Battery cell, battery device and electric device

Abstract

The invention provides a single battery, a battery device and a power utilization device, the single battery comprises a laminated electrode assembly, the laminated electrode assembly comprises a positive pole piece, an isolating membrane and a negative pole piece which are laminated, the negative pole piece comprises a negative current collector and a negative membrane layer arranged on at least one side of the negative current collector, the positive pole piece comprises a positive pole current collector and a positive pole film layer arranged on at least one side of the positive pole current collector, the positive pole film layer comprises a positive pole active material, the positive pole active material comprises lithium-containing transition metal phosphate particles, the compaction density of the positive pole piece is 2.25-2.65 g / cm < 3 >, and the lithium-containing transition metal phosphate particles are uniformly distributed on the positive pole piece. In a sphericity-like area cumulative distribution curve of particles obtained by a tangent plane of the positive electrode film layer along the thickness direction of the pole piece, the sphericity-like degree LA50 is 0.70-0.75, the isolation film comprises a base film and coatings arranged on two sides of the base film, and a bonding layer in each coating is a porous structure continuous layer and comprises a fluorine-containing polymer. The battery monomer disclosed by the invention can give consideration to both energy density and cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a battery cell, a battery device and an electric device. Background Art

[0002] In recent years, with the increasingly wide application scope of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. Among them, lithium iron system batteries have attracted more and more attention in recent years because of their excellent safety performance.

[0003] With the rapid development of lithium iron system batteries, higher requirements have also been put forward for their cycle performance and energy density. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a battery cell, a battery device and an electric device, and the battery cell of the present application can take into account both energy density and cycle performance.

[0005] To achieve the above object, a first aspect of the present application provides a battery cell including a stacked electrode assembly. The stacked electrode assembly includes a stacked positive electrode plate, a separator and a negative electrode plate. The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector. The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes lithium-containing transition metal phosphate particles. The tap density of the positive electrode plate is 2.25 g / cm 3 -2.65 g / cm 3 ³. In the sphericity area cumulative distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the L A50 of sphericity is 0.70 to 0.75, and L A50 represents the sphericity corresponding to the cumulative area ratio of 50% on the vertical axis in the sphericity cumulative distribution curve. The separator includes a base film and coatings provided on both sides of the base film. The coatings include a bonding layer. The bonding layer is a continuous layer with a porous structure. The bonding layer includes a fluoropolymer. The battery cell of the present application can take into account both energy density and the cycle performance of the battery.

[0006] In some embodiments, in the sphericity area cumulative distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode plate, the L A90 of sphericity is 0.80 - 0.90, and L A90It represents the sphericity corresponding to the case where the cumulative area ratio of the vertical axis in the cumulative sphericity distribution curve is 90%. In some embodiments, in the cumulative sphericity area distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the L of the sphericity A10 is 0.50 - 0.55, and L A10 represents the sphericity corresponding to the case where the cumulative area ratio of the vertical axis in the cumulative sphericity distribution curve is 10%. The L of the sphericity A90 and L A10 within the above range indicate that the surface of the particles in the positive electrode film layer is highly smooth and is prone to slip under external force.

[0007] In some embodiments, in the cumulative sphericity distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the concentration of the sphericity (L A90 -L A10 ) / L A50 is 0.45 - 0.55. A small concentration of the sphericity of the positive electrode film layer indicates that the width of the sphericity distribution of the particles in the positive electrode film layer is narrow and the concentration is good.

[0008] In some embodiments, the compaction density of the positive electrode sheet is 2.35 g / cm 3 -2.45 g / cm 3 . Thus, it is beneficial to enable the battery cell to obtain a high energy density.

[0009] In some embodiments, the single-sided coating weight of the positive electrode film layer is 0.33 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 . In some embodiments, the single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25 mm 2 ~0.40 g / 1540.25 mm 2 . Thus, it is beneficial to enable the battery to obtain a relatively high energy density.

[0010] In some embodiments, the porosity of the positive electrode sheet is 23% - 32%. A porosity within this range can ensure both a relatively high compaction density and good wettability of the battery, thereby ensuring that the battery has a high energy density and good cycle performance.

[0011] In some embodiments, the lithium-containing transition metal phosphate particles include a lithium-containing transition metal phosphate matrix and a coating layer located on at least part of the surface of the lithium-containing transition metal phosphate matrix, and the coating layer contains carbon. Carbon has excellent electrical conductivity, which is beneficial to the transmission of electrons. The setting of the carbon coating layer can significantly improve the electronic conductivity of the lithium-containing transition metal phosphate material.

[0012] In some embodiments, the chemical formula of the lithium-containing transition metal phosphate matrix is expressed as Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 , where 0.5 ≤ x1 ≤ 0.8, 0 ≤ y1 ≤ 1.3, 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, N, and P; Y includes one or more of O and F. In some embodiments, the lithium-containing transition metal phosphate includes lithium iron phosphate.

[0013] In some embodiments, the lithium-containing transition metal phosphate contains Ti element. Based on the mass of the lithium-containing transition metal phosphate, the mass content of the Ti element is 0.05% - 0.2%. By including the Ti element, the transport barrier of lithium ions can be reduced, the diffusion rate of lithium ions can be increased, thereby improving the kinetic performance of the battery and enhancing the cycle performance.

[0014] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the electrode, the D A50 of the lithium-containing transition metal phosphate particles is 100 nm - 2.5 μm, and D A50 represents the particle size value corresponding to the cumulative area ratio of 50% on the vertical axis in the area cumulative distribution curve. The design of using a combination of large and small particles for the positive electrode can increase the tap density of the positive electrode, thereby enhancing the energy density of the battery.

[0015] In some embodiments, the thickness of the positive electrode current collector is 12 μm - 20 μm. Using a thicker current collector can improve the overall strength and support of the laminated battery, and at the same time reduce the risk of the electrode sheet wrinkling or breaking during high-pressure rolling.

[0016] In some embodiments, the tap density of the negative electrode sheet is 1.3 g / cm 3 - 1.55 g / cm 3 . In some embodiments, the tap density of the negative electrode sheet is 1.40 g / cm 3 - 1.50 g / cm3 . By keeping the compaction density within the above range, it is beneficial to improve the energy density of the battery.

[0017] In some embodiments, the single-sided coating weight of the negative electrode film layer is 0.15 g / 1540.25mm 2 ~0.207 g / 1540.25mm 2 . In some embodiments, the single-sided coating weight of the negative electrode film layer is 0.17 g / 1540.25mm 2 ~0.2 g / 1540.25mm 2 . Thus, it is beneficial to ensure that the battery has a high energy density.

[0018] In some embodiments, the porosity of the negative electrode plate is 23% - 32%. This can ensure that the battery has a high energy density and good cycling performance.

[0019] In some embodiments, the thickness of the negative electrode current collector is 6μm - 12μm. This can improve the overall strength and support of the laminated battery, and at the same time avoid the risk of the electrode plate wrinkling or breaking during high-pressure rolling.

[0020] In some embodiments, the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes graphite, and the volume average particle size Dv50 of the graphite is 13μm - 22μm. In some embodiments, the volume average particle size Dv50 of the graphite is 14.5μm - 20μm. By using graphite with a particle size in the above range, it is beneficial to increase the compaction density of the electrode plate, thereby increasing the volume energy density of the battery; at the same time, it can ensure that the transmission path of lithium ions in the graphite is appropriate, reducing the risk of adverse effects on battery performance due to too long a path.

[0021] In some embodiments, the fluoropolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer. Such polymers can dissolve in oily solvents, opening the molecular chains to form a relatively uniform slurry. Thus, an overall porous network structure is formed during coating, significantly improving the adhesion to the electrode plate.

[0022] In some embodiments, the single-sided thickness of the adhesive layer is 0.5μm - 2μm. Within this thickness range, the bonding strength between the separator and the electrode plate is within an appropriate range, which is beneficial to the cycling performance and safety performance of the battery monomer.

[0023] In some embodiments, the coating further includes a ceramic layer disposed between the base film and the adhesive layer. Disposing a ceramic layer between the base film and the adhesive layer can improve the wettability of the electrolyte to the separator, promote the flow of the electrolyte, and is beneficial to further improving the performance deterioration problem of the battery cell caused by insufficient electrolyte wetting, thereby being more conducive to improving the cycle performance of the battery monomer.

[0024] In some embodiments, the ceramic layer includes one or more ceramic particles such as aluminum oxide, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, yttrium oxide, zinc oxide, silicon carbide, magnesium fluoride, barium sulfate, barium titanate, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide.

[0025] In some embodiments, the unilateral thickness of the ceramic layer is 0.5 μm - 4 μm. Within this thickness range, the wettability and liquid retention of the electrolyte can be improved, which is beneficial to the cycle performance and safety performance of the battery monomer.

[0026] In some embodiments, the thickness of the base film is 7 μm - 9 μm.

[0027] In some embodiments, the battery monomer contains an electrolyte, and the electrolyte includes a chain carbonate solvent. Based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is 43% - 71%. As a solvent for the electrolyte, the chain carbonate has a lower viscosity than the cyclic carbonate. When the electrolyte includes 43% - 71% of the chain carbonate, the viscosity of the electrolyte is effectively reduced, and the wetting of the electrode assembly is improved.

[0028] In some embodiments, the chain carbonate includes one or both of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). When DMC and EMC are used in combination, it can not only effectively reduce the viscosity of the electrolyte and improve the wettability of the electrolyte, but also will not cause a decrease in the low-temperature performance of the battery.

[0029] In some embodiments, the electrolyte further includes a cyclic carbonate. The cyclic carbonate is beneficial to the dissociation of the lithium salt and improves the conductivity of the electrolyte. In addition, the cyclic carbonate can also form a stable SEI film on the surface of the negative electrode, which is thus beneficial to the improvement of the cycle stability and safety of the battery.

[0030] In some embodiments, based on the total mass of the electrolyte, the mass content of the cyclic carbonate is 14% - 42%. When the mass content of the cyclic carbonate is within the above range, it is beneficial to improve the conductivity of the electrolyte and will not affect the wettability of the electrolyte to the electrode assembly.

[0031] The second aspect of the present application provides a battery device, which includes the battery monomer of the first aspect of the present application.

