Skip to main content
High Volumetric Energy Density (VED) is Critical for Microbatteries

Smaller batteries with higher energy density improve wearable capacity, durability, and functionality

One key attribute of a battery is its capacity, i.e., the amount of energy it can store and then deliver to a product before needing a recharge. How long will your wireless earbuds last if you are constantly talking or listening to music? How long will your smartphone last if you are continuously using the map or playing video games? The battery's energy capacity will determine how long you can use any of those devices before the battery needs recharging.

But it's not just a matter of energy. Batteries are also rated according to how much energy they can store per unit volume. When we want to describe that density in very specific terms, or when we want to compare two batteries to see which one stores more energy for its size, we use a measurement called Volumetric Energy Density, or VED. In short, the higher a battery's VED, the more energy it can store for its size. The sidebar at the end provides more technical details.

Now that we understand the idea of VED, why is it so important? To answer that question, imagine a hearing aid. It needs to be as small as possible to stay comfortable for the user and have a certain shape to fit comfortably inside a person's ear canal. Yet it has a lot of technical pieces inside to help the user hear sounds more clearly. It also needs to last as long as possible before a recharge. Other wearables focused on digital health and sports/fitness also require tiny batteries or microbatteries. At the same time, these devices keep shrinking in size, while offering more features and functionalities. Given those competing design features, a wearables manufacturer needs batteries that are small and contain the required energy. That's why VED is so important: the manufacturers need batteries with the highest VED available.

In the last 20 years, Li-ion coin cell microbatteries have been the only option for these devices. However, Li-Ion is falling short of meeting the increasing demand for energy in smaller forms (also known as form factors). This is for several reasons. First, the materials used in most lithium-ion batteries are either bulky, fragile, or both, which reduces the battery's overall VED. Second, ambient air seeping into the battery can cause damage, and internal battery ingredients must be kept separate from each other to avoid burning. So, the battery needs thick walls, or packaging, to protect against these problems. Unfortunately, thicker walls and interior partitions further reduce VED for a conventional Li-ion battery. This is a problem for standard-size batteries but is an even bigger problem for microbatteries, which might lose a large percentage of VED as a result. Third, remember that a whole new generation of wearables products needs even higher VED batteries for new features and/or longer charge times. Conventional Li-ion coin cell microbatteries are just not meeting these product requirements.

The Ensurge Microbattery offers several improvements over conventional Li-ion batteries, which dramatically improves VED. First, Ensurge uses a very thin stainless steel substrate, rather than the thicker materials of other batteries. This strong yet ultra-thin layer provides much better protection and maintains or even boosts VED. Second, Ensurge uses innovative ultra-compact stacking and packaging of the energy-producing cells within the battery. This further improves VED. Third, the Ensurge microbattery's solid-state electrolyte is inherently safer than a conventional Li-ion battery's liquid electrolyte. Fourth, Ensurge can customize each microbattery's size, so that manufacturers have greater design flexibility.

As a result of all these improvements, the Ensurge Microbattery is the single best microbattery option for wearables and hearables focused on digital health and sports/fitness. Manufacturers can enjoy the full benefits of the highest available VED along with extremely adaptable shapes. This gives manufacturers the freedom to design the next generation of their wearables, their IoT sensors, and their medical devices, according to their consumers' needs, secure in the knowledge that they have access to a microbattery that will fulfill all their requirements.

How is Volumetric Energy Density Calculated? Volumetric Energy Density is the energy or capacity of a battery per unit volume. It is calculated by dividing energy by volume. If two batteries have the same capacity and one is twice as large, then the smaller one has twice the Volumetric Energy Density or VED.

The energy supplied by a battery is measured in Watt-Hours (Wh) or milliWatt-Hours (mWh) for small batteries. A milliWatt is a voltage multiplied by current. Since the voltage of a Lithium battery is nominally 4V, it is common to use Amp-Hours (Ah) or milliAmp-Hour (mAh) as a measure of a battery's capacity. VED then is measured as Watt-Hour/Liter (Wh/L) or milliWatt-Hour/milliLiter (mWh/mL).

NOTE: for this blog, mAh, mWh, and mWh/mL are most relevant as we are focused on microbatteries that supply 1-100 mAh capacity or energy.

About Ensurge Micropower Ensurge is Energizing Innovation™ with the first ultrathin, flexible, reliable, and fundamentally safe solid-state lithium microbattery for the 1-100 milliampere-hour (mAh) class of wearable devices, connected sensors, and beyond. The innovative Ensurge Microbattery enables energy-dense rechargeable products that are ideal for form-factor-constrained applications including hearables (hearing aids and wireless headphones), digital and health wearables, sports and fitness devices, and IoT sensor solutions that use energy harvesting to power everyday things. The company's state-of-the-art manufacturing facility, located in the heart of Silicon Valley, combines patented process technology and materials innovation with the scale of roll-to-roll production methods to bring the advantages of Ensurge technology to established and expanding markets.

High Volumetric Energy Density (VED) is Critical for Microbatteries

10 Jun 2022

Learn how Ensurge Microbattery can energize innovation in your most challenging designs