CN114843443B - Method for evaluating structural stability of positive electrode material - Google Patents

Method for evaluating structural stability of positive electrode material Download PDF

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Publication number
CN114843443B
CN114843443B CN202210512255.0A CN202210512255A CN114843443B CN 114843443 B CN114843443 B CN 114843443B CN 202210512255 A CN202210512255 A CN 202210512255A CN 114843443 B CN114843443 B CN 114843443B
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positive electrode
electrode material
peak
structural stability
peak position
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CN114843443A (en
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段瑞杰
黄本赫
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Svolt Energy Technology Co Ltd
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Svolt Energy Technology Co 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4285—Testing apparatus
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • H01M10/446—Initial charging measures
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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 invention relates to the technical field of batteries, in particular to a method for evaluating structural stability of a positive electrode material. According to the invention, the change of the peak angle of the (003) peak of the ternary positive electrode material in the charging process is tested by an in-situ XRD method, and the structural stability of the positive electrode material is represented. The invention can rapidly evaluate the structural stability of the positive electrode material, and characterizes the change of the unit cell parameters of the positive electrode material in the charge and discharge process by an in-situ XRD test method, so as to achieve the purpose of evaluating the structural stability of the positive electrode material in the charge and discharge process.

Description

Method for evaluating structural stability of positive electrode material
Technical Field
The invention relates to the technical field of batteries, in particular to a method for evaluating structural stability of a positive electrode material.
Background
In the existing lithium ion battery, the performance of the positive electrode material is related to the performance of the whole battery system. Common positive electrode materials include lithium iron phosphate, ternary layered positive electrode materials, lithium cobaltate and the like, wherein the ternary layered positive electrode materials are widely applied and researched by higher working voltage and higher energy density. The structural stability of the positive electrode material determines the cycling stability of the positive electrode material, thereby affecting the cycling performance of the whole battery system.
For stability evaluation of the positive electrode material, a button type full battery or soft package full battery mode is generally adopted to carry out long-time charge and discharge circulation until the discharge capacity of the battery is reduced to 80% of the initial capacity of the battery, capacity loss of the positive electrode material in the whole charge and discharge process of the battery is determined through a reverse buckling test mode, and the positive electrode material is characterized by the capacity reduction rate of the positive electrode material in the battery. Or the intrinsic physical and chemical characteristics of the positive electrode material are represented by means of battery impedance, physical representation and the like so as to represent the advantages and disadvantages of the positive electrode material.
The current method for evaluating the stability of the positive electrode material adopts a charge-discharge circulation method, so that a large amount of test resources and time are consumed, the evaluation period is long, the development period of the positive electrode material and the system is long, and the resource consumption cost is increased; the means of battery impedance and physical characterization can only test static information of the positive electrode material, and can not characterize stability change of the positive electrode material in the charge and discharge process, so that evaluation of the positive electrode material is different.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide a method for evaluating the structural stability of a positive electrode material, which aims to solve the technical problems that in the prior art, a great amount of test resources and time are required to be consumed for evaluating the stability of the positive electrode material by adopting a charge-discharge circulation method, the evaluation period is long, only static information of the positive electrode material can be tested by adopting a battery impedance and physical characterization means, and the stability change of the positive electrode material in the charge-discharge process can not be characterized, so that the evaluation of the positive electrode material is different.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
a method of evaluating structural stability of a positive electrode material, comprising the steps of:
(a) Respectively preparing at least two positive electrode materials to be evaluated into positive electrode plates under the same conditions;
(b) Adopting an in-situ XRD test mould to respectively assemble the positive plates in the step (a) into button cells;
(c) Charging each button cell in the step (b), and simultaneously carrying out in-situ XRD scanning on the positive plate to obtain the peak position of a (003) peak and the charge state of the corresponding button cell in each in-situ XRD scanning process;
(d) The maximum deformation amount B1, the maximum deformation percentage C1, the variable B2 at the end of positive electrode charging, the deformation percentage C2 at the end of positive electrode charging, the deformation rate D1 of positive electrode and the deformation rate D2 at the end of positive electrode charging are obtained according to the following formula:
B1＝A1-A2；
C1％＝(A1-A2)/A1；
B2＝A3-A2；
C2％＝(A3-A2)/A1；
D1＝(A1-A2)/SOC1；
D2＝(A3-A2)/(1-SOC1)；
wherein A1 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 0%; a2 represents a peak position minimum angle of the (003) peak of the positive electrode material during charging; a3 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 100%; SOC1 represents the state of charge of the button cell when the peak position of the (003) peak of the positive electrode material during charging is minimum;
comparing B1, C1% and D1 of each button cell, wherein the smaller B1, C1% and D1 are, the better the structural stability of the positive electrode material corresponding to the button cell is;
and/or comparing B2, C2% and D2 of each button cell, wherein the smaller the B2, C2% and D2, the better the structural stability of the positive electrode material corresponding to the button cell, the better the high voltage performance.
