Function Of Lithium Content Research Articles

On the Description of Electrode Materials Based on the Quantification of Ionic and Electronic Work Functions

During decharging of a lithium ion battery (LIB) electrons are transferred from the cathode material to the outer circuit and lithium ions are transferred into the electrolyte. Here, the energy required to take electrons and lithium ions out of two prototypical cathode materials, LixFePO4 and LixMn2O4 is investigated as a function of the state of lithiation, x [1]. Ionic work functions are measured by thermionic emission, electronic work functions are measured either by thermionic emission or by photoelectron spectroscopy. The work functions measured vary significantly with x for LixFePO4 with moderate, low-dimensional ionic and electronic conductivities but rather little for cubic LixMn2O4 with ca. three orders of magnitude higher ionic and electronic conductivities [2]. The experimental data are supported and rationalized by static energy-landscape calculations and molecular dynamics simulations of the Lithium migration as a function of Lithium content and electric field strength [1]. This study provides new insight into the role of ionic contributions to the energy balance in LIBs. Current efforts are aimed at a complete energetic description of LIBs as previously discussed for LiCoO2 [3].[1] J. Schepp, J. Schuch, J.P. Hofmann, S. Adams, K.-M. Weitzel, to be published[2] M. Park, X. Zhang, M. Chung, G.B. Less, A.M. Sastry, A review of conduction phenomena in Li-ion batteries, Journal of Power Sources 195 (2010) 7904–7929.[3] S. Schuld, R. Hausbrand, M. Fingerle, W. Jaegermann, K.-M. Weitzel, Experimental Studies on Work Functions of Li+ Ions and Electrons in the Battery Electrode Material LiCoO2 A Thermodynamic Cycle Combining Ionic and Electronic Structure, Adv. Energy Mater. 8 (2018) 1703411.

Thermal conductivity of intercalation, conversion, and alloying lithium-ion battery electrode materials as function of their state of charge

Upon insertion and extraction of lithium, materials important for electrochemical energy storage can undergo changes in thermal conductivity (Λ) and elastic modulus (M). These changes are attributed to evolution of the intrinsic thermal carrier lifetime and interatomic bonding strength associated with structural transitions of electrode materials with varying degrees of reversibility. Using in situ time-domain thermoreflectance (TDTR) and picosecond acoustics, we systemically study Λ and M of conversion, intercalation and alloying electrode materials during cycling. The intercalation V2O5 and TiO2 exhibit non-monotonic reversible Λ and M switching up to a factor of 1.8 (Λ) and 1.5 (M) as a function of lithium content. The conversion Fe2O3 and NiO undergo irreversible decays in Λ and M upon the first lithiation. The alloying Sb shows the largest and partially reversible order of the magnitude switching in Λ between the delithiated (18 W m−1 K−1) and lithiated states (<1Wm−1K−1). The irreversible Λ is attributed to structural degradation and pulverization resulting from substantial volume changes during cycling. These findings provide new understandings of the thermal and mechanical property evolution of electrode materials during cycling of importance for battery design, and also point to pathways for forming materials with thermally switchable properties.

Structural and Electrochemical Investigation of High Energy Spinel LiMn1.5Ni0.5O4 Produced at Low Temperature

