Lithium-ion secondary battery, battery device and power-consuming device

Abstract

Lithium-ion secondary battery, characterized in that it comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises lithium-containing transition metal phosphate particles, wherein at least a part of the surface thereof is provided with a carbon coating material, and where the median C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C-value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is greater than or equal to 0.95 and less than or equal to 1.20, and where the concentration of the C-values ​​(C 90 -C 10 ) / C 50 0.01-0.04; where the graphitization C value I G / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1 stands.

Description

TECHNICAL AREA

[0001] The present application relates to the technical field of lithium-ion batteries, in particular a lithium-ion secondary battery, a battery device, a power-consuming device. STATE OF THE ART

[0002] In recent years, secondary batteries have been used in a variety of fields, such as energy storage systems for hydroelectric, thermal, wind and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment and aerospace.

[0003] The active cathode material is a crucial component of lithium-ion secondary batteries, and lithium-containing transition metal phosphate materials possess significant development potential due to their stable structure, good safety, and long cycle life. Given the market demands for energy density and kinetics in lithium-containing transition metal phosphate secondary batteries, it is challenging for existing technology to simultaneously improve upon these performance characteristics, making this a pressing technical problem in the field. REVELATION OF THE INVENTION

[0004] The present application is filed with regard to the above-described subject of investigation and aims to provide a lithium-ion secondary battery that combines high energy density and good kinetic performance.

[0005] A first aspect of the present application provides a lithium-ion secondary battery comprising a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, and wherein the cathode film layer comprises an active cathode material, and wherein the active cathode material comprises lithium-containing transition metal phosphate particles, and wherein at least a part of the surface thereof is provided with a carbon coating material, and wherein the median C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C-value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is greater than or equal to 0.95 and less than or equal to 1.20, and where the concentration of the C-values ​​(C 90 -C 10 ) / C 500.01–0.04; where the graphitization C value I G / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 stands.

[0006] In the embodiment of the present application, the median is C 50 the degree of graphitization is greater than or equal to 0.95 and less than or equal to 1.20, while the concentration of the C values ​​(C 90 -C 10 ) / C 50The graphitization is controlled to 0.01-0.04, indicating that the particles in the cathode film layer have a high degree of graphitization and a high degree of consistency of graphitization. This means that the active cathode material exhibits good uniformity and consistency of the coating. It is also possible to reduce the impedance of particle sliding caused by the low degree of graphitization of the particles in the active cathode material and the resulting local stress concentration. Therefore, the uniform and consistent sliding between the particles of the active cathode material can lead to the electrode foil achieving a higher pressing density under the relatively low roller pressure. At the same time, the uniform and consistent degree of graphitization is conducive to achieving the uniform and consistent insertion and removal of lithium ions.to improve the electrode foil density and the battery energy density while maintaining good kinetic performance. In each embodiment, the median C is 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.96-1.15, optionally 0.98-1.13.

[0007] The median C 50 The degree of graphitization of the cathode film layer within the above range contributes to further improving the sliding ability between the particles and further increasing the pressing density of the electrode foil while maintaining the good kinetic performance of the battery, thereby achieving a balance between the kinetic power and the energy density of the battery.

[0008] In each embodiment, the concentration of C values ​​(C 90 -C 10 ) / C 50 in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.02-0.038, optionally 0.02-0.036.

[0009] The concentration of C values ​​(C 90 -C 10 ) / C 50 Within the above range, this contributes to further improving the consistency of the graphitization degree of the particles in the cathode film layer, improving the consistency of the sliding between the particles, and reducing the inconsistency of the lithium incorporation rate in the cathode film layer due to the poor consistency of the graphitization degree and the resulting local polarization, thereby further improving the kinetic performance of the battery while maintaining the good energy density of the battery.

[0010] In each embodiment, C90 of the graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer is 1.0-1.30, optionally 1.02-1.15.

[0011] C90, the graphitization level within the above range, is closer to the median C. 50 of the degree of graphitization, which indicates that the graphitization degree distribution interval of the particles in the cathode film layer is narrow, contributing to a uniform sliding between the particles to improve the pressing density of the electrode foil.

[0012] In each embodiment, C is 10 of the graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.92-1.10, optionally 0.98-1.08.

[0013] C10 The degree of graphitization within the above range indicates that the various locations in the cathode film layer have a high degree of graphitization, which contributes to the uniform sliding of the particles, reduces the probability of local stress concentrations occurring, and further improves the pressing density of the electrode foil.

[0014] In each embodiment, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with an area of ​​0.001 µm² is 2 -0.06 µm 2 21.00%-27.00% and the area fraction of particles with an area of ​​1.0 µm 2 -4.0 µm 2 12.00%-20.00%.

[0015] Control of the area fraction of particles with an area of ​​0.001 µm 2 -0.06 µm 2 and the area fraction of the particles with an area of ​​1.0 µm 2 -4.0 µm 2The active cathode material within the above range, together with a uniformly high degree of graphitization, allows for uniform particle sliding during the electrode foil compaction process, increasing the electrode foil density while simultaneously reducing negative effects on other battery performance characteristics such as kinetic power, cycle life, and processing power, thus comprehensively improving battery performance.

[0016] In each embodiment, D in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil A50 The particles are 600 nm–800 nm, optionally 650 nm–750 nm, where D A50 refers to the corresponding particle size when the cumulative area distribution of the particles reaches 50% in the cumulative area distribution curve.

[0017] The particle size D A50The number of particles within the above range indicates that a certain number of large particles are present in the cathode film layer. Controlling the average particle size D A50 The particle size within the above area not only improves the transmission efficiency of the roller pressure between the electrode foil particles due to the large contact area between the large-format particles, fully utilizes the skeletal support function of the large-format particles, allows the electrode foil to withstand higher roller pressure and improves the pressing density of the electrode foil, but also reduces the decrease in kinetics caused by the excessive size of the particles and maintains the kinetic performance of the battery while simultaneously improving the pressing density of the electrode foil.

[0018] In each embodiment, the median R in the cumulative distribution curve of the roughness area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 roughness 0.92-0.96.

[0019] The surface area of ​​the particles with median R A50 The roughness within the above area is relatively smooth, and the friction between the particles is relatively small, making it easy to slide under the influence of an external force. Together with the particles having a high degree of graphitization, an increase in the pressing density of the electrode foil at low rolling pressure can be achieved to further improve the energy density of the battery.

[0020] In each embodiment, the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is L A90 Sphericity 0.80-0.95, optionally 0.85-0.93.

[0021] In each embodiment, the median L in the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 Sphericity 0.65-0.85, optionally 0.70-0.80.

[0022] The particles with median L A90 and L A50The sphericity within the above range is approximately spherical, and it is easy for the particles to slide under the influence of an external force, and together with the particles with a high degree of graphitization, an increase in the pressing density of the electrode foil at low rolling pressure can be achieved to further improve the energy density of the battery.

[0023] In each embodiment, the iron dissolution rate of the cathode film layer is 500 ppm-2000 ppm, optionally 500 ppm-1500 ppm.

[0024] The active cathode material, with an iron dissolution rate within the range mentioned above, exhibits a relatively complete and dense carbon coating layer. This layer improves electrical contact between the active cathode materials, increases the electrical conductivity of the active cathode material, reduces its polarization, and further optimizes the kinetic performance of the lithium-ion secondary battery. Simultaneously, the densely coated carbon layer has a low space occupancy rate, and the particle gap is easily compressed by the stress during the roller pressing process. Furthermore, the highly graphitized carbon coating layer is conducive to improving the electrode foil's pressing density and the battery's energy density.

[0025] In each embodiment, the mass content of carbon is 0.8%-1.8%, optionally 0.90%-1.5%, based on the total mass of the active cathode material.

[0026] The active cathode material has a relatively low carbon coating content compared to the active cathode material of the prior art lithium-containing transition metal phosphate, which can further increase the loading of the lithium-containing transition metal phosphate in the cathode foil and improve the energy density of the lithium-ion secondary battery.

[0027] In each embodiment, the lithium and iron antisite defect concentration of the active cathode material is 0.1%-1.5%, optionally 0.3%-1.0%.

[0028] In the embodiment of the present application, the active cathode material with a low lithium iron antisite defect promotes the uniform transport of lithium ions in the solid phase, thereby further improving the kinetic performance of the lithium-ion secondary battery.

[0029] In each embodiment, the lithium-containing transition metal phosphate comprises a component with the following general formula: Li m Fe x P y O j Q q , where Q comprises one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and where 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, 0 <q≤0,1 ist.

[0030] The selection of the appropriate modification element Q improves the ion diffusion path of the active cathode material, improves the lithium ion diffusion rate of the active cathode material, and improves the kinetic performance of the battery.

[0031] In each embodiment, the active cathode material comprises one or more of the following materials: lithium iron phosphate and its doped modified material, as well as coated modified material.

[0032] In each embodiment, the active cathode material comprises titanium, and the mass content of titanium is 2000 ppm-6000 ppm relative to the total mass of the active cathode material.

[0033] The active cathode material in the embodiment of the present application has a high titanium content, and surprisingly, the high addition of titanium does not form a harmful impurity phase that negatively affects the energy density and kinetic performance of the battery, and the reason for this is unclear, but it is suggested that titanium and lithium together with the phosphate ion as well as with other elements form a fast ion conductor which instead improves the kinetic performance of the battery.

[0034] In each embodiment, the powder bulk density of the active cathode material is 0.70 g / cm³. 3 -1.50 g / cm² 3 , optional 0.70 g / cm² 3 -1.20 g / cm² 3 .

[0035] The active cathode material in the embodiment of the present application has a relatively low powder bulk density, and with the help of the high degree of graphitization of the cathode film layer and the good consistency of the degree of graphitization, it is easy for the active cathode material to slide under the action of an external force in order to achieve an increase in the powder compaction density.

[0036] In each embodiment, the powder density of the active cathode material is 2.50 g / cm³ under a pressure of 3 T. 3 -2.70 g / cm² 3 , optional 2.52 g / cm² 3 -2.68 g / cm² 3 .

[0037] With the help of a high degree of graphitization and good consistency of the graphitization degree, the active cathode material can still achieve a high pressing density under the influence of an external force, in order to create a material basis for improving the pressing density of the electrode foil and for the production of a lithium-ion secondary battery with high energy density.

[0038] In each embodiment, the powder resistance of the active cathode material under a pressure of 8MPa is 0.5 Ω·cm-30 Ω·cm, optionally 2 Ω·cm-20 Ω·cm.

[0039] The active cathode material has a high degree of graphitization, therefore it can easily achieve the rapid conduction of electrons between particles via the sp2 structure of carbon on the surface, giving the active cathode material a low powder resistance, which contributes to increasing the solid-phase electron transport rate to further improve the kinetic performance of the battery.

[0040] In each embodiment, the discharge gram capacity of the active cathode material is 135 mAh / g-150 mAh / g at room temperature at a discharge rate of 1 C.

[0041] The high discharge gram capacity of the active cathode material at a C-rate of 1 C indicates that it has good charging and discharging capabilities, which contributes to improving the kinetic performance of the battery.

[0042] In each embodiment, the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, where η is defined as follows: a button cell comprising the active cathode material is charged and discharged twice in a voltage range of 2.0 V to 3.75 V at a C-rate of 0.1 C with a constant current, and subsequently once at a C-rate of 1 C with a constant current. The capacity value extracted in the charge and discharge test at a C-rate of 1 C with a discharge voltage of 3.2 V is recorded as C1, and the capacity value extracted at a discharge voltage of 2.0 V is C2, and n = C1 / C2, and wherein the charging process comprises a constant-voltage charge at a constant voltage of 3.75 V and a constant-voltage cutoff current of 50 µA.

[0043] A high discharge capacity percentage of the active cathode material used in the lithium-ion secondary battery of the embodiment of the present application when discharged to 3.2 V implies that the active cathode material has good kinetic performance. At the same time, the high η value indicates that the lithium-ion secondary battery comprising the active cathode material still exhibits a high voltage when discharged to a low state of charge (SOC), which is conducive to maintaining good performance.

[0044] In each embodiment, the mass content of the conductive medium is 0-1.5% relative to the total mass of the cathode film layer.

[0045] The carbon layer of the active cathode material exhibits a high degree of graphitization and good consistency of graphitization; therefore, the active cathode material has good electronic conductivity, which reduces and even eliminates the use of the conductive agent in the cathode film layer, thus helping to further increase the charging of the active cathode material and improve the energy density of the lithium-ion secondary battery.

[0046] In each embodiment, the mass content of the conductive medium is 0, relative to the total mass of the cathode film layer.

[0047] The active cathode material has extremely good electronic conductivity, which makes it possible to even eliminate the use of the conductive agent in the cathode film layer, which helps to further increase the charging of the active cathode material and improve the energy density of the lithium-ion secondary battery.

[0048] In each embodiment, the cathode film layer further comprises a binder, and, based on the total mass of the cathode film layer, the mass content of the active cathode material is 95.5%-99.5%, optionally 96.5%-99.5%; and the mass content of the binder is 0.5%-3%.

[0049] In each embodiment, the one-sided areal density of the cathode film layer is 300 mg / 1540 mm². 2 -450 mg / 1540 mm 2 .

[0050] A cathode film layer with an areal density within the above range can contribute to improving the energy density of the lithium-ion secondary battery.

[0051] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.51 g / cm³. 3 -2.73 g / cm² 3 .

[0052] The pressure density of the cathode film layer is within the above range, which is beneficial for improving the energy density of the lithium-ion secondary battery.

[0053] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.55 g / cm³. 3 -2.70 g / cm² 3 .

[0054] The pressure density of the cathode film layer is within the above range, which is beneficial for improving the energy density of the lithium-ion secondary battery.

[0055] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.51 g / cm³. 3 -2.73 g / cm² 3 , and in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is 10%-22%.

[0056] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.55 g / cm³. 3 -2.70 g / cm² 3 , and in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is 10%-20%.

[0057] The lower porosity in a cross-sectional area of ​​the cathode film layer in the embodiment of the present application means, on the one hand, that the gradation of large, medium and small particles in the cathode film layer is better while the pressing density is high, and on the other hand, after the same gradation and the same rolling pressure, if the porosity is low, it means that the particles can easily slip against each other, thus reducing the risk of overpressure in the film layer and the risk of stress concentration, and further reducing the probability of demolding of the cathode film during the long cycle process, which contributes to improving the long cycle performance of the battery.

[0058] In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the cathode collector; wherein the lower coating comprises carbon-based particles, wherein the distribution density of the carbon-based particles with a particle size of more than 100 nm in the lower coating is ≤ 10 pcs / 10 µm;

[0059] The lower coating contributes to increasing the electrical conductivity and bond strength of the cathode film layer and the collector, and to reducing demolding of the cathode film layer from the collector during the cycling process, while improving the kinetic performance of the battery. In the high-density electrode foil of the embodiment of the present application, controlling the distribution density of carbon-based particles with a particle size greater than 100 nm to ≤ 10 pcs / 10 µm contributes to reducing the probability of damage to the collector in the high-density electrode foil and further improving the limiting density of the cathode foil.

[0060] In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the cathode collector; wherein the density of the cathode foil in a fully discharged state is greater than or equal to 2.4 g / cm³ 3 is, where the one-sided thickness of the lower coating is 1 µm-4 µm.

[0061] In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the cathode collector; wherein the density of the cathode foil in a fully discharged state is greater than or equal to 2.5 g / cm³ 3 is, where the one-sided thickness of the lower coating is 2 µm-4 µm.

[0062] As the electrode film's density increases, the extrusion effect of large particles of lithium-containing phosphate materials (e.g., with a particle size greater than 1 µm) in the cathode film layer on the bottom coating becomes increasingly significant. Consequently, these large particles tend to create stress concentrations at certain points and even penetrate the collector, damaging the bottom coating. Increasing the thickness of the bottom coating helps to mitigate this stress concentration phenomenon in the electrode film and further increase the electrode film's limiting density.

[0063] A second aspect of the present application provides a battery device comprising at least one lithium-ion secondary battery provided by the first aspect of the present application, wherein the battery device comprises at least one of the battery module, the battery pack and the energy storage battery.

[0064] A third aspect of the present application provides a power-consuming device comprising a lithium-ion secondary battery provided by the first aspect of the present application or a battery device provided by the second aspect of the present application.

