CN108511815B - Method and system for evaluating consistency of lithium ion battery - Google Patents

Method and system for evaluating consistency of lithium ion battery Download PDF

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CN108511815B
CN108511815B CN201810170001.9A CN201810170001A CN108511815B CN 108511815 B CN108511815 B CN 108511815B CN 201810170001 A CN201810170001 A CN 201810170001A CN 108511815 B CN108511815 B CN 108511815B
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lithium ion
grading
batteries
battery
temperature
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CN108511815A (en
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姚丹
彭文
李亚金
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Hefei Gotion High Tech Power Energy Co Ltd
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Hefei Guoxuan High Tech Power Energy 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4207—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells for several batteries or cells simultaneously or sequentially
    • 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]
    • G01R31/3644—Constructional arrangements
    • 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
    • H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
    • H01M10/482—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte for several batteries or cells simultaneously or sequentially
    • 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 discloses a lithium ion battery consistency evaluation method and a lithium ion battery consistency evaluation system, which belong to the field of power battery detection technology and comprise the steps of carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries; carrying out alternating current impedance spectrum test on the lithium ion battery subjected to preliminary grading at low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to preliminary grading; and according to the magnitude of the charge transfer impedance, performing consistency evaluation on the preliminarily graded lithium ion battery. According to the invention, the alternating current impedance test of the battery at low temperature is added to solve the problems that the consistency of the electrical property of the battery at normal temperature is better and the consistency of the battery at low temperature is poorer, so that the reasonable matching of the battery is realized, and the excellent performance of the battery pack during low-temperature and normal-temperature charging and discharging is ensured.

Description

Method and system for evaluating consistency of lithium ion battery
Technical Field
The invention relates to the technical field of power battery detection, in particular to a method for evaluating consistency of a lithium ion battery.
Background
Lithium ion batteries have been successfully used in electric road vehicles because of their high specific energy, high specific power, long service life, wide working range, and the like. Lithium ion batteries for electric road vehicles generally require a plurality of small-capacity low-voltage single batteries to be combined into a high-capacity high-voltage battery pack in a parallel or series connection manner. It is well known that the uniformity of the individual cells within a battery pack is critical to maintaining the performance of the battery pack, and the quality of the uniformity is directly related to the performance and the life of the battery pack.
The method for detecting the consistency of each single battery in the battery industry generally comprises two methods: one method is to classify by detecting the static data of capacity difference, alternating current internal resistance difference and initial voltage difference after the formation and capacity grading of all the single batteries, and then match and screen. The other is a dynamic method, namely, the consistency characteristic of the battery is evaluated by observing the charging and discharging processes.
However, both of the above-described detection methods are intended for detection and evaluation of the consistency of the battery in a normal temperature state, and are not suitable for consistency detection of the battery pack in various environments, particularly in a low-temperature environment. In a low-temperature environment, the conductivity of the important components such as organic electrolyte, active substances, a diaphragm and the like in the battery is greatly reduced, and the battery voltage is possibly reduced to a cut-off voltage at the moment of discharging, so that the battery cannot be discharged and cannot be detected by a dynamic method. Moreover, the internal resistance of each component in the battery is affected by the processing and manufacturing processes, and the inconsistency of the discharge capacity is reflected, so that the internal resistance, the pressure difference and the like at normal temperature cannot be effectively detected.
Therefore, in order to better detect and ensure the consistency of the lithium ion battery pack for the electric road vehicle in a low temperature environment, patent document No. 201010241411.1 discloses testing the consistency of the battery by low temperature direct current internal resistance. Although the mode is simple, large-current charging and discharging equipment is needed, the occupied area of the equipment is large, the price is high, the cost of consistency detection of the single batteries is increased, and the method is not suitable for consistency detection of a large number of single batteries.
Disclosure of Invention
The invention aims to provide a lithium ion battery consistency evaluation method capable of detecting consistency of a large number of single batteries at low temperature.
