Battery cell, battery device, power consuming device, and energy storage device

Abstract

The application provides a battery monomer, a battery device, a power consumption device and an energy storage device. The battery monomer comprises a laminated core, the laminated core comprises a positive pole piece and a negative pole piece, the compaction density of the positive pole piece is 2.3g / cm 3 -2.6g / cm 3 ; the single side density of the positive pole film layer is 0.25g / 15 40.25mm 2 -0.45g / 15 40.25mm 2 ; in the section of the positive pole film layer along the thickness direction of the positive pole piece, the L R1A50 is 0.6-0.8 in the spheroidity area cumulative distribution curve of the particles with R1≥1000nm; and the median number C 50 of the graphitization degree in the cumulative distribution curve of the graphitization degree C obtained by the positive pole film layer under the face scanning mode of the laser microscopic confocal Raman spectrometer is 0.95-1.20. The battery monomer provided by the application has high capacity and good cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery monomer, a battery device, a power utilization device and an energy storage device. BACKGROUND

[0002] In recent years, battery monomers are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] With the pursuit of battery endurance and service life by the market, higher requirements are put forward for battery capacity and cycle performance. However, the prior art is difficult to simultaneously improve the above-mentioned performances, and how to balance the two has become a technical problem to be solved in the field. SUMMARY

[0004] The present application is made in view of the above-mentioned problems, and aims to provide a battery monomer with high capacity and good cycle performance.

[0005] The first aspect of the present application provides a battery monomer, the battery monomer comprising a laminated cell, the laminated cell comprising a positive electrode sheet and a negative electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer comprising lithium-containing transition metal phosphate particles with carbon material arranged on at least part of the surface; the compaction density of the positive electrode sheet is 2.3 g / cm 3 -2.6 g / cm 3 at full discharge state; the single-sided surface density of the positive electrode film layer is 0.25 g / 15-40.25 mm 2 -0.45 g / 15-40.25 mm 2 ; in the section of the positive electrode film layer along the thickness direction of the positive electrode sheet, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm has L R1A50 =0.6-0.8; the cumulative distribution curve of the graphitization degree C value of the positive electrode film layer obtained under the face scanning mode of the laser microscopic confocal Raman spectrometer has a median number C 50 =0.95-1.20 of the graphitization degree; wherein the graphitization degree C value is I G / I D , I G represents the G peak intensity of the Raman spectrum at 1580±100 cm -1 , and I D represents the D peak intensity of the Raman spectrum at 1350±100 cm -1 .

[0006] Studies have shown that stress concentration areas in the film layer are prone to cracking under cyclic expansion, becoming the starting point for film delamination, which is more pronounced in thick-coated cells. Compared to ternary materials, lithium-containing transition metal phosphate structures are more stable and less prone to breakage under high pressure. Lithium-containing transition metal phosphates require higher pressure during electrode compaction to achieve higher compaction density. However, under full-discharge conditions, the compaction density of the positive electrode in a single battery cell exceeds 2.6 g / cm³. 3 This can lead to overpressure on the electrode, increased stress concentration, and a higher risk of film shedding during cycling; while the compaction density of the positive electrode is less than 2.3 g / cm³. 3 This will result in insufficient contact between the positive electrode film particles, leading to increased internal resistance of the battery and affecting the energy density of the individual cells; the single-sided density of the positive electrode film is less than 0.25g / 1540.25mm. 2 This cannot meet the requirements for high energy density; the single-sided density of the positive electrode film is higher than 0.45 g / 1540.25 mm. 2 If the positive electrode film is too thick, the volume expansion during cycling will be significant and the stress concentration will be aggravated, increasing the risk of film shedding.

[0007] Stacked cells are beneficial for improving the space utilization of batteries, thereby further increasing the volumetric energy density and capacity of individual cells. The applicant found that in thick-coated stacked cells, stress concentration usually originates from localized stress generated during compaction. On the one hand, during compaction, particles with low sphericity have sharp stress surfaces and increased sliding friction, making them more prone to stress concentration; on the other hand, lithium-containing transition metal phosphate particles often require high-temperature sintering, which, along with grain boundary melting and particle growth, reduces the sphericity of the particles, with the median sphericity often not exceeding 0.8. When the positive electrode film layer is truncated along the thickness direction of the positive electrode sheet, the cumulative distribution curve of the sphericity area of ​​particles with a particle size R1 satisfying R1≥1000nm, L... R1A50 When the value is less than 0.6, significant local stress will form during particle compaction, significantly increasing the risk of film detachment during cycling; on the other hand, the median C of graphitization degree... 50 Reflecting the degree of order in carbon material layers, a graphitization degree higher than 1.2 indicates lower concentration. Therefore, considering material uniformity, the graphitization degree of carbon material layers is typically not higher than 1.2. 50 When the value is less than 0.95, the slipability of the carbon layer structure decreases, resulting in high friction between particles during compaction and difficulty in slippage. This further increases the stress during the compaction process, thereby increasing the probability of film detachment during the cycle.

[0008] The battery cell provided in this application adopts a thick coating and stacked cell process, and controls the compaction density of the positive electrode sheet to be 2.3 g / cm³ when the battery cell is fully discharged. 3-2.6g / cm 3 ; the single-sided surface density of the positive electrode film layer is 0.25g / 15 40.25mm 2 -0.45g / 15 40.25mm 2 , while improving the capacity of the battery, relieving stress concentration, reducing the probability of film layer falling off, and improving the cycle life of the battery; further, by controlling the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, L R1A50 is 0.6-0.8, and the median value C 50 of the graphitization degree in the cumulative distribution curve of the graphitization degree C obtained by the positive electrode film layer under the face scanning mode of the laser microscopic confocal Raman spectrometer is 0.95-1.20, the sphericity of the large particles in the positive electrode film layer and the graphitization degree of the positive electrode film layer are improved, the local stress generated in the compaction process is improved, thereby further reducing the probability of film layer falling off and improving the cycle life of the battery.

[0009] In summary, the battery cell of the present application has good capacity while improving the capacity diving problem, and the cycle life of the battery is considered.

[0010] In any embodiment, the single-sided coating surface density of the positive electrode film layer is 0.3g / 15 40.25mm 2 - 0.45g / 15 40.25mm 2 .

[0011] In any embodiment, the single-sided coating surface density of the positive electrode film layer is 0.35g / 15 40.25mm 2 - 0.4g / 15 40.25mm 2 .

[0012] The single-sided coating surface density of the positive electrode film layer is further in the above range, which helps to further improve the capacity of the battery and consider the cycle performance.

[0013] In any embodiment, the median value C 50 of the graphitization degree in the cumulative distribution curve of the graphitization degree C obtained by the positive electrode film layer under the face scanning mode of the laser microscopic confocal Raman spectrometer is 1.01-1.13.

[0014] The graphitization degree of the positive electrode film layer is further in the above range, which helps to further improve the easy sliding degree of the particles in the positive electrode film layer, reduce the stress concentration in the positive electrode film layer, and further improve the long cycle stability of the battery cell.

[0015] In any embodiment, in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm, LR1A50 0.65-0.75.

[0016] In any embodiment, in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm has L R1A50 0.67-0.72.

[0017] In the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm has L R1A50 In the range of 0.65-0.75, further in the range of 0.67-0.72, it is beneficial to further reduce the stress concentration at the large particles in the positive electrode film layer of the thick-coated stacked cell, thereby reducing the probability of film layer falling off and improving the cycle life of the battery.

[0018] In any embodiment, the single-sided thickness H of the positive electrode film layer is 70μm-120μm.

[0019] In any embodiment, the single-sided thickness H of the positive electrode film layer is 90μm-120μm.

[0020] The single-sided thickness of the positive electrode film layer in the above range helps to improve the loading capacity of the positive electrode active material in the battery, thereby improving the capacity of the battery.

[0021] In any embodiment, the single-sided thickness H of the positive electrode film layer is 100μm-120μm.

[0022] Increasing the thickness of the positive electrode film layer helps to increase the loading capacity of the positive electrode active material and helps to improve the capacity of the battery. However, the applicant has found that when the single-sided thickness of the positive electrode film layer is greater than or equal to 100μm, the volume expansion of the positive electrode film layer is more significant during the cycle of the battery, thereby generating greater stress, the stress concentration in the positive electrode film layer is more significant, the risk of film layer falling off increases, and further affects the cycle performance of the battery. The embodiments of the present application increase the capacity of the battery by increasing the thickness of the positive electrode film layer, while controlling the sphericity of the particles with a particle size R1 satisfying R1≥1000nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, and the median number C 50 Increasing the degree of slip between particles in the positive electrode film layer reduces the stress concentration generated during the compaction of the tab, thereby improving the capacity of the battery while taking into account the cycle performance of the battery. In any embodiment, based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the tab, the area ratio of the particles with a particle size R1 satisfying R1≥1000nm is 12%-50%.

[0023] In any embodiment, the area proportion of particles with a particle size R1 satisfying R1≥1000 nm is 12%-40% based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0024] The large particles with a particle size R1 satisfying R1≥1000 nm help to improve the compaction density of the positive electrode sheet, thereby improving the volumetric energy density of the battery cell; however, researchers have found that stress concentration is prone to occur at these large particles, increasing the risk of positive electrode film layer peeling. Therefore, the area proportion of particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet is within the range of 12%-50%, and further within the range of 12%-40%, which can not only improve the compaction density of the electrode sheet, but also not excessively increase the probability of film layer peeling, thereby improving the energy density of the thick-coated lithium-containing transition metal phosphate battery while alleviating the capacity drop problem and taking into account the cycle life of the battery.

[0025] In any embodiment, the uniformity of the distribution of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet is less than or equal to 5%.

[0026] In any embodiment, the uniformity of the distribution of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet is 0.2%-2.5%.

[0027] In any embodiment, the uniformity of the distribution of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet is 0.2%-2%.

[0028] The uniformity of the distribution of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet within the above range can effectively reduce the degree of stress concentration in the local area of the film layer, so that the stress in the compaction process of the film layer is uniformly dispersed in the entire area of the film layer, thereby improving the energy density of the battery while reducing the probability of film layer peeling, alleviating the capacity drop problem of the thick-coated lithium-containing transition metal phosphate battery, and improving the cycle life of the battery.

[0029] In any embodiment, in the cumulative distribution curve of the coating value B obtained by the positive electrode film layer under the face scanning mode of the laser microscopic confocal Raman spectrometer, the median number B 50 of the coating value is 0.30-0.60, wherein the coating value B is I P / I D , I P represents the P peak intensity of the Raman spectrum at 948±100 cm -1 , and I D represents the D peak intensity of the Raman spectrum at 1350±100 cm -1 .

[0030] Median value B of the coating value of the positive electrode film layer 50 Within the above range, it is indicated that the carbon material layer of the positive electrode active material is relatively dense and uniform, which is beneficial to improve the uniformity of the positive electrode film layer in the rolling process, and reduce the stress concentration phenomenon in the thick-coated positive electrode film layer. In addition, with the aid of the dense and uniform carbon material layer, the large particles in the positive electrode film layer are more likely to slip during the compaction process, thereby reducing the stress concentration phenomenon at the large particles in the thick-coated positive electrode film layer, reducing the probability of the positive electrode film layer falling off, improving the battery capacity diving problem, and improving the cycle life of the battery.

[0031] In any embodiment, the lithium-containing transition metal phosphate particles in the positive electrode film layer include components represented by the following general formula:

[0032] Li m Fe x P y O j Q q Formula I,

[0033] wherein Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, 0≤q≤0.1.

[0034] In any embodiment, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate, lithium manganese phosphate, fluorinated lithium vanadium phosphate, lithium manganese iron phosphate, and modified materials thereof.

[0035] In any embodiment, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate and doped modified materials, coated modified materials thereof.

[0036] In any embodiment, the iron elution rate of the positive electrode material in the positive electrode film layer is 658 ppm-1921 ppm.

[0037] In any embodiment, the iron elution rate of the positive electrode material in the positive electrode film layer is 658 ppm-1485 ppm.

[0038] In any embodiment, the mass content of titanium element is 500 ppm-8000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0039] In any embodiment, the mass content of titanium element is 1000 ppm-3000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0040] The introduction of titanium element into the lithium-containing transition metal phosphate particles requires the addition of a titanium source during the preparation of the positive electrode active material. The titanium source is often an inert material that can reduce the reactivity of the lithium-containing transition metal phosphate raw material and reduce the increase in particle size. Increasing the graphitization degree of the positive electrode active material often requires a higher sintering temperature or a longer sintering time, but this also increases the size of the particles in the positive electrode film layer, increases the stress concentration of the positive electrode film layer, and causes the positive electrode film layer to fall off. In the embodiments of the present application, by adding a high content of titanium element to the lithium-containing transition metal phosphate particles, the reactivity of the positive electrode active material synthesis raw material is reduced, the positive electrode active material has a high graphitization degree while controlling the large particle ratio, reducing the stress concentration of the positive electrode film layer, and reducing the probability of positive electrode film layer falling off. While improving the energy density of the battery, the cycle life of the battery is also considered.

[0041] At the same time, the doping of titanium element in the positive electrode active material is beneficial to cause lattice distortion, reduce Li-O bond energy, improve lithium ion transmission rate, and improve the kinetic performance of the battery. The lithium ion diffusion in the thick coating film layer is not uniform, often accompanied by a significant lithium ion concentration gradient. The embodiments of the present application improve the solid-phase transmission rate of the positive electrode active material by adding a high content of titanium element to the lithium-containing transition metal phosphate particles, and improve the kinetic problem of the thick electrode sheet battery.

[0042] In any embodiment, the mass content of vanadium element is 500ppm - 5000ppm based on the total mass of lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0043] In any embodiment, the mass content of vanadium element is 500ppm - 3000ppm based on the total mass of lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0044] The vanadium element in the positive electrode film layer can be in multiple valence states, among which +5 valence vanadium (V 5+ ) can be doped at the phosphorus element site, which can cause lattice distortion due to its large radius, expand the diffusion channel of lithium ions, thereby improving the ionic conductivity of the positive electrode active material and improving the kinetic performance of the battery; +3 valence vanadium (V 3+ ) can be doped at the transition metal site to generate lithium vacancies through charge compensation, thereby improving the electronic conductivity of the positive electrode active material. In addition, the uniformity of the distribution of vanadium element in the lithium-containing transition metal phosphate particles is improved, which helps to further improve the kinetic performance of the positive electrode film layer and the reaction uniformity of the positive electrode film layer, thereby further improving the kinetic performance and cycle performance of the battery monomer.

[0045] The mass content of vanadium element in the above range helps to improve the kinetic performance of the positive electrode sheet, and improve the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery. At the same time, the synergistic effect of titanium element, vanadium element and carbon nanotubes in the positive electrode film layer helps to form a good three-dimensional network, further improving the electronic conductivity and ionic conductivity of the positive electrode film layer, thereby further improving the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery.

[0046] In any embodiment, the porosity of the positive electrode film layer is 14%-28%.

[0047] The porosity of the positive electrode film layer is in the above range, the positive electrode film layer has good electrolyte wetting rate and tortuosity, which helps the diffusion of lithium ion liquid phase and solid phase, reduces the concentration polarization of thick electrode sheet, and improves the kinetic performance of the battery. At the same time, it helps to alleviate the volume expansion of the thick-coated electrode sheet during the cycle process, reduce the mechanical stress of the film layer and reduce the stress concentration phenomenon, thereby reducing the risk of film layer falling off of the thick-coated electrode sheet.

[0048] Particularly in thick-coated soft package batteries, the gap between the shell and the electrode sheet is small, the volume occupancy rate of the film layer is large, and the accommodation volume of the electrolyte is reduced. The porosity of the positive electrode film layer in the above range helps to improve the liquid retention rate of the battery core and improve the kinetic performance of the battery.

