Modification Strategy for Constructing Li Gradient Combined with Spinel Phase Coating on Li-Rich Mn-Based Materials

Double-shell Li-rich layered oxide hollow microspheres with sandwich-like carbon@spinel@layered@spinel@carbon shells as high-rate lithium ion battery cathode

Li-rich layered oxide (LRO) cathode material is utilized in anode-free Li metal batteries to provide extra Li inventory, compensating for the constant Li loss during cycling. The Li compensation mechanism of LRO in the anode-free system is elucidated by exploring the reversible/irreversible Li consumption behaviors. Moreover, the relationship between cathode areal capacity, Li inventory, and the cycling performance of the Cu||LRO cell is quantitatively analyzed. The well-designed Cu||LRO anode-free cell demonstrates 51% capacity retention after 60 cycles at a practical areal capacity of 5.0 mAh cm-2, overwhelming the 0.6% capacity retention for Cu||NCM523. Further optimization with an artificial anode protection layer and a fully fluorinated electrolyte enhances the capacity retention of Cu||LRO to 61.4% and 71.5% after 60 cycles, respectively. Combining its low initial Coulombic efficiency and high specific energy, the LRO cathode shows great prospects in the future development of high energy and long lifespan anode-free Li metal batteries.

Multi-strategy synergistic Li-rich layered oxides with fluorine-doping and surface coating of oxygen vacancy bearing CeO2 to achieve excellent cycling stability

Li-rich Mn-based layered oxides (LMLOs) are expected to be the most promising high-capacity cathodes for the next generation of lithium-ion batteries (LIBs). However, the poor cycling stability and kinetics performance of polycrystalline LMLOs restrict their practical applications due to the anisotropic lattice stress and crack propagation during cycling. Herein, B-doped micron-sized single-crystal Co-free LMLOs were obtained by molten-salt (LiNO3 and H3BO3)-assisted sintering. The results reveal that the low-melting-point molten salt can serve as liquid-phase media to improve the efficiency of atomic mass transfer and crystal nucleation and growth. The modified single-crystal LMLO cathodes can resist the accumulation of anisotropic stress and strain during the cycling and reduce interface side reactions, thus achieving excellent high-voltage stability and kinetics performance. The reversible specific capacity of the single crystals is 210.8 mAh g-1 at 1C with a voltage decay rate of 1.95 mV/cycle and up to 161.1 mAh g-1 at 10C with a capacity retention of 81.06% after 200 cycles.

Enhancing the energy densityof lithium-ion batteries (LIBs) remains a critical challenge for advancing next-generation energy storage technologies. Silicon-based anodes offer significantly higher theoretical capacitites, but their practical application is hindered by low initial coulombic efficiency (ICE), leading to substantial lithium loss and rapid full cell performance degradation. Herein, a novel prelithiation agent, lithium borate (LBO), based on the ultralight, cost-effective, and d-orbital-free non-metallic element boron (B) is presented. LBO features a core-shell architecture, consisting of a crystalline Li3BO3 core encapsulated by Li2CO3 and amorphous carbon, delivering an exceptional initial charge capacity of 692 mAh g-1 and superior atmospheric stability with 70% capacity retention after 8 days of ambient exposure. When applied in SiOx||LRLO (Li-rich layered oxide) pouch cells, LBO enhances the gravimetric and volumetric energy density by 14.7% and 21.8%, respectively, while effectively suppressing the irreversible LRLO degradation caused by Li deficiency. This work introduces an element-centric design methodology for prelithiation agents, providing a promising route to propel the development of high-energy-density LIBs.

