WO2023184182A1

WO2023184182A1 - Electrochemical device and electronic device

Info

Publication number: WO2023184182A1
Application number: PCT/CN2022/083833
Authority: WO
Inventors: 关文浩; 陈茂华; 谢远森; 鲁宇浩
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-29
Filing date: 2022-03-29
Publication date: 2023-10-05
Also published as: CN117730426A

Abstract

An electrochemical device (200) and an electronic device. The electrochemical device (200) comprises a negative electrode sheet (120), a positive electrode sheet (110), isolation membranes (130) and an electrolyte, the negative electrode sheet (120) comprising polymeric dielectric material layers (123), and the electrolyte comprising carbonate. By means of providing the polymeric dielectric material layers (123), the surface potential of the negative electrode sheet (120) can be increased, so that the surface potential thereof is higher than the nucleation potential of metal cations, and metal cation deposition of the negative electrode sheet (120) is inhibited; and meanwhile, a carbonate compound in the electrolyte can form on the surface of the negative electrode sheet (120) a stable SEI film having a low impedance, thereby reducing the internal resistance generated by intercalation/deintercalation of metal cations with respect to the negative electrode sheet (120) during a circulation process.

Description

Electrochemical devices and electronic devices

Technical field

The present application relates to the field of electrochemistry, and in particular, to an electrochemical device and an electronic device.

Background technique

Electrochemical devices such as lithium-ion batteries have the advantages of large specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the electronic field. With the rapid development of electric vehicles and mobile electronic devices, people have higher and higher demands for battery energy density, safety, cycle performance and other related requirements.

Among them, the fast charging performance of electrochemical devices is becoming more and more popular among users. As one of the main technical points to improve fast charging performance, the negative electrode plate of electrochemical devices plays an important role in the charge and discharge rate performance of electrochemical devices. . Taking lithium-ion batteries as an example, during the fast charging process, a large number of lithium ions are quickly released from the positive electrode plate, pass through the isolation membrane through mass transfer through the electrolyte, and are embedded in the material of the negative electrode plate. However, when there are flaws in the design of the electrochemical device, When abnormal conditions such as changes in the structure of the electrochemical device occur, lithium ions from the positive electrode sheet may not be quickly embedded into the material of the negative electrode sheet, and lithium ions precipitate on the surface of the negative electrode sheet, resulting in severe capacity loss and even the risk of short circuit.

Contents of the invention

The present application provides an electrochemical device and an electronic device, which can solve the problem of metal cation precipitation from the negative electrode plate in the electrochemical device and reduce the internal resistance of the electrochemical device during the cycle.

In a first aspect, the present application provides an electrochemical device, including a negative electrode piece, a positive electrode piece, and an electrolyte. The negative electrode piece includes a polymer dielectric material layer, and the electrolyte includes carbonate.

In some exemplary embodiments, when the polymer dielectric material layer is placed in an electric field with an electric field intensity of 10 kV/mm to 200 kV/mm for polarization, after the electric field is removed, the polymer dielectric material layer The residual polarization intensity is 50mC/m ² ~ 100mC/m ² .

In some exemplary embodiments, the polymer dielectric material layer includes a polymer dielectric material, the molecular segments of the polymer dielectric material include structural units with polar functional groups, and the polar The functional groups are asymmetrically distributed in the structural units.

In some exemplary embodiments, the polar functional group includes at least one of amide group, fluorine, chlorine, bromine, carboxylic acid group, ester group, and cyano group.

In some exemplary embodiments, the polymer dielectric material includes a copolymer of polyvinylidene fluoride with dielectric effect, a copolymer of polyvinylidene fluoride and trifluoroethylene, and a copolymer of polyvinylidene fluoride and tetrafluoroethylene. At least one of copolymers, odd-numbered nylon dielectric polymers and amorphous dielectric polymers;

The molecular formula of the odd-numbered nylon dielectric polymer is -(HN-(CH ₂ ) _x -CO-)n-, x is an even number, and n is any positive integer;

The amorphous dielectric polymer includes vinylidene dicyanide/vinyl acetate copolymer, vinylidene dicyanide/vinyl benzoate copolymer, vinylidene dicyanide/vinyl propionate copolymer, vinylidene dicyanide/vinyl propionate copolymer, and vinylidene dicyanide/vinyl benzoate copolymer. /At least one of vinylene pivalate copolymer, vinylidene dicyanide/methyl methacrylate copolymer, and vinylidene dicyanide/isobutylene copolymer.

In some exemplary embodiments, the polymer dielectric material satisfies one of the following conditions:

(I) In the copolymer of polyvinylidene fluoride and polytrifluoroethylene, the copolymerization ratio of polytrifluoroethylene is 20 mol% to 70 mol%;

(II) In the copolymer of polyvinylidene fluoride and polytetrafluoroethylene, the copolymerization ratio of the polytetrafluoroethylene monomer is 30 mol% or less;

(III) In the amorphous dielectric polymer, the copolymerization ratio of vinylidene dicyanide is 30 mol% to 80 mol%.

In some exemplary embodiments, the coercive field strength of the polymer dielectric material at 25° C. is greater than 30 kV/mm and less than 200 kV/mm.

In some exemplary embodiments, the thickness of the polymer dielectric material layer is 0.1 μm to 5 μm.

In some exemplary embodiments, the carbonate includes at least one of saturated carbonate or unsaturated carbonate.

In some exemplary embodiments, the saturated carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate.

In some exemplary embodiments, the unsaturated carbonate includes at least one of vinylene carbonate and fluoroethylene carbonate.

In some exemplary embodiments, the electrochemical device satisfies one of the following conditions:

(a) When the polymer dielectric material layer is placed in an electric field with an electric field intensity of 10kV/mm to 200kV/mm for polarization, after the electric field is removed, the residual polarization intensity of the polymer dielectric material layer is 70mC /m ² ~100mC/m ² ;

(b) The coercive field strength of the polymer dielectric material at 25°C is 30kV/mm to 50kV/mm.

