Li2MnO3 Phase Research Articles

Fluorination of Li‐Rich Lithium‐Ion‐Battery Cathode Materials by Fluorine Gas: Chemistry, Characterization, and Electrochemical Performance in Half Cells

AbstractMild fluorination of high‐energy nickel‐cobalt‐manganese (HE‐NCM) materials with low pressures of elementary fluorine gas (F2) at room temperature was systematically studied. The fluorinated HE‐NCM samples were analysed by ion chromatography, inductively coupled plasma mass spectrometry, FT‐IR spectroscopy, powder X‐ray diffraction, magic angle spinning NMR spectroscopy, scanning electron microscopy, thermo‐gravimetric analysis, differential thermal analysis, electrochemical testing, and X‐ray photoelectron spectroscopy. The treatment of the cathode materials with low pressures (a few hundred mbar) of elementary fluorine gas at room temperature led to the elimination of the basic surface film (LiOH, Li2CO3, Li2O, etc.), and the resulting thin amorphous LiF film led to increased capacity and long‐term stability of the battery. Impedance built‐up was greatly reduced for these systems throughout cycling. Fluorination with F2 only causes the formation of O−Me−F bonds (Me=Transition Metal), when treated with F2 at higher pressures. If O−Me−F bonds are formed, it may be detrimental to the electrode surface film resistance and cycle stability of the electrodes. However, it may be that the LiF surface content, which can expand as long as the LiMeO2 structure can be oxidized and Li+ can be extracted, has become too large and thus detrimental. Considering the evolution of differential capacity plots and taking into account the thermodynamic driving force of the F2 treatment, it is likely that the same activation processes that occur electrochemically in Li‐rich materials also occur chemically, when the material is exposed to F2. Differential capacity plots show enhanced Mn4+ reduction peaks upon lithiation, when the material was exposed to F2, only possible after activation of the Li2MnO3 phase. For this reason, we believe fluorination promotes to some extent an activation of this phase.

Electrochemical impedance spectroscopy study of lithium-rich material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 in the first two charge-discharge cycles

Lithium-rich material 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 is successfully prepared by a co-precipitation method. Electrochemical impedance spectroscopy (EIS) is measured under various charge/discharge voltages in the first and second cycles. A reasonable equivalent circuit model is designed for EIS analysis and the fitting curves are aligned well with the experimental curves, suggesting that the proposed equivalent circuit model is an ideal model for lithium battery. According to the analysis on the shape changes of the semicircle in high-frequency and mid-frequency regions during the charging and discharging process, it can be considered that the lithium-rich material is a composite structure of Li2MnO3 phase and LiNi1/3Co1/3Mn1/3O2 phase after its preparation, but it becomes a solid solution structure after the first charging process. The changes of Rct also support above conclusions. According to the changes of the straight line in the low-frequency region and the changes of RSEI during the charging and discharging process, it can be confirmed that the solid electrolyte interphase (SEI) film on the surface of the cathode is gradually formed during the first charging process, and it has been very stable and has stable Li+ migration ability after two cycles. The calculation results of Li+ solid-phase diffusion coefficient also supports above conclusions.

Structural and Electrochemical Analyses on the Transformation of CaFe2O4-Type LiMn2O4 from Spinel-Type LiMn2O4.

Lithium manganese oxides have received much attention as positive electrode materials for lithium-ion batteries. In this study, a post-spinel material, CaFe2O4-type LiMn2O4 (CF-LMO), was synthesized at high pressures above 6 GPa, and its crystal structure and electrochemical properties were examined. CF-LMO exhibits a one-dimensional (1D) conduction pathway for Li ions, which is predicted to be superior to the three-dimensional conduction pathway for these ions. The stoichiometric LiMn2O4 spinel (SP-LMO) was decomposed into three phases of Li2MnO3, MnO2, and Mn2O3 at 600 °C and then started to transform into the CF-LMO structure above 800 °C. The rechargeable capacity (Qrecha) of the sample synthesized at 1000 °C was limited to ∼40 mA h·g–1 in the voltage range between 1.5 and 5.3 V because of the presence of a small amount of Li2MnO3 phase in the sample (=9.1 wt %). In addition, the Li-rich spinels, Li[LixMn2–x]O4 with x = 0.1, 0.2, and 0.333, were also employed for the synthesis of CF-LMO. The sample prepared from x = 0.2 exhibited a Qrecha value exceeding 120 mA h·g–1 with a stable cycling performance, despite the presence of large amounts of the phases Li2MnO3, MnO2, and Mn2O3. Details of the structural transformation from SP-LMO to CF-LMO and the effect of Mn ions on the 1D conduction pathway are discussed.

