Lithium-based cells

The use of LiBF4 in lithium-based cells has been rare because of its inferior ion conductivity until recently, when the thermal instability of LiPEe and the moisture sensitivity became recognized. Attempts to replace LiPEe in lithium ion cells have been made, and the cells based on LiBE4 electrolytes showed improved performance, not only at elevated temperatures up to 50 but, surprisingly, also at low temperatures as well. These observations could bring this salt back to research favor. 

Polymer electrolytes intended for applications in lithium-based cells could be roughly divided into two major classifications (1) those based on neat high polymers, which serve as both solvent to dissolve lithium salts and mechanical matrix to support... 

In lithium-based cells, the essential function of battery separator is to prevent electronic contact, while enabling ionic transport between the positive and negative electrodes. It should be usable on highspeed winding machines and possess good shutdown properties. The most commonly used separators for primary lithium batteries are microporous polypropylene membranes. Microporous polyethylene and laminates of polypropylene and polyethylene are widely used in lithium-ion batteries. These materials are chemically and electrochemically stable in secondary lithium batteries. 

M. Doyle and J. Newman [1995] Modeling the Performance of Rechargeable Lithium-Based Cells Design Correlations for Limiting Cases, Journal of Power Sources, 54, 46-51. 

Alkaline Primary Cells, Fig. 8 Capacity loss on storage of various miniature alkaline cell systems compared to carbon-zinc and lithium-manganese dioxide cells. The lithium-based cells have significantly better storage characteristics compared to alkaline and carbon-zinc cells... 

This Li/CuO cell has an open-circuit voltage of 1.5 V and has the highest specific energy of all solid cathode lithium-based cells. Practical value of 750 W h dmr is obtained. The liquid electrolyte varies from manufacturer to manufacturer, but LiC104 in dioxolane is very often used. The cylindrical cells manufactured by SAFT have practical capacities in the range 0.5 to 3.9 A h. 

CHARACTERIZATION OF ANODES BASED ON VARIOUS CARBONACEOUS MATERIALS FOR APPLICATION IN LITHIUM-ION CELLS... 

This constitutes an interesting industrial problem, since compounds with chemical formula LixMn204 (crystal cell cubic, 0.82 nm space group Fd3m) are found to have interesting electrochemical properties depending on the Li stoichiometry in the structure". This material has a wide potential and it is used for Lithium -based batteries in cell phone applications. 

For the convenience of this discussion, a somewhat arbitrary demarcation was drawn between state-of-the-art (SOA) and novel electrolyte systems, with the former referring to the ones currently used in commercialized lithium ion cells and the latter to the ones improved over the SOA systems but still under development. It should be pointed out that the exact electrolyte compositions in commercialized devices are usually proprietary knowledge, but publications from the affiliated researchers normally disclose sufficient information to reveal the skeletal electrolyte components employed. The distinction made in this review concerning the previously mentioned demarcation is based on such open literature. 

Solid polymer and gel polymer electrolytes could be viewed as the special variation of the solution-type electrolyte. In the former, the solvents are polar macromolecules that dissolve salts, while, in the latter, only a small portion of high polymer is employed as the mechanical matrix, which is either soaked with or swollen by essentially the same liquid electrolytes. One exception exists molten salt (ionic liquid) electrolytes where no solvent is present and the dissociation of opposite ions is solely achieved by the thermal disintegration of the salt lattice (melting). Polymer electrolyte will be reviewed in section 8 ( Novel Electrolyte Systems ), although lithium ion technology based on gel polymer electrolytes has in fact entered the market and accounted for 4% of lithium ion cells manufactured in 2000. On the other hand, ionic liquid electrolytes will be omitted, due to both the limited literature concerning this topic and the fact that the application of ionic liquid electrolytes in lithium ion devices remains dubious. Since most of the ionic liquid systems are still in a supercooled state at ambient temperature, it is unlikely that the metastable liquid state could be maintained in an actual electrochemical device, wherein electrode materials would serve as effective nucleation sites for crystallization. 

This new formulation of electrolytes based on a mixture of EC with a linear carbonate set the main theme for the state-of-the-art lithium ion electrolytes and was quickly adopted by the researchers and manufacturers. Other linear carbonates were also explored, including DEC, ° ethylmethyl carbonate (EMC), ° and propylmethyl carbonate (PMC), ° ° and no significant differences were found between them and DMC in terms of electrochemical characteristics. The direct impact of this electrolyte innovation is that the first generation carbonaceous anode petroleum coke was soon replaced by graphitic anode materials in essentially all of the lithium ion cells manufactured after 1993. At present, the electrolyte solvents used in the over one billion lithium ion cells manufactured each year are almost exclusively based on the mixture of EC with one or more of these linear carbonates, although each individual manufacture may have its own proprietary electrolyte formulation. 

On the other hand, sulfonate (—SOsLi) became the anion of choice because it is highly resistant to oxidation, thermally stable, nontoxic, and insensitive to ambient moisture as compared with LiPFe or LiBp4. As the simplest member of this category (Rp = CFs), lithium triflate (LiTf) received extensive research as a candidate for lithium/lithium ion cells. Other similar salts studied include perfluoroethyl sulfonate (Rp = C2F5), perfluorobutylsulfonate (Rp = and the oligomeric versions that are based on polyether linkages. 

Despite all of these merits, the application of Lilm in lithium ion cells never materialized because it caused severe A1 corrosion in electrolytes based on it. " In situ surface studies using EQCM established a reaction between the Im anion and the A1 substrate in which Al(Im)3 is produced and adsorbed on the A1 surface. Undoubtedly, this corrosion of a key component of the cell by Im greatly restricts the possible application of Lilm, because the role of A1 as a cathode substrate in the lithium-based battery industry is hard to replace, due to its light weight, resistance to oxidation at high potential, excellent processability, and low cost. 

After more than a decade of exploration, the skeletal components of the electrolyte for the commercialized lithium ion devices have been identified. Within the various brands of lithium ion cells, the exact electrolyte composition differs from manufacturer to manufacturer, and the formulas remain proprietary information however, the overwhelming majority of these are apparently based on two indispensable components EC as the solvent and LiPFe as the solute. In most cases, one or more linear carbonates, selected from DMC, DEC, or EMC, are also used as cosolvents to increase the fluidity and reduce the melting point of the electrolyte, thus forming the popular composition consisting of LiPFe/ EC/linear carbonate (s). 

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