Ni-rich layered oxides and Li-rich layered oxides are topics of much research interest as cathodes for Li-ion batteries due to their low cost and higher discharge capacities compared to those of LiCoO2 and LiMn2O4. However, Ni-rich layered oxides have several pitfalls, including difficulty in synthesizing a well-ordered material with all Ni3+ ions, poor cyclability, moisture sensitivity, a thermal runaway reaction, and formation of a harmful surface layer caused by side reactions with the electrolyte. Recent efforts towards Ni-rich layered oxides have centered on optimizing the composition and processing conditions to obtain controlled bulk and surface compositions to overcome the capacity fade. Li-rich layered oxides also have negative aspects, including oxygen loss from the lattice during first charge, a large first cycle irreversible capacity loss, poor rate capability, side reactions with the electrolyte, low tap density, and voltage decay during extended cycling. Recent work on Li-rich layered oxides has focused on understanding the surface and bulk structures and eliminating the undesirable properties. Followed by a brief introduction, an account of recent developments on the understanding and performance gains of Ni-rich and Li-rich layered oxide cathodes is provided, along with future research directions.

Nickel-Rich and Lithium-Rich Layered Oxide Cathodes: Progress and Perspectives

Over the past decade, electrochemical energy storage (EES) devices have greatly improved, as a wide variety of advanced electrode active materials and new device architectures have been developed. These new materials and devices should be evaluated against clear and rigorous metrics, primarily based on the evidence of real performances. A series of criteria are commonly used to characterize and report performance of EES systems in the literature. However, as advanced EES systems are becoming more and more sophisticated, the methodologies to reliably evaluate the performance of the electrode active materials and EES devices need to be refined to realize the true promise as well as the limitations of these fast-moving technologies, and target areas for further development. In the absence of a commonly accepted core group of metrics, inconsistencies may arise between the values attributed to the materials or devices and their real performances. Herein, we provide an overview of the energy storage devices from conventional capacitors to supercapacitors to hybrid systems and ultimately to batteries. The metrics for evaluation of energy storage systems are described, although the focus is kept on capacitive and hybrid energy storage systems. In addition, we discuss the challenges that still need to be addressed for establishing more sophisticated criteria for evaluating EES systems. We hope this effort will foster ongoing dialog and promote greater understanding of these metrics to develop an international protocol for accurate assessment of EES systems.

Towards establishing standard performance metrics for batteries, supercapacitors and beyond.

The layered nickel-rich cathode materials are considered as promising cathode materials for lithium-ion batteries (LIBs) due to their high reversible capacity and low cost. However, several significant challenges, such as the unstable powder properties and limited electrode density, hindered the practical application of the nickel-rich cathode materials with the nickel content over 80%. Herein, important stability issues and in-depth understanding of the nickel-rich cathode materials on the basis of the industrial electrode fabrication condition for the commercialization of the nickel-rich cathode materials are reviewed. A variety of factors threatening the battery safety such as the powder properties, thermal/structural stability are systemically investigated from a material point of view. Furthermore, recent efforts for enhancing the electrochemical stability of the nickel-rich cathode materials are summarized. More importantly, critical key parameters that should be considered for the high energy LIBs at an electrode level are intensively addressed for the first time. Current electrode fabrication condition has a difficulty in increasing the energy density of the battery. Finally, light is shed on the perspectives for the future research direction of the nickel-rich cathode materials with its technical challenges in current state by the practical aspect.

Prospect and Reality of Ni-Rich Cathode for Commercialization

https://iopscience.iop.org/article/10.1149/2.0351701jes/pdf

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes I. Nickel-Rich, LiNixCoyMnzO2

