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

Abstract

Lithium-ion secondary battery, characterized in that the lithium-ion secondary battery comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode current collector and a cathode film layer arranged on at least one side of the cathode current collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises particles of lithium-containing transition metal phosphate which are coated on at least part of their surface with a carbon coating material, wherein in the 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 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%; where in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C 50 greater than or equal to 0.95 and less than or equal to 1.20, where the degree of graphitization is the C-value. G / I D is, where I G a G-peak intensity of the Raman spectrum at 1580±100cm -1 and I D a D peak intensity of the Raman spectrum at 1350±100cm -1 represents.

Description

TECHNICAL AREA

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

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

[0003] Active cathode material is a crucial component of lithium-ion secondary batteries. Lithium transition metal phosphate (LTP) materials are characterized by their stable structure, good safety, and long lifespan, offering broad development potential. As market demands for the energy density and kinetics of secondary batteries in LTP systems increase, achieving simultaneous improvements in these performance characteristics with existing technology is challenging. This has become a technical problem that urgently needs to be addressed in this field. REVELATION OF THE INVENTION

[0004] The present application was filed with regard to the problems mentioned above, and one objective of the present application is to provide a lithium-ion secondary battery that has both high energy density and good dynamic performance.

[0005] The first aspect of the present application provides a lithium-ion secondary battery comprising a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode current collector and a cathode film layer arranged on at least one side of the cathode current collector, wherein the cathode film layer comprises an active cathode material, the active cathode material comprising particles of lithium-containing transition metal phosphate provided on at least a part of their surface with a carbon coating material, wherein 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 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%;where in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C; 50 greater than or equal to 0.95 and less than or equal to 1.20, where the degree of graphitization is the C-value. G / I D is, where I G the G-peak intensity of the Raman spectrum at 1580±100cm -1 and I D the D peak intensity of the Raman spectrum at 1350±100cm -1 represents.

[0006] By controlling the area fraction of particles with a particle size greater than or equal to 1.5 µm in the cathode film layer to greater than or equal to 8.0% and less than or equal to 20.0%, the significant effect of the weak point caused by large particles can be reduced. This has a positive effect on the battery impedance at a low level and improves the battery's dynamic performance. However, this limits the further increase in the electrode film's packing density. The embodiments of the present application further improve the degree of graphitization of the particles in the cathode film layer and the crystallinity of the particles' surface carbon layer by increasing the median C 50The degree of graphitization is controlled to be greater than or equal to 0.95 and less than or equal to 1.20, which facilitates particle sliding in the active cathode material during the roller press film formation process. The particles' easy sliding ability can further increase the compression density of the cathode film layer, thus achieving a balance between kinetic battery performance and energy density.

[0007] In any embodiment, the median of the graphitization degree C in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer is 50 0.97 to 1.13, optionally 1.0 to 1.10.

[0008] The median C 50Increasing the graphitization level of the cathode film layer within the aforementioned range further improves particle sliding, thus compensating for the insufficient gradation caused by the low number of large particles in the cathode film layer. While maintaining the battery's high dynamic performance, the electrode foil density is further improved to achieve a balance between dynamic battery performance and energy density.

[0009] In any embodiment, the concentration of the C-value (C) is determined in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer. 90 -C 10 ) / C 50 0.01 to 0.04.

[0010] The concentration of the C value of the cathode film layer is 0.01-0.04, indicating that the graphitization degree of the surface-coated carbon of the active cathode material is relatively uniform. This means that the active cathode material exhibits good coating uniformity and consistency, thereby reducing the hindrance of sliding caused by the inconsistent graphitization degree of the particles in the active cathode material and the resulting local stress concentration. This uniform sliding between the particles of the active cathode material allows for a higher overall compaction of the electrode foil at relatively low rolling pressure, further improving the pressing density of the electrode foil and the energy density of the battery while maintaining good kinetic battery performance.

[0011] In any embodiment, the concentration of the C-value (C) is determined in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer. 90 -C 10 ) / C 50 0.02 to 0.04.

[0012] The concentration of the C value (C 90 -C 10 ) / C 50 Within the above range, it is advantageous to further improve the consistency of the graphitization degree of the carbon on the surface of the active cathode material and to improve the sliding degree between the particles, further improving the pressing density of the electrode foil and the energy density of the battery while maintaining good kinetic battery performance.

[0013] In any embodiment, the cumulative distribution curve of the graphitization degree C value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, contains the C 90 Degree of graphitization 1.00 to 1.30, optionally 1.02 to 1.15.

[0014] The degree of graphitization C 90 lies within the aforementioned range and thus close to the median graphitization degree C 50 , which indicates that the distribution range of the graphitization degree of the cathode film layer is narrow, which contributes to a uniform sliding between the particles and thus improves the compression density of the cathode foil.

[0015] In any embodiment, the cumulative distribution curve of the graphitization degree C value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, contains the C 10Degree of graphitization 0.92 to 1.10, optionally 0.98 to 1.08.

[0016] The degree of graphitization C 10 within the above area indicates that various locations in the cathode film layer have a high degree of graphitization, which has a positive effect on the uniform sliding of the particles, reduces the probability of a local stress concentration and further improves the pressing density of the electrode foil.

[0017] In any embodiment, the area fraction of particles with a particle size of 1.5 µm to 5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 9.0% to 20.0%.

[0018] In the 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 1.5 µm-5 µm lies within the aforementioned range, which further reduces the hindrance of wetting and diffusion of the electrolyte solution in the cathode film layer by large particles on the surface of the electrode foil, which improves the consistency of the diffusion rate of lithium ions in the particles of the active cathode material, reduces local polarization and improves the kinetic performance of the battery.

[0019] In any embodiment, the area fraction of particles with a particle size of 1.5 µm to 5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10.0% to 20.0%.

[0020] In the course of improving the particle size distribution and increasing the size or proportion of large particles, the introduction of particles with a size of 1.5 µm to 5 µm is unavoidable. The surface area of ​​particles with a size of 1.5 µm–5 µm lies within the aforementioned range, which has a positive effect on the density of the electrode foil and simultaneously takes into account the dynamic performance of the battery.

[0021] In any embodiment, the area fraction of particles with a particle size greater than or equal to 5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 0.

[0022] Studies have shown that particles with a particle size of 5 µm or greater in the cathode film layer significantly impair the wetting of the electrolyte solution into the cathode film layer and the diffusion into the particles of the active material, and the area fraction of particles with a diameter of at least 5 µm is 0, which further reduces the internal resistance of the battery and improves the kinetic performance of the battery.

[0023] In any embodiment, the area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 15.0% - 25.0%, optionally 16.0%-24% and further optionally 16%-20%.

[0024] In the 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 and less than 1.5 µm lies within the above-mentioned range, which has a positive effect on the further improvement of the pressing density of the electrode foil and the improvement of the energy density of the battery while maintaining good battery dynamics.

[0025] In any embodiment, the median of the sphericity L in the cumulative distribution curve of the area of ​​the particle sphericity obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is A50 0.60 to 0.85, optionally 0.65 to 0.80.

[0026] Particles with a median sphericity L A50Within the aforementioned area, they are approximately spherical and tend to slip between the particles when subjected to external forces, which can further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0027] In any embodiment, the median roughness R in the cumulative distribution curve of the particle roughness area obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is R A50 0.92 to 0.96.

[0028] The surface of particles with a median roughness R A50 Within the aforementioned area, the surface is relatively smooth, the friction between the particles is relatively low, and they slip easily under the influence of external forces, which further improves the pressing density of the electrode foil and increases the energy density of the battery.

[0029] In any embodiment, the iron dissolution rate of the cathode film layer is 500 ppm-2000 ppm and can optionally be 500 ppm-1500 ppm.

[0030] The active cathode material, with an iron dissolution rate within the aforementioned range, exhibits a relatively complete and dense carbon coating layer. This layer improves electrical contact between the active cathode materials, enhances their conductivity, reduces their polarization, and further optimizes the kinetic performance of the lithium-ion secondary battery. Simultaneously, the densely coated carbon layer displays a low occupancy rate, and the gaps between the particles are slightly compressed by tension during the rolling process. This can increase both the electrode foil's compaction density and the battery's energy density.

[0031] In any embodiment, the mass content of the carbon element, based on the total mass of the active cathode material, is 0.8% - 1.8% and optionally 0.90% - 1.5%.

[0032] Compared to the active cathode material made of lithium-containing transition metal phosphate in the prior art, the active cathode material has a relatively low carbon coating content, which further increases the charge of the lithium-containing transition metal phosphate in the cathode foil and improves the energy density of the lithium-ion secondary battery.

[0033] In any embodiment, the concentration of lithium iron antisite defects in the active cathode material is 0.1%–1.5%, optionally 0.3%–1.0%.

[0034] The active cathode material in the embodiment of the present application has few lithium iron antisite defects, which has a positive effect on the uniform transfer of lithium ions in the solid phase and further improves the kinetic performance of the lithium-ion secondary battery.

[0035] In any 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, where 0.8 ≤ m ≤ 1.15, 0.9 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 < q < 0.1.

[0036] By selecting a suitable modifying element Q, the ion diffusion path of the active cathode material can be improved, the lithium ion diffusion rate of the active cathode material can be improved, and the kinetic performance of the battery can be improved.

[0037] In any embodiment, the active cathode material comprises one or more lithium iron phosphate and its doped modified material and encapsulating modified material.

[0038] In any embodiment, the active cathode material comprises a titanium element, wherein the mass content of the titanium element is 2000 ppm to 6000 ppm based on the total mass of the active cathode material.

[0039] The active cathode material in the embodiment of the present application has a high titanium content, and surprisingly, the high titanium content does not form a harmful impurity phase that negatively affects the energy density and kinetic performance of the battery. Although the reason for this is not yet clear, it is speculated that the titanium element, phosphate, and other elements (such as the lithium element) together form a fast ion conductor, which in turn improves the kinetic performance of the battery.

[0040] In any embodiment, the powder bulk density in the active cathode material is 0.70 g / cm³. 3 -1.50 g / cm² 3 and can optionally be 0.70 g / cm² 3 -1.20 g / cm² 3 be.

[0041] The active cathode material in the embodiment of the present application has a limited effective gradation that forms spontaneously and a relatively low bulk density. However, due to the high degree of graphitization of the cathode film layer, it can easily slip under the influence of external forces, thereby increasing the compaction density.

[0042] In any embodiment, the powder density of the active cathode material at a pressure of 3 T is 2.50 g / cm³. 3 -2.70 g / cm² 3 and can be 2.52 g / cm² 3 -2.68 g / cm² 3 be.

[0043] Although the area fraction of particles with a particle size greater than or equal to 1.5 µm in the active cathode material is small, the active cathode material can still achieve a high density under external forces due to the high degree of graphitization, thus providing a material basis for improving the density of the electrode foil and for the production of lithium-ion secondary batteries with high energy density.

[0044] In any embodiment, the specific powder resistance of the active cathode material under a pressure of 8 MPa is 0.5 Ω·cm-30.0 Ω·cm and can be 2 Ω·cm-20.0 Ω·cm.

[0045] The active cathode material has a high degree of graphitization, so that the sp 2The structure of the surface carbon facilitates the rapid conduction of electrons between the particles, so that the active cathode material has a low specific powder resistance, which has a positive effect on increasing the solid-phase transfer rate of electrons and further improves the kinetic performance of the battery.

[0046] In any embodiment, the specific discharge capacity of the active cathode material at room temperature and a discharge rate of 1C is 135 mAh / g to 150 mAh / g.

[0047] The active cathode material exhibits a high specific discharge capacity at a 1C rate, indicating that it has good charging and discharging capabilities and positively impacts the improvement of the battery's kinetic performance.

[0048] In any embodiment, the proportion of the discharge capacity of the active cathode material during a discharge to 3.2 V is η≥85%, where η is defined as follows: at room temperature, a button battery containing the active cathode material is charged and discharged twice at a rate of 0.1 C by constant current in the voltage range of 2.0 V to 3.75 V, and then once at a rate of 1 C by constant current, wherein, during a charge and discharge test at a rate of 1 C, the capacity value extracted at 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 recorded as C2, where η=C1 / C2, wherein the charging process includes charging at a constant voltage of 3.75 V, where the reverse current at the constant voltage is 50 µA.

[0049] The high proportion of the discharge capacity of the active cathode material used in the lithium-ion secondary battery of the embodiment of the present application when discharged to 3.2 V indicates that the active cathode material exhibits good kinetic performance. Simultaneously, a high η value indicates that the lithium-ion secondary battery containing the active cathode material still maintains a high voltage when discharged to a low state of charge (SOC), which is conducive to maintaining good performance.

[0050] In any embodiment, the discharge curve of the button battery containing the active cathode material includes a discharge platform in the voltage range of 2.5 V to 2.9 V at 0.1 C.

[0051] The button battery, which contains the active cathode material in the embodiments of the present application, has a new charging and discharging platform in the voltage range of 2.5 V to 2.9 V, which has a positive effect on the discharge range of the battery and the improvement of the energy density of the battery.

[0052] In any embodiment, the mass content of the conductive medium is 0 to 1.5%, optionally 0, relative to the total mass of the cathode film layer.

[0053] The carbon layer of the active cathode material has a high degree of graphitization, which gives the active cathode material good conductivity for electrons, reduces or even eliminates the need for conductive media in the cathode film layer, and further increases the charge capacity of the active cathode material and improves the energy density of the lithium-ion secondary battery.

[0054] In any embodiment, the cathode film layer further comprises a binder, and the mass fraction of the active cathode material is 95.5% to 99.5% based on the total mass of the cathode film layer, or alternatively 96.5% to 99.5%; wherein the mass fraction of the binder is 0.5% to 3%.

[0055] In any embodiment, the one-sided areal density of the cathode film layer is 300 mg / 1540 mm². 2 up to 450 mg / 1540 mm 2 .

[0056] A cathode film layer with an areal density within the aforementioned range can help to improve the energy density of lithium-ion secondary batteries.

[0057] In any embodiment, the density of the cathode film layer is 2.51 g / cm³. 3 up to 2.73 g / cm³ 3 , when the lithium-ion secondary battery is in a completely discharged state.

[0058] In any embodiment, the density of the cathode film layer is 2.55 g / cm³. 3 up to 2.70g / cm² 3 , when the lithium-ion secondary battery is in a completely discharged state.

[0059] The pressure density of the cathode film layer is within the range mentioned above, which has a positive effect on improving the energy density of the lithium-ion secondary battery.

[0060] In any embodiment, the density of the cathode film layer is 2.51 g / cm³. 3 up to 2.73 g / cm³ 3 , when the lithium-ion secondary battery is in a fully discharged state, wherein the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10% to 22%.

[0061] In any embodiment, the density of the cathode film layer is 2.55 g / cm³. 3 up to 2.70g / cm²3 , when the lithium-ion secondary battery is in a fully discharged state, wherein the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10% to 20%.

[0062] Lower porosity in the cross-sectional area of ​​the cathode film layer in the embodiment of the present application means, on the one hand, that the gradation of large, medium, and small particles in the cathode film layer is better and the pressing density is higher. On the other hand, if low porosity is present after the same gradation and the same roller pressure, this means that the particles can slide easily against each other, thereby reducing the risk of overpressure and stress concentration in the film layer and further reducing the probability of cathode film demolding during long cycles, which has a positive effect on improving the long-cycle performance of the battery.

[0063] In any embodiment, the cathode foil comprises a lower coating, wherein the lower coating is arranged between the cathode film layer and the current collector; the lower coating comprises carbon-based particles and the distribution density of the carbon-based particles with a particle size of over 100 nm in the lower coating is less than or equal to 10 pcs / 10 µm.

[0064] The lower coating contributes to improving the conductivity and bonding strength between the cathode film layer and the current collector, reducing demolding of the cathode film layer from the current collector during the cycle, and improving the dynamic performance of the battery. In the high-density electrode foil of the embodiment of the present application, the distribution density of carbon-based particles with a particle size greater than 100 nm in the lower coating is controlled to ≤ 10 particles / 10 µm, which helps to reduce the probability of damage to the current collector in the high-voltage-density electrode foil and further improves the limiting density of the cathode foil.

[0065] In any embodiment, the cathode foil comprises a lower coating, the lower coating being arranged between the cathode film layer and the current collector; the density of the cathode foil in a fully charged state is greater than or equal to 2.4 g / cm³ 3 , where the one-sided thickness of the lower coating is 1 µm-4 µm.

[0066] In any embodiment, the cathode foil comprises a lower coating, the lower coating being arranged between the cathode film layer and the current collector; the density of the cathode foil in the fully charged state is greater than or equal to 2.5 g / cm³ 3 , wherein the one-sided thickness of the lower coating is 2 µm to 4 µm.

[0067] As the electrode film's density increases, the extrusion effect of large lithium phosphate particles (e.g., particle size greater than 1 µm) in the cathode film layer on the lower coating becomes more significant. This can lead to stress concentration at the points where large particles are present, potentially even penetrating the lower coating and damaging the current collector. Increasing the thickness of the lower coating helps to mitigate the stress concentration phenomenon in the electrode film and further increase the electrode film's maximum density.

