Simultaneously increasing the energy and power density of batteries is widely regarded as one of the hurdles preventing EVs from wider acceptance by consumers. Design engineers usually have to compromise between energy and power density as they try to reduce the size and weight of battery packs to meet target performance levels.
So, under the category “look what we have here,” is a development from the engineering wing of the Williams Formula One racing team that seems to provide the best of both worlds. Using what it calls Adaptive Multi-Chem technology, Williams says its solution enables a battery of the same weight as a conventional unit that can deliver longer range without compromising power, or higher power without compromising range.
Two Cell Chemistries
Lithium-ion battery packs are usually made up of a single type of cell, each with the same chemistry, energy density, and power output. Cells are arranged in modules and the modules are assembled into a complete pack. The Williams design uses two different types of cell chemistry, arranged in two separate blocks within the module.
Samsung’s 21700 30T cylindrical cells provide good energy density and more specialized high-performance pouch cells from A123 systems provide the high power. A pouch cell differs from a standard battery pack in that rather than using a metallic cylinder and glass-to-metal electrical feed-through for insulation, conductive foil tabs welded to the electrode and sealed to the pouch carry the positive and negative terminals to the outside.
Here, the pouch cells provide the fast release of energy needed for strong acceleration and, as they become depleted, they can be topped up again from the energy stored in the Samsung cells. Each Adaptive Multi-Chem module has its own integrated, bidirectional dc-dc converter to control the process of energy transfer between the two types of cells.
The new Adaptive Multi-Chem battery pack from William Advanced Engineering builds on the company’s Formula One and Formula E (electric car racing) expertise. (Source: Williams Advanced Engineering)
Williams boasts of a 37% increase in energy density for a target power density and says it uses a compact thermal management system—each module has a self-contained liquid cooling circuit—to provide enough cooling without unnecessary bulk. The company claims a total stored energy of 60 kWh, with a core battery mass of 343 kg (757 lbs.). Peak deployment power is 550 kW (20-second pulse), and peak regeneration power is 550 kW (10-second pulse). What’s more, according to the company, peak power, continuous power, and stored energy of the module can be tailored to individual requirements.
The system is said to be highly adaptable, with independent sizing of energy and power cells through the use of scalable blocks. It can be supplied to customers ready to assemble into battery packs.
Exoskeleton
The new battery module features an exoskeleton manufactured using the company's weight-trimming technology called 223. This production process creates an engineered hinge embedded within a single composite preform of carbon-fiber-reinforced polymer (CFRP). 223 enables the creation of 3D structures from 2D materials, opening the potential for manufacturing techniques previously constrained by cost or production rate. It allows for rapid, low-cost composite production and includes the use of recycled materials.
The 223 exoskeleton improves the battery's structural performance, with the complete base and case weighing just 40 kg, making the entire system 385 kg (849 lbs). It has a high strength-to-weight ratio, better-than-ordinary stiffness, and excellent fatigue and environmental resistance. The technology is particularly relevant to the automotive industry, where reducing weight is seen as one of the primary tools needed to meet increasingly stringent fuel-economy and emissions targets, as well as support for the range required from electric vehicles.
Paul McNamara, Williams Advanced Engineering technical director, concedes that because of the added complexity and integrated electronics, its cost will be higher than a conventional module, “but we hope to get economies of scale as numbers increase.”
Williams Advanced Engineering is the technology and engineering services business of the Williams Group, which also comprises ROKiT Williams Racing in Formula One. Following the in-house development of a Kinetic Energy Recovery System (KERS) for Formula One racing, Williams developed core capabilities in batteries and electrification. These have been applied to Formula E racing, where Williams helped to launch the series and has powered all cars on the grid for the first four seasons of racing and then into vehicles off the racetrack.
Williams lithium-ion Formula E batteries not only are the first to have passed FIA crash testing regulations, but the company reports they also meet stringent air safety regulations in order to be transported around the world to support the global race calendar.
