1. Battery test standards
It can be seen from the statistical table that the formulation or revision of lithium-ion battery standards in China is very active, which is also the need for the market to continuously improve the safety performance of lithium-ion batteries. On the other hand, this also brings more severe challenges to battery manufacturers, requiring battery manufacturers to continuously improve the level of design, production and testing process.
At present, the common test standards for lithium batteries are:
gb/t 18287
iec 61960
iec 60086-4
iec 62133
jis c 8714
ul 1642
ul 2054
2. Take the electrical performance test as an example, a common test
Battery capacity test.
1. Battery capacity
The total battery capacity is expressed in C. The battery capacity is generally expressed in mAh milliampere, and the capacity of a 1mAh battery can be discharged for 1 hour with a constant current current of 1 mAh.
The capacity test of the battery discharge curve at different temperatures and the battery discharge curve at different discharge rates needs to use the static capacity test method (SCT) to measure the usable capacity (including energy) of the battery at different ambient temperaturesDifferent companies and standards have differences in SCT testing methods, but the general idea is similarFor example, in the environment of room temperature (25), the battery manufacturer is fully charged in the manner specified, and then fully shelved in the tested environment and discharged to the cut-off voltage at a rate of 1c (25V), record the released capacity (energy)...In the actual experiment, the test can be repeated 3 times in a row to take the mean value to improve the accuracyCapacity test output: Temperature and capacity (energy) relationship tableTake the capacity c as the x-axis and the voltage v as the y-axisThe point at which the 1C discharge cuts off on the x-axis at different temperatures is the relationship between capacity and temperature.
Test the solution.
In the traditional way, the charge and discharge test is carried out separately with the power supply and the load, but Advics can be realized with a bidirectional power supply.
2. Battery DCIR ACIR test (internal resistance).
As the capacity state of the battery decreases, the internal resistance of the battery increases. The internal resistance of a battery is closely related to its capacity, and the increase of internal resistance of a battery is an important indicator of the deterioration of battery performance.
The research and development results of the annual conference of power supply technology of the international financial telecommunication system show that if the internal resistance of a battery exceeds the normal value of 25, the capacity has been reduced to about 80 of its nominal data capacity, if there is no internal resistance of the battery exceeds the normal value of 50, the market capacity of the battery has been reduced to less than 80 of its nominal capacity, and it needs to be found and replaced in time.
Why test the battery internal resistance:
1. Because the larger the capacity of the battery, the smaller the internal resistance, so the battery capacity can be roughly judged according to the size of the internal resistance.
2. The outstanding performance of battery aging and failure is the increase of internal resistance, so the aging degree of the battery can be quickly judged by testing the internal resistance of the battery.
3. During the maintenance of the battery pack, it is necessary to test the internal resistance of each battery cell frequently, so as to pick out the unit with increased internal resistance and replace it with a good one. The actual equivalent circuit of the battery is more complex. The AC equivalent circuit of the battery shows that under the condition of AC signal, the external characteristics of a battery can be regarded as the electromotive force e, the internal resistance r and the capacitor c in series.
DCIR: Direct Current Resistance. (DC internal resistance is generally given a relatively large current, theoretically the shorter the time, the larger the current, the more accurate the test, mainly considering the electrochemical impedance, and the entire electrochemical system.) ）
ACIR: AC Resistance. (AC internal resistance is the internal resistance of the battery under static conditions, generally giving a small AC disturbance, calculated by the algorithm of a series of equipment, and the strength of physical welding, the contact between the battery case and the cover, etc.).
1.DCIR is a DC resistance at a specific load brightness and discharge current.
2.ACIR typically uses a 1K Hz AC power source and is measured using a four-wire method, the value of which includes the battery resistance and reverse capacitance values, and the formula is impedance = r - j (w * c), which is called AC impedance. Generally speaking, the AC impedance of a battery is less than the DC resistance.
