Lithium-ion rechargeable batteries have a stable position, and reforms are still needed Since Sony's industrialization of lithium-ion batteries in 1992, lithium-ion batteries have become a new type of power supply technology in recent years due to their advantages of high specific energy, long service life, no memory effect, safety, reliability, and fast charge and discharge. Hot spots for development. Lithium-ion batteries are environmentally friendly, non-polluting rechargeable batteries that meet the energy and environmental protection needs of various countries today, and their applications in various industries are rapidly increasing. At present, lithium-ion batteries have been widely used in electronic products such as mobile phones, notebook computers, digital cameras, and MP3, which have largely replaced nickel-cadmium batteries and nickel-metal hydride batteries, accounting for 90% of such applications. In addition, lithium-ion batteries have also begun to become practical in some high-power batteries such as electric vehicles. Table 1 Comparison of lithium ion rechargeable batteries and other batteries However, manufacturers such as mobile phones and video cameras are particularly fond of the light weight characteristics of lithium-ion rechargeable batteries. In terms of energy density per unit weight, lithium-ion batteries are about twice as high as nickel-metal hydride rechargeable batteries and can reach 115Wh / kg. In other words, under the same energy capacity, the weight of the lithium-ion battery pack can be reduced by about half. Therefore, under the special favor of portable device manufacturers, products using lithium-ion rechargeable batteries have been launched successively since 1991, and are very popular. Since then, Matsushita Battery Industries Corporation in 1992, Japan Battery Corporation in 1993, Sanyo Electric, Hitachi and Canada Moli Energy (1990) were put into operation in 1994, establishing the unshakable position of lithium-ion rechargeable batteries in the portable electronic device market . Figure 1 Over-protected rechargeable battery After strengthening the safety protection, the energy density of the lithium ion rechargeable battery continues to increase. At the beginning of practical use in 1990, the energy density per unit volume of lithium-ion batteries was only 190Wh / L; by 2009, 19 years later, this value had increased by about 4 times to 740Wh / L (see Figure 2). But in the same period, the clock frequency of the microprocessor has increased more than 100 times, and the capacity of DRAM has increased by 250 times. Therefore, rechargeable batteries have also been repeatedly cited as progressing too slowly. Figure 2 The capacity of lithium-ion rechargeable batteries continues to increase It is currently in the third period of change. This time is the reform of negative electrode materials. Candidate materials include silicon-based alloys, tin-based alloys and metallic lithium (see Figure 3). Among them, tin alloys have entered practical use. Sony has started to use such materials in camera battery packs launched after the spring of 2005. The 14mm (diameter) × 43mm (length) battery cell has a unit volume energy density of 478Wh / L, which is about 20% higher than that of batteries using traditional materials. Figure 3 Improve energy density
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1.A source of electric current,
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Before 2000, Japan dominated the world in lithium-ion batteries, with output accounting for more than 95% of the world. In recent years, with the rapid rise of China (including Taiwan) and South Korea, Japan's unique pattern has been gradually broken. At present, the market share of lithium-ion batteries in Japan has fallen below 60%, which generally forms a three-thirds world pattern. Although it encountered a global financial turmoil in 2008, its rechargeable battery shipments and sales have increased over the previous year, but this year will still be a severe one. In the future, the rapid development of various electric vehicles will become an important driving force for the advancement of lithium-ion batteries.
The status of lithium-ion batteries is unshakable. In 1989, small-capacity button-type lithium batteries were put into practical use. However, in the summer of 1989, after a number of accidents caused by overheating of mobile phones using lithium batteries, in the early 1990s, the industry took a negative attitude towards the practical prospect of cylindrical rechargeable batteries using lithium materials. However, Sony Energy Tech, a company that specializes in battery manufacturing, broke the deadlock and announced in February of that year that lithium-ion rechargeable batteries had reached practical levels.
Lithium batteries cause accidents because they use metallic lithium as the negative electrode material. After repeated charging and discharging, the negative electrode will form dendrites, which will cause a short circuit between the positive and negative electrodes, causing smoke and fire. The lithium-ion rechargeable battery does not use metal lithium at the positive and negative poles, the positive electrode uses LiCoO2 (lithium cobalt oxide) alloy material, and the negative electrode uses coke-type carbon material. This ensures the safety of the battery, thereby realizing a cylindrical lithium battery.
