Li Sites Research Articles

First-principles study of n- and p-type doping opportunities in LiGaO2

First-principles calculations are presented for Si, Ge, Sn doping of LiGaO2. Both Si and Ge are found to be shallow donors. Sn is found to be a somewhat deeper donor. The site preference is studied and all three group-IV dopants are found to favor the Ga over the Li site when the Fermi level is in the upper part of the gap, corresponding to n-type doping and for Li-rich growth conditions. The prospects for n-type doping are thus favorable. N is found to be amphoteric with both deep donor and acceptor type transition levels. Zn has a significant site competition between Zn (donor) and Zn (acceptor) levels, which would pin the Fermi level in the middle of the gap. Thus, p-type doping cannot be achieved with these dopants.

Correlation between Cation Disordering and the Anionic Redox Chemistry in Li-Rich Layered Oxides

To satisfy our increasing dependence on the high energy storage electronics, Li-rich layered oxides (Li[LixM1-x]O2, M = Ni, Co, Mn, Ru, Ir, etc) have attracted significant attention as cathode materials for lithium-ion batteries in recent years. This class of cathode materials exhibit promising capacities, up to 300 mAh/g, due to accumulative transition metal and oxygen redox reaction1–5. Additional capacity in this class of Li-rich cathode material is attributed to the anionic redox which is irreversible or partially reversible oxygen evolution6,7 and reversible O2-/n- redox1,3,4,8. Luo el at.1 demonstrated that the localized electron holes on oxygen coordinated by Mn4+ and Li+ ions is promoted by the relatively more ionic interactions of O-(Mn/Li) than O-(Ni/Co) interactions at the result of the oxygen oxidation. In our previous study2, at least partially reversible oxygen evolution was observed in 0.4Li2MnO3-0.6LiMn0.5Ni0.5O2 by using Reitveld refinement of high resolution powder diffraction patterns. In the case of 4d (Ru) and 5d (Ir) transition metal-based Li-rich cathode materials, reversible anionic redox was confirmed by X-ray photoelectron spectroscopy (XPS)3,4. Even though the participation of oxygen in redox activity in Li2MnO3 results in partial oxygen evolution with irreversible structural changes9, oxygen redox reaction is stabilized by the reversible peroxo-dimers (O2 n-) formation in the Li2MO3-based (M = Ru, Ir) Li-rich cathode materials due to the high covalent metal-oxygen environment in Ru- and Ir-based lithium-rich cathode materials. However, Seo et al.10 identified the structural and chemical origin of the anionic redox activity which preferentially takes place along the Li-O-Li configurations (non-bonding O 2p states) in Li-rich layered oxides and cation-disordered oxides by using ab initio calculations based on DFT. The electrons in Li-O-Li states are higher energy than those in the other O 2p states owing to their unhybridized O 2p and Li 2s orbitals without taking into account the covalency between the transition metal and oxygen. Through the significant research efforts, anionic redox mechanism seems to be well established. In the case of Na2RuO3, extra anionic capacity is enabled in honeycomb-ordered Na2RuO3 due to the ordered intermediate Na1RuO3 phase which can accommodate the frontier orbital reorganization11, meanwhile, transition metal migration into the empty Li sites is closely associated with the anionic redox as a result of the structural disordering in Li1.17Ni0.21Co0.08Mn0.54O2 5 and Li2IrxSn1-xO3 systems12. It is still under debating whether such manifold anionic chemistry will be solved in terms of transition metals (3d, 4d, and 5d) or alkali metals (Li and Na) or bulk and local structure. In addition, the different reaction mechanism is confirmed between multivalent iridium redox (Ir4+/5.5+)12 and cumulative iridium (Ir4+/5+) and oxygen (O2-/n-) redox13 even in the same C2/m space group of Li2IrO3 materials.Herein, redox mechanism of Li2IrO3 was investigated as a model compound for Li-rich cathode material to understand the key structural differences that lead to anionic redox activity through the synchrotron-based analysis. The local environment, not the composition itself in Li-rich materials, is one of the major factors affecting the redox reaction. We demonstrate that the in-plane disordering in the transition metal layer play a critical role in cation migration and anionic redox, and that cation migration also can trigger the anionic redox reactions. These fundamental insights about Li-rich material family are critical for further development of anionic redox-based cathode materials. In-plane ordering in pristine state with the same composition of Li2IrO3 has a major impact on cation migration and reversible anion redox. Based on the experimental data, detailed findings and discussion will be presented in the 237th ECS meeting.

