1. How are the safety characteristics of lithium-ion batteries achieved?
a. Automatic shutdown protection at 135℃: Utilizing internationally advanced Celgars 2300 PE-PP-PE three-layer composite membrane. When the battery temperature reaches 120℃, the pores on both sides of the PE composite membrane close, increasing the battery's internal resistance and slowing down the internal temperature rise. When the battery temperature reaches 135℃, the PP membrane pores close, breaking the internal circuit and preventing further temperature increases, ensuring battery safety and reliability.
b. Adding additives to the electrolyte: When the battery is overcharged and the battery voltage is higher than 4.2V, the electrolyte additives polymerize with other substances in the electrolyte, the battery internal resistance increases significantly, a large-area open circuit is formed inside the battery, and the battery no longer heats up.
c. Composite battery cover structure: The battery cover adopts a serrated explosion-proof ball structure. When the battery heats up, some of the gas generated during the internal activation process expands, increasing the internal pressure of the battery. When the pressure reaches a certain level, the serration will crack and release gas.
d. Various environmental abuse tests: Various abuse experiments are conducted, such as external short circuit, overcharge, needle penetration, impact, and burning, to examine the battery's safety performance. Simultaneously, temperature shock tests and mechanical performance tests such as vibration, drop, and impact are performed on the battery to examine its performance in real-world usage environments.
2. Why does the constant voltage charging current gradually decrease?
Because when the constant current process ends, the electrochemical polarization inside the battery remains at the same level as during the entire constant current process. During the constant voltage process, under the action of a constant electric field, the concentration polarization of Li+ inside the battery gradually disappears, and the migration number and velocity of ions are manifested as a gradual decrease in current.
3. What is battery capacity?
Battery capacity is divided into rated capacity and actual capacity. The rated capacity of a battery refers to the minimum amount of electricity that the battery should release under certain discharge conditions, as specified or guaranteed during the design and manufacturing process. For Li-ion batteries, the specification is to charge them for 3 hours under constant current (1C) and constant voltage (4.2V) conditions at room temperature. The actual capacity of a battery refers to the actual amount of electricity it releases under certain discharge conditions, primarily affected by the discharge rate and temperature (therefore, strictly speaking, battery capacity should specify the charging and discharging conditions). Common units of capacity include mAh and Ah (1000mAh).
4. What is battery internal resistance?
Internal resistance refers to the resistance encountered by the current flowing through the battery during operation. It consists of two parts: ohmic internal resistance and polarization internal resistance. High internal resistance leads to a lower discharge voltage and shorter discharge time. The magnitude of internal resistance is mainly affected by factors such as the battery's materials, manufacturing process, and structure. It is an important parameter for evaluating battery performance.
Note: The internal resistance in the charging state is generally used as the standard. A dedicated internal resistance meter must be used to measure the battery's internal resistance; a multimeter in ohm mode cannot be used.
5. What is open-circuit voltage?
When fully charged, the open-circuit voltage is approximately 4.1-4.2V; after discharging, it is approximately 3.0V. The battery's state of charge (SOC) can be determined by its open-circuit voltage. What is the operating voltage? The discharging operating voltage is approximately 3.6V.
6. What is the internal air pressure of the battery?
Internal pressure refers to the gas generated during the charging and discharging process of a sealed battery. It is primarily influenced by factors such as battery materials, manufacturing processes, and battery structure. The main cause is the accumulation of gases produced by the decomposition of moisture and organic solutions within the battery. Continuous overcharging at high rates leads to increased battery temperature and internal pressure, which can severely damage battery performance and appearance, causing issues such as leakage, bulging, increased internal resistance, and shortened discharge time and cycle life. Any form of overcharging in Li-ion batteries will severely damage battery performance and may even lead to explosion. Therefore, constant current and constant voltage charging methods must be used during Li-ion battery charging to avoid overcharging.
7. Why must batteries be stored for a period of time before they can be packaged and shipped?
Storage performance is an important parameter for measuring the overall stability of a battery's performance. After a certain period of storage, the battery's capacity and internal resistance are allowed to change to some extent. After a period of storage, the electrochemical properties of the internal components stabilize, allowing us to understand the battery's self-discharge capacity and thus ensure battery quality.
8. Why transform?
After a battery is manufactured, the positive and negative electrode materials inside it are activated through a certain charging and discharging method to improve the battery's charging and discharging performance, as well as its comprehensive performance such as self-discharge and storage. This process is called formation. Battery powder can only show its true performance after it has undergone formation.
9. What is capacity division?
During the manufacturing process, due to technological limitations, the actual capacity of batteries cannot be completely consistent. The process of testing batteries according to their capacity through specific charge and discharge regimes is called capacity grading.
10. What is pressure drop?
The battery is qualitatively charged to over 80%, and its open-circuit voltage is measured. A 5W/2W battery is connected to the positive and negative terminals as a load. A switch is used to disconnect the battery circuit, and the circuit-connecting devices are connected in series. If the voltage drop is no more than 0.4V within 5 seconds after the switch is turned on, it is considered合格 (qualified). This test primarily assesses the battery's load performance.
11. What is static resistance? What is dynamic resistance?
a. Static resistance is the internal resistance of the battery during discharge.
b. Dynamic resistance is the internal resistance of the battery during charging.
12. What welding methods are used for both positive and negative terminals?
a. Ultrasonic welding machine for the positive electrode.
b. Use a spot welding machine for the negative electrode.
13. What is the purpose and location of applying adhesive tape to the battery cells?
a. The battery cell sticker should be positioned so that it does not deform after the battery cell is wound and formed. Adhesive tape should be applied to the bottom to prevent the bottom of the positive electrode plate inside the battery cell from contacting the battery casing and causing a short circuit.
b. Side stickers prevent the battery cell from deforming after winding. Adhesive tape on the bottom prevents the bottom of the positive electrode plate inside the battery cell from contacting the battery casing and causing a short circuit.
14. What are the humidity requirements for the drying room? Why must the battery be weighed before electrolyte filling?
a. Relative humidity is below 6%.
b. Weigh the contents to accurately calculate the injection volume.
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