[0068] A second aspect of the present application relates to a battery device comprising the lithium-ion secondary battery described in the first aspect of the present application, wherein the battery device comprises at least one of a battery module, a battery pack and an energy storage battery.

[0069] The third aspect of the present application further relates to a power-consuming device, wherein the power-consuming device comprises the lithium-ion secondary battery provided in the first aspect of the present application or the battery device provided in the second aspect of the present application.

[0070] An unclaimed aspect of the present application also 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 carbon source comprises polyethylene glycol; wherein the iron source comprises divalent iron; wherein, after milling in a solvent, a mixed slurry is obtained; wherein the volume distribution particle size Dv 50the particle size in the mixed slurry is 1 µm to 4 µm; wherein the mixed slurry is dried and then a precursor powder is obtained; wherein the precursor powder is sintered to obtain the active cathode material; wherein the sintering comprises at least two stages of sintering at constant temperature, wherein the sintering temperature of a high-temperature stage is 750°C to 800°C.

[0071] The area fraction of the large particles on the surface of the cathode film layer produced by the active cathode material manufactured using this process is small, and the active cathode material has a high degree of graphitization, which allows the pressing density of the electrode foil to be slightly increased by slippage between the particles, which has a positive effect on improving the energy density of the battery and also improves the kinetic performance of the battery.

[0072] A further unclaimed aspect of the present application relates to a method for producing a cathode foil, wherein the method comprises the sequential addition and dry mixing of a binder, a conductive agent and an active cathode material produced by the method in a fourth aspect, the subsequent addition of a solvent and stirring to obtain a supplied slurry; wherein the supplied slurry is transferred to at least one side of the current collector and coated, and then dried and hot pressed to obtain the cathode foil.

[0073] In any embodiment, the stirring process comprises a pre-stirring and a main stirring, wherein the stirring speed of the pre-stirring is lower than that of the main stirring, wherein the rotational speed of the pre-stirring is 20 to 30 rpm and the rotational speed of the pre-mixing is 450 to 550 rpm, and wherein the pre-stirring time is 10 to 20 minutes.

[0074] In any embodiment, the hot pressing process comprises at least three hot rolling operations, wherein the hot rolling pressure increases successively, with the hot rolling pressure being 20 to 50 tonnes, 50 to 70 tonnes, and 70 to 90 tonnes respectively; wherein the temperature of the hot roll is 40°C to 80°C, and wherein the electrode foil is heated before the electrode foil enters the hot roll for the first time for compression, with the heating temperature being 40°C to 50°C.

[0075] The active cathode material produced by the aforementioned hot pressing process in combination with the unclaimed manufacturing process of the fourth aspect is advantageous for further reducing the porosity of the cut surface of the cathode film layer, increasing the boundary pressing density of the electrode foil, and improving the energy density of the battery. PRESENTATION OF THE INVENTION Fig. 1 is a scanning electron microscope image of a cross-sectional area of ​​a cathode film layer along the thickness direction of an electrode foil according to an embodiment of the present application; Fig. Figure 2 is a schematic representation of a lithium-ion secondary battery according to an embodiment of the present application; Fig. Figure 3 is a schematic exploded view of a lithium-ion secondary battery according to an embodiment of the present application; Fig.Figure 4 is a schematic representation of a battery module according to an embodiment of the present application; Fig. Figure 5 is a schematic representation of a battery pack according to an embodiment of the present application; Fig. 6 is a schematic exploded view of the in Fig. 5 battery packs shown; Fig. Figure 7 is a schematic diagram of a power-consuming device which, according to an embodiment of the present application, uses the lithium-ion secondary battery as a power source; Fig. Figure 8 is a porosity test diagram of a cross-sectional area of ​​a cathode film layer along the thickness direction of an electrode foil according to an embodiment of the present application. Reference symbol list:

[0076] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Lithium-ion secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover assembly. SPECIFIC EXECUTION FORMS

[0077] In the following, embodiments of the lithium-ion secondary battery, the battery device, and the power-consuming device of the present application are described in detail with appropriate reference to the accompanying drawings. However, an unnecessarily detailed description can be omitted. For example, a detailed description of known facts and a repeated description of essentially the same structure can be avoided. This is to prevent the following description from becoming unnecessarily long and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description serve to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0078] The “ranges” disclosed in this application are defined in terms of a lower limit and an upper limit. A particular range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of that range. The range thus defined can include or exclude the end values ​​and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a particular parameter, it is understood that ranges of 60–110 and 80–120 are also considered. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are listed, all of the following ranges are anticipated: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5.In the present application, unless otherwise specified, the number range "ab" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the number range "0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is simply an abbreviation for these number combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or the like.

[0079] Unless otherwise stated, all embodiments and optional embodiments of the present application may be combined to form new technical solutions, and such technical solutions should be considered to be contained in the disclosure of the present application.

[0080] Unless otherwise stated, all technical features and optional technical features of the present application can be combined to form new technical solutions, and such technical solutions should be considered to be contained in the disclosure of the present application.

[0081] Unless otherwise stated, all steps of the present application may be carried out sequentially or in any order, but preferably sequentially. For example, if a method includes steps (a) and (b), this means that the method may include steps (a) and (b) carried out sequentially, or steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may also include step (c), this means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), or the like.

[0082] In the present application, the terms “several” and “multiple” refer to two or more.

[0083] Unless otherwise stated, the terms used in this application have the generally understood meanings which are usually attributed to those skilled in the art in this field.

[0084] Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods specified in the embodiments of this application. Unless otherwise specified, all parameters were tested at 25°C.

[0085] The battery mentioned in the embodiments of the present application may be a single physical module comprising one or more lithium-ion secondary batteries to provide a higher voltage and capacity. For example, the battery mentioned in this application may comprise a lithium-ion secondary battery, a battery module, a battery pack, or the like.

[0086] A lithium-ion secondary battery is the smallest unit of a battery and can perform charging and discharging independently. Lithium-ion secondary batteries can be cylindrical, rectangular, or other shapes, and the embodiments described in the present application are not limited to these. Fig. Figure 2 shows, as an example, a lithium-ion secondary battery 5 with a cuboid structure.

[0087] A lithium-ion secondary battery comprises an electrode array and an electrolyte.

[0088] The lithium-ion secondary battery may also include an outer casing used to encapsulate the electrode assembly and electrolyte. The outer casing can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. Alternatively, the outer casing can be a soft casing, such as a pouch-like soft casing. The material of the soft casing can be plastic, for example, one or more types of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0089] In some embodiments, the outer packaging, as in Fig.Figure 3 shows a housing 51 and a cover plate 53. The housing 51 can include a base plate and a side plate connected to the base plate, and the base plate and side plates enclose and form a receiving space. The housing 51 has an opening that communicates with the receiving space, and the cover plate 53 is used to cover the opening and close the receiving space. The electrode assembly 52 is encapsulated in the receiving space. The number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more and can be adapted as required.

[0090] The electrode arrangement typically includes a cathode foil and an anode foil, and the anode foil is an electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging, and the cathode foil is an electrode that releases or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0091] If multiple lithium-ion secondary batteries are present, they are connected in series, parallel, or a mixed configuration via a bus component. In some embodiments, the battery can be a battery module; if multiple lithium-ion secondary batteries are present, they are arranged and mounted to form a battery module. In some embodiments, the battery can be a battery pack comprising a housing and a lithium-ion secondary battery, with the lithium-ion secondary battery or battery module being contained within the housing. In some embodiments, the housing can be designed as part of the vehicle's chassis structure. For example, part of the housing can become at least part of a floor panel of the vehicle, or part of the housing can become at least part of a crossmember and a longitudinal member of the vehicle.

[0092] In some embodiments, a battery can be an energy storage device. The energy storage device includes, for example, an energy storage container, an energy storage cabinet, and the like.

[0093] In some embodiments, lithium-ion secondary batteries can be assembled into a battery module, wherein the battery module can comprise several lithium-ion secondary batteries, the number of which can be adjusted depending on the application and capacity of the battery module. Fig. Figure 4 shows a schematic representation of a battery module 4 as an example. As in Fig. As shown in Figure 4, several lithium-ion secondary batteries 5 can be arranged sequentially along the longitudinal direction of battery module 4. Of course, the arrangement can also be any other way. Furthermore, the multiple lithium-ion secondary batteries 5 can be secured by fastening elements.

[0094] Optionally, the battery module 4 can also include an outer shell with a receiving space, and the multiple lithium-ion secondary batteries 5 are received in the receiving space.

[0095] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted depending on the application and capacity of the battery pack.

[0096] Fig. 5 and Fig. Figure 6 shows a schematic representation of a 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 several battery modules 4 arranged within the housing. The housing includes an upper housing 2 and a lower housing 3, with the upper housing 2 serving to cover the lower housing 3 and forming a sealed space for the battery module 4. The arrangement of the multiple battery modules 4 within the housing is arbitrary.

[0097] The material made of lithium-containing transition metal phosphate is frequently used in lithium-ion batteries due to its stable structure, good safety, and long lifespan; however, it has problems with regard to low electronic conductivity and low stacking efficiency, which makes it difficult to further increase the amount of lithium-containing transition metal phosphate in the battery per unit volume effectively, and cannot meet the requirements of high-energy-density batteries.

[0098] To further improve battery energy density and increase electrode density, the common industry approach is to increase the particle size distribution within the electrode foil. Increasing this distribution requires increasing the size or proportion of large particles. However, studies have shown that battery kinetic performance is negatively impacted when the size and proportion of large particles in the electrode foil exceed a certain range. Manufacturing a battery with both high energy density and kinetic performance is a significant engineering challenge that urgently needs to be addressed.

[0099] The first aspect of the present application relates to a lithium-ion secondary battery, wherein the lithium-ion secondary battery comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode current collector and a cathode film layer arranged on at least one side of the cathode current collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises particles of lithium-containing transition metal phosphate provided on at least a part of their surface with a carbon coating material, wherein 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 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%;where in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C; 50 greater than or equal to 0.95 and less than or equal to 1.20, where the degree of graphitization is the C-value. G / I D is, where I G the G-peak intensity of the Raman spectrum at 1580±100cm -1 and I D the D peak intensity of the Raman spectrum at 1350±100cm -1 represents.

[0100] In the 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 1.5 µm is less than 8%, making it difficult to achieve a high cathode foil density. In the 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 1.5 µm is more than 20%. While this contributes to achieving a high cathode foil density, it reduces the contact area between the electrolyte solution and the active cathode material. This hinders the diffusion of lithium ions into the cathode film layer and increases the diffusion path of lithium ions within the particles, leading to strong polarization of the electrode foil, increasing the battery impedance, and significantly degrading the battery's dynamic performance.

[0101] By controlling the area fraction of particles with a particle size of 1.5 µm or more in the cathode film layer to greater than or equal to 8.0% and less than or equal to 20.0%, the significant effect of the large particle vulnerability can be reduced. This helps to keep the battery impedance low and improve the battery's dynamic performance, but limits further increases in the electrode film's packing density. The embodiments of the present application further improve the graphitization degree of the particles in the cathode film layer and the crystallinity of the particles' surface carbon layer by increasing the median C 50The degree of graphitization is controlled to be greater than or equal to 0.95 and less than or equal to 1.20, which facilitates particle sliding in the active cathode material during the roller press film formation process. The particles' easy sliding ability can further increase the compression density of the cathode film layer, thus achieving a balance between kinetic battery performance and energy density.

[0102] In the present application, the term "particle" refers to particles in the cathode film layer whose complete boundaries are visible in the field of view at a certain magnification, for example 10,000x, and defects and scratches may be present inside the particles, but the interior of the particles is not visible with sufficiently complete boundaries to segment the particles.

[0103] In some embodiments, the area fraction of particles with a particle size greater than or equal to 1.5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can optionally be selected as 8.0%, 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 19.0%, 20.0% or a numerical range between any two values.

[0104] In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area statistics of the particles are specific as follows. The cathode film layer is cut along the thickness direction of the electrode foil by an argon ion beam (for example, the following instrument can be used: Leica EM TIC 3X CP, operating voltage: 6 kV, operating time: 6 hours). After the cross-sectional area has been exposed, a scanning electron microscope (for example, the following can be selected: instrument model: Hitachi SU8230, operating voltage: 3 kV, beam current: high, probe model: U (LA100), working distance < 5 mm) is used to observe the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.The image is acquired using a field emission scanning electron microscope in secondary electron mode at the non-edge position in 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 center of the sample), whereby an electron microscope image is acquired at 10,000x magnification, and the particles in the electron microscope image are analyzed using the software ImageJ (1.46r, Win64 version). The specific method for using the software ImageJ is as follows: Loading a scanning electron microscope image to be analyzed, as shown in [reference missing]. Fig.Figure 1 shows the process; particle detection using the Cellpose plug-in software, followed by manual correction; data reading and analysis using the ImageJ software. The specific method for particle detection with the Cellpose plug-in software is as follows: setting the "Segmentation Diameter" parameter (diameter in the "Segmentation" module) to 15 pixels, clicking "run cyto3" for particle detection, and manually marking the particles in the image that are not detected, not detected completely, or detected incorrectly by the software. The particles in the image that are not detected, not detected completely, or detected incorrectly by the software mainly include the following: 1. The particles are too large or have scratches on their surface, which prevents them from being detected or results in incomplete detection;2. When sectioned with the argon ion beam, scratches are created on the particle surface. During detection, the software may incorrectly interpret these scratches as particle boundaries, leading to detection errors. 3. The particle cannot be detected because it is too small. 4. The particles are located at the edge of the electron microscope's field of view, and the particle's interior is penetrated by the edge. The morphology cannot be fully displayed, and the part is detected instead of the whole, resulting in detection errors. For the aforementioned particles that are not detected or exhibit detection errors, manual calibration is performed. The specific procedure is as follows: Deleting the large particles at the edges of the scanning electron microscope that cannot be fully displayed;Determine whether a slit or scratch is present in any other particle that is not detected or exhibits detection errors, wherein, if no slit or scratch is present within the particle, it is judged as a single particle and manually marked according to the manually observed particle boundary; determine, in response to the presence of a slit or scratch inside the particle, whether the slit or scratch penetrates the particle, and if not, determine that it is a single particle and perform manual detection; determine, in response to the slit or scratch penetrating the particle, whether the slit or scratch is linear or irregular; determine, in response to the irregular shape of the slit or scratch, that it is the boundary between particles, splitting the particles along the boundary;Performing a contrast comparison in response to the linear shape of the slit or scratch; determining, in response to an indistinct contrast comparison and the absence of a slit sensation, that the particle is a scratch, which is recognized as a single particle; determining, in response to a strong contrast comparison and the slit sensation, that it is the boundary between particles, which is recognized as two particles. After manual detection, the information irrelevant to the particles is deleted in the automatic image processing process, and the determination and detection of the particles in the image is completed.

[0105] After particle identification and detection, the image is imported into the ImageJ software for analysis, and the scale is adjusted according to the scanning electron microscope image. The particle size and area within the image are then analyzed using the "Feret Diameter" and "Area" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter represents the maximum distance between all parallel lines in the two-dimensional projection of the particle, characterizing its size. The "Area" parameter represents the pixel area of ​​the particle, characterizing its surface area. Particles with a diameter of less than 50 nm exhibit large errors in the statistical process and are difficult to detect accurately. Furthermore, the particle size of the conductive medium is generally less than 50 nm, leading to significant errors in the statistical results.Therefore, in the particle size statistics process of this application, particles with a particle size of less than 50 nm are not counted, and the particle statistics corresponding to the "NaN" indicated by "Area" are discarded. To achieve the statistically significant sample size according to the method described above, each electrode array collects at least 10 scanning electron microscope images with non-overlapping fields of view and counts the area of ​​at least 5000 particles. The sum of the "Area" parameters of particles with a particle size greater than or equal to 1.5 µm and the sum of the "Area" parameters of all particles are calculated as the area of ​​particles with a particle size greater than or equal to 1.5 µm and the total area of ​​the counted particles.The sum of the areas of the particles with a particle size greater than or equal to 1.5 µm divided by the total area of ​​the counted particles is assumed to be the area ratio of the particles with a particle size greater than or equal to 1.5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0106] During the compaction process, the cathode film layer is compacted in the thickness direction. Therefore, the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, compared to the surface of the cathode film layer, can better reflect the actual compaction state of the internal particles of the film layer in a spatial plane. In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area ratio of particles with a particle size greater than or equal to 1.5 µm can intuitively reflect the proportional relationship between the area of ​​some particles in this particle size segment and the total particle area, and thus reflect the particle distribution within this particle size segment.

[0107] It is understood that the particles in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, in particular the particles larger than 50 nm, originate mainly from the active cathode material. Therefore, the embodiments of the present application can accurately and objectively reproduce the distribution of lithium-containing transition metal phosphate particles in the cathode film layer of the electrode foil by observing and counting the particle area in the cross-sectional area of ​​the cathode film layer.

