WO2021189472A1

WO2021189472A1 - Electrochemical device

Info

Publication number: WO2021189472A1
Application number: PCT/CN2020/081836
Authority: WO
Inventors: 张益博; 胡乔舒; 王斌; 邵颖
Original assignee: 宁德新能源科技有限公司
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2021-09-30
Also published as: CN115088127A; CN115088127B

Abstract

An electrochemical device, comprising: a first pole piece, a first porous layer arranged on a surface of the first pole piece, and a second pole piece, wherein the first porous layer includes first polymer fibers and first inorganic particles. In the thickness direction of the first porous layer, the average pore diameter of pores formed by the first polymer fibers in a region away from the first pole piece is A μm, and the average pore diameter of pores formed by the first polymer fibers in a region close to the first pole piece is B μm; the average particle diameter of the first inorganic particles in the region away from the first pole piece is C μm, and the average particle diameter of the first inorganic particles in the region close to the first pole piece is D μm; and the following relationships are satisfied: (a) A > B; and (b) C > D. By means of the electrochemical device, the self-discharge problem and the electrical performance are both improved.

Description

Electrochemical device

Technical field

The present application relates to an electrochemical device and an electronic device including the electrochemical device. More specifically, the present application relates to a lithium ion battery and an electronic device including the lithium ion battery.

Background technique

Lithium-ion batteries have many advantages, such as high energy density, long cycle life, high nominal voltage (>3.7V), and low self-discharge rate. They are widely used in the field of consumer electronics. With the rapid development of electric vehicles and portable electronic devices in recent years, people have higher and higher requirements for the energy density, safety, and cycle performance of lithium-ion batteries, and are looking forward to the emergence of new lithium-ion batteries with comprehensive performance improvements. . Among them, setting a fiber porous layer between the positive and negative electrodes of a lithium-ion battery to replace the traditional ordinary separator is a new technology that has attracted much attention.

The fiber porous layer prepared on the surface of the electrode pole piece by the spinning method can be directly integrated into the surface of the electrode pole piece, without the need for a separate production step of the isolation membrane in the traditional process, which can simplify the production process of lithium ion batteries, and at the same time, due to the spinning preparation The thickness of the fiber porous layer can be made thinner, which can increase the energy density of the lithium ion battery; at the same time, the fiber porous layer prepared by spinning also has a higher porosity than the traditional separator, which can improve the lithium ion battery The ability to retain liquid has therefore received widespread attention.

The disadvantages of the fiber porous layer prepared by the existing spinning technology are obvious. When the pore size of the fiber porous layer is smaller, the fiber distribution is denser, the interface adhesion with the electrode pads is good, and the ability to resist particle piercing is stronger. However, the porosity of the fiber porous layer is low at this time, which is not conducive to ion transmission and assembly. After being formed into a lithium-ion battery, the electrical performance will be adversely affected; when the pore size of the fiber porous layer is larger, the fiber distribution is more sparse and the porosity is higher, which is conducive to ion transmission. At this time, the porous fiber layer has a large porosity and low mechanical strength, which makes its ability to withstand the penetration of particles in the electrode pads weak, which is likely to cause internal short circuits. After being assembled into a lithium-ion battery, there will be excessive self-discharge. problem.

Summary of the invention

The purpose of this application is to provide an electrochemical device with a porous layer provided on the surface of the electrode, which has strong puncture resistance and high electrochemical performance.

The first aspect of the application provides an electrochemical device, including:

A first pole piece, and a first porous layer disposed on the surface of the first pole piece;

Second pole piece

Wherein, the first porous layer includes first polymer fibers and first inorganic particles. In the thickness direction of the first porous layer, the first polymer fibers are located far away from the first pole piece. The average pore diameter of the pores formed in the region is Aμm, the average pore diameter of the pores formed by the first polymer fiber in the region close to the first pole piece is Bμm, and the first inorganic particles are moving away from the first pole piece. The average particle size of the region of is Cμm, and the average particle size of the first inorganic particles in the region close to the first pole piece is Dμm, and the following relationship is satisfied:

(a) A>B;

(b) C>D.

In some embodiments of the first aspect of the present application, the first porous layer includes a first layer and a second layer, the first layer is an area close to the first pole piece, and the second layer is The area away from the first pole piece.

In some embodiments of the first aspect of the present application, the value range of A is 0.05-5, the value range of B is 0.02-3, and the value range of C is 0.01-10. The value of D ranges from 0.01 to 10.

In some implementations of the first aspect of the present application, said A, said B, said C, and said D satisfy at least one of the following relationships:

(a) 1.01≤A/B≤250;

(b) 1.01≤C/D≤500;

(c) 0.1≤C/A≤20;

(d) 0.1≤D/B≤20.

In some embodiments of the first aspect of the present application, in the thickness direction of the first porous layer, the average particle size of the first inorganic particles ranges from a region close to the first pole piece to a distance away from the first pole piece. The area of a pole piece continuously increases.

In some embodiments of the first aspect of the present application, in the thickness direction of the first porous layer, the average pore diameter of the pores formed by the first polymer fiber moves away from the area close to the first pole piece. The area of the first pole piece continuously increases.

In some embodiments of the first aspect of the present application, the diameter of the first polymer fiber is 0.1 nm to 10 μm.

In some embodiments of the first aspect of the present application, the porosity of the first porous layer is 30% to 95%; the thickness of the first porous layer is 1 μm to 20 μm.

