Novel design and facile synthesis of porous carbon nanocomposites for lithium sulfur battery

University of Technology Sydney. Faculty of Science.Rechargeable energy storage devices are being seen as having a crucial role in the powering of myriad portable electronic devices and hybrid electrical vehicles. The composition, morphology, structure and preparation method can affect the electrochemical performance. The properties of electrode materials are of extreme significance for the electrochemical performances of lithium-sulfur batteries. Lithium-sulfur battery based on sulfur cathode has the advantages of high specific capacity, high energy density, low lost and natural abundance of sulfur. These advantages over conventional lithium-ion batteries have driven researchers to make a lot of efforts to understand the redox mechanisms and improve the electrode performance. In order to fully realize the potential of lithium-sulfur battery and to approach commercialization, there are still many problems to overcome. Among them are i) low conductivity nature of sulfur and the discharge product, ii) lithium polysulfide intermediates dissolution and shuttle phenomenon, iii) volumetric expansion upon discharge and iv) lithium metal dendrite formation on anode side. In this thesis, the work is mostly focused on the cathode materials in order to address the first two problems. In the first part of the thesis, we report a rational design and synthesis of 3D hybrid–porous carbon with a hierarchical pore architecture for high performance supercapacitors. It contains nanopores (< 2 nm diameter) and mesopores (2 – 4 nm), derived from carbonization of unique porous metal organic frameworks (MOFs). Owning to the synergistic effect of micropores and mesopores, the hybrid-porous carbon has exceptionally high ion–accessible surface area and low ion diffusion resistance, which is desired for high performance Li-S battery. The initial and 50th cycle discharge capacity 3D hybrid–C/S sulfur cathode are as high as 1343 mAh g⁻¹ and 540 mAh g⁻¹ at a high current rate of 0.5 C. 3D hybrid–C@graphene nanocomposites were prepared by a hydrothermal and chemical vapor deposition method. When applied as an cathode material in lithium-sulfur batteries. 3D hybrid–C@graphene/S nanocomposite exhibited a high lithium storage capacity of 907 mAh g⁻¹. The materials also demonstrated an excellent high rate capacity and a stable cycle performance. 3D porous MXene/S sulfur composite was successfully prepared that demonstrated high reversible capacity, high Coulombic efficiency and excellent cyclability. MXene@graphene/S hybrid sulfur composite were synthesized using a chemical hydrothermal method, exhibiting a high specific capacity of 1284 mAh·g⁻¹ with a superior cycling stability and high rate capabilities. The synthesis of 3D hybrid–C@MXene encapsulated sulfur composites were employed as cathode materials for Li-S batteries. The sulfur composite cathodes delivered a high specific capacity of 1378 mAh/g at 0.1 C current rate and exhibited a stable cycling performance. A rational synthesis of the novel porous N-Ti₃C₂Tₓ nanosheets via the electrostatic self-assembly and effective nitrogen doping process, achieving the porous-modification and nitrogen group surface decoration for porous N-Ti₃C₂Tₓ nanosheets, synchronously. The porous N-doped MXene nanosheets/sulfur composites electrodes with a high sulfur loading exhibits low polarization, stable cycling performance, and excellent rate capability, compared with mixed Ti₃C₂Tₓ/S electrodes showed electrochemical performance, including a high reversible capacity of 1144 mAh g⁻¹ at 0.2 C rate, a high level of capacity retention of 950 mAh g⁻¹ after 200 cycles and good cycling stability with a high sulfur loading of 5.1 mg cm⁻² and high current rate of 2 C rate

Conductive Covalent Organic Frameworks Meet Micro-Electrical Energy Storage: Mechanism, Synthesis and Applications—A Review

Conductive covalent organic frameworks (c-COFs) have been widely used in electrochemical energy storage because of their highly adjustable porosity and modifiable skeletons. Additionally, the fast carrier migration and ion catalysis requirements of micro-electrochemical energy storages (MEESs) are perfectly matched with c-COFs. Therefore, c-COFs show great potential and unlimited prospects in MEESs. However, the main organic component blocks electron conduction, and the internal active sites are difficult to fully utilize, which limits the application of c-COFs. In order to overcome these obstacles, a great deal of research has been conducted on conductivity enhancement. This review first focuses on the exploration of c-COFs in the field of electrical conductivity. Then, the mechanism and explanation of the effect of synthesis on electrical conductivity enhancement are discussed, which emphasizes the range and suitability of c-COFs in MEESs. Finally, the excellent performance characteristics of c-COFs are demonstrated from the MEES perspective, with key points and potential challenges addressed. This review also predicts the direction of development of c-COFs in the future

