Layered LiCoO2 Research Articles

High-Voltage LiNi0.5Mn1.5O4 Thin Film Cathode Prepared By RF Sputtering

Introduction Lithium ion battery is dominant in secondary battery market due to its long cycle life and high energy density compared to other batteries such as nickel hydride and lead acid batteries and thus has been widely used in electronic devices. However, present lithium ion battery, which uses olivine LiFePO4, spinel LiMn2O4 or layered LiCoO2 as cathode materials, cannot meet the requirement of the power sources for transportation applications. With the development of electric vehicles, lithium ion battery with higher energy density is needed. One of the effective ways to enhance the energy density of lithium ion battery is to employ high voltage cathode materials. LiNi0.5Mn1.5O4 cathode has received a great attention for its high potential plateau at around 4.7 V (vs. Li/Li+) and its low price due to enough manganese resource. In this work, LiNi0.5Mn1.5O4 cathode films were deposited by reactive radio-frequency (RF) sputtering on stainless steel substrate. The effects of post-annealing process on the crystallinity and electrochemical performance were examined. As the post-annealed temperature increases, the crystallinity of the thin film becomes better. However, the electrochemical properties did not show the corresponding results. The metal inter-diffusion between stainless steel and LiNi0.5Mn1.5O4film was observed in the annealing process at 600 ℃ or more. Experimental LiNi0.5Mn1.5O4 thin films were fabricated on Stainless Steel substrates. 400 nm-thick LiNi0.5Mn1.5O4 cathode layers were deposited by reactive sputtering using LiNi0.5Mn1.5O4 target. After the deposition, the cathode thin film on stainless steel was crystallized according to various post-annealing temperatures. The electrochemical cell consisted of a Li-metal foil counter electrode, and 1mol/L LiPF6 in a 1:1 solvent mixture of ethylene carbonate and diethyl carbonate as the electrolyte. The cells were assembled in an argon-filled glove box. The structure and crystallinity of the films were investigated using X-ray diffraction (XRD) with Cu Ka radiation. Charge / discharge tests were performed between 2.5 and 5.0 V in the current-rate of 0.05C. The secondary ion mass spectroscopy (SIMS) depth profile measurements were used to analyze the LiNi0.5Mn1.5O4thin films. Results and Discussion The XRD examination of the LiNi0.5Mn1.5O4 thin film on stainless steel substrate obtained from Rf-sputtering method confirmed the spinel crystal structure (Fig. 1). Charge / discharge profiles showed typical curves of spinels such as LiMn2O4 and LiNi0.5Mn1.5O4 at the 1st and 30th cycles (Fig. 2). Among the various post-annealed samples, the 500 °C sample exhibited the best characteristics. The low plateau at about 4 V corresponds to the redox reaction of Mn3+/Mn4+, while the high plateau at about 4.7 V corresponds to the redox reactions of Ni2+/Ni3+ and Ni3+/Ni4+. To investigate the inter-diffusion between the film and the substrate, SIMS depth profile measurements were performed on LiNi0.5Mn1.5O4 thin films at the different post-annealed temperatures (Fig. 3). Above 600 °C, Fe ion and Cr ion were observed in the LiNi0.5Mn1.5O4region. Conclusions Spinel LiNi0.5Mn1.5O4 thin films were successfully prepared on stainless steel substrates by sputtering method. The post-annealed temperature plays an important role in the formation of the LiNi0.5Mn1.5O4film. As the post-annealed temperature increased, the crystallinity of the thin film increased. However, at 600 °C or higher, inter-diffusion occurred between the substrate and the thin film, and secondary phases were formed. As a result, the electrochemical characteristics were deteriorated due to these characteristics. Figure 1

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.

High-throughput computational design of cathode coatings for Li-ion batteries.

Cathode degradation is a key factor that limits the lifetime of Li-ion batteries. To identify functional coatings that can suppress this degradation, we present a high-throughput density functional theory based framework which consists of reaction models that describe thermodynamic and electrochemical stabilities, and acid-scavenging capabilities of materials. Screening more than 130,000 oxygen-bearing materials, we suggest physical and hydrofluoric-acid barrier coatings such as WO3, LiAl5O8 and ZrP2O7 and hydrofluoric-acid scavengers such as Sc2O3, Li2CaGeO4, LiBO2, Li3NbO4, Mg3(BO3)2 and Li2MgSiO4. Using a design strategy to find the thermodynamically optimal coatings for a cathode, we further present optimal hydrofluoric-acid scavengers such as Li2SrSiO4, Li2CaSiO4 and CaIn2O4 for the layered LiCoO2, and Li2GeO3, Li4NiTeO6 and Li2MnO3 for the spinel LiMn2O4 cathodes. These coating materials have the potential to prolong the cycle-life of Li-ion batteries and surpass the performance of common coatings based on conventional materials such as Al2O3, ZnO, MgO or ZrO2.

Localized Mechanical Stress Induced Ionic Redistribution in a Layered LiCoO2 Cathode.