[0049] In any embodiment, the positive electrode film layer further comprises a conductive agent, and the area ratio of the agglomeration area of the conductive agent is 0.5%-2.5% based on the total area of the section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0050] The area ratio of the agglomeration area of the conductive agent in the above range based on the total area of the section of the positive electrode film layer along the thickness direction of the electrode sheet indicates that the conductive agent is uniformly dispersed in the positive electrode film layer, which is easy to form a uniform conductive network, especially helps to reduce the problem of kinetic decline caused by the increase of ion transmission path of thick-coated film layer, reduce the local polarization and even lithium precipitation problem generated during the cycle process of the battery, and improve the cycle life of the battery.

[0051] At the same time, research shows that the first particles of large size in the lithium-containing transition metal phosphate particles are prone to rebound, and the agglomeration area of the conductive agent in the above range can inhibit the rebound of the lithium-containing transition metal phosphate particles by means of uniform distribution of the conductive agent, form mechanical restraint to the particles and even the film layer, improve the cohesion of the film layer, reduce the film layer powder falling and falling off phenomenon, and improve the cycle life of the battery.

[0052] In any embodiment, the positive electrode film layer further comprises a conductive agent, and the area ratio of the agglomeration area of the conductive agent is 0.5%-1.7% based on the total area of the section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0053] In the embodiments of the present application, the area proportion of the agglomeration region of the conductive agent is further within the above range, indicating that the conductive agent is more uniformly distributed in the positive electrode film layer, and the content of the conductive agent is lower, which helps to reduce the occupation of the space of the positive active material by excessive conductive agent, thereby improving the kinetic performance of the battery while further improving the volumetric energy density of the battery.

[0054] In any embodiment, the conductive agent includes carbon nanotubes, which include one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0055] Since the carbon nanotubes have a one-dimensional structure, they can form a network structure in the positive electrode film layer. On the one hand, the high elastic modulus of the carbon nanotubes makes their network structure not only a bridge for stress propagation, but also a restraint for thick-coated positive electrode film layers, which suppresses the rebound of lithium-containing transition metal phosphate particles, effectively alleviates stress concentration and reduces the risk of film layer peeling, thereby improving the battery capacity drop problem; on the other hand, the excellent electrical conductivity of the carbon nanotubes makes their network structure an efficient electron transport channel, even if there is local film layer peeling, the thick electrode sheet can still maintain high electron transport efficiency in the in-plane direction and the thickness direction, thereby delaying the occurrence of the capacity drop problem and further improving the kinetic performance and cycle life of the battery.

[0056] In any embodiment, the conductive agent further includes conductive carbon black.

[0057] The conductive carbon black has a high specific surface area and thus good liquid retention capacity. The thick electrode sheet has a large expansion force during the cycling process, making the electrolyte easy to be squeezed out. The distribution of the conductive carbon black in the positive electrode film layer is beneficial to improve the liquid retention capacity of the thick electrode sheet, further alleviate the capacity drop phenomenon of the battery during the cycling process, and improve the cycle life of the battery.

[0058] In any embodiment, the agglomeration region of the conductive agent includes carbon nanotubes and conductive carbon black.

[0059] The researchers found that carbon nanotubes are prone to agglomeration due to their high surface energy, leading to uneven distribution in the positive electrode film layer and failure to form an effective carbon nanotube network structure. The surface energy of conductive carbon black is close to that of carbon nanotubes, and it can be adsorbed on the surface of carbon nanotubes to form a physical barrier, increase the resistance of carbon nanotube agglomeration, reduce direct contact between carbon nanotubes, and thus inhibit the agglomeration phenomenon and improve the uniformity of carbon nanotubes in the positive electrode film layer. This helps to improve the conductivity of the thick-coated positive electrode film layer and improve the kinetic performance of the battery. On the other hand, it helps to exert the binding effect of carbon nanotubes on the positive electrode film layer, reducing the risk of positive electrode film layer shedding and further improving the kinetic performance and cycle life of the battery. In addition, the agglomeration of carbon nanotubes in the conductive agent agglomeration area will also cause the local ion transport path in the conductive agent agglomeration area to be blocked, and the addition of conductive carbon black can improve the lithium ion transport capacity of this area, reduce local polarization, and further improve the cycle stability of the battery.

[0060] In any embodiment, the mass content C1 of carbon nanotubes satisfies: 0 < C1 ≤ 2.5%, and the mass content C2 of conductive carbon black satisfies: 0 < C2 ≤ 2.5%, based on the mass of the positive electrode film layer.

[0061] The mass content of carbon nanotubes and conductive carbon black within the above range can effectively alleviate the agglomeration of carbon nanotubes and form a good conductive network structure, thereby effectively reducing the stress concentration of the positive electrode film layer and improving the liquid retention rate of the positive electrode tab during long-term cycling, further reducing the risk of tab film layer shedding and the degree of polarization, improving the kinetic performance of the battery, and addressing the capacity drop problem and improving the cycle life of the battery.

[0062] In any embodiment, the positive electrode film layer further comprises a dispersant, and the dispersant comprises hydrogenated nitrile rubber (HNBR).

[0063] HNBR is obtained by hydrogenating and saturating the double bonds of nitrile rubber. Its highly saturated main chain structure makes it have excellent oil resistance, heat resistance, and aging resistance, etc. This allows it to remain stable in different environments and systems when used as a dispersant, and is not prone to degradation or deterioration, thereby effectively exerting the dispersing effect. The HNBR molecular chain contains both polar nitrile groups and non-polar carbon-hydrogen segments. The polar nitrile groups can interact with the surfaces of some polar substances or particles, such as being adsorbed on the surfaces of the dispersed particles through hydrogen bonds, electrostatic interactions, etc.; the non-polar carbon-hydrogen segments have good lipophilicity and can be well stretched and dispersed in non-polar or weakly polar media, allowing the particles to be uniformly dispersed in the medium.

[0064] When HNBR is adsorbed on the surface of particles in the slurry, long-chain molecules of HNBR form a physical barrier around the particles, preventing the particles from approaching and aggregating with each other, so that the particles remain in a relatively independent dispersed state in the system. At the same time, HNBR can reduce the surface tension between the dispersion medium and the dispersed particles, so that the particles are more easily wetted by the medium, thereby promoting the dispersion of the particles in the medium. At the same time, it can also reduce the interfacial energy between the particles, reduce the aggregation phenomenon of the particles due to interfacial energy driving. Further, when the slurry is dried into a film, the elastic network structure of HNBR can buffer the shrinkage stress generated by solvent evaporation, reduce the re-aggregation of the conductive agent due to capillary force in this process, reduce the area ratio of the conductive agent aggregation area, and improve the kinetic performance and cycle life of the battery.

[0065] In any embodiment, the mass content of the dispersant is 0.5%-2% based on the mass of the positive electrode film layer.

[0066] The mass content of the dispersant in the above range can achieve uniform dispersion of particles in the positive electrode film layer while maintaining a high loading of the positive electrode film layer, reduce stress concentration of the thick-coated lithium-containing transition metal phosphate positive electrode film layer, and effectively alleviate the battery capacity drop problem.

[0067] In any embodiment, the battery cell further comprises a separator disposed between the positive electrode sheet and the negative electrode sheet, the separator comprising a base film and a ceramic layer disposed on at least one side of the base film and a bonding layer disposed on the side of the at least one ceramic layer away from the base film, the bonding layer being a continuous layer of porous structure, and the bonding layer comprising a vinylidene fluoride-based polymer.

[0068] In any embodiment, the battery cell further comprises a separator disposed between the positive electrode sheet and the negative electrode sheet, the separator comprising a base film and a ceramic layer disposed on both sides of the base film and a bonding layer disposed on the side of the ceramic layer away from the base film.

[0069] In any embodiment, the vinylidene fluoride-based polymer comprises one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0070] In any embodiment, the vinylidene fluoride-based polymer comprises polyvinylidene fluoride (PVDF).

[0071] The bonding layer of the separator in the prior art usually uses water-based PVDF, which presents an island structure in the separator, which is beneficial to providing a gap for cell swelling on the one hand and facilitating manufacturing on the other hand; however, the contact area of such a separator bonding layer with the electrode sheet is small, and the bonding force is weak.

[0072] The porous structure of the adhesive layer of the separator provided in the embodiments of the present application provides space for the expansion of the thick-coated battery cell, thereby improving the stability thereof. In addition, compared with the adhesive layer in the prior art, the adhesive layer has a larger bonding area with the pole piece, thereby making the bonding between the separator and the pole piece more firm and uniform. Furthermore, the adhesive layer is beneficial to maintaining the interface contact between the separator and the positive electrode film layer when the positive electrode film layer rebounds, thereby reducing the probability of film layer falling off.

[0073] Compared with the wound battery cell, the pressure between the separator and the pole piece in the stacked battery cell is smaller, and the separator and the pole piece are prone to relative displacement, thereby disturbing the film layer and causing the film layer to fall off or drop powder. In addition, the positive and negative electrodes may also be overlapped, thereby increasing the risk of internal short circuit of the battery cell. Therefore, the separator provided in the embodiments of the present application is particularly suitable for the stacked battery cell. The adhesive force between the porous adhesive layer and the pole piece is increased, which is beneficial to improving the adhesive force between the separator and the pole piece and reducing the relative displacement between the separator and the pole piece. This is beneficial to reducing the disturbance to the positive electrode film layer, reducing the probability of film layer falling off, reducing the risk of positive and negative electrode overlap, and reducing the risk of battery cell short circuit.

[0074] In summary, when the vinylidene fluoride-based polymer in the adhesive layer of the embodiments of the present application is selected from the above-mentioned materials, a continuous and uniform porous adhesive layer is formed. First, the adhesive force between the adhesive layer and the pole piece is improved and uniformly distributed, which is beneficial to reducing the stress concentration phenomenon in the thick-coated lithium-containing transition metal phosphate positive electrode film layer and reducing the risk of film layer falling off, thereby further improving the cycle life of the battery. Second, the adhesive layer is stably bonded to the positive electrode pole piece or the negative electrode pole piece, which is beneficial to reducing the direct contact between the positive electrode pole piece and the negative electrode pole piece due to the relative displacement between the pole piece and the separator, reducing the risk of internal short circuit, and improving the safety performance of the battery. Third, the porous adhesive layer is beneficial to maintaining the porosity of the separator and reserving space for the expansion of the battery cell, thereby further improving the cycle life of the battery.

[0075] In any embodiment, the thickness of the base film in the separator is 7-9 μm.

[0076] In any embodiment, the single-sided thickness of the ceramic layer in the separator is 2-4 μm.

[0077] In any embodiment, the single-sided thickness of the adhesive layer in the separator is 1-5 μm.

[0078] The thickness of the adhesive layer is too low, the gap space in the diaphragm is small, and the adhesion between the diaphragm and the pole piece is low. On the one hand, the stress of the film layer increases after the film layer expands, the probability of film layer falling off increases, which affects the cycle life of the battery. On the other hand, the probability of positive negative overlap short circuit increases, thereby affecting the safety performance of the battery. The thickness of the adhesive layer is too large, which occupies a large space of the battery, thereby affecting the volume energy density of the battery. In the embodiments of the present application, the thickness of the adhesive layer is within the above range, which helps to balance the cycle life, safety performance and volume energy density of the battery.

[0079] In any embodiment, the positive electrode film layer is provided with a bottom coating layer at the bottom region close to the positive electrode current collector, the bottom coating layer comprising a conductive agent and a binder, the conductive agent comprising carbon nanotubes and conductive carbon black, and the binder comprising polyvinylidene fluoride (PVDF).

[0080] In any embodiment, the thickness of the bottom coating layer is 0.5-5 μm.

[0081] The bottom coating layer provided in the embodiments of the present application helps to improve the adhesion between the positive electrode film layer and the positive electrode current collector and alleviate the stress concentration phenomenon at large particles, thereby reducing the probability of positive electrode film layer falling off and improving the cycle stability of the battery. At the same time, compared with the direct contact between the positive electrode current collector and the positive electrode film layer, the contact area between the bottom coating layer and the positive electrode film layer is increased, which helps to increase the area of electron transmission between the current collector and the positive electrode film layer, thereby reducing the internal resistance of the pole piece and improving the kinetic performance of the battery.

[0082] In any embodiment, the battery monomer comprises a shell, and the laminated core is accommodated in the shell. The size of the shell in the length direction is L1, the size of the shell in the width direction is W1, and the size of the shell in the thickness direction is H1, wherein 450mm≤L1≤1300mm, 100mm≤W1≤150mm; 14mm≤H1≤22mm.

[0083] In any embodiment, the size of the shell in the length direction is L1, and 450mm≤L1≤650mm.

[0084] When the size L1 of the shell in the length direction satisfies 450mm≤L1≤650mm, the length of the battery monomer is relatively short, which helps to shorten the diffusion path of the current, reduce the internal resistance of the pole piece, thereby reduce the heat generation of the battery and improve its kinetic performance. In addition, the shorter length of the shell helps to shorten the diffusion path of the electrolyte in the infiltration process, improve the infiltration rate and uniformity of the electrolyte, further promote the uniformity of lithium ion deintercalation in the cycle process, alleviate the stress concentration phenomenon, reduce the risk of film layer falling off, and improve the cycle stability of the battery monomer.

[0085] In any embodiment, the size of the shell in the length direction is L1, and 900mm≤L1≤1300mm.

[0086] When the dimension L1 of the shell in the length direction satisfies 900mm≤L1≤1300mm, the dimension of the battery monomer is relatively long, which helps to reduce the volume proportion of the shell in the battery monomer and improve the load proportion of the active material. At the same time, the longer battery monomer can reduce the number of batteries required in the battery module, simplify the structural design of the battery module, and reduce the number and complexity of structural components in the module, thereby improving the space utilization of the battery pack, and further helping to improve the volume energy density of the battery monomer.

[0087] In any embodiment, the material of the shell is a soft package material, and the soft package material includes an aluminum plastic composite film.

[0088] In any embodiment, the material of the shell includes one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), and polyethylene (PE) composite film formed with aluminum.

[0089] The soft package material has a high ductility, so that the shell thereof is more lightweight, thin, and soft, which helps to improve the space utilization of the battery monomer and thereby improve the energy density of the battery monomer. In addition, the high barrier property of aluminum can effectively reduce the penetration of water and oxygen into the battery interior, reduce the decomposition of electrolyte and the oxidation degree of electrode material, and thereby improve the service life of the battery.

[0090] In any embodiment, the capacity of the battery monomer is 95Ah-300Ah at 25℃.

[0091] In any embodiment, the capacity of the battery monomer is 150Ah-190Ah at 25℃.

[0092] The second aspect of the present application provides a battery device, which includes the battery monomer provided in the first aspect of the present application.

[0093] The third aspect of the present application provides a power utilization device, which includes the battery device provided in the second aspect of the present application, and the battery device is used to provide electric energy.

[0094] The fourth aspect of the present application provides an energy storage device, which includes the battery device provided in the second aspect of the present application, and the battery device is used to store electric energy. BRIEF DESCRIPTION OF DRAWINGS

[0095] Figure 1 is a schematic diagram of a separator of an embodiment of the present application;

[0096] Figure 2 is a schematic diagram of a separator of the prior art;

[0097] Figure 3is a schematic view of a surface morphology of a bonding layer according to an embodiment of the present application;

[0098] Figure 4 is a schematic view of a soft-pack jelly-roll battery according to an embodiment of the present application;

[0099] Figure 5 is a schematic view of an electric device according to an embodiment of the present application.

