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.
The practical applications of Li‐rich cathode materials, especially Li‐rich Mn‐based (LRM) cathodes, are hindered by their inherent shortcomings. In this case, the recent understanding of complex reaction mechanisms, the novel modification methods, and the corresponding development trends are comprehensively reviewed. Additionally, other branches and the future opportunities of the Li‐rich cathode materials are also summarized.
VOPO4⋅x H2O has been proposed as a cathode for rechargeable aqueous zinc batteries. However, it undergoes significant voltage decay in conventional Zn(OTf)2 electrolyte. Investigations show the ...decomposition of VOPO4⋅x H2O into VOx in the electrolyte and voltage drops after losing the inductive effect from polyanions.PO43− was thus added to shift the decomposition equilibrium. A high concentration of cheap, highly soluble ZnCl2 salt in the electrolyte further prevents VOPO4⋅x H2O dissolution. The cathode shows stable capacity and voltage retentions in 13 m ZnCl2/0.8 m H3PO4 aqueous electrolyte, in direct contrast to that in Zn(OTf)2 where the decomposition product VOx provides most electrochemical activity over cycling. Sequential H+ and Zn2+ intercalations into the structure are revealed, delivering a high capacity (170 mAh g−1). This work shows the potential issue with polyanion cathodes in zinc batteries and proposes an effective solution using fundamental chemical principles.
The VOPO4⋅x H2O cathode undergoes decomposition and dissolution in rechargeable aqueous Zn batteries. A 13 m ZnCl2/0.8 m H3PO4 aqueous electrolyte is designed to inhibit its degradation, allowing stable capacity and voltage retentions over cycling. Sequential H+ and Zn2+ intercalations into the structure deliver a high capacity of 170 mAh g−1.
P2 layered oxides have attracted more and more attention as cathode materials of high‐power sodium‐ion batteries (SIBs). During the charging process, the release of sodium ions leads to layer slip, ...which leads to the transformation of P2 phase into O2 phase, resulting in a sharp decline in capacity. However, many cathode materials do not undergo P2‐O2 transition during charging and discharging, but form a “Z” phase. It is proved that the iron‐containing compound Na0.67Ni0.1Mn0.8Fe0.1O2 formed the “Z” phase of the symbiotic structure of the P phase and O phase during high‐voltage charging through ex‐XRD and HAADF‐STEM. During the charging process, the cathode material undergoes a structural change of P2‐OP4‐O2. With the increase of charging voltage, the O‐type superposition mode increases to form an ordered OP4 phase, and the P2‐type superposition mode disappears after further charging to form a pure O2 phase. 57Fe‐Mössbauer spectroscopy revealed that no migration of Fe ions is detected. The O–Ni–O–Mn–Fe–O bond formed in the transition metal MO6 (M = Ni, Mn, Fe) octahedron can inhibit the elongation of the Mn–O bond and improve the electrochemical activity so that P2‐Na0.67Ni0.1Mn0.8Fe0.1O2 has an excellent capacity of 172.4 mAh g−1 and a coulombic efficiency close to 99% at 0.1C.
The significant sodium storage mechanism in P2‐Na0.67Ni0.1Mn0.8Fe0.1O2 is revealed in this paper, and the role of Ni2+ and Fe3+ in the phase transition process is linked. Exploring the structural evolution and properties of the “Z” phase is of great significance for the development of high‐performance P2‐NaMO2 sodium‐ion battery cathode materials.
High‐nickel LiNi1−x−yMnxCoyO2 (NMC) and LiNi1−x−yCoxAlyO2 (NCA) are the cathode materials of choice for next‐generation high‐energy lithium‐ion batteries. Both NMC and NCA contain cobalt, an ...expensive and scarce metal generally believed to be essential for their electrochemical performance. Herein, a high‐Ni LiNi1−x−yMnxAlyO2 (NMA) cathode of desirable electrochemical properties is demonstrated benchmarked against NMC, NCA, and Al–Mg‐codoped NMC (NMCAM) of identical Ni content (89 mol%) synthesized in‐house. Despite a slightly lower specific capacity, high‐Ni NMA operates at a higher voltage by ≈40 mV and shows no compromise in rate capability relative to NMC and NCA. In pouch cells paired with graphite, high‐Ni NMA outperforms both NMC and NCA and only slightly trails NMCAM and a commercial cathode after 1000 deep cycles. Further, the superior thermal stability of NMA to NMC, NCA, and NMCAM is shown using differential scanning calorimetry. Considering the flexibility in compositional tuning and immediate synthesis scalability of high‐Ni NMA very similar to NCA and NMC, this study opens a new space for cathode material development for next‐generation high‐energy, cobalt‐free Li‐ion batteries.
