We are all familiar with lithium-ion batteries (LiBs). They power everything from smart phones, laptops, medical devices, electric vehicles and even grid storage. With major companies like CATL, Northvolt, and Tesla currently scaling up their production of LiBs, it is permissible if you’ve forgotten that LiBs are in fact a relatively mature technology. To recap, a typical lithium-ion battery uses carbon (graphite) as an negative electrode and lithium-metal oxide (e.g., NCA, NCM, LCO) as a positive electrode. Using these materials, a LiB’s energy density tops out around 700 Wh/L. Companies are seeking higher energy for space-limited applications, especially electric vehicles, and thus tinkering with the materials inside traditional LiBs to do so. The question bears asking: What then, exactly, are they doing? What comes after LiBs?

Masterbatch In The Plastic Industry

Plastic is one of those materials that we don’t always realize how much it’s involved in our daily lives. From automotive parts to sporting goods, packaging, electronics, and medical devices, we rely on plastics to deliver reliable and quality consumer products. Accordingly, Grand View Research, Inc projects the Global Plastics Market is to reach 654 billion USD by 2020.

What Is Masterbatch And Why Do We Need It?

Before discussion on what a masterbatch is, it is important to note the difference between a polymer and a plastic. A plastic is comprised of a long chain of polymers, whereas polymers are composed of smaller, uniform molecules. Why is this important? Because while all plastics are considered polymers, not all polymers are considered plastics. This knowledge now sets you apart as one of the know-it-alls, and with a proper understanding of this new terminology, we can dive into what a masterbatch is.

Masterbatch a concentrated mixture or pigments and/or additives encapsulated during a heat process into a carrier resign which is then cooled and cut into a granular or pellet shape. This allows for easy processing, storage, consistency and controllability. It can be made from just a simple polymer such as high density polyethylene (HDPE) or something more advanced such as a carbon-fiber composite. No matter the type of masterbatch, they are all made in a similar fashion as seen in the diagram below.

                                    Premix process for manufacturing masterbatch.

Companies will then take the masterbatch, melt it down, and mold it into the end product such as water bottles or packaging. The alternatives to using masterbatch are compounding the materials on site or buying a fully compounded material however both have their own issues. Compounding on site is prone to issues of uneven dispersions and fully compounded material may be more expensive and have less color variety.

Companies looking for improvements from a base plastic masterbatch for higher performance applications, such as sporting goods or automotive parts, will use an enhanced polymer masterbatch that offer improvements in mechanical strength and thermal conductivity. We will cover more about enhanced polymer masterbatches in a later post.

Overall, masterbatch provides companies a convenient way to manufacture polymer or plastic products without requiring extra processing steps or taking up large amounts of storage.

For information on a graphene-enhanced polymer masterbatch, visit www.theglobalgraphenegroup.com/graphene-intermediates

               Electric Vehicle on Fire

It’s no surprise that electronic devices have taken over our daily routines. Not only do we demand the best performance from our phones or laptops, but we demand it everywhere

we go. From hanging out at the beach to taking a hike in the mountains, we take our phones and watches everywhere and we expect them to work. It’s not just portable electronics that are booming right now; almost every major car maker is either currently developing or will develop electric vehicles in some form whether it’s fully electric or a hybrid electric.

         List of OEMs announcements on electric car ambitions, as of April 2017

To get the maximum range out of these electric vehicles, automotive original equipment manufacturers (OEMs) are packing in as many batteries as they can. As electric vehicle performance expectations rise and their designs transition to hold even more powerful batteries, one aspect has struggled to catch up and that is safety.

