CN213878153U

CN213878153U - Pole piece, electrochemical device and electronic device

Info

Publication number: CN213878153U
Application number: CN202022910761.4U
Authority: CN
Inventors: 金娟; 吴飞; 张�浩; 汪颖
Original assignee: Ningde Amperex Technology Ltd; Dongguan Poweramp Technology Ltd
Current assignee: Ningde Amperex Technology Ltd; Dongguan Poweramp Technology Ltd
Priority date: 2020-12-04
Filing date: 2020-12-04
Publication date: 2021-08-03
Anticipated expiration: 2030-12-04

Abstract

Embodiments of the present application provide a pole piece, an electrochemical device, and an electronic device. The pole piece includes a current collector and a first active material layer disposed on the current collector. The first active material layer includes a first portion, a second portion, and a third portion between the first portion and the second portion in a width direction of the pole piece. The density of the first portion and the second portion is greater than the density of the third portion. The embodiment of this application is through controlling the density of the first active material layer to the pole piece, makes the density of the first part of first active material layer and second part all be greater than the density of third part, can make the different positions of pole piece absorb electrolyte at the circulation in-process uniformly to temperature variation is more even, thereby improves electrochemical device's wholeness ability.

Description

Pole piece, electrochemical device and electronic device

Technical Field

The present application relates to the field of electrochemical technologies, and in particular, to a pole piece, an electrochemical device, and an electronic device.

Background

The electrochemical device can generate a large amount of heat in the large-current charging and discharging process, and the heat accumulation can affect the service life and the performance of the electrochemical device. The end of the electrode assembly of the electrochemical device is easy to dissipate heat due to good heat dissipation conditions, and the middle of the electrode assembly is difficult to dissipate heat, which can cause large temperature imbalance. In addition, the electrolyte infiltration on the two sides of the electrode assembly is good, the dynamic performance is good, the electrolyte infiltration in the middle part is poor, and the dynamic imbalance in the electrochemical device is brought. The imbalance in the temperature and the distribution of the electrolyte have an influence on the life and performance of the electrochemical device.

SUMMERY OF THE UTILITY MODEL

The embodiment of the application gives consideration to the energy density and the high-power discharge capacity of the electrochemical device through the control of the pole piece density.

Embodiments of the present application provide a pole piece including a current collector and a first active material layer. A first active material layer is disposed on the current collector, the first active material layer including a first active material. The first active material layer includes a first portion, a second portion, and a third portion between the first portion and the second portion in a width direction of the pole piece. The density of the first portion is greater than the density of the third portion, and the density of the second portion is greater than the density of the third portion.

In some embodiments, the thickness of the first portion is less than the thickness of the third portion, and the thickness of the second portion is less than the thickness of the third portion.

In some embodiments, the pole piece further comprises a material layer disposed between the current collector and the first active material layer. The material layer has a first material layer, a second material layer, and a third material layer corresponding to the first portion, the second portion, and the third portion, respectively. The thickness of the first material layer is larger than that of the third material layer, and the thickness of the second material layer is larger than that of the third material layer.

In some embodiments, the sum of the thicknesses of the first portion and the first material layer is a first thickness, the sum of the thicknesses of the second portion and the second material layer is a second thickness, and the sum of the thicknesses of the third portion and the third material layer is a third thickness, the first thickness, the second thickness, and the third thickness being the same as one another.

In some embodiments, the material layer includes at least one of a second active material, a conductive agent, or a binder.

Another embodiment of the present application provides an electrochemical device including an electrode assembly including a first pole piece, a second pole piece, and a separator. The separator is disposed between the first and second pole pieces. In some embodiments, at least one of the first or second pole pieces is a pole piece as described in any of the above.

In some embodiments, the thickness of the first portion is less than the thickness of the third portion, and the thickness of the second portion is less than the thickness of the third portion. The separation film has fourth, fifth and sixth portions corresponding to the first, second and third portions, respectively, a thickness of the fourth portion being greater than a thickness of the sixth portion, and a thickness of the fifth portion being greater than a thickness of the sixth portion.

