Bengaluru-based Exponent Energy's co-founders Arun Vinayak and Sanjay Byalal, explain the workings of their unique ‘Flexible Energy Stack’ technology and how it will revolutionise the EV sector.
Exponent Energy, a Bengaluru-based startup, has built a battery pack and charging station called E-pack and E-pump, respectively. The startup claims that together they unlock a 0 to 100% rapid charge within 15 minutes for all commercial vehicles, irrespective of the number of wheels. They’re doing this using affordable lithium-ion cells and delivering a warranty of 3,000 charging cycles.
Suffice to say, the ‘Flexible Energy Stack’ they are building could revolutionise the way Indians adopt electric vehicles (EVs). (Above image of co-founders Arun Vinayak and Sanjay Byalal alongside Exponent’s E-Pack)
It was co-founded by Arun Vinayak earlier this year, the founding partner and former Chief Product Officer at Ather Energy, and his former colleague there, Sanjay Byalal. Exponent Energy aims to bridge the relationship between battery cells and chargers to ensure there is less stress on EV batteries, while fully charging them in 15 minutes only.
To give you some context, regular charging solutions take anywhere between four to eight hours to deliver a full charge. Most batteries, meanwhile, last only three years or 1,000-1,200 charge cycles primarily because of the significant degradation they suffer during charging. Finally, the best fast-charging solutions in India are restricted to a few premium EVs, which perform a full charge within 50 minutes and have several caveats to consider.
“If you look at the energy flow in the EV sector, you have the power grid, chargers, battery, and motors. OEMs have figured out how to build great vehicles. They are able to buy batteries and motors and put all of this together and sell a vehicle. The charging partners on the other side are buying chargers and setting them up on the charging stations. But each side is working in isolation, which is why a certain battery and charger don’t seem to work very well. There is an inherent lack of coordination in the EV market today between OEMs, battery makers and charging stations,” says Arun Vinayak, in a conversation with The Better India.
Rapid charging in the current Indian space didn’t work because it was done using bulky and expensive technology like LTO (lithium-titanate-oxide) or supercapacitors. With chargers feeding regular batteries more power than they can handle, it leads to severe battery degradation.
“We’ve simplified energy flow between the battery and charger. This unlocks 15 minute rapid charging on a wide range of regular lithium-ion cells, making it affordable and scalable,” he adds.
How Does it Work?
Until now, the general consensus has been that if you charge an EV battery faster, it will accelerate the degradation process, which is true if you’re taking the brute force approach of dumping as much energy into the battery.
In this regard, fast-charging will ruin battery life, which is why people in the EV space have taken the easy way out by saying they will charge slower and preserve the battery life.
Exponent Energy’s plan to deliver 15 minutes of rapid charging with 3,000 cycle life of affordable lithium-ion cells is made entirely possible by their ability to manage impedance or chaos within a battery cell that restricts the flow of energy. At a very basic level, charging a cell involves ions travelling from cathode to the anode. The faster you charge your batteries, more ions travel from cathode to anode, which results in greater chaos and degradation.
“For the first 800 charging cycles of testing we’ve done, we’ve only lost around 3.5% of capacity and provided a 3,000 life cycle warranty with our batteries thanks to active management of cell impedance across different charging cycles. In comparison, the EV industry in India today has an average warranty of 1,000 life cycles, and loses 20% capacity. By ensuring the charger and battery work seamlessly together, we’ve solved two hard problems, which is charge time and battery life. Most people think these are two opposing problems, but if you approach it right, this is actually just one problem to solve, which comes down to impedance,” explains Arun.
Their charging station is completely future-proofed, offering anywhere between 40 and 800 V and allowing different vehicles and form factors to charge at all sorts of voltages, he claims.
This is unlike battery swap technology, where OEMs are told that they have to only use a battery of only a certain specification and form factor. On the vehicle side, they offer a flexible energy stack. “EV manufacturers today can start working with us by configuring our BMS (battery management system) into their vehicles in the way they want or can just buy the battery pack directly from us. The quickest way is to buy our battery pack, which is modular,” he adds.
Today, they have an LFP (lithium ion phosphate) pack ready, while the NMC (nickel manganese cobalt) pack is being built for market use in three months. These are two of the most popularly used cell chemistries in India.
Thus far, the startup claims to have tested eight different types of cells in the market and successfully rapidly charged all of them from different cell suppliers. Exponent has employed one kind of cell for now, which they will launch in January 2022. This particular solution is a LFP one and it has got a 2 kWh module, but can be put into any configuration to provide any sort of battery pack on request.