Preferably, the positive electrode material includes at least one of ternary positive electrode material, lithium cobaltate, lithium nickel cobalt manganese aluminate, lithium nickel manganese aluminate layered material, and doping modified material of the lithium nickel manganese aluminate layered material.
Preferably, in step (a), the preparation method of each positive electrode sheet specifically includes:
and mixing the positive electrode materials to be evaluated with the same binder, the same conductive agent and the same solvent according to the same proportion to obtain positive electrode slurries respectively, and coating the positive electrode slurries on the surfaces of the same positive electrode current collector respectively and drying the positive electrode slurries.
Preferably, the mass ratio of the positive electrode material, the binder and the conductive agent is (70 to 98): (1-20): (1-20).
Preferably, the binder comprises PVDF.
Preferably, the conductive agent includes at least one of carbon nanotubes, graphene, and conductive carbon black.
Preferably, in step (a), the current during charging is 0.01mA to 1mA and the voltage is 2.7V to 4.4V.
Preferably, the in situ XRD test mold comprises: the device comprises an anode base, two insulating sealing rubber rings, a conductive support bracket, a cathode top cover and two insulating fixing nuts;
an in-situ XRD test window is arranged in the central area of the positive electrode base; the upper surface of the positive electrode base is provided with two screws which are respectively positioned at two opposite sides of the in-situ XRD test window; the side end face of the positive electrode base is provided with a positive electrode lug;
the insulating sealing rubber ring and the positive electrode base are enclosed to form a containing cavity; the accommodating cavity is used for accommodating a laminate of the conductive foil, the positive plate, the diaphragm and the negative plate;
the conductive support bracket is arranged on the upper surface of the laminated body through a ring opening of the insulating sealing rubber ring;
the surface of the negative electrode top cover is respectively provided with two through holes, and the upper ports of the two through holes are respectively provided with an insulating separation rubber ring; the negative top cover is arranged on the upper surfaces of the conductive support bracket and the insulating sealing rubber ring, and two screws respectively penetrate through the two through holes; a negative electrode lug is arranged on the side end face of the negative electrode top cover;
the two insulating fixing nuts are respectively connected with the two screw rods through threads to fix the positive electrode base and the negative electrode top cover.
Preferably, the negative electrode sheet comprises a lithium foil or a graphite negative electrode.
Preferably, in step (c), the in-situ XRD scan is performed at a scan rate of 1 DEG to 10 DEG/min and at a scan interval of 0 to 10min in a scan range of 16 DEG to 20 deg.
Preferably, after the obtaining the peak position of the (003) peak and the corresponding battery capacity in each in-situ XRD scanning process, the method further comprises: and (5) making a charge state-peak position angle curve.
Preferably, the (003) peak detecting the positive electrode material is replaced with the (110) peak detecting the positive electrode material;
the scanning range of the in-situ XRD scanning is 55-65 degrees, the scanning speed is 1-10 degrees/min, and the scanning interval is 0-10 min.
