a secondary battery.

[0094] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes and primarily serves to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through.

[0095] This application does not impose any particular restrictions on the type of secondary battery. For example, the secondary battery can be a lithium-ion battery, a sodium-ion battery, etc. In particular, the secondary battery can be a lithium-ion secondary battery.

[0096] In some embodiments, the secondary battery includes a positive electrode sheet as described in any embodiment of the second aspect of this application, or the secondary battery includes a positive electrode sheet comprising a positive electrode active material as described in any embodiment of the first aspect of this application. Thus, the secondary battery of the embodiments of this application can achieve both high capacity utilization and good cycle performance.

[0097] [Negative electrode plate]

[0098] Secondary batteries also include negative electrode plates.

[0099] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0100] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. As an example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy materials.

[0101] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose particular limitations on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total weight of the negative electrode film layer, the mass percentage content of the negative electrode conductive agent is ≤5 wt%.

[0102] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose particular limitations on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is ≤5 wt% based on the total weight of the negative electrode film layer.

[0103] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is ≤2 wt% based on the total weight of the negative electrode film.

[0104] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0105] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0106] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode sheet described in this application further includes a protective layer covering the surface of the negative electrode film layer.

[0107] Electrolyte

[0108] Secondary batteries also include electrolytes.

[0109] During the charging and discharging process of a secondary battery, active ions repeatedly insert and extract between the positive and negative electrode plates, while the electrolyte acts as a conductor for these active ions. The embodiments of this application do not impose any particular restrictions on the type of electrolyte; it can be selected according to actual needs.

[0110] The electrolyte comprises an electrolyte salt and a solvent. The types of electrolyte salt and solvent are not specifically limited and can be selected according to actual needs.

[0111] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0112] When the secondary battery of this application is a sodium-ion battery, as an example, the electrolyte salt may include, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0113] As an example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ester carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0114] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0115] [Isolation membrane]

[0116] Secondary batteries also include a separator.

[0117] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0118] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0119] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process and / or a stacking process.

[0120] In some embodiments, the secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0121] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0122] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0123] In some implementations, such as Figure 2As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0124] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is then placed in an outer package, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a secondary battery is obtained.

[0125] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0126] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0127] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0128] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0129] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0130] Electrical appliances

[0131] A third aspect of this application provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0132] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0133] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0134] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0135] Example

[0136] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0137] Example

[0138] 1. Preparation of positive electrode sheet

[0139] Aluminum foil with a thickness of 12μm was used as the positive electrode current collector.

[0140] The positive electrode active material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are thoroughly mixed in an appropriate amount of solvent NMP at a weight ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0141] 2. Preparation of negative electrode sheet

[0142] A copper foil with a thickness of 8μm was used as the negative electrode current collector.

[0143] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed thoroughly in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0144] 3. Separating membrane

[0145] Porous polyethylene (PE) membrane is used as the separator.

[0146] 4. Preparation of electrolyte

[0147] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate (EC) and diethyl carbonate (DMC) are mixed at a volume ratio of 1:1 to obtain an electrolyte solvent. Then, lithium salt is mixed with the mixed solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0148] 5. Preparation of secondary batteries

[0149] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained.

[0150] Examples 2 to 17 and Comparative Examples

[0151] Examples 2 to 17 and the comparative examples were prepared using a method similar to that of Example 1. The difference from Example 1 was that at least one of the type and content of the first active material and the type and content of the second active material was adjusted in Examples 2 to 17 and the comparative examples.

[0152] Data for the examples and comparative examples are shown in Tables 1 to 3.

[0153] Test methods

[0154] 1. Cycle performance test of secondary batteries

[0155] At 25°C, the prepared secondary battery was charged at a constant current of 0.33C to the charging cutoff voltage of 4.3V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.5V. Its initial capacity was recorded as C0. Then, it was charged at 0.33C and discharged at 1C, and the discharge capacity Cn of each cycle was recorded until the cycle capacity retention rate (i.e., Cn / C0×100%) reached 80%, and the number of cycles was recorded. A higher number of cycles indicates better cycle performance of the secondary battery.

[0156] Test Results

[0157] The test results are shown in Tables 1 to 3.

[0158] Table 1

[0159]

[0160] Table 2

[0161]

[0162] Table 3

[0163]

[0164] The specific material types are as follows in Tables 1 to 3:

[0165] The chemical formula of the first active substance 1-1 is LiMn 0.6 Fe 0.4 PO4.

[0166] The chemical formula of the first active substance 1-2 is LiFePO4.

[0167] The chemical formula of the second active substance 2-3 is LiNi 0.50 Co 0.30 Mn 0.20 O2.

[0168] The chemical formula of the second active substance 2-4 is LiNi 0.60 Co 0.20 Mn 0.20 O2.

[0169] The chemical formula of the second active substance 2-5 is LiNi 0.80 Co 0.10 Mn 0.10 O2.

[0170] The chemical formula of the second active substance 2-6 is LiNi 0.90 Co 0.05 Mn 0.05 O2.

[0171] The chemical formula of the second active substance 2-7 is LiNi 0.90 Co 0.08 Mn 0.02 O2.

[0172] In Tables 1 to 3, the formula for calculating "cycle life degradation / improvement" is M / N-1, where M is the number of cycles when the cycle life of the example decays to 80% of the initial capacity, and N is the number of cycles when the cycle life of Comparative Example 1 (or Comparative Example 2) decays to 80% of the initial capacity.

