CN116154101A - Electrochemical device and electronic device - Google Patents

Electrochemical device and electronic device Download PDF

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Publication number
CN116154101A
CN116154101A CN202310200234.XA CN202310200234A CN116154101A CN 116154101 A CN116154101 A CN 116154101A CN 202310200234 A CN202310200234 A CN 202310200234A CN 116154101 A CN116154101 A CN 116154101A
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positive electrode
electrolyte
lithium
active material
electrode active
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吴大贝
崔辉
邱亚明
唐超
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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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a positive electrode, a negative electrode and electrolyte; the positive electrode includes a positive electrode active material having P6 3 mc crystal structure; the mass content of boron element on the surface of the positive electrode is n by utilizing X-ray photoelectron spectroscopy analysis 1 The mass content of oxygen element on the surface of the positive electrode is n percent 2 % and n 1 /n 2 >0.2, wherein the electrolyte comprises at least one of lithium difluorooxalato borate, lithium tetrafluoroborate or lithium bistrifluoro methanesulfonimide. Electrochemical device and electronic device provided by the applicationThe device can improve the structural stability of the positive electrode active material in the circulation process under the ultrahigh pressure, and improve the circulation stability of the electrochemical device.

Description

Electrochemical device and electronic device
The present application is a divisional application of chinese invention with application number 202110564152.4 and the name of "electrochemical device and electronic device".
Technical Field
The present application relates to the field of energy storage technology, in particular, to electrochemical devices and electronic devices.
Background
The lithium ion battery is widely applied to the fields of portable electronic products, electric traffic, national defense aviation, energy storage and the like because of the advantages of high energy density, good cycle performance, environmental protection, safety, no memory effect and the like. In order to meet the demands of social development, the search for lithium ion batteries with higher energy and power densities is a highly desirable problem, requiring higher specific capacities and higher voltage platforms for the positive electrode materials used.
In order to obtain higher specific energy, positive electrode active materials are being developed toward high voltage, and current positive electrode active materials are Li with increasing voltage + A great deal of crystal is removed, the crystal structure of the material is damaged irreversibly, so that the lattice oxygen is removed, and the cycle performance of the battery is greatly reduced.
Therefore, there is an urgent need for an electrochemical device to improve the positive electrode interface stability and the cycle stability at high voltage.
Disclosure of Invention
In view of this, the application provides an electrochemical device, which can improve the structural stability of the positive electrode active material under ultra-high pressure in the circulation process and improve the circulation stability of the electrochemical device.
In a first aspect, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive electrode having P6 3 A positive electrode active material of mc crystal structure; the mass content of boron element on the surface of the positive electrode is n by utilizing X-ray photoelectron spectroscopy analysis 1 The mass content of oxygen element on the surface of the positive electrode is n percent 2 % and n 1 /n 2 >0.2。
In the above-described aspects, the positive electrode active material in the electrochemical device has P6 3 The mc crystal structure is stable, and the boron element in the electrolyte is combined to stabilize lattice oxygen in the positive electrode active material under high voltage, so that the structural stability of the positive electrode active material in the circulating process is improved, the oxidation of the electrolyte caused by the loss of active oxygen in the positive electrode active material under high voltage is reduced, and the circulating stability of the electrochemical device under ultrahigh voltage is improved.
With reference to the first aspect, in a possible embodiment, the mass content of the boron element in the positive electrode surface is n 1 ％，5<n 1 <15。
With reference to the first aspect, in a possible embodiment, the mass content of the oxygen element of the positive electrode surface is n 2 ％，8<n 2 <25。
With reference to the first aspect, in a possible embodiment, the electrochemical device has a characteristic peak in a range of 17.5 ° to 19 ° with a half-peak width of 0.05 ° to 0.1 ° in a full charge state using X-ray photoelectron spectroscopy analysis.
With reference to the first aspect, in one possible embodiment, the positive electrode active material satisfies at least one of the following features (a) to (c): (a) The positive electrode active material has an average particle diameter of 8 μm to 30 μm; (b) The tap density of the positive electrode active material is 2.2g/cm 3 To 3g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the (c) The positive electrode active material includes a lithium metal composite oxide having an oxygen element and an M element, wherein the M element includes at least one of Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
With reference to the first aspect, in one possible embodiment, the positive electrode active material includes Li x Na z Co 1- y M y O 2 Wherein, 0.6<x<1.02，0≤y<0.15，0≤z<0.03, M comprises at least one of Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
With reference to the first aspect, in a possible embodiment, the electrolyte includes at least one of lithium difluorooxalato borate, lithium tetrafluoroborate, or lithium bistrifluoro methanesulfonimide.
With reference to the first aspect, in a possible embodiment, the electrolyte includes at least one of lithium difluorooxalato borate, lithium tetrafluoroborate, or lithium bistrifluoro methanesulfonimide.