Test Difficulties:
a.Internal resistance is not a fixed value.
b.Internal resistance cannot be accurately measured using conventional methods.
c.Component errors of test instruments and battery connection cable problems used for testing.
d.In the "Standard Conditions for the Lithium-ion Battery Industry" issued in 2015, it is required that for batteries composed of multi-cell batteries, they should have the ability to detect open-circuit voltage and internal resistance, and the detection accuracy is respectively1mvwith1mω
ACIR Test Solutions.
IT5100 Series Battery Internal Resistance Tester.
Manual or automatic testing of 3 voltage ranges and 7 resistance ranges.
Voltage measurement range: 10 V 1000V
Resistance measurement range: 150 3000
Measure resistance and voltage at a speed of up to 125 seconds at a speed of up to 125 seconds.
It supports statistical operations and stores data via USB.
Comparator function.
DCIR Test Solutions.
In battery pack applications (such as power batteries), it is not possible or convenient to measure AC internal resistance, and the characteristics of the battery pack are generally evaluated by DC internal resistance.
The DC discharge method is a test method that is close to the way batteries work. DC internal resistance calculates DCIR by using the current difference and voltage difference between two different loading currents
3. Cycle life test
Importance of Cycle Life Testing:
Battery life is an important parameter to measure battery performance.
Under a certain charging and discharging system, the number of cycles that the battery can withstand before the battery capacity drops to a certain specified value is called the cycle life of the battery.
As the number of charge and discharge increases, the internal resistance caused by internal oxidation increases, which will make the battery unable to release the stored power, and the life of the battery will gradually be terminated.
The cycle life of the battery is affected by factors such as discharge rate, temperature and charge-discharge cut-off voltage.
4. SOC test
Definition of SOC
SOC (State of Charge), that is, the state of charge, is used to reflect the remaining capacity of the battery, and its value is defined as the ratio of the remaining capacity to the battery capacity, which is often expressed as a percentage. The value range is 0 1, when SoC=0 means that the battery is fully discharged, and when SoC=1 means that the battery is completely full.
When SoC=1, the battery is fully charged.
The battery SoC cannot be measured directly, and its size can only be estimated by parameters such as battery terminal voltage, charge/discharge current, and internal resistance. These parameters are also affected by various uncertain factors such as battery aging, ambient temperature changes, and vehicle driving conditions, so accurate SoC estimation has become an urgent problem in the development of electric vehicles.
The main estimation methods of SOC
The well-known algorithms include the open-circuit voltage method, the ampere-hour integration method and the internal resistance method. Recently, the most studied methods include Kalman filter method, neural network method, etc. New methods are emerging, but most of them are still in the research and discussion stage, and the algorithms in practical application are still dominated by the old methods.
Open-circuit voltage method
The open-circuit voltage of the lithium battery has a clear monotonic correspondence with the charge of the battery, and the battery power can be calculated as long as the accurate open-circuit voltage is obtained. The corresponding curves of the open-circuit voltage and SOC of several battery cells are shown in the figure below.
5. HPPC test
The purpose of HPPC (Hybrid Pulse Power Characterization) test is to determine the dynamic power capability of the battery pack under current pulse conditions, including the 10-second charging power and 10-second discharging power of the battery pack.
The purpose of HPPC testing is to determine the 10-second discharge power and 10-second charging power of the battery pack every 10% SoC. The pulse curve of the test process is shown in the following graph, the charging current is positive, and the discharge current is.
HPPC Test Method
The HPPC test consists of multiple sets of current pulse tests, and the SoC of each group of current pulse tests differs by 10%. The next set of tests is not allowed until the battery has entered electrochemical and thermal equilibrium, typically at 1-hour intervals. The specific test process is as follows:
a) Fully charge the battery as recommended by the manufacturer.
b) Let stand for 1 hour.
c) Constant current pulse test.
d) Discharge 10% SOC
e) Let stand for 1 hour.
f) Repeat c) e) until the battery is 90% drained (or the maximum discharge range specified by the manufacturer).
