CN114397351B - Method for rapidly evaluating cycle performance of lithium iron phosphate positive electrode material - Google Patents
Method for rapidly evaluating cycle performance of lithium iron phosphate positive electrode material Download PDFInfo
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 51
- 238000000034 method Methods 0.000 title claims abstract description 40
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 38
- 238000007600 charging Methods 0.000 claims abstract description 47
- 230000004913 activation Effects 0.000 claims abstract description 17
- 230000010287 polarization Effects 0.000 claims description 16
- 230000003213 activating effect Effects 0.000 claims description 9
- 230000001351 cycling effect Effects 0.000 claims description 9
- 238000004513 sizing Methods 0.000 claims description 4
- 238000001228 spectrum Methods 0.000 claims description 3
- 238000010280 constant potential charging Methods 0.000 claims description 2
- 238000010277 constant-current charging Methods 0.000 claims description 2
- 238000011156 evaluation Methods 0.000 abstract description 4
- 238000000157 electrochemical-induced impedance spectroscopy Methods 0.000 description 43
- 239000000463 material Substances 0.000 description 30
- 238000012360 testing method Methods 0.000 description 15
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 10
- 230000014759 maintenance of location Effects 0.000 description 8
- 239000010405 anode material Substances 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 7
- 239000003792 electrolyte Substances 0.000 description 5
- 229910052759 nickel Inorganic materials 0.000 description 4
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 238000003487 electrochemical reaction Methods 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 238000004146 energy storage Methods 0.000 description 3
- 229910052744 lithium Inorganic materials 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000010406 cathode material Substances 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000005087 graphitization Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 238000012827 research and development Methods 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000012983 electrochemical energy storage Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005562 fading Methods 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/48—Systems using polarography, i.e. measuring changes in current under a slowly-varying voltage
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
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- 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 application provides a method for rapidly evaluating the cycle performance of a lithium iron phosphate positive electrode material. The method comprises the following steps: respectively preparing a lithium iron phosphate positive electrode material to-be-detected sample and a lithium iron phosphate positive electrode material standard sample according to the same process to obtain a to-be-detected sample battery and a standard sample battery; performing activation constant volume treatment under the same condition, respectively charging to a first target voltage, obtaining a charging platform voltage of a sample to be detected and a charging platform voltage of a standard sample through respective charging curves, and respectively collecting EIS spectrograms after first standing to obtain a first resistor of the sample to be detected and a first resistor of the standard sample; the battery is subjected to charge-discharge circulation, and then EIS spectrograms are respectively collected in a full-charge state to obtain a second resistor of a sample to be detected and a second resistor of a standard sample; and comparing and judging the relation between the cycle performance of the sample to be detected and the cycle performance of the standard sample according to the comparison result. The method for rapidly evaluating the cycle performance of the lithium iron phosphate positive electrode material is simple and accurate in evaluation and low in cost.
Description
Technical Field
The application relates to the field of lithium ion batteries, in particular to a method for rapidly evaluating the cycle performance of a lithium iron phosphate positive electrode material.
Background
Electrochemical energy storage is the most mature new energy storage and conversion mode at present, and lithium secondary batteries are the most widely used energy storage devices. The lithium ion battery is ubiquitous in daily life of people, and is a 3C type digital product or a new energy automobile, and the battery heart is needed to be added, so that the performance requirement on the lithium ion battery is higher and higher along with continuous progress of technology. The electrode material of the lithium ion battery plays a decisive role in the performance, and the lithium iron phosphate is one of the first choice positive electrode materials of the power battery and the energy storage battery due to the inherent advantages of low cost, high thermal stability, long cycle life and the like in the current mainstream positive electrode material.
