BYD blade battery – What makes it ultra-safe and comparison with ternary batteries

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BYD India has launched an all-electric MPV e6 for the Indian B2B segment with its 71.7 kWh Blade Battery that claims a WLTC city range of 520 km. BYD’s marketing message about its blade battery is that it’s the safest battery around. In this write-up, Rahul Bollini discusses some of the features and advantages of this battery.

About BYD Blade Battery

BYD first announced the launch of the Blade Battery in March 2020 – as a development set to mitigate concerns about battery safety in EVs.

Specifications of BYD Battery Cell

Blade battery has a prismatic form factor, but it is thinner and longer compared to traditional prismatic Lithium-ion cells. The cell uses LFP cathode chemistry and has a thin blade-like structure that offers structural advantage and better support to the battery pack than regular block-type prismatic cells. The cell has a larger surface area than regular prismatic cells, allowing for better heat dissipation. The cells also allow for slow heat release, lower heat generation, high starting temperature for exothermic reactions, and do not release oxygen during thermal runaway.

Safety Tests undertaken by Blade Battery

The Blade Battery has notably passed the ‘Nail penetration test‘, one of the most stringent safety tests in the industry.

While undergoing nail penetration tests, the Blade Battery emitted neither smoke nor fire after being penetrated, and its surface temperature reached 30 to 60°C. Under the same conditions, the NMC battery exceeded 500°C and violently burned, and while a conventional LFP block battery did not openly emit flames or smoke, its surface temperature reached dangerous temperatures of 200 to 400°C. This implies that EVs equipped with the Blade Battery would be far less susceptible to catching fire, even when severely damaged.

The Blade Battery also passed other extreme tests, such as being crushed, bent, heated in a furnace to 300°C and overcharged by 260%, without resulting in a fire or explosion. It also completed a strength test that saw it being rolled over by a 46-ton heavy truck which it passed without leakage, deformation or smoke, coming out intact and ready to be used in an EV.

In April 2021, BYD announced that all of its pure electric vehicles would come with the Blade Batteries, with nail penetration testing adopted as a brand standard. The first batch of BYD’s sedan HAN EV recently arrived in Brazil, Mexico, Colombia, Uruguay, the Dominican Republic, Costa Rica and the Bahamas. Han EV comes with a range of 605 kilometres and an acceleration of 0 to 100km/h in just 3.9 seconds. e6 launched for India’s B2B market is also equipped with the Blade Battery.

Safety aspect of LFP vs. NMC

A negative chain reaction due to high pressure and high temperature causes thermal runaway in a Lithium-ion cell. Since NMC cells release oxygen as a by-product during thermal runaway, they tend to catch fire very easily. On the other hand, there is no oxygen by-product released in LFP cells during its thermal runaway and hence they don’t catch fire.

NMC cells are preferred in EVs because of their higher volumetric density, which allows for higher energy to be stored, enabling a higher range of electric vehicles. BYD blade battery has a higher volumetric energy density compared to regular block type prismatic cells. Hence, the BYD blade battery has enabled the usage of LFP cells in long-range electric vehicles while addressing safety concerns of catching fire during an incident of thermal runaway.

Blade cells vs regular block type prismatic cells

The size of the BYD Blade cell is larger and has a higher capacity when compared to regular block type prismatic cells.

Using a higher number of smaller capacity regular block type prismatic cells create a mechanical disconnect in a battery pack and leads to less efficient utilization of the space. Regular block type prismatic cells have to be packed as a module first and then the modules are assembled into a final battery pack.

On the other hand, BYD blade cells allow for direct cell to final battery pack assembly, eliminating the need to assemble into modules and increasing the overall volumetric energy density of the final battery pack. The singular cells are arranged together in an array and then inserted into a battery pack. Due to its optimized battery pack structure, the space utilization is increased by over 50% compared to conventional LFP block batteries.

The improvement in the cell architecture and its direct ability to be assembled as a battery pack, has allowed for BYD blade battery to compete with NMC packs in terms of volumetric energy density and offer a similar kind of range. Additionally, NMC battery packs need liquid cooling since they have a lower operating temperature, which takes up more space again and drives up the price of the battery pack. These reasons have made Tesla also consider BYD blade batteries, starting with EVs for the Chinese market.

The author Rahul Bollini has over 6 years of experience as an international Lithium-ion cells R&D consultant and can be reached at bollinienergy@gmail.com.

This article was first published in EVreporter November 2021 Magazine. Click here to subscribe to print editions.