What is a vertically integrated battery company? What are the advantages of battery swapping over battery charging? Roadblocks in the adoption of battery swapping technology? Sharad Bhowmick from EFY spoke to Ganesh Moorthi, CTO of Renon India to find answers to these questions. Ganesh has a deep understanding of Li-Ion chemistries and has spearheaded the technology development of Low Voltage Battery management systems with different AFEs and different architectures.
Q. Please tell me about your company and the idea with which the company was started.
A. We at Renon India Private Limited would like to call ourselves an energy storage company. We aim to become a vertically integrated battery company. This is predominantly because energy storage especially electrical energy storage, technology is still evolving, and we see lithium-ion as one step towards the whole electrification part across different industries.
Renon India Private Limited was started in the year 2019. And at that point in time, if you see the lithium-ion battery pack costs were coming down to less than $200 per kilowatt hour. This was the point of transition because, in 2017, there was this Giga factory watch war, which was happening in all of Europe, America and China. And apart from this, that’s the period when you see a lot of commitment towards curbing pollution, especially carbon emissions, carbon neutral and carbon negative were the buzzwords at that point in time. So, the founders of Renon were really passionate about renewable energies and contributing to greenification of energy.
Q. What do you mean by being a vertically integrated battery company?
A. A vertically integrated battery company can be defined as a company that builds all the core critical components of the battery. I would say, we look at ourselves as battery experts. So, the first and foremost aspect is being a vertically integrated company, i.e. we deal with all technologies and products that are needed to, build a battery pack. And lithium-ion battery pack is something which we would like to build completely in-house.
So, we deal with all the core critical components, the cells, the battery management system, and other value adds that go on top of the battery pack. When we talk about cells, we believe that this is not the right time to enter cell development and cell manufacturing, because the technology is still evolving, it is not yet matured. Hence, we are not touching that space, but apart from that, we are into every other technology related to battery space and are working on each and every aspect including the engineering aspects of building a battery pack.
Q. According to you, apart from the cell, what is the most important component of a battery pack?
A. The second most important component in a battery pack is the battery management system (BMS). In a lead acid battery, you cannot accurately track the different states of the battery pack such as the state of charge, the state of the energy state of power, state of health, whereas the lithium-ion battery packs give accurate information about all their states and also owing to very high energy density and part of density in the battery packs in the lithium-ion battery packs, it also needs to be managed for its safety, moreover, if we manage it effectively, we can achieve the highest efficiency and performance from the battery packs. So, simply put battery management system takes care of the safety efficiency and performance of a lithium-ion battery pack.
There are other electronics which also get coupled with the battery management systems, since the BMS usually has a limited processing capability. Hence, we also need to send our data for processing. So, telematics is also an important component in a battery pack
Q. Can you shed some light on the safety of battery packs and how battery data processing takes place? Does data processing happen in real-time in the BMS, or does it happen over the edge, what is Renon’s approach regarding data processing?
A. Processing at Edge is one of the aspects, processing on the cloud is another aspect and real-time processing at the BMS is the third aspect. We are working on all three aspects to meet the three parameters, i.e., safety, efficiency, and performance. For a safer battery pack, we have a lot of power distribution units within the battery pack. We also integrate multiple different types of sensors into the battery packs, and the battery pack also has a lot of electromechanical systems which is necessary to enhance the safety and connect multiple cells to create a battery pack as a system. So, we also do vertical engineering or basically engineering and in-house development of all the subsystems as well.
Q. What parameters do manufacturers need to consider while selecting Li-Ion cell chemistry for any application?
A. So, one thing that we should understand when we talk about lithium-ion cells is a safety triangle. Because when you work with a lithium-ion cell, you look at three things; one is the amount of energy it can store, the amount of power that it can deliver and the safety of the cell itself.
So, the market always needs a very high energy density. For example: when you buy an electric vehicle you always look for a long-range and that is determined by the energy density of the cells. You also see a lot of two-wheelers and four-wheelers EVs with multiple drive modes such as “sports mode” or “lightning mode”. These modes give you a sudden burst of power so that you can achieve higher speed or high acceleration for a short period. And to support these modes, very high-power density cells are essential. So, the final and most important parameter to consider is safety which depends on the cell’s chemistry. For enhancing safety we prefer more thermally stable cells in order to reduce the risks of thermal throttling.
Q. What cell chemistries are predominantly used in the Indian market and why?
A. In the Indian market, we are predominantly using two lithium ion-based cells, which are basically nickel-manganese-cobalt (NMC), and lithium-Ferro-phosphate (LFP) chemistry cells. When you look at these two cells, each cell’s chemistry offers a different proportion of energy density, power, and thermal stability.