Spinel LiMn1.5Ni0.5O4 (LMNO) materials, without the environmentally toxic Co, are one of the most promising potential cathode materials for lithium ion batteries operated at high voltages. According to the distribution of Mn and Ni within the cubic crystal structure, spinel LMNO can be categorized into either ordered or disordered. Normally, disordered LMNO materials are produced at temperatures which are higher than the theoretical oxygen release temperature of spinel LMNO (715 ℃)[1, 2]. This leads to some Mn4+ atoms being reduced to Mn3+ to maintain the electroneutrality of spinel LMNO. The existence of Mn3+ causes Jahn-Teller distortion and affects the structural stability of spinel LMNO. In order to reduce the amount of Mn3+, high temperature produced LMNO materials are post-annealed at lower temperature, i.e. 700 ℃, to introduce O into spinel LMNO again[3]. Both the high calcination temperatures and the long annealing times increase the preparation cost of the spinel LMNO. In other words, low-temperature calcination without post-annealing would be a preferred way to produce spinel LMNO at lower cost. However, LMNO materials calcinated at 700 ℃ in air show ordered distribution of Mn and Ni, which is supposed to be the reason for poor cycling and rate performance[4, 5]. This indicates changing the ordered distribution of Mn and Ni in 700 ℃ produced LMNO may improve the electrochemical performance.In the present work, different co-precipitation processes are attempted to change the distribution of the Mn and Ni precursors used in the LMNO synthesis. Three different spinel LMNO materials, named as N-, CS- and SW-LMNO, are produced by three hydroxide precursors with stoichiometric Li2CO3 at 700 ℃ without post-annealing. Scanning electron microscope (SEM) images, shown in Figure 1(a) – (c), demonstrate different morphologies of N-, CS- and SW-LMNO. This indicates that different precipitation approaches result in different particle sizes and shapes of spinel LMNO. However, the use of different precipitation processes has little effect on the bulk crystal structure of spinel LMNO, reflected by similar X-ray diffraction (XRD) patterns in Figure 1(d). As shown in Figure 1(e), SW-LMNO shows high initial discharge capacity (140 mAhꞏg-1) at room temperature which is the highest amongst all reported LMNO[6]. SW-LMNO also shows good cycling performance in the first 100 cycles at 1 C (1 C = 150 mAꞏg-1), which are not only better than those of other low-temperature produced spinel LMNO but also comparable with those of most reported high-temperature produced spinel LMNO[7]. This means, this work provides a new strategy to produce high-energy spinel LMNO by controlling the microstructure but save energy consumption. Moreover, transmission electron microscope (TEM), X-ray pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) are performed to explain the reason for improvement of SW-LMNO in comparison with N- and CS-LMNO.Reference[1] A. Manthiram et al. A perspective on the high-voltage LiMn1.5Ni0.5O4 spinel cathode for lithium-ion batteries. Energy & Environmental Science[J]. 2014, 7 (4): 1339-1350[2] M. Kunduraci et al. Effect of oxygen non-stoichiometry and temperature on cation ordering in LiMn2-xNixO4 (0.50≥ x≥ 0.36) spinels. Journal of Power Sources[J]. 2007, 165 (1): 359-367[3] D. W. Shin et al. Role of cation ordering and surface segregation in high-voltage spinel LiMn1.5Ni0.5-xMxO4 (M= Cr, Fe, and Ga) cathodes for lithium-ion batteries. Chemistry of Materials[J]. 2012, 24 (19): 3720-3731[4] Z. Moorhead-Rosenberg et al. Electronic and electrochemical properties of Li1-xMn1.5Ni0.5O4 spinel cathodes as a function of lithium content and cation ordering. Chemistry of Materials[J]. 2015, 27 (20): 6934-6945[5] B. Aktekin et al. Cation ordering and oxygen release in LiNi0. 5-xMn1.5+xO4-y (LNMO): In situ neutron diffraction and performance in Li ion full cells. ACS Applied Energy Materials[J]. 2019, 2 (5): 3323-3335[6] O. Tiurin et al. Atomic layer deposition (ALD) of lithium fluoride (LiF) protective film on Li-ion battery LiMn1.5Ni0.5O4 cathode powder material. [J]. 2020, 448: 227373[7] G. Liang et al. Developing high-voltage spinel LiNi0.5Mn1.5O4 cathodes for high-energy-density lithium-ion batteries: current achievements and future prospects. Journal of Materials Chemistry A[J]. 2020, 8, 15373-15398 Figure 1

(Invited) Thermal, Structural, and Electrochemical Characteristics of Ni-Rich NMCs

