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1. Electrochemical Performance of LixSiON Polymer Electrolytes Derived from an Agriculture Waste Product, Rice Hull Ash

   https://doi.org/10.1021/acsapm.1c00192  

   Temeche, E. ; Zhang, X. ; Laine, R. M. ( March 2021 , ACS applied polymer materials)

   The electrochemical performance of LixSiON (x = 2, 4, and 6) polymer electrolytes derived from the agricultural waste, rice hull ash (RHA, 80−90 wt % SiO2), is reported. Silica can be extracted from RHA by base-catalyzed reaction with hexylene glycol forming the spirosiloxane [(C6H12O2)2Si, SP] that distills from the reaction solution. LixSiON polymer electrolytes form on reacting SP with xLiNH2, offering a low-cost, low- temperature, and green synthesis route. The effect of N and Li+ concentrations in the polymer electrolytes are correlated with ionic and electrical conductivity. X-ray photoelectron spectroscopy studies confirm that N and Li contents increase with increasing LiNH2 content. The amorphous nature and high Li+ contents of the Li6SiON electrolyte provide an optimal ionic conductivity (6.5 × 10−6) at ambient temperature when coated on Celgard. Furthermore, the LixSiON polymer electrolytes offer high Li+ transference numbers (∼0.75−1), enabling assembly of Li symmetric cells with high critical current densities (3.75 mA cm−2). Finally, Li-SPAN (sulfurized, carbonized polyacrylonitrile) half-cells with Li6SiON polymer electrolytes deliver discharge capacities of ∼765 and 725 mAh/g at 0.25 and 0.5 C rates over 50 cycles. 

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2. LiAlO2/LiAl5O8 thin films derived from flame synthesized nanopowders as a potential electro-lyte and coating materials for all solid-state batteries (ASSBs)

   https://doi.org/DOI:10.1021/acsami.0c13021  

   E. Temeche, S. Indris ( July 2020 , ACS applied materials interfaces)

   null (Ed.)

   Recently, γ-LiAlO2 has attracted considerable attention as a coating in Li-ion battery electrodes. However, its potential as a Li+ ceramic electrolyte is limited due to its poor ionic conductivity (<10−10 S cm−1). Here, we demonstrate an effective method of processing LiAlO2 membranes (<50 μm) using nanopowders (NPs) produced via liquid-feed flame spray pyrolysis(LF-FSP). Membranes consisting of selected mixtures of lithium aluminate polymorphs and Li contents were processed byconventional tape casting of NPs followed by thermocompressionof the green films (100 °C/10 kpsi/10 min). The sintered greenfilms (1100 °C/2 h/air) present a mixture of LiAlO2 (∼72 wt %)and LiAl5O8 (∼27 wt %) phases, offering ionic conductivities (>10−6 S cm−1) at ambient with an activation energy of 0.5 eV. This greatly increases their potential utility as ceramic electrolytes for all-solid-state batteries, which could simplify battery designs, significantly reduce costs, and increase their safety. Furthermore, a solid-state Li/Li3.1AlO2/Li symmetric cell was assembled and galvanostatically cycled at 0.375 mA cm−2 current density, exhibiting a transference number ≈ 1. 

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3. Adjusting SiO2 : C mole ratios in rice hull ash (RHA) to control carbothermal reduction to nanostructured SiC, Si3N4 or Si2N2O composites

   https://doi.org/10.1039/D1GC02084F  

   Yu, M. ; Temeche, E. ; Indris, S. ; Laine, R. M. ( September 2022 , Green chemistry)

