Solid Solution Cathode Material Research Articles

Intercalation in Li-ion batteries: thermodynamics and its relation to non-ideal solid-state diffusion

Intercalation is the key phenomenon taking place in lithium-ion batteries: while its thermodynamics sets the equilibrium voltage of active materials, solid-state diffusion of intercalated lithium determines the rate at which the battery can operate. This study revisits the thermodynamics of intercalation by treating the active material as a binary mixture of filled and empty sites, thus relating the equilibrium potential to the chemical potential difference of intercalated lithium. By setting a reference to unitary activity at half state-of-lithiation, the non-ideal behaviour of the active material is quantified via a revisited form of the thermodynamic enhancement factor, revealing that common solid-solution cathode materials as LiNi x Mn y Co1-x-y O2, LiNi0.8Co0.15Al0.05O2, and LiCoO2 show strong super-ideal behaviour. The latter is related to the thermodynamic enhancement of the diffusion coefficient of intercalated lithium. A comprehensive overview of the functional forms of Li diffusion flux according to linear irreversible thermodynamics is provided and related to the chemical diffusion coefficient obtained by conventional characterisation techniques. A literature analysis made on solid-solution cathode active materials reveals that while the chemical diffusion coefficient varies significantly with state-of-lithiation, there exists a convenient functional form of diffusion flux according to linear irreversible thermodynamics that enables a fairly stable diffusion coefficient with state-of-lithiation. This has clear benefits from both modelling and experimental viewpoints and potentially sheds light on the mechanistic fundamentals of solid-state diffusion.

The Effect of Separator and Anode on Electrochemical Characteristics and Crystal Structure of Lithium Ion Battery Cathode Material 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2

Commonly, studies of lithium ion battery (LIB) cathode materials are performed by using lithium metal anode and olefin-based microporous separator. On the other hand, carbon-based anodes and various separators are used in commercial lithium ion batteries. In this work, we studied characteristics of a solid solution cathode material 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2, using graphite as the anode and influence of separator type on structural change of the cathode material was studied.0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 was synthesized by co-precipitation method. The obtained material was characterized by XRD and ICP-AES. The XRD data showed that all major peaks of the synthesized material can be assigned to monoclinic C2/m. We combined three types of separators, polypropylene microporous membranes, OZ-S25 (ceramic coated PET nonwoven) and FPC3012 (nonwoven composed of PET and cellulose) with this anode and cathode.The charge-discharge cycle tests were performed in a bipolar cell using graphite as the anode. When the cathode material was combined with graphite anode, abnormally fast deterioration of cell capacity was observed. To avoid the deterioration, the graphite anode was preprocessed by charging and discharging using lithium metal as the counter electrode. The effect of the preprocess was sufficient only when the Li amount contained in the anode corresponds to at least 10% of the fully charged state. The preprocess could be achieved also by using LiMn1/3Ni1/3Co1/3O2 as the counter electrode. The reason of this improvement is unclear, but SEI formation on graphite anode surface, Li insertion into graphite, or drop in the anode potential might be the reason.Charging and discharging were performed for 5 cycles at 0.1C and 50 cycles at 1C in the voltage range of 2.0 to 4.7 V vs. preprocessed graphite using the various separators above. The figure shows charge and discharge curve for 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 and the preprocessed graphite cell (separator: OZ-S25). The preprocess of the graphite anode stabilized the cell capacity. After the 5th and 55th discharge, the cathode materials were taken out and the average structure was examined by Rietveld method using neutron diffraction measurements at BL20, J-PARC and synchrotron X-ray diffraction measurement at BL19B2, Spring-8. Furthermore, the valence of transition metals after cycle tests was evaluated on XAFS at BL14B2, SPring-8. As a result, with all separators, it was found that the Ni occupancy of the 4g sites, a transition metal layer, decreased, and that of 2c sites, a Li layer, increased. It was also found that the valence of the transition metal after 5 cycles did not differ between the separators. On the other hand, the bond valence sum at each site tended to decrease at the 4g sites and the 2c sites and increase at the 2b sites after 5 cycles. These were the same regardless of the type of the anode, metallic lithium or graphite. It was found that the average crystal structure of the solid solution cathode after 5 cycles was independent from the separator type and the anode type. The result after 55th discharge will be reported on the presentation. Figure 1

Relationship between rate performance and electronic/structural changes during oxygen redox of lithium-rich 4d/3d transition metal oxides

