CN109856557A

CN109856557A - On-line monitoring lithium ion battery electrochemical impedance test method

Info

Publication number: CN109856557A
Application number: CN201910054995.2A
Authority: CN
Inventors: 吴欢欢; 袁雪芹; 邵素霞; 王蓉蓉; 冷飞喜; 姚丹
Original assignee: Gotion High Tech Co Ltd
Current assignee: Gotion High Tech Co Ltd
Priority date: 2019-01-21
Filing date: 2019-01-21
Publication date: 2019-06-07
Anticipated expiration: 2039-01-21
Also published as: CN109856557B

Abstract

The present invention provides an on-line monitoring lithium ion battery electrochemical impedance test method, which can solve the technical problem that the existing test method cannot complete the electrochemical impedance test online. Including S100, place the battery under test in an incubator, and charge the battery under test to a certain SOC state; S200, perform an alternating current impedance (EIS) test on the battery under test, and analyze the impedance values generated by each polarization; S300, put the EIS The battery after the impedance test is connected to the high-precision test cabinet, and current pulses with different gradients are applied to it; S400, the shelving voltage before a certain pulse current I pulse is recorded as U ₀ , and the voltage after pulse t ₂ is recorded as U _t , then △U=U ₀ ‑ U _t , plot △U and pulse current I under different pulse currents, and perform linear fitting, and the obtained slope is the impedance value of the DCR test. The invention combines the direct current method with the alternating current method, and achieves the purpose of online monitoring of the change of the electrochemical impedance of the battery through the direct current impedance test of the small rate current pulse. The experimental process of this method is simple and practical.

Description

A kind of on-line monitoring lithium ion battery electrochemical impedance test method

Technical field

The present invention relates to technical field of lithium ion, and in particular to a kind of on-line monitoring lithium ion battery electrochemical impedance Test method.

Background technique

Internal resistance is a very important performance indicator of battery, has important shadow to the fast charge of battery, heat production, aging It rings.The method for being commonly used to the test internal resistance of cell at present has direct current method (DCR) and alternating current method (EIS).Wherein, direct current method is usually pair Battery carries out the big multiplying power discharging of 3C or 5C, obtains the pulse further according to the ratio between the changing value and pulse current of voltage The impedance magnitude of battery in time.And exchanging rule is the signal disturbance by electrochemical workstation to battery progress by a small margin, The impedance spectra of battery is obtained while keeping stable state inside battery system, passes through the feature of battery impedance spectrogram, fitting point Analyse the available ohmage R generated by the various polarization of battery_s, membrane impedance R_fAnd Charge-transfer resistance R_ct。

Therefore the electrochemical impedance of current battery mainly uses alternating current method to test, this method is a kind of testing impedance side of static state Method needs to remove battery after the certain all numbers of circulation, is placed on testing impedance instrument and carries out testing impedance, therefore, it is impossible to Online testing impedance is carried out to battery, and DC impedance test then can be completed directly in charge and discharge electric cabinet.

Summary of the invention

A kind of on-line monitoring lithium ion battery electrochemical impedance test method proposed by the present invention, can solve existing test Method can not complete the technical issues of testing impedance online.

To achieve the above object, the invention adopts the following technical scheme:

A kind of on-line monitoring lithium ion battery electrochemical impedance test method, comprising the following steps:

S100, mesuring battary is placed in insulating box, then the good temperature of incubator set point charges to mesuring battary a certain SOC state, is shelved；

S200, AC impedance EIS test is carried out to mesuring battary on electrochemical workstation, obtains its EIS impedance spectra, Fitting Analysis obtains the impedance value generated by each polarization, i.e. ohmage Rs, membrane impedance Rf and Charge-transfer resistance Rct； Wherein, R_s+R_f+R_ctFrequency time at inflection point is denoted as t₁；

S300, the battery after EIS testing impedance is connected to high precision measurement cabinet, the small multiplying power of different gradients is carried out to it Current impulse, burst length t₂, the sampling site time of pulse is t_a, the time interval between every subpulse is t_b；

S400, EIS is tested after battery carry out pulsed discharge, when pulsed discharge, putting before a certain pulse current I pulse It sets voltage and is denoted as U₀, pulse t₂Voltage afterwards is denoted as U_t, then △ U=U₀-U_t, then take △ U and pulse electricity under different pulse currents I mapping is flowed, linear fit is carried out, obtained slope is the impedance value of DCR test；

S500, the battery for testing DCR and EIS is placed on high precision measurement cabinet to the circulation for carrying out X multiplying power, every 50 weeks Afterwards, 50%SOC is charged to, its static EIS impedance value, 0.1c < X≤2c are tested in the variation and lower cabinet that its DCR is monitored online.

