Selection of positive/negative materials and technical research of 12v 18650 battery pack

"Higher, faster, stronger" is the well-known Olympic competitive spirit. This motto of the Olympic movement was proposed by Coubertin, the initiator of the modern Olympic movement, and expounds the Olympic movement's spirit of continuous progress and never-satisfied struggle.

Switching to the electric vehicle industry, the power lithium battery, as its heart, is a challenge and research hotspot currently facing the industry in terms of battery material selection and technical research, developing new technologies, supplying higher energy density, and achieving longer driving range.

According to Fang Kaizheng, an expert in the Power Lithium Battery Research Laboratory of the Beijing Work Department of my country Automotive Research Center, the increase in the output of new energy vehicles has driven the increase in power lithium battery supporting batteries. In the first three quarters, the total amount of power lithium battery supporting batteries exceeded 12.1 billion watt-hours, of which the supporting amount for pure electric vehicles was 11 billion watt-hours and the supporting amount for plug-in hybrid vehicles was 1.1 billion watt-hours. Riding on the development trend of the power lithium battery industry, industry researchers are also constantly studying the technical research and development path to improve the energy density of 12v 18650 battery pack and achieve its development goals of "higher energy density, stronger power, and longer endurance".

Diversification of technical routes

Tan Xinxin, deputy director of the Research Institute of Hunan Shanshan Energy Technology Co., Ltd., said that as an important supplier of raw materials in the battery field, Shanshan will consider continuously improving the discharge capacity and charge and discharge voltage of battery materials, and will also consider its power density and calendar life, including cycles, side reactions, etc.

Shanshan Energy is a subsidiary of Shanshan Co., Ltd., established in 2003, with two subsidiaries, Hunan Shanshan New Energy and Ningxia Shanshan New Energy. In the face of challenges such as the future electric vehicle range of 400-500 kilometers and battery life of 10 years or even longer, Hunan Shanshan Research Institute will continue to carry out technical research and development on high-performance power ternary materials to meet the needs of downstream power lithium battery factories.

In terms of material selection, high-nickel ternary materials have become the industry's popular choice. Because it has greater advantages in specific energy than lithium iron phosphate and low-nickel ternary materials. The company's related technology research and development investment has also followed up.

If you want to improve the battery energy density, when selecting materials, Tan Xinxin, director of Hunan Shanshan Research Institute, pointed out: "A high-performance power ternary material is not simply highlighting one or two series. If one series cannot do it, I think it is definitely not a good positive electrode material."

He also mentioned four possible technical research and development routes. The first is the nickel content improvement route that everyone is most familiar with and the most popular; the second is the medium nickel high voltage development route; the third is the high nickel high voltage development route; the fourth is the high voltage LCO development route. From the perspective of energy density, with the increase of nickel content, the overall energy density of the battery will become higher and higher, and the increase in power will also bring improvement. At the same time, high-voltage lithium cobalt oxide has a voltage platform and high capacity, and the overall energy density will also be relatively high.

However, when everyone is talking about high nickel capacity reaching 300Wh/kg or even 400Wh/kg, Tan Xinxin also mentioned that as far as the current situation is concerned, high nickel materials, especially materials with more than 80% nickel content, account for less than 1% of the entire domestic market this year. The promotion and use of high energy density positive electrode materials in China may take some time, and the entire industry must prevent excessive hype and local overheating.

High nickelization of positive electrode materials

In terms of the development trend of 12v 18650 battery pack, there are basically three categories of positive electrode materials. The negative electrode materials are mainly carbon materials, and silicon carbon materials and hot materials are also being studied. Among them, oxides are lithium titanate as an important material choice.

"Positive electrode materials will gradually transition to ternary materials as the main materials," said Chen Yanbin, general manager of Dangsheng Technology. In terms of the research and development of high energy density ternary materials, Dangsheng Technology has always been at the forefront of the industry. By increasing the nickel material content, continuously improving the battery energy density is a feasible technical route. However, what specific technical route to take, for example, whether to go high nickel or high voltage first, may vary from company to company.

