CN113421998A - Electrochemical device and electronic device - Google Patents

Electrochemical device and electronic device Download PDF

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CN113421998A
CN113421998A CN202110686237.XA CN202110686237A CN113421998A CN 113421998 A CN113421998 A CN 113421998A CN 202110686237 A CN202110686237 A CN 202110686237A CN 113421998 A CN113421998 A CN 113421998A
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active material
material layer
lithium manganate
coating
lithium
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CN113421998B (en
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韩翔龙
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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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
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    • 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
    • H01M2004/028—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

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Abstract

The present application provides an electrochemical device and an electronic device, wherein the electrochemical device includes: a positive electrode; the positive electrode includes: a positive electrode current collector, a first active material layer, and a second active material layer; the first active material layer is positioned between the positive electrode current collector and the second active material layer; the first active material layer contains a first type of lithium manganate, the second active material layer contains a second type of lithium manganate, and the mass percentage content of Fe in the first active material layer is larger than that of Fe in the second active material layer. The method can reduce the cost, inhibit the dissolution of Mn and improve the safety performance.

Description

Electrochemical device and electronic device
Technical Field
The present application relates to the field of electrochemical technologies, and in particular, to an electrochemical device and an electronic device.
Background
The price of ternary materials used in the positive electrode of an electrochemical device (such as a lithium ion battery) is high, in order to reduce the cost, some electrochemical devices adopt lithium manganate with low price as a positive electrode material, however, the lithium manganate is easy to react with HF in an electrolyte to dissolve Mn, and during the use process, Mn dissolves into the electrolyte and then deposits to a negative electrode, and finally, an SEI (solid electrolyte interphase) film of the negative electrode is damaged, and lithium is separated out in the charging and discharging process, and the lithium is ignited seriously.
Disclosure of Invention
In some embodiments, the present application provides an electrochemical device comprising: a positive electrode; the positive electrode includes: a positive electrode current collector, a first active material layer, and a second active material layer; the first active material layer is positioned between the positive electrode current collector and the second active material layer; the first active material layer contains a first type of lithium manganate, the second active material layer contains a second type of lithium manganate, and the mass percentage content of Fe in the first active material layer is larger than that of Fe in the second active material layer.
In some embodiments, the mass percentage of Fe in the first active material layer is 800ppm to 10000 ppm; and/or the second active material layer contains not less than 90ppm and less than 800ppm of Fe by mass.
In some embodiments, the particles of the first type of lithium manganate are non-spherical; the particles of the second type of lithium manganate are spherical or spheroidal.
In some embodiments, the first type of lithium manganate comprises LixMnyMzOa(ii) a Wherein M comprises at least one of Nb, B, Mg, Al, Si, P, S, Ti, Cr, Mn, Cu, Zn, Ga, Ge, Y, Zr, Mo, Ag, Ba, W, In, Sn, Pb or Sb; x is 0.9 to 1.2, y is 0.5 to 1.0, z is 0.001 to 0.2, and a is 0.5 to 4.0.
In some embodiments, M comprises Nb, and the atomic ratio of Nb to M is b: 1, wherein b is 0.1 to 1.
In some embodiments, the second type of lithium manganese oxide has an average particle size of 13 μm to 25 μm.
In some embodiments, the electrochemical device further includes a negative electrode including a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including: at least one of Sn, Sb, lithium titanate, a tin-based compound, a silicon-based compound, artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads or graphene.
In some embodiments, the difference between the mass percentage content of Fe of the first active material layer and the mass percentage content of Fe of the second active material layer is 2000ppm to 7000 ppm.
In some embodiments, the first type of lithium manganate is MnO2The prepared lithium manganate and the second type lithium manganate are Mn3O4And (3) preparing the lithium manganate.
In some embodiments, an electronic device is provided that includes an electrochemical device of any of the present applications.
In some embodiments of the application, the second type of lithium manganate has good HF resistance and cannot dissolve out Mn, and the first type of lithium manganate is located in the first active material layer, so that the first type of lithium manganate cannot be in direct contact with an electrolyte, and is not easy to dissolve out Mn, thereby reducing the risk of dissolving out Mn of the positive electrode. In some embodiments of the application, the second active material layer is adopted to protect the first active material layer, so that the dissolution of Mn is prevented, and the overall cost of the anode is reduced by utilizing the low-cost advantage of the first type of lithium manganate, so that the cost of the electrochemical device is reduced, and the safety performance of the electrochemical device is ensured.
