Lithium ion battery, preparation method, battery pack and electric equipment

Abstract

The invention relates to a lithium ion battery and a preparation method thereof, a battery pack and electric equipment, the battery comprises a positive pole piece and a negative pole piece, the positive pole piece comprises a positive active material layer, and the most frequency aperture r1 of the positive pole piece is 50-90nm; the negative electrode plate comprises a negative electrode active material layer, and the most frequency aperture r2 of the negative electrode plate is 900-1500nm. According to the lithium ion battery disclosed by the invention, more effective channels are provided for lithium ion migration only by regulating and controlling the most frequent pore diameters of the positive and negative electrode plates, the diffusion distance and time of lithium ions in the electrode plates are reduced, the charge-discharge performance and the rate capability of the battery are improved, the process requirement is low, the operation is simple and convenient, the expanded production is easy, and the economic benefits of enterprises are improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium batteries, and more specifically, to a lithium ion battery, a preparation method thereof, a battery pack and an electrical device. Background Art

[0002] As a new type of high-voltage and high-energy density power battery, lithium ion secondary batteries have outstanding characteristics such as light weight, high energy density, pollution-free, no memory effect, and long service life, and thus are widely used in new energy vehicles.

[0003] In the prior art, during the preparation process, it is necessary to synchronously control the specific surface area and volume of the macropores and micro-mesopores of the positive and negative electrode plates to improve the rate performance of the lithium ion battery, which requires high process requirements and is inconvenient for actual operation. Summary of the Invention

[0004] The purpose of the present disclosure is to provide a lithium ion battery, a preparation method thereof, a battery pack and an electrical device. By only regulating the most frequent pore diameter of the positive and negative electrode plates, the lithium ion battery provides more effective channels for lithium ion migration, reduces the diffusion distance and time of lithium ions in the electrode, improves the charge and discharge performance and rate performance of the battery, has low process requirements, is easy to operate, is easy to scale up production, and improves the economic benefits of the enterprise.

[0005] To achieve the above purpose, in the first aspect of the present disclosure, a lithium ion battery is provided. The battery includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive electrode active material layer, and the most frequent pore diameter r1 of the positive electrode plate is 50-90 nm; the negative electrode plate includes a negative electrode active material layer, and the most frequent pore diameter r2 of the negative electrode plate is 900-1500 nm.

[0006] Optionally, r1 is 60-85 nm; and / or, r2 is 1050-1200 nm.

[0007] Optionally, in the positive electrode plate, the pore volume of the pores with a pore diameter of 50-90 nm accounts for 50-90% of the total pore volume of the positive electrode plate, preferably 70-90%; and / or, in the negative electrode plate, the pore volume of the pores with a pore diameter of 900-1500 nm accounts for 50%-90% of the total pore volume of the negative electrode plate, preferably 70-90%.

[0008] Optionally, the positive electrode active material layer includes a positive electrode active substance, a first binder and a first conductive agent; The first conductive agent includes carbon nanotubes, carbon black and graphite microflakes. The diameter of the carbon nanotubes is 10-25 nm, and the D 50 particle size of the carbon black is 50-100 nm, and the thickness of the graphite microflakes is 200-400 nm, and the sheet diameter is 0.5-4.5 μm.

[0009] Optionally, the positive electrode active material includes nano-sized lithium iron phosphate particles and micro-sized lithium iron phosphate particles, and the D 50 particle size of the nano-sized lithium iron phosphate particles is 0.1 - 0.4 μm, and the D 50 particle size of the micro-sized lithium iron phosphate particles is 1 - 4 μm.

[0010] Optionally, in the positive electrode active material layer, the mass ratio of the nano-sized lithium iron phosphate particles to the micro-sized lithium iron phosphate particles is 1:(0.67 - 2.33), preferably 1:(1.50 - 2.33).

[0011] Optionally, the positive electrode further includes a positive electrode current collector and a positive electrode conductive coating, the positive electrode conductive coating is located between the positive electrode current collector and the positive electrode active material layer, and the thickness of the positive electrode conductive coating is 0.3 - 1.8 μm.

[0012] Optionally, the negative electrode active material layer includes a negative electrode active material, a second binder, and a second conductive agent; the negative electrode active material includes primary graphite particles and secondary graphite particles, and the D 50 particle size of the primary graphite particles is 3 - 5 μm, and the D 50 particle size of the secondary graphite particles is 20 - 40 μm; In the negative electrode active material layer, the mass ratio of the primary graphite particles to the secondary graphite particles is 1:(2.33 - 9), preferably 1:(4 - 9).

[0013] A second aspect of the present disclosure provides a method for manufacturing a lithium ion battery, the method including: (1) forming a negative electrode active material layer on a negative electrode current collector to obtain a negative electrode tab; the most frequent pore size of the negative electrode tab is 900 - 1500 nm; (2) forming a positive electrode active material layer on a positive electrode current collector to obtain a positive electrode tab; the most frequent pore size of the positive electrode tab is 50 - 90 nm.

[0014] Optionally, the most frequent pore size of the positive electrode tab is 60 - 85 nm; and / or, the most frequent pore size of the negative electrode tab is 1050 - 1200 nm.

[0015] Optionally, in step (1), a negative electrode slurry including a negative electrode active material, a second binder, and a second conductive agent is used to form the negative electrode active material layer; the negative electrode active material includes primary graphite particles and secondary graphite particles, and the D 50 particle size of the primary graphite particles is 3 - 5 μm, and the D 50The particle size is 20 - 40 μm. In the negative electrode active material layer, the mass ratio of the primary graphite particles to the secondary graphite particles is 1:(2.33 - 9), preferably 1:(4 - 9).