[0065] An unclaimed aspect of the present application provides a method for producing an active cathode material, comprising: obtaining a mixed crude material comprising a carbon source, a lithium source, an iron source, and a phosphorus source; wherein the carbon source comprises polyethylene glycol; wherein the iron source comprises iron(II); wherein the molar ratio of iron and phosphorus in the mixed crude material is greater than or equal to 0.95 and less than or equal to 1; milling in a solvent to obtain a mixed slurry; drying the mixed slurry to obtain a precursor powder; sintering the precursor powder to obtain an active cathode material; wherein the sintering comprises at least two constant-temperature sintering stages, the high-temperature sintering temperature being 750°C–800°C.

[0066] The cathode film layer, which is produced from the active cathode material manufactured by the process, has a high degree of graphitization as well as good consistency of the graphitization level, can easily improve the pressing density of the electrode foil by uniform and consistent sliding between the particles and is conducive to improving the energy density of the battery while simultaneously improving the kinetic performance of the battery.

[0067] Another unclaimed aspect of the present application provides a method for producing a cathode foil, wherein the production method comprises: dry mixing of a binder, a conductive agent and an active cathode material obtained by the method in the fourth aspect, adding a solvent, stirring to obtain a shipping slurry; transferring and applying the shipping slurry to at least one side of the collector, drying and hot pressing to obtain a cathode foil.

[0068] In each embodiment, the circulation speed of the dry mixing is 20 rpm-30 rpm and the rotation speed of the dry mixing is 750 rpm-850 rpm.

[0069] In each embodiment, the hot pressing comprises at least three hot rolling presses, wherein the hot rolling pressure increases sequentially and is successively 20 tonnes-50 tonnes, 50 tonnes-70 tonnes and 70 tonnes-90 tonnes; and wherein the hot rolling temperature is 40°C-80°C, and wherein the electrode foil is heated prior to the first entry into the hot rolling press, the temperature of the heating being 40°C-50°C.

[0070] The active cathode material, produced using the above hot pressing process in conjunction with the manufacturing process of the fourth aspect, helps to further reduce the porosity of the cut surface of the cathode film layer, increase the boundary pressing density of the electrode foil, and improve the energy density of the battery. PRESENTATION OF THE INVENTION Fig.Figure 1 shows a scanning electron microscope image of a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil in an embodiment of the present application; Fig. Figure 2 shows a schematic diagram of a lithium-ion secondary battery in an embodiment of the present application; Fig. Figure 3 shows a schematic disassembly diagram of a lithium-ion secondary battery in an embodiment of the present application; Fig. Figure 4 shows a schematic diagram of a battery module in an embodiment of the present application; Fig. Figure 5 shows a schematic diagram of a battery pack in an embodiment of the present application; Fig. Figure 6 shows a schematic disassembly diagram of a battery pack according to Fig. 5; Fig.Figure 7 shows a schematic diagram of a power-consuming device which uses a lithium-ion secondary battery as a power source in an embodiment of the present application; Fig. Figure 8 shows a diagram of a porosity test of a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil in an embodiment of the present application. Reference symbol list: 1 battery pack 2 Upper Case 3 Lower Case 4 battery modules 5 lithium-ion secondary batteries 51 cases 52 Electrode component 53 Cover plate SPECIFIC EXECUTION FORMS

[0071] The following describes in detail embodiments of the lithium-ion secondary battery, the battery device, the current-consuming device, the method for producing an active cathode material, and the method for producing a cathode foil of the present application with reference to the accompanying drawings. However, there will be instances where an unnecessarily detailed description is omitted. For example, detailed descriptions of things that are already well known and repeated descriptions of the same structure are omitted. This is to avoid making the following description unnecessarily long and to facilitate understanding for the person skilled in the art.Furthermore, the attached drawings and the following description serve to provide a person skilled in the art with a complete understanding of the present application and are not intended to limit the subject matter specified in the claims.

[0072] The "range" disclosed here is defined in terms of a lower bound and an upper bound, with a particular range being defined by selecting a lower bound and an upper bound that establish the limits of that range. Ranges defined in this way can include or exclude end values ​​and can be combined in any way; that is, any lower bound can be combined with any upper bound to form a range. For example, if a range of 60-120 and 80-110 is specified for a particular parameter, a range of 60-110 and 80-120 is also to be expected. Furthermore, if the minimum values ​​1 and 2 and the maximum values ​​3, 4, and 5 are specified, the following ranges can be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.Unless otherwise specified, the range "ab" denotes any combination of real numbers between a and b, where both a and b are real numbers. For example, the range "0-5" means that all real numbers between 0 and 5 are listed here, and 0-5 is simply a shorthand representation of the combination of these values. Furthermore, stating that a parameter is an integer ≥ 2 is equivalent to stating that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on.

[0073] Unless expressly stated otherwise, all embodiments and optional embodiments of the present application may be combined to form new technical solutions, and such a technical solution should be considered to be covered by the disclosure of the present application.

[0074] Unless expressly stated otherwise, all technical features of the present application, as well as optional technical features, may be combined to form a new technical solution, and such a technical solution should be considered to be covered by the disclosure of the present application.

[0075] Unless expressly stated otherwise, all steps of the present application may be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out one after the other, or that it may include steps (b) and (a) carried out one after the other. The indication that the method may also include step (c) means, for example, that step (c) may be added to the method in any order; e.g., the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b).

[0076] In the present application, the terms "plural" and "multiple" refer to two or more.

[0077] Unless otherwise stated, the terms used in this application have the known meanings as generally understood by those skilled in the art.

[0078] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined by various test methods commonly used in practice, e.g., according to the test methods specified in the embodiments of this application. Unless otherwise specified, the test temperature for each parameter is 25°C.

[0079] The batteries mentioned in the embodiments of the present application can be a single physical module comprising one or more lithium-ion secondary batteries to achieve a higher voltage and capacity. The batteries mentioned in this application can be, for example, lithium-ion secondary batteries, battery modules, or battery packs.

[0080] The lithium-ion secondary battery is the smallest unit that constitutes the battery and is solely capable of performing the charging and discharging functions. The lithium-ion secondary battery can have the form of a cylinder, a rectangular body, or other shapes, etc., and the embodiments of the present application are not limited thereto. Fig. Figure 2 shows an example of a lithium-ion secondary battery 5 with a rectangular structure.

[0081] The lithium-ion secondary battery comprises an electrode component and an electrolyte.

[0082] The lithium-ion secondary battery may also include an outer casing used to encapsulate the electrode components and the electrolyte. This outer casing can be a rigid housing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. Alternatively, it can be a flexible casing, such as a pouch-like soft casing. The flexible casing can be made of plastic, for example, one or more of the following materials: polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0083] In some embodiments, such as in Fig.As shown in Figure 3, the outer packaging can comprise a housing 51 and a cover plate 53. The housing 51 can include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening that communicates with the receiving cavity, and the cover plate 53 serves to cover the opening to close the receiving cavity. The electrode component 52 is encapsulated within the receiving cavity. The number of electrode components 52 contained in the lithium-ion secondary battery 5 can be one or more and can be adapted as required.

[0084] The electrode component typically comprises a cathode foil and an anode foil, the anode foil being the electrode where the reaction of uptake or lithiation of lithium ions during charging and release or delthiation of lithium during discharging takes place, and the cathode foil being the electrode where the reaction of release or delthiation of lithium ions during charging and uptake or lithiation of lithium during discharging takes place.

[0085] In multiple lithium-ion secondary batteries, the multiple lithium-ion secondary batteries are connected in series, parallel, or a mixed configuration via a sink component. In some embodiments, the battery may be a battery module; in the case of multiple lithium-ion secondary batteries, the multiple lithium-ion secondary batteries are arranged and secured to form a battery module. In some embodiments, the battery may be a battery pack comprising a housing and a lithium-ion secondary battery, with the lithium-ion secondary battery or battery module being housed within the housing. In some embodiments, the housing may be part of a vehicle chassis structure. For example, parts of the housing may be at least part of a vehicle chassis, or parts of the housing may be at least part of a crossmember and a longitudinal member of the vehicle.

[0086] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, and the like.

[0087] In some embodiments, the lithium-ion secondary batteries can be assembled into a battery module, and the number of lithium-ion secondary batteries contained in the battery module can be a plurality, with the exact number being adjustable depending on the application and capacity of the battery module. Fig. Figure 4 is a schematic diagram of battery module 4 as an example. As in Fig.As shown in Figure 4, the multiple lithium-ion secondary batteries 5 in the battery module 4 can be arranged sequentially along a longitudinal direction of the battery module 4. Of course, they can also be arranged in any other desired manner. Furthermore, the multiple lithium-ion secondary batteries 5 can be secured by fastening elements.

[0088] Optionally, the battery module 4 can also include a casing with a receiving space in which the multitude of lithium-ion secondary batteries 5 are housed.

[0089] In some embodiments, the battery modules described above can also be assembled into a battery pack, with the number of battery modules contained in the battery pack being adjustable depending on the application and capacity of the battery pack.

[0090] The Fig. 5 and Fig. Figure 6 shows schematic diagrams of battery pack 1 as an example. As in Fig. 5 and Fig. As shown in Figure 6, the battery pack 1 can comprise a housing and a plurality of battery modules 4 arranged within the housing. The housing comprises an upper housing 2 and a lower housing 3, the upper housing 2 serving to cover the lower housing 3 and form an enclosed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged within the housing in any desired configuration.

[0091] Lithium-containing transition metal phosphates are frequently used in lithium-ion batteries due to their high capacity, structural stability, good safety, and good cycle performance. However, they suffer from problems with low electronic conductivity and low stacking efficiency, which in turn makes it difficult to further improve the charging of lithium-containing transition metal phosphates per unit volume of batteries, and the requirements for high-energy-density batteries cannot be met.

[0092] To further improve battery energy density and increase electrode foil density, the particle size distribution is commonly improved in the industry. Increasing particle size distribution often requires increasing particle size or the ratio of large to small particles. However, increasing the ratio of large particles reduces the battery's kinetic energy, while increasing the ratio of small particles significantly increases processing costs, causes serious side reactions in the battery, and reduces its cycle life. How to further improve electrode foil density to achieve high-energy-density batteries without significantly compromising other battery performance is a pressing technical challenge in this field.

[0093] A first aspect of the present application provides a lithium-ion secondary battery comprising a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, and wherein the cathode film layer comprises an active cathode material, and wherein the active cathode material comprises lithium-containing transition metal phosphate particles, and wherein at least a part of the surface thereof is provided with a carbon coating material, and wherein the median C 50 of the degree of graphitization in the cumulative distribution curve for the C-value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is greater than or equal to 0.95 and less than or equal to 1.20, and where the concentration of the C-values ​​(C 90 -C 10 ) / C 500.01–0.04; where the graphitization C value I G / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm - 1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1 stands.

[0094] In the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, the median C 50A graphitization degree of less than 0.95 indicates poor sliding properties between the particles of the cathode film layer, making it difficult to achieve dense stacking through sliding between particles under pressure. This easily leads to stress concentration and makes it difficult to achieve a high electrode film density. Simultaneously, studies show that increasing the graphitization degree of the cathode film layer often requires increasing the sintering temperature of the active cathode material. While improving process conditions contributes to increasing the graphitization degree of the cathode film layer, it is limited by the uniformity of the temperature field and other factors. Furthermore, increasing the graphitization degree of the particles can easily compromise their homogeneity.The studies indicate that a concentration of C values ​​(C. 90 -C 10 ) / C 50 A value greater than 0.04 leads to an inconsistency in the lithium incorporation rate in the cathode film layer due to the poor consistency of the graphitization degree and then causes local polarization, which is not conducive to improving the kinetic performance of the battery.

[0095] The studies indicate that the median C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C-value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is greater than or equal to 0.95 and less than or equal to 1.20, and simultaneously the concentration of the C-values ​​(C 90 -C 10 ) / C 50is controlled to 0.01-0.04, indicating that the particles in the cathode film layer have a high degree of graphitization and a high degree of consistency of graphitization. This means that the active cathode material exhibits good uniformity and consistency of the coating, and it is possible to reduce the impedance of particle sliding caused by the low degree of graphitization of the particles in the active cathode material and the resulting local stress concentration. Thus, the uniform and consistent sliding between the particles of the active cathode material can lead to the electrode foil achieving a higher pressing density under the relatively low roller pressure. At the same time, the uniform and consistent degree of graphitization is conducive to achieving the uniform and consistent insertion and removal of lithium ions.to improve the electrode foil density and the battery's energy density, based on maintaining good kinetic performance of the battery.

[0096] In the embodiments of the present application, the uniform increase in the degree of graphitization of the particles in the cathode film layer makes it easy for the active cathode material to achieve uniform particle sliding with the aid of the carbon coating material of the particles in the rolling process to form the film, and the pressing density of the electrode foil is further improved, while maintaining the other performance levels of the battery, thus improving the overall performance of the battery.

[0097] Technicians in this field can adjust the graphitization concentration of the cathode film layer in any known way; for example, the adjustment of the graphitization concentration is achieved by selecting the carbon source, adjusting the amount of carbon coating, changing the particle size distribution, controlling the sintering temperature, and the sintering temperature rise rate.

[0098] In the present application, the term "particle" refers to particles in the field of view of the cathode film layer at a certain magnification, e.g. 10,000x, with recognizable complete boundaries, whereby defects and scratches may be present within the particles, but no complete boundaries sufficient to subdivide the particles are recognizable within the particles.

[0099] The particle identification method is as follows: the cathode film layer is cut by the argon ion beam along the thickness direction of the electrode foil (as an example, optional: instrument model: Leica EM TIC 3X CP, operating voltage: 6kV, operating time: 6h), and after exposure of the cut surface, a scanning electron microscope is used (as an example, optional: instrument model: Hitachi SU8230, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) to observe the cut surface of the cathode film layer along the thickness direction of the electrode foil.Images are acquired using a field emission scanning electron microscope (FESEM) in the non-marginal position of the cut surface of the cathode film layer (after observing the edge of the electrode foil under the scanning electron microscope, the field of view is adjusted to the central part of the sample) in secondary electron mode, and the electropherograms are recorded at 10k magnification. The particles in the electropherograms are analyzed using the software ImageJ (1.46r, Win64 version). The ImageJ software is used as follows: Loading the SEM image to be analyzed, as shown in [reference missing]. Fig.Figure 1 shows the process; identifying the particles using the Cellpose plug-in software and manually correcting them based on this; reading and counting the data using ImageJ. The specific method for using the Cellpose plug-in software to identify the particles is as follows: setting the segmentation diameter parameter (diameter in the segmentation module) to 15 pixels, clicking "run cyto3" to identify the particles; manually marking the particles in the image that are not identified, or not fully identified, or incorrectly identified by the software. The particles in the image that are not identified, or not fully identified, or incorrectly identified by the software include, in particular, the following: 1. the particles are too large or there are scratches on the surface of the particles, which prevents them from being identified, or prevents them from being identified completely;2. During the argon ion beam sectioning process, scratches are created on the surface of the particles, and the software may mistakenly interpret these scratches as particle boundaries during the identification process, leading to an identification error; 3. Because the particles are too small, they are not successfully identified; 4. The particles are located at the edge of the electron microscope's field of view, and the interior of the particles is penetrated by the edge, the morphology is not fully displayed, and the local part is identified instead of the whole, resulting in an identification error. The aforementioned unidentified or incorrectly identified particles are calibrated manually, and the specific process is as follows: deleting the particles located at the edges of the scanning electron microscope environment that are not fully displayed;Assess whether or not there is a slit scratch within the other unidentified or incorrectly identified particles; if there is no slit scratch within a particle, it is assessed as a single particle and manually marked according to the manually observed particle boundaries; in response to the presence of a slit scratch within the particle, assess whether the slit scratch runs through the particle; if it does not run through the particle, assess that it is a single particle and manually mark it; in response to the slit scratch running through the particle, assess whether the slit scratch is linear or irregular; in response to the slit scratch being irregular, assess that it is a boundary between the particles and divide the particles along the boundary;In response to the finding that the slit scratch is linear, a contrast comparison is performed; in response to the finding that the contrast comparison is not obvious and there is no cracking effect, the slit scratch is judged as a scratch and marked as a single particle; in response to the finding that the contrast comparison is strong and there is a cracking effect, the slit scratch is judged as a boundary between particles and marked as two particles. After manual marking, the information unrelated to the particles in the automatic image processing is deleted, i.e., the assessment and marking of the particles in the image is complete.

