Li Sites Research Articles

K doping on Li site enables LiTi2(PO4)3/C excellent lithium storage performance

LiTi2(PO4)3 as anode for aqueous lithium ion battery shows promising prospect in energy storage and electronic products owing to stable structure and suitable intercalation/deintercalation voltage of Li ions. However, the performance of LiTi2(PO4)3 needs to be further improved to meet their higher requirements. Herein, K-doped LiTi2(PO4)3/C on Li site was synthesized by sol-gel method combined with heat-treatment. And synthesized sample was used as anode for aqueous lithium ion battery. The main lattice structure and morphology of LiTi2(PO4)3 are not affected by K doping on Li site. And electrochemical property of LiTi2(PO4)3 is obviously improved by K doping. Performance changing trend is in order of Li0.97K0.03Ti2 (PO4)3/C (LCK-3) > Li0.99K0.01Ti2(PO4)3/C (LCK-1) > Li0.95K0.05Ti2(PO4)3/C (LCK-5) > LiTi2(PO4)3/C (LC), which is consistent with the changing trend of lattice volume. LCK-3 demonstrates superb electrochemical property. LCK-3 delivers the discharge capacities of 104.4, 88.9, and 73.1 mAh g−1 at 0.5, 7.0, and 15 C, respectively, 26.7, 42.9, and 53.0 mAh g−1 higher than these of original LC. Moreover, capacity retention of 78.8% for LCK-3 is retained at 6 C even after 1000 cycles, which is much larger than that for LC (60.6%). It is attributed to that K with proper content can widen the pathway for Li ions, which is confirmed by XRD measurement. This can further accelerate the transfer of Li ions in crystal. This work demonstrates that K doping on Li site is a valid method to ameliorate electrochemical performance of LiTi2(PO4)3 in aqueous lithium ion battery.

Sorption of CO2 on NaBr co-doped Li4SiO4 ceramics: Structural and kinetic analysis

Structurally modified and improved NaBr-co-doped Li4SiO4 ceramics were developed for CO2 absorption in low-CO2-concentration atmospheres. Pure and NaCl-doped Li4SiO4 ceramics were also prepared for comparison. The samples were analyzed by X-ray diffraction, Scanning Electron Microscopy, N2 adsorption, X-ray photoelectron spectroscopy, differential scanning calorimetry, and thermogravimetric analyses (dynamic and isothermal). The sorption kinetics were obtained using a double exponential model. The results showed that both Na and Br can be introduced into the Li4SiO4 structure and doped on Li and oxygen sites, respectively. The doped sample presented a Li2O-enriched surface, guaranteeing abundant LiO sites and are significantly different from previous anionic (CO3, F and Cl) doping of Li4SiO4, Br doping also generated macroporous features with small particle size, these favorable characteristics promoted the surface chemisorption kinetics. Moreover, DSC analysis confirmed the formation of the molten phases during CO2 absorption, which helps improve the lithium diffusion kinetics. Here, 0.1 mol NaBr doping was used to reach a maximum absorption capacity (>30.0 wt%) in 15 vol% CO2, suggesting that NaBr-doped Li4SiO4 ceramics have great potential for CO2 capture at high temperature.

Investigation of the Li–Co antisite exchange in Fe-substituted LiCoPO4 cathode for high-voltage lithium ion batteries

Carbon coated olivine Pnma LiCoPO4 (LCP/C) and Fe-substituted LiCo0.8Fe0.2PO4 (LCFP/C) were synthesized by a solvothermal method and their structural features and electrochemical properties were investigated. The electrochemical performance of LCFP/C is better than that of LCP/C, owing to the partial substitution of Co by Fe which effectively suppresses the increasement of antisite exchange between Li+ and Co2+ ions within the structure during cycling, despite a similar amount of Li–Co antisite exchange in pristine LCP/C and LCFP/C samples. Furthermore, direct visualization of Co in Li sites in the pristine samples and after 50 cycles was achieved through high-resolution scanning transmission electron microscopy for both LCP/C and LCFP/C. It was found that LCP/C locally formed a new cation-ordered structure after cycling due to the Li–Co antisite exchange, while the structure of LCFP/C remains almost the same. This study provides direct evidence that Fe substitution reduced the Li–Co exchange and improved the electrochemical cycling life of the LiCoPO4 cathode for high-voltage lithium ion batteries.

