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

Abstract

A 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 current collector and a cathode film layer arranged on at least one side of the cathode current collector, wherein the cathode film layer comprises an active cathode material, the active cathode material comprising lithium-containing transition metal phosphate particles, and wherein at least a part of the surface thereof is provided with a carbon coating material, wherein the percentage area fraction of the particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is greater than or equal to 8.0% and less than or equal to 20.0%, wherein the iron dissolution rate of the cathode film layer is 658 ppm-1921 ppm.

Description

TECHNICAL AREA

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

[0002] In recent years, lithium-ion 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 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 it a pressing technical problem in this field. REVELATION OF THE INVENTION

[0004] In view of the above problem, the present application provides a lithium-ion secondary battery, a battery device, a power-consuming device, a method for producing an active cathode material and a method for producing a cathode foil, which are described below.

[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 current collector and a cathode film layer arranged on at least one side of the cathode current 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, wherein the percentage area fraction of the particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is greater than or equal to 8.0% and less than or equal to 20.0%, and wherein the iron dissolution rate of the cathode film layer is 658 ppm-1921 ppm.

[0006] The percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is less than 8%, which makes it difficult to achieve the high pressure density of the cathode foil.The percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is more than 20%. Although this contributes to achieving a high compression density of the cathode foil, it reduces the contact area between the electrolyte and the active cathode material, hinders the diffusion of lithium ions into the cathode film layer, and increases the diffusion path of the lithium ions in the particles. This further leads to strong local polarization of the electrode foils, increases the battery impedance, and results in a significant deterioration of the battery's kinetic performance.

[0007] By controlling the percentage area fraction of particles with a particle size greater than or equal to 1.5 µm in the cathode film layer to greater than or equal to 8.0% and less than or equal to 20.0%, the significant short-plate effect caused by the large particles can be reduced. This helps to keep the battery impedance low and improve the battery's kinetic performance, but it limits the further improvement of the electrode foil density. In the embodiments of the present application, controlling the iron dissolution rate of the cathode film layer to 658 ppm–1921 ppm, i.e.,By improving the density and completeness of the carbon coating on the surface of the active cathode material, particle movement is facilitated and lattice defects in the lithium-containing transition metal phosphate are reduced. This increases the particle's compressive strength, decreases the likelihood of particle collapse and tearing under high rolling pressure, and improves the compressive density of the electrode foils. Simultaneously, the complete and dense carbon coating material contributes to improved electrical contact between the active cathode materials, enhanced electrical conductivity, and reduced polarization.The low level of lattice defects contributes to smooth lithium-ion transfer channels, thereby improving the lithium-ion transfer rate of the active cathode material and thus achieving a balance between the kinetic performance of the battery and the energy density.

[0008] In each embodiment, the iron dissolution rate of the cathode film layer is 658 ppm–1485 ppm. The cathode film layer with iron dissolution rates in the above range exhibits relatively fewer lattice defects and a more complete and dense carbon coating material. Lower lattice defects contribute to improving the compressive strength and particle slippage in the cathode film layer under high roller pressure; high coating completeness promotes slippage between particles; and a dense coating helps to reduce the carbon layer's volumetric occupancy, further improving the electrode foil's compression density and achieving a balance between the battery's kinetic power and energy density.

[0009] In each embodiment, the median B is 50of the coating value in the cumulative distribution curve for the coating value-B of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.35-0.48; where the coating value-B I P / I D is, where I P for the intensity of the P-peak of the Raman spectrum at 948±100cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 The coating value B can indirectly reflect the thickness of the carbon coating material on the surface of the lithium-containing transition metal phosphate particles. The thinner the carbon coating material, the higher the intensity of the phosphate structure detected in the Raman spectrum and the higher the coating value of the cathode film layer.

[0010] In each embodiment, the percentage area fraction of particles with a particle size of 5 µm or greater in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 0. Research has shown that particles with a particle size of 5 µm or greater in the cathode film layer significantly impair electrolyte infiltration into the cathode film layer and electrolyte diffusion into the active material particles, and the percentage area fraction of particles with a particle size of 5 µm or greater is 0, which leads to a further reduction in the battery's internal resistance and an improvement in the battery's kinetic performance.

[0011] In each embodiment, the percentage area fraction of particles with a particle size of 1.5 µm or greater and less than 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 9.0%–20.0%, optionally 10.0%–20.0%. If the percentage area fraction of particles with a particle size of 1.5 µm or greater and less than 5 µm is within the above range, it is advantageous to improve the pressing density of the electrode foils. At the same time, it is possible to further reduce the hindering effect of large particles on the surface of the electrode foils on the infiltration and diffusion of the electrolyte in the cathode film layer, improve the consistency of the diffusion rate of lithium ions in the particles of the active cathode material, reduce local polarization, and improve the kinetic performance of the battery.

[0012] In each embodiment, the percentage area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 15.0%–25.0%, optionally 16.0%–24.0%. When the percentage area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm is within the above range, it can fill larger gaps in the stacking, form a specific "support structure," reduce the porosity between the particles, and contribute to improving particle contact and overall structural strength. Based on maintaining the good kinetic performance of the battery, the packing density of the electrode foils can be further improved, and the energy density of the battery can be enhanced.

[0013] In each embodiment, the percentage area fraction of particles with a particle size greater than or equal to 200 nm and less than 1500 nm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 73.0%–80.0%, optionally 73.0%–78.0%. The percentage area fraction of particles with a particle size greater than or equal to 200 nm and less than 1500 nm can be determined by testing using the described method. The sum of the areas of the particles with a particle size greater than or equal to 200 nm and less than 1500 nm, divided by the total area of ​​the counted particles, is considered to be the percentage area fraction of particles with a particle size greater than or equal to 200 nm and less than 1500 nm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0014] In each embodiment, 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, 0.95–1.20, optionally 0.98–1.15, and further optionally 1.0–1.10; where the graphitization C value is IG / ID, where IG is the intensity of the G-peak of the Raman spectrum at 1580 ± 100 cm⁻¹ -1 and ID for the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 The higher the degree of graphitization of the carbon on the surface of the active cathode material, the higher the proportion of graphitic structural carbon in the cathode film layer and the easier the particles can slide in the covering material with the help of the highly graphitized carbon structure in order to achieve an increase in the pressing density of the electrode foil.

[0015] 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. The particles with a median L A50 The sphericity within the above area is approximately spherical, and it is easy for the particles to slide from particle to particle under the influence of an external force, which can further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0016] 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 of roughness 0.92-0.96. The surface of the particles whose median R A50The roughness lies within the above range, is relatively smooth, the friction between the particles is relatively low, and it is easy to slip under the influence of external forces, which can further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0017] In each embodiment, the carbon content, based on the total mass of the active cathode material, is 0.8%–1.8%, optionally 0.9%–1.50%. Compared to the prior art active cathode material of lithium-containing transition metal phosphate, this active cathode material has a relatively low carbon coating content, 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.

[0018] 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%. During manufacturing and operation, it is unavoidable that a certain amount of lithium vacancies are present in the crystal structure of the active cathode material. These lithium vacancies 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, thereby forming a lithium and 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, further improving the kinetic performance of the lithium-ion secondary battery.

[0019] 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.

[0020] The selection of the appropriate modification element Q can improve the lattice change rate of the active cathode material in the process of de-embedded lithium, reduce the oxygen activity on the surface of the particles, improve the structural stability of the material and thereby improve the level of the gram capacity game of the material during the cycle and further improve the cycle stability of the lithium-ion secondary battery.

[0021] 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.

[0022] In each embodiment, the active cathode material comprises titanium, and the titanium content, relative to the total mass of the active cathode material, is 2000 ppm–6000 ppm. The high titanium content does not form a harmful impurity phase that negatively affects the energy density and kinetic performance of the battery. The reason for this is unclear, but it is suspected that titanium, together with the phosphate ion and other elements (e.g., lithium), forms a fast-ion conductor, which instead improves the battery's kinetic performance.

[0023] 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 / cm²3 -1.20g / cm² 3 .

[0024] The active cathode material in this embodiment of the present application has a limited effective gradation that forms automatically and has a relatively low powder bulk density, and with the help of the high completeness and density of the carbon coating material of the active cathode material in the cathode film layer, the gaps between the particles can be easily compressed under the action of an external force in order to achieve an increase in the powder compaction density.

[0025] In each embodiment, the powder density of the active cathode material is 2.50 g / cm³ under a pressure of 3T. 3 -2.70 g / cm² 3 , optional 2.52 g / cm² 3 -2.68 g / cm² 3 .

[0026] Although the percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in the cathode film layer is small, this indicates that the surface of the active cathode material has a high density and completeness of the carbon coating material thanks to the cathode film layer with a low iron dissolution rate, which allows a high pressing density to be achieved even under the influence of external forces, and provides 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.

[0027] In each embodiment, the powder resistance of the active cathode material under a pressure of 8 MPa is 0.5 Ω·cm–30.0 Ω·cm, optionally 2.0 Ω·cm–20.0 Ω·cm. The carbon coating material on the surface of the active cathode material exhibits high completeness and density, thus facilitating rapid electron conduction between particles via the coating structure. This results in a low powder resistance for the active cathode material, thereby increasing the electron transport velocity in the solid phase and improving the kinetic performance of the battery.

[0028] In each embodiment, the active cathode material exhibits a discharge gram capacity of 135 mAh / g–150 mAh / g at a discharge rate of 1C. The high discharge gram capacity of the active cathode material at a C-rate of 1C indicates good charge and discharge capability, which contributes to improved battery kinetic performance.

[0029] In each embodiment, the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, wherein 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 rate of 0.1 C at a constant current, and subsequently charged and discharged once at a rate of 1 C at a constant current, wherein the capacity value extracted in the charge and discharge test at a 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 wherein 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.

[0030] A high discharge capacity percentage of the active cathode material used in the lithium-ion secondary battery at a discharge 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, which includes the active cathode material, still maintains a high voltage when discharged to a low state of charge (SOC), which is beneficial for maintaining good performance.

[0031] In each embodiment, a discharge plateau in the voltage range of 2.5 V to 2.9 V is present in the 0.1C discharge curve of the button cell battery, which includes the active cathode material. This helps to extend the battery's discharge interval and improve its energy density.

[0032] In each embodiment, the mass content of the conductive medium is 0-1.5%, optionally 0, relative to the total mass of the cathode film layer.

[0033] The particles in the cathode film layer have a high sphericity, allowing them to be densely stacked during roller pressing and ensuring good contact between them. This results in good electronic conductivity for the particles within the cathode film layer, making it possible to reduce or even eliminate the use of conductive material in the cathode film layer. This further increases the charge of the active cathode material and improves the energy density of the lithium-ion secondary battery.

[0034] In each embodiment, 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%, optionally 96.5%-99.5%; and wherein the mass content of the binder is 0.5%-3%.

[0035] The mass fraction of the active cathode material and the mass fraction of the binder within the above range can effectively improve the active material loading per unit volume of the cathode film layer and maintain better internal bonding strength, reduce the likelihood of powder fall, expansion and cracking problems and improve the energy density of the secondary battery taking safety performance into account.

