The search for better ba​tteries.

Batteries are a game changer. They can store clean energy allowing us to power our transport and homes with clean energy. The race is on to produce batteries with the highest and cheapest energy.

It is difficult to say which will be the next improved battery. The rewards are huge and so too is the competition, and the claims? Impossible to tell.  The puzzle is why the power companies who will be deeply affected by batteries, are not investing in battery research. A Kodak moment?

Energy densities of different batteries

Each atom holds electrons with it's own strength. The difference between the electron holding strength of two atoms/ions, is the theoretical voltage.

For example: from the table on the right, a battery made of Zn and Cu would have a voltage of 0.758 -(-0.345) = 1.083V

In an electric car or plane, we are interested in how much energy can be held in each kilogram of battery. There is a theoretical maximum, and an achieved maximum so far. The lithium ion is at present the most popular car battery, but there are others being developed that may far surpass it. The theoretical  maximum energy densities are giving researchers goals to work towards.

Petrol / gasoline has an energy density of 12,000 kWh/Kg, so it looks as if batteries will never catch up. But, the efficiency of the petrol car is only about 15%. while the efficiency of the electric car is about 70%. So the battery only need to hold 15/70 th of the energy = 2,500 Wh/Kg. And it is even better than that because the electric motor weighs much less than the petrol motor, so we could make do with an even lower figure.

Ion batteries

Ion batteries have​ ions moving between the cathode and anode as electrons flow around the circuit.

Lithium​​ ion 

The e​lectrodes are Lithium and graphite. Lithium ions travel from one electrode to the other carrying the charge to balance the electrons traveling around the circuit.

Lithium batteries are the most popular rechargeable battery at present. More....

There are many types of Lithium Ion batteries. Designed for different applications, or to get around patents. For example: 

• Lithium ferrous phosphate (LFP), SimpliPhi claim 98% efficiency, 5,000 + cyles or 10years.
• lithium manganese oxide (LMO) and
• lithium nickel manganese cobalt oxide (NMC)
• lithium nickel cobalt aluminum oxide (NCA)
• lithium titanate (LTO)
• More: Battery University

Lithium P​olymer

Uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows an exchange of ions (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.   More...

Lifetime of a battery

Battery life depends on the total energy throughput that the active chemicals can tolerate. More

SimplyPhi offer LFP batteries guaranteed for 10 years with daily cycles. It is estimated to last for 5,000+ cycles over 15-20 years. It is 98% efficient, and because of this, needs no cooling. The cost over 10 years is US$0.10/kWh.

Silicon-carbon Nanocomposite Anodes for Li-ion

Researchers have developed a new high-performance anode structure for lithium-ion batteries based on silicon-carbon nanocomposite materials. The material contains rigid and robust silicon spheres with irregular channels to promote the access of lithium ions into the particle mass. With graphite anodes, researchers have achieved stable performance and capacity gains of five times that of regular Li-ion. Manufacturing is said to be simple and low-cost, and the battery is safe and broadly applicable. However, the cycle life is limited due to structural problems when inserting and extracting lithium-ion at high volume. Source: Battery university

Next-​gene​ration lithium-ion batteries

The design is based on replacing the currently used graphite anodes with porous silicon nanoparticles. This follows work done by the same researchers last year using silicon nanowires. The nanowire version actually lasts much longer (2000 recharge cycles) than the current nanoparticle version (200 recharge cycles) and conventional graphite-based designs (500 recharge cycles). But the researchers are confident that the lifespan of the nanoparticle design can be greatly improved in the near future. The problem with nanowires is just that they are relatively hard to mass manufacture, while silicon nanoparticles are readily available. Clean Technica

Magnesium-io​n battery

Magnesium has the advantage of having two charges per atom versus one for lithium. It should be able to take a car 3-5 times as far as a lithium ion battery.

Lithium being small with only one charge passes through membranes very quickly. Magnesium however has 2 charges that attract oxygen containing molecules, and these slow it down.

Toyota, LG, Samsung Hitachi and Pellion are separately researching magnesium ion batteries but are releasing very little information. The battery is due in 2020.

MgFeSiO4 is the cathode material.

The battery is very similar to the Li ion battery so it is not difficult to convert from one to the other. The Tesla gigafactory is equipped to change from lithium to magnesium when the technology is ready.

Pellion paper: Moving Beyond Lithium with Low-Cost, HighEnergy, Rechargeable Magnesium Batteries

The combination of ion-exchanged MgFeSiO4 with a magnesium bis(trifluoromethylsulfonyl)imide–triglyme electrolyte system proposed in this work provides a low-cost and practical rechargeable magnesium battery with high energy density, free from corrosion and safety problems.

