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

Abstract

Lithium-ion secondary battery, characterized in that it comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises lithium-containing transition metal phosphate particles, wherein at least a part of the surface thereof is provided with a carbon coating material, wherein in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1 µm is 30.0%-50.0%; where the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm.

Description

TECHNICAL AREA

[0001] The present application relates to the technical field of lithium-ion batteries, in particular a lithium-ion secondary battery, a battery device 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] As market demands for the lifespan and safety of power-consuming devices have increased, so too have the requirements for the energy density and storage capacity of lithium-ion secondary batteries. However, it is difficult for existing technology to improve these performance levels simultaneously, which has become a pressing technical challenge in this field. REVELATION OF THE INVENTION

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

[0005] A first aspect of the present application provides a lithium-ion secondary battery comprising a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, and wherein the cathode film layer comprises an active cathode material, and wherein the active cathode material comprises lithium-containing transition metal phosphate particles, and wherein at least a part of the surface thereof is provided with a carbon coating material, and wherein in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with a particle size greater than or equal to 1 µm is 30.0%-50.0%; and wherein the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm.

[0006] The embodiment of the present application effectively reduces the magnetic substance content in the cathode film layer while increasing the surface area of ​​the large particles, such that the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm. The electrode foil density in the lithium-ion secondary battery can be improved while maintaining a low self-discharge rate, which contributes to improving the battery's energy density and its long-term maintenance during the storage process.

[0007] In each embodiment, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30.00%-50.00%.

[0008] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm lies within the above range, which can control the content of magnetic substance in the battery, while the pressing density of the electrode foil is improved by gradation, and contributes to improving the energy density of the lithium-ion secondary battery as well as to its long-term maintenance in the storage process.

[0009] In each embodiment, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30.00%-45.00%.

[0010] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with a particle size of 1 µm-5 µm lies within the above range, which allows the migration distance of the lithium ions within the particles to be further taken into account, while improving the packing density and the stability of the capacity storage, and thus enabling the lithium-ion secondary battery to maintain a lower impedance in order to improve the kinetic performance of the battery.

[0011] In each embodiment, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm is 0.05%-0.20%.

[0012] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm lies within the above range, which means that there is a certain number of large particles in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil to improve the pressing density of the electrode foil, and the kinetic performance of the lithium-ion secondary battery is not seriously degraded due to the excessive particle size of the large particles, so that an equilibrium of energy density and kinetic performance of the battery is achieved.

[0013] In each embodiment, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 3.0%-15.0%, optionally 5.0%-12.0% and further optionally 5.0%-10.0%.

[0014] The area fraction of particles with a particle size of 50 nm-200 nm within the above range means that there is a certain number of particles with a particle size of 50 nm-200 nm, which helps to improve the powder density of the active cathode material and the density of the electrode foil by gradation in order to further improve the energy density of the lithium-ion secondary battery.

[0015] In each embodiment, the mass fraction of the magnetic substance in the cathode film layer is less than or equal to 300 ppm, optionally 20-200 ppm.

[0016] The mass content of the magnetic substance within the above range can further mitigate the phenomenon of self-discharge in order to improve the storage stability of the battery capacity.

[0017] In each embodiment, the magnetic substance comprises one or more of Fe, Fe2P, FeP, γ-Fe2O3, Fe2P2O7.

[0018] In each embodiment, the mass content of elemental iron in the cathode film layer is less than 20 ppm, optionally less than or equal to 15 ppm.

[0019] Controlling the mass content of elemental iron within the above range is beneficial for improving the safety performance of the battery.

[0020] 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.

[0021] 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 and further improve the energy density of the lithium-ion secondary battery.

[0022] In each embodiment, the active cathode material comprises titanium, and based on the total mass of the active cathode material, the mass content of titanium is 1500 ppm-8000 ppm, optionally 2500 ppm-8000 ppm, and further optionally 2500 ppm-6000 ppm.

[0023] The active cathode material comprises titanium, and its mass fraction is controlled within the above range. On the one hand, this inhibits particle growth and achieves the purpose of controlling the size of large particles, so that in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm lies within a suitable range; on the other hand, its surface inertia reduces the probability that the local chemical reaction of the raw material is inhomogeneous and generates a magnetic substance.Simultaneously, doping the active cathode material with titanium can improve the electronic conductivity and ion transport rate of the lithium-containing transition metal phosphates and mitigate the negative effects of relatively large particles on the kinetic performance of the active cathode material. By influencing the particle size and the lithium ion transport pathway, a balance is achieved between the energy density and the kinetic power of the battery.

[0024] In each embodiment, the mass fraction of carbon is 0.9%-1.8%, based on the total mass of the active cathode material.

[0025] With respect to the total mass of the active cathode material, the mass fraction of carbon within the above range can not only improve the conductivity of the active cathode material and the kinetic performance of the lithium-ion secondary battery, but also reduce the negative effects of an excessively high carbon content on the charging of the lithium-containing transition metal phosphates, take into account the pressing density of the electrode foil and the impedance of the lithium-ion secondary battery, and simultaneously improve the energy density and kinetic performance of the battery.

[0026] In each embodiment, the median is C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C value of the cathode film layer obtained in the area scanning mode of the laser microconfocal Raman spectrometer, greater than or equal to 0.9 and less than or equal to 1.3, optionally 0.99-1.2, where the graphitization C value IG / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1 stands.

[0027] The active cathode material with a graphitization level within the above range is able to achieve a further improvement in the density of the cathode film layer by means of particle sliding, with the help of the graphitized carbon layer on the surface of the active cathode material, which can easily realize particle sliding in the rolling process for film formation, in order to counteract the negative effect of the particle size on the pressing density of the electrode foil.

[0028] In each embodiment, the median LA50 of the sphericity in the cumulative distribution curve of the sphericity area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 0.60-0.85, optionally 0.65-0.80.

[0029] The particles with median LA50 sphericity within the above range are approximately spherical, and under the influence of an external force, sliding between the particles can easily occur, which helps to further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0030] In each embodiment, the powder density of the active cathode material is 2.48 g / cm³ under a pressure of 3 T. 3 -2.76 g / cm² 3 , optional 2.58 g / cm² 3 -2.76 g / cm² 3 .

[0031] The active cathode material has a high powder density to provide a material basis for improving the pressing density of the electrode foil and for manufacturing a high energy density lithium-ion secondary battery.

[0032] In each embodiment, the powder density of the active cathode material is 2.58 g / cm³ under a pressure of 3 T. 3 -2.76 g / cm² 3 .

[0033] The active cathode material with a density within the above range can further improve the density of the electrode foil and increase the energy density of the battery.

[0034] In each embodiment, the discharge gram capacity of the active cathode material is 135 mAh / g-150 mAh / g at room temperature at a discharge rate of 1 C.

[0035] The active cathode material has a high discharge gram capacity, indicating that the active cathode material has good kinetic performance and contributes to improving the energy density of the lithium-ion secondary battery.

[0036] In each embodiment, the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, where η is defined as follows: a button cell comprising the active cathode material is charged and discharged twice in a voltage range of 2.0 V to 3.75 V at a C-rate of 0.1 C with a constant current, and subsequently once at a C-rate of 1 C with a constant current. The capacity value extracted in the charge and discharge test at a C-rate of 1 C with a discharge voltage of 3.2 V is recorded as C1, and the capacity value extracted at a discharge voltage of 2.0 V is C2, and n = C1 / C2, and wherein the charging process comprises a constant-voltage charge at a constant voltage of 3.75 V and a constant-voltage cutoff current of 50 µA.

[0037] A high discharge capacity percentage of the active cathode material used in the battery according to the embodiment of the present application at a discharge to 3.2 V implies that the active cathode material, although containing a certain proportion of large particles, nevertheless maintains 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.

[0038] In each embodiment, the cathode film layer further comprises a binder and a conductive agent, and, based on the total mass of the cathode film layer, the mass content of the active cathode material is 94%-99.4%, the mass content of the binder is 0.5%-3%, and the mass content of the conductive agent is 0.1%-3%.

[0039] In each embodiment, the one-sided areal density of the cathode film layer is 300 mg / 1540 mm². 2 -450 mg / 1540 mm 2 .

[0040] A cathode film layer with an areal density within the above range can contribute to improving the energy density of the lithium-ion secondary battery.

[0041] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.43 g / cm³. 3 -2.78 g / cm² 3 .

[0042] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.50 g / cm³. 3 -2.75 g / cm² 3 .

[0043] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.43 g / cm³. 3 -2.78 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%-28%.

[0044] In each embodiment, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.5 g / cm³. 3 -2.78 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%.

[0045] The lower porosity 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 cathode film detachment during the long cycle process, which contributes to improving the long cycle performance of the battery.In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the 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;

[0046] The lower coating contributes to increasing the electrical conductivity and bond strength of the cathode film layer and the collector, and to reducing the detachment of the cathode film layer from the collector during the cycling process, while improving the kinetic performance of the battery. This is achieved, for example, in the high-density electrode foil of the embodiment of the present application, when the density of the cathode foil is greater than or equal to 2.4 g / cm³ in the fully discharged state. 3The collector tends to be damaged during the high-pressure compaction process of the electrode foil, and the large-format particles tend to create craters on the collector. Controlling the distribution density of carbon-based particles with a particle size greater than 100 nm to ≤10pcs / 10µm helps to reduce the likelihood of damage occurring to the collector in the high-density electrode foil and to further improve the limiting density of the cathode foil.

[0047] In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the collector; wherein the density of the cathode foil in a fully discharged state is greater than or equal to 2.4 g / cm³ 3 is, where the one-sided thickness of the lower coating is 1 µm-4 µm.

[0048] In each embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the collector; wherein the density of the cathode foil in a fully discharged state is greater than or equal to 2.5 g / cm³ 3 is, where the one-sided thickness of the lower coating is 2 µm-4 µm.

[0049] 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 increases the electrode film's limiting density.

[0050] 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.

[0051] A third aspect of the present application provides a power-consuming device comprising a lithium-ion secondary battery provided by the first aspect of the present application or a battery device provided by the second aspect of the present application.

[0052] An unclaimed aspect of the present application provides a method for producing an active cathode material, comprising: obtaining a mixed crude material comprising a carbon source, a lithium source, an iron source, and a phosphorus source; wherein the molar ratio of lithium and iron in the mixed crude material is greater than 1 and less than 1.05; milling to obtain a mixed slurry, wherein the volume-distributed solid-phase particle size D v 50 in the mixed slurry is 0.3 µm-0.4 µm; drying of the mixed slurry to obtain a precursor powder; sintering of the precursor powder to obtain an active cathode material, the sintering being carried out in an inert gas environment and the total gas flow rate in the sintering process being 1100 m 3 / h-1400 m 3 / h; wherein the sintering comprises an elevated temperature interval and a constant temperature interval, wherein the inert gas flow rate v1 in the elevated temperature interval is higher than the inert gas flow rate v2 in the constant temperature interval; wherein the temperature of the constant temperature interval of the sintering ranges from 770°C to 830°C; wherein the active cathode material comprises lithium-containing transition metal phosphate particles, with at least a portion of its surface being coated with a carbon coating material.

[0053] The active cathode material produced by the unclaimed method not only allows particles larger than 1 µm with a certain area fraction to exist in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, but also ensures that the active cathode material contains a small amount of magnetic substance, which improves the pressing density of the electrode foil, improves the energy density of the lithium-ion secondary battery and ensures that the battery has a low self-discharge level, so that the energy density of the lithium-ion secondary battery can be maintained over a long period during the storage and cycling process of the battery.

[0054] Another unclaimed aspect of the present application provides a method for producing a cathode foil, wherein the production method comprises: dry mixing of a binder, a conductive agent and an active cathode material obtained by the method in the fourth aspect, adding a solvent, stirring to obtain a shipping slurry; transferring and applying the shipping slurry to at least one side of the collector, drying and hot pressing to obtain a cathode foil.

[0055] In each embodiment, the hot pressing comprises at least three hot rolling presses, wherein the hot rolling pressure increases sequentially and is successively 20 tonnes-50 tonnes, 50 tonnes-70 tonnes and 70 tonnes-90 tonnes; and wherein the hot rolling temperature is 40°C-80°C, and wherein the electrode foil is heated prior to the first entry into the hot rolling press, the temperature of the heating being 40°C-50°C.

[0056] The active cathode material, produced using the above hot pressing process in conjunction with the manufacturing process of the fourth aspect, effectively improves the pressing density of the electrode foil while maintaining a low content of magnetic substance, resulting in an improved energy density of the battery while maintaining a low self-discharge.

[0057] In each embodiment, the coating speed of the transfer coating is 1 m / min - 25 m / min.