With reference to the first aspect, in one possible embodiment, the electrolyte satisfies at least one of the following conditions (d) to (f): (d) The electrolyte comprises lithium difluoro-oxalato-borate, wherein the mass of the lithium difluoro-oxalato-borate in the electrolyte is X, and the value range of X is 8-25; (e) The electrolyte comprises lithium difluorooxalato borate, wherein the mass of the lithium difluorooxalato borate in the electrolyte is X%, the electrolyte also comprises lithium tetrafluoroborate, the mass of the lithium tetrafluoroborate in the electrolyte is Y%, the value range of Y is 1-10, and X/Y is more than or equal to 0.8 and less than or equal to 25; (f) The electrolyte comprises lithium difluorooxalato borate, wherein the mass of the lithium difluorooxalato borate in the electrolyte is X percent, the electrolyte further comprises lithium tetrafluoroborate, the mass of the lithium tetrafluoroborate in the electrolyte is Y percent, the electrolyte further comprises lithium bistrifluoromethylsulfonimide, the mass of the lithium bistrifluoromethylsulfonimide in the electrolyte is Z percent, the value range of Z is 2 to 30, and the value of (X+Y)/Z is more than or equal to 0.3 and less than or equal to 17.5.
With reference to the first aspect, in one possible embodiment, 1.16.ltoreq.X+Y)/Z.ltoreq.13.
In a second aspect, the present application provides an electronic device comprising the electrochemical device according to the first aspect.
Compared with the prior art, the application has the following beneficial effects:
the positive electrode active material in the electrochemical device provided by the application has P6 3 The mc crystal structure has high stability, reduces the probability of particle breakage and crystal structure damage, and improves the structural stability of the positive electrode active material in the high-voltage cycling process, thereby improving the cycling performance of the electrochemical device.
The lithium salt in the electrolyte of the electrochemical device can form a positive electrode material solid electrolyte interface film rich in B-O bonds on the surface of the positive electrode active material, and under high voltage, the B-O bonds on the surface of the positive electrode can stabilize lattice oxygen in the positive electrode active material, so that the structural stability of the positive electrode active material in the high voltage circulation process is improved; through modification of the crystal structure of the positive electrode active material, the film forming protection of the positive electrode of the electrolyte is enhanced, and the cycling stability of the electrochemical device under ultrahigh voltage (> 4.55V) is improved.
Detailed Description
The following description is of the preferred embodiments of the present invention, and it should be noted that, for those skilled in the art, it is possible to make several improvements and modifications without departing from the principle of the embodiments of the present invention, and these improvements and modifications are also considered as the protection scope of the embodiments of the present invention.
For simplicity, only a few numerical ranges are explicitly disclosed herein. However, any lower limit may be combined with any upper limit to form a range not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each point or individual value between the endpoints of the range is included within the range, although not explicitly recited. Thus, each point or individual value may be combined as a lower or upper limit on itself with any other point or individual value or with other lower or upper limit to form a range that is not explicitly recited.
In the description herein, unless otherwise indicated, "above" and "below" are intended to include the present number, and the meaning of "multiple" in "one or more" is two or more.
The above summary of the present application is not intended to describe each disclosed embodiment or every implementation of the present application. The following description more particularly exemplifies illustrative embodiments. Guidance is provided throughout this application by a series of embodiments, which may be used in various combinations. In the various examples, the list is merely a representative group and should not be construed as exhaustive.
In a first aspect, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive directionThe electrode includes a positive electrode active material having P6 3 mc crystal structure; the mass content of boron element on the surface of the positive electrode is n by utilizing X-ray photoelectron spectroscopy analysis 1 The mass content of oxygen element on the surface of the positive electrode is n percent 2 % and n 1 /n 2 >0.2。
According to the electrochemical device, the lithium salt in the electrolyte can form the solid electrolyte interface film of the positive electrode material rich in B-O on the surface of the positive electrode active material, and under high voltage, B-O bonds on the surface of the positive electrode can stabilize lattice oxygen in the positive electrode active material, so that the structural stability of the positive electrode active material in the high voltage circulation process is improved; the positive electrode active material has P6 3 And the mc crystal structure has high stability, reduces the probability of particle breakage and crystal structure damage, and improves the structural stability of the positive electrode active material in the high-voltage circulation process. Through modification of a crystal structure, the film forming protection of the positive electrode of the electrolyte is enhanced, and the ultra-high voltage of the electrochemical device can be improved>4.55V).
As used herein, the positive electrode surface refers to an interface formed between an electrolyte and a positive electrode material after charge and discharge. As used herein, the "full charge state" refers to a state when the electrochemical device is charged to 4.55V or more. That is, in the fully charged state of the electrochemical device, the charge potential of the positive electrode is 4.55V or more, specifically, 4.55V, 4.56V, 4.57V, 4.58V, 4.59V, 4.6V, or the like.
As an alternative technical solution of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.
The positive electrode current collector can be a metal foil, a carbon-coated metal foil or a porous metal plate, and preferably aluminum foil.
The positive electrode active material layer includes a positive electrode active material having P6 3 The mc crystal structure, in particular to a hexagonal close-packed crystal structure, has higher stability of the crystal structure, lower probability of particle breakage and crystal structure damage, smaller structural change caused in the process of lithium ion deintercalation and intercalation, and has the advantages of high stability, low cost, and the likeThe stability in air and water is higher, thereby being beneficial to improving the cycle performance and the thermal stability of the lithium ion battery.
As an alternative technical scheme of the application, the positive electrode active material is a lithium metal composite oxide containing oxygen element and M element, wherein the M element comprises at least one of Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
Preferably, the M element comprises at least one of Al, mg, ti, mn or Y.