[0108] In the prior art, a laser particle size analyzer is typically used to count the particle size of the active cathode material using the Malvern laser diffraction method. However, the applicant's investigations show that the lithium-containing transition metal phosphate particles tend to agglomerate, and the test results obtained with the Malvern laser diffraction method, which is based on the laser scattering principle, often measure the particle size of the particle agglomerates. This particle size cannot accurately reflect either the particle size of the particle in the active cathode material or the dispersion state of the active cathode material in the film layer, since the degree of dispersion of the active cathode material in the film layer increases during the slurry preparation and film rolling processes.The test results obtained using the Malvern laser diffraction method are influenced by the particle size, specific surface area, and degree of agglomeration of the active cathode material. Compared to the actual dispersion in the electrode foil, the number of large particles obtained by this test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size determined using the Malvern laser diffraction method cannot correspond to or be analogous with the particle size statistically determined in the embodiments of the present application.

[0109] A person skilled in the art can adjust the particle size using all known processes. For example, the growth rate and time of the cathode material can be controlled by regulating the temperature and time during the production of the positive electrode material. By utilizing the mechanical force of comminution and grinding processes, the raw materials are processed to a target particle size distribution range to achieve particle size adjustment; a sieving and classification device is used to separate the particle sizes of the particle system and obtain the particle size ratio that meets the requirements; the particle size can also be controlled by precisely controlling the feed rate and adjusting the residence time and stress state of the particles in the device.

[0110] Lithium-containing transition metal phosphate refers to a phosphate material containing lithium and a transition metal, which can be detected by all methods known in the art. For example, it can be detected by combining an X-ray diffractometer (XRD) with an energy spectrum analyzer and an inductively coupled plasma mass spectrometer. Lithium-containing transition metal phosphate includes, but is not limited to, lithium iron phosphate, lithium manganese iron phosphate, and doped materials thereof.

[0111] The carbon coating material, arranged on at least a portion of the surface of the lithium-containing transition metal phosphate, can be detected using all methods known in the art. For example, by characterizing the lithium-containing transition metal phosphate using a coupling of a transmission electron microscope and an energy spectrum analyzer, it is possible to observe the carbon coating material arranged on at least a portion of the surface of the lithium-containing transition metal phosphate. It should be noted that the elements in the carbon coating material are not limited to carbon elements, but may also include other non-carbon elements. The carbon coating layer containing the carbon coating material is not limited to a film-like form, but may also comprise an island-like, irregular, or discontinuous encapsulating layer.

[0112] In some embodiments, the median of the graphitization degree C in the cumulative distribution curve of the graphitization degree, namely C-value, of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer is 50 greater than or equal to 0.95 and less than or equal to 1.20, where the degree of graphitization is the C-value. G / I D is, where I G the G-peak intensity of the Raman spectrum at 1580±100cm -1 and I D the D peak intensity of the Raman spectrum at 1350±100cm -1 represents.

[0113] In the present application, the graphitization degree (C-value) of the cathode film layer can be determined by the surface scanning mode of a laser microconfocal Raman spectrometer. Specifically, a laser microconfocal Raman spectrometer (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 extracted to perform a surface scan on its surface or a cross-sectional area along the thickness direction of the electrode foil. The scan area is 45 µm × 45 µm and divided into 10 × 10 grids, with grid vertices serving as test points, a step size of 5 µm, and a total of 100 scan points. This allows for the determination of the C-values ​​at various locations and the cumulative distribution curve of the C-value across the surface scan area.

[0114] In the present application, the cathode film layer can be either a freshly produced cathode film layer or one obtained by dismantling a battery. The surface of the cathode film layer obtained by dismantling the battery inevitably contains electrolyte salt residues. To improve test accuracy, a surface scan of the cut surface of the cathode film layer is preferably performed along the thickness direction of the electrode foil to determine the degree of graphitization of the cathode film layer.

[0115] The graphitization degree (C value) of the cathode film layer is determined by the peak intensity ratio of the G-peak (G-band) and the D-peak (D-band) of the Raman spectrum, and the position of the G-peak is 1580±100cm. -1 , which the carbon sp 2 -Hybrid structure is characterized; the position of the D-peak is at 1350±100 cm -1This characterizes the disordered structure of carbon, where disorder means that there is no regular arrangement between the carbon atoms in the structure. In graphite crystals, carbon atoms in the same layer form sp 2 Hybridization of covalent bonds occurs, and the intermediate layers are subject to van der Waals forces, causing 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 understood that the degree of graphitization in the cathode film layer primarily stems from the graphitized carbon material within the cathode film layer, i.e., from the carbon coating layer of the active cathode material. Although the conductive medium consists of carbon nanotubes rich in sp 2 -Hybrid structure is also a relatively high I c / I p-value, whereby the value represents an extreme value for the cathode film layer in the Raman surface scan test due to its low additive content and small tube diameter, which has no effect on the graphitization degree C 50 in the cathode film layer.

[0116] 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 surface carbon of the active cathode material, the higher the proportion of carbon with a graphitic structure in the cathode film layer. This makes it easier for the particles to slide into the coating layer during the rolling process, thanks to the highly graphitized carbon structure, and the better the electrode foil density can be achieved at low rolling pressure.

[0117] The cumulative distribution curve of the degree of graphitization, namely the C-value, refers to a curve obtained by arranging at least 100 obtained C-values ​​in ascending order, where the degree of graphitization is the horizontal axis and the proportion of the cumulative number is the vertical axis. 50 The C-value corresponds to the percentage of the cumulative number on the vertical axis of the cumulative distribution curve of the degree of graphitization that is 50%. Compared to the point value, the median C 50 The graphitization degree reflects the overall graphitization degree of the particles in the cathode film layer, i.e., the degree of slippage; compared to the mean value, it can reduce the influence of extreme values ​​during the testing process and improve the reliability of the test results.

[0118] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree, namely C-value, of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C 50 optionally selected as 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20 or a numerical range between any two values.

[0119] The degree of graphitization of the active material particles can be adjusted by a person skilled in the art using all known processes. For example, the degree of graphitization of the active material particles can be adapted by regulating the carbon source, optimizing the nucleation process, sintering temperature, sintering time, sintering pressure, and sintering atmosphere. The higher the degree of graphitization of the surface carbon of the active cathode material, the higher the proportion of carbon with a graphitic structure in the cathode film layer. This allows the particles to slide more easily into the coating material with the help of the highly graphitized carbon structure, resulting in a better electrode film density.

[0120] In some embodiments, it is provided that the median value C 50 The degree of graphitization of the cathode film layer is 0.97-1.13 and can optionally be 1.00-1.10.

[0121] The median C 50 Increasing the graphitization level of the cathode film layer within the aforementioned range further improves particle sliding, thus compensating for the insufficient gradation caused by the low number of large particles in the cathode film layer. While maintaining the battery's high dynamic performance, the electrode foil density is further improved to achieve a balance between dynamic battery performance and energy density.

[0122] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the concentration of the C-value (C 90 -C 10 ) / C 50 It is between 0.01 and 0.04.

[0123] Similarly, C 90Referring to the above, the C-value corresponds to the fact that the proportion of the cumulative number of the vertical axis in the cumulative distribution curve of the degree of graphitization, namely the C-value, is 90%, and C 10 The C-value corresponds to the fraction of the cumulative number on the vertical axis of the cumulative distribution curve of the degree of graphitization, namely the C-value, which is 10%. The concentration of the C-value is given by (C 90 -C 10 ) / C 50 expressed. (C 90 -C 10 ) / C 50 It can reflect the magnitude of most C values, is not affected by extreme values, and can also reflect the width of the graphitization degree distribution of particles in the cathode film layer. A low concentration of C in the cathode film layer indicates that the graphitization degree distribution of the surface carbon of the active cathode material is narrow and the concentration is high.

[0124] In some embodiments, the concentration of the C-value (C) is shown in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer. 90 -C 10 ) / C 50 optionally selected as 0.01, 0.02, 0.03, 0.04 or a numeric range between any two values.

[0125] The concentration of the C value of the cathode film layer is 0.01-0.04, indicating that the graphitization degree of the surface-coated carbon of the active cathode material is relatively uniform. This means that the active cathode material exhibits good coating uniformity and consistency, thereby reducing the hindrance of sliding caused by the inconsistent graphitization degree of the particles in the active cathode material and the resulting local stress concentration. This uniform sliding between the particles of the active cathode material allows for a higher overall compaction of the electrode foil at relatively low rolling pressure, further improving the pressing density of the electrode foil and the energy density of the battery while maintaining good kinetic battery performance.

[0126] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the concentration of the C-value (C 90 -C 10 ) / C 50 It is between 0.02 and 0.04.

[0127] The concentration of the C value (C 90 -C 10 ) / C 50 Within the above range, it is advantageous to further improve the consistency of the graphitization degree of the carbon on the surface of the active cathode material and to improve the sliding degree between the particles, further improving the pressing density of the electrode foil and the energy density of the battery while maintaining good kinetic battery performance.

[0128] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the C 90 The degree of graphitization is 1.0 to 1.3, optionally 1.02 to 1.15.

[0129] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree, namely the C value, of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the C 90 The degree of graphitization can optionally be 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.2, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.3 or a numerical range between any two values.

[0130] The degree of graphitization C 90lies within the aforementioned range and thus close to the median graphitization degree C 50 , which indicates that the distribution range of the graphitization degree of the cathode film layer is narrow, which contributes to a uniform sliding between the particles and thus improves the compression density of the cathode foil.

[0131] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the C 10 The degree of graphitization is 0.92 to 1.1, optionally 0.98 to 1.08.

[0132] In some embodiments, it is provided that in the cumulative distribution curve of the graphitization degree, namely the C value, of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the C 10The degree of graphitization can optionally be 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.1 or a numerical range between any two values.

[0133] The degree of graphitization C 10 within the above area indicates that various locations in the cathode film layer have a high degree of graphitization, which has a positive effect on the uniform sliding of the particles, reduces the probability of a local stress concentration and further improves the pressing density of the electrode foil.

[0134] In some embodiments, it is provided that 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 of 1.5 µm to 5 µm is 9.0% to 20.0%.

[0135] In some embodiments, it is provided that in the 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 1.5 µm-5 µm is optionally 9.0%, 10.0%, 11.0%, 12.0%, 13.0%, 14.0%, 15.0%, 16.0%, 17.0%, 18.0%, 19.0%, 20.0% or a numerical range between any two values.

[0136] In the 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 1.5 µm–5 µm can be determined as described above. Specifically, in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the area fraction of particles with a size of 1.5 µm–5 µm is calculated by dividing the sum of the areas of the particles with a size of 1.5 µm–5 µm by the total area of ​​all counted particles.

[0137] In the 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 1.5 µm-5 µm lies within the aforementioned range, which further reduces the hindrance of wetting and diffusion of the electrolyte solution in the cathode film layer by large particles on the surface of the electrode foil, which improves the consistency of the diffusion rate of lithium ions in the particles of the active cathode material, reduces local polarization and improves the kinetic performance of the battery.

[0138] In some embodiments, it is provided that 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 of 1.5 µm to 5 µm is 10.0% to 20.0%.

[0139] In the course of improving the particle size distribution and increasing the size or proportion of large particles, the introduction of particles with a size of 1.5 µm to 5 µm is unavoidable. The surface area of ​​particles with a size of 1.5 µm–5 µm lies within the aforementioned range, which has a positive effect on the density of the electrode foil and simultaneously takes into account the dynamic performance of the battery.

[0140] In some embodiments, it is provided that 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 5 µm is 0.

[0141] In the 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 5 µm can be determined as described above. Specifically, in the 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 5 µm is calculated by dividing the sum of the areas of the particles with a particle size greater than or equal to 5 µm by the total area of ​​all counted particles.

[0142] Studies have shown that particles with a particle size of 5 µm or greater in the cathode film layer significantly impair the wetting of the electrolyte solution into the cathode film layer and the diffusion into the particles of the active material, and the area fraction of particles with a diameter of at least 5 µm is 0, which further reduces the internal resistance of the battery and improves the kinetic performance of the battery.

[0143] In some embodiments, it is provided that in the 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 and less than 1.5 µm is 15.0% - 25.0%, optionally 16.0%-24% and further optionally 16.0%-20.0%.

[0144] In some embodiments, it is provided that in the 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 and less than 1.5 µm is optionally 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25% or a numerical range between any two values.

[0145] In the 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 and less than 1.5 µm can be measured according to the method described above. The sum of the areas of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm, divided by the total area of ​​the counted particles, is taken as the area ratio of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil.

[0146] In the 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 and less than 1.5 µm lies within the above-mentioned range, which has a positive effect on the further improvement of the pressing density of the electrode foil and the improvement of the energy density of the battery while maintaining good battery dynamics.

[0147] In some embodiments, it is provided that in the cumulative distribution curve of the area of ​​particle sphericity obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median of the sphericity L A50 0.60 to 0.85, optionally 0.65 to 0.80.

[0148] The specific method for testing the sphericity of particles in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is as follows: Referring to the method described above in the present application, the particles in the cross-sectional area of ​​the cathode film layer are detected. After particle detection and identification, the images are imported into the ImageJ software for analysis, and the scale is set according to the scanning electron microscope image. The particle size, area, and sphericity of the particles in the image are then analyzed using the analysis functions "Feret Diameter," "Area," and "Round." According to the software manual (ImageJ User Guide IJ 1.46r), the "Round" parameter represents the ratio of the particle's pixel area to the area of ​​a circle with the adjusted long diameter as its diameter, thus characterizing the sphericity of the particles.The closer a particle is to a sphere, the closer the ratio of the pixel area to the area of ​​a circle with the adjusted long diameter as the diameter approaches 1. Therefore, the "Round" parameter of the particles obtained through analysis is used to characterize the sphericity of the particles. Particles with a diameter of less than 50 nm exhibit large errors in the statistical process and are difficult to detect accurately, and the particle size of the conductive medium is generally less than 50 nm, leading to large errors in the statistical results. Therefore, in the particle size statistics process of this application, particles with a particle size of less than 50 nm are not counted, and the particle statistics corresponding to "NaN" indicated by "Round" are discarded.To achieve a statistically significant sample size according to the method described above, each electrode foil collects at least 10 scanning electron microscope images with non-overlapping fields of view. The sphericity of at least 5,000 obtained particles is arranged in ascending order, and the cumulative distribution curve of the particle sphericity in the cathode film layer is obtained with the sphericity as the horizontal axis and the cumulative area fraction as the vertical axis. L. A50 is the sphericity L-value that corresponds to the value at which the cumulative area fraction of the vertical axis in the cumulative distribution curve of the sphericity L-value is 50%.

[0149] In some embodiments, it is provided that in the cumulative distribution curve of the area of ​​particle sphericity, which was obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the L A50the sphericity is 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.705, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85 or a numerical range between any two values.

[0150] A person skilled in the art can adjust the sphericity of the particles through all known processes. For example, the sphericity of the particles can be adjusted through processes such as grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, the addition of surfactants, and adjusting the parameters of each process.

[0151] Particles with a median sphericity L A50 Within the aforementioned area, they are approximately spherical and tend to slip between the particles when subjected to external forces, which can further improve the pressing density of the electrode foil and increase the energy density of the battery.

[0152] In some embodiments, it is provided that in the cumulative distribution curve of the area of ​​particle roughness obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median of the roughness R A50 The value is between 0.92 and 0.96.

[0153] The specific method for testing the roughness of particles in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is as follows: Referring to the method described above in the present application, the particles in the cross-sectional area of ​​the cathode film layer are detected. After particle detection and identification, the images are imported into the ImageJ software for analysis, and the scale is set according to the scanning electron microscope image. The particle size, area, and roughness are then analyzed using the "Feret Diameter," "Area," and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Solidity" parameter is analyzed to represent the ratio of the pixel area to the convex area of ​​the particle. Therefore, the "Solidity" parameter obtained through the analysis is used to characterize the roughness of the particles.According to the definition, the closer the roughness approaches 1, the smoother the particle. Particles with a diameter of less than 50 nm exhibit large errors in the statistical process and are difficult to detect accurately, and the particle size of the conductive medium is generally less than 50 nm, leading to large errors in the statistical results. Therefore, in the particle size statistics process of this application, particles with a size of less than 50 nm are not counted, and the particle statistics corresponding to "NaN" indicated by "Solidity" are discarded. To achieve the statistically significant sample size according to the method described above, each electrode foil collects at least 10 scanning electron microscope images with non-overlapping fields of view. The roughness of at least 5.The 000 obtained particles are arranged in ascending order, and the cumulative distribution curve of the roughness of the particles in the cathode film layer is obtained with the roughness as the horizontal axis and the cumulative area fraction as the vertical axis. R. A50 is the roughness R-value that corresponds to the value at which the cumulative area fraction of the vertical axis in the cumulative distribution curve of the roughness R-value is 50%.

[0154] In some embodiments, it is provided that in the cumulative distribution curve of the area of ​​particle roughness obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median of the roughness R A50 optionally 0.92, 0.93, 0.94, 0.95, 0.96 or a numeric range between any two values.