(c) The thickness of the polymer dielectric material layer is 0.1 μm to 3 μm.

In a second aspect, this application provides a method for preparing an electrochemical device, including:

The polymer dielectric material is first coated on the surface of the negative electrode piece, and then polarized to obtain a polymer dielectric material layer; or,

The polymer dielectric material layer is first subjected to polarization treatment, and then the polarized polymer dielectric material layer is attached to the surface of the negative electrode plate to obtain a polymer dielectric material layer.

In some exemplary embodiments, the polymer dielectric material is placed in a parallel electric field for polarization treatment, and the range of the field strength of the parallel electric field is the correction value of the polymer dielectric material at 25°C. 0.1 times to 6 times the refractory field strength.

In a third aspect, the present application provides an electronic device, including the electrochemical device as described above.

Based on the electrochemical device and electronic device of the present application, the electrochemical device includes a negative electrode piece, a positive electrode piece, and an electrolyte. The negative electrode piece includes a polymer dielectric material layer, and the electrolyte includes carbonate. Setting a polymer dielectric material layer on the surface of the negative electrode piece can increase the surface potential of the negative electrode piece, making its surface potential higher than the nucleation potential of metal cations, inhibiting the precipitation of metal cations from the negative electrode piece, and at the same time, the carbonate compound in the electrolyte can A stable and low-resistance SEI film is formed on the surface of the negative electrode piece, which reduces the internal resistance caused by the insertion/extraction of metal cations in the negative electrode piece during the cycle.

Description of drawings

In order to explain the embodiments of the present application or the technical solutions in the prior art more clearly, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only These are some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a partial cross-sectional view of an electrochemical device implemented in the present application;

Figure 2 is a cross-sectional view of a stacked positive electrode piece and a negative electrode piece of an electrode assembly according to an implementation of the present application;

Figure 3 is a cross-sectional view of a polymer dielectric material layer disposed on the surface of an isolation film according to one implementation of the present application;

Figure 4 is a cross-sectional view of a polymer dielectric material layer disposed on the surface of the isolation film and the surface of the negative electrode sheet in one implementation of the present application;

Figure 5 is a cross-sectional view of a polymer dielectric material layer disposed on the surface of the negative electrode plate in one implementation of the present application;

Figure 6a is a schematic diagram of the α-phase PVDF molecular chain before polarization in one implementation of the present application;

Figure 6b is a schematic diagram of the β-phase PVDF molecular chain before polarization in one implementation of the present application;

Reference signs:

100. Electrode assembly;

110. Positive electrode piece; 111. Positive current collector; 112. Positive active material layer;

120. Negative electrode plate; 121. Negative electrode current collector; 122. Negative electrode active material layer; 123. Polymer dielectric material layer;

130. Isolation film;

200. Electrochemical device;

210. Outer packaging; 210a. Internal space.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

As shown in FIG. 1 , it is a schematic structural diagram of an electrochemical device 200 according to an embodiment of the present application. The electrochemical device 200 includes an outer package 210 , an electrolyte, and an electrode assembly 100 . In this application, the electrode assembly 100 includes a negative electrode piece 120 , a positive electrode piece 110 and an isolation film 130 . The electrode assembly 100 is disposed in the inner space 210a of the outer package 210, and the electrolyte is filled in the inner space 210a of the outer package 210. The electrochemical device 200 is not particularly limited in this application, and may include, but is not limited to, lithium-ion batteries or sodium-ion batteries.

As shown in FIG. 2 , it is a schematic structural diagram of an electrode assembly 100 according to an embodiment of the present application. The electrode assembly 100 includes a positive electrode piece 110 , a negative electrode piece 120 and an isolation film 130 . The isolation film 130 is disposed between the positive electrode piece 110 and the negative electrode. Between the pole pieces 120 to separate the positive pole piece 110 and the negative pole piece 120, the isolation film 130 has ion insulation to prevent the positive pole piece 110 and the negative pole piece 120 from being short-circuited after contact.

The negative electrode piece 120 includes a polymer dielectric material layer 123 , and the polymer dielectric material layer 123 is disposed between the isolation film 130 and the negative electrode piece 120 . As shown in FIGS. 2 to 5 , there is at least one polymer dielectric material layer 123 , and the polymer dielectric material layer 123 can be connected to the surface of at least one of the isolation film 130 and the negative electrode piece 120 . For example, the polymer dielectric material layer 123 can be disposed on the surface of the negative electrode plate 120 and attached to or spaced apart from the isolation film 130; or the polymer dielectric material layer 123 can be disposed on the surface of the isolation film 130 facing the negative electrode plate 120. , and are attached to or spaced apart from the negative electrode piece 120 .

The polymer dielectric material layer 123 includes a polymer dielectric material with dielectric properties. The polymer dielectric material layer 123 is disposed between the isolation film 130 and the negative electrode piece 120 to assist in changing the surface potential of the negative electrode piece 120. For example, when the positively charged side of the polymer dielectric material layer 123 is placed toward the negative electrode piece 120, the surface of the negative electrode piece 120 can be macroscopically charged with positive charge, and the surface potential of the negative electrode piece 120 can be forcibly increased, so that the surface potential of the negative electrode piece 120 can be increased. The potential is higher than the nucleation potential of metal cations, which inhibits the negative electrode plate 120 from dissolving metal cations. When the metal cations reach the surface of the polymer dielectric material layer 123, the self-built electric field inside the polymer dielectric material layer 123 performs negative feedback on the local concentrated metal cation flow, weakening the local large current and uniformizing the negative electrode in advance. The current density on the surface of the sheet 120 suppresses the precipitation of metal cations on the negative electrode sheet 120 .

