CN118209859B - Evaluation and comparison method for matching performance of negative electrode and positive electrode - Google Patents
Evaluation and comparison method for matching performance of negative electrode and positive electrode Download PDFInfo
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- CN118209859B CN118209859B CN202410634798.9A CN202410634798A CN118209859B CN 118209859 B CN118209859 B CN 118209859B CN 202410634798 A CN202410634798 A CN 202410634798A CN 118209859 B CN118209859 B CN 118209859B
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
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Abstract
The invention relates to the technical field of battery manufacturing, and provides an evaluation and comparison method for the matching performance of a negative electrode and a positive electrode. An evaluation method, comprising: and calculating the ratio x of the direct current internal resistance of the battery cell negative electrode in the total internal resistance of the battery cell, wherein x=Rn/Rc, and when the x value calculated in the discharging process is less than or equal to 50% and/or the x value calculated in the charging process is less than or equal to 50% in any SOC state within the SOC range of 0% -100%, the positive electrode material and the positive electrode are good in matching property. The comparison method is to compare the values of x of different battery cells, and the small value of x indicates good matching. The method can provide an intuitive and accurate evaluation means of matching degree information for battery design, helps battery manufacturers optimize the selection and design of anode and cathode materials, and improves the cycle stability and efficiency of the battery.
Description
Technical Field
The invention relates to the technical field of battery manufacturing, in particular to an evaluation and comparison method for the matching performance of a negative electrode and a positive electrode.
Background
The performance of lithium ion batteries depends to a large extent on the degree of matching of the kinetic properties of the anode and cathode materials. The poor matching degree of the dynamic performance can cause the problems of capacity loss, internal resistance increase, cycle life shortening and the like of the battery in the charge and discharge process. Conventional evaluation methods generally rely on complex electrochemical tests and long-term cyclic tests, and thus a new evaluation method is required.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide an evaluation and comparison method for the matching performance of a negative electrode and a positive electrode.
The invention is realized in the following way:
In a first aspect, the present invention provides a method for evaluating the matching between a negative electrode and a positive electrode, including:
calculating the ratio x of the direct current internal resistance of the battery cell negative electrode in the total internal resistance of the battery cell, wherein x=Rn/Rc, when the x value calculated in the discharging process is less than or equal to 50% and/or the x value calculated in the charging process is less than or equal to 50% in any SOC state within the SOC range of 0% -100%, the positive electrode material and the positive electrode material are good in matching property;
the detection and calculation method of the discharge process x comprises the following steps:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
Recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 in a final discharge state by using I constant current discharge t, wherein t is 10-60 s;
discharge rc= (V WE1-VWE2)/I1000 mΩ, discharge rn= (V RE1-VRE2)/I1000 mΩ;
the detection and calculation method of the charging process x comprises the following steps:
Under the state of the measured SOC, discharging t 1 with constant current I 1, and after the state is laid aside until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charging rc= (V WE4-VWE3）/ I2 ×1000mΩ, charging rn= (V RE4-VRE3）/ I2 ×1000mΩ;
The working electrode voltage is the voltage measured when the positive electrode and the negative electrode are connected; the voltage of the reference electrode is the voltage measured when the reference electrode is connected with the negative electrode, and the reference electrode is connected with a metal wire arranged in the electric core;
The measured SOC is any SOC within the range of 0% -100% SOC.
In an alternative embodiment, before detecting and calculating the discharge process or x of the discharge process, further comprises:
Charging and discharging the battery cell for 3-5 times by using standard current, and standing until the battery cell is stable;
charging to full electricity by standard current, and standing to be stable;
Discharging to the measured SOC state with standard current.
In an alternative embodiment, I is 1.0-10.0C; and/or I 1=I2 is 1.0-10.0C;
optionally, the measured SOC is any SOC within a range of 10% -90% SOC.
In an alternative embodiment, the cells include bare cells that lead out the positive and negative electrodes;
At least one metal wire is arranged in the bare cell, a reference electrode is also arranged on the bare cell, and the metal wire is connected with the reference electrode;
optionally, the wire is a copper wire.