[0100] BRIEF DESCRIPTION OF DRAWINGS

[0101] 5: battery cell; 50: case; 20: separator; 201: base film; 202: ceramic layer; 203: bonding layer; X: length direction; Y: width direction; Z: thickness direction. DETAILED DESCRIPTION

[0102] Hereinafter, embodiments of a lithium ion secondary battery, a battery device, an electric device, and an energy storage device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters that are already well known, and repeated description of substantially identical structures, are omitted. This is to avoid the following description from becoming unnecessarily lengthy, and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0103] The ranges disclosed herein are defined by their lower and upper limits. Ranges created by the upper and lower limits are inclusive of the endpoints. Ranges created by the upper and lower limits are also inclusive of any and all sub-ranges subsumed therein. For example, a range of "60% to 120%" is inclusive of at least 60% and 120%, but also includes any and all sub-ranges between (and including) the minimum of about 60% and the maximum of about 120%, that is, all sub-ranges having a limit of less than or equal to 120% in combination with a limit of greater than or equal to 60% also fall within the range of "60% to 120%". Moreover, all statements herein that refer to a range of "from X to Y" are intended to refer to the range of from about X to about Y. For example, a range of "from 60% to 120%" refers to a range of from about 60% to about 120%. Unless otherwise indicated, the use of about in reference to a given value is intended to encompass not only the exact value but also the range of values that is 10% above and below the exact value. For example, a range of "from about 60% to about 120%" is intended to encompass not only the exact range of from 60% to 120% but also a range that is 10% above and below the exact range, that is, a range of from 54% to 126%. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0104] If not specifically specified, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0105] If not specifically specified, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0106] If not specifically specified, all the steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0107] In the present application, the terms "a plurality of" and "a plurality of" refer to two or more.

[0108] Unless otherwise specified, the terms used in the present application have the commonly understood meanings understood by those skilled in the art.

[0109] Unless otherwise specified, the values of the parameters mentioned in the present application can be measured by various test methods commonly used in the art, for example, the test methods given in the examples of the present application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0110] In the examples of the present application, the battery device can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of soft-pack battery cells connected in series, in parallel or in a mixed connection through a busbar component. For example, the battery cell assembly is usually formed by arranging a plurality of soft-pack battery cells; the battery cell assembly can be a battery module, which is formed by arranging and fixing a plurality of soft-pack battery cells into an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with a cable tie.

[0111] The battery device can be a battery pack, which includes a box body and one or more battery cell assemblies accommodated in the box body. The battery cell assembly can be a battery module, which can be accommodated in the box body by fixing the battery module in the box body; the battery cell assembly can also be accommodated in the box body by directly fixing a plurality of soft-pack battery cells in the box body.

[0112] In embodiments of the present application, the case can include a first case and a second case. The first case and the second case are coupled so that an enclosed space is formed inside the case to accommodate the battery cell assembly. The enclosed here means covered or closed, which can be sealed or unsealed. The first case can be a top cover or a bottom plate. For example, the case can 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 an enclosed space is formed inside the case to accommodate the battery cell assembly.

[0113] In embodiments of the present application, the case can be a part of the chassis structure of the vehicle. For example, a part of the case can be at least a part of the floor of the vehicle, or a part of the case can be at least a part of the cross beam and the longitudinal beam of the vehicle.

[0114] In embodiments of the present application, the battery cell can be a secondary battery, which means that the battery cell can be activated by charging after discharging, and the battery cell can be a lithium ion battery. The battery cell can be a flat body.

[0115] The battery mentioned in embodiments of the present application can be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application can include a battery cell, a battery module, or a battery pack, etc.

[0116] The battery cell is the smallest unit that makes up the battery, and it can realize the function of charging and discharging by itself.

[0117] When there are multiple battery cells, the multiple battery cells are connected in series, parallel, or mixed connection through the busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a case and a battery cell, and the battery cell or the battery module is contained in the case. In some embodiments, the case can be a part of the chassis structure of the vehicle. For example, a part of the case can be at least a part of the floor of the vehicle, or a part of the case can be at least a part of the cross beam and the longitudinal beam of the vehicle.

[0118] In some embodiments, the battery can be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0119] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0120] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0121] The battery cell includes an electrode assembly and an electrolyte.

[0122] The electrode assembly generally includes a positive electrode tab and a negative electrode tab, the negative electrode tab being an electrode that undergoes a reaction of absorbing or lithiating lithium ions during charging and releasing or delithiating lithium during discharging, and the positive electrode tab being an electrode that undergoes a reaction of releasing or delithiating lithium ions during charging and absorbing or lithiating lithium during discharging.

[0123] Although lithium-containing transition metal phosphates as positive active materials have significant advantages in cycle stability, their intrinsic specific capacity is significantly lower than that of ternary materials. The applicant found that using a thick coating process in the electrode preparation process becomes an effective technical means to make up for the low capacity of lithium-containing phosphates. However, this process improvement also brings new technical challenges: the thick tab will produce greater volume expansion during long-term cycling, resulting in increased internal stress, which makes the film layer more prone to partially or completely fall off from the tab under stress. The film layer falling off not only causes the loss of positive active materials participating in the charge and discharge reaction, but also forms an "island" effect, that is, some active material particles or between the particles and the conductive agent form isolated areas, which cannot form good electrical contact and thus cannot participate in the charge and discharge reaction of the battery, resulting in a sharp drop in battery capacity; at the same time, this part of the material affects ion transport, increases the internal resistance of the battery, causes local overheating of the battery and increases the risk of thermal runaway, which seriously affects the service life of the battery. Therefore, how to improve the energy density while keeping the battery capacity stable during the cycle process is still a technical problem that needs to be solved urgently.

[0124] The first aspect of the present application provides a battery cell, the battery cell comprising a jelly-roll, the jelly-roll comprising a positive electrode tab and a negative electrode tab, the positive electrode tab comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer comprising lithium-containing transition metal phosphate particles having carbon material disposed on at least part of the surface; the battery cell in a full discharge state, the positive electrode tab having a compaction density of 2.3 g / cm 3 -2.6 g / cm 3 ; the positive electrode film layer having a single-sided surface density of 0.25 g / 15 40.25 mm 2 -0.45 g / 15 40.25 mm 2 ; in a cross-section of the positive electrode film layer along the thickness direction of the positive electrode tab, the particle size R1 satisfies that in the spheroidity area cumulative distribution curve of the particles with R1≥1000 nm, L R1A50 is 0.6-0.8; in the cumulative distribution curve of the graphitization degree C value of the positive electrode film layer obtained under the face scanning mode of the laser microscopic confocal Raman spectrometer, the median number C 50 of the graphitization degree is 0.95-1.20; wherein the graphitization degree C value is I G / I D , I G represents the intensity of the G peak of the Raman spectrum at 1580 ± 100 cm -1 , I D represents the intensity of the D peak of the Raman spectrum at 1350 ± 100 cm -1 .

[0125] Studies have shown that the stress concentration area of the film layer is prone to crack under the action of cyclic expansion, becoming the starting point of film layer peeling, which is more significant in thick-coated battery cells. Compared with ternary materials, lithium-containing transition metal phosphates have more stable structures and are not prone to breakage under high pressure. Lithium-containing transition metal phosphates need to withstand higher pressure during the process of electrode compaction to pursue the increase of compaction density. However, when the battery cell is in the full discharge state, the compaction density of the positive electrode sheet is greater than 2.6 g / cm 3 , which will cause the electrode sheet to be over-pressed, stress concentration to be intensified, and the risk of film layer peeling during the cycle process to be increased; and when the compaction density of the positive electrode sheet is less than 2.3 g / cm 3 , the contact degree of the positive electrode film layer particles will be insufficient, resulting in an increase in the internal resistance of the battery and affecting the energy density of the battery cell; when the single-sided surface density of the positive electrode film layer is less than 0.25 g / 15 40.25 mm 2 , it cannot meet the requirements of high energy density; and when the single-sided surface density of the positive electrode film layer is higher than 0.45 g / 15 40.25 mm 2 , the positive electrode film layer is too thick, the volume expansion during the cycle process is significant, the stress concentration is intensified, and the risk of film layer peeling is increased.

[0126] The laminated battery cell is beneficial to improve the space utilization of the battery, and further improve the volume energy density of the battery cell and the capacity of the battery. The applicant found that in the thick-coated laminated battery cell, the stress concentration is usually derived from the local stress generated during the compaction process. On the one hand, during the compaction process, the force surface of the particles with low sphericity is sharp and is not easy to produce particle slip during the compaction process, and the mutual obstruction between the particles under the action of stress is easy to cause stress concentration. When the particle size R1 in the section of the positive electrode film layer along the thickness direction of the positive electrode sheet satisfies R1≥1000 nm, and the L R1A50 of the cumulative distribution curve of the sphericity area is less than 0.6, a larger local stress will be formed during the compaction process of the particles, and the risk of film layer peeling during the cycle process is significantly increased; on the other hand, the median number C 50 of graphitization degree reflects the order degree of the carbon material layer, and when C 50When less than 0.95, the carbon layer structure slip decreases, resulting in large inter-particle friction during compaction, difficult to slip, further increasing the stress in the compaction process, thereby increasing the probability of film layer falling off during the cycle process. Lithium-containing transition metal phosphate particles often need to be sintered at high temperature, and with the increase of sintering temperature or time, the particle grain boundary melts, the particle grows, and the graphitization degree increases, but the sphericity of the particle decreases. In order to balance the sphericity and graphitization degree of the particles in the film layer, and reduce the short board effect of stress concentration in the compaction process caused by any one of them, the median of the sphericity of the particles with a particle size R1 satisfying R1≥1000nm is often not more than 0.8; and the median of the graphitization degree of the positive electrode film layer C 50 Generally not more than 1.2.

[0127] The battery cell provided in the application adopts the process of thick coating and laminated cell, and controls the compaction density of the positive electrode sheet to be 2.3g / cm 3 -2.6g / cm 3 at full discharge state; the single-sided surface density of the positive electrode film layer is 0.25g / 15 40.25mm 2 -0.45g / 15 40.25mm 2 , while improving the capacity of the battery, relieving stress concentration, reducing the probability of film layer falling off, and improving the cycle life of the battery; further, by controlling the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm in the section of the positive electrode film layer along the thickness direction of the sheet, L R1A50 is 0.6-0.8, and the median of the graphitization degree C 50 is 0.95-1.20 in the cumulative distribution curve of the graphitization degree C value of the positive electrode film layer obtained by the laser microscopic confocal Raman spectrometer in the face scanning mode, the sphericity of the large particles in the positive electrode film layer and the graphitization degree of the positive electrode film layer are improved, the local stress generated in the compaction process is improved, thereby further reducing the probability of film layer falling off and improving the cycle life of the battery.

[0128] In summary, the battery cell of the application has high capacity while improving the capacity diving problem, and the cycle life of the battery is considered.

[0129] In the application, the laminated cell refers to the positive electrode sheet, the separator and the negative electrode sheet stacked together to form a cell.

[0130] In the application, the positive electrode film layer contains lithium-containing transition metal phosphate, but the positive electrode film layer does not simply refer to the positive electrode active material layer, and other film layers connected with the positive electrode active material layer and difficult to distinguish, such as primer layer, liquid retaining layer, etc. are collectively referred to as positive electrode film layer.

[0131] In the present application, the lithium-containing transition metal phosphate refers to a phosphate material containing lithium element and transition metal element, which can be detected by any known method in the art. For example, it can be detected by X-ray diffractometer (XRD) and energy spectrum analyzer, inductively coupled plasma mass spectrometer.

[0132] In the present application, the carbon material arranged on at least part of the surface of the lithium-containing transition metal phosphate particle can be detected by any known method in the art. As an example, the carbon material arranged on at least part of the surface of the lithium-containing transition metal phosphate particle can be observed by transmission electron microscopy and energy spectrum analyzer.

[0133] In the present application, the full discharge state refers to the state after the battery is placed in a 25°C oven environment for 2h, the battery temperature is kept at 25°C, the battery is discharged at 1 / 3C constant current to 2.5V, and then discharged at 0.1C constant current to 2.0V.

[0134] In the present application, the compaction density of the positive electrode tab can be tested by a method known in the art. As an example, the battery is placed in a 25°C oven environment for 2h, the battery temperature is kept at 25°C, the battery is discharged at 1 / 3C constant current to 2.5V, and then discharged at 0.1C constant current to 2.0V, the battery is disassembled, the residual electrolyte is treated with dimethyl carbonate solvent, the tab is dried, and a small round piece with an area of S is cut, the mass W1 is obtained, and the thickness T1 of the positive electrode tab is measured using a micrometer, then the positive electrode film layer of the above weighed tab is wiped off, the mass of the current collector is weighed and recorded as W2, and the thickness T2 of the current collector is measured using a micrometer, then the compaction density PD of the positive electrode tab is (W1-W2) / [(T1-T2)×S].

[0135] In some embodiments, the compaction density of the positive electrode tab of the battery cell in the full discharge state can be selected from 2.3g / cm 3 , 2.31g / cm 3 , 2.32g / cm 3 , 2.33g / cm 3 , 2.34g / cm 3 , 2.35g / cm 3 , 2.36g / cm 3 , 2.37g / cm 3 , 2.38g / cm 3 , 2.39g / cm 3 , 2.40g / cm 3 , 2.41g / cm 3 , 2.42g / cm 3 , 2.43g / cm 3 , 2.44g / cm3 2.45 g / cm 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.50 g / cm 3 2.52 g / cm 3 2.55 g / cm 3 2.60 g / cm 3 or any numerical range between any of the above values.

[0136] In the present application, the single-side coating surface density of the positive electrode film layer is the meaning known in the art, which can be tested by methods known in the art. For example, a single-side coated and cold-pressed positive electrode sheet (if it is a double-side coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first) is punched into a small round piece with an area of S1, weighed, and recorded as M1. Then the positive electrode film layer of the above weighed positive electrode sheet is wiped off, the weight of the current collector is weighed, and recorded as M0. The single-side surface density of the positive electrode film layer is (M1-M0) / S1. In order to ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value is calculated as the test result. The higher the single-side coating surface density of the positive electrode film layer indicates that the load per unit area is increased, which helps to improve the volumetric energy density of the battery cell.

[0137] In some embodiments, the single-side coating surface density of the positive electrode film layer can be selected as 0.25 g / 1540 mm 2 0.26 g / 1540 mm 2 0.27 g / 1540 mm 2 0.28 g / 1540 mm 2 0.29 g / 1540 mm 2 0.30 g / 1540 mm 2 0.31 g / 1540 mm 2 0.32 g / 1540 mm 2 0.33 g / 1540 mm 2 0.34 g / 1540 mm 2 0.35 g / 1540 mm 2 0.36 g / 1540 mm 2 0.37 g / 1540 mm 2 0.38 g / 1540 mm 2 0.39 g / 1540 mm 2 0.40 g / 1540 mm 2 0.41 g / 1540 mm2 0.42 g / 15 40 mm 2 0.43 g / 15 40 mm 2 0.44 g / 15 40 mm 2 0.45 g / 15 40 mm 2 or any numerical range between any two of the above values.

[0138] In some embodiments, the single-sided coating area density of the positive electrode film layer is 0.3 g / 15 40.25 mm 2 - 0.45 g / 15 40.25 mm 2 .

[0139] In some embodiments, the single-sided coating area density of the positive electrode film layer is 0.35 g / 15 40.25 mm 2 - 0.4 g / 15 40.25 mm 2 .

[0140] The single-sided coating area density of the positive electrode film layer is further within the above range, which helps to further improve the capacity of the battery and balance the cycle performance.

