Conversion Chemistry of Cobalt Oxalate for Sodium Storage

Enhancing Benzylamine Electro-Oxidation and Hydrogen Evolution Through in-situ Electrochemical Activation of CoC2O4 Nanoarrays

The sluggish anodic oxygen evolution reaction (OER) seriously restricts the overall efficiency of water splitting. Here, we present an environmentally friendly and efficient aniline oxidation (BOR) to replace the sluggish OER, accomplishing the co-production of H2 and high value-added benzonitrile (BN) at low voltages. Cobalt oxalates grown on cobalt foam (CoC2O4 ⋅ 2H2O/CF) are adopted as the pre-catalysts, which further evolve into working electrocatalysts active for BOR and HER via appropriate electrochemical activation. Thereinto, cyclic voltammetry activation at positive potentials is performed to reconstruct cobalt oxalate via extensive oxidation, resulting in enriched Co(III) species and nanoporous structures beneficial for BOR, while chronoamperometry at negative potentials is introduced for the cathodic activation toward efficient HER with obvious improvement. The two activated electrodes can be combined into a two-electrode system, which achieves a high current density of 75 mA cm-2 at the voltage of 1.95 V, with the high Faraday efficiencies of both BOR (90.0 %) and HER (90.0 %) and the satisfactory yield of BN (76.8 %).

Review and New Perspectives on Non-Layered Manganese Compounds as Electrode Material for Sodium-Ion Batteries

After more than 30 years of delay compared to lithium-ion batteries, sodium analogs are now emerging in the market. This is a result of the concerns regarding sustainability and production costs of the former, as well as issues related to safety and toxicity. Electrode materials for the new sodium-ion batteries may contain available and sustainable elements such as sodium itself, as well as iron or manganese, while eliminating the common cobalt cathode compounds and copper anode current collectors for lithium-ion batteries. The multiple oxidation states, abundance, and availability of manganese favor its use, as it was shown early on for primary batteries. Regarding structural considerations, an extraordinarily successful group of cathode materials are layered oxides of sodium, and transition metals, with manganese being the major component. However, other technologies point towards Prussian blue analogs, NASICON-related phosphates, and fluorophosphates. The role of manganese in these structural families and other oxide or halide compounds has until now not been fully explored. In this direction, the present review paper deals with the different Mn-containing solids with a non-layered structure already evaluated. The study aims to systematize the current knowledge on this topic and highlight new possibilities for further study, such as the concept of entatic state applied to electrodes.

Rod-like Ni0.5Co0.5C2O4·2H2O in-situ formed on rGO by an interface induced engineering: Extraordinary rate and cycle performance as an anode in lithium-ion and sodium-ion half/full cells

Transition metal oxalates have attracted wide attention due to the characteristics of the conversion reaction as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), However, there are huge volume expansion and sluggish circulation dynamics during the reversible Li⁺ and Na⁺ insertion/extraction process, which would lead to unsatisfactory reversible capacity and stability. In order to solve these problems, a rod-like structure Ni_0.5Co_0.5C₂O₄·2H₂O is in-situ formed on the reduced graphene oxide layer (Ni_0.5Co_0.5C₂O₄·2H₂O/rGO) in a glycol-water mixture medium via an interface induced engineering strategy. Benefitting from the synergistic cooperation of nano-diameter rod-like structure and high conductive rGO networks, the experimental results show that the prepared Ni_0.5Co_0.5C₂O₄·2H₂O/rGO electrode has predominant rate performance and ultra-long cycle stability. For the LIBs, it not only exhibits an ultrahigh reversible capacity (1179.9 mA h g^-1 at 0.5 A g^-1 after 300 cycles), but also presents outstanding rate and cycling performance (646.5 mA h g^-1 at 5 A g^-1 after 1200 cycles). Besides, the Ni_0.5Co_0.5C₂O₄·2H₂O/rGO electrode displays remarkable sodium storage capacity of 221.6 mA h g^-1 after 100 cycles at 0.5 A g^-1. Further, the extraordinary electrochemical capability of Ni_0.5Co_0.5C₂O₄·2H₂O/rGO active material is also reflected in two full-cells, assembled using commercial LiCoO₂ as cathode for LIBs and commercial Na₃V₂(PO₄)₃ as cathode for SIBs, both of which can show wonderful specific capacity and cycling stability. It is found in in-situ Raman experiments that the reversible changes of oxalate peaks are monitored in a charge/discharge process, which is scientific evidence for the transform reaction mechanism of metal oxalates in LIBs. These findings not only provide important ideas for studying the charge/discharge storage mechanism but also give scientific basis for the design of high-performance electrode materials.

Understanding the High-Performance Anode Material of CoC2 O4 ⋅2 H2 O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC₂ O₄ ⋅2 H₂ O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC₂ O₄ ⋅2 H₂ O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC₂ O₄ ⋅2 H₂ O. The CoC₂ O₄ ⋅2 H₂ O/rGO electrode delivers a specific capacity of 1011.5 mA h g^-1 at 0.2 A g^-1 after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g^-1 at 0.2 A g^-1 after 100 cycles for sodium storage. Moreover, the full cell CoC₂ O₄ ⋅2 H₂ O/rGO//LiCoO₂ consisting of the CoC₂ O₄ ⋅2 H₂ O/rGO anode and LiCoO₂ cathode maintains 138.1 mA h g^-1 after 200 cycles at 0.2 A g^-1 and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC₂ O₄ ⋅2 H₂ O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.

Nature-Derived Cellulose-Based Composite Separator for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are emerging power sources for the replacement of lithium-ion batteries. Recent studies have focused on the development of electrodes and electrolytes, with thick glass fiber separators (~380 μm) generally adopted. In this work, we introduce a new thin (~50 μm) cellulose–polyacrylonitrile–alumina composite as a separator for SIBs. The separator exhibits excellent thermal stability with no shrinkage up to 300°C and electrolyte uptake with a contact angle of 0°. The sodium ion transference number, tNa+, of the separator is measured to be 0.78, which is higher than that of bare cellulose (tNa+: 0.31). These outstanding physical properties of the separator enable the long-term operation of NaCrO₂ cathode/hard carbon anode full cells in a conventional carbonate electrolyte, with capacity retention of 82% for 500 cycles. Time-of-flight secondary-ion mass spectroscopy analysis reveals the additional role of the Al₂O₃ coating, which is transformed into AlF₃ upon long-term cycling owing to HF scavenging. Our findings will open the door to the use of cellulose-based functional separators for high-performance SIBs.