[0058] The coating rate of the transfer coating is within the above range, which contributes to improving the uniformity of the particle distribution in the coating process, reducing the risk of particle agglomeration in the cathode film layer, reducing the porosity of the cut surface of the cathode film layer, further increasing the boundary pressure density of the electrode foil, and improving the energy density of the battery. PRESENTATION OF THE INVENTION Fig. Figure 1 shows a scanning electron microscope image of a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil in an embodiment of the present application; Fig. Figure 2 shows a schematic diagram of a lithium-ion secondary battery in an embodiment of the present application; Fig. Figure 3 shows a schematic disassembly diagram of a lithium-ion secondary battery in an embodiment of the present application; Fig. Figure 4 shows a schematic diagram of a battery module in an embodiment of the present application; Fig. Figure 5 shows a schematic diagram of a battery pack in an embodiment of the present application; Fig. Figure 6 shows a schematic disassembly diagram of a battery pack according to Fig. 5; Fig. Figure 7 shows a schematic diagram of a power-consuming device which uses a lithium-ion secondary battery as a power source in an embodiment of the present application; Fig. Figure 8 shows a diagram of a porosity test of a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil in an embodiment of the present application. Reference symbol list 1 battery pack 2 Upper Case 3 Lower Case 4 battery modules 5 lithium-ion secondary batteries 51 cases 52 Electrode component 53 Top cover component SPECIFIC EXECUTION FORMS

[0059] The following 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 avoid making the following description 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] Unless expressly stated otherwise, all steps of the present application may be carried out sequentially or randomly, preferably sequentially. For example, the unclaimed 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 statement that the method may also include step (c) means, for example, that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b).

[0064] In the present application, the terms "plural" and "multiple" refer to two or more.

[0065] Unless otherwise stated, the terms used in this application have the known meanings as generally understood by those skilled in the art.

[0066] 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.

[0067] 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 cells, battery modules, or battery packs.

[0068] 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.

[0069] The lithium-ion secondary battery comprises an electrode component and an electrolyte.

[0070] The lithium-ion secondary battery may also include an outer casing used to encapsulate the electrode components and the electrolyte. This outer casing can be a rigid housing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. Alternatively, it can be a flexible casing, such as a pouch-like soft casing. The flexible casing can be made of plastic, for example, one or more of the following materials: polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0071] 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.

[0072] 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.

[0073] 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.

[0074] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, and the like.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] Lithium-containing transition metal phosphates are frequently used in lithium-ion batteries due to their structural stability, good safety, and long lifespan. However, their low electronic conductivity, poor stackability, and low active material loading within the battery prevent them from meeting the requirements of high-energy-density batteries.

[0080] Studies show that increasing the number and proportion of large particles in lithium-containing transition metal phosphate materials is an effective way to increase powder density and the active cathode material loading in the battery. Lithium-containing transition metal phosphate materials often require high-temperature sintering to be formed. The larger the particle size, the greater the solid-phase diffusion between the raw materials and the more the grain boundaries melt, thus increasing energy consumption and sintering temperature. However, experimental results indicate that batteries with large lithium-containing transition metal phosphate particles are associated with high self-discharge.The researchers discovered that this is because, with increasing sintering temperature of the lithium-containing transition metal phosphate material, a carbothermic reduction reaction can easily occur at its lattice defects, and these defects are reduced by the carbon on the surface and other reducing substances (e.g., hydrogen, carbon monoxide, etc.) generated during the manufacturing process to Fe, Fe₂P, and other magnetic substances. Therefore, an increase in large particles in the active cathode material is often accompanied by an increase in the content of magnetic substances.The magnetic substances involved in the charging and discharging process of the lithium-ion secondary battery can easily cause organic substances in the electrolyte to agglomerate and form spikes or points that can easily pierce the diaphragm and create a micro-short circuit inside the lithium-ion secondary battery, resulting in a leakage current path that leads to a gradual reduction in battery capacity without connection to external loads, i.e., an increase in the phenomenon of self-discharge, which degrades the long-term performance of the lithium-ion secondary battery.

[0081] A first aspect of the present application provides a lithium-ion secondary battery comprising a cathode foil, an anode foil, and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, and wherein the cathode film layer comprises an active cathode material, and wherein the active cathode material comprises lithium-containing transition metal phosphate particles, and wherein at least a portion of its surface is provided with a carbon coating material, and wherein, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with a particle size greater than or equal to 1 µm is 30%–50%, as shown in Fig. 1 shown; and wherein the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm.

[0082] It is difficult to achieve a high cathode film density if the area fraction of particles with a size greater than or equal to 1 µm in the cathode film layer is less than 30%. If the area fraction of particles with a size greater than or equal to 1 µm in the cathode film layer exceeds 50%, it is necessary to increase the sintering temperature or sintering time, and the content of magnetic substances will increase, leading to an increase in the self-discharge K-value of the battery cell. While the area fraction of particles with a size greater than or equal to 1 µm can be controlled to between 30.0% and 50.0%, the content of magnetic substances can be adjusted by modifying the gas flow rate, etc.The mass fraction of magnetic substances in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm, thereby reducing the phenomenon of battery self-discharge and simultaneously improving the pressing density of the electrode foil.

[0083] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1 µm is 30.0%–50.0%, thereby fully realizing the effect of gradation during the fabrication and cycle of the electrode foil and effectively improving the electrode foil's compaction density. However, the production of the active cathode material, which includes particles with an area fraction within the above range, often requires a long sintering time at high temperature, leading to an increase in the magnetic substance content. The embodiment of the present application effectively reduces the magnetic substance content in the cathode film layer while increasing the area fraction of the larger particles, such that the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm.The packing density of the electrode foil in the lithium-ion secondary battery can be improved while maintaining a low self-discharge rate, which contributes to improving the battery's energy density and its long-term maintenance during the storage process. 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 discernible complete boundaries, whereby defects and scratches may be present within the particles, but no complete boundaries sufficient for subdivision of the particles are discernible within the particles.

[0084] The particle identification method is as follows: the cathode film layer is cut by the argon ion beam along the thickness direction of the electrode foil (as an example, optional: instrument model: Leica EM TIC 3X CP, operating voltage: 6kV, operating time: 6h), and after exposure of the cut surface, a scanning electron microscope is used (as an example, optional: instrument model: Hitachi SU8230, operating voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) to observe the cut surface of the cathode film layer along the thickness direction of the electrode foil.Images are acquired using a field emission scanning electron microscope (FESEM) in the non-marginal position of the cut surface of the cathode film layer (after observing the edge of the electrode foil under the scanning electron microscope, the field of view is adjusted to the central part of the sample) in secondary electron mode, and the electropherograms are recorded at 10k magnification. The particles in the electropherograms are analyzed using the software ImageJ (1.46r, Win64 version). The ImageJ software is used as follows: Loading the SEM image to be analyzed, as shown in [reference missing]. Fig. Figure 1 shows the process; identifying the particles using the Cellpose plug-in software and manually correcting them based on this; reading and counting the data using ImageJ. The specific method for using the Cellpose plug-in software to identify the particles is as follows: setting the segmentation diameter parameter (diameter in the segmentation module) to 15 pixels, clicking "run cyto3" to identify the particles; manually marking the particles in the image that are not identified, or not fully identified, or incorrectly identified by the software. The particles in the image that are not identified, or not fully identified, or incorrectly identified by the software include, in particular, the following: 1. the particles are too large or there are scratches on the surface of the particles, which prevents them from being identified, or prevents them from being identified completely;2. During the argon ion beam sectioning process, scratches are created on the surface of the particles, and the software may mistakenly interpret these scratches as particle boundaries during the identification process, leading to an identification error; 3. Because the particles are too small, they are not successfully identified; 4. The particles are located at the edge of the electron microscope's field of view, and the interior of the particles is penetrated by the edge, the morphology is not fully displayed, and the local part is identified instead of the whole, resulting in an identification error. The aforementioned unidentified or incorrectly identified particles are calibrated manually, and the specific process is as follows: deleting the particles located at the edges of the scanning electron microscope environment that are not fully displayed;Assess whether or not there is a slit scratch within the other unidentified or incorrectly identified particles; if there is no slit scratch within a particle, it is assessed as a single particle and manually marked according to the manually observed particle boundaries; in response to the presence of a slit scratch within the particle, assess whether the slit scratch runs through the particle; if it does not run through the particle, assess that it is a single particle and manually mark it; in response to the slit scratch running through the particle, assess whether the slit scratch is linear or irregular; in response to the slit scratch being irregular, assess that it is a boundary between the particles and divide the particles along the boundary;In response to the finding that the slit scratch is linear, a contrast comparison is performed; in response to the finding that the contrast comparison is not obvious and there is no cracking effect, the slit scratch is judged as a scratch and marked as a single particle; in response to the finding that the contrast comparison is strong and there is a cracking effect, the slit scratch is judged as a boundary between particles and marked as two particles. After manual marking, the information unrelated to the particles in the automatic image processing is deleted, i.e., the assessment and marking of the particles in the image is complete.

[0085] During the densification process of the cathode film layer, densification occurs in the thickness direction. Therefore, the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is, compared to the surface of the cathode film layer, better able to reflect the actual densification state of the particles within the film layer on a spatial scale. In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with a particle size greater than or equal to 1 µm can intuitively reflect the proportionality of a portion of the particles in the particle size segment to the total area of ​​the particles, thus reflecting the size of the area of ​​the particles in the particle size segment.

[0086] 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 area of ​​the particles in a cross-sectional area of ​​the cathode film layer.

[0087] In the prior art, a laser particle detector is typically used to count the particle size of the active cathode material using the Malvern laser diffraction method. However, the applicant's study shows that, because the lithium-containing transition metal phosphate particles readily agglomerate, the test results obtained using the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of the particle 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, since the dispersion of the active cathode material in the film layer increases during the slurry preparation and roller pressing process to form the film.The test results obtained by the Malvern laser diffraction method are influenced by the particle size, the specific surface area, and the degree of agglomeration of the active cathode material, and compared to the actual dispersion in the electrode foil, the number of large particles obtained by the test is lower than the actual value and the number of small particles is higher than the actual value, 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.

[0088] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1 µm is 30%-50%.

[0089] The unclaimed method for examining the area fraction of particles with a particle size greater than or equal to 1 µm in a cross-section of the cathode film layer along the thickness direction of the electrode foil is as follows: Identifying the particles in the cathode film layer with reference to the method described above in the present application, importing the image after particle evaluation and labeling into the ImageJ software for analysis, completing the scaling according to the scanning electron microscope image, and analyzing the particle size, area, sphericity, and roughness of the particles in a cross-section of the cathode film layer along the thickness direction of the electrode foil using the analysis functions "Feret Diameter," "Area," "Round," and "Solidity." 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 particle size statistical process of the present application, and the statistical data corresponding to particles for which AR, roundness, or solidity are displayed as “NaN” are deleted.The sum of the area parameters for particles with a particle size greater than or equal to 1 µm and the sum of the area parameters for all particles are calculated, and these are used as the area of ​​the particles with a particle size greater than or equal to 1 µm and the total area of ​​the counted particles, respectively. The sum of the areas of the particles with a particle size greater than or equal to 1 µm is divided by the total area of ​​the counted particles, which is used as the area fraction of the particles with an area greater than or equal to 1 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0090] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1 µm is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any value in a range between two of these values.

[0091] Lithium-containing transition metal phosphates refer to phosphate materials comprising lithium and a transition metal element and can be detected by any known method in this field. For example, they can be detected by a combination of X-ray diffraction (XRD) with an energy spectrum analyzer and an inductively coupled plasma mass spectrometer. Lithium-containing transition metal phosphates include, but are not limited to, lithium iron phosphate, lithium manganese iron phosphate, and their dopants.

[0092] The carbon coating layer, which is located on at least part of the surface of the lithium-containing transition metal phosphate, can be detected by any method known in the art. For example, the carbon coating layer located on at least part of the surface of the lithium-containing transition metal phosphate can be observed by characterizing the lithium-containing transition metal phosphate using a combination of transmission electron microscopy and an energy spectrum analyzer.

[0093] In order to fully utilize the capacity of the lithium-containing transition metal phosphate material to increase the energy density, at least part of the surface of the lithium-containing transition metal phosphate material is often coated with a carbon layer to improve the efficiency of electron conduction between the active cathode materials.

[0094] In the present application, the ‘magnetic substance’ refers to a substance that can generate magnetism under the influence of a magnetic field.

