Lithium-rich Oxide Research Articles

Layered lithium-rich oxide nanoparticles: low-temperature synthesis in mixed molten salt and excellent performance as cathode of lithium-ion battery

Layered lithium-rich oxide, 0.5Li2MnO3·0.5LiMn1/3Ni1/3Co1/3O2, is synthesized in a mixed molten salt of KCl and LiCl under 750 °C. Its morphology and structure are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption and desorption isotherm, and its performances as cathode of lithium-ion battery are investigated by charge–discharge test and electrochemical impedance spectroscopy, with a comparison of the samples synthesized via solid-state reaction. It is found that the resulting product consists of uniform nanoparticles, 50 nm in average, which possesses a well crystallite layered structure although its synthesis temperature is low and thus exhibits excellent cyclic stability and rate capability. The resulting product delivers an initial discharge capacity of 268 mAh g−1 at 0.1 C and has a capacity retention of 82% after 100 cycles at 1 C, compared to the 243 mAh g−1 and 73% for the sample synthesized by solid-state reaction under 900 °C.

Insight into the interaction between layered lithium-rich oxide and additive-containing electrolyte

Abstract Electrolyte additives have been found to be effective for the cyclic stability improvement of layered lithium-rich oxide (LRO), which is ascribed to the formation of cathode films derived from the preferential oxidation of the electrolyte additives. However, the detailed mechanism on the formation of the cathode film is unclear. This paper uncovers the interaction between LRO and additive-containing electrolyte through theoretical calculations, electrochemical measurements and physical characterizations. A representative LRO, Li1.2Mn0.54Ni0.13Co0.13O2, is synthesized, and an electrolyte, 1 M LiPF6 in EC/DMC (1/2, in volume) using triethyl phosphite (TEP) as additive, is considered. Charge/discharge tests demonstrate that LRO suffers severe capacity fading and TEP can significantly improve the cyclic stability of LRO. Characterizations from SEM and TEM demonstrate that a cathode film exists on the LRO after cycling in the TEP-containing electrolyte. The theoretical calculations suggest that TEP traps the active oxygen and is then oxidized on LRO preferentially compared to the electrolyte, forming the cathode film. The further characterizations from FTIR and GC, confirm that the preferential combination of TEP with active oxygen is beneficial for the suppression of oxygen evolution, and that the resulting cathode film can suppress the electrolyte decomposition and protect LRO from destruction.

Effect of Li3PO4 coating of layered lithium-rich oxide on electrochemical performance

Abstract A novel composite of layered lithium-rich oxide, Li-Rich@Li 3 PO 4 , coated with Li 3 PO 4 is synthesized through polydopamine template method. Physical characterizations reveal that Li-Rich@Li 3 PO 4 is composed of nanoparticles of 100–200 nm that are coated with a uniform Li 3 PO 4 layer of about 5 nm in thickness. Galvanostatic charge/discharge tests demonstrate enhanced cycling stability and largely increased rate capability of the material after Li 3 PO 4 coating.

Improved Cycling Stability and Fast Charge-Discharge Performance of Cobalt-Free Lithium-Rich Oxides by Magnesium-Doping.

Layered Li-rich, Co-free, and Mn-based cathode material, Li1.17Ni0.25-xMn0.58MgxO2 (0 ≤ x ≤ 0.05), was successfully synthesized by a coprecipitation method. All prepared samples have typical Li-rich layered structure, and Mg has been doped in the Li1.17Ni0.25Mn0.58O2 material successfully and homogeneously. The morphology and the grain size of all material are not changed by Mg doping. All materials have a estimated size of about 200 nm with a narrow particle size distribution. The electrochemical property results show that Li1.17Ni0.25-xMn0.58MgxO2 (x = 0.01 and 0.02) electrodes exhibit higher rate capability than that of the pristine one. Li1.17Ni0.25-xMn0.58MgxO2 (x = 0.02) indicates the largest reversible capacity of 148.3 mAh g-1 and best cycling stability (capacity retention of 95.1%) after 100 cycles at 2C charge-discharge rate. Li1.17Ni0.25-xMn0.58MgxO2 (x = 0.02) also shows the largest discharge capacity of 149.2 mAh g-1 discharged at 1C rate at elevated temperature (55 °C) after 50 cycles. The improved electrochemical performances may be attributed to the decreased polarization, reduced charge transfer resistance, enhanced the reversibility of Li+ ion insertion/extraction, and increased lithium ion diffusion coefficient. This promising result gives a new understanding for designing the structure and improving the electrochemical performance of Li-rich cathode materials for the next-generation lithium-ion battery with high rate cycling performance.