A novel cobalt‐free high‐energy cathode material, high‐nickel LiNi1−x−yMnxAlyO2 (NMA), is reported, with desirable physical and electrochemical properties. Benchmarked against LiNi1−x−yMnxCoyO2 (NMC) and LiNi1−x−yCoxAlyO2 (NCA) of identical Ni content (89 mol%), NMA delivers attractive specific energy, rate capability, cyclability, and thermal stability. Morevoer, NMA offers immediate synthesis scalability without the constraint of a vulnerable cobalt supply chain.
Layered Li‐rich cathode materials with high reversible energy densities are becoming prevalent. However, owing to the activation of low‐potential redox couples and the progressively irreversible ...structural transformation caused by the local adjustment of transition‐metal ions in the intra/interlayer driven by anionic redox, continuous capacity degradation, and voltage decay emerge, thus greatly reducing the energy density and increasing the difficulty of battery system management. Herein, layered Li‐rich cathode materials with higher intralayer configuration entropy have more local structural diversity and higher distortion energy, resulting in superior local structural adaptability with no drastic redox couple evolution, major local structural adjustment, or obvious layered‐to‐spinel phase transition. Consequently, the energy retention of the entropy‐stabilization‐strategy‐enhanced Li‐rich cathode materials is almost twice that of a typical Li‐rich cathode material (Li1.20Mn0.54Ni0.13Co0.13O2, T‐LRM) after 3 months of cyclic testing. Moreover, when cycled at 1 C, the voltage degradation per cycle is less than 0.02%, that is, it results in a voltage loss of only 0.8 mV per cycle, which is excellent performance. This study paves the way for the development of Li‐rich cathode materials with stabilized intralayer atomic arrangements and high local structural adaptability.
Layered Li‐rich cathode materials with higher intralayer configuration entropy have more local structural diversity and higher distortion energy, resulting in superior local structural adaptability: no drastic redox couple evolution, major local structural adjustment, or obvious layered‐to‐spinel phase transition. This leads to high stability of the capacity and voltage, greatly enhancing energy retention.
Aqueous zinc-ion batteries (ZIBs) with low-priced, high-safety, and high synergistic efficiency have captured an ever-increasing amount of consideration and have been expected to be a promising ...choice to replace LIBs. However, the cathode materials of ZIBs reported have many shortcomings such as poor electron and zinc ion conductivity and complicated energy storage mechanisms. In this review, several typical cathode materials for ZIBs in recent years and their detailed energy storage mechanisms are summarized, and various improvement methods to enhance the electrochemical properties of ZIBs are briefly introduced. Eventually, the current problems and the expected development foregrounds of ZIBs are proposed.
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Although lithium-ion batteries (LIBs) have many advantages, they cannot satisfy the demands of numerous large energy storage industries owing to their high cost, low security, and low resource richness. Aqueous zinc-ion batteries (ZIBs) with low cost, high safety, and high synergistic efficiency have attracted an increasing amount of attention and are considered a promising choice to replace LIBs. However, the existing cathode materials for ZIBs have many shortcomings, such as poor electron and zinc ion conductivity and complex energy storage mechanisms. Thus, it is crucial to identify a cathode material with a stable structure, substantial limit, and suitability for ZIBs. In this review, several typical cathode materials for ZIBs employed in recent years and their detailed energy storage mechanisms are summarized, and various methods to enhance the electrochemical properties of ZIBs are briefly introduced. Finally, the existing problems and expected development directions of ZIBs are discussed.
