Carbon Anodes For Sodium-ion Batteries Research Articles

Effect of Vapor Carbon Coating on the Surface Structure and Sodium Storage Performance of Hard Carbon Spheres

Hard carbons have received considerable attention as anode materials for sodium‐ion batteries (SIBs). However, it is still a challenge to improve the plateau capacity and initial coulombic efficiency (ICE) of hard carbons. Herein, a facile vapor carbon‐coating method is used to modify the surface structure of carbon spheres (CS) via the pyrolysis of polypropylene (PP), aiming to seal the exposed pores through a high‐quality carbon layer. CS@2%PP exhibits highly improved sodium storage performance compared to that of the pristine CS, which delivers a plateau capacity of 220 m Ah g−1 and an ICE of 81%. Further investigations show that the improved sodium storage performance of CS@2%PP can be mainly attributed to the reduced structural defects on the surface, lower specific surface area (11.5 m2 g−1), and increased closed pores (12.5%) via carbon coating. The results prove that the surface vapor carbon coating is a facile route to improve the plateau capacity and ICE of hard carbon anodes in SIBs.

Valorizing low cost and renewable lignin as hard carbon for Na-ion batteries: Impact of lignin grade

Lignin, the second most abundant biopolymer and rich in aromatic entities, is a by-product of paper industry and mainly burned to produce energy. Its commercialization for high-value added products remains largely unexplored today. Herein, we explored the preparation of hard carbon anodes for sodium-ion batteries using the two most common lignin grades, i.e, lignin kraft and lignin sulphonate. The lignin kraft hard carbon (LK-HC) shows small specific surface area (1.8 m2 g−1) and a dense random-like morphology while the latter lignin sulphonate hard carbon (LS-HC) presents a high surface area (180 m2 g−1) and spherical particles containing macropores. Their electrochemical performances vs. Na+ revealed a steady capacity of 181 mAh g−1 over cycling for LK-HC, as compared to a capacity of 205 mAh g−1 for LS-HC which fades after 30 cycles due to an impurity-driven growth of a blocking solid electrolyte interphase (SEI). To circumvent this issue, an efficient washing procedure was successfully implemented enabling to obtain (LSW-HC) carbons which deliver a high and stable capacity (284 mAh g−1) along efficiency (78.1%).

Facile and large-scalable synthesis of low cost hard carbon anode for sodium-ion batteries

Although hard carbons are considered to be applied as promising anode materials for sodium-ion batteries (SIBs) with improved specific capacity and good long-term cycle life. However, a significant low initial Coulombic efficiency (ICE) and high cost that consequently impede its use in future commercialization of SIBs. Herein, a cost effective strategy is used to prepare the large-scalable hard carbon (HC) anode material for SIBs, which shows excellent initial reversible capacity of 308 mA h g−1 under the current rate of 50 mA g−1 and considerable higher ICE of 78%. After more than 300 cycles, the material exhibits a specific capacity of 160 mA h g−1 and presenting superior capacity retention more than 94% under current density of 500 mA g−1. The obtained results establish a new technique to construct low cost hard carbon based anode materials for next-generation high performance SIBs.

Nano Hard Carbon Anodes for Sodium-Ion Batteries.

A hindrance to the practical use of sodium-ion batteries is the lack of adequate anode materials. By utilizing the co-intercalation reaction, graphite, which is the most common anode material of lithium-ion batteries, was used for storing sodium ion. However, its performance, such as reversible capacity and coulombic efficiency, remains unsatisfactory for practical needs. Therefore, to overcome these drawbacks, a new carbon material was synthesized so that co-intercalation could occur efficiently. This carbon material has the same morphology as carbon black; that is, it has a wide pathway due to a turbostratic structure, and a short pathway due to small primary particles that allows the co-intercalation reaction to occur efficiently. Additionally, due to the numerous voids present in the inner amorphous structure, the sodium storage capacity was greatly increased. Furthermore, owing to the coarse co-intercalation reaction due to the surface pore structure, the formation of solid-electrolyte interphase was greatly suppressed and the first cycle coulombic efficiency reached 80%. This study shows that the carbon material alone can be used to design good electrode materials for sodium-ion batteries without the use of next-generation materials.

Hard carbons for sodium-ion batteries: Structure, analysis, sustainability, and electrochemistry

Abstract Hard carbons are extensively studied for application as anode materials in sodium-ion batteries, but only recently a great interest has been focused toward the understanding of the sodium storage mechanism and the comprehension of the structure–function correlation. Although several interesting mechanisms have been proposed, a general mechanism explaining the observed electrochemical processes is still missing, which is essentially originating from the remaining uncertainty on the complex hard carbons structure. The achievement of an in-depth understanding of the processes occurring upon sodiation, however, is of great importance for a rational design of optimized anode materials. In this review, we aim at providing a comprehensive overview of the up-to-date known structural models of hard carbons and their correlation with the proposed models for the sodium-ion storage mechanisms. In this regard, a particular focus is set on the most powerful analytical tools to study the structure of hard carbons (upon de-/sodiation) and a critical discussion on how to interpret and perform such analysis. Targeting the eventual commercialization of hard carbon anodes for sodium-ion batteries – after having established a fundamental understanding – we close this review with a careful evaluation of potential strategies to ensure a high degree of sustainability, since this is undoubtedly a crucial parameter to take into account for the future large-scale production of hard carbons.