High-Voltage Sodium and Lithium Nitridophosphates axMy(PO3)3n As Cathode Materials for Sodium-Ion and Lithium-Ion Batteries

Polyanionic compounds stand out as attractive candidates for electrode materials in Na-ion and Li-ion batteries due to their stable 3D framework.1 Furthermore, according to theoretical calculations, N-substituted polyanionic compounds should enable the use of more than one redox couple of transition metals due to the lowering their working voltage.2 Nitridophosphates, with general formula NaxMy(PO3)3N, exhibit an open 3D structure that facilitates the migration of ions at room temperature and enables stable cycling.3,4 In particular, our research has uncovered the remarkably high working voltage of Na3V(PO3)3N (4.0 V vs Na+/Na0 , Figure 1) which, together with Na7V3(P2O7)4, is the highest operating voltage for Na-ion cathode material for the VIV+/VIII+ redox couple.5,6 Moreover, Na3V(PO3)3N can also be used as a cathode in a hybrid Lithium-ion configuration.The Li counterpart Li3V(PO3)3N, can be prepared by chemical ion exchange. Its 6Li ssNMR spectrum exhibits three different peaks that have been assigned to the three independent Li sites and the Li mobility between those sites was probed by 2D exchange spectroscopy (EXSY), as shown in Figure 1c.Aiming to lower the cost and improve the electrochemistry we have further explored the family of nitridophosphates. Seeking for redox-active transition metal we focused on economical and earth abundant 3d metals. Our studies resulted with improving the electrochemical performance of Na2Fe2(PO3)3N vs Na and synthesizing for the first time cobalt nitridophosphate, Na2Co2(PO3)3N with expected electrochemical activity at ~4.5V vs Na+/Na0. Endeavoring to obtain a manganese nitridophosphate we have discovered a new family of compounds which will be also shown.7 1. C. Masquelier and L. Croguennec, Chem. Rev. 113, 6552 (2013).2. M. Armand and M.E.A. y de Dompablo, J. Mater. Chem. 21, 10026 (2011).3. J. Liu, X. Yu, E. Hu, K.-W. Nam, X.-Q. Yang, and P.G. Khalifah, Chem. Mater. 25, 3929 (2013).4. J. Liu, D. Chang, P. Whitfield, Y. Janssen, X. Yu, Y. Zhou, J. Bai, J. Ko, K.-W. Nam, L. Wu, Y. Zhu, M. Feygenson, G. Amatucci, A. Van der Ven, X.-Q. Yang, and P. Khalifah, Chem. Mater. 26, 3295 (2014).5. M. Reynaud, A. Wizner, N. A. Katcho, L.C. Loaiza, M. Galceran, J. Carrasco, T. Rojo, M. Armand, and M. Casas-Cabanas, Electrochemistry Communications 84, 14 (2017).6. C. Deng, S. Zhang, and B. Zhao, Energy Storage Materials 4, 71 (2016).7. A. Wizner, M. Reynaud, J.X. Lian, F. Bonilla, J.-M. Lopez del Amo, J. Carrasco, T. Rojo, M. Armand and M. Casas-Cabanas, submitted. Figure 1

7Li NMR spectra and spin-lattice relaxation in lithium heptagermanate single crystal

7Li NMR spectra and spin-lattice relaxation in Li2Ge7O15 single crystal have been analyzed. It is shown that the NMR spectrum consists of quadrupolar triplets from 7Li (I = 3/2) nuclei located in structurally nonequivalent Li(1) and Li(2) sites (T = 300 K). On heating the quadrupolar splitting decreases as a result of thermal vibrations of 7Li quadrupolar axes whereas NMR lines narrow due to translational motion of lithium ions. Measurements of the spin-lattice relaxation rate T1−1 give information about the time scale and the activation energy of lithium ions motion. The results of NMR studies are compared with findings from electrical conductivity measurements.