In some embodiments of the first aspect of the present application, the weight of the first inorganic particles in the first porous layer per unit area is 0.004 g/m ² to 60 g/m ² .

In some embodiments of the first aspect of the present application, the composition of the first polymer fiber includes polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, poly Among the propylene carbonate, polymethyl methacrylate, polyethylene terephthalate, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene or polyethylene oxide At least one.

In some embodiments of the first aspect of the present application, the first inorganic particles include HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, BaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , SiO ₂ , boehmite, magnesium hydroxide, aluminum hydroxide, lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium germanium thiophosphate, lithium Nitride, SiS ₂ glass, P ₂ S ₅ glass, Li ₂ O, LiF, LiOH, Li ₂ CO ₃ , LiAlO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ At least one of ceramics or garnet ceramics.

In some embodiments of the first aspect of the present application, the second pole piece further includes a second porous layer disposed on the surface of the second pole piece, and the second porous layer includes second polymer fibers And second inorganic particles, the average pore diameter of the pores formed by the second polymer fiber is Eμm, the average particle diameter of the second inorganic particles is Fμm, and the following relationship is satisfied:

(a) A>E;

(b) C>F.

In some embodiments of the first aspect of the present application, the first porous layer and the second porous layer are in contact.

The second aspect of the present application provides an electronic device, including the electrochemical device provided in the first aspect of the present application.

The electrochemical device provided by the solution of the present application has a porous layer on the surface of the pole piece, and the area close to the pole piece has a small pore size and dense fiber distribution. Therefore, it has strong adhesion to the pole piece and has the ability to resist the piercing of the positive and negative particles. Strong; the area far from the pole piece has a large pore size and strong ion conductivity, which is conducive to improving the electrical performance of the electrochemical device; using inorganic particles with different diameters to fill the areas with different pore diameters to further improve the mechanical strength of the porous layer and optimize The pore size distribution of the porous layer reduces the average pore size, thereby improving the self-discharge of the electrochemical device.

In the present application, the term "average particle size" refers to Dv50, and Dv50 represents the particle size that reaches 50% of the cumulative volume from the small particle size side in the volume-based particle size distribution of inorganic particles.

Description of the drawings

In order to explain the embodiments of the present application and the technical solutions of the prior art more clearly, the following briefly introduces the drawings that need to be used in the embodiments and the prior art. Obviously, the drawings in the following description are merely the present invention. For some of the embodiments of the application, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

FIG. 1 is an SEM image of the first porous layer and the second layer of the electrochemical device of Example 1. FIG.

Detailed ways

In order to make the objectives, technical solutions, and advantages of the present application clearer, the following further describes the present application in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative work shall fall within the protection scope of this application.

The electrochemical device of the present application may be any electrochemical device using pole pieces and porous layers, such as lithium ion batteries, super capacitors, etc. The following uses lithium ion batteries as an example for description. Those skilled in the art should understand that the following description is only an example and does not limit the protection scope of the present application.

Second pole piece

(a) A>B;

(b) C>D.

The electrochemical device in this application includes a positive pole piece and a negative pole piece. The first pole piece may be a positive pole piece or a negative pole piece; the first porous layer may be provided on the surface of the positive pole piece. The upper part can also be arranged on the surface of the negative electrode piece; the first porous layer can be arranged on one surface of the positive electrode piece and the negative electrode piece, or can be formed on both surfaces of the positive electrode piece or the negative electrode piece.

In this application, the first porous layer is formed on the first pole piece, one side of which is in contact with the first pole piece, and the other side is not in contact with the first pole piece; the "area close to the first pole piece" is Refers to the area where the porous layer extends from the side in contact with the first pole piece to the middle of the porous layer, and its thickness can be 10% to 90% of the thickness of the porous layer; the “area away from the first pole piece” It refers to the area extending from the side of the porous layer that is not in contact with the first pole piece to the middle of the porous layer, and its thickness can be 10% to 90% of the thickness of the porous layer; wherein, the area close to the first pole piece is The area far away from the first pole piece may be directly connected, or an intermediate area may be included between the area close to the first pole piece and the area far away from the first pole piece. The average pore size of the intermediate area is The application is not limited. By way of example, the aperture of the middle region may be between A and B.

The porous layer in the present application consists of a porous matrix composed of polymer fibers, and inorganic particles are distributed in the porous matrix. In this application, the pore diameters of the pores formed by the polymer fibers in different regions can be understood as the pore diameters of the porous matrix in different regions. The inventor found in research that, without being limited to any theory, the porous layer of the present application, in the area close to the first pole piece, the porous matrix has a smaller average pore size and densely distributed polymer fibers, which can achieve high adhesion to the pole piece. At the same time, the ability to withstand the piercing of the positive and negative electrodes is ensured; the area far away from the first pole piece has a larger average pore size of the porous matrix, a loose distribution of polymer fibers, and provides high ion conductivity. At the same time, filling inorganic particles with a particle size matching the pore size of the porous matrix can effectively fill the voids of the porous matrix, further improve the mechanical strength of the porous layer, optimize the pore size distribution of the porous layer, reduce the average pore size, and improve electrochemistry. The problem of self-discharge of the device.

In some embodiments of the first aspect of the present application, 1.01≤A/B≤250.

In some embodiments of the first aspect of the present application, 1.01≤C/D≤500.

