Electrochemical Deintercalation Research Articles

Self-Oxidated Hybrid Conductive Network Enables Efficient Electrochemical Lithium Extraction Under High-Altitude Environment.

The electrochemical deintercalation method has been considered as an effective way to address the demand for lithium resources due to its environmental friendliness, high selectivity, and high efficiency. However, the performance of electrochemical lithium extraction is closely dependent on the electrode material and needs to be compatible under plateau environments with high-altitude and low-temperature. Herein, an in situ self-oxidation method is conducted to construct a hybrid conductive network on the surface of LiFePO4 (LFP-HN). The introduction of a hybrid conductive network enhanced the interfacial electron/lithium-ion transfer. In addition, structural stability is strengthened through suppressing the intercalation of impurity cations. Consequently, the LFP-HN delivered extremely high lithium extraction capacity (27.42mg g-1), low energy consumption (4.91Wh mol-1), and superior purity (91.05%) in Baqiancuo real brine (4788 m, -10°C). What's more, LFP-HN-based large-scale prototypes are constructed and operated at Baqiancuo, which is calculated to extract 25kg Lithium Carbonate Equivalent per cycle (4.55h, 100 pairs of plates). Based on the excellent performance, the modification strategy developed in this work can be a promising solution for industrial lithium extraction under high-altitude environment.

Exploring the Limits of Fe-Rich Chemistries in Na-Based CaFe2O4-Type Postspinel Oxides.

Structural trends, physical properties, and electrochemical performances of the NaFexRu2-xO4 system have been investigated. Synthesis attempts using both conventional solid-state routes and high-pressure methods were explored for the compositional range 1.0 ≤ x ≤ 1.67. Based on Rietveld refinements against powder X-ray diffraction data, analyses of 57Fe Mössbauer spectroscopy data, and elemental analysis by electron microprobe, the existence of a confined compositional solid solution (1 ≤ x ≤ 1.3) adopting the CaFe2O4-type postspinel structure is demonstrated. This is contrasted with the NaFexTi2-xO4 system, for which no evidence of a solid solution is observed. However, for all explored synthetic routes of NaFexRu2-xO4 compositions, a trivalent iron oxidation state is maintained. Structural analysis and qualitative bond valence energy landscape models reveal that the progressive integration of iron into the postspinel framework results in narrowed sodium ion diffusion channels, restricting electrochemical deintercalation of sodium. Consequently, the CaFe2O4-type iron-rich compounds explored in this study demonstrate limited potential as positive electrode materials for sodium batteries. It is expected that this fundamental insight will help guide the exploration of alternative NaM2O4-based positive electrode materials with similar structure types.

Electrochemically Mediated Lithium Extraction for Energy and Environmental Sustainability

AbstractThe demand for lithium resources is growing rapidly due to the continuous development of the lithium‐ion battery, which plays an important part in the renewable energy industry. Global sources of lithium are ores and brine, of which 59% are distributed in saline brine. However, the significant lithium resources in saline brine have not been fully utilized. The electrochemical deintercalation method (EDM) for lithium extraction from saline brine is a promising technique because of its environmental friendliness, high selectivity, and cost‐effectiveness. Nevertheless, the application of EDM is greatly limited by the easy dissolution of electrode materials like LiMn2O4 and the cost of mass production. Also, there are a few existing review articles on the EDM for lithium extraction. To address this gap, this review provides a comprehensive overview of the current methods for lithium extraction from saline brine, systematically summarizes the technical status of the EDM, and pays special attention to the preparation method and modification of electrode materials. This review gives new insight into the mechanism of EDM and provides a new design strategy for the evaluation methods of EDM.

ZnS/CoS@C Derived from ZIF-8/67 Rhombohedral Dodecahedron Dispersed on Graphene as High-Performance Anode for Sodium-Ion Batteries.