[0155] A skilled person can adjust the roughness of the particles using all known processes. For example, particle roughness can be adjusted through processes such as grinding, polishing, sanding, milling, electroplating, and calendering, as well as by adjusting the parameters of each process.

[0156] The surface of particles with a median roughness R A50 Within the aforementioned area, the surface is relatively smooth, the friction between the particles is relatively low, and they slip easily under the influence of external forces, which further improves the pressing density of the electrode foil and increases the energy density of the battery.

[0157] In some embodiments, the iron dissolution rate of the cathode film layer is provided to be 500 ppm-2000 ppm and optionally 500 ppm-1500 ppm.

[0158] The iron dissolution rate of the cathode film layer can be tested as follows. Specifically, the electrode foil is removed from the battery, cleaned, and then loaded into a small disc with a diameter of 14 mm. Several small disc samples are taken so that the total sample mass is approximately 5 g, which is added to 100.3 g of ascorbic acid solution with a mass concentration of 0.3% (the solvent is ultrapure water). The mixture is stirred for 5 minutes at a speed of 500 revolutions per minute, and the solution is then rapidly aspirated with a 5 mL syringe. The solution is filtered into a test tube using a filter with a hole diameter of 0.45 µm, and 1 mL of the supernatant is pipetted into a glass volumetric flask, diluted 50-fold, and a test is performed using an inductively coupled plasma mass spectrometer (ICP-OES).To determine the iron concentration in the solution, the iron dissolution rate of the cathode film layer is calculated using the formula [(ICP test iron concentration × solution volume / mass of solution involved in volume adjustment) × 100.3 g / (mass of electrode foil of the small disk - mass of current collector of the small disk)], where the solution volume is 50 mL and the mass of the solution involved in volume adjustment is 1 g. Preferably, the mass of the current collector of the small disk is determined by multiplying the thickness of the small disk by its area and density. By measuring with a thickness gauge, the thickness of the small disk can be determined to correspond to the thickness of the current collector in the uncoated area. It is understood that the current collector in the coated area expands during the compaction process, resulting in a slight reduction in thickness compared to the uncoated area.However, the reduction is negligible and has no significant impact on the test results. If the current collector is an aluminum foil, the density is preferably 2.7 g / cm³. 3 .

[0159] In some embodiments, the iron dissolution rate of the cathode film layer can optionally be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm or a numerical range between any two values.

[0160] An expert can adjust the iron dissolution rate of the cathode film layer using any known process. For example, the iron dissolution rate of the cathode film layer is regulated by adjusting the surface coating quality of the cathode film layer, as well as the temperature, time, and pressure during the manufacturing process.

[0161] The iron dissolution rate can indirectly reflect the integrity and density of the carbon coating on the surface of the active cathode material. The lower the iron dissolution rate, the more difficult it is to precipitate iron ions from the carbon coating after acid dissolution; this means that the carbon coating layer on the surface of the active cathode material is more complete and dense. Active cathode materials with an iron dissolution rate within the aforementioned range exhibit a relatively complete and dense carbon coating layer, which can improve electrical contact between the active cathode materials, enhance the conductivity of the active cathode materials, reduce the polarization of the active cathode materials, and further optimize the kinetic performance of the lithium-ion secondary battery.At the same time, the densely coated carbon layer has a low space occupancy rate, and the gaps between the particles are slightly compressed by tension during the rolling process, which can simultaneously increase the pressing density of the electrode foil and the energy density of the battery.

[0162] In some embodiments, the mass content of the carbon element, based on the total mass of the active cathode material, is 0.8% - 1.8% and optionally 0.90% - 1.5%.

[0163] The mass fraction of the carbon element relative to the total mass of the active cathode material can be measured using methods and equipment known in the trade. For example, according to GB / T 21023-2006 "Determination of the total carbon and sulfur content of steel - Infrared absorption method after combustion in a high-frequency induction furnace", the Dekai HCS infrared carbon and sulfur analyzer is used for this determination.

[0164] In some embodiments, it is provided that, based on the total mass of the active cathode material, the mass content of the carbon element can optionally be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% or a numerical range between any two values.

[0165] Compared to the active cathode material made of lithium-containing transition metal phosphate in the prior art, the active cathode material has a relatively low carbon coating content, which further increases the charge of the lithium-containing transition metal phosphate in the cathode foil and improves the energy density of the lithium-ion secondary battery.

[0166] In some embodiments, the concentration of lithium iron antisite defects in the active cathode material is provided to be between 0.1% and 1.5%.

[0167] X-ray diffraction (XRD) data of the sample are acquired using an X-ray diffractometer, and phase analysis is performed. The phase's CIF file is obtained from an open-source website as an initial crystal structure model, including the definition of unit cell parameters, atomic positions, occupation probabilities, and similar parameters. In the initial crystal structure model, taking into account the possibility of an Fe-Li antiposition, the potential Li content at the Fe position and the potential Fe content at the Li position are determined, with the initial value set to 0.1%. The acquired XRD data are then adjusted and refined using the FullProf Suite software, with the parameters being refined in the following order: background parameters, peak intensity, unit cell parameters, and peak shape.If the fitted tip shape and the experimental tip shape are optimally matched and Rwp is less than 10, the refined Li and Fe occupancy probabilities are obtained as the concentration of lithium-iron antisite defects.

[0168] In some embodiments, it is provided that the concentration of the lithium iron antisite defects of the active cathode material can optionally be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a numerical range between any two values.

[0169] An expert can achieve the control of lithium iron antisite defects in the active cathode material through any known process. For example, lithium iron antisite defects in the active cathode material can be controlled by regulating the sintering temperature, sintering time, manufacturing process, stoichiometry of the raw material, and the like.

[0170] During the preparation and cycling process, certain lithium vacancies inevitably form in the crystal structure of the active cathode material. These lithium vacancies not only lead to the oxidation of iron(II) ions to iron ions, but also induce a partial migration of iron ions to lithium sites, resulting in lithium-iron antisite defects. These defects block the one-dimensional diffusion channel of lithium ions and impair the solid-phase transport of lithium ions. The active cathode material in the embodiment of the present application exhibits few lithium-iron antisite defects, which has a positive effect on the uniform transfer of lithium ions in the solid phase and further improves the kinetic performance of the lithium-ion secondary battery.

[0171] In some embodiments, the concentration of lithium iron antisite defects in the active cathode material is provided to be 0.3% to 1.0%.

[0172] In some embodiments, the lithium-containing transition metal phosphate is provided to include 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, where 0.8 ≤ m ≤ 1.15, 0.9 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 ≤ q ≤ 0.1.

[0173] In some embodiments, m may optionally be 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 a numerical range between any two values; where x may optionally be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0 or a numerical range between any two values; where y may optionally be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or a numerical range between any two values; where j can optionally be 3.5, 3.6, 3.7, 3.8, 3.9, 4 or a numeric range between any two values; where q can optionally be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or a numeric range between any two values.

[0174] By selecting a suitable modifying element Q, the ion diffusion path of the active cathode material can be improved, the lithium ion diffusion rate of the active cathode material can be improved, and the kinetic performance of the battery can be improved.

[0175] In some embodiments, the active cathode material comprises one or more lithium iron phosphate and its doped modified material and encapsulating modified material.

[0176] In some embodiments, the active cathode material comprises a titanium element, wherein the mass content of the titanium element is 2000 ppm to 6000 ppm based on the total mass of the active cathode material.

[0177] The type and concentration of elements in the active cathode material can be tested using all methods known in the art. For example, the titanium element and titanium content are tested by inductively coupled plasma emission spectrometry in accordance with Annex C of GB / T 33822-2017.

[0178] In some embodiments, it is provided that, based on the total mass of the active cathode material, the mass content of the titanium element can optionally be 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm or a numerical range between any two values.

[0179] Doping the active cathode material with titanium is advantageous because it causes lattice distortion, reduces the Li-O bond energy, increases the lithium-ion transfer rate, and improves the kinetic performance of lithium-ion secondary batteries. However, in the prior art, the titanium doping concentration in lithium-containing transition metal phosphate is often limited to 3000 ppm because excess titanium is difficult to fully penetrate into the main phase of the lithium-containing transition metal phosphate and can easily become a harmful impurity phase that remains on the surface, negatively impacting battery performance.

[0180] The active cathode material in the embodiment of the present application has a high titanium content, and surprisingly, the high titanium content does not form a harmful impurity phase that negatively affects the energy density and kinetic performance of the battery. Although the reason for this is not yet clear, it is speculated that the titanium element, phosphate, and other elements (such as the lithium element) together form a fast ion conductor, which in turn improves the kinetic performance of the battery.

[0181] In some embodiments, the powder density of the active cathode material is provided for at a pressure of 3T to be 2.50 g / cm³. 3 up to 2.70 g / cm³ 3 amounts.

[0182] In the present application, the term "powder compression density" refers to the process in which, during the compression process, larger gaps are filled by external force through movement and deformation of the powder, the contact area between the particles increases, the attraction between atoms is generated, and the mechanical fit between the particles is improved, thereby increasing the density of the resulting compact, which has a specific density and strength, in g / cm³. 3 is specified.

[0183] The powder density of the active cathode material can be measured using methods and equipment known in the trade. For example, reference can be made to GB / T 24533-2009, and the compaction density meter can be used for the measurement. Specifically, a certain quantity of active cathode material is placed on a special compaction mold (the mold diameter is known), and the mold is hollow in the middle and has a metal disc at the top and bottom. The active cathode material is placed between the metal discs, a metal cylinder is placed on top, and the mold is placed on the compaction density meter, with the base area of ​​the mold being 1.327 cm². 2The pressure is set to 3T. The thickness of the active cathode material under 3T pressure can be read on the device, and the powder density of the active cathode material is ρ=m / v, where v = (S × H), and m is the mass of the active cathode material, S is the base area of ​​the mold, and H is the thickness of the active cathode material after compaction.

[0184] In some embodiments, the powder density of the active cathode material at a pressure of 3T is optionally 2.50g / cm³. 3 , 2.51g / cm³ 3 , 2.52g / cm³ 3 , 2.53g / cm³ 3 , 2.54g / cm³ 3 , 2.55g / cm³ 3 , 2.56g / cm³ 3 , 2.57g / cm³ 3 , 2.58g / cm³ 3 , 2.59g / cm³ 3 , 2.60g / cm² 3 , 2.61g / cm³ 3 , 2.62g / cm³ 3 , 2.63g / cm³ 3 , 2.64g / cm³ 3 , 2.65g / cm³ 3 , 2.66g / cm³ 3 , 2.67g / cm³ 3 , 2.68g / cm³ 3 , 2.69g / cm³3 , 2.70g / cm³ 3 or can be a numerical range between any two values.

[0185] Although the area fraction of particles with a particle size greater than or equal to 1.5 µm in the active cathode material is small, the active cathode material can still achieve a high pressing density under the influence of external forces due to the high degree of graphitization, thus providing a material basis for improving the pressing density of the electrode foil and for the production of lithium-ion secondary batteries with high energy density.

[0186] In some embodiments, the powder density of the active cathode material is provided for at a pressure of 3T to be 2.52g / cm³. 3 up to 2.68g / cm³ 3 amounts.

[0187] In some embodiments, the powder bulk density in the active cathode material is provided to be 0.70 g / cm³. 3 -1.50 g / cm² 3is and optionally 0.70 g / cm² 3 -1.20 g / cm² 3 can amount to.

[0188] The powder bulk density can be measured using all methods known in engineering.

[0189] For example, the electronic balance is switched on, an Erlenmeyer flask is first placed on the balance as a base, and then the balance is zeroed; a vibrating graduated cylinder is taken and placed on the Erlenmeyer flask to weigh it and the weight of the graduated cylinder is recorded; the sample bag is opened and the sample is stirred 3-5 times with a clean sample spoon to mix it thoroughly, and then the sample is transferred evenly into the graduated cylinder; any adhering powder is wiped from the surface of the graduated cylinder with dust-free paper, which is then placed into a zeroed Erlenmeyer flask and weighed;Seal the opening of the measuring cylinder with a sealing film and insert the vibrating measuring cylinder into the appropriate rubber ring of the instrument to ensure that the vibrating measuring cylinder is firmly seated against the rubber ring and perpendicular to the surface of the instrument; set the vibration frequency to 250 times / min on the device and the number of vibrations to 5000, press the button, during which it will vibrate for 20 minutes; remove the TD tube, illuminate the surface of the measuring cylinder with a flashlight, visually read the highest scale value V1 and the lowest scale value V2 and determine the average value V of the two; subtract the mass m0 of the measuring cylinder from the total mass m1 of the measuring cylinder and the sample to obtain the powder mass m, where the bulk density of the sample is given by the density formula ρ = m / v.

[0190] In some embodiments, the powder bulk density of the active cathode material is optionally set to 0.70 g / cm³. 3 , 0.75g / cm² 3 , 0.80g / cm² 3 , 0.85g / cm³ 3 , 0.90g / cm² 3 , 0.95g / cm² 3 , 1.00g / cm² 3 , 1.05g / cm³ 3 , 1.10g / cm² 3 , 1.15g / cm³ 3 , 1.20g / cm² 3 , 1.25g / cm³ 3 , 1.30g / cm² 3 , 1.35g / cm³ 3 , 1.40g / cm² 3 , 1.45g / cm³ 3 , 1.50g / cm² 3 or can be a numerical range between any two values.

[0191] The active cathode material in the embodiment of the present application has a limited effective gradation that forms spontaneously and a relatively low bulk density. However, due to the high degree of graphitization of the cathode film layer, it can easily slip under the influence of external forces, thereby increasing the compaction density.

[0192] In some embodiments, the specific powder resistance of the active cathode material is provided to be 0.5 Ω·cm-30.0 Ω·cm under a pressure of 8 MPa.

[0193] The specific powder resistivity of the active cathode material can be measured using methods and equipment known in the art. For example, reference can be made to GB / T 33822-2017, and a powder resistivity meter (Suzhou Jingge, model ST2722) can be used for the measurement. Specifically, a certain quantity of the active cathode material (e.g., 1 g) is weighed and placed in the feed chamber of the powder resistivity meter, and a pressure of 8 MPa is applied to test the on-resistance and reverse resistance of the active cathode material. The average of these two values ​​is used as the powder resistivity of the active cathode material.

[0194] In some embodiments, it is provided that the specific powder resistance of the active cathode material under a pressure of 8 MPa can optionally be 0.5 Ω·cm, 1 Ω·cm, 2 Ω·cm, 3 Ω·cm, 4 Ω·cm, 5 Ω·cm, 6 Ω·cm, 7 Ω·cm, 8 Ω·cm, 9 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm or a numerical range between any two values.

[0195] The active cathode material has a high degree of graphitization, so that the sp 2 The structure of the surface carbon facilitates the rapid conduction of electrons between the particles, so that the active cathode material has a low specific powder resistance, which has a positive effect on increasing the solid-phase transfer rate of electrons and further improves the kinetic performance of the battery.

[0196] In some embodiments, the specific powder resistance of the active cathode material is provided to be 2.0 Ω·cm-20.0 Ω·cm under a pressure of 8 MPa.

[0197] In some embodiments, the specific discharge capacity of the active cathode material at room temperature and a discharge rate of 1C is 135 mAh / g to 150 mAh / g.

[0198] In the present application, the active cathode material is integrated into a button battery, and its electrical performance is tested using a blue battery tester. At 25 ± 5°C, within the voltage range of 2.0 V to 3.75 V, the battery is charged at 1 C to 3.75 V with a constant current, then paused for 5 minutes. It is then charged to a reverse current of 50 µA with a constant voltage and finally discharged at 1 C to 2.0 V with a constant current. The discharge capacity of the button battery divided by the mass of the active cathode material is assumed to be the specific discharge capacity of the active cathode material at room temperature and a discharge rate of 1 C.

[0199] The preparation and testing process for the button cell battery is as follows: 2.0 g of active cathode material, conductive carbon black, and PVDF are mixed in a mass ratio of 0.9:0.05:0.05, and then an organic solvent, NMP (N-methylpyrrolidone), is added. After thorough mixing and uniform distribution, the mixture is applied with a 150 µm scraper, dried at 100°C for 2 hours, and the cathode foil is pressed at a density of 2.0 g / cm³. 3 - 2.2 g / cm³ 3and preparing with a hole drill into discs with a diameter of 14 mm, then weighing and recording the weight, placing the weighed cathode foil in a vacuum drying chamber (105°C, 1-12 hours, -90 kPa), placing the cathode foil in a glove box after it has dried, and then assembling a battery in the sequence of anode case - nickel foil - lithium disc - separator - cathode foil - cathode case, adding 65-87 µL of electrolyte solution (using a pipette), wherein the electrolyte solution is a mixed solvent of EC (ethylene carbonate) and DMC (1,2-dimethyl carbonate) in a volume ratio of 1:1, and the electrolyte is LiPF6, with the anode placed on top and sealed with a pressure of 650 kg / cm². 2The button battery is inserted into the groove of the sealing machine, and the button battery is removed with insulated tweezers and placed in a dust-free bag, and the glove box is removed and placed in a room with constant temperature for 3 hours to preserve the button battery for testing.

