18650 VS polymer battery: how to avoid the "minefield" of battery selection

As for those who are not familiar with lithium ion batteries, 18650 lithium batteries and lithium polymer battery are more common. Many businessmen will praise their polymer battery in advertising, and describe the disadvantages of 18650 battery.

One issue: confusion of cell types

Basic is same, different types of battery principle 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 battery fool, lithium iron batteries (this is a factory with independent intellectual property rights of iron battery).

Widely refer 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?

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 50000 mAh charging treasure, is likely to be fool people, even more exasperating 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 current voltage to charge is likely to cause the battery heat explosion, lu: su flexible packaging of this was also true of lithium polymer batteries.

Only 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 * 0.91 = 10000 mAh * 0.74 * 0.91 = 6734 mAh (including C said 5 v output capacity effectively, 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).

Issue # 3: rate knowledge blind area of the battery

Lithium battery discharge rate, we usually use the letter "C", 1 C, said the biggest battery discharge, the discharge current for 1 times, for example: 10 C 1 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 to 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 prevents 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.

The page contains the contents of the machine translation.