Technical specifications of lithium-ion batteries

Lithium-ion batteries, as an ideal carrier of electrical energy, are widely used in various fields. When we use lithium-ion batteries, we will pay attention to some technical indicators, as a measure of its performance “good or bad” as the main factors. These main technical indicators are as follows:

1. Capacity
   Battery capacity is an important performance indicator to measure the performance of the battery, which indicates the amount of power the battery can release under certain conditions. Capacity is usually measured in Ampere-hours (Ah), for example, if a battery is 48V 200ah, it means that the battery can store 48V*200ah=9.6KWh, i.e. 9.6 kWh of electricity.
   Battery capacity is divided into actual capacity, theoretical capacity and rated capacity according to different conditions: theoretical capacity refers to the battery active material; participate in the battery reaction given by the amount of electricity, that is, the most ideal state capacity; rated capacity refers to the nameplate indicated that the motor or electrical appliances in the rated operating conditions can be a long time to continue to work the capacity; the actual capacity of the battery in a specific discharge conditions can provide the amount of electricity, which with the temperature, It is directly related to temperature, humidity, charging and discharging multiplication rate, etc., and is usually lower than the rated capacity.
2. Energy Density
   Energy density refers to the energy that can be stored per unit mass or volume of the battery. Energy density has two forms: mass energy density (Wh/kg) and volume energy density (Wh/L).
   The current lithium-ion battery technology has an energy density of about 100 to 200 Wh/kg, which restricts the wide application of lithium-ion batteries, especially in the field of electric vehicles, where a high energy density is the key to improving range.
3. Charge/discharge ratio
   Charge/discharge ratio is a measure of the speed of charging and discharging. This indicator affects the continuous and peak currents of lithium-ion batteries, and its unit is usually C.
   For example, if the rated capacity of a battery is 20Ah, and its rated charge/discharge multiplier is 0.5C, it means that the battery can be charged and discharged repeatedly with a current of 20Ah*0.5C=10A, until the cut-off voltage of charging or discharging. If its maximum discharge multiplier is 10C@10s and its maximum charge multiplier is 5C@10s, then this battery can be discharged with a current of 200A for a duration of 10 seconds and charged with a current of 100A for a duration of 10 seconds.
   The more detailed the definition of the charging and discharging multiplier index, the greater the significance of guidance for use. Especially for lithium-ion batteries, which are used as the power source of electric transportation vehicles, it is necessary to define the continuous and pulse multiplication indexes under different temperature conditions to ensure that lithium-ion batteries are used within a reasonable range.

4.Voltage
Lithium-ion battery voltage, open circuit voltage, operating voltage, charging cut-off voltage, discharge cut-off voltage and other parameters, the unit is V. Open circuit voltage is the battery without any external load or power supply, measuring the potential difference between the positive and negative poles of the battery, which is the open circuit voltage of the battery. Working voltage is the battery external load or power supply, in the working state, there is a current flow, measured by the potential difference between the positive and negative electrodes. Working voltage is related to the composition of the circuit and the operating state of the equipment, is the value of change. Generally speaking, due to the existence of the internal resistance of the battery, the operating voltage is lower than the open-circuit voltage in the discharged state and higher than the open-circuit voltage in the charging state. The charge/discharge cut-off voltage is the maximum and minimum operating voltage that the battery is allowed to reach. Exceeding this limit will cause some irreversible damage to the battery, leading to the degradation of battery performance, and in serious cases, even causing fire, explosion and other safety accidents.

5. Cycle life, calendar life and depth of discharge
   Depth of discharge is the percentage of the battery discharge and the rated capacity of the battery, the battery standard 80% DOD means that 80% of the power discharge.
   Lithium-ion battery life will gradually decline with the use and storage, and there will be more obvious performance. Still take smart phones as an example, after using the phone for a period of time, you can obviously feel the cell phone battery “not durable”, at the beginning may only charge once a day, the back may need to charge twice a day, which is the embodiment of the battery life continues to decline.

Lithium-ion battery life is divided into two parameters: cycle life and calendar life. Cycle life is generally measured in Times, which characterizes the number of times a battery can be charged and discharged. Generally speaking, under ideal temperature and humidity, deep charge and discharge (80% DOD) with rated charge and discharge current, and calculate the number of cycles experienced when the battery capacity decreases to 20% of the rated capacity.
Calendar life is the time span for the battery to reach the end-of-life condition (e.g., 20% capacity decay) after specific operating conditions under the use of environmental conditions. Calendar life is closely aligned with specific usage requirements, and usually requires the specification of specific