Charging principle of mobile phone lithium ion battery
At this stage, smart phones generally use lithium-ion batteries. Lithium-ion batteries were first made in the 1970s. After 20 years of technology accumulation, Sony took the lead in commercializing this technology. When other high-tech battery technologies are still in the conceptual stage, the position of lithium-ion batteries in various product lines can be said to be dominant.
We usually charge our mobile phones every day, but few people have studied how to charge lithium-ion batteries. Simple science, the charging process of lithium-ion batteries will be divided into four stages: low-voltage precharge, constant current charging, constant voltage charging and charging termination.
The charging method of lithium-ion battery is voltage-limited and constant-current. The whole process is controlled by the IC chip. It first checks the voltage condition of the mobile phone rechargeable battery. If the voltage is lower than 3V, it will pre-charge first. At this time, the charging current is the set current. 1/10 of that. When the voltage is raised to 3V, it will enter the standard charging process. At this time, constant current charging will be performed at the set current, and when the battery voltage rises to 4.2V, it will be changed to constant voltage charging while maintaining the charging voltage on the basis of 4.2V. At this time, the charging current will gradually decrease until the current Charging ends when it drops to 1/10 of the set charging current. The charging process of a general lithium-ion battery takes more than 2 hours.
We can also estimate the remaining battery power by measuring the voltage: 4.2V-100%; 3.95V-75%; 3.85V-50%; 3.73V-25%; 3.5V-5%; 2.75V-0%.
Fast charge: inseparable from "P=UI"
So what about fast charging? Everyone knows the basic formula P (power) = U (voltage) I (current). In the case of ensuring that the charger voltage is higher than the battery voltage, fast charging is to allow the charger to adjust the input voltage and output current in real time according to dynamic parameters such as battery voltage, power and even temperature during the charging process. Specifically, there are three methods. .
1. Boost voltage and constant current: In this way, a lot of heat will be generated, and power consumption will increase, which will damage the battery and mobile phone;
2. Constant voltage, increasing current: shunting under parallel circuits, the pressure on each circuit is reduced;
3. Increase the voltage and increase the current: Although this is the fastest way to increase the power and increase the charging speed, it is the same as the first point. At the same time, the increased voltage and current will generate more heat, thereby increasing the battery and the device itself Consumption
After several years of technology accumulation, there are already some representative cases of fast charging on the market.
The Qualcomm QuickCharge1.0 technology announced in 2012 supports a maximum charging power of 10W, which means that the current can reach 2A at a charging voltage of 5V. The QuickCharge 2.0 technology announced in 2013 increased the charging power to 36W on the basis of 1.0, shortening the charging time.
QuickCharge2.0 is divided into two standards, A-level and B-level, and A-level is suitable for mobile phones, tablets and other electronic devices. According to Qualcomm's official data, the maximum charging current of the QuickCharge2.0A standard is 3A. If the charging power is 15W in the case of 5V, the charging speed is faster than the 10W QuickCharge1.0.
To give an example for better understanding, with the use of a 9V/1.67A charger, the charging efficiency of the device will increase by 75%. For example, if you charge a battery with a capacity of 3300mAh for half an hour, QuickCharge2.0 can be charged to 60% after 30 minutes, while the traditional charge is only 12%. In addition, QuickCharge2.0 also supports three voltages: 5V, 9V, and 12V. High-voltage chargers can be adapted to more devices to prevent voltage loss and ensure charging efficiency.
In terms of compatible models, QuickCharge1.0 only supported the models corresponding to the Snapdragon 600 processor, but when switched to QuickCharge 2.0, it can support Snapdragon 200, 400, 410, 615, 800, 801, 805, 810, etc. For processor models, many smartphones currently have support for QuickCharge2.0, including MotoX (second generation), Nexus6, LGGFlex2, Samsung GalaxyNote4, NoteEdge, Sony XperiaZ3, Z3Compact, HTCOneM8, M9, etc., and also include Some models with non-Snapdragon processors, such as the flagship models Samsung S6 and S6edge, actually support QuickCharge2.0.
It should also be noted that QuickCharge2.0 requires a charger with a higher output power. If you use those old chargers, it can still only maintain the normal charging level.
