Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material, a positive electrode binder and a positive electrode conductive agent, the positive electrode binder comprises a first compound, and the positive electrode conductive agent comprises a second compound. The relative dielectric constant of the first compound is epsilon r, the weight-average molecular weight of the first compound is Mw, epsilon r is more than or equal to 15 and less than or equal to 80, and Mw is more than or equal to 700000 and less than or equal to 12000000. The positive pole piece meets the characteristics, so that the secondary battery has relatively high energy density and relatively good dynamic performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density and long life, and are widely used in energy storage devices. With the rapid popularization of new energy vehicles and high-energy-density electronic devices, diversified demands have posed new challenges to lithium-ion batteries, especially the improvement of the energy density and high-current charge and discharge capabilities of lithium-ion batteries, which is currently the focus of attention. Without changing the chemical system, the thick electrode design can reduce the proportion of inactive substances in the lithium-ion battery, thereby increasing the energy density of the lithium-ion battery. However, the high tortuosity caused by the increase in electrode thickness will hinder ion migration and diffusion, resulting in severe polarization of the lithium-ion battery, affecting the kinetic performance and making it difficult to meet the requirements of fast charging. At the same time, high energy density also places higher demands on the electron / ion transport network in the electrode. Therefore, how to optimize the thick electrode conductive network and improve the kinetic performance of lithium-ion batteries is the key to the further development of lithium-ion batteries.

[0003] To improve the high-current charge and discharge capabilities of thick electrode sheets and enhance electron / ion transport, the porosity within the electrode sheets can be increased. However, this reduces the electrode sheet's compaction density, affecting the volumetric energy density of the lithium-ion battery. Therefore, there is an urgent need to provide a lithium-ion battery that combines high energy density with good dynamic performance. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device, which enable the secondary battery to have high energy density and good dynamic performance. The specific technical solution is as follows:

[0005] The first aspect of the present application provides a secondary battery comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode active material, a positive electrode binder and a positive electrode conductive agent, the positive electrode binder comprising a first compound, the relative dielectric constant of the first compound being ε r , the weight average molecular weight of the first compound is Mw, 15≤ε r ≤80, preferably, 30≤ε r≤50; 700000≤Mw≤1200000, preferably, 800000≤Mw≤1100000. When the positive electrode binder in the positive electrode material layer includes a first compound, the relative dielectric constant and weight-average molecular weight of the first compound are within the scope of this application, the first compound has a high relative dielectric constant, which is conducive to the dissociation of lithium salts and increases the content of free lithium ions in the positive electrode plate; and the higher electronegative groups in the first compound are regularly arranged on one side of the skeleton carbon atoms, and the higher electronegative groups can construct a linear lithium ion transmission channel between the positive electrode active materials, which can effectively shorten the lithium ion transmission path, optimize the conductive network of the positive electrode plate, greatly improve the higher ion transmission impedance problem caused by the high tortuosity of the thick plate, better meet the requirements of high energy density electrodes for ion transmission networks, improve the charge and discharge capacity of the secondary battery under large currents, and make the secondary battery have better kinetic performance while having a higher energy density. At the same time, the weight-average molecular weight of the first compound is increased, and the bonding force of the first compound is enhanced, which can correspondingly reduce the amount of the first compound used, correspondingly increase the mass percentage of the positive electrode active material, and improve the energy density of the secondary battery; the conductivity of the first compound itself is relatively poor compared to other components in the positive electrode plate, and reducing the amount of the first compound used can also improve the overall dynamic performance of the positive electrode plate, thereby improving the dynamic performance of the secondary battery.

[0006] In one embodiment of the present application, the average molecular weight of the first compound is Mz, 1.8≤Mz / Mw≤3.5, preferably, 2.0≤Mz / Mw≤2.4. By regulating the value of Mz / Mw within the above range, the molecular weight distribution of the first compound is moderate, the molecular weights of the macromolecular binder and the small molecule binder are both relatively moderate, and the possibility of the macromolecular binder being difficult to melt after heating due to its large molecular weight is reduced, and the possibility of the small molecule binder agglomerating in the positive electrode slurry due to its small molecular weight is reduced.

[0007] In one embodiment of the present application, the first compound comprises at least one of β-polyvinylidene fluoride, a vinylidene fluoride-trifluoroethylene copolymer, or a nanofiller-polyvinylidene fluoride-based composite material. The use of such a first compound, which is a fluoropolymer containing a polar phase, can further shorten the lithium ion transmission path, thereby enhancing the secondary battery's kinetic performance while maintaining a higher energy density.

[0008] In one embodiment of the present application, the ionic conductivity of the first compound is σS / cm, 1.0×10 -4 ≤σ≤5×10 -4By regulating the ionic conductivity of the first compound within the above range, the first compound has a higher ionic conductivity, which can promote lithium ion transmission, further reduce the impedance of the positive electrode sheet, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery.

[0009] In one embodiment of the present application, in the X-ray diffraction spectrum of the first compound, a first characteristic peak exists in the ranges of 19° to 21°, 34° to 35°, and 38° to 41°. The X-ray diffraction spectrum of the first compound satisfies the above characteristics, the first characteristic peak is a characteristic peak of the polar phase (β phase), the dielectric constant of the first compound mainly comes from the β phase, and the high dielectric constant can promote the dissociation of lithium salts; at the same time, it can provide ion transmission channels, shorten the ion transmission path, and improve the kinetic performance of the secondary battery.

[0010] In one embodiment of the present application, in the infrared spectrum of the first compound, at 470 cm -1 Up to 475cm -1 、507cm -1 Up to 515cm -1 、830cm -1 Up to 850cm -1 、1275cm -1 to 1290cm -1 The infrared spectrum of the first compound satisfies the aforementioned characteristics. The groups in the first compound are neatly arranged, the first compound contains a β phase, and the dielectric constant of the first compound primarily comes from the β phase. The high dielectric constant can promote the dissociation of lithium salts and, at the same time, provide ion transport channels, shorten the ion transport path, and improve the kinetic performance of the secondary battery.

[0011] In one embodiment of the present application, the first compound includes silicon, iron, and zinc, and the sum of the mass of the silicon, iron, and zinc in the first compound is W, where W is less than 200 ppm. By regulating the sum of the mass of the silicon, iron, and zinc in the first compound within the above range, the possibility of increased self-discharge of the secondary battery or precipitation of impurity elements on the surface of the negative electrode, which may cause the secondary battery to short-circuit, can be reduced, thereby improving the safety performance of the secondary battery.

[0012] In one embodiment of the present application, the mass change rate of the first compound after immersion in an electrolyte at 85°C for 24 hours is m%, and 15≤m≤45. If the mass change rate of the first compound after immersion in an electrolyte at 85°C for 24 hours is within the above range, the electrolyte can well infiltrate the first compound, the first compound has high ionic conductivity, can promote lithium ion transport, and further improve the kinetic performance of the secondary battery; at the same time, it effectively reduces the rebound phenomenon of the positive electrode sheet, so that the secondary battery has a higher energy density.

[0013] In one embodiment of the present application, the crystallinity of the first compound is X%, 20≤X≤70, preferably, 40≤X≤50. By regulating the crystallinity of the first compound within the above range, the first compound has a higher relative dielectric constant, which is conducive to the dissociation of lithium salts; further shortening the lithium ion transmission path, further improving the kinetic performance of the secondary battery while maintaining a higher energy density.

[0014] In one embodiment of the present application, the melting point of the first compound is Tm°C, 130≤Tm≤175. By regulating the melting point of the first compound within the above range, the processing performance of the positive electrode slurry can be optimized, the stability of the electrode structure can be enhanced, and the cycle life of the secondary battery can be extended.

[0015] In one embodiment of the present application, the crystallization temperature of the first compound is Tc°C, 120 ≤ Tc ≤ 155°C. By regulating the crystallization temperature of the first compound within the above range, the first compound includes a β phase and has a higher relative dielectric constant, which is conducive to the dissociation of lithium salts. In addition, the lithium ion transmission path can be further shortened, thereby further improving the kinetic performance of the secondary battery while maintaining a higher energy density.

[0016] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is w1%, the mass percentage of the positive electrode binder is w2%, and the mass percentage of the positive electrode conductive agent is w3%, and 97.7≤w1≤98.8, 0.7≤w2≤1.3, and 0.5≤w3≤1. By regulating the mass percentages of the positive electrode active material, positive electrode binder, and positive electrode conductive agent within the above ranges, the kinetic performance of the secondary battery is further improved; and with a relatively high mass percentage of the positive electrode active material, the secondary battery has a higher energy density.

[0017] In one embodiment of the present application, the compaction density of the positive electrode material layer is PDg / cm 3, 3.0≤PD≤4.5, preferably, 3.8≤PD≤4.4. By regulating the compaction density of the positive electrode material layer within the above range, the length of the linear lithium ion transmission channel constructed by the highly electronegative groups in the first compound between the positive electrode active materials can be effectively shortened, further shortening the lithium ion transmission path, further improving the kinetic performance of the secondary battery while maintaining a higher energy density.

[0018] In one embodiment of the present application, the contact angle between the positive electrode plate and the electrolyte is θ, 10°≤θ≤60°, preferably, 10°≤θ≤30°. By regulating the contact angle between the positive electrode plate and the electrolyte within the above range, the contact angle between the positive electrode plate and the electrolyte is small, the positive electrode plate has good wettability, the electrolyte can better infiltrate the first compound, the first compound has high ionic conductivity, can promote lithium ion transport, and further improve the kinetic performance of the secondary battery.

[0019] In one embodiment of the present application, the Dv50 of the positive electrode active material satisfies the following conditions: 0.5 μm ≤ Dv50 ≤ 35 μm, preferably 10 μm ≤ Dv50 ≤ 25 μm. By regulating the Dv50 of the positive electrode active material within this range, the particles in the positive electrode material layer are loosely packed, facilitating lithium ion transport and further improving the kinetic performance of the secondary battery. Furthermore, the positive electrode material layer has a higher compaction density, enabling the secondary battery to have a higher energy density.

