Montmorillonite is a typical water-bearing layered silicate mineral with a large specific surface area and strong ion exchange. It is widely used in the preparation of nanocomposites and is also the most commonly used clay mineral in the preparation of composite solid electrolytes. Through organic modification treatment, lithium salt modification treatment on montmorillonite, or by reducing the anisotropy of the electrolyte system, the composite solid electrolyte exhibits higher ionic conductivity.
Organic modification
Organic modification means that through organic intercalation, the compatibility of the smectite filler and the polymer matrix is improved, and the interval between the smectite layers can be enlarged, which is beneficial to the movement of ions between the layers and improves the performance of the electrolyte system.
Lithium-montmorillonite and lithium-montmorillonite intercalated with polyacrylonitrile were used as inorganic fillers to combine with polyacrylonitrile to prepare composite solid electrolytes. Under the same conditions, lithium-montmorillonite intercalated with polyacrylonitrile was used to prepare composite solid electrolytes. The ionic conductivity of the prepared composite solid electrolyte is one order of magnitude higher than the former.
Lithium salt modification
The lithium salt modification treatment is to insert lithium ions between the montmorillonite layers as a lithium source through ion exchange, so that the prepared composite solid electrolyte becomes a single-ion conductor, so as to prevent the movement of anions and cations in the electrolyte to form concentration polarization, resulting in degradation of battery performance .
The use of polyoxyethylene intercalation hectorite can prepare organic-inorganic mixed ion conductor materials. Within a certain temperature range, the ionic conductivity of polyoxyethylene/lithium-montmorillonite composites is much higher than that of lithium-montmorillonite Delithiation, which shows that the negatively charged silicate sheet makes the charge transport carrier in the electrolyte limited to cations.
Reduce the anisotropy of the electrolyte system
The unique layer structure of montmorillonite makes it easy to form a preferred orientation arrangement in the electrolyte system. When the non-conductive layer is perpendicular to the ion current path, the ionic conductivity of the composite electrolyte will be reduced to a certain extent. Therefore, some scholars have proposed that methods such as melt intercalation and ultrasonic stripping should be used to reduce the anisotropy of the electrolyte system to avoid negative effects on ion conductivity.
Compared with the solution intercalation method, the polymer/layered silicate composite prepared by the melt intercalation method can minimize the preferred orientation of the layered silicate, make the material have good isotropy, and avoid the removal of excess due to cleaning. The polymer affects the migration rate of lithium ions.
Intercalation or delaminating montmorillonite has a greater effect on the ionic conductivity of the electrolyte. The exfoliated clay can provide more mobile and conductive ions, and the cations in the intercalated clay will be trapped between the structural unit layers of the clay, resulting in a decrease in ionic conductivity.
Source: Powder Technology Network