[0016] Optionally, in step (2), a positive electrode paste containing a positive electrode active material, a first binder, and a first conductive agent is used to form the positive electrode active material layer; The positive electrode active material includes nano - sized lithium iron phosphate particles and micron - sized lithium iron phosphate particles. The D 50 particle size of the nano - sized lithium iron phosphate particles is 0.1 - 0.4 μm, and the D 50 particle size of the micron - sized lithium iron phosphate particles is 1 - 4 μm.

[0017] Optionally, in the positive electrode active material layer, the mass ratio of the nano - sized lithium iron phosphate particles to the micron - sized lithium iron phosphate particles is 1:(0.67 - 2.33), preferably 1:(1.5 - 2.33).

[0018] Optionally, in step (2), the first conductive agent includes carbon nanotubes, carbon black, and graphite micro - flakes; The diameter of the carbon nanotubes is 10 - 25 nm, the D 50 particle size of the carbon black is 50 - 100 nm, and the thickness of the graphite micro - flakes is 200 - 400 nm, and the sheet diameter is 0.5 - 4.5 μm.

[0019] The third aspect of the present disclosure provides a lithium - ion battery prepared by the method described in the second aspect of the present disclosure.

[0020] The fourth aspect of the present disclosure provides a battery pack, including the lithium - ion battery described in the first aspect or the third aspect of the present disclosure.

[0021] The fifth aspect of the present disclosure provides an electrical device, including the battery described in the first aspect or the third aspect of the present disclosure or the battery pack provided in the fourth aspect of the present disclosure.

[0022] Through the above - mentioned technical solutions, the present disclosure only regulates the most frequent pore diameters of the positive and negative electrode plates, enables the most frequent pore diameters of the positive electrode plate and the negative electrode plate to be within a specific range, provides more effective channels for lithium - ion migration, reduces the diffusion distance and time of lithium ions in the electrode plate, thereby improving the charge - discharge performance and rate performance of the battery; meanwhile, the appropriate most frequent pore diameters of the positive and negative electrode plates contribute to maintaining the structural stability of the electrode plate, reducing material fragmentation and electrode detachment caused by the volume expansion and contraction of the active material during charge - discharge, and extending the cycle life of the battery.

[0023] Other features and advantages of the present disclosure will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present disclosure and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present disclosure, but do not constitute a limitation to the present disclosure. In the accompanying drawings: Figure 1 It is a pore size distribution curve graph of the positive electrode plate and the negative electrode plate in Embodiment 2 of the present disclosure. Specific Embodiments

[0025] The following will describe in detail the specific embodiments of the present disclosure with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not used to limit the present disclosure.

[0026] The first aspect of the present disclosure provides a lithium-ion battery, the battery includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive electrode active material layer, and the most frequent pore size r1 of the positive electrode plate is 50-90 nm; the negative electrode plate includes a negative electrode active material layer, and the most frequent pore size r2 of the negative electrode plate is 900-1500 nm.

[0027] The present disclosure only regulates the most frequent pore size distribution of the positive and negative electrode plates, so that the most frequent pore sizes of the positive and negative electrode plates are within a specific range, providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode plate, thereby improving the charge and discharge performance and rate performance of the battery; at the same time, the appropriate most frequent pore sizes of the positive and negative electrode plates help to maintain the structural stability of the electrode plate, reduce the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and extend the cycle life of the battery; avoid the risk of excessive loss of electrolyte due to too large most frequent pore size, reduce the liquid retention capacity of the battery, avoid uneven distribution of lithium ions inside the electrode plate, and affect the cycle life of the battery; avoid too small most frequent pore size, which limits the migration speed of lithium ions, increases the internal resistance of the battery, and reduces the rate performance of the battery.

[0028] In the present disclosure, the most frequent pore size refers to the pore size value that most frequently appears in the pore size distribution. For example, in Figure 1 in the pore size distribution graph measured by the mercury intrusion method, the highest peak of the ordinate is the most frequent pore size of the positive and negative electrode active material layers.

[0029] In the present disclosure, the most frequent pore size is tested by the mercury intrusion method; it can be tested by intercepting a certain area of the positive / negative electrode plate prepared according to the embodiment, or by intercepting an appropriate size from the positive / negative electrode plate obtained after disassembling the battery for testing.

[0030] In one embodiment, the most frequent pore size r1 of the positive electrode sheet can be any value between 50 and 90 nm, for example, it can be 50 nm, 52 nm, 55 nm, 59 nm, 60 nm, 61 nm, 65 nm, 68 nm, 70 nm, 72 nm, 77 nm, 78 nm, 80 nm, 83 nm, 84 nm, 86 nm, 89 nm, 90 nm, or any value within the range composed of any two of them.

[0031] In one embodiment, the most frequent pore size r2 of the negative electrode sheet can be any value between 900 and 1500 nm, for example, it can be 900 nm, 901 nm, 905 nm, 970 nm, 990 nm, 1000 nm, 1005 nm, 1010 nm, 1130 nm, 1170 nm, 1200 nm, 1210 nm, 1280 nm, 1300 nm, 1305 nm, 1350 nm, 1390 nm, 1400 nm, 1450 nm, 1490 nm, 1500 nm, or any value within the range composed of any two of them.