Li-rich solid solution cathode materials having 3d transition metals or 4d transition metals are the candidate of next generation cathode material. In order to clarify the rate performance of 3d or 4d transition metal oxides, we focused two typical Li-rich solid solution cathodes; Li1.2Ni0.13Co0.13Mn0.54O2 as a model of 3d transition metal oxide and Li1.2Ni0.13Co0.13Ru0.54O2 cathode as a model solid solution cathode containing 4d transition metal. We have applied operando hard and soft X-ray absorption spectroscopies clarify electronic and local distortion of both cathodes. From the results of XAS measurements, the reaction mechanism of Li1.2Ni0.13Co0.13Ru0.54O2 cathode was clearly explained by reversible transition metal redox reaction without the oxygen redox process. The EXAFS analysis suggests that Li1.2Ni0.13Co0.13Ru0.54O2 cathode also had the small distorted structure around Ru compared with around Mn of Li1.2Ni0.13Co0.13Mn0.54O2 cathode. The small distorted structure takes advantages for Li+ diffusion, resulting in the high rate performance of the Li1.2Ni0.13Co0.13Ru0.54O2 cathode.

Optimization of Calcination Temperature in Preparation of a High Capacity Li-Rich Solid-Solution Li[Li0.2Ni0.18Co0.03Mn0.58]O2 Material and Its Cathode Performance in Lithium Ion Battery

In recent years, Li-rich solid-solution layered oxide materials (LLOs) comprising layered LiMO2 (M: transition metals) and Li2MnO3 have attracted much interest as a cathode material for lithium ion battery (LIB) because some materials exhibit capacities as high as 250 mAh g-1 in the voltage range of 2.0 and 4.8 V. Because the Li2MnO3 structure can be reformulated with Li[Li1/3Mn2/3]O2, both of Li2MnO3 and LiMO2 can be considered to be of layered α-NaFeO2-type rock salt structure. The structural compatibility between Li2MnO3, which is electrochemically inactive and has a large theoretical capacity, and LiMO2, which is electrochemically active but offers lower capacity, allows for the structural integration of these components at an atomic level. As a result, the electrochemically inactive Li2MnO3 can participate in the charge/discharge process after activation with oxygen release from the lattice during the charging process and the capacity of LiMO2 can be improved because the Li2MnO3 component acts to stabilize the layered structure of LiMO2 when more than 50% of the Li+ ions are deintercalated. These materials are charged to above 4.5 V (vs. Li/Li+) to fully activate the Li2MnO3 component, and after activation, the cathodes are charged to 4.5 V to reach discharge capacities over 250 mAh g-1. In our previous paper[1], in order to find the optimal composition of the LLOs exhibiting higher cathode performance, which are composed of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2, the selected 75 samples having different composition were synthesized under identical preparation conditions except for the composition and the dependence of the performance of the cathode material on the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the LLO samples was examined in the viewpoint of discharge capacity, retention of discharge capacity, average discharge voltage, energy density and rate capability. In each viewpoint, using ternary phase diagrams of the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the LLO samples, the dependence of each performance on the percentages of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the LLO samples was evaluated. The results concluded that among the LLOs examined Li[Ni0.208Li0.183Co0.033Mn0.575]O2 (Li2MnO3 (55%) - LiNi1/2Mn1/2O2 (35%) - LiNi1/3Co1/3Mn1/3O2 (10%)) possesses the best composition as cathode material for LIBs. In this case, Li[Ni0.208Li0.183Co0.033Mn0.575]O2 was synthesized only under the calcination condition of 900 ℃ for 12 h in air. Changing the calcination temperature can be expected to lead to a structural change and consequently a change in cathode performance. Therefore, in order to clarify the relationship between calcination temperature and cathode performance, in other words, between the degree of crystallinity of LLOs and cathode performance, the LLO samples were synthesized at different calcination temperatures in the rage of 800-1100℃ and their structural and cathode performance analyses were carried out in detail in this study. [1] T. Tsuda, H. Kokubun, Y. Asaoka, K. Miyamoto, Y. Mochizuki, T. Gunji, T. Tanabe, S. Kaneko,T. Ohsaka, F. Matsumoto, Dependences of Discharge Capacity, Retention of Discharge Capacity, Average Discharge Voltage and Energy Density, and Rate Capability on the Composition of xLi2MnO3-yLiNi1/2Mn1/2O2-(1-x-y)LiNi1/3Co1/3Mn1/3O2 Li-rich Solid-Solution Cathode Materials for Li-Ion Battery, ECS Transactions, 75(20) (2017) 173–187.

