CN115832166A

CN115832166A - Positive electrode plate, secondary battery, battery module, battery pack, and electric device

Info

Publication number: CN115832166A
Application number: CN202111117391.1A
Authority: CN
Inventors: 吴燕英; 王星会
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2021-09-23
Filing date: 2021-09-23
Publication date: 2023-03-21
Anticipated expiration: 2041-09-23
Also published as: CN115832166B; WO2023045369A1

Abstract

The application provides a positive pole piece, including coating and current collector, the coating is located at least one surface of current collector, the coating includes first coating and second coating, first coating coats on the current collector surface, the second coating coat in first coating surface, wherein, first coating tortuosity is 3.01 ~ 4.93, the second coating tortuosity is 2.11 ~ 2.87.

Description

Positive electrode plate, secondary battery, battery module, battery pack, and electric device

Technical Field

The application relates to the technical field of lithium batteries, in particular to a positive pole piece, a secondary battery, a battery module, a battery pack and an electric device.

Background

In recent years, with the wider application range of lithium ion batteries, lithium ion secondary batteries are widely used in energy storage power systems such as hydraulic power, thermal power, wind power and solar power stations, and in a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment and aerospace. As lithium ion secondary batteries have been greatly developed, higher requirements are also placed on energy density, cycle performance, safety performance, and the like. In addition, bulk doping and surface coating of the positive electrode active material have a limited effect on modifying the energy density of the lithium ion secondary battery. Therefore, the industry is currently focused on optimizing the structural design of the lithium ion secondary battery. For example, in the case of fixing the cell size and the material chemical system, if the positive electrode plate of the lithium ion secondary battery has a higher coating weight, the active material ratio can be significantly increased, and thus the energy density of the cell can be increased.

However, as the coating amount of the positive electrode plate is increased continuously, the drying of the electrode plate of the lithium ion secondary battery is difficult, so that the baking time and the soaking time are increased correspondingly when the lithium ion secondary battery is produced. Meanwhile, the pole piece is difficult to be fully infiltrated by the electrolyte, the dynamic performance of the lithium ion secondary battery is correspondingly poor, and the performance requirement of the lithium ion secondary battery cannot be met. Therefore, the existing design for the positive electrode plate still needs to be improved.

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide a positive electrode sheet which can improve the rate performance, high/low temperature performance, and safety performance of a secondary battery using the positive electrode sheet, and can improve the dynamic performance of the secondary battery.

Means for solving the problems

In order to achieve the above object, the present application provides a positive electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device.

The utility model provides a positive pole piece, its characterized in that, including the mass flow body and coat in the coating of at least one face of mass flow body, the coating includes first coating and second coating, first coating coats in the surface of mass flow body, the second coating coat in the surface of first coating, wherein, first coating tortuosity is 3.01 ~ 4.93, the second coating tortuosity is 2.11 ~ 2.87.

Therefore, the processing convenience of the positive pole piece, the electrochemical performance and the energy density of the secondary battery are comprehensively considered, and the gradient adjustment of the porosity of the positive pole piece is realized by regulating and controlling the tortuosity of the first coating and the second coating of the positive pole piece. Although the mechanism is not clear, the tortuosity of the positive pole piece is presumed to be in gradient distribution, so that the wettability of the positive pole piece to the electrolyte is improved, the drying time of the positive pole piece is shortened, and the electrochemical performance and the energy density of the lithium ion secondary battery are further improved.

In any embodiment, the coating weight CW of the positive pole piece is more than or equal to 400mg/1540.25cm ² . Therefore, the coating weight CW of the positive pole piece can effectively improve the loading capacity of the positive active substance, and the energy density of the lithium ion secondary battery is ensured.

In any embodiment, the first coating comprises primary particles having Dv50=2 to 4 μm, dv90=4 to 8 μm, and the second coating comprises primary particles having Dv50=2 to 7 μm, dv90=7 to 10 μm, and secondary particles having Dv50=4 to 12 μm, dv90=13 to 30 μm.

Therefore, when the primary particles and the secondary particles are mixed for use and the Dv50 and Dv90 of the primary particles and the secondary particles are in the range, the primary particles can be effectively prevented from being broken in the cold pressing process, and the problem of difficulty in cold pressing of the positive pole piece is further solved. The average particle size of the primary particles in the secondary particles is an average of all the primary particle sizes in a scanning electron microscope image of 10K times.