[0032] The third aspect of the present application provides an electrical device, which includes the battery device of the second aspect of the present application. Description of the Drawings

[0033] Figure 1 It is a scanning electron microscope image of a cross-section of the positive electrode film layer along the thickness direction of the electrode plate in an embodiment of the present application; Figure 2 It is a schematic diagram of the microstructure on the surface of the separator of the present application; Figure 3 It is a schematic diagram of the microstructure on the surface of a conventional separator; Figure 4 It is a schematic diagram of a battery cell in an embodiment of the present application; Figure 5 is Figure 4 The exploded view of the battery cell in an embodiment of the present application shown; Figure 6 It is a schematic diagram of a battery module in an embodiment of the present application; Figure 7 It is a schematic diagram of a battery pack in an embodiment of the present application; Figure 8 is Figure 7 The exploded view of the battery pack in an embodiment of the present application shown; Figure 9 It is a schematic diagram of an electrical device using a secondary battery as a power source in an embodiment of the present application.

[0034] Description of the Reference Numerals 10 Separator of the present application; 11 Porous continuous bonding layer; 111 Pores; 12 Ceramic layer; 20 Conventional separator; 21 Island-shaped binder; 1 Battery pack; 2 Upper box body; 3 Lower box body; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Embodiments

[0035] Hereinafter, embodiments of the battery cell, battery device, and electrical device of the present application specifically disclosed will be described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily long and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the present application.

[0036] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way 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 specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0039] Unless otherwise specified, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out in sequence, or can also include steps (b) and (a) carried out in sequence. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0041] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured using various commonly used testing methods in the art. For example, they can be measured according to the testing methods given in this application.

[0042] At present, lithium iron phosphate system batteries (the positive electrode active material includes lithium-containing transition metal phosphates) have attracted more and more attention due to their better safety performance than ternary system batteries. However, compared with ternary system batteries, the energy density of lithium iron phosphate system batteries is lower. Therefore, in the prior art, the energy density is usually increased by increasing the compaction density of the electrode sheet.

[0043] However, the inventors have found that when the compaction density of the positive electrode film layer is relatively large, especially for laminated batteries, the stress release in the film layer in the later stage of cycling will cause the electrode sheet to be misaligned, the film to peel off, and powder to fall off, which will further cause poor contact between the positive electrode film layer and the separator, and between the positive electrode film layer and the current collector, resulting in an increase in the interfacial resistance and having an adverse effect on the cycling performance of the battery.

[0044] Based on this, the present application provides a new battery cell, battery device, and electrical device, which can obtain excellent cycling performance while having a high energy density. The following will specifically describe the present application and optional implementation manners.

[0045] Battery cell In a first aspect of the present application, a battery cell is provided, which is characterized by including a laminated electrode assembly. The laminated electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet stacked together. The negative electrode sheet includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The positive electrode sheet includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium-containing transition metal phosphate particles. The compaction density of the positive electrode sheet is 2.25 g / cm 3 -2.65 g / cm 3 , in the cumulative sphericality area distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the L A50 of sphericality is 0.7 - 0.75, and L A50 represents the sphericality corresponding to the cumulative area ratio of 50% of the cumulative area of the vertical axis in the cumulative sphericality distribution curve. The separator includes a base film and coatings provided on both sides of the base film. The coatings include a bonding layer, and the bonding layer is a continuous layer with a porous structure. The bonding layer includes a fluoropolymer.

[0046] In the present application, in the laminated battery assembly, the compaction density of the positive electrode sheet is 2.25 g / cm 3 -2.65 g / cm 3 , by adopting a laminated structure and a high compaction density design, the energy density of the battery can be further improved, and the problem that the electrode sheet is prone to cracking at the corners in the winding structure can be avoided. On this basis, the L A50Within the above range, it indicates that the surface of the particles is relatively smooth, and the frictional force between the particles is relatively small, which can improve the slipability between the lithium-containing transition metal phosphate particles. The stress generated during the lithium insertion and extraction process of the electrode can be released through the slip between the particles, thereby alleviating the damage to the electrode structure caused by the stress release of the electrode, reducing the occurrence of misalignment, reducing the risk of poor contact between the positive electrode film layer and the separator, and between the positive electrode film layer and the current collector, reducing the increase in internal resistance, and improving the cycle performance of the battery. Furthermore, by using the separator with the above-mentioned specific adhesive layers on both sides, on the one hand, the continuous film layer enables the adhesive layer to have a larger area in contact with the electrode, enhancing the adhesive force between the separator and the electrode, reducing the occurrence of misalignment, and further enhancing the structural strength and stability of the bare battery cell; on the other hand, the porous structure enables the active ions in the electrolyte to be more easily transported between the separators. Therefore, through the above-mentioned separator, having a good adhesive force with the electrode is beneficial to obtaining a battery cell with a high energy density and a stable cell structure.

[0047] In the present application, the tap density of the positive electrode is the tap density under the condition of 0% SOC (State of Charge). Exemplarily, the tap density under the condition of 0% SOC is 2.25 g / cm 3 、2.26 g / cm 3 、2.27g / cm 3 、2.28 g / cm 3 、2.29 g / cm 3 、2.30 g / cm 3 、2.35 g / cm 3 、2.40 g / cm 3 、2.45g / cm 3 、2.50 g / cm 3 、2.55 g / cm 3 、2.60g / cm 3 、2.65g / cm 3 or within the range between any two values. In some embodiments, the tap density of the positive electrode under the condition of 0% SOC is 2.35 g / cm 3 -2.45g / cm 3 。

[0048] In the present application, the term "particle" refers to a particle with an identifiable complete boundary in the field of view of the positive electrode film layer at a certain magnification, such as 10,000 times. There may be defects and scratches inside the particle, but no complete boundary sufficient to divide the particle can be identified inside the particle.

[0049] The method for identifying particles is as follows: Cut the positive electrode film layer along the thickness direction of the pole piece by an argon ion beam. After exposing the cut surface, use a scanning electron microscope to observe the cut surface of the positive electrode film layer along the thickness direction of the pole piece. Use a field emission scanning electron microscope to collect images in the secondary electron mode at a non-edge position (after observing the edge of the pole piece under the scanning electron microscope, adjust the field of view to the central part of the sample) on the cut surface of the positive electrode film layer, take an electron microscope image at a magnification of 10,000 times, and use ImageJ software (version 1.46r, win64) to analyze the particles in the electron microscope image. The specific method of using ImageJ software is as follows: Load the scanning electron microscope image to be analyzed, as Figure 1 shown; Use the Cellpose plug-in software in it to identify particles, and perform manual correction on this basis; Use Image J to read and count data. The specific method of using the Cellpose plug-in software to identify particles is as follows: Set the segmentation diameter parameter (diameter in the Segmantation module) to 15 pixels, click "run cyto3" to identify particles, and then manually mark the particles in the image that are not recognized by the software, not completely recognized by the software, or have recognition errors. The particles in the image that are not recognized by the software, not completely recognized by the software, or have recognition errors mainly include the following types: 1. Due to the particle being too large or having scratches on the particle surface, the particle cannot be recognized or cannot be completely recognized; 2. During the argon ion beam cutting process, scratches will be generated on the particle surface, and the software may misjudge the scratches as particle boundaries during the recognition process, resulting in recognition errors; 3. Due to the particle being too small, it cannot be successfully recognized; 4. The particle is located at the edge of the electron microscope field of view, and the inside of the particle is penetrated by the edge, and the morphology cannot be completely displayed, and the local part is recognized instead of the whole, resulting in recognition errors. For the above unrecognized or misrecognized particles, manual calibration is performed. The specific process is as follows: Delete the large particles that are located at the four edges of the scanning electron microscope and cannot be completely displayed; Judge whether there are gap scratches inside other unrecognized or misrecognized particles. If there are no gap scratches inside the particle, judge it as a particle, and manually mark it according to the particle boundary observed manually; In response to the presence of gap scratches inside the particle, judge whether the gap scratches penetrate the particle. If they do not penetrate the particle, judge it as a particle and perform manual marking; In response to the gap scratches penetrating the particle, judge whether the gap scratches are linear or irregular; In response to the gap scratches being irregular, judge it as the boundary between particles and divide the particles along this boundary; In response to the gap scratches being linear, perform contrast of contrast; In response to the contrast being not obvious and there being no sense of crack, judge it as a scratch and mark it as a particle; In response to the contrast being strong and there being a sense of crack, judge it as the boundary between particles and mark it as two particles. After manual marking, delete the information irrelevant to the particles during the automatic image processing process, that is, the determination and marking of the particles in the picture are completed.

[0050] The cross-sectional morphology diagram of the positive electrode film layer along the thickness direction of the electrode sheet is as follows Figure 1 shown. Different from the state of the positive electrode active material in the Malvern laser scattering method and also different from the state of the positive electrode active material when directly observing the positive electrode active material by scanning electron microscopy. Under the action of the roller pressure, the particles in the positive electrode film layer show a good dispersion state. Observing the positive electrode film layer is beneficial to effectively characterizing the objective conditions of the particle size, particle area and quantity in the positive electrode film layer.

[0051] It can be understood that the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, especially the particles above 50 nm, mainly come from the positive electrode active material. Therefore, by observing and counting the particle size in the cross-section of the positive electrode film layer in this application, the distribution of the lithium-containing transition metal phosphate particles in the positive electrode film layer in the electrode sheet can be accurately and objectively reflected.

[0052] In the prior art, the Malvern laser diffraction method is usually used to count the particle size of the positive electrode active material. However, the inventors' research shows that due to the easy agglomeration of lithium phosphate, the test results obtained by the Malvern laser diffraction method based on the laser scattering principle often measure the particle size of its particle agglomerates, and cannot truly reflect the particle size of the particles in the positive electrode active material, let alone reflect the dispersion state of the positive electrode active material in the film layer, because the dispersion degree of the positive electrode active material in the film layer will increase during the film-forming rolling process. The test results obtained by the Malvern laser diffraction method are closely related to the particle size, specific surface area and agglomeration degree of the positive electrode active material. Therefore, the particle size obtained by the Malvern laser diffraction method test cannot be equivalent to or analogized to the particle size statistically obtained in this application.

[0053] In this application, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the method for testing the sphericity of particles is as follows: The image after particle determination and identification is imported into ImageJ software for analysis. The scale is set according to the scanning electron microscope image. The Feret diameter and Area of the particle cross-section in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet are analyzed through the "Feret diameter", "Area", "Round", and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter obtained by analysis represents the maximum distance between all parallel lines of the outer contour of the particle cross-section, which characterizes the particle size; the "Area" parameter represents the pixel area of the particle, which characterizes the area of the particle. Since particles with a particle size less than 50 nm have large errors in the statistical process and are difficult to accurately identify, and the particle size of the conductive agent is generally less than 50 nm, which will cause large errors in the statistical results. Therefore, in the particle size statistics process of this application, particles with a particle size less than 50 nm are not counted, and the particle statistical data corresponding to "NaN" displayed in Area is deleted. The "Round" parameter represents the ratio of the pixel area of the particle to the area of a circle with the fitted major axis as the diameter, which can be used to characterize the sphericity of the particle. When the particle is closer to a sphere, the ratio of the pixel area to the area of a circle with the fitted major axis as the diameter is closer to 1. Therefore, the "Round" parameter of the obtained particle is used to characterize the sphericity of the particle.