[0032] In one embodiment, r1 is 60 - 85 nm, and / or r2 is 1050 - 1200 nm. In this embodiment, r1 can be any value between 60 and 85 nm, for example, it can be 60 nm, 61 nm, 62 nm, 63 nm, 64 nm, 66 nm, 67 nm, 69 nm, 70 nm, 71 nm, 72 nm, 74 nm, 75 nm, 76 nm, 77 nm, 79 nm, 80 nm, 81 nm, 83 nm, 84 nm, 85 nm, or any value within the range composed of any two of them; r2 can be any value between 1050 and 1200 nm, for example, it can be 1050 nm, 1055 nm, 1058 nm, 1060 nm, 1062 nm, 1069 nm, 1070 nm, 1075 nm, 1080 nm, 1086 nm, 1090 nm, 1100 nm, 1120 nm, 1130 nm, 1150 nm, 1170 nm, 1200 nm, or any value within the range composed of any two of them. The above embodiments are beneficial to providing more effective channels for lithium-ion migration, reducing the diffusion distance and time of lithium ions in the electrode sheet, and improving the charge-discharge performance and rate performance of the battery; at the same time, it helps to maintain the structural stability of the electrode sheet, reduce the fragmentation of active materials and electrode shedding caused by volume expansion and contraction during charge and discharge, and further improve the cycle life of the battery.

[0033] In one embodiment, in the positive electrode sheet, the volume ratio of pores with a pore diameter of 50 to 90 nm is 50 to 90%, preferably 70 to 90%. In the present disclosure, the volume ratio of pores with a pore diameter of 50 to 90 nm refers to the ratio of the pore volume with a pore diameter of 50 to 90 nm in the pore size distribution curve of the positive electrode sheet to the total pore volume in the positive electrode active material layer, and the volume ratio can be calculated from the pore size distribution curve. In this embodiment, the pore size distribution curve of the positive electrode sheet is formed into a sharp peak type, so that the pore diameter ratio of 50 to 90 nm is larger.

[0034] In one embodiment, in the negative electrode sheet, the volume ratio of pores with a pore diameter of 900 to 1500 nm is 50 to 90%, preferably 70 to 90%. In the present disclosure, the volume ratio of pores with a pore diameter of 900 to 1500 nm refers to the ratio of the pore volume with a pore diameter of 900 to 1500 nm in the pore size distribution curve of the negative electrode sheet to the total pore volume in the negative electrode active material layer, and the volume ratio can be calculated from the pore size distribution curve. In this embodiment, the pore size distribution curve of the electrode sheet is formed into a sharp peak type, so that the pore diameter ratio of 900 to 1500 nm is larger.

[0035] In one embodiment, the positive electrode active material layer includes a positive electrode active material, a first binder, and a first conductive agent; the first conductive agent includes carbon nanotubes, carbon black, and graphite microflakes, the diameter of the carbon nanotubes is 10 to 25 nm, preferably 15 to 20 nm; the D 50 particle size of the carbon black is 50 to 100 nm, preferably 60 to 90 nm; the thickness of the graphite microflakes is 200 to 400 nm, preferably 200 to 300 nm; the flake diameter is 0.5 to 4.5 μm, preferably 1 to 3 μm. The above embodiment is conducive to the construction of a conductive network by carbon nanotubes inside the battery, improving the conductivity of the positive electrode active material, reducing the internal resistance of the lithium battery, reducing the expansion and contraction of the positive electrode active material during charge and discharge, improving the battery life, and at the same time improving the bonding strength of the electrode sheet and reducing the addition amount of the binder; in addition, the blending of multiple conductive agents further facilitates the most frequent pore diameter of the positive electrode sheet to be within an appropriate range, providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode material, thereby improving the charge and discharge performance and rate performance of the battery.

[0036] In the present disclosure, the mass ratios of the positive electrode active material, the first binder, and the first conductive agent in the positive electrode active material layer are not specifically limited and can be conventional ratios in the art. For example, in one embodiment, the mass ratios of the positive electrode active material, the first binder, and the first conductive agent can be (85 to 97):1:(1.5 - 5). In a further embodiment, the mass ratios of the positive electrode active material, the first binder, and the first conductive agent can be calculated according to the feeding ratio in the preparation method.

[0037] In one embodiment, the positive electrode active material layer may further include a first dispersant. The present disclosure does not specifically limit the type of the dispersant, and it may be a conventional type in the art, for example, it may be one or more of carboxymethyl cellulose, polyacrylic acid, polymethyl methacrylate, and polyvinylpyrrolidone; the addition amount of the dispersant is not specially limited and may be a conventional proportion in the art.

[0038] In one embodiment, the positive electrode active material includes nano-scale lithium iron phosphate particles and micro-scale lithium iron phosphate particles. The D 50 particle size of the nano-scale lithium iron phosphate particles is 0.1 - 0.4 μm, and the D 50 particle size of the micro-scale lithium iron phosphate particles is 1 - 4 μm. In the present disclosure, the D 50 particle size can be tested by a particle size diffractometer or can also be tested by a scanning electron microscope.

[0039] In the present disclosure, the composition of the lithium iron phosphate particles is not specifically limited, and it may be a conventional lithium iron phosphate material in the art. For example, the chemical formula may be LiFe （1-x） M x PO4 0 ≤ x ≤ 0.1. In one embodiment, the lithium iron phosphate particles of the present disclosure may be doped with a modifying element M, and M may be one or more of Ti, Zr, Mo, Mn, Mg, V, and C. The doping amount of the modifying element M may be 2000 - 6000 ppm, preferably 2000 - 3000 ppm. In a specific embodiment, the doping amount of the modifying element can be tested by an inductively coupled plasma method (ICP).