Probing the thermal effects of voltage hysteresis in anionic redox-based lithium-rich cathodes using isothermal calorimetry

Probing the thermal effects of voltage hysteresis in anionic redox-based lithium-rich cathodes using isothermal calorimetry

Influence of Li Content on Structure and Electrochemical Performance of Lithium-Rich Cathode Materials for Lithium-Secondary Batteries

Li- and Mn-rich cathode materials win huge attentions due to their extremely high capacity and unique solid solution composite structure. As a composition contains two or more phase, the compatibility of these phases would be critical points to promise high capacity output. We chose both layered structures which have similar oxygen ion arrangement as framework and distinct cations distribution, 1 to found the xLi2MnO3-yLiNi1/3Co1/3Mn1/3O2 cathode materials. From former researches, 2 Li was always used to adjust the ratio of the layered and monoclinic phase. Thus, in this paper the Li content was changed to adjust the composition of the two contained phase. All the precursors of three samples were synthetized though co-precipitation route, after drying and mixing with lithium, the powders were sintered at 900 oC for 15h to obtain the final products. The XRD (X-ray diffraction) were used to investigate the order of crystal structure of these cathode materials, indicating that the ordering of the layered structure was improved with Li content decreased. The intensity of characteristic peaks for monoclinic phase increases with increasing Li content while the ratio of W rohom /W mono decrease from 4.1565 through 3.240 and 3.0789 to 2.44, these results combined with the broaden and split more clearly of (006)/(102) and (108)/(110) doublets indicate the formation of more ordered layered structure as more Li sites were occupied. Electrochemical performance was evaluated by galvanostatic mode at C/10 with cutoff voltage of 4.8V. Results show that the more Li in the structure, the lower polarizing voltage can be obtained, otherwise, the much lower first cycle coulombic efficiency accompanied. Rate capability (not shown) can be improved but with much faster capacity fade and voltage decay. Reference Chen, Y.; Chen, Z.; Xie, K., Effect of Annealing on the First Cycle Performance and Reversible Capabilities of Lithium-Rich Layered Oxide Cathodes. The Journal of Physical Chemistry C 2014.Watanabe, S.; Kinoshita, M.; Nakura, K., Capacity fade of LiNi(1−x−y)CoxAlyO2 cathode for lithium-ion batteries during accelerated calendar and cycle life test. I. Comparison analysis between LiNi(1−x−y)CoxAlyO2 and LiCoO2 cathodes in cylindrical lithium-ion cells during long term storage test. J. Power Sources 2014, 247 (0), 412-422. Figure 1

Quantum-chemical study of 7Li NMR shifts in the context of delithiation of paramagnetic lithium vanadium phosphate, Li3V2(PO4)3 (LVP)

The lithium NMR shifts of three paramagnetic materials important in the charging/discharging processes of lithium vanadium phosphate cathode materials have been studied by large-scale quantum-chemical methodology. Namely, the 7Li NMR shifts of the fully lithiated Li3V2(PO4)3 (LVP3.0), and of the partly delithiated Li2.5V2(PO4)3 (LVP2.5) and Li2V2(PO4)3 (LVP2.0), have been computed and analyzed using a recently proposed approach (A. Mondal, M. Kaupp J. Phys. Chem. C 123 (2019) 8387-8405) that accounts for the Fermi-contact, pseudo-contact, as well as orbital shifts, combining periodic computations with an incremental cluster model. LVP3.0 and LVP2.0 exhibit three and two unique Li sites, respectively, which could be assigned to their experimental 7Li NMR signals. In case of LVP2.0, the computations clearly assigned the signals at 143 ppm and 77 ppm to the Li(1) and Li(2) sites, respectively, even though the latter is connected to Vb(+III d2 sites and the former to Va(+IV) d1 sites. LVP2.5 is the most complex of these three materials, exhibiting a 50% occupation of Li(3) sites, which generates much more complicated Li NMR spectra with seven peaks that partly are closely spaced. Exploring three different occupation patterns, the computations can clearly assign five of the seven signals to one type of Li site and give most probable assignments for the two remaining signals. Notably, the calculations support seven signals to be assigned to LVP2.5, while previous interpretations took two of the signals as being entirely due to contamination by LVP2.0. The accuracy of the computations could probably be improved further by full DFT optimization of large super-cell structures. This work suggests that first-principles computations of NMR shifts of extended paramagnetic solids provide an important tool for the analysis of even rather complex NMR spectra.

