How much do you know about lithium batteries?

For readers who are not familiar with the principles of lithium-ion battery technology, they may be familiar with the words: 18650 lithium battery and lithium polymer battery. Many merchants will praise the polymer battery when they promote their own products but lower the 18650 battery, it is not rigorous.

One of the tricky: confused battery type

The principle of different types of batteries is basically the same, with positive electrode, negative electrode and electrolyte. At present, the nominal voltage of single-phase lithium battery is generally 3.7V, and the positive electrode material is generally lithium cobalt oxide and lithium nickel cobalt manganese oxide (also called three). Element material), lithium iron phosphate or lithium manganate, etc., the anode material is generally graphite, and the electrolyte is generally a lithium hexafluorophosphate solution.

The industry usually uses the size of the lithium battery to identify the battery model. Lithium batteries can be divided into various types according to different rules: high voltage lithium batteries with voltage distinction, standard voltage lithium batteries, standard batteries with different discharge rates (maximum 1C discharge), Rate battery (greater than 1C discharge), as well as pure lithium cobalt oxide battery, ternary lithium battery , lithium- iron battery (which is a factory-floating iron battery with independent intellectual property rights).

Lithium-ion batteries, which are widely mentioned, are distinguished by the material of the package, such as the steel case package represented by 18650 and the early cell phone battery packaged in aluminum case. The mainstream is the lithium-ion battery packaged in aluminum-plastic composite film, which we call lithium polymer battery or soft-package battery.

It is not difficult to identify the battery used in the device. The 18mm battery has a diameter of 18mm, and the thickness of the product specification is necessarily greater than 18mm and longer than 65mm. However, the lower cost of the 18650 determines its market share, so it is hoped that the 18650 can be chosen at a low price.

Tricky 2: no capacity marking

I don't know when to start, many people are always beautiful, I think the higher the battery capacity, the better, but is there really such a large capacity battery?

According to the total capacity currently marked, taking 20000mAh as an example, even if you use imported products, you need 5 parallel processes, let alone more series and parallels of domestic products.

Small and light and portable, it can be 50,000mAh charging treasure, it is likely to be bluffing people, even more irritating is to use product models to mislead consumers, such as 50000M charging treasure, buy back to know, the original 50000M is the product model, and Not charging treasure capacity.

The series-parallel combination of 18650 batteries has high requirements for the consistency of the battery itself. If there is a problem inside a single battery, such as one of the battery packs, the voltage of the battery pack will lower the voltage value of the whole battery and increase the internal resistance. If the original current and voltage are still used for charging, it is very likely to cause the battery to explode and explode. This is also the case with lithium-polymer batteries in aluminum-plastic flexible packaging.

The lithium polymer battery does not explode, but inevitably burns, compared to the 18650 lithium battery packaged in a steel case. Therefore, the battery capacity marked by the product is not as large as possible.

In addition, even if it meets the capacity labeling, how much power can actually be provided? In order to explain this trick more intuitively, we took the close relatives of the emergency power supply - charging treasure.

The capacity of the battery represents the amount of electricity that the battery itself can provide. Just like the pool, the larger the pool, the greater the amount of water stored. The process of charging and discharging is like the process of water storage and discharge in the pool. There must be a pressure difference to form a water flow. To charge a 3.7V battery, it is definitely not possible to charge 3.7V, which requires a higher voltage.

The 10000mAh charging treasure on the market uses a standard voltage battery of 3.7V. When it is necessary to charge the same 3.7V battery (the device battery that uses most lithium batteries is the same 3.7 voltage). Must be boosted to 5V (USB interface standard voltage, except USB-C), the conversion rate of the battery with the "boost board" conversion is 91% (this is still a good battery), in fact, the charging treasure output can The power provided is as follows:

C=C1×(3.7÷5)×0.91=10000mAh×0.74×0.91=6734mAh

(Where C is the 5V effective output capacity and C1 is the battery capacity)

In other words, the charging battery of the nominal 10000mAh capacity battery, in the actual use of the charging treasure can provide the output of the power, according to the optimal calculation is only 6700mAh, then do not be fooled, conscience merchants will mark the battery capacity on the product Also mark the effective output capacity (actual usable capacity).

Catty 3: The blind spot of the rate battery

The discharge rate of lithium battery is generally expressed by the letter 'C'. 1C means that the maximum discharge current of the battery is 1 times discharge. For example, a 1000Ch 10C lithium battery indicates that the maximum discharge current of the battery is 10 times. Then its maximum discharge current is: 10 × 1000 MA = 10A.

Generally speaking, the lithium battery of 1C discharge is a standard battery. The 2C-10C discharge is a small rate battery, and the high frequency rate battery exceeding 10C.

The main difference between the rate battery and the traditional standard battery is that the manufacturing process is different. The standard battery and the small rate battery are mostly made by the pole piece winding process, and the high-rate battery used for the emergency power supply is used for the internal pole piece. The process of lamination is indirectly provided by a simple resolution method. The battery of the winding process will be slightly thicker on both sides, and the flatness is slightly worse, while the lamination process of the lamination process is quite flat.

Because the rate battery is designed to meet the demanding requirements of high current discharge, it uses a thicker pole piece and a thicker lithium ion isolation membrane. The same volume and capacity will be slightly reduced, but sacrificed relative to safety. The small capacity is not enough.

As the emergency starting power supply, the biggest difference with the charging treasure is that the emergency starting power supply needs an instantaneous large current discharge for the vehicle to start the motor for ignition start. At this time, it is necessary to use the "magnification battery" as the power, generally better. Large-magnification batteries use 35C-40C rate discharge, traditional standard batteries may not be able to do the job. If black-hearted merchants use standard batteries to provide power for emergency start-up power products, life expectancy will not be long, and instantaneous high-current discharge is extremely easy to break down. The lithium ion isolation membrane is lightly used for a few times, and the heat is burned on the spot.

The tricky four: "with or without" protection circuit

In the process of using a lithium ion battery or a lithium battery pack, in order to avoid the user's erroneous operation, the battery is heated up, and the electrolyte in the battery is decomposed to generate a gas to increase the internal pressure, which causes precipitation of metal lithium or the like and causes a fire. The protection circuit is evenly used in the lithium-ion battery circuit for various reasons such as the risk of battery rupture and the deterioration of battery characteristics due to over-discharge.

For the protection of lithium-ion rechargeable batteries, the following four protection functions must be available to ensure the safety and reliability of the battery.

Overcharge protection prevents the battery from charging beyond the battery's charge limit voltage. The battery is overcharged, which can easily lead to deterioration of battery characteristics, fire and breakage, and ensure safety.

Over-discharge protection prevents the battery from discharging when the battery discharges. The battery is over-discharged, which directly causes the internal electrochemical performance of the battery to deteriorate. The battery life is affected, and the battery is discarded.

Over current protection prevents MOSFET damage and allows the battery to safely charge within the maximum charge current that it can withstand.

Short-circuit protection prevents direct conduction of positive and negative electrodes due to inadvertent operation, resulting in fire and explosion of the battery, ensuring safety during use and handling.

Therefore, for the cottage emergency start power supply product, the fake circuit is no different from murder, especially the rate battery used in the emergency start power supply, the protection circuit's fraud accounts for about 3-5% of the product cost, but unfortunately only from the appearance is not seen whether there is protection circuit, only by the conscience of the business, so try to buy a big brand.

The page contains the contents of the machine translation.