Whether it is a medical device concept, automotive manufacturing, project, industrial application, or consumer product, companies require large and small battery packs that will ensure their electronic devices and machinery have the longest life cycles without any safety issues. Many of hese battery packs need to be custom made for the specific device before they can be marketed.
Yet, managing your time when undergoing the product development, testing, marketing, and selling of your device can be slowed down when requiring a battery pack made from scratch. It can be a tricky business, as you don't want to build the entire product line before the battery pack development phase is completed. You may find out that the mechanical design of your battery pack will not fit into the device or that the electrical specifications of the battery pack isn't suitable to the power needs of the device.
Here at Epec, we are helping all electronic market segments with their custom battery pack needs with our design and manufacturing capabilities. We can also help you improve your battery pack's time-to-market efforts. There are several validation processes and specification requirements that you should be aware of to eliminate issues early in the design, development, and packaging phases for your battery pack.
In this blog post we will review 5 ways to make time to market improvements when obtaining custom batteries.
Custom battery packs during the assembly process.
Proof of Concept Validation for Battery Pack Power
During your proof of concept for the application, you've determined the electronic device's feasibility, capabilities, and desired functions over a long range of time. Yet, you also need to validate the device's power needs. Certain applications may go through different types of environmental stresses and loads. This can change the way your device functions, as it may require more power to operate than when it is used in a more controlled and stable environment.
For example, there may be times when your device will be used in cold environments, as battery packs will discharge quicker in lower temperatures. So, not only will you have to ensure that the device design will further protect the battery pack in this environment, you also need to figure out the changing power needs of the device to ensure it continues to work as required.
Many companies find that determining the battery life for the device can be a significant hurdle to the process as well as time-consuming. When validating your proof of concept, you should request sample batteries or prototypes that have varying chemistries, housing components, and other requirements (waterproofing and flammability specifications) to use during device testing. By obtaining the sample batteries and prototypes online, you'll be able to create benchtop battery pack prototype data. This necessary data can further hone your battery pack specification requirements when it comes to selecting the appropriate battery chemistry.
Battery Pack Electrical and Mechanical Design
The battery pack's electrical and mechanical designs will need to be created and tested. With the proof of concept validated from the benchtop prototypes, you should be able to narrow down the battery specifications that will work best with the device.
Battery pack requirements may include deciding on:
Then, your engineers should be able to take these designs and change or improve them to ensure that there will be no negative effects created between the materials used for the battery pack and the device, as well as checking that the electrical components will properly connect and provide adequate power to the device. Then, the designs can be passed on to the battery supplier.
3D Printing Mechanical Design Proofing
Tooling the battery pack's enclosure can be a very involved and lengthy process. This procedure can often push out lead times, which can be further delayed if there is even a single dimension or specification that is incorrect regarding the mechanical design. While Epec can improve time-to-market processes by using Fused Deposition Modeling (FDM) to create conceptual models, engineering models, and prototypes of the customized battery pack's enclosure, you can also further shorten the time to market process by using 3D printing.
Since the mechanical and electrical designs have been developed and proven in the last step, you can 3D print the battery pack prototype to verify the mechanical design when placed into the device. This step ensures the battery pack will be formed to fit the device as specified from your mechanical design requirements. We can also use the data collected from the 3D printing process to assist with our tooling procedures when crafting the enclosure.
From this 3D printing proofing phase, you will be able to develop 3D drawings that can benefit the battery supplier (2D drawings of the enclosure's exterior is the minimum that would be required). These drawings can help to give additional details regarding the finish, color, and materials to be used.
Custom Packaging Development and Shipping Requirements
With the mechanical design locked in, you should now move on to the custom packaging design phase. The packaging can vary based on the complexity of the design and the type of battery chemistry that has been selected, such as lithium-based batteries. The battery pack may be supplied in a soft pack or within an enclosure, as you will want to test to ensure that the packaging is up to shipping standards based on where your device will be used.
