Lithium polymer batteries">Lithium polymer batteries generally refer to lithium polymer batteries, also known as lithium polymer batteries, is a chemical nature of the battery. Compared to the previous battery, it has the characteristics of high energy, miniaturization and light weight.
A lithium polymer battery is a battery system that uses polymer materials in at least one or more of the three elements. In lithium polymer battery systems, most of the polymers are used in the cathode and electrolyte. The cathode material is a conductive polymer or inorganic compound used in lithium-ion batteries">lithium-ion batteries, the cathode is often a lithium metal or lithium-carbon interlayer compound, and the electrolyte is a solid or colloidal polymer electrolyte or organic electrolyte. Lithium polymer is more reliable and stable because there is no excess electrolyte in it.
How lithium polymer batteries work
A, lithium-ion battery cell components are as follows.
(1) positive electrode - the active material is generally lithium manganate or lithium cobaltate, lithium nickel cobalt manganate materials, electric bicycles are commonly used lithium nickel cobalt manganate (commonly known as ternary) or ternary + a small amount of lithium manganate, pure lithium manganate and lithium iron phosphate is gradually fading out due to the large size, poor performance or high cost. Conductive electrode fluid using electrolytic aluminum foil with a thickness of 10 - 20 microns.
(2) diaphragm - a specially formed polymer film, the film has a microporous structure, allowing lithium ions to pass freely, while electrons can not pass.
(3) Negative electrode - the active material is graphite, or carbon with a structure similar to graphite, and the conductive collector uses electrolytic copper foil with a thickness of 7-15 microns.
(4) organic electrolyte - dissolved lithium hexafluorophosphate carbonate solvent, polymer use gel electrolyte.
(5) battery shell - divided into steel shell (square type rarely used), aluminum shell, nickel-plated iron shell (cylindrical battery use), aluminum plastic film (soft packaging), etc., and the battery's cap, but also the positive and negative lead ends of the battery.
Second, the working principle of lithium batteries
The following from the lithium battery charging process, the discharge process and battery protection plate three major parts to introduce its working principle:.
1, lithium battery charging process
Lithium battery working principle
The positive electrode of the battery is generated by lithium ions, generated lithium ions from the positive electrode "jump" into the electrolyte, through the electrolyte "crawl" through the small curved hole in the diaphragm, the movement to the negative electrode, and long ago through the external circuit to the negative electrode of electrons combined together. The reaction on the positive electrode is: LiCoO2==Charging==Li1-xCoO2+Xli++Xe(electron) ●The reaction on the negative electrode is: 6C+XLi++Xe=====LixC6In the process of charging, Li+ comes out of the positive electrode LiCoO2, enters the electrolyte, moves to the negative electrode under the action of the external electric field attached to the charger, and enters the negative electrode composed of graphite or coke C in turn. 2. Li-ion battery discharge process
When discharging, electrons and Li+ both act at the same time, in the same direction but on different paths. Li+ "swims" from the negative electrode to the positive electrode, "crawling" through the curved holes in the diaphragm, and "swimming" to the positive electrode, where it combines with the electrons that have long run over. What we usually call the battery capacity refers to the discharge capacity.
There are two types of lithium-ion batteries: liquid lithium-ion batteries (LIB) and lithium polymer batteries (PLIB). Among them, the liquid lithium-ion battery refers to the secondary battery with Li+ embedded compound as the positive and negative electrodes. The positive electrode is LiCoO2, LiNiO2 or LiMn2O4, and the negative electrode is Li-carbon interlayer compound LixC6, and the typical battery system is:
(-)C|LiPF6-EC+DEC|LiCoO2(+)
Anode reaction:LiCoO2=Li1-xCoO2+xLi++xe-
Negative reaction:6C+xLi++xe-=LixC6
Total cell reaction:LiCoO2+6C=Li1-xCoO2+LixC6
The principle of lithium polymer battery is the same as that of liquid lithium, the main difference is that the electrolyte is different from that of liquid lithium. The main structure of the battery consists of three elements: positive electrode, negative electrode and electrolyte. A lithium polymer battery is one that uses at least one or more of these three main structures as the main battery system. In the developed Li-polymer battery system, the polymer materials are mainly used in the anode and electrolyte.
The cathode materials include conductive polymers or inorganic compounds used in general lithium-ion batteries, while the electrolytes can be solid or colloidal polymer electrolytes or organic electrolytes.
3、Battery protection plate
As the name suggests, the battery protection board is mainly for rechargeable batteries (generally refers to lithium batteries) to play a protective role of the integrated circuit board. Lithium batteries (rechargeable) need protection because the lithium battery itself is determined by the material it can not be overcharged, overdischarged, overcurrent, short-circuit and ultra-high temperature charging and discharging, so lithium batteries will always have a protection board and a current fuse. The following figure shows the battery board protection circuit. PTC: positive temperature coefficient thermistor; NTC: negative temperature coefficient thermistor, when the ambient temperature rises, its resistance value decreases, the use of electrical equipment or charging equipment can respond in time to control the internal interruption and stop charging and discharging; U1 is the circuit protection chip, U2 for the two reversed MOSFET switch. The normal state of the battery board U1 CO and DO are output high voltage, the two MOSFETs are open, the battery can be charged and discharged freely.
Charge protection simplified schematic
Overcharge protection: When U1 detects that the battery voltage reaches the overcharge protection threshold, the CO pin outputs a low level, the MOS switch 2 turns from on to off, the charging circuit is shut down, and the charger can no longer charge the battery, thus achieving overcharge protection.
Over-discharge protection: In the process of battery discharge, when U1 detects that the battery voltage is lower than the over-discharge protection threshold, the DO pin changes from high level to low level and MOS switch 1 turns off, so that the battery cannot be discharged again; the battery voltage cannot be lowered again in the over-discharge protection state, requiring the protection circuit to be extremely low current and the control circuit to enter low power consumption. Over-current protection: Under normal conditions, the battery discharges to the load, the current passes through two series-connected MOS tube switches, and the VM pin detects the voltage drop of the two MOS tubes as U. If the load causes U to be abnormal for some reason, the circuit current increases, and when U is greater than a certain value, the DO pin changes from high to low voltage, and MOS switch 1 turns off, thus making the discharge circuit current zero and achieving over The current protection function.
Our daily use of cell phones and notebook batteries are actually lithium-ion batteries, lithium batteries are divided into lithium batteries and lithium-ion batteries, but we are commonly known as lithium batteries. The real lithium battery is rarely used in everyday electronic products due to the high risk of danger. Today's detailed explanation of the working principle and structure of lithium batteries, so that we can understand the full range of lithium batteries.
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