In this application, a polymer dielectric material with a dielectric effect is selected to be used in the polymer dielectric material layer. When the polymer dielectric material layer is placed in an electric field with an electric field intensity of 10kV/mm to 200kV/mm for polarization, After the electric field is removed, the polymer dielectric material layer has residual polarization intensity, and the range of the residual polarization intensity is greater than or equal to 50mC/m ² and less than or equal to 100mC/m ² . The residual polarization strength of the polymer dielectric material layer can be tested using a standard hysteresis loop measuring instrument (model: BZ-MTF-DH1): Place the polymer dielectric material layer with a size of 10cm × 10cm into the test sample box , the dielectric material layer is connected to the signal access terminal of the test host through contact with the probe in the sample box, close the sample box, turn on the power supply of the sample box, adjust the polarization voltage to the electric field strength of 10kV/mm to 200kV/mm, click Start the test, obtain the hysteresis loop of the material, and read the residual polarization intensity.

Wherein, the polymer chain segment of the polymer dielectric material includes structural units with polar functional groups, and each structural unit includes at least one polar functional group. Among them, the polar functional groups are asymmetrically distributed in the structural units, making the positive charge center and negative charge center in each structural unit spatially asymmetrical, so that the polymer chain segment formed after the polymerization of multiple structural units will have a dielectric polarization effect. Furthermore, multiple structural units are asymmetrically distributed in the polymer chain segments. When a polymer dielectric material is polarized in an electric field, the asymmetrically distributed polar functional groups are changed in orientation under the action of an external electric field, and functional groups with the same polarity have the same spatial orientation, resulting in a relatively The larger the dipole moment and the more polar groups on the molecular segments of the polymer dielectric material, the easier it is for the polymer dielectric material to produce spatial polarization under the action of an external electric field.

In some exemplary embodiments, the polar functional group includes at least one of amide group, fluorine, chlorine, bromine, carboxylic acid group, ester group, and cyano group. Taking polymer dielectric materials including polyvinylidene fluoride (PVDF) as an example, Figure 6a is a schematic diagram of the α-phase PVDF molecular chain before polarization, and Figure 6b is a schematic diagram of the β-phase PVDF molecular chain before polarization. , the direction pointed by the arrow in Figure 6a and Figure 6b is the direction of the electric dipole moment of the polar functional group. After the polarization treatment of α-phase PVDF and β-phase PVDF, the polar group fluorine on the molecular chain is changed in the orientation direction, and the orientation tends to be the same, thereby increasing the dipole moment of α-phase PVDF and β-phase PVDF, so that after the electric field is removed There is still residual polarization intensity in α-phase PVDF and β-phase PVDF.

In some exemplary embodiments, the polymer dielectric material includes a copolymer of polyvinylidene fluoride with dielectric effect, a copolymer of polyvinylidene fluoride and trifluoroethylene with dielectric effect, a copolymer of polyvinylidene fluoride with dielectric effect, At least one of a copolymer of polyvinylidene fluoride and tetrafluoroethylene, an odd-numbered nylon-based dielectric polymer with dielectric effect, and an amorphous dielectric polymer with dielectric effect.

The molecular formula of the odd-numbered nylon dielectric polymer is -(HN-(CH ₂ ) _x -CO-)n-, x is an even number, and n is any positive integer.

Amorphous dielectric polymers include vinylidene dicyanide/vinyl acetate copolymer P (VDCN-VAC), vinylidene dicyanide/vinyl benzoate copolymer P (VDCN-VBz), vinylidene dicyanide/propylene Vinyl acid copolymer P (VDCN-VPr), vinylidene dicyanide/vinyl pivalate copolymer P (VDCN-VPiv), vinylidene dicyanide/methyl methacrylate copolymer P (VDCN-MMA) and At least one of vinylidene dicyanotriene/isobutylene copolymer P (VDCN-IB).

In the copolymer of polyvinylidene fluoride and polytrifluoroethylene, the copolymerization ratio of polytrifluoroethylene is 20 mol% to 70 mol%; in the copolymer of polyvinylidene fluoride and polytetrafluoroethylene, the copolymerization ratio of polytetrafluoroethylene monomer The proportion is 30 mol% or less.

In the amorphous dielectric polymer, the copolymerization ratio of vinylidene dicyanide is greater than or equal to 30 mol% and less than or equal to 80 mol%.

In some exemplary embodiments, the coercive field strength of the polymer dielectric material at 25° C. is greater than 30 kV/mm and less than 200 kV/mm. By selecting a polymer dielectric material that satisfies the above-mentioned coercive field strength range and performing polarization treatment on the polymer dielectric material, a built-in layer capable of uniformizing the surface current of the negative electrode plate 120 can be formed in the polymer dielectric material layer 123 . electric field. Preferably, the coercive field strength of the polymer dielectric material at 25°C is 30kV/mm to 50kV/mm. For example, the coercive field strength is 30kV/mm, 35kV/mm, 40kV/mm, 45kV/mm or 50kV/mm. mm etc.

In some exemplary embodiments, the thickness of the polymer dielectric material layer 123 is 0.1 μm to 5 μm. For example, the thickness of the polymer dielectric material layer 123 may be 0.1 μm, 1 μm, 3 μm, 4 μm, or 5 μm, etc. . If the thickness of the polymer dielectric material layer 123 is too thin, it is difficult to form an effective built-in electric field in the polymer dielectric material layer 123 to uniform the current on the surface of the negative electrode piece 120; when the thickness of the polymer dielectric material layer 123 is greater than 0.1 μm. If the polymer dielectric material layer 123 is too thick, it is difficult for metal cations to penetrate the polymer dielectric material layer 123 and migrate into the negative electrode piece 120. At the same time, if the polymer dielectric material layer 123 is too thick, it will occupy more electrochemical devices. 200 internal space 210a, resulting in an increase in the proportion of inactive substances in the electrochemical device 200. In addition, if the polymer dielectric material layer 123 is too thick or too thin, it is not conducive to the bending process of the polymer dielectric material layer 123 with the negative electrode plate 120 or the isolation film 130, and limits the polymer dielectric material layer 123 in the electrochemical device. 200 applications. Preferably, the thickness of the polymer dielectric material layer 123 is 0.1 μm to 3 μm. Preferably, the thickness of the polymer dielectric material layer 123 is 0.1 μm˜3 μm.

