Electrolyte fire retardants

Hexafluorozirconic acid is used ia metal finishing and cleaning of metal surfaces, whereas the fluorozirconates are used in the manufacture of abrasive grinding wheels, in aluminum metallurgy, ceramics industry, glass manufacturing, in electrolytic cells, in the preparation of fluxes, and as a fire retardant (see Abrasives Metal surface treati nts). 

Corrosion inhibitors Cosmetics, drugs Electrical insulation Electrolytic refining Fertilizers Fire retardants Glass and glass wool Herbicides Insecticides Leather tanning Photography Textile dyes Wax emulsifier Wool preservatives... 

Zinc in contact with wood Zinc is not generally affected by contact with seasoned wood, but oak and, more particularly, western red cedar can prove corrosive, and waters from these timbers should not drain onto zinc surfaces. Exudations from knots in unseasoned soft woods can also affect zinc while the timber is drying out. Care should be exercised when using zinc or galvanised steel in contact with preservative or fire-retardant-treated timber. Solvent-based preservatives are normally not corrosive to zinc but water-based preservatives, such as salt formulated copper-chrome-arsenic (CCA), can accelerate the rate of corrosion of zinc under moist conditions. Such preservatives are formulated from copper sulphate and sodium dichromate and when the copper chromium and arsenic are absorbed into the timber sodium sulphate remains free and under moist conditions provides an electrolyte for corrosion of the zinc. Flame retardants are frequently based on halogens which are hygroscopic and can be aggressive to zinc (see also Section 18.10). 

Borax decahydrate occurs in nature as mineral, borax (tincal). It is one of the most common sodium borate ores. The compound has several industrial applications. The refined material is mostly used in household cleaning products. It is used to make pyrex and other horosilicate glasses. Borax is added to fertilizers in small quantities as a source of boron, as a trace nutrient for plants. High purity grade borax is used in cosmetics, toilet products and electrolytic capacitors. It also is used in fire retardants, adhesives and herbicides. 

Other recent developments include the incorporation of a fire retardant, which retards the combustion of the solvent, and a new additive to improve the wetting of the separator. It is difficult to use these additives in the gel-type electrolytes employed in lithium-ion polymer cells. This may be one reason for the lower market share experienced by lithium-ion polymer cells. 

To improve the safety of Li+-ion batteries, some efforts also have been focused on the development of nonflammable electrolytes. One easy approach is the addition of fire retardants into the electrolytes. " ... 

Organic compounds that contain C-F bonds generally show nonflammability or fire-retardant property. Thus, fluoroalkyl-ethers and -esters have been attempted as nonflammable or flame-retardant solvents for LIB electrolytes [88, 89,113]. Fluorinated alkylphosphates, or fluoroalkylphosphates, have higher flame-retardant properties than the corresponding alkylphosphates. Jow and co-workers [104, 114-116] reported a series of fluoroalkylphosphate, i.e., tris(2,2,2-trifluoroethyl) phosphate (TEP), bis(2,2,2-trifluoroethyl)-methyl phosphate (BMP) and (2,2,2-trifluoroethyl)-diethyl phosphate (TDP) (Fig. 2.24), as nonflammable additives or co-solvents of... 

Fig. 2.25 Comparison in flammability of the electrolyte solutions with different fire-retardant...

Feng, J. K. Yao, Y. L. Ai, X. P. Yang, H. X., Tri-(4-methokythphenyl) phosphate a new electrolyte additive with both fire-retardancy and overchaige protection for li-ion batteries,... 

Morford, R. V KeUam III, E. C. Hofmann, M. A. Aflcock, H. R., A fire-retardant oigano-phosphorus gel polymer electrolyte additive for use in rechargeable lithium batteries. Solid State Ionics 2000,133, 171-177. 

Feng JK, Cao YL, Ai XP, Yang HX (2008) Tri-(4-methoxyphenyl) phosphate a new electrolyte additive with both fire-retardancy and overcharge protection for Li-ion batteries. Electrochim Acta 53 8265-8268. doi 10.1016/j.electacta.2008.05.024... 

Research on PAN-based electrolytes started in 1975. PAN attracted much attention due to its simple s)mthesis, good stability, high heat resistance, and fire-retardant property. 

Trimethyl phosphate (TMP) has widespread industrial uses as a fire retardant in plastics production, thus TMP-based electrolytes might be expected to exhibit good performance with no risk of flame. Wang et al. [40] introduced the mechanism underlying flame retardation as follows ... 

Safety and Hazards. The linear carbonate solvents are highly flammable with flash points usually below 30 °C. When the lithium ion cell is subject to various abuses, thermal runaway occurs and causes safety hazards. Although electrode materials and their state-of-charge play a more important role in deciding the consequences of the hazard, the flammable electrolyte solvents are most certainly responsible for the fire when a lithium ion cell vents. The seriousness of the hazard is proportional to the size of the cell, so flame-retarded or nonflammable lithium ion electrolytes are of special interest for vehicle traction batteries. 

Carbon pitch is used for carbon electrodes in electrolytic reduction processes, such as aluminum reduction or the production of electro-steels in arc furnaces. Refractory pitch is used in the manufacture of refractory brick, usually burned magnesite or dolomite, the pores of which are filled with pitch by hot impregnation. Upon firing, the pitch in the brick is converted to carbon by carbonization. The remaining pitch coke within the refractory product retards penetration of molten metals and slags, thus prolonging the life of the brick furnace lining. Coke pitch is used in the production of foundry cores. 

Flame retardant additives are added to the electrolyte to inhibit or delay the onset of radical propagation reaction and prevent the spread of fire when a thermal runaway occurs in a battery. Flame retardant additives have been widely used in other areas such as the plastics and coating industry, and battery flame retardant additives are designed with the same principle. However, more stringent requirements are applied to the battery additives, as the additives must be electrochemically inert, and preferably would have a positive effect on the battery performance. 

Erom the discussion in Section 11.1, it follows that carbonates such as EC, PC, DEC, and DMC can be used as common plasticizers for PAN-based gel elecfrolyfes. Ofher kinds of plasticizer can also be added, for example, ladderlike small molecules confaining -C=N groups, which can favor dissociation of the lithium salt, separation of Li+ ions by the PAN chains, an increase in the ionic conductivity, and reduction of polarization. When a composite plasticizer is added, the ionic conductivity at room temperature may be as high as 4 X IQ- S/cm, with a lithium-ion transference number of 0.6-0.7. However, at high temperature, PAN will cyclize and form a cross-linked structure or carbonize, but will not catch fire, so that gel electrolytes based on PAN have good flame retardant ability. It also reacts with water renmants in the solvents to produce poisonous hydrogen cyanide. 

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