Adsorption of lithium in the manganese hydroxide precipitation processes

Lithium Manganese is an important ingredient in the process of making lithium battery cathode materials. The purpose of this study was to observe the presence of lithium ions in the manganese hydroxide deposition process in mixing MnSO4, LiCl, and NH4OH. The expected result is that the adsorbed lithium ion reacts with manganese hydroxide and settles when sintered at high temperatures. In this experiment, the addition of MnSO4 varied by 5, 10, 15, 20, 25 grams in 200 ml of LiCl solution with a concentration of 10 g / l and ammonia 25% by volume was added. The resulting solids were calcined at 800 °C for 24 hours. The results showed that the best adsorption of lithium ions on the addition of manganese sulfate was 15 g and 25 g. Characterization results obtained by solids have a 3.3% LiMn2O4 phase and 96.7% Li2Mn2O4 at the addition of 15 g manganese sulfate. On the addition of 25 g of manganese sulfate, 36.6% of LiMn2O4 and 63.4% of Li2Mn2O4 were obtained. The success of this study will make it easier for us to synthesize the manufacture of lithium battery cathode materials such as lithium manganese phosphate.

Correlating cycle performance improvement and structural alleviation in LiMn2-xMxO4 spinel cathode materials: A systematic study on the effects of metal-ion doping

LiMn2-xMxO4 (M = Co, Ni, Fe, Cr, Al; x = 0, 0.05, 0.15, 0.2) cathode materials for lithium-ion batteries have been synthesized by an improved solid-state method. Samples were characterized by XRD, SEM, and XPS for their structure, morphology and surface conditions. Their electrochemical performance was also tested. Compared with pristine LiMn2O4, all LiMn2-xMxO4 materials exhibited much better cycling stability between 3.0 V and 4.3 V. LiMn1.85Cr0.15O4 showed a superior cycling stability with a capacity retention of 96.6% after 100 cycles, which is 23% higher than that of the LiMn2O4 phase. The underlying mechanism of the improved cycle performance has been investigated by synchrotron-based X-ray diffraction under operating conditions for batteries. In situ XRD results proved that metal-ion-doped LiMn2O4 could hinder the phase transformation, reduce microstrain and volume shrinkage during cycling and improve their structural stability. The role of the doped metal ions was also confirmed by density functional theory calculations.

FORMATION OF SPINEL STRUCTURE IN SYNTHESIS PROCESS OF Li1.37Mn2O4 USING HYDROTHERMAL METHOD

FORMATION OF SPINEL STRUCTURE IN SYNTHESIS PROCESS OF Li1.37Mn2O4 USING HYDROTHERMAL METHOD. Li1.37Mn2O4 is one form of Li1+xMn2O4 which is engineered from LiMn2O4 phase which is commonly used as a lithium cathode active ingredient. The crucial thing from Li1.37Mn2O4 synthesis is the spinel structure that is formed. This study aims to observe when the spinel structure of Li1.37Mn2O4 starts and when the transformation from a tetragonal structure into spinel occurs. The raw materials used are tetragonal LiOH and tetragonal MnO2. The synthesis was carried out using a hydrothermal method with a temperature of 200 oC with a variation of holding times of 50, 70, 90 and 110 hours. Observation of spinel structure was carried out using XRD and TEM. The results obtained were at the holding times of 50 and 70 hours, the spinel structure had not been formed. The spinel structure begins to form at 90 hours holding time which also indicates that the transformation from the tetragonal structure to spinel occurs at such holding time. The result of a 90-hour holding time is a regular spinel structure but there are still many Mn and Mn-O –based impurities. While the results of the 110-hour holding time produce a perfect yet irregular transformation of the spinel structure.

