CN114665066A - Electrochemical device and electronic device - Google Patents

Electrochemical device and electronic device Download PDF

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Publication number
CN114665066A
CN114665066A CN202210352599.XA CN202210352599A CN114665066A CN 114665066 A CN114665066 A CN 114665066A CN 202210352599 A CN202210352599 A CN 202210352599A CN 114665066 A CN114665066 A CN 114665066A
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negative electrode
negative
active material
electrochemical device
thickness
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Inventor
马胜祥
唐佳
董佳丽
谢远森
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Secondary Cells (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

An electrochemical device includes a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector, a negative electrode undercoat layer, and a negative electrode active material layer; the undercoat layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the undercoat layer; a thickness S (μm) of the negative electrode undercoat layer, a thickness L (μm) of a single-sided negative electrode active material layer, a compacted density P (g/cm) of the negative electrode active material layer3) The relationship between them satisfies: 3.8 is less than or equal to 100 (S/L) + P is less than or equal to 14. The electrochemical device and the negative pole piece thereof can effectively control the matching relation of all parameters by adjustingThe current collector extension risk brought by the volume change of the active material in the process of manufacturing the electrochemical device is avoided; and the breakage of the positive pole piece caused by the extension of the negative pole piece, thereby improving the problems of the wrinkle of the negative pole piece and the deformation of the battery.

Description

Electrochemical device and electronic device
Technical Field
The present disclosure relates to the field of electrochemistry, and more particularly, to an electrochemical device and an electronic device.
Background
Electrochemical devices, such as lithium ion batteries, are widely used in the fields of notebook computers, mobile phones, and new energy electric vehicles, which puts higher demands on the electrochemical devices to maintain low volume expansion while maintaining high energy density. During the charge and discharge of the lithium ion battery, the active material layer expands and contracts along with the movement of lithium ions, so that the copper foil as a current collector is also subjected to a deformation load at each charge and discharge. The stresses generated by the expansion and contraction of such active species are conducted to the current collector through the undercoat layer. If the copper foil is subjected to plastic deformation due to expansion during charging, the copper foil is wrinkled during the next contraction; likewise, if the copper foil is plastically deformed by shrinkage upon discharge, the copper foil risks cracking upon the next expansion.
Disclosure of Invention
In view of the problems in the background art, an object of the present invention is to provide an electrochemical device in which the risk of wrinkling, cracking, and the like of a current collector due to the expansion and contraction of a negative electrode active material layer is effectively reduced, and the risk of battery deformation is reduced.
In order to achieve the above objects, the present application provides an electrochemical device comprising a negative electrode sheet, wherein,
the negative plate comprises a negative current collector, a negative primer layer and a negative active material layer;
the undercoat layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the undercoat layer;
a thickness S (μm) of the negative electrode undercoat layer, a thickness L (μm) of a single-sided negative electrode active material layer, a compacted density P (g/cm) of the negative electrode active material layer3) The relationship between them satisfies:
3.8≤100×(S/L)+P≤14。
in some embodiments, the thickness S (μm) of the negative electrode primer layer, the thickness L (μm) of the single-sided negative electrode active material layer, the compacted density P (g/cm) of the negative electrode active material layer3) The relationship between them satisfies:
4.5≤100×(S/L)+P≤7.5。
in some embodiments, the ratio of the thickness S (μm) of the anode undercoating layer to the thickness L (μm) of the single-sided anode active material layer is 1: 8 to 1: 150.
In some embodiments, the negative primer layer has a thickness S of 1 μm to 5 μm.
In some embodiments, the anode active material layer has an OI value VOIFrom 15 to 25.
In some embodiments, the L ranges from 40 μm to 100 μm.
In some embodiments, the P is 1.1g/cc to 1.8 g/cc.
In some embodiments, the electrochemical device further comprises an electrolyte; in some embodiments, the electrolyte comprises a sulfur-oxygen double bond containing compound; in some embodiments, the sulfur oxygen double bond containing compound has a mass percentage content of M (%) and the specific surface area of the negative electrode active material is a (M) based on the mass of the electrolyte2The/g) satisfies: M/A is more than or equal to 0.3 and less than or equal to 3.
In some embodiments, the compound containing a sulfur-oxygen double bond is selected from at least one of methylene methanedisulfonate, vinyl sulfate, allyl sulfate, 1, 3-propane sultone, 1, 4-butane sultone, ethylene sultone, 1, 3-propene sultone, 1, 4-butene sultone, 1-methyl-1, 3-propene sultone, divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, methyl vinyl sulfone.
In some embodiments, the thickness D (μm) of the negative electrode current collector satisfies: 50 ≤ 400 × (D/L) + VOILess than or equal to 100; wherein, VOIDenotes the orientation index of the negative active material according to VOI＝C004/C110Performing a calculation of C004Is the peak area of 004 characteristic diffraction peak in X-ray diffraction spectrogram of the cathode, C110Is the peak area of the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode.
