LiDFOB

V. Aravindan, P. Vickraman, K. Krishnaraj, Curr. Appl. Phys. 2009, 9, 1474-1479. Li ion conduction in Ti02 filled polyvinyUdenefluoride-co-hexafluoropropylene based novel nanocomposite polymer electrolyte membranes with LiDFOB. 

J. L. Allen, S.-D. Han, P. D. Boyle, W. A. Henderson, J. Power Sources 2011, 196, 9737-9742. Crystal structure and physical properties of lithium difluoro(oxalato)borate (LiDFOB or LiBF20x). 

L. Zhou, W. Li, M. Xu, B. Lucht, Electrochem. Solid-State Lett. 2011, 14, A161-A164. Investigation of the disproportionation reactions and equilibrium of lithium difluorofoxalato) borate (LiDFOB). 

M. Xu, L. Zhou, L. Hao, L. Xing, W. Li, B. L. Lucht, J. Power Sources 2011,196,6794-6801. Investigation and application of lithium difluoro(oxalate)borate (LiDFOB) as additive to improve the thermal stability of electrolyte for lithium-ion batteries. 

Y. Zhu, Y. Li, M. Bettge, D. P. Abraham, J. Electrochem. Soc. 2012, 159, A2109-A2118. Positive electrode passivation by LiDFOB electrolyte additive in high-capacity lithium-ion cells batteries and energy storage. 

M. Hu, J. Wei, L. Xing, Z. Zhou, J. Appl. Electrochem. 2012, 42, 291-296. Effect of hthium difluoro(oxalate) borate (LiDFOB) addihve on the performance of high-voltage hthium-ion batteries. 

Lithium difluoro(oxalato)bQrale (LiDFOB, 8, Hg. 2.18) also shows the same effect as the additive for an electrolyte [74], Lithium bis[salicylato(2-)] borate (LiBSB, 9) [75], lithium bis[croconate]-borate (LiBCB, 10) [76], and lithium bis[l,2-... 

MD simulations were used to study a number of electrolytes of potential interest to lithium battery applications EC DMC/LiPEg [52], EC/LiTESI [53, 54], DMC/ LiTFSI [55], GBL/LiTFSI [55], and acetonitrile doped with LiPEg, LiC104, L1BF4, LiDFOB, LiTFSI [56-58], oligoethers/Li salts [59-61], acetamide/LiTFSI [62],... 

An analogue of LiDFOB is lithium tetrafluoro(oxalato)phosphate (LiPF4C204, or LiFOP), in which phosphorous is the coordination center. This salt was initially synthesized by Prof. Brett Lucht s group at the University of Rhode Island. It has... 

Han S-D, Allen JL, Boyle PD, Henderson WA (2012) Delving into the properties and solution stiucture of nitrile-lithium difluoro(oxalato)borate (LiDFOB) electrolytes for Li-ion batteries. ECS Trans 41 47-51. doi 10.1149/1.4717962... 

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... 

Other than FEC, VC has also been shown to improve Si anode performance [21,22, 35,103], although in some cases the improvement is not as prominent as that of FEC. If FEC indeed protects the Si anode through the VC mechanism, then the LiF generated through the first elimination step may have some positive effect on the Si anode as well. Other additives that work on the Si anode include LiDFOB [35], succinic anhydride [80], alkoxysUanes [108, 118] and tris(pentalluorophenyl) borane [47]. 

Besides LiBOB, other additives have been reported to protect the high voltage cathode and mitigate electrolyte decomposition, including LiDFOB [162], succinic anhydride [66, 122], 1,3-propane sultone [66], tris(hexafluoro- o-propyl) phosphate [127], tris(pentafluorophenyl) phosphine [156], 3-hexylthiophene [3], 1,3-propanediolcyclic sulfate [41], dimethylacetamide [13], triethyl(2-methoxyethyl) phosphonium bis(trifluoromethylsulfonyl)imide [13], glutaric anhydride [16], 4-(trifluoromethyl)-benzonitrile [55], and 1-propylphosphonic acid cyclic anhydride [ 160]. The stmctures of the additives that are not listed in the previous text are shown in Fig. 8. 

The additive research for LiCoP04 is sparser. Few examples include LiBOB [9], shown to mitigate capacity fade at 3 %, LiDFOB [53], which increased capacity retention at 40 cycles from 34 to 69 % at a 5.1 V cut-off potential, and thiophene [152], which increased capacity retention from 15 to 68 % after 30 cycles. Sharabi et al. [Ill] reported that FEC-containing electrolytes with a small amount (0.5-1 %) of trimethlyboroxine additive allowed for 90 % capacity retention after 100 cycles with a 5.2 V cut-off potential. 

Hu M, Wei J, Xing L, Zhou Z (2012) Effect of lithium difluoro(oxalate)borate (LiDFOB) additive on the performance of high-voltage lithium-ion batteries. J Appl Electrochem 42 291-296. doi 10.1007/sl0800-012-0398-0... 

Lithium difluoro(oxaIato)borate (LiDFOB) and lithium bis(fluorosulfonyl)imide (LiFSI) are two promising candidates for lithium ion batteries. Erom previous studies it was obvious that increasing asymmetry of anions would increase both solubility and conductivity of dissolved salts. Therefore, this group synthesized lithium difluoro(oxalato)borate (LiDEOB) [517, 518]. Eor its electrochemical characterizations, see Refs. [181, 530]. 

It is interesting to note that LiDFOB also follows this hydrolysis route and, most importantly, does not produce HF but only borates including BF4, as shown by time-dependent B and F-NMR analysis [181]. 

Figure 17.8 shows the electrochemical behavior of liPFe and the chelatoborates liDFOB and LiBOB atan Al-foil WE all three salts exhibitgood passivation of Al. At lower potentials, the current density i in the first cycle is very low and increases in the case of Li P Fj, first at 3.5 V and above vs Li/ Li due to electrolyte decomposition, much later with LiDFOB from 4.0 to 4.12 V (LiBOB) at an onset current density of 0.25 xA Cm . After reaching a maximum, a constant current appears that decreases further at the re-scan. This shows the formation of a protecting layer on the Al surface. This fact is also proved by the subsequent cycles, which show much later oxidative reactions. The resulting oxidation potential Eox of all three salts after passivation is about 4.9 V vs Li/Li+. LiBOB reaches this value after the third cycle. 

It is worth mentioning that corrosion processes can be investigated in more detail by the use of the electrochemical quartz crystal micro balance (EQCM) [291, 292). Mass changes on the electrode result in very sensitive changes in the resonance frequency of the quartz crystal. Increase of mass, for example, passivation by LiPF or LiDFOB, results in frequency decrease (see Figure 17.8b), whereas corrosion of the surface due to LiOTf is accompanied by mass decrease and a strong frequency increase (see Figure 17.9b) [243]. 

The thermal decomposition temperature of LiPF is low (30°C), and it decomposes easily into PFg and LiF. When it is dissolved in pure solvents, its decomposition temperature rises to 80-130°C, which can avoid the decomposition and polymerization of the electrolyte. In addition, the ionic conductivity of high purity LiPFg in an organic solvent is maximal. It is still the most used lithium salt for lithium-ion battery electrolytes, but LiBOB, LiDFOB, and some organic lithium salts can be used as additives. 

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