Formation Of Li2O2 Research Articles

Gelation of Cathode Electrolytes for Improved Structural Integrity and Enhanced Electrochemical Performance of Li-O2 Batteries

Due to the significantly high theoretical energy density, lithium-oxygen (Li-O2) batteries have been attracting much attention as next generation lithium secondary batteries. Nevertheless, there remain a lot of fundamental challenges to be solved for commercialization of Li-O2 batteries, and the cycling performance of currently reported state-of-the-art Li-O2 batteries is still very poor compared to commercially available Li-ion batteries.[1,2] One of the critical problems for the Li-O2 batteries is the leakage of excess liquid electrolytes from the cathode.[3] During the cell operation, Li2O2 is deposited onto the surface of carbon electrodes, which forces the liquid electrolyte out of the cathode. As a result, the deficiency of liquid electrolytes induces deterioration of the cycling performance. Moreover, the formation of Li2O2 causes serious volume expansion of the carbon cathode, which leads to the structural disintegration of electrodes.[4] To suppress the leakage of electrolytes and disintegration of cathode structures, we are aiming to gelate electrolytes inside the carbon nanotube (CNT) cathodes. Although some gel polymer electrolytes have been reported for Li-O2 batteries so far,[5] gelation of electrolytes inside the cathode has been little investigated. In this study, several types of multi-functional cross-linkers are evaluated to gelate the cathode electrolytes via thermally or UV light-initiated in situ polymerization. By tuning the chemical structure and composition of gelling agents, viscoelastic properties of gels can be broadly controlled. We investigate the effect of gel viscoelasticity and cell restraint pressure on the leakage of electrolyte and mechanical integrity of the CNT cathode, as well as battery performance of the Li-O2 cells. In addition, as another strategy to fabricate CNT-based gel cathodes, solvent-mediated technique is exploited: CNTs, electrolytes, gelling polymers, and volatile solvents are kneaded to form paste films. After evaporation of the solvent, CNT-based gel cathodes were obtained. The relationship between composition and preparation process of the gel cathode and resultant electrochemical performance of Li-O2 cells are studied in detail. We also explore the possibility to reduce the electrolyte amount inside cathodes by gelation toward practically high energy density Li-O2 batteries.

Characterization and Optimization of Co-Doped SnO2 As Anode for Lithium-Ion Batteries

Tin oxide-based materials have been intensively investigated as alternative anodes for lithium-ion batteries due to their high specific capacity, environmental friendliness, non-toxicity, and ease of handling.[1] However, the initial formation of Li2O upon lithiation is essentially irreversible, which has a severe effect on the first cycle coulombic efficiency and the reversibly achievable capacity in general.[2] It has been shown that the incorporation of transition metal dopants can address this issue, as it enables the reversible formation and reformation of Li2O.[3] The choice of the dopant, however, plays a critical role for the long-term cycling stability, rate capability, and eventual energy density of the resulting lithium-ion cells.[4] Herein, we show that the addition of specific combination of different dopants allows for further tailoring the electrochemical properties. We also demonstrate the production of such materials using a scalable continuous hydrothermal flow method. The performance of the best composition (Sn0.9Co0.05Mn0.05O2, SCMO) was further improved by applying a carbonaceous coating. The electrochemical investigation of the coated anode material was conducted in half-cells and in high-energy full-cells using high-voltage LiNi0.5Mn1.5O4 (LNMO) as active material for the cathode (Figure 1).[5] The performance of the full-cells was further enhanced by carefully optimizing the anode composition and fine-tuning the full-cell design, considering electrolytes and different pre-lithiation degrees. Reference s : [1] F. Zoller, D. Böhm, T. Bein, D. Fattakhova-Rohlfing, ChemSusChem., 1 2 , 4140 (2019)[2] I.A. Courtney and J.R. Dahn, J Electrochemical Soc., 144 , 2045 (1997)[3] D. Bresser, S. Passerini and B. Scrosati, Energy Environ. Sci. , 9 , 3348 (2016)[4] Y. Ma et al, Sustain. Energy Fuels, 2 , 2601 (2018)[5] A. Birrozzi et al., Batter. Supercaps, 3 , 284 (2020). Figure 1

(Invited) Challenges in Reversible Electrodeposition and Stripping of Lithium Peroxide for Li-Air Batteries