[0095] The "mass fraction of the magnetic substance in the cathode film layer" can be measured by the following steps: Disassemble the battery to obtain the cathode foil, immerse it in a dimethyl carbonate solvent for 8 hours, dry it, and then sinter the cathode foil under a nitrogen atmosphere at 600°C for 2 hours. During sintering, the cathode collector detaches from the cathode foil. The sintered electrode foil is crushed with a mortar and sieved through a 200-mesh sieve to obtain a cathode material powder. Step 1: Weigh the cathode material powder obtained by the reverse process described above, e.g.80 g, Place in a plastic bucket, add 6 L of deionized water, use a plastic tube to enclose a φ24 mm × 240 mm magnetic rod (with a magnetic induction strength of 6000 GS), and use a heat seal clamp to seal it, and place the magnetic rod in the plastic bucket to seal it together, then set the drum machine speed to 60 rpm and the stirring time to 15 min, place the sealed plastic bucket on the drum machine to stir. Step 2: Prepare another clean plastic bucket, add 5±0.2 L of deionized water to the bucket, rinse the magnetic substances through the plastic tube into the bucket until no sludge block with a surface area greater than or equal to 0.5 cm² remains. 2There is more material present on the surface of the magnetic rod, and then place the magnetic rod in the clean plastic bucket. Close the clean bucket lid, place the plastic bucket on the drum machine, set the drum machine's stirring speed to 60 rpm and the stirring time to 15 minutes, and place the sealed bucket on the stirring device. Repeat step 2 above at least two more times to ensure the accuracy of the extracted magnetic substance quantity.Step 3: Prepare a clean 500 ml beaker, remove the magnetic rod from the bucket and place it in the beaker, use a rinsing bottle to rinse all the magnetic substances on the head of the plastic tube into the beaker, use demagnetized scissors to cut off both sides of the head of the heat shrink tubing and fold them 90° into the top edge of the heat shrink tubing, pull out the magnetic rod and place it in the magnetic rod slot.Using a rinsing bottle, rinse the heat shrink tubing from top to bottom in a zigzag pattern (at least three times on each side), and rinse the magnetic substances into the beaker until no particles remain on the surface of the heat shrink tubing (if there are any hard-to-rinse clumps, scrape them off with the back of a clean ceramic knife, and rinse the contaminants adhering to the ceramic knife into the beaker). Lift the sleeve and rinse the bottom at least three times to ensure that all adsorbed particles of the magnetic substances are collected. Step 4: (1) Place the small magnetic block on the bottom of the beaker and rotate it clockwise from the outside in for at least three rotations, then counterclockwise from the outside in for at least three rotations to adsorb.(2) Repeat step (1) for three rounds, each round of adsorption lasting at least 10 s. (3) Fix the small magnetic block in the center of the beaker bottom with the palm of your hand and hold for longer than 2 s, then slowly pour out the solution by gently tilting the beaker. (4) Place the beaker upright and use a rinsing bottle to rinse the sides of the beaker to ensure that all adhering particles of the magnetic substances are released into the solvent; the amount of solution added is 100–150 mL. (5) Repeat the rinsing in (3) 2–4 times until the liquid in the beaker is clear (no additional solvent needs to be added after the last rinse).Step 5: Add 70 mL of deionized water to the beaker using a syringe, then slowly add 70 mL of hydrochloric acid at a concentration of 36%–38% using another syringe to the beaker. Once the hydrochloric acid dilution is complete, transfer the mixture to a fluoride flask with a sealing cap for storage. Step 6: (1) Using a syringe, inject 15 ± 2 mL of the hydrochloric acid solution prepared in Step 5 into the beaker from which the magnetic substance was extracted, and seal the opening of the beaker with a sealing film. Sonicate the beaker for 2 minutes in an ultrasonic cleaner (power 200 W / frequency 53 kHz). After sonication, wash the beaker with 100 ± 10 mL of deionized water, and repeat the washing process twice. The beaker is filled with 100-150 mL of deionized water, which is to be pumped.The particles of the magnetic substance are captured using a filter membrane with a pore size of 0.45 µm. The filter membrane containing the magnetic substance particles is placed on a substrate for the purity microscope and dried in an oven at 45°C for (15 ± 2) minutes. The mass of the dried filter membrane (containing the magnetic substance particles) is weighed using an electronic balance, and the mass of the empty filter membrane is subtracted to obtain the mass of the magnetic substance. The mass fraction of the magnetic substance relative to the mass fraction of the cathode material powder sample is calculated as the mass fraction of the magnetic substance in the cathode film layer in ppm.

[0096] In some embodiments, the mass fraction of the magnetic substance in the cathode film layer is optionally 20 ppm, 100 ppm, 134.2 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 1000 ppm, 1061.7 ppm, 1450.2 ppm, 1500 ppm, 1980 ppm or any value in a range between any two of these values.

[0097] A person skilled in this field can achieve the regulation of particle area fractions by any known method. For example, the particle size concentration is adjusted by scientifically grading particles of different sizes; the mechanical force of comminution and grinding processes is used to process raw materials to the target range of particle size distribution, thereby achieving the adjustment of particle size and concentration; screening and classification equipment is used to separate the particle sizes within the particle system, thus obtaining a particle size distribution that meets the requirements; and the residence time and force state of the particles in the equipment are adjusted by precisely controlling the feed rate, which also contributes to regulating the particle concentration.

[0098] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30%-50%.

[0099] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any value in a range between two of these values.

[0100] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm lies within the above range, which can control the content of magnetic substance in the battery, while the pressing density of the electrode foil is improved by gradation, and contributes to improving the energy density of the lithium-ion secondary battery as well as to its long-term maintenance in the storage process.

[0101] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30%-45%.

[0102] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of the particles with a particle size of 1 µm-5 µm lies within the above range, which allows the migration distance of the lithium ions within the particles to be further taken into account, while improving the packing density and the stability of the capacity storage, and thus enabling the lithium-ion secondary battery to maintain a lower impedance in order to improve the kinetic performance of the battery.

[0103] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm is 0.05%-0.20%.

[0104] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm is optionally 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2% or any value in a range between two of these values.

[0105] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the fraction of the average equivalent area of ​​the particles with a particle size greater than 1 µm is obtained by dividing the area fraction of the particles with a particle size greater than 1 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil by the total number of particles with a particle size greater than 1 µm cross-sectional area in the cathode film layer along the thickness direction of the electrode foil.In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm lies within the above range, which means that there is a certain number of large particles in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil to improve the pressing density of the electrode foil, and the kinetic performance of the lithium-ion secondary battery is not seriously degraded due to the excessive particle size of the large particles, so that an equilibrium of energy density and kinetic performance of the battery is achieved.

[0106] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 3%-15%, optionally 5%-12% and further optionally 5%-10%.

[0107] In some embodiments, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or any value in a range between two of these values.

[0108] Theoretical studies indicate that, under ideal conditions, spherical particles with a diameter of 314 nm are able to fill the gaps created by the stacking of spherical particles with a diameter of 1 µm, thus increasing particle size distribution and powder density. Particles with diameters of 50 nm to 200 nm are able to fill the gaps between particles with a diameter greater than or equal to 1 µm and work together with them to achieve dense stacking.The area fraction of particles with a particle size of 50 nm-200 nm within the above range means that there is a certain number of particles with a particle size of 50 nm-200 nm, which helps to improve the powder density of the active cathode material and the density of the electrode foil by gradation in order to further improve the energy density of the lithium-ion secondary battery.

[0109] In some embodiments, the mass fraction of the magnetic substance in the cathode film layer is less than or equal to 300 ppm, optionally 20-200 ppm.

[0110] In some embodiments, the mass fraction of the magnetic substance in the cathode film layer is optionally 20 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm or any value in a range between any two of these values.

[0111] The mass content of the magnetic substance within the above range can further mitigate the phenomenon of self-discharge in order to improve the storage stability of the battery capacity.

[0112] In some embodiments, the magnetic substance comprises one or more of Fe, Fe2P, FeP, γ-Fe2O3, Fe2P2O7.

[0113] In some embodiments, the mass content of elemental iron in the cathode film layer is less than 20 ppm, optionally less than or equal to 15 ppm.

[0114] In some embodiments, the mass content of elemental iron in the cathode film layer is optionally 0, 5 ppm, 10 ppm, 15 ppm, 19 ppm or any value in a range between two of these values.

[0115] It is understood that a mass content of elemental iron in the cathode film layer of zero does not necessarily mean that the cathode film layer contains no elemental iron, but merely that the content of elemental iron in it is below the lower detection limit.

[0116] Compared to other magnetic substances, elemental iron is more easily oxidized at the positive electrode and then reduced at the negative electrode. If elemental iron accumulates at the negative electrode to a certain extent, dendrites form, which can lead to diaphragm perforation, causing a short circuit inside the battery and potentially even resulting in fire and explosion, posing a significant safety hazard. Controlling the elemental iron mass content within the range described above is beneficial for improving the battery's safety performance.

[0117] 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.

[0118] In some embodiments, m is optionally 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or any value in a range between any two of these values. x is optionally 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any value in a range between any two of these values. y is optionally 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or any value in a range between any two of these values. j is optionally 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any value in a range between any two of these values. q is optionally 0.01, 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.

[0119] 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 and further improve the energy density of the lithium-ion secondary battery.

[0120] In some embodiments, the active cathode material comprises titanium, and based on the total mass of the active cathode material, the mass content of titanium is 1500 ppm-8000 ppm, optionally 2500 ppm-8000 ppm, and further optionally 2500 ppm-6000 ppm.

[0121] In some embodiments, the mass fraction of titanium, relative to the total mass of the active cathode material, is optionally 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm or any value in a range between two of these values.

[0122] The types and concentrations of elements in the active cathode material can be verified by any known method in this field. For example, the titanium content is verified using inductively coupled plasma emission spectrometry in accordance with Annex C of GB / T 33822-2017.

[0123] Titanium precursors, such as titanium dioxide, are generally surface inert. Their addition during the manufacturing process can reduce the activity of the precursor material mixture. This inhibits particle growth and helps control the size of large particles, ensuring that the proportion of the average equivalent area of ​​particles larger than 1 µm in the cross-sectional area of ​​the cathode film layer, along the thickness direction of the electrode foil, remains within a suitable range. Furthermore, its surface inertness reduces the likelihood of the local chemical reaction of the raw material being inhomogeneous and generating a magnetic substance.Simultaneously, doping the active cathode material with titanium can improve the electronic conductivity and ion transport rate of the lithium-containing transition metal phosphates and mitigate the negative effects of relatively large particles on the kinetic performance of the active cathode material. By influencing the particle size and the lithium ion transport pathway, a balance is achieved between the energy density and the kinetic power of the battery.

[0124] In some embodiments, the mass fraction of carbon is 0.9%-1.8%, based on the total mass of the active cathode material.

[0125] The mass fraction of carbon, relative to the total mass of the active cathode material, can be measured using established methods and equipment. Referring to GB / T 20123-2006 "Determination of the total carbon and sulfur content of steel - Infrared absorption method after combustion in a high-frequency induction furnace," the measurement is performed, for example, using a Dekai HCS infrared carbon and sulfur analyzer.

[0126] In some embodiments, the mass fraction of carbon, relative to the total mass of the active cathode material, is optionally 0.9%, 1%, 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.

[0127] With respect to the total mass of the active cathode material, the mass fraction of carbon within the above range can not only improve the conductivity of the active cathode material and the kinetic performance of the lithium-ion secondary battery, but also reduce the negative effects of an excessively high carbon content on the charging of the lithium-containing transition metal phosphates, take into account the pressing density of the electrode foil and the impedance of the lithium-ion secondary battery, and simultaneously improve the energy density and kinetic performance of the battery.

[0128] In some embodiments, the median is C 50 of the degree of graphitization in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, greater than or equal to 0.9 and less than or equal to 1.3, optionally 0.99–1.2, where the graphitization C value IG / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1 stands.

[0129] In the present application, the graphitization C-value of the cathode film layer can be obtained in the area-scanning mode of a laser microconfocal Raman spectrometer. As an example, a laser microconfocal Raman spectrometer (a high-precision Renishaw laser microconfocal Raman spectrometer) is used, an excitation wavelength of 532 nm is selected, and a suitable amount of the cathode film layer is taken for area scanning of the surface or a cross-sectional area along the thickness direction of the electrode foil. The scanning area is 45 µm × 45 µm, subdivided into 10 × 10 grids, with the vertex of the grid serving as the test point. The step size is 5 µm, and the total number of scan points is 100 to obtain the C-values ​​at various locations and the cumulative distribution curve of the C-values ​​in the area-scanning area.

[0130] 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 traces of electrolyte salt, 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.