The average pore diameter of the polymer fiber formed in different regions is not particularly limited, as long as the purpose of the application can be achieved; for example, the average pore diameter of the pores formed by the first polymer fiber in the region away from the first pole piece may be 50 nm ~5μm, that is, the value range of A is 0.05-5; the average pore diameter of the holes formed by the first polymer fiber in the region close to the first pole piece can be 20nm-3μm, and the value of B is 0.02-3 .

The average particle diameter of the inorganic particles is not particularly limited, as long as the purpose of the application can be achieved; for example, the average particle diameter of the first inorganic particles in the region far away from the first pole piece may be 10 nm to 10 μm, that is, the value of C The value range is 0.01-10, and the average particle diameter of the first inorganic particles in the region close to the first pole piece may be 10 nm-10 μm, that is, the value range of D is 0.01-10.

The inventor also found in the research that in different regions, the average particle size of the inorganic particles and the average pore size of the porous matrix need to have a certain matching relationship. If the average particle size of the inorganic particles is too small, the pores of the porous matrix cannot be effectively filled. , It cannot achieve the purpose of improving the mechanical strength of the porous layer and reducing the average pore diameter of the porous layer; and the average particle size of the inorganic particles is too large, not only cannot effectively fill the pores of the porous matrix of the porous layer, but also causes the overall thickness of the porous layer to be reduced. In some embodiments of the first aspect of this application, 0.1≤C/A≤20; preferably 0.5≤C/A≤3.0; more preferably 1.5; in some embodiments of the first aspect of this application, In other embodiments of the aspect, 0.1≤D/B≤20; preferably 0.5 to 3.0; more preferably 1.5.

In some embodiments of the first aspect of the present application, in the thickness direction of the first porous layer, the average particle size of the first inorganic particles ranges from a region close to the first pole piece to a distance away from the first pole piece. The area of a pole piece increases continuously; for example, it can increase linearly or non-linearly. For example, the pore size of the porous matrix can be changed in a gradient way: that is, it gradually transitions from a small pore area to a mixed area of large pores and small pores, and then transitions In the large aperture area, there is no obvious interface between the large aperture area and the small aperture area.

In other embodiments of the first aspect of the present application, the first porous layer further includes an intermediate layer, the intermediate layer is located between the first layer and the second layer, the first layer, the intermediate layer, and the second layer The average pore size of the layer increases successively, which can be understood as the change of the average pore size of the porous matrix is a sharp change, that is, there is an obvious interface between the large pore area and the small pore area. In some embodiments of the first aspect of the present application, the diameter of the first polymer fiber is 0.1 nm-10 μm. The diameter of the polymer fiber is too small and the strength of the fiber itself is too low. During the preparation or use of the lithium-ion battery, the polymer fiber is easily broken, and the porous layer is pierced by the positive and negative active material particles, causing self-discharge; polymerization; If the diameter of the material fiber is too large, the volume occupied by the polymer fibers in the porous layer is too large. When the porous layer contains nanofibers of the same weight, the pore size of the porous layer may be too large. In the case that the porous layer maintains the same porosity, the content of nanofibers decreases, resulting in a decrease in the strength of the porous layer and an excessively large pore size.

In some embodiments of the first aspect of the present application, the porosity of the first porous layer is 30%-95%. The inventor found in the research that too small porosity will cause blockage of the ion transmission path and hinder the normal charging and discharging of the electrochemical device; too large porosity will cause the porous layer structure to be unstable, and the mechanical strength is too poor to resist the surface of the pole piece. Piercing of particles.

The thickness of the first porous layer is not particularly limited, and is preferably smaller than the thickness of the prior art isolation membrane. For example, the thickness of the porous layer of the present application may be 1 μm to 20 μm, preferably 5 μm to 10 μm. The thickness of the first porous layer is small, which can increase the energy density of the electrochemical device.

The polymer type of the first polymer fiber is not particularly limited, as long as it can form the first porous layer of the present application. For example, the composition of the first polymer fiber may include polyvinylidene fluoride (PVDF), polyimide (PI), polyamide (PA), polyacrylonitrile (PAN), polyethylene glycol (PEG), Polyphenylene ether (PPE), polypropylene carbonate (PPC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyvinylidene fluoride-hexafluoropropylene (PVDF) -HFP), polyvinylidene fluoride-chlorotrifluoroethylene, polyethylene oxide (PEO) or at least one of its derivatives; preferably polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly Vinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyphenylene ether (PPO), polypropylene carbonate (PPC), polyethylene oxide (PEO) At least one of. These polymers may be used alone or in combination of two or more kinds.

The first inorganic particles are not particularly limited. For example, they can be selected from HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, BaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _2. SiO ₂ , boehmite, magnesium hydroxide, aluminum hydroxide, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , where 0<x<2 and 0<y<3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , where 0<x<2, 0<y<1, and 0<z<3), Li _1+x+y (Al,Ga) _x (Ti,Ge) _2-x Si _y P _3-y O ₁₂ , where 0≤x≤1 and 0≤y≤1, lithium lanthanum titanate (Li _x La _y TiO ₃ , where 0<x<2 and 0<y<3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , where 0<x<4, 0<y<1, 0<z<1, and 0 <w<5), lithium nitride (Li _x N _y , where 0<x<4, 0<y<2), SiS ₂ glass (Li _x Si _y S _z , where 0≤x<3, 0<y <2, and 0<z<4), P ₂ S ₅ glass (Li _x P _y S _z , where 0≤x<3, 0<y<3, and 0<z<7), Li ₂ O, LiF , LiOH, Li ₂ CO ₃ , LiAlO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ ceramics or garnet ceramics (Li _3+x La ₃ M ₂ O ₁₂ , Wherein 0≤x≤5, and M is any one of Te, Nb, or Zr) or a mixture of at least two of them.

