As one of the important links in the production of lithium-ion batteries, battery packaging materials are crucial to battery performance, safety and even cost control.
Why Battery Packaging Materials Matters (More Than You Think!)
Think of battery packaging as the protective skin of these energy powerhouses. It’s not just about aesthetics; it’s about safeguarding the delicate internal components and ensuring they function efficiently. Choosing the right packaging materials and design can lead to significant cost savings, thanks to an adequate combination of mechanical, permeation, and seal-strength properties. Over the past decade, three main packaging technologies have become the most common in the lithium-ion battery industry: Cylindrical, Prismatic, and Pouch-based.
Leading suppliers, like Xiaowei, work closely with clients to develop custom enclosures for these three geometries, offering solutions like cans, cases, lids, tabs, rolls, andlaminated films (both aluminum- and polypropylene-based).
Let’s break down these primary packaging styles:
Cylindrical cells often come to mind when people think of batteries – and with good reason! They’re one of the most widely-used models due to their manufacturing ease and mechanical durability.
Cylindrical cells are relatively straightforward to produce and feature a sealed can exterior that can withstand higher internal pressures, with an accessible vent to release excess pressure if necessary for added safety. Cylindrical batteries are commonly found in wireless communications devices, biomedical instruments, power tools – basically any applications where durability and reliability take precedence over size considerations. Furthermore, cylindrical packaging of lithium-ion batteries today are widely available forms.
- Prismatic Cells: As our gadgets became sleeker, the demand for thinner batteries grew, leading to the rise of prismatic cells. Their rectangular design supports thinner cell geometries and can be easily customised to fit specific applications. Interestingly, lithium polymer batteries exclusively use prismatic cell packaging. For these, heavier gauge metals are preferred for casings to help alleviate the risk of bulging from internal pressure.
- Pouch Cells: These are the featherweights of the battery world! Unlike cylindrical and prismatic designs that use hard metallic enclosures, pouch cells are packaged using conductive multi-layer foils. Their electrical contacts are foil tab conduits welded to the electrode and sealed to the pouch material. The big advantages of pouch cells are that they are lighter, less costly, and occupy the least amount of space. This makes them the go-to choice for compact applications like smartphones, tablets, and other portable consumer electronics that need ultra-thin enclosures.
Beyond the main packaging styles, there are also specific materials that make up these solutions, such as battery tab materials (aluminium for positive electrodes, copper for negative), laminated battery tapes (acid-modified polypropylene and polyester for stable pouch cells), and multi-layer aluminium laminate films (available in rolls or preformed pouches).
Shipping Lithium-ion Batteries: A Hazardous Journey
Manufacturing batteries is no easy feat; transporting them between locations requires special care. The U.S. Department of Transportation classifies lithium-ion batteries as hazardous materials under their Hazardous Materials Regulations (HMR; 49 C.F.R Part 171-180), making shipping these items no easy undertaking with numerous rules and packaging requirements in place to guarantee safety.
Shipping lithium-ion batteries is an intricate and complex process; their packaging must meet multiple key criteria in order to fulfill shipping standards, protecting against short circuits, restricting movement within the outer package and avoiding accidental activation of equipment. By meeting all these standards, shipping lithium batteries becomes somewhat more manageable while still demanding thorough attention to details.
- No Metallic Inner Packaging: As a general standard, lithium-ion batteries cannot be packaged in metallic inner packaging. Each battery or cell must be completely enclosed by its inner packaging to prevent contact with other equipment or any conductive material.
- Approved Outer Packaging: The inner packaging (containing the batteries) can then be placed into containers made from materials like metal, wood, fiberboard, or solid plastic boxes, or metal, wood, or plastic drums, or even metal or plastic jerrycans.
- Heavy Batteries: If lithium-ion batteries weigh more than 26.5 pounds and have a strong, impact-resistant outer casing, they can be packed in sturdy outer packaging or protective enclosure casings, such as fully enclosed or wooden slatted crates, on pallets or other handling devices.
- No Movement: A general rule of thumb is that the packaging must prevent any movement or contact with other materials.
- Hazard Labels: Every package must display the appropriate hazard communication label.
Special Situations: Different Batteries, Different Rules
Not all lithium-ion batteries are treated equally when it comes to shipping! Different types of batteries – depending on their condition or purpose – have distinct specifications and packaging requirements:
- Batteries for Recycling or Disposal: Good news here! These are exempt from testing and record-keeping requirements, but they still need to meet typical packaging requirements for lithium-ion batteries.
