In addition to the above-mentioned article on the surface of metal lithium to protect metal lithium and solve various problems of lithium in the electrochemical system, optimizing the negative electrode structure and using new negative electrodes to replace lithium are also important aspects of research in recent years.
Huang et al. creatively proposed a method of adding a graphite intercalation between the separator and the negative electrode to protect lithium, as shown in Figure 1. The graphite layer can be converted into lithiated graphite by short-circuiting with lithium in advance, so that the region where the electrochemical reaction of the electrode occurs is transferred from metal lithium to the vicinity of the graphite layer, avoiding the huge change of the surface morphology after repeated dissolution/deposition of lithium; at the same time, the graphite layer can be used as an artificial SEI film to prevent the corrosion and damage of lithium polysulfide to lithium, reduce the occurrence of side reactions of lithium in the battery system, and improve the utilization rate of active materials; in addition, the high performance of lithium-sulfur batteries is achieved by virtue of the good electrochemical stability of graphite.
The use of lithium-containing anode materials such as lithiated Si/SiOx nanospheres, lithiated silicon nanowires, etc. can replace metal lithium and sulfur cathodes to form a full battery, which can solve the problems of low lithium dendrite and Coulombic efficiency, and make the battery performance stable.
In addition, based on the non-uniformity of the lithium dissolution/deposition process, the structure of the negative electrode current collector has also become an important research direction for the protection of lithium. Researchers from various countries have proposed different materials and structures for lithium storage or as lithium current collectors. Such as hollow carbon microspheres, graphene oxide, 3D porous carbon, polymer nanofibers, 3D structured nano-copper, and glass fiber-modified copper can inhibit the formation and growth of lithium dendrites and improve the non-uniform lithium deposition/dissolution behavior.
All in all, for the metal lithium with the most negative standard electrode potential, the high reactivity is bound to meet the requirements of electrode materials, and it shows great advantages in primary batteries. However, its excessive reactivity brings many adverse effects in lithium secondary batteries. In the lithium-sulfur battery system, the existence of soluble lithium polysulfide complicates the chemical environment of the metal lithium anode, and the reaction between lithium polysulfide and lithium also seriously affects the stability of lithium in the system. The structural damage of the lithium metal anode has become the main reason for the rapid performance degradation of lithium-sulfur batteries. Therefore, the protection of the lithium negative electrode is urgent, and it is also the primary problem that must be solved when the lithium-sulfur battery is on the road to practical use.