[0131] The graphitization C value of the cathode film layer is obtained from the peak intensity ratio of the G-peak (G-band) and the D-peak (D-band) of the Raman spectra, with the position of the G-peak at 1580±100 cm⁻¹ -1 lies and characterizes the sp2 hybrid structure of carbon, and where the position of the D-peak is at 1350±100 cm-1 The C value characterizes the disordered structure of carbon, where disorder means there is no regular arrangement between the carbon atoms in the structure. In graphite crystals, the carbon atoms in the same layer are sp²-hybridized and form covalent bonds, with van der Waals forces acting between the layers, allowing the carbon to slide easily within the graphite structure. Therefore, the C value can characterize the degree of graphitization of the cathode film layer. It is important to understand that the degree of graphitization in the cathode film layer is primarily due to the graphitized carbon material within the cathode film layer, i.e., the carbon coating layer of the active cathode material. Although conductive materials such as carbon nanotubes, which are rich in sp²-hybridized structures, also exhibit relatively high I G / I DDespite 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.

[0132] Therefore, the degree of graphitization of the cathode film layer can also be used to characterize the degree of graphitization of the active cathode material. The higher the degree of graphitization of the carbon on the surface of the active cathode material, and the higher the proportion of graphitic structural carbon in the cathode film layer, the more easily the particles can slide in the coating layer during the rolling process, aided by the carbon structure. This allows for an increase in the pressing density of the electrode foil under low rolling pressure.

[0133] The cumulative distribution curve for the graphitization carbon value is a curve obtained by arranging at least 100 carbon values ​​in order from smallest to largest, with the degree of graphitization on the horizontal axis and the cumulative amount on the vertical axis. 50 A C-value is defined as a value where, in the cumulative distribution curve for the graphitization C-value, the cumulative fraction on the vertical axis is 50%. The median C 50 The graphitization degree, compared to a point value, can reflect the overall graphitization degree, i.e., the sliding ability of the particles in the cathode film layer; and compared to an average value, it can reduce the influence of extreme values ​​in the test process and improve the reliability of the test results.

[0134] A person skilled in this field can regulate the degree of graphitization of the active material particles using any known method. For example, the degree of graphitization of the active material particles can be adjusted by regulating the carbon source, the sintering temperature, the sintering time, the sintering pressure, and the sintering atmosphere.

[0135] In some embodiments, the median C in the cumulative distribution curve for the graphitization C value of the cathode material, obtained in the area-scanning mode of the laser microconfocal Raman spectrometer, is 50 The degree of graphitization can optionally be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.25, 1.3 or any value in a range between two of these values.

[0136] The active cathode material with a graphitization level within the above range is able to achieve a further improvement in the density of the cathode film layer by means of particle sliding, with the help of the graphitized carbon layer on the surface of the active cathode material, which can easily realize particle sliding in the rolling process for film formation, in order to counteract the negative effect of the particle size on the pressing density of the electrode foil.

[0137] In some embodiments, the median LA50 of the sphericity in the cumulative distribution curve of the sphericity area of ​​the particles obtained in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 0.6-0.85, optionally 0.65-0.80.

[0138] The method for verifying the sphericity of particles in a cross-section of the cathode film layer along the thickness direction of the electrode foil is as follows: the particles in the cross-section of the cathode film layer are identified with reference to the method described above in the present application, and the morphology and area of ​​the particles in a cross-section of the cathode film layer along the thickness direction of the electrode foil 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 particle's pixel area 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. LA50 is a sphericity L-value if, in the cumulative distribution curve of the sphericity L-value, the cumulative area fraction on the vertical axis is 50%.

[0139] A person skilled in this field can achieve the regulation of particle sphericity by any known method. For example, particle sphericity can be adjusted by processes such as comminution, polishing, chemical etching, mechanical mixing, extrusion, coating, granulation, addition of surfactants, etc., as well as by adjusting the parameters of the respective processes.

[0140] In some embodiments, 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 optionally 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 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.

[0141] The particles with median LA50 sphericity within the above range are approximately spherical, and under the influence of an external force, sliding between the particles can easily occur, which helps to further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0142] In some embodiments, the powder density of the active cathode material is 2.48 g / cm³ under a pressure of 3 T. 3 -2.76 g / cm² 3 .

[0143] In the present application, the term "powder compaction density" refers to the density (in g / cm³). 3) a blank with a specific density and strength, which is formed in such a way that, with the movement and deformation of the powder in the process of compression by an external force, the larger gaps are filled and the contact area between the particles increases, so that an interatomic attraction is created and the mechanical bond between the particles is strengthened.

[0144] 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 compaction mold (with a known diameter) that is hollow in the center and has a metal disc at the top and bottom. The active cathode material is placed between the metal discs, a metal cylinder is placed on top, the mold is placed on the density measuring device, the pressure is set to 3 T, and the thickness of the active cathode material under this pressure can be read from the device. 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, and S is the base area of ​​the mold, which is 1.327 cm². 2is and H is the thickness of the compacted active cathode material.

[0145] In some embodiments, the powder density of the active cathode material under a pressure of 3 T is optionally 2.48 g / cm³. 3 , 2.49 g / cm³ 3 , 2.50 g / cm³ 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 , 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 or any value within a range between two of these values.

[0146] The active cathode material has a high powder density to provide a material basis for improving the pressing density of the electrode foil and for manufacturing a high energy density lithium-ion secondary battery.

[0147] In some embodiments, the powder density of the active cathode material is 2.58 g / cm³ under a pressure of 3 T. 3 -2.76 g / cm² 3 .

[0148] The active cathode material with a density within the above range can further improve the density of the electrode foil and increase the energy density of the battery.

[0149] In some embodiments, the powder resistance of the active cathode material under a pressure of 8 MPa is 2.0 Ω·cm to 40 Ω·cm.

[0150] The powder resistance of the active cathode material can be measured using methods and equipment known in this field. For example, it can be measured with a powder resistance meter (Suzhou Jingle, model ST2722) in accordance with GB / T 33822-2017. Specifically, a certain amount of active cathode material (e.g., 1 g) is weighed and placed in the loading chamber of the powder resistance meter, a pressure of 8 MPa is applied, the on-resistance and blocking resistance of the active cathode material are tested separately, and the average of the two values ​​is taken as the powder resistance of the active cathode material.

[0151] In some embodiments, the powder resistance of the active cathode material under a pressure of 8 MPa is optionally 2 Ω cm, 3 Ω cm, 4 Ω cm, 5 Ω cm, 6 Ω cm, 7 Ω cm, 8 Ω cm, 9 Ω cm, 10 Ω cm, 11 Ω cm, 12 Ω cm, 13 Ω cm, 14 Ω cm, 15 Ω cm, 16 Ω cm, 17 Ω cm, 18 Ω cm, 19 Ω cm, 20 Ω cm, 21 Ω cm, 22 Ω cm, 23 Ω cm, 24 Ω cm, 25 Ω cm, 26 Ω cm, 27 Ω·cm, 28 Ω·cm, 29 Ω·cm, 30 Ω·cm, 31 Ω·cm, 32 Ω·cm, 33 Ω·cm, 34 Ω·cm, 35 Ω·cm, 36 Ω·cm, 37 Ω·cm, 38 Ω·cm, 39 Ω·cm, 40 Ω·cm or any value in a range between two of these values

[0152] The active cathode material has a low powder resistance, which contributes to improving the capacity utilization of the active cathode material and increasing the energy density of the lithium-ion secondary batteries.

[0153] In some embodiments, the discharge gram capacity of the active cathode material is 135 mAh / g-150 mAh / g at room temperature at a discharge rate of 1 C.

[0154] In the present application, the active cathode material is assembled as a button cell battery to test its electrical performance on a land-based test device. After charging with a constant current from 1°C to 3.75 V within the voltage range of 2.0 V to 3.75 V at 25 ± 5°C, there is a 5-minute pause, followed by charging with a constant voltage up to a cutoff current of 50 µA and subsequent discharging with a constant current of 1 C to 2.0 V. The discharge capacity of the button cell battery is divided by the mass of the active cathode material, thereby determining the discharge gram capacity of the active cathode material at room temperature and a discharge rate of 1 C.

[0155] The manufacturing and testing process of the button cell battery is as follows: Mixing 2.0 g of active cathode material, conductive carbon black, and PVDF in a mass ratio of 0.9:0.05:0.05; adding the organic solvent NMP (N-methylpyrrolidone); mixing thoroughly until homogeneous; applying with a 150 µm scraper; drying at 100°C for 2 hours; and compacting the cathode foil to a density of 2.0 g / cm³. 3 -2.2 g / cm² 3Using a hole punch to cut the cathode foil into a round piece with a diameter of 14 mm, then weighing and recording the weight, placing the weighed cathode foil in a vacuum drying oven (105°C, 1-12 hours, -90 kPa), placing the dried cathode foil in a glove box, assembling it into a battery in the following order: anode tray - nickel mesh - diaphragm - cathode foil - cathode tray, adding 65-87 µL (pipette gun) of electrolyte solution (the electrolyte solution is a solvent mixture of EC (ethylene carbonate), DMC (1,2-dimethyl carbonate) in a volume ratio of 1:1, and the electrolyte LiPF6), placing the button 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.

[0156] It is understood that the discharge gram capacity of the active cathode material can also be determined by disassembling the battery, recovering the cathode foil and testing it after reassembly into a button battery according to the procedure described above.

[0157] In some embodiments, the discharge gram capacity of the active cathode material at room temperature at a discharge rate of 1 C is optionally 135 mAh / g, 140 mAh / g, 141 mAh / g, 142 mAh / g, 143 mAh / g, 144 mAh / g, 145 mAh / g, 146 mAh / g, 147 mAh / g, 148 mAh / g, 149 mAh / g, 150 mAh / g or any value in a range between two of these values.

[0158] The active cathode material has a high discharge gram capacity, indicating that the active cathode material has good kinetic performance and contributes to improving the energy density of the lithium-ion secondary battery.

[0159] In some embodiments, the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, where η is defined as follows: a button cell comprising the active cathode material is charged and discharged twice in a voltage range of 2.0 V to 3.75 V at a C-rate of 0.1 C with a constant current, and subsequently once at a C-rate of 1 C with a constant current. The capacity value extracted in the charge and discharge test at a C-rate of 1 C with a discharge voltage of 3.2 V is recorded as C1, and the capacity value extracted at a discharge voltage of 2.0 V is C2, and n = C1 / C2, and the charging process comprises a constant-voltage charge at a constant voltage of 3.75 V and a constant-voltage cutoff current of 50 µA.

[0160] The value η of the active cathode material can be measured using methods and equipment known in this field. As an example, the button battery is first manufactured according to the procedure described above, and the electrical performance of the manufactured button battery is tested on a land-based test device. This involves charging and discharging the button battery twice at room temperature with a constant current at a C-rate of 0.1 C in the voltage range of 2.0 V to 3.75 V. After being charged with a constant current up to the cutoff voltage, the button battery is charged with a constant voltage to a current of 50 µA and then charged and discharged once with a constant current at a C-rate of 1 C. In the charge / discharge test with a C-rate of 1C, the capacity value when discharging from 3.75 V to a voltage of 3.2 V is recorded as C1, and the capacity value when discharging from 3.75 V to 2.0 V is recorded as C2, and η=C1 / C2.

[0161] In some embodiments, η is optionally 85%, 86%, 87%, 88%, 88.1%, 89%, 90%, 90.1%, 91%, 92%, 92.2%, 93%, 94%, 94.1%, 94.5%, 95%, 95.1% or any value in a range between any two of these values.

[0162] 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%.

[0163] A high discharge capacity percentage of the active cathode material used in the battery according to the embodiment of the present application at a discharge to 3.2 V implies that the active cathode material, although containing a certain proportion of large particles, nevertheless maintains 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.

[0164] In some embodiments, the cathode film layer further comprises a binder and a conductive agent, and, based on the total mass of the cathode film layer, the mass content of the active cathode material is 94%-99.4%, the mass content of the binder is 0.5%-3%, and the mass content of the conductive agent is 0.1%-3%.

[0165] 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.

[0166] 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.

[0167] In some embodiments, the mass fraction of the active cathode material, relative to the total mass of the cathode film layer, is optionally 94%, 95%, 96%, 97%, 98%, 99%, 99.4% or any value in a range between two of these values.

[0168] In some embodiments, the mass content of the binder, relative to the total mass of the cathode film layer, is optionally 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any value in a range between two of these values.

[0169] In some embodiments, the mass fraction of the conductive medium, relative to the total mass of the cathode film layer, is optionally 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any value in a range between two of these values.

[0170] In some embodiments, the one-sided areal density of the cathode film layer is 300 mg / 1540 mm². 2 -450 mg / 1540 mm 2 .