Current Status of Battery Safety

In the news, we are all familiar with electric vehicles catching fire after a crash, vape pens exploding in people’s pockets, and even incidents with cell phones overheating and igniting into flames. These explosions are usually the result of an internal short circuit caused by damage to the battery (e.g., electric vehicle crash), or even an external and uncontrolled temperature increase (e.g., cell phone battery reaches a high temperature). Unfortunately these incidents are prone to occur in situations we often don’t even think twice about, like leaving your phone out in the sun too long or fast charging. Similarly, for electric vehicles, the fact of the matter is that car crashes are inevitable, so there is a risk that a crash can damage the batteries and cause a short circuit. So if short circuits can happen from common acts or acts out of our control, can we find a way to stop them from happening in the first place?

Why do Batteries Catch Fire?

Before we answer that, let’s dive deeper into the causes of batteries catching fire. During an internal short circuit of a battery, the positive and negative electrode materials are physically and electronically brought into contact, giving rise to high local current densities. A prolonged internal short circuit results in self discharge in combination with a local temperature increase. The high temperatures that result from this can cause the electrolyte to decompose through exothermic reactions, which means the decomposition process itself releases even more heat. If the temperature reaches a certain threshold, a thermal runaway event begins causing more and more heat and energy generation until the flash point of the electrolyte is reached causing ignition.

    Overview of the overcharge side reactions at each stages for lithium ion batteries                                                                    with NCM & LMO cathode.

Current Options to Solve the Problem

In industry today, there are a few options to reduce the likelihood of lithium-ion cells from igniting, as well as options to suppress the spreading of fire from cell to cell. One such option is a fireproof casing that holds the many cells together. If an internal short circuit happens in a cell, the runaway reaction is contained in the one cell and does not spread to the dozens of other cells nearby that would create a chain reaction. While this does prevent the ability of the fire from reaching other cells, it does not eliminate the possibility of the cells catching fire in the first place. Another option is attacking the cause of the fires at the source: the battery materials themselves.

The electrolyte is generally the first component of the lithium-ion cells to ignite so this is usually the center of focus in fire prevention. One such method to solve this issue involves the development of a solid-state battery. A solid-state battery is a next-generation battery that uses solid electrodes in tandem with a solid-state electrolyte (SSE) (e.g., ceramics or polymers) instead of the liquid electrolyte found in today’s lithium-ion batteries. While the solid-state battery has a high tolerance against increased temperature and abuse, the SSE it uses is typically expensive to manufacture and inherently weak and inflexible.

Another approach to addressing the flammable electrolyte component is to modify the current liquid electrolyte found in most lithium-ion batteries today. This can be done by changing the chemicals in the solution to raise the inherent temperature at which the chemicals ignite, also known as the flash point. By raising the flash point, the electrolyte is less susceptible to elevated temperatures and prevents the risk of a thermal runaway reaction following a short circuit.

The End Game

The ultimate solution is creating a battery with material components that are inherently non-flammable such as the electrolyte and separator, and pairing them with a casing that localizes any fire that may happen. This combination would give drivers of an electric vehicle the peace of mind that their vehicle will not burst into flames if there is ever a crash or battery overheating.

As battery performance increases so too does the amount of energy they stores which increases the potential for a catastrophic failure if a short circuit were to occur. This calls for a technology that eliminates the possibility of a fire from ever occurring while, ideally, not affecting the battery’s performance. For more information on lithium-ion battery safety, please visit www.theglobalgraphenegroup.com/energy-storage.

Today, mobile devices play an integral part in people’s lives. Almost everyone has at least one smartphone, tablet or wearable device, and many have more. As demands for higher processing speeds and multi-functionality arise, these devices are required to perform efficiently at high rates of power consumption. This demand is further complicated as microprocessor speeds increase but device size remains as compact as ever.

Why Does Thermal Management Matter?

Let’s take a phone for example. When heat is not properly dissipated, thermal stresses build up inside which eventually lead to deteriorated performance before the device ultimately fails. The deteriorated performance results from a significant increase in device temperature known as overheating. Signs of overheating are seen by abrupt, unexpected app shutdowns, frozen screens, or a complete device shutdown. The overheating process consumes battery capacity at a significantly higher rate than normal, and results in having to recharge your battery much sooner than anticipated.