The limited theoretical capacity of traditional cathode materials solely based on transition metal (TM) redox has been a primary factor for the ceiling placed on the energy density of LIBs. In this regard, Li-rich layered oxides (LLOs) have received a great deal of attention, due to their high reversible capacity (> 250 mAh g-1) and high energy density (900 Wh kg-1), courtesy of the TM redox and the additional high-voltage O2- redox.1, 2 Although the electrochemical performance of Co-free LLOs is significantly less satisfactory, developing Co-free cathodes is inevitably a holy grail owing to cobalt’s economic, ethical, and political issues caused by high-cost toxicity. Therefore, studies on Co-free LLOs are necessary for creating long-term benefits for the cathode industry.Unfortunately, Co-free LLOs suffer from capacity and voltage decay on cycling, which for now obviously limits the materials use outside the academics laboratory. It is well accepted that that performance decay is primarily attributed to the irreversible anionic redox and structural degradation in LLOs. The doping strategy has been widely used to address the voltage decay of LLOs.3 While the dopant is typically introduced to the layered R m component, the lithium-rich component (C2/c) in the LLOs, which is the source of anionic redox, has always been ignored.Our team comprehensively investigates the structural involution of LLOs based on a Co-free Li-rich Mn-based Li1.2Ni0.2Mn0.6O2 (LNMO) cathode using in-operando and ex-situ synchrotron-based characterizations. We learned through mechanistic characterization that the transition from the monoclinic (C2/c) to the hexagonal (R-3m) behaviour is an intrinsic behaviour of LLOs for the first time. According to this structure-function relationship, we introduced a small quantity of one electrochemically active metal, ruthenium, into both R-3m and C2/c components in LNMO and found that the oxygen lattice and structural stability can be significantly improved by the site-specific doping against lithiation and delithiation processes.4 Additionally, reducing the irreversible TM migration is key to advancing the performance of layered oxide cathode materials. Contrary to many previous studies that emphasize suppressing cation migration, our team proposed that reversible tetrahedral-octahedral TM migration helps inhibit the formation of undesirable structural changes and phase transformation. The oxidation state of TM, such as Ni, Mn, and Co, are easily trapped into the octahedral sites in the Li layer due to their high octahedral-site splitting energy when a large amount of Li has extracted from the structure. By introducing Cr into LNMO, we found that Cr can migrate reversibly between the tetrahedral and octahedral sites, which makes Cr-doped LNMO possess significantly enhanced structural stability and thus achieve higher electrochemical performance than LNMO.In all, our research focuses on the site-specific doping of the Co-free LLOs and understanding the structure- and chemistry-function relationship of the LLOs. The findings in our work might provide possible pathways for the future design of high-performance cathode materials for lithium-ion batteries and may also apply to developing cathode materials for other energy storage systems.Reference S. Hu, A. S. Pillai, G. Liang, W. K. Pang, H. Wang, Q. Li and Z. Guo, Electrochem. Energy Rev., 2019, 2, 277-311.M. Han, J. Jiao, Z. Liu, X. Shen, Q. Zhang, H.-J. Lin, C.-T. Chen, Q. Kong, W. K. Pang, Z. Guo, R. Yu, L. Gu, Z. Hu, Z. Wang and L. Chen, Adv. Energy Mater., 2020, 10, 1903634.Y. Fan, W. Zhang, Y. Zhao, Z. Guo and Q. Cai, Energy Stor. Mater., 2021, 40, 51-71.Y. Fan, E. Olsson, G. Liang, Z. Wang, A. M. D'Angelo, B. Johannessen, L. Thomsen, B. Cowie, J. Li, F. Zhang, Y. Zhao, W. K. Pang, Q. Cai and Z. Guo, Angew. Chem. Int. Ed., 2022, DOI: 10.1002/anie.202213806.

Zn/Ti dual concentration-gradients surface doping to improve the stability and kinetics for Li-rich layered oxides cathode

In-situ formed hybrid phosphates coating layer enabling co-free Li-rich layered oxides with stable cycle performance

Activation of Oxygen Redox by Inhibited Dynamic Phase Transition for High-Energy Li-Rich Layered Oxide Cathode

