Control Valves: Essential Components for EV Battery Manufacturing and Recycling

The electric vehicle (EV) battery life cycle — manufacture to recycling — appears at first glance to involve discrete manufacturing from start to finish. There are, however, two important steps in battery manufacture and recycling that are reliant on batch processing. The first batch process combines powders and liquids in a mixer to produce battery slurry. The second mixes acids with post-use shredded batteries in a vessel to precipitate out and recapture precious materials.

EV batch processes would be impossible at the volume required without control valves, which are valve bodies — ball, butterfly, angle seat, gate, or solenoid — combined with automated actuation controlled via PLCs. Control valves are also essential in the electrolyte filling process.

Among the many steps in EV battery lifecycle, three rely on control valves: battery slurry production, filling, and battery recycling.

Understanding the vital nature of batch processing and the role control valves play provides a deeper understanding of the complex EV battery manufacturing process. This knowledge gives a deeper appreciation of the marvel of EV battery production.

The Complexities of Battery Slurry Formulation

In every EV battery, the aluminum-foil cathode and the copper-foil anode are coated with a thin film made of a three-component battery slurry. The battery slurry-film layer is essential to battery performance, and its manufacture is a complicated and precise operation. Cathode and anode slurries represent different formulations and are optimized for the role each conductor plays in providing an electric charge and then recharge.

The components of EV battery slurry are:

• active materials that react to lithium ions

• conductive additives that facilitate electron conductivity

• a binding agent that combines the active and conductive materials into a networked agglomeration.

The composition of the slurry and its manufacture are the secret sauce for every battery manufacturer as slurry determines the overall performance of the cathode and anode conductors. Each slurry formulation is proprietary to the battery manufacturer.

Many scientific papers have been written on the materials science of battery slurry composition and processing, and countless suppliers are involved in developing optimized processing and film applying solutions. Consistency and repeatability batch after batch requires the utmost in materials science and process control. Battery slurry manufacture represents a complex interaction of materials added in precise proportions, at exacting intervals, and mechanically mixed to the proper degree so that the slurry meets a host of rheology, dispersal, and sheer properties. Control valves are the means of precise ingress and egress of powders, liquids, and slurries.

A battery gigafactory uses upward of 5,000 control valves in the battery slurry manufacturing process. The valves exhibit fast and repeatable opening and closing based on the slurry formulation process. Each control valve assembly typically comprises a limit switch, pilot valve, positioner, a pneumatically powered linear or rotary actuator, valve body, and filter regulator.

In slurry batch processing, many different types of valves and valve sizes are used. For example, the size of the piping and the pressure exerted by the flow of liquid at one point in the mixing process is so strong that the plant specified the largest Festo DFPD quarter-turn actuators, rated at up to 517 lbf (2300 N) of torque.

Valve Types and Applications

The choice of the control valve begins with the valve body and continues out from there to include the other components such as switches, pilot valves, and actuators. How does one know what type of valve body is best for the material and flow? Many times, the choice of valve type — ball, butterfly, gate, angle seat, or solenoid — rests on installed base or tradition. For example, water treatment facilities tend to use butterfly and gate valves for cost-effective throughput. But some applications, like slurry mixing and battery recycling, fall into a gray area where multiple valve types can fulfill the requirements of the application, and there is not always one right answer or a clear preference.

The principal reason to consider butterfly and gate valves for pipes 2 inches and larger is because these valves scale up to larger sizes more cost effectively than ball, angle seat, and solenoid valves. Butterfly valves have the best price of the two, and they are the easiest and most cost-effective to automate. Thousands of butterfly valves are in use at gigafactories.

Gate valves, on the other hand, are best for slurry, sludge, and high particulate media, as well as proportional control applications. Table 1 shows how the two standard industrial valves compare in relative terms to important considerations for automated applications. A single ★ rating has the lowest relative value in the category while a ★★★ rating offers the highest.

As pressure and/or temperature increases, ball and angle seat valves provide an overall advantage due to the standardization on highly resilient materials like stainless steel housings and PTFE seats. However, the larger an angle seat valve becomes, the lower its pressure rating, losing some of its advantage in this category (Table 2).

For high-cycle-rate applications, start by exploring angle seat valves for pneumatic actuation and solenoid valves for electric actuation. These have the highest lifecycle ratings, while ball and butterfly valves have the lowest. In applications where the valve may only open a few times per day, the number of life cycles are less of priority, and ball and butterfly valves can still be a good choice. Angle seat valves are ideal for controlling the flow of electrolyte into the battery during filling.

When size or weight is an issue — skid applications, for example — angle seat and solenoid valves offer an advantage for automated solutions due to their compact nature with integrated actuating mechanisms.

The design and internal actuation make the angle seat the best selection for fast open and close rates such as filling applications.

After determining the type of valve body required, it is necessary to specify the attributes the valve must have to satisfy the operating conditions. These attributes include type of construction, coating, chemical resistance, pressure rating, diameter, double or single acting, torque requirement, and certificates. Several suppliers, including Festo, offer online configuration tools. These tools help size the selected valve body type and identify all accessories best suited to the application. The engineer simply enters parameters, and the software does the rest. What used to take hours to specify the right valve and then search, sometimes on multiple vendor sites for accessories, now is streamlined thanks to online configuration tools.

The Circular Battery Economy

Recovery of valuable elements within the EV battery is essential for the health and viability of the industry. In recycling used EV batteries, controls valves are required.

Control valves automate the extraction of precious materials from a slurry of shredded EV batteries in a batch process. The valves introduce various acids to the shredded batteries held in a process vessel. The acids precipitate precious materials out of the solution for ease of separation and collection. Valuable materials available for recapture and reuse in lithium-ion batteries include cobalt, gold, lithium, manganese, neodymium, nickel, palladium, platinum, silver, and tantalum.

The process valves and control valves for slurry mixing, electrolyte filling, and battery recycling play crucial parts in the circular battery economy.

This article was written by Jarod Garbe, Industry Segment Manager – E-Mobility, and Lawrence Lin, Business Development Manager – E-Mobility, both at Festo (Islandia, NY). For more information, visit here .

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