Switching ON an electric future

Dr Marc Payne
July 8, 2024

Switching ON an electric future


The role of fluids in advancing electric mobility

Dr Marc Payne, Senior Manager, Advanced Electrification Research, bp

Industry reports suggest that by the mid-2030s, the majority of cars sold globally will be electric. Lubricating fluids in electric vehicles differ significantly from ICE lubricants due to the nature of the environment in which they operate. Therefore, to support the transition to an electric future, the lubricant industry (including Castrol) is diversifying into EV fluids that include e-transmission fluids, e-coolants / e-thermal fluids, and e-greases.

Advanced fluids for next generation vehicles

Electric vehicles need different transmission fluids because components, such as those found in electric motors, are in constant contact with the lubricant, while operating at higher temperatures. In addition, the electric motors can rapidly reach high rotational speeds increasing the torque on gears and bearings which, in turn, increases the stress on the fluids. Furthermore, the fluids need to be compatible with the range of components found in the electric motor and transmission assemblies, including the electrical conducting ones.  Many of these fluids require a different kind of performance to the ones used today in ICE vehicles.

If we look at ultra-fast charging, one of the critical limitations of battery technology is the effect of heat generated during charging on battery life. Thermal management and the right fluids will play an important part in enabling fast charging processes, stable and long-lasting performance. Specialized fluids and greases are therefore vital to enable the power and driving characteristics of long-range, fast-charging vehicles. 

One of the key challenges an EV battery system faces is regulating temperature under increasingly extreme operating conditions such as ultrafast charging and in all types of climates as well as high-performance discharging. This becomes even more challenging when batteries ideally need to operate between temperatures of 20 and 40°C. Currently, most electric cars have either air cooled or indirect liquid cooled battery systems.

[1] bp Energy Outlook 2023

Coming back to transmissions, we see increasing integration of components into one “coolant & lubrication circuit”. known as “wet e-motor”. The benefits of such systems are that the drive unit can be built in a more compact manner, as it no longer requires the transmission be separate from the e-motor and thus the efficiency and power output can be increased due to better heat dissipation. This requires a new generation of transmission fluid formulations to meet both the more severe requirements of EV transmissions but also factors in new requirements such as e-motor compatibility alongside fluid electrical and thermal properties.

Castrol ON is our range of advanced EV Fluids including EV Transmission Fluids, EV Thermal Fluids and EV Greases. Two thirds of the world’s major car manufacturers use Castrol ON EV Fluids as part of their factory fill[2], for service fill and aftermarket.

EV fluids are designed to enhance the performance, range, and durability of electric vehicles.

  • EV-Transmission fluids help extend the life of the drivetrain system and enable EVs to go further on a single charge by unlocking the maximum efficiency of the drivetrain.
  • EV-Thermal fluids help keep batteries cooler, even in extreme conditions, and enable them to tolerate ultra-fast charging as well as high performance discharging through better heat dissipation.
  • EV-Greases enable EVs to perform more efficiently by minimizing temperature spikes and enhancing durability of components while lowering weight.

Castrol is collaborating with major EV car manufacturers to ensure its lubricants and fluids deliver what EV car owners want: to go further on a single charge, enable longer life of transmission and component parts, and ensure long-lasting battery health.

As electric vehicles continue to evolve, we are looking, to shape the way the fluids are defined: pioneering unique performance testing, driving efficiency and economy going beyond the standard requirements of the fluids, taking consumer insights, and engineering technical solutions, advancing technologies that will lead to breakthroughs for the transport of tomorrow.

[2] Source: LMCA data for Top 20 EV OEMs based on total new car sales in 2021

Battery thermal management

Electric vehicles need optimal temperatures for efficient functioning of the battery pack, power electronic systems, and e-motors. When maintained at an optimal temperature, the battery charge, battery health, and capacity are conserved, and the efficiency of an e-motor can be increased. 

The availability of discharge power for starting and acceleration, charge acceptance during regenerative braking, and the health of the battery work at their best at optimal temperatures. As the temperature increases beyond about 40 °C, the battery life, electric vehicle durability, and EV fuel economy degrade. Considering the overall thermal effect of the battery on electric vehicles, battery thermal management is critical. 

