Rechargeable batteries have become deeply integrated into our lives, powering a wide range of energy sources from smartphones and laptops to power tools and never-ending energy systems. In comparison to disposable batteries, these batteries can be used regularly and reduce waste. However, not all rechargeable batteries are structured the same, and understanding their key indicators is crucial for making informed choices. This project will explore the key determining factors that limit the performance and reliability of rechargeable batteries.
- Safety Performance
Unqualified battery performance indicators are not acceptable. The most significant impacts are explosion and leakage. The occurrence of explosions and leaks is mainly related to the internal pressure, structure, and process design of the battery (such as failure of safety valves, lack of protection circuits in lithium-ion batteries, etc.) and improper operations that are prohibited (such as throwing the battery into fire).
Capacity refers to the total amount of electricity that a battery can release under certain discharge conditions. According to the IEC standard and national standards, the rated capacity of nickel-cadmium and nickel-metal hydride batteries is the amount of electricity released when charged at 0.1C for 16 hours and discharged at 0.2C to 1.0V under 20±50C conditions, expressed in C; the rated capacity of lithium-ion batteries is the amount of electricity released when charged at constant temperature, constant current (1C), and constant voltage (4.2V) for 3 hours, and then discharged at 0.2C to 2.75V. The units of battery capacity are mAh and Ah (1Ah = 1000mAh).
Taking AA2300mAh nickel-metal hydride rechargeable batteries as an example, it means that the battery is charged at 230mA (0.1C) for 16 hours and discharged at 460mA (0.2C) to 1.0V, with a total discharge time of 5 hours and a discharged capacity of 2300mAh. Similarly, if discharged at a current of 230mA, the discharge time would be approximately 10 hours.
The internal resistance of a battery refers to the resistance encountered when current flows through the battery. The internal resistance of a charged battery is very low and requires specialized instruments to measure accurately. The commonly known internal resistance of a battery refers to the internal resistance in the charged state, which is the resistance when the battery is fully charged (correspondingly, the internal resistance in the discharged state refers to the internal resistance after the battery is fully discharged. Generally, the internal resistance in the discharged state is larger and less stable than that in the charged state). The larger the internal resistance of a battery, the more energy it consumes internally, and the lower the efficiency of its use. Batteries with high internal resistance generate significant heat during charging, causing a rapid increase in battery temperature, which has a significant impact on both the battery and the charger. As the number of battery usage increases, the internal resistance of the battery will increase to varying degrees due to the consumption of electrolyte and the decrease in the activity of internal chemical substances. Poor quality batteries have a faster rise in internal resistance.
Cycle life refers to the number of repeated charge and discharge cycles that a battery can undergo. Battery life is inversely related to capacity. Generally, nickel-metal hydride batteries can have a cycle life of over 500 cycles. High-capacity batteries have shorter lifespans but can still exceed 200 cycles. The cycle life also closely depends on the charging and discharging conditions. Generally, the larger the charging current (the faster the charging speed), the shorter the cycle life.
Charge Retention Ability
Charge retention ability, commonly referred to as self-discharge, refers to the ability of a battery to retain stored electricity under certain environmental conditions in an open circuit state. Self-discharge is mainly determined by factors such as battery materials, manufacturing processes, and storage conditions. Generally, the higher the temperature, the greater the self-discharge rate. A certain degree of self-discharge in charged batteries is considered normal. Taking nickel-metal hydride batteries as an example, according to the IEC standard, after the battery is fully charged, when stored at a temperature of 20±5°C and a humidity of 65±20%, and left idle for 28 days, the 0.2C discharge time must not be less than 3 hours (which means the remaining capacity is more than 60%). The self-discharge of lithium-ion batteries and dry batteries is much lower.
In conclusion, the core indicators of rechargeable batteries play a vital role in assessing their performance and determining their suitability for various applications. Safety performance, capacity, internal resistance, cycle life, and charge retention ability are key factors to consider when evaluating the quality and reliability of rechargeable batteries. Manufacturers and users alike must prioritize safety, ensuring that batteries meet stringent standards to prevent explosions and leaks. Capacity determines the total amount of energy a battery can provide, while internal resistance affects its efficiency and heat generation during charging. Cycle life indicates the number of charge and discharge cycles a battery can endure before its performance deteriorates. Additionally, charge retention ability measures the battery’s self-discharge rate when left idle. By understanding and monitoring these core indicators, individuals and industries can make informed decisions while selecting and utilizing rechargeable batteries, ultimately promoting the efficient and safe use of energy storage technologies.