The cycle life is an important index for evaluating the performance of the lithium iron phosphate positive electrode material. The main evaluation method at present is to carry out charge and discharge cycles for many times on the assembled battery to judge the capacity retention rate, but the method is very easy to use for hundreds of hours to thousands of hours and takes long time, so that on one hand, the time cost is increased, on the other hand, the test needs to occupy equipment for a long time, and the equipment cost is increased between the test and the test, which is extremely unfavorable for material modification and enterprise production, so that a method for rapidly predicting the cycle life of the battery from the anode material end is needed to save various costs, thereby improving the research and development and production efficiency. At present, related researchers also conduct a plurality of researches in the field of rapid prediction of the cycle life of a lithium ion battery, for example, a patent with publication number CN 110726940A reports a rapid evaluation method of the cycle performance of a high-nickel cathode material of the lithium ion battery, and the quality of the cycle performance of the material is rapidly judged by comparing the positions and the intensities of oxidation peaks of different high-nickel materials meeting the conditions in dQ/dV-V curves of the high-nickel materials in a specified voltage interval. The patent with publication number of CN 106324524A reports a rapid prediction method for the cycle life of a lithium ion battery, which utilizes short-term cycle of an assembled battery, records the capacity retention rate and electrolyte retention rate at a specific cycle interval, and then carries out fitting calculation on the three data so as to predict the cycle life. The patent with publication number of CN 107356877A reports a method for rapidly predicting the cycle life of a lithium ion battery, monitors the graphitization degree of a graphite cathode through XRD test means, and performs fitting calculation according to the cycle number, the capacity retention rate and the graphitization degree so as to predict the cycle life of the battery. However, the reported technologies have limitations of different degrees, the first method is only aimed at specific high-nickel materials, and the drawing of dQ/dV-V curves has extremely high requirements on data precision and is inconvenient for data acquisition; the second method only considers the influence of electrolyte on the cycle performance singly, ignores the influence of the material, especially the positive electrode material, on the cycle performance; the third method is mainly considered from the cathode material end, XRD data are required to be monitored for multiple times, and the requirements and the cost on test equipment are high.
Therefore, how to realize the simple and easy-to-operate fast and accurate prediction of the battery cycle life is still a technical problem faced by the field.
Disclosure of Invention
The purpose of the present application is to provide a method for rapidly evaluating the cycle performance of a lithium iron phosphate positive electrode material, so as to solve the above problems.
In order to achieve the above purpose, the present application adopts the following technical scheme:
a method for rapidly evaluating the cycling performance of a lithium iron phosphate positive electrode material, comprising:
respectively preparing a lithium iron phosphate positive electrode material to-be-detected sample and a lithium iron phosphate positive electrode material standard sample according to the same process to obtain a to-be-detected sample battery and a standard sample battery;
activating and sizing the battery to be tested and the standard battery under the same condition;
respectively charging the activated batteries subjected to constant volume treatment to a first target voltage, obtaining a charging platform voltage of a to-be-detected sample and a charging platform voltage of a standard sample through respective charging curves, and respectively collecting EIS (electrochemical impedance spectroscopy) spectrograms after first standing to obtain a first resistor of the to-be-detected sample and a first resistor of the standard sample;
the battery is subjected to charge-discharge circulation, and then EIS spectrograms are respectively collected in a full-charge state to obtain a second resistor of a sample to be detected and a second resistor of a standard sample;
and comparing the charging platform voltage of the to-be-detected sample with the charging platform voltage of the standard sample, the first resistor of the to-be-detected sample with the first resistor of the standard sample, the second resistor of the to-be-detected sample and the second resistor of the standard sample, and judging the relation between the cycle performance of the to-be-detected sample of the lithium iron phosphate anode material and the cycle performance of the standard sample of the lithium iron phosphate anode material according to the comparison result.
Preferably, the criterion for the judgment is:
if the charging platform voltage of the to-be-detected sample is larger than the charging platform voltage of the standard sample, the first resistance of the to-be-detected sample is larger than the first resistance of the standard sample, and the second resistance of the to-be-detected sample is larger than the second resistance of the standard sample, judging that the cycle performance of the to-be-detected sample of the lithium iron phosphate positive electrode material is lower than that of the standard sample of the lithium iron phosphate positive electrode material;
and if the voltage of the charging platform of the to-be-detected sample is smaller than the voltage of the charging platform of the standard sample, the first resistance of the to-be-detected sample is smaller than the first resistance of the standard sample, and the second resistance of the to-be-detected sample is smaller than the second resistance of the standard sample, judging that the cycle performance of the to-be-detected sample of the lithium iron phosphate positive electrode material is high and Yu Linsuan the cycle performance of the standard sample of the lithium iron phosphate positive electrode material.
Preferably, the activating constant volume treatment comprises:
respectively carrying out constant-current and constant-voltage charging on the battery to be tested and the standard battery to a second target voltage, and then carrying out second standing;
and respectively performing constant-current discharge on the battery to be tested and the standard battery to a third target voltage, and then performing third standing.
Preferably, the second target voltage is 3.7V-4.2V.