[0040] In one embodiment, in the positive electrode active material layer, the mass ratio of the nano-scale lithium iron phosphate particles to the micro-scale lithium iron phosphate particles is 1:(0.67 - 2.33), preferably 1:(1.50 - 2.33). The above embodiment is beneficial to the grading of particles with different particle sizes, making the most frequent pore size of the positive electrode sheet within an appropriate range, which is beneficial to providing more effective channels for the migration of lithium ions, reducing the diffusion distance and time of lithium ions in the electrode sheet, and improving the charge-discharge performance and rate performance of the battery; at the same time, it helps to maintain the structural stability of the electrode sheet, reducing the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improving the cycle life of the battery.

[0041] In one embodiment, the positive electrode further includes a positive current collector and a positive conductive coating, the positive conductive coating is located between the positive current collector and the positive active material layer, the thickness of the positive conductive coating is 0.3 to 1.8 μm, preferably 0.3 to 1 μm. In the present disclosure, the thickness of the conductive coating refers to the single-sided thickness of the conductive coating. In a specific embodiment, the thickness of the conductive coating can be tested by a scanning electron microscope. The above embodiment is beneficial to reducing the interfacial impedance between the positive current collector and the positive active material layer, enhancing the conductivity, improving the problem that the surface of the current collector is prone to electrochemical corrosion, reducing polarization, increasing the adhesion between the positive active material and the current collector, and preventing the corrosion of the current collector by the electrolyte.

[0042] In one embodiment, the negative active material layer includes a negative active material, a second binder, and a second conductive agent; the negative active material includes primary graphite particles and secondary graphite particles, and the D 50 particle size of the primary graphite particles is 3 to 5 μm, and the D 50 particle size of the secondary graphite particles is 20 to 40 μm. In the present disclosure, the D 50 particle size of the negative active material can be tested by a particle size diffractometer or by a scanning electron microscope (SEM). The above embodiment is beneficial to the grading of particles with different particle sizes, making the most frequent pore diameter of the negative active material layer within a suitable range, facilitating the provision of more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode sheet, and improving the charge-discharge performance and rate performance of the battery; at the same time, it helps to maintain the structural stability of the electrode sheet, reducing the breakage and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improving the cycle life of the battery.

[0043] In one embodiment, in the negative active material layer, the mass ratio of the primary graphite particles to the secondary graphite particles is 1:(2.33 to 9), preferably 1:(4 to 9). The above embodiment is beneficial to the grading of particles with different particle sizes, making the most frequent pore diameter of the negative electrode sheet within a suitable range, facilitating the provision of more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode sheet, and improving the charge-discharge performance and rate performance of the battery; at the same time, it helps to maintain the structural stability of the electrode sheet, reducing the breakage and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improving the cycle life of the battery.

[0044] In the present disclosure, the primary graphite particles and the secondary graphite particles have the meanings well-known in the art; the primary graphite particles refer to the original graphite particles that have not undergone any processing; the secondary graphite particles refer to the secondary particles formed by the aggregation of the primary graphite particles. The present disclosure does not make special limitations on the preparation method of the secondary graphite particles, and they can be obtained by conventional methods in the art.

[0045] In one embodiment, the present disclosure does not specifically limit the mass ratios of the negative electrode active material, the second binder, and the second conductive agent in the negative electrode active material layer, which may be conventional ratios in the art. For example, in one embodiment, the mass ratios of the negative electrode active material, the second binder, and the second conductive agent may be (90 - 97):(1 - 5):1. In a specific embodiment, the mass ratios of the negative electrode active material, the second binder, and the second conductive agent may be calculated according to the feeding ratios in the preparation method.

[0046] In one embodiment, the negative electrode active material layer of the present disclosure may further include a second dispersant. The present disclosure does not specifically limit the type of the dispersant, which may be a conventional type in the art. For example, it may be one or more of carboxymethyl cellulose, polyacrylic acid, polymethyl methacrylate, and polyvinylpyrrolidone; the addition amount of the dispersant is not specially limited and may be a conventional ratio in the art.

[0047] In one embodiment, the present disclosure does not specifically limit the first binder and the second binder, which may be conventional types in the art. For example, they may be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride - tetrafluoroethylene - propylene terpolymer, vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene terpolymer, tetrafluoroethylene - hexafluoropropylene copolymer, and fluorinated acrylate resin. The present disclosure does not specifically limit the first conductive agent and the second conductive agent, which may be conventional types in the art. For example, they may be one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0048] The second aspect of the present disclosure provides a method for preparing a lithium - ion battery, the method comprising: (1) forming a negative electrode active material layer on a negative electrode current collector to obtain a negative electrode plate; the most frequent pore size of the negative electrode plate is 900 - 1500 nm; (2) forming a positive electrode active material layer on a positive electrode current collector to obtain a positive electrode plate; the most frequent pore size of the positive electrode plate is 50 - 90 nm.

[0049] In one embodiment, the most frequent pore size of the positive electrode plate is 60 - 85 nm; and / or, the most frequent pore size of the negative electrode plate is 1050 - 1200 nm.