[0100] Lithium-containing transition metal phosphates refer to phosphate materials comprising lithium and a transition metal element and can be detected by any known method in this field. For example, they can be detected by a combination of X-ray diffraction (XRD) with an energy spectrum analyzer and an inductively coupled plasma mass spectrometer. Lithium-containing transition metal phosphates include, but are not limited to, lithium iron phosphate, lithium manganese iron phosphate, and their dopants.

[0101] The carbon coating layer, which covers at least part of the surface of the lithium-containing transition metal phosphate, can be detected by any method known in the art. For example, the carbon coating layer covering at least part of the surface of the lithium-containing transition metal phosphate can be observed by characterizing the lithium-containing transition metal phosphate using a combination of transmission electron microscopy and an energy spectrum analyzer. It should be noted that the elements in the carbon coating layer are not limited to carbon, but may also include other elements besides carbon. The carbon coating layer is not limited to the form of a film, but may also be island-like, irregular, or a discontinuous coating.

[0102] Carbon has excellent electrical conductivity, which facilitates the transfer of electrons, and applying the carbon coating layer can significantly improve the electronic conductivity of the lithium-containing transition metal phosphate material.

[0103] In some embodiments, the median is C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C-value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, greater than or equal to 0.95 and less than or equal to 1.20, where the concentration of the C-values ​​(C 90 -C 10 ) / C 50 0.01–0.04; where the graphitization C value I G / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1stands.

[0104] In the present application, the graphitization C-value of the cathode film layer can be obtained in the area-scanning mode of a laser microconfocal Raman spectrometer. As an example, a laser microconfocal Raman spectrometer (a high-precision Renishaw laser microconfocal Raman spectrometer) is used, an excitation wavelength of 532 nm is selected, and a suitable amount of the cathode film layer is taken for area scanning of the surface or a cross-sectional area along the thickness direction of the electrode foil. The scanning area is 45 µm × 45 µm, subdivided into 10 × 10 grids, with the vertex of the grid serving as the test point. The step size is 5 µm, and the total number of scan points is 100 to obtain the C-values ​​at various locations and the cumulative distribution curve of the C-values ​​in the area-scanning area.

[0105] The cathode film layer in the present application can be either a freshly produced cathode film layer or a cathode film layer obtained by dismantling a battery. The surface of the cathode film layer obtained by dismantling the battery inevitably contains residues of electrolyte salt particles, and to improve the accuracy of the test, an area scan of a cross-sectional area of ​​the cathode film layer is preferably performed along the thickness direction of the electrode foil to characterize the degree of graphitization of the cathode film layer.

[0106] The graphitization C value of the cathode film layer is obtained from the peak intensity ratio of the G-peak (G-band) and the D-peak (D-band) of the Raman spectra, with the position of the G-peak at 1580±100 cm⁻¹ -1lies and characterizes the sp2 hybrid structure of carbon, and where the position of the D-peak is at 1350±100 cm -1The C value characterizes the disordered structure of carbon, where disorder means there is no regular arrangement between the carbon atoms in the structure. In graphite crystals, the carbon atoms in the same layer are sp²-hybridized and form covalent bonds. Van der Waals forces act between the layers, allowing the carbon to slide easily within the graphite structure. Therefore, the C value can characterize the degree of graphitization of the cathode film layer. The higher the value, the higher the degree of graphitization of the carbon material. It is important to understand that the degree of graphitization in the cathode film layer is primarily due to the graphitized carbon material within the cathode film layer, i.e., the carbon coating layer of the active cathode material.Although conductive materials such as carbon nanotubes rich in sp2-hybridized structures also exhibit relatively high IG / ID values, their incorporation into the cathode film layer proves to be an extreme value in the Raman area scanning test of the cathode film layer due to their low additive content and small tube diameters, and they have no effect on the degree of graphitization C. 50 in the cathode film layer.

[0107] Therefore, the degree of graphitization of the cathode film layer can also be used to characterize the degree of graphitization of the active cathode material. The higher the degree of graphitization of the carbon on the surface of the active cathode material, and the higher the proportion of graphitic structural carbon in the cathode film layer, the more easily the particles can slide in the coating layer during the rolling process, aided by the carbon structure. This allows for an increase in the pressing density of the electrode foil under low rolling pressure.

[0108] The cumulative distribution curve for the graphitization carbon value is a curve obtained by arranging at least 100 carbon values ​​in order from smallest to largest, with the degree of graphitization on the horizontal axis and the cumulative amount on the vertical axis. 50A C-value is defined as a value where, in the cumulative distribution curve for the graphitization C-value, the cumulative fraction on the vertical axis is 50%. The median C 50 The graphitization degree, compared to a point value, can reflect the overall graphitization degree, i.e., the sliding ability of the particles in the cathode film layer; and compared to an average value, it can reduce the influence of extreme values ​​in the test process and improve the reliability of the test results.

[0109] A person skilled in this field can regulate the degree of graphitization of the active material particles using any known method. For example, the degree of graphitization of the active material particles can be adjusted by regulating the carbon source and optimizing the nucleation process, sintering temperature, sintering time, sintering pressure, and sintering atmosphere.

[0110] In some embodiments, the median C in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is 50 The degree of graphitization can optionally be 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20 or any value in a range between two of these values.

[0111] With reference to the above statements, C 90 Similarly, a C-value is obtained if, in the cumulative distribution curve for the graphitization C-value, the cumulative quantity fraction of the vertical axis is 90%, and C 10 A C value is reached when, in the cumulative distribution curve for graphitization C values, the cumulative fraction on the vertical axis is 10%. The concentration of C values ​​is expressed as (C 90 -C 10 ) / C50 . (C 90 -C 10 ) / C 50 It is able to reflect both the magnitude of most C values, regardless of polarity, and the width of the distribution of the graphitization degree of the particles in the cathode film layer. The low concentration of C values ​​in the cathode film layer indicates that the distribution of the graphitization degree of the particles in the cathode film layer is narrow and well concentrated.

[0112] In some embodiments, the concentration of C values ​​(C 90 -C 10 ) / C 50 in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, optionally 0.01, 0.02, 0.03, 0.04 or any value in a range between two of these values.

[0113] In some embodiments, the median is C 50of the degree of graphitization in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.96-1.15, optionally 0.98-1.13.

[0114] The median C 50 The degree of graphitization of the cathode film layer within the above range contributes to further improving the sliding ability between the particles and further increasing the pressing density of the electrode foil while maintaining the good kinetic performance of the battery, thereby achieving a balance between the kinetic power and the energy density of the battery.

[0115] In some embodiments, the concentration of C values ​​(C 90 -C 10 ) / C 50in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.02-0.038, optionally 0.02-0.036.

[0116] The concentration of C values ​​(C 90 -C 10 ) / C 50 Within the above range, this contributes to further improving the consistency of the graphitization degree of the particles in the cathode film layer, improving the consistency of the sliding between the particles, and reducing the inconsistency of the lithium incorporation rate in the cathode film layer due to the poor consistency of the graphitization degree and the resulting local polarization, thereby further improving the kinetic performance of the battery while maintaining the good energy density of the battery.

[0117] In some embodiments, C is 90of the graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 1.0-1.3, optionally 1.02-1.15.

[0118] In some embodiments, C in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is 90 The degree of graphitization can optionally be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3 or any value in a range between two of these values.

[0119] C 90 The degree of graphitization within the above range is closer to the median C. 50of the degree of graphitization, which indicates that the graphitization degree distribution interval of the particles in the cathode film layer is narrow, contributing to a uniform sliding between the particles to improve the pressing density of the electrode foil.

[0120] In some embodiments, C is 10 of the graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.92-1.1, optionally 0.96-1.08.

[0121] In some embodiments, C in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is 10The degree of graphitization can optionally be 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1 or any value in a range between two of these values.

[0122] C 10 The degree of graphitization within the above range indicates that the various locations in the cathode film layer have a high degree of graphitization, which contributes to the uniform sliding of the particles, reduces the probability of local stress concentrations occurring, and further improves the pressing density of the electrode foil.

[0123] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with an area of ​​0.001 µm is 2 -0.06 µm 2 21.00%-27.00% and the area fraction of particles with an area of ​​1.0 µm 2 -4.0 µm 2 12.00%-20.00%.

[0124] The area of ​​the particles in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is counted as follows. After particle assessment and labeling, the image is imported into the ImageJ software for analysis. The scale is then adjusted according to the scanning electron microscope image, and the particle size and area are analyzed using the "Feret Diameter" and "Area" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter obtained from the analysis represents the maximum distance between all parallel lines in the two-dimensional projection of the particles, which is used to characterize the particle size; and the "Area" parameter represents the pixel area of ​​the particle to characterize the particle's surface area.Since particles with a size of less than 50 nm are difficult to identify accurately due to large errors in the statistical process, and since the particle size of the conductive medium is generally less than 50 nm, which can cause large errors in the statistical results, particles with a size of less than 50 nm are not counted in the statistical process for the particle size of the present application, and the statistical data corresponding to the particles where Area is displayed as "NaN" are deleted. To achieve the number of statistically significant samples, at least 10 scanning electron microscope images with non-overlapping fields of view are collected for each electrode foil, and the area of ​​at least 5000 particles is counted, summing the "Area" parameters for the particles with an area of ​​0.001 µm. 2 -0.06 µm 2and the sum of the “area” parameters for all particles is calculated, each being defined as the area of ​​the particles with a surface area of ​​0.001 µm² 2 -0.06 µm 2 and the total surface area of ​​the counted particles is used. The sum of the surfaces of the particles with an area of ​​0.001 µm². 2 -0.06 µm 2 is divided by the total area of ​​the counted particles, which is the area fraction of the particles with an area of ​​0.001 µm². 2 -0.06 µm 2 in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, analogously the area fraction of the particles with an area of ​​1.0 µm 2 -4.0 µm 2 receive.

[0125] The morphology of the cut surface of the cathode film layer along the thickness direction of the electrode foil is in Fig.Figure 1 shows this. It differs from the state of the active cathode material in the Malvern laser scattering method and also from the state of the active cathode material when the active cathode material is directly observed by scanning electron microscopy. The particles in the cathode film layer are well dispersed under roller pressure, and observation of the cathode film layer is beneficial for the effective characterization of the particle size, particle area, and number of particles in the cathode film layer.

[0126] During the densification process of the cathode film layer, densification occurs in the thickness direction. Therefore, the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is, compared to the surface of the cathode film layer, better able to reflect the actual density of the particles within the film layer on a spatial scale. In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with a surface area of ​​0.001 µm² can be determined. 2 -0.06 µm 2 and the area fraction of the particles with an area of ​​1.0 µm 2 -4.0 µm 2 intuitively reflect the proportionality of a portion of the particles in the area segment to the total number of particles, which reflects the number of particles in that area segment.

[0127] It is understood that the particles in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, in particular the particles of 50 nm or more, originate mainly from the active cathode material. Therefore, the embodiment of the present application can accurately and objectively reflect the distribution of the lithium-containing transition metal phosphate particles in the cathode film layer of the electrode foil by observing and counting the particle size and the area of ​​the particles in a cross-sectional area of ​​the cathode film layer.

[0128] A person skilled in this field can achieve particle size control through any known method. For example, the growth rate and time of the cathode material are controlled by regulating the temperature and time during the cathode material manufacturing process. The mechanical force of comminution and grinding processes is used to process raw materials to the target particle size distribution, thereby achieving particle size control. Sieving and classification equipment is used to separate the particle sizes within the system, obtaining the particle size fraction that meets the requirements. Finally, the residence time and force state of the particles in the equipment are adjusted by precisely controlling the feed rate, which also contributes to particle size control.

[0129] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with an area of ​​0.001 µm is 2 -0.06 µm 2 21%, 22%, 23%, 24%, 25%, 26%, 27% or any value in a range between two of these values, where the area fraction of the particles has an area of ​​1.0 µm 2 -4.0 µm 2 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or any value in a range between any two of these values.

[0130] Control of the area fraction of particles with an area of ​​0.001 µm 2 -0.06 µm 2 and the area fraction of the particles with an area of ​​1.0 µm 2 -4.0 µm 2The active cathode material within the above range, together with a uniformly high degree of graphitization, allows for uniform particle sliding during the electrode foil compaction process, increasing the electrode foil density while simultaneously reducing negative effects on other battery performance characteristics such as kinetic power, cycle life, and processing power, thus comprehensively improving battery performance.

[0131] In some embodiments, the particle size D in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 the particles 600 nm-800 nm, optionally 650 nm-750 nm, where D A50 refers to the corresponding particle size when the cumulative area distribution of the particles reaches 50% in the cumulative area distribution curve.

[0132] The procedure for testing particle size D A50 The particle size distribution in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is as follows: Referring to the procedure described above, the particle sizes of at least 5000 particles are counted. The particle sizes of the at least 5000 particles obtained are arranged in order from smallest to largest, with the particle size as the horizontal axis and the cumulative area of ​​the particles as the vertical axis, in order to obtain the corresponding particle size when the cumulative area distribution curve of the particles reaches 50%.

[0133] In some embodiments, the particle size D A50of the particles in a cumulative area distribution curve of the particles of the active cathode material, which is obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, optionally 600 nm, 610 nm, 620 nm, 630 nm, 640 nm, 650 nm, 660 nm, 670 nm, 680 nm, 690 nm, 700 nm, 710 nm, 720 nm, 730 nm, 740 nm, 750 nm, 760 nm, 770 nm, 780 nm, 790 nm, 800 nm or any value in a range between two of these values.

[0134] The particle size D A50 The number of particles within the above range indicates that a certain number of large particles are present in the cathode film layer. Controlling the average particle size D A50The particle size within the above area not only improves the transmission efficiency of the roller pressure between the electrode foil particles due to the large contact area between the large-format particles, fully utilizes the skeletal support function of the large-format particles, allows the electrode foil to withstand higher roller pressure and improves the pressing density of the electrode foil, but also reduces the decrease in kinetics caused by the excessive size of the particles and maintains the kinetic performance of the battery while simultaneously improving the pressing density of the electrode foil.

[0135] In some embodiments, the median R in the cumulative distribution curve of the roughness area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 roughness 0.92-0.96.

[0136] The procedure for examining the roughness of particles in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is as follows: Identifying the particles in the cross-sectional area of ​​the cathode film layer with reference to the procedure described above in the present application, importing the image after particle assessment and labeling into the ImageJ software for analysis, completing the scaling according to the scanning electron microscope image, and analyzing the particle size, area, and roughness in the image using the analysis functions "Feret Diameter," "Area," and "Solidity." According to the software manual (ImageJ User Guide IJ 1.46r), the "Solidity" parameter obtained from the analysis represents the ratio of the pixel area to the convex area of ​​the particles. Therefore, the "Solidity" parameter obtained from the analysis is used to characterize the roughness of the particles.The definition makes it clear that the closer the roughness is to 1, the smoother the particle. Since particles with a size of less than 50 nm are difficult to identify accurately due to large errors in the statistical process, and since the particle size of the conductive medium is generally less than 50 nm, which can cause large errors in the statistical results, particles with a size of less than 50 nm are not counted in the statistical process for the particle size of this application, and the statistical data corresponding to particles where solidity is displayed as "NaN" are discarded. To achieve the required number of statistically significant samples, at least 10 scanning electron microscope images with non-overlapping fields of view are collected for each electrode foil.The roughness values ​​of the at least 5000 obtained particles are arranged in order from smallest to largest, and the cumulative distribution curve of the roughness of the particles in the cathode film layer is obtained by taking the roughness as the horizontal axis and the cumulative area fraction as the vertical axis. R. A50 A roughness R-value is obtained when, in the cumulative distribution curve of the roughness R-value, the cumulative area fraction of the vertical axis is 50%.

[0137] In some embodiments, the median R in the cumulative distribution curve of the roughness area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 The roughness can optionally be set to 0.92, 0.93, 0.94, 0.95, 0.96 or any value in a range between any two of these values.

[0138] A person skilled in this field can achieve the regulation of particle roughness using any known method. For example, particle roughness can be adjusted through processes such as milling, polishing, grinding, micro-machining, electroplating, roller burnishing, etc., as well as by adjusting the parameters of the respective processes.

[0139] The surface area of ​​the particles with median R A50 The roughness within the above area is relatively smooth, and the friction between the particles is relatively small, making it easy to slide under the influence of an external force. Together with the particles having a high degree of graphitization, an increase in the pressing density of the electrode foil at low rolling pressure can be achieved to further improve the energy density of the battery.

[0140] In some embodiments, L in the cumulative distribution curve of the sphericity area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A90 Sphericity 0.80-0.95, optionally 0.85-0.93.