Investigation of Various Factors for Capacity Fading of Li-Rich Solid Solution Cathode

Introduction Development of high capacity cathode materials with good cycleability is one of the most important tasks to improve the energy density of lithium ion batteries. Li-rich solid solution cathode materials have been focused as promising materials to solve this task. So far, we have focused on and investigated Li1.08Mn0.54Ni0.13Co0.13O2 (LMNC) as a composition to realize good cycleability in the solid solution cathode materials, and found that the control of depth of charge is effective to improve its cycleability. For example, the limited charging up to 280 mAh g-1 improves the discharge capacity retention of 393rd cycle against 4thcycle to 70% from 33% for fully-charging. In this study, various factors such as crystal structure, particle morphology and solid-electrolyte interphase in the initial several cycles were investigated to realize the better cycleability. Experimental LMNC was synthesized by sol-gel method. As starting materials, LiNO3, Mn(NO3)2・6H2O, Ni(NO3)2・6H2O, Co(NO3)2・7H2O and citric acid were dissolved into water (250 ml). The precursor sol was dried at 120 oC for 12 h and sintering at 800 oC for 10 h to obtain LMNC. To identify a crystal structure of the sample, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) were conducted. Composite electrodes were made by coating slurry that contained the prepared sample, acetylene black and PVDF in a weight ratio of 80 : 10 : 10 on Al foil as a current collector. NMP was used as a solvent. 2032 coin type cell was assembled with lithium metal as anode, 3-dimensionally ordered macroporous polyimide separator as separator and 1.0 mol dm-3 LiPF6 / EC : DMC = 1 : 2 in volume as electrolyte in argon atmosphere. Charge-discharge test was carried out at 30 oC and current density = 250 mA g-1. The constant current charge was carried out from 2.0 to 4.8 V, and then the constant voltage charge at 4.8 V was conducted until the current decreased to 0.01 C (CCCV mode). After charge and discharge of each cycle from 1st to 3rd cycles, the cathodes were analyzed by XRD and Raman spectroscopy. After 90thcycles, the cathodes were observed by Transmission Electron Microscope (TEM). Results and discussion Figure 1 shows TEM images of the LMNC before and after cycles. Figure 1 (a) image shows highly crystallized while (b) image shows a partly change of crystal. These images suggests that the crystallinity of LMNC particles decreases after cycles. In addition, an amorphous layer was observed on the surface of cycled particles. Figure 2 shows the Raman spectra of before and after cycles. This measurement was conducted under argon atmosphere by air tight cell. The peak of LMNC was observed at 600 cm-1, the peaks of 1400 and 1600 cm-1 attribute to carbon peaks. The peak of LMNC shifted to 625 - 630 cm-1 at charge state. However after discharging, it returned again to 600 cm-1. This peak shift corresponds to the crystal structure change from layer to spinel (LiMn2O4) (2). The XRD patterns of LMNC before and after cycles shown in Figure 3. The peaks for cathode after cycles are identified to R-3m. Peaks of spinel structure were not observed. From the result of Raman and XRD, structure changes occur only near the surface of LMNC at charge state. The super lattice peaks at around 20o was not observed after cycles. This means disordering of Li/Mn cations in the transition metal rich layer. AS a result of this disordering, Li ion can not easy to intercalate and de-intercalate. This causes the capacity decay at 1st to 3rdcycles. References (1) K. Sasaki et al, The Battery Symposium in Japan abstract book p204 (2015) (2) F. Amalraj et al, J. Electrochem. Soc.160, A324 – A337 (2013) Acknowledgement TEM observations were supported by Mr. Shinoda of National Institute for Materials Science (NIMS) Battery Research Platform. Figure 1

The Examination of the Composition of xLi2MnO3-yLiNi0.5Mn0.5O2-zLiNi1/3Co1/3Mn1/3O2 Solid-Solution Cathode Materials Exhibiting High Capacity, Discharge Voltage and Rate Performance