[0141] In the present application, the term "particle" refers to a particle in the field of view of the positive electrode film layer under a certain magnification, for example, 10 thousand times, which has an identifiable complete boundary. There can be defects and scratches inside the particle, but the complete boundary inside the particle cannot be identified enough to divide the particle. The positive electrode film layer in the present application can be a freshly prepared positive electrode film layer or a positive electrode film layer obtained by disassembling the battery.

[0142] In the present application, the particle identification method is as follows: the positive electrode film layer is cut along the thickness direction of the pole piece by argon ion beam (as an example, the device model: Leica EMTIC3XCP, working voltage: 6kV, working time: 6h can be selected), and the cut surface is observed by scanning electron microscope (as an example, the device model: Hitachi SU8230, working voltage: 3kV, beam current: high, probe model: U (LA100), working distance < 5mm can be selected) after the cut surface is exposed. The cut surface of the positive electrode film layer along the thickness direction of the pole piece is observed by field emission scanning electron microscope. The image is collected by secondary electron mode at a non-edge position in the cut surface of the positive electrode film layer (after observing the edge of the pole piece under the scanning electron microscope, the field of view is adjusted to the center part of the sample), and the electron microscope image is taken at a magnification of 10k. The particles in the electron microscope image are analyzed by ImageJ software (1.46r, win64 version). The use method of ImageJ software is as follows: load the scanning electron microscope image to be analyzed; identify the particles by using the Cellpose plug-in software, and manually correct on this basis; read and count the data by using ImageJ. The specific method of identifying particles by using the Cellpose plug-in software is as follows: set the segmentation diameter parameter (Segmantation module diameter) to 15 pixels, click “runcyto3” to identify particles; manually identify the particles in the image that are not identified by the software or not completely identified by the software or have errors in identification. The particles in the image that are not identified by the software or not completely identified by the software or have errors in identification mainly include the following: 1, due to the fact that the particles are too large or the particles have scratches on the surface, the particles cannot be identified or cannot be completely identified; 2, during the argon ion beam cutting process, scratches will be generated on the surface of the particles, and the software may misjudge the scratches as the boundaries of the particles during the identification process, thereby generating identification errors; 3, due to the fact that the particles are too small, the particles are not successfully identified; 4, the particles are located at the edge of the electron microscope field of view, the particles are penetrated by the edge, the morphology cannot be completely displayed, and the local instead of the whole is identified, thereby generating identification errors.For the above-mentioned unrecognizable or misidentified particles, manual calibration is performed, and the specific process is as follows: deleting the particles located at the edge of the scanning electron microscope, which cannot completely display the large particles; judging whether there is a gap mark in the interior of other unrecognizable or misidentified particles, if there is no gap mark in the interior of the particles, judging that it is one particle, and manually identifying it according to the particle boundary observed by manual observation; in response to the existence of a gap mark in the interior of the particle, judging whether the gap mark penetrates the particle, if not, judging that it is one particle, and performing manual identification; in response to the gap mark penetrating the particle, judging whether the gap mark is linear or irregular; in response to the gap mark being irregular, judging that it is the boundary between particles, and dividing the particles along the boundary; in response to the gap mark being linear, performing contrast; in response to the contrast being not obvious and having no crack feeling, judging that it is a scratch, and identifying it as one particle; in response to the contrast being strong and having a crack feeling, judging that it is the boundary between particles, and identifying it as two particles. After manual identification, the information unrelated to the particles in the automatic processing of the image is deleted, that is, the determination and identification of the particles in the picture are completed.

[0143] In the present application, the sphericity test method of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab is as follows: the particles in the section of the positive electrode film layer are identified by referring to the method described above, and the appearance of the particles in the section of the positive electrode film layer along the thickness direction of the tab is analyzed by using the "shape description" analysis function in ImageJ. According to the software manual (ImageJ User Guide IJ 1.46r), the "Round" parameter obtained by analysis represents the ratio of the pixel area of the particle to the area of the circle with the fitted long diameter as the diameter, which can be used to characterize the sphericity of the particle. The closer the particle is to a sphere, the closer the ratio of the pixel area to the area of the circle with the fitted long diameter is to 1. Therefore, the "Round" parameter of the particle obtained by analysis is used to characterize the sphericity of the particle. The sphericity of at least 1000 particles with a particle size R1 satisfying R1≥1000 nm is arranged in order from small to large, and the sphericity is taken as the horizontal axis and the cumulative area ratio is taken as the vertical axis to obtain the sphericity cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm in the positive electrode film layer. R1A1 50 is the sphericity L value corresponding to the cumulative area ratio of 50% of the vertical axis in the sphericity L value cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm.

[0144] In some embodiments, in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, L R1A50Optionally 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.705, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80 or any numerical range between any two of them.

[0145] The person skilled in the art can realize the regulation of the sphericity of the particles by any process known. As an example, the regulation of the sphericity of the particles can be realized by processes such as grinding, polishing, chemical etching, mechanical stirring, extrusion, coating, granulation, addition of surfactants, etc., as well as adjustment of the parameters of each process.

[0146] In the present application, the graphitization degree C value cumulative distribution curve refers to the curve obtained by arranging the obtained at least 100 C values in order from small to large, taking the graphitization degree as the horizontal axis and the cumulative quantity ratio as the vertical axis. C 50 The median C of the graphitization degree is the C value corresponding to the cumulative quantity ratio of 50% on the vertical axis of the graphitization degree C value cumulative distribution curve. 50 Compared with the point value, the graphitization degree of the particles in the positive electrode film layer can reflect the overall graphitization degree, i.e. the easy sliding degree; compared with the mean value, the influence of extreme values in the test process can be reduced, and the confidence of the test result can be improved.

[0147] The graphitization degree C value of the positive electrode film layer can be obtained by the face scanning mode of the laser microscopic confocal Raman spectrometer. As an example, specifically, a laser microscopic confocal Raman spectrometer (high-precision Renishaw laser microscopic confocal Raman spectrometer) is used, the excitation wavelength of 532 nm is selected, an appropriate amount of positive electrode film layer is taken, the surface thereof or the section along the thickness direction of the pole piece is face-scanned, the scanning area is 45 μm x 45 μm, which is divided into 10 x 10 grids, the grid vertices are taken as the test points, the step length is 5 μm, and the total number of scanning points is 100 points, thereby obtaining the C values of different sites and the C value cumulative distribution curve of the face scanning area. The positive electrode film layer in the present application can be a freshly prepared positive electrode film layer or a positive electrode film layer obtained by disassembling from a battery. The surface of the positive electrode film layer obtained by disassembling from a battery inevitably has residual electrolyte salt particles. In order to improve the test accuracy, the section along the thickness direction of the pole piece is preferably face-scanned to characterize the graphitization degree of the positive electrode film layer.

[0148] The graphitization degree C value of the positive electrode film layer is obtained by the peak intensity ratio of the G peak (G-band) and the D peak (D-band) of the Raman spectrum, the G peak position is 1580 ± 100 cm -1 , which represents the sp 2 hybrid structure of carbon; the D peak position is 1350 ± 100 cm -1characterizes the disordered structure, where disorder means that there is no regular arrangement of carbon atoms in the structure. In graphite crystals, carbon atoms in the same layer are sp 2 hybridized to form covalent bonds, and van der Waals forces between layers, making the carbon of the graphite structure easy to slip. Therefore, the C value can characterize the graphitization degree of the positive electrode film layer. It can be understood that the graphitization degree in the positive electrode film layer mainly comes from the carbon material in the positive electrode film layer that has been subjected to graphitization treatment, i.e., the carbon material layer of the positive electrode active material. Although the carbon material of the positive electrode active material is rich in sp 2 The carbon nanotube conductive agent with the hybrid structure also has a relatively high I G / I D However, due to its low addition content and small tube diameter, its addition in the positive electrode film layer shows an extreme value in the Raman area scanning test of the positive electrode film layer, and does not affect the graphitization degree C 50 Therefore, the graphitization degree of the positive electrode film layer can also be used to characterize the graphitization degree of the positive electrode active material.

[0149] A person skilled in the art can realize the regulation of the graphitization degree of the active material particles by any process known. As an example, regulating the carbon source, sintering temperature, sintering time, sintering pressure, and sintering atmosphere can all realize the adjustment of the graphitization degree of the active material particles.

[0150] The higher the graphitization degree of the surface carbon of the positive electrode active material, the higher the proportion of the carbon of the graphite structure in the positive electrode film layer, and the easier the particles slip with the help of the carbon structure with high graphitization degree in the coating layer, reducing the stress concentration phenomenon in the pole piece.

[0151] In some embodiments, the median value C 50 may be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, or any numerical range between any two of them.

[0152] In some embodiments, the median value C 50 is 1.01-1.13.

[0153] The graphitization degree of the positive electrode film layer is further within the above range, which helps to further improve the easy-slipping degree of the particles in the positive electrode film layer, reduce the stress concentration in the positive electrode film layer, and further improve the long cycle stability of the battery cell.

[0154] In some embodiments, in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm has L R1A50 is 0.65-0.75.

[0155] In some embodiments, in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm has L R1A50 is 0.67-0.72.

[0156] In the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000nm has L R1A50 In the range of 0.65-0.75, further in the range of 0.67-0.72, it is beneficial to further reduce the stress concentration at the large particles in the positive electrode film layer of the thick-coated stacked cell, thereby reducing the probability of film layer falling off and improving the cycle life of the battery.

[0157] In some embodiments, the single-sided thickness H of the positive electrode film layer is 70μm -120μm.

[0158] In some embodiments, the single-sided thickness H of the positive electrode film layer is 90μm -120μm.

[0159] The thickness of the positive electrode film layer can be detected by any means known in the art. As an example, the thickness of the positive electrode film layer in the section of the positive electrode tab along the thickness direction is measured by scanning electron microscopy.

[0160] In some embodiments, the single-sided thickness H of the positive electrode film layer can be selected from 70μm, 71μm, 72μm, 73μm, 74μm, 75μm, 76μm, 77μm, 78μm, 79μm, 80μm, 81μm, 82μm, 83μm, 84μm, 85μm, 86μm, 87μm, 88μm, 89μm, 90μm, 91μm, 92μm, 93μm, 94μm, 95μm, 96μm, 97μm, 98μm, 99μm, 100μm, 101μm, 102μm, 103μm, 104μm, 105μm, 106μm, 107μm, 108μm, 109μm, 110μm, 111μm, 112μm, 113μm, 114μm, 115μm, 116μm, 117μm, 118μm, 119μm, 120μm or any numerical range between any two of them.

[0161] The single-sided thickness of the positive electrode film layer in the above range is helpful to improve the active material loading in the positive electrode of the battery, thereby improving the capacity of the battery.

[0162] In some embodiments, the single-side thickness H of the positive electrode film layer is 100-120 pm.

[0163] Increasing the thickness of the positive electrode film layer helps to increase the loading of the positive electrode active material and helps to increase the capacity of the battery. However, the applicant has found that when the single-side thickness of the positive electrode film layer is greater than or equal to 100 pm, the volume expansion of the positive electrode film layer is more significant during the cycling of the battery, thereby generating greater stress, the stress concentration phenomenon in the positive electrode film layer is more significant, the risk of film layer peeling increases, and thus the cycling performance of the battery is affected. The embodiments of the present application increase the capacity of the battery by increasing the thickness of the positive electrode film layer, while controlling the median value C of the graphitization degree in the cumulative distribution curve of the graphitization degree C obtained by the positive electrode film layer in the laser microscopic confocal Raman spectrometer under the face scanning mode, the degree of slip between the particles in the positive electrode film layer is increased, and the stress concentration generated during the compaction of the electrode sheet is reduced, thereby increasing the capacity of the battery while taking into account the cycling performance of the battery. 50

[0164] In some embodiments, based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the electrode sheet, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm is 12%-50%.

[0165] It can be understood that the particles in the 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, the embodiments of the present application can accurately and objectively reflect the distribution of the lithium-containing transition metal phosphate particles in the positive electrode film layer by observing and counting the particle area in the section of the positive electrode sheet along the thickness direction of the electrode sheet.

[0166] In the prior art, a laser particle size analyzer is usually used to count the particle size of the positive electrode active material by Malvern laser diffraction method. However, the applicant's research shows that because the lithium-containing transition metal phosphate particles are prone to agglomeration, the test results obtained by the Malvern laser diffraction method according to the principle of laser scattering are often the particle size of the particle agglomerates, and cannot truly reflect the particle size of the particles in the positive electrode active material, nor can they 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 be improved during the processes of slurry preparation and film rolling. The test results obtained by the Malvern laser diffraction method are affected by the particle size, specific surface area and agglomeration degree of the positive electrode active material, and compared with the true dispersion state in the electrode sheet, the number of large particles obtained by the test is lower than the actual value, and the number of small particles is higher than the actual value. Therefore, the particle size obtained by the Malvern laser diffraction method cannot be equivalent or analogous to the particle size obtained by the counting of the embodiments of the present application. ​

[0167] The area ratio of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the pole piece is tested as follows: the particles of the positive electrode film layer are identified according to the method described above, the picture after the particle determination and identification is imported into ImageJ software for analysis, the scale is set according to the scanning electron microscope picture, and the particle size, area, sphericity and roughness of the particles in the section of the positive electrode film layer along the thickness direction of the pole piece are statistically analyzed by using the analysis functions of “Feret diameter”, “Area”, “Round” and “Solidity”. 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 represents the particle size of the particle; the “Area” parameter obtained represents the pixel area of the particle. Since the particles with a particle size less than 50 nm have a large error 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 a large error in the statistical result, therefore, in the particle size statistical process of the present application, the particles with a particle size less than 50 nm are not counted, and the particle statistical data corresponding to the particles with AR, Round or Solidity display as “NaN” are deleted. The sum of the “Area” parameters of the particles with a particle size R1 satisfying R1≥1000 nm and the sum of the “Area” parameters of all particles are calculated as the area of the particles with a particle size R1 satisfying R1≥1000 nm and the total area of the counted particles, respectively. The area ratio of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the pole piece is calculated by dividing the sum of the areas of the particles with a particle size R1 satisfying R1≥1000 nm by the total area of the counted particles.

[0168] In some embodiments, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the pole piece can be selected as 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 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 numerical range between any two of them.

[0169] In some embodiments, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the pole piece is 12%-40%.

[0170] The large particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab help to improve the compaction density of the positive electrode tab, thereby improving the volumetric energy density of the battery cell; however, the researchers found that stress concentration is prone to occur at these large particles, increasing the risk of positive electrode film layer peeling. Therefore, the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab is in the range of 12%-50%, and further in the range of 12%-40%, which can both improve the compaction density of the positive electrode tab and not cause too high peeling probability of the positive electrode film layer, thereby improving the energy density of the thick-coated lithium-containing transition metal phosphate battery while relieving the capacity diving problem and taking into account the cycle life of the battery.

[0171] In some embodiments, the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab is less than or equal to 5%.

[0172] The distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab can be tested by methods known in the art. As an example, the section of the positive electrode film layer along the thickness direction of the positive electrode tab is divided into three layers of equal thickness (when a bottom coating layer is coated on the positive electrode current collector surface before coating the positive electrode active material layer, the region from the positive electrode film layer close to the positive electrode current collector 5 μm to the surface of the positive electrode film layer away from the positive electrode current collector is divided into three layers of equal thickness along the thickness direction of the positive electrode tab), namely the lower layer close to the positive electrode current collector, the upper layer away from the positive electrode current collector, and the middle layer between the upper layer and the lower layer; 10 non-overlapping fields are randomly selected in the upper layer, the middle layer and the lower layer respectively, and scanning electron microscope images are taken at 10k magnification; the 10 scanning electron microscope images taken in each layer are respectively imported into ImageJ software for analysis, and the area ratio of the particles with a particle size R1 satisfying R1≥1000 nm in the 10 images corresponding to the upper layer, the middle layer and the lower layer is obtained according to the above-mentioned "area ratio test method of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab", and a total of three values are obtained. The range of the three values of the upper layer, the middle layer and the lower layer is the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, wherein the range is the difference between the maximum value and the minimum value of the three values of the upper layer, the middle layer and the lower layer. The smaller the distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the positive electrode tab, the more uniform the distribution of the large particles with a particle size R1 satisfying R1≥1000 nm in the positive electrode film layer, which helps to reduce the stress concentration phenomenon at the large particles in the positive electrode film layer and reduce the probability of delamination and peeling, thereby improving the cycle performance of the battery.

