Synthesis of novel hard mesoporous carbons and their application as anodes for Li and Na ion batteries

Mesoporous-microporous carbons, were obtained from the pyrolysis of resol polymerized in the presence of tetraethoxysilane (TEOS) and the triblock copolymer PEO ₁₄₀ -PPO ₃₉ -PEO ₁₄₀ (F108). Carbons Cx-y (x = TEOS/F108 M ratio; y = synthesis temperature) exhibit interconnected porosity measured by N ₂ adsorption with high BET area and micro-mesoporous volume. According to this information and that obtained by Raman, XRD and CO ₂ adsorption, the carbons are described as hard carbons. As conductive additive-free anodes for Li- ion coin cells (LIBs), the carbons Cx-y present high initial specific capacity, being the highest for C70-100 (670 mAh/g) with high capacity retention: 500 mAh/g at 27 mA/g, 68 cycles and rate capability: 100 mAh/g at 1365 mA/g, 56 cycles. The C70-100 improved efficiency is attributed to the highest mesoporosity and lowest non-graphitizing hard carbon nature and surface activity. As anodes for Na-ion batteries (NIBs), these carbons present higher first discharge capacities ∼ 780-420 mAh/g and initial capacity, ∼192-109 mAh/g, than graphite. C90-150 with the lowest irreversible capacity is promising anode for NIBs. This result is due to its higher hard carbon nature and surface activity than C70-100 and lower porosity than C70-100 and C90-100, allowing more stability in carbon-sodium intercalation and less electrolyte decomposition, respectively.