Preparation of Li-B alloys as anode material for production of lithium batteries has been extensively studied. (1,2) However, many questions remained unexplained. So¬me ambiguities also remained regarding the existence of a LiB3 compound and the dissolution of boron in lithium melt. Preparation of Li-B alloys is very challen¬ging, because it is carried out at relatively high temperatures, where molten Li is highly reactive. An argon-filled dry-box, containing less than 0.1 ppm of oxygen and water, was used in synthesis protocol. Li-metal and crystalline boron were heated in electric furnace in a pure iron crucible. The processes for the preparation and characterization of Li-B alloys are described in detail in previously published publications (3,4). It is interesting that in the present time most of researchers avoid the classic metallurgical preparation of Li-B alloys. There are some do¬cu¬men¬ted procedures using metallurgical approaches, which significantly differs from ours (5), due to a highly demanding experimental work.
In the present work we report on the development of materials that origi¬na¬te from Li-B system and could lead to the preparation and application of 2-D boron ma¬terials – i.e. borophenes – graphene analogs. Borophenes are promising new class of materials, due to their exceptional physical and mechanical properties, which offer a wide range of applications, especially for energy conversion and storage devices. It is hard to say that borophenes have been synthesized as pure 2-D material. We believe that Li-B alloys, which we began to develop in the early 1990s can be used for this purpose (1,2).
Using extensive research work and quantum chemical calculations (ab initio MO) we explained the mechanisms of formation of Li-B alloys and so-called "dissolution" of the boron in the melt of metalic lithium (6,7 and 8). We found that the LiB3 composition is not actually an alloy, but rather interstitial solid Li so¬lu¬tion, which is incorporated into B12 interstices in the β-rombohedral boron. We also found that Li incorporation increases the unit cell of the boron which then causes local disorder and micro stress in its crystal lattice. Using X-ray powder diffrac¬ti¬on, we have shown that due to this stress, the surface of the crystalline boron peels off, which leads to the formation of layered boron material.
We prepared Li-B alloy, by metallurgical process and with H2O/HCl(aq.) solution remained lithium was etched away. This material was then purified and exfoliated in water suspensions, filtered and dried in vacuum oven at elevated tem¬pe¬rature. Detailed synthesis procedure will be published elsewhere. The resulting material was then morphologically characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), chemically with energy-dis¬per¬sive X-ray spectroscopy (EDS), and Electron energy loss spectroscopy (EELS). The material was further characterized by powder XRD, evolved gas analysis (EGA), Brunauer-Emmett-Teller analysis (BET) and electrochemical methods.
Within the material we found layered, amorphous, material which is stable at relatively high temperature and could be borophene. We tested this material as an anode in Li-ion batteries, as a supercapacitor and as an additive to spectrally se¬le¬c¬tive coatings for concentrated solar power plants (CSPs). All results confirmed un¬usual behavior of material.