[0050] The method of the present disclosure only regulates the most frequent pore sizes of the positive and negative electrode sheets, so that the most frequent pore sizes of the positive and negative electrode sheets are within a specific range, providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode sheets, thereby improving the charge-discharge performance and rate performance of the battery; at the same time, the appropriate pore sizes of the positive and negative electrode sheets contribute to maintaining the structural stability of the electrode sheets, reducing the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and prolonging the cycle life of the battery. The method of the present disclosure has low process requirements, is easy to operate, is easy to scale up production, and is beneficial to improving the economic benefits of enterprises.

[0051] In one embodiment, in step (1), the negative electrode active material layer is formed by using a negative electrode paste containing a negative electrode active material, a second binder, and a second conductive agent; the negative electrode active material includes primary graphite particles and secondary graphite particles, and the D 50 particle size of the primary graphite particles is 3 to 5 μm; the D 50 particle size of the secondary graphite particles is 20 to 40 μm. The above embodiment is beneficial to making the most frequent pore size of the negative electrode sheet within a suitable range, beneficial to providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode sheet, and improving the charge-discharge performance and rate performance of the battery; at the same time, it helps to maintain the structural stability of the electrode sheet, reduces the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improves the cycle life of the battery.

[0052] In one embodiment, in step (1), in the negative electrode paste, the mass ratio of the primary graphite particles to the secondary graphite particles is 1:(2.33 to 9), preferably 1:(4 to 9). The above embodiment is beneficial to the grading of particles with different particle sizes, making the most frequent pore size of the negative electrode sheet within a suitable range, beneficial to providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode sheet, and improving the charge-discharge performance and rate performance of the battery; at the same time, it helps to maintain the structural stability of the electrode sheet, reduces the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improves the cycle life of the battery.

[0053] In one embodiment, the positive electrode active material layer is formed by using a positive electrode paste containing a positive electrode active material, a first binder, and a first conductive agent; the positive electrode active material includes nano-scale lithium iron phosphate particles and micro-scale lithium iron phosphate particles, and the D 50 particle size of the nano-scale lithium iron phosphate particles is 0.1 to 0.4 μm, and the D 50The particle size is 1 - 4 μm. The above embodiments are conducive to keeping the most frequent pore size of the positive electrode plate within a suitable range, which is conducive to providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode plate, and improving the charge-discharge performance and rate performance of the battery. At the same time, it helps to maintain the structural stability of the electrode plate, reduce the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improve the cycle life of the battery.

[0054] In the positive electrode slurry, the mass ratio of the nano-scale lithium iron phosphate particles to the micro-scale lithium iron phosphate particles is 1:(0.67 - 2.33), preferably 1:(1.50 - 2.33). The above embodiments are conducive to the grading of particles with different particle sizes, keeping the most frequent pore size of the positive electrode plate within a suitable range, which is conducive to providing more effective channels for lithium ion migration, reducing the diffusion distance and time of lithium ions in the electrode plate, and improving the charge-discharge performance and rate performance of the battery. At the same time, it helps to maintain the structural stability of the electrode plate, reduce the fragmentation and shedding of the active material caused by the volume expansion and contraction of the active material during charge and discharge, and further improve the cycle life of the battery.

[0055] In the present disclosure, the preparation methods of the nano-scale lithium iron phosphate particles and the micro-scale lithium iron phosphate particles can be conventional methods in the art. For example, they can be obtained by low-temperature liquid-phase synthesis, hydrothermal synthesis, high-temperature solid-phase method, carbothermal reduction method, etc. 50 Lithium iron phosphate particles with a particle size within the scope of the present disclosure.

[0056] In one embodiment, in step (2), the first conductive agent includes carbon nanotubes, carbon black, and graphite microflakes. The diameter of the carbon nanotubes is 10 - 25 nm, preferably 15 - 20 nm. The 50 particle size of the carbon black is 50 - 100 nm, preferably 60 - 90 nm. The thickness of the graphite microflakes is 200 - 400 nm, preferably 200 - 300 nm, and the flake diameter is 0.5 - 4.5 μm, preferably 1 - 3 μm. The above embodiments are conducive to the construction of a conductive network by carbon nanotubes inside the battery, improving the conductivity of the positive electrode active material, reducing the internal resistance of the lithium battery, reducing the expansion and contraction of the positive electrode active material during charge and discharge, improving the battery life, and at the same time improving the adhesion strength of the electrode plate and reducing the addition amount of the binder.

[0057] In the present disclosure, the mass ratio of the carbon nanotubes, the carbon black, and the graphite microflakes in the positive electrode paste is not specifically limited and can vary within a wide range. For example, it can be (10~5):(3~0.5):1. The above embodiments are conducive to constructing a conductive network of carbon nanotubes inside the battery, improving the conductivity of the positive electrode active material, reducing the internal resistance of the lithium battery, reducing the expansion and contraction of the positive electrode active material during charge and discharge, increasing the battery life, and at the same time improving the bonding strength of the electrode sheet and reducing the addition amount of the binder.

[0058] In one embodiment, the method further includes: mixing a third conductive agent and a third binder to form a conductive coating paste, coating the conductive coating paste on the positive electrode current collector to form a positive electrode conductive coating; and then coating the positive electrode paste on the positive electrode conductive coating to form the positive electrode active material layer on the positive electrode conductive coating, obtaining a positive electrode including a positive electrode active material layer and a conductive coating; wherein the thickness of the conductive coating is 0.3~1.8 μm.