Thanks to a high theoretical energy density combined to a relatively high operation voltage around 3 Volts versus Li+/Li, the non-aqueous Li-Air battery is a good candidate for future electric cars with an increased driving range. In principle, this battery relies on the reversible electrochemical reaction between the metallic Li and the gaseous O2 in presence of a non-aqueous electrolyte where Li+ ions and dissolved O2 molecules diffuse and react to form the ideal discharge product lithium peroxide Li2O2. However, this apparently simple reaction process appears to be more complicated when put into practice.Considering the Li-O2 discharge process, there are two main models proposed in the literature to explain the Oxygen Reduction Reaction which were unified in a single mechanism process where Li2O2 formation goes through a surface reaction or/and a solution reaction1, depending on system parameters such as the applied potential or the solvent properties. Using an electrochemical quartz crystal microbalance (EQCM) we studied the products formed in discharge as well as the reversibility of the reactions from a mass point of view during cycling.2 Regarding the Li-O2 charge process, the Li2O2 decomposition occurring is a rather sluggish and incomplete process. A lot of efforts was made in this area by the research community, and several approaches were proposed to facilitate and fasten the Li2O2 decomposition: the use of solid state catalyst of several kind (doped carbon, non-precious materials...) or soluble catalysts also called redox mediators, such as for example TTF3 (tetrathiafulvalene), TEMPO4 (2,2,6,6-tetramethylpiperidinyloxyl), Cobalt Bis(terpyridine)5, lithium iodide6 (LiI). The mobile redox mediators, electron-hole transfer agents, aid the oxidation of Li2O2 as has been reported previously. In our EQCM study we activated in situ the TTF and confirms its usefulness on the mass reversibility of the deposition/dissolution of Li2O2 during cycling2. Later on, we performed a detailed study of the effect of LiI redox mediator on the formation and decomposition of Li2O2.7 We showed that the solvent could drastically change the mechanism of decomposition during charge8. Finally, we will discuss the parameters able to influence the most the deposition and stripping of Li2O2 in a non-aqueous medium. Reference s : 1 L. Johnson, C. Li, Z. Liu, Y. Chen, S. A. Freunberger, J. M. Tarascon, P. C. Ashok, B. B. Praveen, K. Dholakia, P. G. Bruce, Nature Chemistry, 6, 1091 – 1099 (2014). 2 S. Schaltin, G. Vanhoutte, M. Wu, F. Bardé, J. Fransaer, Phys. Chem. Chem. Phys. , 17, 12575 – 12586 (2015). 3 Y. Chen, S. A. Freunberger, Z. Peng, O. Fontaine, and P. G. Bruce, Nature Chemistry, 5, 489 – 494 (2013). 4 Y. Hase, J. Seki, T. Shiga, F. Mizuno, H. Nishikoori, H. Iba, K. Takechi, Chem. Commun., 52, 12151 – 12154 (2016). 5 Koffi P.C. Yao, J. T. Frith, S. Youssef Sayed, F. Bardé, J. R. Owen, Y. Shao-Horn, N. Garcia-Araez, J. Phys. Chem. C, 120 (30), 16290 – 16297 (2016). 6 Y. Qiao, S. Wu, Y. Sun, S. Guo, J. Yi, P. He, H. Zhou, ACS Energy Letters, 2, 8, 1869 – 1878 (2017). 7 M. Tulodziecki, G.M. Leverick, C.V; Amanchukwu, Y. Katayama, D.G. Kwabi, F. Bardé, P. Hammond, Y. Shao-Horn, Energy Environ. Sci., 10, 1828, (2017). 8 G. Leverick, M. Tułodziecki, R. Tatara, F. Bardé, Y. Shao-Horn, Joule, Vol. 3, Issue 4, 1106-1126, (2019).

Germanium Oxide Negative Electrodes - Tuning Synthesis Conditions Towards High-Energy and High-Power Lithium-Ion Cells