Solid-state batteries (SSBs) using a solid electrolyte show potential for providing improved safety as well as higher energy and power density compared with conventional Li-ion batteries. However, two critical bottlenecks remain: the development of solid electrolytes with ionic conductivities comparable to or higher than those of conventional liquid electrolytes and the creation of stable interfaces between SSB components, including the active material, solid electrolyte and conductive additives. Although the first goal has been achieved in several solid ionic conductors, the high impedance at various solid/solid interfaces remains a challenge. Recently, computational models based on ab initio calculations have successfully predicted the stability of solid electrolytes in various systems. In addition, a large amount of experimental data has been accumulated for different interfaces in SSBs. In this Review, we summarize the experimental findings for various classes of solid electrolytes and relate them to computational predictions, with the aim of providing a deeper understanding of the interfacial reactions and insight for the future design and engineering of interfaces in SSBs. We find that, in general, the electrochemical stability and interfacial reaction products can be captured with a small set of chemical and physical principles. The reliable operation of solid-state batteries requires stable or passivating interfaces between solid components. In this Review, we discuss models for interfacial reactions and relate the predictions to experimental findings, aiming to provide a deeper understanding of interface stability.

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Understanding interface stability in solid-state batteries

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes II. Lithium-Rich, xLi2MnO3⋅(1-x)LiNiaCobMncO2

Li-rich electrode materials of the family xLi2MnO3·(1−x)LiNiaCobMncO2 (a + b + c = 1) suffer a voltage fade upon cycling that limits their utilization in commercial batteries despite their extremely high discharge capacity, ≈250 mA h g−1 Li-rich, 035Li2MnO3·065LiNi035Mn045Co020O2, is exposed to NH3 at 400 °C, producing materials with improved characteristics: enhanced electrode capacity and a limited average voltage fade during 100 cycles in half cells versus Li Three main changes caused by NH3 treatment are established First, a general bulk reduction of Co and Mn is observed via X-ray photoelectron spectroscopy and X-ray absorption near edge structure Next, a structural rearrangement lowers the coordination number of CoO and MnO bonds, as well as formation of a surface spinel-like structure Additionally, Li+ removal from the bulk causes the formation of surface LiOH, Li2CO3, and Li2O These structural and surface changes can enhance the voltage and capacity stability of the Li-rich material electrodes after moderate NH3 treatment times of 1–2 h

High-Temperature Treatment of Li-Rich Cathode Materials with Ammonia: Improved Capacity and Mean Voltage Stability during Cycling

We present the results of our in situ X-ray diffraction (XRD) and Raman spectroscopy measurements for the first Li-ion extraction/insertion (charge/discharge) processes of nickel-rich Li1+x(NiyCozMnz)wO2 (0.005<x<0.03; y:z=8:1, w is nearly 1) electrodes in Li cells. These cells were of a special design that provide in situ (at-work) measurements during electrochemical polarization and can be used for regular cycling tests of practical Li-battery electrodes. By using XRD measurements, it was established that, upon Li+ extraction, these cathode materials demonstrate structural transformations of the hexagonal phase (space group R-3m) H1 to another hexagonal phase H2 (with a lower Li-ion content in the lattice) and to domains comprising both of these two phases, coexisting at potentials E≈4.2–4.3 V. The above phases differ by the a and c lattice constants, which is in agreement with literature results. Evolution of the lattice constants with the electrode potential upon charge/discharge is shown to be in correlation with the differential capacity dQ/dE versus E plots and with some Raman parameters calculated from complementary in situ studies of these cathode materials by Raman spectroscopy.

Li+‐Ion Extraction/Insertion of Ni‐Rich Li1+x(NiyCozMnz)wO2 (0.005<x<0.03; y:z=8:1, w≈1) Electrodes: In Situ XRD and Raman Spectroscopy Study

https://iopscience.iop.org/article/10.1149/2.0681506jes/pdf

Ji-Yong Shin

Papers

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes I. Nickel-Rich, LiNixCoyMnzO2

Review—Recent Advances and Remaining Challenges for Lithium Ion Battery Cathodes II. Lithium-Rich, xLi2MnO3⋅(1-x)LiNiaCobMncO2

High-Temperature Treatment of Li-Rich Cathode Materials with Ammonia: Improved Capacity and Mean Voltage Stability during Cycling

Li+‐Ion Extraction/Insertion of Ni‐Rich Li1+x(NiyCozMnz)wO2 (0.005<x<0.03; y:z=8:1, w≈1) Electrodes: In Situ XRD and Raman Spectroscopy Study

Studies of Aluminum-Doped LiNi0.5Co0.2Mn0.3O2: Electrochemical Behavior, Aging, Structural Transformations, and Thermal Characteristics