[0059] The present disclosure does not specifically limit the third conductive agent and the third binder used in the positive electrode conductive coating, and they can be of conventional types in the art. For example, the third conductive agent can be one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the third binder can be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0060] The third aspect of the present disclosure provides a lithium-ion battery prepared by the method described in the second aspect of the present disclosure.

[0061] In one embodiment, the battery includes a separator, and the separator can be of conventional types in the art. The present disclosure does not specifically limit this, and for example, it can include a base film, a coating, and an adhesive layer. The base film can be one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride; the coating can be a polyvinylidene fluoride coating (PVDF) and / or a pseudo-boehmite coating (ALOOH); the adhesive layer can be an adhesive layer formed by polyvinylidene fluoride.

[0062] The battery of the present disclosure can include but is not limited to single cells, battery modules, battery packs, etc. That is, the actual application forms of the battery provided by the present disclosure can be but are not limited to the listed products, and can also be other application forms. When the battery is a single cell, it includes at least one of cylindrical batteries, square batteries, etc.

[0063] The fourth aspect of the present disclosure provides a battery pack including the battery described in the first aspect or the third aspect of the present disclosure.

[0064] The fifth aspect of the present disclosure provides an electrical device, including the battery described in the first aspect or the third aspect of the present disclosure, or the battery pack described in the fourth aspect of the present disclosure.

[0065] It should be noted that the above electrical device can be any conventional electrical device, such as but not limited to computers, electric vehicles, air conditioners, refrigerators, washing machines, microwave ovens, printers, fax machines, etc.

[0066] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited thereby. Unless otherwise specified, the reagents used in the present disclosure are all battery grade and are obtained through commercial channels.

[0067] In the following examples of the present disclosure, the D 50 particle size of the positive electrode active material is tested by scanning electron microscopy (SEM). The test method includes: intercepting a 0.5 cm * 0.5 cm part of the positive electrode sheet, magnifying it 2000 times under the scanning electron microscope, taking 50 SEM pictures, and measuring the particle sizes of 50 positive electrode active material particles in each SEM picture, and taking the average value to obtain the D 50 particle size of the positive electrode active material; The D 50 particle size of the negative electrode active material is tested by scanning electron microscopy (SEM). The test method includes: intercepting a 0.5 cm * 0.5 cm part of the negative electrode sheet, magnifying it 2000 times under the scanning electron microscope, taking 50 SEM pictures, and measuring the particle sizes of 50 negative electrode active material particles in each SEM picture, and taking the average value to obtain the D 50 particle size of the negative electrode active material; The D 50 particle size of the carbon black is tested by scanning electron microscopy (SEM). The test method includes: intercepting a 0.5 cm * 0.5 cm part of the positive electrode sheet, magnifying it 2000 times under the scanning electron microscope, taking 50 SEM pictures, and measuring the particle sizes of 50 carbon black particles in each SEM picture, and taking the average value to obtain the D 50 ; The tube diameter of the carbon nanotubes is tested by scanning electron microscopy (SEM). The test method includes: observing the cross-section of the positive electrode sheet under SEM, selecting at least 5 regions at different positions, testing no less than 3 discrete carbon nanotubes in each region, and the total sample size should be ≥ 15, and calculating the average value of the carbon nanotube diameters; The sheet diameter of the graphite microflakes is tested by scanning electron microscopy (SEM), including: intercepting a 0.5 cm * 0.5 cm part of the positive electrode sheet, magnifying it 2000 times under the scanning electron microscope, taking 50 SEM pictures, and measuring the lengths of 50 graphite microflakes in each SEM picture, and taking the average value to obtain the sheet diameter of the graphite microflakes; The thickness of the graphite microflakes was tested by scanning electron microscopy (SEM). The testing method included: intercepting a 0.5 cm * 0.5 cm part of the positive electrode sheet, magnifying it 2000 times under the scanning electron microscope, taking 50 SEM images. Among them, the thickness of 50 graphite microflakes in each SEM image was measured, and the average value was taken to obtain the thickness of the graphite microflakes; The most frequent pore size and the proportion of pore volume of the positive electrode sheet and the negative electrode sheet were tested by mercury intrusion porosimetry (the testing standard is GB / T 21650.1 - 2008).

[0068] Example 1 Preparation of the negative electrode sheet: The artificial graphite active material, conductive agent (conductive carbon black SP), dispersant (carboxymethyl cellulose CMC), and binder (styrene - butadiene rubber SBR) were mixed in a mass ratio of 95:1:1.5:2.5. The powder material and deionized water were stirred into a negative electrode slurry by a homogenizer and evenly coated on the copper foil, and after drying, a negative electrode active material layer was formed; among them, the artificial graphite particles used in this Example 1 included: D 50 Primary artificial graphite particles with a particle size of 3 μm, D 50 Secondary artificial graphite particles with a particle size of 20 μm, and the mass ratio was 1:9; the D of conductive carbon black SP 50 The particle size was 50 nm.