In some embodiments, the negative current collector comprises copper foil and has a thickness D of 4 μm to 20 μm.
In some embodiments, the tensile strength of the negative electrode current collector is x (mpa), and satisfies: X/D is more than or equal to 60 and less than or equal to 100.
In some embodiments, at room temperature, the elongation of the negative electrode current collector is δ (%), δ ranges from 3 to 10, and satisfies: l/delta is more than or equal to 4 and less than or equal to 20.
In some embodiments, the porosity of the negative electrode sheet is Z (%), and Z ranges from 20 to 50, and satisfies: Z/D is more than or equal to 1 and less than or equal to 8.
In some embodiments, the adhesive force F (N/m) between the anode active material layer and the anode current collector satisfies: f is more than or equal to 10 and less than or equal to 30, and the value range of the resistance of the negative electrode is 3-30m omega.
In some embodiments, the negative active material of the negative active material layer includes at least one of natural graphite, artificial graphite, hard carbon, or soft carbon.
In some embodiments, the negative primer layer includes at least one of carbon black, carbon nanotubes, graphite, acetylene black, graphene.
In some embodiments, the present application also provides an electronic device comprising the electrochemical device described above.
The application at least comprises the following beneficial effects:
according to the electrochemical device and the negative pole piece thereof, all parameters are adjusted within the range of the electrochemical device, so that the current collector extension risk caused by the volume change of active substances in the charging and discharging processes of the electrochemical device can be effectively controlled; and the breakage of the positive pole piece caused by the extension of the negative pole piece, thereby improving the problems of the wrinkle of the negative pole piece and the deformation of the battery.
Detailed Description
Exemplary embodiments are described more fully below, however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.
(electrochemical device)
The electrochemical device may be a capacitor, a lithium ion battery, a sodium ion battery, or a zinc ion battery. For example, a lithium ion capacitor, a lithium ion primary battery, or a lithium ion secondary battery may be used.
The electrochemical device comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte.
The application provides a matching relation between negative active material and under coat, mass flow body, through the relation between restriction negative active material and the under coat, including the thickness of under coat, the thickness of mass flow body, the thickness of negative pole piece, the compaction density of negative pole piece, negative pole piece OI value. The undercoat is matched with a proper negative active material and a current collector, so that the risks of wrinkling, cracking and the like of the current collector caused by the expansion and contraction of a negative active material layer are effectively improved, the deformation risk of the battery is reduced, and simultaneously, the electrolyte contains sulfur-oxygen double bonds, so that the cycle performance and the dynamic performance of the electrochemical device are further improved.
[ negative electrode sheet ]
In some embodiments, the negative electrode sheet includes a negative electrode current collector, a negative electrode undercoat layer, and a negative electrode active material layer.
In some embodiments, the primer layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the primer layer. The current collector and the negative electrode material can be tightly linked through the bottom coating between the current collector and the negative electrode material, so that not only can stress be conducted and the binding power be improved, but also the conductivity of the negative electrode material layer can be improved, and the electrochemical performance of the negative electrode material layer can be improved. In some embodiments, the current collector comprises copper foil.
For convenience, the negative plate expansion parameter is defined as follows: j100 × (S/L) + P, K400 × (D/L) + VOI(ii) a J and K can represent the XY expansion rate of the lithium ion battery negative plate.
In some embodiments, the thickness S (μm) of the negative electrode primer layer, the thickness L (μm) of the single-sided negative electrode active material layer, the compacted density P (g/cm) of the negative electrode active material layer3) The relationship between them satisfies:
3.8≤100×(S/L)+P≤14。
in some embodiments, the thickness S (μm) of the negative electrode primer layer, the thickness L (μm) of the single-sided negative electrode active material layer, the negative electrode active material layerCompacted density P (g/cm) of the layer of sexual material3) The relationship between them satisfies:
4.5≤100×(S/L)+P≤7.5。
under the condition of specific compaction density, if the thickness ratio of the base coat to the active material is too small, the base coat cannot be tightly connected with the current collector and the active material layer, and the risk of powder falling and the like exists, so that the conductivity of the battery is influenced; when the compaction density is adjusted, the thickness ratio of the bottom coating to the active material is adjusted at the same time, so that the negative plate meets the conditions that the energy density is not less than 4.5 and not more than 100 x (S/L) + P is not more than 7.5, and the electrochemical device has good low expansion performance and good dynamic performance under the condition of not reducing the energy density or the cycle life.
In some embodiments, the thickness S of the negative primer layer is 1 μm to 5 μm. The undercoat layer can improve the adhesion between the active material layer and the current collector and contribute to release of stress generated when the active material layer expands in the XY direction. Too high a thickness of the undercoat layer may result in a decrease in energy density of the battery; and the charge transfer resistance increases after the relative thickness of the undercoat layer exceeds a certain value.
