Deep analysis of the three major paths for power cells to increase energy density

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In 2017, the state's subsidies for new energy vehicles fell by a larger margin than in 2016. According to informed sources, some small-scale new energy vehicle companies have been forced to change due to subsidies, and the remaining new energy vehicle manufacturers have begun to make great efforts to improve product performance and quality. But how do these companies that hold their positions survive, and how to solve the problems of increasing the energy density of new energy vehicles' power batteries? Wang Dong, director of the National 863 Electric Vehicle Major Power Battery Test Center, said that the battery energy density is not simply the energy density of the battery level, but the battery level, which is the energy density of the system. Standards have also been raised to the system level.

So how to improve the energy density of the power battery system?

Improve light weight level and indirectly increase power density of power battery

In the past, new energy vehicle manufacturers used steel materials to make electric vehicle power battery trays. Now many companies are mainly based on aluminum alloy materials. The density of the aluminum alloy is 2.7 g/c m3, and the aluminum alloy is excellent in terms of compression and welding. The magnesium alloy has a density of 1.8 g/cm3 and the carbon fiber is 1.5 g/cm3. These materials are used to produce battery trays, which will greatly improve the lightweight level of new energy vehicles. Wang Zidong believes that lightweight technology is still evolving, and more lightweight materials will be available in the future. He said that not only should the weight of the battery tray material be studied, but also the weight of the material should be considered from the power battery unit to the system, so as to maximize the energy density of the power battery.

Lightweight needs to reduce the weight of the parts, but it does not reduce the strength of the parts, so the material's robustness needs to be considered. In addition, the use of lighter materials will face the problem of rising costs. Therefore, in the case that the cost of the power battery has not been greatly reduced, it is imperative to develop a lightweight and reliable material that is more reliable and economical. In this regard, foreign research and development is better. In 2016, Volvo announced that the lightweight battery of electric vehicles has entered the practical testing stage. Volvo said that if the current electric vehicle battery is completely replaced with a new lightweight material, it can reduce the weight of the car by more than 15%, and the material cost is lower and more environmentally friendly. However, China's research and application in this area is still lagging behind, and efforts must be made to catch up with the pace of foreign companies.

Tangled iron lithium or ternary is not as good as layout silicon carbon anode

As the two major domestic technology routes, the energy density of lithium iron phosphate and ternary materials has increased in recent years. Because the energy density of the ternary is higher, and the subsidy policy is more inclined to high-energy density products, all major battery companies regard the ternary battery as the main force of the company's next-generation products. For example, Tianjin shares said that it has mass-produced ternary cell core energy of 215 wh/kg, and will mass produce 230 Wh/kg in 2017. Recently, it will focus on developing high-nickel ternary material batteries; BAK 18650 cylinder The third-generation 2.9Ah product has been mass-produced with an energy density of approximately 218Wh/Kg. Currently, the development of high-nickel 811/NCA system is focused. However, Shen Wei, general manager of BYD Co., Ltd. believes that although the ternary and iron-lithium have a large difference in monomer energy density, they are almost the same in terms of system energy density after grouping, and also in terms of cost and battery storage difficulty. There is no big difference. Therefore, Shen Wei suggested that enterprises should consider starting from the negative electrode materials of power batteries in the planning of improving the energy density of power batteries, and apply silicon materials (such as silicon oxide anode materials) in mass production products to improve the overall energy density of the battery pack. .

Change battery size to increase system energy density

Changing the battery size is still an effective way to increase battery energy density. Although Tesla chose the 18650 technology route to successfully attract many domestic power battery companies to follow, but because of the small capacity of 18650 batteries, generally around 2-4Ah, the number of series and parallel is too much, the probability of single failure is greater. As a result, its application in the mainstream new energy passenger car and passenger car field is limited. In 2017, Tesla, the first to use 18650 batteries, turned its attention to the 21700 battery and has already achieved mass production. According to Tesla CEO Musk, when the Model 3 car with 21700 battery is launched, it will re-examine whether to use Model 21700 battery to manufacture Model S and Model X models. Once approved, the 21700 battery is likely to fully replace the 18650 battery on the Tesla. It is understood that after using 21700 batteries, Tesla will reduce the number of required batteries by about 1/3 due to the same energy, which will reduce the number of metal connectors in the entire package, thus further reducing the weight of the battery pack. The energy density of the car will be partially improved. This approach also provides a reference for domestic 18650 battery companies in improving energy density and reducing costs. It is understood that the current domestic 18650 battery companies basically recognize Tesla's way, and are also in the relevant layout. Among them, Shenzhen BAK, Far East Foster, Lions New Energy and other cylindrical battery companies have clearly announced that they will put into production 21700 batteries in the future capacity expansion, and Yiwei Lithium's first 21700 production line has been officially put into production, Lishen's 21700 The production line is also about to go into production.

Similarly, for soft and square batteries, changing the size can also increase the system's energy density to some extent.

In the post-subsidy era, the market needs electric vehicles that truly meet the needs of consumers. The power battery of a new energy vehicle is by no means a parallel connection with a small-capacity battery, or it is as simple as amplifying a small-capacity battery. Power battery companies should consider the overall perspective of new energy vehicles, improve the energy density of power batteries in a variety of ways, and gradually free consumers from "mileage anxiety."