In any embodiment, the primary particle blending ratio in the second coating layer is 10 to 50% with respect to the total mass of the positive electrode active material; the ratio of the Dv50 of the secondary particles to the Dv50 of the primary particles is 1.5 to 10. Therefore, when the primary particles are in the range of the mixing proportion, the tortuosity of the positive pole piece can be effectively regulated and controlled, and the distribution state of the porosity of the positive pole piece is improved. When the ratio of the Dv50 of the secondary particles to the Dv50 of the primary particles is within the above range, the situation that the secondary particles are broken in the cold pressing process can be effectively improved, and the problem that the positive pole piece is difficult to cold press is further improved.

In any embodiment, the first coating layer has a thickness of 20 to 140 μm and the second coating layer has a thickness of 20 to 140 μm. Therefore, when the thicknesses of the first coating and the second coating are within the range, the positive pole piece has better processing performance, and is convenient to be wound into a battery cell and assembled into a secondary battery.

In any embodiment, the compacted density of the first coating layer is greater than the compacted density of the second coating layer. Therefore, the porosity and the tortuosity of the positive pole piece are regulated and controlled by enabling the compaction density of the first coating to be larger than that of the second coating, and the positive pole piece is guaranteed to have high positive active material loading capacity while the wettability of the positive pole piece to electrolyte is improved.

In any embodiment, the first coating layer has a compaction of 2.5 to 2.8g/cc and the second coating layer has a compaction of 2.1 to 2.5g/cc. Thus, when the compacted density of the first coating layer is within the above range, the first coating layer can be loaded with more positive electrode active material, and the positive electrode active material particles can be sufficiently contacted. When the compaction density of the second coating is within the range, the electrolyte can be fully immersed in the second coating, so that the wettability of the positive pole piece to the electrolyte is improved.

In any embodiment, the first coating has a porosity of 16 to 20%; the porosity of the second coating is 26-30%. Therefore, when the first coating and the second coating are in the range, the wettability of the positive pole piece to the electrolyte can be effectively improved, and the drying time of the positive pole piece can be shortened.

In any embodiment, the positive electrode active material is LiNi _x Co _y Mn _z Fe _a Al _b P _c O ₂ (wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0 and less than or equal to 4). Therefore, the lithium ion secondary battery can have higher energy density and better electrochemical performance by selecting the positive active material with high gram capacity and good cycle performance.

A second aspect of the present application provides a secondary battery comprising the positive electrode sheet of the first aspect of the present application.

A third aspect of the present application provides a battery module including the secondary battery of the second aspect of the present application.

A fourth aspect of the present application provides a battery pack including the battery module of the third aspect of the present application.

A fifth aspect of the present application provides an electric device including at least one selected from the secondary battery of the second aspect of the present application, the battery module of the third aspect of the present application, or the battery pack of the fourth aspect of the present application.

Effects of the invention

The application provides a positive pole piece, secondary battery, battery module, battery package, electric installation. The first coating and the second coating adopt different cold pressing pressures to regulate and control the tortuosity of the first coating and the second coating of the positive pole piece, so that the tortuosity of the first coating is greater than that of the second coating, and the tortuosity of the positive pole piece is in gradient distribution, thereby improving the wettability of the positive pole piece on electrolyte and shortening the drying time of the positive pole piece on the premise of ensuring that the positive pole piece has higher coating weight, and further improving the electrochemical performance and the dynamic performance of the lithium ion secondary battery.

Drawings

Fig. 1 is a schematic view of the tortuosity of the positive electrode sheet of the present application.

Fig. 2 is a scanning electron micrograph of example 2 of the present application.

Fig. 3 is a schematic view of a secondary battery according to an embodiment of the present application.

Fig. 4 is an exploded view of the secondary battery according to the embodiment of the present application shown in fig. 3.

Fig. 5 is a schematic view of a battery module according to an embodiment of the present application.

Fig. 6 is a schematic diagram of a battery pack according to an embodiment of the present application.

Fig. 7 is an exploded view of the battery pack according to the embodiment of the present application shown in fig. 6.

Fig. 8 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Description of reference numerals:

L _t the actual path length of the substance through the pore medium; l is ₀ A media distance; 1, a battery pack;2, putting the box body on the box body; 3, discharging the box body; 4 a battery module; 5 a secondary battery; 51 a housing; 52 an electrode assembly; 53 a cap assembly.

Detailed Description

Hereinafter, embodiments of the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device of the present application are specifically disclosed in detail with reference to the accompanying drawings as appropriate. But a detailed description thereof will be omitted. For example, detailed descriptions of already known matters and repetitive descriptions of actually the same configurations may be omitted. This is to avoid unnecessarily obscuring the following description, and to facilitate understanding by those skilled in the art. The drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner may or may not include endpoints and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the

minimum range values

1 and 2 are listed, and if the

maximum range values

3,4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 to 5" have been listed herein, and "0 to 5" is simply an abbreviated representation of the combination of these numbers. In addition, when a parameter is an integer of 2 or more, 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, or the like.

