Electrochemical synthesis of carbon-metal fluoride nanocomposites as cathode materials for lithium batteries

Herein we have demonstrated an electrochemical method for the synthesis of carbon-metal fluoride nanocomposites (CMNFCs). Electrochemical intercalation of transition metal ions into graphite fluoride (CFx) resulted in the formation of CMNFCs. As a proof-of-concept, we have synthesized C-FeF2 and C-NiF2 nanocomposites by the electrochemical intercalation of Fe2+ and Ni2+ into CFx from corresponding non-aqueous electrolytes. The C-FeF2 and C-NiF2 nanocomposites synthesized by this method showed high reversible capacity and cycling stability compared to chemically synthesized analogs as cathode materials for lithium batteries. The reversible capacity of chemically synthesized C-FeF2 is 181 mAh g-1, whereas electrochemically synthesized material is 349 mAh g-1 after 20 cycles. The better cycling performance of electrochemically synthesized C-FeF2 was attributed to the homogeneous distribution of FeF2 nanoparticles within the carbon matrix enabled by the electrochemical intercalation of Fe2+. The electrochemical method described here is emission-free, cost-effective, occurs at room temperature, and extendable to the synthesis of several other CMFNCs. Moreover, it might provide new avenues for the synthesis of advanced functional materials

Electrochemical synthesis of carbon-metal fluoride nanocomposites as cathode materials for lithium batteries

Herein we have demonstrated an electrochemical method for the synthesis of carbon-metal fluoride nanocomposites (CMFNCs). Electrochemical intercalation of transition metal ions into graphite fluoride (CF$_{x}$) resulted in the formation of CMFNCs. As a proof-of-concept, we have synthesized C-FeF$_{2}$ and C-NiF$_{2}$ nanocomposites by the electrochemical intercalation of Fe$^{2+}$ and Ni$^{2+}$ into CF$_{x}$ from corresponding non-aqueous electrolytes. The C-FeF$_{2}$ and C-NiF$_{2}$ nanocomposites synthesized by this method showed high reversible capacity and cycling stability compared to chemically synthesized analogs as cathode materials for lithium batteries. The reversible capacity of chemically synthesized C-FeF$_{2}$ is 181 mAh g$^{-1}$, whereas electrochemically synthesized material is 349 mAh g$^{-1}$ after 20 cycles. The better cycling performance of electrochemically synthesized C-FeF$_{2}$ was attributed to the homogeneous distribution of FeF$_{2}$ nanoparticles within the carbon matrix enabled by the electrochemical intercalation of Fe$^{2+}$. The electrochemical method described here is emission-free, cost-effective, occurs at room temperature, and extendable to the synthesis of several other CMFNCs. Moreover, it might provide new avenues for the synthesis of advanced functional materials

Ionically conducting inorganic binders: a paradigm shift in electrochemical energy storage

Among the key components in batteries, binders play a vital role by interconnecting active materials and conductive additives and facilitating the coating of electrode materials on the desired substrates thus enabling the flexible fabrication of batteries. Further, they aid in buffering volume changes that arise in electrode materials and enhance their cycling stability. Presently, polyvinylidene fluoride-based binders are employed widely, despite their high cost, non-eco-friendliness, and energy inefficiency. Several water processable binders have been investigated as alternatives, but they suffer from various intrinsic issues. Here, we reveal the potential of several ionically conducting inorganic binders (ICIBs). These ICIBs are not only ionically conducting, but also water processable, chemically compatible, eco-friendly, low-cost, thermally stable (>1000 °C), emission-free, and importantly, safe to use. These inorganic binders outperformed standard polyvinylidene fluoride-based binders in several aspects. Surprisingly, ICIBs are absorbing the exothermic heat evolved by charged cathode materials at high temperatures, which will significantly enhance the safety of the batteries. The unique intrinsic ionic conductive properties combined with binding abilities enabled the flexible processing and functioning of solid-state batteries, otherwise challenging due to the mechanical rigidity, chemical incompatibility, and interfacial issues posed by solid electrolytes. The inorganic binders introduced here will make battery manufacturing and recycling more energy-efficient, eco-friendly, flexible, safe, and above all, cost-effective

