140
6 Nanomaterials for Batteries
with a potential of above 4.4 V relative to the aluminum current collector (relative
to Li/Li
+ ). LiC(SO 2 CF 3 ) 3 was first prepared by Dominey. It also has good thermal
stability and electrochemical stability. At temperatures above 300 °C, decomposition
begins to occur. It also has good conductivity which is only about 10% smaller
than LiTFSI in the same electrolyte system. When LiC(SO 2 CF 3 ) 3 based organic
electrolytes are used in lithium-ion batteries, there is no corrosion problem for
aluminum or stainless-steel electrode current collectors. This superior stability is
mainly due to LiC(SO 2 CF 3 ) 3 that has a large anion, a steric hindrance effect attached
to the central carbon atom and a high degree of delocalization of the negative charge.
6.2.3.4 New Type Electrolyte Lithium Salt
Although LiPF 6 has good electrical conductivity and oxidation/reduction stability,
meanwhile, LiPF 6 has the disadvantages of poor thermal stability and easy hydrolysis, which has brought considerable difficulties for the production and use of LiPF 6 .
Therefore, finding cheap electrolyte lithium salt as a substitute for LiPF 6 is the development direction of electrolyte lithium salt. The research work in this area mainly
includes two aspects: (1) complex lithium borate compound; (2) complex lithium
phosphate compound.
The complex lithium borate has good environmental friendliness, so it has received
some attention in the research of electrolyte lithium salt. There are more than 10
complex lithium borate compounds that have been studied successively, but the
complex lithium borate compounds have low conductivity, which limits their application. Li-BOB (lithium bisoxalatoborate) is a representative of this type of lithium
salt, and not only has the Al current collector better oxidation stability in LiBOBbased electrolytes than in LiPF 6 -based electrolytes, but also in PC-based electrolytes,
it exhibits a unique SEI film-forming function. The complexed lithium phosphate
compound is basically a new compound formed by replacing fluorine in LiPF 6 with
a trifluoromethyl group or a perfluoroalkyl group. LiFAP(liPF 3 (C 2 F 5 ) 3 ) is a typical
representative of this type of lithium salt. Compared with LiPF 6 , LiFAP has certain
advantages because it does not exist HF, and FAP—has high stability and low reactivity, which prevents the malignant interaction between electrodes and electrolytes
and thus protects the electrode active materials. Although the research and development of new electrolyte lithium salts have achieved a lot of results, LiPF 6 will
still be the main electrolyte lithium salt in consideration of performance, price, and
production process.
6.2.4 Separator
The separator itself is not only a good conductor of electrons, but also has the property
of passing through the electrolyte ions. The separator material must have good chemical and electrochemical stability, good mechanical properties, and high infiltration
6 Nanomaterials for Batteries
with a potential of above 4.4 V relative to the aluminum current collector (relative
to Li/Li
+ ). LiC(SO 2 CF 3 ) 3 was first prepared by Dominey. It also has good thermal
stability and electrochemical stability. At temperatures above 300 °C, decomposition
begins to occur. It also has good conductivity which is only about 10% smaller
than LiTFSI in the same electrolyte system. When LiC(SO 2 CF 3 ) 3 based organic
electrolytes are used in lithium-ion batteries, there is no corrosion problem for
aluminum or stainless-steel electrode current collectors. This superior stability is
mainly due to LiC(SO 2 CF 3 ) 3 that has a large anion, a steric hindrance effect attached
to the central carbon atom and a high degree of delocalization of the negative charge.
6.2.3.4 New Type Electrolyte Lithium Salt
Although LiPF 6 has good electrical conductivity and oxidation/reduction stability,
meanwhile, LiPF 6 has the disadvantages of poor thermal stability and easy hydrolysis, which has brought considerable difficulties for the production and use of LiPF 6 .
Therefore, finding cheap electrolyte lithium salt as a substitute for LiPF 6 is the development direction of electrolyte lithium salt. The research work in this area mainly
includes two aspects: (1) complex lithium borate compound; (2) complex lithium
phosphate compound.
The complex lithium borate has good environmental friendliness, so it has received
some attention in the research of electrolyte lithium salt. There are more than 10
complex lithium borate compounds that have been studied successively, but the
complex lithium borate compounds have low conductivity, which limits their application. Li-BOB (lithium bisoxalatoborate) is a representative of this type of lithium
salt, and not only has the Al current collector better oxidation stability in LiBOBbased electrolytes than in LiPF 6 -based electrolytes, but also in PC-based electrolytes,
it exhibits a unique SEI film-forming function. The complexed lithium phosphate
compound is basically a new compound formed by replacing fluorine in LiPF 6 with
a trifluoromethyl group or a perfluoroalkyl group. LiFAP(liPF 3 (C 2 F 5 ) 3 ) is a typical
representative of this type of lithium salt. Compared with LiPF 6 , LiFAP has certain
advantages because it does not exist HF, and FAP—has high stability and low reactivity, which prevents the malignant interaction between electrodes and electrolytes
and thus protects the electrode active materials. Although the research and development of new electrolyte lithium salts have achieved a lot of results, LiPF 6 will
still be the main electrolyte lithium salt in consideration of performance, price, and
production process.
6.2.4 Separator
The separator itself is not only a good conductor of electrons, but also has the property
of passing through the electrolyte ions. The separator material must have good chemical and electrochemical stability, good mechanical properties, and high infiltration