In some exemplary embodiments, the polymer dielectric material layer 123 further includes an adhesive, and the weight ratio of the polymer dielectric material to the adhesive is 0.05˜0.15:1. The adhesive includes at least one of N-methylpyrrolidone, propylene glycol, glycerol or glycol.

In this application, the electrolyte includes carbonate, and the carbonate includes at least one of saturated carbonate or unsaturated carbonate. The carbonate in the electrolyte can form a stable and low-resistance SEI film (solid electrolyte interface, solid electrolyte interface film) on the surface of the negative electrode piece 120, reducing the risk of metal cations intercalating/extracting from the negative electrode piece 120 during the cycle. The internal resistance generated reduces the internal resistance during the circulation process of the electrochemical device, which can further improve the performance of the electrochemical device.

In some exemplary embodiments, the saturated carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate. In some exemplary embodiments, the unsaturated carbonate includes at least one of vinylene carbonate and fluoroethylene carbonate.

The electrolyte in this application also includes lithium salts. This application has no special restrictions on lithium salts. Any lithium salt known in the art can be used, as long as the purpose of this application can be achieved. For example, the lithium salts can include LiTFSI, 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 or LiPO ₂ F At least one of ₂ etc.

The electrolyte in this application also includes other non-aqueous solvents. Other non-aqueous solvents are not particularly limited as long as they can achieve the purpose of this application. For example, the non-aqueous solvents may include carboxylate compounds, ether compounds, nitrile compounds or other At least one of organic solvents and the like, for example, may include, but is not limited to, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate or tert-acetate. At least one of butyl esters.

The positive electrode sheet 110 includes a positive current collector 111 and a positive active material layer 112 . The positive active material layer 112 is provided on at least one surface of the positive current collector 111 . The negative electrode sheet 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 . The negative electrode active material layer 122 is provided on at least one surface of the negative electrode current collector 121 . The negative active material layer 122 has a pore structure to form spaces where metal cations are embedded. The polymer dielectric material layer 123 is provided on the surface of the negative active material layer 122 .

The negative electrode sheet 120 of the present application is not particularly limited. The negative active material layer 122 can be any negative active material layer 122 in the prior art. The negative active material layer 122 includes natural graphite, artificial graphite, hard carbon, soft carbon, silicon, and silicon. At least one of carbon or silicon oxide; the negative electrode current collector 121 can be any negative electrode current collector 121 known in the art, such as copper foil, aluminum foil, aluminum alloy foil or composite current collector.

The isolation membrane 130 of the present application is not particularly limited. For example, the isolation membrane 130 may be made of a material that is stable to the electrolyte of the present application, so that the ions in the electrolyte can pass through the isolation membrane 130, so that the ions in the electrolyte can It can move between the positive electrode piece 110 and the negative electrode piece 120. For example, the isolation film 130 may include polyethylene (PE) or the like.

When the polymer dielectric material layer 123 is disposed on the surface of the negative electrode active material layer 122 or the surface of the isolation film 130, the polymer dielectric material in the polymer dielectric material layer 123 can be stable with the negative electrode active material layer 122 and the isolation film 130. Ground connection, not easy to be stripped.

In the thickness direction X of the negative electrode sheet 120 , the polymer dielectric material layer 123 completely covers the negative electrode active material layer 122 .

The isolation film 130 is disposed between the positive electrode piece 110 and the negative electrode piece 120 . The negative electrode piece 120 , the isolation film 130 and the positive electrode piece 110 can be stacked or wound in sequence along the thickness direction X of the negative electrode piece 120 .

The positive electrode sheet 110 of the present application is not particularly limited. The positive active material layer 112 includes nickel cobalt manganese ternary material, nickel cobalt aluminum material, lithium iron phosphate, lithium cobalt oxide, lithium manganate, lithium iron manganese phosphate or lithium titanate. At least one of; the positive electrode current collector 111 can be any positive electrode current collector 111 known in the art, such as aluminum foil, aluminum alloy foil or composite current collector, etc., and the positive electrode active material layer 112 can be any positive electrode active material layer 112 in the prior art. .

The electrode assembly 100 also includes a positive electrode tab and a negative electrode tab. The positive electrode tab is electrically connected to the positive electrode current collector 111 , and the negative electrode tab is electrically connected to the negative electrode current collector 121 . When the electrode assembly 100 is disposed in the electrochemical device 200, the positive electrode tab and the negative electrode tab are used to electrically connect with the external circuit to charge and discharge the electrochemical device 200, and to monitor the internal working status of the electrochemical device 200.

An embodiment of the present application also provides a method for preparing the electrode assembly 100, which is used to prepare the electrode assembly 100 as described above. Preparation methods include:

The polymer dielectric material is first coated on the surface of at least one of the isolation film 130 and the negative electrode piece 120, and then polarized to obtain the polymer dielectric material layer 123; or, the polymer dielectric material is first coated on the surface of at least one of the isolation film 130 and the negative electrode piece 120. Perform polarization treatment, and then attach the polarized polymer dielectric material to the surface of at least one of the isolation film 130 and the negative electrode piece 120 to obtain the polymer dielectric material layer 123; the polymer dielectric material layer The polarization electric field in 123 can effectively improve the surface potential of the negative electrode piece 120, thereby improving the state of metal cations deposited on the surface of the negative electrode piece 120.

