In 2019, the Nobel Prize in Chemistry was awarded to John Bannister Goodenough, Michael Stanley Whittingham, and Akira Yoshino for their pioneering work on lithium batteries. 

Lithium was once a metal with very limited use in electronics.  But by the late-20^th century, this lightweight metal became a powerful tool for solving the energy needs of devices large and small.

To help commemorate the ongoing work being done in this field, this article will explore the history of lithium in electronics; as well as its future implications.

Introduction

Lithium’s name comes from the Greek “lithos,” meaning: stone.  Despite being very near the start of the periodic table, it was discovered relatively recently: in 1817 by Swedish chemist: Johan August Arfvedson.  As the very lightest of all metals, lithium will float on water; but will also ignite in its famously violent reactions.  Lithium has the highest specific heat of any solid element, making it unparalleled as a heat-exchanger. 

In its early years, chemists applied lithium fluoride to patented processes for reducing alumina into metallic aluminum using electric currents.  But it wasn’t until after the Second World War that lithium production erupted.

In the years to come, lithium would begin to see use in batteries, thanks to the innovative research of solid-state physicists.  Initial uses of lithium batteries were limited.  But as the new battery chemistry began to see commercial applications, lithium-based energy storage grew into a billion-dollar industry.

Lithium In Batteries

To be clear, lithium can be present in cells and batteries.  A cell is a single energy source, and it isn’t until two or more cells are stacked together that the system can appropriately be called a battery.

When a smartphone or other device uses a lithium battery, the battery terminals provide connections to two different conductive (often metallic) materials inside each cell.  Those materials are barricaded from each other by a separator material.  The conductors are immersed in an electrolyte.  The combination of the different conductive surfaces and the electrolyte make up the battery’s two electrodes.  Normally the electrolyte is a liquid or gel, but there are solid electrolytes being developed in 2019 that are made of polymers or ceramic materials.

Inside the battery, any buildup of positive or negative electric charge on the conducting electrodes will attract chemicals that have the opposite charge.  These charged chemicals are called ions.  Being very small, the ions—and the charge they carry—can migrate through the electrolyte to meet the opposing conductor.  When the ions reach an electrode, one of two electrochemical reactions will take place depending on the charge of the ion.

• At the battery anode: an oxidation reaction will take place.  Oxidation means a material has increased its electrical charge. 
• At the battery cathode, a reduction reaction will take place.  Reduction is the opposite of oxidation, and is the process of gaining an electron (i.e.: adding -1 to the charge already on the material).
• A mnemonic for remembering this is “RED CAT.”  That is, “reduction happens at the cathode.”

When the battery anode and cathode are connected to an electrical circuit, electrons will flow from the anode, through the circuit, and to the cathode.  Note: this direction runs counter to the conventional model of charge flow, which depicts electricity as traveling from a positive voltage to a negative voltage.

Throughout the 20^th century, battery engineers have used many electrode materials.  But it’s specifically the primary (non-rechargeable) lithium battery that provides a distinctly large amount of energy for its small size and weight.  “Primary” means they are effectively one-time-use devices.  They do however outperform rechargeable lithium batteries in the amount of energy they can store for their size and weight.

As of 2019, the storable energy a lithium cell can hold is about 2 to 5 times greater than zinc anode batteries.  These lithium cells also have a higher electrochemical potential than comparable battery chemistries.  Typically this potential is between 3.0 and 4.0 V per cell.  The primary lithium cell is often used in watches and fitness trackers thanks to its small size. 

Beyond the primary lithium battery, there are many sub-types of lithium batteries: way too many to cover here in any detail.  But just to name a few:

Lithium-ion batteries are rechargeable.  Their chemistry varies vastly from the primary lithium type, and they contain very little metallic lithium.  Unlike more conventional batteries: lithium-ion batteries are a large family of battery chemistries that all operate based on using charged lithium ions as the battery’s charge carrier.  Others tend to use hydrogen or hydroxide ions.  The positive electrode is typically a lithium metal oxide such as Lithium Cobalt Oxide (LCO) or Lithium Manganese Oxide (spinel).  But there are still many variations within the lithium-ion battery family: each having its own unique advantages and disadvantages.

