Nickel-rich Layered Cathode Research Articles

Superior Electrochemical and Kinetics Performance of LiNi0.8Co0.15Al0.05O2 Cathode by Neodymium Synergistic Modifying for Lithium Ion Batteries

The nickel-rich layered cathode material LiNi0.8Co0.15Al0.05O2 (NCA) is receiving enormous attention for its high energy density and low cost. Nevertheless, its wide application is limited by its unsatisfactory cycle performance and rate performance. In this study, the synergetic modification of the Nd2AlO3N coating and Nd3+ doping is realized to enhance the electrochemical performance of NCA. The Nd2AlO3N coating can protect the electrode-electrolyte interface and inhibit the side reactions. In the meantime, the Nd3+ doping, with the larger ion radius of Nb3+ and stronger Nd-O bond energy, can effectively enhance the kinetics performance and stabilize the crystal structure of the NCA cathode material. The modified materials with above characters demonstrate an excellent electrochemical stability and kinetics performance, among which the Nd4000 sample has the quite best performance, and its capacity/capacity retention still reach 168 mAh·g−1/91% after 200 cycles, which are distinctly higher than the pristine 144.6 mAh·g−1/78.5%. The electrochemical impedance spectra and cyclic voltammetry results also demonstrate that the charge transfer resistance and electrode polarization are suppressed with neodymium modifying during the cycle, and the lithium ion diffusion coefficient is significantly increased compared with the pristine sample.

A Novel Core-shell Structured Nickel-rich Layered Cathode Material for High-energy Lithium-ion Batteries

A Novel Core-shell Structured Nickel-rich Layered Cathode Material for High-energy Lithium-ion Batteries

Structural elucidation of the degradation mechanism of nickel-rich layered cathodes during high-voltage cycling.

Phase transition occurring during cycling plays a fundamentally important role in the cycling performance of nickel-rich cathodes. Here, splitting of two O3 phases, rather than the often observed O1 phases in the conventional LiCoO2 electrode, was discovered in LiNi0.85Co0.10Mn0.05O2 at a high-voltage region (>4.6 V). Such degradation could be mitigated via Al doping.

Ethylviologen Hexafluorophosphate as Electrolyte Additive for High-Voltage Nickel-Rich Layered Cathode

The present study demonstrates the use of ethylviologen hexafluorophosphate as an electrolyte additive for nickel-rich cathode. This additive can significantly improve the capacity retention and cycling efficiency of the Li-ion batteries. The cell with 0.2 wt % additive exhibits much-improved capacity retention compared to the cell with reference electrolyte. The LiNi0.8Mn0.1Co0.1O2/C full-cell cycled in 0.2 wt % additive exhibits obvious enhancement in its cycling stability with the capacity retention of 81.6% of its initial discharge capacity after 100 cycles. Electrochemical impedance spectroscopy studies show that the ethylviologen hexafluorophosphate additive slows down impedance rise by effectively stabilizing the solid electrolyte interface during prolonged cycling. This improved cycling performance is attributed to the formation of a stable passive layer by preferential decomposition of additive prior to the oxidative breakdown of the electrolyte solvent molecules. The effect of the additive by forming a passivation layer on cathode surface via a sacrificial decomposition reaction was evidenced by surface characterization using X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy.

A novel synthesis strategy to improve cycle stability of LiNi0.8Mn0.1Co0.1O2 at high cut-off voltages through core-shell structuring

Nickel-rich cathode materials have attracted considerable interest because of their high specific capacities, voltage ranges, and low cost. However, serious capacity attenuation and poor rate performance limit their application. This study proposes a novel strategy to improve the cycle stability of the nickel-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) layer material by designing core-shell LiNi0.8Co0.1Mn0.1O2 (CS-NCM811). CS-NCM811 is designed by the characteristic reaction between dimethylglyoxime (C4H8N2O2) and nickel ion to form Ni(C4H7N2O2)2. The CS-NCM811 is characterized with high nickel content in its core and high manganese content on its surface, leading to a high capacity and excellent cycle stability. The capacity retention of CS-NCM811 was 72.8%, much higher than that of NCM811 (47.1%) after 500 cycles at a rate of 5 C. Not only is this method a novel strategy to design high capacity cathode materials but also provides some new insights into the cycle stability of nickel-rich layered cathode materials.