[0173] In some embodiments, the distribution uniformity of the particles with the particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet can be selected as 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 1%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, or any numerical range between any two of the above values.

[0174] In some embodiments, the distribution uniformity of the particles with the particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet is 0.2%-2.5%.

[0175] In some embodiments, the distribution uniformity of the particles with the particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet is 0.2%-2%.

[0176] The distribution uniformity of the particles with the particle size R1 satisfying R1≥1000 nm in the section of the positive electrode film layer along the thickness direction of the electrode sheet within the above range can effectively reduce the stress concentration degree in the local area of the film layer, so that the stress in the film layer compaction process can be uniformly dispersed in the entire area of the film layer, thereby improving the energy density of the battery while reducing the probability of film layer falling off, alleviating the capacity diving problem of the thick-coated lithium-containing transition metal phosphate battery, and improving the cycle life of the battery.

[0177] In some embodiments, in the cumulative distribution curve of the coating value B obtained by the positive electrode film layer under the face scanning mode of the laser microscope confocal Raman spectrometer, the median of the coating value B 50 is 0.30-0.60, wherein the coating value B is I P / I D , I P represents the P peak intensity of the Raman spectrum at 948±100 cm -1 , and I D represents the D peak intensity of the Raman spectrum at 1350±100 cm -1 .

[0178] The B-value cumulative distribution curve refers to arranging the obtained at least 100 B-values in ascending order, taking the B-value as the horizontal axis and the cumulative quantity proportion as the vertical axis to obtain a curve. In order to reduce the influence of the extreme value of the coating value caused by the non-particle region in the positive electrode film layer on the test results, the median B 50 The compactness of the carbon material layer on the positive electrode active material is evaluated. B 50 The B-value is the B-value corresponding to the cumulative quantity proportion of 50% on the vertical axis of the B-value cumulative distribution curve.

[0179] In the present application, the coating value B-value of the positive electrode film layer can be obtained by scanning with a laser microscopic confocal Raman spectrometer. As an example, specifically, a laser microscopic confocal Raman spectrometer (high-precision Renishaw laser microscopic confocal Raman spectrometer) is used, the excitation wavelength of 532 nm is selected, and an appropriate amount of positive electrode film layer is taken to scan the surface or the section along the thickness direction of the electrode sheet. The scanning area is 45 μm x 45 μm, which is divided into 10 x 10 grids, the grid vertices are taken as the test points, the step is 5 μm, and the total number of scanning points is 100 points. Thus, the B-values of different sites and the B-value cumulative distribution curve of the scanning area are obtained. The positive electrode film layer in the present application can be a freshly prepared positive electrode film layer or a positive electrode film layer obtained by disassembling from a battery. The surface of the positive electrode film layer obtained by disassembling from a battery inevitably has residual electrolyte salt particles. In order to improve the test accuracy, the section along the thickness direction of the electrode sheet is preferably scanned to characterize the coating value of the positive electrode film layer.

[0180] The coating value B-value of the positive electrode film layer is obtained by the peak intensity ratio of the P peak (P-band) and the D peak (D-band) of the Raman spectrum, the P peak position is 948 ± 100 cm -1 , which represents the phosphate PO4 3- structure; the D peak position is 1350 ± 100 cm -1 , which represents the disordered structure, wherein disorder indicates that there is no regular arrangement between carbon atoms in the structure. In the test process, the excitation wavelength of 532 nm is selected, and the test depth is shallow. Therefore, in the test results obtained by scanning the positive electrode film layer in the laser microscopic confocal Raman spectrometer, the carbon structure peak exhibits higher intensity than the phosphate structure peak.

[0181] A person skilled in the art can realize the regulation of the coating value of the active material particles by any known process. As an example, regulating the type of carbon source, the addition amount of carbon source, the sintering temperature, the sintering time, the sintering pressure, and the sintering atmosphere can all realize the adjustment of the coating value of the active material particles. The coating value B-value can reflect the compactness of the carbon material layer on the surface of the lithium-containing transition metal phosphate particles. The more compact the carbon material layer, the lower the intensity of the phosphate structure detected in the Raman spectrum, and the smaller the coating value B-value of the positive electrode film layer.

[0182] In some embodiments, the positive electrode film layer further comprises a coating layer arranged on at least part of the surface of the lithium-containing transition metal phosphate particles, and the positive electrode film layer has a median value B of the coating value B in the cumulative distribution curve of the coating value B obtained by the laser microscope confocal Raman spectrometer in the face scanning mode, and the coating value B is in the range of 0.1 to 0.5. 50 Optionally, 0.3, 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, 0.52, 0.53, 0.54, 0.55, 0.56, 0.57, 0.58, 0.59, 0.6, or any numerical range between any two of the above values.

[0183] The median value B of the coating value B of the positive electrode film layer 50 The above range indicates that the carbon material layer of the positive electrode active material is relatively dense and uniform, which is beneficial to improve the uniformity of the slip of the positive electrode film layer during the rolling process, and reduce the stress concentration phenomenon in the thick-coated positive electrode film layer. In addition, with the aid of the dense and uniform carbon material layer, the large particles in the positive electrode film layer are more likely to slip during the compaction process, thereby reducing the stress concentration phenomenon at the large particles in the thick-coated positive electrode film layer, reducing the probability of the positive electrode film layer falling off, improving the battery capacity diving problem, and improving the cycle life of the battery.

[0184] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer comprise a component represented by the following general formula:

[0185] Li m Fe x P y O j Q q Formula I,

[0186] wherein Q comprises one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, 0≤q≤0.1.

[0187] In some embodiments, m can be selected from 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or any numerical range between any two of them; x can be selected from 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or any numerical range between any two of them; y can be selected from 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, or any numerical range between any two of them; j can be selected from 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any numerical range between any two of them; q can be selected from 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any numerical range between any two of them.

[0188] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium fluorophosphate, lithium manganese iron phosphate, and modified materials thereof.

[0189] In some embodiments, the lithium-containing transition metal phosphate particles in the positive electrode film layer include one or more of lithium iron phosphate and doped modified materials, coated modified materials thereof.

[0190] In some embodiments, the iron elution rate of the positive electrode material in the positive electrode film layer is 658 ppm-1921 ppm.

[0191] The iron elution rate of the positive electrode material in the positive electrode film layer can be tested by a method known in the art. As an example, 7.5 g of positive electrode material powder obtained by scraping the powder from the positive electrode film layer sample is weighed and added to 100.3 g of ascorbic acid solution with a mass concentration of 0.3% (solvent is ultrapure water). After stirring at a speed of 500 revolutions per minute for 305 minutes, the solution is quickly sucked using a 5 mL syringe, filtered into a test tube using a filter head with a pore size of 0.45 μm, and 1 mL of supernatant is sucked using a pipette and added to a glass volumetric flask for dilution by 50 times. An inductively coupled plasma optical emission spectrometer (ICP-OES) is used for testing to obtain the concentration of iron elements in the solution. The iron elution rate of the positive electrode material in the positive electrode film layer is calculated by the formula: (ICP test iron element concentration x solution volume / involved constant solution mass) x 100.3 g / positive electrode material powder mass, the solution volume is 50 mL, and the involved constant solution mass is 1 g.

[0192] In some embodiments, the iron elution rate of the cathode material in the cathode film layer can be 658 ppm, 700 ppm, 800 ppm, 890 pm, 900 ppm, 1000 ppm, 1058 pm, 1076 pm, 1100 ppm, 1143 pm, 1200 ppm, 1236 pm, 1300 ppm, 1311 pm, 1384 pm, 1349 pm, 1400 ppm, 1485 pm, 1500 ppm, 1531 pm, 1600 ppm, 1700 ppm, 1800 ppm, 1921 ppm, or any numerical range between any two of them.

[0193] In some embodiments, the iron elution rate of the cathode material in the cathode film layer is 658 ppm-1485 ppm.

[0194] The iron element eluted in the cathode material mainly comes from the lithium-containing transition metal phosphate in the cathode active material. The iron elution rate depends on the number of lattice defects of the lithium-containing transition metal phosphate on one hand, and the completeness and density of the carbon material layer on the surface of the cathode active material on the other hand. The lower the iron elution rate means that the lithium-containing transition metal phosphate has fewer lattice defects, which is beneficial to reducing the corrosion of the lattice in a weak acid environment; and the more complete and dense the carbon material layer on the surface of the cathode active material, the more the iron ion is inhibited from being eluted in a weak acid environment. The cathode material with an iron elution rate within the above range has relatively few lattice defects and a complete and dense carbon material layer, which is beneficial to improving the pressure resistance and easy sliding degree of the particles in the cathode film layer under large roller pressure, improving the compaction density of the cathode film layer and reducing the stress concentration in the cathode film layer, improving the energy density of the battery and also improving the battery capacity diving problem.

[0195] In some embodiments, the mass content of titanium element is 500 ppm-8000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the cathode film layer.

[0196] The types and contents of elements in the lithium-containing transition metal phosphate particles in the cathode film layer can be tested by any known method in the art. As an example, the titanium element and content are tested by inductively coupled plasma emission spectrometry according to Appendix C of GB / T 33822-2017.

[0197] In some embodiments, the mass content of titanium element is selected from 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5500 ppm, 6000 ppm, 6500 ppm, 7000 ppm, 7500 ppm, 8000 ppm, or any numerical range between any two of them, based on the total mass of lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0198] In some embodiments, the mass content of titanium element is 1000 ppm-3000 ppm, based on the total mass of lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0199] The introduction of titanium element into lithium-containing transition metal phosphate particles requires the addition of a titanium source in the preparation process of the positive electrode active material. The titanium source is often an inert material, which can reduce the reactivity of the lithium-containing transition metal phosphate raw material and reduce the particle size growth. Increasing the graphitization degree of the positive electrode active material often requires a higher sintering temperature or a longer sintering time, but this will also increase the size of the particles in the positive electrode film layer, increase the stress concentration of the positive electrode film layer, and cause the film layer to fall off. In the embodiments of the present application, by adding a high content of titanium element into the lithium-containing transition metal phosphate particles, the reactivity of the positive electrode active material synthesis raw material is reduced, and the positive electrode active material is synthesized with high graphitization degree while controlling the proportion of large particles, reducing the stress concentration of the positive electrode film layer, and reducing the probability of film layer falling off. The battery cycle life is improved while improving the battery energy density.

[0200] At the same time, the doping of titanium element in the positive electrode active material is beneficial to cause lattice distortion, reduce Li-O bond energy, improve lithium ion transmission rate, and improve the kinetic performance of the battery. The lithium ion diffusion in the thick coating film layer is not uniform, often accompanied by a significant lithium ion concentration gradient. The embodiments of the present application improve the solid-phase transmission rate of the positive electrode active material by adding a high content of titanium element into the lithium-containing transition metal phosphate particles, and improve the kinetic problem of the thick electrode sheet battery.

[0201] In some embodiments, the mass content of vanadium element is 500 ppm-5000 ppm, based on the total mass of lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0202] The type and content of elements in the lithium-containing transition metal phosphate particles in the positive electrode film layer can be tested by any known method in the art. As an example, the content of vanadium element is tested by inductively coupled plasma atomic emission spectrometry according to Appendix C of GB / T 33822-2017.

[0203] In some embodiments, the mass content of vanadium element is selected from 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, 1100 ppm, 1200 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, 1800 ppm, 1900 ppm, 2000 ppm, 2100 ppm, 2200 ppm, 2300 ppm, 2400 ppm, 2500 ppm, 2600 ppm, 2700 ppm, 2800 ppm, 2900 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0204] In some embodiments, the mass content of vanadium element is 500 ppm - 3000 ppm, based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

[0205] The vanadium element in the positive electrode film layer can be in multiple valence states, wherein the +5 valence vanadium (V 5+ ) can be doped at the phosphorus element site, which can cause lattice distortion due to its large radius, expand the diffusion channel of lithium ions, thereby improving the ionic conductivity of the positive electrode active material and the kinetic performance of the battery; the +3 valence vanadium (V 3+ ) can be doped at the transition metal site to generate lithium vacancies through charge compensation, thereby improving the electronic conductivity of the positive electrode active material. In addition, the uniformity of the distribution of vanadium element in the lithium-containing transition metal phosphate particles is improved, which helps to further improve the kinetic performance of the positive electrode film layer and the reaction uniformity of the positive electrode film layer, thereby further improving the kinetic performance and cycle performance of the battery monomer.

[0206] The mass content of vanadium element in the above range helps to improve the kinetic performance of the positive electrode sheet and the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery. At the same time, the titanium element, vanadium element and carbon nanotubes in the positive electrode film layer synergistically work together to help form a good three-dimensional network, further improving the electronic conductivity and ionic conductivity of the positive electrode film layer, thereby further improving the kinetic performance of the thick-coated lithium-containing transition metal phosphate battery.

[0207] In some embodiments, the porosity of the positive electrode film layer is 14% - 28%.

[0208] In the present application, the porosity of the positive electrode film layer can be tested in the following manner. The cross-section scanning electron microscope image of the positive electrode film layer obtained in the manner described above is imported into ImageJ software, a straight line tool is selected, a ruler length in the image is marked using the straight line, "Analyze Set Scale" is clicked, and the ruler parameters are set in the software according to the ruler length in the image. A rectangular tool is selected, the part of the image outside the ruler area is selected, the selected area is copied using "Image Duplicate", the image format is adjusted using "Image Type 8 bit"; "Analyze Set Measurements" is selected, and the following five options are selected: "Area", "Mean gray value", "Area Fraction", "Limit to threshold", and "Feret's diameter", wherein "Decimal places" is selected as 3, "Image"-"Adjust"-"Threshold" is selected in sequence, 0 and 100 are set in sequence in the "Threshold" box, and the porosity data in the cross-section electron microscope image can be derived using the Analyze-Measure function. The porosity picture is obtained by using "Image"-"Overlay"-"Flatten"; "Apply" in "Threshold" is clicked, and "Analyze"-"Analyze Particles" is clicked, and the four columns on the left are checked, and the porosity statistical data is obtained.

[0209] It can be understood that in the embodiments of the present application, the "pores" in the cross-section of the positive electrode film layer are identified by image color difference and threshold. The "pores" are not the pore data obtained by the exhaust test, and are mainly used to represent the gap between the particles in the cross-section of the positive electrode film layer. This method is better than the exhaust method because the porosity obtained by the exhaust method is related to the pores between the particles and the pores in the carbon material layer on the surface of the particles, and cannot objectively reflect the pores between the particles.

[0210] In some embodiments, the porosity of the positive electrode film layer can be selected as 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, or any numerical range between any two of them.

[0211] The porosity of the positive electrode film layer is within the above range, the positive electrode film layer has good electrolyte impregnation rate and tortuosity, which helps the diffusion of lithium ion liquid phase and solid phase, helps to reduce the concentration polarization of thick electrode sheet, and improves the kinetic performance of the battery. At the same time, it helps to alleviate the volume expansion of thick coated electrode sheet during the cycle process, reduce the mechanical stress of the film layer and reduce the stress concentration phenomenon, thereby reducing the risk of film layer falling off of thick coated electrode sheet.

