Long-Life Nickel-Rich Layered Oxide Cathodes with a Uniform Li2ZrO3 Surface Coating for Lithium-Ion Batteries

Constructing a Protective Pillaring Layer by Incorporating Gradient Mn4+ to Stabilize the Surface/Interfacial Structure of LiNi0.815Co0.15Al0.035O2 Cathode

Nickel-rich layered oxides are regarded as very promising materials as cathodes for lithium-ion batteries because of their environmental benignancy, low cost, and high energy density. However, insufficient cycle performance and poor thermotic characteristics induced by structural degradation at high potentials and elevated temperatures pose challenging hurdles for nickel-rich cathodes. Here, a protective pillaring layer, in which partial Ni²⁺ ions occupy Li slabs induced by gradient Mn⁴⁺, is integrated into the primary particle of LiNi_0.815Co_0.15Al_0.035O₂ to stabilize the surface/interfacial structure. With the stable outer surface provided by the enriched Mn⁴⁺ gradient concentration and the pillar effect of the NiO-like phase, Mn-incorporated quaternary cathodes show enhanced structural stability and improved Li⁺ diffusion as well as lithium-storage properties. Compared with the severe capacity fade of a pure layered structure, the cathode with gradient Mn⁴⁺ exhibits more stable cycling behavior with a capacity retention of 80.0% after 500 cycles at 5.0 C.

Multishell Precursors Facilitated Synthesis of Concentration-Gradient Nickel-Rich Cathodes for Long-Life and High-Rate Lithium-Ion Batteries

The rational design of concentration-gradient (CG) structure is demonstrated as an available approach to improve the electrochemical performances of high-energy nickel-rich cathodes for lithium-ion batteries (LIBs). However, the complicated preparing processes, especially the CG-precursors, generally result in the less-than-ideal repeatability and consistency that is regarded as an extreme challenge for the widespread commercialization. Thus, the innovative strategy with facile steps and the feasibility of large-scale preparation for commercialized applications should be urgently developed. Herein, through the temperature-tunable cation diffusion, the feasibility of controllable preparation of nickel-rich CG-LiNi_0.7Co_0.15Mn_0.15O₂ (NCM) from multishell precursors is first demonstrated. As expected, the Li/CG-NCM half cells show much enhanced cycle-life, rate property, and safety because of the mitigated side-reactions and fast Li⁺ kinetics. Besides, the Li₄Ti₅O₁₂/CG-NCM full cells also exhibit long-term lifespan, 95% capacity retention even after 2000 cycles, and high-rate behaviors. Importantly, by contrast with the conventional techniques that prepare CG cathodes from CG precursors, the proposed new synthesis strategy from multishell precursors is suitable for large-scale preparation. Overall, this multishell precursor-facilitated synthesis probably promotes the practical applications of CG cathodes for state-of-the-art LIBs and also can be easily expanded to controllably preparing spinel- and olive-type CG cathodes.

Revealing the role of NH4VO3 treatment in Ni-rich cathode materials with improved electrochemical performance for rechargeable lithium-ion batteries

Although Ni-rich layered oxides are considered a candidate of next-generation cathode materials, their inherent properties, such as surface lithium residues and structural destruction, cause detrimental electrochemical performance, especially at elevated temperatures. Here, a facile ball-milling method is proposed to remove the lithium residues and enhance the electrochemical performance of LiNi0.6Co0.2Mn0.2O2. After NH4VO3 treatment, a lithium ion-conductive Li3VO4 coating layer is found on the LiNi0.6Co0.2Mn0.2O2 surface at heat-treatment temperatures of 300 and 450 °C, with a small part of vanadium ions diffusing into the surface lattice. When the temperature surpasses 600 °C, almost all vanadium ions dope into the bulk structure. The complex relationships between the post-sintering temperature and surface structure and their impact on electrochemical properties are discussed in detail. Electrochemical tests show that 0.5 wt% NH4VO3 treated LiNi0.6Co0.2Mn0.2O2 at 450 °C exhibits much improved cycling stability (96.1% cycling retention at 0.5C after 100 cycles and 97.2% after 50 cycles at 55 °C), rate capability (117.0 mA h g-1 at 5C), and storage property (4683 ppm lithium residue amount after storing in air for 7 days). Such superior performance is ascribed to the Li3VO4 coating layer that inhibits the electrolyte decomposition and helps create a stable and thinner cathode-electrolyte interface, resulting in decreased interfacial resistance. In addition, this coating layer suppresses internal micro-stress and phase transformation from a layered to spinel and rock-salt structure, which increases the structural integrity of LiNi0.6Co0.2Mn0.2O2 during repeated charge-discharge cycling.

Construction of uniform ZrO2 nanoshells by buffer solutions

The growth kinetics of ZrO₂ could be well-tuned in buffer solutions, which led to uniform ZrO₂ nanoshells.