Lithium Extraction Mechanism in Li-Rich Li2MnO3 Involving Oxygen Hole Formation and Dimerization

Lithium-rich oxide electrodes with layered structures have attracted considerable interest because they can deliver high energy densities for lithium-ion batteries. However, there is significant debate regarding their redox chemistry. It is apparent that the mechanism of lithium extraction from lithium-rich Li2MnO3 is not fully understood, especially in relation to the observed O2 evolution and structural transformation. Here, delithiation and kinetic processes in Li2MnO3 are investigated using ab initio simulation techniques employing high level hybrid functionals as they reproduce accurately the electronic structure of oxygen hole states. We show that Li extraction is charge-compensated by oxidation of the oxide anion, so that the overall delithiation reaction involves lattice oxygen loss. Localized holes on oxygen (O–) are formed as the first step but are not stable leading to oxygen dimerization (with O–O ∼ 1.3 A) and eventually to the formation of molecular O2. Oxygen dimerization facilitates Mn migr...

Effect of Lithium Content on Spinel Phase Evolution in Lithium-Rich Layered Oxides LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (0.8 ≤ x ≤ 1.6) for Li-Ion Batteries

Lithium-rich oxides LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (x=1.6, 1.4, 1.2, 1.0, 0.8) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. The baseline composition x=1.4 had been previously determined as having the best electrochemical performance due to its small primary particle size and homogeneous distribution of nano-domains consisting of (C2/m) and (R3¯m) phases. In this study, the Rietveld refinement results indicate the presence of two phases at high lithium levels (x=1.6 and 1.4): Li2MnO3 (C2/m) and Li M O2 ( M = Ni, Co, Mn) (R3¯m); the latter contains Ni2+ and Ni3+. At low lithium levels (x=1.2, 1.0, and 0.8) an additional spinel phase Li M 2O4 (Fd3¯m) emerges, which is known to affect the electrochemical performance of the oxide. Structural analysis reveals that the spinel phase contains mixed transition metals Ni, Co, and Mn as [Li+,Co2+][Ni2+,Co3+,Mn4+]2O4. A low lithium level is found to induce primary particle growth, as well as Co and Ni segregation within the secondary particles. These results are expected to contribute to material optimization and commercialization of lithium-rich oxide cathodes.

Lithium-Rich Layered Cathode Materials Containing 3d and 4d Transition Metals for Lithium Ion Battery