[0212] Particularly in thick-coated soft-pack batteries, the gap between the shell and the electrode sheet is small, the volume occupancy of the film layer is large, and the accommodation volume of the electrolyte is reduced. The porosity of the positive electrode film layer is within the above range, which helps to improve the liquid retention rate of the battery and improve the kinetic performance of the battery.

[0213] In some embodiments, the positive electrode film layer further comprises a conductive agent, and the area ratio of the agglomeration region of the conductive agent is 0.5%-2.5% based on the total area of the cross section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0214] In this application, the area ratio of the agglomeration region of the conductive agent based on the total area of the cross section of the positive electrode film layer along the thickness direction of the electrode sheet can be tested by the following method. The cross section of the positive electrode film layer along the thickness direction of the electrode sheet is observed by scanning electron microscopy using the similar method described above, and the area of the conductive agent agglomeration region in the scanning electron microscope image is measured at 3k magnification. Since the conductive agent is generally a carbon-based material, such as conductive carbon black, carbon nanotubes, etc., under high magnification of the scanning electron microscope, the agglomerated conductive agent can be seen, and the conductive agent agglomeration region often appears as a black agglomeration compared to other regions in the positive electrode film layer. With the help of image analysis software, the conductive agent agglomeration region refers to the region in the scanning electron microscope image where the conductive agent is obviously agglomerated and appears black. Specifically, the scanning electron microscope image at 3k magnification is imported into ImageJ, the black conductive agent agglomeration region with a Feret greater than or equal to 2 μm is selected, and the sum of the areas of the selected regions is calculated as the area of the conductive agent agglomeration region. The area ratio of the agglomeration region of the conductive agent is the ratio of the area of the conductive agent agglomeration region to the total area of the imported scanning electron microscope image. Randomly take 3 scanning electron microscope images with non-overlapping ranges, and calculate the average value of the area ratio of the agglomeration region of the conductive agent as the "area ratio of the agglomeration region of the conductive agent based on the total area of the cross section of the positive electrode film layer along the thickness direction of the electrode sheet".

[0215] In some embodiments, the positive electrode film layer further comprises the conductive agent, and the area percentage of the agglomerated region of the conductive agent is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any numerical range between any two of the above values, based on the total area of the cross section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0216] The area percentage of the agglomerated region of the conductive agent within the above range, based on the total area of the cross section of the positive electrode film layer along the thickness direction of the electrode sheet, indicates that the conductive agent is uniformly distributed in the positive electrode film layer, which is conducive to forming a uniform conductive network, and is particularly helpful in reducing the problem of kinetic decline caused by the increase of ion transmission path in thick coating film layers, reducing the local polarization and even lithium precipitation problems generated during the cycle of the battery, and improving the cycle life of the battery.

[0217] Meanwhile, research shows that the first particles of large size in the lithium-containing transition metal phosphate particles are prone to rebound, and the agglomerated area of the conductive agent within the above range can inhibit the rebound of the lithium-containing transition metal phosphate particles by means of uniform distribution of the conductive agent, mechanically bind the particles and even the film layer, improve the cohesion of the film layer, reduce the film layer powder and shedding phenomenon, and improve the cycle life of the battery.

[0218] In some embodiments, the positive electrode film layer further comprises the conductive agent, and the area percentage of the agglomerated region of the conductive agent is 0.5%-1.7%, based on the total area of the cross section of the positive electrode film layer along the thickness direction of the electrode sheet.

[0219] In the embodiments of the present application, the area percentage of the agglomerated region of the conductive agent is further within the above range, indicating that the conductive agent is more uniformly distributed in the positive electrode film layer, and the content of the conductive agent is lower, which helps to reduce the occupation of the space of the positive electrode active material while improving the kinetic performance of the positive electrode film layer, thereby further improving the volume energy density of the battery while improving the kinetic performance of the battery.

[0220] In some embodiments, the conductive agent comprises carbon nanotubes, and the carbon nanotubes comprise one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0221] In the present application, the term "carbon nanotube" refers to a tube-shaped structure formed by carbon atoms in sp 2Graphene sheets formed by hybrid bonding curl to form nanomaterials with several to tens of layers of coaxial hollow cylindrical tubes. The diameter is usually in the range of several to tens of nanometers, and the length can vary from microns to centimeters, presenting a high aspect ratio. According to the number of layers of graphene sheets, they can be divided into single-walled carbon nanotubes (SWCNTs), few-walled carbon nanotubes (FWCNTs), and multi-walled carbon nanotubes (MWCNTs). Carbon nanotubes have excellent electrical conductivity and high elastic modulus.

[0222] Since carbon nanotubes have a one-dimensional structure, they can form a network structure in the positive electrode film layer. On the one hand, the high elastic modulus of carbon nanotubes makes their network structure not only a bridge for stress propagation, but also has a binding effect on thick coated positive electrode film layers, inhibiting the rebound of lithium-containing transition metal phosphate particles, effectively relieving stress concentration and reducing the risk of film layer peeling, thereby improving the battery capacity drop problem; on the other hand, the excellent electrical conductivity of carbon nanotubes makes their network structure an efficient electron transport channel, even if there is local film layer peeling, the thick electrode sheet can still maintain high electron transport efficiency in the in-plane and thickness directions, thereby delaying the occurrence of the capacity drop problem and further improving the kinetic performance and cycle life of the battery.

[0223] In some embodiments, the conductive agent further includes conductive carbon black.

[0224] Conductive carbon black has a high specific surface area and thus good liquid retention capacity. The thick electrode sheet has a large expansion force during the cycling process, making it easy for the electrolyte to be squeezed out. The distribution of conductive carbon black in the positive electrode film layer is beneficial to improving the liquid retention capacity of the thick electrode sheet, further alleviating the capacity drop phenomenon of the battery during the cycling process, and improving the cycle life of the battery.

[0225] In some embodiments, the agglomerated region of the conductive agent includes carbon nanotubes and conductive carbon black.

[0226] The researchers found that carbon nanotubes are prone to agglomeration due to their high surface energy, leading to uneven distribution in the positive electrode film layer and failure to form an effective carbon nanotube network structure. The surface energy of conductive carbon black is close to that of carbon nanotubes, which can be adsorbed on the surface of carbon nanotubes to form a physical barrier, increase the resistance of carbon nanotube agglomeration, reduce direct contact between carbon nanotubes, and thus inhibit the agglomeration phenomenon and improve the uniformity of carbon nanotubes in the positive electrode film layer. On the one hand, this helps to improve the conductivity of the thick-coated positive electrode film layer and improve the kinetic performance of the battery; on the other hand, it helps to exert the binding effect of carbon nanotubes on the positive electrode film layer, reduces the risk of the positive electrode film layer falling off, and further improves the kinetic performance and cycle life of the battery. In addition, the agglomeration of carbon nanotubes in the conductive agent agglomeration area will also cause the local ion transport path of the conductive agent agglomeration area to be blocked, and the addition of conductive carbon black can improve the lithium ion transport capacity of this area, reduce local polarization, and further improve the cycle stability of the battery.

[0227] In some embodiments, the mass content C1 of carbon nanotubes satisfies: 0 < C1 ≤ 2.5%, and the mass content C2 of conductive carbon black satisfies: 0 < C2 ≤ 2.5%, based on the mass of the positive electrode film layer.

[0228] In some embodiments, the mass content C1 of carbon nanotubes can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any numerical range between any two of them, based on the mass of the positive electrode film layer.

[0229] In some embodiments, the mass content C2 of conductive carbon black can be selected as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any numerical range between any two of them, based on the mass of the positive electrode film layer.

[0230] The mass content of carbon nanotubes and conductive carbon black within the above range can effectively alleviate the agglomeration of carbon nanotubes and form a good conductive network structure, thereby effectively reducing the stress concentration of the positive electrode film layer and improving the liquid retention rate of the positive electrode tab during long-term cycling, further reducing the risk of the positive electrode tab film layer falling off and the degree of polarization, improving the kinetic performance of the battery, and addressing the capacity drop problem and improving the cycle life of the battery.

[0231] In some embodiments, the positive electrode film layer further comprises a dispersant, and the dispersant comprises hydrogenated nitrile rubber (HNBR).

[0232] HNBR is obtained by hydrogenation of nitrile rubber, and its highly saturated main chain structure makes it have excellent oil resistance, heat resistance and aging resistance, etc. This makes it stable in different environments and systems when used as a dispersant, and is not prone to degradation or deterioration, thereby effectively playing a dispersing role. The HNBR molecular chain contains both polar nitrile groups and non-polar carbon-hydrogen segments. The polar nitrile groups can interact with some polar substances or particle surfaces, such as adsorbing on the surface of the dispersed particles through hydrogen bonds, electrostatic interactions, etc.; the non-polar carbon-hydrogen segments have good lipophilicity and can be well stretched and dispersed in non-polar or weakly polar media, allowing the particles to be uniformly dispersed in the medium.

[0233] When HNBR adsorbs on the surface of the particles in the slurry, its long-chain molecules form a physical barrier around the particles, preventing the particles from coming close to each other and aggregating, so that the particles remain in a relatively independent dispersed state in the system. At the same time, HNBR can reduce the surface tension between the dispersion medium and the dispersed particles, making it easier for the particles to be wetted by the medium, thereby promoting the dispersion of the particles in the medium. At the same time, it can also reduce the interfacial energy between the particles, reducing the aggregation of the particles driven by interfacial energy. Further, when the slurry is dried into a film, the elastic network structure of HNBR can buffer the shrinkage stress generated by solvent evaporation, reduce the re-aggregation of the conductive agent due to capillary force during this process, reduce the area ratio of the conductive agent aggregation area, and improve the kinetic performance and cycle life of the battery.

[0234] In some embodiments, the mass content of the dispersant is 0.5%-2% based on the mass of the positive electrode film layer.

[0235] In some embodiments, the mass content of the dispersant can be selected as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, or any numerical range between any two of them, based on the mass of the positive electrode film layer.

[0236] The mass content of the dispersant in the above range can achieve uniform dispersion of the particles in the positive electrode film layer while maintaining a high loading of the positive electrode film layer, reduce stress concentration in the thick-coated lithium-containing transition metal phosphate positive electrode film layer, and effectively alleviate the battery capacity drop problem.

[0237] In some embodiments, the battery cell further includes a separator 20 disposed between the positive electrode and the negative electrode. The separator 20 includes a base film 201, a ceramic layer 202 disposed on at least one side of the base film 201, and an adhesive layer 203 disposed on the side of the ceramic layer 202 away from the base film 201. The adhesive layer 203 is a continuous layer with a porous structure and includes a vinylidene fluoride polymer.

[0238] In some embodiments, the battery cell further includes a separator disposed between the positive electrode and the negative electrode. The separator includes a base film, ceramic layers disposed on both sides of the base film, and an adhesive layer disposed on both sides of the ceramic layers away from the base film.

[0239] In some embodiments, the vinylidene fluoride polymer includes one or more of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP).

[0240] In some embodiments, vinylidene fluoride polymers include polyvinylidene fluoride (PVDF).

[0241] In existing technologies, the adhesive layer of the diaphragm typically uses aqueous PVDF, which exhibits an island-like structure within the diaphragm, such as... Figure 2 As shown, this is beneficial for providing a gap for cell expansion and also facilitates manufacturing; however, the contact area between such a separator adhesive layer and the electrode is small, and the adhesion is weak.

[0242] The diaphragm provided in this application uses a continuous porous layer as the adhesive layer, such as... Figure 1 and Figure 3 As shown, its porous structure provides space for the expansion of the thick-coated cell, improving its stability; at the same time, compared with the adhesive layer in the prior art, it has a larger bonding area with the electrode, thus making the bonding between the separator and the electrode more firm and uniform; furthermore, when the positive electrode film rebounds, it helps to maintain the interfacial contact between the separator and the positive electrode film, reducing the probability of film detachment.

[0243] It is understandable that a continuous adhesive layer may break and deform into a blocky structure during electrode manufacturing or cycling due to contact with or compression of the positive or negative electrode. The continuous structure referred to in this application means that, at the microscopic level, such as under a scanning electron microscope or optical microscope, the adhesive layer of the separator is continuous. To reflect the true morphology of the separator, during sampling, it is preferable to sample in areas of the battery where the separator's adhesive layer is not bonded to the positive or negative electrode. For example, sampling can be performed at locations beyond the positive and negative electrode; or sampling can be performed near the surface of the electrode assembly. This sampling area has less adhesion to the positive or negative electrode, providing a better reflection of the separator's true state.

[0244] Compared with the wound cell, the extrusion between the separator and the pole piece in the stacked cell is small, and the separator and the pole piece are prone to relative displacement, thereby disturbing the film layer and causing the film layer to be prone to powder falling or peeling off. In addition, it can also cause the positive and negative poles to be overlapped with each other, thereby increasing the risk of internal short circuit of the cell. Therefore, the separator provided in the embodiments of the present application is particularly suitable for the stacked cell. The adhesion between the porous adhesive layer and the pole piece is increased, which helps to improve the adhesion between the separator and the pole piece and reduce the relative displacement between the separator and the pole piece. This not only helps to reduce the disturbance to the positive pole film layer and the probability of film layer peeling off, but also helps to reduce the risk of positive and negative pole overlapping and causing the cell to short circuit.

[0245] In summary, when the vinylidene fluoride-based polymer in the adhesive layer is selected from the above-mentioned materials, a continuous and uniform porous adhesive layer is formed. First, the adhesion between the adhesive layer and the pole piece is improved and uniformly distributed, which helps to reduce the stress concentration phenomenon in the thick-coated lithium-containing transition metal phosphate positive pole film layer and reduce the risk of film layer peeling off, thereby further improving the cycle life of the battery. Second, the adhesive layer is stably bonded to the positive pole or the negative pole, which helps to reduce the direct contact between the positive pole and the negative pole due to the relative displacement of the pole and the separator, thereby reducing the risk of internal short circuit and improving the safety performance of the battery. Third, the porous adhesive layer helps to maintain the porosity of the separator and reserve space for the expansion of the cell, thereby further improving the cycle life of the battery.

[0246] In some embodiments, the material of the base film can include, but is not limited to, one or more of glass fiber, non-woven fabric, polyethylene (PE), and polypropylene (PP).

[0247] In some embodiments, the ceramic layer includes one or more of aluminum oxide (Al2O3), zirconium oxide (ZrO2), titanium oxide (TiO2), silicon oxide (SiO2), and boron nitride (BN).

[0248] The ceramic particles have flame retardancy and high hardness value, and are not easy to deform under heat, so the dimensional stability is excellent. The thermal conductivity of the ceramic material is low, which can further prevent certain thermal runaway points in the battery from expanding to form overall thermal runaway, thereby improving the safety performance of the battery monomer.

[0249] In some embodiments, the thickness of the base film in the separator is 7-9 μm.

[0250] In some embodiments, the thickness of the base film in the separator can be selected as 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, or a numerical range between any two values.

[0251] In some embodiments, the single-side thickness of the ceramic layer in the separator is 2-4 μm.

[0252] In some embodiments, the single-side thickness of the ceramic layer in the separator can be selected to be 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or a numerical range between any two of them.

[0253] In some embodiments, the single-side thickness of the adhesive layer in the separator is 1 μm-5 μm.

[0254] In some embodiments, the single-side thickness of the adhesive layer in the separator can be selected to be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a numerical range between any two of them.

[0255] In the present application, "thickness" has the meaning known in the art and can be measured using methods and instruments known in the art. As an example, a high-precision micrometer (e.g., Mitutoyo 293-100, with a precision of 0.1 μm) can be used for testing.