[0020] In one embodiment of the present application, the thickness of the positive electrode current collector is H1 μm, 7≤H1≤20, preferably, 8≤H1≤12. By adjusting the thickness of the positive electrode current collector within the above range, the thickness of the positive electrode current collector is smaller, which can enable the secondary battery to have a higher energy density.

[0021] In one embodiment of the present application, the porosity of the positive electrode material layer is P%, 18.7≤P≤35.3; based on the total pore volume of the positive electrode material layer, the volume percentage of pores with a pore diameter greater than 50 nm is V1%, 74≤V1≤97. By regulating the porosity of the positive electrode material layer and the volume percentage of pores with a pore diameter greater than 50 nm within the above ranges, the length of the linear lithium ion transport channel constructed by the more electronegative groups in the first compound between the positive electrode active materials can be effectively shortened, further shortening the lithium ion transport path and further improving the kinetic performance of the secondary battery.

[0022] In one embodiment of the present application, the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles is S1%, and 81≤S1≤92. By regulating the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles within the above range, the lithium ion transmission path can be effectively shortened, improving the kinetic performance of the secondary battery. In addition, the corrosion of the positive electrode active material particles by the electrolyte can be effectively reduced, further improving the kinetic performance and cycle performance of the secondary battery.

[0023] In one embodiment of the present application, the positive electrode conductive agent includes conductive carbon and carbon nanotubes. The conductive carbon includes at least one of Super P, carbon nanofibers, flake graphite, acetylene black, Ketjen black, carbon dots, or graphene. The use of these conductive carbons can further optimize the conductive network of the positive electrode sheet, facilitate electron transport, further reduce the impedance of the positive electrode sheet, further improve the charge and discharge capacity of the secondary battery at high currents, and further enhance the kinetic performance of the secondary battery.

[0024] In one embodiment of the present application, the positive electrode conductive agent includes conductive carbon and carbon nanotubes. In the Raman spectrum of carbon nanotubes, at 1300 cm -1 to 1400cm -1 There is a peak intensity of I in the range D The third characteristic peak at 1550cm -1 to 1650cm -1 There is a peak intensity of I in the range G The fourth characteristic peak, 0.72≤I D / I G ≤0.77. By regulating I D / I G The value of is within the above range, which is beneficial to optimizing the conductive network of the positive electrode material layer. At the same time, the carbon nanotubes also have high conductivity, further improving the kinetic performance of the secondary battery.

[0025] In one embodiment of the present application, the positive electrode conductive agent includes conductive carbon and carbon nanotubes, wherein the diameter of the carbon nanotubes is D nm, where 4 ≤ D ≤ 20. By regulating the diameter of the carbon nanotubes within the above range, the positive electrode slurry has better processing performance while providing a higher effective conductive area, further improving the dynamic performance of the secondary battery.

[0026] In one embodiment of the present application, in a scanning electron microscope image of the positive electrode material layer within an area of ​​85 μm × 120 μm, the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer is S2%, and 47.8≤S2≤57.7. By regulating the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer within the above range, the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer is higher, which can further optimize the conductive network of the positive electrode sheet, facilitate electron transport, and further enhance the kinetic performance of the secondary battery.

[0027] In one embodiment of the present application, the bonding force between the positive electrode material layer and the positive electrode current collector is FN / m, 13.00≤F≤28.29. By regulating the bonding force between the positive electrode material layer and the positive electrode current collector within the above range, the positive electrode material layer and the positive electrode current collector are in closer contact, which can further shorten the lithium ion transmission path and further improve the dynamic performance of the secondary battery.

[0028] In one embodiment of the present application, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, or lithium iron phosphate. By selecting such positive electrode active materials, the secondary battery has both high energy density and good kinetic performance.

[0029] In one embodiment of the present application, the thickness of the positive electrode material layer on one side of the positive current collector is H2μm, with 44.44≤H2≤66.67. By regulating the thickness of the positive electrode material layer on one side of the positive current collector within this range, the lithium ion transmission path can be further shortened, further improving the kinetic performance of the secondary battery and simultaneously enabling the secondary battery to have a higher energy density.

[0030] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0031] Beneficial effects of this application:

[0032] The present application provides a secondary battery and an electronic device, wherein the secondary battery comprises a positive electrode plate, the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, the positive electrode material layer comprises a positive electrode active material, a positive electrode binder and a positive electrode conductive agent, the positive electrode binder comprises a first compound, and the relative dielectric constant of the first compound is ε r , the weight average molecular weight of the first compound is Mw, 15≤ε r ≤80, 700000≤Mw≤1200000. The positive electrode sheet meets the above characteristics, which can make the secondary battery have high energy density and good dynamic performance.

[0033] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0035] Figure 1 This is a scanning electron microscope image of backscattered electrons on the surface of the positive electrode material layer of Example 1-1 of the present application;

[0036] Figure 2 This is a distribution diagram of the positive electrode active material, positive electrode binder, and positive electrode conductive agent in the positive electrode material layer of Example 1-1 of the present application;

[0037] Figure 3 This is an X-ray diffraction spectrum of the first compound β-polyvinylidene fluoride of Example 1-1 of the present application;

[0038] Figure 4 This is the infrared spectrum of the first compound β-polyvinylidene fluoride in Example 1-1 of the present application. DETAILED DESCRIPTION

[0039] The following will be combined with the embodiments of the present application and the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0040] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0041] The first aspect of the present application provides a secondary battery comprising a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode active material, a positive electrode binder and a positive electrode conductive agent, the positive electrode binder comprising a first compound, the relative dielectric constant of the first compound being ε r , the weight average molecular weight of the first compound is Mw, 15≤ε r ≤80, preferably, 30≤ε r ≤50; 700000≤Mw≤1200000, preferably, 800000≤Mw≤1100000. For example, ε rThe value of can be 15, 20, 30, 40, 50, 60, 70, 80 or a range consisting of any two of the above values; the value of Mw can be 700000, 750000, 800000, 850000, 900000, 950000, 1000000, 1050000, 1100000, 1150000, 1200000 or a range consisting of any two of the above values. Relative dielectric constant ε r refers to the dielectric constant ε of the first compound and the dielectric constant ε of vacuum r0 The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its thickness direction, or on both surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a portion of the positive electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0042] The inventors have found that when the positive electrode binder in the positive electrode material layer includes a first compound, the relative dielectric constant and weight-average molecular weight of the first compound are within the scope of this application, the first compound has a higher relative dielectric constant, which is conducive to the dissociation of lithium salts and increases the content of free lithium ions in the positive electrode plate; and the groups with higher electronegativity in the first compound are regularly arranged on one side of the skeleton carbon atoms. The groups with higher electronegativity can construct a linear lithium ion transmission channel between the positive electrode active materials, which can effectively shorten the lithium ion transmission path, optimize the conductive network of the positive electrode plate, greatly improve the higher ion transmission impedance problem caused by the high tortuosity of the thick plate, better meet the requirements of high energy density electrodes for the ion transmission network, improve the charge and discharge capacity of the secondary battery under large current, and make the secondary battery have better kinetic performance while having a higher energy density. At the same time, the weight-average molecular weight of the first compound is increased, and the binding force of the first compound is enhanced, which can correspondingly reduce the amount of the first compound used, correspondingly increase the mass percentage of the positive electrode active material, and improve the energy density of the secondary battery; the first compound itself has a poor conductivity relative to other components in the positive electrode plate, and reducing the amount of the first compound used can also improve the overall dynamic performance of the positive electrode plate, thereby improving the dynamic performance of the secondary battery. When the relative dielectric constant of the first compound is too small, for example, less than 15, the transmission path of lithium ions in the positive electrode plate is highly tortuous, affecting the migration and diffusion of lithium ions, the polarization of the secondary battery is large, affecting the charge and discharge capacity of the secondary battery under large currents, and affecting the dynamic performance of the secondary battery; when the relative dielectric constant of the first compound is too large, for example, greater than 80, the dielectric loss of the first compound is high, which will cause more energy to be dissipated in the form of heat, resulting in energy loss of the secondary battery; it may also aggravate the decomposition of the electrolyte, leading to aggravated side reactions, and affecting the cycle performance of the secondary battery. When the weight average molecular weight of the first compound is too small, for example, less than 700,000, the bonding force between the positive electrode material layer and the positive electrode current collector will be low, affecting the kinetic performance and cycle performance of the secondary battery; when the weight average molecular weight of the first compound is too large, for example, greater than 1,200,000, the first compound is easy to entangle and difficult to disperse, affecting the processing performance of the secondary battery. Therefore, by regulating the positive electrode binder in the positive electrode material layer to include the first compound, the relative dielectric constant and weight average molecular weight of the first compound are within the scope of this application, so that the secondary battery can have better kinetic performance while having a higher energy density. In this application, "high current" refers to a current of 2C and above.

[0043] In one embodiment of the present application, the average molecular weight of the first compound is Mz, 1.8≤Mz / Mw≤3.5, preferably, 2.0≤Mz / Mw≤2.4. For example, the value of Mz / Mw can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5 or a range consisting of any two of the above values. The value of Mz / Mw can reflect the molecular weight distribution of the first compound. By regulating the value of Mz / Mw within the above range, the molecular weight distribution of the first compound is moderate, the molecular weights of the macromolecular binder and the small molecule binder are relatively moderate, and the possibility of the macromolecular binder not being easily melted after heating due to its large molecular weight is reduced, and the possibility of the small molecule binder agglomerating in the positive electrode slurry due to its small molecular weight is reduced. In the present application, 1260000≤Mz≤4200000.

