Electroreduction of Carbon Dioxide to Acetate using Heterogenized Hydrophilic Manganese Porphyrins.

The electrochemical reduction of carbon dioxide (CO2 ) to value-added chemicals is a promising strategy to mitigate climate change. Metalloporphyrins have been used as a promising class of stable and tunable catalysts for the electrochemical reduction reaction of CO2 (CO2 RR) but have been primarily restricted to single-carbon reduction products. Here, we utilize functionalized earth-abundant manganese tetraphenylporphyrin-based (Mn-TPP) molecular electrocatalysts that have been immobilized via electrografting onto a glassy carbon electrode (GCE) to convert CO2 with overall 94 % Faradaic efficiencies, with 62 % being converted to acetate. Tuning of Mn-TPP with electron-withdrawing sulfonate groups (Mn-TPPS) introduced mechanistic changes arising from the electrostatic interaction between the sulfonate groups and water molecules, resulting in better surface coverage, which facilitated higher conversion rates than the non-functionalized Mn-TPP. For Mn-TPP only carbon monoxide and formate were detected as CO2 reduction products. Density-functional theory (DFT) calculations confirm that the additional sulfonate groups could alter the C-C coupling pathway from *CO→*COH→*COH-CO to *CO→*CO-CO→*COH-CO, reducing the free energy barrier of C-C coupling in the case of Mn-TPPS. This opens a new approach to designing metalloporphyrin catalysts for two carbon products in CO2 RR.

Insight into the failure mechanism of large-scale cylindrical lithium-sulphur cells.

Li-S batteries with a sulphur loading content of 5 mg cm-2 were produced as large-scale 18 650 cylindrical cells. We have found that a key failure mode of cylindrical Li-S battery cells is the severe capacity fading during the galvanostatic charge-discharge process due to the corrosion of the electrodes, the electrolyte decomposition, and the severe polysulphide shuttling effect.

Core-shell structure of LiMn2O4 cathode material reduces phase transition and Mn dissolution in Li-ion batteries.

Although the LiMn2O4 cathode can provide high nominal cell voltage, high thermal stability, low toxicity, and good safety in Li-ion batteries, it still suffers from capacity fading caused by the combination of structural transformation and transition metal dissolution. Herein, a carbon-coated LiMn2O4 cathode with core@shell structure (LMO@C) was therefore produced using a mechanofusion method. The LMO@C exhibits higher cycling stability as compared to the pristine LiMn2O4 (P-LMO) due to its high conductivity reducing impedance growth and phase transition. The carbon shell can reduce direct contact between the electrolyte and the cathode reducing side reactions and Mn dissolution. Thus, the cylindrical cell of LMO@C//graphite provides higher capacity retention after 900 cycles at 1 C. The amount of dissoluted Mn for the LMO@C is almost 2 times lower than that of the P-LMO after 200 cycles. Moreover, the LMO@C shows smaller change in lattice parameter or phase transition than P-LMO, indicating to the suppression of λ-MnO2 phase from the mixed phase of Li1-δMn2O4 + λ-MnO2 when Li-delithiation at highly charged state leading to an improved cycling reversibility. This work provides both fundamental understanding and manufacturing scale demonstration for practical 18650 Li-ion batteries.

Free carbonate-based molecules in the electrolyte leading to severe safety concerns of Ni-rich Li-ion batteries.

The safety of Li-ion batteries is one of the most important factors, if not the most, determining their practical applications. We have found that free carbonate-based solvent molecules in the hybrid electrolyte system can cause severe safety concerns. Mixing ionic liquids with a carbonate-based solvent as the co-solvent at a fixed salt concentration of 1 M LiPF6 can lead to free carbonate-based molecules causing poor charge storage performance and safety concerns.

Reducing the Energy Band Gap of Cobalt Hydroxide Nanosheets with Silver Atoms and Enhancing Their Electrical Conductivity with Silver Nanoparticles.

Although cobalt hydroxide (Co(OH)2) has been attracting attention in several applications, its photoelectrochemical property has not yet been fully investigated. In this work, tuning the energy band gap of Co(OH)2 nanosheets with silver atoms and enhancing their electrical conductivity with silver nanoparticles were then focused. A Ag-doped α-Co(OH)2 thin film was successfully synthesized via an electrodeposition method. The optical properties of the as-prepared materials were characterized by UV-vis and fluorescence lifetime spectroscopies and further confirmed by density functional theoretical calculation. It was found that Ag atoms between adjacent layers of Co(OH)2 can reduce its electronic band gap to 2.45 eV (α-Co(OH)2) as compared to 2.85 eV of ß-Co(OH)2. In terms of electrochemical properties, silver nanoparticles (AgNPs) can enhance the electrical conductivity of Co(OH)2 nanosheets, leading to faster charge transfer reducing the internal resistance and significantly increasing the overall charge storage performance. Interestingly, under light illumination, Ag-doped α-Co(OH)2 exhibits ca. 0.8 times lower charge storage capacity as compared to that under the dark condition. This is because the photoelectrons can be recombined with the generated holes in the conduction band. The charge storage mechanisms of Ag-doped α-Co(OH)2 operated under dark conditions and light irradiation were further studied and confirmed using in situ electrochemical X-ray absorption spectroscopy (XAS). Overall, the in situ XAS supports the electrochemical result. This finding may pave a way to further develop photoactive advanced functional materials of metal hydroxides and oxides.

Optimization of the Electrode Properties for High-Performance Ni-Rich Li-Ion Batteries.