EV Thermal Fluids can reduce the maximum temperatures which the cells reach and minimise temperature variances between the cells during ultra-fast charging and discharging (Figure 1). This enables ultra-fast charging while protecting against battery cell degradation. One of the next big challenges for electrified vehicles Is enabling high power (300kW) ultra-fast charging events to be sustained for longer. This means drivers will have the convenient fast charge they are seeking. Current technology vehicles may sustain 300kW charging for a short time (less than 10 minutes). Through simulations, Castrol has demonstrated that immersion cooled battery designs with Castrol ON EV fluid can sustain maximum charge powers for much longer without overheating.

image 8

Figure 1:  Performance and Durability: Immersion cooling improves the thermal gradient and peak temperature of cells under fast charging vs indirect cooling.

Castrol is now part of a consortium on a UK government sponsored research project to develop an 800V immersion cooled battery system which will demonstrate the advantages of these new technology batteries. Other partners include BMW UK and TAE Power Solutions

At present, most battery packs are thermally managed using water-glycol-based coolants housed within channels within a baseplate or within a cooling ribbon that regulate the temperature of the cells, the dielectric Castrol ON EV Thermal Fluids are formulated specifically for immersion cooling. This enables significant improvements in thermal management and excellent electrical protection in a range of operating conditions, at high and low ambient temperatures[3], for a longer battery life[4].

[3] Versus indirect cooled battery system

[4] Castrol EV Fluids benefits are demonstrated in bespoke testing and development

A preconception within the industry is that dielectric immersion fluids are more viscous than water-glycol. While that holds true for the 1st generation of Castrol ON EV Thermal Fluids work carried out by the Advanced Electrification Research team has resulted in Castrol’s 2nd generation immersion fluids, which exhibit similar viscosity to 50:50 water/glycol fluids at 30 °C (see figure 2).  This decrease in viscosity between the two Castrol ON EV Thermal Fluid generations reduces the pump power required in an immersion cooled battery system; increasing efficiency.

image 10

Figure 2:  Temperature viscosity profiles for Castrol ON gen 1 and gen 2 fluids versus 50:50 water/glycol.

Below 30 °C, the 2nd generation EV thermal fluid has even lower viscosity than water glycol. This means that Castrol’s 2nd Generation ON EV Thermal fluids require similar or lower pumping powers to that of water-glycol based systems hence optimising the efficiency and effectiveness of the temperature management process.


Figure 3:  Immersion thermal management fluids prevent thermal propagation events

Castrol’s Advanced Electrification Research team continues to optimise thermal management performance through joint co-engineering programmes with partners, anticipating the multi-faceted technical challenges resulting from ever-increasing demands for greater battery and powertrain performance.

Investing for the future

“We are committed to supporting the electrification of transport and the take-up of electric vehicles. The growth of EV fluids is a huge opportunity, and we aim to be the market leader in this sector. The significant £50 million investment in Pangbourne will allow us to build additional strategic technologies and capabilities to further advance EV fluids for the future. The facilities will also be an amazing showcase to demonstrate our integrated technology expertise to customers as we help drive the transition to EVs.” Michelle Jou, CEO Castrol

We are also working to support other industries reduce their carbon emissions through electrification – for example, we’re working to support the electrification of sea travel and ports, commercial vehicles, electric motorbikes, and support our industrial customers throughout this transition too.

Advanced EV Fluid technologies and engineering can also be applied to other industries such as thermal management fluids for data centres where demand is rising exponentially.

BP has invested approximately £50 million (around $60 million)in a new, state-of-the-art Advanced Electrification testing centre and analytical laboratory in the UK that is planned to open by mid-2025. The new facilities will be located at bp’s existing global headquarters for its Castrol business in Pangbourne, Berkshire. The site already undertakes research and development of fuels, lubricants and EV fluids and aims to become a leading hub for fluid technologies and engineering in the UK.

Dr Marc Payne, Senior Manager, Advanced Electrification Research, bp

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Dr Marc Payne
Senior Manager, Advanced Electrification Research bp

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