Preferably, the constant-current constant-voltage charge and the constant-current discharge are both performed at 0.01C to 0.1C.
Preferably, the time of the second rest and the third rest is 5min-30min respectively and independently.
Preferably, the activation constant volume treatment is performed 1-3 times.
Preferably, the charging to the first target voltage is performed under a condition of 0.01C to 0.1C;
the first target voltage is 3.7V-4.2V, and the first standing time is 1h-5h.
Preferably, the charge-discharge cycle is performed at 0.5C-5C for 10-30 cycles.
Preferably, the polarization voltage of the electrochemical workstation used for acquiring the EIS spectrogram is 10mV, and the frequency is 100000Hz-0.001Hz.
Compared with the prior art, the beneficial effects of this application include:
according to the method for rapidly evaluating the cycle performance of the lithium iron phosphate positive electrode material, the cycle performance of the lithium iron phosphate positive electrode material is rapidly evaluated by measuring and comparing the charging platform voltage and the resistance of the sample to be tested and the standard sample. The operating voltage of the lithium iron phosphate positive electrode material was about 3.4V (vs. Li/Li + ) The more the charging voltage platform moves forward and the larger the various resistances obtained by EIS map fitting are, the more serious the material is affected by polarization (comprising ohmic polarization, electrochemical polarization and concentration polarization), and three reasons of polarization on the main recyclable lithium loss, material structural damage and internal resistance increase affecting the material circulation performance are embodied, and the main factors affecting the circulation performance of the lithium iron phosphate anode material on the market at present are the primary particle size and carbon coating condition of the material. For the primary particle size, the excessive particle size can cause pulverization of the material to block an infiltration channel of the electrolyte, so that polarization is caused; too small particle size results in severe side reactions, accelerated consumption of recyclable lithium ions, and a loss of capacity. For carbon coating, the coating layer is too thick, the electrochemical reaction on the surface of the material is affected, and the polarization is increased; the coating is uneven, the local iron dissolution is aggravated, the consumption of the recyclable lithium ions is accelerated, and the capacity fading is accelerated. These influencing factors can be characterized by polarization differences, so that the cycle performance of the lithium iron phosphate anode material can be rapidly judged by using the method.
The method only needs a small amount of charge and discharge cycles to collect data, thereby greatly reducing the time and equipment cost and accelerating the research and development and production cycle. The influence of polarization on the cycle performance is reflected through the collected data, three main reasons of the main recyclable lithium loss, the structural damage and the internal resistance increase of the material are reflected, the influence of polarization on the cycle performance is judged by utilizing the deviation of the voltage of the charging platform and the fitting of EIS maps to each resistor, and the prediction result is more comprehensive and accurate.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate certain embodiments of the present application and therefore should not be considered as limiting the scope of the present application.
FIG. 1 is LFP of example 1 A And LFP S The charging curve comparison graph, the initial EIS comparison graph, the EIS comparison graph after 25 circles of circulation and the long-circulation comparison graph;
FIG. 2 is LFP of example 2 A And LFP S The charging curve comparison graph, the initial EIS comparison graph, the EIS comparison graph after 25 circles of circulation and the long-circulation comparison graph;
FIG. 3 is LFP in example 3 A And LFP S Charging curve comparison graph, initial EIS comparison graph, EIS comparison graph after 15 circles of circulation and long circulation comparison graph;
FIG. 4 is LFP in a control experiment S EIS and long cycle plots after 25 cycles at 1C and 4C currents;
FIG. 5 is LFP of comparative example 1 S Unactivated constant volume and activated constant volume initial EIS contrast diagram, unactivated constant volume LFP S A 25-circle circulation chart is passed;
FIG. 6 is LFP of comparative example 2 A 、LFP B And LFP S Long cycle comparison graph.
Detailed Description
The term as used herein:
"prepared from … …" is synonymous with "comprising". The terms "comprising," "including," "having," "containing," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.
The conjunction "consisting of … …" excludes any unspecified element, step or component. If used in a claim, such phrase will cause the claim to be closed, such that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of … …" appears in a clause of the claim body, rather than immediately following the subject, it is limited to only the elements described in that clause; other elements are not excluded from the stated claims as a whole.