[0141] The procedure for examining the sphericity of particles in a cross-section of the cathode film layer along the thickness direction of the electrode foil is as follows: Identifying the particles in the cross-section of the cathode film layer with reference to the procedure described above in the present application, importing the image after particle assessment and labeling into the ImageJ software for analysis, completing the scaling according to the scanning electron microscope image, and analyzing the particle size, area, and sphericity of the particles in the image using the analysis functions "Feret Diameter," "Area," and "Round." According to the software manual (ImageJ User Guide IJ 1.46r), the parameter "Round" obtained from the analysis represents the ratio of the particle's pixel area to the area of ​​a circle with the adjusted longitudinal diameter as its diameter and can be used to characterize the particle's sphericity.The closer the particle is to a sphere, the closer the ratio of the pixel area to the area of ​​the circle with the adjusted longitudinal diameter (diameter) is to 1. Therefore, the "Round" parameter of the particles, obtained from the analysis, is used to characterize the sphericity of the particles. Since particles with a size of less than 50 nm are difficult to identify accurately due to large errors in the statistical process, and since the particle size of the conductive medium is generally less than 50 nm, which can cause large errors in the statistical results, particles with a size of less than 50 nm are not counted in the statistical process for the particle size of this application, and the statistical data corresponding to particles where Round is displayed as "NaN" are deleted.To obtain a statistically significant number of samples, at least 10 scanning electron microscope images with non-overlapping fields of view are acquired for each electrode foil. The sphericities of the at least 5000 particles obtained are arranged in order from smallest to largest value, and the cumulative distribution curve of the particle sphericity in the cathode film layer is obtained by taking the sphericity as the horizontal axis and the cumulative area fraction as the vertical axis. L. A90 A sphericity L-value is obtained if, in the cumulative distribution curve of the sphericity L-value, the cumulative area fraction of the vertical axis is 90%.

[0142] In some embodiments, L in the cumulative distribution curve of the sphericity area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A90The sphericity 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95 represents any value in a range between two of these values.

[0143] A person skilled in this field can achieve the regulation of particle sphericity by any known method. For example, particle sphericity can be adjusted by processes such as comminution, polishing, chemical etching, mechanical mixing, extrusion, coating, granulation, addition of surfactants, etc., as well as by adjusting the parameters of the respective processes.

[0144] In some embodiments, the median L in the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 Sphericity 0.65-0.85, optionally 0.70-0.80.

[0145] L A50A sphericity L-value is obtained if, in the cumulative distribution curve of the sphericity L-value, the cumulative area fraction of the vertical axis is 50%.

[0146] In some embodiments, L in the cumulative distribution curve of the sphericity area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 The sphericity can optionally be 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.705, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85 or any value in a range between any two of these values.

[0147] The particles with median L A90 and L A50The sphericity within the above range is approximately spherical, and it is easy for the particles to slide under the influence of an external force, and together with the particles with a high degree of graphitization, an increase in the pressing density of the electrode foil at low rolling pressure can be achieved to further improve the energy density of the battery.

[0148] In some embodiments, the iron dissolution rate of the cathode film layer is 500 ppm-2000 ppm, optionally 500 ppm-1500 ppm.

[0149] The iron dissolution rate of the cathode film layer can be tested as follows. Specifically, the electrode foil is removed from the battery, washed, and then punched into a small disc with a diameter of 14 mm. A large number of small disc samples are taken so that the total mass of the samples is approximately 5 g. These are added to 100.3 g of a 0.3% mass concentration ascorbic acid solution (the solvent being high-purity water). The solution is stirred at 500 revolutions per minute for 5 minutes and then rapidly aspirated with a 5 mL syringe. It is then filtered into a test tube using a 0.45 µm orifice filter head. Using a pipette gun, 1 mL of the supernatant is aspirated and placed in a glass volumetric flask for 50-fold dilution. The result is then tested using an inductively coupled plasma mass spectrometer (ICP-OES).To obtain the iron concentration in the solution using the following formula: [(ICP test concentration of iron × volume of solution / mass of solution used for analysis) × 100.3 g / (mass of electrode foil of small disk - mass of collector of small disk)], where the volume of the solution is 50 mL and the mass of the solution used for analysis is 1 g, the iron dissolution rate of the cathode film layer is calculated. Preferably, the collector mass of the small disk is obtained by multiplying the thickness of the small disk by the area and by the density. The thickness of the small disk can be determined by measuring the thickness of the collector in the uncoated area using a thickness gauge. Although the collector in the coated area expands during compaction, resulting in a slight reduction in thickness compared to the uncoated area,This has no undue impact on the test results, as the reduction is negligible. If the collector is an aluminum foil, the density is preferably 2.7 g / cm³. 3 In some embodiments, the iron dissolution rate of the cathode film layer is optionally 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, or any value in a range between two of these values.

[0150] A person skilled in this field can regulate the iron dissolution rate of the cathode film layer using any known method. For example, the iron dissolution rate of the cathode film layer can be regulated by controlling the surface coating quality of the cathode film layer, the temperature, the time, and the pressure during the manufacturing process.

[0151] The iron dissolution rate reflects the completeness and density of the carbon coating on the surface of the active cathode material. The lower the iron dissolution rate, the fewer iron ions can be precipitated from the carbon coating layer after the acid dissolves; that is, the more complete and dense the carbon coating layer on the surface of the active cathode material. Active cathode material with an iron dissolution rate within the range described above exhibits a relatively complete and dense carbon coating layer, which is capable of improving electrical contact between the active cathode materials, increasing the electrical conductivity of the active cathode material, reducing its polarization, and further optimizing the kinetic performance of the lithium-ion secondary battery.At the same time, the densely coated carbon layer has a low space occupancy rate, and the particle gap is slightly compressed by the tension during the roller pressing process, and with the highly graphitized layer of the carbon coating, it is more conducive to improving the pressing density of the electrode foil and the energy density of the battery.

[0152] In some embodiments, the mass content of carbon is 0.8%-1.8%, optionally 0.90%-1.5%, based on the total mass of the active cathode material.

[0153] The mass fraction of carbon, relative to the total mass of the active cathode material, can be measured using methods and equipment known in this field. Referring to GB / T 21023-2006 "Determination of the total carbon and sulfur content of steel - Infrared absorption method after combustion in a high-frequency induction furnace", the measurement is carried out, for example, using a Dekai HCS infrared carbon and sulfur analyzer.

[0154] In some embodiments, the mass fraction of carbon, relative to the total mass of the active cathode material, is optionally 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% or any value in a range between two of these values.

[0155] The active cathode material has a relatively low carbon coating content compared to the active cathode material of the prior art lithium-containing transition metal phosphate, which can further increase the loading of the lithium-containing transition metal phosphate in the cathode foil and improve the energy density of the lithium-ion secondary battery.

[0156] In some embodiments, the lithium and iron antisite defect concentration of the active cathode material is 0.1%-1.5%, optionally 0.3%-1.0%.

[0157] XRD data of the sample are acquired using an X-ray diffractometer. The sample is analyzed for its physical phase, and a CIF file of the physical phase, obtained from an open-source website, is used as the initial crystal structure model, including the definition of cellular parameters, atomic positions, and occupation probabilities. In the initial crystal structure model, the possible Li content at the Fe position and the possible Fe content at the Li position, taking into account the possibility of an antipodal Fe-Li position, are determined, and the initial value is set to 0.1%. The acquired XRD data are then fitted and refined using FullProf Suite software, with the parameters being refined in the following order: background parameters, peak intensity, cellular parameters, and peak shape.If the fitted and experimental peak shapes are equipped with the best and Rwp is less than 10, the occupation probability of refined Li and Fe is obtained, which is used as the lithium and iron antisite defect concentration.

[0158] In some embodiments, the lithium and iron antisite defect concentration of the active cathode material is optionally 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any value in a range between two of these values.

[0159] A person skilled in this field can control the lithium and iron antisite defects of the active cathode material using any known method. For example, the control of lithium and iron antisite defects in the active cathode material can be achieved by controlling the sintering temperature, the sintering time, the manufacturing process, the stoichiometric ratio of the raw material, and the like.

[0160] During manufacturing and operation, a certain number of lithium voids are unavoidable in the crystal structure of the active cathode material. These voids not only lead to the oxidation of iron(II) ions to iron(III) ions, but also induce the partial migration of iron(III) ions to lithium sites, forming a lithium-iron antisite defect. This defect blocks the one-dimensional diffusion channel of lithium ions and impairs the solid-phase transport of lithium ions. In the embodiment of the present application, the active cathode material with a low lithium-iron antisite defect promotes the uniform transport of lithium ions in the solid phase, thereby further improving the kinetic performance of the lithium-ion secondary battery.

[0161] In some embodiments, the lithium-containing transition metal phosphate comprises a component with the following general formula: LimFexPyOjQq, where Q comprises one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and where 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, 0 <q≤0,1 ist.

[0162] In some embodiments, m is optionally 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or any value in a range between any two of these values. x is optionally 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any value in a range between any two of these values. y is optionally 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or any value in a range between any two of these values. j is optionally 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any value in a range between any two of these values. q is optionally 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value in a range between any two of these values.

[0163] The selection of the appropriate modification element Q improves the ion diffusion path of the active cathode material, improves the lithium ion diffusion rate of the active cathode material, and improves the kinetic performance of the battery.

[0164] In some embodiments, the active cathode material comprises one or more of the following materials: lithium iron phosphate and its doped modified material, as well as coated modified material.

[0165] In some embodiments, the active cathode material comprises titanium, and the mass content of titanium is 2000 ppm-6000 ppm relative to the total mass of the active cathode material.

[0166] The types and concentrations of elements in the active cathode material can be verified by any known method in this field. For example, the titanium content is verified using inductively coupled plasma emission spectrometry in accordance with Annex C of GB / T 33822-2017.

[0167] In some embodiments, the mass fraction of titanium, relative to the total mass of the active cathode material, is optionally 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm or any value in a range between two of these values.

[0168] Doping with titanium in the active cathode material leads to lattice distortion, reduces the Li-O binding energy, increases the lithium-ion transport rate, and improves the kinetic performance of the lithium-ion secondary battery. However, in the prior art, the titanium doping content in the lithium-containing transition metal phosphate often cannot exceed 3000 ppm, as too much titanium is difficult to fully penetrate into the bulk phase of the lithium-containing transition metal phosphate and tends to become a harmful impurity phase that remains on the surface and negatively affects battery performance.

[0169] The active cathode material in the embodiment of the present application has a high titanium content, and surprisingly, the high addition of titanium does not form a harmful impurity phase that negatively affects the energy density and kinetic performance of the battery, and the reason for this is unclear, but it is suggested that titanium and lithium together with the phosphate ion as well as with other elements form a fast ion conductor which instead improves the kinetic performance of the battery.

[0170] In some embodiments, the powder bulk density of the active cathode material is 0.70 g / cm³. 3 -1.50 g / cm² 3 , optional 0.7 g / cm² 3 -1.20 g / cm² 3 .

[0171] The powder bulk density can be obtained by testing with any method known in this field.

[0172] As an example, an electronic balance is switched on; first, an Erlenmeyer flask is used as a base and placed on the electronic balance; then the electronic balance is zeroed; a bulk density graduated cylinder is taken and placed on the Erlenmeyer flask to weigh the graduated cylinder and record the weight; the sample bag is opened, and the sample in the bag is stirred with a clean sample spoon for 3-5 rotations to mix it well; then the sample is transferred stably into the graduated cylinder; the powder adhering to the surface is wiped off with a dust-free paper; then the graduated cylinder is placed in the zeroed Erlenmeyer flask for weighing;The opening of the measuring cylinder is sealed with a sealing film, and the bulk density measuring cylinder is inserted into a suitable rubber ring of the device to ensure that the bulk density measuring cylinder is firmly connected to the rubber ring and is perpendicular to the surface of the device; the vibration frequency on the device is set to 250 times / min and the number of vibrations to 5,000 times, the button is pressed, and the device vibrates for 20 minutes; then the TD tube is removed, and the surface of the measuring cylinder is illuminated with a flashlight; using the method of visual inspection, the highest scale reading V1 and the lowest scale reading V2 are taken to obtain the average value V of the two; the mass m0 of the measuring cylinder is subtracted from the mass m1 of the measuring cylinder and the mass m of the sample to obtain the powder mass m, and the bulk density of the sample is obtained using the density formula p = m / v.

[0173] In some embodiments, the powder bulk density of the active cathode material is optionally 0.70 g / cm³. 3 , 0.80 g / cm² 3 , 0.90 g / cm² 3 , 1.00 g / cm² 3 , 1.10 g / cm² 3 , 1.20 g / cm² 3 , 1.30 g / cm² 3 , 1.40 g / cm² 3 , 1.50 g / cm² 3 or any value within a range between two of these values.

[0174] The active cathode material in the embodiment of the present application has a relatively low powder bulk density, and with the help of the high degree of graphitization of the cathode film layer and the good consistency of the degree of graphitization, it is easy for the active cathode material to slide under the action of an external force in order to achieve an increase in the powder compaction density.

[0175] In some embodiments, the powder density of the active cathode material is 2.50 g / cm³ under a pressure of 3 T. 3 -2.70 g / cm²3 , optional 2.52 g / cm² 3 -2.68 g / cm² 3 .

[0176] In the present application, the term "powder compaction density" refers to the density (in g / cm³). 3 ) a blank with a specific density and strength, which is formed in such a way that, with the movement and deformation of the powder in the process of compression by an external force, the larger gaps are filled and the contact area between the particles increases, so that an interatomic attraction is created and the mechanical bond between the particles is strengthened.

[0177] The powder density of the active cathode material can be measured using methods and equipment known in this field. For example, it can be measured with a density measuring device according to GB / T24533-2009. Specifically, a certain quantity of the active cathode material is placed on a special compaction mold (with a known diameter), which is hollow in the middle and has a metal disc at the top and bottom.The active cathode material is placed between the metal discs, a metal cylinder is placed on top, the mold is placed on the device for measuring the compression density, the base area of ​​the mold being 1.327 cm2, the pressure is set to 3 T, and the thickness of the active cathode material under the pressure of 3 T can be read from the device, and the powder compression density of the active cathode material is ρ=m / v, where v=(S×H), m is the mass of the active cathode material, S is the base area of ​​the mold, and H is the thickness of the compressed active cathode material.

[0178] In some embodiments, the powder density of the active cathode material is optionally 2.52 g / cm³ under a pressure of 3 T. 3 , 2.53 g / cm³ 3 , 2.54 g / cm³ 3 , 2.55 g / cm³ 3 , 2.56 g / cm³ 3 , 2.57 g / cm³ 3 , 2.58 g / cm³ 3 , 2.59 g / cm³ 3 , 2.60 g / cm³ 3 , 2.61 g / cm³ 3 , 2.62 g / cm³3 , 2.63 g / cm³ 3 , 2.64 g / cm³ 3 , 2.65 g / cm³ 3 , 2.66 g / cm³ 3 , 2.67 g / cm³ 3 , 2.68 g / cm³ 3 or any value within a range between two of these values.

[0179] With the help of a high degree of graphitization and good consistency of the graphitization degree, the active cathode material can still achieve a high pressing density under the influence of an external force, in order to create a material basis for improving the pressing density of the electrode foil and for the production of a lithium-ion secondary battery with high energy density.

[0180] In some embodiments, the powder resistance of the active cathode material under a pressure of 8 MPa is 0.5 Ω·cm-30 Ω·cm, optionally 2 Ω·cm-20 Ω·cm.

[0181] The powder resistance of the active cathode material can be measured using methods and equipment known in this field. For example, it can be measured with a powder resistance meter (Suzhou Jingle, model ST2722) in accordance with GB / T33822-2017. Specifically, a certain amount of active cathode material (e.g., 1 g) is weighed and placed in the loading chamber of the powder resistance meter, a pressure of 8 MPa is applied, the on-resistance and blocking resistance of the active cathode material are tested separately, and the average of the two values ​​is taken as the powder resistance of the active cathode material.

[0182] In some embodiments, the powder resistance of the active cathode material under a pressure of 29400 N is optionally 0.5 Ω·cm, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm or any value in a range between any two of these values.

[0183] The active cathode material has a high degree of graphitization, therefore it can easily achieve the rapid conduction of electrons between particles via the sp2 structure of carbon on the surface, giving the active cathode material a low powder resistance, which contributes to increasing the solid-phase electron transport rate to further improve the kinetic performance of the battery.