(a) A>E;

(b) C>F.

In this application, the first porous layer can be directly processed on the surface of the first pole piece. When assembling the electrochemical device, it contacts and bonds with the second pole piece; in a preferred embodiment of the present application, The surface of the second pole piece is provided with a second porous layer. When the electrochemical device is assembled, the second porous layer is in contact with the first porous layer, which can further improve the adhesion between the pole piece and the porous layer.

In some embodiments of the first aspect of the present application, the diameter of the second polymer fiber may be 0.1 nm to 10 μm. The diameter of the second polymer fiber may be the same as or different from that of the first polymer fiber.

In some embodiments of the first aspect of the present application, the porosity of the second porous layer is 30%-95%. The porosity of the second porous layer may be the same as or different from that of the first porous layer.

The thickness of the second porous layer is not particularly limited, and may be, for example, 1 μm to 5 μm.

The weight of the second inorganic particles in the second porous layer is not particularly limited, for example, it may be 0.004 g/m ² to 60 g/m ² , and the weight of the second inorganic particles may be the same as the weight of the first inorganic particles. Or different.

The polymer type of the second polymer fiber is not particularly limited, as long as it can form the second porous layer of the present application. For example, the composition of the second polymer fiber may include polyvinylidene fluoride (PVDF), polyimide (PI), polyamide (PA), polyacrylonitrile (PAN), polyethylene glycol (PEG), Polyphenylene ether (PPE), polypropylene carbonate (PPC), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyvinylidene fluoride-hexafluoropropylene (PVDF) -HFP), polyvinylidene fluoride-chlorotrifluoroethylene, polyethylene oxide (PEO) or at least one of its derivatives; preferably polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), poly Vinylidene fluoride (PVDF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyphenylene ether (PPO), polypropylene carbonate (PPC), polyethylene oxide (PEO) At least one of. These polymers may be used alone or in combination of two or more; the polymer used in the second polymer fiber may be the same as or different from the first polymer fiber.

The second inorganic particles are not particularly limited. For example, they can be selected from HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, BaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , TiO _2. SiO ₂ , boehmite, magnesium hydroxide, aluminum hydroxide, lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , where 0<x<2 and 0<y<3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , where 0<x<2, 0<y<1, and 0<z<3), Li _1+x+y (Al,Ga) _x (Ti,Ge) _2-x Si _y P _3-y O ₁₂ , where 0≤x≤1 and 0≤y≤1, lithium lanthanum titanate (Li _x La _y TiO ₃ , where 0<x<2 and 0<y<3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , where 0<x<4, 0<y<1, 0<z<1, and 0 <w<5), lithium nitride (Li _x N _y , where 0<x<4, 0<y<2), SiS ₂ glass (Li _x Si _y S _z , where 0≤x<3, 0<y <2, and 0<z<4), P ₂ S ₅ glass (Li _x P _y S _z , where 0≤x<3, 0<y<3, and 0<z<7), Li ₂ O, LiF , LiOH, Li ₂ CO ₃ , LiAlO ₂ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ ceramics or garnet ceramics (Li _3+x La ₃ M ₂ O ₁₂ , Wherein 0≤x≤5, and M is any one of Te, Nb, or Zr) or a mixture of at least two of them.

In the electrochemical device of the present application, the second inorganic particles may be the same as or different from the first inorganic particles.

In this application, the method of depositing polymer fibers and inorganic particles is not particularly limited, and can be carried out by using deposition methods known in the art. For example, the porous matrix is prepared by electrospinning, air spinning or centrifugal spinning, so The inorganic particles are filled in the porous matrix by electrodeposition. The order of depositing polymer fibers and inorganic particles is not particularly limited, as long as the porous layer of the present application can be formed, and the porous layer of the present application includes a porous matrix formed by polymer fibers and inorganic particles distributed in the porous matrix. For example, the polymer fibers and inorganic particles of corresponding particle size can be deposited at the same time.

The porous layer of the present application can be implemented with any spinning equipment known in the art, and is not particularly limited, as long as the purpose of the application can be achieved, and any spinning equipment known in the art can be used. For example, the electrospinning equipment can be Yongkang Leye Elite series, etc.; the air spinning equipment can be the air jet spinning machine of Nanjing Genus New Material; the centrifugal spinning equipment can be the centrifugal spinning machine of Sichuan Zhiyan Technology. The electrodeposition method can be implemented with any equipment known in the art, and is not particularly limited, as long as the purpose of the application can be achieved. For example, the electrostatic spraying equipment of Samez, France can be used.