The transportation sector is continuously transitioning from combustion engines towards fully electric vehicles and lithium-ion batteries (LIBs) are the energy storage device of choice due to their high volumetric and gravimetric energy density.1 However, to meet future targets in terms of driving range and re-/charging times, the state-of-the-art graphite anode graphite needs to be replaced with materials offering even higher energy densities and, especially, better power capabilities.2 Alloying metal-oxides such as ZnO and SnO2 have been widely studied, since they offer high theoretical specific capacities (988 mAh g-1 and 1494 mAh g-1, respectively), while being environmentally friendly and non-toxic. Furthermore, such alloying metal oxides have high densities, which promises higher volumetric capacities compared to graphite. However, these high densities, in combination with the high overall Li+ uptake, result in pronounced volume expansion upon cycling. Furthermore, the eventually irreversible Li2O formation limits the practically achievable specific capacities to the alloying contribution only. It has been shown that this limitation can be overcome by introducing a transition metal (e.g., Fe, Co) into the lattice, leading to a reversible Li2O formation and favorable de-/lithiation kinetics.3,4 This concept of transition metal doping has recently also been transferred to germanium oxide – another example for a Li+ alloying oxide with an even higher theoretical specific capacity (i.e., 2152 mAh g-1) - and was shown to partially enable re-oxidation of germanium to germanium oxide, though (so far) only for the initial cycles.5 Within this study, we tackled the problem from a more comprehensive perspective and elaborate on the effect of different synthesis conditions, the introduction of Fe into GeO2, as well as the impact of different germanium oxide phases on the electrochemical performance. The latter aspect is, indeed, commonly overlooked so far when studying metal oxide anodes. The highly complementary techniques employed include, amongst others, in situ/operando characterization methods such as in situ high temperature XRD, operando XRD and operando dilatometry. Ultimately, we realized lithium-ion cells comprising lithium-rich Li1.2Mn0.6Ni0.2O2 cathodes with a specific energy of about 400 Wh kg-1 and stable cycling for more than 350 cycles. N. Nitta, F. Wu, J. T. Lee, and G. Yushin, Mater. Today, 18, 252–264 (2015).J. Asenbauer et al., Sustain. Energy Fuels (2020).D. Bresser et al., Chem. Mater., 25, 4977–4985 (2013).Y. Ma et al., Sustain. Energy Fuels, 2, 2601–2608 (2018).J. Wu, N. Luo, S. Huang, W. Yang, and M. Wei, J. Mater. Chem. A, 7, 4574–4580 (2019).

Improved Ionic Conductivity and Li Dendrite Suppression Capability toward Li7P3S11-Based Solid Electrolytes Triggered by Nb and O Cosubstitution.

It is still a big challenge to simultaneously enhance the ionic conductivity, dendrite suppression capability, and interfacial compatibility of sulfide solid electrolytes. In this work, a novel Li7P2.88Nb0.12S10.7O0.3 solid electrolyte is prepared via Nb and O cosubstitution of glass-ceramic Li7P3S11. This sulfide-based electrolyte possesses a high ionic conductivity (3.59 mS cm-1) at 298 K, improved critical current density (1.16 mA cm-2), and excellent interfacial compatibility between the sulfide electrolyte and Li2S active material. The improved electrochemical stability of the sulfide solid electrolyte against metallic lithium is attributed to the formation of Nb and Li2O at the interface, which can induce uniform Li deposition and prevent further side reaction. The all-solid-state Li/Li2S batteries based on this electrolyte exhibit remarkably enhanced cycling stability and rate performance.

In Situ X-Ray Photoelectron Spectroscopy for All-Solid-State Batteries: Analysis of Lithiation and Delithiation Reactions of Silicon Thin-Film Electrode