Structural and Electrochemical Impacts of Mg/Mn Dual Dopants on the LiNiO2 Cathode in Li-Metal Batteries.

Doping chemistry has been regarded as an efficient strategy to overcome some fundamental challenges facing the "no-cobalt" LiNiO2 cathode materials. By utilizing the doping chemistry, we evaluate the battery performance and structural/chemical reversibility of a new no-cobalt cathode material (Mg/Mn-LiNiO2). The unique dual dopants drive Mg and Mn to occupy the Li site and Ni site, respectively. The Mg/Mn-LiNiO2 cathode delivers smooth voltage profiles, enhanced structural stability, elevated self-discharge resistance, and inhibited nickel dissolution. As a result, the Mg/Mn-LiNiO2 cathode enables improved cycling stability in lithium metal batteries with the conventional carbonate electrolyte: 80% capacity retention after 350 cycles at C/3, and 67% capacity retention after 500 cycles at 2C (22 °C). We then take the Mg/Mn-LiNiO2 as the platform to investigate the local structural and chemical reversibility, where we identify that the irreversibility takes place starting from the very first cycle. The highly reactive surface induces the surface oxygen loss, metal reduction reaching the subsurface, and metal dissolution. Our data demonstrate that the dual dopants can, to some degree, mitigate the irreversibility and improve the cycling stability of LiNiO2, but more efforts are needed to eliminate the key challenges of these materials for battery operation in the conventional carbonate electrolyte.

Crystal structure and lithium ionic transport behavior of Li site doped Li7La3Zr2O12

Doping some elements on Li site of LLZO is an effective method to stabilize it as cubic phase and improve Li+ conductivity. The reported possible Li site elements calculated by first principle are Be, B, Al, Fe, Zn, Ga and the Ga-doped LLZO shows the a higher conductivity than other LLZO. However, whether these elements all can stable LLZO as cubic phase are needed to be verified and the reason of Ga exhibits higher conductivity is not clear enough. In this work, all these elements are tried to be doped on Li site and the results show that the Al, or Fe, or Ga can stable LLZO as cubic phase while the others does not. The Ga-doped LLZO exhibits the highest conductivity of 1.31×10−3 S•cm-1 due to the transform of group space from Ia-3d to I-43d, shorter distances between different Li+, and Ga can improve the grain size.

Essential structural and experimental descriptors for bulk and grain boundary conductivities of Li solid electrolytes

ABSTRACT We present a computational approach for identifying the important descriptors of the ionic conductivities of lithium solid electrolytes. Our approach discriminates the factors of both bulk and grain boundary conductivities, which have been rarely reported. The effects of the interrelated structural (e.g. grain size, phase), material (e.g. Li ratio), chemical (e.g. electronegativity, polarizability) and experimental (e.g. sintering temperature, synthesis method) properties on the bulk and grain boundary conductivities are investigated via machine learning. The data are trained using the bulk and grain boundary conductivities of Li solid conductors at room temperature. The important descriptors are elucidated by their feature importance and predictive performances, as determined by a nonlinear XGBoost algorithm: (i) the experimental descriptors of sintering conditions are significant for both bulk and grain boundary, (ii) the material descriptors of Li site occupancy and Li ratio are the prior descriptors for bulk, (iii) the density and unit cell volume are the prior structural descriptors while the polarizability and electronegativity are the prior chemical descriptors for grain boundary, (iv) the grain size provides physical insights such as the thermodynamic condition and should be considered for determining grain boundary conductance in solid polycrystalline ionic conductors.

The effect of gallium substitution on the structure and electrochemical performance of LiNiO2 in lithium-ion batteries

Ga-doped LiNiO2 is reinvestigated. Ga is suggested to occupy the Li site. Detailed structural and electrochemical characterization is provided.

