Cinnamon-Derived Hierarchically Porous Carbon as an Effective Lithium Polysulfide Reservoir in Lithium-Sulfur Batteries.

Lithium-sulfur batteries are attractive candidates for next generation high energy applications, but more research works are needed to overcome their current challenges, namely: (a) the poor electronic conductivity of sulfur, and (b) the dissolution and migration of long-chain polysulfides. Inspired by eco-friendly and bio-derived materials, we synthesized highly porous carbon from cinnamon sticks. The bio-carbon had an ultra-high surface area and large pore volume, which serves the dual functions of making sulfur particles highly conductive and acting as a polysulfide reservoir. Sulfur was predominantly impregnated into pores of the carbon, and the inter-connected hierarchical pore structure facilitated a faster ionic transport. The strong carbon framework maintained structural integrity upon volume expansion, and the unoccupied pores served as polysulfide trapping sites, thereby retaining the polysulfide within the cathode and preventing sulfur loss. These mechanisms contributed to the superior performance of the lithium-sulfur cell, which delivered a discharge capacity of 1020 mAh g-1 at a 0.2C rate. Furthermore, the cell exhibited improved kinetics, with an excellent cycling stability for 150 cycles with a very low capacity decay of 0.10% per cycle. This strategy of combining all types of pores (micro, meso and macro) with a high pore volume and ultra-high surface area had a synergistic effect on improving the performance of the sulfur cathode.

Designing High-Performance Nanostructured P2-type Cathode Based on a Template-free Modified Pechini Method for Sodium-Ion Batteries.

Layered oxides are promising cathode materials for sodium-ion batteries because of their high theoretical capacities. However, many of these layered materials experience severe capacity decay when operated at high voltage (>4.25 V), hindering their practical application. It is essential to design high-voltage layered cathodes with improved stability for high-energy-density operation. Herein, nano P2-Na2/3(Mn0.54Ni0.13Co0.13)O2 (NCM) materials are synthesized using a modified Pechini method as a prospective high-voltage sodium storage component without any modification. The changes in the local ionic state around Ni, Mn, and Co ions with respect to the calcination temperature are recorded using X-ray absorption fine structure analysis. Among the electrodes, NCM fired at 850 °C (NCM-850) exhibits excellent electrochemical properties with an initial capacity and energy density of 148 mAh g-1 and 555 Wh kg-1, respectively, when cycled between 2 and 4.5 V at 160 mA g-1 along with improved cyclic stability after 100 charge/discharge cycles. In addition, the NCM-850 electrode is capable of maintaining a 75 mAh g-1 capacity even at a current density of 3200 mA g-1. In contrast, the cell fabricated with NCM obtained at 800 °C shows continuous capacity fading because of the formation of an impurity phase during the synthesis process. The obtained capacity, rate performance, and energy density along with prolonged cyclic life for the cell fabricated with the NCM-850 electrodes are some of the best reported values for sodium-ion batteries as compared to those of other p2-type sodium intercalating materials.

Nanoscale Manipulation of Spinel Lithium Nickel Manganese Oxide Surface by Multisite Ti Occupation as High-Performance Cathode.

A novel two-step surface modification method that includes atomic layer deposition (ALD) of TiO2 followed by post-annealing treatment on spinel LiNi0.5 Mn1.5 O4 (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn2 O4 (TMO)-like spinel phase resulting from the reaction of TiO2 with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO-like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO2 growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic-scale surface structural modification using ALD and post-treatment, which is of great importance for the future design of cathode materials.

Efficient Method of Designing Stable Layered Cathode Material for Sodium Ion Batteries Using Aluminum Doping.

Despite their high specific capacity, sodium layered oxides suffer from severe capacity fading when cycled at higher voltages. This key issue must be addressed in order to develop high-performance cathodes for sodium ion batteries (SIBs). Herein, we present a comprehensive study on the influence of Al doping of Mn sites on the structural and electrochemical properties of a P2-Na0.5Mn0.5-xAlxCo0.5O2 (x = 0, 0.02, or 0.05) cathode for SIBs. Detailed structural, morphological, and electrochemical investigations were carried out using X-ray diffraction, cyclic voltammetry, and galvanostatic charge-discharge measurements, and some new insights are proposed. Rietveld refinement confirmed that Al doping caused TMO6 octahedra (TM = transition metal) shrinkage, resulting in wider interlayer spacing. After optimizing the aluminum concentration, the cathode exhibited remarkable electrochemical performance, with better stability and improved rate performance. Electrochemical impedance spectroscopy (EIS) measurements were performed at various states of charge to probe the surface and bulk effects of Al doping. The material presented here exhibits exceptional stability over 100 cycles within a 1.5-4.3 V window and outperforms several other Mn-Co-based cathodes for SIBs. This study presents a facile method for designing structurally stable cathodes for SIBs.

Engineering the Pores of Biomass-Derived Carbon: Insights for Achieving Ultrahigh Stability at High Power in High-Energy Supercapacitors.

