Preparation of long-term cycling stable ni-rich concentration-gradient NCMA cathode materials for li-ion batteries

Aluminium-sodium targeted co-doping to boost the electrochemical stability of full concentration gradient Ni-rich LiNi0.80Co0.05Mn0.15O2 cathodes

Structural engineering of full concentration gradient (FCG) offers promising prospects for improving the interface and thermal stability of Ni-rich layered cathodes. However, the Ni content in the core of FCG cathode particle is higher than that on the surface, resulting in rapid structural deterioration at the particle core during cycling. To directionally strengthen the structural stability at the cores of FCG cathode particles, this study proposes a dual-cation targeted co-doping strategy that coordinates gradient Al doping with uniform Na doping. Al-Na co-doped FCG Li1-yNayNi0.80Co0.05Mn0.15-xAlxO2 (FNCM-AxNy) cathodes were successfully prepared through a combined in-situ and wet-chemistry method. As confirmed in experimental and theoretical studies, the particle core is structurally stabilized by the directional distribution of Al and Na within the particles, the formation of strong AlO bonds, and the provision of Na pillar ions in the bulk, which alleviate lattice shrinkage and structural collapse of the particles during the cycling process. Moreover, Al-Na co-doping enhances the diffusion kinetics by widening the ion- diffusion channels and reducing the diffusion barriers. Consequently, the capacity retention of the as-prepared FNCM-A0.1N1 cathode (co-doped with 0.1 mol% Al and 1 mol% Na) after 200 cycles at a rate of 1C reached 93 %, considerably outperforming both the pristine cathode (81 %) and the Al-doped cathode (87 %). Our study provides a novel idea to enhance the electrochemical stability by targeting strengthening the structural stability at the particle core of FCG Ni-rich layered cathodes.

Building an entropy-assisted enhanced surface on ultrahigh nickel cathodes to improve electrochemical stability

Increasing the Ni content in Ni-rich cathodes to over 90% can further enhance the energy density and reduce costs. However, this aggravates the issue of lattice oxygen release due to the instability of the layered structure. In this work, an entropy-stabilized surface strategy is used to process ultrahigh nickel cathode LiNi0.96Co0.03Mn0.01O2 (NCM). Utilizing the low solid solubility of high-valent elements W, Mo and Nb in NCM, the simultaneous introduction of W, Mo and Nb ions will aggregate on the outer surface of NCM, which in turn forms a composite entropy assisted enhancement surface. This entropy assisted enhancement surface consists of a composite lithium compound coating and a high-entropy rock salt phase, which inhibits the loss of surface lattice oxygen and reduces the corrosion of cathode particles by electrolyte decomposition products. Furthermore, the formation of the entropy assisted enhancement surface retains the role of refined primary particles, thereby further enhancing the mechanical properties. NCM modified with composite entropy assisted enhancement surface (HE03) exhibits a capacity of 234.5 mAh g-1 at 0.1C with a capacity retention of 96.7% after 100 cycles at 0.5C. This entropy-stabilizing strategy enables the ultrahigh nickel cathodes to display high specific capacity of and improved cycling stability, presenting a promising modification approach.

Systematic study of Co-free LiNi0.9Mn0.07Al0.03O2 Ni-rich cathode materials to realize high-energy density Li-ion batteries

The growing use of EVs and society's energy needs require safe, affordable, durable, and eco-friendly high-energy lithium-ion batteries (LIBs). To this end, we synthesized and investigated the removal of Co from Al-doped Ni-rich cathode materials, specifically LiNi0.9Co0.1Al0.0O2 (NCA-0), LiNi0.9Mn0.1Al0.0O2 (NMA-0), LiNi0.9Mn0.07Al0.03O2 (NMA-3), intending to enhance LIB performance and reduce the reliance on cobalt, a costly and scarce resource. Our study primarily focuses on how the removal of Co affects the material characteristics of Ni-rich cathode material and further introduces aluminum into the cathode composition to study its impacts on electrochemical properties and overall performance. Among the synthesized samples, we discovered that the NMA-3 sample, modified with 3 mol% of Al, exhibited superior battery performance, demonstrating the effectiveness of aluminum in promoting cathode stability. Furthermore, the Al-modified cathode showed promising cycle life under normal and high-temperature conditions. Our NMA-3 demonstrated remarkable capacity retention of ∼ 88 % at 25 °C and ∼ 81 % at 45 °C after 200 cycles at 1C, within a voltage range of 2.8-4.3 V, closely matching the performances of conventional NCM and NCA cathodes. Without cobalt, the cathodes exhibited increased cation disorder leading to inferior rate capabilities at high C-rates. In-situ transmission XRD analysis revealed that the introduction of Al has reduced the phase change and provided much-needed stability to the overall structure of the Co-free NMA-3. Altogether, the findings suggest that our aluminum-modified NMA-3 sample offers a promising approach to developing Co-free, Ni-rich cathodes, effectively paving the way toward sustainable, high-energy-density LIBs.

Understanding Electrochemical Performance Enhancement with Quaternary NCMA Cathode Materials

Ni-rich cathode materials show promise for use in lithium-ion batteries. However, a significant obstacle to their widespread adoption is the structural damage caused by microcracks. This research paper presents the synthesis of Ni-rich cathode materials, including LiNi0.8Co0.1Mn0.1O2 (referred to as NCM) and Li(Ni0.8Co0.1Mn0.1)0.98Al0.02O2 (referred to as NCMA), achieved through the high-temperature solid-phase method. Electrochemical (EC) testing results reveal the impressive EC performance of NCMA. NCMA exhibited a discharge capacity of 141.6 mAh g-1 and maintained a cycle retention rate of up to 74.92% after 300 cycles at a 1 C rate. In contrast, the NCM had a discharge capacity of 109.7 mAh g-1 and a cycle retention rate of 61.22%. Atomic force microscopy showed that the Derjaguin-Muller-Toporov (DMT) modulus value of NCMA exceeded that of NCM, signifying a greater mechanical strength of NCMA. Density functional theory calculations demonstrated that the addition of aluminum during the delithiation process led to the mitigation of anisotropic lattice changes and the stabilization of the NCMA structure. This improvement was attributed to the relatively stronger Al-O bonds compared to the Ni(Co, Mn)-O bonds, which reduced the formation of microcracks by enhancing NCMA's mechanical strength.

Decoding the puzzle: recent breakthroughs in understanding degradation mechanisms of Li-ion batteries

Lithium-ion batteries (LIBs) remain at the forefront of energy research due to their capability to deliver high energy density. Understanding their degradation mechanism has been essential due to their rapid engagement in modern electric vehicles (EVs), where battery failure may incur huge losses to human life and property. The literature on this intimidating issue is rapidly growing and often very complex. This review strives to succinctly present current knowledge contributing to a more comprehensible understanding of the degradation mechanism. First, this review explains the fundamentals of LIBs and various degradation mechanisms. Then, the degradation mechanism of novel Li-rich cathodes, advanced characterization techniques for identifying it, and various theoretical models are presented and discussed. We emphasize that the degradation process is not only tied to the charge-discharge cycles; synthesis-induced stress also plays a vital role in catalyzing the degradation. Finally, we propose further studies on advanced battery materials that can potentially replace the layered cathodes.