When an equivalent, concentration, or other value or parameter is expressed as a range, preferred range, or a range bounded by a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. For example, when ranges of "1 to 5" are disclosed, the described ranges should be construed to include ranges of "1 to 4", "1 to 3", "1 to 2 and 4 to 5", "1 to 3 and 5", and the like. When a numerical range is described herein, unless otherwise indicated, the range is intended to include its endpoints and all integers and fractions within the range.
In these examples, the parts and percentages are by mass unless otherwise indicated.
"parts by mass" means a basic unit of measurement showing the mass ratio of a plurality of components, and 1 part may be any unit mass, for example, 1g may be expressed, 2.689g may be expressed, and the like. If we say that the mass part of the a component is a part and the mass part of the B component is B part, the ratio a of the mass of the a component to the mass of the B component is represented as: b. alternatively, the mass of the A component is aK, and the mass of the B component is bK (K is an arbitrary number and represents a multiple factor). It is not misunderstood that the sum of the parts by mass of all the components is not limited to 100 parts, unlike the parts by mass.
"and/or" is used to indicate that one or both of the illustrated cases may occur, e.g., a and/or B include (a and B) and (a or B).
A method for rapidly evaluating the cycling performance of a lithium iron phosphate positive electrode material, comprising:
respectively preparing a lithium iron phosphate positive electrode material to-be-detected sample and a lithium iron phosphate positive electrode material standard sample according to the same process to obtain a to-be-detected sample battery and a standard sample battery;
activating and sizing the battery to be tested and the standard battery under the same condition;
respectively charging the battery subjected to the activation constant volume treatment to a first target voltage, obtaining a charging platform voltage of a to-be-detected sample and a charging platform voltage of a standard sample through respective charging curves, and respectively collecting EIS spectrograms after first standing to obtain a first resistor of the to-be-detected sample and a first resistor of the standard sample;
the battery is subjected to charge-discharge circulation, and then EIS spectrograms are respectively collected in a full-charge state to obtain a second resistor of a sample to be detected and a second resistor of a standard sample;
and comparing the charging platform voltage of the to-be-detected sample with the charging platform voltage of the standard sample, the first resistor of the to-be-detected sample with the first resistor of the standard sample, the second resistor of the to-be-detected sample and the second resistor of the standard sample, and judging the relation between the cycle performance of the to-be-detected sample of the lithium iron phosphate anode material and the cycle performance of the standard sample of the lithium iron phosphate anode material according to the comparison result.
The main function of activating constant volume is to make the active material of electrode material fully participate in the reaction so as to make it reach an optimum state. The activation is complete as the activation treatment capacity reaches the maximum value at the activation current and remains unchanged. In general, a newly assembled battery may cause slow electrochemical reaction, incomplete capacity release due to insufficient contact between an electrolyte and an electrode active material, various resistances may be large when tested through EIS, and activation may be performed in several cycles of starting a cycle without performing an activation direct cycle test, so that the EIS data of the test may be inaccurate. Generally, the smaller the activation current, the more fully activated.
In an alternative embodiment, the criteria for the determination are:
if the charging platform voltage of the to-be-detected sample is larger than the charging platform voltage of the standard sample, the first resistance of the to-be-detected sample is larger than the first resistance of the standard sample, and the second resistance of the to-be-detected sample is larger than the second resistance of the standard sample, judging that the cycle performance of the to-be-detected sample of the lithium iron phosphate positive electrode material is lower than that of the standard sample of the lithium iron phosphate positive electrode material; and if the voltage of the charging platform of the to-be-detected sample is smaller than the voltage of the charging platform of the standard sample, the first resistance of the to-be-detected sample is smaller than the first resistance of the standard sample, and the second resistance of the to-be-detected sample is smaller than the second resistance of the standard sample, judging that the cycle performance of the to-be-detected sample of the lithium iron phosphate positive electrode material is high as Yu Linsuan of the standard sample of the lithium iron phosphate positive electrode material.
In an alternative embodiment, the activation constant volume treatment comprises:
respectively charging the battery to be tested and the standard sample battery to a second target voltage at constant current and constant voltage, and then carrying out second standing;
and discharging the battery to be tested and the standard battery to a third target voltage in a constant current manner respectively, and then performing third standing.
In an alternative embodiment, the second target voltage is 3.7-4.2V.
Alternatively, the second target voltage may be any value between 3.7V, 3.8V, 3.9V, 4.0V, 4.1V, 4.2V, or 3.7-4.2V.
In an alternative embodiment, both the constant current constant voltage charge and the constant current discharge are performed at 0.01C to 0.1C.