Germanium as a donor dopant in garnet electrolytes

Cubic Li7La3Zr2O12 (LLZO) garnet electrolytes continue to be viewed as an enabler of all-solid-state lithium battery technologies, or as protective membranes for next-generation lithium battery systems. Supervalent dopants at the lithium sublattice are commonly used to stabilise the conductive cubic phase, through the creation of lithium vacancies. The use of germanium (Ge4+) as a higher valent dopant substituting for Li+ was studied here and shown to stabilise the cubic LLZO phase through substitution of x = 0.10 mol of Ge (at the tetrahedral 24d Li sites of the space group Ia-3d, based on the neutron powder diffraction result). This substitution preference follows that of Al3+ (having a similar ionic radius and reported to reside at 24d sites), but with a lower critical concentration for cubic phase stabilisation, in agreement with charge neutrality arguments to obtain the required Li content (ca. 6.4–6.6 per formula unit) for optimum conductivity. The x = 0.10 composition gave the highest bulk Li ion conductivity of 2.8 × 10−4 S cm−1 at 25 °C, on the order of reported values for Al-doped LLZO. Surface chemical analysis using time of flight secondary ion mass spectrometry showed Ge homogeneously distributed within the grains as well as some Li-, O- and Ge- enrichment along the grain boundaries. Cyclic voltammetry of the cells containing Ge-doped LLZO showed a redox stability up to +5 V.

Promoting the Cyclic Performance and Boosting Li+transport of LiV3O8 Via Ca Doping

As one of the most promising cathodes for rechargeable Lithium ion battery, LiV3O8 commonly suffers from inevitably complicated phase transitions and sluggish kinetics. Here, we develop a Ca doping technique totackle this long-standing issue of instability and improve the rate performance of LiV3O8. The dopants are found to reside in the Li site ofLiV3O8, where works as a pillar to increase the a axis distance facilitating Li diffusion, stabilizing the structure and suppressing the phase transition during cycling. This doped LiV3O8 displays an exceptionally high capacity of 280 mAh g-1, cyclability with 87% capacity retention over 100 cycles and significantly enhanced rate capability.

Investigation of Li Ion Dynamics in Garnet Oxide Li6.5La3Zr1.5Ta0.5O12 Using Molecular Dynamics Simulation

To overcome the safety issue of liquid electrolytes in conventional lithium-ion batteries, various solid-state inorganic electrolytes have been studied. Among them, lithium garnet oxides have been attracting research interests due to their high ionic conductivity, Li7-xLa3Zr2-xTaxO12 (LLZTO) with have a at room temperature with a maximum value around x = 0.51,2. There are two different structures of lithium garnet oxides, a cubic structure with space group Iad and a tetragonal phase with space group I41/acd. The cubic structure has two types of Li sites, i.e., tetrahedral (Td) 24d sites and octahedral (Oh) 48g sites. The tetragonal structure has four types of Li sites, i.e., Td-8a, Td-16e, Oh-16f, and Oh-32g sites. The fully empty 16e sites and fully occupied the other sites in tetragonal structure makes its conductivity about 2 orders lower than the cubic phase. However, the complexity of structure hindered the understanding of the mechanism of lithium ion conduction. In this paper, we performed molecular dynamics (MD) simulation on Li6.5La3ZrTaO12 based on classic MD simulation from both the interatomic potential and DFTB methods to study its structure and properties including lattice parameters, diffusion parameters, ionic conductivities, dielectric constants, and elastic moduli. The results are extracted through correlation function that was used for simple liquids3. The consistency of our results with the reported experimental ones helped us to understand the Li diffusion mechanism. References (1) Y. X. Wang and W. Lai "High Ionic Conductivity Lithium Garnet Oxides of Li7-xLa3Zr2-xTaxO12 Compositions," Electrochem. Solid State Lett. 2012, 15, A68-A71. http://dx.doi.org/10.1149/2.024205esl(2) Y. T. Li, J. T. Han, C. A. Wang, H. Xie, and J. B. Goodenough "Optimizing Li+ conductivity in a garnet framework," J. Mater. Chem. 2012, 22, 15357-15361. http://dx.doi.org/10.1039/c2jm31413d(3) In Theory of Simple Liquids (Fourth Edition); J.-P. Hansen and I. R. McDonald, Eds.; Academic Press: Oxford, 2013, p i.

