At present, lithium-ion batteries have become the basic power supply for mobile electronic devices such as mobile phones and notebook computers, and have also begun to be applied to light electric vehicles and hybrid electric vehicles. However, due to the rapid increase in demand, the cost of lithium-ion batteries has become increasingly prominent. Due to the increase in battery energy density, battery safety accidents have also been reported. At present, the lithium-ion battery industry is about to undergo major structural adjustments. The industrialization of power and energy storage batteries is accompanied by the development of materials, processes and equipment in the direction of major technological innovations.
Using a variety of methods to improve the safety of safety batteries involves many aspects of materials, battery design, manufacturing, and application. Simply changing the cathode material does not completely guarantee the safety of the battery. Only the main materials should carefully choose the anode material, electrolyte and battery separator. For example, the anode material used as the lithium ion battery is carbon material, metal oxide and alloy. Graphite material is still the main anode material of today's lithium ion battery. However, its safety performance is lower than that of hard carbon materials, and the spinel lithium titanate anode material has higher safety performance. The use of a new membrane that can withstand higher temperatures and an electrolyte with a flame retardant is also a technical means to improve the safety of lithium-ion batteries.
The main factors affecting the safety of lithium-ion batteries are the electrode material of the battery, the electrolyte, the manufacturing process and the conditions of use. The weight of a lithium-ion battery used in a mobile phone is about 20 grams. The basic requirement is that the probability of a safety accident is less than one in a million. This is the minimum standard acceptable to the public. The actual situation is more than one in ten thousand. Be small. The weight of the lithium-ion battery pack used in electric bicycles ranges from 3 kg to 4 kg, which is more than 100 times larger than that of mobile phones. Pure electric cars will use batteries of 300 kg to 400 kg. As for the weight of electric buses or electric trucks, the battery weight will be It is 1500 kg to 2000 kg, and it is 75,000 times to 100,000 times that of "mobile phone". As battery capacity increases, the likelihood of a safety incident increases dramatically. Therefore, when a lithium ion battery is used as a power battery, it is necessary to improve its safety performance. The larger the unit cell, the higher the safety index required to be achieved. For example, lithium cobalt oxide and graphite commonly used in mobile phone batteries are used as positive and negative materials for lithium ion power batteries, and the safety of batteries after large-scale operation cannot be guaranteed.
At the beginning of the development of lithium-ion battery electric vehicles in China, there have been several explosions and combustion accidents. One of the main reasons is the use of lithium cobalt oxide as the cathode material for batteries. At that time, finding a positive electrode material for replacing lithium cobaltate to solve the safety problem was the top priority for the developer of the lithium-ion battery. The safety of high-power lithium-ion batteries in China has been well resolved during the 10th Five-Year Plan period. The use of a modified lithium manganate material reduces the oxidation of the positive electrode, and the content of active lithium is also lower than that of lithium cobaltate. The capacity of lithium manganate batteries produced in mass production in Japan is not large. For example, the batteries for the 3000 electric vehicles in Tokyo are 216 13Ah lithium manganese oxide batteries.
Lithium iron phosphate is safer for the positive electrode. In terms of the positive electrode, lithium iron phosphate (LiFePO4) has high thermal stability in the charged state, low oxidizing ability to the electrolyte, and better safety, and can be used to make a larger battery. The theoretical capacity of LiFePO4 is 170 mAh/g, which is 3.5V with respect to the metal lithium voltage. The actual reversible capacity of the material can exceed 160 mAh/g. Compared with other materials, the chemical diffusion coefficient of lithium ions in LiFePO4 is low, and the electron conductance at room temperature is much lower than other cathode materials. It is necessary to improve the material properties and achieve application by reducing the material size and coating the conductive agent. The defects are low density, large battery volume and high electrolyte usage. The current research hotspot is to develop new synthetic methods of lithium iron phosphate and modify the materials to improve the comprehensive performance of lithium iron phosphate.