To improve energy densities of lithium-ion batteries meant for vehicle applications, the battery community is increasingly turning to Ni-rich NMC cathode materials. These materials, with compositions LiNixMnyCozO2: x+y+z≈1, x>y, are particularly attractive because they have higher practical capacities than NMC formulations where the Ni and Mn contents are matched. However, this comes at the expense of lower thermal stability of delithiated (charged) materials and shorter cycle lives. Utilizing a number of surface and bulk sensitive synchrotron techniques, our group has studied the thermal properties of fully and partially chemically delithiated NMC-622 and NMC-811 as a function of lithium content and temperature. As expected, changes in the bulk structures are observed at lower temperatures for compositions with lower Li and/or higher Ni content. As the temperature increases, phase conversion generally progresses as follows: Layered--> disordered-->LiMn2O4-type spinel-->M3O4-type spinel-->MO rock salt Several of these bulk reactions are associated with progressive reduction of Ni and Co with concomitant loss of oxygen. Interestingly, bulk-sensitive hard XAS and surface-sensitive soft XAS experiments suggest that, in some cases, apparent metal oxidation initially occurs close to the temperatures at which phase changes occur, rather than reduction. This can be explained in part by temperature-induced changes in M-O bond covalency, which act as a portent that a bulk reaction is about to occur. Lithium migration from one region in a particle to another may also explain discrepancies between surface and bulk metal oxidation states. In addition to lithium migration, Ni migration has been directly observed in heated particles using in situ synchrotron nanotomography. Full field X-ray spectromicroscopy also reveals considerable heterogeneity in the distribution of metal oxidation states as samples are heated, with reduction and, by inference, bulk phase change, occurring sooner in smaller primary particles than in larger ones. These observations suggest that strategies such as particle size and morphology engineering may help to improve the thermal characteristics of Ni-rich NMCs.

Mechanical Properties of Two-Dimensional Materials (Graphene, Silicene and MoS2 Monolayer) Upon Lithiation

The mechanical stability of electrode materials in lithium-ion batteries (LIBs) is critical for their safe usage. Two-dimensional (2D) materials have been widely studied to be used as electrode materials for LIBs. In this paper, the mechanical properties of several typical 2D materials, including graphene, silicene and MoS2 monolayer upon lithium intercalation were studied, based on the density functional theory calculations with the model developed by Topsakal and Ciraci (Appl Phys Lett 96:091912, 2010). It was found that the in-plane stiffness of 2D materials decreases with increases of lithium concentration. In-plane stiffness decreased about 9.8% at lithium concentration of 0.184 Li/A2 for graphene and 6.0% at a concentration of 0.153 Li/A2 for silicene. The evolution of in-plane stiffness of MoS2 monolayer as a function of lithium concentration and electron-doping concentration were compared. The in-plane stiffness of MoS2 monolayer decreased with increases of Li and electron concentration, which revealed that the electron doping effect is the mechanism causing the decrease of the mechanical stability of electrode materials upon lithiation.

Ionic and Electronic Transport Properties of Lithium-Metal-Oxygen Systems

Mixed conducting spinel (e. g. LixMn1.5Ni0.5O4 ) and layer structure materials (NCA, NMC) have been used as cathode for lithium ion batteries due to their high energy and power density. Ionic and electronic transport properties of these materials play an important role to help designing particle morphology and loading of active materials in order to get better electrochemical performances. Also these compounds can be ordered or disordered depending on the arrangement of Mn and Ni in the crystal structure. The charge-discharge behavior of ordered and disordered structures has been tested by several research groups. However still it is not clear which structural composition is suitable for a high performance battery. It is also not clearly understood if the rate performance of the material is limited by bulk transport properties or interfacial reactions. Here we report on the electronic and ionic conductivity and diffusivity of these materials which has been determined separately by using ion and electron blocking cell configurations as a function of lithium concentration on sintered dense pellets. For spinel, the disordered phase exhibits about fifteen time higher electronic conductivity than the ordered phase at room temperature in the lithiated state. The conductivities of the partially delithiated ordered phase measured at a given temperature increase monotonically with increasing delithiation at x = ~0.3 and beyond that the electronic conductivity is almost leveled up. In contrast, the electronic conductivity of disordered phase initially decreases with delithiation and comes down to the level of lithiated ordered phase. After that it exhibits almost the same electron conducting behavior as of ordered phase [1, 2]. The lithiated ordered and disordered phases exhibit the same order of magnitude of ionic conductivity and diffusivity. On the other hand electronic conductivity of layer structure materials gradually increase with increasing the state of charge whereas ionic diffusivity gradually decreases up to 50% state of charge and again increases on further charging [3, 4]. Chemical diffusion during electrochemical use is limited by lithium transport, but is fast enough over the entire state-of-charge range to allow charge/discharge of micron-scale particles at practical C-rates. References R. Amin and I. Belharouk, J. Power Sources, 348 (2017) 311–317.R. Amin and I. Belharouk, J. Power Sources, 348 (2017) 318–325.R. Amin,Y.-M. Chiang, J. Electrochem. Soc. , 163 (8), (2016) A1512-A1517.R. Amin, D. B Ravnsbæk, Y.-M. Chiang, J. Electrochem. Soc. 162 (7) (2015) A1163-A1169.

