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KR-20260066253-A - METHOD FOR INSPECTING LOW VOLTAGE FAILURE AND METHOD FOR PREPARING SECONDARY BATTERY USING SAME

KR20260066253AKR 20260066253 AKR20260066253 AKR 20260066253AKR-20260066253-A

Abstract

The present invention relates to a low-voltage defect inspection method and a secondary battery manufacturing method using the same. It provides a low-voltage defect inspection method applicable to a mass production line and a secondary battery manufacturing method using the same, which can inspect low-voltage defects of a secondary battery early and within a short period of time based on non-destructive electrochemical evaluation (EIS, electrochemical impedance spectroscopy).

Inventors

  • 손기현
  • 나균일

Assignees

  • 주식회사 엘지에너지솔루션

Dates

Publication Date
20260512
Application Date
20241104

Claims (8)

  1. An EIS measurement step of measuring a secondary battery using electrochemical impedance spectroscopy (EIS) to acquire EIS data at the above-mentioned set time intervals; A peak frequency extraction step of obtaining a distribution of relaxation times (DRT) plot from EIS data for each of the above-mentioned set time intervals, and extracting P1, the frequency value at which the first peak occurs, and P2, the frequency value at which the second peak occurs, from each DRT plot; I1 extraction step for extracting I1, which is the maximum intensity value corresponding to the P1 value extracted from each DRT plot; A ΔI1 calculation step for obtaining ΔI1, which is the value of the time change of I1 for each DRT plot I1 value; A ΔP2 calculation step for calculating ΔP2, which is the value of the time change of P2 for each DRT plot P2 value; and A low voltage defect inspection method comprising a low voltage prediction step for predicting a low voltage defect of a secondary battery to be measured based on the above ΔI1 and the above ΔP2.
  2. In paragraph 1, A low voltage defect inspection method in which, in the above EIS measurement step, the setting time is 0.5 to 4 days.
  3. In paragraph 1, A low-voltage defect inspection method in which, in the above EIS measurement step, the electrochemical impedance spectroscopy is performed in a frequency band of 5 Hz to 1 MHz.
  4. In paragraph 1, A low-voltage defect inspection method in which the above secondary battery is a secondary battery immediately after the pre-aging process.
  5. In paragraph 1, A low voltage defect inspection method in which, in the above I1 extraction step, each DRT plot I1 value is fitted with the function I1(t) of the following Equation 1 for the above set time t: [Mathematical Formula 1] In the above equation, I1(t) is a value corresponding to the maximum intensity value of the secondary battery under analysis at time t during EIS measurement, I1(0) is a value corresponding to the maximum intensity value of the secondary battery under analysis at time t=0 during EIS measurement, and λ is a constant as the reduction rate.
  6. In paragraph 5, In the above ΔI1 calculation step and ΔP2 calculation step, The above ΔI1 is defined by the following mathematical formula 2, and A low-voltage defect inspection method in which the above ΔP2 is defined by the following mathematical formula 3: [Mathematical Formula 2] [Mathematical Formula 3] In the above equation, t1 and t2 are the set times, and P2(t) is the P2 value corresponding to the DRT plot measured at the set time t.
  7. In paragraph 6, A low-voltage defect inspection method in which, in the above low-voltage prediction step, the defect status of the secondary battery is predicted by the following mathematical formula 4: [Mathematical Formula 4] In the above equation, α and β are weights, and Defect Score is a constant value representing the correlation with the low voltage defect of the secondary battery under analysis.
  8. Step of making an electrode by kneading, applying, and drying the electrode material; A step of forming a unit cell by stacking the above electrodes and separators; A step of rolling the unit cell or preparing a plurality of the unit cells and then stacking and combining them to form an electrode assembly; A step of housing the above electrode assembly in a battery case; Step of injecting an electrolyte into the battery case and sealing the battery case; A pre-aging step to ensure that the above electrolyte is sufficiently impregnated into the electrode and the separator of the electrode assembly; A step of analyzing a secondary battery in which the pre-aging step has been performed using the low-voltage defect inspection method of claim 1; An activation step of charging the above secondary battery to a power level above a certain level; A degassing (DGS) step for removing gas inside the battery case generated in the activation step above; and A method for manufacturing a secondary battery comprising a re-sealing step of resealing the battery case.