[0054] Arrange the sphericities of at least 5000 obtained particles in ascending order. Use the sphericity as the horizontal axis and the cumulative area ratio as the vertical axis to obtain the cumulative distribution curve of the sphericity of particles in the positive electrode film layer. L A50 It is the sphericity L value corresponding to the cumulative area ratio of 50% on the vertical axis in the cumulative distribution curve of the sphericity L value.

[0055] The sphericity L A50 Compared with the point value, it can reflect the overall sphericity of the particles in the positive electrode film layer, that is, the degree of approximation to a sphere; compared with the mean value, it can reduce the influence of extreme values in the test process and improve the confidence level of the test results.

[0056] In this application, in the cumulative distribution curve of the sphericity area of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the sphericity L of the particles A50 Is 0.70, 0.71, 0.72, 0.73, 0.74, 0.75 or the numerical range between any two of them.

[0057] In some embodiments, in the cumulative distribution curve of the sphericity area of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the concentration of the sphericity is 0.45 - 0.55, and the concentration = (L A90-L A10 ) / L A50 . Exemplarily, (L A90 -L A10 ) / L A50 can optionally be 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55, or a numerical range between any two of them.

[0058] In the cumulative sphericality area distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the test method for the concentration degree of sphericality is as follows: Referring to the sphericality test method described above in this application, and so on, L A90 is the L value corresponding to when the cumulative area ratio of the vertical axis in the cumulative distribution curve of the sphericality L value is 90%, and L A10 is the L value corresponding to when the cumulative area ratio of the vertical axis in the cumulative distribution curve of the sphericality L value is 10%. The concentration degree of sphericality is represented by (L A90 -L A10 ) / L A50 . (L A90 -L A10 ) / L A50 can not only reflect the sphericality size of most particles, but also be unaffected by extreme values, and can also reflect the width of the sphericality distribution of the particles in the positive electrode film layer. The concentration degree of the sphericality L value of the positive electrode film layer indicates that the width of the sphericality distribution of the particles in the positive electrode film layer is narrow and the concentration is good.

[0059] In the prior art, the compaction density of the electrode sheet is usually increased by increasing the particle grading. The increase in particle grading is often accompanied by an increase in large particles and small particles. Lithium-containing transition metal phosphate is a ceramic material, and during the high-temperature sintering process, the grain boundaries melt and the particles grow. The sintering of large particles often requires a higher sintering temperature or a longer sintering time and more grain boundary melting. Therefore, in the prior art, the sphericality of large particles is relatively low, which in turn leads to a decrease in the overall level and concentration degree of the particle sphericality.

[0060] This application realizes uniform and consistent slippage between particles by improving the sphericality of the particles and increasing the concentration degree of the particle sphericality, reduces the slippage blockage and stress concentration caused by excessive local sphericality, so that the stress generated during the charge and discharge process of the electrode sheet can be released through the slippage between the particles, thereby ensuring that the battery cell has excellent electrical performance.

[0061] In some embodiments, in the cumulative sphericality area distribution curve of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the L of the sphericality A90 is 0.80 - 0.90, and / or the L A10 is 0.50 - 0.55. Exemplarily, the L of the sphericalityA90 is 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90 or a numerical range between any two of them. Exemplarily, the sphericity L A10 is 0.50, 0.51, 0.52, 0.53, 0.54, 0.55 or a numerical range between any two of them. The sphericity L A10 , L A90 within the above range indicates that most particles have a high sphericity, avoiding extreme morphological differences and preventing excessive voids and stress concentration caused by bridging between particles, which is beneficial to uniform slip.

[0062] In some embodiments, the single-sided coating weight of the positive electrode film layer is 0.33 g / 1540.25mm 2 ~0.43 g / 1540.25mm 2 . Exemplarily, the single-sided coating weight is 0.33 g / 1540.25mm 2 , 0.34 g / 1540.25mm 2 , 0.35 g / 1540.25mm 2 , 0.36 g / 1540.25mm 2 , 0.37 g / 1540.25mm 2 , 0.38 g / 1540.25mm 2 , 0.39 g / 1540.25mm 2 , 0.40 g / 1540.25mm 2 , 0.41 g / 1540.25mm 2 , 0.42 g / 1540.25mm 2 , 0.43 g / 1540.25mm 2 or a numerical range between any two of them. In some embodiments, the single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25mm 2 ~0.40 g / 1540.25mm 2 . Thus, it is beneficial to enable the battery to obtain a high energy density.

[0063] In some embodiments, the porosity of the positive electrode plate is 23% - 32%. Exemplarily, the porosity of the positive electrode plate is 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32% or a numerical range between any two of them. When the porosity is within this range, it can ensure that the battery has a high tap density and good wettability, thereby ensuring that the battery has a high energy density and good cycling performance.

[0064] In this application, the porosity is tested by the gas displacement method with reference to GB / T 24586-2009. After the electrode sheet / separator is impregnated in DMC and cleaned and dried, it is tested using a true density meter AccuPyc Ⅱ 1340. Among them, the percentage of the pore volume in the electrode sheet accounting for the total volume of the electrode sheet is the porosity of the electrode sheet, and the calculation formula is: porosity = (V - V0) / V × 100%, where V0 is the true volume and V is the apparent volume.

[0065] In some embodiments, the lithium-containing transition metal phosphate particles include a lithium-containing transition metal phosphate matrix and a coating layer located on at least a part of the surface of the lithium-containing transition metal phosphate matrix, and the coating layer contains carbon elements. Carbon has excellent electrical conductivity and is beneficial to the transmission of electrons. The setting of the carbon coating layer can significantly improve the electron conductivity of the lithium-containing transition metal phosphate material and make up for the defect of poor electron conduction performance of the lithium-containing transition metal phosphate material.

[0066] The carbon coating layer provided on at least a part of the surface of the lithium-containing transition metal phosphate can be detected by any well-known method in the art. As an example, by using a transmission electron microscope and an energy spectrum analyzer in combination to characterize the lithium-containing transition metal phosphate, the carbon coating layer provided on at least a part of the surface of the lithium-containing transition metal phosphate can be observed. It should be noted that the elements in the carbon coating layer are not limited to carbon elements, and there may also be other non-carbon elements. The carbon coating layer is not limited to a film shape, but also includes island shapes, irregular shapes or discontinuous coating layers.

[0067] In some embodiments, the chemical formula of the lithium-containing transition metal phosphate matrix is expressed as Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 , where 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 0.8, 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; X includes one or more of S, Si, Cl, B, C, N, P; Y includes one or more of O, F. In some embodiments, the lithium-containing transition metal phosphate includes lithium iron phosphate.

[0068] The lithium-containing transition metal phosphate contains Ti. For example, lithium iron phosphate contains Ti. Additionally, based on the mass of the lithium-containing transition metal phosphate, the mass content of the Ti element is 0.05% to 0.2%. Exemplarily, the mass content of the Ti element is 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.2% or any numerical range between any two of them. By including the Ti element, the transport barrier of lithium ions can be reduced, and the diffusion rate of lithium ions can be increased, thereby improving the kinetic performance of the battery and enhancing the cycle performance.

[0069] In some embodiments, in the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the D of the lithium-containing transition metal phosphate particles A50 is 100 nm to 2.5 μm. The positive electrode adopts a design with a combination of large and small particles, which can improve the tap density of the positive electrode, thereby enhancing the energy density of the battery. Exemplarily, D A50 is 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm or any numerical range between any two of them.

[0070] In this application, as the D A50 testing method, it can be carried out as follows: In the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the D of the particles A50The calculation method is as follows. The image after particle determination and identification is imported into the ImageJ software for analysis according to the method described above. The scale is set according to the scanning electron microscope image. The particle size and area of the particles in the cross-section of the positive electrode film layer along the thickness direction of the electrode are analyzed through the "Feret diameter", "Area", "Round", and "Solidity" analysis functions. According to the software manual (ImageJ User Guide IJ 1.46r), the "Feret" parameter obtained by analysis represents the maximum distance between all parallel lines in the two-dimensional projection of the particle, which characterizes the particle size; and the "Area" parameter obtained represents the pixel area of the particle. Since particles with a particle size less than 50 nm have large errors in the statistical process and are difficult to accurately identify, and the particle size of the conductive agent is generally less than 50 nm, which will cause large errors in the statistical results. Therefore, in the particle size statistics of this application, particles with a particle size less than 50 nm are not statistically counted, and the particle statistical data corresponding to "NaN" displayed by AR or Round or Solidity are deleted. According to the above method, to meet the sample size with statistical significance, at least 10 non-overlapping scanning electron microscope images are collected for each electrode, and the particle sizes of at least 5000 particles are statistically counted. The particle sizes of at least 5000 obtained particles are arranged in ascending order. With the particle size as the horizontal axis and the cumulative area ratio calculated through the "Area" of the particles as the vertical axis, the area cumulative distribution curve of the particles in the positive electrode film layer is obtained. D A50 It is the particle size value corresponding to when the cumulative area ratio on the vertical axis in the area cumulative distribution curve is 50%.

[0071] In some embodiments, the thickness of the positive current collector is 12 μm to 20 μm. Exemplarily, the thickness of the positive current collector is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm or any numerical range between any two of them. Using a thicker current collector can improve the overall strength and support of the laminated battery, and at the same time reduce the risk of the electrode wrinkling or breaking during high-pressure rolling.

[0072] As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector. In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0073] During the charge and discharge process of the battery, the insertion and extraction and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode active materials in the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0074] In the list of positive electrode active materials in the present application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0075] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0076] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In the present application, the lithium-containing transition metal phosphate particles of the positive electrode active material can be prepared by the following method, and the method includes the following steps.

[0078] S1, obtaining a mixed raw material including a carbon source, a lithium source, an iron source, and a phosphorus source, wherein the molar ratio of lithium to iron in the mixed raw material is greater than or equal to 1 and less than or equal to 1.05, and after grinding, a mixed slurry is obtained.

[0079] S2, drying the mixed slurry to obtain a precursor powder.

