Invented by LEE; Jung Seong, KIM; Yang Seob, CHOI; Hyeon Seon, LEE; Yeon Ho, HAN; Byong Joon, KIM; Hye Mi, KIM; Nam Ju, LEE; Jae Yeon, LEE; Woo Sung, PARK; Sang Hyun, LEE; Chan Kyu, JO; Jung Mo, SAMSUNG SDI CO., LTD.

Let’s dive straight into a fascinating invention that could change the way rechargeable lithium batteries perform and last. This blog will help you understand this new separator technology, why it matters, how it stands out from what came before, and what makes it special. If you use electronics, work in battery research, or are curious about new energy tech, keep reading—this could be the breakthrough you’ve been waiting for.

Background and Market Context

Rechargeable lithium batteries power many things in our lives. From phones and laptops to electric cars and even power tools, they keep our world running. As we use these devices more, the need for batteries that last longer, store more energy, and stay safe becomes even more important.

In the past, battery fires and swelling have made headlines. Sometimes, batteries get too hot and become dangerous. This usually happens because of something inside the battery called a separator. The separator is a thin layer that keeps the battery’s positive and negative sides from touching each other. If it fails, the battery can short circuit and overheat.

Most separators today are made from thin plastic films, like polyethylene or polypropylene. They have tiny holes that let lithium ions move between the battery’s two sides. But these films can shrink or melt when they get too hot, especially if the battery is overcharged or damaged. That shrinkage can cause big safety problems. So, companies and scientists are always searching for new ways to make separators that are stronger, safer, and more reliable.

With electric cars becoming more popular and with more devices demanding higher battery capacity, the pressure is on. Battery makers want separators that not only stop short circuits but also help batteries carry more energy, charge faster, and last longer. A separator that does all this, while being cost-effective, is like finding the Holy Grail of battery tech.

This is where the new invention comes in. The patent application we’re discussing presents a separator with a unique coating design. The aim is to solve safety, stability, and performance issues in a way that works for today’s (and tomorrow’s) batteries. Let’s explore why this is needed, and what makes it different from other solutions.

Scientific Rationale and Prior Art

To understand what’s new, it helps to look at what’s already out there. Traditional separators are made using materials like polyethylene because it’s cheap and easy to process. However, these separators can’t handle high temperatures well; they shrink or melt if things get too hot inside the battery. If the separator fails, the positive and negative parts of the battery can touch, causing a short circuit, which can lead to overheating or fire.

Some battery makers have tried adding ceramic particles (like alumina, boehmite, or silica) to the separator surface. These ceramic coatings improve heat resistance and help the separator keep its shape at high temperatures. But, simply mixing ceramic powder into a coating and putting it on the plastic film isn’t enough. If the coating isn’t uniform, or if the binder holding the particles together isn’t strong or well-chosen, the separator may still shrink—or the ceramic coating may crack and fall off. This causes safety and reliability problems.

Another challenge is that adding ceramic materials and binders can increase the separator’s resistance. High resistance slows down the movement of lithium ions between the battery’s positive and negative sides, which reduces battery performance. So, the trick is to make a separator that is both strong (to prevent shrinkage and fires) and allows ions to move easily (to keep the battery powerful and long-lasting).

Some earlier inventions tried to solve these problems by using different kinds of polymers as binders, or mixing in different kinds of particles. Others used adhesives to make the separator stick better to the battery electrodes (the positive and negative sides). But each of these had trade-offs: improved safety but worse performance, or better performance but less safety.

For example, one popular prior art method was to use polyvinylidene fluoride (PVDF) as a binder for the ceramic particles. PVDF is good because it helps the coating stick and is pretty stable, but it doesn’t help much with ion movement, and can make the separator more resistant. Other patents used acrylic binders, which have some advantages for ion mobility, but may not be as heat-resistant, or may not hold the ceramic particles as tightly.

There are even more complex solutions, like making separators with multiple layers—each with its own coating and composition. But these can be expensive to manufacture, or may not work as well in real batteries. And as batteries get thinner and more powerful, the requirements for a good separator become even more strict. A good separator has to be thin (to maximize battery energy), strong (to prevent failures), and allow ions to move quickly (to keep performance high).

The patent we’re looking at builds on all these earlier ideas, but with a new twist. It combines a smart choice of binder materials, a carefully chosen particle size and shape for the ceramic filler, and a special adhesive layer—all designed to work together for better safety, strength, and battery performance. It addresses the trade-offs seen in prior art by carefully balancing the components and how they’re put together. Let’s see how.

Invention Description and Key Innovations

The heart of this invention is a separator with a multi-layer coating. It’s built on a thin, porous plastic film, which is the base. On top of this film, the inventors add two special layers—a heat-resistant layer and an adhesive layer. These layers are chosen and designed to work together, giving the separator new properties that make it safer and better performing in rechargeable lithium batteries.