Comparing Operando XRD and Dems to Investigate Metal-Substituted LiNiO2

LiNiO₂ (LNO) has been introduced as cathode active material for Li‐ion batteries in 1990 [1]. After years of intensive research, it emerged that several instability issues plague the material, so that it was abandoned in favor of isostructural metal‐substituted compounds called NCA (for lithium nickel cobalt aluminum oxide) and NCM (lithium nickel cobalt manganese oxide). These sacrifice a certain amount of specific energy in exchange for stability, durability and safety [2]. With few exceptions, NCA and NCM are nowadays the industrial standard when it comes to automotive applications. However, the continuous push towards electric cars with longer driving range is synonym, for these compounds, with increasing the nickel content (which is already beyond 80%), eventually leading back again to LiNiO₂. For this reason, we synthesized a series of LiNiO2 samples, where Ni is substituted by low amounts of other elements (< 5%). We implement a characterization strategy based on operando XRD, differential electrochemical mass spectrometry (DEMS) and ex situ TEM, enabling us to track, in real time upon battery charge and discharge (i.e., as Li is extracted/inserted from/into LNO, respectively), the evolution of the material´s crystal structure, the transformation of its surface and the evolution of gaseous products. We place particular emphasis on the behavior of LNO at high state of charge (> 4.1 V), where the transition between the hexagonal phases H2 and H3, whose unit cell volume is very different, induces significant mechanical strain in the material [3]. The H2 and H3 phases are also thermodynamically metastable [4] and decompose towards off-stoichiometric Li1-zNi1+zO2, with release of O2[5], a reaction we can observe by DEMS and TEM. With this combined strategy, we aim at understanding which element, if any, can sufficiently stabilize LNO in the charged state. Bibliography Dahn, J.R., U. Vonsacken, and C.A. Michal, Structure and Electrochemistry of Li1+-yNiO2 and a New Li2NiO2 Phase with the Ni(OH)2 Structure. Solid State Ionics, 1990. 44(1-2): p. 87-97. Myung, S.-T., et al., Nickel-Rich Layered Cathode Materials for Automotive Lithium-Ion Batteries: Achievements and Perspectives. ACS Energy Letters, 2017. 2(1): p. 196-223. Yoon, C.S., et al., Structural Stability of LiNiO2 Cycled above 4.2 V. ACS Energy Letters, 2017. 2(5): p. 1150-1155. Das, H., et al., First-Principles Simulation of the (Li–Ni–Vacancy)O Phase Diagram and Its Relevance for the Surface Phases in Ni-Rich Li-Ion Cathode Materials. Chemistry of Materials, 2017. 29(18): p. 7840-7851. Bianchini, M., et al., There and back again - The journey of LiNiO2 as cathode active material. Angew Chem Int Ed Engl, 2018: p. 10.1002/anie.201812472.

Effect of flower-like Ni(OH)2 precursors on Li+/Ni2+ cation mixing and electrochemical performance of nickel-rich layered cathode

Nickel-rich metal oxide layered cathode is the most potential material for high specific capacity Li-ion battery. However, the unstable cycle performance and undesirable rate capacity limit its further application. Herein, we propose a methodology of using nanoflakes assembled flower-like Ni(OH)2 microspheres as self-sacrificing precursors to synthesize nickel-rich layered LiNi0.8Co0.1Mn0.1O2. The morphologies of precursors have significant influences on the oxidation degree of Ni2+ during sintering, Li+/Ni2+ cation mixing and electrochemical performance of lithiation materials. The sample (NCM-NF1) synthesized through dense deposit nanoflakes assembled flower-like Ni(OH)2 precursor exhibits the best cycle stability and rate capacity among three samples. Between 2.8 V and 4.3 V, the NCM-NF1 exhibits a capacity retention of 98% after 60 cycles at 0.2 C; between 2.8 V and 4.6 V, the NCM-NF1 delivers a discharge capacity of 218.2 mA h g−1 at 0.2 C and 170.9 mA h g−1 at 5 C. The satisfactory electrochemical performance of NCM-NF1 could be attributed to the lower Li+/Ni2+ cation mixing and weaker polarization.