[0173] As shown in Tables 1 to 3, in Comparative Examples 1 and 2, the cycle performance of polyanionic materials as positive electrode active materials is relatively poor; compared to the comparative examples, the combined... Figure 7 In this embodiment, the positive electrode active material combines a polyanionic material of a specific molecular formula and a ternary material of a specific molecular formula. The voltage platforms between the first active material and the second active material are relatively close, which is beneficial to jointly exert the capacity of both materials and improve the cycle performance of the secondary battery.

[0174] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A positive electrode active material, comprising: The first active substance includes Li 1+x Fe 1-y A y P 1-z Q z Compounds of O4 and their modified compounds, wherein 0 ≤ x < 1, 0 ≤ y ≤ 0.8, 0 ≤ z ≤ 0.1, A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and Q includes one or more of B, Si, N, S, F, Cl, and Br; and The second active substance, including a compound with the molecular formula Li h Ni j Co k M1 d M2 e O f R g and its modified compounds, where 0.75 ≤ h ≤ 1.2, 0.38 < j < 1, 0.03 < k < 0.50, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 includes one or both of Mn or Al, M2 includes one or more of the group consisting of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Ba, Y, W, and Nb, and R includes one or more of the group consisting of N, F, S, and Cl Specifically, a coin cell half-cell is formed by combining a positive electrode sheet containing the aforementioned positive electrode active material per unit area with a lithium sheet per unit area, and charged at a 0.1C rate to obtain a capacity-voltage derivative curve. The capacity-voltage derivative curve includes: The first peak value α, whose unit is V, and the x-coordinate corresponding to the first peak value α is v1; and The second peak value β is in V, and the horizontal coordinate corresponding to the second peak value β is v2; α-β≤0.25, v2<v1.

2. The positive electrode active material according to claim 1, wherein, 3.5 < v1 < 4.0; and / or 3.3 < v2 < 3.

6.

3. The positive electrode active material according to claim 1 or 2, wherein, A coin cell half-cell is formed by combining a positive electrode sheet containing the first active material per unit area with a lithium sheet per unit area. The cell is charged at a rate of 0.1C to obtain a first relationship curve between the state of charge (SOC) and its corresponding open-circuit voltage (OCV). The voltage plateau in the first relationship curve between 0% and 10% SOC is denoted as m, and its unit is V. A coin cell half-cell is formed by combining a positive electrode sheet containing the second active material per unit area with a lithium sheet per unit area. The cell is charged at a rate of 0.1C to obtain a second relationship curve between the state of charge (SOC) and its corresponding open-circuit voltage (OCV). The voltage plateau in the second relationship curve between 0% and 10% SOC is denoted as n, and its unit is V. Where mn≤0.

15.

4. The positive electrode active material according to any one of claims 1 to 3, wherein, The first active substance satisfies at least one of the following conditions: (1) 0 ≤ x ≤ 0.3; (2) 0 ≤ y ≤ 0.

7.

5. The positive electrode active material according to any one of claims 1 to 4, wherein the first active material satisfies at least one of the following conditions: (I) A includes one or more of Ti, V, Ni, Co and Mg; (II) Q includes one or more of B, Si, N and S.

6. The positive electrode active material according to any one of claims 1 to 5, wherein, The first active substance includes LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 One or more of PO4 and LiFePO4.

7. The positive electrode active material according to any one of claims 1 to 6, wherein, The second active substance satisfies at least one of the following conditions: (a) 0.50 ≤ j < 1; (b) M2 includes one or more of Mg, Ti, Ba and Nb.

8. The positive electrode active material according to claim 7, wherein, 0.50≤j≤0.95。 9. The positive electrode active material according to any one of claims 1 to 8, wherein, The second active material includes LiNi 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.70 Co 0.20 Mn 0.10 O2, LiNi 0.50 Co 0.30 Mn 0.20 O2, LiNi 0.60 Co 0.20 Mn 0.20 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2, LiNi 0.90 Co 0.05 Mn 0.05 One or more of O2.

10. The positive electrode active material according to any one of claims 1 to 9, wherein, Based on the mass of the positive electrode active material, the mass percentage of the first active material is A%; Based on the mass of the positive electrode active material, the mass percentage of the second active material is B%. The positive electrode active material satisfies the following condition: 1.5 ≤ A / B ≤ 9.

0.

11. The positive electrode active material according to claim 10, wherein, 2.3≤A / B≤4.

0.

12. The positive electrode active material according to claim 10, wherein, 60≤A≤90。 13. The positive electrode active material according to claim 10, wherein, 70≤A≤80。 14. The positive electrode active material according to claim 10, wherein, 10≤B≤40。 15. The positive electrode active material according to claim 10, wherein, 20≤B≤30。 16. The positive electrode active material according to any one of claims 1 to 15, wherein, The first active material includes one or both of single-crystal particles and single-crystal-like particles; and / or The second active material includes one or more of single crystal particles, quasi-single crystal particles, and polycrystalline particles.

17. The positive electrode active material according to claim 16, wherein, The second active material includes polycrystalline particles.

18. A positive electrode sheet, comprising a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer comprising a positive electrode active material as described in any one of claims 1 to 17.

19. A secondary battery comprising the positive electrode as described in claim 18.

20. An electrical device comprising the secondary battery as described in claim 19.

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