News provided by Digital Energy Storage: The 13th China International Energy Storage Conference was held in Hangzhou from May 24 to 26, jointly directed by the Department of Energy Conservation and Comprehensive Utilization of the Ministry of Industry and Information Technology and the Department of Energy Conservation, Science and Technology and Equipment of the National Energy Administration, organized by the China Chemical and Physical Power Industry Association and supported by more than 240 organizations.

More than 1011 industry chain supply chain enterprises from different fields such as industry authorities, domestic and foreign institutions in China, scientific research institutions, power grid enterprises, power generation enterprises, system integrators, financial institutions, etc., 5417 guests attended the conference, of which 245 enterprises displayed the whole industry chain of new energy storage, covering system integration, cells, PCS, BMS, containers, fire protection, testing and certifications.

In the afternoon of May 25, Tao Zhiyong, R&D Director of Shenzhen Topband Battery Co., Ltd. was invited to share a keynote report in the special session on lithium-ion battery and energy storage system design, which is entitled " Design and Process Development Trend of Energy Storage Battery Cells ". The following is the main content of the report:

Zhiyong Tao: Good afternoon, experts, guests and peers! I am very pleased to share with you my speech "Design and Process Development Trend of Energy Storage Battery Cells".

First of all, I would like to present my opinion that the future of energy storage battery is to develop in the direction of large capacity, low cost, high safety and long life. Of course, a while ago academician Ouyang proposed a large-capacity lithium iron cells have the risk of deflagration, but we believe that the general direction will not change, leaving us with the technical problems need to work together to solve. 

What choices should we make around the three core indicators of energy storage battery cells? I'll share from the following aspects: packaging form, cell structure, process, charging and discharging methods, material system and control method.

Cylindrical cells in the small and medium capacity of the energy storage system still has its unique advantages, especially in these two years the process of large cylindrical cells has been greatly improved. We are now looking at this all-pole lug process has been a great improvement over the previous models with single or dual pole lugs such as 18650 or 21700, the main improvement is the flow and thermal conductivity. Thanks to the progress of the process, large cylindrical cells are widely used in a large part of energy storage systems, but it also has its limitations.

Pouch cells, its unique advantage of is that the energy density can be particularly high, which is the highest in the three types of packaging. In addition, it is also suitable for large rate discharge, especially over 30C or more, which is very suitable for pouch cell. The main problem of pouch cell is that the cost is really high, the whole process is slightly complicated, and the cost of PACK is relatively high, because you have to make a bracket for it and do rigid treatment. Therefore, at present, there are not many domestic companies using pouch cells for PACK or energy storage, Pylon technologies is one of them, but there are not many choices. 

Topband Battery independently develops and produces these three types of battery cells, so we have made a brief internal summary, from the analysis of economy and safety as well as performance, we came to such a conclusion. We consider that used in energy storage, especially for large energy storage, prismatic aluminum shell slightly superior, followed by perhaps cylindrical, the comparison of this figure is to share the results.

Next, I would like to share with you issue of material selection. Just now the guests also introduced the situation of the power battery. In the past decade, whether it is power batteries or energy storage batteries, we have gone a long way in the pursuit of high energy density, from the earliest 111 NMC system, to 523, 622, 811, to the extreme is "high nickel + silicon carbon", coupled with solid-state electrolyte, energy density can be more than 400wh/kg. There is another option, that is, to reduce the high nickel system, choose the nickel 55 system, so why choose it? Because the high nickel material is indeed very high energy density, but safety is slightly worse than other systems, so the industry has another choice, is to do a single crystallization of nickel 55 system. Because the polycrystalline NMC, it has a problem, that is, in the cycle process is inevitable to produce grain boundary splitting, will bring safety and lifespan problems to the battery cells.

Lithium iron phosphate battery, we can see from this graph, its thermal stability is indeed much better than the NMC system, pure material, its decomposition temperature is much higher than the NMC system. As you can see, the graph on the right, in the Hot Box Test, at 180 degrees, lithium iron system basically does not produce thermal runaway phenomenon.

