Nd2O3 encapsulation-assisted surface passivation of Ni-rich LiNi0.8Co0.1Mn0.1O2 active material and its electrochemical performance

Surface Modification on Nickel Rich Cathode Materials for Lithium-Ion Cells: A Mini Review

Nickel-rich (Ni-rich) layered oxides are considered as the most promising cathode candidates for lithium-ion cells owing to their high theoretical specific capacity. However, the higher nickel content endows structural deformation through unwanted phase transitions and parasitic side reactions that lead to capacity fading upon prolonged cycling. Hence, a deep understanding of the chemistry and structural behaviour is essential for developing Ni-rich Lithium Nickel Cobalt Manganese oxide (NCM) cathode-based high-energy batteries. The present review focuses on the different challenges associated with Ni-rich NCM materials and surface modification as a strategy to solve the issues associated with NCM materials, assessment of several coating materials, and the recent developments in the surface modification of Ni-rich NCMs, with an in-depth discussion on the impact of coating on the degradation mechanism.

Quantifying Dissolved Transition Metals in Battery Electrolyte Solutions with NMR Paramagnetic Relaxation Enhancement

Transition metal dissolution is an important contributor to capacity fade in lithium-ion cells. NMR relaxation rates are proportional to the concentration of paramagnetic species, making them suitable to quantify dissolved transition metals in battery electrolytes. In this work, ⁷Li, ³¹P, ¹⁹F, and ¹H longitudinal and transverse relaxation rates were measured to study LiPF₆ electrolyte solutions containing Ni²⁺, Mn²⁺, Co²⁺, or Cu²⁺ salts and Mn dissolved from LiMn₂O₄. Sensitivities were found to vary by nuclide and by transition metal. ¹⁹F (PF₆^-) and ¹H (solvent) measurements were more sensitive than ⁷Li and ³¹P measurements due to the higher likelihood that the observed species are in closer proximity to the metal center. Mn²⁺ induced the greatest relaxation enhancement, yielding a limit of detection of ∼0.005 mM for ¹⁹F and ¹H measurements. Relaxometric analysis of a sample containing Mn dissolved from LiMn₂O₄ at ∼20 °C showed good sensitivity and accuracy (suggesting dissolution of Mn²⁺), but analysis of a sample stored at 60 °C showed that the relaxometric quantification is less accurate for heat-degraded LiPF₆ electrolytes. This is attributed to degradation processes causing changes to the metal solvation shell (changing the fractions of PF₆^-, EC, and EMC coordinated to Mn²⁺), such that calibration measurements performed with pristine electrolyte solutions are not applicable to degraded solutions-a potential complication for efforts to quantify metal dissolution during operando NMR studies of batteries employing widely-used LiPF₆ electrolytes. Ex situ nondestructive quantification of transition metals in lithium-ion battery electrolytes is shown to be possible by NMR relaxometry; further, the method's sensitivity to the metal solvation shell also suggests potential use in assessing the coordination spheres of dissolved transition metals.

Enhanced electrochemical performance of cobalt oxide layers coated LiNi0.8Co0.1Mn0.1O2 by polyvinylpyrrolidone-assisted method cathode for Li-ion batteries

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) stands out among many cathode materials for lithium-ion batteries due to its high energy density. However, the Li-Ni mixing phenomenon and the side reactions between the active cathode material and the electrolyte during the charging and discharging process have hindered its commercial application. Co₃O₄ is a transition metal oxide with a spinel structure that can provide Li⁺ embedding sites for NCM811 and is considered a competitive coating material. Here, we use polyvinylpyrrolidone (PVP) as the assisting material and Co(NO₃)₂·6H₂O as the cobalt source to form a uniform and continuous Co₃O₄ coating on the surface the of NCM811 by a simple wet chemical method. The formed coating can avoid direct contact between NCM811 and the electrolyte, enhance the structural stability of the material surface, and reduce the polarization of the electrode during cycling. The experimental results demonstrate that the performance of the modified cathode materials is higher than that of NCM811, with a higher initial specific capacity (183.59 mAh·g^-1 at 0.1C), specific capacity (151.10 mAh·g^-1 at 2C) and cycle performance. The performances are better than those of many oxide coating materials at this research stage and provide a potential solution for the practical application of NCM811 lithium-ion batteries that provide high energy.