Dry Processed Nickel-Rich Layered Transition Metal Oxide Cathode Electrode

Lithium ion battery is a key driver for the proliferation of clean transportation. While its high energy density and operating life time are favorable, the overall cost is limiting widespread adoption. Since the first commercial lithium ion batteries produced by Sony in 1991 for consumer electronics, energy density and life time have gradually improved with the development of new electrode materials such as high capacity LiNixMnyCozO2, LiNi0.8Co0.15Al0.05O2 and silicon, and electrolyte additive such as vinylene carbonate1 and fluoroethylene carbonate2. Recently nickel-rich layered cathode and high capacity silicon anode have been incorporated into commercial lithium ion battery to further increase energy density. While electrode materials have advanced, electrode manufacturing process has largely remained the same, reaching a plateau in coating width, line speed, electrode energy density and production cost. To address these critical needs, Maxwell Technologies has developed a dry battery electrode coating technology with differentiating attributes. Maxwell’s unique solvent-free coating process used to commercialize ultracapacitors can be adapted to produce electrodes using current state-of-the-art lithium ion battery chemistries and advanced materials3-5 with advantages over conventional wet coating process. The benefits are lower CO2 emission, lower capex and opex cost, improved energy density and the ability to process moisture sensitive or reactive materials. To demonstrate these attributes, we have advanced our dry electrode process development using nickel-rich layered cathode materials to improve energy density, increase cycle life and reduce cell manufacturing cost. We have produced dry electrodes using LiNi0.6Mn0.2Co0.2O2, LiNi0.8Mn0.1Co0.1O2 and LiNi0.8Co0.15Al0.05O2 in roll-to-roll format and characterized their electrochemical performances in small and large capacity pouch cells. Dry process demonstration for prelithiated materials has also been established. This paper will report the physical properties of nickel-rich layered dry cathode film produced at the lab and pilot production level and their electrochemical performance with coating loading of 30-40mg/cm2 per coating side, which is significantly heavier than a typical wet cast electrode in the range of 20-24mg/cm2 per coating side in commercial high energy 18650 cell.

LiNi0.8Co0.15Al0.05O2 cathodes exhibiting improved capacity retention and thermal stability due to a lithium iron phosphate coating

Nickel-rich layered cathode materials for lithium ion batteries, e.g., LiNi0.8Co0.15Al0.05O2, have garnered considerable academic and industrial research interests, due to their higher specific energy and lower cost than the widely commercialized LiCoO2. To be more widely deployed in electric vehicles, Ni-rich cathodes with further improved thermal stability and energy densities need to be developed. Herein, we use an industrially viable fusion mixing method to apply LiFePO4 nanoparticles as a coating on LiNi0.8Co0.15Al0.05O2. The LiFePO4 coating helps to reduce the formation of cathode-electrolyte interface layer and the extent of cation mixing in LiNi0.8Co0.15Al0.05O2, which lowers electrochemical polarizations and charge transfer impedance. Compared to pristine LiNi0.8Co0.15Al0.05O2, the LiNi0.8Co0.15Al0.05O2- LiFePO4 composite in a full pouch cell exhibits a higher reversible capacity of 210 mAh·g−1 and capacity retention (>95% after 100 cycles) when it is charged up to 4.5 V. In situ calorimetric measurements show that the temperature rise in LiNi0.8Co0.15Al0.05O2- LiFePO4 pouch cells at higher rates (>C/2) is lower than in pristine LiNi0.8Co0.15Al0.05O2 by 10 °C. The coating strategy in this work can be applied to other nickel-rich and Li-rich cathodes.