In a specific embodiment of the present application, the positive electrode active material has the chemical formula of Li x Na z Co 1-y M y O 2 Wherein, 0.6<x<0.85，0≤y<0.15，0≤z<0.03, M comprises at least one of Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
The electrochemical device has a characteristic peak having a half-width of 0.05 DEG to 0.1 DEG in a range of 17.5 DEG to 19 DEG in a full charge state by X-ray photoelectron spectroscopy analysis.
Specifically, characteristic peaks in the XRD spectrum of the positive electrode active material may be located at 17.5 °, 18 °, 18.5 °, 19 °, or the like, and the half-width of the characteristic peaks may be 0.05 ° to 0.1 °.
In some embodiments of the present application, the positive electrode active material includes, but is not limited to
Li 0.63 Co 0.985 Al 0.015 O 2 、Li 0.6 Na 0.01 Co 0.985 Al 0.015 O 2 、Li 0.7 Na 0.01 Co 0.985 Al 0.015 O 2 、DD210838I-DIV
Li 0.8 Na 0.01 Co 0.985 Al 0.015 O 2 、Li 0.7 Na 0.01 Co 0.98 Al 0.02 O 2 、Li 0.7 Na 0.01 Co 0.975 Al 0.025 O 2 、Li 0.7 Na 0.015 Co 0.985 Al 0.015 O 2 、Li 0.7 Na 0.02 Co 0.985 Al 0.015 O 2 、Li 0.7 Na 0.01 Co 0.983 Al 0.015 Mg 0.002 O 2 、Li 0.7 Na 0.01 Co 0.984 Al 0.015 Ti 0.001 O 2 、Li 0.7 Na 0.01 Co 0.994 Al 0.003 Mg 0.002 Ti 0.001 O 2 。
In some embodiments of the present application, the average particle diameter Dv50 of the positive electrode active material is 8 μm to 30 μm, and the average particle diameter may specifically be 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, or 30 μm, or the like, but may of course be other values within the above range, and is not limited thereto. The average particle diameter is too large, the diffusion path of lithium ions in large-particle-diameter particles is longer, the larger the resistance to be overcome by diffusion is, the crystal deformation and volume expansion of the positive electrode active material caused by the embedding process are continuously accumulated, so that the embedding process is gradually difficult to carry out, the particle diameter of the positive electrode active material is controlled below 30 mu m, the electrochemical dynamic performance and the rate capability in the charge and discharge process can be improved, the polarization phenomenon is reduced, and the battery has higher specific capacity, coulombic efficiency and cycle performance. The average particle size is too small, the specific surface area of the positive electrode active material is often larger, the surface side reaction is increased, the particle size of the positive electrode active material is more than 8 mu m, the particle size of the positive electrode active material is ensured not to be too small, the surface side reaction of the material is reduced, the agglomeration among particles of the positive electrode active material with too small particle size can be effectively inhibited, and the battery is ensured to have higher rate performance and cycle performance.
The tap density of the positive electrode active material is 2.2g/cm 3 To 3g/cm 3 . The tap density can be specifically 2.2g/cm 3 、2.3g/cm 3 、2.4g/cm 3 、2.5g/cm 3 、2.6g/cm 3 、2.7g/cm 3 、2.8g/cm 3 、2.9g/cm 3 Or 3g/cm 3 And the like, but may be any other value within the above range, and is not limited thereto. The tap density of the positive electrode active material is in the above range, which is advantageous for improving the specific capacity and energy density of the battery and improving the electricityRate performance and cycle performance of the cell.
Alternatively, the particles of the positive electrode active material may include primary particles and/or secondary particles.
The crystal structure of the positive electrode active material may be measured by an X-ray powder diffractometer, for example, a Brucker D8A_A25 type X-ray diffractometer manufactured by Brucker AxS, germany, using CuK alpha rays as a radiation source, and the wavelength of the radiation
Figure SMS_1
The scan 2 theta angle ranges from 10 deg. to 90 deg., and the scan rate is 4 deg./min.
The tap density of the positive electrode active material may be conveniently measured using instruments and methods well known in the art, such as a tap density meter, for example, FZS 4-4B-type tap density meter.
The average particle diameter Dv50 of the positive electrode active material is a meaning well known in the art, and the particle size test method is referred to in GB/T19077-2016. For example, it may be conveniently measured using a laser particle size analyzer, such as the Mastersizer model 3000 laser particle size analyzer available from Markov instruments, UK.
Further, the positive electrode active material layer further includes a binder and a conductive agent.
The binder may be one or more of styrene-butadiene rubber (SBR), aqueous acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA).
The conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
The above positive electrode may be prepared according to a conventional method in the art. The positive electrode active material, and optionally, a conductive agent and a binder are typically dispersed in a solvent (e.g., N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry, and the positive electrode slurry is coated on a positive electrode current collector, and subjected to processes such as drying, cold pressing, and the like to obtain a positive electrode.
Because the positive electrode active material of the first aspect of the application is adopted, the positive electrode has higher comprehensive electrochemical performance and safety performance.
Further, the anode may be an anode active material layer including an anode current collector and disposed on the anode current collector. For example, the anode current collector includes two opposite surfaces, and the anode active material layer is stacked on either or both of the two surfaces of the anode current collector.
