lithium 3400mah 3.7v 18650 battery technology for portable power

　　A typical laptop battery can hold more than 50W of energy, and great care must be taken in its design, construction, and use to ensure that safe limits are not exceeded. Few circuit design engineers want or need to be battery experts, but they must ensure that the system's battery blocks can safely complete their mission and that the main system monitors the operation of the battery blocks during operation. To meet these constraints, you must understand how a battery block is specified, what types of testing and inspection it requires, and how your application monitors the health of the battery block as it works.

　　Due to their high energy capacity, lithium-ion batteries have become the mainstream for powering portable consumer devices. However, safety considerations also force manufacturers to package the battery cells in a battery block, which generally contains fuses, monitoring circuits, fuel gauges, SMBus (system management bus) interfaces, and authorization circuits. The industry-standard 18650 battery cell is the same size as an AA battery, but even if the device uses a single cell, it requires that the battery cell be packaged as a battery block that contains safety circuitry and insurance.

　　In addition to chemical and technical characteristics, it is also necessary to choose a lithium 3400mah 3.7v 18650 battery cell supplier with a stable supply chain to ensure a stable supply of battery blocks and cells. Lithium-ion cores have become increasingly difficult to obtain for a variety of reasons, including batch recalls, factory closures and material shortages in recent years. Combine these issues with rising transportation costs, unfavorable exchange rates, increasing demand for lithium-ion batteries in consumer electronics, power tools, automobiles, and rising battery cell prices, and you can see why a stable supply chain must as a priority criterion for selecting battery suppliers.

　　In the early 1990s, Sony became the first manufacturer of lithium 3400mah 3.7v 18650 battery cells and remains the largest battery cell supplier with Panasonic. Cost-sensitive small and medium-volume products can buy battery blocks off-the-shelf in stores, which come from thousands of small and medium-sized suppliers in China. But don't be too concerned with price when choosing a battery pack: it's rarely cost-effective to try to perform quality testing during incoming factory inspections, and field failures of battery packs are a source of danger. For cost-conscious low-volume applications, store-bought battery blocks are a viable route, but don’t let price be the deciding factor. High-volume applications can often determine the development costs of a custom battery block. In addition, small and medium-volume applications that require high quality and high power (such as medical applications) can afford a higher price and justify a customized battery block.

　　You can work with a battery cell supplier or a battery block design studio to develop a custom battery block. A valuable communication tool when working with battery block suppliers is a set of power curves that represent the application over time under different operating modes, including temperature limits. Power tools may have a discharge curve that corresponds to high current pulses during cutting or drilling operations. The amplitude and timing of the pulses vary with the shape of the material. A device with an RF transceiver will also have pulse spikes when transmitting and must provide continuous current to the display and other functions. Ask your battery block supplier to demonstrate with prototype battery blocks that their design can meet all power curve requirements.

　　Robin Tichy, marketing manager for Micropower Electronics, a custom battery block designer and manufacturer, said some of the company's medical application customers require that each battery be tested and that the test should include a complete charge and discharge cycle to ensure that the company has assembled it correctly. Each battery block has sufficient capacity. In some cases, the company must also develop a custom tester specifically for the production line. Some customers only require a simple voltage test to ensure correct assembly, while other customers only require the manufacturer to test product samples. If your battery block design requires the use of a relatively cheap power IC, which calibrates the battery block and measures the charge in and out of the battery, counts the coulomb value, and then each battery block must be charged and discharged individually after assembly. This calibration increases manufacturing costs and the overall price of the battery block. Tichy recommends weighing the pros and cons of using a more expensive fuel gauge, such as Texas Instruments' ImpedanceTrack series, which does not require an initial charge-discharge cycle.