Preferably, in step (b), the peak position of the (003) peak and the voltage of the button cell corresponding to the peak position are obtained in each in-situ XRD scanning process, and a cell voltage-peak position angle curve is produced.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the change of the peak angle of the (003) peak of the ternary positive electrode material in the charging process is tested by an in-situ XRD method, and the structural stability of the positive electrode material is represented. The method can rapidly evaluate the structural stability of the positive electrode material, and the cell parameter change of the positive electrode material in the charge-discharge process is represented by an in-situ charge XRD test method so as to evaluate the structural stability of the positive electrode material in the charge-discharge process.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of the structure of an in situ XRD (X-ray diffraction) test die according to the invention;
FIG. 2 is the results of the in situ XRD test in example 1;
fig. 3 is a plot of state of charge versus peak position for positive electrode material a, positive electrode material b in example 1;
fig. 4 is a graph showing capacity retention rate of the positive electrode material a and the positive electrode material b in comparative example 1;
fig. 5 is a plot of state of charge versus peak position for positive electrode material c, positive electrode material d in example 2;
fig. 6 is an XRD curve of the ternary cathode material.
Reference numerals:
1-positive electrode base, 2-normal position XRD test window, 3-positive electrode tab, 4-conductive foil, 5-positive plate, 6-diaphragm, 7-negative plate, 8-insulating sealing rubber ring, 9-conductive support bracket, 10-negative electrode top cover, 11-negative electrode tab, 12-insulating fixing nut, 13-insulating separation rubber ring, 14-screw rod and 15-through hole.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
The invention relates to a method for evaluating the structural stability of a positive electrode material, which comprises the following steps:
(a) Respectively preparing at least two positive electrode materials to be evaluated into positive electrode plates under the same conditions;
(b) Adopting an in-situ XRD test mould to respectively assemble the positive plates in the step (a) into button cells;
(c) Charging each button cell in the step (b), and simultaneously carrying out in-situ XRD scanning on the positive plate to obtain the peak position of a (003) peak and the charge state of the corresponding button cell in each in-situ XRD scanning process;
(d) The maximum deformation amount B1, the maximum deformation percentage C1, the variable B2 at the end of positive electrode charging, the deformation percentage C2 at the end of positive electrode charging, the deformation rate D1 of positive electrode and the deformation rate D2 at the end of positive electrode charging are obtained according to the following formula:
B1＝A1-A2；
C1％＝(A1-A2)/A1；
B2＝A3-A2；
C2％＝(A3-A2)/A1；
D1＝(A1-A2)/SOC1；
D2＝(A3-A2)/(1-SOC1)；
wherein A1 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 0%; a2 represents a peak position minimum angle of the (003) peak of the positive electrode material during charging; a3 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 100%; SOC1 represents the state of charge of the button cell when the peak position of the (003) peak of the positive electrode material during charging is minimum;
comparing B1, C1% and D1 of each button cell, wherein the smaller B1, C1% and D1 are, the better the structural stability of the positive electrode material corresponding to the button cell is;
and/or comparing B2, C2% and D2 of each button cell, wherein the smaller the B2, C2% and D2, the better the structural stability of the positive electrode material corresponding to the button cell, the better the high voltage performance.
The method is simple to operate and short in test period, and can greatly shorten the evaluation time of the positive electrode material and shorten the research and development period. A quick and simple testing method is provided for the development of the high-voltage system anode material, and the development efficiency of the high-voltage system battery is improved.
The smaller the B1, the C1 percent and the D1 are, the smaller the structural deformation of the positive electrode material in the charge-discharge cycle process is, and the better the crystal structure stability is; conversely, the larger B1, C1 and D1 are, the larger the structural deformation of the positive electrode material in the charge-discharge cycle process is, and the poorer the crystal structure stability is.
The smaller the B2, the C2 percent and the D2 are, the smaller the structural deformation of the positive electrode material at the charging terminal is, the better the crystal structure stability is, the better the high-voltage performance of the positive electrode material is, and the positive electrode material is more suitable for manufacturing a high-voltage system positive electrode material; conversely, the larger B2, C2% and D2 are, the larger the structural deformation of the positive electrode material at the charging terminal is, the worse the crystal structure stability is, the worse the high-voltage performance of the positive electrode material is, and the positive electrode material is not suitable for manufacturing a high-voltage system positive electrode material.
In one embodiment, the positive electrode material includes a positive electrode material having a crystal structure of Hexagonal (R-3 m).