[0080] S3. Sinter the precursor powder, including: after the first sintering at a first temperature, conduct a second sintering at a second temperature of 750°C - 800°C.

[0081] S4. Conduct crushing to obtain the positive electrode active material; the crushing includes using air jet milling, and the classification frequency of the air jet milling is 18 Hz - 24 Hz, and the crushing air pressure is 0.45 MPa - 0.65 MPa.

[0082] The preparation method provided by this application improves the sphericity of the particles in the positive electrode active material by regulating the lithium-iron ratio, sintering temperature, and crushing process, such that the median L of the sphericity in the cumulative area distribution curve of the sphericity of the particles obtained from the cross-section along the thickness direction of the electrode sheet A50 is 0.70 - 0.75.

[0083] In some embodiments, the iron source includes divalent iron, and can be one or more of ferrous oxalate, ferrous carbonate, and ferrous nitrate.

[0084] In some embodiments, the lithium source includes one or more of lithium dihydrogen phosphate, lithium phosphate, lithium carbonate, and lithium acetate.

[0085] In some embodiments, the carbon source includes a polymer carbon source, and can be one or more of polyethylene glycol and polyvinyl alcohol.

[0086] During the sintering process, the divalent iron source will preferentially decompose to generate a large amount of ferrous oxide, which serves as the nucleation site to generate nanocrystalline nuclei of lithium-containing transition metal phosphate. At the same time, the polymer carbon source has a relatively low decomposition temperature, and the iron element on the surface of the nanocrystalline nuclei will further catalyze the decomposition of the carbon source, such that the carbon coating material on the surface of the positive electrode active material can have a relatively high degree of graphitization at a relatively low sintering temperature, reducing the resistivity of the positive electrode active material, and at the same time improving the compactness and uniformity of the carbon coating material coated on the surface of the lithium-containing transition metal phosphate.

[0087] In some embodiments, based on the total mass of the carbon source, the mass content of polyethylene glycol is 1.0% - 4.0%.

[0088] The polymer carbon source has a relatively low decomposition temperature and graphitization temperature, such that the carbon coating material on the surface of the positive electrode active material can decompose to form a carbon layer at a relatively low sintering temperature, hindering the growth and sintering of the lithium-containing transition metal phosphate grains, and being beneficial to reducing the particle size of the positive electrode active material particles.

[0089] In some embodiments, the lithium source and the phosphorus source can be the same substance.

[0090] In some embodiments, the iron source includes ferrous oxalate, the lithium source and the phosphorus source include lithium dihydrogen phosphate, and the carbon source includes polyethylene glycol.

[0091] In some embodiments, the atomic molar ratio of lithium element to iron element in the lithium source and the iron source may be selected as 1.00, 1.01, 1.02, 1.03, 1.04, 1.05 or the numerical range between any two of them.

[0092] When the atomic molar ratio of lithium element to iron element is 1, it belongs to the ideal stoichiometric ratio, which can maintain the best electrochemical performance, optimize the reversible deintercalation ability of lithium ions during charge and discharge, and has good crystal structure stability to improve the cycle life and reduce the probability of the appearance of impurity phases. However, in actual production, in order to compensate for the lithium loss during the sintering process, the molar ratio of lithium to iron elements needs to be adjusted to be slightly higher than 1.

[0093] In some embodiments, the slurry further includes a titanium source. Optionally, the titanium source includes one or more of titanium dioxide, tetrabutyl titanate, titanium nitrate, and titanic acid.

[0094] The titanium source often has low surface activity. 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, make the lithium-containing transition metal phosphate form smaller particles during sintering, contribute to improving the sphericity of the particles, and thus enhance the overall structural stability of the material.

[0095] In some embodiments, lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol, and titanium dioxide are mixed evenly and ground in an organic solvent to obtain a mixed raw material. The organic solvent can effectively reduce the occurrence of side reactions, improve the purity and consistency of the material. Moreover, the organic solvent has good volatility and is easier to remove during the subsequent drying process, and will not remain inside the material, resulting in pores inside the material and affecting the denseness and structural stability of the material.

[0096] In some embodiments, the mixed slurry obtained after grinding includes at least two ball milling-demagnetization cycles, and each of the ball milling and demagnetization independently satisfies one or more of the following conditions.

[0097] (1) The grinding balls for the ball milling are one or more of zirconia balls, silicon nitride zirconia balls, and ceramic zirconia balls.

[0098] (2) The diameter of the grinding balls for the first ball milling is 5 mm - 6 mm, and the diameter of the grinding balls for the second ball milling is 0.5 mm - 0.7 mm.

[0099] (3) The rotation speed of the first ball milling is 1400 rpm - 1600 rpm, and the rotation speed of the second ball milling is 400 rpm - 600 rpm.

[0100] (4) The first ball milling time is 150 - 200 min, and the second ball milling time is 140 min - 180 min.

[0101] (5) The demagnetization method is permanent magnet iron removal.

[0102] (6) The demagnetization intensity of the demagnetization is greater than or equal to 8000 GS.

[0103] Through at least two combinations of ball milling - demagnetization, large - particle materials can be quickly processed and further refined in a shorter time. In this way, it is possible to effectively avoid non - uniform particle size caused during ball milling, reduce the agglomeration phenomenon between particles, improve the conductivity and cycle stability of the battery, and at the same time improve the overall production efficiency while ensuring the performance of the final product.

[0104] In some embodiments, the volume - distribution particle size D of the particles in the mixed slurry V50 is 1.0 μm - 4.0 μm.

[0105] The volume - distribution particle size D of the particles in the mixed slurry V50 Within the above range, on the one hand, it can increase the activity of the particles to a certain extent, and at the same temperature, some cathode active material particles with a particle size of 1 μm - 1.5 μm can be generated, improving the compaction density of the electrode sheet and the energy density of the battery; on the other hand, it can improve the catalytic decomposition efficiency of iron elements on the surface of the crystal nucleus for the carbon source, improve the coating quality of the carbon source, and improve the uniformity and graphitization degree of the carbon - coated material coating, thereby further improving the compaction density of the electrode sheet and the energy density of the battery.

[0106] In some embodiments, the first sintering satisfies one or more of the following conditions.

[0107] (1) The heating rate is greater than or equal to 2 °C / min.

[0108] (2) The first temperature is 300 °C - 400 °C.

[0109] (3) The holding time is 2 h - 6 h.

[0110] The second sintering is carried out at the second temperature (750 °C - 800 °C) and optionally satisfies one or more of the following conditions.

[0111] (1) The heating rate is greater than or equal to 3 °C / min.

[0112] (2) The holding time is 8 h - 15 h.

[0113] Using a relatively high heating rate to quickly rise to the target temperature is beneficial to the uniform growth of particles and reduces the presence of larger - sized particles.

[0114] By controlling the sintering temperature in the sintering process, the speed of the sintering diffusion rate can be controlled. At high temperatures, the diffusion of the particle surface increases, the defects in the particles will be repaired, and the lattice will be rearranged. Through recrystallization, the defects on the particle surface are eliminated, the grain structure of the particles is more orderly, the size of the particles gradually increases, and it helps to smooth the particle surface and promote the particle to develop into a spherical shape. The sintering temperature also affects the graphitization rate of the carbon source. Kinetics, carbon atoms gain more energy and can overcome the original energy barrier, causing them to rearrange more violently in the lattice. The sintering time affects the degree of reaction. If the sintering time is too short, the diffusion and rearrangement of the lithium-containing transition metal phosphate and the carbon source are not completely completed; if the sintering time is too long, the particles will grow abnormally, the grains inside the particles will coarsen, the material structure will tend to be unstable, the bonding force between the particles will be enhanced, and agglomeration will occur.

[0115] In addition, in the present application, the classification frequency of airflow crushing is 18Hz-24Hz, and the crushing air pressure is 0.45MPa-0.65MPa. The classification frequency in airflow crushing refers to the operating frequency of the classification device in airflow crushing, which is usually related to the classification efficiency and particle size distribution of the particles. A higher classification frequency will screen the particles in the airflow more times, so that larger particles are screened out, leaving smaller particles. And a higher classification frequency is likely to increase the number of collisions of particles, so that irregular particles are further impacted, so that the particle shape tends to be spherical. In addition, high air pressure will cause the particles to be subjected to greater impact force, and the collision between particles will be more intense, which will cause the surface of the particles to be subjected to stronger impact and wear, and large particles can be crushed into small particles, and the collision between particles will be more intense, and the surface will be more easily trimmed, which improves the sphericity of the particles. However, too high classification frequency and crushing pressure will cause the agglomerated particles to further crack and break after being dispersed into primary particles, affecting the predetermined particle gradation distribution and making the carbon coating material incomplete, which is manifested as increased iron dissolution, negatively affecting the slip of particles during rolling, and increasing the contact and reaction between lithium-containing transition metal phosphates and external factors such as electrolytes, which is not conducive to the cycle performance and life of the battery. Therefore, it is necessary to control the classification frequency and crushing pressure of air flow crushing within a suitable range.

[0116] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0117] Negative electrode In the present application, the negative electrode tab includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material. As an example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite surfaces of the negative electrode current collector.

[0118] In some embodiments, the tap density of the negative electrode tab is 1.3 g / cm 3 -1.55 g / cm 3 . Exemplarily, the tap density is 1.30 g / cm 3 、1.35 g / cm 3 、1.40 g / cm 3 、1.41 g / cm 3 、1.42 g / cm 3 、1.43 g / cm 3 、1.44 g / cm 3 、1.45 g / cm 3 、1.46 g / cm 3 、1.47 g / cm 3 、1.48 g / cm 3 、1.49 g / cm 3 、1.50 g / cm 3 、1.51 g / cm 3 、1.52 g / cm 3 、1.53 g / cm 3 、1.54 g / cm 3 、1.55 g / cm 3 or any value range between any two of them. Optionally, the tap density of the negative electrode tab is 1.40 g / cm 3 -1.50 g / cm 3 . By making the tap density within the above range, it is beneficial to improve the energy density of the battery. The tap density of the negative electrode tab in the present application is the tap density measured under the condition of 0% SOC (State of Charge).