Lithium-Ion Battery Operation, Degradation, and Aging Mechanism in Electric Vehicles: An Overview

Understanding the aging mechanism for lithium-ion batteries (LiBs) is crucial for optimizing the battery operation in real-life applications. This article gives a systematic description of the LiBs aging in real-life electric vehicle (EV) applications. First, the characteristics of the common EVs and the lithium-ion chemistries used in these applications are described. The battery operation in EVs is then classified into three modes: charging, standby, and driving, which are subsequently described. Finally, the aging behavior of LiBs in the actual charging, standby, and driving modes are reviewed, and the influence of different working conditions are considered. The degradation mechanisms of cathode, electrolyte, and anode during those processes are also discussed. Thus, a systematic analysis of the aging mechanisms of LiBs in real-life EV applications is achieved, providing practical guidance, methods to prolong the battery life for users, battery designers, vehicle manufacturers, and material recovery companies.

Nickel-Rich Layered Cathode Materials for Lithium-Ion Batteries

Nickel-rich layered transition metal oxides are considered as promising cathode candidates to construct next-generation lithium-ion batteries to satisfy the demands of electrical vehicles, because of the high energy density, low cost, and environment friendliness. However, some problems related to rate capability, structure stability, and safety still hamper their commercial application. In this Review, beginning with the relationships between the physicochemical properties and electrochemical performance, the underlying mechanisms of the capacity/voltage fade and the unstable structure of Ni-rich cathodes are deeply analyzed. Furthermore, the recent research progress of Ni-rich oxide cathode materials through element doping, surface modification, and structure tuning are summarized. Finally, this review concludes by discussing new insights to expand the field of Ni-rich oxides and promote practical applications.

Bifunctional Surface Coating of LiNbO3 on High-Ni Layered Cathode Materials for Lithium-Ion Batteries

High-Ni cathode materials with a layered structure generally suffer from structural instability induced by a highly reactive Ni component, especially at the surface. Crystalline LiNbO₃, with excellent thermal stability and ionic conductivity, has the potential to considerably enhance the interfacial stability of these cathode materials. By optimizing the crystalline coating of bifunctional LiNbO₃ on a high-Ni cathode material, we are able to improve cycle performance and rate capability by minimizing the direct exposure of Ni with electrolytes. Since a LiNbO₃ coating layer directly affects electrochemical performance, we also focus on the correlation of LiNbO₃ crystallinity with electrochemical behaviors of Li⁺ in the cathode materials. We show that the Li⁺ conducting behaviors are closely related to the crystallinity of LiNbO₃. Highly crystalline LiNbO₃ effectively suppresses the structural changes of the cathode materials by facilitating strain relaxation induced by repeated Li⁺ intercalation and deintercalation into and from the host structure. Moreover, it offers strong enhancement in mechanical and thermal stabilities at elevated temperatures above 60 °C. In this regard, this research provides a practical solution for successfully utilizing high-Ni layered cathode materials in commercial LIBs.

Synthesis of a fine LiNi0.88Co0.09Al0.03O2 cathode material for lithium-ion batteries via a solvothermal route and its improved high-temperature cyclic performance

Nickel–Cobalt–Aluminum (NCA) cathode materials for lithium-ion batteries (LIBs) are conventionally synthesized by chemical co-precipitation. However, the co-precipitation of Ni²⁺, Co²⁺, and Al³⁺ is difficult to control because the three ions have different solubility product constants. This study proposes a new synthetic route of NCA, which allows fabrication of fine and well-constructed NCA cathode materials by a high temperature solid-state reaction assisted by a fast solvothermal process. The capacity of the LiNi_0.88Co_0.09Al_0.03O₂ as-synthesized by the solvothermal method was 154.6 mA h g⁻¹ at 55 °C after 100 cycles, corresponding to 75.93% retention. In comparison, NCA prepared by the co-precipitation method delivered only 130.3 mA h g⁻¹ after 100 cycles, with a retention of 63.31%. Therefore, the fast solvothermal process-assisted high temperature solid-state method is a promising candidate for synthesizing high-performance NCA cathode materials.

Nickel–Cobalt–Aluminum (NCA) cathode materials for lithium-ion batteries (LIBs) are conventionally synthesized by chemical co-precipitation.