Lithium Ion Battery Electrolyte Formulation Introduction

Lithium-ion battery electrolytes are non-aqueous liquid electrolytes composed of organic solvents and electrolyte lithium salts. Of course, there are solid electrolytes. What are they made of? Let’s take a look.

1. Liquid lithium ion battery electrolyte

The choice of electrolyte has a great impact on the performance of lithium-ion batteries. It must be chemically stable, especially not easy to decompose at higher potentials and higher temperature environments, and has higher ionic conductivity (>10-3s) /cm), and must be inert to the anode and cathode materials, and can not corrode them.

Conductive salts include LiCIO4, LiPF6, LiBF6, LiA SF6 and LiOSO2CF3, and their electrical conductivity is in the order of LiAsF6>LiPF6>LiCIO4>LiBF6>LiOSO2CF3. LiClO4 is prone to safety problems such as explosion due to its high oxidizability, which is generally limited to experimental studies; LiAsF6 has high ionic conductivity, easy purification and good stability, but contains toxic As, and its use is restricted;

LiBF6 has poor chemical and thermal stability and low electrical conductivity. LiO SO2CF3 has poor electrical conductivity and has a corrosive effect on the electrode, so it is rarely used; although LiPF6 will undergo decomposition reaction, it has high ionic conductivity, so the current lithium ion The battery basically uses LiPF6. Currently, most of the electrolytes used in commercial lithium-ion batteries use LiPF6 EC2DMC, which has higher ionic conductivity and better electrochemical stability.

2. Solid electrolyte

The direct use of metallic lithium as anode material has a high reversible capacity, its theoretical capacity is as high as 3862mAh-g-1, which is more than ten times that of graphite materials, and the price is lower. It is regarded as the most attractive new generation of lithium-ion batteries. The anode material, but will produce dendritic lithium. Using solid electrolyte as ion conduction can inhibit the growth of dendritic lithium, making it possible for metallic lithium to be used as an anode material. In addition, the use of solid electrolyte can avoid the shortcomings of liquid electrolyte leakage, and the battery can be made into a thinner (only 0.1mm thick), higher energy density, and smaller volume high-energy battery.

The solid polymer electrolyte has the characteristics of good flexibility, film-forming properties, stability, and low cost. It can be used as a separator between positive and negative electrodes and as an electrolyte for transferring ions.

Solid polymer electrolytes can generally be divided into dry solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE). SPE solid polymer electrolyte is mainly based on polyethylene oxide (PEO). Its disadvantage is that the ion conductivity is low, which can only reach 10-40cm at 100°C.

Adding a liquid organic solvent with high dielectric constant and low molecular weight such as PC to the solid polymer electrolyte can greatly improve the solubility of the conductive salt. The electrolyte formed is the GPE gel polymer electrolyte, which has a high temperature at room temperature. Ionic conductivity, but in the process of use, it will leak out and become invalid. Gel polymer lithium ion batteries have been commercialized.

3. Gel electrolyte

The main components of the gel polymer electrolyte are basically the same as the liquid organic electrolyte, except that the liquid organic electrolyte is adsorbed on the gel polymer matrix. Therefore, in addition to the above conditions, it should also have the adhesion between the electrode active material Good adhesion, all solvents are fixed in the polymer matrix, there is no free organic solvent, to ensure no leakage, good bending performance and high mechanical strength.

Lithium-ion battery electrolyte should meet:

A Lithium ion has high conductivity, which is 3×10-3~2×10-2S/cm in a wide temperature range;

B has a wide electrochemical window, that is, it is stable in a wide voltage range (for lithium-ion batteries, it must be stable at 4.5V) without decomposition reaction, that is, it has good oxidation stability.

C is chemically stable, that is, it basically does not react with the electrode materials of the battery system such as the positive electrode, the negative electrode, the current collector, the separator, and the adhesive;

D is guaranteed to be liquid in a wide temperature range, generally hope the temperature range is -40~+700C

E has good solvation properties for ions;

F is non-toxic, low vapor pressure, safe to use;

G can promote the reversible reaction of the electrode as much as possible, and has good compatibility with the electrode;

H is easy to prepare and low in cost.