First, the development trend of lithium battery is introduced. In recent years, the development trend of power battery is very rapid. By 2025, the total sales of new energy vehicles will reach 6.6 million units, and the rapid growth in pure electric and PHEV has surpassed that of hybrid vehicles. By 2025, the entire estimated capacity will reach 85GWH, but in the morning, experts also said that the entire power battery capacity has exceeded the demand for electric vehicles, but the demand for high-end batteries is still lacking.
The state has also made a specific plan for the development of power batteries. By 2020, the energy density should reach 300 watt-hours per kilogram, the cost should be less than 1.5, and the later to reach 300 watt-hours per kilogram, the cost is less than 0.8 yuan. The life span reaches 1500 times. The energy density of the new lithium-ion battery will reach 400 watt-hours per kilogram, and the new system should reach 500 watt-hours per kilogram.
The state plans for the entire battery. From 2020 to 2025, there will be a technical requirement in 2030, and the requirements will be continuously improved. The energy density should be higher and higher, especially the cost of the system, from 1.3 yuan / The watt hour dropped to 0.8 yuan / watt hour.
The first phase is from 2016 to 2020, this is an upgrade phase of technology. First, the monomer energy density should reach 300 watt-hours per kilogram, and the cost should be reduced by 50% to 0.6 yuan/watt hour. This is a monomer with an energy density of 250. From 2014 to 2015, the cost of power batteries is still between 2.5 yuan and 3 yuan, but in 2017 it has quickly dropped to between 1.6 yuan and 2 yuan, the whole is very in line with the market demand for power batteries.
The second and third phases, which I have already mentioned before, will not be repeated.
The key to the development of a power battery is nothing more than these aspects. It is very simple to say, but it is very difficult to do. The first one is that the one-time requirement is very high, except for the single unit, especially after the group is one-off. In terms of safety, because it is related to the safety of people's lives and property, it must be done in terms of safety. Low cost, high power density, maintenance free, good high and low temperature performance, environmental friendliness, long cycle life and fast charging.
Lithium battery power battery system development route, from the current point of view is still in the lithium iron phosphate, ternary and lithium manganese oxide plus carbon system, the current energy density has reached 160 to 200 watt hours, and will continue to develop later From the high nickel system, NMC, NCA and high nickel nickel manganese system plus carbon, can achieve 200 to 280 watt hours per kilogram. To achieve 250 to 400, in addition to policy cooperation, the application of core materials such as silicon carbon, tin and other materials is required. To be more than 400 or more, basically the system needs to change, like the application of new systems such as lithium-sulfur batteries and lithium air mentioned by several professors.
In terms of technical routes, we will elaborate on these three aspects.
At present, there are three types of power batteries in terms of shape, square, cylindrical, and soft. In terms of the market ratio of these products, soft-pack batteries have shown a very rising trend in recent years. In some high-end fields, For example, the batteries of Water and Nissan are all used in flexible packaging batteries. The proportion of flexible packaging batteries is expected to exceed 50% in future trends. Compared with other two square and cylindrical batteries, the flexible packaging battery has the biggest advantage of safety performance. Because it is a flexible package, it is sealed by PP film, so the internal pressure is relatively low, generally 2 to 3 kg. The pressure will be released. The cylindrical and square lithium batteries are passed through a soft port or a laser welding method, and the pressure is generally about 10 to 15 kg. Therefore, if the explosion-proof valve cannot be fully opened, the explosion may occur, so the safety performance of the flexible package is slightly better when compared with the three shapes.
There are also flexible packaging that has advantages in terms of charging and discharging. Since 1997, flexible packaging has been applied in the field of MP3 and digital batteries. In 2001, it was applied to mobile phones and Bluetooth headsets. In 2004, it was applied to aircraft models. Since 2005, it has been used in LEV, electric bicycles and tablets. In the following years, it began to focus on the application of power batteries. In fact, from the analysis of data, the growth rate of power batteries in recent years has exceeded the growth rate of consumer. The history of the development of flexible packaging is basically the growth of the excellent technical team.
From the perspective of the new energy automobile industry chain, it is mainly divided into upper, middle and lower reaches, and the upstream is mainly the mineral resources of nickel ore, graphite, lithium ore and positive and negative materials. The middle reaches are mainly the core material, positive electrode, negative electrode, electrolyte, diaphragm and some other materials. The middle is our battery manufacturing and PACK assembly. Downstream is the consumer electronics such as mobile phones, as well as power tools, electric bicycles, electric new energy vehicles and energy storage systems.
Analysis of the cost of new energy vehicles, power batteries have basically occupied 50% of the cost of new energy vehicles, so why so many large passenger car manufacturers must have their own battery manufacturers and PACK manufacturers, which is the core technology of new energy vehicles It can also be seen from the cost.
From the analysis of the cost of the entire power battery, the positive electrode accounts for about 35% to 50%. Recently, after the price of the positive electrode material has increased, basically, the entire cost has accounted for 50% of the entire power battery. Others such as electrolytes and diaphragms account for about 10%.
