Lithium-ion Battery Introduction

- May 10, 2018-

Lithium-ion battery: It is a secondary battery (rechargeable battery), which mainly depends on the movement of lithium ions between positive and negative electrodes. During the charge and discharge process, Li+ intercalates and deintercalates between the two electrodes: During charging, Li+ is deintercalated from the positive electrode, and the negative electrode is in the lithium-rich state through the electrolyte; the opposite occurs during discharge.

(1) Positive electrode: The active material is usually lithium manganate or lithium cobaltate, lithium nickel-cobalt-manganese oxide material, and lithium-nickel-cobalt-manganate (commonly known as ternary) or ternary + small amount of lithium manganate is commonly used for electric bicycles. Lithium manganate and lithium iron phosphate gradually fade out due to their bulkiness, poor performance, or high cost. The lead electrode fluid uses an electrolytic aluminum foil having a thickness of 10 to 20 μm.

(2) Separator - a specially formed polymer film, the film has a microporous structure, allowing free passage of lithium ions, and electrons can not pass.

(3) Anode: The active material is graphite, or graphite-like carbon, and the conductive current collector uses an electrolytic copper foil having a thickness of 7-15 μm.

(4) Organic Electrolyte - A carbonate solvent in which lithium hexafluorophosphate is dissolved, and a gel-like electrolyte is used in the polymer.

(5) The battery case - is divided into steel (rarely used square), aluminum shell, nickel plated iron shell (cylindrical battery use), aluminum plastic film (flexible packaging), etc., as well as the battery cap, but also the positive battery Negative lead terminal.


Lithium-ion battery operating principle

Lithium-ion batteries use a carbon material as a negative electrode and a lithium-containing compound as a positive electrode. There is no metallic lithium, and only lithium ions exist. This is a lithium-ion battery. A lithium ion battery is a generic name for a battery that uses a lithium ion intercalation compound as a positive electrode material. Lithium-ion battery charge and discharge process, is the insertion and removal of lithium ions. In the process of intercalation and deintercalation of lithium ions, it is accompanied by the embedding and deintercalation of equivalent electrons with lithium ions (it is customary that the positive electrode is represented by embedding or deintercalating and the negative electrode is inserted or unplugged). During the charging and discharging process, lithium ions are inserted/removed from/inserted into/out/inserted between the positive and negative electrodes, and are vividly referred to as “rocking chair batteries”.

When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as a negative electrode has a layered structure, and it has many micropores. Lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions are embedded, the higher the charging capacity. Similarly, when the battery is discharged (ie, we use the battery), the lithium ions embedded in the carbon layer of the negative electrode escape and move back to the positive electrode. The more lithium ions returning to the positive electrode, the higher the discharge capacity.

The general lithium battery charging current is set between 0.2C and 1C, the greater the current, the faster the charging, and the greater the battery heat. Moreover, excessive current charging does not allow full capacity because the electrochemical reaction inside the battery takes time. Just like pouring beer, if you pour it too quickly, you will get a bubble and you will not be full.


              Lithium-ion battery advantages

1) High voltage

The working voltage of the single cell battery is as high as 3.7-3.8V (3.2V for lithium iron phosphate), which is three times that of the Ni-Cd and Ni-MH batteries.

2) Larger than the energy

The actual specific energy that can be achieved is about 555Wh/kg, that is, the material can reach a specific capacity of 150mAh/g or more (3 - 4 times Ni-Cd, 2 - 3 times Ni-MH), which is close to its theory. About 88% of the value.

3) long cycle life

Generally can reach more than 500 times, or even more than 1000 times, lithium iron phosphate can reach more than 2,000 times. For small-current discharge appliances, the battery life will double the competitiveness of the appliance.

4) Good safety performance

No pollution, no memory effect. As Li-ion's predecessor lithium battery, due to the easy formation of dendrite metal lithium short circuit, reducing its application areas: Li-ion does not contain cadmium, lead, mercury and other elements that are environmentally polluting: some processes (such as sintered The major drawback of Ni-Cd batteries is the "memory effect", which severely restricts the use of batteries, but Li-ion does not have this problem at all.

5) Small self-discharge

The self-discharge rate of Li-ion charged at room temperature after 1 month storage is about 2%, which is much lower than 25-30% of Ni-Cd and 30-35% of Ni-MH.

6) Fast charge

The 1C charge can reach 80% of the nominal capacity for 30 minutes, and the phosphor-iron battery can reach 90% of the nominal capacity for 10 minutes.

7) Working temperature

Operating temperature is -25~45°C. With the improvement of electrolyte and positive electrode, it is expected to widen to -40~70°C.


Lithium-ion battery disadvantages


Unlike other rechargeable batteries, the capacity of lithium-ion batteries will slowly degrade, depending on the number of uses, but also with temperature. This phenomenon of decline can be expressed in terms of reduced capacity, or it can be expressed in terms of increased internal resistance.

Recovery rate

About 1% of new products from the factory need to be recycled for various reasons.

Not tolerate overcharge

When overcharged, excessively embedded lithium ions are permanently fixed in the crystal lattice and cannot be released, resulting in a short battery life.


During overdischarge, excessive lithium ions are desorbed from the electrode, which can cause the lattice to collapse and shorten the lifetime.



Lithium metal battery

Lithium batteries are a kind of energy storage batteries using metal lithium as the electrode. Their specific energy is very high. They were divided into disposable batteries and rechargeable lithium batteries in the early days. However, after accidents occurred in rechargeable lithium batteries, they are rarely seen in the civilian market. Rechargeable lithium battery. Lithium-ion rechargeable batteries actually utilize the difference in the concentration of lithium ions for energy storage and discharge, and there is no lithium metal in the battery.

Lithium metal batteries with the same principle as ordinary dry batteries, it is the use of metal lithium as an electrode, through the corrosion of metal lithium or called oxidation to generate electricity, run out of waste, can not be charged.

Difference between lithium metal battery and lithium ion battery

The main difference is that the lithium metal battery is a disposable battery, and the lithium ion battery is a rechargeable battery! Lithium metal battery is the same as the principle of ordinary dry battery. It uses metal lithium as the electrode, and generates electricity by the corrosion or oxidation of metal lithium. When it is used up, it is wasted and cannot be charged; Lithium-ion battery is usually made of lithium cobaltate as the positive electrode. Carbon is used as a negative electrode, an electrolyte is filled in the middle to form an ion-free channel, and a separator is used to separate the positive and negative electrodes from short circuit. When charging, lithium ions leaching from the lithium cobalt oxide due to the electric field, free to pass through the pores in the separator in the electro-hydraulic, and reach the negative electrode to react with carbon to form lithium carbide; on the contrary, the discharge process returns the lithium ion to the positive electrode. Lithium-ion battery charge and discharge process.