[0200] It is understood that the specific discharge capacity of the active cathode material can also be determined by disassembling the battery, obtaining the cathode foil, assembling it into a button battery according to the method above, and then testing it.

[0201] In some embodiments, the specific discharge capacity of the active cathode material at room temperature and a discharge rate of 1C may optionally be 135mAh / g, 136mAh / g, 137mAh / g, 138mAh / g, 139mAh / g, 140mAh / g, 141mAh / g, 142mAh / g, 143mAh / g, 144mAh / g, 145mAh / g, 146mAh / g, 147mAh / g, 148mAh / g, 149mAh / g, 150mAh / g or a numerical range between any two values.

[0202] The active cathode material exhibits a high specific discharge capacity at a 1C rate, indicating that it has good charging and discharging capabilities and positively impacts the improvement of the battery's kinetic performance.

[0203] In some embodiments, it is provided that the proportion of the discharge capacity of the active cathode material during a discharge to 3.2 V is η≥85%, where η is defined as follows: at room temperature, a button battery containing the active cathode material is charged and discharged twice at a rate of 0.1 C by constant current in the voltage range of 2.0 V to 3.75 V, and then once at a rate of 1 C by constant current, wherein, during a charge and discharge test at a rate of 1 C, the capacity value extracted at 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 recorded as C2, where η=C1 / C2, wherein the charging process includes charging at a constant voltage of 3.75 V, where the reverse current at the constant voltage is 50 µA.

[0204] The η-value of the active cathode material can be measured using methods and equipment known in engineering. As an example, a button battery is first prepared according to the procedure described above, and its electrical performance is tested using a blue electrical tester. Specifically, the button battery is charged and discharged twice at a constant current rate of 0.1 C in the voltage range of 2.0 V to 3.75 V. After charging at a constant current up to the reverse voltage, it is charged at a constant voltage to a current of 50 µA and then charged and discharged once at a constant current rate of 1 C. During the 1 C charge and discharge test, the capacity value for a discharge from 3.75 V to 3.2 V is recorded as C1, and the capacity value for a discharge from 3.75 V to 2.0 V is recorded as C2, where η = C1 / C2.

[0205] In some embodiments, it is provided that η can be selected as 85%, 86%, 87%, 88%, 88.1%, 89%, 90%, 90.1%, 91%, 92%, 92.2%, 93%, 94%, 94.1%, 94.5%, 95%, 95.1% or a numerical range between any two values.

[0206] In some embodiments, the proportion of the discharge capacity η of the active cathode material in the newly manufactured lithium-ion secondary battery is ≥ 88% when discharged to 3.2 V. After the newly manufactured lithium-ion secondary battery has been charged and discharged for a period of time at a rate of 0.1 C by constant current in the voltage range of 2.0 V to 3.75 V, the proportion of the discharge capacity η of the active cathode material can be maintained at ≥ 85% when discharged to 3.2 V.

[0207] The high proportion of the discharge capacity of the active cathode material used in the lithium-ion secondary battery of the embodiment of the present application when discharged to 3.2 V indicates that the active cathode material exhibits good kinetic performance. Simultaneously, a high η value indicates that the lithium-ion secondary battery containing the active cathode material still maintains a high voltage when discharged to a low state of charge (SOC), which is conducive to maintaining good performance.

[0208] In some embodiments, it is provided that in the discharge curve of the button battery containing the active cathode material, a discharge platform in the voltage range of 2.5 V to 2.9 V is present at 0.1 C.

[0209] The discharge platform typically refers to a range in which the voltage is relatively stable during the charging and discharging process of the battery. As the battery discharges, current flows out, and the battery voltage initially drops, but then reaches a relatively stable range where the voltage changes only slightly; this stable voltage range is called the discharge platform.

[0210] A button battery can be manufactured by disassembling the cathode foil of a lithium-ion secondary battery and combining it with lithium metal. Assembly and manufacturing can also be carried out according to the method described above. In the present application, the active cathode material is incorporated into a button battery, and its electrical performance is tested using a blue battery tester. Within the voltage range of 2.0 V to 3.75 V, it is charged at 0.1 C to 3.75 V with a constant current, then paused for 5 minutes, then charged to a reverse current of 50 µA with a constant voltage, and finally discharged at 0.1 C to 2.0 V with a constant current.

[0211] The discharge curve shows that the standard charge and discharge platform voltage of lithium-containing transition metal phosphate is typically between 3.2 V and 3.65 V. The button cell battery containing the active cathode material in the embodiments of the present application has a new charge and discharge platform in the voltage range of 2.5 V to 2.9 V, which has a positive effect on the battery's discharge range and improves its energy density. At the same time, this also confirms the assumption that the active cathode material of the embodiment of the present application contains a fast ion conductor.

[0212] In some embodiments, it is provided that the mass content of the conductive medium is 0 to 1.5% relative to the total mass of the cathode film layer.

[0213] In some embodiments, it is provided that, based on the total mass of the cathode film layer, the mass content of the conductive medium can be selected as 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a numerical range between any two values.

[0214] In some embodiments, the conductive medium is provided to comprise at least one of superconducting carbon, acetylene carbon black, carbon black, Ketjen carbon black, carbon dot, carbon nanotube, graphene and carbon nanofiber.

[0215] The carbon layer of the active cathode material has a high degree of graphitization, which gives the active cathode material good conductivity for electrons, reduces or even eliminates the need for conductive media in the cathode film layer, and further increases the charge capacity of the active cathode material and improves the energy density of the lithium-ion secondary battery.

[0216] In some embodiments, it is provided that, based on the total mass of the cathode film layer, the mass content of the conductive medium is 0.

[0217] The active cathode material has an extremely high conductivity for electrons, so that a conductive agent does not even need to be added to the cathode film layer, which has a beneficial effect on further increasing the charge quantity of the active cathode material and improving the energy density of the lithium-ion secondary battery.

[0218] In some embodiments, the cathode film layer also comprises a binder, and the mass fraction of the active cathode material, based on the total mass of the cathode film layer, is 95.5% to 99.5%, or alternatively 96.5% to 99.5%; wherein the mass fraction of the binder is 0.5% to 3%.

[0219] In some formulations, the binder is provided for to comprise 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.

[0220] In some embodiments, it is provided that, based on the total mass of the cathode film layer, the mass content of the active cathode material can be selected as 95.5%, 96%, 96.5%, 97%, 98%, 99%, 99.5% or a numerical range between any two values.

[0221] In some embodiments, it is provided that, based on the total mass of the cathode film layer, the mass content of the binder can be selected as 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a numerical range between any two values.

[0222] In some embodiments, the one-sided areal density of the cathode film layer is 300 mg / 1540 mm². 2 up to 450 mg / 1540 mm 2 amounts.

[0223] In the present application, the areal density of the cathode film layer on one side has a well-known meaning in the art and can be tested using methods known in the art. For example, a cathode foil coated and densified on one side is taken (if it is a double-sided cathode foil, the cathode film layer on one side can be wiped off first), which is punched into small discs with an area of ​​S1, the weight of which is weighed and recorded as M1. Then the cathode film layer of the weighed cathode foil is wiped off, and the weight of the current 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 the average value calculated as the test result.

[0224] In some embodiments, the one-sided areal density of the cathode film layer is specified as 300 mg / 1540 mm². 2 , 310 mg / 1540 mm 2 , 320 mg / 1540 mm 2 , 330 mg / 1540 mm 2 , 340 mg / 1540 mm 2 , 350 mg / 1540 mm 2 , 360 mg / 1540 mm 2 , 370 mg / 1540 mm 2 , 380 mg / 1540 mm 2 , 390 mg / 1540 mm 2 , 400 mg / 1540 mm 2 , 410 mg / 1540 mm 2 , 420 mg / 1540 mm 2 , 430 mg / 1540 mm 2 , 440 mg / 1540 mm 2 , 450 mg / 1540 mm 2 or a numerical range between any two values ​​can be selected.

[0225] A cathode film layer with an areal density within the aforementioned range can help to improve the energy density of lithium-ion secondary batteries.

[0226] In some embodiments, the pressure density of the cathode film layer is specified as 2.51 g / cm³.3 up to 2.73 g / cm³ 3 is the value when the lithium-ion secondary battery is in a completely discharged state.

[0227] In some embodiments, the pressure density of the cathode film layer is provided for to be 2.55 g / cm³. 3 up to 2.70g / cm² 3 is the value when the lithium-ion secondary battery is in a completely discharged state.

[0228] In the present application, the fully discharged state refers to the state in which the battery is placed in an oven environment at 25°C and left for 2 hours, maintaining the battery temperature at 25°C, and the battery is discharged to 2.5 V with a constant current at 1 / 3 C and then discharged to 2.0 V with a constant current at 0.1 C.

[0229] The density of the cathode film layer can be tested using established methods. For example, the battery is placed in a 25°C oven environment 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, after which the battery is disassembled to obtain the cathode film.The remaining electrolyte solution is treated with dimethyl carbonate solvent, the electrode is dried and cut into small discs with an area of ​​S, whose mass is W1, and the thickness T1 of the cathode foil is measured with a micrometer, then the cathode film layer is wiped from the weighed electrode foil, the mass of the current collector being weighed and recorded as W2, and a micrometer is used to measure the thickness of the current collector T2, and then the compression density of the cathode film layer is PD = (W1 - W2) / [(T1 - T2) × S].

[0230] In some embodiments, it is provided that in the fully discharged state the density of the cathode film layer of the lithium-ion secondary battery is 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 / cm³3 , 2.61 g / cm³ 3 , 2.62 g / cm³ 3 , 2.63 g / cm³ 3 , 2.64 g / cm³ 3 , 2.65 g / cm³ 3 , 2.66 g / cm³ 3 , 2.67 g / cm³ 3 , 2.68 g / cm³ 3 , 2.69 g / cm³ 3 , 2.70 g / cm³ 3 , 2.71 g / cm³ 3 , 2.72 g / cm³ 3 , 2.73 g / cm³ 3 or a numerical range between any two values ​​can be selected.

[0231] In some embodiments, it is provided that after the compaction process the compression density of the cathode film layer is 2.63 g / cm³. 3 up to 2.85 g / cm³ 3 amounts.

[0232] In some embodiments, it is provided that after the compaction process the compression density of the cathode film layer of the lithium-ion secondary battery is 2.63 g / cm³. 3 , 2.64g / cm³ 3 , 2.65 g / cm³ 3 , 2.66 g / cm³ 3 , 2.67g / cm³ 3 , 2.68 g / cm³ 3 , 2.69 g / cm³ 3 , 2.70g / cm³ 3 , 2.71g / cm³3 , 2.72g / cm³ 3 , 2.73g / cm³ 3 , 2.74g / cm³ 3 , 2.75g / cm³ 3 , 2.76g / cm³ 3 , 2.77 g / cm³ 3 , 2.78 g / cm³ 3 , 2.79 g / cm³ 3 , 2.80g / cm² 3 , 2.81g / cm³ 3 , 2.82g / cm³ 3 , 2.83g / cm³ 3 , 2.84g / cm³ 3 , 2.85g / cm³ 3 or a numerical range between any two values ​​can be selected.

[0233] In the present application, the term "densification" refers to the densification of the cathode film layer by mechanical pressure during the battery assembly process in order to improve its density and conductivity.

[0234] In some embodiments, it is provided that after the forming process the compression density of the cathode film layer is 2.53 g / cm³. 3 up to 2.73g / cm³ 3 amounts.

[0235] In some embodiments, it is provided that after the formation process the compression density of the cathode film layer of the lithium-ion secondary battery is 2.53 g / cm³. 3 , 2.54g / cm³ 3 , 2.55 g / cm³ 3 , 2.56 g / cm³ 3 , 2.57g / cm³ 3 , 2.58 g / cm³ 3 , 2.59 g / cm³ 3 , 2.60g / cm² 3 , 2.61g / cm³ 3 , 2.62g / cm³ 3 , 2.63g / cm³ 3 , 2.64g / cm³ 3 , 2.65g / cm³ 3 , 2.66g / cm³ 3 , 2.67 g / cm³ 3 , 2.68 g / cm³ 3 , 2.69 g / cm³ 3 , 2.70g / cm³ 3 , 2.71g / cm³ 3 , 2.72g / cm³ 3 , 2.73g / cm³ 3 or a numerical range between any two values ​​can be selected.

[0236] In the present application, the formation refers to the formation of a stable solid electrolyte interface (SEI film) and an electrode structure through electrochemical reactions during the first charging and discharging process of the battery.

[0237] It is understandable that, due to the rebound of the electrode foil during the cycling process, 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.

[0238] The pressure density of the cathode film layer is within the range mentioned above, which has a positive effect on improving the energy density of the lithium-ion secondary battery.

[0239] In some embodiments, the pressure density of the cathode film layer is specified as 2.51 g / cm³. 3 up to 2.73 g / cm³ 3is, where the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10% to 22%.

[0240] In some embodiments, the pressure density of the cathode film layer is specified as 2.55 g / cm³. 3 up to 2.70 g / cm³ 3 is, wherein the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10% to 20%.

[0241] In some embodiments, it is provided that the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil can be selected as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22% or a numerical range between any two values.

[0242] The porosity of the cathode film layer can be tested in the cross-sectional area along the thickness direction of the electrode foil as follows. The scanning electron microscope (SEM) image of the cross-sectional area of ​​the cathode film layer, obtained as described above, in the thickness direction of the electrode foil, is imported into the ImageJ software. A straight line tool is selected, a straight line is used to mark the scale length in the image, and by clicking "Analyze Set Scale," the scale parameters in the software are set according to the scale length in the image.The rectangle tool is selected, the portion of the image outside the scale range is selected, "Image Duplicate" is used to copy the selected area, and "Image Type 8 bit" is used to adjust the image format. "Analyze Set Measurements" is selected, and the following five options are chosen: "Area," "Mean gray value," "Area Fraction," "Limit to threshold," and "Feret's diameter," with "Decimal places" set to 3. Then, "Image" - "Adjust" - "Threshold" is selected. In the "Threshold" field, 0 and 100 are set consecutively, and then the Analyze-Measure function is used to export the pore data from the electron microscope image of this section.Exporting is done by using "Image" - "Overlay" - "Flatten" to obtain the pore image; clicking "Apply" in "Threshold", then clicking "Analyze" - "Analyze Particles", and by selecting the four columns on the left, the pore statistics can be obtained.

[0243] It is understandable that in the embodiments of the present application, the "pore" in the cross-sectional area of ​​the cathode film layer is detected by using image color differences and threshold values. This "pore" is not the pore data obtained in the exhaust gas test, but is primarily used to characterize the cross-sectional area between particles in the cross-sectional area of ​​the cathode film layer. This method is superior to the blow-out method because the porosity obtained with the blow-out method is related to the pores between the particles and the holes in the carbon layer with which the surface of the lithium iron phosphate particles is coated, and thus cannot objectively reflect the pores between the particles.

[0244] As in Fig.As shown in Figure 8, a lower porosity in the cross-sectional area of ​​the cathode film layer tested using this method means, on the one hand, that the gradation of large, medium, and small particles in the cathode film layer is better and the pressing density is higher, and on the other hand, low porosity at the same gradation and roller pressure means that the particles slide easily from one another, thereby reducing the risk of overpressure and stress concentration in the film layer and further reducing the probability of cathode film demolding during long cycles, which has a positive effect on improving the long-cycle performance of the battery.

[0245] In some embodiments, the cathode foil comprises a lower coating, the lower coating being arranged between the cathode film layer and the current collector; the lower coating comprises carbon-based particles and the distribution density of the carbon-based particles with a particle size of over 100 nm in the lower coating is less than or equal to 10 pcs / 10 µm.

[0246] Carbon-based particles are particles with carbon as their main component, which include, but are not limited to, conductive carbon, soot, and the like.

[0247] The lower coating contributes to improving the conductivity and bonding strength between the cathode film layer and the current collector, reducing demolding of the cathode film layer from the current collector during the cycle, and improving the dynamic performance of the battery. For example, in the high-density electrode foil of the embodiment of the present application, if the density of the cathode foil in the fully discharged state is greater than or equal to 2.4 g / cm³ 3The current collector is easily damaged during the high-pressure compaction process of the electrode foil, with large particles tending to form depressions on the current collector, and controlling the distribution density of carbon-based particles with a particle size of over 100 nm in the lower coating to ≤ 10 particles / 10 µm helps to reduce the probability of damage to the current collector in the high-voltage-density electrode foil and to further improve the limiting compaction density of the cathode foil.

[0248] The distribution density of carbon-based particles with a particle size greater than 100 nm in the lower coating can be controlled using the above method, wherein the cathode film layer is cut with an argon ion beam along the thickness direction of the electrode foil and a scanning electron microscope image or a microscopic image is taken, wherein the size of the carbon particles in the lower coating is determined using a statistical method, and wherein the number of carbon-based particles with a particle size greater than 100 nm per 10 µm in the lower coating is counted at least 5 times and the average value is calculated.