Electrochemical supercapacitors with high energy density are promising devices due to their simple construction and long-term cycling performance. The development of a supercapacitor based on electrical double-layer charge storage with high energy density that can preserve its cyclability at higher power presents an ongoing challenge. Herein, we provide insights to achieve a high energy density at high power with an ultrahigh stability in an electrical double-layer capacitor (EDLC) system by using carbon from a biomass precursor (cinnamon sticks) in a sodium ion-based organic electrolyte. Herein, we investigated the dependence of EDLC performance on structural, textural, and functional properties of porous carbon engineered by using various activation agents. The results demonstrate that the performance of EDLCs is not only dependent on their textural properties but also on their structural features and surface functionalities, as is evident from the electrochemical studies. The electrochemical results are highly promising and revealed that the porous carbon with poor textural properties has great potential to deliver high capacitance and outstanding stability over 300 000 cycles compared with porous carbon with good textural properties. A very low capacitance degradation of around 0.066 % per 1000 cycles, along with high energy density (≈71 Wh kg-1 ) and high power density, have been achieved. These results offer a new platform for the application of low-surface-area biomass-derived carbons in the design of highly stable high-energy supercapacitors.

Facile hydrothermal synthesis and characterization of Co2GeO4/r-GO@C ternary nanocomposite as negative electrode for Li-ion batteries.

Ternary nanocomposite of Co2GeO4/r-GO@C is synthesized by single step hydrothermal method followed by calcination. The XRD analysis reveals the formation of cubic structured Co2GeO4 and their corresponding functional groups identified through Raman analysis. The TEM analysis assures that uniform distribution of Co2GeO4 nanoparticles on the r-GO layers. The Galvanostatic charge-discharge (GCD) curve demonstrates that the initial discharge capacity of pristine Co2GeO4, Co2GeO4/r-GO and Co2GeO4/r-GO@C composite is 1400, 1284 and 1594mAhg-1 at 50mAg-1, respectively. The cycling stability curve shows the specific capacity of 609, 970 and 1180mAhg-1 for pristine, Co2GeO4/r-GO and Co2GeO4/r-GO@C composite, respectively over 15 cycles. The ternary composite of Co2GeO4/r-GO@C delivers the discharge capacity of 323mAhg-1 at high current density of 1Ag-1 over 500 cycles with capacity retention of 71%. The rate capability curve indicates that Co2GeO4/r-GO@C composite shows the better rate capability.

Highly stable Na2/3 (Mn0.54 Ni0.13 Co0.13 )O2 cathode modified by atomic layer deposition for sodium-ion batteries.

For the first time, atomic layer deposition (ALD) of Al2 O3 was adopted to enhance the cyclic stability of layered P2-type Na2/3 (Mn0.54 Ni0.13 Co0.13 )O2 (MNC) cathodes for use in sodium-ion batteries (SIBs). Discharge capacities of approximately 120, 123, 113, and 105 mA h g(-1) were obtained for the pristine electrode and electrodes coated with 2, 5, and 10 ALD cycles, respectively. All electrodes were cycled at the 1C discharge current rate for voltages between 2 and 4.5 V in 1 M NaClO4 electrolyte. Among the electrodes tested, the Al2 O3 coating from 2 ALD cycles (MNC-2) exhibited the best electrochemical stability and rate capability, whereas the electrode coated by 10 ALD cycles (MNC-10) displayed the highest columbic efficiency (CE), which exceeded 97 % after 100 cycles. The enhanced electrochemical stability observed for ALD-coated electrodes could be a result of the protection effects and high band-gap energy (Eg =9.00 eV) of the Al2 O3 coating layer. Additionally, the metal-oxide coating provides structural stability against mechanical stresses occurring during the cycling process. The capacity, cyclic stability, and rate performance achieved for the MNC electrode coated with 2 ALD cycles of Al2 O3 reveal the best results for SIBs. This study provides a promising route toward increasing the stability and CE of electrode materials for SIB application.

LiMnBO3 nanobeads as an innovative anode material for high power lithium ion capacitor applications.

A novel approach was made to fabricate lithium ion hybrid capacitor (Li-HC) having LiMnBO3 nanobead (LMB-NB) anode and polyaniline nanofiber (PANI) cathode in 1 M LiPF6 organic electrolyte. LMB-NB and PANI nanofibers were synthesized using urea assisted microwave-solvothermal method and chemical polymerization process, respectively. The PANI/LMB-NB cell showed improved electrochemical capacitive behavior as compared to activated carbon (AC)/LMB-NB cell due to the characteristic conductivity and the morphological feature of PANI as well as LMB-NB electrodes. A discharge capacitance (DCcell) of ∼125 F g(-1) was obtained at a current density of 1 A g(-1) between the potential range 0 and 3 V for PANI/LMB-NB cell, while AC/LMB-NB cell delivered only 77 F g(-1) at the same current density. Moreover, PANI/LMB-NB cell exhibited excellent rate performance with the DCcell of about 55 F g(-1) at 2.25 A g(-1) and still retained 94% of the initial value after 30 000 charge-discharge cycles. In addition, maximum energy and power densities of 42 Wh kg(-1) and 5350 W kg(-1), respectively, were achieved from PANI/LMB-NB cell. The obtained DCcell, energy, and power densities along with prolonged cyclic life for PANI/LMB-NB cell are some of the best ever reported values for Li-HC as compared to the cells constructed with various lithium intercalating materials.