[0171] In the present application, the areal density of the cathode film layer on one side has a meaning known in the art and can be tested by methods known in the art. For example, a cathode foil coated and densified on one side (in the case of a cathode foil coated on both sides, the cathode film layer on one side can be wiped off first) is taken, punched, and cut into a small disc with an area of ​​S1, weighed, and recorded as M1. Then, the cathode film layer of the cathode foil, which was weighed as described above, is wiped off, and the weight of a collector is weighed and recorded as M0. The areal density of the cathode film layer on one side is given by: (M1 - M0) / S1. To ensure the accuracy of the test results, several sets (e.g., 10 sets) of the samples to be tested can be tested, and an average value can be calculated as the test result.

[0172] In some embodiments, the one-sided areal density of the cathode film layer is optionally 300 mg / 1540 mm². 2 , 310mg / 1540 mm 2 , 320mg / 1540 mm 2 , 330mg / 1540 mm 2 , 340mg / 1540 mm 2 , 350mg / 1540 mm 2 , 360mg / 1540 mm 2 , 370mg / 1540 mm 2 , 380mg / 1540 mm 2 , 390mg / 1540 mm 2 , 400mg / 1540 mm 2 , 410mg / 1540 mm 2 , 420mg / 1540 mm 2 , 430mg / 1540 mm 2 , 440mg / 1540 mm 2 , 450mg / 1540 mm 2 or any value within a range between two of these values.

[0173] A cathode film layer with an areal density within the above range can contribute to improving the energy density of the lithium-ion secondary battery.

[0174] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.43 g / cm³. 3-2.78 g / cm² 3 .

[0175] In the present application, a fully discharged state refers to a state in which, after the battery has been stored in an oven environment at 25°C for 2 hours and the temperature of the battery has been maintained at 25°C, the battery is discharged to 2.5 V with a constant current of 1 / 3 C and then discharged to 2.0 V with a constant current of 0.1 C.

[0176] The density of the cathode film layer can be tested using methods known in this field. For example, the battery is placed in an oven environment at 25°C and stored for 2 hours. While maintaining the battery temperature at 25°C, the battery 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 film in the fully discharged state of the lithium-ion secondary battery. The remaining electrolyte solution is treated using the solvent dimethyl carbonate. The electrode film is dried and cut into a small disc with area S. The mass is weighed and recorded as W1. Using a micrometer, the thickness T1 of the cathode film is measured. The cathode film layer is then wiped from the weighed electrode film. The mass of the collector is weighed and recorded as W2.and the thickness T2 of the collector is measured using a hundredths micrometer, then the compression density PD of the cathode film layer = (W1-W2) / [(T1-T2) xS].

[0177] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is optionally 2.43 g / cm³. 3 , 2.44 g / cm³ 3 , 2.45 g / cm³ 3 , 2.46 g / cm³ 3 , 2.47 g / cm³ 3 , 2.48 g / cm³ 3 , 2.49 g / cm³ 3 , 2.50 g / cm³ 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 , 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 or any value within a range between two of these values.

[0178] 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.

[0179] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.50 g / cm³. 3 -2.75 g / cm² 3 .

[0180] In some embodiments, the compression density of the cathode film layer after treatment by the compaction process is 2.55 g / cm³. 3 -2.90 g / cm² 3 .

[0181] In some embodiments, the compression density of the cathode film layer after treatment by the compaction process is optionally 2.55 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 , 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 / cm³ 3 , 2.90 g / cm³ 3 any value within a range between two of these values.

[0182] In the present application, “densification” means the compaction of the cathode film layer by mechanical pressure during the battery assembly process in order to improve its compactness and conductivity.

[0183] In some embodiments, the density of the cathode film layer after treatment by the forming process is 2.43 g / cm³. 3 -2.78 g / cm² 3 .

[0184] In some embodiments, the density of the cathode film layer after treatment by the forming process is optionally 2.43 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 , 2.78 g / cm³ 3 any value within a range between two of these values.

[0185] 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.

[0186] It is understood that the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is somewhat lower than the density of the cathode film layer after compaction and formation, because the electrode foil rebounds during the cycling process.

[0187] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.43–2.78 g / cm³. 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%-28%.

[0188] In some embodiments, the density of the cathode film layer in the fully discharged state of the lithium-ion secondary battery is 2.5–2.78 g / cm³. 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%.

[0189] 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%, 23%, 24%, 25%, 26%, 27%, 28% or any value in a range between two of these values.

[0190] The porosity of the cathode film layer can be examined in a cross-section along the thickness direction of the electrode foil as described below. Import the scanning electron microscope image of the cross-section of the cathode film layer along the thickness direction of the electrode foil, obtained using the method described above, into the ImageJ software. Select the straight line tool, use a straight line to mark the length of the scale in the image, click "Analyze Set Scale", and adjust the scale parameters in the software according to the length of the scale in the image.Select the rectangle tool, select the portion of the image outside the scale range, use "Image Duplicate" to duplicate the selected area, use "Image Type 8 bit" to adjust the image format; select "Analyze Set Measurements" and select the following five options: "Area", "Mean gray value", "Area Fraction", "Limit to threshold", "Feret's diameter", selecting 3 for "Decimal places", and successively selecting "Image" - "Adjust" - "Threshold", and successively setting the "Threshold" position to 0 and 100, thereby enabling the Analyze-Measure function to export the pore data in the scanning electron microscope image of the section surface.Use "Image"-"Overlay"-"Flatten" to export and obtain the pore image; click "Apply" in "Threshold", then click "Analyze"-"Analyze Particles", and check the four columns on the left to obtain the pore statistics.

[0191] 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. As in Fig. As shown in Figure 8, the “pore” is not the porosity data obtained in the exhaust gas test, but is mainly used to characterize the cross-sectional area between the particles in the cut surface of the cathode film layer, 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 reflected.The lower porosity in a cross-sectional area of ​​the cathode film layer, determined using this method, means, on the one hand, that the gradation of large, medium, and small particles in the cathode film layer is better while the pressing density is high, and on the other hand, after the same gradation and the same rolling pressure, if the porosity is low, it means that the particles can easily slip against each other, thus reducing the risk of overpressure in the film layer and the risk of stress concentration, and further reducing the probability of demolding of the cathode film during the long cycle process, which contributes to improving the long cycle performance of the battery.

[0192] In some embodiments, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the 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; where the carbon-based particles refer to particles with carbon as the main component, including but not limited to conductive carbon, soot, etc.

[0193] The lower coating contributes to increasing the electrical conductivity and bond strength of the cathode film layer and the collector, and to reducing the detachment of the cathode film layer from the collector during the cycling process, while improving the kinetic performance of the battery. This is achieved, for example, in the high-density electrode foil of the embodiment of the present application, when the density of the cathode foil is greater than or equal to 2.4 g / cm³ in the fully discharged state. 3The collector tends to be damaged during the high-pressure compaction process of the electrode foil, and the large-format particles tend to create craters on the collector. Controlling the distribution density of carbon-based particles with a particle size greater than 100 nm to ≤10pcs / 10µm helps to reduce the likelihood of damage occurring to the collector in the high-density electrode foil and to further improve the limiting density of the cathode foil.

[0194] In some embodiments, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the collector; wherein the lower coating comprises carbon-based particles, wherein the distribution density of the carbon-based particles with a particle size greater than 100 nm in the lower coating is 0.1 pcs / 10 µm, 1 pcs / 10 µm, 1.5 pcs / 10 µm, 2 pcs / 10 µm, 2.5 pcs / 10 µm, 3 pcs / 10 µm, 3.5 pcs / 10 µm, 4 pcs / 10 µm, 4.5 pcs / 10 µm, 5 pcs / 10 µm, 5.5 pcs / 10 µm, 6 pcs / 10 µm, 6.5 pcs / 10 µm, 7 pcs / 10 µm, 7.5 pcs / 10 µm, 8 pcs / 10 µm, 8.5 pcs / 10 µm, 9 pcs / 10 µm, The quantity can be 9.5pcs / 10µm, 10pcs / 10µm, or any value in a range between any two of these values.

[0195] 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.

[0196] 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 v 50 of the carbon-based particles added during the manufacturing process of the lower coating are in the 20-60 nm range 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.

[0197] In some embodiments, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the collector; wherein the density of the cathode foil in a fully discharged state is greater than or equal to 2.4 g / cm³3 is, where the one-sided thickness of the lower coating is 1-4 µm.

[0198] In some embodiments, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the collector; wherein the density of the cathode foil in a fully discharged state is greater than or equal to 2.5 g / cm³ 3 is, where the one-sided thickness of the lower coating is 2-4 µm.

[0199] 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 increases the electrode film's limiting density.

[0200] In some embodiments, the one-sided thickness of the lower coating can be 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4 µm or any value in a range between two of these values.

[0201] The thickness of the bottom coating on one side can be checked as follows. As described above, the cathode film layer is cut along the thickness direction of the electrode foil using an argon ion beam. A scanning electron microscope image is taken, and the thickness of the bottom coating on one side is measured by taking a point at 1 µm intervals along the length of the electrode foil. The thickness of the bottom coating is then averaged after measuring the thickness at 10 points. It should be noted that anomalous points must be avoided when taking measurements.Areas of the lower coating with thicknesses of less than 50 nm and thicknesses of more than 4 µm; these anomalous points are mainly due to extreme variations in the thickness of individual areas caused by the extrusion of anomalous stress concentrations during the densification process of the electrode foil, and these anomalous points have no statistical significance. In some embodiments, the thickness of the cathode collector is less than or equal to 17 µm, optionally 13–15 µm.

[0202] In some embodiments, the thickness of the cathode collector is optionally 13 µm, 14 µm, 15 µm, 16 µm, 17 µm or any value in a range between two of these values.

[0203] 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.).

[0204] A cathode collector with a thickness within the above range contributes to increasing the charging of the unit mass of the battery and the energy density of the lithium-ion secondary battery.

[0205] 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 130 mg / 1540 mm². 2 -220 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.

[0206] In some embodiments, the one-sided areal density of the anode film layer is optionally 130 mg / 1540 mm². 2 , 140mg / 1540 mm 2 , 150mg / 1540 mm 2 , 160mg / 1540 mm 2 , 170mg / 1540 mm 2 , 180mg / 1540 mm 2 , 190mg / 1540 mm 2 , 200mg / 1540 mm 2 , 210mg / 1540 mm 2 , 220mg / 1540 mm 2 or any value within a range between two of these values.

[0207] In some embodiments, the compression density of the anode film layer is 1.40 g / cm³. 3-1.75 g / cm² 3 .

[0208] In some embodiments, the compression density of the anode film layer is optionally 1.40 g / cm³. 3 , 1.45 g / cm³ 3 , 1.50 g / cm² 3 , 1.55 g / cm³ 3 , 1.60 g / cm³ 3 , 1.70 g / cm³ 3 , 1.75 g / cm³ 3 or any value within a range between two of these values.

[0209] 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.

[0210] The areal density and the compression density of the anode film layer are within the above range, which helps to match the cathode film layer in order to increase the energy density of the lithium-ion secondary battery.

[0211] In some embodiments, the anode collector can be a metal foil or a composite collector. For example, a copper foil can be used as the metal foil. The composite collector can comprise a base layer of polymeric material and a metal layer formed on at least one surface of the polymeric base layer. The composite collector can be formed by depositing metallic material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0212] In some embodiments, the anode film layer comprises a negative active material. The negative active material may be a negative active material known in the art for use in batteries. For example, the negative active material may comprise at least one of the following: synthetic graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may be at least one of monomeric silicon, silicon oxides, silicon-carbon complexes, silicon-nitrogen complexes, and silicon alloys. The tin-based material may be at least one of monolithic tin, tin oxide compounds, and tin alloys.However, the present application is not limited to these materials, and other conventional materials that can be used as negative active materials in batteries may also be used. It is possible to use only one of these negative active materials or to use more than two in combination.

[0213] In some embodiments, the anode film layer optionally further comprises a binder. This binder may be at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0214] 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.

[0215] In some embodiments, the anode film layer optionally includes further additives, such as thickening agents (e.g. sodium carboxymethylcellulose (CMC-Na)), etc.

[0216] In some embodiments, the anode foil can be produced as follows: Dispersing the components described above for the production of the anode foil, such as the negative active material, the conductive agent, the binder and other components, in a solvent (e.g. deionized water) to form an anode slurry; applying the anode slurry to the anode collector and obtaining the anode foil after drying, compaction and other processes.

[0217] 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 needed. For example, the electrolyte can be in liquid, gel, or solid form.

[0218] In some embodiments, an electrolyte solution is used for the electrolyte. This electrolyte solution consists of an electrolyte salt and a solvent.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] 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.