Alternatively, the constant-current constant-voltage charge and the constant-current discharge are both performed under a condition of any one value between 0.01C, 0.05C, 0.1C, or 0.01C to 0.1C.
In an alternative embodiment, the second rest and the third rest are each independently for a period of 5min to 30min.
Optionally, the time of the second standing and the third standing are each independently any value between 5min, 10min, 15min, 20min, 25min, 30min or 5min-30min.
In an alternative embodiment, the activation constant volume treatment is performed 1-3 cycles.
Alternatively, the activation constant volume treatment may be performed 1, 2, or 3 turns.
In an alternative embodiment, the charging to the first target voltage is performed at 0.01C to 0.1C;
optionally, the charging is performed under a condition that the first target voltage is any value between 0.01C, 0.05C, 0.1C, or 0.01C-0.1C;
the first target voltage is 3.7-4.2V, and the first standing time is 1-5 h.
Alternatively, the first target voltage may be any value between 3.7V, 3.8V, 3.9V, 4.0V, 4.1V, 4.2V, or 3.7-4.2V, and the first rest time may be any value between 1h, 2h, 3h, 4h, 5h, or 1h-5h.
In an alternative embodiment, the charge-discharge cycle is performed at 0.5-5C for 10-30 cycles.
Alternatively, the charge-discharge cycle may be performed at any value between 0.5C, 1C, 2C, 3C, 4C, 5C, or 0.5-5C, and the number of turns may be 10 turns, 15 turns, 20 turns, 25 turns, 30 turns, or any integer between 10-30 turns.
In an alternative embodiment, the polarization voltage of the electrochemical workstation used to acquire the EIS spectra is 10mV and the frequency is 100000Hz-0.001Hz.
Embodiments of the present application will be described in detail below with reference to specific examples, but it will be understood by those skilled in the art that the following examples are only for illustration of the present application and should not be construed as limiting the scope of the present application. 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.
Example 1
Lithium iron phosphate material A to be measured (marked as LFP A ) And a lithium iron phosphate standard (LFP) of known cycle performance S ) And assembling the battery according to the same process under the same condition, standing for 12h, and performing three-circle charge-discharge activation constant volume in a battery test system after the electrolyte is fully soaked.
The specific activation constant volume comprises: charging to 3.8V at constant current and constant voltage of 0.1C, standing for 10min, discharging to 2.0V at constant current of 0.1C, and standing for 10min.
To activate LFP A And LFP S The battery is charged to 3.8V with a constant current and a constant voltage of 0.1C, an initial EIS spectrogram is collected under a full-charge state after standing for 3 hours, then 25 cycles of charge and discharge are carried out with a 1C current, and the EIS spectrograms of the battery and the initial EIS spectrogram are collected under the full-charge state.
FIG. 1 (a) shows LFP of example 1 A And LFP S Is a comparison of the 0.1C charge curve; (b) Is LFP in example 1 A And LFP S Is a comparison graph of the initial EIS of (C); (c) Is LFP in example 1 A And LFP S EIS comparison graph after 25 circles of circulation; (d) Is LFP in example 1 A And LFP S Is a long cycle comparison graph of (c).
LFP by analyzing and comparing the charge voltage-capacity curve obtained in the above step A To a greater extent than LFP than the 3.4V curve voltage plateau S Curve, comparing the collected initial EIS spectrogram LFP A The combined resistance of the battery is greater than LFP S And a battery. After 25 cycles, the capacity retention rate of the two is 100%, but the EIS spectrograms collected after 25 cycles show that each resistance is increased and LFP A Greater than LFP of battery S Battery, thereby judging LFP A The cycle performance of the material is lower than LFP S The material, and consequently the long cycling of both cells, also illustrates this.
Example 2
The procedure and other conditions were the same as in example 1, except that the following conditions were used:
the lithium iron phosphate material a to be tested was exchanged for another lithium iron phosphate material B to be tested (noted LFPB).
FIG. 2 (a) is the LFP of example 2 B And LFP S Is a comparison of the 0.1C charge curve; (b) Is LFP in example 2 B And LFP S Is a comparison graph of the initial EIS of (C); (c) Is LFP in example 2 B And LFP S EIS comparison graph after 25 circles of circulation; (d) Is LFP in example 2 B And LFP S Is a long cycle comparison graph of (c).
