Spinel/Layered Heterostructured Lithium-Rich Oxide Nanowires as Cathode Material for High-Energy Lithium-Ion Batteries

Ni/Mg Dual Concentration-Gradient Surface Modification to Enhance Structural Stability and Electrochemical Performance of Li-Rich Layered Oxides

Li-rich layered oxides (LRLOs), with the advantages of high specific capacity and low cost, are considered as candidates for the next-generation cathode of lithium-ion batteries (LIBs). Unfortunately, sluggish kinetics and interfacial degradation lead to capacity loss and voltage decay of the material during cycling. To address these issues, we propose a Ni/Mg dual concentration-gradient modification strategy for LRLOs. From the center to the surface of the modified materials, the contents of Ni and Mg are gradually increased while the content of Mn is decreased. The high Ni content on the surface increases the proportion of cationic redox, elevating the operating voltage and accelerating reaction kinetics. Moreover, the doped Mg on the surface of the material acting as a stabilizing pillar suppresses the migration of transition metals, stabilizing the layered structure. Therefore, the material with the Ni/Mg dual concentration-gradients delivers a superior electrochemical performance, exhibiting a suppressed voltage decay of 2.8 mV per cycle during 200 cycles (1 C, 2-4.8 V) and an excellent rate capability of 94.84 mAh/g at 7C. This study demonstrates a synergic design to construct high-performance LRLO cathode materials for LIBs.

Dual Strategies with Anion/Cation Co-Doping and Lithium Carbonate Coating to Enhance the Electrochemical Performance of Lithium-Rich Layered Oxides

Lithium-rich layered oxides (LLOs, Li1.2 Mn0.54 Ni0.13 Co0.13 O2 ) are widely used as cathode materials for lithium-ion batteries due to its high specific capacity, high operating voltage and low cost. However, the LLOs are faced with rapid decay of charge/discharge capacity and voltage, as well as interface side reactions, which limit its electrochemical performance. Herein, the dual strategies of sulfite/sodium ion co-doping and lithium carbonate coating were used to improve it. It founds that modified LLOs achieve 88.74 % initial coulomb efficiency, 295.3 mAh g-1 first turn discharge capacity, in addition to 216.9 mAh g-1 at 1 C, and 87.23 % capacity retention after 100 cycles. Mechanism research indicated that the excellent electrochemical performance benefits from the doping of both Na+ and SO3 2- , and it could significantly reduce the migration energy barrier of Li+ and promote Li+ migration. Meanwhile, anion and cation are co-doped greatly reduces the band gap of LLOs and increase its electrical conductivity, and its binding effect on Li+ is weakened, making it easier for Li+ to shuttle through the material. In addition, the lithium carbonate coating significantly inhibits the occurrence of interfacial side reactions of LLOs. This work provides a theoretical basis and practical guidance for the further development of LLOs with higher electrochemical performance.

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.

Challenges and Recent Advances in High Capacity Li-Rich Cathode Materials for High Energy Density Lithium-Ion Batteries

Li-rich cathode materials have attracted increasing attention because of their high reversible discharge capacity (>250 mA h g^-1 ), which originates from transition metal (TM) ion redox reactions and unconventional oxygen anion redox reactions. However, many issues need to be addressed before their practical applications, such as their low kinetic properties and inefficient voltage fading. The development of cutting-edge technologies has led to cognitive advances in theory and offer potential solutions to these problems. Herein, a recent in-depth understanding of the mechanisms and the frontier electrochemical research progress of Li-rich cathodes are reviewed. In addition, recent advances associated with various strategies to promote the performance and the development of modification methods are discussed. In particular, excluding Li-rich Mn-based (LRM) cathodes, other branches of the Li-rich cathode materials are also summarized. The consistent pursuit is to obtain energy storage devices with high capacity, reliable practicability, and absolute safety. The recent literature and ongoing efforts in this area are also described, which will create more opportunities and new ideas for the future development of Li-rich cathode materials.