Drawings
The above and other features, advantages and aspects of various embodiments of the present disclosure will become more apparent by referring to the following detailed description when taken in conjunction with the accompanying drawings. Throughout the drawings, the same or similar reference numbers refer to the same or similar elements. It should be understood that the drawings are schematic and that elements and elements are not necessarily drawn to scale.
Fig. 1 is a schematic diagram of a positive electrode of an embodiment of the disclosure.
Fig. 2 is a schematic of the change in cycling capacity for example 1 and comparative example 1 of the present disclosure.
Fig. 3 is a schematic of the change in cycling capacity for example 2 and comparative example 2 of the present disclosure.
Fig. 4 is a schematic graph of the capacity fade for example 3 and comparative example 3 of the present disclosure.
Fig. 5 is a schematic graph of the capacity fade for example 4 and comparative example 4 of the present disclosure.
Detailed Description
Embodiments of the present application will be described in more detail below. While certain embodiments of the present application have been illustrated, it should be understood that the present application may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather are provided for a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are for illustrative purposes only and are not intended to limit the scope of the present application.
To reduce the cost of electrochemical devices (e.g., lithium ion batteries), some technologies employ MnO2The lithium manganate prepared for the raw material is used as the anode material of an electrochemical device, but the lithium manganate reacts with HF in an electrolyte in the using process to dissolve Mn, and finally an SEI film of a negative electrode is damaged. In other techniques, the use of more costly Mn3O4The prepared lithium manganate is low in Mn dissolution risk, but the lithium manganate is high in cost, low in gram-volume and limited in application.
In some embodiments, the present disclosure provides an electrochemical device, which may be a lithium ion battery, comprising: a positive electrode; as shown in fig. 1, the positive electrode includes: a positive electrode collector 10, a first active material layer 11, and a second active material layer 12; as the positive electrode collector 10, an aluminum foil, a copper foil, or the like can be used. The first active material layer 11 is located between the positive electrode collector 10 and the second active material layer 12; the first active material layer 11 contains a first type of lithium manganate, the second active material layer 12 contains a second type of lithium manganate, and the mass percentage content of Fe in the first active material layer 11 is larger than the mass percentage content of Fe in the second active material layer 12.
In some embodiments, the first type of lithium manganate is MnO2The prepared lithium manganate and the second type lithium manganate are Mn3O4The prepared lithium manganate and the second lithium manganate have better HF resistance and are not easy to dissolve Mn, and because the first lithium manganate is positioned on the first active material layer 11 and the first active material layer 11 is positioned between the second active material layer 12 and the positive current collector 10, the first lithium manganate cannot be in direct contact with the electrolyte and can also be in direct contact with the electrolyteMn is not easy to dissolve out, thereby reducing the risk of dissolving out Mn and improving the safety performance. In some embodiments of the present application, the second active material layer 12 is used to protect the first active material layer 11, prevent Mn from dissolving out, and reduce the overall cost of the positive electrode by taking advantage of the low cost of the first type of lithium manganate. Therefore, some embodiments of the present disclosure ensure the safety of the electrochemical device while reducing the cost of the electrochemical device.
It is understood that the raw material may have some residue during the process of preparing lithium manganate due to the limitation of the manufacturing process. Therefore, in practice, it is possible to measure whether or not the first active material layer 11 includes MnO2To judge whether the material for preparing the first type of lithium manganate is MnO or not2. For using MnO2The first kind of lithium manganate is prepared, the first active material layer 11 comprises MnO2. Similarly, it is possible to measure whether or not Mn is included in second active material layer 123O4To determine whether the material for preparing the second type lithium manganese oxide is Mn3O4. For the use of Mn3O4The second type lithium manganese oxide was prepared, and the second active material layer 12 included Mn3O4。
In some embodiments of the present disclosure, the first active material layer 11 includes an elemental iron and/or an iron compound, and the second active material layer 12 includes an elemental iron and/or an iron compound. In some embodiments, the first and second lithium manganate types comprise iron and/or iron compounds, and for using MnO2First kind of prepared lithium manganate, MnO2The iron content in the raw material is higher, and Mn is adopted3O4Second type of lithium manganese acid prepared as raw material, Mn used therefor3O4The iron content in the raw material is low, so that the mass percentages of Fe in the prepared first type lithium manganate and the second type lithium manganate are different, and further, the mass percentages of Fe in the first active material layer 11 using the first type lithium manganate and the second active material layer 12 using the second type lithium manganate are different.