Magnesium-doped Li[Li0.2Mn0.54Ni0.13Co0.13]O2 cathode with high rate capability and improved cyclic stability

Mg-doped Li[Li0.2Mn0.54 − x/3Ni0.13 − x/3Co0.13 − x/3Mgx]O2 (x = 0, 0.005, 0.007, 0.01, and 0.02) cathode materials have been synthesized by mixing Mn0.54Ni0.13Co0.13(CO3)0.8 precursor, Li2CO3, and MgO, followed by high-temperature solid-state method. X-ray diffraction (XRD) results show that Mg-doped samples have enlarged interlayer distance and orderly layered structure. Scanning electron microscope (SEM) results indicate that all the samples have similar morphologies. Electrochemical tests indicate that Mg doping facilitates the activation of Li2MnO3 phase and suppresses the transformation from layered to spinel-like phase. Mg-doped samples possess improved cyclic and rate performance. The Li[Li0.2Mn0.54 − x/3Ni0.13 − x/3Co0.13 − x/3Mgx]O2 (x = 0.01) sample delivers a capacity retention of 92.07% compared with 75.25% of the undoped one after 200 cycles at 250 mA g−1 and exhibits the discharge capacity of 198.56 mAh g−1 at 500 mA g−1. The reasons for the improved electrochemical performance are the enlarged interslab spacing and the enhanced structural stability.

A Novel Material Design for Li-Rich Cathode Material’s Long-Term Cycling and High Volumetric Energy Density

Fast development of portable electronic devices (such as a smart phone, iPad, and Galaxy Note) and electrified vehicles (such as EVs and HEVs) require better and smaller lithium ion batteries as their energy storages. What is needed for the cathode of the lithium ion battery is a material capable of higher energy density. However, not only the development of cathode material but also the commercialization of high energy density anode material has been limited due to the cathode material’s much lower energy density compared to anode material. In this regard, Li-rich material (Li2MnO3-LiMO2, M=Ni, Mn and Co) that has 150 % higher energy density than commercialized LiCoO­2 is the unique next generation cathode material to solve the problem. In the past decade, many researches have focused on the surface stabilization method of this material to improve its intrinsic problems of poor cycle/ rate capability and such surface treatment methods have been demonstrated in a few examples, including AlF3 coating and spinel heterostructures, yielding noticeable improvements in rate and cycle ability. Although such surface treatments showed improved rate and cycle performances, the realization of the Li-rich material’s high volumetric energy density and long-term cycle life which are more critical factors for the commercialization of Li-rich material still remained unsatisfied. For instance, AlF3 coated Li-rich LNCMO has abrupt capacity fade after 100 cycles, while it showed good rate and cycle capability within 100 cycles. Hence, new active material design, instead of simple surface modification methods such as coating or doping, is required to solve above previous limits. Here we demonstrate a novel approach for lithium storage, which is a material design of a secondary structure which consists of large primary particle with a novel activation method using simple chemical treatment, to achieve superior long-term cycle life with high volumetric energy density. In this design, the large primary particle effectively reduced its surface area producing markedly decreased surface instability reaction as well as high tap density. Interestingly, the chemical approach activates only surface Li2MnO3 phase of large primary particle and the very surface activation effectively overcome the activation problem, which is limit of large primary particle have. This novel concept is very meaningful in that it is the first and unique method to achieve cathode material’s high volumetric energy density with long-term cycle life. As a result, this novel designed material affords remarkable battery performance with high volumetric energy density of ~1980 Wh L-1 and extremely high cycle retention of 90% during 300 cycles.

Effects of Nanofiber Architecture and Antimony Doping on the Performance of Lithium-Rich Layered Oxides: Enhancing Lithium Diffusivity and Lattice Oxygen Stability

Li-rich layered oxides (LLOs) with high specific capacities are favorable cathode materials with high-energy density. Unfortunately, the drawbacks of LLOs such as oxygen release, low conductivity, and depressed kinetics for lithium ion transport during cycling can affect the safety and rate capability. Moreover, they suffer severe capacity and voltage fading, which are major challenges for the commercializing development. To cure these issues, herein, the synthesis of high-performance antimony-doped LLO nanofibers by an electrospinning process is put forward. On the basis of the combination of theoretical analyses and experimental approaches, it can be found that the one-dimensional porous micro-/nanomorphology is in favor of lithium-ion diffusion, and the antimony doping can expand the layered phase lattice and further improve the lithium ion diffusion coefficient. Moreover, the antimony doping can decrease the band gap and contribute extra electrons to O within the Li2MnO3 phase, thereby enhancing electronic conductivity and stabilizing lattice oxygen. Benefitting from the unique architecture, reformative electronic structure, and enhanced kinetics, the antimony-doped LLO nanofibers possess a high reversible capacity (272.8 mA h g-1) and initial coulombic efficiency (87.8%) at 0.1 C. Moreover, the antimony-doped LLO nanofibers show excellent cycling performance, rate capability, and suppressed voltage fading. The capacity retention can reach 86.9% after 200 cycles at 1 C, and even cycling at a high rate of 10 C, a capacity of 172.3 mA h g-1 can still be obtained. The favorable results can assist in developing the LLO material with outstanding electrochemical properties.