Structural, thermodynamic, and local probe investigations of the honeycomb material Ag3LiMn2O6

Here we present the structural and magnetic properties of the new honeycomb material ${\mathrm{Ag}}_{3}{\mathrm{LiMn}}_{2}{\mathrm{O}}_{6}$. The system $\mathrm{Ag}[{\mathrm{Li}}_{1/3}{\mathrm{Mn}}_{2/3}]{\mathrm{O}}_{2}$ belongs to a quaternary $3R$-delafossite family and crystallizes in a monoclinic symmetry with space group $C\phantom{\rule{0.16em}{0ex}}2/m$, and the magnetic ${\mathrm{Mn}}^{4+}\phantom{\rule{0.28em}{0ex}}(S=3/2)$ ions form a honeycomb network in the $ab$ plane. An anomaly around 50 K and the presence of antiferromagnetic (AFM) coupling (Curie-Weiss temperature ${\ensuremath{\theta}}_{CW}\ensuremath{\sim}\ensuremath{-}51\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) were inferred from our magnetic susceptibility data. The magnetic specific heat clearly manifests the onset of magnetic ordering in the vicinity of 48 K, and the recovered magnetic entropy, above the ordering temperature, falls short of the expected value, implying the presence of short-range magnetic correlations. An asymmetric Bragg peak (characteristic of two-dimensional order), seen in neutron diffraction, gains intensity even above the ordering temperature, thus showing the existence of short-range spin correlations. Our electron spin resonance (ESR) experiments corroborate the bulk magnetic data. Additionally, the ESR line broadening upon approaching the ordering temperature ${T}_{\mathrm{N}}$ could be described in terms of a Berezinskii-Kosterlitz-Thouless scenario with ${T}_{\mathrm{KT}}=40(1)\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The $^{7}\mathrm{Li}$ NMR line shift probed as a function of temperature tracks the static susceptibility (${K}_{\mathrm{iso}}$) of magnetically coupled ${\mathrm{Mn}}^{4+}$ ions. The $^{7}\mathrm{Li}$ spin-lattice relaxation rate ($1/{T}_{1}$) exhibits a sharp decrease below about 50 K. A critical divergence is absent at the ordering temperature perhaps because of the filtering out of the antiferromagnetic fluctuations at the Li site, i.e., at the centers of the hexagons in the honeycomb network. Combining our bulk and local probe measurements, we establish the presence of an ordered ground state for the honeycomb system ${\mathrm{Ag}}_{3}{\mathrm{LiMn}}_{2}{\mathrm{O}}_{6}$. Our ab initio electronic structure calculations suggest that in the $ab$ plane, the nearest-neighbor (NN) exchange interaction is strong and AFM, while the next-NN and the third-NN exchange interactions are FM and AFM, respectively. The interplanar exchange interaction is found to be relatively small. In the absence of any frustration the system is expected to exhibit long-range, AFM order, in agreement with experiment.

