I. Battery voltage (V)

1. Open circuit voltage (OCV)

The voltage of the lithium battery when it is not connected to an external circuit or load can generally be tested with a multimeter.

2. Operating voltage (WV)

The potential difference between the positive and negative terminals of the battery under applied load, that is, when there is current flowing through the battery in the circuit. When the battery is working, there will be current flowing through the battery, because of the internal resistance and load resistance of the battery itself, the battery operating voltage is always lower than the open circuit voltage.

3. Discharge cut-off voltage (DCV) :

Refers to the battery in the case of electric energy, the set voltage reached when the discharge is finished, the general set voltage is 3.0V or above, overdischarge will have an irreversible impact on the battery.

4. Charging limit voltage (LCV) : The current charging system is generally CC (constant current charging) +CV (constant voltage charging), which is the voltage that changes from constant current to constant voltage charging during the charging process.

Ⅱ. Battery capacity (Ah or mAh)

Step 1 Define

Battery capacity refers to the amount of electricity released by the battery under certain conditions (discharge rate, temperature, termination voltage, etc.), which is one of the important indicators of battery electrical performance.

Step 2: Capacity

It is expressed in C and the unit is Ah (ampere-hour) or mAh (milliampere-hour).

Ⅲ. Calculation formula

C=It, battery capacity (Ah) = current (A) x discharge time (h).

Step 4 Classify

The capacity of the battery can be divided into rated capacity, theoretical capacity and actual capacity.

1) Rated capacity

That is, the capacity indicated on the battery packaging is the lowest capacity released under standard conditions according to the standards promulgated by the state or relevant departments.

2) Theoretical capacity

A theoretical value calculated according to Faraday's law based on the mass of the active substance.

3) Actual capacity

According to the actual situation of the battery, the battery capacity released under a certain charge and discharge system. It is related to the situation of the battery itself, such as SOC, SOH, etc., and it is also related to the charge and discharge system.

Three. Battery internal resistance (mΩ)

Step 1 Define

The internal resistance of a battery is the resistance it receives when it flows through a current. The internal resistance of the battery is mainly affected by the material of the battery, the production process, the battery structure and other factors.

Step 2 Classify

It includes ohm internal resistance and polarization internal resistance.

Ohmic internal resistance: depends on the electrode material, electrolyte, diaphragm resistance, contact resistance between materials, and contact resistance with the shell composition. When a battery is discharged, the ohm resistance obeys Ohm's law.

Internal resistance to polarization: It is mainly the resistance caused by electrochemical polarization and concentration polarization when the battery flows through the current. The polarization resistance increases with the increase of current density, but it is not linear, and usually increases linearly with the logarithmic increase of current density.

The internal resistance of the battery is not a constant and changes over time during discharge because the composition of the active substance, electrolyte concentration and temperature are constantly changing.

Ⅳ. Charge Cycle life

Step 1 Define

The secondary battery experiences a charge and discharge called a cycle or a cycle, and the capacity of the battery will gradually decrease after repeated charge and discharge. Generally, lithium batteries will be charged and discharged under standard conditions, and when the battery capacity is reduced to 80%, the number of cycles the battery undergoes is the cycle life.

2. Influencing factors

There are mainly incorrect use of the battery, the battery material of the battery itself, the composition and concentration of the electrolyte, the charge and discharge rate, the discharge depth (DOD%), the temperature, the production process, etc., all have an impact on the cycle life of the battery.

Ⅴ. Battery Power (Wh)

Step 1 Define

Refers to the amount of energy stored by the battery, generally expressed in Wh or KWh.

2. Calculation formula

Energy (Wh) = rated voltage (V) x working current (A) x working time (h).

Ⅵ. Energy density (Wh/Kg)

Step 1 Define

It is the energy released per unit mass or unit volume of the battery, that is, the volume specific energy or mass specific energy refers to the energy released per unit volume or mass, usually expressed by the volume energy density (Wh/L) or.

2. Calculation formula

Volume energy density (Wh/L) = battery capacity (Ah) × average discharge platform (V)/ battery volume (L)

Mass Energy density (Wh/kg) = battery capacity (Ah) x average discharge platform (V)/ battery weight (Kg)

Ⅶ. Battery discharge platform

It refers to the voltage in the part of the discharge curve where the voltage basically remains level under a certain charge and discharge system.

The higher, longer and more stable the discharge platform of the general battery, the better the discharge performance of the battery. Industry standards require 1C discharge platforms to be more than 70%.

Ⅷ. Self-discharge rate (% / month)

Step 1 Define

In the storage process of the battery, because of the impurities of the battery material and the impurities brought into the production process, some side reactions inside the battery, etc., lead to the battery in the process of placement, the capacity will gradually decline, and the ratio of the reduced capacity to the battery capacity is called the self-discharge rate.

2. Reasons

The instability of the electrode in the electrolyte, the side reactions caused by impurities inside the battery, etc., cause the active substance to be consumed, the chemical energy converted to electric energy is reduced, and the battery capacity is reduced.

3. Influencing factors

The ambient temperature has a great influence on the battery, and too high temperature will accelerate the self-discharge of the battery.

Step 4 Show

The expression method and unit of battery capacity attenuation (self-discharge rate) are: %/ month or %/ year.

Ⅸ. Depth of charge and discharge (SOC, DOD)

Charge depth: the ratio of the amount of charge to the nominal capacity, generally expressed by SOC.

Discharge depth: The discharge depth is the ratio of the discharge quantity to the nominal capacity. Generally denoted by DOD.

For example, the capacity of a battery with a capacity of 20Ah becomes 4Ah after discharge, which can be called 80%DOD. If the battery has a capacity of 10Ah after charging, the charging depth can be 50%SOC.

Ⅹ. Charge, discharge ratio (A)

Step 1 Define

Discharge rate: refers to the current value required when releasing its rated capacity (C) within a specified time, which is numerically equal to a multiple of the rated capacity of the battery. For example, if the discharge rate is 2C, the discharge current of the battery is: 2* the capacity of the battery (unit is A).

Charging rate: that is, the speed of charging, its value is also equal to the speed of the rated capacity of the battery.

2. Classification of discharge rate

Low magnification (< 0.5C), medium magnification (0.5-3.5C), high magnification (3.5-7.0C), super magnification (> 7.0C).

During the discharge process, the battery exceeds the specified discharge termination voltage value of the battery and continues to discharge, which may cause the internal pressure of the battery to rise, and the reversibility of the positive and negative active substances to be damaged, so that the capacity of the battery is significantly reduced.

Ⅺ. Over charge

When the battery is charging, after reaching the full state, if it continues to charge, it may lead to increased internal pressure of the battery, battery deformation, night leakage, etc., the performance of the battery will be significantly reduced and damaged, and even dangerous explosion.

Ⅻ. Load capacity

When the positive and negative ends of the battery are connected to the electrical appliance, the output power that drives the electrical appliance to work is the load capacity of the battery.

XIII. Battery internal pressure

The internal pressure of a battery is the pressure formed by the gas produced during charging and discharging. It is mainly affected by the battery material manufacturing process, structure and other use process factors.

XIV. Battery formation

After the battery is assembled and injected, the positive and negative active substances are activated through a certain charge and discharge method to improve the battery's charge and discharge performance and self-discharge, storage and other comprehensive properties. Only after the battery has been formed can its true performance be reflected. At the same time, the separation process in the formation process can improve the consistency of the battery pack and improve the performance of the final battery pack.