Lithium-Carbon Fluoride Battery

The lithium-carbon fluoride (Li-CFJ battery offers impressive capabilities in terms of energy density of 500 to 700 Wh/kg or 700 to 1,000 Wh/L and a wide operating temperature range from -60° to 160°C. Its major performance capabilities and potential applications can be summarized as follows  

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Lithium functions as the anode in the battery s chemical system. When considering using lithium batteries, it is crucial to take a look at the material used for the cathode. There are a number of cathode and depolarizer materials used in conjunction with the lithium metal anode to make up the generic term lithium batteries. These materials, which include manganese dioxide, sulphur dioxide, carbon fluoride, thionyl chloride and lead iodide, greatly influence the properties and characteristics of lithium batteries (Table 38.2). 

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

Some of the earliest concepts came from Japan, where Matsuchita developed the Li/(CF) battery that was used, for example, in fishing floats. Lithium fluoride and carbon are the final reaction products, but the cell potential of 2.8—3.0 V suggests a different electrochemical reaction. It was proposed that lithium initially intercalates the carbon monofluoride lattice and subsequently the lithium fluoride is formedF Li + (CF)n — L CF)n C + LiF. Although much work... 

Fluorination of graphite at high temperature (300-500° C) gives a white powder which approximates to the composition (CF) . X-ray studies indicate that the fluorine atoms are strongly bonded to carbon but are contained between the graphite layers [140]. Graphite fluorides have similar properties to PTFE and have been exploited commercially as speciality lubricants and in high-performance lithium batteries [141]. 

Chen ZH, Christensen L, Dahn JR (2004) Mechanical and electrical properties of poly (vinylidene fluoride-tetrafiuoroethylene-propylene)/super-S carbon black swelled in liquid solvent as an electrode binder for lithium-ion batteries. J Appl Polym Sci 91 2958-2965... 

To overcome the stability problem, it is obvious that an alternative approach to material synthesis would be needed. In this respect a recent report suggested that iron oxide encapsulated in meso- and macroporous carbon can be used as anode in Li batteries and reaches a greatly improved reversibility and rate performance. At the same time, a similar structure for a cathode material based on iron and lithium fluoride was synthesized and investigated. It was demonstrated that encapsulation of transition metal-metal fluoride in nanocarbon might be an effective strategy to improve the cycling performance of such a cathode material. ... 

Inappropriate matching of the physicochemical properties of the binder with the carbon material may influence dramatically upon the electroactive area via blocking of the SPE film or simply decreasing the electroactive surface area. Another point to be considered is the cost of the binders. For example, fluoropolymers such Nafion, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are commonly used as binder in electrode preparation in the field of lithium-ion batteries or fuel cells. However, the curing process has to be soft in most cases... 

The electrochemically active electrode materials in Li-ion batteries are a lithium metal oxide for the positive electrode and lithiated carbon for the negative electrode. These materials are adhered to a metal foil current collector with a binder, typically polyvinylidene fluoride (PVDF) or the copolymer polyvinylidene fluoride-hexafluroropropylene (PVDF-HFP), and a conductive diluent, typically a high-surface-area carbon black or graphite. The positive and negative electrodes are electrically isolated by a microporous polyethylene or polypropylene separator film in products that employ a liquid electrolyte, a layer of gel-polymer electrolyte in gel-polymer batteries, or a layer of solid electrolyte in solid-state batteries. 

Carbonate-based electrolytes are used in lithium-ion batteries. The main components of the SEI are Li2C03, lithium oxides, and lithium alkyl carbonate (R0C02Li). When a fluoride is used as supporting salt for the electrolyte, the SEI film usually contains LiF. If LiC104 is used, the SEI film will contain Cl. Their detailed SEI contents are related to the electrolyte composition. 

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