   We report here extracting SiO2 as spirosiloxane [(CH3)2C(O)CH2CH(O)CH3]2Si from rice hull ash (RHA) to carefully control the SiO2 : C mole ratios, allowing direct carbothermal reduction to SiC, Si3N4, or Si2N2O without the need to add extra carbon and as a mechanism to preserve the original nanocomposite structure. We can adjust SiO2 : C ratios from 2 : 15 to 13 : 35 simply by reacting RHA with hexylene glycol (HG) with catalytic base to distillatively extract SiO2 to produce silica depleted RHA (SDRHA) with SiO2 contents of 40–65 wt% and corresponding carbon contents of 60–35 wt% with specific surface areas (SSAs) of >400 m2 g−1. On heating SDRHA40–65 at 1400–1500 °C in an Ar, N2, or N2–H2 atmosphere, XRD patterns reveal formation of SiC, Si3N4, or Si2N2O as the major phase with some residual hard carbon. SEM studies reveal mixtures of particles and whiskers in the products, which show BET specific surface areas >40 m2 g−1 after oxidative removal of excess carbon. Dilute acid and boiling water prewashing of RHA with milling eliminates typical product impurities compared to those found using conventional carbothermal reduction of agricultural wastes, which qualifies the resulting composites as components for electrochemical energy storage devices among other applications, to be reported elsewhere. 

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4. Silicon carbide (SiC) derived from agricultural waste potentially competitive with silicon anodes

   https://doi.org/10.1039/D2GC00645F  

   Yu, M. ; Temeche, E. ; Indris, S. ; Lai, W. ; Laine, R. M. ( April 2022 , Green chemistry)

   Biomass-derived materials offer low carbon approaches to energy storage. High surface area SiC w/wo 13 wt% hard carbon (SiC/HC, SiC/O), derived from carbothermal reduction of silica depleted rice hull ash (SDRHA), can function as Li+ battery anodes. Galvanostatic cycling of SiC/HC and SiC/O shows capacity increases eventually to >950 mA h g−1 (Li1.2–1.4SiC) and >740 mA h g−1 (Li1.1SiC), respectively, after 600 cycles. Post-mortem investigation via XRD and 29Si MAS NMR reveals partial phase transformation from 3C- to 6H-SiC, with no significant changes in unit cell size. SEMs show cycled electrodes maintain their integrity, implying almost no volume expansion on lithiation/delithiation, contrasting with >300% volume changes in Si anodes on lithiation. Significant void space is needed to compensate for these volume changes with Si in contrast to SiC anodes suggesting nearly competitive capacities. 6Li MAS NMR and XPS show no evidence of LixSi, with Li preferring all-C environments supported by computational modeling. Modeling also supports deviation from the 3C phase at high Li contents with minimal volume changes. 

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5. Silica depleted rice hull ash (SDRHA), an agricultural waste, as a high-performance hybrid lithium-ion capacitor

   https://doi.org/10.1039/D0GC01746A  

   E. Temeche, M. Yu ( July 2020 , Green chemistry)

   null (Ed.)

   Rice hull ash (RHA, an agricultural waste) produced during combustion of rice hulls to generate electricity consists (following dilute acid leaching) of high surface area SiO2 (80–90 wt%) and 10–20 wt% carbon (80 m2 g−1 total). RHA SiO2 is easily extracted by distillation (spirosiloxane) producing SDRHA, which offers an opportunity to develop “green” hybrid lithium-ion capacitors (LICs) electrodes. SDRHA consists of 50–65 wt% SiO2 with the remainder carbon with a specific surface area of ≈220 m2 g−1. SDRHA microstructure presents a highly irregular and disordered nanocomposite composed of nanosilica closely connected via graphene layers enhancing Li-ion mobility during charge/discharge process. SDRHA electrochemicalproperties were assessed by assembling Li/SDRHA half-cells and LiNi0.6Co0.2Mn0.2O2 (NMC622)-SDRHA full-cells. The half-cell delivered a high specific capacity of 250 mA h g−1 at 0.5C and retained a capacity of 200 mA h g−1 at 2C for 400 h. In contrast to the poor cycle performance of NMC based batteries at high C-rates, the hybrid full-cell demonstrated a high specific capacitance of 200 F g−1 at 4C. In addition, both the half and full hybrid cells demonstrate excellent coulombic efficiencies (∼100%). These results suggest that low cost and environmentally friendly SDRHA, may serve as a potentialalternative electrode material for LICs. 

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