[0044] In one embodiment of the present application, the first compound includes at least one of β-polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer or nanofiller-polyvinylidene fluoride based composite material. The above-mentioned β-polyvinylidene fluoride is a fluorine-containing polymer containing β crystal form (polar phase); the above-mentioned vinylidene fluoride-trifluoroethylene copolymer includes poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) (P(VDF-TrFE-CTFE)); the above-mentioned nanofiller-polyvinylidene fluoride based composite material refers to a multiphase composite material with a synergistic dielectric enhancement effect formed by introducing a functional filler with a high dielectric constant (ε>100) by physical or chemical methods using polyvinylidene fluoride (PVDF) as a matrix. The functional filler is a nanofiller, and the nanofiller includes at least one of BaTiO3 or SrTiO3. The nanofiller-polyvinylidene fluoride based composite material includes at least one of PVDF / BaTiO3 composite material or PVDF / SrTiO3 composite material. The above-mentioned first compound is selected. The above-mentioned first compound is a fluorine-containing polymer containing a polar phase. The above-mentioned first compound has a high relative dielectric constant, which is conducive to the dissociation of lithium salts and further increases the content of free lithium ions in the positive electrode plate; and the groups with higher electronegativity in the first compound are arranged more regularly on one side of the skeleton carbon atoms. The groups with higher electronegativity can construct a linear lithium ion transmission channel between the positive electrode active materials, which can further shorten the lithium ion transmission path, further optimize the conductive network of the positive electrode plate, further reduce the ion transmission impedance, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery while having a higher energy density.

[0045] In one embodiment of the present application, the ionic conductivity of the first compound is σS / cm, 1.0×10 -4 ≤σ≤5×10 -4For example, the value of σ can be 1.0×10 -4 , 1.5×10 -4 , 2.0×10 -4 , 2.5×10 -4 , 3.0×10 -4 , 3.5×10 -4 , 4.0×10 -4 , 4.5×10 -4 , 5×10 -4 Or a range consisting of any two of the above values. By regulating the ionic conductivity of the first compound within the above range, the first compound has a higher ionic conductivity, which can promote lithium ion transport, further reduce the impedance of the positive electrode sheet, further improve the charge and discharge capacity of the secondary battery under high current, and further improve the kinetic performance of the secondary battery.

[0046] In one embodiment of the present application, in the X-ray diffraction spectrum of the first compound, a first characteristic peak exists in the ranges of 19° to 21°, 34° to 35°, and 38° to 41°. The X-ray diffraction spectrum of the first compound satisfies the above characteristics, the first characteristic peak is a characteristic peak of the polar phase (β phase), the dielectric constant of the first compound mainly comes from the β phase, and the high dielectric constant can promote the dissociation of the lithium salt; at the same time, the β phase represents the neat arrangement of electronegative groups, which can provide ion transmission channels, shorten the ion transmission path, reduce the impedance of the positive electrode sheet, improve the charge and discharge capacity of the secondary battery under large current, and improve the kinetic performance of the secondary battery.

[0047] In one embodiment of the present application, in the infrared spectrum of the first compound, at 470 cm -1 Up to 475cm -1 、507cm -1 Up to 515cm -1 、830cm -1 Up to 850cm -1 、1275cm -1 to 1290cm -1 A second characteristic peak exists within the range. The infrared spectrum of the first compound meets the above characteristics. The groups in the first compound are neatly arranged, the first compound contains a β phase, and the dielectric constant of the first compound mainly comes from the β phase. The high dielectric constant can promote the dissociation of lithium salts. At the same time, the groups in the first compound are neatly arranged, which can provide ion transmission channels, shorten the ion transmission path, reduce the impedance of the positive electrode, improve the charge and discharge capacity of the secondary battery under high current, and improve the kinetic performance of the secondary battery.

[0048] In one embodiment of the present application, the first compound includes silicon, iron and zinc, and the sum of the masses of silicon, iron and zinc in the first compound accounts for W, W < 200ppm. Exemplarily, the value of W can be less than 200ppm, 180ppm, 160ppm, 140ppm, 120ppm, 100ppm, 80ppm, 60ppm, 40ppm, 20ppm. Silicon, iron and zinc are impurity elements in the first compound. By regulating the sum of the masses of silicon, iron and zinc in the first compound to be within the above range, the content of impurity elements in the first compound is small, which can reduce the possibility of increased self-discharge of the secondary battery or precipitation of impurity elements on the surface of the negative electrode sheet causing a short circuit in the secondary battery, thereby improving the safety performance of the secondary battery.

[0049] In one embodiment of the present application, the mass change rate of the first compound after immersion in the electrolyte at 85°C for 24 hours is m%, and 15≤m≤45. For example, the value of m can be 15, 17, 19, 20, 25, 27, 29, 30, 35, 37, 39, 40, 45, or a range consisting of any two of the above values. The mass change rate of the first compound after immersion in the electrolyte at 85°C for 24 hours can reflect the swelling properties of the first compound in the electrolyte. If the mass change rate of the first compound after immersion in the electrolyte at 85°C for 24 hours is within the above range, the electrolyte can well infiltrate the first compound, the first compound has a high ionic conductivity, can promote lithium ion transmission, further reduce the impedance of the positive electrode sheet, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery; at the same time, it effectively reduces the rebound phenomenon of the positive electrode sheet, so that the secondary battery has a higher energy density.

[0050] In one embodiment of the present application, the crystallinity of the first compound is X%, 20≤X≤70, preferably, 40≤X≤50. Exemplarily, the value of X can be 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 or a range consisting of any two of the above values. The dielectric constant of the first compound mainly comes from the crystalline phase. By regulating the crystallinity of the first compound within the above range, the first compound has a higher relative dielectric constant, which is conducive to the dissociation of lithium salts and further increases the content of free lithium ions in the positive electrode sheet; and the more electronegative groups in the first compound can construct a linear lithium ion transmission channel between the positive electrode active materials, which can further shorten the lithium ion transmission path, further optimize the conductive network of the positive electrode sheet, further reduce the ion transmission impedance, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery while having a higher energy density.

[0051] In one embodiment of the present application, the melting point of the first compound is Tm°C, 130 ≤ Tm ≤ 175. For example, the value of Tm can be 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, or a range consisting of any two of the above values. By regulating the melting point of the first compound within the above range, the processing performance of the positive electrode slurry can be optimized, the stability of the electrode structure can be enhanced, and the cycle life of the secondary battery can be extended.

[0052] In one embodiment of the present application, the crystallization temperature of the first compound is Tc°C, 120≤Tc≤155. For example, the value of Tc can be 120, 125, 130, 135, 140, 145, 150, 152, 155, or a range consisting of any two of the above values. Changes in crystallization temperature may change the crystal form distribution and affect the ratio of polar phase to non-polar phase in the first compound. Different crystal forms have different dielectric constants and mechanical properties, which in turn affect the polarization and ion transport efficiency of the first compound. By regulating the crystallization temperature of the first compound within the above range, the first compound contains a β phase and has a higher relative dielectric constant, which is conducive to the dissociation of lithium salts and further increases the content of free lithium ions in the positive electrode plate; and the more electronegative groups in the first compound can construct a linear lithium ion transmission channel between the positive electrode active materials, which can further shorten the lithium ion transmission path, further optimize the conductive network of the positive electrode plate, further reduce the ion transmission impedance, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery while having a higher energy density.

[0053] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is w1%, the mass percentage of the positive electrode binder is w2%, and the mass percentage of the positive electrode conductive agent is w3%. 97.7≤w1≤98.8, 0.7≤w2≤1.3, and 0.5≤w3≤1. For example, the value of w1 can be 97.7, 97.8, 97.9, 98.0, 98.1, 98.2, 98.3, 98.4, 98.5, 98.6, 98.7, 98.8, or a range consisting of any two of the above values; the value of w2 can be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, or a range consisting of any two of the above values; and the value of w3 can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a range consisting of any two of the above values. By regulating the mass percentage of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent within the above range, the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent all have appropriate mass percentages. The first compound can increase the content of free lithium ions in the positive electrode plate and effectively shorten the lithium ion transmission path. The conductive network of the positive electrode plate is further optimized, and the kinetic performance of the secondary battery is further improved. In addition, the mass percentage of the positive electrode active material is relatively high, and the secondary battery has a higher energy density.

[0054] In one embodiment of the present application, the compaction density of the positive electrode material layer is PDg / cm 3 , 3.0≤PD≤4.5, preferably, 3.8≤PD≤4.4. Exemplarily, the value of PD can be 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, 4.4, 4.5 or a range consisting of any two of the above values. By regulating the compaction density of the positive electrode material layer within the above range, the positive electrode material layer has a suitable porosity, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent in the positive electrode material layer have a suitable spacing, which can effectively shorten the length of the linear lithium ion transmission channel constructed by the more electronegative groups in the first compound between the positive electrode active materials, further shorten the lithium ion transmission path, further optimize the conductive network of the positive electrode sheet, further reduce the ion transmission impedance, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery while having a higher energy density.

[0055] In one embodiment of the present application, the contact angle between the positive electrode plate and the electrolyte is θ, 10°≤θ≤60°, preferably, 10°≤θ≤30°. Exemplarily, θ can be 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60° or a range consisting of any two of the above values. By regulating the contact angle between the positive electrode plate and the electrolyte within the above range, the contact angle between the positive electrode plate and the electrolyte is small, the positive electrode plate has good wettability, the electrolyte can better infiltrate the first compound, the first compound has high ionic conductivity, can promote lithium ion transmission, further reduce the impedance of the positive electrode plate, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery.

[0056] In one embodiment of the present application, the Dv50 of the positive electrode active material satisfies the following: 0.5μm≤Dv50≤35μm, preferably, 10μm≤Dv50≤25μm. Exemplarily, the value of Dv50 can be 0.5, 1, 5, 9, 10, 11, 15, 19, 20, 21, 25, 29, 30, 31, 35 or a range consisting of any two of the above values. By regulating the Dv50 of the positive electrode active material within the above range, the positive electrode material layer has a suitable porosity and compaction density, and the particles in the positive electrode material layer are loosely stacked, which is conducive to lithium ion transmission, further reducing the impedance of the positive electrode sheet, further improving the charge and discharge capacity of the secondary battery under large current, and further improving the kinetic performance of the secondary battery; at the same time, the positive electrode material layer has a higher compaction density, which can make the secondary battery have a higher energy density.