In an alternative embodiment, the method for detecting and calculating the discharging process x and the charging process x includes:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 in a discharge final state by using I constant current discharge t;
After the rest is carried out until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
Recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I=I2,t=t2 =10-60 s by using an I 2 constant current charging t 2;
The measured SOC is any SOC within the range of 0% -100% SOC.
In an alternative embodiment, when the x value is within 35-50% in any SOC state within the range of 0-100% SOC, the anode material and the cathode are good in matching.
In a second aspect, the present invention provides a method for comparing the quality of matching between a negative electrode and a positive electrode, comprising:
Comparing the direct current internal resistances of the cathodes of different cells in the charging process and/or the discharging process with the ratio x of the total internal resistance of the cells, wherein the cell with small x value has good matching performance, and x=rn/Rc;
the detection and calculation method of the discharge process x comprises the following steps:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
Recording the working electrode voltage V WE2 and the reference electrode voltage V RE2 of the final discharge state by using I 1 constant-current discharge t, wherein t is 10-60 s;
discharge rc= (V WE1-VWE2)/I1000 mΩ, discharge rn= (V RE1-VRE2)/I1000 mΩ;
the detection and calculation method of the charging process x comprises the following steps:
Under the state of the measured SOC, discharging t 1 with constant current I 1, and after the state is laid aside until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charging rc= (V WE4-VWE3）/ I2 ×1000mΩ, charging rn= (V RE4-VRE3）/ I2 ×1000mΩ;
The working electrode voltage is the voltage measured when the positive electrode and the negative electrode are connected; the voltage of the reference electrode is the voltage measured when the reference electrode is connected with the negative electrode, and the reference electrode is connected with a metal wire arranged in the electric core;
The measured SOC is any SOC within the range of 0% -100% SOC.
In an alternative embodiment, before detecting and calculating the discharge process or x of the discharge process, further comprises:
Charging and discharging the battery cell for 3-5 times by using standard current, and standing until the battery cell is stable;
charging to full electricity by standard current, and standing to be stable;
Discharging to the measured SOC state with standard current.
In an alternative embodiment, I is 1.0-10.0C; and/or I 1=I2 is 1.0-10.0C;
optionally, the measured SOC is any SOC within a range of 10% -90% SOC.
In an alternative embodiment, the method for detecting and calculating the discharging process x and the charging process x includes:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 of a discharge final state by I 1 constant-current discharge t;
After the rest is carried out until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
Recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t=t2 =10-60 s by using an I 2 constant current charging t 2;
The measured SOC is any SOC within the range of 0% -100% SOC.
The invention has the following beneficial effects:
The method for evaluating and comparing the matching performance of the negative electrode and the positive electrode provided by the embodiment of the invention evaluates or compares the matching performance of the negative electrode and the positive electrode by detecting and calculating the ratio of the direct current internal resistance of the negative electrode to the total internal resistance of the battery core as x (Rn/Rc), and the method can provide an intuitive and accurate evaluation means of matching degree information for battery design, help battery manufacturers optimize the selection and design of positive and negative electrode materials and improve the cycle stability and efficiency of the battery.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a three-electrode cell;
FIG. 2 is a statistical plot of the negative discharge DCIR duty cycle (i.e., x-value);
FIG. 3 is a statistical plot of the negative charge DCIR duty cycle (i.e., x-value);
Fig. 4 is a graph showing the percentage of normal temperature cycle capacity trend of the batteries according to example 1 and example 2;
Fig. 5 is a graph showing the high-temperature cycle capacity percentage trend of the batteries according to examples 1 and 2;
Fig. 6 is a high-temperature storage capacity retention rate trend chart of the batteries according to examples 1 and 2;
fig. 7 is a high-temperature storage capacity recovery rate trend chart of the batteries according to examples 1 and 2.