In order to realize the purpose, the invention adopts the technical scheme that:
on one hand, the method for evaluating the consistency of the lithium ion battery comprises the following steps:
carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
carrying out alternating current impedance spectrum test on the lithium ion battery subjected to the preliminary grading at a low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to the preliminary grading;
and according to the magnitude of the charge transfer impedance, performing consistency evaluation on the preliminarily graded lithium ion battery.
Preferably, the alternating current impedance spectrum test at low temperature is performed on the preliminarily graded lithium ion battery to obtain the charge transfer impedance of the preliminarily graded lithium ion battery, and the method specifically includes:
charging the lithium ion battery subjected to primary grading to the same charge state at normal temperature;
placing the lithium ion batteries with the same charge state in a low-temperature environment until the internal and external parts of the batteries reach preset temperatures;
and carrying out low-temperature alternating current impedance spectrum test on the batteries with the internal and external temperatures reaching the preset temperature to obtain the charge transfer impedance of the batteries.
Preferably, according to the magnitude of the charge transfer impedance, performing consistency evaluation on the preliminarily graded lithium ion battery, specifically including:
taking the average value of the charge transfer impedances of all the lithium ion batteries with the difference values of the charge transfer impedances within the difference standard range as a grading standard;
and according to the grading standard, a plurality of lithium ion batteries in the same gear form a battery pack.
Preferably, the temperature range of the low-temperature environment is-20 ℃ to 0 ℃.
Preferably, the step of performing formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain the lithium ion batteries after preliminary grading specifically includes:
carrying out formation treatment on a plurality of lithium ion batteries with the same nominal capacity, carrying out voltage detection on the formed batteries, and screening out the batteries with qualified voltage values;
and (3) aging the battery with a qualified voltage value at a high temperature, grading and standing, and grading the lithium ion battery according to the voltage reduction value, the internal resistance value and the capacity value to obtain the preliminarily graded lithium ion battery.
Preferably, the high-temperature aging temperature of the battery with qualified voltage value is 40-45 ℃, and the standing time is 12-13h in the capacity grading and standing treatment.
Preferably, in the lithium ion battery subjected to the primary grading treatment according to the voltage reduction value, the internal resistance difference standard and the capacity difference standard, the grading conditions are specifically as follows:
the value of the capacity difference standard is 10-20% of the nominal capacity of the single battery, the value of the internal resistance difference standard is 10-20% of the nominal internal resistance of the single battery,
and the voltage reduction value is the voltage difference delta V measured twice before and after the same battery is placed still, and the delta V is less than 30 mV.
In another aspect, a system for evaluating lithium ion battery consistency includes:
the formation and capacity grading processing module is used for carrying out formation and capacity grading processing on a plurality of lithium ion batteries with the same nominal capacity to obtain the lithium ion batteries subjected to primary grading;
the alternating current impedance spectrum testing module is used for carrying out alternating current impedance spectrum testing on the lithium ion battery subjected to the preliminary grading at a low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to the preliminary grading;
and the consistency evaluation module is used for carrying out consistency evaluation on the lithium ion battery subjected to the preliminary grading according to the size of the charge transfer impedance.
Preferably, the alternating current impedance spectrum testing module specifically includes:
the charging unit is used for charging the lithium ion battery subjected to the preliminary grading to the same charge state at normal temperature;
the low-temperature processing unit is used for placing the lithium ion batteries with the same charge state in a low-temperature environment until the internal and external parts of the batteries reach preset temperatures;
and the test unit is used for carrying out low-temperature alternating current impedance spectrum test on the batteries with the inside and the outside reaching the preset temperature to obtain the charge transfer impedance of the batteries.
In another aspect, a system for evaluating lithium ion battery consistency is provided, comprising:
a memory for storing a plurality of program instructions;
a processor for loading a plurality of program instructions stored in memory to perform:
carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
carrying out alternating current impedance spectrum test on the lithium ion battery subjected to the preliminary grading at a low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to the preliminary grading;
and according to the magnitude of the charge transfer impedance, performing consistency evaluation on the preliminarily graded lithium ion battery.