[0036] In each embodiment, the cathode film layer has a one-sided areal density of 300 mg / 1540 mm². 2 -450 mg / 1540 mm 2A cathode film layer with an areal density within the above range can contribute to improving the energy density of the lithium-ion secondary battery.

[0037] In each embodiment, when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.51 g / cm³. 3 -2.73 g / cm² 3 .

[0038] In each embodiment, when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.55 g / cm³. 3 -2.70 g / cm² 3 .

[0039] 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.

[0040] In each embodiment, the cathode film layer meets at least one of the following conditions: (1) when the lithium-ion secondary battery is in a fully discharged state, 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) when the lithium-ion secondary battery is in the fully discharged state, 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%.

[0041] The lower porosity in a cross-sectional area of ​​the cathode film layer 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.

[0042] In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the current collector, and wherein the lower coating satisfies at least one of the following conditions: (1) the lower coating comprises carbon-based particles, and the distribution density of the carbon-based particles with a particle size greater than 100 nm in the lower coating is ≤ 10 pcs / 10 µm; (2) the packing 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.

[0043] The lower coating helps to increase the electrical conductivity and bonding strength of the cathode film layer and the collector, and to reduce the demolding of the cathode film layer from the collector during the cycle process, while improving the kinetic performance of the battery.

[0044] 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.

[0045] A second aspect provides a battery device comprising a lithium-ion secondary battery according to the first aspect of the present application.

[0046] A third aspect of the present application provides a power-consuming device comprising at least one of the lithium-ion secondary battery according to the first aspect of the present application or the battery device according to the second aspect of the present application.

[0047] A method for producing an active cathode material is provided, wherein the manufacturing process comprises: obtaining a mixed raw material comprising a carbon source, a lithium source, an iron source, and a phosphorus source, wherein the carbon source comprises a polymeric carbon source, wherein the mass fraction of the trivalent iron element in the iron source is less than or equal to 0.08%, and wherein the molar ratio of lithium to iron in the mixed raw material is greater than or equal to 1 and less than or equal to 1.05; milling to obtain a mixed slurry; drying the mixed slurry to obtain a precursor powder; sintering the precursor powder to obtain an active cathode material after decomposition; wherein the sintering comprises a first temperature and a second temperature, and wherein the second temperature for sintering is 750°C–800°C.

[0048] The polymeric carbon source has a relatively low decomposition temperature and a relatively low graphitization temperature, which allows the carbon coating material on the surface of the active cathode material to decompose at a low sintering temperature to form a carbon layer. This layer 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. Controlling the mass fraction of the trivalent iron element helps to improve the homogeneity and consistency of the carbon coating material.On the one hand, the manufacturing process optimizes the quality of the carbon coating through the use of the carbon source, the iron source and the regulation of the sintering parameters, improves the distribution of the particle size and reduces the crystal defects in the active cathode material, and on the other hand provides a material basis for the production of the cathode film layer.

[0049] A method for producing a cathode film is provided, the manufacturing process comprising: dry mixing of a binder, a conductive agent, and an active cathode material prepared by the above manufacturing process; 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 current collector; drying and hot pressing to obtain a cathode film layer.

[0050] 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 before the first entry into the hot rolling press, and wherein the temperature of the heating is 40 °C-50 °C.

[0051] The stirring process comprises a pre-stirring and a main stirring, the main stirring having a rotational speed of 20 rpm-30 rpm and an internal rotational speed of 1450 rpm-1550 rpm.

[0052] The active cathode material, produced using the above hot pressing process in conjunction with the manufacturing process, 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.

[0053] The above explanation represents only a general outline of the technical solution of the present application. In conjunction with the content of the description, the present invention can be implemented so that the technical measures of the present application can be understood more clearly. The specific embodiments of the present application are explained in more detail below so that the above and other objectives, features, and advantages of the present application become more apparent and can be easily understood. 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 in an embodiment of the present application. Reference symbol list: 1 battery pack 2 Upper Case 3 Lower Case 4 battery modules 5 Secondary battery 51 cases 52 Electrode component 53 Cover plate SPECIFIC EXECUTION FORMS

[0054] The following section describes in detail embodiments of the lithium-ion secondary battery, the battery device, and the power-consuming device 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 will be left out. This is to prevent the following description from becoming unnecessarily long and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description serve to ensure the complete understanding of the present application by those skilled in the art and are not intended to limit the subject matter specified in the claims.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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).

[0059] In the present application, the terms "plural" and "multiple" refer to two or more.

[0060] Unless otherwise stated, the terms used in this application have the known meanings as generally understood by those skilled in the art.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] The lithium-ion secondary battery comprises an electrode component and an electrolyte.

[0065] The lithium-ion secondary battery may also include an outer casing used to encapsulate the electrode component and the electrolyte. The outer casing can be a rigid housing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. Alternatively, the outer casing 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).

[0066] 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.

[0067] 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.

[0068] 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.

[0069] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, and the like.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Lithium-containing transition metal phosphate materials are frequently used in lithium-ion batteries due to their structural stability, good safety, and long lifespan. 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.

[0075] To further improve the battery's energy density and increase the electrode foil's density, the industry typically increases the particle size distribution within the electrode foil. Increasing this particle size distribution requires increasing the proportion of large particles. However, research shows that the battery's kinetic performance is negatively affected when the proportion of large particles in the electrode foil exceeds a certain threshold. The engineering challenge of developing a battery that combines both energy density and kinetic performance must be addressed within this field of study.

[0076] The first aspect of the present application provides a lithium-ion secondary battery, the lithium-ion secondary battery comprising a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode current collector and a cathode film layer arranged on at least one side of the cathode current 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, wherein the percentage area fraction of the particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is greater than or equal to 8.0% and less than or equal to 20.0%, and wherein the iron dissolution rate of the cathode film layer is 658 ppm-1921 ppm.

[0077] The percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is less than 8%, which makes it difficult to achieve a high pressing density of the cathode foil.The percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is greater than 20%. Although this contributes to achieving a high compression density of the cathode foil, it reduces the contact area between the electrolyte and the active cathode material, hinders the diffusion of lithium ions into the cathode film layer, and increases the diffusion path of the lithium ions in the particles. This further leads to strong local polarization of the electrode foils, increases the battery impedance, and results in a significant deterioration of the battery's kinetic performance.

[0078] By controlling the percentage area fraction of particles with a particle size greater than or equal to 1.5 µm in the cathode film layer to greater than or equal to 8.0% and less than or equal to 20.0%, the significant short-plate effect caused by the large particles can be reduced. This helps to keep the battery impedance low and improve the battery's kinetic performance, but it limits the further improvement of the electrode foil's packing density. In the embodiments of the present application, controlling the iron dissolution rate of the cathode film layer to 658 ppm–1921 ppm, i.e.,By improving the density and completeness of the carbon coating on the surface of the active cathode material, particle movement is facilitated and lattice defects in the lithium-containing transition metal phosphates are reduced. This increases the particle's compressive strength, decreases the likelihood of particle collapse and tearing under high rolling pressure, and improves the compressive density of the electrode foils. Simultaneously, the complete and dense carbon coating material contributes to improved electrical contact between the active cathode materials, enhanced electrical conductivity, and reduced polarization.The low level of lattice defects contributes to smooth lithium-ion transfer channels, thereby improving the lithium-ion transfer rate of the active cathode materials and achieving a balance between the battery's kinetic performance and energy density.

[0079] Lithium-containing transition metal phosphate refers to a phosphate material comprising lithium and a transition metal element and can be detected by any known method in this field. For example, it can be detected by a combination of an X-ray diffractometer (XRD) and an energy spectrum analyzer.

[0080] The carbon coating material, which is located on at least a portion 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 material arranged on at least a portion 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.

[0081] 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.

[0082] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is greater than or equal to 8.0% and less than or equal to 20.0%.

[0083] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is optionally 8.0%, 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 19.0%, 20.0% or any value in a range between two of these values.

[0084] In a cross-section of the cathode film layer along the thickness direction of the electrode foil, the particle identification procedure 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 cross-section, 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 cross-section 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 procedure 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.

[0085] The particle area in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is counted as follows: The images after particle determination and identification were imported into the ImageJ software for analysis, and the scale was set according to the scanning electron microscope diagram. The specific procedure is as follows: Import the image after particle evaluation and labeling into the ImageJ software for analysis. Complete the scale setting according to the scanning electron microscope image. The specific process is as follows: The pixel length of the scale in the electron microscope image is measured using the straight line tool, and the ratio of the pixel length to the length represented by the scale (as in Fig.Figure 1 shows a scale length of 5.00 µm, which is used as the base scale, and the actual length can then be determined by calculating the pixel length. The particle size of particles in images is 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 obtained from the analysis represents the pixel size 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 therefore not counted in the statistical process for particle size in the present application. According to the above procedure, in order to achieve the number of statistically significant samples, no fewer than 10 scanning electron microscope images were taken of each electrode foil, and the area of ​​no fewer than 5000 particles was counted. The sum of the area parameters of the particles with a size of more than or equal to 1.5 µm and the sum of the area parameters of all particles were calculated as the area of ​​the particles with a size of more than or equal to 1.5 µm and the area of ​​the particles with a size of 1.5 µm, respectively.The total area of ​​the counted particles is calculated. The sum of the areas of the particles with a particle size of 1.5 µm or greater, divided by the total area of ​​the counted particles, is considered the percentage of the area of ​​particles with a particle size of 1.5 µm or greater in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0086] 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 and distribution within the cathode film layer.

[0087] During the pressing process of the cathode film layer, the compression occurs in the thickness direction, and 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 represent the actual compression state of the particles within the film layer on a spatial scale. The percentage of surface area occupied by particles with a particle size greater than or equal to 1.5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can directly represent the ratio of the particle area in this particle size range to the total particle area, thus reflecting the particle distribution within this size range.

[0088] 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 area of ​​the particles in a cross-sectional area of ​​the cathode film layer.

[0089] In the prior art, the particle size of the active cathode material is usually determined using the Malvern laser diffraction method. However, the applicant's research shows that, since lithium-containing phosphate readily agglomerates, the test results obtained using the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of the agglomerates. This does not accurately reflect the particle size of the particles in the active cathode material, and even less so the dispersion of the active cathode material in the film layer, as the dispersion of the active cathode material in the film layer increases during the roller pressing process for film formation.The test results obtained by the Malvern laser diffraction method are closely related to the particle size, the specific surface area and the degree of agglomeration of the active cathode material, so that the particle size obtained by the Malvern laser diffraction method cannot be equivalent or analogous to the particle size obtained by the embodiment of the present application.

[0090] A person skilled in the art 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 its production. 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 system are adjusted by precisely controlling the feed rate, which also helps to regulate the particle concentration.

[0091] In some embodiments, the iron dissolution rate of the cathode film layer is 658 ppm-1921 ppm.

