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67776 2009 年 09 月 01 日 23:00 Reading (loading. ..) Comments (1) Category: Personal Diary
Lithium-ion batteries have become the battery of choice for portable electronic products. The battery capacity of high density, price competitive, the next few years will continue to be the market mainstream. However, lithium has been hidden danger of explosion. As more and more widely applied, explosions also endless. In fact, through proper system design and batteries battery level determined,
cheap gucci heels, lithium-ion batteries can be very safe. Explosion proof electric lines and the current core technologies are mature, should be fewer and fewer explosions.
characteristics of lithium-ion battery Lithium is the chemical periodic table on the diameter of the smallest and most active metal. Small size, so the capacity of high density, well received by consumers and engineers welcome. However, the chemical properties are too active, then brought a high risk. Lithium metal when exposed to air, with oxygen to produce intense oxidation of the explosion. To enhance the security and voltage, scientists have invented the graphite and lithium cobalt oxide and other materials to save the lithium atom. The molecular structure of these materials, forming a small nanometer scale storage grid that can be used to store the lithium atom. Thus, even if the battery case rupture, oxygen access, also due to oxygen molecules too large to get into these small cells, making the lithium atoms to avoid contact with oxygen will not explode. This principle of lithium-ion battery, it makes people get high-capacity density, but also to achieve security.
lithium-ion battery charging, the cathode of lithium atoms lose electron, the oxidation of lithium ions. Lithium-ion through the electrolyte to the cathode to travel into the cathode cell, and get an electronic, revert to the lithium atom. Discharge, the entire process upside down. To prevent the battery terminals directly touch and short circuit the battery would add a paper membrane with many pores, to prevent short circuits. Good separator in the battery temperature is too high can also be automatically closed pores, so that lithium ion can not pass through to strips to prevent accidents from taking place.
overcharge protection to lithium cell voltage higher than 4.2V, it will start generating side effects. Overcharge voltage higher, also followed the higher the risk. After the voltage is above 4.2V lithium batteries, cathode materials, the number of lithium atoms in the remaining less than half of the cells often break down at this time, so have a permanent decline in battery capacity. If you continue to charge, because the cell has been filled with negative lithium atom, the follow-up of lithium metal will be accumulated at the anode surface. The lithium atoms from the cathode surface to the direction of lithium ion to grow dendrites. The lithium metal crystal will pass through the diaphragm
paper, the positive and negative terminal. Sometimes short-circuit the battery prior to the first explosion, this is because the overcharge process, electrolyte and other materials will produce gas cracking, making the battery casing or pressure valve Guzhang broken, so that with the accumulation of oxygen into the surface of the lithium atoms in the anode reaction and then explode. Therefore, the lithium battery charger, be sure to set the voltage limit, it can take into account the battery life, capacity, and safety. The ideal charge voltage limit of 4.2V.
discharge lithium batteries have a voltage limit. When the batteries voltage is below 2.4V, the part of the material will begin to be destroyed. Also, because the battery will self-discharge, discharge voltage will be lower the longer, therefore, best not to put 2.4V discharge stopped. Discharge from 3.0V to 2.4V Li-ion battery during this period, the energy released only about 3% of battery capacity. Therefore, 3.0V is the ideal cut-off voltage of discharge.
charge and discharge, in addition to voltage limits, current limits are also necessary. Current is too large, too late to enter the lithium-ion cells, will gather on the surface. These lithium-ion access to electronic, it will produce lithium atoms in the crystal surface, which, like overcharging, may cause danger. If the battery case rupture, it will explode.
Therefore, the protection of lithium-ion batteries, at least to include: charge voltage limit, lower limit of discharge voltage and current limit of three. General lithium batteries, in addition to lithium batteries, but will have a protection board, this board is mainly to provide protection of the three protection. However, the protection of the three protection board is obviously not enough, the global lithium battery explosion or frequent. To ensure the safety of the battery system must be cause of the explosion of the battery, a more careful analysis.
explosion explosive type of battery cells can be categorized as a class form the external short circuit, an internal short circuit and overcharge three. Here external means external batteries, including the insulation within the battery pack caused by poor design and other short-circuit.
a short circuit when the external batteries, electronic components and failed to cut off the circuit when the internal batteries will generate heat, resulting in vaporization of some of the electrolyte, the battery cover stretch. When the battery to 135 degrees internal temperature is high, the quality of a good separator, will pore closed, terminated or near termination of the electrochemical reaction,
gucci shoes, the current dip, the temperature slowly dropped, and thus avoid the explosion. However, poor pore closure rate, or the membrane pores will not close the paper, let the battery temperature continues to rise, more electrolyte evaporation, and finally the battery case bursting, and even the battery temperature is raised to the materials burn and explode.