Lithium-ion batteries (LIBs) have become the state-of-the-art power source for portable appliances, such as notebook computers, cellular phones, and digital cameras, and a prime candidate for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and electric vehicles (EVs) because of their high energy density, high power density, superior cyclability and safety. The development of a higher capacity cathode material in particular is a matter of great urgency for the automobile industry because the currently attainable capacity of commercially available cathode materials for Li-ion batteries, such as LiCoO2 and LiMn2O4, is much lower than that of anode materials, which limits the expansion of LIB usage. A great deal attention has recently been focused on the Li-rich solid-solution layered cathode material Li2MnO3-LiMO2 (M = Co, Ni, etc.), which exhibits a discharge capacity of more than 200 mAhg-1 when operated above 4.6 V. The structural compatibility between Li2MnO3, which is electrochemically inactive and has a large theoretical capacity, and LiMO2, which is electrochemically active but has lower capacity, allows for the structural integration of these components at the atomic level. As a result, the electrochemically inactive Li2MnO3 can participate in the charge/discharge process after activation with oxygen release from the lattice during the charging process, while the capacity of LiMO2 can be improved by the stabilization of the layered LiMO2 structure by the Li2MnO3 component when more than 50% of the Li+ ions are deintercalated. In this study, the performance of the cathode material was investigated in detail by varying the charge/discharge voltage limits, cycle numbers, and current densities during pre-treatment [1] to reduce the duration of the pre-cycling process. In addition, search of composition of Li2MnO3-LiMO2 (M = Co, Ni, etc.) which exhibits high capacity and its duration and do not exhibit the decrease in the average discharge voltage with charge/discharge cycles was done. Specifically, the examined cathode material is considered to be solid-solution of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2. The relationship between the percentage of Li2MnO3, LiCo1/3Ni1/3Mn1/3O2 and LiNi0.5Mn0.5O2 in the solid-solution cathode material and the cathode performance mentioned above was examined with the half coin cells that were fabricated with the cathode and Li metal anode.

Investigation on Average and Local Crystal Structures and Electronic Structure Change of Li-Rich Solid Solution Cathode Material 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 during Charge-Discharge Process Using Neutron Beam and Synchrotron X-Ray Sources and First-Principles Calculations

Significant progress continues to be made with regard to on high capacity lithium ion batteries in order to meet the requirement for the electric power and electric vehicles. The solid solution cathode material of Li2MnO3 and LiMO2 (M = Mn, Ni, Co) have attracted attention over the last ten years because they deliver high discharge capacity [1]. On the other hand, it was reported as the one of the problems that discharge voltage of this material decreases by repeating charge and discharge process. But the mechanism of the voltage fade is not clear. To commercialize the solid solution materials, it is necessary to solve the problem. In this study, we focused on the above problem. Our previous report described a transition metal rearrangement that occurs between 4.6 and 3.3 V during the initial discharge process [2]. In this paper, the average and local crystal structures, and the electronic structure of pristine (0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2) and samples after 1st discharge and after 5th discharge were investigated using a combination of a pair distribution function (PDF) analysis and first-principles calculations. 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 was synthesized by coprecipitation method, and its average crystal structure was determined by Rietveld analysis using powder neutron diffraction measurements (BL20, J-PARC) and synchrotron X-ray diffraction measurements (BL02B2, SPring-8). In addition, we carried out first-principle calculation (VASP-code, WIEN2k-code) in order to discuss the electronic state theoretically. Also, we used Pair Distribution Function (PDF) analysis using neutron total scattering (BL21, J-PARC) and synchrotron X-ray total scattering (BL04B2, SPring-8) in order to discuss the detailed local structure. To discuss the structural changes associated with the repeating charge and discharge process, we carried out X-ray absorption spectroscopy in addition to VASP-code and PDF analysis using synchrotron X-ray total scattering. First, the average and local crystal structures, and the electronic structure of 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 were investigated using a combination of a pair distribution function (PDF) analysis and first-principles calculations. The results of a Rietveld analysis using neutron diffraction data showed that 0.4Li2MnO3- 0.6LiMn1/3Ni1/3Co1/3O2 belonged to space group C2/m. Based on the site occupancy results, Mn was localized at 4g sites, and Ni and Co were present at both 4g and 2b sites. Both the maximum entropy method using synchrotron X-ray diffraction data, and calculations using WIEN2k, showed that the covalencies between Mn at 2b sites and O at8j sites in the transition metal layer, and between 2c and 8j sites in the lithium layer, were relatively low. A PDF analysis using both synchrotron X-ray and neutron total scattering data produced good fits to the observed data, and identified local differences in the average structure, such as the precise locations of Li and O. Although some distortion existed, the refined structure contained Mn-O6, Ni-O6, and Co-O6 tetrahedra. The bond lengths corresponded to the ionic radii, so that the valence of Mn, Ni and Co in this material before charging was tetravalent, between divalent and trivalent, and trivalent, respectively. These results were consistent with the valence obtained from the density of states calculated by the WIEN2k code, thus confirming that the local structural model was appropriate. Second, the structural changes associated with the repeating charge and discharge using after 1st discharge and after 5th discharge were investigated. By the comparison of this material before charge, after 1st discharge and after 5th discharge using PDF analysis, it was indicated that Li deviated from the plane of Li layer associated with the repeating charge and discharge. While the bond distance of Mn-O and Co-O was longer, that of Ni-O was shorter. From the results, the both the valences of Mn and Ni approached to trivalent with the repeating charge and discharge,. These local structural changes related to the decrease of discharge voltage by repeating charge and discharge. Acknowledgement This work was supported in part by JSPS KAKENHI Grant Number 25420718. [1] M.M. Thackeray, et al., J. Mater. Chem. 15, 2257 (2005). [2] Y. Idemoto et al, Electrochimica Acta, , 153, 399(2015).