[0227] 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.

[0228] A third aspect of the present application provides a power-consuming device comprising a lithium-ion secondary battery provided by the first aspect of the present application. An unclaimed aspect of the present application provides a method for producing an active cathode material, comprising: obtaining a mixed raw material comprising a carbon source, a lithium source, an iron source, and a phosphorus source; wherein the molar ratio of lithium and iron in the mixed raw material is greater than 1 and less than 1.05; milling to obtain a mixed slurry, wherein the volume-distributed solid-phase particle size D v50 in the mixed slurry is 0.3 µm-0.4 µm; drying of the mixed slurry to obtain a precursor powder; sintering of the precursor powder to obtain an active cathode material, the sintering being carried out in an inert gas environment and the total gas flow rate in the sintering process being 1100 m 3 / h-1400 m 3 / h; wherein the sintering comprises an elevated temperature interval and a constant temperature interval, wherein the inert gas flow rate v1 in the elevated temperature interval is higher than the inert gas flow rate v2 in the constant temperature interval; wherein the temperature of the constant temperature interval of the sintering ranges from 770°C to 830°C; wherein the active cathode material comprises lithium-containing transition metal phosphate particles, with at least a portion of its surface being coated with a carbon coating material.

[0229] In some embodiments, the temperature of the constant temperature sintering interval is optionally 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C or any value in a range between any two of these values.

[0230] High-temperature sintering facilitates the increase in the area fraction of particles with a particle size greater than or equal to 1 µm in the cathode film layer.

[0231] In some embodiments, the molar ratio of lithium and iron in the mixed raw material can optionally be 1.01, 1.02, 1.03, 1.04 or any value in a range between two of these values.

[0232] The molar ratio of lithium and iron in the mixed raw material is greater than 1, which helps to replenish lithium during the sintering process of the active cathode material, increase the crystallinity of the crystals, and improve the capacity of the active cathode material; however, the study has shown that an excessively high molar ratio of lithium and iron in the raw material can lead to incomplete chemical reactions in a local area during the sintering process of the active cathode material, thereby increasing the probability of the formation of the magnetic substance such as Fe2P.A molar ratio of lithium and iron in the mixed raw material within the above range helps to improve the pressing density of the electrode foil and the energy density of the lithium-ion secondary battery, while keeping the battery at a low self-discharge level, so that the energy density of the lithium-ion secondary battery can be maintained over a long period of time during the storage and cycling process of the battery.

[0233] In this application, the term “D” represents v 50" the corresponding particle size when the percentage of the cumulative particle size distribution of the sample particle size obtained by the Malvern laser scattering method reaches 50%.

[0234] In some embodiments, the volume-distributed solid-phase particle size D is v50 in the mixed slurry optionally 0.3 µm, 0.31 µm, 0.32 µm, 0.33 µm, 0.34 µm, 0.35 µm, 0.36 µm, 0.37 µm, 0.38 µm, 0.39 µm, 0.4 µm or any value in a range between two of these values.

[0235] The particle size of the solid phase in the mixed slurry after milling lies within the range mentioned above, indicating that the raw material has a small particle size, resulting in relatively high activity. This suggests that diffusion of the solid phase likely occurs during the high-temperature sintering process, leading to particle size of 1 µm or larger with a specific surface area fraction. Simultaneously, the solid phase particle size within this range in the mixed slurry after milling helps to reduce the likelihood of generating magnetic substances due to uneven chemical reactions in the local area caused by excessively high raw material activity.

[0236] In some embodiments, the inert gas comprises one or more of the gases nitrogen, neon, and helium.

[0237] In some embodiments, sintering is carried out in an inert gas environment and the total gas flow rate in the sintering process is 1100 m³ / h. 3 / h, 1200m 3 / h, 1300m 3 / h, 1350m 3 / h, 1400 m 3 / h or any value in a range between two of these values.

[0238] The total gas flow rate in the sintering process is within the above range, which helps to reduce the partial pressure of the reducing atmosphere and decrease the possibility of local reduction and increase of the magnetic substances.

[0239] During the heating process, the precursor raw materials undergo intensive chemical reactions with each other, and an increase in gas flow helps to mitigate the phenomena of overpressure in the local reduction atmosphere, uneven reaction, and high concentrations of magnetic substances. In the constant-temperature process, slow solid-phase diffusion occurs between the precursor raw materials to achieve particle growth, and maintaining a relatively low gas flow is beneficial for preserving the stability of the temperature field in the sintering process, thus ensuring uniform particle growth.

[0240] In some embodiments, v1:v2 is optionally 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1 or any value in a range between any two of these values.

[0241] The active cathode material produced by this process not only allows particles larger than 1 µm with a specific area fraction to exist in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, but also ensures that the active cathode material contains a small amount of magnetic substance, which improves the pressing density of the electrode foil, improves the energy density of the lithium-ion secondary battery and ensures that the battery has a low self-discharge level, so that the energy density of the lithium-ion secondary battery can be maintained over a long period during the storage and cycling process of the battery.

[0242] In some embodiments, the iron source is an iron-containing compound.

[0243] In some embodiments, the iron source comprises at least one of iron(III) hydroxide, iron(II) chloride, iron(III) trioxide, iron(III) phosphate, iron(III) pyrophosphate, iron(II) oxalate, iron powder, iron(III) nitrate, iron(III) tetroxide and iron(III) hydroxide.

[0244] In some embodiments, the phosphorus source is a phosphate compound.

[0245] In some embodiments, the phosphorus source comprises at least one of phosphoric acid, iron phosphate, diammonium phosphate and diammonium hydrogen phosphate.

[0246] In some embodiments, the iron source and the phosphorus source can be the same substance. In some embodiments, iron phosphate is used as the iron and phosphorus source.

[0247] In some embodiments, the lithium source comprises one or more of lithium carbonate, lithium dihydrogen phosphate, lithium oxalate, lithium oxide, lithium hydroxide, and lithium acetate.

[0248] In some embodiments, the lithium source comprises lithium carbonate.

[0249] In some embodiments, the carbon source comprises one or more of glucose, polyethylene glycol, citric acid, sucrose, starch, fructose, lactose, polyaniline, polyacrylonitrile and polyvinylpyrrolidone.

[0250] In some embodiments, the carbon source comprises glucose and polyethylene glycol.

[0251] 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.

[0252] In some embodiments, the volume distribution coefficient of the solid phase (D) is V90 - D V10 ) / Dv 50 in the mixed slurry 1.8-3.0.

[0253] In some embodiments, the volume distribution coefficient of the solid phase (D) is V90 - D V10 ) / D v 50 in the mixed slurry optionally 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 or any value in a range between any two of these values.

[0254] A volume distribution coefficient of the solid phase in the mixed slurry within the above range indicates a uniform particle size distribution of the raw material, which contributes to improving the homogeneity of the solid-phase reaction during the subsequent sintering and reduces the risk of locally reduced material concentration, increased reduction, and magnetic material aggregation due to uneven mixing of the raw material.

[0255] In some embodiments, the precursor powder has a volume-distributed particle size D v 50 of 5 µm-60 µm.

[0256] In some embodiments, the precursor powder is obtained by spray drying the mixed slurry.

[0257] In some embodiments, the sintering is a primary sintering process comprising at least two constant temperature intervals: a first constant temperature interval with a constant temperature of 400°C-500°C, and a first constant temperature interval with a constant temperature time of 3-8 hours; the primary sintering has a maximum constant temperature of 770°C-820°C and is processed at this maximum temperature for 8-15 hours.

[0258] In some embodiments, the maximum constant temperature of the primary sintering is optionally 770°C, 780°C, 790°C, 800°C, 810°C, 820°C or any value in a range between any two of these values.

[0259] In some embodiments, the processing time at constant temperature at maximum temperature is 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, or any value in a range between two of these values.

[0260] Sintering at a high temperature in the above temperature range helps to increase the particle size of the active cathode material, so that large particles of 1 µm or more can have a certain area fraction in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, thereby increasing the pressing density of the electrode foil and at the same time reducing the rise of the reducing atmosphere due to an excessively high sintering temperature and controlling the probability of generating a magnetic substance, such as Fe2P, from the reduction, in this way a balance is achieved between the energy density and the storage stability of the battery.

[0261] In some embodiments, the sintering consists of at least two sintering processes, wherein a primary sintered product is obtained after the first sintering process and the second sintering process takes place after grinding the primary sintered product.

[0262] In some embodiments, the first sintering takes place at a sintering temperature of 720°C-780°C and a sintering time of 6-12 hours.

[0263] In some embodiments, the first sintering takes place at a sintering temperature that is optionally 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C or any value in a range between two of these values.

[0264] In some embodiments, the sintering time of the first sintering is optionally 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value in a range between any two of these values.

[0265] In some embodiments, the second sintering takes place at a sintering temperature of 770°C-830°C and a sintering time of 6-12 hours.

[0266] In some embodiments, the second sintering takes place at a sintering temperature that is optionally 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C or any value in a range between any two of these values.

[0267] In some embodiments, the sintering time of the second sintering is optionally 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours or any value in a range between any two of these values.

[0268] In some embodiments, the second sintering after milling the primary sintered product comprises the following: separate milling after adding a carbon source to the primary sintered product, wherein D v 50 of a first group of ground particles is 1.40 µm-2.0 µm; where D v50 of a second group of ground particles 0.35 µm-0.45 µm; mixing the first group of ground particles with the second group of ground particles in a mass ratio of 30:70-70:30 to obtain mixed intermediate particles, the mixed intermediate particles being subjected to a second sintering.

[0269] In some embodiments, the second sintering after milling the primary sintered product comprises the following: separate milling after adding a carbon source to the primary sintered product, wherein D v 50 of a first group of ground particles optionally 1.4 µm, 1.45 µm, 1.5 µm, 1.55 µm, 1.6 µm, 1.65 µm, 1.7 µm, 1.75 µm, 1.8 µm, 1.9 µm, 2 µm or any value in a range between two of these values.

[0270] In some embodiments, the second sintering after milling the primary sintered product comprises the following: separate milling after adding a carbon source to the primary sintered product, wherein D v 50 of a second group of ground particles optionally 0.35 µm, 0.36 µm, 0.37 µm, 0.38 µm, 0.39 µm, 0.4 µm, 0.41 µm, 0.42 µm, 0.43 µm, 0.44 µm, 0.45 µm or any value in a range between two of these values.

[0271] In some embodiments, it is possible to mix the first group of ground particles with the second group of ground particles in a mass ratio of 30:70, 40:60, 50:50, 60:40, 70:30 to obtain mixed intermediate particles.

[0272] The two-sintering process can effectively shorten the sintering time in the high-temperature interval, thereby reducing the risk and probability of magnetic substance formation during high-temperature sintering. Furthermore, the particle activity can be controlled by adjusting the particle size of the two groups of milled products in the second sintering process, ensuring that the active cathode material simultaneously exhibits a specific area fraction of large particles. This increases the electrode foil density and improves the energy density of the lithium-ion secondary battery, while simultaneously resulting in a low self-discharge level. This allows the energy density of the lithium-ion secondary battery to be maintained for extended periods during storage and cycling.

[0273] Another unclaimed aspect of the present application provides a method for producing a cathode foil, wherein the production method comprises: dry mixing of a binder, a conductive agent and an active cathode material obtained by the method in the fourth aspect, adding a solvent, stirring to obtain a shipping slurry; transferring and applying the shipping slurry to at least one side of the collector, drying and hot pressing to obtain a cathode foil.

[0274] In some embodiments, the hot pressing comprises at least three hot rolling presses, wherein the hot rolling pressure increases sequentially and is successively 20-50 tonnes, 50-70 tonnes and 70-90 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, the temperature of the heating being 40°C-50°C.

[0275] The active cathode material, produced using the above hot pressing process in conjunction with the manufacturing process of the fourth aspect, effectively improves the pressing density of the electrode foil while maintaining a low content of magnetic substance, resulting in an improved energy density of the battery while maintaining a low self-discharge.

[0276] In some embodiments, the coating speed of the transfer coating is 1 m / min–25 m / min. In some embodiments, the coating speed of the transfer coating is optionally 1 m / min, 2 m / min, 3 m / min, 4 m / min, 5 m / min, 6 m / min, 7 m / min, 8 m / min, 9 m / min, 10 m / min, 11 m / min, 12 m / min, 13 m / min, 14 m / min, 15 m / min, 16 m / min, 17 m / min, 18 m / min, 19 m / min, 20 m / min, 21 m / min, 22 m / min, 23 m / min, 24 m / min, 25 m / min, or any value in a range between any two of these values.