Layered Li-rich Mn-based oxides are believed to be a good candidate for cathode material in the next generation of lithium-ion batteries. However, they have some disadvantages, such as low initial coulombic efficiency, low rate capacity, and deficient cyclability. To overcome these shortcomings, various approaches, such as elemental doping, have been adopted. In this study, Al-doped Li1.21Mn0.54Ni0.125Co0.125O2 were successfully synthesized using the sol–gel method. Samples were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), surface-area analysis, field emission scanning electron microscopy and transmission electron microscopy (TEM). Measurements of galvanostatic charge discharge and electrochemical impedance spectroscopy were also performed to evaluate the electrochemical performance of the prepared samples. The XRD patterns showed that all the samples with the structure of 0.55Li2MnO3.0.45LiNi0.33Mn0.33Co0.33O2 had a composite material with two individual layered structures that are integrated with each other. By doping Al, the lattice parameters of the samples changed. The first discharge capacity of the Al-doped specimens was lower than that of the pristine sample. In cycling performance results, it is clear that cyclic behavior and capacity stability rate in doped samples have improved compared to the undoped sample, and in the meantime, the sample with 0.05 aluminum doping has shown the best performance. Optimal performance of the doped specimens can be related to lower load transfer resistance and better structural stability.

Engineering of surface oxygen vacancies in Co-free concentration-gradient Li-rich cathodes for high-capacity batteries

Lithium-rich manganese-based cathodes (LR) are valuable cathode materials for the next generation of lithium-ion batteries (LIBs) with high-energy density. However, the fast voltage/capacity decay on cycling is the major obstacle for the practical application induced by the less-than-ideal anionic redox reactions and structure distortion. Herein, in order to tackle these challenges, a perovskite-like La2Li0.5Co0.5O4 (LLCO) material is selected as protective surface to stabilize the Li1.2Mn0.54Ni0.13Co0.13O2 (LR) substrate through wet chemical coating method. Versatile structure/phase characterizations and electrochemical tests exhibit that the LLCO can not only minish the oxygen evolution and enhance the structure stability, but also restrain the electrolyte corrosion and increase the mechanical strength of cathode materials. Moreover, the coated LLCO with high electronic/ionic conductivity dramatically accelerates the energy storage kinetic, thereby displaying the improved rate performance. Specifically, the optimized LR@LLCO sample (1LLCO) exhibits a high capacity of 250.6 mAh·g−1 after 100 cycles at 0.1 C and excellent capacity retention of 82.6% after 200 cycles at 2 C. This work provides a new idea for the modification of LR cathodes toward commercial high-performance LIBs.

Low initial Coulombic efficiency (ICE) is an obstacle for practical application of Li-rich Mn-based layered oxides (LLOs), which is closely related with the irreversible oxygen evolution owing to the overoxidized reaction of surface labile oxygen. Here we report a NH4 F-assisted surface multicomponent integration technology to accurately control the ICE, by which oxygen vacancies, spinel-layered coherent structure, and F-doping are skillfully integrated on the surface of treated LLOs microspheres. Though the regulation on the removed amount of labile oxygen by surface integrated structure, the ICE of LLOs cathodes can adjust from starting value to 100 %. X-ray absorption spectroscopy, refined X-ray diffraction, and scanning transmission electron microscopy show that the removed labile oxygen mainly comes from Li2 MnO3 -like structure. Even operating at a high cut-off voltage of 5 V, the capacity retention of integrated sample at 200 mA g-1 is still larger than 98 % after 100 cycles.

Li-rich layered oxide (LLO) cathodes possess high theoretical capacity and voltage, but constructing cathodes with high active material fractions to achieve high energy density in all-solid-state batteries (ASSBs) remains challenging. In this work, it is demonstrated that the main limitation to electrochemical performance lies not in interfacial instability but in sluggish Li+ transport arising from intra- and interparticle voids. Intraparticle voids are found to hinder ion diffusion within polycrystalline LLO, while extensive interparticle voids are introduced in reduced-particle-size LLO due to particle aggregation under limited solid-state electrolyte content. In these aggregated domains, Li+ conduction is restricted to isolated LLO regions and the intrinsically low ionic conductivity of LLO further aggravates transport limitations. To address these issues, a composite cathode with a Li3InCl6 coating was designed to improve the interfacial contact and Li+ conduction pathways. The resulting ASSB delivers 245.2 mAh/g at 0.1 C, retains 80.9% capacity after 250 cycles at 0.3 C, and maintains 75.9 mAh/g at 5 C with only 27.5 wt % Li3InCl6. This work provides a practical cathode design strategy for realizing high-energy-density LLO-based halide ASSBs.

Enhanced long-term cyclability in Li-Rich layered oxides by electrochemically constructing a LixTM3-xO4-type spinel shell