Layered rock salt type structure such as LiCoO2 and Li(Mn,Co,Ni)O2 have been used as the cathode materials for lithium ion battery. However, the practical capacity is not enough to require the future demand for the large-scaled energy devices such as electric vehicles or electricity storage systems. The high capacity cathode materials should be developed for the next generation battery system. Layered lithium-rich oxides (xLi2MnO3-(1-x)Li(Mn,Co,Ni)O2) are one of promising candidates and the many researchers have studied them [1-4]. For the practical applications, the irreversible reaction in the initial charge-discharge, the capacity fade and the voltage decrease should be addressed. Recently, the lithium-rich compounds containing 4d transition metals were reported as the interesting cathode materials [5]. In this study, layered lithium-rich compounds containing 3d and 4d transition metals were synthesized and the reaction mechanism was investigated. These knowledges will be useful to develop the next-generation cathode materials. The cathode materials were synthesized by the polymerized complex method. Metal sources were dissolved into nitric acid and citric acid and ethylene glycol were added into this solution with stirring and heated at 200 °C. The obtained polymer was calcined at 400°C for 3 hours. The precursor was pressed into pellets (10 mm diameter) and heated at 850°C for 48 hours. The obtained powders were characterized by X-ray diffraction and scanning electron microscopy. For the charge-discharge measurements, the prepared powder, acetylene black and polyvinylidene difluoride binder were mixed at a weight ratio of 8:1:1 with 1-methyl-2-pyrrolidone solvent. The slurry was coated on the Al foil and dried in a vacuum oven at 80°C. The electrodes were roll-pressed and used as the working electrode. Li foil was used as the counter electrode material and 1 mol/L LiPF6 in a 3:7 volume ratio of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) was used as the electrolyte. The two-electrode cells were assembled in an argon-filled glove box. X-ray diffraction study showed the prepared samples exhibit the layered rock salt structure without distinct impurities. Scanning electron microscopy showed the particle size of the powder was sub-micrometer. The charge-discharge capacity of this material was about 200 mAh/g. The charge-discharge profile represented a gradual slope and low polarization compared with the case of xLi2MnO3-(1-x)Li(Mn,Co,Ni)O2. Moreover, the irreversible reaction at the high potential caused by oxygen evolution did not occur in the first cycle and showed good cycle performance. This result suggested that lithium-rich layered oxides containing 3d and 4d transition metals have one of promising cathode materials. We will discuss the reaction mechanism of this system in the presentation. [1] M.M. Thackeray, S.-H. Kang, C.S. Johnson, J.T. Vaughey, R. Benedek, S.A. Hackney, J. Mater. Chem., 17 (2007) 3112. [2] T.A. Arunkumar, Y. Wu, A. Manthiram, Chem. Mater., 19 (2007) 3067. [3] F. Mantia, F. Rosciano, N. Tran, P. Novák, J. Electrochem. Soc., 156 (2009) A823. [4] N. Yabuuchi, K. Yoshii, S. Myung, I. Nakai, S. Komaba, J. Am. Chem. Soc., 133 (2011) 4404. [5] M. Sathiya, G. Rousse, K. Ramesha, C. P. Laisa, H. Vezin, M. T. Sougrati, M. L. Doublet, D. Foix, D. Gonbeau, W. Walker, A. S. Prakash, M. Ben Hassine, L. DuPont, J. M. Tarascon, Nat. Mater., 12 (2013) 827.

Effect of lithium content on spinel phase evolution in the composite material LixNi0.25Co0.10Mn0.65O(3.4 + x) / 2 (0.8 ≤ x ≤ 1.6) for Li-ion batteries

The composite material LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (x=1.6, 1.4, 1.2, 1.0, 0.8) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. The Rietveld refinement results indicate the presence of two phases at high lithium levels (x=1.6 and 1.4): Li2MnO3 (C2/m) and LiMO2 (MNi, Co, Mn) (R3¯m); the latter contains Ni2+ and Ni3+. At low lithium levels (x=1.2, 1.0, and 0.8) an additional spinel phase LiM2O4 (Fd3¯m) emerges, which is known to affect the electrochemical performance of the oxide. Structural analysis reveals that the spinel phase contains mixed transition metals Ni, Co, and Mn as [Li+,Co2+][Ni2+,Co3+,Mn4+]2O4. A low lithium level is found to induce primary particle growth, as well as Co and Ni segregation within the secondary particles. These results are expected to contribute to material optimization and commercialization of lithium-rich oxide cathodes.

Tuning the Electronic Structure of the Metal–Oxygen Group by Silicon Substitution in Lithium-Rich Manganese-Based Oxides for Superior Performance

Si-doped layered manganese-based lithium-rich oxides were used as cathodes for lithium-ion batteries. The silicon-doped electrode exhibits exceptional specific capacity as well as rate capability compared to those of the pristine sample. In particular, the modified cathode shows noticeable enhancement in thermal stability, wherein the heat release is reduced and the position of the exothermic peak increases by 60 °C. First-principles calculations suggest that Si atoms occupy sites of transition metals in Si-doped Li-rich materials, which gives rise to an appreciable downshift of the O 2p band relative to that of the pristine sample.