In addition to QuickCharge2.0, the MediaTek platform also launched fast charging technologies PumpExpress and PumpExpressPlus in February last year and May of this year, respectively. The official claims that the charging speed can be increased by 45% and must be used with specific chargers.
Two fast charging specifications
1. PumpExpress provides fast DC charger with output power less than 10W (5V), controlled output voltage: 5V/4.8V/4.6V/4.4V/4.2V/4.0V/3.8V/3.6V, mainstream output power: 5V/1A&5V/1.5A;
2. The output power supplied by PumpExpressPlus for the charger is greater than 15W. The difference is that the controlled output voltage has three new levels of 12V, 9V and 7V, which are 12V/9V/7V/5V/4.8V/4.6V/4.4V /4.2V/4.0V/3.8V/3.6V;
The principle of PumpExpress technology is mainly built into the PMIC power management integrated circuit, which allows the charger to determine the initial voltage required for charging according to the current. At this time, the PMIC sends a pulse current command to the charger through the USB Vbus (USB voltage), and the charger follows the command Adjust the output voltage to obtain the maximum charging current when the voltage is finally increased to 5V.
When charging with constant current, the current sent to the battery keeps decreasing. According to the figure above, it can be seen that the voltage and current on the reverse transformer composed of Nsec to Naux change, and the Naux output current is sent to the Vsense pin. The Vsense circuit calculates the current change, and then increases the voltage of the Npri transformer, so that the output voltage of the secondary coil Nsec is also increased. According to the formula P=UI, the power output to the mobile phone charging IC is increased; it is guaranteed that when the battery voltage is close to 4.2V, it will continue to execute from P=UI (5V×very small current) to P=UI (greater than 5V) The adjustment of the voltage × very small current) realizes the purpose of fast charging the battery.
In terms of products, the MT6630 platform first used PumpExpress technology. Later PumpExpressPlus was mainly used in new platforms such as MT6575 and MT6732. For example, the familiar mCharge technology of Meizu MX5 is based on PumpExpressPlus, as well as other mobile phones that use MTK solutions.
VOOC flash charging technology
QuickCharge2.0 and PumpExpress technologies have one thing in common. They are to achieve fast charging by increasing the charging voltage of mobile phones. However, OPPO’s fast charging ideas are obviously more radical, using a low voltage and increasing current method, such as Find7 equipment. It is a charging mode of 5V voltage + 5A current, which can charge 75% of the electricity in 30 minutes.
Two different hardware designs in the VOOC flash charging system are the 7-pin microUSB interface and 8 metal contact batteries. Generally speaking, the conventional microUSB interface has 5 pins, while the mobile phone battery has 4 to 5 contacts, but OPPOFind7 has 7 pins and 8 contacts. The extra pins and contacts can form a similar block The series channel of the battery to increase the charging speed.
Since VOOC flash charging technology is not a platform-based technology, it currently only supports OPPO's own products, such as OPPOFind7, N3, and R7, and must be used with flash charging chargers, which has greater limitations.
What is the future battery technology?
Compared with the previous two years, fast charging technology has become more mature now. When the new battery technology encounters a bottleneck, fast charging technology can be said to solve the urgent need. Especially when you are away from home, or when you cannot charge for a long time when dealing with an emergency, fast charging technology can win you more time. Therefore, it is not difficult to predict that fast charging technology may become the standard configuration of every mobile phone in the future.
Of course, in the end, we still look forward to new breakthroughs in battery technology itself. Although many technologies are now in the conceptual stage, there are several more reliable conjectures that deserve attention.
One theory is that lithium-ion batteries will be replaced by lithium-sulfur batteries. Because traditional lithium-ion batteries will deposit lithium metal after a period of use, which will cause the battery capacity to expand and explode. This is an important reason why lithium-ion batteries cannot be used for a long time.
During the research process, it was discovered that the use of lithium sulfur instead of traditional lithium polymer can not only achieve higher charging capacity, but also reduce the appearance of lithium metal deposits to enhance stability. In fact, the design is to add a thin layer of silica (glass) to the sulfide to make it easier to separate the sulfur from the electrolyte and pass between the electrodes.
Another feasible method is the new technology of lithium metal anode. The essence of this method is to compress the volume of lithium-ion batteries to ensure that the smart phone is light and thin, and at the same time obtain more power by reducing the volume of the battery and the number of new batteries.