Rate Performance Modification of a Lithium-Rich Manganese-Based Material through Surface Self-Doping and Coating Strategies

Lithium-rich manganese-based materials are currently considered to be highly promising cathode materials for next-generation lithium-ion batteries due to their high specific capacity (>250 mA h g^-1) and low cost. A key challenge for the commercialization of these lithium-rich manganese-based materials is their poor rate performance, which is caused by the low electronic conductivity and increasing interface charge transfer resistance produced by the side reaction during the cycling procedure. In this work, we try to improve the rate performance of a lithium-rich manganese-based material Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ using a collaborative approach with Co-doping and Na_xCoO₂-coating methods. Cobalt doping can improve the electronic conductivity, and Na_xCoO₂ coating provides a convenient lithium-ion diffusion channel and moderately alleviates the inevitable decrease in cycling stability caused by cobalt doping. Under the synergistic effect of these two modification strategies, the surface and internal dynamics of the Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ material are enhanced and its rate performance is considerably improved without decay of the cycle stability.

Promoting the Reversible Oxygen Redox Reaction of Li-Excess Layered Cathode Materials with Surface Vanadium Cation Doping

Li-excess layered cathode (LLC) materials have a high theoretical specific capacity of 250 mAh g-1 induced by transition metal (cationic) and oxygen (anionic) redox activity. Especially, the oxygen redox reaction related to the activation of the Li2MnO3 domain plays the crucial role of providing a high specific capacity. However, it also induces an irreversible oxygen release and accelerates the layered-to-spinel phase transformation and capacity fading. Here, it is shown that surface doping of vanadium (V5+) cations into LLC material suppresses both the irreversible oxygen release and undesirable phase transformation, resulting in the improvement of capacity retention. The V-doped LLC shows a high discharge capacity of 244.3 ± 0.8 mAh g-1 with 92% retention after 100 cycles, whereas LLC delivers 233.6 ± 1.1 mAh g-1 with 74% retention. Furthermore, the average discharge voltage of V-doped LLC drops by only 0.33 V after 100 cycles, while LLC exhibits 0.43 V of average discharge voltage drop. Experimental and theoretical investigations indicate that doped V-doping increase the transition metal-oxygen (TM-O) covalency and affect the oxidation state of peroxo-like (O2) n - species during the delithiation process. The role of V-doping to make the oxygen redox reversible in LLC materials for high-energy density Li-ion batteries is illustrated here.

O2-Type Li0.78[Li0.24Mn0.76]O2 Nanowires for High-Performance Lithium-Ion Battery Cathode

Continued improvement in the electrochemical performance of Li-Mn-O oxide cathode materials is key to achieving advanced low-cost Li-ion batteries with high energy densities. In this study, O2-type Li_0.78[Li_0.24Mn_0.76]O₂ nanowires were synthesized by a solvothermal reaction to produce P2-type Na_5/6[Li_1/4Mn_3/4]O₂ nanowires, which were then subjected to molten salt Li-ion exchange. The resulting nanowires have diameters less than 20 nm and lengths of several micrometers. The full-Mn-based nanowires cathode material delivers a reversible capacity of 275 mAh g^-1 at 0.1 C and 200 mAh g^-1 at a high current rate of 15 C with a capacity retention of more than 80% and the voltage decay was dramatically suppressed after 100 cycles. This excellent performance is ascribed to the highly stable oxygen redox reaction and lack of layered-to-spinel phase transition in the O2-type structure during cycling.

Al2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 nanotubes as cathode materials for high-performance lithium-ion batteries

Li-rich manganese-based layered cathode Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCO) nanotubes are synthesized by electrospinning and surface coated with different amounts of amorphous Al₂O₃.

Improved Electrochemical Performances of LiCoO2 at Elevated Voltage and Temperature with an In Situ Formed Spinel Coating Layer

Although various cathode materials have been explored to improve the energy density of lithium-ion batteries, LiCoO₂ is still the first choice for 3C consumer electronics due to the high tap density and high volumetric energy density. However, only 0.5 mol of lithium ions can be extracted from LiCoO₂ to avoid side reactions and irreversible structure change, which typically occur at high voltage (>4.2 V). To improve the electrochemical performances of the LiCoO₂ cathode material at high cut-off voltage and elevated temperature for higher energy density, an in situ formed spinel interfacial coating layer of LiCo _xMn_{2- x}O₄ is achieved by the reaction of the surface region of the LiCoO₂ host. The capacity retention of the modified LiCoO₂ cycled at a high voltage of 4.5 V is significantly increased from 15.5 to 82.0% after 300 cycles at room temperature, due to the stable spinel interfacial inhibiting interfacial reactions between LiCoO₂ and the electrolyte as confirmed by impedance spectroscopy. We further demonstrated that LiCoO₂ with the spinel interfacial layer also exhibits an excellent cycling stability at a high temperature of 45 °C.