[0119] In some embodiments, the single-sided coating weight of the negative electrode film layer is 0.150 g / 1540.25 mm 2 ~0.207 g / 1540.25 mm 2 . Exemplarily, the single-sided coating weight is 0.150 g / 1540.25 mm 2 、0.155 g / 1540.25 mm 2 、0.160 g / 1540.25 mm2 、0.165 g / 1540.25 mm 2 、0.170 g / 1540.25 mm 2 、0.175 g / 1540.25 mm 2 、0.180 g / 1540.25 mm 2 、0.185 g / 1540.25 mm 2 、0.190 g / 1540.25 mm 2 、0.195 g / 1540.25 mm 2 、0.200 g / 1540.25 mm 2 、0.207 g / 1540.25 mm 2 or a numerical range between any two of them. Optionally, the single-sided coating weight of the negative electrode film layer is 0.170 g / 1540.25 mm 2 ~0.200 g / 1540.25 mm 2 . By making the single-sided coating weight of the negative electrode film layer within the above range, it is possible to ensure that the battery has a high energy density.

[0120] In some embodiments, the porosity of the negative electrode plate is 23% - 32%. Exemplarily, the porosity of the negative electrode plate is 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32% or a numerical range between any two of them. A porosity within this range can simultaneously ensure that the battery has a high tap density and good wettability, thereby ensuring that the battery has a high energy density and good cycling performance.

[0121] In some embodiments, the thickness of the negative electrode current collector is 6 μm - 12 μm. Exemplarily, the thickness of the negative electrode current collector is 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm or a numerical range between any two of them. Using a thicker current collector can improve the overall strength and support of the stacked cell, and at the same time can also avoid the risk of the electrode plate wrinkling or breaking during high-pressure rolling.

[0122] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer 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 (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0123] The negative electrode active material can be the negative electrode active material for batteries known in the art. In some embodiments, the negative electrode active material includes graphite, and the volume average particle size Dv50 of the graphite is 13 μm to 22 μm. Exemplarily, the volume average particle size Dv50 is 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, or a numerical range between any two of them. Optionally, the volume average particle size Dv50 of the graphite is 14.5 μm to 20 μm. By using graphite with a particle size in the above range, it is beneficial to increase the compaction density of the electrode sheet, thereby increasing the volume energy density of the battery; at the same time, it can ensure that the transmission path of lithium ions in the graphite is appropriate, reducing the risk of adverse effects on battery performance due to too long a path.

[0124] However, as the negative electrode active material, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. As an example, the negative electrode active material may further include soft carbon and / or hard carbon.

[0125] In some embodiments, the negative electrode film layer may further optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0126] In some embodiments, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0127] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickener (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0128] In some embodiments, the negative electrode sheet can be prepared in the following manner: Dispersing the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; Coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet can be obtained.

[0129] Separator The separator of the present application includes a base film and coatings provided on both sides of the base film. The coatings include a bonding layer, the bonding layer is a continuous layer with a porous structure, and the bonding layer includes a fluoropolymer.

[0130] The adhesive layer is a porous and continuous layer structure, which is mainly constructed by an oil-based binder, that is, the binder is dispersed with an organic solvent and then coated into a film. The adhesive layer formed thereby is a continuous structure (see Figure 2 , which schematically shows the microstructure of the surface of the separator 10 of the present application). Such a structure is different from the adhesive layer constructed by a traditional water-based binder, which mainly disperses the binder with an aqueous solvent and then coats it into a film, so that the formed adhesive layer has an island-like structure (see Figure 3 , which schematically shows the microstructure of the surface of the separator 20 formed by a traditional water-based binder). Although the adhesive layer with an island-like structure is convenient for manufacturing, the bonding area is small and the bonding force is weak. This problem is particularly obvious in the stacked battery, which will cause the misalignment of the electrodes of the stacked battery, and further affect the cycle performance. Therefore, the battery cell of the present invention adopts a stacked electrode assembly and at the same time adopts a separator with a continuous adhesive layer having the above-mentioned porous structure on both sides, so that there is a good bonding force between the electrode and the separator, thereby obtaining a battery cell with a high energy density and a stable cell structure. For the adhesive layer, on the one hand, the continuous film layer enables the adhesive layer to have a larger area in contact with the electrode, enhancing the bonding force between the separator and the electrode; on the other hand, the porous structure enables the active ions in the electrolyte to be more easily transported between the separators.

[0131] The morphology of the continuous layer of the porous structure of the adhesive layers on both sides of the separator can be observed by an electron microscope. For example, the separator can be disassembled from the battery cell, and after cleaning the surface, it can be observed under, for example, a scanning electron microscope. In order to reflect the true morphology of the separator, during the sampling process, it is preferably sampled in the area where the adhesive layer of the separator in the battery does not bond with the positive electrode or the negative electrode. As an example, sampling is performed at the position of the separator where the projection exceeds the positive electrode and the negative electrode; or sampling is performed on the separator near the surface of the electrode assembly. In these sampling areas, the bonding between the separator and the positive electrode or the negative electrode is less, and the true state of the separator can be better reflected.

[0132] In addition, it can be understood that the continuous structure may become blocky due to contact with the positive electrode or the negative electrode or being squeezed during the manufacturing or cycling process of the electrode. The continuous structure referred to in the present application does not mean that the adhesive layer is continuous throughout the battery. Instead, it refers to a continuous network layer with a porous structure at the microscopic level, such as when observed under an electron microscope, rather than an island-like structure.

[0133] This application has no special restrictions on the type of the base film, and any publicly known porous structure base film with good chemical stability and mechanical stability can be selected. In some embodiments, the material of the base film includes one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The base film can be a single-layer film or a multi-layer composite film, without any special restrictions. When the base film is a multi-layer composite film, the materials of each layer can be the same or different, without any special restrictions. Optionally, the base film is polyethylene.

[0134] In some embodiments, the thickness of the base film is 7μm - 9μm, and this thickness range is beneficial to improving the safety performance of the battery cell. Exemplarily, the thickness of the base film is any value among 7μm, 8μm, 9μm or a value within the range composed of any two of these values.

[0135] The coating is located on both sides of the base film and includes a bonding layer, and the bonding layer is a continuous layer with a porous structure. In some embodiments, the bonding layer is arranged in contact with the surface of the base film. In some other embodiments, there are other interposed layers between the bonding layer and the base film, for example, the ceramic layer detailed below.

[0136] The bonding layer includes a fluoropolymer. The fluoropolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-chlorotrifluoroethylene-tetrafluoroethylene-hexafluoropropylene copolymer. Optionally, the fluoropolymer includes polyvinylidene fluoride PVDF. Such polymers can be dissolved in oily solvents to open the molecular chains to form a relatively uniform slurry. Thus, an overall porous network structure is formed during coating, significantly improving the bonding force with the electrode sheet.

[0137] In some embodiments, the thickness of one side of the bonding layer is 0.5μm - 2μm. Within this thickness range, the bonding strength between the separator and the electrode sheet is within a suitable range, which is beneficial to the cycle performance and safety performance of the battery cell. Exemplarily, the thickness of the one-sided bonding layer is any value among 0.15μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.5μm, 1.6μm, 1.8μm, 2μm or a value within the range composed of any two of these values.

[0138] The "thickness of one side of the bonding layer" mentioned in this application refers to the average thickness of the film layer where the bonding material exists, without counting the part of the pores in the film layer where there is no bonding material.

[0139] In some embodiments, the coating further includes a ceramic layer disposed between the base film and the adhesive layer. The ceramic layer includes one or more ceramic particles such as alumina, boehmite, silica, magnesia, titania, stannic oxide, calcium oxide, zirconia, barium sulfate, yttria, zinc oxide, silicon carbide, magnesium fluoride, barium titanate, aluminum hydroxide, magnesium hydroxide, or calcium hydroxide. Optionally, the ceramic layer includes alumina and / or boehmite.

[0140] Disposing a ceramic layer between the base film and the adhesive layer can improve the wettability of the electrolyte to the separator, promote the flow of the electrolyte, and is beneficial to further improving the performance deterioration problem of the battery cell caused by insufficient electrolyte wetting, thereby being more conducive to improving the cycle performance of the battery monomer.

[0141] In some embodiments, the average particle size of the ceramic material is 0.2 μm to 2.5 μm; optionally, it is 0.5 μm to 1.5 μm. Controlling the average particle size of the ceramic material within the above range is beneficial to improving the liquid retention capacity of the separator membrane, thereby being beneficial to further improving the lithium plating situation, and further being beneficial to improving the cycle performance and safety performance of the battery monomer. Exemplarily, the average particle size of the ceramic material is any value among 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 2.5 μm or a value within the range composed of any two numerical values.

[0142] In some embodiments, the single-sided thickness of the ceramic layer is 0.5 μm - 4 μm. Within this thickness range, the wettability and liquid retention of the electrolyte can be improved, which is beneficial to the cycle performance and safety performance of the battery monomer. Exemplarily, the thickness of the single-sided ceramic layer is any value among 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm or a value within the range composed of any two numerical values.

[0143] The presence of the adhesive layer and the optional ceramic layer in the separator membrane disassembled from the electrode assembly can be observed by scanning electron microscopy (SEM).

[0144] In order to reflect the true morphology of the separator membrane, during the sampling process, it is preferably sampled in the area where the adhesive layer of the separator membrane in the battery does not bond with the positive electrode plate or the negative electrode plate. As an example, it is sampled at the part of the separator membrane that projects beyond the positive electrode plate and the negative electrode plate; or it is sampled at the separator membrane near the surface of the electrode assembly. The bonding between such a separator membrane sampling area and the positive electrode plate or the negative electrode plate is less, and it can better reflect the true state of the separator membrane.

[0145] The specific method can adopt the following method for measuring the coating thickness, and observe from the cross-section of the separator film along the thickness direction. In addition, the morphology of the coating can also be observed by observing the surface of the separator film under a scanning electron microscope (SEM). As mentioned above, after disassembling the separator film from the battery cell and sampling in a suitable area, clean the surface of the separator film sample, and the surface of the separator film can be observed by SEM. Refer to Figure 2 The schematic diagram of the microstructure of the surface of the separator film. According to the separator film 10 of the present application, the morphology of the porous continuous adhesive layer 11 on the surface can be seen as a continuous film layer with a porous structure including a plurality of pores 111. If there is a ceramic layer, the ceramic particles in the ceramic layer 12 below the adhesive layer can be observed from the pores 111 of the adhesive layer 11. Different from the separator film of the present application, Figure 3 The schematic diagram of the microstructure of the surface of the conventional separator film 20 obtained by using the conventional aqueous adhesive coating method is shown. Refer to Figure 3 , the surface of the conventional separator film 20 also has a ceramic layer 12, and there are island-shaped adhesives 21 on the ceramic layer 12. By comparing Figure 2 and Figure 3 , it can be seen that the adhesive layer of the present application has a much larger adhesive area.