The negative current collector may employ copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.
The anode active material layer typically includes an anode active material, and optionally, a conductive agent, a binder, and a thickener.
Examples of the negative electrode active material may include, but are not limited to, natural graphite, artificial graphite, mesocarbon microbeads (abbreviated as MCMB), hard carbon, soft carbon, silicon-carbon composite, li-Sn alloy, li-Sn-O alloy, sn, snO, snO 2 Or spinel structured lithiated TiO 2 -Li 4 Ti 5 O 12 At least one of Li metal and Li-Al alloy. Wherein the silicon-carbon composite means that it contains at least about 5 wt% silicon based on the weight of the silicon-carbon anode active material.
The conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers, the binder may be one or more of Styrene Butadiene Rubber (SBR), aqueous acrylic resin and carboxymethyl cellulose (CMC), and the thickener may be carboxymethyl cellulose (CMC). However, the present application is not limited to these materials, and other materials that can be used as a negative electrode active material, a conductive agent, a binder, and a thickener for a lithium ion battery may be used.
The above-described negative electrode may be prepared according to a conventional method in the art. The negative electrode active material, the optional conductive agent, the binder and the thickener are generally dispersed in a solvent, wherein the solvent can be deionized water to form uniform negative electrode slurry, the negative electrode slurry is coated on a negative electrode current collector, and the negative electrode is obtained after the procedures of drying, cold pressing and the like.
The separator is not particularly limited, and any known porous separator having electrochemical stability and chemical stability may be used, and may be, for example, a single-layer or multi-layer film of one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
On the basis of modifying the positive electrode active material, if the electrolytic liquid system is further improved, the interface of the positive electrode active material can be better stabilized, and side reaction between the positive electrode active material and the electrolyte is inhibited, so that the removal of lattice oxygen of the positive electrode active material is reduced, and the cycle performance of the electrochemical device is improved.
The electrolyte comprises an organic solvent, lithium salt and an additive.
As an alternative solution of the present application, the lithium salt in the electrolyte may include at least one of lithium difluorooxalato borate, lithium tetrafluoroborate, or lithium bistrifluoromethylsulfonimide. It can be understood that the lithium salt contains boron element, which is favorable for forming a B-O bond on the surface of the positive electrode when the electrolyte is in contact reaction with the surface of the positive electrode under high voltage, stabilizing lattice oxygen in the positive electrode active material and improving the structural stability of the positive electrode active material in the high voltage circulation process.
As an optional technical scheme of the application, the electrolyte comprises lithium difluoroborate (LiDFOB), the mass of the lithium difluoroborate (LiDFOB) in the electrolyte is X%, and the value range of X is 8 to 25. Specifically, the mass of lithium difluorooxalato borate (LiDFOB) in the electrolyte may be specifically 8%, 10%, 12%, 14%, 25%, or the like, and other values within the above range are also possible.
As an alternative solution of the present application, the electrolyte further includes lithium tetrafluoroborate (LiBF 4 ) The lithium tetrafluoroborate (LiBF 4 ) The mass of the electrolyte is Y, the value range of Y is 1 to 10, and X/Y is more than or equal to 0.8 and less than or equal to 25.
Specifically, lithium tetrafluoroborate (LiBF 4 ) The mass in the electrolyte may be specifically 1%, 2%, 4%, 5%, 6%, 7%, 8% or 10%, etc., and of course, may be within the above rangeOther values within.
The ratio of X/Y may be specifically 0.8, 1,2, 4, 6, 8, 10, 12, 14 or 25, or the like, but may be any other value within the above range.
As an optional technical scheme of the application, the electrolyte further comprises lithium bis (trifluoromethanesulfonyl imide) (LiTFSI), the mass of the lithium bis (trifluoromethanesulfonyl imide) (LiTFSI) in the electrolyte is Z%, the value range of Z is 2 to 30, and the value of Z is more than or equal to 0.3 and less than or equal to (X+Y)/Z is more than or equal to 17.5.
Specifically, the mass of lithium bistrifluoromethylsulfonylimide (LiTFSI) in the electrolyte may be specifically 2%, 4%, 6%, 8%, 11%, 15%, 20% or 30%, or the like, and other values within the above range may be also possible.
The ratio of (x+y)/Z may be specifically 0.3, 1,2,3, 6, 7, 9, 10, 11, 12, 13, 14, 15, 17.5, or the like, but may be any other value within the above range.
The organic solvent may include one or more of cyclic carbonate, chain carbonate, and carboxylate. For example, it may be: at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methylethyl carbonate (DEC), dimethyl carbonate (DMC), sulfolane (SF), γ -butyrolactone (γ -BL), propylethyl carbonate, methyl Formate (MF), ethyl formate (MA), ethyl Acetate (EA), ethyl Propionate (EP), propyl Propionate (PP), methyl propionate, methyl butyrate, ethyl butyrate, fluoromethyl carbonate, diethyl fluorocarbonate, and the like.
The electrolyte may further include a functional additive selected from at least one of Vinylene Carbonate (VC), vinyl sulfate (DTD), propane Sultone (PS), fluoroethylene carbonate (FEC), tris (trimethylsilyl) phosphate (TMSP), adiponitrile (ADN), succinonitrile (SN), 1,3, 6-Hexanetrinitrile (HTCN), or 1,2, 3-tris (2-cyanooxy) propane (TCEP).
