Polymer-based solid electrolyte with ultra thermostability exceeding 300 °C for high-temperature lithium-ion batteries in oil drilling industries

High-temperature lithium-ion batteries (HLBs) are a crucial component in logging while drilling (LWD) equipment, facilitating the date acquisition, analysis, and transmission in myriametric deep formation. Conventional batteries are unable to guarantee a reliable power supply for LWD operations in extreme high-temperature conditions encountered at depths exceeding 10,000 m. Moreover, the development of dedicated batteries for these applications is progressing at a relatively slow pace. In light of these considerations, we put forth a novel proposal: a composite solid-state electrolyte (CSE) for HLB. Poly (ether ether ketone) (PEEK) nanofiber membranes, which are thermally stable at temperatures exceeding 350 °C, were prepared and subsequently composited with Li₇La₃Zr₂O₁₂ (LLZO) by the vacuum filtration method. At room temperature, the PEEK-LLZO composite exhibits ionic conductivity of 1.11 mS·cm ⁻¹ and demonstrates stability in lithium-lithium symmetric cells for up to 3500 h. The initial discharge specific capacity was recorded at 132.9 mAh·g ⁻¹ at 0.5 C rate, declining to 86.6 % after 500 cycles. Density Functional Theory (DFT) simulations were employed to elucidate the lithium-ion transport mechanisms within the CSE system. It is noteworthy that the CSE displays remarkable thermal stability, with a performance threshold exceeding 300 °C. The ionic conductivity of the CSE system reaches 2.40 mS·cm ⁻¹ at 250 °C, representing a twofold increase compared to the LLZO system and an elevenfold increase compared to the LiTFSI molten salt system. Moreover, the initial discharge specific capacity of the CSE was determined to be 123.3 mAh·g ⁻¹ at 250 °C and a 1 C rate, retaining 92.8 % of its capacity after 50 cycles. These findings suggest that the CSE exhibits high safety, excellent cycling stability, and considerable potential for application in high-temperature lithium-ion batteries.