Controlling the transport of ions within electrodes is highly desirable for the operation of rechargeable ion batteries. Here, for the first time, we report the role of mechanical stress in controlling the redistribution of lithium ions in a layered LiCoO2 electrode at a resolution of ∼100 nm. Under a higher stress field, more active redistribution of lithium ions was observed along the grain boundaries than the interiors of the layered LiCoO2. The dynamic force ramping test proved the external stress field (<100 nN) is capable of inducing the resistive-switching effect of the layered LiCoO2. The comparison test on the highly ordered pyrolytic graphite (HOPG) substrate further demonstrated the improved current responses from the layered LiCoO2 resulted from the deficiency of lithium ions, rather than the increase of tip-sample contact area. Our findings will pave the road for a full understanding of how mechanical stimulus can affect the distribution of ions in the layered electrodes of rechargeable ion batteries.

Strain imaging of a LiCoO2 cathode in a Li-ion battery

Li-ion batteries have been recognized as promising devices for a sustainable society. Layered LiCoO2 and graphite are commonly used as electrode materials for Li-ion batteries. When charging and discharging, Li-ions are extracted or inserted into the interlayers, which causes changes in volume. Scanning probe microscopy (SPM) can allow high resolution imaging of these volume changes, which enables us to investigate Li-ion migration without destruction. We observed volume changes in the LiCoO2 cathode using SPM and successfully imaged the distribution of the volume changes corresponding to the LiCoO2 particles. Volume changes in the interspace were significantly larger than those in the particles. The large volume changes are caused by electrolyte flux induced by changes in concentration of Li ions. The volume changes were greatly reduced when the electrolyte dried out. The dry-out and infiltration of electrolyte between the LiCoO2 particles and the current collector spread out with the procedure of degradation of the batteries. The boundaries between the dry-out and infiltration regions acted as barriers of electrolyte flux.

Strategies and Advances in the Structural Design of Lithium Metal Oxide Electrodes

Of the three categories of cathode materials that dominate today’s lithium-ion battery industry, i.e., those with layered, spinel and olivine-type structures, layered lithium-metal-oxide systems remain the most attractive category for providing high energy densities. Although LiCoO2 (LCO) and LiNi0.8Co0.15Al0.05O2 (NCA) remain attractive electrodes for portable consumer electronics devices and heavier duty applications (e.g., transportation), they suffer from structural and chemical instabilities at high charging potentials that limit the practical energy output of the cells. While spinel lithium-manganese-oxide (LMO) and olivine lithium-iron-phosphate (LFP) electrodes provide superior thermal stability over layered LCO and NCA electrodes, they are disadvantaged by their low theoretical specific capacity and low packing densities, respectively, relative to the best layered systems. The discovery that layered lithium- and manganese-rich metal oxide electrode structures, derived from the incorporation of a Li2MnO3 component, can deliver their theoretical capacity (250-260 mAh/g) [1, 2], albeit at relatively low current rates when charged continuously above 4.5 V, has resulted in worldwide efforts to bring these electrodes to the market. Despite this advance, these lithium- and manganese-rich electrodes lack structural instability when cycled, which is not surprising given that layered-LiMnO2transforms to a spinel-type structure during repeated charge and discharge [3]. This presentation will report on recent approaches and efforts at Argonne National Laboratory to design stabilized high capacity electrode materials by exploring the phase space of structurally-integrated lithium-metal-oxide materials through a combination of processing, compositional, structural, electrochemical and theoretical studies. The concept of designing structurally-integrated electrodes for lithium-ion cells was sparked by the existence of composite structures such as gamma-MnO2, which has been used prolifically over the years in LeClanché dry cells and alkaline cells [4]. Gamma-MnO2 occurs in nature [5] and can also be made synthetically by chemical or electrochemical methods [6]; its structure is comprised of a predominant electroactive-active component, ramsdellite-MnO2, integrated with a beta-MnO2 (rutile-type) component that is significantly less reactive to lithium uptake and provides stability to the overall electrode structure. References Z.H. Lu, J.R. Dahn, J. Electrochem. Soc. 149, A815 (2002).M.M. Thackeray, C.S. Johnson, J.T. Vaughey, N. Li, S.A. Hackney, J. Mater. Chem. 15, 2257 (2005).P. G. Bruce, A. R. Armstrong, R. L. Gitzendanner, J. Mater. Chem. 9, 193 (1999).M.M. Thackeray, S.-H. Kang, C.S. Johnson, J.T. Vaughey, R. Benedek, S.A. Hackney, J. Mater. Chem. 17, 3112 (2007).J. E. Post, Proc. Natl. Acad. Sci. USA, 96, 3447 (1999).Y. Chabre and J. Pannetier, Prog. Solid St. Chem. 23, l (1995). Acknowledgments Funding for this work from the Office of Vehicle Technologies of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, is gratefully acknowledged. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Control of Lattice Orientation and Interface of LiCoO2 for All Solid State Batteries

