What progress has been made in the application research of cascade power battery in power storage

At the 8th China international energy storage conference held recently, Yang kai, director of the research office of energy storage battery ontology technology of China electric power research institute co., LTD., delivered a wonderful speech entitled "research on the application of cascade power battery in power storage" in the special session of energy storage power station.

The speech is as follows:

Yang kai: hello, everyone. I'm Yang kai from China electric power research institute. Today, I'd like to share with you some of our work on battery utilization. Because cascade utilization battery is now a hot topic, China institute of electrical technology has been working on this topic for about five or six years since 2012. First understand phase using the technical background, the background we know more from various fields, because of our country's electric cars now has entered a rapid development period, sold 777000 units in 2017, is expected to more than 1 million vehicles in 2018, which is associated with the electric car battery retired quantity increases gradually, to his retirement in 2020 will reach 20 GWH, by the year 2025 is expected to reach 90 GWH. With such a large number of retired power batteries, cascade utilization is quite necessary.

The so-called cascade utilization is to re-adapt the retired power battery and reuse it in some occasions with relatively low utilization rate. At present, there are three applications of cascade utilization, the first is the cascade electric vehicle, the second is the power grid energy storage, and the third is the application of communication base station.

For arrangement in the meaning of exploitation, we summarize mainly has three aspects: one is that it can prolong the service life of the battery, improve the value of the whole life cycle use, if in the stage of the pilot used the battery will still be able to profit, it also can reduce the application in the field of electric vehicles in disguised forms when purchasing batteries cost; The second aspect is energy storage. If cascade utilization can be applied to power grid energy storage, compared with the new battery, it will reduce the cost of energy storage project, and also reduce the cost of user electricity in the process of energy storage. The third aspect is the embodiment of the full use of resources, with better environmental benefits.

At present, in the industry of cascade utilization, many demonstration projects have been done at home and abroad. In China, there are mainly byd, baic new energy, iron tower group, state grid corporation of China, southern grid, etc., and some demonstration projects have been done. Technology in the use of phase as main development at present, the technology of main including battery status evaluation, after retiring from the electric vehicle batteries, it is what kind of state of health, the value of how much can be applied to another is sorting the reorganization, is another pilot use safety of battery is reduced, the safety management has some work to do. From the analysis of domestic and international technology development trends, we can basically judge that there are two development trends. The first is the application of cascade utilization battery from the early stage of disassembling the battery into a single unit, to the current mainstream technology trend is the application of the whole module. The second trend is the scale of demonstration projects from the initial kilowatt to the current megawatt.

At present, we believe that the application of power storage is an effective means of large-scale consumption of retired batteries. At present, new energy power generation can probably absorb the decommissioned batteries of 120GWh, and cascade utilization of batteries brings opportunities to the low cost of power. At present, there is another significant advantage of cascade utilization battery in the aspect of power energy storage. It is because the scenes of power energy storage are very rich, which can provide some application scenes for retired batteries with different performances. Here are five main scenarios that I won't go into.

The second aspect is to introduce some of the work we have done in battery cascade utilization in recent years.

We rely on the new energy storage of 2016 approved by the state key laboratory of parallel operation control, we in the use of phase state estimation, life prediction, system integration, economic evaluation, etc. The research work, we in Zhang Bei energy storage experiment base also made several demonstration project, I introduce some work today.

We mainly studied three types of batteries. One battery is the battery retired from the 2008 Olympic Games electric cars. This is the lithium manganese acid battery, which was retired in 2012. The second category is the batteries used in the K9 electric vehicle in shenzhen, which were retired in 2015. The third category is the batteries used in the xuejiadao electric vehicle in Qingdao, which were retired in 2016.

The retired lithium manganate battery is the kind of battery that was retired in 2012. After our tests, the main capacity of these batteries is about 55 ampere-hours. Theoretically, 80% of the batteries used in electric cars will be retired, but this battery has only 50% to 60% capacity here. From the internal resistance, we can also see that its dispersion is relatively large, the initial internal resistance, the new battery is 0.5 -- 0.6, the dispersion is relatively large after retirement, the largest is 1.5 ohm, so we divided it into about 6 gears. In terms of the capacity retention rate, it should be said that about half of the battery capacity retention rate is still relatively good, which can account for more than 95%.

We measured the power and temperature rise characteristics of this battery. From the perspective of calorific value, the temperature rise is about 5 degrees at 50 amperes. We calculated its actual service life according to this battery. We chose one scenario, which was under UPS condition, and we did the adaptability evaluation. We calculated the capacity retention rate and the formula of shelving, and the expected service life of this battery was about 3 years under UPS condition. And as an evaluation of peak-to-trough application, if the battery is in peak-to-trough condition, its service life is about 1,500 times. As a smooth working condition, we chose four batteries, one is about the same capacity, internal resistance of different, the second is internal resistance, almost capacity changes, made prediction in smooth condition, you can see the performance of this battery in smooth condition performance is not very good, can be seen from the figure with poor retention capacity.

