Major challenges in the development of solid-state batteries using garnet-type solid-state electrolytes (SSEs) include suppressing dendrite growth, improving moisture stability, and reducing interfacial resistance. Prior attempts to remove surface impurities of SSEs through dry polishing caused high interfacial resistance that proves this method to be unviable. Further, several efforts on depositing thin-film protective layers on SSEs without understanding surface chemistry failed to demonstrate improved electrochemical performance. Here, we report the simultaneous removal of the surface impurities and protection of the SSE against air and moisture by regulating its surface chemistry. In situ X-ray photoelectron spectroscopy (XPS) studies revealed that primary surface contaminants such as lithium carbonate (Li 2 CO 3 ) and lithium hydroxide on the SSE, Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZT), could be removed by either argon-ion sputtering at 227 °C or annealing at 777 °C in ultrahigh vacuum conditions. To protect the cleaned LLZT surface from further ambient contamination, in situ atomic layer deposition was used to deposit ∼3 nm-thick h-BN using tris(dimethylamino)borane and ammonia precursors at 450 °C. Intermittent XPS analysis confirmed the absence of Li 2 CO 3 formation and the stability of h-BN-coated LLZT pellets for over 2 months of exposure to atmospheric air and moisture. Electrochemical impedance spectroscopy studies revealed that an ultrathin layer of ∼3 nm h-BN drastically reduced the interfacial resistance from 1145 to 18 Ω cm 2 (∼65× reduction). Li plating/stripping studies revealed a constant polarization of 27 mV at a 0.5 mA cm −2 current density over prolonged cycling and a high critical current density of 0.9 mA cm −2 . An all-solid-state battery using a LiFePO 4 cathode exhibited a stable capacity of 130 mAh g −1 for over 100 cycles and a negligible capacity fade-off of 0.11 mAh g −1 per cycle at an average Coulombic efficiency of 98.4%.
Electro- and photocatalytic reduction of N2 to NH3 – the nitrogen reduction reaction (NRR) – is an environmentally- and energy-friendly alternative to the Haber-Bosch process for ammonia production. There is a great demand for the development of novel semiconductor-based electrocatalysts with high efficiency and stability to perform this process under visible light irradiation and ambient conditions. Herein we report electro-, and photocatalytic NRR with transition metal dichalcogenides (TMDCs), viz MoS2 and WS2. Improved acid treatment of bulk TMDCs yields exfoliated TMDCs (exTMDCs) only a few layers thick with ~10 % S vacancies. Linear scan voltammograms on exMoS2 and exWS2 electrodes reveal significant NRR activity for exTMDC-modified electrodes, which is greatly enhanced by visible light illumination. Spectral measurements confirm ammonia as the main reaction product of electrocatalytic and photocatalytic NRR, and the absence of hydrazine byproduct. Femtosecond-resolved transient absorption studies provide direct evidence of interaction between photo-generated excitons/trions with N2 adsorbed at S vacancies. DFT calculations corroborate N2 binding to exMoS2 at S-vacancies, with substantial pi-backbonding to activate dinitrogen. Our findings suggest that chemically functionalized exTMDC materials could fulfill the need for highly-desired, inexpensive catalysts for the sustainable production of NH3 using sunlight under neutral pH conditions.
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Currently, the demand for lithium-ion batteries is high due to its application in portable electronics, electric vehicles, and grid energy storage.1-2 The safety threat imposed by the liquid organic electrolyte can be eliminated by employing solid-state electrolytes (SSEs) that would also potentially enable the use of lithium metal anode (highest theoretical capacity, 3861 mAh g-1).3 Among several SSEs, garnet-type SSEs are comparatively stable with metallic lithium and they possess a wide electrochemical stability window.4 However, there are several unaddressed issues like the high interfacial resistance, instability of garnets in moisture containing atmosphere, propagation of lithium dendrites, etc. that hinders their practical application.3 Our investigation focuses on the removal of the detrimental lithium carbonate and lithium hydroxide layers from the surface of the garnets using two methods, namely argon-ion sputtering and ultra-high vacuum annealing. Precise control of the surface contaminant removal was achieved using in-situ X-ray photoelectron spectroscopy (XPS).5 The pristine garnet surface was found to be extremely atmosphere sensitive through XPS measurements. To overcome the sensitivity issue, atomic layer deposition (ALD) of 3 nm of h-BN was carried out using tris(dimethylamino)borane and ammonia precursors at 450 oC. The initial layers close to the garnet were present in an oxidized form (BNxOy) due to the oxygen-rich composition of garnet and the h-BN was capped over these layers, which were confirmed using angle-resolved XPS. The interfacial resistance drastically reduced from 1145 to 18 Ω cm2 through these processes. The inherent insulating nature of h-BN blocked the leakage of electrons across the solid-electrolyte and prevented the propagation of lithium dendrites. This enabled the plating and stripping of lithium in a symmetrical cell at a current density of 0.5 mA cm-2 with uniform polarization for over 200 hours. All-solid-state battery assembled using LiFePO4 cathode and Li anode exhibited stable cycling with a capacity of 130 mAh g-1 with minimum capacity fade. References: Rajendran, S.; Tang, Z.; George, A.; Cannon, A.; Neumann, C.; Sawas, A.; Ryan, E.; Turchanin, A.; Arava, L. M. R., Inhibition of Lithium Dendrite Formation in Lithium Metal Batteries via Regulated Cation Transport through Ultrathin Sub‐Nanometer Porous Carbon Nanomembranes. Advanced Energy Materials, 2021, 11(29), 2100666.Gopalakrishnan, D.; Alkatie, S.; Cannon, A.; Rajendran, S.; Thangavel, N. K.; Bhagirath, N.; Ryan, E. M.; Arava, L. M. R., Anisotropic Mass Transport Using Ionic Liquid Crystalline Electrolyte to Suppress Lithium Dendrite Growth. Sustainable Energy & Fuels 2021, 5, 1488-1497.Rajendran, S.; Pilli, A.; Omolere, O.; Kelber, J.; Arava, L. M. R., An All-Solid-State Battery with a Tailored Electrode-Electrolyte Interface Using Surface Chemistry and Interlayer-Based Approaches. Chemistry of Materials 2021, 33 (9), 3401-3412.Rajendran, S.; Thangavel, N. K.; Mahankali, K.; Arava, L. M. R., Toward Moisture...
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