Compared with the prior art, the invention has the following technical effects: the invention adds the alternating current impedance test of the battery under the specific charging State (SOC) at low temperature in addition to the conventional screening detection of the consistency of voltage, internal resistance, capacity, storage voltage drop and the like at normal temperature, so as to solve the problems of better electrical property consistency of the battery under the normal temperature condition and poorer consistency under the low temperature condition, realize reasonable matching of the battery and ensure that the battery pack has excellent performance at low temperature and normal temperature charging and discharging.
Drawings
The following detailed description of embodiments of the invention refers to the accompanying drawings in which:
FIG. 1 is a schematic flow chart of a method for evaluating lithium ion battery consistency;
FIG. 2 is an EIS spectrum of 8 cells tested at-10 ℃;
FIG. 3 is a schematic diagram of a system for evaluating lithium ion battery consistency;
fig. 4 is a comparative graph illustrating the discharge of batteries leased using the method of the present invention and the prior art method at a rate of 0.5C at a low temperature of-10C.
Detailed Description
To further illustrate the features of the present invention, refer to the following detailed description of the invention and the accompanying drawings. The drawings are for reference and illustration purposes only and are not intended to limit the scope of the present disclosure.
As shown in fig. 1, the present embodiment discloses a method for evaluating lithium ion battery consistency, which includes the following steps S101 to S103:
s101, carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
s102, carrying out alternating current impedance spectrum test on the lithium ion battery subjected to preliminary grading at a low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to preliminary grading;
and S103, according to the size of the charge transfer impedance, performing consistency evaluation on the preliminarily graded lithium ion battery.
As a further preferable scheme, the step S101 specifically includes:
(1) voltage screening: charging and discharging multiple lithium ion batteries with nominal capacity of 16.5Ah for the first time to obtain a battery state of 3.2 + -0.02V, standing at room temperature for 1 day, measuring the voltage of the battery, and recording as V1. According to the voltage of the measuring cell, V1The single lithium ion battery A with the battery of more than or equal to 3.2V qualified by judgment1。
(2) Capacity grading treatment: after the battery with qualified size and appearance is judged, the battery is subjected to capacity grading and standing treatment, and the lithium ion battery A is subjected to capacity grading and standing treatment1Aging in a high temperature aging room with the high temperature aging condition set at 40-45 deg.C for 12-13 h.
(3) Sorting the batteries: and grading the single lithium ion battery according to the obtained discharge capacity C value, the voltage reduction value and the internal resistance value of the battery. The specific screening conditions are as follows:
a. the voltage reduction value is that delta V is less than or equal to 30mV, wherein the delta V is the voltage difference measured twice before and after the same battery is placed still;
b. the value of the standard deviation of the capacity is 10 to 20 percent of the nominal capacity of the single battery;
c. the value of the standard deviation of the internal resistance is 10 to 20 percent of the nominal internal resistance of the single battery.
Screening the lithium ion batteries according to the three standards, wherein the selected battery is Ac1。
Specifically, in practical application, an automatic voltage and internal resistance sorting device may be adopted to sequentially sort the voltage and internal resistance of the batteries of each grade according to the capacity grading identification, and perform grading according to the standard that the voltage difference is less than 30mV and the alternating current internal resistance difference is less than 0.5 mohm.
More preferably, in step S102: the lithium ions A after the preliminary grading are carried outc1The method comprises the following steps of testing alternating current impedance spectrum of a battery at low temperature to obtain charge transfer impedance of the lithium ion battery after primary grading, and specifically comprises the following steps:
(1) a is to bec1The battery is charged to the same state of charge, requiring a state of charge of 25-75%.
(2) Battery A after the preliminary gradingc1And standing the battery in a constant-temperature environment bin for more than 5 hours to ensure that the inside and the outside of the battery reach the temperature set in the environment bin in advance.
It should be noted that the low temperature range in the environmental chamber is any temperature point in the range of-20 ℃ to 0 ℃.