In some embodiments, the L ranges from 40 μm to 100 μm. A decrease in the thickness of the active material layer may decrease the energy density of the battery; when the thickness of the active substance layer is increased, the XY direction expansion is large, because the thickness of the pole piece is too large, the stress release is too large after the active substance is fully charged, the XY direction expansion and the charge transfer impedance of the pole piece can be directly increased, and the dynamic performance of the battery is not facilitated.
In some embodiments, the ratio of the thickness S (μm) of the anode undercoating layer to the thickness L (μm) of the single-sided anode active material layer is 1: 8 to 1: 150. If the thickness of the bottom coating is too thick, the expansion in the XY direction is reduced, but the thickness of the pole piece is also increased, and the energy density of the battery is influenced; therefore, the above-described collocation needs to be satisfied between the undercoat layer and the active material layer of the current collector.
In some embodiments, the anode active material layer has an OI value VOIIs 10 to 25. The larger the OI value is, the more the particles are distributed in an angle parallel to the current collector, and after the pole piece is fully filled, the expansion in the Z direction is increased and the expansion in the XY direction is reduced; too large OI value will lead toResulting in too little porosity of the pole piece.
In some embodiments, the P is 1.1g/cc to 1.8 g/cc.
The compaction density of the negative pole piece is too low, so that most particles are distributed in the direction vertical to the current collector, and although the infiltration of electrolyte and the reduction of charge transfer impedance are facilitated, graphite embedded lithium after full charge causes overlarge XY direction expansion, so that the whole deformation of the battery is also unfavorable, and the problems of first effect reduction, pole piece demoulding and the like are caused.
The excessive compaction density of the negative plate can cause most particles to be arranged at an angle parallel to the current collector, and as a result, the electrolyte infiltration is poor, the contact area between the material and the electrolyte is greatly reduced, so that the ion embedding or separation is seriously hindered, the charge transfer impedance is remarkably increased, and the dynamic performance of the lithium ion battery is not facilitated.
In some embodiments, the thickness D (μm) of the negative electrode current collector satisfies: 50 ≤ 400 × (D/L) + VOILess than or equal to 100; wherein, VOIDenotes the orientation index of the negative active material according to VOI＝C004/C110Performing a calculation of C004Is the peak area of 004 characteristic diffraction peak in X-ray diffraction spectrogram of the cathode, C110Is the peak area of the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode.
When the thickness and the tensile strength of the current collector meet the relationship, the negative pole piece can remarkably reduce the XY expansion rate of the pole piece while maintaining the energy density of the battery. The negative current collector can effectively release the stress in the XY direction generated by the negative active material layer in the circulation process when the thickness of the current collector, the thickness of the single surface of the negative active material layer and the orientation index of the negative active material meet the relationship, so that the circulation stress of the active material layer is balanced, and the expansion of the thickness is prevented from being amplified by the uneven stress in the XY direction; the thickness of the current collector has little influence on the internal liquid phase transfer impedance; the current collector has an excessively small thickness, and expansion in the XY direction is difficult to suppress. In some embodiments, 55 ≦ 400 × (D/L) + V is preferredOI≤80。
In some embodiments, the negative current collector comprises copper foil and has a thickness D of 4 μm to 20 μm. In some embodiments, the tensile strength of the negative electrode current collector is x (mpa), and satisfies: X/D is more than or equal to 60 and less than or equal to 100.
In some embodiments, at room temperature, the elongation of the negative electrode current collector is δ (%), δ ranges from 3 to 10, and satisfies: l/delta is more than or equal to 4 and less than or equal to 20.
In some embodiments, the negative electrode has a porosity of Z (%), wherein Z ranges from 20 to 50, and satisfies: Z/D is more than or equal to 1 and less than or equal to 8.
In some embodiments, the adhesion force F (N/m) between the negative active material layer and the negative current collector satisfies: f is more than or equal to 10 and less than or equal to 30, and the value range of the resistance of the negative electrode is 3-30m omega.
In some embodiments, the negative active material of the negative active material layer includes at least one of natural graphite, artificial graphite, hard carbon, or soft carbon.
In some embodiments, the negative primer layer includes at least one of carbon black, carbon nanotubes, graphite, acetylene black, graphene.
[ electrolyte ]
In some embodiments, the electrochemical device further comprises an electrolyte.
In some embodiments, the electrolyte includes a compound containing a double bond of sulfur and oxygen.
In some embodiments, the sulfur oxygen double bond containing compound has a mass percentage content of M (%) and the specific surface area of the negative electrode active material is a (M) based on the mass of the electrolyte2The/g) satisfies: M/A is more than or equal to 0.3 and less than or equal to 3.