[0069] Preparation of the positive electrode sheet: The preparation of the conductive coating included: mixing the binder (PVDF) and the conductive agent (carbon black) in a mass ratio of 19:1 to form a conductive coating slurry, coating it on the aluminum foil, and after drying, a conductive coating was formed. The single - side thickness of the conductive coating was 1.8 μm; After mixing the lithium iron phosphate active material, conductive agent, and binder (polyvinylidene fluoride PVDF) in a mass ratio of 97:2:1, the powder material and NMP were stirred into a positive electrode slurry by a homogenizer and evenly coated on the conductive coating, and after drying, a positive electrode including a positive electrode active material layer and a conductive coating was formed; among them, the lithium iron phosphate used was LiFePO4, and the content of Ti was 2500 ppm; the lithium iron phosphate included D 50 Nanoscale lithium iron phosphate particles with a particle size of 0.1 μm and D 50 Micron - scale lithium iron phosphate particles with a particle size of 4 μm, and the mass ratio of the nanoscale lithium iron phosphate particles to the micron - scale lithium iron phosphate particles was 1:2.33; the positive electrode conductive agent included carbon nanotubes (CNTs), conductive carbon black, and graphite microflakes. The tube diameter of the carbon nanotubes was 20 nm, the D of the conductive carbon black 50 The particle size was 100 nm, the diameter of the graphite microflakes was 0.5 μm, and the thickness was 300 nm. The mass ratio of the carbon nanotubes, conductive carbon black, and graphite microflakes was 8:1:1; Electrolyte preparation: Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1 to obtain an organic solvent. Then, dissolve the thoroughly dried lithium salt LiPF6 in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L. Separator: Use a polyethylene film as the separator.

[0070] Preparation of lithium-ion battery: Stack the above-mentioned positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator placed between the positive and negative electrode sheets to play an isolation role, and then wind them to obtain a bare battery core. Place the bare battery core in an outer packaging shell, dry it, inject the electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0071] Examples 2 - 12 The methods of Examples 2 - 12 are the same as those of Example 1, except that the particle sizes and mass ratios of the positive and negative active materials used are different. The specific differences are shown in Table 1.

[0072] Comparative Examples 1 - 5 The methods of Comparative Examples 1 - 5 are the same as those of Example 1, except that the particle sizes and mass ratios of the positive and negative active materials used are different. The specific differences are shown in Table 1.

[0073] Table 1

[0074] Test Examples Test the pore size distribution of the positive and negative electrode sheets obtained in the above examples and comparative examples. At the same time, test the lithium-ion batteries assembled in the examples and comparative examples. The test results are shown in Table 2; the test results of the pore size distribution of the positive and negative electrode sheets of Example 2 are as Figure 1 shown.

[0075] The method for testing the battery power performance is as follows: (1) Battery DC internal resistance test: Discharge the battery at a constant current of 0.33C (0.6A) to 2.0V at room temperature, and charge it at a constant current of 0.33C to 50% SOC (charge amount 0.9A). Discharge at a constant current of 1.5C (2.7A) for 30s, record the voltage before and after discharge, and calculate the discharge DCIR (mΩ) = (voltage before discharge - voltage after discharge) / discharge current * 1000; (2) Cycle performance test: At 25°C, charge the lithium-ion batteries prepared in the examples and comparative examples at a rate of 3C and discharge at a rate of 1C, and conduct a full charge and discharge cycle test until the capacity of the lithium-ion battery decays to 80% of the initial capacity, and record the number of cycles.

[0076] Table 2

[0077] Comparative Example 1 uses nano-scale lithium iron phosphate particles as the positive electrode active material. Due to the high production process difficulty, high cost, and low tap density of nano-scale lithium iron phosphate, it cannot meet the energy density requirements.

[0078] According to the data in Table 2, compared with Comparative Examples 1 to 5, in the most frequent pore size range of the positive electrode sheet and the negative electrode sheet of the present disclosure in Examples 1 to 12, the DC internal resistance of the battery is smaller and the cycle performance is better.

[0079] Comparing with Examples 7 and 11, it can be known that in Example 2, the particle sizes of the primary graphite particles and the secondary graphite particles in the negative electrode active material are within the preferred range of the present disclosure, the most frequent pore size of the negative electrode is within the preferred range of the present disclosure, the DC internal resistance of the battery is smaller, and the cycle performance is better.

[0080] Comparing with Example 8, it can be known that in Example 2, the mass ratio of the nano-scale particles to the micro-scale particles in the positive electrode active material is within the preferred range of the present disclosure, the most frequent pore size of the positive electrode is within the preferred range of the present disclosure, the DC internal resistance of the battery is smaller, and the cycle performance is better.

[0081] Comparing with Example 9, it can be known that in Example 2, the mass ratio of the primary graphite particles and the secondary graphite particles in the negative electrode active material is within the preferred range of the present disclosure, the most frequent pore size of the negative electrode is within the preferred range of the present disclosure, the DC internal resistance of the battery is smaller, and the cycle performance is better.

[0082] Comparing with Example 10, it can be known that in Example 2, the particle size range of the nano-scale particles to the micro-scale particles in the positive electrode active material is within the preferred range of the present disclosure, the most frequent pore size of the positive electrode is within the preferred range of the present disclosure, the DC internal resistance of the battery is smaller, and the cycle performance is better.

[0083] Comparing with Example 12, it can be known that in Example 2, the thickness range of the positive electrode conductive coating is within the preferred range of the present disclosure, the most frequent pore size of the positive electrode is within the preferred range of the present disclosure, the DC internal resistance of the battery is smaller, and the cycle performance is better.

[0084] The preferred embodiments of the present disclosure have been described in detail above in conjunction with the accompanying drawings. However, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0085] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any suitable manner. To avoid unnecessary repetition, the present disclosure will not separately describe various possible combination manners.

[0086] In addition, any combination can be made among various different embodiments of the present disclosure, as long as it does not violate the idea of the present disclosure, and the same shall be regarded as the content disclosed by the present disclosure.