Designing and Modifying of Lithium-Rich Layered Compound Based on Anion Redox

Lithium ion batteries have been increasingly urged with high energy density and long cycle life to meet the increasing requirements for portable electronics, use of renewable energy and electric vehicles. The availability of the appropriate cathode material is crucial for the development of lithium ion batteries with high energy density. Lithium rich manganese-based layered oxides (LRMO), proposed by Amine, are considered to be the next generation promising cathode material owing to their high capacity and low cost. However, capacity fading and voltage decay hinder its application in practice. To overcome these problems, tremendous efforts have been made to realize electrochemical performance improvement, including partial element doping and the coating of active materials. The high capacity of LRMO is contributed by multiple electron process consisted of metal and oxygen redox. Many previous work demonstrated that the active oxygen redox is caused by the overlap between O 2p band and transition metal (TM) 3d band. Though providing extra capacity, the oxygen redox also brings the unstability of layered structure when gives excess electrons out. In our works, we proposed a general strategy to tune the electronic structure of layered oxides to improve the cycle performance by introducing polyanions into the local structure. We incorporated boron atoms into LRMO structure and found that boron atoms show high covalence with oxygen than metal atoms. This undermined the covalence of TM-O bond and lowered the top level of oxygen 2p band, which decreased overlap area between TM 3d band and O 2p band. We at last demonstrated a better LRMO cathode with higher stability (capacity retention is 94% at 20 mA/g for 80 cycles). The oxygen redox is essential for the multiple electron process providing high capacity. However, anionic redox has also been proved in conventional layered oxides like LiCoO2 and LiNi1/3Co1/3Mn1/3O2, but they show terrible stability and deliver capacity less than 200 mA h/g though with high theoretical capacity of about 270 mA h/g. This provokes a question about why these two types of layered oxides show different stability though with similar layered structure. In order to figure it out, we took a series of in situ investigation to study the geometric and electronic structural evolution of Li2RuO3 during charging/discharging, a typical lithium rich layered oxide with both of cation and anion redox. We found that lithium rich oxides show higher stability than conventional layered structure due to the superlattice structure. The extra lithium atoms in the transition metal layer will make the structure flexible and facilitate the distortion caused by oxygen redox upon deep delithiation. This enhances the stability of layered structure during lithiation and delithiation. Anionic redox can be deemed as a double-edged sword since it can provide extra capacity in the price of structural stability. Only when the anions give proper amounts of electrons can ensure high capacity and acceptable stability. Therefore, controllable anionic redox is required to develop optimal cathodes. We presented a work by doping different amounts of boron atoms in Li2RuO3. We found that Li2RuBxO3 (B=0, 0.02, 0.05, 0.1) show distinctive charge/discharge behavior since boron atoms can tune the electronic structure of oxygen and change the redox path. The obtained materials show different reversibility due to the variant redox path. This work is of great importance for the instruction of modification of such lithium rich layered oxides. Furthermore, anionic redox is instructive for the designing of new kinds of lithium rich high capacity electrodes. As studied in our work, we aware that the recipe of high capacity electrodes is multiple electron process, flexible structure and enough lithium ions. In addition to oxygen, sulfur is probably accessible to the multiple electron process as well. Hence, we developed lithium rich layered sulfides with high capacity of 200 mA h/g, which has a lower voltage and higher stability and safety compared with LRMO, and mild voltage decay is presented. This work will open a new scope for the development of high capacity electrodes. In summary, anionic redox is mysterious and needs to be deeply investigated, and it provides us a new direction for the modifying and designing of cathode materials. From oxygen to sulfur to selenium to tellurium, anions give amounts of possibilities for the developing of high capacity electrodes.