Comparing these two chemistries, LFP chemistry is more thermally stable chemistry compared to NMC however, LFP cells are at least 30 to 40 percent low in terms of energy density compared to NMC cells.
Q. What about the cells having solid electrolytes, do these have better thermal stability than the existing cells?
A. People are talking about the industry moving towards solid electrolytes, the solid electrolytes are supposed to have more safety because it is solid instead of gel. Because in a gel the anode and cathode cannot shut securely within a cell. However, they have their own pros and cons that is not commercialized and still, the industry is researching on. So, just simply to say liquid electrics have been in the research and in study for the past 50 years, while solid electrolytes are being studied only for the last three to four years. So we have a lot more time to go in order to select a collection to commit to which means ideally, right now we have to work with liquid electrolytes, which are prone to internal shots and goods, which is the major reason for thermal runaway failure. Right. And in that, we have to choose the chemistries which are more thermally stable, and which have less options in order to enter into thermal runaway. Right. So all this is something we talk about something called internal abuse, which is a short circuit, which happens because of cycling of the sales, the chemical degradation of the electrolyte, which happens within the cell.
Q. Battery pack is a complex system, so is it correct to say that the development of battery pack is a cross-functional engineering problem requiring knowledge of multiple fields and not only electrical or chemical engineering?
A. Yes, you’re very right, it’s a cross-functional engineering problem. And we have to find the right midpoint across all the verticals of mechanical, electrical and thermal functions. Moreover, we have to take into account all the worst-case scenarios of abuse and then come up with an engineering solution which can protect the battery from an abuse perspective. External abuse is an engineering problem, while, Internal abuse is more of cell quality, inspection, understanding measurement, analysis, prognostics, etc. But I think the first and foremost point is to take care of the internal abuse and the second point is to take care of the external abuse.
Q. What’s the importance of selecting the right battery?
A. The selection of the right cell is crucial for both the performance and safety of the battery pack. To enhance the safety of the battery pack, each cell in the battery pack needs to be inspected individually before placing it in the battery.
Q. No two cells are identical, they have different internal resistances, battery health, etc. So, before placing it in the battery pack you must test each individual cell. So, can you talk more about the testing protocols and the type of battery you have developed?
A. We at Renon give a lot of importance to cell qualification, cell characterization and cell testing. So, for us cell testing actually means 100 per cent inspection of cells before production or before putting that cell into a battery pack. But even before that, there are a lot of evaluations that we do at the cell level here and before bringing the cells into a battery pack level. So, we perform we follow is standards, the Indian standards for cell characterization, and cell performance, and then we also follow some international standards to understand the different capacities and different characterization of the cells.
The two major methods employed today are Cell Grading and Cell Sorting. However, they are not sufficient and need additional quality assurance techniques on top of it. In addition to the cell quality assurance, 100% BMS inspection at incoming quality inspection for the balancing current, pre-discharge functionality and upper/lower protections across voltage, current and temperature are very critical. Keeping energy density and safety in mind for fleet and consumer applications, Renon has employed high-quality NMC cells in its swappable battery pack, Groot which are tested for at least a couple of cycles for its capacity, open-circuit voltage and impedance. The nominal voltage of the battery pack is 57.65V and it has a rated energy of 2.04 kWh.
Q. What are the most essential features of a BMS?
A. The BMS is important for the safety of the battery pack. It tracks the different states of the battery pack such as the state of charge, the state of the energy state of power, the state of health, etc. The right BMS can help us extract the highest efficiency and performance from the battery packs
The BMS takes care of safety by setting the limits and hence avoids either over-charging or over-discharging of your battery off your cell after a particular voltage. Similarly, there is a particular limit to the current that you can draw from the cell. And the third thing is about the temperature the electrochemical cells work very differently degrade very differently at different temperatures, and there is a safe operating temperature limit for lithium-ion chemistry right now. So, the BMS also prevents that by setting limits across temperature limits.
The BMS also need to perform an important safety function called cell balancing. The BMS balances by burning the extra energy that is present in the additional cell, this way of balancing is called passive balancing. There’s a more advanced balancing technique known as active cell balancing where we actually transfer energy from the highest energy cell to the lowest energy state.
Q. Which method of cell balancing is preferred by the industry?
A. In the industry, mostly passive balancing is being used because that doesn’t make a lot of difference in the mobility applications. When it comes to large capacity, very critical applications’ active balancing will be often needed.
Q. What are the takeaways of the new battery policy the government has launched recently?