All embodiments and alternative embodiments of the present application may be combined with each other to form new solutions, if not specifically stated.

All technical and optional features of the present application may be combined with each other to form new solutions, if not otherwise specified.

All steps of the present application may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, reference to the process further comprising step (c) means that step (c) may be added to the process in any order, for example, the process may comprise steps (a), (b) and (c), may also comprise steps (a), (c) and (b), may also comprise steps (c), (a) and (b), etc.

The terms "comprises" and "comprising" as used herein mean either open or closed unless otherwise specified. For example, the terms "comprising" and "comprises" may mean that other components not listed may also be included or included, or that only listed components may be included or included.

In this application, the term "or" is inclusive, if not otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or not present); a is false (or not present) and B is true (or present); or both a and B are true (or present).

Positive pole piece

In an embodiment of this application, this application has proposed a positive pole piece, including the current collector and coat in the coating of at least one face of current collector, the coating includes first coating and second coating, first coating coats in the surface of current collector, the second coating coat in the surface of first coating, wherein, first coating tortuosity is 3.01 ~ 4.93, the second coating tortuosity is 2.11 ~ 2.87.

With reference to FIG. 1, tortuosity is the actual path length L through which material passes in the pore medium _t Distance from medium (thickness))L ₀ The ratio of (a) to (b). In the positive electrode plate, L _t Is the actual path length, L, of lithium ions through the positive electrode active material particles ₀ Is the thickness of the coating layer of the positive pole piece.

Although the mechanism is not clear, the applicant has surprisingly found that: if the tortuosity of the positive pole piece is higher, the electrolyte is difficult to infiltrate the positive pole piece, and the diffusion performance of lithium ions in the electrolyte is relatively poor. On the contrary, the lower the tortuosity of the positive electrode sheet, the more the electrolyte can fully infiltrate the positive electrode sheet, and the lithium ion diffusion performance in the positive electrode sheet is better, but the content of the positive active material in the positive electrode sheet is lower, so the energy density of the lithium ion secondary battery can be reduced to a certain extent by using the positive electrode sheet with lower tortuosity.

According to the positive electrode plate, the first coating and the second coating are arranged on the surface of the current collector, and corresponding regulation and control means (such as mixing of primary particles and secondary particles and different cold compaction densities) are adopted to enable the tortuosity of the first coating to be larger than that of the second coating, so that the positive electrode plate has high active material loading capacity and excellent dynamic performance: the first coating has larger tortuosity, so that the positive pole piece is ensured to have higher positive active material loading capacity, and the energy density of the lithium ion secondary battery is obviously improved; meanwhile, the second coating has smaller tortuosity, so that the electrolyte can fully infiltrate the positive plate, lithium ions can be favorably diffused in the positive plate, the lithium ion secondary battery is ensured to have better dynamic performance, and the cycle performance and other electrochemical performances of the lithium ion secondary battery are further improved.

In some embodiments, the coating amount CW of the positive electrode sheet is 400mg/1540.25cm or more in order to increase the coating amount of the positive electrode active material of the positive electrode sheet and thereby increase the energy density of the lithium ion secondary battery ² 。

In some embodiments, the first coating comprises primary particles having Dv50=2 to 4 μm, dv90=4 to 7 μm, and the second coating comprises primary particles having Dv50=2 to 7 μm, dv90=7 to 10 μm, and secondary particles having Dv50=4 to 12 μm, dv90=13 to 30 μm.

Referring to fig. 2, fig. 2 is a Scanning Electron Microscope (SEM) image of a cross section of the positive electrode tab of the present application. The size of the primary particles of the positive electrode active material of the first coating layer is significantly smaller than the size of the secondary particles of the positive electrode active material of the second coating layer. The average particle size of the primary particles in the secondary particles is an average of all the primary particle sizes in a scanning electron microscope image of 10K times. Therefore, the primary particles and the secondary particles are mixed, and when the Dv50 and Dv90 of the primary particles and the secondary particles are within the range, the secondary particles can be prevented from being broken in the cold pressing process, so that the problem of difficulty in cold pressing of the positive pole piece is solved, and meanwhile, the tortuosity of the coating can be regulated and controlled, so that the tortuosity of the first coating is greater than that of the second coating, and the positive pole piece has high positive active material loading capacity and excellent wettability.