The content of the sulfur-oxygen double bond compound is related to the specific surface area of the negative active material, and when M/A is more than or equal to 0.3 and less than or equal to 3, the expansion of the pole piece in the XY direction can be satisfied, and the dynamic performance is good. The sulfur-oxygen double bond compound is too low, and SEI formed on the negative electrode is incomplete, so that slight lithium precipitation and high charge transfer resistance are caused; and if the content of the sulfur-oxygen double bond compound is too high, slight lithium precipitation and excessive charge transfer resistance are caused.
[ Positive electrode sheet ]
The positive pole piece comprises a positive current collector and a positive diaphragm.
The positive current collector is a metal, such as, but not limited to, aluminum foil.
The positive diaphragm is arranged on the surface of the positive current collector. The positive electrode membrane contains a positive electrode active material. When the electrochemical device is a lithium ion battery: the positive active material may be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, olivine-structured lithium-containing phosphate, such as lithium cobaltate or lithium manganate, but the present application is not limited to these materials, and other conventionally known materials that may be used as positive active materials for lithium ion batteries may also be used.
In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode binder is used to improve the binding properties between positive electrode active material particles and between the positive electrode active material particles and a current collector. In some embodiments, the positive electrode binder comprises at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon. In some embodiments, acetylene black is included.
In some embodiments, the method for preparing the positive electrode sheet is a method for preparing a positive electrode sheet that can be used for an electrochemical device, which is well known in the art. In some embodiments, in the preparation of the positive electrode slurry, a solvent is generally added, and the positive electrode active material is dissolved or dispersed in the solvent after adding a binder and, if necessary, a conductive material and a thickener to prepare the positive electrode slurry. The solvent is evaporated during the drying process. The solvent is a solvent known in the art that can be used as the positive electrode active material layer, such as but not limited to N-methylpyrrolidone (NMP).
[ separator ]
In some embodiments, the separator is polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer composite film thereof.
In some embodiments, the separator is a single layer separator or a multilayer separator.
In some embodiments, the release film is coated with a coating. In some embodiments, the coating comprises at least one of an organic coating selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyimide, acrylonitrile-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, acrylic acid-styrene copolymer, polydimethylsiloxane, sodium polyacrylate, sodium carboxymethylcellulose, and an inorganic coating selected from SiO, and the inorganic coating is selected from a group consisting of a silicone oxide, a silicone2、Al2O3、CaO、TiO2、ZnO、MgO、ZrO2、SnO2At least one of them.
The form and thickness of the separator are not particularly limited. The method for preparing the separator is a method for preparing a separator that can be used in an electrochemical device, which is well known in the art.
[ case ]
In some embodiments, the positive electrode sheet, the separation film, and the negative electrode sheet are sequentially stacked, such that the separation film is located between the positive electrode sheet and the negative electrode sheet, and then wound to obtain a wound battery (or called an electrode assembly), the battery is placed in a casing, an electrolyte is injected, and after vacuum packaging, standing, formation, air-bleed molding, and the like, an electrochemical device can be obtained.
In other embodiments, the electrochemical device is used in conjunction with a circuit protection board.
The shell is a hard shell or a flexible shell. The hard shell is made of metal, for example. The flexible housing is, for example, a metal plastic film, such as an aluminum plastic film, a steel plastic film, or the like.
(electronic device)
The present application also provides an electronic device comprising the above electrochemical device, the electronic device of the present application being any electronic device such as, but not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable 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 power tool, a flashlight, a camera, a large-sized household battery, a lithium ion capacitor. Note that the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, and an air vehicle, in addition to the above-exemplified electronic devices. The air transport carrier device comprises an air transport carrier device in the atmosphere and an air transport carrier device outside the atmosphere.
[ test ]
Some specific examples and comparative examples are listed below to better illustrate the present application. In the following examples, reagents, materials and instruments used are commercially available unless otherwise specified.
The lithium ion batteries of the present application are all prepared according to the following method:
(1) preparation of positive pole piece
Mixing positive electrode active material lithium cobaltate (molecular formula is LiCoO)2) Mixing acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder according to a weight ratio of 96: 2, and then fully stirring and mixing in a proper amount of N-methylpyrrolidone (NMP) solvent to form uniform anode slurry; coating the slurry on a current collector Al foil, drying, cold pressing and splitting to obtain the positive pole piece.
(2) Preparation of negative plate
The current collector adopts copper foil, and after negative active material graphite, thickener carboxymethyl cellulose sodium (CMC) and binder Styrene Butadiene Rubber (SBR) are mixed according to the weight ratio of 95: 2: 3, the mixture is fully stirred and mixed in a proper amount of deionized water solvent to form uniform negative slurry; the slurry was coated on the above copper foil previously coated with a primer (default used copper foil thickness was 6 μm, tensile strength was 450MPa, elongation was 4%), dried, cold pressed, and stripped to obtain a negative electrode sheet. The conductive carbon material of the bottom coating is at least one selected from carbon black, carbon nano tubes, graphite, acetylene black and graphene.
