Recently, Hitachi has developed a 48V lithium-ion battery pack with high power output suitable for small-displacement vehicles for medium-hybrid vehicles. Due to its system's good fuel consumption reduction effect and high cost performance, it is expected to be popular in China and Europe. The 48V system currently on the market is mainly used for micro-hybrid and weak hybrid vehicles. The lithium-ion battery pack developed by Hitachi this time further expands the application of the 48V system in the field of hybrid vehicles.

　　48V system concept

　　In order to more effectively save energy, reduce emissions, and improve fuel economy, people have found a new system between the transformation of the engine itself and the replacement of a completely new power system, that is, the hybrid power system. Nowadays, a hybrid system is widely used, that is, in a car with a gasoline and diesel engine, an electric motor is added, and the two engines work together. The initial micro-hybrid system is to add a belt-driven starter motor (BSG) to the starter motor (usually 12V) on the traditional internal combustion engine. The motor is a stop-start integrated motor to control the start of the engine. And stop, thereby canceling the idle speed of the engine, reducing fuel consumption and emissions, that is, the so-called 12V micro-mixing system has the function of automatic start and stop.

　　The 48V system is an improvement to the 12V micro-hybrid automatic start-stop system. The voltage of the system is 48V. The traditional lead-acid battery is replaced by a power lithium-ion battery with an energy of less than one kilowatt-hour, and the traditional starter motor and generator are replaced by a BSG motor. It is equivalent to an enhanced version of the automatic start-stop system. In addition to the automatic start-stop function, it can also provide auxiliary power when necessary.

　　The source of the 48V system

　　The concept of the 48V system originated from the joint launch of several German vehicle manufacturers including Audi, BMW, Daimler, Porsche and Volkswagen in 2011 and the development of the LV148 standard. In June 2013, the European Union approved the 2020 carbon dioxide emission standard, which requires that the average carbon dioxide emission level of new cars be controlled at 95 g/km by 2020; if European car manufacturers cannot meet the requirements for CO2 emission restrictions in the future, they will face A fine of up to 95 Euros per gram per car per excess. This compulsory standard has prompted OEMs and component suppliers to reduce the fuel consumption of vehicles from different technical routes. The 48V system has become the focus of attention in the industry due to its increased limited cost and significant energy-saving and emission-reduction advantages.

　　Compared with the advantages of the 12V micro-hybrid system, Hong Yinglin, Delphi Parker’s Asia Pacific New Energy Product Manager, gave us an example: “For example, air conditioners. When a traditional car is waiting for a red light, the engine is idling, and the belt-driven air conditioner compressor can Continue to work, the air conditioner will still be cooled. But for cars with start-stop function, they need to switch to electric air conditioners when they wait for the red light, otherwise the passengers have to endure the environment without air conditioning when the red light or traffic jam. An electric air-conditioning compressor The minimum power is 2.5kw. If 12V is used for power supply, the grid will be unbearable, and 48V will be no problem. In addition, the 48V side can also provide power for active suspension, electric steering, electric heaters, etc."

　　At present, the mainstream in the Japanese market is a strong hybrid vehicle equipped with a high-voltage battery of more than 100V, which uses a lithium-ion rechargeable battery module of more than 100V. Although it can greatly improve the fuel efficiency of hybrid vehicles (HEV), it is a special component And the cost of withstand voltage components is high. Using a 48V system will also increase the cost, but compared to the cost of a pure electric vehicle or a strong hybrid car, the 48V system can save 40% to 60% of the cost, and the 48V lithium-ion rechargeable battery module can also increase the cost by 10-15%. Fuel efficiency.

　　One of the keys to the 48V system specification is the lithium-ion battery technology, which can provide a higher (3 times) energy density than the lead-acid chemical battery, and reduce the size and weight. The 48V lithium-ion battery has better charging performance and can more efficiently store the energy recovered by the car’s braking, which can provide more and more electronic loads (such as front seat heating, heated windshield, rear Shock absorber) provides more power.　　 48V lithium ion battery system application status

　　One of the keys to the 48V system is lithium-ion battery technology. Compared with lead-acid batteries and nickel-hydrogen batteries, lithium-ion batteries have higher energy density and better charge and discharge performance. The voltage of lithium-ion batteries is as high as 3.7V. In order to meet the voltage requirements of electric vehicles, it is necessary to connect single batteries in series and parallel to form a battery pack to meet the high-energy and high-power conditions required for electric vehicles. Under normal circumstances, the car power system regards the battery pack as a single battery. During the start and stop of the car, the entire battery pack undergoes frequent charging and discharging processes. The battery pack is composed of single cells, and the absolute consistency of the battery cells cannot be guaranteed before leaving the factory. If a battery in the battery pack has undergone multiple charge/discharge cycles, its state of charge cannot be periodically balanced with other batteries , It will eventually enter a deep discharge state, which will cause damage and eventually cause a battery pack failure. Therefore, we need a battery detection system (BMS: Battery Management System) to monitor and measure the overall condition of the battery pack and individual batteries, including voltage, current, and charge. Status, etc., and replace the single battery in time to extend the endurance and service life of the battery pack.

　　The 48V lithium-ion battery pack newly developed by Hitachi this time contains BMS substrates, battery cells, relays, and fuse packs in the same box. It has strong assembly and high reliability. This battery pack can accelerate and decelerate the vehicle. As well as energy regeneration during braking, it supports the efficient operation of hybrid vehicles' engines and motors.

　　At present, the 48V lithium-ion battery packs on the market generally consist of 12 to 13 single cells, which are mostly used in the field of small pure electric vehicles such as electric bicycles, electric motorcycles, electric tricycles, etc., as well as power tools; mainly for vehicles Lithium-ion power battery manufacturers include AVIC Lithium, CITIC Guoan Mengguli and Wanxiang Group.

　　In the field of hybrid vehicles, the 48V lithium-ion battery pack system is mainly used in micro-hybrid or weak-hybrid systems, and is at the level of research and development and limited production. In response to the development of more energy-efficient automotive products, car giants are developing automotive products that use 48V automatic start-stop systems. The world's leading industry research organization IHS released a report that by 2025, 48V mild hybrid vehicles will account for more than half of all hybrid vehicles, and 95% of mild hybrid vehicles will adopt the 48V solution.

　　The 48V lithium-ion battery pack developed by Hitachi this time can be applied to moderate hybrid electric vehicles, with higher input power and output power, and the battery cells have excellent low temperature resistance, and the output density is the same as that of the previous Hitachi battery cells. 1.5 times, both good fuel consumption reduction effect and high cost performance have played a role in promoting the popularization of mid-mixed vehicles in China and Europe.