A set of LixSiON (x = 2, 4, 6) polymer precursors to a novel solid-state electrolyte system were synthesized starting from rice hull ash (RHA), an agricultural waste, providing a green route towards the assembly of all solid-state batteries (ASSBs). Silica, ∼90 wt% in RHA, can be catalytically (alkali base) dissolved (20–40 wt%) in hexylene glycol (HG) and distilled directly from the reaction mixture as the spirosiloxane [(C6H14O2)2Si, SP] at 200 °C. SP can be lithiated using controlled amounts of LiNH2 to produce LixSiON oligomers/polymers with MWs up to ∼1.5 kDa as characterized by FTIR, MALDI-ToF, multinuclear NMR, TGA-DTA, XRD, XPS, SEM and EDX. XPS analyses show that Li contents depend solely on added LiNH2
but found N contents are only ≤1 at%. NH2 likely is removed as NH3 during sample preparation (vacuum/ overnight). In contrast, MALDI indicates N contents of ∼5–30 at% N with shorter drying times (vacuum/ minutes). 7Li NMR positive chemical shifts suggest that precursor bound Li+ ions dissociate easily, ben- eficial for electrochemical applications. The 7Li shifts correlate to Li contents as well as Li+ conductivities. 1H, 13C and 29Si NMRs of the Li6SiON precursor show fluxional behavior implying high Li+ mobility. Dense microstructures are observed for Li4SiON and Li6SiON pellets heated to 200 °C/2 h/N2. Impedance studies suggest that ionic conductivities increase with Li content; the Li6SiON precursor offers the highest ambient conductivity of 8.5 × 10−6 S cm−1 after heating to 200 °C/2 h/N2.
more »
« less
Electrochemical Performance of LixSiON Polymer Electrolytes Derived from an Agriculture Waste Product, Rice Hull Ash
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.
more »
« less
- Award ID(s):
- 1926199
- NSF-PAR ID:
- 10357008
- Date Published:
- Journal Name:
- ACS applied polymer materials
- Volume:
- 3
- ISSN:
- 2637-6105
- Page Range / eLocation ID:
- 2144-2152
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Sulfide solid‐state electrolytes have remarkable ionic conductivity and low mechanical stiffness but suffer from relatively narrow electrochemical and chemical stability with electrodes. Therefore, pairing sulfide electrolytes with the proper cathode is crucial in developing stable all‐solid‐state Li batteries (ASLBs). Herein, one type of thioantimonate ion conductor, Li6+
x Gex Sb1−x S5I, with different compositions is systematically synthesized and studied, among these compositions, an outstanding ionic conductivity of 1.6 mS cm−1is achieved with Li6.6Ge0.6Sb0.4S5I. To improve the energy density and advance the interface compatibility, a metal sulfide FeS2cathode with a high theoretical capacity (894 mAh g−1) and excellent compatibility with sulfide electrolytes is coupled with Li6.6Ge0.6Sb0.4S5I in ASLBs without additional interface engineering. The structural stabilities of Li6.6Ge0.6Sb0.4S5I and FeS2during cycling are characterized by operando energy dispersive X‐ray diffraction, which allows rapid collection of structural data without redesigning or disassembling the sealed cells and risking contamination by air. The electrochemical stability is assessed, and a safe operating voltage window ranging from 0.7≈2.4 V (vs. In–Li) is confirmed. Due to the solid confinement in the ASLBs, the Fe0aggregation and polysulfides shuttle effects are well addressed. The ASLBs exhibit an outstanding initial capacity of 715 mAh g−1at C/10 and are stable for 220 cycles with a high capacity retention of 84.5% at room temperature. -
more » « less
Tantalum‐doped lithium lanthanum zirconate garnet (Li7−
x La3Zr2−x Tax O12[LLZTO]) has received interest as a solid electrolyte for solid‐state lithium batteries due to its good electrochemical properties and ionic conductivity. However, the source of discrepancies for reported values of ionic conductivity in nominally or nearly equivalent compositions of LLZTO is not completely clear. Herein, synthesis‐related factors that may contribute to the differences in performance of garnet electrolytes are systematically characterized. The conductivity of samples with composition Li6.4La3Zr1.4Ta0.6O12prepared by various methods including solid‐state reaction (SSR), combustion, and molten salt synthesis is compared. Varying levels of elemental inhomogeneity, comprising a variation in Ta and Zr content on the level of individual LLZTO particles, are identified. The elemental inhomogeneity is found to be largely preserved even after high‐temperature sintering and correlated with reduced ionic conductivity. It is shown that the various synthesis and processing‐related variables in each of the preparation methods play a role in these compositional variations, and that even LLZTO synthesized via conventional, high‐temperature SSR can exhibit substantial variability in local composition. However, by improving reagent mixing and using LLZTO powder with low agglomeration and small particle size distribution, the compositional uniformity, and hence, ionic conductivity, of sintered garnet electrolytes can be improved. -
more » « less
Abstract Polymer–ceramic composite electrolytes are emerging as a promising solution to deliver high ionic conductivity, optimal mechanical properties, and good safety for developing high‐performance all‐solid‐state rechargeable batteries. Composite electrolytes have been prepared with cubic‐phase Li7La3Zr2O12(LLZO) garnet and polyethylene oxide (PEO) and employed in symmetric lithium battery cells. By combining selective isotope labeling and high‐resolution solid‐state Li NMR, we are able to track Li ion pathways within LLZO‐PEO composite electrolytes by monitoring the replacement of7Li in the composite electrolyte by6Li from the6Li metal electrodes during battery cycling. We have provided the first experimental evidence to show that Li ions favor the pathway through the LLZO ceramic phase instead of the PEO‐LLZO interface or PEO. This approach can be widely applied to study ion pathways in ionic conductors and to provide useful insights for developing composite materials for energy storage and harvesting.
-
null (Ed.)Polyethylene oxide (PEO)-based polymers are commonly studied for use as a solid polymer electrolyte for rechargeable Li-ion batteries; however, simultaneously achieving sufficient mechanical integrity and ionic conductivity has been a challenge. To address this problem, a customized polymer architecture is demonstrated wherein PEO bottle-brush arms are hyperbranched into a star architecture and then functionalized with end-grafted, linear PEO chains. The hierarchical architecture is designed to minimize crystallinity and therefore enhance ion transport via hyperbranching, while simultaneously addressing the need for mechanical integrity via the grafting of long, PEO chains ( M n = 10,000). The polymers are doped with lithium bis(trifluoromethane) sulfonimide (LiTFSI), creating hierarchically hyperbranched (HB) solid polymer electrolytes. Compared to electrolytes prepared with linear PEO of equivalent molecular weight, the HB PEO electrolytes increase the room temperature ionic conductivity from ∼2.5 × 10 –6 to 2.5 × 10 −5 S/cm. The conductivity increases by an additional 50% by increasing the block length of the linear PEO in the bottle brush arms from M n = 1,000 to 2,000. The mechanical properties are improved by end-grafting linear PEO ( M n = 10,000) onto the terminal groups of the HB PEO bottle-brush. Specifically, the Young’s modulus increases by two orders of magnitude to a level comparable to commercial PEO films, while only reducing the conductivity by 50% below the HB electrolyte without grafted PEO. This study addresses the trade-off between ion conductivity and mechanical properties, and shows that while significant improvements can be made to the mechanical properties with hierarchical grafting of long, linear chains, only modest gains are made in the room temperature conductivity.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acsapm.1c00192