In some embodiments of the present application, the positive electrode of the electrochemical device has a double-layer coating structure by the firstThe active material layer 11 reduces the manufacturing cost, and the contact between the first type lithium manganate in the first active material layer 11 and the HF is reduced through the second active material layer 12, so that the safety performance is improved. In some embodiments of the present application, MnO is utilized2The first kind of lithium manganate prepared has the advantages of low cost and Mn3O4The prepared second lithium manganese oxide has the advantage of high stability, and the cost can be reduced and the controllable risk of Mn dissolution can be ensured by a double-layer coating mode.
In some embodiments of the present disclosure, the mass percentage content of Fe in the first active material layer 11 is 800ppm to 10000ppm, optionally 2100ppm to 8000 ppm; in some embodiments, the mass percentage content of Fe in the second active material layer 12 is 90ppm to 800 ppm. In some examples, limiting the mass percentage of Fe in first active material layer 11 and second active material layer 12 to the above range may indicate that the first type of lithium manganate is formed using MnO2The prepared lithium manganate and the second type lithium manganate are Mn3O4And (3) preparing the lithium manganate.
In some embodiments of the present disclosure, the difference between the mass percentage content of Fe in first active material layer 11 and the mass percentage content of Fe in second active material layer 12 is 2000ppm to 7000 ppm.
In some embodiments of the present disclosure, the particles of the first type of lithium manganate are non-spherical; the particles of the second type of lithium manganate are spherical or spheroidal. In some embodiments, the spherical or spheroidal lithium manganese dioxide of the second type can be in sufficient contact with the electrolyte to protect the first active material layer. Since the first type of lithium manganate particles are non-spherical, contact with the electrolyte can be reduced, and elution of Mn can be further prevented.
In some embodiments of the present disclosure, the first type of lithium manganate comprises LixMnyMzOa(ii) a Wherein M comprises at least one of Nb, B, Mg, Al, Si, P, S, Ti, Cr, Mn, Cu, Zn, Ga, Ge, Y, Zr, Mo, Ag, Ba, W, In, Sn, Pb or Sb; x is 0.9 to 1.2, y is 0.5 to 1.0, z is 0.001 to 0.2, and a is 0.5 to 4.0.
In some embodiments of the present disclosure, M comprises Nb in an atomic ratio of Nb to M of b: 1, wherein b is 0.1 to 1. In some embodiments, Nb in the first type of lithium manganate can stabilize the structure of the first type of lithium manganate, thereby improving the structural stability. If b is less than 0.1, the effect on improving structural stability may not be significant.
In some embodiments of the disclosure, the second type of lithium manganate has an average particle size of 13 μm to 25 μm. In some embodiments, the average particle size of the second type lithium manganese oxide may be, for example, a Dv50 value of the second type lithium manganese oxide, and when the average particle size of the second type lithium manganese oxide is too small, the contact area with the electrolyte may be increased, which is not favorable for structural stability, and when the average particle size of the second type lithium manganese oxide is too large, the rate capability may be reduced. Optionally, the second type of lithium manganese oxide has an average particle size of 18 μm.
In some embodiments of the present disclosure, the first active material layer 11 and the second active material layer 12 further include a conductive agent and a binder, the conductive agent may be conductive graphite, carbon fiber, carbon nanotube, or the like, and the binder may be polyvinylidene fluoride.
In some embodiments of the present disclosure, the electrochemical device further includes a negative electrode including a negative electrode current collector and a negative electrode active material layer, the negative electrode current collector may employ an aluminum foil, a copper foil, or the like, and the negative electrode active material layer includes: at least one of Sn, Sb, lithium titanate, a tin-based compound, a silicon-based compound, artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads or graphene. In some embodiments, the negative electrode further comprises a conductive agent, a thickening agent and a binder, the conductive agent can adopt conductive graphite, the thickening agent can adopt sodium carboxymethyl cellulose, and the binder can adopt styrene butadiene rubber.