[0057] In the present application, Dv50 means the particle size at which the volume accumulation reaches 50% from the smallest particle size in the volume-based particle size distribution of the material.

[0058] In one embodiment of the present application, the thickness of the positive electrode current collector is H1 μm, 7 ≤ H1 ≤ 20, preferably, 8 ≤ H1 ≤ 12. For example, the value of H1 can be 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range consisting of any two of the above values. By regulating the thickness of the positive electrode current collector within the above range, the thickness of the positive electrode current collector is smaller, which can enable the secondary battery to have a higher energy density.

[0059] In one embodiment of the present application, the porosity of the positive electrode material layer is P%, 18.7≤P≤35.3; based on the total pore volume of the positive electrode material layer, the volume percentage of pores with a pore diameter greater than 50 nm is V1%, and 74≤V1≤97. For example, the value of P can be 18.7, 19, 20, 22, 24, 26, 28, 30, 32, 34, 35, 35.3, or a range consisting of any two of the above values; the value of V1 can be 74, 76, 79, 80, 83, 86, 89, 90, 93, 96, 97, or a range consisting of any two of the above values. By regulating the porosity of the positive electrode material layer and the volume percentage of pores with a pore diameter greater than 50 nm within the above range, the positive electrode material layer has a suitable number and size of pores, which can effectively shorten the length of the linear lithium ion transmission channel constructed by the more electronegative groups in the first compound between the positive electrode active materials, further shortening the lithium ion transmission path, further improving the charge and discharge capacity of the secondary battery under large current, and further improving the kinetic performance of the secondary battery.

[0060] In one embodiment of the present application, the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles is S1%, 81≤S1≤92. For example, the value of S1 can be 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, or a range consisting of any two of the above values. By regulating the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles within the above range, the positive electrode binder is more evenly distributed on the surface of the positive electrode active material particles, and the positive electrode binder covers a larger area on the surface of the positive electrode active material particles, which is conducive to the first compound to construct a linear lithium ion transmission channel between the positive electrode active materials, which can effectively shorten the lithium ion transmission path, improve the charge and discharge capacity of the secondary battery under large current, and improve the dynamic performance of the secondary battery; and the positive electrode binder covers the surface of the positive electrode active material particles, which can effectively reduce the corrosion of the electrolyte on the positive electrode active material particles, further improving the dynamic performance and cycle performance of the secondary battery.

[0061] In one embodiment of the present application, the positive electrode conductive agent includes conductive carbon and carbon nanotubes, and the conductive carbon includes at least one of Super P, carbon nanofibers, flake graphite, acetylene black, Ketjen black, carbon dots or graphene. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The selection of the above-mentioned conductive carbon can further optimize the conductive network of the positive electrode plate, facilitate electron transmission, further reduce the impedance of the positive electrode plate, further improve the charge and discharge capacity of the secondary battery under high current, and further enhance the kinetic performance of the secondary battery.

[0062] In one embodiment of the present application, the positive electrode conductive agent includes conductive carbon and carbon nanotubes. In the Raman spectrum of carbon nanotubes, at 1300 cm-1 to 1400cm -1 There is a peak intensity of I in the range D The third characteristic peak at 1550cm -1 to 1650cm -1 There is a peak intensity of I in the range G The fourth characteristic peak, 0.72≤I D / I G ≤0.77. For example, I D / I G The value of can be 0.72, 0.73, 0.74, 0.75, 0.76, 0.77 or a range consisting of any two of the above values. D / I G The value of I can characterize the surface defects or sidewall modification degree of carbon nanotubes. D / I G The larger the value of , the more surface defects of the carbon nanotubes, which is more conducive to the dispersion of carbon nanotubes and the optimization of the conductive network of the positive electrode material layer. However, too many surface defects of carbon nanotubes will affect the conductivity of carbon nanotubes. By regulating I D / I G When the value of is within the above range, the number of surface defects of the carbon nanotubes is appropriate, which is beneficial to the dispersion of the carbon nanotubes and the optimization of the conductive network of the positive electrode material layer. At the same time, the carbon nanotubes also have high conductivity, further reducing the impedance of the positive electrode sheet, further improving the charge and discharge capacity of the secondary battery under large current, and further improving the kinetic performance of the secondary battery.

[0063] In one embodiment of the present application, the positive electrode conductive agent includes conductive carbon and carbon nanotubes, and the diameter of the carbon nanotubes is Dnm, 4≤D≤20. For example, the value of D can be 4, 6, 8, 10, 12, 14, 16, 18, 20, or a range consisting of any two of the above values. By regulating the diameter of the carbon nanotubes within the above range, the positive electrode slurry has better processing performance while providing a higher effective conductive area, further reducing the impedance of the positive electrode sheet, further improving the charge and discharge capacity of the secondary battery under large current, and further improving the dynamic performance of the secondary battery.

[0064] In one embodiment of the present application, in a scanning electron microscope image within the range of 85μm×120μm of the positive electrode material layer, the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer is S2%, 47.8≤S2≤57.7. For example, the value of S2 can be 47.8, 50, 51, 52, 53, 54, 55, 56, 57, 57.7 or a range consisting of any two of the above values. By regulating the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer within the above range, the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer is higher, which can further optimize the conductive network of the positive electrode sheet, facilitate electron transmission, further reduce the impedance of the positive electrode sheet, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the kinetic performance of the secondary battery.

[0065] In one embodiment of the present application, the bonding force between the positive electrode material layer and the positive electrode current collector is FN / m, 13.00≤F≤28.29. For example, the value of F can be 13.00, 15.00, 17.00, 19.00, 20.00, 23.00, 25.00, 27.00, 28.29 or a range consisting of any two of the above values. By regulating the bonding force between the positive electrode material layer and the positive electrode current collector within the above range, the bonding force between the positive electrode material layer and the positive electrode current collector is greater, and the positive electrode material layer and the positive electrode current collector are in closer contact, which can further shorten the lithium ion transmission path, further improve the charge and discharge capacity of the secondary battery under large current, and further improve the dynamic performance of the secondary battery.

[0066] In one embodiment of the present application, the positive electrode active material includes at least one of lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide or lithium iron phosphate. The above-mentioned lithium nickel cobalt manganese oxide may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95),LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3At least one of O2 (NCM111). By selecting the above-mentioned positive electrode active materials, the secondary battery has high energy density and good dynamic performance.

[0067] In one embodiment of the present application, the thickness of the positive electrode material layer on one side of the positive current collector is H2 μm, and 44.44 ≤ H2 ≤ 66.67. For example, the value of H2 can be 44.44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 66.67, or a range consisting of any two of the above values. By regulating the thickness of the positive electrode material layer on one side of the positive current collector within the above range, the positive electrode material layer has a suitable porosity and compaction density, which can effectively shorten the length of the linear lithium ion transmission channel constructed between the positive electrode active material by the more electronegative groups in the first compound, further shortening the lithium ion transmission path, further improving the charge and discharge capacity of the secondary battery under high current, and further improving the kinetic performance of the secondary battery; at the same time, the secondary battery has a higher energy density.

[0068] The present application does not particularly limit the method for regulating the relative dielectric constant of the first compound, as long as the purpose of the present application can be achieved. For example, a commercially available first compound with a different relative dielectric constant can be selected.

[0069] The present application does not particularly limit the manner in which the weight average molecular weight and average molecular weight of the first compound are regulated, as long as the purpose of the present application can be achieved. For example, a commercially available first compound having a different weight average molecular weight can be selected, and the weight average molecular weight of the first compound can be tested in combination with the test method of "Molecular Weight and Molecular Weight Distribution Test" in this application, and the first compound having the desired weight average molecular weight can be selected. For example, a commercially available first compound having a different average molecular weight can be selected, and the average molecular weight of the first compound can be tested in combination with the test method of "Molecular Weight and Molecular Weight Distribution Test" in this application, and the first compound having the desired average molecular weight can be selected.

[0070] The present application does not particularly limit the method for regulating Mz / Mw, as long as the purpose of the present application can be achieved. For example, the Mz / Mw value can be regulated by regulating the respective values ​​of Mz and Mw, and the regulation method is as described above.

[0071] The present application does not particularly limit the method for regulating the crystallinity and crystallization temperature of the first compound, as long as the purpose of the present application can be achieved. For example, the crystallinity and crystallization temperature of the first compound can be regulated by regulating the cooling rate, reaction temperature, and reaction time during the preparation of the first compound. For example, the preparation method of the first compound and the molecular structure of the first compound can also affect the crystallinity and crystallization temperature of the polymer.

[0072] The present application does not particularly limit the method for regulating the melting point of the first compound, as long as the purpose of the present application can be achieved. For example, the average molecular weight of the first compound, the weight average molecular weight of the first compound, the molecular chain structure, and the crystal distribution of the first compound may affect the melting point of the first compound.

[0073] The present application does not particularly limit the method for regulating the mass percentage of the positive electrode active material, positive electrode binder, and positive electrode conductive agent, as long as the purpose of the present application can be achieved. For example, the mass percentage of the positive electrode active material can be regulated by regulating the mass of the added positive electrode active material; the mass percentage of the positive electrode binder can be regulated by regulating the mass of the added positive electrode binder; and the mass percentage of the positive electrode conductive agent can be regulated by regulating the mass of the added positive electrode conductive agent.

[0074] The present application does not particularly limit the method for regulating the compaction density of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the compaction density of the positive electrode material layer can be regulated by regulating the cold pressing pressure during the cold pressing process.