[0092] In some embodiments, the iron dissolution rate of the cathode film layer is optionally 658 ppm, 700 ppm, 800 ppm, 890 ppm, 900 ppm, 1000 ppm, 1058 ppm, 1076 ppm, 1100 ppm, 1143 ppm, 1200 ppm, 1236 ppm, 1300 ppm, 1311 ppm, 1384 ppm, 1349 ppm, 1400 ppm, 1485 ppm, 1500 ppm, 1531 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1921 ppm, or any value in a range between any two of these values.

[0093] The iron dissolution rate of the cathode film layer can be tested using methods known in the technical field. For example, the electrode foil is removed from the battery, washed, and then placed in a small disk with a diameter of 14 mm. Numerous small disk 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 305 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 drawn up and placed in a glass volumetric flask for 50-fold dilution.and using an inductively coupled plasma mass spectrometer (ICP-OES) to obtain the concentration of iron element in the solution according to the following formula: [(ICP test concentration of iron element × 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 expands in the coated area during pressing,This results in a slight reduction in thickness compared to the uncoated area, but this has no undue impact on the test results, as the reduction is negligible. Preferably, if the collector is an aluminum foil, the density is preferably 2.7 g / cm³. 3 .

[0094] A person skilled in this field can regulate the iron dissolution rate of the cathode material using any known method. For example, the iron dissolution rate of the cathode material is regulated by controlling the surface coating quality of the cathode material, the temperature, time, and pressure during the manufacturing process. Furthermore, the battery design, the oxidizer content in the electrolyte solution, the battery's operating temperature, and the intensity of charging and discharging can also influence the iron dissolution rate during battery operation. The iron dissolution rate of the cathode film layer originates primarily from the active cathode substances of the lithium-containing transition metal phosphate within the cathode film layer, which can be reflected in the completeness and density of the carbon coating on the surface of the active cathode material from the side view.The lower the iron dissolution rate, the fewer iron ions can be precipitated from the carbon coating material after the acid dissolves; that is, the more complete and dense the carbon coating material is on the surface of the active cathode material. An iron dissolution rate of the cathode film layer within the range above indicates that the active cathode material has a relatively complete and dense carbon coating, capable of improving electrical contact between the active cathode materials, increasing their electrical conductivity, reducing their polarization, and further optimizing the kinetic performance of the lithium-ion secondary battery.At the same time, the highly complete structure of the carbon coating material makes the particles susceptible to stress slippage during the roller pressing process, which can simultaneously increase the pressing density of the electrode foil and the energy density of the battery.

[0095] In some embodiments, the iron dissolution rate of the cathode film layer is 658 ppm-1485 ppm.

[0096] The cathode material, whose cathode film layers have iron dissolution rates in the range mentioned above, exhibits relatively fewer lattice defects and more complete and dense carbon coating materials. Lower lattice defects contribute to improving the compressive strength and particle slippage in the cathode film layer under high roller pressure; high coating completeness promotes slippage between particles; and a dense coating helps to reduce the carbon layer's volumetric occupancy, further improve the electrode foil's compression density, and achieve a balance between the battery's kinetic power and energy density.

[0097] In some embodiments, the median B 50of the coating value in the cumulative distribution curve for the coating value-B of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, 0.35-0.48; where the coating value-B I P / I D is, where I P for the intensity of the P-peak of the Raman spectrum at 948±100cm -1 and ID for the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 stands.

[0098] In the present application, the coating value B can be obtained by an area-scanning mode of the 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 B values ​​at various locations and the cumulative distribution curve of the B values ​​in the area-scanning area.

[0099] 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 along the thickness direction of the electrode foil is preferably carried out to characterize the coating value of the cathode film layer.

[0100] The coating value B of the cathode film layer is obtained from the peak intensity ratio of the P-peak (P-band) and the D-peak (D-band) of the Raman spectra, with the position of the P-peak at 948±100cm -1 lies and the phosphate PO4 3- -structure characterized, and where the position of the D-peak is at 1350±100cm-1 The Raman spectrum is characterized by its disordered structure, where disorder means there is no regular arrangement between the carbon atoms in the structure. The Raman spectrum is a surface analyzer with a detection depth of 10 nm, so the carbon structure peaks of the cathode film layer exhibit higher intensity in the area-scanning mode of the laser microconfocal Raman spectrometer compared to the phosphate structure peaks, which are more prevalent in the bulk phase.

[0101] A person skilled in the art can regulate the coating value of the active material particles by any known method. For example, the coating value of the active material particles can be adjusted by regulating the type of carbon source, the amount of carbon source added, the sintering temperature, the sintering time, the sintering pressure, and the sintering atmosphere.

[0102] The coating value B can indirectly reflect the thickness of the carbon coating material on the surface of the lithium-containing transition metal phosphate particles. The thinner the carbon coating material, the higher the intensity of the phosphate structure detected in the Raman spectrum and the higher the coating value of the cathode film layer.

[0103] The cumulative distribution curve of coating value B is the curve obtained when at least 100 B values ​​are arranged in order from smallest to largest, using the coating value as the horizontal axis and the cumulative number fraction as the vertical axis. B50 is the B value when the cumulative number fraction on the vertical axis of the cumulative distribution curve of coating value B is 50%.

[0104] In some embodiments, the median B 50The coating value of the cathode film layer can optionally be 0.35, 0.36, 0.37, 0.38, 0.39, 0.398, 0.4, 0.41, 0.42, 0.43, 0.432, 0.44, 0.443, 0.445, 0.448, 0.449, 0.45, 0.453, 0.459, 0.46, 0.47, 0.48 or any value in a range between two of these values.

[0105] To reduce the influence of the extreme value of the coating value due to the non-particle-like region in the cathode film layer on the test results, the median B was 50 The coating value is used to evaluate the thickness of the carbon coating material on the active cathode material. The median B 50The coating value of the cathode film layer lies within the above range, indicating that the thickness of the carbon coating material on the active cathode material is small, which contributes to a further reduction in the volume occupied by the carbon coating material, a further improvement in the pressing density of the electrode foil, and to establishing a balance between the kinetic power and the energy density of the battery.

[0106] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 0.

[0107] The percentage of surface area covered by particles with a size greater than or equal to 5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can be determined using the method described above. In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area of ​​particles with a size greater than or equal to 5 µm, divided by the total area of ​​all counted particles, is considered the area fraction of particles with a size greater than or equal to 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0108] Research shows that particles with a particle size of more than or equal to 5 µm in the cathode film layer significantly impair the infiltration of the electrolyte in the cathode film layer and the diffusion of the electrolyte into the active material particles, and the percentage area fraction of particles with a particle size of more than or equal to 5 µm is 0, which leads to a further reduction of the internal resistance of the battery and an improvement in the kinetic performance of the battery.

[0109] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 1.5 µm and less than 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 8.0%–20.0%, optionally 10.0%–20.0%.

[0110] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 1.5 µm and less than 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is optionally 8.0%, 9.0%, 9.02%, 10.0%, 11.0%, 12.0%, 12.81%, 13.0%, 14.0%, 14.58%, 14.62%, 14.92%, 15.0%, 15.31%, 15.39%, 15.46%, 16.0%, 16.02%, 16.89%, 17.0%, 18.0%, 19.0%, 20.0%, or any value in a range between two of these values.

[0111] The percentage area of ​​particles with a particle size greater than or equal to 1.5 µm and less than 5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can be determined using the above method. In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area of ​​the particles with a particle size greater than or equal to 1.5 µm and less than 5 µm, divided by the total area of ​​the counted particles, is considered the area fraction of particles with a particle size greater than or equal to 1.5 µm and less than 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0112] Improving particle size distribution and increasing the percentage of surface area covered by large particles inevitably necessitates the inclusion of particles with a size greater than or equal to 1.5 µm and less than 5 µm. At the intersection of the cathode film layer along the thickness direction of the electrode foil, if the surface area covered by particles with a size greater than or equal to 1.5 µm and less than 5 µm falls within the aforementioned range, it is beneficial to improve the electrode foil's compaction density. Simultaneously, it is possible to further reduce the inhibiting effect of large particles on the electrode foil surface on electrolyte infiltration and diffusion within the cathode film layer, improve the consistency of the lithium ion diffusion rate within the active cathode material particles, reduce local polarization, and enhance the battery's kinetic performance.

[0113] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 1 µm and less than 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 15.0%-25.0%, optionally 16.0%-24.0%.

[0114] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 1 µm and less than 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is optionally 15.0%, 16.0%, 17.0%, 18.0%, 18.28%, 18.41%, 18.88%, 19.0%, 19.23%, 19.31%, 19.66%, 19.70%, 20.0%, 20.25%, 20.89%, 21.0%, 22.0%, 23.0%, 23.88%, 24.0%, 25.0%, or any value in a range between two of these values.

[0115] The percentage area of ​​particles with a particle size greater than or equal to 1 µm and less than 1.5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can be determined using the above method. In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area of ​​the particles with a particle size greater than or equal to 1 µm and less than 1.5 µm, divided by the total area of ​​the counted particles, is considered the area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0116] In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, if the area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm lies within the range described above, it can fill larger gaps in the stacking, form a specific "support structure," reduce the porosity between the particles, and contribute to improving particle contact and overall structural strength. Based on maintaining the good kinetic performance of the battery, the electrode foil's packing density can be further improved, and the battery's energy density can be enhanced.

[0117] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 200 nm and less than 1500 nm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 73.0%-80.0%, optionally 55%-65%.

[0118] In some embodiments, the percentage area fraction of particles with a particle size of more than or equal to 200 nm and less than 1500 nm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is optionally 73.0%, 74.0%, 75.0%, 75.07%, 75.10%, 75.24%, 75.42%, 75.45%, 75.67%, 75.83%, 76%, 76.21%, 76.66%, 77.0%, 78.0%, 78.57%, 79.0%, 80.0%, or any value in a range between two of these values.

[0119] In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the percentage area fraction of particles with a particle size greater than or equal to 200 nm and less than 1500 nm can be determined using the above procedure. The sum of the areas of particles with a particle size greater than or equal to 200 nm and less than 1500 nm, divided by the total area of ​​all counted particles, is considered the percentage area fraction of particles with a particle size greater than or equal to 200 nm and less than 1500 nm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0120] The percentage area fraction of particles with a particle size of more than or equal to 200 nm and less than 1500 nm in the cathode film layer within the above range can further improve the consistency of the diffusion rate of the lithium ions, leading to an improvement in the kinetic performance of the lithium-ion secondary battery, increasing the utilization rate of the active substances and thereby improving the energy density of the battery.

[0121] 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, 0.95–1.20, optionally 0.98–1.15 and further optionally 1.0–1.10; 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±100cm -1 and I Dfor the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 stands.

[0122] In the present application, the graphitization C-value can be obtained by an area-scanning mode of the 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.

[0123] 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.