(3) Preparation of the separator
PE porous polymer film with thickness of 7um as isolating film
(4) Preparation of the electrolyte
Mixing EC, DMC and DEC at a weight ratio of 1: 1 under dry argon atmosphere, adding LiPF6Mixing uniformly to form a basic electrolyte, wherein LiPF6The content of (B) was 12.5%. And adding a compound containing sulfur-oxygen double bonds into the basic electrolyte according to percentage.
(5) Preparation of lithium ion battery
And winding the positive plate, the negative plate and the isolating membrane to prepare an electrode assembly, and then welding terminals, packaging aluminum foil, packaging, injecting liquid, standing, forming, exhausting and forming to prepare the lithium ion battery.
The lithium ion battery prepared by the method is tested for performance. In the examples, the kinds and contents of substances or additives used, and the results of performance tests of lithium ion batteries are shown in tables 1 to 4, wherein the contents of the respective additives are weight percentages calculated based on the mass of the electrolyte. Unless otherwise specified, DCR as used herein refers to the direct current resistance of a lithium ion battery at 10% state of charge (SOC).
And then testing the performance of the lithium ion battery.
[ measurement of parameters of negative electrode sheet ]
(1) Pole piece OI value VOI：
And (4) disassembling the tested battery to obtain a negative plate, and soaking the negative plate in Ethyl Methyl Carbonate (EMC) for cleaning. XRD is tested by adopting a Brookfield X-ray diffractometer according to the general rule of X-ray diffraction analysis and the method for measuring the lattice parameters of the artificial graphite, namely JIS K0131-. Different peak position changes represent different unit cell sizes of the graphite, the graphitization process of the graphite material can be reflected, and the peak area is obtained by integrating the peak intensity and the half-peak width. Wherein VOI represents the orientation of the negative active materialIndex according to VOI＝C004/C110Calculating, wherein C004 is the peak area of 004 characteristic diffraction peak in X-ray diffraction spectrogram of the cathode, and C110Is the peak area of the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode.
(2) Pole piece compaction density P:
standing the tested battery at 25 deg.C for 5 min, constant-current charging the lithium ion battery to 3.85V (50% SOC) at 0.7C, disassembling the battery in a drying room, and recording the mass (g/cm) of the negative plate in unit area after the electrolyte is volatilized2) And the thickness (cm) of the negative plate (the number of collection points is more than 14). The compacted density PD of the negative plate is the mass (g/cm) of the negative plate in unit area2) The thickness (cm) of the negative electrode sheet.
(3) Pole piece adhesion test
And disassembling the tested battery to obtain a negative plate with two sides coated with the negative material, and soaking the negative plate in Ethyl Methyl Carbonate (EMC) for cleaning. Taking a pole piece with two sides coated with negative materials, wherein the pole piece is about 15-20 cm; pasting the pole piece on a steel plate by using a 3M double-sided adhesive tape; testing the pole piece by using a material testing machine INSTRON 3365 to obtain the relation between force and distance; and calculating to obtain the pole piece adhesion value.
(4) Tensile strength test of negative current collector
And disassembling the battery to be tested to obtain a negative plate, and removing the negative active material and the bottom coating to obtain a negative current collector. The negative electrode current collector was cut at a test temperature of 25 ℃ to have a length x width of 200mm x 15mm, and the tensile properties were tested by a universal material testing machine 5848 at a tensile rate of 50mm/min, the tensile strength and elongation of which were calculated from the maximum load and the elongation at length at the time of breaking the specimen.
(5) Porosity test of negative plate
And (4) disassembling the battery to be tested to obtain a negative plate, and soaking the negative plate in Ethyl Methyl Carbonate (EMC) for cleaning. The measurement was carried out by a gas displacement method using an American Macmor Rutach densitometer (ACCUPYC II 1345). The percentage of the pore volume in the pole piece in the total volume of the pole piece is the porosity of the pole piece, and the calculation formula is as follows: porosity ═ V-V0)/V × 100%, where V0 is the true volume and V is the apparent volume.
(6) And testing the resistance of the negative plate:
and (4) disassembling the tested battery to obtain a negative plate, and soaking the negative plate in Ethyl Methyl Carbonate (EMC) for cleaning. And measuring the resistivity of the pole piece by adopting a four-probe method. The apparatus used for the four-probe method test was a precision dc voltage current source (model SB 118), four copper plates 1.5cm long by 1cm wide by 2mm thick were fixed on a line at equal intervals, the distance between the two copper plates in the middle was L (1cm to 2cm), and the base material for fixing the copper plates was an insulating material. During testing, the lower end faces of four copper plates are pressed on a tested pole piece, the copper plates at two ends are connected with direct current I, voltage V is measured at the two copper plates in the middle, the values of I and V are read three times, the average value of I and V is obtained, and V/I is the pole piece resistance at the tested position.