[0075] The present application does not particularly limit the method for regulating the contact angle between the positive electrode sheet and the electrolyte, as long as the purpose of the present application can be achieved. For example, the contact angle between the positive electrode sheet and the electrolyte can be regulated by regulating the type and / or mass percentage of the positive electrode binder in the positive electrode material layer.

[0076] This application does not particularly limit the method for regulating the Dv50 of the positive electrode active material, as long as the objectives of this application can be achieved. For example, the Dv50 of the positive electrode active material can be regulated by grinding the positive electrode active material. For example, the Dv50 of the positive electrode active material can be regulated by controlling the grinding time. For example, when other conditions remain unchanged, extending the grinding time decreases the Dv50 of the positive electrode active material; shortening the grinding time increases the Dv50 of the positive electrode active material.

[0077] The present application does not particularly limit the method for adjusting the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, commercially available positive electrode current collectors of different thicknesses can be selected.

[0078] The present application does not particularly limit the method for regulating the porosity of the positive electrode material layer and the volume percentage of pores with a pore diameter greater than 50 nm, as long as the objectives of the present application can be achieved. For example, the porosity of the positive electrode material layer and the volume percentage of pores with a pore diameter greater than 50 nm can be regulated by regulating the mass percentage of the positive electrode active material, the positive electrode binder, the positive electrode conductive agent, and / or the Dv50 of the positive electrode active material.

[0079] The present application does not particularly limit the method for regulating the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles, as long as the purpose of the present application can be achieved. For example, the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles can be regulated by regulating the mass percentage of the positive electrode active material and the positive electrode binder.

[0080] The present application does not particularly limit the method for regulating the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer can be regulated by regulating the mass percentage of the positive electrode conductive agent.

[0081] The present application does not particularly limit the method for regulating the bonding force between the positive electrode material layer and the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the bonding force between the positive electrode material layer and the positive electrode current collector can be regulated by regulating the type and distribution of the positive electrode binder and the mass percentage of the positive electrode binder.

[0082] The present application does not particularly limit the method for regulating the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode material layer can be regulated by regulating the compaction density of the positive electrode material layer.

[0083] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0084] In the present application, the secondary battery also includes a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along the thickness direction of itself, or on two surfaces of the negative electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector, etc.

[0085] The negative electrode material layer of the present application includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x(0.5<x<1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O 12 , Li-Al alloy or metallic lithium. The negative electrode material layer of the present application also includes a negative electrode binder and a negative electrode conductive agent. The present application has no particular restrictions on the negative electrode binder and the negative electrode conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the negative electrode binder may include but is not limited to polyvinylidene fluoride (PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyamide, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, styrene-butadiene rubber (SBR), polypropylene, polyethylene, polyetherimide, a copolymer of propylene derivatives or at least one of carboxymethyl cellulose salts. The above-mentioned carboxymethyl cellulose salts may include but are not limited to at least one of sodium carboxymethyl cellulose, potassium carboxymethyl cellulose or lithium carboxymethyl cellulose. The negative electrode conductive agent may be at least one of the above-mentioned positive electrode conductive agents. The present application has no particular restrictions on the mass ratio of the negative electrode active material, the negative electrode binder and the negative electrode conductive agent in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0086] The present application does not particularly limit the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm. The present application does not particularly limit the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 250 μm.

[0087] In the present application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt and a non-aqueous solvent. The lithium salt may include various lithium salts commonly used in the art, such as at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvent. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorocarbonate compound. The above-mentioned chain carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (EMC). The cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound may include but is not limited to at least one of fluorinated ethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or caprolactone. The above-mentioned ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the weight percentage of the lithium salt and the non-aqueous solvent, as long as the purpose of the present application can be achieved.

[0088] In the present application, the secondary battery also includes a diaphragm. The diaphragm is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0089] In the present application, the diaphragm may include a base film and a surface treatment layer. The base film may be a non-woven fabric or a composite film having a porous structure, and the material of the base film may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the base film, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder for the diaphragm. The present application does not particularly limit the above-mentioned inorganic particles, and for example, it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application does not particularly limit the separator binder, and for example, it can be at least one of the aforementioned negative electrode binders. The polymer layer comprises a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0090] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0091] The present application does not particularly limit the type of secondary battery, which may include any device that generates an electrochemical reaction. In the present application, secondary batteries may include but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), lithium polymer secondary batteries or lithium ion polymer secondary batteries, etc.

[0092] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging. Among them, the packaging bag is a packaging bag known in the art, and the present application does not limit this.

[0093] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0094] The present application does not particularly limit the type of electronic device, and the electronic device may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0095] Example

[0096] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0097] Test methods and equipment:

[0098] Positive electrode binder sampling method:

[0099] Disassemble the lithium-ion battery and remove the positive electrode sheet. Cut the positive electrode sheet into 1cm×1cm samples and scrape the positive electrode material layer on the positive electrode current collector aluminum foil with a blade to separate the positive electrode material layer from the positive electrode current collector. Place the positive electrode material layer powder in a vacuum dryer at 60°C for 12 hours to remove the electrolyte and moisture. Dissolve the dried positive electrode material layer powder in N-methylpyrrolidone (NMP) with a mass ratio of positive electrode material layer powder to NMP of 1:20; centrifuge at 5000rpm for 10 minutes to separate the supernatant (containing the positive electrode binder) and the precipitate (containing the positive electrode active material and positive electrode conductive agent). After evaporating the solvent from the supernatant at 50°C, vacuum dry at 60°C for 6 hours to obtain the positive electrode binder powder. The positive electrode binder is sampled using the above method in the following relative dielectric constant test, molecular weight and molecular weight distribution test, ionic conductivity test, X-ray diffraction test, infrared spectrum test, element mass ratio test, mass change rate test, crystallinity test, melting point test, and crystallization temperature test.

[0100] Relative dielectric constant test:

[0101] (1) Sample processing: The positive electrode binder powder was pressed into a disc (20 mm in diameter and 0.5 mm in thickness) with uniform thickness at 200°C and 10 MPa using a hot press. The disc was placed in a vacuum drying oven at 120°C and dried for 4 hours to remove moisture (moisture content <0.1 wt%) to obtain a disc sample.

[0102] (2) Electrode Preparation: Circular gold electrodes (15 mm in diameter, 50 nm in thickness) were deposited on both sides of the wafer sample using vacuum evaporation, ensuring close contact between the gold electrodes and the wafer sample. Silver glue was used to connect copper wires to the gold electrodes to avoid contact resistance.

[0103] (3) Test process: Initial calibration: Without placing the wafer sample, measure the parasitic capacitance (C0) and residual inductance (L0) of the fixture, and perform open circuit / short circuit compensation in the LCR meter. Install the sample: Place the wafer sample with gold electrodes deposited on the surface in the fixture, and adjust the spacing so that the gold electrodes are in close contact with the surface of the wafer sample (pressure ≈ 5N, to avoid excessive compression causing thickness changes). Parameter settings: frequency: 10Hz, test voltage: 1V (small signal to avoid ferroelectric domain reversal), temperature setting: 25℃. Data acquisition: Measure the capacitance (C) and loss factor (tanδ), and record the readings at this frequency. After the frequency point stabilizes, take the average of 3 measurements. Thickness measurement: Use a micrometer to measure the thickness (d) of the wafer sample with an accuracy of ±1μm.

[0104] (4) Data processing: Calculation of relative dielectric constant: ε r =(C×d) / (ε0×A).

[0105] Where: C is the measured capacitance; d is the thickness of the wafer sample; A is the effective area of ​​the gold electrode (πr 2 , r=7.5mm), ε0 is the dielectric constant of vacuum, and the standard value is 8.8541878128×10 -12 F / m.

[0106] Molecular weight and molecular weight distribution test:

[0107] In accordance with the national standard "Gel Permeation Chromatography (GPC) Using Tetrahydrofuran as Eluent" (GB / T 21863-2008), an ultra-high performance polymer chromatograph (ACQUITY APC) and an ACQUITY differential refractive index detector (DID) were used. The test steps are as follows: (1) Preheating: Install the chromatographic column and tubing, turn on the console, test power, and then open the Empower test software. (2) Parameter setting: injection volume: 10 μL to 50 μL (depending on sample concentration); pump flow rate: 0.2 mL / min; mobile phase: 30 mol / L LiBr in N-methylpyrrolidone (NMP); sealing cleaning liquid: isopropanol; pre-column: PL gel 10 μm MiniMIX-B Guard (size: 50 mm × 4.6 mm × 2); analytical phase: PL gel 10 μm MiniMIX-B (size: 250 mm × 4.6 mm); standard: polystyrene; run time: 30 min; detector: ACQUITY differential refractive index (RI) detector; column oven temperature: 90 °C; detector temperature: 55 °C. (3) Sample testing: a. Preparation of standard sample solution and test sample solution: Weigh 0.005g of standard sample narrow distribution polystyrene (PS) and test sample positive electrode binder powder respectively and add 2mL of mobile phase liquid to prepare 2.5mg / mL standard sample solution and test sample solution, and place them in the refrigerator for more than 8h; b. Standard / test sample solution test: Edit the sample group to be tested, select the established sample group method, wait for the baseline to stabilize, click the run queue, and start testing the sample. (4) Data processing: Based on the relationship between retention time and molecular weight, use the chemical workstation to establish a calibration curve, integrate and quantify the sample spectrum, and the chemical workstation automatically generates molecular weight (including weight average molecular weight and average molecular weight) and molecular weight distribution results.

[0108] Ionic conductivity test:

[0109] (1) At 25°C, the positive electrode binder powder is loaded into a mold and pressed into a dense cylindrical sample, making the cylindrical sample uniform and free of cracks.

[0110] (2) Platinum, an ion-conducting material, is coated on both sides of the cylindrical sample to form a symmetrical electrode structure.

[0111] (3) Connect an impedance analyzer to measure the frequency response of the cylindrical sample. The measured frequency range is 0.00001 Hz to 1000000 Hz, and the amplitude is 5 mV.