As an alternative technical scheme of the application, the electrolyte comprises a heterocyclic sulfonate compound with a structure shown as a formula I, wherein the mass of the heterocyclic sulfonate compound in the electrolyte is 0.1-2%;
Figure SMS_2
wherein M is Na or K; x is O or S;
R 1 、R 2 、R 3 each independently selected from at least one of hydrogen, halogen, and aldehyde groups.
Specifically, the mass of the heterocyclic sulfonate compound in the electrolyte may be specifically 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%, or the like, but may be other values within the above range, and is not limited thereto.
Specifically, the heterocyclic sulfonate compound is selected from at least one of the following compounds:
Figure SMS_3
/>
Figure SMS_4
due to the adoption of the P6 3 Positive electrode active material having mc crystal structure, and LiDFOB and LiBF in the electrolyte 4 Or the positive film forming additives of LiTFSI are mutually matched and act together to stabilize lattice oxygen of the positive active material under high voltage, stabilize the structure of the positive active material and improve the cycling stability of the electrochemical device under high voltage.
As an optional technical solution of the present application, the electrochemical device of the present application further includes a separator disposed between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the electrochemical device are not particularly limited in the present application, and may be any of those disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic, etc., formed from a material that is stable to the electrolyte of the present application.
As an alternative solution of the present application, the release film may comprise a substrate layer and a coating layer. In some embodiments, the substrate layer is a nonwoven, film, or composite film having a porous structure. In some embodiments, the material of the substrate layer may include or be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. In some embodiments, the material of the substrate layer may include or be selected from a polyethylene porous film, a polypropylene porous film, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film, or the like.
The coating layer may be, but is not limited to, a polymer layer, an inorganic layer, or a mixed layer formed of a polymer and an inorganic substance. The coating layer thickness is 0.5 μm to 10 μm, and may be specifically 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 6 μm, 8 μm or 10 μm, etc.
As an alternative solution of the present application, the inorganic layer includes inorganic particles, and the inorganic particles may include or be selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The average particle diameter of the inorganic particles is 0.001 μm to 3 μm, specifically, 0.001 μm, 0.01 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 1.8 μm, 2 μm, 2.5 μm or 3 μm, etc., and is not limited herein.
As an optional technical solution of the present application, the polymer layer includes a binder, and the binder is at least one selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoroethylene copolymer (PVDF-HFP), polyvinylpyrrolidone (PVP), polyacrylate, pure acrylic emulsion (anionic acrylic emulsion formed by copolymerizing acrylate and a special functional monomer), styrene-acrylic emulsion ((styrene-acrylate emulsion) obtained by emulsion copolymerization of styrene and acrylate monomer), and styrene-butadiene emulsion (SBR obtained by emulsion copolymerization of butadiene and styrene).
Those skilled in the art will appreciate that the electrochemical device of the present application may be a lithium ion battery, or any other suitable electrochemical device. The electrochemical device in the embodiments of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include all kinds of primary batteries, secondary batteries, solar cells, or capacitors, without departing from the disclosure of the present application. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
The present application is further illustrated below in conjunction with specific embodiments. It should be understood that these examples are illustrative only of the present application and are not intended to limit the scope of the present application.
1. Preparation of positive electrode active material
1) Preparation of P6 3 Li of mc structure 0.73 Na 0.02 CoO 2
Step (1): the molar ratio of the cobaltosic oxide to the sodium carbonate powder is 0.75:1, mixing in proportion; sintering the uniformly mixed powder for 46h in oxygen atmosphere at 800 ℃ to obtain P6 3 Na of mc structure 0.75 CoO 2 ；
Step (2): na is mixed with 0.75 CoO 2 Mixing with lithium nitrate uniformly according to the molar ratio of Na to Li of 0.75:5, reacting for 6 hours at 300 ℃ in air atmosphere, washing reactants with deionized water for multiple times, washing the reactants with molten salt, and drying the powder to obtain the product with P6 3 Li of mc structure 0.73 Na 0.02 CoO 2 。
2) Preparation of P6 3 Li of mc structure x Na z Co 1-y Al y O 2
Step (1): cobalt chloride and aluminum sulfate are mixed according to the mole ratio of Co to Al of 1-y: y, adding the mixture into deionized water, adding precipitator sodium carbonate and complexing agent ammonia water to adjust the PH value to 7, and precipitating; the precipitate was then sintered at 600℃for 7h and ground to give (Co 1-y Al y ) 3 O 4 And (3) powder.
