Oxide Cathodes For Li-Ion Batteries Research Articles

Jahn-Teller Distortions and Phase Transitions in LiNiO2: Insights from Ab Initio Molecular Dynamics and Variable-Temperature X-ray Diffraction.

The atomistic structure of lithium nickelate (LiNiO2), the parent compound of Ni-rich layered oxide cathodes for Li-ion batteries, continues to elude a comprehensive understanding. The common consensus is that the material exhibits local Jahn-Teller distortions that dynamically reorient, resulting in a time-averaged undistorted R3̅m structure. Through a combination of ab initio molecular dynamics (AIMD) simulations and variable-temperature X-ray diffraction (VT-XRD), we explore Jahn-Teller distortions in LiNiO2 as a function of temperature. Static Jahn-Teller distortions are observed at low temperatures (T < 250 K) via AIMD simulations, followed by a broad phase transition that occurs between 250 and 350 K, leading to a highly dynamic, displacive phase at high temperatures (T > 350 K), which does not show the four short and two long bonds characteristic of local Jahn-Teller distortions. These transitions are followed in the AIMD simulations via abrupt changes in the calculated pair distribution function and the bond-length distortion index and in X-ray diffraction via the monoclinic lattice parameter ratio, amon/bmon, and δ angle, the fit quality of an R3̅m-based structural refinement, and a peak sharpening of the diffraction peaks on heating, consistent with the loss of distorted domains. Between 250 and 350 K, a mixed-phase regime is found via the AIMD simulations where distorted and undistorted domains coexist. The repeated change between the distorted and undistorted states in this mixed-phase regime allows the Jahn-Teller long axes to change direction. These pseudorotations of the Ni-O long axes are a side effect of the onset of the displacive phase transition. Antisite defects, involving Li ions in the Ni layer and Ni ions in the Li layer, are found to pin the undistorted domains at low temperatures, impeding cooperative ordering at a longer length scale.

Elucidating degradation mechanisms of Co-free high-Ni layered oxide cathodes for Li-ion batteries via advanced X-ray-based characterization methods

High-Ni layered oxide cathodes without Co are being investigated as potential cathode materials for Li-ion batteries with high energy density. By decreasing the Co content, these cathodes not only boost energy density but also alleviate concerns about the supply instability and fluctuating cost of Co raw materials. However, the elevated Ni content in the layered oxides causes distinct chemo-mechanical degradation mechanisms that inhibit their commercial application. In order to gain insight into the degradation process at various scales, from the atomic to the particle and the electrode levels, and to devise ways to prevent degradation, multi-scale characterization methods are essential. In this review, we critically evaluate the role of Co substitution in high-Ni layered oxides and the impact of Co content on the chemo-mechanical degradation process. Furthermore, the use of advanced X-ray-based characterization methods, which have helped shed light on the degradation mechanisms of high-Ni cathodes, is also discussed.

Al, Zr dual-doped cobalt-free nickel-rich cathode materials for lithium-ion batteries

Nickel-rich and cobalt-free cathode materials have obvious advantages in the aspects of energy density and economic efficiency. However, these materials are restricted from being used in commercial lithium-ion batteries due to the problems of poor structural stability and rate capability. In this study, the aluminum and zirconium dual-doped Co-free Ni-rich LiNi0.96Mn0.04O2 cathode material (NMAZ) is prepared by a facile high-temperature solid-phase method. The obtained NMAZ shows low cation disordering degree owing to the stability of transition metal slabs induced by strong Al–O and Zr–O bonds. Besides, the kinetics of lithium-ion diffusion is significantly improved by larger c-axis and the fast lithium-ion conducting Li2ZrO3 layer on the interface. As a result, NMAZ shows an improved capacity retention of 70.3% at 1C after 100 cycles under an elevated temperature (45 ​°C), compared with 50.5% of pure LiNi0.96Mn0.04O2. In addition, it exhibits splendid rate performance even at higher C-rate and better thermal stability compared to bare LiNi0.96Mn0.04O2. Hence, the Al, Zr dual-doped modification is beneficial to improving the structural stability and electrochemical performance of the Ni-rich and Co-free layered oxide cathodes for Li-ion batteries.