[0112] (4) Perform AC impedance measurements and obtain Nyquist and Bode plots.

[0113] (5) According to the equivalent circuit model, the ionic conductivity of the positive electrode binder is calculated using the following formula:

[0114] Ionic conductivity of positive electrode binder = L2 / (A2×R b ); where: L2 is the thickness of the cylindrical sample, A2 is the cross-sectional area of ​​the cylindrical sample, R b is the bulk resistance of the cylindrical sample, obtained from the intersection of the semicircular arc and the oblique line at the high-frequency end.

[0115] X-ray diffraction (XRD) test:

[0116] The cathode binder was tested using an X-ray powder diffractometer (Bruker D8 ADVANCE) with a Cu Kα target. The voltage was 40 kV, the current was 40 mA, the scanning angle range was 5° to 80°, the scanning step size was 0.00836°, and the time per step was 0.3 s. Silicon powder (15% by weight of the cathode binder) was added. Using the internal standard method, the peak position of the silicon standard was used to calibrate the instrument and test errors. The characteristic peak positions of the cathode binder were then calculated to obtain the X-ray diffraction spectrum of the cathode binder.

[0117] Infrared spectrum test:

[0118] The positive electrode binder powder was tested by Fourier transform infrared spectroscopy using a Thermo Fisher Nicolet iS20 FTIR spectrometer. The reference standard was the national standard "Fourier transform infrared spectrometer" (GB / T 21186-2007). The infrared spectrum of the positive electrode binder was obtained by the potassium bromide tablet method.

[0119] Element mass ratio test:

[0120] The element types and mass proportions of the different elements in the positive electrode binder were determined using an inductively coupled plasma emission spectrometer (ICP, PE7000DV spectrometer manufactured by PerkinElmer, USA). 0.2 g of the positive electrode binder powder was weighed and dissolved in a 42% nitric acid solution. The nitric acid solution in which the positive electrode binder was dissolved was then tested to determine the element types and mass proportions of the different elements in the positive electrode binder, and the sum of the mass proportions of the corresponding elements was calculated.

[0121] Quality change rate test:

[0122] Dissolve the positive electrode binder powder in NMP at a ratio of 7 wt % to obtain a slurry. This slurry was then placed in an aluminum box and baked at 85°C for 48 h to obtain a film (to completely dry the film). Record the initial film weight as m0. Soak the film in an electrolyte at 85°C for 24 h, remove it, wipe the film surface dry with dust-free paper, and weigh it as m1. The mass change rate (m (%)) = (m1 - m0) / m0. This electrolyte was used in Example 1-1.

[0123] Crystallinity test:

[0124] Differential scanning calorimetry (DSC) was used to determine the crystallinity of the positive electrode binder. First, 10 mg of the positive electrode binder powder was sealed in an aluminum crucible and melted and quenched at 200°C to eliminate the thermal history. Then, the temperature was raised to 200°C at 10°C / min under a nitrogen atmosphere. The melting peak was recorded and the melting enthalpy (ΔH) was calculated by integration. f ), crystallinity of positive electrode binder = ΔH f / ΔH 0 f , ΔH 0 f The melting enthalpy for 100% crystallinity is 100%. After testing, the initial and secondary scan data must be compared to ensure repeatability is less than 5%. Calibration with a Sn standard ensures instrument accuracy. The instrument used for this test is a differential scanning calorimeter (NETZSCH, DSC214 Polyma).

[0125] Melting point test:

[0126] The melting point of the positive electrode binder was tested using differential scanning calorimetry (DSC). An aluminum crucible was used, the positive electrode binder powder weighed 10 mg, and the test temperature range was from room temperature to 400°C at a heating rate of 10°C / min. The instrument used for the test was a differential scanning calorimeter (Netzsch, model DSC214 Polyma).

[0127] Crystallization temperature test:

[0128] The crystallization temperature of the positive electrode binder was determined using differential scanning calorimetry (DSC). 10 mg of positive electrode binder powder was sealed in an aluminum crucible and heated to 200°C at 10°C / min to eliminate the thermal history. The temperature was then cooled to room temperature at -10°C / min. The crystallization exothermic peak during the cooling process was recorded. The peak temperature of the crystallization exothermic peak was the crystallization temperature of the positive electrode binder. The instrument used for the test was a differential scanning calorimeter (brand: NETZSCH, instrument model: DSC214 Polyma).

[0129] Compaction density test:

[0130] Disassemble the lithium-ion battery, remove the positive electrode sheet, clean the positive electrode sheet with dimethyl carbonate (DMC), and dry the positive electrode sheet. Select the area on the positive electrode sheet including the double-sided positive electrode material layer and cut it into 10 pieces with an area of ​​1540.25mm using a cutting machine. 2 Weigh the small discs and take the average value M. Then measure the thickness of the discs with a caliper and take the average value H3. Then wipe off the positive electrode material layer from the ten discs, weigh them, and take the average value M0. Then measure the thickness of the positive electrode current collector with a caliper and take the average value H1. The compacted density of the positive electrode material layer, PD, = (M - M0) / [1540.25 × (H3 - H1)].

[0131] Contact angle test between positive electrode and electrolyte:

[0132] The contact angle between the positive electrode and the electrolyte is measured using the sessile drop method. First, the positive electrode is laid flat on a substrate (keeping it flat), then 0.02 mL of electrolyte is dropped onto the positive electrode sample. The image of the drop is captured by a high-resolution camera, and the angle is automatically measured by software using an optical contact angle meter. The test result is the contact angle between the positive electrode and the electrolyte.

[0133] Dv50 test:

[0134] The lithium-ion battery was discharged at a constant current of 0.2C to 3.0V and then disassembled. The positive electrode sheet was removed, cleaned with DMC, and air-dried. The dried positive electrode sheet was randomly cut from the area on the surface of the positive electrode sheet where the positive electrode material layer was provided. The sheet was placed in a muffle furnace and calcined at 600°C for 2 hours. The powder on the surface of the positive electrode sheet was scraped off with a knife to obtain positive electrode active material particles. The particle size of the positive electrode active material particles was measured using a Malvern particle size analyzer (model: MasterSizer2000). 0.02g of positive electrode active material particles was added to a 50mL clean beaker, followed by 20mL of dispersant ethanol. The sample dispersion was completely dispersed in the ethanol using a 120W ultrasonic cleaner. The sample dispersion was then tested using a Malvern particle size analyzer to obtain the particle size Dv50 of the positive electrode active material particles.

[0135] Porosity and pore size distribution test:

[0136] (1) The lithium-ion battery was discharged at a constant current of 0.5C to 3.0V, and then disassembled to obtain the positive electrode sheet. The positive electrode sheet was then immersed in DMC at room temperature for 30 minutes and dried. (2) The positive electrode sheet obtained in step (1) was cut into 30 cm × 2 cm samples, dried at 120°C for 2 hours, and then degassed in a degassing chamber for 12 hours. The porosity and pore size distribution of the positive electrode material layer were then measured using a mercury intrusion instrument. The mercury intrusion instrument model was MicroActive AutoPore V 9605, and the pressure was set to 33,000 psia.

[0137] Test on the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles:

[0138] Lithium-ion batteries were disassembled to obtain positive electrode sheets. These sheets were then immersed in DMC at room temperature for 60 minutes, removed, and air-dried at room temperature. The dried sheets were then cut into 5 mm × 5 mm samples. The samples were characterized using a Philips XL-30 field emission scanning electron microscope (SEM) under the following test conditions: an accelerating voltage of 10 kV, a 10-spot raster, a working distance of 10 mm, and a magnification of 1000x. Backscattered electrons were used to obtain SEM images of the positive electrode material layer surface. Within the 85 μm × 120 μm SEM image, the distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles was analyzed and calculated using IMG Analysis digital image analysis software.

[0139] Raman spectroscopy test:

[0140] The Raman spectrum of carbon nanotubes was measured using a laser microconfocal Raman spectrometer (model HR Evolution, HORIBA Scientific Instruments Division). -1 The peak intensity at I D , at 1580cm -1 The peak intensity at I G . I of carbon nanotubes D / I G The value of is obtained by the following method: the carbon nanotube powder is placed on a Raman test sample table, and the Raman spectrum of the carbon nanotube powder is measured to obtain I D / I G The value was tested 12 times and the average value was the I D / I G value.

[0141] Carbon nanotube diameter test:

[0142] (1) disassembling a lithium-ion battery to obtain a positive electrode; (2) soaking the positive electrode in DMC at room temperature for 60 minutes, taking it out, and drying it at room temperature; (3) taking the positive electrode obtained in step (2), and obtaining a cross-section of the positive electrode material layer on the positive electrode by liquid nitrogen brittle fracture; (4) observing the cross-section by SEM (model: Philips XL-30 field emission scanning electron microscope), measuring the diameters of a total of no less than 30 carbon nanotubes in 10 areas, and taking the average value as the diameter of the carbon nanotube.

[0143] Distribution ratio test of positive electrode conductive agent on the surface of positive electrode material layer:

[0144] Lithium-ion batteries were disassembled to obtain positive electrode sheets. These sheets were then immersed in DMC at room temperature for 60 minutes, removed, and air-dried at room temperature. The dried sheets were then cut into 5 mm × 5 mm samples. The samples were characterized using a Philips XL-30 field emission scanning electron microscope (SEM) under the following test conditions: an accelerating voltage of 10 kV, a 10-spot raster, a working distance of 10 mm, and a magnification of 1000x. Scanning electron micrographs of the positive electrode material layer surface were obtained using a Beisanse 2 electron microscope. Within the 85 μm × 120 μm SEM image, the ratio of the positive electrode conductive agent area to the total area was analyzed and calculated using IMG Analysis digital image analysis software, representing the distribution ratio of the positive electrode conductive agent.