[0184] In some embodiments, the discharge gram capacity of the active cathode material is 135 mAh / g-150 mAh / g at room temperature at a discharge rate of 1 C.

[0185] In the present application, the active cathode material is assembled as a button cell battery to test its electrical performance on a land-based test device. After charging with a constant current from 1°C to 3.75 V within the voltage range of 2.0 V to 3.75 V at 25 ± 5°C, there is a 5-minute pause, followed by charging with a constant voltage up to a cutoff current of 50 µA and subsequent discharging with a constant current of 1 C to 2.0 V. The discharge capacity of the button cell battery is divided by the mass of the active cathode material, thereby determining the discharge gram capacity of the active cathode material at room temperature and a discharge rate of 1 C.

[0186] The manufacturing and testing process of the button cell battery is as follows: Mixing 2.0 g of active cathode material, conductive carbon black, and PVDF in a mass ratio of 0.9:0.05:0.05; adding the organic solvent NMP (N-methylpyrrolidone); mixing thoroughly until homogeneous; applying with a 150 µm scraper; drying at 100°C for 2 hours; and compacting the cathode foil to a density of 2.0 g / cm³. 3 -2.2g / cm² 3Using a hole punch to make the cathode foil into a round piece with a diameter of 14 mm, then weighing and recording the weight, placing the weighed cathode foil in a vacuum drying oven (105°C, 1-12 hours, -90 kPa), placing the dried cathode foil in a glove box, assembling it into a battery in the following order: anode tray - nickel mesh - diaphragm - cathode foil - cathode tray, adding 65-87 µL (pipette gun) of electrolyte solution (the electrolyte solution is a solvent mixture of EC (ethylene carbonate), DMC (1,2-dimethyl carbonate) in a volume ratio of 1:1, and the electrolyte LiPF6), placing the button battery with the anode facing upwards into the groove of the sealing machine, with a sealing pressure of 650 kg / cm², removing the button battery with insulated tweezers and loading it into a Dust-free bag, remove glove box, store in a thermostatic room for 3 hours,to obtain the button battery for the test.

[0187] It is understood that the discharge gram capacity of the active cathode material can also be determined by disassembling the battery, recovering the cathode foil and testing it after reassembly into a button battery according to the procedure described above.

[0188] In some embodiments, the discharge gram capacity of the active cathode material at room temperature at a discharge rate of 1 C is optionally 135 mAh / g, 136 mAh / g, 137 mAh / g, 138 mAh / g, 139 mAh / g, 140 mAh / g, 141 mAh / g, 142 mAh / g, 143 mAh / g, 144 mAh / g, 145 mAh / g, 146 mAh / g, 147 mAh / g, 148 mAh / g, 149 mAh / g, 150 mAh / g or any value in a range between any two of these values.

[0189] The high discharge gram capacity of the active cathode material at a C-rate of 1 C indicates that it has good charging and discharging capabilities, which contributes to improving the kinetic performance of the battery.

[0190] In some embodiments, the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, where η is defined as follows: a button cell comprising the active cathode material is charged and discharged twice in a voltage range of 2.0 V to 3.75 V at a C-rate of 0.1 C with a constant current, and subsequently once at a C-rate of 1 C with a constant current. The capacity value extracted in the charge and discharge test at a C-rate of 1 C with a discharge voltage of 3.2 V is recorded as C1, and the capacity value extracted at a discharge voltage of 2.0 V is C2, and n = C1 / C2, and the charging process comprises a constant-voltage charge at a constant voltage of 3.75 V and a constant-voltage cutoff current of 50 µA.

[0191] The value η of the active cathode material can be measured using methods and equipment known in this field. As an example, the button battery is first manufactured according to the procedure described above, and the electrical performance of the manufactured button battery is tested on a land-based test device. This involves charging and discharging the button battery twice at room temperature with a constant current at a C-rate of 0.1 C in the voltage range of 2.0 V to 3.75 V. After being charged with a constant current up to the cutoff voltage, the button battery is charged with a constant voltage to a current of 50 µA and then charged and discharged once with a constant current at a C-rate of 1 C. In the charge / discharge test with a C-rate of 1C, the capacity value when discharging from 3.75 V to a voltage of 3.2 V is recorded as C1, and the capacity value when discharging from 3.75 V to 2.0 V is recorded as C2, and η=C1 / C2.

[0192] In some embodiments, η is optionally 85%, 86%, 87%, 88%, 88.1%, 89%, 90%, 90.1%, 91%, 92%, 92.2%, 93%, 94%, 94.1%, 94.5%, 95%, 95.1% or any value in a range between any two of these values.

[0193] In some embodiments, the active cathode material in the newly manufactured lithium-ion secondary battery is discharged to 3.2 V with a discharge capacity percentage η ≥ 88%. After charging and discharging the newly manufactured lithium-ion secondary battery at a C-rate of 0.1 C in a voltage range of 2.0 V to 3.75 V over a period of time with a constant current, the discharge capacity percentage η of the active cathode material discharged to 3.2 V can be maintained at ≥ 85%.

[0194] A high discharge capacity percentage of the active cathode material used in the lithium-ion secondary battery of the embodiment of the present application when discharged to 3.2 V implies that the active cathode material has good kinetic performance. At the same time, the high η value indicates that the lithium-ion secondary battery comprising the active cathode material still exhibits a high voltage when discharged to a low state of charge (SOC), which is conducive to maintaining good performance.

[0195] In some embodiments, the mass content of the conductive medium is 0-1.5% relative to the total mass of the cathode film layer.

[0196] In some embodiments, the mass fraction of the conductive medium, relative to the total mass of the cathode film layer, is optionally 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any value in a range between two of these values.

[0197] In some embodiments, the conductive agent comprises at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dot, carbon nanotubes, graphene and carbon nanofibers.

[0198] The carbon layer of the active cathode material exhibits a high degree of graphitization and good consistency of graphitization; therefore, the active cathode material has good electronic conductivity, which reduces and even eliminates the use of the conductive agent in the cathode film layer, thus helping to further increase the charging of the active cathode material and improve the energy density of the lithium-ion secondary battery.

[0199] In some embodiments, the mass fraction of the conductive medium is 0, relative to the total mass of the cathode film layer.

[0200] The active cathode material has extremely good electronic conductivity, which makes it possible to even eliminate the use of the conductive agent in the cathode film layer, which helps to further increase the charging of the active cathode material and improve the energy density of the lithium-ion secondary battery.

[0201] In some embodiments, the cathode film layer further comprises a binder, and, based on the total mass of the cathode film layer, the mass content of the active cathode material is 95.5%-99.5%, optionally 96.5%-99.5%; and the mass content of the binder is 0.5%-3%.

[0202] In some embodiments, the binder comprises at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0203] In some embodiments, the mass fraction of the active cathode material, relative to the total mass of the cathode film layer, is optionally 95.5%, 96.0%, 96.5%, 97%, 98%, 99%, 99.5% or any value in a range between two of these values.

[0204] In some embodiments, the mass content of the binder, relative to the total mass of the cathode film layer, is optionally 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any value in a range between two of these values.

[0205] In some embodiments, the one-sided areal density of the cathode film layer is 300 mg / 1540 mm². 2 -450 mg / 1540 mm 2 .

[0206] In the present application, the areal density of the cathode film layer on one side has a meaning known in the art and can be tested by methods known in the art. For example, a cathode foil coated and densified on one side (in the case of a cathode foil coated on both sides, the cathode film layer on one side can be wiped off first) is taken, punched, and cut into a small disc with an area of ​​S1, weighed, and recorded as M1. Then, the cathode film layer of the cathode foil, which was weighed as described above, is wiped off, and the weight of a collector is weighed and recorded as M0. The areal density of the cathode film layer on one side is given by: (M1 - M0) / S1. To ensure the accuracy of the test results, several sets (e.g., 10 sets) of the samples to be tested can be tested, and an average value can be calculated as the test result.

[0207] In some embodiments, the one-sided areal density of the cathode film layer is optionally 300 mg / 1540 mm². 2 , 310mg / 1540 mm 2 , 320mg / 1540 mm 2 , 330mg / 1540 mm 2 , 340mg / 1540 mm 2 , 350mg / 1540 mm 2 , 360mg / 1540 mm 2 , 370mg / 1540 mm 2 , 380mg / 1540 mm 2 , 390mg / 1540 mm 2 , 400mg / 1540 mm 2 , 410mg / 1540 mm 2 , 420mg / 1540 mm 2 , 430mg / 1540 mm 2 , 440mg / 1540 mm 2 , 450mg / 1540 mm 2 or any value within a range between two of these values.

[0208] A cathode film layer with an areal density within the above range can contribute to improving the energy density of the lithium-ion secondary battery.

[0209] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.51 g / cm³. 3-2.73 g / cm² 3 .

[0210] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.55 g / cm³. 3 -2.70 g / cm² 3 .

[0211] In the present application, a fully discharged state refers to a state in which, after the battery has been stored in an oven environment at 25°C for 2 hours and the temperature of the battery has been maintained at 25°C, the battery is discharged to 2.5 V with a constant current of 1 / 3 C and then discharged to 2.0 V with a constant current of 0.1 C.

[0212] The compression density of the cathode film layer can be tested using methods known in this field.As an example, the battery is placed in an oven environment at 25°C and stored for 2 hours. While the battery temperature is maintained at 25°C, it is discharged to 2.5 V at a constant current of 1 / 3 C and then to 2.0 V at a constant current of 0.1 C. The battery is then disassembled to obtain a cathode foil. The remaining electrolyte solution is treated using the solvent dimethyl carbonate. The electrode foil is dried and cut into a small disc with area S to obtain mass W1. Using a micrometer, the thickness T1 of the cathode foil is measured. The cathode film layer is then wiped from the weighed electrode foil. The mass of the collector is weighed and recorded as W2. The thickness T2 of the collector is measured using a micrometer. The density PD of the cathode film layer is then = (W1-W2) / [(T1-T2) [xS].

[0213] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is optionally 2.51 g / cm³. 3 2.52g / cm² 3 , 2.53g / cm³ 3 , 2.54g / cm³ 3 , 2.55g / cm³ 3 , 2.56g / cm³ 3 , 2.57g / cm³ 3 , 2.58g / cm³ 3 , 2.59g / cm³ 3 , 2.60g / cm² 3 , 2.61g / cm³ 3 , 2.62g / cm³ 3 , 2.63g / cm³ 3 , 2.64g / cm³ 3 , 2.65g / cm³ 3 , 2.66g / cm³ 3 , 2.67g / cm³ 3 , 2.68g / cm³ 3 , 2.69g / cm³ 3 , 2.70g / cm³ 3 , 2.71g / cm³ 3 , 2.72g / cm³ 3 , 2.73g / cm³ 3 or any value within a range between two of these values.

[0214] The pressure density of the cathode film layer is within the above range, which is beneficial for improving the energy density of the lithium-ion secondary battery.

[0215] In some embodiments, the compression density of the cathode film layer after treatment by the compaction process is 2.63 g / cm³. 3 -2.85 g / cm² 3 .

[0216] In some embodiments, the compression density of the cathode film layer after treatment by the compaction process is optionally 2.63 g / cm³. 3 , 2.64g / cm³ 3 , 2.65g / cm³ 3 , 2.66g / cm³ 3 , 2.67g / cm³ 3 , 2.68g / cm³ 3 , 2.69g / cm³ 3 , 2.70g / cm³ 3 , 2.71g / cm³ 3 , 2.72g / cm³ 3 , 2.73g / cm³ 3 , 2.74g / cm³ 3 , 2.75g / cm³ 3 , 2.76g / cm³ 3 , 2.77g / cm³ 3 , 2.78g / cm² 3 , 2.79 g / cm³ 3 , 2.80g / cm³ 3 , 2.81g / cm³ 3 , 2.82g / cm³ 3 , 2.83g / cm³ 3 , 2.84g / cm³ 3 , 2.85g / cm³ 3 or any value within a range between two of these values.

[0217] In the present application, compaction means compacting the cathode film layer by mechanical pressure during the battery assembly process to improve its compactness and conductivity.

[0218] In some embodiments, the density of the cathode film layer after treatment by the forming process is 2.52 g / cm³. 3 -2.73 g / cm² 3 .

[0219] In some embodiments, the density of the cathode film layer after treatment by the forming process is optionally 2.52 g / cm³. 3 , 2.53g / cm³ 3 , 2.54g / cm³ 3 , 2.55g / cm³ 3 , 2.56g / cm³ 3 , 2.57g / cm³ 3 , 2.58g / cm³ 3 , 2.59g / cm³ 3 , 2.60g / cm² 3 , 2.61g / cm³ 3 , 2.62g / cm³ 3 , 2.63g / cm³ 3 , 2.64g / cm³ 3 , 2.65g / cm³ 3 , 2.66g / cm³ 3 , 2.67g / cm³ 3 , 2.68g / cm³ 3 , 2.69g / cm³ 3 , 2.70g / cm³3 , 2.71g / cm³ 3 , 2.72g / cm³ 3 , 2.73g / cm³ 3 or any value within a range between two of these values.

[0220] In the present application, the formation refers to the formation of a stable solid electrolyte interface (SEI film) and electrode structure through the electrochemical reaction during the first charge / discharge cycle of the battery.

[0221] It is understood that the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is somewhat lower than the density of the cathode film layer after compaction and formation, because the electrode foil rebounds during the cycling process.

[0222] The pressure density of the cathode film layer is within the above range, which is beneficial for improving the energy density of the lithium-ion secondary battery.

[0223] In some embodiments, the density of the cathode film layer is 2.51 g / cm³. 3 -2.73 g / cm² 3 , and in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is 10%-22%.

[0224] In some embodiments, the density of the cathode film layer is 2.55 g / cm³. 3 -2.70 g / cm² 3 , and in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is 10%-20%.

[0225] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is optionally 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22% or any value in a range between two of these values.

[0226] The porosity of the cathode film layer can be examined in a cross-section along the thickness direction of the electrode foil as described below. Import the scanning electron microscope image of the cross-section of the cathode film layer along the thickness direction of the electrode foil, obtained using the method described above, into the ImageJ software. Select the straight line tool, use a straight line to mark the length of the scale in the image, click "Analyze Set Scale", and adjust the scale parameters in the software according to the length of the scale in the image.Select the rectangle tool, select the portion of the image outside the scale range, use "Image Duplicate" to duplicate the selected area, use "Image Type 8 bit" to adjust the image format; select "Analyze Set Measurements" and select the following five options: "Area", "Mean gray value", "Area Fraction", "Limit to threshold", "Feret's diameter", selecting 3 for "Decimal places", and successively selecting "Image" - "Adjust" - "Threshold", and successively setting the "Threshold" position to 0 and 100, thereby enabling the Analyze-Measure function to export the pore data in the scanning electron microscope image of the section surface.Use "Image"-"Overlay"-"Flatten" to export and obtain the pore image; click "Apply" in "Threshold", then click "Analyze"-"Analyze Particles", and check the four columns on the left to obtain the pore statistics.

[0227] It is understood that in the embodiment of the present application, the “pores” in the cut surface of the cathode film layer are identified by the color difference and the threshold of the image, as in Fig.Figure 8 illustrates that the "pore" is not the porosity data obtained in the exhaust gas test, but is mainly used to characterize the cross-sectional area between the particles in the cut surface of the cathode film layer. This method is superior to the exhaust gas method because the porosity obtained by the exhaust gas method is related to the pores between the particles and also to the pores in the carbon layer coated on the surface of the lithium iron phosphate particles, and therefore the pores between the particles cannot be objectively reflected.

[0228] The lower porosity in a cross-sectional area of ​​the cathode film layer, determined using this method, means, on the one hand, that the gradation of large, medium, and small particles in the cathode film layer is better while the pressing density is high, and on the other hand, after the same gradation and the same rolling pressure, if the porosity is low, it means that the particles can easily slip against each other, thus reducing the risk of overpressure in the film layer and the risk of stress concentration, and further reducing the probability of demolding of the cathode film during the long cycle process, which contributes to improving the long cycle performance of the battery.

[0229] In some embodiments, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the cathode collector; wherein the lower coating comprises carbon-based particles, wherein the distribution density of the carbon-based particles with a particle size of more than 100 nm in the lower coating is ≤ 10 pcs / 10 µm;

[0230] where the carbon-based particles refer to particles with carbon as the main component, including but not limited to conductive carbon, soot, etc.