Oxygen Loss in Layered Oxide Cathodes for Li-Ion Batteries: Mechanisms, Effects, and Mitigation.

Layered lithium transition metal oxides derived from LiMO2 (M = Co, Ni, Mn, etc.) have been widely adopted as the cathodes of Li-ion batteries for portable electronics, electric vehicles, and energy storage. Oxygen loss in the layered oxides is one of the major factors leading to cycling-induced structural degradation and its associated fade in electrochemical performance. Herein, we review recent progress in understanding the phenomena of oxygen loss and the resulting structural degradation in layered oxide cathodes. We first present the major driving forces leading to the oxygen loss and then describe the associated structural degradation resulting from the oxygen loss. We follow this analysis with a discussion of the kinetic pathways that enable oxygen loss, and then we address the resulting electrochemical fade. Finally, we review the possible approaches toward mitigating oxygen loss and the associated electrochemical fade as well as detail novel analytical methods for probing the oxygen loss.

Impact of Nickel on Next-Generation Li-Rich Oxide Cathodes for Li-Ion Batteries

As developments in lithium-ion batteries have focused on improving energy density, cycle life, and reducing cost, an important class of layered oxides with excess lithium, Li[Li,Ni,Mn,Co]O2, has been heavily studied as a next-generation electrode material. However, our limited understanding of the underlying electrochemical mechanisms hinders our ability to mitigate the negative impacts of these mechanisms, and has to date prevented commercialization. Previous studies have shown that these materials show a myriad of simultaneous mechanisms including changes in the nickel oxidation state, reversible oxygen redox accounting for capacities exceeding the theoretical limit1, oxygen gas release decreasing cycle efficiency2, as well as structural transformations leading to voltage fade3. Due to this complex mixture of electrochemical processes, model systems have been used extensively to observe these processes one at a time.This work on model systems is continued here by studying materials that show both nickel and oxygen redox but no structural transformations during cycling. This builds on work performed on Li-Fe-Sb-O and Li-Fe-Te-O where oxygen gas release was found to reduce Fe during charging of the electrode, an unexpected observation that has not been seen in other materials until the present study4. Given that nickel, and not iron, is of interest for next-generation materials, herein we use Li-Ni-Sb-O and Li-Ni-Te-O as model systems to better understand the electrochemical consequences of combining Ni and O redox processes during cycling. Herein, we show extensive electrochemical tests, ex-situ powder X-ray diffraction, online electrochemical mass spectrometry, X-ray absorption near-edge spectroscopy (XANES) and X-ray photoemission spectroscopy (XPS). Results show limited oxygen release takes place from the particle surfaces only, coupled with a marked contrast between the nickel oxidation states at the surface (as seen by XPS) and those of the bulk of the particles (seen with XANES). XPS data also demonstrates a reduction of surface nickel during oxygen gas release, confirming that the mechanism identified with Li-Fe-Sb-O does in fact occur in Ni-containing materials, though this is limited to the particle surface. Despite this surface effect, the reversibility of the nickel in the bulk is lost resulting in poor long-term cycling. Given that a great deal of work is currently being done to maximize the amount of nickel in next-generation electrode material, the consequences of nickel use in Li-rich oxides observed here are of high importance to further our understanding of these important materials.

High Pressure Effect on Structural and Electrochemical Properties of Anionic Redox-Based Lithium Transition Metal Oxides

Summary The richness of anionic redox chemistry in the solid state offers new opportunities and a possible paradigm shift in energy storage. The excess capacity that goes beyond conventional theoretical values is attributed to the anionic redox in Li-rich transition metal oxide cathodes for Li-ion batteries. Their electrochemical behavior is thermodynamically determined by structural evolution. To better understand the electrochemical dependence on structural factors, we have induced structural modifications in pristine and electrochemically activated Li1.144Ni0.136Co0.136Mn0.544O2 through high-pressure treatment. A unique cyclical change of structural reordering is observed in the anionic redox-activated material during operando pressure sweep, characterized by a periodic evolution of superlattice peak intensity in synchrotron X-ray diffraction patterns. During the structural reordering period, the bulk compressibility of the material decreases, even becoming negative. These insights elucidate the structural flexibility and metastability of anionic redox-based materials, which can undergo large compressions and structural modifications while delivering good electrochemical properties.