Wherein, the battery to be studied in the step S100 includes all battery systems (rectangular, cylinder, full battery, half electricity Pond etc.).

Battery need to be same state when carrying out EIS and DCR test in the step S100.

Ac impedance measurement (EIS) in the step S200 includes current disturbing and voltage disturbance both of which.

The burst length that DC impedance is tested in the step S300 is R in EIS impedance spectrum_s+R_f+R_ctFrequency at inflection point Time, i.e. t₂=t₁。

Pulse sampling site time range is 0.0001s≤t in the step S300_a≤ 1s, preferably 1ms-10ms.

Pulse current range is 0 < I≤1c in the step S300, and spacing gradient can choose 0.02-0.2c, preferably 0.1c- 0.2c。

Pulse sampling site time range is t in the step S300_b>=30min, preferably 30min.

The time of DCR pulse sliced is electrochemical impedance in first week EIS spectrogram in cyclic process in the step S500 The frequency time of inflection point.

As shown from the above technical solution, on-line monitoring lithium ion battery electrochemical impedance test method of the invention is chosen Burst length of the frequency time as direct current method testing impedance in AC impedance spectroscopy at the inflection point of electrochemical impedance region, and arteries and veins It rushes the small multiplying power electric current that electric current is chosen within 1C and online prison is reached by the DC impedance test of this small multiplying power current impulse Control battery electrochemical impedance variations purpose.

When the burst length of direct current method testing impedance is chosen for the inflection point in electrochemical impedance region in AC impedance spectroscopy Between, pulse current chooses the small multiplying power electric current within 1C, and verifying obtains accurately measuring the electrochemistry of battery by direct current method Impedance, and then achieve the purpose that battery electrochemical impedance variations are monitored online by direct current method, this method experimentation is simple, practical Property is strong.

Detailed description of the invention

Fig. 1 is the flow diagram of the method for the present invention；

Fig. 2 is the EIS impedance spectra of example 1；

Fig. 3 is the Linear Fit Chart of the DCR (0.464s) of example 1；

Fig. 4 is the impedance value of the DCR test of example 1；

Fig. 5 is 500 weeks DCR of circulation of example 1 compared with EIS impedance；

Fig. 6 is the EIS impedance spectra of example 2；

Fig. 7 is the Linear Fit Chart of the DCR (0.293s) of example 2；

Fig. 8 is the impedance value of the DCR test of example 2；

Fig. 9 is 500 weeks DCR of circulation of example 2 compared with EIS impedance.

Specific embodiment

In order to make the object, technical scheme and advantages of the embodiment of the invention clearer, below in conjunction with the embodiment of the present invention In attached drawing, technical scheme in the embodiment of the invention is clearly and completely described, it is clear that described embodiment is A part of the embodiment of the present invention, instead of all the embodiments.

As shown in Figure 1, on-line monitoring lithium ion battery electrochemical impedance test method described in the present embodiment, including S100, mesuring battary is placed in insulating box, then the good temperature of incubator set point charges to a certain SOC state to mesuring battary, puts It sets；

S500, the battery for testing DCR and EIS is placed on high precision measurement cabinet to the circulation for carrying out 1C multiplying power, every 50 Zhou Hou charges to 50%SOC, its static EIS impedance value is tested in the variation and lower cabinet that its DCR is monitored online.

It is described in detail below in conjunction with specific example:

Example 1: when ternary lamination full battery 50%SOC, the test of direct current method electrochemical impedance:

(1) full battery to be studied is placed in 25 DEG C of insulating boxs, charges to 50%SOC, shelves 1h；

(2) AC impedance (EIS) test, voltage disturbance, forcing frequency are carried out to mesuring battary on electrochemical workstation For 5mv, its EIS impedance spectra is obtained, Fitting Analysis obtains the impedance value generated by each polarization；Wherein, as shown in Fig. 2, Rs+ Frequency time at Rf+Rct inflection point is denoted as t₁；

EIS fitting data is as follows:

SOC/%	R_s/Ω	R_f/Ω	R_ct/Ω	R_s+R_f+R_ct/Ω	f/Hz	t₁/s
							50	0.200	0.093	0.347	0.640	2.15	0.464