Market Opportunities for Thermal Management Components in Smartphones, Yole                                                               Development, November 2017

On top of that, the batteries in most cell phones are lithium-ion batteries and they are extremely sensitive to heat. Exposure to elevated temperatures speeds up their aging process and, in turn, cuts the battery life short.

How Do We Combat Overheating?

With the help of thermal management technology, there are ways to handle this thermal dilemma. Recall that heat transfer may occur from one place to another via conduction, convection, or radiation. Conduction is the transfer of heat energy by direct contact, convection is the movement of heat by actual motion of matter, and radiation is the transfer of energy with the help of electromagnetic waves. Both convection and radiation have been shown to have minimal effect on cooling in mobile devices, [1] therefore conduction is the best solution.

Difference between convection, conduction, radiation

How Can We Conduct Heat Away from the Source Efficiently?

Heat spreaders, by introducing a solid conduction path between the components and the case, effectively minimize the temperature of hot spots and evenly distribute localized heat flux over a large area, which helps dissipate heat more efficiently. Due to their low profile and conformability, heat spreaders can be placed in close proximity to the microprocessor (i.e., heat source) and minimize the thermal resistance effects that would otherwise result from air gaps. While heat pipes and thermal interface materials have also been explored as options for thermal management, heat spreaders have proven to be the ideal choice.

What Is In A Heat Spreader?

Materials that have been used in heat spreaders include metals, composites, and graphite. Metals such as aluminum and copper have stood out as the best options owing to their relatively high thermal conductivity (237 and 401 W/m-K respectively) and relatively low costs. Copper’s more isothermal base has led to its use over aluminum as it reduces spreading resistance [2].

Composites of steel sandwiched with aluminum, copper, or graphite have also been explored to impart bending resistance and thermal conductivity in the device, but still present a weight:volume ratio challenge. The need to balance thermal management performance with overall device weight has resulted in concerns about the use of metals.

Graphite has recently become a more desirable material for thermal management in mobile devices due to its thermal conductivity (500 W/m-k) and low density, which is 4 times less than copper. It is conformable and has the ability to minimize contact resistance; however, the brittle nature of graphite presents limitations to the manufacturing process.

So What Is The Answer?

The next generation of thermal management is expected to fall on the shoulders of graphene. Graphene’s excellent thermal conductivity (up to 5,300 W/m-K) allows it to be leveraged in anything ranging from phones to drones in the form of thermal foils and thermal pastes. Not only does graphene offer exceptional thermal conductivity, but it also acts as an electromagnetic shield (EMI) and is very lightweight so it won’t add significantly to the weight of the device.

Summary:

· As more power is required for devices, more efficient methods of cooling are needed to prevent overheating.

· Overheating due to poor thermal management can cause app failures, frozen screens and even compete device shutdown.

· Thermal management via conduction is the best route to efficiently cool electronic devices.

· Heat spreaders can be made from metals such as aluminum and copper, composites of steel, and graphite, but each pose their own set of challenges.

· Graphene, the next generation of thermal management materials, offers exceptional thermal conductivity while also being lightweight.

Sources:

[1] T. T. Lee, “Thermal management of handheld telecommunication products « electronics cooling magazine –focused on thermal management, TIMs, fans, heat sinks, CFD software, LEDs/lighting,” in Electronics

Cooling, 2016. [Online]. Available: http://www.electronics-cooling.com/1998/05/thermal-management-ofhandheld-telecommunication-products/. Accessed: Jun. 28, 2016.

[2] A. McWilliams, “The market for thermal management technologies – SMC024K,” in BCC Research, 2016. [Online]. Available: http://www.bccresearch.com/market-research/semiconductor-manufacturing/the-marketfor- thermal-management-technologies-report-smc024k.html. Accessed: Jun. 28, 2016.