All solid state batteries are widely investigated as next generation batteries because they do not suffer from leakage, volatilization, and flammability of liquid electrolyte. Both bulk type and thin film solid batteries have attract great attention. LiCoO2 thin film has been commonly used as the cathode material for solid state batteries due to its high capacity, operating voltage and long cycle life. Because of the importance of the solid-solid interface for the performance of the battery and stability during cycling, i.e. its life time, the interface of substrate/LiCoO2 and LiCoO2/solid electrolyte during the preparation of the solid battery and possible intermediate products in the interlayer attract great attention recently. [1] The deposition parameters has a big influence on the film quality in terms of structure, morphology and electrochemical properties. In the case of layered LiCoO2, lithium-ion diffusion rely on vacancy hopping mechanism within the lithium plane, showing a predominant two dimensional path. Therefore, different orientation of lattice could influence the intercalation properties of LiCoO2 thin film deposited. [2] A primary challenge in all solid state battery is the difficulty of rapidly moving charge across solid/solid interface within the electrodes and across the electrode/electrolyte interface. The consecutive study on electrode and/or electrolyte has achieved great progress for the last decades. However, interfaces still dominate the interfacial impedance during electrochemical reaction. The optimization of interface of substrate/LiCoO2 and LiCoO2 /solid electrolyte could direct the further improvement of current all solid state batteries. Both lithium ion mobility and electrochemical reaction of LiCoO2 thin film with the solid electrolyte and the substrate are related to the interfacial resistance, which could be minimized through controlling growth orientation of LiCoO2during deposition.[3] Therefore, the ionic transportation across solid/solid interface and electrode/electrolyte interface are increased, leading to improved electrochemical performance. In this work, we optimize the deposition parameter to get high crystalline HT-LiCoO2 with hexagonal structure and good electrochemical performance firstly. Next, we study on sputtering deposition of LiCoO2 with different orientation in order to study the LiCoO2/substrate and LiCoO2/solid state electrolyte interface. The compositional (XPS), microstructural (XRD, Raman, SEM) and electrochemical properties of the sputtering LiCoO2thin films with different orientation are investigated. For the study of interface, we will adopt advanced technique to investigate the chemical/physical changes at the interface layers. Reference [1] Luntz, Alan C., et al. The journal of physical chemistry letters 6.22 (2015): 4599-4604. [2] Bates, J. B., et al. Journal of The Electrochemical Society 147.1 (2000): 59-70. [3] Yoon, Yongsub, et al. Journal of Power Sources226 (2013): 186-190.

LiCoO2 degradation Behavior in the High-Voltage Phase-Transition Region and Improved Reversibility with Surface Coating

Introduction Layered LiCoO2, which is the most common cathode material used for Li-ion batteries, exhibits phase transitions from the O3 phase to the H1-3 and O1 phases at charge voltages exceeding 4.5 V (vs. Li+/Li) [1]. These phase transitions were believed to result in poor charge/discharge reversibility in the high-voltage region [2]; however, the detailed degradation mechanism has not been elucidated. Additionally, the charge/discharge performance of active materials can be improved with surface coatings. Certain types of coating have been reported to suppress the capacity fade exhibited by LiCoO2, even above 4.5 V [3]. In this study, we examined in detail the degradation behavior of LiCoO2and the suppression effect of a coating at a charge voltage of 4.7 V. Experimental LiCoO 2 powder with a secondary particle diameter of 7 μm (Nippon Chemical Industrial) was used as the active material. An Al-oxide coating was formed using a sol-gel method [4]. The surface structures of bare and coated LiCoO2 samples were evaluated using field emission scanning electron microscopy and Cs-corrected scanning transmission electron microscopy (Cs-STEM) combined with energy-dispersive X-ray spectroscopy. The electrochemical characteristics of the samples were examined in pouch cells with a Li-metal counter electrode. A 1.0 mol dm-3 of LiPF6 in ethylene carbonate+diethyl carbonate (EC+DEC; 1:2 by volume) was used as the electrolyte. The cells were cycled between 2.5 and 4.7 V. Initial charge/discharge and cycle performance were evaluated at current densities of 0.05 and 0.2 C, respectively. Here, 1 C was defined as 274 mAh g-1, which is the theoretical capacity of LiCoO2. Results and Discussion Figure 1 shows the charge/discharge curves of bare and coated LiCoO2 during the cycle test. The bare LiCoO2 exhibits considerably decreased capacity and increased polarization, whereas these changes are remarkably suppressed in coated LiCoO2. Because coated LiCoO2 shows voltage plateaus in the relatively high-voltage region between the 1st and 20thcycles, phase transitions in this region can be assumed to be fairly reversible. Figure 2 shows a cross-sectional transmission electron microscopy (TEM) image of bare LiCoO2 after the cycle test. The entire surface of the bare LiCoO2 sample is covered by an altered layer with a thickness of several nanometers. High-resolution STEM revealed that this altered layer has a spinel-like (Co3O4-like) crystal structure, which should exhibit poor Li-ion conductivity. This structure could explain why the formation of this layer substantially increases the polarization of bare LiCoO2. Furthermore, instances of pitting corrosion (approximately 10 nm in size) occur at the grain-boundary surfaces of bare LiCoO2 (Fig. 2). These result from Co dissolution into the electrolyte and lead to intrinsic capacity fade. In contrast, formation of the spinel-like layer and pitting corrosion were suppressed in the coated LiCoO2. The LiCoO2 degradation mechanism in the high-voltage phase-transition region will be discussed by comparing the results for bare and coated LiCoO2samples. Acknowledgements This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING) project of NEDO, Japan.