The preparation method of the electrode assembly 100 also includes disposing the polymer dielectric material layer 123 between the isolation film 130 and the negative electrode piece 120, and disposing the isolation film 130 between the negative electrode piece 120 and the positive electrode piece 110 to obtain an electrode. Components 100. Among them, after the polymer dielectric material is polarized, the charges on opposite sides of the formed polymer dielectric material layer 123 are also made different, and in the assembled electrode assembly 100, the polymer dielectric material layer 123 The positively charged side is disposed toward the negative electrode piece 120, so that the surface of the negative electrode piece 120 can be positively charged macroscopically, and the surface potential of the negative electrode piece 120 is forcibly increased, making its surface potential higher than the nucleation potential of metal cations, inhibiting The negative electrode piece 120 precipitates metal cations.

In some exemplary embodiments, a method for polarizing a polymer dielectric material includes: placing the polymer dielectric material in a parallel electric field for polarization treatment, and the field strength range of the parallel electric field is the polymer dielectric 0.1 times to 6 times the coercive field strength of the material at 25°C. The time range for placing the polymer dielectric material in a parallel electric field for polarization treatment can be 30 minutes.

The polymer dielectric material can be disposed on the surface of the isolation film 130 or the negative electrode piece 120 in an amorphous state, and then undergoes polarization treatment. For example, the amorphous state includes powder or slurry. The polymer dielectric material can also be disposed on the surface of the isolation film 130 or the negative electrode piece 120 in a shaped state and after polarization treatment. For example, the shaped state includes a film, a sheet, etc.

When the polymer dielectric material is disposed on the surface of the isolation film 130 or the negative electrode piece 120 in an amorphous state, it can be mixed with an adhesive, coated on the surface of the isolation film 130 or the negative electrode piece 120 and dried, and then polarized. chemical treatment to form a polymer dielectric material layer 123.

When the polymer dielectric material is processed into a finalized state, it can be bonded to the surface of the isolation film 130 or the negative electrode piece 120, or it can be initially connected to the surface of the isolation film 130 or the negative electrode piece 120, and then polarized to form a polymer dielectric material. After the electrical material layer 123 is formed, during the subsequent processing of the electrochemical device 200, for example, in the formation step of the electrochemical device 200, at least one of pressure and heat treatment is performed on the polymer dielectric material layer 123, so that The polymer dielectric material layer 123 is fixed on the isolation film 130 or the negative electrode piece 120 .

The outer packaging in this application is not particularly limited, and any well-known outer packaging in the art can be used. For example, it can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.; it can also be a soft bag, such as a bag-type soft bag, a soft bag, etc. The bag may be made of aluminum plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

This application also provides an electronic device, including the above electrochemical device 200, which may include, for example, a car, a mobile phone, etc.

Taking the electrochemical device 200 as a lithium-ion battery as an example, the present application will be described in further detail below with reference to specific embodiments.

Example 1

Preparation of polymer dielectric material layer 123:

(1) Provide powdered α-phase polyvinylidene fluoride (PVDF) as a polymer dielectric material and N-methylpyrrolidone (NMP) as a binder. The α-phase PVDF polymer dielectric material has a coercive field strength at 25°C. is 50kV/mm, disperse the powdery α-phase PVDF polymer dielectric material in N-methylpyrrolidone, stir to disperse the α-phase PVDF evenly, and obtain a dielectric slurry, in which the weight ratio of α-phase PVDF to NMP is 0.12, that is, the solid content of the dielectric slurry is 12%.

(2) Use a scraper to evenly apply the dielectric slurry on one surface of the polyethylene (PE) isolation film 130 with a thickness of 15 μm, and place it in a vacuum drying oven to dry at 80°C. After drying, the thickness of the polymer dielectric material attached to the surface of the isolation film 130 is 1 μm (that is, the thickness of the subsequently obtained polymer dielectric material layer 123 attached to the surface of the isolation film 130 is 1 μm).

(3) The isolation film 130 with the polymer dielectric material attached to the surface is placed in the parallel electric field of the polarization device for polarization. The polarization device includes a positive pressure plate and a negative pressure plate for generating a parallel electric field. The positive pressure plate and the negative pressure plate are used to generate parallel electric fields. The parallel electric field direction is from the positive pressure plate to the negative pressure plate. The polymer dielectric material is placed close to the negative pressure plate. The parallel electric field strength is 50kV/mm and the polarization time is 30 minutes. After polarization, the α-phase polyvinylidene fluoride and N - Methyl pyrrolidone forms a polymer dielectric material layer 123 on the surface of the isolation film 130, and the polymer dielectric material layer 123 and the isolation film 130 are cut into specifications of (42mm×62mm) for use. The residual polarization intensity of the polymer dielectric material layer 123 is 53 mC/m ² .

Preparation of positive electrode piece 110:

Mix the cathode active material (LiNi _0.8 Co _0.1 Mn _0.1 O ₂ ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.0:1.5, and add N-methylpyrrolidone (NMP) As a solvent, prepare a slurry with a solid content of 0.75 and stir evenly. The slurry is evenly coated on the positive electrode current collector 111 aluminum foil, and dried at 90°C to obtain a single-sided coated positive electrode piece 110 with a coating thickness of 70 μm. Cut the single-sided coated positive electrode piece 110 The specifications of (38mm×58mm) are ready for use.

Preparation of negative electrode piece 120:

Mix artificial graphite, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) at a weight ratio of 97:1.0:2.0, add N-methylpyrrolidone (NMP) as a solvent, and prepare a slurry with a solid content of 0.8 ingredients and stir evenly. The slurry is evenly coated on the two opposite surfaces of the copper foil of the negative electrode current collector 121, and dried at 80°C to obtain the negative electrode current collector 121 with negative electrode active material layers 122 on both sides, and cut into (40mm× 60mm) specification is ready for use, in which the thickness of each negative active material layer 122 is 100 μm. In the subsequent preparation process of the lithium ion battery, the polymer dielectric material layer 123 is disposed toward the negative electrode active material layer 122 , that is, a negative electrode including the polymer dielectric material layer 123 , the negative electrode active material layer 122 and the negative electrode current collector 121 is formed. Pole piece 120.