In some embodiments, in the second coating layer, the primary particle blending ratio is 10 to 50% and the ratio of the secondary particle Dv50 to the primary particle Dv50 is 1.5 to 10 with respect to the total mass of the positive electrode active material. Therefore, when the mixing proportion of the primary particles is in the range, the cold pressing performance of the positive pole piece can be obviously improved. When the ratio of the Dv50 of the secondary particles to the Dv50 of the primary particles is within the above range, the situation that the secondary particles are broken in the cold pressing process can be effectively improved, and the problem that the positive pole piece is difficult to cold press is further improved.

In some embodiments, the first coating has a thickness of 20 to 140 μm and the second coating has a thickness of 20 to 140 μm. Therefore, when the thicknesses of the first coating and the second coating are within the range, the positive pole piece has good processing performance, and is convenient to be subsequently wound into a battery cell to be assembled into the secondary battery.

In some embodiments, the first coating layer has a compacted density that is greater than the compacted density of the second coating layer from the standpoint of controlling tortuosity and porosity of the first coating layer and the second coating layer.

Therefore, the porosity and the tortuosity of the positive pole piece are regulated and controlled by enabling the compacted density of the first coating to be larger than that of the second coating, and the loading capacity of the positive pole piece with a high positive active material is guaranteed while the wettability of the positive pole piece to electrolyte is improved.

In some embodiments, the first coating has a compaction of 2.5 to 2.8g/cc and the second coating has a compaction of 2.1 to 2.5g/cc.

Therefore, when the compacted densities of the first coating and the second coating are within the range, the tortuosity of the first coating is high, the positive active material content is high, the particles are in close contact, the tortuosity of the second coating is small, the electrolyte can fully infiltrate the positive pole piece, and the dynamic performance of the positive pole piece is remarkably improved.

In some embodiments, the porosity of the first coating is 16 to 20%; the porosity of the second coating is 26-30%.

Therefore, when the porosity of the first coating layer and the porosity of the second coating layer are within the above ranges, the performance of the positive electrode sheet has both high active material coating amount and excellent electrolyte wettability. Therefore, the energy density of the lithium ion secondary battery is obviously improved, the diffusion capacity of lithium ions in the positive pole piece is improved, and the dynamic performance of the lithium ion secondary battery is further improved.

In some embodiments, the positive electrode active material is LiNi _x Co _y Mn _z Fe _a Al _b P _c O ₂ (wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0 and less than or equal to 4).

Therefore, the performance of the positive pole piece can better fit the characteristics of an electrochemical system, and the performance requirement of the lithium ion secondary battery is further met.

The average volume distribution particle diameter Dv50 is a particle diameter corresponding to 50% of the cumulative volume distribution percentage of the positive electrode active material. The average volume distribution particle diameter Dv90 is a particle diameter corresponding to 90% of the cumulative volume distribution percentage of the positive electrode active material. In the present application, the volume average particle diameter Dv50 of the positive electrode active material may be determined by a laser diffraction particle size analysis method. For example, with reference to the standard GB/T19077-2016, using a laser particle Size analyzer (e.g., malvern Master Size 3000).

Imbibition rate test method:

absorbing 2mm of electrolyte by using a capillary tube, vertically placing the capillary tube on a cold-pressed pole piece, standing for 200 seconds, and observing the residual height of the electrolyte in the capillary tube;

imbibition rate = (2 mm-residual height) × capillary cross-sectional area × (1.0 g/cm) ³ (electrolyte density)/time tortuosity test method:

in the present application, the tortuosity of the positive electrode sheet can be tested by mercury intrusion methods, for example, with reference to the standard GB/T21650.1-2008, using a pore size analyzer (e.g., poremaster60 GT).

Tortuosity is calculated according to the following formula:

τ＝(2.23-1.13Vρ _Hg )(0.92y) ^1+E

wherein, the first and the second end of the pipe are connected with each other,

v: mercury volume; ρ is a unit of a gradient _Hg Mercury density; s: the total area of the positive pole piece;

△V _i : a change in pore volume; d _i : an average pore diameter; e: the porosity index.

The secondary battery, the battery module, the battery pack, and the electric device according to the present invention will be described below with reference to the drawings as appropriate.

In one embodiment of the present application, a secondary battery is provided.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. In the process of charging and discharging the battery, active ions are embedded and separated back and forth between the positive pole piece and the negative pole piece. The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The isolating membrane is arranged between the positive pole piece and the negative pole piece, mainly plays a role in preventing the short circuit of the positive pole and the negative pole, and can enable ions to pass through.

[ Positive electrode sheet ]

The positive pole piece is the positive pole piece of this application first aspect.

[ negative electrode sheet ]

The negative pole piece includes the negative pole mass flow body and sets up the negative pole rete on the negative pole mass flow body at least one surface, the negative pole rete includes negative pole active material.