LFP by analyzing and comparing the resulting charge voltage-capacity curve B To a degree of 3.4V deviation from the curve voltage plateau of less than LFP S Curve, comparing the collected initial EIS spectrogram LFP B The combined resistance of the battery is smaller than LFP S And a battery. After 25 cycles, the capacity retention rate of the two is 100%, but the EIS spectrograms collected after 25 cycles show that each resistance is increased and LFP B Battery cellIn LFP S Battery, thereby judging LFP B The cycle performance of the material is superior to LFP S The materials, and subsequently the long cycling of both cells, can also be demonstrated.
Example 3
The procedure and other conditions were the same as in example 1, except that the following conditions were used:
activating and constant volume treatment: charging to 3.9V at constant current and constant voltage at 0.1C, standing for 20min, discharging to 2.0V at constant current at 0.1C, and standing for 20min. And setting the charge-discharge circulation current to be 2C, and collecting EIS data for comparison after 15 circles of circulation.
FIG. 3 (a) is the LFP of example 3 A And LFP S Is a comparison of the 0.1C charge curve; (b) Is LFP in example 3 A And LFP S Is a comparison graph of the initial EIS of (C); (c) Is LFP in example 3 A And LFP S EIS comparison graph after 15 circles of circulation; (d) Is LFP in example 3 A And LFP S Is a long cycle comparison graph of (c).
LFP by analyzing and comparing the charge voltage-capacity curve obtained in the above step A To a greater extent than LFP than the 3.4V curve voltage plateau S Curve, comparing the collected initial EIS spectrogram LFP A The combined resistance of the battery is greater than LFP S And a battery. After 15 cycles, the capacity retention rate of the two is 100%, but the EIS spectrograms collected after 15 cycles show that each resistance is increased and LFP A Greater than LFP of battery S Battery, thereby judging LFP A The cycle performance of the material is lower than LFP S The material, and consequently the long cycling of both cells, also illustrates this.
Control test
To illustrate the effect of current magnitude on the evaluation results, the following control tests were performed:
the procedure and other conditions were the same as in example one, with the following different condition parameters:
and (3) carrying out charge and discharge circulation on the battery assembled by the activated standard sample LFP material under the current of 4C.
FIG. 4 (a) shows LFP in the control of the present application S EIS comparison plot after 25 cycles at 1C and 4C currents; (b) For LFP in control experiments S Long cycle comparison plots at 1C and 4C currents.
Analysis and comparison of the standard LFP S The EIS of the battery after 25 circles of circulation under 4C is found that each resistance is larger than the EIS of the battery after 25 circles of circulation under 1C, which shows that the circulation performance of the standard sample under 4C is poorer than that of the battery under 1C, and the subsequent long circulation of the battery under two currents can be also illustrated. The reason for this difference is that the greater the charge and discharge current, the greater the polarization, and the more the polarization is, the more the resistance is increased on the EIS spectrum, and the greater the polarization, the poorer the cycle performance of the corresponding battery.
Comparative example 1
The procedure and other conditions were the same as in example one, with the following different condition parameters:
and directly collecting an initial EIS spectrogram of the assembled standard sample LFP material battery without activating and fixing the volume, and carrying out charge and discharge circulation under the current of 1C.
FIG. 5 (a) shows LFP of comparative example 1 of the present application S An initial EIS contrast plot of unactivated constant volume and activated constant volume; (b) LFP of comparative example 1 with constant volume unactivated S A 25-turn cycle chart was run at 1C current.
Analysis and comparison of unactivated constant volume and activated constant volume LFP S The initial EIS curve of the material shows that each resistance value of the unactivated constant volume is larger than that of the activated constant volume, which indicates that the active material which is not subjected to the activated constant volume does not fully participate in the reaction, and the optimal state of the electrochemical reaction is not achieved. The cycling data in fig. 5 (b) also shows that the discharge capacity retention rate of the material without activation sizing increases slowly during cycling, indicating that the material is being activated during cycling. The integrated data may result in less accurate data collected without the activation constant volume process.
Comparative example 2
The procedure and other conditions were the same as in example one, with the following different condition parameters:
lithium iron phosphate a, lithium iron phosphate B and lithium iron phosphate S were subjected to a long cycle test at a current level of 1C.
FIG. 6 is LFP of comparative example 2 of the present application A 、LFP B And LFP S Long cycle comparison graph.