Metal sulfides are highly promising anode materials for sodium-ion batteries due to their high theoretical capacity and ease of designing morphology and structure. In this study, a metal-organic framework (ZIF-8/67 dodecahedron) was used as a precursor due to its large specific surface area, adjustable pore structure, morphology, composition, and multiple active sites in electrochemical reactions. The ZIF-8/67/GO was synthesized using a water bath method by introducing graphene; the dispersibility of ZIF-8/67 was improved, the conductivity increased, and the volume expansion phenomenon that occurs during the electrochemical deintercalation of sodium was prevented. Furthermore, vulcanization was carried out to obtain ZnS/CoS@C/rGO composite materials, which were tested for their electrochemical properties. The results showed that the ZnS/CoS@C/rGO composite was successfully synthesized, with dodecahedrons dispersed in large graphene layers. It maintained a capacity of 414.8 mAh g-1 after cycling at a current density of 200 mA g-1 for 70 times, exhibiting stable rate performance with a reversible capacity of 308.0 mAh g-1 at a high current of 2 A g-1. The excellent rate performance of the composite is attributed to its partial pseudocapacitive contribution. The calculation of the diffusion coefficient of Na+ indicates that the rapid sodium ion migration rate of this composite material is also one of the reasons for its excellent performance. This study highlights the broad application prospects of metal-organic framework-derived metal sulfides as anode materials for sodium-ion batteries.

Rapid synthesis and characterizations of defect-enhanced WO3-δ thin film electrode for effective energy storage application in asymmetric supercapacitor devices

Oxygen vacancy-doped WO3-δ thin film electrode with improved conductivity and high areal capacitance was synthesized via mild electrochemical oxygen de-intercalation of electrodeposited WO3 thin film. The X-ray diffraction (XRD) analysis revealed the presence of monoclinic phase W18O49 of the doped thin film electrode. Raman spectroscopy analysis confirmed the presence of lower valence W5+ in the WO3-δ film. Electrical characterizations of doped WO3-δ and undoped WO3 films show that the doped electrode exhibits far lower sheet resistance and resistivity than the undoped WO3 sample. Mott-Schottky analysis of the samples shows that the vacancy-doped WO3-x possesses a higher donor concentration than the stoichiometric WO3. Electrochemical characterizations by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD,) and electrochemical impedance spectroscopy (EIS) confirmed the superior pseudocapacitive charge storage metrics via its improved volumetric capacitance of 366.12 F·cm−3 (16.0 mF·cm−2) and reduced equivalent series as well as charge transfer resistance over WO3 thin film. This study demonstrated the synthesis of oxygen vacancy-doped WO3-δ thin film using a homemade two-electrode cell facility instead of the popular energy-consuming vacuum-assisted film deposition under controlled-atmosphere conditions. Besides, the vacancy-doped WO3-δ electrode shows a strong charge storage capability in the far negative operating potential range, indicating its suitability as an anode electrode for fabricating high-energy asymmetric supercapacitors.

Biochemical fulvic acid derived amorphous carbon modified microcrystalline graphite as low-cost anode for potassium-ion storage

Graphite anode has great potential toward potassium ion storage for abundant reserves, yet it suffers from the large volume expansion and slow diffusion rate. Herein, the low-cost biochemical fulvic acid-derived amorphous carbon (BFAC) is employed to modify the natural microcrystalline graphite (BFAC@MG) by a simple mixed carbonization strategy. The BFAC smooths the split layer and folds on the surface of microcrystalline graphite and builds the heteroatom-doped composite structure, which effectively alleviates the volume expansion caused by K+ electrochemical de-intercalation processes, together with improving electrochemical reaction kinetics. As expected, the optimized BFAC@MG-0.5 exhibits superior potassium-ion storage performance, which delivers a high reversible capacity (623.8 mAh g−1), excellent rate performance (147.8 mAh g−1 at 2 A g−1), and remarkable cycling stability (100.8 mAh g−1 after 1200 cycles). As a practical device application, the potassium-ion capacitors are assembled using the BFAC@MG-0.5 anode and commercial activated carbon cathode, which exhibits a maximum energy density of 126.48 Wh kg−1 and superior cycle stability. Significantly, this work demonstrates the potential of microcrystalline graphite as the host anode material for potassium-ion storage.