Lithium Rich Layered Sulfides As a New-Type Cathode for Lithium Ion Batteries

Recent years more and more attention are paid on the exploration of lithium rich high capacity electrodes since the growing demand for high energy density lithium ion batteries for electric vehicles. In addition to the well-known lithium rich manganese based layered oxides, several lithium rich systems were proposed like ruthenium, molybdenum, and niobium based layered oxides[1-4]. Based on these work, we studied the recipe for the high capacity layered oxide cathodes and summarize it to be three aspects, namely sufficient lithium ions, multiple electron process, and flexible structure, of which the importance for the stabilization of the layered structure was demonstrated in our recent work[5]. The multiple electron process is usually realized by both the redox of metal and oxygen in these lithium rich oxides. However, though the oxygen ions can provide extra electrons accounting for the high capacity, excess oxidation of oxygen ions will result in destabilization of the structure and large irreversible capacity. Furthermore, the activation of the oxygen redox often happens at high voltage range, proposing quite high requirements for the electrolytes and leading to the unsafety concerns. Sulfur would be more superior choice than oxygen since polysulfide ions is more stable than peroxides or superoxides. On the other hand, sulfides have relatively lower voltage than oxides and provides access for the multiple electron process happening at a lower voltage range. The higher top of sulfur p state also will increase the electron mobility and thus the conductivity of the cathode. So the developing of lithium rich layered sulfides is a feasible route for the development of high capacity cathodes. In this work, we have developed a kind of lithium rich layered sulfides Li1.2Ti0.6Co0.2S2 for the first time based on the layered Li2MnO3-like structure Li2TiS3. Layered Li2TiS3 can’t deliver substantial capacity since the sole redox of sulfur will destabilize the structure. However, after we introduced active transition metal ions cobalt in the layered structure to substitute Ti atoms, the compound Li1.2Ti0.6Co0.2S2 can deliver capacity of more than 200 mA h/g at 20 mA/g. The first charge can only deliver 100 mAh/g which is contributed only by sulfur redox. On the later discharge, the capacity was increased to 200 mA h/g with a new redox of Ti4+/3+ is activated. The as-prepared new lithium rich layered sulfides can contribute more than 150 mA h/g for 100 cycles. The average voltage is only 2.4 V and will offer large safety than existing cathodes. This work will open a new area for the developing of lithium rich high capacity electrodes.

Understanding the Structural Evolution of Multiple Cationic Centres during Electrochemical Cycling of Lithium Rich Layered Li2Ru1-XFexO3

Lithium rich layered cathode materials have recently garnered a lot of attention as high capacity cathodes in Li-ion batteries, and their possible use for vehicular applications. However, they have been shown to be poor in terms of high power performance and long-term stability[1], these issues are mainly attributed to the structural changes occurring in the material during electrochemical cycling[2]. The understanding of these changes are still at an infant stage. In this work, we concentrate on the formation and study of the effect of partial substitution of ruthenium with iron in a Lithium rich ruthenium oxide (Li2RuO3). The purpose of substituting ruthenium with iron is to be able to understand the effect of multiple redox centers on the electrochemical performance of Lithium rich layered cathodes. Apart from having an active redox couple (Fe3+/Fe4+) in our interest region (3 - 4.6V vs. Li), iron is cost effective and environmentally benign. Li2Ru1-xFexO3 (0<x<1)was synthesised using a high temperature ceramic route [3]. Rietveld refinement of the X-ray diffraction pattern was carried out to confirm the formation of a pure phase. Initial electrochemical measurements conducted at 20 mA g-1 show a high reversible capacity of ≈240 mAh g-1 in an organic electrolyte using Li as the counter electrode. This was accomplished by the reversible removal/insertion of ≈1.4 moles of Lithium from the host structure. This is beyond the capacity that can be expected due to the ruthenium and iron redox couples alone (≈ 174 mAh g-1). Apart from the high capacity, it was observed that the material had a much-reduced voltage decay during cycling, when compared to other ruthenium based Lithium rich layered cathodes[1, 4-6]. In order to understand the structural changes, responsible for the extra capacity, in-operando X-ray diffraction measurements were made using a specially designed electrochemical cell [7]. The results obtained contribute to a unique insight into the charge storage mechanism of Lithium rich layered cathode materials and will help in the future development of new chemistries involving Lithium rich layered materials for energy storage applications Reference1. Sathiya, M., et al., Origin of voltage decay in high-capacity layered oxide electrodes. Nat Mater, 2015. 14(2): p. 230-238.2. Hong, J., et al., Review—Lithium-Excess Layered Cathodes for Lithium Rechargeable Batteries. Journal of The Electrochemical Society, 2015. 162(14): p. A2447-A2467.3. Kobayashi, H., et al., Structure and lithium deintercalation of Li 2− x RuO 3. Solid State Ionics, 1995. 82(1): p. 25-31.4. Sathiya, M., et al., Reversible anionic redox chemistry in high-capacity layered-oxide electrodes. Nat Mater, 2013. 12(9): p. 827-835.5. Sathiya, M., et al., High Performance Li2Ru1–y Mn y O3 (0.2≤ y≤ 0.8) Cathode Materials for Rechargeable Lithium-Ion Batteries: Their Understanding. Chemistry of Materials, 2013. 25(7): p. 1121-1131.6. Kalathil, A.K., et al., Influence of Ti4+ on the Electrochemical Performance of Li-Rich Layered Oxides - High Power and Long Cycle Life of Li2Ru1–xTixO3 Cathodes. ACS Applied Materials & Interfaces, 2015. 7(13): p. 7118-7128.7. Hartung, S., et al., Note: Electrochemical cell for in operando X-ray diffraction measurements on a conventional X-ray diffractometer. Review of Scientific Instruments, 2015. 86(8): p. 086102.