[0231] The lower coating contributes to increasing the electrical conductivity and bonding strength of the cathode film layer and the collector, and to reducing the demolding of the cathode film layer from the collector during the cycling process, while improving the kinetic performance of the battery. This is achieved, for example, in the high-density electrode foil of the embodiment of the present application, when the density of the cathode foil is greater than or equal to 2.4 g / cm³ in the fully discharged state. 3The collector tends to be damaged during the high-pressure compaction process of the electrode foil, and the large-format particles tend to create craters on the collector. Controlling the distribution density of carbon-based particles with a particle size greater than 100 nm to ≤10pcs / 10µm helps to reduce the likelihood of damage occurring to the collector in the high-density electrode foil and to further improve the limiting density of the cathode foil.

[0232] The distribution density of carbon-based particles with a particle size greater than 100 nm in the lower coating can be determined by the method described above, wherein the cathode film layer is cut along the thickness direction of the electrode foil using an argon ion beam, and wherein a scanning electron microscope image or a microscopic image is taken, and wherein the size of the carbon particles in the lower coating is determined by the counting method, and wherein the number of carbon-based particles with a particle size greater than 100 nm contained in each 10 µm in the lower coating is counted, and wherein the counting is carried out for not fewer than 5 times to determine the average value.

[0233] The lower coating in the embodiment of the present application can be produced by any known manufacturing process, such as pre-sieving or centrifugation and other processes to remove large particles of the carbon-based material in the manufacturing process of the carbon-based particles, so that D V50 The carbon-based particles added during the manufacturing process of the bottom coating are in the range of 20nm-60nm and DV90 is less than or equal to 70nm, and the bottom coating is obtained by mixing, stirring the carbon-based material and the binder and applying it to the collector.

[0234] In some embodiments, the density of the cathode foil in a fully discharged state is greater than or equal to 2.4 g / cm³. 3 , and the one-sided thickness of the lower coating is 1 µm-4 µm.

[0235] In some embodiments, the density of the cathode foil in a fully discharged state is greater than or equal to 2.5 g / cm³. 3 , and the one-sided thickness of the lower coating is 2 µm-4 µm.

[0236] As the electrode film's density increases, the extrusion effect of large particles of lithium-containing phosphate materials (e.g., with a particle size greater than 1 µm) in the cathode film layer on the bottom coating becomes increasingly significant. Consequently, these large particles tend to create stress concentrations at certain points and even penetrate the collector, damaging the bottom coating. Increasing the thickness of the bottom coating helps to mitigate this stress concentration phenomenon in the electrode film and further increase the electrode film's limiting density.

[0237] The thickness of the bottom coating on one side can be checked as follows. As described above, the cathode film layer is cut along the thickness direction of the electrode foil using an argon ion beam. A scanning electron microscope image is taken, and the thickness of the bottom coating on one side is measured by taking a point at a distance of 1 m along the length of the electrode foil. The thickness of the bottom coating is then averaged after measuring the thickness at 10 points. It should be noted that anomalous points must be avoided when taking measurements.Areas of the lower coating with thicknesses of less than 50 nm and thicknesses of more than 4 µm; these anomalous points are mainly due to extreme variations in the thickness of individual areas caused by the extrusion of anomalous stress concentrations in the compaction process of the electrode foil, and these anomalous points have no statistical significance.

[0238] In some embodiments, the thickness of the cathode collector is less than or equal to 17 µm, optionally 13 µm-15 µm.

[0239] In some embodiments, the thickness of the cathode collector is optionally 13 µm, 14 µm, 15 µm, 16 µm, 17 µm or any value in a range between two of these values.

[0240] In some embodiments, the cathode collector can be a metal foil or a composite collector. For example, an aluminum foil can be used as the metal foil. The composite collector can comprise a base layer of polymeric material and a metal layer formed on at least one surface of the polymeric base layer. The composite collector can be formed by depositing metallic material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0241] In some embodiments of the lithium-ion secondary battery, the anode foil comprises an anode collector and an anode film layer arranged on at least one side of the anode collector, wherein the areal density of the anode film layer on one side is 140 mg / 1540 mm². 2 -221 mg / 1540 mm 2 is; and / or wherein the compression density of the anode film layer is 1.40 g / cm³ 3 -1.75g / cm² 3 amounts.

[0242] The one-sided areal density and the compression density of the anode film layer can be tested using similar methods to those previously described for the cathode film layer.

[0243] The areal density and the compression density of the anode film layer are within the above range, which is beneficial for improving the energy density of the lithium-ion secondary battery.

[0244] In some embodiments, the anode collector can be a metal foil or a composite collector. For example, a copper foil can be used as the metal foil. The composite collector can comprise a base layer of polymeric material and a metal layer formed on at least one surface of the polymeric base layer. The composite collector can be formed by depositing metallic material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0245] In some embodiments, the anode film layer comprises a negative active material. The negative active material may be a negative active material known in the art for use in batteries. For example, the negative active material may comprise at least one of the following: synthetic graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may be at least one of monomeric silicon, silicon oxides, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may be at least one of monolithic tin, tin oxide compounds, and tin alloys.However, the present application is not limited to these materials, and other conventional materials that can be used as negative active materials in batteries may also be used. It is possible to use only one of these negative active materials or to use more than two in combination.

[0246] In some embodiments, the anode film layer optionally further comprises a binder. This binder may be at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0247] In some embodiments, the anode film layer optionally further comprises a conductive material. The conductive material can be at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dot, carbon nanotubes, graphene, and carbon nanofibers.

[0248] In some embodiments, the anode film layer optionally includes further additives, such as thickening agents (e.g. sodium carboxymethylcellulose (CMC-Na)), etc.

[0249] In some embodiments, the anode foil can be produced as follows: Dispersing the components described above for the production of the anode foil, such as the negative active material, the conductive agent, the binder and other components, in a solvent (e.g. deionized water) to form an anode slurry; applying the anode slurry to the anode collector and obtaining the anode foil after drying, compaction and other processes.

[0250] In some embodiments, the lithium-ion secondary battery includes an electrolyte. The electrolyte serves as an ion conductor between the cathode foil and the anode foil. The present application does not impose any specific restrictions regarding the type of electrolyte, which can be selected as required. For example, the electrolyte can be liquid, gel, or solid.

[0251] In some embodiments, an electrolyte solution is used for the electrolyte. This electrolyte solution consists of an electrolyte salt and a solvent.

[0252] In some embodiments, the electrolyte salt may be at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(trifluorosulfonyl) amide, lithium bis(trifluoromethanesulfonyl) amide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalic acid borate, lithium di(oxalic acid) borate, lithium difluorodioxygenophosphate and lithium tetrafluorooxalic acid phosphate.

[0253] In some embodiments, the solvent may be at least one of ethylidene carbonate, propylidene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylenepropyl carbonate, ethylenepropyl carbonate, butylidene carbonate, ethylidene fluorocarbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0254] In some embodiments, the electrolyte optionally includes an additive. This additive may, for example, include a film-forming additive for the negative electrode and a film-forming additive for the positive electrode, and may also include an additive that can improve certain battery properties, such as an additive to improve the battery's overcharge performance, an additive to improve the battery's high- or low-temperature performance, etc.

[0255] In some embodiments, the lithium-ion secondary battery further comprises a separating film. The present application does not impose any specific restrictions regarding the type of separating film, and any known separating film with a porous structure and good chemical and mechanical stability can be selected.

[0256] In some embodiments, the separating film material can be at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separating film can be a single-layer film or a multi-layer composite film without any particular restriction. If the insulating film is a multi-layer composite film, the materials of the layers can be the same or different without any particular restriction.

[0257] In some embodiments, the cathode foil, the anode foil and the separating film can be assembled into an electrode component by a winding process or a stacking process.

[0258] In some embodiments, the lithium-ion secondary battery may include an outer packaging. The outer packaging can be used to encapsulate the electrode component and electrolyte described above.

[0259] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a rigid casing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. The outer packaging of the secondary battery can also be a soft casing, such as a bag-like soft casing. The soft casing can be made of plastic, and examples of such plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0260] A second aspect of the present application provides a battery device comprising at least one lithium-ion secondary battery provided by the first aspect of the present application, wherein the battery device comprises at least one of the battery module, the battery pack and the energy storage battery.

[0261] A third aspect of the present application provides a power-consuming device comprising a lithium-ion secondary battery provided by the first aspect of the present application.

[0262] An unclaimed aspect of the present application provides a method for producing an active cathode material, comprising: obtaining a mixed crude material comprising a carbon source, a lithium source, an iron source, and a phosphorus source; wherein the carbon source comprises polyethylene glycol; wherein the iron source comprises iron(II); wherein the molar ratio of iron and phosphorus in the mixed crude material is greater than or equal to 0.95 and less than or equal to 1; milling in a solvent to obtain a mixed slurry; drying the mixed slurry to obtain a precursor powder; sintering the precursor powder to obtain an active cathode material; wherein the sintering comprises at least two constant-temperature sintering stages, the high-temperature sintering temperature being 750°C–800°C.

[0263] The manufacturing process provided by the embodiment of the present application improves the degree of graphitization of the active cathode material by regulating the molar ratio of iron and phosphorus in the mixed raw material and also uses polyethylene glycol as a carbon source. Together with controlling the sintering temperature and the catalytic reduction of iron(II), the degree of graphitization of the particles in the cathode film layer is uniformly increased. This provides a material basis for the production of a cathode film layer with a median C 50 of the degree of graphitization of greater than or equal to 0.95 and less than or equal to 1.20 and a concentration of the C values ​​(C 90 -C 10 ) / C 50 created from 0.01-0.04.

[0264] The cathode film layer, which is produced from the active cathode material manufactured by the process, has a high degree of graphitization as well as good consistency of the graphitization level, can easily improve the pressing density of the electrode foil by uniform and consistent sliding between the particles and is conducive to improving the energy density of the battery while simultaneously improving the kinetic performance of the battery.

[0265] In some embodiments, the iron source comprises iron(II), optionally one or more of iron(II) oxalate, iron(II) carbonate and iron(II) nitrate.

[0266] During the sintering process, the iron(II) source preferentially decomposes to generate a large amount of iron oxide, which serves as a nucleation site for the formation of nanocrystalline cores of the lithium-containing transition metal phosphate. Simultaneously, the polymeric carbon source has a relatively low decomposition temperature, and the iron element present on the surface of the nanocrystalline cores further catalyzes the decomposition of the carbon source. This allows the carbon coating layer on the surface of the active cathode material to exhibit a relatively high degree of graphitization at a relatively low sintering temperature. This reduces the electrical resistance of the active cathode material while simultaneously improving the density and uniformity of the carbon coating layer on the surface of the lithium-containing transition metal phosphate.

[0267] In some embodiments, the phosphorus source comprises one or more of lithium dihydrogen phosphate, phosphoric acid, and ammonium dihydrogen phosphate.

[0268] In some embodiments, the lithium source and the phosphorus source may be the same substance.

[0269] In some embodiments, the iron source comprises iron(II) oxalate, wherein the lithium source and the phosphorus source comprise lithium dihydrogen phosphate, and wherein the carbon source comprises polyethylene glycol.

[0270] In some embodiments, the atomic molar ratio of the elements iron and phosphorus in the iron source and the phosphorus source is 0.95:1.0-1.0:1.0.

[0271] In some embodiments, the atomic molar ratio of the elements iron and phosphorus in the iron source and the phosphorus source is optionally 0.95:1.0, 0.96:1.0, 0.97:1.0, 0.98:1.0, 0.99:1.0, 1.0:1.0 or any value in a range between two of these values.

[0272] An iron-to-phosphorus ratio that is too high or too low can lead to structural instability. A ratio that is too low can result in incomplete lithium occupancy, reducing the ionic conductivity and structural stability of the material, while a ratio that is too high can lead to an iron excess, which impairs the electrochemical stability and capacity performance of LiFePO4. An appropriate iron-to-phosphorus ratio can promote uniform crystal growth and prevent particle aggregation or excessive variations in particle size during the synthesis process.If the iron-phosphorus ratio is too high, excess iron ions can form large particles during the reaction, which impairs the uniformity of the particle size; conversely, if the iron-phosphorus ratio is too low, the phosphate may not be able to fully participate in the reaction, leading to incomplete particle growth, which also impairs the uniformity of the particles.

[0273] In some embodiments, the iron(II) oxalate has a particle size D10 greater than or equal to 3 µm, a particle size D50 of 50 µm-80 µm and a particle size D90 of less than or equal to 150 µm.

[0274] In this application, the terms “D10”, “D50” and “D90” represent the corresponding particle size when the percentage of the cumulative particle size distribution of the sample particle size obtained by the Malvern laser scattering method reaches 10%, 50% and 90% respectively.

[0275] Controlling the particle size of iron(II) oxalate D10 to greater than or equal to 3 µm can reduce the proportion of small iron(II) oxalate particles and control the reactivity during the milling process. Controlling the particle sizes D50 and D90 of the iron(II) oxalate helps to ensure uniform mixing of the raw materials during milling, resulting in a mixed slurry with homogeneous components and particle size, and improving the consistency of the particle size of the produced lithium-containing transition metal phosphate.

[0276] In some embodiments, the mass content of the trivalent iron element is less than or equal to 0.08%.

[0277] In some embodiments, the mass content of the trivalent iron element is optionally 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08% or any value in a range between two of these values.

[0278] Controlling the mass fraction of trivalent iron helps improve the uniformity and consistency of the carbon coating layer. An excessively high trivalent iron content preferentially depletes the carbon source, leading to poor quality and thickness consistency of the carbon layer deposited between the particles. On the one hand, the uneven thickness of the carbon coating layer impairs the compaction between the particles, and on the other hand, local carbon depletion impairs the overlap of the conductive network between the particles, negatively impacting the effective increase in the electrode foil's compaction density and the improvement of its kinetics.

[0279] In some embodiments, the lithium source comprises one or more of lithium dihydrogen phosphate, lithium phosphate, lithium carbonate, and lithium acetate.

[0280] In some embodiments, the carbon source comprises a polymeric carbon source, optionally one or more of polyethylene glycol and polyvinyl alcohol.

[0281] In some embodiments, the mass content of the carbon source is 1-4% relative to the total mass of the cathode film layer.

[0282] The polymeric carbon source has a relatively low decomposition and graphitization temperature, which allows the carbon coating layer on the surface of the active cathode material to decompose at a low sintering temperature to form a carbon layer that inhibits the growth of the lithium-containing transition metal phosphate grains and sinter growth, and helps to reduce the particle size of the active cathode material particles.

[0283] At the same time, the polymeric carbon source typically has a high molecular weight or a long molecular chain, and a stable skeletal structure can easily be formed through crosslinking or orientation during heat treatment, and this order can be maintained during high-temperature carbonization, which is conducive to the directed growth of graphite crystals; simultaneously, the entanglement and crosslinking of long chains are conducive to the reduction of structural defects and the reduction of crystal lattice disruption due to chain breaking in the carbonization process, which can increase the degree of graphitization.

[0284] The organic molecules in the carbon source will decompose at high temperature, releasing carbon atoms that can cover and fill the tiny gaps or defects on the surface of the active material and reduce surface roughness. The coating formed by the polymeric carbon source has a high degree of graphitization and a dense carbon structure, which is beneficial for optimizing the surface roughness of the active cathode material.

[0285] In some embodiments, the polyethylene glycol has a weight-average molecular weight of less than 10000.

[0286] In some embodiments, the weight-average molecular weight of the polyethylene glycol is optionally 1500, 2000, 3000, 4000, 6000, 8000 or any value in a range between two of these values.

[0287] The use of a polyethylene glycol with a weight-average molecular weight of less than 10000 allows the control of the decomposition rate during sintering to form a layer of carbon coating of suitable and uniform thickness.

[0288] In some embodiments, the moisture content of the polyethylene glycol is less than or equal to 0.5%.

[0289] If the moisture content of the polyethylene glycol is high, the moisture can disrupt the decomposition process, causing incomplete or uneven decomposition rates during sintering. Excess moisture can also lead to uneven distribution of the molten polyethylene glycol during sintering, affecting the uniformity of the carbon layer and resulting in an unstable or delaminating carbon coating layer.

[0290] In some embodiments, the moisture content of the polyethylene glycol is optionally 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or any value in a range between two of these values.

[0291] In some embodiments, the polyethylene glycol has a pH value of 5-7.

