Atomically topological interlocking enables near-zero-strain lithium-rich manganese-based oxide cathodes

The pursuit of high-energy-density lithium-ion batteries (LIBs) hinges upon the relentless development of advanced cathode materials. The inherent high operating voltage renders oxide cathodes the most favored option for this objective. Even with the exceptional capacity of ∼300 mAh/g exhibited by lithium-rich manganese oxide cathodes, the cell-level energy density at present remains constrained at 400 Wh/kg. Consequently, a transformative breakthrough is urgently needed to revolutionize oxide cathode materials with ultrahigh capacity (>300 mAh/g) and thereby enable the design of LIBs for a broad range of applications. In this Focus Review, the electrochemical performances of various oxide cathodes are comprehensively scrutinized, with particular emphasis on those characterized by a Li/O ratio greater than 0.6 (Li1+xTM1–xO2, x > 0.2, where TM denotes transition metal). We emphasize that the construction of multidimensional defects offers a promising means of resolving the present quandary regarding the trade-off between structural stability and capacity for high-capacity oxide cathodes.

Despite their ultrahigh specific capacity, lithium‐rich layered oxide cathodes are still plagued by challenges such as poor cycle stability and notorious voltage decay, which are primarily attributed to surface issues such as the release of lattice oxygen and interfacial side reactions. In this study, a facial strategy of gradient fluorination is adopted to construct a thin but robust LiF‐rich cathode electrolyte interface (CEI), highly enhancing the stability of the interface of lithium‐rich oxides. Experimental results and theoretical calculations both demonstrate that the stable CEI not only promotes oxygen participation in redox reactions and simultaneously inhibits oxygen release and structural transition, but also facilitates the transport kinetics of lithium ions. As a result, the gradient fluorinated lithium‐rich cathode delivers highly enhanced rate performance (133 mAh g−1 at 5 C), superior cycling stability with a capacity retention of 81.9% after 100 cycles at 1 C (250 mAh g−1), and alleviated voltage fade (only 1.75 mV per cycle). Moreover, a unique formation mechanism for LiF‐rich surfaces is proposed according to theoretical calculations. This work not only provides a fresh understanding of the CEI formation mechanism, but also show a promising avenue for designing LiF‐rich CEIs applicable to other layered oxide cathodes.

Apart from conventional redox chemistries, exploring high-voltage anionic redox processes, such as pure oxygen or high-valent transition metal ion redox, poses challenges due to the instability of O nonbonding or O-dominant energy states. These states are associated with destructive behaviors in layered oxide cathodes, including local structural distortion, cationic disordering, and oxygen gas evolution. In this study, we suppress first-cycle voltage hysteresis and irreversible O2 evolution in Li-rich oxide cathodes through covalency competition induced by the substitution of electropositive groups. We found that the nonequivalent electron distribution within an asymmetric MA-O-MB backbone (metal-to-metal charge transfer via oxygen ligands) increases electron density on electronegative transition metal ions, preventing them from reaching unstable oxidation states within an operating voltage range. This phenomenon is observed across diverse transition metal combinations, providing insights into controlling unnecessary oxygen redox activity. Our findings open new avenues for controlling intrinsic redox chemistry and enabling the rational design of high-energy density Li-rich oxide cathodes.

Using molten-salts as a thermal processing medium for cobalt-free lithium-rich cathode material

Reversible anionic (oxygen) redox in lithium-rich cathode oxides has been becoming a blooming research topic to further boost the energy density in lithium-ion batteries. There are numerous experimental observations and theoretical calculations to illustrate the importance of defects on anionic redox activity, but how the defects on the surface and bulk control the kinetics of anionic redox is not well understood. Here, we uncover this intriguing ambiguity on the correlation among defects states, Li-ion diffusion, and oxygen redox reaction. It is found that the surface-defective microstructure has fast Li-ion diffusion to achieve superior cationic redox activities/kinetics, whereas the bulk-defective microstructure corresponds to a slow Li-ion diffusion to result in poor cationic redox activities/kinetics. By contrast, both surface and bulk defects can be of benefit to the enhancement of oxygen redox activities/kinetics. Moreover, a positive correlation is also established among charge-transfer resistance, interface reaction charge-transfer activation energy, and oxygen redox activity in these electrode materials. This study on defect-anionic activity provides a new insight for controlling anionic redox reaction in lithium-rich cathode materials for real-world application.

The Cover Feature illustrates the protection effects of the cathodes interfacial layer after adding the methyl diphenylphosphinite (MDP) additive into the electrolyte. MDP participates in the interfacial reaction of cathodes through the peroxidation behavior, and forms a robust protective film with interaction between the P−O species and transition-metal elements. The film prevents the cathodes being attacked by HF in the electrolyte, leading to an enhanced high-temperature performance of lithium-rich oxide cathodes. More information can be found in the Article by Y. Ma and co-workers on page 1569 in Issue 12, 2018 (DOI: 10.1002/celc.201800061).