Preparation of electrolyte:

In a dry argon atmosphere, mix ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1:1 to obtain an organic solvent. Add lithium salt LiPF ₆ to the organic solvent. Dissolve and mix uniformly to obtain a basic electrolyte, add vinylene carbonate and fluoroethylene carbonate to the basic electrolyte, and mix uniformly to obtain an electrolyte, in which the mass percentage of lithium salt is 12.5%, and the mass percentage of vinylene carbonate is 12.5%. The mass percentage is 1.5%, and the mass percentage of fluoroethylene carbonate is 5%.

Preparation of lithium-ion batteries:

The above-mentioned cut negative electrode current collector 121 with the negative electrode active material layer 122 on both sides is placed in the middle, and the above-mentioned cut positive electrode tabs 110 are respectively arranged on both sides of it, and between each positive electrode tab 110 and the negative electrode The above-mentioned isolation film 130 with the polymer dielectric material layer 123 attached is disposed between the active material layers 122, and the polymer dielectric material layer 123 faces the negative electrode active material layer 122. The negative electrode tab 120, the two layers of positive electrode tabs 110 and Two layers of isolation films 130 are laminated along the thickness direction The positive electrode piece 110 is electrically connected to the positive ear to obtain the electrode assembly 100. The electrode assembly 100 is placed into the inner space 210a of the aluminum-plastic film outer package 210, and is injected into the inner space 210a of the outer package 210 through the opening of the outer package 210. After the electrolyte is added, the opening of the outer package 210 is sealed to obtain a laminated lithium-ion battery.

Example 2

The difference from Example 1 is that powdery β-phase polyvinylidene fluoride (PVDF) is provided as the polymer dielectric material. The coercive field strength of β-phase PVDF polymer dielectric material is 30kV/mm at 25℃. The residual polarization intensity of the polymer dielectric material layer 123 is 92mC/m ² .

Example 3

The difference from Example 1 is that a powdery copolymer of polyvinylidene fluoride and polytetrafluoroethylene (PVDF-PTFE, in which the copolymerization ratio of polytetrafluoroethylene monomer is 25 mol%) is provided as a polymer dielectric material. The coercive field strength of polyvinylidene fluoride copolymer is 30kV/mm at 25℃. The residual polarization intensity of the polymer dielectric material layer 123 is 98 mC/m ² .

Example 4

The difference from Embodiment 3 is that the thickness of the polymer dielectric material layer 123 is 0.1 μm. The residual polarization intensity of the polymer dielectric material layer 123 is 94mC/m ² .

Example 5

The difference from Embodiment 3 is that the thickness of the polymer dielectric material layer 123 is 3 μm. The residual polarization intensity of the polymer dielectric material layer 123 is 95 mC/m ² .

Example 6

The difference from Embodiment 3 is that the thickness of the polymer dielectric material layer 123 is 5 μm. The residual polarization intensity of the polymer dielectric material layer 123 is 93mC/m ² .

Example 7

The differences from Example 1 are:

Preparation of negative electrode piece 120:

Mix artificial graphite, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) at a weight ratio of 97:1.0:2.0, add N-methylpyrrolidone (NMP) as a solvent, and prepare a slurry with a solid content of 0.8 ingredients and stir evenly. The slurry is evenly coated on the two opposite surfaces of the copper foil of the negative electrode current collector 121, and dried at 80°C to obtain the negative electrode sheet 120 with the negative electrode active material layer 122 on both sides, and the following preparation method is used to prepare the high The molecular dielectric material layer 123 is disposed on the surface of the negative active material layer 122 facing away from the negative current collector 121 to obtain the negative electrode piece 120 .

Among them, the preparation of the polymer dielectric material layer 123 includes:

(1) Provide powdered copolymer of polyvinylidene fluoride and polytetrafluoroethylene (PVDF-PTFE, in which the copolymerization ratio of polytetrafluoroethylene monomer is 25 mol%) as a polymer dielectric material, N-methylpyrrolidone (NMP) As a binder, powdered PVDF-PTFE has a coercive field strength of 50KV/mm at 25°C. Disperse powdered PVDF-PTFE in N-methylpyrrolidone (NMP) and stir to make PVDF- The PTFE is dispersed evenly, and a dielectric slurry with a solid content of 12% is obtained. Use a scraper to evenly apply the dielectric slurry on the surface of each negative active material layer 122 facing away from the negative current collector 121. After drying in a vacuum drying oven at 80°C, each layer of polymer dielectric material and adhesive will form The thickness of the layer structure is all 0.1 μm (that is, the thickness of the subsequently obtained polymer dielectric material layer 123 is 0.1 μm).

(2) Place the above-mentioned negative electrode piece 120 with polymer dielectric material and adhesive on both sides in the parallel electric field of the polarization device, perform polarization, and attach the polymer dielectric material to the positive electrode of the polarization device. Place the pressure plate with the parallel electric field strength of 100kV/mm and the polarization time of 30 minutes. Then flip the negative electrode piece 120 and place the polymer dielectric material on the other side of the negative electrode piece 120 against the positive pressure plate of the polarization device. The curing time is 30 minutes. The polymer dielectric material and the adhesive form the polymer dielectric material layer 123 on the surface of the negative electrode piece 120. The negative electrode piece 120 is cut into (42mm×62mm) specifications for use. The residual polarization intensity of the polymer dielectric material layer 123 is 95 mC/m ² .

Preparation of electrolyte:

In a dry argon atmosphere, mix ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1:1 to obtain an organic solvent. Add lithium salt LiPF ₆ to the organic solvent. Dissolve and mix evenly to obtain a basic electrolyte, add fluorinated ethylene carbonate to the basic electrolyte, and mix evenly to obtain an electrolyte, in which the mass percentage of lithium salt is 12.5%, and the mass percentage of fluorinated ethylene carbonate is 12.5%. is 5%.

