Improving the Structural Stability of Li-Rich Layered Cathode Materials by Constructing an Antisite Defect Nanolayer through Polyanion Doping

Dual modification of phosphate toward improving electrochemical performance of LiNiO2 cathode materials

Lithium nickel oxide (LiNiO2) cathode materials are featured with high capacity and low cost for rechargeable lithium-ion batteries but suffer from severe structure and interface instability. Bulk doping together with surface coating has been proven to be an efficient approach to improve the inner structure and interfacial stability of the LiNiO2 cathode material. Nevertheless, the role of anion doping seems to be quite different from that of cation doping, and a deep insight will be desirable for the structure design of the LiNiO2 cathode material. In this paper, PO43--doped and Li3PO4-coating of dual modification of LiNiO2 are achieved via a facile approach. It is demonstrated that the PO43- anions are doped into the tetrahedron vacant sites of the crystal structure, alleviating the phase transition and improving the reversibility of crystal structure. Besides, the Li3PO4 coating layer ameliorates the interface stability to restrain the side reactions. Therefore, the dual modification enhances overall structural stability of the material to provide excellent performance. Moreover, the consumption of the Li residues by the formation of Li3PO4 coating layer, and the enlarged interlayer spacing of the crystal structure by PO43- doping can facilitate the Li+ ions diffusion, resulting in a superior rate capability.

Electrochemical coupling in subnanometer pores/channels for rechargeable batteries

Subnanometer pores/channels (SNPCs) play crucial roles in regulating electrochemical redox reactions for rechargeable batteries. The delicately designed and tailored porous structure of SNPCs not only provides ample space for ion storage but also facilitates efficient ion diffusion within the electrodes in batteries, which can greatly improve the electrochemical performance. However, due to current technological limitations, it is challenging to synthesize and control the quality, storage, and transport of nanopores at the subnanometer scale, as well as to understand the relationship between SNPCs and performances. In this review, we systematically classify and summarize materials with SNPCs from a structural perspective, dividing them into one-dimensional (1D) SNPCs, two-dimensional (2D) SNPCs, and three-dimensional (3D) SNPCs. We also unveil the unique physicochemical properties of SNPCs and analyse electrochemical couplings in SNPCs for rechargeable batteries, including cathodes, anodes, electrolytes, and functional materials. Finally, we discuss the challenges that SNPCs may face in electrochemical reactions in batteries and propose future research directions.

Function and Application of Defect Chemistry in High-Capacity Electrode Materials for Li-Based Batteries

Current commercial Li-based batteries are approaching their energy density limitation, yet still cannot satisfy the energy density demand of the high-end devices. Hence, it is critical to developing advanced electrode materials with high specific capacity. However, these electrode materials are facing challenges of severe structural degradation and fast capacity fading. Among various strategies, constructing defects in electrode materials holds great promise in addressing these issues. Herein, we summarize a series of significant defect engineering in the high-capacity electrode materials for Li-based batteries. The detailed retrospective on defects specification, function mechanism, and corresponding application achievements on these electrodes are discussed from the view of point, line, planar, volume defects. Defect engineering can not only stabilize the structure and enhance electric/ionic conductivity, but also act as active sites to improve the ionic storage and bonding ability of electrode materials to Li metal. We hope this review can spark more perspectives on evaluating high-energy-density Li-based batteries.

High-Efficiency Electrolyte for Li-Rich Cathode Materials Achieving Enhanced Cycle Stability and Suppressed Voltage Fading Capable of Practical Applications on a Li-Ion Battery

Li-rich cathodes have been in considerable attention for their high reversible capacity. However, they have serious problems like poor cycling with intense capacity decay and voltage fading, which restrict their access to practical applications. In this work, a facile and efficient strategy is proposed to alleviate these intrinsic issues with a high-efficiency electrolyte system. This special electrolyte enables Li-rich cathodes to deliver superior integrated performance with a high initial discharge capacity of 301 mAh·g^-1, outstanding cycling stability with a capacity retention of 88% at 0.5 C over 500 cycles, and a remarkable rate capability of 136 mAh·g^-1 at 5 C, respectively. What is more, the voltage fading is largely suppressed. Physical and electrochemical characterizations demonstrate that the robust CEI film formed on the cathode surface contributes to the improved electrochemical performance. This work provides a new approach to surmount defects of Li-rich materials and will largely promote their practical applications on Li-ion batteries.