Effects of Nanofiber Architecture and Antimony Doping on the Performance of Lithium-Rich Layered Oxides: Enhancing Lithium Diffusivity and Lattice Oxygen Stability

Li-rich layered oxides (LLOs) with high specific capacities are favorable cathode materials with high-energy density. Unfortunately, the drawbacks of LLOs such as oxygen release, low conductivity, and depressed kinetics for lithium ion transport during cycling can affect the safety and rate capability. Moreover, they suffer severe capacity and voltage fading, which are major challenges for the commercializing development. To cure these issues, herein, the synthesis of high-performance antimony-doped LLO nanofibers by an electrospinning process is put forward. On the basis of the combination of theoretical analyses and experimental approaches, it can be found that the one-dimensional porous micro-/nanomorphology is in favor of lithium-ion diffusion, and the antimony doping can expand the layered phase lattice and further improve the lithium ion diffusion coefficient. Moreover, the antimony doping can decrease the band gap and contribute extra electrons to O within the Li₂MnO₃ phase, thereby enhancing electronic conductivity and stabilizing lattice oxygen. Benefitting from the unique architecture, reformative electronic structure, and enhanced kinetics, the antimony-doped LLO nanofibers possess a high reversible capacity (272.8 mA h g^-1) and initial coulombic efficiency (87.8%) at 0.1 C. Moreover, the antimony-doped LLO nanofibers show excellent cycling performance, rate capability, and suppressed voltage fading. The capacity retention can reach 86.9% after 200 cycles at 1 C, and even cycling at a high rate of 10 C, a capacity of 172.3 mA h g^-1 can still be obtained. The favorable results can assist in developing the LLO material with outstanding electrochemical properties.

Unravelling the Structure and Electrochemical Performance of Li-Cr-Mn-O Cathodes: From Spinel to Layered

To explore a new series of cathode materials with high electrochemical performance, the spinel-layered (1 - x)[LiCrMnO₄]· x[Li₂MnO₃·LiCrO₂] ( x = 0, 0.25, 0.5, 0.75, and 1) composites are synthesized with the sol-gel method. X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, and Raman spectra reveal that the structure of the (1 - x)[LiCrMnO₄]· x[Li₂MnO₃·LiCrO₂] cathode materials evolves from spinel to hybrid spinel-layered and layered structures with the increase of the Li concentration. Test results reveal that the structure and electrochemical performance of (1 - x)[LiCrMnO₄]· x[Li₂MnO₃·LiCrO₂] ( x = 0.25, 0.5 and 0.75) composites have the characteristics of both spinel ( x = 0) and Li-rich layered phases ( x = 1). In particular, x = 0.5 and 0.75 electrodes exhibit relatively high capacity retention and rate capability, which is mainly ascribed to the synergistic effect of the spinel and Li-rich layered phases, the 3D Li-ion diffusion channels of the spinel phase, and the low charge-transfer resistance ( R_ct) and Warburg diffusion impedance ( W_o).

Exposing the {010} Planes by Oriented Self-Assembly with Nanosheets To Improve the Electrochemical Performances of Ni-Rich Li[Ni0.8Co0.1Mn0.1]O2 Microspheres

A modified Ni-rich Li[Ni_0.8Co_0.1Mn_0.1]O₂ cathode material with exposed {010} planes is successfully synthesized for lithium-ion batteries. The scanning electron microscopy images have demonstrated that by tuning the ammonia concentration during the synthesis of precursors, the primary nanosheets could be successfully stacked along the [001] crystal axis predominantly, self-assembling like multilayers. According to the high-resolution transmission electron microscopy results, such a morphology benefits the growth of the {010} active planes of final layered cathodes during calcination treatment, resulting in the increased area of the exposed {010} active planes, a well-ordered layer structure, and a lower cation mixing disorder. The Li-ion diffusion coefficient has also been improved after the modification based on the results of potentiostatic intermittent titration technique. As a consequence, the modified Li[Ni_0.8Co_0.1Mn_0.1]O₂ material exhibits superior initial discharges of 201.6 mA h g^-1 at 0.2 C and 185.7 mA h g^-1 at 1 C within 2.8-4.3 V (vs Li⁺/Li), and their capacity retentions after 100 cycles reach 90 and 90.6%, respectively. The capacity at 10 C also increases from 98.3 to 146.5 mA h g^-1 after the modification. Our work proposes a novel approach for exposing high-energy {010} active planes of the layered cathode material and again confirms its validity in improving electrochemical properties.