In some embodiments of the present disclosure, an electrochemical device comprises: an isolation film; the separator includes: at least one of a polypropylene single-layer diaphragm, a polyethylene single-layer diaphragm, a polypropylene/polyethylene/polypropylene three-layer composite diaphragm, a diaphragm which takes polyethylene terephthalate non-woven fabrics as a base material and is provided with a nano ceramic impregnated coating, or a diaphragm which takes polyolefin mixed resin coated on a porous base material.
In some embodiments of the present disclosure, it is preferred,the electrochemical device comprises an electrolyte, wherein the electrolyte comprises a solvent and a lithium salt, and the solvent is selected from one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), Ethyl Propyl Carbonate (EPC), ethyl butyl carbonate (BEC), dipropyl carbonate (DPC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), gamma-butyrolactone (gamma-BL), Vinylene Carbonate (VC) and Propylene Sulfite (PS) in any proportion; the lithium salt is selected from lithium hexafluorophosphate (LiPF)6) Lithium tetrafluoroborate (LiBF)4) Lithium hexafluoroarsenate (LiAsF)6) Lithium perchlorate (LiClO)4) Lithium trifluoromethanesulfonate (CF)3SO3Li) or several kinds in any proportion.
In some embodiments of the present application, the electrochemical device is a wound lithium ion battery or a stacked lithium ion battery.
In some embodiments of the present application, the electrochemical device may be a lithium ion battery, and the lithium ion battery may be a secondary battery (e.g., a lithium ion secondary battery), a primary battery (e.g., a lithium primary battery, etc.), and the like, but is not limited thereto.
Embodiments of the present application also provide electronic devices including the electrochemical devices described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a large household battery, and the like.
The present application will be better illustrated by the following examples, in which a lithium ion battery is used as an example.
The following describes a method of testing various parameters of the present application.
And (3) cycle testing: the lithium ion battery was charged to 4.2V at 25 ℃ with a constant current of 0.5C. Then, the mixture was charged at a constant voltage of 4.2V until the current became 0.05C, and the mixture was allowed to stand for 5 min. Then discharging to 2.8V at constant current of 1.0C, and standing for 2 min. This was taken as a cycle and the discharge capacity C was recorded0Repeating the above cycle for 1000 times, recording discharge capacity C once per cycle, and calculating cycle capacity retention rate C/C0X 100%, the amount of Mn eluted was measured after the end of 1000 cycles.
And (3) testing the calendar life: charging the lithium ion battery to 100%, standing at 45 +/-2 ℃ or 70 +/-2 ℃, and charging the lithium ion battery to 4.2V at a constant current of 0.5 ℃. Then charging with constant voltage of 4.2V until the current is 0.05C, standing for 5min, fully charging and standing for 24 h; then discharging to 2.8V at constant current of 1.0C, and standing for 2 min. This was taken as a cycle and the discharge capacity C was recorded0The cycles were repeated 100 times, the discharge capacity C was recorded every 1 cycle, and the cycle capacity retention rate C/C was calculated0 X 100%, the amount of Mn eluted was measured after the end of 80 cycles.
The method for testing the average particle size of lithium manganate comprises the following steps: the particle distribution of lithium manganate was measured by a laser particle size analyzer (model MasterSizer3000) to obtain Dv50 of the particle distribution. The particle Dv50 refers to the particle size corresponding to 50% by volume of the cumulative particle size distribution of the sample.
The method for testing the mass percentage content of Fe in the active material layer comprises the following steps: taking 1 g of samples at three different positions in the active material layer respectively, testing the mass percentage content of Fe in the samples by using an inductively coupled plasma atomic emission spectrometer (ICP), and taking the average value of the obtained three values as the mass percentage content of Fe in the active material layer.