[0249] The lower coating in embodiments of the present application can be realized by any known manufacturing process, such as pre-sieving or centrifugation in the manufacturing process of carbon-based particles to remove large particles of the carbon-based material, so that the carbon-based particles added in the manufacturing process of the lower coating have a D V50 from 20 to 60 nm and a D V90 of less than or equal to 70 nm, and the carbon-based material is mixed with the binder, stirred and applied to the current collector to obtain the bottom coating.

[0250] In some embodiments, the density of the cathode foil in the fully charged state is greater than or equal to 2.4 g / cm³. 3 , wherein the one-sided thickness of the lower coating is 1 µm to 4 µm.

[0251] In some embodiments, the density of the cathode foil in the fully discharged state is greater than or equal to 2.5 g / cm³. 3 , wherein the one-sided thickness of the lower coating is 2 µm to 4 µm.

[0252] As the electrode film's density increases, the extrusion effect of large lithium phosphate particles (e.g., particle size greater than 1 µm) in the cathode film layer on the lower coating becomes more significant. This can lead to stress concentration at the points where large particles are present, potentially even penetrating the lower coating and damaging the current collector. Increasing the thickness of the lower coating helps to mitigate the stress concentration phenomenon in the electrode film and further increase the electrode film's maximum density.

[0253] The thickness of the bottom coating on one side can be checked as follows. As in the method above, the cathode film layer is sliced ​​along the thickness direction of the electrode foil by an argon ion beam, and a scanning electron microscope image is acquired. Along the length of the electrode foil, the thickness of the bottom coating on one side is measured at points spaced 1 µm apart, and an average value is calculated after measuring the thickness at 10 points. It should be noted that abnormal locations must be avoided when taking measurements.The area in the lower coating with a thickness of less than 50 nm and a thickness of more than 4 µm; these abnormal spots are mainly due to the extreme thickness variations of individual areas caused by abnormal stress concentrations and extrusion during the compaction of the electrode foil, and are not statistically significant.

[0254] In some embodiments, the thickness of the cathode current collector is provided to be less than or equal to 17 µm and can be selected between 13 µm and 15 µm.

[0255] In some embodiments, the thickness of the cathode current collector is provided to be 13 µm, 14 µm, 15 µm, 16 µm, 17 µm or a numerical range between any two values.

[0256] In some embodiments, the cathode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector can comprise a base layer of polymer material and a metal layer formed on at least one surface of the polymer base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, or the like) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), or the like).

[0257] In some embodiments of the lithium-ion secondary battery, the anode foil comprises an anode current collector and an anode film layer arranged on at least one side of the anode current collector, and the one-sided areal density of the anode film layer is 140 mg / 1540 mm². 2 up to 221 mg / 1540 mm 2 ; and / or the density of the anode film layer is 1.40 g / cm³ 3 up to 1.75 g / cm³ 3 .

[0258] The one-sided areal density and compression density of the anode film layer can be tested using a similar method to that described above for the cathode film layer.

[0259] The areal density and compression density of the anode film layer are within the aforementioned ranges, which has a positive effect on improving the energy density of the lithium-ion secondary battery.

[0260] In some embodiments, the anode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector can comprise a base layer of polymer material and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, or the like) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), or the like).

[0261] In some embodiments, the anode film layer comprises an active anode material. The active anode material can be any battery active anode material known in the art. For example, the active anode material can comprise at least one of the following materials: synthetic graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, silicon-oxygen compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy.However, the present application is not limited to these materials, and other conventional materials suitable for use as active battery anode materials may also be used. These active anode materials may be used alone or in combination with one or more of them.

[0262] In some embodiments, the anode film layer optionally includes a binder. The binder can be selected from at least one of the following: 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).

[0263] In some embodiments, the anode film layer optionally includes a conductive material. The conductive material can be selected from at least one of the following: superconducting carbon, carbon black, carbon black, Ketjen carbon black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0264] In some embodiments, the anode film layer may optionally include other additives, such as a thickening agent (e.g. sodium carboxymethylcellulose (CMC-Na)).

[0265] In some embodiments, it is provided that the anode foil can be produced by the following method: Dispersing the above-mentioned components for the production of the anode foil, such as the active anode material, the conductive agent, the binder and all other components in a solvent (such as deionized water) to form an anode slurry; the anode slurry is applied to the anode current collector and after processes such as drying and compaction, the anode foil can be obtained.

[0266] In some embodiments, the lithium-ion secondary battery comprises an electrolyte. The electrolyte conducts ions between the cathode foil and the anode foil. For the present application, there are no specific restrictions regarding the type of electrolyte, which can be selected as required. For example, the electrolyte can be liquid, gel-like, or completely solid.

[0267] In some embodiments, the electrolyte takes the form of an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0268] In some embodiments, it is provided that the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorobisoxalatophosphate and lithium tetrafluorooxalate phosphate.

[0269] In some embodiments, it is provided that the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0270] In some embodiments, the electrolyte solution may optionally include an additive. The additive may, for example, include an additive that forms the anode film and an additive that forms the cathode film, and may also include an additive that can improve certain battery properties, such as an additive that improves the battery's overcharge performance, an additive that improves the battery's performance at high or low temperatures, or the like.

[0271] In some embodiments, the lithium-ion secondary battery also includes a separating film. The present application does not impose any specific restrictions regarding the type of insulating membrane, and any known separating film with a porous structure and good chemical and mechanical stability can be selected.

[0272] In some embodiments, the separating film material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separating film can be a single-layer membrane or a multi-layer composite membrane without any particular restriction. If the separating film is a multi-layer composite membrane, the materials of the individual layers can be the same or different without any particular restriction.

[0273] In some embodiments, it is provided that an electrode arrangement can be produced from the cathode foil, the anode foil and the separating film by a winding process or a lamination process.

[0274] In some embodiments, the lithium-ion secondary battery may include an outer packaging. The outer packaging can be used to package the electrode assembly and the electrolyte.

[0275] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer packaging of the secondary battery can also be a soft packaging, such as a bag-like soft packaging. The material of the soft packaging can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate, among others.

[0276] A second aspect of the present application provides a battery device comprising a lithium-ion secondary battery provided by the first aspect of the present application, and the battery device comprises at least one of a battery module, a battery pack and an energy storage battery.

[0277] A third aspect of the present application relates to a power-consuming device comprising the lithium-ion secondary battery described in the first aspect of the present application.

[0278] An unclaimed aspect of the present application relates to a process 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 carbon source comprises polyethylene glycol; wherein the iron source comprises divalent iron; wherein, after milling in a solvent, a mixed slurry is obtained; wherein the volume distribution particle size D V50 the particle size in the mixed slurry is 1 µm to 4 µm; wherein the mixed slurry is dried and then a precursor powder is obtained; wherein the precursor powder is sintered to obtain the active cathode material; wherein the sintering comprises at least two stages of sintering at constant temperature, wherein the sintering temperature of a high-temperature stage is 750°C to 800°C.

[0279] The manufacturing process provided by embodiments of the present application adjusts the content of large particles in the active cathode material by controlling the sintering temperature and the particle size of the precursor. Simultaneously, the degree of graphitization of the active cathode material is further improved by using polyethylene glycol as a carbon source in combination with sintering temperature control and catalytic reduction with divalent iron. This provides a material basis for the production of a cathode film layer in which, in a cross-sectional area along the thickness direction of the electrode foil, the area fraction of particles with a particle size greater than or equal to 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%, and the median degree of graphitization C 50 greater than or equal to 0.95 and less than or equal to 1.20.

[0280] In some embodiments, it is provided that the volume distribution particle size D V50 The particle size in the mixed slurry is 1 µm to 4 µm.

[0281] In the present application, the term “Dv” refers to 50 “to the particle size that is present when the percentage of the cumulative particle size distribution of the sample volume reaches 50%, measured using the Malvern laser scattering method;

[0282] In some embodiments, it is provided that the volume distribution particle size D V50 The particle size in the mixed slurry can be chosen as 1 µm, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4.0 µm or a numerical range between any two values.

[0283] The volume distribution particle size D V50The particles in the mixed slurry within the above range can, on the one hand, increase the activity of the particles to a certain degree and, at the same temperature, partially generate particles of the active cathode material with a particle size of 1 µm to 2 µm, thereby improving the pressing density of the electrode foil and the energy density of the battery; on the other hand, this can improve the catalytic decomposition efficiency of the iron element on the surface of the crystal nuclei towards the carbon source, improve the coating quality of the carbon source, improve the uniformity and graphitization degree of the carbon coating layer, and further improve the pressing density of the electrode foil and the energy density of the battery.

[0284] The area fraction of the large particles on the surface of the cathode film layer produced by the active cathode material manufactured using this process is small, and the active cathode material has a high degree of graphitization, which allows the pressing density of the electrode foil to be slightly increased by slippage between the particles, which has a positive effect on improving the energy density of the battery and also improves the kinetic performance of the battery.

[0285] In some embodiments, the iron source is provided to be divalent iron, which can be selected from one or more of iron(II) oxalate, iron(II) carbonate and iron(II) nitrate.

[0286] In some embodiments, the lithium source is provided to comprise one or more of lithium dihydrogen phosphate, lithium phosphate, lithium carbonate and lithium acetate.

[0287] In some embodiments, the carbon source is provided to comprise a polymer carbon source which can be selected from one or more of polyethylene glycol and polyvinyl alcohol.

[0288] In some embodiments, the phosphorus source is provided to comprise one or more of lithium dihydrogen phosphate, phosphoric acid and ammonium dihydrogen phosphate.

[0289] In some embodiments, it is provided that the lithium source and the phosphorus source can be the same substance.

[0290] In some embodiments, the iron source comprises iron(II) oxalate, the lithium source and the phosphorus source comprise lithium dihydrogen phosphate, and the carbon source comprises polyethylene glycol.

[0291] During the sintering process, the divalent iron source preferentially decomposes, producing a large amount of iron(II) oxide, which serves as a nucleation site for the formation of nanocrystal nuclei for lithium-containing transition metal phosphate. Simultaneously, the polymer carbon source exhibits a relatively low decomposition temperature, and the iron element on the surface of the crystal nuclei further catalyzes the decomposition of the carbon source. This results in a carbon coating layer on the surface of the active cathode material exhibiting a relatively high degree of graphitization at a lower sintering temperature, reducing the resistivity of the active cathode material and improving the density and uniformity of the carbon coating layer on the surface of the lithium-containing transition metal phosphate.Furthermore, the uniform deposition of carbon on the surface of the lithium-containing transition metal phosphate further hinders the growth of the crystal grains of the lithium-containing transition metal phosphate and reduces the likelihood that the particles of the active cathode material will grow into large particles with a particle size of over 1.5 µm.

[0292] In some embodiments, it is provided that the particle size D 10 of iron(II) oxalate greater than or equal to 3 µm, the particle size D 50 50 µm to 80 µm and the particle size D 90 less than or equal to 150 µm.

[0293] In the present application, the terms “D 10 ", „D 50 " and "D 90"each the particle sizes that are present when the percentage of the cumulative particle size distribution of the sample volume reaches 10%, 50% and 90%, as measured by the Malvern laser scattering method.

[0294] By controlling the particle size D 10 By reducing the particle size of iron(II) oxalate to greater than or equal to 3 µm, the proportion of small iron(II) oxalate particles can be reduced and the reaction activity during the milling process can be controlled. By controlling the particle size D 50 and D 90 The iron(II) oxalate allows the raw materials to be mixed uniformly during the grinding process, resulting in a mixed slurry with consistent components and uniform particle sizes, thus improving the particle size consistency of the produced lithium-containing transition metal phosphate.

[0295] In some embodiments, it is provided that the mass content of trivalent iron element is less than or equal to 0.08%.

[0296] In some embodiments, it is provided that the mass content of the trivalent iron element can be selected as 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08% or a numerical range between any two values.

[0297] Controlling the mass fraction of trivalent iron improves the uniformity and consistency of the carbon coating layer. Excessive trivalent iron content initially depletes the carbon source, leading to inconsistencies in the quality and thickness of the enveloping carbon layer between the particles. This uneven thickness impairs the compaction between the particles, while a local carbon deficiency reduces the overlap of the conductive network between the particles, hindering effective improvement of the electrode foil's density and dynamics.

[0298] In some embodiments, the atomic molar ratio of the lithium element and the iron element in the lithium source and the iron source is 1.0 : 1.0 to 1.05 : 1.0.

[0299] In some embodiments, the atomic molar ratio of the lithium element and the iron element in the lithium source and the iron source can be selected as 1.0:1.0, 1.01:1.0, 1.02:1.0, 1.03:1.0, 1.04:1.0, 1.05:1.0, or a numerical range between any two values. In some embodiments, the carbon source comprises a polymer carbon source, which can be selected from one or more polyethylene glycols and polyvinyl alcohols.

[0300] In some embodiments, it is provided that, based on the total mass of the cathode film layer, the mass content of the carbon source is 1% to 4%.

[0301] The polymer carbon source has a relatively low decomposition temperature and graphitization temperature, so the carbon coating layer on the surface of the active cathode material can be decomposed at a relatively low sintering temperature to form a carbon layer that hinders the growth and sintering of the crystal grains of lithium-containing transition metal phosphate and has a positive effect on reducing the particle size of the active cathode material particles.

[0302] Nowadays, the polymer carbon source typically has a higher molecular weight or longer molecular chains, which can easily form a stable skeletal structure through crosslinking or orientation during heat treatment, and this order is retained during high-temperature carbonization, which promotes the directed growth of graphite crystals; meanwhile, the interlinking and crosslinking between long chains help to reduce structural defects and the crystal lattice disruption caused by chain breaks during the carbonization process, thereby improving the degree of graphitization.

[0303] The organic molecules in the carbon source decompose at high temperature, releasing carbon atoms. These carbon atoms can cover and fill the tiny gaps or defects on the surface of the active material, thus reducing the surface roughness. The encapsulating layer formed from the polymer carbon source exhibits a high degree of graphitization and a denser carbon structure, which facilitates the optimization of the surface roughness of the active cathode material.

[0304] In some embodiments, it is provided that the weight-average molecular weight of polyethylene glycol is less than 10,000.

[0305] In some embodiments, it is provided that the weight-average molecular weight of polyethylene glycol can be set to 1500, 2000, 3000, 4000, 6000, 8000 or a numerical range between any two values.

[0306] By using polyethylene glycol with a weight-average molecular weight of less than 10,000, the decomposition rate during sintering can be controlled to form a carbon coating layer of a suitable and uniform thickness.

[0307] In some embodiments, the water content of the polyethylene glycol is provided for to be less than or equal to 0.5%.

[0308] If the water content in the polyethylene glycol is high, the water can impair the decomposition process and lead to incomplete or uneven decomposition during sintering. Excessive moisture can also lead to an uneven distribution of the molten polyethylene glycol during the sintering process, which affects the uniformity of the carbon layer and can cause the carbon coating layer to become unstable or detach.

[0309] In some embodiments, it is provided that the water content of polyethylene glycol can be selected between 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% or a numerical range between any two values.

[0310] In some embodiments, the pH value of polyethylene glycol is specified as being between 5 and 7.

[0311] Polyethylene glycol with a pH of 5 to 7 exhibits high stability and is not degraded by excessive acidity during mixing, especially under high-temperature conditions, which can lead to premature decomposition and compromise the quality of the coating layer. If polyethylene glycol is alkaline, it can impair the stability of other components and cause dissolution or oxidation of metal ions, which in turn affects the performance of the final active cathode material.

[0312] In some embodiments, the slurry is provided to also include a titanium source, optionally comprising one or more of titanium dioxide, tetrabutyl titanate, titanium nitrate and titanic acid.

[0313] A titanium source often exhibits lower surface activity, and the inclusion of the titanium source in the slurry can reduce the activity of the lithium-containing transition metal phosphate precursor, inhibit the particle growth of the lithium-containing transition metal phosphate during high-temperature sintering, and form smaller lithium-containing transition metal phosphate particles during the sintering process.

[0314] Titanium acts as a crystal lattice stabilizer, with titanium elements usually in the form of Ti 4+enters the crystal lattice of the lithium-containing transition metal phosphate, and some titanium ions can take the position of iron ions, making the crystal structure more stable and reducing the possibility of a reversal of lithium ions and iron ions, especially at high temperature or during charging and discharging with high current.

[0315] Meanwhile, titanium doping helps to improve the sphericity of the particles and reduce the roughness of the particles, thereby improving the overall structural stability of the material.

[0316] In some embodiments, the sintering process comprises at least two stages of sintering at constant temperature, wherein the sintering temperature of the low-temperature stage is 300°C to 400°C, the heat preservation time is 2 hours to 6 hours, and the sintering temperature of the high-temperature stage is 750°C to 800°C, the heat preservation time is 8 hours to 15 hours.

[0317] In some embodiments, the temperature increase rate from the low-temperature stage to the high-temperature stage is greater than or equal to 5°C / min.

[0318] Using a higher temperature rise rate to quickly heat up to the target temperature promotes uniform particle growth and reduces the presence of particles with a particle size greater than or equal to 1.5 µm.

