There are few subjects as hot as batteries. Vilified because they can catch fire and we don’t know how to recycle them, they are also an indispensable part of the ecological transition: they are a highly efficient method of storing electricity. Nevertheless, to understand the role they will and could play, we need to ask some complex questions: don’t they consume too much metal? Are they suitable for all uses? What technologies are available? What are the risks ? What are the innovations ?
We’ll answer these questions here. We’ll look at..:
- Battery basics
- Lithium-ion batteries, which currently dominate the market
- Other mature or obsolete technologies
- Battery problems, particularly in terms of safety.
- Battery innovations, such as the development of “redox flow” batteries.
I. Batteries in general
Let’s take a look at how batteries work, how much they cost, and what we can do to improve them.
How batteries work
The first battery was invented in late 1799 by Alessandro Volta. However, the date often used is 1800, when he submitted his invention to the Royal Society, where it was read on June 26. His battery was a stack of zinc and copper disks separated by a felt pad soaked in salt water.
Volta’s battery worked as follows: the oxidation of zinc released a Zn2 ion and 2 electrons. The copper, however, did not react with these electrons, which in fact reacted with the water in the soaked cloth. The reaction is electrolysis of the water, producing dihydrogen: 2H2O e- => 2HO- H2. If you touched the top and bottom of the column, the current would flow through you.
This is the fundamental principle of batteries: a flow of electrons and a flow of ions, chemical energy is transformed into electrical energy (and vice versa).
Here, chemical energy is fixed at the start. In the case of batteries, it is “acquired”: charging the battery will generate a chemical reaction, which will go in the opposite direction when discharged.
Price and production
Batteries have long had one problem: they’re heavy. For a long time, this meant that electric vehicles were little more than gadgets. Lithium-ion batteries have changed that, being able to store a good amount of energy per unit weight. Their price has fallen by 97% since their introduction in 1991.
Vehicle batteries are estimated to average $156/kWh in 2019. (IAE 2020, p.29) According to Bloomberg, the price has dropped from $1,100 in 2010 to $137/kWh in 2020, with plans to reach as low as $58/kWh in 2030.
Possible innovations
There are many avenues for improvement. First of all, the cells themselves can be improved: we can choose the chemical reaction that will take place and the electrode materials, the cell manufacturing methods and other engineering aspects. We can also improve heat management, or the“packs” that the cells will form. There are also battery management systems (BMS), which optimize the battery’s behavior during operation. The most modern systems extend the service life of lithium-ion cells from 9 to 17.5%. (IAE 2020, p.45)
In terms of applications, automotive batteries are the subject of the most patents. In 2000, they rose from around ten per year, compared with ~80 for portable applications, to 736 per year in 2018, compared with 298 for portable applications. (IAE 2020, p.47)
II. Lithium-ion batteries, the leading technology
First commercialized by Sony in 1991, lithium-ion batteries dominate the portable electronics market.
They also dominate innovation in this field: in 2018, 2,547 battery-related patents concerned Li-ion cells and only 462 concerned other cell types. (IAE 2020, p.6) These batteries accounted for 93% of stationary energy storage systems, excluding STEP in 2018. (ibid, p.32)
The principle of lithium-ion batteries
Lithium-ion batteries are based on the exchange of lithium ions between a cathode (composed of various lithium and cobalt-based alloys) and an anode (often graphite) separated by an electrolyte. In the discharge phase, the Li ion migrates towards the cathode, generating an electric current, and vice versa in the charge phase.
A liquid or gel electrolyte, often based on lithium hexafluorophosphate (LiPF
6), facilitates the process.
The reasons for their success are essentially that they can store a lot of energy per unit weight (energy density, 100-265Wh/kg); have a good power-to-weight ratio (300-1500W/kg); and have a low self-discharge rate (<10%/year);
Variations in lithium-ion batteries
There are several types of lithium-ion batteries. For example, cathodes can use different mixtures:
- Lithium and cobalt oxide (LiCoO2, LCO): high voltage, energy density, stability and cost. Used in portable electronics.