Icon: 1-an aluminum plastic film; 2-bare cell; 3-positive electrode; 4-negative electrode; 5-a reference electrode; 6-copper wire.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. 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 features and capabilities of the present invention are described in further detail below in connection with the examples.
The method for evaluating the matching performance of the negative electrode and the positive electrode provided by the embodiment of the invention comprises the following steps:
calculating the ratio x of the direct current internal resistance of the battery cell negative electrode in the total internal resistance of the battery cell, wherein x=rn/Rc, when the x value calculated in the discharging process is less than or equal to 50% and/or the x value calculated in the charging process is less than or equal to 50% in any SOC state (for example, 1%, 10%, 20%, 50%, 78, 90% or 100%) within the SOC range of 0% -100%, the matching property of the negative electrode material and the positive electrode is good;
the detection and calculation method of the discharge process x comprises the following steps:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
Recording the working electrode voltage V WE2 and the reference electrode voltage V RE2 of the final discharge state by using I 1 constant-current discharge t, wherein t is 10-60 s;
discharge rc= (V WE1-VWE2)/I1000 mΩ, discharge rn= (V RE1-VRE2)/I1000 mΩ;
the detection and calculation method of the charging process x comprises the following steps:
Under the state of the measured SOC, discharging t 1 with constant current I 1, and after the state is laid aside until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charging rc= (V WE4-VWE3）/ I2 ×1000mΩ, charging rn= (V RE4-VRE3）/ I2 ×1000mΩ;
The working electrode voltage is the voltage measured when the positive electrode and the negative electrode are connected; the voltage of the reference electrode is the voltage measured when the reference electrode is connected with the negative electrode, and the reference electrode is connected with a metal wire arranged in the electric core;
The measured SOC is any SOC within the range of 0% -100% SOC.
The method for comparing the quality of the matching of the cathodes and the anodes of different battery cells provided by the embodiment of the invention comprises the following steps:
Comparing the direct current internal resistances of the cathodes of different cells in the charging process and/or the discharging process with the ratio x of the total internal resistance of the cells, wherein the cell with small x value has good matching performance, and x=rn/Rc;
the detection and calculation method of the discharge process x comprises the following steps:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
Recording the working electrode voltage V WE2 and the reference electrode voltage V RE2 of the final discharge state by using I 1 constant-current discharge t, wherein t is 10-60 s;
discharge rc= (V WE1-VWE2)/I1000 mΩ, discharge rn= (V RE1-VRE2)/I1000 mΩ;
the detection and calculation method of the charging process x comprises the following steps:
Under the state of the measured SOC, discharging t 1 with constant current I 1, and after the state is laid aside until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charging rc= (V WE4-VWE3）/ I2 ×1000mΩ, charging rn= (V RE4-VRE3）/ I2 ×1000mΩ;
The working electrode voltage is the voltage measured when the positive electrode and the negative electrode are connected; the voltage of the reference electrode is the voltage measured when the reference electrode is connected with the negative electrode, and the reference electrode is connected with a metal wire arranged in the electric core;
The measured SOC is any SOC within the range of 0% -100% SOC.
The ratio of the direct current internal resistance of the negative electrode in the total internal resistance of the battery cell is x (Rn/Rc), and the contribution degree of the negative electrode material in the internal resistance of the battery cell is reflected by the ratio; the magnitude of the internal resistance directly influences the dynamic performance of the battery cell, so that the proportion also reflects the dynamic performance allowance of the negative electrode material compared with the positive electrode material, and the smaller the internal resistance of the negative electrode is, the larger the dynamic performance allowance is, similar to the N/P value in the battery cell (under the same condition, the positive-to-negative electrode capacity exceeds the allowance of the positive electrode capacity).