[0319] In some embodiments, it is provided that lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol and titanium dioxide are uniformly mixed and ground in an organic solution to obtain a mixed raw material.

[0320] Organic solvents can effectively reduce the occurrence of side reactions and improve the purity and consistency of materials. Furthermore, organic solvents exhibit high volatility and are more easily removed during the subsequent drying process. They also do not remain in the material, preventing the formation of air pockets and compromising its compactness and structural stability.

[0321] In some embodiments, it is provided that, based on the total mass of the mixed raw material, the mass fraction of the carbon source in the mixed raw material is 5% to 7%.

[0322] In some embodiments, it is provided that, based on the total mass of the mixed raw material, the mass fraction of the carbon source in the mixed raw material can be selected as 5%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7% or a numerical range between any two values.

[0323] By controlling the mass fraction of the carbon source within the aforementioned range, the material's conductivity can be improved, and the negative effects on the specific capacitance of the cathode foil and the battery's energy density can be reduced. An excessively thick carbon layer not only occupies the effective space of the active material but can also lead to structural instability.

[0324] In some embodiments, the solvent is provided to include water and its mixture.

[0325] In some embodiments, the process of obtaining the mixed raw material, comprising a carbon source, a lithium source, an iron source and a phosphorus source, involves adding the carbon source, the lithium source, the phosphorus source and the iron source to the solvent and mixing and stirring, with a stirring speed of 1400 to 2200 rpm.

[0326] In some embodiments, it is provided that obtaining the precursor powders after drying the mixed slurry includes obtaining the precursor powders after spray drying the mixed slurry.

[0327] In some embodiments, the product is subjected to airflow pulverization to obtain the active cathode material after the precursor has been sintered.

[0328] In some embodiments, the classification frequency during airflow pulverization is 18 Hz to 24 Hz and the pulverization air pressure is 0.45 MPa to 0.65 MPa.

[0329] The classification frequency in airflow pulverization refers to the operating frequency of the classification device during airflow pulverization, which is typically related to classification efficiency and the particle size distribution. A higher classification frequency filters the particles in the airflow more frequently, resulting in larger particles being filtered out and smaller particles remaining. Furthermore, a higher classification frequency can increase the number of particle collisions, causing irregular particles to be struck more forcefully, resulting in smoother particle surfaces and a more spherical shape.

[0330] High air pressure causes the particles to be subjected to a greater impact force and the collisions between the particles to become more intense, thus subjecting the surface of the particles to stronger shocks and abrasion, and large particles can be broken down into smaller particles, and the collisions between the particles become more intense, and the surface can be trimmed more easily, thereby improving the sphericity and surface flatness of the particles.

[0331] However, excessively high classification frequency and pulverizing air pressure cause the agglomerated particles to break down into primary particles, which are then further torn and fractured. This impairs the predetermined particle size distribution and results in an incomplete carbon coating layer. Consequently, there is increased iron dissolution, which negatively impacts particle sliding during roller pressing. Furthermore, it leads to increased contact and reaction between the lithium-containing transition metal phosphate and external factors such as the electrolyte solution, negatively affecting the battery's cycle performance and lifespan. Therefore, it is essential to control the classification frequency and pulverizing air pressure of the airflow pulverization process within an appropriate range.

[0332] A further unclaimed aspect of the present application relates to a method for producing a cathode foil, wherein the method comprises the sequential addition and dry mixing of a binder, a conductive agent and an active cathode material produced by the method in a fourth aspect, the subsequent addition of a solvent and stirring and controlling the viscosity to obtain a supplied slurry; wherein the supplied slurry is transferred to at least one side of the current collector and coated, and then dried and hot pressed to obtain the cathode foil.

[0333] In some embodiments, the stirring process includes a pre-stirring and a main stirring, wherein the stirring speed of the pre-stirring is lower than that of the main stirring, wherein the rotational speed of the pre-stirring is 20 to 30 rpm and the rotational speed of the pre-mixing is 450 to 550 rpm, and wherein the pre-stirring time is 10 to 20 minutes.

[0334] In some embodiments, the hot pressing process comprises at least three hot rolling operations, wherein the hot rolling pressure increases successively, with the hot rolling pressure being 20 tonnes to 50 tonnes, 50 tonnes to 70 tonnes and 70 tonnes to 90 tonnes respectively; wherein the temperature of the hot roll is 40°C to 80°C, wherein the electrode foil is heated before the electrode foil enters the hot roll for the first time for compression, wherein the heating temperature is 40°C to 50°C.

[0335] The active cathode material produced by the above-mentioned hot pressing process in combination with the manufacturing process of the fourth aspect in the embodiments of the present application is advantageous in order to further reduce the porosity of the cut surface of the cathode film layer, to increase the boundary pressing density of the electrode foil and to improve the energy density of the battery.

[0336] Furthermore, the present application also provides for a power-consuming device, wherein the power-consuming device comprises at least one of the secondary batteries, battery modules, or battery packs provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device or as an energy storage unit for the power-consuming device. The power-consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, and the like), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, and the like), electric trains, ships and satellites, energy storage systems, and the like.

[0337] Depending on the usage requirements, a secondary battery, a battery module or a battery pack can be selected as the power-consuming device.

[0338] Fig. Figure 7 shows an example of a power-consuming device. This device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. To meet the power-consuming device's requirements for high performance and energy density of the secondary battery, a battery pack or battery module can be used.

[0339] As another example, the device could be a mobile phone, a tablet computer, a laptop computer, or the like. The device typically needs to be lightweight and thin, and a secondary battery can be used as a power source. Examples of implementation

[0340] The following are exemplary embodiments of the present application. These embodiments are examples and serve only to illustrate the present application; they should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the technical literature or the product instructions must be followed. The reagents and instruments used, without manufacturer information, are exclusively commercially available products. Exemplary embodiment 1(1) Production of active cathode material

[0341] Lithium dihydrogen phosphate, iron(II) oxalate, polyethylene glycol, and titanium dioxide are uniformly mixed and ground in methanol to obtain a mixed raw material. The ratio of lithium dihydrogen phosphate to iron(II) oxalate is such that the molar ratio of lithium to iron is 1.03 : 1.0. The particle size D 10 The diameter of iron(II) oxalate is 6.1 µm, the particle size D 50 is 60.5 µm and the particle size D 90 The particle size is 105.5 µm, and the mass content of the Fe element in the iron(II) oxalate is 30.9% and the mass content of the trivalent iron element is 0.03%.

[0342] The mixed raw material is ground several times in a ball mill and demagnetized to obtain a mixed slurry. The number and duration of grinding are controlled, as is the particle size D. V50 The particle size of the mixed slurry after grinding is 3.0 µm.

[0343] The mixed slurry is spray-dried to obtain a dry precursor powder material, and the dry precursor powder material has a light yellow appearance and a uniform color.

[0344] The precursor powder material is placed in a sintering furnace and heated under a nitrogen atmosphere at a rate of 2°C / min from 25°C to 350°C and held at this temperature for 3 hours. The temperature is then increased at a rate of 5°C / min to a second temperature of 770°C and held at this temperature for 10 hours, followed by cooling.

[0345] The material obtained is crushed by an airflow pulverization process with a classification frequency of 22 Hz and a pulverization pressure of 0.55 MPa to obtain a carbon-coated active cathode material made of lithium iron phosphate.

[0346] The mass content of carbon element in the active cathode material is 1.2%, the median of the sphericity L A50 The median roughness R is 0.719. A50 The coefficient of performance (COP) is 0.939, the concentration of lithium iron antisite defects is 0.62%, and the powder bulk density is 1.04 g / cm³. 3 The powder compaction density at a pressure of 3T is 2.57 g / cm³. 3 The specific powder resistance at a pressure of 8 MPa is 5.58 Ω·cm. The specific discharge capacity at a 1C discharge rate is 141.4 mAh / g; there is a discharge platform in the voltage range of 2.5 V to 2.9 V, and the proportion of the discharge capacity at the 3.2 V discharge platform is 90.52%. (2) Production of the cathode foil:

[0347] 2.2 wt% PVDF, 0.8 wt% conductive carbon black, and 97.0 wt% active cathode material are added sequentially and dry mixed. N-methylpyrrolidone is then added, the mixture is stirred, and the viscosity is adjusted to obtain a supplied slurry. The supplied slurry is transferred and applied to the bottom coating of the current collector aluminum foil. The bottom coating comprises carbon black and PVDF in a mass ratio of 1:1, with a dispersion density of carbon-based particles larger than 100 nm in the bottom coating of ≤ 10 particles / 10 µm, and a thickness of 2 µm. After drying and hot pressing, a cathode film layer with a one-sided areal density of 350 mg / 1540 cm² is obtained. 2 receive.

[0348] The stirring process includes pre-stirring and main stirring, and the stirring speed during pre-stirring is lower than during main stirring, and the rotational speed during pre-stirring is 25 rpm, the rotational speed is 500 rpm, and the duration of pre-stirring is 15 minutes.

[0349] The hot pressing process comprises three hot rolling pressing processes, and the hot rolling pressing pressure increases successively, reaching 35 tons, 55 tons and 75 tons respectively; the temperature of the hot roll being 65°C, with the electrode foil being heated before the electrode foil enters the hot roll for the first time for compaction, the heating temperature being 50°C.

[0350] The electrode foil density is the limiting electrode foil density, and the test procedure for the limiting electrode foil density is as follows: the limiting electrode foil density in this embodiment is 2.68 g / cm³. 3 .

[0351] In the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, 17,707 particles were counted. This results in 79 particles with a particle size between 1.5 µm and 5 µm being present in the cross-sectional area of ​​the cathode film layer, representing 14.58% of the area. There are no particles larger than 5 µm, with the area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm being 19.70%. The median C 50 The graphitization degree of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer is 1.02, C 90 is 1.04, C 10 is 1.0 and the concentration of the C value (C 90 - C 10 ) / C 50 is 0.034.

[0352] The iron dissolution rate of the cathode film layer is 1076 ppm. (3) Production of the anode foil:

[0353] 95.5 wt% active anode material (artificial graphite), 1.0 wt% conductive agent (conductive carbon black), 2.0 wt% binder (styrene-butadiene rubber (SBR)), and 1.5 wt% thickener (sodium carboxymethylcellulose (CMC)) are mixed, augmented with deionized water, stirred, and dispersed to form an anode slurry. The anode slurry is then applied to the surface of both sides of the copper foil. After both sides are coated, it is dried, cold-pressed, cut, and sliced ​​to produce the anode foil. The coated single-sided areal density is 165 mg / 1540 mm². 2 and the density is 1.60 g / cm³ 3 . (4) Production of the release film

[0354] Polypropylene film is used as a separating film. (5) Preparation of the electrolyte solution

[0355] In a glovebox with an argon atmosphere (H2O< 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) / dimethyl carbonate (DMC) are mixed uniformly in a volume ratio of 1:1, the lithium salt LiPF6 is added and dissolved in the organic solvents, the LiPF6 content in the solution is 1 mol / l, and it is stirred uniformly to obtain an electrolyte solution. (6) Battery manufacturing:

[0356] The cathode foil, the separator film and the anode foil are stacked in sequence, and the separator film should be able to separate the cathode from the anode, obtaining a bare battery core by winding, which is placed in an outer packaging, and the electrolyte solution is added, and after packaging, forming, blowing and other processes, a lithium-ion battery is finally obtained.

[0357] The manufacturing processes of embodiments 2 and 3 are basically the same as those of embodiment 1, with the exception that the sintering temperature of the precursor powder material is adjusted. Example 2

[0358] The precursor powder material is placed in a sintering furnace and heated under a nitrogen atmosphere at a rate of 2°C / min from 25°C to 350°C and held at this temperature for 3 hours. The temperature is then increased at a rate of 5°C / min to a second temperature of 755°C and held at this temperature for 10 hours, followed by cooling. Example 3

[0359] The precursor powder material is placed in a sintering furnace and heated under a nitrogen atmosphere at a rate of 2°C / min from 25°C to 350°C and held at this temperature for 3 hours. The temperature is then increased at a rate of 5°C / min to a second temperature of 790°C and held at this temperature for 10 hours, followed by cooling.

[0360] The manufacturing processes of embodiments 4 and 5 are essentially the same as those of embodiment 1, with the exception that the particle size D V50 the mixed slurry is adjusted after grinding. Example 4

[0361] The mixed raw material is ground several times in a ball mill and demagnetized to obtain a mixed slurry. The number and duration of grinding are controlled, as is the particle size D. V50 The particle size of the mixed slurry after grinding is 4.0 µm. Example 5

[0362] The mixed raw material is ground several times in a ball mill and demagnetized to obtain a mixed slurry. The number and duration of grinding are controlled, as is the particle size D. V50 The particle size of the mixed slurry after grinding is 1.5 µm. Example 6

[0363] The manufacturing process of embodiment 6 is basically the same as that of embodiment 1, with the exception that no conductive carbon black is added during the manufacture of the cathode foil:

[0364] 97.8 wt% active cathode material and 2.2 wt% PVDF are mixed, then N-methylpyrrolidone is added, stirred and dispersed to produce a cathode slurry.

[0365] The manufacturing processes of embodiments 7 and 8 are essentially the same as those of embodiment 1, except that the carbon source is adapted in the process for producing an active cathode material. Example 7

[0366] Lithium dihydrogen phosphate, iron(II) oxalate, a mixture of polyethylene glycol and glucose, and titanium dioxide are mixed uniformly in methanol and ground. The ratio of lithium dihydrogen phosphate to iron(II) oxalate is such that the molar ratio of lithium to iron is 1.03 : 1.0. The mass ratio of polyethylene glycol to glucose is 3:1. Example 8

[0367] Lithium dihydrogen phosphate, iron(II) oxalate, a mixture of polyethylene glycol and glucose, and titanium dioxide are mixed uniformly in methanol and ground. The ratio of lithium dihydrogen phosphate to iron(II) oxalate is such that the molar ratio of lithium to iron is 1.03 : 1.0. The mass ratio of polyethylene glycol to glucose is 1:3.

[0368] The manufacturing process of Comparative Example 1 is basically the same as the manufacturing process of Exemplary Example 1, except that the carbon source is replaced by glucose and the sintering temperature of the precursor powder material is adjusted. Comparative example 1

[0369] Lithium dihydrogen phosphate, iron(II) oxalate, glucose, and titanium dioxide are uniformly mixed and milled in methanol to obtain a mixed raw material. The precursor powder is placed in a sintering furnace and heated under a nitrogen atmosphere at a rate of 2°C / min from 25°C to 350°C, and held at this temperature for 3 hours. The temperature is then increased at a rate of 5°C / min to a second temperature of 803°C and held at this temperature for 10 hours, followed by cooling.

[0370] The manufacturing process of comparative example 2 is basically the same as that of embodiment 1, with the exception that the sintering temperature of the precursor powder material and the particle size D V50 the mixed slurry is adjusted after milling and the carbon source is replaced by glucose. Comparative example 2

[0371] Lithium dihydrogen phosphate, iron(II) oxalate, glucose, and titanium dioxide are uniformly mixed and milled in methanol. The mixed raw material is milled several times in a ball mill and demagnetized to obtain a mixed slurry. The number and duration of milling are controlled, and the particle size D is adjusted. V50 The mixed slurry has a particle size of 4.0 µm after milling. The mixed slurry is spray-dried to obtain a dry precursor powder material, which has a light yellow appearance and a uniform color. The precursor powder material is placed in a sintering furnace and heated under a nitrogen atmosphere at a rate of 2°C / min from 25°C to 350°C and held at this temperature for 3 hours. The temperature is then increased at a rate of 5°C / min to a second temperature of 750°C and held at this temperature for 10 hours, followed by cooling. Performance tests 1. Energy density test

[0372] The lithium-ion secondary battery is held at 25°C for 2 hours to ensure its temperature is 25°C. After charging the lithium-ion secondary battery at 0.33C to a reverse charge voltage of 3.65 V at 25°C, charging continues at a constant voltage at the reverse charge voltage until the current reaches 0.05C and charging is blocked (where C represents the nominal capacity of the lithium-ion secondary battery). After being held at 25°C for 1 hour, the lithium-ion secondary battery is discharged at 0.33C at 25°C to a reverse charge voltage of 3.65 V, and the total discharge energy of the lithium-ion secondary battery is recorded as E0.

[0373] The length, width, and height of the battery cell are measured, and the volume of the battery cell is calculated as V0 = length * width * height. The volume energy density of a lithium-ion secondary battery = discharge energy E0 of the lithium-ion secondary battery / volume V0 of the lithium-ion secondary battery. 2. Test procedure for DC resistance (DCR)

[0374] Charge at 25°C with a constant current of 0.33C to 3.65V, then charge with constant voltage to a current of 0.05C, then discharge at 0.33C to 20% SOC, stand for 5 minutes, then discharge for 30 seconds with a 3C pulse, stand for 40 seconds, then charge for 40 seconds at 3C, charge with a constant current of 0.33C to 3.65V after standing for 5 minutes, then charge with constant voltage to 0.05C, then discharge at 0.33C to 10% SOC, stand for 5 minutes, then discharge for 30 seconds with a 3C pulse, stand for 40 seconds, then charge for 40 seconds at 3C, stand for 5 minutes, then full charge at 0.33C, then discharge at 0.33C to 50% SOC, then stand for 2 hours at -25°C. Then discharge for 30 seconds with a 1C pulse, then stand for 10 minutes, then stand for 2 hours at 25°C, then charge with a constant current of 0.33C to 3.65V, then charge with a constant voltage to 0.05C, then discharge at 0.33C to 20% SOC, then stand for 2 hours below -25°C.Then discharge for 30 seconds with a 1C pulse, then stand for 10 minutes.