Development and Characterization of Li(NixMnyCo1-x-y)O2 Layered Cathode Materials for Lithium Ion Batteries

Lithium ion batteries are now widely used especially in mobile applications as a power source. In the case of Li-ion batteries, certain properties such as energy density, cycle life, safety, electrical conductivity and rate capability have great importance. LiCoO2 has been used as a cathode material for Li-ion batteries for many years. However, capacity of the currently used layered LiCoO2 cathodes is limited to perform 50% of its theoretical capacity (140 mAh/g) [1]. In this regard, novel layered Li(Ni1/3Mn1/3Co1/3)O2 cathode materials have been investigated as an alternative cathodes searching for higher capacity, cycle life, rate capability and safety. Li(Ni1/3Mn1/3Co1/3)O2 cathodes exhibit higher capacity that of close to 200 mAh/g with enhanced safety [2]. This high capacity can be associated with the improved chemical stability. However, the rate capability is the most important deficiency which should be improved for new layered Li(Ni1/3Mn1/3Co1/3)O2cathode materials. Moreover, the electrochemical performance of cathode is strongly affected by powder properties such as morphology, surface area and composition. Therefore, spray pyrolysis method was used to obtain spherical fine-sized morphology followed by heat treatment will to obtain better electrochemical activity [3]. The precursor powders were prepared using aquaous solution via spray pyrolysis. Li(NixMnyCo1-x-y)O2 cathode material was produced by using solutions of lithium nitrate (LiNO3), nickel (II) nitrate hexahydrate (N2NiO6.6H2O), manganese (II) nitrate tetrahydrate (Mn (NO3).4H2O and cobalt (II) nitrate hexahydtare (Co(NO3)2.6H2O) with the mole ratio of 1:1/3:1/3:1/3, repectively. The total concentration of the solution is 0.5 M with additives of citric acid and ethylene glycol. Spray pyrolysis was used to obtain spherical fine-sized particles which then heat treated between 800⁰C - 1000⁰C. Different time-temperature combinations were tried and an undefined peak of new layered Li(Ni1/3Mn1/3Co1/3)O2 was observed which heat treated at 1000⁰C. Therefore, temperature range between 800⁰C and 900⁰C was chosen as heat treatment temperature. X-Ray Diffraction (XRD) pattern of obtained layered Li(Ni1/3Mn1/3Co1/3)O2cathode material showed good [006]/[102] and [108]/[110] doublets indicating layered structure and good hexagonal ordering as shown in Figure 1. Figure 1. XRD spectrum of layered Li(Ni1/3Mn1/3Co1/3)O2cathode materials produced by using spray pyrolysis and then heat treated. Precursor concentration, droplet size, gas flow rate and temperature are the main parameters affecting the particle properties. Therefore, these parameters were optimized to obtain particles with spherical fine-sized and narrow size distribution. The morphology of Li(NixMnyCo1-x-y)O2 observed by scanning electron microscopy (SEM) and average particle size was between 0.4 and 0.6 μm, as shown in Figure 2. Li(NixMnyCo1-x-y)O2cathode materials will be investigated focusing on the improvement of capacity, cycle life and especially rate capability via doping elements. With proper cathode composition, experimental parameters, electrode design and doping elements, improved electrochemical properties was achieved. Figure 2. SEM images of studied layered Li(Ni1/3Mn1/3Co1/3)O2 cathode materials produced by using spray pyrolysis and then heat treated. Figure 1

