Basic Parameters of Lithium Batteries

Summary of technical parameters of lithium iron batteries. Lithium-ion battery cells are composed of positive and negative electrodes, electrolytes and diaphragms. In the power lithium battery system, each parameter can characterize the different performance of the system. As an electrochemical power source, lithium iron batteries naturally have characteristic parameters such as voltage, internal resistance, capacity, energy, and power.

Technical parameters of lithium iron batteries

Generally speaking, when we use lithium batteries, we will pay attention to some technical indicators as the main factors to measure the "good or bad" performance of lithium batteries.

What do the specifications, size, charge and discharge, and current resistance of lithium batteries represent? Generally, we say how many volts and how many ampere-hours, which is not difficult to understand. It refers to voltage and capacity. For example: 48V30AH, which is the specification of lithium batteries. It is also one of the parameters of lithium batteries. Let's take a look at the common parameters of lithium batteries!

1. Capacity

The unit of capacity is generally "mAh" or "Ah", and there is a difference between rated capacity and actual capacity when in use. Rated capacity refers to the total amount of electricity that a fully charged lithium-ion battery can provide when it is discharged to the cut-off voltage at a certain discharge rate under laboratory conditions. The actual capacity is generally not equal to the rated capacity. It is directly related to temperature, humidity, charge and discharge rate, etc. In general, the actual capacity is slightly smaller than the rated capacity, and sometimes even much smaller than the rated capacity. For example, in the winter in the north, if a mobile phone is used outdoors, the battery capacity will drop rapidly.

2. Energy density

Energy density refers to the amount of electricity that can be stored and released by a battery per unit volume or unit weight. There are two units: Wh/kg and Wh/L, which represent weight specific energy and volume specific energy respectively. The amount of electricity here is the integral of the capacity (Ah) and the operating voltage (V) mentioned above. When applied, the energy density indicator is more instructive than the capacity.

The improvement of the energy density of lithium-ion batteries is a slow process, far lower than Moore's Law in the integrated circuit industry. This has caused a scissors gap between the performance improvement of electronic products and the energy density improvement of batteries, and it continues to expand over time.

3. Charge and discharge rate

This indicator will affect the continuous current and peak current of lithium batteries when they are working, and its unit is generally C. The current value corresponding to the charge and discharge rate multiplied by the working voltage can get the continuous power and peak power indicators of lithium-ion batteries.

The more detailed the definition of the charge and discharge rate indicator is, the greater the guiding significance for use. Especially for lithium-ion batteries as the power source of electric vehicles, it is necessary to specify the continuous and pulse rate indicators under different temperature conditions to ensure that lithium-ion batteries are used within a reasonable range.

4. Voltage

The voltage of lithium batteries includes some parameters such as open circuit voltage, working voltage, charge cut-off voltage, and discharge cut-off voltage.

5. Life

The life of iron-lithium batteries is divided into two parameters: cycle life and calendar life. Cycle life is generally measured in times, which represents the number of times the battery can be charged and discharged in cycles. Of course, there are conditions here. Generally, it is to perform deep charge and discharge at the rated charge and discharge current under ideal temperature and humidity, and calculate the number of cycles experienced when the battery capacity decays to 80% of the rated capacity.

6. Internal resistance

Inside the lithium iron battery, lithium ions move from one pole to the other. The factors that hinder the movement of ions in the process together constitute the internal resistance of the lithium battery. Its main parts include the physical internal resistance of the conductive parts; the inherent impedance of electrochemical substances such as motor materials, diaphragms and electrolytes; the temporary increase in the resistance to the movement of lithium ions when there is current inside the battery; these three parts together constitute the main body of the internal resistance.

The internal resistance is most sensitive to temperature. Under different temperatures, the internal resistance value can change greatly. One of the important reasons for the decline in lithium battery performance at low temperatures is that the internal resistance of the battery is too large at low temperatures.

7. Power

The power here should be more accurately referred to as specific power, which is the charge and discharge power capacity of a single cell or the charge and discharge power capacity of a cell per unit mass or unit volume. Whether a lithium battery can be charged and discharged at high power has been determined when it is designed.

8. Consistency of battery packs

This parameter is quite interesting. Even if the battery cells of the same specification and model are grouped, the battery packs have great differences in voltage, capacity, internal resistance, life and other performance. When used in electric vehicles, the performance indicators often do not reach the original level of the single cell.