- Lithium nickel manganese cobalt oxide (LiNixMnyCozO2, NMC): high voltage, energy density and capacity. Less good thermal and chemical stability, and cobalt is expensive. Used in electric vehicles and portable electronics.
- Lithium nickel cobalt aluminum oxide (LiNiCoAlO2, NCA): high energy density, high capacity, but less safety. Used in electric vehicles and portable electronics.
- Lithium and manganese oxide (LiMn2O4, LMO)
- Lithium iron phosphate (LiFePO4, LFP). These materials are less expensive, have good durability, high power density and good safety. Several major companies, including Apple, Tesla and Volkswagen, have announced their interest in this type of battery. Tesla is already using them.
The same goes for anodes:
- Lithium titanium oxide (LTO): good safety, long life, fast charge/discharge, low energy density, low capacity, low voltage. Used in stationary batteries and small electric vehicles.
- Carbon (graphite): low cost, good voltage, energy density and stability, but poor fast-charge performance at low temperatures. Widely used.
- Lithium. Not used.
- Silicone (IAE 2020, p.68) Silicone has interesting energy aspects (captures 9 times more lithium ions than graphite and has a better energy density), but is not very durable, notably because it expands when it absorbs lithium ions. This is an avenue being explored by Tesla.
IAE estimates that these batteries will reach a density of around 275Wh/kg (2020, p.29)
Another important area of innovation is the use of solid electrolyte. The liquid or gel electrolytes currently used in lithium-ion batteries tend to pose a fire hazard. The number of patents on this subject is rising steadily, from 6 in 2000 to 36 in 2010, and 211 in 2018. (IAE 2020, p.71)
III. Other and older mature technologies
While lithium-ion batteries have established themselves, there are other axes that have existed or that remain.
Zebra batteries (sodium-nickel chloride)
Zebra batteries(Zeolite Battery Research Africa), combining sodium, chlorine and nickel, were popular in the late 90s as a replacement for nickel-cadmium (NiCd) technology in cars, and were banned in the 2000s by European Directive 2002/95/EC on the grounds of their dangerousness.
The equivalence is as follows: 2Na NiCL2 <=> 2NaCl Ni. Voltage is 2.58V at 300°C.
These batteries have a high energy capacity and good efficiency, but they operate at high temperatures (around 300°C), which poses problems, particularly in terms of service life.
Their density is around 90-120Wh/kg. Among the few companies using this technology is a Swiss manufacturer, Innovenergy, which emphasizes the ecological benefits of using common, non-hazardous materials. It acknowledges, however, that these batteries “are very expensive because they are not manufactured in low-cost countries and do not benefit from the economies of scale associated with high production volumes.”
IV. Battery problems
Safety issues
Stationary battery installations in Great Britain have been described as “time bombs”. A fire could quickly spread from one battery to another, and toxic fumes could be generated. A fire in Illinois forced the evacuation of a nearby village in 2021. A Tesla stationary battery caught fire in Australia. In 2020, a container caught fire in France.
More worryingly, the lithium ion battery of an electric scooter stored indoors exploded on December 31, 2021, devastating the room it was in.
Perhaps the most famous safety problem is that of the Samsung Galaxy Note 7 smartphone, which caused the lithium-ion battery to explode.
IRSN has published a summary on lithium batteries, mainly concerning private individuals:
- Electrical risk: electrification or electric arc in the event of battery short-circuit or during battery disconnection operations.
- Chemical risk: exposure to hazardous electrolytes or electrodes containing toxic oxides, e.g. in the event of thermal runaway of the battery or, in another context, during battery recycling.
- Fire – explosion risk following a malfunction. Electrolytes are often combustible or flammable, and “lithium and some of its alloys react violently with humidity The energy contained in the battery, if it loses its “straitjacket”, will diffuse and promote fire. (IRSN)
Lithium cells and batteries are also classified as “hazardous materials”, so their transport and storage are strictly regulated. (IRSN) The toxicity of lithium has also prompted the European Commission to consider classifying it in category “1A” for reproductive toxicity in 2022, following an ECHA opinion to this effect.