In some embodiments, a sum of thicknesses of the first portion and the fourth portion is a fourth thickness, a sum of thicknesses of the second portion and the fifth portion is a fifth thickness, a sum of thicknesses of the third portion and the sixth portion is a sixth thickness, and the fourth thickness, the fifth thickness, and the sixth thickness are the same as each other.

In some embodiments, the electrode assembly is a laminate structure, and the first active material layer includes a central region and a peripheral region surrounding the central region. The central region is part of the third portion and the peripheral region includes the first portion, the second portion, and part of the third portion. The density of the peripheral region is greater than the density of the central region.

In some embodiments, the electrode assembly is in a winding structure, a density of the third portion near a winding start end is less than a density of the third portion far from the winding start end in a winding direction, the winding direction being perpendicular to a length direction of the pole piece.

Embodiments of the present application also provide an electronic device including the above electrochemical device.

The embodiment of this application is through controlling the density of the first active material layer to the pole piece, makes the density of the first part of first active material layer and second part all be greater than the density of third part, can make the different positions of pole piece absorb electrolyte at the circulation in-process uniformly to temperature variation is more even, thereby improves electrochemical device's wholeness ability.

Drawings

Fig. 1 shows a front view of a pole piece of an embodiment of the present application.

Fig. 2 shows a front view of a pole piece of another embodiment of the present application.

Fig. 3 shows a front view of a pole piece of another embodiment of the present application.

Fig. 4 shows a front view of a pole piece of another embodiment of the present application.

Fig. 5 shows a front view of a pole piece of another embodiment of the present application.

Fig. 6 shows a schematic view of an electrochemical device of an embodiment of the present application.

Fig. 7 shows a schematic view of a portion of an electrochemical device of an embodiment of the present application.

Fig. 8 shows a top view of a pole piece of an embodiment of the present application.

Detailed Description

The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.

Fig. 1 shows a front view (cross-sectional view in the width direction of the pole piece) of the pole piece of an embodiment of the present application. The pole piece may include a current collector 10 and a first active material layer 11 disposed on the current collector 10, the first active material layer 11 including a first active material, it being understood that the first active material layer 11 may further include a conductive agent and a binder.

The first active material layer 11 includes a first portion 111, a second portion 112, and a third portion 113 between the first portion 111 and the second portion 112 in the width direction of the pole piece. It should be understood that although the first portion 111, the second portion 112 and the third portion 113 are distinguished by dashed lines in fig. 1, there may not be a demarcation at the dashed lines in practice. In some embodiments, the density of the first portion 111 and the second portion 112 is greater than the density of the third portion 113. It is to be understood that the ratio of the width of the first portion 111 or the second portion 112 to the width of the active material layer 11 may be set as desired, for example, (0,1/3], although other suitable values may be used.

In the present application, the density of the first portion 111 may be the compacted density of the first portion 111, i.e. the bulk density of the material contained in the first portion 111. The thickness h of the first portion 111 can be measured by cutting a pole piece with a certain area s, scraping the first portion 111 and weighing m, so that the density of the first portion 111 is m/(s × h).

In some embodiments, the density of each of the first and

second portions

111 and 112 may be greater than the density of the third portion 113 by forming more of the first active material at the first and

second portions

111 and 112. For example, the coating weights of the first part 111 and the second part 112 are 120g/mm²The cold pressing thickness is 60 mu m, and the density is 2g/cm³The third portion 113 had a coating weight of 60g, a cold-pressed thickness of 60 μm and a density of 1g/cm³. By enabling the densities of the first portion 111 and the second portion 112 to be greater than the density of the third portion 113, and enabling the third portion 113 with smaller density to have more gaps, the electrolyte of the third portion 113 can be conveniently infiltrated, the problem that the electrolyte is difficult to infiltrate at the third portion 113 is solved, the infiltration of the electrolyte is more uniform, and the high-power discharge capacity of the electrochemical device is favorably improved. In addition, since the density of the first and

second portions

111 and 112 is large, the energy density of the electrochemical device is also improved. Therefore, the design of the pole piece gives consideration to the energy density and the high-power discharge capacity of the electrochemical device, and the overall performance of the electrochemical device is improved。