Example 1
Preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96: 0.8: 0.8: 2.4 in N-methylpyrrolidone solution to form slurry 1. Using aluminum foil as the front surfaceAnd (3) a positive current collector (16 μm), and coating the slurry 1 on the positive current collector to form a coating layer 1. Adding Mn3O4The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96: 0.8: 0.8: 2.4 in N-methylpyrrolidone solution to form slurry 2. And coating the slurry 2 on the coating 1 to form a coating 2, and drying, cold pressing and cutting to obtain the anode. The lithium manganese oxide in the coating 1 contains Nb, and the molecular formula is LiMn1.96Nb0.04O4The magnetic impurity (magnetic impurity is Fe element) was 3000ppm, lithium manganese oxide in the coating 2 was spherical particles, Dv50 was 18.0 μm, and the magnetic impurity (magnetic impurity is Fe element) was 150 ppm. Coating 1: the weight ratio of the coating 2 is 1: 9 coat weight of coating 1 was 0.020kg/m2The coating weight was 0.18kg/m2。
Preparation of a negative electrode: mixing artificial graphite (V)Negative pole0.1V), styrene butadiene rubber and sodium carboxymethyl cellulose according to the weight ratio of 97.7: 1.0: the proportion of 1.3 is dissolved in deionized water to form cathode slurry. Copper foil is adopted as a negative current collector (8 mu m), and the negative slurry is coated on the negative current collector (coating weight is 0.070 kg/m)2) And drying, cold pressing and cutting to obtain the cathode.
Preparing an electrolyte: under the environment with the water content of less than 10ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): propyl propionate: Vinylene Carbonate (VC): 20: 30: 20: 28: 2, weight ratio) are mixed according to the weight ratio of 10: 90 are formulated to form an electrolyte.
Preparing an isolating membrane: selecting single-layer polypropylene (PP) as a diaphragm, and having air permeability of 76secs/100cm3。
Preparing a lithium ion battery: and stacking the negative electrode, the positive electrode and the isolating membrane in sequence to enable the isolating membrane to be positioned between the positive electrode and the negative electrode to play an isolating role, and then winding the components into an electrode assembly. The electrode assembly was then packed in an aluminum plastic film pouch and, after dehydration at 80 ℃, a dry electrode assembly was obtained. And then injecting the electrolyte into a dry electrode assembly, and completing the preparation of the lithium ion battery through the working procedures of vacuum packaging, standing, formation, shaping and the like.
Comparative example 1
Comparative example 1 differs from example 1 only in the preparation of the positive electrode and the remaining steps are the same.
Preparing a positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96: 0.8: 0.8: and 2.4, dissolving the mixture in the N-methyl pyrrolidone solution to form positive electrode slurry. Coating the anode slurry on an aluminum foil, and drying, cold pressing and cutting to obtain the anode. The molecular formula of lithium manganate is LiMn1.96Nb0.04O4Coating weight 0.2kg/m2The magnetic impurity (Fe element as a magnetic impurity) was 3000 ppm.
The results of the performance tests of example 1 and comparative example 1 are shown in fig. 2, and it can be seen from fig. 2 that the cycle performance of example 1 is significantly better than that of comparative example 1, the elution amount of Mn after 1000 cycles of example 1 is 600ppm, and the elution amount of Mn of comparative example 1 is 1500 ppm. This is probably because the double coating was used in example 1, and the Mn in coating 2 in example 1 was3O4The prepared lithium manganate protects MnO in the coating 12The prepared lithium manganate reduces the contact of lithium manganate in the coating 1 and electrolyte, thereby reducing the dissolution of Mn. While the positive electrode of comparative example 1 has only coating 1 and no coating 2, MnO2The prepared lithium manganate is corroded by HF in the electrolyte, so that Mn is seriously dissolved out, and the cycle performance is reduced.
Example 2
Preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96.2: 0.6: 0.8: 2.4 in N-methylpyrrolidone solution to form slurry 1. The slurry 1 was coated on a positive current collector using aluminum foil as the positive current collector (16 μm), to form a coating layer 1. MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95.7: 0.9: 0.9: the ratio of 2.5 was dissolved in N-methylpyrrolidone solution to form slurry 2. And coating the slurry 2 on the coating 1 to form a coating 2, and drying, cold pressing and cutting to obtain the anode. Lithium manganese oxide in coating 1Has Nb and Mg, and the molecular formula is LiMn1.94Nb0.05Mg0.01O4The magnetic impurity (magnetic impurity is Fe element) was 3800ppm, lithium manganate in the coating layer 2 was spherical particles, Dv50 was 25 μm, and the magnetic impurity (magnetic impurity is Fe element) was 100 ppm. Coating 1: the weight ratio of the coating 2 is 2: 8, coat weight of coat 1 was 0.040kg/m2The coating weight was 0.16kg/m2。
Preparation of a negative electrode: mixing artificial graphite (V)Minus 10.1V), Si (V)Minus 20.6V), styrene butadiene rubber and sodium carboxymethyl cellulose in a weight ratio of 92.8: 4.9: 1.0:1.3 (corresponding to a ratio of artificial graphite to Si of 95: 5) and prepared as in example 1.