Nowadays, high-energy-density cathode materials are increasingly becoming the mainstream of the battery industry. It is reported that domestic cathode material production companies with leading product technology have begun to study and produce high-nickel ternary materials. Some types of high-nickel ternary materials, such as 622 and 811, have also begun small-scale production, and some companies have already conducted trials in downstream companies. Moreover, the capacity ratios of 622 and 811 can reach 160mAh/g and 180mAh/g, respectively, which are a certain degree of improvement over the current 532 and 111 types.

To make high-nickel materials, problems such as life and storage safety must be solved, and optimization must be achieved from the precursor, deliquescence, doping, and surface. Regarding whether there is a problem with the life of high-nickel materials, Chen Yanbin also said that Dangsheng Technology's R&D technology can ensure that the life will not be affected on the basis of increasing the capacity by 20 mAh.

Increase research and development of negative electrode materials

At present, the batteries developed by domestic battery companies are basically lithium iron phosphate batteries, which are widely used in passenger cars, special vehicles, buses, etc. Yan Huiqing said: "To improve the energy density of lithium iron phosphate, we must first make a good negative electrode. We have been continuously developing negative electrode materials and making high-energy-density lithium iron phosphate batteries. From the perspective of powder processing, positive, negative or ternary materials have similar technologies in improving the overall compaction density and capacity of the battery. Therefore, we are also developing high-energy-density lithium iron phosphate batteries, striving to increase the battery capacity and compaction density. Especially the compaction density, so we made spherical lithium iron phosphate. At the same time, we apply high-end negative electrode materials to it, thereby improving the energy density of the entire lithium iron phosphate battery."

In contrast, industrial technology Lv Xuelong, a senior researcher at the Institute's Materials Research Department, believes: "In fact, last year, some battery manufacturers began to mention the use of ternary materials for mixing. The second solution is to use lithium iron phosphate directly as a positive electrode material to improve energy density. Other academic research units, such as Harbin Institute of Technology, also have technologies involving lithium vanadium phosphate. The difference is that it seems that for positive electrode material manufacturers, there is no effective solution for lithium vanadium phosphate at this stage."

Now the requirements for the range of electric vehicles are getting higher and higher. For 12v 18650 battery pack, if its energy density is required to be doubled, its technical difficulties exist in many aspects.

Su Jinran, deputy chief engineer of Tianjin Lishen Battery Co., Ltd. (referred to as "Lishen"), analyzed that it does take some effort to reach 350 watt-hours/kilogram under the current lithium-ion system. There is still some need for discussion on NCA, nickel materials, silicon-carbon negative electrode materials, etc., but the actual use of silicon-carbon negative electrode materials in 12v 18650 battery pack still needs to overcome some technical difficulties, such as its cycle characteristics, expansion characteristics, etc.

It is estimated that by 2020, the energy density of domestic lithium-ion 12v 18650 battery pack will reach 350 watt-hours/kilogram. In this regard, Su Jinran believes that this will require very high technology. If the current lithium battery system is used alone, it may be difficult to achieve this energy density value.

Therefore, some new power lithium battery positive electrode materials, negative electrode materials and even diaphragm materials should be studied in depth. If there is no breakthrough in these aspects, the improvement of technical level may be limited. Lishen also has a special team working on this.

From the perspective of the battery material system, Xiao Chengwei, director of the 18th Institute of my country Electronics Technology Group Corporation, said that the negative electrode material of the battery is basically carbon-based, and the positive electrode material will also have major changes, including lithium manganese oxide, lithium cobalt oxide and other materials.

From the perspective of the overall development industry trend, it is hoped that through the selection of some different material systems, hybrid lithium batteries with higher and higher industrial energy density can be developed to achieve large-scale application in the field of new energy vehicles.

However, Xiao Chengwei analyzed that from the current technical development roadmaps issued by the state and the next subsidy policy, the state is still guiding the direction of high-energy-density batteries. While various battery companies are trying to increase the energy density of lithium iron phosphate batteries as much as possible, they will also increase their efforts to develop and promote some products of ternary batteries in the next step.

Power lithium battery research and development technology is an important factor affecting the promotion and application of electric vehicles. As one of the important indicators of power lithium battery performance, improving energy density is only one of the methods. The entire power lithium battery industry must also reduce costs and improve the overall performance of 12v 18650 battery pack by improving power density, service life, and developing new material technologies.

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