What is the battery capacity and internal resistance of lithium-ion batteries?
Reply Battery capacity problem：The capacity of lithium-ion batteries is divided into three types, rated capacity, theoretical capacity and actual capacity. The rated capacity of the battery refers to the minimum capacity provided by the battery specified or guaranteed when the battery is designed and manufactured under certain discharge conditions, discharged to the final voltage, is the capacity of the battery specified during the design and production. The actual capacity of the battery refers to the actual power released by the battery under certain discharge conditions, which will be affected by many factors, mainly the discharge rate of the battery and the temperature during discharge, strictly speaking, the battery capacity The discharge conditions should be specified. Generally speaking, the capacity of a battery refers to the amount of power that the battery can store, and the unit of capacity is mAh. To give an example: if there is a battery with a nominal capacity of 10000mAh, and it is discharged with a current of 100mA, then the battery can work for 100 hours. Of course, this is the ideal situation. In practice, we also need to consider whether the output current can be constant, whether the temperature at which the output current is at a constant, etc. These all need to be looked at according to the actual situation.
Reply Battery internal resistance problem：The internal resistance of a lithium-ion battery refers to the resistance inside the battery through which the current flows when the battery is working. It includes ohmic internal resistance and polarization internal resistance. Polarization internal resistance includes electrochemical polarization internal resistance and concentration pole.化 internal resistance. The ohmic internal resistance mainly refers to the electrode material resistance, the diaphragm material resistance, the electrolyte material resistance, and the contact resistance of each part, which of course is also related to the size, structure, size, and assembly of the battery. The internal resistance of a lithium-ion battery is not a constant, it will change with time during the process of charging and discharging. This is because the composition of the active material in the battery, the concentration and temperature of the electrolyte are constantly changing. The ohmic internal resistance follows Ohm’s law, and the polarization internal resistance increases with the increase of current density, but they are not linear. It often increases linearly as the logarithm of the current density increases. The internal resistance of different types of batteries is also different, even the same type of batteries, due to the inconsistency of internal chemical characteristics, their internal resistance is also different. The internal resistance of the battery is very small, so we generally use Haou’s units to define it. Internal resistance is an important indicator to measure battery performance. Under normal circumstances, a battery with a small internal resistance has a strong high-current discharge capacity, and a battery with a large internal resistance has a weak discharge capacity. In general measurement occasions, we require that the internal resistance measurement accuracy error of the battery must be controlled within plus or minus 5%. Such a small resistance value and such a precise requirement must be measured with a dedicated instrument.