The earliest synthesis method of lithium iron phosphate was the solid phase reaction method of JB Goodenough. The method is simple and convenient, and easy to operate. The disadvantage is that the synthesis cycle is long and the batch stability of the product is difficult to control. How to prevent the oxidation of ferrous iron during heat treatment and powder processing is a key control point for synthesis. At present, there are many carbothermal reduction methods, coprecipitation methods, hydrothermal methods, and spray pyrolysis methods developed by R&D teams.
At present, companies that can produce lithium iron phosphate in the world include Valence, A123, and Phostech. There are also many enterprises that are conducting industrial development of lithium iron phosphate in China. According to Internet surveys, 80% of domestic well-known lithium battery cathode material suppliers have announced that they are developing and producing lithium iron phosphate related products. Compared with the "international professional players", from the perspective of investment in research and development and time, it is still in its infancy.
Lithium iron phosphate is still very young compared to other lithium battery materials. Some people say that the battery used in electric tools, some people say that it will be applied to the battery of electric buses, the initial development is to be encouraged.
Japan has a monopoly position in the field of lithium-ion batteries. Sony, Sanyo Electric, Panasonic Battery, NEC and other famous companies have established large-scale lithium-ion battery production lines, and most manufacturers are not only maintaining and expanding the output of the original brands, but also Use their respective advantages to develop new products for lithium-ion power batteries. Japan’s new Sunshine Program has launched a lithium-ion battery development program for vehicles since 1992, investing more than $1 billion in research and development, and achieving technological and technological breakthroughs. Toyota Motor Co., Ltd. has begun mass production of on-board lithium-ion rechargeable batteries for use in some models of the small car "Vitz" that was launched in February 2003. The stability has been tested by the market. Lithium-ion batteries produced by Hitachi, NEC, Mitsubishi and other companies are used in electric vehicles and hybrid electric vehicles in batches. Fuji Heavy Industries introduced the lithium-ion battery Electric Vehicle "R1e" for lithium electroplating designed for Tokyo Electric Power. In the mode, it can be filled with 80% in 15 minutes and about 80km in 1 charge. The maximum speed is 100km/h. Tokyo Electric Power introduced 30 more R1e in 2006. In addition, approximately 3,000 vehicles are introduced in total after the fiscal year. In general, Japan is still the leading country in power battery technology. Its power battery and its key material mass production technology have matured, and its performance has almost met the demand of electric vehicles.
Using a variety of methods to improve the safety of safety batteries involves many aspects of materials, battery design, manufacturing, and application. Simply changing the cathode material does not completely guarantee the safety of the battery. Only the main materials should carefully choose the anode material, electrolyte and battery separator. For example, the anode material used as the lithium ion battery is carbon material, metal oxide and alloy. Graphite material is still the main anode material of today's lithium ion battery. However, its safety performance is lower than that of hard carbon materials, and the spinel lithium titanate anode material has higher safety performance. The use of a new membrane that can withstand higher temperatures and an electrolyte with a flame retardant is also a technical means to improve the safety of lithium-ion batteries.
The main factors affecting the safety of lithium-ion batteries are the electrode material of the battery, the electrolyte, the manufacturing process and the conditions of use. The weight of a lithium-ion battery used in a mobile phone is about 20 grams. The basic requirement is that the probability of a safety accident is less than one in a million. This is the minimum standard acceptable to the public. The actual situation is more than one in ten thousand. Be small. The weight of the lithium-ion battery pack used in electric bicycles ranges from 3 kg to 4 kg, which is more than 100 times larger than that of mobile phones. Pure electric cars will use batteries of 300 kg to 400 kg. As for the weight of electric buses or electric trucks, the battery weight will be It is 1500 kg to 2000 kg, and it is 75,000 times to 100,000 times that of "mobile phone". As battery capacity increases, the likelihood of a safety incident increases dramatically. Therefore, when a lithium ion battery is used as a power battery, it is necessary to improve its safety performance. The larger the unit cell, the higher the safety index required to be achieved. For example, lithium cobalt oxide and graphite commonly used in mobile phone batteries are used as positive and negative materials for lithium ion power batteries, and the safety of batteries after large-scale operation cannot be guaranteed.
