High-Temperature-Annealed Multi-Walled Carbon Nanotubes as High-Performance Conductive Agents for LiNi_0.5Co_0.2Mn_0.3O₂ Lithium-Ion Batteries

In this work, the high yield of MWNTs was prepared by chemical vapor deposition (CVD) method, followed by annealing at 2000–2800 °C, and the effects of high annealing temperature on metal impurities and defects in multi-walled carbon nanotubes (MWNTs) was explored. Furthermore, the annealed MWNTs were dispersed using a sand mill to make a conductive slurry, and finally the cathode LiNi0.5Co0.2Mn0.3O2 was added to the assembled batteries, and the application of MWNTs (slurry) as conductive agents in LiNi0.5Co0.2Mn0.3O2 (NCM) cathode materials by sand-mill dispersion on the performance of lithium-ion batteries was investigated. The results indicate that high temperature annealing can effectively remove the residual metal impurities from MWNTs and the defects in MWNTs gradually decreases as the temperature rises. In addition, 2 wt% of MWNTs (slurry) in LiNi0.5Co0.2Mn0.3O2 is sufficient to form an electronically conductive network; as a result, the electronic conductivity and the high rates performance of the LiNi0.5Co0.2Mn0.3O2 batteries were greatly improved. The LiNi0.5Co0.2Mn0.3O2 battery with MWNTs slurries annealed at 2200 ℃ as a conductive additive displays the highest initial discharge capacity of 173.16 mAh·g−1 at 0.1 C. In addition, after 100 cycles, a capacity retention of 95.8% at 0.5 C and a discharge capacity of 121.75 mAh·g−1 at 5 C were observed. The multi-walled carbon nanotubes used as conductive agents in LiNi0.5Co0.2Mn0.3O2 (NCM) cathode materials show excellent battery behaviors, which would provide a new insight for the development of high-performance novel conductive agents in lithium-ion batteries

Coalbed methane accumulation conditions and enrichment models of Walloon Coal measure in the Surat Basin, Australia

The coal measure of Middle Jurassic Walloon Subgroup is the main reservoir of coalbed methane (CBM) reservoirs in the Surat Basin, Australia, and it is a set of typical low-rank, high-yield coal measure. To figure out the CBM accumulation conditions and enrichment models of this coal measure, its distribution characteristics, source rock characteristics, reservoir characteristics and preservation conditions were investigated based on mud logging, experimental and testing data. Then, based on the analysis results of gas origin and gas bearing property of this coal measure, 3 CBM development areas in northeastern Surat Basin were analyzed and compared in terms of its gas enrichment model, and favorable conditions for CBM accumulation and enrichment of Walloon coal measure (WCM) was summarized. It is indicated that tectonic movements, groundwater conditions and macerals provide favorable conditions for gas generation of Walloon coal. The roof, floor and interbed of this coal measure are lithologically tight, presenting a good sealing capacity. Besides, the Walloon CBM reservoir is a mixed origin gas reservoir with the secondary biogenic methane as the dominant component formed in a monocline structure jointly sealed by hydrodynamic force and lithology. CBM enrichment is controlled by 3 factors, i.e., local structure, methane generating capacity of coal bed and underground hydrodynamic force, and it can be divided into 3 models, i.e., anticline model, syncline model and slope model, among which, the CBM enrichment degree of the former two models is higher. Finally, different from other CBM reservoirs, the Walloon CBM reservoir satisfies four favorable conditions in CBM accumulation and enrichment, including dual-carbon source, efficient methane generation, moderate hydrodynamic force and double sealing. Keywords: Australia, Surat Basin, Jurassic, Walloon coal measure, CBM, CBM accumulation condition, CBM enrichment mode