[0277] The coating rate of the transfer coating is within the above range, which contributes to improving the uniformity of the particle distribution in the coating process, reducing the risk of particle agglomeration in the cathode film layer, reducing the porosity of the cut surface of the cathode film layer, further increasing the boundary pressure density of the electrode foil, and improving the energy density of the battery.

[0278] Furthermore, the present application provides a power-consuming device comprising at least one lithium-ion secondary battery, a battery module, a battery pack, and an energy storage battery provided by the present application. The lithium-ion secondary battery, the battery module, and the battery pack can be used as a power source for the power-consuming device or as an energy storage unit for the power-consuming device. The power-consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0279] Depending on requirements, a lithium-ion secondary battery, a battery module or a battery pack can be selected as the power-consuming device.

[0280] 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.

[0281] 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

[0282] 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 identification are all commercially available products. Exemplary embodiment 1(1) Production of the active cathode material

[0283] Lithium carbonate, iron phosphate, titanium dioxide, glucose, and polyethylene glycol are added to water and mixed in a premixing vessel at a speed of 1400 rpm and demagnetized by a demagnetizing rod with a magnetic field strength of 10000 Gs, wherein the ratio of lithium carbonate to iron phosphate is such that the molar ratio of lithium to iron is 1.03:1.0, wherein the mass content of glucose is 6% compared to the total amount of raw materials and the mass content of polyethylene glycol is 5% compared to the total amount of raw materials, and after homogeneous mixing, a mixed raw material with a solids content of 40% is obtained; The number of particles of the magnetic substance in the lithium carbonate is less than or equal to 500 pcs / kg, the particle size D V10 of the material is greater than or equal to 1 µm, the particle size D v 50 is 6 µm and the particle size D V90is less than or equal to 40 µm; and the number of particles of the magnetic substance in the iron phosphate is less than or equal to 95 pcs / kg and the morphology has an approximately spherical shape; the number of particles of the magnetic substance of glucose is less than or equal to 500 pcs / kg; the molecular weight of polyethylene glycol is 1500 and the number of particles of the magnetic substance is less than or equal to 150 pcs / kg.

[0284] The mixed raw materials undergo two grinding and demagnetization cycles in a sand mill. After one hour of coarse grinding, the coarsely ground raw materials are demagnetized using a permanent magnet separator with a demagnetization intensity greater than or equal to 8000 Gs. The demagnetized raw materials then undergo fine grinding. During the grinding process, the temperature of the slurry is controlled to less than 40°C to obtain a mixed slurry; the particle size of the solid phase D v D50 in the mixed slurry is 0.35 µm, and spray drying is carried out to obtain dry precursor powder. D50 after drying is 55.0 µm; the number of particles of the magnetic substance is less than or equal to 70 pcs / kg.

[0285] The precursor powder is subjected to two-stage heat sintering in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: heating at a rate of 2°C / min from 25°C to 450°C (the first heating segment) and holding for 3 hours; heating at a rate of 5°C / min from 450°C to 780°C (the second heating segment) and holding for 12 hours; wherein the gas flow rate of the heating segment is greater than that of the constant temperature segment, with a ratio of 1.5:1 and a total gas flow rate of 1350 cm³ / h. 3 / h, and wherein cooling takes place after heating; after air stream comminution, a carbon-coated lithium iron phosphate material with D v 50 of 1.0 µm-2.0 µm were obtained.

[0286] The above-mentioned D50, D v 50 and D V90 refer to the data obtained through the Malvern laser scattering test.

[0287] Based on the total mass of the active cathode material, the mass fraction of carbon is 1.25% and the mass fraction of titanium is 4000 ppm. Under a pressure of 3 T, the powder density of the active cathode material is 2.52 g / cm³. 3 , where the discharge gram capacity at room temperature is 141.4 mAh / g at a discharge rate of 1 C. The active cathode material is discharged to 3.2 V with a discharge capacity percentage η of 92.5%. (2) Production of the cathode foil

[0288] 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 distribution density of carbon-based particles with a particle size greater than 100 nm in the bottom coating is ≤10 pcs / 10 µm, and the thickness of the bottom coating is 2 µm. A cathode film layer with a one-sided areal density of 350 mg / 1540 cm² is obtained. 2 The coating is obtained after drying and hot pressing. The transfer speed of the coating is 20 m / min.

[0289] The hot pressing process comprises at least three hot rolling presses, wherein the hot rolling pressure increases sequentially and is successively 40 tonnes, 60 tonnes and 80 tonnes; and wherein the hot rolling temperature is 60°C, and wherein the electrode foil is heated before the first entry into the hot rolling press, the temperature of which is 40°C.

[0290] The electrode foil's compressive density, its limiting compressive density, and the test procedure for the limiting compressive density of the electrode foil are described below; the limiting compressive density of the electrode foil in this embodiment is 2.63 g / cm³. 3 .

[0291] In a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30%, wherein in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the fraction of the average equivalent area of ​​particles with a particle size greater than 1 µm is 0.127%, and wherein in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 6.34%, and wherein the mass fraction of the magnetic substance in the cathode film layer is 20 ppm, and wherein the mass fraction of elemental iron is 0 (lower than the lower detection limit and is recorded as 0).In the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, the median C is. 50 of the graphitization degree 1.00, the median LA50 of the sphericity of the particles in the cathode film layer 0.715 and the porosity of the cross-sectional area of ​​the cathode film layer 15.991%. (3) Production of the anode foil:

[0292] 95.5 wt% of the negative active material (artificial graphite), 1.0 wt% of the conductive agent (conductive carbon black), 2.0 wt% of the binder (styrene-butadiene rubber (SBR)), and 1.5 wt% of the thickener (sodium carboxymethylcellulose (CMC)) are mixed, augmented with deionized water, stirred, and dispersed to produce an anode slurry. The anode slurry is then applied to both surfaces of the copper foil, and after both sides are coated, the anode foil is produced by drying, compacting, cutting, and stacking. The density of the coated single-sided surface is 164 mg / 1540.25 mm². 2 and the density is 1.60 g / cm³ 3 . (4) Production of the release film

[0293] Polypropylene film is used as a separating film. (5) Preparation of the electrolyte solution:

[0294] In a glove box with an argon atmosphere (H2O<0.1ppm, O2<0.1ppm), the organic solvent ethylene carbonate (EC) / dimethyl carbonate (DMC) is homogeneously mixed in a volume ratio of 1:1, and the lithium salt LiPF6 is added to dissolve it in the organic solvent, and the content of LiPF6 in the solution is 1 mol / L, and it is stirred homogeneously to obtain the electrolyte solution. (6) Battery manufacturing:

[0295] 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 secondary battery is finally obtained. Example 2

[0296] The manufacturing process of embodiment 2 is essentially the same as that of embodiment 1, and the difference lies in the sintering process of the active cathode material, namely:

[0297] The precursor powder is subjected to two-stage heat sintering in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: heating at a rate of 2°C / min from 25°C to 450°C (the first heating segment) and holding for 3 hours; heating at a rate of 5°C / min from 450°C to 800°C (the second heating segment) and holding for 12 hours; wherein the gas flow rate of the heating segment is greater than that of the constant temperature segment, with a ratio of 1.5:1 and a total gas flow rate of 1350 cm³ / h. 3 / h, and wherein cooling takes place after heating; after air stream comminution, a carbon-coated lithium iron phosphate material with D v 50 of 1.0 µm-2.0 µm were obtained. Example 3

[0298] The manufacturing process of embodiment 3 is essentially the same as that of embodiment 1, and the difference lies in the sintering process of the active cathode material, namely:

[0299] The precursor powder is subjected to two-stage heat sintering in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: heating at a rate of 2°C / min from 25°C to 450°C (the first heating segment) and holding for 3 hours; heating at a rate of 5°C / min from 450°C to 820°C (the second heating segment) and holding for 12 hours; wherein the gas flow rate of the heating segment is greater than that of the constant temperature segment, with a ratio of 1.5:1 and a total gas flow rate of 1350 cm³ / h. 3 / h, and wherein cooling takes place after heating; after air stream comminution, a carbon-coated lithium iron phosphate material with D v 50 of 1.0 µm-2.0 µm were obtained. Example 4

[0300] The manufacturing process of embodiment 4 is essentially the same as that of embodiment 1, and the difference lies in the fact that the amount of titanium source added is adjusted in the manufacturing process of the active cathode material, so that the mass content of titanium is 2500 ppm relative to the mass of the active cathode material. Example 5

[0301] The manufacturing process of embodiment 5 is essentially the same as that of embodiment 1, and the difference lies in the fact that the amount of titanium source added is adjusted in the manufacturing process of the active cathode material, so that the mass content of titanium is 1500 ppm relative to the mass of the active cathode material. Example 6

[0302] The manufacturing process of embodiment 6 is essentially the same as that of embodiment 1, and the difference lies in the sintering process of the active cathode material, and the difference includes in particular the following two points: (2) The carbon source in the mixed raw material is only glucose, and the mass of glucose is 5.7 wt% compared to the mass of iron phosphate; (3) The heating and sintering process differs. The precursor powder is sintered at least twice in a nitrogen atmosphere, with the first sintering temperature being 750°C and the holding time being 8 hours, in order to obtain the primary sintered product.

[0303] To the primary sintered product, 1.5 wt% (based on the mass of the primary sintered product) of glucose, 3.0 wt% (based on the mass of the primary sintered product) of polyethylene glycol, and a titanium source are added, and the mixture is milled homogeneously and divided into two groups for the second milling. The milling parameters of the two groups are different, and D v 50 of the ground particles of the first group are ground to 2.0 µm and D v 50% of the ground particles from the second group are adjusted to 0.35 µm. The ground particles from the first and second groups are mixed in a mass ratio of 30:70 and spray-dried for the second sintering. The second sintering temperature is 800°C and the holding time is 10 hours.

[0304] The ratio of titanium in the titanium source in the mixed raw material to the titanium in the titanium source added to the primary sintered product is 5:2, with the mass fraction of titanium being 6000 ppm based on the total mass of the active cathode material. Example 7

[0305] The manufacturing process of embodiment 7 is essentially the same as that of embodiment 6, and the difference lies in the fact that that D v 50 of the ground particles of the first group 1.5 µm and D v 50% of the ground particles of the second group have a particle size of 0.40 µm. The ground particles of the first and second groups are mixed in a mass ratio of 70:30 and spray-dried for the second sintering. Comparative example 1

[0306] The manufacturing process of comparative example 1 is essentially the same as that of embodiment 1, and the difference lies in the fact that the following processes differ in the manufacturing process of the active cathode material:

[0307] The mixed raw materials undergo two grinding and demagnetization cycles in a sand mill. After one hour of coarse grinding, the coarsely ground raw materials are demagnetized using a permanent magnet separator with a demagnetization intensity greater than or equal to 8000 Gs. The demagnetized raw materials then undergo fine grinding. During the grinding process, the temperature of the slurry is controlled to less than 40°C to obtain a mixed slurry; the particle size of the solid phase D v The particle size in the mixed slurry is 0.5 µm, and spray drying is carried out to obtain dry precursor powder.

[0308] The precursor powder is subjected to two-stage temperature sintering in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: heating at a rate of 2°C / min from 25°C to 450°C (the first heating segment) and holding for 3 hours; heating at a rate of 5°C / min from 450°C to 765°C (the second heating segment) and holding for 12 hours; wherein the gas flow rate of the heating segment is greater than that of the constant temperature segment, and wherein the ratio is 1:1 and the total gas flow rate is 1350 cm³. 3 / h, and wherein cooling takes place after heating; after air stream comminution, a carbon-coated lithium iron phosphate material with D v 50 of 1.0 µm-2.0 µm were obtained. Comparative example 2

[0309] The manufacturing process of comparative example 2 is essentially the same as that of embodiment 1, and the difference lies in the fact that the following processes differ in the manufacturing process of the active cathode material:

[0310] Lithium carbonate, iron phosphate, titanium dioxide, glucose, and polyethylene glycol are added to water and mixed in a premixing vessel at a speed of 1400 rpm and demagnetized by a demagnetizing rod with a magnetic field strength of 8000 Gs-12000 Gs, wherein the ratio of lithium carbonate to iron phosphate is such that the molar ratio of lithium to iron is 1.05:1.0, wherein the mass content of glucose is 6% compared to the total amount of raw materials and the mass content of polyethylene glycol is 5% compared to the total amount of raw materials, and after homogeneous mixing, a mixed raw material with a solids content of 40% is obtained;

[0311] The mixed raw materials undergo two grinding and demagnetization cycles in a sand mill. After one hour of coarse grinding, the coarsely ground raw materials are demagnetized using a permanent magnet separator with a demagnetization intensity greater than or equal to 8000 Gs. The demagnetized raw materials then undergo fine grinding. During the grinding process, the temperature of the slurry is controlled to less than 40°C to obtain a mixed slurry; the particle size of the solid phase D v D50 in the mixed slurry is 0.35 µm, and spray drying is carried out to obtain dry precursor powder. D50 after drying is 50-60 µm; the number of particles of the magnetic substance is less than or equal to 70 pcs / kg.