[0124] 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±100cm -1 lies and the sp 2-Hybrid structure of carbon is characterized, and the position of the D-peak is at 1350±100cm -1 lies and characterizes the disordered structure, where disorder means that there is no regular arrangement between the carbon atoms in the structure. In graphite crystals, the carbon atoms in the same layer are sp 2 -hybridized and form covalent bonds, with van der Waals forces acting between the layers, allowing for a slight sliding of the carbon in the graphite structure. Therefore, the C value can characterize the degree of graphitization of the cathode film layer. 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 material of the active cathode material. Although conductive materials such as carbon nanotubes, which are rich in sp 2-hybridized structures are also relatively high I G / I D Despite exhibiting 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 influence on the degree of graphitization C. 50 in the cathode film layer. Therefore, the degree of graphitization of the cathode film layer can also characterize the degree of graphitization of the active cathode material.

[0125] The cumulative distribution curve of graphitization degree-C value is the curve obtained when at least 100 C values ​​are arranged in order from smallest to largest, using the graphitization degree as the horizontal axis and the cumulative number of values ​​as the vertical axis. 50The C-value is determined when the cumulative number fraction on the vertical axis of the curve of the cumulative distribution of graphitization degree-C-value is 50%. The median C 50 The degree of graphitization, compared to a point value, can reflect the degree of graphitization of the particles in the cathode film layer, i.e., the degree of ease of particle sliding; and compared to a mean value, it can reduce the influence of extreme values ​​in the test process and improve the reliability of the test results.

[0126] The higher the degree of graphitization of the carbon on the surface of the active cathode material, the higher the proportion of graphitic structural carbon in the cathode film layer and the easier it is for the particles to slide in the covering material with the help of the highly graphitized carbon structure, in order to achieve an increase in the pressing density of the electrode foil.

[0127] A person skilled in the art 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 (which can be selected as cross-linked PEG), the sintering temperature, the sintering time, the sintering pressure, the sintering atmosphere, and the nucleation process. The higher the degree of graphitization of the carbon on the surface of the active cathode material, the higher the proportion of graphitic structural carbon in the cathode film layer, and the more easily the particles can slide within the coating material with the aid of the highly graphitized carbon structure, thus increasing the electrode film's density.

[0128] In some embodiments, the median is C 50of the graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer optionally 0.95, 0.96, 0.97, 0.98, 0.99, 0.993, 1, 1.005, 1.008, 1.01, 1.012, 1.015, 1.02, 1.021, 1.03, 1.032, 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.

[0129] 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 the sphericity 0.65-0.85, optionally 0.70-0.80, where the sphericity L value is the ratio between the particle area and the area of ​​the fitted circle.

[0130] The test procedure for particle sphericity, which is obtained in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, is as follows: The particles in the cross-sectional area of ​​the cathode film layer are identified according to the procedure described above in the present application, and the morphology of the particles in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil and the area of ​​the particles are analyzed using the "Shape Description" and "Area" analysis functions in ImageJ. According to the software manual (ImageJ User Guide IJ 1.46r), the "Area" parameter obtained from the analysis represents the pixel area of ​​the particle, and the "Round" parameter represents the ratio of the pixel area of ​​the particle to the area of ​​a circle with the adjusted longitudinal diameter as its diameter.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 as the diameter is to 1. Therefore, the "Round" parameter of the particles obtained from the analysis is used to characterize the sphericity of the particles. The sphericities of the at least 5000 obtained particles are arranged in order from smallest to largest value, and the cumulative distribution curve of the sphericity area of ​​the particles 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. A50 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 50%.

[0131] In some embodiments, the median is L A50the sphericity 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, optionally 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 two of these values.

[0132] A person skilled in the art 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.

[0133] The particles with a median L A50The sphericity within the above area is approximately spherical, and it is easy for the particles to slide from particle to particle under the influence of an external force, which can further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0134] 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.

[0135] 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 test procedure for median R A50The roughness is determined as follows: The particles in the cut surface of the cathode film layer are identified according to the method described above in the present application, and the morphology of the particles in the cut surface of the cathode film layer along the thickness direction of the electrode foil is analyzed using the "Shape Description" analysis function in ImageJ. 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. As the definition shows, the closer the roughness is to 1, the smoother the particle.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 area 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%.

[0136] In some embodiments, the median R is A50 The roughness in the cumulative distribution curve of the roughness surface of the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is optionally 0.92, 0.93, 0.94, 0.95, 0.96 or lies in a range of values ​​in between.

[0137] A person skilled in the art can achieve the regulation of particle roughness by any known method. For example, particle roughness can be adjusted by processes such as milling, polishing, grinding, micro-energy machining, electroplating, roller burnishing, etc., as well as by adjusting the parameters of the respective processes.

[0138] The surface of the particles whose median R A50 The roughness lies within the above range, is relatively smooth, the friction between the particles is relatively low, and it is easy to slip under the influence of external forces, which can further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0139] In some embodiments, the mass content of carbon is 0.8%-1.8%, optionally 0.9%-1.5%, based on the total mass of the active cathode material.

[0140] 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.

[0141] 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.

[0142] In comparison to the active cathode material of the lithium-containing transition metal phosphate in the prior art, the active cathode material has a relatively low carbon coating content, 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.

[0143] 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%.

[0144] 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.

[0145] 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 any two of these values.

[0146] A person skilled in the art can achieve the control of the lithium and iron antisite defect concentration of the active cathode material by any known method. For example, the control of the lithium and iron antisite defects of 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.

[0147] During manufacturing and operation, a certain number of lithium vacancies are unavoidable in the crystal structure of the active cathode material. These lithium vacancies 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 blocking of the one-dimensional diffusion channel of lithium ions impairs solid-phase lithium ion transport.

[0148] The active cathode material in the embodiments of the present application exhibits a low lithium and iron antisite defect, which indirectly confirms that the active cathode material in the embodiments of the present application has a low content of lattice defects. This contributes to reducing the risk of particles collapsing and breaking under high rolling pressure and to improving the pressing density of the electrode foil. Simultaneously, a more uniform transfer of lithium ions in the solid phase is achieved, further improving the energy density and kinetic performance of lithium-ion secondary batteries.

[0149] In some embodiments, 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.

[0150] 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.

[0151] In some embodiments, 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.

[0152] In some embodiments, 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.

[0153] In some embodiments, 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.

[0154] In some embodiments, 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.

[0155] The selection of the appropriate modification element Q can improve the lattice change rate of the active cathode material in the process of de-embedded lithium, reduce the oxygen activity on the surface of the particles, improve the structural stability of the material and thereby improve the level of the gram capacity game of the material during the cycle and further improve the cycle stability of the lithium-ion secondary battery.

[0156] 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.

[0157] In some embodiments, 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.

[0158] Both the type and the content of the elements in the active cathode material can be tested according to any known methods in the relevant technical field. For example, the titanium content is tested using inductively coupled plasma emission spectrometry with reference to Annex C of GB / T 33822-2017.

[0159] Doping with titanium in the active cathode material leads to lattice distortion, reduces the Li-O bond energy, increases the lithium ion diffusion 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 impacts battery performance.

[0160] 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, together with the phosphate ion as well as with other elements (e.g. lithium), forms a fast ion conductor which instead improves the kinetic performance of the battery.

[0161] 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 .

[0162] The powder bulk density can be tested according to known methods in this technical field. For 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 inside is stirred with a clean sample spoon for 3-5 revolutions to mix it thoroughly; then the sample is transferred stably into the graduated cylinder; any powder adhering to the surface is wiped off with 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 bulk density measuring cylinder 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 ρ = m / v.

[0163] In some embodiments, the powder bulk density of the active cathode material is optionally 0.70 g / cm³. 3 , 0.80 g / cm³ 3 , 0.90 g / cm³ 3 , 1.00 g / cm² 3 , 1.10 g / cm³ 3 , 1.20 g / cm³ 3 , 1.30 g / cm³ 3 , 1.40 g / cm³ 3 , 1.50 g / cm² 3 or any value within a range between two of these values.

[0164] The active cathode material in this embodiment of the present application has a limited effective gradation that forms automatically and has a relatively low powder bulk density, and with the help of the high completeness and density of the carbon coating material of the active cathode material in the cathode film layer, the gaps between the particles can be easily compressed under the action of an external force in order to achieve an increase in the powder compaction density.

[0165] In some embodiments, the powder density of the active cathode material is 2.50 g / cm³ under a pressure of 3T. 3 -2.70 g / cm² 3 , optional 2.52 g / cm² 3 -2.68 g / cm² 3 .

[0166] In the present application, the term ‘powder compression density’ refers to the density (in g / cm3) of 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 is increased, so that an interatomic attraction is created and the mechanical bond between the particles is strengthened.

[0167] 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 using a density measuring device according to GB / T 24533-2009. Specifically, a certain quantity of the active cathode material is placed on a special mold for compression (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, and the mold is placed on the density measuring device. The base area of ​​the mold is 1,327 cm². 2The 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 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 pressed active cathode material.

[0168] In some embodiments, the powder density of the active cathode material is optionally 2.50 g / cm³ under a pressure of 3T. 3 , 2.51 g / cm³ 3 , 2.52 g / cm³ 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 / cm³ 3 , 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 , 2.69 g / cm³ 3, 2.70 g / cm³ 3 or any value within a range between two of these values.

[0169] Although the percentage area fraction of particles with a particle size greater than or equal to 1.5 µm in the cathode film layer is small, this indicates that the surface of the active cathode material has a high density and completeness of the carbon coating material thanks to the cathode film layer with a low iron dissolution rate, which allows a high pressing density to be achieved even under the influence of external forces, and provides 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.

[0170] In some embodiments, the powder resistance of the active cathode material under a pressure of 8 MPa is 0.5 Ω·cm-30.0 Ω·cm, optionally 2.0 Ω·cm-20.0 Ω·cm.

[0171] The powder resistance of the active cathode material can be measured according to known methods and equipment in this technical field. For example, it can be measured using a powder resistance meter (Suzhou Jingle, model ST2722) with reference to GB / T 33822-2017. Specifically, a certain quantity 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 the 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.

[0172] In some embodiments, the powder resistance of the active cathode material under a pressure of 8 MPa is optionally 0.5 Ω-cm, 1 Ω-cm, 2 Q-cm, 3 Ωcm, 4 Ω-cm, 5 Ω-cm, 6 Ω-cm, 7 Ω-cm, 8 Ω-cm, 9 Q-cm, 10 Ω-cm, 15 Ω-cm, 20 Ω-cm, 25 Ωcm, 30 Ω-cm or any value in a range between any two of these values.

[0173] The carbon coating material on the surface of the active cathode material exhibits high completeness and density, making rapid electron conduction between the particles easily achievable with the help of the coating structure, thus giving the active cathode material a low powder resistance, leading to an increase in the solid phase electron transfer rate and a further improvement in the kinetic performance of the battery.

[0174] In some embodiments, the active cathode material has a discharge gram capacity of 135 mAh / g-150 mAh / g at a discharge rate of 1 C.

[0175] In the present application, the active cathode material is assembled as a button cell battery to test its electrical properties using a land-based test device. After charging with a constant current of 1C to 3.75V in the voltage range of 2.0V to 3.75V 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 1C to 2.0V. 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 1C.

