14.08.2021

Inside Electric: Batteries

The UR-1 race aircraft is fully electric and the energy is, naturally speaking, stored in the batteries.

Batteries are widely used and a variety have become available on the market. Talking about EVs (electric vehicles) has also become a regular topic of conversation for many.

This energy-storage system is hardly new and has a long, truly fascinating history. Previously, powering an EV with a battery was not a prerogative for even the most visionary science-fiction writers.

Below, we outline the history of the battery and how it has made its way into the first Swiss all-electric race plane. We answer: when have batteries being invented? How much have they improved since then? What type of battery are we using for the UR-1 airplane, our Swiss electric aircraft?

History

The first battery was invented in 1799 by the famous Italian physicist, Alessandro Volta. His pioneering device, called a voltaic pile, consisted of a stack of copper and zinc plates, separated by brine-soaked paper-disks.

In 1836, the English chemist John Frederic Daniell created a new energy-storage device called the Daniell Cell after analyzing the voltaic pile. While this became the first practical battery, it is some twenty years later that the French physicist, Gaston Planté, put together the Lead-acid battery. Today, this remains the battery system used to power the average car’s electric system.

In the first decade of the 21st Century, existing EVs used Nickel-metal hydride batteries. This technology was quickly substituted for the Lithium-ion polymer one, which can be found in many everyday devices, including PED (portable electric devices), wheelchairs, and cars.

Basic functioning

The basic functioning of every battery remains essentially the same: two electrodes are connected by a circuit and separated by an electrolyte.

Generally, the energy is produced through the chemical reaction between the materials of the electrodes. In simple terms, the anode loses electrons, which flow through the circuit to the cathode. This “movement” provokes a chemical reaction which is the source of the energy is released into the circuit. This energy can then be used to power electric motors, for example.

Explanatory schematic section of the operation of a lithium-ion battery
Credit: University of Pau

Most popular batteries

There are many types of batteries, each having properties more adapted to certain applications. The most common ones include the Lead-acid battery, the Nickel-metal hydride (NiMH), and the Lithium-ion polymer (LiPo).

Lead-acid

Anode Cathode Electrolyte Use Case Specific Energy Density (Wh/kg) Life Cycle (80% discharge) Main Hazard
LeadLead 
dioxide
Sulfuric acid Automotive 30 50 200 300 Acid spillage 

The Lead-acid batteries are mostly used in automotive. These batteries are powerful, cheap, and easily rechargeable. However, they are heavy and don't like to be completely empty over a long period.

Nickel-metal hydride (NiMH)

Anode Cathode Electrolyte Use Case Specific Energy Density (Wh/kg) Life Cycle (80% discharge) Main Hazard
Metal hydrideNickel 
oxyhydroxide
Potassium hydroxideCommon devices60 120 300 500 Low

The Nickel-metal hydride batteries are well known. These small batteries are the ones we insert into home devices such as cameras or TV remote controllers. The difference between these and Alkaline batteries is that the NiMH battery is rechargeable and safer.

Nickel-metal hydride batteries were also used in the automotive sector and many EVs were built with this kind of energy storage device. However, these were soon replaced by the Lithium-ion polymer batteries, which have better energy density per weight and volume.

Lithium-ion polymer (LiPo)

Anode Cathode Electrolyte Use Case Specific Energy Density (Wh/kg) Life Cycle (80% discharge) Main Hazard
GraphiteLithium metal oxidesPolymerelectric motors150 190 1'000-2'000 Fire and explosions

Unlike most batteries on the market, the LiPo battery consists of a solid polymer electrolyte. This kind of electrolyte was investigated for the purpose of preventing the formation of dendrite, a problem which used to appear in lithium-ion batteries.

This structure offers the opportunity to have a long-lasting battery hardwearing, that is light in weight and has a high energy density. Additionally, unlike other battery forms, they do not suffer from any memory effect when charged before being emptied completely.

Our choice

At Pie Aeronefs SA, we chose Lithium-ion polymer batteries for our first Swiss electric race aircraft. This kind of battery offers the best balance between power output and safety, despite the fire risks inherently found in Lithium-ion batteries.

Details

In our UR-1 batteries, the anode consists of graphite material and the cathode of lithium cobalt oxide. The Nominal Voltage of our batteries is 3.7 V, and the Typical Capacity is 5000 mAh.

Placement

Our batteries are arranged in the wing of our UR-1 Swiss electric aircraft. This idea was inspired by the arrangement of fuel in conventional aircraft.

This becomes challenging when it comes to batteries. Indeed, we have to create a sophisticated structure able to support the weight of the battery. This consists of building a wing with appropriate rigidity, as a flexible wing may damage the batteries.

To prevent any risk of fire, we designed an original battery fire protection system in addition to a liquid cooling system. More information on this will be available soon.

Section of the wing of the Swiss electric aircraft UR-1
The six purple packs represent the six batteries in each side of the wing.

Pros and cons of the LiPo Battery

Pros:

  • Twice higher energy density than standard batteries
  • High Power Output
  • No memory effect ;
  • Less upkeep effort required than other batteries
  • Easier to dispose of (no toxic cadmium)

Cons:

  • Fire risks (without appropriate fire prevention system)
  • Low endurance
  • Expensive
  • Fragile

It is important to note that the fire risk and the low endurance of Lithium-ion polymer batteries are inherent problems of this technology and are present in all LiPo cells.

Discover our fire protection system in a next article. Stay tuned.