[0312] The precursor powder is subjected to two-stage temperature sintering in a nitrogen atmosphere to obtain lithium iron phosphate cathode material: heating at a rate of 2°C / min from 25°C to 450°C (the first heating segment) and holding for 3 hours; heating at a rate of 5°C / min from 450°C to 820°C (the second heating segment) and holding for 12 hours; wherein the ratio of the gas flow volume of the heating segment to that of the constant temperature segment is 1:1, and wherein the total gas flow is 900 cm³ 3 / h, and wherein cooling takes place after heating; after air stream comminution, a carbon-coated lithium iron phosphate material with D v 50 of 1.0 µm-2.0 µm were obtained. Performance test 1. Self-discharge K-value test

[0313] Charging at 25°C with a constant current of 0.05 C to 3.0 V and then charging at a constant voltage to a current of 0.05 C, and testing the open-circuit voltage V1 in V after storage for 24 hours at 25°C, and retesting the open-circuit voltage V2 in V after further storage for 24 hours, and the self-discharge K-value is 1000×(V1-V2) / 48 in mV / h. 2. DCR test

[0314] Charge at 25°C to 3.65V with a constant current of 0.33C, then charge with a constant voltage to a current of 0.05C, then discharge to 20% SOC at 0.33C, store for 5 min, then pulse discharge at 3C for 30 s, store for 40 s, then charge at 3C for 40 s, store for 5 min, then charge to 3.65V with a constant current of 0.33C and charge at a constant voltage to 0.05C, then discharge at 0.33C to 10% SOC, store for 5 min, then pulse discharge at 3C for 30 s, store for 40 s, then charge at 3C for 40 s, store for 5 min, then full charge at 0.33C, then discharge at 0.33C to 50% SOC, then store at -25°C for 2 hours and pulse discharge at 1C for 30 s, store for 10 min, then store at 25°C for 2 hours, charge to 3.65 V with a constant current of 0.33 C, then charge with a constant voltage to 0.05 C, then discharge at 0.33 C to 20% SOC, then store at -25°C for 2 hours and pulse discharge at 1C for 30 s, store for 10 min.

[0315] 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) / pulse current. 3. Test of the electrode foil's limiting compressive strength

[0316] After double-sided coating, the electrode foil is compacted using a roller press to test its elongation and evaluate its flexibility. Increasing the roller press pressure produces electrode foils with varying densities. As the pressure increases, the electrode foil's density increases, its ductility increases, and its flexibility decreases. Excessive ductility is likely to cause warping, while insufficient flexibility is likely to lead to brittle fracture. Therefore, the lower of the two densities, defined as the limiting density, is determined when the electrode foil's ductility reaches 8% or the number of times it can be flexibly folded (3).

[0317] The compression density is calculated from the mass of the cathode film layer / volume of the cathode film layer. 4. Ductility test

[0318] Laying the electrode foil on a horizontal table, cutting the electrode foil into sections, each strip being approximately 100 cm long; removing the copper foil of the substrate at the edge of the electrode foil, taking care to keep the cut edge of the electrode foil parallel to the MD direction of the electrode foil (perpendicular to the direction of the pressure roller) to ensure that the electrode foil is completely covered by the coating; using a steel ruler to measure the lengths between the marking points at the head and tail of the electrode foil and the positions of equal width in the longitudinal direction, estimating the length to the nearest 0.1 mm, and recording the length before compaction;and wherein, after compaction, the length between the corresponding marker points is recorded, and wherein (length after compaction - length before compaction) / length before compaction is used as the ductility.; 5. Testing the number of times flexible folding can be performed

[0319] Cutting the cathode foil into a test sample measuring 20×100 mm 2Fold this in the middle in the forward direction, flatten it with a 2kg pressure roller, and unfold it against the light to check if the gap is translucent. If no translucency occurs, fold it in the opposite direction and flatten it with a 2kg pressure roller, and check it against the light again. This process is repeated until the gap is translucent, and the number of folds is recorded. Repeat the test three times and take the average value as reference data for the flexibility of the electrode foil. Test result

[0320] *0 in the examples means that the lower detection limit is not exceeded, which makes an accurate determination of the quantity difficult.

[0321] By comparing the exemplary embodiments and the comparative examples, it is evident that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1 µm is 30%-50%; wherein the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm, which contributes to the lithium-ion secondary battery achieving a high electrode foil density, while the battery has a low self-discharge K-value, enabling the battery to have both a high energy density and good storage performance.

[0322] If, in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30%-45%, the lithium-ion secondary battery achieves a high pressing density of the electrode foil, while at the same time the battery can exhibit a low self-discharge K-value based on good kinetic performance and high capacity.

[0323] If the mass fraction of titanium is 2500 ppm–8000 ppm relative to the total mass of the active cathode material, the activity of the raw material can be reduced by the surface inertness of the titanium source, thereby reducing the probability of an uneven local chemical reaction and the generation of a high content of magnetic substances, while at the same time it is beneficial to control the proportion of the average equivalent area of ​​the particles of 1 µm or more in order to achieve a balance between the storage stability and the kinetic performance of the lithium-ion secondary battery.

[0324] By comparing embodiments 1, 2, 6, 7 and the other embodiments, it is evident that when the mass fraction of the magnetic substance in the cathode film layer is 20-200 ppm, it contributes to maintaining a high density of the electrode foil of the lithium-ion secondary battery, while the battery can have a low self-discharge K-value, and the lithium-ion secondary battery further improves the kinetic performance while achieving a balance between high energy density and good storage performance.

[0325] 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 20123-2006

[0125]

Claims

[1] Lithium-ion secondary battery, characterized by that it comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode collector and a cathode film layer arranged on at least one side of the cathode collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises lithium-containing transition metal phosphate particles, wherein at least a part of the surface thereof is provided with a carbon coating material, wherein in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1 µm is 30.0%-50.0%; where the mass fraction of the magnetic substance in the cathode film layer is greater than or equal to 20 ppm and less than or equal to 1980 ppm. [2] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30.00%-50.00%. [3] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 1 µm-5 µm is 30.00%-45.00%. [4] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the proportion of the average equivalent area of ​​particles with a particle size greater than 1 µm is 0.05%-0.20%. [5] Lithium-ion secondary battery according to claim 1, characterized by, that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 3.0%-15.0%. [6] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 5.0%-12.0%. [7] Lithium-ion secondary battery according to claim 1, characterized by , that in a cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a particle size of 50 nm-200 nm is 5.0%-10.0%. [8] Lithium-ion secondary battery according to claim 1, characterized by that the mass fraction of the magnetic substance in the cathode film layer is less than or equal to 300 ppm. [9] Lithium-ion secondary battery according to claim 8, characterized by, that the mass fraction of the magnetic substance in the cathode film layer is 20 ppm-200 ppm. [10] Lithium-ion secondary battery according to claim 1, characterized by , that the magnetic substance comprises one or more of Fe, Fe2P, FeP, γ-Fe2O3, Fe2P2O7. [11] Lithium-ion secondary battery according to claim 1, characterized by , that the mass content of elemental iron in the cathode film layer is less than 20 ppm. [12] Lithium-ion secondary battery according to claim 11, characterized by that the mass content of elemental iron in the cathode film layer is less than or equal to 15 ppm. [13] Lithium-ion secondary battery according to claim 1, characterized by , that the lithium-containing transition metal phosphate includes a component with the following general formula: Li m Fe x P y O j Q q , where Q comprises one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, and where 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, 0 <q≤0,1 ist. [14] Lithium-ion secondary battery according to claim 1, characterized by , that the active cathode material comprises titanium, wherein the mass content of titanium is 1500 ppm-8000 ppm relative to the total mass of the active cathode material. [15] Lithium-ion secondary battery according to claim 14, characterized by , that the active cathode material comprises titanium, wherein the mass content of titanium is 2500 ppm-8000 ppm relative to the total mass of the active cathode material. [16] Lithium-ion secondary battery according to claim 14, characterized by , that the active cathode material comprises titanium, wherein the mass content of titanium is 2500 ppm-6000 ppm relative to the total mass of the active cathode material. [17] Lithium-ion secondary battery according to claim 1, characterized by, that, based on the total mass of the active cathode material, the mass fraction of carbon is 0.9%-1.8%. [18] Lithium-ion secondary battery according to claim 1, 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 greater than or equal to 0.9 and less than or equal to 1.3, where the graphitization C value I G / I D is, where I G for the intensity of the G-peak of the Raman spectrum at 1580±100 cm -1 and I D for the intensity of the D-peak of the Raman spectrum at 1350±100 cm -1 stands. [19] Lithium-ion secondary battery according to claim 18, characterized by that the median C 50The graphitization degree in the cumulative distribution curve for the graphitization C value of the cathode film layer, obtained in the area scanning mode of the laser microconfocal Raman spectrometer, is 0.99-1.

2. [20] Lithium-ion secondary battery according to claim 1, 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 0.60-0.

85. [21] Lithium-ion secondary battery according to claim 20, 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.

80. [22] Lithium-ion secondary battery according to claim 1, characterized by, that under a pressure of 3 T the powder density of the active cathode material is 2.48 g / cm³ 3 -2.76 g / cm² 3 amounts. [23] Lithium-ion secondary battery according to claim 22, characterized by , that under a pressure of 3 T the powder density of the active cathode material is 2.58 g / cm³ 3 -2.76 g / cm² 3 amounts. [24] Lithium-ion secondary battery according to claim 1, characterized by , that the active cathode material has a discharge gram capacity of 135 mAh / g-150 mAh / g at room temperature at a discharge rate of 1 C. [25] Lithium-ion secondary battery according to claim 1, characterized by, that the active cathode material is discharged to 3.2 V with a discharge capacity percentage η ≥ 85%, where η is defined such that a button battery comprising the active cathode material is charged and discharged twice in a voltage range of 2.0 V to 3.75 V at a C-rate of 0.1 C at a constant current and subsequently charged and discharged once at a C-rate of 1 C at a constant current, wherein the capacity value extracted in the charge and discharge test at a C-rate of 1 C at a discharge voltage of 3.2 V is recorded as C1, and wherein the capacity value extracted at a discharge voltage of 2.0 V is C2, and wherein n=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. [26] Lithium-ion secondary battery according to claim 1, characterized by, that the cathode film layer further comprises a binder and a conductive agent, wherein, based on the total mass of the cathode film layer, the mass content of the active cathode material is 94%-99.4%, the mass content of the binder is 0.5%-3% and the mass content of the conductive agent is 0.1%-3%. [27] Lithium-ion secondary battery according to claim 1, characterized by , that the one-sided areal density of the cathode film layer is 300 mg / 1540 mm² 2 -450 mg / 1540 mm 2 amounts. [28] Lithium-ion secondary battery according to claim 1, characterized by , that in the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.43 g / cm³ 3 -2.78 g / cm² 3 amounts. [29] Lithium-ion secondary battery according to claim 1, characterized by , that in the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.50 g / cm³ 3 -2.75 g / cm² 3 amounts. [30] Lithium-ion secondary battery according to claim 1, characterized by that the cathode film layer meets at least one of the following conditions: (1) In the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.43 g / cm³. 3 -2.78 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%-28%; (2) In the fully discharged state of the lithium-ion secondary battery, the density of the cathode film layer is 2.50 g / cm³. 3 -2.78 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%. [31] Lithium-ion secondary battery according to claim 1, characterized bythat the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the collector; and wherein the lower coating satisfies at least one of the following conditions: (1) the lower coating comprises carbon-based particles, wherein the distribution density of the carbon-based particles with a particle size of more than 100 nm in the lower coating is ≤ 10 pcs / 10 µm; (2) the density of the cathode foil in a fully discharged state is greater than or equal to 2.4 g / cm³ 3 , and the one-sided thickness of the lower coating is 1 µm-4 µm; (3) the density of the cathode foil in a fully discharged state is greater than or equal to 2.5 g / cm³ 3 , and the one-sided thickness of the lower coating is 2 µm-4 µm. [32] Battery device, characterized by, that it comprises a lithium-ion secondary battery according to one of claims 1 to 31, wherein the battery device comprises at least one of a battery module, a battery pack and an energy storage battery. [33] Power-consuming device, characterized by , that it comprises a lithium-ion secondary battery according to any one of claims 1 to 31.

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