[0176] 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 pressing the cathode foil to a density of 2.0 g / cm³. 3 -2.2 g / cm² 3Using a punch machine to make the cathode foil into a round disc 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 - lithium disc - 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) and DMC (1,2-dimethyl carbonate) in a volume ratio of 1:1, and the electrolyte is LiPF6), placing the button cell battery with the anode facing upwards into the groove of the sealing machine, applying a sealing pressure of 650 kg / cm² 2The process involves removing the button battery with insulated tweezers and placing it in a dust-free bag, removing the glove box, and storing it in a thermostatic room for 3 hours to preserve the button battery for testing.

[0177] It is understood that the discharge gram capacity of the active cathode material can also be determined by disassembling the battery, obtaining the cathode foil and testing after reassembly into a button battery according to the procedure described above.

[0178] In some embodiments, the discharge gram capacity of the active cathode material at a discharge rate of 1C is optionally 135 mAh / g, 140 mAh / g, 142.4 mAh / g, 145 mAh / g, 150 mAh / g or any value in a range between two of these values.

[0179] The high discharge gram capacity of the active cathode material at a discharge rate of 1C indicates its good charge and discharge capability, which contributes to improving the kinetic performance of the battery.

[0180] In some embodiments, 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 rate of 0.1 C at a constant current and subsequently charged and discharged once at a rate of 1 C at a constant current, wherein the capacity value extracted in the charge and discharge test at a rate of 1 C at a discharge voltage of 3.2 V is recorded as C1, where the capacity value extracted at a discharge voltage of 2.0 V is C2, 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.

[0181] In some embodiments, the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 88.

[0182] The η-value of the active cathode material can be measured according to known methods and equipment in this technical 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 apparatus at room temperature. This involves charging and discharging the button battery twice 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 cut-off 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.

[0183] In some embodiments, η is optionally 85%, 86%, 87%, 88%, 88.1%, 89%, 90%, 90.1%, 91%, 91.1%, 92%, 92.2%, 93%, 94%, 94.1%, 94.5%, 95%, 95.1%, or any value in a range between any two of these values.

[0184] 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%.

[0185] A high discharge capacity percentage of the active cathode material used in the lithium-ion secondary battery of the embodiment of the present application at a discharge 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 at a discharge to a low state of charge (SOC), which is conducive to maintaining good performance.

[0186] In some embodiments, a discharge plateau in a voltage range of 2.5 V to 2.9 V is present in a 0.1C discharge curve of the button battery, which includes the active cathode material.

[0187] The discharge plateau generally refers to a range of the battery's voltage where it remains relatively stable and unchanged during charging and discharging. As the battery discharges, current flows out, causing the voltage to initially drop, but then it enters a relatively stable range. Within this range, voltage fluctuations are very small; this stable voltage range is known as the discharge plateau.

[0188] The button cell battery can be manufactured by dissecting the cathode foil in the lithium-ion secondary battery and combining it with lithium metal. It can also be assembled and manufactured using the method described above.

[0189] In the present application, the active cathode material is assembled as a button cell battery to test its electrical properties using a land-based tester. After charging to 3.75 V at a constant current of 0.1 C in the voltage range of 2.0 V to 3.75 V, the battery was paused for 5 minutes, charged at a constant voltage up to a cutoff current of 50 µA, and then discharged to 2.0 V at a constant current of 0.1 C.

[0190] The discharge curves show that the standard voltage of the charge and discharge plateau for lithium-containing phosphates typically lies between 3.2 V and 3.65 V. The button cell battery, which comprises the active cathode material in the embodiment of the present application, exhibits a new discharge plateau in the voltage range of 2.5 V to 2.9 V, which contributes to an extension of the battery's discharge interval and an improvement in the battery's energy density. At the same time, this confirms the assumption that the active cathode material of the embodiments of the present application comprises a fast-ion conductor.

[0191] In some embodiments, the mass content of the conductive medium is 0-1.5% relative to the total mass of the cathode film layer.

[0192] In some embodiments, the mass fraction of the conductive medium relative to the total mass of the active cathode material 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.

[0193] 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.

[0194] The active cathode material exhibits a high density and high completeness of the carbon coating material, so that the active cathode material has good electronic conductivity and it is possible to reduce the use of the conductive agent in the cathode film layer, which contributes to a further increase in the charge of the active cathode material and to improving the energy density of the lithium-ion secondary battery.

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

[0196] The active cathode material has very good electronic conductivity and it is possible to eliminate the use of the conductive agent in the cathode film layer, which contributes to a further increase in the charge of the active cathode material and to improving the energy density of the lithium-ion secondary battery.

[0197] In some embodiments, 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%, optionally 96.5%-99.5%, and the mass content of the binder is 0.5%-3.0%.

[0198] 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.

[0199] 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%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5% or any value in a range between two of these values.

[0200] In some embodiments, the mass fraction of the binder, based on 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.

[0201] The mass fraction of the active cathode material and the mass fraction of the binder within the above range can effectively improve the active material loading per unit volume of the cathode film layer and maintain better internal bonding strength, reduce the likelihood of powder fall, expansion and cracking problems and improve the energy density of the secondary battery taking safety performance into account.

[0202] In some embodiments, the cathode film layer has a one-sided areal density of 300 mg / 1540 mm². 2 -450 mg / 1540 mm 2 .

[0203] 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 on one side and pressed (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 round 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 then calculated as (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.

[0204] In some embodiments, the one-sided areal density of the cathode film layer is optionally 300 mg / 1540 mm². 2 , 310 mg / 1540 mm 2 , 320 mg / 1540 mm 2 , 330 mg / 1540 mm 2 , 340 mg / 1540 mm 2 , 350 mg / 1540 mm 2 , 360 mg / 1540 mm 2 , 370 mg / 1540 mm 2 , 380 mg / 1540 mm 2 , 390 mg / 1540 mm 2 , 400 mg / 1540 mm 2 , 410 mg / 1540 mm 2 , 420 mg / 1540 mm 2 , 430 mg / 1540 mm 2 , 440 mg / 1540 mm 2 , 450 mg / 1540 mm 2 or any value within a range between two of these values.

[0205] A cathode film layer with an areal density in the above range can contribute to the energy density of lithium-ion secondary batteries.

[0206] In some embodiments, when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.51 g / cm³.3 -2.73 g / cm² 3 .

[0207] In some embodiments, when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.55 g / cm³. 3 -2.70 g / cm² 3 .

[0208] In the present application, a fully discharged state means: storing the battery at 25°C for 2 hours, waiting until the temperature of the battery is maintained at 25°C, and discharging the battery with a constant current of 1 / 3 C to 2.5 V and then discharging the battery with a constant current of 0.1 C to 2.0 V.

[0209] The compression density of the cathode film layer can be tested according to known methods in this technical 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 round 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 determined. =(W1-W2) / [(Ti-T2)×S].

[0210] In some embodiments, the density of the cathode film layer when the lithium-ion secondary battery is in a fully discharged state is optionally 2.51 g / cm³. 3 , 2.52 g / cm³ 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 / cm³ 3 , 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 , 2.69 g / cm³ 3 , 2.70 g / cm³ 3 , 2.71 g / cm³ 3 , 2.72 g / cm³ 3 , 2.73 g / cm³ 3 or any value within a range between two of these values.

[0211] In some embodiments, the density of the cathode film layer after a pressing treatment is 2.63 g / cm³. 3 -2.85 g / cm² 3.

[0212] In some embodiments, the compression density of the cathode film layer after a pressing treatment is optionally 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 , 2.69 g / cm³ 3 , 2.70 g / cm³ 3 , 2.71 g / cm³ 3 , 2.72 g / cm³ 3 , 2.73 g / cm³ 3 , 2.74 g / cm³ 3 , 2.75 g / cm³ 3 , 2.76 g / cm³ 3 , 2.77 g / cm³ 3 , 2.78 g / cm³ 3 , 2.79 g / cm³ 3 , 2.80 g / cm³ 3 , 2.81 g / cm³ 3 , 2.82 g / cm³ 3 , 2.83 g / cm³ 3 , 2.84 g / cm³ 3 , 2.85 g / cm 3 or any value within a range between two of these values.

[0213] In the present application, the term "pressing" refers to the pressing of the cathode film layer by mechanical pressure during the battery assembly process to improve its compactness and conductivity.

[0214] In some embodiments, the density of the cathode film layer after treatment by the forming process is 2.51 g / cm³. 3 -2.73 g / cm² 3 .

[0215] In some embodiments, the density of the cathode film layer after treatment by the forming process is optionally 2.51 g / cm³. 3 , 2.52 g / cm³ 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 / cm³ 3 , 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 , 2.69 g / cm³ 3 , 2.70 g / cm³ 3 , 2.71 g / cm³ 3 , 2.72 g / cm³ 3 , 2.73 g / cm³ 3 or any value within a range between two of these values.

[0216] 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.

[0217] It is understood that the compression density of the cathode film layer when the lithium-ion secondary battery is in a fully discharged state is somewhat lower than the compression density of the cathode film layer after pressing and forming, because the electrode foil bounces off during the cycling process.

[0218] 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.

[0219] In some embodiments, the density of the cathode film layer is 2.51 g / cm³. 3 -2.73g / 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%.

[0220] In some embodiments, the density of the cathode film layer is 2.55 g / cm³. 3 -2.70g / 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%.

[0221] 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.

[0222] The porosity of the cathode film layer in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can be tested using the following procedure. Import the scanning electron microscope image of the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, obtained using the above procedure, into the ImageJ software, select the straight line tool, use a straight line to mark the length of the scale in the image, click on "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 porosity 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”, checking the four columns on the left to obtain the porosity statistics.

[0223] 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 value of the image. The "pore “This 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, and this method is better than 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 represented.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 roller 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.

[0224] In some embodiments, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the current 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.

[0225] Where carbon-based particles refer to particles with carbon as the main component, including but not limited to conductive carbon, soot, etc.

[0226] The lower coating contributes to increasing the electrical conductivity and bond 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 in the high-density electrode foil of the embodiment of the present application, for example, 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 pressing process of the electrode foil at high pressure, and the large-format particles tend to create craters on the collector. Controlling the distribution density of carbon-based particles with a particle size of more 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.

[0227] 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.

[0228] 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 lower coating are in the range of 20-60 nm and D V90 less than or equal to 70 nm, and the bottom coating is obtained by mixing, stirring the carbon-based material and the binder and applying it to the collector.

[0229] 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;

[0230] 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;

[0231] 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.

[0232] The thickness of the bottom coating on one side can be tested 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 average thickness value is then calculated after measuring the thickness of the bottom coating 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 m; 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 pressing process of the electrode foil, and these anomalous points have no statistical significance.

[0233] In some embodiments, the thickness of the cathode current collector is less than or equal to 17 µm, optionally 13 µm-15 µm.

[0234] In some embodiments, the thickness of the cathode current collector is optionally 13 µm, 14 µm, 15 µm, 16 µm, 17 µm or any value in a range between two of these values.

[0235] 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.).

[0236] In some embodiments, 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 -1.75 g / cm² 3 amounts.

[0237] 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.

[0238] 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.