Conductive Covalent Organic Frameworks Meet Micro-Electrical Energy Storage: Mechanism, Synthesis and Applications&mdash;A Review

Conductive covalent organic frameworks (c-COFs) have been widely used in electrochemical energy storage because of their highly adjustable porosity and modifiable skeletons. Additionally, the fast carrier migration and ion catalysis requirements of micro-electrochemical energy storages (MEESs) are perfectly matched with c-COFs. Therefore, c-COFs show great potential and unlimited prospects in MEESs. However, the main organic component blocks electron conduction, and the internal active sites are difficult to fully utilize, which limits the application of c-COFs. In order to overcome these obstacles, a great deal of research has been conducted on conductivity enhancement. This review first focuses on the exploration of c-COFs in the field of electrical conductivity. Then, the mechanism and explanation of the effect of synthesis on electrical conductivity enhancement are discussed, which emphasizes the range and suitability of c-COFs in MEESs. Finally, the excellent performance characteristics of c-COFs are demonstrated from the MEES perspective, with key points and potential challenges addressed. This review also predicts the direction of development of c-COFs in the future

Spinel LiMn₂O₄ Cathode Materials in Wide Voltage Window: Single-Crystalline versus Polycrystalline

Single-crystal (SC) layered oxides as cathodes for Li-ion batteries have demonstrated better cycle stability than their polycrystalline (PC) counterparts due to the restrained intergranular cracking formation. However, there are rare reports on comparisons between single-crystal LiMn2O4 (SC-LMO) and polycrystalline LiMn2O4 (PC-LMO) spinel cathodes for Li-ion storage. In this work, the Li-ion storage properties of spinel LiMn2O4 single-crystalline and polycrystalline with similar particle sizes were investigated in a wide voltage window of 2–4.8 V vs. Li/Li+. The SC-LMO cathode exhibited a specific discharge capacity of 178 mA·h·g−1, which was a bit larger than that of the PC-LMO cathode. This is mainly because the SC-LMO cathode showed much higher specific capacity in the 3 V region (Li-ion storage at octahedral sites with cubic to tetragonal phase transition) than the PC-LMO cathode. However, unlike layered-oxide cathodes, the PC-LMO cathode displayed better cycle stability than the SC-LMO cathode. Our studies for the first time demonstrate that the phase transition-induced Mn(II) ion dissolution in the 3 V region rather than cracking formation is the limiting factor for the cycle performance of spinel LiMn2O4 in the wide voltage window

Spinel LiMn2O4 Cathode Materials in Wide Voltage Window: Single-Crystalline versus Polycrystalline

Single-crystal (SC) layered oxides as cathodes for Li-ion batteries have demonstrated better cycle stability than their polycrystalline (PC) counterparts due to the restrained intergranular cracking formation. However, there are rare reports on comparisons between single-crystal LiMn2O4 (SC-LMO) and polycrystalline LiMn2O4 (PC-LMO) spinel cathodes for Li-ion storage. In this work, the Li-ion storage properties of spinel LiMn2O4 single-crystalline and polycrystalline with similar particle sizes were investigated in a wide voltage window of 2–4.8 V vs. Li/Li+. The SC-LMO cathode exhibited a specific discharge capacity of 178 mA·h·g−1, which was a bit larger than that of the PC-LMO cathode. This is mainly because the SC-LMO cathode showed much higher specific capacity in the 3 V region (Li-ion storage at octahedral sites with cubic to tetragonal phase transition) than the PC-LMO cathode. However, unlike layered-oxide cathodes, the PC-LMO cathode displayed better cycle stability than the SC-LMO cathode. Our studies for the first time demonstrate that the phase transition-induced Mn(II) ion dissolution in the 3 V region rather than cracking formation is the limiting factor for the cycle performance of spinel LiMn2O4 in the wide voltage window

Facile Synthesis of Crumpled Nitrogen-Doped MXene Nanosheets as a New Sulfur Host for Lithium-Sulfur Batteries