[0145] Adhesion test:

[0146] (1) Disassemble the lithium-ion battery, remove the positive electrode, clean the positive electrode with DMC, and then dry the positive electrode;

[0147] (2) Take the dried positive electrode sheet and cut a sample with a width of 30 mm and a length of 100 mm using a blade;

[0148] (3) Apply special double-sided tape to the steel plate with a width of 20 mm and a length of 90 mm;

[0149] (4) Stick the sample cut in step (2) on the double-sided tape with the test surface facing downward;

[0150] (5) Insert a paper tape with a width equal to the width of the specimen and a length of 180 mm under the specimen and secure it with wrinkle glue;

[0151] (6) Turn on the power of the Sansi tensile testing machine, the indicator light will light up, and adjust the position of the limit block;

[0152] (7) Fix the sample prepared in step (5) on the test bench, set the speed to 10 mm / min, the test range to 0 mm to 40 mm, and pull the paper tape in a 90° direction until the test is completed to obtain the bonding force between the positive electrode material layer and the positive electrode current collector.

[0153] Charging time to 100% state of charge (SOC) test:

[0154] In an environment of (25±3)℃, the lithium-ion battery is charged to 4.5V at a constant current of 1.0C, then to 4.52V at a constant current of 1.5C, then to 4.53V at a constant current of 3C, then to 4.55V at a constant current of 6C, then to 4.58V at a constant current of 10C, and then changed to constant voltage charging to a cutoff current of 0.025C. The state of charge of the lithium-ion battery obtained is 100% SOC, and the charging time to reach this state is the charging time to 100% SOC.

[0155] 3C discharge capacity retention rate (3C DC ratio) test:

[0156] In an environment of (25±3)℃, the lithium-ion battery was charged to 4.5V at a constant current of 1.0C, then to 4.52V at a constant current of 1.5C, then to 4.53V at a constant current of 3C, then to 4.55V at a constant current of 6C, then to 4.58V at a constant current of 10C, and then changed to constant voltage charging to a cutoff current of 0.025C; left for 30min; discharged using a 0.2C rate current to a set voltage (for the positive electrode active material, the LCO voltage is 3.0V) and a discharge capacity of D0; left for 5min ; Then charge at a constant current of 1.0C to 4.5V, then charge at a constant current of 1.5C to 4.52V, then charge at a constant current of 3C to 4.53V, then charge at a constant current of 6C to 4.55V, then charge at a constant current of 10C to 4.58V, and then change to constant voltage charging to a cutoff current of 0.025C; leave for 30 minutes; use 3C rate current to discharge until the voltage is the set value (for the positive electrode active material, the LCO voltage is 3.0V), the discharge capacity is D1, then 3C discharge capacity retention rate (%) = D1 / D0×100%.

[0157] Volume energy density test:

[0158] In an environment of (25±3)℃, the lithium-ion battery is charged to 4.5V at a constant current of 1.0C, then to 4.52V at a constant current of 1.5C, then to 4.53V at a constant current of 3C, then to 4.55V at a constant current of 6C, then to 4.58V at a constant current of 10C, and then changed to constant voltage charging to a cutoff current of 0.025C; set aside for 30 minutes, and discharge at a rate current of 0.2C to a voltage of 3.0V, and then stand for 5 minutes. The energy of the above discharge process is recorded as the discharge energy E. Calculate the volume V (mm) of the lithium-ion battery 3 ) = length × width × height.

[0159] Volumetric energy density (Wh / L) = E / V × 10 6 .

[0160] Example 1-1

[0161] <Preparation of positive electrode sheet>

[0162] The positive electrode active material lithium cobalt oxide (LiCoO2, LCO), the positive electrode conductive agent Super P, the positive electrode conductive agent multi-walled carbon nanotubes, and the positive electrode binder first compound β-polyvinylidene fluoride are mixed in a weight ratio of 98.2:0.3:0.3:1.2, and N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry is 75wt%; the positive electrode slurry is evenly coated on one surface of the positive electrode current collector aluminum foil, and dried at 120°C for 1h to obtain a positive electrode sheet with a single-side coated positive electrode material layer; wherein the coating weight of the positive electrode material layer is 0.02g / cm 2 The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. After drying under vacuum conditions at 120°C for 1 hour, cold pressing, cutting, and slitting, a positive electrode sheet with a specification of 74mm×867mm is obtained. Among them, the thickness H1 of the positive electrode current collector is 10μm; the compaction density PD of the positive electrode material layer is 4.4g / cm 3 ; The thickness H2 of the single-sided positive electrode material layer is 45.45μm.

[0163] <Preparation of negative electrode sheet>

[0164] The negative electrode active material artificial graphite, the negative electrode binder sodium carboxymethyl cellulose (CMC-Na), and the negative electrode binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 95:2:3, and deionized water was added as a solvent. The mixture was stirred and mixed to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was evenly coated on one surface of an 8 μm thick negative electrode current collector copper foil and dried at 120°C to obtain a negative electrode sheet coated with a 50 μm thick negative electrode material layer on one side. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. The sheet was dried under vacuum at 120°C for 1 hour, and then cold pressed, cut, and slit to obtain a negative electrode sheet with a specification of 78 mm × 875 mm. The compaction density during the cold pressing process was 1.75 g / cm 3 .

[0165] <Preparation of Electrolyte>

[0166] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a weight ratio of 1:1:1 to create a base solvent. Lithium hexafluorophosphate (LiPF6) was then added and mixed thoroughly to create an electrolyte. The weight percentage of the lithium salt, LiPF6, was 12.5% ​​based on the mass of the electrolyte, with the remainder being the base solvent.

[0167] <Preparation of Separator>

[0168] A polyethylene (PE) film with a thickness of 15 μm is used.

[0169] <Preparation of lithium-ion batteries>

[0170] The prepared positive electrode sheet, separator, negative electrode sheet, and separator are stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The electrodes are then wound to form an electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then filled with electrolyte. The lithium-ion battery is then vacuum packaged, allowed to stand, formed, degassed, and trimmed.

[0171] Example 1-2 to Example 1-16

[0172] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0173] Example 1-17 to Example 1-19

[0174] The process is the same as Example 1-1 except that the cooling rate and reaction temperature during the preparation of the first compound are adjusted so that the crystallinity of the first compound is as shown in Table 1.

[0175] Example 1-20 to Example 1-24

[0176] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0177] Example 1-25 to Example 1-26

[0178] The process is the same as Example 1-1 except that the cooling rate and reaction temperature during the preparation of the first compound are adjusted so that the crystallinity of the first compound is as shown in Table 1.

[0179] Examples 1-27

[0180] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0181] Example 1-28 to Example 1-29

[0182] The process is the same as Example 1-1 except that the cooling rate and reaction temperature during the preparation of the first compound are adjusted so that the crystallinity of the first compound is as shown in Table 1.

[0183] Example 2-1 to Example 2-6

[0184] Except that the milling time was adjusted so that the Dv50 of the positive electrode active material was as shown in Table 2, the rest was the same as Example 1-1.

[0185] Example 2-7 to Example 2-14

[0186] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0187] Example 2-15 to Example 2-19

[0188] Except that the cold pressing pressure in the cold pressing process was adjusted so that the compaction density of the positive electrode material layer was as shown in Table 2, the rest was the same as Example 1-1.

[0189] Example 2-20 to Example 2-25

[0190] Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-1.

[0191] Comparative Examples 1 to 6

[0192] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0193] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0194]

[0195]

[0196]

[0197] From Examples 1-1 to 1-29 and Comparative Examples 1 to 6, it can be seen that when the positive electrode binder in the positive electrode material layer includes a first compound and the relative dielectric constant and weight-average molecular weight of the first compound are within the scope of this application, the prepared lithium-ion battery has a shorter charging time to 100% SOC, a higher 3C discharge capacity retention rate, and a volume energy density, indicating that the lithium-ion battery has a higher energy density while also having better kinetic performance. In Comparative Examples 1 to 6, the relative dielectric constant and / or weight-average molecular weight of the first compound are not within the scope of this application, and the prepared lithium-ion batteries have a longer charging time to 100% SOC, a lower 3C discharge capacity retention rate, and a volume energy density, indicating that the lithium-ion battery has a lower energy density and poorer kinetic performance.

[0198] The type of the first compound typically affects the kinetic performance and energy density of the lithium-ion battery. As can be seen from Examples 1-1, 1-2, and 1-5, by adjusting the type of the first compound within the scope of this application, the prepared lithium-ion batteries have a shorter charge to 100% SOC time, a higher 3C discharge capacity retention rate, and a higher volumetric energy density, indicating that the lithium-ion battery has both high energy density and good kinetic performance.

[0199] The Mz / Mw value generally affects the kinetic performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-6, 1-16, and 1-24, by adjusting the Mz / Mw value within the range of this application, the prepared lithium-ion batteries have a shorter charge to 100% SOC time, a higher 3C discharge capacity retention rate, and a higher volumetric energy density, indicating that lithium-ion batteries have both higher energy density and better kinetic performance.

[0200] The crystallinity of the first compound generally affects the kinetic performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 1-17, 1-19, 1-25, 1-26, 1-28, and 1-29, by regulating the crystallinity of the first compound within the scope of this application, the prepared lithium-ion batteries have a shorter charge to 100% SOC time, a higher 3C discharge capacity retention rate, and a higher volumetric energy density, indicating that the lithium-ion batteries have both higher energy density and better kinetic performance.

[0201] The melting point of the first compound generally affects the cycle life, kinetic performance, and energy density of a lithium-ion battery. As can be seen from Examples 1-1, 1-3, 1-5, and 1-20, by adjusting the melting point of the first compound within the scope of this application, the prepared lithium-ion batteries have a shorter charge to 100% SOC time, a higher 3C discharge capacity retention rate, and a higher volumetric energy density, indicating that the lithium-ion batteries have both higher energy density and better kinetic performance.