A novel low-cobalt single-crystal lithium-rich manganese-based layered oxide cathodes with enhanced electrochemical performances

Lithium-rich manganese-based oxides (LRMOs) exhibit high specific capacity exceeding 250 mAh g-1, making them promising candidates for next-generation lithium-ion batteries. However, oxygen evolution during cycling destabilizes the crystal structure, leading to capacity fading. By precisely controlling the oxygen/nitrogen (O2/N2) ratio during sintering, this work achieves a significant reduction in bulk oxygen vacancy content and enhances lattice oxygen stability. The O50 sample sintered under 50%O2/50%N2 atmosphere ratio demonstrates exceptional performance with 96.7% capacity retention (216.5 mAh g-1) after 300 cycles at 1 C rate (1 C = 200 mA g-1). Remarkably, it maintains delivering 155.0 mAh g-1 at 5 C and 133.2 mAh g-1 at 10 C, showing superior rate capability. Structural characterization reveals this atmosphere-controlled sintering strategy simultaneously enhances bulk oxygen stability and surface oxygen vacancy generation, providing a simple yet effective strategy for the design of high-performance LRMOs.

A layered lithium-rich manganese-based oxide cathode, containing R3̅m (LiTMO2, TM = Mn, Ni, Co) and C2/m (Li2MnO3) nanodomains, utilizes both transition metals and oxygen redox to yield substantial energy density. However, the inherent heterogeneous nature and distinct nanodomain redox chemistries of layered lithium-rich oxides will inevitably cause pernicious lattice strain and structural displacement, which can hardly be eliminated by conventional doping or coating strategies and result in accelerated performance decay. Herein, we incorporate a strain-inhibiting perovskite phase coherently grown within the layered structure to effectively restrain the displacement and lattice strain during uneven Li-ion extraction. The enhanced mechanochemical stability of the designed cathode benefits the persistent structure and reversible oxygen redox, thereby achieving high initial Coulombic efficiency and stable cycling and voltage profiles. Our approach of lattice engineering alleviates the strain and displacement caused by inhomogeneous reactivity between heterogeneous nanodomains and promotes the development of advanced cathode materials with long durability.

Energy storage via anionic redox provides extra capacity for lithium-rich manganese-based oxide cathodes at high voltage but causes gradual structural collapse and irreversible capacity loss with generation of On - (0 ≤ n < 2) species upon deep oxidation. Herein, the stability and reversibility of anionic redox reactions are enhanced by a simple sulfur-assisted surface modification method, which not only modulates the material's energy band allowing feasible electron release from both bonding and antibonding bands, but also traps the escaping On - via an as-constructed SnS2- x - σ Oy coating layer and return them to the host lattice upon discharge. The regulation of anionic redox inhibits the irreversible structural transformation and parasitic reactions, maintaining the specific capacity retention of as-modified cathode up to 94% after 200 cycles at 100mA g-1 , along with outstanding voltage stability. The reported strategy incorporating energy band modulation and oxygen trapping is promising for the design and advancement of other cathodes storing energy through anion redox.

Stabilizing Structure and Performances of Lithium Rich Layer-Structured Oxide Cathode Materials

Energy-tuned photoelectron spectroscopy demonstrates the surface preferential oxidation of oxygen for the Li-rich cathode material Li1.2Ni0.2Mn0.6O2 upon charge.

Extensive research interest has been garnered by lithium-rich manganese-based layered oxides (LMNC), primarily driven by their high specific capacity and economic advantage. However, LMNC suffers from severe irreversible oxygen release, surface–interface side reactions, and structural degradation, which lead to rapid voltage and capacity fading during cycling, significantly hindering their commercial application. Herein, a synergistic modification strategy of “Yttrium doping–ZrO2 coating” is proposed for the Y-LMNC@ZrO2 composite cathode. First-principle calculations confirm that Y-doping enhances lattice oxygen stability owing to the strong Y–O bond, effectively suppressing oxygen loss during delithiation. Meanwhile, the ZrO2 coating layer considerably reduces side reactions at the electrode–electrolyte interface. Experimental results show that after 200 cycles at 1C, the Y-LMNC@ZrO2 electrode exhibits an excellent electrochemical performance, achieving a high discharge capacity of 172.3 mAh g–1 and maintaining a capacity retention of 92.34% after cycling. In full-cell tests, the Y-LMNC@ZrO2 sample exhibits an 13.36% improvement in capacity retention after 100 cycles compared with the unmodified sample. These results demonstrate that as-prepared Y-LMNC@ZrO2 is a promising high-performance cathode material for lithium-ion batteries.

Nanoscale characterization of charged/discharged lithium-rich thin film cathode by scanning probe microscopy techniques

Challenges and solutions of lithium-rich manganese-based layered oxide cathode materials