Electrochemical Analysis of Factors Affecting the Kinetic Capabilities of an Ionic Liquid Electrolyte

As an alternative to conventional carbonate-based electrolytes, ionic liquid (IL) electrolytes exhibit several advantageous characteristics including non-flammability, negligible volatility, high electrochemical and thermal stability, and the ability to form robust yet conductive passivation layers on a number of high-energy electrode materials. However, IL electrolytes traditionally suffer from poor rate performance owing to their high viscosity and low ionic conductivity as compared to traditional electrolyte solutions. The following study will assess the kinetic capabilities of an IL electrolyte paired with a high-energy, nickel-rich layered cathode. The effects of temperature, electrode mass loading, and electrode composition are investigated in order to form an understanding of the kinetically limiting factors. Cycling tests performed at elevated temperatures not only show that IL electrolytes enable stable high-temperature operation but that elevated temperatures facilitate substantial improvements in rate capabilities. Analysis by electrochemical impedance spectroscopy ultimately illuminates a critical correlation between electrode wettability and rate performance. The trends established by this study will to help inform the optimal performance of IL electrolytes in high-rate applications.

High-Energy Nickel-Rich Layered Cathode Stabilized by Ionic Liquid Electrolyte

In order to meet the critical energy-storage challenges of the future, a next-generation lithium-ion battery will need to achieve a higher energy density and longer cycle life. While increasing the nickel content in layered LiMO2 (M = Ni, Mn, Co) significantly improves the capacity of the material, nickel-rich cathodes cycled in conventional organic electrolytes commonly suffer from crystallographic phase transformation and the growth of a resistive interfacial layer, both of which result in voltage fade and capacity degradation during cycling. However, pairing a nickel-rich cathode with an appropriate ionic liquid (IL) electrolyte enables exceptional cycling stability and energy retention. This work demonstrates how a pyrrolidinium-based IL electrolyte not only allows for cycling to higher voltages but shows a 95% energy retention and average discharge capacity of 189 mAh g−1 over 150 cycles between 3 and 4.5 V vs. Li/Li+ with a nickel-rich layered cathode. Based on electrochemical and crystallographic analyses, the exceptional performance of the cells cycled in IL is attributed to the stability of the electrode-electrolyte interfacial layer formed by the IL which protects the active material and suppresses the structural degradation commonly observed in nickel-rich cathodes.

Controllable TiO2 coating on the nickel-rich layered cathode through TiCl4 hydrolysis via fluidized bed chemical vapor deposition.

Surface coating of metal oxides is an effective approach for enhancing the capacity retention of a nickel-rich layered cathode. Current conventional coating techniques including wet chemistry methods and atomic layer deposition are restricted by the difficulty in perfectly balancing the coating quality and scale-up production. Herein, a highly efficient TiO2 coating route through fluidized bed chemical vapor deposition (FBCVD) was proposed to enable scalable and high yield synthesis of a TiO2 coated nickel-rich cathode. The technological parameters including coating time and TiCl4 supply rate were systematically studied, and thus a utility TiO2 deposition rate model was deduced, promoting the controllable TiO2 coating. The FBCVD TiO2 deposition mechanism was fundamentally analyzed based on the TiCl4 hydrolysis principle. The amorphous and uniform TiO2 coating layer is compactly attached on the particle surface, forming a classical core–shell structure. Electrochemical evaluations reveal that the TiO2 coating by FBCVD route indeed improves the capacity retention from 89.08% to 95.89% after 50 cycles.

Cyclic carbonate for highly stable cycling of high voltage lithium metal batteries

