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A cell-holder for battery pack prototype with composite flame-retardant material and 3D printing

News International-French

18 Mar 2020

Professional 3D printing supplier CRP Technology shows strategic use of advanced technology in the development of EVs. It has manufactured cell pouch frames for Energica Motor Company, to test on battery pack prototypes, both for the racing and the production sides. The cell pouch frames were created using laser sintering technology and composite flame-retardant material.

A cell-holder for battery pack prototype with composite flame-retardant material and 3D printing

First Italian manufacturer of supersport electric motorcycles, Energica Motor Company is an innovator in the EV market.

Thanks to the close involvement in the MotoE racing series (Energica was chosen by Dorna as single manufacturer for FIM Enel MotoE World Cup. The first edition of the World Cup concluded recently, celebrating rider Matteo Ferrari from Team Trentino Gresini MotoE as championship winner) Energica’s technological advancement had an important boost, being able to count on an element of competitive advantage represented by MotoE itself: Energica have an exclusive testing ground to try new technical solutions – with some of the best riders worldwide. This support proved to be unlike anything else for Energica R&D, both for the racing and the production sides.

Since its establishment, Energica has availed itself the partnership with CRP Technology. CRP Technology is worldwide innovator of additive manufacturing with Windform materials for LS technology. CRP was born – like Energica – from the entrepreneurial vision of Cevolini family.

The following case study explains how CRP Technology supported Energica in developing and manufacturing of cell pouch frame. The cell frames were tested on battery pack prototypes, both for the racing and the production sides.

The challenge
Energica motorcycles use a high-energy lithium polymer (Li-NMC) battery.

The battery is contained in sealed housing: battery cells, the Battery Management System (BMS) and all the necessary systems to ensure the safety of the vehicle.

Left: Energica Ego battery pack ready to be mounted - Right: Battery pack mounted (detail)

Energica is a manufacturer that has designed, patented and adopted a cooling system for the battery pack that is superior to usual ones thanks to its specific ventilation paths that limit the stress on the batteries. This provides considerable benefits to both performance of the vehicle and the life of the battery.

Energica’s R&D department carries out research on new cells placed on the market, in order to evaluate their use in industrial production. This activity allows Energica to be at the forefront of the most advanced technology.

The activity starts from the validation of the single cell (initial screening) and evolves in testing battery pack prototypes on the road. The tests conducted on the cells are part of Energica’s know-how, and therefore cannot be disclosed in detail.

In this specific case, the study was conducted on pouch cells.

In order to carry out the tests required by Energica procedure, the team of engineers at Energica decided to provide each pouch cell with a surrounding case, with the function of support and reinforcement.

Pouch cell (screenshot) with 3D printed casing and cooling system. The casing has been manufactured in Windform FR2 flame-retardant + glass-fiber reinforced composite material

To test the battery pack prototype on the road, the casing of each pouch cell had to be manufactured using a high-performance material with mechanical properties and using advanced technology that met Energica’s requirements.

3D printed pouch cell casings manufactured by CRP Technology using selective laser sintering technology and Windform FR2 for testing. User/client: Energica Motor Company

Due to these reasons, Energica has relied on CRP Technology: Experience and know-how gained in over many years of activity as supplier of innovative and cutting-edge technological solutions for the most competitive and demanding industrial sectors, CRP Technology has supported Energica from the early stages of design and development to the construction of the cell casing with professional 3D printing and Windform material.

The solution
Following the examination of Energica’s needs and the analysis of the 3D files of the application, CRP Technology has opted to use selective laser sintering technology with Windform FR2, the new material from Windform Top-Line family of high performance composite material for additive manufacturing, which is flame retardant and glass-fiber reinforced.

Engineer Franco Cevolini, CTO and VP at CRP Technology, states:

“Having built functional prototypes of pouch cell casings for various tests, including road tests. It was clear we should use a material with specific characteristics, namely: polyamide-based material, electrically insulated, stiff, resistant to temperature and flame retardant.”