Understanding the Li and Na Intercalation in Si Clathrate Frameworks

Tetrel (Si, Ge, Sn) clathrates are host-guest structures that display novel electrochemical reactions with Li and Na due to their unique cage structure. One area of interest for Tetrel clathrates is the possibility of topotactic Li/Na insertion into the clathrate framework due to the open cage structure. The type II clathrate Na24-x(Si,Ge)136 is unique because the structure can be obtained without guest atoms in the clathrate framework. Figure 1 shows a crystal model schematic of the two unique polyhedral cages that comprise the type II Si clathrate structure: the dodecahedra (Si20, grey) and the hexakaidecahedra (Si28, blue). The structure usually forms with Na guest atoms (yellow) in the center of these cages, but when heated (300 – 500 °C ) under vacuum, the Na atoms diffuse and evaporate out of the structure resulting in a guest free clathrate, Si136.1 Once Na is removed the structure, Li intercalation into the vacant cages becomes possible.2 During the lithiation of the guest-free type II Si clathrate (Na1Si136), there is plateau at 0.30 V vs Li/Li+ which corresponds to Li intercalation into the vacant cages of the clathrate structure.2,3 With synchrotron powder X-ray diffraction, we confirm that Li intercalation is occurring in a topotactic fashion into the framework and identify the Li positions in the two types of cages. In the Si20 cage, Li is found near the center of the cages with a slightly split position, while Li in the Si28 cage is found very off-center, coordinated off the hexagonal faces. Density functional theory (DFT) calculations corroborate the Li positions in both cages. Next, we demonstrate that by using a voltage cutoff of 0.26 V, reversible Li insertion is possible as evidenced by the reproducible voltage profile. Due to the very low volume expansion (0.23 %) and reasonable capacity and voltage (230 mAh/g at 0.30 V), the type II Si clathrate has possible applications as an anode for Li-ion rechargeable batteries.In contrast to the room temperature intercalation of Li, we find that electrochemical deintercalation of Na from the type II structure requires high temperatures (350-450 °C) and overpotentials to achieve. We demonstrate electrochemical desodiation using a novel high temperature approach using a Na beta-alumina solid electrolyte.4 By using DFT to calculate the migration barriers for Na and Li, we demonstrate that the large differences between Li and Na intercalation originates from the much higher migration barriers for Na (1.0 - 2.0 eV) in the type II structure when compared to Li (0.2 eV). Based on these results, design rules for intercalation into Tetrel frameworks will be discussed and other promising open Tetrel frameworks highlighted. Figure 1: Crystal model schematic of the two types of polyhedral in the type II Si clathrate structure: the dodecahedra (grey) and the hexakaidecahedra (blue). Si atoms are orange and Na atoms are yellow. References (1) Krishna, L.; Baranowski, L. L.; Martinez, A. D.; Koh, C. A.; Taylor, P. C.; Tamboli, A. C.; Toberer, E. S. Efficient Route to Phase Selective Synthesis of Type II Silicon Clathrates with Low Sodium Occupancy. CrystEngComm 2014, 16, 3940–3949.(2) Langer, T.; Dupke, S.; Trill, H.; Passerini, S.; Eckert, H.; Pöttgen, R.; Winter, M. Electrochemical Lithiation of Silicon Clathrate-II. J. Electrochem. Soc. 2012, 159, A1318–A1322.(3) Dopilka, A.; Weller, J. M.; Ovchinnikov, A.; Childs, A.; Bobev, S.; Peng, X.; Chan, C. K. Structural Origin of Reversible Li Insertion in Guest‐Free, Type II Silicon Clathrates. Adv. Energy Sustain. Res. 2021, 2000114.(4) Dopilka, A.; Childs, A.; Bobev, S.; Chan, C. K. Solid-State Electrochemical Synthesis of Silicon Clathrates Using a Sodium-Sulfur Battery Inspired Approach. J. Electrochem. Soc. 2021, 168, 020516. Figure 1

