lithium ion battery

What should you know when buying a lithium ion battery

In today’s age of electronic information, almost all the devices we use every day need batteries. If you don’t know much about lithium ion battery, you may be confused by the jargon when shopping for them. So this article is for you. We will not talk about the complex and professional lithium ion battery principle, but will introduce some battery knowledge which is simple and easy to understand, and useful for buying a lithium ion battery. It will you to get rid of confusion.After understand this article, I believe you will be handy when choosing. You will know you should consider what aspects to choose a suitable lithium ion battery combined with your own application scenarios.

you should consider what aspects to choose a suitable lithium ion battery

1.Primary battery and rechargeable battery

Primary battery: It can discharge only once. After discharging, it cannot be recharged and reused. With the same capacity, the mass and volume of the primary battery are larger than those of the general rechargeable battery. The self-discharge of the primary battery is much smaller than that of the secondary battery, but the internal resistance is much larger than that of the secondary battery, so the load capacity is lower. Its disadvantage is that it will produce a large amount of waste batteries and have a certain impact on the environment.

Lithium ion battery is rechargeable battery

Rechargeable battery: After discharge, they can be rechargeable with the specified charger and re-discharged. They can be used repeatedly. Lithium ion battery is rechargeable battery.

2.Current

The directional movement of charge forms a current. The current, which can be electrons moving through A wire or ions moving through an electrolyte in positive and negative electrodes, is measured in amperes (A).

3.Voltage

Voltage is the potential difference between two ends of a battery,  is measured in volts (V).

4.Energy

Energy is a measure of the amount of Energy that can be stored in a battery, usually is measured in kilowatt hours (kWh)

5.Capacity

The amount of electric energy stored in a battery is expressed in ampere hours (Ah), a unit related to the energy. The capacity of a battery can be divided into rated capacity and actual capacity. The rated capacity of the battery refers to the minimum amount of power that should be released under certain discharge conditions when the battery is designed and manufactured. For lithium ion battery,IEC standards stipulate that the rated capacity of the battery is the amount of power released when the battery is discharged from 0.2C to 2.75V after charging for 3 h under the control of constant current (1C) and constant voltage (4.2V) at room temperature. And the actual capacity of the battery refers to the actual power released by the battery under certain discharge conditions. It is mainly affected by the discharge rate and temperature (so strictly speaking, the battery capacity should specify the charge and discharge conditions). The standard states that the actual capacity of a battery should be greater than or equal to its rated capacity, so the vast majority of batteries manufactured by a responsible manufacturer are not less than their rated capacity.

The capacity of a lithium ion battery can be divided into rated capacity and actual capacity

6.Charge

The process of using external power to increase the voltage and capacity of a battery; At this point electrical energy is converted into chemical energy.

(1) Charge characteristic: the characteristics of the battery when charging, such as charging curve, charging capacity, charging rate, charging depth, charging time, etc.

(2) Charge curve: the voltage of a battery changes with time when it is being charged

(3) Capacity density: the amount of electricity released per unit mass or volume, usually expressed in mAh or mAhkg. It is also called specific capacity or gram capacity.

(4) Energy density: the energy released per unit mass or volume, generally expressed by WhL or Whikg. Lithium ion battery has a high energy density, so they are smaller in size and mass for the same energy requirements.

(5) End-of-charge voltage: also known as limited charge voltage, refers to the voltage when the battery reaches the full charging state during the specified constant current charge period, that is, the voltage when the battery is fully charged.

(6) Over charge: the process of continuing charging beyond the specified charge termination voltage. The battery life is affected when over change is happen. The most direct manifestation of overcharge is: the battery is obviously hot, because the battery has been saturated, if the battery continues to charge, it is difficult to raise the voltage of the battery, it will be emitted in the form of heat, which will cause permanent damage to the battery. In general, lithium ion battery chargers will automatically stop charging when they reach the charging termination voltage.

The lithium ion battery life is affected when over change is happen

(7) Constant voltage charge: the process of charging the battery under a constant voltage. Generally set the end-of-charge current, when the current is less than this value, the charging process ends.