[0239] 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 a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0240] In some embodiments, the anode film layer comprises an active anode material. The active anode material may be an active anode material known in the art for use in batteries. For example, the active anode 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 monolithic 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 active anode materials in batteries may also be used. It is possible to use only one of these active anode materials or to use more than two in combination.

[0241] In some embodiments, the anode film layer optionally 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).

[0242] 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.

[0243] In some embodiments, the anode film layer optionally includes further additives, such as thickening agents (e.g. sodium carboxymethylcellulose (CMC-Na)), etc.

[0244] 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 active anode 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, pressing and other processes.

[0245] 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.

[0246] In some embodiments, an electrolyte solution is used for the electrolyte. This electrolyte solution consists of an electrolyte salt and a solvent.

[0247] 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.

[0248] 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.

[0249] 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.

[0250] 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.

[0251] 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.

[0252] 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.

[0253] 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.

[0254] 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.

[0255] 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.

[0256] A third aspect of the present application provides a power-consuming device comprising a lithium-ion secondary battery according to the first aspect of the present application.

[0257] A method for producing an active cathode material is provided, wherein the manufacturing process comprises: obtaining a mixed raw material comprising a carbon source, a lithium source, an iron source, and a phosphorus source, wherein the carbon source comprises a polymeric carbon source, wherein the mass fraction of the trivalent iron element in the iron source is less than or equal to 0.08%, and wherein the molar ratio of lithium to iron in the mixed raw material is greater than or equal to 1 and less than or equal to 1.05; milling to obtain a mixed slurry; drying the mixed slurry to obtain a precursor powder; sintering the precursor powder to obtain an active cathode material after decomposition; wherein the sintering comprises a first temperature and a second temperature, and wherein the second temperature for sintering is 750°C–800°C.

[0258] On the one hand, the manufacturing process optimizes the quality of the carbon coating through the use of the carbon source, the iron source and the regulation of the sintering parameters, improves the distribution of the particle size and reduces the crystal defects in the active cathode material, and on the other hand provides a material basis for the production of the cathode film layer.

[0259] The iron source comprises divalent iron, possibly one or more of iron(II) oxalate, iron(II) carbonate and iron nitrate.

[0260] During the sintering process, the divalent iron source preferentially decomposes to produce a large amount of iron oxide, which serves as a nucleation site for the formation of nanocrystalline crystal 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 crystal cores within the nanocrystal cores further catalyzes the decomposition of the carbon source. This allows the carbon coating material on the surface of the active cathode material to exhibit a relatively high degree of graphitization at a relatively low sintering temperature, reducing the electrical resistance of the active cathode material and simultaneously improving the density and homogeneity of the carbon coating material on the surface of the lithium-containing transition metal phosphate.Furthermore, the uniform deposition of carbon on the surface of the lithium-containing transition metal phosphate further hinders the growth of the lithium-containing transition metal phosphate grains and reduces the likelihood that the particles of the active cathode material will grow into large particles with a particle size of more than 1.5 µm.

[0261] In some embodiments, the iron oxalate has a particle size D 10 of greater than or equal to 3 µm, a particle size D 50 of 50-80 µm and a particle size D 90 of less than or equal to 150 µm.

[0262] In the present application, the terms “D 10 “, “D 50 “ and “D 90 “ of the particle size when the percentage of the cumulative particle size distribution of the particle size of the sample obtained by the Malvern laser scattering test reaches 10%, 50% or 90% respectively.

[0263] Control of particle size D 10 Iron oxalate particles larger than or equal to 3 µm can reduce the proportion of smaller iron oxalate particles and control its reactivity during the milling process. Controlling the particle size D 50 , D 90 The addition of iron(II) oxalate helps to mix the raw materials uniformly during the milling process, to obtain a mixed slurry with consistent components and uniform particle size, and to improve the consistency of the particle size of the produced lithium-containing transition metal phosphate.

[0264] In some embodiments, the mass content of the trivalent iron element is less than or equal to 0.08%.

[0265] In some embodiments, the mass fraction 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.

[0266] Controlling the mass fraction of trivalent iron helps improve the homogeneity and consistency of the carbon coating material. An excessive amount of trivalent iron preferentially depletes the carbon source, resulting in inconsistencies in the quality and thickness of the carbon layer deposited between the particles. On the one hand, this uneven thickness of the carbon coating material impairs the compression between the particles; on the other hand, local carbon depletion affects the overlap of the conductive network between the particles, negatively impacting the effective increase in the electrode foil's compression density and the improvement of its kinetics.

[0267] In some embodiments, the lithium source comprises one or more of lithium dihydrogen phosphate, lithium phosphate, lithium carbonate, or lithium acetate.

[0268] In some embodiments, the carbon source comprises a polymeric carbon source, optionally one or more of polyethylene glycol, polyvinyl alcohol.

[0269] In some embodiments, the mass content of the carbon source is 1-4%, based on the total mass of the mixed raw material.

[0270] The polymeric carbon source has a relatively low decomposition and graphitization temperature, so the carbon coating material on the surface of the active cathode material can decompose at a low sintering temperature and form a carbon layer that inhibits the growth of the lithium-containing transition metal phosphate grains and the growth of the sintering, which is beneficial to reducing the particle size of the active cathode material particles.

[0271] 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; at the same time, the entanglement and crosslinking of long chains are conducive to the reduction of structural defects and the reduction of lattice disruption due to chain breakage in the carbonization process, which can increase the degree of graphitization.

[0272] 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, thus reducing surface roughness. The coating material formed from the polymeric carbon source exhibits a higher degree of graphitization and a denser carbon structure, which is advantageous for optimizing the surface roughness of the active cathode material.

[0273] In some embodiments, the polyethylene glycol has a weight-average molecular weight of 10,000 and below.

[0274] Polyethylene glycols with a weight-average molecular weight of less than 10,000 have shorter carbon chains, which makes it easy to control the decomposition rate during sintering in order to form a carbon coating material of suitable and uniform thickness.

[0275] In some embodiments, the polyethylene glycol has a water content of less than or equal to 0.5%.

[0276] If the water content of the polyethylene glycol is high, the moisture can disrupt the decomposition process and cause incomplete or uneven decomposition rates during sintering. Excess moisture can also lead to uneven distribution of the molten polyethylene glycol during sintering, which impairs the homogeneity of the carbon layer and results in instability or delamination of the carbon coating material.

[0277] In some embodiments, the water 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.

[0278] In some embodiments, the polyethylene glycol has a pH value of 5-7.

[0279] Polyethylene glycol with a pH of 5-7 is more stable and is not degraded by excessive acidity during mixing, especially at high temperatures, which can lead to rapid decomposition and impair the coating quality. Alkaline polyethylene glycol can compromise the stability of other components, leading to dissolution or oxidation reactions of metal ions and affecting the performance of the finished active cathode material.

[0280] In some embodiments, the phosphorus source comprises one or more of lithium dihydrogen phosphate, phosphoric acid, and ammonium dihydrogen phosphate.

[0281] In some embodiments, the lithium source and the phosphorus source may be the same substance.

[0282] In some embodiments, the iron source comprises iron(II) oxalate, the lithium source and the phosphorus source comprise lithium dihydrogen phosphate, and the carbon source comprises polyethylene glycol.

[0283] In some embodiments, the atomic molar ratio of the lithium elements and the iron elements in the lithium source and the iron source is 1.00-1.05.

[0284] In some embodiments, the atomic molar ratio of lithium element and iron element in the lithium source and the iron source is optionally 1.00, 1.01, 1.02, 1.03, 1.04, 1.05 or any value in a range between two of these values.

[0285] When the atomic molar ratio of lithium to iron is 1, this is the ideal stoichiometric ratio for maintaining optimal electrochemical performance, optimizing the reversible de-embedding of lithium ions during charging and discharging, and achieving good crystal structure stability to improve cycle life and reduce the likelihood of heterogeneous phase formation. However, in actual manufacturing, the molar ratio of lithium to iron must be adjusted to slightly more than 1 to compensate for lithium loss during sintering.

[0286] 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.

[0287] 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.

[0288] Titanium is used as a lattice stabilizer, and the titanium element usually occurs in the form of Ti 4+ into the lattice of the lithium-containing transition metal phosphate, 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.

[0289] At the same time, doping with titanium helps to improve the sphericity of the particles and reduce the roughness of the particles, thereby increasing the overall structural stability of the material.

[0290] In some embodiments, lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol and titanium dioxide are homogeneously mixed and ground in an organic solvent to obtain the mixed raw material.

[0291] 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, which makes it easier to remove during the subsequent drying process and prevents it from remaining in the material, thus avoiding the formation of pores and impairing the material's density and structural stability.

[0292] In some embodiments, obtaining a mixed slurry after milling comprises at least two ball mill demagnetization cycles, wherein the ball mill demagnetization independently satisfies one or more of the following conditions: (1) The grinding balls for ball grinding are one or more of zirconium oxide balls, silicon zirconium nitride balls and ceramic zirconium balls. (2) the diameter of the grinding balls for a first ball grinding is 5mm-6mm, and the diameter of the grinding balls for the second ball grinding is 0.5mm-0.7mm; (3) the speed for the first ball grinding is 1400 rpm-1600 rpm, and the speed for the second ball grinding is 400 rpm-600 rpm; (4) the grinding time for the first grinding of the balls is 150 min-200 min, and the grinding time for the second grinding of the balls is 140 min-180 min; (5) the demagnetization method is permanent magnetic iron removal; (6) the demagnetization has a demagnetization strength greater than or equal to 8000 GS.

[0293] By combining at least two ball mill demagnetization processes, it is possible to quickly process materials with large particles and further refine them in a shorter time. This effectively avoids the uneven particle size that arises during ball milling, reduces the phenomenon of agglomeration between particles, improves the electrical conductivity and cycle stability of the battery, and also increases overall production efficiency while ensuring the performance of the final product.

[0294] In some embodiments, the particle size of the volume distribution D is v50 of the particles in the mixed slurry 1.0 µm-4.0 µm.

[0295] For the purposes of this application, the term “D” means V50 “the particle size at which the cumulative percentage of the size distribution of the sample volume tested by the Malvern laser scattering method reaches 50%;

[0296] In some embodiments, the particle size of the volume distribution D v50 The particle size in the mixed slurry can optionally be 1 µm, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4.0 µm or any value in a range between two of these values.

[0297] The particle size of the volume distribution D V50The particles in the mixed slurry in the above range can, on the one hand, increase the activity of the particles to a certain degree and enable the generation of some particles from active cathode material with a particle size of 1 µm-1.5 µm at the same temperature, as well as improve the pressing density of the electrode foil and the energy density of the battery; on the other hand, it can improve the catalytic decomposition efficiency of the iron element on the surface of the crystal core to the carbon source, improve the coating quality of the carbon source and the coating homogeneity and graphitization of the carbon material, which further improves the pressing density of the electrode foil and the energy density of the battery.

[0298] In some embodiments, drying the mixed slurry to obtain a precursor powder includes spray drying the mixed slurry to obtain the precursor powder.