Магний-ионды батареяға арналған ұнтақ висмут негізіндегі анодтық материал және оның қасиеттері

In this work an intercalation anode material synthesized on the base of the powdered bismuth is presented. The uniformly distribution of carbon paste suspension over the substrate surface was found out by scanning-electron microscopy. The regularities of electrochemical intercalation and deintercalation of magnesium ions into the electrode created on the base of powdered bismuth in a solution of 0.25 mol/L Mg(N(SO2CF3)2)2 on the base of acetonitrile were studied. The cyclic voltammograms with the results of scanning electron microscopy and atomic emission analysis indicate that in the cathode area the reduction processes proceed with the formation of an intermetallic compound – MgxBiy; two peaks were observed at the reverse course which were conceivably corresponding to two-stage magnesium oxidation. According to cyclic voltammograms by the difference in the potential of peaks in the forward and reverse directions it was established that the processes of reduction and oxidation of magnesium ions into intercalation material were irreversible. The diffusion coefficients of intercalation and deintercalation into the electrode material were calculated using the Rendles-Shevchik equation; they were 3.12·10-11 sm2/s and 1.85·10-11 sm2/s, respectively. X-ray diffraction (XRD) results demonstrated the cubic structure of the bismuth crystal lattice with altered parameters corresponding to inter-metallide formation. At galvanostatic cycling of the synthesized anode material a capacity of up to 104 mA·h·g-1 at current load 1C was achieved. Such results can be a good indicator for the development of magnesium-ion power sources.

NMR Study of LiCo0.96Al0.04O2 As a Positive Electrode Material for Li-Ion Batteries: Homogeneity and Role of Doping on Mechanisms

LiCoO2 (LCO) is one of the most widely used positive electrode materials in lithium-ion batteries due to its high volumetric energy density which can be further improved by charging at high voltages. However, working at high potential (above 4.3 V vs. Li+/Li) causes a deterioration in cycling performance induced by structural instabilities, electrolyte oxidation and Co dissolution. Extensive studies have been devoted to increasing energy density by increasing the cutoff voltage. The substitution of cobalt with various metals is one of the classic methods, the choice of aluminum as dopant for example is based on several criteria: low cost and non-toxicity, a similar radius for Al3+ compared to Co3+ (0.535 Å vs. 0.545 Å) facilitates the replacement of the latter and maintains the structure leading to the complete solid solution LiCo1-yAlyO2.We will focus here on LiCo0.96Al0.04O2, synthesized by the solid route and characterized by 7Li, 27Al and 59Co Nuclear Magnetic Resonance (NMR) and synchrotron X-Ray Diffraction (XRD). In addition to the characterization of the mean structure by XRD, the NMR allows us to study the local environments of the different nuclei. 27Al MAS NMR and synchrotron XRD studies revealed that the Al-doping in this material is homogeneous. 7Li MAS NMR indicates that its stoichiometry (Li/M=1.00) is ideal. The electrochemical study has shown that the phase transitions occurring during delithiation of LiCoO2, were partially eliminated by aluminum doping even with a low doping amount and the high potential mechanisms appear to be different. In order to better understand the role of Al-doping on the mechanisms involved during cycling, several phases LixCo0.96Al0.04O2 were prepared by electrochemical deintercalation and studied by 7Li, 59Co, and 27Al NMR and by XRD.During lithium deintercalation, Co3+ is oxidized to Co4+ then one unpaired electron is generated in the t2g band of Co atoms (t2g 5eg 0). For 0.8 ≤ x ˂ 1.00 the 7Li MAS NMR shows that the system behaves locally as two phase domain: domain with localized electrons and domain with delocalized ones on Con+ ions (Knight shift), even for very low amount of deintercalation (x=0.98), thus the XRD results confirm the existence of the biphasic domain. Whereas, a single phase domain is observed for the deintercalated materials with 0.4 ≤ x ≤ 0.8 and also at the NMR time of scale a single signal (Knight shift) is observed. This signal increases in intensity at the expense of 0 ppm and shifts to the higher isotropic displacement values up to x=0.5 then decreases, thus the evolution of the chex lattice parameter is correlated with the signal shift. For x = 0.3 and x = 0.2: a new broad signal appears probably due to formation of new Li environment in stacking faulted layers (O1 type). These different contributions will be more detailed on the presentation.