“We are working with OEMs on one side and ensuring our battery packs work very well with their vehicles and setting up charging stations ourselves through charging partners. We’ve installed these charging stations in our Bengaluru office and next month we will launch our first charging station outside the office premises. Setting up a charging network is not really a problem for us given that we’ve got experience in it,” says Arun.
Testing these battery packs, meanwhile, has been extensive. Besides 800 charging cycles in lab conditions, the company claims to have also done thousands of kilometers on the road on their three and four-wheeler demo vehicles. In their laboratories, they have thermal chambers that supply rapid charge of their battery packs at 50℃ ambient temperature. They stress the battery with almost 8 years worth of testing of vibrations, heat and stress within a month. So far, they claim to have spent a lot of time and money on reliability testing.
But how do they ensure the 3,000 charge cycles warranty? Most cell degradation happens while charging. Think of charging as rolling a boulder up the hill. You’re increasing the potential energy of the cell. It’s a very stressful process, creating a lot of heat, stress and internal damage. Discharging energy from a cell is like rolling a boulder down a hill, and thus much easier. If you give a car racer your EV, what will happen is that you’ll probably run out of battery range much sooner and your battery might heat up and de-rate, but it won’t actually damage the cell.
What damages the battery cell is charging because the internal resistance while charging (impedance) is almost four times more while charging as compared to discharging. Batteries catch fire only while charging because the battery management system (BMS) is inaccurate and is often charging the battery blind.
“In a given battery you have hundreds of cells and you need all of them to work in sync. If one cell goes kaput then your whole battery breaks down. If one cell is imbalanced and hits its limit during charging, the other cell also has to stop charging. Therefore, this results in the undercharging of the battery. On the other hand, if the BMS hasn’t sensed that a particular cell has crossed its limit and you keep charging it and overfill one cell with energy, that’s when you have fires starting. We have a BMS which is 10 times more accurate in reading what’s happening inside the battery and has one of the fastest balancing circuits,” claims Arun.
The second problem is that most chargers perform a constant current charge profile, i.e. they dump energy at a constant rate. As a result of this approach, you fundamentally spike impedance internally and this creates a lot of damage.
“What we are able to do is ensure that we slow the whole process down whenever required and speed it up whenever we can. Since we have a variable profile and can sense what’s happening inside a cell, the charger and cell can coordinate better to ensure there is less stress. When you remove that resistance, energy flows smoothly, charging time comes down, damage reduces and that’s why we are able to solve both these problems,” he adds.
Inspiration Behind Exponent Energy
Exponent Energy’s larger problem statement is to get India to ‘go electric tomorrow’. When Arun joined Ather Energy in 2014 as a founding partner alongside Tarun Mehta and Swapnil Jain, no one in India believed in EVs. In 2018, Ather launched their first product (an e-scooter), which got people’s attention, but critics maintained that this was not a profitable venture. However, this has changed now.
As Sanjay says, “In India, commercial vehicles today roughly represent 10% of total vehicles sold in the country yet consume 70% of on-road energy. It’s an energy-hungry segment rushing to go electric and needs a dependable rapid charging network that helps them keep going. To fulfill this demand, we intend to actively collaborate with all major stakeholders.”
“Having built products like e-scooters and charging points, I felt that this was a problem we solved. My personal learning curve was flattening out. The second thing I noticed sometime around 2018-19 is a distinct change in the public discourse surrounding EVs from consumers, investors, battery manufacturers, the government and OEMs,” says Arun.
But most people were still buying very mediocre technology from China. A lot of people started coming to Ather and started asking for their technology. It sparked a thought with Arun that there could be an underlying technology that multiple OEMs could use.
However, Ather’s technology was built from a very vertically integrated point of view and it just didn’t make sense for anyone else to use it. Of course, there were OEMs like Hero that decided to use Ather’s charging port, but he realised that if they wanted to provide that technology, it had to be a separate company focusing on that problem.
“The 0 to 1 shift where EVs drive better than ICE vehicles has happened. However, the 1 to 100 scale is shackled by how complex and disrupted energy flow is for EVs today—specifically between chargers and batteries—leading to terrible charge times and battery life. The Indian EV space has massive potential ($206 Bn cumulatively by 2030). But to get there, we need to simplify energy for EVs by solving crucial deep tech problems. A rapid charging solution agnostic of battery capacity, cell chemistry and the number of wheels on a vehicle is the first of many innovations that will unlock exponential scale for everyone.” says Arun.
(Edited by Yoshita Rao)