In one embodiment, the positive electrode material includes at least one of a ternary positive electrode material, lithium cobaltate, lithium nickel cobalt manganese aluminate, lithium nickel manganese aluminate layered material, and a doping modified material of the lithium nickel manganese aluminate layered material. In one embodiment, the ternary positive electrode material includes a nickel cobalt manganese ternary positive electrode material (NCM) or a nickel cobalt aluminum ternary positive electrode material (NCA), or the like.
In one embodiment, in step (a), the preparation method of each positive electrode sheet specifically includes:
and mixing the positive electrode materials to be evaluated with the same binder, the same conductive agent and the same solvent according to the same proportion to obtain positive electrode slurries respectively, and coating the positive electrode slurries on the surfaces of the same positive electrode current collector respectively and drying the positive electrode slurries.
In one embodiment, the mass ratio of the positive electrode material, the binder, and the conductive agent is (70 to 98): (1-20): (1-20). In one embodiment, the mass ratio of the positive electrode material, the binder, and the conductive agent includes, but is not limited to, 70:1: 20. 75:15: 10. 80:10:10 or 90:5:5, etc.
In one embodiment, the binder comprises PVDF.
In one embodiment, the conductive agent includes at least one of carbon nanotubes, graphene, and conductive carbon black.
In one embodiment, the solvent comprises N-methylpyrrolidone (NMP).
In one embodiment, in step (a), the current during charging is 0.01mA to 1mA and the voltage is 2.7V to 4.4V.
In one embodiment, the current during charge and discharge includes, but is not limited to, 0.02mA, 0.05mA, 0.1mA, 0.2mA, 0.3mA, 0.4mA, 0.5mA, 0.6mA, 0.7mA, 0.8mA, 0.9mA, or 1mA.
In one embodiment, the in-situ XRD test mold is schematically shown in fig. 1, and comprises: the device comprises a positive electrode base 1, two insulating sealing rubber rings 8, a conductive support bracket 9, a negative electrode top cover 10 and two insulating fixing nuts 12; the center area of the positive electrode base 1 is provided with an in-situ XRD test window 2.
The upper surface of the positive electrode base 1 is provided with two screws 14, and the two screws 14 are respectively positioned on two opposite sides of the in-situ XRD test window 2 and are perpendicular to the positive electrode base 1.
The side end face of the positive electrode base 1 is provided with a positive electrode lug 3.
The insulating sealing rubber ring 8 and the positive electrode base 1 are enclosed to form a containing cavity; the accommodating cavity is used for accommodating a laminated body of the conductive foil 4, the positive electrode plate 5, the diaphragm 6 and the negative electrode plate 7, the laminated body is sequentially provided with the conductive foil 4, the positive electrode plate 5, the diaphragm 6 and the negative electrode plate 7 from bottom to top, and electrolyte is arranged in the diaphragm. The electrolyte is conventional electrolyte of lithium ion batteries.
The conductive support bracket 9 is arranged at the upper end of the laminated body through a ring opening of the insulating sealing rubber ring 8.
Two through holes 15 are respectively formed in the surface of the negative electrode top cover 10, and insulating separation rubber rings 13 are respectively arranged at upper ports of the two through holes 15; the negative top cover 10 is arranged on the upper surfaces of the conductive support bracket 9 and the insulating sealing rubber ring 8, and two screws respectively penetrate through the two through holes 15; the two insulating fixing nuts 12 are respectively connected with the two screw rods 14 through threads to fix the positive electrode base 1 and the negative electrode top cover 10.
The side end face of the negative electrode top cover 10 is provided with a negative electrode tab 11.
The in-situ XRD test die used in the invention is a buckling die matched with test equipment, and in the in-situ XRD test, different XRD equipment is used, and the matched in-situ XRD test dies are different. So long as the change of the (003) peak of the positive electrode material in the charge-discharge process can be tested.
In one embodiment, the negative electrode sheet comprises a lithium foil or graphite negative electrode.
In one embodiment, in step (c), the in situ XRD scan is performed at a scan rate of 1 DEG/min to 10 DEG/min and at a scan interval of 0 to 10min in a scan range of 16 DEG to 20 deg.