(3) battery after EIS testing impedance is connected to high precision measurement cabinet, different current impulses, pulse is carried out to it Electric current I=0.2c, 0.4c, 0.6c, 0.8c, 1c, burst length are R in EIS impedance spectra_s+R_f+R_ctFrequency time at inflection point 0.464s, sampling site time when pulse are 0.001s, and the time interval between every subpulse is 30min；

(4) when pulsed discharge, the shelved voltage before a certain pulse current I pulse is denoted as U₀, pulse t₂Voltage after s is denoted as U_t, then △ U=U₀-U_t, then take △ U and pulse I under different pulse currents to map, carry out linear fit, obtained slope is The impedance value of DCR test；As shown in Figure 3 and Figure 4,

(5) impedance value that more above-mentioned alternating current method and direct current method measure.

The calculation formula of relative deviation are as follows: o '=| R_DCR(Xs)-R_EIS|/R_EIS* 100, relative deviation is about within 15%, can To think that both impedance detecting method differences can be ignored.

SOC/%	DCR(0.464s)/Ω	R²	EIS_Rs+Rf+Rct/Ω	Relative deviation/%
					50	0.707	1	0.64	10.47

The impedance value that above data can be seen that two methods measurement is closer to, and relative deviation is about 10.47%, Therefore, can be with the variation of direct current method measurement battery electrochemical impedance, and then achieve the purpose that on-line monitoring.

(6) battery for testing DCR and EIS is placed on high precision measurement cabinet to the circulation for carrying out 1C multiplying power, every 50 weeks Afterwards, 50%SOC is charged to, its static EIS impedance value is tested in the variation and lower cabinet that its DCR (0.464s) is monitored online.Such as Shown in Fig. 5 and following table；

Cycles	1	50	100	150	200	250	300	350	400	450	500
												EIS(R_s+R_ct+R_f)	0.64	0.645	0.691	0.681	0.666	0.702	0.712	0.706	0.718	0.715	0.72
DCR(0.464s)	0.707	0.711	0.762	0.759	0.755	0.77	0.775	0.778	0.783	0.78	0.786
												Relative deviation/%	10.47	10.23	10.27	11.45	13.36	9.69	8.85	10.20	9.05	9.09	9.17

During recycling 500 weeks as can be seen from the above data, the impedance value and direct current method that are measured by static AC method The impedance value of on-line monitoring is close, relative deviation be 8.3%~

11.79%, difference can be ignored.It therefore, can be with the battery of direct current method on-line monitoring in cyclic process Electrochemical impedance.

Example 2: when tertiary cathode half-cell 50%SOC, the test of direct current method electrochemical impedance

(1) positive half-cell to be studied is placed in 25 DEG C of insulating boxs, charges to 50%SOC, shelves 1h；

(2) AC impedance (EIS) test, voltage disturbance, forcing frequency are carried out to mesuring battary on electrochemical workstation For 5mv, its EIS impedance spectra is obtained, Fitting Analysis obtains the impedance value generated by each polarization.Wherein, R_s+R_f+R_ctInflection point The frequency time at place is denoted as t₁；As shown in Figure 6.

EIS fitting data is as follows:

(3) battery after EIS testing impedance is connected to high precision measurement cabinet, different current impulses, pulse is carried out to it Electric current I=0.2c, 0.4c, 0.6c, 0.8c, 1c, burst length are R in EIS impedance spectra_s+R_f+R_ctFrequency time at inflection point 0.293s, sampling site time when pulse are 0.001s, and the time interval between every subpulse is 30min；

(4) when pulsed discharge, the shelved voltage before a certain pulse current I pulse is denoted as U₀, pulse t₂Voltage after s is denoted as U_t, then △ U=U₀-U_t, then take △ U and pulse I under different pulse currents to map, carry out linear fit, obtained slope is The impedance value of DCR test；As shown in Figure 7 and Figure 8；

SOC/%	DCR(0.292s)/Ω	R²	EIS_Rs+Rf+Rct/Ω	Relative deviation/%
					50	0.619	0.9999	0.586	5.63

From the above data, it can be seen that the impedance value of two methods measurement is closer to, relative deviation is about 5.63%, Therefore, can be with the variation of direct current method measurement battery electrochemical impedance, and then achieve the purpose that on-line monitoring.