[ test of electrochemical Performance of Battery ]
(1) Swelling test of negative plate along X/Y direction
Standing the tested battery at 25 ℃ for 5 minutes, charging the lithium ion battery to 4.4V at a constant current of 0.7C, and then charging to 0.05C at a constant voltage of 4.4V; and (3) disassembling the battery in a drying room, cutting out part of the negative plate, testing the width of the negative plate along the X/Y direction by using a CCD (charge coupled device), and comparing the width with the width of the pole piece collected after cold pressing to obtain the expansion rate of the pole piece along the X/Y axis direction.
(2) Dynamic performance test
Standing the tested battery at 25 ℃ for 5 minutes, charging the lithium ion battery to 4.4V at a constant current of 2C, and then charging to 0.05C at a constant voltage of 4.4V; standing for 5 min, discharging at constant current of 0.5C to 3V, and standing for 5 min. And repeating the charge-discharge process for 10 times, fully charging the battery, disassembling the battery in a drying room, and observing the lithium separation condition on the surface of the negative plate. And counting the areas of gray and golden yellow parts on the surface of the negative plate, wherein the area of the gray part is the area of the lithium analysis part.
The percentage of the area of lithium precipitation is equal to the partial area of lithium precipitation/the total area of the negative plate is equal to 100 percent
The more the area of lithium deposition, the worse the kinetics and the worse the charging ability, the smaller the area of lithium deposition, the better the kinetics and the charging ability.
(3) Electrochemical Impedance Spectroscopy (EIS)
a) The preparation and the lithium plating of the three-electrode battery are consistent, as the preparation method of the lithium ion battery is the same, in the preparation process of the lithium ion battery, a copper wire is connected into the battery as a reference electrode, the contact position of the copper wire is a blank area of a negative current collector without an active substance layer, the copper wire is close to a tab position but is not in contact with the tab, then the lithium is plated for 6 hours in the contact areas of the copper wire and the negative current collector by the current of 20 muA respectively, and the EIS is tested after the lithium plating is finished.
b) EIS testing step: the lithium-plated three-electrode battery is connected to a Bio-Logic VMP3B electrochemical workstation produced by the French Biaroje company for testing, the frequency range of the test is 30mHz to 50kHz, the amplitude is 5mV, and after data are collected, the data are analyzed by adopting an impedance complex plan to obtain the data of Rct.
(4) Lithium ion liquid phase transfer impedance (Rion)
The lithium ion batteries were tested in a Bio-Logic VMP3B electrochemical workstation, manufactured by Pioney corporation, France, with a frequency range of 30mHz to 50kHz and an amplitude of 5 mV. And analyzing the data by adopting an impedance complex plan after the data are collected to obtain the lithium ion liquid phase transfer impedance (Rion).
(5) DC impedance test (DCR)
Charging the lithium ion battery to 4.45V at a constant current of 1.5C at 0 ℃, and then charging to 0.05C at a constant voltage; standing for 30 minutes; discharge was performed at 0.1C for 10 seconds (0.1 second was tapped once and the corresponding voltage value U1 was recorded), and discharge was performed at 1C for 360 seconds (0.1 second was tapped once and the corresponding voltage value U2 was recorded). The charging and discharging steps were repeated 5 times. "1C" is a current value at which the battery capacity is completely discharged within 1 hour. The DCR is calculated according to the following formula: r ═ (U2-U1)/(1C-0.1C).
Table 1 shows the relationship between the electrode sheet expansion parameter J, the electrode sheet XY expansion rate and the charge transfer impedance Rct of different cathode sheets adopted in examples 1-7 and comparative examples 1-5 under different primer layer thicknesses, electrode sheet thicknesses and electrode sheet compaction densities.
TABLE 1 parameters of examples 1-7 and comparative examples 1-5
Figure BDA0003576381870000131
Comparing examples 1-7 and comparative examples 1-3 in Table 1, it can be seen that the XY expansion ratio of examples 1-5 is smaller than that of comparative example 1, and the charge transfer resistance is also smaller than that of comparative example 1, and the pole piece expansion parameter J in each example satisfies 3.8. ltoreq. J.ltoreq.14, at which time the primer layer can improve the adhesion between the active material layer and the current collector and help release the stress generated when the active material layer expands in the XY direction; and the conductive agent on the bottom coating is beneficial to improving the conductivity of the lithium ion battery and is reflected in the reduction of charge transfer resistance. The ratio of the thickness of the undercoat layer to the thickness of the negative active material layer in comparative example 1 is low, so that the undercoat layer cannot form an effective slow-release effect on cyclic stress under similar compacted density conditions, and is not favorable for XY-direction expansion and cell dynamic performance.