In one embodiment, in step (c), the scanning speed includes, but is not limited to, 1 °/min, 2 °/min, 3 °/min, 4 °/min, 5 °/min, 6 °/min, 7 °/min, 8 °/min, 9 °/min, or 10 °/min.
In one embodiment, the scan interval includes, but is not limited to, 0min, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, or 10min.
In one embodiment, after the obtaining of the peak position of the (003) peak and its corresponding battery capacity during each in situ XRD scan, further comprises: and (5) making a charge state-peak position angle curve.
In one embodiment, detecting the (003) peak of the positive electrode material is replaced by detecting the (110) peak of the positive electrode material.
The scanning range of the in-situ XRD scanning is 55-65 degrees, the scanning speed is 1-10 degrees/min, and the scanning interval is 0-10 min.
Besides the change of the peak position of the (003) peak, the structural stability of the positive electrode material can be represented by the change of the peak position of the (110) peak at 55-65 degrees, the peak intensity of the (110) peak is relatively weak, and the test effect is not obvious.
In one embodiment, in step (b), the peak position of the (003) peak and the corresponding battery voltage during each in-situ XRD scan are obtained, and a battery voltage-peak position angle curve is produced.
In one embodiment, the structural stability of the positive electrode material can be further determined by testing the peak position of the (003) peak and the corresponding battery voltage during in-situ XRD scanning and making a battery voltage-peak position angle curve. The voltage of the battery is given by a device test, and in the charging process, the device records the charging time and the voltage of the battery, and obtains a voltage-peak position angle curve according to an XRD scanning curve corresponding to the charging time.
The following is a further description of specific examples, comparative examples, and figures.
The XRD profile of the ternary positive electrode material is shown in fig. 6, and the position and type of the peak can be determined.
Example 1
A method of evaluating structural stability of a positive electrode material, comprising the steps of:
(1) Mixing a ternary positive electrode material a and a ternary positive electrode material b to be compared with conductive carbon black, PVDF and NMP solvents respectively to form uniform slurry, wherein the mass ratio of the positive electrode material to the binder to the conductive agent is 80:10:10, respectively coating the slurry on a conductive aluminum foil, and drying NMP solvent to prepare a positive plate a and a positive plate b of the positive electrode material.
(2) The positive electrode tab a and the positive electrode tab b were assembled into a button cell for testing using the in-situ XRD test mold in fig. 1, respectively, in which the negative electrode tab was a lithium foil.
(3) And charging the button cell to be tested with small current (0.1 mA), wherein the charging voltage range is 2.7V-4.4V.
(4) While charging, the positive plate a and the positive plate b respectively perform in-situ XRD scanning, the scanning range is 16-20 degrees, the scanning speed is 2 degrees/min, no-interval scanning is performed, and the scanning result is shown in figure 2.
(5) The peak position of the (003) peak and the battery state of charge at the peak position during each XRD scan are obtained, and a state of charge-peak position angle curve is produced, as shown in FIG. 3.
(6) The maximum deformation amount B1 of the positive electrode, the maximum deformation percentage C1 of the positive electrode and the positive electrode deformation rate D1 are obtained according to the following formula:
B1＝A1-A2；
C1％＝(A1-A2)/A1；
D1＝(A1-A2)/SOC1；
wherein A1 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 0%; a2 represents a peak position minimum angle of the (003) peak of the positive electrode material during charging; SOC1 represents the state of charge of the button cell when the peak position of the (003) peak of the positive electrode material during charging is minimum;
comparing the structural stability of the ternary positive electrode material a and the ternary positive electrode material b: from the test results, the values of B1, C1% and D1 of the ternary positive electrode material a are all greater than the values of B1, C1% and D1 of the ternary positive electrode material B, so that the structural stability of the ternary positive electrode material B is better.
Example 2
A method of evaluating structural stability of a positive electrode material, comprising the steps of:
(1) Mixing the ternary positive electrode material c and the ternary positive electrode material d to be compared with conductive carbon black, PVDF and NMP solvents respectively to form uniform slurry, wherein the mass ratio of the positive electrode material to the binder to the conductive agent is 80:10:10, coating the slurry on a conductive aluminum foil, and drying NMP solvent to prepare a positive plate c and a positive plate d of the positive electrode material.