Biochars from various biomass types as precursors for hard carbon anodes in sodium-ion batteries

Last years have shown an explosion of interest about biochars. Until now, the applications targeted have mostly been in the fields of energy or agronomy. But high-added value applications in the field of electrochemistry, such as hard carbon precursor in anodes for sodium ion batteries, become more and more mentioned as promising uses to investigate. The present study aims at evaluating the feasibility of using biochars from various biomass types for this application and drawing links between biomass properties and the resulting hard carbon electrochemical performance. To achieve this goal, hard carbons were obtained by high-temperature slow pyrolysis of four woody and agricultural biomasses. These hard carbons were prepared as anodes, characterized regarding structural and textural properties and finally tested during successive cycles to assess electrode performances and correlate them with biomass composition. Whatever biomass, the hard carbon could be used in cells and thus biomass appears as a promising feedstock for this application. However, there are apparent differences between biomasses concerning coulombic efficiency and to some extent, cycle stability. Hence resinous wood appears to be the most suitable precursor, while wheat straw would be the least one, probably because of its too high surface area or inorganic element content. Based on these observations, hypotheses were suggested about the influence of lignin and hemicelluloses composition as well as of inorganic elements. To our knowledge, this study is pioneering in proposing a systematic study approach to understand the influence of different biomass properties in a hard carbon electrode for sodium-ion batteries.

Hard carbon anodes of sodium-ion batteries: undervalued rate capability

The rate capability of hard carbon has long been underestimated in prior studies that used carbon/Na two-electrode half-cells. Through a three-electrode cell setup, we discover that it is the overpotential of the sodium counter electrode that drives the half-cells to the lower cutoff potential prematurely during hard carbon sodiation, particularly at high current rates, which prevents the hard carbon anode from being fully sodiated.

Novel D-Glucose Derived Hard Carbon Anode for Sodium-Ion Batteries

The synthesis and characterization of a hard carbon anode material for room-temperature sodium-ion battery is being reported. The carbon material was prepared via two-step process including hydrothermal carbonization (HTC) and pyrolysis. Similar carbon materials were recently synthesized and investigated by our group as supercapacitor electrode materials [1,2]. Sodium-ion batteries have emerged as a promising candidate for large-scale energy storage due to sodium’s abundance and low cost of raw materials. However, significant work is needed on the development of Na-ion intercalation anodes [3,4]. The materials were investigated using SEM, HR-TEM, gas sorption techniques and Raman spectroscopy. Electrochemical characterization has been carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge method (GCD). The glucose derived carbon particles have a round shape and consist of both ordered and disordered graphitic domains, as can be seen from HR-TEM images (Figure 1a). The electrode slurry was prepared by mixing the carbon active material, conductive additive (Super P) and polyvinylidene difluoride (PVdF) binder in a 75:15:10 mass ratio. The mixed slurry was cast onto copper foil using doctor-blade technique. The cast electrodes were dried under vacuum for 24h. The half-cells (EL-Cell GmbH) were assembled in an Argon-filled glovebox (O2 < 0.1 ppm, H2O < 0.1 ppm). Sodium metal was used as counter and reference electrode and 1M NaClO4 in propylene carbonate (PC) as the electrolyte. Cyclic voltammograms measured at 0.5 mV s-1 potential scan rate are shown in Figure 1b. The identical shape of the CVs indicates good reversibility. Very well developed peaks at E = 10 mV and E = 100 mV suggest that reversible Na-ion intercalation is taking place in the material. However, the electrode seems to exhibit some capacitive properties in the potential region from 225 mV to 1 V, after which the current density drops suggesting that the electrode is charged positively and therefore Na-ions are replaced by bigger and more solvated ClO4 - anions. Galvanostatic charge-discharge curves in Figure 1c show discharge capacity values of 250 mAh g-1 at 50 mA g-1 current density. The half-cells were cycled between 0.005 and 1.5 V vs Na/Na+. The effect of co-intercalating solvents [5–8] will be analysed using electrochemical techniques together with ex situ/in situ Raman spectroscopy data. Acknowledgements The present study was supported by the Estonian Centre of Excellence in Science project 3.2.0101.11-0030, Estonian Energy Technology Program project 3.2.0501.10-0015, Material Technology Program project 3.2.1101.12-0019, Project of European Structure Funds 3.2.0601.11-0001, Estonian target research project IUT20–13, NAMUR project 3.2.0304.12-0397 and projects 3.2.0302.10-0169 and 3.2.0302.10-0165.

Mechanistic insights into sodium storage in hard carbon anodes using local structure probes.

Operando23Na solid-state NMR and pair distribution function analysis experiments provide insights into the structure of hard carbon anodes in sodium-ion batteries. Capacity results from "diamagnetic" sodium ions first adsorbing onto pore surfaces, defects and between expanded layers, before pooling into larger quasi-metallic clusters/expanded carbon sheets at lower voltages.

Long cycle life microporous spherical carbon anodes for sodium-ion batteries derived from furfuryl alcohol

Sub-micron carbon spheres with high porosity are synthesized and tested as sodium-ion battery anodes. At a 1C rate, 1000 cycles (Na (de)insertion) are achieved with a capacity of 115 mA h g−1 @ 0.2V average.

Predicting capacity of hard carbon anodes in sodium-ion batteries using porosity measurements

We report an inverse relationship between measurable porosity values and reversible capacity from sucrose-derived hard carbon as an anode for sodium-ion batteries (SIBs). Materials with low measureable pore volumes and surface areas obtained through N2 sorption yield higher reversible capacities. Conversely, increasing measurable porosity and specific surface area leads to sharp decreases in reversible capacity. Utilizing a low porosity material, we thus are able to obtain a reversible capacity of 335mAhg−1. These findings suggest that sodium-ion storage is highly dependent on the absence of pores detectable through N2 sorption in sucrose-derived carbon.