551235 polymer battery.How does fast charging of mobile phones affect battery life?

　　The latest Meizu PRO6 is also equipped with fast charging technology. One of its posters has this sentence: "Why do they never talk about battery life when they talk about fast charging?"

　　Quickly learn about lithium-ion batteries

　　First of all, we need to understand the charging and discharging principles of lithium-ion batteries. The battery has two poles: the positive electrode is lithium compound, and the negative electrode is graphite.

　　Charging and discharging are all conversions of electrical energy and chemical energy. During the movement of lithium ions in the positive and negative electrodes, they are also changing into different compounds.

　　We can think of lithium ions as cars equipped with electric charges: when charging, due to the electric field, all the cars drive to the negative electrode to store a certain amount of energy (lithium ions are embedded in the micropores of the graphite carbon layer of the negative electrode); when discharging, These charged lithium ion cars run to the positive electrode due to chemical reactions (the deintercalation of lithium ions makes the positive electrode in a lithium-rich state). In this process, a current supply is formed.

　　Ideally, as long as the chemical structure of the positive and negative electrode materials basically does not change, the reversibility of battery charge and discharge is very good, and the lithium-ion battery can ensure long-term circulation.

　　Fast charging mainly ensures that lithium ions are quickly embedded from the positive electrode and quickly embedded in the negative electrode, without causing the deposition of lithium ions.

　　However, when the current increases, a semipermeable membrane (SEI membrane) on the surface of the electrode negative electrode (graphite) will rupture to a certain extent, causing the electrode material and the electrolyte to react with each other. In addition, the increase in temperature will also cause side effects inside the battery. The reaction destroys the chemicals on the battery, resulting in reduced reversibility (that is, the lithium-ion car cannot be driven back and forth) and the battery capacity will continue to decrease.

　　This is what we often feel, even though it is fully charged, why is the battery less and less able to withstand use?

　　Take the lithium battery of a DJI drone as an example. A 4480mAh 68Wh lithium battery with a voltage of 15.2V only takes 1.5h to fully charge (compared to an iPhone 6splus battery with a capacity of 2750mAh and a voltage of 3.8V). However, the lithium battery of a DJI drone Battery life is only 200 cycles. The decrease in battery life is noticeable.

　　According to the latest report from DIGITIMES, Apple has recently been working on upgrading battery charging technology and is preparing to use 15V to 20V charging equipment to improve battery efficiency and promote new IC technology. However, the equipment provider of PWMIC also said that this requires taking great risks.

　　Fast charging protection mode

　　The fast charging solutions of the three companies will all have battery temperature monitoring solutions. When increasing the voltage, it is inevitable that the temperature will increase. If you play large-scale games while using Qualcomm QC's fast charging technology, due to chip control, the external voltage is limited to ensure that your phone will not become seriously hot, but the charging efficiency will decrease.

　　VOOC flash charging uses segmented charging current control and multi-line settings of charging cables and batteries. To put it simply, one battery was charged before, and now it is divided into several batteries and charged separately.

　　In terms of safety, because fast charging has a "handshake protocol", the output voltage and current will be coordinated before charging.

　　Lithium battery charging is divided into three parts: constant current precharge (CCPre-charge), high current constant current charge (CCFastCharge) and constant voltage charge (CV).

　　After the mobile phone's power is exhausted, the voltage drops. When it is lower than a certain value, the charger will use a relatively low current to precharge the lithium battery. After a period of time, when the lithium battery voltage is higher than the predetermined value, it will enter the second stage of high current and constant current charging. At this time, appropriately increasing the current can speed up the charging speed.

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