Influence of brønsted-acid and cation-exchange sites on ethene adsorption in ZSM-5

Abstract Differential heats of adsorption were measured for ethane and ethene on a siliceous ZSM-5, H-[Al]ZSM-5, H-[Fe]ZSM-5, Li-[Al]ZSM-5, H(Zn)-[Al]ZSM-5, and H(Zn)-[Fe]ZSM-5 at 195 K in order to characterize the nature of interactions between the olefin functional group and both Bronsted sites and exchanged metal cations. On siliceous ZSM-5, the differential heats for ethane and ethene were both 31 ± 1 kJ/mol, independent of coverage. While the additional interaction of ethane with Li and Zn-cation sites was negligible and only about 2 kJ/mol with Bronsted sites, the additional heats of adsorption for ethene were negligible on Li sites, 8 kJ/mol on Bronsted sites, and 14 kJ/mol Zn sites. Results were similar for exchanged [Al]ZSM-5 and [Fe]ZSM-5. Density functional theory calculations with different dispersion-corrected generalized gradient approximation functionals correctly predict the increased interaction of ethene with acid sites but overestimate the strength of interaction of proton and Li with C C double bonds.

In Situ Electrochemical Zn2+-Doping for Mn-Rich Layered Oxides in Li-Ion Batteries

Mn-rich layered oxide materials have been considered as promising cathode materials for large scale Li-ion batteries because Mn is more inexpensive than Co and Ni. In this connection, a variety of doped-materials have been examined to improve the electrochemical performance of Mn-rich cathode materials. Doped-materials are conventionally synthesized using solid state synthesis at high temperatures, where most dopants are located at transition metal sites. The amount of redox-active transition metals decreases with increasing the amount of dopants in transition metals sites, resulting in the reduced reversible capacity of doped-materials. This paper demonstrates an in situ electrochemical doping of Zn2+ that is site-selective. Li+ at Li sites in Mn-rich layered oxides is selectively replaced by Zn2+ during cycling. Zn2+ ions in electrolytes are irreversibly inserted to Li sites in delithiated Mn-rich cathode materials during discharge, leading to the formation of Zn2+-doped Mn-rich layered oxides, [Li1–xZn...

Mg-doped Li1.133Ni0.2Co0.2Mn0.467O2 in Li site as high-performance cathode material for Li-ion batteries

Li- and Mn-rich layered oxides as cathode materials attract considerable attention owing to the superior capacity. However, their practical applications are still hindered by the inherent drawbacks such as the poor rate capability. Based on the structure characteristics that Li diffuses through two-dimensional lithium ion diffusion tunnel during intercalation/extraction, enlarging Li layer spacing is an effective strategy to increase Li+ diffusion coefficient and enhance rate capability. In this work, Mg-doping in Li site is employed to enhance the electrochemical performance of Li1.133Ni0.2Co0.2Mn0.467O2. With the ionic radius similar to that of Li+, Mg2+ is more suitable to occupy Li site and enlarge lattice parameter c which is critical to Li layer spacing and lithium ion diffusion coefficient. Consequently, Li1.123Mg0.010Ni0.2Co0.2Mn0.467O2 exhibits high initial capacity of 308 mAh g−1 at 25 mA g−1 and better rate capability as high as 166.1 mAh g−1 at 625 mA g−1 under 2.0–4.8 V vs. Li/Li+. Its ionic conductivity at 4.1 V during charge and 3.7 V during discharge is 4.1 ∗ 10−12 cm2·s−1 and 9.2 ∗ 10−13 cm2·s−1, 6.10 times and 6.07 times higher than that of pristine sample, indicating that magnesium doping facilitates the migration and diffusion of Li+ due to the enlargement of lithium ion diffusion channel.