As an example, the negative electrode current collector has two surfaces opposite in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two surfaces opposite to the negative electrode current collector.

In the secondary battery of the present application, the negative current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In the secondary battery of the present application, a negative active material for a battery known in the art may be used as the negative active material. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate and the like. The silicon-based material can be at least one selected from the group consisting of elemental silicon, a silicon oxy compound, a silicon carbon compound, a silicon nitrogen compound and a silicon alloy. The tin-based material may be selected from at least one of elemental tin, tin-oxygen compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative active material may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In the secondary battery of the present application, the negative electrode film layer may further optionally include a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In the secondary battery of the present application, the negative electrode film layer may further optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In the secondary battery of the present application, the negative electrode film layer may further optionally include other additives, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In the secondary battery of the application, the negative pole piece can be prepared in the following way: dispersing the components for preparing the negative electrode plate, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (such as deionized water) to form negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and drying, cold pressing and the like to obtain the negative electrode pole piece.

[ electrolyte ]

The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The electrolyte is not particularly limited and may be selected as desired. For example, the electrolyte may be liquid, gel, or all solid.

In the secondary battery of the present application, the electrolyte is an electrolytic solution. The electrolyte includes an electrolyte salt and a solvent.

In the secondary battery of the present application, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorodioxaoxalato phosphate, and lithium tetrafluorooxalato phosphate.

In the secondary battery of the present application, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

In the secondary battery of the present application, the electrolyte may further optionally include an additive. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.

[ separator ]

In the secondary battery of the present application, the secondary battery further includes a separator. The type of the separator is not particularly limited, and any known separator having a porous structure and good chemical and mechanical stability may be used.

In the secondary battery of the present application, the material of the separator may be at least one selected from the group consisting of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In the secondary battery of the present application, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In the secondary battery of the present application, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and electrolyte.

In the secondary battery of the present application, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

The shape of the secondary battery is not particularly limited, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 3 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to fig. 4, the overwrap may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and a cover plate 53 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

Fig. 5 is a battery module 4 as an example. Referring to fig. 5, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.

Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the battery modules may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.

Fig. 6 and 7 are a battery pack 1 as an example. Referring to fig. 6 and 7, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3, and an enclosed space for accommodating the battery module 4 is formed. A plurality of battery modules 4 may be arranged in any manner in the battery box.

In addition, this application still provides a power consumption device, power consumption device includes at least one in secondary battery, battery module or the battery package that this application provided. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.

As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.

Fig. 8 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.

As another example, the device may be a cell phone, tablet, laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.

Examples

Hereinafter, examples of the present application will be described. The following description of the embodiments is merely exemplary in nature and is in no way intended to limit the present disclosure. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

Example 1

The positive active material LiFePO of the first coating layer ₄ The conductive agent Super P and the binder polyvinylidene fluoride (PVDF) are fully stirred and uniformly mixed in an N-methylpyrrolidone (NMP) solvent system according to the weight ratio of 97 to 1, and then the mixture is coated on an Al foil to be dried and cold-pressed, so that a first coating is obtained.

Then, the positive active material LiFePO of the second coating layer is added ₄ The positive electrode plate is prepared by the steps of mixing a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) according to a weight ratio of 97 to 1 in an N-methylpyrrolidone (NMP) solvent system, fully stirring and uniformly mixing, coating the mixture on a first coating by extrusion coating or transfer coating, and drying and cold pressing the coating.

In the first coating layer, dv50=2.0 μm, dv90=4.0 μm, and the compacted density of the primary particles is: 2.6g/cc, coating thickness 22.5 μm, coat weight CW =90mg/1540.25cm ² The cold pressure was 40T.

In the second coating layer, dv50=5.5 μm, dv90=8.2 μm for the primary particles, and Dv50=7.3 μm, dv90=25 μm for the secondary particles, wherein the blending ratio of the primary particles is 30%, and the compaction density is: 2.2g/cc, coating thickness 91.5 μm, coat weight CW =310mg/1540.25cm ² The cold pressure was 10T.

Example 2

The positive active material LiFePO of the first coating layer ₄ The preparation method comprises the following steps of 1, fully stirring and uniformly mixing a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solvent system according to a weight ratio of 97.

Then, the second coating of the anode active material LiFePO is added ₄ The positive electrode plate is prepared by the steps of mixing a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) according to a weight ratio of 97 to 1 in an N-methylpyrrolidone (NMP) solvent system, fully stirring and uniformly mixing, coating on a first coating, drying, and cold pressing.

Wherein, in the first coating, dv50=2.0 μm, dv90=4.0 μm of the primary particles, the compacted density is: 2.6g/cc, coating thickness 22.5 μm, coat weight CW =90mg/1540.25cm ² The cold pressure was 40T.

