CoCO3 micrometer particles stabilized by carbon nanofibers networks as composite electrode for enhanced rate and cyclic performance of lithium-ion batteries

Recent Advances on Synthesis of CoCO3 with Controlled Morphologies

Cobalt carbonates and derivatives represent most promising cost-effective materials for energy storage, conversion and upgrading. Morphology determines the performances, as size, shape and electronic configuration are key factors for tunable properties in the area of batteries, catalysis, magnetics and plasmonics. However, there is lack of insights in literature on morphological control of cobalt carbonates during hydrothermal and solvothermal conditions. Therefore, this review provides detailed discussion on synthesis, formation mechanism and morphological control of nanosheets, wires, spheres and cubes of cobalt carbonates. Furthermore, the influence of experimental conditions and plausible mechanism which govern the growing processes were further discussed in details. The outcome of this short review will offer insights into rational design of inexpensive metal carbonates for numerous other energy and environment applications.

Preparation of Small-Particle and High-Density Cobalt Carbonate Using a Continuous Carbonate Precipitation Method and Evaluation of Its Growth Mechanism

Spherical CoCO₃ powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH₄HCO₃, and without a template. The effects of the concentration of ammonium carbonate, process pH, and feeding rate on the tap density and apparent density of cobalt carbonate were investigated. It was found that the apparent and tap density values of 4.4 µm of cobalt carbonate were 1.27 g/cm³ and 1.86 g/cm³, respectively, when the initial concentration of NH₄HCO₃ solution was 60 g/L, the pH was 7.15–7.20, and the feeding rate of cobalt chloride was 2 L/h. The anisotropic growth process of the crystal lattice plane of CoCO₃ under the aforementioned optimal conditions were studied. The results demonstrated that the crystal grew fastest along the (110) facet orientation, which was the dominant growth surface, determining the final morphology of the primary particles. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results demonstrated that the primary particle morphology of the cobalt carbonate was a nanosheet. The unit cell of cobalt carbonate, of a hexagonal structure in the horizontal direction, grew horizontally along the (110) facet orientation, while 20–35 unit cells of the carbon carbonate were stacked along the c-axis in the thickness direction. Finally, the sheet-shaped particles were agglomerated into dense spherical secondary particles, as presented through the crystal re-crystallization model.

Cobalt Hydroxide Carbonate/Reduced Graphene Oxide Anodes Enabled by a Confined Step-by-Step Electrochemical Catalytic Conversion Process for High Lithium Storage Capacity and Excellent Cyclability with a Low Variance Coefficient

Transition metal carbonates/hydroxides have attracted much attention as appealing anode materials due to their considerable reversible electrochemical catalytic conversion capacity. However, their serious positive or negative trends with cycles caused by the electrochemical catalytic conversion seriously affect their practical applications. Herein, novel one-dimensional cobalt hydroxide carbonate (CHC) nanomaterials are tightly anchored on reduced graphene oxide (RGO) sheets via a facile one-pot hydrothermal synthesis, forming surface-confined domains to further restrict the electrochemical catalytic conversion process. The analysis on the cycled electrodes at varied potentials confirms that the added capacity of CHC arises from the step-by-step reversible reactions of Li₂CO₃ and LiOH under the electrochemical catalysis of Co metal generated by the conversion reaction of CHC. The reversible reaction of Li₂CO₃ is followed closely by that of LiOH in the discharge process, while the order is opposite in the charge process. Such a step-by-step electrochemical catalytic conversion process could confine each other to accommodate the volume change and avoid side reactions. The confined effect is further enhanced by limiting the width and length of the CHC, which are determined by regulating the nucleation and growth of CHC on the surface of RGO, leading to an extraordinary cyclability. The optimized CHC/RGO hybrid maintains a high reversible capacity of 1110 mA h g^-1 after 100 cycles at 0.1 A g^-1, which is much higher than the theoretical value of CHC (506 mA h g^-1) on the basis of the recognized conversion reaction. Furthermore, it keeps high reversible capacities of 755 and 506 mA h g^-1 after 200 cycles at 1 and 2 A g^-1, respectively, exhibiting a high-rate cyclability with the lowest coefficient of variance of 9.4% among the reported ones. The confined step-by-step electrochemical catalytic conversion process facilitates high lithium storage capacity and satisfactory cyclability with a pretty low variance coefficient.