Structure and performance of Na+ and Fe2+ co-doped Li1-xNaxMn0.8Fe0.2PO4/C nanocapsule synthesized by a simple solvothermal method for lithium ion batteries

Na+ and Fe2+ were co-doped at the Li and Mn site of LiMnPO4/C through a simple solvothermal method. Researches show that Li1-xNaxMn0.8Fe0.2PO4/C nanocapsule is generated through the self-assembly without surfactant. The simultaneous successfully doping of Na+ and Fe2+, which is proved by the EDS and XPS of Li0.97Na0.03Mn0.8Fe0.2PO4/C (LN-3), does not cause the rearrangement of cation. The particle sizes of nanocapsule decrease gradually with the doping of Na+. The pyrolytic carbon with excellent conductivity is coated on the surface of nanocapsule. The crystal of LN-3 nanocapsule with regular diffraction lattice is well developed. The doping of Na+ does not change the potential of electrochemical reaction. Cathode LN-3 delivers the maximum electrochemical performance. Its specific capacity at 0.05 C, 1 C and 5 C are improved to 141.7, 125.0 and 89.5 mAh·g−1, which is partially resulting from the enhanced diffusion coefficient of lithium ions. The capacity retention ratio in 200 cycles at 0.5 C is 96.65%. The ex-situ XRD patterns after 200 cycles are nearly unchanged and the structure is proved to be very stable. The doping of Na+ can also inhibit the dissolution of Mn2+ and Fe2+ in the electrolyte.

Defects, Lithium Mobility and Tetravalent Dopants in the Li3NbO4 Cathode Material

The defect processes of oxides such as self-diffusion impact their performance in electrochemical devices such as batteries and solid oxide fuel cells. The performance of lithium ion batteries can be improved by increasing the Li-ion diffusion. In that respect Li3NbO4 is identified as a positive electrode material for rechargeable lithium ion batteries. Here, we employ static atomistic scale simulations to examine the defect properties, doping behaviour and lithium ion migration paths in Li3NbO4. The present calculations show a correct reproduction of experimentally observed crystal structure of Li3NbO4. The Li-Nb anti-site defect is found to be the dominant intrinsic defect process suggesting that a small concentration of Li on Nb sites and Nb on Li sites is present. Vacancy assisted long range lithium diffusion paths were examined and our calculations reveal that the lowest activation energy (1.13 eV) migration path is two dimensional forming a zig-zag shape. Subvalent doping by Ge on the Nb site is thermodynamically favourable process and a potential strategy to incorporate extra Li in the form of Li interstitial in Li3NbO4. The results presented herein can motivate further experimental work for the development of Li3NbO4 based batteries.

Effect of ionic substitutions on the physicochemical, morphological, and electrochemical properties of lithium-rich vanadium phosphate and pyrophosphate compounds

The new Na/Cr-bisubstituted lithium vanadium monodiphosphate compound (LNVCPP) Li9-xNaxV2.8Cr0.2(P2O7)3(PO4)2, where x = 0.0, 0.5, 1.0, 1.5, and 2.0 have been prepared via simple sol–gel combustion route. The as-prepared materials are characterized by XRD, FESEM, and EDX. The XRD data indicate the presence of single phase of Li9-xNaxV2.8Cr0.2 (P2O7)3(PO4)2 (x = 0.0–2.0) with trigonal structure. Both cycle performance and rate capability have shown improvement with moderate Na-doping content. Cell of Li8.5Na0.5V2.8Cr0.2(P2O7)3(PO4)2 cathode delivers a specific discharge capacity of 53 mAhg−1 after 35 cycles in comparison with the other samples. The optimum ratio Li8.5Na0.5VCPP coated with carbon delivers a specific discharge capacity of about 75 mAhg−1 after 25 cycles. Therefore, it presents the good electrochemical rate and cyclic stability. The enhancement of the rate and cyclic capability may be attributed to the optimizing particle size, morphologies, and structural stability with the proper amount of Na-doping (x = 0.5) in Li sites.

High Rate Li-Ion Batteries with Cation-Disordered Cathodes

Summary Cation disordering in electrode materials for Li-ion batteries is deemed as an undesired structural feature for achieving high electrochemical activity owing to sluggish Li diffusion in the structure. Therefore, extensive efforts have been made to develop electrode materials having a well cation-ordered structure. We report a new class of cation-disordered material that can achieve reasonable Li diffusion by controlling the way of the cation distribution rather than the degree of cation disordering itself. The fully cation-disordered LiFeSO4F, activated by changes in the synthesis temperature and the Li/Fe ratio, delivers a substantially improved electrochemical performance. It exhibits a superior rate capability up to 100 C (36-s discharge) with ∼ 60 mAh/g and excellent capacity retention for 2,500 cycles at 5 C charge/20 C discharge rate. These results extend the scope of electrode materials to include cation-disordered materials and provide new opportunities for designing them for high-performance Li-ion batteries.