Electrochemical Calorimetry of Li1.2Ni0.15Mn0.55Co0.1O2

Introduction Li-rich oxides, Li(Li x Me1-x )O2 (Me = Co, Ni, Mn), are promising positive electrode active materials for lithium-ion cells because of their ability to deliver capacities over 250 mAhg-1.[1, 2] However, the mechanisms responsible for their unique voltage profiles, such as the activation voltage plateau in the 1st delithiation cycle and voltage hysteresis during cycling, are not fully understood. Electrochemical calorimetry is a powerful tool to observe reversible / irreversible reactions during charge and discharge of the electrode. In addition, the observed reversible heat flow can be described in terms of the change in configurational entropy of lithium ions (DS) in the structure, the heat of polarization, and side reactions. DS is also obtained using the temperature dependence of the open circuit voltage (dE/dT). Here, we compare the heat flow during charge and discharge, open circuit voltage (OCV), and dE/dT to evaluate reversible and irreversible reaction factors of the Li-rich oxides. Experimental All data reported here are obtained on the cathode material denoted as Li(Li0.2Ni0.15Mn0.55Co0.1)O2= (0.5Li2MnO3 - 0.5LiNi0.375Co0.25Mn0.375O2). Coin-type half cells containing c.a. 10 mg cathode material with counter lithium metal were prepared, and the heat flow during charge and discharge was observed using an isothermal microcalorimeter. We also measured OCV and dE/dT at every 2.5 % state of charge (SOC), and correlated the values to the obtained heat flow. In the case of OCV assumption, the relaxation time of OCV (t) was also determined. Results and Discussion As is well known, the lithium-rich oxide material shows the wide voltage plateau only during the 1st cycle.[3] We observed a large gap between the 1st cycle charge voltage and OCV (Figure 1(a)) and also large exothermic heat in the corresponding region (capacity > 100 mAhg-1) as shown in Figure 1(b). dE/dT values are negative (which means endothermic reaction during charge as shown in Figure 1(b); £). The estimated total heat flow (red dots), taking into consideration the heat of polarization from OCV (Figure 1(b); œ) is obviously lower than the observed heat flow (blue line). This observation suggests large irreversible exothermic heat flow for oxide capacities >100 mAhg-1. In addition, the relaxation time constant (Figure 1(c); °) also drastically increases in the corresponding region, which suggests that the irreversible reactions are slower than the reversible reactions. The heat flow during the 2nd charge cycle is distinctly different from that of the 1st cycle. However, the gap between observed heat flow (blue line in Figure 1 (e)) and the estimated one from dE/dT and heat of polarization (Figure 1 (e); œ) remained, which indicates the persistence of irreversible reactions. These irreversible heat flows may be associated with the energy required to induce structural changes within the oxide particles. In our presentation we will discuss the origins of the oxide voltage hysteresis using the heat flow, dE/dT, OCV, and the OCV relaxation times (t) obtained from the charge and discharge cycles. Figure 1

