CN102004204B - Method for detecting false solder of battery pack - Google Patents

Abstract

The invention discloses a method for detecting false welding of a battery pack, which comprises a battery pack in which n single cells are connected in series through electrode terminals; charging the battery pack with a current not less than 2C rate, and simultaneously detecting the voltage U of each single cell _i ; when the voltage U _i of the i-th cell is greater than a predetermined value, that is, the i-th cell has a virtual weld; where i and n are natural numbers, and i is the number of the cell. The test method provided by the present invention can detect the connection virtual solder joints in the battery pack very quickly, easily and accurately, and find out the position of the virtual solder joints in time to maintain the battery pack, not only for the normal use of the battery pack, but also to ensure that the battery pack Safe applications in electric vehicles.

Description

A method for detecting virtual welding of battery packs

【Technical field】

The invention relates to a power battery pack, in particular to a detection method for a virtual welding connection in the power battery pack. the

【Background technique】

Rechargeable lithium batteries have a wide range of applications, such as laptop batteries, mobile phone batteries, power tools, network equipment and other personal electronic devices. The power source required by these devices is a lightweight battery with medium or smaller power output requirements. However, on other devices, rechargeable lithium batteries can also provide higher power than the above-mentioned devices require. For example, high-output lithium batteries can be used as industrial power supply equipment, high-power communication facilities, electric vehicles, etc. In the field of electric vehicles, the maturation of high-output lithium-ion battery systems is an obvious driver. the

To achieve high output of lithium batteries, multiple single cells need to be connected in series or in parallel to improve battery energy or battery output efficiency. In the prior art, multiple single batteries are usually connected in series or in parallel by electrode terminal welding connection, screw connection, etc. When the battery pack is applied to an electric vehicle, the battery may be desoldered or soldered due to the following reasons Unreliable connection: The design of the battery cell connection is unreasonable; after a long period of vibration, the connection of the battery becomes loose or disconnected. When the latter kind of virtual soldering occurs, it is difficult to find the virtual soldering point by means of visual observation, and the existence of the virtual soldering point seriously affects the charging and discharging of the battery pack, and is more likely to cause safety problems of the battery pack. Therefore, it is extremely important to find the position of the false welding as soon as possible and maintain the battery with the false welding. the

【Content of invention】

The technical problem solved by the invention is a problem that is difficult to find when the connection of the power battery pack is unreliable such as weak welding during use in the prior art. In particular, it provides an easy-to-implement method for detecting the weak welding of the battery pack. the

The invention provides a method for detecting the virtual welding of a battery pack, comprising a battery pack in which n cells are connected in series through electrode terminals; charging the battery pack with a current not less than 2C rate, and simultaneously detecting the voltage U _i of each cell ; When the voltage U _i of the i-th single cell is greater than a predetermined value, that is, the i-th single cell has a virtual weld; where i and n are natural numbers, and i is the number of the single cell.

The method for detecting the virtual welding of the battery pack provided by the present invention is to charge the battery pack with a large current (the current is greater than or equal to 2C), and then test the voltage of each single cell when it is discharged with a high current, if the measured voltage is greater than a predetermined value Or the charging limit voltage of the lithium battery can determine the position of the virtual solder joint in the battery pack, which takes a very short time (about 0.1 seconds), so it is very simple and can accurately detect the virtual solder joints in the battery pack. Finding the location of the virtual welding in time and maintaining the battery pack will not only ensure the normal use of the battery pack, but also ensure the safe application of the battery pack in electric vehicles. the

【Description of drawings】

FIG. 1 is a schematic diagram of a specific test point distribution of the potential of a single battery in the test method provided by the present invention. the

Fig. 2 is a schematic diagram of the charging voltage curve of the battery pack in the specific embodiment provided by the present invention. the

【Detailed ways】

The detailed content of the method for testing the virtual welding of a battery pack provided by the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. the

The invention provides a method for detecting the virtual welding of a battery pack, comprising a battery pack in which n cells are connected in series through electrode terminals; charging the battery pack with a current not less than 2C rate, and simultaneously detecting the voltage U _i of each cell ; When the voltage U _i of the i-th single cell is greater than a predetermined value, that is, the i-th single cell has a virtual weld; where i and n are natural numbers, and i is the number of the single cell. Wherein, the predetermined value is generally the charging limit protection voltage value of the lithium battery, and may also be a value about 0.3V higher than the charging platform of the single battery. Lithium batteries with different positive electrode material systems have different charging protection voltage values. For example, the charging protection voltage of lithium iron phosphate material as the positive electrode material is 3.8V; and the charging protection voltage of lithium manganate material as the positive electrode material is 4.2V.