Si is an attractive anode material for next-generation lithium batteries including all-solid-state batteries because it has a high theoretical capacity density (4200 mAh g-1). However, Si suffers from the irreversible capacity loss related to the severe volume expansion/shrinkage during the lithiation/delithiation processes. In liquid-type batteries, the main cause of the capacity loss is the continuous formation/decomposition of the solid electrolyte interphase (SEI) on the Si anodes [1]. However, the capacity loss of the Si anode is also regarded as a serious issue even in all-solid-state batteries without using electrolyte solution. Thus, a fundamental understanding of the lithiation/delithiation reactions of the Si anode is important to solve the problem. X-ray photoelectron spectroscopy (XPS) enables us to analyze the elemental composition, oxidation states, and electronic structure of the sample surface. In situelectrochemical XPS, which can measure the same position of a sample under the operational condition for batteries, allows a stepwise analysis of the reactions without interference from variation and inhomogeneity of samples [2]. Here, lithiation/delithiation reactions of an amorphous Si electrode in a thin-film cell is investigated by using an XPS apparatus equipped with an applying voltage system [3]. The amorphous Si with a thickness of about 100 nm is formed on the Li6.6La3Zr1.6Ta0. 4O12 (LLZT) sheet by radio-frequency magnetron sputtering, and the Cu is further coated on the sputtered Si layer by DC sputtering. During the Cu deposition, a stainless-steel stencil mask is used to yield an uncoated amorphous Si part with a diameter of about 2 mm as an analytical region for the XPS measurements. The Li metal layer is thermally deposited on the other side of LLZT. After the thin-film cell with the final structure of [Cu/Si(100 nm)/LLZT(500 µm)/Li metal(1.3 µm)] is connected to the sample holder in an Ar-filled glove box, it is transferred to the XPS apparatus by using a vacuum suitcase to prevent from exposing to open air. The cell is cycled between 0.01 and 1.2 V at 0.02C (1.245 µA) in UHV chamber of the XPS apparatus. The Si surface is observed by XPS before/after the lithiation/delithiation processes. The galvanostatic potential profiles show that the capacity for the first lithiation and delithiation processes is 3160 and 2977 mAh g-1, respectively. A broad Li 1s peak appears after the first lithiation process, confirming the Li insertion to the Si electrode. According to the peak fitting, the Li 1s peak is composed of lithium-silicide (LixSi), Li2O, and Li2CO3. The Li2O and Li2CO3 are possibly formed by the reaction of the lithium-silicide surface with a trace amount of residual gas from the vacuum chamber and LLZT. The Li2O and Li2CO3 contribute to the irreversible capacity loss because these components remain even after the subsequent delithiation process. In the Si 2p region, peaks originated from bulk Si (Si0) at 99.1 eV and Si suboxide (SiOx) at 101.9 eV are shifted to lower binding energy side. These peak shifts indicate the formation of lithium-silicide (LixSi) and lithium-silicate (Li4SiO4) due to the insertion of Li ions to each layer. Based on the calculation using the peak intensities and known physical parameters, it is proposed that the Si electrode has a surface structure of [Li2O (2.5 nm)/Li4SiO4 (0.9 nm)/LixSi] at this state. In addition, the composition of the LixSi is estimated to be Li3.27Si from the charge integration and the thickness of each layer. After the subsequent delithiation process, the Li4SiO4 peak remains in the same position. In contrast to the immobility of the Li4SiO4 peak, the LixSi peak is shifted back to the higher binding energy side, but it does not completely return to the original position of the Si0 peak. The composition of the lithium-silicide phase at this state is estimated to be Li0.14Si. Therefore, Li trapped in Li0.14Si and formation of Li4SiO4, Li2O, and Li2CO3 contribute to the irreversible capacity loss of the Si electrode.

(Invited) A Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium-Oxygen Batteries

Reactive oxygen species or superoxide (O2 -) to damage or age biological cells is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from the superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C60) was used as a superoxide disproportionation chemo-catalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm-2) with 0.5 mAh cm-2 cut-off survived up to 50 cycles after MA-C60 was introduced to electrolyte. Moreover, the SOD-mimetic catalyst increased capacity: e.g., more than six-fold increase at 0.2 mA cm-2. Experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60.