Synthesis and electrochemical properties of Li1.2Mn0.54Ni0.13Co0.13O2 cathode material for lithium-ion battery

The layered Li1.2Mn0.54Ni0.13Co0.13O2 lithium-rich manganese-based solid solution cathode material has been synthesized by a simple solid-state method. The as-prepared material has a typical layered structure with R-3m and C2/m space group. The synthesized Li1.2Mn0.54Ni0.13Co0.13O2 has an irregular shape with the size range from 200 to 500 nm, and the primary particle of Li1.2Mn0.54Ni0.13Co0.13O2 has regular sphere morphology with a diameter of 320 nm. Electrochemical performances also have been investigated. The results show that the cathode material Li1.2Mn0.54Ni0.13Co0.13O2 prepared at 900 °C for 12 h has a good electrochemical performance, which can deliver a high initial discharge capacity of 233.5, 214.2, 199.3, and 168.1 mAh g−1 at 0.1, 0.2, 0.5, and 1 C, respectively. After 50 cycles, the capacity retains 178.0, 166.3, 162.1, and 155.9 mAh g−1 at 0.1, 0.2, 0.5, and 1 C, respectively. The results indicate that the simple method has a great potential in synthesizing manganese-based cathode materials for Li-ion batteries.

Change of Average and Local Crystal Structure and Electronic Structure of Li-Rich Solid Solution Cathode Material 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 during Charge-Discharge Process Using First-Principles Calculations and Neutron Beam and Synchrotron X-Ray Sources

In recent years, lithium-ion battery has been expected in order to meet the requirement for the electric vehicles and electric power. The solid solutions of Li2MnO3 and LiMO2 (M = Mn, Ni, Co, etc.) have attracted attention over the last 10 years because they deliver high discharge capacity[1]. On the other hand, it was reported as the one of the problems that discharge voltage of this material decreases by repeating charge and discharge process. But the mechanism of the voltage fade is not clear. To commercialize the solid solution materials, it is necessary to solve the problem. In this study, we focused on the above problem. Our previous report described a transition metal rearrangement that occurs between 4.6 and 3.3 V during the initial discharge process[2]. We synthesized the 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 by coprecipitation method, and its average crystal structure was discussed by Rietveld analysis using powder neutron diffraction measurements(BL20, J-PARC) and synchrotron X-ray diffraction measurements(BL02B2, SPring-8). In addition, we carried out first-principle calculation (VASP-code, WIEN2k-code) in order to discuss the electronic state theoretically. Also, we used Pair Distribution Function (PDF) analysis using synchrotron X-ray total scattering(BL04B2, SPring-8) and neutron total scattering(BL21, J-PARC) in order to discuss the detailed local structure. To discuss the structural changes associated with the repeating charge and discharge process, we carried out X-ray absorption spectroscopy in addition to VASP-code and PDF analysis using synchrotron X-ray total scattering. First, the average and local crystal structures, and the electronic structure of 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 were investigated using a combination of a pair distribution function (PDF) analysis and first-principles calculations. The results of a Rietveld analysis using neutron diffraction data showed that 0.4Li2MnO3-0.6LiMn1/3Ni1/3Co1/3O2 belonged to space group C2/m. Based on the site occupancy results, Mn was localized at 4g sites, and Ni and Co were present at both 4g and 2b sites. Both the maximum entropy method using synchrotron X-ray diffraction data, and calculations using WIEN2k, showed that the covalencies between Mn at 2b sites and O at8j sites in the transition metal layer, and between 2c and 8j sites in the lithium layer, were relatively low. A PDF analysis using both synchrotron X-ray and neutron total scattering data produced good fits to the observed data, and identified local differences in the average structure, such as the precise locations of Li and O. Although some distortion existed, the refined structure contained Mn-O6, Ni-O6, and Co-O6 tetrahedra. The bond lengths corresponded to the ionic radii, so that the valence of Mn, Ni and Co in this material before charging was tetravalent, between divalent and trivalent, and trivalent, respectively. These results were consistent with the valence obtained from the density of states calculated by the WIEN2k code, thus confirming that the local structural model was appropriate. Second, the structural changes associated with the repeating charge and discharge using after first discharge and after fifth discharge were investigated. By the comparison of this material before charge, after first discharge and after fifth discharge using PDF analysis, it was indicated that Li deviated from the plane of Li layer associated with the repeating charge and discharge. While the bond distance of Mn-O and Co-O was longer, that of Ni-O was shorter. From the results, the both the valences of Mn and Ni approached to trivalent. These local structural changes related to the decrease of discharge voltage by repeating charge and discharge. Acknowledgement This work was supported in part by JSPS KAKENHI Grant Number 25420718. [1] M.M. Thackeray, et al., J. Mater. Chem. 15, 2257 (2005). [2] Y. Idemoto et al, Electroch imica Acta, , 153, 399(2015).

