Effects of Nb doping on the performance of 0.5Li2MnO3·0.5LiNi1/3Co1/3Mn1/3O2 cathode material for lithium-ion batteries

Recent advances in lithium-rich manganese-based cathodes for high energy density lithium-ion batteries

The development of society challenges the limit of lithium-ion batteries (LIBs) in terms of energy density and safety. Lithium-rich manganese oxide (LRMO) is regarded as one of the most promising cathode materials owing to its advantages of high voltage and specific capacity (more than 250 mA h g^-1) as well as low cost. However, the problems of fast voltage/capacity fading, poor rate performance and the low initial Coulombic efficiency severely hinder its practical application. In this paper, we review the latest research advances of LRMO cathode materials, including crystal structure, electrochemical reaction mechanism, existing problems and modification strategies. In this review, we pay more attention to recent progress in modification methods, including surface modification, doping, morphology and structure design, binder and electrolyte additives, and integration strategies. It not only includes widely studied strategies such as composition and process optimization, coating, defect engineering, and surface treatment, but also introduces many relatively novel modification methods, such as novel coatings, grain boundary coating, gradient design, single crystal, ion exchange method, solid-state batteries and entropy stabilization strategy. Finally, we summarize the existing problems in the development of LRMO and put forward some perspectives on the further research.

On the disparity in reporting Li-rich layered oxide cathode materials

Lithium-rich layered oxides are considered one of the most promising cathode materials for next generation lithium-ion batteries due to their extraordinary specific capacity of over 280 mA h g^-1 and superior energy density of over 1000 W h kg^-1. Despite the excellent performance, LRLOs still suffer from low Coulombic efficiency, serious capacity/voltage decay upon cycling, voltage hysteresis, short lifespan, and poor rate capability. Driven by the thirst for high-energy-density battery technologies, various strategies have been developed to address these issues with great progress being achieved in the past several years. However, the emerging disparity among the published results severely precludes meaningful comparisons between different LRLOs and material modification strategies, which has become an impediment to the development and commercialization of LRLOs. Although the significance of standardization has been recognized in the battery community, the standardization of LRLOs is worth particular attention due to their complicated compositions and unique electrochemical properties. This perspective analyzes the underlying parameters that can cause varied and even controversial results observed in LRLOs, from the synthesis procedure to the electrochemical evaluation procedure, followed by preliminary suggestions for the standard protocols of chemical compositions, synthesis pathways, calcination conditions, electrode preparation, battery fabrication, and battery testing. Hopefully, this perspective can help build a reliable baseline for LRLO research, thus aligning the huge research effort toward the practical applications of LRLOs.

Understanding and Control of Activation Process of Lithium-Rich Cathode Materials

Lithium-rich materials (LRMs) are among the most promising cathode materials toward next-generation Li-ion batteries due to their extraordinary specific capacity of over 250 mAh g−1 and high energy density of over 1 000 Wh kg−1. The superior capacity of LRMs originates from the activation process of the key active component Li2MnO3. This process can trigger reversible oxygen redox, providing extra charge for more Li-ion extraction. However, such an activation process is kinetically slow with complex phase transformations. To address these issues, tremendous effort has been made to explore the mechanism and origin of activation, yet there are still many controversies. Despite considerable strategies that have been proposed to improve the performance of LRMs, in-depth understanding of the relationship between the LRMs’ preparation and their activation process is limited. To inspire further research on LRMs, this article firstly systematically reviews the progress in mechanism studies and performance improving attempts. Then, guidelines for activation controlling strategies, including composition adjustment, elemental substitution and chemical treatment, are provided for the future design of Li-rich cathode materials. Based on these investigations, recommendations on Li-rich materials with precisely controlled Mn/Ni/Co composition, multi-elemental substitution and oxygen vacancy engineering are proposed for designing high-performance Li-rich cathode materials with fast and stable activation processes.

Graphical abstract

The “Troika” of composition adjustment, elemental substitution, and chemical treatment can drive the Li-rich cathode towards stabilized and accelerated activation.