Confined-Space-Induced Side Reactions in Li-O2 Electrochemistry

Rechargeable lithium-oxygen battery (LOB) is one of potentially promising candidates for next-generation batteries of which criteria typically set as > 500 Wh kg-1 in a full-cell configuration [1]. However this rechargeable battery system suffers from a wide spectrum of side reactions at the all main components, i.e. anode, electrolyte, and cathode, and also at their interfaces [2-5]. Therefore, the suppression of side reactions is a key challenge in LOB. Especially, understanding mechanism of side reactions occurring at the interface of porous cathode/electrolyte is important to improve the basic electrochemical properties of LOB, therefore, is also essential to enhance the battery performances of LOB. In our previous works, we prepared a variety of porous-carbon-based cathodes to investigate the effects of heteroatom doping or hierarchical porestructures in Li-O2 electrochemistry [6-9], and found that a porestructure gives considerably strong influences to electrochemical growth/decomposition of Li2O2 at a solid-liquid interface in porous electrodes. Driven by these previous findings, in this work, we aimed to understand further details of the Li-O2 electrode process in porous solids by, and show here that unfavorable side reactions in porous electrodes are induced if the reaction takes place at confined-spaces.In our study, we controlled the electrochemical growth of Li2O2 in a porous electrode by changing current densities, and therefore can selectively form Li2O2 at macropores or mesopores/macropores confirmed by nitrogen adsorption/desorption experiments and X-ray diffractometry. Furthermore, operando gas analysis, combining electrochemical experiments and on-line mass spectrometry, revealed that the Li2O2 formed in macropores can almost solely proceed the electrochemical decomposition reaction for O2 generation, on the other hand, Li2O2 in mesopores generate a considerable amount of CO2, even around 3.5 V vs Li/Li+. These results indicated that a confinement space could trigger Li2O2 to unfavorable side reactions to form CO2. Therefore, a fine control of porestructure in cathodes is important for LOB not only to improve round trip energy efficient but also to obtain reversible Li2O2 formation, i.e. O2 + 2Li+ + 2e − ↔ Li2O2 [10].In the presentation, a detailed mechanism will be explained how confined-space-induced side reactions are proceeded.[1] M. Ue, K. Sakaushi, K. Uosaki, Materials Horizons, DOI: 10.1039/D0MH00067A (2020).[2] B. D. McCloskey, D. S. Bethune, R. M. Shelby, G. Girishkumar, A. C. Luntz, J. Phys. Chem. Lett., 2, 1161 (2011).[3] B. D. McCloskey, A. Speidel, R. Scheffler, D. C. Miller, V. Viswanathan, J. S. Hummelshøj, J. K. Nørskov, A. C. Luntz, J. Phys. Chem. Lett., 3, 997 (2012).[4] W.-J. Kwak, Rosy, D. Sharon, C. Xia, H. Kim, L. R. Johnson, P. G. Bruce, L. F. Nazar, Y.-K. Sun, A. A. Frimer, M. Noked, S. A. Freunberger, D. Aurbach. Chem. Rev., DOI: 10.1021/acs.chemrev.9b00609 (2020).[5] T. Liu, J. P. Vivek, E. W. Zhao, J. Lei, N. Garcia-Araez, C. P. Grey, Chem. Rev., DOI: 10.1021/acs.chemrev.9b00545 (2020).[6] K. Sakaushi, T.-P. Fellinger, M. Antonietti, ChemSusChem, 8, 1156 (2015).[7] K. Sakaushi, S.-J. Yang, T.-P. Fellinger, M. Antonietti, J. Mater. Chem. A, 3, 11720 (2015).[8] K. Sakaushi, M. Antonietti, Bull. Chem. Soc. Jpn., 88, 386 (2015).[9] K. Sakaushi, M. Antonietti, Acc. Chem. Res., 48, 1591 (2015).[10] K. Sakaushi, H. Asahina, K. Uosaki, in preparation.

Ultrasmall SnO2 directly grown on commercial C45 carbon as lithium-ion battery anodes for long cycling performance

Development of high-performance SnO2 anodes is hampered by its peculiar electrochemical behavior, characterized by two processes: conversion and alloying reactions. The conversion reaction being irreversible leads to specific capacities lower than theoretical, however rational design of nanosized SnO2 can mitigate this issue, though SnO2 low conductivity and electrode pulverization justify the need of carbon matrices. Some carbon structures proved to be strongly effective at laboratory-scale, but most are too expensive or complicated to obtain for scaling-up. Herein, we exploit the high concentration of oxide and carboxylic surface functional groups of C-NERGY™ Super C45 carbon black for one-pot synthesis of ultrafine SnO2 nanoparticles over the carbon surface. These functional groups accomplish the hydrolysis/oxidation of SnCl2, resulting in finely dispersed SnO2 nanoparticles (5 nm in average size) growth over C45. Presence of oxygen species on C45 surface, accessible to tin, prevent fast formation of Li2O, allowing to achieve high capacity and extreme electrode stability. The assembled cells with SnO2/C45 exhibit for more than 400 cycles the reversible capacity of 560 mA h g−1 per pure SnO2 (after subtracting C45 contribution) at 1C, demonstrating prolonged cycling operation thus providing an interesting opportunity for scalable production of stable and high-capacity battery anodes alternatively to graphite.