The type of the lithium ion battery according to the present application is not limited, and can be any type of lithium ion battery, such as button type, cylindrical type, soft pack type lithium ion battery and the like. The lithium ion battery according to the present application includes a positive electrode, a negative electrode, an electrolyte, and a porous layer according to the present application. In an embodiment of the present application, the first porous layer may be formed on both surfaces of the positive pole piece, and then follow the manner of the negative pole piece, the first porous layer + the positive pole piece + the first porous layer The lamination is carried out to form a lithium ion battery laminate in which there is no porous layer on the surface of the negative electrode piece. In another embodiment of the present application, the first porous layer may be formed on both surfaces of the negative electrode piece, and then follow the order of the first porous layer + negative electrode piece + first porous layer and positive electrode piece. Lithium-ion battery laminates are formed by stacking in the same manner. In other embodiments of the present application, the first porous layer may be formed on both surfaces of the positive pole piece, the second porous layer is formed on the negative pole piece, and then the second porous layer + negative pole piece + The second porous layer, the first porous layer + the positive pole piece + the first porous layer are laminated to form a lithium ion battery laminate; or the first porous layer is formed on both surfaces of the negative pole piece , The second porous layer is formed on the positive pole piece, and then laminated in the manner of second porous layer + positive pole piece + second porous layer, first porous layer + negative pole piece + first porous layer , Forming a lithium ion battery laminate. The laminated body formed in the above-mentioned embodiment may continue to be laminated in the above-mentioned order, or it may be directly wound to form a multilayer lithium ion battery laminated body. This application does not limit the stacking mode, and those skilled in the art can make a selection according to the actual situation.

In the embodiments of the present application, the positive pole piece is not particularly limited, as long as the purpose of the present application can be achieved. For example, the positive pole piece usually includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. Wherein, the positive electrode current collector is not particularly limited, and may be any positive electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collector. The positive electrode active material is not particularly limited, and can be any positive electrode active material in the prior art. For example, the active material is selected from lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium iron phosphate, lithium cobalt oxide, and manganese acid. At least one of lithium and lithium iron manganese phosphate.

Optionally, the positive pole piece may further include a conductive layer located between the positive electrode current collector and the positive electrode active material. The composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art.

In the embodiments of the present application, the negative pole piece is not particularly limited, as long as it can achieve the purpose of the present application. For example, the negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material layer, and the positive electrode active material layer includes a positive electrode active material. Wherein, the negative electrode current collector is not particularly limited, and any negative electrode current collector known in the art can be used, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collectors. The negative active material is not particularly limited, and any negative active material known in the art can be used. For example, it may include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, silicon carbon, silicon oxygen compound, soft carbon, hard carbon, lithium titanate, or niobium titanate.

The electrolyte of the lithium ion battery is not particularly limited, and any electrolyte known in the art can be used, and the electrolyte can be any of a gel state, a solid state, and a liquid state. For example, the liquid electrolyte includes a lithium salt and a non-aqueous solvent.

The lithium salt is not particularly limited, and any lithium salt known in the art can be used as long as the purpose of the application can be achieved. For example, the lithium salt can be selected from LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ CF ₃ ) ₃ and at least one of _{LiPO 2} F _2. _{For example, LiPF 6} can be used as the lithium salt.

The non-aqueous solvent is not particularly limited, as long as it can achieve the purpose of the present application. For example, as the non-aqueous solvent, at least one of carbonate compounds, carboxylate compounds, ether compounds, nitrile compounds, and other organic solvents can be selected.

For example, the carbonate compound can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC), methyl ethyl carbonate Ester (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), carbonic acid 1 ,2-Difluoroethylene, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1 -Fluoro-2-methylethylene, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluorocarbonate- At least one of 2-methylethylene and trifluoromethylethylene carbonate.

Another aspect of the present application provides an electronic device including the electrochemical device according to the present application.

Test Methods:

Weight of inorganic particles per unit area of porous layer:

Disassemble the lithium-ion battery after discharging to obtain an electrode pad with a porous layer on the surface. A ^{sample of the porous layer with a cross-sectional area of S m 2} is taken, and then the inorganic particles in the sample are separated, dried at 110 ℃, and then weighed. Weight, the weight is mg, and the value of m/S is the weight of the inorganic particles in the porous layer per unit area.

Porosity of porous layer:

The lithium ion battery is disassembled after discharge to obtain an electrode pad with a porous layer on the surface, a part of the porous layer sample is cut, and the porosity of the porous layer is tested by a conventional mercury intrusion method.

Self-discharge rate K value of lithium ion battery:

Discharge the lithium-ion battery to 3.0V at a current of 0.5C, let it stand for 5 minutes, then charge the lithium-ion battery at a constant current of 0.5C to 3.85V, and then charge a constant voltage of 3.85V to a current of 0.05C, Let it stand for two days in an environment of 25℃±3℃, test and record the voltage OCV1 at this time. Next, let the lithium ion battery continue to stand in an environment of 25℃±3℃ for two days, test and record the voltage OCV2 at this time, and obtain the K value by the following formula: K(mV/h)=(OCV2-OCV1)/48h *1000.

Capacity retention rate:

Charge the lithium-ion battery at a constant current of 0.5C to 4.4V, and then charge at a constant voltage of 4.4V to a current of 0.05C, let it stand for 10 minutes in an environment of 25℃±3℃, and then use a current of 0.5C Discharge to 3.0V, record the first discharge capacity as Q ₁ , repeat the cycle for 50 times, record the discharge capacity at this time as Q ₅₀ , obtain the capacity retention rate η after 50 cycles by the following formula: η=Q ₅₀ /Q ₁ * 100%.