Insights into the Phase Transformation and Degradation Mechanisms of Al and Al-Alloys for Lithium-Ion Battery Anodes

Despite the tremendous progress made towards understanding the alloying and dealloying mechanisms in new lithium-ion battery anode materials like silicon and tin, the large volumetric changes that are intrinsic to these materials seem difficult to overcome in the absence of additional coating or nano-structuring methods that inherently increase cost and decrease capacity. Thus, the most likely candidate to replace graphite in the future may not be that which has the absolute highest capacity, but one that has an optimal balance between cost, capacity and processing complexity. Aluminum has significant advantages over other alloy anodes because of its low cost, high abundance, and wide variety of film and foil processing options. If the high theoretical capacity of aluminum (ca. 1 Ah/g or 2.7 Ah/cm3) can be even partially realized, it would be a significant improvement over conventional carbon-based anode materials. Despite the great promise of aluminum as an anode material in lithium-ion batteries, it typically suffers from fast capacity fading upon cycling. Unfortunately, the depth of knowledge concerning the degradation mechanisms of aluminum-based anode electrodes is still scarce. In this work, aluminum and aluminum-based alloys are used to investigate the lithiation, delithiation, and degradation mechanisms in this industrially-friendly materials system. Various in situ and ex situ microscopy methods are employed, along with conventional electrochemical cycling and characterization techniques, to investigate the phase transformations associated with the Al-Li system, in particular from the α-phase (Al) to the β-phase (AlLi), during charging and discharging. Furthermore, substrate curvature methods are used which allow for quantitative insights into the mechanical properties of the film as a function of lithium content. Scanning electron microscopy investigations of the surface morphological evolution of the aluminum-based thin-film electrodes indicate that irreversible damage depends more on the depth of discharge than on the volume contraction during delithiation [1]. These results suggest that aluminum-based anodes may be highly suitable for future lithium-ion battery anodes and implications for commercially available aluminum foils as anode materials will be discussed. [1] M. H. Tahmasebi, D. Kramer, R. Mönig, and S. T. Boles, “Insights into Phase Transformations and Degradation Mechanisms in Aluminum Anodes for Lithium-Ion Batteries,” J. Electrochem. Soc., vol. 166, no. 3, pp. A5001–A5007, 2019.

Effects of Thermal Exposure on the Structure Evolution of LiNi0.8Mn0.1Co0.1O2

High energy nickel-rich NMC (LiNixMnyCozO2; x+y+z≈1, x≥y+z) cathodes offer promising theoretical high capacity cell metrics. As the nickel content increases, the cathode exhibits a decrease in capacity retention, structural stability, and thermal stability. Herein, the thermal stability of chemically delithiated NMC-811 is investigated as a function of lithium content. A myriad of synchrotron characterization techniques are used to understand the role of the transition metals on structure stability at elevated temperatures. The in-situ heating experiments capture both chemical and morphological changes within the material that yield key particle size information on thermal stability. The bulk and surface sensitive techniques capture intermediate states between the transition metal 3d-oxygen 2p bonds at low temperatures, which inevitably can lead structural changes. This work demonstrates the importance in developing robust cathode materials for lithium ion batteries.

In situ and Operando Raman Spectroscopy of Layered Transition Metal Oxides for Li-ion Battery Cathodes

In situ and operando Raman spectroscopy is proposed to provide unique means for deeper fundamental understanding and further development of layered transition metal LiMO2 (M=Ni,Co,Mn) oxides suitable for Li-ion battery applications. We compare several spectro-electrochemical cell designs and suggest key experimental parameters for obtaining optimum electrochemical performance and spectral quality. Studies of the most practically relevant LiMO2 compositions are exemplified with particular focus on two experimental approaches: (1) lateral and axial Raman mapping of the electrode’s (near-) surface to monitor inhomogeneous electrode reactions and (2) time-dependent single-particle spectra during cycling to analyze the LixMO2 lattice dynamics as a function of lithium content. Raman Spectroscopy is claimed to provide a unique real-time probe of the M-O bonds, which are at the heart of the electrochemistry of LiMO2 oxides and govern their stability. We highlight the need for further fundamental understanding of the relationships between the spectroscopic response and oxide lattice structure with particular emphasis on the development of a theoretical framework linking the position and intensity of the Raman bands to the local LixMO2 lattice configuration. The use of complementary experimental techniques and model systems for validation also deserve further attention. Several novel LiMO2 compositions are currently being explored, especially containing dopings and coatings, and Raman Spectroscopy could offer a highly dynamic and convenient tool to guide the formulation of high specific charge and long cycle life LiMO2 oxides for next-generation Li-ion battery cathodes.

