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Technical Support / Technical articles

Lithium Ion Battery Forced Internal Short Circuit Test Analysis (2)
  • Test Steps:

    (1) Charging for the test sample;

    (2) Disassemble the battery and placed small nickel;

    (3) Involution battery and make the battery up to the test temperature;

    (4) Pressure on it.

    Detailed Test Steps Operation:

    1. Charging for the Test Sample:

      Single battery internal short circuit test is aimed for a full charged battery.

      The Battery Charging Condition is:

    Respectively testing under the upper temperature and lower temperature stable for 1-4 hours later, using the upper charging voltage and largest charging current, charging until to 0.05 C. The upper and lower test temperature is the highest temperature and lowest temperature on the surface of the battery when the battery using upper charging voltage and largest charging current. The upper and lower test temperature in the charging condition was selected and formulate according to the material properties of lithium-ion battery. JIS C 8714 respectively proposed the upper temperature 45 ℃ and lower temperature 10 ℃, and the maximum charge voltage of 4.25 V, and this condition is proposed aimed to the universal lithium ion (Cobalt acid lithium negative - carbon anode) batteries material in nowadays marketing, not include all lithium batteries.

    If adopt new limits of upper and lower test temperature and charging voltage, it requires to carry out a certain experiment and adding data basics. To determine the new upper charging voltage investigation content includes: structure stability of the positive pole material, cathode material of lithium absorption and the structure stability of the electrolyte material properties. To ensure a new upper and lower test temperature investigation content including: structure stability of the positive pole material and the structure stability of the electrolyte material properties.  Need to make sure that the new limit test temperature of the security of rechargeable batteries, and add in the new limit test temperature 5 ℃ suitable  for JIS C 8714 charging condition of clause 5.1, and conform to the test requirements in 5.2 ~ 5.2. Based on the absorption of lithium ion cathode material, lithium ion movement degree of electrolyte etc. ( relative to the temperature).
    2. Dismantling and Place the Small Nickel

    Dismantling the single cells in the surrounding temperature Is 20 ℃± 5 ℃, dew point below -25 ℃, and in the positive active material,  the negative active material, the anode aluminum foil and the cathode active material place a small nickel shown below. The reason to dismantling the single battery under dew point below 25 ℃ is to prevent moisture influent  the battery's internal chemical environment. This step should be done as soon as possible, in order to minimize the influence of steam and water vapor to the battery characteristics in the electrolyte dismantling process.
    3. Lapped Battery and Make a New Battery Test Temperature

    Lapped the single battery cell which has been placed in nickel, avoid loose and mark in the position which placed nickel. Then put in sealed polyethylene bags, and the after sealing the  polythene bags into the sealing bag made of aluminium foil, respectively in the upper (lower) test temperature plus (minus) 5 ℃ condition placed for (plus or minus 15) 45 min. This step is to restore the electrode body before the collapse of the state, and to prepare for the next dentures test. The reason to put lapped good single cell in a sealed bag is mainly to prevent evaporation of electrolyte and the natural environment influence on battery chemical state, therefore, it should be chosen as small as possible volume bags. In addition, in the upper (lower) plus (minus) 5 ℃ in test temperature placed for (plus or minus 15) 45 min to is in order to make the electrode body up to the test temperature when pressure testing.

    4. Pressure Step

    In the lower and upper temperature condition, use the pressure equipment in the picture below, at the rate of 0.1 mm/s pressure on the single battery position which placed a small nickel, at the same time using the voltmeter monitor the change of single battery output voltage. When observed there are more than 50 MV voltage drop, or when the pressure reaches requirements ( 800 n for cylindrical battery, 400 n for square battery ), then can stop the reduced pressure tool and maintain for 30 s, and then put out the pressure. Using so slow pressure speed as 0.1 mm/s, can better control the internal short circuit time and severe level, When 50 MV pressure drop appeared in the pressure process, it express that the battery has been pierce  the battery diaphragm under the pressure and caused a short circuit in the single cell within a small nickel, then is no need to continue to put pressure on at this time; If pressure has up to 800 n ( square battery  400 n) there is still no voltage drop appears, that means the single battery diaphragm can effectively prevent small nickel piercing and can also prevent the single battery mixed with small metal particles from internal short circuit.




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