In situ graphitized hard carbon xerogel: A promising high-performance anode material for Li-ion batteries
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To address the challenges of capacity fading and poor electronic conductivity of hard carbons as anode in Li-ion batteries (LIBs), we report here the catalytic graphitization of resorcinol–formaldehyde xerogel (RFX)-derived hard carbon via a single-step synthesis by incorporating two transition metal catalysts (Co and Ni) with different loadings (5 and 10%) at a modest temperature of 1100 °C. Loading of both the catalysts affects the extent of graphitization and other physiochemical properties that have a direct influence on the anodic performance of as graphitized RFX-derived hard carbon. A 10% Ni catalyst in RFX-derived carbon induces the highest degree of graphitization of 81.4% along with partial amorphous carbon and nickel phases. This improved crystallinity was conducive enough to facilitate rapid electron and Li-ion transfer while the amorphous carbon phase contributed to higher specific capacity, resulting in overall best anodic performance as ever reported for RFX-derived carbon. A specific capacity of 578 mAh/g obtained after 210 cycles at 0.2 C with coulombic efficiency greater than 99% confirms the potential of graphitized RFX-derived carbon as an anode for high-performance LIBs.
Introduction Due to the depletion of conventional fossil fuels and the inconsistency of renewable energy resources, energy storage is of much importance than its availability [1]. Efficient devices are required to store energy harvested from renewable resources [1, 2]. Rechargeable lithium-ion battery (LIB) is one such device among many which stores energy electrochemically and is widely used in portable devices, hybrid electric vehicles and to store energy in grids due to the characteristic features like cost-effectiveness, no pollution, long cyclic life and higher working voltages [3, 4, 5, 6, 7, 8, 9]. In principle, Li-ion moves in between two electrodes during charge/discharge cycles. As the electrodes host the Li-ion, the electrodes must be good ionic/electronic conductor. The characteristics of anode material directly influence the electrochemical performance, and hence, it plays an important role in LIBs [5, 6, 7]. Carbonaceous materials outmaneuver other materials as anode due to their wide range of availability in different forms, good electronic conductivity, and stable cyclic performance [10, 11, 12]. Among the carbon-based anodes, graphite represents the most favored material and it is widely used in marketable LIBs because of its reasonable reversible lithium
storage by intercalation/de-intercalation, long cyclic life, overall stability, low voltage hysteresis. and high energy efficiency [12, 13]. However, the natural reserves of macro-crystalline graphite are scarce and led researchers to prepare synthetic graphite from soft carbons by heat-treating them at very high temperatures between 2500 and 3000 °C which involves heavy energy penalty [14, 15, 16]. The process of graphitizing the soft carbons is not only energy intensive but these carbons are also limited with capacity when tested as anode and hence restric
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