Biomass-derived carbon materials as anodes for rechargeable batteries

Abstract

Lithium-ion batteries (LIBs) power most of the portable electronic devices nowadays. However, the geographically limited lithium resources have led to the rapid rise of the battery price. Therefore, new battery technologies that do not rely on lithium must be developed.Sodium-ion batteries (NIBs) are one of the promising alternatives that can replace LIBs, because of not only the abundance of sodium resources but also the significantly lower cost of sodium than lithium. To develop the NIB technology, it is imperative to find a suitable anode material that can reversibly interact with sodium ions. Amongst the available anode materials reported in the literature, carbonaceous materials are promising. While graphite has been successfully used as the anode for LIBs, it shows very poor performance for NIBs owing to the larger ionic radius of sodium than lithium, making the former difficult to intercalate into graphite. Therefore, carbon materials with an enlarged interplanar separation that can accommodate larger sodium ions would make it a suitable candidate as anodes for NIBs. Hard carbon materials derived from biomass have been shown to hold a great promise for NIBs in this regard. Biomass is a widely available resource, especially in Australia. Utilising such naturally abundant biomass precursors for producing carbon material lowers the reliance on non-renewable fossil fuel resources, thus making material production sustainable and economic. In addition, such hard carbons derived from biomass have larger interlayer spacing and defects which allow efficient sodium-ion storage. Therefore, this PhD project aims to develop such biomass-based hard carbon anode materials for NIBs.Research results collected in this thesis project have shown that biomass-derived carbon materials display promising electrochemical properties in both LIB and NIB cells. It was found in this project that flame deposited carbon nanoparticles from coconut oil exhibited a second-cycle discharge capacity of about 277 mA h g-1 in NIBs and of about 741 mA h g-1 in LIBs at a current density of 100 mA g-1. Good cycling stability, rate performance, and high coulombic efficiency are the key properties of the carbon nanoparticles. In another work, binder-free carbon electrodes with a three-dimensional architecture prepared by using a one-step fabrication protocol delivered a specific discharge capacity of 764 mA h g-1 at a current density of 50 mA g-1 with an exceptional cycling stability in a LIB cell. In a NIB cell, the electrode exhibited a discharge capacity of 241 mA h g-1 in the second cycle at a current density of 50 mA g-1 and remained stable over prolonged cycling.Further, the focus of the thesis was laid on improving the performance of such carbon materials for NIBs. Spinifex nanocellulose derived hard carbons were prepared and used as anodes for NIBs. This carbon produced by using a low-temperature carbonization protocol delivered a superior performance as an anode for NIBs with a specific capacity of 386 mA h g-1 at 20 mA g-1 on par with graphite-based anodes for LIBs. To further enhance the performance of such carbon anodes for NIBs, a raw mango powder derived carbon material enriched with nitrogen-containing functional groups was developed for NIBs. A reversible specific capacity of ~520 mA h g-1 at a current density of 20 mA g-1 along with an excellent rate performance were obtained. When cycled at a high current density of 1 A g-1, the nitrogen-rich carbon was stable for over 1000 cycles delivering a capacity of ~204 mA h g-1. In all, the thesis brings out the importance of biomass-derived carbons for rechargeable batteries and puts forth synthesis and optimisation strategies for improving the electrochemical properties of such carbons for NIBs.In summary, this thesis successfully demonstrates different synthesis strategies to prepare biomass derived hard carbon materials as anodes for rechargeable batteries. Such carbon materials produced from biomass are cost-effective and sustainable. Novel strategies like flame-deposition methods have been implemented in the present thesis project to prepare carbon nanoparticles with superior electrochemical performance in LIBs and NIBs. In addition, a scalable carbon production from native Australian biomass spinifex was demonstrated as superior anodes for NIBs. The microstructure of hard carbons reported in the thesis revealed that larger interlayer spacing and defects enhance the sodium-ion storage. Strategies to further improve the performance of such carbon materials by introducing heteroatoms like nitrogen was successfully demonstrated in the thesis. The works presented in the thesis could inspire future research in exploring such hard carbon material with tunable surface chemistries for sodium-ion storage.