Insight into self-discharge of layered lithium-rich oxide cathode in carbonate-based electrolytes with and without additive

Self-discharge behavior of layered lithium-rich oxide as cathode of lithium ion battery in a carbonated-based electrolyte is understood, and a simple boron-containing compound, trimethyl borate (TMB), is used as an electrolyte additive to suppress this self-discharge. It is found that layered lithium-rich oxide charged under 4.8 V in additive-free electrolyte suffers severe self-discharge and TMB is an effective electrolyte additive for self-discharge suppression. Physical characterizations from XRD, SEM, TEM, XPS and ICP-MS demonstrate that the crystal structure of the layered lithium-rich oxide collapses due to the chemical interaction between the charged oxide and electrolyte. When TMB is applied, the structural integrity of the oxide is maintained due to the protective cathode film generated from the preferential oxidation of TMB.

Synthesis and performances of Li-Rich@AlF3@Graphene as cathode of lithium ion battery

A novel composite of layered lithium-rich oxide with AlF3 and graphene, Li-Rich@AlF3@Graphene, is synthesized as high performance cathode of lithium ion battery in terms of rate capability and cyclic stability. Physical characterizations from X-ray diffraction, scanning electron microscope and transmission electron microscope, demonstrate that the layered lithium-rich oxide in Li-Rich@AlF3@Graphene is composed of uniform nanoparticles of 100nm, which are coated with a layer of 2nm AlF3 and wrapped with graphene sheets. Charge/discharge tests indicate that the naked lithium-rich oxide exhibits poor cyclic stability and rate capability as cathode of lithium ion battery, which can be improved to some extent by the only contribution of AlF3 but significantly by the concurrent contribution of AlF3 and graphene.

Layered Lithium-Rich Oxide Nanoparticles Doped with Spinel Phase: Acidic Sucrose-Assistant Synthesis and Excellent Performance as Cathode of Lithium Ion Battery.

Nanolayered lithium-rich oxide doped with spinel phase is synthesized by acidic sucrose-assistant sol-gel combustion and evaluated as the cathode of a high-energy-density lithium ion battery. Physical characterizations indicate that the as-synthesized oxide (LR-SN) is composed of uniform and separated nanoparticles of about 200 nm, which are doped with about 7% spinel phase, compared to the large aggregated ones of the product (LR) synthesized under the same condition but without any assistance. Charge/discharge demonstrates that LR-SN exhibits excellent rate capability and cyclic stability: delivering an average discharge capacity of 246 mAh g(-1) at 0.2 C (1C = 250 mA g(-1)) and earning a capacity retention of 92% after 100 cycles at 4 C in the lithium anode-based half cell, compared to the 227 mA g(-1) and the 63% of LR, respectively. Even in the graphite anode-based full cell, LR-SN still delivers a capacity of as high as 253 mAh g(-1) at 0.1 C, corresponding to a specific energy density of 801 Wh kg(-1), which are the best among those that have been reported in the literature. The separated nanoparticles of the LR-SN provide large sites for charge transfer, while the spinel phase doped in the nanoparticles facilitates lithium ion diffusion and maintains the stability of the layered structure during cycling.

In Situ Formed Layered-Layered Metal Oxide as Bifunctional Catalyst for Li-Air Batteries

