CN105510847A - Method for screening consistency of lithium ion batteries - Google Patents

Abstract

The invention discloses a method for screening the consistency of lithium ion batteries. The method comprises the following steps of (i) randomly selecting sample groups of which the number is N from a tested group, carrying out constant-current discharging by 0.2 C to 1 C under a 25+/-5 DEG C environment until preset discharge end voltage is achieved, and standing for a certain time; (ii) carrying out constant-current charging by 0.2 C to 1 C until preset charging end voltage is achieved, changing constant-current charging into constant-voltage charging until the current is reduced to be 0.05 C, recording capacity data, and calculating corresponding mean values of Q and R; (iii) testing open-circuit voltage of a sample by using a tester, obtaining Ui (wherein i is equal to 1, 2, . . . N), and calculating a corresponding mean value of U; (iv) calculating a confidence interval; (v) carrying out matching and screening on batteries in the batch according to the confidence interval, and matching the batteries positioned in the confidence interval into groups. The method disclosed by the invention has the advantages that during a screening process, internal resistance, capacity and multiple factors of temperature, humidity and the like of a testing environment are comprehensively considered, and the service life of a lithium battery pack is prolonged.

Description

The conforming screening technique of lithium ion battery

Technical field

The present invention relates to lithium ion battery production technical field, be specifically related to the conforming screening technique of a kind of lithium ion battery.

Background technology

Lithium ion battery, owing to having the features such as high energy storage density, long-life, low self-discharge rate, environmental pollution be little, becomes the main power source of digital product and new-energy automobile gradually.

Single lithium battery voltage is generally only 3.0V ~ 4.0V (nominal voltage is 3.6V), and finite capacity, so in the high-power system such as electric motor car, electric tool, need the lithium battery series, parallel of tens joints, joint up to a hundred to use in groups.

Due to limitation prepared by technique, even with batch cell produced, the otherness of voltage, capacity, internal resistance and self-discharge rate also can be there is.If use without the random combo of screening, these differences seriously will reduce the serviceable life of integral battery door group, so be necessary to carry out conforming examination to battery.

Conventional screening method comprises voltage combo method, capacity combo method, internal resistance matching method.They respectively have relative merits, and such as voltage method is simple to operate, but do not consider loads change; Volumetric method need be carried out according to specific discharge and recharge condition, and spended time is long, and testing cost is high; Though internal resistance method can complete measurement fast, cause degree of accuracy not high due to the impact of polarization resistance cannot be removed.

The production run of battery can not avoid dust and impurity completely, and their existence can cause inside battery micro-short circuit and then cause self-discharge phenomenon.Between monomer, the difference of self-discharge rate also can have influence on the performance and used life of integral battery door group, so during combo, there is a need to screen self-discharge rate difference.

Summary of the invention

Instant invention overcomes the deficiencies in the prior art, provide a kind of lithium ion battery conforming screening technique, for improving the serviceable life of lithium battery group.

Consider the problems referred to above of prior art, according to an aspect disclosed by the invention, the present invention by the following technical solutions:

The conforming screening technique of a kind of lithium ion battery, it comprises:

I) from tested group, random selecting quantity is the sample group of N, under 25 DEG C ± 5 DEG C environment, put a final voltage with 0.2C ~ 1C constant-current discharge to what preset, shelve a period of time;

II) be charged to default end of charge voltage with the constant current of 0.2C ~ 1C again, turn constant-voltage charge and reduce to 0.05C to electric current, recording capacity data group Q _i, (i=1,2 ... N), internal resistance data group R _i(i=1,2 ... and ask for corresponding average N),

III) then sample is shelved a period of time after, use tester survey its open-circuit voltage, obtain U _i, (i=1,2 ... and ask for corresponding average N),

IV) carry out fiducial interval calculating:

(1) standard deviation is asked for:

$S_R=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{R}-R_i)}^2};$

$S_Q=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{Q}-Q_i)}^2};$

$S_U=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{U}-U_i)}^2};$

(2) sampling average error is asked for:

${\mathrm{\μ}}_R=S_R/\sqrt{N};$

${\mathrm{\μ}}_Q=S_Q/\sqrt{N};$

${\mathrm{\μ}}_U=S_U/\sqrt{N};$

(3) permissible error σ is calculated:

σ _R＝μ _R*t；

σ _Q＝μ _Q*t；

σ _U＝μ _U*t；

Wherein, t is be that standardized normal distribution is tabled look-up the value obtained according to degree of confidence p, degree of freedom v;

(4) fiducial interval of internal resistance, capacity, self-discharge rate three parameters is asked for:

R fiducial interval: $[\stackrel{\_}{R}-{\mathrm{\σ}}_R,\stackrel{\_}{R}+{\mathrm{\σ}}_R];$

Q fiducial interval: $[\stackrel{\_}{Q}-{\mathrm{\σ}}_Q,\stackrel{\_}{Q}+{\mathrm{\σ}}_Q];$

U fiducial interval: $[\stackrel{\_}{U}-{\mathrm{\σ}}_U,\stackrel{\_}{U}+{\mathrm{\σ}}_U];$

V) according to fiducial interval, combo examination is carried out to this batch of battery, will the battery pairing of fiducial interval be positioned in groups.

In order to realize the present invention better, further technical scheme is:

According to one embodiment of the invention, described IV) carry out fiducial interval calculating: t for be 80% ~ 99% according to degree of confidence p, degree of freedom v is 31 ~ ∞, the relation of v and sample number is: v=N-1.

According to another embodiment of the invention, described III) sample of step is positioned over 40 DEG C ± 2 DEG C ~ 45 DEG C ± 2 DEG C, under the environment of 90% ~ 95%, and standing time is 5 ~ 10 days.

The present invention can also be:

According to another embodiment of the invention, described I) sample number N>30 in step.

Compared with prior art, one of beneficial effect of the present invention is:

The conforming screening technique of a kind of lithium ion battery of the present invention, can in conjunction with concrete condition, from the viewpoint of realizing cost, battery performance requirement etc., setting and adjustment accuracy of instrument, degree of confidence p and degree of freedom v etc., duration is shelved in self discharge, requires higher, select measuring accuracy, degree of confidence, degree of freedom also corresponding larger, the present invention has considered internal resistance, capacity, and the multinomial factor such as the humiture of test environment, thus improves the serviceable life of lithium battery group.

Accompanying drawing explanation

In order to clearer explanation present specification embodiment or technical scheme of the prior art, below the accompanying drawing used required in the description to embodiment or prior art is briefly described, apparently, the accompanying drawing that the following describes is only the reference to some embodiments in present specification, for those skilled in the art, when not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.

Fig. 1 is t value table corresponding to different degree of confidence, degree of freedom;

Fig. 2 is the workflow schematic diagram of the method for the invention.

Embodiment

Below in conjunction with embodiment, the present invention is described in further detail, but embodiments of the present invention are not limited thereto.

In view of the problem that background technology is mentioned, consider the internal resistance of lithium battery, capacity, the feature of self-discharge rate statistical probability all in standardized normal distribution, the invention provides a kind of by multinomial to the voltage of lithium battery, internal resistance, capacity, self-discharge rate, ambient temperature and humidity, examination duration, testing cost etc. combined factors consideration, in conjunction with the consistance screening method that paired sample inspection principle in statistics completes, through practice test, compared with prior art simple and practical, reliability is high, effectively can reduce monomer battery core difference in lithium battery group, improve the serviceable life of whole group.Particularly, as shown in Figure 2, the conforming screening technique of a kind of lithium ion battery, after completing size, outward appearance, printing, the basic test such as (comprising shock, fall, vibrate) safely, carry out group gas-mixing screening to the consistance with batch lithium battery, step is as follows:

Step one, first from tested group, random selecting quantity is the sample group of N (N>30), under 25 DEG C ± 5 DEG C environment, with 0.2C ~ 1C constant-current discharge to the final voltage of regulation, shelves 1h ~ 3h;

Step 2, be charged to the final voltage of regulation with the constant current of 0.2C ~ 1C, turn constant-voltage charge to electric current reduces to 0.05C; Shelve 1h ~ 3h, use capacity and internal resistance test device, recording capacity data group Q _i, (i=1,2 ... N), internal resistance data group R _i(i=1,2 ... and ask for corresponding average N),

Step 3, for accelerate self discharge, shorten and shelve the time, consider that self-discharge rate and hot and humid environment are proportionate, sample is sent into 40 DEG C ± 2 DEG C ~ 45 DEG C ± 2 DEG C, under the ageing environment of 90% ~ 95%, after shelving 5 ~ 10 days (120h ~ 240h), use tester to survey its open-circuit voltage, obtain U _i, (i=1,2 ... and ask for corresponding average N),