Micron-sized single-crystal cathodes for sodium-ion batteries

Confining the particle-electrolyte interactions to the particle surface in electrode materials is vital to develop sustainable and safe batteries. Micron-sized single-crystal particles offer such opportunities. Owing to the reduced surface area and grain boundary-free core, particle-electrolyte interactions in micron-sized single-crystal particles will be confined to the particle surface. Here, we reveal the potential of such materials in sodium-ion batteries. We synthesized and investigated the chemical, electrochemical, and thermal properties of single-crystalline P2-type Na(0.7)Mn(0.9)Mg(0.1)O(2) as a cathode material for sodium-ion batteries. Single-crystalline Na(0.7)Mn(0.9)Mg(0.1)O(2) with a mean particle size of 8.1 μm exhibited high cycling and voltage stability. In addition, the exothermic heat released by the charged single-crystal Na(0.7)Mn(0.9)Mg(0.1)O(2) cathodes was four times lower than that of the corresponding polycrystalline Na(0.7)Mn(0.9)Mg(0.1)O(2). This significantly enhances the thermal stability of electrode materials and possibly mitigates thermal runaways in batteries. Surprisingly, single crystals of Na(0.7)Mn(0.9)Mg(0.1)O(2) were relatively stable in water and ambient atmosphere

Unlocking the potential of weberite-type metal fluorides in electrochemical energy storage

Sodium-ion batteries (NIBs) are a front-runner among the alternative battery technologies suggested for substituting the state-of-the-art lithium-ion batteries (LIBs). The specific energy of Na-ion batteries is significantly lower than that of LIBs, which is mainly due to the lower operating potentials and higher molecular weight of sodium insertion cathode materials. To compete with the high energy density of LIBs, high voltage cathode materials are required for NIBs. Here we report a theoretical investigation on weberite-type sodium metal fluorides (SMFs), a new class of high voltage and high energy density materials which are so far unexplored as cathode materials for NIBs. The weberite structure type is highly favorable for sodium-containing transition metal fluorides, with a large variety of transition metal combinations (M, M’) adopting the corresponding Na2MM’F7 structure. A series of known and hypothetical compounds with weberite-type structure were computationally investigated to evaluate their potential as cathode materials for NIBs. Weberite-type SMFs show two-dimensional pathways for Na+ diffusion with surprisingly low activation barriers. The high energy density combined with low diffusion barriers for Na+ makes this type of compounds promising candidates for cathode materials in NIBs

Insight into Sulfur Confined in Ultramicroporous Carbon

Here, we provide a deeper insight into the state of sulfur confined in ultramicroporous carbon (UMC) and clarify its electrochemical reaction mechanism with lithium by corroborating the results obtained using various experimental techniques, such as X-ray photoelectron spectroscopy, electron energy loss spectroscopy, in situ Raman spectroscopy, and in situ electrochemical impedance spectroscopy. In combination, these results indicate that sulfur in UMC exists as linear polymeric sulfur rather than smaller allotropes. The electrochemical reactivity of lithium with sulfur confined in UMC (pore size ≤0.7 nm) is different from that of sulfur confined in microporous carbon (≤2 nm, or ultramicroporous carbon containing significant amount of micropores) and mesoporous carbon (>2 nm). The observed quasi-solid-state reaction of lithium with sulfur in UMC with a single voltage plateau during the discharge/charge process is due to the effective separation of solvent molecules from the active material. The size of carbon pores plays a vital role in determining the reaction path of lithium with sulfur confined in UMC

Validation of QTL mapping and transcriptome profiling for identification of candidate genes associated with nitrogen stress tolerance in sorghum