Impact of Nickel on Next-Generation Li-Rich Oxide Cathodes for Li-Ion Batteries

As developments in lithium-ion batteries have focused on improving energy density, cycle life, and reducing cost, an important class of layered oxides with excess lithium, Li[Li,Ni,Mn,Co]O2, has been heavily studied as a next-generation electrode material. However, our limited understanding of the underlying electrochemical mechanisms hinders our ability to mitigate the negative impacts of these mechanisms, preventing commercialization. Previous studies have shown that these materials show a myriad of simultaneous mechanisms including changes in the nickel oxidation state, reversible oxygen redox accounting for capacities exceeding the theoretical limit1, oxygen gas release decreasing cycle efficiency2, as well as structural transformations leading to voltage fade3. Due to this complex mixture of electrochemical processes, model systems have been used extensively to observe these processes one at a time.This work on model systems is continued here by studying materials that show both nickel and oxygen redox but no structural transformations during cycling. This builds on work performed on Li-Fe-Sb-O and Li-Fe-Te-O where oxygen gas release was found to reduce Fe during charging of the electrode, an unexpected observation that had not been seen in other materials4. Given the use of nickel rather than iron in next-generation materials, herein we use Li-Ni-Sb-O and Li-Ni-Te-O as model systems to better understand the electrochemical contribution of Ni and O during cycling. The materials have been studied using extensive electrochemical tests, ex-situ powder X-ray diffraction, online electrochemical mass spectrometry, X-ray absorption near-edge spectroscopy and X-ray photoemission spectroscopy. Results show limited oxygen release from the particle surfaces only, coupled with a marked contrast between the nickel oxidation states at the surface (XPS) and those of the bulk of the particles (XANES). XPS data also demonstrates a slight reduction in surface nickel during oxygen gas release, confirming that the mechanism identified with Li-Fe-Sb-O does in fact occur in Ni-containing materials, though this is limited to the particle surface. Given that a great deal of work is currently being done to maximize the amount of nickel in next-generation electrode material, the consequences of nickel use in Li-rich oxides observed here are of high importance to further our understanding of the limitations of these materials that are currently preventing their commercialization. 1. McCalla, E. et al, Science 2015, 350 (6267), 1516.2. Jung, R. et al, Journal of The Electrochemical Society 2017, 164 (7), A1361-A1377.3. Gallagher, K. G et al, Electrochemistry Communications 2013, 33, 96-98.4. McCalla, E. et al, Journal of the American Chemical Society 2015, 137 (14), 4804-4814.

Correction: Identifying the anionic redox activity in cation-disordered Li1.25Nb0.25Fe0.50O2/C oxide cathodes for Li-ion batteries

Correction for ‘Identifying the anionic redox activity in cation-disordered Li1.25Nb0.25Fe0.50O2/C oxide cathodes for Li-ion batteries’ by Mingzeng Luo et al., J. Mater. Chem. A, 2020, 8, 5115–5127, DOI: 10.1039/C9TA11739C.

Layered Oxide Cathodes for Li-Ion Batteries: Oxygen Loss and Vacancy Evolution

Loss of oxygen in layered transition-metal oxides is a major reason for the structural degradation and thus the fade of electrochemical performance in the cathodes for Li-ion batteries. Via in situ...

Origin of charge compensation and its effect on the stability of oxide cathodes for Li-ion batteries: The case of orthosilicates

The charge-compensation mechanism and host stability of a cathode play the central role in determining its reversible capacity. Here, first-principle calculations are presented to study the charge compensation and its effect on the stability of orthosilicates, Li2−xTMSiO4 (TM = Fe, Mn), as the promising high-capacity cathode materials for Li-ion batteries. The charge compensation in Li2−xTMSiO4 upon delithiation is found to be achieved first by a combined reversible TM and oxygen redox process, originating from the dynamic response of their electronic structures to the Li ions (or electrons) removal and the associated charge transfer from the O to Fe ions, and then by the irreversible formation of O vacancy (VO) that destroys the host stability of these materials. Whether the formation of VO in these materials upon delithiation would occur is demonstrated to be essentially determined by the energy level of their highest occupied electronic states and can be understood by the defect charge transition mechanism which provides a quantitative way to estimate to what extent the oxygen redox could be reversibly used in a cathode that being important for the future design of high-capacity cathode materials.