Step (2): will (Co) 1-y Al y ) 3 O 4 The molar ratio of Na to Co of the powder to the sodium carbonate powder is z: mixing the proportions of y; the evenly mixed powder is put in oxygen atmosphere at 800 DEG CSintering for 46h under the condition to obtain Na z Co 1-y Al y O 2 。
Step (3): na is mixed with z Co 1-y Al y O 2 The molar ratio of Na to Li with lithium nitrate is z: mixing at a ratio of 10x, reacting at 300 ℃ in air atmosphere for 6 hours, washing reactants with deionized water for multiple times, cleaning with molten salt, and drying powder to obtain the product with P6 3 Li of mc structure x Na z Co 1-y Al y O 2 。
3) Preparation of P6 3 Li of mc structure x Na z Co 1-y M y O 2
Li x Na z Co 1-y M y O 2 With Li x Na z Co 1-y Al y O 2 The preparation methods are basically the same, except that the types and/or contents of the doping elements M are different, and specifically, M is selected from Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
4) non-P6 3 Li of mc structure 0.58 Na 0.01 Co 0.985 Al 0.015 O 2
Step (1): adding cobalt chloride and aluminum sulfate into deionized water according to the molar ratio of cobalt to aluminum of 0.985:0.015, adding precipitator sodium carbonate and complexing agent ammonia water, and regulating the pH value to 7 to precipitate; the precipitate was then sintered and ground to obtain (Co 0.985 Al 0.015 ) 3 O 4 And (3) powder.
Step (2): will (Co) 0.985 Al 0.015 ) 3 O 4 The molar ratio of the powder to the lithium carbonate is 0.58: mixing at a ratio of 0.985, sintering in air at 1000deg.C for 12 hr, cooling, grinding and sieving to obtain Li with R-3m structure 0.58 Na 0.01 Co 0.985 Al 0.015 O 2 。
2. Preparation of the Positive electrode
The positive electrode active material Li prepared above x Na z Co 1-y M y O 2 Conductive carbon black (Super P), binder polyvinylidene fluoride (PVDF) in weight ratio 97:1.4:1.6, adding the mixture into N-methyl pyrrolidone (NMP) and fully stirring and mixing the mixture to form uniform anode slurry; wherein the solid content of the positive electrode slurry is 72wt%; uniformly coating the anode slurry on an anode current collector aluminum foil; and drying the coated aluminum foil, cold pressing, cutting, slitting and drying under vacuum conditions to obtain the anode.
3. Preparation of negative electrode
Mixing negative electrode active material artificial graphite, conductive carbon black (Super P), thickener sodium carboxymethylcellulose (CMC) and binder styrene-butadiene rubber (SBR) according to the weight ratio of 96.4:1.5:0.5:1.6, adding deionized water, and stirring uniformly to obtain negative electrode slurry, wherein the solid content of the negative electrode slurry is 54wt%. The negative electrode slurry is coated on a negative electrode current collector copper foil, then dried, cold-pressed, cut into pieces, welded with tabs and dried to obtain the negative electrode.
4. Preparation of a separator film
Selecting Polyethylene (PE) isolating film with thickness of 9 mu m, passing through polyvinylidene fluoride (PVDF) slurry and Al 2 O 3 And (5) coating and drying the slurry to obtain the final isolating film.
5. Preparation of electrolyte
Uniformly mixing Ethylene Carbonate (EC), propylene Carbonate (PC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) according to the mass ratio of EC to PC to EMC=20 to 20 to 40 to 30 in a dry argon environment, and then uniformly mixing fully dried lithium salt LiPF 6 (1 mol/kg) was dissolved in the above nonaqueous solvent, and finally the additive or lithium salt in the examples was added to the base electrolyte, and the electrolyte was obtained by mixing uniformly.
6. Preparation of lithium ion batteries
Sequentially stacking the positive electrode, the isolating film and the negative electrode, enabling the isolating film to be positioned between the positive electrode and the negative electrode to play a role in isolation, and then winding to obtain a bare cell; and (3) placing the bare cell in an aluminum plastic film of an outer packaging foil after welding the tab, injecting the prepared electrolyte into the dried bare cell, and performing procedures such as vacuum packaging, standing, formation, shaping, capacity testing and the like to obtain the soft-package lithium ion battery (the thickness is 3.3mm, the width is 39mm, and the length is 96 mm).
Performance test:
(1) Cycle performance test
The lithium ion batteries prepared in the examples and the comparative examples are charged to 4.6V at a constant current of 3C (the capacity of the soft-pack battery is 2000 mAh) and then charged to 0.05C at a constant voltage of 4.6V, the charging capacity at this time is recorded as the first-cycle charging capacity of the lithium ion battery, then the lithium ion battery is left stand for 5min, and then discharged to 3.0V at a constant current of 1C and left stand for 5min, and the discharging capacity at this time is recorded as the first-cycle discharging capacity of the lithium ion battery, namely the initial capacity of the lithium ion battery. And carrying out 200-cycle charge and discharge tests on the lithium ion battery according to the method, and detecting to obtain the discharge capacity of the 200 th cycle. Capacity retention (%) at 25 ℃ for 200 cycles=discharge capacity at 200 th cycle/first cycle discharge capacity x 100%.
The lithium ion batteries prepared in the examples and the comparative examples are charged to 4.6V at a constant current of 3C (the capacity of the soft-pack battery is 2000 mAh) and then charged to 0.05C at a constant voltage of 4.6V, the charging capacity at the moment is recorded as the first-ring charging capacity of the lithium ion battery, then the lithium ion battery is left stand for 5min, and then discharged to 3.0V at a constant current of 1C and left stand for 5min, wherein the discharging capacity at the moment is recorded as the first-ring discharging capacity of the lithium ion battery, namely the initial capacity of the lithium ion battery, in a cyclic charging and discharging process. And carrying out 200-cycle charge and discharge tests on the lithium ion battery according to the method, and detecting to obtain the discharge capacity of the 200 th cycle. 200 cycles of capacity retention (%) at 45 ℃ =discharge capacity at 200 cycles/first cycle discharge capacity×100%.