The lithium metal battery (LMB) is one of the most promising next-generation battery systems due to its ultrahigh energy density. However, problematic dendrite formation and low Coulombic efficiency (CE) greatly limit its practical application. Carbonate electrolyte solvents are still indispensable for the operation of LMBs using a transition metal oxide cathode. We determined the impact of different cyclic carbonates, which actively participate in the formation of the solid-electrolyte interface (SEI), on the stable cycling of LMBs using a nickel-rich layered cathode LiNi0.6Mn0.2Co0.2O2 (NMC622). The substitution of fluorine atoms in the cyclic carbonate profoundly enhances the stability of the lithium metal anode while fluoroalkyl and alkoxy substituents are detrimental. Cyclic carbonate trans-difluoroethylene carbonate (DFEC) was identified as a novel SEI enabler on the lithium metal anode, facilitating the formation of a protective SEI with relatively high lithium fluoride content. A Li/NMC622 cell utilizing DFEC electrolyte solvent as SEI enabler displayed a capacity retention larger than 82% after 400 cycles and an average CE of 99.95%. In contrast, the cycling retention after 400 cycles for a Li/NMC622 cell using monofluoroethylene carbonate was only 31% with an average CE of 99.73%. Other fluoroalkyl or alkoxy cyclic carbonates do not provide improved stabilization of the lithium metal anode over ethylene carbonate. The fundamental studies in this work provide critical insight for the further development of advanced electrolytes in LMBs.

Chemically-induced cathode–electrolyte interphase created by lithium salt coating on Nickel-rich layered oxides cathode

Nickel-rich layered transition metal oxides have been highlighted as advanced cathode materials; however, their poor cycling performance at elevated temperatures is a critical hurdle that limits the expansion of their applications. We propose a novel approach for the development of a chemically induced cathode–electrolyte interphase on cathodes using a lithium tetra(trimethylsilyl) borate as a functional precursor. This precursor contains a silyl-borate functional group that forms the cathode–electrolyte interphase layer via chemical reactions, which mitigates electrolyte decomposition and scavenges fluoride species. The precursor is prepared by a convenient one-step synthesis and it readily forms a nanoscale artificial cathode–electrolyte interphase layer through chemical reactions with cathode material during the mixing process used for the preparation of cathode slurries. Our first-principles calculations reveal a thermodynamically favorable reaction between lithium tetra(trimethylsilyl) borate and the fluoride species. We demonstrate that the artificial cathode–electrolyte interphase layer effectively mitigates electrolyte decomposition and the dissolution of transition metal components, thereby improving the interfacial stability of cathodes. As a result, a cell cycled with lithium tetra(trimethylsilyl) borate-modified cathode material shows comparable cycling retention at room temperature and much improved cycling performance at a high temperature after 100 cycles.

Origin of Carbon Dioxide Evolved during Cycling of Nickel-Rich Layered NCM Cathodes.

Gas formation caused by parasitic side reactions is one of the fundamental concerns in state-of-the-art lithium-ion batteries because gas bubbles might block local parts of the electrode surface, hindering lithium transport and leading to inhomogeneous current distributions. Here, we elucidate on the origin of CO2, which is the dominant gaseous species associated with the layered lithium nickel cobalt manganese oxide (NCM) cathode, by implementing isotope labeling and electrolyte substitution in differential electrochemical mass spectrometry-differential electrochemical infrared spectroscopy measurements. Li2CO3 on the NCM surface was successfully labeled with 13C via a process that involves its removal followed by intentional growth. In situ gas analytics on such NCM samples with 13C-labeled Li2CO3 clearly indicate that Li2CO3 decomposition contributes to CO2 evolution, especially during the first charge. At the same time, the greater contribution of electrolyte decomposition was indicated by the large amount of 12CO2 observed. Employment of butyronitrile as the electrolyte solvent in further measurements helped determine that the majority of electrolyte decomposition occurs via a reaction that involves the lattice oxygen of NCM.

Accelerated Evolution of Surface Chemistry Determined by Temperature and Cycling History in Nickel-Rich Layered Cathode Materials.