Thermal stability of 5 V LiCoMnO4 spinels with LiF additive

The thermal stability of LiCoMnO4 and LiCoMnO4 with 1 wt.-% LiF as an additive was compared upon heating in air. The stoichiometries of samples heat-treated at 700, 800, 900 and 1000 °C were analyzed by means of inductively coupled plasma optical emission spectroscopy for cation contents, inert gas fusion analysis for oxygen, and nuclear reaction analysis for fluorine contents, revealing that the sample chemistries remain constant except for oxygen. The oxygen content of the samples correlates with the Li2MnO3 secondary phase fraction, which forms upon heating, as is shown by X-ray powder diffraction. For each temperature, a greater amount of Li2MnO3 is formed in the samples with LiF addition than in the single LiCoMnO4 samples. In situ high-temperature X-ray powder diffraction between 650 and 950 °C demonstrates that LiCoMnO4 with LiF addition exhibits the same kind of decomposition reactions upon heating and cooling as the sample without LiF addition. However, for the samples with LiF addition, the formation of the decomposition product, Li2MnO3, is accelerated due to the excess Li through LiF addition, i.e. the stability of the spinel phase decreases due to the supply of lithium. Since lithium is consumed by Li2MnO3 formation and fluorine remains in the samples, we can also conclude that the fluorine anion is incorporated into the spinel or Li2MnO3 phase upon heating LiCoMnO4 and LiF together.

Enhanced Electrochemical Performance of Li1.2Mn0.54Ni0.13Co0.13O2 via L-Ascorbic Acid-Based Treatment as Cathode Material for Li-Ion Batteries

Low rate performance and poor cyclic performance are vital factors undermining the practical application of Li-rich layered oxides as the cathode material for advanced Li-ion batteries. Herein, we demonstrate a significant enhancement in rate capability and cyclic performance of Li1.2Mn0.54Ni0.13Co0.13O2 via an L-ascorbic acid-based treatment. The discharge capacity ratio at different current rates (0.5C/0.05C) increases from 70.4% to 79.9% after L-ascorbic acid-based modification. Furthermore, the remaning energy for the modified sample after the 100th cycle is 628.6 Wh Kg−1, which is 35.6% higher than the energy density of pristine sample (463.5 Wh Kg−1). The enhancement in electrochemical performance of the L-ascorbic acid treated Li1.2Mn0.54Ni0.13Co0.13O2 is attributed to the co-contribution of chemical activation of Li2MnO3 phase, exposure of high proportion of Li-conducting-favorable faces at the particle surface, increase in specific surface area and in-situ formation of minor spinel phase under the surface.

Structural and Electrochemical Properties of Spherical LiMgxMn2–xO4 (x ≤ 0.10) for Secondary Lithium Ion Batteries

A series of spherical LiMgxMn2–xO4 (x ≤ 0.10) cathode materials were successfully synthesized by a co-precipitation technique and solid state route. The morphologies and crystal structures of LiMgxMn2–xO4 were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. All LiMgxMn2–xO4 samples exhibited a single phase LiMn2O4 spinel structure with good crystallinity. Mg2+ ions could completely occupy the octahedral (16d) site to substitute Mn3+ and Mn4+ ions. The effect of Mg2+ ions on the electrochemical performance of LiMgxMn2–xO4 was investigated by galvanostatic charge–discharge test and electrochemical impedance spectroscopy (EIS). The results showed that the Mg-doped LiMn2O4 possessed better cycling stability. For the LiMg0.06Mn194O4, the initial discharge capacity was 115 mAh/g and remained 111 mAh/g after 50 cycles at a constant current density of 148 mA/g (1 C-rate) during the voltage range 3.0–4.3 V. The capacity retention could reach 96.5%, which was higher than that of the LiMn2O4.