You will also need to understand all shipping requirements. If transporting lithium-based batteries, your company and shipping department will need to be certified to be in compliance with DOT regulations. Becoming familiar with US38.3 transportation requirements will ensure that the packaging design will pass all rigorous shipping and transportation testing to gain approval.
Market Segment Determination
While your engineers will be developing the electrical and mechanical designs for the battery pack that will be handed over to the battery supplier, you and your team will need to decide on the market segment that will be using your devices. While this seems obvious from the proof of concept stage of your device, the battery pack design and build can impact your ability to offer these devices to certain industries unless you receive the appropriate certifications.
Specific industries that will require testing and documentation include medical, aerospace, and the military. Some of these requirements include serialization of the battery pack as well as the components in the device for medical applications. In military and aerospace, companies will need the battery packs to pass all Highly Accelerated Life Testing (HALT) and Highly Accelerated Stress Screen Testing (HAST) requirements before being placed into use to check for any rapid fatigue or defects. Other companies may have certification requirements to check for shock and vibration limits, extreme temperatures, and other factors.
To pass these certifications, your device and custom battery pack will need to be thoroughly tested. Your team will be able to evaluate which markets will require certifications, the types of tests that will be performed, and how many sample quantities will be needed that will undergo the testing. In addition, companies that require certification testing will usually have a timeline on how long testing will take place.
With all this information, you can better time when testing and certification will be completed so that your custom battery packs can then be manufactured and shipped to your site to meet your production deadlines. You'll also be able to develop a time frame if testing reveals any design flaws with the device that will need to be addressed.
Reducing the Developmental Timeline
From the validation phase to the marketing research, performing these initial steps can allow battery suppliers to speed up the battery pack development process. Then, we can move on to the scope of the project and the production phases. By supplying as much information as possible, a battery supplier will begin their design and manufacturing procedures. Here at Epec, this process is as follows:
Summary
Always be aware that lead times will vary significantly from the moment a battery chemistry is selected, especially when selecting lithium-based batteries due to regulatory requirements. Having thorough documentation for the battery supplier from the offset and being available for the battery pack application reviews and the scope refinement phases will help to improve the time to market for your battery packs. Also, the moment that you have a device concept that will require a battery pack, contact an approved battery pack assembler, such as Epec. We can help you determine the type of documentation and data that will be needed to make our development process move quickly.
In many universities and startup-scale battery R&D environments, the coin cell is the default form factor to evaluate battery systems. However, in applications such as electric vehicles (EV), “cells” are typically manufactured in pouch, prismatic, or cylindrical form factors, which are then assembled into “modules”, “packs”, and then integrated into the EV product. In order to achieve stringent safety and performance requirements, a high level of precision, uniformity, stability, and automation have become necessary in the battery manufacturing process.
This work is a summary of CATL’s battery production process collected from publicly available sources in Chinese media (ref.1,2,3). CATL (Contemporary Amperex Technology Co. Limited) is the largest battery manufacturer in the world, and its battery production process is sophisticated and highly automated. Although much of the details of the manufacturing process are proprietary, we have identified and outlined the 3 main production stages and 14 key processes below from publicly available sources as an introduction to battery manufacturing.
The industrial production of lithium-ion batteries usually involves 50+ individual processes. These processes can be split into three stages: electrode manufacturing, cell fabrication, formation and integration.
Equipment plays a critical role in determining the performance and cost of lithium-ion batteries. Mirroring the three manufacturing stages, equipment can be divided into three categories as well: the 1st stage equipment (Mixer, Coater, Roller Press, Splitting Machine, Filming Machine, Die-cutting Machine, etc.), the 2nd stage equipment (Winding/lamination machine, electrolyte injection machine, packaging equipment), and the 3rd stage equipment (Charging and discharging machines, testing equipment, etc.). The capital cost for each of these three stages represents approximately 40%, 30%, 30% of the cost of the production line.
