Key Technology of 48V Lithium Battery System

Recently, Hitachi has developed a 48V lithium-ion battery pack suitable for small-displacement vehicles for hybrid vehicles. It is expected to be popular in China and Europe because of its good system performance in reducing fuel consumption and high cost. At present, the 48V system on the market is mainly used for micro-hybrid and weakly hybrid vehicles. The lithium-ion battery pack developed by Hitachi has further developed the application of the 48V system in the field of hybrid vehicles.

The concept of the 48V system

In order to more effectively save energy and reduce emissions and improve fuel economy, people have found a new system between the transformation of the engine itself and the replacement of a new power system, which is a hybrid system. It is now commonly used in hybrid systems, that is, in the car of the steam engine, plus an electric motor, the two engines work together. The initial micro-mixing system was equipped with a belt-driven start-up motor (BSG) on a conventional internal combustion engine start-up motor (usually 12V), which is a Station-Start integrated motor used to control the engine. Start and stop, this eliminates the idle speed of the engine and reduces fuel consumption and emissions, which is called the 12V micro-mixing system and has the function of automatic start and stop.

The 48V system is an improvement of the 12V micro-hybrid automatic starting and stopping system. The system has a voltage of 48V. The powerful lithium-ion battery with energy less than one degree is used instead of the traditional lead-acid battery, and the BSG motor is used instead of the traditional start-up motor and generator. Equivalent to an enhanced version of the automatic start and stop system, in addition to the automatic start and stop function, but also can provide auxiliary power when necessary.

Source of the 48V system

The concept of the 48V system was first derived from several German vehicle manufacturers in 2011, including Audi, BMW, Daimler, Porsche and Volkswagen, and developed the LV 148 standard. In June 2013, the EU approved the 2020 CO2 emission standard, which requires that the average CO2 emission level of new cars be controlled at 95 g/km by 2020; European car manufacturers will face fines of up to Euro95 per gram per vehicle if they fail to meet the CO2 emission restrictions in the future. This mandatory standard has prompted vehicle manufacturers and parts suppliers to reduce vehicle fuel consumption from different technical routes. The 48V system has become the focus of attention of the industry because of its advantages in increasing limited costs to save energy and reduce emissions.

Advantages and Key Technologies of the 48V System

Yingfeiling believes that the development of the 48V system is based on the following points:

Although the 12V startup is low-cost, CO2 emission reduction is limited;

High-pressure hybrid power emission reduction, but the system cost increased more;

48V to close to the cost of the 12V startup system;

Provide performance close to high-pressure hybrid technology;

CO2 emission reductions of up to 15 percent or more;

The system cost target is less than 1,000 euros;

Load other than power systems can be provided for more advanced and energy-efficient designs.

Compared to the advantage of the 12V micro-mixing system, Hongyinglin, manager of new energy products in the Asia-Pacific region of Delphi Parker, gave us an example: "For example, when a traditional car is waiting for a red light, the engine is idle, and the belt-driven air-conditioning compressor can continue to work. Air conditioning is still cooled. However, for a car with a stop function, it is necessary to switch to electric air conditioning when waiting for a red light, otherwise, passengers will have to endure the environment without air conditioning when waiting for a red light or traffic jam. An electric air-conditioning compressor has a minimum power of 2.5 kW. If it is powered by 12V, the grid will be unbearable. With 48V, there will be no problem. In addition, the 48V side can also supply power to active suspension, electric steering, electric warm wind and so on. "

At present, the mainstream in the Japanese market is a strong hybrid vehicle equipped with a high-voltage battery of 100V or higher. The lithium-ion rechargeable battery module of 100V or more is used, and although the hybrid vehicle (HEV) can greatly improve fuel efficiency, the special component is and the pressure component is costly. Using a 48V system will also increase the cost, but compared to the cost of a pure electric car or a strong hybrid car, the 48V system can save 40% to 60%, and the 48V lithium-ion rechargeable battery module can also increase 10 to 15%. Fuel efficiency.

One of the keys to the 48V system specifications is lithium-ion battery technology, which can provide higher (3 times) energy density, size, weight, and other reductions than lead-acid chemical batteries. The 48V lithium-ion battery has better-charging performance and can store vehicle braking recovery energy more efficiently, providing more power for the increasing number of electronic loads required in the car (such as front seat heating, heating windshield, rear shock absorber).

An application status of 48V lithium-ion battery system

One of the keys to the 48V system is lithium-ion battery technology. Lithium-ion batteries have higher energy density and better charging and discharging performance than lead-acid batteries and nickel-metal hydrogen batteries. Lithium-ion cells have a single voltage of up to 3.7 V. In order to meet the voltage requirements used in electric vehicles, it is necessary to use single cells in series to form batteries in parallel to meet the high energy and high power conditions required for electric vehicles. Under normal circumstances, the automotive power supply system will regard the battery pack as a single cell. During the process of driving and stopping the car, the entire battery pack undergoes frequent charging and discharge processes. The battery pack is composed of monomers and can not guarantee the absolute consistency of the cell monomer before the factory. If one cell in the battery pack undergoes multiple charge/discharge cycles, its charging state cannot be periodically balanced with other cells. Eventually, it will enter a deep discharge state, resulting in damage and eventually a battery failure. Therefore, we need a battery detection system(BMS: Battery Management System) to monitor and measure the overall situation of the battery and individual cells, including voltage, current, charge state, etc.., Replace individual cells in time to extend battery life and service life.

The newly developed 48V lithium-ion battery pack by Hitachi is a BMS substrate, battery monomer, Relay, and fuse group loaded in the same box. It can be highly assembled and reliable. This battery pack can accelerate and decelerate in vehicles. As well as the energy regeneration supply during braking, it supports the efficient operation of hybrid engine and motor.

At present, the 48V lithium-ion battery pack on the market is generally composed of 12 to 13 monomer cells, which are mostly used in the field of small pure electric vehicles such as electric bicycles, electric motorcycles, electric tricycles, and electric tools. The main manufacturers of lithium-ion power batteries for vehicles are AVIC Lithium, and CITIC UNITA Guli and Wanxiang Group.

In the field of hybrid vehicles, the 48V lithium-ion battery system is mainly used in micro-mixing or weak hybrid power systems and is at the level of R&D and limited production. Under the requirements of developing more energy-efficient automotive products, the car giant is developing automotive products that use the 48V automatic start and stop system. By 2025, 48V light hybrids will account for more than half of all hybrids, and 95 % of light hybrids will use the 48V scheme, according to a report released by IHS, the world's leading industry research institute.

The 48V lithium-ion battery pack developed by Hitachi can be applied to moderately hybrid electric vehicles, with higher input power and output power, and the battery monomer has excellent performance in low-temperature resistance, and the output density is 1.5 times that of Hitachi battery monomer., The combination of good effect of reducing fuel consumption and high cost performance has played a role in promoting the popularity of China and Europe.

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