[0299] In some embodiments, the sintering of the precursor powder to obtain an active cathode material comprises at least two sintering processes.

[0300] In some embodiments, the first sintering of at least two sinterings satisfies one or more of the following conditions: (1) a heating rate greater than or equal to 2 °C / min; (2) a holding temperature of 300 °C-400 °C; (3) a holding time of 2-6 hours.

[0301] In some embodiments, the second sintering of at least two sinterings satisfies one or more of the following conditions: (1) a heating rate greater than or equal to 3 °C / min; (2) a holding temperature of 750 °C-800 °C; (3) a holding time of 8-15 hours.

[0302] Using a higher heating rate to quickly raise the temperature to the target temperature facilitates uniform particle growth and reduces the presence of particles with a particle size greater than or equal to 1.5 µm.

[0303] By controlling the sintering temperature in the first and second sintering processes, the rate of sinter diffusion can be controlled. At high temperatures, diffusion at the particle surface increases, defects in the particles are repaired, and the crystal lattice is rearranged. Through recrystallization, defects on the particle surface are eliminated, the grain structure of the particles becomes more ordered, and the particle size gradually increases, which contributes to the smoothing of the particle surface and promotes the development of the particles into a spherical shape. The sintering temperature also affects the graphitization rate of the carbon source; kinetically, the carbon atoms gain more energy and are able to overcome the initial energy barriers, thus enabling more drastic rearrangements within the lattice.The sintering time affects the extent of the reaction: if the sintering time is too short, the diffusion and rearrangement of the lithium-containing transition metal phosphate and the carbon source are not completely completed; if the sintering time is too long, the particles become unusually large, the grains within the particles become coarser, the structure of the material becomes unstable, the adhesion between the particles is increased, and agglomeration occurs.

[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 classification frequency of the airflow comminution is 18 Hz-24 Hz and the comminution air pressure is 0.45 MPa-0.65 MPa.

[0306] The classification frequency in airflow comminution refers to the operating frequency of the classification device during airflow comminution, which is typically related to classification efficiency and the particle size distribution. At a higher classification frequency, the particles in the airflow are sieved more frequently, thus separating out the larger particles and leaving the smaller ones behind. Furthermore, a higher classification frequency is likely to increase the number of particle collisions, resulting in irregular particles being further blasted, leading to smoother particle surfaces and a more spherical shape.

[0307] Due to the high air pressure, the particles are subjected to a stronger impact, the collision between the particles is more intense, which means that the surface of the particles is subjected to strong impact and abrasion, large particles can be broken down into smaller particles, the collision between the particles is more intense, the surface is easier to trim, improving the sphericity of the particles and the surface flatness.

[0308] However, excessively high classification frequency and comminution 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 material incomplete, manifesting as increased iron dissolution. It also negatively impacts particle slippage during roller pressing, 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 classification frequency and comminution pressure of the airflow within a suitable range.

[0309] A method for producing a cathode film is provided, the manufacturing process comprising: dry mixing of a binder, a conductive agent, and an active cathode material prepared by the above manufacturing process; 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 current collector; drying and hot pressing to obtain a cathode film layer.

[0310] In some embodiments, the stirring comprises a pre-stirring and a main stirring, wherein the main stirring has a rotational speed of 20 rpm-30 rpm and an intrinsic rotational speed of 1450 rpm-1550 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 before the first entry into the hot rolling press, and wherein the temperature of the heating is 40°C-50°C.

[0312] The above hot pressing process is applied to work in conjunction with the active cathode material produced by the above manufacturing process, which helps to further reduce the porosity of the cut surface of the cathode film layer, increase the final pressing density of the electrode foil and improve the energy density of the battery.

[0313] Furthermore, the present application provides a power-consuming device, the power-consuming device comprising at least one of the secondary batteries of the present application, a battery module, and a battery pack. The 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 can 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 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 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 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. Example 11. Production of the active cathode material

[0318] Mixing lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and titanium dioxide and milling in methanol to obtain the mixed raw material. The ratio of lithium dihydrogen phosphate to iron oxalate is determined such that the atomic molar ratio of lithium to iron is 1.03; the particle size D90 of iron oxalate is 100 nm, and the mass fraction of the trivalent iron element is 0.03%.

[0319] The mixed raw material was ground several times in a ball mill and demagnetized to obtain a mixed slurry.

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

[0321] The precursor powder material was placed in a sintering furnace and heated from 25°C to a first temperature of 350°C at 2°C / min under a nitrogen atmosphere and held at this temperature for 3 hours, then heated to a second temperature of 770°C at 5°C / min and held at this temperature for 10 hours, and finally cooled.

[0322] The material obtained was crushed by an airflow crushing process with a classification frequency of 22 Hz and a crushing air pressure of 0.55 MPa to obtain a carbon-coated active lithium iron phosphate cathode material.

[0323] The mass content of the carbon element in the active cathode material obtained through production is 1.144%, and the lithium and iron antisite defect concentration is 0.58%, with a powder bulk density of 1.05 g / cm³. 3 The powder compaction density under 3T pressure is 2.57 g / cm³. 3, and the specific powder resistance under a pressure of 8 MPa is 6 Ω-cm; the discharge gram capacity at a discharge rate of 1 C is 142.4 mAh / g; there is a discharge plateau in a voltage range of 2.5 V to 2.9 V, and the discharge capacity percentage of the 3.2 V discharge plateau is 91.1%. 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 cm³ is obtained. 2This product is obtained after drying and hot pressing. The stirring process includes a pre-stirring and a main stirring, the main stirring having a rotational speed of 25 rpm and a rotational speed of 1500 rpm.

[0325] 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; wherein the hot rolling temperature is 65°C, wherein the electrode foil is heated before the first entry into the hot rolling press, wherein the temperature of the heating is 50°C.

[0326] The electrode foil density is the limiting electrode foil density, and the test procedure for the limiting electrode foil density is described below; the limiting electrode foil density in this embodiment is 2.67 g / cm³. 3 .

[0327] In the produced cathode film layer, the statistical results in the cross-sectional area along the thickness direction of the electrode foil show that in the cross-sectional area of ​​the cathode film layer, the area fraction of particles with a particle size of more than or equal to 1.5 µm and less than 5 µm is 14.58%, of more than 5 µm is 0%, of more than or equal to 1 µm and less than 1.5 µm is 19.70%, and of more than or equal to 200nm and less than 1500nm is 75.07%.

[0328] The median B 50 The coating value of the cathode film layer, obtained by an area-scanning mode of the laser microconfocal Raman spectrometer, is 0.443. The median C 50The degree of graphitization obtained by an area-scanning mode of the laser microconfocal Raman spectrometer is 1.021. In the cumulative distribution curve of the particle sphericity number obtained in a cross-section of the cathode film layer along the thickness direction of the electrode foil, the median L A50 The sphericity is 0.722. In the cumulative distribution curve of the roughness number of particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median R is A50 The roughness is 0.943. The iron dissolution rate of the cathode film layer is 1058 ppm. 3. Production of the anode foil:

[0329] 95.5 wt% of the active anode 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, pressing, cutting, and stacking. The density of the coated single-sided surface is 165 mg / 1540 mm². 2 and the density is 1.60 g / cm³ 3 . 4. Production of the release film

[0330] Polypropylene film is used as a separating film. 5. Preparation of the electrolyte solution

[0331] 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 Production

[0332] 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.

[0333] The manufacturing process of embodiment 2 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.02.

[0334] The manufacturing process of embodiment 3 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.01.

[0335] The manufacturing process of embodiment 4 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.05.

[0336] The manufacturing process of embodiment 5 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the mass content of the trivalent iron element in iron(II) oxalate is 0.80%.

[0337] The manufacturing process of embodiment 6 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the carbon source is replaced by polyethylene glycol + glucose, wherein the mass ratio of polyethylene glycol to glucose is 3:1.

[0338] The manufacturing process of embodiment 7 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the carbon source is replaced by polyethylene glycol + glucose, wherein the mass ratio of polyethylene glycol to glucose is 2:1.

[0339] The manufacturing process of embodiment 8 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the carbon source is replaced by polyethylene glycol + glucose, wherein the mass ratio of polyethylene glycol to glucose is 1:2.

[0340] The manufacturing process of embodiment 9 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the carbon source is replaced by polyethylene glycol + glucose, wherein the mass ratio of polyethylene glycol to glucose is 1:3.

[0341] The manufacturing process of embodiment 10 is essentially the same as that of embodiment 1, with the difference that no conductive carbon black is added in the manufacturing step of the cathode foil.

[0342] The manufacturing process of embodiment 11 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the second temperature is 755 °C.

[0343] The manufacturing process of embodiment 12 is essentially the same as that of embodiment 1, with the difference that in the manufacturing step of the active cathode material the carbon source is replaced by polyethylene glycol + glucose, wherein the mass ratio of polyethylene glycol to glucose is 1:3, wherein the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.05.

[0344] The manufacturing process of Comparative Example 1 is essentially the same as that of Exemplary Example 1, with the difference that in the manufacturing step of the active cathode material the carbon source polyethylene glycol is replaced by glucose, wherein the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.05, and wherein the second temperature is 810 °C.

[0345] The manufacturing process of Comparative Example 2 is essentially the same as that of Exemplary Example 1, with the difference that in the manufacturing step of the active cathode material the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.01, and wherein the second temperature is 745 °C.

[0346] The manufacturing process of Comparative Example 3 is essentially the same as that of Exemplary Example 1, with the difference that in the manufacturing step of the active cathode material the carbon source polyethylene glycol is replaced by glucose, wherein the ratio of lithium dihydrogen phosphate and iron(II) oxalate brings the atomic molar ratio of lithium and iron to 1.06, and wherein the second temperature is 740 °C. Performance test 1. Limiting compressive strength of the electrode foil

[0347] After double-sided coating, the electrode foil is pressed using a roller press to test its elongation and flexibility. Increasing the roller press pressure produces electrode foils with varying densities. As the pressure increases, the electrode foil's density also increases, while its ductility decreases. Excessive ductility is likely to cause warping, and insufficient flexibility is likely to lead to brittle fracture. Therefore, the lower of the two densities, where the electrode foil's ductility is 8% or the number of times it can be flexibly folded, is defined as the limiting density.

[0348] The compression density is calculated from the mass of the cathode film layer / volume of the cathode film layer.

[0349] The test procedure for ductility is as follows:

[0350] Place the electrode foil on a horizontal table; cut the electrode foil into sections, each strip being approximately 100 cm long; remove 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; use 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 record the length before pressing;and wherein, after pressing, the length between the corresponding marking points is recorded, and wherein (length after pressing - length before pressing) / length before pressing is used as the ductility.

[0351] The number of times the flexible folding is tested as follows.

[0352] 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 2 kg 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 2 kg 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. 2. Energy density test

[0353] 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 25°C at 0.33C until the discharge cutoff voltage reaches 2.5V. Record the total discharge energy of the lithium-ion secondary battery as E0.

[0354] Measuring the length, width, and height of the lithium-ion secondary battery and calculating the volumetric value of the lithium-ion secondary battery, V0=length*width*height.