Formation of an Anti-Core–Shell Structure in Layered Oxide Cathodes for Li-Ion Batteries

The layered → rock-salt phase transformation in the layered dioxide cathodes for Li-ion batteries is believed to result in a “core–shell” structure of the primary particles, in which the core region remains as the layered phase while the surface region undergoes a phase transformation to the rock-salt phase. Using transmission electron microscopy, here we demonstrate the formation of an “anti-core–shell” structure in cycled primary particles with a formula of LiNi0.80Co0.15Al0.05O2, in which the surface and subsurface regions remain as the layered structure while the rock-salt phase forms as domains in the bulk with a thin layer of the spinel phase between the rock-salt core and the skin of the layered phase. Formation of this anti-core–shell structure is attributed to oxygen loss at the surface that drives the migration of oxygen from the bulk to the surface, thereby resulting in localized areas of significantly reduced oxygen levels in the bulk of the particle, which subsequently undergoes phase transfo...

A review of Ni-based layered oxides for rechargeable Li-ion batteries

This article reviews Ni-based layered oxide cathodes for Li-ion batteries, primarily from a materials design perspective.

Understanding the Degradation Mechanism of Lithium Nickel Oxide Cathodes for Li-Ion Batteries.

The phase transition, charge compensation, and local chemical environment of Ni in LiNiO2 were investigated to understand the degradation mechanism. The electrode was subjected to a variety of bulk and surface-sensitive characterization techniques under different charge-discharge cycling conditions. We observed the phase transition from the original hexagonal H1 phase to another two hexagonal phases (H2 and H3) upon Li deintercalation. Moreover, the gradual loss of H3-phase features was revealed during the repeated charges. The reduction in Ni redox activity occurred at both the charge and the discharge states, and it appeared both in the bulk and at the surface over the extended cycles. The degradation of crystal structure significantly contributes to the reduction of Ni redox activity, which in turn causes the cycling performance decay of LiNiO2.

Identifying the redox activity of cation-disordered Li-Fe-V-Ti oxide cathodes for Li-ion batteries.

Cation-disordered oxides have recently shown promising properties on the way to explore high-performance intercalation cathode materials for rechargeable Li-ion batteries. Here, stoichiometric cation-disordered Li2FeVyTi1-yO4 (y = 0, 0.2, 0.5) nanoparticles are studied. The substitution of V for Ti in Li2FeVyTi1-yO4 increases the content of active transition metals (Fe and V) and accordingly the amount of Li(+) (about (1 + y)Li(+) capacity per formula unit) that can be reversibly intercalated. It is found that Fe(3+)/Fe(2+) and V(4+)/V(3+) redox couples contribute to the overall capacity performance, whereas Ti(4+) remains mainly inert. There is no evidence for the presence of Fe(4+) species after charging to 4.8 V, as confirmed from the ex situ(57)Fe Mössbauer spectroscopy and the Fe K-edge absorption spectra. The redox couple reactions for iron and vanadium are examined by performing in situ synchrotron X-ray absorption spectroscopy. During charging/discharging, the spectral evolution of the K-edges for Fe and V confirms the reversible Fe(3+)/Fe(2+) and V(4+)/V(3+) redox reactions during cycling between 1.5 and 4.8 V.