[0202] The crystallization temperature of the first compound generally affects the cycle life, kinetic performance, and energy density of the lithium-ion battery. As can be seen from Examples 1-1, 1-3, 1-5, 1-20, and 1-21, by regulating the crystallization temperature of the first compound within the scope of this application, the prepared lithium-ion batteries have a shorter charge to 100% SOC time, a higher 3C discharge capacity retention rate, and a higher volumetric energy density, indicating that the lithium-ion battery has both higher energy density and better kinetic performance.

[0203] The combined mass ratio of silicon, iron, and zinc in the first compound typically affects the safety, kinetics, and energy density of a lithium-ion battery. As can be seen from Examples 1-1 and 1-27, by regulating the combined mass ratio of silicon, iron, and zinc in the first compound within the scope of this application, the prepared lithium-ion batteries exhibited shorter charge times to 100% SOC, higher 3C discharge capacity retention rates, and higher volumetric energy densities, demonstrating that lithium-ion batteries possess both higher energy density and better kinetics.

[0204] Depend on Figure 1 It can be seen that in Example 1-1, the white particles with clear outlines are the positive electrode active material. The scanning electron microscope image of the backscattered electrons on the surface of the positive electrode material layer of Example 1-1 can be obtained after software processing. Figure 2 .Depend on Figure 2 It can be seen that the white particles with clear outlines are positive electrode active materials, the gray or light gray parts on the surface of the positive electrode active material particles or between the positive electrode active material particles are positive electrode binders, and the yellow surface and mesh-like distribution parts are positive electrode conductors. The positive electrode binder and positive electrode conductor are evenly distributed on the surface of the positive electrode active material particles or between the positive electrode active material particles.

[0205] Depend on Figure 3 It can be seen that in the X-ray diffraction spectrum of the first compound β-polyvinylidene fluoride, first characteristic peaks exist in the ranges of 19° to 21°, 34° to 35°, and 38° to 41°.

[0206] Depend on Figure 4It can be seen that in the infrared spectrum of the first compound β-polyvinylidene fluoride, at 470 cm -1 Up to 475cm -1 、507cm -1 Up to 515cm -1 、830cm -1 Up to 850cm -1 、1275cm -1 to 1290cm -1 There is a second characteristic peak in the range.

[0207]

[0208]

[0209] The Dv50 of the positive electrode active material generally affects the kinetic performance and energy density of lithium-ion batteries. As can be seen from Examples 1-1, 2-1, and 2-6, by regulating the Dv50 of the positive electrode active material within the scope of this application, the prepared lithium-ion batteries have shorter charge times to 100% SOC, higher 3C discharge capacity retention rates, and higher volumetric energy densities, demonstrating that lithium-ion batteries possess both higher energy density and better kinetic performance.

[0210] I D / I G The value of usually affects the kinetic performance of lithium-ion batteries. From Examples 1-1, 2-7 to 2-10, it can be seen that by regulating I D / I G The value of is within the scope of this application, and the prepared lithium-ion battery has a shorter charging time to 100% SOC, a higher 3C discharge capacity retention rate and volume energy density, indicating that the lithium-ion battery has good kinetic performance and also has a higher energy density.

[0211] The diameter of carbon nanotubes generally affects the kinetic performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-11, and 2-14, by adjusting the diameter of the carbon nanotubes within the scope of this application, the prepared lithium-ion batteries have shorter charge times to 100% SOC, higher 3C discharge capacity retention rates, and higher volumetric energy densities, demonstrating that the lithium-ion batteries have both good kinetic performance and high energy density.

[0212] The compaction density of the positive electrode material layer usually affects the kinetic performance and energy density of the lithium-ion battery. It can be seen from Example 1-1, Example 2-15 to Example 2-19 that by regulating the compaction density of the positive electrode material layer within the scope of this application, the prepared lithium-ion battery has a shorter charging time to 100% SOC, a higher 3C discharge capacity retention rate and volume energy density, indicating that the lithium-ion battery has a higher energy density while also having better kinetic performance. In Example 1-1, Example 2-15 to Example 2-19, as the compaction density of the positive electrode material layer increases, the porosity of the positive electrode material layer becomes smaller, the contact angle between the positive electrode sheet and the electrolyte becomes larger, the electrolyte infiltration becomes worse, the lithium-ion battery takes longer to charge to 100% SOC, the 3C discharge capacity retention rate becomes smaller, and the kinetic performance of the lithium-ion battery becomes worse. Compared with Example 1-1, the compaction density of Example 2-18 and Example 2-19 is larger, which may affect the energy density of the lithium-ion battery to a certain extent, and the energy density of the lithium-ion battery is reduced.

[0213] The thickness of the positive electrode current collector usually affects the energy density of the lithium-ion battery. It can be seen from Examples 1-1, 2-20 to 2-25 that by regulating the thickness of the positive electrode current collector within the scope of this application, the prepared lithium-ion battery has a shorter charging time to 100% SOC, a higher 3C discharge capacity retention rate and volume energy density, indicating that the lithium-ion battery has a higher energy density and better dynamic performance. In Examples 1-1, 2-20 to 2-25, the thickness of the positive electrode current collector of Examples 2-20 and 2-21 is smaller than that of Example 2-22. The thinner the positive electrode current collector, the lower the energy density of the lithium-ion battery.

[0214] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0215] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0216] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent, the positive electrode binder comprising a first compound, the relative dielectric constant of the first compound being ε r , the weight average molecular weight of the first compound is Mw, 15≤ε r ≤80,700000≤Mw≤1200000.

2. The secondary battery according to claim 1, wherein 30≤ε r ≤50, and / or, 800000≤Mw≤1100000.

3. The secondary battery according to claim 1, wherein The average molecular weight of the first compound is Mz, 1.8≤Mz / Mw≤3.

5.

4. The secondary battery according to claim 3, wherein 2.0≤Mz / Mw≤2.

4.

5. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1) The first compound includes at least one of β-polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, or nanofiller-polyvinylidene fluoride-based composite materials; (2) The ionic conductivity of the first compound is σS / cm, 1.0×10 -4 ≤σ≤5×10 -4 ; (3) In the X-ray diffraction spectrum of the first compound, first characteristic peaks are present in the ranges of 19° to 21°, 34° to 35°, and 38° to 41°; (4) In the infrared spectrum of the first compound, at 470 cm -1 Up to 475cm -1 、507cm -1 Up to 515cm -1 、830cm -1 Up to 850cm -1 、1275cm -1 to 1290cm -1 There is a second characteristic peak in the range; (5) The first compound includes silicon, iron, and zinc, and the sum of the mass of the silicon, iron, and zinc in the first compound is W, where W is less than 200 ppm; (6) The mass change rate of the first compound after immersion in the electrolyte at 85°C for 24 hours is m%, and 15≤m≤45.

6. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1) The crystallinity of the first compound is X%, 20≤X≤70; (2) The melting point of the first compound is Tm°C, 130≤Tm≤175; (3) The crystallization temperature of the first compound is Tc°C, 120≤Tc≤155.

7. The secondary battery according to claim 1, wherein The crystallinity of the first compound is X%, and 40≤X≤50.

8. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1) The compaction density of the positive electrode material layer is PD g / cm 3 , 3.0≤PD≤4.5; (2) The contact angle between the positive electrode sheet and the electrolyte is θ, 10°≤θ≤60°; (3) The Dv50 of the positive electrode active material satisfies the following conditions: 0.5 μm ≤ Dv50 ≤ 35 μm; (4) The thickness of the positive electrode current collector is H1 μm, 7≤H1≤20.

9. The secondary battery according to claim 1, which satisfies at least one of the following characteristics: (1) The compaction density of the positive electrode material layer is PD g / cm 3 , 3.8≤PD≤4.4; (2) The contact angle between the positive electrode sheet and the electrolyte is θ, 10°≤θ≤30°; (3) The Dv50 of the positive electrode active material satisfies the following conditions: 10 μm ≤ Dv50 ≤ 25 μm; (4) The thickness of the positive electrode current collector is H1 μm, 8≤H1≤12.

10. The secondary battery according to claim 1, wherein The porosity of the positive electrode material layer is P%, 18.7≤P≤35.3; based on the total pore volume of the positive electrode material layer, the volume percentage of pores with a pore diameter greater than 50 nm is V1%, 74≤V1≤97.

11. The secondary battery according to claim 1, wherein The distribution ratio of the positive electrode binder on the surface of the positive electrode active material particles is S1%, 81≤S1≤92.

12. The secondary battery according to claim 1, wherein The positive electrode conductive agent includes conductive carbon and carbon nanotubes, and the positive electrode conductive agent meets at least one of the following characteristics: (1) The conductive carbon comprises at least one of Super P, carbon nanofiber, flake graphite, acetylene black, Ketjen black, carbon dots or graphene; (2) In the Raman spectrum of the carbon nanotubes, at 1300 cm -1 to 1400cm -1 There is a peak intensity of I in the range D The third characteristic peak at 1550cm -1 to 1650cm -1 There is a peak intensity of I in the range G The fourth characteristic peak, 0.72≤I D / I G ≤0.77; (3) The diameter of the carbon nanotube is D nm, 4≤D≤20.

13. The secondary battery according to claim 1, wherein In a scanning electron microscope image of the positive electrode material layer within a range of 85 μm×120 μm, the distribution ratio of the positive electrode conductive agent on the surface of the positive electrode material layer is S2%, and 47.8≤S2≤57.

7.

14. The secondary battery according to claim 1, wherein The bonding force between the positive electrode material layer and the positive electrode current collector is FN / m, 13.00≤F≤28.

29.

15. The secondary battery according to claim 1, wherein The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide or lithium iron phosphate.

16. The secondary battery according to claim 1, wherein The thickness of the positive electrode material layer on one side of the positive electrode current collector is H2 μm, and 44.44≤H2≤66.

67. 17 . An electronic device comprising the secondary battery according to claim 1 .

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