In the second coating layer, dv50=5.5 μm and Dv90=8.2 μm for the primary particles, dv50=7.3 μm and Dv90=25 μm for the secondary particles, the blending ratio of the primary particles is 40%, and the compacted density is: 2.2g/cc, coating thickness 91.5 μm, coat weight CW =310mg/1540.25cm ² The cold pressure was 20T.

Example 3

In the second coating layer, dv50=5.5 μm and Dv90=8.2 μm for the primary particles, dv50=7.3 μm and Dv90=25 μm for the secondary particles, the blending ratio of the primary particles is 20%, and the compacted density is: 2.2g/cc, coating thickness 91.5 μm, coat weight CW =310mg/1540.25cm ² The cold pressure was 30T.

Example 4

The positive active material LiFePO of the first coating layer ₄ The conductive agent Super P and the binder polyvinylidene fluoride (PVDF) are fully stirred and uniformly mixed in an N-methylpyrrolidone (NMP) solvent system according to the weight ratio of 97 to 1, and then coated on an Al foil by extrusion coating or transfer coating, dried and cold pressed to obtain a first coating.

Then, the second coating of the anode active material LiFePO is added ₄ The positive electrode plate is prepared by the steps of mixing a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) according to a weight ratio of 97 to 1 in an N-methylpyrrolidone (NMP) solvent system, fully stirring and uniformly mixing, coating the mixture on a first coating by extrusion coating or transfer coating, and drying and cold pressing the coating.

Wherein, in the first coating, dv50=2.0 μm, dv90=4.0 μm of the primary particles, the compacted density is: 2.6g/cc, coating thickness 70 μm, coat weight CW =279mg/1540.25cm ² The cold pressure was 30T.

In the second coating layer, dv50=5.5 μm and Dv90=8.2 μm for the primary particles, dv50=7.3 μm and Dv90=25 μm for the secondary particles, the blending ratio of the primary particles is 30%, and the compacted density is: 2.2g/cc, coating thickness 91.5 μm, coat weight CW =121mg/1540.25cm ² The cold pressure was 15T.

Example 5

Wherein, in the first coating, dv50=2.0 μm, dv90=4.0 μm of the primary particles, the compacted density is: 2.7g/cc, coating thickness 62 μm, coat weight CW =258mg/1540.25cm ² The cold pressure was 55T.

In the second coating layer, dv50=5.5 μm and Dv90=8.2 μm for the primary particles, dv50=7.3 μm and Dv90=25 μm for the secondary particles, the blending ratio of the primary particles is 30%, and the compacted density is: 2.2g/cc, coating thickness 42 μm, coat weight CW =142mg/1540.25cm ² The cold pressure was 50T.

Comparative example 1

Then, the second coating of the anode active material LiFePO is added ₄ A conductive agent Super P, a binder polyvinylidene fluoride (PVDF)And (2) fully stirring and uniformly mixing in an N-methylpyrrolidone (NMP) solvent system in a weight ratio of 97.

Wherein, in the first coating, dv50=2.0 μm, dv90=4.0 μm of the primary particles, the compacted density is: 2.6g/cc, coating thickness 22.5 μm, coat weight CW =90mg/1540.25cm ² The cold pressure was 70T.

In the second coating layer, dv50=5.5 μm and Dv90=8.2 μm for the primary particles, dv50=7.3 μm and Dv90=25 μm for the secondary particles, the blending ratio of the primary particles is 5%, and the compacted density is: 2.2g/cc, coating thickness 91.5 μm, coat weight CW =310mg/1540.25cm ² The cold pressure was 21T.

Comparative example 2

In the second coating layer, dv50=5.5 μm and Dv90=8.2 μm for the primary particles, dv50=7.3 μm and Dv90=25 μm for the secondary particles, the blending ratio of the primary particles is 60%, and the compacted density is: 2.2g/cc, coating thickness 91.5 μm, coat weight CW =310mg/1540.25cm ² The cold pressure was 60T.

The parameters of the positive electrode sheets of examples 1 to 5, comparative example 1 and comparative example 2 are shown in table 1.

Table 1: parameters of the positive electrode sheets of examples 1 to 5 and comparative examples 1 and 2

The positive electrode sheets of examples 1 to 5, comparative example 1 and comparative example 2 were tested for the liquid-suction rate and the tortuosity, respectively. The test results are shown in table 2 below.

Table 2: results of liquid suction Rate test and tortuosity test of examples 1 to 5 and comparative examples 1 and 2

In addition, secondary batteries were prepared as follows from the positive electrode sheets of examples 1 to 5, comparative example 1, and comparative example 2, respectively, and performance tests were performed. The test results are shown in table 3 below.

