Multifunctional Batteries Inspired by Mammal Fat

Innovation: Academia

University of Michigan

2020

Image: Hans-Jurgen Mager / Unsplash / CC BY SA - Creative Commons Attribution + ShareAlike

Modify Material Characteristics

The materials found in living systems are variable, yet often made from the same basic building blocks. For example, all insect exoskeletons consist of a material called chitin. Because material resources are limited, each material within or used by a given living system must frequently serve multiple purposes. Therefore, living systems have strategies to modify materials’ softness, flexibility, and other characteristics. To ensure survival, the benefits of these modifications must outweigh the living system’s energy and material expenditure to generate them. For example, spiders store the liquid components of spider silk in a gland, converting them into silk thread when needed. Some threads have different characteristics, such as elasticity and UV reflectance, than others.

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Modify Size/Shape/Mass/Volume

Many living systems alter their physical properties, such as size, shape, mass, or volume. These modifications occur in response to the living system’s needs and/or changing environmental conditions. For example, they may do this to move more efficiently, escape predators, recover from damage, or for many other reasons. These modifications require appropriate response rates and levels. Modifying any of these properties requires materials to enable such changes, cues to make the changes, and mechanisms to control them. An example is the porcupine fish, which protects itself from predators by taking sips of water or air to inflate its body and to erect spines embedded in its skin.

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Manage Mechanical Wear

A living system is subject to mechanical wear when two parts rub against each other or when the living system comes in contact with abrasive components in its environment, such as sand or coral. Some abrasive components are a constant force, such as finger joints moving, while others occur infrequently, such as a sand storm moving across a desert. Living systems protect from mechanical wear using strategies appropriate to the level and frequency of the source, such as having abrasion-resistant surfaces, replaceable parts, or lubricants. For example, human joints like shoulders and knees move against each other all day, every day. To protect from mechanical wear, a lubricant reduces friction between the cartilage and the joint.

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Manage Impact

An impact is a high force or mechanical shock that happens over a short period of time, such as a hammer hitting a nail rather than a hand pushing slowly against a wall. Because of their speed and force, impacts don’t allow materials to slowly adjust to the force, which can lead to cracks, ruptures, and complete breakage. Therefore, living systems have strategies that can absorb, dissipate, or otherwise survive that force without the need to add large amounts of material. For example, the Toco toucan’s large beak is very lightweight, yet can withstand impacts because it’s made of a composite material with rigid foam inside and layers of a hard, fibrous material outside.

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Store Energy

Once a living system captures energy or transforms one energy form into another, it must frequently save that energy for future use. But energy is difficult to store in some forms. So living systems need strategies to either use energy quickly, or to convert it from forms that are difficult to store (such as electrical or kinetic) to more storable forms. For example, grasshoppers store energy as potential energy in an elastic material in their tendons. When they need to jump, that energy converts into kinetic energy, providing the force needed to escape predators.

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Structural batteries from University of Michigan are made of zinc to increase the energy density of the battery and optimize material usage.

Benefits

Increased efficiency
Non-toxic
Multifunctional

Applications

Manufacturing
Transportation
Small robotics

UN Sustainable Development Goals Addressed

Goal 11: Sustainable Cities & Communities

The Challenge

Robots are currently designed to carry single lithium ion batteries that can take up about 20% of the carrying capacity and overall weight. This limits the amount of work a robot can perform, reducing its productivity.

Innovation Details

The batteries function as both an energy source and a structural material that protects the robots. This mimics the multifunctionality of mammalian fat tissues to store energy and protect the internal organs. The battery is non-toxic, zinc-based, and can be conformed to a variety of shapes to protect other parts of the robot. These body-integrated batteries could achieve 72 times as much capacity than the typical single lithium-ion battery. The battery works by passing hydroxide ions between a zinc electrode and the air side through an electrolyte membrane. That membrane is partly a network of aramid nanofibers — the carbon-based fibers found in Kevlar vests — and a new water-based gel. The gel helps shuttle the hydroxide ions between the electrodes. The battery is made from cheap, abundant and largely nontoxic materials, making it more environmentally friendly than traditional batteries. The gel and aramid nanofibers will not catch fire if the battery is damaged, unlike the flammable electrolyte in lithium ion batteries.

Biological Model

Mammals utilize a layer of fat to both provide insulation for internal organs and store energy for later use.

References

Journal article

Biomorphic structural batteries for robotics

Science Robotics

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