　　The IEEE1625 standard targets rechargeable batteries for portable computing and covers the testing requirements for laptop battery blocks. Following the recall of battery packs by Dell, HP, Apple and other notebook computer manufacturers, the IEEE announced in late 2006 that it would modify the test requirements specified by IEEE1625. The organization is still revising the standard and plans to publish it in 2009 (Reference 3). IEEE1725 is another standard, which is oriented to the testing of mobile phones and battery blocks. In addition, UL (Guarantee Laboratory) 1642 covers electronic, mechanical and environmental testing of lithium-ion batteries. Rich Chamberlain, vice president of engineering at battery supplier Boston-power, said that the industry considers the UL1642 specification to be the minimum test, especially in the notebook computer market, and most manufacturers in the industry have to do more testing to ensure the safety of battery blocks.

　　The features of the battery block can also serve as a differentiating feature, and your customers may pay more money for it, or the feature may influence the customer's purchasing decision. For example, a customer may wish to pay more for a battery pack that has a longer run time, or a shorter recharge time. Similarly, the total cost of ownership of a battery module to the end user includes not only the battery cells, power management circuitry and packaging, but also the number of cycle life cycles: more cycles means longer life.

　　lithium 3400mah 3.7v 18650 battery cells are not off-the-shelf commodities, but they can be finely tuned, such as changing the chemistry of the anode and cathode, their thickness, and the composition of the internal separators. Chamberlain recommends that system designers communicate with battery cell suppliers and battery block designers to select battery cells based on the performance needs and dimensions of their designs, or even customize a battery cell. Boston-power's original product, which it began offering in 2007, was the Sonata battery block, which designers could use in laptop designs. The Sonata's launch coincided with Dell and Sony's battery block recalls. Sonata's safety features include more stable chemical reactions within the battery cells, patented current control circuitry, new thermal fuses, and pressure relief vents.

　　Chamberlain used the battery cell structure in the Sonata as an example to illustrate how safety considerations in battery block design complement performance needs. He said: "A typical laptop battery block uses a six-cell structure of three series and two parallel. The current passing through the parallel battery cells will be divided, and because the impedance characteristics of these battery cells are slightly different, the current will flow through these cells. The method of cells is also slightly different, thus resulting in differences in cell life and safety issues. Sonata cells have a larger format than ordinary cells: we connect three cells in series, without a parallel structure. This seems relatively simple, But this change in the battery block can provide a lot of performance and safety improvements." Another example of battery cell customization is the thickness of the electrode: by controlling the thickness, it can be optimized for high energy storage or high power. The development of a custom battery cell does not take long: According to Chamberlain, it only takes six months to modify one of the chemical components in the battery cell. Other larger changes may take more time. But he said: "Unless you talk to a battery cell supplier, you never know how long it will last."

　　Because a battery block contains circuitry such as lithium-ion cells, it is important for system designers to work with battery block designers to understand the role of power management circuitry in the battery block to ensure safety and performance. Smart battery blocks can communicate with the host to report the battery's charge status and health conditions, such as life cycle, temperature, charge and discharge current and voltage thresholds, providing the highest level of safety and performance. This circuit is often part of a battery block fuel gauge, which is also responsible for the charge symbol on a laptop or cell phone display.

　　The battery block circuit can have a fuel gauge IC, an analog front end including overcharge protection and cell balancing, and an overvoltage protection IC). If the temperature of a battery block exceeds a certain preset limit (usually 50°C), the power safety circuit will temporarily cut off the power supply to the battery block through one of the two charge and discharge safety MOSFETs connected in series with the battery cell. Once the temperature drops within the operating temperature range, the circuit turns the MOSFET back on and power is restored to the battery block.

　　You may have experienced this: Your phone or laptop shuts down when it's been exposed to sunlight or left in a hot car for too long. Then after a period of cooling, they can resume working. However, if the temperature continues to be high, or the current remains within an unsafe range, the circuit will cause a chemical fuse to blow, permanently cutting off the battery block. Once the chemical fuse blows out, the battery block is irrecoverable and needs to be returned to the recycling center.

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