The development of new energy vehicle power battery systems involves materials, chemistry, mechanics, thermodynamics, heat transfer, fluid mechanics, electricity, systems and control. Its key technologies include battery pack assembly technology, thermal management technology, power management technology and safety Tube

　　The development of new energy vehicle power lithium battery systems involves materials, chemistry, mechanics, thermodynamics, heat transfer, fluid mechanics, electricity, systems and control. Its key technologies include battery pack assembly technology, thermal management technology, power management technology and Safety management technology, etc. Vehicle power lithium battery system technology has become a bottleneck for the popularization of electric vehicles. It needs to be explored and broken through from many aspects such as material development, battery design, processing and manufacturing, system integration, and business models.

　　1. Classification of new energy vehicle power lithium batteries

　　New energy vehicle power lithium batteries can be divided into two categories: batteries and fuel cells. Batteries are used in pure electric vehicles (EV), hybrid electric vehicles (HEV) and plug-in hybrid electric vehicles (PHEV); fuel cells Dedicated to fuel cell vehicles (FCV).

　　1.1 Battery

　　Low temperature lithium iron phosphate battery 3.2V 20A -20℃ charging, -40℃ 3C discharge capacity ≥70%

　　Charging temperature: -20~45℃ -Discharge temperature: -40~+55℃ -40℃ Support maximum discharge rate: 3C -40℃ 3C discharge capacity retention rate ≥70%

　　Batteries are the only power source for the drive system in pure electric vehicles, mainly including nickel, nickel metal hydride and lithium-ion batteries. Currently, lithium-ion batteries are in a stage of rapid development, and are used in new energy vehicles such as the Nissan Leaf, Toyota Prius plug-in, Tesla Model S, GM Volt, Ford Focus EV and BMW i3. In addition, lithium resources are relatively abundant and the price is not expensive. It can be said that lithium-ion batteries are currently the most promising power lithium batteries in the market. The performance comparison of Category 4 batteries is shown in Figure 1.

　　1.2 Fuel power cell

　　A fuel power cell is a device in which fuel and oxidant react directly to convert their chemical energy into electrical energy through electrode reactions. Fuel-powered cells do not need to be charged and have the advantages of high specific energy, long service life, less maintenance work, and the ability to continuously supply high power. In addition, fuel cell vehicles can achieve the same driving range as fuel vehicles.

　　According to different electrolytes, fuel cells can be divided into five categories: alkaline fuel cells, phosphoric acid fuel cells, proton exchange membrane fuel cells, molten carbonate fuel cells and solid oxide fuel cells. At present, proton exchange membrane fuel cells are widely used in fuel cell vehicles and will be a very competitive battery type in the field of lithium battery power for new energy vehicles in the future.

　　2. Overview of new energy power lithium battery industry technology

　　Low temperature and high energy density 18650 3350mAh-40℃ 0.5C discharge capacity ≥60%

　　Charging temperature: 0~45℃ Discharge temperature: -40~+55℃ Specific energy: 240Wh/kg -40℃ Discharge capacity retention rate: 0.5C Discharge capacity ≥ 60%

　　Since the usage methods of vehicle power lithium batteries are quite different in different types of new energy vehicles, their performance requirements are quite different. HEV has a gasoline engine as the power source, which places more emphasis on acceleration performance and climbing ability, so it pays more attention to the specific power of the battery (requiring up to 800 to 1200W/kg); PHEV and EV are completely powered by batteries and place more emphasis on continued driving after charging. capacity, so more attention is paid to the specific energy of the battery (required to reach 100-160Wh/kg)

　　Due to significant differences in their respective properties, materials, costs, etc., the use prospects of different types of power lithium batteries are different. At present, the most mature technology is nickel-metal hydride power lithium battery, but the most successful commercialization is lithium-ion battery, and fuel power battery is widely regarded as a long-term goal.

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