[0355] Volume energy density of the lithium-ion secondary battery = Discharge energy E0 of the lithium-ion secondary battery / Volume V0 of the lithium-ion secondary battery. 3. DCR test procedure

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

[0358] The batteries of each embodiment and comparison example are manufactured separately according to the above procedure, and the performance parameters are measured, and the results are shown in Table 1 below. Table 1 carbon source Content of the trivalent iron element in iron oxalate / wt.% Lithium-iron ratio Second temperature / °C Conductive agent content / wt. % Area fraction of particles with a particle size ≥1.5µm and <5 µm / % Area fraction of particles with a particle size ≥5µm / % Iron dissolution rate / ppm Example 1 PEG 0,03 1,03 770 0,80 14,62 0 1058 Example 2 PEG 0,03 1,02 770 0,80 13,70 0 890 Example 3 PEG 0,03 1,01 770 0,80 12,81 0 658 Example 4 PEG 0,03 1,05 770 0,80 15,46 0 1485 Example 5 PEG 0,80 1,03 770 0,80 15,31 0 1349 Execution- PEG: Glucose 0,03 1,03 770 0,80 14,92 0 1143 example 6 =3:1 Example 7 PEG: Glucose=2:1 0,03 1,03 770 0,80 15,39 0 1236 Example 8 PEG: Glucose=1:2 0,03 1,03 770 0,80 16,02 0 1384 Example 9 PEG: Glucose=1:3 0,03 1,03 770 0,80 16,89 0 1531 Example 10 PEG 0,03 1,03 770 0 14,58 0 1076 Example 11 PEG 0,03 1,03 755 0,80 9,02 0 1311 Example 12 PEG: Glucose=1:3 0,03 1,05 770 0,80 18,21 0 1921 Comparative example 1 Glucose 0,03 1,05 810 0,80 21,78 0 2365 Comparative example 2 PEG 0,03 1,01 745 0,80 7,20% 0 487 Comparative example 3 Glucose 0,03 1,06 740 0,80 9,63 0 2105 Continuation of Table 1 B 50 Area fraction of particles with a particle size ≥200nm and <1500nm / % Area fraction of particles with a particle size ≥1µm and <1.5µm / % Compressed density in a fully discharged state / cm³ 3 DC internal resistance at 25 °C, 3 °C, 20% SOC / mΩ DC internal resistance -25 °C, 1 °C, 50% SOC / mΩ Energy density Wh / L Example 1 0,443 75,10 19,66 2,55 43,4 388,0 444,8 Example 2 0,437 75,47 20,28 2,53 44,35 391,6 441,5 Example 3 0,432 75,83 20,89 2,51 45,3 395,2 438,1 Example 4 0,450 75,24 18,41 2,58 47,7 395,2 449,8 Example 5 0,448 75,45 19,23 2,57 46,2 423,7 426,2 Example 6 0,445 75,42 20,25 2,56 45,2 421,3 446,5 Example 7 0,449 75,67 19,31 2,57 45,4 411,4 448,1 Example 8 0,453 76,21 18,88 2,58 46,7 421,7 447,5 Example 9 0,459 76,66 18,28 2,59 48,2 428,8 446,9 Example 10 0,443 75,07 19,70 2,56 43,6 390,1 443,3 Example 11 0,398 78,57 23,88 2,51 40,0 356,2 438,1 Execution- 0,465 73,78 15,57 2,60 49,3 441,9 437,4 example 12 Comparative example 1 0,489 72,34 14,72 2,63 50,3 454,0 446,7 Comparative example 2 0,345 81,02 25,23 2,38 47,7 430,7 415,6 Comparative example 3 0,480 79,02 22,50 2,43 40,9 368,6 424,8

[0359] As can be seen from the data comparison of the exemplary embodiments and the comparative examples, if the percentage area fraction of the particles with a particle size of more than or equal to 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%, and if the iron dissolution rate of the cathode film layer is 658 ppm–1921 ppm, the battery has a high cathode film density, a high energy density, and offers good kinetic performance.

[0360] As can be seen from the comparison of embodiments 9, 12 and the other embodiments, the DC internal resistance of the battery can be further reduced if the iron dissolution rate of the cathode film layer is 658 ppm-1485 ppm.

[0361] As can be seen from the data comparison of the exemplary embodiments and the comparative examples, it is beneficial for the further improvement of the pressing density and the energy density of the cathode foil if the percentage area fraction of the particles with a particle size of more than or equal to 1.5 µm and less than 5 µm is 9.0%-20.0%.

[0362] As can be seen from the comparison between embodiment 11 and other embodiments, it is beneficial for a further improvement in the energy density of the battery if the percentage area fraction of the particles with a particle size of more than or equal to 200 nm and less than 1500 nm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 73.0%–78.0%.

[0363] 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

[0140] Suzhou Jingle, model ST2722

[0171]

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 current collector and a cathode film layer arranged on at least one side of the cathode current collector, wherein the cathode film layer comprises an active cathode material, the active cathode material comprising lithium-containing transition metal phosphate particles, and wherein at least a part of the surface thereof is provided with a carbon coating material, wherein the percentage area fraction of the particles with a particle size of more than or equal to 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is greater than or equal to 8.0% and less than or equal to 20.0%, wherein the iron dissolution rate of the cathode film layer is 658 ppm-1921 ppm. [2] Lithium-ion secondary battery according to claim 1, characterized by, that the iron dissolution rate of the cathode film layer is 658 ppm-1485 ppm. [3] Lithium-ion secondary battery according to one of claims 1 or 2, characterized by that the median B 50 of the coating value in the cumulative distribution curve for the coating value-B of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.35-0.48; where the coating value-B I P / I D is, where I P for the intensity of the P-peak of the Raman spectrum at 948±100cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 stands. [4] Lithium-ion secondary battery according to any one of claims 1 to 3, characterized by , that the percentage area fraction of particles with a particle size of more than or equal to 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 0. [5] Lithium-ion secondary battery according to any one of claims 1 to 4, characterized by , that the percentage area fraction of particles with a particle size of more than or equal to 1.5 µm and less than 5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 9.0%-20.0%, optionally 10.0%-20.0%. [6] Lithium-ion secondary battery according to any one of claims 1 to 5, characterized by , that the percentage area fraction of particles with a particle size of more than or equal to 1 µm and less than 1.5 µm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 15.0%-25.0%, optionally 16.0%-24.0%. [7] Lithium-ion secondary battery according to any one of claims 1 to 6, characterized by, that the percentage area fraction of particles with a particle size of more than or equal to 200 nm and less than 1500 nm in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 73.0%-80.0%, optionally 73.0%-78.0%. [8] Lithium-ion secondary battery according to claims 1 to 7, characterized by 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 0.95–1.20, optionally 0.98–1.15, and further optionally 1.0–1.10; 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±100cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100cm -1 stands. [9] Lithium-ion secondary battery according to any one of claims 1 to 8, characterized by , that 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, the median LA50 of the sphericity is 0.65-0.85, optionally 0.70-0.

80. [10] Lithium-ion secondary battery according to any one of claims 1 to 9, 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 RA50 of the roughness is 0.92-0.

96. [11] Lithium-ion secondary battery according to any one of claims 1 to 10, characterized by , that, based on the total mass of the active cathode material, the mass content of carbon is 0.8%-1.8%, optionally 0.9%-1.50%. [12] Lithium-ion secondary battery according to any one of claims 1 to 11, characterized by that the lithium and iron antisit defect concentration of the active cathode material is 0.1%-1.5%, optionally 0.3%-1.0%. [13] Lithium-ion secondary battery according to any one of claims 1 to 12, 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. [14] Lithium-ion secondary battery according to any one of claims 1 to 13, 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. [15] Lithium-ion secondary battery according to any one of claims 1 to 14, 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. [16] Lithium-ion secondary battery according to any one of claims 1 to 15, characterized by that 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 is; and / or that under a pressure of 3T the powder density of the active cathode material is 2.50 g / cm³ 3 -2.70 g / cm² 3 , optional 2.52 g / cm² 3 -2.68 g / cm² 3 amounts. [17] Lithium-ion secondary battery according to any one of claims 1 to 16, characterized by , that the powder resistance of the active cathode material under a pressure of 8MPa is 0.5 Ω·cm-30.0 Ω·cm, optionally 2.0 Ω·cm-20.0 Ω·cm. [18] Lithium-ion secondary battery according to any one of claims 1 to 17, characterized by , that the active cathode material has a discharge gram capacity of 135 mAh / g-150 mAh / g at a discharge rate of 1 C. [19] Lithium-ion secondary battery according to any one of claims 1 to 18, 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 rate of 0.1 C at a constant current and subsequently charged and discharged once at a rate of 1 C at a constant current, wherein the capacity value extracted in the charge and discharge test at a rate of 1 C at a discharge voltage of 3.2 V is recorded as C1, wherein the capacity value extracted at a discharge voltage of 2.0 V is C2, where η=C1 / C2, 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. [20] Lithium-ion secondary battery according to any one of claims 1 to 19, characterized by, that in a 0.1C discharge curve of the button battery, which includes the active cathode material, there is a discharge plateau in a voltage range of 2.5 V to 2.9 V. [21] Lithium-ion secondary battery according to any one of claims 1 to 20, characterized by , that, relative to the total mass of the cathode film layer, the mass content of the conductive medium is 0-1.5%, optionally 0. [22] Lithium-ion secondary battery according to any one of claims 1 to 21, 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%, optionally 96.5%-99.5%; wherein the mass content of the binder is 0.5%-3%. [23] Lithium-ion secondary battery according to any one of claims 1 to 22, characterized by that the cathode film layer has a one-sided areal density of 300mg / 1540mm 2 -450mg / 1540mm 2 has. [24] Lithium-ion secondary battery according to any one of claims 1 to 23, characterized by , that when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.51g / cm³ 3 -2.73g / cm² 3 amounts. [25] Lithium-ion secondary battery according to any one of claims 1 to 24, characterized by , that when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.55 g / cm³ 3 -2.70 g / cm² 3 amounts. [26] Lithium-ion secondary battery according to any one of claims 1 to 25, characterized by that the cathode film layer meets at least one of the following conditions: (1) when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.51 g / cm³ 3 -2.73 g / cm² 3, 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) when the lithium-ion secondary battery is in a fully discharged state, the density of the cathode film layer is 2.55 g / cm³ 3 -2.70 g / cm² 3 , 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%. [27] Lithium-ion secondary battery according to any one of claims 1 to 26, characterized by that the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the current collector; and wherein the lower coating satisfies at least one of the following conditions: (1) the bottom coating comprises carbon-based particles, and the distribution density of the carbon-based particles with a particle size of more than 100 nm in the bottom 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. [28] Battery device, characterized by , that it comprises a lithium-ion secondary battery according to any one of claims 1 to 27, wherein the battery device comprises at least one of a battery cell, a battery module, a battery pack and an energy storage battery. [29] Power-consuming device, characterized bythat it comprises a lithium-ion secondary battery according to any one of claims 1 to 27 or a battery device according to claim 28.

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