Preparation of lithium-ion batteries:

The above-mentioned cut negative electrode piece 120 with the polymer dielectric material layer 123 on both sides is placed in the middle, and the cut positive electrode pieces 110 are respectively placed on both sides of the negative electrode piece 120 in the thickness direction X. A polyethylene (PE) isolation film 130 with a thickness of 15 μm is placed between each positive electrode piece 110 and the negative electrode piece 120. The negative electrode piece 120 with a polymer dielectric material layer 123 on both sides, the two layers of the positive electrode piece 110 and Two layers of isolation films 130 are laminated along the thickness direction Connect, the positive electrode lug is electrically connected to the positive electrode piece 110 to obtain the electrode assembly 100. Place the electrode assembly 100 into the inner space 210a of the aluminum-plastic film outer package 210, and inject it into the inner space 210a of the outer package 210 through the opening of the outer package 210. After the electrolyte is added, the opening of the outer package 210 is sealed to obtain a laminated lithium-ion battery.

Example 8

The difference from Embodiment 7 is that the thickness of the polymer dielectric material layer 123 is 1 μm, and the residual polarization intensity of the polymer dielectric material layer 123 is 92 mC/m ² .

Example 9

The difference from Embodiment 7 is that the thickness of the polymer dielectric material layer 123 is 3 μm, and the residual polarization intensity of the polymer dielectric material layer 123 is 90 mC/m ² .

Example 10

The difference from Embodiment 7 is that: the thickness of the polymer dielectric material layer 123 is 5 μm, and the residual polarization intensity of the polymer dielectric material layer 123 is 90 mC/m ² ;

Preparation of electrolyte:

In a dry argon atmosphere, mix ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1:1:1 to obtain an organic solvent, and add lithium salt to the organic solvent LiPF ₆ is dissolved and mixed evenly to obtain an electrolyte, in which the mass percentage of lithium salt is 12.5%.

Example 11

The differences from Embodiment 7 are:

Preparation of the polymer dielectric material layer 123: The polymer dielectric material is nylon 7, and the coercive field strength of nylon 7 is 97KV/mm at 25°C. Prepare nylon 7 into a nylon 7 film with a thickness of 5 μm (molecular formula is -(HN-(CH ₂ ) ₆ -CO-) _n -, brand: Taiwan Chemical Fiber Co., Ltd., grade: NP4000), place the nylon 7 film Air polarization is performed in a parallel electric field, the parallel electric field strength is 280kV/mm, and the polarization time is 30 minutes. After the polarization is completed, the nylon 7 film forms a polymer dielectric material layer 123, and the polymer dielectric material layer 123 is The positively charged surface is attached to the surface of the negative active material layer 122 facing away from the negative current collector 121 . The residual polarization intensity of the polymer dielectric material layer 123 is 98 mC/m ² .

Preparation of electrolyte:

In a dry argon atmosphere, mix ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1:1 to obtain an organic solvent. Add lithium salt LiPF ₆ to the organic solvent. Dissolve and mix evenly to obtain an electrolyte solution, in which the mass percentage of lithium salt is 12.5%.

Example 12

The differences from Example 1 are:

Preparation of the polymer dielectric material layer 123: The polymer dielectric material is powdered vinylidene dicyanide and vinyl acetate copolymer (P(VDCN-VAC)). P(VDCN-VAC) is coercive at 25°C. The field intensity is 200KV/mm. Powdered P(VDCN-VAC) is dispersed in N-methylpyrrolidone (NMP), and the P(VDCN-VAC) is dispersed evenly by stirring to obtain a dielectric slurry with a solid content of 12%. Use a scraper to evenly coat one surface of the isolation film 130 with the dielectric slurry, place it in a vacuum drying oven to dry at 80°C, and then place it in a parallel electric field for polarization. The parallel electric field field strength is 300kV/mm. The time is 30 minutes. After the polarization is completed, P(VDCN-VAC) and N-methylpyrrolidone form the polymer dielectric material layer 123. The residual polarization intensity of the polymer dielectric material layer 123 is 76 mC/m ² .

Preparation of electrolyte:

In a dry argon atmosphere, mix ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate in a mass ratio of 1:1:1:1 to obtain an organic solvent. Add lithium salt LiPF ₆ to the organic solvent. Dissolve and mix uniformly to obtain a basic electrolyte, add vinylene carbonate to the basic electrolyte, and mix uniformly to obtain an electrolyte, in which the mass percentage of lithium salt is 12.5% and the mass percentage of vinylene carbonate is 1.5 %.

Example 13

The differences from Example 1 are:

The polymer dielectric material is a powdery copolymer of vinylidene dicyanide and methyl methacrylate (P(VDCN-MMA)). The coercive field strength of P(VDCN-MMA) at 25°C is 200KV/mm. Powdered P(VDCN-MMA) is dispersed in N-methylpyrrolidone, and stirred to disperse P(VDCN-MMA) evenly to obtain a dielectric slurry with a solid content of 12%. Use a scraper to evenly coat the dielectric slurry on the surface of the isolation film 130, place it in a vacuum drying oven to dry at 80°C, and then place it in a parallel electric field for air polarization. The parallel electric field field strength is 300kV/mm, and the polarization time for 30 minutes. After the polarization is completed, P(VDCN-MMA) and N-methylpyrrolidone form the polymer dielectric material layer 123. The residual polarization intensity of the polymer dielectric material layer 123 is 88 mC/m ² .