mainly because of internal short circuit copper foil and aluminum foil membrane perforation burr, or dendrite lithium atom caused by the worn diaphragm. The small needle-like metal, can cause micro-short circuit. Because, there are some very fine needle resistance, therefore, the current may not be significant. Department of copper foil burrs created during the production process can be observed phenomenon is battery drain too fast, most batteries can be factory or assembly plant screening program. Moreover, since small glitches, sometimes blows, making the battery back to normal. Thus, short-circuit caused the explosion due to micro-burr the probability is not high.
this argument, you can plant from the internal batteries are often charged shortly after the negative battery voltage is low, but the explosion rarely get statistical support. Therefore, the internal short circuit caused an explosion, caused mainly because of the overcharge. Because, after overcharging pole piece is filled with needle-like crystals of lithium metal, piercing points are everywhere, everywhere, in the event of micro-short circuit. Therefore,
gucci outlet, the battery temperature will gradually rise, the last high-temperature gas to the electrolyte. This situation, whether the material temperature combustion and explosion, or the case was first bursting, so that the air inside a heated metal oxide and lithium, are explosive ending.
but overcharge caused by internal short circuit caused this explosion, not necessarily in charge at the time. Battery temperature is not possible to make materials with high combustion gases generated by the battery cover is not enough to bursting, consumers on the termination charge, with phone out. At this time a large number of micro-heat generated by short circuit, the battery temperature rises slowly, over a period of time before the explosion. Description of all consumers to find the phone when you pick up the phone very hot, throw away after the explosion.
the above type of explosion, we can focus on the explosion to prevent overcharge, external short circuit to prevent, and improve safety of batteries
all of three. Which overcharge is the Prevention and electronic protection to prevent external short circuit, battery and battery system design and assembly of a larger relationship. Batteries to enhance the focus on security, chemical and mechanical protection, and more related to the battery cell manufacturer.
design
only because hundreds of millions of global mobile phone to achieve security, security protection, the failure rate must be less than one hundred million to one. Because the circuit board failure rates are generally much higher than one hundred million to one. Therefore, the battery system must be more than prescribe the security line of defense. A common mistake is designed charger (adaptor) to charge batteries directly. This will overcharge protection responsibility, entirely to the protection of the battery pack on board. Although the protective plate failure rate is not high, but even the low failure rate to one in a million chance of the world every day, there will be an explosion or accident.
battery systems such as the can over charge, over discharge, over current are two security respectively, the failure rate of each protection if it is one ten thousandth, two protection failure rate can be reduced to one to one hundred million. Common battery charging system block diagram below, contains two parts, charger and battery pack. Also includes charger adapter (Adaptor), and charge controller in two parts. AC converted to DC adapter, DC charger controller is the maximum current limit and maximum voltage. Battery protection board and the battery cell contains two parts, and a PTC to limit the maximum current.
text box: AC-DC adapter text box: Charging Current Limit pressure limiting the text box: Charger text box: protection board over charge, over-let flow, etc. Protective text box: batteries text box: only text box silicon: the battery core
mobile phone battery systems, for example, over charge protection system using the charger output voltage is set at 4.2V or so, to reach the first layer of protection, so even if the battery pack protection board failure, the battery will not be overcharge And dangerous. Second protection is to protect the board over charge protection, usually set to 4.3V. Thus, protection board usually do not have to be responsible for cutting off the charging current, abnormally high voltage only when the charger only when needed action. Over-current protection is limited by the protection board and tape to be responsible, which is two protection against over-current and external short circuit. Due to excessive discharge will be used in the process of electronic products. Therefore, the general design of electronic products by the circuit board to provide the first to protection, the protection plate on the battery pack provides the second safety. When the electronics detect the supply voltage drops below 3.0V, it should automatically shut down. If the product design is not design this feature, the protection board to 2.4V in the voltage is low, close the discharge circuit.
In short, the battery system design, must be over charge, over discharge, over current, respectively, and provide two electronic protection. Which is the second safety protection board. After charging the protection plate removed, if the battery will explode on behalf of the poor design.
Although this method provides two protection, but as consumers, after the charger broken, often will buy non-original charger to recharge, and battery charger industry, based on cost considerations, often the charge controller removed, to reduce costs. Result, bad money drives out good money, the market there have been many bad charger. This makes the loss of overcharge protection first and most important line of defense. The overcharge caused by battery explosion is the most important factor, therefore, poor battery charger can be called the bombing culprits.
course, not all of the battery system programs are used as shown above. In some cases, the battery pack will have charge controller design. For example: Many laptop computers plus the battery bar,
gucci bikinis, there is charge controller. This is because the laptop will charge controller is generally done in the computer, only to give consumers an adapter. Therefore, notebook computer battery packs applied, you must have a charge controller to ensure that the external battery charging using the adapter security. In addition, the use of car cigarette lighter charging products, and sometimes will do in the battery charge controller group.