[0292] Polyethylene glycol with a pH of 5-7 is more stable and does not decompose during mixing due to excessive acidity, especially at high temperatures, which can lead to premature decomposition and compromise coating quality. Alkaline polyethylene glycol can impair the stability of other components, potentially causing dissolution or oxidation reactions of metal ions and affecting the performance of the finished active cathode material.

[0293] In some embodiments, the slurry further comprises a titanium source, which optionally includes one or more of titanium dioxide, tetrabutyl titanate, titanium nitrate and titanic acid.

[0294] The titanium source tends to have low surface activity, and the inclusion of the titanium source in the slurry can decrease the activity of the lithium-containing transition metal phosphate precursor, inhibit the particle growth of the lithium-containing transition metal phosphate during the high-temperature sintering process, and allow the lithium-containing transition metal phosphate to form smaller particles during the sintering process.

[0295] Titanium is used as a lattice stabilizer, and the titanium element usually enters the lattice of the lithium-containing transition metal phosphate in the form of Ti4+, and some of the titanium ions can take the place of the iron ions, making the crystal structure more stable and reducing the possibility of inversion of the lithium and iron ions, especially at high temperatures or during charging and discharging with high currents.

[0296] In some embodiments, lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol and titanium dioxide are homogeneously mixed in an organic solvent and ground to obtain the mixed raw material.

[0297] The organic solvent can effectively reduce the occurrence of side reactions and improve the purity and consistency of the material. Furthermore, the organic solvent has good volatility and can be more easily removed during the subsequent drying process, thus preventing the phenomenon of the organic solvent remaining in the material, which leads to the formation of pores and impairs the material's density and structural stability.

[0298] In some embodiments, the mass fraction of the carbon source in the mixed raw material is 5%-7%, based on the total mass of the mixed raw material.

[0299] In some embodiments, the mass fraction of the carbon source in the mixed raw material, based on the total mass of the mixed raw material, is optionally 5%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7% or any value in a range between two of these values.

[0300] By controlling the mass of the carbon source so that it contains lithium within the aforementioned ranges, the electrical conductivity of the material can be improved and the negative impact on the specific capacitance of the cathode foil and the energy density of the battery can be reduced. An excessively thick carbon layer not only occupies valuable space within the active material but can also lead to structural instability.

[0301] In some embodiments, the solvent comprises water and mixtures thereof.

[0302] In some embodiments, obtaining a mixed raw material comprising a carbon source, a lithium source, an iron source and a phosphorus source includes adding the carbon source, the lithium source, the phosphorus source, and the iron source to the solvent for mixing and stirring, and stirring at a speed of 1400 rpm to 2200 rpm.

[0303] In some embodiments, drying the mixed slurry to obtain a precursor powder includes spray drying the mixed slurry to obtain the precursor powder.

[0304] In some embodiments, the product is subjected to airflow comminution after sintering of the precursor to obtain the active cathode material.

[0305] In some embodiments, the sorting frequency of the airflow comminution is 18 Hz-24 Hz and the comminution air pressure is 0.45 MPa-0.65 MPa.

[0306] The sorting frequency in airflow comminution refers to the operating frequency of the sorting device during airflow comminution, which is generally related to sorting efficiency and the particle size distribution. At a higher sorting frequency, the particles in the airflow are sieved more frequently, so that larger particles are removed and smaller particles remain. A higher sorting frequency likely increases the number of particle collisions, so irregular particles are further blasted, resulting in smoother particle surfaces and a more spherical shape.

[0307] High air pressure causes the particles to be subjected to a stronger impact and the collision between the ponds to be more intense, which results in the surface of the particles being subjected to strong impact and wear, causing the particles to be broken down into smaller ponds, the collision between the particles to be more intense and the surface to be easier to trim, which improves the sphericity and surface flatness of the particles.

[0308] However, excessively high sorting frequency and crushing air pressure cause the agglomerated particles to be dispersed into primary particles, which then begin to crack and break down further. This affects the predetermined particle size distribution and renders the carbon coating layer incomplete, manifesting as increased iron dissolution. It also negatively impacts particle displacement during rolling, increases contact and reaction between the lithium-containing transition metal phosphate and the electrolyte solution, and is detrimental to maintaining cycle performance and battery lifespan. Therefore, it is essential to control the sorting frequency and crushing air pressure within a suitable range.

[0309] A further unclaimed aspect of the present application provides a method for producing a cathode foil, wherein the production method comprises: dry mixing a binder, a conductive agent and an active cathode material produced by the production method in the fourth aspect, adding a solvent, stirring and adjusting the viscosity to obtain a shipping slurry; transferring and applying the shipping slurry to at least one side of the collector, drying and hot pressing to obtain a cathode foil.

[0310] In some embodiments, the circulation speed of the dry mixing is 20 rpm-30 rpm and the rotation speed of the dry mixing is 750 rpm-850 rpm.

[0311] In some embodiments, the hot pressing comprises at least three hot rolling presses, wherein the hot rolling pressure increases sequentially and is successively 20 tonnes-50 tonnes, 50 tonnes-70 tonnes and 70 tonnes-90 tonnes; and wherein the hot rolling temperature is 40°C-80°C, and wherein the electrode foil is heated prior to the first entry into the hot rolling press, the temperature of the heating being 40°C-50°C.

[0312] The active cathode material in the embodiment of the present application, which is produced using the above hot pressing method in conjunction with the manufacturing method of the fourth aspect, contributes to further reducing the porosity of the cut surface of the cathode film layer, increasing the boundary pressing density of the electrode foil and improving the energy density of the battery.

[0313] Furthermore, the present application provides a power-consuming device comprising at least one lithium-ion secondary battery, battery module, or battery pack provided by the present application. The lithium-ion secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device or as an energy storage unit for the power-consuming device. The power-consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0314] Depending on requirements, a lithium-ion secondary battery, a battery module or a battery pack can be selected as the power-consuming device.

[0315] Fig. Figure 7 shows an example of the power-consuming device. The power-consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium-ion secondary battery of this power-consuming device, a battery pack or battery module can be used.

[0316] Another example of such a device is a mobile phone, a tablet, a laptop, etc. The device usually needs to be light and thin and can use a lithium-ion secondary battery as a power source. Examples of implementation

[0317] The following describes exemplary embodiments of the present application. The embodiments described below are exemplary, serve to explain the present application, and cannot be construed as limiting the present application. Unless specific techniques or conditions are indicated in the exemplary embodiments, they correspond to the techniques or conditions described in the relevant literature or to the information in the product specification. The reagents or instruments used, without manufacturer information, are all commercially available products. Exemplary embodiment 1(1) Production of the active cathode material

[0318] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and titanium dioxide in a solvent until homogeneous. The ratio of iron(II) oxalate to lithium dihydrogen phosphate results in a molar ratio of iron to phosphorus of 0.965:1.0.

[0319] The mixed raw materials are repeatedly ball-milled and demagnetized in a ball mill to obtain the mixed slurry. The number of milling passes and the milling time are controlled, as is the particle size D. v50 The particle size of the mixed slurry after grinding is 3.0 µm.

[0320] The mixed slurry is spray-dried to obtain the dried precursor powder material, and the dried precursor powder material has a light yellow appearance and a uniform color.

[0321] The precursor powder material is placed in a sintering furnace and heated under a nitrogen atmosphere at 2°C / min from 25°C to 350°C and kept at this temperature for 3 hours, then heated at 5°C / min to a second temperature of 770°C and kept at this temperature for 10 hours, and after completion, cooling is carried out.

[0322] The obtained lithium iron phosphate cathode material is crushed by the airflow comminution process to obtain the carbon-coated active lithium iron phosphate cathode material.

[0323] The mass fraction of the carbon element in the active cathode material is 1.103%, the median L A50 The sphericity is 0.720, L A90 is 0.895 and the median R A50 The roughness is 0.941, and the lithium and iron antisit defect concentration is 0.55%, the powder bulk density is 1.04 g / cm³. 3The powder density under a pressure of 3 T is 2.572 g / cm³. 3 , and the specific resistance of the powder under a pressure of 8 MPa is 5.90 Ω-cm; the discharge gram capacity at a discharge rate of 1 C is 143.8 mAh / g; the discharge capacity percentage of the 3.2V discharge platform is 91.0%. (2) Production of the cathode foil

[0324] 2.2 wt% PVDF, 0.8 wt% conductive carbon black, and 97.0 wt% active cathode materials are added sequentially and dry mixed. N-methylpyrrolidone is then added, the mixture is stirred, and the viscosity is adjusted to obtain the shipping slurry. The shipping slurry is transferred and applied to the bottom coating of the collector aluminum foil. The bottom coating consists of carbon black and PVDF in a mass ratio of 1:1. The particle size distribution of carbon-based particles greater than 100 nm in the bottom coating is ≤10 pcs / 10 µm, and the thickness of the bottom coating is 2 µm. A cathode film layer with a one-sided areal density of 350 mg / 1540 cm² is obtained after drying and hot pressing.

[0325] The circulation speed of the dry mixing is 25 rpm / 30 rpm and the rotation speed of the dry mixing is 800 rpm.

[0326] The hot pressing process comprises at least three hot rolling presses, wherein the hot rolling pressure increases sequentially and is successively 35 tonnes, 55 tonnes and 75 tonnes; and wherein the hot rolling temperature is 65°C, and wherein the electrode foil is heated before the first entry into the hot rolling press, the temperature of which is 50°C.

[0327] The electrode foil's compressive density, the limiting compressive density of the electrode foil, and the test procedure for the limiting compressive density of the electrode foil are described below; the limiting compressive density of the electrode foil in this embodiment is 2.68 g / cm³. 3 .

[0328] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, 17,857 particles are counted, and the results show that the area fraction of the particles with an area of ​​0.001 µm 2 -0.06 2 23.84% and the area fraction of the particles with an area of ​​1.0 µm 2 -4.0 µm 2 15.01%. The median C 50 The degree of graphitization of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 1.018, C 90 is 1.041, C 10 is 1.007 and the concentration of the C values ​​(C 90 -C 10 ) / C 50 It is 0.033.

[0329] The iron dissolution rate of the cathode film layer is 1041 ppm. (3) Production of the anode foil:

[0330] 95.5 wt% of the negative active material (artificial graphite), 1.0 wt% of the conductive agent (conductive carbon black), 2.0 wt% of the binder (styrene-butadiene rubber (SBR)), and 1.5 wt% of the thickener (sodium carboxymethylcellulose (CMC)) are mixed, augmented with deionized water, stirred, and dispersed to produce an anode slurry. The anode slurry is then applied to both surfaces of the copper foil, and after both sides are coated, the anode foil is produced by drying, compacting, cutting, and stacking. The density of the coated single-sided surface is 165 mg / 1540 mm². 2 and the pressing density 1.60g / cm³ 3 . (4) Production of the release film

[0331] Polypropylene film is used as a separating film. (5) Preparation of the electrolyte solution:

[0332] In a glove box with an argon atmosphere (H2O<0.1ppm, O2<0.1ppm), the organic solvent ethylene carbonate (EC) / dimethyl carbonate (DMC) is homogeneously mixed in a volume ratio of 1:1, and the lithium salt LiPF6 is added to dissolve it in the organic solvent, and the content of LiPF6 in the solution is 1 mol / L, and it is stirred homogeneously to obtain the electrolyte solution. (6) Battery manufacturing:

[0333] The cathode foil, separator film, and anode foil are stacked in sequence, and the separator film should be able to play the role of insulating the cathode and the anode, and the bare electrical core is obtained by winding, and the bare electrical core is placed in the outer packaging into which the electrolyte solution is injected, and through the processes of encapsulation, formation, and exhaust, the lithium-ion battery is finally obtained.

[0334] The manufacturing process of embodiments 2 and 3 is essentially the same as that of embodiment 1, and the difference lies in the fact that the carbon source is set in the raw material. Example 2

[0335] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and glucose (mixed in a mass ratio of 3:1) and titanium dioxide in a solvent until a homogeneous state is achieved. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.965:1.0. Example 3

[0336] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and glucose (mixed in a mass ratio of 1:3) and titanium dioxide in a solvent until a homogeneous state is achieved. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.965:1.0.

[0337] The manufacturing process of embodiment 4 is essentially the same as that of embodiment 3, and the difference lies in the fact that the sintering temperature of the precursor powder material is adjusted. Example 4

[0338] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and glucose (mixed in a mass ratio of 1:3) and titanium dioxide in a solvent until a homogeneous state is achieved. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.965:1.0.

[0339] The precursor powder material is placed in a sintering furnace and sintered under a nitrogen atmosphere in two stages to obtain a lithium iron phosphate cathode material: the temperature is increased from 25°C to 350°C at a heating rate of 2°C / min and the temperature is held for 3 hours; the temperature is increased from 350°C to 780°C at a heating rate of 5°C / min and the temperature is held for 10 hours; and after completion, cooling is carried out.

[0340] The manufacturing process of embodiments 5 and 6 is essentially the same as that of embodiment 1, and the difference lies in the fact that the sintering temperature of the precursor powder material is adjusted. Example 5

[0341] The precursor powder material is placed in a sintering furnace and sintered under a nitrogen atmosphere in two stages to obtain a lithium iron phosphate cathode material: the temperature is increased from 25°C to 350°C at a heating rate of 2°C / min and the temperature is held for 3 hours; the temperature is increased from 350°C to 755°C at a heating rate of 5°C / min and the temperature is held for 10 hours; and after completion, cooling is carried out. Example 6

[0342] The precursor powder material is placed in a sintering furnace and sintered in two stages under a nitrogen atmosphere to obtain a lithium iron phosphate cathode material: the temperature is increased from 25°C to 350°C at a heating rate of 2°C / min and the temperature is held for 3 hours; the temperature is increased from 350°C to 790°C at a heating rate of 5°C / min and the temperature is held for 10 hours; and after completion, cooling is carried out.

[0343] The manufacturing process of embodiments 7 and 8 is essentially the same as that of embodiment 1, and the difference lies in the adjustment of the molar ratio of iron and phosphorus. Example 7

[0344] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and titanium dioxide in a solvent until homogeneous. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.955:1.0. Example 8

[0345] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and titanium dioxide in a solvent until homogeneous. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.975:1.0.

[0346] The manufacturing process of embodiment 9 is essentially the same as that of embodiment 1, and the difference lies in the fact that no conductive carbon black is added during the manufacture of the cathode foil:

[0347] 97.8 wt% of the active cathode material and 2.2 wt% of PVDF are mixed, and then N-methylpyrrolidone is added; the positive electrode slurry is prepared by stirring and dispersing.

[0348] The manufacturing process of comparative example 1 is essentially the same as that of embodiment 1, and the difference lies in the fact that the sintering temperature of the carbon source is set in the raw material and the precursor powder material. Comparative example 1

[0349] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, glucose, and titanium dioxide in a solvent until homogeneous. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.965:1.0.

[0350] The precursor powder material is placed in a sintering furnace and sintered under a nitrogen atmosphere in two stages to obtain a lithium iron phosphate cathode material: the temperature is increased from 25°C to 350°C at a heating rate of 2°C / min and the temperature is held for 3 hours; the temperature is increased from 350°C to 740°C at a heating rate of 5°C / min and the temperature is held for 10 hours; and after completion, cooling is carried out.

[0351] The manufacturing process of comparative example 2 is essentially the same as that of embodiment 1, and the difference lies in the adjustment of the molar ratio of iron and phosphorus and the sintering temperature of the precursor powder material. Comparative example 2

[0352] Mixing and grinding lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and titanium dioxide in a solvent until homogeneous. The ratio of lithium dihydrogen phosphate to iron(II) oxalate results in a molar ratio of iron to phosphorus of 0.955:1.0.

[0353] The precursor powder material is placed in a sintering furnace and sintered under a nitrogen atmosphere in two stages to obtain a lithium iron phosphate cathode material: the temperature is increased from 25°C to 350°C at a heating rate of 2°C / min and the temperature is held for 3 hours; the temperature is increased from 350°C to 810°C at a heating rate of 5°C / min and the temperature is held for 10 hours; and after completion, cooling is carried out. Performance test 1. Energy density test

[0354] Store the lithium-ion secondary battery for 2 hours at 25°C to ensure its temperature is 25°C. Charge the lithium-ion secondary battery at 25°C at 0.33C until the cutoff voltage of 3.65V is reached. Continue charging at a constant voltage at this cutoff voltage until the current reaches 0.05C, at which point charging is stopped (where C represents the nominal capacity of the lithium-ion secondary battery). After storing the lithium-ion secondary battery for 1 hour at 25°C, discharge it at 0.33C until the discharge cutoff voltage reaches 3.65V, and record the total discharge energy of the lithium-ion secondary battery as E0.