The inventors have further researched and found that the joints between the single battery and the adjacent single battery may be the joints with the most false welds in the battery pack, whether it is a battery pack connected by electrode terminal welding, or connected by other methods such as screws. The battery pack, all of that. In order to enable the present invention to more conveniently test the virtual solder joint between the single battery and the adjacent single battery, the present invention is further preferably carried out according to the following method. the

As shown in the accompanying drawing 1 of the description, it shows a specific schematic diagram of the distribution of the potential test points of the single battery in the test method provided by the present invention, wherein, n sections of single battery 1 are connected in series by welding the electrode terminals 2 to form a battery pack, and the welding points 3 places in the picture. the

First, calibrate the potential V ₁ of the negative electrode terminal of the battery pack = 0V, starting from the negative electrode terminal of the battery pack, test the potentials V ₂ , ..., V _i , ... of the negative electrode terminals of each single battery in sequence , V _n-1 , V _n , V _n+1 . As shown in Figure 1, the welding point 3 between the first cell and the second cell is located between the V ₁ potential test point and the V ₂ potential test point, and the i-th cell and the i-th cell The welding point 3 between the +1 single cells is located between the V _i potential test point and the V _i+1 potential test point, and there is no welding point between the negative electrode terminal and the positive electrode terminal of the nth single cell, Therefore, U _i =V _i+1 -V _i .

In the same way, the method of the present invention is also completely feasible from the positive terminal of the battery pack as the starting point of the test. Calibrate the potential V' ₁ of the positive electrode terminal of the battery pack = 0V, start from the positive electrode terminal of the battery pack, and test the potential V' _i of the positive electrode terminal of each single battery sequentially, the i-th single battery The connection points with the i+1th cell are distributed between two adjacent potential test points, therefore, U′ _i =V′ _i −V′ _i+1 .

Through the above steps, the voltage U _i of the single battery during high-current charging can be tested separately. When the voltage U _i is greater than the predetermined value, it can be judged that the electrode terminal between the i-th cell and the i+1-th cell is welded False welding occurs.

The inventors of the present invention unexpectedly found that when a high-magnification current passes through the welding place, if the welding place is normal, the voltage obtained by testing each potential test point can normally represent the voltage value of each node. Nearby voltage values fluctuate greatly in a short period of time. the

The inventor further found that if there is a false weld at a certain point of the battery pack, when a large current passes through, the contact resistance between the batteries will increase, and the voltage of a single battery will rise sharply during charging, causing the battery pack to fail to charge. Therefore, the detection method of the present invention uses a high-rate current to rapidly increase the contact resistance at the virtual weld, and the current is at least 2C. the

In the method of the present invention, for charging the battery pack with a large current, it is further preferred to charge the battery pack with a charge greater than or equal to 2C and less than or equal to 3C. If the current is less than 2C, the purpose of the test cannot be achieved, but if it is too large, there may be unsafe factors in the test. Therefore, the range of greater than or equal to 2C and less than or equal to 3C is more appropriate. the

Example

Detect the virtual solder joints of a battery pack. The capacity of the battery pack is 50A, and 10 single cells are formed in series by welding electrode terminals. The positive electrode material system of the single battery adopts lithium iron phosphate material, and the charging protection voltage is 3.8V. the

First, set the potential detection points as shown in Figure 1 of the specification, where n is 10. Then charge the battery pack at 2C, wherein the charging current is 100A, the duration is 0s-1.2s, and the interval is 0.1s, and the voltage of each single battery is detected, and the voltage of the single battery is recorded as U ₁ -U ₁₀ . After charging, the voltage of each single battery returns to normal. The test results are shown in Table 1, and the test curves are shown in Figure 2.