Li-Rich Layered/Spinel Heterostructured Special Morphology Cathode Material with High Rate Capability for Li-Ion Batteries

Li-rich material 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 with a layered/spinel heterostructure is synthesized by a simple strategy. On the basis of structure and morphology analyses, it is revealed that the as-prepared Li-rich material possesses both porous micronano structure and integral layered-spinel heterostructure. Moreover, the obtained layered-spinel cathode material possesses prominent electrochemical characteristics, especially its rate capability. The initial discharge capacity of the as-prepared material is 269 mAh g–1 with a high Coulombic efficiency of 90.3%. The material delivers discharge capacities of 239 mAh g–1 at 0.5C, 195 mAh g–1 at 5C, and 175.8 mAh g–1 even at 10C. Also, the capacity retention of the cell is still as high as 80% at high current density (5C) after 200 cycles. The addition of spinel can inhibit the collapse of the material structure and voltage fading upon cycling. The 3D spinel Li4Mn5O12 phase in the Li-rich compound could provide a fast Li-ion diffusion pathway and a poro...

Ion transport and phase transformation in thin film intercalation electrodes

AbstractThin film battery electrodes of the olivine structure LiFePO4and the spinel phase LiMn2O4are deposited through ion-beam sputtering. The intercalation kinetics is studied by cyclo-voltammetry using variation of the cycling rate over 4 to 5 orders of magnitude. The well-defined layer geometry allows a detailed quantitative analysis. It is shown that LiFePO4clearly undergoes phase separation during intercalation, although the material is nano-confined and very high charging rates are applied. We present a modified Randles–Sevcik evaluation adapted to phase-separating systems. Both the charging current and the overpotential depend on the film thickness in a systematic way. The analysis yields evidence that the grain boundaries are important short circuit paths for fast transport. They increase the electrochemical active area with increasing layer thickness. Evidence is obtained that the grain boundaries in LiFePO4have the character of an ion-conductor of vanishing electronic conductivity.

Toward Positive Electrode Materials with High-Energy Density: Electrochemical and Structural Studies on LiCo x Mn2-x O4 with 0 ≤ x ≤ 1.

To obtain positive electrode materials with higher energy densities (Ws), we performed systematic structural and electrochemical analyses for LiCoxMn2–xO4 (LCMO) with 0 ≤ x ≤ 1. X-ray diffraction measurements and Raman spectroscopy clarified that the samples with x ≤ 0.5 are in the single-phase of a spinel structure with the Fd3̅m space group, whereas the samples with x ≥ 0.75 are in a mixture of the spinel-phase and Li2MnO3 phase with the C2/m space group. The x-dependence of the discharge capacity (Qdis) indicated a broad maximum at x = 0.5, although the average operating voltage (Eave) monotonically increased with x. Thus, the W value obtained by Qdis × Eave reached the maximum (=627 mW h·g–1) at x = 0.5, which is greater than that for Li[Ni1/2Mn3/2]O4. Furthermore, the change in the lattice volume (ΔV) during charge and discharge reactions approached 0%, that is, zero-strain, at x = 1. Because ΔV for x = 0.5 was smaller than that for Li[Ni1/2Mn3/2]O4, the x = 0.5 sample is found to be an alternative positive electrode material for Li[Ni1/2Mn3/2]O4 with a high W.

Influence of ammonium hydroxide solution on LiMn2O4 nanostructures prepared by modified chemical bath method

LiMn2O4 (LMO) powders were prepared by modified chemical bath deposition (CBD) method by varying ammonium hydroxide solution (AHS). The volume of the AHS was varied from 5 to 120mL in order to determine the optimum volume that is needed for preparation of LMO powders. The effect of AHS volume on the structure, morphology, and electrochemical properties of LMO powders was investigated. The X-ray diffraction (XRD) patterns of the LMO powders correspond to the cubic spinel LMO phase. It was found that the XRD peaks increased in intensity with increasing volume of the AHS up to 20mL. The estimated average grain sizes calculated using the XRD patterns were found to be in the order of 66 ± 1nm. It was observed that the estimated average grain sizes increased up to 20mL of AHS. The scanning electron microscopy (SEM) results revealed that the AHS volume does not influence the surface morphology of the prepared nano-powders. Elemental energy dispersive (EDS) analysis mapping conducted on the samples revealed homogeneous distribution of Mn and O for the sample synthesized with 120mL of AHS. The UV–Vis spectra showed a red shift with an increase in AHS up 20mL. The cyclic voltammetry and galvanostatic charge/discharge cycle testing confirmed that 20mL of AHS has superior lithium ion kinetics and electrochemical performance.