Understanding the electrochemical superiority of 0.6Li[Li1/3Mn2/3]O2-0.4Li[Ni1/3Co1/3Mn1/3]O2 nanofibers as cathode material for lithium ion batteries

Solid solution cathode materials 0.6Li[Li1/3Mn2/3]O2-0.4Li[Ni1/3Co1/3Mn1/3]O2 with different morphologies were synthesized by electrospinning and coprecipitation method respectively. The field-emission scanning electron microscope images verified the successful formation of nanofibers for electrospinning and nanoparticles for coprecipitation and the nanofibers showed larger specific surface area according to the Brurauer Emmerr Teller procedure. The X-ray powder diffraction patterns and the corresponding lattice parameter refinements showed that both samples can be indexed to hexagonal α-NaFeO2 layered structure with space group of R-3m. And the material prepared by electrostatic spinning method has a tight atomic arrangement in the layer yet the different dimensions do not influence the intercalation and deintercalation of lithium ion through the interlayer. The discharge capacity of nanofibers electrode is 302.3mAhg−1 at 0.05C and the initial columbic efficiency is 76.2%, which are higher than 282.7mAhg−1 and 68.2% of the nanoparticles electrode. The nanofibers electrode also presented better cycleability and rate capability, especially performed capacity of 126.6mAhg−1 at 5C, much higher than that of 109.4mAhg−1 for nanoparticles electrode. The step-by-step cyclic voltammetry revealed that the nanofibers electrode performs higher discharge voltage platform and enhanced discharge energy density. The excellent electrochemical performance of nanofibers electrode is ascribed to the better conductivity and superior lithium ion diffusion ability according to the electrochemical impedance spectrum measurement.

Synthesis and electrochemical characteristics of Li1.2(Ni0.2Mn0.6)x(Co0.4Mn0.4)y(Ni0.4Mn0.4)1−x−yO2 (0 ≤ x + y ≤ 1) cathode materials for lithium ion batteries

According to the tetrahedral phase diagram of LiNiO2–LiCoO2–LiMnO2–Li2MnO3, a series of Li1.2(Ni0.2Mn0.6)x(Co0.4Mn0.4)y(Ni0.4Mn0.4)1−x−yO2 (0 ≤ x + y ≤ 1) have been designed to explore new Li-rich solid solution cathode materials.

Structural Stability in the Initial Discharge Process of the Li-Rich Solid Solution Cathode Material Li7/6Mn3/6Ni1/6Co1/6O2 using Neutron and Synchrotron X-Ray Sources