And evaluating the matching degree of the dynamic performance of the anode and cathode material system according to the direct current internal resistance ratio of the anode. If the internal DC resistance of the negative electrode is too high, the dynamic properties of the negative electrode material and the positive electrode material may be not matched, and the type and proportion of the materials need to be adjusted or the electrode structure needs to be optimized; if the direct current internal resistance of the negative electrode is too low, the dynamic performance of the negative electrode material is far higher than that of the positive electrode material, the positive electrode material may become a limiting factor under the condition of high-current charge and discharge, so that the battery performance is reduced; and if the internal DC resistance of the anode is moderate, the matching degree of the dynamic performance of the anode and cathode materials is good. Ideally, the internal resistance (i.e., dynamic performance) of the positive and negative electrodes should be kept balanced to ensure stability and efficiency of the battery during charge and discharge, thereby improving the cycle life of the battery.
The inventor researches find that when the detected x value is less than or equal to 50% in any SOC state within the range of 0% -100%, the matching property of the anode material and the anode of the battery cell is good. Therefore, the method for evaluating the matching performance of the negative electrode and the positive electrode provided by the application judges whether the matching performance of the negative electrode material and the positive electrode of the battery cell is good or bad by detecting and calculating the x value of the charging process and/or the discharging process and judging whether the x value is less than or equal to 50 percent. Therefore, the evaluation method provided by the application has good guiding significance for selecting proper anode and cathode materials before manufacturing the battery cell.
Preferably, in any SOC state within the range of 0% -100%, when the x value is within 35% -50%, the matching property of the anode material and the cathode is good.
And as the x value can be detected and calculated, the comparison of the matching performance of different cathodes and anodes can be realized by comparing the x values of different electric cores. Therefore, the comparison method provided by the application has good guiding significance for selecting proper anode and cathode materials before manufacturing the battery core.
Alternatively, the measured SOC is, for example, any SOC in the range of 10% -90% SOC.
Optionally, the evaluation method and the comparison method provided by the application specifically include:
S1, three-electrode cell construction
A three electrode system was constructed comprising a Working Electrode (WE), a Counter Electrode (CE) and a Reference Electrode (RE). The working electrode represents the positive or negative electrode of the cell, the counter electrode is used for applying current, and the reference electrode is used for providing stable potential reference.
Specifically, as shown in fig. 1, the battery cell comprises a bare battery cell and an aluminum plastic film 1 coated on the surface of the bare battery cell, wherein the bare battery cell 2 leads out a positive electrode 3 and a negative electrode 4;
At least one metal wire (generally 1-3) is arranged in the bare cell, a reference electrode 5 is also arranged on the bare cell 2, and the metal wire is connected with the reference electrode 5.
The wire is preferably provided with a plurality of wires, and the plurality of wires can be used for preventing the wire in the test from being broken and not being tested continuously, even if one wire is broken, the other wires can be tested in standby.
Optionally, the wire is a copper wire 6.
The specific manufacturing method is as follows:
(1) Selecting positive and negative electrode materials to be evaluated, preparing electrode plates according to a battery cell manufacturing process, and preparing bare battery cells through a lamination or winding process;
(2) And (3) taking 1-3 copper wires (the outer layer of the copper wires is provided with a polyurethane protective layer) with the diameter of 10 mu m, soaking one end of the copper wires in concentrated sulfuric acid to remove the polyurethane protective layer, electrifying the copper wires, then plugging the copper wires into the bare cell obtained in the step (1), leaking the other end of the copper wires during packaging, performing protective treatment to prevent the copper wires from being broken, ensuring that the copper wires are not contacted with positive and negative electrode lugs and each other, and subsequently completing the manufacture of a finished cell according to a normal cell manufacturing process.
S2, preparation before measurement
The battery cell prepared in the step S1 is subjected to capacity calibration and direct current internal resistance test under different SOCs, and meanwhile, the voltages of a working electrode and a reference electrode are monitored, and the whole test process is carried out at normal temperature (22-28 ℃), and the specific test method is as follows:
(1) Charging and discharging the experimental battery cell for 3-5 times by using standard current, and placing the experimental battery cell until the experimental battery cell is stable (the placing time can be 30min, for example), when the extremely difference of the continuous 3 times of test results is less than 3% of rated capacity, the test can be ended in advance, the average value of the last 3 times of test results is taken as the calibrated capacity, and the calculation is participated in when the electrochemical performance is counted later;
(2) Charging to full electricity with standard current, and standing to be stable (the standing time can be 30min, for example);
(3) Discharge to the measured SOC state (e.g., 10%, 20%, 30%, 50%, 70%, 80%, or 90%) at standard current.