[0256] If the thickness of the adhesive layer is too low, the void space in the separator is small and the adhesion between the separator and the electrode sheet is low. On the one hand, the probability of film layer peeling increases after the film layer expands, affecting the cycle life of the battery. On the other hand, the probability of positive and negative overlap short circuit increases, thereby affecting the safety performance of the battery. If the thickness of the adhesive layer is too large, the space occupancy rate of the battery is large, thereby affecting the volumetric energy density of the battery. In the embodiments of the present application, the thickness of the adhesive layer is within the above range, which helps to balance the cycle life, safety performance and volumetric energy density of the battery.

[0257] In some embodiments, the positive electrode film layer is provided with a bottom coating layer at the bottom region close to the positive current collector, the bottom coating layer comprising a conductive agent and a binder, the conductive agent comprising carbon nanotubes and conductive carbon black, and the binder comprising polyvinylidene fluoride (PVDF).

[0258] In some embodiments, the thickness of the bottom coating layer is 0.5 μm-5 μm.

[0259] In some embodiments, the thickness of the bottom coating layer can be selected to be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, or a numerical range between any two of them.

[0260] The bottom coating layer provided in the embodiments of the present application helps to improve the adhesion between the positive electrode film layer and the positive current collector and alleviate the stress concentration phenomenon at large particles, thereby reducing the probability of positive electrode film layer peeling and improving the cycle stability of the battery. At the same time, compared with the direct contact between the positive current collector and the positive electrode film layer, the contact area between the bottom coating layer and the positive electrode film layer is increased, which helps to increase the area of electron transmission between the current collector and the positive electrode film layer, thereby reducing the internal resistance of the electrode sheet and improving the kinetic performance of the battery.

[0261] In some implementations, such as Figure 4 As shown, the battery cell 5 includes a housing 50, and the stacked cells are housed inside the housing 50. The housing 50 has a length dimension of L1 in the X direction, a width dimension of W1 in the Y direction, and a thickness dimension of H1 in the Z direction. Wherein, 450mm≤L1≤1300mm, 100mm≤W1≤150mm, and 14mm≤H1≤22mm.

[0262] In some implementations, L1 can be selected as 450mm, 480mm, 490mm, 500mm, 510mm, 520mm, 530mm, 540mm, 550mm, 560mm, 570mm, 580mm, 590mm, 600mm, 610mm, 620mm, 630mm, 640mm, 650mm, 660mm, 670mm, 680mm, 690mm, 700mm, 710mm, 720mm, 750mm, 800mm, 850mm, 900mm, 950mm, 1000mm, 1050mm, 1100mm, 1150mm, 1200mm, 1250mm, 1300mm, or any value range between the two.

[0263] In some implementations, W1 can be selected as 100mm, 110mm, 120mm, 130mm, 140mm, 150mm or any value range between the two.

[0264] In some implementations, H1 can be selected as 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21mm, 22mm or any value range between the two.

[0265] In some embodiments, the length dimension of the housing is L1, where 450mm ≤ L1 ≤ 650mm.

[0266] When the length dimension L1 of the casing satisfies 450mm≤L1≤650mm, the length of the battery cell is shorter, which helps to shorten the current diffusion path, reduce the internal resistance of the electrode, thereby reducing the heat generation of the battery and improving its dynamic performance. In addition, the shorter casing length helps to shorten the diffusion path of the electrolyte during the wetting process, improve the wetting rate and uniformity of the electrolyte, further promote the uniformity of lithium ion insertion and extraction during cycling, alleviate stress concentration, reduce the risk of film peeling, and improve the cycle stability of the battery cell.

[0267] In some embodiments, the length dimension of the housing is L1, where 900mm ≤ L1 ≤ 1300mm.

[0268] When the length dimension L1 of the shell satisfies 900mm≤L1≤1300mm, the size of the battery monomer is relatively long, which helps to reduce the volume ratio of the shell in the battery monomer and improve the load ratio of the active material. At the same time, the longer battery monomer can reduce the number of batteries required in the battery module, simplify the structural design of the battery module, and reduce the number and complexity of structural components in the module, thereby improving the space utilization of the battery pack, and further helping to improve the volumetric energy density of the battery monomer.

[0269] In some embodiments, as shown in FIG. 1, the material of the shell 50 is a soft package material, and the soft package material includes an aluminum plastic composite film. Figure 4

[0270] In some embodiments, the material of the shell includes one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), polyethylene (PE) and aluminum composite film.

[0271] The soft package material has a high ductility, so that the shell is more lightweight, soft, and helps to improve the space utilization of the battery monomer, thereby improving the energy density of the battery monomer. In addition, the high barrier property of aluminum can effectively reduce the penetration of water and oxygen into the battery, reduce the decomposition of electrolyte and the oxidation degree of electrode material, thereby improving the service life of the battery.

[0272] In some embodiments, the capacity of the battery monomer is 95Ah-300Ah at 25℃.

[0273] In some embodiments, the capacity of the battery monomer is 150Ah-190Ah at 25℃.

[0274] In the present application, the capacity of the battery monomer is the meaning known in the art, which can be tested by the method known in the art. As an example, at 25℃, charge to 3.65V at 0.5C charge rate, then charge to 0.05C at 3.65V constant voltage, stand for 10min, then discharge to 2.5V at 1C discharge rate, and the discharge capacity of the battery monomer is taken as the capacity of the battery monomer.

[0275] ​In some embodiments, the capacity of the battery cell can be selected from 95 Ah, 100 Ah, 105 Ah, 110 Ah, 115 Ah, 120 Ah, 125 Ah, 130 Ah, 135 Ah, 140 Ah, 145 Ah, 150 Ah, 155 Ah, 158 Ah, 159 Ah, 160 Ah, 161 Ah, 165 Ah, 170 Ah, 175 Ah, 178 Ah, 180 Ah, 185 Ah, 190 Ah, 200 Ah, 210 Ah, 220 Ah, 230 Ah, 240 Ah, 250 Ah, 270 Ah, 280 Ah, 290 Ah, 300 Ah, or any range between any two of the above values, at 25 °C.

[0276] The second aspect of the present application provides a battery device comprising the battery cell provided by the first aspect of the present application.

[0277] The battery device disclosed in the embodiments of the present application can be used in a power consumption device using the battery device as a power source or a variety of energy storage systems using the battery device as an energy storage element. In addition to being used in vehicles, the battery device can be used in, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, the electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric plane toys, etc. The spacecraft can include airplanes, rockets, space shuttles, and spaceships, etc.

[0278] The third aspect of the present application provides a power consumption device using the battery device as a power source, wherein the power consumption device comprises at least one of the battery cell, the battery module, or the battery pack provided by the present application. The battery cell, the battery module, or the battery pack can be used as a power source of the power consumption device, or can be used as an energy storage unit of the power consumption device. As the power consumption device, the battery cell, the battery module, or the battery pack can be selected according to the use requirements.

[0279] Figure 5 The power consumption device is an example. The power consumption device disclosed in the embodiments of the present application can be a fuel car, a gas car, or a new energy car, which can be a pure electric car, a hybrid car, or a range extended car, etc. The vehicle is internally provided with a battery device, which can be arranged at the bottom, the head, or the tail of the vehicle. The battery device can be used for power supply of the vehicle, for example, the battery device can be used as an operating power source of the vehicle. The vehicle can further comprise a controller and a motor, and the controller is used to control the battery device to supply power to the motor, for example, for the working power demand of the vehicle during starting, navigation, and driving. In some embodiments of the present application, the battery device can not only be used as an operating power source of the vehicle, but also be used as a driving power source of the vehicle, instead of or partially instead of fuel or natural gas to provide driving power for the vehicle.

[0280] The fourth aspect of the present application provides an energy storage device using a battery device as a power source. The energy storage device can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system.

[0281] Embodiment

[0282] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application. If a specific technology or condition is not specified in the embodiments, the technology or condition described in the literature in the art or according to the product manual is used. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be obtained by purchase.

[0283] Embodiment 1

[0284] (1) Preparation of positive active material

[0285] Lithium dihydrogen phosphate, ferrous oxalate, carbon source, titanium dioxide, and vanadium pentoxide were mixed uniformly in methanol and ground to obtain a mixed raw material. The molar ratio of lithium dihydrogen phosphate and ferrous oxalate was 1.025:1.0, so that the molar ratio of lithium and iron was 1.025:1.0. The carbon source included polyethylene glycol with a weight average molecular weight of 500, polyethylene glycol with a weight average molecular weight of 2000, and polyethylene glycol with a weight average molecular weight of 4000 in a mass ratio of 2:6:2. The particle size D 10 was 6.5 μm, the particle size D 50 was 62 μm, and the particle size D 90 was 108 μm. The mass content of Fe element in the ferrous oxalate was 30.5%, and the mass content of trivalent iron element was 0.03%.

[0286] The mixed raw material was ball milled in a ball mill for multiple times and de-magnetized to obtain a mixed slurry. The milling times and time were controlled, and the particle size Dv 50 of the milled mixed slurry was 3.15 μm.

[0287] The mixed slurry was spray dried to obtain a dry precursor powder material, and the appearance of the dry precursor powder material was light yellow and uniform in color.

[0288] The precursor powder material was placed in a sintering furnace, and the temperature was raised from 25°C to 360°C at a rate of 2°C / min under a nitrogen atmosphere and kept at this temperature for 3.5 h. Then the temperature was raised to a second temperature of 785°C at a rate of 5°C / min, and kept at this temperature for 10 h. After the end of the process, the temperature was lowered and cooled. The mass content of Ti element was 1050 ppm and the mass content of V element was 950 ppm based on the total mass of the positive active material.

[0289] The obtained material is broken by airflow crushing method with a classification frequency of 21 Hz and a wind volume of 0.54 MPa, to obtain a lithium iron phosphate positive electrode active material with a carbon material on the surface.

[0290] The D10, D50, D90 and Dv50 above refer to data obtained by a Malvern laser scattering method.

[0291] (2) Preparation of the positive electrode tab

[0292] The positive electrode active material, the conductive agent and the binder polyvinylidene fluoride are mixed in a solvent N-methyl pyrrolidone at a mass ratio of 94.1:1.9:3, and then a dispersant HNBR with a mass ratio of 1% is added, and the mixture is fully mixed and stirred in a stirring tank to prepare a positive electrode slurry. The stirring includes pre-stirring and main stirring, the stirring speed of the pre-stirring is lower than that of the main stirring, the pre-stirring has a revolution speed of 25 rpm and a rotation speed of 500 rpm, and the pre-stirring time is 15 min. After the stirring process is completed, the positive electrode slurry is transported to a coating process; the conductive agent includes conductive carbon black and multi-walled carbon nanotubes at a mass ratio of 0.9:1, the specific surface area of the conductive carbon black is 80 m 2 / g, the oil absorption value is 180 mL / 100 g, the average length of the carbon nanotube is 20 μm, and the specific surface area is 280 m 2 / g.

[0293] The positive electrode slurry is transferred and coated onto an aluminum foil and dried, and hot pressing is performed to obtain a positive electrode tab with a single-sided surface density of the positive electrode film layer of 0.38 g / 15 40.25 mm 2 , and a compacted density of 2.36 g / cm 3 . Here, the compacted density refers to the compacted density under the full discharge state of the battery monomer.

[0294] The hot pressing process includes three times of hot roller pressing process, the hot roller pressing pressure increases in turn, and the hot roller pressing pressure is 35 tons, 55 tons and 75 tons in turn; the hot roller temperature is 65°C; before the first time of entering the hot roller compaction, the tab is heated, and the heating temperature is 50°C.

[0295] The positive electrode tab is slitted and punched into a specified shape, and the punched positive electrode tab is sorted according to the weight by a weighing sorting machine, so as to be stacked by a stacking machine.

[0296] In the section of the positive electrode film layer along the thickness direction of the tab, the median number L R1A50 of the sphericity in the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm is 0.721; and the median number C 50is 1.11; the area ratio of particles with a particle size R1 satisfying R1≥1000 nm is 35.28% based on the total area of the section of the positive electrode film layer along the thickness direction of the electrode sheet; the distribution uniformity of particles with a particle size R1 satisfying R1≥1000 nm is 1.97% in the section of the positive electrode film layer along the thickness direction of the electrode sheet; the median value B of the positive electrode film layer coating value B is 0.441; the iron dissolution rate of the positive electrode material is 976 ppm; the area ratio of the agglomeration region of the conductive agent is 1.91% based on the total area of the section of the positive electrode film layer along the thickness direction of the electrode sheet; and the porosity of the positive electrode film layer is 15.06%. 50 is 0.441; the iron dissolution rate of the positive electrode material is 976 ppm; the area ratio of the agglomeration region of the conductive agent is 1.91% based on the total area of the section of the positive electrode film layer along the thickness direction of the electrode sheet; and the porosity of the positive electrode film layer is 15.06%.

[0297] (3) Preparation of the negative electrode sheet

[0298] A mixture of artificial graphite and natural graphite (weight ratio of 1:1), a conductive agent, conductive carbon black, a binder, styrene-butadiene rubber (SBR), and a thickening agent, carboxymethyl cellulose sodium (CMC), were mixed uniformly at a weight percentage of 96:0.5:2.0:1.5, and deionized water was added. After stirring and dispersing, a negative electrode slurry was obtained. The negative electrode slurry was coated on a copper foil substrate, and after drying, compaction, slitting, and sheeting, a negative electrode sheet was obtained.

[0299] The negative electrode sheet was divided into strips and punched into a specified shape, and the punched negative electrode sheet was sorted by weight using a weighing sorting machine for use in a sheet stacking machine.

[0300] (4) Separator

[0301] Polyvinylidene fluoride (PVDF) was dissolved in N-methyl pyrrolidone (NMP), and after stirring uniformly, polyethylene glycol (PEG) was added as a pore-forming agent and stirred and mixed thoroughly to obtain a bonding layer solution. The bonding layer solution was applied to the above-mentioned base film with ceramic layers on both sides, and after pre-volatilization at 80°C and drying at 110°C, the PEG was dissolved out in deionized water to obtain a porous structure bonding layer separator.

[0302] The thickness of the base film is 8 μm, the thickness of the single-sided ceramic layer is 3 μm, and the thickness of the single-sided bonding layer is 1 μm.

[0303] (5) Electrolyte

[0304] In an argon atmosphere glove box (H2O<0.1 ppm, O2<0.1 ppm), organic solvents, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed uniformly.

[0305] Lithium hexafluorophosphate was then added and dissolved in the organic solvent to obtain a concentration of 1.05 mol / L of lithium hexafluorophosphate in the electrolyte, and vinylene carbonate (VC) was added and stirred uniformly to obtain the electrolyte of Example 1.

[0306] wherein the mass content of dimethyl carbonate is 26%, the mass content of methyl ethyl carbonate is 43.3%, the mass content of ethylene carbonate is 17.3%, and the mass content of vinylene carbonate is 0.9%, based on the total mass of the electrolyte.

[0307] (6) Preparation of the battery

[0308] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order using a stacking machine, and the separator can isolate the positive electrode and the negative electrode, to obtain a stacked cell. The stacked cell is subjected to a rubberizing process, and the stacked cell after the rubberizing process is placed in an outer package. The outer package is an aluminum plastic film made of an inner layer of polypropylene, an intermediate layer of aluminum foil, and an outer layer of nylon. The aluminum plastic film outer package is obtained by a pit forming machine and trimming to obtain a target shape and size. The aluminum plastic film is then heat-sealed to satisfy the sealing tension of the aluminum plastic film ≥ 25 N / 8 mm. The battery is vacuum baked, left to stand, and electrolyte is injected using a flat needle, sealed, and then the soft package battery is subjected to hot pressing and cold pressing. The temperature of the hot pressing is 45°C, the time is 2 minutes, and the pressure is 90 kg / cm 2 . The temperature of the cold pressing is 25°C, the time is 2 minutes, and the pressure is 90 kg / cm 2 . Finally, the battery monomer is obtained through processes such as formation, vacuum exhaust, and edge cutting. The size of the battery monomer in the length direction is 600 mm, in the width direction is 125 mm, and in the thickness direction is 20 mm.

