The lithium air, or Li–O2, battery system is a promising electrochemical energy storage system because of its very high theoretical specific energy, as required by automotive applications. Fundamental research has resulted in much progress in mitigating detrimental (electro)chemical processes; however, the detailed structural evolution of the crystalline Li2O2 and LiOH discharge products, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure operando under realistic electrochemical conditions. This study uses Rietveld refinement of operando X-ray diffraction data during a complete discharge–charge cycle to reveal the detailed structural evolution of Li2O2 and LiOH crystallites in 1,2-dimethoxyethane (DME) and DME/LiI electrolytes, respectively. The anisotropic broadened reflections confirm and quantify the platelet crystallite shape of Li2O2 and LiOH and show how the average crystallite shape evolves during discharge and charge. Li2O2 is shown to form via a nucleation and growth mechanism, whereas the decomposition appears to start at the smallest Li2O2 crystallite sizes because of their larger exposed surface. In the presence of LiI, platelet LiOH crystallites are formed by a particle-by-particle nucleation and growth process, and at the end of discharge, H2O depletion is suggested to result in substoichiometric Li(OH)1–x, which appears to be preferentially decomposed during charging. Operando X-ray diffraction proves the cyclic formation and decomposition of the LiOH crystallites in the presence of LiI over multiple cycles, and the structural evolution provides key information for understanding and improving these highly relevant electrochemical systems.

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The vanadium pentoxide (V2O5)/graphene nanocomposite films have been synthesized by direct intercalation method using V2O5 sol and graphene. The structure of the films was investigated with X-Ray Diffraction (XRD). The electrochemical properties of the nanocomposite films were studied by cyclic voltammetry and chronoamperometry with the standard three-electrode configuration. The optical properties were characterized by UV–Visible spectrophotometer. The intercalation of graphene improves the stability and reversibility of the V2O5 xerogel films. The response rate of the V2O5/graphene nanocomposite films is enhanced. The optical modulatory range of the V2O5/graphene nanocomposite films is 1.5 times larger than that of V2O5 xerogel films. These results demonstrate that the nanocomposite films can be used potentially in fast switching electrochromic devices.

decomposition (oxygen evolution reaction, OER) of Li 2 O 2 according to the reaction 2Li O Li O 2 discharge charge 2 2. [1] Therefore, the performance of this battery is determined by the reversibility of Li 2 O 2 redox and the electrolyte stability. [1] The morphology and mechanism of Li 2 O 2 deposition depends on the relative stability of the intermediate LiO 2 product in the electrolyte and the time scale of the Li 2 O 2 formation on the cathode surface. While LiO 2 stability is determined by the stabilization of the Li + both through the solvation strength of the electrolyte (quantified by the donor number (DN)) and the association strength of the counter anion, [5][6][7] the time scale determines to what extent the intermediate LiO 2 species are solvated. [8] In an intermediate DN electrolyte, such as tetraethylene glycol dimethyl ether (TEGDME), the nucleation and growth of toroidal Li 2 O 2 particles were proposed to occur via the solution dismutase mechanism at low current rates, whereas at fast rates quasi-amorphous thin films were observed on electrode surface. [8] Porous carbon based materials have been extensively explored as O 2 gas diffusion electrodes because of their high surface area, low weight, and low cost. Unfortunately, the discharge product Li 2 O 2 reacts with carbon and the electrolyte at high potentials that characterize the OER process, and forms byproducts that clog the electrode pores, resulting in capacity fading and poor cycling stability. [9,10] Significant efforts have been expended in mitigating these side reactions by employing several combinations of noble metals (Au, Ru/RuO 2 , and Pt), [11][12][13][14][15][16][17][18][19][20][21] transition metal oxides (MnO 2 , Co/CoO/Co 3 O 4 , NiO, and TiO 2 ), [22][23][24][25][26][27][28][29][30][31][32][33] and metal-related compounds, [34][35][36][37][38][39][40] both as catalysts and conductive matrices to improve the energy efficiency and cycle life of the LiO 2 batteries.Most often the reported cycling performance of LiO 2 systems is based on capacity-limited cycling, rather than the preferred potential-limited cycling where the full electrode capacity is utilized. Capacity-limited cycling performance of batteries makes it difficult to quantify if improved cycling stability can be attributed to the specific role of electrode or to the continuous consumption of new active sites on the electrode surface is delivered. To date, the only electrode systems that have displayed improved reversible Li 2 O 2 formation and decomposition during potential limited cycling in aprotic LiO 2 batteries are porous gold, [14] metallic RuO 2 , [41,42] the metallic porous Although the high energy density of LiO 2 chemistry is promising for vehicle electrification, the poor stability and parasitic reactions associated with carbonbased cathodes and the insulating nature of discharge products limit their rechargeability and energy density. In this study, a cathode material consisting of α-Fe 2 O 3 nanoseeds and carbon nanotubes (CNT) is presented, which...

A sodium ion-conducting polymer electrolyte based on polyvinyl pyrrolidone (PVP) complexed with NaClO(4) was prepared using the solution-cast technique. The cathode film of V(2)O(5) xerogel modified with polyvinyl pyrrolidone was prepared using the sol-gel method. Investigations were conducted using X-ray diffractometry (XRD), Fourier transformation infrared (FT-IR) spectroscopy. The ionic conductivity and transference number measurements were performed to characterize the polymer electrolyte for battery applications. The transference number data indicated that the conducting species in these electrolytes are the anions. Using the electrolyte, electrochemical cells with a configuration Na/(PVP + NaClO(4))/V(2)O(5) modified by (PVP) were fabricated and their discharge profiles studied.