Nature Published 11 July 2014

Sodium-ion battery

The problem with the sodium ion battery is the cathode material. If it can be solved then we may get a very cheap battery. Various research teams have announced promising progress.

• University of Texas at Austin: Professor John Goodenough who invented the Li-ion battery is using the mineral Eldfellite - NaFe(SO₄)₂, so named because it was found recently on the rim of Eldfell, a volcano in Iceland.
• Kansas State University are trying graphene,
• University of Maryland are working on an “expanded” graphite anode.
• Purdue University, “tailored” carbon and tin.

Na-ion batteries work in the same way as Li-ion batteries. During discharge, Na⁺ ions migrate from the anode to the cathode, while the balancing electrons travel to the cathode via an external circuit, where they can be used to perform electrical work. At the cathode, the arriving electrons are accommodated by utilising a redox couple while the sodium ions intercalate into the cathode structure – this process is reversible on charging.

Ref: Chemistry World

Alumin​ium-io​n batteries

After 30 years of research scientists at  Stanford University have managed to produce an aluminium ion cell. It has  one quarter the energy per KG of a lithium ion, but can charge and discharge more than 10 times faster. It does not degrade after more than 7,500 cycles, whereas a Li ion battery degrades after 1-3,000 cycles.

The electrodes are Al foil and pyrolytic or foamed graphite. 

The liquid electrolyte of 1-ethyl-3-methylimidazolium chloride and anhydrous aluminum chloride. This electrolyte contains mobile AlCl4- ions, which are exchanged between the anode and cathode as it charges and discharges.

Ref: Nature April 2015

Al cell performance over 7,500 cycles of charge and discharge.

Graphite foam

Fluorid​e ion 

Research is being done on using fluoride or chloride ions to carry the charge. The theoretical energy density is higher than lithium ion batteries.

Ionic electrolyte

Boulder Ionics claim their electrolyte will increase the performance of lithium batteries.

Sulfur batteries

Metal sulfur batteries promise high power densities at very low cost.

Sodium-su​lfur

Sodium sulfur batteries are being used in some power stations and for leveling the output from wind farms. The advantage is that it is a liquid metal battery and crystals do not grow and short circuit the battery or push the plates out of shape.

The Na and S are kept molten by normal heat released by charging and discharging.

Lithi​u​m-sulfur

By virtue of the low atomic weight of lithium and the moderate weight of sulfur, lithium-sulfur batteries offer a very high specific energy of 550Wh/kg, about three times that of Li-ion, and a specific power potential of 2,500W/kg. During discharge, lithium dissolves from the anode surface, and reverses itself when charging by plating itself back onto the anode. Li-S has a cell voltage of 2.10V, has good cold temperature discharge characteristics, can be recharged at –60C (–76F) and is environmentally friendly. Sulfur as main ingredient is abundantly available.

A typical Li-ion has a graphite anode that hosts lithium ions much like a hotel books guests and then it releases the ions to the cathode on discharge. In Li-S, graphite is replaced by lithium metal, a catalyst that provides double duty as electrode and supplier of lithium ions. The Li-S battery gets rid of “dead weight” by replacing the metal oxide cathode of a Li-ion with cheaper and lighter sulfur. Sulfur has the added advantage of being able to double-book lithium atoms, something Li-ion cannot do.

Challenges with lithium-sulfur are limited cycle life of only 40 to 50 charges/discharges and poor stability at higher temperature. Sulfur is lost during cycling by shuttling away from the cathode and reacting with the lithium anode. Other problems are poor conductivity and a degradation of the sulfur cathode. Since 2007, Stanford engineers have experimented with nanowire. Trials with graphene also show good results.

Source: Battery university

Researchers have been trying to make Li S batteries working for 20 years.

Oxis Energy in Abingdon, UK. It says it has run large cells for an impressive 900 cycles, at energy densities that match current Li-ion cells. 

Oxis is aiming at 4-500 Wh/kg and US$ 125/kWh with 1-2,000 cycles.

Oxis is working with Lotus Engineering, headquartered in Ann Arbor, Michigan. Source: Nature

Magn​esium-Sulfur

This has a high the​oretical energy of  4,000 Wh/Kg so there is research into this combination.   Patent

Metal-air batteries

Metal air batteries have been primary cells meaning they are not rechargeable. They have very high energy densities, much higher than Li ion batteries at 150 Wh/Kg.

Research effort has been on making these rechargeable.