Na2S Treatment and Coherent Interface Modification of the Li-Rich Cathode to Address Capacity and Voltage Decay

Li-rich and Mn-based layered oxides are the most promising candidates for next-generation high energy density cathode materials. However, inherent problems including poor rate performance, continuous capacity degradation, and voltage fading hinder their commercial utilization. Herein, a lattice- and interfacial-modified Li_1.2Mn_0.54Co_0.13Ni_0.13O₂ with a pristine-layered bulk structure, Na- and S-doped transition phase, and epitaxially grown Na₂Mn (SO₄)₂ (C2/c symmetry) layer were constructed by Na₂S treatment. The monoclinic Na₂Mn(SO₄)₂ not only acts as an interface protective layer, alleviating the harmful electrode-electrolyte reactions, but also promotes formation of oxygen vacancy in the layered structure, enhancing reversibility of oxygen redox. The Na and S surface lattice doping leads to enhanced Li⁺ diffusion and alleviates the chance of oxygen release. With the positive effects provided by the stable interfacial layer and lattice modification, the modified cathodes with moderate Na₂S treatment shows alleviated capacity and voltage decay and enhanced electrochemical kinetics. Especially, the washed cathode with 3 wt % Na₂S treatment delivers a discharge specific capacity of 305 at 0.1 C and 219 mA h g^-1 at 1 C, as well as 93.15% capacity retention and 88.20% voltage retention after 200 cycles at 1 C.

Interfacial Regulation of Ni-Rich Cathode Materials with an Ion-Conductive and Pillaring Layer by Infusing Gradient Boron for Improved Cycle Stability

Ni-rich cathodes LiNi_xCo_yAl_1-x-yO₂ (0.8 < x < 1) with high energy density, environmental benignity, and low cost are regarded as the most promising candidate materials for next-generation lithium batteries. Unfortunately, capacity fading derived from unstable surface properties and intrinsic structural instability under extreme conditions limits large-scale commercial utilization. Herein, an interface-regulated Ni-rich cathode material LiNi_0.87Co_0.10Al_0.03O₂ with a layer (R3̅m) core, a NiO salt-like (Fm3̅m) phase, and an ultrathin amorphous ion-conductive LiBO₂ (LBO) layer is constructed by gradient boron incorporation and lithium-reactive coating during calcination. The ultrathin LBO layer not only exhausts residual lithium species but also acts as a layer for Li⁺ transport and insulation of detrimental reaction. The NiO salt-like phase in the subsurface could enhance the structural stability of the layer core for the pillar effects. With the positive role provided by the functional hybrid surface layer and boron doping, the modified cathode exhibits enhanced Li⁺ conductivity, structural stability, reversibility of the H2-H3 phase transition, suppressed side reactions, ameliorated transition-metal dissolution, and excellent electrochemical performance. Especially, a 1% wt boron-modified cathode delivers a discharge capacity of 211.99 mA h g^-1 in the potential range of 3.0-4.3 V at 0.2 C and excellent cycle life with a capacity retention of 89.43% after 200 cycles at 1 C.

Formation and Effect of Residual Lithium Compounds on Li-Rich Cathode Material Li1.35[Ni0.35Mn0.65]O2

Li-rich cathode materials are regarded as ideal cathode materials, owing to their excellent electrochemical capacity. However, residual lithium compounds, which are formed on the surface of the materials by reacting with moisture and carbon dioxide in ambient atmosphere, can impair the surface structure, injure the capacity, and impede the electrode fabrication using Li-rich materials. Exposure to air atmosphere causes the formation of residual lithium compounds; the formation of such compounds is believed to be related to humidity, temperature, and time during handling and storage. In this study, we demonstrated for the first time an artificial strategy for controlling time, temperature, and humidity to accelerate exposure. The formation and effect of residual lithium compounds on Li-rich cathode material Li_1.35[Ni_0.35Mn_0.65]O₂ were systematically investigated. The residual lithium compounds formed possessed primarily an amorphous structure and were partially coated on the surface. These compounds include LiOH, Li₂O, and Li₂CO₃. Li₂CO₃ is the major component in residual lithium compounds. The presence of residual lithium compounds on the material surface led to a high discharge capacity loss and large discharge voltage fading. Understanding the formation and suppressing the effect of residual lithium compounds will help prevent their unfavorable effects and improve the electrochemical performance.