A New Class of Ternary Compound for Lithium Ion Battery

As for conventional cathode materials for lithium ion battery (LIB), such as LiMO2 (M=Ni, Co, Mn), LiFePO4, LiMn2O4, the ratio of Li to metal (Li/M) is 1 or less, which constrains their specific capacities to be in the range of 100-180 mAh/g. As an alternative, lithium rich material (LRM) possesses Li/M ratio of higher than 1, providing more than one reversible (de)intercalation Li+ ions per metal. LMR is able to deliver capacity of higher than 250 mAh/g, making it the most promising candidate for next generation high-energy LIBs. Li2MnO3, one of the most important family members of LRM, has attracted extensive interest in the research community. Li2MnO3 has been composited with layered compounds such as LiMO2 (M=Ni, Co, Mn), LiFeO2 and Li2RuO3 to form solid solutions of xLi2MnO3•(1-x)LiMO2 (M=Ni, Co, Mn),1 xLi2MnO3•(1-x)LiFeO2 2 and xLi2MnO3•(1-x)Li2RuO3.3 These LMR layered solid solutions deliver high capacity of more than 250 mAh/g due to the involvement of anionic redox electrochemistry during charge/discharge process besides of cationic redox electrochemistry. However, LRM layered oxides suffer from the structural transformation from layered-to-spinel phase, leading to severe voltage decay and capacity loss upon cycling. Cation substitution has been reported as an effective strategy to suppress the structural transformation for lithium rich layered oxides. For example, Sathiya et al. investigated the effect of Sn4+ doping on electrochemical properties of Li2RuO3 LRM and it is revealed Sn4+ could slow down or prevent trapping of metal ions in interstitial tetrahedral sites due to its larger ionic radius, resulting in enhanced cycling performance and less voltage decay.4 Based on the aforementioned work, we propose to partially substitute Mn4+ ions in Li2MnO3 structure by Sn4+ ions to synthesize Li2MnO3- Li2SnO3 solid solution, in which case the Sn4+ ions could block migration pathway of Mn4+ ions from transition metal layer to Li layer and therefore suppress the structural transformation upon cycling. Li2MnO3 shares a similar crystal structure as Li2SnO3 with the same oxide-ion lattice filled alternatively by Li layers and honeycomb LiM2 layers. Due to the minor distortion of the oxygen stacking, C2/c space group is usually chosen to describe Li2SnO3 and C2/m is regarded better to describe Li2MnO3 structure. The similarity in structure implies the possibility to form Li2MnO3-Li2SnO3 solid solution. However, since Sn4+ ion (0.69 Å) has a much larger radius than Mn4+ ion (0.54 Å), the substitution of Sn4+ ions for Mn4+ ions in Li2MnO3 lattice cause severe lattice distortion and thus brings extra lattice energy, leading to phase separation once the substitution exceeds a certain limit. Attempt of synthesizing a single 0.5Li2MnO3-0.5Li2SnO3 solid solution phase always failed by high-temperature solid-state reaction. Instead, a composite of Li2MnO3 and Li2SnO3 mixture phase was obtained because of phase separation. In order to buffer the lattice distortion resulted from large radius difference between Mn4+ and Sn4+ ions, we introduce a third element of Ru, whose ionic radius (0.62 Å) is in between Mn4+ and Sn4+ ions, to assist the formation of 0.5Li2MnO3-0.5Li2SnO3 solid solution. It is found that, for the first time, with the increment of Ru content incorporated in the Li2RuO3-Li2MnO3-Li2SnO3 ternary system, it gradually evolves from composite into single-phase solid solution. Electrochemical performance of this ternary oxide series have been systematically investigated in this work. This novel strategy opens a new avenue to extend the limit for forming solid solutions and significantly enriches electrode family members for lithium ion batteries. Figure 1