[0146] In the embodiment of the present application, the thickness of the base film, the single-sided thickness of the adhesive layer, and the single-sided thickness of the ceramic layer have their conventional meanings in the art. The thickness of the base film and the coating in the separator film can be detected by methods and equipment well-known in the art. For example, a newly prepared separator film can be taken as a sample, or a discharged battery cell (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, the separator film is obtained from the battery cell, and the separator film is dried and used as a sample. Cut the separator film along the thickness direction with an ion beam cutter to expose the cross-section. Subsequently, use a scanning electron microscope to measure the thickness of the cross-section of the separator film and its respective layers. Adjust the microscope to an appropriate magnification, and the base film, ceramic layer, and adhesive layer of the separator film can be completely observed. Then, perform a mapping test on the separator film. The coating containing the distribution of metal elements in the test results is the ceramic layer, and the coating with higher carbon and fluorine element contents is the adhesive layer. Then, measure the thickness T1 of the ceramic coating and the thickness t1 of the adhesive layer on one side of the base film respectively. According to the above operation steps, further measure the thicknesses T2, T3, T4, T5 of the ceramic layer and the thickness values t2, t3, t4, t5 of the organic coating in another 4 different fields of view. Calculate the average value respectively to obtain the thicknesses of the ceramic coating and the adhesive layer.

[0147] The specific materials of the adhesive layer and the optional ceramic layer can be tested by the following methods: For the separator disassembled from the battery cell at 0% state of charge (SOC) from the electrode assembly, for the separator with only the adhesive layer, the separator can be placed in a suitable solvent (such as N-methylpyrrolidone, NMP) to dissolve the adhesive layer and then tested with an infrared spectrometer, or directly tested with an infrared spectrometer on the surface of the entire separator sample. The type of the adhesive layer material can be identified by identifying the characteristic peaks in the infrared spectrum. For the separator with an adhesive layer and a ceramic layer, the separator can be placed in a suitable solvent (such as NMP), ultrasonically treated at 60 °C for 60 min to remove the coating on the separator, then the solid material is collected, and the solid material is subjected to X-ray diffraction test. The type of the ceramic material can be determined by the XRD test pattern. In addition, the separator can be placed in a suitable solvent (such as NMP), the adhesive layer is dissolved and then tested with an infrared spectrometer, or directly tested with an infrared spectrometer on the surface of the entire separator sample. The type of the adhesive layer material can be identified by identifying the characteristic peaks in the infrared spectrum.

[0148] In some embodiments, the thickness of the base film is 7 μm - 9 μm. Exemplarily, the thickness of the base film is 7 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, 7.5 μm, 7.6 μm, 7.7 μm, 7.8 μm, 7.9 μm, 8.0 μm, 8.1 μm, 8.2 μm, 8.3 μm, 8.4 μm, 8.5 μm, 8.6 μm, 8.7 μm, 8.8 μm, 8.9 μm, 9 μm or any value range between any two of them.

[0149] In some embodiments, the porosity of the separator is 28% - 50%. Exemplarily, the porosity is 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50% or any value range between any two of them. Optionally, the porosity of the separator is 31% - 40%. By making the porosity of the separator within the above range, it is possible to reduce the influence on the migration rate of lithium ions between the positive and negative electrodes while enabling the separator to have appropriate mechanical strength.

[0150] The present application does not particularly limit the preparation method of the separator. Exemplarily, it can be prepared by the following method.

[0151] The separator with a ceramic layer is first coated with the ceramic layer. Ceramic particles and a binder (e.g., with a mass ratio of 5:1, and a thickener if any) for forming the ceramic layer are dispersed in a solvent (e.g., N-methylpyrrolidone NMP) to form a ceramic layer slurry. The ceramic layer slurry is coated on both sides of the base film, and after drying to remove the solvent, a separator with ceramic layers on both sides of the base film is obtained.

[0152] Next, the adhesive layer is coated. A fluoropolymer (such as PVDF, with a final mass content of 20%) is dissolved in an organic solvent (such as NMP), and then a pore-forming agent (such as PEG, with a final mass content of 15%) is added and mixed evenly to obtain an adhesive layer solution. The liquid is coated on the surface of the ceramic layer (for those without a ceramic layer, it can be directly coated on the surface of the base film), and part of the solvent is pre-evaporated at 80°C, and then dried at 110°C. The dried separator is immersed in deionized water to dissolve and wash away PEG, thereby forming a porous adhesive layer.

[0153] Electrolyte The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. There is no specific limitation on the type of electrolyte in this application, and it can be selected according to requirements.

[0154] In some embodiments, the electrolyte includes a chain carbonate solvent. Based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is 43%-71%. Exemplarily, based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is any value among 43%, 45%, 50%, 52%, 54%, 56%, 58%, 60%, 62%, 65%, 70%, 71% or a value within the range composed of any two numerical values. Optionally, based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is 52%-62%. As a solvent for the electrolyte, the chain carbonate has a lower viscosity than the cyclic carbonate. When the electrolyte includes 43%-71% of the chain carbonate, the viscosity of the electrolyte is effectively reduced, and the wetting of the electrode assembly is improved.

[0155] In some embodiments, the chain carbonate includes one or both of dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). Optionally, the chain carbonate solvent includes DMC and EMC. Further optionally, the chain carbonate is DMC and EMC.

[0156] DMC has a lower viscosity than EMC and can play a greater role in reducing the viscosity of the electrolyte. However, DMC has a higher crystallization temperature, so its low-temperature performance is relatively poor and it is prone to crystallization at low temperatures. When DMC is used in combination with EMC, it can not only effectively reduce the viscosity of the electrolyte and improve the wettability of the electrolyte, but also will not cause a decline in the low-temperature performance of the battery.

[0157] The present application places no particular limitation on the ratio of DMC to EMC, which can be adjusted as needed. In some embodiments, based on the total mass of the electrolyte, the mass content of DMC is 8% - 43%. Exemplarily, based on the total mass of the electrolyte, the mass content of DMC is any value among 8%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 43% or a value within the range composed of any two of these numerical values. When the content of DMC in the electrolyte is within the above range, its function of reducing the viscosity of the electrolyte can be fully exerted, and at the same time, the low-temperature performance of the battery will not be affected.

[0158] In some embodiments, the electrolyte further includes cyclic carbonates. Cyclic carbonates are beneficial to the dissociation of lithium salts and improve the conductivity of the electrolyte. In addition, cyclic carbonates can also form a stable SEI film on the surface of the negative electrode, thereby contributing to the improvement of the cycle stability and safety of the battery.

[0159] In some embodiments, the cyclic carbonate may include ethylene carbonate (EC) and / or propylene carbonate (PC).

[0160] In some embodiments, based on the total mass of the electrolyte, the mass content of the cyclic carbonate is 14% - 42%. Exemplarily, based on the total mass of the electrolyte, the mass content of the cyclic carbonate is any value among 14%, 17%, 20%, 23%, 24%, 26%, 28%, 30%, 32%, 33%, 36%, 39%, 42% or a value within the range composed of any two of these numerical values. Optionally, based on the total mass of the electrolyte, the mass content of the cyclic carbonate is 23% - 33%. When the mass content of the cyclic carbonate is within the above range, it is beneficial to improve the conductivity of the electrolyte and will not affect the wettability of the electrolyte to the electrode assembly.

[0161] The present application places no particular limitation on the electrolyte salt. In some embodiments, the electrolyte salt includes a lithium salt. The lithium salt includes one or more selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. Optionally, the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorophosphate, and lithium bis(fluorosulfonyl)imide.

[0162] In some embodiments, based on the total mass of the electrolyte, the mass content of the electrolyte salt is 8% - 18%, optionally 11% - 15%.

[0163] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc. Exemplarily, the additives include one or more of vinylene carbonate, fluoroethylene carbonate, and fluorobenzene. Based on the total mass of the electrolyte, the mass content of the additives is 0.4% - 5%, optionally 0.7% - 3%. Exemplarily, in the electrolyte, the mass content of the additives is any value among 0.5%, 0.7%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a value within the range composed of any two of these numerical values.

[0164] In the present application, the battery cell includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly functioning to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0165] In some embodiments, the battery cell may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0166] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0167] The present application has no particular limitation on the shape of the battery cell, and it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 is a battery cell 5 with a square structure as an example.

[0168] In some embodiments, referring to Figure 5 , the outer package may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator are formed into an electrode assembly 52 through a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte infiltrates in the electrode assembly 52. The number of the electrode assemblies 52 included in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0169] Battery device In a second aspect of the present application, a battery device is provided. The battery device (Battery Apparatus) of the present application may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly (Battery Cell Assembly) may include a plurality of the battery cells provided in the first aspect above, and the plurality of battery cells are connected in series, parallel, or in a hybrid connection through a busbar component.

[0170] In some embodiments, the battery cell assembly (Battery Cell Assembly) is generally formed by arranging a plurality of battery cells.

[0171] As an example, the battery cell assembly may be a battery module (Battery Module), and the battery module is formed by arranging and fixing a plurality of battery cells into an independent module. As an example, the battery module may be formed by bundling a plurality of battery cells with cable ties.

[0172] As an example, the battery cell assembly may also be accommodated in a box by directly fixing a plurality of battery cells to the box.

[0173] As an example, the box may include a first box body and a second box body. The first box body and the second box body are snapped together so that a closed space is formed inside the box to accommodate the battery cell assembly. The "closed" here means covering or closing, which may be sealed or non-sealed. The first box body may be a top cover or a bottom plate.

[0174] As an example, the box may include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame so that a closed space is formed inside the box to accommodate the battery cell assembly.

[0175] In some embodiments, the box may be part of the chassis structure of a vehicle. For example, a part of the box may form at least a part of the floor of the vehicle, or a part of the box may form at least a part of the crossbeam and longitudinal beam of the vehicle.

[0176] In some embodiments, the battery device may be a battery pack (battery Pack), and the battery pack includes a box and one or more battery cell assemblies, and the battery cell assemblies are accommodated in the box.

[0177] The technical solutions described in the embodiments of the present application are applicable to various electrical devices using battery cells, such as mobile phones, portable devices, laptop computers, battery cars, electric toys, electric tools, vehicles, ships, and spacecrafts, etc. For example, spacecrafts include airplanes, rockets, space shuttles, and spaceships, etc.

[0178] Figure 6 This is the battery module 4 as an example. Refer toFigure 6 In the battery module 4, multiple battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the multiple battery cells 5 may be fixed by fasteners.

[0179] Optionally, the battery module 4 may further include a housing having an accommodation space, and the multiple battery cells 5 are accommodated in the accommodation space.