Lithium-air (​Li-air)

Lithium-air batteries are an exciting research frontier because they could store far more energy than current lithium ion batteries. They borrow the idea from zinc-air and the fuel cell in that they breathe air. The battery uses a catalytic air cathode that supplies oxygen, an electrolyte and a lithium anode. Scientists anticipate an energy storage potential that is 5–10 times larger than that of Li-ion but they speculate that it will take one to two decades before the technology can be commercialized. Depending on materials used, Li-ion-air will produce voltages in between 1.7 and 3.2V/cell. IBM, the University of California and others are developing the technology. The theoretical specific energy of lithium-air is 13kWh/kg; aluminum-air has similar qualities, with an 8kWh/kg theoretical specific energy.

Li-air experiences the sudden death syndrome. The battery requires lithium and oxygen to operate but these components form lithium peroxide films that produce a barrier and prevent electron movement. This results in a sudden reduction in the battery's storage capacity. Scientists are experimenting with additives to prevent the film formation. Air purity is also said to be challenge as the air we breathe in our cities is not clean enough for lithium-air.    Source: Battery university

Lith​ium air

Lithium-air battery can theoretically deliver an astonishing 10 times more energy density than even today’s best lithium ion technology. That is about the energy density of petrol / gasoline.  

The problem is water in the air will react with lithium so it needs a membrane to allow only oxygen through.

POLYPLUS has made a major breakthrough in the development of protected lithium metal electrodes that enable the development of batteries with unprecedented energy density. The protected lithium electrode (PLE) developed at POLYPLUS is remarkably stable in aggressive environments including almost all aqueous and non-aqueous electrolytes. POLYPLUS currently is focused on the development of rechargeable and non-rechargeable Lithium-Air, Lithium-Seawater and Lithium-Sulfur batteries.

PolyPlus is developing rechargeable and non-rechargeable Li-Air, and Li-Seawater batteries based on protected Li electrodes.

At a nominal potential of about 3 volts, the theoretical specific energy for a lithium/air battery is over 5,000 Wh/kg for the reaction forming LiOH and 11,000 Wh/kg for the reaction forming Li2O2 or for the reaction of lithium with dissolved oxygen in seawater, rivaling the energy density for hydrocarbon fuel cells and far exceeding Li-ion battery chemistry that has a theoretical specific energy of about 400 Wh/kg.

PolyPlus intends to first commercialize non-rechargeable Li/Air and Li/Seawater batteries followed by the introduction of rechargeable Li/Air.

The projected energy density and specific energy for commercial Li-Air batteries is on the order of 1000 Wh/l and 1000 Wh/kg.

Lithium/Seawater batteries which use the ocean as the positive electrode are even more energy dense and should be introduced commercially at about 1500 Wh/l and 1500 Wh/kg.   Source

Sod​ium-air

Lithium air cells have proved very difficult due to side reactions such as the formation of Li₂CO₃ and the enature of lithium oxide..

Sodium doesn't seem to have these complications and should be very cheap. BASF is working on this.

The oxi​de layer

When lithium reacts with oxygen, it forms LiO2 (lithium oxide), which is highly unstable and found only as an intermediate species in Li-air batteries, after which it turns into Li2O2. On the other hand, sodium and oxygen form NaO2 (sodium superoxide), a more stable compound. Since NaO2 doesn't decompose, the reaction can be reversed during charging. Physics News

Zinc​-air

New work by ZAF Energy Systems has improved the zinc air battery.

They claim a lithium cell has 200 watt hours per kilogram; and the new zinc air battery can store 400 watt hours per kilogram. Zinc is one third of the cost of lithium and because of it's energy density, half the mass is needed. 

The zinc air batteries also are nonflammable.

Several other companies and research labs have reported breakthroughs in creating a zinc-air battery, including Eos Systems and Fluidic Energy.

The first product to be released by ZAF will be a home-energy storage unit with 1,000 D-sized cells. The rechargable unit, which will cost about $10,000, will be the size of a small refrigerator. It will be certified for residential, commercial and medical backup energy storage needs, with a 48-kilowatt hour capacity, enough to meet the average two-day needs of the average ho​usehold.

They have developed the first solid-state electrolyte to be used in a battery. Instead of a typical liquid or paste alkaline electrolyte, the ZAF battery uses a solid polymer electrolyte that limits the amount of oxygen that can pass through, while allowing ions to pass freely. This substantially increases the number of recharges and extends the battery life.

The electrolyte in the ZAF battery has been proven rechargeable at 500 charges. If the battery in an electric vehicle has a range of 800 kM, then with 500 recharges, that’s 400,000 kM.

The problem of dendrites forming in zinc batteries are solved with a new anode and electrolyte designs that both limit dendrite growth and prevent shorting.

Source: Clean Technica

Aluminiu​m Air

Aluminium air batteries are primary batteries which are non chargeable. However some are claiming they are rechargeable.