Example

Preparation Example 1: Preparation of negative pole piece

The negative active material artificial graphite, conductive carbon black, and styrene-butadiene rubber are mixed in a weight ratio of 96:1.5:2.5, and deionized water is added as a solvent to prepare a slurry with a solid content of 0.7, and stir it evenly. The slurry was uniformly coated on one surface of a copper foil of a negative electrode current collector with a thickness of 10 μm and dried at 110° C. to obtain a negative electrode piece with a thickness of 150 μm on a single side coated with a negative electrode active material layer. The above steps were repeated on the other surface of the negative electrode current collector to obtain a negative electrode sheet coated with a 150 μm thick negative electrode active material layer on both sides. Then, cut the negative pole piece into a size of 41mm×61mm for later use.

Preparation Example 2: Preparation of positive pole piece

The positive electrode active material lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 0.75. Stir well. The slurry was uniformly coated on one surface of the positive electrode current collector aluminum foil and dried at 90° C. to form a positive electrode active material layer with a thickness of 100 μm on one side of the positive electrode current collector. Repeat the above steps on the other surface of the aluminum foil of the positive electrode current collector to obtain a positive electrode piece coated with a positive electrode active material layer of 100 μm on both sides. After the coating is completed, cut the positive pole piece into a size of 38mm×58mm for use.

Preparation Example 3: Preparation of electrolyte

In a dry argon atmosphere, first mix ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) as a solvent at a mass ratio EC:EMC:DEC=30:50:20, and then Add lithium hexafluorophosphate to the solvent, dissolve and mix uniformly, and obtain an electrolyte with a lithium salt concentration of 1.15 mol/L.

The following examples illustrate the preparation of the porous layer according to the present application. In these embodiments, a negative pole piece is taken as an example for description, and a first porous layer is deposited on both surfaces of the negative pole piece. It should be understood that the first porous layer may also be deposited on both surfaces of the positive pole piece, or a first porous layer may be deposited on one surface of the negative pole piece and one surface of the positive pole piece, respectively, These embodiments can also achieve the purpose of this application. Those skilled in the art should understand that these embodiments are also within the protection scope of the present application.

Example 1

Preparation of slurry A: The first inorganic particles of aluminum oxide (Al ₂ O ₃ ) and the binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 90:10, and the solvent N-methylpyrrolidone ( NMP), formulated into slurry A with a solid content of 0.4, in which the average particle size of the first inorganic particles is 60 nm.

Preparation of slurry B: The first inorganic particles of aluminum oxide (Al ₂ O ₃ ) and the binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 90:10, and the solvent N-methylpyrrolidone ( NMP), formulated into slurry B with a solid content of 0.4, in which the average particle size of the first inorganic particles is 300 nm.

Disperse polyvinylidene fluoride in dimethylformamide/acetone (7:3) solvent, stir evenly until the slurry viscosity is stable, and obtain a solution with a mass fraction of 25%. Use the above solution to prepare by electrospinning. A first layer with a thickness of 3μm and an average pore diameter of 20nm was prepared on one surface of the negative electrode piece obtained in Example 1. While electrospinning, using the above-mentioned slurry A as the raw material, the electrospray method was used to the Al ₂ O ₃ particles filled in the first layer, wherein an average particle size of Al ₂ O ₃ particles was 60 nm; gas is then spun through a method of preparing a thickness 9μm thereabove, the average pore size of 100nm In the second layer, while air-spinning, using the above-mentioned slurry B as the raw material, the Al ₂ O ₃ particles are filled in the second layer by the electrospray method, wherein the average particle size of the _{Al 2} O _{3 particles is} 300nm (the micrograph of the second layer of the first porous layer is shown in Figure 1);

Among them, the diameter of the polymer fiber (component is PVDF) in the first layer and the second layer is 100nm, and the porosity of the first porous layer formed by the first layer and the second layer is 80%. The weight per unit area of the first inorganic particles in the first porous layer formed with the second layer is 4.5 g/m ² .

In a completely consistent method, the above steps are also completed on the other surface of the negative pole piece to obtain a negative pole piece coated with the first porous layer on both sides.

One surface of the positive electrode sheet obtained in Preparation Example 2 was electrospinned to prepare a second porous layer (component PVDF) with a thickness of 3 μm and an average pore diameter of 20 nm. While spinning, use Slurry A, using electrospray method to fill Al ₂ O ₃ inorganic particles between the second polymer fibers, the average particle size of the particles is 60 nm;

Wherein, the diameter of the polymer fiber of the second porous layer is 100 nm; the porosity of the second porous layer is 80%.

In a completely consistent method, the above steps are also completed on the other surface of the positive pole piece to obtain a positive pole piece with double-sided coating.

Example 2

The average particle size of the inorganic particles filled in the first layer except the first porous layer on the surface of the negative electrode piece is 400 nm; the average particle size of the inorganic particles filled in the second layer is 2000 nm;

The average particle size of the inorganic particles filled in the second porous layer on the surface of the positive pole piece is 400 nm;

The rest is the same as in Example 1.

Example 3

Except for the first porous layer on the surface of the negative electrode, the average pore size of the first layer is 50nm, and the average particle size of the filled inorganic particles is 100nm; the average pore size of the second layer is 500nm, and the average particle size of the filled inorganic particles is 1000nm;

The average pore diameter of the second porous layer on the surface of the positive pole piece is 50 nm, and the average particle diameter of the filled inorganic particles is 100 nm;

The rest is the same as in Example 1.

Example 4

Except that the average pore size of the second layer of the first porous layer of the negative electrode piece is 1000 nm, and the average particle size of the filled inorganic particles is 2000 nm; the rest is the same as in Example 3.