[0180] Figure 7 and Figure 8 is the battery pack 1 as an example. Refer to Figure 7 and Figure 8 In the battery pack 1, a battery box and multiple battery modules 4 arranged in the battery box may be included. The battery box includes a first box body 2 and a second box body 3. The first box body 2 can cover the second box body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in the battery box in any manner.

[0181] Power-consuming device A third aspect of the embodiments of the present application further provides an electrical device. The electrical device of the present application will be described below with reference to the accompanying drawings as appropriate.

[0182] The electrical device mentioned in the embodiments of the present application includes the battery device provided in the second aspect of the present application. The battery device can be used as the power supply of the electrical device or as the energy storage unit of the electrical device. The electrical device may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0183] Figure 9 is the electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the electrical device for the battery, a battery pack or a battery module may be used.

[0184] Another example of the device may be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thinness and lightness, and battery cells may be used as the power supply.

[0185] Embodiment Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific technologies or conditions noted in the embodiments, the technologies or conditions described in the literature in the art or according to the product specifications are followed. For the reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0186] Example 1 (1) Preparation method of the positive electrode material S1, Lithium dihydrogen phosphate, ferrous oxalate, polyethylene glycol, and titanium dioxide are mixed evenly in methanol and then ground to obtain a mixed raw material. Among them, the ratio of lithium dihydrogen phosphate to ferrous oxalate is adjusted so that the atomic molar ratio of lithium to iron is 1.03.

[0187] S2, The mixed slurry is spray-dried to obtain a dried precursor powder, and the appearance of the dried precursor powder is light yellow and uniform in color.

[0188] S3, The precursor powder is placed in a sintering furnace. Under a nitrogen atmosphere, it is heated from 25°C to the first temperature of 350°C at a rate of 2°C / min and held at this temperature for 3 h, and then heated to the second temperature of 770°C at a rate of 5°C / min and held at this temperature for 10 h. After that, it is cooled down.

[0189] S4, The obtained material is crushed by the method of air flow crushing with a classification frequency of 21 Hz and an air volume with a crushing air pressure of 0.55 MPa to obtain a carbon-coated lithium iron phosphate positive electrode active material.

[0190] (2) Preparation of the positive electrode sheet The positive electrode active material (chemical formula LiFePO4. D A50 is 750 nm), polyvinylidene fluoride, conductive carbon black, and carboxymethyl cellulose are mixed in a weight ratio of 97:2:1 and then added to the solvent N-methylpyrrolidone, stirred evenly to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector aluminum foil (thickness 15 um) to form a positive electrode film layer (the coating weight per side is 0.38 g / 1540.25 mm 2 , and the coating thickness per side is 102.8 μm), and after drying, it is cold-pressed under the condition of a roll pressure of 55 tons to obtain a positive electrode sheet (the porosity is 28.4%).

[0191] (3) Preparation of the negative electrode sheet The anode material graphite (volume average particle size Dv50 is 15 μm) is fully stirred and mixed with the conductive agent Super-P, the dispersant CMC, and the binder SBR in a mass ratio of 96.4:0.4:1.0:2.2 in an appropriate amount of deionized water to form an anode slurry; the anode slurry is coated on a copper foil (8um) to form an anode film layer (the single-sided coating weight of the anode film layer is 0.185 g / 1540.25mm 2 , and the single-sided coating thickness is 82 μm), and after drying and cold pressing, an anode electrode sheet (porosity is 29%) is obtained.

[0192] (4) Preparation of electrolyte In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed evenly. Then lithium hexafluorophosphate is added and dissolved in the organic solvent to make the concentration of lithium hexafluorophosphate in the electrolyte 1.05 mol / L, and vinylene carbonate (VC) is added and stirred evenly to obtain the electrolyte of Example 1.

[0193] Among them, based on the total mass of the electrolyte, the mass content of dimethyl carbonate is 27.2%, the mass content of ethyl methyl carbonate is 29.9%, the mass content of ethylene carbonate is 28.1%, and the mass content of vinylene carbonate is 2.6%.

[0194] (5) Separator A 7μm polyethylene film is used as the base film. The ceramic material alumina powder (particle size 1μm) and the binder polyvinylidene fluoride (PVDF) are added to the solvent N-methylpyrrolidone (mass ratio of alumina:PVDF:solvent is 5:1:10) and mixed evenly to make a ceramic layer slurry. The ceramic layer slurry is coated on both sides of the base film and dried to form a ceramic layer. PVDF is added to the solvent N-methylpyrrolidone and mixed evenly, and then polyethylene glycol (PEG) as a pore-forming agent is added to make a binder layer solution, where the mass content of PVDF is 20% and the mass content of PEG is 10%. The binder layer solution is coated on the ceramic layer, pre-volatilized at 80°C and dried at 110°C, and then immersed in deionized water to dissolve polyethylene glycol to obtain a separator. The single-sided thickness of the ceramic layer of the obtained separator is measured to be 1.6μm, the single-sided thickness of the binder layer is 0.65μm, and the porosity of the separator is 35% by the following method.

[0195] (6) Preparation of battery monomer Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an insulating role, and then form an electrode assembly through the stacking process. Place the electrode assembly in an outer package, inject the above-mentioned electrolyte after drying, and obtain a battery cell through processes such as vacuum packaging, standing, formation, and shaping.

[0196] Performance test of the electrode sheet (1)Compaction density under the condition of 0% SOC The compaction density of the electrode sheet is determined by measuring the single-sided coating weight (g / cm 2 ) of the electrode sheet per unit area and the thickness (cm) of the single-sided coating on the electrode sheet (the number of sampling points > 10). Among them, the compaction density PD of the negative electrode sheet = the single-sided coating weight (g / cm 2 ) of the electrode sheet per unit area / the thickness (cm) of the single-sided coating on the electrode sheet.

[0197] Testing method for single-sided coating weight of electrode sheet After the battery cell is fully discharged and disassembled, take an appropriate amount of the electrode sheet, soak it in DME for 1 h and then take it out for drying. Cut 10 electrode sheets of the same size and weigh them. The average weight of the 10 electrode sheets is recorded as m1; then wipe off the active material coatings on both sides of the 10 electrode sheets and weigh the weight of the substrate. The average weight of the 10 substrates is recorded as m2; then the single-sided coating weight of the electrode sheet = (m2 - m1) / 2.

[0198] Measuring method for thickness of single-sided coating on electrode sheet After the battery cell is fully discharged and disassembled, take an appropriate amount of the electrode sheet in the double-sided coating area, soak it in DME for 1 h and then take it out for drying. Use a micrometer to measure the total thickness at 15 different positions of the electrode sheet, and take the average value and record it as t1; then measure the thickness of the substrate at 15 different positions of the electrode sheet, and take the average value and record it as t2; then the thickness of the single-sided coating on the electrode sheet = (t1 - t2) / 2.

[0199] (2)Determination of L A10 、L A50 、L A90 of sphericity Determination is carried out with reference to the specific test method described above. Among them, L A50 is the sphericity corresponding to the proportion of the cumulative area on the vertical axis in the sphericity cumulative distribution curve being 50%; L A10 is the sphericity corresponding to the proportion of the cumulative area on the vertical axis in the sphericity cumulative distribution curve being 10%; L A90 is the sphericity corresponding to the proportion of the cumulative area on the vertical axis in the sphericity cumulative distribution curve being 90%.

[0200] Characteristics test of the separator (1)Coating thickness The isolation film was polished along the thickness direction using an argon ion cross-section polisher (such as the IB-09010 CP type argon ion cross-section polisher from JEOL, Japan) (argon gas flow rate 0.12 MPa, polishing time 90 min) to obtain the cross-section of the isolation film along the thickness direction. It was observed under a field emission scanning electron microscope that the base film, ceramic layer, and bonding layer were present simultaneously in the field of view. At 5 different fields of view, 5 sites were respectively selected to measure the thicknesses of the ceramic layer and bonding layer on the side of the base film, and the average value was calculated.

[0201] (2) Porosity of the isolation film The porosity of the isolation film was measured in accordance with Standard GB / T 24586-2009.

[0202] Performance test of the battery cell (1) Test of volume energy density At 25 °C, the battery cell was charged at a constant current of 0.33C to the cut-off voltage of 3.65V, and then charged at a constant voltage of 3.65V until the current reached 0.05C. At this time, the secondary battery was in a fully charged state. After the fully charged secondary battery was left standing for 5 min, it was discharged at a constant current of 0.33C to the cut-off voltage of 2.5V, and the discharge energy was recorded as Q0.

[0203] The length, width, and thickness of the battery cell were measured, and the volume of the battery cell was calculated and denoted as V; then the volume energy density of the battery = Q0 / V, unit: Wh / L.

[0204] (2) Test method for DCR growth rate At 25 °C, after charging at a constant current of 0.33C to 3.65V, charging at a constant voltage until the current reached 0.05C, then discharging at 1 / 3C to 50% SOC, leaving standing for 5 min, discharging with a 3C pulse for 30 s, leaving standing for 40 s, and charging with a 3C current for 40 s, and then leaving standing for 10 min.

[0205] The voltage before and after the pulse discharge was recorded, and the formula for calculating DCR was DCR = (voltage before the pulse discharge after the standing end - voltage before the standing after the pulse discharge) / pulse current.

[0206] The DCR before the cycle was tested according to the above process and denoted as R0, and the DCR after 2000 cycles was denoted as R1. Then the growth rate of DCR after 2000 cycles = (R1 - R0) / R0 * 100% Cycle test method At 25 °C, the lithium-ion secondary battery was charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V until the current reached 0.05C; left standing for 10 min; then discharged at a constant current of 0.33C to 2.5V; the above steps were cycled 2000 times.

[0207] Example 2-6 The preparation method of Example 2-6 is similar to that of Example 1, except that the preparation method of the positive electrode sheet is adjusted as shown in Table 1.

[0208] Example 7-11 The preparation method of Example 7-11 is similar to that of Example 1, except that the compaction density of the electrode sheet is adjusted by adjusting the roll pressure during cold pressing of the electrode sheet.

[0209] Comparative Example 1 The preparation method of Comparative Example 1 is similar to that of Example 7, except that the preparation method of the positive electrode sheet is adjusted as shown in Table 1.

[0210] Comparative Example 2 The preparation method of Comparative Example 2 is similar to that of Example 1, except that the compaction density of the electrode sheet is adjusted by adjusting the roll pressure during cold pressing of the electrode sheet to 65 tons.