Preparation of electrolyte:

Comparative example 1

The differences from Example 1 are:

No polymer dielectric material is provided between the separator and the negative electrode piece 120;

Preparation of electrolyte:

The electrode assembly 100 and the electrochemical device 200 in each embodiment and comparative example were tested using the following methods:

Negative electrode piece 120 lithium precipitation rate:

Under the condition that the test temperature is 25℃, charge to 4.3V with a constant current at a certain rate, the rate is not less than 3C, then charge with a constant voltage to 0.05C, let it stand for 5 minutes and then discharge to 2.8V at 1C. The capacity obtained in the above steps is the initial capacity of the lithium-ion battery. Charge and discharge the lithium-ion battery at the same rate as the previous step for a cycle test. After 10 cycles, disassemble the battery and observe whether lithium is precipitated from the negative electrode plate 120. The lithium deposition rate of the negative electrode piece 120 is regarded as the lithium deposition rate of the negative electrode piece 120 .

Internal resistance (mΩ):

Use the DC discharge method to test the internal resistance of the lithium-ion battery. Use a large current of 40A to instantly discharge the lithium-ion battery for 3 seconds. Measure the voltage drop U at this time. The internal resistance value of the cell can be obtained through U/40A.

Examples 1-13 and Comparative Example 1 respectively include the four electrolyte solutions in Table 1.

Table 1

The parameter settings and test results of the above-mentioned Examples 1-19 and Comparative Example 1 are shown in Table 2.

Table 2

It can be seen from Examples 1-13 and Comparative Example 1 that the polymer dielectric material layer 123 is included in the lithium ion battery, and when the electrolyte includes carbonate, the polymer dielectric material layer 123 can improve the surface of the negative electrode plate 120 potential, inhibiting the precipitation of metal cations on the negative electrode piece 120. At the same time, the carbonate compound in the electrolyte can form a stable and low-impedance SEI film on the surface of the negative electrode piece 120, reducing the embedding of metal cations in the negative electrode piece 120 during the cycle. /The internal resistance generated by the disengagement can therefore increase the lithium elution rate of the negative electrode plate 120 and reduce the internal resistance during the lithium-ion battery cycle, thereby improving the performance of the lithium-ion battery.

It can also be seen from Table 2 that whether the polymer dielectric material layer 123 is located on the side of the isolation film facing the negative active material layer 122 or on the surface of the negative active material layer 122, it can improve the lithium deposition problem of the negative electrode piece 120; Optimizing the thickness of the polymer dielectric material layer 123 within the scope of this application can further improve the lithium elution from the negative electrode plate 120 and enhance the overall performance of the lithium-ion battery.

In the drawings of this embodiment, the same or similar numbers correspond to the same or similar components; in the description of this application, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation or a specific orientation. Construction and operation, therefore the terms describing the positional relationships in the drawings are only for illustrative purposes and cannot be understood as limitations of the patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims

An electrochemical device is characterized in that it includes a negative electrode piece, a positive electrode piece, a separation film and an electrolyte. The negative electrode piece includes a polymer dielectric material layer, and the electrolyte includes carbonate.
The electrochemical device according to claim 1, characterized in that when the polymer dielectric material layer is placed in an electric field with an electric field intensity of 10 kV/mm to 200 kV/mm for polarization, and the electric field is removed, the high polymer dielectric material layer The residual polarization intensity of the molecular dielectric material layer is 50mC/m 2 ~ 100mC/m 2 .
The electrochemical device according to claim 1, wherein the polymer dielectric material layer includes a polymer dielectric material, and the molecular segments of the polymer dielectric material include structural units with polar functional groups. , and the polar functional groups are asymmetrically distributed in the structural unit.
The electrochemical device according to claim 3, characterized in that

The polar functional group includes at least one of amide group, fluorine, chlorine, bromine, carboxylic acid group, ester group and cyano group.
The electrochemical device according to claim 3, characterized in that

The polymer dielectric materials include copolymers of polyvinylidene fluoride with dielectric effect, copolymers of polyvinylidene fluoride and trifluoroethylene, copolymers of polyvinylidene fluoride and tetrafluoroethylene, and odd-numbered nylon dielectric materials. at least one of a polymer and an amorphous dielectric polymer;

The molecular formula of the odd-numbered nylon dielectric polymer is -(HN-(CH 2 ) x -CO-)n-, x is an even number, and n is any positive integer;

The amorphous dielectric polymer includes vinylidene dicyanide/vinyl acetate copolymer, vinylidene dicyanide/vinyl benzoate copolymer, vinylidene dicyanide/vinyl propionate copolymer, vinylidene dicyanide/vinyl propionate copolymer, and vinylidene dicyanide/vinyl benzoate copolymer. /At least one of vinylene pivalate copolymer, vinylidene dicyanide/methyl methacrylate copolymer, and vinylidene dicyanide/isobutylene copolymer.
The electrochemical device according to claim 5, characterized in that the polymer dielectric material satisfies one of the following conditions:

(I) In the copolymer of polyvinylidene fluoride and polytrifluoroethylene, the copolymerization ratio of polytrifluoroethylene is 20 mol% to 70 mol%;

(II) In the copolymer of polyvinylidene fluoride and polytetrafluoroethylene, the copolymerization ratio of the polytetrafluoroethylene monomer is 30 mol% or less;

(III) In the amorphous dielectric polymer, the copolymerization ratio of vinylidene dicyanide is 30 mol% to 80 mol%.
The electrochemical device according to claim 1, wherein the coercive field strength of the polymer dielectric material at 25° C. is greater than 30 kV/mm and less than 200 kV/mm.
The electrochemical device according to claim 1, wherein the thickness of the polymer dielectric material layer is 0.1 μm to 5 μm.
The electrochemical device according to claim 1, wherein the carbonate includes at least one of saturated carbonate or unsaturated carbonate;

The saturated carbonate includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate;

The unsaturated carbonate includes at least one of vinylene carbonate and fluoroethylene carbonate.
An electronic device, characterized by comprising the electrochemical device according to any one of claims 1 to 9.