Detailed explanation of the basic principles of lithium batteries

The core working logic of lithium batteries is to achieve reversible conversion of chemical energy and electrical energy through the directional migration of lithium ions between the positive and negative electrodes. This process of "ion shuttle" may seem simple, but it contains intricate principles of materials science and electrochemistry. ​

Core composition and role division

The basic structure of a lithium battery includes four core components: positive electrode, negative electrode, electrolyte, and separator

Positive electrode: usually composed of compounds containing lithium (such as lithium cobalt oxide, lithium iron phosphate, etc.), it is a "temporary warehouse" for lithium ions, releasing them during discharge and storing them during charging. ​

Negative electrode: The mainstream material is graphite (some new batteries use silicon-based materials), and its layered structure can adsorb lithium ions like a sponge, forming stable embedded compounds. ​

Electrolyte: It is mostly an organic solution or solid electrolyte, which provides a migration channel for lithium ions and isolates electrons (preventing short circuits). ​

Diaphragm: A porous film that allows lithium ions to pass through but prevents electrons from crossing, ensuring that only ion exchange occurs between the positive and negative electrodes rather than direct electron flow. ​

Energy conversion during discharge

When the battery supplies power to the device, the entire system functions like a precision collaborative 'energy factory':

The lithium atom (Li) at the negative electrode loses electrons (e ⁻) and becomes a positively charged lithium ion (Li ⁺)

Electrons flow to the positive electrode through an external circuit, forming a current to drive the operation of devices (such as lighting up a phone screen or driving a motor to rotate)

Lithium ions move towards the positive electrode through the micropores of the separator via the electrolyte solution

At the positive electrode, lithium ions combine with electrons and positive electrode materials to complete the "embedding" process, converting chemical energy into electrical energy

During this process, the crystal structure of the positive and negative electrode materials will undergo slight expansion (especially the negative electrode graphite), but high-quality materials can restore their original state through their own elasticity, ensuring cycling stability. ​

The reverse process during charging

When charging from an external power source, the entire reaction proceeds in reverse:

The voltage provided by the power supply forces electrons to flow from the positive electrode to the negative electrode

Lithium ions in the positive electrode material are "squeezed out" (deintercalation process) and re-enter the electrolyte

Lithium ions cross the separator again, return to the negative electrode and obtain electrons, reducing to lithium atoms embedded in the graphite layer

Electricity is converted into chemical energy and stored until it is released during the next discharge

It is worth noting that the migration speed of lithium ions during the charging process is closely related to the current intensity: during high current fast charging, if lithium ions do not have time to embed into the negative electrode, metal lithium dendrites may precipitate on the surface, which not only consumes active lithium, but also may puncture the separator and cause short-circuit hazards - this is also the core reason why advanced battery management systems (BMS) are needed to regulate fast charging technology. ​

This working principle based on lithium ion migration enables lithium batteries to have high voltage (cell voltage 3.2-4.2V, far exceeding the 1.2V of nickel hydrogen batteries) and high energy density characteristics, while avoiding the problem of metal lithium dendrite growth in traditional batteries (a fatal defect of early lithium metal batteries), laying the foundation for commercial applications.