The pole piece used in the comparative example 3 has lower compaction density, which is beneficial to the infiltration of electrolyte and the reduction of Rct, but the graphite is embedded with lithium after full charge to a certain extent, so that the expansion in the XY direction is increased, and the problems of first effect reduction, pole piece demoulding and the like can be caused.
The pole piece used in the comparative example 4 has too high compaction density, at this time, although the expansion parameter J of the pole piece is more than 3.8 and the expansion of the pole piece in the XY direction is less than or equal to 0.5%, the too high compaction density can cause most particles to be arranged at an angle parallel to the current collector, consequently, the electrolyte infiltration is poor, the contact area of the material and the electrolyte is greatly reduced, so that the ion embedding or the ion separation is seriously hindered, the Rct is remarkably increased, and the dynamic performance of the lithium ion battery is not facilitated.
The ratio of the thickness of the primer to the thickness of the pole piece used in comparative example 5 is higher, which results in a pole piece expansion parameter J larger than 14, and although the pole piece has smaller XY direction expansion, no benefit is obtained from the energy density direction.
In conclusion, when J is more than or equal to 4.5 and less than or equal to 7.5, the XY-direction expansion rate of the negative plate can be obviously reduced while the battery keeps higher energy density and dynamic performance, and the XY-direction expansion rate of the negative plate when the negative plate is fully charged is less than or equal to 0.5 percent.
Table 2 shows the effect of the physical parameters of the copper foil of the current collector and the OI value of the negative electrode sheets of examples 8 to 12 and comparative examples 6 to 9 on the XY expansion ratio and liquid phase transfer resistance of the electrode sheets at a primer thickness of 1.5 μm and a compacted density of 1.50 g/cc.
TABLE 2 parameters of examples 8 to 12 and comparative examples 6 to 9
Figure BDA0003576381870000141
It can be seen from comparison between examples 8-12 and comparative examples 7-8 in table 2 that when the expansion parameter K is greater than or equal to 50, the XY-direction expansion of the electrode sheet is less than or equal to 0.4%, which is probably because when the current collector thickness, the single-side thickness of the negative active material layer, and the orientation index of the negative active material satisfy the above relationship, the negative current collector can effectively release the XY-direction stress generated in the negative active material layer during the cycle process, so that the cycle stress of the active material layer is balanced, the thickness expansion is prevented from being amplified by the uneven XY-direction cycle stress, and the XY-direction expansion can also be improved by the Z-direction release after the electrode sheet is fully charged.
When the OI value of the pole piece in the comparative example 6 is more than or equal to 25, the wettability of the material and the electrolyte is poor, and the liquid phase transfer impedance is obviously increased. Comparative example 7 used an electrode sheet with too small an OI value and the particle arrangement tended to be perpendicular to the current collector direction, resulting in too much XY expansion after full charge. Therefore, the pole piece OI value is 15-25, and small liquid phase transfer impedance can be considered while small expansion in the XY direction is ensured.
The copper foil used in comparative example 9 had an excessively large thickness, where K > 100, and had a very large effect on the energy density of the battery although the XY direction swelling was small. Therefore, the thickness of the copper foil is 6-10 mu m, K is more than or equal to 50 and less than or equal to 100, and excellent XY direction expansion performance can be obtained while excessive energy density is not lost.
Table 3 lists the effect of primer thickness, S ═ O double bond compound content in the electrolyte on the dynamic performance at a sheet compaction density of 1.50g/cc for a sheet thickness of 6 μm for a copper foil and 65 μm for a sheet thickness.
TABLE 3 parameters of examples 13 to 17 and comparative examples 10 to 11
Figure BDA0003576381870000151
Examples 14 and 17 and comparative examples 10 to 11 show that when the content of the S ═ O compound is controlled to 0.5 to 1%, the SEI film thickness and the resistance of the surface of the negative electrode can be reduced, and the kinetic properties can be improved; when the content of the S ═ O compound is 2 to 3%, the DCR resistance increases.
The content of the S-O compound is related to the specific surface area of the negative active material, and when M/A is more than or equal to 0.3 and less than or equal to 3, the expansion of the pole piece in the XY direction is within the range of the weight 1 and the pole piece has good dynamic performance.
In comparative example 10, the ratio of M/a was too low, and the SEI formed by the electrolyte at the negative electrode was incomplete, thus causing slight lithium precipitation and higher DCR resistance; the higher S ═ O compound content in comparative example 11 caused more serious lithium deposition and excessive DCR resistance.
Table 4 lists the effect of different negative electrode sheets on the adhesion and resistance of the negative electrode sheet at different primer thicknesses.