However, the performance of the lithium-ion battery at the beginning of practical use was not significantly better than the main competitor at the time-nickel-metal hydride rechargeable batteries (see Table 1). For example, the energy density per unit volume of a lithium-ion rechargeable battery in early 1993 was 220Wh / L (this is the value of a cylindrical battery with a diameter of 18mm × 65mm in length, the same below), which is only about 20 higher than the 180Wh / L of a nickel-metal hydride battery %. Moreover, lithium-ion rechargeable batteries also have many shortcomings, such as "no voltage compatibility with dry batteries", "difficult charge control", "high internal resistance, unable to charge and discharge with large currents", "difficult to parallel, difficult to achieve Capacity battery pack "etc.
Improve safety and avoid accidents Since 1990, lithium-ion rechargeable batteries have basically developed along the two main lines of high density and ensuring safety. In order to promote the miniaturization and weight reduction of products, manufacturers of portable electronic equipment strongly demand to increase the energy density of batteries. However, the higher the density, the higher the risk of fire and smoke. The accident must never happen again! The fire accident in the summer of 1989 lingered in the minds of battery technicians: if another accident occurred, the rechargeable battery using lithium material would ruin the future.
Therefore, at the beginning of the practical use of lithium-ion rechargeable batteries, battery manufacturers implemented strict safety measures called "over-protection". In order to ensure safety even when the battery is in an overdischarge / overcharge state due to misoperation, the manufacturer has configured three safety structures for the battery: PTC (positive temperature coefficient) thermistor, safety valve, and diaphragm. Figure 1 shows an example of a safety circuit. When an abnormal temperature rise is detected, the load of the battery unit can be cut off electrically to avoid danger.
In addition, equipment manufacturers developing mobile phones, cameras, and notebook computers have also played an important role in ensuring battery safety. At that time, all equipment manufacturers set up test plans for acceptance, such as nail penetration test, high temperature / low temperature working test, and heating test in a pan. Based on a series of test results, equipment manufacturers will raise existing problems with battery manufacturers, and put forward many opinions on how to improve the structure of battery cells and design safety circuits. Under such close cooperation of hard work, until the early 20th century, there was no major accident in the lithium ion rechargeable battery, and the market developed very smoothly.
Improve materials to improve performance
The improvement of energy density basically relies on the improvement of the positive and negative electrode materials, the adjustment of the battery structure, and the improvement of the manufacturing process. There have been three major changes in materials in 19 years, which have accelerated the increase in energy density time and time again. The first occurred between 1994 and 1995, and the anode material changed from coke-based carbon material to graphite-based carbon material. This change increased the energy density by about 20%. In the following 8-9 years, the combination of LiCoO2 for the positive electrode and graphite-based carbon materials for the negative electrode has been maintained. The second change occurred between 2002 and 2003. The cathode material changed from LiCoO2 to a mixture of LiCoO2 and Li (Ni-Co-Mn) O2, and the energy density was increased by about 10%.
In January 2007, the Panasonic Electric Appliance Industry and the Panasonic Battery Industry successfully achieved an energy density per unit volume of up to 740 Wh / L by using an alloy material as the anode material. The company did not disclose the specific situation of this alloy material. It has not been mass-produced until March this year, but it is expected to be put into practical use in the near future. In addition, battery products that use silicon-based alloys and lithium metal as negative electrodes to greatly increase energy density are also in the process of trial production.
Since 2006, the lithium-ion rechargeable batteries used in notebook computers, mobile phones and other products have experienced abnormal heat accidents again, potentially posing a fire hazard. Battery manufacturers such as Sony, Panasonic Battery Industry, and Sanyo Electric have all recycled battery packs in large quantities. The reason is that the metal powder is mixed in the manufacturing process, and it is said that the equipment manufacturer improperly handles the charge and discharge management. The equipment manufacturers faced the rebuttal and blamed each other.
In fact, the real reason has not yet been determined. For this purpose, we should thoroughly investigate the cause, recognize the seriousness of "recurrence of an accident, and ruin the future", learn from the spirit of time-consuming development of the senior technical personnel of both parties to ensure safety at all costs, and work together,
2.A volt meter,
3.A switching matrix used to connect the current source and the volt meter to all of the contact points in a cable.
In addition to these parts a cable tester may also have a microcontroller and a display to automate the testing process and show the testing results.