(1) Preparation of secondary battery

The positive electrode piece used in each of the examples and comparative examples was the positive electrode piece described above.

Artificial graphite serving as a negative electrode active material, acetylene black serving as a conductive agent, styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) serving as a thickening agent are mixed according to a weight ratio of 90:5:2:2:1, fully stirring and uniformly mixing in a deionized water solvent system, coating on a copper foil, drying, and cold pressing to obtain the negative pole piece.

A porous polymer film made of Polyethylene (PE) was used as a separator. And overlapping the positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive and negative electrodes to play an isolating role, and winding to obtain the bare cell. The bare cell was placed in an outer package, and an electrolyte was injected and packaged to obtain a secondary battery using the positive electrode sheets in each of the examples and comparative examples.

(2) Secondary battery ac impedance test

The electrochemical impedance of the secondary battery prepared as described above was measured using an electrochemical workstation (model: VMP3, manufacturer: bio-logic, france) setting the frequency range of the normal full-cell test to 500 kHz-30 mHz and the amplitude to 5 mV.

(3) Discharge rate test of secondary battery

Each secondary battery prepared above was allowed to stand at a constant temperature of 25 ℃ for 30 minutes. Discharging to 2.5V at constant current of 0.33C, discharging to 2.0V at constant current of 0.33C, standing for 1 hr, charging to 3.65V at constant current of 0.33C, charging at constant voltage with cutoff current of 0.05C, standing for 30 min, discharging to 2.5V at constant current of 0.33C, discharging to 2.0V at constant current of 0.33C, and recording discharge capacity C ₀ Standing for 1 hour, charging to 3.65V at 0.33C under constant current, charging at constant voltage, stopping current at 0.05C, and standing for 30 minutes.

Discharge capacity C was recorded as 1C to 2.5V,1C to 2.0V ₁ Then, the mixture is kept stand for 1 hour, and is charged to 3.65V by a 0.33C constant current, and is charged at a constant voltage, and is kept stand for 30 minutes by a 0.05C cutoff current. The retention ratio of 1C discharge capacity was (C) ₁ /C ₀ )*100％。

Discharge to 2.5V at 2C, 2.0V at 2C and recording the discharge capacity C ₂ And then left to stand for 30 minutes. The retention ratio of 2C discharge capacity is (C) ₂ /C ₀ )*100％。

(4) High and low temperature performance test of secondary battery

Performance test at 25 ℃: each of the secondary batteries prepared above was placed in a 25 ℃ high and low temperature box (model: SM-012PF, manufacturer: guangdong Sanzhi Co., ltd.) respectively, discharged to 2.5V at 1C, discharged to 2.0V at 1C, then left to stand for 5 minutes, charged to 3.65V at a constant current at 1C, charged at a constant voltage, and cut-off current at 0.05C, and the discharge capacity C was recorded ₀ Then, the mixture was left to stand for 30 minutes, discharged to 2.5V at 1C, discharged to 2.0V at 1C, then left to stand for 30 minutes, charged to 3.65V at a constant current at 1C, charged at a constant voltage with a cutoff current of 0.05C, and then left to stand for 5 minutes.

Retention ratio of discharge capacity at 25 ℃ of (C) ₀ /C ₀ )*100％。

-25 ℃ performance test: adjusting the temperature of the high-low temperature box to-25 ℃, standing each prepared secondary battery for 120 minutes,discharge capacity C was recorded as 1C to 2.5V,1C to 2.0V ₁ And then left to stand for 5 minutes.

Retention ratio of discharge capacity at-25 ℃ of (C) ₁ /C ₀ )*100％。

60 ℃ performance test: the secondary batteries prepared above were allowed to stand for 120 minutes by adjusting the high and low temperature chambers to 25 ℃, charged to 3.65V at a constant current of 1C, charged at a constant voltage with a cutoff current of 0.05C, and then allowed to stand for 5 minutes. Adjusting the temperature of the high-low temperature chamber to 60 ℃, standing each secondary battery prepared above for 120 minutes, discharging to 2.5V according to 1C, discharging to 2.0V according to 1C, and recording the discharge capacity C ₂ And then left to stand for 5 minutes.

