Lithium-ion rechargeable battery, referred to as lithium-ion battery, is a secondary battery (also called rechargeable battery) widely used in modern electronic equipment. Based on the Reversible Embedding and deembedding process of lithium ions, it realizes the storage and release of energy through the movement of lithium ions between the positive electrode and the negative electrode. This article will introduce in detail the basic working principle, structural composition, charging and discharging process and performance characteristics of lithium ion rechargeable battery.

I. Basic concepts of lithium ion batteries

lithium ion battery is a kind of battery that can be charged and discharged for many times and belongs to the category of secondary battery. Different from the primary battery, the lithium ion battery can be charged by an external power supply during use to restore its stored electric energy, thus realizing recycling. Its core working mechanism is the reversible movement of lithium ion (Li +) between the positive and negative poles of the battery.

The birth of lithium ion battery solves the problems of low energy density, large weight, short life and so on existing in traditional battery, making it an important power source in the fields of consumer electronics, electric vehicles, energy storage systems and so on.

II. Structure and composition of lithium ion battery

lithium Ion battery mainly consists of the following parts:

1. positive electrode (cathode)
   

2. Negative electrode (anode)
   the negative electrode generally adopts carbon materials such as graphite, which can embed lithium ions. During the charging process, lithium ions are removed from the positive electrode, migrated and embedded into the negative electrode; When discharging, lithium ions are removed from the negative electrode and migrated back to the positive electrode.

3. Electrolyte
   electrolyte is a liquid or solid medium that can conduct electricity, usually lithium salt (such as LiPF) dissolved in organic solvent. It provides channels for the migration of lithium ions and prevents electrons from flowing directly through electrolyte to prevent short circuit.

4. Diaphragm
   the diaphragm is a kind of porous membrane, which is located between the positive and negative poles, allowing lithium ions to pass through, but preventing direct contact between the positive and negative poles and avoiding short circuit of the battery.

5. Collector fluid
   the positive and negative electrode materials are coated on the metal foil, which are respectively used as the positive and negative electrode collecting fluid of the battery, and are responsible for the collection and conduction of electrons.

III. Working principle of lithium ion battery

charging process

when the lithium ion battery is connected to an external power source for charging, the external power source pushes the electrons from the positive electrode to the negative electrode. At the same time, lithium ions are disembedded from the positive electrode, migrated to the negative electrode surface through electrolyte and diaphragm, and embedded in the lattice structure (usually graphite interlayer) of the negative electrode material. At this time, the negative electrode stores a large amount of lithium ions and electrons, and the battery is in a high-energy state.

The simplified charging reaction formula can be expressed:

• positive pole: Li **** xCoO **& rarr; Li *** x** & delta;CoO **+ & delta;Li** + & delta;e**
• negative pole: C + & delta;Li's + & delta;e's & rarr; Li & delta;C

discharge process

when the battery supplies power to external devices, lithium ions are de-embedded from the negative electrode, passing through electrolyte and diaphragm, and migrating back to the positive electrode. At the same time, electrons flow along the external circuit, forming current and driving the load to work. Lithium ions are reembedded in the lattice of the positive electrode material to release the stored energy.

the simplified discharge reaction formula is:

• negative pole: Li & delta;C & rarr; C + & delta;Li **+ & delta;e *
• positive pole: Li *** x **& delta;CoO** + & delta;Li **+ & delta;e** & rarr; Li **xCoO *

through the above process, lithium ions are continuously migrated between the two poles to realize the charge and discharge cycle of the battery.

IV, lithium ion battery performance characteristics

1. high energy density
   compared with traditional batteries, lithium-ion batteries have higher energy density, that is, they can store more electric energy per unit weight and volume. This makes lithium-ion batteries very suitable for portable electronic devices and electric vehicles.

2. No memory effect
   many traditional rechargeable batteries have "memory effect", that is, charging without full discharge will reduce the battery capacity. Lithium-ion batteries basically do not have such problems. Users can charge and discharge at any time, making them more flexible to use.

3. low self-discharge rate
   the self-discharge rate of lithium-ion batteries is relatively low, and the power loss is relatively small when they are not used for a long time, thus ensuring the standby time of the equipment.

4. Long cycle life
   under the condition of reasonable use and maintenance, lithium-ion battery can complete hundreds to thousands of charge and discharge cycles with a long life.

5. Lightweight design
   lithium ion battery is light in weight and small in size, which is suitable for equipment design of various sizes and shapes.

6. Wide operating temperature range
   lithium ion battery can work in a wide temperature range. Although extreme high temperature or low temperature will affect the performance and service life, its overall adaptability is better.

V. Safety and management of lithium ion batteries

although lithium-ion batteries have superior performance, their safety problems cannot be ignored. The internal materials of the battery have strong chemical activity. Under abnormal conditions such as overcharge, short circuit, mechanical damage or high temperature, it may lead to thermal runaway, causing combustion or explosion.

Therefore, modern lithium-ion batteries are usually equipped with battery management systems (BMS)., monitor and manage the voltage, current, temperature and other parameters of the battery in real time to prevent overcharge, overdischarge and overtemperature, and ensure the safe and stable operation of the battery.

In addition, the battery design also adopts multiple protection measures, such as safety valve, diaphragm technology, flame retardant electrolyte, etc., to further improve the safety performance of the battery.

VI. Precautions for charging and discharging lithium ion batteries

in order to prolong the service life of lithium ion batteries and ensure safety, users should pay attention to the following points during use:

1. avoid overcharging and overdischarging
   overcharging will cause the internal pressure of the battery to rise, and overdischarging will damage the active material of the battery, which will shorten the battery life.

2. Avoid high temperature environment
   high temperature accelerates battery aging and even causes safety accidents. Storage and use should try to avoid exposure and high temperature environment.

3. Use a matching charger
   use original or standard charging equipment to avoid current instability or abnormal voltage.

4. Prevent mechanical damage
   

5. Avoid idle for a long time
   when not in use for a long time, it is recommended to keep the battery power between 30% and 50% to avoid full discharge.

Lithium-ion rechargeable battery is a secondary battery that relies on the Reversible Embedding and disembedding of lithium ions between positive and negative electrodes to realize energy storage and release. Its light, efficient, long service life and low self-discharge rate make it the preferred power supply for modern electronic equipment and electric vehicles. Through reasonable management and use, lithium-ion batteries can provide lasting power for our life and work safely and stably.