As shown in fig. 2, in some embodiments, the thickness d1 of the first portion 111 and the thickness d2 of the second portion 112 are both less than the thickness d3 of the third portion 113. In some embodiments, if the thicknesses of the first portion 111, the second portion 112, and the third portion 113 are not uniform, the thicknesses may refer to average thicknesses of the respective regions. As shown in fig. 3, the thickness d1 of the first portion 111 and the thickness d2 of the second portion 112 are both less than the thickness d3 of the third portion 113. In some embodiments, the thickness d1 of the first portion 111 and the thickness d2 of the second portion 112 may be the same. As also shown in fig. 3, in some embodiments, the thickness of the first active material layer 11 continuously decreases from the third portion 113 to the first portion 111 and from the third portion 113 to the second portion 112; in some embodiments, the thickness of the first active material layer 11 may also be discretely reduced from the third portion 113 to the first portion 111 and from the third portion 113 to the second portion 112.

In some embodiments, different thicknesses at different regions may be achieved by differences in the cold pressing pressure of the different regions. Therefore, the first portion 111 and the second portion 112 are large in density and small in thickness, and the third portion 113 is small in density and large in thickness, so that the electrolyte of the third portion 113 can be conveniently infiltrated, the problem that the electrolyte is difficult to infiltrate at the third portion 113 is solved, the infiltration of the electrolyte is more uniform, and the high-power discharge capacity of the electrochemical device is improved.

As shown in fig. 4, in some embodiments, the pole piece further includes a material layer 12 disposed between the current collector 10 and the first active material layer 11. In some embodiments, the material layer 12 has a first material layer 121, a second material layer 122, and a third material layer 123 corresponding to the first portion 111, the second portion 112, and the third portion 113 of the first active material layer 11, respectively. In some embodiments, the thickness d4 of the first material layer 121 and the thickness d5 of the second material layer 122 are both greater than the thickness d6 of the third material layer 123. By making the thickness d4 of the first material layer 121 and the thickness d5 of the second material layer 122 both greater than the thickness d6 of the third material layer 123, the deficiency of the thicknesses of the first part 111 and the second part 112 can be made up, the overall thickness of the pole piece tends to be balanced, and the surface flatness of the pole piece is improved.

In some embodiments, the material layer 12 includes at least one of a second active material, a conductive agent, or a binder.

In some embodiments, the material layer 12 includes a second active material, which may further increase the energy density. In some embodiments, the material layer 12 includes a conductive agent, and a conductive layer is disposed between the first active material layer 11 and the current collector 10, so as to improve the conductive capability between the first active material layer 11 and the current collector 10, and further improve the high-rate discharge capability. In some embodiments, the material layer 12 includes an adhesive, so that the adhesion of the edge of the pole piece is better, the first portion 111 and the second portion 112 of the first active material layer 11 and the current collector 10 are less prone to peeling, the problems of powder falling and demolding of the pole piece during processing such as slitting or die cutting are prevented, and the safety, reliability and service life of the pole piece are improved.

In some embodiments, the sum of the thicknesses of the first portion 111 and the first material layer 121 is a first thickness (d1+ d4), the sum of the thicknesses of the second portion 112 and the second material layer 122 is a second thickness (d2+ d5), the sum of the thicknesses of the third portion 113 and the third material layer 123 is a third thickness (d3+ d6), and the first thickness, the second thickness, and the third thickness are the same as each other, i.e., d1+ d4, d2+ d5, d3+ d 6. Therefore, the thickness of the pole piece is guaranteed to be uniform.

In some embodiments, as shown in fig. 5, the thickness of the material layer 12 increases continuously from the third material layer 123 to the first material layer 121 and from the third material layer 123 to the second material layer 122. In some embodiments, the thickness of the material layer 12 may also increase discretely from the third material layer 123 to the first material layer 121 and from the third material layer 123 to the second material layer 122.

In some embodiments, the conductive agent comprises at least one of conductive carbon black, conductive graphite, acetylene black, conductive carbon fibers, carbon nano-segments, graphene, or metal powder. In some embodiments, the binder comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, or styrene butadiene latex. In some embodiments, the mass ratio of the conductive agent to the binder in the material layer 12 is 2:8 to 8:2, although other suitable materials and mass ratios may be used.