New Insights into the Mechanism of Enhanced Performance of Li[Ni0.8Co0.1Mn0.1]O2 with a Polyacrylic Acid-Modified Binder

A binder is an important component in lithium-ion batteries and plays a significant role in maintaining the properties of active substances. Most studies in the field of binders have only focussed on physical properties such as bonding performance. Here, a polyacrylic acid-modified binder was designed and adapted to Li[Ni_0.8Co_0.1Mn_0.1]O₂, which enhanced the electrochemical stability of Li[Ni_0.8Co_0.1Mn_0.1]O₂ from 30.2 to 66.6% (300 cycles at 1 C). We for the first time discovered that this was caused by a chemical reaction between polyacrylic acid and the residual lithium on the surface during the cycling, which formed a lithium propionic acid coating layer and maintained the stability of the layered structure.

Investigation of the structure and performance of Li[Li0.13Ni0.305Mn0.565]O2 Li-rich cathode materials derived from eco-friendly and simple coating techniques

Constructing uniform nanoceramic coating layers is a well-known challenge in the field of coating materials. Herein, Al₂O₃-coated Li[Li_0.13Ni_0.305Mn_0.565]O₂ (LLNM) Li-rich cathode materials are successfully prepared through a dry prilling coating (DPC) method. The structures and electrochemical performances of the Al₂O₃-coated products are systematically examined. Typically, the cycling stability is enhanced and voltage degradation upon cycling is reduced, benefiting from the unique and controllable nano-sized Al₂O₃ coating layer. Moreover, metal ion dissolution is avoided when using the DPC method, which is eco-friendly and suitable for large scale production.

Constructing uniform nanoceramic coating layers is a well-known challenge in the field of coating materials.

Flexible Li[Li0.2Ni0.13Co0.13Mn0.54]O2/Carbon Nanotubes/Nanofibrillated Celluloses Composite Electrode for High-Performance Lithium-Ion Battery

Rapidly-growing demand for wearable and flexible devices is boosting the development of flexible lithium ion batteries (LIBs). The exploitation of flexible electrodes with high mechanical properties and superior electrochemical performances has been a key challenge for the rapid practical application of flexible LIBs. Herein, a flexible composite electrode was prepared from the mixed solutions of Li[Li_0.2Ni_0.13Co_0.13Mn_0.54]O₂ (LLOs), carbon nanotubes(CNTs), and nanofibrillated celluloses (NFCs) via a vacuum filtration method. The resulting LLOs/CNTs/NFCs electrode delivered an initial discharge capacity of 253 mAh g⁻¹ at 0.1 C in the voltage range from 2.0 to 4.6 V, and retained a reversible capacity of 178 mAh g⁻¹ with 83% capacity retention after 100 cycles at 1 C. The LLOs/CNTs/NFCs electrode exhibited excellent flexibility along with repeated bending in the bending test. The LLOs/CNTs/NFCs electrode after bending test remained a discharge capacity of 149 mAh g⁻¹ after 100 cycles at 1 C, and the corresponding capacity retentions was 76%. The excellent electrochemical performance and high flexibility can be ascribed to the framework formed by CNTs with high conductivity and NFCs with good mechanical properties. The results imply that the as-fabricated electrode can be a promising candidate for the flexible LIBs.

Structure and electrochemical performance modulation of a LiNi0.8Co0.1Mn0.1O2 cathode material by anion and cation co-doping for lithium ion batteries

Ni-rich layered transition metal oxides show great energy density but suffer poor thermal stability and inferior cycling performance, which limit their practical application. In this work, a minor content of Co and B were co-doped into the crystal of a Ni-rich cathode (LiNi_0.8Co_0.1Mn_0.1O₂) using cobalt acetate and boric acid as dopants. The results analyzed by XRD, TEM, XPS and SEM reveal that the modified sample shows a reduced energy barrier for Li⁺ insertion/extraction and alleviated Li⁺/Ni²⁺ cation mixing. With the doping of B and Co, corresponding enhanced cycle stability was achieved with a high capacity retention of 86.1% at 1.0C after 300 cycles in the range of 2.7 and 4.3 V at 25 °C, which obviously outperformed the pristine cathode (52.9%). When cycled after 300 cycles at 5C, the material exhibits significantly enhanced cycle stability with a capacity retention of 81.9%. This strategy for the enhancement of the electrochemical performance may provide some guiding significance for the practical application of high nickel content cathodes.

Ni-rich layered transition metal oxides show great energy density but suffer poor thermal stability and inferior cycling performance, which limit their practical application.