What are electrolytes

What is an electrolyte? An electrolyte and an electrolyte are not the same. It should be said that the electrolyte contains an electrolyte, because the electrolyte is a solid state, which generally refers to a substance in an ionic state. The electrolyte is dissolved in a liquid solvent to form an electrolyte, which means that it can conduct electricity. A liquid will have different material formulations due to different use environments, but the function is the same, that is, it has the function of conducting electricity. The electrolyte or electrolyte we usually say is mainly divided into biological electrolyte or electrolyte and battery electrolyte and electrolyte. Next, we will interpret electrolytes and electrolytes from the two directions of bioconductive liquids and battery conductive liquids.
1. Electrolyte and electrolyte for battery
(1) Two forms of battery electrolyte and electrolyte
1) Liquid electrolyte and electrolyte
Liquid electrolyte, its solvent is anhydrous organic matter, and most use mixed solvent. The common organic liquid electrolyte is generally a system composed of 1 molL lithium salt/mixed carbonate solvent. As a medium for the transfer of charge and mass transfer, the electrolyte suitable for lithium-ion batteries should generally meet the following requirements:
A. It has high conductivity in a wide temperature range, preferably above (1~2)×10-3S/cm, and the lithium ion migration number is as high as possible; B. The liquid temperature range (liquid range) is wide , at least in the range of -20~80 ℃; C. Good chemical stability, basically no reaction with electrode active materials (such as positive and negative materials), current collectors, diaphragms, etc.
D. It has good compatibility with electrode materials and can form a stable and effective passivation film;
E. Good electrochemical stability and high decomposition voltage to reduce the self-discharge of the battery and the increase of the internal pressure of the battery during operation; F. High flash point and ignition point, good safety; G. Environmental friendliness, decomposition products are harmful to the environment Less affected.
The above requirements are an important guarantee for realizing low internal resistance, long life and high safety of lithium-ion batteries. The selection of lithium salts, organic solvents, and the optimization of electrolyte solutions determine the cycle efficiency, operating voltage, operating temperature, and storage period of the battery, which is one of the key technologies for the development of lithium-ion batteries. In a sense, the liquid electrolyte of lithium-ion battery plays a decisive role in battery performance.
After decades of research and practice, the electrolyte used in lithium-ion batteries has been basically formed. Commercial electrolytes generally choose LiPF6 as the lithium salt, and the solvents are mostly ethylene carbonate (EC) and dimethyl carbonate (DMC) or A mixed solvent composed of diethyl carbonate (DEC). In addition, there are a small number of electrolyte systems used for special purposes. These electrolyte systems support the commercialization of lithium-ion batteries and future research and development.
2) Solid or colloidal electrolytes and electrolytes
The use of solid electrolyte can avoid the shortcomings of liquid electrolyte leakage, and can also make the battery thinner (the thickness is only 0.1mm), higher energy density, and smaller high-energy battery. Destructive experiments show that solid-state lithium-ion batteries have high safety performance. After destructive experiments such as nail penetration, heating, short circuit and overcharge, liquid electrolyte lithium-ion batteries will have safety problems such as night leakage and explosion. There are no other safety issues other than a slight increase. Solid polymer electrolytes have the characteristics of good flexibility, film-forming properties, stability, and low cost, and can be used as separators between anode and cathode electrodes and as electrolytes for transferring ions. Solid polymer electrolytes can generally be divided into dry solid polymer electrolytes and gel polymer electrolytes. Solid polymer electrolytes are mainly based on polyethylene oxide. The disadvantage is that the ionic conductivity is low. In solid polymer electrolytes, ionic conduction mainly occurs in the amorphous region, and migration is carried out by the movement of polymer chains. Polyoxyethylene is easy to crystallize due to the high regularity of its molecular chain, and crystallization reduces ionic conductivity. Therefore, in order to improve the ionic conductivity, on the one hand, it can reduce the crystallinity of the polymer and improve the mobility of the chain, and on the other hand, it can improve the solubility of the conductive salt in the polymer. Destruction of the crystalline properties of the polymer by means of grafting, block, cross-linking, and copolymerization can significantly improve its ionic conductivity. In addition, the addition of inorganic complex salts can also improve the ionic conductivity. Adding a liquid organic solvent with low dielectric constant and relative molecular mass to the solid polymer electrolyte can greatly improve the solubility of the conductive salt. The formed electrolyte is a gel polymer electrolyte, which has high ionic conductivity at room temperature. , but it will fail due to the liquid separation during use. Gel polymer lithium-ion batteries have been commercialized.
(2) What types of battery electrolytes and electrolytes are there?
There are many chemical formulations of battery electrolytes and electrolytes, which will vary according to the type of battery and the application performance of the battery, but the purpose is to make the battery have better performance and efficiency in the application.
In terms of battery types, electrolytes include lead-acid batteries, lithium batteries, gel batteries, nickel-metal hydride batteries, fuel cells, capacitor batteries, low-temperature batteries, and high-temperature batteries. These electrolytes are all formulated with mineral chemicals, and their electrical conductivity is much higher than that of biological electrolytes, and at the same time, they will destroy biological functions.
2. Biological electrolytes and electrolytes
Biological electrolytes are biological fluids that sustain life. They cannot conduct large currents, but they conduct electricity faster than non-biological electrolytes. Generally speaking, the biological electrolyte of the same species has the same electrolyte in the same part of the body; the electrolyte of different organisms will be different.
Electrolytes are ions present in body fluids, which can maintain the osmotic pressure of body fluids and maintain the normal distribution of fluids in the body. They are the main components of body fluids and participate in important physiological and biochemical processes in the body. Under normal circumstances, the body has a perfect buffering and regulating system; through the compensation of the buffering system, lungs and kidneys, it maintains a stable state of water, electrolyte and acid-base balance.
The main cations in body fluid electrolytes are potassium (K+), sodium (Na+), magnesium (Mg2+) and calcium (Ca2+), and the main anions include chloride (C1–), phosphate (HPO42–, H2PO4–), bicarbonate ( HCO3–), sulfate (SO42-)), and organic anions such as lactic acid and protein.