(2) The button cell for testing was assembled using the in-situ XRD test mold in fig. 1, in which the negative electrode sheet was lithium foil.
(3) And charging the button cell to be tested with small current (0.1 mA), wherein the charging voltage range is 2.7V-4.4V.
(4) And charging, and respectively carrying out in-situ XRD scanning on the positive plate c and the positive plate d, wherein the scanning range is 16-20 degrees, the scanning speed is 2 degrees/min, and no interval scanning is carried out.
(5) The peak position of the (003) peak and the battery state of charge at the peak position during each XRD scan are obtained, and a state of charge-peak position angle curve is produced as shown in fig. 5.
(6) The positive electrode charging end variable B2, the positive electrode charging end deformation percentage C2% and the positive electrode charging end deformation rate D2 are obtained according to the following formula:
B2＝A3-A2；
C2％＝(A3-A2)/A1；
D2＝(A3-A2)/(1-SOC1)；
wherein A2 represents a peak position minimum angle of the (003) peak of the positive electrode material during charging; a3 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 100%; SOC1 represents the state of charge of the button cell when the peak position of the (003) peak of the positive electrode material during charging is minimum;
comparing the structural stability of the ternary positive electrode material c and the ternary positive electrode material d under high voltage: as shown by the test result, the values of B2, C2% and D2 of the ternary positive electrode material D are larger than the values of B2, C2% and D2 of the ternary positive electrode material C, so that the ternary positive electrode material C has better high-voltage structural stability and is more suitable for a high-voltage system.
Comparative example 1
The evaluation method of the ternary cathode material in the prior art comprises the following steps:
and (3) respectively mixing the ternary positive electrode material a and the ternary positive electrode material b to be compared in the embodiment 1 with conductive carbon black and PVDF according to the mass ratio (positive electrode material: binder: conductive agent=80:10:10) by using NMP as a solvent to form uniform slurry, coating the uniform slurry on a conductive aluminum foil, and drying the NMP solvent to prepare positive electrode plates a and b of the positive electrode materials to be evaluated.
(2) And assembling the positive plate a and the positive plate b into a battery a and a battery b through the processes of die cutting, assembling, liquid injection and pre-charge formation.
(3) Battery a and battery b were subjected to charge-discharge cycle test to form charge-discharge capacity decay curves as shown in fig. 4.
The results of the evaluation method in this comparative example showed that the battery cycle degradation of the positive electrode sheet b was smaller, the structural stability was better, and the results were consistent with those of example 1.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (13)

1. A method for evaluating structural stability of a positive electrode material, comprising the steps of:
(a) Respectively preparing at least two positive electrode materials to be evaluated into positive electrode plates under the same conditions;
(b) Adopting an in-situ XRD test mould to respectively assemble the positive plates in the step (a) into button cells;
(c) Charging each button cell in the step (b), and simultaneously carrying out in-situ XRD scanning on the positive plate to obtain the peak position of a (003) peak and the charge state of the corresponding button cell in each in-situ XRD scanning process;
(d) The maximum deformation amount B1, the maximum deformation percentage C1, the variable B2 at the end of positive electrode charging, the deformation percentage C2 at the end of positive electrode charging, the deformation rate D1 of positive electrode and the deformation rate D2 at the end of positive electrode charging are obtained according to the following formula:
B1=A1-A2；
C1%=（A1-A2）/A1；
B2=A3-A2；
C2%=（A3-A2）/A1；
D1=（A1-A2）/SOC1；
D2=（A3-A2）/（1-SOC1）；
wherein A1 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 0%; a2 represents a peak position minimum angle of the (003) peak of the positive electrode material during charging; a3 represents a peak position angle of the (003) peak of the positive electrode material when the state of charge of the button cell is 100%; SOC1 represents the state of charge of the button cell when the peak position of the (003) peak of the positive electrode material during charging is minimum;
comparing B1, C1% and D1 of each button cell, wherein the smaller B1, C1% and D1 are, the better the structural stability of the positive electrode material corresponding to the button cell is;
and/or comparing B2, C2% and D2 of each button cell, wherein the smaller the B2, C2% and D2, the better the structural stability of the positive electrode material corresponding to the button cell, the better the high voltage performance.