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Then look at the safety, from most of the industry or the national standard test, lithium iron is the highest rate of adoption, so at present, if you are doing energy storage, if from the perspective of safety, lithium iron phosphate is still a most preferable. From the lithium iron system in recent years, we are still pursuing the route of high-voltage solid-state route, the current high-voltage solid-state technology can reach about 2.65 g/cm³, the previous years or in about 2.4 g/cm³. Lithium iron raw material manufacturers now after efforts to improve the sintering process, can basically meet the requirements of lithium iron energy density maximization.  

Now I would like to talk about the popular lithium manganese iron phosphate, it has also done a large-scale pilot test in our company, the conclusion is that the energy density is really high, about 20% higher than lithium iron. Theoretically it can be increased by 25%, but in fact, because there are still some differences in the ratio of iron and manganese between domestic suppliers, plus it mainly improves the platform voltage, so it may not feel obvious, but we think it is a potential backup option for the energy storage system. Lithium manganese iron phosphate may also have to solve the problem of the discharge curve on the load of electricity, generally used to mix and match with NMC lithium iron manganese or lithium manganate to make some optimization adjustments to the curve. I predict that in the next year or the year after, lithium manganese iron phosphate products will have a certain scale. Next, I will talk about the application scenario of sodium ion battery in energy storage system. Our company has a few years of research on sodium ion battery energy storage, in fact, sodium ion battery has several advantages, first of all, its cost can be very low, theoretically speaking, it should be able to reduce costs than lithium iron to at least 30% or more. From the point of view of its technical route, at present the domestic basically choose layer oxide is the main, Prussian blue and Prussian white is less. The negative electrode basically uses hard carbon, but in the past ten years, the domestic hard carbon technology progress is not fast, but in the past two years the development and industrialization of hard carbon has accelerated significantly, this is because in the past two years the price of lithium carbonate rose too fast, so that the lithium industry cost pressure is great, continued production will lose money, to be able to deliver successfully and profitably, so accelerate the launch of sodium ion batteries.

At present, the fastest progress in the development of sodium ion batteries is the hard carbon and layer oxide, the current energy density of domestic company can be achieved 160wh/kg, cycle life up to about 3000 times. There is still a bit of a gap from our requirements for energy storage, so we still have to observe sodium ion batteries until the end of this year and next year. I will briefly talk about the key issues in structural design. Now the battery  cell used in large capacity energy storage, basically is the heteropolar column, its main advantage is heat dissipation and temperature rise. As you can see from this picture, the left picture is the hetero-pole, its average temperature rise is much lower than homopolar column, basically, the industry is more recognized like this structural design, there are two ways to facilitate heat dissipation: the first is to have a length-to-width ratio close to 1, and the second is to design the poles and lugs as wide as possible. Diaphragm coating and pole edge coating are now commonly used in the industry to dissipate heat and remove burrs and improve the consistency of the battery.

The next thing I'd like to share with you is the cost control in terms of energy storage cells. From this structure chart can be seen, the largest cost is the cathode, in extreme cases, can account for 57%, the highest price of lithium carbonate had reached 600,000 / ton. Now it has come down, but the highest percentage is still cathode. In fact, we reduce the cost of those few ways, to meet the performance requirements, do not waste, with standardization to replace customization. Because the customization has to have a gradual climbing process, and then there is a scale process, so as far as possible to use standardization, try to replace the complex structure with a simple structure, reduce logistics costs, in order to achieve the purpose of cost reduction of the battery cell. The second is to do subtraction, which has a lot of programs, just now the guests also mentioned CTC and CTP, remove the intermediate links, remove excessive conductive agent, remove the unnecessary electrolyte dosage. In order to reduce the amount of one percent, we may need to do a lot of experiments. Because of the need to figure out the impact between battery life and the reduction, most of the battery factory's development time is actually spent in the process of observation and repeated verification.