(8) Constant current charge: the process of charging the rechargeable battery at a constant current. Generally set the end-of-charge voltage, when the voltage reaches this value, the charging process ends. For example, a lithium ion battery is charged with constant current and constant voltage, and the battery is charged with constant current in the first stage. At this stage, the battery voltage rises with time, and when the voltage reaches the set upper limit, it enters the second stage and then carries out constant voltage charge with the upper limit voltage. In the constant voltage charging stage, the charging current gradually decreases with time until the current drops to the set minimum value, which can be considered as the battery is full and the charging ends. Constant current and constant voltage charging mode has high charging efficiency, and less damage to the lithium ion battery.

7.Discharge

The process by which electric current flows from a battery through an external circuit and chemical energy is converted to electrical energy.

lithium ion battery chemical energy is converted to electrical energy

(1) Discharge characteristic: the characteristics displayed when the battery is discharged. Such as discharge curve, discharge capacity, discharge rate, discharge depth, discharge time and so on.

(2) Discharge curve: the voltage changes with time when the battery is discharged.

(3) Discharge capacity: the amount of energy discharged when the battery is discharged. It is generally expressed by the product of time and current, such as Ah, mAh(1Ah=3600C).

(4) Discharge rate: a measure of the speed of discharge. It is the current value required by the battery to discharge its rated capacity within a specified time. It is a multiple of the rated capacity of the battery in terms of data value, usually represented by the letter C. When the discharge is completed in 1 hour, it is called 1C discharge; When the discharge is completed in 5 hours, it is called 0.2c discharge. And if the rate increases, the discharge time will decrease, 2C is means that the discharge is completed in half an hour.

(5) Depth of discharge: a measure of discharge degree, which is the percentage of discharge capacity to the total discharge capacity.

(6) Duration time: the total discharge time of the battery under a certain external load before the specified termination voltage.

(7) Nominal voltage: the average voltage in the whole process of 0.2c discharge of the battery.

Nominal capacity: Battery discharge capacity when 0.2c.

Residual capacity: Residual capacity of the battery.

(8) Over discharge: discharge continues when the end-of-discharge voltage is lower than the specified voltage. It is easy to leak or affect the service life of the battery.

8.Self discharge

Lithium ion battery has a very low self-discharge rate

The capacity loss process when there is no connection with external load. Lithium ion battery has a very low self-discharge rate. The average self-discharge rate of different types of lithium ion battery is about 1% to 5% per month.

9.Utilization

Percentage of actual discharge capacity to theoretical capacity.

10.Open circuit voltage

The voltage between the positive and negative terminals when the battery is not loaded.

11.Closed circuit voltage

It also known as working voltage, the voltage between the positive and negative terminals when the battery is loaded. Compared to other types of battery, such as nickel-based battery and lead-acid battery, lithium ion battery has a higher working voltage. The working voltage of lithium ion battery is generally 3.2 to 3.8 V, so lithium ion battery require fewer cells for the same assembly voltage.

12.Internal resistance

The resistance to current flowing through the battery during operation. The resistance between the positive and negative ends of the battery is the sum of the resistance of the collector, the active substance of the electrode, the diaphragm and the electrolyte. A large battery internal resistance reduces the battery discharge voltage and shortens the discharge time. The smaller the value, the better the performance.

13.Shelf/storage life

The time that the battery can be placed under certain parts without load to achieve the performance degradation to a specified degree.

14.Cycle life of lithium ion battery

the cycle life of lithium ion battery can reach thousands

The number of charge and discharge times that can occur when the capacity and other battery performance meet the specified requirements. Lead-acid batteryhave a cycle life of about 300 to 500 cycles, while the cycle life of lithium ion battery can reach thousands.

15.Memory Effect

When the battery in discharge if the capacity is not used up, then after charging the battery, the discharge capacity can only reach the level of the last discharge, any method is impossible to restore its rated capacity. Lithium ion battery have no memory effect. So you don’t have to wait until the battery runs out to charge it.

16.Liquid leakage

It means the leakage of electrolyte from a battery. But that rarely happens with lithium ion battery, which are completely sealed during manufacturing.

17.Short circuit

The state of the internal positive and negative electrode of battery forming electrical path: mainly due to the destruction of the diaphragm mixed with conductive impurities, the formation of dendrites, etc.

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