Summary of 18650 Lithium ion Battery Knowledge.
Summary of Lithium ion Battery Knowledge: Lithium ion battery manufacturers will introduce the basic knowledge of lithium-ion to students. Lithium ion batteries are developed from lithium batteries. So before getting to know lithium-ion batteries, let's first introduce them.
The main components of lithium-ion batteries
(1) Battery cover
(2) Positive electrode - active material is lithium cobalt oxide
(3) Diaphragm - a special composite membrane
(4) Negative electrode - active material is carbon
(5) Organic electrolyte
(6) Battery case
The superior performance of lithium-ion batteries
The superiority of lithium-ion batteries that we often talk about is related to traditional nickel cadmium batteries (Ni/Cd) and nickel hydrogen batteries (Ni/MH). So, what are the advantages of lithium-ion batteries?
(1) High working voltage
(2) Greater than energy
(3) Long cycle life
(4) Low self discharge rate
(5) No memory effect
(6) No pollution
The following is a comparison of the performance of nickel cadmium, nickel hydrogen, and lithium-ion batteries:
Technical parameters: Nickel cadmium battery, nickel hydrogen battery, lithium-ion battery
Working voltage (V) 1.21.23.6
Weight specific energy (Wh/Kg) 5065105-140
Volume specific energy (Wh/l) 150200300
Charge and discharge life (times) 5005001000
Self discharge rate (%/month) 25-3030-356-9
Is there a memory effect? Yes No
Whether there is pollution or not
(Note: The charging rate is all 1C)
The working principle of lithium-ion batteries
As we all know, the positive electrode material of lithium-ion batteries is lithium cobalt oxide, and the negative electrode is carbon.
The working principle of lithium-ion batteries refers to their charging and discharging principles. When charging the battery, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move through the electrolyte to the negative electrode. As the negative electrode, carbon has a layered structure with many micropores. Lithium ions that reach the negative electrode are embedded into the micropores of the carbon layer. The more lithium ions embedded, the higher the charging capacity.
Similarly, when discharging the battery (i.e. the process of using the battery), the lithium ions embedded in the negative carbon layer are released and move back to the positive electrode. The more lithium ions return to the positive electrode, the higher the discharge capacity. The battery capacity we usually refer to is the discharge capacity.
It is not difficult to see that during the charging and discharging process of lithium-ion batteries, lithium ions move from the positive electrode to the negative electrode and then to the positive electrode. If we metaphorically compare lithium-ion batteries to a rocking chair, where the two ends of the rocking chair are the two poles of the battery, and lithium-ion batteries are like excellent athletes running back and forth between the two ends of the rocking chair. So, experts have given lithium-ion batteries a cute name - rocking chair batteries.
The assembly process of lithium-ion batteries
The process technology of lithium-ion batteries is very strict and complex, and here we can only briefly introduce a few of the main processes.
1. Pulping: Mix specialized solvents and adhesives with powdered positive and negative electrode active substances, stir evenly at high speed, and make a paste like positive and negative electrode substance.
2. Coating: Apply the prepared slurry evenly on the surface of the metal foil, dry it, and make positive and negative electrode pieces separately.
3. Assembly: Place the positive electrode sheet, separator, negative electrode sheet, and separator in the order from top to bottom, roll them up to make the battery core, and then complete the assembly of the battery through processes such as electrolyte injection and sealing to produce the finished battery.
4. Chemical conversion: Use specialized battery charging and discharging equipment to conduct charging and discharging tests on finished batteries, inspect each battery, screen out qualified finished batteries, and wait for delivery.
Safety characteristics of lithium-ion batteries
Lithium ion batteries have been widely used in people's daily lives, so their safety performance should definitely be the first assessment indicator for lithium-ion batteries. There are very strict international standards for assessing the safety performance of lithium-ion batteries, and a qualified lithium-ion battery should meet the following conditions in terms of safety performance.
(1) Short circuit: no fire, no explosion
(2) Overcharging: No fire, no explosion
(3) Hot box test: No fire, no explosion (150 ℃ constant temperature for 10 minutes)
(4) Needle puncture: Non explosive (use a 3mm nail to penetrate the battery)
(5) Flat impact: No fire, no explosion (10kg heavy object hits battery from a height of 1M)
(6) Burning: Non explosive (gas flame barbecue battery)
How are the safety characteristics of lithium-ion batteries achieved?
In order to ensure the safe and reliable use of lithium-ion batteries, experts have conducted very strict and meticulous battery safety design to achieve battery safety assessment indicators.
(1) Diaphragm 135 ℃ automatic shutdown protection
Adopting internationally advanced Celgard2300PE-PP-PE three-layer composite film. When the battery temperature reaches 120 ℃, the PE film holes on both sides of the composite film close, the internal resistance of the battery increases, and the internal temperature of the battery slows down. When the battery temperature reaches 135 ℃, the PP film holes close, the internal circuit of the battery breaks, and the battery no longer heats up, ensuring the safety and reliability of the battery.
(2) Add additives to the electro-hydraulic system
When the battery is overcharged and the voltage is higher than 4.2V, the electrolyte additives aggregate with other substances in the electrolyte, causing a significant increase in the internal resistance of the battery. This results in a large area of open circuit inside the battery, and the battery no longer heats up.
(3) Composite structure of battery cover
The battery cover adopts a scratch explosion-proof structure. When the battery is heated up, some of the gas generated during the activation process inside the battery expands, and the internal pressure of the battery increases. When the pressure reaches a certain level, the scratch ruptures and deflates.
(4) Various environmental abuse tests
Conduct various abuse tests, such as external short circuit, overcharge, needle puncture, flat plate impact, incineration, etc., to investigate the safety performance of the battery. Simultaneously conduct temperature shock tests and mechanical performance tests such as vibration, drop, and impact on the battery to investigate its performance in actual usage environments.
Lithium ion battery is a new type of green and environmentally friendly battery
Caring for the environment and protecting the earth is an unshirkable responsibility for each and every one of us. How can we reflect our environmental philosophy in action?
As battery consumers, we should purchase and use new green and environmentally friendly batteries; As a battery manufacturer, we should produce new green and environmentally friendly batteries. Only through the joint efforts of everyone can we create and protect our beautiful and harmonious natural environment.
New green and environmentally friendly batteries refer to a type of high-performance, pollution-free battery that has been put into use or is currently under development in recent years. The lithium-ion batteries, nickel metal hydride batteries, mercury free alkaline zinc manganese batteries that are currently widely used, as well as lithium or lithium-ion plastic batteries, fuel cells, and electrochemical energy storage supercapacitors that are being developed and researched, all belong to the category of new green and environmentally friendly batteries. In addition, the widely used solar cells that utilize solar energy for photovoltaic conversion (also known as photovoltaic power generation) also belong to this category.