[0211] According to the same test method as in Example 1, the performance of the battery monomers prepared in Examples 2 to 9 and Comparative Examples 1 and 2 was measured, and the specific results are shown in Table 1.

[0212] Table 1

[0213] As can be seen from Table 1, in Examples 1 to 6, at the same positive electrode compaction density, the sphericity L of the lithium iron phosphate particles A50 is in the range of 0.70 to 0.75, which can reduce the DCR growth rate during the cycling of the battery cell. The increase in DCR during cycling is related to problems such as the wrinkling and deformation of the electrode sheet caused by stress concentration during the cycling of the electrode sheet. The deformation of the electrode sheet will affect the interface contact between the electrode sheet and the separator, affecting the normal insertion and extraction of lithium ions, thereby leading to an increase in the internal resistance of the battery cell. Using lithium iron particles with a higher sphericity can release the stress generated during the insertion and extraction of lithium in the electrode sheet through the slip between the particles, thereby alleviating the damage to the electrode sheet structure caused by stress concentration in the electrode sheet and improving the battery performance.

[0214] In Examples 7 to 11, using lithium iron particles with the same sphericity, by making the compaction density in the range of 2.25 g / cm 3 -2.65 g / cm 3 range, as the compaction density of the positive electrode sheet increases, the volumetric energy density of the battery increases accordingly.

[0215] By comparing Example 7 with Comparative Example 1, it can be seen that the compaction density of Comparative Example 1 is the same as that of Example 7, but due to the sphericity L A50 being outside the range of 0.70 to 0.75, the DCR growth rate is significantly higher than that of Example 7. In addition, by comparing Examples 7 to 11 with Comparative Example 2, it can be seen that although the sphericity LA50 The same, but the compaction of comparative example 2 is too high, the contact pressure between particles increases, which may cause particle deformation or rupture, resulting in increased side reactions during charging and discharging, and increased impedance; on the other hand, the residual stress of the pole piece is higher after high-pressure rolling, and the deintercalation of lithium ions during charging and discharging will further aggravate stress concentration, leading to particle contact failure, pole piece structure degradation, forming a local "dead zone", and increasing interface impedance. Therefore, the DCR growth rate in comparative example 2 is very large, and the technical effect of the present application cannot be obtained.

[0216] Examples 12-14 The preparation methods of Examples 12-14 are similar to those of Example 1, except that the isolation membranes are different and are adjusted as shown in Table 2.

[0217] Comparative Example 3 The preparation method of Comparative Example 3 is similar to that of Example 1, except that a polypropylene film (thickness 12 um) is used as the isolation film.

[0218] Comparative Example 4 The preparation method of comparative example 4 is similar to that of example 1, except that the isolation membrane is different. Specifically, the adhesive layer of the isolation membrane adopts a traditional water-based adhesive layer. In the preparation of the isolation membrane of example 1, water is used instead of N-methylpyrrolidone, and polyethylene glycol is not added.

[0219] Through testing, it was found that the single-side thickness of the ceramic layer of the obtained isolation membrane was 1.6um; the single-side thickness of the bonding layer was 0.65um, and the bonding layer was an island structure and was discontinuous.

[0220] Table 2

[0221] It can be seen from Table 2 that by using the separator of the present application, the DCR growth rate of the laminated battery during the cycle can be reduced and the battery energy density can be improved. In contrast, Comparative Examples 3 and 4 use separators different from those of the present application, which cannot take into account both energy density and cycle performance, and cannot achieve the technical effect of the present application.

[0222] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that, It includes a laminated electrode assembly, and the laminated electrode assembly includes a positive electrode tab, a separator, and a negative electrode tab which are stacked. The negative electrode tab includes a negative current collector and a negative electrode film layer provided on at least one side of the negative current collector. The positive electrode tab includes a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes lithium-containing transition metal phosphate particles. The compaction density of the positive electrode sheet is 2.25 g / cm 3 -2.65 g / cm 3 , In the cumulative area distribution curve of the sphericity of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the L of the sphericity A50 is 0.70 to 0.75, and L A50 represents the sphericity corresponding to the cumulative area ratio of 50% on the vertical axis in the cumulative distribution curve of the sphericity. The separator includes a base film and coatings provided on both sides of the base film. The coatings include a bonding layer, and the bonding layer is a continuous layer with a porous structure. The bonding layer includes a fluoropolymer.

2. The battery cell according to claim 1, characterized in that, In the cumulative area distribution curve of the sphericity of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, the L of the sphericity A90 is 0.80 - 0.90, and L A90 represents the sphericity corresponding to when the cumulative area ratio of the vertical axis in the cumulative distribution curve of the sphericity is 90%.

3. The battery cell according to claim 1 or 2, characterized in that, In the cumulative area distribution curve of the sphericity of the particles obtained from the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, L A10 is 0.50 - 0.55, and L A10 represents the sphericity corresponding to the cumulative area ratio of 10% on the vertical axis in the cumulative distribution curve of sphericity.

4. The battery cell according to claim 3, characterized in that, In the cumulative area distribution curve of the sphericity of the particles obtained from the cross-section of the positive electrode film layer in the thickness direction of the electrode sheet, the concentration of sphericity (L A90 -L A10 ) / L A50 is 0.45 - 0.

55.

5. The battery cell according to claim 1 or 2, characterized in that, The tap density of the positive electrode sheet is 2.35 g / cm 3 - 2.45 g / cm 3 .

6. The battery cell according to claim 1 or 2, characterized in that, The single-sided coating weight of the positive electrode film layer is 0.33 g / 1540.25 mm 2 ~0.43 g / 1540.25 mm 2 .

7. The battery cell according to claim 1 or 2, characterized in that, The single-sided coating weight of the positive electrode film layer is 0.36 g / 1540.25 mm 2 ~0.40 g / 1540.25 mm 2 .

8. The battery cell according to claim 1 or 2, characterized in that, The porosity of the positive electrode tab is 23% - 32%.

9. The battery cell according to claim 1 or 2, characterized in that, The lithium-containing transition metal phosphate particles include a lithium-containing transition metal phosphate matrix and a coating layer located on at least a part of the surface of the lithium-containing transition metal phosphate matrix. The coating layer contains carbon.

10. The battery cell according to claim 9, characterized in that, The chemical formula of the lithium-containing transition metal phosphate matrix is expressed as Li x1 A y1 Me a1 M b1 P 1-c1 X c1 Y z1 , Wherein, 0.5 ≤ x1 ≤ 1.3, 0 ≤ y1 ≤ 0.8, 0.9 ≤ x1 + y1 ≤ 1.3; 0.9 ≤ a1 ≤ 1.5, 0 ≤ b1 ≤ 0.5, 0.9 ≤ a1 + b1 ≤ 1.5; 0 ≤ c1 ≤ 0.5; 3 ≤ z1 ≤ 5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, Ce; X includes one or more of S, Si, Cl, B, C, N, P; Y includes one or more of O, F.

11. The battery cell according to claim 9, wherein, The lithium-containing transition metal phosphate includes lithium iron phosphate.

12. The battery cell according to claim 9, characterized in that, The lithium-containing transition metal phosphate contains Ti element. Based on the mass of the lithium-containing transition metal phosphate, the mass content of the Ti element is 0.05% - 0.2%.

13. The battery cell according to claim 1 or 2, characterized in that, In the cross-section of the positive electrode film layer along the thickness direction of the electrode sheet, D of the lithium-containing transition metal phosphate particles A50 is 100 nm to 2.5 μm, and D A50 represents the particle size value corresponding to 50% of the cumulative area ratio of the vertical axis in the area cumulative distribution curve.

14. The battery cell according to claim 1 or 2, characterized in that, The thickness of the positive current collector is 12μm - 20μm.

15. The battery cell according to claim 1 or 2, characterized in that, The compaction density of the negative electrode plate is 1.3 g / cm 3 - 1.55 g / cm 3 .

16. The battery cell according to claim 1 or 2, characterized in that, The compaction density of the negative electrode plate is 1.40 g / cm 3 - 1.50 g / cm 3 .

17. The battery cell according to claim 1 or 2, characterized in that, The single-sided coating weight of the negative electrode film layer is 0.15 g / 1540.25 mm 2 ~0.207 g / 1540.25 mm 2 .

18. The battery cell according to claim 1 or 2, characterized in that, The single-sided coating weight of the negative electrode film layer is 0.17 g / 1540.25mm 2 ~0.2 g / 1540.25mm 2 .

19. The battery cell according to claim 1 or 2, characterized in that, The porosity of the negative electrode tab is 23% - 32%.

20. The battery cell according to claim 1 or 2, characterized in that, The thickness of the negative current collector is 6μm - 12μm.

21. The battery cell according to claim 1 or 2, characterized in that, The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes graphite. The volume average particle size Dv50 of the graphite is 13μm - 22μm.

22. The battery cell according to claim 21, wherein, The volume average particle size Dv50 of the graphite is 14.5μm - 20μm.

23. The battery cell according to claim 1, characterized in that, The fluoropolymer includes one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

24. The battery cell according to claim 1, characterized in that, The unilateral thickness of the bonding layer is 0.15μm - 2μm.

25. The battery cell according to claim 1, wherein The coating further includes a ceramic layer provided between the base film and the bonding layer.

26. The battery cell according to claim 25, wherein, The ceramic layer comprises one or more ceramic particles of alumina, boehmite, silicon oxide, magnesium oxide, titanium oxide, tin oxide, calcium oxide, zirconium oxide, barium sulfate, yttrium oxide, zinc oxide, silicon carbide, magnesium fluoride, barium titanate, aluminum hydroxide, magnesium hydroxide or calcium hydroxide.

27. The battery cell according to claim 25, wherein, The single-side thickness of the ceramic layer is 0.5 μm - 4 μm.

28. The battery cell according to claim 1, wherein The thickness of the base film is 7 μm - 9 μm.

29. The battery cell according to claim 1 or 2, characterized in that, The battery cell contains an electrolyte, and the electrolyte comprises a chain carbonate solvent. Based on the total mass of the electrolyte, the mass content of the chain carbonate solvent is 43% - 71%.

30. The battery cell according to claim 29, wherein, The chain carbonate comprises one or both of dimethyl carbonate and ethyl methyl carbonate.

31. The battery cell according to claim 29, wherein The electrolyte further comprises a cyclic carbonate.

32. The battery cell according to claim 31, wherein Based on the total mass of the electrolyte, the mass content of the cyclic carbonate is 14% - 42%.

33. A battery device, characterized in that, Comprising the battery cell according to any one of claims 1 to 32.

34. An electrical device, characterized in that, Comprising the battery device according to claim 33.

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