Nickel-rich layered cathode materials have the potential to enable cheaper and higher energy lithium ion batteries. However, these materials face major challenges (e.g., surface reconstruction, microcracking, potential oxygen evolution) that can hinder the safety and cycle life of lithium ion batteries. Many studies of nickel-rich materials have focused on ways to improve performance. Understanding the effects of temperature and cycling on the chemical and structural transformations is essential to assess the performance and suitability of these materials for practical battery applications. The present study is focused on the spectroscopic analysis of surface changes within a strong performing LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material. We found that surface chemical and structural transformations (e.g., gradient metal reduction, oxygen loss, reconstruction, dissolution) occurred quicker and deeper than expected at higher temperatures. Even at lower temperatures, the degradation occurred rapidly and eventually matched the degradation at high temperatures. Despite these transformations, our performance results showed that a better performing nickel-rich NMC is possible. Establishing relationships between the atomic, structural, chemical, and physical properties of cathode materials and their behavior during cycling, as we have done here for NMC811, opens the possibility of developing lithium ion batteries with higher performance and longer life. Finally, our study also suggests that a separate, systematic, and elaborate study of surface chemistry is necessary for each NMC composition and electrolyte environment.

Stabilization of Nickel-Rich Layered Cathode Materials of High Energy Density by Ca Doping

Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. LixCoO2 has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase LiNixMnyCo1-x-yO2 (NMC, both x and y 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound Li(Ni0.83Co0.12Mn0.05)O2, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

Electrochemical Performance of Dry Battery Electrode

Li ion battery has been a key research and development topic in energy storage industry in past decade because of considerable consumer demand and market growth including consumer electronics and transportation. A significant effort is focused on development of new chemistry of battery materials such as nickel-rich layered cathode and high capacity silicon anode. Unlike recently reported solvent-free electrode manufacturing variants such as electrostatic spray coating1, dry powder painting2 and isothermal hot-pressing3, Maxwell Technologies unique heritage solvent-free dry electrode process4 used to commercialized Ultracapacitor electrodes can be adapted to existing lithium ion battery chemistries and advanced materials. Maxwell dry electrode manufacturing demonstrative benefits over conventional slurry wet coating process includes, (i)environmentally benign due to elimination of toxic solvent, (ii) lower cost by reducing capital and operating expenditures, resulting from elimination of solvent recovery and recycling system, (iii) improved energy and power density afforded by unique dense high loading electrode microstructures. Maxwell Technologies has applied its proprietary dry electrode process to produced lithium ion battery cathode and anode electrode with unparalleled energy density and enhance cycle life over conventional wet coated electrodes. We have demonstrated dry robust process capability, incorporating current and advanced chemistries such as graphite, silicon, metal alloy, and nickel-rich layered transition metal oxides. In addition, we have demonstrated roll-to-roll dry process scalability using common and advanced battery material chemistries. This paper presents physical properties of self-supporting dry electrode film and electrochemical performance of dry battery electrode in half cell and full cell. We will share electrochemical performance of dry battery electrode produced at the lab-level and pilot-level in single layer pouch cell as well as multilayer stacked pouch cell platform with capacity raging from about 200mAh to about 15Ah.

Multifunctional NiTiO3nanocoating fabrication based on the dual-Kirkendall effect enabling a stable cathode/electrolyte interface for nickel-rich layered oxides

A novel multifunctional NiTiO3nanocoating is fabricated based on the dual-Kirkendall effect, enabling high cyclability and rate capability for nickel-rich layered cathode material.

Spray pyrolysis synthesis of nickel-rich layered cathodes LiNi1−2xCoxMnxO2 (x = 0.075, 0.05, 0.025) for lithium-ion batteries

In this study we report a series of nickel-rich layered cathodes LiNi1−2xCoxMnxO2 (x = 0.075, 0.05, 0.025) prepared from chlorides solution via ultrasonic spray pyrolysis. SEM images illustrate that the samples are submicron-sized particles and the particle sizes increase with the increase of Ni content. LiNi0.85Co0.075Mn0.075O2 delivers a discharge capacity of 174.9 mAh g−1 with holding 93% reversible capacity at 1 C after 80 cycles, and can maintain a discharge capacity of 175.3 mAh g−1 at 5 C rate. With increasing Ni content, the initial specific capacity increases while the cycling and rate performance degrades in some extent. These satisfying results demonstrate that spray pyrolysis is a powerful and efficient synthesis technology for producing Ni-rich layered cathode (Ni content > 80%).