The problem of materials
Note that lithium isn’t the only metal that will come under strain with the development of batteries.
In 2019, global lithium production will be 77 kt. One tonne of lithium can be obtained by :
- recycling 28 t of batteries,
- the extraction of 250 t of ore,
- the extraction of 750 t of brine.
In 2018, 60% of the world’s lithium is used to manufacture batteries
https://www.inrs.fr/metiers/energie/utilisation-batteries-lithium.html
An NMC 622 battery, for example, contains mainly copper (17%), electrolyte solution (15%) and aluminum (8%). The cathodes, which represent 31% of the weight, are composed of 16% manganese, 55% nickel, 10% lithium and 19% cobalt. The anodes represent 22% of the weight and are made of graphite (IAE 2020, p.49)
Cobalt is problematic, as much for its environmental and social impact as for its price. Carmakers in particular are trying to reduce its use.
The price of lithium exploded in 2022, having increased more than 5-fold, although it should be noted that lithium is not a rare metal. The problem lies more in its insufficient exploitation. France, for example, has significant lithium resources (BRGM), as does Germany.
Recyclability
The “main processing methods for lithium batteries are hydrometallurgy and pyrometallurgy” (IRSN)
In 2018, 193 kt of battery waste declared collected.
Currently in France, less than 10% of lithium batteries are recycled.
https://www.inrs.fr/metiers/energie/utilisation-batteries-lithium.html
Price and scale of stationary batteries
Finally, there’s a more fundamental issue for batteries: their price and scale. A recent project illustrates this well: an electricity storage battery farm designed to be coupled with a photovoltaic installation was recently launched. The 900MWh facility will occupy 16 hectares and will be able to release a maximum of 409 MW, equivalent to the energy produced by a French nuclear reactor in one hour. It would be the largest in the world. This begs the question: why not build a nuclear reactor instead?
This question will become all the more acute with the development of small, modular 4th generation nuclear reactors, which are not only more flexible, but also extraordinarily safe.
Stationary batteries will play an important role in the ecological transition, but their role will always be to smooth out peaks and troughs, and they are out of the question for storage beyond a few days or weeks, and above all for seasonal storage, which is the real challenge for intermittent energies.
V. Batteries of the future
The need for batteries is set to grow, both as a result of the development of electric vehicles and for a new use: stationary batteries. As intermittent energies develop, short-, medium- and long-term electricity storage devices are needed.
Numerous innovations are therefore being developed to improve existing batteries, whether for mobile or stationary use. Chemistry
Lithium-air batteries
Lithium-air or lithium-oxygen batteries use oxygen from the air to operate. The cathode is made of porous carbon and the anode of lithium. When charged, . Conversely, when discharged, lithium ions (Li ) migrate and combine with oxygen to form lithium peroxide (Li2O2) on the cathode. In other words, electricity prevents lithium from oxidizing.
This technology is the subject of much interest, as its batteries would be much lighter and more compact than lithium-ion batteries. Indeed, in theory, they could reach 3.5 kWh/kg! Of course, this is still a long way off. In 2022, a Japanese group is said to have developed a lithium-air battery capable of storing 500Wh/kg.
One of the problems with this technology is its instability. In 2020, South Korean researchers (Korea Advanced Institute of Science and Technology, KAIST) are said to have developed nanoparticles capable of stabilizing it. There are also “contamination” problems. Other components in the air can react to produce LiOH or Li2CO3, for example. Lithium peroxide itself can “foul” the cathode and cause problems. Coatings are being developed to counter these mechanics. (Wu and Yu 2019)
Sodium-ion batteries
The principle of sodium-ion batteries is similar to that of lithium-ion batteries, but uses sodium, which is much more common and less expensive. Their advantages are good specific power and fast charging. Their disadvantage is a lower storage capacity per unit weight.