Lithium-polymer (or Lipo) batteries use a polymeric electrolyte. 

Lithium-air batteries (also called lithium-oxygen batteries): use a special device called an air cathode that draws in oxygen from the surroundings as a supply of ions.

Lithium-sulfur batteries are an emerging technology with very high theoretical energy density.

So why do some Lithium batteries catch fire?  To reiterate, Lithium is a dangerously-reactive metal.  But in accidents that make headlines, it’s actually the flammable organic electrolyte, solvents, and oxides that fuel fires.  Lithium-ion batteries hold more energy than other batteries of the same mass, so they naturally release more energy during incidents. 

These incidents (i.e.: failure modes) can be generalized as the following sequence of events.  First, the battery sustains internal damage due to misuse, mishandling, defect, etc.  Then the damage results in a short circuit between the anode and cathode.  From there, the following events take place:

1. The short circuit will drive a high internal electric current through the battery.
2. The electric current generates heat within the battery (per Joule’s Law of Heating). 
3. The heat increases the battery rate of reaction (per the Arrhenius equation).
4. The accelerated rate of reaction increases the electric current further.

Each event above triggers the next in a loop called thermal runaway until the battery reaches extreme temperatures.  Lithium battery fires can reach temperatures near 900 °C.

Because the danger is readily acknowledged by the scientific community, system designers may design safety features into the battery itself.  These safety measures may include:

• Fuses to interrupt short circuit conditions, and reduce heating by cutting off charge flow;
• Blocking diodes to avoid reverse voltages and imbalanced charging between neighboring cells;
• Thermal cutoffs to shut off the entire battery if temperatures are elevated above a threshold;
• Thermal fuses to render the battery temporarily unusable if temperatures are elevated;
• Thermistors to report the temperature to an outside circuit, such as a microprocessor.

Even the very shape of coin and pin-style batteries are designed to prevent accidental reversal of the battery—basically mistake-proofing the installation process.

These (and other) safety measures come as a cost of using the best battery elements in electronics. 

Lithium In Motion Detectors

In alarm security applications, the heat-sensing crystal: Lithium Tantalate (LiTaO3) can track an intruder’s body heat to reveal them.  This works because the Lithium Tantalate has a useful property called pyroelectricity (“pyro” being Greek for “fire”).  A pyroelectric material will generate a temporary voltage in response to a change in its temperature.  If the temperature goes steady, the voltage fades.  Such capability is useful in detecting the motion of heated objects such as humans and intruders

Pyroelectric sensors belong to a group of devices called thermal infrared detectors.  Security alarm devices using this technique are called “PIR” sensors: which stands for “pyroelectric infrared,” or sometimes simply “passive infrared.”  As the target traverses the sensor’s field of view, the pyroelectric effect increases.  What makes this approach unique is how the detector rejects visible light, and how it can’t be fooled by camouflage.  It emits no laser, no microwaves, or anything else that would give away its position.  Therefore, this use case is called “passive” infrared.  It’s important to note that pyroelectricity isn’t thermoelectricity.  The two effects are similar.

Electronic circuits and processors that receive electrical signals from the material are executing a form of measurement called pyrometry.  A typical sensor layer is the so-called “dual element detector,” which is amplified by a junction field-effect transistor (JFET).  This setup is paired with a specialized lens called a multi-fresnel lens and an evaluation circuit.  The aim of the most advanced systems is to develop detectors with the highest possible signal-to-noise ratio the technology can offer.

One of the biggest drawbacks in pyroelectric detectors is they are sensitive to acceleration and are slightly microphonic.  If a pyroelectric detector is mechanically excited by movement, the material will generate an electrical signal independently of any objects in view.