Example 5

Except that the average pore diameter of the second layer of the first porous layer of the negative electrode piece is 5000 nm, and the average particle diameter of the filled inorganic particles is 10000 nm; the rest is the same as in Example 3.

Example 6

Except for the first porous layer on the surface of the negative electrode, the average pore size of the first layer is 80nm, and the average particle size of the filled inorganic particles is 300nm; the average pore size of the second fiber layer is 400nm, and the average particle size of the filled inorganic particles is 1500nm ；

The average pore diameter of the second porous layer on the surface of the positive pole piece is 80 nm, and the average particle diameter of the filled inorganic particles is 300 nm;

The rest is the same as in Example 1.

Example 7

Except for the surface of the negative pole piece, the first porous layer has an average pore size of 100 nm, and the average particle size of the filled inorganic particles is 10 nm; the average pore size of the second layer is 1000 nm, and the average particle size of the filled inorganic particles is 100 nm;

The average pore diameter of the second porous layer on the surface of the positive pole piece is 100 nm, and the average particle diameter of the filled inorganic particles is 10 nm;

The rest is the same as in Example 1.

Example 8

Except for the first porous layer on the surface of the negative pole piece, the average pore diameter of the first layer is 100 nm, and the average particle diameter of the filled inorganic particles is 200 nm; the average pore diameter of the second fiber layer is 500 nm, and the average particle diameter of the filled inorganic particles is 1000 nm;

The average pore diameter of the second porous layer on the surface of the positive pole piece is 100 nm, and the average particle diameter of the filled inorganic particles is 200 nm;

The rest is the same as in Example 1.

Example 9

Except for the first porous layer on the surface of the negative pole piece, the average pore size of the first layer is 120nm, and the average particle size of the filled inorganic particles is 12nm; the average pore size of the second layer is 600nm, and the average particle size of the filled inorganic particles is 60nm;

The average pore size of the second porous layer on the surface of the positive pole piece is 120nm, and the average particle size of the filled inorganic particles is 12nm;

The rest is the same as in Example 1.

Example 10

Except for the first porous layer on the negative electrode sheet, the average particle size of the inorganic particles filled in the first layer is 120 nm, and the average particle diameter of the inorganic particles filled in the second layer is 600 nm;

The average particle size of the second porous layer filled with inorganic particles on the surface of the positive pole piece is 120 nm;

The rest is the same as in Example 9.

Example 11

Except for the first porous layer on the negative electrode, the average particle size of the inorganic particles filled in the first layer is 400 nm, and the average particle size of the inorganic particles filled in the second layer is 2000 nm;

The average particle size of the second porous layer filled with inorganic particles on the surface of the positive pole piece is 400 nm;

The rest is the same as in Example 9.

Example 12

Except for the first porous layer on the negative electrode, the average particle size of the inorganic particles filled in the first layer is 1200 nm, and the average particle diameter of the inorganic particles filled in the second layer is 6000 nm;

The average particle size of the second porous layer filled with inorganic particles on the surface of the positive pole piece is 1200 nm;

The rest is the same as in Example 9.

Example 13

Except for the first porous layer on the surface of the negative pole piece, the average pore size of the first layer is 180nm, and the average particle size of the filled inorganic particles is 2000m; the average pore size of the second layer is 500nm, and the average particle size of the filled inorganic particles is 10000nm;

The average pore size of the second porous layer on the surface of the positive pole piece is 180 nm, and the average particle size of the filled inorganic particles is 2000 nm;

The rest is the same as in Example 1.

Example 14

Except for the first porous layer on the surface of the negative pole piece, the average pore diameter of the first layer is 1000 nm, and the average particle diameter of the filled inorganic particles is 100 m; the average pore diameter of the second layer is 5000 nm, and the average particle diameter of the filled inorganic particles is 5000 nm;

The average pore diameter of the second porous layer on the surface of the positive pole piece is 1000 nm, and the average particle diameter of the filled inorganic particles is 100 nm;

The rest is the same as in Example 1.

Example 15

Except for the first porous layer on the surface of the negative pole piece, the average pore size of the first layer is 3000nm, and the average particle size of the filled inorganic particles is 8000m; the average pore size of the second layer is 5000nm, and the average particle size of the filled inorganic particles is 10000nm;

The average pore diameter of the second porous layer on the surface of the positive pole piece is 3000 nm, and the average particle diameter of the filled inorganic particles is 8000 nm;

The rest is the same as in Example 1.

Example 16

Except that the second porous layer is not provided, the rest is the same as in Example 6.

Example 17

In addition to controlling the weight of inorganic particles in the first porous layer to 4 mg/m ² ;

The rest is the same as in Example 6.

Example 18

In addition to controlling the weight of inorganic particles in the first porous layer to 60 g/m ² ;

The rest is the same as in Example 6.

Example 19

Except that polyacrylonitrile (PAN) is used as the raw material to prepare the first porous layer and the second porous layer, the rest is the same as in Example 6.

Example 20

Except that polyethylene oxide (PEO) is used as a raw material to prepare the first porous layer and the second porous layer, the rest is the same as in Example 6.

Full battery preparation:

The negative pole piece with the first porous layer prepared in each embodiment and the positive pole piece prepared in the preparation example are opposed and stacked. After fixing the four corners of the entire laminated structure with adhesive tape, it is placed in an aluminum plastic film, and after top-side sealing, liquid injection, and packaging, a lithium-ion laminated battery is finally obtained.

