EV adoption has begun around the world but to allow true mass adoption at scale where EVs are > 50% market share, we have to have affordable and scalable solutions for the three main problems that plague EVs today:
- Life & Efficiency
Range anxiety and Availability of charging are the primary blockers for mass adoption of EVs. The following will enable replication of the refueling model seen for ICE vehicles:
- Setup of EV Fast Charging and Battery Swapping stations
- Develop technologies that allow Extreme Fast Charge within 5 minutes
- Setting up a Charging Station costs between Rs. 1 Lakh for a Slow AC Charger to Rs. 40 Lakhs for a DC Fast Charger. As per the guidelines set by the Indian Govt., it is compulsory to set up an EV Charging station every 3 kms in cities and 25 kms on Highways on both sides. Today, India is at < 5% of the total mandated amount and there are multiple companies in India installing chargers at a growth rate of 30% annually. Companies such as Bolt, Magenta and ElectricPe are setting up AC Slow Charge points that require users to bring their own DC charger whereas companies such as Zeon, Statiq and Tata are setting up Standardized CCS2 and GB/T DC Fast Chargers that plug directly into vehicles.
Slow Wall Socket Charger DC Fast Charger
Charging in residential areas will likely be limited to 3 kW - 15 A Socket charging due to the absence of any high tension lines or high power transformers. Users will be able to use their own premises or charge using a publicly installed Socket Charger Point. A 15A Socket at an Office, Shopping Complex, Apartment Society or Flat will in ideal conditions enable a Scooter or Three Wheeler to charge within 45 minutes depending on Battery Size. Cars such as the Nexon EV will require > 60 kW chargers to enable the same. Setting up Large DC chargers is expensive, space consuming and requires specific grid allocation. This makes Fast Chargers prevalent only in specific City and Highway locations as shown below.
- The second part of the problem is the Time taken to Charge Vehicles. There is no technical limitation from a charger’s perspective as multiple chargers worldwide (Tesla, ABB, Tata Power, Statiq, Delta, Ionity) can deliver over 100 kW of continuous power, enough to fast charge a Tata Nexon in less than 30 minutes. But most vehicles cannot charge within 15 minutes and the limiting factor is the Battery Pack.
Life & Efficiency
Life of EVs today is a function of Battery life. The body and electronics of a vehicle last over 7 years but the first component to give away is almost always the Battery Pack. Multiple companies around the world are working to obtain more than 10 years of Battery life by creating and modifying cell chemistries. Today’s standard NMC and NCA Chemistries in ideal conditions allow ~1000 cycles (depending on manufacturer) which equates to 1 full ride and charge everyday for 3-5 years. LFP batteries provide over 2000 cycles but for 20% less range over life. The market standard cell for most Battery Packs used in 2 and 3 wheelers in India is an NMC based 18650 delivering around 600 cycles with 20% degradation over life, < 3 years of life. The battery packs are not engineered for life or efficiency and thus are able to deliver less than half of the rated capacity of the cell. Using advanced battery pack design, predictive battery modeling and optimized charge algorithms, the objective over the coming years would be to improve Battery Life by >30%.
Fire safety of EVs is entirely dependent on Battery Health and Temperature. Most EV Li Batteries are composed of NMC or LFP Chemistries which operate extremely well between 15-40oC and observe a massive capacity reduction less than -10oC and above 40oC. Most battery packs have internal hardware or software enabled cut offs that do not allow a battery to go past 60oC. Beyond 60oC, Li-ion cells can experience a rapid thermal rise if operated in high ambient temperatures and beyond ~90oC cells can experience an uncontrollable exothermic reaction referred to as Thermal Runaway.
The release of thermal energy of one cell then spreads to another thus creating a chain of reactions resulting in an explosive fire. Certain chemistries such as LFP are ~10% safer as they allow higher activation temperatures and lesser energy release in a thermal runaway scenario but all Li-ion cells create huge fire safety risks when allowed to attain high temperatures. The engineering of the module and pack that encompasses the cell is the real key to fire prevention and mitigation.
Being able to predict and protect from Thermal Runaway is one of the key purposes of a battery pack. Thermal runaway happens due to three main reasons:
- Poor Cell Quality: Battery cells are composed of sheets of positive and negative electrodes precisely rolled up in a metal container. When the Anode (positive) and Cathode (negative) within a cell touch, it is referred to as a Short Circuit. A poorly manufactured batch of cells can contain contaminants and also allow excess deformation thus leading to a short circuit. High quality cells are precisely manufactured, rigorously quality checked and have internal safety mechanisms to lower the possibility and impact of a short circuit. 95% of cells being used in Indian battery packs today come from China. The cell quality themselves are responsible for 10% of the fire cases observed.
- Overcharging: This is the primary reason for most Battery Fires. Li-ion cells can only be charged up to a max voltage beyond which the cell starts to expand and bulge which then leads to a short circuit. A well engineered battery pack measures and monitors voltage and temperature accurately and precisely across multiple locations. Battery Packs also have an internal cut off mechanism to disable charging once the charging thresholds have been reached. Robust battery architectures which can stand abuse charging conditions are the key to ensuring no over charge related fires. Systems not engineered well will not be able to cut off charge in every scenario, thus leading to short circuit due to overcharge and then eventually Thermal Runaway.
- Excess Temperature: Li-ion batteries are at a fire risk when temperatures reach close to 60oC. Battery packs with no thermal management can observe temperatures rise beyond 60oC when the ambient reaches 45oC thus increasing the risk and probability of failure. Advanced battery packs are engineered to disallow temperatures over 50oC no matter what the scenario or weather condition. Moreover even if one cell short circuits, Batteries are supposed to contain fires and thus disallow thermal runaway. In the scenario where a cell exceeds 100oC, the system should be engineered to absorb the impact of one cell catching fire and not let it spread to other cells. There should be no thermal runaway impact on the vehicle or user. Mild smoke release for a couple of minutes with no visible fire or explosion is the only acceptable scenario.
Engineering a battery pack for 100% Fire safety is thus a combination of Cell Selection, Thermal and Voltage Management and error proof Manufacturing.