Best practices in Li

Delhi-based Inverted, founded in 2017, started supplying EV battery packs in early 2020. Today, it is one of the leading suppliers of Lithium-ion battery packs for light electric vehicles in India and also caters to stationary energy storage applications. In this chat with the co-founder Raghav Jain, we discuss the best practices for battery pack manufacturing and ensuring battery performance and safety.

For e-mobility applications, we largely focus on the electric two-wheeler and three-wheeler vehicles. At present, every month, we supply about 10,000 battery packs for e-2Ws, 1000-1500 packs for the e-3W L3 category and ~ 200 for the e-3W L5 category.

AIS 156 Amendment 3 is a welcome step, which was desperately needed to build greater reliability and safety in battery packs. There were many such initiatives that we were already working on, so when the notification came, we were well-prepared for most of the requirements.

However, one requirement took us by surprise. As per the standard, the batteries need to be able to withstand a temperature of 300 degrees Celsius – if the thermal runaway happens, the propagation should not spread to the other neighbouring cells. To fulfil this requirement, we explored multiple thermal management solutions suitable for the Indian context. It took us three months of rigorous testing in our R&D lab to fine-tune and figure out the right solution from a mass production perspective. The solution that we have now implemented is technology agnostic andsuitable for any battery chemistry, including NMC and LFP.

There are four broad facets to be considered while designing a battery pack.

Moreover, we do not rush the process of design and exhaustively look at all four aspects before moving to production. We have put in place proper DFMEA and PFMEA systems to take all failure modes into consideration while designing the battery pack.

We follow a rigorous six-month evaluation process before onboarding any cell supplier.

We get a thousand samples from a new potential cell supplier, which are subjected to lifecycle testing. This accelerated testing for about thousand-plus cycles tells us what kind of capacity retention the cells have in ideal conditions. Then we subject the cells to various C rates and different conditions simulating the actual usage scenario. This is done for 50 cycles to see the deviation between the IDC curve and the real conditions. The cells are also subjected to another set of tests, including a crush test, drop test and nail penetration, before we approve them for the intended application.

Before deploying for mass production, we subject all the cells to a hundred per cent grading as per capacity, voltage, and IR. So, we can see if there is any deviation from this sample cell, and we refrain from working with that particular cell supplier. Also, we ensure that we work with highly reputed manufacturers, so there's a limited deviation from the specifications.

If you look up battery packs sold in 2020, they were extremely rudimentary.

Initially, most people looked at batteries as a standalone product and not in the context of the vehicle. However, now OEMs are way more selective in their approach. The industry has significantly moved forward, and people are talking about vehicle integration testing, lifecycle testing and thermal solutions. OEMs care about details and ask questions, such as which connectors are being used. This is a significant shift in the approach, and companies are conscious of finding the right battery pack for their applications, which seldom happened before 2020. Now, there is also greater awareness at the consumer end, who are asking tough questions. So automatically, there is greater awareness in the ecosystem overall. Additionally, the latest battery standards by MoRTH are driving the industry towards understanding the battery pack in depth.

When we started out, we were using imported off-the-shelf BMS available in the market. However, in the last 18 months, we have developed our own battery management system on the 18s platform (batteries built on a 48V or a 60V platform). For anything which is above the 18s platform, we are dependent on an external vendor for BMS as of today.

However, we are committed to having our own design for the battery management system. We intend to indigenize the BMS across the range of batteries we make and handle the design and component selection ourselves. We are working on a deep SOC/SOH algorithm, and we want to embed the same in the BMS.

We are focused on developing in-house capabilities for everything apart from the cell, whether it is the extrusion, die cast, thermal material, the BMS or the busbars. We have already indigenized most of the battery pack components and aim to indigenize the rest in the next couple of months.

This interview was first published in EVreporter May 2023 magazine, which can be accessed here.

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