Electrolyte Optimization of a Substituted-LiCo1-xFexPO4 Cathode
An alternative approach involves the use of electrolyte additives for improved passivation layer formation (2-3). This approach, however, does not affect any structural changes that may occur within the cathode (i.e., additives are not as effective in stabilizing the cathode structure as doped metals). The use of additives can nevertheless improve the high-temperature performance of the cell and ensure a longer cycle life (4).
This study utilizes a joint cathode/electrolyte research approach. A next-generation LiCoPO4-doped cathode was used (developed by ARL) that is less insulating than traditional LiCoPO4, as indicated by a shorter CV step requirement. Various electrolyte additives were examined with the new cathode to further optimize the performance. These additives include tris(hexafluoro-iso-propyl)phosphate (HFiP), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), fluoroethylene carbonate (FEC) and Trimethylboroxine (TMB). While investigating the properties of the new cathode material, the electrolyte mixture was optimized for high-capacity cycling. This study has yielded a high-efficiency cell with a long cycle-life that is stable at room temperature and elevated temperatures.
The authors wish to express their gratitude to the DOE ABR program for partial financial support.
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