The electrochemical activity of a Li-air battery cathode catalyst derived from the lithium rich layered-layered metal oxide of the formula 0.5Li2MnO3.0.5LiMn0.5Ni0.35Co0.15O2 is reported. The catalyst formed in-situ by electrochemically de-lithiating this metal oxide embedded in a high surface area carbon matrix behaved as a bifunctional catalyst for O2 reduction reaction (ORR) and O2 evolution reaction (OER) in a non-aqueous Li-O2 cell. Cyclic voltammetry (CV) in both half and full cells revealed enhanced OER and ORR catalytic activity by: i-) displaying a more positive potential shift during ORR, ii-) stabilizing the initial ORR product LiO2, and iii-) showing an additional potential step in the oxidation of the ORR products. In the CV of catalyzed cells, a reduction peak appeared before the main peroxide (O22−) formation peak suggesting that the catalyst stabilizes the superoxide (O2−) formed prior to the formation of peroxide. Evidence for LiO2 as the initial discharge product was obtained from both the Raman spectrum and X-ray diffraction (XRD) pattern of Li-air cell cathodes after galvanostatic discharge to 2 V. Surface features for the discharged cathodes obtained from Field Emission Scanning Electron Microscope (FESEM) unveiled dissimilar morphologies for the discharge products from catalyzed and uncatalyzed cells, originating from different nucleation mechanisms. The catalyzed cells exhibited longer cycle life than uncatalyzed cells under similar cycling conditions.

Improving High Voltage Interfacial and Structural Stability of Layered Lithium-Rich Oxide Cathode by Using a Boracic Electrolyte Additive

In this work, a boracic electrolyte additive trimethyl borate (TMB) was investigated to improve the interfacial and structural stability of layered lithium-rich oxide (LLO) at high operating potential. The LLO in electrolyte with 2% TMB additive shows high capacity retention of 84.5% after 300 cycles at 0.5 C and good rate capability of 120 mAh g−1 at 4 C rate, comparing to 17.9% after 250 cycles and 65 mAh g−1 at 4 C rate of baseline electrolyte. The results from DFT calculation, dQ/dV, EIS, chronoamperometry and physical characterizations indicate that TMB has higher oxidation activity than baseline electrolyte. The preferential oxidation of TMB generates an effective protective film on the LLO surface, which greatly restrains the continuous oxidation of baseline electrolyte and enhances the structural stability of electrode, leading to excellent cyclic and rate performances of LLO at high operating potential.

The roles of nickel/manganese in electrochemical cycling of lithium-rich Mn-based nickel cathode materials

Lithium-rich oxides have attracted much attention due to their potential application as cathode materials in lithium ion batteries, but still suffer from voltage decay and capacity fading upon cycling. Understanding the effect of active-mass elements on the deterioration of cycling performance would be beneficial for finding a suitable route to address these challenging problems. Herein, a Li-rich Mn-based nickel oxide Li1.231Mn0.592Ni0.2O2 was synthesized. We have mainly employed dQ/dV plots to elucidate the electrochemical process changes during cycling. Our results demonstrate that the influence of Ni is more sensitive than that of Mn, and the Ni redox peak is gradually disappeared upon cycling, but the electrode reaction of Mn is relatively stable with the shape of the corresponding dQ/dV plots are unchanged, though a small shift to low potential occurs. Moreover, the capacity contribution of Ni is decreased with the extent of cycling, but the capacity contribution of Mn is increased.

Understanding the roles of anionic redox and oxygen release during electrochemical cycling of lithium-rich layered Li4FeSbO6.

Li-rich oxides continue to be of immense interest as potential next generation Li-ion battery positive electrodes, and yet the role of oxygen during cycling is still poorly understood. Here, the complex electrochemical behavior of Li4FeSbO6 materials is studied thoroughly with a variety of methods. Herein, we show that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides. Moreover, we directly demonstrate the limited reversibility of the oxygenated species (O2(n-); n = 1, 2, 3) for the first time. We also find that during charge to 4.2 V iron is oxidized from +3 to an unusual +4 state with the concomitant formation of oxygenated species. Upon further charge to 5.0 V, an oxygen release process associated with the reduction of iron +4 to +3 is present, indicative of the reductive coupling mechanism between oxygen and metals previously reported. Thus, in full state of charge, lithium removal is fully compensated by oxygen only, as the iron and antimony are both very close to their pristine states. Besides, this charging step results in complex phase transformations that are ultimately destructive to the crystallinity of the material. Such findings again demonstrate the vital importance of fully understanding the behavior of oxygen in such systems. The consequences of these new aspects of the electrochemical behavior of lithium-rich oxides are discussed in detail.