Self-Standing 3D Thin Film Cathodes for Micobatteries

While the microelectronic industry is advancing at a rapid pace with smaller and smaller devices, the implementation of microelectro-mechanical systems (MEMS) on the market strongly depends on the availability of on-board power sources. However, traditional rechargeable batteries based on liquid electrolyte are not applicable due to the restrictions for on-chip design, size and inherent risk of leakage, which give rise to the development of all-solid-state thin film lithium-ion microbattery technology. As more energy is required in microelectronic devices, two-dimensional (2D) thin film microbatteries are no longer the ideal battery design because the limited footprint area results in a compromise between energy density and power density for the build-in power source. A move to all-solid-state three-dimensional (3D) architectures has been proposed as a promising approach to tackle this challenge and achieve both high energy and power densities within the footprint area [1]. 3D microbatteries generally require the fabrication of 3D nanoarchitectured electrodes with large capacity at high charge/discharge rates and long-term cycling capability. Without using binders or conductive additives, the direct fabrication of nanoarchitectures for the electrode materials on conductive substrates represents a new class of electrodes: 3D self-supported electrodes. Except as the key component for constructing 3D microbatteries, the 3D self-supported electrodes using flexible substrates (such as metal foil and carbon cloth) can be ideal electrodes for flexible lithium-ion batteries. Active research efforts have been devoted to the synthesis and characterization of various 3D self-supported electrodes on different conductive substrates. However, most of the previous works focused on the preparation of 3D self-supported nanoarchitectures for anode materials such as Si, Co3O4, and TiO2 [2], while very limited work has been reported on the 3D self-supported nanoarchitectures for cathode materials. The difficulty lies in the fact that the synthesis of cathode materials such as LiCoO2 and LiMn2O4 involves high temperature treatment, which is difficult for retaining the nanostructures after heat treatment. In this work, we present a new "hydrothermal lithiation" method to construct 3D LiCoO2 and LiMn2O4 nanoarrays on metal substrates [3,4]. Mesoporous low-temperature LiCoO2 nanowire arrays can be directly prepared by a two-step hydrothermal method and they can be easily converted into chain-like high-temperature LiCoO2 nanowire arrays through further calcination. The layered LiCoO2 nanowire arrays exhibit both high gravimetric capacity and areal capacity, while maintaining good cycling stability and rate capability. Similar method was used to prepare vertically aligned porous LiMn2O4 nanowall arrays, comprising highly crystallized spinel nanoparticles, on various conductive substrates without high temperature treatment. The "hydrothermal lithiation" can effectively convert Mn3O4 spinel nanowall arrays into LiMn2O4 spinel nanowall arrays without severe morphology change. The binder-free three-dimensional porous LiMn2O4 nanowall arrays exhibit high specific reversible capacity up to 131 mAh g-1 (or 0.29 mAh cm-2) as well as outstanding cycling stability and rate capability, making them promising as cathodes for both three-dimensional thin film lithium-ion microbatteries. The 3D cathode design and the effective low-temperature synthesis route will lead to new opportunities to develop high-performance microbatteries and flexible lithium-ion batteries.

Progress in surface coating on LiNi&amp;lt;sub&amp;gt;0.8&amp;lt;/sub&amp;gt;Co&amp;lt;sub&amp;gt;0.15&amp;lt;/sub&amp;gt;Al&amp;lt;sub&amp;gt;0.05&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; cathode materials for lithium-ion batteries

Cathode materials with high energy density and long life are currently the focus in the research and development of advanced lithium-ion batteries. Compared to traditional commercial layered LiCoO2, the nickel-rich cathode material with typical composition of LiNi0.8Co0.15Al0.05O2 (NCA) has attracted intensive interest because of advantages of low cost and high specific capacity (i.e., ~200 mAh/g). However, this promising cathode material suffers from problems, such as severe irreversible capacity loss and poor performance at high temperature due to the mixed cation distribution of Li/Ni and the presence of high-valent Ni on charge that poses structural instability and strong oxidizing ability. There are generally two strategies to address the issues, namely, cation doping and the more extensively employed surface coating. In this article, we review recent progress made in surface coating of NCA cathode materials. Currently, the materials used for coating NCA mainly include carbonaceous materials (e.g., graphene), oxides and composite oxides (e.g., SiO2, CeO2, TiO2, and Li2O-2B2O3), fluorides (AlF3), lithium-containing compounds (e.g., LiCoO2), phosphates (e.g., AlPO4 and Co3(PO4)2) and polymers (e.g., polyaniline). The surface-coated NCA shows better cycling performance as compared to the raw material. The effect of coating on electrode properties varies among different coated materials. The coating of oxides/fluorides/phosphates reduces the corrosion of electrolyte on the electrode and suppresses the side reaction between the electrolyte and the electrode, giving rise to better capacity retention. Carbonaceous materials and composite oxides exert similar protective effect and help to improve the electrical and ionic conductivity. Some stable lithium-containing compounds are coated on NCA to form a core-shell structure, facilitating both Li+ insertion/delithiation and electron conduction with reduced electrode polarization and enhanced electrode stability. The coating methods also affect the electrode performance. Coating can be achieved through mechanical or chemical ways. The former is to mechanically mix the coating material and the raw NCA material by stirring or milling. Mechanical coating is simple in processing but is energy consuming and may incur structural/morphological break. Chemical coating is to generate in situ the coated material on the surface of raw material via chemical reactions. Complicated procedures are often required to make the coating layer uniformly distributed on target materials. As the coated materials are generally electrochemically inactive, their amount should be kept minimized to reduce expense of available capacity. Additionally, the type of coated materials and the thickness of coating layer should be optimized to make full advantage of coating. As a result of surface modification, the cyclability and thermal stability of NCA cathode materials can be greatly improved as compared to the pristine uncoated electrode.