In some embodiments, although it is illustrated in fig. 1 to 5 that the first active material layer 11 is disposed on only one side of the current collector 10, it is understood that the first active material layer 11 may be disposed on both sides of the current collector 10.

As shown in fig. 6, an embodiment of the present application also provides an electrochemical device 60, the electrochemical device 60 including an electrode assembly including a first pole piece 61, a second pole piece 62, and a separator 63 disposed between the first pole piece 61 and the second pole piece 62. In some embodiments, at least one of the first pole piece 61 and the second pole piece 62 is a pole piece as described above. In some embodiments, the first pole piece 61 may be a positive pole piece, and the second pole piece 62 may be a negative pole piece. In some embodiments, the first pole piece 61 may be a negative pole piece, and the second pole piece 62 may be a positive pole piece.

For better explanation, the positive electrode tab 61 and the separator 63 will be described below as an example, and the negative electrode tab 62 and the separator 63 may be disposed correspondingly.

In some embodiments, as described above, the thickness d1 of the first portion 111 and the thickness d2 of the second portion 112 are both less than the thickness d3 of the third portion 113. In some embodiments, as shown in fig. 7, the isolation film 63 includes an isolation film substrate 631 and an isolation film coating 632. In some embodiments, the thickness of the isolation film 63 may not be uniform, which may be caused by the non-uniform thickness of the isolation film substrate 631, the non-uniform thickness of the isolation film coating 632, or both. For convenience of explanation, the following description will be given by taking the example of the uneven thickness of the separator coating 632, but this is not intended to limit the present application. As shown in fig. 7, the release film coating 632 includes a first coating 6321, a second coating 6322, and a third coating 6323, and the first coating 6321 and the second coating 6322 each have a thickness greater than that of the third coating 6323. In some embodiments, the separation film 63 has fourth, fifth, and sixth portions corresponding to the first, second, and

third portions

111, 112, and 113 of the first active material layer 11, respectively, which are the corresponding portions of the first, second, and

third coating layers

6321, 6322, and 6323 plus the separation film substrate 631, respectively. Since the thickness of each of the first and

second coating layers

6321 and 6322 is greater than that of the third coating layer 6323 and the thickness of the release film substrate 631 is uniform, the thickness d7 of the first portion and the thickness d8 of the second portion are greater than the thickness d9 of the third portion.

In some embodiments, the sum of the thicknesses of the first portion 111 and the fourth portion is a fourth thickness (d1+ d7), the sum of the thicknesses of the second portion 112 and the fifth portion is a fifth thickness (d2+ d8), the sum of the thicknesses of the third portion 113 and the sixth portion is a sixth thickness (d3+ d9), and the fourth thickness, the fifth thickness, and the sixth thickness are the same as one another, i.e., d1+ d7 ═ d2+ d8 ═ d3+ d 9. In this manner, the thickness of the electrode assembly of the electrochemical device 60 is made uniform throughout by the thickness of the separation film 63.

In some embodiments, as described above, the pole piece may further include the material layer 12, and the material layer 12 and the separator 63 may jointly ensure that the thickness of the electrode assembly of the electrochemical device 60 is uniform throughout, for example, d1+ d4+ d7 ═ d2+ d5+ d8 ═ d3+ d6+ d 9.

In some embodiments, the electrode assembly is a wound structure in which the first pole piece 61, the separator 63, and the second pole piece 62 are sequentially wound in layers. The density of the third portion 113 near the winding start end is less than the density of the third portion 113 far from the winding start end in the winding direction, which is perpendicular to the length direction of the pole piece. That is, the density of the third portion 113 near the initial portion of the winding structure is smaller, and the number of voids is relatively larger, which is beneficial to promoting the infiltration of the electrolyte, and overcomes the problem of uneven infiltration of the electrolyte at the inner side and the outer side of the winding structure. In addition, since the density of the portion of the third portion 113 away from the starting end of the winding structure is greater, the energy density of the electrochemical device 60 can also be increased.