(3) The cells were subjected to alternating current impedance (EIS) testing using an electrochemical workstation. Wherein the set parameters are as follows: frequency of 10-2～105The amplitude was 5 mV. An EIS curve graph is obtained, and the electrochemical transfer impedance value is obtained after Zview fitting, as shown in FIG. 2, the EIS curve graph of the batteries No. 1 and No. 2 in the sequence along the arrow direction in FIG. 2 is the EIS curve graph of the battery No. 8.
More preferably, in step S103: according to the magnitude of the charge transfer impedance, consistency evaluation is carried out on the lithium ion battery subjected to preliminary grading, and the method specifically comprises the following steps:
selecting a value, such as 10%, between the range of the standard deviation of the internal resistance of 10-20%, and taking the average value of the impedance with the difference standard of the charge transfer impedance of 10% (namely 10% of the nominal internal resistance of the single battery) as the grading standard. And grading the plurality of single batteries subjected to the test according to the grading standard.
The scheme increases the charge transfer impedance test of the battery at low temperature, effectively solves the problems that each single battery has good electrical property consistency under the condition of normal temperature and the electrical properties of each single battery have large difference under the condition of low temperature, is suitable for detecting large-scale batteries, realizes reasonable battery matching and ensures that the battery pack has excellent performance during low-temperature and normal-temperature charging and discharging.
As shown in fig. 2, a 0.5C constant current discharge at a temperature of-10 ℃ was performed, and discharge capacity data were collected as shown in table 1:
TABLE 1
Figure BDA0001585311780000061
Figure BDA0001585311780000071
The test results in table 1 show that the grading of the conventional capacity internal resistance test at normal temperature does not reflect the consistency of the low-temperature discharging capacity of the battery, and the low-temperature charge transfer resistance value is very consistent with the low-temperature discharging capacity of the battery.
As shown in fig. 4, according to the method of the present invention, the tested low temperature transfer impedance value is used as a grading standard, the batteries are graded according to the standard of the average value of the direct current low temperature charge transfer impedance of all the batteries with the difference of the low temperature charge transfer impedance of each battery being less than 10%, the battery is combined by 7S2P by using the single batteries with the same grade to obtain a 22.4V16Ah battery pack, and fig. 4 is a graph of the battery pack discharging at 0.5C rate at the low temperature of-10 ℃. The battery pack numbered 1-1 in the figure is obtained by sorting and matching by adopting the method of the invention, the battery pack numbered 2-1 is obtained by screening the voltage difference, the internal resistance difference and the capacity difference by adopting a common method, and as can be seen from the figure 4, the battery pack obtained by adopting the method of the invention has small voltage reduction at the moment of heavy current discharge at low temperature, high discharge capacity and good consistency among the battery packs.
In addition to conventional screening detection of consistency such as voltage, internal resistance, capacity, storage voltage drop and the like at normal temperature, the charge transfer impedance detection at low temperature is added for evaluating the electrochemical characteristics of the battery at low temperature, so that the consistency of the electrical performance of each single battery at low temperature is ensured, reasonable matching of the battery is realized, and the battery pack has excellent performance during low-temperature and normal-temperature high-rate charge and discharge. The method can quickly, comprehensively and effectively evaluate the consistency of the electrical properties of the batteries, particularly evaluate the characteristics of the batteries in a special low-temperature use environment, effectively solve the common problems that each single battery shows good consistency at normal temperature and the electrical properties greatly differ at low temperature, and can be popularized and applied to detection of large-batch batteries and screening of battery matching.
As shown in fig. 3, the present embodiment discloses a system for evaluating lithium ion battery consistency, which includes:
a formation and grading processing module 10, configured to perform formation and grading processing on multiple lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
an ac impedance spectrum testing module 20, configured to perform an ac impedance spectrum test at a low temperature on the preliminarily graded lithium ion battery to obtain a charge transfer impedance of the preliminarily graded lithium ion battery;
and the consistency evaluation module 30 is configured to perform consistency evaluation on the preliminarily graded lithium ion batteries according to the magnitude of the charge transfer impedance.