Additionally, many of these systems are only able to detect the presence of a moving object in their surveillance area, but not the direction of motion.  To ascertain the direction of motion, alternative detectors use asymmetrically-shaped sensors combined with signal shape analysis that can estimate the target’s direction of travel.

Lithium In Communications

Lithium Tantalate can also convert electricity to mechanical energy and back again.  The property of generating electricity from mechanical pressure is called piezoelectricity (“piezo” being Greek for “pressure”).  By sending an electric signal into the material, a tiny wave of pressure will propagate across the crystalline lithium tantalate and then create a voltage at the other end.  This effect is responsible for the acceleration sensitivity and resulting noise in the lithium tantalite-based motion detector.

But there is an upside to the piezoelectric effect of the material.  If the material has a transmitted electrode at one end, and a receiving electrode installed at the far end, the receiving electrodes will recover some transmitted signals better than others.  This makes lithium tantalate (and the similar lithium niobate) useful as an electronic filter.  These filters are called Surface Acoustic Wave, or “SAW” filters.  SAW filters are versatile components for smartphones and other wireless devices.

Likewise, the effect has been used in a niche device called the piezoelectric transformer.  Like the SAW filter, the piezoelectric transformer has a set of input and output electrodes.  But the intended use is voltage conversion.  Voltages going into the input terminals can be stepped up to higher voltages, much like a magnetic transformer, but without the large size and weight associated with the magnetic counterpart.  Presently, the effect can be accomplished using the ceramic material: PZT (lead zirconate titanate), however, the elimination of lead in consumer goods has made lithium niobite a more attractive alternative.  The piezoelectric transformer is being used in high-voltage applications like compact florescent backlighting for electronic displays.

Lithium In Terahertz Detectors

The capabilities don’t end there.  When applied as a thin-film, lithium tantalate can detect terahertz-range radiation.  The terahertz bands are a large slice of the electromagnetic spectrum that has yet to be widely used outside of research and niche scientific applications.  They cover frequencies between 300 GHz and 10 Terahertz (basically placing them between microwaves and infrared). 

First, thin-film lithium tantalite will absorb terahertz radiation.  This raises its temperature, and—like the motion sensor—a measurable voltage will appear that can be captured and processed.  Researchers have even made it generate its own terahertz signals using laser pulses.  The applications range from medical imaging and diagnostics to airport security and horizon detection for satellites.

Conclusion

With the upcoming conversion from fossil fuels to electric vehicles, the future of lithium…like its demand will be massive.  In 2017, the commodities forecaster Roskill estimated lithium demand to grow throughout 2027 as electric vehicles begin to compete on price with fossil fuels.  In 2018, the U.S. geological survey noted that lithium supply security had become a top priority to the tech sectors of the U.S. and Asia.  This has the potential to draw billions in capital investment toward lithium production and possibly lithium recycling.

Right now, the lithium battery’s biggest competitors are fossil fuels like gasoline and diesel.  These fuels are highly energetic.  Gasoline has a nominal specific energy of over 12,000 Wh/kg, compared to only 200 Wh/kg for lithium polymer batteries.  Of course, the internal combustion engine has its own inefficiencies, so the gap is smaller than these figures alone indicate.  The industry goal is to boost this figure to around 350 Wh/kg usable energy at the lithium cell level.

Where battery safety is a concern, materials scientists are hard at work creating better countermeasures for the future.  For example, in 2017 researchers at Stanford University created a new method for releasing an internal flame retardant.  And scientists are investigating solid electrolytes as a durable and safer alternative to liquid electrolytes.  While lithium-ion chemistries may contain some toxic materials such as cobalt, they are less dangerous than other active materials used in lead-acid or nickel-cadmium batteries.

So, will lithium become the preferred energy source of the future?  Only time will tell how the community will face this most formidable challenge.

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