As the aluminum anode is consumed by contact with oxygen, hydrated aluminum forms as a byproduct. That material can be recycled and used to create a new aluminum anode, which is why the batteries are referred to as rechargeable. Periodically, the aluminum anode will have to be replaced. The recycling would need to be recycled in a factory.

So they are not rechargeable.

Alcoa partnered with Phinergy in 2013 with plans for a 2017 debut.

They have the potential to drive an electric car 8 times as far as Li ion.

Other batteries

Lithium-metal (Li-metal)

Most lithium-metal batteries are non-rechargeable. Moli Energy of Vancouver was first to mass-produce a rechargeable Li-metal battery for mobile phones, but occasional shorts from lithium dendrites caused thermal runaway conditions and the batteries were recalled in 1989. Li-metal has a very high specific energy. In 2010, a trial Li-metal-polymer with a capacity of 300Wh/kg was tested in an experimental electric vehicle (this compares to 80Wh/kg for the Nissan Leaf). DBM Energy, the German manufacturer of this battery, claims 2,500 cycles, short charge times and competitive pricing if the battery were mass-produced. Safety remains a major issue.  Source: Battery university
 

Solid-state Lithium

The solid electrolyte (SE) uses metallic lithium as anode material. This provides a higher energy density than in the oxidized format of lithium-ion, but lithium anodes have been tried before and battery manufacturers were forced to discontinue production because of safety issues. Lithium tends to form metal filaments, or dendrites, that cause short circuits. Scientists try to overcome this invasion by using a polymer as separators and electrolyte.

The key objectives for the -solid-state lithium ion battery are achieving sufficient conductivity at cooler temperatures, as well as increasing the cycle count, a weak point with most solid-state battery designs. Prototypes of the solid-state lithium ion only reach 100 cycles.

Targeted applications are load leveling for renewable energy source and EVs by cashing in on short charge times. Solid-state batteries promise to store twice the energy to regular Li-ion but the loading capabilities will be lower, making them less suited for power tools and applications requiring high current loading. Commercialization can take 10 years or longer.

 Source: Battery university

Lithium ​water battery

With the lithium protected from water by a special membrane, it is possible to make a 3 V battery with an high energy density of about about 1,500 Wh/kg

Micro​ lithium

Newly created “micro-batteries” that are only a few millimeters in size are now the most powerful batteries in the world. The new batteries, created by researchers at the University of Illinois, greatly out-power “even the best supercapacitors,” while being only a fraction of their size.

“They pack such a punch that a driver could use a cellphone powered by these batteries to jump-start a dead car battery – and then recharge the phone in the blink of an eye,”  University of Illinois press release.

The unusual property of these batteries is they have high power transmission and high energy storage. 

Clean technica   Nature

The graphic illustrates a high power battery technology from the University of Illinois. Ions flow between three-dimensional micro-electrodes in a lithium ion battery.

Image credit: Beckman Institute for Advanced Science and Technology

Molte​n metal

Two layers of molten metal as electrodes, separated by their different densities and by a layer of molt​en-salt electrolyte. The metal layers swell or shrink as ions pass between them, storing or releasing energy. Because everything is liquid, there is nothing that could crack after thousands of cycles, as solid electrodes might.

The metal​ would be kept molten by internal resistance in  the charging and discharging processes.

Ambri systems have developed a liquid metal battery based on molten lithium  floating on a molten salt, floating in turn on molten antimony and lead.  It operates at 450^oC with an efficiency of 75%.

During discharge, electrons move from the lithium into the circuit, leaving litium as an ion. It migrates through the salt into the antinomy/lead layer to form an alloy. This reverses during charging.

Lead acid

Invented in 1959, it powered the first electric cars in the late 1800s. They are cheap and hold charge for a long time. However they have low energy density and need maintenance and replacement quite often.

More: Lead Acid

Lead acid Ultrabattery

CSIRO has developed a new type of lead acid battery that combines the advantages of ultra capacitors with Lead acid batteries..

UltraBattery® is a completely new class of lead-acid technology: a hybrid, long-life lead-acid energy storage device that operates very efficiently in continuous Partial State of Charge (PSoC) use, without frequent overcharge maintenance cycles.

It is an energy-storing lead-acid battery with the quick charge acceptance, power discharge, and longevity of a capacitor.

Low grade heat battery

At low to warm temperatures, such as 60C. a cell made of Prussian blue nanoparticles and ferrocyanide can be charged, then when it is cooled to say 15C, the cell discharges more energy than was used to charge it. The cell converts heat to electricity.

The efficiency at this stage is only about 2%. The theoretical Carnot limit is 10%.

It will be useful in specialised areas, but is unlikely to be a mass produced product.

References:

http://batteryuniversity.com/learn

How electrochemical cells work

All about batteries

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