6.5 Lithium-Sulfur Battery
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addition, oxides can significantly increase the volumetric energy density of lithiumsulfur batteries. Metal oxides can not only be used as pure sulfur additives for lithiumsulfur batteries, but also be directly added to carbon composite materials to obtain
composite positive electrode materials.
Metal Sulfide
With the gradual enrichment of metal supplied synthesis methods, researchers try
to add it to the positive electrode of lithium-sulfur batteries. Metal sulfides have a
strong affinity for sulfur-containing substances and can well limit the loss of positive
electrode active materials. Lithium sulfide cathode materials have been the most
widely studied of all metal sulfides. Since the sulfur composite positive electrode does
not contain lithium in traditional lithium-sulfur batteries, the lithium metal negative
electrode needs to provide a lithium source. In this way, the lithium negative electrode
will undergo structural changes during the reaction process, causing potential safety
hazards to the lithium-sulfur battery system. Researchers have developed sulfide
materials to replace pure sulfur cathode materials, which has eliminated the impact
of structural changes in lithium metal anodes (e.g., MnS, CuS, ZnS, SnS 2 , and NiS 2 ).
However, sulfides generally have poor conductivity and must be compounded with
other conductive materials.
Other Metal Compounds
Most metal oxides are poorly conductive, so the use of metal oxides alone as cathode
materials for lithium-sulfur batteries may impede electron transport, resulting in
reducing sulfur utilization and rate capability. For example, TiN–S composite positive
electrode has a high conductivity, a strong porous skeleton, and a good adsorption
capacity, and the assembled lithium-sulfur battery shows excellent cycle stability
(Cui et al. 2016). Recent studies have shown that nanostructured metal carbides have
a strong adsorption effect on polysulfides, such as TiC and WC can adsorb polymers
and promote polysulfide reduction reactions. Due to the microcrystalline size (about
25 nm) and a large number of active sites, TiC cathode materials can be used in
lithium-sulfur batteries to improve the cycling performance. It has a steady specific
capacity of 860 mAh g
−1 in 100th cycle (Al Salem et al. 2016), which is instructive
for the next step.
6.5.4.6 Lithium Sulfide Electrode Materials
Lithium sulfide (Li 2 S) as the final discharge product of lithium-sulfur batteries has
attracted attention due to its higher theoretical specific capacity (1166 mAh/g). Li 2 S
does not require metallic lithium as a negative electrode compared to the sulfur
electrode material, which can reduce the safety problems caused by the lithium metal
dendrite. However, its poor electronic and ionic conductivity, and its high solubility in
electrolytes must be solved, the typical methods to use are carbon-coated or porous
Li 2 S-filled materials to improve its electrical conductivity and inhibit polysulfide
from dissolving in the electrolyte.
181
addition, oxides can significantly increase the volumetric energy density of lithiumsulfur batteries. Metal oxides can not only be used as pure sulfur additives for lithiumsulfur batteries, but also be directly added to carbon composite materials to obtain
composite positive electrode materials.
Metal Sulfide
With the gradual enrichment of metal supplied synthesis methods, researchers try
to add it to the positive electrode of lithium-sulfur batteries. Metal sulfides have a
strong affinity for sulfur-containing substances and can well limit the loss of positive
electrode active materials. Lithium sulfide cathode materials have been the most
widely studied of all metal sulfides. Since the sulfur composite positive electrode does
not contain lithium in traditional lithium-sulfur batteries, the lithium metal negative
electrode needs to provide a lithium source. In this way, the lithium negative electrode
will undergo structural changes during the reaction process, causing potential safety
hazards to the lithium-sulfur battery system. Researchers have developed sulfide
materials to replace pure sulfur cathode materials, which has eliminated the impact
of structural changes in lithium metal anodes (e.g., MnS, CuS, ZnS, SnS 2 , and NiS 2 ).
However, sulfides generally have poor conductivity and must be compounded with
other conductive materials.
Other Metal Compounds
Most metal oxides are poorly conductive, so the use of metal oxides alone as cathode
materials for lithium-sulfur batteries may impede electron transport, resulting in
reducing sulfur utilization and rate capability. For example, TiN–S composite positive
electrode has a high conductivity, a strong porous skeleton, and a good adsorption
capacity, and the assembled lithium-sulfur battery shows excellent cycle stability
(Cui et al. 2016). Recent studies have shown that nanostructured metal carbides have
a strong adsorption effect on polysulfides, such as TiC and WC can adsorb polymers
and promote polysulfide reduction reactions. Due to the microcrystalline size (about
25 nm) and a large number of active sites, TiC cathode materials can be used in
lithium-sulfur batteries to improve the cycling performance. It has a steady specific
capacity of 860 mAh g
−1 in 100th cycle (Al Salem et al. 2016), which is instructive
for the next step.
6.5.4.6 Lithium Sulfide Electrode Materials
Lithium sulfide (Li 2 S) as the final discharge product of lithium-sulfur batteries has
attracted attention due to its higher theoretical specific capacity (1166 mAh/g). Li 2 S
does not require metallic lithium as a negative electrode compared to the sulfur
electrode material, which can reduce the safety problems caused by the lithium metal
dendrite. However, its poor electronic and ionic conductivity, and its high solubility in
electrolytes must be solved, the typical methods to use are carbon-coated or porous
Li 2 S-filled materials to improve its electrical conductivity and inhibit polysulfide
from dissolving in the electrolyte.