[0355] Measuring the length, width, and height of the battery cell and calculating the volumetric value of the battery cell, V0 = length * width * height. Volume energy density of the lithium-ion secondary battery = lithium-ion secondary battery discharge energy E0 / volume V0 of the lithium-ion secondary battery. 2. DCR test procedure

[0356] Charge at 25°C to 3.65V with a constant current of 0.33C, then charge with a constant voltage to a current of 0.05C, then discharge to 20% SOC at 0.33C, store for 5 min, then pulse discharge at 3C for 30 s, store for 40 s, then charge at 3C for 40 s, store for 5 min, then charge to 3.65V with a constant current of 0.33C and charge at a constant voltage to 0.05C, then discharge at 0.33C to 10% SOC, store for 5 min, then pulse discharge at 3C for 30 s, store for 40 s, then charge at 3C for 40 s, store for 5 min, then full charge at 0.33C, then discharge at 0.33C to 50% SOC, then store at -25°C for 2 hours and pulse discharge at 1C for 30 s, store for 10 min, then store at 25°C for 2 hours, charge to 3.65 V with a constant current of 0.33 C, then charge with a constant voltage to 0.05 C, then discharge at 0.33 C to 20% SOC, then store at -25°C for 2 hours and pulse discharge at 1C for 30 s, store for 10 min.

[0357] Recording the voltage at this point before and after each pulse discharge to calculate the DCR under different conditions, where the calculation formula is: DCR=(voltage before pulse discharge after the end of storage - voltage after pulse discharge before storage) / pulse current. 3. Limiting compressive strength of the electrode foil

[0358] After double-sided coating, the electrode foil is compacted using a roller press to test its elongation and evaluate its flexibility. Increasing the roller press pressure produces electrode foils with varying densities. As the pressure increases, the electrode foil's density increases, its ductility increases, and its flexibility decreases. Excessive ductility is likely to cause warping, while insufficient flexibility is likely to lead to brittle fracture. Therefore, the lower of the two densities, defined as the limiting density, is determined when the electrode foil's ductility reaches 8% or the number of times it can be flexibly folded (3).

[0359] The compression density is calculated from the mass of the cathode film layer / volume of the cathode film layer.

[0360] The test procedure for ductility is as follows:

[0361] Laying the electrode foil on a horizontal table, cutting the electrode foil into sections, each strip being approximately 100 cm long; removing the copper foil of the substrate at the edge of the electrode foil, taking care to keep the cut edge of the electrode foil parallel to the MD direction of the electrode foil (perpendicular to the direction of the pressure roller) to ensure that the electrode foil is completely covered by the coating; using a steel ruler to measure the lengths between the marking points at the head and tail of the electrode foil and the positions of equal width in the longitudinal direction, estimating the length to the nearest 0.1 mm, and recording the length before compaction;and wherein, after compaction, the length between the corresponding marker points is recorded, and wherein (length after compaction - length before compaction) / length before compaction is used as the ductility.;

[0362] The number of times the flexible folding is checked as follows.

[0363] Cutting the cathode foil into a test sample measuring 20×100 mm 2; Fold this in the middle in the forward direction, flatten it with a 2kg pressure roller and unfold it against the light to check if the gap is translucent or not; if no translucency occurs, it is folded in the opposite direction and flattened with a 2kg pressure roller, and it is checked again against the light, and so on, until the gap is translucent, and the number of folds is recorded; repeat the test three times and take the average value as reference data for the flexibility of the electrode foil. Test result Table 1 carbon source Sintering temperature / °C Fe / P Mass content of the conductive agent Graphitization degree C 50 Concentration of C values D A50 / nm Area fraction of particles with an area of ​​0.001µm 2 - 0.06µm 2 / % Area fraction of particles with an area of ​​1 µm 2 -4µm 2 / % Example 1 PEG 770 0,965 0,80% 1,018 0,033 730 23,84 15,01 Example 2 PEG:PEG:Glucose=3:1 770 0,965 0,80% 1,012 0,034 733 23,55 15,29 Example 3 PEG:Glucose=1:3 770 0,965 0,80% 0,987 0,036 735 23,10 15,59 Example 4 PEG:Glucose=1:3 780 0,965 0,80% 1,016 0,04 746 22,34 17,11 Example 5 PEG 755 0,965 0,80% 0,965 0,028 702 26,01 12,89 Example 6 PEG 790 0,965 0,80% 1,125 0,04 767 21,45 19,78 Execution- PEG 770 0,955 0,80% 1,029 0,032 736 22,63 15,87 example 7 Example 8 PEG 770 0,975 0,80% 1,005 0,036 724 24,76 14,21 Example 9 PEG 770 0,965 0,00% 1,018 0,033 730 23,84 15,01 Comparison example 1 glucose 740 0,965 0,80% 0,92 0,045 637 27,54 11,66 Comparison example 2 PEG 810 0,955 0,80% 1,16 0,054 815 20,01 21,88 Table 2 Electrode foil pressure density after full discharge and formation g / cm³ 3 Energy density Wh / L DCR25°C3C20%SOC / mΩ DCR-25°C1C50%SOC / m Ω 2,56 445,0 43,1 387,9 Example of implementation 11 2,57 446,7 44,9 407,3 Example of implementation 12 2,58 444,3 47,4 426,3 Example of implementation 13 2,6 447,6 47,8 430,6 Example of implementation 14 2,52 438,4 40,6 360,0 Implementation example 2,61 446,5 47,5 425,9 15 Example of implementation 16 2,57 444,0 45,5 424,8 Example of implementation 17 2,54 441,7 41,2 371,2 Example of implementation 18 2,56 448,7 43,5 391,2 Example of implementation 19 2,4 418,4 44,6 401,5 Comparative example 1 2,62 443,6 50,6 454,2 Comparative example 2

[0364] From the comparison between the exemplary embodiments and the comparative examples, it is evident that the median C 50of the degree of graphitization in the cumulative distribution curve for the graphitization C-value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is greater than or equal to 0.95 and less than or equal to 1.20, where the concentration of the C-values ​​(C 90 -C 10 ) / C 50 0.01-0.04; the battery maintains a low internal resistance (especially with low impedance at a low SOC) while improving the electrode foil density, which allows the battery to improve the electrode foil density and the battery energy density while maintaining good kinetic performance.

[0365] From the comparison of embodiment 5 with embodiments 1-4 and 6-9, it is evident that, in the cumulative distribution curve for the graphitization C-value of the cathode material obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, the median C 50 The graphitization level is 0.98-1.13, and it contributes to improving the pressing density of the electrode foil based on maintaining a low impedance of the battery and to improving the energy density of the battery based on maintaining good kinetic performance of the battery.

[0366] From a comparison of embodiments 4 and 6 with embodiment 2, it is evident that when the concentration of the C values ​​(C 90 -C 10 ) / C 50In the cumulative distribution curve for the graphitization C-value of the cathode material, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.02-0.038 indicates that the coating of the active cathode material has a high uniformity, which contributes to a further improvement in the kinetic performance of the battery based on maintaining a good pressing density of the electrode foil and the energy density of the battery.

[0367] From the comparison of embodiment 9 with embodiment 1, it is evident that the lithium-ion secondary battery of the embodiments of the present application still exhibits good kinetic performance when no conductive means is added, and at the same time the energy density of the lithium-ion secondary battery can be further improved.

[0368] It should be noted that the present application is not limited to the embodiments mentioned above. The embodiments mentioned above are only examples, and embodiments within the scope of the technical solution of the present application that have essentially the same composition as the technical idea and have the same effect are included in the technical scope of the present application. Furthermore, within the scope of the present application, other possibilities for constructing the embodiments by combining some of the constituent elements of the embodiments and applying various deformations to the embodiments that a person skilled in the art can imagine without departing from the subject matter of the present application are also included. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] GB / T 21023-2006

[0153] Suzhou Jingle, Model ST2722

[0181]

Claims

[1] Lithium-ion secondary battery, characterized by that it comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises lithium-containing transition metal phosphate particles, wherein at least a part of the surface thereof is provided with a carbon coating material, and where the median C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C-value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is greater than or equal to 0.95 and less than or equal to 1.20, and where the concentration of the C-values ​​(C 90 -C 10 ) / C 50 0.01-0.04; where the graphitization C value I G / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1 stands. [2] Lithium-ion secondary battery according to claim 1, characterized by that the median C 50 The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.96-1.

15. [3] Lithium-ion secondary battery according to claim 1, characterized by that the median C 50 The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.98-1.

13. [4] Lithium-ion secondary battery according to claim 1, characterized by , that the concentration of C values ​​(C 90 -C 10 ) / C 50 in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.02-0.

038. [5] Lithium-ion secondary battery according to claim 1, characterized by , that the concentration of C values ​​(C 90 -C 10 ) / C 50 in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.02-0.

036. [6] Lithium-ion secondary battery according to claim 1, characterized by that C 90The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 1.0-1.

30. [7] Lithium-ion secondary battery according to claim 1, characterized by that C 90 The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 1.02-1.

15. [8] Lithium-ion secondary battery according to claim 1, characterized by that C 10 The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.92-1.

10. [9] Lithium-ion secondary battery according to claim 1, characterized by that C 10The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.98-1.

08. [10] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles has an area of ​​0.001 µm 2 -0.06 µm 2 21.00%-27.00% and the area fraction of particles with an area of ​​1.0 µm 2 -4.0 µm 2 12.00%-20.00%. [11] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil D A50 the particle size is 600 nm-800 nm, where D A50refers to the corresponding particle size when the cumulative area distribution of the particles reaches 50% in the cumulative area distribution curve. [12] Lithium-ion secondary battery according to claim 11, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil D A50 the particle size is 650 nm-750 nm, where D A50 refers to the corresponding particle size when the cumulative area distribution of the particles reaches 50% in the cumulative area distribution curve. [13] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the roughness area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median R A50 The roughness is 0.92-0.

96. [14] Lithium-ion secondary battery according to claim 1, characterized by, that in the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, L A90 the sphericity is 0.80-0.

95. [15] Lithium-ion secondary battery according to claim 14, characterized by , that in the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, L A90 the sphericity is 0.85-0.

93. [16] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median L A50 the sphericity is 0.65-0.

85. [17] Lithium-ion secondary battery according to claim 16, characterized by, that in the cumulative distribution curve of the sphericity surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median L A50 the sphericity is 0.70-0.

80. [18] Lithium-ion secondary battery according to claim 1, characterized by that the iron dissolution rate of the cathode film layer is 500 ppm-2000 ppm. [19] Lithium-ion secondary battery according to claim 18, characterized by , that the iron dissolution rate of the cathode film layer is 500 ppm-1500 ppm. [20] Lithium-ion secondary battery according to claim 1, characterized by , that, based on the total mass of the active cathode material, the mass content of carbon is 0.8%-1.8%. [21] Lithium-ion secondary battery according to claim 20, characterized by , that, based on the total mass of the active cathode material, the mass content of carbon is 0.90%-1.5%. [22] Lithium-ion secondary battery according to claim 1, characterized by , that the lithium and iron antisit defect concentration of the active cathode material is 0.1%-1.5%. [23] Lithium-ion secondary battery according to claim 22, characterized by , that the lithium and iron antisit defect concentration of the active cathode material is 0.3%-1.0%. [24] Lithium-ion secondary battery according to claim 1, characterized by , that the lithium-containing transition metal phosphate includes a component with the following general formula: Li m Fe x P y O j Q q , where Q comprises one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and where 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, 0 <q≤0,1 ist. [25] Lithium-ion secondary battery according to claim 1, characterized by, that the active cathode material comprises one or more of the following materials: lithium iron phosphate and its doped modified material, as well as coated modified material. [26] Lithium-ion secondary battery according to claim 1, characterized by , that the active cathode material comprises titanium, wherein the mass content of titanium is 2000 ppm-6000 ppm relative to the total mass of the active cathode material. [27] Lithium-ion secondary battery according to claim 1, characterized by that the powder bulk density of the active cathode material is 0.70 g / cm³ 3 -1.50 g / cm² 3 amounts. [28] Lithium-ion secondary battery according to claim 27, characterized by that the powder bulk density of the active cathode material is 0.70 g / cm³ 3 -1.20 g / cm² 3 amounts. [29] Lithium-ion secondary battery according to claim 1, characterized by , that under a pressure of 3 T the powder density of the active cathode material is 2.50 g / cm³3 -2.70 g / cm² 3 amounts. [30] Lithium-ion secondary battery according to claim 29, characterized by , that under a pressure of 3 T the powder density of the active cathode material is 2.52 g / cm³ 3 -2.68 g / cm² 3 amounts. [31] Lithium-ion secondary battery according to claim 1, characterized by , that the powder resistance of the active cathode material under a pressure of 8 MPa is 0.5 Ω·cm-30 Ω·cm. [32] Lithium-ion secondary battery according to claim 31, characterized by , that the powder resistance of the active cathode material under a pressure of 8 MPa is 2 Ω·cm-20 Ω·cm. [33] Lithium-ion secondary battery according to claim 1, characterized by , that the active cathode material has a discharge gram capacity of 135 mAh / g-150 mAh / g at room temperature at a discharge rate of 1 C. [34] Lithium-ion secondary battery according to claim 1, characterized by, that the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, where η is defined such that a button battery comprising the active cathode material is charged and discharged twice in a voltage range of 2.0 V to 3.75 V at a C-rate of 0.1 C at a constant current and subsequently charged and discharged once at a C-rate of 1 C at a constant current, wherein the capacity value extracted in the charge and discharge test at a C-rate of 1 C at a discharge voltage of 3.2 V is recorded as C1, and wherein the capacity value extracted at a discharge voltage of 2.0 V is C2, and where η=C1 / C2, and wherein the charging process comprises a constant voltage charge with a constant voltage of 3.75 V and a constant voltage cut-off current of 50 µA. [35] Lithium-ion secondary battery according to claim 1, characterized by, that, relative to the total mass of the cathode film layer, the mass content of the conductive medium is 0-1.5%. [36] Lithium-ion secondary battery according to claim 1, characterized by , that, relative to the total mass of the cathode film layer, the mass content of the conductive medium is 0. [37] Lithium-ion secondary battery according to claim 1, characterized by , that the cathode film layer further comprises a binder, wherein, based on the total mass of the cathode film layer, the mass content of the active cathode material is 95.5%-99.5%; and wherein the mass content of the binder is 0.5%-3%. [38] Lithium-ion secondary battery according to claim 37, characterized by , that, based on the total mass of the cathode film layer, the mass content of the active cathode material is 96.5%-99.5%. [39] Lithium-ion secondary battery according to claim 1, characterized by , that the one-sided areal density of the cathode film layer is 300 mg / 1540 mm²2 -450 mg / 1540 mm 2 amounts. [40] Lithium-ion secondary battery according to claim 1, characterized by , that in the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.51 g / cm³ 3 -2.73 g / cm² 3 amounts. [41] Lithium-ion secondary battery according to claim 1, characterized by , that in the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.55 g / cm³ 3 -2.70 g / cm² 3 amounts. [42] Lithium-ion secondary battery according to claim 1, characterized by that the cathode film layer meets at least one of the following conditions: (1) In the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.51 g / cm³. 3 -2.73 g / cm² 3, and in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is 10%-22%; (2) In the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.55 g / cm³. 3 -2.70 g / cm² 3 , and in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the porosity of the cathode film layer is 10%-20%. [43] Lithium-ion secondary battery according to claim 1, characterized by that the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the cathode collector; and wherein the lower coating satisfies at least one of the following conditions: (1) the lower coating comprises carbon-based particles, wherein the distribution density of the carbon-based particles with a particle size of more than 100 nm in the lower coating is ≤ 10 pcs / 10 µm; (2) the density of the cathode foil in a fully discharged state is greater than or equal to 2.4 g / cm³ 3 , and the one-sided thickness of the lower coating is 1 µm-4 µm; (3) the density of the cathode foil in a fully discharged state is greater than or equal to 2.5 g / cm³ 3 , and the one-sided thickness of the lower coating is 2 µm-4 µm. [44] Battery device, characterized by , that it comprises a lithium-ion secondary battery according to any one of claims 1 to 43, wherein the battery device comprises at least one of a battery module, a battery pack and an energy storage battery. [45] Power-consuming device, characterized by, that it comprises a lithium-ion secondary battery according to any one of claims 1 to 43 or a battery device according to claim 44.

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