First-principles study of BC3 monolayer as anodes for lithium-ion and sodium-ion batteries applications

In this paper we have studied the stability, mobility and voltage profile of alkali metal intercalated BC3 monolayer (MxBC3), for 0 < x ≤ 1 and M = Li, Na. Firstly, our calculations have the objective to identify the lower energy of Li and Na adsorption sites by using the density functional theory, then we calculate the minor diffusion energies of Na and Li on the surface of BC3 monolayer as shown by the total density of states of MxBC3 (M = Li, Na). Moreover, we showed that BC3 monolayer has changed his semiconductor character to metallic character after the adsorption of Li and Na on his surface. Importantly, we have demonstrated that BC3 monolayer has a higher theoretical capacity (582,63 mA h/g) as compared to Mo2C, VS2, MoS2, and graphite. Finally, we show that monolayer BC3 has a low average open-circuit voltage of 0.48 V for Li and 0.79 V for Na. These results highlight suggest that BC3 monolayer can be a promising anode material both for lithium-ion and sodium-ion batteries.

Rapid and Tunable Assisted-Microwave Preparation of Glass and Glass-Ceramic Thiophosphate "Li7P3S11" Li-Ion Conductors.

Glass and glass-ceramic samples of metastable lithium thiophosphates with compositions of 70Li2S-30P2S5 and Li7P3S11 were controllably prepared by using a rapid assisted-microwave procedure in under 30 min. The rapid preparation times and weak coupling of the evacuated silica ampules with microwave radiation ensure minimal reactivity of the reactants and the container. The microwave-prepared samples display comparable conductivity values with more conventionally prepared (melt quenched) glass and glass-ceramic samples, on the order of 0.1 and 1 mS cm-1 at room temperature, respectively. Rietveld analysis of synchrotron X-ray diffraction data acquired with an internal standard quantitatively yields phase amounts of the glassy and amorphous components, establishing the tunable nature of the microwave preparation. X-ray photoelectron spectroscopy and Raman spectroscopy confirm the composition and the appropriate ratios of isolated and corner-sharing tetrahedra in these semicrystalline systems. Solid-state 7Li nuclear magnetic resonance (NMR) spectroscopy resolves the seven crystallographic Li sites in the crystalline compound into three main environments. The diffusion behavior of these Li environments as obtained from pulsed-field gradient NMR methods can be separated into one slow and one fast component. The rapid and tunable approach to the preparation of high quality "Li7P3S11" samples presented here coupled with detailed structural and compositional analysis opens the door to new and promising metastable solid electrolytes.

Mg2+-doped LiFePO4/C cathode from expired lithium carbonate and ferrous sulfate tablets

The wide application and oversupply of various medicines are inevitably accompanied by the production of massive amounts of expired medicines, which can trigger the environmental contamination and waste of resources if these are not reasonably managed. For this reason, the efforts were made to recycle two expired medicines (lithium carbonate (Li2CO3) and ferrous sulfate (FeSO4) tablets) simultaneously into magnesium ion-doped lithium iron phosphate (LiFePO4; LFP)/carbon (C) powders through a facile high-temperature solid-state reaction. In addition, the economic feasibility was analyzed and discussed. The results suggested that 0·51 wt% magnesium ions were successfully doped into the lithium (Li) site of LFP/carbon, and the corresponding molecular formula was Li0·92Mg0·04FePO4/C, which resulted in the double effects: a decrease in the unit cell volume and an increase in the electronic conductivity. Furthermore, the magnesium ion/LFP/carbon cathode also exhibited better electrochemical lithium-storage performance compared with the undoped LFP/carbon cathode, indicating high application feasibility in lithium-ion batteries. Additionally, the recycling process was economically profitable, which would stimulate the development of the circular economy of waste expired medicines and lithium-ion batteries.

