Improvements on High Temperature Lithium Oxyhalide Primary Battery for Downhole Tools Power Applications

Abstract Commercial lithium oxyhalide batteries have a very flat voltage curve. It is challenging to determine a battery's remaining capacity during and after powering downhole drilling tools. It is wasteful and environmentally hazardous to dispose of lightly used battery packs. Through innovations in battery cell design and electrolyte formulation, laboratory cells showed multiple voltage plateaus allowing easy estimation of remaining capacity at room temperature. Prototyped DD-size batteries validated the unique feature at high temperatures. If the batteries are used in downhole drilling and measurement tools, non-productive time may be shortened, and costs reduced over time. Small coin cells were assembled in an inert argon gas filled glovebox. The assembled coin cell, lithium metal foil disk, carbon electrode, and other cell components were weighted to determine electrolyte weight accurately. Carbon black electrodes were prepared by coating carbon black paste on nickel foam substrate. After overnight air drying, coated nickel foam was hot pressed to 1 mm thickness at 230 °C. DD-size cells were prototyped at a battery vendor with selected cell configurations. Performance of coin cells and prototyped DD-size cells were measured during constant current discharge tests. Discharge voltage curves of baseline coin cells mimicking commercial battery products were flat at 3.4 until sudden voltage crash at the end of discharge. Coin cells OP-33 and OP-36, with the improved design and electrolyte formula, showed two main voltage plateaus. The higher voltage plateau was around 3.85-3.60 V, and the lower voltage plateau was around 3.50-3.40 V. The sharp voltage transition from 3.60 V to 3.50 V was easy for a user or a battery management system to detect. Capacity percentage in the higher voltage plateau and the lower voltage plateau depends on the energy active chemical compositions of electrolyte. A cell design and electrolyte formulation were selected to prototype scaled-up DD-size cells. Three repeating DD-size cells were discharged at 150 °C. The overall sloping voltage curves and the obvious voltage transition between two discharge stages around 3.5 V can greatly facilitate battery capacity estimation. As of today, there is no commercial high temperature lithium oxyhalide primary battery with such a unique feature of staged and sloping battery voltage shape for capacity estimation. Compared to capacity estimation by charge counting method utilized in some battery monitoring chips, capacity estimation based on voltage change is much simpler, more accurate, and consumes less battery energy without needs of frequent current measurement and charge calculation. Any previously lightly discharged battery pack can be easily determined whether further usage is possible for the next downhole tools power application, which saves cost and reduces battery waste.