Interfacial Kinetics and Ionic Diffusivity of Electrodeposited MoS2 Film a Battery Electrode

The MoS2 is deployed in various fields of applications including rechargeable battery, hydrogen storage, solar cell, catalysis and electronic transistors. The ionic diffusivity and interfacial exchange current density, are important parameters, play a vital role for the optimization of device performances which are not systematically studied for this material. Additive-free dense film of MoS2 has been fabricated by electrodeposition technique and annealed at different temperatures in argon and sulfur atmosphere. The as-deposited and heat treated film is characterized by XRD, SEM, SIMS and XPS. The measurements of interfacial charge transfer kinetics and lithium ion diffusivity is performed in the half cell configuration (Li/separator/LixMoS2 film) as a function of lithium content. The exchange current density at the electrode/electrolyte interface is found to be barely vary with the degree of lithiation (~0.09-0.08mA/cm2) at (x=0.01-0.25). The ionic diffusivity of the phase is found to be ~5x10-12cm2s-1 and ~5x10-11cm2s-1, respectively, and does not vary much with the degree of lithiation. From the obtained results it appears that the charge transfer resistance during electrochemical measurement is limited by the interfacial kinetics over the measured state-of-charge. Down size particle with higher surface area is required to be used as a battery electrode of the material for real life application.

Interfacial Kinetics and Ionic Diffusivity of the Electrodeposited MoS2 Film.

The transition-metal disulfide (MoS2) is a fantastic material used in diverse fields of applications. Ionic diffusivity and interfacial exchange current density are model parameters that play a crucial role for the optimization of device performances, which are not clearly known for this material. The additive-free dense film of MoS2 has been deposited by a facile electrodeposition approach and characterized by structural, morphological, and compositional analyses. This report provides the characterization of interfacial charge-transfer kinetics and diffusion of lithium ion in the MoS2 films as a function of lithium concentration at 25 °C temperature. The interfacial exchange current density is observed to be varied barely, ∼0.069-0.066 mA/cm2, with the change of lithium content, from x = 0.01-0.25, in Li xMoS2. The ionic diffusivity of the film is found to be in the range of ∼3 × 10-11-10-11 cm2 s-1 and does not vary much with the measured lithium concentration window. The electrochemical performances of the material are limited by the transport of lithium ion and interfacial kinetics over the measured state of lithium content. A submicron-size particle with high surface area is needed to be used as an electrode of the material for practical C-rates.

Volume Changes of Graphite Anodes Revisited: A Combined Operando X-ray Diffraction and In Situ Pressure Analysis Study

Lithium intercalation into graphite is one of the electrochemically best studied solid-state reactions, and its application in lithium-ion batteries was a pioneering step in the development of advanced electrochemical storage devices. Therefore, one might expect that virtually any aspect of this important reaction has been examined both qualitatively and quantitatively. All the more, it is surprising that there are only a few experimental studies on the volume expansion of graphite, especially under cycling conditions. To the best of our knowledge, there exists no comprehensive set of structural data as a function of lithium content. Here, we present this missing information using combined results from electrochemical testing and operando X-ray diffraction. The changes in lattice parameters and unit cell volume are examined and related to the different intercalation stages and phase transition regimes. A total volume expansion (from space-group-independent evaluation) of 13.2% is observed when C6 is fully...

A molecular dynamics study of lithium-containing aprotic heterocyclic ionic liquid electrolytes.

Classical molecular dynamics simulations were performed on twelve different ionic liquids containing aprotic heterocyclic anions doped with Li+. These ionic liquids have been shown to be promising electrolytes for lithium ion batteries. Self-diffusivities, lithium transference numbers, densities, and free volumes were computed as a function of lithium concentration. The dynamics and free volume decreased with increasing lithium concentration, and the trends were rationalized by examining the changes to the liquid structure. Of those examined in the present work, it was found that (methyloxymethyl)triethylphosphonium triazolide ionic liquids have the overall best performance.