Layered Li2RuO3–LiCoO2 composite as high-performance cathode materials for lithium-ion batteries

Lithium-rich transition metal oxides are attractive cathode materials providing high energy densities for lithium-ion batteries. A layer-structured Li2RuO3-LiCoO2 composite was synthesized by the solid-state reaction method. In the as-prepared composite, Li2RuO3 component not only serves as the electrochemical active phase providing large reversible capacity, but also improves the structural stability of layered LiCoO2 at high potential. Electrochemical measurements show the composite has high reversible specific capacity and good capacity retention. Particularly, the initial discharge specific capacity can reach 240mAh/g at current density of 0.13C between 2.0V and 4.5V. It also exhibits an excellent cycling stability with capacity retention of 75% after 50 cycles. The present work suggests choosing appropriate transition metal M and M′ for Li2MO3-LiM′O2 composite should be an efficient strategy for designing new cathode materials.

(Invited) Elucidation of Lithiation Process As a Function of Structural and Chemical Transformations in Li2MnO3

The layered Li2MnO3 is a key component in the Li/Mn-rich cathode materials, and provides a representative end-member for the spectrum of compositions reported in the literature. While exhibiting excellent initial capacity, the Li excess materials suffer from voltage fade, high impedance, and poor rate capability, particularly in the Mn-rich, high Li excess concentration regime. In this talk we present insights about the Li electrochemical reactivity of Li2MnO3, from first-principles calculations. In particular, we elucidate the bulk lithiation/delithiation mechanism in pristine bulk LixMnO3 for 1< x < 2, involving coherent Li migration from the two Li-containing layers. Surprisingly, and contrary to expectations from available experimental results, we find that the pristine material exhibits excellent Li mobility enabling a Li rate capability on par with the well-known layered LiCoO2. For lower Li contents (x < 1), we have previously shown that Li2MnO3 becomes increasingly unstable towards manganese migration into the Li layer as well as oxygen loss at the surface. We systematically investigate the influence of these factors on the lithiation/delithiation process, which provides a hypothesis for the experimentally observed slow, and increasingly poor, electrochemical response of this material.

(Invited) High-Throughput DFT Thermochemistry Applied to the Design of Cathode Coatings Forlithium-Ion Batteries

We present a high-throughput (HT) density functional theory (DFT) based framework to identify new functional coatings that can suppress cathode degradation in Li-ion batteries. This HT framework is based on reaction models that describe the thermodynamic and electrochemical stabilities and acid-scavenging capabilities of oxide materials. Using the framework, we search for coatings with different functionalities including physical barriers, hydrofluoric acid (HF) barriers and HF scavengers, by screening more than 130,000 candidate oxide materials. Employing two alternative material selection methods, namely, weighted-sum and rank aggregation multi-objective optimization, we predict new promising physical and HF-barrier coating materials such as WO3, LiAl5O8, ZrP2O7, Hf2P2O9, TaPO5, CaSn4(PO4)6, and new or under-explored HF-scavengers such as Sc2O3, Li2CaGeO4, Li3NbO4, TaBO4, LiBO2, Mg3(BO3)2, Ca5(BO3)3F, Ca2Ta2O7 and Li2MgSiO4. Using principal component analysis, we show that the the likelihood of discovery of effective HF-scavenger coatings is highest in silicates and borates among all oxides. We further present a new HT design strategy where thermodynamically optimal HF-scavenger coatings for a given cathode material can be found by (i) incorporating the cathode material itself in the chemical space, (ii) evaluating the cathode-coating reactivity, and (iii) monitoring cathode reactivity in electrochemical (charge and discharge) and HF-attack reactions. Examples of such optimal coatings we found include Li2SrSiO4, Li2CaSiO4 and CaIn2O4 coatings for the layered LiCoO2 and Li2GeO3, Li2TiSiO5, Li4NiTeO6, Ca2Mn3O8, and Li2MnO3 for the spinel LiMn2O4 cathodes. These candidate coating materials have the potential to prolong the cycle-life of lithium-ion batteries and surpass the performance of common coating technologies based on conventional materials such as Al2O3, ZnO, MgO or ZrO2. This work was performed in collaboration with Muratahan Aykol, Soo Kim, Vinay I. Hegde, David Snydacker, Zhi Lu, Shiqiang Hao, Scott Kirklin, and Dane Morgan.

