Lithium hexafluorophosphate

Lithium hexafluorophosphate (LiPFs) is the most frequently used salt in commercially available secondary lithium-ion batteries. As mentioned above, liPFe moderately fulfills most of the required properties. LiPFg is up to now one of the most eflflcient salts in lithium-ion batteries. Its conductivity is similar to that of LiAsFfi in blends of organic solvents (e.g., 10.7 mS-cm in 1 M EC/DMC at ambient temperature [80]). 

Another drawback of LiPFis is its sensitivity to moisture. It produces HF with water and thus prevents the use of Mn-spinels as cathode materials, so great effort has to be undertaken to achieve high purity grades of used solvents and a moisture-free fabrication environment. 

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Anhydrous silver hexafluorophosphate [26042-63-7] AgPF, as well as other silver fluorosalts, is unusual in that it is soluble in ben2ene, toluene, and xylene and forms 1 2 molecular crystalline complexes with these solvents (91). Olefins form complexes with AgPF and this characteristic has been used in the separation of olefins from paraffins (92). AgPF also is used as a catalyst. Lithium hexafluorophosphate [21324-40-3] LiPF, as well as KPF and other PF g salts, is used as electrolytes in lithium anode batteries (qv). 

Lithium hexafluorophosphate is thermally unstable in the solid state [52], where it decomposes at about 30 °C [53], In solvents and solvates it is more stable. Decomposition begins in the range from 80 °C [53] to about 130 °C [13], yielding scarcely soluble LiF and the Lewis acid PF5 which in turn initiates polymerization of cyclic... 

Lithium hexafluoroarsenate is thermally stable [54, 55] but shows environmental risks due to possible degradation products [56-58], even though it is itself not very toxic. Its LD 50 value is similar to that of lithium perchlorate [55]. Just like lithium hexafluorophosphate, it can initiate the polymerization of cyclic ethers. Polymerization may be inhibited by tertiary amines [59], or 2-methylfuran [60], yielding highly stable electrolytes. 

As the electrolyte, 1M solution of Lithium hexafluorophosphate in the mixture of ethylene carbonate and diethyl carbonate (1M LiPF6 EC DEC=1 1 - electrolyte LP-40 by Merck) was used. 

Lithium tetrafluoroborate, (LiBF4), lithium hexafluorophosphate, (LiPF6), lithium hexafluoroarsenate, (LiAsF ), lithium trifluoromethane sulfonate, (LiSOjCFj), are the electrolyte salts of the 21st Century. The performance of lithium ion cells, primary and secondary lithium cells depends on the purity of these compounds. Several hundred tons of these materials have been produced and many more tons — and perhaps thousands of tons — will be required in the near future. One of the largest automotive producers predicts that there may be a market for 10-15 million pounds of these salts. The demand for Lithium ion primary cells is also very huge in electronics, computers, communication systems and military applications. 

Lithium hexafluorophosphate, LiPF6, is prepared by dissolving LiF in AHF and passing PF5 as pure gas or generated in situ as shown below ... 

A high-yielding single step method for preparing poly(9-fluroenone) by electrolyti-cally polymerizing fluorene in the presence of propylene carbonate and lithium hexafluorophosphate is described. 

By using coupled TG-FTIR, direct evidence of the decomposition of lithium hexafluorophosphate has been obtained by Teng et al. [112]. Their studies showed that LiPFg is stable under normal temperature when the content of water... 

LiPFf. Lithium hexafluorophosphate is used almost exclusively in commercial Li-ion batteries. This salt has thus far demonstrated the best balance of essential properties necessary for a primary Li-ion electrolyte salt [12, 40], In aprotic solvents, the resulting electrolytes have some of the highest conductivity values measured. LiPEg-based electrolytes react to form a stable interface with the A1... 

M. Ishikawa, M. Morita, M. Asao, Y. Matsuda, J. Electrochem. Soc. 1994, 141, 1105-1108. Charge/discharge characteristics of carbon fiber with graphite structure in organic electrolytes containing hthium trifluoromethanesulfate and lithium hexafluorophosphate. 

Most liquid electrolytes used in commercial lithium-ion cells are nonaqueous solutions, in which roughly 1 mol dm of lithium hexafluorophosphate (LiPF ) salt is dissolved in a mixture of carbonate solvents selected from cyclic carbonates, e.g., ethylene carbonate (EC) and propylene carbonate (PC), and linear carbonates, e.g., dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), as listed in Table 2.1 [1]. 

The standard composition of an electrolyte in LlBs is a mixture of cycUc carbonates (such as ethylene carbonate (EC) and propylene carbonate (PC)) and chain carbonates (such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC abbreviated as MEC below), and diethyl carbonate (DEC)), to which about 1 mol/L of a lithium salt (such as lithium hexafluorophosphate (LiPF )) is added. Ube Industries, Ltd. discovered that if small amounts of impurities exist in the electrolyte, decomposition current generated from the impurities begins to flow, which leads to the formation of undesirable thick SET This spurred the development of a pioneering high-grade purification process for the base electrolyte in 1997 [16]. High purity is a key feature of functional electrolytes developed by Ube Industries, Ltd. and enables production of transparent and chemically stable electrolytes, in contrast to the conventional electrolytes which were less stable and brown owing to its low purity (Fig. 3.1). 

Another key battery component is the electrolyte. While many possible electrolytes are being developed, we have selected lithium hexafluorophosphate (LiPFe) in a solvent of EC and DMC. Little information exists on the production of LiPFe, so its impact, although estimated on the basis of data presented by Espinosa et al. [12], is somewhat uncertain. Given the potentially harmfiil nature of the compound, it is of interest to consider what its fate may be during the battery recycling process, which we address in Section 4. 

Polyselenophene (Fig. 16c) has been prepared. However, due to the difficulty in obtaining the monomer, the polymer has not been extensively investigated. Polymers of selenophene prepared electrochemically under appropriate conditions yield films with maximum conductivities of 10"- S cm [330,331]. Samples of p-doped selenophene produced chemically have conductivities on the same order of magnitude [332]. Applying 3-10 V between two electrodes in an electrolyte of 0.1 to 1 M lithium tetrafluoroborate or lithium perchlorate dissolved in benzonitrile or propylene carbonate gives polyselenophene films, as does the combination of tetrabutylammonium tetrafluoroborate in benzonitrile. However, other salts such as lithium hexafluoroarsenate, lithium hexafluorophosphate, tetrabutylammonium perchlorate, or silver perchlorate in combination with solvents such as acetonitrile or nitrobenzene were reported to produce either powders or no products at all [330,331,333]. 

The electrolyte solution consists of a lithium salt in an organic solvent. Commonly used salts include lithium hexafluorophosphate, lithium perchlorate, lithium tetra-fluoroborate, lithium hexafluoroarsenate, lithium hexafluorosilicate, and lithium tetraphen)dborate. Organic solvents used in the electrolyte solution are ethylene carbonate, dieth)d carbonate, dimethyl carbonate, methyl ethyl carbonate, and propylene carbonate, to name the most important ones. When a lithium ion battery is charged, the positive lithium ions move from the positive electrode to the negative one. The process to insert the lithium ions into the graphite electrode is called intercalation. When the cell is discharging, the reverse occurs. 

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