The effects of alkali metal ions with different ionic radii substituting in Li sites on the electrochemical properties of Ni-Rich cathode materials

The influences of alkali metal ions with different ionic radii substituting in Li sites on structure and electrochemical performances of Ni-rich cathode are systematically investigated. Li0.99M0.01Ni0.8Co0.1Mn0.1O2 (M = Li, Na, K, Rb) are synthesized by calcining Ni0.8Co0.1Mn0.1(OH)2 with lithium carbonate and other alkali carbonates. Diffraction analysis shows doping with alkali metal ions will not change the host layered structure. Specifically, alkali metal ion with appropriate ionic radius (Na+) dopes in Li site can enlarge Li slab space, decrease cation mixing and stabilize crystal structure by acting as “pillar ions”; while, the K+ and Rb+ ions with larger ionic radii dope in Li sites will block Li+ diffusion and cause lattice distortion. The capacity retention of the bare, Na+, K+ and Rb+ doped samples after 200 cycles at 1C within 2.8–4.3 V is 93.2%, 96.8%, 88.7% and 92.9%, respectively. The experimental results and theoretical calculations reveal that doping ions with appropriate ionic radii in Li sites are in favor of Li+ diffusion, while doping ions with overlarge ionic radii will deteriorate the structure and electrochemical performances of the cathode. We believe this study will benefit the future works for the Li-site doping of layered materials.

Crystal Structural Framework of Lithium Super‐Ionic Conductors

AbstractAs technologically important materials for solid‐state batteries, Li super‐ionic conductors are a class of materials exhibiting exceptionally high ionic conductivity at room temperature. These materials have unique crystal structural frameworks hosting a highly conductive Li sublattice. However, it is not understood why certain crystal structures of the super‐ionic conductors lead to high conductivity in the Li sublattice. In this study, using topological analysis and ab initio molecular dynamics simulations, the crystal structures of all Li‐conducting oxides and sulfides are studied systematically and the key features pertaining to fast‐ion conduction are quantified. In particular, a unique feature of enlarged Li sites caused by large local spaces in the crystal structural framework is identified, promoting fast conduction in the Li‐ion sublattice. Based on these quantified features, the high‐throughput screening identifies many new structures as fast Li‐ion conductors, which are further confirmed by ab initio molecular dynamics simulations. This study provides new insights and a systematic quantitative understanding of the crystal structural frameworks of fast ion‐conductor materials and motivates future experimental and computational studies on new fast‐ion conductors.

Local metallic and structural properties of the strongly correlated metal LaNiO3 using 8Li β–NMR

We report $\beta$-detected NMR of ion-implanted $^{8}$Li in a single crystal and thin film of the strongly correlated metal LaNiO$_{3}$. In both samples, spin-lattice relaxation measurements reveal two distinct local metallic environments, as is evident from $T$-linear Korringa $1/T_{1}$ below 200 K with slopes comparable to other metals. A small, approximately temperature independent Knight shift of $\sim 74$ ppm is observed, yielding a normalized Korringa product characteristic of substantial antiferromagnetic correlations, but, we find no evidence for a magnetic transition from 4 to 310 K. Two distinct, equally abundant $^{8}$Li sites is inconsistent with the widely accepted rhombohedral structure of LaNiO$_{3}$, but cannot be simply explained by either of the common alternative orthorhombic or monoclinic distortions.

An Entropically Stabilized Fast-Ion Conductor: Li3.25[Si0.25P0.75]S4

We report on a family of lithium fast ion conductors, Li3+x[SixP1–x]S4, that exhibit an entropically stabilized structure type in a solid solution regime (0.15 < x < 0.33) with superionic conductivity above 1 mS·cm–1. Exploration of the influence of aliovalent substitution in the thermodynamically unstable β-Li3PS4 lattice using a combination of single crystal X-ray and powder neutron diffraction, the maximum entropy method, and impedance spectroscopy reveals that substitution induces structural splitting of the localized Li sites, effectively stabilizing bulk β-Li3PS4 at room temperature and delocalizing lithium ion density. The optimal material, Li3.25[Si0.25P0.75]S4, exhibits inherent entropic site disorder and a frustrated energy landscape, resulting in a high conductivity of 1.22 mS·cm–1 that represents an increase of three orders of magnitude compared to bulk β-Li3PS4 and one order of magnitude higher than the nanoporous form. The enhanced ion conduction and lowered activation barrier with increasin...