Crumpled nitrogen-doped MXene nanosheets with strong physical and chemical coadsorption of polysulfides are synthesized by a novel one-step approach and then utilized as a new sulfur host for lithium-sulfur batteries. The nitrogen-doping strategy enables introduction of heteroatoms into MXene nanosheets and simultaneously induces a well-defined porous structure, high surface area, and large pore volume. The as-prepared nitrogen-doped MXene nanosheets have a strong capability of physical and chemical dual-adsorption for polysulfides and achieve a high areal sulfur loading of 5.1 mg cm(-2). Lithium-sulfur batteries, based on crumpled nitrogen-doped MXene nanosheets/sulfur composites, demonstrate outstanding electrochemical performances, including a high reversible capacity (1144 mA h g(-1) at 0.2C rate) and an extended cycling stability (610 mA h g(-1) at 2C after 1000 cycles).</p

Supercapacitors of Nanocrystalline Covalent Organic Frameworks—A Review

Due to their highly changeable porosity and adaptable skeletons, covalent organic frameworks (COFs) have been frequently used in supercapacitors. Additionally, COFs are a wonderful match for supercapacitors’ requirements for quick carrier migration and ion catalysis. COFs exhibit significant potential and limitless opportunities in electrochemical storage supercapacitors. The applicability of COFs has, nonetheless, been limited because the primary organic component prevents electron conduction and the interior active sites are challenging to fully utilize. The conductivity enhancement of COFs has been the subject of extensive research to solve these challenges. This review begins by outlining the features of COFs in the context of their use in supercapacitors and their methods of synthesis. The application of previously published COF materials in supercapacitors were evaluated including electrode materials and solid-state devices. Finally, essential aspects and potential problems are discussed as the exceptional performance characteristics of COFs are illustrated from a supercapacitor standpoint. This review also forecasts the future of COF-based supercapacitor development

Supercapacitors of Nanocrystalline Covalent Organic Frameworks&mdash;A Review

Due to their highly changeable porosity and adaptable skeletons, covalent organic frameworks (COFs) have been frequently used in supercapacitors. Additionally, COFs are a wonderful match for supercapacitors&rsquo; requirements for quick carrier migration and ion catalysis. COFs exhibit significant potential and limitless opportunities in electrochemical storage supercapacitors. The applicability of COFs has, nonetheless, been limited because the primary organic component prevents electron conduction and the interior active sites are challenging to fully utilize. The conductivity enhancement of COFs has been the subject of extensive research to solve these challenges. This review begins by outlining the features of COFs in the context of their use in supercapacitors and their methods of synthesis. The application of previously published COF materials in supercapacitors were evaluated including electrode materials and solid-state devices. Finally, essential aspects and potential problems are discussed as the exceptional performance characteristics of COFs are illustrated from a supercapacitor standpoint. This review also forecasts the future of COF-based supercapacitor development

Achieving High Performance Electrode for Energy Storage with Advanced Prussian Blue-Drived Nanocomposites—A Review

Recently, Prussian blue analogues (PBAs)-based anode materials (oxides, sulfides, selenides, phosphides, borides, and carbides) have been extensively investigated in the field of energy conversion and storage. This is due to PBAs’ unique properties, including high theoretical specific capacity, environmental friendly, and low cost. We thoroughly discussed the formation of PBAs in conjunction with other materials. The performance of composite materials improves the electrochemical performance of its energy storage materials. Furthermore, new insights are provided for the manufacture of low-cost, high-capacity, and long-life battery materials in order to solve the difficulties in different electrode materials, combined with advanced manufacturing technology and principles. Finally, PBAs and their composites’ future challenges and opportunities are discussed

Boosting the capacitance of MOF-derived carbon-based supercapacitors by redox-active bromide ions

Supercapacitors have attracted tremendous attention due to their merits of excellent cycling stability, remarkable power density and low cost. Nevertheless, the low energy density of supercapacitors has encumbered their further development for practical applications. Development of advanced high-energy supercapacitors is considered to be of crucial importance. In this work, the capacitance of MOF-derived carbon-based supercapacitor is dramatically improved by addition of soluble redox-active LiBr electrolyte additive. The post analysis of this redox-active electrolytes reveal that the Br−/Br2 couple are the main pseudocapacitance contribution in the early cycles stages (<140 cycles), which gradually reaches an equilibrium state and converts into Br–/Br3– redox couples after 160 cycles. The achieved specific capacitance of the assembled supercapacitors is up to 825.6 F g−1 in the added-bromide-ion (ABI) electrolyte. The performance is over seven-fold as high as bromide-free (BF) electrolyte at current density of 1 A g−1