Effects of defect chemistry and kinetic behavior on electrochemical properties for hydrothermal synthesis of LiFePO4/C cathode materials

Abstract Lithium iron phosphate cathode materials for lithium ion batteries were synthesized successfully by hydrothermal synthesis method using LiOH·H2O and FeSO4·7H2O as resources of Li and Fe, respectively. The X-ray diffraction, the scanning electron microscopy, the surface areas, the Fourier transform infrared spectra and electrochemical properties of LiFePO4/C cathode materials prepared at different pH values were investigated. The solubility product principle is reasonable to illustrate the chemical composition of the final products in the hydrothermal process. A full Rietveld refinement of X-ray diffraction patterns and Fourier transform infrared spectra results of pure LiFePO4/C prepared at pH 8, 9, 10 supports that cation mixing is the intrinsic characteristic of LiFePO4/C synthesized by hydrothermal process. The lithium diffusion kinetics is affected by the interaction between the occupation of Fe on Li sites and the diffusion path length. In the applied pH range, there is an optimal pH value of 10 for the formation, morphology, and lithium diffusion kinetics, and hence the best electrochemical performances of LiFePO4/C. The mechanisms of nucleation and crystal growth, the defect chemistry and the kinetic behavior are widely discussed in the study, and are essential for optimizing the properties of LiFePO4.

Self-supporting lithiophilic N-doped carbon rod array for dendrite-free lithium metal anode

Carbon materials as host matrix of lithium (Li) anode attract more and more attention in order to inhibit uncontrollable dendritic growth of Li. Powdery carbon materials are usually synthesized and loaded on current collector by binder. The pore structure and active site of powdery materials will be easily destroyed during cycling. Herein, a self-supporting carbon film consisting of nitrogen (N)-doped carbon rod array (NCRA) with high N content and large surface area skeleton is developed as Li host matrix to regulate Li metal nucleation and suppress dendrites growth. The NCRA matrix exhibits low lithium loss mass and good long-term cycling stability during Li plating/stripping. The loss mass of Li in each cycle on NCRA is less than 0.01 mg cm−2 at 1.0 mA cm−2 and the value is much smaller than that (0.063 mg cm−2) on Cu foil. The Li|NCRA@Li symmetric cell has ultralong lifespan beyond 620 h and small voltage hysteresis of less than 40 mV at 2.0 mA cm−2. The good electrochemical performance is ascribed to the stable self-supporting array structure for the storage of Li and abundant lithiophilic active sites for uniform Li electrodeposition in NCRA host matrix. Therefore, the dendritic growth of Li is effectively inhibited. This study provides a promising self-supporting lithiophilic NCRA as host material of Li anode to promote practical application in next-generation lithium-metal based batteries.

Оптические аномалии в кристаллах LiNbO-=SUB=-3-=/SUB=- : Mg

We have established that increase in magnesium concentration in LiNbO3:Mg(0.19-5.91 mol% MgO) crystals leads to re-structuring in defective structure and optical anomalies connected with the re-structuring. The anomalies have threshold character. Optical uniformity of crystals was shown to increase at Mg concentration close to a threshold one ~3.0 mol% MgO. IR-absorption spectrum in the area of stretching vibrations of OH groups shifts to a high-frequency area (~50 cm-1 in comparison with other crystals), when Mg concentration nears the second threshold. At this sharp decrease in protons amount and jump-like shift of an absorption edge in the shortwave region are also observed. The shift was shown to be caused by the fact that at 5.5 mol% MgO all point defects NbLi are substitutes by Mg cations and with an increase in Mg concentration, Mg cations occupy Li and Nb sites forming point defects MgLi and MgNb.