Preferably, the ac impedance spectrum testing module 20 specifically includes:
the charging unit is used for charging the lithium ion battery subjected to the preliminary grading to the same charge state at normal temperature;
the low-temperature processing unit is used for placing the lithium ion batteries with the same charge state in a low-temperature environment until the internal and external parts of the batteries reach preset temperatures;
and the test unit is used for carrying out low-temperature alternating current impedance spectrum test on the batteries with the inside and the outside reaching the preset temperature to obtain the charge transfer impedance of the batteries.
On the other hand, this embodiment also discloses an evaluation system for lithium ion battery consistency, which includes:
a memory for storing a plurality of program instructions;
a processor for loading a plurality of program instructions stored in memory to perform:
carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
carrying out alternating current impedance spectrum test on the lithium ion battery subjected to the preliminary grading at a low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to the preliminary grading;
and according to the magnitude of the charge transfer impedance, performing consistency evaluation on the preliminarily graded lithium ion battery.
It should be understood that the consistency evaluation system in this embodiment corresponds to the consistency evaluation method, and the above and other operations and/or functions of each module in the consistency evaluation system respectively implement corresponding processes of each method in fig. 1, and are not described herein again for brevity.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (8)

1. A method for evaluating consistency of a lithium ion battery is characterized by comprising the following steps:
carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
and carrying out alternating current impedance spectrum test on the lithium ion battery subjected to preliminary grading at low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to preliminary grading, wherein the test comprises the following steps:
charging the lithium ion batteries subjected to primary grading to the same charge state, wherein the required charge state is 25-75%, then placing the batteries in a constant-temperature environment bin for standing for more than 5 hours, so that the internal and external parts of the batteries reach the preset temperature of the environment bin, and the low temperature range in the environment bin is-20-0 ℃;
and (3) carrying out alternating current impedance test on the battery by utilizing an electrochemical workstation, wherein the set parameters are as follows: frequency of 10-2~105Amplitude of 5mVObtaining an EIS curve chart, and fitting by using Zview to obtain an electrochemical transfer impedance value;
according to the size of the charge transfer impedance, consistency evaluation is carried out on the lithium ion battery subjected to preliminary grading, and the consistency evaluation method specifically comprises the following steps:
taking the average value of the charge transfer impedances of all the lithium ion batteries with the difference values of the charge transfer impedances within the difference standard range as a grading standard;
and according to the grading standard, a plurality of lithium ion batteries in the same gear form a battery pack.
2. The method for evaluating the consistency of the lithium ion batteries according to claim 1, wherein the step of performing an alternating current impedance spectrum test on the preliminarily classified lithium ion batteries at a low temperature to obtain the charge transfer impedance of the preliminarily classified lithium ion batteries specifically comprises the steps of:
charging the lithium ion battery subjected to primary grading to the same charge state at normal temperature;
placing the lithium ion batteries with the same charge state in a low-temperature environment until the internal and external parts of the batteries reach preset temperatures;
and carrying out low-temperature alternating current impedance spectrum test on the batteries with the internal and external temperatures reaching the preset temperature to obtain the charge transfer impedance of the batteries.
3. The method for evaluating the consistency of lithium ion batteries according to any one of claims 1 to 2, wherein the step of performing chemical composition and capacity grading on a plurality of lithium ion batteries with the same nominal capacity to obtain the lithium ion batteries after preliminary grading specifically comprises:
carrying out formation treatment on a plurality of lithium ion batteries with the same nominal capacity, carrying out voltage detection on the formed batteries, and screening out the batteries with qualified voltage values;
and (3) aging the battery with a qualified voltage value at a high temperature, grading and standing, and grading the lithium ion battery according to the voltage reduction value, the internal resistance value and the capacity value to obtain the preliminarily graded lithium ion battery.
4. The method for evaluating the consistency of the lithium ion batteries according to claim 3, wherein the batteries with qualified voltage values are subjected to high-temperature aging and capacity grading standing treatment, wherein the high-temperature aging temperature is 40-45 ℃, and the standing time is 12-13 h.