(2) The positive plate after formation is analyzed and tested by utilizing X-ray photoelectron spectroscopy:
fully placing the formed battery cell to 3V, disassembling the battery cell in a glove box, taking part of positive plates, washing with Dimethylaminoethyl Methacrylate (DM), airing for 48 hours in the glove box, sealing the positive plates with a sample bag, performing X-ray photoelectron spectroscopy analysis (namely positive electrode surface), and generally selecting O and B elements from test elements, thereby obtaining a positive electrode surface related X-ray photoelectron spectroscopy analysis map and related element mass percentages. The test data are shown in table 1.
Following the above preparation procedure, batteries of examples 1 to 13 and comparative examples 1 and 2 were obtained, in which:
electrolyte no LiPF in examples 1 to 13 6 The positive electrode active material is P6 3 Li of mc structure 0.63 Na 0.01 Co 0.985 Al 0.015 O 2 The method comprises the steps of carrying out a first treatment on the surface of the The types and the masses of the lithium salt added to the electrolyte are shown in Table 1, and the other conditions are the same as those of comparative example 2.
LiPF having 1mol/kg lithium salt in comparative example 1 6 The positive electrode active material is non-P6 3 Li of mc structure 0.58 Na 0.01 Co 0.985 Al 0.015 O 2 。
LiPF having 1mol/kg lithium salt in comparative example 2 6 The positive electrode active material is P6 3 Li of mc structure 0.63 Na 0.01 Co 0.985 Al 0.015 O 2 。
The mass content of each element and the mass content ratio of boron element and oxygen element in the positive electrode XPS test after the formation of the comparative example 1 and the example 7 are shown in the table 1.
TABLE 1
Figure SMS_5
The test results of examples 1 to 13 and comparative examples 1 and 2 are shown in table 2:
TABLE 2
Figure SMS_6
/>
Figure SMS_7
It is noted that "/" indicates that the component is not added or not present.
From the test data of examples 1 to 6 in the above table, it can be seen that as the lipfob content in the electrolyte increases, the ratio of the boron element mass content to the oxygen element mass content on the surface of the positive electrode after formation increases gradually, since the increase of the ratio of the boron element mass content to the oxygen element mass content means that more B-O bonds can be formed in the interface, which is favorable for stabilizing lattice oxygen in the positive electrode active material, the cycle capacity retention rate of the battery at normal temperature (25 ℃) or high temperature (45 ℃) increases first, the basic change after the cycle capacity retention rate is not obvious, and the appropriate concentration and the boron/oxygen element mass content ratio on the surface of the positive electrode cooperate with the positive electrode active material to improve the cycle stability of the battery at voltage.
From the test data of examples 2, 7 to 10 in the above table, it can be seen that, as LiBF in electrolyte 4 The increase of the content is beneficial to stabilizing lattice oxygen in the positive electrode active material, the cyclic capacity retention rate is increased, and the cyclic stability of the battery under voltage is improved.
From the test data of examples 8, 11 to 13 in the above table, it can be seen that, as the content of LiTFSI in the electrolyte increases, the ratio of the mass content of boron element to the mass content of oxygen element on the positive electrode surface after formation increases insignificantly, and LiTFSI can slightly improve the high voltage cycle because LiTFSI is higher than litfsob and LiBF 4 More stable and can provide stable lithium ion transport.
Since examples 1 to 13 employ P6 3 Positive electrode active material of mc structure, which is excellent in structural stability during high voltage cycle due to lattice oxygen in the crystal structure, and the electrolytes of examples 1 to 13 contain boron element, boron element and P6 3 The positive electrode active material with the mc structure has synergistic effect, and can stabilize lattice oxygen on the surface of the positive electrode material, thereby improving high-voltage circulation.
As can be seen from the test data of comparative example 1 and examples 1 to 10,since the positive electrode active material in comparative example 1 was non-P6 3 Li of mc structure 0.58 Na 0.01 Co 0.985 Al 0.015 O 2 The lattice structure is unstable, and in the high-voltage circulation process, lattice oxygen in the lattice of the positive electrode active material is removed, and the electrolyte is oxidized, so that the circulation capacity retention rate of the battery at normal temperature (25 ℃) or high temperature (45 ℃) is obviously reduced.
From the test data of comparative example 2 and examples 1 to 10, although the positive electrode active material was P6 3 Li of mc structure 0.63 Na 0.01 Co 0.985 Al 0.015 O 2 But does not contain LiTFSI, liDFOB or LiBF in the electrolyte 4 No boron element can form a B-O bond with oxygen element, which is not beneficial to stabilizing lattice oxygen in the positive electrode material, and electrolyte LiPF 6 The positive electrode film forming ability of the electrolyte is smaller than that of the electrolyte LiDFOB, so that the stable positive electrode interface film is not formed, and the battery cycle capacity retention rate is also obviously reduced.