The 1st stage: electrode manufacturing
The first stage in battery manufacturing is the fabrication of positive and negative electrodes. The main processes involved are: mixing, coating, calendering, slitting, electrode making (including die cutting and tab welding). The equipment used in this stage are: mixer, coating machine, roller press, slitting machine, electrode making machine.
Mixing — Electrode slurry preparation process
To produce an electrode slurry, the raw active materials are combined with solvent, binder, and additives. Slurry mixing is the first step of the electrode manufacturing process, and the process is done separately for cathode and anode materials. The key measurable characteristics of this process (viscosity, density, solid content) will directly affect the quality of the battery and the uniformity of the electrode. In the mixing process, the formulation of raw materials, mixing steps, mixing time are all important parameters.
From the very first step of adding components, the sequence of materials mixing could affect the final electrode’s electrochemical performance. Starting from dry-blending of active materials and conductive carbon, followed by adding solvent could result in lower slurry viscosity, which could enable higher solid content and faster drying, but with trade-off on the rate capability. In contrast, with conductive additives dispersing in binder then incorporate active material will result in a porous conductive framework which subsequently aids the electrochemical performance(ref.).
To achieve a viable electrode slurry, two of the main criteria is if the slurry is stable and processable. Due to interactions between the slurry particles (van der Waals attractions, hydrogen bonding and electrostatic forces) the agglomerations are inevitable. Thus the addition of a dispersant is always needed in the mixing process. Although mixing is a relatively low cost process, the time needed to ensure sufficient slurry dispersion could be a constraint on throughput.
CATL cell manufacturing-slurry mixing
Additionally, in the mixing process the air quality must be strictly controlled to prevent any dust particles or impurities from contaminating the electrode slurry. For cathode slurry preparation in particular, moisture should be well controlled for high-Ni containing cathode materials to prevent corrosion of aluminum foil. Strategies to mitigate the corrosion include pH adjustment, by the addition of phosphoric acid; or interface modifications through applying metal oxide coating on the active material or using carbon primary coating on the current collector.
Coating — Coat and dry the electrode slurry on the current collector foil
Coating (equipment: coater) refers to the process of evenly applying the electrode slurry onto the aluminum (cathode) and copper (anode) metal foils and the drying process that follows. In large scale manufacturing such as in CATL’s process, the coating method used is a tensioned web over slot die with backing roll. In the slot die coater, the slurry is dispersed through a slot gap onto the moving metal foil. Below is an illustration of slot die coating:
Slot die coating illustration from Durr
Slot-die coating has the advantage of being capable of operating at speeds demanded by industry (up to 300ft/min) and is proficient in achieving even coating thicknesses with precision. Electrode drying is integrated in the continuous coater. During drying, three competing physical processes are happening simultaneously: evaporation of the solvent, diffusion of the binder, and sedimentation of the particles(ref.). In large scale manufacturing, air flotation is applied to assure equal drying to prevent edge curling and leaving an equal amount of residual solvent on both sides. The flotation dryer line could be as long as 70 m, with drying temperatures ranging from RT to 150 °C. Drying temperature and speed could make a big difference on the distribution of each component in the electrode. Coatings dried at 150 °C had 3 times as much binder at the surface layer than on the substrate layer, while a coating dried at RT (room temperature) was more uniform (ref.).
Air flotation illustration from Durr
The quality of the coating and drying processes profoundly affects the uniformity, consistency, safety, and cycle life of the manufactured battery. Non-uniformity or defects introduced at this stage on either side of the electrodes will result in poor electrochemical performance of the battery and can cause serious safety issues.
Coating thickness and mass loading should be precisely controlled, and to avoid foil tearing and failure (the main limiting factor in line speed), the coater’s rolling speed and tension must be precisely calibrated. For example, CATL’s current production line utilizes copper foils that are 6um in thickness, 4000 meters in length, and a rolling speed of 80 m/min during the coating process.