**2. Results and discussion of various topics**

#### **2.1 Sulfur, selenium and tellurium batteries**

Many efforts have focused on the cathode material design, electrolyte optimizations, separator modification, still some of the challenges remain due to slow kinetics, electrolyte compatibility, and inferior cycling stability. Hence, there are many

possibilities for the development of more reliable sulfur, selenium tellurium (SSTs) batteries. He et al. [5] showed schematic representation of various components for the development of lithium-ion batteries based on SST as shown in **Figure 1**. The carbonbased materials, conductive materials, and their nanostructure with a porous matrix refereed as a host due to low electrical conductivity of SSTs (S and Se) and the soluble properties of the chalcogenide. Therefore, the host materials can provide necessary contact with SSTs to reduce the formation of inactive regions and satisfy the adsorbing as well as accommodation of soluble active materials. Therefore, the mass loading of SSTs cathodes can efficiently be increased. The various approaches such as melting diffusion, chalcogen vaporization are used to increase the mass loading of active SSTs into the conductive host materials. An introduced of metal atoms to form a bonding with SSTs is another possible method for reducing the reaction barriers in Al-SSTs batteries.

## *2.1.1 Al-sulfur batteries*

The most abundant high-surface-area carbon porous materials are possible to absorb the SSTs materials, which is more impartment for limiting chalcogenide dissolution [28]. Thus, well-designed porous structure carbon materials composites can enhance not only the charge transport but also improve the retention of SSTs cathode during electrochemical reaction [29]. Therefore, carbon materials are attractive to be host for the insulating S with a regular matrix. A melt-diffusion method was conducted to prepare the S/activated carbon cloth (ACC) composite cathode material in Al-S battery as shown in **Figure 1a**. As prepared ACC material exhibited type I adsorption, corresponding to microporous structure with a pore size below 2 nm. The Brunnauer-Emmett-Teller (BET) measurement showed that after compositing of S into the ACC, specific surface area decreased from 2376.6 to 1532.8 m<sup>2</sup> g−1 and also decreased to its micropore volume from 0.93 to 0.61 cm3 g−1, indicating that the S material was uniformly impregnate into the microporous structure. The Al-S battery based on S/ACC cathode exhibited a high specific capacity of 1320 mA h g−1 and discharged voltage about 0.65 V as shown in **Figure 2b**.

The microporous structure ACC host consists of pore size less than 2 nm and can effectively provide the fast solid-state reaction kinetics favoring to its ready electron

#### **Figure 1.**

*Perspective for Al-SSTs batteries. Reprinted from ref. [5].*

*Advanced Chalcogen Cathode Materials for Lithium-Ion Batteries DOI: http://dx.doi.org/10.5772/intechopen.103042*

#### **Figure 2.**

*The galvanostatic charge/discharge curves of a, b) Al-S battery, c, d) Al-Se battery (n* ≥ *1), and e, f) Al-Te battery. Reprinted from ref. [5].*

access, large reaction area, and decreasing the ionic diffusion length. Similarly, a free-standing CNF host was also introduced in Al-S battery as shown in 2b. The carbon nanofiber with a diameter of 100–200 nm occupies between the interspaces in micrometer scale level. This CNF structure provides a spacious, robust, conductive matrix to accommodate the active S and their products. The S and EMIC/AlCl3 slurry dispersed into the freestanding CNF host, the Al-S battery exhibited a good capacity of 1250 mAhg−1. These above free-standing carbon materials not only provide a conductive matrix for S materials, but also reduce the side reaction from the binder, thereby enhanced stability of Al-S battery. The porous carbonized Cu-based metal organic frameworks (MOFs) called as HKUST-1-C also introduced as a host to the S in Al-S batteries [30]. The HKUST-1-C carbon materials exhibited high hierarchical porous structure with surface area of 179 m2 g−1 and a pore sizes in <5 nm range.

These are more suitable for being host in S cathode batteries. The metallic Cu can react with polysulfides to form S-Cu ionic clusters, thereby reducing the kinetic barrier of the electrochemical conversion reaction and facilitating the reversibility of S during charge/discharge processes. Therefore, the S@HKUST-1-C cathode battery exhibited a stable performance with a reversible capacity of 600 mA h g−1 at the 75th cycle and retained 460 mA h g−1 even after 500 cycles at 1 A g−1. These results indicate that the metallic material provides a valuable strategy to develop stable Al-S batteries. A nitrogen-doped hierarchical porous carbon called as HPCK used as a host for S in Al-S batteries [31]. Hierarchical micro-, meso-, and macro-pores of HPCK was prepared by carbonizing a N-rich polymer precursor combined with zinc nitrate and followed by a KOH etching process. Interestingly, KOH etching process greatly improved the surface area (2513 m<sup>2</sup> g−1) and created more micro- and meso-pores. The Al-S batteries based on S/HPCK cathode delivered a capacity of 1027 mA h g−1 at 0.2 A g−1 for 50 cycles and exhibited excellent cyclic ability of 405 mA h g−1 at 1 A g−1 for 700 cycles. The hierarchical porous structure of HPCK with high surface area and large pores confined S materials. The huge macropores provide fast ion transport in the electrolyte. Therefore, the porous carbon powders, metal content along with structure optimization for host are impartment factors for Al-S batteries.