Thermal Behaviour of LixMeO2 (Me=Co or Ni+Mn+Co) Cathode Materials

The main challenge for electric vehicles, smaller portable devices and high capacity stationary storage facilities is their safety behaviour under normal and abusive operation conditions. The most commonly used cathodes in lithium-ion batteries (LIB) for portable applications contain lithium cobalt oxide (LiCoO2) as active material. The susceptibility of LiCoO2 cathodes to thermal runaway was previously reported in the framework of safety studies for energy storage systems [1]. The partial substitution of Co by other transition metals was much exploited. One of the main benefits of cells containing electrodes with new chemistries, such as lithium nickel manganese cobalt oxide (Li(NiMnCo)O2, isostructural with the layered LiCoO2), is the improved thermal stability in the fully charged state (delithiated cathodes). LIB with cathodes containing Li(NiMnCo)O2 perform better during thermal runaway tests than those with LiCoO2 [2,3]. Understanding the heat balance between the amounts of heat generated and dissipated in LIB during operation, when the concentration of Li in the electrode varies, is a critical issue. To improve battery safety, thermal management systems (TMS) were introduced to control the operation of high energy and high power batteries. Therefore, knowledge of bulk electrode thermal properties such as thermal conductivity, thermal diffusivity and specific heat capacity are required to optimize TMS design models and for increasing the predictability of multiscale simulations [4]. The thermodynamic properties of LiMeO2 (Me=Ni+Mn+Co) materials for LIB with layered structure were measured by calorimetry up to 973 K. Heat increment and specific heat capacity of samples with Ni:Mn:Co ratio of 1:1:1 and 4:4:2 were determined by transposed drop calorimetry and differential scanning calorimetry. These studies on active materials were extended to cathode level for samples with 1:1:1 stoichiometry. The cathodes under investigation were tape-casted composite thick films, both containing LiMeO2 active material mixed with additives (binder and carbon black), deposited on aluminium current collector foils. To compare the currently studied alternative material (Me=Ni+Mn+Co and Ni:Mn:Co=1:1:1) with the traditional LiCoO2, cathodes with Me=Co were also prepared using the same method and additionally investigated. Due to the presence of the additives, the thermophysical properties of the cathodes were studied as a function of temperature up to 573 K [5]. Thermal diffusivity was measured directly on cathode samples by laser flash analysis, whereas specific heat capacity measurements were performed using differential scanning calorimetry on samples prepared from the composite contained in the cathode sheet. These heat capacity data, together with those for aluminium, were used to predict the cathodes respective heat capacities. Furthermore, the transport properties were also studied as a function of lithium concentration x in the Li x MeO2 cathodes (0≤x≤1). The compositions, which were investigated in this work, were produced by electrochemical titration. The values of x were determined by laser induced breakdown spectroscopy through surface and bulk analysis for homogeneity in lithium concentration [6]. All cathode samples for the laser flash measurements were used in a dry state, without liquid electrolyte in the pores of the composite. Since most of the cell and battery pack models consider a homogeneously distributed mixture of liquid electrolyte in the porous electrodes, data provided in this study could contribute to the improvement of such models through the implementation of dry areas which coexist within cell layers [7]. These areas represent sources of ageing and degradation and lead to thermal gradients across the cells which are up to now neglected in the state of the art of the TMS. The results presented in this work are the first experimental data of this kind which combine application oriented and fundamental research. Furthermore, our temperature and concentration dependent data are critical for significantly improving simulation studies of the thermal behaviour of LIB, including thermal runaway, since current approaches assume bulk properties to be independent of temperature and lithiation degree due to lack of measured data.

