Lithium recovery from geothermal brine – an investigation into the desorption of lithium ions using manganese oxide adsorbents

Spinel type lithium manganese oxides (LMOs) are promising adsorption materials for selective recovery of lithium from salty brines. In this work a lithium-ion sieve material, H$_{1.6}$Mn$_{1.6}$O$_{4}$, derived from Li$_{1.6}$Mn$_{1.6}$O$_{4}$4, a spinel type LMO, was successfully prepared via hydrothermal synthesis. This lithium-ion sieve, H$_{1.6}$Mn$_{1.6}$O$_{4}$, was then used in laboratory tests to adsorb Li+ from a generic LiCl solution and geothermal brine from Bruchsal geothermal power plant. Desorption experiments were performed with the following desorption solutions: ammonium peroxydisulfate ((NH$_{4}$)$_{2}$S$_{2}$O$_{8}$), sodium peroxydisulfate (Na$_{2}$S$_{2}$O$_{8}$), acetic acid (CH$_{3}$COOH), sulfuric acid (H$_{2}$SO$_{4}$), carbonic acid (H$_{2}$CO$_{3}$), ascorbic (C$_{6}$H$_{8}$O$_{6}$) and hydrochloric acid (HCl). The results showed that C$_{6}$H$_{8}$O$_{6}$ led to adsorbent destruction and only small amount of lithium was desorbed with H$_{2}$CO$_{3}$. CH$_{3}$COOH and (NH$_{4}$)$_{2}$S$_{2}$O$_{8}$ showed the best desorption performance with high lithium recovery and low Mn dissolution. The kinetic experiments indicate that more than 90% of equilibrium was reached after 4 hours. A decline in the adsorption/desorption capacity was measured for all desorption agents after eight cycles in the long-term experiments. These long-term tests revealed that higher lithium recovery in desorption with HCl and CH$_{3}$COOH was achieved compared to (NH$_{4}$)$_{2}$S$_{2}$O$_{8}$. On the other hand, the use of CH$_{3}$COOH and (NH$_{4}$)$_{2}$S$_{2}$O$_{8}$ seems to be advantageous to HCl because of lower Mn dissolution. According to the XRD results, the spinel structure of the treated adsorbents was preserved, but a weakening of the peak intensity was observed. Analyzing the adsorbent composition after eight cycles, an accumulation of competing ions was observed. This was especially remarkable when acetic acid was used

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved

Electrochemical Li Storage Properties of Carbon-Rich B–C–N Ceramics

Amorphous BCN ceramics were synthesized via a thermal conversion procedure of piperazine–borane and pyridine–borane. The synthesized BC₂N and BC₄N ceramics contained, in their final amorphous structure, 45 and 65 wt % of carbon, respectively. Elemental analysis revealed 45 and 65 wt % of carbon for BC₂N and BC₄N, respectively. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed the amorphous nature of studied compounds. Lateral cluster size of carbon crystallites of 7.43 and 10.3 nm for BC₂N and BC₄N, respectively, was calculated from Raman spectroscopy data. This signified a higher order of the carbon phase present in BC₄N. The electrochemical investigation of the low carbon BC₂N composition as anodes for Li-ion batteries revealed initial capacities of 667 and 235 mAh·g⁻¹ for lithium insertion/extraction, respectively. The material with higher carbon content, BC₄N, disclosed better reversible lithium storage properties. Initial capacities of 1030 and 737 mAh·g⁻¹ for lithium insertion and extraction were recovered for carbon-rich BC₄N composition. Extended cycling with high currents up to 2 C/2 D revealed the cycling stability of BC4N electrodes. Cycling for more than 75 cycles at constant current rates showed a stable electrochemical behavior of BC₄N anodes with capacities as high as 500 mAh·g⁻¹

SiCN Ceramics as Electrode Materials for Sodium/Sodium Ion Cells – Insights from ²³Na In‐Situ Solid‐State NMR