Fig. 8 shows a top view of the active material layer 11. In some embodiments, the electrode assembly is a laminate structure. As shown in fig. 8, the first active material layer 11 includes a central region 81 and a peripheral region 82 surrounding the central region 81. In some embodiments, the central region 81 is part of the third portion 113 and the peripheral region 82 comprises the first portion 111, the second portion 112, and a portion of the third portion 113, wherein the first portion 111, the second portion 112, and the portion of the third portion 113 are schematically distinguished by a dashed line, and indeed there may be no boundary between them. In some embodiments, the density of the peripheral region 82 is greater than the density of the central region 81. Because the density of the central area 81 is relatively small, and the gaps are relatively more, the infiltration of the electrolyte is facilitated, and the problem that the central area 81 is not beneficial to the infiltration of the electrolyte is solved. In addition, since the density of the peripheral region 82 is high, the energy density of the electrochemical device can be increased.

In some embodiments, the thickness of the peripheral region 82 may be less than the thickness of the central region 81, e.g., the thickness of the first active material 11 may decrease discretely or continuously from the central region 81 to the peripheral region 82. In some embodiments, the overall uniformity of the thickness of the electrode assembly of the electrochemical device 60 may be achieved by the material layer 12 and the separation film 63, which may be referred to the above description and will not be described herein.

Therefore, through the gradient design of the density from the middle to the two sides of the pole piece, a multilayer gradient with the kinetic performance sequentially increased from the two sides to the middle can be formed, the electrolyte infiltration performance and the temperature change balance between the two sides and the middle of the electrode assembly of the electrochemical device are ensured, and the energy density and the high-power discharge capacity of the electrochemical device are improved. In addition, through setting up the material layer that thickness changes, guaranteed the whole even of pole piece thickness on the one hand, on the other hand guarantees that the adhesion of pole piece both sides is better, prevents the pole piece in the course of working such as slitting or cross cutting powder falling and the demoulding problem. In addition, the overall uniformity of the thickness of the electrode assembly of the electrochemical device is ensured by providing the separation film having a varying thickness.

In some embodiments, when the first electrode sheet 61 is a positive electrode sheet, the current collector 10 may be an aluminum foil, but other positive electrode current collectors commonly used in the art may also be used. In addition, the first active material layer 11 may include a positive electrode active material, a binder, and a conductive agent. The positive active material may include at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium nickel manganate. The conductive agent in the first active material layer 11 of the positive electrode tab 61 may include at least one of conductive carbon black, ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. The binder in the first active material layer 11 of the positive electrode tab 61 may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefin, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber, or polyvinyl alcohol. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the first active material layer 11 may be 92 to 98.5: 0.5-3: 1 to 5. It should be understood that the above description is merely an example, and any other suitable material, thickness, and mass ratio may be employed for the first active material layer 11 of the positive electrode tab 61.

In some embodiments, when the first pole piece 62 is a negative pole piece, the current collector 10 may be at least one of a copper foil, a nickel foil, or a carbon-based current collector, although other negative pole current collectors commonly used in the art may also be used. In addition, the first active material layer 11 may include a negative active material, a binder, and a conductive agent. The negative active material may include at least one of artificial graphite, natural graphite, hard carbon, mesocarbon microbeads, a silicon alloy, a tin alloy, or pure silicon. The conductive agent in the first active material layer 11 of the negative electrode tab 62 may include at least one of conductive carbon black, ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers. The binder in the first active material layer 11 of the negative electrode tab 62 may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefin, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethylcellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber, or polyvinyl alcohol. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent, and the binder in the first active material layer 11 may be 92 to 98.5: 0.5-3: 1 to 5. It will be appreciated that the above description is merely an example and that any other suitable mass ratio may be employed.

The second active material may be the same or different from the first active material.

In some embodiments, the release film substrate 631 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the isolation film 63 is in the range of about 5 μm to 500 μm.