Step 4, degree of confidence of carrying out are p (80% ~ 99%), and fiducial interval when degree of freedom is v (relation of 31 ~ ∞, v and sample number is: v=N-1) calculates:

(1) standard deviation is asked for:

$S_R=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{R}-R_i)}^2};$

$S_Q=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{Q}-Q_i)}^2};$

$S_U=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{U}-U_i)}^2};$

(2) sampling average error is asked for:

${\mathrm{\μ}}_R=S_R/\sqrt{N};$

${\mathrm{\μ}}_Q=S_Q/\sqrt{N};$

${\mathrm{\μ}}_U=S_U/\sqrt{N};$

(3) permissible error σ is calculated:

σ _R＝μ _R*t；

σ _Q＝μ _Q*t

σ _U＝μ _U*t；

Wherein, t is table look-up the degree of confidence p, the degree of freedom that obtain " distribution of t bilateral " when being v, also the t value of i.e. standardized normal distribution, as shown in Figure 1;

(4) ask for internal resistance, capacity, self-discharge rate (namely hot and humid shelve after open-circuit voltage) fiducial interval of three parameters:

R fiducial interval: $[\stackrel{\_}{R}-{\mathrm{\σ}}_R,\stackrel{\_}{R}+{\mathrm{\σ}}_R];$

Q fiducial interval: $[\stackrel{\_}{Q}-{\mathrm{\σ}}_Q,\stackrel{\_}{Q}+{\mathrm{\σ}}_Q];$

U fiducial interval: $[\stackrel{\_}{U}-{\mathrm{\σ}}_U,\stackrel{\_}{U}+{\mathrm{\σ}}_U];$

Step 5, carry out combo examination according to fiducial interval to this batch of battery, by internal resistance, capacity with agingly shelve rear voltage and fall into battery pairing in fiducial interval in groups, all the other are rejected, and complete examination.

Another embodiment:

Below for the conformity classification combo of certain brand ferric phosphate lithium cell (3.2V 3.5AH), the present invention is described in detail:

I) first random selecting 225 cells from tested group, under 25 DEG C ± 5 DEG C environment, with 0.2C constant-current discharge to 2.5V, shelve 1h;

II) be charged to 3.2V with the constant current of 0.2C ~ 1C, turn constant-voltage charge and send a telegraph till stream is down to 0.05C, shelve 1h, use capacity tester and internal resistance test device, recording capacity data group Q _i, (i=1,2 ... 225), internal resistance data group R _i(i=1,2 ... 225), data group typing Excel is shown, utilize " AVERAGE " function to obtain average

III) sample is sent into 45 DEG C ± 2 DEG C, under the environment of 95%, shelve 7 days, then survey its voltage, obtain U _i, (i=1,2 ... 225), corresponding average obtained by typing Excel table

IV) to choose degree of confidence be 95%, degree of freedom is ∞, carries out fiducial interval calculating:

(1) " STDEV " function of Excel is utilized to ask for standard deviation:

$S_R=\sqrt{\frac{1}{225}*{\mathrm{\Σ}}_{i=1}^{225}{(\stackrel{\‾}{R}-R_i)}^2};$

$S_Q=\sqrt{\frac{1}{225}*{\mathrm{\Σ}}_{i=1}^{225}{(\stackrel{\‾}{Q}-Q_i)}^2};$

$S_U=\sqrt{\frac{1}{225}*{\mathrm{\Σ}}_{i=1}^{225}{(\stackrel{\‾}{U}-U_i)}^2};$

(2) sampling average error is asked for:

${\mathrm{\μ}}_R=S_R=/\sqrt{225};$

${\mathrm{\μ}}_Q=S_Q/\sqrt{225};$

${\mathrm{\μ}}_U=S_U/\sqrt{225};$

(3) permissible error σ is calculated:

σ _R＝μ _R*1.960；

σ _Q＝μ _Q*1.960；

σ _U＝μ _U*1.960；

Wherein, " 1.960 " for looking into T value table, by bilateral degree of confidence be 95%, sample number is that the corresponding hurdle of ∞ obtains;

(3) fiducial interval of voltage three parameters after internal resistance, capacity, self discharge is asked for:

R fiducial interval: $[\stackrel{\_}{R}-{\mathrm{\σ}}_R,\stackrel{\_}{R}+{\mathrm{\σ}}_R];$

Q fiducial interval: $[\stackrel{\_}{Q}-{\mathrm{\σ}}_Q,\stackrel{\_}{Q}+{\mathrm{\σ}}_Q];$

U fiducial interval: $[\stackrel{\_}{U}-{\mathrm{\σ}}_U,\stackrel{\_}{U}+{\mathrm{\σ}}_U];$

V) carry out examination and rejecting according to fiducial interval, it is one group that battery internal resistance, capacity and self-discharge rate fallen in fiducial interval is compiled, and all the other are rejected.

In this instructions, each embodiment adopts the mode of going forward one by one to describe, and what each embodiment stressed is the difference with other embodiment, identical similar portion cross-reference between each embodiment.

Spoken of in this manual " embodiment ", " another embodiment ", " embodiment ", etc., refer to the specific features, structure or the feature that describe in conjunction with this embodiment and be included at least one embodiment of the application's generality description.Multiple place occurs that statement of the same race is not necessarily refer to same embodiment in the description.Furthermore, when describing specific features, structure or a feature in conjunction with any embodiment, what advocate is also fall within the scope of the invention to realize this feature, structure or feature in conjunction with other embodiments.

Although with reference to multiple explanatory embodiment of the present invention, invention has been described here, but, should be appreciated that, those skilled in the art can design a lot of other amendment and embodiment, these amendments and embodiment will drop within spirit disclosed in the present application and spirit.More particularly, in the scope of and claim open in the application, multiple modification and improvement can be carried out to the building block of subject combination layout and/or layout.Except the modification of carrying out building block and/or layout is with except improvement, to those skilled in the art, other purposes also will be obvious.

Claims (4)

1. the conforming screening technique of lithium ion battery, is characterized in that it comprises:

I) from tested group, random selecting quantity is the sample group of N, under 25 DEG C ± 5 DEG C environment, with 0.2C ~ 1C constant-current discharge to the final discharging voltage preset, then shelves a period of time;

II) be charged to described default end of charge voltage with the constant current of 0.2C ~ 1C again, then turn constant-voltage charge and reduce to 0.05C to electric current, recording capacity data group Q _i, (i=1,2 ... N), internal resistance data group R _i(i=1,2 ... and ask for corresponding average N),

III) then sample is shelved a period of time after, use tester survey its open-circuit voltage, obtain U _i, (i=1,2 ... and ask for corresponding average N),

IV) carry out fiducial interval calculating

(1) standard deviation is asked for:

$S_R=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{R}-R_i)}^2};$

$S_Q=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{Q}-Q_i)}^2};$

$S_U=\sqrt{\frac{1}{N}*{\mathrm{\Σ}}_{i=1}^N{(\stackrel{\‾}{U}-U_i)}^2};$

(2) sampling average error is asked for:

${\mathrm{\μ}}_R=S_R/\sqrt{N};$

${\mathrm{\μ}}_Q=S_Q/\sqrt{N};$

${\mathrm{\μ}}_U=S_U/\sqrt{N};$

(3) permissible error σ is calculated:

σ _R＝μ _R*t；

σ _Q＝μ _Q*t；

σ _U＝μ _U*t；

Wherein, t is be that standardized normal distribution is tabled look-up the value obtained according to degree of confidence p, degree of freedom v;

(4) fiducial interval of internal resistance, capacity, self-discharge rate three parameters is asked for:

R fiducial interval:

Q fiducial interval:

U fiducial interval:

V) according to fiducial interval, combo examination is carried out to this batch of battery, will the battery pairing of fiducial interval be positioned in groups.

2. the conforming screening technique of lithium ion battery according to claim 1, is characterized in that described IV) carry out fiducial interval calculating: t for be 80% ~ 99% according to degree of confidence p, degree of freedom v is 31 ~ ∞, the relation of v and sample number is: v=N-1.

3. the conforming screening technique of lithium ion battery according to claim 1, is characterized in that described III) sample of step is positioned over 40 DEG C ± 2 DEG C ~ 45 DEG C ± 2 DEG C, under the environment of 90% ~ 95%, and standing time is 5 ~ 10 days.

4. the conforming screening technique of lithium ion battery according to claim 1, is characterized in that described I) sample number N>30 in step.