Li2ZrO3 -Coated Li1.2Ni0.2Mn0.8O2 for the High Performance Cathode Material in Lithium Ion Batteries

Introduction Recently, high energy density lithium ion batteries (LIBs) play an important role in the field of portable and electronic devices and electrical vehicles. Although conventional layered LiCoO2 cathode material has good electrical properties, the capacity of current LiCoO2 is around 160 mAhg-1 with lithium utilization in the structure less than 50%. Moreover, their cost and safety requirement are still problems for the adoption of lithium ion technology for these large-battery application. In this reasons, during the past two decades, several cathode materials have been emerged as an alternative layered structure compounds, such as olivine phosphates (LiMPO4; M = Fe, Co, Ni, and Mn) and spinel oxides (LiM2O4; M = Mn, Ni and Co), however these still have a relatively low capacity. To overcome this problem, Over-lithiated Layered Oxide (OLO) materials have been considered one of the promising cathode materials for the next generation of cathode materials. Among them, 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 which is known as high capability (250 mAhg-1) has excellent electrochemical performance and stability at higher cut-off voltage beyond 4.8 V. However, its severe capacity fading during high current rates is generally related to the unstable structure and the side reaction with electrolytes cause problems while cathode carries out beyond 4.8 in a range of high voltage. Herein, we reports Li2ZrO3 -coated Li1.2Ni0.2Mn0.8O2 for high performance cathode material in lithium ion batteries. The concept is both to decrease the interface resistance by crystallization of the surface layer and cover the particles with Li2ZrO3that would suppress the particles against side reactions with the electrolyte. In addition, it can circumvent the loss of transition-metal ions of oxygen, without changing the electronic and ionic conductivities. In this study, X-ray diffraction, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Electrochemical Impedance Spectroscopy and various Charge-discharge measurements were also performed to further investigate the effect of surface-coating layer. Experimental To make samples, OLO was made by adding Zirconium isopropoxide was added in the mixed powder and then mixed by hand. After pelletizing, it was put in Alumina crucible and calcinated in 900 °C for 10 hours (heating rate is 5 °C/min). After calcination, powder was filtered using D.I water to remove the residue of LiOH. Resulting powder was dried at 60oC (overnight). Electrode slurry has been made of 92% of cathode materials, 4% of Denka black, 4% of PVdF. The slurry was casted on the Al foil for current collector and assembled with 2032 coin cell. Result and discussion Surface modification of cathode electrodes with lithium zirconia oxide gives rise to the better rate properties than pristine OLO. Figure 1

Performance Optimization for Nanoscale Nickel Manganese Cobalt Oxide (NMC) Li-Ion Battery Cathode

Cathode materials with high energy storage capacity, thermal stability and extended cycle life are remaining challenges in Li-ion batteries[1]. Materials that are considered for Li-ion battery cathodes include Li-containing layered oxides, spinel oxides, phosphates, fluorophosphates, and silicates. Requirements are that they must be capable of dedoping lithium during charge, and undergo lithium doping during discharge. Layered LiCoO2 has been used in the first generation of commercial cathode material introduced by Sony Corporation in 1991. It was selected due to its reversibility, dischargecapacity, charge/discharge efficiency, discharge curve and other properties. The theoretical capacity of LiCoO2 is 274 mAh/g, however, practically attainable capacity is only 120-130 mAh/g in the potential window of 2.8 to 4.2 V[2]. Other layered materials such as LiNiO2 and LiMn2O4 and their doped derivatives (LiNixCoyO2 and LiMn1-xCoxO2 are also being investigated because of relatively high capacity (180-200 mAh/g), however the capacity fading and conversion from layered to spinel structure under cycling remain challenging[3].The mixed oxide LiNi0.33Mn0.33Co0.33 (NMC) has received much attention in recent years because of its higher charging voltage up to 4.7 V, lower cost, low toxicity, good thermal stability and most importantly attainable specific capacity of 200 mAh/g. However, this complex material also suffers from capacity fading during cycling. The capacity reduces from 175 mAh/g to 140 mAh/g after 50 cycles discharge at 1C rate when cycled to 4.5 V[4]. The fading is typically prescribed to either (a) the formation of cathode electrolyte interface (CEI) layer due to the decomposition of electrolyte or (b) the loss oftransition metal ions from the cathode during charging and discharging at high voltage, or both. For LiFePO4 cathode materials it has been demonstrated that smaller particle sizes can improve performance due to shorter diffusion paths and higher surface-to-volume ratios[5]. However several concerns arise when shifting from micron sized to nanoscale battery materials. One is the electrical connectivity of each nanoparticle to the current collector and another is higher electrolyte/particle contact area resulting in increased CEI formation. In this work we explore the effects of particle size(micron and nanoscale) of the NMC cathode materials, the effects of charging potential limits and the effects of the electrolyte additives on the performance and cycle life. Charge/discharge cycling, electrochemical impedance spectroscopy (EIS), x-ray diffractometry (XRD), scanning electron microscopy (SEM), Raman spectroscopy and in-situ x-ray absorption spectroscopy (XAS) techniques are used to understand the lithiation/delithiation mechanisms and capacity fading phenomena in those cathodes with the goal of finding reasonable mitigation approaches to challenges with nanoscale battery materials. The presentation will summarize the results of this investigation and will suggest performance optimization strategy for improved capacity retention innanoscale NMC cathodes.