The choice of current during the test depends on the BSF (Battery Size F) provided by the battery manufacturer
actor) coefficient, if the BCF coefficient cannot be determined, you can choose 5C current or 75% IMAX
6. Circuit overcharge and overdischarge withstand test
What is the impact of overcharge and overdischarge on battery performance?
Overcharging refers to the act of continuing to charge the battery after it has been fully charged after a certain charging process. In order to prevent the battery from overcharging, it is necessary to control the charging end, so the accuracy of the charging termination voltage is a very important parameter.
Battery over-discharge can have catastrophic consequences for the battery, especially if the battery is over-discharged at a high current, or repeated over-discharge has a greater impact on the battery. The discharge test requires the battery to be discharged at different temperatures, observe the changes of the battery, and record the capacity of the battery.
The cut-off voltage of the battery cell exceeds 425V is considered overcharged.
Overcharging may lead to leakage, deformation, and a certain degree of voltage as the charge deepens after the constant voltage fails (the general limit is 6.).0v) will cause **.
Solution: Add PCB board protection outside the battery, or set up a protective circuit and or time limit device in the charger (i.e., the charging limit is 25 hours) to prevent the battery from overcharging.
What is overdischarge?What are the adverse consequences of over-discharge?How to avoid it?
The cut-off voltage of 1c discharge cell is not less than 275V, 3C or more discharge cut-off voltage is not less than 3If the 0V discharge state continues, it is overdischarged.
Over-discharge can lead to leakage, zero voltage, and negative voltage, which is one of the main causes of impaired battery performance.
Solution: Add a PCB board outside the battery or design a protective circuit or time limit device in the charger to prevent over-discharge. ）
Other tests
Balanced charge/discharge test.
Dynamic condition simulation test.
Balanced charge/discharge test.
Battery temperature test. Self-discharge.
3. Test solutions:
Battery testing difficulties.
The measurement time is relatively long, and there are phenomena such as abnormal data and computer crash.
In the case of conventional power supply loads, the power loss is large.
The wiring ignites instantaneously.
It is difficult to analyze dynamic value measurements.
Lithium battery overshoot and overdischarge have natural, first-class and other hazards.
ITS5300 Battery Charge and Discharge Test System
Battery Test System Features:
1 Energy feedback test system.
2. Constant current, constant voltage, constant flow constant pressure, slope, ladder, etc.
3 Internal resistance test.
4 Battery temperature monitoring.
5 Battery cycle charge and discharge test.
6 Battery capacity test.
6. Battery overcharge, overdischarge rate bearing capacity test.
7. Power battery charge retention ability test.
8. Battery performance test at different temperatures, including charge and discharge performance test and efficiency test.
9. High-speed current pulse test.
10. Battery cycle test.
11 BMS communication function.
12 channels of parallel extended power (master-slave parallel & current sharing technology.
13.Sound and light emergency stop, anti-reverse connection and anti-ignition protection, power-off memory protection function, all-round charge and discharge protection function, etc.
Software testing interface
What you see on the screen now is a schematic diagram of the two power battery packs during the test, a matrix is a power battery pack, and these small squares, each small square represents a single cell in the power battery pack, and the display of this graphic is very clear and clear. So, how do our engineers know how each cell is working at any time?In different states, the small squares corresponding to the single cell will show different colors. The green color in the diagram indicates normal operation, and if there are alarms and protections, they are shown in yellow and red. The blue color indicates the selected cell, and its series of test parameters and curves are displayed below. You can display the graph in full screen and overlay multiple curves.
Advantages: Comply with national standards and be compatible with a variety of protocols.
Rich and complete test items.
Professional software. It is modular, easy to configure and maintain.
Battery cell test protocols.
Battery module test protocol.
Battery pack test scheme.
Fuel cell test solutions.
Solar cell test protocols