Table 1 Test results

time(s) U ₁ (V) U ₂ (V) U ₃ (V) U ₄ (V) U ₅ (V) U ₆ (V) U ₇ (V) U ₈ (V) U ₉ (V) U ₁₀ (V) 0.0 3.288 3.29 3.287 3.287 3.318 3.318 3.289 3.291 3.318 3.319 0.1 3.288 3.29 3.287 3.287 3.318 3.318 3.289 3.291 3.318 3.319 0.2 3.288 3.29 3.287 3.287 3.318 3.318 3.289 3.291 3.318 3.319 0.3 3.288 3.29 3.287 3.287 3.318 3.318 3.289 3.291 3.318 3.319 0.4 3.576 3.623 3.626 3.585 3.318 3.318 3.289 3.291 3.318 3.319 0.5 3.576 3.623 3.626 3.585 3.781 3.669 3.614 3.583 3.318 3.319

[0024] time(s) U ₁ (V) U ₂ (V) U ₃ (V) U ₄ (V) U ₅ (V) U ₆ (V) U ₇ (V) U ₈ (V) U ₉ (V) U ₁₀ (V) 0.6 3.576 3.623 3.626 3.585 3.781 3.669 3.614 3.583 3.318 3.319 0.7 3.576 3.623 3.626 3.585 3.781 3.669 3.614 3.583 3.675 3.688 0.8 3.576 3.623 3.626 3.585 3.781 3.669 3.614 3.583 3.675 3.688 0.9 3.576 3.623 3.626 3.585 3.781 3.669 3.614 3.583 3.675 3.688 1.0 3.594 3.641 3.654 3.598 3.781 3.669 3.614 3.583 3.675 3.688 1.1 3.594 3.641 3.654 3.598 3.781 3.669 3.614 3.583 3.675 3.688 1.2 3.594 3.641 3.654 3.598 3.808 3.693 3.637 3.592 3.675 3.688

From the above table 1 and the accompanying drawing 2 in the manual, it can be clearly seen that when U ₅ is charged for 0.4 to 0.5s (the time lag of the charging equipment exists accordingly), the voltage suddenly rises to 3.781V, which rises by 0.63V in only 0.1s, which is far It is higher than the voltage increase of other single cells; and when it reaches the charging protection voltage in 1.2s, it stops charging. It shows that there is a false welding between the fifth and sixth sections of the single battery.

Therefore, the method for detecting the virtual welding of the battery pack provided by the present invention can detect the virtual solder joints in the battery pack very quickly, easily and accurately, and find the position of the virtual soldering in time to maintain the battery pack. use, and can ensure the safe application of battery packs in electric vehicles. the

Claims (5)

1. a method that detects false solder of battery pack comprises that n joint cell is through the electric battery of electrode terminal series connection; Electric battery is carried out the charging that electric current is not less than the 2C multiplying power, detect simultaneously the voltage U of every joint cell _iVoltage U when i joint cell _iDuring greater than predetermined value, i.e. i joint cell generation rosin joint; Wherein i, n are natural number, and i is the cell numbering.

2. the method for detection false solder of battery pack according to claim 1, wherein, described predetermined value is cell charge protection magnitude of voltage.

3. the method for detection false solder of battery pack according to claim 1 wherein, is demarcated the extreme electromotive force V of described electric battery negative electricity ₁=0V, from the negative electricity of electric battery extremely, test successively the electromotive force V of the negative electrode terminal of every joint cell _i, the tie point of described i joint cell and i+1 joint cell is distributed between adjacent two potential test points, therefore, and U _i=V _I+1-V _i

4. the method for detection false solder of battery pack according to claim 1 wherein, is demarcated the electromotive force V ' of described electric battery positive electricity end ₁=0V from the positive electricity end of electric battery, tests the electromotive force V ' of the anode electrode terminal of every joint cell successively _i, the tie point of described i joint cell and i+1 joint cell is distributed between adjacent two potential test points, therefore, and U ' _i=V ' _i-V ' _I+1

5. the method for the described detection false solder of battery pack of any one according to claim 1-4 wherein, is carried out electric current more than or equal to the charging of 2C less than or equal to 3C to electric battery.

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