Resolving atomic-scale phase transformation and oxygen loss mechanism in ultrahigh-nickel layered cathodes for cobalt-free lithium-ion batteries

Summary Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials.

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Layer spacing gradient (NaLi)1−xCoO2 for electrochemical Li extraction

Reversible electrochemical potassium deintercalation from >4 V positive electrode material K6(VO)2(V2O3)2(PO4)4(P2O7)

Reversible electrochemical deintercalation of potassium from the K6(VO)2(V2O3)2(PO4)4(P2O7) phosphate-pyrophosphate-oxide of potassium and vanadium (IV,V) obtained through a ceramic route has been demonstrated. The material has been tested as a high voltage positive electrode (cathode) for K-ion batteries, demonstrating 53% of the theoretical capacity of 88 mAh/g at the current density C/50 in the 1.8–4.4 V vs K/K+ potential range. The crystal structures of K6(VO)2(V2O3)2(PO4)4(P2O7) in the pristine, charged and discharged states were refined by Rietveld method from powder X-ray diffraction data using a structure model with stochastic orientation of the pyrophosphate groups (space group Pnma, a = 6.9891(1)Å, b = 13.3735(2)Å, c = 14.2495(2)Å in the pristine state). In spite of deintercalation of bulky K+ cations, the cell volume change upon charge amounts to 0.9% rendering K6(VO)2(V2O3)2(PO4)4(P2O7) a “low strain” cathode. The potassium (de)intercalation occurs equally from two distinct crystallographic sites through a single ~4.2 V sloped plateau featuring solid-solution-like behavior, which was demonstrated by operando powder X-ray diffraction. The evaluation of diffusion barriers from the first principles has been conducted by the nudged elastic band method for two ordered arrangements of the pyrophosphate groups derived from the refined disordered structure. The diffusion barriers along crystallographic direction b for both investigated ordered variants were found to be below 0.3 eV.

Atomic-scale observation of phase transition of MgMn2O4 cubic spinel upon the charging in Mg-ion battery

Direct observation of demagnesiated structure of MgMn2O4 spinel oxides at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. Upon the Mg ions extraction from MgMn2O4 spinel oxides, structural transition from cubic to tetragonal phases was observed. The phase transition is a result of Mn octahedral distortion due to cooperative Jahn–Teller distortion of six-coordinate MnIII (t2g3–eg1). On the basis of HAADF/ABF micrographs and electron energy-loss spectrometer (EELS), it is suggested that Mn3+/Mn4+ and/or Mn3+/Mn5+ redox couples play a crucial role in the first electrochemical Mg deintercalation. This is the first report on observation of cubic-tetragonal phase transition in charged spinel MgMn2O4 which shed new insight into the magnesium storage mechanism in this important cathode material for Mg-ion batteries.

Crystal structure and cathode properties of delithiated Li1-xMn1/3Ni1/3Co1/3O2 for Mg rechargeable batteries

The crystal structure and electrode properties of delithiated Li1-xMn1/3Ni1/3Co1/3O2 as a Mg rechargeable battery cathode material were investigated. Electrochemically delithiated Li0.3Mn1/3Ni1/3Co1/3O2 and Li0.4Mn1/3Ni1/3Co1/3O2 in a Mg cell exhibited capacities of approximately 50 and 80 mAh g−1, respectively. On the other hand, chemically delithiated Li0.1Mn1/3Ni1/3Co1/3O2 and Li0.4Mn1/3Ni1/3Co1/3O2 exhibited capacities of approximately 40 and 130 mAh g−1, respectively. Synchrotron X-ray diffraction was performed to refine the crystal structure of these two chemically delithiated samples and their crystal structures were analyzed in detail. Although Li0.4Mn1/3Ni1/3Co1/3O2 was identified as a monophase of a hexagonal crystal system (R3¯m), Li0.1Mn1/3Ni1/3Co1/3O2 was identified as two phases of the hexagonal O3-type (R3¯m) and the trigonal O1-type (P3¯m1). Therefore, the Li deficient O3 structure is considered to be more suitable than O1 structure in the electrochemical intercalation and deintercalation of Mg ions.