Role of Li Distribution in High Li Conductivity of Li x (Ge,P)3S12

Li x (GeP)2S12 (LGPS) is a lithium superionic conductor with the obvious potential application as an electrolyte for all-solid-state batteries that could be safer and have higher power compared to conventional batteries using liquid electrolytes. Li10GeP2S12 shows an exceptionally high conductivity of 12 mS/cm at room temperature [1], and doubling of the conductivity to 25 mS/cm was attained in the related compound Li9.54Si1.74P1.44S11.7Cl0.3 [2]. LGPS has a complicated structure. The backbone is a framework of GeS4 and PS4 tetrahedra where there are (Ge,P) shared sites and P-only sites. Li is four-folded coordinated with S and occupy four types of sites, Li1 to Li4. (Li1)S4 and (Li3)S4 form a one-dimensional chain and this is considered to be the primary Li diffusion route. The original article [1] claimed that the Li1 site is clearly double-split while the other Li sites are not split. However, in our presentation we show that the Li3 site is actually double-split at room temperature and triple-split at 10K. Li splitting means that there are more local minima for Li, which in turn results in increased complexity in Li migration paths. Understanding and controlling of Li splitting is important to further enhance Li conductivity. Both Li1 and Li3 sites, which are found to split, take part in the primary Li conduction path and therefore the intriguing high Li conductivity of LGPS should be strongly influenced by fine details of the Li potential. Our first principles calculations show that that neither Li1 nor Li3 sites splits in Li12Ge3S12 where all Li sites are occupied, and reducing the Li concentration, or introducing Li vacancies, was found to be necessary for splitting of these Li sites. Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; Mitsui, A., A lithium superionic conductor. Nat. Mater. 2011, 10 (9), 682.Kato, Y.; Hori, S.; Saito, T.; Suzuki, K.; Hirayama, M.; Mitsui, A.; Yonemura, M.; Iba, H.; Kanno, R., High-power all-solid-stae batteries using sulfide superionic conductors. Nature Energy 2016, 1 (4), 16030.

Molecular Analysis of Transport Characteristics of Li Ion in Solid State Electrolyte

These days, the demands for a new technology for producing energy without consuming fossil fuels are increasing. One reason is, for example, strict regulations of emitting CO2 and NO on cars like Euro 6 in European countries. It is predicted these regulations will be much stricter in many countries in the future. Also, the demands for a new battery that is smaller and has higher energy outputs for smartphones and computers are increasing in the 21 century. So, one of the solutions for the problems in the 21 century is inventing new battery without emitting CO2 and NO. Above all, lithium ion battery is given attention as the one of the new batteries because it has high energy density and can be stored for a long time. Lithium ion battery has some merits such as rechargeable battery, high energy density and large range of operating temperatures. With these benefits, lithium ion battery is used for electronic vehicles (EV), cellphones and computers. However, lithium ion battery has some demerits. Because its electrolyte is liquid, liquid leak and automatic firing occurs and it has low degree of design freedom. One of the solutions for these problems is all solid-state lithium ion battery whose electrolyte is solid. In our study, as the material for the electrolyte Li7La3Zr2O12 (LLZ) is chosen. LLZ can treat easily due to high chemical stability of Li ions and high ion conductivity at high temperatures. In previous research, it was revealed that LLZ has phase transition from tetragonal phase to cubic phase at about 900 K. It was also found that there are no sites in tetragonal LLZ but some sites in cubic LLZ. That is, it means LLZ has no sites below 900K and some sites above 900K. Above all, the transport mechanism of Li ion in both tetragonal LLZ and cubic LLZ at 300K was revealed by Ab-initio MD simulation. However, how the structure property of LLZ influences the transport property of Li ion at various temperatures was not revealed. The objective of this research is to reveal how the structure property of LLZ influences the transport property of Li ion in LLZ at various temperatures by molecular dynamics (MD) simulation. In this research, we simulated the self-diffusivity of Li ion from 300K to 1100K with 100K decrements. As the analysis of transport property, we calculated self-diffusion coefficients and root-mean square deviation (RMSD) of each Li ion. As the analysis of structure property, we calculated the lattice parameters and Li-Li’s radius distribution function (RDF). As the simulation system, we constructed the initial structure at first, performed NVT or NPT simulation for 225 ps to reach equilibrium state and after that started sampling for 1ns. Firstly we found a peak at 2.5Å from the results of RDF. The result is consistent with the fact that the distance between Li site and the nearest other Li site is about 2.5Å from other research. From the result of self diffusion coefficient of Li ion against temperature, we found the slope from 500K to 900K is different from the slope from 900K to 1100K. It can be considered that the difference is due to the difference of the transport mechanisms of Li ion in each LLZ phases. From the results of RMSD, we found that the temperature dependence on RMSD is large. From 600K to 800K we found some Li ions jumped to the neighboring sites and change the places. It is called “a synchronous collective motion”. From 900K to 1100K the synchronous collective motion was not seen in the graphs. From these results and the fact that there is some sites in LLZ from 900K but no sites below 900K, it can be said that Li ions move as synchronous collective motion below 900 while they do not move as synchronous collective motion but as the motion through the vacant sites from 900K to 1100K.