TABLE 4 parameters for examples 19-23 and comparative example 12
Figure BDA0003576381870000161
In examples 19 to 23 and comparative example 12, when the thickness of the undercoat layer was 1.5 to 3 μm, the increase in the thickness of the undercoat layer was advantageous in terms of the adhesion effect between the negative active material and the current collector, and the negative electrode sheet had low resistance; when the thickness of the primer layer is further increased, the resistance of the pole piece is obviously increased, so that the thickness of the primer layer is not required to be excessively large. The primer used in comparative example 12 has too small a thickness, which results in too small a pole piece adhesion, and the negative pole piece resistance increases significantly, which is detrimental to the cell dynamics.
The above-disclosed features are not intended to limit the scope of practice of the present disclosure, and therefore, all equivalent variations that are described in the claims of the present disclosure are intended to be included within the scope of the claims of the present disclosure.

Claims (13)

1. An electrochemical device comprising a negative electrode sheet, wherein,
the negative plate comprises a negative current collector, a negative primer layer and a negative active material layer;
the undercoat layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the undercoat layer;
a thickness S (μm) of the negative electrode undercoat layer, a thickness L (μm) of a single-sided negative electrode active material layer, a compacted density P (g/cm) of the negative electrode active material layer3) The relationship between them satisfies:
3.8≤100×(S/L)+P≤14。
2. the electrochemical device according to claim 1,
a thickness S (μm) of the negative electrode undercoat layer, a thickness L (μm) of the single-sided negative electrode active material layer, and a compacted density P (g/cm) of the negative electrode active material layer3) The relationship between them satisfies:
4.5≤100×(S/L)+P≤7.5。
3. the electrochemical device according to claim 1,
the ratio of the thickness S (mum) of the negative electrode base coat to the thickness L (mum) of the single-sided negative electrode active material layer is 1: 8 to 1: 150.
4. The electrochemical device according to claim 1,
the thickness S of the negative electrode bottom coating is 1-5 μm;
the negative electrode active material layer has an OI value VOIFrom 15 to 25;
the value range of the L is 40-100 mu m;
the P is 1.1g/cc to 1.8 g/cc.
5. The electrochemical device according to claim 1,
the electrochemical device further comprises an electrolyte;
the electrolyte comprises a compound containing a sulfur-oxygen double bond;
the sulfur-oxygen double bond-containing compound has a mass percentage content of M (%) and a specific surface area of the negative electrode active material of A (M) (%), based on the mass of the electrolyte2The/g) satisfies: M/A is more than or equal to 0.3 and less than or equal to 3.
6. The electrochemical device according to claim 5,
the compound containing the sulfur-oxygen double bond is selected from at least one of methylene methane disulfonate, vinyl sulfate, allyl sulfate, 1, 3-propane sultone, 1, 4-butane sultone, ethylene sultone, 1, 3-propylene sultone, 1, 4-butene sultone, 1-methyl-1, 3-propylene sultone, divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone and methyl vinyl sulfone.
7. The electrochemical device according to claim 1,
the thickness D (mum) of the negative current collector satisfies: 50 ≤ 400 × (D/L) + VOI≤100；
Wherein, VOIDenotes the orientation index of the negative active material according to VOI＝C004/C110Performing a calculation of C004Is the peak area of 004 characteristic diffraction peak in X-ray diffraction spectrogram of the cathode, C110Is the peak area of the 110 characteristic diffraction peak in the X-ray diffraction spectrum of the negative electrode.
8. The electrochemical device according to claim 1,
the negative current collector comprises copper foil, and the thickness D is 4-20 μm;
the tensile strength of the negative current collector is X (MPa), and the following requirements are met: X/D is more than or equal to 60 and less than or equal to 100.
9. The electrochemical device according to claim 1,
at room temperature, the elongation of the negative current collector is delta (%), the value range of delta is 3-10, and the following conditions are met: l/delta is more than or equal to 4 and less than or equal to 20.
10. The electrochemical device according to claim 7,
the porosity of the negative plate is Z (%), the value range of Z is 20-50, and the following conditions are met: Z/D is more than or equal to 1 and less than or equal to 8.
11. The electrochemical device according to claim 1,
the binding force F (N/m) between the negative active material layer and the negative current collector satisfies: f is more than or equal to 10 and less than or equal to 30, and the value range of the resistance of the negative electrode is 3-30m omega.
12. The electrochemical device according to claim 1,
the negative active material of the negative active material layer includes at least one of natural graphite, artificial graphite, hard carbon, or soft carbon;
the negative electrode bottom coating comprises at least one of carbon black, carbon nano tubes, graphite, acetylene black and graphene.
13. An electronic device comprising the electrochemical device of claims 1-12.
CN202210352599.XA 2022-03-31 2022-03-31 Electrochemical device and electronic device Pending CN114665066A (en)

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