Background: Quantitative trait loci (QTLs) detected in one mapping population may not be detected in other mapping populations at all the time. Therefore, before being used for marker assisted breeding, QTLs need to be validated in different environments and/or genetic backgrounds to rule out statistical anomalies. In this regard, we mapped the QTLs controlling various agronomic traits in a recombinant inbred line (RIL) population in response to Nitrogen (N) stress and validated these with the reported QTLs in our earlier study to find the stable and consistent QTLs across populations. Also, with Illumina RNA-sequencing we checked the differential expression of gene (DEG) transcripts between parents and pools of RILs with high and low nitrogen use efficiency (NUE) and overlaid these DEGs on to the common validated QTLs to find candidate genes associated with N-stress tolerance in sorghum. Results: An F7 RIL population derived from a cross between CK60 (N-stress sensitive) and San Chi San (N-stress tolerant) inbred sorghum lines was used to map QTLs for 11 agronomic traits tested under different N-levels. Composite interval mapping analysis detected a total of 32 QTLs for 11 agronomic traits. Validation of these QTLs revealed that of the detected, nine QTLs from this population were consistent with the reported QTLs in earlier study using CK60/China17 RIL population. The validated QTLs were located on chromosomes 1, 6, 7, 8, and 9. In addition, root transcriptomic profiling detected 55 and 20 differentially expressed gene (DEG) transcripts between parents and pools of RILs with high and low NUE respectively. Also, overlay of these DEG transcripts on to the validated QTLs found candidate genes transcripts for NUE and also showed the expected differential expression. For example, DEG transcripts encoding Lysine histidine transporter 1 (LHT1) had abundant expression in San Chi San and the tolerant RIL pool, whereas DEG transcripts encoding seed storage albumin, transcription factor IIIC (TFIIIC) and dwarfing gene (DW2) encoding multidrug resistance-associated protein-9 homolog showed abundant expression in CK60 parent, similar to earlier study. Conclusions: The validated QTLs among different mapping populations would be the most reliable and stable QTLs across germplasm. The DEG transcripts found in the validated QTL regions will serve as future candidate genes for enhancing NUE in sorghum using molecular approaches

Greener, Safer and Better Performing Aqueous Binder for Positive Electrode Manufacturing of Sodium Ion Batteries

P2-type cobalt-free MnNi-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their high reversible capacity and well chemical stability. However, the phase transformations during repeated (dis)charge steps lead to rapid capacity decay and deteriorated Na+ diffusion kinetics. Moreover, the electrode manufacturing based on polyvinylidene difluoride (PVDF) binder system has been reported with severely defluorination issue as well as the energy intensive and expensive process due to the use of toxic and volatile N-methyl-2-pyrrolidone (NMP) solvent. It calls for designing a sustainable, better performing, and cost-effective binder for positive electrode manufacturing. In this work, we investigated inorganic sodium metasilicate (SMS) as a viable binder in conjunction with P2-Na0.67Mn0.55Ni0.25Fe0.1Ti0.1O2 (NMNFT) cathode material for SIBs. The NMNFT-SMS electrode delivered a superior electrochemical performance compared to carboxy methylcellulose (CMC) and PVDF based electrodes with a reversible capacity of ~161 mAh/g and retaining ~83 % after 200 cycles. Lower cell impedance and faster Na+ diffusion was also observed in this binder system. Meanwhile, with the assistance of TEM technique, SMS is suggested to form a uniform and stable nanoscale layer over the cathode particle surface, protecting the particle from exfoliation/cracking due to electrolyte attack. It effectively maintained the electrode connectivity and suppressed early phase transitions during cycling as confirmed by operando XRD study. With these findings, SMS binder can be proposed as a powerful multifunctional binder to enable positive electrode manufacturing of SIBs and to overall reduce battery manufacturing costs

Unlocking the potential of weberite-type metal fluorides in electrochemical energy storage

Sodium-ion batteries (NIBs) are a front-runner among the alternative battery technologies suggested for substituting the state-of-the-art lithium-ion batteries (LIBs). The specific energy of Na-ion batteries is significantly lower than that of LIBs, which is mainly due to the lower operating potentials and higher molecular weight of sodium insertion cathode materials. To compete with the high energy density of LIBs, high voltage cathode materials are required for NIBs. Here we report a theoretical investigation on weberite-type sodium metal fluorides (SMFs), a new class of high voltage and high energy density materials which are so far unexplored as cathode materials for NIBs. The weberite structure type is highly favorable for sodium-containing transition metal fluorides, with a large variety of transition metal combinations (M, M’) adopting the corresponding Na2MM’F7 structure. A series of known and hypothetical compounds with weberite-type structure were computationally investigated to evaluate their potential as cathode materials for NIBs. Weberite-type SMFs show two-dimensional pathways for Na+ diffusion with surprisingly low activation barriers. The high energy density combined with low diffusion barriers for Na+ makes this type of compounds promising candidates for cathode materials in NIBs