Preparing an electrolyte: the same as in example 1.
Preparing an isolating membrane: selecting single-layer Polyethylene (PE) as a diaphragm, coating ceramic on one side of the diaphragm, and ensuring that the air permeability is 85secs/100cm3。
Preparing a lithium ion battery: the same as in example 1.
Comparative example 2
Comparative example 2 is different from example 2 only in the preparation of the positive electrode, and the rest is the same.
Preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95.7: 0.9: 0.9: 2.5 is dissolved in the N-methyl pyrrolidone solution to form the anode slurry. Coating the anode slurry on an aluminum foil, and drying, cold pressing and cutting to obtain the anode. The molecular formula of lithium manganate is LiMn1.94Nb0.05Mg0.01O4Coating weight 0.2kg/m2The magnetic impurity (Fe element as a magnetic impurity) was 3800 ppm.
The results of the performance tests of example 2 and comparative example 2 are shown in fig. 3, and it can be seen from fig. 3 that the cycle performance of example 2 is significantly better than that of comparative example 2, the elution amount of Mn of example 2 after 1000 cycles is 400ppm, and the elution amount of Mn of comparative example 2 is 1600 ppm. The elution of Mn in example 2 is lower than that in example 1, probably because the lithium manganate in example 2 contains Mg, the structural stability of the lithium manganate is further improved, and the precipitation of Mn is prevented.
Example 3:
preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96.2: 0.6: 0.8: 2.4 in N-methylpyrrolidone solution to form slurry 1. An aluminum foil is used as a positive current collector (16 μm), and the slurry 1 is coated on the positive current collector and dried to form the coating 1. Adding Mn3O4The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95.7: 0.9: 0.9: the ratio of 2.5 was dissolved in N-methylpyrrolidone solution to form slurry 2. And coating the slurry 2 on the coating 1 to form a coating 2, and drying, cold pressing and cutting to obtain the anode. The lithium manganese oxide in the coating 1 contains Nb and Zr and has a molecular formula of LiMn1.94Nb0.05Zr0.01O4The magnetic impurity (magnetic impurity is Fe element) was 3800ppm, lithium manganate in the coating layer 2 was spherical particles, Dv50 was 13 μm, and the magnetic impurity (magnetic impurity is Fe element) was 120 ppm. Coating 1: the weight ratio of the coating 2 is 5: 5 coating weight of coating 1 was 0.080kg/m2The coating weight of the coating layer 2 was 0.08kg/m2。
Preparation of a negative electrode: mixing natural graphite (V)Negative pole0.1V), artificial graphite (V)Negative pole0.1V), styrene butadiene rubber and sodium carboxymethyl cellulose are dissolved in deionized water according to the weight ratio of 30:67.7:1.0:1.3 to form cathode slurry. The copper foil is adopted as a negative current collector, and the negative slurry is coated on the negative current collector (the coating weight is 0.080 kg/m)2) And drying, cold pressing and cutting to obtain the cathode.
Preparing an electrolyte: lithium hexafluorophosphate was formulated with a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): Ethyl Methyl Carbonate (EMC): Vinylene Carbonate (VC): 20: 30: 20: 28: 2, weight ratio) at a water content of less than 10ppm to form an electrolyte at a weight ratio of 8: 92.
Preparing the isolating membrane by selecting a polypropylene/polyethylene/polypropylene three-layer composite membrane, coating ceramic on one surface of the membrane, and enabling the air permeability to be 200secs/100cm3。
Preparing a lithium ion battery: the same as in example 1.
Comparative example 3
Comparative example 3 is different from example 3 only in the preparation of the positive electrode, and the rest is the same.
Preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95.7: 0.9: 0.9: 2.5 is dissolved in the N-methyl pyrrolidone solution to form the anode slurry. And coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and cutting to obtain the positive electrode. The molecular formula of lithium manganate is LiMn1.94Nb0.05Zr0.01O4The magnetic impurity (Fe element as magnetic impurity) was 3800ppm, and the coating weight was 0.2kg/m2。
The results of the performance test of example 3 and comparative example 3 are shown in FIG. 4, in which the 80-calendar-life Mn of example 3 was dissolved out at 1000ppm and the 80-calendar-life Mn of comparative example 3 was dissolved out at 3000 ppm. This is because the double-layer coating method adopted in example 3 reduces the contact of lithium manganate in the coating layer 1 with the electrolyte, thereby suppressing elution of Mn from the coating layer 1.
Example 4:
preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96: 0.8: 0.8: 2.4 in N-methylpyrrolidone solution to form slurry 1. An aluminum foil is used as a positive current collector (16 mu m), and the slurry 1 is coated on the positive current collector and dried to form a coating 1. Adding Mn3O4The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95.7: 0.9: 0.9: the ratio of 2.5 was dissolved in N-methylpyrrolidone solution to form slurry 2. And coating the slurry 2 on the coating 1 to form a coating 2, and drying, cold pressing and cutting to obtain the anode. The lithium manganate in the coating 1 contains Nb, and the molecular formula of the lithium manganate is LiMn1.95Nb0.05O4The magnetic impurity (magnetic impurity is Fe element) was 7000ppm, lithium manganese oxide in the coating 2 was spherical particles, Dv50 was 15 μm, and the magnetic impurity (magnetic impurity is Fe element) was 90 ppm. The weight ratio of coating 1 to coating 2 was 15:85,the coating weight of coating 1 was 0.032kg/m2The coating weight of coating 2 was 0.179kg/m2。
Preparation of a negative electrode: the same as in example 1.
Preparing an electrolyte: the same as in example 1.
Preparing an isolating membrane: selecting a polypropylene/polyethylene/polypropylene three-layer composite diaphragm, coating ceramic on one side, and having the air permeability of 200secs/100cm3。
Preparing a lithium ion battery: the same as in example 1.
Comparative example 4
Comparative example 4 is different from example 4 only in the preparation of the positive electrode.
Preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95.7: 0.9: 0.9: 2.5 is dissolved in the N-methyl pyrrolidone solution to form the anode slurry. Coating the anode slurry on an aluminum foil, and drying, cold pressing and cutting to obtain the anode. The molecular formula of lithium manganate is LiMn1.95Nb0.05O4The magnetic impurity (Fe element) was 7000ppm, and the coating weight was 0.2kg/m2。
The results of the performance tests of example 4 and comparative example 4 are shown in fig. 5, and it can be seen from fig. 5 that the storage performance of the lithium ion battery of example 4 is better than that of the lithium ion battery of comparative example 4, the Mn at 80 calendar life of example 4 is dissolved out 1500ppm, and the Mn at 80 calendar life of comparative example 4 is dissolved out 4000ppm, because the coating 2 protects the lithium manganate in the coating 1 and reduces the Mn dissolution in the double-layer coating manner adopted in example 4.
Example 5:
preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 96: 0.8: 0.8: 2.4 in N-methylpyrrolidone solution to form slurry 1. The slurry 1 was coated on a positive current collector using aluminum foil as the positive current collector (16 μm), to form a coating layer 1. MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95: 1.1: 1.4: 2The ratio of 5 was dissolved in a solution of N-methylpyrrolidone to form slurry 2. And coating the slurry 2 on the coating 1, and drying, cold pressing and cutting to obtain the anode. The lithium manganese oxide in the coating 1 contains Nb and Al, and the molecular formula is LiMn1.92Nb0.05Al0.02O4The magnetic impurity (Fe element) was 6000ppm, lithium manganese oxide in the coating 2 was spherical particles, Dv50 was 20 μm, and the magnetic impurity was 190 ppm. Coating 1: the weight ratio of the coating 2 is 15:85, coating weight of coating 1 was 0.032kg/m2The coating weight was 0.179kg/m2。
Preparation of a negative electrode: mixing artificial graphite (V)Negative pole0.08V), styrene butadiene rubber and sodium carboxymethyl cellulose according to the weight ratio of 97.7: 1.0: the ratio of 1.3 was dissolved in deionization to form a negative electrode slurry. Copper foil is used as a negative current collector (8 mu m), and the negative slurry is coated on the negative current collector (coating weight is 0.085 kg/m)2) And drying, cold pressing (the thickness of the pole piece is 0.12mm) and cutting to obtain the negative pole.