Further, examples 14 to 23 were prepared according to the above preparation method, the positive electrode active materials in examples 14 to 23 are shown in table 2, and the other conditions were the same as in example 5; the test results of examples 5, 14 to 23 and comparative example 1 are shown in table 3:
TABLE 3 Table 3
Figure SMS_8
As can be seen from a comparative analysis of the data in table 2, examples 5, 14 to 23 of the present application have P6 3 Li of mc structure x Na z Co 1-y M y O 2 The characteristic peak of the (002) crystal face is between 17.5 and 19 degrees, the half-peak width of the characteristic peak is between 0.05 and 0.1 degrees, and the boron element contained in the electrolyte and the positive electrode active material act cooperatively, so that the stability of the positive electrode active material to air, water and carbon dioxide can be improved, and the cycling stability of the battery under normal temperature or high temperature environment and high voltage can be improved.
Further, examples 24 to 29 were produced according to the above production methods, and the electrolytes of examples 24 to 29 were different in the amount of the compound represented by formula I-1 added, with the other conditions being the same as example 5; the test results of examples 5 and 24 to 29 are shown in table 4:
TABLE 4 Table 4
Figure SMS_9
From the test data of examples 5 and 24 to 29 in Table 3, it is understood that the cyclic capacity retention rate of the battery varies as the amount of the compound of formula I-1 increases as shown in Table 4, since the compound of formula I-1 facilitates the formation of a stable solid electrolyte membrane at the interface of the positive electrode, and the boron-containing lithium salt and P6 3 The positive electrode active material with the mc structure has synergistic effect, reduces side reaction of electrolyte, and further improves the cycle performance of the battery.
While the preferred embodiment has been described, it is not intended to limit the scope of the claims, and any person skilled in the art can make several possible variations and modifications without departing from the spirit of the invention, so the scope of the invention shall be defined by the claims.

Claims (9)

1. An electrochemical device includes a positive electrode, a negative electrode, and an electrolyte; it is characterized in that the method comprises the steps of,
the positive electrode includes a positive electrode having P6 3 A positive electrode active material of mc crystal structure; the mass content of boron element on the surface of the positive electrode is n by utilizing X-ray photoelectron spectroscopy analysis 1 The mass content of oxygen element on the surface of the positive electrode is n percent 2 % and n 1 /n 2 >0.2；
The electrolyte comprises at least one of lithium difluorooxalato borate, lithium tetrafluoroborate or lithium bistrifluoromethylsulfonimide.
2. The electrochemical device of claim 1, wherein 5<n 1 <15。
3. The electrochemical device according to claim 1, wherein the positive electrode active material has a characteristic peak having a half-peak width of 0.05 ° to 0.1 ° in a range of 17.5 ° to 19 ° using X-ray photoelectron spectroscopy in a full charge state of the electrochemical device.
4. The electrochemical device of claim 1, wherein the positive electrode active material satisfies at least one of the following features (a) to (c):
(a) The positive electrode active material has an average particle diameter of 8 μm to 30 μm;
(b) The tap density of the positive electrode active material is 2.2g/cm 3 To 3g/cm 3 ；
(c) The positive electrode active material includes a lithium metal composite oxide having an oxygen element and an M element, wherein the M element includes at least one of Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
5. The electrochemical device of claim 1, wherein the positive electrode active material comprises Li x Na z Co 1- y M y O 2 Wherein, 0.6<x<1.02，0≤y<0.15，0≤z<0.03, M comprises at least one of Al, mg, ti, mn, fe, ni, zn, cu, nb, cr or Zr.
6. The electrochemical device of claim 1, wherein the electrolyte satisfies at least one of the following conditions (d) to (f):
(d) The electrolyte comprises lithium difluoro-oxalato-borate, wherein the mass of the lithium difluoro-oxalato-borate in the electrolyte is X, and the value range of X is 8-25;
(e) The electrolyte comprises lithium difluorooxalato borate, wherein the mass of the lithium difluorooxalato borate in the electrolyte is X%, the electrolyte also comprises lithium tetrafluoroborate, the mass of the lithium tetrafluoroborate in the electrolyte is Y%, the value range of Y is 1-10, and X/Y is more than or equal to 0.8 and less than or equal to 25;
(f) The electrolyte comprises lithium difluorooxalato borate, wherein the mass of the lithium difluorooxalato borate in the electrolyte is X percent, the electrolyte further comprises lithium tetrafluoroborate, the mass of the lithium tetrafluoroborate in the electrolyte is Y percent, the electrolyte further comprises lithium bistrifluoromethylsulfonimide, the mass of the lithium bistrifluoromethylsulfonimide in the electrolyte is Z percent, the value range of Z is 2 to 30, and the value of (X+Y)/Z is more than or equal to 0.3 and less than or equal to 17.5.
7. The electrochemical device of claim 1, wherein the electrolyte comprises a heterocyclic sulfonate compound of the structure of formula I, the heterocyclic sulfonate compound being present in the electrolyte in an amount of 0.1% to 2% by mass;
Figure FDA0004109138150000011
wherein M is Na or K; x is O or S;
R 1 、R 2 、R 3 each independently selected from at least one of hydrogen, halogen, and aldehyde groups.
8. The electrochemical device of claim 7, wherein the heterocyclic sulfonate compound is selected from at least one of the following:
Figure FDA0004109138150000021
/>
Figure FDA0004109138150000022
Figure FDA0004109138150000023
/>
9. an electronic device, characterized in that it comprises the electrochemical device according to any one of claims 1 to 8.
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