Polymer-derived silicon carbonitride ceramic (SiCN) is used as an electrode material to prepare cylindrical sodium/sodium ion cells for solid-state NMR investigations. During galvanostatic cycling structural changes of the environment of sodium/sodium ions are investigated by applying ²³Na in-situ solid-state NMR. Changes of the signals assigned to sodium metal, intercalated sodium cation and sodium cation originating from the electrolyte are monitored as well as the occurrence of an additional signal in the region of metallic sodium. The intensity of this additional signal changes periodically with the cycling process indicating the reversibility of structures formed and deformed during the galvanostatic cycling. To identify interactions of sodium/sodium ions with the SiCN electrode materials, the cycled SiCN material is studied by ²³Na ex-situ MAS NMR at high spinning rates of 20 and 50 kHz to obtain appropriate spectral resolution

Impact of blending with polystyrene on the microstructural and electrochemical properties of SiOC ceramic

In this work, we present the electrochemical behavior and microstructural analysis of silicon oxycarbide (SiOC) ceramics influenced by an addition of polystyrene (PS). Polymer-derived ceramics were obtained by pyrolysis (1000 degrees C, Ar atmosphere) of different polysiloxanes prepared by sol-gel synthesis. This method is very effective to obtain desired composition of final ceramic. Two alkoxysilanes phenylthriethoxysilane and diphenyldimethoxysilane were used as precursors. Before pyrolysis polysiloxanes were mixed with PS using toluene as a solvent. Blending with PS affects the microstructure and free carbon content in the final ceramic material. Free carbon phase has been confirmed to be a major lithium storage host. Nevertheless, we demonstrate here that capacity does not increase linearly with increasing carbon content. We show that the amount of SiO4 units in the SiOC microstructure increases the initial capacity but decreases the cycling stability and rate capability of the material. Furthermore, the microstructure of the free carbon influences the electrochemical performance of the ceramic: More ordered graphitic clusters favor better rate capability performance

Determination of the chemical diffusion coefficient of Li-ions in carbon-rich silicon oxycarbide anodes by electro-analytical methods

The diffusion coefficient of Li-ions (DLi+) within carbon-rich silicon-oxycarbide ceramic anodes of specific chemical composition SiO0.95C3.72 is determined by potentiostatic and galvanostatic intermittent titration technique (PITT, GITT) and electrochemical impedance spectroscopy (EIS). The estimated values for DLi+ range between 10−9 and 10−11 cm2 s−1, dependent on the applied method. The observed variation of DLi+ is in a comparable range as reported for disordered carbons, well reflecting the Li-ion storage in the segregated free carbon phase in the amount of about 43 wt-% within the SiOC microstructure. However, in contrast to graphite and disordered carbons, the diffusion coefficient of lithium within carbon-rich SiOC is less potential dependent. This feature is discussed with respect to the particular morphology of the free carbon phase

Carbon-rich SiOC anodes for lithium-ion batteries: Part II. Role of thermal cross-linking

This paper presents the study of lithium insertion into carbon-rich polymer-derived silicon oxycarbide (SiOC) ceramics, synthesized by a thermal treatment of commercially available polysiloxane at 400 °C, followed by pyrolysis at 1100 and 1300 °C. The investigated samples demonstrate a similar chemical composition and provide a high amount of free carbon as separate phase within their microstructure. XRD- and Raman-measurements led us to identify the free carbon phase as a mixture of disordered carbon, nano-crystalline graphite and graphene sheets. This advantageous composition offers a large variety of Li-Ion storage sites, providing high lithiation capacities and reliable cycling behavior. In particular the 1100 °C sample demonstrates a stable reversible capacity of 521 mAhg− 1 at a cycling current of 37 mAg− 1, which is significantly higher than the theoretical capacity of graphite. The inferior performance of the 1300 °C sample with 367 mAhg− 1 at 37 mAg− 1 is attributed to a changed microstructure, namely an increased carbon organization within the free carbon phase and SiC crystallization at this temperature. In both cases, the thermal cross-linking leads to much better electrochemical properties than observed for directly pyrolyzed samples

