Battery electrolytes are a central component of a battery. “Electrolytes” is an imprecise collective term for media that are electrically conductive due to the charged atoms (ions) or charged molecules (ions) that they contain.
Most battery electrolytes are liquid and are therefore referred to as electrolyte solutions: In lead-acid batteries, for example, it is sulfuric acid, the electrolyte diluted with water, which acts as the solvent. But it can also be molten salts (molten salt) e.g. liquid, inorganic salts (at elevated temperature), as in thermal batteries, or solids (solid electrolyte).-.
In lithium-ion batteries (LIB), water-free organic electrolyte solutions are used. The absence of water makes it possible to store much more energy in LIB’s than in aqueous batteries. In today’s (2023) environmentally friendly electric cars, batteries are installed that mostly use liquid electrolytes. Mobility 4.0 will also only see batteries with liquid electrolytes for the time being.
Similar to lithium-ion, supercapacitors also use anhydrous organic electrolyte solutions.
However, solid state electrolytes are the subject of current research and are not yet available as standard in commercial batteries (2023). There is hope to incorporate pure lithium metal into rechargeable LIBs through the use of solid-state electrolytes. Unlike liquid electrolytes, solid-state electrolytes completely prevent the growth of dendrites in the battery cell. This could significantly increase the energy density of lithium-based batteries, which is particularly desired in electric aviation, but also in e-mobility.
It is also possible to combine ionic polymers (polyelectrolytes, e.g. Nafion) or non-ionic polymers (e.g. Polethylene Oxide, PEO) and solvents as electrolytes, in which case they are referred to as gel electrolytes. Such gel electrolytes are popular because they have the ionic conductivity of liquid electrolytes, but are solid and do not leak. Such battery types are commercially available and are colloquially referred to as “polymer batteries.”
Various additives can be added to electrolytes. If an electrolyte is not sufficiently electrically conductive, conductive salts are added to it to improve the electrical conductivity. This is the case in most lithium-ion batteries, for example.
Battery additives usually help to improve the stability of a battery. Many other additives can be added to an electrolyte to improve certain properties in a battery. Wetting battery additives, for example, ensure better wetting of the electrodes with the electrolyte. So-called redox shuttles (redox-active compounds) prevent dangerous chemical reactions from occurring in lithium-ion batteries due to overcharging.
An important factor limiting the performance of lithium-ion batteries is the degradation of the cathode material, which can be caused by dissolution of transition metals, interfacial reactions, loss of contact with conductive particles, and so on. Although all transition metals in the cathode (such as Mn, Ni, Co, Fe, and Zn) are susceptible to dissolution, manganese showed the greatest tendency to decompose.
This is a major reason for the decrease in capacitance in spinel electrodes and other cathodes containing manganese. Metal dissolution leads to structural disorder of the cathode and also the growth and degradation of the SEI layer on the anode.
One way to solve these problems is to use additives that can form an effective surface film
on the cathode. Film-forming cathode additives are designed to oxidize before the solvents and cover the electrode surface to prevent oxidative decomposition of the electrolytes.
Other additives for batteries are used to form polymer-like films on the surfaces of battery electrodes in the hope of preventing the formation of lithium metal dendrites and zinc metal dendrites.
Power density is the power per mass or volume unit.
The specific power density and the gravimetric power density are power per mass (W/kg).
The volumetric power density is power per volume (W/L)
Circular economy, trade in Li-ion batteries waste will remain essential in markets where economically viable recycling can take place. Promoting circular economy and value chains for Li-ion batteries require clear rules on the waste status, transport, storage, safety regulations, trade facilitation, standards for battery design, product lifetime, and regulatory targets for waste collection and recycling rates.
The energy density describes the amount of energy that can be stored in a battery per mass or per volume. There is a “volumetric energy density”, sometimes short-abbreviated as “energy density” and the specific energy density also called as the gravimetric energy density. Therefore, the amount of energy per kg (Wh/kg) or the amount of energy per litre (Wh/L).
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