Structural Distribution of Redox-Active Oxygen Governing Chemical Reversibility in Li- and Mn-Rich Layered Oxides

Li- and Mn-rich layered oxides (LMR) come into the spotlight due to anomalously high capacities under O redox. However, O redox also incurs undesirable situations: voltage fade, inhomogeneous kinetics and low coulombic efficiency, limiting a practical use. Herein, through a comparative study on LMR (Li1.15Mn0.51Co0.17Ni0.17O2) having different distributions of redox-active oxygen in a structural arrangement, we reveal the origin of irreversible properties of LMR, which appear mainly at low voltage redox region (LVRR, ~3.0V). Focusing on chemical reversibility at LVRR, real-time simultaneous observations on competitive TM-O redox behavior and TM occupancies in Li sites were conducted using operando fine-interval X-ray absorption spectroscopies. First-principles calculations demonstrate that the dispersed arrangement of redox-active oxygen stabilizes TM-O coordination, leading to restrained TM migration and reversible O redox. The enlightenment of chemical reversibility which considers the real-time changes in electronic/crystalline structures provides a new perspective on a structural design for ideal future LMR.

Lithium Intercalation Edge Effects and Doping Implications for Graphite Anodes

The interface between electrolyte and graphite anodes plays an important role for Li intercalation and has significant impact on the charging/discharging performance of lithium ion batteries (LIBs). However, atomistic understanding of interface effects that would allow to rationally tune the interface is largely missed. In this work, we comprehensively study the energetics of Li near the main non-basal surfaces of graphite, namely the armchair and zigzag edges. Compared with the bulk, both graphite edges provide stronger absorbing Li sites (i.e., sub-surface sites that lithiate at higher voltages). Furthermore, this effect is significantly more pronounced at the zigzag edge compared to the armchair edge due to its unique electronic structure. The “peculiar” topologically stabilized electronic surface state found at zigzag edges strongly interacts with lithium; thereby changing Li diffusion behavior at the surface as well. Finally, boron/nitrogen doping was identified as a promising strategy to tune the Li intercalation behaviors at both edge systems, which might give some guidance for the modification of graphite anodes with a view enhance intercalation kinetics.

Rapid response of photorefraction in vanadium and magnesium co-doped lithium niobate

Vanadium and magnesium co-doped LiNbO3 (LN) crystals were grown, and their photorefractive properties were studied in the visible spectral region. At 488 nm the shortest response time of 80 ms was achieved for an LN crystal co-doped with 0.1 mol% V2O5 and 6.0 mol% MgO, which is the more rapid than other reported doped LN crystals in the same wavelength region. The sensitivity of this crystal reaches 17 cm J−1 with an adequate diffraction efficiency of 4.0%. A schematic diagram for energy level is proposed and discussed. Through the analysis of defect structure and absorption spectra, we found that the change of the vanadium ions occupancy from Li sites to Nb sites is responsible for significant shortening the response time. The rapid response of vanadium and magnesium co-doped LN crystal can play an excellent role in the field of dynamic holography and practical holographic 3D-storage applications.