Analysis and Modeling of Oxide Reduction Processes for Uranium Oxides

This article describes a kinetic model for the reduction process of used oxide nuclear fuel with molten LiCl at 650°C. In this process, metal oxides, primarily UO2, react to form metallic U and Li2O. As UO2 is gradually reduced, metallic U and Li2O form in molten LiCl, in and through which Li2O dissolves and diffuses. To capture the prescribed chemical and physical phenomena, two classical kinetic models are integrated sequentially to describe Li2O formation, dissolution, and diffusion behaviors. The first part of the integrated model uses a shrinking core kinetics to explain the formation, dissolution, and diffusion of Li2O while accounting for the expanding metallic uranium layer. The second part of the integrated model begins with the completion of Li2O dissolution and deals with the diffusion of excess Li2O in the metallic uranium layer. A Fick's second law without an external source describes the second part of the process behavior. The integrated model explains engineering scale kinetic measurement data from the literature with the effective Li2O diffusion coefficient range between 2 and 6 (10−5cm2/sec).

1,2-dimethyl-3-propylimidazolium iodide as a multiple-functional redox mediator for Li-O2 batteries: In situ generation of a “self-defensed” SEI layer on Li anode

How to develop a homogeneous redox mediator (RM) towards both ORR and OER and how to prevent the shuttle effect are two main issues for Li-O2 batteries thus far. Here, we firstly report 1,2-dimethyl-3-propylimidazolium iodide (DMPII), which serves multiple functions as a RM for discharge capacity promotion, a RM for charge potential reduction, and a Li anode protector for shuttling suppression by in situ generating a “self-defensed” SEI layer. Benefiting from these advantages, a cell with DMPII displays a stable cyclability with a low terminal charge potential of ~3.6 V till the cell death, a considerable rate performance, and a good reversibility associated with Li2O2 formation and degradation. Based on the experimental and density functional theory (DFT) calculation results, a working mechanism for a cell operation is also proposed. These results represent a promising progress in the development of multiple-functional RM for Li-O2 batteries. Moreover, we expect that this work gives an insight into the in situ protection of Li metal anode for board applications (e.g., Li-S batteries, all-solid-state Li-ion batteries, etc.).

Novel and highly efficient catalyst for Li–O2 battery: Porous LaCo0.6Ni0.4O3 nanofibers decorated with ultrafine Co3O4 nanoparticles

It is crucial to design effective cathode catalysts for high performance of Li–O2 batteries (LOBs). Herein, porous LaCo0.6Ni0.4O3 nanofibers decorated with ultrafine Co3O4 nanoparticles (Co3O4@LCN NFs) are designed and employed as cathode catalyst for LOBs. The X-ray photoelectron spectroscopy measurement results suggested that uniform dispreading of Co3O4 nanoparticles on LCN NFs surface could largely increase the surface chemisorbed oxygen, resulting in enhanced catalytic activity. Furthermore, with the assistance of Co3O4 nanoparticles, Co3O4@LCN NFs can significantly facilitate O2 adsorption and diffusion, Li2O2 nucleation/decomposition and the formation of tiny sheet-like Li2O2, thereby achieving a low charge overpotential. A high specific capacity of 11,288 mA h g−1, a low charge voltage plateau of 3.72 V at first cycle and excellent cycle stability of 116 cycles at 1000 mA g−1 are obtained for LOBs with Co3O4@LCN NFs.

Catalysts based on carbon nanotubes modified by N, Pt, or PtCo for oxygen reaction catalysis in nonaqueous electrolyte containing lithium ions

The effect of carbon nanotube (CNT) surface modification by oxygen– and nitrogen–containing groups on the activity of Pt–containing catalysts supported on these CNT (Pt/CNT and PtCo/CNT) studied in the oxygen reaction in aprotic electrolyte containing lithiumсations. It is shown, that modification of the CNT surface by oxygen– and nitrogen–containing groups enhances the polarization capacity of the material that characterizes the value of the electrochemically active surface area and lowers the overpotential of the oxygen reduction reaction (ORR). Synthesis of platinum or its alloy (PtCo) on modified CNT allowed establishing the relationship between the activity of these catalysts in the oxygen reaction in aprotic electrolyte and the synthesis conditions and CNT pretreatment. The catalytic effect of modification by platinum consists in a decrease in the ORR overpotential with formation of Li2O2 and its further anodic decomposition and in an increase in the reversibility degree. It is shown that the sites on which Pt nanoparticles are fixed on the CNT surface are oxygen–containing groups. The most probable result of synthesis of PtCo alloy on CNT is the binding of cobalt to nitrogen in nitrogen–containing groups and then to platinum (N–Co–Pt).