The retention ratio of discharge capacity at 60 ℃ was (C) ₂ /C ₀ )*100％。

(5) Secondary battery DC impedance test

And (3) standing each secondary battery prepared in the above step for 30 minutes in a constant temperature environment of 25 ℃, discharging to 2.5V according to a constant current of 0.33C, standing for 30 minutes, charging to 3.65V according to a constant current of 0.33C, then charging at a constant voltage, stopping current at 0.05C, and then standing for 30 minutes. Discharge to 2.5V at 0.33C and recording discharge capacity C ₀ And standing for 30 minutes, charging to 3.65V at a constant current of 0.33C, then charging at a constant voltage, cutting off the current of 0.05C, and then standing for 5 minutes. Discharge at 0.33C and cut-off current of 0.5C ₀ (the SOC was 50% in this step for each secondary battery prepared as described above), left for 1 hour, and the voltage U at that time was recorded ₁ Discharge at current I =5C for 30 seconds, recording voltage U at this time ₂ And then left to stand for 5 minutes. DCR resistance = (U) ₁ -U ₂ )/I。

Table 2: results of Performance test of examples 1 to 5 and comparative examples 1 and 2

From the above results, it is understood that in the positive electrode sheets of examples 1 to 5, since the porosity of the positive electrode sheet is distributed in a gradient manner by using the positive electrode active material having small particles for the first coating layer and by increasing the cold compaction density so that the tortuosity of the first coating layer is higher than that of the second coating layer, good effects are obtained in all of the rate capability, high and low temperature performance, and wettability of the electrolyte solution of the secondary battery. And, the kinetic performance of the lithium ion secondary battery is also improved.

In contrast, the blending ratio of the primary particles of the second coating layer in the positive electrode sheet obtained in comparative example 1 is only 5%, the blending ratio of the primary particles of the second coating layer in the positive electrode sheet obtained in comparative example 2 is up to 60%, and the tortuosity of the positive electrode sheet is large. Thus, the diffusion resistance R of comparative examples 1 and 2 _f And the dynamic performance is not effectively improved.

In addition, in example 1, the diffusion resistance R was smaller in example 2 and example 3 than in example 2 and example 3, although the diffusion resistance R was smaller in example 2 and example 3 _f The dynamic performance, high and low temperature performance and rate performance of the material are all improved. But the continuous improvement of the mixing ratio of the primary particles in the second coating layer has no obvious effect on the dynamic performance of the lithium ion secondary battery.

The present application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments having substantially the same configuration as the technical idea and exhibiting the same operation and effect within the technical scope of the present application are all included in the technical scope of the present application. In addition, various modifications that can be conceived by those skilled in the art are applied to the embodiments and other embodiments are also included in the scope of the present application, in which some of the constituent elements in the embodiments are combined and constructed, without departing from the scope of the present application.

Claims

1. The positive pole piece is characterized by comprising a current collector and a coating coated on at least one surface of the current collector, wherein the coating comprises a first coating and a second coating, the first coating is coated on the surface of the current collector, the second coating is coated on the surface of the first coating,

wherein the first coating has a tortuosity of 3.01-4.93, and the second coating has a tortuosity of 2.11-2.87.

2. The positive electrode sheet according to claim 1, wherein the total coating amount CW of the positive electrode sheet is 400mg/1540.25cm or more ² 。

3. The positive electrode sheet according to any one of claims 1 or 2, wherein the first coating layer comprises primary particles having Dv50=2 to 4 μm and Dv90=4 to 8 μm, and the second coating layer comprises primary particles having Dv50=2 to 7 μm and Dv90=7 to 10 μm, and secondary particles having Dv50=4 to 12 μm and Dv90=13 to 30 μm.

4. The positive electrode sheet according to any one of claims 1 to 3,

in the second coating layer, the mixing proportion of the primary particles is 10-50% of the total mass of the positive electrode active material,

the ratio of the secondary particle Dv50 to the primary particle Dv50 is 1.5 to 10.

5. The positive electrode sheet according to any one of claims 1 to 4,

the thickness of the first coating is 20-140 μm, and the thickness of the second coating is 20-140 μm.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein the first coating layer has a compacted density greater than that of the second coating layer.

7. The positive electrode sheet according to claim 6, wherein the first coating layer has a compaction of 2.5 to 2.8g/cc and the second coating layer has a compaction of 2.1 to 2.5g/cc.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein the porosity of the first coating layer is 16 to 20%; the porosity of the second coating is 26-30%.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein the positive electrode active material is LiNi _x Co _y Mn _z Fe _a Al _b P _c O ₂ Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, a is more than or equal to 0 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.8, and c is more than or equal to 0 and less than or equal to 4.

10. A secondary battery comprising the positive electrode sheet according to any one of claims 1 to 9.

11. A battery module characterized by comprising the secondary battery according to claim 10.

12. A battery pack comprising the battery module according to claim 11.

13. An electric device comprising at least one selected from the secondary battery according to claim 10, the battery module according to claim 11, and the battery pack according to claim 12.