How Much You Know 18650 Battery And Li-polymer Battery ?

- Mar 04, 2017-

lipo battery.jpg

From left to right, respectively, for standard 18650 lithium batteries, Al compound packing film for  lithium ion battery, and RC lithium ion batteries used for emergency power.



 3.7 V / 5000 mah soft package polymer    power: 10.5 Wh

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3575175means battery size:3.5mmX75mmX175mm

3200mah  battery.jpg

voltage:11.1V 3pcs 3.7v battery cell series packed

One issue: confusion of cell types

For lithium ion battery technology principle unfamiliar readers, 18650 lithium-ion batteries and lithium polymer battery estimate is to listen to at most two words, many businessmen in advertising their products will praise god polymer battery, 18650 battery on the ground, it is not too serious.

In fact, the principle of different types of cells are basically the same, has the positive and negative, and the electrolyte, the current mainstream single lithium batteries nominal voltage is 3.7 V, commonly the anode materials are generally cobalt acid lithium cobalt, nickel manganese acid lithium (also called ternary material), manganese acid lithium or lithium iron phosphate, etc., general for graphite anode materials, electrolyte is six lithium fluoride phosphate solution in general.Industry often use lithium batteries battery model to identify the overall size, lithium battery can be divided into several types according to different rules, such as voltage distinguish standard of high-pressure lithium batteries, lithium batteries, battery discharge ratio distinguishing them (maximum 1 c discharge), the ratio of batteries (greater than 1 c discharge), and according to the positive electrode material to distinguish pure cobalt acid lithium batteries, the ternary lithium batteries, lithium iron batteries (that is, a factory fool with independent intellectual property rights of iron battery).Widely referred to lithium ion batteries to distinguish between the shell encapsulating material according to more, such as represented by 18650 steel shell encapsulation and early phone battery with aluminum shell encapsulation.The mainstream is lu: su composite film packaging of the lithium ion battery, we call it a lithium polymer battery or flexible packaging. 

To identify equipment used by the battery is not difficult, 18650 battery 18 mm diameter thickness to the thickness of the product specification must be greater than 18 mm, longer than 65 mm.But 18650 lower cost decided to its market share, so I hope cheap can choose 18650, hope thin might as well choose lithium-polymer battery.

The capacity of issue # 2: there is no moral integrity
Don't know when to start, many people are always in great beauty, feel the battery capacity is higher, the better, but there really is such a large capacity of the battery?Above 18650 batteries, import brands so far only 18650 product capacity production can achieve the maximum capacity of 4100 mah, domestic general is hovering around 2600 mah.According to the current common with a total capacity of 20000 mah, for example, if the use of imported products is also need 5 parallel technology together, not to mention the domestic products of more series-parallel.Small light and portable, easily 30000 mah, 50000 mah charging treasure, a see will know that is disarming, more can spirit is to mislead consumers with product model, such as 50000 m charging treasure, buy back just know, original 50000 m is the product model, rather than charging capacity. 

18650 battery series parallel combination consistency have high requirements for the battery itself, if a single battery internal problems, such as one of the batteries in the battery pack is low voltage, then certainly will drag down the whole battery voltage value and increase resistance, if still use the original battery by current voltage is likely to cause the battery heat explosion, lu: su flexible packaging of lithium polymer battery this is true, but relatively steel shell encapsulation 18650 li-ion battery, lithium polymer battery will not explode, but inevitably occur.So the product labeling of the battery capacity is not the bigger the better.

In addition, even in conformity with the capacity of annotation, but in fact can provide power is how many?In order to more intuitive on this issue, we take the emergency start Cousins, the power of the charging treasure to grasp.Battery capacity represents itself, battery can provide power, just like pool, the bigger the pool to save the water, the greater the charge and discharge process is like a pool of water storage and water process, must want to have pressure difference to form water.For 3.7 V battery, will not filling with 3.7 V voltage, it need higher voltage.With 10000 mah charging treasure on the market for internal use standard is 3.7 V voltage of the battery, when the need for the same built-in 3.7 V battery charging device (currently the vast majority of batteries with lithium battery equipment are the same 3.7 voltage), must step up to 5 V (except USB interface standard voltage, USB - C), with the "clamp" rise of the battery in the transformation the conversion rate of 91% (this is a good battery), actually charging treasure output power provided by the following formula:

C = C1 * (5) present 3.7 * 3.7 = 10000 mah * 0.74 * 0.91 = 6734 mah
Effective output capacity (including C said 5 v, C1) represents the battery capacity

That is to say, the nominal capacity of 10000 mah battery charging treasure, charging treasure can provide output in the practical use of electricity, according to the optimal calculation and only 6700 mah, later don't be fool, conscience, merchants will be on the product label and identify the effective output capacity of the battery capacity (the actual usable capacity).


discharge current for 1 times

Example: a 10 c 1000 mah lithium batteries, said 10 times the maximum discharge current for the battery, is the largest discharge current: 10 x 1000 ma = 10 a. 

Usually we say 1 c discharge lithium battery is a standard battery, 2 c - 10 c for small ratio of battery discharge, more than 10 c for high rate batteries. 

Ratio of batteries and the traditional standard cell main difference is that the different craft, standard cells and small ratio of batteries with extremely winding process, that quick starting power supply using high rate battery its internal plate is made by the lamination process, it also provides a simple and easy to distinguish indirect method, winding technology on both sides of the battery will be slightly thick, flatness is a bit poor, and lamination process the ratio of the battery is fairly flat founder.As the ratio of batteries is in order to meet the demanding large current discharge requirements, it adopted the thicker sheet, the thicker lithium ion separation membrane, the same volume, capacity will be slightly reduced, but relative to the safety, small capacity of sacrifice is not of the word. 

With charging treasure as emergency launch power, the biggest difference is that the emergency start power is the need for instantaneous large current discharge, ignition start-up for vehicle starting motor, which need to use "ratio" battery as power, general good big ratio battery 35 c - 40 c discharge, the traditional standard cell is not qualified for this job, if the "dirty" businessman with a standard battery to provide power for emergency start power products, life doesn't grow, instantaneous large-current discharge breakdown lithium ion separation membrane, extremely easy to light several times is used, or fever burned on the spot. 

Issue 4: "optional" protection circuit
In lithium ion battery or lithium battery in use process, in order to avoid the user error caused by the operation of the battery, the battery with the decomposition of the electrolyte in the produced gas pressure rises, make its cause caused a fire and precipitation of metal lithium batteries the risk of rupture, and over discharge, degrade battery features a variety of reasons, such as in the lithium ion battery circuit and protection circuit must be used.The protection of lithium ion rechargeable batteries, must have the following four protection function, to ensure the safety and reliability of the battery.Overcharge protection, prevent over the battery charge limits when the battery voltage, battery overcharge, easy to cause the characteristics of battery degradation, fire and break, to ensure safety.Put protection, prevent over the battery discharge limits when the battery discharge voltage, the battery discharge, led directly to the battery internal electrochemical performance degradation, light affect the service life of the battery, or dead batteries.Overcurrent protection to prevent the destruction of the MOSFET, lets batteries are able to withstand the maximum charging current value of the security charge.Short circuit protection, prevent due to careless operation, will directly is the cathode conduction, battery caused by the fire explosion etc, to ensure safety when using and handling.So for fake emergency start power products would be tantamount to murder the non-existing of protection circuit, especially the emergency start power by using the ratio of the battery, the protection circuit of fraud about 3-5% cost of product, but only from the appearance is don't see any protection circuit, can only by merchants conscience, so try to choose and buy the big brands.

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