Structural batteries are multifunctional materials or

structures A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...

, capable of acting as an

electrochemical energy storage Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in ...

system (i.e.

batteries Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

) while possessing mechanical integrity. They help save weight and are useful in transport applications such as

electric vehicle An electric vehicle (EV) is a vehicle that uses one or more electric motors for propulsion. It can be powered by a collector system, with electricity from extravehicular sources, or it can be powered autonomously by a battery (sometimes c ...

s and

drones Drone most commonly refers to: * Drone (bee), a male bee, from an unfertilized egg * Unmanned aerial vehicle * Unmanned surface vehicle, watercraft * Unmanned underwater vehicle or underwater drone Drone, drones or The Drones may also refer to: ...

, because of their potential to improve system efficiencies. Two main types of structural batteries can be distinguished: embedded batteries and laminated structural electrodes.

Embedded batteries

Embedded batteries represent

multifunctional An MFP (multi-function product/printer/peripheral), multi-functional, all-in-one (AIO), or multi-function device (MFD), is an office machine which incorporates the functionality of multiple devices in one, so as to have a smaller footprint in a ...

structures where

lithium-ion battery A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also s ...

cells are efficiently embedded into a

composite structure Composite or compositing may refer to: Materials * Composite material, a material that is made from several different substances ** Metal matrix composite, composed of metal and other parts ** Cermet, a composite of ceramic and metallic materia ...

, and more often sandwich structures. In a sandwich design, state-of-the-art

lithium-ion batteries A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also see ...

are embedded forming a core material and bonded in between two thin and strong face sheets (e.g. aluminium). In-plane and bending loads are carried by face sheets while the battery core takes up transverse shear and compression loads as well as storing the

electrical energy Electrical energy is energy related to forces on electrically charged particles and the movement of electrically charged particles (often electrons in wires, but not always). This energy is supplied by the combination of electric current and electr ...

. The

structure can then be used as a load-bearing as well as an energy storage material.

Laminated structural electrodes

In laminated structural electrodes the

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...

material possesses an intrinsic

load-bearing A load-bearing wall or bearing wall is a wall that is an active structural element of a building, which holds the weight of the elements above it, by conducting its weight to a foundation structure below it. Load-bearing walls are one of the ear ...

and energy storage function. Such batteries are also called massless batteries, since in theory vehicle body parts could also store energy thus not adding any additional weight to the vehicle as additional batteries would not be needed. An example for such batteries are those based on a zinc

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemoni ...

, manganeseoxide

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction i ...

and a fiber/ polymer composite electrolyte. The structural electrolyte enables stable charge and discharge performance. This assembly has been demonstrated in an

unmanned aerial vehicle An unmanned aerial vehicle (UAV), commonly known as a drone, is an aircraft without any human pilot, crew, or passengers on board. UAVs are a component of an unmanned aircraft system (UAS), which includes adding a ground-based controlle ...

. A commonly proposed structural battery is based on a

carbon fiber reinforced polymer Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

(CFRP) concept. Here,

carbon fibers Carbon fibers or carbon fibres (alternatively CF, graphite fiber or graphite fibre) are fibers about in diameter and composed mostly of carbon atoms. Carbon fibers have several advantages: high stiffness, high tensile strength, high stren ...

serve simultaneously as

electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials dep ...

and structural reinforcement. The lamina is composed of

that are embedded in a matrix material (e.g. a

polymer A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and ...

). Multiple layers of

are impregnated with a matrix that enables load transfer between the fibers but also

lithium-ion A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also see ...

transport, unlike commonly used

vinylester Vinyl ester resin, or often just vinyl ester, is a resin produced by the esterification of an epoxy resin with acrylic or methacrylic acids. The "vinyl" groups refer to these ester substituents, which are prone to polymerize and thus an inhibitor i ...

epoxy Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional ...

matrices. This type of energy storage system can be based on a nickel or on

chemistry. The laminate is made of the combination of a negative

, a separator and a positive

, embedded in an ionically conductive and structural electrolyte. In the laminated structural

concept,

can be used to

intercalate Intercalation may refer to: *Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite *Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar follo ...

e.g. lithium-ions (structural

); similarly, to commercially available

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

anodes. The structural cathode consists of

coated with electrochemically active species, e.g. lithium oxide particles. An example of a structural battery exploiting a

carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

negative electrode and

lithium iron phosphate Lithium iron phosphate or lithium ferro-phosphate (LFP) is an inorganic compound with the formula . It is a gray, red-grey, brown or black solid that is insoluble in water. The material has attracted attention as a component of lithium iron phosph ...

positive electrode was demonstrated to be capable of lighting an

LED A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (cor ...

. Some separator material is used in between the two structural

to prevent short-circuits. However, the CFRC concept described above is still being researched.

References

{{Reflist Electric power systems components Energy storage Battery (electricity)