Analysis of the long cycle comparison plots of the three lithium iron phosphate materials at 1C reveals that the cycle performance of the three lithium iron phosphate materials provided by the conventional charge-discharge cycle was compared, and that the performance fluctuation was not large in the first 300 cycles, and the cycle performance could not be compared, 600 hours were required if only the test time required for constant current charge and constant current discharge during these 300 cycles were considered, and longer time was required if the constant voltage charge and rest steps required for each cycle were taken into consideration. It is obvious from this: the conventional method is adopted to compare the cycle performance difference time cost is huge, and the cost is brought about by the loss of the detection instrument and the economic cost brought about by the electric energy consumption. By adopting the method provided by the invention, the EIS data is collected after 10-30 cycles, the test time is greatly shortened, and the time of the conventional test means is basically only one tenth of that of the conventional test means.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should 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 corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.
Furthermore, those skilled in the art will appreciate that while some embodiments herein include some features but not others included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the present application and form different embodiments. For example, in the claims below, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is only for enhancement of understanding of the general background of the application and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Claims (7)
1. A method for rapidly evaluating the cycling performance of a lithium iron phosphate positive electrode material, comprising:
respectively preparing a lithium iron phosphate positive electrode material to-be-detected sample and a lithium iron phosphate positive electrode material standard sample according to the same process to obtain a to-be-detected sample battery and a standard sample battery;
activating and sizing the battery to be tested and the standard battery under the same condition;
respectively charging the battery subjected to the activation constant volume treatment to a first target voltage, obtaining a charging platform voltage of a to-be-detected sample and a charging platform voltage of a standard sample through respective charging curves, and respectively collecting EIS spectrograms after first standing to obtain a first resistor of the to-be-detected sample and a first resistor of the standard sample; the charging is carried out under the condition of 0.01-0.1C until the first target voltage; the first target voltage is 3.7V-4.2V, and the first standing time is 1h-5h;
the battery is subjected to charge-discharge circulation, and then EIS spectrograms are respectively collected in a full-charge state to obtain a second resistor of a sample to be detected and a second resistor of a standard sample; the charge and discharge cycle is carried out for 10-30 circles under the condition of 0.5-5C;
comparing the charging platform voltage of the to-be-detected sample with the charging platform voltage of the standard sample, the first resistance of the to-be-detected sample with the first resistance of the standard sample, the second resistance of the to-be-detected sample with the second resistance of the standard sample, and judging the relation between the cycle performances of the to-be-detected sample of the lithium iron phosphate positive electrode material and the standard sample of the lithium iron phosphate positive electrode material according to the comparison result;
the judgment standard is as follows:
if the charging platform voltage of the to-be-detected sample is larger than the charging platform voltage of the standard sample, the first resistance of the to-be-detected sample is larger than the first resistance of the standard sample, and the second resistance of the to-be-detected sample is larger than the second resistance of the standard sample, judging that the cycle performance of the to-be-detected sample of the lithium iron phosphate positive electrode material is lower than that of the standard sample of the lithium iron phosphate positive electrode material;
and if the voltage of the charging platform of the to-be-detected sample is smaller than the voltage of the charging platform of the standard sample, the first resistance of the to-be-detected sample is smaller than the first resistance of the standard sample, and the second resistance of the to-be-detected sample is smaller than the second resistance of the standard sample, judging that the cycle performance of the to-be-detected sample of the lithium iron phosphate positive electrode material is high and Yu Linsuan the cycle performance of the standard sample of the lithium iron phosphate positive electrode material.
2. The method of claim 1, wherein the activating constant volume treatment comprises:
respectively carrying out constant-current and constant-voltage charging on the battery to be tested and the standard battery to a second target voltage, and then carrying out second standing;
and respectively performing constant-current discharge on the battery to be tested and the standard battery to a third target voltage, and then performing third standing.
3. The method of claim 2, wherein the second target voltage is 3.7V-4.2V.
4. The method according to claim 2, wherein the constant-current constant-voltage charge and the constant-current discharge are both performed at 0.01C to 0.1C.
5. The method of claim 2, wherein the second and third standstill times are each independently from 5min to 30min.
6. The method of claim 1, wherein the activating constant volume treatment is performed 1-3 turns.
7. The method of any one of claims 1-6, wherein the polarization voltage of the electrochemical workstation used to acquire the EIS spectrum is 10mV and the frequency is 100000Hz to 0.001Hz.
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