Comparative example 1

Except that neither the first porous layer nor the second porous layer is filled with inorganic particles; the rest is the same as in Example 11.

Comparative example 2

Except that the first layer, the second layer and the second porous layer of the first porous layer are all filled with inorganic particles with an average particle size of 2000 nm; the rest is the same as in Example 11.

Comparative example 3

Except that the first layer, the second layer and the second porous layer of the first porous layer are all filled with inorganic particles with an average particle size of 400 nm; the rest is the same as in Example 11.

Comparative example 4

Except that the first layer of the first porous layer on the surface of the negative pole piece is filled with inorganic particles with an average particle size of 80 nm; the rest is the same as in Example 14.

Comparative example 5

Except that the second layer of the first porous layer on the surface of the negative electrode piece is filled with inorganic particles with an average particle size of 2500 nm; the rest is the same as in Example 2.

The data and test results of each embodiment and comparative example are shown in Table 1.

By comparing Example 11 of the present application with Comparative Examples 1, 2, and 3, it can be seen that when inorganic particles of different particle diameters are filled into the regions of the porous layer with different pore diameters, the self-discharge problem is significantly improved (K Value decreased); the cycle performance of the battery has also been improved (high cycle capacity retention rate).

Comparing Example 14 with Comparative Example 4, and comparing Example 2 with Comparative Example 5, it can be seen that when the particle size of the filled inorganic particles is too large or too small, the self-discharge problem or cycle performance cannot be achieved. Improvement, and only when the ratio of the particle diameter of the filled inorganic particles to the pore diameter of the porous layer satisfies 0.1-20, can the self-discharge problem and cycle efficiency be improved or improved.

The above are only preferred embodiments of this application, and are not intended to limit this application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included in the protection of this application. Within the range.

Claims

An electrochemical device, which includes:

A first pole piece, and a first porous layer disposed on the surface of the first pole piece;

Second pole piece

Wherein, the first porous layer includes first polymer fibers and first inorganic particles. In the thickness direction of the first porous layer, the first polymer fibers are located far away from the first pole piece. The average pore diameter of the pores formed in the region is Aμm, the average pore diameter of the pores formed by the first polymer fiber in the region close to the first pole piece is Bμm, and the first inorganic particles are moving away from the first pole piece. The average particle size of the region of is Cμm, and the average particle size of the first inorganic particles in the region close to the first pole piece is Dμm, and the following relationship is satisfied:

(a) A>B;

(b) C>D.
The electrochemical device according to claim 1, wherein the first porous layer comprises a first layer and a second layer, the first layer is a region close to the first pole piece, and the second layer Is the area away from the first pole piece.
The electrochemical device according to claim 1, wherein the value range of A is 0.05 to 5, the value range of B is 0.02 to 3, and the value range of C is 0.01 to 10. The value range of D is 0.01～10.
The electrochemical device according to any one of claims 1 to 3, wherein the A, the B, the C, and the D satisfy at least one of the following relationships:

(a) 1.01≤A/B≤250;

(b) 1.01≤C/D≤500;

(c) 0.1≤C/A≤20;

(d) 0.1≤D/B≤20.
The electrochemical device according to claim 1, wherein in the thickness direction of the first porous layer, the average particle size of the first inorganic particles is from a region close to the first pole piece to a distance away from the The area of the first pole piece continuously increases.
The electrochemical device according to claim 1, wherein, in the thickness direction of the first porous layer, the average pore diameter of the pores formed by the first polymer fiber is from a region close to the first pole piece to The area away from the first pole piece continuously increases.
The electrochemical device according to claim 1, wherein the diameter of the first polymer fiber is 0.1 nm to 10 μm.
The electrochemical device according to claim 1, wherein:

The porosity of the first porous layer is 30% to 95%; the thickness of the first porous layer is 1 μm to 20 μm.
The electrochemical device according to claim 1, wherein the weight of the first inorganic particles in the first porous layer per unit area is 0.004 g/m 2 to 60 g/m 2 .
The electrochemical device according to claim 1, wherein the composition of the first polymer fiber includes polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, Polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene or polyethylene oxide At least one of.
The electrochemical device according to claim 1, wherein the first inorganic particles comprise HfO 2 , SrTiO 3 , SnO 2 , CeO 2 , MgO, NiO, CaO, BaO, ZnO, ZrO 2 , Y 2 O 3 , Al 2 O 3 , TiO 2 , SiO 2 , boehmite, magnesium hydroxide, aluminum hydroxide, lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium germanium thiophosphate, Lithium nitride, SiS 2 glass, P 2 S 5 glass, Li 2 O, LiF, LiOH, Li 2 CO 3 , LiAlO 2 , Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2- At least one of GeO 2 ceramics or garnet ceramics.
The electrochemical device according to claim 1, wherein the second pole piece further comprises a second porous layer disposed on the surface of the second pole piece, and the second porous layer comprises a second polymer Fibers and second inorganic particles, the average pore diameter of the pores formed by the second polymer fiber is Eμm, the average particle diameter of the second inorganic particles is Fμm, and the following relationship is satisfied:

(a) A>E;

(b) C>F.
The electrochemical device according to claim 12, wherein the first porous layer and the second porous layer are in contact.
An electronic device comprising the electrochemical device according to any one of claims 1-13.