In some embodiments, a release film coating 632 is disposed on at least one surface of the release film substrate 631, the release film coating 632 including inorganic particles selected from alumina (Al) and a binder₂O₃) Silicon oxide (SiO)₂) Magnesium oxide (MgO), titanium oxide (TiO)₂) Hafnium oxide (HfO)₂) Tin oxide (SnO)₂) Cerium oxide (CeO)₂) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)₂) Yttrium oxide (Y)₂O₃) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the binder of the barrier film coating 632 is selected from at least one of polyvinylidene fluoride, copolymers of vinylidene fluoride-hexafluoropropylene, polyamides, polyacrylonitrile, polyacrylates, polyacrylic acids, polyacrylates, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

In some embodiments, the electrochemical device 60 comprises a lithium ion battery, although the application is not so limited. In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent. The lithium salt is selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆One or more of LiBOB or lithium difluoroborate. For example, LiPF is selected as lithium salt₆Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be selected from carbonate compounds, carboxylate compounds, ether compounds, other organic solvents, or combinations thereof.

The carbonate compound may be selected from a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

The chain carbonate compound may be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), or a combination thereof. The fluoro carbonate compound may be selected from Fluoro Ethylene Carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof.

The carboxylate compound may be selected from methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.

The ether compound may be selected from dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

The other organic solvent may be selected from the group consisting of dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, or combinations thereof.

In some embodiments of the present application, taking a lithium ion battery as an example, a positive electrode plate, a separator, and a negative electrode plate are sequentially wound or stacked to form an electrode member, and then the electrode member is placed in, for example, an aluminum plastic film for packaging, and an electrolyte is injected into the electrode member for formation and packaging, so as to form the lithium ion battery. And then, performing performance test on the prepared lithium ion battery.

Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.

Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Claims

1. A pole piece, comprising:

a current collector;

a first active material layer disposed on the current collector, the first active material layer including a first active material;

wherein, in the width direction of the pole piece, the first active material layer comprises a first part, a second part and a third part positioned between the first part and the second part, the density of the first part is greater than that of the third part, and the density of the second part is greater than that of the third part.

2. The pole piece of claim 1 wherein the thickness of the first portion is less than the thickness of the third portion and the thickness of the second portion is less than the thickness of the third portion.

3. The pole piece of claim 1, further comprising a material layer disposed between the current collector and the first active material layer,

the material layers include a first material layer, a second material layer, and a third material layer corresponding to the first portion, the second portion, and the third portion, respectively,

the thickness of the first material layer is larger than that of the third material layer, and the thickness of the second material layer is larger than that of the third material layer.

4. The pole piece of claim 3 wherein the sum of the thicknesses of the first portion and the first material layer is a first thickness, the sum of the thicknesses of the second portion and the second material layer is a second thickness, and the sum of the thicknesses of the third portion and the third material layer is a third thickness, the first thickness, the second thickness, and the third thickness being the same as one another.

5. An electrochemical device comprising an electrode assembly, the electrode assembly comprising:

a first pole piece;

a second pole piece;

a separator disposed between the first and second pole pieces;

wherein at least one of the first or second pole pieces is a pole piece according to any one of claims 1 to 4.

6. The electrochemical device of claim 5, wherein a thickness of the first portion is less than a thickness of the third portion, a thickness of the second portion is less than a thickness of the third portion,

the isolation film comprises a fourth portion, a fifth portion and a sixth portion which correspond to the first portion, the second portion and the third portion respectively, the thickness of the fourth portion is larger than that of the sixth portion, and the thickness of the fifth portion is larger than that of the sixth portion.

7. The electrochemical device according to claim 6, wherein a sum of thicknesses of the first portion and the fourth portion is a fourth thickness, a sum of thicknesses of the second portion and the fifth portion is a fifth thickness, a sum of thicknesses of the third portion and the sixth portion is a sixth thickness, and the fourth thickness, the fifth thickness, and the sixth thickness are the same as each other.

8. The electrochemical device according to claim 5, wherein the electrode assembly has a winding structure in which a density of the third portion near a winding start end is less than a density of the third portion away from the winding start end in a winding direction perpendicular to a length direction of the electrode sheet.

9. An electronic device characterized by comprising the electrochemical device according to any one of claims 5 to 8.