Phase structure and electrochemical performance control of 0.5Li2MnO3⋅0.5LiNi1/3Co1/3Mn1/3O2 based on the concentration adjustment in a molten salt synthesis system

The lithium-rich layered 0.5Li2MnO3⋅0.5LiNi1/3Co1/3Mn1/3O2 material was simply prepared by the molten-salt method. Effect of reactant concentration on phase and electrochemical performance was systemically studied by the X-ray diffraction, the galvanostatical charge/discharge and the dQ/dV profile, respectively. It can be confirmed that the obtained phase is sensitive to the reactant concentration. The spinel structure LiMn2O4 or Li4Mn5O12 phase easily occurs, when reactant concentration is low during the molten salt synthesis of Lithium-rich cathode material. The 0.5Li2MnO3–0.5LiNi1/3Co1/3Mn1/3O2 material with partial Li4Mn5O12 phase shows the higher specific capacity, and delivers a initial discharge capacity of 191 mAh g− 1 under a 20 mA g− 1 current rate, and then increases to the maximum value of 250 mAhg− 1. The discharge plateau of 2.5 V and the redox peaks at 2.55, 4.6 V give the electrochemical evidence of the existing Li4Mn5O12 phase, which also results in the higher specific capacity. Formation of partial Li4Mn5O12 phase reduces the initial discharge voltage, but mitigates the decay rate of voltage at the higher discharge current rate.

Highly stable Li1.2Mn0.54Co0.13Ni0.13O2 enabled by novel atomic layer deposited AlPO4 coating

Lithium-rich layered material is one of the most promising candidates of cathode materials for next-generation electric vehicles. However, one of the major issues that pertains to this material is the oxygen release during initial charge, which results in low initial coulombic efficiency (CE), intense electrolyte oxidation and thermal instability. In this study, we have conducted aluminum phosphate (AlPO4) coating via atomic layer deposition (ALD) approach to protect the surface of this cathode material powders. It was found that part of the C2/m Li2MnO3 phase turned into a spinel-like phase during the ALD process. The oxygen release has been effectively suppressed by such transformation, the initial CE increased from 75.2% for the bare electrode to 86.2% for the electrode with only 5 ALD cycles of AlPO4 coating. Furthermore, AlPO4 was also found to be more effective in improving the thermal stability of the cathode material comparing to bare or Al2O3 coated samples. Our study has provided a new possible solution towards cathode materials with high thermal resistance via conformal coating.

Spinel-layered integrate structured nanorods with both high capacity and superior high-rate capability as cathode material for lithium-ion batteries

Spinel phase LiMn2O4 was successfully embedded into monoclinic phase layeredstructured Li2MnO3 nanorods, and these spinel-layered integrate structured nanorods showed both high capacities and superior high-rate capabilities as cathode material for lithium-ion batteries (LIBs). Pristine Li2MnO3 nanorods were synthesized by a simple rheological phase method using α-MnO2 nanowires as precursors. The spinel-layered integrate structured nanorods were fabricated by a facile partial reduction reaction using stearic acid as the reductant. Both structural characterizations and electrochemical properties of the integrate structured nanorods verified that LiMn2O4 nanodomains were embedded inside the pristine Li2MnO3 nanorods. When used as cathode materials for LIBs, the spinel-layered integrate structured Li2MnO3 nanorods (SL-Li2MnO3) showed much better performances than the pristine layered-structured Li2MnO3 nanorods (L-Li2MnO3). When charge–discharged at 20 mA·g−1 in a voltage window of 2.0–4.8 V, the SL-Li2MnO3 showed discharge capacities of 272.3 and 228.4 mAh·g−1 in the first and the 60th cycles, respectively, with capacity retention of 83.8%. The SL-Li2MnO3 also showed superior high-rate performances. When cycled at rates of 1 C, 2 C, 5 C, and 10 C (1 C = 200 mA·g−1) for hundreds of cycles, the discharge capacities of the SL-Li2MnO3 reached 218.9, 200.5, 147.1, and 123.9 mAh·g−1, respectively. The superior performances of the SL-Li2MnO3 are ascribed to the spinel-layered integrated structures. With large capacities and superior high-rate performances, these spinel-layered integrate structured materials are good candidates for cathodes of next-generation high-power LIBs.