last line of defense electronic protection measures if failed, the last line of defense, it is necessary to provide the batteries. The security level of batteries, the batteries can be based on whether the external short circuit and overcharge to approximate hierarchical. As the battery before the explosion, if an internal lithium atoms deposited on the surface, explosive power will be even greater. Moreover,
gucci sunglasses, due to overcharge consumers to use inferior protection often only line of defense in the charger, so batteries against overcharge capacity than the capacity of external short circuit resistance is more important. If the external short-circuit the batteries will not explode, could be a star. The explosion will not overcharge the batteries, you can get two stars. Then the safety level of batteries, there is zero stars to three stars, four grades. Taiwan made the Japanese system and the battery cell, usually can reach the highest level of three stars, Chinese made batteries to uneven. The following table is a common lithium batteries market, the level of security.
security level is not too short not explode explosive charge on behalf of manufacturers
★ ★ ★ O O Japan factory, will yuan, should electricity
★ ★ O X continental level plant
★ X O mainland secondary plant
☆ X X mainland three plants
batteries against external short circuit method, usually including the use of high-quality paper and use the pressure valve diaphragm two measures. In which the best high-quality diaphragm, external short circuit Ninety-nine per cent of the battery will not explode. Pressure valve will have side effects. For example, battery charge, the pressure valve burst if too early, let oxygen into the cause the explosion. In addition, the precision of Chinese-made pressure valve is not *. Aluminum aluminum production plants in China, less than one percent of the pressure valve in the industry claim that the pressure range of work, there was only one per cent can be *, II. Therefore, assembly plant, in order to ensure that short-circuit the battery will not explode, the best way is to experiment on directly. As long as the battery fully charged, and then placed in explosion-proof box to determine the short circuit short circuit capacity.
battery cell resistance to overcharge method is very complex and must consider the chemical formula, the shell mechanical properties, and related electronic components. General system using battery charge to a voltage, so that additives start to react, on the one hand increase the resistance on the one hand the energy into heat energy, in order to achieve 1C/12V overcharge 6 hours, not the explosion safety. For the string and use the battery, and sometimes together with supporting electronic components or precision of the pressure valve.
China, nearly half of the system batteries can short-circuit tests, but most of them can not overcharge test. Also, because the electronic protection, the most likely line of defense is the collapse of the overcharge protection, and over charge arising from the explosion also the most serious. Therefore, the core of the anti-overcharge the battery capacity is related to the industry in the choice of battery cells, the focus of the focus. For single use battery, at least to be able to reach 1C/6V overcharge 6 hours does not explode. Batteries used in series, at least through 1C/12V overcharge 6 hours. In order to use inferior charger in the case of consumers, ensure the safety of the battery pack.
attribution
battery explosion, the analysis of cause of the blast, the first step is to determine the attribution of responsibility. If this is the site of short circuit in the explosive and the external battery pack, it must be the failure of two electronic protection, and batteries have also failed to pass the test of short-circuit. Then protect the sheet manufacturer, batteries manufacturer, PTC manufacturers, and assembly manufacturers have a responsibility. But the chances of this happening is not high. If the short circuit in the battery pack's internal parts, the most likely is due to insulation failure and lead batteries failed the short circuit test. Therefore, the assembly plant and the plant has a responsibility batteries. If it is too explosive charge, usually guided by the charger voltage is too high to protect the plate temperature is too high due to the failure of temporary or permanent, and failure to prevent overcharging of batteries. Since all batteries are only to ensure that plants do not explode when the batteries short-circuit,
not guarantee overcharge without explosion. Assembly plant also will be on the product label, only use original charger 『』. Therefore, the charger works the greatest responsibility and communication lines, protect the plate, followed by manufacturers and assembly plants. There are many chargers, although the output voltage is 4.2V marked about the actual voltage is over 5V. In this case, the responsibility is clearly in the charger works with the communications line. If the charger manufacturer's label accurately the voltage higher than 5V, the results of communications lines also sell it to consumers when the cell phone charger, then the communication line will bear the greatest responsibility.
identification of the professional battery explosion is very high, and the cost is not Zi. As assembly plants throughout the supply chain, the actor will change the safety role of batteries. Therefore, unclear responsibilities, often need to first pay the cost. Therefore, the choice of safe batteries,
gucci sunglasses 2011, especially batteries against overcharge on the assembly plant of paramount importance.
Note
consumer lithium-ion battery system, if properly designed, for the over charge, over discharge, over current protection are two instances e, and batteries may also pass Short-circuit test and had been fully tested. So, security should be no fear, consumers can safely use.
buy the charger, it is best to buy the original charger. Buy non-original charger, do not believe in the value of manufacturers indicated output voltage. Communication lines should be asked about the amount of electricity form the output voltage charger base, voltage below 4.3V before use. Must use the charger voltage is above 4.3V, the best end in the phone charging plug. Do not put non-original battery in the charger base of non-original charge, most are like the explosion occurred.
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