Lithium‐ and manganese‐rich layered oxides (LMLOs, ≥ 250 mAh g−1) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and ...oxygen release induced chemo‐mechanical breakdown. Herein, a Co‐free single‐crystalline LMLO, that is, LiLi0.2Ni0.2Mn0.6O2 (LLNMO‐SC), is prepared via a Li+/Na+ ion‐exchange reaction. In situ synchrotron‐based X‐ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro‐strain are observed in LLNMO‐SC compared to its polycrystalline counterpart (LLNMO‐PC) during the charge–discharge process. Specifically, the as‐synthesized LLNMO‐SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li‐ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long‐term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO‐SC decreases by only ≈0.2 V after 100 cycles at 28 mA g‐1 between 2.0 and 4.8 V, which is much lower than that of LLNMO‐PC (≈0.5 V). Such a single‐crystalline strategy offers a promising solution to constructing stable high‐energy lithium‐ion batteries (LIBs).
A Li+/Na+ ion‐exchange reaction is reported to synthesize the Co‐free single‐crystalline LiLi0.2Ni0.2Mn0.6O2 (LLNMO‐SC). In situ synchrotron‐based X‐ray diffraction and absorption spectroscopy are utilized to investigate the structural evolution of LLNMO‐SC and its polycrystalline counterpart (LLNMO‐PC) during electrochemical cycling. The origin of mitigated voltage decay in LLNMO‐SC is unraveled upon long‐term cycling.
The novelty of the work: This review introduces briefly the strategies of regenerating cathode materials from spent lithium-ion battery. Regeneration can achieve not only the recycle of valuable ...metals in lithium-ion batteries but also the reutilization of recovered metals.
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•New cathode materials can be directly regenerated from spent LIBs.•Regeneration strategies can directly recycle different types of spent LIBs.•Regenerated cathode materials show excellent electrochemical performances.•Ideal economic benefits can be obtained through regeneration processes.
The recycle and reutilization of spent lithium-ion batteries for environmental protection and resource reclamation has arousing rising attention. Numerous studies placed the only emphasis on the recovery of target metals, whereas the application of recovered materials has been ignored. Recently, regeneration, a novel and efficient treatment method, can achieve not only the recycle of valuable metals in lithium-ion batteries but also the reutilization of recovered metals. Accordingly, the recycle of spent lithium-ion batteries for new cathode materials has aroused extensive attention. This paper summarizes existing processes and technologies of regenerating cathode materials from cathode scraps of lithium-ion batteries. In the meantime, the common cathode materials regenerated by diverse synthetic routes are systematically analyzed. Besides, metal impurity elements are discussed, which are likely to lead to the inferior electrochemical properties of the regenerative cathode materials. Lastly, the existing challenges and suggestions for regeneration process are proposed. This paper can lay a theoretical basis and guidance for regenerating and reutilizing the cathode materials by recycling spent lithium-ion batteries.
Li‐rich Mn‐based cathode materials (LRMs) are potential cathode materials for high energy density lithium‐ion batteries. However, low initial Coulombic efficiency (ICE) severely hinders the ...commercialization of LRM. Herein, a facile oleic acid‐assisted interface engineering is put forward to precisely control the ICE, enhance reversible capacity and rate performance of LRM effectively. As a result, the ICE of LRM can be precisely adjusted from 84.1% to 100.7%, and a very high specific capacity of 330 mAh g−1 at 0.1 C, as well as outstanding rate capability with a fascinating specific capacity of 250 mAh g−1 at 5 C, are harvested. Theoretical calculations reveal that the introduced cation/anion double defects can reduce the diffusion barrier of Li+ ions, and in situ surface reconstruction layer can induce a self‐built‐in electric field to stabilize the surface lattice oxygen. Moreover, this facile interface engineering is universal and can enhance the ICEs of other kinds of LRM effectively. This work provides a valuable new idea for improving the comprehensive electrochemical performance of LRM through multistrategy collaborative interface engineering technology.
Introduced cation/anion double defects can reduce the interface charge transfer resistance and enhance the Li+ ion diffusion coefficient. The induced in situ surface reconstruction layer can increase the electronic conductivity and stabilize the surface lattice oxygen. As a result, the initial Coulombic efficiency of Li‐rich Mn‐based cathode material is controlled precisely.
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