The standard current refers to standard charge and discharge current corresponding to the type or kind of the battery cell prepared in the step S1.
S3, discharge x value test
(1) Recording the stable working electrode voltage V WE1 and the reference electrode voltage V RE1 under the state of SOC;
(2) Recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 in a final discharge state by using I constant current discharge t, wherein t is 10-60 s;
The discharge x value is calculated by the formula x=rn/Rc, discharge rc= (V WE1-VWE2)/I1000 mΩ, discharge rn= (V RE1-VRE2)/I1000 mΩ.
S4, charging x value test
(1) Under the state of the measured SOC, the constant current discharge t 1 is carried out by I 1, and after the voltage value is stable (the rest time can be 3 hours for example), the working electrode voltage V WE3 and the reference electrode voltage V RE3 are recorded;
(2) Recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charge rc= (V WE4-VWE3）/ I2 x 1000mΩ, charge rn= (V RE4-VRE3）/ I2 x 1000mΩ) is calculated by the formula x=rn/Rc to obtain the charge x value.
Preferably, in order to make the evaluation result or the comparison result more accurate, both the discharge x value and the charge x value can be selected for testing, and preferably, the discharge x value test is performed first and then the charge x value test is performed in a continuous test mode. The method comprises the following steps:
(1) After step S2, recording the stable working electrode voltage V WE1 and the reference electrode voltage V RE1 in the measured SOC state;
(2) Recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 in a discharge final state by using I constant current discharge t;
(3) After the rest is carried out until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
(4) Recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t=t2 =10-60 s by using an I 2 constant current charging t 2;
The measured SOC is any SOC within the range of 0% -100% SOC.
The method for continuously measuring the discharge x value and the charge x value is equivalent to the constant current discharge process in the process of measuring the discharge x value and the constant current discharge process in the process of measuring the charge x value.
Preferably, I is 1.0 to 10.0C (e.g., 1C, 2C, 3C, 5C, 8C, or 10C); and/or I 1=I2 is 1.0 to 10.0c (e.g., 1C, 2C, 3C, 5C, 8C, or 10C).
Example 1
The present example provides a negative electrode (negative electrode # 1) whose active ingredient is single-particle graphite.
And (3) taking lithium iron phosphate as an anode, and assembling the lithium iron phosphate into a 2.5Ah small soft-package battery cell of a three-electrode system.
The charge x value and the discharge x value in 10% soc, 50% soc and 90% soc states were respectively tested as follows. The method comprises the following steps:
a) Charging and discharging for 3 times at standard current of 0.5C, and standing for 30min; taking the average value of 3 discharge capacities as a calibration capacity C 0;
b) Charging to full power at standard current of 0.5C, and standing for 30min;
c) Discharging to 90% soc at standard current 0.5C;
d) Standing for 3h, recording the stabilized working electrode voltage V WE1 and the reference electrode voltage V RE1;
e) 1.0C constant current discharge for 60s, recording the working electrode voltage V WE2 at the end of discharge, reference electrode voltage V RE1 (sampling frequency: 0.01 s);
Discharge rc= (V WE1-VWE2）/1 c 1000mΩ, discharge rn= (V RE1-VRE2)/1 c 1000mΩ;
f) Standing for 3h, recording the stabilized working electrode voltage V WE3 and the reference electrode voltage V RE3;
g) 1.0C constant current charge for 60s, recording working electrode voltage V WE4 at the end of charge, reference electrode voltage V RE4 (sampling frequency: 0.01 s);
Charging rc= (V WE4-VWE3)/1 c 1000mΩ, charging rn= (V RE4-VRE3)/1 c 1000mΩ;
h) Repeating the steps c) to g) for 2 times to finish charge and discharge Rc and Rn under 50% SOC and 10% SOC.