2. The method of assessing the structural stability of a positive electrode material of claim 1, wherein said positive electrode material comprises at least one of a ternary positive electrode material, lithium cobaltate, lithium nickel cobalt manganese aluminate, lithium nickel manganese aluminate layered material, and a doping modified material of said lithium nickel manganese aluminate layered material.
3. The method for evaluating structural stability of a positive electrode material according to claim 1, wherein in step (a), the method for producing each positive electrode sheet specifically comprises:
and mixing the positive electrode materials to be evaluated with the same binder, the same conductive agent and the same solvent according to the same proportion to obtain positive electrode slurries respectively, and coating the positive electrode slurries on the surfaces of the same positive electrode current collector respectively and drying the positive electrode slurries.
4. The method for evaluating structural stability of a positive electrode material according to claim 3, wherein the mass ratio of the positive electrode material, the binder and the conductive agent is (70 to 98): (1-20): (1-20).
5. The method of evaluating the structural stability of a positive electrode material according to claim 3, wherein the binder comprises PVDF.
6. The method for evaluating the structural stability of a positive electrode material according to claim 3, wherein the conductive agent comprises at least one of carbon nanotubes, graphene, and conductive carbon black.
7. The method of claim 1, wherein in step (a), the current during charging is 0.01ma to 1ma and the voltage is 2.7v to 4.4v.
8. The method of assessing the structural stability of a positive electrode material of claim 1, wherein said in situ XRD test pattern comprises: the device comprises an anode base, two insulating sealing rubber rings, a conductive support bracket, a cathode top cover and two insulating fixing nuts;
an in-situ XRD test window is arranged in the central area of the positive electrode base; the upper surface of the positive electrode base is provided with two screws which are respectively positioned at two opposite sides of the in-situ XRD test window; the side end face of the positive electrode base is provided with a positive electrode lug;
the insulating sealing rubber ring and the positive electrode base are enclosed to form a containing cavity; the accommodating cavity is used for accommodating a laminate of the conductive foil, the positive plate, the diaphragm and the negative plate;
the conductive support bracket is arranged on the upper surface of the laminated body through a ring opening of the insulating sealing rubber ring;
the surface of the negative electrode top cover is respectively provided with two through holes, and the upper ports of the two through holes are respectively provided with an insulating separation rubber ring; the negative top cover is arranged on the upper surfaces of the conductive support bracket and the insulating sealing rubber ring, and two screws respectively penetrate through the two through holes; a negative electrode lug is arranged on the side end face of the negative electrode top cover;
the two insulating fixing nuts are respectively connected with the two screw rods through threads to fix the positive electrode base and the negative electrode top cover.
9. The method of evaluating the structural stability of a positive electrode material according to claim 8, wherein the negative electrode sheet comprises a lithium foil or a graphite negative electrode.
10. The method for evaluating structural stability of a positive electrode material according to claim 1, wherein in the step (c), the scanning range of in-situ XRD scanning is 16 ° to 20 °, the scanning speed is 1 °/min to 10 °/min, and the scanning interval is 0 to 10min.
11. The method of claim 1, wherein after the obtaining the peak position of the (003) peak and the corresponding battery capacity during each in-situ XRD scan, further comprising: and (5) making a charge state-peak position angle curve.
12. The method of evaluating the structural stability of a positive electrode material according to claim 1, wherein the detection of the (003) peak of the positive electrode material is replaced with the detection of the (110) peak of the positive electrode material;
the scanning range of the in-situ XRD scanning is 55-65 degrees, the scanning speed is 1-10 degrees/min, and the scanning interval is 0-10 min.
13. The method according to claim 1, wherein in step (b), the peak position of the (003) peak and the voltage of the button cell corresponding to the peak position are obtained during each in-situ XRD scan, and a cell voltage-peak position angle curve is produced.
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