High‐Performance Li–O2 Batteries Based on All‐Graphene Backbone

AbstractThe Li–O2 battery is one of the most captivating energy storage forms due to its extraordinarily high energy density and the readily its the ready availability of oxygen. However, significant challenges lie ahead on both the anode and cathode sides before the technology can be finally deployed to benefit human life. Herein, a two‐birds‐one‐stone tactic is implemented to fabricate high‐performance and flexible Li–O2 batteries utilizing only one structural backbone composed of graphene oxide aerogel embedding hollow NiCo2O4 microspheres for both the anode and cathode. While the composite Li anode fabricated through lithium infusion exhibits an ultrahigh capacity of 3398.4 mAh g−1 and significantly inhibits dendrite growth and volume expansion, the freestanding oxygen cathode demonstrates great capability in promoting energy efficiency by catalyzing reversible Li2O2 formation. When coupled together, the resultant Li–O2 batteries manifest a superb long‐term cycling stability with highly reversible discharge/charge for more than 400 cycles, apart from the remarkable mechanical deformability demonstrated by flexible pouch cells. By employing a full spectrum of ex situ and operando spectroscopic and microscopic tools, mechanistic insights into the remarkable Li–O2 performance are given.

Utilizing a Photocatalysis Process to Achieve a Cathode with Low Charging Overpotential and High Cycling Durability for a Li-O2 Battery.

The practical applications of non-aqueous lithium-oxygen batteries are impeded by large overpotentials and unsatisfactory cycling durability. Reported here is that commonly encountered fatal problems can be efficiently solved by using a carbon- and binder-free electrode of titanium coated with TiO2 nanotube arrays (TNAs) and gold nanoparticles (AuNPs). Ultraviolet irradiation of the TNAs generates positively charged holes, which efficiently decompose Li2 O2 and Li2 CO3 during recharging, thereby reducing the overpotential to one that is near the equilibrium potential for Li2 O2 formation. The AuNPs promote Li2 O2 formation, resulting in a large discharge capacity. The electrode exhibits excellent stability with about 100 % coulombic efficiency during continuous cycling of up to 200 cycles, which is due to the carbon- and binder-free composition. This work reveals a new strategy towards the development of highly efficient oxygen electrode materials for lithium-oxygen batteries.

Utilizing a Photocatalysis Process to Achieve a Cathode with Low Charging Overpotential and High Cycling Durability for a Li‐O2 Battery

AbstractThe practical applications of non‐aqueous lithium‐oxygen batteries are impeded by large overpotentials and unsatisfactory cycling durability. Reported here is that commonly encountered fatal problems can be efficiently solved by using a carbon‐ and binder‐free electrode of titanium coated with TiO2 nanotube arrays (TNAs) and gold nanoparticles (AuNPs). Ultraviolet irradiation of the TNAs generates positively charged holes, which efficiently decompose Li2O2 and Li2CO3 during recharging, thereby reducing the overpotential to one that is near the equilibrium potential for Li2O2 formation. The AuNPs promote Li2O2 formation, resulting in a large discharge capacity. The electrode exhibits excellent stability with about 100 % coulombic efficiency during continuous cycling of up to 200 cycles, which is due to the carbon‐ and binder‐free composition. This work reveals a new strategy towards the development of highly efficient oxygen electrode materials for lithium‐oxygen batteries.

Molten salt synthesis of CoFe2O4 and its energy storage properties

In this article, we report simple and scalable one-pot molten salt synthesis of CoFe2O4 as electrode material for Lithium ion batteries. X-ray diffraction studies along with Rietveld analysis showed a pure phase of CoFe2O4 with space group Fd-3m and crystallite size of 54 nm. As an anode material CoFe2O4 showed high initial discharge/charge capacity of 1556/1093 mA h g−1 and a reversible capacity of 926 mA h g−1 after 30 cycles with columbic efficiency of 99%. A relatively high reversible capacity of 594 mA h g−1 was observed at high current density of 1C (916 mA g−1) which shows the better reversibility of CoFe2O4 at high current density. As the current was reduced to 0.1C reversible capacity of 899 mA h g−1 was retained suggesting high rate performance of CoFe2O4. The long-term stability test, carried out using galvanostatic charge/discharge (GC) at a current density of 0.5C, showed a reversible capacity of 369 mA h g−1 at the end of 200th cycle. The structural and morphological evaluation of the sample after cycling, using ex-situ X-ray diffraction and ex-situ transmission electron microscopy, confirmed structural degradation and formation of metal nanoparticles, Li2O and amorphous nature of electrode material. The one-pot molten salt synthesis approach is quite simple and can be extended for large-scale production of electrode materials.

