6.5 Lithium-Sulfur Battery
185
Carbonate Solvent System
Due to the certain solubility of polysulfide in this system, the active material can have
a high reaction activity in the reaction process, so as to ensure the smooth progress
of the redox reaction. Currently used ether solvents mainly include Tetrahydrofuran
(Cyclic ethers such as THF) and 1–3-dioxolane (DOL); ethylene glycol dimethyl
ether (DME), triethylene glycol dimethyl ether (TGDME) and tetraethylene glycol
dimethyl ether (TEGDME). The results show that chain ethers have good solubility
of polysulfide ions, making the sulfur electrode reaction process proceed smoothly.
In particular, DOL easily undergoes ring-opening polymerization reaction on the
surface of the metal lithium negative electrode, so that it can form a layer of elastic and
stable protective film, which is conducive to improving the stability of metal lithium
during cycling. Therefore, chains and cyclic ethers are often used to improve the
electrochemical performance of lithium-sulfur batteries (Choi et al. 2007). Among
them, DOL and DME are the most commonly used mixed solvents in a volume ratio
of 1:1.
6.5.6.2 Solid Electrolyte
Theoretically, the use of a solid electrolyte can completely avoid the deterioration of the electrochemical performance caused by the dissolution of polysulfide
ions. However, the solid itself has intrinsic defects such as low room temperature
conductivity and large interface contact resistance. It needs to work at relatively high
temperatures, thus limiting its application in lithium-sulfur batteries. If the active
material surface is evenly coated with a solid electrolyte membrane, the problem
of high contact resistance between the active material and the electrolyte in the allsolid-state lithium-sulfur battery can be effectively overcome, and the electrochemical performance of the system is greatly improved. For example, the nanocomposite polymer electrolyte NCPE(PEO 20 LiCF 3 − SO 3 Li 2 S + 10wt% ZrO 2 ) and the
nanoscale Li 2 S − Li 3 PS 4 core–shell structure (Hassoun and Scrosati 2010; Suo et al.
2013).
6.5.6.3 Solvent-In-Salt Electrolyte System
A new type of dual-function electrolyte system “Solvent-in-Salt” (SIS) was proposed
in 2013 and applied in lithium-sulfur batteries. At the same time, two key technical
challenges of dissolving polysulfide ions and stabilizing metal lithium negative electrodes were solved (Fig. 6.23). By using a conventional ether system as a solvent,
lithium salt concentration is greatly increased, and a large amount of free solvent
molecules are complexed with a lithium salt. Also, the dissolution of polysulfide ions
in the electrolyte is effectively suppressed, and the “multi-sulfide ion shuttle effect” of
polysulfide ions dissolved in the electrolyte during charging is avoided. The serious
overcharge of the battery was prevented, the circulating Coulombic efficiency was
185
Carbonate Solvent System
Due to the certain solubility of polysulfide in this system, the active material can have
a high reaction activity in the reaction process, so as to ensure the smooth progress
of the redox reaction. Currently used ether solvents mainly include Tetrahydrofuran
(Cyclic ethers such as THF) and 1–3-dioxolane (DOL); ethylene glycol dimethyl
ether (DME), triethylene glycol dimethyl ether (TGDME) and tetraethylene glycol
dimethyl ether (TEGDME). The results show that chain ethers have good solubility
of polysulfide ions, making the sulfur electrode reaction process proceed smoothly.
In particular, DOL easily undergoes ring-opening polymerization reaction on the
surface of the metal lithium negative electrode, so that it can form a layer of elastic and
stable protective film, which is conducive to improving the stability of metal lithium
during cycling. Therefore, chains and cyclic ethers are often used to improve the
electrochemical performance of lithium-sulfur batteries (Choi et al. 2007). Among
them, DOL and DME are the most commonly used mixed solvents in a volume ratio
of 1:1.
6.5.6.2 Solid Electrolyte
Theoretically, the use of a solid electrolyte can completely avoid the deterioration of the electrochemical performance caused by the dissolution of polysulfide
ions. However, the solid itself has intrinsic defects such as low room temperature
conductivity and large interface contact resistance. It needs to work at relatively high
temperatures, thus limiting its application in lithium-sulfur batteries. If the active
material surface is evenly coated with a solid electrolyte membrane, the problem
of high contact resistance between the active material and the electrolyte in the allsolid-state lithium-sulfur battery can be effectively overcome, and the electrochemical performance of the system is greatly improved. For example, the nanocomposite polymer electrolyte NCPE(PEO 20 LiCF 3 − SO 3 Li 2 S + 10wt% ZrO 2 ) and the
nanoscale Li 2 S − Li 3 PS 4 core–shell structure (Hassoun and Scrosati 2010; Suo et al.
2013).
6.5.6.3 Solvent-In-Salt Electrolyte System
A new type of dual-function electrolyte system “Solvent-in-Salt” (SIS) was proposed
in 2013 and applied in lithium-sulfur batteries. At the same time, two key technical
challenges of dissolving polysulfide ions and stabilizing metal lithium negative electrodes were solved (Fig. 6.23). By using a conventional ether system as a solvent,
lithium salt concentration is greatly increased, and a large amount of free solvent
molecules are complexed with a lithium salt. Also, the dissolution of polysulfide ions
in the electrolyte is effectively suppressed, and the “multi-sulfide ion shuttle effect” of
polysulfide ions dissolved in the electrolyte during charging is avoided. The serious
overcharge of the battery was prevented, the circulating Coulombic efficiency was