I would like to share the issue of life optimization of energy storage cells. At present, it can be seen that the purpose of our energy storage conference is all about improving the cost performance of the battery cells and reducing the cost of the battery cells' life cycle. The most critical thing here is to make the battery life as long as possible so that the cost in the life cycle will be low. If you want to do industrial and commercial storage, the battery life is not more than 10,000 times, the cost may not be controlled down, or even loss money. In our 20 years of lithium development history, the improvement of battery life is really fast, the early lithium battery life is 300 times, 500 times, NMC is 500-1000 times, the earliest lithium iron for 1500 times, now the highest can reach more than 10,000 times, which cannot be achieved without the efforts of the material factory,  electrolyte factory, the improvement of equipment precision and automation.

In particular, we tend to ignore the impact of the battery structure design, when the cells are done, but the consistency is not good, the PACK structure is not good, will affect the life of the battery. From our entire development of energy storage batteries, the impact is from materials, structure, consistency, which is the most important issue. According to the different prismatic, cylindrical, pouch, the direction of adjustment is also different, each type of battery cells will have some relative differences in focus. Talk about some of the measures that our company is now doing to help improve the energy storage battery cell, including the way of charging and discharging, many head enterprises may also be used the same way. In other words, when charging, if you can use high current in the initial stage, and use a small flow rate to replenish when it is almost full, this will relatively improve the life of the battery, which requires some fine-tuning of the charging method in the system design of the battery. In fact, its basic principle is very simple. When it starts charging, in the case of fast charging, there is basically no concentration polarization, and when it is almost full, from the electrochemical point of view, the concentration polarization becomes a major control method to reduce the current, which is conducive to reducing the loss of the battery.

And then share with you some of the advantages of large-capacity energy storage battery cells and the risks to be avoided. In the past two years, battery factories, including the head enterprises to make the battery cells bigger and bigger, are based on the idea that in order to reduce the cost, whether it is the cost of the housing per unit area, or the cost of the PACK, reduce the connector, we all want to make the battery cells bigger. But there is a risk of making it bigger, when the battery is thick, heat dissipation is not easy to solve, the thickness from 30mm to 70 and 80mm, the middle pole piece of heat dissipation is certainly worse than the side, and it is difficult to compensate by heat dissipation, air duct design is also difficult to eliminate excessive temperature differences, so we need to fully understand the problem. Increase the thickness of the shell, which makes it difficult to dissipate heat, reduces the amount of electrolyte, there is also the risk of insufficient circulation, thinning the diaphragm, there is the risk of short circuit, so when we do energy storage battery cells, whether it is the design, or process, there are many factors to consider. What I listed here is only a part of the risk for your reference. There are many reports today emphasizing the development direction of large-capacity battery cell, which is the consensus of the industry. Large-capacity encountered a variety of problems, we also have to face frankly, how to solve? I think we may have to do the class blade double-headed column battery, we are all working in this direction, simply thicken or in a certain design point such as stack electrode density, these are not very feasible. The direction of optimization of energy storage battery cell design is to get a balance of heat dissipation, cost and lifetime, which is the direction we think the future.

I will share the future trend of energy storage battery manufacturing process. First of all, the manufacturing trend is basically in the direction of automation, and digitalization and high precision are the basis of automation. We have been making battery cells for so long and found that 40% of the abnormalities occur in the front production process, from batching to production. If these processes are done well, there are basically no serious abnormalities or relatively few abnormalities in the later stages. We have been making battery cells for so long and found that 40% of the abnormalities occur in the front production process, from batching to production. If these processes are done well, there are basically no serious abnormalities or relatively few abnormalities in the later stages. For the stirring process in the front section of the battery, I think the future trend must be continuous pulping, which has the advantage of reliability and efficiency are greatly improved. Because the traditional way is a kind of probability stirring, the probability and efficiency of each stirring is relatively low. This is the principle and equipment of continuous pulping. From the development of lithium battery, the coating process, from the earliest single-sided coating to now popular double-layer coating, the future will also develop to double-sided coating. In fact, the main equipment factories now provide double-sided coating, but the current usage rate is not very high in battery cells factory. The benefits are obvious, fast and efficient. The laser die-cutting is also a trend.

