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A new refrigerant fluid allows a battery to be charged 41% faster

Castrol and Sprint Power are collaborating on a project to develop ultra-fast charging battery cells and packs for fuel cell electric vehicles (BEVs) and fuel cell hybrids (FCHEVs) through the use of a new cooling fluid.

Two battery modules designed by Sprint Power, which will use Castrol ON thermal fluids for electric vehicles, are charged to 80% in just 12 minutes. This will make vehicles an even more viable alternative for those who have not yet chosen electric mobility.

The collaboration between Castrol and Sprint Power is the fruit of the CELERITAS Project, a €11.2 million scheme, with €5.5 million funded through APC 18, with the aim of addressing current consumer concerns in relation to current electric vehicle charging speeds. In addition to Castrol and Sprint Power, the consortium includes BMW, AMTE Power, Clas-SiC and Eltrium.

The UK’s Sprint Power is a leading company in electric propulsion systems, power electronics and battery systems. It has developed two battery systems, one for electric applications and the other for hybrid applications, which integrate all the system’s electronics and incorporate various charging protocols to save weight and space. They also integrate an 800 V to 14 V DC-DC converter, a battery management system (BMS), and “direct cooling” capability, in which the cells are immersed in a cooling solution not conductive.

Castrol ON Electric Vehicle Thermal Fluid is specifically formulated for direct cooled applications to ensure these Sprint Power battery systems can charge faster and offer more performance and protection. In addition, Castrol is using its state-of-the-art modeling and testing facilities; This is to ensure that both Sprint Power battery systems benefit from an optimized final design. And, in addition, it must also be ensured that it is capable of withstanding the most demanding conditions that ultra-fast charging entails.

Advanced battery modules

Sprint Power battery modules feature a modular cell block that can be tailored for a variety of applications, from sports cars to electric vertical takeoff and landing (eVTOL) vehicles.

The hybrid battery module has been configured for its potential application in hydrogen cell electric vehicles. It has an optimized design, with a power/weight ratio of 3 kW/kg excluding the DC-DC converter. The module can supply 5 kWh of useful energy, with a maximum charge/discharge rate of 230 kW (105 kW continuous). In the most performance version, designed for application in sports cars, the figure increases to 76 kWh of useful energy with a maximum charge/discharge rate of 800 kW (700 kW continuous).

An integrated unidirectional 800 V to 14 V converter supports a maximum power output of 3.5 kW from a compact 0.8 kW/l high power pack. As with everything else in the Sprint Power battery module, the DC-DC converter has been designed to be very efficient, with a maximum efficiency rating of 97%.

The module incorporates Sprint Power’s master BMS, which includes a security microcontroller to support cybersecurity, diagnose faults, and is compatible with CHAdeMO or CCS charging standards. The system can supply a voltage of 8-16 V and has been tested for operation at temperatures ranging from −40°C to 85°C. A slave BMS offers configurable support for battery modules of various sizes between 5 and 12 cells.

Castrol’s expertise in fluids

The thermal management Most of the current battery modules for electric vehicles are made with water-glycol-based coolants, which are lodged in the channels and regulate the temperature of the cells. In contrast, the battery modules being developed under the CELERITAS Project use Castrol ON electric vehicle thermal fluid, an innovative dielectric liquid that circulates inside the module and comes into direct contact with the individual battery cells. This translates into faster charging and significant improvements in thermal management across a range of operating conditions, at high and low ambient temperatures, for longer battery life.

In an independently performed modeling study with the same variables, Castrol ON electric vehicle thermal fluid showed a 41% faster charging compared to water-glycol fluids. Using Castrol fluid, the battery charged 80% in 10 min, compared to 14.1 min when using existing water-glycol fluids.

By cooling the battery cells individually, Castrol dielectric fluid will also help avoid the risk of “thermal runaway”, where high temperatures cause irreversible failure of individual battery cells as a result of overcharging or short circuiting. Thermal runaway can develop into thermal spread, where heat from the damaged cell is transferred by convection and conduction to adjacent cells, a process that can lead to catastrophic failure of the entire battery module. With direct cooling systems, temperature spikes in individual cells are less likely and, if they do occur, can be quenched at the source, unlike refrigerants used in indirect cooling systems.

Extensive simulation and testing

Castrol’s long experience in modeling and simulation has given both parties a better understanding of how Castrol dielectric fluid will circulate inside battery modules. This has allowed the Sprint Power team to optimize the battery module design to improve its thermal performance. Simulation tests will also allow the team to perform thermal runaway tests.

Optimized fluid dynamic testing will then allow Castrol to identify potential improvements in future products in the ON range.

Castrol’s state-of-the-art battery testing facilities will be used from early 2023 to test functional prototypes to help ensure they deliver the required performance, durability and safety. The facilities have the capacity to test battery packs at temperatures ranging from −40°C to 85°C, and up to a maximum of 1,200 V DC and 600 kW.

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