Surface/Interfacial Structure and Chemistry of High-Energy Nickel-Rich Layered Oxide Cathodes: Advances and Perspectives

The urgent prerequisites of high energy-density and superior electrochemical properties have been the main inspiration for the advancement of cathode materials in lithium-ion batteries (LIBs) in the last two decades. Nickel-rich layered transition-metal oxides with large reversible capacity as well as high operating voltage are considered as the most promising candidate for next-generation LIBs. Nonetheless, the poor long-term cycle-life and inferior thermal stability have limited their broadly practical applications. In the research of LIBs, it is observed that surface/interfacial structure and chemistry play significant roles in the performance of cathode cycling. This is due to the fact that they are basically responsible for the reversibility of Li⁺ intercalation/deintercalation chemistries while dictating the kinetics of the general cell reactions. In this Review, the surface/interfacial structure and chemistry of nickel-rich layered cathodes involving structural defects, redox mechanisms, structural evolutions, side-reactions among others are initially demonstrated. Recent advancements in stabilizing the surface/interfacial structure and chemistry of nickel-rich cathodes by surface modification, core-shell/concentration-gradient structure, foreign-ion substitution, hybrid surface, and electrolyte additive are presented. Then lastly, the remaining challenges such as the fundamental studies and commercialized applications, as well as the future research directions are discussed.

Ni-Rich LiNi0.8Co0.1Mn0.1O2 Oxide Coated by Dual-Conductive Layers as High Performance Cathode Material for Lithium-Ion Batteries

Ni-rich materials are appealing to replace LiCoO₂ as cathodes in Li-ion batteries due to their low cost and high capacity. However, there are also some disadvantages for Ni-rich cathode materials such as poor cycling and rate performance, especially under high voltage. Here, we demonstrate the effect of dual-conductive layers composed of Li₃PO₄ and PPy for layered Ni-rich cathode material. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy show that the coating layers are composed of Li₃PO₄ and PPy. (NH₄)₂HPO₄ transformed to Li₃PO₄ after reacting with surface lithium residuals and formed an inhomogeneous coating layer which would remarkably improve the ionic conductivity of the cathode materials and reduce the generation of HF. The PPy layer could form a uniform film which can make up for the Li₃PO₄ coating defects and enhance the electronic conductivity. The stretchy PPy capsule shell can reduce the generation of internal cracks by resisting the internal pressure as well. Thus, ionic and electronic conductivity, as well as surface structure stability have been enhanced after the modification. The electrochemistry tests show that the modified cathodes exhibited much improved cycling stability and rate capability. The capacity retention of the modified cathode material is 95.1% at 0.1 C after 50 cycles, whereas the bare sample is only 86%, and performs 159.7 mAh/g at 10 C compared with 125.7 mAh/g for the bare. This effective design strategy can be utilized to enhance the cycle stability and rate performance of other layered cathode materials.

Atomic Layer Deposition of Stable LiAlF4 Lithium Ion Conductive Interfacial Layer for Stable Cathode Cycling

Modern lithium ion batteries are often desired to operate at a wide electrochemical window to maximize energy densities. While pushing the limit of cutoff potentials allows batteries to provide greater energy densities with enhanced specific capacities and higher voltage outputs, it raises key challenges with thermodynamic and kinetic stability in the battery. This is especially true for layered lithium transition-metal oxides, where capacities can improve but stabilities are compromised as wider electrochemical windows are applied. To overcome the above-mentioned challenges, we used atomic layer deposition to develop a LiAlF₄ solid thin film with robust stability and satisfactory ion conductivity, which is superior to commonly used LiF and AlF₃. With a predicted stable electrochemical window of approximately 2.0 ± 0.9 to 5.7 ± 0.7 V vs Li⁺/Li for LiAlF₄, excellent stability was achieved for high Ni content LiNi_0.8Mn_0.1Co_0.1O₂ electrodes with LiAlF₄ interfacial layer at a wide electrochemical window of 2.75-4.50 V vs Li⁺/Li.

Mitigating the Surface Degradation and Voltage Decay of Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Material through Surface Modification Using Li2ZrO3

In the quest to tackle the issue of surface degradation and voltage decay associated with Li-rich phases, Li-ion conductive Li₂ZrO₃ (LZO) is coated on Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (LNMC) by a simple wet chemical process. The LZO phase coated on LNMC, with a thickness of about 10 nm, provides a structural integrity and facilitates the ion pathways throughout the charge-discharge process, which results in significant improvement of the electrochemical performances. The surface-modified cathode material exhibits a reversible capacity of 225 mA h g^-1 (at C/5 rate) and retains 85% of the initial capacity after 100 cycles. Whereas, the uncoated pristine sample shows a capacity of 234 mA h g^-1 and retains only 57% of the initial capacity under identical conditions. Electrochemical impedance spectroscopy reveals that the LZO coating plays a vital role in stabilizing the interface between the electrode and electrolyte during cycling; thus, it alleviates material degradation and voltage fading and ameliorates the electrochemical performance.

High-voltage positive electrode materials for lithium-ion batteries

The ever-growing demand for advanced rechargeable lithium-ion batteries in portable electronics and electric vehicles has spurred intensive research efforts on high-voltage positive electrode materials over the past decade.