Windform FR2 was the choice because it is has all these characteristics.

Eng. Cevolini comments:

“To be more specific, flame retardant characteristics are very important, because it guarantees self-extinguishing in case of operating anomalies, which are a result of a temporary voltage peak, with consequent localized melting, followed by combustion initiation. As example: If an ignition/combustion occurred in a localized portion of the cell casing, and the polymer were flame retardant, then the combustion would be extinguished. Instead, if the material were not flame retardant, then serious problems would arise, because the combustion would degenerate into a fire. Windform FR2 prevents such an occurrence.”

Stiffness is also very important, Cevolini states:

“The material chosen for the pouch casing had to have a high mechanical performance in order to guarantee an overall stiffness to the battery pack prototype. In order to withstand the volumetric expansion that cells undergo during the charge and discharge cycles."

Indeed, the expansion generates pressure: the cell casings therefore had to be able to withstand these stresses.

Outcome
After Energica Motor Company’s approval, CRP Technology 3D Printing Department proceeded with the manufacturing and delivery of the pouch casings.

This technology has allowed, once again, to highlight the perfect combination of selective laser sintering technology and Windform composite materials.

Thanks to Windform FR2, indeed, in a very short time and with good and highly promising results in terms of mechanical, electrical and thermal features, it was possible to carry out all the tests on the battery pack prototype and testing protocols required by Energica.

In-depth analysis: potential issues of pouch cells and their resolution using 3D printing and windform FR2 composite material

  • Issue no.1: Swelling

Swelling can occur as part of gas generation during charge and discharge. It is a concern, which should not be underestimated.
 

Pouch cell with casing (screenshot). Direction of swelling indicated by red arrows

Giampiero Testoni, CTO at Energica Motor Company:

“In a test-ready battery pack prototype (images 7 and 8), each cell must be in position and not move. Stability must be assured by the cell casing. Therefore, cell casings play a fundamental role: they must be resistant and contain the swelling of the cell, without breaking.”

Left: Pouch cell battery pack prototype (screenshot); Right: test-ready pouch cell battery pack prototype

Energica, assisted by CRP Technology, has verified that Windform FR2 and selective laser sintering process guarantee a high level of precision of the pouch cells to maintain their position inside the battery pack.

Testoni adds:

“The cell casings in Windform FR2 allow a certain degree of freedom of movement” to swell and contract without deforming, without going out of position, without interfering with one another.”

  • Issue no.2: Heat rejection

Swelling of pouch cells generates heat that must be dissipated. To aid this heat rejection a metal plate with two lateral structures is attached to each pouch cell and holder. The function of the plate is cooling: the heat is transferred to the lateral structures and dissipated to the outside, in combination with the cooling system patented by Energica.
 

Exploded view of pouch casing with pouch cell and cooling system. The heat is transferred to the plate and brought to the external sides (red arrows) for dissipation (blue arrows)

Figure below represent the area most affected by the increase in heat. This section must not undergo deformation: any loss of preload of the screw could generate sparks with the potential of fire.
 

Left: Exploded view of pouch casing with pouch cell and cooling system. Circled in red, the area most affected by heat increase. The area must stay stiff; Right: Detail of the area of the pouch casing most affected by heat increase

Engineer Franco Cevolini adds:

“When a polymer begins to heat up, it loses its mechanical characteristics and undergoes deformation. It does not happen with Windform FR2 because it is a composite material and it preserves its stiffness. Windform FR2 deflection temperature under load is higher than any other non-composite materials with the same flame-retardant characteristics”.

Giampiero Testoni, CTO Energica Motor Company:

“We rely on CRP Technology and its 3D Printing Department because they have the right composite material to satisfy every need, in particular to support a complex project such as Energica electric motorcycles. I am not referring to an ordinary motorcycle, but to a high voltage and power, electric motorcycle that has specific needs. CRP Technology is the right partner to support customers in their everyday challenges.”