Let’s break down each part in simple terms:

1. The Heat-Resistant Layer

This layer is made from a blend of two parts: a binder and a filler. The binder is a “(meth)acryl-based” polymer, which means it is made from building blocks derived from acrylic acid, hydroxyalkyl (meth)acrylate, and (meth)acrylamido sulfonic acid. This special mix of building blocks gives the binder the following advantages:

• Good adhesion: It helps the ceramic filler stick tightly to the base film, so the coating stays intact even when the separator is bent or flexed.
• High heat resistance: The polymer structure helps the separator keep its shape at high temperatures (up to 150°C or more), reducing shrinkage and the risk of short circuits.
• Low resistance: The design of the polymer allows lithium ions to move more easily through the separator, so the battery can still deliver a lot of power.
• Improved dispersibility: The binder helps the ceramic particles spread out evenly in the coating, making the layer uniform and stable.

The filler in this layer is a ceramic powder, such as boehmite, with a particle size carefully controlled between about 250 and 350 nanometers. This is important—if the particles are too small, they may clump up or make the coating too dense, increasing resistance. If they’re too big, the coating may become rough or weak. By picking just the right size and shape (like plate-shaped or cubic), the inventors get a strong, thin, and even coating that helps prevent heat shrinkage and keeps the separator robust.

By using a high ratio of filler to binder (as much as 10 to 50 times more filler than binder by mass), the layer can be made very thin and still provide strong protection against heat. This means the separator stays lightweight and doesn’t take up too much room inside the battery.

2. The Adhesive Layer

On top of the heat-resistant layer, the inventors add an adhesive layer. This layer helps the separator stick firmly to the battery’s positive and negative electrodes. Why is this important? Good adhesion means the separator won’t slip or move during battery assembly or use, which keeps the battery stable and safe.

The adhesive binder is a clever mix of two kinds of fluorine-based polymers. One type has a hydroxyl or carboxylic acid group (which helps it bond well when wet), and the other type does not have these groups (which helps it bond well when dry). By mixing them in just the right ratio, the separator gets both “wet” and “dry” bonding strength. That means it stays stuck to the electrodes whether the battery is dry or soaked with electrolyte.

This adhesive layer is also thin but tough, and it’s made using special PVDF (polyvinylidene fluoride) copolymers, often with hexafluoropropylene. This choice means the separator can be processed with low-boiling-point solvents, which is safer and less costly in manufacturing. It also means the separator’s air permeability stays high—important for letting lithium ions move freely.

3. The Porous Substrate

The base film is a porous plastic, usually polyethylene or polypropylene, which is already widely used in batteries. What’s important here is that the coating layers are thin compared to the base film—often only about 10% to 50% as thick. That keeps the separator thin, light, and efficient, while still adding the new properties from the special coatings.

What Does This Mean for Batteries?

The result is a separator that checks all the boxes:

• Low heat shrinkage: Even after spending an hour at 150°C, the separator shrinks less than 6.5%, and often much less (as low as 1% in some tests). This means the separator keeps working even in tough conditions, making battery fires or failures much less likely.
• Low resistance: The membrane resistance is less than 1 ohm, which is very good for a coated separator. This lets batteries charge and discharge quickly, keeping performance high.
• Strong bonding: The separator sticks tightly to the battery electrodes, both wet and dry, which improves battery assembly and helps the device last longer.
• High air permeability: The separator lets lithium ions move easily, so the battery doesn’t lose capacity or power.
• Good processability: The coating layers can be made thin and uniform, and can be processed with safer, low-boiling-point solvents, helping manufacturing be safer and less expensive.

Practical Example:

In real-world tests, batteries made with this separator showed high capacity, stable cycling, and improved safety over those made with older separators. For example, tests showed the separator’s heat shrinkage was often below 2%, and its membrane resistance was around 0.85 ohms or less. Even after being stressed, the separator kept its shape and stayed stuck to the electrodes. This means that batteries using this separator should be safer, longer-lasting, and more powerful—just what the market wants.

Why This Matters

This invention is important because it solves a long-standing problem for battery makers: how to make a separator that is both safe and high performing, without making batteries thicker, heavier, or more expensive. By carefully choosing the binder chemistry, the filler size and shape, and the adhesive layer design, the inventors have created a separator that works better than what’s come before.

As a bonus, the technology is flexible. The coating composition can be adjusted for different battery types or performance needs. For example, the ratio of binder to filler, or the types of fluorine-based polymers in the adhesive layer, can be tweaked to balance bonding strength, resistance, and other properties.

For battery manufacturers, this means a smoother path to safer, more reliable, and higher-performing batteries—whether for electric cars, mobile devices, or energy storage.

Conclusion

We’re living in a time when better batteries can change everything—from smartphones that last longer to electric cars that drive farther and charge faster. But as batteries get more powerful, the need for safe, reliable separators grows even stronger. This new separator invention, with its smart combination of heat-resistant coatings, strong yet thin adhesive layers, and carefully chosen materials, could set a new standard for safety and performance.

By addressing the weaknesses of earlier designs and providing real, measurable improvements, this separator could help usher in a new era for rechargeable lithium batteries. If you care about battery safety, performance, or just want the next generation of devices to be even better, keep an eye on this technology. Its thoughtful design and proven results make it a potential game-changer in the world of energy storage.

Want to learn more or see how this technology could fit into your products? Reach out to battery experts or patent professionals for advice—this is one innovation you don’t want to miss.

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