Claims

1. A lithium-ion battery, characterized in that, The battery includes a positive electrode plate and a negative electrode plate. The positive electrode plate includes a positive electrode active material layer, and the most frequent pore diameter r1 of the positive electrode plate is 50-90 nm; the negative electrode plate includes a negative electrode active material layer, and the most frequent pore diameter r2 of the negative electrode plate is 900-1500 nm.

2. The battery according to claim 1, wherein, r1 is 60-85 nm; and / or, r2 is 1050-1200 nm.

3. The battery according to claim 1, wherein, In the positive electrode plate, the ratio of the pore volume with a pore diameter of 50-90 nm to the total pore volume of the positive electrode plate is 50-90%, preferably 70-90%; and / or, In the negative electrode plate, the ratio of the pore volume with a pore diameter of 900-1500 nm to the total pore volume of the negative electrode plate is 50%-90%, preferably 70-90%.

4. The battery according to any one of claims 1-3, wherein, The positive electrode active material layer includes a positive electrode active substance, a first binder, and a first conductive agent; The first conductive agent includes carbon nanotubes, carbon black, and graphite micropieces. The diameter of the carbon nanotubes is 10 to 25 nm, and the D 50 particle size of the carbon black is 50 to 100 nm. The thickness of the graphite micropieces is 200 to 400 nm, and the sheet diameter is 0.5 to 4.5 μm.

5. The battery according to claim 4, wherein, The positive electrode active material includes nanoscale lithium iron phosphate particles and micron-scale lithium iron phosphate particles. The D 50 particle size of the nanoscale lithium iron phosphate particles is 0.1 to 0.4 μm, and the D 50 particle size of the micron-scale lithium iron phosphate particles is 1 to 4 μm.

6. The battery according to claim 5, wherein, In the positive electrode active material layer, the mass ratio of the nanoscale lithium iron phosphate particles to the micron-scale lithium iron phosphate particles is 1:(0.67-2.33), preferably 1:(1.50-2.33).

7. The battery according to claim 1, wherein, The positive electrode further includes a positive electrode current collector and a positive electrode conductive coating. The positive electrode conductive coating is located between the positive electrode current collector and the positive electrode active material layer, and the thickness of the positive electrode conductive coating is 0.3-1.8 μm.

8. The battery according to any one of claims 1-7, wherein, The negative electrode active material layer includes a negative electrode active substance, a second binder, and a second conductive agent; The negative electrode active material includes primary graphite particles and secondary graphite particles, and the D 50 particle size of the primary graphite particles is 3 to 5 μm, and the D 50 particle size of the secondary graphite particles is 20 to 40 μm; In the negative electrode active material layer, the mass ratio of the primary graphite particles to the secondary graphite particles is 1:(2.33-9), preferably 1:(4-9).

9. A method for preparing a lithium-ion battery, characterized in that, The method includes: (1) Forming a negative electrode active material layer on a negative electrode current collector to obtain a negative electrode plate; the most frequent pore diameter of the negative electrode plate is 900-1500 nm; (2) Forming a positive electrode active material layer on a positive electrode current collector to obtain a positive electrode plate; the most frequent pore diameter of the positive electrode plate is 50-90 nm.

10. The method according to claim 9, wherein, The most frequent pore diameter of the positive electrode plate is 60-85 nm; and / or, the most frequent pore diameter of the negative electrode plate is 1050-1200 nm.

11. The method according to claim 9, wherein, In step (1), a negative electrode paste containing a negative electrode active substance, a second binder, and a second conductive agent is used to form the negative electrode active material layer; The negative electrode active material includes primary graphite particles and secondary graphite particles, and the D 50 particle size of the primary graphite particles is 3 to 5 μm, and the D 50 particle size of the secondary graphite particles is 20 to 40 μm. In the negative electrode active material layer, the mass ratio of the primary graphite particles to the secondary graphite particles is 1:(2.33 to 9), preferably 1:(4 to 9).

12. The method according to claim 9, wherein In step (2), a positive electrode paste containing a positive electrode active substance, a first binder, and a first conductive agent is used to form the positive electrode active material layer; The positive electrode active material includes nanoscale lithium iron phosphate particles and micron-scale lithium iron phosphate particles, and the D 50 particle size of the nanoscale lithium iron phosphate particles is 0.1 to 0.4 μm, and the D 50 particle size of the micron-scale lithium iron phosphate particles is 1 to 4 μm.

13. The battery according to claim 12, wherein, In the positive electrode active material layer, the mass ratio of the nanoscale lithium iron phosphate particles to the micron-scale lithium iron phosphate particles is 1:(0.67-2.33), preferably 1:(1.5-2.33).

14. The method according to claim 9, wherein, In step (2), the first conductive agent includes carbon nanotubes, carbon black, and graphite microflakes; The diameter of the carbon nanotubes is 10 to 25 nm, and the D 50 particle size of the carbon black is 50 to 100 nm. The thickness of the graphite microflakes is 200 to 400 nm, and the flake diameter is 0.5 to 4.5 μm.

15. A lithium-ion battery prepared by the method according to any one of claims 9-14.

16. A battery pack, characterized in that, Including the lithium-ion battery according to any one of claims 1-8 and claim 15.

17. An electrical device, characterized in that, Including the lithium-ion battery according to any one of claims 1-8 and claim 15 or the battery pack according to claim 16.

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