High-voltage 18650 3.7v battery charging methods and development status

　　High-voltage 18650 3.7v battery charging methods and development status. At present, lithium-ion batteries have the advantages of high operating voltage, high specific energy, light weight, long life, and low self-discharge, and are widely used in various electronic products, power tools, and model toys. Conventional electrical equipment has small operating current and long standby time, and conventional lithium-ion batteries can meet their usage requirements. As the pace of life accelerates, people prefer lithium-ion batteries to have good fast charging capabilities to shorten battery charging time. This requires the use of high-voltage lithium-ion batteries that can be charged and discharged quickly. The editor will introduce the charging method and development status of high-voltage lithium-ion batteries.

　　Background of high-voltage 18650 3.7v battery development

　　In order to design high-energy-density lithium-ion batteries, in addition to continuously optimizing their space utilization, increasing the compaction density and gram capacity of the battery's positive and negative electrode materials, highly conductive carbon nanometers and polymer binders are used to improve the positive and negative electrodes. In addition to the active material content, increasing the operating voltage of lithium-ion batteries is also one of the important ways to increase battery energy density.

　　The cut-off voltage of lithium-ion batteries is gradually transitioning from the original 4.2V to 4.35V, 4.4V, 4.45V, 4.5V and 5V. Among them, 5V nickel-manganese lithium-ion batteries have excellent characteristics such as high energy density and high power and will be One of the important directions for the future development of new energy vehicles and energy storage. With the continuous development of power supply R&D technology, lithium-ion batteries with higher voltage and higher energy density will gradually come out of the laboratory and serve consumers in the future.

　　High voltage lithium ion battery charging method

　　1. Ordinary series charging

　　At present, 18650 3.7v battery packs are generally charged in series. This is mainly because the series charging method has a simple structure, low cost, and is easier to implement. However, due to the differences in capacity, internal resistance, attenuation characteristics, self-discharge and other performance between single lithium-ion batteries, when charging 18650 3.7v battery packs in series, the single 18650 3.7v battery with the smallest capacity in the battery pack will It is fully charged first, but at this time, other batteries are not fully charged yet. If the batteries continue to be charged in series, the fully charged single 18650 3.7v battery may be overcharged.

　　Overcharging of lithium-ion batteries will seriously damage the performance of the battery, and may even cause explosions and personal injuries. Therefore, in order to prevent overcharging of single lithium-ion batteries, 18650 3.7v battery packs are generally equipped with a battery management system when used. The management system protects each single 18650 3.7v battery from overcharging. During series charging, if the voltage of a single 18650 3.7v battery reaches the overcharge protection voltage, the battery management system will cut off the entire series charging circuit and stop charging to prevent this single battery from being overcharged, which will cause other problems. Lithium-ion batteries cannot be fully charged.

　　2. The battery management system and charger coordinate and cooperate with series charging

　　The battery management system is the device that has the most comprehensive understanding of the performance and status of the battery. Therefore, establishing a connection between the battery management system and the charger allows the charger to understand the battery information in real time, thereby more effectively solving the battery charging problem. Some problems arise.

　　The principle of the battery management system and charger coordinating the charging mode is: the battery management system monitors the current status of the battery (such as temperature, single cell voltage, battery operating current, consistency, temperature rise, etc.) and uses these parameters Estimate the maximum allowable charging current of the current battery; during the charging process, the battery management system and the charger are connected through communication lines to achieve data sharing.

　　3. Parallel charging

　　In order to solve the problem of overcharging and undercharging of some single cells in the battery pack, a parallel charging method has been developed.

　　However, the parallel charging method requires the use of multiple low-voltage, high-current charging power sources to charge each single battery. It has the disadvantages of high charging power cost, low reliability, low charging efficiency, and thick connection wire diameter. Therefore, there is currently no large-scale charging method. The range uses this charging method.

　　4. Large current charging in series and parallel charging with small current

　　Since the above three charging methods all have certain problems, a charging method that is most suitable for high-voltage battery packs, especially electric vehicle battery packs, has been developed, which uses a battery management system and a charger to coordinate and cooperate with series high-current charging and constant voltage. Current-limited parallel low-current charging mode.

　　Its main purpose is to reduce the shortcomings of the poor charging effect of the coordinated charging method of BMS and charger when there are a large number of batteries connected in series in the battery pack, so that the consistency between single cells is relatively poor. Coordinate with the charging mode for maximum effect.

　　Development status of high-voltage lithium-ion batteries

　　At present, domestic and foreign battery manufacturers for mobile phones and other digital electronic products are moving in the direction of high-voltage lithium-ion batteries. High-voltage and high-energy-density lithium-ion batteries will have greater market space in high-end mobile phones and portable electronic devices. Cathode materials and electrolytes are key materials for improving the high voltage of lithium-ion batteries. Among them, the use of modified high-voltage lithium cobalt oxide and high-voltage ternary materials will become more mature and common.

　　As the voltage of high-voltage lithium-ion batteries increases, some safety properties will be reduced during use, so they have not been used in bulk in power vehicles. At present, the battery cathode materials used in power vehicles are mainly ternary materials and lithium iron phosphate. In order to increase energy density to meet demand, high-nickel cathode materials such as 811NCM and NCA, high-capacity silicon-carbon anodes, or improving battery space utilization are generally selected to improve energy density and battery life.

　　Generally speaking, high-voltage lithium-ion batteries refer to batteries with a single charging cut-off voltage higher than 4.2V. For example, the cut-off voltage of lithium-ion batteries used in mobile phones develops from 4.2V to 4.3V, 4.35V, and then to 4.4V. . At present, 4.35V and 4.4V lithium-ion batteries have been maturely used in the market. 4.45V and 4.5V have also begun to be favored by the market and will gradually develop and mature.

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