[0375] The voltage is recorded before and after each pulse discharge and the DCR is calculated under different conditions, and the formula for calculation is DCR = (voltage before pulse discharge after standstill - voltage before standstill after pulse discharge) / pulse current. 3. Limiting compressive strength of the electrode foil

[0376] The double-sided coated electrode foil is compacted using a roller press to test its elongation and evaluate its flexibility after compaction. Increasing the roller press pressure allows for the production of electrode foils with varying densities. As the pressure increases, the density, elongation, and flexibility of the electrode foil all increase. Excessive elongation can easily lead to distortion, while insufficient flexibility can result in brittle fracture. Therefore, the lower of the two densities corresponding to an elongation of 8% or a number of 3 flexible folds is defined as the limiting density.

[0377] The compression density is calculated from the mass of the cathode film layer / the volume of the cathode film layer.

[0378] The test procedure for elongation is as follows:

[0379] Lay the electrode foil flat on a horizontal tabletop and cut it into pieces, each approximately 100 cm long; remove the copper foil substrate at the edge of the electrode foil, ensuring that the cut edge of the electrode foil runs parallel to the MD direction of the electrode foil (perpendicular to the direction of the press roller) to guarantee that part of the electrode foil is completely covered with the coating; measure the length between the marked points at positions of equal width longitudinally at the front and rear ends of the electrode foil using a steel ruler, estimating the length to the nearest 0.1 mm and recording the length before compaction; record the length between the corresponding marked points after compaction and use (length after compaction - length before compaction) / length before compaction as the elongation of the electrode foil.

[0380] The following describes the test procedure for the number of flexible folds.

[0381] The cathode foil is used in test samples measuring 20 × 100 mm. 2 Cut; after folding the test samples forward, flatten them with a 2 kg roller, unfold them, and check the gap against the light to see if there is light transmission. If not, fold them backward, flatten them with a 2 kg roller, and check against the light again. Repeat this process until light passes through the gap, and note the number of folds. The test is repeated three times, and the average value is used as reference data for the flexibility of the electrode foil. Test results Table 1 carbon source The particle size of the mixed slurry after milling is D V50 µm Sintering temperature ur / °C Mass content of the conductive agent Degree of graphitization C 50 Area fraction of particles with a particle size of 1.5µm - 5 µm Area fraction of particles with a particle size greater than or equal to 1 µm and less than 1.5 µm Example 1 PEG 3,0 770 0,80% 1,02 14,58% 19,70% Example 2 PEG 3,0 755 0,80% 0,97 9,02% 23,97% Example 3 PEG 3,0 790 0,80% 1,13 19,43% 16,02% Execution- PEG 4,0 770 0,80% 1,00 12,37% 20,88% example 4 Example 5 PEG 1,5 770 0,80% 1,04 15,78% 19,12% Example 6 PEG 3,0 770 0,00% 1,02 14,58% 19,70% Example 7 PEG:Glucose = 3:1 3,0 770 0,80% 1,01 15,35% 19,31% Example 8 PEG:Glucose = 1:3 3,0 770 0,80% 0,99 17,21% 18,18% Comparison example 1 glucose 3,0 803 0,80% 1,07 20,33% 14,45% Comparison example 2 glucose 4,0 750 0,80% 0,93 9,12% 25,21% Table 2 Degree of graphitization C 10 Degree of graphitization C 90 C-value concentration Median of Sphericity L A50 Density g / cm³ 3 the electrode foil after formation and complete discharge Example 1 1,00 1,04 0,034 0,719 2,56 Example 2 0,955 0,983 0,029 0,738 2,51 Example 3 1,1 1,144 0,039 0,702 2,6 Example 4 0,988 1,018 0,030 0,723 2,53 Example 5 1,021 1,058 0,036 0,714 2,58 Example 6 1,00 1,04 0,034 0,719 2,56 Execution 0,996 1,031 0,035 0,712 2,57 Example 7 Example 8 0,976 1,013 0,037 0,689 2,59 Comparison example 1 1,03 1,08 0,047 0,67 2,59 Comparison example 2 0,915 0,962 0,051 0,739 2,45 Table 3 DCR25°C, 3C,20%SOC / mΩ DCR25°C, 3C,10%SOC / mΩ DCR-25°C 1C50%SOC / mΩ DCR-25°C, 1C,20%SOC / mΩ Energy density Wh / L Example 1 43,3 60,9 388,2 445,6 445,0 Example 2 40,7 57,0 360,3 410,0 436,7 Example 3 47,7 67,6 426,3 494,7 444,9 Example 4 42,0 58,7 377,0 430,9 440,0 Example 5 45,6 64,5 411,9 467,0 448,3 Example 6 43,8 60,4 390,1 448,9 448,7 Example 7 45,1 64,0 408,4 464,4 446,7 Example 8 48,4 68,7 427,4 496,0 445,5 Comparative example 1 49,9 71,9 454,2 527,2 441,0 Comparative example 2 42,1 58,6 372,9 424,5 426,7

[0382] From the comparison between the exemplary embodiments and the comparative examples, it can be seen that in the 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 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%; in the cumulative distribution curve of the graphitization degree C value of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the compression density of the cathode foil is improved when the median graphitization degree C 50 greater than or equal to 0.95 and less than or equal to 1.20, while the battery maintains a low internal resistance (especially a low impedance at low SOC), so that the battery has both good energy density and dynamic performance.

[0383] From the comparison between embodiments 1-8 and comparative example 2, it can be seen that in the cumulative distribution curve of the graphitization degree C value of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median C 50 The degree of graphitization is 0.97-1.13, which is advantageous for improving the pressing density of the electrode foil while maintaining the low impedance of the battery, thereby improving the energy density of the battery while maintaining good kinetic battery performance.

[0384] From the comparison between embodiments 2, 8 and comparative example 1, embodiments 3-7, it is evident that in the cumulative distribution curve of the graphitization degree C value of the cathode film layer, which was obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median C 50 The graphitization level is 1.0-1.10, which helps to maintain a low impedance of the battery while achieving a high pressing density of the electrode foil, thus achieving a balance between the dynamic performance and the energy density of the battery.

[0385] From the comparison between embodiment 2 and embodiments 1, 3-8, it can be seen that 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 of 1.5-5 µm is 10.0-20.0%, which has a positive effect on improving the pressing density of the electrode foil while maintaining the low impedance of the battery, thereby improving the energy density of the battery while maintaining good kinetic battery performance.

[0386] From the comparison between embodiment 6 and embodiment 1, it can be seen that the lithium-ion secondary battery of the embodiment of the present application still exhibits good dynamic performance even without the addition of a conductive medium, so that the energy density of the lithium-ion secondary battery can be further improved.

[0387] It should be noted that the present application is not limited to the embodiments mentioned above. The embodiments mentioned above are merely examples, and all embodiments that exhibit essentially the same structure and effects as the technical idea within the technical solution of the present application are all included within the technical scope of the present application. Furthermore, other embodiments in which various modifications conceivable by a person skilled in the art are added to the embodiments, and some components of the embodiments are combined to form the other embodiments, are also included within the scope of the present application without departing from the core of the present application. QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] GB / T 21023-2006

[0163]

Claims

[1] Lithium-ion secondary battery, characterized by , that the lithium-ion secondary battery comprises a cathode foil, an anode foil and an electrolyte, wherein the cathode foil comprises a cathode current collector and a cathode film layer arranged on at least one side of the cathode current collector, wherein the cathode film layer comprises an active cathode material, wherein the active cathode material comprises particles of lithium-containing transition metal phosphate which are coated on at least part of their surface with a carbon coating material, wherein in the 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 1.5 µm is greater than or equal to 8.0% and less than or equal to 20.0%; where in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C 50 greater than or equal to 0.95 and less than or equal to 1.20, where the degree of graphitization is the C-value. G / I D is, where I G a G-peak intensity of the Raman spectrum at 1580±100cm -1 and I D a D peak intensity of the Raman spectrum at 1350±100cm -1 represents. [2] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C 50 0.97 to 1.

13. [3] Lithium-ion secondary battery according to claim 1, characterized by, that in the cumulative distribution curve of the graphitization degree C value of the cathode film layer obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the median of the graphitization degree C 50 1.0 to 1.

10. [4] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the concentration of the C-value (C 90 -C 10 ) / C 50 It is between 0.01 and 0.

04. [5] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the graphitization degree C-value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the concentration of the C-value (C 90 -C 10 ) / C 50It is between 0.02 and 0.

04. [6] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the graphitization degree C value of the cathode film layer, obtained in a surface scan mode of the laser microconfocal Raman spectrometer, the C 90 for the degree of graphitization 1.00- 1.

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

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

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

08. [10] Lithium-ion secondary battery according to claim 1, characterized by , that in the 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 1.5 µm to 5 µm is 9.0% to 20.0%. [11] Lithium-ion secondary battery according to claim 1, characterized by , that in the 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 1.5 µm to 5 µm is 10.0% to 20.0%. [12] Lithium-ion secondary battery according to claim 1, characterized by , that in the 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 5 µm is 0. [13] Lithium-ion secondary battery according to claim 1, characterized by , that in the 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 and less than 1.5 µm is 15.0% to 25.0%. [14] Lithium-ion secondary battery according to claim 13, characterized by , that in the 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 and less than 1.5 µm is 16.0% to 24%. [15] Lithium-ion secondary battery according to claim 13, characterized by, that in the 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 and less than 1.5 is between 16% and 20%. [16] Lithium-ion secondary battery according to claim 1, characterized by , that in the cumulative distribution curve of the particle sphericity region obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median of the sphericity L A50 0.60 to 0.

85. [17] Lithium-ion secondary battery according to claim 16, characterized by , that in the cumulative distribution curve of the particle sphericity region obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median of the sphericity L A50 The value is between 0.65 and 0.

80. [18] Lithium-ion secondary battery according to claim 1, characterized by, that in the cumulative distribution curve of the particle roughness range obtained from the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil, the median of the roughness R A50 The value is between 0.92 and 0.

96. [19] Lithium-ion secondary battery according to claim 1, characterized by that the iron dissolution rate of the cathode film layer is 500 ppm to 2000 ppm. [20] Lithium-ion secondary battery according to claim 1, characterized by , that the iron dissolution rate of the cathode film layer is 500 ppm to 1500 ppm. [21] Lithium-ion secondary battery according to claim 1, characterized by , that the mass content of the carbon element is 0.8% to 1.8% based on the total mass of the active cathode material. [22] Lithium-ion secondary battery according to claim 21, characterized by , that the mass content of the carbon element is 0.90% to 1.5% based on the total mass of the active cathode material. [23] Lithium-ion secondary battery according to claim 1, characterized by , that the concentration of lithium iron antisite defects in the active cathode material is 0.1% to 1.5%. [24] Lithium-ion secondary battery according to claim 23, characterized by , that the concentration of lithium iron antisite defects in the active cathode material is 0.3% to 1.0%. [25] 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, C1, Br, where 0.8 ≤ m ≤ 1.15, 0.9 ≤ x ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j ≤ 4, 0 < q ≤ 0.

1. [26] Lithium-ion secondary battery according to claim 1, characterized by, that the active cathode material comprises one or more of lithium iron phosphate and its doped modified material and encapsulating modified material. [27] Lithium-ion secondary battery according to claim 1, characterized by , that the active cathode material comprises a titanium element, wherein the mass content of the titanium element is 2000 ppm to 6000 ppm based on the total mass of the active cathode material. [28] Lithium-ion secondary battery according to claim 1, characterized by , that the powder bulk density of active cathode material is 0.70 g / cm³ 3 up to 1.50 g / cm² 3 is; and / or that the powder density of the active cathode material at a pressure of 3T is 2.50 g / cm³. 3 up to 2.70 g / cm³ 3 amounts. [29] Lithium-ion secondary battery according to claim 28, characterized by , that the powder bulk density of active cathode material is 0.70 g / cm³ 3 up to 1.20 g / cm³ 3is; and / or that the powder density of the active cathode material at a pressure of 3T is 2.52g / cm³. 3 up to 2.68g / cm³ 3 amounts. [30] Lithium-ion secondary battery according to claim 1, characterized by , that the specific powder resistance of the active cathode material under a pressure of 8 MPa is 0.5 Ω·cm to 30.0 Ω·cm. [31] Lithium-ion secondary battery according to claim 30, characterized by , that the specific powder resistance of the active cathode material under a pressure of 8 MPa is 2 Ω·cm to 20.0 Ω·cm. [32] Lithium-ion secondary battery according to claim 1, characterized by , that the specific discharge capacity of the active cathode material at room temperature and a discharge rate of 1C is 135 mAh / g to 150 mAh / g. [33] Lithium-ion secondary battery according to claim 1, characterized by, that the proportion of the discharge capacity of the active cathode material during a discharge to 3.2 V is η≥85%, where η is defined as follows: at room temperature, a button battery containing the active cathode material is charged and discharged twice at a rate of 0.1 C by constant current in the voltage range of 2.0 V to 3.75 V, and then once at a rate of 1 C by constant current, wherein in a charge and discharge test at a rate of 1 C, the capacity value extracted at 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 recorded as C2, where η= C1 / C2, wherein the charging process includes charging at a constant voltage of 3.75 V, where the reverse current at the constant voltage is 50 µA. [34] Lithium-ion secondary battery according to claim 1, characterized by, that in the discharge curve of the button battery containing the active cathode material, a discharge platform in the voltage range of 2.5 V to 2.9 V is present at 0.1 C. [35] Lithium-ion secondary battery according to claim 1, characterized by , that, relative to the total mass of the cathode film layer, the mass content of the conductive medium is 0 to 1.5%. [36] Lithium-ion secondary battery according to claim 35, characterized by , that based on the total mass of the cathode film layer, the mass content of the conductive medium is 0. [37] Lithium-ion secondary battery according to claim 1, characterized by that the cathode film layer also comprises a binder and that the mass fraction of the active cathode material, based on the total mass of the cathode film layer, is 95.5% to 99.5%; wherein the mass fraction of the binder is 0.5% to 3%. [38] Lithium-ion secondary battery according to claim 37, characterized by, that the mass content of the active cathode material, based on the total mass of the cathode film layer, is 96.5% to 99.5%. [39] Lithium-ion secondary battery according to claim 1, characterized by , that the one-sided areal density of the cathode film layer is 300 mg / 1540 mm² 2 up to 450 mg / 1540 mm 2 amounts. [40] Lithium-ion secondary battery according to claim 1, characterized by that the density of the cathode film layer is 2.51 g / cm³ 3 up to 2.73 g / cm³ 3 is the value when the lithium-ion secondary battery is in a completely discharged state. [41] Lithium-ion secondary battery according to claim 40, characterized by that the density of the cathode film layer is 2.55 g / cm³ 3 up to 2.70 g / cm³ 3 is the value when the lithium-ion secondary battery is in a completely discharged state. [42] Lithium-ion secondary battery according to claim 1, characterized bythat the cathode film layer meets at least one of the following conditions: (1) The density of the cathode film layer is 2.51 g / cm³ 3 up to 2.73 g / cm³ 3 , when the lithium-ion secondary battery is in a fully discharged state, wherein the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10% to 22%; (2) the density of the cathode film layer is 2.55g / cm³ 3 up to 2.70g / cm² 3 , when the lithium-ion secondary battery is in a fully discharged state, wherein the porosity of the cathode film layer in the cross-sectional area of ​​the cathode film layer along the thickness direction of the electrode foil is 10% to 20%. [43] 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 cathode current collector; wherein the lower coating satisfies at least one of the following conditions: (1) the lower coating comprises carbon-based particles and the distribution density of the carbon-based particles with a particle size of over 100 nm in the lower coating is less than or equal to 10 pcs / 10 µm; (2) the density of the cathode foil in the fully charged state is greater than or equal to 2.4 g / cm³ 3 , wherein the one-sided thickness of the lower coating is 1 µm to 4 µm; (3) The density of the cathode foil in the fully charged state is greater than or equal to 2.5 g / cm³ 3 , wherein the one-sided thickness of the lower coating is 2 µm to 4 µm. [44] Battery device, characterized by, that the battery device comprises a lithium-ion secondary battery according to any one of claims 1 to 43, wherein the battery device comprises at least one of a battery module, a battery pack and an energy storage battery. [45] Power-consuming device, characterized by that the battery device comprises a lithium-ion secondary battery according to any one of claims 1 to 43 or a battery device according to claim 44.

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