This approach is being developed by the French start-up Tiamat, as well as by the Chinese giant CATL, which has announced a sodium-ion battery for 2021 that charges very quickly (15 minutes to 80% charge), has good cold tolerance (retains 90% of its capacity at -20°C) and has an energy density of 160 Wh/kg.
Redox flow batteries
Redox flow batteries are very special batteries: the cathodes and anodes themselves are a relatively neutral porous matrix. The “active” substance in each pole is two electrolyte solutions (anolyte and catholyte), which are injected from reservoirs. In the middle, a proton exchange membrane (as in PEM fuel cells) separates the two.
They have several advantages: they are modular (parts can be easily replaced), have economies of scale, and can be recharged instantaneously when needed (behaving rather like a fuel cell). What’s more, electrolytes also act as a heat transfer medium, facilitating temperature regulation. Their disadvantages are relatively low voltage, low energy density and the need for pumps to circulate the electrolyte, which reduces efficiency.
They are therefore particularly suited to stationary storage, their energy storage capacity being limited mainly by the size of their reservoirs. What’s more, they enable long-term storage.
There are several variants. Some batteries use only vanadium, based on the reactions “V3 e- <=> V2 “ in the anolyte and “VO2 H20 <=> VO2 2H e-“ in the catholyte. The mass density is of the order of 15-25Wh/kg (Lourenssen et al. 2019)
This reaction delivers a voltage of 1.26V, but the cost and availability of vanadium are a hindrance.
Other batteries use zinc and bromide. The reaction at the anolyte is “Zn <=> Zn2 2e-“ and “Br2 2e- <=> 2Br-“ at the catholyte. This is the solution adopted by Redflow.
Various research projects
- Polypeptide batteries. https://www.enerzine.com/une-nouvelle-batterie-polypeptidique-recyclable-sans-metal-qui-se-degrade-a-la-demande/34189-2021-05
- IAE 2020, Innovation in Batteries and Electricity Storage, https://www.iea.org/reports/innovation-in-batteries-and-electricity-storage
- Fordham and Magill Allison, Safety of Grid Scale Lithium-ion Battery Energy Storage Systems, https://www.researchgate.net/publication/352158070_Safety_of_Grid_Scale_Lithium-ion_Battery_Energy_Storage_Systems
- IRSN, Les batteries au lithium, Connaître et prévenir les risques, 2021 https://www.inrs.fr/media.html?refINRS=ED 6407
- EIA, “Solar power and batteries account for 60% of planned new U.S. electric generation capacity”, https://www.eia.gov/todayinenergy/detail.php?id=51518#
- BRGM, Ressources métropolitaines en lithium et analyse du potentiel par méthodes de prédictivité, report BRGM/RP-6821-FR, December 2018
- Feixiang Wu, Yan Yu, Toward True Lithium-Air Batteries, Joule, Volume 2, Issue 5, 2018, Pages 815-817, ISSN 2542-4351, https://doi.org/10.1016/j.joule.2018.04.019. (https://www.sciencedirect.com/science/article/pii/S2542435118301806)
- G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, and W. Wilcke,“Lithium-Air Battery: Promise and Challenges“, The Journal of Physical Chemistry Letters, 20101 (14), 2193-2203 DOI: 10.1021/jz1005384
- Kyle Lourenssen, James Williams, Faraz Ahmadpour, Ryan Clemmer, Syeda Tasnim, Vanadium redox flow batteries: A comprehensive review, Journal of Energy Storage, Volume 25, 2019, 100844, ISSN 2352-152X, https://doi.org/10.1016/j.est.2019.100844. (https://www.sciencedirect.com/science/article/pii/S2352152X19302798)
- Jean-Jacques Samueli and Jean-Claude Boudenot, “L’invention de la pile électrochimique par Volta”, Bibnum [Online], Physics, online September 01, 2008, accessed January 30, 2023. URL : http://journals.openedition.org/bibnum/719