Description

Method for inspecting low voltage failure and method for preparing a secondary battery using the same The present invention relates to a low-voltage defect inspection method and a secondary battery manufacturing method using the same. It relates to a low-voltage defect inspection method applicable to a mass production line that can inspect low-voltage defects of a secondary battery early and for a short period of time based on non-destructive electrochemical impedance spectroscopy (EIS), and a secondary battery manufacturing method using the same. Generally, rechargeable batteries are batteries capable of repeated use through the processes of discharging, which converts chemical energy into electrical energy, and charging, which converts electrical energy into chemical energy. Types include nickel-cadmium (Ni-Cd) batteries, nickel-hydrogen (Ni-MH) batteries, lithium-metal batteries, lithium-ion (Li-ion) batteries, and lithium-ion polymer batteries. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. The charging and discharging of a lithium secondary battery proceeds as the process of lithium ions being intercalated and deintercalated from the lithium metal oxide of the positive electrode to the negative electrode is repeated. A secondary battery can generally be manufactured by housing an electrode assembly, in which a cathode, a separator, and an anode are stacked and assembled, together with an electrolyte in a case such as a cylindrical can or a prismatic pouch. Specifically, a unit cell is manufactured by cutting, stacking, etc., a cathode, separator, and anode in a pre-designed manner. The manufactured unit cells can be manufactured into an electrode assembly by stacking, folding, or rolling a predetermined quantity. Subsequently, the electrode assembly is placed in a battery case, an electrolyte is injected, and then sequentially undergoes steps such as sealing, pre-aging, activation, degassing (DGS), re-sealing, and performance testing to be shipped as a secondary battery product. These lithium secondary batteries may experience various types of defects due to various causes during the manufacturing process or use. In particular, some completed secondary batteries exhibit voltage drop behavior exceeding their self-discharge rate, a phenomenon that can be referred to as a low-voltage defect. Such low-voltage failures in secondary batteries are typically caused by structural defects, such as internal metal foreign matter or folding of the current collector. When such structural defects occur, lithium deposition accelerates and can grow into dendrites. These dendrites can cause internal short circuits in the secondary battery, leading to battery failure or damage, and in severe cases, ignition. Therefore, in the production of secondary batteries, a low-voltage test is required after the aforementioned processes of liquid injection, sealing, pre-aging, activation, degassing (DGS), re-sealing, and performance testing. However, since it typically takes several days, for example about five days, to perform this test, a problem of reduced productivity occurs. Therefore, there is a need for technology capable of inspecting low-voltage defects non-destructively in a short period of time. FIG. 1 is a block diagram illustrating the low-voltage defect inspection method of the present invention. Figure 2 is a graph of the distribution of relaxation times (DRT) for the EIS measurement of a normal battery. Figure 3 is a DRT graph for EIS measurements of a low-voltage expected battery. Hereinafter, embodiments according to the present invention will be described in detail with reference to the attached drawings. In this process, the size or shape of components illustrated in the drawings may be exaggerated for clarity and convenience of explanation. Furthermore, terms specifically defined in consideration of the configuration and operation of the present invention may vary depending on the intent or convention of the user or operator. The definitions of such terms should be based on the content throughout this specification. The low-voltage defect inspection method of the present invention is an inspection method capable of predicting low-voltage defects that exhibit a phenomenon showing voltage drop behavior exceeding the self-discharge rate, which may occur due to various causes during the secondary battery manufacturing process or use. According to the present invention, it is possible to predict secondary batteries with a high probability of low-voltage defects. For example, the charging and discharging of a lithium secondary battery proceeds through the repeated process of lithium ions intercalating and deintercalating from the lithium metal oxide of the positive electrode to the negative electrode. Low-voltage defects in secondary batteries are often caused by defect