Electrochemical Performance of Full Concentration Gradient Cathode for Lithium-Ion Batteries

Worldwide effort is being devoted to development of lithium-ion batteries for consumer devices, plug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EV), which require higher energy, increased safety, and lower cost. Most commercial lithium-ion batteries use a layered LiCoO2 as the cathode material, but LiCoO2has a limited practical capacity of about 140 mAh/g. A high capacity cathode material with high packing density is thus being sought to improve the energy density of lithium-ion batteries with improved safety. Recently, some novel design structures cathode material are reported, such as core-shell, gradient material. First, a co-precipitation process is used to synthesize core-shell or gradient structure spherical precursor, then using this precursor to prepare a same structure cathode material. Using this new process, it is easy to control the elements distribution inside of single particles. This concept make it is possible to achieve the high capacity, cycling life and safety for a cathode material. So the composition design is based on those, high Ni in bulk material for high capacity and high Mn on the surface for safety with certain Co are investigated. In this study, we investigated a full concentration gradient material, and the average composition is closed to Li1.0Ni0.6Co0.2Mn0.2O2. The material was synthesized by a solid-state reaction from full concentration gradient spherical precursor Ni0.6Co0.2Mn0.2(OH)2 and LiOH precursors. The full concentration gradient spherical precursor Ni0.6Co0.2Mn0.2(OH)2was prepared by a co-precipitation process. It exhibited uniform spherical particle shape with 15-mm diameter and high tap density of 2.7 g/cc. The electrochemical performance of the material was evaluated in a coin-cell. When the current density was 16 mA/g (C/10), the discharge capacities were about 191 mAh/g. The significant improvement in tap density and the high capacity of this material makes it a potential cathode material for high energy battery application. Acknowledgments The authors acknowledge the financial support of the U.S. Department of Energy, FreedomCAR & Vehicle Technologies Office, under Contract No. DE-AC02-06CH11357. Figure 1

Fast discharge process of layered cobalt oxides due to high Na⁺ diffusion.

Sodium ion secondary battery (SIB) is a low-cost and ubiquitous secondary battery for next-generation large-scale energy storage. The diffusion process of large Na+ (ionic radius is 1.12 Å), however, is considered to be slower than that of small Li+ (0.76 Å). This would be a serious disadvantage of SIB as compared with the Lithium ion secondary battery (LIB). By means of the electrochemical impedance spectroscopy (EIS), we determined the diffusion constant (D) of Na+ in thin films of O3- and P2-type NaCoO2 with layered structures. We found that the D values (~ 0.5–1.5 × 10−10 cm2/s) of Na+ are higher than those (< 1 × 10−11 cm2/s) of Li+ in layered LiCoO2. Especially, the D values of O3-NaCoO2 are even higher than those of P2-NaCoO2, probably because O3-NaCoO2 shows successive structural phase transitions from the O3, O’3, P’3, to P3 phases with Na+ deintercalation. We further found that the activation energy (ED ~ 0.4 eV) for the Na+ diffusion is significantly low in these layered cobalt oxides. We found a close relation between the relative capacity and the renormalized discharge rate ( = L2/DT, where L and T are the film thickness and discharge time, respectively).

Review—Li-Rich Layered Oxide Cathodes for Next-Generation Li-Ion Batteries: Chances and Challenges

Since their commercialization Li-ion batteries have relied on the use of layered oxides (LiMO2) as positive electrodes. Over the years, via skilful chemical substitution their performances have drastically improved in terms of safety and capacity, which has nearly doubled (280 mAh/g) with the recent arrival of Li-rich NMC, i.e. layered LiCoO2 in which Co has been simultaneously replaced by Mn, Ni and Li. This review will aim to describe the chemical rationale which has led to this material evolution prior to focus on Li-rich NMC phases which are sources of excitement but challenges as well. The benefits of going back to fundamentals to rationalize and understand the new science at work with these Li-rich NMC phases will be stressed and illustrated by the discovery of a new reversible anionic redox process. Issues regarding voltage fade and limited rate capability which are plaguing their present utilization in commercial Li-ion cells will be addressed as well and solutions proposed. Owing to such advances, layered oxides which are over performing spinel or polyanionic-based compounds have a bright future.

A rapid combustion route to synthesize high-performance nanocrystalline cathode materials for Li-ion batteries

Nanocrystalline spinel LiMn2O4 and layered LiCo1−xMnxO2 (x = 0–0.15) cathode materials were synthesized by a rapid combustion route in combination with an annealing treatment using common filter paper as the template and ethanol as the fuel. The structure, morphology and electrochemical properties of the materials were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The spinel LiMn2O4 annealed at 750 °C shows excellent cycling stability (capacity retention is 92% after 200 cycles), high coulombic efficiency (>99%) and good rate capability. The layered LiCoO2 shows high initial capacity (168.9 mAh g−1) and good rate capability, but its capacity retention is only 74% after 80 cycles owing to the nanosize effect. After doping a small quantity of Mn (x = 0.05), the cycling performance of the Mn-doped sample was significantly improved compared with that of the pristine LiCoO2 (capacity retention is 87% after 80 cycles).