At the beginning of the development of lithium-ion battery electric vehicles in China, there have been several explosions and combustion accidents. One of the main reasons is the use of lithium cobalt oxide as the cathode material for batteries. At that time, finding a positive electrode material for replacing lithium cobaltate to solve the safety problem was the top priority for the developer of the lithium-ion battery. The safety of high-power lithium-ion batteries in China has been well resolved during the 10th Five-Year Plan period. The use of a modified lithium manganate material reduces the oxidation of the positive electrode, and the content of active lithium is also lower than that of lithium cobaltate. The capacity of lithium manganate batteries produced in mass production in Japan is not large. For example, the batteries for the 3000 electric vehicles in Tokyo are 216 13Ah lithium manganese oxide batteries.
Lithium iron phosphate is safer for the positive electrode. In terms of the positive electrode, lithium iron phosphate (LiFePO4) has high thermal stability in the charged state, low oxidizing ability to the electrolyte, and better safety, and can be used to make a larger battery. The theoretical capacity of LiFePO4 is 170 mAh/g, which is 3.5V with respect to the metal lithium voltage. The actual reversible capacity of the material can exceed 160 mAh/g. Compared with other materials, the chemical diffusion coefficient of lithium ions in LiFePO4 is low, and the electron conductance at room temperature is much lower than other cathode materials. It is necessary to improve the material properties and achieve application by reducing the material size and coating the conductive agent. The defects are low density, large battery volume and high electrolyte usage. The current research hotspot is to develop new synthetic methods of lithium iron phosphate and modify the materials to improve the comprehensive performance of lithium iron phosphate.
The earliest synthesis method of lithium iron phosphate was the solid phase reaction method of JB Goodenough. The method is simple and convenient, and easy to operate. The disadvantage is that the synthesis cycle is long and the batch stability of the product is difficult to control. How to prevent the oxidation of ferrous iron during heat treatment and powder processing is a key control point for synthesis. At present, there are many carbothermal reduction methods, coprecipitation methods, hydrothermal methods, and spray pyrolysis methods developed by R&D teams.
At present, companies that can produce lithium iron phosphate in the world include Valence, A123, and Phostech. There are also many enterprises that are conducting industrial development of lithium iron phosphate in China. According to Internet surveys, 80% of domestic well-known lithium battery cathode material suppliers have announced that they are developing and producing lithium iron phosphate related products. Compared with the "international professional players", from the perspective of investment in research and development and time, it is still in its infancy.
Lithium iron phosphate is still very young compared to other lithium battery materials. Some people say that the battery used in electric tools, some people say that it will be applied to the battery of electric buses, the initial development is to be encouraged.
Japan has a monopoly position in the field of lithium-ion batteries. Sony, Sanyo Electric, Panasonic Battery, NEC and other famous companies have established large-scale lithium-ion battery production lines, and most manufacturers are not only maintaining and expanding the output of the original brands, but also Use their respective advantages to develop new products for lithium-ion power batteries. Japan’s new Sunshine Program has launched a lithium-ion battery development program for vehicles since 1992, investing more than $1 billion in research and development, and achieving technological and technological breakthroughs. Toyota Motor Co., Ltd. has begun mass production of on-board lithium-ion rechargeable batteries for use in some models of the small car "Vitz" that was launched in February 2003. The stability has been tested by the market. Lithium-ion batteries produced by Hitachi, NEC, Mitsubishi and other companies are used in electric vehicles and hybrid electric vehicles in batches. Fuji Heavy Industries introduced the lithium-ion battery Electric Vehicle "R1e" for lithium electroplating designed for Tokyo Electric Power. In the mode, it can be filled with 80% in 15 minutes and about 80km in 1 charge. The maximum speed is 100km/h. Tokyo Electric Power introduced 30 more R1e in 2006. In addition, approximately 3,000 vehicles are introduced in total after the fiscal year. In general, Japan is still the leading country in power battery technology. Its power battery and its key material mass production technology have matured, and its performance has almost met the demand of electric vehicles.
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