INTRODUCTION Significant progress continues to be made with regard to research on high capacity lithium ion batteries. In particular, the solid-solution xLi(Li1/3Mn2/3)O2-(1-x)Li(Mn1/3Ni1/3Co1/3)O2 has become the focus of attention as an active cathode material since it exhibits a high discharge capacity of 200 m×A×h×g-1 or greater by charging above 4.5 V vs. Li/Li+[1]. but loss of oxygen and Li2O occurred in the higher voltage region, which caused irreversible capacity and degradation of cycle performance. On the other hand, this system, however, is still characterized by many unknowns, including its crystal structure change during charge-discharge process and the origin of the high discharge capacity. So as to resolve this problem, in this study, we performed the neutron and synchrotron X-ray diffraction measurement for Li-rich solid solution cathode material Li7/6Mn3/6Ni1/6Co1/6O2, and analyzed the average structural change in the initial discharge process. Additionally, we tried to clarified changes of the local and electronic structures during the initial discharge process using pdf (pair distribution function) method by neutron and synchrotron X-ray total scattering and X-ray absorption fine structure (XAFS). 2. EXPERIMENTAL We prepared Li7/6Mn3/6Ni1/6Co1/6O2 solid solution material by a copricipitation method. These samples were characterized by X-ray diffraction, ICP-AES. Their cathode properties were investigated by charge-discharge cycle tests. In order to clarify the average and electronic structures[2], we measured neutron (iMATERIA: J-PARC) and synchrotron X-ray diffraction (BL19B2, BL02B2: SPring-8), and then performed the Rietveld (RIETAN-FP, Z-code) and MEM (maximum entropy method) analyses (Dysnomia, Z-MEM). As for the local structure investigation, the PDF method was applied to the neutron(Nomad: SNS) and synchrotron X-ray (BL04B2: SPring-8) total scattering patterns. In addition, XAFS spectra were measured (BL14B2: SPring-8, BL7C: KEK-PF ). These analyses were carried out for the cathodes of Li7/6Mn3/6Ni1/6Co1/6O2 in the initial discharge process changing discharge depth as well as pristine samples. 3. RESULTS AND DISCUSSION Li7/6Mn3/6Ni1/6Co1/6O2 is assigned to space group C2/m, which is associated with an ordered arrangement within the transition metal layer. In order to study in detail the structural change in the initial discharge process changing discharge depth(2.0, 3.3, 3.5, 3.8, 4.8 V vs Li/Li+ at the peak of dQ/dV plot), the average structures was analyzed by Rietveld method using neutron and synchrotron X-ray difrraction. From the neutron diffraction results, a significant reduction of the a -axis and bond length of 2c(Li)-4h(Li) were only show by in the first discharge process and not show. In the second dischrage process. We also examined the local structural change by neutron and synchrotron X-ray total scattering and XAFS. The atomic distances estimated from pair distribution function G(r) were different from those of the average structure analysis. Since there are differences in local structure and the average structure, the PDF analysis were required to clarify the refined local structures. PDF analysis was performed (Fig.1), each sample fitted the observed value G obs(r) very well, and it was possible to express a peak, which cannot be expressed with the average structure G ave(r), with the local structure G local(r). From the PDF analysis, the peak shape around 0.6nm was changed and it is suggeted local structure changes during discharge process. Acknowledgement This work was supported by JSPS KAKENHI Grant Number 25420718 and Tokyo Ohka Foundation for the Promotion of Science and Technology. [1] M.M. Thackeray, et al., J. Mater. Chem. 15, 2257 (2005). [2] Y. Idemoto et al, Electrochemistry, 80(10), 791(2012).

Polaron states and migration in F-doped Li2MnO3

Abstract Li2MnO3 compound is one essential component of the Li-rich solid solution cathode material (mLi2MnO3⋅nLiMO2, M = Mn, Ni, Co, etc.) for lithium ion batteries. The intrinsic insulating nature of the electronic structure determines that the electronic conductivity of the Li2MnO3 compound is low, which is unfavorable to the fast charge/discharge performance of the battery. In this paper, we demonstrate that F doping can create polaron states in the Li2MnO3 lattice from first principles calculations. The small polaron migration energy barrier in the Li2MnO3 lattice is about 0.27 eV. It is also observed that the polaron state is strongly trapped by the F atom, which decreases the efficiency of the doping enhanced electronic conductivity.

Synthesis of layered cathode material 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 by an improved co-precipitation method for lithium-ion battery

The layered 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 lithium-rich manganese-based solid solution cathode material has been synthesized by two-step co-precipitation method. X-ray diffraction studies reveal that the as-prepared material has a typical layered structure with R-3m and C2/m space group. The surface morphology of the [Mn4/6Ni1/6Co1/6]CO3 precursor and cathode material 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 have been examined using scanning electron microscopy. Electrochemical performances, including discharge capacity, cycling performance and rate capability also have been investigated. The results show that the cathode material 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 prepared by two-step co-precipitation method has a good electrochemical performance, which can deliver a high initial discharge capacity of 276.70 mAh g−1 at the current density of 25 mA g−1. When cycling at 125 mA g−1, the material indicates an initial discharge capacity of 211.31 mAh g−1 and 196.64 mAh g−1 after 50 cycles, capacity retention is 93.06% and its coulombic efficiencies is greater than 98% at each charge/discharge cycling. Furthermore, the as-prepared material 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2 also shows an excellent rate capacity.