The Effect of Ni Oxidation State on Li-Rich Layered Oxides

Li-rich layered oxides (LLO) are being studied intensively as an upgrade over current layered oxide cathodes for Li-ion batteries due to their increased discharge capacity.1 There are several issues, however, that need to be overcome before LLO can be adopted for commercial use. One of the largest issues is the voltage decay and the subsequent energy decrease, which is caused by the slow transformation of the layered phase into a 3 V spinel-like phase, which occurs due to Mn4+ ions being reduced to Mn3+ during cycling.2 It has recently been reported that incorporating Ni3+ ions into LLO and reducing the Mn4+ content can suppress the voltage decay.3 Our study uses a systematic approach to investigate the effect of Ni3+ ions on LLO with the series Li1.2Mn0.6-x Ni0.2+x O2 with x = 0.00, 0.02, 0.05, 0.10, 0.15, and 0.20, which produce Ni oxidation states of, respectively, 2.00+, 2.18+, 2.40+, 2.67+, 2.86+, and 3.00+. All the materials displayed the expected X-ray diffraction patterns, which consist of the R-3m structure with additional superstructure peaks due to Li/Mn ordering. The (003)/(104) peak ratio, which is a measure of cation mixing, generally decreases with increasing Ni oxidation state. This is because Ni3+ ions (0.56 Ǻ) are smaller than Ni2+ ions (0.69 Ǻ), so there is less Li/Ni cation mixing. Increasing the Ni oxidation state has several effects on the first charge-discharge cycle as well. It increases the sloping-voltage region because there are less insulating Mn4+ ions. It decreases the plateau-voltage region because a decrease in Mn4+ ions reduces the amount of Li2MnO3-like phase in the material and the decrease in Li/Ni cation mixing enhances this effect. Despite the decreased plateau-region capacity, the irreversible capacity loss (IRC) increases, which in turn causes the discharge capacity to decrease generally. The increased IRC may be caused by undesirable side reactions similar to those experienced by layered oxides with high nickel content. Figure 1(a) displays the first discharge cycle dQ/dV data, which show a large decrease in the size of the Mn4+ reduction peak at ~ 3.3 V and increase in the Ni reduction peaks at ~ 4.3 V and ~ 3.8 V, suggesting that increasing the Ni oxidation state could avoid the reduction of Mn4+. Increasing the Ni oxidation state also generally increases the cyclability of these materials. Due to the decrease in the plateau-region capacity and Mn4+ reduction that a higher Ni oxidation state causes, the conversion to the 3 V spinel-like phase is suppressed, resulting in increased cyclability. Because of these effects, the voltage decay is also reduced with increasing Ni oxidation state. Figures 1(b) and (c) show, respectively, the voltage curves for the materials at their 2nd and 40thcycles. Besides the sample with a Ni oxidation state of 2.67+, the increased Ni oxidation state decreases the voltage decay upon extended cycling. The presentation will also focus on the synthesis of another series of materials with Co in order to increase the capacity of the materials. 1. H. Yu and H. Zhou, The Journal of Physical Chemistry Letters, 4, 1268 (2013). 2. E.-S. Lee and A. Manthiram, Journal of Materials Chemistry A, 2, 3932 (2014). 3. M. N. Ates, S. Mukerjee and K. M. Abraham, Journal of The Electrochemical Society, 161, A355 (2014). Figure 1: Electrochemical data for materials with varying Ni oxidation states: (a) first discharge cycle dQ/dV data, (b) 2nd charge-discharge cycle voltage plots, and (c) 40th charge-discharge cycle voltage plots. Figure 1

Non-isothermal electrochemical model for lithium-ion cells with composite cathodes

Transition metal oxide cathodes for Li-ion batteries offer high energy density and high voltage. Composites of these materials have shown excellent life expectancy and improved thermal performance. In the present work, a comprehensive non-isothermal electrochemical model for a Lithium ion cell with a composite cathode is developed. The present work builds on lithium concentration-dependent diffusivity and thermal gradient of cathode potential, obtained from experiments. The model validation is performed for a wide range of temperature and discharge rates. Excellent agreement is found for high and room temperature with moderate success at low temperatures, which can be attributed to the low fidelity of material properties at low temperature. Although the cell operation is limited by electronic conductivity of NCA at room temperature, at low temperatures a shift in controlling process is seen, and operation is limited by electrolyte transport. At room temperature, the lithium transport in Cathode appears to be the main source of heat generation with entropic heat as the primary contributor at low discharge rates and ohmic heat at high discharge rates respectively. Improvement in electronic conductivity of the cathode is expected to improve the performance of these composite cathodes and pave way for its wider commercialization.

High Performance Oxide Cathodes for Li-ion Batteries

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