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Opinion piece by Venkat Rajaraman – Chief Executive Officer, Cygni Energy Pvt Ltd
Prof Jeff Dahn’s (Dalhousie University, Canada) seminal paper, which got published after 3 years of extensive research, is touted as the “Benchmark for New Battery Technologies”. Though this paper does not describe any brand new chemistry, it is a composite of industry’s best practices. The secret sauce is the electrolyte, with novel additives and other changes that can make the battery last longer. The paper also focuses on single crystal cathode (powder of cathode material made into a single crystal so that it doesn’t react with the surrounding electrolyte) as well as the best of cathode, anode and electrolyte materials to set the bar for achieving a million mile battery.
When Elon Musk cited Prof’s Dahn’s research and announced Tesla’s million-mile battery, it took the EV world by storm. Tesla’s Model S proudly boasts of a range of 400 miles on a single charge. Tesla attributes this to a superior battery, better vehicle design, significant mass reduction, increased drive unit efficiency, maximised regenerative braking and reduced aerodynamic drag. With a range of 400 miles per charge cycle, one would need 2500 cycles to achieve the million-mile mark.
In Western world, EV batteries are already outlasting the electric vehicles they are fitted in. Most EV batteries are warrantied to last for 8 to 10 years or 100,000 miles. Tesla’s recent Impact Report notes less than 20% degradation after 200,000 miles. Nissan has estimated that its battery in the Nissan Leaf will last well over 10 years based on battery degradation data. For today’s cars, 200,000 km is considered good. It looks like a million-mile battery can beat not by a few thousand of kilometres but by 800,000 km!!
In India, we are still far behind. Two-wheelers and Three-wheelers dominate about 80% of the automotive market. In the extended range electric two-wheeler category, the Okinawa iPraise claims a range of 160 km, while the Revolt RV and Hero Photon claim a range of 150 km and 110 km respectively (all in Eco mode). Almost all other EVs are below the 100 km range. Revolt’s RV400 also carries the highest battery warranty of 8-years and 150,000 km. Hero Electric also recently offered a 5-year warranty on their battery packs. Most other manufacturers offer a 3 year standard warranty, while some offer even lower.
Many prospective buyers in India are still worried about how long the battery will last and how the vehicle’s capacity and range will decline over time. These concerns are real, especially for the two-wheeler and three-wheeler segment. At the very best, the batteries are warranted for about 3-5 years or 1000 cycles (at 80-100 km per charge, this translates to about 80,000 km). If the batteries are warrantied to maintain a good health over a much longer number of cycles, say 2500 cycles, it would go a long way toward assuaging the concerns of the customers.
What does it take to create a million mile battery for India? While the term “million-mile battery” at first glance, comes off as no more than a marketing gimmick and a great tag-line, it quickly gets across the concept of a battery that lasts forever and signifies durability. For India, the exact milestone could vary, but presumably, anything above 350,000 km for a battery would be pretty good (where it outshines the equivalent ICE vehicle).
Battery is all about trade-offs across various metrics such as safety, cost, energy density and life span. You optimize on one vector, mostly at the cost of one or more of other vectors. So how does one resolve this conundrum?
Battery Chemistry: Chemistry plays a vital role in the battery life. LFP chemistry is generally known to be long lasting, safe and cheapest of all Li-Ion battery technologies. LFP chemistry also guarantees a higher cycle life, with some of the Tier-1 manufacturers offering more than 4000 cycles. Prof’s Dahn’s brilliant paper shows that long-lasting NMC and NCA chemistry is also round-the-corner. Solid-state batteries, once commercially available, also boast of very high cycle life. What else can be done to increase the life of the battery? Let’s see some common industry practices to improve the battery life:
Depth of Discharge: The cycle life of the battery has an inverse relation to the depth of discharge. The higher the depth of discharge, the lower the life of the battery. Actual cycle life may vary with battery chemistry but in general, this relationship holds true. So, one easy way to extend the life of the battery is to reduce the depth of discharge allowing for a higher number of cycles. Of course, this has cost implications and is, at best, a trade-off between cost and cycle-life.
Temperature is Vital: Another key factor that affects the cycle life of a battery is the temperature. By allowing the cut-off voltage to dynamically change with the battery temperature, the life of the battery can be extended.
The C-Rate: The rate of charge and discharge affects the cycle life. The higher the rate of discharge, generally the lower the cycle life. It again depends on the battery chemistry. LFP can handle a higher rate of discharge as compared to NMC or NCA chemistry batteries. If the rate of discharge can be controlled and throttled lower at higher temperature, then one can extend the life of the batteries.
Dynamic Thresholds: Batteries degrade with each charge-discharge cycle. By dynamically adjusting the cut-off thresholds with the number of cycles, the life of the battery can be improved. More advanced techniques include incorporation of the cell characterisation data/results from the characterisation equipment into the Battery Management System (BMS) so that the battery pack is optimised for that particular batch of cells and chemistry.
With the e-commerce boom, the last mile delivery and logistics sector is experiencing significant growth. Last mile delivery companies like Dunzo, Delhivery, Shadowfax etc, are carrying out over 2 million deliveries per month with a daily range of 60-80 km. A million-mile battery (or in this case a 350,000 km battery), could still last well over 12 years!! For these companies, with more focus towards operational cost reduction and clear shift towards EV for last mile delivery, a long-lasting battery is the need of the hour.
India’s ACC PLI scheme for batteries clearly focuses on Cycle Life as a parameter for the Rs18,100 Crore incentive and it is envisioning cycle life of 4000 cycles and above. Though it may not be anytime soon the major OEM’s announce a million-mile battery for India, it is definitely not far-away! Such durable batteries will accelerate our transition to decarbonisation and make EVs to be loved by everyone, truly immortalising the Duracell Bunny slogan “Batteries that last and lasts forever“.
Opinion piece by Venkat Rajaraman – Chief Executive Officer, Cygni Energy Pvt Ltd.
Venkat is the Founder/CEO of Cygni Energy, a leading storage technology company with cutting-edge expertise in EV Batteries (2W & 3W) and Energy Storage Systems (Telecom etc). Cygni has deployed over 75MWh of storage solutions in technical partnership with IIT Madras. Venkat has over 25 years of experience in Product Design and Engineering and has a master’s degree in Electrical Engineering from Stanford University.