We conducted 7 safety tests on this battery according to the standards of 2006. The battery could pass all 7 safety tests, and it could not catch fire or explode. Because of this we made a energy storage system, battery pack in daxing electric taxis charge in power plant, the product after participating in operation, the loop is less than 100 times, sharply reduce battery performance, is the consistency of the battery too scattered, dispersed quickly, the battery when we in the assembly, it is split into monomer, after a very fine sorting, reorganization, and formed a new modules and systems, even so, its performance also fell sharply. Therefore, we can basically judge that the salty food produced before 2012 is of little value because of its limited production capacity.

Now let's look at the second battery, the 200 ampere-hour lithium iron phosphate battery, which was retired from the K9 bus. At the beginning, it was 200 amperes, and by the time we got it to about 150 to 160, we could see that the battery had very little dispersion and good consistency. The capacity was basically between 145 and 160, and the internal resistance didn't increase much. The capacity retention rate was also very good.

It can be seen that the performance of the battery in the charging and discharging process is good. In terms of the uplift characteristics, we have measured the temperature at 0.5c, 1C and 2C. In the state of 0.5c, the temperature rises by about 2 degrees, 1C by more than 5 degrees, and 2C by more than 10 degrees. Therefore, we suggest that the temperature rise should be controlled within 5 degrees considering its safe use.

In the safety test, the battery also appeared to bulge, but through these safety tests, there is no problem.

We focused on battery life analysis, and this battery we did 100 percent DOD, full charge, 80 percent DOD and 20 percent DOD, and you can see that this battery, at 100 percent DOD, tested 4,000 cycles, still had 93 percent capacity, 80 percent DOD tested 5,000 times, and had 91 percent capacity.

For this battery, we have built a 250 kilowatt /1 megawatt hour energy storage system, which is installed in the energy storage laboratory of zhangbei energy storage experimental base of state grid. This system is mainly used to smooth the wind power and make some frequency modulation. It has been nearly a year and a half since the installation of this system in March 2016, and the system operation is relatively stable.

The third type of battery is lithium iron phosphate battery, which was retired from Qingdao. The initial capacity of this battery is 22 hours. After retirement, 60% of the battery capacity is above 19 hours, and the dispersion is not high. Similarly, we have also measured its multiplier and temperature rise. It can be seen that the temperature rise of this battery is about 1 degree below 0.5c, and the temperature rise of 1C is no more than 3 degrees. In this case, both 0.5c and 1C are fine.

Another is the high and low temperature charge-discharge characteristics. You can see that this battery can be charged up to 90% even at zero degrees. There was also no problem with weather safety tests.

Life characteristics, after the battery 100% DOD circulation 1400 times, the capacity retention rate is about 93%, 80% DOD circulation 2000 times, the capacity retention rate is about 90%, 28 days of self-discharge use performance is also good, about 98%.

This battery is now in the charge of project construction of xuji group, and the institute of electrical technology provides technical support to make a set of 3MW/9MWh system, which is currently planned to be installed in the second phase of the national wind power storage and transportation demonstration project, mainly for wind power smoothing, photovoltaic absorption and tracking plan. The system is currently under installation and debugging.

Finally, some conclusions are made based on the work we have done in the past few years. First of all, we think that not all of the power battery is suitable for making arrangement in use, as we described above to the first demonstration project, basically, you can see in the early years (before 2012) of the battery, because the technical level of the battery itself and preparation level is not high, after electric vehicle application stage, pilot use value is lower, and the safe hidden trouble. The second is the cascade utilization countries, some key technologies still need to be broken through, such as rapid performance evaluation technology, including health status evaluation and residual value evaluation. The second is the selection and reorganization of low cost. In the stage of cascade utilization, low cost is considered as the most critical index, because it is to realize its low cost. If the cost cannot be reduced in each link, it is difficult to compete with the abandoned power. Another reason is that the potential safety hazard may be increased compared with the new battery. Therefore, in the cascade utilization, the safety warning, including the later safety protection, should be more considerate than the new battery. Thirdly, for retired power batteries in different states, appropriate application scenarios should be selected. In the field of power storage, batteries can be used in certain scenarios according to different performance stages to ensure the safe use of batteries and give full play to the residual value of each stage of cascade utilization.

For the prospect of this technology, first of all, for retired batteries, its performance is definitely getting better and better. As can be seen from the demonstration projects we have just done, the latter two demonstration projects we have introduced are still very good, with better and better performance and continuously lower price. The second aspect, power battery the whole the history data, communications protocol, pilot using battery again retired link now consider more and more perfect, many enterprises have now consciously, at the time of the power battery application consider good pilot using stage of retirement in the future, so can reduce the cost of pilot using the link relatively, improve the economic benefit of it. From 2016 to 2018, various ministries and commissions of the state have issued nearly 15 policies successively, which mentioned the use of echelon. It can be said that the state attaches great importance to this issue. In addition, the national key research and development plan has also deployed relevant contents. That is to say, from the technical level and the policy level, we believe that the cascade utilization technology is still very promising in terms of power storage.

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