The measured discharge and charge x values for different SOC states are recorded in fig. 2 and 3.
Example 2
This embodiment is substantially the same as embodiment 1, except that: negative electrode 2# is taken as a negative electrode, and the active component is secondary particle graphite.
The measured discharge and charge x values for different SOC states are recorded in fig. 2 and 3.
As can be seen from fig. 2 and 3, in example 1, the assembled battery cell of negative electrode 2# is adopted, and the x value measured under each SOC state is smaller than negative electrode 1#, which indicates that the negative electrode 2# is well matched with the positive electrode and is well matched with the negative electrode 1#; the x value measured under each SOC state of the negative electrode 2# is in the range of 35% -50%, which indicates that the matching property of the negative electrode 2# and the positive electrode is good.
Experimental example
The cells of examples 1 and 2 were tested for normal temperature cycle performance and high temperature cycle performance as shown in fig. 4 and 5;
the cells of examples 1 and 2 were tested for high temperature storage capacity retention and recovery as shown in fig. 6 and 7.
As can be seen from fig. 4 to 7, in the application example of the 2.5Ah small soft package, the normal temperature and high temperature cycle performance of the negative electrode 2# is better; and the high-temperature storage performance is excellent, so that the evaluation method for the matching performance of the cathode and the anode provided by the embodiment of the invention is reliable.
The 90% soc discharge DCIR and 10% soc charge DCIR of negative electrode 1# are > 50%, while the 90% soc discharge DCIR and 10% soc charge DCIR of negative electrode 2# are < 50%; compared with the negative electrode 1#, the normal-high-temperature cycle life of the negative electrode 2# is prolonged by about 1000 weeks and 500 weeks respectively, and the high-temperature storage is only 1-2.4% lower; the comprehensive service life of the negative electrode No. 2 with the DCIR ratio less than 50% is obviously longer than that of the negative electrode No. 1, and the comparison method for the matching performance of the negative electrode and the positive electrode provided by the embodiment of the invention is reliable.
In summary, the method for evaluating and comparing the matching performance of the negative electrode and the positive electrode provided by the embodiment of the invention evaluates or compares the matching performance of the negative electrode and the positive electrode by detecting and calculating the ratio of the direct current internal resistance of the negative electrode to the total internal resistance of the battery core as x (Rn/Rc), so that the method is convenient and easy to implement, has reliability and has good guiding significance for selecting proper positive and negative electrode materials before manufacturing the battery core.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (12)
1. The method for evaluating the matching performance of the negative electrode and the positive electrode is characterized by comprising the following steps:
Calculating the ratio x of the direct current internal resistance of the battery cell negative electrode in the total internal resistance of the battery cell, wherein x=Rn/Rc, and when the x value calculated in the discharging process and the x value calculated in the charging process are both in the range of 35-50% in any SOC state in the range of 0-100%, the positive electrode material and the positive electrode material are indicated to have good matching property;
the detection and calculation method of the discharge process x comprises the following steps:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
Recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 in a final discharge state by using I constant current discharge t, wherein t is 10-60 s;
discharge rc= (V WE1-VWE2)/I1000 mΩ, discharge rn= (V RE1-VRE2)/I1000 mΩ;
the detection and calculation method of the charging process x comprises the following steps:
Under the state of the measured SOC, discharging t 1 with constant current I 1, and after the state is laid aside until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charging rc= (V WE4-VWE3）/ I2 ×1000mΩ, charging rn= (V RE4-VRE3）/ I2 ×1000mΩ;
The working electrode voltage is a voltage measured when the positive electrode and the negative electrode are connected; the reference electrode voltage is measured when the reference electrode and the negative electrode are connected, and the reference electrode is connected with a metal wire arranged in the electric core;
the measured SOC is any SOC in the range of 0% -100% SOC.