An electrochemical investigation of oxygen adsorption on Pt single crystal electrodes in a non-aqueous Li+ electrolyte

Cyclic voltammetry has been used to probe the initial stages of oxygen reduction and oxidation in lithium-containing dimethyl sulfoxide at well-defined Pt single crystal electrodes in order to elucidate any catalytic effects ascribable to surface structure. In contrast to previous work involving sodium-oxygen, lithium-oxygen studies did not yield any significant differences for reaction on the three basal planes of platinum. Rather, all three planes generated a similar voltammetric response. However, by judicious use of various potential sweep limits, the formation of superoxide together with both a “conformal” or surface adlayer of lithium peroxide (Li2O2) together with a “microcrystallite” surface Li2O2 phase was resolved. Voltammetric peak intensity versus sweep rate measurements confirmed that superoxide electrooxidation was diffusion limited whereas electrooxidation of the two Li2O2 phases displayed behaviour typical of a surface-confined process. Under steady-state conditions for the formation of superoxide, it was found that for both the conformal and microcrystallite Li2O2 phases, electrooxidation followed zero-order kinetics, pointing to the importance of free surface sites in facilitating these reactions. A marked change in the rate of Li2O2 formation was found to coincide with a coverage of 0.25 monolayers, as measured by the charge density of the conformal Li2O2 electrooxidation peak. We postulate that electron tunnelling through both the conformal Li2O2 layer and microcrystallites deposited on this surface layer coincides with this coverage and accounts for such behaviour. This phenomenon of electron tunnelling through single conformal and mixed conformal/microcrystallite structures should prove vitally important in governing the overall electrooxidation rate.

In Situ Observation of Lithiation and Delithiation Reactions of a Silicon Thin Film Electrode for All-Solid-State Lithium-Ion Batteries by X-ray Photoelectron Spectroscopy.

In situ X-ray photoelectron spectroscopy is applied to electrochemical lithiation/delithiation processes of an amorphous Si electrode sputter-deposited on a Li6.6La3Zr1.6Ta0.4O12 solid electrolyte. After the first lithiation, a broad Li peak appears at the Si surface, and peaks corresponding to bulk Si and Si suboxide significantly shift to lower binding energy. The appearance of the Li peak and shift of the Si peaks confirm the formation of lithium-silicide and lithium-silicates due to the lithiation of Si and native suboxide. The composition of lithium-silicide is estimated to be Li3.44Si by quantitative analysis of electrochemical response and photoelectron spectra. Peak fitting analysis shows the formation of Li2O and Li2CO3 due to side reactions. Upon the following delithiation, the peak corresponding to Li3.44Si phase shifts back to higher binding energy to form Li0.15Si phase, while lithium-silicates, Li2O, and Li2CO3 remained as irreversible species. Thus, electrochemical reactions accompanied with lithiation/delithiation processes are successfully observed.

Revealing the Li2O2 Nucleation Mechanisms on CeO2 Catalysts for Lithium‐Oxygen Batteries

AbstractThe addition of ceria (CeO2) nanoparticles to the cathode of a lithium‐oxygen battery results in increased capacity, lower overpotentials and better cyclability. To shed light on the mechanisms of this performance enhancement, we have investigated the early stages of Li2O2 nucleation at stoichiometric and reduced ceria surfaces by means of atomistic simulations based on density functional theory. Adsorption energies are stronger on ceria than on graphene, that is, nucleation mainly would take place on the oxide. The adsorption process of O2 is the one that determines the nucleation sites for the Li2O2 formation on the different CeO2 surfaces. The LiO2 intermediate is adsorbed at the O2 reduction sites. On the reduced (100) surface, the LiO2 tends to adsorb dissociatively, opening up the possibility to the formation of other species than the desired end‐product, Li2O2. On the contrary, optimal properties are found for the reduced (110) surface, which should therefore be the most active surface for Li2O2 nucleation among all low‐index surfaces of ceria. These findings could pave the route to produce better cathodes for Li‐oxygen batteries by the addition of carefully designed ceria nanoparticles, which maximizes the exposition of the most favorable facet.