Electrolytes anion receptors

A variety of organoboron polymer electrolytes were successfully prepared by hydroboration polymerization or dehydrocoupling polymerization. Investigations of the ion conductive properties of these polymers are summarized in Table 7. From this systematic study using defined organoboron polymers, it was clearly demonstrated that incorporation of organoboron anion receptors or lithium borate structures are fruitful approaches to improve the lithium transference number of an ion conductive matrix. 

Unfortunately, these aza-ethers showed limited solubility in the polar solvents that are typically preferred in nonaqueous electrolytes, and the electrochemical stability window of the LiCl-based electrolytes is not sufficient at the 4.0 V operation range required by the current state-of-the-art cathode materials. They were also found to be unstable with LiPFe. Hence, the significance of these aza-ether compounds in practical applications is rather limited, although their synthesis successfully proved that the concept of the anion receptor is achievable by means of substituting an appropriate core atom with strong electron-withdrawing moieties. 

X. Sun, H. S. Lee, S. Lee, X. Q. Yang, J. McBreen, Electrochem. Solid-State Lett. 1998, 1, 239-240. A novel lithium battery electrolyte based on Uthium fluoride and a tris(pentafluorophenyl) borane anion receptor in DME. 

Lee HS, Yang XQ, Sun X, McBreen J (2001) Synthesis of a new family of fluorinated boronate compounds as anion receptors and studies of their use as additives in lithium battery electrolytes. J Power Sources 97-98 566-569... 

LiLF, Lee HS, LiH, YangXQ, Nam KW, Yoon WS, McBreen J, Huang XJ (2008) New electrolytes for lithium ion batteries using LiF salt and boron based anion receptors. J Power Sources 184 517-521... 

LiF. This eonfirms that PFPTFBB is a bifunetional electrolyte additive, serving as both redox shuttle and anion receptor [17]. 

Boron-containing compounds, especially those with only three substitutions, are mostly known for their functions as anion receptors. However, some of these compounds are also capable of forming an SEl, making them bi-functional additives [78]. The lithium salts with tetra-substituted boron anions such as LiBOB and LiDFOB can serve as SEI-forming additives in electrolytes based on other salts... 

While additives meant to improve the SEl certainly constitute a major portion of the additive research for Li-ion batteries, many other additives aim to improve different aspects of the Li-ion batteries, such as the safety characteristics, ionic conductivity of the electrolyte, and high/low temperature performance of the electrolyte. For example, researchers have developed redox shuttle and overcharge shutdown additives to protect the battery from overcharge and the resulting thermal mnaway, flame retardant additives to reduce the flammability of the electrolyte, and anion receptors to enhance the ionic conductivity and increase the lithium transference number. These additives may not be critical to the cell performance, but may be very important and possibly necessary in commercial batteries. 

Ion receptors are developed to bind to the cations or anions of the lithium salt in the electrolyte to promote ion dissociation and, therefore, increase ionic conductivity of the electrolyte. Although both cation and anion receptors have been shown to improve the ionic conductivity of electrolytes, cationic receptors slow down the mobility of Li" and, hence, reduce the Li ion transference number. In contrast, anion... 

As mentioned above, the primary purpose of anion receptors is to increase the ionic conductivity and Li ion transference number, although in some battery systems, the conductivity cannot be improved [73]. However, even in the early days of anion receptor research, researchers found other uses of these interesting molecules. To begin with, anion receptors can greatly increase the solubility of salts that are otherwise almost insoluble in organic electrolytes, such as LiF [70, 119, 138], Li20, and Li202 (Fig. 10) [150]. Electrolytes based on these salts that are traditionally... 

Xie B, Lee HS, Li H, Yang XQ, McBreen J, Chen LQ (2008) New electrolytes using Li20 or Li202 oxides and tris(pentafluorophenyl)borane as boron based anion receptor for lithium batteries. Electrochem Commun 10 1195-1197. doi 10.1016/j.elecom.2008.05.043... 

Alkyl-substituted and phenyl-substituted borate anion receptors have been investigated as electrolyte additives in lithium-ion batteries (58). These compoimds, triphenyl borate and trimethyl borate, are shown in Figure 2.12. 

The behavior of the anion receptor TPEPB in a 1 M LiCl04 electrolyte in EC/DMC (1/2.5 v/v) was studied by Lee et al. [425]. The transference number of the lithium cation was enhanced by increasing the TPFPB content from 0.22 (0 M TPFPB) to 0.55 (0.1 M TPFPB), measured by the potentiostatic polarization method of Bruce and Vincent (see Section 17.4.6.4). The total ionic conductivity decreased due to the decreasing anionic conductivity, but the cationic conductivity increased. The interaction between TPFPB and Cl04, resulting in formation of a complex and advanced dissociation of LiCl04, was shown by FTIR analysis. 

X 10 S cm". This approach is seemingly espedally useful for battery electrolytes, because the transference number of the lithium ion is increased recently, Weng et al. [519] reported an improved synthesis of tetrafluoro-catechol [105] that is a starting material for the fluorinated boronate ester, 2-(pentafluorophenyl)-tetrafluoro-l,3,2-benzodioxaborole (PFPTFBB). PEPTEBB acts as an anion receptor. In addition, it is an effective redox shuttle for overcharge protection of lithium-ion batteries. Conceptually, this approach is similar to the use of lithium salts with large anions or the immobilization of anions at polymer backbones. 

Sun X, Lee HS, Yang XQ, McBreen J (2002) LFsing a boron-based anion receptor additive to improve the thermal stability of LiPFe-based electrolyte for lithium batteries. Electrochem Solid State Lett 5 A248-A251... 

Lee HS, Yang XQ, Nam KW, Wang X (2012) Huorinated arylboron oxalate as anion receptors and additives for non-aqueous battery electrolytes. US Patent 2012/0183866 A. Accessed 19 July 2012... 

Obtained in acetonitrile solution containing 0.2 mol dm-3 BuJNBF4 as supporting electrolyte. Solutions were 1 x 10-3 mol dm 3 in receptor and potentials were obtained with reference to an Ag/Ag electrode. Coulometric investigations suggest Et values represent a two-electron reduction process. b Cathodic shift in reduction potential produced by presence of anions (up to 4 equiv) added as their tetrabutylammonium salts. Precipitation of complex observed no CV could be obtained. Obtained in acetonitrile solution. 

Electrolyte stimulation is chiefly a function of monovalent cations in all animals that have been studied. Consequently, the receptor sites are thought to he anionic The pH relationships of stimulation also indicate that strongly acidic (e.g.. PO, or SOj- ) receptor groups are involved. Calculations... 

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