(Invited) Screening Plus Testing of Cathode Materials for Ca and Mg Batteries

While the current state-of-the-art in rechargeable batteries is the Li-ion technology, research efforts are intensified towards the development of alternative technologies to satisfy the ever-increasing demand for enhanced energy density. The development of rechargeable batteries based on the intercalation reaction of multivalent cations (Ca2+, Mg2+, Al3+) is a current challenge for electrochemical energy storage. Designing such batteries demands the identification of competitive electrode materials and electrolytes for each particular active ion. In the last years, we have combined computational and experimental techniques in the search of potential cathode materials that could reversibly insert Mg/Ca ions [1-4]. First principles calculations are used to predict three fundamental electrochemical properties of materials: average intercalation voltage, specific capacity and ionic mobility. Benchmarking the computational results with experimental evidences is a necessary step to accelerate reliable materials design based on DFT calculations. Therefore, our experimental investigations comprise the synthesis, characterization and electrochemical testing of materials. In this work, we confront computational and experimental results for selected oxides, nitrides, sulphides and silicate materials. We will show that the combined computational/experimental approaches lead to proof of concept and rationalization for the reversible electrochemical intercalation and deintercalation of calcium in TiS2 [4]. Acknowledgments: Authors are grateful for financial support from Ministerio de Ciencia e Innovación (grant MAT2014-53500-R), the European Union H2020-FETOPEN funded project CARBAT-766617 and Toyota Motor Europe.

Paul Hagenmuller's contribution to solid state chemistry: A scientometric analysis

Paul Hagenmuller (1921−2017) is an important figure of French solid-state chemistry, who enjoyed scientific and institutional recognition. He published 796 papers and has been cited more than 16,000 times. This paper explores Hagenmuller's work using scientometric analysis to reveal the impact of his work, his main research topics and his collaborations. Although Hagenmuller was a recognized scientist, a subset of his work, now highly cited, attracted little attention at the time of publication. To understand this phenomenon, we detect and study papers with delayed recognition, also called 'Sleeping Beauties' (SBs). In scientometrics, SBs are publications that go unnoticed, or 'sleep' for a long time before suddenly attracting a lot of attention in terms of citations. We identify 7 SBs published between 1965 and 1985, and awakened between 1993 and 2010. The first SB reports the discovery of the clathrate structure of silicon. The second reports the isolation of four new phases with the formula NaxCoO2 (x < =1). The five other SBs investigate the electrochemical intercalation and deintercalation of sodium, and the structure and properties of layered oxides. Through interviews with his coworkers, we attempt to identify the reasons for the delayed recognition and the context of the renewed interest in those papers.

Electrochemical Behavior of Graphitized Carbon Nanospheres in a Propylene Carbonate-Based Electrolyte Solution

Electrochemical lithium-ion intercalation and deintercalation at carbonaceous materials in propylene carbonate (PC)-based electrolyte solution depends on the graphitization degree of the material. In this study, graphitized carbon nanospheres (GCNSs) heat-treated at 2900°C (GCNS-2900) and 2600°C (GCNS-2600) showed the reversible lithium-ion intercalation and deintercalation in PC-based electrolyte solutions, despite their high graphitization degree. Moreover, in situ Raman spectroscopy and transmission electron microscopy (TEM) were performed to further understand the electrochemical behavior. According to the Raman spectra, the cointercalation of PC with lithium ions and partial exfoliation was observed only in GCNS-2900. The TEM images revealed that GCNS-2900 exhibited structural collapses due to the concentration of stress in the ridges of a polyhedron during the graphitization process. Such collapses were responsible for the cointercalation of PC with lithium ions and partial exfoliation in GCNS-2900. The control of the graphitization degree, including the stacking order, suppression of edges and structural collapses, and a suitable arrangement of graphene layers should effectively suppress the destruction of graphite and improve the first coulombic efficiency in PC-based electrolyte solutions.