Part I: Electronic and ionic transport properties of the ordered and disordered LiNi0.5Mn1.5O4 spinel cathode

Abstract Here, we report on the electronic and ionic conductivity and diffusivity of the ordered (P4332) and disordered ( F d 3 ¯ m ) LiNi0.5Mn1.5O4 spinel material, which have been determined by using ion and electron blocking cell configurations as a function of lithium concentration and temperature. The disordered phase exhibits about fifteen-time higher electronic conductivity than the ordered phase at room temperature in the lithiated state. Upon delithiation, the electronic conductivity of the ordered LiNi0.5Mn1.5O4 phase increases and reaches the same levels observed for the disordered phase. The ionic conductivity and diffusivity of LiNi0.5Mn1.5O4, in the ordered and disordered forms, are in the range of ∼1 × 10−9 S/cm and ∼5 × 10−9 cm2/s, respectively. Both phases exhibit similar activation energies for the ionic conductivity and diffusivity, i.e. 0.70 ± 0.2eV and 0.74 ± 0.2eV, respectively. It can be concluded from the obtained results that the electrochemical performance of LiNi0.5Mn1.5O4, whether ordered or disordered, is limited by lithium transport, but is fast enough to allow charge/discharge of micron-scale particles at practical C-rates.

Part-II: Exchange current density and ionic diffusivity studies on the ordered and disordered spinel LiNi 0.5 Mn 1.5 O 4 cathode

Abstract Additive-free pellets of Li1-xNi0.5Mn1.5O4 have been prepared for the purpose of performing ionic diffusivity and exchange current density studies. Here we report on the characterization of interfacial charge transfer kinetics and ionic diffusivity of ordered (P4332) and disordered ( F d 3 ¯ m ) Li1-xNi0.5Mn1.5O4 as a function of lithium content at ambient temperature. The exchange current density at the electrode/electrolyte interface is found to be continuously increased with increasing the degree of delithiation for ordered phase (∼0.21–6.5 mA/cm2) at (x = 0.01–0.60), in contrast the disordered phase exhibits gradually decrease of exchange current density in the initial delithiation at the 4 V plateau regime (x = 0.01–0.04) and again monotonously increases (0.65–6.8 mA/cm2) with further delithiation at (x = 0.04–0.60). The ionic diffusivity of ordered and disordered phase is found to be ∼5 × 10−10cm2s−1 and ∼10−9cm2s−1, respectively, and does not vary much with the degree of delithiation. From the obtained results it appears that the chemical diffusivity during electrochemical use is limited by lithium transport, but is fast enough over the entire state-of-charge range to allow charge/discharge of micron-scale particles at practical C-rates.

Understanding the Origins of Higher Capacities at Faster Rates in Lithium-Excess LixNi2–4x/3Sbx/3O2

The lithium-excess LixNi2–4x/3Sbx/3O2 (LNSO) materials were previously shown to demonstrate higher capacities and improved cyclability with increasing lithium content. While the performance trend is promising, observed capacities are much lower than theoretical capacities, pointing to a need for further understanding of active redox processes in these materials. In this work, we study the electrochemical behavior of the LNSO materials as a function of lithium content and at slow and fast rates. Surprisingly, Li1.15Ni0.47Sb0.38O2 (LNSO-15) exhibits higher discharge capacities at faster rates and traverses distinct voltage curves at slow and fast rates. To understand these two peculiarities, we characterize the redox activity of nickel, antimony, and oxygen at different rates. While experiments confirm some nickel redox activity and oxygen loss, these two mechanisms cannot account for all observed capacity. We propose that the balance of the observed capacity may be due to reversible oxygen redox and that t...

Surface Morphology and Surface Stability against Oxygen Loss of the Lithium-Excess Li2MnO3 Cathode Material as a Function of Lithium Concentration.

There is a growing appreciation for the role of surface reactivity and subsequent reconstruction affecting the performance of high-voltage, high-capacity Li-ion cathode materials. In particular, the promising Li-excess materials are known to exhibit significant vulnerability toward oxygen release, which can cause surface densification and impede Li intercalation. Here we focus on the end member, Li2MnO3, as a Li-excess, Mn-rich representative of this class of materials and systematically elucidate all possible stoichiometric low Miller index surfaces with various cation ordering on each surface. We apply surface cation reconstruction rules that depend on the local environment, including target Mn-Li site exchanges, and optimize the resulting surface Li configurations using metadynamics. The equilibrium Wulff shape shows dominant (001), (010) surface facets, and almost all facets exhibit favorable Mn reconstruction. Most importantly, we find that while all equilibrium LixMnO3 surfaces become unstable toward oxygen release for x < 1.7, some facets are consistently more resistant than others which may provide a design metric for more stable particle morphologies and enhanced surface oxygen retention.