Several factors affecting the life of the power battery are mainly from the positive electrode, the negative electrode, and the electrolyte and the separator. The positive electrode material is also introduced in front of the positive electrode material. For example, there are some coating, doping, and granular precursors. Performance will affect the life of our power battery.
The positive electrode material mainly requires small redox change positioning, chemical stability, particle, morphology, material matching, and its ionic conductivity, high current charge and discharge performance. The negative electrode is also the same. It is desirable to form a good SDI film, which can quickly accommodate lithium ions, can be quickly charged and discharged, and discharge is very good.
In terms of electrolytes, we have studied new material combinations, as well as film-forming additives for SEI films, as well as some over-charged additives, because our new national standard requires ternary requirements, requiring its voltage to be EC-charged, high. The voltage test at 1.5 times should be able to pass. Therefore, in the electrolyte, there is also a combination of positive electrode coating to pass this test.
The electrolyte should have additives for corrosion prevention, and additives for lowering internal resistance, improving surface activity, and improving positive film formation performance. On the diaphragm side, I saw that the former Chinese Academy of Sciences teacher also introduced that we are in the diaphragm, because the safety performance is required in the power battery application, so its heat shrinkage ability is good, and the ion conductor can quickly pass the ion conductor. The coated diaphragm also has a high voltage resistant diaphragm.
The comparison of several existing materials is not repeated here. At present, there are several choices for cathode materials. One is that we use the most, which is ternary 523, 622, and even 811. These may still be in the laboratory stage, and there is no mass production. There is also a binary type of nickel-manganese, which may require a relatively high voltage, 5 volts, and the nickel-cobalt-lithium ternary material used by Tesla, as well as negative lithium. We are very optimistic. Because it does not have a particularly expensive metal such as nickel and cobalt, the energy density is very high. If this material can be applied very well, the cost of the power battery can be reduced immediately. There are also some sodium and potassium ions behind, which can reduce costs.
Our capacity analysis of different ternary materials, with the addition of nickel content, its capacity will be higher and higher, but it is necessary to meet some high-voltage electrolytes, membranes, such as some processing technology matching .
In terms of electrolytes, some new lithium salts are used to match this system, for example, some ODFB, including some of the current TFSI and FFSI salts, including some low-temperature lithium difluorophosphate, by forming a protective film on the positive electrode, The reaction between the ternary and the positive electrode electrolyte is increased to increase the life of the battery.
The lithium-rich manganese is mainly at 2 to 4.8 volts and can exert a capacity of 250 mAh or more. However, due to some structural problems of this material and some limitations faced by it, many experts may not be optimistic about this material, but because of its low lithium diffusion efficiency, its platform will gradually reduce these shortcomings, including scientific research. Institutions and many companies have not used this material well. In fact, some doping, modification, nanocrystallization and improved coating can be gradually overcome. At present, there are already good results in our laboratory.
There is also a lithium manganese iron phosphate which is mainly capable of improving its voltage platform, maintaining the safety performance of lithium iron phosphate and increasing the energy density. This is also a promising material, and this material is relatively mature. There are also some new sodium salts, sodium iron sulfate and other materials mentioned above, which are not new materials synthesized by lithium phosphate, and are also new materials, which can reduce the cost.
The negative electrode is currently mentioned by everyone, that is, silicon carbon, but because of the characteristics of silicon carbon itself, such as its expansion and its punctual efficiency, everyone has tried to solve this problem. Including lithium, including some compounding with carbon, to avoid its shortcomings, to apply its advantages. Silicon nanocrystallization, and graphene doping, as well as PV connectors are used to better use silicon carbon, and then with the electrolyte.
In addition to the material aspect, it is also very important in the battery process. This is also affecting the life of our power battery. The first point is the one-time coating. Coating is a basic part of the power battery. If this program is not done well. It is very difficult to make a battery with very good performance. So in terms of coating, in fact, the degree of automation in China has reached a level. Now we will apply this squeeze coating, which can control the accuracy of plus or minus 1 and control by Xre or β-ray. Density is controlled in closed loop. In addition, the consistency of the compaction density in the production process also has a great influence on the performance of the battery, especially in the compaction of the negative electrode, which has a great influence on the cycle of the battery and the energy. There is also moisture control. There are also chemical conversion technologies. Flexible packaging has certain advantages in chemical conversion technology. It can use high temperature pressurized technology, cylindrical or aluminum shell batteries. Aluminum shell batteries currently use negative pressure, about one atmosphere, but soft packs can add several The pressure can make the positive and negative electrodes more closely contact, and can form a dense film when held, maintaining its later performance.
There is also the amount of liquid retention. Some experts say that the battery will be replenished after the battery is taken back, so that its secondary life can be improved and used twice. In fact, the amount of rehydration is also very important at the first time, which directly affects the use of long loops of the battery.
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