I will mention the most headache in the production process of battery is the impurities and burr control and the design of the stacked sheet and coiling. For energy storage batteries, especially prismatic cell, more than 70% are selected for coiling. Coiling has its problems, you can look at this chart, no matter what kind of pressed cell process you take, there will always be deformation, that deformation in the small cell or thin time is not obvious, but after making a large and thick battery cell will have such problems. I will mention the most headache in the production process of battery is the impurities and burr control and the design of the stacked sheet and coiling. For energy storage batteries, especially prismatic cell, more than 70% are selected for coiling. Coiling has its problems, you can look at this chart, no matter what kind of pressed cell process you take, there will always be deformation, that deformation in the small cell or thin time is not obvious, but after making a large and thick battery cell will have such problems. As you can see in the right corner, this deformation will bring about a marginal effect of lithium migration during the charging and discharging of the cell, which will bring about a difference in the expansion force during cycling. If you are doing a laminated sheet, you will find that the expansion force of the battery in the cycle is much smaller than that of the coiled one, which is the effect of force. So why now some lithium battery companies in making large-capacity energy storage cells, it is to choose the laminated sheet, is a comprehensive consideration, in addition to manufacturing efficiency,  performance and late expansion force, expansion force if not well controlled, it will destroy the entire finished product structural. Energy storage battery process development trend, I think the most important is the integration of manufacturing, in fact, now we have basically achieved, is to integrate several key processes through the integration of equipment together to do integration, to improve efficiency and reduce logistics.

At the same time, certain processes may be eliminated in the future. There may be no more stirring in the future, and the dry powder will be pressed all over the foil directly by spraying or pressing. It is even possible that if the consistency is good, the battery does not need capacity sorting, because capacity sorting does not have much economic value, if the consistency of the capacity is very good, CPK reaches 2.0 or more, it is possible to cancel capacity sorting. In addition, in the future, the manufacturing of battery cells or battery pack, will gradually popularize visual monitoring or visual rectification, will greatly improve the efficiency of manufacturing. The future of lithium manufacturing may have new optimization options in the future, such as three-dimensional simulation production, including energy consumption, energy consumption in the decade has been reduced by 30%, and should continue to decline.

Next I will briefly introduce our company-Shenzhen Topband Battery Co. Ltd., Topband Battery has now achieved continuous pulping, integrated manufacturing, environmental protection factory and energy saving factory. In the material system, the company mainly for lithium iron phosphate, the future will be sodium ion and lithium manganese iron phosphate to do the next generation of evaluation. In the field of application of the battery cell, small capacity energy storage products adapted to large cylindrical cell, the company currently produces 33140-15Ah, 40140-20Ah large cylindrical cells, can perfectly match the 0.5kWh-3kWh portable energy storage products, the whole life of more than 2 years, size of PACK is relatively small, cost-effective.

Topband Battery's large capacity prismatic cells for energy storage are designed to last more than 10,000 times, with low temperature rise, less than 1 degree for 0.5C discharge, less than 5 degrees for 1C discharge, and better heat dissipation performance. 100Ah square cells can be used in home energy storage products, with a single module design of 5.12kwh, and different capacities in series and in parallel according to different electricity demand, to meet the household electricity demand of 150Ah. Square cells can be used in industrial and commercial energy storage products, the company is currently developing 100kWh, 200kWh standard industrial and commercial storage products, all using the 150Ah cells.

Topband battery is committed to become a world-class and reliable supplier of lithium battery products r, I hope to do more in-depth communication and technology sharing with industry colleagues on battery technology, thank you!  Forward: Digital Energy Storage News Center