- Prototype Batteries: Similar to recycling batteries, prototypes are exempt from testing and record-keeping requirements. However, they have a few extra rules:
- You have the option of using non-combustible, non-flammable cushioning to prevent vibration and contact with other materials.
- If a prototype battery weighs more than 60 pounds, it must be contained in individual packaging.
- Shipping papers for prototypes must include the specific phrase: “Transport in accordance with §173.185”.
- Damaged or Recalled Batteries: These are the most sensitive to ship and have the strictest guidelines to prevent potential thermal runaway or leakage hazards. They may only be transported by highway, rail, or vessel.
- Each damaged battery must be placed in individual, non-metallic packaging.
- The inner packaging MUST be made of cushioning material that is non-combustible, non-conductive, and absorbent.
- This individual packaging must then be contained by outer packaging made from metal, wooden, or solid plastic boxes, or metal, plywood, or plastic drums.
- The outer packaging also needs to display specific labels, such as “Damaged/defective lithium ion battery” and/or “Damaged/defective lithium metal battery”. Companies like Ameripak specialize in providing safe and compliant packaging for these highly hazardous damaged, defective, or recalled (DDR) batteries.
A Closer Look: The Magic of Pouch Cell Packaging
Pouch cells’ secret sauce lies in their packaging: aluminum-plastic film is flexible yet sturdy allowing for compact form factors suited for portable electronics to electric vehicles alike. Because pouch cells optimize space usage while decreasing weight consumption significantly without compromising performance levels or performance potentials they remain an industry favorite when looking to increase efficiency without compromising performance levels.
The main purpose of this soft pack packaging is to create a perfectly isolated environment for the cell, keeping the inside in a vacuum, oxygen-free, and water-free state. Why so strict? Because the dynamic electrochemical reactions inside lithium-ion batteries are super sensitive to water and oxygen. If these elements interact with the electrolyte, they can produce hydrofluoric acid (HF), which is a major contributor to degradation and a shortened battery life.
The aluminum-plastic film itself is a marvel of engineering, typically made of three main layers:
- The Outer Layer: Usually nylon, this layer protects the middle layer, reduces scratches and dirt, ensures a good appearance, and most importantly, prevents air (especially oxygen) from penetrating to maintain the battery’s internal environment. It also helps ensure the aluminum foil can deform well. Sometimes, PET is used instead of nylon for better chemical resistance, though this might reduce the depth of the punch pit.
- The Middle Layer: This layer is primarily aluminum foil and provides specific thickness and strength to prevent water vapor penetration and external damage to the core.
- The Inner Layer: Typically made of PP (polypropylene) material, this layer is crucial for encapsulation, insulation, and preventing the aluminum layer from contacting the electrolyte.
Sometimes, a decorative or special protective layer might be added outside the PET/nylon to improve the battery’s luster, though this increases the cost.
How are these layers brought together into a sealed pouch? Essentially, mechanical high temperatures – usually about 230degC (446degF) – play an essential part. Heat is transferred carefully through outer layers into each polypropylene (PP) layer before finally coming together to fuse together in perfect conditions of temperature, pressure, and time for an air-tight seal that ensures tight security of each pouch.
The encapsulation process itself involves several precise steps:
- PP Top-Sealing: This is often the trickiest part! It involves folding and aligning the packaging foil, fine-tuning tab positions, loading and aligning the battery core, and then performing heat sealing.
- Side Seal: Encapsulating the core after the top seal is complete.
- Corner Sealing: This prevents the seal from breaking at the corners of the folded foil.
- Vacuum Encapsulation: After the electrolyte is injected, the airbag is sealed under vacuum to prevent leakage and water vapor entry.
- Secondary Encapsulation (Degassing): This is the process of venting and sealing the battery cores after chemical formation, also performed under vacuum conditions.
At each step in this process, every detail matters: temperature, time, pressure and vacuum degree are carefully considered in order to create an airtight seal and ensure optimal battery performance and safety. Achieve this delicate balancing act successfully is key for its overall success and safety.
Finding Your Perfect Packaging Partner
As a leading one-stop battery manufacturing service provider, XIAOWEI provides a complete set of solutions for both manufacturing and transportation. With rich experience in lithium battery manufacturing, we are able to design packaging that not only meets strict government transportation regulations, but also meets the unique needs of customers, ensuring that your lithium-ion batteries are transported safely and in compliance with regulations, and often provide UN-certified packaging solutions.
We hope that this in-depth discussion will give you a clearer understanding of how much thinking and technology is behind each lithium-ion battery packaging!