Using a Battery to Synthesize New Vanadium Oxides

AbstractSodium electrochemical deintercalation in a battery was used as a route to synthesize new vanadium oxides. Sodium layered oxides were used as positive electrode materials in batteries and sodium was electrochemically deintercalated up to a precise composition resulting in the discovery of a new phase Na1/2VO2. As for many vanadium oxides, this compound presents a magnetic transition, slightly above room temperature, around 325 K, as well as a structural transition involving displacements of vanadium ions. The discovery of this new vanadium oxide and the study of its unique electronic properties have only been possible because the battery permits the synthesis of this new phase at room temperature. This shows that many more new systems could be explored using electrochemical (de)intercalation in a battery and new materials that would be impossible to synthesize by classical solid state reaction could be obtained.

Structural and optical properties of alumina passivated amorphous Si slanted columnar thin films during electrochemical Li-ion intercalation and deintercalation observed by in situ generalized spectroscopic ellipsometry

The authors report on the structural and optical property changes of alumina passivated amorphous Si slanted columnar thin films during electrochemical Li-ion intercalation and deintercalation determined by in situ generalized spectroscopic ellipsometry. The cyclic voltammetry investigations versus Li/Li+ are performed at a rate of 1 mV/s, while Mueller matrix generalized spectroscopic ellipsometry data are collected. Through a best-match model analysis utilizing the homogeneous biaxial layer approach, temporal anisotropic optical constants are obtained. The authors observe a strong anisotropic electrochromic response with maximum changes of ∼18% in the anisotropic refractive indices and ∼750% in the anisotropic extinction coefficients. Furthermore, the thin films reversibly expand and contract by ∼35%. A comparative analysis of the temporal optical constant response to the changes in overall optical anisotropy of the electrode reveals six transient regions throughout the Li-ion intercalation and deintercalation cycle of the highly ordered three-dimensional nanostructures. The transients correspond to electrochemical potential regions which show limited charge transfer, metalization or demetalization, and swelling or deswelling of the nanostructures. Furthermore, the electrochemical potential regions in which the transients are observed here are very similar to those previously reported for Li-ion intercalation and deintercalation of silicon nanowires using structural analysis techniques, where four distinct phases of Li-Si alloy formation were revealed. The authors find that at low Li contributions, swelling and deswelling occur preferentially along the slanted columns, while at high Li contributions, swelling and deswelling occur preferentially within the intercolumnar space.

Electrochemical deintercalation kinetics of 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 studied by EIS and PITT

The charge transfer resistances (Rct) and chemical diffusion coefficients of lithium ions (DLi+) in 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 at various potentials in the first charge process were systematically tested by EIS and PITT. In the initial stage of the charging process, Rct gradually decreased to a minimum value of 68.5 Ω at 4.0 V. Then it sharply increased to 977.5 Ω at 4.8 V. The main reason was the activation of Li2MnO3 component started to decompose to Li2O and MnO2 at about 4.5 V. The DLi+ obtained from EIS and PITT was greatly dependent on the potential and it in the range of 10−16 to 10−12 cm2 s−1and 10−14 to 10−13 cm2 s−1, respectively. The DLi+ variation tendency with cell potential obtained from EIS and PITT was consistent with each other and with a maximum value at 4.0 V. The low Li+ diffusion coefficients was due to the high kinetic barrier associated with oxygen loss, surface and structural rearrangement. The results showed that the kinetic of 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3O2 was controlled by lithium-ion diffusion in the low voltage (<4.0 V) and controlled by charge transfer resistance in the high voltage (>4.3 V).