Elevated electrochemical performance of (NH4)3AlF6-coated 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 cathode material via a novel wet coating method

A novel wet method of (NH4)3AlF6 coating was explored to enhance the electrochemical performance of Mn-based solid-solution cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2. The X-ray powder diffraction patterns show that the coating material is pure-phase (NH4)3AlF6 and both pristine and coated samples can be indexed to hexagonal α-NaFeO2 layered structure with space group of R-3m. The field-emission scanning electron microscope images and the energy dispersive X-ray spectroscopy show that (NH4)3AlF6 is successfully coated on the surface of active particle. The (NH4)3AlF6 coated electrodes exhibit improved electrochemical performance, for instance, the initial charge-discharge efficiency was promoted by 5% (NH4)3AlF6 coating, the 1wt.% and 3wt.% coated electrodes deliver elevated cycling ability which is ascribed to the lower resistance between electrode and electrolyte as indicated by AC impedance measurement at different cycles. In addition, the coated-electrodes also give enhanced rate capability particularly for 1wt.% NAF-coated electrode performing surprising capacity of 143.4 mAh g−1 at 5C higher than that of 109.4 mAh g−1 for pristine electrode. Furthermore, the 1wt.% NAF-coated electrode also shows improved cycle and rate performance at 55°C.

Enhanced oxygen reducibility of 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 cathode material with mild acid treatment

Solid solution cathode material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 has been synthesized by a co-precipitation method and a mild acid was adopted to give rise to the H+/Li+ exchange reaction. The inductively coupled plasma-atomic emission spectrometry (ICP-AES) and atomic absorption spectroscopy (AAS) data show that the H+/Li+ exchange reaction actually occurs and the chemical composition is H0.06Li1.15Ni0.13Co0.14Mn0.55O2.03 after the material was treated. The X-ray powder diffraction patterns indicates that the structure doesn't change through the H+/Li+ exchange reaction and remains the hexagonal α-NaFeO2 layered structure with space group of R-3m. The field-emission scanning electron microscope (SEM) and transmission electron microscope (TEM) images show that there are traces of erosion on the surface of the H+/Li+ exchanged sample. The initial charge–discharge curve measured at 0.05C (12.5 mA g−1) demonstrates that the H+/Li+ exchanged electrode delivers a capacity of up to 314.0 mAh g−1 and coulombic increased initial efficiency. Cycle voltammetry (CV) measurement confirms this is attributed to the improvement of the reduction catalytic activity of oxygen released during the initial charging. The processed electrode also displays improved rate performance.

A Na4Fe(CN)6/NaCl solid solution cathode material with an enhanced electrochemical performance for sodium ion batteries

A Na4Fe(CN)6/NaCl solid solution was synthesized and investigated as a cathode material for sodium ion batteries. Pure Na4Fe(CN)6 and NaCl do not work as cathode materials for sodium ion batteries, while a sample of Na4Fe(CN)6/NaCl demonstrated a remarkably enhanced Na+ insertion/extraction capability and electrochemical performance, due to the cation vacancies and interconnected cages generated in the solid solution framework.

2413 Liイオン二次電池固溶体正極材料中のLi拡散に関する第一原理計算

2413 Liイオン二次電池固溶体正極材料中のLi拡散に関する第一原理計算

Local Structure of Li-rich Layered Cathode Material Li[Ni0.17Li0.2Co0.07Mn0.56]O2

The local structure of Li[Ni0.17Li0.2Co0.07Mn0.56]O2 was analyzed by high resolution scanning transmission electron microscopy (HR-STEM) and X-ray absorption spectroscopy (XAS). The HR-STEM images clearly showed a new type of stacking fault, as well as visual patterns of Li-ordering in the transition-metal (TM) layers. The XAS data showed that the valence states of the component TMs are Ni(II), Co(III) and Mn(IV), suggesting that some of the Li(I) in the TM layers of Li2MnO3 structure is replaced by Ni(II). Based on the results obtained, a detailed structural model for Li-rich solid-solution cathode materials was proposed.

Novel Lithium-Ion Cathode Materials Based on Layered Manganese Oxides

Lithium manganese oxides with a two-dimensional layered crystal structure are of high fundamental and technological interest as cathode materials for rechargeable lithium-ion batteries, due to the safety, low cost, and low toxicity of manganese-based materials. However, basic problems such as the collapse of the layer structure during cycling of the battery have proven difficult to solve. This collapse usually leads to poor rate performance and to evolution of steps in the voltage profile, both of which are undesirable for practical applications. This article highlights important recent work on stabilization of the layered crystal structure of lithium manganese oxide. In particular we focus on the use of layered manganese oxide as a base for developing novel complex solid–solution cathode materials with improved capacity, cycling stability, and safety.