2. The method of evaluating according to claim 1, further comprising, before detecting and calculating the discharge process or x of the discharge process:
Charging and discharging the battery cell for 3-5 times by using standard current, and standing until the battery cell is stable;
charging to full power by the standard current, and standing to be stable;
discharging to the measured SOC state with the standard current.
3. The method according to claim 1, wherein I is 1.0 to 10.0c;
And/or I 1=I2 is 1.0-10.0C.
4. The evaluation method according to claim 1, wherein the measured SOC is any SOC in a range of 10% -90% SOC.
5. The evaluation method according to claim 1, wherein the battery cell includes a bare cell that leads out the positive electrode and the negative electrode;
The bare cell is internally provided with at least one metal wire, the bare cell is also provided with a reference electrode, and the metal wire is connected with the reference electrode.
6. The method of evaluating according to claim 5, wherein the wire is a copper wire.
7. The evaluation method according to claim 1, wherein the detection and calculation method of the discharging process x and the charging process x comprises:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 in a discharge final state by using I constant current discharge t;
After the rest is carried out until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
Recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I=I2,t=t2 =10-60 s by using an I 2 constant current charging t 2;
the measured SOC is any SOC in the range of 0% -100% SOC.
8. The method for comparing the quality of the matching between the cathode and the anode is characterized by comprising the following steps:
Comparing the direct current internal resistances of the cathodes of different battery cells in the charging process and the discharging process to obtain the ratio x of the total internal resistance of the battery cells, wherein the battery cells with small x values have good matching performance within the range of 35-50%, and x=rn/Rc;
the detection and calculation method of the discharge process x comprises the following steps:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
Recording the working electrode voltage V WE2 and the reference electrode voltage V RE2 of the final discharge state by using I 1 constant-current discharge t, wherein t is 10-60 s;
Discharge rc= (V WE1-VWE2）/ I1 x 1000mΩ, discharge rn= (V RE1-VRE2）/ I1 x 1000mΩ);
the detection and calculation method of the charging process x comprises the following steps:
Under the state of the measured SOC, discharging t 1 with constant current I 1, and after the state is laid aside until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t1=t2 =10-60 s by using an I 2 constant current charging t 2;
Charging rc= (V WE4-VWE3）/ I2 ×1000mΩ, charging rn= (V RE4-VRE3）/ I2 ×1000mΩ;
The working electrode voltage is a voltage measured when the positive electrode and the negative electrode are connected; the reference electrode voltage is measured when the reference electrode and the negative electrode are connected, and the reference electrode is connected with a metal wire arranged in the electric core;
the measured SOC is any SOC in the range of 0% -100% SOC.
9. The method of comparing of claim 8, further comprising, prior to detecting and calculating the discharge event or x of the discharge event:
Charging and discharging the battery cell for 3-5 times by using standard current, and standing until the battery cell is stable;
charging to full power by the standard current, and standing to be stable;
discharging to the measured SOC state with the standard current.
10. The comparison method according to claim 8, wherein I is 1.0 to 10.0c;
And/or I 1=I2 is 1.0-10.0C.
11. The comparison method according to claim 8, wherein the measured SOC is any SOC in the range of 10% -90% SOC.
12. The comparison method according to claim 8, wherein the detecting and calculating method of the discharging process x and the charging process x includes:
Recording a stable working electrode voltage V WE1 and a reference electrode voltage V RE1 under the measured SOC state;
recording a working electrode voltage V WE2 and a reference electrode voltage V RE2 of a discharge final state by I 1 constant-current discharge t;
After the rest is carried out until the voltage value is stable, recording the working electrode voltage V WE3 and the reference electrode voltage V RE3;
Recording the charging final working electrode voltage V WE4 and the reference electrode voltage V RE4,I1=I2,t=t2 =10-60 s by using an I 2 constant current charging t 2;
the measured SOC is any SOC in the range of 0% -100% SOC.
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