Preparing an electrolyte: under an environment with a water content of less than 10ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): methyl ethyl carbonate (EMC): 10: 40: 25: 25, weight ratio) were mixed in a weight ratio of 12.5: 87.5 to form an electrolyte.
Preparing an isolating membrane: the same as in example 1.
Preparing a lithium ion battery: the same as in example 1.
Comparative example 5
Comparative example 5 is different from example 5 only in the preparation of the positive electrode, and the rest is the same.
Preparation of the positive electrode: MnO of2The prepared lithium manganate, the conductive carbon black, the carbon nano tube and the polyvinylidene fluoride are mixed according to the weight ratio of 95: 1.1: 1.4: 2.5 is dissolved in the N-methyl pyrrolidone solution to form the anode slurry. Coating the anode slurry on an aluminum foil, and drying, cold pressing and cutting to obtain the anode. The molecular formula of lithium manganate is LiMn1.92Nb0.05Al0.02O4Magnetic impurities (Fe element) 6000ppm, and a coating layer 0.2kg/m2。
As a result of the test, the 80-calendar-life Mn elution of example 5 was 500ppm, and the 80-calendar-life Mn elution of comparative example 5 was 900 ppm. In example 5, the lithium manganate in the coating layer 1 is protected by the coating layer 2 by means of double-layer coating, so that elution of the lithium manganate in the coating layer 1 is suppressed, and elution amount of Mn is reduced.
The statistics in the examples and comparative examples are shown in Table 1.
TABLE 1
Figure BDA0003124798130000131
Figure BDA0003124798130000141
Remarking: the first active material layer is a coating 1 and the second active material layer is a coating 2.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims (10)

1. An electrochemical device, comprising:
a positive electrode, the positive electrode comprising: a positive electrode current collector, a first active material layer, and a second active material layer; the first active material layer is positioned between the positive electrode current collector and the second active material layer;
the first active material layer contains a first type of lithium manganate, the second active material layer contains a second type of lithium manganate, and the mass percentage content of Fe in the first active material layer is larger than that of Fe in the second active material layer.
2. The electrochemical device according to claim 1, wherein at least one of the following conditions is satisfied:
the mass percentage of Fe in the first active material layer is 800ppm to 10000 ppm; or
The second active material layer contains Fe in a percentage by mass of not less than 90ppm and less than 800 ppm.
3. The electrochemical device according to claim 1, wherein at least one of the following conditions is satisfied:
the first type of lithium manganate particles are non-spherical; or
The particles of the second type of lithium manganese oxide are spherical or spheroidal.
4. The electrochemical device according to claim 1,
the first type of lithium manganate comprises LixMnyMzOa；
Wherein M comprises at least one of Nb, B, Mg, Al, Si, P, S, Ti, Cr, Mn, Cu, Zn, Ga, Ge, Y, Zr, Mo, Ag, Ba, W, In, Sn, Pb or Sb;
x is 0.9 to 1.2, y is 0.5 to 1.0, z is 0.001 to 0.2, and a is 0.5 to 4.0.
5. The electrochemical device according to claim 4,
m comprises Nb, and the atomic ratio of Nb to M is b: 1, wherein b is 0.1 to 1.
6. The electrochemical device according to claim 1,
the average particle size of the second type of lithium manganese oxide is 13 to 25 μm.
7. The electrochemical device of claim 1, further comprising a negative electrode current collector and a negative electrode active material layer comprising at least one of Sn, Sb, lithium titanate, tin-based compounds, silicon-based compounds, artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, or graphene.
8. The electrochemical device according to claim 1,
the difference between the mass percentage content of Fe in the first active material layer and the mass percentage content of Fe in the second active material layer is 2000ppm to 7000 ppm.
9. The electrochemical device of claim 1, wherein said first type of lithium manganate is MnO-based2The second kind of lithium manganate is Mn3O4And (3) preparing the lithium manganate.
10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.
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