High hole concentration Li-doped NiZnO thin films grown by photo-assisted metal–organic chemical vapor deposition

High hole concentration Li-doped NiZnO thin films were grown by metal–organic chemical vapor deposition (MOCVD). The crystalline, optical, electrical, and morphological characteristics of the NiZnO films were studied as a function of lithium content. The resistance of the films decreased and the hole concentration greatly increased with increasing lithium content. However, the crystalline and optical properties were observed to degrade as the lithium content was increased. To relieve the degradation, a photo-assisted MOCVD method was used in order to restrict this degradation and this represents a new way to obtain stable high hole concentration NiZnO films.

In-Situ Stress Evolution in Thin Film Electrodes during Electrochemical Cycling in Li-Batteries

Electrochemical cycling induced mechanical damage of electrode materials actively contributes towards the performance degradation of lithium-ion batteries. The correlation between mechanical damage and performance degradation in anode materials that show large volume changes, such as silicon, graphite and tin, has been amply demonstrated. On the hand, typical oxide electrodes undergo only a few % volume changes, and the non-reversible nature of the crystal structure evolution as a function of lithium concentration in such electrodes is, in general, believed to be the limiting factor for performance degradation. For example, cycling in LixCoO2 is generally limited to 0≤x≤0.5, mainly, due to the irreversibility associated with the crystal structure changes beyond further Li extraction/re-insertion. However, due to their brittle nature only a few % volume changes can have significant implication on the mechanical damage leading to performance degradation for such ceramic oxide electrodes. Thus, the issue of electrochemical cycling induced mechanical degradation in oxide electrodes is being actively explored in recent years [1-2]. In this work, we present in-situ stress evolution of i) two canonical cathode systems, namely layered LiCoO2 and spinel LiMn2O4 and ii) one conversion electrode system, Co3O4 in thin film configuration to quantify the driving force leading to the mechanical degradation. In-situ stress evolution in thin film electrodes was measured by monitoring the change in the elastic substrate curvature during electrochemical cycling in a suitably designed beaker cell using multiple-beam optical sensing (MOS) method. Thin films of the electrodes were prepared using solution deposition technique. Structural characterizations using XRD and Raman spectroscopy showed predominant presence of desired (poly)crystalline phases in the as prepared samples. In addition, SEM images also revealed the presence of dense microstructural features in the as prepared films. During Li-extraction from layered LixCoO2, there was almost linear increase in compressive stress up to ~50% Li removal, which is consistent with its lattice parameter evolution during Li removal [3], and a maximum compressive stress of ~0.35 GPa was observed for x~0.5. Upon lithiation there was almost reversible stress evolution in LixCoO2. Similar behavior was also observed for subsequent cycles as well, while limiting the upper charging cut-off voltage to 4.3V. On the other hand, initial delithiation from spinel LixMn2O4 induces tensile stress up to ~4.1V, beyond which the induced stress reverses direction (termed as “compressive drop”) with further delithiation (up to 4.3 V). This reversal of stress evolution in the later stages of delithiation from spinel LixMn2O4 is in apparent contradiction with the lattice parameter evolution of spinel LixMn2O4 during lithium extraction [4]. Upon lithium re-insertion (up to 3.5V), induced compressive stress increases linearly. The subsequent cycles (in the 4V region), however, did not show any “compressive drop” during later stages of delithiation and the induced stress evolved reversibly during delithiation-lithiation. The origin of this first cycle “compressive drop” in spinel LiMn2O4 is not known at present. In an attempt to establish the origin of the observed first cycle “compressive drop” in spinel LiMn2O4 thin films, stress measurement data varying multiple parameters including cathode film thickness, reannealing a cycled electrode will be presented. The effect of stress evolution in these thin film electrodes during cycling as a function of cycling voltage window and current density will also be presented and discussed in the light of their crystal structural changes. References D. J. Miller, C. Proff, J. G. Wen, D. P. Abraham and J. Bareno, Adv. Energy Mater., 3, 1098 (2013).W. H. Woodford, W. C. Carter and Y. M. Chiang, Energy Environ. Sci., 5, 8014 (2012).J. N. Reimers and J. R. Dahn, J. Electrochem. Soc., 139, 2091 (1992).Y. Xia and M. Yoshio, J. Electrochem. Soc., 143, 825 (1996).