[0309] The preparation method of Example 2-10 is basically the same as that of Example 1, except that the preparation method of the positive active material is adjusted, as follows:

[0310] Example 2

[0311] The preparation method of Example 2 is basically the same as that of Example 1, except that in the preparation of the positive active material, the second temperature is adjusted to 765°C.

[0312] Example 3

[0313] The preparation method of Example 3 is basically the same as that of Example 1, except that in the preparation of the positive active material, the second temperature is adjusted to 735°C.

[0314] Example 4

[0315] The preparation method of Example 4 is basically the same as that of Example 1, except that in the preparation of the positive active material, the carbon source is replaced by polyethylene glycol with a molecular weight of 500 and polyethylene glycol with a molecular weight of 2000 in a mass ratio of 2:8.

[0316] Example 5

[0317] The preparation method of Example 5 is basically the same as that of Example 1, except that in the preparation of the positive active material, the carbon source is replaced by polyethylene glycol with a molecular weight of 500.

[0318] Example 6

[0319] The preparation method of Example 6 is basically the same as that of Example 1, except that in the preparation of the positive active material, the carbon source is replaced by polyethylene glycol with a molecular weight of 2000.

[0320] Example 7

[0321] The preparation method of Example 7 is basically the same as that of Example 3, except that in the preparation of the positive active material, the carbon source is replaced by polyethylene glycol with a molecular weight of 500 and glucose with a mass ratio of 2:8.

[0322] Example 8

[0323] The preparation method of Example 8 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, the coating weight is adjusted, and the hot roller pressure, hot roller temperature, transfer coating speed, and heating temperature before first entering the hot roller compaction are adaptively adjusted, so that the cold-pressed positive electrode film layer has a single-sided surface density of 0.43 g / 15 40.25 mm 2 ; and the thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0324] Example 9

[0325] The preparation method of Example 9 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet, the coating weight is adjusted, and the hot roller pressure, hot roller temperature, transfer coating speed, and heating temperature before first entering the hot roller compaction are adaptively adjusted, so that the cold-pressed positive electrode film layer has a single-sided surface density of 0.26 g / 15 40.25 mm 2 ; and the thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0326] Example 10

[0327] The preparation method of Example 10 is basically the same as that of Example 1, except that the hot roller pressure, hot roller temperature, transfer coating speed, and heating temperature before first entering the hot roller compaction are adjusted, so that the positive electrode sheet has a single-sided surface density of 0.41 g / 15 40.25 mm 2 and a compaction density of 2.52 g / cm 3 . Here, the compaction density refers to the compaction density under the full discharge state of the battery monomer. The thickness of the battery is appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0328] Comparative Example 1

[0329] Comparative Example 1 was prepared in substantially the same manner as Example 3, except that in the preparation of the positive active material, the carbon source was replaced with glucose.

[0330] Comparative Example 2

[0331] Comparative Example 2 was prepared in substantially the same manner as Example 1, except that in the preparation of the positive electrode sheet, the coating weight was adjusted, and the heat roller pressure, heat roller temperature, speed of transfer coating, and heating temperature before first entering the heat roller compaction were adaptively adjusted, so that the cold-pressed positive electrode film layer had a single-sided surface density of 0.24 g / 15 40.25 mm 2 ; and the thickness of the battery was appropriately adjusted while keeping the number of positive electrode sheets, separators, and negative electrode sheets unchanged.

[0332] Test Method

[0333] 1. Capacity of the battery monomer

[0334] At 25°C, charge to 3.65V at a charge rate of 0.5C of the nominal capacity of the battery monomer, then charge to 0.05C at 3.65V constant voltage, stand for 10 min, then discharge to 2.5V at a discharge rate of 1C, stand for 10 min, calculate the capacity C in the discharge process by the formula C = I x t, unit Ah.

[0335] 2. Cycle number corresponding to capacity decay to 80%

[0336] At 25°C, charge to 3.65V at a charge rate of 0.5C of the nominal capacity of the battery monomer, then charge to 0.05C at 3.65V constant voltage, stand for 10 min, then discharge to 2.5V at a discharge rate of 1C, stand for 10 min, the above one charge-discharge is a cycle, until the battery capacity decays to 80% of the nominal capacity, stop testing, recorded as cycle number @ 80% SOH.

[0337] Test Results

[0338] The test results of the above examples and comparative examples are shown in Table 1.

[0339] Table 1

[0340]

[0341] As can be seen from the comparison of the examples and the comparative examples, the battery monomer comprises a laminated cell, the laminated cell comprises a positive pole piece and a negative pole piece, 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 lithium-containing transition metal phosphate particles with carbon material arranged on at least part of the surface; the battery monomer is in a full discharge state, the compaction density of the positive pole piece is 2.3 g / cm 3 -2.6 g / cm 3 ; the single-sided surface density of the positive pole film layer is 0.25 g / 15 40.25 mm 2 -0.45 g / 15 40.25 mm 2 , in the section of the positive pole film layer along the thickness direction of the positive pole piece, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.6-0.8; in the graphitization degree C value cumulative distribution curve of the positive pole film layer obtained in the face scanning mode of the laser microscopic confocal Raman spectrometer, the median number C50 of the graphitization degree is 0.95-1.20, and the battery monomer helps to improve the cycle stability of the battery in the long cycle process while maintaining good capacity.

[0342] As can be seen from the comparison of examples 1-3, in the section of the positive pole film layer along the thickness direction of the positive pole piece, the sphericity area cumulative distribution curve of the particles with a particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.65-0.75, in the range of 0.67-0.72, and the battery monomer has good long cycle stability.

[0343] As can be seen from the comparison of examples 1, examples 3-6 and example 7, in the graphitization degree C value cumulative distribution curve of the positive pole film layer obtained in the face scanning mode of the laser microscopic confocal Raman spectrometer, the median number C 50 of the graphitization degree is further selected from 1.01-1.13, which helps to further improve the long cycle stability of the battery monomer.

[0344] As can be seen from the comparison of examples 1 and examples 8-10, the single-sided coating surface density of the positive pole film layer is further in the range of 0.35 g / 15 40.25 mm 2 -0.4 g / 15 40.25 mm 2 , which helps to further balance the capacity and long cycle stability of the battery.

[0345] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A battery cell, characterized by The battery cell includes an electrode assembly and an electrolyte, the battery cell includes a laminated core, the laminated core includes a positive electrode sheet and a negative electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, the positive electrode film layer includes lithium-containing transition metal phosphate particles with carbon material arranged on at least part of the surface, the lithium-containing transition metal phosphate particles include titanium elements, the mass content of the titanium elements is 500-8000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer; The battery cell in full discharge state, the compaction density of the positive pole piece is 2.3g / cm 3 -2.6g / cm 3 ; The single side surface density of the positive electrode film layer is 0.25 g / 15 40.25 mm 2 -0.45 g / 15 40.25 mm 2 ; In a section of the positive electrode film layer along the thickness direction of the positive electrode tab, the particle size R1 satisfies R1≥1000 nm, and in a cumulative distribution curve of sphericity of the particles with the particle size R1 satisfying R1≥1000 nm, L R1A50 is 0.6-0.8, and L R1A150 is a sphericity L value corresponding to a cumulative area ratio of 50% of the longitudinal axis in the cumulative distribution curve of the sphericity L value of the particles with the particle size R1 satisfying R1≥1000 nm. The graphitization degree C value cumulative distribution curve of the positive electrode film layer obtained under the laser microscopic confocal Raman spectrometer face scanning mode, wherein the median of the graphitization degree C 50 is 0.95-1.20; wherein, the graphitization degree C value is I G / I D , I G represents the G peak intensity of the Raman spectrum at 1580±100cm -1 , I D represents the D peak intensity of the Raman spectrum at 1350±100cm -1 ; The area ratio of particles with a particle size R1 satisfying R1≥1000 nm is 12-50% based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the electrode sheet. The distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm is less than or equal to 5% in the section of the positive electrode film layer along the thickness direction of the electrode sheet.

2. The battery cell of claim 1, wherein, The single side surface density of the positive electrode film layer is 0.3 g / 15 40.25 mm 2 -0.45 g / 15 40.25 mm 2 .

3. The battery cell according to claim 1 or 2, characterized in that, The graphitization degree C value cumulative distribution curve of the positive electrode film layer obtained under the laser microscope confocal Raman spectrometer face scanning mode, the median number C of the graphitization degree is 1.01-1.

13. 50 1.01-1.

13.

4. The battery cell of claim 3, wherein, The single side surface density of the positive electrode film layer is 0.35 g / 15 40.25 mm 2 -0.4 g / 15 40.25 mm 2 .

5. The battery cell of claim 4, wherein, In a cross section of the positive electrode film layer in the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles having a particle size R1 satisfying R1≥1000 nm has L R1A50 0.65-0.

75.

6. The battery cell of claim 4, wherein, In a cross section of the positive electrode film layer in the thickness direction of the positive electrode tab, the sphericity area cumulative distribution curve of the particles having a particle size R1 satisfying R1≥1000 nm has L R1A50 of 0.67-0.

72.

7. The battery cell according to claim 1 or 2, characterized in that, The single-side thickness H of the positive electrode film layer is 70-120 μm.

8. The battery cell according to claim 1 or 2, characterized in that, The single-side thickness H of the positive electrode film layer is 90-120 μm.

9. The battery cell according to claim 1 or 2, characterized in that, The single-side thickness H of the positive electrode film layer is 100-120 μm.

10. The battery cell according to claim 1 or 2, characterized in that, The area ratio of particles with a particle size R1 satisfying R1≥1000 nm is 12-40% based on the total area of the particles in the section of the positive electrode film layer along the thickness direction of the electrode sheet; and / or, The distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm is 0.2-2.5% in the section of the positive electrode film layer along the thickness direction of the electrode sheet.

11. The battery cell according to claim 1 or 2, characterized in that, The distribution uniformity of the particles with a particle size R1 satisfying R1≥1000 nm is 0.2-2% in the section of the positive electrode film layer along the thickness direction of the electrode sheet.

12. The battery cell according to claim 1 or 2, characterized in that, The median value B of the coating value in the cumulative distribution curve of the coating value B obtained by the positive electrode film layer under the laser microscopic confocal Raman spectrometer face scanning mode 50 is 0.30-0.60, wherein the coating value B is I P / I D , wherein I P represents the intensity of the P peak of the Raman spectrum at 948±100cm -1 , I D represents the intensity of the D peak of the Raman spectrum at 1350±100cm -1 .

13. The battery cell of claim 1, wherein, The lithium-containing transition metal phosphate particles in the positive electrode film layer include a component represented by the following general formula: Li m Fe x P y O j Q q Formula I, In the formula, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, Br, 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.

1.

14. The battery cell of claim 1, wherein, The iron elution rate of the positive electrode material in the positive electrode film layer is 658-1921 ppm.

15. The battery cell of claim 1, wherein, The iron elution rate of the positive electrode material in the positive electrode film layer is 658-1485 ppm.

16. The battery cell of claim 1, wherein, The mass content of the titanium elements is 1000-3000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

17. The battery cell of claim 1, wherein, The lithium-containing transition metal phosphate particles include vanadium elements, and the mass content of the vanadium elements is 500-5000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

18. The battery cell of claim 1, wherein, The lithium-containing transition metal phosphate particles include vanadium elements, and the mass content of the vanadium elements is 500-3000 ppm based on the total mass of the lithium-containing transition metal phosphate particles in the positive electrode film layer.

19. The battery cell of claim 1, wherein, The porosity of the positive electrode film layer is 14-28%.

20. The battery cell of claim 1, wherein, The positive electrode film layer further comprises a conductive agent, and an area proportion of an agglomeration region of the conductive agent is 0.5%-2.5% based on a total area of a cross section of the positive electrode film layer along a thickness direction of the electrode sheet.

21. The battery cell of claim 20, wherein, The area proportion of the agglomeration region of the conductive agent is 0.5%-1.7%.

22. The battery cell of claim 20, wherein, The conductive agent comprises carbon nanotubes, and the carbon nanotubes comprise one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

23. The battery cell of claim 20, wherein, The conductive agent further comprises conductive carbon black.

24. The battery cell of claim 20, wherein, The agglomeration region of the conductive agent further comprises carbon nanotubes and conductive carbon black.

25. The battery cell of claim 24, wherein, A mass content C1 of the carbon nanotubes satisfies 0 26. The battery cell of claim 1, wherein, The positive electrode film layer further comprises a dispersing agent, and the dispersing agent comprises hydrogenated nitrile rubber (HNBR).

27. The battery cell of claim 26, wherein, A mass content of the dispersing agent is 0.5%-2% based on a mass of the positive electrode film layer.

28. The battery cell of claim 1, wherein, The battery monomer further comprises a separator arranged between the positive electrode sheet and the negative electrode sheet, and the separator comprises a base film, ceramic layers arranged on both sides of the base film, and a bonding layer arranged on a side of at least one of the ceramic layers away from the base film, the bonding layer is a continuous layer of a porous structure, and the bonding layer comprises a vinylidene fluoride-based polymer.

29. The battery cell of claim 28, wherein, The separator satisfies at least one of the following conditions: (1) a thickness of the base film is 7 μm-9 μm; (2) a single-side thickness of the ceramic layer is 2 μm-4 μm; (3) a single-side thickness of the bonding layer is 1 μm-5 μm.

30. The battery cell of claim 1, wherein, The positive electrode film layer is provided with a bottom coating layer at a bottom region close to the positive electrode current collector, and the bottom coating layer satisfies at least one of the following conditions: (1) the bottom coating layer comprises a conductive agent and a bonding agent, the conductive agent comprises carbon nanotubes and conductive carbon black, and the bonding agent comprises polyvinylidene fluoride (PVDF); (2) a thickness of the bottom coating layer is 0.5 μm-5 μm.

31. The battery cell of claim 1, wherein, The battery monomer comprises a shell, the jellyroll is accommodated in the shell, a length direction dimension of the shell is L1, a width direction dimension of the shell is W1, and a thickness direction dimension of the shell is H1, wherein 450 mm≤L1≤1300 mm, 100 mm≤W1≤150 mm, and 14 mm≤H1≤22 mm.

32. The battery cell of claim 31, wherein, The length direction dimension of the shell is L1, and 450 mm≤L1≤650 mm.

33. The battery cell of claim 31, wherein, The length direction dimension of the shell is L1, and 900 mm≤L1≤1300 mm.

34. The battery cell of claim 31, wherein, The material of the shell is a soft package material, and the soft package material comprises an aluminum plastic composite film, and the aluminum plastic composite film comprises a composite film formed by one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), nylon, polyethylene terephthalate (PET), and polyethylene (PE) and aluminum.

35. The battery cell of claim 1, wherein, The capacity of the battery monomer is 95 Ah-300 Ah at 25 °C.

36. The battery cell of claim 1, wherein, The capacity of the battery monomer is 150 Ah-190 Ah at 25 °C.

37. A battery device, characterized by The battery monomer comprises the battery monomer according to any one of claims 1-36.

38. An electrical device, comprising: The electrical device includes the battery device of claim 37 for providing electrical energy.

39. An energy storage device, comprising: The energy storage device includes the battery device of claim 37 for storing electrical energy.

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