Composite materials based on polymer-derived SiCN ceramic and disordered hard carbons as anodes for lithium-ion batteries

New composite materials based on polymer-derived SiCN ceramics and hard carbons were studied in view of its application as anodes for lithium-ion batteries. Two kinds of composites were prepared by pyrolysis of the preceramic polysilazane (HTT1800, Clariant) at 1000 °C in Ar atmosphere mixed with hard carbons derived from potato starch (HC_PS) or with a hard carbon precursor, namely potato starch (PS), denoted as HTT/HC_PS and HTT/PS composites, respectively. Thermal gravimetric analysis suggests possible reactions between the preceramic polymer and the carbon precursor. The HTT/PS composites contain higher amount of oxygen and appear to be more homogeneous than that of the HTT/HC_PS composite. Raman analysis confirms the presence of highly disordered carbon in the composites by the appearance of the well-pronounced D band at 1347 cm−1. The materials are amorphous with a significant fraction of single graphene sheets as confirmed by X-ray diffraction. The HTT/PS composite exhibits a high-recovered capacity (434 mAh g−1 when charging with a current of 36 mA g−1) and outstanding cyclability for 400 cycles even at high current rates (90 mAh g−1 when charging with 3600 mA g−1). These properties make the composite a candidate anode material for high power energy devices

Lithium insertion into carbon-rich SiOC ceramics: Influence of pyrolysis temperature on electrochemical properties

Carbon-rich silicon oxycarbide ceramics (SiOC) prepared via thermal conversion of polyorganosiloxane demonstrate high lithiation capacity and reliable rate capability when used as anode material in Li-ion batteries. The electrochemical properties of carbon-rich SiOC are strongly related to microstructure and phase composition, dependent on final pyrolysis temperature. Both, the increasing organization of free carbon segregated within the microstructure and the gradual degradation of the amorphous Si–O–C network with increasing pyrolysis temperature (Tpyr) lead to reduced capacities and changing voltage profiles. Within our study, the highest registered capacity of 660 mAh g−1 for Tpyr = 900 °C dropped below 80 mAh g−1 for SiOC pyrolyzed at 2000 °C. A continuous decrease in capacity is observed, when increasing Tpyr stepwise by 100 °C, which can be explained by major microstructural changes. First, the free carbon within the ceramic microstructure organizes toward higher ordered configurations, as determined by Raman spectroscopy. Second, X-ray powder diffraction demonstrates a decomposition of the amorphous Si–O–C network resulting in SiC crystallization and growth of SiC domains. Simultaneously, FTIR spectroscopy shows a strong increase of Si–C vibration with Tpyr, while Si–O vibration diminishes and almost disappears after annealing at 1700–2000 °C. According to our study we find, that i) increasing carbon organization provides less Li-ion storing sites, ii) gradual Si–O–C network decomposition reduces the structural stability of the free carbon phase and iii) formation of electrochemically inactive SiC account for reduced capacities and changing voltage profiles with increasing Tpyr

On the Reversible Sodium Plating/stripping Reaction in Porous SiCN(O) Ceramic: A Feasibility Study

Sodium-ion batteries (SIBs) are a cost-effective and sustainable alternative to lithium-ion batteries (LIBs), which might be independent of rare raw materials. These advantages come at the expense of low energy density. Sodium metal batteries (SMBs) can provide a possible solution. In this work, we present the use of a porous silicon carbonitride (SiCN(O)) ceramic as an anodic matrix for reversible Na-plating. The role of the pores is investigated and the plating mechanism allowing reversible and uniform plating/stripping of sodium is also presented. Electrochemical studies show a stable and reversible capacity gain of around 60 mAh/g beyond the insertion capacity of the SiCN(O) ceramic over 100 cycles