5. The method for evaluating the consistency of the lithium ion batteries according to claim 3, wherein in the lithium ion batteries subjected to the primary grading treatment according to the voltage reduction value, the internal resistance difference standard and the capacity difference standard, the grading conditions are specifically as follows:
the value of the capacity difference standard is 10-20% of the nominal capacity of the single battery, the value of the internal resistance difference standard is 10-20% of the nominal internal resistance of the single battery,
and the voltage reduction value is the voltage difference delta V measured twice before and after the same battery is placed still, and the delta V is less than 30 mV.
6. A system for evaluating lithium ion battery consistency is characterized by comprising:
the formation and capacity grading processing module is used for carrying out formation and capacity grading processing on a plurality of lithium ion batteries with the same nominal capacity to obtain the lithium ion batteries subjected to primary grading;
the alternating current impedance spectrum testing module is used for carrying out alternating current impedance spectrum testing on the preliminarily graded lithium ion battery at low temperature to obtain the charge transfer impedance of the preliminarily graded lithium ion battery, and comprises the following steps:
charging the lithium ion batteries subjected to primary grading to the same charge state, wherein the required charge state is 25-75%, then placing the batteries in a constant-temperature environment bin for standing for more than 5 hours, so that the internal and external parts of the batteries reach the preset temperature of the environment bin, and the low temperature range in the environment bin is-20-0 ℃;
and (3) carrying out alternating current impedance test on the battery by utilizing an electrochemical workstation, wherein the set parameters are as follows: frequency of 10-2~105Obtaining an EIS curve chart with the amplitude of 5mV, and obtaining an electrochemical transfer impedance value after Zview fitting;
the consistency evaluation module is used for performing consistency evaluation on the preliminarily graded lithium ion battery according to the magnitude of the charge transfer impedance, and specifically comprises the following steps:
taking the average value of the charge transfer impedances of all the lithium ion batteries with the difference values of the charge transfer impedances within the difference standard range as a grading standard;
and according to the grading standard, a plurality of lithium ion batteries in the same gear form a battery pack.
7. The system for evaluating consistency of lithium ion batteries according to claim 6, wherein the alternating current impedance spectrum testing module specifically comprises:
the charging unit is used for charging the lithium ion battery subjected to the preliminary grading to the same charge state at normal temperature;
the low-temperature processing unit is used for placing the lithium ion batteries with the same charge state in a low-temperature environment until the internal and external parts of the batteries reach preset temperatures;
and the test unit is used for carrying out low-temperature alternating current impedance spectrum test on the batteries with the inside and the outside reaching the preset temperature to obtain the charge transfer impedance of the batteries.
8. A system for evaluating lithium ion battery consistency is characterized by comprising:
a memory for storing a plurality of program instructions;
a processor for loading a plurality of program instructions stored in memory to perform:
carrying out formation and grading treatment on a plurality of lithium ion batteries with the same nominal capacity to obtain preliminarily graded lithium ion batteries;
and carrying out alternating current impedance spectrum test on the lithium ion battery subjected to preliminary grading at low temperature to obtain the charge transfer impedance of the lithium ion battery subjected to preliminary grading, wherein the test comprises the following steps:
charging the lithium ion batteries subjected to primary grading to the same charge state, wherein the required charge state is 25-75%, then placing the batteries in a constant-temperature environment bin for standing for more than 5 hours, so that the internal and external parts of the batteries reach the preset temperature of the environment bin, and the low temperature range in the environment bin is-20-0 ℃;
and (3) carrying out alternating current impedance test on the battery by utilizing an electrochemical workstation, wherein the set parameters are as follows: frequency of 10-2~105Obtaining an EIS curve chart with the amplitude of 5mV, and obtaining an electrochemical transfer impedance value after Zview fitting;
according to the size of the charge transfer impedance, consistency evaluation is carried out on the lithium ion battery subjected to preliminary grading, and the consistency evaluation method specifically comprises the following steps:
taking the average value of the charge transfer impedances of all the lithium ion batteries with the difference values of the charge transfer impedances within the difference standard range as a grading standard;
and according to the grading standard, a plurality of lithium ion batteries in the same gear form a battery pack.
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