(6) battery for testing DCR and EIS is placed on high precision measurement cabinet and carries out charge and discharge, after 50 weeks, charging To 50%SOC, its static EIS impedance value is tested in the variation and lower cabinet that its DCR (0.292s) is monitored online.If Fig. 9 is under Shown in table；

11.79%, difference can be ignored.It therefore, can be with the electricity of direct current method on-line monitoring battery in cyclic process Chemical impedance.

To sum up alternating current method is measured the frequency time at electrochemical impedance inflection point as direct current method impedance by the embodiment of the present invention The burst length of test, and small multiplying power current impulse is combined, realize that battery electrochemical impedance, which is monitored online, by DC impedance method becomes The purpose of change has good application value.

The above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations；Although with reference to the foregoing embodiments Invention is explained in detail, those skilled in the art should understand that: it still can be to aforementioned each implementation Technical solution documented by example is modified or equivalent replacement of some of the technical features；And these modification or Replacement, the spirit and scope for technical solution of various embodiments of the present invention that it does not separate the essence of the corresponding technical solution.

Claims

1. an on-line monitoring lithium-ion battery electrochemical impedance test method, is characterized in that: comprise the following steps:

S100, place the battery to be tested in an incubator, set the temperature in the incubator, then charge the battery to be tested to a certain SOC state, and set it aside;

S200, perform the AC impedance EIS test on the battery to be tested on the electrochemical workstation, obtain its EIS impedance spectrum, and obtain the impedance values generated by each polarization by fitting and analysis, namely, the ohmic impedance Rs, the membrane impedance Rf and the charge transfer impedance Rct; Among them, the frequency time at the inflection point of R _s + R _f + R _ct is recorded as t ₁ ;

S300. Connect the battery after the EIS impedance test to a high-precision test cabinet, and perform current pulses with different gradients of small rate on it. The pulse time is t ₂ , the pulse sampling time is t _a , and the time interval between each pulse is t 2 . is t _b ;

S400. Perform pulse discharge on the battery after the EIS test. During pulse discharge, the shelving voltage before the pulse of a certain pulse current I is recorded as U ₀ , and the voltage after the pulse t ₂ is recorded as U _t , then △U = U ₀ - U _t , and then plot △U and pulse current I under different pulse currents, perform linear fitting, and the obtained slope is the impedance value of the DCR test;

S500. Put the tested DCR and EIS battery on a high-precision test cabinet for X-rate cycle, after every 50 weeks, charge it to 50% SOC, monitor the change of its DCR online and test its static EIS impedance value under the cabinet , 0.1 c <X ≤ 2c.

2. The method for testing the electrochemical impedance of an on-line monitoring lithium-ion battery according to claim 1, wherein the temperature of the incubator in the step S100 is 0°C to 45°C.

3 . The method for testing the electrochemical impedance of lithium-ion batteries on-line according to claim 2 , wherein the temperature of the incubator in the step S100 is 25° C. 4 .

4. online monitoring lithium ion battery electrochemical impedance testing method according to claim 1, is characterized in that: the pulse time of DC impedance test in described step S300 is R _s + R _f + R _ct inflection point in the EIS impedance spectrum frequency time, ie t ₂ = t ₁ .

5 . The method for testing the electrochemical impedance of lithium-ion batteries with on-line monitoring according to claim 1 , characterized in that: in the step S300 , the pulse sampling time range is 0.0001s ≤ t _a ≤ 1 s. 6 .

6 . The method for testing the electrochemical impedance of lithium-ion batteries with on-line monitoring according to claim 5 , wherein the pulse sampling time range in the step S300 is 1ms≦t _a ≦10ms. 7 .

7. online monitoring lithium ion battery electrochemical impedance testing method according to claim 1, is characterized in that: in described step S300, pulse current range is 0＜1≤1c.

8. The method for testing the electrochemical impedance of an on-line monitoring lithium-ion battery according to claim 1, characterized in that: in the step S300, the time range of the pulse sampling point is t _b ≥ 30 min.

9. The method for testing the electrochemical impedance of an on-line monitoring lithium-ion battery according to claim 1, wherein the small rate current pulses of different gradients in the step S300 are selected from 0.02 to 0.2 c.

10 . The method for testing the electrochemical impedance of an on-line monitoring lithium ion battery according to claim 9 , wherein in the step S300 , 0.1 c - 0.2 c is selected for the small rate current pulses of different gradients. 11 .