The microstructure of the electrodes in lithium-ion batteries (LIBs) strongly affects their gravimetric and volumetric energy and power as well as their cycle life. Especially, the effect of the microstructure in the case of next-generation Ni-rich cathode materials has not yet been investigated. A comprehensive understanding of the calendering process is therefore necessary to find an optimal level of the electrode microstructure that can enhance lithium-ion transportation, minimize plastic deformation, and improve conductivity. This work therefore aims to investigate the effect of microstructure and wettability on the electrode kinetics of next-generation Ni-rich LiNi0.88Co0.09Al0.03O2-based 18650 cylindrical cells, which were produced at the semiautomation scale of the pilot plant. Thus, all materials, electrodes, and the battery production are in quality control as the same level of commercial LIBs. With the optimized microstructure and other properties including a finely tuned compaction degree of 17.54%, a thickness of 188 µm, a sheet resistivity of 36.47 mΩ cm-2, a crystallite size of 88.85 nm, a porosity of 26.03%, an electrode Brunauer-Emmett-Teller (BET) surface area of 1.090 m2 g-1, an electrode density of 2.529 g cm-3, and an electrolyte uptake capability of 47.8%, the optimized LiNi0.88Co0.09Al0.03O2 18650 cylindrical cells exhibit excellent high-rate capacity retention, fast Li-ion diffusion, and low internal resistance. The optimized electrode microstructure of next-generation Ni-rich cathode materials could be an effective strategy toward the real application of next-generation Ni-rich LIBs.

Effect of fluoroethylene carbonate on the transport property of electrolytes towards Ni-rich Li-ion batteries with high safety.

Transport phenomena and the solvation structure of lithium ions (Li+) and hexafluorophosphate anions (PF6-) in electrolytes with different fluoroethylene carbonate (FEC) concentrations as well as the electrochemical performance and safety of Ni-rich Li-ion battery cells at the 18650 cylindrical cell level are investigated. We have found that the electrolyte with an optimized FEC concentration (25% v/v) can effectively enhance the transport property in terms of the Li+ transference number and contact ion pair (CIP) ratio leading to high performance and safety of practical 18650 cylindrical LIBs.

A 3D free-standing lithiophilic silver nanowire aerogel for lithium metal batteries without lithium dendrites and volume expansion: in operando X-ray diffraction.

A 3D free-standing lithiophilic silver nanowire aerogel (AgNWA) can stop the dendritic growth of lithium metal at the initial nucleation process. The 3D structure can also suppress the infinite volume expansion of lithium during cycling. The active AgNWA scaffold can serve as a Li reservoir to compensate for the irreversible consumption of Li. The lithiated AgNWA anode was coupled with a lithium iron phosphate (LFP) cathode in a full-cell configuration providing much higher performance than the Li//LFP cell.

Photoactive Zn-air batteries using spinel-type cobalt oxide as a bifunctional photocatalyst at the air cathode.

Spinel-type cobalt oxide (Co3O4) was synthesized and used as a photoactive bifunctional electrocatalyst towards the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) at the air cathode of zinc-air batteries (ZABs). The Co3O4 having direct and indirect band gap energies of ca. 2.20 eV and ca. 1.35 eV can absorb visible light, generating photogenerated carriers and photoelectrons via the photoelectric effect. Upon exposure to visible light, the Co3O4 electrode exhibits ca. 30% higher current density than that under dark conditions and provides around 10-20% lower OER and ORR overpotentials than those under the dark conditions. Under visible light, the specific capacity of the as-fabricated photoactive ZAB cell is improved by ca. 10% as compared to that under dark conditions.

High-Performance Li-Ion Batteries Using Nickel-Rich Lithium Nickel Cobalt Aluminium Oxide-Nanocarbon Core-Shell Cathode: In Operando X-ray Diffraction.

Nickel-rich layered, mixed lithium transition-metal oxides have been pursued as a propitious cathode material for the future-generation lithium-ion batteries due to their high energy density and low cost. Nevertheless, acute side reactions between Ni4+ and carbonate electrolyte lead to poor cycling as well as rate performance, which limits their large-scale applications. Here, core-shell like LiNi0.8Co0.15Al0.05O2 (NCA)-carbon composite synthesized by a solvent-free mechanofusion method is reported to solve this issue. Such a core-shell structure exhibits a splendid rate as well as stable cycling when compared to the physically blended NCA. In operando X-ray diffraction studies show that both materials experience anisotropic structural change, i.e., stacking c-axis undergoes a gradual expansion followed by an abrupt shrinkage; meanwhile, the a-axis contracts during the charging process and vice versa. Interestingly, the core-shell material displays a significantly high reversible capacity of 91% in the formation cycle at 0.1C and a retention of 84% at 0.5C after 250 cycles, whereas pristine NCA retains 71%. The robust mechanical force assisted dry coating obtained by the mechanofusion method shows improved electrochemical performance and demonstrates its practical feasibility.

Insight into the effect of additives widely used in lithium-sulfur batteries.

The interaction between the reactive lithium metal surface and LiNO3 results in the formation of LixNOy clusters, which can protect the Li metal anode and suppress the shuttling effect of lithium polysulfides via the dipole-dipole interaction called the lithium bond.

Polyaniline-grafted hydrolysed polyethylene as a dual functional interlayer/separator for high-performance Li-S@C core-shell batteries.

A modified hydrolysed polyethylene with polyaniline was used as a dual functional interlayer/separator for high-performance lithium-sulphur batteries (LSBs) to reduce the migration of soluble polysulphide intermediates. Also, the sulphur cathode was encapsulated with carbon nanoparticles with a S@C core-shell structure using a solvent-free coating process. The chemical interaction between the imine group of the quinoid ring in the PANI structure and the polysulphides reducing the shuttle effect as well as the high electrical conductivity and less volume change of the carbon encapsulated sulphur can provide high-performance Li-S@C core-shell batteries.